Wikipedia:Reference desk/Archives/Science/2014 May 22

= May 22 =

Quitting Smoking and Weight Gain
Not a medical question, just can't seem to find an accurate answer and am curious. Disclaimer out of the way - gaining weight is associated with quitting smoking. From what I've read, thus far, I've heard that this is due to three different things: smoking increases metabolism, increased eating, changes in gut flora. The common amount of weight gain is supposed to be around 10 pounds - but I've also read that that number isn't useful for individuals since some smokers gain a much larger amount that skews it. So, here's my question (I'm hoping that there is some reliable data to actually look at): what is the primary cause of this weight gain, is it harder to reverse gain after quitting, what determines who will gain a lot as opposed to a little? Essentially, how does this all work? --back to the disclaimer: when I can't sleep, I just google random things that pop into my head, this happened to be one of those things; but, since I can't find any really rock solid details, now I'm even more curious. Thank you for any help (sorry for the ridiculously long question):-) Phoenixia1177 (talk) 08:00, 22 May 2014 (UTC)


 * This recent review article says "The mechanism of weight gain includes increased energy intake, decreased resting metabolic rate, decreased physical activity and increased lipoprotein lipase activity." (and also lists several complicating factors, e.g. age, genetics, heavy smoking, etc.) . This google scholar search has many relevant articles, some seem are more focused than the general review . SemanticMantis (talk) 13:52, 22 May 2014 (UTC)


 * I suspect that the sense of taste plays a role, too, although that's a bit difficult to quantify, so less likely to be studied by science. I certainly know that for me, a nonsmoker, the smell of cigarettes makes me lose my appetite.  Interestingly, it's not the tobacco itself, as pipe tobacco, which is relatively pure, doesn't cause this effect.  Specifically, I suspect it's the ammonia they add to cigarettes, to draw out the flavor, that turns my stomach.  I once bought a candy bar from a vending machine and immediately spit it out as inedible.  I went back and looked at the rest of the vending machine to find they had cigarettes in there ! StuRat (talk) 14:00, 22 May 2014 (UTC)


 * There may be multiple factors here, but probably one of them is serotonin. Nicotine is known to increase the release of serotonin in the brain, and one of the effects of serotonin is to suppress appetite.  So quitting smoking means less serotonin, which means more appetite. Looie496 (talk) 17:34, 22 May 2014 (UTC)


 * Another factor is that some people eat sweets (candies) to distract themselves when they have cravings; the additional energy intake is what causes weight gain.

Genetic engineering to alter genes
You can add genes to cells with a vector such as a virus. How do you remove or alter existing genes? 203.45.159.248 (talk) 08:40, 22 May 2014 (UTC)
 * Well, when adding genes to a specific location, you would make a vector containing the gene of interest (plus a selection marker) flanked on either side by a stretch of DNA that is the same as the genomic region you're planning on inserting the gene into, this to facilitate the homologous recombination. Now imagine doing the same, but instead of the gene of interest, you put nothing in between the flanking genomic regions. You would remove from the genome any sequence that is in between the flanking regions. Also note that it's not necessary to remove the whole gene of interest from the genome to knock out the function, just the first exon or so is normally enough. Now, in practice you wouldn't have nothing in between your flanking regions, you would still introduce something to help with selection, like an antibiotic resistance gene, or a fluorescent protein. Note that this is the traditional way of doing things, these days with things like CRISPR the methods can be different, though the basic principle is the same. Fgf10 (talk) 08:52, 22 May 2014 (UTC)

I have -4 power in my left eye but almost neutral in my right eye. If i stop to use the spectacle then what problem may arise ?
I have -4 power on my left which is in X-axis in some degree rotation due to which my contact lens always move when i blink my eyes and everything go blur. What kind of contact lens is suitable for me? — Preceding unsigned comment added by Zonex shrestha (talk • contribs) 09:40, 22 May 2014 (UTC)
 * Wikipedia's reference desk will not answer requests for medical advice. See an eyecare professional, who can answer this question.  -- Jayron  32  09:42, 22 May 2014 (UTC)


 * We also do it gently, so as to avoid putting people off. IBE (talk) 02:49, 23 May 2014 (UTC)


