Engineering many-body quantum dynamics by disorder

Going beyond the currently investigated regimes in experiments on quantum transport of ultracold atoms in disordered potentials, we predict a crossover between regular and quantum-chaotic dynamics when varying the strength of disorder. Our spectral approach is based on the Bose-Hubbard model describing interacting atoms in deep random potentials. The predicted crossover from localized to diffusive dynamics depends on the simultaneous presence of interactions and disorder, and can be verified in the laboratory by monitoring the evolution of typical experimental initial states.Comment: 4 pages, 4 figures (improved version), to be published in PR

Langmuir cells and mixing in the upper ocean

The presence of surface gravity waves at the ocean surface has two important effects on turbulence in the oceanic mixed layer (ML): the wave breaking and the Langmuir cells (LC). Both these effects act as additional sources of turbulent kinetic energy (TKE) in the oceanic ML, and hence are important to mixing in the upper ocean. The breaking of high wave-number components of the wind wave spectrum provides an intense but sporadic source of turbulence in the upper surface; turbulence thus injected diffuses downward, while decaying rapidly, modifying oceanic near-surface properties which in turn could affect the air-sea transfer of heat and dissolved gases. LC provide another source of additional turbulence in the water column; they are counter-rotating cells inside the ML, with their axes roughly aligned in the direction of the wind (Langmuir I., Science, 87 (1938) 119). These structures are usually made evident by the presence of debris and foam in the convergence area of the cells, and are generated by the interaction of the wave-field–induced Stokes drift with the wind-induced shear stress. LC have long been thought to have a substantial influence on mixing in the upper ocean, but the difficulty in their parameterization have made ML modelers consistently ignore them in the past. However, recent Large Eddy Simulations (LES) studies suggest that it is possible to include their effect on mixing by simply adding additional production terms in the turbulence equations, thus enabling even 1D models to incorporate LC-driven turbulence. Since LC also modify the Coriolis terms in the mean momentum equations by the addition of a term involving the Stokes drift, their effect on the velocity structure in the ML is also quite significant and could have a major impact on the drift of objects and spilled oil in the upper ocean. In this paper we examine the effect of surface gravity waves on mixing in the upper ocean, focusing on Langmuir circulations, which is by far the dominant part of the surface wave contribution to mixing. Oceanic ML models incorporating these effects are applied to an observation station in the Northern Adriatic Sea to see what the extent of these effects might be. It is shown that the surface wave effects can indeed be significant; in particular, the modification of the velocity profile due to LC-generated turbulence can be large under certain conditions. However, the surface wave effects on the bulk properties of the ML, such as the associated temperature, while significant, are generally speaking well within the errors introduced by uncertainties in the external forcing of the models. This seems to be the reason why ML models, though pretty much ignoring surface wave effects until recently, have been reasonably successful in depicting the evolution of the mixed layer temperature (MLT) at various timescales

Mean-Field- and Classical Limit of Many-Body Schr\"odinger Dynamics for Bosons

We present a new proof of the convergence of the N-particle Schroedinger dynamics for bosons towards the dynamics generated by the Hartree equation in the mean-field limit. For a restricted class of two-body interactions, we obtain convergence estimates uniform in the Planck constant , up to an exponentially small remainder. For h=0, the classical dynamics in the mean-field limit is given by the Vlasov equation.Comment: Latex 2e, 18 page

Some integrals ocurring in a topology change problem

In a paper presented a few years ago, De Lorenci et al. showed, in the context of canonical quantum cosmology, a model which allowed space topology changes (Phys. Rev. D 56, 3329 (1997)). The purpose of this present work is to go a step further in that model, by performing some calculations only estimated there for several compact manifolds of constant negative curvature, such as the Weeks and Thurston spaces and the icosahedral hyperbolic space (Best space).Comment: RevTeX article, 4 pages, 1 figur

Heterogeneity in District-Level Transmission of Ebola Virus Disease during the 2013-2015 Epidemic in West Africa.

