Science desk
< January 30	<< Dec \| January \| Feb >>	February 1 >

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.

January 31

Star formation

Is it right that stars can blow up and their remains recondense to form new stars? Is it also right that this cycle cannot continue forever but must gradually wind down? —Preceding unsigned comment added by 86.135.27.52 (talk) 00:03, 31 January 2011 (UTC)[reply]

In two words, yes and yes. in more words, i'm not sure where to start, perhaps with Stellar evolution and entropy.. feel free to come back if you have any more specific questions. Vespine (talk) 00:19, 31 January 2011 (UTC)[reply]

Also take a look at Metallicity. As stars age, they burn Hydrogen into heavier elements. When they "blow up" (into red giants, or even supernovae), some or all of the material of the star is ejected from the star. This can become part of a later population of stars. But not all of the ejected material is Hydrogen. The heavy elements have a number of interesting effects (they catalyse different fusion processes in the star), but, in particular, they cannot themselves fuse in the same way Hydrogen does. Eventually, a region of space will run out of Hydrogen to form stars from. --Stephan Schulz (talk) 00:32, 31 January 2011 (UTC)[reply]

(Edit Conflicts) Yes to both questions.

As is detailed in Star formation (surprise!), stars form from condensing clouds of interstellar gases and dust. Some of the gases are left over from the initial creation of the universe in the Big Bang, but this only made Hydrogen (H) and Helium (He) (and maybe a little Lithium (Li)): all other gases and (non H/He) dust have been created by nuclear fusion processes within stars (see Stellar nucleosynthesis) and then dispersed when they exploded as novae or supernovae; some of the H and He will also have been cycled through those stars without being consumed in nuclear fusion.

However, only a small proportion of stars explode. Most (see Stellar evolution) simply use up all their nuclear fuel and then gradually cool down (although the Universe has not yet existed long enough for any of the resultant white dwarfs to stop glowing from their fusion-created heat). Also, some of the material forms not stars but planets and associated materials, which do not get redispersed much. Even when a star does explode, some of its material usually remain concentrated as a white dwarf, neutron star or black hole.

Because these processes 'lock up' some of the universe's material, the amount available for forming new generations of stars is continually diminishing, and will (presumably) eventually run out. When that happens no new stars will form, no fusion will occur, and all the white dwarfs, planetary material, and so on will gradually cool down by radiation which will heat up the colder interstellar (and intergalactic) clouds until everything in the universe is at a uniform (very low) temperature - this is called the Heat death of the universe.

However, the Heat death scenario assumes that the universe eventually stops its expansion and becomes static. If it continues to expand indefinitely, the result may instead be what is called the 'Big Freeze', which may not look much different. If however the universe stops expanding and begins to contract, it may be able to restart star formation for a while before eventually coalescing into a Big Crunch, after which the prognosis is unclear. 87.81.230.195 (talk) 00:43, 31 January 2011 (UTC)[reply]

Thanks for the great answers! I have one more question... does anyone have any clue about the maximum number of times that any material will be recycled through different stars? I'm not expecting an exact answer, but something more along the lines of whether the answer is 3 or one million... 86.135.27.52 (talk) 00:56, 31 January 2011 (UTC)[reply]

Depending on how you define "material", closer to 3 (I'd put it somewhere from 10 to 100). The percentage of hydrogen fused by a star varies based on the mass of a star. The sun will fuse, ballpark, 10-20% of its hydrogen, with larger stars fusing less and smaller ones fusing more (red dwarfs, being convective, fuse nearly all of their hydrogen, albeit on much longer time frames). As for the "depending" -- well, a good chunk of that fused hydrogen, now helium, will get fused later on, either in that star or reconstituted in another future star. Is it still the same material? Still, though, there is a finite number of fusion progressions available before net energy becomes negative. Much of those heavy elements end up as the starting mass for black holes. Now, granted, at the end of all this, you can still have the material out and about somewhere (Earth's heavy elements are basically all supernova ash), and so you can get outlier cases where a bit of material cycles as unburnable stellar ash over and over and over, but odds are that a black hole will vacuum it up sooner or later. — Lomn 02:15, 31 January 2011 (UTC)[reply]

