Wikipedia:Reference desk/Archives/Science/2009 November 29

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 29

Solutes

When I dash salt into a bowl of water, it seems as though the salt falls and 'drags water with it down into the water' upon hitting the surface, but when I dash paprika, it seems as though the paprika falls and 'pulls the water' along its own surface, causing the paprika to rapidly spread along the surface. Does this happen because the salt is immediately ionized and falls into the water, while paprika doesn't ionize and isn't nearly as readily brought into solution, and perhaps because of surface tension, fails to be incorporated? DRosenbach ^{(Talk | Contribs)} 01:10, 29 November 2009 (UTC)

Paprika will not likely dissolve appreciably at all. Most of the compounds in paprika are hydrophobic and/or insoluble in water. If you shake the mixture, you can generate a Suspension, but that is not at all the same thing as a solution. As far as the visual effect of the mixing of the two, well, I can't make much comment on that as I really don't understand what you are getting at (the difference between "drag" and "pull".) But for sure, the way in which salt mixes with water (which is a true solution, see solvation for more details) and the way in which paprika mixes with water are very different. --Jayron32 02:03, 29 November 2009 (UTC)

Salt being dropped into water "falls into the water," while paprika dropped into water does not "fall in," but spreads out onto the surface. Try it in a white vessel and you'll see the effect. DRosenbach ^{(Talk | Contribs)} 02:28, 29 November 2009 (UTC)

What you're probably seeing is most likely a surface tension effect. Individual grains of salt are larger and more massive than individual specks of paprika powder; table salt is also a denser material than paprika. Consequently, each grain of salt exerts a substantially greater force per unit area on the water's surface and is more likely to fall through. The other factor is that I expect paprika (being dried plant matter) is probably appreciably more hydrophobic than salt; the salt is much more readily wetted by water. TenOfAllTrades(talk) 02:56, 29 November 2009 (UTC)

May be some component of the Paprika has a surfactant effect? That would explain the phenomenos described. Dauto (talk) 03:44, 29 November 2009 (UTC)

Most herbs and spices are used for their volatile oils, which explains the hydrophobia you're seeing. --Sean 15:19, 30 November 2009 (UTC)

Coffee problem

I was given the following problem: if you have a cup of coffee that's too warm to drink, and you want to cool it as quickly as possible, should you add cream immediately or after?

My first thought was that the cream should be added later, because the coffee will cool down faster when it is warmer (owing to the greater difference in temperature between the coffee and the air). But then I thought, the cream will do a better job of decreasing the temperature of the coffee if it is added immediately, because that is when the difference in temperature between the coffee and cream is greatest. So which is: immediately or later? —Preceding unsigned comment added by 24.200.1.37 (talk) 03:30, 29 November 2009 (UTC)

Haha, my first concern would be more of preventing precipitation due to solubility issues (and keeping everything supersaturated), but I think adding it first would be more rapid, if your target temperature is above ambient temperature. Of course, adding creamer later will help to achieve lower cooling temperatures, but I don't think that's your goal. (You could also perform an empirical experiment...) John Riemann Soong (talk) 03:45, 29 November 2009 (UTC)

This question is a classic. It's such a classic in fact, that I think it's a homework question. But you could always google for the answer, there are probably hundreds of sites that explain it, and would do a better job than a few paragraphs here. Ariel. (talk) 03:47, 29 November 2009 (UTC)

The question isn't a homework one, but yes I did try to google it. The problem is, everyone seems to ignore the fact that that the cream will be a more effective cooler if it is added immediately, thereby making the correct answer ambiguous.

Well, what do you mean by "cool down faster". Do you mean the total time between the starting temperature and the final temperature OR do you mean the instantaneous rate of change of the temperature at any given point along the way. Depending on which definition of "faster" you mean, will result in a different approach to finding the answer. --Jayron32 03:49, 29 November 2009 (UTC)

Total time.

I think adding it later works better exactly for the reasons you provided. Dauto (talk) 03:51, 29 November 2009 (UTC)

But the reasons I gave work against each other...

