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visits member for 1 year, 9 months
seen Jul 7 '13 at 22:47

Feb
2
answered Instrumentation handbook
Jan
27
comment Travel direction of lightning
that's one of my favorite youtube videos.
Jan
26
comment Have we managed to make a perfect vacuum?
@user44430, UHV is mostly limited by H2, not N2 or O2. This is because (1) most pumps (turbopumps, ion pumps, etc.) preferentially pumps heavier molecules and (2) the hydrogen load is from the walls of the vacuum chamber. Air leaking into a vacuum chamber is negligible in most systems.
Jan
26
comment Have we managed to make a perfect vacuum?
In most UHV (ultra high vacuum) systems, including mine, the main component is by far hydrogen molecules (H2). They're light and very difficult to pump out. For that reason, many pumps in the UHV range focus solely on pumping hydrogen (e.g., titanium sublimation or non-evaporable getters).
Jan
21
answered Non-destructive measurement of qbits
Jan
21
comment What can the D-Wave quantum computer do?
@Lagerbaer: I think D-wave has a fantastic PR department, for exactly the same reason. They make a lot of incorrect claims and hype their system, which is exactly what a PR department is supposed to do. As a scientist, I find the whole thing highly disturbing.
Jan
20
comment Temperature in space
Temperature is NOT a measure of kinetic energy. It is a measure of how much energy is required to change the energy of a system. Truth be told, temperature can be somewhat subtle in many situations, as the answers clearly demonstrate in this one.
Jan
20
answered How were the crystal lattices of elements determined to perfection ? (Ex:- That of a copper is a cubic lattice )
Jan
13
comment Can all quantum superpositions be realized experimentally?
Beware of question like, "Can ... be realized experimentally?" Do you mean that, theoretically, can an experiment realize it? I would argue that's not the same as, "Can an experiment realize ..."? (More below on my answer.)
Jan
13
comment Rutherford's Gold Foil Experiment
As the older professors say: things are easy for us youngin' grad students. I can go to dinner while I acquire data, unlike poor Marsden and Geiger.
Jan
13
revised Can all quantum superpositions be realized experimentally?
added 512 characters in body
Jan
13
answered Can all quantum superpositions be realized experimentally?
Jan
12
comment Does a quantum phase transition have latent heat?
Some do, some don't. Just like classical phase transitions, quantum ones can be first order (with latent heat) or second order (without) -- or something else. Most of the traditional examples that leap to my mind are second order.
Jan
12
comment Why are so many forces explainable using inverse squares when space is three dimensional?
Feynman had an interesting comment: nature tends to be described by laws that can be understood or mathematically expressed in qualitatively different ways. Take a look at Ch. 8 of lecture 2 of the Messenger Series (research.microsoft.com/apps/tools/tuva/#data=3|||).
Jan
12
comment Alkali atom in oscilating electromagnetic field
The rotating wave approximation can be confusing. I originally learned it in the context of a spin-1/2 particle in a magnetic field, where the coordinates of the spin and real space match. It's a little more confusing in general problems, where the real space and spin space coordinate systems are nontrivially related.
Jan
11
awarded  Nice Answer
Jan
11
revised Alkali atom in oscilating electromagnetic field
added 181 characters in body
Jan
11
answered Alkali atom in oscilating electromagnetic field
Jan
11
answered Why is a critical system equal to a gapless system?
Jan
9
comment Where does energy for high and low tides come from?
This is why we always see the same face of the moon: there are no longer tides on the moon. Tidal forces lead to friction, which locks the precessional and rotational rates.