Wikipedia:Reference desk/Archives/Science/2012 March 16

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March 16

Meteorology question

Reading through the Dodge City, Kansas National Weather Service forecast discussion today I came upon something that somewhat confuses me (not something that happens often being a meteorology student). It says (I apologize in advance for the all caps, but that's what NWS products use) "FRIDAY EVENING COULD BRING MORE WIDELY SCATTERED CONVECTION HOWEVER AS THE LEADING EDGE OF A LEFT FRONT QUADRANT JET MAY PRODUCE A THERMALLY INDIRECT VERTICAL CIRCULATION NEAR THE OKLAHOMA LINE IN THE EVENING."[1] The part that confuses me is the part about "the leading edge of a left front quadrant jet may produce a thermally indirect vertical circulation", as this is not a concept I have come across before. I also seem to have seen something related to this on the evening TV weather forecast here (2:30 into the video). First, what does the forecast discussion part mean? Second, what is the meteorology behind it (i.e. how does the part that's confusing me cause the convection mentioned in the first part)? Thanks in advance, Ks0stm ^{(T•C•G•E)} 00:09, 16 March 2012 (UTC)

I am not sure, but I think "jet" here refers to a front from the jet stream mixed in vertically from downward convection. Npmay (talk) 01:15, 16 March 2012 (UTC)

They appear to have dropped the word streak. See here and here and here. CambridgeBayWeather (talk) 17:17, 16 March 2012 (UTC)

Can a black hole also be, or contain, a neutron star?

If so, would that be ascertainable? Aside from a certain mass range, what else if anything might give evidence for it? Thanks, Rich Peterson198.189.194.129 (talk) 00:33, 16 March 2012 (UTC)

Sort of. Many black holes would have been neutron stars if they were less massive. You can not ascertain anything about the contents of a black hole directly, but you can infer quite a bit about its mass and former composition from the remnants of its formation. As for the matter in a black hole which was there upon its formation, most of it is in a frame of reference where it is a very hot and compressed quark-gluon plasma I believe, but I'm not sure, and nobody really knows what the physical state of a singularity is. Everything that falls into the black hole (even a moment) after its formation is, in its own frame of reference, trapped in a state of being continually stretched and heated. Npmay (talk) 01:07, 16 March 2012 (UTC)

I remember reading that large black holes could exist without being very dense. It was a popular science magazine.(not Popular Science)198.189.194.129 (talk) 01:10, 16 March 2012 (UTC)

Supermassive black holes under a string-theoretical interpretation can be less dense than ordinary matter. There is a discussion of this in Fuzzball_(string_theory)#Physical_characteristics. Npmay (talk) 01:13, 16 March 2012 (UTC)

Neutron stars often spin fast, could that give the black hole containing it an angular momentum that we could observe? Or could "Hawking radiation" be affected by the nature of the stuff inside? Thanks, Richard Peterson198.189.194.129 (talk) 01:21, 16 March 2012 (UTC)

Yes, the collapse of a spinning neutron star would produce a rotating black hole, and we could in theory, if we got close enough, measure its rotation by frame dragging or the Penrose process. Smurrayinchester 10:09, 16 March 2012 (UTC)

Just to clarify, a neutron star cannot be in a black hole and still be considered a neutron star. Once it collapses or falls past the event horizon, the material will inevitably fall into the singularity within finite time. Hawking radiation is not affected by the composition of the black hole. Goodbye Galaxy (talk) 18:28, 16 March 2012 (UTC)

As for the density, the claim that black holes aren't very dense is based on a measure of average density, with the region contained by the event horizon considered the volume. Not only can we not see past the event horizon, we can't sense what's beyond it through any means. That also means the gravity field of the black hole beyond the event horizon is the same no matter the internal distribution of mass. As for whether you'd see evidence in the hawking radiation, I have no idea, but physicists can't seem to agree on how you'd "read" the radiation anyway. Someguy1221 (talk) 01:26, 16 March 2012 (UTC)

Could cold dark matter have accumulated in orange dwarf stars?

