I'm impressed. Very clever, but you've forgotten about the coordinate transformations of relativity. Assuming I remember my grad school E&M correctly, if one does a full calculation relativistically, the force arising from a body moving in a straight line at uniform speed does in fact appear to come from where the body would be predicted to be at the time that the signal is received, not the time that it is sent. Of course, if the body curves suddenly, this simple result breaks down (since own can't anticipate how it would curve). The situation with co-orbitting bodies is more complex, but the basic idea is the same: the full relativistic calculation with retardation effects (i.e. finite signal propagation) eliminates the naive nonphysical effects. One does, however, see things like precession of the perihelion from GR, which is absent in the Newtonian approximation.
Yes there is a voltage. My point was that you can't get the voltage by multiplying the E field by the wavelength, because the E field is perpendicular to the wavevector. V ~ int E dot dr. E dot dr is zero if you direct dr along the wavevector.
Thinking in terms of classical mechanics, how far does an electron travel in one half-cycle of an optic wave? Even if the electron is accelerated ballistically (without scattering), in a typical sunlight field strength it goes some very very tiny distance in that time- not even an atom's worth. At that frequency and field strength, it's interband transitions (or plasmon excitations in the appropriate geometry, but that's anoher story).
Hmmm. The electric field of EM radiation is transverse (perpendicular) to the direction of propagation (i.e. wavelength) so the potential difference doesn't build up in that direction.
The problem here is likely timescales: light has a VERY high frequency (10^17 Hertz roughly, if I did my math right). At that frequency one doesn't push the electrons back and forth like a kinetic particle in the usual diode treatments so much as one excites interband transtions, which is how a regular solar cell works.
The EPR 'paradox' isn't a problem at the level of physics. Quantum theory (even non-relativistic) makes very clear predictions about the statistical properties of measurements on spatially separated but correlated particles, and experiments agree. There is no violation of causality. No information propagates faster than the speed of light. Certainly the effect is weird, and it conflicts with some of our naive (i.e. non-quantum) intuitions of how to interpret a physical theory, but there is no logical contradiction and no need to extend or modify the quantum theory to account for experiment.
Wavefunction 'collapse' has some interesting details to be worked out, and some deep matters of interpretation that could use clarification, but it also to date presents no conflicts between experimental results and theoretical predictions. Wavefunctions follow the time-dependent Schrodinger equation, always. It's just when the quantum mechanics extends substantially into macroscopic systems with very large numbers of degrees of freedom, the dynamics of the many-body correlated wavefunction becomes quite complex and our regular intuitions can't keep up very well.
One thing to keep in mind is that wavefunctions do not exist, according to a reasonable definition of exist. The only thing that exists is that which can be measured, that which is physically observable, that which is accessible to an experimental observation. A wavefunction is not physically observable. It is a mathematical tool used to make predictions about experimental results. The simultaneity of collapse of a wavefunction isn't like the simultaneous collapse of say an egg carton. All physical properties related to the process of collapse of an egg carton can be measured by experiment as a function of distance across the carton: density, shear forces, stresses, shape, etc. Not so for a wavefunction.
Yes, everyone can make intelligent choices within the confines of their scope of action. But what forces set the boundaries on their scope of possible action?
It's not bona fide slave labor, so it's ok? Everything else goes? Deplorable working conditions are associated with industrial revolutions for at least a couple reasons. (1) Abject rural poverty as you mention. Anything to help people escape that. And taking nasty dirty jobs to pull oneself out of poverty is a positive part of that process. (2) Rapid economic change without rule of law and democratic institutions tends to concentrate political power in the economic elite. The elite accrue a much larger fraction of the economic value of a process than they suffer the environmental cost (environmental cost is roughly equal per person, if anything favoring those rich enough to be able to afford to live elsewhere, and the $ gain is not equal).
Does the government as a whole really want to shut them down? Certainly they want to give that appearance, but they apparently haven't been very effective at it...
