Wikipedia:Reference desk/Archives/Science/2009 December 22

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December 22

Manned landing on Venus

Assuming an astronaut could be found who was daft enough to risk being cooked to death in the event of equipment failure (we will assume he brings cyanide capsules with him) how long could he stay outside on the surface of Venus with the best conceivable refrigerated heat resistant spacesuit? Supposing the refrigeration was powered by radioisotope Stirling generators, would the heat difference be enough to power it? We will assume a a large heatsink attached. [Trevor Loughlin]80.0.109.64 (talk) 02:23, 22 December 2009 (UTC)

At 750 K and 90 atmospheres pressure, I don't think anything that looked like a spacesuit would be adequately protective. Dragons flight (talk) 03:47, 22 December 2009 (UTC)

How much mass do you budget for the suit and cooling equipment? The surface gravity on Venus is slightly less than on Earth. The surface temperature is around 460 Celsius, slightly cooler than the cleaning cycle temperature temperature of a Self cleaning oven [1]. A rigid suit or rover with the insulation of such an oven might protect for a brief EVA, comparable to the self-cleaning ovens 3 hour clean cycle, with supplementary active cooling. A long coolant line extending from the ship might allow sufficient mobility to explore a bit, plant a flag, snap photos, and collect rocks like on the initial 2 1/2 hour Apollo 11 EVA. We know that a number of Soviet Venus landers survived for an hour or so, but the internal temperature of the probes is not stated in the articles such as Venera 14. Also, there was no return from the surface attempted. As opposed to a heat engine, with the shielding needed for the radioisotope to drive some other cooling apparatus, why not have tanks of liquified oxygen and nitrogen to cool him as they boil and furnish a breathable atmosphere? A more instant problem than staying cool is avoidance of crushing, since the surface atmospheric pressure is 93 Bar, or the equivalent of being 924 meters below the surface of the ocean. An actively cooled rover on treads might work better than a spacesuit, which implies a suit intended to protect from vacuum. An unmanned mission with a rover which proved the technology for a short surface stay and sample return to Earth would likely precede a manned mission. The main additional benefit of a manned Venus mission would be hero creation (either live for a parade, or mourned). Carl Sagan in a 1970's book (revised after his death by someone else in 2000) doubted a near-term Venus manned mission would be possible, but discussed a mission to float in the clouds of the planet in an airship. It would be an exciting ride. Edison (talk) 04:15, 22 December 2009 (UTC)

It's instructive to see what happened to the Russian Venera probes - according to Venera#Flight_data_for_all_Venera_missions, many of those chunky craft were crushed by the huge air pressure - or succumbed to the heat and the sulphuric acid rain in the upper atmosphere. Few lasted more than an hour. There is very little sunlight - so no solar panels for power. Air conditioning at those temperatures is tough - the cooling coils would have to be hotter than the planet's atmosphere. Venus is a pretty amazingly hostile place. I don't think we'll see manned missions there anytime soon. As the technology of things like spacesuits improves to where such a mission could maybe be possible - so the technology of the robots that could do a vastly better job will have improved immeasurably compared to what we have now. I could believe a robotic mission with a human in orbit to control them without the long signal delays to Earth. A completely immersive virtual-reality mission would just be so much easier than sending live humans to the surface. SteveBaker (talk) 04:30, 22 December 2009 (UTC)

The Russians are developing the Venera D series orbiter/lander for circa 2016-2018, and once considered a 30 day lifetime, but later reduced it to 1 day or so [2] or even the old 1 hour design to have a bigger mass budget for scientific instruments as opposed to heavy cooling systems. The solar brightness is like an overcast day, so I agree with Steve that solar panels are not a good prospect. With the moderate winds at the surface (.3 to 1 meter/second average)and high density (able to roll small rocks) what are the prospects for wind generated power? Presumably radioisotopes would be the "standard" power source. If electronics are to operate at some high ambient temperature (likely cooled some from the surface temperature) are solid state electronics or vacuum tubes a better prospect, at least for the final RF output stage? Edison (talk) 05:12, 22 December 2009 (UTC)

I found some discussion of what cooling and power generation the Soviets used on the Veneras. Phase-change materials which melted at 30 C were popular for cooling. Simple batteries and turbines were used for power. At [3] see comments by Guest_DonPMitchell_ at his post May 17 2006, 06:05 PM. Edison (talk) 06:21, 22 December 2009 (UTC)

If you don't expect the lander to last more than an hour or so then batteries will be more than adequate. For longer missions turbines or RTGs seem like the best options. Solar panels would work - you don't need much light to get usable amounts of power and Venus has very long days - but they wouldn't be my first choice. --Tango (talk) 13:07, 22 December 2009 (UTC)

Couldn't you use aerogel and liquid nitrogen as cooling? Aerogel is very very light, so you could make the walls really think, reducing heat transfer to almost nothing. With liquid air for cooling you don't need a complicated refrigeration system. Possibly the biggest problem is the pressure. Maybe there is some way of designing a craft with no voids, and let it pressurize (but that wouldn't work with the aerogel). Is there a light weight, low thermal conduction liquid, that is not very compressible? (Yah, I know, if only...) Still, if you assume a pressurized (reverse-pressurized?) vessel, would aerogel not be enough for handling the heat? Ariel. (talk) 08:08, 22 December 2009 (UTC)

