Wikipedia:Reference desk/Archives/Science/2011 September 1

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September 1

What would it look like inside of a gas giant like Jupiter?

Do we have any idea of what it might look like? Is it possible for a man in a space suit to survive this? ScienceApe (talk) 03:09, 1 September 2011 (UTC)

Too dark to read :-) --Trovatore (talk) 03:15, 1 September 2011 (UTC)

Right, since the light from the Sun wouldn't penetrate very far through the thick atmosphere. If you had your own light source, the thick atmosphere would still quickly absorb it, but perhaps you could see a short distance. In that case, you'd see clouds of various colors, depending on where you happened to be, or perhaps oceans of various colors, depending on the chemical mix, if you were near the core. Of course, all of this assumes that you don't die instantly from the chemicals, winds/currents, and temperatures. I imagine something more like a bathysphere than a space-suit would be needed to withstand the extreme forces. StuRat (talk) 03:57, 1 September 2011 (UTC)

I'm pretty sure Jupiter is oozing ionizing radiation at a rate that would require some very protective environments. The effect of going even within a few hundred thousand miles of the planet unprotected would probably be acute radiation poisoning. --Jayron32 04:03, 1 September 2011 (UTC)

[1] See this link. It is artist Adolf Schaller's impression of the great red storm as viwed from within Jupiter, ignore the alien balloons. I would guess, that if you descended 1000 km into Jupiter, you would no longer see the sun, but the area should be continuely lit up by the perpertual lightning flashes. There should be a lack of proper statification between cloud layers such as that which exists higher up. It is not to say it doesn't exist, just that they aren't as clearly distinguishable. It should appear like a glowing fog that seems to extend indefinitely in all directions, don't forget the strong winds. Plasmic Physics (talk) 05:04, 1 September 2011 (UTC)

Actually, after the first 100 km or so (at a pressure of roughly 10 atmospheres) the Jovian atmosphere is expected to have warmed enough that none of the available materials condense any more. An observer who made it that far might essentially pass below the clouds and have a visibility extending for kilometers (assuming that they bring their own light source, or perhaps see via lightning). Dragons flight (talk) 05:28, 1 September 2011 (UTC)

At what depth would black body radiation from the core light up the surroundings? Plasmic Physics (talk) 12:00, 1 September 2011 (UTC)

I'm not sure exactly, but not too deep, I imagine. According to Jupiter#Internal structure, the temperature at the boundary of the metallic hydrogen is 10,000K and that's 78% of the way to the surface. Black body radiation becomes visible at about 1,000K, by 10,000K you are well into the ultraviolet. However, it's difficult to say how useful black body radiation would be to see by. Since everything around you would be roughly the same temperature, it would all glow the same colour. You might be able to make out objects by their brightness (consider an oven heated to 3000K - while the air is at 3000K and therefore is red hot, the density is so low that you hardly see it and what you actually see is the walls of the oven glowing red), but the extent to which you can see otherwise is the extent to which the objects aren't perfect black bodies. If we need objects to not be black bodies in order to see them (black bodies are, after all, black), then we can no longer approximate them as black bodies and it makes it difficult to work with. --Tango (talk) 18:41, 1 September 2011 (UTC)

AFAIK if the only major source of light was from black-body radiation, then the light would be coming with equal intensity from all directions (and with the same intensity from any object within visual range as from the background!), so you'd end up in pretty much the same situation as in a flat-light whiteout -- only this would be more of a redout/yellow-out, and would be even worse because (1) all the objects are glowing at the same intensity and color as the background, so are nearly invisible; and (2) the light itself would be bright enough to overwhelm the eyes, as in snow blindness. 67.169.177.176 (talk) 05:32, 2 September 2011 (UTC)

This may be a shot in the dark, but what if I change my question? At what depth would the brightness of the transmitted light from the core equal the intensity of sunlight above jupiter. It would be a complete guess since no one actually knows the internal properties of Jupiter with absolute certainty. Plasmic Physics (talk) 04:06, 3 September 2011 (UTC)

Prob'ly not that deep, since Jupiter doesn't get a whole lot of sunlight to begin with. FWIW 67.169.177.176 (talk) 05:36, 3 September 2011 (UTC)