Considering the age of the Universe and the time it takes for stars to form, live, and die, most stars are either first or second generation (i.e. either formed from the initial material from the Big Bang or from the direct result of those stars "dying"). Our sun is a second-generation star, IIRC. There are likely some third or fourth generation stars out there, but with each successive generation there are probably orders or magnitude fewer stars to be found. --Jayron32 15:38, 31 January 2011 (UTC)[reply]

No, this is something of a confusion. Our sun is a Population I (or "metal-rich") star, as are most stars in our vicinity. Population II stars are metal-poor stars that formed earlier. The hypothesized Population III stars would be the very first stars, formed before the interstellar medium had been enriched by an earlier generation of stars. Since "metals" (for astronomers, everything except for Hydrogen and Helium) catalyze certain fusion processes, population III stars could become extremely large before fusion became strong enough to generate enough light pressures to stop the further increase in size. Such large stars have a very short lifetime (compared to the universe, or our sun - Hypergiants like Eta Carinae live only a few million years), so the PI-PIII classification does not correspond directly to the number of generations. --Stephan Schulz (talk) 16:32, 31 January 2011 (UTC)[reply]

color changing mug

A Chemical Engineering org I worked with gave me this wonderful mug. It's black but when you pour hot coffee in it, it changes color and reveals the group's logo. Any idea how it works? --Lenticel ^(talk) 01:31, 31 January 2011 (UTC)[reply]

My guess is the mug uses thermochromic liquid crystals, making it a kind of liquid crystal thermometer, similar to a mood ring. Red Act (talk) 01:47, 31 January 2011 (UTC)[reply]

Thanks for the explanation--Lenticel ^(talk) 02:39, 31 January 2011 (UTC)[reply]

By the way, if it's like the ones my wife and I bought about 20 years ago, be careful how you wash it. We found that the thermochromic layer was not well bonded to the mug and was very easily damaged. Of course, the technology may have improved since then. Incidentally, on ours that layer was black at room temperature and turned clear with heat, revealing the pattern painted underneath. --Anonymous, 04:00 UTC, January 31, 2011.

Identify unknown mineral

Hi. I have a very small sample of a mineral, and need some help in identifying it. I have discerned the following properties:

Type: Non-metallic
Colour: Red to reddish-brown
Crystal shape: Nearly amorphous, some flat sides, slightly irregular
Morphology: Tar-like appearance, may have layers, smooth with creases
Rock form: Igneous appearance, two 'parallelogram' sides (opposite at angle), two long nearly 'triangular' sides (opposite), one rhombus-like 'trapezoidial' side, one small 'triangle' side (opposite aforementioned)
Angles: 50° to 130°
Other minerals: At least two, one may be quartz, other mineral is greenish-brownish-black and earthy striated appearance
Mohs hardness: >6.0 (scratches stainless steel and glass)
Lustre: Waxy or resinous
Diaphaneity: Translucent to opaque
Specific gravity: ~3 - 5 (imprecise method)
Reactions: No visible reaction w/ brown vinegar

Any idea what the mineral might be? Thanks. ~A H 1^(TCU) 03:30, 31 January 2011 (UTC)[reply]

I have uploaded an image. For the other lower-quality images, see here and here. ~A H 1^(TCU) 19:33, 31 January 2011 (UTC)[reply]

I would suggest Jasper from the colour and hardness, although the S.G. would be less than you measured, any idea where it came from? Mikenorton (talk) 19:46, 31 January 2011 (UTC)[reply]

First, u must know is streak, it is very important if it's not white.--Chris.urs-o (talk) 20:02, 31 January 2011 (UTC)[reply]

I found the mineral sample as a piece of gravel on a paved road surface near a river. When I measured the specific gravity, I used a floating container in water and compared the volume displaced by the "rock" to the water-volume-equivalent (mass) displaced by the rock, thus it is an extremely imprecise method. I am unable to test the streak as I do not have an "unglazed porcelain tile" handy, though attempting to crush the rock produced a white powdery surface and pinkish edges. ~A H 1^(TCU) 20:11, 31 January 2011 (UTC)[reply]

Something must scratch the mineral, just tell me the colour of the streak. The characteristics of the streak (mineralogy) and of the cleavage (crystal) (angle n surface, if u could use a hammer), would be nice. --Chris.urs-o (talk) 20:33, 31 January 2011 (UTC)[reply]