A craft with no voids would obviously have to be unmanned, I thought we were talking about manned missions (unmanned ones have already happened and if we can make a lander than lasts an hour then we can make one that lasts a few days, we just have to decide if it is worth the effort - all such missions show rapidly diminishing returns). If you want to have a thick aerogel insulator then you need to build a pressurised rover rather than a spacesuit - a spacesuit that thick would be immobile. I think that probably is the way to go. I don't think you need liquid nitrogen for cooling - liquid nitrogen is about -200°C, we're talking about cooling the craft to about 20°C, so we just need something colder than that. Water would be fine. Just let it evaporate and it will cool the craft. --Tango (talk) 13:07, 22 December 2009 (UTC)

As a side note, does anyone know what the thermal conduction of a dewar flask is? And can you add it to Thermal conductivity? Ariel. (talk) 08:08, 22 December 2009 (UTC)

It will depend on the quality of the dewar flask. I'm sure the expensive ones labs use to keep LN₂ cold have lower conductivity than the cheap ones used to take coffee on picnics. --Tango (talk) 13:11, 22 December 2009 (UTC)

Brief side-note - when I worked in a lab, we used to use ordinary picnic flasks to store small amounts of LN2. Without the tops being screwed on, of course. :) Tevildo (talk) 23:55, 22 December 2009 (UTC)

Presumably that was for short periods of time, though? The evaporative cooling required to keep it cold with the lid off would be quite significant, so you would run out of LN2 pretty quickly (I'd guess 10's of minutes, but I don't have much experience with LN2), I'd think. --Tango (talk) 01:21, 23 December 2009 (UTC)

Well, it was just to transfer the LN2 from the main tank to the vacuum system - "storage" is perhaps the wrong word. However, you could certainly retain a reasonably-full flask for a couple of hours - "10's of minutes" is the right order of magnitude, if a little on the pessimistic side. Tevildo (talk) 01:57, 23 December 2009 (UTC)

A visit to Venus leads to a lifetime on Mercury. Cuddlyable3 (talk) 23:49, 22 December 2009 (UTC)

snoring while "awake"

OK. I snore. The other night, I was snuggling with my toddler at bedtime and he was soon fast asleep. As I lay there (I really relish the snuggle time!), my wife quietly came into the room. I let her know that I would be joining her momentarily. However, she said I was snoring really loud. I swear I wasn't even asleep! So here is my question: how can I be snoring so loudly that I don't wake up yet when my wife quietly opened the door, I reacted as if I was never asleep. How can I be "asleep" enough to snore yet "awake" enough to respond to my wife's entrance to the bedroom? —Preceding unsigned comment added by 99.250.117.26 (talk) 05:24, 22 December 2009 (UTC)

You were in fact sleeping. This has happened to me many times; I insist "But I wasn't sleeping!" and am laughed at. Comet Tuttle (talk) 07:22, 22 December 2009 (UTC)

When you are asleep, your sub-conscious brain filters out the expected sound of snoring (expected by your sub-conscious brain, even if you believe you don't snore), and wakes you only when you hear an unexpected noise or a sound that you know you should respond to. We all experience this - if not with snoring then with normal household sounds. Dbfirs 08:54, 22 December 2009 (UTC)

I've had the same experience as a passenger in a car. I must have been fast asleep (at least, my mum who was driving insists I was and I seem to have missing time) but as soon as she pulled off the motorway onto a sliproad for the services I was awake and fully alert and instinctively looked round to see what was going on. My sub-concious must have been listening to what was going on and detected a change in the road noise so woke me up. --Tango (talk) 13:14, 22 December 2009 (UTC)

It happens to me every night. I can quite categorically say I am not sleeping. Most of the time I don't even have my eyes closed, but can even be reading! I can even have a conversation as CT says above. The only explanation I have ever come up with is that the part of the brain concerned with filtering out the sound made by air moving through a restricted broncho-nasal passage (snoring) kicks in at a point where a degree of physical relaxation is achieved.--TammyMoet (talk) 09:02, 22 December 2009 (UTC)

Having open eyes, reading and having conversations does not preclude being asleep, of course. See sleep walking. --Tango (talk) 15:58, 22 December 2009 (UTC)

But being sentient and aware usually does! In other words, I am conscious, self-aware and can remember what has happened. --TammyMoet (talk) 18:27, 22 December 2009 (UTC)

Being able to remember it is pretty conclusive evidence of being awake! Sentience and awareness are difficult to define. --Tango (talk) 01:22, 23 December 2009 (UTC)

Just to expand a bit more on my initial query: what stage or level of sleep would I be in to be able to filter out my snoring yet be able to awake instantaneously? —Preceding unsigned comment added by 99.250.117.26 (talk) 04:59, 23 December 2009 (UTC)

I would guess (from limited experience) that any stage other than deep sleep allows this. Dogs seem to be much more proficient than most humans at waking on significant sounds. Our article on (Slow-wave sleep) mentions that this level of sleep usually diminishes as we get older, and this correlates with an observed increased ability to wake "on demand" from our auditory system. Dbfirs 09:35, 25 December 2009 (UTC)

Reading while thinking about other stuff...

