Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.
This seems like a question with a very wide scope. If this matter can be used as fuel, sure, the energy costs, benefits, efficiency will of course vary depending on the materials, available other materials and technologies used. Also taken into consideration could be the transformations matter can have over time (oil comes from organic material for instance, which can be used as energy source to produce light)... —PaleoNeonate – 07:16, 27 September 2017 (UTC)[reply]
That is what the sun does, continually. Wymspen (talk) 09:51, 27 September 2017 (UTC)[reply]
Relevant link: nuclear fusion (one can hardly assume the OP will know it). Depending on the definition of "matter", a standard fire may qualify too (no mass is lost, but the energy comes from material changes in matter). TigraanClick here to contact me 11:04, 27 September 2017 (UTC)[reply]
"No mass is lost" is true for alll practical purposes but technically incorrect. "Too little mass is lost to measure" would be correct. Every time energy is emitted, mass is lost. This is detailed in our article about Mass–energy equivalence. It takes a lot of light to equal a very small mass. The Grand Coulee Dam's turbines put out roughly 7 gigawatts per hour. The output of the dam for four hours reduces the mass of the Columbia River by roughly one gram. This mass is sent away through the power lines in the form of electrical energy, and some of it goes to electrical devices such as lights or computer monitors where it is converted to light. When the light from your computer monitor hits the walls of the room you are in, the walls become a tiny bit warmer and a very tiny bit heavier. (warmer object weight more. spinning balls weigh more. charged batteries weigh more. A jar of pickles on the top shelf weighs more...) Also see Conservation of energy and Conservation of mass. --Guy Macon (talk) 12:35, 27 September 2017 (UTC)[reply]
I'm not sure that a jar of pickles on the top shelf does weigh more than it does at floor level :) The increase in weight due to added gravitational potential energy is mg2h/c2, but the *decrease* in weight due to the decrease in g with height is approximately 2mgh/R where R is the radius of the Earth (this assumes h << R). Taking g = 10 m/s2, c = 3 x 108 m/s and R = 6.3 x 106 m, we have mg2h/c2 is approximately 10-16 mgh, whereas 2mgh/R is approximately 3 x 10-7 mgh. So decrease in weight due to lower g >> increase in weight due to higher E. Gandalf61 (talk) 16:06, 27 September 2017 (UTC)[reply]
(Guy slaps himself with a wet trout). Of course. Rookie mistake, saying "weighs" when I should have said "masses". The gain in mass from the added kinetic energy is tiny compared to the fact that gravity pulls less at higher altitudes. I haven't done the calculations but I am guessing that both are tiny compared to a speck of dust landing on the pickle jar or the barometric pressure changing and affecting the buoyancy of the jar. Thanks for the correction. --Guy Macon (talk) 03:50, 28 September 2017 (UTC)[reply]
How does DEPT-45/90/135 work in geometric terms?[edit]
Distortionless enhancement by polarization transfer is a type of 13C-NMR that works by shining two different frequencies of radio waves at a sample. One interacts with protons, one interacts with 13C nuclei. Somehow this causes the 13C nuclei eventually to get a detectable amount of energy by virtue of changing the orientation of their spin relative to the magnetic field, in a way that is affected by how many protons they were bound to. Somehow it works out that a pulse of 0.5 pi-halved units makes all of them show a positive phase, then 1 makes only C-H show up, then 1.5 makes CH2 negative and the others positive. Every review will explain that this works. But ... how the heck does that make any sense? Any explanations welcome, even on the "simpler" aspects of how the polarization transfer really works. Wnt (talk) 11:08, 27 September 2017 (UTC)[reply]
As a start (I only have a moment to post now), we're dealing with spin polarization and controlling the population inversion of nuclei that are spin coupled to each other. Here's a set of NMR lectures that goes into some of the underlying physics of NMR, with polarization transfer being in lecture #5. DMacks (talk) 14:09, 27 September 2017 (UTC)[reply]
