Wikipedia:Reference desk/Archives/Science/2016 April 7

Science desk
< April 6	<< Mar | April | May >>	April 8 >

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.

April 7

Rotating sphere

While I don't begin to understand the equations at Frame-dragging#Mathematical derivation of frame-dragging, I don't see anything there that looks as if it is modelling the messy atomic nature of real-life matter. It looks too mathematically "exact". Do the equations assume an idealised kind of perfectly smooth and uniform matter? If so, how can one even in principle determine whether a perfect sphere of such matter is rotating or not, given that the sphere rotated through any angle is completely indistinguishable from the original? 86.161.61.4 (talk) 01:56, 7 April 2016 (UTC)

We can tell the sphere is rotating or stationary by its effect on the surrounding region of spacetime; that is even though the sphere itself is perfectly symmetrical, and thus visually indistinguishable whether it is rotating or not, the effects on the surrounding region of spacetime are detectable and measurable, and can be used to deduce the axis, direction, and speed of rotation of the object in question. The Kerr metric describes how so. --Jayron32 02:02, 7 April 2016 (UTC)

Thanks, well I understand that is what the frame-dragging equations say, but I still have a hard time understanding how it is even defined whether the sphere is rotating when, as I say, the sphere rotated through any angle seems completely indistinguishable from the original in every respect (assuming granularity of real-life matter is not modelled). Is the "frame-dragging" the only way that the rotation can be detected? I suppose since we are talking about a hypothetical type of matter, it would possibly depend on other hypothesised properties of the matter, but if it is perfectly uniform in every respect then I don't really see how hypothesising other properties would help. 86.161.61.4 (talk) 02:35, 7 April 2016 (UTC)

I don't genuinely understand general relativity, but note that a moving mass generates gravitomagnetic force. Gravity waves and gravity and gravitomagnetism are all aspects of some big messy tensor math. When a sphere turns that contains mass, it induces fields around it vaguely like how a continuous loop of current in a superconductor generates a magnetic field. I don't actually have any idea how accurate that metaphor is or how far it goes, but at least it should illustrate that the sphere isn't really homogeneous. Wnt (talk) 02:46, 7 April 2016 (UTC)

In the absence of gravity, you could throw a tomato at it and see what happens to the stain, or scratch it and see what happens to the scratch, or hit it with a hammer and see how the sound waves propagate. If it's frictionless, rigid and indestructible, then maybe there is no way to tell and maybe there's no meaningful sense in which it is rotating. But perfectly rigid objects can't exist in special or general relativity because of the light-speed limit. In general relativity, you can't have rotation without frame dragging (as far as I know), so the field is enough to distinguish a rotating from a non-rotating sphere. -- BenRG (talk) 03:45, 7 April 2016 (UTC)

Bounce light off of it and you'll get a different doppler shift depending on whether you are shining light on the part rotating towards you or the part rotating away. (Assuming the magic sphere reflects light anyway.) Push on it and gyroscopic effects will affect the result, etc. Even for a smooth classical mass, there are definite differences that one could measure. Dragons flight (talk) 07:56, 7 April 2016 (UTC)

@Dragons flight: If a sphere is perfectly smooth, light would either have to reflect from it or transmit through it. Either way, I'm not clear that the Doppler shift would come into play. I would ass-u-me that the reflection off a moving mirror should be the same as from a stationary one? Wnt (talk) 16:48, 9 April 2016 (UTC)

A photon reflection is properly understood as occurring in the rest frame of the mirror. A mirror moving at velocity v, relative to the observer, will appear to change the frequency of the light be a factor of $\left(1-{v \over c}\right)$ in the low velocity limit. Such effects are small but reliably measurable. Different parts of a rotating mirror ball which show a different amount of doppler distortion due the surface velocity at the point of the reflection. Dragons flight (talk) 17:41, 9 April 2016 (UTC)

