Wikipedia:Reference desk/Archives/Science/2012 April 30

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April 30

Fibrosis

Do all infections and inflammations cause scar tissue to form in the area affected? — Preceding unsigned comment added by 138.253.210.6 (talk) 08:17, 30 April 2012 (UTC)

I don't think so otherwise the common cold would scar nasal tissue, and that's obviously not true. I stand to be corrected though. --TammyMoet (talk) 09:30, 30 April 2012 (UTC)

No. Small areas of damage to the body are fixed by regrowing the original tissue, with a few exceptions, like nerve cells. Thus, no damage should be apparent once this process is complete. However, this is too slow for large areas of damage, so scar tissue is used, instead. Unfortunately, we lack the ability to gradually replace scar tissue with normal tissue, so scars become permanent. StuRat (talk) 15:30, 30 April 2012 (UTC)

Kinased oligonucleotides

Hello. What's a "kinased oligonucleotide", and how does it differ from a "normal" oligonucleotide? Thanks! Leptictidium (mt) 10:25, 30 April 2012 (UTC)

Does protein kinase have the information you need? SpinningSpark 15:48, 30 April 2012 (UTC)

Kinases are enzymes that facilitate the addition of phosphate groups to other molecules; a 'kinased' oligonucleotide is therefore one to which a phosphate has been added (generally to the 5' end) through the use of an enzyme (most often T4 or T7 polynucleotide kinase). TenOfAllTrades(talk) 15:49, 30 April 2012 (UTC)

Why it's not just called a phosphorylated oligo is beyond me..... Fgf10 (talk) 17:01, 30 April 2012 (UTC)

Probably historical accident. I'm guessing that the T4 PNK method was either the first, the cheapest, or the most popular method for some period of time (and may still be—I've never done much work in the area) and it has just stuck. The term phosphorylated is definitely also used; it is slightly broader in its meaning, however, in that it can also cover oligos that were phosphorylated using other mechanisms (that is, not with a kinase) or at the other (3') end of the strand. If it makes you feel better, Google suggests that phosphorylated oliogos outnumber their kinased brethren on the web by about three to one. TenOfAllTrades(talk) 13:12, 1 May 2012 (UTC)

Think of it from the worker's point of view. He has these oligos, he has to "kinase" them, and then he has "kinased oligos". Wnt (talk) 05:11, 3 May 2012 (UTC)

How many neurons can fire at once?

I've read the average neuron in the human brain can fire 200 times per second. How many neurons can actually sustain this rate simultaneously? How many usually do? Is this limited by physical constraints (e.g. ability to feed in and dissipate energy) or by neurological bottlenecks? NeonMerlin 12:11, 30 April 2012 (UTC)

I suspect that while the (limitted) supply of nutrients will enforce an upper limit of how many many neurons can simulataneously fire at maxiumum rate, electric disturbance will impose a lower limit. Every neuron that fires creates an electric field that propagates out through the bulk of the brain. If you get enough firing simultaneously and rythmically, the electric fields will add, perhaps creating a field strong enough to fire more neurons. This could avalanche thru the brain causing loss of functioning until nutrients and/or neurotransmitters are finally expended. Any comments from those who have studied epilepsy? Ratbone58.170.164.197 (talk) 14:49, 30 April 2012 (UTC)

the high Amplitude of Delta wave production indicates synchronized firing of many neurons (at low frequency). I believe Exploding head syndrome and Life review are other examples of simultaneous activity of large percentage of neurons. --Digrpat (talk) 22:00, 30 April 2012 (UTC)

Does this mean that EHS or seizures could (at least in theory) result if the executive functions were somehow artificially accelerated too much? (The idea of such acceleration was what motivated the question, because I've read about the "executive bottleneck" hypothesis and am interested in cognitive enhancement.) NeonMerlin 12:17, 1 May 2012 (UTC)

200 Hz is a rate you only see in brief bursts, usually not more than 5 or 10 spikes. There are areas of the brain where most of the neurons run constantly at 50 Hz or more, but those areas only make up a small fraction of the total brain. In the cerebral cortex, the great majority of neurons fire at overall time-averaged rates of 10 Hz or less, although individual neurons can ramp up quite a bit from that for brief periods when they are active. During an epileptic seizure the rates go up substantially, but I don't have any figures -- I'm pretty sure the max rate is far below 200 Hz, though. Looie496 (talk) 04:20, 1 May 2012 (UTC)

Hydraulics/Pressure question

I have a box with a shaft passing through it. The box (completely insulated of course) is filled with a hydraulic fluid maintained at a certain pressure (say, 10 bar). When the shaft rotates (say, at 1500 RPM), will the pressure acting on the walls of the box change? If so, how? 117.216.154.47 (talk) 12:39, 30 April 2012 (UTC)

