User:RJFJR/referencedesknotes

Re-focusing photographs

copied from reference desk

Could it be possible for an out-of-focus photo to be brought into focus by some kind of algorithm or equipment? It seems to me that all the necessary information must be in the photo, and although the information is scrambled up, the scrambling must occur in a predictable way. Presumably I'm wrong? "Sharpen" filters that work by edge-detection are not at all what I mean. 81.131.18.168 (talk) 10:44, 9 April 2010 (UTC)

See deconvolution microscopy, and more generally deconvolution for the theoretical basis of this approach. My impression is that detailed information is required about the whole optical system for this to work effectively, making it impractical for normal photography, however I am no expert on optics. I know that one approach in biological microscopy is to image a perfectly spherical bead of known diameter, and use this to work out the deconvolution parameters needed. 131.111.185.69 (talk) 11:19, 9 April 2010 (UTC)

(ec) Computational photography studies that problem. Here are a few links you might find interesting: Light fields and computational photography, Synthetic Aperture Focusing using a Shear-Warp Factorization of the Viewing Transform, and the MultiCamera. It really helps to have redundant information, (for example, many separate photographs - though there are other ways to have redundant information), so that an algorithm can extract additional information to help focus the image. This video, Synthetic Aperture focusing, shows a series of processed results from a "single image" generated by the multi-camera (you can consider this a single camera with a huge synthetic aperture, or you can consider it 128 cameras with normal apertures). In either case, though, these algorithms require additional (redundant) information which is not contained in an ordinary photograph - your post implies that de-focusing is "information scrambling" (which is correct, but your terminology is a bit imprecise.) However, your assumption that this "scrambling" is predictable is not exactly right - it's only predictable if we have additional information - how the image was defocused, or some knowledge about the 3D setup of the scene, etc.

If you have a fairly powerful computer (~ 1 GB of RAM and a pretty fast processor), you can use this browser-based demo to play with synthetic-aperture focusing on a series of test photographs. If you're a programmer, the project source code is available, so you don't have to run this inside a web-browser (for obvious performance reasons!) Nimur (talk) 11:23, 9 April 2010 (UTC)

If you know exactly how the blur occurred then you can calculate a point spread function, and do the inverse convolution. However there is still a problem of noise. Any noise will be amplified. compression artifacts will be counted as noise too, so you need to perform this on a non compressed and high quality image. Without knowing the way the picture was corrupted, you can attempt blind deconvolution. As far as I know there were not any stable algorithms or methods using a limited CPU to get a good result. Graeme Bartlett (talk) 12:41, 9 April 2010 (UTC)

Adaptive optics may also be relevant. StuRat (talk) 13:01, 9 April 2010 (UTC)

Using a plenoptic lens you have more data in the digital image. [2] Bwbuckley (talk) 02:59, 7 March 2011 (UTC)

Enzyme for digesting pork?

copied from reference desk

Yesterday someone told me they had been raised vegetarian and so had trouble digesting pork because they didn't produce a necessary digestive enzyme. What enzyme would that be? RJFJR (talk) 19:53, 9 April 2010 (UTC)

I've heard vegetarians claim this too, but this and this would both indicate that it's not true; that your body generates the requisite digestive enzymes regardless of your diet. In the unlikely case that your friend is a panda, she can still digest meat, but may have lost the taste for it. -- Finlay McWalter • Talk 20:06, 9 April 2010 (UTC)

The gut bacteria will be different. And it takes a while before you change the colony composition. So you need to change your diet slowly to let the bacteria adjust. Ariel. (talk) 20:23, 9 April 2010 (UTC)

Digestion of meat (protein) is mostly done by proteases in the stomach at low pH. Intestinal bacteria may play a secondary role, but it is a minor one. See Gut flora#Functions for a run-down of their major roles in the human digestive tract. These bacteria are more relevant to the digestion of carbohydrates, starches and to some extent even cellulose; but protein is pretty much chemically digested by gastric acid. Nimur (talk) 21:21, 9 April 2010 (UTC)

Gastric acid starts the process, but trypsin and other pancreatic proteases do the main job of digesting all proteins, either plant or animal source. Vegetarians can certainly digest pork: they just notice a change in stool appearance and composition related to a different set of undigestible excreta. alteripse (talk) 02:49, 10 April 2010 (UTC)

liquid becoming solid at higher temperature?

copied from reference desk

There was something on the radio this morning about a substance that might be used for medical treatments that is a liquid when chilled but a solid at body temperature. Is this actually a reversable phase change or is it more like a thermoset glue? (If it's the former, is there a name for this property?) RJFJR (talk) 18:40, 17 September 2010 (UTC)

This news item sounds like what you are remembering. DMacks (talk) 19:16, 17 September 2010 (UTC)

That's it: "a injectable formulation derived from natural sugar chains that exists as a liquid when cooled and becomes a solid at body temperature." RJFJR (talk) 19:19, 17 September 2010 (UTC)

Thermoreversibilty I think could be the word. Poloxamer gels exhibit this property. They are nowhere as strong as the gels we are used to though. Perhaps that why they want to develop them further. They would have the property of keeping damaged cells from leaking out their contents out all over the place but are not up to the job just yet. --Aspro (talk) 19:46, 17 September 2010 (UTC)

The article Thermosetting polymer deals with the process in general terms; this sounds like the use of bioorganic molecules like sugars and polysacharrides to develop materials with similar properties. --Jayron32 19:47, 17 September 2010 (UTC)

Here we go: Temperature Induced Gelation. It is probably the next sec of 5.2.2. Cellulose derivatives which is applicable because cellulose is only sugar. Here's a patent as well.[3]--Aspro (talk) 20:11, 17 September 2010 (UTC)

Oh and I forgot to say: I found the patent because as always Wikipedia has an article about it (Poloxamer) and it was under references. Thermoreversible also appease to be the commonly accepted term for this property.Here is another example of its use. [4] Does this fully answer your question?--Aspro (talk) 21:22, 17 September 2010 (UTC)

Link

• Echium vulgare (Viper's bugloss)

• category of icons

Stay with me, buddy; we're gonna make it through this

From reference desk, I'd ben wondering about this

On television and in movies, wounded people are often encouraged to stay concious. Is this necessary to improve chances of survival? Why not just let them be unconscious and continue rescue efforts while they sleep? --90.215.213.167 (talk) 01:51, 24 October 2010 (UTC)

It's more dramatic to see the Wounded Hero struggle. However, some injuries--e.g. concussion--carry a danger if the patient loses consciousness. → ROUX ₪ 01:54, 24 October 2010 (UTC)

WRONG —Preceding unsigned comment added by Kj650 (talk • contribs) 03:29, 24 October 2010 (UTC)

Could you be more specific, please? → ROUX ₪ 03:31, 24 October 2010 (UTC)

WP:OR here: I suspect that, because an injured person who is verifiably conscious, is not dead, this is reassuring to the others around. Fighting to stay conscious also demonstrates that the injured person has not "given up". Bielle (talk) 05:27, 24 October 2010 (UTC)

With a (suspected) concussion loosing consciousness or sleeping is not dangerous. The problem is that going to sleep can mask serious injury. That's why the recommendation is not to let the person go to sleep have a head injury - you want to make sure they are not seriously injured (which you would notice by altered consciousness states, pupils of different sizes, etc.). From this people extrapolate a little too far.

The only other thing I can think of is that a conscious person can help in their recovery, but for example pinpointing injuries (pain), and giving a medical history. But besides that I can not think of any reason not to let the person become unconscious - in fact one of the first treatments for serious head wounds is a medically induced coma. Physically forcing (shaking) a person to stay awake can probably injure them more! (However all that said, I would be reassured if a doctor could confirm/deny what I wrote.) Ariel. (talk) 08:02, 24 October 2010 (UTC)

There can be a number of reasons to keep the casualty awake. For example a study discussed here into pre-hospital deaths from road accidents "showed that at least 39% and up to 85% of preventable pre-hospital deaths may be due to airway obstruction”. Much easier to monitor and remedy airway problems in a conscious person. Another serious risk with accident victims or people suffering from blood loss is hypothermia. At least two reasons you want to keep someone awake who's at risk of this, firstly again problems are easier to monitor in a conscious patient, and secondly the body temperature naturally decreases during sleep, so thereby heightening risks of hypothermia. Of course once a person has been transferred to professional care and a proper medical facility the equation changes completely. --jjron (talk) 11:55, 24 October 2010 (UTC)

U.S. Army FM 21-11 First Aid for Soldiers [5] has a special wounds chapter entitled Proper First Aid for Head Injuries. This chapter outlines numerous procedures if the victim loses consciousness - but at no time does it suggest trying to keep the victim awake. Nimur (talk) 16:53, 24 October 2010 (UTC)

The most significant mortal risk in loss of consciousness is loss of airway. An unconscious person cannot protect their airway, so no gag reflex. That means you can inhale stuff (blood, snot, vomit, bone, brain, whatever) into your lungs (aspiration pneumonia) and this can progress to ARDS. Then you have a really good chance of dying. In hospital we have plenty of technology at our disposal to artificially maintain airways. We just need to be aware of the problem! But in the field, the best means of protecting an airway is to keep the victim conscious. Failing that there's airway manoeveres like jaw thrust. If there 's a seriously life-threatening head injury, then unconsciousness may be as preventable as nightfall, but deterioration of milder injuries may be prevented when the victim stays awake. Mattopaedia ^{Say G'Day!} 05:38, 25 October 2010 (UTC)

Category:Articles with sections that need to be turned into prose

Need to cook steaks; not embarass myself

copied from the misc reference desk for my notes.

So, I have been informed by my wife we are going to host an old fashioned cookout for her boss and his spouse. My wife wants me to grill steaks. Now, on the rare occasion (Ouch, bad pun that I did not intend) that I grill steaks myself (as opposed to going to a restaurant), I usually just get a cheap cut, cook it hot & fast, a dash of salt & pepper, and eat it bloody with a can of cold beer to wash it down. Needless to say, that is not exactly what my wife has in mind. I'm pretty confident in my ability to grill the steaks to preference (medium, medium rare, etc), but suggestions on a good cut of meat and marinating/tenderizing methods would be really helpful. (PS- I'm cooking with gas if it matters, and would prefer to stay away from fillets if at all possible.) Quinn ^☂THUNDER 19:47, 11 April 2011 (UTC)

Personally my favourite it a Bavette, but I understand that it's not necessarily considered the best cut (Flank steak apparently). In terms of how to cook 'em I tend to leave that to the chefs in the restaurant but someone will be a long in a min to give some advice i'm sure. ny156uk (talk) 20:30, 11 April 2011 (UTC)

Good grilling steak is steak that is lean and cut from one muscle. For that reason, the fatty gristly stuff (the meat "nearer the hoof and horn") is usually reserved for long, slow, low heat methods like proper barbecue and crock pot and braising. The nice lean cuts are found farther from the "hoof and horn", and generally do much less work for the animal, so have less gristle and have a softer, more tender texture.

I would recommend one of the following:

• The T-bone or its cousin the Porterhouse, which are basically the "man cut". When cartoon writers want to put a steak in their animation, and want you to know instantly that its a steak, they draw a T-bone.
• The Filet mignon is the gold standard of steak cuts. Its quite lean, takes well to high heat, and has no rind, bone, or anything else to mess up the meat. Its all good eating.
• The Top sirloin is a decent cut as well, has a bit more gristle than the filet mignon, but it is often just as lean.
• The flank steak. While this breaks the "horn and hooves" rule, the flank steak has some unique properties that make it good for grilling. With a flank steak, rather than grill each individual portion, you grill the whole thing, and then cut the grilled roast into thin slices across the grain, exposing the rare inner meat. This treatment is usually called London broil or carne asada (our carne asada says that the dish is made with sirloin, but the all of best carne asada I have had has been flank steak). If you cut the meat really thin, it is a great dish.
• A standing rib roast, AKA Prime rib. Like the flank steak, this is usually cooked as a whole roast, and the cut into slices. Unlike the flank steak, prime rib is best cut and served in big, thick slices. Also, the prime rib is ideally suited for big parties where people have different tastes and want different levels of doneness. Pieces cut from the end of this large roast will be more well done, while pieces cut from the center will be rarer. Good for trying to get every guest what they want without driving yourself crazy trying to grille a bunch of steaks to different levels of doneness. If more guests want more well-done meat, just leave the whole roast in longer. If everyone likes it rare, leave it in a bit shorter.