@Dragons flight: Oh, I should have qualified that! I understand if the mirror is moving toward the symmetry point of the reflection (or away) there has to be a Doppler shift - the wavefronts get stacked up as the light gets less and less travel time before coming back. But a sphere rotating in place is not moving toward you or away (well, it might be, but no more than if it were not rotating). I expect each wave from the source strikes the sphere and comes to your eye along the same path distance, and they remain spaced at the same distance as when they were emitted, i.e. at the same wavelength. Wnt (talk) 23:50, 9 April 2016 (UTC)

If you look at an element on the equator of a rotating object, sometimes that element is moving closer to you and sometimes it is moving away. That is enough. The local motion will affect the reflection of light directed at a small portion of the sphere. Dragons flight (talk) 12:22, 10 April 2016 (UTC)

It's not representing anything atomic. It's macro field equations generally applied to black holes but are also seen in any rotating mass. Rotating sphere's have symmetry but when it is so massive that the rotation induces a change in space-time around the object. Normally we think of conic solutions for gravity and solve for the static field. In simplified way, the rotation changes the static field and that change forces the body to follow the rotation. That's "frame dragging" as the reference frame is dragged around the rotating body without any angular momentum being supplied by the reference fram. That defies Newton mechanics where rotation doesn't affect attraction and it's also more than simply adding mass/energy to the rotating body. It appears to physically alter space-time and all matter/energy have dynamic solution based on rotation and their location within the ergosphere. The effect is greatest at the sphere's equator and disappears at the poles. I believe it also means that point-mass models fail GR for rotating black holes as do singularities. The rotating mass has a volume and the disappearing affect at the poles is how jets are formed. Lense–Thirring precession is frame dragging with more familiar masses. It's written more intuitively than the complex equations surrounding black holes and shows that rotating bodies with volume and mass can be identified with a gyroscope. --DHeyward (talk) 07:14, 7 April 2016 (UTC)

In the Einstein field equations, the rotational motion enters through the energy-momentum tensor which has a component for mass or energy density but also components for mass or energy fluxes. Icek~enwiki (talk) 10:16, 9 April 2016 (UTC)

how is this happening?

what is going on here scientifically speaking? how has this remained in this state for so long? if you google image it there's even people sitting on top of it...Old Man of the Lake 68.48.241.158 (talk) 05:28, 7 April 2016 (UTC)

There is a suggested answer in the first reference given in the article (from which, incidentally, at least some of the article is plagiarised): Some have suggested that when the Old Man slipped into the lake, he had rocks bound within his roots. This might naturally make him float vertically, though no rocks appear to still be there. At any rate, the submerged end could become heavier over time through being waterlogged. Acting like the wick on a candle, the shorter upper portion of the Old Man remains dry and light. This apparent equilibrium allows the log to be very stable in the water.. Henry^Flower 05:58, 7 April 2016 (UTC)

26 feet is below the waterline, 4 feet above. That volume below the waterline must displace the entire weight of the log. The weight below the waterline seems to be concentrated in the lower section. That places the center of mass far below the surface and makes it stable. Unless there is a change in mass, it's very stable. --DHeyward (talk) 09:24, 7 April 2016 (UTC)

So, how long could this go on for? how did it begin? rolled in there and first floated horizontally? how will it eventually end?68.48.241.158 (talk) 12:15, 7 April 2016 (UTC)

see, the vertical answer above now..but what about the rest? — Preceding unsigned comment added by 68.48.241.158 (talk) 12:17, 7 April 2016 (UTC)

If the waterlogged wood is denser than the wood that's out in the air, then it's easy to see how it remains stable. If it was firmly attached by roots to the bottom of the lake - yet close enough to the shore for the top to be poking out of the water, then the section that's below water would become waterlogged - and therefore denser than the top part - and when the roots eventually gave way (possibly in a storm or something), it would float away in the current position.

In future, what happens depends a lot on the nature of the lake water and the above-water climate. In some conditions, wood can remain underwater for centuries and still be relatively intact. If so then we'd expect the top section to gradually erode away. This would result in the tree gradually rising in the water to maintain equilibrium. If the newly exposed (waterlogged) wood dries out fast enough, then the tree would gradually move upwards to compensate for the loss of above-water wood - the log would probably remain stable for decades or longer. But if the below-water wood starts to decay and slough off at a higher rate than the above-water wood goes away - then the entire tree will slide slowly underwater - until it's sufficiently water logged to sink completely. Various combinations of above and below water decay could produce other results.

