23,150 research outputs found
Model for reflection and transmission matrices of nanowire end facets
Nanowires show a large potential for various electrooptical devices, such as
light emitting diodes, solar cells and nanowire lasers. We present a direct
method developed to calculate the modal reflection and transmission matrix at
the end facets of a waveguide of arbitrary cross section, resulting in a
generalized version of the Fresnel equations. The reflection can be
conveniently computed using Fast Fourier Transforms. We demonstrate that the
reflection is qualitatively described by two main parameters, the modal field
confinement and the average Fresnel reflection of the plane waves constituting
the waveguide mode.Comment: 11 pages,14 figure
Effect of an atom on a quantum guided field in a weakly driven fiber-Bragg-grating cavity
We study the interaction of an atom with a quantum guided field in a weakly
driven fiber-Bragg-grating (FBG) cavity. We present an effective Hamiltonian
and derive the density-matrix equations for the combined atom-cavity system. We
calculate the mean photon number, the second-order photon correlation function,
and the atomic excited-state population. We show that, due to the confinement
of the guided cavity field in the fiber cross-section plane and in the space
between the FBG mirrors, the presence of the atom in the FBG cavity can
significantly affect the mean photon number and the photon statistics even
though the cavity finesse is moderate, the cavity is long, and the probe field
is weak.Comment: Accepted for Phys. Rev.
Codeless GPS Applications to Multi-Path: CGAMP
Cordless Global Positioning System (GPS) Applications to Multi-Path (CGAMP) is meeting the challenge of exploiting the L-band signals from the Global Positioning System (GPS) satellites for the measurement of the impulse response of radio transmission channels over space-Earth paths. This approach was originally suggested by E. K. Smith and has been pursued by J. Lemmon, without an affordable implementation being identifiable. In addition to the high cost of a suitable P code correlating GPS receiver, there is also the major impediment of the often announced Department of Defense policy of selective availability/anti-spoof (SA/AS) that clouds reliable access to the wideband (20 MHz) P channel of the GPS signals without cryptographic access. A technique proposed by MacDoran utilizes codeless methods for exploiting the P channel signals implemented by the use of a pair of antennas and cross correlation signal detection
Prescription-induced jump distributions in multiplicative Poisson processes
Generalized Langevin equations (GLE) with multiplicative white Poisson noise
pose the usual prescription dilemma leading to different evolution equations
(master equations) for the probability distribution. Contrary to the case of
multiplicative gaussian white noise, the Stratonovich prescription does not
correspond to the well known mid-point (or any other intermediate)
prescription. By introducing an inertial term in the GLE we show that the Ito
and Stratonovich prescriptions naturally arise depending on two time scales,
the one induced by the inertial term and the other determined by the jump
event. We also show that when the multiplicative noise is linear in the random
variable one prescription can be made equivalent to the other by a suitable
transformation in the jump probability distribution. We apply these results to
a recently proposed stochastic model describing the dynamics of primary soil
salinization, in which the salt mass balance within the soil root zone requires
the analysis of different prescriptions arising from the resulting stochastic
differential equation forced by multiplicative white Poisson noise whose
features are tailored to the characters of the daily precipitation. A method is
finally suggested to infer the most appropriate prescription from the data
Missing Transverse-Doppler Effect in Time-Dilation Experiments with High-Speed Ions
Recent experiments with high-speed ions have investigated potential
deviations from the time-dilation predicted by special relativity (SR). The
main contribution of this article is to show that the SR predictions are
matched by the experimental results only when the transverse Doppler effect in
the observed emissions from the ions are neglected in the analysis. However,
the Doppler effect in the emission cannot be neglected because it is similar to
the time dilation effect. Thus, the article highlights the need to consider
Doppler emission effects when validating SR time dilation using high-speed ion
experiments.Comment: 3 pages, 3 figure
Demixing of aqueous polymer two-phase systems in low gravity
When polymers such as dextran and poly(ethylene glycol) are mixed in aqueous solution biphasic systems often form. On Earth the emulsion formed by mixing the phases rapidly demixes because of phase density differences. Biological materials can be purified by selective partitioning between the phases. In the case of cells and other particulates the efficiency of these separations appears to be somewhat compromised by the demixing process. To modify this process and to evaluate the potential of two-phase partitioning in space, experiments on the effects of gravity on phase emulsion demixing were undertaken. The behavior of phase systems with essentially identical phase densities was studied at one-g and during low-g parabolic aircraft maneuvers. The results indicate the demixing can occur rather rapidly in space, although more slowly than on Earth. The demixing process was examined from a theoretical standpoint by applying the theory of Ostwald ripening. This theory predicts demizing rates many orders of magnitude lower than observed. Other possible demixing mechanisms are considered
Growth gradients in fish larvae *
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72250/1/j.1095-8649.1983.tb02886.x.pd
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