Thanks again. Richard Peterson198.189.194.129 (talk) 03:16, 16 March 2012 (UTC)

I don't have an answer for you, but why do you specifically pick that one kind of star? Someguy1221 (talk) 03:21, 16 March 2012 (UTC)

If your dark matter does not inter-act with normal mater or itself, then any that falls into a star should just come out the other side and not stop. So it would be difficult to accumulate, as the dark matter would hve to lose momentum to stay in the star. Graeme Bartlett (talk) 04:56, 16 March 2012 (UTC)

Dark matter is still under the influence of gravitation, so why wouldn't it accumulate in a gravitational well? SkyMachine ⁽⁺⁺⁾ 08:28, 16 March 2012 (UTC)

As Graeme said, it needs to lose momentum and energy in order to accumulate. Ordinary matter does that via radiation or collisions. Dark matter particles do not radiate and they do not (or at best weakly) interact with each other, so that is not possible. Dark matter requires complicated collective processes that redistribute the energy and allow it to accumulate, so-called violent relaxation (that redirect is a bit useless...). And that (as far as we know) only works on larger scales, say small galaxies and up. --Wrongfilter (talk) 09:04, 16 March 2012 (UTC)

(ec)Because there's nothing to stop it when it gets there. The most you'd get is dark matter orbiting the well. Now, these are "weakly interacting", rather than "non-interacting", so they will inevitably collide with something given infinite time. Someguy1221 (talk) 09:06, 16 March 2012 (UTC)

Is this the same situation with regard to black holes? Would the dark matter only orbit around or pass by rather than being trapped? SkyMachine ⁽⁺⁺⁾ 09:22, 16 March 2012 (UTC)

No. If a dark matter particle should pass the event horizon of the black hole, it is trapped, just like everything else. Someguy1221 (talk) 09:39, 16 March 2012 (UTC)

I asked about orange stars because I've read they can be very old, and have had time to accumulate the stuff. I was thinking time to accumulate is an important factor, because once it's there, it won't readily leave, even in a nova? Perhaps an even better sort of object for me to inquire about would be a very ancient white dwarf, which could be just as old as an orange star, but would have stronger gravity...It does seem to me it could be orbiting, but orbiting far inside the star, for a long time, then, if and after any interactions, probably drop to a lower orbit inside the star?--Rich Peterson198.189.194.129 (talk) 17:41, 16 March 2012 (UTC)

What's the evidence that dark matter doesn't interact with itself? Wnt (talk) 23:54, 16 March 2012 (UTC)

It could, it very well could. But in the simplest models that allow dark matter to hardly ever interact with normal matter, it also hardly ever interacts with itself. Someguy1221 (talk) 00:41, 17 March 2012 (UTC)

No one has mentioned it, but the assumption that weakly interacting massive particles might accumulate in stars has been the basis for a variety of experiments. For example, if they accumulate significantly in the sun, and if they can self-annihilate, then one signature could be a excess of very high energy neutrinos coming from the sun. Super Kamiokande and similar neutrino telescopes have looked for such signals, though so far we don't yet have a definitive detection. The possibility of such dark matter accumulating in stars has been studied in a great deal of detail, though what one expects depends on the properties that are assumed for the unseen dark matter. Dragons flight (talk) 02:39, 17 March 2012 (UTC)