No, think about it in terms of energy. Mixing the cream and the coffee doesn't change the total heat energy in the cream and coffee system. The only way the heat of the system changes is by the coffee getting rid of it to the environment as it cools. Rckrone (talk) 07:37, 29 November 2009 (UTC)

Add the cream immediately to the hot coffee because that increases the volume of liquid in contact with the cup hence reducing the thermal resistance between liquid and atmosphere. But add that cream gently without stirring to avoid heating by Turbulence kinetic energy. OTOH if you have a very cold spoon you know where to stick it. Cuddlyable3 (talk) 11:28, 29 November 2009 (UTC)

The simplest way to find out is to try it out ourselves. All you need is a thermometer, a clock and some coffee. With two cups you don't even need to measure time. Too bad I don't have all of these right now, else I would do the experiment myself.--131.188.3.20 (talk) 14:32, 29 November 2009 (UTC)

The heat loss will be in proportion to the temperature difference between the coffee and its surroundings. If the 'cream' is at room temperature rather than chilled, then the temperature difference will be greater if you do not add it to the coffee. If the 'cream' (do Americans really use cream rather than milk - all that saturated fat and calories - somehow I'm not surprised) is chilled, then leave it in the fridge until the last moment. Case solved. 89.240.199.137 (talk) 15:23, 29 November 2009 (UTC)

This is indeed a classic. There are probably a dozen conflicting possibilities...these are the ones I immediately recall:

1. The rate at which energy is lost from the coffee is proportional to the difference in temperature with the environment. (See Newton's law of cooling) So hot coffee loses heat energy faster than cooler coffee. Adding the cream at the end should be the right thing to do if you want cooler coffee.
2. Cream lightens the color of the surface of the coffee - that changes it's thermal emissivity - so it radiates heat differently.
3. Adding cream increases the volume of the liquid - which increases the surface area - which improves heat loss.
4. When you add the cream, you induce turbulance in the coffee which allows the hotter coffee in the center of the volume to swirl out to the edges where it'll cool more effectively.
5. If you take the cream out of the fridge when you first make the coffee - it's warming up towards air temperature while you're thinking about adding it. That heat ends up in the coffee when you mix it. If you added the cream immediately, that extra heat would not be accumulated.
6. If you are using a cup with a narrow base and a wide rim - then as you add more cream, the exposed surface area of the coffee to the air increases. If you use a cylindrical mug - then that's not a factor. If you use one of those cups that has a narrower rim than base (I have one of those) - then the reverse is the case.

I'm sure there were others too. Short answer: It's crazy complicated - which is why people like to argue about it - it's like the ridiculous "Airplane on a treadmill" - except this one is actually hard to answer. I believe that for "normal" shapes of coffee cups and normal coffee/cream ratios and normal room temperatures - the nice Mr Newton was right and you should add the cream at the last moment if you want the coolest coffee possible in the time available. SteveBaker (talk) 16:41, 29 November 2009 (UTC)

That's right, and stir the coffee vigorously (and blow on it at the same time) whilst you are waiting to add the cream. Dbfirs 17:50, 29 November 2009 (UTC)

I don't understand why there is any question. Cool it down means to reach a certain lower temperature point. Why would you delay adding the cooler liquid? You are trying to reach a target temperature in the shortest possible time. And no other factors are supplied in the question as posed. Given the wide range of possible factors that are not specified, it is possible that that target temperature could be reached almost instantaneously. Bus stop (talk) 17:58, 29 November 2009 (UTC)

If that was the case we would be solving a stupid problem. I would rather solve a more interesting problem and assume that you cannot reach the target temperature simply by pouring the cream and therefore waiting to the last minute is the right answer. Dauto (talk) 18:30, 29 November 2009 (UTC)

I experience this problem every single day and my solution is this: add more milk than usual. Take it right to the temperature you want it at, right away. If we are taking a scientific view then Steve Baker's first point is the most pertinent. Vranak (talk) 18:33, 29 November 2009 (UTC)

Obviously if you have enough (and can tolerate enough) cream to drop the temperature to the desired amount immediately - then you should - but that's just a rather uninteresting special case of a more general problem. If Newton's law of cooling is the only issue then the best algorithm is:

• Calculate the coffee temperature at which adding the maximum allowed amount of cream will bring the temperature to the ideal value more or less instantly. Call this 't_addcream'.
• Assume that the ambient air temperature is 't_ambient'.
• Grab the hot (black) coffee: call it's temperature 't_coffee'.
• While the t_coffee is greater than t_addcream - wait.
• Add the cream.

