Wikipedia:Reference desk/Archives/Science/2013 June 18

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June 18

Homozygote-to-heterozygote assortative mating

Are there any known examples of heterozygous genetic traits subject to assortative mating, but for which homozygotes prefer heterozygous mates and vice-versa? (This would be equivalent to the same allele coding a disassortative recessive trait and an assortative dominant trait. The reason I ask is that if autism-spectrum disorders were partly the result of a partially dominant trait, then people "square enough for the peg and round enough for the hole" would more often become partners and parents of those that needed them, as I have anecdotal evidence to suggest.) NeonMerlin 03:25, 18 June 2013 (UTC)

I have no answer here, only the observation that the same thought had occurred to me. I think the 'square enough/round enough' phenomenon you're describing is what's known as the 'broader autism phenotype'. If anyone can supply some genetics insight here, I'd be fascinated. Thanks! AlexTiefling (talk) 11:37, 18 June 2013 (UTC)

That article mentions disassortative mating, which I think is what you want (heterozygous mating with homozygous preferentially and v/v) - it's a keyword that will pull up things like [1]. You might also be curious about [2] (MHC disassortative mating?). Note that our article gives the opposite speculation - assortative mating - about autism. Wnt (talk) 21:57, 18 June 2013 (UTC)

Audio Source Signatures and Transforming

Given samples of two sources/instruments/voices performing/speaking the same piece in identical fashion is it possible to workout a transform between the two so that given new samples of one, we could transform it into a decent approx. of the other? For example, given a violin and an acoustic guitar playing various scales at various rates, could we generate an algorithm to map violin pieces to guitar pieces? What about for voices and speaking (This is my primary interest, but the situation is interesting in general)? Finally, what about less specific cases, for example: changing a male voice into a "female" voice (not a specific one, just removing male characteristics and adding feminine ones); or, with music, changing a string instrument to a brass version of it? I'd be interested in any information pertaining to this, including info on what characterizes one source from another (and the science/mathematics of it). Thank you for any help:-)Phoenixia1177 (talk) 04:52, 18 June 2013 (UTC)

To give you an entry into the literature, what you are asking for in technical terminology is a digital filter that transforms a recording of a violin into something that sounds like a guitar, or a recording of a male voice into something that sounds like a female voice. All of these things can be done, but some are simple and others required a very sophisticated filter. The main thing that gives a sound source its character is its power spectrum, but there are other important things too -- for example a guitar is plucked while a violin is usually played with a bow, and it is very difficult to transform a plucked sound into a bowed sound. Looie496 (talk) 15:06, 18 June 2013 (UTC)

This is definitely not easy stuff. There is software out there (eg this one) that can extract the pitch and duration of notes from simple music. (This is generally called "music-to-MIDI" because MIDI is the lingua franca of music synthesis) - and once you have that, you can relatively easily produce synthesized music played on any other instrument for which good synthesis exists. But if you have complicated polyphony or lots of different instruments playing different parts, then extracting the note information is much harder - perhaps impossible. Some software can do this in realtime - so that you can play music on a guitar and have it sound like a pipe organ or a xylophone...but, again, it's quite limited. Most good software takes longer to do the transcription than the music takes to play - so you can only use it on recordings.

There are "voice changers" out there (just google "voice changer" and you'll see a bazillion of them) - but they mostly just shift the pitch of the voice up and down or add distortion of one kind or another. They don't change other "characteristics" that might identify the gender of the speaker.

There is software out there that can make synthetic voices from sound samples of real people. I heard a very convincing demo of Winston Churchill reading some modern text that was created by dumping all of his recorded speeches into some analysis software - deducing the characteristics of his voice and then using that to synthesize his new speech. But software like this is quite new and specialized - it would probably require you paying a company who specializes in this kind of thing to do that work for you. I don't think the process is entirely automatic either.

SteveBaker (talk) 15:05, 18 June 2013 (UTC)

Thank you both for the answers:-) In general, I have an interest in this subject, but I do have an oddly specific need for a part of it. Supposing that I, a man, recorded my voice speaking with a female rhythm, vocabulary choices, inflection, etc. what would I need to do to it, mathematically, to make it passably feminine? I'm not wanting to do anything nefarious, but am making an fps for my own interest and use and don't feel like hunting down voice actors. Obviously, what I'm proposing isn't going to end up with a great sound for female characters, but it sounds fun and a neat side project to learn something from. (I've acted both male and female roles extensively, and written them, so I can imitate how a female speaks outside of actual physical properties.) On this elaboration, additionally, would it be feasible to modify a given masculine voice to sound like a different male speaker more easily? Phoenixia1177 (talk) 05:57, 19 June 2013 (UTC)

With regard to voice transformation, some work was done by NASA in the 1960's with a view to using analogue methods of bandwidth compression, which were never used. I remember they published an interesting paper, the essentials of which are: 1) the human voice comprises 3 frequency bands, low, originating in the chest & contributing to the quality of the voice; midband originating in the throat, contributing mainly to the the speech evelope and to the identity of the speeker, and high, originating in the mouth, contributing the intellence (ie conveyed meaning) of the speech. To convert male speech into female sounding speech, you need to suppress the mids and substitue new mids at higher pitch and with less harmonic structure. For best illusion, you need to shift the lows up in pitch a bit. You need to leave the highs alone, or you'll get a Donald Duck voice with poor diction. None of this is easy. I cannot find the NASA paper now, but this may give you some clues for your own search.

If you have (or a friend has) good electronics construction skills, you may find it easier to try the 1940's VODER approach - using a key or finger controlled electronic voice. See http://www.davidszondy.com/future/robot/voder.htm. Scroll down until you find the video clip. Do not be discouraged by the sound quality - the machine was built by a chap interested in encription and novelty, not high quality sound. Operators needed to build up considerable skill to operate this machine. However, about 30 years ago, myself and some other workers revisited the VODER idea for helping children who had lost their voice due to cancer and for who a throat box artifical larynch is not a option. The usual approach was to give them a pocket computer with a text-to-speech program, but the sound is so unnatural that people tended to ignore it. Or a device with some pre-recorded emergency messages ("please, where is the toilet?", "please phone my mum on 456-98765") which also tended to get ignored. And conversations were impossible due to the delay in typing. The idea was that they could take everywhere a pocket size VODER machine, which might be possible with 1980's electronics instead of 1940's electronics. We found that producing a tolerable child voice to match the child was not difficult, but we coudn't do an adult (male or female) voice, as to do that you need a full size hi-fi loudspeaker. We found that using the key arrangement of an English stenography/court reporter machine (which is a bit like a multi-key computer mouse, with 5 keys positioned to naturally fall under each thumb and finger tip. Different combinations of key pressed simultanously code for each steno "sound") and the right choice in key coding with pressure coded volume, made it easy to learn. A bright 8-year old could learn to make useful speech in a few hours, sounding much better than computer text-to-speech software, and could easily do it fast enough for a natural conversation. With the steno keyblock in the right hand, and a pitch control in the left, they could do a pretty good job at singing! Our project was not very successful however. Batteries then were not good enough, and we couldn't make it cheap enough. — Preceding unsigned comment added by 124.182.180.102 (talk) 07:01, 19 June 2013 (UTC)