Keep in mind also that all these nice heavy metals are now released into the food chain. Long-run that's everyone's problem.
How similar is an interesting question- in each country it's a nasty job, but is there any information on the relative working conditions, the level of education of the workers as to the health and environmental issues, and the avenues of recourse for workers in cases of abuse? Any correlation with the degree of democracy?
This demo (which works very well) shows conservation of momentum. The tennis ball or basketball bounced alone will hit the floor with velocity V relative to the floor and rebound with velocity -V relative to the floor. When you drop the tennisball/basketball combo, the basketball hits the floor first, rebounding with velocity -V as before. The tennis ball, which is still moving downwards, then immediately collides with it at a relative velocity of 2V. The tennis ball rebounds with velocity -2V relative to the basketball, which is itself moving upwards at velocity -V, so the tennis ball moves upwards at -3V relative to the ground. Since the height attained goes as the square of the velocity (kinetic energy going like velocity squared and potential energy change due to gravity being linear in the distance ascended) the tennis ball travels nine times higher.
I've also done this demo with three balls stacked on each other. It's much harder to get them all aligned, but when it works, the topmost ball goes (optimally) forty nine times higher than when bounced alone.
Note that the momentum conservation equations that give the perfect reversal of relative velocity assume that one object in the collision is much more massive than the other (i.e. basketball versus earth and tennis ball versus basketball). In this limit, the velocity of the more massive object is essentially unchanged by the collision.
Once, for fun, I calculated that if you extended the stack of balls to something like 20 that the topmost ball would attain orbital velocity:-).
Unlike usage of the average random piece of software,
*everyone* votes, and many feel it to be
personally important, so
I suspect quite a few people may hack on this particular system.
IBM Fortran Compiler on RS/6000
on
Pet Bugs?
·
· Score: 2
Compile short fortran program
"Internal compiler error. Please contact IBM representative"
Re-compile from command line using command history. Compiled fine.
Historically, increased CMOS speeds have come from
one thing: shrink the features. Atoms being small,
this works for quite some number of doublings.
Techniques such as strained Si, alternative gate
dielectrics, etc. are a qualitative change in
strategy. They have potential to help, but they
don't have the long-term extendability
that we've seen from shrinkage.
Let's say strained Si gives a factor
of 8 in mobility. That's great, but in 3-4 years
it's done and we need some other idea orthogonal
to the previous one. Having to come up with a
qualitatively new enhancement every 3 years
is very different from the make-it-smaller world
to date.
1100 is mentioned near the beginning. A later
paragraph states:
Another reason is the high production cost. As part of the final manufacturing process, the foam must be heated to temperatures as high as 3,000 degrees Celsius or more than 5,000 degrees Fahrenheit. "That's a tremendous amount of energy," says Conway. And as such, the ovens are necessarily very small and the yield of material is often very modest.
If you heat it up hot enough in the presence of
oxygen, it will burn. So will a diamond, for that
matter. The 3000 degree heat treatment
that they use during synthesis must be done
in an inert atmosphere. Coal burns more
easily than diamonds, I'd guess, but both
are carbon with fairly similar heats of
combustion. Local carbon bonding comes in
two main forms, sp2 (triangular) and sp3 (tetrahedral) bonding; the binding energies of
the two are quite close and both will happily
burn in the presence of oxygen, at high
temperatures.
Just finished reading the pdf of the manuscript.
My biggest concern is the magnitude of the observed
effect- a few standard deviations above background.
The data acquisition runs lasted 7 or 12 hrs (or
for several iterated 300s runs with another detector). The question raised here is, if you've
got marginal statistics (particularly for an
exceptional effect, if truly observed), then why not run
the experiment longer, like a month? That should
yield a strong enough signal that statistics are no
longer an issue. With a small set of runs, there
lies a risk of subconsicously self-selecting a fraction of the runs as the 'good' ones. I'm not saying that's
what happened, but it can't be ruled out based on
the data at hand.