SteveBaker (talk) 19:19, 8 April 2016 (UTC)

The catch here is that if the wood can become waterlogged enough to sink, then why doesn't the top part, being near the water, get waterlogged until it all sinks? "Wicking" is a sort of nice explanation, except what kind of wicking keeps the interior of a saturated object dry? Now, I could wish for data about how far it sticks above the waterline relative to monthly humidity conditions, but it seems more plausible that there would simply be stable buoyancy in some or all of the log, and some inclusion pulling it down on one end. Wnt (talk) 23:57, 9 April 2016 (UTC)

it seems bizarre to say the least that this has been stable going on 150 years now...apparently it has been though...I mean it can't last forever...but could it last 500 more years?? or is this totally unrealistic? why hasn't the exposed part decayed away? why hasn't the submerged part decayed away?68.48.241.158 (talk) 19:46, 10 April 2016 (UTC)

Sharks' food choice - surfers vs. scuba divers

Do sharks avoid biting scuba divers (maybe due to the neoprene suit)? All attacks I read about seem to be against surfers. Wouldn't it be easier for a shark to bite someone who is underwater? --Scicurious (talk) 11:54, 7 April 2016 (UTC)

Not if they're in a shark cage. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:37, 7 April 2016 (UTC)

These may help you in your research: [1] and [2] and [3] and [4] and [5] The last one looks most promising, it seems to be a database of known shark attacks, which would allow one to categorize attacks by type of sharks, where and when the attack occurred, etc. --Jayron32 13:04, 7 April 2016 (UTC)

The hypothesis I've heard is that, from below, surfers on paddle boards look like seals, so sharks attack in a case of mistaken identity. They rarely actually eat a surfer, and this seem to support the idea that it's not intentional predation. StuRat (talk) 16:58, 7 April 2016 (UTC)

On TV shows I've seen about sharks, they reiterate what you're saying. It's as if the shark takes a bite out of you and thinks, "Oh, that's not a seal", and goes swimming off looking for other prey, oblivious to the screams of the victim. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:30, 7 April 2016 (UTC)

And let's not forget to note that shark attacks on humans are altogether rare. And in most attacks that do happen, the shark doesn't want to eat the human. They're either defending themselves or their territory or mistake the human for a prey animal. --71.110.8.102 (talk) 19:37, 7 April 2016 (UTC)

They're afraid of the bubbles (until habituated). 78.98.62.173 (talk) 20:38, 7 April 2016 (UTC)

I don't know this, but I'd assume a shark can tell a lot more about a human under the water than one on top of a board. Wnt (talk) 16:51, 9 April 2016 (UTC)

Covalent bonds

I'm a high school student. We've learned that Covalent bonds form exclusively between Non-Metals and Ionic between Metals and Non-Metals. However, a question came today on what type of bonds are present in TiCl4 (Titanium(IV) Chloride). What should be the answer? — Preceding unsigned comment added by Imad Sawal (talk • contribs) 12:45, 7 April 2016 (UTC)

