161,216 research outputs found
Wind tunnel investigations of model rotor noise at low tip speeds
Experimental and related analytical results on model rotor rotational and broadband noise obtained in the anechoic wind tunnel and rotor facility are summarized. Factors studied include various noise sources, effects of helicopter performance parameters on noise generated by a model main rotor, appropriate scaling laws for the various types of main rotor noise, and the effects of intensity and size scales of injected turbulence on the intensity and spectra of broadband noise
Separator plugs for liquid helium
Work performed during Summer 1984 (from June to Sept. 30) in the area of porous media for use in low temperature applications is discussed. Recent applications are in the area of vapor - liquid phase separation, pumping based on the fountain effect and related subsystems. Areas of potential applications of the latter are outlined in supplementary work. Experimental data have been developed. The linear equations of the two-fluid model are inspected critically in the light of forced convection evidence reported recently. It is emphasized that the Darcy permeability is a unique throughput quantity in the porous media application areas whose use will permit meaningful comparisons of data not only in one lab but also within a group of labs doing porous plug studies
Single spin- and chiral-glass transition in vector spin glasses in three-dimensions
Results of Monte Carlo simulations of XY and Heisenberg spin glass models in
three dimensions are presented. A finite size scaling analysis of the
correlation length of the spins and chiralities of both models shows that there
is a single, finite-temperature transition at which both spins and chiralities
order.Comment: 5 pages, 5 figures. Replaced by published versio
Are All Static Black Hole Solutions Spherically Symmetric?
The static black hole solutions to the Einstein-Maxwell equations are all
spherically symmetric, as are many of the recently discovered black hole
solutions in theories of gravity coupled to other forms of matter. However,
counterexamples demonstrating that static black holes need not be spherically
symmetric exist in theories, such as the standard electroweak model, with
electrically charged massive vector fields. In such theories, a magnetically
charged Reissner-Nordstrom solution with sufficiently small horizon radius is
unstable against the development of a nonzero vector field outside the horizon.
General arguments show that, for generic values of the magnetic charge, this
field cannot be spherically symmetric. Explicit construction of the solution
shows that it in fact has no rotational symmetry at all.Comment: 6 pages, plain TeX. Submitted to GRF Essay Competitio
Optical Study of the Free Carrier Response of LaTiO3/SrTiO3 Superlattices
We used infrared spectroscopic ellipsometry to investigate the electronic
properties of LaTiO3/SrTiO3 superlattices (SLs). Our results indicated that,
independent of the SL periodicity and individual layer-thickness, the SLs
exhibited a Drude metallic response with sheet carrier density per interface
~3x10^14 cm^-2. This is probably due to the leakage of d-electrons at
interfaces from the Mott insulator LaTiO3 to the band insulator SrTiO3. We
observed a carrier relaxation time ~ 35 fs and mobility ~ 35 cm^2V^-1s^-1 at 10
K, and an unusual temperature dependence of carrier density that was attributed
to the dielectric screening of quantum paraelectric SrTiO3.Comment: 4 pages, 4 figure
Diagrammatic analysis of the two-state quantum Hall system with chiral invariance
The quantum Hall system in the lowest Landau level with Zeeman term is
studied by a two-state model, which has a chiral invariance. Using a
diagrammatic analysis, we examine this two-state model with random impurity
scattering, and find the exact value of the conductivity at the Zeeman energy
. We further study the conductivity at the another extended state
(). We find that the values of the conductivities at
and do not depend upon the value of the Zeeman energy
. We discuss also the case where the Zeeman energy becomes a
random field.Comment: 14P, Late
Dilaton test of connection between AdS_3 X S^3 and 5D black hole
A 5D black hole(M) is investigated in the type IIB superstring theory
compactified on ST. This corresponds to AdSST in the near horizon with asymptotically flat space. Here the
harmonic gauge is introduced to decouple the mixing between the dilaton and
others. On the other hand we obtain the BTZ balck
hole(AdSST) as the non-dilatonic solution. We calculate
the greybody factor of the dilaton as a test scalar both for a 5D black
hole(MST) and the BTZ black hole(AdSST). The result of the BTZ black hole agrees with the greybody
factor of the dilaton in the dilute gas approximation of a 5D black hole.Comment: revised version to appear in classical and quantum gravity, 15 pages
with RevTe
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