Deeply subrecoil two-dimensional Raman cooling

We report the implementation of a two-dimensional Raman cooling scheme using sequential excitations along the orthogonal axes. Using square pulses, we have cooled a cloud of ultracold Cesium atoms down to an RMS velocity spread of 0.39(5) recoil velocity, corresponding to an effective temperature of 30 nK (0.15 T_rec). This technique can be useful to improve cold atom atomic clocks, and is particularly relevant for clocks in microgravity.Comment: 8 pages, 6 figures, submitted to Phys. Rev.

Levy distribution in many-particle quantum systems

Levy distribution, previously used to describe complex behavior of classical systems, is shown to characterize that of quantum many-body systems. Using two complimentary approaches, the canonical and grand-canonical formalisms, we discovered that the momentum profile of a Tonks-Girardeau gas, -- a one-dimensional gas of $N$ impenetrable (hard-core) bosons, harmonically confined on a lattice at finite temperatures, obeys Levy distribution. Finally, we extend our analysis to different confinement setups and demonstrate that the tunable Levy distribution properly reproduces momentum profiles in experimentally accessible regions. Our finding allows for calibration of complex many-body quantum states by using a unique scaling exponent.Comment: 7 pages, 6 figures, results are generalized, new examples are adde

Three-dimensional Simulations of Disk Accretion to an Inclined Dipole: I. Magnetospheric Flow at Different Theta

We present results of fully three-dimensional MHD simulations of disk accretion to a rotating magnetized star with its dipole moment inclined at an angle Theta to the rotation axis of the disk. We observed that matter accretes from the disk to a star in two or several streams depending on Theta. Streams may precess around the star at small Theta. The inner regions of the disk are warped. The warping is due to the tendency of matter to co-rotate with inclined magnetosphere. The accreting matter brings positive angular momentum to the (slowly rotating) star tending to spin it up. The corresponding torque N_z depends only weakly on Theta. The angular momentum flux to the star is transported predominantly by the magnetic field; the matter component contributes < 1 % of the total flux. Results of simulations are important for understanding the nature of classical T Tauri stars, cataclysmic variables, and X-ray pulsars.Comment: 26 pages, 22 figures, LaTeX, macros: emulapj.sty, avi simulations are available at http://www.astro.cornell.edu/us-rus/inclined.ht

Exact and explicit probability densities for one-sided Levy stable distributions

We study functions g_{\alpha}(x) which are one-sided, heavy-tailed Levy stable probability distributions of index \alpha, 0< \alpha <1, of fundamental importance in random systems, for anomalous diffusion and fractional kinetics. We furnish exact and explicit expression for g_{\alpha}(x), 0 \leq x < \infty, satisfying \int_{0}^{\infty} exp(-p x) g_{\alpha}(x) dx = exp(-p^{\alpha}), p>0, for all \alpha = l/k < 1, with k and l positive integers. We reproduce all the known results given by k\leq 4 and present many new exact solutions for k > 4, all expressed in terms of known functions. This will allow a 'fine-tuning' of \alpha in order to adapt g_{\alpha}(x) to a given experimental situation.Comment: 4 pages, 3 figures and 1 tabl

Cirrhosis Diagnosis and Liver Fibrosis Staging: Transient Elastometry Versus Cirrhosis Blood Test.

INTRODUCTION: Elastometry is more accurate than blood tests for cirrhosis diagnosis. However, blood tests were developed for significant fibrosis, with the exception of CirrhoMeter developed for cirrhosis. We compared the performance of Fibroscan and CirrhoMeter, and classic binary cirrhosis diagnosis versus new fibrosis staging for cirrhosis diagnosis. METHODS: The diagnostic population included 679 patients with hepatitis C and liver biopsy (Metavir staging and morphometry), Fibroscan, and CirrhoMeter. The prognostic population included 1110 patients with chronic liver disease and both tests. RESULTS: Binary diagnosis: AUROCs for cirrhosis were: Fibroscan: 0.905; CirrhoMeter: 0.857; and P=0.041. Accuracy (Youden cutoff) was: Fibroscan: 85.4%; CirrhoMeter: 79.2%; and P&lt;0.001. Fibrosis classification provided 6 classes (F0/1, F1/2, F2±1, F3±1, F3/4, and F4). Accuracy was: Fibroscan: 88.2%; CirrhoMeter: 88.8%; and P=0.77. A simplified fibrosis classification comprised 3 categories: discrete (F1±1), moderate (F2±1), and severe (F3/4) fibrosis. Using this simplified classification, CirrhoMeter predicted survival better than Fibroscan (respectively, χ=37.9 and 19.7 by log-rank test), but both predicted it well (P&lt;0.001 by log-rank test). Comparison: binary diagnosis versus fibrosis classification, respectively, overall accuracy: CirrhoMeter: 79.2% versus 88.8% (P&lt;0.001); Fibroscan: 85.4% versus 88.2% (P=0.127); positive predictive value for cirrhosis by Fibroscan: Youden cutoff (11.1 kPa): 49.1% versus cutoffs of F3/4 (17.6 kPa): 67.6% and F4 classes (25.7 kPa): 82.4%. CONCLUSIONS: Fibroscan\u27s usual binary cutoffs for cirrhosis diagnosis are not sufficiently accurate. Fibrosis classification should be preferred over binary diagnosis. A cirrhosis-specific blood test markedly attenuates the accuracy deficit for cirrhosis diagnosis of usual blood tests versus transient elastometry, and may offer better prognostication