I recall a discussion of this topic a few years ago here. It should be possible to build a floating probe like a bathyscaphe, with a small pressure vessel for instruments and controls and a large buoyancy chamber which causes the craft to float at a desired altitude. Instruments could monitor pressure, temperature, wind speed, electromagnetic disturbances, composition of the atmosphere,and radiation. The buoyancy bag or chamber could have radiators to dissipate heat, prolonging the operating time. A rocket could be used to send a capsule to the upper atmosphere for data recovery, if radio propagation were impossible to an orbiting relay satellite. Edison (talk) 19:17, 1 September 2011 (UTC)

How would the radiators work? A radiator needs to be hotter than the ambient temperature in order to work. For something like a car, that's fine, since the heat in generated by the engine and the car is surrounded by cool air. Since it is the ambient temperature that is causing the craft to heat up, it can't get hotter than that. You would need some kind of heat pump connected to the radiator if you were going to get any cooling from it. --Tango (talk) 00:09, 2 September 2011 (UTC)

Yes, a working fluid could be used in a heat pump (or refrigerator). Alternatively, the evaporation of a fluid or sublimation of a solid could be used in a one-pass sacrificial way to keep an instrument capsule cool for a while to prolong the data collection capability. Such a more passive cooling system might offer a shorter operating life at a large saving of mass. The Russian Venera probes of the 1970's could operate for 50 minutes at 475C and 90 atmospheres, just buy prechilling and then using some sort of circulating fluid. The Galileo Jupiter atmosphere probe descended for about an hour and failed at 23 atmospheres and 153C. There is no surface, just a density gradient. If the Galileo probe could descend to a fairly dense area, couldn't a probe be made to float at some density level? Apparently that probe was able to get out a radio signal to an orbiter after considerable descent through the atmosphere, reducing the need for a rocket to rise to a higher level to transmit, though the lightning at some levels should produce considerable interference. From a level of atmospheric poor radio propagation or high interference, it might also be possible to release a buoy with a flotation bag which could rise to a higher level to transmit. Edison (talk) 20:28, 2 September 2011 (UTC)

The high pressure and temperature would likely overwhelm any spacecraft. ~AH1 ^(discuss!) 23:44, 2 September 2011 (UTC)

It clearly would, eventually, but we might want to keep it working for a while before it failed, and having it "float" at some density level seems like a possibility, with less power required than having it "fly" with engines, and longer lifetime than if it just plunges down until crushed/melted like the Galileo probe. Active cooling could keep an outer shell from melting or collapsing for a time dependent on the supply of coolant or the power supply with active cooling. I've seen electric arc furnaces which operate for a considerable time with the temperature in the pot high enough to melt the metal of the outer crucible did it not have active cooling flow (there's a ceramic lining, just as a Jupiter probe could have an insulating ceramic shell). The Lockheed SR-71 Blackbird from the 1960's operated with the outer surfaces above 260C, with active cooling of the surfaces. Rocket motors commonly actively cool parts of the combustion chamber which would otherwise melt by circulating fuel through them. Fuel and oxidized could both be used this way. On some planets, a craft could carry oxygen and use the atmosphere as fuel. Doesn't sound like this would work on Jupiter. Edison (talk) 20:40, 4 September 2011 (UTC)

An idea for an arbitrary surface designation: the first encountered critical point - the first depth at which any of the components of the atmosphere is critical. Where is the first depth like this, and what component is it? I don't expect hydrogen to be the first component to be critical. Plasmic Physics (talk) 03:57, 3 September 2011 (UTC)

I don't remember off the top of my head, but the first component to be critical (excluding trace components, of course) would prob'ly be either water or ammonia -- I'm not sure which one, though. 67.169.177.176 (talk) 05:47, 3 September 2011 (UTC)

DNA polymers

Are there any standard techniques that create polymers of repeating sequences of DNA? I am having a hard time searching due to the fact that a DNA molecule is commonly referred to as a "polymer" of nucleotides, rather than of a specific sequence. 184.98.162.93 (talk) 03:19, 1 September 2011 (UTC)