The case that Bus stop and Vernak describe are just trivial subsets of this more general solution.

There are all sorts of corner cases where more extreme initial conditions would favor adding the cream at the outset and then waiting - but Bus stop is basically incorrect in 'typical' cases where t_coffee is greater than t_addcream - because Newton's law of cooling says that the coffee will lose heat energy much faster if t_coffee is a lot bigger than t_ambient than if it's closer to t_ambient. Cooling the coffee down by adding the cream before t_addcream will cause the coffee to remain higher than t_target for much longer than if you waited for the black coffee to cool to t_addcream naturally. SteveBaker (talk) 19:12, 29 November 2009 (UTC)

This sounds like it would be a good problem for Mythbusters. Of course it lacks the excitement of blowing something up or inflicting pain. I suppose the pain could come from one of the cast having to drink the hot or not so hot coffee. As long as the volumes and temperatures of coffee (as poured and at the highest allowed drinking temperature) and cream are unspecified, the problem may have multiple solutions. The standard answer [1] is that adding the cream immediately leads to the coffee being warmer, say 15 minutes later, because of Newton's cooling law leading to greater heat loss during the long period of high delta temp if the coffee goes uncreamed until it is to be consumed. Conversely, coffee goes from brewing temp to a safe drinking temp quicker if you wait to add the cream [2] If I recall correctly, some science popularizer like [Isaac Asimov]] or Mr. Wizard said this many years ago (no citation readily available). Edison (talk) 22:15, 29 November 2009 (UTC)

Some original research with hot chocolate - mmmm! Can't tell the differenc6, gonna have to try again :) hydnjo (talk) 01:30, 30 November 2009 (UTC)

Guys! We've had this question before - so often that I wrote the official Wikipedia Reference Desk Coffee And Milk Simulator some time back (in response to our December 29, 2008 query). Our best responses can be found by searching the archives. The decisive conclusion is that adding milk later always causes the coffee to end colder, but it takes a lot of work (or a lot of milk) to have a very significant effect. Nimur (talk) 03:17, 30 November 2009 (UTC)

That is a wonderous thing of great beauty Nimur!

But it misses a bunch of second order effects that can dramatically overturn the decision in some cases. As the graph shows, the amount of gain you get by dumping the cream in late isn't all that great and it could be overwhelmed by effects such as the increase in the volume of the liquid.

I'm playing Devil's advocate here - because I believe that your simulation is 'good enough' in common cases. But suppose the "cup" is a tall, thin cylinder such that the area of the base of the cup and the liquid exposed to the air at the top is negligable compared to the area of the sides of the cup. If you increase the volume if liquid by 10% by adding the cream - then you also increase the surface area by close to 10%. Newton's law of cooling says that the rate of heat loss is proportional to the temperature difference multiplied by the surface area - so if adding the cream drops the temperature difference by less than it increases the surface area - then adding the cream early results in cooler coffee than adding it later.

This is complicated though - if the cup itself is made of a material like steel that's a good conductor of heat then the "surface area" exposed to the ambient air is the area of steel in contact with the air - plus the surface area of the coffee. In this situation, then as the surface area of the liquid increases the area of hot steel that's exposed to the cooler air decreases and we're back with adding the cream as late as possible - but for a new and interesting reason. But if the material that the cup is made of is a good insulator then the reverse might be the case. For more conical coffee cups - the amount of surface area increase gained when you add the cream is disproportionately in the region where the liquid meets the ambient air rather than the porcelain of the cup - which alters the rate of heat flow across the interface. Just this one complicating factor (and there are MANY more) means that there isn't a clean answer in every possible case.