 * See here. Count Iblis (talk) 11:20, 22 May 2014 (UTC)


 * If your lens is designed to correct astigmatism at all, it ought to be weighted to keep its alignment; if it's not meant to correct astigmatism, then I can't guess why blinking has that effect. I've had no such trouble as you describe in about seven years, though sometimes when I put them on they take a few minutes to settle at the proper angle. —Tamfang (talk) 07:21, 23 May 2014 (UTC)

Persistance of Electromagnetic radiation
Do electromagnetic radiation persist even in a reduced scale and in that case can electromagnetic radiation from distant past be detected and amplified and thus people can witness events from arbritrary past without affecting the past that is travel backward in time.Why is in not research directed to develop theory and contrivance to achieve this in reality.In time travel page there is a reference to such claims.When stars stars several light years away are detected why is this not possible.I want to ask that staying in this planet can people travel back in history or visualise it in some television type of device.Do laws of physics pose a barrier to this and then why cannot these barriers circumvented when technology has advanced to a state where traces of gamma radiation from distant space detected and analysed, then why not local visible EMR.Cannot be there any EMR from past in atmosphere.Sorry for my absurd insane naive question. 117.194.253.103 (talk) 16:19, 22 May 2014 (UTC)


 * Certainly. We can detect electromagnetic radiation from the "Big Bang".  That's because it takes time for light to get from one point to another.  If we do some absurd approximations of reality, we can hypothesize of a perfectly sealed box containing perfect (non-absorbing) mirrors.  If we turn on, then immediately turn off, the a light source inside such a box, I don't see why said photons shouldn't remain there in perpetuity.  The problem is that no such box, and no such mirrors actually exist; even the best mirrors absorb enough light that said photons would dissipate within fractions of a second.  -- Jayron  32  16:39, 22 May 2014 (UTC)


 * As far as why we can't view our own history this way, the EM radiation from a human event is absurdly small compared with that given off by a star. In either case, the level reduces dramatically as it spreads out into space, but the star starts with so much EM radiation that it's still detectable above the background noise.  Not so for human events.


 * A secondary problem is that we can't observe the Earth from very far away. And, if we send a space ship there to observe, it will move much slower than the speed of light, meaning the "past" it observes once it arrives there will have happened long after the ship was launched.


 * Reflected EM waves are one way around this problem, using a natural body which has been there all along. The Moon can reflect radio waves, for example, to lets us hear a couple seconds into our past.  With anything more distant than the Moon, the reflection would again be too weak to detect above the noise. StuRat (talk) 17:46, 22 May 2014 (UTC)


 * We can see light from the past of distant stars because they are distant and also extremely intense. EM radiation travels in basically a straight line unless something reflects or refracts it or until it gets absorbed. Any EM radiation from Earth from 100 years ago that hasn't been absorbed by something already is 100 light years away now. Since it's mostly going out in all directions, the intensity is decreasing with the square of the distance. Trying to see any sort of reflection would be like shining a flashlight at a hand mirror a mile away and then using a solar panel placed behind the flashlight to try to collect the reflected light. Even in the middle of the night it would be nearly impossible, but we're constantly generating EM radiation, so it would be more like trying to do it during the middle of the day, and trying to somehow sort out what's reflected from the flashlight and what's ambient light. Mr.Z-man 18:14, 22 May 2014 (UTC)


 * So we can imagine the following thought-experiment. Suppose we launch a gigantic mirror out into space - and use it to look back at ourselves through a similarly gigantic telescope.  If the mirror was 10 light years away, we'd be able to watch what was happening on earth 20 years ago.   This sounds like a fun way to look into the past...something that historians would kill to own.  But there is a fundamental problem...even in principle.   To get the mirror 10 light years away will take more than 10 years to do - because our spaceship can't fly faster than the speed of light.  And once the mirror is out there, it'll be another 10 years before the light reflected from it gets back to us to see.   So the oldest event that such a mirror could possibly see would be from the moment of it's own launch!   We can't ever see back to a point before the moment we decided to do it!  So rather than go to all that trouble, why not just put a satellite into low earth orbit with a big camera and lots of storage space and simply record the events on earth, replaying them as needed in the future.  Such a device still can't see past the day it was first turned on - but it's a lot less trouble to make and doesn't need a near-light-speed rocket to get it up there where we need it.   The only way we can see into the past like that is if there is some kind of large deep-space mirror that's already out there courtesy of a freak of nature - or a handy alien civilization.  SteveBaker (talk) 19:36, 22 May 2014 (UTC)