Just always remember to choose the highest quality steaks regardless of which cut you choose. You'll want a steak that has "marbling" (tiny flecks of fat) throughout the meat, rather than streaks. Paying extra for top-grade beef from a specialty butcher may be worth it, if you are cooking to impress. --Jayron32 20:40, 11 April 2011 (UTC)

My father-in-law manages a steakhouse, and his secret ingredient for steaks is a needle tenderizer (sample here at Amazon; not to be confused with the hammer shown at meat tenderizer). The more tender cuts (filet mignon particularly) also tend to have less beefy flavor, so a good tenderizer lets you get beefy-and-tender out of something like top sirloin, which is my preferred steak cut. From there, I agree with your seasoning method of salt and pepper, applying it before grilling. You can also do things like add stuff on top when you're done cooking -- butter mixed with spices or herbs, sauteed mushrooms and onions, sharp cheese crumbles -- that fancy up the steak without making the process of cooking the steak any different. — Lomn 20:53, 11 April 2011 (UTC)

And, as always with red meat, do not be tempted to serve it as soon as it's done. Take it off the flame but keep it warm with foil, leave it for a few (up to 5) minutes, and only then serve it. This makes it much more juicy and tender than it would otherwise have been. -- Jack of Oz [your turn] 21:05, 11 April 2011 (UTC)

Damn this thread is manly! Let me just ad that if you want something a little less cro-magnon, salmon, catfish, and shark steaks all grill nicely. You've got to be a bit careful with the salmon, because unlike the other two it will flake, but grill it skin-on or in foil and it'll be fine. and if you've never had grilled shark... mmmmMMmmmm... --Ludwigs2 22:58, 11 April 2011 (UTC)

I regret having to disagree with Jack above insofar as his welcome advice on not serving the meat immediately after frying in butter or grilling for about 5 minutes. Make that 15 minutes resting between 2 warmed plates that can also be used for serving upon and I will applaud his instructions. And if necessary, re-warm the steaks before serving. But resting (of the steaks) is essential to de-stress the meat after cooking - and it gives you time to prepare the vegetables etc, 92.4.39.69 (talk) 23:53, 11 April 2011 (UTC)

The time needed to let it sit depends on the size of the pieces and the heat they were cooked at. I try for 10 minutes, but have a habit of cutting that (pun intended) short when the smell becomes irresistible. It doesn't simply make the meat juicier, it literally keeps the juice in the meat rather than running out all over the plate when it gets sliced. As far as advice goes, that wait after grilling is the simplest (and cheapest) way to make a steak more presentable for someone you want to impress. Matt Deres (talk) 13:02, 12 April 2011 (UTC)

Rump steak is excellent - much to preferred over the more expensive sirloin. It is tender and has a rich, meaty taste. No need to season it before cooking, but beurre maitre d' is a good accompaniment, as is some proper English mustard (not the week and wandery stuff they have abroad). DuncanHill (talk) 13:17, 12 April 2011 (UTC)

Rump, or round (in the U.S.), is a great cut of meat for certain applications. You can make a decent London Broil out of it (as with flank), but as a big hunk-o-rare-steak it doesn't work as well as other cuts, without substantial tenderizing (the needle tenderizer noted above may help a lot). I use round a lot in my cooking, especially for applications like pot roast and beef stew because it has a fantasticly beefy flavor and it stands up well to long cooking times; but as a grilled steak it has very tough, stringy muscle fibers. Remember that this is the main muscle that the animal uses to walk with; which is a two edged sword. More work means that the muscle has a higher concentration of myoglobin and related compounds, which is what provides that "beefy" flavor; however conversely it also has muscle fibers which are denser and thicker and more reslient, and thus of a tougher texture, and must be treated right before and during cooking. The OP specifically stated he wanted a steak which required less preperation; so perhaps the Filet Mignon makes a better steak for his purposes. --Jayron32 15:50, 12 April 2011 (UTC)

I'm sorry Jayron, but that is absolute nonsense. Rump does not need tenderising and works exceptionally well as a big hunk of rare steak. It may be that your American "round" steak is either something completely different, or from very poor quality animals. If anyone tried to tenderise a bit of rump that I was going to eat, I'd probably tenderise him. Rump needs no preparation. DuncanHill (talk) 19:33, 12 April 2011 (UTC)

Rump steak is not "round steak" - as the charts at Category:Cuts of beef make clear. DuncanHill (talk) 19:40, 12 April 2011 (UTC)

That explains some of the confusion. When I looked at the rump steak link earlier, it redirected to round, which I assumed was the same cut (being unfamiliar with the term). If the link had been accurate, I would not have been led to making the wrong conclusions about the texture of the steak in question. Mea culpa. Please let this be a lesson to everyone in the future. I am always wrong. Feel free to let that inform your understanding of my answers. My wrongness must be understood as absolute and permanent. I apologize for misleading everyone with my wrongness. I have struck my answer because it was clearly wrong, and DuncanHill is of course fully correct in it being absolute nonsense. --Jayron32 20:04, 12 April 2011 (UTC)

I hadn't followed the rump steak link when I made it - I had forgotten just how US-centric much of Wikipedia is. There has been some prior discussion on the round steak talk page about the issue, so I have nominated the redirect for deletion (we do need an article there though) and removed the erroneous references to rump from the round steak article. I dread looking at all the other cuts of beef articles - from the charts it looks like we will need a lot of dabbing. DuncanHill (talk) 20:12, 12 April 2011 (UTC)

I was puzzled by Jayron's (now stricken) comments on "rump" (my favourite cut), but all is clear now that Duncan has shown that he meant "topside" or "silverside". We do need some work on the articles. Dbfirs 22:25, 12 April 2011 (UTC)

What, no Ribeye mentions? I personally prefer a good ribeye to all the others. Just a bit of salt and pepper, a bit of red left in the middle. Hmmm...I'm getting hungry. Tex (talk) 16:06, 12 April 2011 (UTC)

Ooh. Yes, ribeye is very good. I did mention it in a roundabout way; ribeye steak is the same cut as a standing rib roast, just cut and grilled as a steak rather than as a roast. It is a tasty bit of cow... --Jayron32 20:06, 12 April 2011 (UTC)

Flank steak is delicious marinated in a tamari-garlic marinade and served with grilled onions and green peppers. Best served well done in my opinion. -- Mwalcoff (talk) 22:12, 12 April 2011 (UTC)

FTL neutrinos

Is it true? What are the implications for physics? --70.134.53.27 (talk) 15:27, 23 September 2011 (UTC)

Presumably you're interested in recent announcements by CERN, as reported in this BBC article - Speed-of-light experiments give baffling result at Cern? Here's the official press release, OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso. If you're interested in the implications, consider reading the papers linked from that, or watching the broadcast seminar, featuring a QA session.

Here's the pre-print, Measurement of the neutrino velocity with the OPERA detector in the CNGS beam. The claim is that tau neutrinos arrived 60.7 ns earlier than they should have, after a flight of 730 km. Unfortunately, as always, high energy physics is much more complicated than that: the tau neutrinos did not fly the entire distance; they are produced somewhere en-route out of muon neutrinos. If you want to understand the details, ... the research is outlined in the paper and websites.

In my opinion, the best way to assess the "implications" of the experiment is first to establish an understanding of the sources of error, and the methods used to control those errors. As a skeptical scientist, I believe it is more probable that a large team of physicists measured time and distance incorrectly, as a result of invalid statistical data processing; but it's also possible that the behavior of 15,000 neutrinos did actually violate all other known physical observations. After you review the data and experimental presentation, and if you believe all experimental errors are accounted for, the next step would be to undertake an explanation for the speed. Finally, you could proceed to derive physical consequences that follow from this apparent violation of the "speed limit." Nimur (talk) 16:47, 23 September 2011 (UTC)

I have to correct you on the tau neutrinos - as far as I know only a single tau neutrino has so far been seen at the OPERA detector (I remember reading that they expect a total of only 11 tau neutrinos over the several years of the research project). Many more muon neutrinos have been detected, and the recent preprint on arXiv states that there were "about 16000" neutrino events detected by OPERA. And since we know about neutrino oscillation, we actually shouldn't talk about tau neutrinos, muon neutrinos and electron neutrinos but about ν₁, ν₂ and ν₃; then e.g. beta decay creates a certain superposition of the 3 neutrinos characteristic for the electron, and there is another superposition for the muon and another one for the tauon. Icek (talk) 18:48, 23 September 2011 (UTC)

(Merged from "Exceeding the speed of light" above - Wnt (talk) 17:59, 23 September 2011 (UTC))

[6] Now i am not a science guy but nothing could exceed the speed of light right?but than whats this? — Preceding unsigned comment added by 175.110.242.217 (talk) 08:10, 23 September 2011

(Merged from #Neutrinos above - Wnt (talk) 17:55, 23 September 2011 (UTC))

Sorry to be the first cranky neutrino question after the CERN release of data, and this is probably a very stupid question. Is there a good reason to think that neutrinos must have a positive mass? I'm sure there must be, but I can't see it in our article neutrino. Our article says that neutrinos must have a non-zero mass, and that our main source of information on the masses depends on the squares of the masses (if I'm reading that right)? Please disappoint me with a reasonable explanation, or I'll be too excited to sleep :P 86.164.78.26 (talk) 21:59, 22 September 2011 (UTC)

Okay, we need to distinguish three different things here:

1. Negative mass. This has nothing directly to do with tachyons. Tachyons don't have negative mass.
2. Negative mass-squared (also called imaginary mass) in classical relativistic particle theory. Classical particles with negative m² go faster than light.
3. Negative mass-squared in relativistic field theory. This is mathematically related to the classical particle case, but the practical upshot is very different. In a field theory, the mass-squared behaves like a spring constant—if you think of the field as a rubber sheet then the higher the mass, the more resistant the sheet is to stretching. If the mass-squared is negative, then not only does the sheet not resist stretching but it actually pushes in the same direction you pull it, leading to an exponential feedback loop if the field is even slightly disturbed. The only way for this to make any sense is if there's a counterbalancing effect that comes into play at larger amounts of stretching, so the sheet only stretches to the point that these opposing effects balance each other. This actually happens in the Standard Model with the Higgs field, and is called tachyon condensation. The result is a field that behaves for practical purposes like it has a positive mass-squared.

I know nothing about this new announcement from OPERA except that they claim to have found actual superluminal propagation. This sounds like the second case above, but modern particle physics is built on quantum field theory, where the second case is irrelevant; "tachyons" don't propagate superluminally in quantum field theory. So, if this is real, it would pretty much require rebuilding modern particle physics from the ground up. It could be a quantum gravity effect, and this might give a hint as to the right theory of quantum gravity. But more likely it's experimental error. -- BenRG (talk) 23:05, 22 September 2011 (UTC)

Might you be referring to the Reuters article that they are travelling faster than light? I just got it linked to me. Excitement should be withheld as it's almost certainly an error, but honestly, given the fact that the scientists aren't crackpots, my heart did rush a little when I got to the end of the article without indication that they're crackpots. SamuelRiv (talk) 23:21, 22 September 2011 (UTC)

[7]. Nil Einne (talk) 00:54, 23 September 2011 (UTC)

Here's the preprint. The official announcement doesn't happen until 4PM Friday in Geneva (13 hours from now). As that blog post says, it's way too early to get excited about this. -- BenRG (talk) 01:01, 23 September 2011 (UTC)

Note from some reports [8] [9] it appears that while the team think there is a possibility their results are correct and would be confirmed by independent replication and that would obviously be their preference, they think the more likely explanation is there's an error they didn't notice. Some further comment on the Sn1987A neutrinos [10] Nil Einne (talk) 01:08, 23 September 2011 (UTC)

The news reports on the report said the neutrinos travelled through the Earth faster than the speed of light in vacuum. What would be the speed of light through dirt and rocks, ignoring the fact that dirt and rocks would absorb the light? Edison (talk) 14:13, 23 September 2011 (UTC)

Can one talk about the speed of light through totally opaque media? Whatever the answer is, it's not faster than it would be a vacuum, so how would that get you anything? --Mr.98 (talk) 19:29, 23 September 2011 (UTC)

opacity is not an absolute characteristic, it is relative. Even dirt and rocks allow EM to propagate through it, albeit not very well, but there is still a "speed of light". —Akrabbim^talk 19:44, 23 September 2011 (UTC)

Well, that's true. I was thinking only about visual frequencies, which are not very penetrative, but of course there are lots of forms of EM. But either way, it's going to be slower than in a vacuum. --Mr.98 (talk) 22:57, 23 September 2011 (UTC)

http://xkcd.com/955/. Deor (talk) 14:36, 23 September 2011 (UTC)

Perhaps they pass through the 8th dimension. Wnt (talk) 17:32, 23 September 2011 (UTC)

Just as likely as The 5th Dimension. Edison (talk) 17:45, 23 September 2011 (UTC)

Ah, but the neutrino oscillation overthruster allows it to tap into the dimension of space inside solid matter.^[11] ;) Wnt (talk) 18:07, 23 September 2011 (UTC)

Perhaps even the Sixth dimension? Hot damn! SamuelRiv (talk) 18:19, 23 September 2011 (UTC)

All kidding aside, I almost wonder if there could be something to this idea. The passage with solid matter is what distinguishes these neutrinos from the ones from distant supernovae. Now a standard force like electromagnetism, so far as I understand from a previous discussion here, can be modeled as an extra dimension, a bending of space just like gravity. But neutrinos ignore this force, so they shouldn't be slowed by the Earth's optical refractive index. Is it conceivable that some obscure force acting on the neutrino could have a different kind of refractive effect, where passing through solid matter actually makes them go faster than passing through empty space? As if there were some other dimension in which space could be bent, but one which is bent in the vacuum, but which can be straightened out by matter? (Almost surely this is bogus - yes, I know that calculation is quite indirect and errors or unspectacular physics oddities could slip in in many places, but if we want to imagine a way to explain the result if it were real...) Wnt (talk) 02:35, 24 September 2011 (UTC)

Err, don't most neutrinos detected go through a lot of solid matter? My understanding is that most neutrino detectors are deep underground to avoid cosmic ray contamination. I don't think passing through matter (which is an imprecise way of saying "didn't interact with any matter", right?) is really the distinguishing factor here. The distinguishing factor is that these guys claim to know when they created the neutrino, precisely, which is exactly what we don't know with regards to supernovae or stars. Right? --Mr.98 (talk) 04:45, 24 September 2011 (UTC)

While the neutrinos measured from SN 1987A did travel a relatively long path through the Earth (if you look at the 3 neutrino detectors mentioned in the article, they are all so far north that the supernova couldn't have been visible from their position at any time of day; and for neutrino detectors with direction sensitivity the neutrinos from above are usually discarded as far as I know, because there is more background of muons being created when cosmic rays hit the atmosphere), that wouldn't have much effect on the average speed from the Large Magellanic Cloud to the Solar System.

Maybe it is some kind of near-field effect like it also occurs in electromagnetic dipole radiation, but that's just something that came to my mind now without any calculations to back it up. In any case, if information really travels faster than light, then causality is broken or special relativity is wrong. Icek (talk) 13:26, 24 September 2011 (UTC)

The world's observatories did a great job on some of these supernovae, but 60 ms precision is surely beyond them! However accurately the neutrinos speed was measured relative to their travel time to Earth, any small variation within the Earth would have gone unnoticed, I would say.

It doesn't break causality or special relativity to go faster than the speed of light, if that speed is measured in water, glass, etc. Only the speed of light in vacuum counts, because it is the fastest and most fundamental speed. But what if it isn't? What if there's some slightly faster speed of light that applies in this case? Wnt (talk) 14:27, 24 September 2011 (UTC)

Of course I mean the speed of light in vacuum. Assuming that the Lorentz transformation is correct, then you could indeed send a message into your own past (you only need a neutrino emitter in the vicinity of the neutrino detector which receives the information from the neutrino detector; the neutrino emitter has to be moving at a very high speed away from the original neutrino source and emit neutrinos towards a detector close to the original source; from the rest frame it will look as if the neutrinos from the fast moving emitter are moving backwards in time).