@DMacks: I'm hoping you come back ... among other reasons, because you didn't actually link the lectures! Wnt (talk) 10:34, 29 September 2017 (UTC)[reply]
Yikes! Real Life is kicking my butt here. But [1] is it. DMacks (talk) 20:36, 29 September 2017 (UTC)[reply]
@DMacks: Thanks - this is is a tremendously helpful resource ... but I feel like I need a tremendous amount of help. On the narrow issue of how DEPT works, it gives three graphs. The first graph shows that the radio signal to the hydrogen maximally increases the C13 vector in CH by 90 degrees by pi/2. The second shows it increasing it in CH2 by 90 degrees by pi/4, i.e. the same graph twice as fast, with it going through zero at pi/2, then negative at 3pi/4. And then the third shows CH3... which also goes maximal at pi/4, but reaches a minimum at pi/2, and then bounces off the axis to go to another maximum at 3pi/4! It's like sin(rad), sin(2*rad), 2-cos(4*rad) for some reason. The explanation is "it relies on the creation and manipulation of multiple quantum magnetization (the 13C π / 2 pulse) which we cannot see or represent with vectors." A huge improvement on writing a mysterious table with +, -, 0 ... but still mysterious.
The "editing" seems related to causing population inversions with precisely tuned frequencies - though for simply affecting all H, I suppose it doesn't have to be all that tuned... just to H. I could be wrong, but I was inferring that NMR is somehow summing up both absorption and emission of radio photons, so that if a population is inverted it gives a signal of opposite sign from one non-inverted. And the JCH/2 indicates how long it takes the precession of a carbon coupled to an H (seeing some slight increase or decrease of the magnetic field via effects from the other nucleus) to get precisely out of step with the other.
A key aspect throughout all this NMR seems to be that despite all the "nucleus has a quantum spin with two directions" stuff, it seems absolutely unavoidable to think in terms of what I would have thought were "hidden variables" in any other QM context. I mean, we seem to have to accept that each and every atomic nucleus has its own precise spin vector in some precise direction that precesses precisely according to the applied magnetic field, even when the radio signal is off (which can be refocused by inverting it) to get precisely out of step during the JCH time interval. I mean, I wonder... given that this works, then could weird sorts of Bohmian mechanics see equally abstruse applications to chemistry or nuclear fusion involving equally precise aiming of electrons and nucleons in space??? Wnt (talk) 19:56, 30 September 2017 (UTC)[reply]
Can a person's eye color (or other purely genetic info) be deduced from an analysis of his/her saliva sample? 2601:646:8E01:7E0B:3805:A6E1:1618:EEB8 (talk) 11:48, 27 September 2017 (UTC)[reply]
Assuming the saliva produces a good DNA sample, current (since 2009) tests are more than 90% accurate in detecting if a person has blue eye color. Detecting brown eye color is not over 90% accurate as well. I assume that if you demonstrate that a person does not have brown or blue eye color, you are left with green. The blue-brown tests are down to using only 6 positions on the human genome. So, your sample needs to have all 6 of those positions undamaged. 209.149.113.5 (talk) 11:53, 27 September 2017 (UTC)[reply]
It also assumes the color is constant. I've hazel eyes which are mostly brownish now but on occasion they've been quite green. Nothing to do with envy or anything else I know of :) Dmcq (talk) 16:58, 27 September 2017 (UTC)[reply]
Brown covers amber (amber is brown with extra collagen). Blue covers grey (gray is blue with extra collagen). Hazel is a mix of brown and green. As for consistency of eye color - it can change. My eyes permanently changed from brown to blue when I was in my early 20s. 209.149.113.5 (talk) 12:24, 28 September 2017 (UTC)[reply]
I was boiling some meat and boiled it far longer than I meant to. There was nothing wrong with the result. Could meat be preserved by boiling it indefinitely? Could I still eat a piece of meat after boiling it for a year? — Preceding unsigned comment added by 85.76.43.174 (talk • contribs)
Hiroo Onoda's autobiography, about how he spent more than 30 years in a jungle on Lubang Island, describes his techniques for keeping beef by boiling it. He even has a few drawings of Dakota pits, in case you want to boil the beef on the down-low.