I tried using tools such as a clamp and a hammer to create powder from the mineral, and it appears noticeably white, at least compared to the mineral itself. Any cleavage of the mineral is likely not distinct, but may come in roughly rhombus-shaped thin layers. However, I unfortunately lost the sample down the drain when attempting to wash it, so any further tests will at least momentarily be unlikely verifiable. By the way, the sample itself could have originated almost anywhere. The actual geographical location where I found it though, is Southern Ontario. ~A H 1^(TCU) 19:42, 1 February 2011 (UTC)[reply]

There are few minerals that don't have a white streak. There are few minerals with Mohs above 6.0. Lemon juice (citric acid) is better than vinegar (acetic acid). Wheathering changes the colour surface, a macro picture of the cleaved surface is better. The density is not precise enough; streak, mohs and density identify at least the mineral family/ mineral group. We'r at Mikenorton's suggestion: Jasper (SiO₂, Commons:Category: Heliotrop). Try Mindat.org, Rhodonite MnSiO₃, Orthoclase KAlSi₃O₈ ?--Chris.urs-o (talk) 05:46, 5 February 2011 (UTC)[reply]

Damiana

does Damiana lower testosterone like weed does — Preceding unsigned comment added by Tommy35750 (talk • contribs) 04:34, 31 January 2011 (UTC)[reply]

According to most of the sources here, many herbalists claim that it stimulates testosterone production, and acts as an aphrodisiac [1]. On the other hand, one author has stated that the claims of aphrodisiac qualities are an "herbal hoax"[2]. Either way, I'm certainly not seeing anything claiming that it reduces testosterone levels. -- Mesoderm (talk) 05:17, 31 January 2011 (UTC)[reply]

Paternity

Hello, i had sexual intercouse with a woman 10 months ago. I ejaculated in her oral cavity, not in her vagina. Now she has had a baby and claims i am the father, which i can't as i disposed no jizz in her vagina. Am i the father and what can i do?—Preceding unsigned comment added by 77.17.27.62 (talk) 10:22, 31 January 2011

It's easier to become a father than you might think. While it's not very likely in the individual case, sperm can get into the vagina from other ways of intercourse. You can request a paternity test (but try to be diplomatic about it). If its yours, you'd better cherish and support it. --Stephan Schulz (talk) 10:33, 31 January 2011 (UTC)[reply]

Even with perfect use, coitus interruptus has a failure rate of about 4% per year, i.e., out of 100 couples who use coitus interruptus correctly every time they have sex for a year, 4 women will become pregnant. It is thought that the primary cause of failure in the case of perfect use is preseminal fluid picking up some sperm from a previous ejaculation. So this is not necessarily a case of paternity fraud. Red Act (talk) 15:10, 31 January 2011 (UTC)[reply]

In her mouth? Kittybrewster ☎ 17:07, 31 January 2011 (UTC)[reply]

It is possible she either accidentaly or deliberately transferred it. SpinningSpark 17:39, 31 January 2011 (UTC)[reply]

I had thought something similar initially but a careful reading suggests the OP's described scenario is ambigious. He said 'i had sexual intercouse with a woman 10 months ago. I ejaculated in her oral cavity.' This may mean he solely had receptive oral sex and his penis never went anywhere near his partner's vagina, it may also mean he had vaginal intercourse (which is a common meaning for sexual intercourse) but withdrew before ejaculation (i.e. coitus interruptus) to ejaculate in his partner's mouth. In the later scenario, Red Act's reply is clearly relevant Nil Einne (talk) 18:13, 31 January 2011 (UTC)[reply]

Yes, my interpretation of the question is that vaginal sex occurred prior to the oral ejaculation. Red Act (talk) 02:42, 1 February 2011 (UTC)[reply]

You sound very much like Boris Becker after his intercourse with Ermakowa. He accused here that she stole his sperm and impregnated herself later. The whole thing was a big hype and was called the "Samenraub" Afair.--Stone (talk) 19:33, 31 January 2011 (UTC)[reply]

In theory, simple tooth brushing can cause bacteremia, so I suppose that human microorganisms might also penetrate to the bloodstream by this means. And bleeding occurs normally during ovulation, at least briefly within the ovary as it ruptures, and perhaps for a longer duration in unusual cases. This makes me think that it is theoretically possible to have a conception which, though not immaculate, is certainly unexpected. However, the odds of this probably rank up there with getting hit by a meteor - I'd need to look up the original bacteremia data to make even a wild guess. Of course in practice, I expect a paternity test is what is needed to find the truth. Wnt (talk) 00:12, 1 February 2011 (UTC)[reply]

