| Topic: |
Science > Physics |
| User: |
"Gregory L. Hansen" |
| Date: |
29 Sep 2004 07:29:17 PM |
| Object: |
Crystal structure without diffraction? |
I've been reading about how things like the band structure and densities
of states relate to macroscropic properties of crystals, like the optical
properties, coefficients of thermal expansion, heat capacity, etc. I
wondered, then, how much we can tell about a crystal's structure from
strictly macroscopic and thermodynamic properties, without x-rays or
neutrons beams or the like. Maybe it wouldn't have been information
available in the 19th century because you have to get them pretty darn
cold to see some of the important stuff. At the very least you could
learn some things about the symmetries from the macroscopic angles, if a
coefficient has different magnitudes in different directions, etc.
When doing crystallography I know there's a phase problem in that what is
recorded on the photographic film, the CCD, whatever, is an intensity,
|psi* psi|^2. That phase information is lost. Could data from, e.g.
polarimetry, or from surface acoustic waves, help to recover that?
Strictly speaking, I've probably seen all the theory that's required to
answer my own question. But darnit, the many body problem isn't easy.
--
"Yes, I revere you much, honored ones, and wish to fart in response." --
Aristophanes, Clouds
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| User: "Rob Woodside" |
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| Title: Re: Crystal structure without diffraction? |
01 Oct 2004 11:36:29 AM |
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(Gregory L. Hansen) wrote in message news:<cjfk0t$fap$1@hood.uits.indiana.edu>...
I've been reading about how things like the band structure and densities
of states relate to macroscropic properties of crystals, like the optical
properties, coefficients of thermal expansion, heat capacity, etc. I
wondered, then, how much we can tell about a crystal's structure from
strictly macroscopic and thermodynamic properties, without x-rays or
neutrons beams or the like. Maybe it wouldn't have been information
available in the 19th century because you have to get them pretty darn
cold to see some of the important stuff. At the very least you could
learn some things about the symmetries from the macroscopic angles, if a
coefficient has different magnitudes in different directions, etc.
When doing crystallography I know there's a phase problem in that what is
recorded on the photographic film, the CCD, whatever, is an intensity,
|psi* psi|^2. That phase information is lost. Could data from, e.g.
polarimetry, or from surface acoustic waves, help to recover that?
Strictly speaking, I've probably seen all the theory that's required to
answer my own question. But darnit, the many body problem isn't easy.
Steno, a contempory of Newton, noticed the constancy of interfacial
angles on corresponding faces of two different crystals of the same
mineral. Around 1800 Hauy realized the law of rational indices,
whereby crystal faces intersected crystallographic axes with rational
numbers due to the stacking of identical units. I've forgotten who
introduced point groups, but it must have been shortly after the
Bravais brothers in 1814. Now a macroscopic crystal that had a
sufficient variety of faces could be assigned a point group and axial
ratios. The rest of 19th century crystallography catalogued these.
Remarkably with the advent of x-ray diffraction, people were amazed
that the 19th century axial ratios were just the axial ratios for the
unit cell and the 19th century crystallographer were almost always
right. To get the space groups from the point groups one has to
resolve the mirror planes and rotation axes into glide planes and
screw axes. Knowing space group and unit cell is still a long way from
the actual structure, but with some chemical knowledge and a simple
compound one could guess the structure. Finally by the middle of the
20th century, the Patterson function allowed one to set up an
algorithm that would settle down to the actual structure starting from
initial guesses as to where the atoms were and defeat the loss of
phase.
How to do better? Certainly if one had an x-ray laser and could take
x-ray holographs, one could recover the phases directly. Another
possibility is with the new microscopes (Scanning tunnelling, atomic
force). If a crystal face is clean enough and flat enough, one can see
how the atoms are arranged in that plane, modulo surface relaxation.
Doing this with two faces that span 3-space would give the structure.