There are natural processes that do this, see Repeated sequence (DNA) for some threads to follow. Much of it is junk DNA and doesn't appear to code for any known protein, but some may have other functions, such as telomeres. --Jayron32 03:24, 1 September 2011 (UTC)

I'm aware of that. I was specifically looking for laboratory techniques. 184.98.162.93 (talk) 03:27, 1 September 2011 (UTC)

Sure, if you synthesize a sequence ABBBBBC you can use PCR to make many of those, and if you have an enzyme which will convert ...BBB-C and A-BBB... to ...BBBBBB... (these are well understood but you or someone else will have to find a link as I'm pressed for time) then you just let that stew for as long as you need to make long strings of B. 216.239.45.21 (talk) 03:32, 1 September 2011 (UTC)

In concept making a repeated sequence is just a simple case of synthetic DNA. But in practice DNA that repeats precisely can cause special problems - "unclonable DNA"^[2][3], triple helix and other exotic structure formation, and all manner of improper annealing. For a common lab inadvertency, consider the typical 100 or 123 bp DNA ladder which, if heated by some overeager grad student trying to get it into solution, somehow transforms into what appears to be a single high molecular weight band. One wonders how the DNA figures out just how to anneal when there are anywhere from 1 to 30 identical sequences in each piece ... but somehow it figures out a remarkably sharp solution, at least, given that it is too high of a molecular weight for the gel and you probably don't have a useful standard to compare it to... Methods of multimerizing the insertion of restriction fragments into a plasmid exist; there's rolling circle replication; and as mentioned PCR methods can work, if properly done. (Note for example that misaligned annealing can allow extension of more repeats...) Still, this is one of those things that can turn truly terrible, depending on exactly what you're trying to accomplish. Wnt (talk) 09:07, 2 September 2011 (UTC)

genealogical research: Hepatic dropsy

One of my ancestors is listed as having died from hepatic dropsy after an illness of 4 months. Any suggestions as to a modern diagnostic term? Thanks in advance bcatt (talk) 06:34, 1 September 2011 (UTC)

Here is a list of archaic medical diagnoses, which are interesting in their own right. If you scroll down you will find a reference to "hepatic dropsy". It seems to be an accumulation of fluid dependant on liver disease. Richard Avery (talk) 07:08, 1 September 2011 (UTC)

(ec) Sounds like a euphemism for cirrhosis. Nimur (talk) 07:13, 1 September 2011 (UTC)

This may correspond to abdominal ascites, which is itself a symptom of liver disease such as cirrhosis. --TammyMoet (talk) 08:19, 1 September 2011 (UTC)

Thanks for all the helpful answers. bcatt (talk) 20:22, 1 September 2011 (UTC)

Multi-cylinder engine

why do indicated power in each cylinder of a multi cylinder engine vary? is it necessary for indicated power to be same in all the cylinders? what are the consequences if the indicated powers vary and dont vary in the cylinders of the same multi cylinder engine?? — Preceding unsigned comment added by Saritha2616 (talk • contribs) 07:43, 1 September 2011 (UTC)

"Include a meaningful title. Do not write "Question" or "Query", but write a few words that briefly tell the volunteers the subject of the question." Plasmic Physics (talk) 08:55, 1 September 2011 (UTC)

I added a meaningful title. Indicated power per individual cylinder is a theoretical value and I don't know of an engine where it is not by design the same for all cylinders. Different values could introduce imbalance leading to vibration and even crankshaft failure.

The horsepower of a four-stroke internal combustion engine is:

HP= MEP x CID x RPM/(33,000 x 12 x 2)

where

MEP = theoretical mean effective pressure acting on the piston top through its stroke. It is divided by the work of 1 hp (33,000 ft-lb)

CID = piston top area times crankshaft's stroke length, which is divided by 12 to convert the value to feet

RPM = revolutions per minute. which is divided by 2 because the cylinder fires every other revolution.