Somewhat irrespective of the pressure within the box, as any practical fluid will have a finite viscosity, the rotating shaft will tend to drag round the fluid with it, the the thereby rotating fluid will try to drag round the box as well. If the box is not externally constrained, then it will rotate at the same speed as the shaft. If the box is externally prevented from rotating, then there will be power dissipated in the fluid. If viscosity is sufficient, the power absorbed in the fluid will raise its' temperature. All practical fluids expand slightly with temperature, so if the box is trulely rigid, and the seals perfect, infinite pressure could in theory be attained. In practice, at reasonable speeds like 1500 RPM, things will be different. Practical fluids show a marked decrease in viscosity with temperature, and (usually) a very slight decrease in viscosity with pressure. This means that in practice, you are likely to have the fluid temperature settle at a slightly raised temperature with little change in pressure (depending on the box & shaft dimensions, perhaps not even measurable), as it will settle at a temperature just great enough to reduce the viscosity so as to absorb just enough power to maintain that temperature. See http://en.wikipedia.org/wiki/Viscosity Ratbone58.170.164.197 (talk) 14:38, 30 April 2012 (UTC)

I know this is a stupid followup question, but here goes. Due to the rotation of the fluid, won't there be any "centrifugal force" acting on each fluid particle, and hence, won't the pressure in the radial direction increase? — Preceding unsigned comment added by 117.216.154.47 (talk) 18:34, 30 April 2012 (UTC)

It's not a stupid question at all. I should have thought of it myself. However, for centrifugal force to result in pressure on the walls of the box, there must be sufficient centrifugal force to overcome internal cohesive (atomic) forces within the fluid, added to the static pressure, forming tiny pockets of vacuum. This could be achieved by making the radial size of the box large enough with respect to the given RPM. If the box is externally constrained from rotating, it may be difficult to get the fluid rotating fast enough. Below the critical speed, there will be no pockets of vacuum and no increase in pressure due to centrifugal force at all. Ratbone124.182.4.180 (talk) 04:17, 1 May 2012 (UTC)

fever to being cold

If someone went from a fever to being cold constantly and very fast would it be enough to kill (I am asking this out of curiosity). --86.41.70.125 (talk) 14:57, 30 April 2012 (UTC)

Not sure what you mean:

1) If they go from feeling hot to feeling cold, this can be a sign of disease, but how they feel won't directly effect their health.

2) If the temperature in the environment suddenly changes, this can cause shock, and potentially could kill you do to a heart attack. However, lots of people do just that, like the Polar Bear Club and those who go from a hot sauna to rolling naked in the snow.

3) If you mean your core body temperature suddenly changes by a large amount, that certainly would be unhealthy, perhaps shattering bones and teeth, but this isn't possible. StuRat (talk) 15:39, 30 April 2012 (UTC)

No I mean if one was to from fever to being cold and then get a fever again and being cold again then it gets repeated over and over again would it be enough to kill them. --86.45.153.97 (talk) 16:13, 1 May 2012 (UTC)

You just repeated the same thing again. If I didn't understand the first time, then repeating it won't help. Which of the 3 I listed do you mean ? If you mean something else, try explaining it using different words. Specifically, please tell me precisely what is making them hot or cold, and whether they really are hot and cold or merely feel that way. StuRat (talk) 18:26, 1 May 2012 (UTC)

I mean is someone going from being hot to cold repeatly for a period of time. --86.45.153.65 (talk) 19:57, 1 May 2012 (UTC)

You still haven't said what is causing them to get hot and then cold. Without knowing that, I can't answer. Is the temperature around them changing rapidly ? StuRat (talk) 20:12, 1 May 2012 (UTC)

Does the op mean changing illnesses? 99.43.78.36 (talk) 17:44, 2 May 2012 (UTC)

when the body is under attack there are a number of different defences, you may already know there are white blood cells that seek out foreign bodies and attack them, there are other defences and different levels as well.

Just as humans, plants, animals all die if they are exposed to extreme environments, some of the pathogens (bugs) we get can only survive in narrow temperature ranges. This is not a real problem, because in a 'carrier' (a person who has the illness but does not die from it) the temperature is kept nice and constant and the bug lives a good life, sometimes that person doesn't notice anything. Ideally the bug can pass from person to person and live a good life without those people falling ill, this is common, we have a LOT of 'bugs' in and on us.

when the bug is doing damage and out of control, and the few white cells can't keep up with preventing damage, because bugz are getting mathematically out of hand, then a system wide attack can be conducted. Your body heats up in an attempt to literally cook the bugz, and if that does not work, it will try to freeze the bug to death, and try to repeat that if required. You can die with a fever, or the fever can break and you come back stronger, with an immune system that responds instantly to a known enemy. Hard to say which way things will go, depends on what you have caught. Personally I trust the fundamental systems and if I feel cold I rug and cover up and help my body cook the bad things out, and help freeze on the other hand. If fever is a bad idea paracetamol usually interrupts the natural response and stabilises the temperature, at which point the battle may or may not still be won. you'd be more likely to be a carrier obviously if the bug overwhelmed you and your immune system surrendered after it had a weapon taken away. Penyulap ☏ 10:00, 6 May 2012 (UTC)

Parasitic pepper twin ?

