Wikipedia:Reference desk/Archives/Science/2010 October 20

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October 20

Pancreatin

what is the optimum temperature for pancreatin? —Preceding unsigned comment added by 24.86.167.133 (talk) 00:01, 20 October 2010 (UTC)

Presumably Normal human body temperature. --Jayron32 02:45, 20 October 2010 (UTC)

Though a fair assumption, it's not necessarily right. Enzymes tend to function better at higher temperatures, but temperature rise will also eventually cause denaturation. There's no saying optimum function will occur at body temp, it will often be something a bit above. Just to add a complexity, some enzymes have their peak function below body temp. This (old) research paper suggests pancreatin is nearly twice as active at 50°C than at body temperature, but that it denatures quite quickly at that temperature. I think it says something about 40°C being optimal (for the relationship between speed of reaction and rate of denaturation), but you can read it up yourself to figure out the details. --jjron (talk) 06:06, 20 October 2010 (UTC)

P-v curve problem

i have got struck up is a very fundamental graph.which says Graph isothermal pv curve is above polytropic and below it adiabatic compression curve.but from p=c/v,p=c/v^1.2 and p=c/v^1.4 gives the reverse. Also at upper junction how cum at a point v=v^1.2=v^1.4 could be true for a given v=v1.please clarify.—Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 10:25, 20 October 2010

err got some clarificatiojn in wiki books ..wikibooks but i would love to have some comment at point of intersection of curves which have v=v^1.4=v^1.2 etc... kindly help. —Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 10:40, 20 October 2010

Acrylonitrile butadiene styrene

are most vacuums made from Acrylonitrile butadiene styrene —Preceding unsigned comment added by Kj650 (talk • contribs) 14:18, 20 October 2010 (UTC)

Do you mean vacuum flasks? If so, no reason why not, apart from a higher cost than some other thermoplastics. I think that it used to me more commonly used for such things before the raw material prices went up. Mikenorton (talk) 14:24, 20 October 2010 (UTC)

no, vacuum cleaners —Preceding unsigned comment added by Kj650 (talk • contribs) 15:53, 20 October 2010 (UTC)

how much would it cost a fit 20 year old to go die on Mars with a 5% chance of dying sooner

if a fit young man wanted a one way trip to mars just long enough to be the first person to die there, but also accepted a 5% risk of dying sooner than on the surface of mars (i.e. in mission-related problems that prevented his reaching the martian surface, or indeed mars at all) then how much would the mission cost him? How about if we increase the acceptable probability of a failed mission to 10%? 20%? 50%? —Preceding unsigned comment added by 85.181.48.193 (talk) 16:05, 20 October 2010 (UTC)

It's not really possible to answer your question. First of all we have no way to calculate the the probability of a failed mission. Any numbers you hear are just wild guesses. Also, the mission will cost about the same no matter the probability. Probability is all about random events. You can handle those with redundancy, but that's about it. And redundancy doesn't really increase costs all that much. What costs a lot is planning and engineering. Reducing planning or engineering does not change the probability - it just changes if it will work or not. There is some effect where you can plan for a random event - so in that sense reducing the planning costs, and hurt the mission success rate, but it's not really possible to calculate this. Anyway, just for an order of magnitude, the cost is going to be in the hundreds of billions. Ariel. (talk) 17:07, 20 October 2010 (UTC)

Well, the problem is that manned space travel is already safer than 50% - reliable estimates place it around 98% safe, whatever that means. So accepting a more risky mission doesn't reduce costs. (How would you reduce to a 50% survival rate? Only carry the LD-50 of oxygen and food, and no more? Would that reduce mission costs in any perceivable way?) If the objective is cost-reduction, cost-cutting life-support is probably not the way to go. Consider taking a look at the budget-breakdown, of say the Apollo missions - and apply some strategy to cut costs. For example, if Project Apollo had sent 1 man instead of 3, how much money would have been saved, how greatly would the scientific mission change, and how much extra risk would have been added?