If you think there is some slightly faster "speed of light" applying in this case (because there is actually no way that light moves in a straight line from CERN to Gran Sasso?), then what would happen if you build a long straight tube from CERN to Gran Sasso? You could repeat the Michaelson-Morley experiment with light sent through the tube and with the interferometer traveling at various speeds (obviously there are many practical problems with these experiments, but in principle they can be done). Would the neutrinos travel slower because the tube exists, or what else would happen (things could be arranged so that the measured neutrinos would move through the soil close to the tube, but not through the vacuum inside the tube)? Icek (talk) 14:58, 24 September 2011 (UTC)

To disclose fully, I don't know (but ought to) whether the Lorentz transformation or electrical formulas involving c would be noticeably inaccurate if they should be using the hypothetical super-fast c accessible to neutrinos passing through solid matter, but instead are using a somewhat slower measure of light passing through a vacuum. On the other hand, since I'm just handwaving anyway, for all I know the neutrino path might be one of these straighter-than-straight non-Euclidean geometry things in 11 dimensions. Alas, my imagination has gotten beyond what I know. But I'm skeptical that the Michaelson-Morley experiment applies, because you can't use it to come up with anything important when a medium slows the speed of light, so why would you be able to use it if it speeds it up? Wnt (talk) 03:41, 25 September 2011 (UTC)

Nature News has printed the extra dimension idea (citing a professor emeritus......)^[12] but without the assistance of Buckeroo Banzai they still have failed to make the connection with the space inside solid matter. ;) Wnt (talk) 17:00, 25 September 2011 (UTC)

—Wow, only on weekends!  :) All kidding aside, I think that this discovery may actually be slightly less revolutionary than it first appears.

It was always my understanding (please feel free to correct me, if I err) that Albert Einstein theorized that the speed of light in a vacuum was a universal speed limit, by claiming that as something approached light speed, the flow of time—relative to it—would proportionately slow down, or "dilate." By extension, as said object hit light speed, time would stop, rendering any further acceleration (speed / time) impossible. There are two "gaps" in this hypothesis, however.

1.) Einstein himself never said that something couldn't travel faster than light speed if it were ALREADY moving that fast when it was created.

2.) Niels Bohr (to whom we owe the current atomic model, along with Ernest Rutherford) in one of his arguments with Einstein, even went so far as to propose that a particle travelling at, say, 9/10 of light speed, may even be able to "quantum jump" to 1-1/10 of light speed.

Long story short, I don't believe AT ALL that Einstein was mistaken in his theories; rather, CERN may have just confirmed the existence of the very first Tachyon! Pine (talk) 21:00, 24 September 2011 (UTC)

As I said above, tachyons are violating causality. For a tachyon at speed v you only need a tachyon emitter traveling faster than ${\frac {2v}{1+{\frac {v^{2}}{c^{2}}}}}$ (a speed which is below c). Send a tachyon from a stationary tachyon emitter to a tachyon detector traveling along the moving tachyon emitter. When the moving tachyon detector detects a tachyon, the moving tachyon emitter shall emit a tachyon back at the stationary tachyon emitter, and it will arrive there before the original tachyon was emitted, as can be calculated using Lorentz transformations. Icek (talk) 22:13, 24 September 2011 (UTC)

This is a really problematic argument because it makes an assumption about emitter vs receiver that isn't even logically coherent. It assumes that you can always choose to emit a tachyon going "forward in time", where "time" is for some reason the coordinate time of your rest frame. I see no reason why the world should work that way in any case, but a more serious problem is that the tachyon's worldline can go forward in time with respect to the rest frames of both endpoint labs, i.e., it can be "emitted" on both ends by this definition. Obviously this makes no sense from a causality perspective. The most obvious solution is to impose some kind of global Lorentz-violating causality relation, perhaps coincident with the rest frame of the cosmic microwave background. But if you do that then of course your procedure for sending a signal into the past no longer works. -- BenRG (talk) 22:54, 24 September 2011 (UTC)

Special relativity, as it existed in 1905, could accommodate faster-than-light travel in a certain limited sense, if you didn't worry too much about causality. But a lot has happened since then. As I said earlier in this thread, quantum field theory, which is the foundation of modern physics, can't deal with faster-than-light particles. It does have a concept of "tachyons," but they don't go faster than light, despite the name. If this phenomenon is real then it undermines the foundations of quantum field theory and everything is potentially up in the air, even basic concepts like "mass" and "speed". -- BenRG (talk) 22:54, 24 September 2011 (UTC)

I'll just note a disagreement with the idea that FTL must equal time travel - this assumes that relativity always applies, but FTL is clearly beyond relativity anyway. I am rather fond of the idea that an absolute rest frame can be defined at any point in space; most of the matter we see stays within 0.1c or so of this rest frame. Provided that under hypothetical new laws of physics an FTL particle is never permitted to move backward in time relative to the locally defined rest frame, it could never possibly move in a complete closed circle in spacetime. Of course there is no shred of evidence for this, but we cannot dismiss FTL a priori based on time travel paradoxes. (And it is also very much possible that time travel is possible, and the single past and the single future simply reconcile their fates as best they may) Wnt (talk) 03:48, 25 September 2011 (UTC)

Here's a good readable summary of the experiment, by Chad Orzel. -- BenRG (talk) 23:17, 24 September 2011 (UTC)

Inform

This is from User talk:Card Zero 04:33, 28 December 2011 (UTC) Could you tell me more about your experience trying to use Inform and why you rated it 'interesting rather than good' in your post at the reference desk? RJFJR (talk) 20:58, 25 December 2011 (UTC)

Sure. I should maybe have mentioned that I was referring to Inform 7, which is radically different from Inform 6. It seems that 6 is a sensible and mundane language tailored for writing text adventures, similar to some others such as ADRIFT - so I gather from browsing Interactive Fiction Competition results. I haven't ever used 6 (except as one or two little inclusions within code written in 7).

Inform 7 is an extraordinary effort to allow the writing of adventure games in natural language, for the benefit of writers of fiction rather who aren't programmers. It's simultaneously brilliant, absurd, rational, and awkward, like a conlang. Some problems:

• Turning English phrases into aliases for 6's keywords and symbols isn't a royal road to high-level abstraction. You can't say "computer, create an adventure game with the following characteristics ..." and continue as if having a conversation or writing a novel. It just means that now you have to memorise an arcane set of English phrases instead of the usual keywords and symbols.
• Some of the English words which are now magically endowed with the power to control the workings of the game may in fact be words you want to use as part of the game, particularly as the names of objects, causing conflicts and confusion.
• Some of the English words which you naturally try to use to control the workings of the game may in fact be slightly incorrect, and so are interpretted differently (perhaps interpretted as the names of objects), causing conflicts and confusion. Beware trying to write in a natural style!
• Though the compiler tries to understand natural language, it isn't, of course, an actual AI, so it constantly fails to understand what you mean. One example of this which features in the manual is the problem with saying "The Airport is west of the Airport Road" . If an "Airport Road" already exists, then "The Airport" will be understood as an abbreviated reference to it (in the same way that you might create a "School of Dance and Occult Sciences" and then refer to it later as just "The School"). The outcome is that there will be no airport, and the airport road will be west of itself. The way out of the problem is to use the keyword called ... so now there is the situation where saying "east of the Airport Road is a room called the Airport" means something significantly different from "east of the Airport Road is the Airport". More subtle syntax, waiting to trip you up. Note also the absurdity of using the keyword room to describe every location, such as an airport or a road.
• The task of writing a game - or the nature of the things I attempt to achieve - pulls against using natural language. For instance, I began writing a game set on an ocean liner. Many of the rooms would be cabins, which would all have certain characteristics in common. Inform 7 allows you to associate adjectives with object types, so that you can say, for instance, "a window can be triangular", and create some rules about triangular things, and thereafter declare that certain windows are triangular. This is fine for common adjectives, but how do you say "like a cabin"? I ended up writing "A room can be cabinoid." My code tends to fill up with strange semi-nonsense words in this way.
• Something similar to the inner platform effect can occur. There are a lot of special-purpose pieces of syntax for entities such as transparent containers. This is fine if you work with what's supplied. If on the other hand you want to create fundamental, low-level effects that the language designers hadn't thought of, you can get into terrible kludgy knots. I had a lot of trouble with a game where I tried to start the player in darkness, and I found myself constantly fighting against the built-in rules for the scope of vision.
• You can write libraries to achieve effects and make those effects portable from one game to another - for instance, there's a much-used library for dealing with opening and closing objects that have locks on. My workflow seemed often to follow this pattern:

1. Begin writing a game.
2. Realise a special effect is needed.
3. Begin writing a library to deal with it.
4. Several days pass. Continue trying to debug the library so it works in every imaginable situation.
5. Give up. Begin a new game.

I found Inform 7 delightful, but was almost entirely unproductive with it - I never got a game written to a standard where I'd let it out in public. This was alright because writing in Inform 7 is itself a lot like playing a text adventure, in the classic guess-the-verb idiom. It was five years ago that I did most of my dabbling with Inform; if I began again (as I suddenly feel the urge to) I could probably supply you with a longer and more detailed rant about it.  Card Zero  (talk) 19:50, 27 December 2011 (UTC)

Probabilities of extremely rare events

I can't find it now but I thought I saw something in one of the list of open problems (can't remember if it was the list for math, philosophy or science) that contained an entry for assigning probabilities to extremely rare events, such as events that haven't been observed yet. I thought an example was assigning a probability to the sun won't rise tomorrow. Does this ring a bell for anyone? RJFJR (talk) 19:34, 14 January 2012 (UTC)

It definitely sounds like an appropriate example, as the number varies substantially depending on whether you live in Fairbanks. Wnt (talk) 19:56, 14 January 2012 (UTC)

Assigning probabilities to events that haven't happened yet... I don't think this is an open problem in mathematics or statistics. I think this is a shortcoming of the way we educate people about probability. Our article, Probability theory, lays out the formalisms that are needed to calculate probabilities; in reality, there are a lot of prerequisite pieces of information that must be known a priori to make a meaningful estimate of the probability of an event. In engineering, we use Bayesian estimation when we are unsure of the prerequisite knowledge... in a sense, quantifying our uncertainty about our estimates. But even still, the best Bayesian algorithm cannot calculate probabilities for events outside of the domain it is designed for.

In a lot of science fiction, characters severely abuse the terminology of probability for dramatic effect: C-3PO famously quotes the odds for "successfully navigating an asteroid field is approximately 3,720 to 1." While it may make for exciting storytelling, his statement is entirely meaningless! Probability does not apply to such a statement! How many ways can we tear this quote apart? Natural language processing and computational semantics - what does "success" mean? For that matter, what does "asteroid field" mean? Certainly, the odds should be different in a "less dangerous" asteroid field! But C-3PO doesn't say "the odds of exiting this asteroid field..." - a stunning display of linguistic imprecision to preceed such a precise numerical conclusion! From the standpoint of probability, it's pretty meaningless to "calculate odds" for sophisticated behaviors and phenomena; nor will it translate ambiguous human language expressions into precise quantifiable results. That's just not what probability does, and I don't think future probability researchers will "solve" this. The only "open problem" here is, how do we educate people about the way probability really works, so that they can correctly and effectively use it to inform their decisions when it actually is useful. (Like, "what's the probability of winning money while gambling?" Sadly, while this is actually an easy problem to calculate odds for, surprisingly few gamblers use that information to make smart decisions). Nimur (talk) 20:22, 14 January 2012 (UTC)

Well, there are methods for doing this. If you know the constituent probabilities, you can figure the final probability, as in the Drake equation. In your example, if you can estimate the probabilities of all the different ways the Sun could fail to rise in the morning, then you could get the total probability. StuRat (talk) 21:22, 14 January 2012 (UTC)

As demonstrated at Chernobyl and Fukushima, for example. Wnt (talk) 23:04, 14 January 2012 (UTC)

At Fukushima, they seemed to have made an error is assuming that the plant failing, the power supply off the electrical grid failing, and the diesel backup generators failing were all independent events. So, if you figure each of those has a 1/1000 chance, you then get a 1 in a billion chance of all three happening at once. The reality, though, is that any quake large enough to severely damage the reactors would likely also take out the grid and backup generators. StuRat (talk) 23:22, 14 January 2012 (UTC)

"oops, didn't think of that" (tm) ;-). Someone calculating might have missed the relationship between the factors. In all, they didn't think of the probability of a higher than estimated tsunami wave. Electron9 (talk) 14:39, 15 January 2012 (UTC)

There is also a finite probability for you to arise out of thin air, then experience the present moment you are experiencing now, and then vanishing into thin air again.Count Iblis (talk) 00:31, 15 January 2012 (UTC)

Name of set

The Abel-Ruffini theorem article says "The theorem says that not all solutions of higher-degree equations can be obtained by starting with the equation's coefficients and rational constants, and repeatedly forming sums, differences, products, quotients, and radicals (n-th roots, for some integer n) of previously obtained numbers."

What do you call the set of numbers that are statable by a finite number of sums, differences, products, quotients and radicals of integers? Is there a common name for this? RJFJR (talk) 16:37, 7 September 2012 (UTC)

"Numbers defined by radicals"? — Quondum 18:20, 7 September 2012 (UTC)

Sounds like irrational numbers, to me, unless we include roots of negative numbers, in which case we have complex numbers. StuRat (talk) 18:29, 7 September 2012 (UTC)

They will be irrational, but not all irrational numbers fit that description. The square root of two, for instance, is irrational but can be described in terms of radicals (I just described it that way). --Tango (talk) 22:30, 8 September 2012 (UTC)

Shouldn't your example be an irrational number which can't be described in terms of "repeatedly forming sums, differences, products, quotients, and radicals" to prove your point ? I would think any irrational number could be defined in that way, if we allow for an infinite series. However, when adding the restriction that it be a finite series, then you may well be right. StuRat (talk) 00:40, 9 September 2012 (UTC)

There are more irrationals (aleph1) than there are formulas constructable in a finite number of symbols. I was wondering if they might be related to the computable numbers. RJFJR (talk) 18:44, 7 September 2012 (UTC)

Just have to jump in here — there are $2^{\aleph _{0}}$ irrationals. This may or may not equal $\aleph _{1}$ — the statement that these are equal is the continuum hypothesis, and its truth value is not known.