What you're learning is called a heuristic or a "rule of thumb". The main purpose of the learning you are doing in your class is to train you to learn how to apply abstract rules (like "nonmetal + nonmetal = covalent bonds") to specific situations, (like "What kind of bonding would you predict would happen in TiCl4"). Pedagogically, students usually need to learn the basic principles of abstract thinking like that (of the type "If A then B, If B then C. Now, Tell me about the relationship between A and C), that is just applying abstract rules to specific examples. Actual deep Chemistry content is still delivered, but at a very superficial level. The next thing you would be taught is more complex heuristics, such as electronegativity, which is still a heuristic rule, but a more complicated one than the "nonmetal + nonmetal = covalent" rule (in this case, it is "If the difference in electronegativity between the elements is below a certain threshold, the bond is covalent). Now, that's a more complicated rule, but it's still a rule of thumb, and still doesn't get down to the deep understanding of exactly what a bond is, and what makes a covalent bond work. After you had learned that, THEN you would go into concepts such as molecular orbitals and valence bond theory and hybridization theory and start to get into the behavior of electrons at at the basic level, and then you would be expected to use those principles to be able to determine the sort of bonding that is happening. This type of learning model, starting with the simplest (easiest but most inaccurate model) and building towards the complex (hardest to understand but more accurate model) is called Instructional scaffolding, or sometimes derisively as the Lie-to-children, not in the sense of being misleading, but in the sense of simplifying complex concepts at the early stages, to prepare the learner to better understand the more complex concepts at the later stages.

If that was too TL;DR for you, here's the simple explanation: If your teacher taught you that "nonmetal + nonmetal = covalent" and "metal + nonmetal = ionic" and that is all they taught you, then for this task, they expect you to apply that concept to the problems they gave you. Whether or not at this point such thinking is correct in all cases is irrelevant to the educational task, because they are building towards something more complex you should learn later. --Jayron32 13:17, 7 April 2016 (UTC)

Chloride is the anion (negatively charged ion) Cl⁻ found in common salt NaCl. Wikipedia has an ar-ticle about Titanium tetrachloride a volatile liquid with industrial uses, whose molecular formula (TiCl₄) might be read as tickle. AllBestFaith (talk) 15:55, 7 April 2016 (UTC)

Indeed. I know the correct answer because I have two chemistry degrees, and by the end of my Freshman year of college, I had been taught quite enough information to know how to work that out. That's not the question the OP asked, which was more about what their teacher expects as the "correct answer". We would need to know on what basis the teacher is assessing the student, and what the purpose of the lesson is. --Jayron32 17:24, 7 April 2016 (UTC)

Just a question: In University senior year, do they still label them "orbitals" or is the Lie-to-children thing still applied :) --DHeyward (talk) 07:21, 8 April 2016 (UTC)

No, the word "orbital" is still used, even though electrons don't properly "orbit". The language is what the language is, etymological fallacy and all. All chemists use the term, they just understand that electrons are not little rigid balls carving circular paths around the nucleus. --Jayron32 09:43, 8 April 2016 (UTC)

• Honestly, if the OP is really interested in learning about chemical bonding from the horse's mouth, they could do no better than to pick up a copy of (or read it for free online) The Nature of the Chemical Bond by Linus Pauling. That work is the sine qua non of the subject, and really, everything in a modern HS or College chemistry textbook that has been said about bonding for the past 50 years or so is basically taken straight from Pauling's mouth. The great thing about The Nature of the Chemical Bond is that, for what is a pretty dense topic, it's quite readable and understandable. Pauling, besides being perhaps the most brilliant chemist in history, was a pretty good writer as well. He does get into some deep mathematical analysis, but his prose is understandable even to the lay person with little mathematical background; that is if you skim the math and trust that he's smarter than you and know what he's doing, his conclusions based on that Math are written in fairly plain and understandable language, and it's quite easy to get all the basic principles of bonding even if you don't have much background in the subject. --Jayron32 00:58, 8 April 2016 (UTC)

Taking Jayron's cue: the expected answer, given the rules, is ionic; but lo! in real life it's covalent. So there must be something more going on than the rules suggest, etc. 'Scuse me whilst I go & read some Pauling & eat Vitamin C like sherbert. --Tagishsimon (talk) 03:46, 8 April 2016 (UTC)

Indeed. The thing with TiCl4 is that all the heuristics would get it wrong, even electronegativity. Even comparisons to other Ti (IV) compounds. TiO2, Titanium (IV) oxide, is a clearly ionic high-melting crystaline solid. TiCl4 is a liquid, so clearly covalent. And yet they both contain Titanium (IV), and Chlorine and Oxygen are very close in terms of electronegativity, the difference is not nearly enough to explain the huge game in bond character. Real chemistry is messy. --Jayron32 13:21, 8 April 2016 (UTC)

