1,422 research outputs found
Fast tuning of superconducting microwave cavities
Photons are fundamental excitations of the electromagnetic field and can be
captured in cavities. For a given cavity with a certain size, the fundamental
mode has a fixed frequency {\it f} which gives the photons a specific "color".
The cavity also has a typical lifetime , which results in a finite
linewidth {\it f}. If the size of the cavity is changed fast compared
to , and so that the frequency change {\it f} {\it
f}, then it is possible to change the "color" of the captured photons. Here we
demonstrate superconducting microwave cavities, with tunable effective lengths.
The tuning is obtained by varying a Josephson inductance at one end of the
cavity. We show data on four different samples and demonstrate tuning by
several hundred linewidths in a time . Working in the few
photon limit, we show that photons stored in the cavity at one frequency will
leak out from the cavity with the new frequency after the detuning. The
characteristics of the measured devices make them suitable for different
applications such as dynamic coupling of qubits and parametric amplification.Comment: 2nd International Workshop on Solid-State Quantum Computing, June
2008, Taipei, Taiwa
Remote sensing of Earth terrain
Remote sensing of earth terrain is examined. The layered random medium model is used to investigate the fully polarimetric scattering of electromagnetic waves from vegetation. The model is used to interpret the measured data for vegetation fields such as rice, wheat, or soybean over water or soil. Accurate calibration of polarimetric radar systems is essential for the polarimetric remote sensing of earth terrain. A polarimetric calibration algorithm using three arbitrary in-scene reflectors is developed. In the interpretation of active and passive microwave remote sensing data from the earth terrain, the random medium model was shown to be quite successful. A multivariate K-distribution is proposed to model the statistics of fully polarimetric radar returns from earth terrain. In the terrain cover classification using the synthetic aperture radar (SAR) images, the applications of the K-distribution model will provide better performance than the conventional Gaussian classifiers. The layered random medium model is used to study the polarimetric response of sea ice. Supervised and unsupervised classification procedures are also developed and applied to synthetic aperture radar polarimetric images in order to identify their various earth terrain components for more than two classes. These classification procedures were applied to San Francisco Bay and Traverse City SAR images
Polarimetric clutter modeling: Theory and application
The two-layer anisotropic random medium model is used to investigate fully polarimetric scattering properties of earth terrain media. The polarization covariance matrices for the untilted and tilted uniaxial random medium are evaluated using the strong fluctuation theory and distorted Born approximation. In order to account for the azimuthal randomness in the growth direction of leaves in tree and grass fields, an averaging scheme over the azimuthal direction is also applied. It is found that characteristics of terrain clutter can be identified through the analysis of each element of the covariance matrix. Theoretical results are illustrated by the comparison with experimental data provided by MIT Lincoln Laboratory for tree and grass fields
Polarimetric scattering from layered media with multiple species of scatterers
Geophysical media are usually heterogeneous and contain multiple species of scatterers. In this paper a model is presented to calculate effective permittivities and polarimetric backscattering coefficients of multispecies-layered media. The same physical description is consistently used in the derivation of both permittivities and scattering coefficients. The strong permittivity fluctuation theory is extended to account for the multiple species of scatterers with a general ellipsoidal shape whose orientations are randomly distributed. Under the distorted Born approximation, polarimetric scattering coefficients are obtained. These calculations are applicable to the special cases of spheroidal and spherical scatterers. The model is used to study effects of scatterer shapes and multispecies mixtures on polarimetric signatures of heterogeneous media. The multispecies model accounts for moisture content in scattering media such as snowpack in an ice sheet. The results indicate a high sensitivity of backscatter to moisture with a stronger dependence for drier snow and ice grain size is important to the backscatter. For frost-covered saline ice, model results for bare ice are compared with measured data at C band and then the frost flower formation is simulated with a layer of fanlike ice crystals including brine infiltration over a rough interface. The results with the frost cover suggest a significant increase in scattering coefficients and a polarimetric signature closer to isotropic characteristics compared to the thin saline ice case