Just read the reading article and didn't see any mention of the phenomenon whereby you're reading a passage but your mind wanders. Some part of your brain continues to methodically process the passage but the bulk of your consciousness is focused on something else entirely. Eventually, you "come to" and realize you haven't been "getting" any of the last X paragraphs you read, despite the fact that you quite clearly have actually read them. I find the frequency of this event is directly proportional to how mentally tired I am. More fatigue = more reading without reading. I'd be delighted to learn the science behind this! 218.25.32.210 (talk) 08:38, 22 December 2009 (UTC)

You have two "brains". One is your conscious brain, the other is the automatic/background brain. (Not the same thing as your subconscious.) The second brain is used when you are driving on automatic, or doing other automatic things during the day while not thinking about them (walking a familiar route, eating, lots of other things things too). This is useful, so that you can think, while doing other things. This is not limited to reading (which is why it's not in that article). This can be very beneficial if you learn to control it. For example while giving a speech, have this "second brain", say the words you planned, while "you" are thinking of the next words. Have you ever typed one word, while planning to type something else entirely? Ever have a conversation, with apparently normal responses, and after have no memory of what you said, because you were thinking of something else? This is also related to how you can catch an object thrown at you, faster than you can think to do it. There are probably multiple independent "thinking" structures in the brain (each one doing something else, talk, read, eat, walk, etc), and not a single consciousness. Each independent structure can work independently, meanwhile the "master consciousness" can control them directly, let them work on their own (i.e. react to the environment, like walk without hitting a wall), or give them instructions to act in a certain way, but on their own. It's quite amazing that with all the background going on, you still perceive yourself as one being. PS. This is all my personal experience of consciousness. I assume other people are the same, since everyone I know can walk and drive automatically. Ariel. (talk) 08:59, 22 December 2009 (UTC)

Well, no -- there is no reason to think we have "two brains" or anything like it. The fact that things like this occur is well known, but we really don't understand the science behind them except in the vaguest way. They are an aspect of consciousness, which we don't understand very well at all. I could tell you a few facts, such as which parts of the brain are active when you are experiencing something that you are going to remember (the hippocampus in particular is one), but I don't think they add up to a real understanding. Looie496 (talk) 15:38, 22 December 2009 (UTC)

There are certainly 'layers' of processing going on in the brain. Something in your retina detects lines and curves - something else in your visual cortex puts together lines and curves and recognizes letters and small bits of words, then yet higher levels of processing assembles the words and extracts meaning from the text - and yet higher levels track things like story and character development and such. You can see children who are learning to read acquiring each 'level' of processing in turn. But competent adult readers have pushed those lower level functions into such an autonomic part of the brain that we're no longer conscious of that low level recognition. Once you reach that stage, it's possible for the higher level functions to go off at a tangent and start thinking about other things without 'shutting down' the lower level processes.

You can convince yourself of this "layering" of the reading process by trying to quickly name the colors of the words in the image to your right here. DO NOT READ THE WORDS - JUST NAME THE COLORS THAT THE WORDS ARE PRINTED IN.

People who are competent readers find this very hard to do! Our lower level autonomic 'reading system' refuses to give us the colors but instead processes the words and tells us what the words say. Small children who have only just learned how to read find this test very easy - but the more you read, the harder it becomes. SteveBaker (talk) 17:47, 22 December 2009 (UTC)

That's called the Stroop effect, just as a by-the-way. I didn't mean to say that the mind/brain lacks internal structure (which would be a ridiculous thing for a neuroscientist to say), just that it can't be decomposed into "two brains" in any meaningful way. Looie496 (talk) 18:53, 22 December 2009 (UTC)

Thanks for the Stroop link - I didn't know that! But I agree about the "two brains" thing. What we have is a classical "top down" software implementation. It's amazing that the brain so often does things in ways that are so strikingly similar to computer software. SteveBaker (talk) 13:01, 23 December 2009 (UTC)

Odd that it should be "top down" while at the same time massively, obscenely parallel. Felis cheshiri (talk) 15:22, 23 December 2009 (UTC)

It's also annoyingly hard for people like me who are partially colorblind! Nyttend (talk) 00:29, 24 December 2009 (UTC)

M-theory

If a string is a one dimensional brane, and a brane can be and are dimensional barriers according to some theroies, then wouldn't a string also be a dimensional barier? —Preceding unsigned comment added by 74.67.89.61 (talk) 10:35, 22 December 2009 (UTC)

Difficult to answer that without knowing what you mean by "dimensional barrier". Where does that term come from ? Gandalf61 (talk) 14:00, 22 December 2009 (UTC)

According to some theories are four dimensional universe is seperated from othe dimensions by a brane, our universe is on a brane, that is what i mean. —Preceding unsigned comment added by 74.67.89.61 (talk) 00:19, 23 December 2009 (UTC)

You have now posted three questions about this, and not had an answer (apart from the response from Gandalf61 above). This suggests that either

• there is nobody here who knows about the subject (unlikely), or
• your questions are so basic or vague that nobody is sure how much of the subject you understand, and so nobody knows how to answer you helpfully.