Bottom line is that the simulation is missing some important details that can definitely change the outcome.

As a long-time veteran of this particular debate - I can tell you that the large number of sophisticated arguments makes any kind of simplistic answer invalid for all but the simplest of cases - and that's why this debate dragged on for so long back in the early days of the Internet.

Think about this one, for example: If you add cream slowly (like if you're making Irish coffee) and it floats on top of the coffee instead of mixing properly - then it forms an insulating layer (and as a highly fatty liquid, it's a better insulator than black coffee) - that reduces the amount of heat lost to the air from the hot coffee beneath.

It's really complicated.

SteveBaker (talk) 04:46, 30 November 2009 (UTC)

That's freakin' awesome. :) --Sean 14:49, 30 November 2009 (UTC)

I totally agree with Steve's nitpicks - I assume many things; most notably, uniform mixing, which is probably the worst assumption. Steve brings up weird-shaped vessels, which could also throw things out of whack. Fortunately the simulation is open-source:

Simulation Code, in GNU Octave

clear;close all;
room_ambient_temp = 25;

tau_nlc = 60;   % Time constant (Seconds) for the cooling
r_nlc = 1/tau_nlc; % constant for Newton's Law of Cooling in the form dT/dt = -r(T-Tamb)

% Initial coffee and milk parameters
coffee_volume = 300;   % mL
coffee_temp0  = 100;   % degrees C
milk_volume   = 30;    % mL
milk_temp0    = 5;     % degrees C

% Initialize the coffee and milk parameters
coffee1_temp(1) = (coffee_temp0*coffee_volume + milk_temp0*milk_volume)/(coffee_volume+milk_volume)
coffee2_temp(1) =  coffee_temp0;

%%Loop over time, measured after 2:00 PM, in seconds
for t = [1:60*30]
    coffee1_temp(t+1) = coffee1_temp(t) - r_nlc*(coffee1_temp(t)-room_ambient_temp);
    coffee2_temp(t+1) = coffee2_temp(t) - r_nlc*(coffee2_temp(t)-room_ambient_temp);
    

    % At time 2:10, add milk to Coffee #2
    if (t == 60*10)
        coffee2_temp(t+1) = (coffee2_temp(t)*coffee_volume + milk_temp0*milk_volume)/(coffee_volume+milk_volume)
    end
    
end


%% Plotting, including time-stamped x-axis
time_labels = datenum(2008, 12, 29, 14, 0, 0) + 1/(24*60*60)*[0:60*30];
plot(time_labels,coffee1_temp, 'r'); hold on;
plot(time_labels,coffee2_temp, 'b');
datetick('x', 16);
xlim([datenum(2008, 12, 29, 14, 0, 0), datenum(2008, 12, 29, 14, 20, 0)]);
legend('Coffee 1 - Milk Added at 2:00', 'Coffee 2 - Milk Added at 2:10');
xlabel('Time');
ylabel('Temperature (Celsius)');
title(['Hot Coffee Simulation with \tau = ' , num2str(tau_nlc) , ' sec']);

So fellow milk/coffee enthusiasts can feel free to write plugins for various additional parameters and I'll throw those into my web interface. Nimur (talk) 15:03, 30 November 2009 (UTC)

I was (gnomically) waiting for those already engaged in this conversation to say so, but WOW! Nimur, posting open-source code for GNU Octave so that anyone can run and tweak this model is just so cool. Wikipedia at its finest! -- Scray (talk) 04:30, 1 December 2009 (UTC)

Cope elimination

Can you do it with a six-membered transition state? (I'm guessing not, because of the electron-pushing?) John Riemann Soong (talk) 03:48, 29 November 2009 (UTC)

Molecular structure

Does anyone know what the wiggly line means in the molecular structure diagram in the top right-hand corner of Amphetamine? —Preceding unsigned comment added by 86.138.105.112 (talk) 04:00, 29 November 2009 (UTC)

