Wikipedia:Reference desk/Archives/Science/2012 January 25

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January 25

Complexity and dynamism of systems

I am searching for literature that argues that changes in a complex environment should not be handled with fast reactions as this can have unpredictable consequences (because the environment is complex and, thus, it is not easy to understand/control). On the other hand I am searching for literature that argues that changes in a dynamic environment should not be handled with predefined "hard-wired" solutions as a system needs to remain flexible for a dynamic environment. Any ideas (maybe from the systems theory literature)? Top-journals preferred. 130.149.229.180 (talk) 07:57, 25 January 2012 (UTC)

Maybe there's an analogy to be made from another field. In curve-fitting, there's often the tendency to put in too many constraints, which causes the generated curves to become unpredictable and "lumpy". Better curve-fitting is often achieved by ignoring some of the data points, to get a smooth curve through most of them. StuRat (talk) 08:06, 25 January 2012 (UTC)

That sounds interesting, but is a bit too far away from what my topic is about (firm networks). 130.149.229.180 (talk) 10:04, 25 January 2012 (UTC)

A good starting point could also be literature that states that a "preventive" strategy fits to a complex environment, whereas a "reactive" strategy fits to a dynamic environment. Any ideas? 130.149.229.180 (talk) 10:04, 25 January 2012 (UTC)

Backpedaling a bit, you don't need a 'complex' system to show that fast reactions can be wrong. The system dynamics textbook "Business dynamics - Systems thinking and modeling for a complex world" by Sterman showcase examples of how taking corrective actions based on your immediate perception can make matters worse, typically because of time-delays. The classic example is a shower. You're in the shower and the water is too cold. You immediately turn the hot-water knob and keep turning it until the water temperature is to your liking. But because of the pipes and hose, there's a time-delay between turning on the hot water and actually feeling it. Therefore you have actually turned the knob too far and you'll soon get burned by the hot water.

This is a common pattern related to feedback loops, which can also be generalized to market economies or any other system. The aforementioned textbook is sort of a 'complex systems 101' course, with concepts that need to be established before one move on to more, well.. 'complex' things :-)

Another topic which may fit your second topic is organizational resilience which deals with how a system, instead of being robust to outside influence, should be able to change its form and organizational structure, so as to preserve its intended function. There should be some literature on this. EverGreg (talk) 11:53, 26 January 2012 (UTC)

A massive sun storm

I am an Iranian researcher , whom is studying about solar system with some new ideas for formation mechanism of system. As you will see in my work, the base discussion has some differences with existing model ,due to the result of my recent works.(of entering role of solar CNO cycle products to be carried by solar wind ,to solar wind effects in some chemical complexes in planets atmosphere and body and in addition discussions about the resulting mass increasing of Jovian planets )--Akbarmohammadzade (talk) 10:42, 25 January 2012 (UTC) Too I have new ideas for opposite rotation of VENUS ,that is preparing for publish .--Akbarmohammadzade (talk) 10:42, 25 January 2012 (UTC)

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(NEWS):A wave of charged particles from an intense solar storm is pummeling the Earth right now, which may trigger stunning aurora displays and cause minor disruptions to satellites over the next two days, NASA scientists say. (Jan. 24) Photo By NASA/SDO

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The question:how much mass can be ejected from sun body per such storm which can surround whole sun surface by particles and send those particles by solar wind ?>--Akbarmohammadzade (talk) 10:42, 25 January 2012 (UTC)

See Coronal mass ejection which has some figures as to size and frequency. --Jayron32 12:15, 25 January 2012 (UTC)

Earth life elsewhere

Are there any extremophiles currently living on Earth that could potentially live on Mars, or Europa, or any other planet/moon in our solar system? Obviously we don't exactly know the conditions of such environments (well, we've got a decent handle on Mars), but is it even remotely possible? Goodbye Galaxy (talk) 14:56, 25 January 2012 (UTC)

Beer microbes have lived for a long time in the vacuum of space on the space station, so I think there might be some that could survive on Mars, perhaps. Beer Microbes in space 217.158.236.14 (talk) 15:47, 25 January 2012 (UTC)

There is a possibility that we may have already exported Bacillus safensis to Mars. Tardigrades are also extremely tough and could probably survive on the surface of Mars, but I think they would need a source of water and food in order to reproduce. But maybe the tardigrades could eat the bacteria .... Gandalf61 (talk) 15:50, 25 January 2012 (UTC)

Chemotrophs, specifically chemosynthetic autotrophs, e.g. many archaea found at hydrothermal vents could potentially colonize Europa or Enceladus, or any place that has liquid water oceans with sources of 'food', e.g. sulfides. (We do not yet know for sure if those moons have those conditions, but it's not unreasonable to think they might) SemanticMantis (talk) 16:17, 25 January 2012 (UTC)

On Earth it is possible to find life that can live in virtually any liquid water by digesting even small amounts of dissolved minerals. The tolerances of various different kinds of microbes cover essentially the full range of temperature, pressure, pH and salinity under which liquid water can occur on Earth. So pretty much anywhere in the solar system that there is persistent liquid water would be tolerable to some form of Earth microbe. That potentially includes the Martian subsurface once one goes deep enough to warm up enough to allow for ground water. It would also include the subsurface oceans that are suggested to exist on Enceladus and Europa. Dragons flight (talk) 16:50, 25 January 2012 (UTC)

