136,082 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
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
The performance of modified jatropha-based nanofluid during turning process
The industry's extensive use of petroleum-based metalworking fluid (MWF) harms the environment
and humans. The production of bio-based MWF, especially from crude jatropha oil (CJO), has therefore taken
numerous initiatives. This aimed to formulate newly modified jatropha oil (MJO) with the addition of 0.05wt.%
hBN and 0.05wt.% MoS2 as the nanofluid for MWF. The performance of the nanofluids was determined
through the turning process in terms of cutting temperature, workpiece surface roughness, tool life and tool
wear of the tool lubricated by the nanofluids. The performance of the nanofluid samples was compared with
the synthetic ester (SE). From the results, after conducted 100mm axial cutting length MJO+hBN+MoS2
recorded the lowest in cutting temperature and surface roughness compared to all samples. The result shows
that MJO+hBN+MoS2 has longer tool life (6500mm) compared to SE (6000mm). Abrasion and adhesion were
observed as the dominant tool wear mechanism. In conclusion, MJO+hBN+MoS2 shows better machining
performance and has the potential to be an environmentally friendly metalworking fluid
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