Bell peppers often have something "extra" inside. It looks like a small pepper, itself, and is often tadpole shaped (but curled up). They are usually attached at the stem, but other times are not attached at all, rather rattling around inside. Is this a parasitic twin ? StuRat (talk) 16:11, 30 April 2012 (UTC)

It's known as an "internal proliferation" and is a form of Parthenocarpy according to this - see also this. Mikenorton (talk) 16:15, 30 April 2012 (UTC)

OK, thanks for the info. I'll mark this resolved. StuRat (talk) 18:12, 1 May 2012 (UTC)

Resolved

Engineering at university

At most universities, are engineering modules taught by a wide range of schools/departments e.g. Maths department, environmental sciences department etc or is it all taught by an engineering department? 80.195.94.171 (talk) 16:26, 30 April 2012 (UTC)

This is very much school-specific. My undergraduate university, which offered accredited degrees in Electrical Engineering and Computer Science, (and many other engineering and non-engineering fields), had certain mathematics courses that could be taken via the math department or via the computer science department. Certain classes were considered "interchangeable," and others required specific departmental course codes. In my graduate program, specific modules were recommended to be taught by individual professors, irrespective of their department. Many professors officially sat in multiple departments, e.g., the physics and computer science and the mathematics department, for reasons of academic politics - so I had the option to list a few courses as either a physics, or as a math, or as a computer science class - even though it was the same material and the same classroom. It's difficult to get statistics for "most" universities, but a good place to begin checking is the accreditation requirements for universities in your region.

For example, my undergraduate institution's accrediting board was the ABET. Here's an overview of what that exactly means: Proud to be an ABET Accredited Program. Roughly, this means that an independent board of academic experts, not affiliated with the university, has certified that our required mathematics and engineering courses are "very rigorous," and meet exacting standards, which-ever department actually is responsible for delivering the instruction. Nimur (talk) 16:55, 30 April 2012 (UTC)

Here in the UK you'll see an engineering department at most universities, but undergrads can be expected to have to trot to the maths department (and others) for the occasional lecture. LukeSurl ^{t c} 23:27, 30 April 2012 (UTC)

Ex-UK lecturer here: my old department used to provide modules for other departments so we used to have to teach our subject area in other departments. Sometimes this meant I'd have to teach in places such as art studios, machine rooms or draughting rooms. So it's not the case that the students would have to move around: lecturers also moved. I guess it depended on what was easiest to timetable. --TammyMoet (talk) 02:00, 1 May 2012 (UTC)

When I did my Bachelor of Engineering course, not only were math subjects taught by the Math Department, physics subjects taught by the Physics department, and the one solitary chemistry unit taught by the Chemistry department, in the fisrt two years of the (4 year) course, the university compelled you to do what they called "broadening units" with the stated intent of making you a more balanced man. For broadening units, you could pick whatever units from any uni course you liked, subject to timetable conflicts and subject prerequisites. I chose psychology and journalism units - and never regreted it.

At least here in Australia, universities providing engineering and certain other degrees considered to have academic significance (eg medicine) have for many years compelled undergrads to first do a "common first year", the first year of an Arts degree, or even a whole Arts degree. This is driven because the standard of education in Australian high schools has been slowly dropping for years - I believe the USA also has this problem. High school graduates used to be well equiped to tackle a solid degree, but they are not now.

At the Uni I went to, the allocation of rooms was another matter. I think the central administration used some sort of computer program to allocate rooms, and to the computer a room was a room was a room... We were continually walking from one end of campus to the other. It kept us fit.