I think we need to start panspermia-ing our solar system with these bacteria as soon as possible! All of our eggs are in one basket! Goodbye Galaxy (talk) 19:52, 25 January 2012 (UTC)

Scientists, however, take the exact opposite approach, zealously sterilizing anything going to another planetary body so as to avoid contaminating the environment of extremophiles that might already be there. Also, in the event that humanity is utterly destroyed, knowing that yeast yet lives on Phobos would seem to be of little comfort or value. — Lomn 14:07, 26 January 2012 (UTC)

Heh, I think that actually would comfort me a lot. But yeah, I'll revise my opinion to: we should start pansermia-ing planets and moons immediately after conclusively determining that life is not already present. Goodbye Galaxy (talk) 02:49, 27 January 2012 (UTC)

Get ready for a long wait, recalling that absence of evidence is not evidence of absence ;) SemanticMantis (talk) 23:16, 27 January 2012 (UTC)

Bacterium in the bloodstream

Suppose you put a single bacterium (e. g. some common non-pathogenic variant of Escherichia coli) into the bloodstream. What is the mean lifetime of the bacterium before it is killed by immune cells? Icek (talk) 19:12, 25 January 2012 (UTC)

Don't think there is any definitive answer to such a question. The immune response differers from one individual to another. So to get any figure at all, one would have to do such an experiment on a large cohort. As this 'one microbe' scenario would not provide any useful scientific data, it is unlikely that any such studies have been conducted. With a few exceptions, one microbe would not be able to establish an ongoing infection, so again, this scenario is of not much interest. Moreover, in vivo studies like this are impossibly hard to do--Aspro (talk) 20:26, 25 January 2012 (UTC)

Agreed. There are even cases where that one microbe might be something for which the person has no immunity (either because it's a "super-bug" or because the person's immune system is compromised), and it spreads until it kills them. StuRat (talk) 21:05, 25 January 2012 (UTC)

A "super-bug" refers to a bacterium which is resistant to multiple antibiotics, it has nothing to do with the presence or otherwise of immunity. Also, a non-pathogenic bacterium (as specified in the question) would likely be killed by the innate immune system, e.g. by a macrophage before the development of adaptive immunity. This is because a non-pathogenic bacterium will not have evolved any immune evasion mechanisms allowing it to avoid being killed in this way, therefore even someone with a compromised immune system may not succumb to a non-pathogenic organism if it is primarily the adaptive immune system which is compromised (as is the case in AIDS). However they may be more susceptible to opportunistic pathogens, that normally aren't very good at evading the immune system, but can do it if the task is made easier by a compromised immune system. This is actually a very interesting question - what component of the immune system would be most likely to kill a non-pathogenic microbe first, and how long does that component normally take to act? My guess would be that phagocytosis would get there first, although a complement response triggered by a bound natural antibody, or a circulating antibody generated due to a previous exposure might be a good contender. I'm not sure though, as although I study immunology I have never actually thought about which component would "win" in this situation. If I have time later (when I am not meant to be working instead of browsing wikipedia) I might look this up a bit more thoroughly. Of course, as Aspro says the experiment won't have been done directly, but we should be able to get pretty far by extrapolation. Equisetum (talk | contributions) 12:12, 26 January 2012 (UTC)

They did list a non-pathogenic bacterium in their example, but didn't specify that they were only interested in the case of a non-pathogenic bacterium. A super-bug does mean it has multiple antibiotic resistance, but, of course, they are likely to also be at least partially resistant to our own immune response, or there would be no need to use antibiotics on them in the first place. A bacterium that always dies immediately when introduced to the human bloodstream is not going to be classified as a super bug. StuRat (talk) 18:16, 26 January 2012 (UTC)

Sorry, reading through my post I sounded a bit snappy - that wasn't my intent. I agree with you that anything that would be called a "super-bug" in reality would be a dangerous pathogen in addition to being drug resistant, therefore capable of immune evasion or resistance. Oh, and I've thought of another possible candidate for the fastest way the immune system could kill a bacterium: antimicrobial peptides. Equisetum (talk | contributions) 14:41, 27 January 2012 (UTC)

Thanks, apology accepted. StuRat (talk) 18:32, 27 January 2012 (UTC)

Thanks for the answers so far, especially Equisetum. I should limit the question to non-pathogenic bacteria. Icek (talk) 11:11, 27 January 2012 (UTC)

Okay, I posed the question to the people in my lab and they were pretty emphatic that the alternative complement pathway would kill the bacterium first. This pathway doesn't require the initial binding of antibody and so is much faster (and I'm embarrassed to say that I forgot all about it). Sorry I don't have any references to back this up, but it seems reasonable and I trust their view on this. Equisetum (talk | contributions) 14:50, 27 January 2012 (UTC)

Radiation from airport x-ray machines

How much radiation does an operator of a traditional (not a backscatter X-ray ) x-ray machine get? 88.8.69.246 (talk) 23:30, 25 January 2012 (UTC)

That depends. Read page 31 of this PDF. Von Restorff (talk) 02:30, 26 January 2012 (UTC)