I suggest that you talk about what you do understand and where that information comes from - if it is a Wikipedia article, cite it; if not, does the article string theory not help? - and then pose your question again more clearly in that context. --ColinFine (talk) 17:25, 24 December 2009 (UTC)

Snow defrosting on cars - patterns

Noticed something the other day and have a theory but though - why not ask here...so I will...My neighbour has a Mercedes C-Class and when the snow on the bonnet (hood for American's?) started to melt it did so in a 'pattern'. The pattern was - numerous circles of no-snow, with lines of no-snow. What caused this? My assumption is that this is a reverse-impression of the inside of the bonnet and that the extra thickness creates these 'warmer' parts where the snow doesn't last as long. It seemed that a number of cars on the street all had a different 'pattern' so figured it could be something to do with heat in that way. Anybody? 194.221.133.226 (talk) 12:21, 22 December 2009 (UTC)

Something like this? or this? SpinningSpark 16:45, 22 December 2009 (UTC)

The underside of the bonnet (hood) generally contains a lot of stiffening material and crumple-zones - also (depending on the model of car) padding to keep the noise levels down, and a kind of blanket of material that's designed to melt in an engine fire and act to extinguish it (or at least slow it down. Evidently, the ability of the heat from the engine to get up through the structure to melt the ice depends on the thickness of the metal, the amount and shape of the padding, etc. SteveBaker (talk) 17:34, 22 December 2009 (UTC)

Wow, all these years I've been brushing off my car before I start it, I've been missing out. Now I can't wait until the next snow so I can see what pattern shows up on my hood! APL (talk) 17:49, 22 December 2009 (UTC)

How is gasoline delivered to gas stations?

In the US, gasoline is sold in three grades (87, 89, 91 93) based on their octane ratings. Gasoline is delivered to gas stations using tanker trucks. Based on appearance alone, it is not clear whether the tanks on these vehicles have internal compartments. How are the different grades of gasoline delivered? Are they

• delivered separately?
• delivered by the same trucks that have internal compartments in their tanks?
• delivered as regular-grade gasoline with some octane-boosting additive added on delivery?
• delivered separately, with the mid-grade gasoline being a blend of the regular-grade and the premium-grade gasoline?

--173.49.11.197 (talk) 13:37, 22 December 2009 (UTC)

Personal experience from being a night clerk at a BP back in 1991... Each grade of gas is delivered by a different truck. -- kainaw™ 13:54, 22 December 2009 (UTC)

(EC) Crude oil is pulled from the ground or offshore. It is taken to a terminal or FPSO and then transferred to tanker ships. These ships drop crude off at a refinery. The oil refinery generates various grades of refined product, which include gasoline, kerosene, jet fuel, and other products. The various fuel types and different grades of gasoline are placed in to Refined Product Pipelines, such as these operated by Sunoco (not to be confused with crude oil pipelines like the Trans-Alaska Pipeline, which operate differently in both the business-sense and technical details). The various grades of gasoline are pushed into the pipeline in series; the goal is to prevent mixing by carefully controlling the laminar flow of fluid in the pipeline, but understand that there are engineering tolerances to this process. Different grades and even different brands of fuel from different refineries can be streamed into the pipeline, and by minimizing the mixing, can be extracted later. Each unit of refined product is contractually obligated to be delivered from an entry-point (a specific refinery, owned by a specific integrated or downstream company like Shell or BP or Valero) and is contractually obligated to be withdrawn from the pipeline at some other location (hundreds of kilometers away from the refinery) at a specific company's terminal. As each slug of refined product comes out, it is assayed and sorted to the appropriate separate storage tank for its product grade. Sometimes, additional processing is performed at these terminals, adding a few additives like Chevron Techron. But this doesn't change the octane rating of the fuel (not much, anyway). Finally, the gasoline from each separate storage tank is put into a separate local transport truck for each grade (as Kainaw corroborated above), and then trucked to consumer fueling stations (which have the recognizable brand-names you are familiar with), as well as airports, industrial facilities, and anywhere else that needs large quantities of refined product. Nimur (talk) 13:58, 22 December 2009 (UTC)

Thanks for the comprehensive explanation. --173.49.11.197 (talk) 14:22, 22 December 2009 (UTC)

Not sure if you were asking about this, but the tanks in the truck are divided into compartments, or have baffles (walls with slots or holes in them). This is to keep all the liquid from sloshing around whenever the truck starts or stops. The momentum of the liquid would make the truck uncontrollable otherwise. For some reason our article on Tanker truck does not mention this. The article on Tanker ship links to Free Surface Effect which mentions it. Ariel. (talk) 17:22, 22 December 2009 (UTC)

At least some trucks have separate sections that can (in principle) each have a different product.[4] My WP:OR in USA is that I usually see one truck with several hoses, each going into a different underground tank, and each tank (well okay, the cover over the access ports) is color-coded for a different octane rating. DMacks (talk) 17:31, 22 December 2009 (UTC)

FYI: Gasoline is sold in the US in 93 and (rarely) 95 octane grades - it depends on where you live. SteveBaker (talk) 17:29, 22 December 2009 (UTC)

Thanks. I meant to say 87, 89, and 93 in the question but I mistyped it. I don't recall seeing 95-grade gasoline sold around here. Is it for some special applications? --173.49.11.197 (talk) 18:17, 22 December 2009 (UTC)

