2,340 research outputs found
Giant Magnetoresistance Oscillations Induced by Microwave Radiation and a Zero-Resistance State in a 2D Electron System with a Moderate Mobility
The effect of a microwave field in the frequency range from 54 to 140
on the magnetotransport in a GaAs quantum well with AlAs/GaAs
superlattice barriers and with an electron mobility no higher than
is investigated. In the given two-dimensional system under
the effect of microwave radiation, giant resistance oscillations are observed
with their positions in magnetic field being determined by the ratio of the
radiation frequency to the cyclotron frequency. Earlier, such oscillations had
only been observed in GaAs/AlGaAs heterostructures with much higher mobilities.
When the samples under study are irradiated with a 140- microwave
field, the resistance corresponding to the main oscillation minimum, which
occurs near the cyclotron resonance, appears to be close to zero. The results
of the study suggest that a mobility value lower than
does not prevent the formation of zero-resistance states in magnetic field in a
two-dimensional system under the effect of microwave radiation.Comment: 4 pages, 2 figur
CRIMINAL LAW—GIVE ME FREEDOM!: HOW AMBIGUOUS FEDERAL SUPERVISED RELEASE CONDITIONS UNDERMINE THE PURPOSE OF THE SENTENCING REFORM ACT
Vagueness, as the word suggests, is inherently uncertain. This Note addresses the issues of vagueness presented by unclear supervised release conditions, as well as discusses the split of authority pertaining thereto. Specifically, the condition discussed throughout the Note prohibits defendants from frequenting places where controlled substances are illegally present. Because federal appellate courts differ as to the condition’s meaning and its application, the existing circuit split will be thoroughly discussed. The main issues with the condition demonstrate a lack of attentiveness and forethought of the sentencing judges that ultimately impose undue hardships onto the defendants wishing to enter back into society. Furthermore, due to the lack of clarity of the proscribed terms, defendants may be uncertain as to what behavior is permitted and what act may result in re-incarceration. Since the proscribed terms are subject to varying interpretations, the defendants subject to this condition may find it difficult to obey. This Note will argue that the imposition of vague supervised release conditions is contradictory to the rehabilitative purpose of supervised release, and will urge the sentencing courts to exercise greater caution when imposing terms of federal supervision. This will ensure that defendants are not subject to unclear terms that may be unintentionally violated
Scanning probe methods for studying surface structures - history of development and recent possibilities
Nonequilibrium stationary states with ratchet effect
An ensemble of particles in thermal equilibrium at temperature , modeled
by Nos\`e-Hoover dynamics, moves on a triangular lattice of oriented semi-disk
elastic scatterers. Despite the scatterer asymmetry a directed transport is
clearly ruled out by the second law of thermodynamics. Introduction of a
polarized zero mean monochromatic field creates a directed stationary flow with
nontrivial dependence on temperature and field parameters. We give a
theoretical estimate of directed current induced by a microwave field in an
antidot superlattice in semiconductor heterostructures.Comment: 4 pages, 5 figures (small changes added
Twinkling pulsar wind nebulae in the synchrotron cut-off regime and the gamma-ray flares in the Crab Nebula
Synchrotron radiation of ultra-relativistic particles accelerated in a pulsar
wind nebula may dominate its spectrum up to gamma-ray energies. Because of the
short cooling time of the gamma-ray emitting electrons, the gamma-ray emission
zone is in the immediate vicinity of the acceleration site. The particle
acceleration likely occurs at the termination shock of the relativistic striped
wind, where multiple forced magnetic field reconnections provide strong
magnetic fluctuations facilitating Fermi acceleration processes. The
acceleration mechanisms imply the presence of stochastic magnetic fields in the
particle acceleration region, which cause stochastic variability of the
synchrotron emission. This variability is particularly strong in the steep
gamma-ray tail of the spectrum, where modest fluctuations of the magnetic field
lead to strong flares of spectral flux. In particular, stochastic variations of
magnetic field, which may lead to quasi-cyclic gamma-ray flares, can be
produced by the relativistic cyclotron ion instability at the termination
shock. Our model calculations of the spectral and temporal evolution of
synchrotron emission in the spectral cut-off regime demonstrate that the
intermittent magnetic field concentrations dominate the gamma-ray emission from
highest energy electrons and provide fast, strong variability even for a
quasi-steady distribution of radiating particles. The simulated light curves
and spectra can explain the very strong gamma-ray flares observed in the Crab
nebula and the lack of strong variations at other wavelengths. The model
predicts high polarization in the flare phase, which can be tested with future
polarimetry observations.Comment: 5 pages, 3 figures, MNRAS in pres
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