2,397 research outputs found
SSME structural dynamic model development
A mathematical model of the Space Shuttle Main Engine (SSME) as a complete assembly, with detailed emphasis on LOX and High Fuel Turbopumps is developed. The advantages of both complete engine dynamics, and high fidelity modeling are incorporated. Development of this model, some results, and projected applications are discussed
Conditions for one-dimensional supersonic flow of quantum gases
One can use transsonic Bose-Einstein condensates of alkali atoms to establish
the laboratory analog of the event horizon and to measure the acoustic version
of Hawking radiation. We determine the conditions for supersonic flow and the
Hawking temperature for realistic condensates on waveguides where an external
potential plays the role of a supersonic nozzle. The transition to supersonic
speed occurs at the potential maximum and the Hawking temperature is entirely
determined by the curvature of the potential
Critical properties and Bose Einstein Condensation in dimer spin systems
We analyze the spin relaxation time for a system made of weakly
coupled one dimensional ladders.This system allows to probe the dimensional
crossover between a Luttinger liquid and a Bose-Einstein condensateof magnons.
We obtain the temperature dependence of in the various dimensional
regimes, and discuss the experimental consequences.Comment: 4 pages, RevTeX 4, 3 EPS figure
Spin picture of the one-dimensional Hubbard model: Two-fluid structure and phase dynamics
We propose a scheme for investigating the quantum dynamics of interacting
electron models by means of time-dependent variational principle and spin
coherent states of space lattice operators. We apply such a scheme to the
one-dimensional hubbard model, and solve the resulting equations in different
regimes. In particular, we find that at low densities the dynamics is mapped
into two coupled nonlinear Schroedinger equations, whereas near half-filling
the model is described by two coupled Josephson junction arrays. Focusing then
to the case in which only the phases of the spin variables are dynamically
active, we examine a number of different solutions corresponding to the
excitations of few macroscopic modes. Based on fixed point equation of the
simpler among them, we show that the standard one-band ground state phase space
is found.Comment: 10 pages, 1 figure, to appear on Phys. Rev.
New Young Star Candidates in BRC 27 and BRC 34
We used archival Spitzer Space Telescope mid-infrared data to search for
young stellar objects (YSOs) in the immediate vicinity of two bright-rimmed
clouds, BRC 27 (part of CMa R1) and BRC 34 (part of the IC 1396 complex). These
regions both appear to be actively forming young stars, perhaps triggered by
the proximate OB stars. In BRC 27, we find clear infrared excesses around 22 of
the 26 YSOs or YSO candidates identified in the literature, and identify 16 new
YSO candidates that appear to have IR excesses. In BRC 34, the one
literature-identified YSO has an IR excess, and we suggest 13 new YSO
candidates in this region, including a new Class I object. Considering the
entire ensemble, both BRCs are likely of comparable ages, within the
uncertainties of small number statistics and without spectroscopy to confirm or
refute the YSO candidates. Similarly, no clear conclusions can yet be drawn
about any possible age gradients that may be present across the BRCs.Comment: 54 pages, 19 figures, accepted by A
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