12,034 research outputs found
Wash water recovery system
The Wash Water Recovery System (WWRS) is intended for use in processing shower bath water onboard a spacecraft. The WWRS utilizes flash evaporation, vapor compression, and pyrolytic reaction to process the wash water to allow recovery of potable water. Wash water flashing and foaming characteristics, are evaluated physical properties, of concentrated wash water are determined, and a long term feasibility study on the system is performed. In addition, a computer analysis of the system and a detail design of a 10 lb/hr vortex-type water vapor compressor were completed. The computer analysis also sized remaining system components on the basis of the new vortex compressor design
Phase separation in the bosonic Hubbard model with ring exchange
We show that soft core bosons in two dimensions with a ring exchange term
exhibit a tendency for phase separation. This observation suggests that the
thermodynamic stability of normal bose liquid phases driven by ring exchange
should be carefully examined.Comment: 4 pages, 6 figure
The Stochastic Green Function (SGF) algorithm
We present the Stochastic Green Function (SGF) algorithm designed for bosons
on lattices. This new quantum Monte Carlo algorithm is independent of the
dimension of the system, works in continuous imaginary time, and is exact (no
error beyond statistical errors). Hamiltonians with several species of bosons
(and one-dimensional Bose-Fermi Hamiltonians) can be easily simulated. Some
important features of the algorithm are that it works in the canonical ensemble
and gives access to n-body Green functions.Comment: 12 pages, 5 figure
Giant anharmonicity suppresses superconductivity in AlH under pressure
The anharmonic self energy of two zone boundary phonons were computed to
lowest order for AlH in the structure at 110 GPa. The
wavevector and branch index corresponding to these modes are situated in a
region of phase space providing most of the electron-phonon coupling. The self
energies are found to be very large and the anharmonic contribution to the
linewidth of one of the modes studied could be distinguished from the
electron-phonon linewidth. It is found that anharmonicity suppresses the
electron-phonon coupling parameter , providing a possible explanation
for the disagreement between experiment and previous theoretical studies of
superconductivity in this system.Comment: 10 pages, 4 figure
Quantum phases of mixtures of atoms and molecules on optical lattices
We investigate the phase diagram of a two-species Bose-Hubbard model
including a conversion term, by which two particles from the first species can
be converted into one particle of the second species, and vice-versa. The model
can be related to ultra-cold atom experiments in which a Feshbach resonance
produces long-lived bound states viewed as diatomic molecules. The model is
solved exactly by means of Quantum Monte Carlo simulations. We show than an
"inversion of population" occurs, depending on the parameters, where the second
species becomes more numerous than the first species. The model also exhibits
an exotic incompressible "Super-Mott" phase where the particles from both
species can flow with signs of superfluidity, but without global supercurrent.
We present two phase diagrams, one in the (chemical potential, conversion)
plane, the other in the (chemical potential, detuning) plane.Comment: 7 pages, 10 figure
Ring Exchange and Phase Separation in the Two-dimensional Boson Hubbard model
We present Quantum Monte Carlo simulations of the soft-core bosonic Hubbard
model with a ring exchange term K. For values of K which exceed roughly half
the on-site repulsion U, the density is a non-monotonic function of the
chemical potential, indicating that the system has a tendency to phase
separate. This behavior is confirmed by an examination of the density-density
structure factor and real space images of the boson configurations. Adding a
near-neighbor repulsion can compete with phase separation, but still does not
give rise to a stable normal Bose liquid.Comment: 12 pages, 23 figure
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