Dynamics of a classical Hall system driven by a time-dependent Aharonov--Bohm flux

We study the dynamics of a classical particle moving in a punctured plane under the influence of a strong homogeneous magnetic field, an electrical background, and driven by a time-dependent singular flux tube through the hole. We exhibit a striking classical (de)localization effect: in the far past the trajectories are spirals around a bound center; the particle moves inward towards the flux tube loosing kinetic energy. After hitting the puncture it becomes ``conducting'': the motion is a cycloid around a center whose drift is outgoing, orthogonal to the electric field, diffusive, and without energy loss

A constant of quantum motion in two dimensions in crossed magnetic and electric fields

We consider the quantum dynamics of a single particle in the plane under the influence of a constant perpendicular magnetic and a crossed electric potential field. For a class of smooth and small potentials we construct a non-trivial invariant of motion. Do to so we proof that the Hamiltonian is unitarily equivalent to an effective Hamiltonian which commutes with the observable of kinetic energy.Comment: 18 pages, 2 figures; the title was changed and several typos corrected; to appear in J. Phys. A: Math. Theor. 43 (2010

Propagators weakly associated to a family of Hamiltonians and the adiabatic theorem for the Landau Hamiltonian with a time-dependent Aharonov-Bohm flux

We study the dynamics of a quantum particle moving in a plane under the influence of a constant magnetic field and driven by a slowly time-dependent singular flux tube through a puncture. The known adiabatic results do not cover these models as the Hamiltonian has time dependent domain. We give a meaning to the propagator and prove an adiabatic theorem. To this end we introduce and develop the new notion of a propagator weakly associated to a time-dependent Hamiltonian.Comment: Title and Abstract changed, will appear in Journal of Mathematical Physic

Adjoint approach to the physical characterization of a shallow-water environment

In underwater acoustics a variety of different applications of adjoint models has been proposed in recent years. Adjoints have been derived for normal modes and for both the standard parabolic equation and Claerbout’s wide-angle approximation. This paper reviews the analytic nonlocal boundary control approach proposed in an earlier paper by the authors [Meyer & Hermand, ‘‘Optimal nonlocal boundary control of the wide-angle parabolic equation for inversion of a waveguide acoustic field,’’ J. Acoust. Soc. Am. 117, 2937–2948 (2005)] and presents a numerical extension that allows direct inversion of the geoacoustic parameters that are embedded in a discrete representation of the nonlocal boundary condition at the water-sediment interface. The effectiveness of this numerical adjoint approach for the physical characterization of a shallow-water environment is illustrated with applications for geoacoustic inversion and ocean acoustic tomography. In particular, it is shown how a joint inversion across multiple frequencies can enhance the performance of the optimization process, especially for the case of a sparse receiver array spanning part of the water column. In an additional example we combine the two applications and discuss the feasibility of geoacoustic inversion in the presence of an uncertain sound-speed profile

A numerical adjoint parabolic equation (PE) method for tomography and geoacoustic inversion in shallow water

Recently, an analytic adjoint-based method of optimal nonlocal boundary control has been proposed for inversion of a waveguide acoustic field using the wide-angle parabolic equation [Meyer and Hermand, J. Acoust. Soc. Am. 117, 2937–2948 (2005)]. In this paper a numerical extension of this approach is presented that allows the direct inversion for the geoacoustic parameters which are embedded in a spectral integral representation of the nonlocal boundary condition. The adjoint model is generated numerically and the inversion is carried out jointly across multiple frequencies. The paper further discusses the application of the numerical adjoint PE method for ocean acoustic tomography. To show the effectiveness of the implemented numerical adjoint, preliminary inversion results of water sound-speed profile and bottom acoustic properties will be shown for the YELLOW SHARK ’94 experimental conditions

Validation of adjoint-generated environmental gradients for the acoustic monitoring of a shallow water area

In the framework of the recent Maritime Rapid Environmental Assessment sea trial MREA07/BP'07 [Le Gac&Hermand, 2007] that was conducted in the same area south of the island of Elba as the earlier Yellow Shark trial (YS94), this paper examines the original YS94 acoustic data and the recent MREA07 oceanographic data to demonstrate adjoint-based acoustic monitoring of environmental parameters in Mediterranean shallow waters. First, adjoint-generated environmental gradients are validated for the application in geoacoustic inversion where the bottom acoustic parameters of the YS94 layered seabed are determined from the long-range waterborne propagation of a multi-frequency signal. Then, for the application in ocean acoustic tomography, the temporal variability of the MREA07/BP'07 oceanographic data is analyzed in terms of empirical orthogonal functions and the adjoint-based inversion scheme is used to track the time-varying sound speed profile of the experimental transect

Resonance distribution in open quantum chaotic systems

In order to study the resonance spectra of chaotic cavities subject to some damping (which can be due to absorption or partial reflection at the boundaries), we use a model of damped quantum maps. In the high-frequency limit, the distribution of (quantum) decay rates is shown to cluster near a ``typical'' value, which is larger than the classical decay rate of the corresponding damped ray dynamics. The speed of this clustering may be quite slow, which could explain why it has not been detected in previous numerical data.Comment: 4 pages. Compared with version 2, we have slightly modified the figures, corrected some misprints, and added the values for the fits in figure

Evaluation of the Sustainability of an Intervention to Increase HIV Testing

BACKGROUND Sustainability—the routinization and institutionalization of processes that improve the quality of healthcare—is difficult to achieve and not often studied. OBJECTIVE To evaluate the sustainability of increased rates of HIV testing after implementation of a multi-component intervention in two Veterans Health Administration healthcare systems. DESIGN Quasi-experimental implementation study in which the effect of transferring responsibility to conduct the provider education component of the intervention from research to operational staff was assessed. PATIENTS Persons receiving healthcare between 2005 and 2006 (intervention year) and 2006 and 2007 (sustainability year). MEASUREMENTS Monthly HIV testing rate, stratified by frequency of clinic visits RESULTS The monthly adjusted testing rate increased from 2% at baseline to 6% at the end intervention year and then declined reaching 4% at the end of the sustainability year. However, the stratified, visit-specific testing rate for persons newly exposed to the intervention (i.e., having their first through third visits during the study period) increased throughout the intervention and sustainability years. Increases in the proportion of visits by patients who remained untested despite multiple, prior exposures to the intervention accounted for the aggregate attenuation of testing during the sustainability year. Overall, the percentage of patients who received an HIV test in the sustainability year was 11.6%, in the intervention year 11.1%, and in the pre-intervention year 5.0% CONCLUSIONS Provider education combined with informatics and organizational support had a sustainable effect on HIV testing rates. The effect was most pronounced during patients' early contacts with the healthcare system.Health Services Research & Development Service (SDP 06–001