3,727 research outputs found
Periodic and Quasi-Periodic Compensation Strategies of Extreme Outages caused by Polarization Mode Dispersion and Amplifier Noise
Effect of birefringent disorder on the Bit Error Rate (BER) in an optical
fiber telecommunication system subject to amplifier noise may lead to extreme
outages, related to anomalously large values of BER. We analyze the Probability
Distribution Function (PDF) of BER for various strategies of Polarization Mode
Dispersion (PMD) compensation. A compensation method is proposed that is
capable of more efficient extreme outages suppression, which leads to
substantial improvement of the fiber system performance.Comment: 3 pages, 1 figure, Submitted to IEEE Photonics Letter
Detection Of Brugia Malayi And Brugia Pahangi Parasites By Biotinlabeled Dna Probes
Morphologically, the larvae of Brugian parasites are difficult to differentiate by conventional methods. Recently, radioactive labeled DNA probes2'3 have been developed to distinguish the larvae of these parasites. However, these probes have a short shelf-life and are hazardous to the users. Two oligonucleotide DNA probes have been tested, one is specific for B.malayi and the other specific for B.pahangi. They were each labeled with Biotin in three different ways by using : a one-tailed 30mer biotinylated uridine residues, a two-tailed 30mer biotinylated uridine-thymidine residues. The dot blot assays were tested at various temperatures (30°C-80°C) using different concentrations of parasite DNAs (12.8ng-0.1ng). Our preliminary results indicated that the sensitivity and specificity of the biotinylated DNA probes, with a two-tailed 45mer biotinylated residues, were highly acceptable for field use
Dynamical heterogeneities in a supercooled Lennard-Jones liquid
We present the results of a large scale molecular dynamics computer
simulation study in which we investigate whether a supercooled Lennard-Jones
liquid exhibits dynamical heterogeneities. We evaluate the non-Gaussian
parameter for the self part of the van Hove correlation function and use it to
identify ``mobile'' particles. We find that these particles form clusters whose
size grows with decreasing temperature. We also find that the relaxation time
of the mobile particles is significantly shorter than that of the bulk, and
that this difference increases with decreasing temperature.Comment: 8 pages of RevTex, 4 ps figure
Enhanced fluctuations of the tunneling density of states near bottoms of Landau bands measured by a local spectrometer
We have found that the local density of states fluctuations (LDOSF) in a
disordered metal, detected using an impurity in the barrier as a spectrometer,
undergo enhanced (with respect to SdH and dHvA effects) oscillations in strong
magnetic fields, omega _c\tau > 1. We attribute this to the dominant role of
the states near bottoms of Landau bands which give the major contribution to
the LDOSF and are most strongly affected by disorder. We also demonstrate that
in intermediate fields the LDOSF increase with B in accordance with the results
obtained in the diffusion approximation.Comment: 4 pages, 4 figure
Photometric Calibration of the Swift Ultraviolet/Optical Telescope
We present the photometric calibration of the Swift UltraViolet/Optical
Telescope (UVOT) which includes: optimum photometric and background apertures,
effective area curves, colour transformations, conversion factors for count
rates to flux, and the photometric zero points (which are accurate to better
than 4 per cent) for each of the seven UVOT broadband filters. The calibration
was performed with observations of standard stars and standard star fields that
represent a wide range of spectral star types. The calibration results include
the position dependent uniformity, and instrument response over the 1600-8000A
operational range. Because the UVOT is a photon counting instrument, we also
discuss the effect of coincidence loss on the calibration results. We provide
practical guidelines for using the calibration in UVOT data analysis. The
results presented here supersede previous calibration results.Comment: Minor improvements after referees report. Accepted for publication in
MNRA
Density anomaly in a competing interactions lattice gas model
We study a very simple model of a short-range attraction and an outer shell
repulsion as a test system for demixing phase transition and density anomaly.
The phase-diagram is obtained by applying mean field analysis and Monte Carlo
simulations to a two dimensional lattice gas with nearest-neighbors attraction
and next-nearest-neighbors repulsion (the outer shell). Two liquid phases and
density anomaly are found.
The coexistence line between these two liquid phases meets a critical line
between the fluid and the low density liquid at a tricritical point. The line
of maximum density emerges in the vicinity of the tricritical point, close to
the demixing transition
String-like Clusters and Cooperative Motion in a Model Glass-Forming Liquid
A large-scale molecular dynamics simulation is performed on a glass-forming
Lennard-Jones mixture to determine the nature of dynamical heterogeneities
which arise in this model fragile liquid. We observe that the most mobile
particles exhibit a cooperative motion in the form of string-like paths
(``strings'') whose mean length and radius of gyration increase as the liquid
is cooled. The length distribution of the strings is found to be similar to
that expected for the equilibrium polymerization of linear polymer chains.Comment: 6 pages of RevTex, 6 postscript figures, uses epsf.st
Electron focusing, mode spectroscopy and mass enhancement in small GaAs/AlGaAs rings
A new electron focusing effect has been discovered in small single and
coupled GaAs/AlGaAs rings. The focusing in the single ring is attributed solely
to internal orbits. The focusing effect allows the ring to be used as a small
mass spectrometer. The focusing causes peaks in the magnetoresistance at low
fields, and the peak positions were used to study the dispersion relation of
the one-dimensional magnetoelectric subbands. The electron effective mass
increases with the applied magnetic field by a factor of , at a magnetic
field of . This is the first time this increase has been measured
directly. General agreement obtains between the experiment and the subband
calculations for straight channels.Comment: 13 pages figures are available by reques
Polyhedral Cosmic Strings
Quantum field theory is discussed in M\"obius corner kaleidoscopes using the
method of images. The vacuum average of the stress-energy tensor of a free
field is derived and is shown to be a simple sum of straight cosmic string
expressions, the strings running along the edges of the corners. It does not
seem possible to set up a spin-half theory easily.Comment: 15 pages, 4 text figures not include
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