It means that both enantiomers prolly have similar properties on the body -- e.g. chirality doesn't matter. John Riemann Soong (talk) 04:13, 29 November 2009 (UTC)

• Thanks, do you mean that there are "left-handed" and "right-handed" versions of the molecule, but the structure diagram is not distinguishing between them (it could represent either)? 86.138.105.112 (talk) 04:29, 29 November 2009 (UTC)
  • That's exactly right. There are two non-superimposible mirror image versions (i.e. "left" and "right" handed), the wavy line indicates that the actual version doesn't matter to the discussion at hand, or that there is a racemic mixture of the two versions under discussion. --Jayron32 04:38, 29 November 2009 (UTC)
    • Got it, thanks! 86.138.105.112 (talk) 04:46, 29 November 2009 (UTC)

Earth's season

Hi! my question is how the season change occur in earth? and a season is same all around the world? i.e same season occur in all countries? —Preceding unsigned comment added by Nirmal kumaran (talk • contribs) 07:36, 29 November 2009 (UTC)

No, at any given time, the entire world does not experience the same season. What the current season is depends on where you are. See Season. Red Act (talk) 08:12, 29 November 2009 (UTC)

Seasons are reversed in the Northern hemisphere vs the Southern hemisphere (winter in one is summer in the other, spring is autumn, and vice versa). The nearer to one or other pole you are, the more extreme the seasons are. There basically aren't any seasons in the tropics (although you do get wet season and dry season in some places). The seasons are caused by the axial tilt of the Earth, which means sunlight hits a particular place on the Earth at different angles at different times of year (or, put another way, the sun gets higher in the sky during summer than winter). Sunlight shining directly on the ground heats it up more than sunlight hitting the ground at a glancing angle. --Tango (talk) 11:41, 29 November 2009 (UTC)

And in addition, when the sun is higher in the sky, you also get more hours of daylight, so the sun has more time to heat things up. --Anonymous, 07:53 UTC, November 30, 2009.

The greatest effect by far is the angle at which the sunlight hits the ground, as Tango said. --121.127.200.51 (talk) 09:07, 30 November 2009 (UTC)

Wrong -- that's true if you're relatively near the equator, but the length of the day becomes a more important factor as you get nearer to the poles. Especially once you pass the Arctic or Antarctic Circle and you start getting continuous daylight in one part of the year and continuous night in another part! --Anonymous, 21:40 UTC, November 30, 2009.

However, the usual effects of seasons are sometimes altered by oscillations such as ENSO. ~AH1^(TCU) 01:47, 2 December 2009 (UTC)

Evaporating water

When evaporating water , are you creating new oxygen?

Evaporating water doesn't create oxygen or anything else. The water molecules (H₂O) stay exactly the same. 86.134.90.230 (talk) 12:12, 29 November 2009 (UTC).

Agreed. Evaporated water becomes water vapor, not free oxygen. StuRat (talk) 13:18, 29 November 2009 (UTC)

For more details see liquid and gas. In water, the H₂O molecules are all stuck to each other, when it evaporates all that happens is the H₂O molecules seperate from each other, but they remain intact H₂O molecules. There are means of seperating the H's from the O's to give you H₂ gas and O₂ gas, but this usually involves much more energy than is typical of evaporation. --Jayron32 20:34, 29 November 2009 (UTC)

However, water has strange properties. It does not have a set condensation nor an evaporation point, because there is supercooled water and mist can from from a puddle under sunlight below freezing, or from one's breath (which is condensation that can occur either above or below freezing). The presence of air also seems to have an effect on this. ~AH1^(TCU) 01:46, 2 December 2009 (UTC)

How do I prevent wrinkles around my eyes

I'm 27 and just starting to see wrinkles. Oh no! How do I prevent wrinkles as I get into my thirties? —Preceding unsigned comment added by 92.224.206.187 (talk) 12:25, 29 November 2009 (UTC)