We have not yet made a full harvest with this new microscope
technology and my hope is that we can use it for not just structures,
but to TEST theories of crystal growth and finally understand what
causes a particular morphology.
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| User: "zigoteau" |
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| Title: Re: Crystal structure without diffraction? |
30 Sep 2004 03:33:38 AM |
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(Gregory L. Hansen) wrote in message news:<cjfk0t$fap$1@hood.uits.indiana.edu>...
Hi, Greg,
I've been reading about how things like the band structure and densities
of states relate to macroscropic properties of crystals, like the optical
properties, coefficients of thermal expansion, heat capacity, etc. I
wondered, then, how much we can tell about a crystal's structure from
strictly macroscopic and thermodynamic properties, without x-rays or
neutrons beams or the like. Maybe it wouldn't have been information
available in the 19th century because you have to get them pretty darn
cold to see some of the important stuff. At the very least you could
learn some things about the symmetries from the macroscopic angles, if a
coefficient has different magnitudes in different directions, etc.
When doing crystallography I know there's a phase problem in that what is
recorded on the photographic film, the CCD, whatever, is an intensity,
psi* psi=|psi|^2. That phase information is lost. Could data from, e.g.
polarimetry, or from surface acoustic waves, help to recover that?
That's a bit like saying that you don't need satellites for
observations of the earth. In both cases, the hi-tech data provides
information, and provides it in a form, that would only be available
using the older measurement techniques at great expense. What's more,
the new techniques provide a different way of looking at the data and
new intuitions that are priceless.
I'm sure you know all about silicon. The stable form under ambient
conditions has a cubic unit cell. It takes a while thinking about it
before you can reconcile a cube with the fact that the four bonds
around any silicon atom point to the corners of a tetrahedron. The
three principal axes of the cube are in fact the directions bisecting
the angle between pairs of bonds. Now if any crystal with cubic
symmetry has a macroscopically-measurable materials parameter which is
naturally the element of a matrix, or a tensor of the fourth degree,
then that parameter must be isotropic. This is the case for the
dielectric constant, the elastic tensor and the coefficient of thermal
expansion. So the information that such measurements give you about
what's going on at the atomic level is extremely sparse. It's
negative, ruling out certain arrangements but not supporting any of
the remaining possibilities very strongly.
There is a phenomenon that the length of papers using a given
measurement technique is in inverse proportion to the amount of
information it provides. The smaller the amount of information, the
more you can argue about what it all means.
Strictly speaking, I've probably seen all the theory that's required to
answer my own question. But darnit, the many body problem isn't easy.
No pain, no gain. I happen to be made up of over 1e30 atoms, almost
all in intimate contact with their neighbors, so the solution to the
many body problem has special significance to me.
Cheers,
Zigoteau.
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| User: "Andy Resnick" |
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| Title: Re: Crystal structure without diffraction? |
30 Sep 2004 03:40:11 PM |
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Gregory L. Hansen wrote:
I've been reading about how things like the band structure and densities
of states relate to macroscropic properties of crystals, like the optical
properties, coefficients of thermal expansion, heat capacity, etc. I
wondered, then, how much we can tell about a crystal's structure from
strictly macroscopic and thermodynamic properties, without x-rays or
neutrons beams or the like. Maybe it wouldn't have been information
available in the 19th century because you have to get them pretty darn
cold to see some of the important stuff. At the very least you could
learn some things about the symmetries from the macroscopic angles, if a
coefficient has different magnitudes in different directions, etc.
When doing crystallography I know there's a phase problem in that what is
recorded on the photographic film, the CCD, whatever, is an intensity,
|psi* psi|^2. That phase information is lost. Could data from, e.g.
polarimetry, or from surface acoustic waves, help to recover that?
Strictly speaking, I've probably seen all the theory that's required to
answer my own question. But darnit, the many body problem isn't easy.
