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| bio | website | |
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| location | ||
| age | ||
| visits | member for | 2 years, 4 months |
| seen | Apr 13 at 15:08 | |
| stats | profile views | 42 |
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Jun 22 |
comment |
Energy efficiency of antimatter producion Also, even if you could get antimatter stored in considerable quantities, with efficiency close to 1 (not bigger). What would you do with it? Eletron-positron pairs anihilate into 500 keV gamma rays, which is very bad for propulsion. Photons this hard can´t just be reflected for push. You would have to find materials that would absorb and thermalize them, and then eject these. I don't think this is much better than what we already do, at much higher costs. |
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Jun 22 |
accepted | Imaginary pertubation to a Hamiltonian: how is it the same as rotation to imaginary time? |
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Jun 21 |
comment |
Imaginary pertubation to a Hamiltonian: how is it the same as rotation to imaginary time? (...) he uses exactly this substitution to get $Z[J]$. Of course, the potential for a free scalar field is proportional to $q^2$, but wouldn't adding the whole $i\epsilon H$ mess up the momentum integral you need to get from the hamiltonian to the lagrangean? The bothering point here is that this $i \epsilon$ factor will be the one (on page 185) dictating the path of integration to get the propagator. |
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Jun 21 |
comment |
Imaginary pertubation to a Hamiltonian: how is it the same as rotation to imaginary time? Yes, I noticed it would be far simpler to add $i \epsilon H$ but, when the author goes on to quantizing a scalar field (page 182) |
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Jun 21 |
awarded | Critic |
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Jun 21 |
accepted | What is the relation between (physicists) functional derivatives and Fréchet derivatives |
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Jun 20 |
asked | Imaginary pertubation to a Hamiltonian: how is it the same as rotation to imaginary time? |
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Jun 19 |
comment |
What is the relation between (physicists) functional derivatives and Fréchet derivatives That´s exactly my problem with this definition (Dirac delta subtleties apart). It seems your are defining the partial derivative in the specific direction of $\delta_y$, but this very definition is used everywhere as the partial derivative in any direction (are they all the same?). Another way of expressing my problem: is the first equality below valid? Why? (I tried to follow your notation, $f_y$ means f calculated at point $y$): $$ \frac{\delta F}{\delta (f_y)}[f] = \frac{\delta F}{\delta (\delta_y)}[f] = \lim_{\epsilon \to 0} \frac{1}{\epsilon} ( F[f + \epsilon \delta_y] - F[f]). $$ |
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Jun 19 |
awarded | Editor |
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Jun 19 |
revised |
What is the relation between (physicists) functional derivatives and Fréchet derivatives Corrected Spelling |
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Jun 19 |
awarded | Supporter |
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Jun 19 |
answered | Why does paper become transparent when smeared with oil but not (so much) with water? |
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Jun 19 |
awarded | Teacher |
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Jun 19 |
answered | Why is paper more frangible when it is wet? |
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Jun 18 |
asked | What is the relation between (physicists) functional derivatives and Fréchet derivatives |
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Jan 21 |
awarded | Student |
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Jan 21 |
awarded | Scholar |
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Jan 21 |
accepted | Understanding boundary conditions on slices of AdS5 |
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Jan 21 |
asked | Understanding boundary conditions on slices of AdS5 |