The PubChem database entry for Titanium(IV) chloride shows a 2D structure of charged atoms but lists 5 covalently-bonded units consistent with a non-polar tetrahedral structure. Further, TiCl4 is soluble in toluene and chlorocarbons, as are other non-polar species. However, from a high temperature mixture with other metal chlorides the Titanium ion can be extracted by electrolysis, [6] AllBestFaith (talk) 16:11, 8 April 2016 (UTC)

Wow. I wonder how much of a biochemistry you could have going on the right exoplanet with TiCl4 as the solvent... Wnt (talk) 17:28, 9 April 2016 (UTC)

what % ethylene is polyethylene made of?

what % ethylene is polyethylene made of?

polyethylene is what resin is made from, polyethylene is the main material in plastic bags. — Preceding unsigned comment added by Joro613 (talk • contribs) 12:49, 7 April 2016 (UTC)

I'm not sure I follow the question. The question is either 100% or 0% or something in between, depending on what you mean. Let me explain the three possibilities

• polyethylene is a polymer made up of ethylene monomer units. Since there is only one monomer unit , ethylene, and nothing else polyethylene is 100% ethylene. (in contrast, nylon is composed of two alternating monomer units, so could be said to be 50% of one and 50% of the other, I suppose).
• That being said, the final product should contain none of the original ethylene. It's a chemical reaction that creates polyethylene out of ethylene units, so the final product (the polyethylene) has already reacted and thus there's none of the ethylene left. So the answer could be "0%"
• THAT being said, the actual reaction that turns ethylene into polyethylene isn't as simple as leaving a bunch of ethylene around and letting it become polyethylene on its own. There are several different steps along the way, various other chemicals are used to react, etc. So, if you take into account the other chemicals in the reaction mixture that GETS you from ethylene --> polyethylene, it would be some other % of the total amount of the reaction mixture.

So, first you'd need to clarify which of those amounts you are really looking for. --Jayron32 13:25, 7 April 2016 (UTC)

Polyethylene (a solid) is made from Ethylene (a gas) either by Coordination polymerization or by Radical polymerization. Both the plastic and the gas are organic Hydrocarbon compounds of Carbon and Hydrogen atoms with covalent bonds. The Wikipedia articles linked here can serve well as an introduction to Organic chemistry. AllBestFaith (talk) 15:34, 7 April 2016 (UTC)

How many notes can the average human sing?

I know I can sing at middle C and two octaves above middle C. Is this normal? 140.254.136.179 (talk) 16:57, 7 April 2016 (UTC)

The Wikipedia article titled vocal range would be where you should start researching the answer to your question. --Jayron32 17:19, 7 April 2016 (UTC)

Two octaves is not bad I suppose. Minnie Ripperton could do five octaves. Depends on the trousers if you are a man.--178.101.224.162 (talk) 23:22, 7 April 2016 (UTC)

Example videos: Maria Carey (5 - 7 octave), Tim Foust (5 octave), (9 octaves ?). AllBestFaith (talk) 01:23, 8 April 2016 (UTC)

Yes, these men had exceptionally long trousers as well as exceptionally wide vocal ranges. --DHeyward (talk) 07:59, 8 April 2016 (UTC)

Yes what? Castrati to whom your "these men" links are neither average humans, normal nor noted for wide vocal range. The article notes that the lower part of the voice sounds like a "super-high" tenor. AllBestFaith (talk) 14:26, 8 April 2016 (UTC)

You asked how many notes, not the range of the voice. Given that there are an enormous infinite of gradations between one tone and the other (called being flat, or off-key by musicians) you could probably manage a few thousand very slightly different notes (though it might not be called singing by everyone). 217.44.50.87 (talk) 10:40, 8 April 2016 (UTC)

We assume the OP intends different pitch notes. In Western song music the Equal temperament scale of 12 intervals (11 notes) per octave is standard. Arab singers can use twice as many intervals per octave but are not noted for wide vocal range. AllBestFaith (talk) 14:11, 8 April 2016 (UTC)

Based on my personal experience as a choral singer, two octaves is pretty typical, maybe a bit larger than the average amateur singer.

