The point is not for you, the student, to have an idea of what your fellow classmates think. Rather, the point is for me, the professor, to have an idea of how well the students have understood what I am presenting.
The "show of hands" approach doesn't work; the students quickly figure out who the smart kids in the class are, and wait to copy thier answers. Writing things down on paper doesn't work either, because it takes too long.
Also, if you can easily understand everything your professor is telling you, you aren't the student she needs to worry about. You would probably be able to learn the subject matter on your own, with or without a professor. Most of the time, the ones who really need the extra explanation are either very well aware of the fact (in which case, they are unlikely to ask questions during lecture for fear of looking stupid), or are so totally out to sea that they don't even realize they don't understand what is going on. In the former case, the clicker gives the students a chance to let the professor know, in a nonthreatening way, that they don't understand what is going on. In the latter case, the students can see (whithout a strong negative impact on their grade) that they don't understand what's going on.
There have also been a lot of comments about how hackable these systems are. If you know enough to be able to hack one of these, more power to you. Again, you're not the student I'm trying to reach. You will do fine in my class, with or without my help.
To those of you who have only negative things to say about these systems, what would make them better? The idea of immediate, automated assessment is really attractive to me as an educator.
You should have bought the CLP-550. I avoided the CLP-500 for just this reason (and the fact that I heard bad things about its OS X support, as well). The CLP-550 supports Postscript, and works fine from my Mac, my Linux box, and my Windows box.
Another advantage to the CLP-550 over the 500 is that the 550 comes with full toner cartridges; the cartridges which ship with the 500 are only half full.
I don't understand how companies can sell printers that don't support Postscript. On the other hand, this seems to be a case where a company heard complaints from its customers, and corrected thier bad practices (the toner issue, and Postscript support).
Just out of interest, how many games have you heard about where you have to stop domestic terrorists?
One springs to mind immediately. Deus Ex. At least, you start out fighting domestic terrorism. You end up fighting an international conspiracy which has taken control of several governments. The really great thing about it, IMO, is that the moral decisions you make are rarely black and white.
Two others:
Why we Sleep, by James Horne, and Why we Nap
(edited) by Claudio Stampi. The first is a good overview of sleep research in general, and specifically addresses some of the claims that are made about the purposes of sleep. Horne looks at several arguments (he agrees with some, and disagrees with others) but more importantly gives pointers to the research which supports or refutes each claim.
The second is a book dealing with polyphasic sleep and chronobiology. Some of the findings presented there seem to have been missed by much of the sleep research community.
Both books are fairly technical, but this is news for nerds, right?
On a related note, sleep research is an area in which there are a lot of (widely) divergent views, all with some amount of data to back them up. Anyone who doesn't acknowledge this fact is not giving you the whole story. As a couple of examples, a number of hormones are released in different amounts thoughout the day (and night). In some cases, this is linked to sleep, but in others, the rhythm is linked to other zeitgebers without being directly related to sleep. Since most people sleep at night and are awake during the day, researchers have to be very careful to separate the two.
Also, experimental methods can be very important. Some of the methods used to limit sleep (or one particular phase of sleep) have caused other trauma which may have been responsible for some of the results. And finally, much research has been done on rats or other small mammals, and then extrapolated to humans. The problem is that humans (unlike rats) have a big enough brain to relax without sleeping. Since the only way for a rat to relax is for it to sleep, there are a number of effects which are tied to being relaxed which some researchers have instead tied to being asleep. Horne's book covers all of these points in detail (as well as several others).
There's an amusing story about Feynman and an abacus salesman in Brazil (found in Surely you're Joking, Mr. Feynman). Feynman was eating in a cafe where he often went, and an abacus salesman came in, trying to sell to the staff. He challenged them to some math problems, and (apparently by chance) they suggested he compete with Feynman instead. They started with an addition problem, and the abacus guy won by quite a bit. They moved on to multiplication, and the abacus won again, but not by very much. Sensing a challenge, the abacus salesman suggests they do cube roots. Quoting now:
"Cube roots! He wants to do cube roots by arithmetic! It's hard to find a more difficult fundamental problem in arithmetic. It must have been his topnotch exercize in abacus-land.
"He writes a number on some paper--any old number--and I still remember it: 1729.03. He starts working on it, mumbling and grumbling: "Mmmmmmmmagmmmmbrrr"--he's working like a demon! He's poring away, doing this cube root.
Meanwhile I'm just sitting there.
One of the waiters says, "What are you doing?"
I point to my head. "Thinking!" I say. I write down 12 on the paper. After a little while I've got 12.002.
The man with the abacus wipes the sweat off his forehead: "Twelve!" he says.
"Oh, no!" I say. "More digits! More digits!" I know that in taking a cube root by arithmetic, each new digit is even more work than before. It's a hard job."