The actual powers delivered by the cylinders will vary with their conditions and are usually not identical. Source. Cuddlyable3 (talk) 09:44, 1 September 2011 (UTC)

Autumn is when? (Northern Hemisphere)

Why not just say it begins when the Autumnal Equinox is 23rd Sept 2011. They tell us that there is temperature lag and so it is 1st Sept 2011 due to meteorology. If there is a LAG due to weather why is it not in October then?... this makes no sense to me! — Preceding unsigned comment added by 92.30.154.8 (talk) 12:09, 1 September 2011 (UTC)

Meteorologists use the 1st of September, December, March and June as their season start points. However, folk tradition has them starting on the equinoxes and the solstices. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:16, 1 September 2011 (UTC)

The article Autumn notes the various starting dates for Autumn in different regions. Some cultures regard the autumnal equinox as mid-autumn and others define Autumn in whole months i.e. Sept/Oct/Nov in Northern hemisphere. Cuddlyable3 (talk) 12:20, 1 September 2011 (UTC)

Starting fall in October would be a larger lag than having it start in September but keep it in mind that both of them are lags. No lag would be if the Equinox coincided with the middle of the Fall season, not its beginning, so starting Fall at the equinox is already a lag of one and a half months. Dauto (talk) 12:55, 1 September 2011 (UTC)

Not really. Winter starts on about December 21 and ends on about March 20. And the midpoint, around Groundhog Day, is typically the coldest stretch of winter, at least in the American midwest. Likewise, late July and early August, the midpoint of summer, are typically the hottest days. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:08, 1 September 2011 (UTC)

Yes, the designations are decently aligned with the weather, by design. What Dauto means is that the weather and the season designations lag behind the Earth's orbit. The period of least direct sunlight is centered around the winter solstice, which is before the coldest time of year. Rckrone (talk) 16:11, 1 September 2011 (UTC)

The Midwest US I have experienced seems to short autumn and spring a bit to extend winter and summer. Typically around here, summer starts early June and ends mid September and Winter starts late November and ends in mid March. Googlemeister (talk) 14:26, 1 September 2011 (UTC)

These definitions are always a bit fuzzy around the edges, since cultural definitions vary so much, as do local weather conditions, and other issues. In the U.S. at least, the season are traditionally delineated by holidays or observances. Summer lasts from Memorial Day (last weekend in May) to Labor Day (First weekend in September), with autumn lasting until Thanksgiving (fourth Thursday in November), winter lasting until Spring Break (usually first weeks of March) and thus spring lasting until Memorial Day. --Jayron32 17:05, 1 September 2011 (UTC)

To clarify a bit:

1) First, let's start with the assumption that summer is to be the hottest season and winter the coldest, by which I mean we want to gather all the (contiguous) hottest days together and call them summer and all the (contiguous) coldest days and call them winter.

2) If there was no thermal lag, then the hottest day would also be the longest day (the summer solstice), and the shortest day (the winter solstice) would be the coldest day. Those would then be right in the middle of summer and winter, respectively.

3) However, to adjust for the thermal lag, those events actually mark the start of summer and winter, respectively. Astronomers did this because they still felt these astronomical events should play some roll in determining the season.

4) Meteorologists apparently thought that this was a bit of an over-adjustment, and moved the season starts back about 3 weeks to the start of those months. Of course, wanting to have an easy to remember point where each season starts instead of determining the exact time of the solstices and equinoxes also was a factor. StuRat (talk) 17:42, 1 September 2011 (UTC)

Astronomically (and calendarically) the equinoces and solstices are the starting points of the seasons. Meteorologically, the first days of March, June, September, and December are the starting points of the seasons. If the Earth had no atmosphere (and therefore no thermal lag,) the Earth's temperature would be greatest on the equinoces and solstices, much like StuRat said up there. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:31, 1 September 2011 (UTC)

... so "astronomically" (as in most documents written by astronomers), the equinoxes and solstices are the mid-points of the seasons, not the start. Dbfirs 07:12, 2 September 2011 (UTC)

No. If there was no thermal lag, that would likely be the case, but, since there is, astronomers chose to have those events define the start of each season. StuRat (talk) 16:28, 2 September 2011 (UTC)

No, folklore in some regions chose to do this. Astronomers usually use the Celtic model and refer to the "midsummer solstice" etc. Dbfirs 21:30, 4 September 2011 (UTC)

No atmosphere would certainly reduce the thermal lag, but oceans and the continents would still exhibit some thermal lag. StuRat (talk) 00:21, 2 September 2011 (UTC)