Anyway, as I often bring up when the question of costs are raised on such questions - cost only really means something if you have a large statistical average - a market price. In other words, because there is no market for one-manned missions to Mars with 5% survival rate, there is no "price". You can't walk into the spacecraft store and buy a rocket. So it's meaningless to ask how much it "costs" in such point-blank terms. You need to evaluate things like - "who is capable of accomplishing this goal", and "how much will they prioritize it," and "how many support people are required," and "will the government permit us to do it," and so on. Those questions do not have straightforward dollar-value costs. When the Federal Government decided to fund Project Apollo, they did dedicate a specific budget for it - but it was part of an international movement toward space exploration - the costs (and benefits) in terms of the political and geopolitical capital are impossible to count. Could you launch a space-craft to Mars? Well, it all depends - are you a rocket-scientist? Can you afford the many-years-long process to design and build such an enormous rocket? Will somebody try to stop you? (Large rockets are suspiciously similar to large missiles and attract negative attention). So, you can't count the dollar-cost by itself. It's a meaningless parameter in such an enormous endeavor. Nimur (talk) 17:13, 20 October 2010 (UTC)

When engineers calculate risk percentages, they are using a specific (and often controversial) methodology known as quantitative risk assessment. It takes a huge amount of time to figure out said risks and teams of trained engineers to do so. We can't just hand wave on here and come up with meaningful numbers, much less correlate them to costs. The kind of study you are requesting is far beyond the capacity of the Reference Desk. --Mr.98 (talk) 18:39, 20 October 2010 (UTC)

We could do an approximation though I would think. Find out how much dV the spacecraft would need to get into orbit, and then to get to mars. The weight of the spacecraft needed to hold 1 human and 6-12 months of food, water and O2. Since he doesn't need to survive on the surface, we don't need to worry about slowing the spacecraft down when it gets to mars and it can just crash into the surface. Googlemeister (talk) 19:27, 20 October 2010 (UTC)

You're right :( (OP here). I was expecting too much from the Reference Desk. It's just that you never let me down before - I came to rely on you too much. I need to grow up. :( —Preceding unsigned comment added by 85.181.48.193 (talk) 22:12, 20 October 2010 (UTC)

Please do not send your corpse to Mars. NASA spends a lot of effort ridding their Mars probes of any organic material so that we do not contaminate the place. It would not be good if some bacteria from your gut propagated across the planet. —Arctic Gnome (talk • contribs) 03:06, 21 October 2010 (UTC)

NASA spent far more money for "man-rated" spacecraft components in the moon race. A booster might be fine for firing a weapon, or putting an unmanned satellite in orbit, but many components would be more expensive when they were upgraded to a reliabilty level, with longer mean time between failures, more thorough testing, and redundant backup systems. It certainly cost more to provide a booster with some thrust level and deltaV capability when the expected failure rate was 1 in 10,000 than when 1 in 100 was acceptable. The question is a very sensible one, but the answers may not be easily obtained. Somewhere in the early NASA reports one might find the relative cost of a booster or a guidance system for a manned spacecraft versus a similar ballistic missile system or satellite booster. Edison (talk) 19:50, 21 October 2010 (UTC)

exploring mars

Can someone give me a quick outline of what scientists would do to send a probe to mars, collect samples, analysie them and find evidence of life, then set up an operation to mine some valuable mineral there and ship it back to earth? just a series of points, step by step would be sufficient. If I need more on some parts, I can always come back later.

148.197.121.205 (talk) 16:06, 20 October 2010 (UTC)

Have you looked at NASA's official Mars Program website? They have many sub-pages geared toward all kinds of audiences, ranging from kindergarteners to students to professional scientists. There are presently a few active missions, listed here, as well as several historical missions. Every mission has its own web portal - and each page includes a "planning", "budget", "science", "results", and multimedia links. Scan over these portals - compare the Mars missions launched in the 1970s (like Viking Lander) to those in the 1990s-2000s-era (like Mars Pathfinder) or Mars Science Laboratory, one of the newest. There are also pages for future missions, from those almost-launched to those still in planning phase, and even hypothetical long-range projects. Nimur (talk) 16:15, 20 October 2010 (UTC)