“
When we shot a cow, we cut the meat up, skewered it and dried it over a fire at night. During the ten days required for this, we ate boiled beef. Piled on pieces of wood, the liver and other innards were cooked in a makeshift steamer. Small pieces of meat were boiled in a pot until the water was gone. To keep it from getting moldy, it was reheated every day.
He also describes a lot of gastrointestinal distress, and other systematic problems related to bad food:
“
For the first three days, we would have fresh meat, broiled or stewed, two times a day. Presumable because of the meat's high calory count, as I ate, my body temperature climbed until I felt hot to the soles of my feet. It was hard to breathe when walking and impossible to climb a tree. My head would always feel a little giddy. I found that if I drank the milk of green coconuts as a vegetable substitute when I ate meat, my temperature would soon return to normal.
”
“
On the fourth day we piled as much meat as possible in a pot and boiled it. By heating this up once every day and a half or two days after that, we kept it from spoiling, and the flavor held up for a week or ten days. While we were eating the boiled meat, we dried what was left for future consumption. We called this dried meat "smoked beef." ...From one cow, we could make about 250 slices of smoked beef. By eating only one slice apiece each day, we could make the meat last for about four months.
Also see perpetual stew. Note that, as stated above, it isn't necessary to boil it continuously, but only periodically, to keep it from spoiling. Boiling continuously will cause the structure to break down more quickly, making it mushy. Bones, on the other hand, could use far more boiling to become soft enough to eat. Also note that boiling continuously, especially with the lid off, will concentrate whatever impurities were in the water, which must be constantly replenished. That likely includes salt, but also perhaps copper, lead, etc. The materials the pot is made from will also tend to find their way into the stew, so pewter and maybe aluminum should be avoided. StuRat (talk) 18:02, 27 September 2017 (UTC)[reply]
A bit of yes and no here: “boiling” think was used in the old generic sense to mean reheating as one doesn't boil meat. What is important is the critical control point for the foods being cooked. Once cooked they can be kept 63 deg C or above until served. Even so, this is not perpetual. In the 19th century some quacks still thought that life spontaneously evolved because they 'scientifically' demonstrated that if one boiled a broth then sealed the glass vessel, the broth still went on to turn into something horrid. Eventually we came understand, that some bacteria survive boiling temperatures. Perpetual stews (when done as one's grandmother and her grand mother did before) ensure that the pH is too low for pathogenic bacteria to thrive in. They are not only safe but delicious. It gets even more complicated when one gets to putrefied flesh. Fish don't need any artificial heat to turn the flesh into fish source. Yet 99% of the readers here have probably enjoyed purified juices with their meal without knowing it. Aspro (talk) 19:46, 27 September 2017 (UTC)[reply]
Purified, putrified, or both? If that's a typo, it's a whole nother meaning. μηδείς (talk) 21:15, 28 September 2017 (UTC)[reply]
Putrified as in Garum. The inter-cellular enzymes rot the flesh making it putrid and for a few months very smelly of purification. Ie. Smells like rotten fish as that is what it is! Aspro (talk) 13:45, 30 September 2017 (UTC)[reply]
". . . one doesn't boil meat." Ahem! {The poster formerly known as 87.81.230.195} 2.217.210.199 (talk) 23:39, 27 September 2017 (UTC)[reply]
As I said above 'boil' is used in the generic sense. No one that knows how to cook actual boils meat – they simmer it – despite your reference. Consider boiled meat , Take your time, etc. Boiled meat tastes like cheap convenience microwave ready meals. And although I love my pressure cooker I never use it for meat - unless it is for bone broth (for the pets).Aspro (talk) 14:10, 30 September 2017 (UTC)[reply]
"Could meat be preserved by boiling it indefinitely?" Short answer NO. If you boiled the water indefinitely the meat in it will be what's the word, deconstructed into basic components. The proteins will be broken and what you have left is not "meat" but I don't know what it is. The best way I can put it is basic components. From the article in cooking, it says "When proteins are heated they become denatured (unfolded) and change texture." 110.22.20.252 (talk) 07:19, 28 September 2017 (UTC)[reply]
