14,829 research outputs found
Thermodynamic properties and bulk viscosity near phase transition in the Z(2) and O(4) models
We investigate the thermodynamic properties including equation of state, the
trace anomaly, the sound velocity and the specific heat, as well as transport
properties like bulk viscosity in the Z(2) and O(4) models in the Hartree
approximation of Cornwall-Jackiw-Tomboulis (CJT) formalism. We study these
properties in different cases, e.g. first order phase transition, second order
phase transition, crossover and the case without phase transition, and discuss
the correlation between the bulk viscosity and the thermodynamic properties of
the system. We find that the bulk viscosity over entropy density ratio exhibits
an upward cusp at the second order phase transition, and a sharp peak at the
1st order phase transition. However, this peak becomes smooth or disappears in
the case of crossover. This indicates that at RHIC, where there is no real
phase transition and the system experiences a crossover, the bulk viscosity
over entropy density might be small, and it will not affect too much on
hadronization. We also suggest that the bulk viscosity over entropy density
ratio is a better quantity than the shear viscosity over entropy density ratio
to locate the critical endpoint.Comment: 19 pages, 30 figures, 1 tabl
Deduction of the quantum numbers of low-lying states of 6-nucleon systems based on symmetry
The inherent nodal structures of the wavefunctions of 6-nucleon systems have
been investigated. The existence of a group of six low-lying states dominated
by L=0 has been deduced. The spatial symmetries of these six states are found
to be mainly {4,2} and {2,2,2}.Comment: 8 pages, no figure
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Two-phase flow and oxygen transport in the perforated gas diffusion layer of proton exchange membrane fuel cell
Liquid water transport in perforated gas diffusion layers (GDLs)is numerically investigated using a three-dimensional (3D)two-phase volume of fluid (VOF)model and a stochastic reconstruction model of GDL microstructures. Different perforation depths and diameters are investigated, in comparison with the GDL without perforation. It is found that perforation can considerably reduce the liquid water level inside a GDL. The perforation diameter (D = 100 μm)and the depth (H = 100 μm)show pronounced effect. In addition, two different perforation locations, i.e. the GDL center and the liquid water break-through point, are investigated. Results show that the latter perforation location works more efficiently. Moreover, the perforation perimeter wettability is studied, and it is found that a hydrophilic region around the perforation further reduces the water saturation. Finally, the oxygen transport in the partially-saturated GDL is studied using an oxygen diffusion model. Results indicate that perforation reduces the oxygen diffusion resistance in GDLs and improves the oxygen concentration at the GDL bottom up to 101% (D = 100 μm and H = 100 μm)
Paper Session I-A - Advanced Liquid Feed Experiment (ALFE)
During the Advanced Spacecraft Feed System Study, conducted by the McDonnell Douglas Astronautics Company (MDAC) under contract to the Astronautics Laboratory - Air Force Systems Command (AL/AFSC), several key fluid system components were developed for potential application to a new generation of highly reliable, storable propellant spacecraft. These components demonstrated the capability to electronically control the pressurization schedule in the propellant feed tanks, to accurately gauge the available on board propellants, and to reliably track the propellant usage throughout the mission. In comparison with conventional mechanical regulators and capacitance type propellant gaging systems, they afford lower system cost and weight. When integrated with an attitude control system (ACS) tank designed for unlimited replenishment from main engine propellant tanks, overall system operatibility, on-orbit life, maintainability, and flexibility can be significantly enhanced
First excited band of a spinor Bose-Einstein condensate
The analytical expression of the fractional parentage coefficients for the
total spin-states of a spinor N-boson system has been derived. Thereby an
S-conserved theory for the spinor Bose-Einstein condensation has been proposed.
A set of equations has been established to describe the first excited band of
the condensates. Numerical solution for Na has been given as an example.Comment: 6 pages, 3 figure
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