24,798 research outputs found
Spectra and binding energy predictions of chiral interactions for 7Li
Using the no-core shell model approach, we report on the first results for
7Li based on the next-to-next-to-leading order chiral nuclear interaction.
Both, two-nucleon and three-nucleon interactions are taken into account. We
show that the p-shell nuclei are sensitive to the subleading parts of the
chiral interactions including three-nucleon forces. Though chiral interactions
are soft, we do not observe overbinding for this p-shell nucleus and find a
realistic description for the binding energy, excitation spectrum and radius.Comment: 12 pages, 12 figure
Design and application of squeeze film dampers for turbomachinery stabilization
The steady-state transient response of the squeeze film damper bearing was investigated. Both the steady-state and transient equations for the hydrodynamic bearing forces are derived; the steady-state equations were used to determine the damper equivalent stiffness and damping coefficients. These coefficients are used to find the damper configuration which will provide the optimum support characteristics based on a stability analysis of the rotor-bearing system. The effects of end seals and cavitated fluid film are included. The transient analysis of rotor-bearing systems was conducted by coupling the damping and rotor equations and integrating forward in time. The effects of unbalance, cavitation, and retainer springs are included. Methods of determining the stability of a rotor-bearing system under the influence of aerodynamic forces and internal shaft friction are discussed
An algebraic interpretation of the Wheeler-DeWitt equation
We make a direct connection between the construction of three dimensional
topological state sums from tensor categories and three dimensional quantum
gravity by noting that the discrete version of the Wheeler-DeWitt equation is
exactly the pentagon for the associator of the tensor category, the
Biedenharn-Elliott identity. A crucial role is played by an asymptotic formula
relating 6j-symbols to rotation matrices given by Edmonds.Comment: 10 pages, amstex, uses epsf.tex. New version has improved
presentatio
Asymptotics of 10j symbols
The Riemannian 10j symbols are spin networks that assign an amplitude to each
4-simplex in the Barrett-Crane model of Riemannian quantum gravity. This
amplitude is a function of the areas of the 10 faces of the 4-simplex, and
Barrett and Williams have shown that one contribution to its asymptotics comes
from the Regge action for all non-degenerate 4-simplices with the specified
face areas. However, we show numerically that the dominant contribution comes
from degenerate 4-simplices. As a consequence, one can compute the asymptotics
of the Riemannian 10j symbols by evaluating a `degenerate spin network', where
the rotation group SO(4) is replaced by the Euclidean group of isometries of
R^3. We conjecture formulas for the asymptotics of a large class of Riemannian
and Lorentzian spin networks in terms of these degenerate spin networks, and
check these formulas in some special cases. Among other things, this conjecture
implies that the Lorentzian 10j symbols are asymptotic to 1/16 times the
Riemannian ones.Comment: 25 pages LaTeX with 8 encapsulated Postscript figures. v2 has various
clarifications and better page breaks. v3 is the final version, to appear in
Classical and Quantum Gravity, and has a few minor corrections and additional
reference
Kleinian Geometry and the N=2 Superstring
This paper is devoted to the exploration of some of the geometrical issues
raised by the superstring. We begin by reviewing the reasons that
-functions for the superstring require it to live in a
four-dimensional self-dual spacetime of signature , together with some
of the arguments as to why the only degree of freedom in the theory is that
described by the gravitational field. We then move on to describe at length the
geometry of flat space, and how a real version of twistor theory is relevant to
it. We then describe some of the more complicated spacetimes that satisfy the
-function equations. Finally we speculate on the deeper significance of
some of these spacetimes.Comment: 30 pages, AMS-Te
From non-Hermitian effective operators to large-scale no-core shell model calculations for light nuclei
No-core shell model (NCSM) calculations using ab initio effective
interactions are very successful in reproducing experimental nuclear spectra.
The main theoretical approach is the use of effective operators, which include
correlations left out by the truncation of the model space to a numerically
tractable size. We review recent applications of the effective operator
approach, within a NCSM framework, to the renormalization of the
nucleon-nucleon interaction, as well as scalar and tensor operators.Comment: To be submited to J. Phys. A, special issue on "The Physics of
Non-Hermitian Operators
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