Wnt, it seems like you are pushing way past the boundaries of "theoretically". That scenario is not even remotely possible; others have given much more plausible answers above. Let's stick with relevant references and not wild guesses. --- Medical geneticist (talk) 01:06, 1 February 2011 (UTC)[reply]

But science is supposed to be fun.... ;) Wnt (talk) 01:17, 2 February 2011 (UTC)[reply]

The OP's statement that the "Had sexual intercourse" with the paramour before "ejaculating in her mouth" provides ample possibility of introduction of his sperm in her vagina. Genetic testing might be informative. (This does not constitute medical advice, but I once watched the Jerry Springer Show). Edison (talk)

Monatomic elements?

Is there such a thing in nature? [3] <-- Is there any truth to this or is it all basically pseudo-science? -- œ ^™ 10:52, 31 January 2011 (UTC)[reply]

The noble gases are monatomic gases, but the idea that there are macroscopic amounts of precious metals in a stable monatomic form at normal temperatures and pressures makes no sense. The article that you link to is definitely pseudo-science. Gandalf61 (talk) 11:27, 31 January 2011 (UTC)[reply]

This was discussed recently; see Wikipedia:Reference desk/Archives/Science/2011 January 27#ORME Orbitally Rearranged Monoatomic Elements. –Henning Makholm (talk)

Most of that site is pure balderdash, but nuclear isomers including superdeformation and hyperdeformation of nuclei are real. And I do think that this phenomenon one day will be the basis of some very important technology... Wnt (talk) 00:23, 1 February 2011 (UTC)[reply]

However, the idea that nuclear isomers would have a different enough electron structure be relevant for chemical bonding sounds firmly like balderdash. There's the isomeric shift, but that's rather more subtle. –Henning Makholm (talk) 02:02, 1 February 2011 (UTC)[reply]

WiFi laptop or home PC amateur radio packet network equivalent

I know that armature radio has a packet radio relay system which can serve as a network with each station becoming essentially a switch. Is there a way for home computers and laptops with WiFi to set up such a network as well? I ask because even in my neighborhood whenever I try to set up my WiFi I get a list of connections I might log onto. --Inning (talk) 13:04, 31 January 2011 (UTC)[reply]

Yes, the general term for such is a wireless ad hoc network, and WiFi supports such capability. Note, though, that those connections you're seeing (almost certainly) aren't configured for that purpose. — Lomn 14:15, 31 January 2011 (UTC)[reply]

How might one configure those connections for such a purpose in the event of an emergency? 19:43, 31 January 2011 (UTC) — Preceding unsigned comment added by Inning (talk • contribs)

You might be better asking these questions on the computing/IT ref des. CS Miller (talk) 19:59, 31 January 2011 (UTC)[reply]

With wifi, the short answer is "you won't". Wifi is a very short-range network type intended to transfer data between computers -- it's not capable of cross-linking into a ham radio system or other useful emergency response system. Additionally, the hardware to run a standard no-config-needed wifi network is dirt cheap and readily available -- just grab any $50 router off the shelf at a store and plug it in. Ad hoc wifi has very little real purpose or utility. — Lomn 21:05, 31 January 2011 (UTC)[reply]

That said, your search engine of choice (or your operating system help files) will readily tell you how to use ad hoc networking for your particular system. — Lomn 21:07, 31 January 2011 (UTC)[reply]

...so you are saying I can not log onto my neighbors WiFi and in turn have him log onto one down the street , etc until a link of WiFi's make up a network that reaches across town and eventually to the next town, county, state and country? --Inning (talk) 02:10, 1 February 2011 (UTC)[reply]

In principle, I see no reason that you couldn't, provided you've got enough suitably equipped computers to bridge the inevitable network gaps. The effort and cooperation needed, however, is unlikely to ever materialize, nor is there any compelling use case beyond "to see if it can be done" (a motivation which has a rich tradition on the internet, to be sure). But if you want wireless computer communication in the event of emergency, plan on some combination of data-rich mobile service or satellite internet -- protocols designed for the purpose at hand. — Lomn 04:21, 1 February 2011 (UTC)[reply]