I am skeptical that dark matter is weakly interacting massive particles at all, because there seems to be no actual evidence for their existence, there is no theory of supermassive black hole formation which does not involve aggregation of smaller primordial black holes over time, none of the gravitational microlensing or wide binary star orbit studies have ruled out massive compact halo object dark matter more than a few hundred stellar masses on average, and a relatively small fluctuation in the rate of spacetime expansion between the inflationary epoch and nucleosynthesis would allow for the additional baryons necessary. Furthermore, all particle dark matter theories are unable to explain the cuspy halo problem and the dwarf galaxy problem. Moreover, dozens of intermediate mass black holes have been confirmed in the past couple years, up from two which were known prior. This is a minority view not held by those who stand to gain research grants from the construction of particle dark matter detectors, but I predict in a few years the black holes will prevail over particles. There is a full account of these issues at Talk:Dark matter#Draft table. And in answer to the original question, if an intermediate mass black hole collided or entered a close enough orbit with a dwarf star, it would siphon its matter, producing x-rays in the accretion disk over a time period depending on how direct the collision happened to be. Npmay (talk) 04:51, 17 March 2012 (UTC)

Is ac supply used for driver circuits?

usually driver circuits are fed with dc ,but my project is designed using ac ,could any one say why ac is implemented? — Preceding unsigned comment added by Ishusri (talk • contribs) 07:26, 16 March 2012 (UTC)

This question cannot be answered as insufficient information has been given. Driver of what? What kind of driver? What do you mean by "fed" - power? signal? What is the project about? Keit120.145.44.170 (talk) 10:08, 16 March 2012 (UTC)

My guess is this is some sort of hobbyist project and the OP is thinking of a power supply module (probably a constant current one although perhaps a constant voltage one) functioning as an LED driver or similar. And the OP is saying many such commercial or hobbyist modules are designed for DC input (which from my limited experience is often true baring ones designed for mains voltage). And the OP wants to know if you can design one suitable for AC input. There's of course no reason you can't design a module that can take AC input and some modules are in fact suitable for AC input (as I said mains voltage ones are an obvious example). Just add some sort of rectification to a DC design is probably the simplest option. You will of course need to consider whether your design needs smoothing etc. However if you're working with mains voltage or other AC input above extra-low voltage, you should make sure you know what you are doing for safety reasons, which you very likely don't if you didn't think of rectification. Nil Einne (talk) 12:41, 16 March 2012 (UTC)

I agree. But the OP could be on about lots of other things - for example he/she might be a student doing some sort of mechatronics course, and his/her class has had a lecture on stepper motor drivers, which normally get powered from DC. Sometimes lecturers throw in a project or assignment question about using a standard stepper motor driver integrated circuit to control a multi-phase AC motor instead of a stepper motor. And the answer is usually yes it can, if you connect it up right and program it right - but to do it you need real understanding, not just the ability to regurgitate the text book & copy datasheet circuits. Homework in other words - if so show you made an effort first. The OP's english is inconsistent - did he mean "could any one say[explain] how ac is implemented?" - or did he mean "could any one say why DC is normally implemented?" Keit60.230.199.158 (talk) 15:42, 16 March 2012 (UTC)

The reason I felt a school or university project was unlikely is it would seem surprising they would be assigned such a project with so little knowledge of basic electronics as to not think of the possibility of rectification. But you're right, another possibly more likely possibility is that it wasn't a matter that they didn't think of rectification, but rather they want to know why their project uses AC. (I somehow misread their last sentence as being a question of whether it's possible to use AC but rereading it it sounds more like a question of why AC is used.) Nil Einne (talk) 17:34, 17 March 2012 (UTC)

Please don't advise connecting a home project to the mains to a user who may well not understand what they are doing. SpinningSpark 16:43, 17 March 2012 (UTC)

Actually I clearly stated they should not do so if they don't understand what they are doing, which as I also said, they almost definitely do not do if they needed to ask about it. (I also acknowledged the existance of common products which do use mains voltage as examples since they are from my experience the most common examples by far. I didn't see this as a problem since amongst other things it doesn't particularly sound like the OP is interested in using commercial modules and if they were, since OP hadn't already found them, I thought it unlikely my acknowledging their existance would prompt them to.) But do remember it's easily possible they are dealing with AC voltage which is generally consider safe (below 24V) so there's no reason not to answer the general question (although as I noted above, I may have misinterpeted the question anyway) about the possibility of using AC voltage just because one of the more likely AC voltages is mains voltage. Particularly if a clear cut warning is provided that they should not deal with any dangerous voltages without knowing what they are doing. (If the OP had suggested they were dealing with mains voltage or other dangerous voltages then it may be a good idea just to not answer even the general question but I think it's difficult to make that case here.) Nil Einne (talk) 17:41, 17 March 2012 (UTC)

