10,735 research outputs found
Development of a prototype automatic controller for liquid cooling garment inlet temperature
The development of a computer control of a liquid cooled garment (LCG) inlet temperature is descirbed. An adaptive model of the LCG is used to predict the heat-removal rates for various inlet temperatures. An experimental system that contains a microcomputer was constructed. The LCG inlet and outlet temperatures and the heat exchanger outlet temperature form the inputs to the computer. The adaptive model prediction method of control is successful during tests where the inlet temperature is automatically chosen by the computer. It is concluded that the program can be implemented in a microprocessor of a size that is practical for a life support back-pack
Velocity field distributions due to ideal line vortices
We evaluate numerically the velocity field distributions produced by a
bounded, two-dimensional fluid model consisting of a collection of parallel
ideal line vortices. We sample at many spatial points inside a rigid circular
boundary. We focus on ``nearest neighbor'' contributions that result from
vortices that fall (randomly) very close to the spatial points where the
velocity is being sampled. We confirm that these events lead to a non-Gaussian
high-velocity ``tail'' on an otherwise Gaussian distribution function for the
Eulerian velocity field. We also investigate the behavior of distributions that
do not have equilibrium mean-field probability distributions that are uniform
inside the circle, but instead correspond to both higher and lower mean-field
energies than those associated with the uniform vorticity distribution. We find
substantial differences between these and the uniform case.Comment: 21 pages, 9 figures. To be published in Physical Review E
(http://pre.aps.org/) in May 200
Hyperk\"ahler Arnold Conjecture and its Generalizations
We generalize and refine the hyperk\"ahler Arnold conjecture, which was
originally established, in the non-degenerate case, for three-dimensional time
by Hohloch, Noetzel and Salamon by means of hyperk\"ahler Floer theory. In
particular, we prove the conjecture in the case where the time manifold is a
multidimensional torus and also establish the degenerate version of the
conjecture. Our method relies on Morse theory for generating functions and a
finite-dimensional reduction along the lines of the Conley-Zehnder proof of the
Arnold conjecture for the torus.Comment: 13 page
A Bayesian approach to the estimation of maps between riemannian manifolds
Let \Theta be a smooth compact oriented manifold without boundary, embedded
in a euclidean space and let \gamma be a smooth map \Theta into a riemannian
manifold \Lambda. An unknown state \theta \in \Theta is observed via
X=\theta+\epsilon \xi where \epsilon>0 is a small parameter and \xi is a white
Gaussian noise. For a given smooth prior on \Theta and smooth estimator g of
the map \gamma we derive a second-order asymptotic expansion for the related
Bayesian risk. The calculation involves the geometry of the underlying spaces
\Theta and \Lambda, in particular, the integration-by-parts formula. Using this
result, a second-order minimax estimator of \gamma is found based on the modern
theory of harmonic maps and hypo-elliptic differential operators.Comment: 20 pages, no figures published version includes correction to eq.s
31, 41, 4
Bearing tester data compilation, analysis and reporting and bearing math modeling, volume 1
Thermal and mechanical models of high speed angular contact ball bearings operating in LOX and LN2 were developed and verified with limited test data in an effort to further understand the parameters that determine or effect the SSME turbopump bearing operational characteristics and service life. The SHABERTH bearing analysis program which was adapted to evaluate shaft bearing systems in cryogenics is not capable of accommodating varying thermal properties and two phase flow. A bearing model with this capability was developed using the SINDA thermal analyzer. Iteration between the SHABERTH and the SINDA models enable the establishment of preliminary bounds for stable operation in LN2. These limits were established in terms of fluid flow, fluid inlet temperature, and axial load for a shaft speed of 30,000 RPM
On the Alexandrov Topology of sub-Lorentzian Manifolds
It is commonly known that in Riemannian and sub-Riemannian Geometry, the
metric tensor on a manifold defines a distance function. In Lorentzian
Geometry, instead of a distance function it provides causal relations and the
Lorentzian time-separation function. Both lead to the definition of the
Alexandrov topology, which is linked to the property of strong causality of a
space-time. We studied three possible ways to define the Alexandrov topology on
sub-Lorentzian manifolds, which usually give different topologies, but agree in
the Lorentzian case. We investigated their relationships to each other and the
manifold's original topology and their link to causality.Comment: 20 page
The oxygen isotope effect in the ab-plane reflectance of underdoped YBa_2Cu_3O_{7-delta}
We have measured the effect of oxygen isotope substitution on the ab-plane
reflectance of underdoped YBCO. The frequency shift of the transverse optic
phonons due to the substitution of O-16 by O-18 yields an isotope effect of the
expected magnitude for copper-oxygen stretching modes with alpha=0.5 +- 0.1.
The reflectance shoulder at 400 - 500 cm^-1 shows a much smaller exponent of
alpha=0.1 +- 0.1 in the normal state and alpha=0.23+- 0.1 in the
superconducting state. These observations suggest that the shoulder is of
electronic origin and not due to a phonon mode as has been suggested recently.Comment: 4 pages 2 figure
Optimal rotations of deformable bodies and orbits in magnetic fields
Deformations can induce rotation with zero angular momentum where dissipation
is a natural ``cost function''. This gives rise to an optimization problem of
finding the most effective rotation with zero angular momentum. For certain
plastic and viscous media in two dimensions the optimal path is the orbit of a
charged particle on a surface of constant negative curvature with magnetic
field whose total flux is half a quantum unit.Comment: 4 pages revtex, 4 figures + animation in multiframe GIF forma
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