Mean-field analysis of a dynamical phase transition in a cellular automaton model for collective motion

A cellular automaton model is presented for random walkers with biologically motivated interactions favoring local alignment and leading to collective motion or swarming behavior. The degree of alignment is controlled by a sensitivity parameter, and a dynamical phase transition exhibiting spontaneous breaking of rotational symmetry occurs at a critical parameter value. The model is analyzed using nonequilibrium mean field theory: Dispersion relations for the critical modes are derived, and a phase diagram is constructed. Mean field predictions for the two critical exponents describing the phase transition as a function of sensitivity and density are obtained analytically.Comment: 4 pages, 4 figures, final version as publishe

Shock experiments in range of 10-45 GPa with small multidomain magnetite in porous targets

Peer reviewe

Ropivacaine decreases tissue oxygen saturation following peripheral nerve block in children

Background: Local anesthetics can cause vasoconstriction and disrupt neuronal impulses, reducing regional blood flow and increasing tissue oxygen consumption. This could alter regional oxygen supply and demand. Because microcirculation modifies during development and oxygen consumption kinetics differ between children and adults, we aimed to assess effects of ropivacaine Peripheral Nerve Block (PNB) on regional tissue saturation in children and young adults using Near-Infrared Spectroscopy (NIRS). Methods: Following Institutional Review Board approval and informed consent, 20 patients undergoing PNB for various orthopedic surgeries were studied. NIRS sensors were placed on the operative limb, contralateral limb, and forehead. Tissue saturations (rSO2) were recorded at baseline and every 5 minutes for 60 minutes following ropivacaine PNB. Mean rSO2 was assessed with repeated measures ANOVA. Correlation of tissue rSO2 with cerebral oximetry was calculated and significance determined with student’s t-test. Results: In all patients, blocked limb rSO2 decreased significantly compared to control limb 20 minutes after injection and remained lower. Control limb rSO2 and cerebral oximetry did not change over time. Non-blocked limb rSO2 demonstrated weak but significant correlation with cerebral oximetry while blocked limb rSO2 showed no correlation. Mean change in blocked limb rSO2 from baseline was significantly negative compared to a net positive mean change in the non-blocked limb. Conclusions: Decreased rSO2 following PNB suggests reduced local blood flow due to vasoconstriction, increased tissue oxygen consumption, or both. Changes in rSO2 provide an opportunity to develop NIRS as a non-invasive tool to identify successful PNB. Local anesthetic-induced decline in rSO2 could have implications in operative settings with ischemia or low-flow

Daubechies wavelets as a basis set for density functional pseudopotential calculations

Daubechies wavelets are a powerful systematic basis set for electronic structure calculations because they are orthogonal and localized both in real and Fourier space. We describe in detail how this basis set can be used to obtain a highly efficient and accurate method for density functional electronic structure calculations. An implementation of this method is available in the ABINIT free software package. This code shows high systematic convergence properties, very good performances and an excellent efficiency for parallel calculations.Comment: 15 pages, 11 figure

Three‐dimensional forward stratigraphic modelling of the sedimentary architecture of meandering‐river successions in evolving half‐graben rift basins

The spatial organisation of meandering‐river deposits varies greatly within the sedimentary fills of rift basins, depending on how differential rates of fault propagation and subsidence interplay with autogenic processes to drive changes in fluvial channel‐belt position and rate of migration, avulsion frequency and mechanisms of meander‐bend cut off. This set of processes fundamentally influences stacking patterns of the accumulated successions. Quantitative predictions of the spatio‐temporal evolution and internal architecture of meandering fluvial deposits in such tectonically active settings remain limited. A numerical forward stratigraphic model—the Point‐Bar Sedimentary Architecture Numerical Deduction (PB‐SAND)—is applied to examine relationships between differential rates of subsidence and resultant fluvial channel‐belt migration, reach avulsion and channel‐deposit stacking in active, fault‐bounded half‐grabens. The model is used to reconstruct and predict the complex morphodynamics of fluvial meanders, their generated channel belts, and the associated lithofacies distributions that accumulate as heterogeneous fluvial successions in rift settings, constrained by data from seismic images and outcrop successions. The 3D modelling outputs are used to explore sedimentary heterogeneity at various spatio‐temporal scales. Results show how the connectivity of sand‐prone geobodies can be quantified as a function of subsidence rate, which itself decreases both along and away from the basin‐bounding fault. In particular, results highlight the spatial variability in the size and connectedness of sand‐prone geobodies that is seen in directions perpendicular and parallel to the basin axis, and that arises as a function of the interaction between spatial and temporal variations in rates of accommodation generation and fault‐influenced changes in river morphodynamics. The results have applied significance, for example, to both hydrocarbon exploration and assessment of groundwater aquifers. The expected greatest connectivity of fluvial sandbody in a half‐graben is primarily determined by the complex interplay between the frequency and rate of subsidence, the style of basin propagation, the rates of migration of channel belts, the frequency of avulsion and the proportion and spatial distribution of variably sand‐prone channel and bar deposits