Second concern is the accuracy of the shock
hydrodynamic simulations, both the assumption of
perfect spherical symmetry (which is crucial to
a high concentration of energy at the very center)
and the treatment of the complex interactions in
the plasma during compression (Born-Mayer potentials, as used here, are outside their
realm of validity when the substance ionizes, I
suspect).
I'm not prepared to say "obviously wrong,"
(open mind = good) but there are red flags...
If gas taxes and vehicle registration fees are
reduced commensurately, then driving at off-peak
times would be cheaper than before.
That gives a new money-saving option to
the poor, one which was not previously
available.
The fundamental issue is fairness of road
usage: if you drive during rush hour, then
you are slowing down hundreds or thousands
of other cars by virtue of your contribution to
congestion. That's a cost that you should pay
whatever your income level.
As regards the poor, the sad fact is that life
as a whole is unfair to the poor:-(. Best to
design pricing models that imposes fair
costs for burdens imposed on others, and
then independently establish
programs that explicitly give the poor a leg
up on everything at once, like better education
and social programs to get at root causes. If
access to transportation is one of those root
causes, then slide the pricing scale in some
manner.
[Full disclosure: I'm a professor at Penn State
in one of the departments that you list.]
The most important skill to learn in college
is how to think rigorously and creatively.
From your brief description of interests, I'd
also add analytically to the list.
Any challenging technical or scientific job
requires continuous learning after graduation-
college is to learn how to learn.
My own bias (no prizes for guessing what
department I'm in!) is physics: it's something
of a liberal arts degree for the 21st century.
Quite possibly an undergrad physics degree
won't teach you any 'useful' facts:-),
but it will teach you how to analysis complex problems rigorously and analytically.
Same applies to the other majors you listed
too, of course. You won't go wrong in any of
them so long as you challenge yourself.
Interesting question. The BEC is characterized
by the total number of particles (atoms) within.
Call it N. If the constituent atoms are radioactive, and one waits for decay products of
a single radioactive decay to be detected
in an external detector, then one will find
an N-1 atom condensate, plus one set of decay
products. Which atom decayed? Atoms (of the same
isotope of the same element) in their
ground (lowest-energy) states
are indistinguishable entities, even in non-BEC systems
(ever try to tell two electrons or two protons
apart? same works for assemblages of same:-).
It so happens that this indistinguishabilty has
few experimental consequences at normal temperatures, but more profound consequences at
very low temperatures. So one can't say which
atom decayed- the question is ill defined.
By the way, researchers at Rice University (Randall G. Hulet et al.) made
a condensate before Wolfgang Ketterle's group at MIT. MIT was third. Wolfgang is a great phycisist and gives a spectacular talk, but I bet
the Rice people are feeling a bit left out about now, for good reason.
I agree the user can do with the content
whatever they want in terms of immediate
personal display on their browser and later
fair use. But as content provider I do
have one fundamental right- the ability to
not provide content when I don't want to. If
the content provider wants to ask a question
first (e.g. "will you be adding ad links?"),
in expectation of an honest answer, before
deciding whether to provide content, they should
be able to do that. They can't here.
I see this more as a negotiated compromise
between the user and the website they are viewing.
The user can send the site a request "I'd like
to view
your site, but I'll be adding a bunch of ad links"
and the site should be able to respond "Sorry, you
can view this content, but only if you omit the
ad links" or "OK go ahead" or
"Sorry- you can't view it at all in that case."
I don't have a problem with these sorts of ad
links, but only if as website owner, I can participate in a negotiation on how
my site content can be used. The companies
distributing these tools are using my content
to their direct financial benefit and my direct
financial cost- that's ok, but they need to
ask permission first and enter into an agreement with me, either directly or on case-by-case through automated negotiations with
the users of their software.