I bet one could extract quite a bit of information by simply determining
the cleavage planes of a good quality crystal. Lots of other
macroscopic measurements could be performed as well (piezoelectricty,
for example: squeeze it and there is electrical activity). There's an
incredible paper written around the turn of the century that discusses
how to cleave a diamond to maximize it's asthetics (sp?)
http://www.folds.net/diamond_design/index.html
Then there's the mechanical stress-strain measurements performed by
Wertheim in the 1840's- he's another brilliant chap who killed himself,
in the tradition of Boltzmann...
Euler literally wrote the book on linear elasticity. Hamilton did a
fair bit on crystal optics.
Solid mechanics and continuum mechanics have been around longer than any
other branch of physics.
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
CWRU School of Medicine
tanspose 'op' for mail
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| User: "" |
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| Title: Re: Crystal structure without diffraction? |
29 Sep 2004 11:55:41 PM |
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In article <cjfk0t$fap$1@hood.uits.indiana.edu>, (Gregory L. Hansen) writes:
I've been reading about how things like the band structure and densities
of states relate to macroscropic properties of crystals, like the optical
properties, coefficients of thermal expansion, heat capacity, etc. I
wondered, then, how much we can tell about a crystal's structure from
strictly macroscopic and thermodynamic properties, without x-rays or
neutrons beams or the like. Maybe it wouldn't have been information
available in the 19th century because you have to get them pretty darn
cold to see some of the important stuff. At the very least you could
learn some things about the symmetries from the macroscopic angles, if a
coefficient has different magnitudes in different directions, etc.
Certainly.
When doing crystallography I know there's a phase problem in that what is
recorded on the photographic film, the CCD, whatever, is an intensity,
|psi* psi|^2.
Aye, that's the eternal problem.
That phase information is lost. Could data from, e.g.
polarimetry, or from surface acoustic waves, help to recover that?
It may. Especially if (as it happens at time), the diffraction data
(even at the absence of phase) limits the possibilities to few
distinct cases. Then, using additional data, you can pick one over
the other.
Strictly speaking, I've probably seen all the theory that's required to
answer my own question. But darnit, the many body problem isn't easy.
That's for sure:-)
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "Gregory L. Hansen" |
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| Title: Re: Crystal structure without diffraction? |
30 Sep 2004 09:27:06 AM |
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In article <hlM6d.3$45.411@news.uchicago.edu>,
<mmeron@cars3.uchicago.edu> wrote:
In article <cjfk0t$fap$1@hood.uits.indiana.edu>,
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) writes:
When doing crystallography I know there's a phase problem in that what is
recorded on the photographic film, the CCD, whatever, is an intensity,
|psi* psi|^2.
Aye, that's the eternal problem.
That phase information is lost. Could data from, e.g.
polarimetry, or from surface acoustic waves, help to recover that?
It may. Especially if (as it happens at time), the diffraction data
(even at the absence of phase) limits the possibilities to few
distinct cases. Then, using additional data, you can pick one over
the other.
I think this must be one of those "Yes, in principle" things. Not so
useful when all the easy structures have been figured out decades ago and
now you're trying to figure out a protein.
--
"For every problem there is a solution which is simple, clean and wrong."
-- Henry Louis Mencken
.
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| User: "" |
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| Title: Re: Crystal structure without diffraction? |
30 Sep 2004 04:18:08 PM |
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In article <cjh53q$105$1@hood.uits.indiana.edu>, (Gregory L. Hansen) writes:
In article <hlM6d.3$45.411@news.uchicago.edu>,
<mmeron@cars3.uchicago.edu> wrote:
In article <cjfk0t$fap$1@hood.uits.indiana.edu>,
(Gregory L. Hansen) writes:
When doing crystallography I know there's a phase problem in that what is
recorded on the photographic film, the CCD, whatever, is an intensity,
|psi* psi|^2.
Aye, that's the eternal problem.
That phase information is lost. Could data from, e.g.
polarimetry, or from surface acoustic waves, help to recover that?