There must be hundreds of different anti-wrinkle products - lotions, eyepads, Botox, etc.. We can't really recommend one. The problem with judging these products (except Botox, I suppose, but that is only a temporary solution and has plenty of side effects) is that it is several years, at least, before you can really assess their effectiveness, so you aren't likely to get useful advice by just asking your friends what they would recommend. I've had a quick look for academic papers doing proper comparisons of treatments, but I haven't found anything useful... --Tango (talk) 13:03, 29 November 2009 (UTC)

Wouldn't drinking adequate amounts of water, getting adequate sleep, and not smoking, all be a good idea if wrinkles around the eyes are trying to be avoided? Bus stop (talk) 13:08, 29 November 2009 (UTC)

Also avoid sunlight and/or wear hats and sunscreen to prevent damage from UV light. StuRat (talk) 13:12, 29 November 2009 (UTC)

I got my first wrinkle round my eyes aged 48. I attribute this to: 1. Good bone structure on my face. 2. Not having children. 3. Never smoking. 4. I only wash my face once a day. 5. I try and sleep 8 hours a night. 6. I've used moisturising cream daily since I was aged 14. --TammyMoet (talk) 13:21, 29 November 2009 (UTC)

And 7. You got lucky. One datapoint really isn't useful. --Tango (talk) 13:23, 29 November 2009 (UTC)

Thanks Tammy. That washing once per day: is it with ice cold, cold, lukewarm, warm, hot, or steaming hot water? How long do you shower? 92.230.65.123 (talk) 14:41, 29 November 2009 (UTC)

I wash with hot water, and I have a bath once a day. And yes I agree: I got lucky. --TammyMoet (talk) 16:17, 29 November 2009 (UTC) And I forgot something quite important: I'm about 4 stone overweight. Thin people don't have the layer of fat which makes their face fill out, and are more prone to wrinkles. --TammyMoet (talk) 16:18, 29 November 2009 (UTC)

Avoid squinting, smiling, frowning, scowling or laughing. And don't smoke.[3] Fences&Windows 13:38, 29 November 2009 (UTC)

One more piece of advice. Stop worrying about wrinkles. Worrying gives you wrinkles... Dauto (talk) 14:59, 29 November 2009 (UTC)

Have a healthy balanced diet. Take exercise. Stay slim. Don't smoke, avoid alcohol. My pet theory is that drinkers (and smokers) look older than their years. 89.240.199.137 (talk) 15:27, 29 November 2009 (UTC)

You will get more and more wrinkles around your eyes. Laugh and smile as much as you can. Nothing is more attractive than smile wrinkles. DVdm (talk) 17:20, 29 November 2009 (UTC)

Get new parents. A large proportion of your wrinkles are a product of genes; some is likely environement, but it may be difficult to seperate the wrinkles you have just because of your genetic make up versus the wrinkles you have because you abused your skin. --Jayron32 20:37, 29 November 2009 (UTC)

Forgot to add - stay out of the sun. If you live in a sunny area, the wrinkles may be sun-damage, and you can look forward to other skin problems from sun-damage in the future. 78.147.183.186 (talk) 22:34, 29 November 2009 (UTC)

Screw it! Just keep trying to look like Clint ;) hydnjo (talk) 01:21, 30 November 2009 (UTC)

What happens after a Pulmonary embolism?

Our article doesn't explain what happens to the blood from the lungs, assuming the patient survives and recovers without need for surgery. Where does the blood go? --Dweller (talk) 17:03, 29 November 2009 (UTC)

I'm not sure what blood you're referring to, but if you mean the initial blood clot (assuming it's a thrombotic P.E.), it is either broken down by fibrinolysis, or the thrombus is organized and recanalized so that a new channel forms through the clot. See this section of our thrombus article (only #3, #4, and maybe #2 apply if the patient "survives and recovers" as you say). Blood flow is restored most rapidly in the first day or two, then improvement gradually slows [4]. It's often impaired permanently, but may be recovered to some degree. - Draeco (talk) 18:06, 29 November 2009 (UTC)

Perhaps you were referring to "blood in the cavity surrounding the lungs" instead of "blood in the lungs." DRosenbach ^{(Talk | Contribs)} 23:16, 29 November 2009 (UTC)

