5,614 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 simple background-independent hamiltonian quantum model
We study formulation and probabilistic interpretation of a simple
general-relativistic hamiltonian quantum system. The system has no unitary
evolution in background time. The quantum theory yields transition
probabilities between measurable quantities (partial observables). These
converge to the classical predictions in the limit. Our main tool
is the kernel of the projector on the solutions of Wheeler-deWitt equation,
which we analyze in detail. It is a real quantity, which can be seen as a
propagator that propagates "forward" as well as "backward" in a local parameter
time. Individual quantum states, on the other hand, may contain only "forward
propagating" components. The analysis sheds some light on the interpretation of
background independent transition amplitudes in quantum gravity
Can appearance conversations explain differences between gay and heterosexual men's body dissatisfaction?
Men's body dissatisfaction is prevalent and a serious health concern as it is associated with negative outcomes including depression, disordered eating, and anabolic steroid abuse. Gay men are particularly vulnerable to body dissatisfaction, perhaps due to heightened sociocultural appearance pressures experienced in gay subculture. Appearance conversations represent an underresearched, but potentially potent, mechanism of appearance pressures. The current study explored whether differences in the frequency of engaging in appearance conversations accounted for differences in body dissatisfaction and associated risk factors among gay and heterosexual men. A purposeful sample of gay (N = 77, Mage = 32.57) and heterosexual (N = 78, Mage = 25.30) men were recruited from community organizations in the United Kingdom. Participants completed an online questionnaire assessing appearance conversations, body dissatisfaction, appearance orientation, and internalization of appearance ideals. Gay men reported more frequent engagement in positive and negative appearance conversations and greater body dissatisfaction, appearance orientation, and general internalization than heterosexual men. Moreover, frequency of appearance conversations mediated the relationship between sexuality and the majority of study variables, including body dissatisfaction (ps<.05). These findings suggest that appearance conversations are an important sociocultural influence on male body image and that they are important in understanding the differences between gay and heterosexual men's body dissatisfaction and associated risk factors. © 2013 American Psychological Association
Simplicial minisuperspace models in the presence of a massive scalar field with arbitrary scalar coupling
We extend previous simplicial minisuperspace models to account for arbitrary
scalar coupling \eta R\phi^2.Comment: 24 pages and 9 figures. Accepted for publication by Classical and
Quantum Gravit
Gauge invariance of parametrized systems and path integral quantization
Gauge invariance of systems whose Hamilton-Jacobi equation is separable is
improved by adding surface terms to the action fuctional. The general form of
these terms is given for some complete solutions of the Hamilton-Jacobi
equation. The procedure is applied to the relativistic particle and toy
universes, which are quantized by imposing canonical gauge conditions in the
path integral; in the case of empty models, we first quantize the parametrized
system called ``ideal clock'', and then we examine the possibility of obtaining
the amplitude for the minisuperspaces by matching them with the ideal clock.
The relation existing between the geometrical properties of the constraint
surface and the variables identifying the quantum states in the path integral
is discussed.Comment: 23 page
Spacetime states and covariant quantum theory
In it's usual presentation, classical mechanics appears to give time a very
special role. But it is well known that mechanics can be formulated so as to
treat the time variable on the same footing as the other variables in the
extended configuration space. Such covariant formulations are natural for
relativistic gravitational systems, where general covariance conflicts with the
notion of a preferred physical-time variable. The standard presentation of
quantum mechanics, in turns, gives again time a very special role, raising well
known difficulties for quantum gravity. Is there a covariant form of
(canonical) quantum mechanics? We observe that the preferred role of time in
quantum theory is the consequence of an idealization: that measurements are
instantaneous. Canonical quantum theory can be given a covariant form by
dropping this idealization. States prepared by non-instantaneous measurements
are described by "spacetime smeared states". The theory can be formulated in
terms of these states, without making any reference to a special time variable.
The quantum dynamics is expressed in terms of the propagator, an object
covariantly defined on the extended configuration space.Comment: 20 pages, no figures. Revision: minor corrections and references
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On the interpretation of time-reparametrization-invariant quantum mechanics
The classical and quantum dynamics of simple time-reparametrization-
invariant models containing two degrees of freedom are studied in detail.
Elimination of one ``clock'' variable through the Hamiltonian constraint leads
to a description of time evolution for the remaining variable which is
essentially equivalent to the standard quantum mechanics of an unconstrained
system. In contrast to a similar proposal of Rovelli, evolution is with respect
to the geometrical proper time, and the Heisenberg equation of motion is exact.
The possibility of a ``test clock'', which would reveal time evolution while
contributing negligibly to the Hamiltonian constraint is examined, and found to
be viable in the semiclassical limit of large quantum numbers.Comment: 13 pages, set in REVTeX. One figure available by FAX from
[email protected]
Consistent Histories in Quantum Cosmology
We illustrate the crucial role played by decoherence (consistency of quantum
histories) in extracting consistent quantum probabilities for alternative
histories in quantum cosmology. Specifically, within a Wheeler-DeWitt
quantization of a flat Friedmann-Robertson-Walker cosmological model sourced
with a free massless scalar field, we calculate the probability that the
univese is singular in the sense that it assumes zero volume. Classical
solutions of this model are a disjoint set of expanding and contracting
singular branches. A naive assessment of the behavior of quantum states which
are superpositions of expanding and contracting universes may suggest that a
"quantum bounce" is possible i.e. that the wave function of the universe may
remain peaked on a non-singular classical solution throughout its history.
However, a more careful consistent histories analysis shows that for arbitrary
states in the physical Hilbert space the probability of this Wheeler-DeWitt
quantum universe encountering the big bang/crunch singularity is equal to
unity. A quantum Wheeler-DeWitt universe is inevitably singular, and a "quantum
bounce" is thus not possible in these models.Comment: To appear in Foundations of Physics special issue on quantum
foundation
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
Oxygen-derived species: their relation to human disease and environmental stress.
Free radicals and other reactive oxygen species (ROS) are constantly formed in the human body, often for useful metabolic purposes. Antioxidant defenses protect against them, but these defenses are not completely adequate, and systems that repair damage by ROS are also necessary. Mild oxidative stress often induces antioxidant defense enzymes, but severe stress can cause oxidative damage to lipids, proteins, and DNA within cells, leading to such events as DNA strand breakage and disruption of calcium ion metabolism. Oxidative stress can result from exposure to toxic agents, and by the process of tissue injury itself. Ozone, oxides of nitrogen, and cigarette smoke can cause oxidative damage; but the molecular targets that they damage may not be the same
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