 * There should be such a mirror - the light that lenses all the way around a neutron star or black hole. Has anyone ever calculated how much signal you can get that way?  I mean, it sounds ridiculous, but that's what I thought about seeing extrasolar planets. Wnt (talk) 20:35, 22 May 2014 (UTC)

3D printers
It's looking like my expensive, high-tech 3D printer is actually a pile of junk that breaks every few days, falls apart for no reason, and costs a lot to keep repairing... Whilst I would love to get a proper expensive model, from what I've seen they cost at least ten times as much, money I don't have right now, so I'll have to resort to buying a nice cheap one, in fact if this experience is anything to go on, something as cheap as possible, so I don't regret having wasted even more money.

Trouble is, back when I bought this, there were basically three different models available for less than £2000 whereas now there are about 50, and I have no idea which are any good, which are available in my country, how much they cost, and so on.

What I need is some place where I can find out which 3D printer options there are in the UK, giving the actual price, including shipping, tax and so on, and preferably with some example of what they can do. That or just someone's recommendation of a reasonably cheap but good model to look at.

213.104.128.16 (talk) 16:55, 22 May 2014 (UTC)


 * If you need one, but can't afford to buy one that's reliable, it might make sense to rent (hire) one, find a timeshare arrangement with others in the same predicament, or simply pay others who have the device to do the 3D printing for you. This will hopefully only be a temporary arrangement, until the cost of quality 3D printers comes down.  This will avoid the problems of high expense and low reliability you currently have from being on the bleeding edge.  Also, trying out various machines in this way will give you better insight into which one you might want to buy and which to avoid. StuRat (talk) 17:53, 22 May 2014 (UTC)


 * Sadly, they still do need a fair bit of tweaking and adjusting to play nicely. Things like getting the bed perfectly level and having the head tracking across it at perfect height is a pain to manage - adjusting temperatures and flow rates according to the kind of plastic and the ambient temperature in the room - and maybe according to the nature of the thing you're trying to make...they are definitely not "plug and play" like a 2D printer. There are companies who are working hard to get rid of those issues - but I have to say that I can't think of any sub $3,000 device that's going to work without a lot of tweaking and adjusting.  There was a great review of the market in Make Magazine a few months ago - there was a special edition which did a head-to-head trial of 23 different low-cost printers.   The problem is that since then, nearly all of the printers have come out with newer versions, etc...so the marketplace is changing faster than the reviewers can keep up.  SteveBaker (talk) 19:22, 22 May 2014 (UTC)


 * I canna help but make a quick reference to an old song:  Enjoy... :) Wnt (talk) 19:39, 22 May 2014 (UTC)


 * Yeah - that's a great analogy! When cars first appeared, you expected to have to stop and fix minor breakdowns and to tweak and adjust - but as they became more popular, they got more reliable and needed less and less special care.  The owner's manual for my '63 Mini lists things you have to inspect and adjust every 1000 miles - with more things every 3000.  My 2012 MINI needs nothing whatever done to it except filling the gas tank until the 25,000 mile service.  Not even an oil change.   Low cost (by which I mean "less than $20,000") 3D Printers are still pretty much at the first stage. SteveBaker (talk) 20:32, 22 May 2014 (UTC)


 * Odd thing is, the actual printing is going quite well, it's the mechanics of the printer itself that doesn't work, screws coming loose, bits breaking off, parts getting jammed or stuck. Hence why I'm thinking getting a cheaper model might not really make much difference, but could at least give me a spare to use whenever either one is needing repairs. 213.104.128.16 (talk) 20:08, 22 May 2014 (UTC)


 * If screws are coming loose, you might want to get some "threadlock" at your local auto-parts store...that at least is an easy fix.


