41,176 research outputs found
Turbulence Time Series Data Hole Filling using Karhunen-Loeve and ARIMA methods
Measurements of optical turbulence time series data using unattended
instruments over long time intervals inevitably lead to data drop-outs or
degraded signals. We present a comparison of methods using both Principal
Component Analysis, which is also known as the Karhunen--Loeve decomposition,
and ARIMA that seek to correct for these event-induced and mechanically-induced
signal drop-outs and degradations. We report on the quality of the correction
by examining the Intrinsic Mode Functions generated by Empirical Mode
Decomposition. The data studied are optical turbulence parameter time series
from a commercial long path length optical anemometer/scintillometer, measured
over several hundred metres in outdoor environments.Comment: 8 pages, 9 figures, submitted to ICOLAD 2007, City University,
London, U
Humidity contribution to C_n^2 over a 600m pathlength in a tropical marine environment
We present new optical turbulence structure parameter measurements, C_n^2,
over sea water between La Parguera and Magueyes Island (17.6N 67W) on the
southwest coast of Puerto Rico. The 600 meter horizontal paths were located
approximately 1.5 m and 10 m above sea level. No data of this type has ever
been made available in the literature. Based on the data, we show that the
C_n^2 measurements are about 7 times less compared to equivalent land data.
This strong evidence reinforces our previous argument that humidity must be
accounted for to better ascertain the near surface atmospheric turbulence
effects, which current visible / near infrared C_n^2 bulk models fail to do. We
also explore the generalised fractal dimension of this littoral data and
compare it to our reference land data. We find cases that exhibit monofractal
characteristics, that is to say, the effect of rising temperatures during the
daylight hours upon turbulence are counterbalanced by humidity, leading to a
single characteristic scale for the measurements. In other words, significant
moisture changes in the measurement volume cancels optical turbulence increases
due to temperature rises. Figures available as JPG only.Comment: 7 pages, 4 figures, 1 table, SPIE Photonics West 2007, paper 6457B-2
Spectroscopic analyses of Fe and water in clays: A Martian surface weathering study
Martian surface morphology suggests the presence of liquid H2O on Mars in the past. Reflectance spectra of the Martian surface include features which correspond to the crystal field transitions of iron, as well as features supporting the presence of ice and minerals containing structural OH and surface water. Researchers initiated further spectroscopic studies of surface iron and water and structural OH in clays in order to determine what remotely obtained spectra can indicate about the presence of clays on Mars based on a clearer understanding of the factors influencing the spectral features. Current technology allows researchers to better correlate the low frequency fundamental stretching and bending vibrations of O-H bonds with the diagnostic near infrared overtone and combination bands used in mineral characterization and identification
Applying the Hilbert--Huang Decomposition to Horizontal Light Propagation C_n^2 data
The Hilbert Huang Transform is a new technique for the analysis of
non--stationary signals. It comprises two distinct parts: Empirical Mode
Decomposition (EMD) and the Hilbert Transform of each of the modes found from
the first step to produce a Hilbert Spectrum. The EMD is an adaptive
decomposition of the data, which results in the extraction of Intrinsic Mode
Functions (IMFs). We discuss the application of the EMD to the calibration of
two optical scintillometers that have been used to measure C_n^2 over
horizontal paths on a building rooftop, and discuss the advantage of using the
Marginal Hilbert Spectrum over the traditional Fourier Power Spectrum.Comment: 9 pages, 11 figures, proc. SPIE 626
Divergence and Shannon information in genomes
Shannon information (SI) and its special case, divergence, are defined for a
DNA sequence in terms of probabilities of chemical words in the sequence and
are computed for a set of complete genomes highly diverse in length and
composition. We find the following: SI (but not divergence) is inversely
proportional to sequence length for a random sequence but is length-independent
for genomes; the genomic SI is always greater and, for shorter words and longer
sequences, hundreds to thousands times greater than the SI in a random sequence
whose length and composition match those of the genome; genomic SIs appear to
have word-length dependent universal values. The universality is inferred to be
an evolution footprint of a universal mode for genome growth.Comment: 4 pages, 3 tables, 2 figure
Quantum error correction of coherent errors by randomization
A general error correction method is presented which is capable of correcting
coherent errors originating from static residual inter-qubit couplings in a
quantum computer. It is based on a randomization of static imperfections in a
many-qubit system by the repeated application of Pauli operators which change
the computational basis. This Pauli-Random-Error-Correction (PAREC)-method
eliminates coherent errors produced by static imperfections and increases
significantly the maximum time over which realistic quantum computations can be
performed reliably. Furthermore, it does not require redundancy so that all
physical qubits involved can be used for logical purposes.Comment: revtex 4 pages, 3 fig
Self-optimization of optical confinement in ultraviolet photonic crystal slab laser
We studied numerically and experimentally the effects of structural disorder
on the performance of ultraviolet photonic crystal slab lasers. Optical gain
selectively amplifies the high-quality modes of the passive system. For these
modes, the in-plane and out-of-plane leakage rates may be automatically
balanced in the presence of disorder. The spontaneous optimization of in-plane
and out-of-plane confinement of light in a photonic crystal slab may lead to a
reduction of the lasing threshold.Comment: 5 pages, 5 figure
Universal Torsion-Induced Interaction from Large Extra Dimensions
We consider the Kaluza-Klein (KK) scenario in which only gravity exists in
the bulk. Without the assumption of symmetric connection, the presence of brane
fermions induces torsion. The result is a universal axial contact interaction
that dominates those induced by KK gravitons. This enhancement arises from a
large spin density on the brane. Using a global fit to Z-pole observables, we
find the 3 sigma bound on the scale of quantum gravity to be 28 TeV for n=2. If
Dirac or light sterile neutrinos are present, the data from SN1987A increase
the bound to \sqrt{n}M_S >= 210 TeV.Comment: 9 pages REVTeX, 1 postscript figure, uses axodraw.st
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