Feynman goes on to explain the approximate method he used to get the result, and then gives his analysis:
"I realized something: he doesn't know numbers. With the abacus, you don't have to memorize a lot of arithmetic combinations; all you have to do is learn how to push the little beads up and down. You don't have to memorize 9 + 7 = 16; you just know that when you add 9 you push a ten's bead up and pull a one's bead down. So we're slower at basic arithmetic, but we know numbers.
Furthermore, the whole idea of an approximate method was beyond him, even though a cube root often cannot be computed exactly by any method. So I never could teach him how I did cube roots or explain ho lucky I was that he happened to choose 1729.03."
The rest of that chapter (entitled "Lucky Numbers") talks about his experiences in trying to improve his mental math skills. Definitely worth a read.
Seymour Papert, who holds the Lego chair for learning research at MIT (and who created Logo) wrote a book called the Connected Family which addresses this issue. The book is available at amazon,
and there's a companion website.
In a nutshell, he recommends using meaningful projects to teach programming concepts in an environment like that provided by Logo.
Yes, it is worth thinking about the environmental impact. But, when doing so, it's important to know what we're talking about. As you said, the ocean plays a very important role in the climate system. About half of the heat transport between the equator and the poles takes place in the ocean.
You seem a little confused about two points, however. First, there are two sources of forcing for ocean currents; density (heat and salt) and the wind. The two are related but distinct. The wind driven circulation is affected by the density profile, but not really driven by it. The Gulf Stream (as well as most other surface currents) are driven by wind, rather than density. People are still trying to work out some of the details, but this has been pretty well understood since the late 1940s. So, unless the annual mean winds were to drastically change, the Gulf Stream isn't going to "shut down". Since the prevailing winds are a function of the differential heating of the earth, and it's rotation, this isn't too likely.
Now, having said that, there is some concern that a significant disruption in annual mean temperature (such as would be necessary to melt the polar ice caps) could shut down the thermohaline circulation, so that is something we should at least consider. The climate system is really complicated, though, and contains a lot of nonlinear feedback mechanisms, and it isn't clear exactly what would happen if we had such a disruption.
In any event, the amount of energy one could extract from the ocean in this way isn't going to affect the density profile very much; you can't get away from either conservation of energy or the second law of thermodynamics. So yes, we should think about the environmental effects of our actions, but we should do so carefully and sensibly. This is going to have a much smaller effect on the environment than a coal burning plant producing the same amount of power (and no fresh water).
So, if there is a reverse gradient, then doesn't that also mean that there is going to be extrordinary convection currents as the heated (and less dense) material rises to the surface. While there logically would also have to be a down current, the mediums would have to be really turbulent.
Actually, it's a little more complicated than that. The density of a fluid parcel (such as in the atmosphere) depends on several factors, including temperature, pressure, and composition (for example, water vapor content in Earth's atmosphere, or salinity in the ocean). The distribution of all of these properties affect the stability of an atmosphere. So, it is possible to have a stable atmosphere that is heated at the bottom, as long as the lapse rate (the change of temperature with height) isn't too large.
The question `how large is too large?' depends on the details of the atmosphere in question.
This website has some numbers for various atmospheres in our solar system. With a measured lapse rate of about 7.7 K/km, there probably isn't a lot of spontaneous convection
due to purely thermal forcing going on on Venus.
Of course, turbulence can be forced in a wide variety of ways, so the absence of strong convection doesn't mean there isn't turbulence on Venus.
Slashdot Mirror
The "show of hands" approach doesn't work; the students quickly figure out who the smart kids in the class are, and wait to copy thier answers. Writing things down on paper doesn't work either, because it takes too long.
Also, if you can easily understand everything your professor is telling you, you aren't the student she needs to worry about. You would probably be able to learn the subject matter on your own, with or without a professor. Most of the time, the ones who really need the extra explanation are either very well aware of the fact (in which case, they are unlikely to ask questions during lecture for fear of looking stupid), or are so totally out to sea that they don't even realize they don't understand what is going on. In the former case, the clicker gives the students a chance to let the professor know, in a nonthreatening way, that they don't understand what is going on. In the latter case, the students can see (whithout a strong negative impact on their grade) that they don't understand what's going on.
There have also been a lot of comments about how hackable these systems are. If you know enough to be able to hack one of these, more power to you. Again, you're not the student I'm trying to reach. You will do fine in my class, with or without my help.
To those of you who have only negative things to say about these systems, what would make them better? The idea of immediate, automated assessment is really attractive to me as an educator.
I don't understand how companies can sell printers that don't support Postscript. On the other hand, this seems to be a case where a company heard complaints from its customers, and corrected thier bad practices (the toner issue, and Postscript support).