But briefly, here's the process. (This is really more a current-state-of-affairs - NASA operates differently today than it did in 1970! NASA is now more of a program coordinator more than a system-integrator). The Federal Government will decide a decade-long NASA budget; the NASA program office will decide how to prioritize Mars exploration over the next few years, and if the money situation is good, it will decide to plan a mission. (This process takes multiple years, so it's worth bringing up). The amount of money determines many things: number of scientists who will work on the project; size of the spacecraft; and so on. These parameters determine the limitations of the scientific capabilities of the spacecraft. After those things are decided, a scientific program officer will try to accomplish a series of scientific goals by packing on as many instruments as she/he can afford to budget. Each instrument is sub-contracted out to major research institutions (usually, "famous" research universities are the lead for a sub-project - so, the Mars Atomic Force Microscope might be designed by Stanford and the camera might get contracted to Cal Tech), and then these principle investigators might sub-contract smaller parts of each instrument to other schools in a collaborative process). When these subcontractors are done researching the instrument-design, and the specifications and capabilities are finalized, usually a large contractor like Northrop Grumman or Lockheed Martin will build the flight-ready version, and these are all packaged up and sent to NASA. One contractor will be designated the lead for the mission and will be responsible for taking all the sub-parts and assembling them into a flight-ready spacecraft. Finally, NASA engineers will orchestrate the launch, and then the mission operations are handled jointly between the research organizations and NASA. Typically, the scientific data is returned to Earth in the form of low level data products, (like binary-code-files still in S-band-radio bit-order) and post-processed by NASA into high level data products (like photographs and mass-spectrometry charts). The are returned to each instrument designer, who analyzes the scientific results. Feedback is given to NASA, who might send new commands to the rover, or change the flight-profile of the orbiter, or so on, to help the scientists get better data. After the operation completes, (i.e., the spacecraft runs out of battery, or the Congress cancels the funding for the people who operate the ground-stations, or so on), the project "ends", and the data is made available to the public and the scientific community for further analysis. Nimur (talk) 16:27, 20 October 2010 (UTC)

We have a related article, Mars sample return mission, though it is way less ambitious than your scenario. Comet Tuttle (talk) 17:07, 20 October 2010 (UTC)

For Mars it is easy case, after pathfinder Mars got the target for everybody. (Other planets are far more complicated targets for landers). So you have every few years a lander with geology, biology, chemistry, meteorology ... instruments. So chose a biology or chemistry instrument you think will go to Mars on the next missions and join the group of the scientist who is the PI of the instrument. Than you are the scientist who is cooperating with others to send something to Mars. SAM on Mars Science Laboratory or LMC and MOMA on Exomars are the next oportunities I think (COI). Than the instrument has to detect life. (This is strongly depending on the definition you put into what qualifies for life.) The next point: "to mine valuable minerals" is the only point which does not make any sense. There is nothing of value on Mars if you subtract the costs for the transport. Even diamonds, helium-3 would be to expensive to transport it back to earth.--Stone (talk) 21:13, 20 October 2010 (UTC)

Inreality: Scientists have not the power to send anything to space, Wernher von Braun was the last one to be able to talk a president into a mission. NASA is driven by scientists, but also by politics. For ESA, JAXA, Roscosmos ISRO and CNSA all this works even more different in many ways. The us and soviet space program was not so focused on the science in former years, to go to the moon was done because it is difficult. There was also always a strong military component in all developments including the rockets the re-entry the cameras, even the Salyut program. This can come back if the situation on our little globe changes again. A man moon walk of a chinese astronaut would give the old and very boring space race a new pace and one new competitor. In the reality the life of the scientist is sometime more cruel, for example the Chandrayaan-1 mission and the Chang'e 2 due to the instruments which were already part of other moon missions yielded less science informations than what a scientist would wanted to have. These missions where driven by the need to demonstrate technical capabilities. Other missions are driven by lobbying certain very important things like helium-3 on the moon, which is not needed for at least long enough that the return to the moon is not necessary for another two decades. Scientist must deal with the missions they get. There are 100 concept studies around and one is piked out than everybody has to adapt to that new mission. If there is a ir spectrometer on the new Jupiter mission and you have built a ir spectrometer for the not selected Saturn mission you will try to get into that project as co-investigator with hardware at the AO. To get onto the mission you need heritage this is the most used word in the business before the AO (announcement of opportunity) famous does not buy you anything in that business, the space heritage does. At the ESA level you have also to be in the right country, if there are 10 instruments and already the camera and the magnetometer and the uv-vis spectrometer are built by German PIs you have no chance to get on the mission with another German instrument. DLR will not have enough money to pay for all the instruments. The instruments are not financed by ESA, but by the national agencies. A cruel example what happens to missions is the DAWN mission which was cancelled to show that the new NASA director has a strong leadership personality. There are people out there who tried this lets go to mars and find life for decades and still sit in the lab and have no instrument on any mission.--Stone (talk) 21:17, 20 October 2010 (UTC)