I think it is beyond time the OP came back and clarified what he wants. Keit58.170.182.237 (talk) 04:13, 18 March 2012 (UTC)

Milk

There were some creamy deposits on the inside of my milk carton, that left solid clumps in my milk. The milk I bought was whole pasteurised and organic. The milk smelt ok and tasted ok but I was sick, what could these deposits have been? — Preceding unsigned comment added by 92.8.72.150 (talk) 09:49, 16 March 2012 (UTC)

That would be milk fat. Most likely the milk was frozen, which undoes the homogenization process which previously mixed the cream into the milk. The cream naturally "rises to the top", hence that expression, but freezing tends to make the cream stick to the outside of the container.

Separated milk is not dangerous, and this is how people had their milk for most of human history. However, the milk may tastes too thin without the fat mixed in, since you're used to it that way. I assume by "I was sick" you mean you found the substance disgusting, not that you literally were sick.

As far as preventing this, is it possible it froze in your refrigerator ? If so, you may need to move it to a different part of the refrigerator or turn the temp up a bit. If it was frozen some time before you bought it, then you might want to buy a different brand or from a different store. Another option is to buy skim milk (nonfat milk), which doesn't contain enough fat to clump up. Of course, if you're not used to it, that stuff tastes like water. StuRat (talk) 10:04, 16 March 2012 (UTC)

I'm not sure the OP is saying the milk made them sick. I think they're saying that they were already sick, and so their ability to smell or taste might have been hindered (as often happens when one has a cold, for example). --Mr.98 (talk) 13:33, 16 March 2012 (UTC)

I interpreted "The milk smelt ok and tasted ok but I was sick…" to mean that the milk made the person sick, or caused some kind of sickness. I think some clarification is in order, as Mr.98's understanding of that wording makes sense too. Bus stop (talk) 13:45, 16 March 2012 (UTC)

The IP is from the UK so they could mean that the milk made them vomit. See here. CambridgeBayWeather (talk) 17:11, 16 March 2012 (UTC)

Now, I thought that "but I was sick" meant that the op was mentally ill and lacked the mental capacity to discern if the milk was good or not. I have a good idea : maybe you could ASK for clarification. — Preceding unsigned comment added by 165.212.189.187 (talk) 17:31, 16 March 2012 (UTC)

google satellite

Where do the 1930 satellite images on Google Earth come from? The satellite article says the first satellite was in 1957 109.162.115.155 (talk) 18:35, 16 March 2012 (UTC)

Which images? Juliancolton (talk) 18:44, 16 March 2012 (UTC)

They're aerial not satellite. Google Earth already uses lots of modern USGS aerial photos, so it's never just been satellite imagery only. 87.113.82.247 (talk) 18:50, 16 March 2012 (UTC)

(yes, despite them labelling the overhead imagery button "satellite"). 87.113.82.247 (talk) 18:52, 16 March 2012 (UTC)

quick chemistry question

I have the mass (g) and volume (mL) of something and I need to find M (molarity) and mol...I can't figure this out so do you know if I'm missing something? — Preceding unsigned comment added by 142.132.6.24 (talk) 19:18, 16 March 2012 (UTC)

Try molecular weight or molar mass. 74.65.209.218 (talk) 19:47, 16 March 2012 (UTC)

OP here. How about just using grams and mL to get moles? Is there a way to do that? — Preceding unsigned comment added by 142.132.70.14 (talk) 01:11, 17 March 2012 (UTC)

