15,788 research outputs found
Fabrication of thick structures by sputtering
Deposit, 5500-gram of Cu-0.15 wt % Zr alloy, sputtered onto copper cylinder to average thickness of 12.29 mm. Structure was achieved with high-rate sputter deposition for about 100 hours total sputtering time. Material had twice the strength of unsputtered material at temperatures to 723 K and equivalent strength at nearly 873 K
Performance interface document for users of Tracking and Data Relay Satellite System (TDRSS) electromechanically steered antenna systems (EMSAS)
Satellites that use the NASA Tracking and Data Relay Satellite System (TDRSS) require antennas that are crucial for performing and achieving reliable TDRSS link performance at the desired data rate. Technical guidelines are presented to assist the prospective TDRSS medium-and high-data rate user in selecting and procuring a viable, steerable high-gain antenna system. Topics addressed include the antenna gain/transmitter power/data rate relationship; Earth power flux-density limitations; electromechanical requirements dictated by the small beam widths, desired angular coverage, and minimal torque disturbance to the spacecraft; weight and moment considerations; mechanical, electrical and thermal interfaces; design lifetime failure modes; and handling and storage. Proven designs are cited and space-qualified assemblies and components are identified
Testing models of inflation with CMB non-gaussianity
Two different predictions for the primordial curvature fluctuation bispectrum
are compared through their effects on the Cosmic Microwave Background
temperature fluctuations. The first has a local form described by a single
parameter f_{NL}. The second is based on a prediction from the warm
inflationary scenario, with a different dependence on wavenumber and a
parameter f_{WI}. New expressions are obtained for the angular bispectra of the
temperature fluctuations and for the estimators used to determine and
f_{WI}. The standard deviation of the estimators in an ideal experiment is
roughly 5 times larger for f_{WI} than for f_{NL}. Using 3 year WMAP data gives
limits -375<f_{WI}<36.8, but there is a possibility of detecting a signal for
f_{WI} from the Planck satellite.Comment: 13 pages, 5 figures in ReVTe
Neutrino Dark Energy and Moduli Stabilization in a BPS Braneworld Scenario
A braneworld model for neutrino Dark Energy (DE) is presented. We consider a
five dimensional two-branes set up with a bulk scalar field motivated by
supergravity. Its low-energy effective theory is derived with a moduli space
approximation (MSA). The position of the two branes are parametrized by two
scalar degrees of freedom (moduli). After detuning the brane tensions a
classical potential for the moduli is generated. This potential is unstable for
dS branes and we suggest to consider as a stabilizing contribution the Casimir
energy of bulk fields. In particular we add a massive spinor (neutrino) field
in the bulk and then evaluate the Casimir contribution of the bulk neutrino
with the help of zeta function regularization techniques. We construct an
explicit form of the 4D neutrino mass as function of the two moduli. To recover
the correct DE scale for the moduli potential the usual cosmological constant
fine-tuning is necessary, but, once accepted, this model suggests a stronger
connection between DE and neutrino physics.Comment: 26 pages, 1 EPS figur
Phase-Insensitive Scattering of Terahertz Radiation
The nonlinear interaction between Near-Infrared (NIR) and Terahertz pulses is
principally investigated as a means for the detection of radiation in the
hardly accessible THz spectral region. Most studies have targeted second-order
nonlinear processes, given their higher efficiencies, and only a limited number
have addressed third-order nonlinear interactions, mainly investigating
four-wave mixing in air for broadband THz detection. We have studied the
nonlinear interaction between THz and NIR pulses in solid-state media
(specifically diamond), and we show how the former can be frequency-shifted up
to UV frequencies by the scattering from the nonlinear polarisation induced by
the latter. Such UV emission differs from the well-known electric-field-induced
second harmonic (EFISH) one, as it is generated via a phase-insensitive
scattering, rather than a sum- or difference-frequency four-wave-mixing
process
Heat-kernel coefficients of the Laplace operator on the D-dimensional ball
We present a very quick and powerful method for the calculation of
heat-kernel coefficients. It makes use of rather common ideas, as integral
representations of the spectral sum, Mellin transforms, non-trivial commutation
of series and integrals and skilful analytic continuation of zeta functions on
the complex plane. We apply our method to the case of the heat-kernel expansion
of the Laplace operator on a -dimensional ball with either Dirichlet,
Neumann or, in general, Robin boundary conditions. The final formulas are quite
simple. Using this case as an example, we illustrate in detail our scheme
---which serves for the calculation of an (in principle) arbitrary number of
heat-kernel coefficients in any situation when the basis functions are known.
We provide a complete list of new results for the coefficients
, corresponding to the -dimensional ball with all the
mentioned boundary conditions and .Comment: 29 pages, LaTex, lines had been cut in the previous version by
transmission, no further change
One loop effective potential in heterotic M-theory
We have calculated the one loop effective potential of the vector multiplets
arising from the compactification to five dimensions of heterotic M-theory on a
Calabi-Yau manifold with h^{1,1}>1. We find that extensive cancellations
between the fermionic and bosonic sectors of the theory cause the effective
potential to vanish, with the exception of a higher order curvature term of the
type which might arise from string corrections.Comment: Latex, 28 pages, 1 figur
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