3,157 research outputs found
Novel Quaternary Dilute Magnetic Semiconductor (Ga,Mn)(Bi,As): Magnetic and Magneto-Transport Investigations
Magnetic and magneto-transport properties of thin layers of the
(Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor grown by the
low-temperature molecular-beam epitaxy technique on GaAs substrates have been
investigated. Ferromagnetic Curie temperature and magneto-crystalline
anisotropy of the layers have been examined by using magneto-optical Kerr
effect magnetometry and low-temperature magneto-transport measurements.
Postgrowth annealing treatment has been shown to enhance the hole concentration
and Curie temperature in the layers. Significant increase in the magnitude of
magnetotransport effects caused by incorporation of a small amount of Bi into
the (Ga,Mn)As layers revealed in the planar Hall effect (PHE) measurements, is
interpreted as a result of enhanced spin-orbit coupling in the (Ga,Mn)(Bi,As)
layers. Two-state behaviour of the planar Hall resistance at zero magnetic
field provides its usefulness for applications in nonvolatile memory devices.Comment: 10 pages, 3 figures, to be published in the Proceedings of ICSM-2016
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The truncated moment problem on N0
We find necessary and sufficient conditions for the existence of a probability measure on N0, the nonnegative integers, whose first n moments are a given n-tuple of nonnegative real numbers. The results, based on finding an optimal polynomial of degree n which is nonnegative on N0 (and which depends on the moments), and requiring that its expectation be nonnegative, generalize previous results known for n=1, n=2 (the Percus–Yamada condition), and partially for n=3. The conditions for realizability are given explicitly for n≤5 and in a finitely computable form for n≥6. We also find, for all n, explicit bounds, in terms of the moments, whose satisfaction is enough to guarantee realizability. Analogous results are given for the truncated moment problem on an infinite discrete semi-bounded subset of R
Signal reconstruction in the EM end-cap calorimeter and check with cosmic data in the region 0< eta <3.2
In 2007, the electromagnetic end-cap calorimeter joined the ATLAS commissioning effort. Since then, calibration and cosmic muon runs are taken regularly, allowing to set-up, debug and test in situ the signal reconstruction. These are the first data in the 1.4500 MeV) have been used to perform a systematic and quantitative comparison between data and predicted physics pulse shapes in a coherent way over the entire calorimeter coverage, 0< eta <3.2. This represents the first attempt to unify barrel and end-cap in situ data in a common analysis. Results are similar in the barrel and the end-cap, only slightly worse for the latter as expected from its more complex geometry. This is the first proof of the quality of an ATLAS-like signal reconstruction in the end-caps, despite its challenging aspect, and gives confidence that the energy reconstruction is in good control over the complete electromagnetic calorimeter coverage 0< eta <3.2
Covariance systems
We introduce new definitions of states and of representations of covariance
systems. The GNS-construction is generalized to this context. It associates a
representation with each state of the covariance system. Next, states are
extended to states of an appropriate covariance algebra. Two applications are
given. We describe a nonrelativistic quantum particle, and we give a simple
description of the quantum spacetime model introduced by Doplicher et al.Comment: latex with ams-latex, 23 page
Von Neumann equations with time-dependent Hamiltonians and supersymmetric quantum mechanics
Starting with a time-independent Hamiltonian and an appropriately chosen
solution of the von Neumann equation we construct
its binary-Darboux partner and an exact scattering solution of
where is time-dependent and not
isospectral to . The method is analogous to supersymmetric quantum mechanics
but is based on a different version of a Darboux transformation. We illustrate
the technique by the example where corresponds to a 1-D harmonic
oscillator. The resulting represents a scattering of a soliton-like
pulse on a three-level system.Comment: revtex, 3 eps file
Where to Next for Optimizing Adherence in Large-scale Trials of CPAP?
Large-scale randomized trials of positive airway pressure (PAP) efficacy have been largely negative yet PAP adherence was notably sub-optimal across the trials. To address this limitation, evidence-based PAP adherence protocols embedded within the larger trial protocol are recommended. The complexity of such protocols will be dependent on adequacy of resources, including funding and inclusion of behavioral scientist experts on the scientific team, and trial-specific considerations (e.g., target population) and methods. Recommendations for optimizing PAP adherence in large-scale trials are set forth that address rigor and reproducibility
Quantum feedback with weak measurements
The problem of feedback control of quantum systems by means of weak
measurements is investigated in detail. When weak measurements are made on a
set of identical quantum systems, the single-system density matrix can be
determined to a high degree of accuracy while affecting each system only
slightly. If this information is fed back into the systems by coherent
operations, the single-system density matrix can be made to undergo an
arbitrary nonlinear dynamics, including for example a dynamics governed by a
nonlinear Schr\"odinger equation. We investigate the implications of such
nonlinear quantum dynamics for various problems in quantum control and quantum
information theory, including quantum computation. The nonlinear dynamics
induced by weak quantum feedback could be used to create a novel form of
quantum chaos in which the time evolution of the single-system wave function
depends sensitively on initial conditions.Comment: 11 pages, TeX, replaced to incorporate suggestions of Asher Pere
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Generalized early warning signals in multivariate and gridded data with an application to tropical cyclones
Tipping events in dynamical systems have been studied across many applications, often by measuring changes in variance or autocorrelation in a one-dimensional time series. In this paper, methods for detecting early warning signals of tipping events in multidimensional systems are reviewed and expanded. An analytical justification of the use of dimension-reduction by empirical orthogonal functions, in the context of early warning signals, is provided and the one-dimensional techniques are also extended to spatially separated time series over a 2D field. The challenge of predicting an approaching tropical cyclone by a tipping-point analysis of the sea-level pressure series is used as the primary example, and an analytical model of a moving cyclone is also developed in order to test predictions. We show that the one-dimensional power spectrum indicator may be used following dimension-reduction or over a 2D field. We also show the validity of our moving cyclone model with respect to tipping-point indicators.
Many dynamical systems experience sudden shifts in behavior, often referred to as tipping points or critical transitions. A volume of work is dedicated to detecting and predicting these critical transitions, often making use of generic early warning signal (EWS) indicators based on autocorrelation1,2
and increasing variance.3,4
Similar indicators based on other scaling properties of the time series, namely, detrended fluctuation analysis (DFA)5,6
and power spectrum scaling,7
have also been used. Other methods have estimated parameters to fit a model to the data, both for detecting critical transitions8–10
and for predicting future transitions dynamics
Complete positivity of nonlinear evolution: A case study
Simple Hartree-type equations lead to dynamics of a subsystem that is not
completely positive in the sense accepted in mathematical literature. In the
linear case this would imply that negative probabilities have to appear for
some system that contains the subsystem in question. In the nonlinear case this
does not happen because the mathematical definition is physically unfitting as
shown on a concrete example.Comment: extended version, 3 appendices added (on mixed states, projection
postulate, nonlocality), to be published in Phys. Rev.
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