30,224 research outputs found
A novel wideband dynamic directional indoor channel model based on a Markov process
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Results from the National Aeronautics and Space Administration remote sensing experiments in the New York Bight, 7-17 April 1975
A cooperative operation was conducted in the New York Bight to evaluate the role of remote sensing technology to monitor ocean dumping. Six NASA remote sensing experiments were flown on the C-54, U-2, and C-130 NASA aircraft, while NOAA obtained concurrent sea truth information using helicopters and surface platforms. The experiments included: (1) a Radiometer/Scatterometer (RADSCAT), (2) an Ocean Color Scanner (OCS), (3) a Multichannel Ocean Color Sensor (MOCS), (4) four Hasselblad cameras, (5) an Ebert spectrometer; and (6) a Reconafax IV infrared scanner and a Precision Radiation Thermometer (PRT-5). The results of these experiments relative to the use of remote sensors to detect, quantify, and determine the dispersion of pollutants dumped into the New York Bight are presented
Characterization of causes of signal phase and frequency instability Final report
Characteristic instabilities in phase and frequency errors of reference oscillator
The Murchison Widefield Array: Design Overview
The Murchison Widefield Array (MWA) is a dipole-based aperture array
synthesis telescope designed to operate in the 80-300 MHz frequency range. It
is capable of a wide range of science investigations, but is initially focused
on three key science projects. These are detection and characterization of
3-dimensional brightness temperature fluctuations in the 21cm line of neutral
hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10,
solar imaging and remote sensing of the inner heliosphere via propagation
effects on signals from distant background sources,and high-sensitivity
exploration of the variable radio sky. The array design features 8192
dual-polarization broad-band active dipoles, arranged into 512 tiles comprising
16 dipoles each. The tiles are quasi-randomly distributed over an aperture
1.5km in diameter, with a small number of outliers extending to 3km. All
tile-tile baselines are correlated in custom FPGA-based hardware, yielding a
Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point
spread function (PSF) quality. The correlated data are calibrated in real time
using novel position-dependent self-calibration algorithms. The array is
located in the Murchison region of outback Western Australia. This region is
characterized by extremely low population density and a superbly radio-quiet
environment,allowing full exploitation of the instrumental capabilities.Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Proceedings
of the IEE
A discussion of dynamic stability measurement techniques
Techniques for the measurement of the dynamic stability of linear systems are discussed. Particular attention is given to an analysis of the errors in the procedures, and to methods for calculating the system damping from the data. The techniques discussed include: transient decay, moving block analysis, spectral analysis, random decrement signatures, transfer function analysis, and parameter identification methods. The special problems of rotorcraft dynamic stability testing are discussed
Discovery of Strange Kinetics in Bulk Material: Correlated Dipoles in CaCu3Ti4O12
Dielectric spectroscopy of CaCu3Ti4O12 was performed spanning broad ranges of
temperature (10-300K) and frequency (0.5Hz-2MHz). We attribute the permittivity
step-fall to the evolution of Kirkwood-Fr\"oehlich dipole-correlations;
reducing the moment-density due to anti-parallel orienting dipoles, with
decreasing temperature. Unambiguous sub-Arrhenic dispersion of the associated
loss-peak reveals the prime role of strange kinetics; used to describe
nonlinearity-governed meso-confined/fractal systems, witnessed here for the
first time in a bulk material. Effective energy-scale is seen to follow thermal
evolution of the moment density, and the maidenly estimated correlation-length
achieves mesoscopic scale below 100K. Temperature dependence of correlations
reveals emergence of a new, parallel-dipole-orientation branch below 85K. Novel
features observed define a crossover temperature window connecting the
single-dipoles regime and the correlated moments. Conciling known results, we
suggest a fractal-like self-similar configuration of Ca/Cu-rich sub-phases;
resultant heterogeneity endowing CaCu3Ti4O12 its peculiar electrical behaviour.Comment: 19 pages, 5 figures, 44 reference
Spectral partitioning of time-varying networks with unobserved edges
We discuss a variant of `blind' community detection, in which we aim to
partition an unobserved network from the observation of a (dynamical) graph
signal defined on the network. We consider a scenario where our observed graph
signals are obtained by filtering white noise input, and the underlying network
is different for every observation. In this fashion, the filtered graph signals
can be interpreted as defined on a time-varying network. We model each of the
underlying network realizations as generated by an independent draw from a
latent stochastic blockmodel (SBM). To infer the partition of the latent SBM,
we propose a simple spectral algorithm for which we provide a theoretical
analysis and establish consistency guarantees for the recovery. We illustrate
our results using numerical experiments on synthetic and real data,
highlighting the efficacy of our approach.Comment: 5 pages, 2 figure
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