14,757 research outputs found
Local field effect as a function of pulse duration
In this note we give semiclassical consideration of the role of pulse
duration in observation of local field effects in the regime of optical
switching. We show that the main parameter governing local field influence is
the ratio of peak Rabi frequency corresponding to medium inversion and Lorentz
frequency of the medium. To obtain significant local field effect, this
parameter should be near unity that is valid only for long enough pulses. We
also discuss the role of relaxation and pulse shape in this processes.Comment: 4 pages, 3 figure
A prototype system for detecting the radio-frequency pulse associated with cosmic ray air showers
The development of a system to detect the radio-frequency (RF) pulse
associated with extensive air showers of cosmic rays is described. This work
was performed at the CASA/MIA array in Utah, with the intention of designing
equipment that can be used in conjunction with the Auger Giant Array. A small
subset of data (less than 40 out of a total of 600 hours of running time),
taken under low-noise conditions, permitted upper limits to be placed on the
rate for pulses accompanying showers of energies around eV.Comment: 53 pages, LaTeX, 19 figures, published in Nuclear Instruments and
Methods. Revised version; some references update
Nonlinear Transport Near a Quantum Phase Transition in Two Dimensions
The problem of non-linear transport near a quantum phase transition is solved
within the Landau theory for the dissipative insulator-superconductor phase
transition in two dimensions. Using the non-equilibrium Schwinger round-trip
Green function formalism, we obtain the scaling function for the non-linear
conductivity in the quantum disordered regime. We find that the conductivity
scales as at low field but crosses over at large fields to a universal
constant on the order of . The crossover between these two regimes
obtains when the length scale for the quantum fluctuations becomes comparable
to that of the electric field within logarithmic accuracy.Comment: 4.15 pages, no figure
Fermi-Edge Singularities in the Mesoscopic X-Ray Edge Problem
We study the x-ray edge problem for a chaotic quantum dot or nanoparticle
displaying mesoscopic fluctuations. In the bulk, x-ray physics is known to
produce deviations from the naively expected photoabsorption cross section in
the form of a peaked or rounded edge. For a coherent system with chaotic
dynamics, we find substantial changes and in particular that a photoabsorption
cross section showing a rounded edge in the bulk will change to a slightly
peaked edge on average as the system size is reduced to a mesoscopic (coherent)
scale.Comment: 4 pages, 3 figures, final version as published in PR
Properties of iterative Monte Carlo single histogram reweighting
We present iterative Monte Carlo algorithm for which the temperature variable
is attracted by a critical point. The algorithm combines techniques of single
histogram reweighting and linear filtering. The 2d Ising model of ferromagnet
is studied numerically as an illustration. In that case, the iterations
uncovered stationary regime with invariant probability distribution function of
temperature which is peaked nearly the pseudocritical temperature of specific
heat. The sequence of generated temperatures is analyzed in terms of stochastic
autoregressive model. The error of histogram reweighting can be better
understood within the suggested model. The presented model yields a simple
relation, connecting variance of pseudocritical temperature and parameter of
linear filtering.Comment: 3 figure
SPT5 affects the rate of mRNA degradation and physically interacts with CCR4 but does not control mRNA deadenylation
The CCR4-NOT complex has been shown to have multiple roles in mRNA metabolism, including that of transcriptional elongation, mRNA transport, and nuclear exosome function, but the primary function of CCR4 and CAF1 is in the deadenylation and degradation of cytoplasmic mRNA. As previous genetic analysis supported an interaction between SPT5, known to be involved in transcriptional elongation, and that of CCR4, the physical association of SPT5 with CCR4 was examined. A two-hybrid screen utilizing the deadenylase domain of CCR4 as a bait identified SPT5 as a potential interacting protein. SPT5 at its physiological concentration was shown to immunoprecipitate CCR4 and CAF1, and in vitro purified SPT5 specifically could bind to CAF1 and the deadenylase domain of CCR4. We additionally demonstrated that mutations in SPT5 or an spt4 deletion slowed the rate of mRNA degradation, a phenotype associated with defects in the CCR4 mRNA deadenylase complex. Yet, unlike ccr4 and caf1 deletions, spt5 and spt4 defects displayed little effect on the rate of deadenylation. They also did not affect decapping or 5\u27 - 3\u27 degradation of mRNA. These results suggest that the interactions between SPT5/SPT4 and the CCR4-NOT complex are probably the consequences of effects involving nuclear events and do not involve the primary role of CCR4 in mRNA deadenylation and turnover
STM Studies of Synthetic Peptide Monolayers
We have used scanning probe microscopy to investigate self-assembled
monolayers of chemically synthesized peptides. We find that the peptides form a
dense uniform monolayer, above which is found a sparse additional layer. Using
scanning tunneling microscopy, submolecular resolution can be obtained,
revealing the alpha helices which constitute the peptide. The nature of the
images is not significantly affected by the incorporation of redox cofactors
(hemes) in the peptides.Comment: 4 pages, 3 figures (4 gifs); to appear in the Proceedings of the
XIIth Int. Winterschool on Electronic Properties of Novel Materials
"Molecular Nanostructures", Kirchberg/Tyrol, Febr. 199
Fluctuations of g-factors in metal nanoparticles: Effects of electron-electron interaction and spin-orbit scattering
We investigate the combined effect of spin-orbit scattering and
electron-electron interactions on the probability distribution of -factors
of metal nanoparticles. Using random matrix theory, we find that even a
relatively small interaction strength %(ratio of exchange constant and mean
level %spacing \spacing ) significantly increases -factor
fluctuations for not-too-strong spin-orbit scattering (ratio of spin-orbit rate
and single-electron level spacing 1/\tau_{\rm so} \spacing \lesssim 1), and
leads to the possibility to observe -factors larger than two.Comment: RevTex, 2 figures inserte
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