At first the proteins might just be broken down to amino acids, which are still nutritious. But, yes, eventually they would be broken down further, into something non-nutritious. There are other processes which cause decomposition besides microbes. Food in cans breaks down eventually, even though sterile. These processes would likely be accelerated at higher temps. Rancidification is one such process. StuRat (talk) 03:10, 30 September 2017 (UTC)[reply]
Besides inadequate dietary intake, are there any other causes of Pantothenic acid deficiency? The article is rather vague. Also, what is the treatment protocol for Pantothenic acid deficiency in a hospital setting? Thanks for your time. 116.58.233.152 (talk) 19:06, 27 September 2017 (UTC)[reply]
Don't take this as gospel but people with ME who find their guts play them up (i.e. unable to absorb essential vitamins) often end up noticing that their feet feel hot. Supplementation with Pantothenic Acid relieves the symptoms. No idea if this also occurs in Beriberi but one can imagine it does for the gross similarities not observed with with pure thiamine deficiencies. Aspro (talk) 20:07, 27 September 2017 (UTC)[reply]
Part of the problem is that the enzymes that that are being synthesized have redundant parts, making the biochemical pathways more complex than they needs to be, making us susceptible to diseases that affect these pathways. As pointed out here this is a likely consequence of the enzymes being relics from the the RNA world. Count Iblis (talk) 00:08, 28 September 2017 (UTC)[reply]
In general, white looks like the plainest color. But on a computer screen, black looks like the plainest color. What special properties do computer screens have?? Georgia guy (talk) 22:55, 27 September 2017 (UTC)[reply]
How do you propose we quantify "plainness"? --Jayron32 23:29, 27 September 2017 (UTC)[reply]
In the case where the monitor uses LCD (see Thin-film-transistor liquid-crystal display for details), pixels are made of multiple subpixels which can sometimes be perceived. Other technologies also have their own artifacts; the black color is usually produced by non-activated regions or using a separate more uniform layer. —PaleoNeonate – 23:42, 27 September 2017 (UTC)[reply]
The point is that color are qualia. I can't even define "red" in a satisfactory way that would have meaning without referencing something red; aesthetic opinions about colors and how they make the OP feel are entirely undefined, and there's no meaningful way to explain why he decides to feel certain ways about colors. --Jayron32 01:05, 29 September 2017 (UTC)[reply]
I suspect that the difference is between reflected light and emitted light. Most surfaces reflect light, while computer screens emit light (some have backlights the emit light, and an intermediate layer that absorbs light, but that detail's not relevant here). StuRat (talk) 00:53, 28 September 2017 (UTC)[reply]
Left: An additive colour scheme, as used in computer displays. Right: A subtractive colour scheme, as used in printing. To add a bit to this: reflected light (like light reflecting off paper or a painted wall) has "subtractive colour" - the light starts as white, and certain frequencies get absorbed by the material they reflect off, and if all the frequencies are absorbed you get black. Emitted light (like light from a computer screen) has "additive colour" - the absence is black, and as you add frequencies of light it becomes white. Smurrayinchester 08:26, 28 September 2017 (UTC)[reply]
There is little difference between subtractive colour on a reflective device and additive colour for a luminescent device – that's the point of them. They both emit light according to the additive model. Andy Dingley (talk) 09:33, 28 September 2017 (UTC)[reply]
Rate of drinking water affects the urging to urinate[edit]
I claim that drinking water real slowly, taking hours to drink the whole glass of water, doesn't make me feel more urging to urinate, while drinking faster would more likely feel more urging to urinate within an hour or so. Is it true that the rate of drinking water affects the amount of water ending up as urine and therefore the degree of increase of urge? PlanetStar 23:03, 27 September 2017 (UTC)[reply]
Sure. The sooner you drink a given ounce of water, the sooner it is absorbed into your bloodstream, the sooner it is removed by your kidneys and the sooner it ends up in your bladder. So, if you slowly drink water, it will slowly accumulate in your bladder, and if you quickly drink it, it will quickly accumulate there.
