10,381 research outputs found
Poincar\'{e} gauge theory of gravity
A Poincar\'{e} gauge theory of (2+1)-dimensional gravity is developed.
Fundamental gravitational field variables are dreibein fields and Lorentz gauge
potentials, and the theory is underlain with the Riemann-Cartan space-time. The
most general gravitational Lagrangian density, which is at most quadratic in
curvature and torsion tensors and invariant under local Lorentz transformations
and under general coordinate transformations, is given. Gravitational field
equations are studied in detail, and solutions of the equations for weak
gravitational fields are examined for the case with a static, \lq \lq spin"less
point like source. We find, among other things, the following: (1)Solutions of
the vacuum Einstein equation satisfy gravitational field equations in the
vacuum in this theory. (2)For a class of the parameters in the gravitational
Lagrangian density, the torsion is \lq \lq frozen" at the place where \lq \lq
spin" density of the source field is not vanishing. In this case, the field
equation actually agrees with the Einstein equation, when the source field is
\lq \lq spin"less. (3)A teleparallel theory developed in a previous paper is
\lq \lq included as a solution" in a limiting case. (4)A Newtonian limit is
obtainable, if the parameters in the Lagrangian density satisfy certain
conditions.Comment: 27pages, RevTeX, OCU-PHYS-15
Asymmetric Non-Abelian Orbifolds and Model Building
The rules for the free fermionic string model construction are extended to
include general non-abelian orbifold constructions that go beyond the real
fermionic approach. This generalization is also applied to the asymmetric
orbifold rules recently introduced. These non-abelian orbifold rules are quite
easy to use. Examples are given to illustrate their applications.Comment: 30 pages, Revtex 3.
Analysis of dynamic characteristics of fluid force induced by labyrinth seal
Flow patterns of the labyrinth seal are experimentally investigated for making a mathematical model of labyrinth seal and to obtain the flow induced force of the seal. First, the flow patterns in the labyrinth chamber are studied on the circumferential flow using bubble and on the cross section of the seal chamber using aluminum powder as tracers. And next, the fluid force and its phase angle are obtained from the measured pressure distribution in the chamber and the fluid force coefficients are derived from the fluid force and the phase angle. Those are similar to the expression of oil film coefficients. As a result, it is found that the vortices exist in the labyrinth chambers and its center moves up and down periodically. The pressure drop is biggest in the first stage of chambers and next in the last stage of chambers
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