Note that the cavity around both lungs would be pleural. :-) StuRat (talk) 03:34, 30 November 2009 (UTC)

I'm going to use that one! DRosenbach ^{(Talk | Contribs)} 13:03, 1 December 2009 (UTC)

Excellent point (and pun); it's also interesting to note singular pleural human cases PMID 16714521, PMID 14602881. The cases described there highlight what I think is a great "did you know" fact - bison have a communication between the right and left pleural cavities that may help explain the ease with which Native Americans hunted them, and their near-extinction by white hunters - any injury causing pneumothorax (such as an arrow or bullet into the lung) would be rapidly fatal. I see plenty of human medical sources for this information, and lots of Google hits, but I don't have a veterinary reference at hand that I would consider definitive. -- Scray (talk) 14:39, 1 December 2009 (UTC)

Ah. I thought blood actually entered the lungs (coughing blood is cited as a symptom). I just wondered how it would drain from there, given that blood isn't supposed to go there! If blood doesn't enter the lung, how does the PE cause people to cough blood? --Dweller (talk) 10:30, 30 November 2009 (UTC)

Hemoptysis may result from pulmonary infarction, i.e. death of lung tissue due to inadequate perfusion. The lung has a dual blood supply from pulmonary and bronchial arterioles, and there are anastomoses between these circulations. With small PEs (in the pulmonary artery), the bronchial circulation provides adequate perfusion to sustain the lung tissue; however, in certain vulnerable distributions, or with a large enough PE, the bronchial circulation can be overwhelmed (or even stagnate due to the anastomoses) leading to infarction. When that happens, lung tissue (including vascular walls) dies, and blood does leak into the airways (alveoli, then bronchi, etc) resulting in hemoptysis. The dead tissue eventually gets remodeled through processes like organization by agents that include alveolar macrophages. The center of that dead area generally remains a scar (or, less commonly, a cavity), whereas the peripheral portions may recover some function. The blood itself can be removed completely by the mucociliary escalator then through the digestive tract or simply by coughing, though some will have to be cleared locally, e.g. by macrophages that may process the iron for re-use, though some will remain for a time as characteristic hemosiderin-laden macrophages. BTW, I'm reminded of my comment in this thread, in which I suggested that the connection between the airway and the esophagus might not be totally detrimental. -- Scray (talk) 12:33, 30 November 2009 (UTC)

Thanks Scray. I understood some of that. You're saying (I think) that there are mechanisms (including, but not limited to coughing) that will get rid of blood from the lungs, it won't just sit there. --Dweller (talk) 13:50, 30 November 2009 (UTC)

In any case, it won't remain as blood - some will be coughed up or cleared by the "escalator" to which I referred, but the blood that remains will be broken down with components cleared in various ways. The plasma (serum, really, since the fibrinogen and clotting factors will be consumed in a fibrin-based clot) will be cleared by lymphatics, the platelets will become part of the local clot, the white cells will most likely die there, and along with the red blood cells will be trapped in the clot. Organization of that clot will result in entry and activation of phagocytic cells, primarily macrophages, that will ingest the debris. Most components of blood cells (proteins, lipids, sugars, nucleic acids) are readily broken down; however, the Heme is difficult for the body to metabolize, and the iron therein requires special handling. Phagocytosis of red blood cells by macrophages often results in accumulation of hemosiderin that may remain for a long time in the tissue (described in that article) and draining lymph nodes, but iron can be recycled through pathways involving ferritin and transferrin. If some of this jargon is not clarified by the linked articles, please ask. -- Scray (talk) 15:52, 30 November 2009 (UTC)

Citing this CDC webpage

Hi, how would I cite this webpage (I use ref-works)? [5]

Many thanks 188.220.144.215 (talk) 22:23, 29 November 2009 (UTC)

Do you mean for use on Wikipedia? If so, you can use the {{Cite web}} template which will correctly format it for you. Otherwise, it depends which of the many citation styles you are required to use in your document. SpinningSpark 00:24, 30 November 2009 (UTC)