Ratbone124.182.4.180 (talk) 03:34, 1 May 2012 (UTC)

Mechanical engineers often need computer science subjects (for control systems), management is a common topic on engineering courses (for project management etc), and some civil engineers study architecture, as well as the usual mathematics courses. There's a lot of potential subjects, and they may be taught by lecturers from other departments, or on courses run by other departments, or even by engineering faculty/department lecturers. --Colapeninsula (talk) 08:50, 1 May 2012 (UTC)

In the U.S., at least, I am pretty sure it is similar to the Australian example above. At most universities in the U.S., one would only take the engineering specific courses in the Engineering department. Thus, while a Chemical Engineer would need to take calculus and organic chemistry and fluid dynamics, it would be usual to take the calculus class from the Math department, the organic chemistry from the Chemistry department, and the Fluid Dynamics class from the Chemical Engineering department. This may be more efficient for the university, as Calculus is going to be the same whether it is used by a Chemical Engineer or an Economist, so they can sit in the same room and learn about integrals and differentials next to each other, so there's no real need to teach a sepetate "chemical engineer only" calculus class. --Jayron32 18:14, 1 May 2012 (UTC)

At my (American) university that I attend now, we do have an engineering section of calculus, with TAs who are engineers, that focuses towards applications of calculus in engineering. At a different school I have attended, they had two sets of chemistry classes, one in the liberal arts school, and another in the engineering/hard science school. In general though, I think Jayron32 is correct, at least in my experience. Buddy431 (talk) 18:40, 1 May 2012 (UTC)

At my undergrad school, the main required calculus course was taught by the math department and from a "pure" viewpoint. The engineers probably didn't think they needed quite so many proofs, but it was considered important to teach them to them anyway, for culture. --Trovatore (talk) 18:45, 1 May 2012 (UTC)

It's part of the long and continuous debate in education on the value of a liberal arts education versus a vocational education. The former aims to train a "complete citizen" by giving them the tools they need to do many jobs, and also to be a more complete citizen, fully engaged with the culture, history, and society. The latter focuses purely on skills that train one for their job, ignoring the rest. --Jayron32 23:32, 1 May 2012 (UTC)

A further comment on something touched on by Nimur above - a reflection on the administrative/political/acreditation quirks of universities - Australian ones at least. I did my bachelor degree in electronic engineering - comprising a common first year (a mix of just about anything, not even engineering of any sort), then 3 futher years specialising in electronics with significant amounts of Math from the Math Dept and some physics from Physics dept. In third year, us electronics students got programmed to do a unit called "Control Systems 304". In Uni nomenclature, the 3 in "304" means a third year unit, the 0 means its supposed to be of only moderate intellectual and workload challenge, and the 4 means something about revison of the unit since the degree was acredited, and whether or not it needs just specific other units done first, or the whole previous year. Electrical students got programmed to do a unit called "Feedback Modelling 316". The "1" in 316 means that the unit is of higher intellectual and workload challenge. Mechanical engineers got to do a unit called something else again. We all went to the same room and got taught the same thing by the same lecturer! Each subject unit was allocated so many points. The points for CS304 were different to FM316. To be awarded a degree, you needed a total of x many points - thus the importance?? of each unit varies depending on the degree you are doing. At exam time, we got to do the same exam papers labelled with all three subject names and codes. So the same subject, actually about various forms of negative feedback, is supposedly easy or difficult depending on what degree your are doing! What utter nonsense. Many other subjects were similar. Keit120.145.52.89 (talk) 04:07, 2 May 2012 (UTC)

highest decibel rating of any fling insect.

i asked this question in the entertaiment section but i hope i can get also answers here. Wich insect has the loudest decuibel rating when the insect flies? — Preceding unsigned comment added by Saludacymbals (talk • contribs) 20:23, 30 April 2012 (UTC)

Considering "loudest" to mean the highest decibel rating, I think you are looking for a massive insect that is also in some sense a poor flyer. Echoing some comments from the other Q: As Alansplodge pointed out, a dragonfly can be large, but are amazing fliers and quite quiet. Bumblebees are loud, but are not so loud as a cicada or cicada killer, perhaps in part due to mass differences. I have never heard a Hercules beetle or Goliathus goliatus in flight, but I would think the latter could easily be louder yet, perhaps the loudest. One interesting aspect of your question is that it would be relatively straightforward to gather some big bugs and do some audio testing, but somehow I think nobody has :) SemanticMantis (talk) 00:11, 1 May 2012 (UTC)

Since none of our photos give a good sense of scale, check out G. goliathus here [1]. SemanticMantis (talk) 00:16, 1 May 2012 (UTC)

so is even a cicadfa when it flyes loud?(article edited) Secmantimantis i meant any insect! — Preceding unsigned comment added by Saludacymbals (talk • contribs) 10:11, 1 May 2012 (UTC)

Yes, cicadas are loud flyers. In the USA, it is the loudest insect flight I commonly hear. green fruit beetles are also loud, but I think cicadas are louder. (This is all original research). Among all insects, I guessed the large beetles that I listed above might be loudest. I've looked through the scientific literature, and the only relevant material I found comes from bat research. For example, this paper [2] discusses how insect wing beats reflect sonar signals. This is not the same as loudness, but it's a start. SemanticMantis (talk) 13:12, 1 May 2012 (UTC)