4,743 research outputs found
Lateral fluid forces acting on a whirling centrifugal impeller in vaneless and vaned diffuser
Fluid forces on a rotating centrifugal impeller in whirling motion were studied. A two dimensional impeller installed in a parallel-walled vaneless and vaned diffuser whirled on a circular orbit with various positive and negative angular velocities. It is shown that the fluid forces exert a damping effect on the rotor in most operating conditions, but become excitatory when the impeller operates at very low partial discharge while rotating far faster than the whirl speed. The fluid forces were expressed in terms of mass, damping and stiffness matrices. Impellers with the same geometry and whirl condition are calculated. Quantitative agreement is obtained especially in positive whirl
Prandtl number of lattice Bhatnagar-Gross-Krook fluid
The lattice Bhatnagar-Gross-Krook modeled fluid has an unchangeable unit
Prandtl number. A simple method is introduced in this letter to formulate a
flexible Prandtl number for the modeled fluid. The effectiveness was
demonstrated by numerical simulations of the Couette flow.Comment: 4 pages, uuencoded postscript fil
Itinerant-localized dual character of a strongly-correlated superfluid Bose gas in an optical lattice
We investigate a strongly-correlated Bose gas in an optical lattice.
Extending the standard-basis operator method developed by Haley and Erdos to a
boson Hubbard model, we calculate excitation spectra in the superfluid phase,
as well as in the Mott insulating phase, at T=0. In the Mott phase, the
excitation spectrum has a finite energy gap, reflecting the localized character
of atoms. In the superfluid phase, the excitation spectrum is shown to have an
itinerant-localized dual structure, where the gapless Bogoliubov mode (which
describes the itinerant character of superfluid atoms) and a band with a finite
energy gap coexist. We also show that the rf-tunneling current measurement
would give a useful information about the duality of a strongly-correlated
superfluid Bose gas near the superfluid-insulator transition.Comment: 10 pages, 4 figure
Magnetic response of nonmagnetic impurities in cuprates
A theory of the local magnetic response of a nonmagnetic impurity in a doped
antiferromagnet, as relevant to the normal state in cuprates, is presented. It
is based on the assumption of the overdamped collective mode in the bulk system
and on the evidence, that equal-time spin correlations are only weakly
renormalized in the vicinity of the impurity. The theory relates the Kondo-like
behavior of the local susceptibility to the anomalous temperature dependence of
the bulk magnetic susceptibility, where the observed increase of the Kondo
temperature with doping reflects the crossover to the Fermi liquid regime and
the spatial distribution of the magnetization is given by bulk
antiferromagnetic correlations.Comment: 5 pages, 3 figure
Detection of an X-Ray Hot Region in the Virgo Cluster of Galaxies with ASCA
Based on mapping observations with ASCA, an unusual hot region with a spatial
extent of 1 square degree was discovered between M87 and M49 at a center
coordinate of R. A. = 12h 27m 36s and Dec. = (J2000). The X-ray
emission from the region has a 2-10 keV flux of ergs
s cm and a temperature of keV, which is
significantly higher than that in the surrounding medium of keV. The
internal thermal energy in the hot region is estimated to be ergs with a gas density of cm. A power-law
spectrum with a photon index is also allowed by the data. The hot
region suggests there is an energy input due to a shock which is probably
caused by the motion of the gas associated with M49, infalling toward the M87
cluster with a velocity km s.Comment: 12 pages, 3 figures, accepted to ApJ
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