(But it is certainly true that there are at least $\aleph _{1}$ irrationals, and that's a possible reading of your claim, so apologies if that's what you meant.) --Trovatore (talk) 20:32, 7 September 2012 (UTC)

Nope. Pi is a computable number, but not a number defined by radicals (the latter set is presumably a proper subset of the former). — Quondum 19:05, 7 September 2012 (UTC)

You're right. And I now see where you liked Numbers defined by radicals to and that is the answer. Thank you. RJFJR (talk) 20:24, 7 September 2012 (UTC)

"The maximal solvable extension of Q", or "Q^solv" are names. You might have been thinking of constructible numbers which form a subfield, not computable numbers.John Z (talk) 20:55, 7 September 2012 (UTC)

I suspect that "Numbers defined by radicals" is a strictly informal term (perhaps "Numbers contructible from radicals" would be better). John's suggestion would be unambiguous (though I'd have to rely on him that it is in fact the same set; for example, there are solutions to the cubic and quartic equations that I'd assume are in Q^solv but are not constructible from only real radicals of real rumbers and integers). — Quondum 06:33, 8 September 2012 (UTC)

I thought it was called the surd field? Huh, that's red. I know I've seen it somewhere. --Trovatore (talk) 08:40, 8 September 2012 (UTC)

Surd field sounds like a good, snappy, short name, but a quick google seems to show that it used for what we are calling constructible numbers, and should probably redirect there. Quondum, I think you are referring to the fact that the solutions to say a rational cubic with 3 real roots may involve radicals of complex numbers, but by the cubic & quartic formulas they sit in Q^solv. Abel-Ruffini just says that Q^solv is strictly smaller than Q, the algebraic closure of the rationals, the Algebraic numbers, and in particular the roots of most equations with degree bigger than 4 are not in Q^solv. Galois theory identifies extensions with solvable Galois group with ones definable by radicals.John Z (talk) 21:00, 8 September 2012 (UTC)

John, yes, that is what I meant. I'm a bit out of my depth here, but it sounds like you're saying that a cubic with 3 real roots is expressible using radicals (by which we mean here real radicals of real numbers, starting with integers), which I was under the impression is impossible in general. I suspect that solvability is critically dependent on the field (R or C). For example, x² + 1 is an irreducible element over R, but is factorizable over C, and related subtleties may affect the interpretation of Galois theory. Or something like that – as I said, this is a bit beyond me. — Quondum 23:20, 8 September 2012 (UTC)

No, you are right, you can't always get all the roots of a cubic with three real roots by only using real radicals of real numbers. You may have to take roots of complex numbers, but that is OK since Q[i] for instance is an extension with a solvable (abelian, even cyclic) galois group; you get it by taking radicals. When we have enough roots of unity in the base, cyclic extensions - ones with cyclic galois group - correspond to taking an nth root of something in the base. Solvable extensions, ones with solvable galois groups correspond to taking iterated radicals. The maximal solvable extension is built up by taking all the iterated radicals, as RJFJR wants. Take all the roots of stuff in Q. Adjoin them to Q & you get some field. Then take all the roots of stuff in there, and go on ad infinitum.

So to get the solution of such a cubic, you can think of taking an extension adjoining i, or the square root of some negative number (given in the cubic formula) & then take some cube root of something in that extension to get the solution of some cubic using the cubic formula. The imaginary parts can cancel out and you land back in R, but to write the solution using radicals, taking them in fields not embeddable in R is necessary.

Another interesting & even more important, probably, subfield of Q^solv is Q^ab, the maximal abelian extension of Q, the biggest extension of Q with abelian galois group. It is a real, non-obvious theorem, the Kronecker–Weber theorem, that this is the same field as that gotten by adjoining all roots of 1, the same field as taking all Cyclotomic fields together.John Z (talk) 00:05, 9 September 2012 (UTC)

Name of Game?

There was a game I remember from middle school where one player selected a four digit number and the other player guessed a number and was told how many digits were in the correct place and how many were the right digit but in the wrong place. We called it bullseye because the right number ion the right place was called a bullseye (and in the wrong place was called a hit.) Does anyone know what this game is called? (I want to see if I can find a discuss of strategies online.) Thanks. RJFJR (talk) 16:05, 18 November 2012 (UTC)

Bulls and cows. -- Finlay McWalterჷTalk 16:15, 18 November 2012 (UTC)

Never knew that. I knew it as Mastermind. Mingmingla (talk) 18:16, 18 November 2012 (UTC)

Invicta Plastics (on whom we don't have an article!) always used to get very annoyed if any publication missed out the space ("Mastermind" rather than "Master Mind"). Cf "Biro". Tevildo (talk) 19:03, 18 November 2012 (UTC)

I would guess that "Mastermind", without the space, can't be copyrighted, being a single English word. StuRat (talk) 23:36, 18 November 2012 (UTC)

I would guess that copyright is completely irrelevant; this would be a trademark issue, and quite certainly single English words can be trademarked. Your confusion may be that descriptive English words cannot be trademarked (at least under US law.) So, I couldn't trademark "MILK" for the brand name of my bovine product. However, I could very well trademark "MILK" for my line of footwear. --jpgordon^{::==( o )} 02:15, 19 November 2012 (UTC)

I had thought you were describing Mastermind. Loved that game. μηδείς (talk) 22:53, 18 November 2012 (UTC)

Very similar to what I remember as "bagels". WP has bagel (game), which redirects to a page that describes it. --Trovatore (talk) 02:19, 19 November 2012 (UTC)

Power Plant Efficiency

Consider a power plant running on petroleum. The fuel has a certain amount of chemical energy and it produces a certain amount of electrical energy. How would I find an estimate for its efficiency? (It doesn't have to be very accurate, I just want to compare it to the efficiency of a car's engine... which I also haven't estimated yet. All I've got so far is the thermodynamic efficiency based on temperature of the furnace versus ambient temperature and I don't think that is going to be a good estimate.) Thank you. RJFJR (talk) 00:32, 3 September 2013 (UTC)

Typical diesel engine generator sets run at about 42 to 45% overall thermodynamic efficiency. You can verify this by going to manufacturer's or dealer's websites (eg Caterpillar) and downloading data sheets for any model of your choice. This applies over the range for small portable gensets to huge power stations. Coal fired and oil fired steam turbine power stations run at somewhat less efficiency, especially older power stations, but the fuel (coal or heavy bunker oil) is much cheaper.

Typical gasoline car engines run at around 22 to 27% thermodynamic efficiency at best throttle setting. Diesel engines in power generation service are considerably more efficient than car engines because 1) they operate at higher compression ratios (typically 15:1 vs 9:1), they do not thottle the intake air, and because they operate at a constant RPM, the design can be optimised for that RPM. Also, turbo charging, which can only be applied to a limitted extent set by detonation on a gasoline engine, can be applied to a diesel engine to a much larger degree limitted only by mechanical and thermal stresses. By recovering heat energy from the exhaust and putting it to use, turbocharging raises thermodynamic efficiency as well as power output. A minor factor: The combustion temperatures in a gasoline engine are higher, especially at part throttle, because the combustion is stochiometric. A diesel engine operates with excess air. The higher combustion temperatures in gasoline engines mean a higher proportion of heat lost to the coolant, lowering efficiency.

On light loads, the efficiency of a diesel engine falls off not as bad as it does for a gasoline engine (because the intake air is not throttled, and because combustion tempertures go down).

However, if a large gasoline engine is designed to run only at a specific optimum RPM, no expense is spared, and is operated by trained personell, its efficiency can approach that of a diesel engine. For example Word War 2 vintage Merlin and Pratt & Witney aircraft engines.

58.170.175.173 (talk) 01:41, 3 September 2013 (UTC)

45% efficiency for a diesel generator sounds high, but are you only looking as far as the output terminals of the generator, and neglecting losses in transformers and transmission and distribution? Edison (talk) 02:16, 3 September 2013 (UTC)

Correct, the figure applies only to the extent of the generator terminals. Losses in transmission and distribution can be any sort of value and I assumed the OP didn't want it included. For example, a genset in use at a mine site will have only simple local distribution, and distribution losses may be only 1% or less. But a municipal power station feeding a state-wide grid will encounter transmission and dustribution losses very much greater. For this reason, electric automobiles recharged from the electricity mains are rarely a global carbon advantage, even though their internal efficiency may be 90% or better, or 80% if you include the losses in the charger. For the figure for gasoline engines I gave, it applies to to mechnical output at the flywheel, and does not include losses in the gearbox and differential. 58.170.175.173 (talk) 02:29, 3 September 2013 (UTC)

2D shell theorem?

Shell theorem says it applies to spherically symmetric objects. If I limit it to two dimensions does it apply to radially symmetric objects? (I can't write the problem in a form I can find the integral for.) RJFJR (talk) 21:29, 7 September 2013 (UTC)

There is a version of the shell theorem that holds in any dimension, but with the appropriate Newtonian potential. In three dimensions, this is a 1/r law (for the potential) or equivalently a 1/r² law (for the force). In two dimensions, on the other hand, it's a log(r) law (for the potential) or equivalently a 1/r law (for the force). (In n≠2 dimensions, the potential is $Cr^{n-2}$ for some constant C depending only on the dimension.) You can get from the three dimensional to the two dimensional result by dimensional reduction (extend a two dimensional body to an infinite cylinder in three dimensions by adding a z axis). Hope this helps, Sławomir Biały (talk) 00:16, 8 September 2013 (UTC)

Thank you very much. RJFJR (talk) 01:44, 8 September 2013 (UTC)

Why does salt amplify flavors in food?

When you add anything else to food it just makes the dish taste more like whatever you added yet salt makes other things taste more strongly, why is that?Bastardsoap (talk) 12:50, 8 September 2013 (UTC)

I'm not entirely sure that it does. However one suggestion I've seen in a few cook books is that salt pulls liquids from inside of cells to the surface by osmosis and that this brings more flavor to the surface where it's more easily tasted.

Of course it's not just salt, Monosodium glutamate (MSG) has a reputation for enhancing whatever flavor the food already has - but that too is a somewhat dubious claim because MSG has an innate umami flavor of its own. SteveBaker (talk) 13:10, 8 September 2013 (UTC)

Wouldn't sugar have an equal osmotic effect in equal concentrations?Bastardsoap (talk) 13:17, 8 September 2013 (UTC)

Perhaps it does? We add it to foods in similar ways. SteveBaker (talk) 13:42, 9 September 2013 (UTC)

I found National Center for Biotechnology Information - Taste and Flavor Roles of Sodium in Foods: A Unique Challenge to Reducing Sodium Intake which says; "Added salt improves the sensory properties of virtually every food that humans consume, and it is cheap. There are many reasons for adding salt to foods. The main reason is that, in many cases, added salt enhances the positive sensory attributes of foods, even some otherwise unpalatable foods; it makes them “taste” better. For people who are accustomed to high levels of salt in their food, its abrupt absence can make foods “taste” bad." It continues; "One understood mechanism by which sodium-containing compounds may improve overall flavor is by the suppression of bitter tastes.". Alansplodge (talk) 13:39, 8 September 2013 (UTC)

Suppression of bitter tastes is not a mechanism, doesn't tell you anything about how it does thisBastardsoap (talk) 15:51, 8 September 2013 (UTC)

I'm almost certain that McGee will have something to say on this subject in On Food and Cooking (how much detail he will go into I cannot say - it's a big book, but the guy has a lot of ground to cover). I will have a look in my copy when I get home in about 8 hours. If I don't post back here within 12 hours feel free to bug me on my talk page because that will mean I've forgotten. Equisetum (talk | contributions) 14:17, 9 September 2013 (UTC)

Teaching myself General Relativity

I am thinking about teaching meyself GR with the only the internet and maybe a few texts I can buy in an ebook format and no expert guidance. Is this a achivable goal? How much time should I set aside for it? And what resources (Ideally available online on a digital format) would you recomend for it?Diwakark86 (talk) 15:28, 7 March 2014 (UTC)

This depends heavily on your background. Are you familiar with linear algebra and calculus? If so, you should be able to teach yourself basic GR, albeit with difficulty. Check out Introduction to General Relativity by Lewis Ryder and Leonard Susskind's lecture series at Stanford University: [13]. --Bowlhover (talk) 16:03, 7 March 2014 (UTC)

The answer to that question is going to depend a lot on where you're starting from, and where you're hoping to get to. MIT offers an open courseware version of their course in general relativity 8.962, which I expect would give a reasonable working knowledge of the topic. If you were to actually take the course, you'd be looking at three hours per week of lectures, times fifteen weeks, plus probably at least as much time spent on assignments and homework to try to apply what you had learnt—call it a hundred-plus hour commitment all told.

However, that presupposes that you are prepared to take a graduate-level course, and that you already have a reasonably firm grasp of the prerequisite material. From the syllabus,

The course catalog lists Differential Equations (18.03), Linear Algebra (18.06), and Electromagnetism II (8.07) as prerequisites. Students should also be familiar with Lagrangians and action principles, Green's functions, and numerical analysis (some homework assignments require the numerical solution of systems of differential equations).

There's some pretty heavy mathematical lifting involved in GR. (Note that the prerequisite courses specified each have their own list of prerequisites as well.) There's a lot of foundational knowledge that you would be expected to have to build on. You haven't specified what level of knowledge and experience you're coming in with, so it's hard to say how long it would take you to get up to speed.

The other side of the question is what you are hoping to do with it. General relativity is something that physicists can study and work with (and argue over) for entire careers; there's a very, very long road between knowing something about GR and knowing most of GR. TenOfAllTrades(talk) 16:12, 7 March 2014 (UTC)

Here are: a simple introduction, a too-simple introduction and several videos about GR. 84.209.89.214 (talk) 16:58, 7 March 2014 (UTC)

zeroes of infinite sums

Can someone refer me to some material on how to find the zeroes of functions that are defined as infinite sums? RJFJR (talk) 23:18, 22 April 2015 (UTC)

I don't think there is any general method. Can you give a little more context? Are you looking for exact solutions, or approximations within some tolerance, or approximations within an arbitrarily small tolerance? Are the sums power series or trigonometric series or something else? --Trovatore (talk) 23:27, 22 April 2015 (UTC)

It seems like you try to decide Riemann Hypothesis, don't you? HOOTmag (talk) 23:33, 22 April 2015 (UTC)

Assuming that you have uniform estimates on the truncation error (e.g., for a uniformly convergence series), you can use the method of bisection to locate individual zeros. In more favorable cases, standard numerical methods like Newton's method can be used, but one needs to be careful that the series converges in an appropriately strong sense. Sławomir Biały (talk) 23:39, 22 April 2015 (UTC)

A power series can be treated like this. Truncate the series and compute the zeroes of the resulting polynomial by the the Durand-Kerner method. Bo Jacoby (talk) 09:17, 23 April 2015 (UTC).

That result is probably not useful for the full series, since analytic functions in general need not have roots at all, such as with the exponential function, nor have a uniform limit for the position of the zeros.--Jasper Deng (talk) 09:08, 24 April 2015 (UTC)

The result is useful when the series converges around a root. Bo Jacoby (talk) 07:02, 24 April 2015 (UTC).