One springs to mind immediately. Deus Ex. At least, you start out fighting domestic terrorism. You end up fighting an international conspiracy which has taken control of several governments. The really great thing about it, IMO, is that the moral decisions you make are rarely black and white.
The second is a book dealing with polyphasic sleep and chronobiology. Some of the findings presented there seem to have been missed by much of the sleep research community.
Both books are fairly technical, but this is news for nerds, right?
On a related note, sleep research is an area in which there are a lot of (widely) divergent views, all with some amount of data to back them up. Anyone who doesn't acknowledge this fact is not giving you the whole story. As a couple of examples, a number of hormones are released in different amounts thoughout the day (and night). In some cases, this is linked to sleep, but in others, the rhythm is linked to other zeitgebers without being directly related to sleep. Since most people sleep at night and are awake during the day, researchers have to be very careful to separate the two.
Also, experimental methods can be very important. Some of the methods used to limit sleep (or one particular phase of sleep) have caused other trauma which may have been responsible for some of the results. And finally, much research has been done on rats or other small mammals, and then extrapolated to humans. The problem is that humans (unlike rats) have a big enough brain to relax without sleeping. Since the only way for a rat to relax is for it to sleep, there are a number of effects which are tied to being relaxed which some researchers have instead tied to being asleep. Horne's book covers all of these points in detail (as well as several others).
"Cube roots! He wants to do cube roots by arithmetic! It's hard to find a more difficult fundamental problem in arithmetic. It must have been his topnotch exercize in abacus-land.
"He writes a number on some paper--any old number--and I still remember it: 1729.03. He starts working on it, mumbling and grumbling: "Mmmmmmmmagmmmmbrrr"--he's working like a demon! He's poring away, doing this cube root.
Meanwhile I'm just sitting there.
One of the waiters says, "What are you doing?"
I point to my head. "Thinking!" I say. I write down 12 on the paper. After a little while I've got 12.002.
The man with the abacus wipes the sweat off his forehead: "Twelve!" he says.
"Oh, no!" I say. "More digits! More digits!" I know that in taking a cube root by arithmetic, each new digit is even more work than before. It's a hard job."
Feynman goes on to explain the approximate method he used to get the result, and then gives his analysis:
"I realized something: he doesn't know numbers. With the abacus, you don't have to memorize a lot of arithmetic combinations; all you have to do is learn how to push the little beads up and down. You don't have to memorize 9 + 7 = 16; you just know that when you add 9 you push a ten's bead up and pull a one's bead down. So we're slower at basic arithmetic, but we know numbers.
Furthermore, the whole idea of an approximate method was beyond him, even though a cube root often cannot be computed exactly by any method. So I never could teach him how I did cube roots or explain ho lucky I was that he happened to choose 1729.03."
The rest of that chapter (entitled "Lucky Numbers") talks about his experiences in trying to improve his mental math skills. Definitely worth a read.
Seymour Papert, who holds the Lego chair for learning research at MIT (and who created Logo) wrote a book called the Connected Family which addresses this issue. The book is available at amazon, and there's a companion website. In a nutshell, he recommends using meaningful projects to teach programming concepts in an environment like that provided by Logo.
You seem a little confused about two points, however. First, there are two sources of forcing for ocean currents; density (heat and salt) and the wind. The two are related but distinct. The wind driven circulation is affected by the density profile, but not really driven by it. The Gulf Stream (as well as most other surface currents) are driven by wind, rather than density. People are still trying to work out some of the details, but this has been pretty well understood since the late 1940s. So, unless the annual mean winds were to drastically change, the Gulf Stream isn't going to "shut down". Since the prevailing winds are a function of the differential heating of the earth, and it's rotation, this isn't too likely.
Now, having said that, there is some concern that a significant disruption in annual mean temperature (such as would be necessary to melt the polar ice caps) could shut down the thermohaline circulation, so that is something we should at least consider. The climate system is really complicated, though, and contains a lot of nonlinear feedback mechanisms, and it isn't clear exactly what would happen if we had such a disruption.
In any event, the amount of energy one could extract from the ocean in this way isn't going to affect the density profile very much; you can't get away from either conservation of energy or the second law of thermodynamics. So yes, we should think about the environmental effects of our actions, but we should do so carefully and sensibly. This is going to have a much smaller effect on the environment than a coal burning plant producing the same amount of power (and no fresh water).
The article mentioned something about voice chat. I imagine that compressing the audio would be pretty important, to conserve bandwidth.
The question `how large is too large?' depends on the details of the atmosphere in question. This website has some numbers for various atmospheres in our solar system. With a measured lapse rate of about 7.7 K/km, there probably isn't a lot of spontaneous convection due to purely thermal forcing going on on Venus.
Of course, turbulence can be forced in a wide variety of ways, so the absence of strong convection doesn't mean there isn't turbulence on Venus.