Thermodynamics question

If we extract the maximum possible amount of work out of a system consisting solely of one litre of water at 10 degrees and one litre of water at 90 degrees, then what is the final state of that system? (I'm assuming that there is no external external "environment" with which the system can exchange heat. All we have in the universe is the two reservoirs of water.)

On the one hand, it seems it can't be two litres of water at 50 degrees because simply mixing the initial reservoirs would produce that state without any work being done (prompting the question "where did the energy go?"). On the other hand, it seems counterintuitive that it should be two litres of water at some lower temperature. 86.135.26.218 (talk) 17:54, 20 October 2010 (UTC)

See Carnot efficiency. You can't just use the formula directly, though: the efficiency will drop as the reservoirs near one another's temperature. Assuming constant heat capacity, we can write ${\dot {c}}=(\eta -1){\dot {h}}=-{\frac {c}{h}}{\dot {h}}$ (also derivable from the entropic rule $dS_{c}=-dS_{h}$), so ${\frac {d}{dt}}\log c=-{\frac {d}{dt}}\log h$ and the logarithms approach one another at equal speed. They will therefore meet at the geometric mean of the absolute temperatures, which happens to be 47.5 °C. The temperature is lower than the average precisely because you took some of the energy away to do work (and the presence of the cold reservoir was what allowed you to do so). --Tardis (talk) 18:32, 20 October 2010 (UTC)

Oh, thanks! I guess that makes sense. 86.135.26.218 (talk) 19:09, 20 October 2010 (UTC).

• However, could you look at this, where I asked if one litre of water at 90 degrees plus one litre at 10 degrees in some sense contained more energy than two litres at 50 degrees. The answer given by Wnt was "yes", and the implication seemed to be that it was "yes" because of the energy (work) that could be extracted in the way that we've been discussing here. However, if the end result after the work has been extracted is two litres at 47.5 degrees, rather than 50 degrees, then this argument rather seems to fall apart? 86.135.26.218 (talk) 20:43, 20 October 2010 (UTC).

What Wnt was getting at was (as was linked later by Gr8xoz) exergy, which is closely related to the (confusingly named) concept of thermodynamic free energy. In that previous question, your two systems had the same amount of actual energy, but arranged differently: in the separated case, there is less entropy and more (that is, positive) exergy, and so some of that same amount of energy is "available" — can be recovered with a heat engine. Since the ability to do work is an important notion of energy, it is true that "in some sense" the separated quantities of water have more energy; what they have is more useful energy. But since in fact they have the same absolute amount of energy, when you do use the heat engine the exergy that you remove shows up as reduced true energy in the result. --Tardis (talk) 21:59, 20 October 2010 (UTC)

Thank you. 86.135.26.218 (talk) 00:51, 21 October 2010 (UTC)

Animal nutritional requirements

Humans need varied diets in order to meet all of their nutritional requirements. How is it that many animals seem to be able to thrive on relatively less varied diets? Simply to say that they are adapted to those diets, and we are not, is not an answer; since animals' bodies are as complex as our own, it would seem that they would have similarly complex needs. John M Baker (talk) 18:57, 20 October 2010 (UTC)