I was hoping for an answer like "read chapter 5 of book XYZZY for a general overview". I'm not sure what is knowable. They tell me there is a zero to zeta around .5 + 14.***i (or something) but I don't know how they found it. And when I try to think about finding the zeroes of complex valued functions of a complex argument my intuition gets confused. I think you pointed me in the right direction: I need to go back and look in my old numerical analysis book about how if you truncate the series you can bound how close the zero is. Thank you. RJFJR (talk) 17:47, 23 April 2015 (UTC)

For the zeta function specifically, the complex argument of zeta is under control on the critical line, so the problem of finding zeros is effectively reduced to finding zeros of a single real function. See Titchmarsh "The Zeros of the Riemann zeta-function", 1935, Proceedings of the Royal Society, Vol 151, No 873 pp. 234-255. Parts of that paper are readable. Sławomir Biały (talk) 20:50, 23 April 2015 (UTC)

Our Z function and Riemann–Siegel formula and links therein may help, and they cite how people found such zeros. The Z function is rigged to be real on the critical line by the functional equation, so intuition won't get so confused. :-)John Z (talk) 06:05, 25 April 2015 (UTC)

Thank you, everyone. (I think I need to get out my old text books and review some.) RJFJR (talk) 22:54, 25 April 2015 (UTC)

Neural network sufficiency

Universal approximation theorem

Impossibility fallacy

By my bad luck or by some other cause, I have many times seen and heard people dismissing ideas or designs on the basis that "if this could be done this would have been done already", or "this has not been done, therefore this can not be done". What is the name of this fallacy? I have read our list of fallacies but I haven't found a close enough match. Did I miss it? What's the proper name of this fallacy? Thanks in advance, Dr Dima (talk) 04:52, 3 August 2015 (UTC)

Max Beerbohm came close to this when he said: Anything that is worth doing has been done frequently. Things hitherto undone should be given, I suspect, a wide berth. -- Jack of Oz ^{[pleasantries]} 05:56, 3 August 2015 (UTC)

It's perfectly rational to have less confidence in a claimed discovery if it's something that would likely have been discovered earlier if it were true. -- BenRG (talk) 06:17, 3 August 2015 (UTC)

(It's also rational to put less trust in someone's claims on learning that they're a politician, even though that's called "argumentum ad hominem", and to be more trusting of a physicist's claims about physics than a non-physicist's, even though that's called "appeal to authority". So it is still possible that the hasn't-been-done-before argument appears on lists of fallacies under some name, since they are bogus anyway. Someone should come up with a nice Latin name for the belief that it's wrong to pursue a line of argument that appears on these lists.) -- BenRG (talk) 07:18, 3 August 2015 (UTC)

We do have it. Faulty generalization is the term. It is most likely true of a sample that most inventions fail uniqueness. Yet we know the population has invention. That the sample doesn't reflect the population is a truism in statistics. Or perhaps more understandably, the population of all things exceeds the sample of known inventions. It is a "faulty generalization" to claim all things is bound by all known things. --DHeyward (talk) 06:53, 3 August 2015 (UTC)

Is there actually anyone who believes that claims of new discoveries are false because nothing remains to be discovered? I think "an extraordinary claim requires extraordinary proof" is closer to what people mean when they say "this has not been done, therefore this can not be done". If you produce the unicorn you claim to have caught and it passes all their tests, then they'll believe you, but not before. This saying doesn't appear on lists of fallacies, but that's fine because it isn't a fallacy. -- BenRG (talk) 07:18, 3 August 2015 (UTC)

Agree, but if people mean it literally, then it is a logical fallacy. Supdiop (Talk🔹Contribs) 08:13, 3 August 2015 (UTC)

• It is not always a fallacy, because the reasoning can be valid if certain extra premises are added. When it is a fallacy, formally it is the fallacy of the undistributed middle. Looie496 (talk) 12:47, 3 August 2015 (UTC)

• Yes, if it is something seemingly obvious, then you would expect that somebody would have tried it before. For example, if you could pour saltwater into a normal car engine and get it to run, somebody would have figured that out by now. On the other hand, there might be some new technology which could find a way to extract energy from saltwater (I'm not saying there is, just that we can't discount the possibility because it hasn't been done before). StuRat (talk) 16:17, 3 August 2015 (UTC)

This is really a matter of probability and perhaps of Occam's razor. Without additional information of some kind, if you are unsure of whether something could be done, and it hasn't - the odds are much higher that it can't be done than that it can. It's not certain though - so this is a statement that should be modified by the word "probably"..."If this were possible, it would probably have been done already". Occam's razor might also apply here - that's another tool of inexactitude that never the less proves useful. StuRat's example of running a car on water is a great example of that. It hasn't been done - and the laws of physics strongly suggest that it can't ever be done *BUT* there may be laws of physics of which we're currently unaware that might make it possible. Occam's razor says that the simplest explanations are the best - and it's certainly simpler to assume that water-fuelled cars are impossible (because physics forbids them) than it is to assume that they'll eventually be possible (because we'll discover new laws of physics to make it so).

SteveBaker (talk) 17:21, 3 August 2015 (UTC)

Density of solids at extreme pressures

Can someone point me to a graph or equation that describes what happens to the density of solids at extreme pressures? (The density of a solid is pretty constant at normal pressures but what about cases like the density of iron at the pressure of the center of the Earth?) RJFJR (talk) 20:53, 3 August 2015 (UTC)

The Center for Rock Abuse is probably the preeminent experimental rock-crushing laboratory in the United States; they reside in the Petroleum Engineering department at Colorado School of Mines. Here's a list of their research publications. If you're interested in more observational science, Earthquake and Volcano Deformation is a good book on solid mechanics as it pertains to the massive stresses, strains, and pressures of geological processes.

If what you really seek is details about iron in the center of the earth, the models are much more diverse and a lot harder to validate empirically: you can find lots of references in our article on the inner core. Almost everything we know about this region is deduced from teleseismic soundings of earthquakes: the density can be inferred by estimating the speed of sound at which earthquake P-waves propagate.

Nimur (talk) 21:24, 3 August 2015 (UTC)

School song question

(from help)

Can someone point me to the information on whether including the lyrics of school songs in articles about schools is appropriate? RJFJR (talk) 16:40, 5 September 2015 (UTC)

• @RJFJR: According to the WikiProject on schools, the lyrics of a school song should not be included on the school's article. Lyrics in the public domain can be placed on Wikisource and linked to in the article however. See WP:WPSCHOOLS/AG#WNTI for this information. --Stabila711 (talk) 17:15, 5 September 2015 (UTC)

Thank you. RJFJR (talk) 18:56, 5 September 2015 (UTC)

Can Audiopedia links be added? are they automatically added?

Can audiopedia articles be linked/templated into wikipedia articles? Is there a bot doing so?

I found Audiopedia videos of spoken wikipedia articles meant for the blind.

Audiopedia seems to be sponsored by the BBC. http://www.telegraph.co.uk/technology/news/8865357/BBC-to-open-vast-radio-archive-online.html

There is an Audiopedia user https://en.wikipedia.org/wiki/User:Audiopedia

here is an example wikipedia spoken recording. https://www.youtube.com/watch?v=vOgcIIy4mtw&ab_channel=Audiopedia

Informati:on https://www.youtube.com/channel/UCV63FScHnShoobfaENC8R_Q/about Description We provide a free service targeted to blind and visually-impaired internet users. Wikipedia is the largest database of knowledge ever known to mankind, and yet it is essentially inaccessible to individuals with limited vision. Note that all text is licensed under CC-BY-SA, and all images are also creative commons (various licenses).

Thank you,CuriousMind01 (talk) 16:24, 12 September 2015 (UTC)

Hey CuriousMind01. That YouTube channel is unconnected with Wikipedia, and it is a copyright violation of Wikipedia, so we would certainly never properly link to them, automatically or otherwise. However, the copyright issue could be fixed to give proper attribution to Wikipedia's authors under our licenses (they do make an attempt to comply at their about page, woefully short of the mark). Wikipedia already has spoken versions of articles, and, as of now, there are 1,165 in the category for them. We also have a project dedicated to producing them. I do see some advantages to having a YouTube channel for others. For example, any normal format can be uploaded to YouTube using a billion devices, whereas there are many hoops to jump through here, because of the requirements that the upload be in a free and open-source software codec and container (see Vorbis & Ogg). Also, even though a human's reading is almost always many times better than a program's, it can be tasked with creating them 24 hours a day and allow access for people where they don't have it now. But even if we concede that, it would be better to have such a program to do so here rather than linked to off-site. I would support setting that up but as with everything here, it requires someone willing to take the time and having the know-how to do it.--Fuhghettaboutit (talk) 17:05, 12 September 2015 (UTC)

Hi, Audiopedia doesn't seem to be in any copyright violation per the terms in: https://en.wikipedia.org/wiki/Wikipedia:Copyrights, because the content is offered by WP for free to all.

I think what they are doing is legal, creating computer generated spoken WP text articles, offered for free for use of the blind, and citing the WP article name and an image. It would be great if WP did the same, like you wrote it takes time and skills. Thank you, CuriousMind01 (talk) 18:25, 12 September 2015 (UTC)

Hi again CuriousMind01. As I said about that page "(they do make an attempt to comply at their about page, woefully short of the mark)". I actually linked for you the copyright policy page you linked back to me above, and have a quite a lot of experience in copyright enforcement, application and interpretation. I do think it's important for you to understand what the copyright issue is, so you, being involved and possibly in a position to help here – maybe even in some manner informing Audiopedia of the problem so they can become compliant and we could link their efforts – are armed with the knowledge to know what the problem actually is and how it can be fixed.

Wikipedia content is not "offered by WP for free to all". There are two basic problems with this statement. First, Wikipedia does not own the copyright to (the vast majority of) its content at all, its authors do, personally, whatever they contribute, so long as it is sufficiently creative to be subject to copyright protection. Second, most of that content is co-licensed under two free copyright licenses: the 1) CC-By-SA 3.0 Unported License, and under the GFDL, which, simplifying, require that copyright attribution be given to to the authors in a "reasonable manner" to comply with the licenses. We further agree by contributing, that such copyright attribution credit to us, the authors of an article, can be provided by (in addition to stating one or more free licenses they are reusing the content under), include a direct line notice of the page at this site where its page history is available, so that a person viewing the re-used content is informed of, and can easily and directly navigate to, the page being re-used and therefore can see the identity of the content authors in its history. This can be done by posting at the reuse site a) a hyperlink (where possible) or b) URL to the Wikipedia page or pages being re-used (emphasis added as this becomes important in the next paragraph), or c) a list of all authors, which you would find in the page history/ies (generally this last option is only done where a page has very few authors).

What this means in practice is that each one of the Audiopedia files needs a clear notice stating the license and saying what specific Wikipedia page its content comes from, by the methods I've outlined. This is not provided by vague notice somewhere that all text is "is licensed under CC-BY-SA". Every one of those videos is infringing on the copyright of the authors in the content of the page being read, and will be until a compliant full and direct notice is provided for the specific Wikipedia page by one of the methods I've outlined – it's really not all that difficult to comply but they don't come close. Best regards--Fuhghettaboutit (talk) 19:16, 12 September 2015 (UTC)

Thanks Fuhghettaboutit. Copyright is a complicated subject(to me).

Are these statements correct? For each Audiopedia Youtube video speaking a Wikipedia article,Audiopedia would have to state they are complying with these 2 licenses: 1. https://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License 2. https://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License and write the URL the wikipedia article which is being spoken (re-used).

State the intent of the spoken re-use is to assist the blind and visually impaired to make a use of Wikipedia articles, for free from Audiopedia.

Thanks again--CuriousMind01 (talk) 17:59, 13 September 2015 (UTC)

CuriousMind01, close but not quite. They would need to comply with at least one of those two license, they could select either or both. In either case, they would need to provide a link to the original page history, or the original Wikipedia page, which itself has a link to the history. A permalink to the version they used would be preferable. They would also need to be clear that their content is under the same license, and that people may use it on the same conditions. They would not need to state their intent, as Wikipedia's license are not in any way conditioned upon intent (they might want to, but that would be their choice). Indeed if they chose to charge for their services, Wikipedia's license would permit it if the above conditions were complied with.DES ^(talk) 18:26, 13 September 2015 (UTC)

Life expectancy in Medieval Europe

This claim intrigued me. Are there reliable sources for medieval life expectancy? Our article on longevity doesn't have pre-Victorian era stats, although it does make the excellent point that any such statistic would need to strip out infant mortality to have any value when assessing the claims about the Templars. --Dweller (talk) Become old fashioned! 14:07, 30 March 2016 (UTC)

• A 14th-century man in Halesowen, England who survived to age 20 could expect to live another 21-28 years, depending on social status. In the 15th century, this increased to 33 years after age 20 (i.e., 53 years of age total). Adult female mortality was greater because of death in childbirth and exposure to infections while caretaking for others. (see Gilchrist 2012)
• Various studies estimated the average lifespans for monks as: 29-30 years (Westminister Abbey); 33.12 years (primarily Christchurch Cathedral Priory, Canterbury), 31 years (some other houses) - apparently lifespan depended on the wealth of the monastery (Oliva 1998).
• McKitterick 2004 says that the records are better for men then they are for women and that "Fifty or fifty-five years was a lifespan readily attained by the greater and the powerful, who did not always take the best care of themselves. This would be true if kings or prelates ... and of fighting men active on the field of battle or in tournaments ... More telling still is the fact that, in 1194, an appraisal of the men at arms in the service of the king of France shows that 10 per cent of the sergeants were under twenty, 56 per cent were between twenty-one and thirty-nine, a further 20 per cent were in their forties, while 14 per cent were over fifty, each and every one of them still bearing arms."
• Butler 2014 writes: "the life expectancy of those in later medieval England was quite modest. For men who survived the perils of infancy and childhood, one might reasonably hope to reach ... around forty years of age. Because of the dangers of childbirth, women's life expectancy was even shorter. Archaeological data proposed an average date of death for adult women of around thirty-three."
  • Neutrality^talk 14:45, 30 March 2016 (UTC)

  That should be held up as the model Ref Desk answer: Loads of references, no personal speculation. Brilliant. --Jayron32 14:51, 30 March 2016 (UTC)

  Thanks! Neutrality^talk 14:55, 30 March 2016 (UTC)

Agreed, that's excellent, thank you. --Dweller (talk) Become old fashioned! 20:33, 30 March 2016 (UTC)

Growing Bismuth crystals

What is the best way of growing nice looking Bismuth crystals starting from the metal in 'shot' form?--178.100.75.110 (talk) 23:30, 10 June 2016 (UTC)

Google and Youtube are covered in instructions for these. You could have saved yourself a wait by going direct. Richard Avery (talk) 07:33, 11 June 2016 (UTC)

@Richard Avery: We shouldn't be looking to defer to search engines. They may serve up several sites, but which is best? And will those searches remain usable, will those sites remain in operation? The goal is to bring back the information and integrate it here, just as we do for encyclopedia articles and for the same reason. Someday Google is going to start charging and a lot of the world will lose access, the people who don't matter anyway but still would like to know. Wnt (talk) 15:02, 11 June 2016 (UTC)

Best method? Practice.