Thank you for the response, very interesting. Unfortunately, I'm not good with electronics, nor do I know anyone who is. However, I will track down the NASA paper; it sounds quite useful. The VODER looks intriguing, I'll have to read up on it more; looking around on this topic has led me to a lot of articles on speech synthesis, which while different is related and fascinating. Thank you very much:-)Phoenixia1177 (talk) 07:16, 19 June 2013 (UTC)

my 2001 bmw 740i is rattling

what do i do? i can't figure it out and ain't got no money. it rattles upon slow acceleration and is a light vibrator noise coming from my right rear wheel. — Preceding unsigned comment added by 108.212.70.237 (talk) 05:38, 18 June 2013 (UTC)

I'm not a mechanic, but my personal opinion is that your wheels need to be balanced. Lucky for you, this can be done pretty easily and inexpensively at most tire shops. (BTW, if you "ain't got no money", perhaps you might consider selling your luxury BMW and buying a more affordable car to make ends meet?) 24.23.196.85 (talk) 06:13, 18 June 2013 (UTC)

Hmmm.. A 2001 740i could have been purchased for as low as $5000 if in poor condition and with no maintenance logs, even though it is a top line luxury vehicle. Sometimes young guys buy these before realising that a car costs a lot more to own than the purchase price, so the question could be genuine. Check the driveline: Check each universal joint. These rwd cars have a split prop shaft like trucks and some GM cars. Check the prop shaft carrier/bearing underneath the center of the car. When the resient mounting fails you get just the symptoms you describe. If the carrier and bearing are ok and the universal joints are ok, check things like engine mounts and suspension components. Note that if engine is misfiring one cylinder this can combine with other problems to cause rattles during mild acceleration. Also note that if te car has been correctly serviced by properly certified mechanics since new, all these faults are just about impossible. — Preceding unsigned comment added by 124.182.43.219 (talk) 10:20, 18 June 2013 (UTC)

I agree with the above suggestion. If you don't think you can do the checks yourself, look for an underbody shop that will provide a free inspection. They'll lift it up, look over things, and show you exactly what has gone wrong and what needs to be replaced. They'll provide you with an estimate, which I would expect to be $75-$250 in labor (assuming you're in the US) on top of the normal cost of the parts, depending on the exact problem. From there you can decide whether it is worth it to handle the repair on your own or not. 209.131.76.183 (talk) 14:30, 18 June 2013 (UTC)

It is unfortunate that you don't have the money to get it looked at by a professional. Wheel vibration has to be taken very seriously because the causes can be anything from something as simple as a balance weight fallen off of the rim - all the way up to a problem with wheel bearings or a broken axle that can literally cause the wheel to fall off at freeway speeds! With a car as old as this one, wheel bearing issues are quite likely - and if the car was for sale at a suspiciously cheap price, that could easily be the reason why!

It often takes an expert to figure out which of those things it is. At the very least, I'd want to get it put up on a lift so that the wheel and it's associated suspension parts can be examined properly. When you know how serious the problem is, you can judge whether you can fix it yourself, or whether you can afford to get someone to fix it for you - or maybe it's a problem you can just decide to live with (very unlikely in the case of wheel vibration!).

If you absolutely must do something yourself:

• I suppose it could be something as simple as a loose lug nut or a bad tire (look for suspicious bulges or other signs that it's not perfectly round and smooth)...those are things you can easily check - but it's relatively unlikely.
• You could jack up that corner of the car (make sure it's in gear or in park and with the parking brake on!) until the wheel is just off of the ground by a half inch or so - then try to wobble the wheel with your hands - both side-to-side and up-and-down. If you don't know what to expect (and I guess you don't), try the same thing with the wheel that's not causing vibration. Does they feel the same? If you can feel a definite difference between them then you probably have a wheel bearing problem - which is quite serious and potentially dangerous. If that's the problem then you're in a position where "If you have to ask the question - you're not qualified to fix it" - and this is going to cost you serious money to get it fixed. BMW's are amongst the more expensive cars to get work done on.
• Going to a cheap tire place and asking them to balance the wheel might help - and shouldn't cost an arm and a leg.
• Failing that, try to find a garage who will assess the problem for no charge - some places will do that. That would at least tell you whether this is something potentially life-threatening - or just an annoyance that should be fixed to avoid premature tire wear or something.

General "rattles" are only to be expected in a car of this age - and they may well be exacerbated by your wheel wobble - so get that seen to first. A rattle can be anything from a loose dashboard panel to a bent exhaust heat baffle to a broken motor mount! There is no way we can diagnose it for you without a lot more information.

I have to say: If you want a cheap car - then don't buy a cheap luxury car - those things are hard to maintain, the parts are expensive - and if you need professional help, remember that mechanics who specialize in luxury cars charge prices that only luxury car owners can afford!

If you have visions of becoming a "shade tree mechanic" and doing the work yourself then you need to start with something older, smaller and simpler!

SteveBaker (talk) 14:49, 18 June 2013 (UTC)

This is a rear wheel drive car with 4-wheel independent suspension, so a broken axle is most unlikely - the symptoms would be quite a bit more dramatic (think: extreme grinding noises; unable to move). However, a fauly wheel bearing is a possible cause of the rear wheel vibration only, especially if the car has high mileage and a history of poor maintenance (faults like this always come back to poor maintenance, which in turn is indicated if the purchase price was low). I agree with the rest of Steve's comments. The corrollary to them is that taking luxury cars to average mechanics can cost you even more than the expensive specialist mechanics. Simply because the average mechanic sees GM cars, Fords, Toyotas, etc all the time. Experience with them gives them the ability to diagnose faults straight away without having to puzzle them out with logical thinking. And they can get on the phone to their parts supplier (if they don't already have the parts) right away and call out a list off the top of their head. For car they hardly ever see they'll have to a) obtain/download the relavent parts manual (a story in itself these days) b) study it, c) work out what parts they need, d) find out where to get them and order and d) when they parts arrive, realise they need something else. And YOU pay for the time. The practical advantage of luxury cars is minimal these days anyway. All the major brands all have good design and good safety. The benefit of buying high end luxury cars is being able to say "look at me - I am a big success - I can afford it" - which does not apply if you bought an old cheapie. Back in the 1960's makes like BMW, Mercedes had clear advantages over GM and Ford, with their all-independent suspension, proper auto aircon, durability, and safety, but the gap has closed a lot now. Now you pay for the name. — Preceding unsigned comment added by 124.182.180.153 (talk) 23:18, 18 June 2013 (UTC)

Possible improvements in Wikipedia entry on Milankovitch Cycles

The image in question

Introduction:

James Hansen's book, "Storms of My Grandchildren" make it clear that our understanding of Ice Ages, which has come about from a combination of Milankovitch Theory with much hard work by geologists on coring and complex analyses of those cores, is at the centre of our understanding of what is likely to happen to us as Global Warming picks up pace.

Unfortunately, even though I am a climate physicist of 40 years experience, engaged on writing a popular book on this subject, I cannot yet say I understand Milankovitch theory as described in this article (or any other popular books on the subject) well enough to write a simple but authoritative account of it for my readers.

I am not blaming the authors of the article at all for this -- it is genuinely a brute of a subject for anyone to get one's head around, and I have learned a lot from what they say.

