7,549 research outputs found
Wave spectra of a shoaling wave field: A comparison of experimental and simulated results
Wave profile measurements made from an aircraft crossing the North Carolina continental shelf after passage of Tropical Storm Amy in 1975 are used to compute a series of wave energy spectra for comparison with simulated spectra. Results indicate that the observed wave field experiences refraction and shoaling effects causing statistically significant changes in the spectral density levels. A modeling technique is used to simulate the spectral density levels. Total energy levels of the simulated spectra are within 20 percent of those of the observed wave field. The results represent a successful attempt to theoretically simulate, at oceanic scales, the decay of a wave field which contains significant wave energies from deepwater through shoaling conditions
SAGE III aerosol extinction validation in the Arctic winter: comparisons with SAGE II and POAM III
The use of SAGE III multiwavelength aerosol extinction coefficient measurements to infer PSC type is contingent on the robustness of both the extinction magnitude and its spectral variation. Past validation with SAGE II and other similar measurements has shown that the SAGE III extinction coefficient measurements are reliable though the comparisons have been greatly weighted toward measurements made at mid-latitudes. Some aerosol comparisons made in the Arctic winter as a part of SOLVE II suggested that SAGE III values, particularly at longer wavelengths, are too small with the implication that both the magnitude and the wavelength dependence are not reliable. Comparisons with POAM III have also suggested a similar discrepancy. Herein, we use SAGE II data as a common standard for comparison of SAGE III and POAM III measurements in the Arctic winters of 2002/2003 through 2004/2005. During the winter, SAGE II measurements are made infrequently at the same latitudes as these instruments. We have mitigated this problem through the use of potential vorticity as a spatial coordinate and thus greatly increased of the number of coincident events. We find that SAGE II and III extinction coefficient measurements show a high degree of compatibility at both 1020 nm and 450 nm except a 10–20% bias at both wavelengths. In addition, the 452 to 1020 nm extinction ratio shows a consistent bias of ~30% throughout the lower stratosphere. We also find that SAGE II and POAM III are on average consistent though the comparisons show a much higher variability and larger bias than SAGE II/III comparisons. In addition, we find that SAGE II and POAM III data sets are not well correlated at and below 18 km. Overall, we find both the extinction values and the spectral dependence from SAGE III are robust and we find no evidence of a significant defect within the Arctic vortex
Reducing Polarization Mode Dispersion With Controlled Polarization Rotations
One of the fundamental limitations to high bit rate, long distance,
telecommunication in optical fibers is Polarization Mode Dispersion (PMD). Here
we introduce a conceptually new method to reduce PMD in optical fibers by
carrying out controlled rotations of polarization at predetermined locations
along the fiber. The distance between these controlled polarization rotations
must be less than both the beat length and the mode coupling length of the
fiber. This method can also be combined with the method in which the fiber is
spun while it drawn. The incidence of imperfections on the efficiency of the
method is analysed.Comment: 4 page
Detection of single electron spin resonance in a double quantum dot
Spin-dependent transport measurements through a double quantum dot are a
valuable tool for detecting both the coherent evolution of the spin state of a
single electron as well as the hybridization of two-electron spin states. In
this paper, we discuss a model that describes the transport cycle in this
regime, including the effects of an oscillating magnetic field (causing
electron spin resonance) and the effective nuclear fields on the spin states in
the two dots. We numerically calculate the current flow due to the induced spin
flips via electron spin resonance and we study the detector efficiency for a
range of parameters. The experimental data are compared with the model and we
find a reasonable agreement.Comment: 7 pages, 5 figures. To be published in Journal of Applied Physics,
proceedings ICPS 200
Ratchet Cellular Automata
In this work we propose a ratchet effect which provides a general means of
performing clocked logic operations on discrete particles, such as single
electrons or vortices. The states are propagated through the device by the use
of an applied AC drive. We numerically demonstrate that a complete logic
architecture is realizable using this ratchet. We consider specific
nanostructured superconducting geometries using superconducting materials under
an applied magnetic field, with the positions of the individual vortices in
samples acting as the logic states. These devices can be used as the building
blocks for an alternative microelectronic architecture.Comment: 4 pages, 3 figure
A flexible flight display research system using a ground-based interactive graphics terminal
Requirements and research areas for the air transportation system of the 1980 to 1990's were reviewed briefly to establish the need for a flexible flight display generation research tool. Specific display capabilities required by aeronautical researchers are listed and a conceptual system for providing these capabilities is described. The conceptual system uses a ground-based interactive graphics terminal driven by real-time radar and telemetry data to generate dynamic, experimental flight displays. These displays are scan converted to television format, processed, and transmitted to the cockpits of evaluation aircraft. The attendant advantages of a Flight Display Research System (FDRS) designed to employ this concept are presented. The detailed implementation of an FDRS is described. The basic characteristics of the interactive graphics terminal and supporting display electronic subsystems are presented and the resulting system capability is summarized. Finally, the system status and utilization are reviewed
- …