In addition to this effect, note that the kidneys will remove less water than you drink, if you are dehydrated, until you are properly hydrated. So, slowly drinking water when dehydrated will produce very little urine at all. Also, water leaves the body in other ways, such as sweat and respiration, so if you drink water slowly enough, it may largely be disposed of in these ways, with little left for urine. StuRat (talk) 00:46, 28 September 2017 (UTC)[reply]
If you drink water quickly then you will produce urine quickly. However, the total volume of water that ends up as urine is not affected by how fast you drink it. Rather, water in must equal water out. The kidneys achieve homeostasis by reacting against changes in blood solute concentration and blood pressure. Drinking pure water dilutes the blood and increases blood pressure. C0617470r (talk) 07:43, 28 September 2017 (UTC)[reply]
Depending on climate there can be an "insensible loss" of water by breathing; also, in dry climates sweating can at times be far less noticeable. Together, a person can need far more water in a desert, even when not noticeably sweating, than in a humid area; so if the same amount were consumed over a long period, most of the water would be lost by these mechanisms and anti-diuretic hormone would still keep the urine production low. Wnt (talk) 10:39, 29 September 2017 (UTC)[reply]
frankly dangerous medical speculation about user's own symptoms
The following discussion has been closed. Please do not modify it.
It seems to me that drinking cold water would usually make my stomach gurgle more readily and more often than warm water. It could be because as cold water warms up in the stomach it produces bubbles as warm water don't hold air as well as cold water. But at some other times drinking hot water would be the most effective when there's something in the intestine blocking the flow of water because the hot water has greater power to go through and dissolve the blockage more easily than what cold water does. Is my belief correct that cold water would make the stomach gurgle more easily in the empty stomach? PlanetStar 23:03, 27 September 2017 (UTC)[reply]
The alimentary canal is not a simple piece of plumbing. Any liquid drunk, whether hot or cold, will exchange heat with the body and reach normal internal temperature within a very short time, long before it could reach the intestines. What nature of "blockage" do you think could exist, that would be dissolved by additional water but not by normal digestive juices? (That additional fluid intake will help constipation by softening dry stools, or slowing their formation, is not disputed.) {The poster formerly known as 87.81.230.195} 2.217.210.199 (talk) 23:51, 27 September 2017 (UTC)[reply]
A blockage is an undigested food that would eventually be digested or excreted out as waste that it can be managed by water. Often as soon as I lay my belly down right after drinking water, gurgles would start. As cold water warms in the body it release bubbles; the colder the water I drink, the more quickly and more bubbles water releases as colder water warms up faster at the start while taking longer to warm up, therefore producing more intense and longer lasting gurgles. That's my theory. PlanetStar 00:29, 28 September 2017 (UTC)[reply]
There are quite a few ways to die from a self-diagnosed "blockage" of the alimentary canal, including tumors, torsions, diverticulitis and so forth. Having had 2/3 of my colon removed and told I had a 60% chance of survival, please see a doctor if you need to discuss your symptoms. WP:DISCLAIMER. μηδείς (talk) 03:02, 28 September 2017 (UTC)[reply]
Intestinal obstruction is a medical emergency which will cause death within a few hours without immediate surgery. Chronic Type 2 diabetes is something rather different which no longer requires destructive surgery - a lining has been developed which coats the alimentary canal and prevents absorption. 92.8.220.234 (talk) 13:06, 28 September 2017 (UTC)[reply]