Force-Free Models of Magnetically Linked Star-Disk Systems

Disk accretion onto a magnetized star occurs in a variety of astrophysical contexts, from young stars to X-ray pulsars. The magnetohydrodynamic interaction between the stellar field and the accreting matter can have a strong effect on the disk structure, the transfer of mass and angular momentum between the disk and the star, and the production of bipolar outflows, e.g., plasma jets. We study a key element of this interaction - the time evolution of the magnetic field configuration brought about by the relative rotation between the disk and the star - using simplified, largely semianalytic, models. We first discuss the rapid inflation and opening up of the magnetic field lines in the corona above the accretion disk, which is caused by the differential rotation twisting. Then we consider additional physical effects that tend to limit this expansion, such as the effect of plasma inertia and the possibility of reconnection in the disk's corona, the latter possibly leading to repeated cycles in the evolution. We also derive the condition for the existence of a steady state for a resistive disk and conclude that a steady state configuration is not realistically possible. Finally, we generalize our analysis of the opening of magnetic field lines by using a non-self-similar numerical model that applies to an arbitrarily rotating (e.g. keplerian) disk.Comment: 75 pages, 22 figures, 2 tables. Submitted to Astrophysical Journa

Dicke-Type Energy Level Crossings in Cavity-Induced Atom Cooling: Another Superradiant Cooling

This paper is devoted to energy-spectral analysis for the system of a two-level atom coupled with photons in a cavity. It is shown that the Dicke-type energy level crossings take place when the atom-cavity interaction of the system undergoes changes between the weak coupling regime and the strong one. Using the phenomenon of the crossings we develop the idea of cavity-induced atom cooling proposed by the group of Ritsch, and we lay mathematical foundations of a possible mechanism for another superradiant cooling in addition to that proposed by Domokos and Ritsch. The process of our superradiant cooling can function well by cavity decay and by control of the position of the atom, at least in (mathematical) theory, even if there is neither atomic absorption nor atomic emission of photons.Comment: 15 pages; 8 figure

Mean-field limit of systems with multiplicative noise

A detailed study of the mean-field solution of Langevin equations with multiplicative noise is presented. Three different regimes depending on noise-intensity (weak, intermediate, and strong-noise) are identified by performing a self-consistent calculation on a fully connected lattice. The most interesting, strong-noise, regime is shown to be intrinsically unstable with respect to the inclusion of fluctuations, as a Ginzburg criterion shows. On the other hand, the self-consistent approach is shown to be valid only in the thermodynamic limit, while for finite systems the critical behavior is found to be different. In this last case, the self-consistent field itself is broadly distributed rather than taking a well defined mean value; its fluctuations, described by an effective zero-dimensional multiplicative noise equation, govern the critical properties. These findings are obtained analytically for a fully connected graph, and verified numerically both on fully connected graphs and on random regular networks. The results presented here shed some doubt on what is the validity and meaning of a standard mean-field approach in systems with multiplicative noise in finite dimensions, where each site does not see an infinite number of neighbors, but a finite one. The implications of all this on the existence of a finite upper critical dimension for multiplicative noise and Kardar-Parisi-Zhang problems are briefly discussed.Comment: 9 Pages, 8 Figure

Photonic superdiffusive motion in resonance line radiation trapping - partial frequency redistribution effects

The relation between the jump length probability distribution function and the spectral line profile in resonance atomic radiation trapping is considered for Partial Frequency Redistribution (PFR) between absorbed and reemitted radiation. The single line Opacity Distribution Function [M.N. Berberan-Santos et.al. J.Chem.Phys. 125, 174308 (2006)] is generalized for PFR and used to discuss several possible redistribution mechanisms (pure Doppler broadening, combined natural and Doppler broadening and combined Doppler, natural and collisional broadening). It is shown that there are two coexisting scales with a different behavior: the small scale is controlled by the intricate PFR details while the large scale is essentially given by the atom rest frame redistribution asymptotic. The pure Doppler and combined natural, Doppler and collisional broadening are characterized by both small and large scale superdiffusive Levy flight behaviors while the combined natural and Doppler case has an anomalous small scale behavior but a diffusive large scale asymptotic. The common practice of assuming complete redistribution in core radiation and frequency coherence in the wings of the spectral distribution is incompatible with the breakdown of superdiffusion in combined natural and Doppler broadening conditions

Large phenotype jumps in biomolecular evolution

By defining the phenotype of a biopolymer by its active three-dimensional shape, and its genotype by its primary sequence, we propose a model that predicts and characterizes the statistical distribution of a population of biopolymers with a specific phenotype, that originated from a given genotypic sequence by a single mutational event. Depending on the ratio g0 that characterizes the spread of potential energies of the mutated population with respect to temperature, three different statistical regimes have been identified. We suggest that biopolymers found in nature are in a critical regime with g0 in the range 1-6, corresponding to a broad, but not too broad, phenotypic distribution resembling a truncated Levy flight. Thus the biopolymer phenotype can be considerably modified in just a few mutations. The proposed model is in good agreement with the experimental distribution of activities determined for a population of single mutants of a group I ribozyme.Comment: to appear in Phys. Rev. E; 7 pages, 6 figures; longer discussion in VII, new fig.