582 research outputs found
Influence of impeller and diffuser geometries on the lateral fluid forces of whirling centrifugal impeller
Lateral fluid forces on two-dimensional centrifugal impellers, which whirl on a circular orbit in a vaneless diffuser, were reported. Experiments were further conducted for the cases in which a three-dimensional centrifugal impeller, a model of the boiler feed pump, whirls in vaneless and vaned diffusers. The influence of the clearance configuration between the casing and front shroud of the impeller was also investigated. The result indicated that the fluid dynamic interaction between the impeller and the guide vanes induces quite strong fluctuating fluid forces to the impeller, but nevertheless its influence on radial and tangential force components averaged over a whirling orbit is relatively small
Superfluid Fermi atomic gas as a quantum simulator for the study of neutron-star equation of state
We theoretically propose an idea to use an ultracold Fermi gas as a quantum
simulator for the study of the neutron-star equation of state (EoS) in the
low-density region. Our idea is different from the standard quantum simulator
that heads for {\it perfect} replication of another system, such as a Hubbard
model discussed in high- cuprates. Instead, we use the {\it
similarity} between two systems, and theoretically make up for the difference
between them. That is, (1) we first show that the strong-coupling theory
developed by Nozi\`eres-Schmitt Rink (NSR) can quantitatively explain the
recent EoS experiment on a Li superfluid Fermi gas in the BCS
(Bardeen-Cooper-Schrieffer)-unitary limit far below the superfluid phase
transition temperature . This region is considered to be very
similar to the low density region (crust regime) of a neutron star (where a
nearly unitary -wave neutron superfluid is expected). (2) We then
theoretically compensate the difference that, while the effective range is negligibly small in a superfluid Li Fermi gas, it cannot be
ignored ( fm) in a neutron star, by extending the NSR theory
to include effects of . The calculated EoS when
fm is shown to agree well with the previous neutron-star EoS in the low density
region predicted in nuclear physics. Our idea indicates that an ultracold
atomic gas may more flexibly be used as a quantum simulator for the study of
other complicated quantum many-body systems, when we use, not only the
experimental high tunability, but also the recent theoretical development in
this field. Since it is difficult to directly observe a neutron-star interior,
our idea would provide a useful approach to the exploration for this mysterious
astronomical object.Comment: 29 pages, 7 figure
Multipole particle in relativity
We discuss the motion of extended objects in a spacetime by considering a
gravitational field created by these objects. We define multipole moments of
the objects as a classification by Lie group SO(3). Then, we construct an
energy-momentum tensor for the objects and derive equations of motion from it.
As a result, we reproduce the Papapetrou equations for a spinning particle.
Furthermore, we will show that we can obtain more simple equations than the
Papapetrou equations by changing the center-of-mass.Comment: 22 pages, 2 figures. Accepted for publication in Phys. Rev.
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