The Ebola virus disease (EVD) epidemic in West Africa in 2013-2015 spread heterogeneously across the three hardest-hit countries Guinea, Liberia and Sierra Leone and the estimation of national transmission of EVD provides little information about local dynamics. To investigate district-level transmissibility of EVD, we applied a statistical modelling approach to estimate the basic reproduction number (R0) for each affected district and each country using weekly incident case numbers. We estimated growth rates during the early exponential phase of the outbreak using exponential regression of the case counts on the first eight weeks since onset. To take into account the heterogeneity between and within countries, we fitted a mixed effects model and calculated R0 based on the predicted individual growth rates and the reported serial interval distribution. At district level, R0 ranged from 0.36 (Dubréka) to 1.72 (Beyla) in Guinea, from 0.53 (Maryland) to 3.37 (Margibi) in Liberia and from 1.14 (Koinadugu) to 2.73 (Western Rural) in Sierra Leone. At national level, we estimated an R0 of 0.97 (95% CI 0.77-1.18) for Guinea, 1.26 (95% CI 0.98-1.55) for Liberia and 1.66 (95% CI 1.32-2.00) for Sierra Leone. Socio-demographic variables related to urbanisation such as high population density and high wealth index were found positively associated with R0 suggesting that the consequences of fast urban growth in West Africa may have contributed to the increased spread of EVD

HIV Protease Inhibitors: Advances in Therapy and Adverse Reactions, Including Metabolic Complications

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90068/1/phco.19.4.281.30937.pd

Magnitude and Duration of Elevated Gastric pH in Patients Infected with Human Immunodeficiency Virus After Administration of Chewable, Dispersible, Buffered Didanosine Tablets

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90191/1/phco.24.16.1539.50959.pd

The Moment of Inertia and the Scissors Mode of a Bose-condensed Gas

We relate the frequency of the scissors mode to the moment of inertia of a trapped Bose gas at finite temperature in a semi-classical approximation. We apply these theoretical results to the data obtained in our previous study of the properties of the scissors mode of a trapped Bose-Einstein condensate of $^{87}$Rb atoms as a function of the temperature. The frequency shifts that we measured show quenching of the moment of inertia of the Bose gas at temperatures below the transition temperature - the system has a lower moment of inertia that of a rigid body with the same mass distribution, because of superfluidity.Comment: 14 pages, 5 fig

Collective oscillations of a classical gas confined in harmonic traps

Starting from the Boltzmann equation we calculate the frequency and the damping of the monopole and quadrupole oscillations of a classical gas confined in an harmonic potential. The collisional term is treated in the relaxation time approximation and a gaussian ansatz is used for its evaluation. Our approach provides an explicit description of the transition between the hydrodynamic and collisionless regimes in both spherical and deformed traps. The predictions are compared with the results of a numerical simulation.Comment: 6 pages, revtex, 2 figures include

Supersymmetric Scenarios with Dominant Radiative Neutralino Decay

The radiative decay of the next-to-lightest neutralino into a lightest neutralino and a photon is analyzed in the MSSM. We find that significant regions of the supersymmetric parameter space with large radiative BR's (up to about 100%) do exist. The radiative channel turns out to be enhanced when the neutralino tree-level decays are suppressed either "kinematically" or "dynamically". In general, in the regions allowed by LEP data and not characterized by asymptotic values of the SuSy parameters, the radiative enhancement requires tan beta ~= 1 and/or M_1 ~= M_2, and negative values of \mu. We present typical specific scenarios where these "necessary" conditions are fulfilled, relaxing the usual relation M_1=(5/3)*tan^2(th_W)*M_2. The influence of varying the stop masses and mixing angle when the radiative decay is enhanced is also considered. Some phenomenological consequences of the above picture are discussed.Comment: 32 pages, LaTeX file + 23 figures embedded with epsf.sty. In this revised version, Eq.(3) plus some related notations and text passages have been changed. Minor error corrected in Fig.12(a). The numerical analysis and the conclusions of the paper are not affected. (Includes the erratum to appear in Phys. Rev. D.) Source and ps files are also available at ftp://hpteo.roma1.infn.it/pub/preprints/ambr-mele/Rome1-1148/ or at http://feynman.physics.lsa.umich.edu/~ambros/Physics.html#1