Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals

We report on the thermally activated flux flow dependency on the doping dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found clearly that irrespective of the doping ratio, magnetoresistivity showed a distinct tail just above the Tc, offset associated with the thermally activated flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature dependence of the activation energy follows the relation U(T, B)=U_0 (B) (1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence of the activation energy follows a power law of U_0 (B)~B^(-{\alpha}) where the exponent {\alpha} is changed from a low value to a high value at a crossover field of B=~2T, indicating the transition from collective to plastic pinning in the crystals. Finally, it is suggested that the 3D vortex phase is the dominant phase in the low-temperature region as compared to the TAFF region in our series samples

Anomalous kinetics of attractive A+B→0A+B \to 0 reactions

We investigate the kinetics of $A+B \to 0$ reaction with the local attractive interaction between opposite species in one spatial dimension. The attractive interaction leads to isotropic diffusions inside segregated single species domains, and accelerates the reactions of opposite species at the domain boundaries. At equal initial densities of $A$ and $B$, we analytically and numerically show that the density of particles ($\rho$), the size of domains ($\ell$), the distance between the closest neighbor of same species ($\ell_{AA}$), and the distance between adjacent opposite species ($\ell_{AB}$) scale in time as $\rho \sim t^{-1/3}$, $\ell_{AA} \sim t^{1/3}$, and $\ell \sim \ell_{AB} \sim t^{2/3}$ respectively. These dynamical exponents form a new universality class distinguished from the class of uniformly driven systems of hard-core particles.Comment: 4 pages, 4 figure

Nonlinear Response of Cylindrical Shells to Underwater Explosion: Testings and Numerical Prediction Using USA/DYNA3D / June 1, 1991 - March 1, 1992

The views expressed are those of the authors and do not reflect the offical policy or position of DoD or US Government.Nonlinear 3-D Dynamic Analysis Code (VEC/DYNA3D) has been interfaced with Underwater Shock Analysis Code (USA) and capabilities were developed to perform numerical analysis of submerged and semi-submerged marine structures subjected to underwater explosion. A series of numerical analysis were performed to determine the elastic and elasto-plastic responses of cylindrica shell type structures. The results were favorably compared with those of underwater explosion testings. The coupled code USA/DYNA3D makes possible to predict shock-induced damage response of naval structure. In addition, numerical sensitivity analyses were undertaken to determine the importance of various physical and numerical modeling factors. This study showed clearly three types of response modes of cylinder subjected to a side-on explosion: accordion mode, breathing mode and whipping mode.This report was prepared for and funded by both Defense Nuclear Agency, Alexandria, VA 20311 and Naval Postgraduate School, Monterey, CA 93943.Approved for public release; distribution is unlimited

Response of dual-layered structures subjected to shock pressure wave

The response of coated, metallic structures subjected to shock pressure waves is studied. The coating is either an elastic material or nearly incompressible rubber of variable stiffness separating the structure from an air or water medium. The stress, nodal velocity, and internal energy of the coated structure are compared to a system without a coating (homogeneous system) to examine the effect of various coating types and configurations on the response of the structure to shock conditions. The results show that a mismatch of impedance, pc0, between the coating and structure governs the degree of energy exchange between the coating and structure at the interface. The impedance mismatch between the structure and a rubber coating at the threshold value is termed the critical difference. If the impedance mismatch exceeds the critical difference, the dynamic response will be more adverse. A softer coating generally has a smaller impedance and tends to concentrate stress wave energy in the underlying structureDefense Nuclear Agency, Alexandria, VAhttp://archive.org/details/responseofdualla00brasMIPR No. 94-573N

Coupling of lattice Boltzmann and finite element methods for fluidstructure interaction application

In order to analyze the fluid-structure interaction between a flow and a flexible structure, an algorithm was presented to couple the lattice Boltzmann method (LBM

Emergence of skew distributions in controlled growth processes

Starting from a master equation, we derive the evolution equation for the size distribution of elements in an evolving system, where each element can grow, divide into two, and produce new elements. We then probe general solutions of the evolution quation, to obtain such skew distributions as power-law, log-normal, and Weibull distributions, depending on the growth or division and production. Specifically, repeated production of elements of uniform size leads to power-law distributions, whereas production of elements with the size distributed according to the current distribution as well as no production of new elements results in log-normal distributions. Finally, division into two, or binary fission, bears Weibull distributions. Numerical simulations are also carried out, confirming the validity of the obtained solutions.Comment: 9 pages, 3 figure