There is also 91 - gas stations here in Texas are split about 50/50 between the ones that sell 91 and those that sell 93. I've only seen 95 sold in a couple of places. One is the gas station inside DFW airport - I can only imagine that some kind of airport service vehicle benefits from 95. It's so hard to find that I doubt that any normal vehicle requires it - but high-compression engines do perform a little better with it - especially in European cars that are often designed to take advantage of the higher octane stuff that you find around Europe. My turbo MINI Cooper definitely runs better on 93 than 91 (more power and better fuel economy) and you may even get a "Check Engine" light if you run it on 89. I think it does better still on 95 (or 93 with a third of a bottle of octane booster!) - but I don't have any hard numbers to back that up - so it might just be observer-bias.SteveBaker (talk) 18:34, 22 December 2009 (UTC)

By the way, in high-altitude states, regular is only 85. Apparently you don't need as high an octane number there. I'm not sure exactly why. Maybe with a lower partial pressure of oxygen, compression ignition is less likely? Does that mean you need higher cetane number diesel fuel? --Trovatore (talk) 21:32, 22 December 2009 (UTC)

It's not the lower partial pressure of oxygen, it's the lower overall pressure. Premature ignition is caused by the absolute pressure in the cylinder, so since the engine's compression ratio doesn't change at higher altitude, the lower starting pressure means that the final pressure of the fuel-air mixture is also lower. --Carnildo (talk) 01:38, 24 December 2009 (UTC)

Suicide jump balloon

In a recent CSI episode, a guy jumped from a building with the intent of committing suicide, but the police anticipated this and had the LVFD set up a big balloon on the street level -- does such a balloon really have the potential to save a jumper, assuming he lands in an un-awkward position, or does such a balloon not really exist? DRosenbach ^{(Talk | Contribs)} 14:06, 22 December 2009 (UTC)

What you saw was an air bag used primarily for movie stunts. Yes, they do exist (see: [5]) and in principle can be designed to stop a human falling from any height (though 50-100 ft would be a common _target). The limitation is that a person needs to land horizontally in the center of the bag, which is okay for a stuntman, but a jumper who was serious about killing himself would just have to dive head first or move over a few feet so he missed the center of the bag. Also, they are big things that have to be inflated and maintained with air blowers, etc. It seems very unlikely that you could set one up without the jumper noticing (as happened in CSI). Dragons flight (talk) 14:37, 22 December 2009 (UTC)

Remarkably, someone has looked at (primarily suicidal) 'jumpers' versus (primarily accidental) 'fallers' in a clinical setting. The abstract is free, but you'll need a subscription for the full (but brief) note: WP Burdick, (2004), "Jumpers and Fallers: a Comparison of the Distribution of Skeletal Injury" Clinical Radiology 44(2):192-3. While 'jumpers' tended to have more severe injuries overall (possibly due to deliberate choice of greater starting heights), they also had a greater likelihood of landing feet-first — implying either an instinctive resistance to going head-first, or a deliberate last-second backing-out. Many 'jumpers' also had significantly more severe injuries to the dominant – usually right – side of their bodies, suggesting a deliberate attempt to break their falls using their stronger side. 'Fallers' tended to have a uniform left-right distribution of injuries and a greater number of skull fractures, presumably due to surprise and lack of psychological preparedness. (One caveat — the study I've linked to only reports on fracture cases arriving at a particular trauma center by air ambulance, so the very-obviously-fatal cases would be triaged out, and very minor injuries would not be included.)

I haven't seen the CSI episode in question and am therefore unaware of the height from which the individual purportedly jumped, the size and position of the air bag, or the nature of the jumper's landing. I can't comment on whether or not the episode allowed sufficient time for bag placement and inflation, or whether or not the blowers would have been audible above traffic and wind noise at altitude. However, it is at least plausible that instinctual responses might tend to guide the jumper into a feet-first landing — regardless of whether or not it was a 'serious' attempt. Even a suboptimal body orientation might be sufficiently cushioned by an airbag to allow the jumper to survive, albeit with lower-extremity injuries. Worth noting is that there are many substantiated reports of survival by skydivers who have suffered a complete failure of their 'chutes. Usually these rare survivors have severe and traumatic injuries, but then again, they usually don't have an airbag to land on. TenOfAllTrades(talk) 18:34, 22 December 2009 (UTC)

The guy jumped from...eh...50 or so stories, but from the time the cops showed up, it was less than 5 minutes until the jump -- not nearly enough time to get the bag opened. The episode was in the original Las Vegas CSI and was entitled "Death is better" or something of that nature. I'd say the poetic license of allowing such a huge bag to be fully operational in way less time than it would actually require is fine -- certainly much more acceptable than obvious errors that creep into episodes, like mislabeling tooth numbers in the post-mortem exam in the previous episode eititled "Appendicitement." Thanx to all for your comments. DRosenbach ^{(Talk | Contribs)} 18:48, 22 December 2009 (UTC)

A giant inflatable gas bag being transported and inflated in under five minutes without a jumper noticing, (Or incidentally changing his jump location) and then perfectly landing on the gas bag is all less obvious than miss-numbered teeth? You must be a dentist. APL (talk) 02:38, 23 December 2009 (UTC)

I'd have thought something like a bouncy castle would be too hard. Would they be better just having people stretching a strong sheet of something like canvas between them which would allow the jumper to be slowed over a longer distance? Dmcq (talk) 00:27, 23 December 2009 (UTC)

