9,035 research outputs found
Harmonically Trapped Quantum Gases
We solve the problem of a Bose or Fermi gas in -dimensions trapped by mutually perpendicular harmonic oscillator potentials. From the
grand potential we derive their thermodynamic functions (internal energy,
specific heat, etc.) as well as a generalized density of states. The Bose gas
exhibits Bose-Einstein condensation at a nonzero critical temperature
if and only if , and a jump in the specific heat at if and
only if . Specific heats for both gas types precisely coincide as
functions of temperature when . The trapped system behaves like an
ideal free quantum gas in dimensions. For we recover
all known thermodynamic properties of ideal quantum gases in dimensions,
while in 3D for 1, 2 and 3 one simulates behavior reminiscent of
quantum {\it wells, wires}and{\it dots}, respectively.Comment: 14 pages including 3 figures and 3 table
Cooper pairs as bosons
Although BCS pairs of fermions are known not to obey Bose-Einstein (BE)
commutation relations nor BE statistics, we show how Cooper pairs (CPs),
whether the simple original ones or the CPs recently generalized in a many-body
Bethe-Salpeter approach, being clearly distinct from BCS pairs at least obey BE
statistics. Hence, contrary to widespread popular belief, CPs can undergo BE
condensation to account for superconductivity if charged, as well as for
neutral-atom fermion superfluidity where CPs, but uncharged, are also expected
to form.Comment: 8 pages, 2 figures, full biblio info adde
Flavour constraints on scenarios with two or three heavy squark generations
We re-assess constraints from flavour-changing neutral currents in the kaon
system on supersymmetric scenarios with a light gluino, two heavy generations
of squarks and a lighter third generation. We compute for the first time limits
in scenarios with three heavy squark families, taking into account QCD
corrections at the next-to-leading order. We compare our limits with those in
the case of two heavy families. We use the mass insertion approximation and
consider contributions from gluino exchange to constrain the mixing between the
first and second squark generation. While it is not possible to perform a
general analysis, we assess the relevance of each kind of flavour- and
CP-violating parameters. We also provide ready to use magic numbers for the
computation of the Wilson coefficients at 2 GeV for these scenarios.Comment: 23 pages, 14 figures; v3: matches published version (contains
improvements in the presentation and clarifications
Real time phase-slopes calculations by correlations using FPGAs
J. Trujillo Sevilla ; M. R. Valido ; L. F. RodrĂguez Ramos ; E. Boemo ; F. Rosa ; J. M. RodrĂguez Ramos, “Real time phase-slopes calculations by correlations using FPGAs,” Proc. SPIE 7015, Adaptive Optics Systems, 70153B (July 11, 2008), Norbert Hubin; Claire E. Max; Peter L. Wizinowich
, 7015 (Issue) 70153B, (2008). Copyright © 2008 SPIE Society of Photo‑Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.ELT laser guide star wavefront sensors are planned to handle an expected amount of data to be overwhelmingly large
(1600x1600 pixels at 700 fps). According to the calculations involved, the solutions must consider to run on specialized
hardware as Graphical Processing Units (GPUs) or Field Programmable Gate Arrays (FPGAs), among others.
In the case of a Shack-Hartmann wavefront sensor is finally selected, the wavefront slopes can be computed using
centroid or correlation algorithms. Most of the developments are designed using centroid algorithms, but precision ought
to be taken in account too, and then correlation algorithms are really competitive.
This paper presents an FPGA-based wavefront slope implementation, capable of handling the sensor output stream in a
massively parallel approach, using a correlation algorithm previously tested and compared to the centroid algorithm.
Time processing results are shown, and they demonstrate the ability of the FPGA integer arithmetic in the resolution of
AO problems.
The selected architecture is based in today’s commercially available FPGAs which have a very limited amount of
internal memory. This limits the dimensions used in our implementation, but this also means that there is a lot of margin
to move real-time algorithms from the conventionalThis work has been partially supported by “Programa Nacional de Diseño y Producción Industrial" (Project DPI 2006-
07906) of the “Ministerio de Educación y Ciencia" of the Spanish Government, and by “European Regional
Development Fund" (ERDF)
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