It may. Especially if (as it happens at time), the diffraction data
(even at the absence of phase) limits the possibilities to few
distinct cases. Then, using additional data, you can pick one over
the other.
I think this must be one of those "Yes, in principle" things. Not so
useful when all the easy structures have been figured out decades ago and
now you're trying to figure out a protein.
--
As my thesis advisor (many years ago) used to say, "at any given point
in the history of science, all the easy problems have been dealt with,
already":-) Pretty tautological, when you think about it. But, yes,
proteins can be a *****.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
.
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| User: "Gregory L. Hansen" |
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| Title: Re: Crystal structure without diffraction? |
30 Sep 2004 07:30:46 PM |
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In article <kK_6d.9$45.710@news.uchicago.edu>,
<mmeron@cars3.uchicago.edu> wrote:
In article <cjh53q$105$1@hood.uits.indiana.edu>,
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) writes:
I think this must be one of those "Yes, in principle" things. Not so
useful when all the easy structures have been figured out decades ago and
now you're trying to figure out a protein.
--
As my thesis advisor (many years ago) used to say, "at any given point
in the history of science, all the easy problems have been dealt with,
already":-) Pretty tautological, when you think about it. But, yes,
proteins can be a *****.
There was a time when you could roll balls down an inclined plane, or
watch a chandelier swing, and it would be cutting-edge research. But
even the easy stuff now needs a vacuum deposition rig, or a dilution
refrigerator, or a nuclear reactor.
Fractals gave us a brief time when you could spill coffee on a napkin and
call it science. But they've moved beyond that now.
--
"Usenet is like a herd of performing elephants with diarrhea -- massive,
difficult to redirect, awe-inspiring, entertaining, and a source of
mind-boggling amounts of excrement when you least expect it. "
-- Gene Spafford, 1992
.
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| User: "Andy Resnick" |
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| Title: Re: Crystal structure without diffraction? |
01 Oct 2004 07:18:14 AM |
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Gregory L. Hansen wrote:
In article <kK_6d.9$45.710@news.uchicago.edu>,
<mmeron@cars3.uchicago.edu> wrote:
In article <cjh53q$105$1@hood.uits.indiana.edu>,
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) writes:
I think this must be one of those "Yes, in principle" things. Not so
useful when all the easy structures have been figured out decades ago and
now you're trying to figure out a protein.
--
As my thesis advisor (many years ago) used to say, "at any given point
in the history of science, all the easy problems have been dealt with,
already":-) Pretty tautological, when you think about it. But, yes,
proteins can be a *****.
There was a time when you could roll balls down an inclined plane, or
watch a chandelier swing, and it would be cutting-edge research. But
even the easy stuff now needs a vacuum deposition rig, or a dilution
refrigerator, or a nuclear reactor.
Fractals gave us a brief time when you could spill coffee on a napkin and
call it science. But they've moved beyond that now.
I disagree with this assessment- discovering or synthesizing new
knowledge has never been trivial. As for "inclined planes and swinging
chandeliers", the technical difficulties with making a perfectly flat,
straight and smooth channel of any reasonable length is considerable
without modern machinery- try it. Fabricating a well-characterized
pendulum is likewise difficult without modern manufacturing methods.
As for the difficult development of the theoretical framework required
to understand *why* one would want to swing a pendulum or roll something
down a slope, I would recommend reading "History of Mechanics" by Rene
Dugas. The progression of statics (balanced lever arms and geometry,
basically) to dynamics is fascinating reading.
Additionally, there is plenty of interesting science that one may do
without a vacuum deposition rig, a dilution refrigerator, or a nuclear
reactor. Certainly one benefits from a well-appointed lab, but
electrophysiology is not much more than a decent voltmeter. What
distinguishes the good experimental scientist from the hack is the
ability to use what is available, as opposed to having the latest toy to
play with. And besides, all a theorist needs, or has ever needed, is a
piece of chalk!