As the vocal range article mentions, there are different ideas of what it means to "sing" a note. Probably many people can squeak or grunt into an amplified microphone over many octaves. Here's a video of Matthew Curtis actually singing beautifully over three octaves. That's more than most people can manage. Julie Andrews, famous for her wide range, had a useful range of three octaves and change ([7]). (She's still alive but I think her range is smaller now.) -- BenRG (talk) 16:47, 8 April 2016 (UTC)

Vocal range and acoustics are a huge field of research, with variances and qualities of both populations and individuals well studied, but in searching for a direct answer to the OP's question, I was surprised at the dearth of sources directly on point as to the "average range". Its probably a result of the fact that researchers recognize the complexities A) of the sort raised by BenRG above as to what it means to properly sing a note, B) the question of innate capability between realized potential (this article speaks to that issue briefly), and C) the difficulty of a getting a testing group reflecting the true human average, controlled for environment and natural variance.

Still, I did find this paywalled source (which unfortunately does not reflect much of anything of its findings in its abstract...) and this, for what little clarity they can provide. This source is more about the relevant musical theory than any specific empirical measurements, but it does have some relevant observations. Note also that we have Category:Singers with a three-octave vocal range, Category:Singers with a four-octave vocal range, Category:Singers with a five-octave vocal range, Category:Singers with a six-octave or greater vocal range--though you'll want to check the refs on the articles for the individual singers before you look at any of them as exemplars of the range they are purported to have. Snow ^{let's rap} 19:46, 8 April 2016 (UTC)

How to dissolve the chemical that wrecks circuit traces?

What chemical does one use to get rid of the damage with the green/blue color to circuit board traces that EEVblog #696 shows at 8:07 ? It should be possible to have something that react with the attacking chemical and binds to it harder than the underlying copper trace. Removal by braiding is likely to just make the damage worse. Bytesock (talk) 18:19, 7 April 2016 (UTC)

The "attacking chemical" is actually ordinary Verdigris and the "underlying copper traces" are gone. Google "remove verdigris" for general info on removing verdigris. That being said, if you remove the verdigris, there won't be anything left. Instead google "repair pc board traces". --Guy Macon (talk) 19:39, 7 April 2016 (UTC)

I interpretate that as there's no trace left. So the way to fix it is to add a wire, glue a new trace etc. Complete replacement in other words. ? (short of photographing and making a new board) Bytesock (talk) 11:48, 8 April 2016 (UTC)

The green colour of the circuit board shows that it most likely and certainly is epoxy fibre. The protective coating spayed over the top of the PCB (printed circuit board) would perhaps be a two-part polyester resin (for this 1984 era) . The chemicals that dissolve polyurethane resin may also attack the epoxy. Which means it will lift the copper tracks from the board. Just have to go back to basics. See you see this site for help and advice :Coating Removal, Identification of Coating--Aspro (talk) 20:21, 7 April 2016 (UTC)

Outpatient procedure complication and mortality rates

Anyone know of a single source for outpatient procedures' complication and mortality rates? I have a list of 8 procedures I'm interested in. Was trying to find a single source before going to look up each individual procedure (e.g., liposuction, wisdom teeth extraction, etc.) I found http://riskcalculator.facs.org/ but it seems to be only for more major surgeries. If anyone knows, I'd appreciate it. Please ping me in reply. Thanks! EvergreenFir (talk) Please {{re}} 22:09, 7 April 2016 (UTC)

@EvergreenFir: Hard question as I would look at different sources depending on whether it was an absolute mortality rate or a comparative rate to inpatient care of the same procedure. Comparative is difficult because the rates change (i.e. an outpatient procedure may have no waiting list, with a 10% post-op mortality rate, an in-patient identical procedure may have a 3 year waiting list with 20% dying before the procedure and a 1% post-op mortality rate - what would you compare?). The other question would be whether it's directly attributed to the procedure (i.e. "die on the table") or whether it includes post-op complications such as infections. Do you have more details? --DHeyward (talk) 08:26, 8 April 2016 (UTC)

