2,319 research outputs found
Study of quasi-optical circuit techniques in varactor multipliers
Quasi-optical circuit techniques in varactor multiplier
Study of quasi-optical circuit techniques in varactor multipliers
Quasi-optical circuit techniques in varactor multiplier
Killing vectors in asymptotically flat space-times: I. Asymptotically translational Killing vectors and the rigid positive energy theorem
We study Killing vector fields in asymptotically flat space-times. We prove
the following result, implicitly assumed in the uniqueness theory of stationary
black holes. If the conditions of the rigidity part of the positive energy
theorem are met, then in such space-times there are no asymptotically null
Killing vector fields except if the initial data set can be embedded in
Minkowski space-time. We also give a proof of the non-existence of non-singular
(in an appropriate sense) asymptotically flat space-times which satisfy an
energy condition and which have a null ADM four-momentum, under conditions
weaker than previously considered.Comment: 30 page
Microwave characterization of slotline on high resistivity silicon for antenna feed network
Conventional silicon wafers have low resistivity and consequently unacceptably high value of dielectric attenuation constant. Microwave circuits for phased array antenna systems fabricated on these wafers therefore have low efficiency. By choosing a silicon substrate with sufficiently high resistivity it is possible to make the dielectric attenuation constant of the interconnecting microwave transmission lines approach those of GaAs or InP. In order for this to be possible, the transmission lines must be characterized. In this presentation, the effective dielectric constant (epsilon sub eff) and attenuation constant (alpha) of a slotline on high resistivity (5000 to 10 000 ohm-cm) silicon wafer will be discussed. The epsilon sub eff and alpha are determined from the measured resonant frequencies and the corresponding insertion loss of a slotline ring resonator. The results for slotline will be compared with microstrip line and coplanar waveguide
Relativistic Acoustic Geometry
Sound wave propagation in a relativistic perfect fluid with a non-homogeneous
isentropic flow is studied in terms of acoustic geometry. The sound wave
equation turns out to be equivalent to the equation of motion for a massless
scalar field propagating in a curved space-time geometry. The geometry is
described by the acoustic metric tensor that depends locally on the equation of
state and the four-velocity of the fluid. For a relativistic supersonic flow in
curved space-time the ergosphere and acoustic horizon may be defined in a way
analogous the non-relativistic case. A general-relativistic expression for the
acoustic analog of surface gravity has been found.Comment: 14 pages, LaTe
Attenuation of epsilon(sub eff) of coplanar waveguide transmission lines on silicon substrates
Attenuation and epsilon(sub eff) of Coplanar Waveguide (CPW) transmission lines were measured on Silicon substrates with resistivities ranging from 400 to greater than 30,000 ohm-cm, that have a 1000 angstrom coating of SiO2. Both attenuation and epsilon(sub eff) are given over the frequency range 5 to 40 GHz for various strip and slot widths. These measured values are also compared to the theoretical values
Phase Transitions in Hexane Monolayers Physisorbed onto Graphite
We report the results of molecular dynamics (MD) simulations of a complete
monolayer of hexane physisorbed onto the basal plane of graphite. At low
temperatures the system forms a herringbone solid. With increasing temperature,
a solid to nematic liquid crystal transition takes place at K
followed by another transition at K into an isotropic fluid.
We characterize the different phases by calculating various order parameters,
coordinate distributions, energetics, spreading pressure and correlation
functions, most of which are in reasonable agreement with available
experimental evidence. In addition, we perform simulations where the
Lennard-Jones interaction strength, corrugation potential strength and dihedral
rigidity are varied in order to better characterize the nature of the two
transitions through. We find that both phase transitions are facilitated by a
``footprint reduction'' of the molecules via tilting, and to a lesser degree
via creation of gauche defects in the molecules.Comment: 18 pages, eps figures embedded, submitted to Phys. Rev.
The Exact Geometry of a Kerr-Taub-NUT Solution of String Theory
In this paper we study a solution of heterotic string theory corresponding to
a rotating Kerr-Taub-NUT spacetime. It has an exact CFT description as a
heterotic coset model, and a Lagrangian formulation as a gauged WZNW model. It
is a generalisation of a recently discussed stringy Taub-NUT solution, and is
interesting as another laboratory for studying the fate of closed timelike
curves and cosmological singularities in string theory. We extend the
computation of the exact metric and dilaton to this rotating case, and then
discuss some properties of the metric, with particular emphasis on the
curvature singularities.Comment: 14 pages, 3 figure
The Efroimsky formalism adapted to high-frequency perturbations
The Efroimsky perturbation scheme for consistent treatment of gravitational
waves and their influence on the background is summarized and compared with
classical Isaacson's high-frequency approach. We demonstrate that the Efroimsky
method in its present form is not compatible with the Isaacson limit of
high-frequency gravitational waves, and we propose its natural generalization
to resolve this drawback.Comment: 7 pages, to appear in Class. Quantum Gra
Distributional energy momentum tensor of the extended Kerr geometry
We generalize previous work on the energy-momentum tensor-distribution of the
Kerr geometry by extending the manifold structure into the negative mass
region. Since the extension of the flat part of the Kerr-Schild decomposition
from one sheet to the double cover develops a singularity at the branch surface
we have to take its non-smoothness into account. It is however possible to find
a geometry within the generalized Kerr-Schild class that is in the
Colombeau-sense associated to the maximally analytic Kerr-metric.Comment: 12 pages, latex2e, amslatex and epsf macro
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