Since you say you use RefWorks, it sounds like you're not looking for a Wikipedia template. Ref-works does not represent a citation format, in fact it supports many of them. I think what you want is a breakdown of MMWR into conventional fields. I Google'd "how to cite mmwr" and got a variety of useful resources, including this one which gives the APA format for a MMWR citation. MMWR is a little odd among journals (which are what RefWorks is used for most), but I would map it this way:

• Authors: Centers for Disease Control and Prevention
• Title: Update: Measles --- United States, January--July 2008
• Journal: Morbidity and Mortality Weekly Report
• Date of publication: 22 Aug 2008
• Volume: 57
• Issue: 33
• Pages: 893 - 896

Hope this helps. -- Scray (talk) 00:45, 30 November 2009 (UTC)

hydride donation to amides

When a hydride attacks an amide, does it attack the carbonyl carbon or the amide nitrogen? The nitrogen would be more positive, wouldn't it? John Riemann Soong (talk) 22:27, 29 November 2009 (UTC)

Recognising, just with a glance, that a squeleton is the one of an americain

Hello. I'm French. Recently, watching an episode of the serial "Bones", we saw something difficult to explain. I asked the question on the French Reference desk (called l'Oracle) and got good informations but no good answers. That's why I try the same thing here.

The situation took place in Norway. A squeleton is discovered, after some seconds of observation, the specialist says that it's the squeleton of an American. We think it's mean white, caucasien from the USA.

The squeleton is sent to the USA where the Dr Brennan, at the same speed, gets to the same conclusion.

We must give more informations. The squeleton is not old enought to be from World War 1 or 2.

Considering that all the ancestors of the white americans came from Europe, how a single glance to a squeleton can lead to such a conclusive conclusion ?-Reims (Champagne area)-France---Joël DESHAIES (talk) 22:47, 29 November 2009 (UTC)

This is not necessarily possible in reality. Oftentimes, in television series (such as Bones) facts are embellished or "bent" (I believe in French, this would be "ont dénaturé") to further the plot line. Intelligentsium 23:49, 29 November 2009 (UTC)

Perhaps from a dental filling? A lot of different kinds of dental restorative materials have been used, so perhaps the skeleton had a dental filling made of a material that was only used in the US at the time of the filling? Or depending on the skeleton's age, perhaps from a relative lack of cavities? Water fluoridation was first used in the US. Colorado brown stain on the teeth would be an indication, too. Or perhaps the skeleton had an intramedullary rod, or surgical screw or plate or wire of a type that was only used in the US at the time of a bone fracture? It does seem like a well-written script would explain anything along those lines, though, if it's used as an important plot device. Or maybe the script did give a plausible explanation, but that part got edited out due to the episode running over time. Red Act (talk) 01:08, 30 November 2009 (UTC)

I googled and found that this episode is called "Mayhem on a Cross". Several links around the web indicate that the identification as American was due to the visible orthodonture. Perhaps if you watched this episode dubbed it was lost in translation? P.S. it's spelled "skeleton" in English. --Sean 15:05, 30 November 2009 (UTC)

The speed of the reaction Ca(OH)2+CO2

What is the approximate speed of the reaction between calcium hydroxide in suspension and carbon dioxide in air at standart conditions? Renaldas Kanarskas (talk) 22:48, 29 November 2009 (UTC)

How much of each? Without a quantity, the only answer I can provide is: slowly. Intelligentsium 23:53, 29 November 2009 (UTC)

Imagine 1 gr of Ca(OH)2 mixed with 1 gr of water. This suspension is lying on the glass in our room, concentration of CO2 in air is 0,04%. As water evaporates, new quantities are being added immediatly. Renaldas Kanarskas (talk) 00:21, 30 November 2009 (UTC)

I don't actually know the answer, but you may be rate limited by how fast CO₂ dissolved in the water. So a thin layer with high surface area will react quicker than a lump. You could reduce this variation by saying dry Ca(OH)₂. Graeme Bartlett (talk) 20:57, 2 December 2009 (UTC)