28,315 research outputs found
Axial instability of rotating relativistic stars
Perturbations of rotating relativistic stars can be classified by their
behavior under parity. For axial perturbations (r-modes), initial data with
negative canonical energy is found with angular dependence for all
values of and for arbitrarily slow rotation. This implies instability
(or marginal stability) of such perturbations for rotating perfect fluids. This
low -instability is strikingly different from the instability to polar
perturbations, which sets in first for large values of . The timescale for
the axial instability appears, for small angular velocity , to be
proportional to a high power of . As in the case of polar modes,
viscosity will again presumably enforce stability except for hot, rapidly
rotating neutron stars. This work complements Andersson's numerical
investigation of axial modes in slowly rotating stars.Comment: Latex, 18 pages. Equations 84 and 85 are corrected. Discussion of
timescales is corrected and update
Calculation of compressible flow about three-dimensional inlets with auxiliary inlets, slats and vanes by means of a panel method
An efficient and user oriented method was constructed for calculating flow in and about complex inlet configurations. Efficiency is attained by: (1) the use of a panel method; (2) a technique of superposition for obtaining solutions at any inlet operating condition; and (3) employment of an advanced matrix iteration technique for solving large full systems of equations, including the nonlinear equations for the Kutta condition. User concerns are addressed by the provision of several novel graphical output options that yield a more complete comprehension of the flowfield than was possible previously
Ferromagnetism of He Films in the Low Field Limit
We provide evidence for a finite temperature ferromagnetic transition in
2-dimensions as in thin films of He on graphite, a model system
for the study of two-dimensional magnetism. We perform pulsed and CW NMR
experiments at fields of 0.03 - 0.48 mT on He at areal densities of 20.5 -
24.2 atoms/nm. At these densities, the second layer of He has a
strongly ferromagnetic tendency. With decreasing temperature, we find a rapid
onset of magnetization that becomes independent of the applied field at
temperatures in the vicinity of 1 mK. Both the dipolar field and the NMR
linewidth grow rapidly as well, which is consistent with a large (order unity)
polarization of the He spins.Comment: 4 figure
Nuclear Multifragmentation Critical Exponents
We show that the critical exponents of nuclear multi-fragmentation have not
been determined conclusively yet.Comment: 3 pages, LaTeX, one postscript figure appended, sub. to
Phys.Rev.Lett. as a commen
Classical simulation of quantum many-body systems with a tree tensor network
We show how to efficiently simulate a quantum many-body system with tree
structure when its entanglement is bounded for any bipartite split along an
edge of the tree. This is achieved by expanding the {\em time-evolving block
decimation} simulation algorithm for time evolution from a one dimensional
lattice to a tree graph, while replacing a {\em matrix product state} with a
{\em tree tensor network}. As an application, we show that any one-way quantum
computation on a tree graph can be efficiently simulated with a classical
computer.Comment: 4 pages,7 figure
Persistent current in superconducting nanorings
The superconductivity in very thin rings is suppressed by quantum phase
slips. As a result the amplitude of the persistent current oscillations with
flux becomes exponentially small, and their shape changes from sawtooth to a
sinusoidal one. We reduce the problem of low-energy properties of a
superconducting nanoring to that of a quantum particle in a sinusoidal
potential and show that the dependence of the current on the flux belongs to a
one-parameter family of functions obtained by solving the respective
Schrodinger equation with twisted boundary conditions.Comment: 5 pages, 1 figur
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