What if one put a click-through license on one's
website: "Each page of this site is to be viewed
in its entirely, without filtering." If a website
user can opt in to a device that filters
and modifies content of the
site, then a website owner should be able to opt
out of that. Symmetry. It takes two to tango.
Slashdot Mirror
At least the ones to deep pages...
I'm impressed. Very clever, but you've forgotten about the coordinate transformations of relativity. Assuming I remember my grad school E&M correctly, if one does a full calculation relativistically, the force arising from a body moving in a straight line at uniform speed does in fact appear to come from where the body would be predicted to be at the time that the signal is received, not the time that it is sent. Of course, if the body curves suddenly, this simple result breaks down (since own can't anticipate how it would curve). The situation with co-orbitting bodies is more complex, but the basic idea is the same: the full relativistic calculation with retardation effects (i.e. finite signal propagation) eliminates the naive nonphysical effects. One does, however, see things like precession of the perihelion from GR, which is absent in the Newtonian approximation.
How come no-one has written an algorithm to remove the channel logo? Should be possible with some image recognition and...
Yes there is a voltage. My point was that you can't get the voltage by multiplying the E field by the wavelength, because the E field is perpendicular to the wavevector. V ~ int E dot dr. E dot dr is zero if you direct dr along the wavevector.
Thinking in terms of classical mechanics, how far does an electron travel in one half-cycle of an optic wave? Even if the electron is accelerated ballistically (without scattering), in a typical sunlight field strength it goes some very very tiny distance in that time- not even an atom's worth. At that frequency and field strength, it's interband transitions (or plasmon excitations in the appropriate geometry, but that's anoher story).
Hmmm. The electric field of EM radiation is transverse (perpendicular) to the direction of propagation (i.e. wavelength) so the potential difference doesn't build up in that direction.
The problem here is likely timescales: light has a VERY high frequency (10^17 Hertz roughly, if I did my math right). At that frequency one doesn't push the electrons back and forth like a kinetic particle in the usual diode treatments so much as one excites interband transtions, which is how a regular solar cell works.
The EPR 'paradox' isn't a problem at the level of physics. Quantum theory (even non-relativistic) makes very clear predictions about the statistical properties of measurements on spatially separated but correlated particles, and experiments agree. There is no violation of causality. No information propagates faster than the speed of light. Certainly the effect is weird, and it conflicts with some of our naive (i.e. non-quantum) intuitions of how to interpret a physical theory, but there is no logical contradiction and no need to extend or modify the quantum theory to account for experiment.
Wavefunction 'collapse' has some interesting details to be worked out, and some deep matters of interpretation that could use clarification, but it also to date presents no conflicts between experimental results and theoretical predictions. Wavefunctions follow the time-dependent Schrodinger equation, always. It's just when the quantum mechanics extends substantially into macroscopic systems with very large numbers of degrees of freedom, the dynamics of the many-body correlated wavefunction becomes quite complex and our regular intuitions can't keep up very well.
One thing to keep in mind is that wavefunctions do not exist, according to a reasonable definition of exist. The only thing that exists is that which can be measured, that which is physically observable, that which is accessible to an experimental observation. A wavefunction is not physically observable. It is a mathematical tool used to make predictions about experimental results. The simultaneity of collapse of a wavefunction isn't like the simultaneous collapse of say an egg carton. All physical properties related to the process of collapse of an egg carton can be measured by experiment as a function of distance across the carton: density, shear forces, stresses, shape, etc. Not so for a wavefunction.
Yes, everyone can make intelligent choices within the confines of their scope of action. But what forces set the boundaries on their scope of possible action?
It's not bona fide slave labor, so it's ok? Everything else goes? Deplorable working conditions are associated with industrial revolutions for at least a couple reasons. (1) Abject rural poverty as you mention. Anything to help people escape that. And taking nasty dirty jobs to pull oneself out of poverty is a positive part of that process. (2) Rapid economic change without rule of law and democratic institutions tends to concentrate political power in the economic elite. The elite accrue a much larger fraction of the economic value of a process than they suffer the environmental cost (environmental cost is roughly equal per person, if anything favoring those rich enough to be able to afford to live elsewhere, and the $ gain is not equal).