Bismuth crystal growing is great fun and low complexity for equipment, but the crystals grow in liquid phase bismuth just where you can't see them. So there's an awful lot about learning the best growth profiles (timing) by repeated experiment, rather than observation.

I'd also suggest an Indian grocers as a source of handy stainless containers in a range of sizes. Then get enough bismuth to work easily with - it's annoying to try and grow them in a teaspoon. A small electric hotplate is useful, but as the thermal mass is high you only need rough power control, not necessarily closed loop control of temperature. A non-contact IR thermometer is cheap and useful though. If you fancy a small electronics project, then PID controller modules are cheap (China via eBay) and that will make you a handy workshop hotplate with temperature control. Andy Dingley (talk) 09:39, 11 June 2016 (UTC)

template for citation not specific enough?

Is there an inline template for indicating that a foot note isn't specific enough for a person to determine what is being cited as a reference? RJFJR (talk) 18:10, 30 December 2016 (UTC)

See Category:Inline_cleanup_templates. There is {{where}} and {{when}} for example and many others. RudolfRed (talk) 18:15, 30 December 2016 (UTC)

Thank you. I went through the list again and didn't find quite what I was looking for but I was able to refine the citation. I'll keep a copy of your answer for future use. RJFJR (talk) 18:46, 30 December 2016 (UTC)

I'm having the same problem, and the closest I've found is {{Full citation needed}}. 71.41.210.146 (talk) 21:05, 30 December 2016 (UTC)

Tool to sort category by article size?

Is there a tool that will list the articles in a category sorted by size of the article? (I don't know of one but I'd feel silly if the only reason I never found it is because I never asked.) Thank you. RJFJR (talk) 16:09, 3 February 2017 (UTC)

I don't know such a tool. An incategory: search like incategory:"Jazz events" will display the size. It's not sorted but may be better than nothing. PrimeHunter (talk) 16:25, 3 February 2017 (UTC)

Hello @RJFJR:, PetScan has the ability to sort its output depending on article size (and to restrict the list with specified size limits). I just tested the sort feature with a small cat, and it seems to work fine. GermanJoe (talk) 16:30, 3 February 2017 (UTC)

Thank you! I'm glad I asked. RJFJR (talk) 18:08, 3 February 2017 (UTC)

Can hydrogen conduct electricity?

Science news had an article about Jupiter that said there is a theory that its magnetic field is caused by circulating electric currents in one of the planet's outer layers of molecular hydrogen. Does hydrogen conduct electricity? It does as a plasma but how about when it isn't ionized? Does it need a certain pressure? RJFJR (talk) 14:20, 28 June 2017 (UTC)

See metallic hydrogen. As is defining for a metal, this involves delocalized electrons (free to move) as a "cloud" within the metal, thus conduction. Yes, it takes a great deal of pressure. Andy Dingley (talk) 14:25, 28 June 2017 (UTC)

Is that the only time hydrogen would conduct? (No one has proved metallic hydrogen exists and it was proposed it might exist at the core of Jupiter but the layer described in the article is an outer layer so probably not sufficient pressure for metallic.) RJFJR (talk) 14:31, 28 June 2017 (UTC)

It is estimated that metallic hydrogen extend ~80% of the radius of Jupiter. That's fairly "outer" to me. Dragons flight (talk) 00:16, 29 June 2017 (UTC)

Here's a paper on the topic of metallization in Jupiter's atmosphere. Mikenorton (talk) 14:32, 28 June 2017 (UTC)

Thank you. RJFJR (talk) 14:42, 28 June 2017 (UTC)

If hydrogen is heated to a plasma (which some may say is not really hydrogen anymore because it is a different state of matter) that will conduct. As will any other element in a plasmic state. Aspro (talk) 21:57, 28 June 2017 (UTC)

But Jupiter's atmosphere isn't thought to be a plasma. Andy Dingley (talk) 22:20, 28 June 2017 (UTC)

• Ionic hydrogen H⁺ conducts in solution. μηδείς (talk) 00:09, 29 June 2017 (UTC) (surprised that's a redlink. Maybe it should redirect to acid?)
  • I think you may be looking for the Grotthuss mechanism? Double sharp (talk) 07:36, 29 June 2017 (UTC)
  • Hydron (chemistry) ; i made the redirect Gem fr (talk) 12:38, 29 June 2017 (UTC)

Citation tool

from help

Is there any tool for easily citing web pages, by just entering the URL?--Freshman404^Talk 11:38, 14 September 2017 (UTC)

Not exactly, but Refill and ProveIt both do something similar, as does the inbuilt RefToolbar. Yunshui ^雲_水 11:40, 14 September 2017 (UTC)

• Yes. Two good ones I've used are Yadkard and User:Ark25/RefScript#How to use the script. For the RefScript thing, use the old method of installation. Thanks. Lourdes 12:03, 14 September 2017 (UTC)

Pinging Freshman404... Lourdes 12:06, 14 September 2017 (UTC)

Freshman404 Not sure I understand the first comment "not exactly". If you are using the visual editor, and click on the cite button, then enter the URL, it can often create a reference. It isn't 100% but it's north of 90%. Referencing, which used to be a challenging task is now relatively easy in many cases. Tools such as refill a useful for cleaning up existing articles with improper references, but I wouldn't use it for for a new reference. Not only does the site automatically convert URLs, drop in an ISBN, PMID or DOI , and in many cases it will complete a reference for you. (Some people realize this, however there were some editors who are unhappy with the initial rollout of visual editor and vowed never to use it again. If anyone made that file they should try again because references along make it worthwhile. Plus, it handles tables nicely now.--S Philbrick(Talk) 14:42, 14 September 2017 (UTC)

In addition, if the URL is already saved as a reference it is ridiculously easy to fix. Click on edit to invoke the visual editor, click on the reference number, click on convert, click on insert and save. If the article has a half dozen or more I use refill but fewer than that is just as easy to let visual editor do the work.--S Philbrick(Talk) 14:59, 14 September 2017 (UTC)

@Sphilbrick: Thanks for your kind answer. I know that. I was looking for Yadkard, which "Lourdes" mentioned. Freshman404^Talk 15:00, 14 September 2017 (UTC)

As an example, I just improve six references in Jeanette Pohlen-Mavunga In less than a minute. (As a tip, if you have more than one reference to change start at the end.) — Preceding unsigned comment added by Sphilbrick (talk • contribs) 15:04, 14 September 2017 (UTC) --S Philbrick(Talk) 15:07, 14 September 2017 (UTC)

If Yadkard works for you, then great, but I looked at it and thought it seemed like more work than VE. Do you think I am missing something? What does Yadkard do that VE cannot do faster and easier? Serious question, if it is a useful tool, I'd like to use it, but my quick review suggested it may have been useful pre-VE, but is now redundant.--S Philbrick(Talk) 15:07, 14 September 2017 (UTC)

Convergence of Taylor expansion

I asked Wolfram Alpha to show me the Taylor expansion of x^.5 at 1 so I could check my math. But it included a region of convergence. Can someone tell me how to determine the region of convergence? RJFJR (talk) 23:45, 17 June 2018 (UTC)

@RJFJR: For one-variable Taylor series, the Cauchy–Hadamard theorem provides a straightforward formulaic way to determine the radius of convergence. In this case, we have a Taylor series given by ${\sqrt {x}}=-\sum _{n=0}^{\infty }{\frac {(2n-3)!!}{n!(-2)^{n}}}(x-1)^{n}=-\sum _{n=0}^{\infty }{\frac {(2n-3)!!}{(2n)!!(-1)^{n}}}(x-1)^{n}$ from which we clearly see that the limit superior of the nth root of the absolute value of the nth term is 1 as $n\to \infty$, yielding a radius of convergence of 1. This can perhaps more easily be demonstrated using the ratio test. Since we took the expansion about $x=1$, the result follows.--Jasper Deng (talk) 00:14, 18 June 2018 (UTC)

Longest User Talk pages

Is there a way to find the largest user talk pages on Wikipedia? Please {{ping}} me when you respond. --Jax 0677 (talk) 20:22, 18 July 2018 (UTC)

@Jax 0677: Does Wikipedia:Database reports/Long pages#All pages work for you? PrimeHunter (talk) 21:05, 18 July 2018 (UTC)

 Jax 0677: I ran a query for you, here, but you have already found the largest. Sam Sailor 21:58, 18 July 2018 (UTC)

• Reply - @Sam Sailor:, can you please teach me how to run such a query? --Jax 0677 (talk) 17:10, 19 July 2018 (UTC)

​Sure. Feed the following

SELECT
  page_title,
  page_len
FROM page
WHERE page_len > 600000
AND page_namespace = 3
AND page_title NOT LIKE "%/%"
ORDER BY page_len ASC;

into Quarry. Sam Sailor 18:02, 19 July 2018 (UTC)

multi column lists

{{div col|colwidth=20em}} {{div col end}}

Limits

I managed to find a page online that told me that lim n->inf (1-1/n)^n is 1/e but it doesn't have an explanation. Also I'd like to read more about this kind of limit. Can someone point me to some material on this? Thank you. RJFJR (talk) 18:16, 1 February 2019 (UTC)

See the last formula in Exponential function#Formal definition. The limit is an example of an Indeterminate form, specifically 1^∞. As such it can be solved be applying L'Hôpital's rule. --RDBury (talk) 22:48, 1 February 2019 (UTC)

It may be circular logic to use L'Hôpital's rule as the calculus itself is based on the above limit in part. Ruslik_Zero 08:25, 2 February 2019 (UTC)

True, you wouldn't use L'Hôpital's rule to prove the limit if you were trying to prove derivative formula's from scratch. But once you've established derivative formulas then L'Hôpital is fair game and probably the easiest method for evaluating an indeterminate form, especially if you didn't bother keeping track of all the ingredients that were used to prove those derivative formulas. The same sort of issue comes up with derivatives of trig functions and I've had more than one frustrated Calc I student who didn't understand why they had to learn the squeeze theorem to find the limit of sin x/x when it's so much easier to use L'Hôpital. In any case, the OP just asked for some links, not proofs, and I think L'Hôpital is still relevant. --RDBury (talk) 12:20, 2 February 2019 (UTC)

If you're familiar with the Taylor series for exp(x), you know $e^{x}=1+x+{x^{2} \over {2!}}+\cdots$ and if x is near zero, you can ignore the higher order terms. So you get $e^{x}\approx 1+x$ when x is small. Substituting $x=-1/n$, that means $e^{-1/n}\approx 1-{1/n}.$ Raising both sides to the nth power, you get $e^{-1}\approx \left(1-1/n\right)^{n}$ q.e.d. 173.228.123.166 (talk) 10:41, 2 February 2019 (UTC)

• you can ignore the higher order terms is faulty logic. The correct calculation needs to take care of the residual: $e^{x}\approx 1+x+O(x^{2})$ (see big O notation), hence $e^{-{\frac {1}{n}}}\approx 1-{\frac {1}{n}}+O({\frac {1}{n^{2}}})$, hence $\left(e^{-{\frac {1}{n}}}\right)^{n}\approx \left(1-{\frac {1}{n}}+O({\frac {1}{n^{2}}})\right)^{n}$. The right hand side of that latter equation is equivalent to $\left(1-{\frac {1}{n}}\right)^{n}+O({\frac {1}{n}})$ where the residual goes to zero as n grows large, which means we are in the clear, but it is not always necessarily the case when manipulating Taylor series.

For an example of what the faulty logic may lead you, consider ${\frac {e^{2x}-2x-1}{x^{2}}}$. Its limit as x goes to 0 is 1, but if you had truncated the Taylor series to $e^{2x}\approx 1+2x$ "because we can ignore the higher order terms", you would have erroneously deduced the limit was 0. Making the computation with the residual yields ${\frac {e^{2x}-2x-1}{x^{2}}}={\frac {1+2x+O(x^{2})-2x-1}{x^{2}}}=O(1)$, and the fact that the residual does not tend to 0 as x goes to 0 in the end results shows you need more terms in the Taylor series. Tigraan^{Click here to contact me} 14:03, 2 February 2019 (UTC)

Thank you everybody. (I never paid enough attention to those 1^inf indeterminate forms. I'll go study up on it now. And the calculations using big-O notation is great to see.) RJFJR (talk) 00:38, 3 February 2019 (UTC)

Calculations of observable universe

Is there an article here (or external reference) explaining the math behind current observable universe radius? I tried to use Hubble's law as a linear approximation and found that value should be 37 bly, didn't get similar result of 46.1 bly. I may be missing other information on calculation. Thank you, Almuhammedi (talk) 17:30, 26 February 2019 (UTC)

Does Observable universe#Size help? It doesn't mention Hubble's law, but discusses other models and calculations to determine the size of the universe. --Jayron32 17:44, 26 February 2019 (UTC)

Unfortunately, it still doesn't explain how the 46.5 was achieved mathematically. Almuhammedi (talk) 04:05, 27 February 2019 (UTC)

What you're looking for is in this book reference: [14], which shows how to calculate the distance to a light source based on redshift, scale factor and Hubble's constant. The book actually shows the derivation of this relationship in a variety of general relativistic models, and this formula belongs to the flat version of the FLRW metric. This relationship depends on assumptions about the nature and history of the universe, but there is considerable agreement that the universe looks like flat FLRW back to the time of last scattering. Someguy1221 (talk) 04:42, 27 February 2019 (UTC)

note:Noncommutative logic

Martian core

Composition of Mars says Mars has a molten iron core but no convection. Any idea why it wouldn't have convection if the core is molten? Isn't it cooling so it should have a temperature gradient? RJFJR (talk) 00:58, 19 March 2020 (UTC)

