5,623 research outputs found
Changes of instability thresholds of rotor due to bearing misalignments
The influence of bearing misalignment upon the dynamic characteristics of statistically indeterminant rotor bearing systems is investigated. Both bearing loads and stability speed limits of a rotor may be changed significantly by magnitude and direction of bearing misalignment. The useful theory of short journal bearings is introduced and simple analytical expressions, governing the misalignment problem, are carried out. Polar plots for the bearing load capacities and stability maps, describing the speed limit in terms of misalignment, are presented. These plots can be used by the designer to estimate deviations between calculation and experimental data due to misalignment effects
Sound Mode Hydrodynamics from Bulk Scalar Fields
We study the hydrodynamic sound mode using gauge/gravity correspondence by
examining a generic black brane background's response to perturbations. We
assume that the background is generated by a single scalar field, and then
generalize to the case of multiple scalar fields. The relevant differential
equations obeyed by the gauge invariant variables are presented in both cases.
Finally, we present an analytical solution to these equations in a special
case; this solution allows us to determine the speed of sound and bulk
viscosity for certain special metrics. These results may be useful in
determining sound mode transport coefficients in phenomenologically motivated
holographic models of strongly coupled systems.Comment: 17 pages. Corrections made to one of the gauge invariant equations
(66). This equation was not used in the other main conclusions of the paper,
so the rest of the results are unchange
A shear spectral sum rule in a non-conformal gravity dual
A sum rule which relates a stress-energy tensor correlator to thermodynamic
functions is examined within the context of a simple non-conformal gravity
dual. Such a sum rule was previously derived using AdS/CFT for conformal
Supersymmetric Yang-Mills theory, but we show that it does
not generalize to the non-conformal theory under consideration. We provide a
generalized sum rule and numerically verify its validity. A useful byproduct of
the calculation is the computation of the spectral density in a strongly
coupled non-conformal theory. Qualitative features of the spectral densities
and implications for lattice measurements of transport coefficients are
discussed.Comment: 13 pages, 3 figures. v5: Typos in Eq. (60) fixed. v4: References
added, matches published version. v3: Minor typographical corrections. v2:
References and some discussion in Appendix A have been added; conclusions
unchange
Systematic Review – Final: Have arid land springs restoration projects been effective in restoring hydrology, geomorphology, and invertebrates and plant species composition comparable to natural springs with minimal anthropogenic disturbance?
The aim of this review is to examine the effectiveness of springs restoration projects in the southwestern United States in restoring hydrology, geomorphology, and plant and invertebrates species composition to condiitions comparable with natural springs with minimal anthropogenic disturbances
Probing Hadronic Structure with The Decay
We compute the branching ratio for and
in chiral perturbation theory and find that
both decays should be observable at CEBAF. With sufficiently low thresholds on
the invariant mass a branching ratio of may be observed
for . For the decay
mode we predict a branching ratio of . The dependence of the
M1 and E2 amplitudes on the momentum transfer will provide a useful test of
chiral perturbation theory which predicts variation over the
allowed kinematic range.Comment: 6 pages, 3 figures, UCSD/PTH 93-06, QUSTH-93-02, Duke-TH-93-4
The effective mass of two--dimensional 3He
We use structural information from diffusion Monte Carlo calculations for
two--dimensional 3He to calculate the effective mass. Static effective
interactions are constructed from the density-- and spin structure functions
using sumrules. We find that both spin-- and density-- fluctuations contribute
about equally to the effective mass. Our results show, in agreement with recent
experiments, a flattening of the single--particle self--energy with increasing
density, which eventually leads to a divergent effective mass.Comment: 4 pages, accepted in PR
Second order hydrodynamics for a special class of gravity duals
The sound mode hydrodynamic dispersion relation is computed up to order
for a class of gravitational duals which includes both Schwarzschild and
Dp-Brane metrics. The implications for second order transport coefficients are
examined within the context of Israel-Stewart theory. These sound mode results
are compared with previously known results for the shear mode. This comparison
allows one to determine the third order hydrodynamic contributions to the shear
mode for the class of metrics considered here.Comment: 20 page
Development of an in-line filter to prevent intrusion of NO2 toxic vapors into A/C systems
The hypergolic propellant nitrogen tetroxide (N2O4 or NTO) is routinely used in spacecraft launched at Kennedy Space Center (KSC) and Cape Canaveral Air Station (CCAS). In the case of a catastrophic failure of the spacecraft, there would be a release of the unspent propellant in the form of a toxic cloud. Inhalation of this material at downwind concentrations which may be as high as 20 parts per million (ppm) for 30 minutes in duration, may produce irritation to the eyes, nose and respiratory tract. Studies at both KSC and CCAS have shown that the indoor concentrations of N2O4 during a toxic release may range from 1 to 15 ppm and depend on the air change rate (ACR) for a particular building and whether or not the air conditioning (A/C) system has been shut down or left in an operating mode. This project was initiated in order to assess how current A/C systems could be easily modified to prevent personnel from being exposed to toxic vapors. A sample system has been constructed to test the ability of several types of filter material to capture the N2O4 vapors prior to their infiltration into the A/C system. Test results will be presented which compare the efficiencies of standard A/C filters, water wash systems, and chemically impregnated filter material in taking toxic vapors out of the incoming air stream
Nonrelativistic Chern-Simons Vortices on the Torus
A classification of all periodic self-dual static vortex solutions of the
Jackiw-Pi model is given. Physically acceptable solutions of the Liouville
equation are related to a class of functions which we term
Omega-quasi-elliptic. This class includes, in particular, the elliptic
functions and also contains a function previously investigated by Olesen. Some
examples of solutions are studied numerically and we point out a peculiar
phenomenon of lost vortex charge in the limit where the period lengths tend to
infinity, that is, in the planar limit.Comment: 25 pages, 2+3 figures; improved exposition, corrected typos, added
one referenc
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