Does the government as a whole really want to shut them down? Certainly they want to give that appearance, but they apparently haven't been very effective at it...
Keep in mind also that all these nice heavy metals are now released into the food chain. Long-run that's everyone's problem.
How similar is an interesting question- in each country it's a nasty job, but is there any information on the relative working conditions, the level of education of the workers as to the health and environmental issues, and the avenues of recourse for workers in cases of abuse? Any correlation with the degree of democracy?
Umm, mainland China is not democratic.
This demo (which works very well) shows conservation of momentum. The tennis ball or basketball bounced alone will hit the floor with velocity V relative to the floor and rebound with velocity -V relative to the floor. When you drop the tennisball/basketball combo, the basketball hits the floor first, rebounding with velocity -V as before. The tennis ball, which is still moving downwards, then immediately collides with it at a relative velocity of 2V. The tennis ball rebounds with velocity -2V relative to the basketball, which is itself moving upwards at velocity -V, so the tennis ball moves upwards at -3V relative to the ground. Since the height attained goes as the square of the velocity (kinetic energy going like velocity squared and potential energy change due to gravity being linear in the distance ascended) the tennis ball travels nine times higher.
:-).
I've also done this demo with three balls stacked on each other. It's much harder to get them all aligned, but when it works, the topmost ball goes (optimally) forty nine times higher than when bounced alone.
Note that the momentum conservation equations that give the perfect reversal of relative velocity assume that one object in the collision is much more massive than the other (i.e. basketball versus earth and tennis ball versus basketball). In this limit, the velocity of the more massive object is essentially unchanged by the collision.
Once, for fun, I calculated that if you extended the stack of balls to something like 20 that the topmost ball would attain orbital velocity
That's why I always do this with a suspended bowling ball instead.
The initial password assigned to the hacked account was OnlneAp16501. I wonder if the merchant before them had password OnlneAp16500? Sigh.
Unlike usage of the average random piece of software, *everyone* votes, and many feel it to be personally important, so I suspect quite a few people may hack on this particular system.
Compile short fortran program
"Internal compiler error. Please contact IBM representative"
Re-compile from command line using command history.
Compiled fine.
Historically, increased CMOS speeds have come from one thing: shrink the features. Atoms being small, this works for quite some number of doublings. Techniques such as strained Si, alternative gate dielectrics, etc. are a qualitative change in strategy. They have potential to help, but they don't have the long-term extendability that we've seen from shrinkage. Let's say strained Si gives a factor of 8 in mobility. That's great, but in 3-4 years it's done and we need some other idea orthogonal to the previous one. Having to come up with a qualitatively new enhancement every 3 years is very different from the make-it-smaller world to date.
If you heat it up hot enough in the presence of oxygen, it will burn. So will a diamond, for that matter. The 3000 degree heat treatment that they use during synthesis must be done in an inert atmosphere. Coal burns more easily than diamonds, I'd guess, but both are carbon with fairly similar heats of combustion. Local carbon bonding comes in two main forms, sp2 (triangular) and sp3 (tetrahedral) bonding; the binding energies of the two are quite close and both will happily burn in the presence of oxygen, at high temperatures.
Just finished reading the pdf of the manuscript. My biggest concern is the magnitude of the observed effect- a few standard deviations above background. The data acquisition runs lasted 7 or 12 hrs (or for several iterated 300s runs with another detector). The question raised here is, if you've got marginal statistics (particularly for an exceptional effect, if truly observed), then why not run the experiment longer, like a month? That should yield a strong enough signal that statistics are no longer an issue. With a small set of runs, there lies a risk of subconsicously self-selecting a fraction of the runs as the 'good' ones. I'm not saying that's what happened, but it can't be ruled out based on the data at hand.