While it is like a bouncy castle, it isn't inflated anywhere near as much so it will compress more. Catching someone in a sheet would be very difficult - for a start, you can't hold it very high above the ground so the distance you can slow them over is fairly small. It would also require significant strength and training from the people holding it to make sure they relax the sheet at just the right rate. --Tango (talk) 01:28, 23 December 2009 (UTC)

The "stunt" type fall arresting balloons are filled with a lot of air and have quite large vents so they constantly have to be pumped with air to keep them inflated. When a person lands on them a lot of air escapes as their fall is arrested. If they were just a big balloons full of air the deceleration would be much too fast to prevent serious injury or death. The fabric must offer "just" the right amount of resistance to stop you hitting the ground hard, but not enough to be too hard it self. An interesting related thing I learned when I did a sky diving course, which illustrates the point: if you freefall onto an open parachute of someone who has already deployed below you, the impact will likely be enough to kill you. This is something you have to be particularly aware of if you are jumping with a big group. Vespine (talk) 04:13, 23 December 2009 (UTC)

It's not so great for the person below you, either :-/ --Trovatore (talk) 10:42, 23 December 2009 (UTC)

LEDs

Resolved

An LED comprises a semiconductor diode. Does a diode comprise an anode and a cathode? ~~ Dr Dec (Talk) ~~ 17:50, 22 December 2009 (UTC)

It would appear so: ~~ Dr Dec (Talk) ~~ 17:59, 22 December 2009 (UTC)

eur.... a diode is made of an pn junction I wouldn't describe any of the constituent parts as electrodes. It is a continuous piece of silicon whose doping properties change along its length. —Preceding unsigned comment added by 92.17.229.48 (talk) 17:01, 23 December 2009 (UTC)

A thermionic diode (or vacuum tube, as some people call them) has a cathode and an anode. A semiconductor diode is similar in some ways, but doesn't have those discrete items. --ColinFine (talk) 17:34, 24 December 2009 (UTC)

To clarify - a semiconductor diode has a cathode and anode, but doesn't comprise a cathode and anode. Even a vacuum diode doesn't (solely) comprise a cathode and anode - as a minimum, it also has a heater. Tevildo (talk) 22:30, 24 December 2009 (UTC)

That ain't necessarily so, there are such things as directly heated cathodes and photo-cathodes which require no additional electrodes. @92.17.229.48, even diffused junction diode terminals are still referred to as anode and cathode even though, as you say, there have probably not been any made with electrodes this century. Another point of note is the same terminals are still called anode and cathode on a diode even when it is reverse biased - strictly speaking the names should be reversed as well but they are not by convention. SpinningSpark 23:00, 24 December 2009 (UTC)

epidemiology of symptomatic osteoarthritis

Hi all the article on osteoarthritis says that 80% of people aged 65 have radiological evidence of OA but only 60% have symptoms of osteoarthritis. Therefore if I've worked this out correctly the article claims that 75% of people aged 65 who have radiological symptoms are symptomatic. Clicking on the citation number 6 brings up an article on NSAIDs which has nothing to do with the previous statment. I would like to find a good reference for the epidemiology of symptomatic osteoarthritis. I have a book called Crash course in orthapaedics and rheumatology which claims that the prevalence of symptomatic OA is around 20% - which is a big difference to wikipedia article's estimation. Please help! Thanks, RichYPE (talk) 17:51, 22 December 2009 (UTC)

As far as epidemiology goes, it's based on what's believed to be a representative cohort -- that's because, obviously, the actual number of X's per Y's aren't tallied. While radiographic evidence of osteoarthritis may or may not itself be subjective (let's assume for this discussion that radiographic evaluation is the gold standard of testing for the ailment), I'd say that symptomatic anything is certainly subjective. The perception of pain is highly subjective and what one may consider merely uncomfortable another may consider dastardly painful. While I cannot comment on the NSAIDS article being used to cite something out of context, I will say that symptomaticity is so subjective that in some minds, it's nearly worthless. DRosenbach ^{(Talk | Contribs)} 18:43, 22 December 2009 (UTC)

Why so many people at Amundsen-Scott South Pole Station?

The article shows pictures of office-block sized habitations, and says that up to 200 people are there during the Antartic "summer". My question is, what on earth do 200 people find to do there? What keeps 200 people busy full-time+ ? Why can't you just use remote-controlled instruments instead? Seem like a waste of money. 84.13.44.90 (talk) 18:53, 22 December 2009 (UTC)

IceCube Neutrino Observatory. Dauto (talk) 19:27, 22 December 2009 (UTC)

The above is just one example out of many lines of research regularly undertaken at the station. Dauto (talk) 19:56, 22 December 2009 (UTC)

We also have an article for South Pole Telescope. As I recall, IceCube's construction is currently better funded than all the other NSF programs on the continent combined with an appropriation of something like $275M over 8 years (it's a line item in the Congressional Budget for NSF). IceCube makes up roughly half the staff at pole during summer. Some of the rest are general station personnel, e.g. cooks and administrators, and rest are associated with the other experiments and programs. Dragons flight (talk) 21:00, 22 December 2009 (UTC)

I've been reading the blogs and journals of people at various Antarctic stations, and much of what they do is construction and maintainence: the environment is very hard on equipment. For example, in the network of remotely-controlled Antarctic weather stations, about a quarter of them are broken down at any given time, and it may take a year or two before someone manages to repair or replace one that's broken.