My question:

Could the Reference Desk kindly get me into email contact with the authors of the article? In particular, with whoever provided the box, found on the right side of the first page of this article? Whoever the person is who came up with this box, it's clearly got nearly all of what I need to understand. I would like to email back and forth with him/her to explain what I am trying to do, and to work out some wording that satisfies both me and that person as a description of the physical things that govern the summer warming of icecaps. What's already there is very good. However, my purpose is to explain the observational history of the past few centuries that led to these astrophysical results, and this is the area where I most need the advice of the authors of the article. (Ivars Peterson's "Newton's Clock: Chaos in the Solar System", Freeman and Co 1993, unfortunately just misses giving what I need). 06:45, 18 June 2013 (UTC)~ — Preceding unsigned comment added by Neergtrish (talk • contribs)

Hi. Firstly, it's probably worth pointing out that almost all Wikipedia articles are collaborative efforts, so it's unlikely that there is a single 'author' of the article, which seems to be what you're looking for. Nevertheless, if you want to find out who has contributed to the article, simply click 'View History' at the top of the article and you will be able to see all the changes made throughout its history.

As for the image in the top right, this was added on 3rd June 2009 by Incredio. If you wish to contact them, the best way would be through their talk page. Some editors allow others to email them through Wikipedia's EmailUser, but Incredio has not enabled this, so on-Wiki communication is the only way.

Alternatively, since this is the reference desk, we may be able to help. If you post the questions you have about the article, maybe we can find some sources to aid your understanding. - Cucumber Mike (talk) 07:55, 18 June 2013 (UTC)

The basic problem here is that this just isn't how Wikipedia works. It's a collaborative environment - the idea is that any discussions you may wish to have about the content of the article should be publicly available to anyone who wishes to be involved in editing the article - either now, or in years to come. That discussion forms a valuable record of why particular editing choices were made. Hence private email communication between editors about article content is generally considered inappropriate - even in cases where the user allows you to communicate with them in private. By far the best thing for you to do here is to raise your concerns on the "Talk" page of the article itself - generally your input will be seen as interesting and valuable - so long as it is constructive and on-topic. Beware though that most of the time people here have little respect for your personal qualifications (after all On the Internet, nobody knows you're a dog) and you'll need to make your points by linking to reference information such as books and scientific papers that back up whatever point you're trying to make.

Another part of Wikipedia culture that's important here is encapsulated in the Be Bold philosophy. It's perfectly OK (indeed, encouraged) for you to dive in and fix the article yourself. If there is some problem with what you write, it may get reverted - or improved in some way by another editor - and that should be the starting point for a discussion thread on the corresponding talk page. It's more efficient to make a change to the article and only to discuss it if people disagree than it is to debate each change before it goes into the article.

If you absolutely must have private email communication, you could try enabling that for your own account and posting a request to the editors' talk page requesting that (s)he contact you via email. However, don't be surprised if the don't. Most editors (myself included) would prefer to keep communications about article content on the relevant talk page.

Wikipedia is a very different way of working than you may be used to - but it's surprisingly productive - and the outcomes are usually good. SteveBaker (talk) 14:07, 18 June 2013 (UTC)

• The article (for convenience) is Milankovitch cycles, and I've added a thumbnail of the image in question here. Note that the creator, Incredio, has not edited Wikipedia since November 2012, and therefore is probably not paying attention to his or her talk page (but you never know). Looie496 (talk) 14:51, 18 June 2013 (UTC)

Yeah - but there are plenty of other people working on the article - and a vibrant, active talk page. If our OP raises his issues there, I'm quite sure that they'll be properly discussed and any problems swiftly dealt with or explained. SteveBaker (talk) 23:58, 18 June 2013 (UTC)

What's this turtle doing?

These two photos were taken just a few days ago in Vermont. I'm guessing that it's a common snapping turtle. It was a bit aggravated by me being as close as I was and I didn't want to bother it too much. What was it likely doing? Would the other two, for lack of a better word, divots in the soil next to the road in the foreground of the second image have been dug out by the turtle? Was she(?) laying eggs? There wasn't a large body of water near by. She was scratching at the dirt when I found her. Thanks, Dismas|^(talk) 07:11, 18 June 2013 (UTC)

Yes, laying eggs I think. They live is small streams, don't they ? So you might not know there's one nearby. Since turtles don't exactly travel long distances on land, I'd expect the stream it came from to be quite close (maybe even a drainage culvert). They don't seem to understand the danger of roads, either, unfortunately. StuRat (talk) 07:31, 18 June 2013 (UTC)

Snapping turtles prefer standing water, not flowing streams. They like warmer elevated areas for nesting, that roadside would have met both those requirements. μηδείς (talk) 16:54, 18 June 2013 (UTC)

Can neutrinos undergo gravitational lensing?

Thanks!76.218.104.120 (talk) 11:28, 18 June 2013 (UTC)

Yes. Like all elementary particles, neutrinos have mass/energy - therefore their paths are affected by gravity, and therefore they undergo gravitational lensing. Gandalf61 (talk) 11:36, 18 June 2013 (UTC)

More specifically, high-energy neutrinos (the only ones that we can detect directly) will follow paths that are essentially indistinguishable from the paths of photons in terms of gravitational lensing. — Quondum 13:58, 18 June 2013 (UTC)

Complex space & Quantum mechanics

I don't have a background in particle physics, but I have been doing some reading. I recently picked up on some ideas brought up with Imaginary time and the complex plane. So is it possible to project an imaginary axis on a 3D, maybe as (x,y,z,i), n-dimensional Euclidean space? I could only assume this logic could be used to explain occurrences such as particle-wave duality. In a similar way this little diagram (http://commons.wikimedia.org/wiki/File:Dualite.jpg) shows how what we may see as 2 separate figures may in fact be the same because we fail to see a superfluous axis of space. Bugboy52.4 ¦ =-= 13:51, 18 June 2013 (UTC)

I assume you mean the coordinates (x,y,z,it), since i is not a variable. If that's the case than yes, there's value in that approach as a way to better understand Minkowski space, but that is not related to the concept of particle-wave duality. Dauto (talk) 15:40, 18 June 2013 (UTC)

If you're thinking about complex numbers, three spatial dimensions, and time, the classic object building off of those is the quaternions. I'm not aware of applications to quantum mechanics, but they have been used for many types of theoretical physics, and you might enjoy reading up on them anyway.

“ Time is said to have only one dimension, and space to have three dimensions. […] The mathematical quaternion partakes of both these elements; in technical language it may be said to be "time plus space", or "space plus time": and in this sense it has, or at least involves a reference to, four dimensions. And how the One of Time, of Space the Three, Might in the Chain of Symbols girdled be. ”

— William Rowan Hamilton. Enjoy, SemanticMantis (talk) 19:12, 18 June 2013 (UTC)

What are the extra j and k axis in quaternions and its application in physics? this is fascinating, Id like to learn more. Oh and I was just considering the possibility since particles can appear and reappear or have a superposition then maybe we are only visualizing these particles from the perspective of our space because they are moving through an extra dimention. Bugboy52.4 ¦ =-= 23:05, 18 June 2013 (UTC)

The j and k are extra imaginary components - that is j^2 = k^2 = -1. Note that quaternions do not obey commutativity of product: ij = k, ji = -k for instance. Your ideas about particle-wave duality are off the mark. It has nothing to do with extra dimensions. Particle-wave duality really is simply a symptom of the inadequacy of the concepts of particles and waves to begin with. Dauto (talk) 03:47, 19 June 2013 (UTC)

I noticed that as well, how a product was able to have 2 seperate qoutients. Is there anywhere I can read more indept about this cerriculurly? 99.38.224.22 (talk) 04:36, 19 June 2013 (UTC)

If you like the quaternions than you might enjoy the octonions as well. The octonions have 7 different imaginary units. They do not obey commutativity like the quaternions plus they also do not obey associativity. That is (AB)C may be different from A(BC). Dauto (talk) 13:45, 19 June 2013 (UTC)

Quaternions are just mathematical conveniences - it's not that they have any particular physical significance. I use them a lot in 3D computer graphics to represent three-dimensional rotations because they have some particularly nice properties that are a huge improvement over using three angles or a 3x3 matrix. SteveBaker (talk) 00:35, 20 June 2013 (UTC)

Siphoning gasoline - which cars to choose?