The answer should probably be at or linked from essential nutrient, though it's not :-(. The short answer is that different organisms can manufacture different substances than others. To take an extreme example, plants have different requirements than animals because they can use photosynthesis to create simple sugars and animals cannot. By that same token, humans can manufacture their own vitamin D₃, while presumably other animals cannot. So humans don't need to eat vitamin D₃, while a different animal would. Matt Deres (talk) 20:20, 20 October 2010 (UTC)

If you're interested in the extremes of human diet, our article on Inuit diet might be of use. While the traditional diet is varied per see, it still contains a very high amount of animal-based product (blubber, organs, flesh, blood, etc.) with no noted long-term health effects. Matt Deres (talk) 01:01, 21 October 2010 (UTC)

Do you know if anyone has done research to see if the inuit have different biochemistry to most of us? I know that people in Peru living at high altitutes have evolved a different form of haemoglobin and larger lungs, so it's not inconceivable that the inuit differ in some way, allowing them to consume such a diet. Smartse (talk) 10:48, 21 October 2010 (UTC)

One important example is our inability to synthesise vitamin C whereas most animals can, as well as all plants. Presumably, we lost the ability to produce it ourselves because at some stage in our evolution we were gaining enough from our diet, that when our genes mutated, it made no difference to our survival. Our brain also needs fairly large amounts of the omega fatty acids (in particular very long chain PUFAs) which can only be obtained from some foods. The case of docosahexaenoic acid (more valuable than gold apparently) is really strange because although we can produce it ourselves, most of our life the genes are only expressed at a low level, meaning we have to eat hundreds of grams of omega 3s (like Alpha-linolenic acid to produce one gram of docosahexaenoic acid. The VLC-PUFAs are synthesised a lot by algae (and then accumulate in the marine foodchain) and our inability to synthesise them may be linked to the theory that we were semi-aquatic at some point in our evolution (tried to find an article on this but failed) and so were getting enough from our diets. Then there are the essential amino acids that we can't synthesise ourselves. I'm not sure how unique this inability is amongst animals. Smartse (talk) 10:48, 21 October 2010 (UTC)

The aquatic ape hypothesis is based on much unnecessary assumptions. 67.243.7.240 (talk) 21:40, 22 October 2010 (UTC)

It should also be noted that the difference between a healthy diet and a diet which you can survive on for a long time with (relatively) minor health issues are quite different. People can survive (long term) on a pretty unvaried diet and the standard of 'health' for a human is very different to that for your average animal (e.g. non pet based animals won't necessarily live long enough for the ill-effects of their diet to have an impact). ny156uk (talk) 22:07, 20 October 2010 (UTC)

Note also that our digestive systems are different compared to most animals as a result of evolutionary adaption to eating cooked foods. In a BBC's Horizon documentary last year, volunteers were put on the same diet as normally given to Chimps. That didn't work well :) . Our digestive systems are very limited; it demands far less resources to digest the food we eat compared to our closest realted relatives, making room for us to have a big brain. Count Iblis (talk) 22:25, 20 October 2010 (UTC)

B.t.w., I think the point made in that documentary was that by cooking foods we can absorb more nutrients, even with a more limted digestive system. The reason why we have a big brain and a Chimp hasn't is simply because we get can get more nutrients for our brain, despite expending far less effort to digest food. Count Iblis (talk) 22:30, 20 October 2010 (UTC)

Be careful Iblis, (good-natured nitpicking follows) Humans ancestors had bigger brains than chimps long before they started cooking. While your point is interesting and cooking/digestions surely play a role in evolution of brain size, I'd hesitate to say that this is `the reason' humans have larger brains than chimps. SemanticMantis (talk) 16:26, 21 October 2010 (UTC)

"Cooking allowed humans to have bigger brains" is a theory most prominently fronted by primatologist Richard Wrangham, as in his book Catching Fire: How Cooking Made Us Human. It's gotten a fair amount of media play, although the Wrangham article notes it's controversial in anthropological circles, saying that opponents claim bigger brains were due to meat eating. -- 140.142.20.229 (talk) 17:18, 22 October 2010 (UTC)

voice

What is the voice effect in this clip called —Preceding unsigned comment added by 217.211.193.135 (talk) 20:44, 20 October 2010 (UTC)

