4,236 research outputs found
Consequences of negative differential electron mobility in insulated gate field effect transistors
We study the consequences of negative differential electron mobility in
insulated gate field effect transistors (FETS) using the field model. We show
that, in contrast to the case of the monotonic velocity saturation model, the
field distributions in a short-channel FET may be described by the gradual
channel approximation even for high drain-to-source voltages. The
current-voltage dependence of the short-channel FET should have a branch with a
negative slope. The FET exhibits a negative differential resistance and may
show convective or absolute instability, depending on the applied voltages. The
fluctuation growth is governed by the diffusion law with a negative effective
diffusion coefficient.Comment: 4 pages, 2 figure
Orbit equivalence rigidity for ergodic actions of the mapping class group
We establish orbit equivalence rigidity for any ergodic, essentially free and
measure-preserving action on a standard Borel space with a finite positive
measure of the mapping class group for a compact orientable surface with higher
complexity. We prove similar rigidity results for a finite direct product of
mapping class groups as well.Comment: 11 pages, title changed, a part of contents remove
Formation of plasma around a small meteoroid: 1. Kinetic theory
This article is a companion to Dimant and Oppenheim [2017] https://doi.org/10.1002/2017JA023963.This paper calculates the spatial distribution of the plasma responsible for radar head echoes by applying the kinetic theory developed in the companion paper. This results in a set of analytic expressions for the plasma density as a function of distance from the meteoroid. It shows that at distances less than a collisional mean free path from the meteoroid surface, the plasma density drops in proportion to 1/R where R is the distance from the meteoroid center; and, at distances much longer than the mean‐free‐path behind the meteoroid, the density diminishes at a rate proportional to 1/R2. The results of this paper should be used for modeling and analysis of radar head echoes.This work was supported by NSF grant AGS-1244842. (AGS-1244842 - NSF
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Studies of the beam-beam interaction for the LHC
We have used the beam-beam simulation code CBI to study the beam-beam interaction for the LHC. We find that for nominal LHC parameters, and assuming only one bunch per beam, there are no collective (coherent) beam-beam instabilities. We have investigated the effect of sweeping one of the beams around the other (a procedure that could be used as a diagnostic for head-on beam-beam collisions), We find that this does not cause any problems at the nominal current, though at higher currents there can be beam blow-up and collective beam motion. (4 refs)
Stimulated wave of polarization in spin chains
Stimulated wave of polarization, triggered by a flip of a single spin,
presents a simple model of quantum amplification. Previously, it has been found
that such wave can be excited in a 1D Ising chain with nearest-neighbor
interactions, irradiated by a weak resonant transverse field. Here we explore
models with more realistic Hamiltonians, in particular, with natural
dipole-dipole interactions. Results of simulations for 1D spin chains and rings
with up to nine spins are presented.Comment: 15 pages, 5 figure
Electrocardiogram derived respiration during sleep
The aim of this study was quantify the ECG Derived Respiration (EDR) in order to extend the capabilities of ECG-based sleep analysis. We examined our results in normal subjects and in patients with Obstructive Sleep Apnea Syndrome (OSAS) or Central Sleep Apnea. Lead 2 ECG and three measures of respiration (thorax and abdominal effort, and oronasal flow signal) were recorded during sleep studies of 12 normal and 12 OSAS patients. Three parameters, the R-wave amplitude (RWA), R-wave duration (RWD), and QRS area, were extracted from the ECG signal, resulting in time series that displayed a behavior similar to that of the respiration signals. EDR frequency was correlated with directly measured respiratory frequency, and averaged over all subjects. The peak-to-peak value of the EDR signals during the apnea event was compared to the average peak-to-peak of the sleep stage, containing the apnea. 1
Does event structure influence children's motion event expressions
This study focuses on understanding of event structure, in particular therelationship between Manner and Path. Narratives were elicited from twenty 3-year-olds and twenty adults using 6 animated motion events that were divided into two groups based on Goldberg's (1997) distinction between causal (Manner-inherent; e.g. roll down) and non-causal (Manner-incidental; e.g. spin while going up) relationships between Manner and Path. The data revealed that adults and children are sensitive to differences between inherent and incidental Manner. Adults significantly reduced use of canonical syntactic constructions for Manner-incidental events, employing other constructions. Children, however, while significantly reducing use of canonical syntactic constructionsfor Manner-incidental events, did not exploit alternative constructions. Instead, they omitted Manner from their speech altogether. A follow-up lexical task showed that children had knowledge of all omitted Manners. Given that this strategic omission of Manner is not lexically motivated, the results are discussed in relation to implications for pragmatics and memory load
Collective Decoherence of Nuclear Spin Clusters
The problem of dipole-dipole decoherence of nuclear spins is considered for
strongly entangled spin cluster. Our results show that its dynamics can be
described as the decoherence due to interaction with a composite bath
consisting of fully correlated and uncorrelated parts. The correlated term
causes the slower decay of coherence at larger times. The decoherence rate
scales up as a square root of the number of spins giving the linear scaling of
the resulting error. Our theory is consistent with recent experiment reported
in decoherence of correlated spin clusters.Comment: 4 pages, 4 figure
Improved Analysis of J/psi Decays into a Vector Meson and Two Pseudoscalars
Recently, the BES collaboration has published an extensive partial wave
analysis of experimental data on J/psi -> phi pi+pi-, J/psi -> omega pi+pi-,
J/psi -> phi K+K- and J/psi -> omega K+K-. These new results are analyzed here,
with full account of detection efficiencies, in the framework of a chiral
unitary description with coupled-channel final state interactions between pi-pi
and K-bar K pairs. The emission of a dimeson pair is described in terms of the
strange and nonstrange scalar form factors of the pion and the kaon, which
include the final state interaction and are constrained by unitarity and by
matching to the next-to-leading-order chiral expressions. This procedure allows
for a calculation of the S-wave component of the dimeson spectrum including the
f_0(980) resonance, and for an estimation of the low-energy constants of Chiral
Perturbation Theory, in particular the large N_c suppressed constants L_4^r and
L_6^r. The decays in question are also sensitive to physics associated with OZI
violation in the 0++ channel. It is found that the S-wave contributions to phi
pi+pi-, phi K+K- and omega pi+pi- given by the BES partial-wave analysis may be
very well fitted up to a dimeson center-of-mass energy of ~1.2 GeV, for a large
and positive value of L_4^r and a value of L_6^r compatible with zero. An
accurate determination of the amount of OZI violation in the J/psi -> phi
pi+pi- decay is achieved, and the S-wave contribution to omega K+K- near
threshold is predicted.Comment: 18 pages, 6 figures, title changed, accepted version for PR
Compound transfer matrices: Constructive and destructive interference
Scattering from a compound barrier, one composed of a number of distinct
non-overlapping sub-barriers, has a number of interesting and subtle
mathematical features. If one is scattering classical particles, where the wave
aspects of the particle can be ignored, the transmission probability of the
compound barrier is simply given by the product of the transmission
probabilities of the individual sub-barriers. In contrast if one is scattering
waves (whether we are dealing with either purely classical waves or quantum
Schrodinger wavefunctions) each sub-barrier contributes phase information (as
well as a transmission probability), and these phases can lead to either
constructive or destructive interference, with the transmission probability
oscillating between nontrivial upper and lower bounds. In this article we shall
study these upper and lower bounds in some detail, and also derive bounds on
the closely related process of quantum excitation (particle production) via
parametric resonance.Comment: V1: 28 pages. V2: 21 pages. Presentation significantly streamlined
and shortened. This version accepted for publication in the Journal of
Mathematical Physic
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