An assessment of the newest magnetar-SNR associations

Anomalous X-ray Pulsars and Soft-Gamma Repeaters groups are magnetar candidates featuring low characteristic ages ($\tau = {P\over{2 {\dot P}}}$). At least some of them they should still be associated with the remnants of the explosive events in which they were born, giving clues to the type of events leading to their birth and the physics behind the apparent high value of the magnetar magnetic fields. To explain the high values of $B$, a self-consistent picture of field growth also suggests that energy injection into the SNR is large and unavoidable, in contrast with the evolution of {\it conventional} SNR. This modified dynamics, in turn, has important implications for the proposed associations. We show that this scenario yields low ages for the new candidates CXOU J171405.7-381031/CTB 37B and XMMU J173203.3-344518/G353.6-0.7, and predicted values agree with recently found ${\dot P}$, giving support to the overall picture.Comment: Contributed talk to the ASTRONS 2010 Conference, Cesme, Turkey, Aug. 2-6 201

Optical Dipole Trapping beyond Rotating Wave Approximation: The case of Large Detuning

We show that the inclusion of counter-rotating terms, usually dropped in evaluations of interaction of an electric dipole of a two level atom with the electromagnetic field, leads to significant modifications of trapping potential in the case of large detuning. The results are shown to be in excellent numerical agreement with recent experimental findings, for the case of modes of Laguerre-Gauss spatial profile.Comment: 13 pages, 2 figure

Electrolytes between dielectric charged surfaces: Simulations and theory

We present a simulation method to study electrolyte solutions in a dielectric slab geometry using a modified 3D Ewald summation. The method is fast and easy to implement, allowing us to rapidly resum an infinite series of image charges. In the weak coupling limit, we also develop a mean-field theory which allows us to predict the ionic distribution between the dielectric charged plates. The agreement between both approaches, theoretical and simulational, is very good, validating both methods. Examples of ionic density profiles in the strong electrostatic coupling limit are also presented. Finally, we explore the confinement of charge asymmetric electrolytes between neutral surfaces

Role of three-body interactions in formation of bulk viscosity in liquid argon

With the aim of locating the origin of discrepancy between experimental and computer simulation results on bulk viscosity of liquid argon, a molecular dynamic simulation of argon interacting via ab initio pair potential and triple-dipole three-body potential has been undertaken. Bulk viscosity, obtained using Green-Kubo formula, is different from the values obtained from modeling argon using Lennard-Jones potential, the former being closer to the experimental data. The conclusion is made that many-body inter-atomic interaction plays a significant role in formation of bulk viscosity.Comment: 4 pages, 3 figure

Pion mass effects on axion emission from neutron stars through NN bremsstrahlung processes

The rates of axion emission by nucleon-nucleon bremsstrahlung are calculated with the inclusion of the full momentum contribution from a nuclear one pion exchange (OPE) potential. The contributions of the neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) processes in both the nondegenerate and degenerate limits are explicitly given. We find that the finite momentum corrections to the emissivities are quantitatively significant for the non-degenerate regime and temperature-dependent, and should affect the existing axion mass bounds. The trend of these nuclear effects is to diminish the emissivities

Holonomic constraints : an analytical result

Systems subjected to holonomic constraints follow quite complicated dynamics that could not be described easily with Hamiltonian or Lagrangian dynamics. The influence of holonomic constraints in equations of motions is taken into account by using Lagrange multipliers. Finding the value of the Lagrange multipliers allows to compute the forces induced by the constraints and therefore, to integrate the equations of motions of the system. Computing analytically the Lagrange multipliers for a constrained system may be a difficult task that is depending on the complexity of systems. For complex systems, it is most of the time impossible to achieve. In computer simulations, some algorithms using iterative procedures estimate numerically Lagrange multipliers or constraint forces by correcting the unconstrained trajectory. In this work, we provide an analytical computation of the Lagrange multipliers for a set of linear holonomic constraints with an arbitrary number of bonds of constant length. In the appendix of the paper, one would find explicit formulas for Lagrange multipliers for systems having 1, 2, 3, 4 and 5 bonds of constant length, linearly connected.Comment: 13 pages, no figures. To appear in J. Phys. A : Math. The