I'm just watching something postapocalyptic and they need to siphon gasoline from abandoned cars. How would they know which contain the right type? Are there just two (diesel and unleaded)? Would it still be good after 20 years sat in the tank? — Preceding unsigned comment added by 89.241.228.217 (talk) 15:35, 18 June 2013 (UTC)

This is harder than it looks, because the nature of fuel can vary between countries and even between regions. (Of all of these the most comical, and I would think lucrative for the right people, is Opal (fuel); but I think it still is subject to stability issues despite the lower volatility) See Gasoline#Stability to get started. Wnt (talk) 16:15, 18 June 2013 (UTC)

Not hard at all - every car parts store sells siphons - and locking gas caps to prevent theft from your own car. And how many times have you had to alter your car when you went on vacation? Rmhermen (talk) 17:29, 18 June 2013 (UTC)

The neck of the gas tank is a different diameter for gasoline and diesel - in an effort to prevent people from accidentally grabbing the wrong hose at the gas station and filling their car with the wrong stuff...so it's easy to tell which is which if you know what you're looking for. Also, many cars now have stickers inside the gas cap telling you what octane range you need - which would also be a clue.

However, after 20 years, gasoline (and probably diesel too) is going to be almost useless for running a car on. The lighter fractions of the complex chemical brew will evaporate off and leave only the heavier fractions. As gasoline gets more than a year old - it gets harder and harder to start you car using it, and eventually, it flat out doesn't work. SteveBaker (talk) 19:25, 18 June 2013 (UTC)

Well, the "Opal" I mentioned has fewer volatiles - however, I think that the main problem isn't loss of volatiles, but reaction with oxygen to cause gummy deposits. I would allow for the possibility that ingenious postapocalyptic people can modify engines to be more robust (or find ancient relics or modern eco-prototypes that can choke down anything) but not be able to reach in and turn the key on a car they find beside the road, even with that battery they were carrying around in their backpack for such occasions. But I don't know these things well - it would be nice to hear an actual mechanic chime in. Wnt (talk) 20:56, 18 June 2013 (UTC)

There are details about what happens to "old" gasoline here Gasoline#Stability - suffice to say that 20 year old gasoline is going to be fairly useless as a fuel for cars. Incidentally - I checked up on diesel - and the problem is pretty much the same. This BP document says that diesel fuel is not "useable" after 6 to 12 months depending on temperature.

Truly, after just a few years, the gasoline in car tanks would be very poor for running cars...after 20 years, there's no chance. SteveBaker (talk) 23:53, 18 June 2013 (UTC)

All the above makes some assumptions. Internal combustion engines all around the world have used all sorts of horrible fuels, so long as you have air fuel and spark a mechanic will eventually get an SI engine to run, and a diesel engine is in theory not much less flexible. Greglocock (talk) 01:52, 19 June 2013 (UTC)

Usually diesel engine is more fuel flexible than gasoline engine, it can burn any heavy flammable liquid provided it have enough heat, but unfortunately they cannot accept gas like natural gas or woodgas, they need a ignition source for that 118.136.5.235 (talk) 11:44, 19 June 2013 (UTC)

Our Multifuel article discusses this - some military engines are designed to run on a crazily wide variety of fuels. Years ago, I had a friend who was a tank commander - he always claimed that his tank could run on anything from scotch whiskey to margarine - although that seems a little unlikely to me.

There are consumer vehicles out there marketted as Flexible-fuel vehicles - with that little green leaf logo on the back (which appears to be there to mislead people into thinking that these are somehow better for the environment)! Flex-fuel really means that the engine can cope with widely varying levels of ethanol mixed into the gasoline - but that wouldn't help them to run on 20 year old gasoline.

So, I suppose, our intrepid post-apocalypse folk had better find a suitable tank to be driving around in - and then they can run it on just about anything they can find out there. Of course that's not without problems. Most modern tanks are only able to drive an average of around 200 miles between breakdowns.

SteveBaker (talk) 13:05, 19 June 2013 (UTC)

The most multifuel engine so far is a gas turbine, and it could be improvised by attaching a combustion chamber to a turbocharger (see http://www.pfranc.com/projects/turbine/top.htm for example) and attaching another turbocharger turbine to the exhaust of it, it could be used for shaft power but it is much much much better to connect it to a electric generator

Source:Chrysler Turbine Car The article even said that it could run out of tequila, but the only problem and that is so huge is its directly connected to the wheel, and gas turbine is known as inefficient at idle — Preceding unsigned comment added by 118.136.5.235 (talk) 01:51, 20 June 2013 (UTC)

In a post-apocalyptic scenario, if you wanted to get from A to B and didn't care about the health of your engine at the end of it, then a normal diesel engine will run on a mixture of diesel fuel and gasoline/petrol. I accidentally put the wrong fuel in my old Peugot and pressed on regardless - it ran ok if a bit hesitantly. However, two weeks later, the head gasket failed resulting in a repair bill greater than the value of the car. Lesson learnt, but if it's the end of the world you might not be too fussy. Alansplodge (talk) 12:18, 20 June 2013 (UTC)

In the first year or two after "the big one", you might be right - but sooner or later, cars that still run are going to get rarer and rarer. If you take a perfectly well maintained modern car and leave it parked in the street for 20 years, it's not going to run again without a hell of a lot of restoration work! Such cars are occasionally found these days - the classic car nuts call them "Barn finds" (and yes, we have an article about that!) - because they are often found in disused barns. Here, for example is what a nice Jaguar XK120 looks like after it's been parked for 30 years.

So, 20 years after the apocalypse, once you do get a car running, it's likely that you most definitely WILL care about keeping it running. Just jumping into another one in the local baseball field parking lot, tossing out the skeletal remains of the driver, then turning the key and driving away from the encroaching zombie herd simply isn't going to work!

SteveBaker (talk) 16:50, 20 June 2013 (UTC)

Generic medications

I am a physician and today at work a dispute arose between our pharmacist and myself. Some of my patients complain that the medications they take often change their appearance in color and shape. They claim that some of the generic variants are in fact ineffective and they refuse to take them. I believe that there might be a scientific explanation why this happens. Different generic manufacturers probably use different fillers (clays) and in some cases the active chemical (medication) gets bound to them and passes the GI tract thus decreasing bio availability. Our pharmacist contends that all generics are tightly regulated by the FDA and such an event is not possible.

The question is: are the fillers regulated by the FDA?

