Superfluid-insulator transition and BCS-BEC crossover in dirty ultracold Fermi gas

Superfluid-insulator transition in an ultracold Fermi gas in the external disorder potential of the amplitude $V_0$ is studied as a function of the concentration of the gas $n$ and magnetic field $B$ in the presence of the Feshbach resonance. We find the zero temperature phase diagrams in the plane ($B,n$) at a given $V_0$ and in the plane $(V_0, n)$ at a given $B$. Our results for BEC side of the diagram are also valid for the superfluid-insulator transition in a Bose gas.Comment: Reference added, typos correcte

Experimental study of the jamming transition at zero temperature

We experimentally investigate jamming in a quasi-two-dimensional granular system of automatically swelling particles and show that a maximum in the height of the first peak of the pair correlation function is a structural signature of the jamming transition at zero temperature. The same signature is also found in the second peak of the pair correlation function, but not in the third peak, reflecting the underlying singularity of jamming transition. We also study the development of clusters in this system. A static length scale extracted from the cluster structure reaches the size of the system when the system approaches the jamming point. Finally, we show that in a highly inhomogeneous system, friction causes the system to jam in series of steps. In this case, jamming may be obtained through successive buckling of force chains.Comment: 15 pages, 17 figure

Density of States for a Specified Correlation Function and the Energy Landscape

The degeneracy of two-phase disordered microstructures consistent with a specified correlation function is analyzed by mapping it to a ground-state degeneracy. We determine for the first time the associated density of states via a Monte Carlo algorithm. Our results are described in terms of the roughness of the energy landscape, defined on a hypercubic configuration space. The use of a Hamming distance in this space enables us to define a roughness metric, which is calculated from the correlation function alone and related quantitatively to the structural degeneracy. This relation is validated for a wide variety of disordered systems.Comment: Accepted for publication in Physical Review Letter

Surface versus bulk characterization of the electronic inhomogeneity in a VO_{2} film

We investigated the inhomogeneous electronic properties at the surface and interior of VO_{2} thin films that exhibit a strong first-order metal-insulator transition (MIT). Using the crystal structural change that accompanies a VO_{2} MIT, we used bulk-sensitive X-ray diffraction (XRD) measurements to estimate the fraction of metallic volume p^{XRD} in our VO_{2} film. The temperature dependence of the p$^{XRD}$ was very closely correlated with the dc conductivity near the MIT temperature, and fit the percolation theory predictions quite well: $\sigma$ $\sim$ (p - p_{c})^{t} with t = 2.0$\pm$0.1 and p_{c} = 0.16$\pm$0.01. This agreement demonstrates that in our VO$_{2}$ thin film, the MIT should occur during the percolation process. We also used surface-sensitive scanning tunneling spectroscopy (STS) to investigate the microscopic evolution of the MIT near the surface. Similar to the XRD results, STS maps revealed a systematic decrease in the metallic phase as temperature decreased. However, this rate of change was much slower than the rate observed with XRD, indicating that the electronic inhomogeneity near the surface differs greatly from that inside the film. We investigated several possible origins of this discrepancy, and postulated that the variety in the strain states near the surface plays an important role in the broad MIT observed using STS. We also explored the possible involvement of such strain effects in other correlated electron oxide systems with strong electron-lattice interactions.Comment: 27 pages and 7 figure

Pressure dependence of the Boson peak in glassy As2S3 studied by Raman Scattering

A detailed pressure-dependence study of the low-energy excitations of glassy As2S3 is reported over a wide pressure range, up to 10 GPa. The spectral features of Boson peak are analysed as a function of pressure. Pressure effects on the Boson peak are manifested as an appreciable shift of its frequency to higher values, a suppression of its intensity, as well as a noticeable change of its asymmetry leading to a more symmetric shape at high pressures. The pressure-induced Boson peak frequency shift agrees very well with the predictions of the soft potential model over the whole pressure range studied. As regards the pressure dependence of the Boson peak intensity, the situation is more complicated. It is proposed that in order to reach proper conclusions the corresponding dependence of the Debye density of states must also be considered. Employing a comparison of the low energy modes of the crystalline counterpart of As2S3 as well as the experimental data concerning the pressure dependencies of the Boson peak frequency and intensity, structural or glass-to-glass transition seems to occur at the pressure ~4 GPa related to a change of local structure. Finally, the pressure-induced shape changes of the Boson peak can be traced back to the very details of the excess (over the Debye contribution) vibrational density of states.Comment: To appear in J. Non-Cryst. Solids (Proceedings of the 5th IDMRCS, Lille, July 2005

