7,483 research outputs found
A new facility to study three dimensional viscous flow and rotor-stator interaction in turbines
A description of the Axial Flow Turbine Research Facility (AFTRF) being built at the Turbomachinery Laboratory of the Pennsylvania State University is presented. The purpose of the research to be performed in this facility is to obtain a better understanding of the rotor/stator interaction, three dimensional viscous flow field in nozzle and rotor blade passages, spanwise mixing and losses in these blade rows, transport of wake through rotor passage, and unsteady aerodynamics and heat transfer of rotor blade row. The experimental results will directly feed and support the analytical and the computational tool development. This large scale low speed facility is heavily instrumented with pressure and temperature probes and has provision for flow visualization and laser Doppler anemometer measurement. The facility design permits extensive use of the high frequency response instrumentation on the stationary vanes and more importantly on the rotating blades. Furthermore it facilitates detailed nozzle wake, rotor wake, and boundary layer surveys. The large size of the rig also has the advantage of operating at Reynolds numbers representative of the engine environment
A Closed Contour of Integration in Regge Calculus
The analytic structure of the Regge action on a cone in dimensions over a
boundary of arbitrary topology is determined in simplicial minisuperspace. The
minisuperspace is defined by the assignment of a single internal edge length to
all 1-simplices emanating from the cone vertex, and a single boundary edge
length to all 1-simplices lying on the boundary. The Regge action is analyzed
in the space of complex edge lengths, and it is shown that there are three
finite branch points in this complex plane. A closed contour of integration
encircling the branch points is shown to yield a convergent real wave function.
This closed contour can be deformed to a steepest descent contour for all sizes
of the bounding universe. In general, the contour yields an oscillating wave
function for universes of size greater than a critical value which depends on
the topology of the bounding universe. For values less than the critical value
the wave function exhibits exponential behaviour. It is shown that the critical
value is positive for spherical topology in arbitrary dimensions. In three
dimensions we compute the critical value for a boundary universe of arbitrary
genus, while in four and five dimensions we study examples of product manifolds
and connected sums.Comment: 16 pages, Latex, To appear in Gen. Rel. Gra
Peroxisomes and Glyoxysomes Edited by R. Kindl and P.B. Lazarow Annals of the New York Academy of Sciences Vol. 386, New York Academy of Sciences; New York, 1982 xii + 550 pages. $102 (approx. £62)
Ionizing radiation damage to DNA: Molecular aspects Edited by S.S. Wallace and R.B. Painter; Wiley-Liss; New York, 1990; xx + 331 pages; $98
Advances in inflammation research, vol. 8 Edited by G. Weissman Raven Press; New York, 1984 xi + 251 pages. $61.50
Approximate Decoherence of Histories and 't Hooft's Deterministic Quantum Theory
This paper explores the possibility that an exactly decoherent set of
histories may be constructed from an approximately decoherent set by small
distortions of the operators characterizing the histories. In particular, for
the case of histories of positions and momenta, this is achieved by doubling
the set of operators and then finding, amongst this enlarged set, new position
and momentum operators which commute, so decohere exactly, and which are
``close'' to the original operators. The enlarged, exactly decoherent, theory
has the same classical dynamics as the original one, and coincides with the
so-called deterministic quantum theories of the type recently studied by 't
Hooft. These results suggest that the comparison of standard and deterministic
quantum theories may provide an alternative method of characterizing emergent
classicality. A side-product is the surprising result that histories of momenta
in the quantum Brownian motion model (for the free particle in the
high-temperature limit) are exactly decoherent.Comment: 41 pages, plain Te
Commuting Position and Momentum Operators, Exact Decoherence and Emergent Classicality
Inspired by an old idea of von Neumann, we seek a pair of commuting operators
X,P which are, in a specific sense, "close" to the canonical non-commuting
position and momentum operators, x,p. The construction of such operators is
related to the problem of finding complete sets of orthonormal phase space
localized states, a problem severely constrained by the Balian-Low theorem.
Here these constraints are avoided by restricting attention to situations in
which the density matrix is reasonably decohered (i.e., spread out in phase
space). Commuting position and momentum operators are argued to be of use in
discussions of emergent classicality from quantum mechanics. In particular,
they may be used to give a discussion of the relationship between exact and
approximate decoherence in the decoherent histories approach to quantum theory.Comment: 28 pages, RevTe
The role of the quantum properties of gravitational radiation in the dete ction of gravitational waves
The role that the quantum properties of a gravitational wave could play in
the detection of gravitational radiation is analyzed. It is not only
corroborated that in the current laser-interferometric detectors the resolution
of the experimental apparatus could lie very far from the corresponding quantum
threshold (thus the backreaction effect of the measuring device upon the
gravitational wave is negligible), but it is also suggested that the
consideration of the quantum properties of the wave could entail the definition
of dispersion of the measurement outputs. This dispersion would be a function
not only of the sensitivity of the measuring device, but also of the
interaction time (between measuring device and gravitational radiation) and of
the arm length of the corresponding laser- interferometer. It would have a
minimum limit, and the introduction of the current experimental parameters
insinuates that the dispersion of the existing proposals could lie very far
from this minimum, which means that they would show a very large dispersion.Comment: 19 pages, Latex (use epsfig.sty
Quantum cosmology with a curvature squared action
The correct quantum description for a curvature squared term in the action
can be obtained by casting the action in the canonical form with the
introduction of a variable which is the negative of the first derivative of the
field variable appearing in the action, only after removing the total
derivative terms from the action. We present the Wheeler-DeWitt equation and
obtain the expression for the probability density and current density from the
equation of continuity. Furthermore, in the weak energy limit we obtain the
classical Einstein equation. Finally we present a solution of the wave
equation.Comment: 8 pages, revte
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