"Meteorologically" in Europe. In North America, I think meteorologists use the astronomical definition, because the lag is a bit longer here than in Europe. At least, if they don't, it's plausible that they could (in California, for example, the hottest month is not infrequently September). --Trovatore (talk) 20:39, 1 September 2011 (UTC)

California has gotten a bit slow since medical marijuana got legal there, hm...? --Jayron32 21:46, 1 September 2011 (UTC)

There is, of course, the Mid-Autumn Festival. ~AH1 ^(discuss!) 23:39, 2 September 2011 (UTC)

Calculate airline security

How are airline security statistics calculated? Accidents/km, Accidents/starts? Deaths/km, ... ? Quest09 (talk) 12:12, 1 September 2011 (UTC)

Many countries have a transport safety authority that collects this data. Cuddlyable3 (talk) 12:23, 1 September 2011 (UTC)

Air safety might be relevant at least as a starting point. Bus stop (talk) 12:38, 1 September 2011 (UTC)

Nice, but when they say: airline x is on the top 10 most secure airlines, how do they came to the conclusion? You have airlines like Qatar or Singapore Airlines, which fly many km for each start, and you have regional airlines, which start more and fly less km. What would be a fair comparison here? (provided the assumption that accidents happen mainly at start and landing). Quest09 (talk) 13:04, 1 September 2011 (UTC)

See Air_safety#Statistics — there are a few different metrics used, and they give different results. (Note also the bit at the end regarding the difference between what airline insurers use and what airline press releases use.) Air does pretty well when you are talking about the amount of time or the distances covered, obviously, but does much less well when you talk about deaths per trip (because the number of deaths per accident is very high, and the most dangerous parts of flying are the takeoffs and the landings, not the in-between time). --Mr.98 (talk) 13:53, 1 September 2011 (UTC)

It's interesting to look at the numbers per passenger-hour and compare them to the numbers per passenger-journey. The average air journey appears to be roughly 4 hours long; the average car trip is about 20 minutes. In other words, the duration of the average automobile trip – and, I suspect, of the vast majority of automobile trips – are substantially shorter than virtually all air journeys. TenOfAllTrades(talk) 14:13, 1 September 2011 (UTC)

And the time for flights gets even worse once you figure in all the extra time needed for a flight:

1) Drives to and from airports at both ends (these also should be considered in relative safety calculations).

2) Time to go through security (may involve waiting in line).

3) Time to check in and check luggage (may involve waiting in line).

4) Time to go from terminal to car and vice versa, which may involve waiting for, then taking a bus to move you between lot and terminal, or time to walk that distance.

5) Extra safety cushion time you need to allow. In some cases, we've been advised to arrive up to 3 hours before a scheduled departure.

6) Time to board and exit plane (including waiting for others to do so).

7) Time plane spends taxiing or waiting for clearance.

8) Time spent due to flight delays and cancellations (requiring rebooking).

9) Time spent reserving flight, especially if you want to compare prices.

10) Time spent when switching planes, for non-direct flights, and also the additional time due to such flights not going straight toward the final destination.

For example, I used to regularly travel between Detroit and Toronto. Fortunately, there were direct flights, which took about 40 minutes, from tires off the runway to back on, versus a 4 hour drive. However, once all the other time was added in, I found it was quicker to drive. StuRat (talk) 17:58, 1 September 2011 (UTC)

irrelevant discussion of airplane flight time issues
The following discussion has been closed. Please do not modify it.
...which is totally irrelevant to the risk question. I mean, is there anyone here who doesn't know that air travel takes a lot of time? The reason it was brought up has to do with risk safety, but I can't see how your 10 point list above contributes to that discussion at all, unless I'm missing something. --Mr.98 (talk) 22:37, 1 September 2011 (UTC)

Yes, you're missing quite bit. I specifically mentioned that the risk from the drive to and from the airport should be figured in, but there are also risks in some of those other steps, like getting from the parking lot to the terminal and back. And, if you are comparing risk versus time spent, the issue does come up of whether you consider the time spent to be only when the plane is in the air or the entire time of the trip, from door to door. I'd argue that (total risk)/(total time spent) would be the best metric. StuRat (talk) 00:27, 2 September 2011 (UTC)

