333 research outputs found
Nonadiabatic quantum pumping in mesoscopic nanostructures
We consider a nonadiabatic quantum pumping phenomena in a ballistic narrow
constriction. The pumping is induced by a potential that has both spatial and
temporal periodicity characterized by and . In the zero frequency
() limit, the transmission through narrow constriction exhibits
valley structures due to the opening up of energy gaps in the pumping region --
a consequence of the periodicity. These valley structures remain robust in
the regime of finite , while their energies of occurrence are shifted
by about . The direction of these energy shifts depend on the
directions of both the phase-velocity of the pumping potential and the
transmitting electrons. This frequency dependent feature of the valley
structures gives rise to both the asymmetry in the transmission coefficients
and the pumping current. An experimental setup is suggested for a possible
observation of our nonadiabatic quantum pumping findings.Comment: 4 pages, 2 figure
Anomalous oxidation of Fe-Si alloys under a low oxygen pressure at 800 °C
The authors acknowledge financial support by NSFC of China under the research projects (Nos. 50971129 and 51371183).Abstract The oxidation of three Fe-xSi alloys (x = 5, 9, 13 at.%) under 10−20 atm O2 at 800 °C formed in all cases SiO2 layers. For Fe-5Si this layer broke down and healed up periodically forming an anomalous internal oxidation zone with spherical and net-shaped SiO2 particles. The SiO2 layer formed on the other two alloys spalled off due to the growth and thermal stress accumulated. The critical silicon content needed for its external oxidation on Fe-Si alloys calculated according to an extension of Wagner's theory under the present experimental conditions is significantly smaller than the experimental results.PostprintPeer reviewe
Nonlinear atom optics and bright gap soliton generation in finite optical lattices
We theoretically investigate the transmission dynamics of coherent matter
wave pulses across finite optical lattices in both the linear and the nonlinear
regimes. The shape and the intensity of the transmitted pulse are found to
strongly depend on the parameters of the incident pulse, in particular its
velocity and density: a clear physical picture for the main features observed
in the numerical simulations is given in terms of the atomic band dispersion in
the periodic potential of the optical lattice. Signatures of nonlinear effects
due the atom-atom interaction are discussed in detail, such as atom optical
limiting and atom optical bistability. For positive scattering lengths, matter
waves propagating close to the top of the valence band are shown to be subject
to modulational instability. A new scheme for the experimental generation of
narrow bright gap solitons from a wide Bose-Einstein condensate is proposed:
the modulational instability is seeded in a controlled way starting from the
strongly modulated density profile of a standing matter wave and the solitonic
nature of the generated pulses is checked from their shape and their
collisional properties
Leading order analysis of neutrino induced dimuon events in the CHORUS experiment
We present a leading order QCD analysis of a sample of neutrino induced
charged-current events with two muons in the final state originating in the
lead-scintillating fibre calorimeter of the CHORUS detector. The results are
based on a sample of 8910 neutrino and 430 antineutrino induced opposite-sign
dimuon events collected during the exposure of the detector to the CERN Wide
Band Neutrino Beam between 1995 and 1998. % with GeV
and GeV collected %between 1995 and 1998. The analysis yields a
value of the charm quark mass of \mc = (1.26\pm 0.16 \pm 0.09) \GeVcc and a
value of the ratio of the strange to non-strange sea in the nucleon of , improving the results obtained in similar analyses
by previous experiments.Comment: Submitted to Nuclear Physics
Charged-Particle Multiplicities in Charged-Current Neutrino-- and Anti-Neutrino--Nucleus Interactions
The CHORUS experiment, designed to search for
oscillations, consists of a nuclear emulsion target and electronic detectors.
In this paper, results on the production of charged particles in a small sample
of charged-current neutrino-- and anti-neutrino--nucleus interactions at high
energy are presented. For each event, the emission angle and the ionization
features of the charged particles produced in the interaction are recorded,
while the standard kinematic variables are reconstructed using the electronic
detectors. The average multiplicities for charged tracks, the pseudo-rapidity
distributions, the dispersion in the multiplicity of charged particles and the
KNO scaling are studied in different kinematical regions. A study of
quasi-elastic topologies performed for the first time in nuclear emulsions is
also reported. The results are presented in a form suitable for use in the
validation of Monte Carlo generators of neutrino--nucleus interactions.Comment: 17 pages, 5 figure
Associated Charm Production in Neutrino-Nucleus Interactions
In this paper a search for associated charm production both in neutral and
charged current -nucleus interactions is presented. The improvement of
automatic scanning systems in the {CHORUS} experiment allows an efficient
search to be performed in emulsion for short-lived particles. Hence a search
for rare processes, like the associated charm production, becomes possible
through the observation of the double charm-decay topology with a very low
background. About 130,000 interactions located in the emulsion target
have been analysed. Three events with two charm decays have been observed in
the neutral-current sample with an estimated background of 0.180.05. The
relative rate of the associated charm cross-section in deep inelastic
interactions, has been
measured. One event with two charm decays has been observed in charged-current
interactions with an estimated background of 0.180.06 and the
upper limit on associated charm production in charged-current interactions at
90% C.L. has been found to be .Comment: 10 pages, 4 figure
Measurement of B(D_s+ -> mu+ nu_mu)/B(D_s+ -> phi mu+ nu_mu) and Determination of the Decay Constant f_{D_s}
We have observed purely-leptonic decays of
from a sample of muonic one prong decay events
detected in the emulsion target of Fermilab experiment E653. Using the yield measured previously in this experiment, we obtain
. In addition, we extract the decay constant .Comment: 15 pages including one figur
Measurement of charm production in neutrino charged-current interactions
The nuclear emulsion target of the CHORUS detector was exposed to the
wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy from
1994 to 1997. In total about 100000 charged-current neutrino interactions with
at least one identified muon were located in the emulsion target and fully
reconstructed, using newly developed automated scanning systems. Charmed
particles were searched for by a program recognizing particle decays. The
observation of the decay in nuclear emulsion makes it possible to select a
sample with very low background and minimal kinematical bias. 2013
charged-current interactions with a charmed hadron candidate in the final state
were selected and confirmed through visual inspection. The charm production
rate induced by neutrinos relative to the charged-current cross-section is
measured to be sigma(nu_mu N -> mu- C X)/sigma(CC) = (5.75 +-0.32 stat +-0.30
syst)%. The charm production cross-section as a function of the neutrino energy
is also obtained. The results are in good agreement with previous measurements.
The charm-quark hadronization produces the following charmed hadrons with
relative fractions (in %): f_Dzero = 43.7+-4.5, f_Lambda_c^plus = 19.2+-4.2,
f_Dplus = 25.3+-4.2, and f_D_splus = 11.8+-4.7.Comment: 16 pages, 5 figure
Observation of a first candidate in the OPERA experiment in the CNGS beam
The OPERA neutrino detector in the underground Gran Sasso Laboratory (LNGS)
has been designed to perform the first detection of neutrino oscillations in
direct appearance mode through the study of the
channel. The hybrid apparatus consists of an emulsion/lead target complemented
by electronic detectors and it is placed in the high energy long-baseline CERN
to LNGS beam (CNGS) 730 km away from the neutrino source. Runs with CNGS
neutrinos were successfully carried out in 2008 and 2009. After a brief
description of the beam, the experimental setup and the procedures used for the
analysis of the neutrino events, we describe the topology and kinematics of a
first candidate charged-current event satisfying the kinematical
selection criteria. The background calculations and their cross-check are
explained in detail and the significance of the event is assessed.Comment: 19 pages, 3 figure
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