 * There is really no substitute for knowing in great detail what every little bit does - so when it goes wrong, you can easily and confidently find and fix the problem. My 3D printer is temperamental as all hell - but at least when something goes wrong, I can fix it without much grief.   It's mostly made from laser-cut plywood - and since I also own two laser cutters, I have made various replacement parts and redesigned some of the bits that fail.   That would be impossibly annoying if I was in a production setting - but fortunately, right now, I'm just exploring what these machines can do and trying to figure out how to make money if I were to own a bunch of them.


 * SteveBaker (talk) 20:32, 22 May 2014 (UTC)


 * Ever make any replacement parts in the 3D printer itself ? StuRat (talk) 16:10, 23 May 2014 (UTC)


 * No - my 3D printer only has one plastic part (a large gear wheel) - and I doubt it'll need replacing anytime soon. However, member of the RepRap project (which more or less started the 3D printer revolution) routinely make a large percentage of the parts for a new 3D printer using previous generations of the same printer.  I also made lots of parts for my #2 laser cutter using my #1 laser cutter - and parts for the #1 laser cutter were made on a commercial laser cutter that I had access to at the time.


 * Uh oh. Berserkers, here we come! --Trovatore (talk) 00:55, 24 May 2014 (UTC)


 * "Now that we no longer need the humans for repairs, we can begin our plan to liquidate them !". StuRat (talk) 00:57, 24 May 2014 (UTC)


 * The machine on the left made all of the plastic parts for the machine on the right...but as you can see, not much of the machine was made of plastic back then. Each new generation of RepRap has more printable parts - so they are definitely edging towards being able to make one machine using another. SteveBaker (talk) 04:09, 24 May 2014 (UTC)


 * Not something I'm into yet but I've some ideas for models and intend just sending off for them to be printed rather than getting my own printer at least to start with. By the time I've spent enough for one printer they should be quite a bit better is my thought and I'm more interested in getting good models. Dmcq (talk) 17:25, 23 May 2014 (UTC)


 * As a disclaimer, I've read a fair bit about but never actually owned a 3D printer due to cost reasons. While I somewhat agree with SteveBaker, I also think it's useful to look for a good community, particularly if you don't have much experience with 3D printers or the various mechanical parts that make up one. Personally, I'm partial to the various RepRap derivatives, particularly those who are still associated with the original community, both because of their strong open source heritage and also as being one of the early drivers of low cost 3D printers. They are strongly DIY, but as hinted at, they do have a good community . Of course that still leaves many, many options.
 * I would take care of any Kickstarter projects, even those which have launched already. While there has undoutedly been some goodies there, many of them overpromised and under delivered and even if you're buying after the Kickstarter when the product is being sold, you need to be careful that the printer doesn't have numerous flaws relating to trying and failing to meet their Kickstarter promises (or simply the fact that the designers aren't very good but jumped on the Kickstarter/3D printer bandwagon because it seemed cool). However there are other 3D printers with decent communities and printers outside the RepRap one, I'm simply less familiar with them.
 * Of course, you shouldn't expect unpaid strangers to fix all your problems for you, but a good community be able to offer advice when you do have problems which you can't work out how to fix yourself after resonable efforts on your part. It will also be a useful place to get help in making sure your printer is working properly in the first instance which will likely reduce problems in the future.
 * As SB has said, you should expect regular maintenence although a decent printer set up properly should generally be able to print for more than a 'few days', I'm presuming 'a few' here means under 10, probably under a week. This applies even if you buy an already assembled but cheap printer, although personally I would suggest looking in to something with some assembly isn't a bad idea since you'll probably end up having to do a fair amount of similar stuff over time any way.
 * (I'm actually partial to the Ormerod myself, but that's partially because of the price and it sounds like your budget is higher. But also because I'm quite interested in the 3 or more colour/plastic idea, and RepRapPro, the designers, of the Ormerod seems to be one of the few RepRap or really any very low cost printer which is working on that. I admit the fact that the designer is one of the RepRap pioneers also helps. In particular, based on what you've said, I'm not sure if I'd recommend it here. Amongst other things, the Ormerod was a fairly major redesign and correspondingly had a number of flaws but it's still at its first version. On the flip side, the connection with RS and the large number of users has meant a fairly large community has developed around it, even compared to other RepRaps.)
 * Nil Einne (talk) 18:30, 23 May 2014 (UTC)

Self-detonating buildings
To be clear, this question is not about anecdotes, including the 9/11 Truthers, though they inspire the question. Strictly as a matter of published science or serious policy discussion in openly published, reputable sources, has there ever been a discussion of any idea to pre-place explosives in certain very tall and/or vulnerable buildings so that if their structural integrity is compromised by an attack or natural disaster, they could be brought down in a clean footprint rather than starting a chain of falling dominoes that takes out half the city?