Lipid content and biomass analysis in autotrophic and heterotrophic algal species

Biofuels are a form of renewable energy derived from living matter, typically plants. The push for biofuels began in order to decrease the amount of carbon dioxide (CO2) released into the atmosphere, as biofuels are essentially carbon neutral. The idea is the same amount of CO2 the plants took in to perform photosynthesis will then be released in the burning of the biofuels. Algae is an excellent source of biofuels because it grows quickly and is versatile in terms of the type of fuel it can produce. The two most common mechanisms for algae growth are heterotrophic or photoautotrophic. Heterotrophically grown algae uses an exogenous energy source, such as glucose, and uses the energy stored in it to perform cellular functions. Glucose also serves as a source of carbon and hydrogen, which are the primary elements found in lipids. In addition heterotrophic algae requires other nutrients for survival, such as water, vitamins, and inorganic ions. Algae grown photoautotrophically uses pigments in cellular photoreceptors to convert energy from light into adenosine triphosphate (ATP), an energy source, and to produce glucose. It also requires water, vitamins, and inorganic ions like the heterotrophic algae does. Some algal species, such as Chlorella zofingiensis, can be grown both photoautotrophically and heterotrophically. This algae species will be the subject of our experiment. Our experiment seeks to discover the most efficient way of growing algae to produce the highest amount of lipids. In addition to serving as a key component of cell and organelle membranes, lipids are a common form of high efficiency, long-term energy storage for living organisms, which is why lipids are extracted and processed to form biofuels. We propose growing one species of algae photoautotrophically by providing it with proper amounts of light but eliminating any glucose available. We will also grow the same species heterotrophically, with exogenous access to glucose, but eliminating all exposure to light sources. Finally, we will grow the same species mixotrophically with access to both glucose and light. Once the algae is grown, it will be harvested and analyzed for its lipid profile to determine which algae sample has the highest percent lipid content. We will also measure the percent biomass of each sample to determine which primary energy source leads to the greatest amount of total algal growth, percent organic material, and percent lipid content. We predict the algae grown with access to both sunlight and exogenous glucose will produce both the highest lipid content and the highest percent of biomass

Screening of charged spheroidal colloidal particles

We study the effective screened electrostatic potential created by a spheroidal colloidal particle immersed in an electrolyte, within the mean field approximation, using Poisson--Botzmann equation in its linear and nonlinear forms, and also beyond the mean field by means of Monte Carlo computer simulation. The anisotropic shape of the particle has a strong effect on the screened potential, even at large distances (compared to the Debye length) from it. To quantify this anisotropy effect, we focus our study on the dependence of the potential on the position of the observation point with respect with the orientation of the spheroidal particle. For several different boundary conditions (constant potential, or constant surface charge) we find that, at large distance, the potential is higher in the direction of the large axis of the spheroidal particle

Origin of Superconductivity in Boron-doped Diamond

Superconductivity of boron-doped diamond, reported recently at T_c=4 K, is investigated exploiting its electronic and vibrational analogies to MgB2. The deformation potential of the hole states arising from the C-C bond stretch mode is 60% larger than the corresponding quantity in MgB2 that drives its high Tc, leading to very large electron-phonon matrix elements. The calculated coupling strength \lambda ~ 0.5 leads to T_c in the 5-10 K range and makes phonon coupling the likely mechanism. Higher doping should increase T_c somewhat, but effects of three dimensionality primarily on the density of states keep doped diamond from having a T_c closer to that of MgB2.Comment: Four pages with two embedded figures, corrected fig1. (To appear in Physical Review Letters(2004)

Phonon spectral function for an interacting electron-phonon system

Using exact diagonalzation techniques, we study a model of interacting electrons and phonons. The spectral width of the phonons is found to be reduced as the Coulomb interaction U is increased. For a system with two modes per site, we find a transfer of coupling strength from the upper to the lower mode. This transfer is reduced as U is increased. These results give a qualitative explanation of differences between Raman and photoemission estimates of the electron-phonon coupling constants for A3C60 (A= K, Rb).Comment: 4 pages, RevTeX, 2 eps figur