Transport properties and structures of vortex matter in layered superconductors

In this paper we analyze the structure, phase transitions and some transport properties of the vortex system when the external magnetic field lies parallel to the planes in layered superconductors. We show that experimental results for resistivity are qualitatively consistent with numerical simulations that describe the melting of a commensurate rotated lattice. However for some magnetic fields, the structure factor indicates the occurrence of smectic peaks at an intermediate temperature regime.Comment: 8 pages, 8 eps figure

Numerical Analysis of the Big Bounce in Loop Quantum Cosmology

Loop quantum cosmology homogeneous models with a massless scalar field show that the big-bang singularity can be replaced by a big quantum bounce. To gain further insight on the nature of this bounce, we study the semi-discrete loop quantum gravity Hamiltonian constraint equation from the point of view of numerical analysis. For illustration purposes, we establish a numerical analogy between the quantum bounces and reflections in finite difference discretizations of wave equations triggered by the use of nonuniform grids or, equivalently, reflections found when solving numerically wave equations with varying coefficients. We show that the bounce is closely related to the method for the temporal update of the system and demonstrate that explicit time-updates in general yield bounces. Finally, we present an example of an implicit time-update devoid of bounces and show back-in-time, deterministic evolutions that reach and partially jump over the big-bang singularity.Comment: 5 pages, 3 figures, new title, replaced with version accepted for publicatio

Physical consequences of P≠\neqNP and the DMRG-annealing conjecture

Computational complexity theory contains a corpus of theorems and conjectures regarding the time a Turing machine will need to solve certain types of problems as a function of the input size. Nature {\em need not} be a Turing machine and, thus, these theorems do not apply directly to it. But {\em classical simulations} of physical processes are programs running on Turing machines and, as such, are subject to them. In this work, computational complexity theory is applied to classical simulations of systems performing an adiabatic quantum computation (AQC), based on an annealed extension of the density matrix renormalization group (DMRG). We conjecture that the computational time required for those classical simulations is controlled solely by the {\em maximal entanglement} found during the process. Thus, lower bounds on the growth of entanglement with the system size can be provided. In some cases, quantum phase transitions can be predicted to take place in certain inhomogeneous systems. Concretely, physical conclusions are drawn from the assumption that the complexity classes {\bf P} and {\bf NP} differ. As a by-product, an alternative measure of entanglement is proposed which, via Chebyshev's inequality, allows to establish strict bounds on the required computational time.Comment: Accepted for publication in JSTA

Automated EEG spectrum analysis system

A computer system has been designed to acquire EEG data from monkeys and to perform the spectral and statistical analysis. The system is capable of processing two channels simultaneously, acquire 64 Kbytes of EEG data for each channel on floppy disk, do the spectrums and averages of the spectrums, and calculate the histogram amplitudes of 13 frequency bands in a range of 0-71.1 Hz. The software gives the user a lot of choices with respect to data acquisition and processing. The relative spectral power differences between no-drug and drug experiments give information about the drug effects on the central nervous system. The present system is easier to control with respect to previous similar systems because it is capable of performing the experiments in an automated manner without any human intervention. Another quality of the system is the simplicity and small space needed. Being based on software, the system is very flexible and easy to extend. One of the features of the new system is new programs for the statistical comparisons can be done automatically. Another feature is related to the extension of the system to process 15 channels simultaneously. Experiments have been performed to validate the system using the previous system results. Results are presented to show the quality of the system. Investigations have been done into other ways of analyzing the spectral data in order to improve the system. The results of this system can be successfully used in classifying new drugs

Distortion of Globular Clusters by Galactic Bulges

One of the external fields that influences the population of globular clusters is that due to galactic bulges. In extreme situations, perigalactic distances $r_p \le 100$ pc, globular clusters could suffer total disruption in a single passage. A more common scenario is that for cluster orbits with $r_p \ge 200$ pc. We investigate the effects of tidal forces from a bulge on the shape of globular clusters for this type of encounters. We find distortions characterized by ``twisting isophotes'' and consider the potential for observability of this effect. In the Milky Way, a typical globular cluster must pass within several hundred pc of the center to experience substantial distortion, and it is possible that this has happened recently to one or two present day clusters. We estimate that this distortion could be observed even for globulars in dense fields toward the bulge. In more extreme environments such as giant ellipticals or merger products with newly formed globulars, this effect could be more common, extending out to orbits that pass within 1 kpc of the bulge center. This would lead to a substantial shift in the eccentricity distribution of globulars in those galaxies.Comment: 12 pages, 8 figure