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
CWRU School of Medicine
tanspose 'op' for mail
.
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| User: "Gregory L. Hansen" |
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| Title: Re: Crystal structure without diffraction? |
01 Oct 2004 09:31:23 AM |
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In article <cjjhvc$9f1$1@eeyore.INS.cwru.edu>,
Andy Resnick <axr67@op.cwru.edu> wrote:
Gregory L. Hansen wrote:
In article <kK_6d.9$45.710@news.uchicago.edu>,
<mmeron@cars3.uchicago.edu> wrote:
In article <cjh53q$105$1@hood.uits.indiana.edu>,
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) writes:
I think this must be one of those "Yes, in principle" things. Not so
useful when all the easy structures have been figured out decades ago and
now you're trying to figure out a protein.
--
As my thesis advisor (many years ago) used to say, "at any given point
in the history of science, all the easy problems have been dealt with,
already":-) Pretty tautological, when you think about it. But, yes,
proteins can be a *****.
There was a time when you could roll balls down an inclined plane, or
watch a chandelier swing, and it would be cutting-edge research. But
even the easy stuff now needs a vacuum deposition rig, or a dilution
refrigerator, or a nuclear reactor.
Fractals gave us a brief time when you could spill coffee on a napkin and
call it science. But they've moved beyond that now.
I disagree with this assessment- discovering or synthesizing new
knowledge has never been trivial.
There's no doubt about that. As Mati mentioned, they had to know that
watching chandeliers swinging, or rolling balls down inclined planes were
a good thing to study, and meaningfully interpret it. That's not so
obvious if you hadn't already grown up with F=ma.
As for "inclined planes and swinging
chandeliers", the technical difficulties with making a perfectly flat,
straight and smooth channel of any reasonable length is considerable
without modern machinery- try it.
It's still something that could be attempted by a craftsman in his
workshop. Compare that with a modern craftsman testing the standard
model in his garage.
Fabricating a well-characterized
pendulum is likewise difficult without modern manufacturing methods.
This one is pretty easy, I think. They had thread, they had musket balls
and other small, dense objects. They could easily do as well as a
modern freshman physics lab. Finding a time standard to characterize the
swinging would be harder.
As for the difficult development of the theoretical framework required
to understand *why* one would want to swing a pendulum or roll something
down a slope, I would recommend reading "History of Mechanics" by Rene
Dugas. The progression of statics (balanced lever arms and geometry,
basically) to dynamics is fascinating reading.
Additionally, there is plenty of interesting science that one may do
without a vacuum deposition rig, a dilution refrigerator, or a nuclear
reactor. Certainly one benefits from a well-appointed lab, but
electrophysiology is not much more than a decent voltmeter. What
distinguishes the good experimental scientist from the hack is the
ability to use what is available, as opposed to having the latest toy to
play with. And besides, all a theorist needs, or has ever needed, is a
piece of chalk!
With the caveat that the experimental scientist, using what's available,
may have to find something else to research.
--
"Very well, he replied, I allow you cow's dung in place of human
excrement; bake your bread on that." -- Ezekiel 4:15
.
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| User: "Andy Resnick" |
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| Title: Re: Crystal structure without diffraction? |
01 Oct 2004 01:02:10 PM |
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Gregory L. Hansen wrote:
In article <cjjhvc$9f1$1@eeyore.INS.cwru.edu>,
Andy Resnick <axr67@op.cwru.edu> wrote:
<snip>
As for "inclined planes and swinging
chandeliers", the technical difficulties with making a perfectly flat,
straight and smooth channel of any reasonable length is considerable
without modern machinery- try it.
It's still something that could be attempted by a craftsman in his
workshop. Compare that with a modern craftsman testing the standard
model in his garage.
Fabricating a well characterized
pendulum is likewise difficult without modern manufacturing methods.