@DHeyward: Honestly would be fine with any, so long as it was consistent and I could compare procedures apples-to-apples. Would prefer both "die on the table" and long term, but would settle for either. For complications, same thing. As for wait list, I'm interested in post-procedure only. EvergreenFir (talk) Please {{re}} 17:41, 8 April 2016 (UTC)

UK's NIH might be my first choice for data. They have waitlists and they are now trying to move to more outpatient care which is more difficult and should have more scholarly papers. The U.S. data overall would be harder to compare apples to apples because it's generally not random difference in method or recent or controlled. Patients getting inpatient service are sicker, generally, in the U.S. as insurance companies set some of the service standards and approve admissions (e.g. a person who gets an inpatient abortion is likely to be an emergency or complications while the normal procedure is outpatient but I doubt there is any scholarly data that could reasonably be used for mortality rates comparing inatient vs. outpatient, it's just normal vs. emergency - I was looking for that type of data a few weeks ago so that's why it popped into my head). Next choice would be VA but they don't often publish and use industry standards (the wait list is just a bonus). Let me look fore som NIH data. --DHeyward (talk) 18:17, 8 April 2016 (UTC)

It's not clear to me that OP wants to compare inpatient to outpatient at all. E.g. the example of wisdom teeth - isn't that almost entirely done outpatient? If there's no need to compare inpatient to outpatient, then many more data sources become available. I was interpreting the "apples-to-apples" to mean the same method was used to assess complications for wisdom teeth extraction and liposuction, not a method to compare wisdom teeth between inpatient and outpatient procedures. SemanticMantis (talk) 19:22, 8 April 2016 (UTC)

Just outpatient is fine. I'll check out NIH though EvergreenFir (talk) Please {{re}} 03:13, 9 April 2016 (UTC)

Washing clothes

This is a SERIOUYS QUESTION> What is the best way of washing clothes in order to remove those unsightly marks on certain undergarments? I cant find anything in the pedia to answer this Q. --178.101.224.162 (talk) 23:19, 7 April 2016 (UTC)

I would recommend stain removal soap. And soaking in water. Graeme Bartlett (talk) 23:55, 7 April 2016 (UTC)

Depends on the stain I suppose... non-chlorine bleach (usually hydrogen peroxide) will get most organic-based stains out when used with detergent (thinking poo, blood, mold, etc.). I find that the Resolve stain stick (looks like a deodorant stick) works very well for old grease/oil stains. That might help for the stains bras sometimes get. Jezebel has a lovely article about getting panties clean (link). EvergreenFir (talk) Please {{re}} 23:56, 7 April 2016 (UTC)

For really soiled stuff like diapers, Grandma used simple washing soda and borax followed by vinegar. It didn't bring them up 'brilliant white' because the don't contain any bluey colour chemical enhancers but they were clean. After the diapers have been rinsed in clean water, wash in dilute vinegar (washing soda is chemically basic, so this helps to neutralize what’s liquid is left in the cloth and makes it feel softer – which what you want next to a baby's bum). You can wash them in modern detergents after though, if you wish (but the modern detergents cost more per wash). Note: Some modern detergents work at low temperatures but washing soda and borax needs water to be very hot. Not marketed today because its too cheap and 'unbranded.' Being unbranded no corporation would be willing to spend the high cost of advertising for something they can not claim to be their own unique product. Sham, when its so much cheaper and effective.--Aspro (talk) 00:17, 8 April 2016 (UTC)

Think reusable nappies (diapers if you are American). It is normal for them to get faecal stains. Buy a tub of nappy cleanser, and follow the instructions. It should work fine unless your diet contains a lot of strong artificial colourings. (I suspect your initial question didn't get taken seriously because you used the slang expression "skid marks"). 217.44.50.87 (talk) 08:55, 8 April 2016 (UTC)