Alternatively, are there sound architectural reasons to conclude that no skyscraper, no matter what is done to it, could ever really go over sideways and push over its neighbors in a chain reaction? Wnt (talk) 20:44, 22 May 2014 (UTC)


 * The sound architectural reason that there are no pre-placed explosives in a building is that they're forbidden by building codes - they're illegal. Building codes extensively regulate hazardous materials in any given structure: concentrated alcohol, for instance, which can be remarkably dangerous in a fire. Buildings which contain explosives in any quantity are ... (consults 2012 International Building Code) ... are classified as H-1 (high-hazard at highest level) occupancies (as opposed to business or residential occupancies, like most high rise buildings). The IBC limits any building containing explosives to one story, no matter what construction material it is. Building codes and fire codes are predicated on the subordination of protection of property to the protection of life.


 * As for falling over sideways, most things will fall straight down unless they're given a strong reason to do otherwise, and in controlled demolitions great care is taken to create a consistent line of weakened structure so that something that is supposed to lay over sideways really does that instead of falling in a heap. Buildings really don't want to move, and they're not designed for dynamic loading (beyond earthquake, vehicle/machinery and wind loads), so they don't necessarily fail intuitively under extreme conditions. Buildings are composed of lots of individual parts and are unlikely to act as a unit after the weakest components have failed. However, one failure mode of the John Hancock Tower could have had it fall over sideways. The Citicorp Building could have fallen diagonally in some circumstances (both cases are documented in their respective articles). That's not to say they'd keel over as a unit, it would have almost certainly been messier than that.


 * In no case would any sane building inspector or fire marshal ever countenance any form of explosives in any building occupied by anyone other than someone who is directly involved in handling explosives. Speaking as an architect, I'd expect to lose my license if I proposed anything of the sort. I'd certainly be uninsured, as would the destructible building.  Acroterion   (talk)   21:09, 22 May 2014 (UTC)


 * Indeed. Murphy's Law:  The installation of any self-destruct device, will, sooner or later, be triggered off by some unforeseen circumstances or by some numbskull, at a totally inappropriete time. Having said that, buildings are engineered to fail gracefully.  For example, one of the great benefits of steel re-inforced concrete it that under severe overload, cracking and spalling occurs well below the level of overload that will cause catastrophic failure.  The building manager has thus time to carry out corrective action.  Multi-story buildings are engineered so that core load bearing structures do not fail until the fire destruction is at a level where evacuation should be either complete or too late. 139.168.241.56 (talk) 02:40, 23 May 2014 (UTC)


 * It would be interesting to figure out just how much it would take to push a building over sideways. I assume a nuclear explosion of sufficient force on one side would do it.  Would a direct hit by an F5 hurricane or F5 tornado do it ?  How about if a dam bursts and it's slammed into by a wall of mud and/or water the same height as the building ?  How about a tsunami the height of a building ? StuRat (talk) 03:47, 23 May 2014 (UTC)


 * A tsunami the height of a building would almost certainly do it; a hurricane or tornado, no way. 24.5.122.13 (talk) 06:21, 23 May 2014 (UTC)


 * It'd have to be calculated on a case-by-case basis. A tall building, narrow in plan on one side and broad in the other direction, with a solid, firmly-connected wall infill and perhaps a soft first level (like a high lobby or pillars) might fall over if hit by a shock broadside on. A building with extensive glazing, differently proportioned, would probably just lose its curtain wall and internal partitions, but still remain mostly standing. Once the exterior wall surface is compromised, the primary structure presents relatively little for the shock to react against. That's essentially what happened at the St. John's Regional Medical Center (Missouri) in Joplin, Missouri that took a direct hit from the EF-4/5 2011 Joplin tornado. The building was pushed around (it rotated slightly), but not pushed over.  Acroterion   (talk)   14:26, 23 May 2014 (UTC)