Stu's comment is most certainly not irrelevant (although appearing detailed and lengthy). Under discussion are the irrelevant parts of a trip that are included in the statistics in comparison with automobiles. Stu is reminding us that there are many irrelevant fragments to an airline flight that are included in the total hours upon which airline statistics are based. --DeeperQA (talk) 23:14, 1 September 2011 (UTC)

I would totally disagree with adding risk from the drive to and from the airport as part of the air travel risk since you are driving, not the airline. That would be equivalent to adding the risk of crossing the street to get to your car into the driving statistics. The two things are not really part of each other. You could live across the street from the airport if you wanted (at least at some airports) Googlemeister (talk) 13:16, 2 September 2011 (UTC)

If you try to determine the relative safety between driving directly to a destination, or flying, and fail to consider all of the risks involved with either, you will reach the wrong conclusion. And saying "you could move next to the airport" is also irrelevant. You could also buy an armored truck to make your drive safer. What matters is how things really are, not how they theoretically could be. As for considering the risk of walking across the street to get in your car (assuming your car is so parked), that would be appropriate, but, of course, you need to walk to your car whether driving directly or driving to the airport, so this cancels out when determining relative risks.

Your method reminds me of DNA analysis, where they say that 2 DNA samples match with only a 1 in a trillion (or some ridiculously large number) chance of them being wrong. What that is is the chance that two different people will have identical DNA at all the points checked. They completely neglect the much higher risk that the lab technician will screw up and test the same sample twice, say after being distracted by a phone call. StuRat (talk) 16:39, 2 September 2011 (UTC)

I too disagree. Factoring in the not-in-air time is irrelevant for airplane risk. Factoring in the time waiting for the baggage carosel or the switching between planes is also totally irrelevant. StuRat is complaining that airplanes are often quite time consuming despite their apparent speed. No one disputes this, but it is totally irrelevant for the question of safety statistics. Whether you spend 5 hours or 5 minutes waiting in the airport lobby for a layover does not have any effect on the safety of airplanes as a means of transportation, as I think should be completely obvious. Your time and means of going to and from the airport has nothing to do with airplane safety by itself; it is a completely separate variable. --Mr.98 (talk) 14:29, 2 September 2011 (UTC)

I don't think "risk per minute" is itself a very good metric, but, if you use it, you should use total risk over total time. If you don't do so, you could claim "there's X risk in a single hour-long flight, so if you fly 10 hour-long flights a day there would be 10X risk per day". However, when you consider that the one hour flight takes 4 hours overall, that would mean that 10 flights a day would take 40 hours a day, clearly an impossibility. Personally, I think "risk per mile (or km)" is the most useful measure of safety, but I would still include the total risk of the trip, from door to door, as the best method of deciding on the safest course of action. I would also use the straight-line distance you intend to travel (door to door), rather than counting extra miles you need to travel to make connecting flights or because the roads don't go directly where you want them to go. StuRat (talk) 16:55, 2 September 2011 (UTC)

As for when it would be appropriate to ignore total risk, and only focus on the risk of the flight itself, that would make sense for airline safety officials, assuming they have no authority to improve safety of passengers before they board and after they exit. However, the passengers aren't only concerned with their safety while on the plane, but for the entire trip, so, for them, the entire risk is relevant. StuRat (talk) 17:10, 2 September 2011 (UTC)

This is quite, quite silly. The time you spend on the ground is irrelevant. It does not have anything to do with the risk of flight. Calculating risks is not concerned with the practicality of multiplying the risks, it's concerned about comparing different outcomes. Comparing irrelevant metrics leads to irrelevant results. Think it through a bit. Risk per mile has its own obvious problems, which we've already discussed above. Each of the measures gives different results, as discussed above, and you really do have to take them all into consideration when comparing risks. You need not invent your reasoning on this from scratch, StuRat, as risk assessors have been discussing this for decades. --Mr.98 (talk) 21:51, 2 September 2011 (UTC)

I find it sometimes helps to view the extreme situation, in cases like this. Imagine the country is in a civil war, and the road to your destination is clear, but there are major battles around the airport. In such a case, would you still argue that the trip to and from the airport is irrelevant in calculating whether taking a plane or driving is safer ?

