6,301 research outputs found
Digital filter suppresses effects of nonstatistical noise bursts on multichannel scaler digital averaging systems
Digital filter suppresses the effects of nonstatistical noise bursts on data averaged over multichannel scaler. Interposed between the sampled channels and the digital averaging system, it uses binary logic circuitry to compare the number of counts per channel with the average number of counts per channel
Non-linear screening of external charge by doped graphene
We solve a nonlinear integral equation for the electrostatic potential in
doped graphene due to an external charge, arising from a Thomas-Fermi (TF)
model for screening by graphene's electron bands. In particular, we study
the effects of a finite equilibrium charge carrier density in graphene,
non-zero temperature, non-zero gap between graphene and a dielectric substrate,
as well as the nonlinearity in the band density of states. Effects of the
exchange and correlation interactions are also briefly discussed for undoped
graphene at zero temperature. Nonlinear results are compared with both the
linearized TF model and the dielectric screening model within random phase
approximation (RPA). In addition, image potential of the external charge is
evaluated from the solution of the nonlinear integral equation and compared to
the results of linear models. We have found generally good agreement between
the results of the nonlinear TF model and the RPA model in doped graphene,
apart from Friedel oscillations in the latter model. However, relatively strong
nonlinear effects are found in the TF model to persist even at high doping
densities and large distances of the external charge.Comment: 12 pages including 6 figure
A three-dimensional hard spheres theory of scattering of gas atoms from a solid surface
Three dimensional model of monatomic gases interacting with solid surfaces represented by similar, noninteracting hard sphere
Reconnection in Marginally Collisionless Accretion Disk Coronae
We point out that a conventional construction placed upon observations of
accreting black holes, in which their nonthermal X-ray spectra are produced by
inverse comptonization in a coronal plasma, suggests that the plasma is
marginally collisionless. Recent developments in plasma physics indicate that
fast reconnection takes place only in collisionless plasmas. As has recently
been suggested for the Sun's corona, such marginal states may result from a
combination of energy balance and the requirements of fast magnetic
reconnection.Comment: Revised in response to referee. Accepted ApJ. 11 pp., no figures.
Uses aastex 5.0
Ghost Interference with Optical Parametric Amplifier
The 'Ghost' interference experiment is analyzed when the source of entangled
photons is a multimode Optical Parametric Amplifier(OPA) whose weak limit is
the two-photon Spontaneous Parametric Downconversion(SPDC) beam. The visibility
of the double-slit pattern is calculated, taking the finite coincidence time
window of the photon counting detectors into account. It is found that the
coincidence window and the bandwidth of light reaching the detectors play a
crucial role in the loss of visibility on coincidence detection, not only in
the 'Ghost' interference experiment but in all experiments involving
coincidence detection. The differences between the loss of visibility with
two-mode and multimode OPA sources is also discussed.
PACS: 42.65.Yj, 42.50.Dv, 42.65.L
Smoothing effect and delocalization of interacting Bose-Einstein condensates in random potentials
We theoretically investigate the physics of interacting Bose-Einstein
condensates at equilibrium in a weak (possibly random) potential. We develop a
perturbation approach to derive the condensate wavefunction for an amplitude of
the potential smaller than the chemical potential of the condensate and for an
arbitrary spatial variation scale of the potential. Applying this theory to
disordered potentials, we find in particular that, if the healing length is
smaller than the correlation length of the disorder, the condensate assumes a
delocalized Thomas-Fermi profile. In the opposite situation where the
correlation length is smaller than the healing length, we show that the random
potential can be significantly smoothed and, in the meanfield regime, the
condensate wavefunction can remain delocalized, even for very small correlation
lengths of the disorder.Comment: The word "screening" has been changed to "smoothing" to avoid
confusions with other effects discussed in the literature. This does not
affect the content of paper, nor the results, nor the physical discussio
Missing and Quenched Gamow Teller Strength
Gamow-Teller strength functions in full spaces are calculated with
sufficient accuracy to ensure that all the states in the resonance region have
been populated. Many of the resulting peaks are weak enough to become
unobservable. The quenching factor necessary to bring into agreement the low
lying observed states with shell model predictions is shown to be due to
nuclear correlations. To within experimental uncertainties it is the same that
is found in one particle transfer and (e,e') reactions. Perfect consistency
between the observed peaks and the calculation is
achieved by assuming an observation threshold of 0.75\% of the total strength,
a value that seems typical in several experimentsComment: 11 pages, 6 figures avalaible upon request, RevTeX, FTUAM-94/0
Experimental studies of ECRH/ECCD effects on Tearing Mode stability using the new TCV real-time control system
Abstract GP9.00075 submitted for the DPP10 Meeting of The American Physical Society
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
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