I've never looked into this with planets, but I am familiar with stars. I assume they're somewhat similar. Heat can be moved out by convection, by radiation (in stars) or by conduction (in planets). As heat moves out by radiation/conduction and the core cools, the temperature gradient drops. If the temperature gradient is less steep than adiabatic, the medium is stable and no convection will happen, although cooling will continue by radiation or conduction. Also see lapse rate, which is about gasses, but the same applies to liquids. The adiabatic lapse rate for liquids is much closer to zero than that for gasses. PiusImpavidus (talk) 10:54, 19 March 2020 (UTC)

This paper by Stevenson in 2001 suggests that there was convection in Mars' core at an earlier stage in its evolution - see Figure 3 in that paper. Mikenorton (talk) 16:56, 19 March 2020 (UTC)

Here's the cool (*rimshot*) article for this general topic: Earth's internal heat budget. (Focuses on Earth, but there's some discussion of other planets.) --47.146.63.87 (talk) 18:46, 19 March 2020 (UTC)

Pizza Mexicana

Pizza Mexicana with ham or pepperoni, pineapple and jalapeño peppers is a popular style of pizza in the Nordic countries. How similar is it to pizza that is actually eaten in Mexico? JIP | Talk 11:50, 27 April 2020 (UTC)

The idea of putting tinned pineapple on pizza is credited to Sam Panopoulos, a Greek-Canadian, in Ontario in 1962 (so maybe Pizza Canadensis?). Alansplodge (talk) 12:08, 27 April 2020 (UTC)

What makes it a pizza "Mexicana" in the Nordic countries is the jalapeño peppers, as Mexican cuisine is associated with spiciness. Is this true also for genuine Mexican pizza? JIP | Talk 12:17, 27 April 2020 (UTC)

It is (so far as I can tell) though, a universal phenomena for every culture to say "this food comes from this foreign culture" and it either has nothing to do with that culture or is only vaguely related. Mexicans sometimes do put jalapenos on their pizza, but the only things listed in that article that I couldn't order on a pizza back in South Carolina were chorizo and tripas. Ian.thomson (talk) 12:45, 27 April 2020 (UTC)

By the way, see below. Mexicans don't particularly put anything on their pizza. The paragraph you cite is referenced to a cookbook recipe for Taco Bell's Mexican Pizza, not to any native Mexican-made pizza. I wouldn't take anything said in that paragraph as referring to anything about Mexicans and their pizza-eating habits, rather to an American fast food chain creating a pizza-like dish with Americanized "Mexican"-type ingredients. --Jayron32 13:25, 27 April 2020 (UTC)

While we're going down this rabbit hole, in Mexican cuisine, there is a dish with pork, hot peppers, and pineapple known as tacos al pastor, which is based on the Eastern Mediterranean style of food known as shawarma/döner kebab/gyros. It's interesting that there's both an Eastern Med (Greek/Lebanese/etc) connection and a pineapple connection, through pineapple is not otherwise well represented in either the cuisine of Mexico or of the Eastern Med. --Jayron32 12:22, 27 April 2020 (UTC)

Also, there's really not a "genuine" Mexican pizza. In Mexico, any pizza that you're likely to get will be from American chain restaurants (Dominos Pizza, Papa Johns, Pizza Hut, etc.) and the like, they don't really have a native "pizza culture". While Wikipedia has a tiny section on Mexican pizza, what this really is is an American invention that consist of putting typical Mexican ingredients, like salsa roja and taco-seasoned ground beef (which is itself an American approximation of actual Mexican cuisine, and mostly unknown in Mexico) on a pizza. There's not a typical "Mexican pizza", there's whatever random Mexicany-type ingredients the restaurant that made it decided to put on it (and, those ingredients generally don't include pineapple). --Jayron32 12:31, 27 April 2020 (UTC)

Right, it's fusion cuisine. Similarly, American Chinese cuisine has little to do with food actually consumed in China, even though it's often referred to as "Chinese food" in the U.S.; it was created by Chinese immigrants to the U.S. who adapted some elements of Chinese cuisine to American tastes. For that matter, the global idea of "pizza" is itself an Italian-American dish that is loosely based on traditional Mediterranean flatbreads. In turn, American culture exported it across the world and then other cultures put their own twists on it. Good old cultural exchange! Tex-Mex is another good example. --47.146.63.87 (talk) 21:54, 27 April 2020 (UTC)

"...the global idea of "pizza" is itself an Italian-American dish that is loosely based on traditional Mediterranean flatbreads." A bit of US-centrism there. In Australia, the first pizza shops were established by Italian immigrants who had come directly to Australia without going via the US. I doubt they knew much at all about what was happening in America. Its culture had not begun to dominate in those days. HiLo48 (talk) 23:54, 27 April 2020 (UTC)

I'd also note that even if something is a an American fast food chain, what it served in a certain country can often be a complicated mix of American influence and local influence, depending somewhat on the management and freedom allowed. What people expect from the restaurant is likewise likely to be a complicated mix of what they expect from what kind of food, which will be influence by its American origins, and their local palates. Cost and east of production also comes into play.

For example, I'm fairly sure the reason Domino's in NZ and Australia have butter chicken inspired pizzas is not because someone in the US thought that's a good idea, it's because managers in NZ or Australia most of who are probably born in NZ/Australia thought they could come up with something which would be popular with the Kiwi and Aussie palates. I believe this is probably also the reason for the common apricot chicken pizza. And while possibly the Domino's lava cake was invented in the US, I strongly suspect the idea for a durian one originated from someone (if not multiple people) in South East Asia. Likewise the sambal sauce was probably the idea of a Malaysian or maybe Singaporean [15].

And it's not like locally grown chains or restaurants aren't likely influenced by the norms influenced in part by the US either. Hell Pizza came from NZ. But they have the same influences from the US, from Italy, from Australia etc that US pizza chains here tend to have. They have more freedom, and operate far more upmarket, which affects what they offer but I'm unconvinced this means their pizzas are more "Kiwi" than Domino's or Pizza Hut.

Mexico may in some ways have a stronger influence from US managers and tastes given it's geographical proximity, still with supposedly 120 million pizzas in 2016 [16], most I'm fairly sure for locals and not American tourists, I would be surprised if there is no Mexican influence on what goes on pizzas in Mexico. This is not to say you could identify anything as being distinctly Mexican about pizzas in Mexico, but rather you also can't simply say it's just American influence or an American idea of what is Mexican. In reality both are surely at play with both Mexicans in Mexico and Americans having a role.

You get the same thing in other areas e.g. the Kiwiburger. Fried chicken including spicy fried chicken at McDonald's in Malaysia. Nasi Lemak McD. The season Prosperity burger at McDonald's in Malaysia and I think Singapore. Hot and spicy being a permanent menu item at KFC in Malaysia and some other places, and being hotter than the one you get in NZ (and I expect Australia). It seems there's currently no fish burger at KFC in Malaysia, but from what I gather, they've had various attempts and it's lasted a lot longer there than it did the US. (It seems Jamaica is possibly another place?)

I've even heard anecdotal reports of Nando's restaurants in NZ making the mistake of following the South African norms for what 'hot', 'medium' and 'mild' means, to the surprise of customers for who 'hot' means something like 'medium' or maybe even less in South Africa. There's also the interesting case of Kenny Rogers Roasters, which is dead in the US but survived in Malaysia with some presence in other parts of Asia.

Nil Einne (talk) 06:14, 28 April 2020 (UTC)

Classic Peanuts: what does S/w mean?

In a recent Classic Peanuts strip: Woodstock is typing as Snoopy dictates. "Kindest regards, Snoopy S/w". Snoopy walks away and Woodstock adds "Dictated but not read".

What does the "S/w" mean?

Thank you, RJFJR (talk) 21:44, 28 April 2020 (UTC)

Snoopy/Woodstock, meaning typed by Woodstock for Snoopy. Meters (talk) 21:55, 28 April 2020 (UTC)

Yes, this is how it used to be done when typing was considered a menial task that the boss should not waste his time on, but should have a secretary to do it. Normally the notation would show the full initials of boss and secretary, like RMN/rmw, but Snoopy and Woodstock both have one-word full names, so in their case it's just S/w. If the boss didn't bother checking the typed letter for correctness, the secretary might add "Dictated but not read". --76.71.6.31 (talk) 22:20, 28 April 2020 (UTC)

[17-joke gap] —Tamfang (talk) 01:14, 29 April 2020 (UTC)

??? ?Baseball Bugs ^{What's up, Doc?} carrots? 03:14, 29 April 2020 (UTC)

He means he recognized the initials I used in my example. --76.71.6.31 (talk) 06:42, 30 April 2020 (UTC)

Very good. :) And, fittingly, the cartoon was dated near the time when Nixon started firing people as the scandal heated up. ?Baseball Bugs ^{What's up, Doc?} carrots? 11:17, 30 April 2020 (UTC)

Hm, I was taught to use a colon for that; a slash would mean signed by Woodstock with authority delegated from Snoopy, possibly without Snoopy's specific knowledge. —Tamfang (talk) 00:52, 29 April 2020 (UTC)

I googled "Woodstock dictated but not read", and it found the cartoon, which was originally dated April 27, 1973.[17] ?Baseball Bugs ^{What's up, Doc?} carrots? 03:14, 29 April 2020 (UTC)

How to Indicate a Typist's Initials in a Letter says: "Type the initials of the letter writer in capital letters, followed by a slash or colon. Add the typist’s initials in lowercase letters. For example, if the letter writer's name is Andrew Benson, and the typist's name is Carrie Dale, the typist line should appear as follows: AB/cd, or AB:cd". Alansplodge (talk) 12:01, 29 April 2020 (UTC)

Change colors for my display?

Is there a way I can change how internal links are shown to me so the colors are more distinct between visited and unvisited internal links? Thank you. RJFJR (talk) 14:10, 22 May 2020 (UTC)

See Help:Link color. PrimeHunter (talk) 14:45, 22 May 2020 (UTC)

Advice on cleaning up references?

Hi. Any advice on how to improve references either using refill or manually? RJFJR (talk) 01:08, 1 November 2020 (UTC)

Hello RJFJR. You seem to be using refill okay. There is one thing to be aware of (if you aren't already) a reference has to be completely bare for refill to work - like this https://www.rte.ie/entertainment/book-reviews/2001/0315/445335-outofme/ - If there is anything else - dates - author name - even a period at the end of the url https://www.rte.ie/entertainment/book-reviews/2001/0315/445335-outofme/. refill will skip the link. As to manual fixes the first thing I do is run the url at Citer. It fixes a fair amount but you do need to look at the whole ref that it creates to make sure it is okay. For instance it will format a url from Amazon but it won't give it a proper title. Now the ones that are still left bare need to be fixed completely by hand. What I do then is have two or more windows open on my computer. I'll have the editing field for the article in one window. I find the bare url - copy/paste it into a second windows browser and hit enter to see what comes up. Quite often you will find the link is dead so you can slap a {{dead link|date=November 2020}} template on the reference in the article. If something does come up then I have a blank cite web template in my sandbox (which is in a third window) {{cite web |url= |title= |last= |first= |date= |website= |format=PDF|access-date=2020-11-01}} that I copy paste it into the article. I then start to fill the fields with the info available by more copy pasting. Please note my blank template has the "|format=PDF" That is because PDFs will make up the majority of the bare urls that refill and citer won't fix. It is a field I have to remember to remove for those urls that aren't PDFs. Also, there are many sources that don't have enough info to fill all the fields so you can skip or remove them. After you hit "show preview" or "save" it is worth going to the reference section and taking a look at things. Sometimes you will make an error in the formatting. Sometimes a bare url will slip through. Also there might be red messages pointing out that there are things other than formatting that need looking at - for example the "|website=" field doesn't like it if you include the whole url |website=https://www.rte.ie is wrong while |website=www.rte.ie will make the red warning go away. I know this is a brief recap (probably too brief) of some of the ins and outs of formatting bare urls manually. I've been working on them for several years and have gotten used to some of their quirks. I still make mistakes but things can always be fixed with further edits. You will, naturally, get more adept at dealing with them as your editing continues. Best regards. MarnetteD|Talk 04:26, 1 November 2020 (UTC)

Test page

User:RJFJR/referencedesknotes/test

procedure using rationals are dense

It should be easy to do this, and it is easy to prove it can be done, but I can't define an easy way to do it:

Let a be an irrational number (it's trivial if it's rational) and b an arbitrarily small positive rational number. What is a procedure to return 2 distinct rational numbers from the interval (a,a+b) ?

(There might be a way that starts calculate a rational approximation b*ceil(a/b) but I'm not sure and I think there should be something better...)

Thank you, RJFJR (talk) 20:40, 22 December 2020 (UTC)

I don't think it's possible to give an answer until you explain how the irrational number a is presented. The obvious setup would be to think of your procedure as a program in a language that has an oracle that gives, say, decimal digits of a, or otherwise gives arbitrarily good rational approximations to a, but then the problem is trivial, so you must be asking something else. What are you asking exactly? --Trovatore (talk) 21:30, 22 December 2020 (UTC)

If you have a procedure to produce one rational value in the interval (a, a+b) for arbitrary positive rational b, then you can also produce one for b/2, b/3, and so on, and the sequence of numbers thus produced contains a descending subsequence that converges to a – which gives an infinity of rationals between a and a+b. As Trovatore says, it is not possible to give a procedure independent of the presentation. Here is a similar but seemingly much simpler problem: Given a real number a, produce an integer i such that i > a. It sounds trivial, but it is not. An even simpler problem, but only seemingly: Given a real number a, report whether a > 0. If you have a procedure for doing that, I can solve the original problem (assuming I may appeal to Markov's principle).  --Lambiam 22:04, 22 December 2020 (UTC)

If one is allowed to use the ceiling function, as suggested in the question, the problem is not hard to solve, using the property that x ≤ ceil(x) < x + 1. Let n be a sufficiently large positive integer – how large it needs to be, we'll see later. Then, by the property of the ceiling function, na ≤ ceil(na) < na + 1. Take c = ceil(na)/n, so by dividing everything in the inequation by n, we obtain a ≤ c < a + 1/n. Since a is irrational, the first inequality is strict: a < c < a + 1/n, or, equivalently, c ∈ (a, a + 1/n). We are almost done; all we need is to pick a value for n such that 1/n ≤ b. That is easy: take n = ceil(1/b).  --Lambiam 22:50, 22 December 2020 (UTC)

If you take the infinite expansion of an irrational number a as a continued fraction – which can be computed if you can use the ceiling function and therefore the floor function – and take every second approximant (the second, the fourth, and so on), this gives a descending sequence of rationals that converges to a. For example, for π, that descending sequence goes like 22/7, 355/113, 104348/33215, 312689/99532, ... . For an approximant p/q in that sequence (in simplified form), it is the case that a − p/q < 1/q². So all approximants p/q for which q² ≥ 1/b satisfy a < p/q < a + b.  --Lambiam 07:38, 23 December 2020 (UTC)

Thanks everyone. By procedure I didn't mean a computer subroutine, I meant the kind of description they give in a math book, and I should have said ceiling instead of ceil (I was distracted by realizing I don't know the wikimarkup for the math extension to do that little right angle upsidedown L for ceiling.) The answer about sufficiently large n and how to determine it is sufficiently large is the kind of thing I was looking for. Thank you. RJFJR (talk) 19:39, 23 December 2020 (UTC)

The markup for the math extension is standard LaTeX: <math>\lceil x\rceil</math>, which renders as $\lceil x\rceil$. Or you can use Unicode characters, as in ⌈''x''⌉, which renders as ⌈x⌉. The amputee brackets actually have character entity references that are not difficult to remember: you can use ⌈''x''⌉ instead.  --Lambiam 20:41, 23 December 2020 (UTC)

Lean

Lean (proof assistant)

Baking formulas

(from Quora) If baking is such an exact science, why do recipes so often have measurements that round off to suspiciously standard sizes (e.g., one cup, one teaspoon, rather than .93 cups and 1.27 teaspoons)? No professional baker or pastry chef uses volume measures. We ditched those forever ago and went with beam and finally, digital scales. Also, we don't use recipes. That's for cooks. We use formulas.