Monte Carlo simulations of random copolymers at a selective interface

We investigate numerically using the bond--fluctuation model the adsorption of a random AB--copolymer at the interface between two solvents. From our results we infer several scaling relations: the radius of gyration of the copolymer in the direction perpendicular to the interface ($R_{gz}$) scales with $\chi$, the interfacial selectivity strength, as $R_{gz}=N^{\nu}f(\sqrt{N}\chi)$ where $\nu$ is the usual Flory exponent and $N$ is the copolymer's length; furthermore the monomer density at the interface scales as $\chi^{2\nu}$ for small $\chi$. We also determine numerically the monomer densities in the two solvents and discuss their dependence on the distance from the interface.Comment: Latex text file appended with figures.tar.g

Preparation of distilled and purified continuous variable entangled states

The distribution of entangled states of light over long distances is a major challenge in the field of quantum information. Optical losses, phase diffusion and mixing with thermal states lead to decoherence and destroy the non-classical states after some finite transmission-line length. Quantum repeater protocols, which combine quantum memory, entanglement distillation and entanglement swapping, were proposed to overcome this problem. Here we report on the experimental demonstration of entanglement distillation in the continuous-variable regime. Entangled states were first disturbed by random phase fluctuations and then distilled and purified using interference on beam splitters and homodyne detection. Measurements of covariance matrices clearly indicate a regained strength of entanglement and purity of the distilled states. In contrast to previous demonstrations of entanglement distillation in the complementary discrete-variable regime, our scheme achieved the actual preparation of the distilled states, which might therefore be used to improve the quality of downstream applications such as quantum teleportation

Many worlds in one

A generic prediction of inflation is that the thermalized region we inhabit is spatially infinite. Thus, it contains an infinite number of regions of the same size as our observable universe, which we shall denote as \O-regions. We argue that the number of possible histories which may take place inside of an \O-region, from the time of recombination up to the present time, is finite. Hence, there are an infinite number of \O-regions with identical histories up to the present, but which need not be identical in the future. Moreover, all histories which are not forbidden by conservation laws will occur in a finite fraction of all \O-regions. The ensemble of \O-regions is reminiscent of the ensemble of universes in the many-world picture of quantum mechanics. An important difference, however, is that other \O-regions are unquestionably real.Comment: 9 pages, 2 figures, comments and references adde

Critical exponents for random knots

The size of a zero thickness (no excluded volume) polymer ring is shown to scale with chain length $N$ in the same way as the size of the excluded volume (self-avoiding) linear polymer, as $N^{\nu}$, where $\nu \approx 0.588$. The consequences of that fact are examined, including sizes of trivial and non-trivial knots.Comment: 4 pages, 0 figure

Mixtures of Bosonic and Fermionic Atoms in Optical Lattices

We discuss the theory of mixtures of Bosonic and Fermionic atoms in periodic potentials at zero temperature. We derive a general Bose--Fermi Hubbard Hamiltonian in a one--dimensional optical lattice with a superimposed harmonic trapping potential. We study the conditions for linear stability of the mixture and derive a mean field criterion for the onset of a Bosonic superfluid transition. We investigate the ground state properties of the mixture in the Gutzwiller formulation of mean field theory, and present numerical studies of finite systems. The Bosonic and Fermionic density distributions and the onset of quantum phase transitions to demixing and to a Bosonic Mott--insulator are studied as a function of the lattice potential strength. The existence is predicted of a disordered phase for mixtures loaded in very deep lattices. Such a disordered phase possessing many degenerate or quasi--degenerate ground states is related to a breaking of the mirror symmetry in the lattice.Comment: 11 pages, 8 figures; added discussions; conclusions and references expande