You may be interested in today's news stories about the Open Mesh Project (wireless mesh networking, mesh network)^{[4], [5]}. It sounds like this idea - which I should say grumpily, should have been a major focus by somebody somewhere before major protests and internet blackouts broke out - may finally get the attention it needs. Wnt (talk) 01:25, 2 February 2011 (UTC)[reply]

Brace, brace

I've noticed that the advised position to brace for impact on cheap flights (e.g. Ryanair or Easyjet) would place my head hard against the seat in front, with tension in my neck. I'm just under six feet tall, which I suppose is about average height for a 26 year old male in the UK. Could the intention be that a quick cervical dislocation would reduce/prevent my suffering in the event of a collision? --129.215.47.59 (talk) 16:55, 31 January 2011 (UTC)[reply]

I think the idea is to protect you from injuries like whiplash in the case of light impacts. Of course, if your plane ploughs headlong into the side of a mountain, there is not much you can do. Also, it's not just cheap providers who offer this advice - it's standard across industry. I don't have any references for this, but I can tell you I have never flown on the providers you mention and I have seen this advice on pretty much every flight I have been on. --KägeTorä - (影虎) (TALK) 17:03, 31 January 2011 (UTC)[reply]

We do have an article about it: Brace for impact. --KägeTorä - (影虎) (TALK) 17:07, 31 January 2011 (UTC)[reply]

The general idea with a brace position is: you're going to end up in that position anyway in a hard deceleration. By pre-positioning yourself in that position, you reduce blunt head trauma and whiplash involved with getting your head into that position from the crash. Whatever then happens, was going to happen anyway. Arakunem^Talk 17:08, 31 January 2011 (UTC)[reply]

The brace position will soon be adapted to the air-bags used in some planes.--Stone (talk) 19:04, 31 January 2011 (UTC)[reply]

Incidentally, some people seem to believe that the brace position was designed to kill you (to lessen the insurance payout). Mythbusters did an episode on it, finding this not true, and that the position does really help reduce neck and head injury: [6]. Buddy431 (talk) 04:38, 1 February 2011 (UTC)[reply]

I understand that passengers would be better off if all the seats faced backwards, which I whjat I'd prefer. 92.28.247.121 (talk) 18:42, 1 February 2011 (UTC)[reply]

The proposal for rear-facing airplane seats was discussed somewhere and the conclusion seemed to be that the only way to get passengers to accept it would be to replace the windows with TV screens showing moving clouds, and have a dummy cockpit door at the back wall of the plane. Cuddlyable3 (talk) 20:48, 1 February 2011 (UTC)[reply]

About half the passengers in trains are happy going backwards. Actually what I would prefer would be something like bunks that you could lie flat on. I think you could squeeze as many or more in if they were stacked zig-zagged and in alternate directions so that everyone got a double height above their cheast and head. 2.97.220.121 (talk) 20:26, 2 February 2011 (UTC)[reply]

Forward facing seats are simply what people have become used to by not being given a choice. The first commercial aircraft, such as the Boeing 307, often had seats facing in both directions, similar to a train. Some even had bars with barstools so you could swivel around and face whichever way you liked - including face down on the floor when the plane hit turbulence. -- kainaw ™ 20:42, 2 February 2011 (UTC)[reply]

The difference between aircraft and train seats is that aircraft frequently operate with a significant pitch angle. The RAF passenger VC10s used to operate with rearward facing passenger seating and I can confirm from personal experience of several transatlantic crossings courtesy of Crab Air that the sensation of being about to fall forward out the seat the whole time quickly gets quite wearing. Zeusfaber (talk) 23:03, 2 February 2011 (UTC)[reply]

But unless you are taking-off and landing at different altitudes, don't you have as much up-pitch as down-pitch? 92.15.14.91 (talk) 17:31, 3 February 2011 (UTC)[reply]

ear piercing (2)

A follow up to semi-archived discussion above: (copied text removed) –Henning Makholm (talk) 19:48, 31 January 2011 (UTC)[reply]

Also, is the a time when closing of the piercing is impossible?Accdude92 (talk) 11:26 am, Today (UTC−6)

Could you try asking your question with more detail? I don't understand. Comet Tuttle (talk) 18:43, 31 January 2011 (UTC)[reply]

Insulated windows

I am not sure if this question has been answered before, but here goes:

My parents built a new house last spring/summer. They had energy efficuent windows installed. Several times over the course of this winter (central Ontario, Canada), they have noted frost (sometimes significant amounts) on the insides of all of the windows. When they enquired about this, the builder told them that there was too much moisture in the air. Personally, I don't buy this. I have had new windows installed in my home (several years ago) and while there may be some condensation at times (eg. after a hot shower), there has never been any kind of frost. So, while there may, indeed, be excessive moisture in the air of my parent's home, there is no way that I can think of that frost would develop unless there was something wrong with the windows construction and/or installation. The cold air from outside needs to somehow get inside to freeze the condensed moisture; properly built and installed windows should not do this. What do others think? Physics is not my forte . . . 76.75.136.254 (talk) 17:40, 31 January 2011 (UTC)[reply]

Googling for "condenstation windows", I found this guy, who claims that the condensation might be a sign that they did a good job, because it means the house is properly sealed up and thus trapping all of the moisture inside. Drafty houses let in the dry winter air, which lowers the relative humidity, making condensation less of a problem. It sounds like they sealed up your windows properly, and your parents need to get a dehumidifier. -- Mesoderm (talk) 18:04, 31 January 2011 (UTC)[reply]

I think the OP is implying that the windows are sub-standard because they are letting heat out (hence the frost), not because of the condensation per se. But I have no idea whether or not this would be normal at Canadian temperatures. SpinningSpark 18:42, 31 January 2011 (UTC)[reply]

Oh, yes. I see that now. Sorry. -- Mesoderm (talk) 18:50, 31 January 2011 (UTC)[reply]

This is very odd. We had -26°C last winter and no more than -10°C during the day and the 20 year old double glass isolation windows showed a lot of condensation but no ice not even in the bedroom where the heating was very low at that time.--Stone (talk) 19:01, 31 January 2011 (UTC)[reply]

It really does depend on the temperature gradient between outside and inside. If you keep the room very cool, and it is extremely cold outside, then frost would be normal. I regularly get quite a thickness of internal frost in single-glazed unheated rooms, but frost on the inside shouldn't happen in a heated room with efficient double glazing except in really extreme conditions. Drawing curtains across at night might make frost more likely. Do you have a guarantee on the windows, or any specification on their insulation rating? Are they sealed units? It sounds as if there is some convection of freezing air somewhere. Dbfirs 19:53, 31 January 2011 (UTC)[reply]

Thanks for the feedback everyone. All of the rooms are well heated but there is frost formation whether or not the curtins are drawn. A dehumidifier was recommended but, as I note, nothing should be frosting over (in my opinion). Frost develops not only where the upper and lower window meet but also on the glass and sil itself. Is there a way to measure or determine if there is a problem with the window construction or installation? 76.75.136.254 (talk) 21:12, 31 January 2011 (UTC)[reply]

Just feel the temperature with your hand. Compare the temperature of various windows, and also compare it to some external walls. A double paned window should be somewhat colder than the walls if the walls are insulated, and about the same temperature as uninsulated walls. Feel also for drafts near the window, and feel the edges of the window (not the glass, the frame), because maybe they didn't insulate the edges. Make sure they actually used double paned glass (it's easy to tell, just look inside the window at the edge). Ariel. (talk) 03:08, 1 February 2011 (UTC)[reply]

If the frame and sills are frosting first, it sounds like they are the cheaper ones without the hollow cavities having been filled with polyurethane foam; See diagram. Between the frames and sill, where they meet the walls, lintels and so on, there should also be foam sealant (often bright yellow), to keep out moisture and draughts. Also, the optimum air gap is 16 mm and with two sheets of glass -that's 24 mm total. The paper work that your parents signed (contract), agreeing to have them installed, should give details as to who's frames (or Window System) they are. From that, you can find out from the manufacture, what specifications and standards they meet. They also need to know the manufacture, in case they need to order new parts for repairs.--Aspro (talk) 14:07, 1 February 2011 (UTC)[reply]

Often the coldest part of a window is the frame. Glass can be made relatively efficient in terms of thermal efficiency, although there are limits. The frames are harder to make energy-efficient do while retaining sufficient stiffness to support the glass and to seal, since stiff materials tend to also be conductive. Single-pane glass has a U-value of about 1.3 (lower is better). Plain double-pane glass, U= about 0.49, triple clear about 0.34 and double glazing with low-e coating and argon fill about 0.30. Super-efficiency windows might reach 0.15. This is in contrast with normal wall construction, which in Canada should have a U value of about 0.05, so even efficient windows are the cold spot. The temperature of a glass or frame surface is related to the temperature gradient through the assembly, and the right combination of temperature and relative humidity might produce condensation or frost, so the answer is: it depends. Frame construction, glazing options and construction details all play a part. Acroterion _(talk) 16:07, 1 February 2011 (UTC)[reply]