Second concern is the accuracy of the shock hydrodynamic simulations, both the assumption of perfect spherical symmetry (which is crucial to a high concentration of energy at the very center) and the treatment of the complex interactions in the plasma during compression (Born-Mayer potentials, as used here, are outside their realm of validity when the substance ionizes, I suspect).
I'm not prepared to say "obviously wrong," (open mind = good) but there are red flags...
If gas taxes and vehicle registration fees are reduced commensurately, then driving at off-peak times would be cheaper than before. That gives a new money-saving option to the poor, one which was not previously available.
The fundamental issue is fairness of road usage: if you drive during rush hour, then you are slowing down hundreds or thousands of other cars by virtue of your contribution to congestion. That's a cost that you should pay whatever your income level.
As regards the poor, the sad fact is that life as a whole is unfair to the poor :-(. Best to
design pricing models that imposes fair
costs for burdens imposed on others, and
then independently establish
programs that explicitly give the poor a leg
up on everything at once, like better education
and social programs to get at root causes. If
access to transportation is one of those root
causes, then slide the pricing scale in some
manner.
[Full disclosure: I'm a professor at Penn State in one of the departments that you list.]
The most important skill to learn in college is how to think rigorously and creatively. From your brief description of interests, I'd also add analytically to the list. Any challenging technical or scientific job requires continuous learning after graduation- college is to learn how to learn.
My own bias (no prizes for guessing what department I'm in!) is physics: it's something of a liberal arts degree for the 21st century. Quite possibly an undergrad physics degree won't teach you any 'useful' facts :-),
but it will teach you how to analysis complex problems rigorously and analytically.
Same applies to the other majors you listed too, of course. You won't go wrong in any of them so long as you challenge yourself.
Interesting question. The BEC is characterized by the total number of particles (atoms) within. Call it N. If the constituent atoms are radioactive, and one waits for decay products of a single radioactive decay to be detected in an external detector, then one will find an N-1 atom condensate, plus one set of decay products. Which atom decayed? Atoms (of the same isotope of the same element) in their ground (lowest-energy) states are indistinguishable entities, even in non-BEC systems (ever try to tell two electrons or two protons apart? same works for assemblages of same :-).
It so happens that this indistinguishabilty has
few experimental consequences at normal temperatures, but more profound consequences at
very low temperatures. So one can't say which
atom decayed- the question is ill defined.
By the way, researchers at Rice University (Randall G. Hulet et al.) made a condensate before Wolfgang Ketterle's group at MIT. MIT was third. Wolfgang is a great phycisist and gives a spectacular talk, but I bet the Rice people are feeling a bit left out about now, for good reason.
I agree the user can do with the content whatever they want in terms of immediate personal display on their browser and later fair use. But as content provider I do have one fundamental right- the ability to not provide content when I don't want to. If the content provider wants to ask a question first (e.g. "will you be adding ad links?"), in expectation of an honest answer, before deciding whether to provide content, they should be able to do that. They can't here.
I see this more as a negotiated compromise between the user and the website they are viewing. The user can send the site a request "I'd like to view your site, but I'll be adding a bunch of ad links" and the site should be able to respond "Sorry, you can view this content, but only if you omit the ad links" or "OK go ahead" or "Sorry- you can't view it at all in that case."
I don't have a problem with these sorts of ad links, but only if as website owner, I can participate in a negotiation on how my site content can be used. The companies distributing these tools are using my content to their direct financial benefit and my direct financial cost- that's ok, but they need to ask permission first and enter into an agreement with me, either directly or on case-by-case through automated negotiations with the users of their software.
What if one put a click-through license on one's
website: "Each page of this site is to be viewed
in its entirely, without filtering." If a website
user can opt in to a device that filters
and modifies content of the
site, then a website owner should be able to opt
out of that. Symmetry. It takes two to tango.