Why, when, and how fast innovations are adopted

When the full stock of a new product is quickly sold in a few days or weeks, one has the impression that new technologies develop and conquer the market in a very easy way. This may be true for some new technologies, for example the cell phone, but not for others, like the blue-ray. Novelty, usefulness, advertising, price, and fashion are the driving forces behind the adoption of a new product. But, what are the key factors that lead to adopt a new technology? In this paper we propose and investigate a simple model for the adoption of an innovation which depends mainly on three elements: the appeal of the novelty, the inertia or resistance to adopt it, and the interaction with other agents. Social interactions are taken into account in two ways: by imitation and by differentiation, i.e., some agents will be inclined to adopt an innovation if many people do the same, but other will act in the opposite direction, trying to differentiate from the "herd". We determine the conditions for a successful implantation of the new technology, by considering the strength of advertising and the effect of social interactions. We find a balance between the advertising and the number of anti-herding agents that may block the adoption of a new product. We also compare the effect of social interactions, when agents take into account the behavior of the whole society or just a part of it. In a nutshell, the present model reproduces qualitatively the available data on adoption of innovation.Comment: 11 pages, 13 figures (with subfigures), full paper (EPJB 2012) on innovation adoption mode

Calcium-Activated Potassium Channels Inhibition in Autonomically Stimulated Human Atrial Myocytes

The autonomic nervous system has been reported to play a major role in the generation and maintenance of atrial fibrillation. Various investigations have suggested small-conductance calcium-activated potassium (SK) channels as potential targets for more effective pharmacological therapies. In this study, we used in silico modeling and simulation to investigate the effects of SK channel inhibition on the action potential (AP) of autonomically stimulated human atrial cardiomyocytes. The Grandi AP model, with a new formulation for the ISK current, was used to represent human atrial electrophysiology. Choliner-gic stimulation by different concentrations of acetylcholine (ACh) hyperpolarized the AP and shortened the AP duration (APD) in a dose-dependent manner, with up to 7 mV resting membrane potential elevation and >200 ms APD shortening for 1 µM ACh at 1 Hz pacing frequency. Additional ß-adrenergic stimulation by 1 µM Isoproterenol (Iso) partially attenuated the effects of cholinergic stimulation by prolonging the APD by 41.6%. ISK inhibition was able to reverse the effects of cholinergic activation, but only for moderate ACh doses and when combined with 1 µM Iso, leading to 58.3% prolongation of the AP stimulated with 0.01 µM ACh. In conclusion, ISK inhibition combined with ß-adrenergic stimulation can be effective in antagonizing cholinergic effects on human atrial myocytes

An ADM 3+1 formulation for Smooth Lattice General Relativity

A new hybrid scheme for numerical relativity will be presented. The scheme will employ a 3-dimensional spacelike lattice to record the 3-metric while using the standard 3+1 ADM equations to evolve the lattice. Each time step will involve three basic steps. First, the coordinate quantities such as the Riemann and extrinsic curvatures are extracted from the lattice. Second, the 3+1 ADM equations are used to evolve the coordinate data, and finally, the coordinate data is used to update the scalar data on the lattice (such as the leg lengths). The scheme will be presented only for the case of vacuum spacetime though there is no reason why it could not be extended to non-vacuum spacetimes. The scheme allows any choice for the lapse function and shift vectors. An example for the Kasner $T^3$ cosmology will be presented and it will be shown that the method has, for this simple example, zero discretisation error.Comment: 18 pages, plain TeX, 5 epsf figues, gzipped ps file also available at http://newton.maths.monash.edu.au:8000/preprints/3+1-slgr.ps.g

The H=xp model revisited and the Riemann zeros

Berry and Keating conjectured that the classical Hamiltonian H = xp is related to the Riemann zeros. A regularization of this model yields semiclassical energies that behave, in average, as the non trivial zeros of the Riemann zeta function. However, the classical trajectories are not closed, rendering the model incomplete. In this paper, we show that the Hamiltonian H = x (p + l_p^2/p) contains closed periodic orbits, and that its spectrum coincides with the average Riemann zeros. This result is generalized to Dirichlet L-functions using different self-adjoint extensions of H. We discuss the relation of our work to Polya's fake zeta function and suggest an experimental realization in terms of the Landau model.Comment: 5 pages, 3 figure