A basic baguette is as simple as sin. Its formula is:

100% flour

70% water

2% salt

2% IY (instant yeast)

174% total

Say I want 20 small baguettes at 10 oz each? That's 200 oz of dough.

200/174=1.15

Now, multiply 1.15 times each percentage above. We are now dealing with 115 oz of flour. Every other ingredient is expressed as a percentage of 115.

You're gonna end up with an exact amount of dough. Almost. The hydration of the dough will change based upon atmospheric humidity. Damp flour absorbs less water, dry flour (think winter furnaces) will need more water.

Refs in lead

user:Elmidae I looked and didn't find anything in the MOS about not having refs in the lead (but I didn't look all that hard.) Can you point to something in the MOS that discusses this? RJFJR (talk) 18:15, 18 January 2021 (UTC)

@RJFJR: it's at MOS:LEADCITE. I've always taken the standard to be "only put refs in lead if statement is likely to be challenged, otherwise keep it free of refs". None of these seem controversial, so I'd move them out. In addition ref 3 is ONLY in the lede, which is a definite no-no, and should be attached to wherever that item is treated in the text body. - Probably should just do this but I was in NPP mode at the time and not intending to do much copy-editing along the way. --Elmidae (talk · contribs) 19:19, 18 January 2021 (UTC)

@Elmidae: Thank you. That was what I was looking for and couldn't find. (That page also answered something I'd been meaning to look at and hadn't gotten to.) RJFJR (talk) 22:25, 18 January 2021 (UTC)

Refill2

Hi, MarnetteD. Refill2 can't fix PDFs when they are references. Since not fixing them bugs me... do you have any suggestions or procedures for them? Thank you in advance. RJFJR (talk) 17:26, 5 February 2021 (UTC)

TGIF RJFJR. There is some good news regarding formatting PDFds. Reflinks has recently been resurrected. It can format many - though not all - PDFs. It will also format several other urls that refill skips. You do have to click on "interactive" in the upper left corner and then click "all unformatted links" before copy pasting the article title in the page title field. Another benefit is that it will put PDFs into an editing field so even if it doesn't fix them they are ready for manual formatting. Now if you haven't used it before it takes a little getting used to but I think you will get the hang of it fairly quickly. As always I'll try to help with any questions that come up. Best regards. MarnetteD|Talk 17:55, 5 February 2021 (UTC)

grammar for a language

I've been told that when linguists study a language they record the lexicon (vocabulary) and they write a grammar for it. What would such a grammar look like? I don't think my town library would have a linguistics specific grammar for me to examine and when I try to imagine documenting the grammar for English I imagine a horribly long and complicated result. By the way, my background is in software so when we studied computer grammars we studied context-free grammars and context-sensitive grammars but I don't know if a grammar for a natural language would be documented like that. Thank you. RJFJR (talk) 19:00, 20 March 2021 (UTC)

For example: Modern Swahili Grammar. Alansplodge (talk) 19:28, 20 March 2021 (UTC)

As I recall, an unabridged dictionary will often have a grammar section in front, in addition to a pronunciation guide. One thing about computer languages is that they are primarily instructions to do specific tasks, so they have a much smaller vocabulary and grammar. <-Baseball Bugs ^{What's up, Doc?} carrots-> 19:57, 20 March 2021 (UTC)

Most modern computer languages have indeed an infinite vocabulary, since they allow for identifiers and strings of any length. In principle the same is true of languages (like German) which support composite words. But in that case you can still break it down to a finite elementary vocabulary. What makes (most) computer languages simpler ist the grammar, not the vocabulary. --Stephan Schulz (talk) 17:39, 21 March 2021 (UTC)

Computer languages aren't too much like natural languages, since there is generally an exact definition of what is part of the language and what isn't, and if there is an error, then the running of the program usually stops at that point with an error-message which may or may not be helpful. Mathematical grammars in the Chomsky hierarchy have been used in attempts to parse human languages with computer software, but linguists don't generally use them when writing grammar-books covering human languages... AnonMoos (talk) 18:15, 21 March 2021 (UTC)

It's been a long loooong time back, but I remember seeing what I now know are context-free grammars for parts of English and German back in high school. Things like a sentence being composed of a noun phrase, a verb phrase, and an optional noun phrase, with a noun phrase being (e.g.) a noun, or an adjective followed by a noun phrase. It was by no means complete, but it covered the basic cases... --Stephan Schulz (talk) 18:39, 21 March 2021 (UTC)

Does any computer language have an infinite number of reserved words? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:53, 22 March 2021 (UTC)

Those are what linguists call "toy grammars" (or "a grammar for a toy subset of English language" on the Chomsky hierarchy article), which only handle a very small fraction of the sentences in a language. Theoretical linguists devising a new syntactic theory are sometimes enamored with mathematical grammar frameworks, but this is much less common in the case of practical linguists writing a book-length description of the grammar of one specific language. Incorporating a simplified version of the Aspects of the Theory of Syntax transformational theory into language textbooks for high-schoolers or even junior-high-schoolers was a slightly strange educational fad of the second half of the 1960s and early 1970s which did not last. I doubt it did any harm, but I doubt that it did much good in accomplishing educational goals, either... AnonMoos (talk) 01:19, 22 March 2021 (UTC)

The method a linguist will use to describe the grammar of a language depends very much both on the background of the linguist and the intended audience. If that audience is formed by aspiring language learners, the vast majority of whom are not linguists, they had better use an informal description with paradigm tables and example sentences. AFAIK, no one has ever attempted to give a formal description of the full complexity of any natural language. A scholarly work like The Cambridge Grammar of the English Language runs up to 1178 pages, while the earlier A Comprehensive Grammar of the English Language ends on page 1779. Neither can lay claim to being complete. Whether a sentence is grammatically acceptable is not always a simple yes-no issue; a native speaker's grammar sense may tell them a sentence is a bit off, but not really wrong.  --Lambiam 22:27, 20 March 2021 (UTC)

Name for how to compare probablistic models?

I'm sure there is a whole lot of material on how to do this but I don't know what it is called.

Suppose I've got some probablistic models (e.g. weather forecasts that say 20% or 40% likely rain on Tuesday and then it does or doesn't rain that day) and I want to check a bunch of predictions vs results and determine which is best. (So one prediction is slightly off for a lot of days and another is usually right but occasionally really off, determine which is better.)

What do I look up to study on this kind of mathematical question? Thank you. RJFJR (talk) 03:49, 29 March 2021 (UTC)

Model selection. --116.86.4.41 (talk) 08:26, 29 March 2021 (UTC)

Thank you. (Reading the related articles will be very interesting.) RJFJR (talk) 14:23, 29 March 2021 (UTC)

note to self: *In forecasting and prediction, the Brier score is a measure of forecast skill based on MSE.

Does colored newspaper ink contain heavy metals?

I was told that the colored ink in newspaper contained heavy metals (and to keep those pages out of the garden). That was a long time ago. There is now a lot more color in the newspaper. Are they still based on heavy metals? Thank you. RJFJR (talk) 04:30, 21 January 2022 (UTC)

Not according to this source: "Today’s newspaper uses ink that is 100 percent non-toxic. Inks of all colors and black and white are included." What I see in sources^[18][19] is that volatile organic compounds are considered more of a problem than pigments, an issue that is resolved if the newspaper uses soy ink. But this source mentions cadmium yellow as a common newspaper-ink pigment; the heavy metal cadmium is toxic.  --Lambiam 12:32, 21 January 2022 (UTC)

So are non-coloured newspapers now safe for Fish and chips as they were in my youth? Martin of Sheffield (talk) 14:26, 21 January 2022 (UTC)

Perhaps if liberally sprinkled with salt and vinegar. What was considered safe in your youth may no longer be generally recognized as safe today, though.  --Lambiam 14:17, 23 January 2022 (UTC)

At the time of chips-in-newspaper (before about 1970?), they were cooked either in beef dripping (in the North of England and Scotland) or lard. Much healthier! Alansplodge (talk) 22:50, 23 January 2022 (UTC)

In the era of typesetting, the printing press probably contained heavy metals like lead, and could transfer some to the paper. Nowadays these methods are not so common. Also Phthalocyanine Blue BN a common blue pigment contains copper. Copper is an essential metal for plants. Graeme Bartlett (talk) 22:20, 23 January 2022 (UTC)

filtering a category

Is there an easy way to filter Category:Articles needing cleanup from June 2022 to only see entries that aren't added as having bare url? RJFJR (talk) 23:20, 25 June 2022 (UTC)

@RJFJR: I'm not sure if there is an user script that can do so directly, but you can search for them using CirrusSearch: Special:Search/deepcategory:"Articles needing cleanup from June 2022" -hastemplate:"Cleanup bare URLs". NguoiDungKhongDinhDanh 23:42, 25 June 2022 (UTC)

SAT Solver's non-existence certificate

So apparently a SAT Solver can return a certificate to prove its conclusion that there are no solutions. I don't know what the certificate for this would look like. Can someone point me to some information on non-existence certificates? Thank you. RJFJR (talk) 22:04, 25 June 2022 (UTC)

I don't know what I'm looking at here but I see the words Certified UNSAT ... 3 different UNSAT certificate types ... Certified UNSAT solver output example, is this any help?  Card Zero  (talk) 22:52, 25 June 2022 (UTC)

As defined in that document it is basically the same as the proof of unsatisfiability. Not as snappy as a certificate of satisfiability (being the satisfying assignment), but still, checking a proof is much easier than finding one.  --Lambiam 08:15, 26 June 2022 (UTC)

Thank you. I think I understand the idea now. RJFJR (talk) 18:36, 26 June 2022 (UTC)

English tense of "is eaten"

In the sentence "This type of rice is eaten all over the world." what tense is represented by 'is eaten'? RJFJR (talk) 04:53, 26 April 2023 (UTC)

Present tense, passive voice. --Wrongfilter (talk) 05:10, 26 April 2023 (UTC)

More specifically, the simple present.  --Lambiam 09:39, 26 April 2023 (UTC)

Damn it, never good enough... But, isn't "simple" more of an aspect? --Wrongfilter (talk) 12:08, 26 April 2023 (UTC)

True, but then you could just have said "Present tense", full stop.  --Lambiam 14:58, 26 April 2023 (UTC)

I could have, but I suspect that the passive voice is what actually prompted the question. I hope you didn't take offense, my comment was thoroughly tongue in cheek. --Wrongfilter (talk) 15:35, 26 April 2023 (UTC)

My seconds will contact your seconds.  --Lambiam 20:22, 26 April 2023 (UTC)

These days, we have to say "My seconds will reach out to your seconds. (*vomit*) -- Jack of Oz ^{[pleasantries]} 21:16, 26 April 2023 (UTC)

I see now. I was trying to figure out why that form to be was in there and it threw me. (I was trying to figure out how to explain to a non-native speaker of English why it should be is eaten rather than is ate.) Thank you. RJFJR (talk) 01:57, 27 April 2023 (UTC)

Template to tag a reference to user-generated content?

from help desk

Is there an inline template for tagging a reference to indicate it is to user generated content, like twitter, and should be replaced with a better reference? RJFJR (talk) 02:38, 30 April 2023 (UTC)

{{user-generated source}}/{{user-generated inline}} * Pppery * _{it has begun...} 02:40, 30 April 2023 (UTC)

Differential Equation

Does the differential equation x² * d²x/dt² = k have a name? (All I've figured out about this so far is that I don't remember enough about differential equations. I'm not getting anything on solving it except errors.) Thank you. RJFJR (talk) 02:45, 23 May 2024 (UTC)

As to a solution, you could guess that one might be some power of $t$ and accordingly substitute $x=At^{p}$ (where $A$ and $p$ are constants), then solve for $p$ and then solve for $A$. catslash (talk) 09:02, 23 May 2024 (UTC)

Then, since nothing in the equation depends on the absolute value of $t$, you could apply an arbitrary time-shift to get a slightly more general solution $x=A(t-t_{0})^{p}$. catslash (talk) 09:20, 23 May 2024 (UTC)

You're right. Thank you. p=2/3, I was not expecting that. I appreciate it. RJFJR (talk) 14:14, 23 May 2024 (UTC)

This is an autonomous second order equation. If you write ${\ddot {x}}-{\frac {k}{x^{2}}}=0$ and multiply with ${\dot {x}}$, you find ${\frac {d}{dt}}({\frac {1}{2}}{\dot {x}}^{2}+{\frac {k}{x}})=0$ so ${\frac {1}{2}}{\dot {x}}^{2}+{\frac {k}{x}}=C$ for some constant $C$. Solve for ${\dot {x}}$ and you get a separable first order equation. —Kusma (talk) 14:35, 23 May 2024 (UTC)

Thank you. I need to dig out the old textbook and start reading. RJFJR (talk) 19:25, 23 May 2024 (UTC)