Vibrato possibly? Dismas|^(talk) 20:45, 20 October 2010 (UTC)

Sounds to me like a talk box, as used by Peter Frampton in this clip. Looie496 (talk) 21:07, 20 October 2010 (UTC)

However there are also some other tricks that produce similar effects, as summarized in Robotic voice effects. Looie496 (talk) 21:14, 20 October 2010 (UTC)

Isn't that autotune? Ariel. (talk) 22:33, 20 October 2010 (UTC)

Agreed. ---Sluzzelin talk 22:48, 20 October 2010 (UTC)

Bismuth toxicity

The article about bismuth says that it isn't toxic, but don't bismuth samples contain toxic amounts of thallium produced through radioactive decay? --70.250.212.44 (talk) 23:06, 20 October 2010 (UTC)

Well, no it doesn't. It says that it has "unusually low toxicity for a heavy metal"; in particular, it's less toxic than lead, antimony, or polonium. Not exactly a ringing endorsement!

As an aside, I'm not too happy about the way the toxicity information is phrased in the polonium article. It's talking mainly about the radioactive effects, which I presume are dominant, but that's not what "toxicity" means to me. Radioactivity is more like a physical effect; I expect "toxicity" to refer to chemical ones. --Trovatore (talk) 07:34, 22 October 2010 (UTC)

The half-life of Bismuth-209 is ridiculously long. That means that you'd need ridiculously long times to accumulate much thallium. Someone on here can surely calculate whether or not a sample of Bismuth-209 created during the Big Bang would have enough thallium in it to be toxic. My back-of-the-envelope read of the relevant numbers (toxic dose of thallium, half-life of bismuth) says "no", but I'm not very quantitative. --Mr.98 (talk) 23:23, 20 October 2010 (UTC)

The Big Bamg did not create any bismuth. 174.58.107.143 (talk) 02:42, 21 October 2010 (UTC)

My point was just that even if you assume it was created at the same time as the Big Bang (which is ridiculous because all bismuth on Earth is probably much, much newer than that), there still shouldn't be enough to be toxic. But I wasn't clear about that. --Mr.98 (talk) 11:48, 21 October 2010 (UTC)

I calculate that 1 Mole (unit) of Bismuth (about 200 g, or about half a pound) that's 13.75 billion years old (the age of the universe) would have about 4.4*10¹⁴ atoms of Thallium, or 0.15 micrograms. The "safe" level of exposure to thallium is 0.1 mg per cubic meter in the air in a workplace [1]. The risk from such a tiny amount in the Bismuth is miniscule. One of the more common routes of ingesting thallium is through food: This study found that people typically ingest something like 5 micrograms (0.005 milligrams) a day. If you're eating bismuth for fun, you have other things to worry about than Thallium poisoning. Buddy431 (talk) 02:58, 21 October 2010 (UTC)

Note that the bismuth is refined from the ore before use, which will tend to reduce the thallium content. Once refined, the radiogenic production of new thallium is so slow that it was only even discovered in 2003, so it is completely negligible in the context of toxicity. Physchim62 (talk) 08:36, 21 October 2010 (UTC)

Mass spectrometry

Ions with smaller masses are deflected more than ones with greater mass, but what about ones with the same mass but different charges (e.g. ²⁵Mg²⁺ and ²⁵Mg⁺)? --70.250.212.44 (talk) 23:20, 20 October 2010 (UTC)

The ones with the bigger charge experience greater deflection - the basic formula underlying mass spec is ${\vec {F}}=q({\vec {B}}\times {\vec {v}})$; increasing q obviously increases the force and thus the deflection you end up with.--81.153.109.200 (talk) 00:11, 21 October 2010 (UTC)

Strictly, mass spectrometry and similar experimental set-ups measure mass per charge ratio, and not mass properly. But for most cases, the charge is known (it is +1), or can be discerned from prior knowledge of the expected composition. In complicated mass-spec experimental setups, there is some redundancy (e.g., both Mg+ and Mg²⁺ may be present) - and a variety of empirical and numerical techniques exist to estimate the true distribution. Nimur (talk) 00:14, 21 October 2010 (UTC)