Thanks, - Alex — Preceding unsigned comment added by 168.178.74.53 (talk) 16:27, 18 June 2013 (UTC)

They are in Canada. I doubt the US would be different. I have found, personally, with one specific drug, that the original and one of the generics work for me, but not another of the generics. My pharmacist says that this is not uncommon on an individual basis. Bielle (talk) 16:37, 18 June 2013 (UTC)

• You should take a look at Generic drug#Quality standards. Ironically, it includes a statement that, "A physician survey in the US found only 17% of prescribing physicians correctly identified the USFDA's standards for bioequivalency of generic drugs". Looie496 (talk) 16:48, 18 June 2013 (UTC)

(Let me note that we are flirting dangerously close here to Wikipedia's prohibition against giving medical advice -- the fact that the questioner identifies as a physician isn't really relevant.) Looie496 (talk) 16:52, 18 June 2013 (UTC)

No, we are not. And yes, it isn't. --Stephan Schulz (talk) 17:54, 18 June 2013 (UTC)

Kainaw's criterion is not being breached. We can certainly answer this question. SteveBaker (talk) 19:14, 18 June 2013 (UTC)

I believe that it's well known that the packaging of generics can make a difference. Our article generic drug says "A generic drug must contain the same active ingredients as the original formulation. According to the U.S. Food and Drug Administration (FDA), generic drugs are identical or within an acceptable bioequivalent range to the brand-name counterpart with respect to pharmacokinetic and pharmacodynamic properties. By extension, therefore, generics are considered (by the FDA) identical in dose, strength, route of administration, safety, efficacy, and intended use." - which suggests that (in the USA at least) your patient's fears are unfounded. However, the article goes on to say "The FDA's use of the word "identical" is very much a legal interpretation, and is not literal." - so these generics are "legally identical" but maybe not actually identical.

Later in that article, under Generic_drug#Efficacy - it describes a study done in 2009 on oxybutynin that showed that the generic version was less effective - and the image there shows a clear difference in the rate at which bupropion is released between the generic and the original version of the drug. Our Bioequivalence article has more to say on the matter.

So, yes, there are probably some small differences. The question is whether these differences are sufficient to be truly noticeable by your patients. Clearly the FDA don't think they should be.

We should also suspect that a nocebo effect is taking place here - because the patients disbelieve that the generic is as good ("How can it possibly be as good? It's cheaper!") they are getting a reverse-placebo effect that is making them genuinely sicker for reasons unrelated to the content of the drug itself. They simply lost confidence in it and the nocebo effect did the rest.

An alternative hypothesis for what you're seeing is that (randomly) some patients get better after a while on the treatment and some get worse - regardless of whether they are taking the generic or the original drug. The ones who get better don't say anything - and the ones who didn't switch to the generic don't attribute their change to the treatment because it didn't change. But the patients who (by chance) get worse right around the time they switched to the generic version will always attribute the change to the first thing that comes to mind - which is that the generic drug doesn't work as well. Since you're only hearing from the ones who have something to complain about - you're going to see a rather severe "confirmation bias" effect going on here.

In terms of what you can do about it - that's a tougher matter. Having an authority figure (such as a doctor) boldly assert that the generic is utterly identical and just as good as the original might well have an effect - but we're into the realms of psychology and "bedside manner" rather than hard science. Worse still, if you yourself now have doubts over the generic drug - then that might well be subconsciously passed onto the patients, which would be a clear case where the nocebo effect could happen.

SteveBaker (talk) 19:14, 18 June 2013 (UTC)

I am the original poster. Thanks to everyone who responded. I am not sure I am doing this post correctly, I've never before posted answers. One of the later contributors extrapolated on the difference between generic and brand names. This is not my situation at all. We are talking about a perceptible difference between two generics. Today's case in one of many in my practice. In the environment I work in everything might be suspect (I am a prison psychiatrist. I see up to 30 patients a day). This case however stands out. The man said that he had taken citalopram for 7 years and it always worked for him. Two weeks ago he was given citalopram from a different maker and now he is complaining that it is not working, he is getting depressed.

About 15 or 20 years ago I read an article about an attempt to compare the bio availability of brand name Tegretol with various generic carbamazepines. Surprisingly some of the generics appeared to have substantially better bio availability than the brand name medication. That article led me to believe that the fillers are responsible for the difference and that they are not regulated.

Thanks. - Alex — Preceding unsigned comment added by 168.178.74.53 (talk) 20:17, 18 June 2013 (UTC)

One important consideration is that even though generics need to meet the same standards as all other drugs, they are in fact much less closely monitored. Also, because the profit margins are significant smaller for generic drugs than for branded drugs that not yet off patent, there is a very real and very significant pressure to cut manufacturing and distribution costs. That's a situation that is simply ripe for abuse. See for example the massive criminal fraud that pervaded generic manufacturer Ranbaxy: http://features.blogs.fortune.cnn.com/2013/05/15/ranbaxy-fraud-lipitor/ DrMatthias (talk) 20:28, 18 June 2013 (UTC)

There's also the possibility that the generics are outright counterfeits. You might want to have the patient return to the original med while you have the new generic tested, and also monitor any other patients who were switched to the new med. I personally am highly suspicious of any change to prescribed meds ("If it ain't broke, don't fix it").

As for differences in the binder, my dad had an interesting case where he was using a pill cutter on the name brand to split it into two, but then the generic equivalent just shattered into sharp shards when he tried to use it there. StuRat (talk) 20:38, 18 June 2013 (UTC)

The differences between generic and branded is likely to be similar to that between one generic and another. They certainly do differ in the binders and other non-active ingredients that they use - but (in theory) that's not supposed to make any difference because the FDA requires them not to. My previous comments about nocebo and observer bias still apply. It would probably be unethical - but I'd be strongly tempted to get a batch of the generic that your patient did fine on and dunk them into some food coloring to make them look like something else. If he continues to claim that it's not working then you may suspect the nocebo/observer-bias effect. Sadly, that doesn't help you to do anything about it. SteveBaker (talk) 23:42, 18 June 2013 (UTC)

There's also the possibility that your supplier may have supplied you with counterfeit drugs. I remembered last year in the UK we had a scare about this and I found this article (if you can get past the spam ads) confirming that the US also suffered. --TammyMoet (talk) 11:36, 19 June 2013 (UTC)

Generating electricity by evaporating water

Theoretically, if the relative humidity is r and the ambient temperature is T, then given N molecules of water, you can extract approximately an amount of W = -N k T Log(r) of work by letting the water evaporate (this is assuming the ideal gas law for water vapor, I leave this as an exercise for the Ref Deskers). This means that at a relative humidity of 60% at 20 C, one liter of water could theoretically generate about 69 kJ of energy.