Reminds me of a real-life case. Last year, my Dad was in need of heart surgery. We asked what the risk was, and the surgeon gave us a rather low risk of death. Based on that, we decided to go ahead. He survived the surgery, but then died of a post-operative infection. We found out later, that the low number they gave us was only for death on the operating table, and that the total risk was much higher. We would have made a different decision had we been informed of the total risk entailed by the surgery. What's even worse, the doctor probably considers the surgery to have been a success, and will continue to recommend it, based on his faulty metric, even though a large portion of the patients die as a result of the surgery. StuRat (talk) 22:50, 2 September 2011 (UTC)

@StuRat: If there's a major battle going on around the airport, do you really expect said airport to continue normal flight operations? 67.169.177.176 (talk) 05:51, 3 September 2011 (UTC)

If the battles are in between you and the airport, they may still be a safe distance from the airport itself. Also, if people are trying to evacuate, and the airport is their last hope, they might keep it open longer than would seem to be safe. StuRat (talk) 05:57, 3 September 2011 (UTC)

True, but in the second case you don't have a choice -- it's either go to the airport and try to evacuate no matter what the risk, or stay put and get killed where you are. As they say, one choice is no choice at all. 67.169.177.176 (talk) 09:00, 3 September 2011 (UTC)

Perhaps people on the far side of the airport would use it to evacuate, since they would have to pass through the battle zone on your side of the airport to take the road out, but on your side of the airport, beyond the battle zone, the road is clear. StuRat (talk) 18:02, 3 September 2011 (UTC)

I live on one extreme side of a quite large city. The airport is way on the other side. Driving to the airport is quite a challenge. If I choose instead to drive to another big city where I can avoid that trip across town, I save a lot of hassles of all kinds. HiLo48 (talk) 03:05, 3 September 2011 (UTC)

Systolic vs. diastolic pressure as a severity indicator

For many years I heard that for people who have hypertension or are at risk of it, the blood pressure # that they should pay more attention to is the diastolic pressure. Recently on a TV program the voice-over said that the higher of the two numbers (i.e. the systolic pressure) is the one that people should be watching. Has there been a change in our understanding of the relative significance of the two numbers as a hypertension severity indicator? --173.49.82.36 (talk) 12:28, 1 September 2011 (UTC)

Both systolic and diastolic pressures should be controlled. Using the standards adopted by the American Society of Hypertension, adult blood pressure should be below 140/90 unless the person has diabetes or chronic kidney disease, then it should be below 130/80. To be below 140/90, systolic blood pressure must be below 140 and diastolic blood pressure must be below 90. In general, it is easier to lower systolic blood pressure with medication than it is to lower diastolic blood pressure. So, those with high diastolic and controlled systolic are in a particular risk group where more than simple medication may be necessary to control hypertension. But, millions of dollars are spent developing new medications to treat hypertension. So, the risk of high diastolic blood pressure is decreasing to the point that most hypertension specialists don't consider systolic or diastolic control to be any different. They just pick the medication that best treats the type of hypertension a patient has. -- kainaw™ 13:42, 1 September 2011 (UTC)

Is the difference between the two numbers significant? ~AH1 ^(discuss!) 23:34, 2 September 2011 (UTC)

I assume that you are asking about the Pulse pressure, defined as the difference between the systolic and diastolic pressures. That (linked) article addresses its significance. -- Scray (talk) 04:43, 3 September 2011 (UTC)

medical student

is medical student takes admission for mehran university? if yes so, for which department? — Preceding unsigned comment added by 182.182.84.18 (talk) 15:41, 1 September 2011 (UTC)

Not the appropriate venue for asking, but try [4] -- MacAddct1984 ^{(talk • contribs)} 20:21, 1 September 2011 (UTC)

Co-occurring disorder(s)

Is it possible to have many different types of mental illnesses. And if it is possible, is it likely? If there is a Wikipedia article on what I'm asking, please point me in the right direction. Thanks. Lighthead ^þ 19:14, 1 September 2011 (UTC)