Remote control also has the problem of communication: the South Pole is so far south that it can't contact satellites in geosynchronous orbit -- contact with the rest of the world is only possible when a relay satellite in an inclined orbit comes into view. Supporting 200 people at the South Pole for six months costs much less than putting up a few satellites. --Carnildo (talk) 01:57, 24 December 2009 (UTC)

To be cynical also, the US reserves the right to claim under theAntarctic Treaty System. A continual presence on the continent might help in any future territorial claim. Polypipe Wrangler (talk) 12:13, 26 December 2009 (UTC)

Would cannibalism have saved Captain Scott?

Robert Falcon Scott and his companions died while returning from the south pole, due to running out of food during a storm. If they had turned to cannibalism and eaten their first casulty, who I think was Oakes, is there any reason not to think that the remainder of them would have survived? 84.13.44.90 (talk) 19:03, 22 December 2009 (UTC)

Wikipedia is not a good reference source for alternative history, most of the time :) --Dr Dima (talk) 20:37, 22 December 2009 (UTC)

And to your question directly - no, the three remaining explorers probably would not have survived even if they'd eaten Oakes' corpse. Hunger contributed to their death but was not the sole cause. --Dr Dima (talk) 20:40, 22 December 2009 (UTC)

What were the other causes then? 84.13.44.90 (talk) 21:09, 22 December 2009 (UTC)

You (both) mean Oates, by the way, though he was not the first of the 5-man polar party to die - that was Edgar Evans. AndrewWTaylor (talk) 21:03, 22 December 2009 (UTC)

I said three remaining explorers, didn't I? :) . The question was specifically about Oates, not Evans. And yes, the name is spelled Oates, not Oakes, so my bad. --Dr Dima (talk) 22:30, 22 December 2009 (UTC)

I'm asking if turning cannibal in that situation (for the Scott party or any other humans under similar conditions) would enable the march north to be continued, or if there are other problems that would result in not succeeding. Not really an alternative-history question. 84.13.44.90 (talk) 21:09, 22 December 2009 (UTC)

Just by looking over the article on Scott, it sounds like they needed a lot more than some meat to save them. Even with full stomachs the cold would have gotten to them before long, and they were a long way from the end of their journey. The only possible scenario is that the weather remarkably improved just after they died, leading to the thesis that if they had food to hold on for a few more days they would have been able to complete the journey. This is, of course, impossible to know. --66.195.232.121 (talk) 21:47, 22 December 2009 (UTC)

Any idea how soon the weather improved? 67.243.1.21 (talk) 01:08, 26 December 2009 (UTC)

Scott was very short on fuel as well as rations, so the Scott expedition members were frostbitten and dehydrated. They were also suffering from snow blindness. So, as I said, hunger was not the sole cause of their death. While fact-checking I was amazed to find that we have an entire article devoted to Comparison of the Amundsen and Scott Expeditions. It is very good. --Dr Dima (talk) 22:39, 22 December 2009 (UTC)

Of course we have! hydnjo (talk) 02:15, 23 December 2009 (UTC)

Would a coffee-grinder grind flax seeds?

I would like to grind flax seeds, because unground flax seeds go straight through you without being digested, and flax seed oil (also known as linseed oil) turns rancid very easily and is also rather expensive. My question is, would a small electric coffee bean grinder also be able to grind flax seeds? Flax seeds are much smaller than coffee beans. If not, what else could grind or open flax seeds easily? I do not think I have the patience to use a pestle and mortar. Thanks 84.13.44.90 (talk) 21:30, 22 December 2009 (UTC)

I suspect that a coffee grinder will turn flax seeds (or any oily kernel) into an unappetizing oily goo somewhat like peanut butter. It will also be very hard to impossible to clean. At least that happened when we tried to make ground peanuts for Chinese cooking... --Stephan Schulz (talk) 21:43, 22 December 2009 (UTC)

You could try putting it in a blender. If I was grinding the sort of amount I think you are, I would use my wand blender with the smaller container attachment. I've ground already coarsely ground almonds finer using this method. You might, of course, end up with an oily goo, but you could probably eat that. If you were only grinding a tablespoon or two, I'd use a pestle and mortar. 86.176.191.243 (talk) 23:22, 22 December 2009 (UTC)

I use a small coffee grinder to grind up all kinds of spices and it works a treat on anything that is dry. Stephan is right that cleaning it afterwards is a problem, especially if you want to use it for a different flavoured material next (maybe coffee for instance). The problem is the blade is not removable like it is on a food blender, but maybe there are models out there with a removable blade if you look around. SpinningSpark 01:45, 23 December 2009 (UTC)

It says here to "Grind flaxseeds in a coffee or seed grinder in order to enhance their digestibility and therefore their nutritional value." I find it available in supermarkets. It is called flax seed meal, and it comes in a type of vacuum packaging that ground coffee sometimes comes packed in too. Bus stop (talk) 01:52, 23 December 2009 (UTC)