This one is pretty easy, I think. They had thread, they had musket balls
and other small, dense objects. They could easily do as well as a
modern freshman physics lab. Finding a time standard to characterize the
swinging would be harder.
At the risk of flogging a dead topic, let me toss this out:
First of all, 'The Standard Model" is not the be-all and end-all of
physics. That's a limited view of physics, and that view has
contributed mightily to the marginalization of physics in education.
The reductionism view of reality, of finding the bottom stratum of
existence, is played out. The standard model will never be used to
explain the function of even the simplest protein molecule, let alone a
complete signaling pathway which regulates the expression of a
particular gene. Science in general, of which physics is a small but
vital component, is often practiced *and advanced* by using simple,
existing equipment in a new ingenious way- the scanning probe microscope
is a good example of that.
Back to the supposed ease of fabricating inclined planes and pendulums
in the 1500s, or even earlier. One could not go to the store and buy
these things, nor the equipment to fabricate these things. Could you
build a lathe or forge with which to make your scientific equipment?
What about glassblowing? Now factor in all the daily crap one needed to
do just to survive- there was no leisure class back then. There was no
real merchant class or professional class, other than doctors and
lawyers. Most of the scientists back then made their own materials and
equipment to study. And were employed by royalty, in order to peruse
their (a)vocation.
Let's talk about stability: design a pendulum that will swing with
minimal friction, whose properties will not change with temperature and
humidity, and whose properties can not only readily duplicated, but can
be controlled. Simply tying a thread around a nail will give poor
results. There was no aluminum, steel, ceramic, etc. etc. I don't
know how readily available wire was back then, but I expect there wasn't
much to be had, given there was no household electricity. There were no
clocks, no thermometers, no engines. Paper was expensive.. Look at the
instruments used for science back then- they were like jewelry, because
they were horribly expensive to manufacture, just like today.
Let's not denigrate the contributions of medieval scientists: Jean
Buridan, William of Ockham, and many, many others:
http://www.hannibal.cnyric.org/TeacherWebs/Cburch/activityfiles/abbrevPhysicsTimeResearchList.htm
Look at how much was done before Galileo, never mind before Newton and
Huyghens (a reliable clock...)!
Science today is no more difficult than it was then. Perhaps more
sophisticated, but not necessarily.
<snip>
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
CWRU School of Medicine
tanspose 'op' for mail
.
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| User: "Timo Nieminen" |
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| Title: Re: Crystal structure without diffraction? |
03 Oct 2004 08:20:08 PM |
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On Fri, 1 Oct 2004, Gregory L. Hansen wrote:
Andy Resnick <axr67@op.cwru.edu> wrote:
I disagree with this assessment- discovering or synthesizing new
knowledge has never been trivial.
There's no doubt about that. As Mati mentioned, they had to know that
watching chandeliers swinging, or rolling balls down inclined planes were
a good thing to study, and meaningfully interpret it. That's not so
obvious if you hadn't already grown up with F=ma.
As for "inclined planes and swinging
chandeliers", the technical difficulties with making a perfectly flat,
straight and smooth channel of any reasonable length is considerable
without modern machinery- try it.
It's still something that could be attempted by a craftsman in his
workshop. Compare that with a modern craftsman testing the standard
model in his garage.
We have (had?) a rolling balls down inclined planes to measure g 1st year
undergad experiment. Accuracy was woeful. (Not necessarily a bad thing for
a 1st year undergrad experiment - I also liked the one where I vs V was
measured for a couple of diodes and compared to (simplistic) theory. I had
little sympathy and few mark for the quartet who decided to trust the
theory and fabricate data to match.)
OTOH, one can home-build a Geiger counter. Is the theory sufficient to
predict decay rates with worthwhile precision? In any case, there is no
lack of worthwhile measurements that can be made with better accuracy and
precision.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
.
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| User: "Timo Nieminen" |
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| Title: Re: Crystal structure without diffraction? |
03 Oct 2004 08:10:59 PM |
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On Fri, 1 Oct 2004, Andy Resnick wrote:
And besides, all a theorist needs, or has ever needed, is a
piece of chalk!