No a simple answer to this but generally having any one mental disorder doesn't bar an individual from having on other. However, a genetic disposition to having some disorders may protect someone from developing a disorder that is associated with some other set of genes. It also is unlikely to be the result of just one gene (for say schizophrenia) but a combination of several. Genes, it must be remembered, are normally protective, which is why they survive. Even the gene responsible for Huntington's disease is thought to have a protective effect against getting a particular physical condition (I forget which). Then there are disorders that are the result of bad experiences etc., and it possible to have several of those.--Aspro (talk) 19:58, 1 September 2011 (UTC)

But what makes me wonder is that the symptoms oftentimes overlap. It may sound funny, but it almost seems as if the whole field of psychology is a kind of pseudoscience. It seems to be a whole lot of guessing. Especially as relates to diagnosis. Lighthead ^þ 20:10, 1 September 2011 (UTC)

In most cases the DSM (the "bible" of diagnosis in the US) will describe a set of symptoms as a single condition of a mixed type, rather than as two superimposed conditions (for example, a schizoaffective disorder rather than a combination of schizophrenia and an affective disorder). But this is essentially arbitrary. Looie496 (talk) 21:26, 1 September 2011 (UTC)

I have both Asperger's and Tourette's syndromes. Plasmic Physics (talk) 00:20, 2 September 2011 (UTC)

That would have made for a FAR funnier Rain Man. I mean nothing personal by that, my intention is not to make light of your condition. Vespine (talk) 00:38, 2 September 2011 (UTC)

The entertainment industry has done a terrible job of stereotypeing Tourette's. Not everyone swears uncontrolably as in the Southpark episode. In fact, a large portion of us express non-verbal symptons. Plasmic Physics (talk) 01:01, 2 September 2011 (UTC)

That would be an example of coprolalia. ~AH1 ^(discuss!) 23:31, 2 September 2011 (UTC)

An individual may have many disorders simultaneously, as the disorders typically are not mutually exclusive, though this may increase comorbidity. However, the cause is rarely purely genetic, or even biological. ~AH1 ^(discuss!) 23:31, 2 September 2011 (UTC)

Thanks for all the information; I'll chew it all over. Lighthead ^þ 19:59, 5 September 2011 (UTC)

solar cells

Are their there solar cells which are more efficient in low light? --DeeperQA (talk) 22:47, 1 September 2011 (UTC)

Wait, solar cells posses other solar cells? Plasmic Physics (talk) 00:13, 2 September 2011 (UTC)

There is no correlation between luminous intensity and efficiency. A solar cell is as efficient in low light as it is in strong light. Assuming you are talking about an efficiency ratio. Plasmic Physics (talk) 00:53, 2 September 2011 (UTC)

Unfortunately, solar light includes infrared frequency and when concentrated increases the surface temperature of the surface it is absorbed by. I would imagine that at some point efficiency becomes less until the surface is so hot it melts at which point efficiency is zero. Some plants must have less light in order to do well and grow while other plants need more light. In either case the rate of growth is directly dependent on the amount of sunlight all other factors being the same. --DeeperQA (talk) 02:34, 2 September 2011 (UTC)

Plant life is not comparable in this context, it opperates and is affect in a completely different way. You could simply filter out infrared light, if your goal is maintain a low temperature. Plasmic Physics (talk) 03:33, 2 September 2011 (UTC)

But, of course, when visible light or UV is absorbed it also produces heat. StuRat (talk) 03:47, 2 September 2011 (UTC)

One method is to use mirrors to concentrate the low light onto the solar cells. Since mirrors are less expensive than solar cells, this can provide a cheaper alternative to covering the same area with solar cells. However, note that in full light, the excess heat might damage the solar cells. StuRat (talk) 03:54, 2 September 2011 (UTC)

I saw "floating" solar panels on tv a while ago. The water that the solar cells float on provides plenty of cooling allowing a configuration of mirrors to concentrate far more light onto them then they would normally tolerate. Vespine (talk) 04:58, 2 September 2011 (UTC)

See solar cell efficiency and fill factor. The materials of the photovoltaic cells may affect its absorptive capabilities, for example the usual silicon-based cells vs. organic ones. ~AH1 ^(discuss!) 23:27, 2 September 2011 (UTC)