Handheld missile/rocket launchers with multiple missiles

Are there any handheld rocket/missile launchers that can carry multiple missiles/rockets? ScienceApe (talk) 18:38, 31 January 2011 (UTC)[reply]

The M202 FLASH fits that description. --Daniel 18:40, 31 January 2011 (UTC)[reply]

While not a missile/rocket launcher, there is also the M32 Multiple Grenade Launcher, as well as others. --KägeTorä - (影虎) (TALK) 18:47, 31 January 2011 (UTC)[reply]

Fliegerfaust qualifies if "effectiveness" isn't one of the requirements ;) . Vespine (talk) 21:34, 31 January 2011 (UTC)[reply]

what the species name?

hi. i found a funny pic of a baby monkey online. here is the link: http://www.superlaugh.com/pets/babymonkey.jpg please, could you tell what species that baby belong to? —Preceding unsigned comment added by 62.0.34.93 (talk) 20:38, 31 January 2011 (UTC)[reply]

It's a macaque. I'm not sure about the specific species, but possibly a Toque Macaque. CS Miller (talk) 22:41, 31 January 2011 (UTC)[reply]

Processing of metals: casting

When using a pattern for hot metal casting, which kind of pattern volatilizes when the metal is poured? —Preceding unsigned comment added by 208.54.5.54 (talk) 21:22, 31 January 2011 (UTC)[reply]

Usually a pattern is used to make one or more moulds, and the molten metal is then poured into the moulds and allowed to cool. In many applications, each mould is then destroyed to allow removal of the cast object. I have not heard of volatile moulds or patterns. You could investigate investment casting and the lost-wax casting process. Dolphin (t) 21:31, 31 January 2011 (UTC)[reply]

When I was at school we used expanded polystyrene to make a shape, then formed damp sand around this. We poured aluminium into the mould and the polystyrene vapourized, leaving an aluminium shape. Whether this is still considered safe, I'm not qualified to comment. --Phil Holmes (talk) 22:03, 31 January 2011 (UTC)[reply]

See also evaporative-pattern casting. Our entire article on casting (metalworking) has lots of interesting stuff, actually. TenOfAllTrades(talk) 03:59, 1 February 2011 (UTC)[reply]

Parachutes

Why do parachutes have holes in them? 74.15.137.130 (talk) 22:25, 31 January 2011 (UTC)[reply]

See Parachute#Round types. Basically, it reduces flapping around. I think it also increases drag by forcing the air to flow around the interior of the chute, rather than creating a high-pressure cell. --T H F S W (T · C · E) 22:33, 31 January 2011 (UTC)[reply]

How does it reduce oscillations? 74.15.137.130 (talk) 00:13, 1 February 2011 (UTC)[reply]

If you drop a piece of paper it slides back and forth as the air spills first from one side then the other. By putting a hole in the middle all the air spills from there instead of the sides, which stops it from doing that. Ariel. (talk) 03:02, 1 February 2011 (UTC)[reply]

To clarify a bit, the holes help the parachute keep its shape. It is simplest to explain with the round "WWII" style parachutes. If you just have a closed fabric "cup", inverted, the air rushing into the parachute from the bottom needs a way to get out. If you don't have a hole in the middle, it gets out by tipping the entire cup shape on its side, which does a pretty terrible job of actually slowing you down. By putting a hole in the middle, the inrushing air is "funneled" out the hole in the center, which prevents the chute from tipping over or collapsing. Now, with all of the inrushing air escaping out the top, the chute is able to maintain its inverted cup shape, and thus help to trap most of the air, and thus slow you down. The same principles apply to the rectangular shaped parachutes, but its just organized a bit differently. --Jayron32 05:37, 1 February 2011 (UTC)[reply]

And you can tug on a pair of handles just before you hit the ground which close the holes and slow you down. Alansplodge (talk) 09:24, 1 February 2011 (UTC)[reply]

Also, per the article, vents enable a certain amount of steering.--Shantavira|^{feed me} 10:25, 1 February 2011 (UTC)[reply]