The question is if we can generate electricity using a process that involves evaporating water. One can think of the following process. If we have two cups of water and we add salt to one cup, then one can generate electricity using electrodes one of which can absorb sodium ions, the other electrode can absorb chlorine ions. When the electrodes are saturated one puts them in the cup of water without salt, electricity will then run in the other direction as the ions from the electrodes dissolve into the water. This process exploits the difference in salt concentration of the two cups of water and it has been tested in practice. So, we can just use this process until the salt concentrations are equal. Then we wait until all the water has evaporated away, we then get the salt back and we can start the same process again. But this seems to me a cumbersome process that doesn't generate a lot of power. Count Iblis (talk) 17:01, 18 June 2013 (UTC)

This building can power seven conventional 60W light bulbs. Good thing we have LED light bulbs nowadays :) Wnt (talk) 20:52, 18 June 2013 (UTC)

I don't see how evaporation contributes to the energy generation there. Looie496 (talk) 17:42, 18 June 2013 (UTC)

Yup - and given that the world is neither short of salty water nor fresh(ish) water, why bother with the evaporation at all? Just swap the water over at the appropriate stage... AndyTheGrump (talk) 17:46, 18 June 2013 (UTC)

See osmotic power. You could certainly increase the concentration of some salt via evaporation and then use the resulting gradient to provide power. It's probably not very effective, though. --Stephan Schulz (talk) 17:58, 18 June 2013 (UTC)

There are of course other ways that evaporation of water can provide power - hydroelectricity is in most cases ultimately driven by the process... AndyTheGrump (talk) 18:09, 18 June 2013 (UTC)

One form of Ocean Thermal Energy Conversion involves warm surface water evaporating under reduced pressure, the vapor then driving a huge low-pressure turbine (essentially an enclosed windmill) and finally condensing on contact with cold deep-sea water. (Personally, I'm not so sure this would work at all -- and even if it does, it would be EXTREMELY inefficient because of the low temperature difference.) 24.23.196.85 (talk) 01:23, 19 June 2013 (UTC)

Merkel

How much does Angela Merkel weight in atomic mass units? --Wissbegieriges (talk) 18:16, 18 June 2013 (UTC)

Well, Ms Merkel's weight does not seem to be published anywhere I could find. This says that an average 58 year old caucasian woman weighs 70kg - and that the 25/75 percentile span is +/- 10kg. She doesn't appear to be excessively large or skinny - so that's a reasonable range. An atomic mass unit is 1.6x10^-27 so just divide one by the other and you'll have your answer - somewhere between 36,000,000,000,000,000,000,000,000,000 and 48,000,000,000,000,000,000,000,000,000. SteveBaker (talk) 18:44, 18 June 2013 (UTC)

Problems with the definition of the newton in relativity

If the newton is the force required to accelerate a 1 kg object at 1 m/(s^2), then that seems to be only accurate classically, because F=ma is not valid relativistically. In my opinion the Newton should be defined as the force that will cause a 1 kg m/s change in an object's momentum if exerted over the course of a single second. But do we actually gain by using a relativistic definition of the newton?--Jasper Deng (talk) 19:27, 18 June 2013 (UTC)

Forces need to be treated with a Lorentz transform when considering relativistic reference frames. If you do this correctly, "all the math works out." See Lorentz invariance with respect to momentum and force. Nimur (talk) 21:17, 18 June 2013 (UTC)

But the problem is, we have:

$\mathbf {F} ={\frac {d\mathbf {p} }{dt}}={\frac {d}{dt}}({\frac {m\mathbf {v} }{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}})={\frac {m\mathbf {a} }{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}+{\frac {mva\mathbf {v} }{c^{2}({\sqrt {1-{\frac {v^{2}}{c^{2}}}}})^{3}}}$

(if my differentiation is correct)

which means, a constant force does not lead to a uniform acceleration, so 1 N does not exactly produce an acceleration of 1 m/s^2 for a 1 kg object.--Jasper Deng (talk) 21:39, 18 June 2013 (UTC)

Note relativistic mass. In fact, this equation can be derived from the assumption that momentum remains conserved while mass increases, if I understand correctly. Wnt (talk) 22:02, 18 June 2013 (UTC)

Usually, when we refer to the mass of an object, we refer to its rest mass, I'm pretty sure.--Jasper Deng (talk) 23:40, 18 June 2013 (UTC)

When we refer to mass and we know we are worried about relativistic reference frames, we don't leave the interpretation up to chance! Specify what you mean. For example, the article I linked expressly defines inertial mass and invariant mass. The article defines and uses a different mathematical symbol for each value. Things get way too confusing if everyone is interpreting "mass" to mean different things! Nimur (talk) 00:19, 19 June 2013 (UTC)

I never really grokked what Lorentz transforms were for-- so thanks OP for the question and Nimur for the answer! SemanticMantis (talk) 02:23, 19 June 2013 (UTC)

The definition of the Newton doesn't specify which kind of mass is referred to.--Jasper Deng (talk) 05:39, 19 June 2013 (UTC)

Oh, is that so? Perhaps you aren't looking hard enough: there's a whole club full of unit nerds who get together and standardize this sort of definition - accounting for all sorts of theoretical and practical specifics. The more pedantically one nitpicks at such things, the more pedantic the responses have to become. Nimur (talk) 06:04, 19 June 2013 (UTC)

None of that is necessary. The Newton is defined as equivalent to 1 kg m / s^2. That definition works in relativety just as well as in classic physics. Dauto (talk) 03:32, 19 June 2013 (UTC)

Not really. For example, torque is measured in N m, which is equivalent to the joule, but is clearly a different kind of quantity.--Jasper Deng (talk) 05:37, 19 June 2013 (UTC)

Your statement is correct but misses the point. The Newton is not defined as a specific force acting on a specific mass creating an specific acceleration. It is defined as specific combination of base units. Now, if you really must see a unit definition as a description of a specific experimental set up (and believe me, you don't - but if you must) than just add the requirement that the accelerating object is at rest. Dauto (talk) 13:34, 19 June 2013 (UTC)

The meter, second, the kilogram, that's way too many quantities! The meter and the second are not independent physical quantities, mass and energy are the also the same quantites up to a conversion factor. So, you can just as well dump the Newton and work with e.g. the unit of power. Count Iblis (talk) 12:01, 19 June 2013 (UTC)

% fat-free

I'm wondering about how (under US regulations) a product can claim to be 97% fat-free when it's 80% fat. Any ideas? — kwami (talk) 23:04, 18 June 2013 (UTC)

On the face of it, that seems impossible - so I'm guessing there is something missing in your description. What exactly is the product and what are the other claimed ingredients? SteveBaker (talk) 23:20, 18 June 2013 (UTC)

Is that like those "low fat oils?" Either they have replaced it for soemthing else, or I don't know. OsmanRF34 (talk) 23:50, 18 June 2013 (UTC)

Varying definitions of "fat". HiLo48 (talk) 00:http://images.google.com/11, 19 June 2013 (UTC)

OK, it could have low saturated fat, or low monounsaturated fat, or low cis fat or whatever. But I doubt the marketing people are not aware that they are playing with the ignorance of the people who associate fat = bad, so low fat = good. OsmanRF34 (talk) 01:20, 19 June 2013 (UTC)

This page says "When a label claims to be 95 percent free, it is not saying—contrary to popular belief—that only 5 percent of the calories come from fat. The legal definition of 95 percent fat free is 95 percent of the weight of the product doesn’t contain fat". ( spam filtered 3fatchicks.com/does-95-percent-fat-free-mean-that-only-5-percent-of-the-calories-come-from-fat/ ). Perhaps not the most reliable source, but I think they're on to something, regarding the labels being regulated by weight, not calorie content. When I googled for this, I also found this link from the US FDA[www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/LabelingNutrition/ucm064911.htm], but it doesn't load for me. SemanticMantis (talk) 02:34, 19 June 2013 (UTC)

I typically see this with luncheon meats. I doubt weight alone would account for it, as I don't think sliced meat contains that much water. Even 98%-fat-free chicken soup is only 35% fat.[3] Weight would account for this meat,[4] which is 97% fat-free and 19% fat, but I've come across meats with similar claims that are 70 or 80% fat by calories. I can't figure that out. — kwami (talk) 05:12, 19 June 2013 (UTC)