You need the know the molar mass. A mole of iron is a lot heavier than a mole of hydrogen. Someguy1221 (talk) 02:00, 17 March 2012 (UTC)

What is "something"? The information you give is not enough. So if somebody told you, here is something that weighs X and has volume Y, he hasn't given you enough info. If he said, here's 120ml solution of 10g Na3O2H7C14X11P4Be2 in an unknown liquid, then you can calculate molarity. 84.197.178.75 (talk) 14:33, 17 March 2012 (UTC)

Or if it's a gas at known pressure and temperature, then the mass and volume are sufficient. 22.4 liters = 1 mole at STP 84.197.178.75 (talk) 14:38, 17 March 2012 (UTC)

need a non-phosphate buffer system that yields a pH of near-neutral (7 +/- 0.4)

I can't use phosphate buffers for organic acids because they encourage algal blooms. What system is optimal? 74.65.209.218 (talk) 19:31, 16 March 2012 (UTC)

What exactly is the application of this? It's pretty easy to just search for lists of different buffers. For example, you can read a list of some buffers used in microscopy here [2]. What's best really depends on the application though. Buddy431 (talk) 21:27, 16 March 2012 (UTC)

He's trying to help his aquarium plants grow without harming his fish: Wikipedia:Reference_desk/Science#feeding_plants_carbon. StuRat (talk) 22:08, 16 March 2012 (UTC)

Will 200 mM sodium acetate/methanol work? Npmay (talk) 23:08, 16 March 2012 (UTC)

Is that OK for fish ? StuRat (talk) 23:20, 16 March 2012 (UTC)

Oh, no, it is not! Sorry I missed that this was for an aquarium. Methanol and sodium acetate are likely to kill and season fish and plants, respectively. Npmay (talk) 05:02, 17 March 2012 (UTC)

You really can't pick random laboratory buffering systems and expect them to work in an aquarium, at least not on a stable, long-term basis. If you're looking to buffer an aquarium, you really only have two choices, and it's not really a "choice", as which one you use is determined by the type of tank you're keeping. The first option is bicarbonate/carbonate buffering, which basically amounts to throwing limestone chips into the tank (the term for aquarium buffering capacity, KH, derives from the German for "carbonate hardness"). The equillibria a little more complex than an intro chem titration, due to the multiple species, multiple pKas and precipitation effects, so even though the pKas might not line up, the buffering tends to work out, especially in a CO₂ injected tank. The one drawback is that dissolving limestone increases your GH (overall hardness), which doesn't work so well for soft water tanks (note that soft water is not the same as softened water - don't use water that's been through a water softener for aquaria, due to the salt content). If you want to maintain a soft water tank, you need to use humic acid to do your buffering, or as the aquarium wonks call it, "blackwater" (because it tints the water). You can either make it yourself by extracting peat moss, or you can buy "blackwater extract" from well-stocked aquarium supply stores (e.g. [3]). From your call for a pH of 7.0, it looks like you might be trying to maintain a soft water tank - be sure to test the GH of your source water if you go down that path. (Note that commercial companies also sell buffering agents which contain secret ingredients which may not be either of the two above.)

By the way, although they're nice blokes an all, Wikipedia & the RefDesk probably isn't the best place to get your aquarium maintenance information. There are gobs of sites on the web about how to maintain a tank (especially a planted tank), including many knowledgeable specialty forums who would be happy to answer your questions. My first stop suggestion, though, is the Aquaria FAQs at the Krib [4], as well as the assembled usenet post there (e.g. general plant info, CO₂ and water hardness, carbonate buffering]). The posts may be a bit old, but they still contain valid information. I'm not really hooked into the current planted tank web forums, but doing a Google search for /planted aquarium forum/ gave at least six options on the front page alone, so it's likely you'll be able to find a friendly and knowledgeable community to help you out. (If one is populated by jerks, feel free to move on to a different one.) -- 71.217.13.130 (talk) 03:37, 17 March 2012 (UTC)