3,377 research outputs found
Spacecraft antenna systems Final engineering report, Oct. 1963 - Jan. 1966
Spacecraft communication system with reliable, beam-steering antenn
High-gain self-steering microwave repeater, volume 1 Final engineering report, Jan. 1966 - Apr. 1969
Engineering model of high gain self steering microwave transponder and application to satellite communication link
Absolute conservation law for black holes
In all 2d theories of gravity a conservation law connects the (space-time
dependent) mass aspect function at all times and all radii with an integral of
the matter fields. It depends on an arbitrary constant which may be interpreted
as determining the initial value together with the initial values for the
matter field. We discuss this for spherically reduced Einstein-gravity in a
diagonal metric and in a Bondi-Sachs metric using the first order formulation
of spherically reduced gravity, which allows easy and direct fixations of any
type of gauge. The relation of our conserved quantity to the ADM and Bondi mass
is investigated. Further possible applications (ideal fluid, black holes in
higher dimensions or AdS spacetimes etc.) are straightforward generalizations.Comment: LaTex, 17 pages, final version, to appear in Phys. Rev.
Advanced microwave radiometer antenna system study
The practicability of a multi-frequency antenna for spaceborne microwave radiometers was considered in detail. The program consisted of a comparative study of various antenna systems, both mechanically and electronically scanned, in relation to specified design goals and desired system performance. The study involved several distinct tasks: definition of candidate antennas that are lightweight and that, at the specified frequencies of 5, 10, 18, 22, and 36 GHz, can provide conical scanning, dual linear polarization, and simultaneous multiple frequency operation; examination of various feed systems and phase-shifting techniques; detailed analysis of several key performance parameters such as beam efficiency, sidelobe level, and antenna beam footprint size; and conception of an antenna/feed system that could meet the design goals. Candidate antennas examined include phased arrays, lenses, and optical reflector systems. Mechanical, electrical, and performance characteristics of the various systems were tabulated for ease of comparison
Generalized Virasoro anomaly and stress tensor for dilaton coupled theories
We derive the anomalous transformation law of the quantum stress tensor for a
2D massless scalar field coupled to an external dilaton. This provides a
generalization of the Virasoro anomaly which turns out to be consistent with
the trace anomaly. We apply it together with the equivalence principle to
compute the expectation values of the covariant quantum stress tensor on a
curved background. Finally we briefly illustrate how to evaluate vacuum
polarization and Hawking radiation effects from these results.Comment: enlarged version of hep-th/0307096 containing the quantum stress
tensor for arbitrary geometries and discussion of the Hawking effect. To
appear in Phys. Lett.
Paramagnon dispersion in -FeSe observed by Fe -edge resonant inelastic x-ray scattering
We report an Fe -edge resonant inelastic x-ray scattering (RIXS) study of
the unusual superconductor -FeSe. The high energy resolution of this
RIXS experiment (55meV FWHM) made it possible to resolve
low-energy excitations of the Fe manifold. These include a broad peak
which shows dispersive trends between 100-200meV along the and
directions of the one-Fe square reciprocal lattice, and which can
be attributed to paramagnon excitations. The multi-band valence state of FeSe
is among the most metallic in which such excitations have been discerned by
soft x-ray RIXS
The Dimensional-Reduction Anomaly in Spherically Symmetric Spacetimes
In D-dimensional spacetimes which can be foliated by n-dimensional
homogeneous subspaces, a quantum field can be decomposed in terms of modes on
the subspaces, reducing the system to a collection of (D-n)-dimensional fields.
This allows one to write bare D-dimensional field quantities like the Green
function and the effective action as sums of their (D-n)-dimensional
counterparts in the dimensionally reduced theory. It has been shown, however,
that renormalization breaks this relationship between the original and
dimensionally reduced theories, an effect called the dimensional-reduction
anomaly. We examine the dimensional-reduction anomaly for the important case of
spherically symmetric spaces.Comment: LaTeX, 19 pages, 2 figures. v2: calculations simplified, references
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Dream Girl, Give Back My Dream To Me
https://digitalcommons.library.umaine.edu/mmb-vp/4186/thumbnail.jp
Down By The Nile
https://digitalcommons.library.umaine.edu/mmb-vp/5149/thumbnail.jp
QCD Pressure and the Trace Anomaly
Exact relations between the QCD thermal pressure and the trace anomaly are
derived. These are used, first, to prove the equivalence of the thermodynamic
and the hydrodynamic pressure in equilibrium in the presence of the trace
anomaly, closing a gap in previous arguments. Second, in the temporal axial
gauge a formula is derived which expresses the thermal pressure in terms of a
Dyson-resummed two-point function. This overcomes the infrared problems
encountered in the conventional perturbation-theory approach.Comment: 9 pages plain te
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