If you had a drop of oil in a gallon of water, it would be 99.9999....% fat free by weight, and 100% fat by calories. This probably explains the other products, since they just bulk out the product with something with negligable calorie value (not just water, fibre is another example of a food type with nearly no calorie value). Of course, if the small amount of fat is contributing that much to the percentage of calories, the overall calorie content is probably less than the normal version. MChesterMC (talk) 08:25, 19 June 2013 (UTC)

From the the soup link, there are 2.5g of fat in 120mL (~120g) of soup. 2.5/120*100 = 2.08% fat, or just about 98% stuff that isn't fat. Since about 98% of the stuff in the soup isn't fat, it's reasonable for the manufacturers to call it 98% fat free. In terms of energy content (i.e. calories), at a rough approximation, (2.5g fat)*9cal/g = 22.5 calories from fat (the linked label has 25 calories from fat, which is close enough) and (10g carbohydrates)*4cal/g = 40 calories from carbohydrates, which account for 62.5 (or 65) of the 70 calories listed on the label. So fat, although only being 2% of the mass, accounts for about 35% of the calories. A similar calculation could be done using the linked information on chicken breasts.--Wikimedes (talk) 10:13, 19 June 2013 (UTC)

OK, so to summarize: We believe that the 97% and 80% numbers that our OP is seeing are percentages of different things. The 97% is the percentage of fat by weight and the 80% is percentage of calories that come from fat.

So imagine something like a bowl of lettuce with some small amount of cheese crumbled onto it. Suppose that 97% of the food is lettuce, which has almost no calories at all and 3% is cheese, which is almost all fat and therefore contributes 80% of the calories in that product. You'd be correct in saying that the meal is 97% fat-free, and that 80% of the calories come from fat.

Which number you care about is tricky. If you're trying to lose weight then neither number matters - all you should care about is serving size and calories per serving. If you're trying to eliminate fat from your diet, then the 97% fat-free number is the one you care about.

SteveBaker (talk) 12:43, 19 June 2013 (UTC)

Yes, I understand that. But chicken soup should be an extreme, as it's mostly water. I don't understand how luncheon meat, which has relatively little water (or fiber) can have a more extreme discrepancy than soup. — kwami (talk) 04:56, 20 June 2013 (UTC)

Can you give us some specifics? What brand of lunchmeat? Care to post a photo of the nutrition label, or at least transcribe it? --Trovatore (talk) 07:37, 20 June 2013 (UTC)

As for the soup, did you compare with this one? The difference of the calories is big. Oda Mari (talk) 09:42, 20 June 2013 (UTC)

In the US products which are basically 100% fat can be labelled "fat free", due to rounding down and absurdly small portion sizes. Pam cooking spray comes to mind: [5]. This requires some serious double-think to comprehend. StuRat (talk) 09:09, 20 June 2013 (UTC)

Ha, good find! SemanticMantis (talk) 15:00, 20 June 2013 (UTC)

I've never encountered the suggestion that 'X% fat free' should refer to energy (ie calories) rather than mass. Is this something that is done in the US? It seems obvious that the amount of fat in a thing is measured by the actual amount of fat in it. AlexTiefling (talk) 09:20, 20 June 2013 (UTC)

I've not encountered it before either. It's not done in the US.--Wikimedes (talk) 12:38, 20 June 2013 (UTC)

OK - so let's look at an actual can of spam with US labelling: PICTURE HERE.

Six servings per can - the can is about 3" tall - so you get a couple of 1/4" thick slices in a serving - which seems reasonable if you do not intend to die in the immediate future! It has 180 calories, of which 140 are from fat. So 78% of the calories are from fat. Total fat content is 25% of your daily value.

None of the percentages on the can are percentages by weight, or by calorie value. The "25%" number isn't 25% of the product - it's saying that if you eat four portions of spam (two thirds of a can) then you're getting the US government's recommended daily value of fat in your diet. We're also told that in a 56 gram "serving", there is 16 grams of "total fat" - so 28% of the weight of the spam is fat.

Conclusion: 78% of the calories are from fat. 28% of the weight is fat. The amount of fat is 25% of your recommended daily amount.

None of those numbers are remotely close to what the OP is seeing...so we need to know where those 97% and 80% numbers are coming from - they clearly aren't anywhere on the label of a "luncheon meat" product. SteveBaker (talk) 14:26, 20 June 2013 (UTC)

Yes, but the "X% fat free" labeling is usually not on the nutrition label, it's an advertising feature, usually on the front. For the spam above, the front of the can MIGHT say "72% fat free." -- because, by weight 28% is fat, and 72% is not. Here is a working link to the US FDA CODE OF FEDERAL REGULATIONS [6]. According to that,

“ (6) The term "_ percent fat free" may be used on the label or in the labeling of foods, provided that:

(i) The food meets the criteria for "low fat" in paragraph (b)(2) or (b)(3) of this section

”

-- spam probably doesn't meet the "low fat" requirements, but a similar product (e.g. spam lite) may well do so. SemanticMantis (talk) 15:13, 20 June 2013 (UTC)

Er, the 'X% fat free' figures clearly relate to the proportion of fat (however measured) in the product itself. All the percentages printed on the Spam can are percentages of the DV (or RDA, as we call it over here) of each of those things that one serving supplies. So you're comparing apples with oranges. Certainly the Spam can doesn't provide an answer to my question - the number of calories from fat is shown as an absolute figure, not a percentage. AlexTiefling (talk) 15:19, 20 June 2013 (UTC)

WARNING TO RESPONDANTS: A major problem with this discussion:

• In UK English, "Luncheon meat" means spam and stuff like spam: minced up meat of dubious origins, ("mechanically recovered head meat" is a nicely evocative turn of phrase isn't it?!), often with large and visible chunks of fat in it, typically packed in aspic and sold in a can.
• In US English, "Luncheon meat" (aka "Lunch meat") means thin slices of lean, pre-cooked, and mostly recognisable meat of the kind you might find on a delicatessen counter or pre-packaged in a plastic tub.

VERY different products! So when answering, it's going to be necessary to define which of those things you mean! SteveBaker (talk) 14:26, 20 June 2013 (UTC)

Thanks, Steve! I try to keep track of pondial differences, but that's one that had so far escaped my notice. --Trovatore (talk) 19:26, 20 June 2013 (UTC)

To be honest, even after close to 20 years of living in the US, it was a new one on me too. I only really understood the difference while looking for a luncheon meat nutritional label on Google images earlier today! SteveBaker (talk) 20:41, 20 June 2013 (UTC)

I was referring to US regulations, and so to deli-type meats, not Spam. I understand that "fat-free" is by weight, so I'm not surprised that something may be 97% fat-free at the same time it's 35% fat by calories, and I know that serving sizes may be made small enough to contain 0.5g fat, which is then rounded off to zero and claimed to be 0% fat. I've even seen butter substitutes that are both 100% fat-free and 100% fat, but those are exceptional cases. What I couldn't figure out was how deli-type meats could be 97% fat-free and 80% fat, as weight, water content, and rounding would not seem to be enough to explain them. I was hoping someone here would be familiar with this, but if not, I'll try to jot down the details the next time I'm at the market. — kwami (talk) 22:51, 20 June 2013 (UTC)

If you could snap a cellphone photo of the packaging - that would be best of all! SteveBaker (talk) 14:23, 21 June 2013 (UTC)

Cleaning the shower stall.