General Relativistic Effects in the Core Collapse Supernova Mechanism
We apply our recently developed code for spherically symmetric, fully general
relativistic (GR) Lagrangian hydrodynamics and multigroup flux-limited
diffusion neutrino transport to examine the effects of GR on the hydrodynamics
and transport during collapse, bounce, and the critical shock reheating phase
of core collapse supernovae. Comparisons of models computed with GR versus
Newtonian hydrodynamics show that collapse to bounce takes slightly less time
in the GR limit, and that the shock propagates slightly farther out in radius
before receding. After a secondary quasistatic rise in the shock radius, the
shock radius declines considerably more rapidly in the GR simulations than in
the corresponding Newtonian simulations. During the shock reheating phase, core
collapse computed with GR hydrodynamics results in a substantially more compact
structure from the center out to the stagnated shock. The inflow speed of
material behind the shock is also increased. Comparisons also show that the
luminosity and rms energy of any neutrino flavor during the shock reheating
phase increases when switching from Newtonian to GR hydrodynamics, and
decreases when switching from Newtonian to GR transport. This latter decrease
in neutrino luminosities and rms energies is less in magnitude than the
increase that arise when switching from Newtonian to GR hydrodynamics, with the
result that a fully GR simulation gives higher neutrino luminosities and harder
neutrino spectra than a fully Newtonian simulation of the same precollapse
model.Comment: 35 pages, 23 figure
Decay rate and renormalized frequency shift of a quantum wire Wannier exciton in a planar microcavity
The superradiant decay rate and frequency shift of a Wannier exciton in a
one-dimensional quantum wire are studied. It is shown that the dark mode
exciton can be examined experimentally when the quantum wire is embedded in a
planar microcavity. It is also found that the decay rate is greatly enhanced as
the cavity length is equal to the multiple wavelength of the emitted
photon. Similar to its decay rate counterpart, the frequency shift also shows
discontinuities at resonant modes.Comment: 12 pages, 2 figures. To appear in P. R. B. September 200
An attenuating mutation in a neurovirulent Sindbis virus strain interacts with the IPS-1 signaling pathway in vivo
The AR86 strain of Sindbis virus causes lethal neurologic disease in adult mice. Previous studies have identified a virulence determinant at nonstructural protein (nsP) 1 position 538 that regulates neurovirulence, modulates clearance from the CNS, and interferes with the type I interferon pathway. The studies herein demonstrate that in the absence of type I interferon signaling, the attenuated mutant exhibited equivalent virulence to S300 virus. Furthermore, both S300 and nsP1 T538I viruses displayed similar neurovirulence and replication kinetics in IPS-1-/- mice. TRIF dependent signaling played a modest role in protecting against disease by both S300 and nsP1 T538I, but did not contribute to control of nsP1 T538I replication within the CNS, while MyD88 played no role in the disease process. These results indicate that the control of the nsP1 T538I mutant virus is largely mediated by IPS-1-dependent RLR signaling, with TRIF-dependent TLR signaling also contributing to protection from virus-induced neurologic disease
Bound states of L-shaped or T-shaped quantum wires in inhomogeneous magnetic fields
The bound state energies of L-shaped or T-shaped quantum wires in inhomogeous
magnetic fields are found to depend strongly on the asymmetric parameter
, i.e. the ratio of the arm widths. Two effects of
magnetic field on bound state energies of the electron are obtained. One is the
depletion effect which purges the electron out of the OQD system. The other is
to create an effective potential due to quantized Landau levels of the magnetic
field. The bound state energies of the electron in L-shaped or T-shaped quantum
wires are found to depend quadratically (linearly) on the magnetic field in the
weak (strong) field region and are independent of the direction of the magnetic
field. A simple model is proposed to explain the behavior of the magnetic
dependence of the bound state energy both in weak and strong magnetic field
regions.Comment: 4 pages, 4 figure
Safety Intelligence and Legal Machine Language: Do We Need the Three Laws of Robotics?
In this chapter we will describe a legal framework for Next Generation Robots (NGRs) that has safety as its central focus. The framework is offered in response to the current lack of clarity regarding robot safety guidelines, despite the development and impending release of tens of thousands of robots into workplaces and homes around the world. We also describ
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