Overuse of non-prescription analgesics by dental clinic patients

<p>Abstract</p> <p>Background</p> <p>Many patients present to dental clinics for treatment of painful conditions. Prior to seeking treatment, many of these patients will self-medicate with non-prescription analgesics (NPA), and some will unintentionally overdose on these products. The objective of this study is to describe the use of NPA among dental patients.</p> <p>Methods</p> <p>All adult patients presenting to an urban dental clinic during a two-week period in January and February of 2001 were approached to participate in this research project. Trained research assistants using a standardized questionnaire interviewed patients. Patient demographics and the NPA usage over the 3 days preceding the office visit were recorded. We defined a supra-therapeutic dose as any dose greater than the total recommended daily dose stated on package labeling.</p> <p>Results</p> <p>We approached 194 patients and 127 participated. The mean age of participants was 35.5 years, 52% were male. Analgesic use preceding the visit was reported by 99 of 127 patients, and most (81/99) used a NPA exclusively. Fifty-four percent of NPA users were taking more than one NPA. NPA users reported using ibuprofen (37%), acetaminophen (27%), acetaminophen/aspirin combination product (8%), naproxen (8%), and aspirin (4%). Sixteen patients reported supra-therapeutic use of one or more NPA (some ingested multiple products): ibuprofen (14), acetaminophen (3), and naproxen (5).</p> <p>Conclusion</p> <p>NPA use was common in patients presenting to a dental clinic. A significant minority of patients reported excessive dosing of NPA. Ibuprofen was the most frequently misused product, followed by naproxen and acetaminophen. Though mostly aware of the potential toxicity of NPA, many patients used supra-therapeutic dosages.</p

SCAR is a primary regulator of Arp2/3-dependent morphological events in Drosophila

The Arp2/3 complex and its activators, Scar/WAVE and Wiskott-Aldrich Syndrome protein (WASp), promote actin polymerization in vitro and have been proposed to influence cell shape and motility in vivo. We demonstrate that the Drosophila Scar homologue, SCAR, localizes to actin-rich structures and is required for normal cell morphology in multiple cell types throughout development. In particular, SCAR function is essential for cytoplasmic organization in the blastoderm, axon development in the central nervous system, egg chamber structure during oogenesis, and adult eye morphology. Highly similar developmental requirements are found for subunits of the Arp2/3 complex. In the blastoderm, SCAR and Arp2/3 mutations result in a reduction in the amount of cortical filamentous actin and the disruption of dynamically regulated actin structures. Remarkably, the single Drosophila WASp homologue, Wasp, is largely dispensable for these numerous Arp2/3-dependent functions, whereas SCAR does not contribute to cell fate decisions in which Wasp and Arp2/3 play an essential role. These results identify SCAR as a major component of Arp2/3-dependent cell morphology during Drosophila development and demonstrate that the Arp2/3 complex can govern distinct cell biological events in response to SCAR and Wasp regulation

Universal Formulae for Percolation Thresholds

A power law is postulated for both site and bond percolation thresholds. The formula writes $p_c=p_0[(d-1)(q-1)]^{-a}d^{\ b}$, where $d$ is the space dimension and $q$ the coordination number. All thresholds up to $d\rightarrow \infty$ are found to belong to only three universality classes. For first two classes $b=0$ for site dilution while $b=a$ for bond dilution. The last one associated to high dimensions is characterized by $b=2a-1$ for both sites and bonds. Classes are defined by a set of value for $\{p_0; \ a\}$. Deviations from available numerical estimates at $d \leq 7$ are within $\pm 0.008$ and $\pm 0.0004$ for high dimensional hypercubic expansions at $d \geq 8$. The formula is found to be also valid for Ising critical temperatures.Comment: 11 pages, latex, 3 figures not include

Classical Spin Models with Broken Continuous Symmetry: Random Field Induced Order and Persistence of Spontaneous Magnetization

We consider a classical spin model, of two-dimensional spins, with continuous symmetry, and investigate the effect of a symmetry breaking unidirectional quenched disorder on the magnetization of the system. We work in the mean field regime. We show, by numerical simulations and by perturbative calculations in the low as well as in the high temperature limits, that although the continuous symmetry of the magnetization is lost, the system still magnetizes, albeit with a lower value as compared to the case without disorder. The critical temperature at which the system starts magnetizing, also decreases with the introduction of disorder. However, with the introduction of an additional constant magnetic field, the component of magnetization in the direction that is transverse to the disorder field increases with the introduction of the quenched disorder. We discuss the same effects also for three-dimensional spins.Comment: 12 pages, 12 figures, RevTeX

Analytic solution of the fractional advection diffusion equation for the time-of-flight experiment in a finite geometry

A general analytic solution to the fractional advection diffusion equation is obtained in plane parallel geometry. The result is an infinite series of spatial Fourier modes which decay according to the Mittag-Leffler function, which is cast into a simple closed form expression in Laplace space using the Poisson summation theorem. An analytic expression for the current measured in a time-of-flight experiment is derived, and the sum of the slopes of the two respective time regimes on logarithmic axes is demonstrated to be -2, in agreement with the well known result for a continuous time random walk model. The sensitivity of current and particle number density to variation of experimentally controlled parameters is investigated in general, and the results applied to analyze selected experimental data.Comment: 10 pages, 6 figure