Recently moved into a house with a glassed-in shower stall - which has a whitish film coating the surface that looks like hard water deposits or soap residue or something. So far, we've tried to clean it with:

• Calcium Lime Rust aka "CLR" - (now Phosphate-free)
• CLR-brand shower cleaner
• Scrubbing Bubbles
• Vinegar with Baking soda
• Bar Keepers Friend
• Hard work with various scrubbers and cloths.

Result so far...nothing, zip, nada. Shower still has deposits on glass. I was quite surprised that CLR didn't get it clean - but maybe the new phosphate-free formulation isn't effective.

Any suggestions? OK...any PRACTICAL suggestions?!  :-)

SteveBaker (talk) 23:35, 18 June 2013 (UTC)

I would try Acetic acid or Citric acid in reasonable concentrations (say 25% of Acetic acid). Adding baking soda is counterproductive, as it will neutralize the acid. --Stephan Schulz (talk) 23:48, 18 June 2013 (UTC)

OK - I double checked with my g/f and she has tried vinegar by itself...same problem. But according to Vinegar, the white vinegar we used is only 8% acetic acid - so maybe need to get some of the real thing. We're planning to try some neat lemon juice. SteveBaker (talk) 00:16, 19 June 2013 (UTC)

Be careful with the "real thing", if by that you mean glacial acetic acid. I understand that it's fairly nasty stuff. My dad said just the odor would knock you off your feet. --Trovatore (talk) 00:19, 19 June 2013 (UTC)

Over here, 25% Acedic acid is sold in 1/2l and 1l bottles, as "Essigessenzce" (essence of vinegar). It's primarily marketed as a food product (dilute 5-1 with wine, juice, or, boringly, water, to make various vinegars), but also for cleaning. --Stephan Schulz (talk) 06:47, 19 June 2013 (UTC)

Is it possible to reduce white vinegar (reduce in the cooking sense, not chemical)? Does it form an azeotrope, or can you obtain glacial without burning it? Plasmic Physics (talk) 00:22, 19 June 2013 (UTC)

If it corrodes metal should you reduce it in a Teflon coated kitchen vessel, under good ventilation or outside? Plasmic Physics (talk) 00:28, 19 June 2013 (UTC)

I don't remember off the top of my head, but the WP data page on acetic acid doesn't show any azeotropes on the distillation curve -- so yes, if you heat the stuff hot enough (116 C or more) you can get glacial acid. WARNING -- DO NOT try this at home without BOTH a fume hood AND a gas mask, because the smell would knock you out cold! (I know from experience -- I've accidentally inhaled just a tiny whiff of glacial acetic acid vapor, and it almost burned my nose right off!) Also, whatever you do, DO NOT concentrate acetic acid in a metal container -- it will undergo a single displacement reaction, forming the corresponding metal acetate (i.e. burning a hole in the metal) and releasing hydrogen gas (which could cause an explosion if you're using an open flame as your heat source). And no, a Teflon-coated saucepan WILL NOT do -- the Teflon degrades over time with high temperatures, and can also easily become scratched during normal use, exposing the metal underneath. Use a glass or plastic container instead. 24.23.196.85 (talk) 01:55, 19 June 2013 (UTC)

Except for being highly toxic and a disposal issue (i.e. you don't want it in the water supply), chromic acid will clean the white off of rice. It's great at getting sparkling glass, though it is nasty stuff. IIRC, you make it with a 50/50 mixture of concentrated sulfuric acid with a saturated solution of sodium dichromate. But again, it's so nasty, unless you have a means of using it in a well-ventilated space, avoid all skin contact, have proper breathing protection, and are scrupulously careful to properly dispose of every drop you use, it's probably not practical. But if chromic acid doesn't get it clean, it isn't meant to be clean. --Jayron32 01:16, 19 June 2013 (UTC)

Yes, maybe Steve Baker is scrubbing like mad a frosted glass. OsmanRF34 (talk) 01:22, 19 June 2013 (UTC)

Maybe not even deliberately frosted. Glass can become etched, and if it is etched, it can be as scrupulously clean and look milky or cloudy. --Jayron32 01:59, 19 June 2013 (UTC)

"Home is where you can scratch where it etches." ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:25, 19 June 2013 (UTC)

Hmmm, I thought I mentioned: "OK...any PRACTICAL suggestions" ?? :-) I don't think I'll be using chromic or glacial acetic acids!

@Stephan: I'll see if I can find some of this "Essigessence" stuff. Thanks!

I corrected the spelling above (too many languages for one head). Amazon seems to have 20% vinegar, which I guess would be close enough. --Stephan Schulz (talk) 14:07, 19 June 2013 (UTC)

@OsmanRF34: Yes, I considered the possibility that it's deliberately frosted - but it's clearly too subtle for that...also it exhibits a pattern that looks exactly like water droplets.

@Jayron: That's a definite possibility at this point...but it's hard to imagine how that would have happened. Perhaps calcium deposits from the water were scrubbed into the glass by some previous aggressive effort to clean it without chemical assistance. Are those deposits hard enough to scratch glass?

SteveBaker (talk) 12:05, 19 June 2013 (UTC)

(Oh - and incidentally, you don't need to distil your own glacial acetic acid - you can buy a bottle for $17 on Amazon.com!) SteveBaker (talk) 12:29, 19 June 2013 (UTC)

Perhaps nail polish remover and peroxide will clean it? Plasmic Physics (talk) 13:12, 19 June 2013 (UTC)

Nah, better not try that, not unless you have an affinity for explosive showers. Plasmic Physics (talk) 13:15, 19 June 2013 (UTC)

Now that is an effective test of the Wikipedia disclaimer. Please note acetone peroxide is one of those potent explosives used only by nutjobs because of a tendency to spontaneously explode when least expected, though most consumer formulations of hydrogen peroxide shouldn't be nearly concentrated enough (I think). Wnt (talk) 15:22, 19 June 2013 (UTC)

Have you tried undiluted bleach? this can remove soap scum and fungus pretty well. Graeme Bartlett (talk) 21:49, 19 June 2013 (UTC)

Use dilute hydrochloric acid from a pool supply store. We use it for removing calc build-up in pipes on an industrial scale, and also it cleans the glass windows on the work utes up real good. 39.214.158.84 (talk) 22:36, 19 June 2013 (UTC)

CONCLUSION : Figuring that the glass is probably etched rather than having some very resistant material on the surface, we tried using some of that Rain-X stuff that you put on car windshields to make them repel water better. It worked wonderfully! The haze is now invisible - and as a bonus, the water sheets off of it more easily. The only likely downside is that we'll have to re-do it periodically. Thanks for all of the advice! SteveBaker (talk) 00:28, 20 June 2013 (UTC)

Steve, I know you like do it yourself challenges. I've heard it is possible to take lightly etched glass and restore it using polishing compound and buffing machines. The goal is of course to polish out the surface and make it smooth again. I've never tried it myself, and I suspect there is a substantial risk of making things worse, but if you are feeling adventurous then I suppose you could look into trying that. Dragons flight (talk) 06:15, 20 June 2013 (UTC)

Yes, but at that point, simply replacing the three panes of glass would be a lot easier! Anyway - RainX seems to work well. SteveBaker (talk) 13:56, 20 June 2013 (UTC)