Of course, one can always say that the stuff one can do with a piece of
chalk is the hard stuff. For the easy stuff, one needs a computer [1].
[1] With all the usual reservation concerning people who can do the insane
analytical stuff with ease but can't program their way out of a wet paper
bag, and taxonomies that include computational theoretical physics as a
part of theoretical physics (doing computational theoretical applied
physics and computational theoretical experimental physics, I can grok the
floppy flaccidity of such taxonomies from experience).
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
.
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| User: "Rene Tschaggelar" |
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| Title: Re: Crystal structure without diffraction? |
01 Oct 2004 05:42:03 AM |
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Gregory L. Hansen wrote:
In article <kK_6d.9$45.710@news.uchicago.edu>,
<mmeron@cars3.uchicago.edu> wrote:
In article <cjh53q$105$1@hood.uits.indiana.edu>,
glhansen@steel.ucs.indiana.edu (Gregory L. Hansen) writes:
I think this must be one of those "Yes, in principle" things. Not so
useful when all the easy structures have been figured out decades ago and
now you're trying to figure out a protein.
--
As my thesis advisor (many years ago) used to say, "at any given point
in the history of science, all the easy problems have been dealt with,
already":-) Pretty tautological, when you think about it. But, yes,
proteins can be a *****.
There was a time when you could roll balls down an inclined plane, or
watch a chandelier swing, and it would be cutting-edge research. But
even the easy stuff now needs a vacuum deposition rig, or a dilution
refrigerator, or a nuclear reactor.
The ball on a tilted plane was not that trivial because
they didn't had counters with nanosecond resolution and
accuracy. Nor at one time they had the (functional-)
analysis as we know it today.
Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
.
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| User: "" |
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| Title: Re: Crystal structure without diffraction? |
30 Sep 2004 10:26:27 PM |
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In article <cji8fm$ef1$1@hood.uits.indiana.edu>, (Gregory L. Hansen) writes:
In article <kK_6d.9$45.710@news.uchicago.edu>,
<mmeron@cars3.uchicago.edu> wrote:
In article <cjh53q$105$1@hood.uits.indiana.edu>,
(Gregory L. Hansen) writes:
I think this must be one of those "Yes, in principle" things. Not so
useful when all the easy structures have been figured out decades ago and
now you're trying to figure out a protein.
--
As my thesis advisor (many years ago) used to say, "at any given point
in the history of science, all the easy problems have been dealt with,
already":-) Pretty tautological, when you think about it. But, yes,
proteins can be a *****.
There was a time when you could roll balls down an inclined plane, or
watch a chandelier swing, and it would be cutting-edge research. But
even the easy stuff now needs a vacuum deposition rig, or a dilution
refrigerator, or a nuclear reactor.
Yes, true. Though I'm sure that those early experiments with inclined
planes were anything but simple for those involved. Figuring out what
to look for and how to discard spurious effects is only simple after
you already know what you're doing. But, one thing that is true, in
those bygone days an average person (well, not a peasant but a country
squire for sure) with scientific interests could've set up and perform
experiments using easily available means. Not anymore.
Fractals gave us a brief time when you could spill coffee on a napkin and
call it science. But they've moved beyond that now.
Till next time:-) There are always these brief anomalies, but they
don't stay.
As a general rule, you're an area of "known stuff" which, being known,
is perceived as simple, and an area of "unknown stuff" where you're no
idea what's going on. And the boundary between these two areas is
said "cutting edge of science". That's where things are tough, but
not quite impossible.
Exceptions occur during brief periods where suddenly a whole new area
opens for research. Then, for a while, there are more interesting
facts and ideas than people working on them and everyboy has a good
chance to lay his hands on somtehtin new and interesting. It is like
the historical situation of a new continent being opened for
exploration.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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