I use a blender for grounding peanuts to make Apam Balik aka Ban Chien Kueh and many other transliterations of the name from various Chinese dialects which is similar to Indonesian Martabak. It makes them fairly fine although you can control the process somewhat by how long you grind them (because of my purpose I prefer them fairly coarse although not as coarse as the stuff they sell as chopped nuts) and can also be a bit uneven if you don't do it for long enough (again something I prefer). I found it better and easier then trying to bash the nuts in a bag (which tends to lead to the bag breaking) or in a mortar and pestle (which I found results in the nuts jumping out at the early stages although my mortar and pestle may be a bit small for that sort of thing). However I do do a resonably quantity at a time. Nil Einne (talk) 11:54, 23 December 2009 (UTC)

I have a blender, but like other blenders the blades are too high up for the small quantities I want to deal with. The flax seeds only have to be opened rather than ground, so I'd be interested to hear of any suggestions as to how that could be done easily. 92.29.68.169 (talk) 13:27, 23 December 2009 (UTC)

Lipid mobilization and utilization from adipose tissue

Apologies if this is explained somewhere, but I cannot get a full understanding (if one exists) of the full biochemical and cellular process involved in the mobilization and utilization of fat stored in adipose tissue. I would like to understand the following, with the asumption that this is an ongoing dynamic state that simply gets accelerated into lipid release under conditions that dictate the utilization of stored fat:

a. what is the normal status of lipid stored in adipose tissue, in the condition where their is neither an excess of metabolites for the body nor a shortage? b. what are the stimuli that induce fat mobilisation from the adipose tissue, is it exclusively glucagon mediated activity or are there other metabolic stimuli that contribute to the mobilisation? c. what are the consequences of these stimuli, i.e. what are the cascade of events that occur within the adipose cell and what is the mechanism of action such that the stored lipid (triglyceride) is released? d. assuming the triglycerides are released into the interstitial space, what happens next? excuse my lack of knowledge, but are they directly absorbed by the lymphatic vessels and ultimately released into the blood circulation where they undergo initial metabolic breakdown to glycerol and free fatty acids which can then undergo cellular uptake and be metabolised by classic metabolic pathways, or is there metabolic action in the interstitial space before the lymphatic tissue can absorb and transport the gycerol and free fatty acid, or is their a completely different outcome? e. this said, when fat is mobilised from adipose tissue, what dictates the specific areas of this mobilistion - I am trying to get some cellular understanding of why if (for example) a person wants to lose abdominal fat, this is practically the last area that a patient will see fat breakdown from

Any insights into this area or direction on a treatise which covers these questions would be greatly appreciated, I understand the absorption of fat from dietary intake, but not the mobilization of fat from its storage site in the adipose tissue. —Preceding unsigned comment added by 99.54.67.12 (talk) 21:37, 22 December 2009 (UTC) --99.54.67.12 (talk) 15:41, 23 December 2009 (UTC)R Owen, Houston

You are asking a very complicated series of questions, which is probably why no one has attempted to answer them yet... This topic is covered in great detail in any number of textbooks, although it is fair to say that the details are still being worked out by scientists working in the field. Here are some articles you can look at (though some are in need of significant work): lipid, adipose tissue, adipocyte, fatty acid, triglyceride, fatty acid metabolism, lipase, hormone-sensitive lipase, lipolysis.

Here are some incomplete answers to your questions:

• a) (from Adipocyte: "fat stored is in a semi-liquid state, and is composed primarily of triglycerides and cholesteryl ester." In the steady-state, the body nearly always has some adipose stores. Obviously, the amount of excess caloric intake will dictate how much fat is stored.
• b) The hormone-sensitive lipase (HSL) enzyme is partly regulated by glucagon, which is secreted when the blood sugar is low; however, the stronger effect is probably from insulin, which inhibits HSL under conditions where blood glucose is normal or high. As blood glucose levels fall, insulin secretion from the pancreas decreases, and HSL is released from inhibition. The more complete answer to this question (especially in regard to the regulation of lipolysis in adipocytes) probably relates to the regulation of a different lipase enzyme, called "adipose triglyceride lipase" which according to this article is also involved in metabolism of triglycerides in adipocytes.
• c) (from Lipid#Biological_functions): "The adipocyte, or fat cell, is designed for continuous synthesis and breakdown of triacylglycerols". This process is controlled by complex hormone cascades (see b). The actual biochemistry that happens inside of the adipocyte is not really well covered in our articles, unfortunately. You could have a look at this article, which from the abstract details some of those mechanisms. The end result is that the adipocyte releases free fatty acids and glycerol.
• d) The triglycerides are broken down in the adipocyte and released as free fatty acids into the blood stream (not the lymphatics, I believe). From the blood stream, they can either be used by muscle cells for energy production via fatty acid oxidation or absorbed by the liver and packaged into lipoproteins.
• e) I'm not aware of "regional" control of fat mobilization, although there's no reason to think that it couldn't happen (through a paracrine rather than endocrine mechanism). My guess is that what you observe about abdominal fat being the hardest to get rid of, is that there's just more fat deposited in certain regions of the body, and therefore those regions take the longest to be depleted.

Hopefully that's enough to get you started. Enjoy! --- Medical geneticist (talk) 14:06, 24 December 2009 (UTC)

bubbles

What causes soap to forarm bubbles? —Preceding unsigned comment added by Accdude92 (talk • contribs) 22:39, 22 December 2009

Soap bubble is your friend :) --Dr Dima (talk) 22:44, 22 December 2009 (UTC)