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In this paper, we study Klein tunneling in random media. To this purpose, we simulate the propagation of a relativistic Gaussian wavepacket through a graphene sample with randomly distributed potential barriers (impurities). The simulations, based on a relativistic quantum lattice Boltzmann method, permit to compute the transmission coefficient across the sample, thereby providing an estimate for the conductivity as a function of impurity concentration and strength of the potentials. It is found that the conductivity loss due to impurities is significantly higher for wave-packets of massive particles, as compared to massless ones. A general expression for the loss of conductivity as a function of the impurity percentage is presented and successfully compared with the Kozeny-Carman law for disordered media in classical fluid dynamics., Comment: 12 pages, 38 figures

We provide numerical evidence that electronic pre-turbulent phenomena in graphene could be observed, under current experimental conditions, through detectable current fluctuations, echoing the detachment of vortices past localized micron-sized impurities. Vortex generation, due to micron sized constriction, is also explored with special focus on the effects of relativistic corrections to the normal Navier-Stokes equations. These corrections are found to cause a delay in the stability breakout of the fluid as well as a small shift in the vortex shedding frequency. Finally, a relation between the Strouhal number, a dimensionless measure of the vortex shedding frequency, and the Reynolds number is provided under conditions of interest for future experiments., Comment: 5 pages, 8 figures

We present a new lattice kinetic method to simulate fluid dynamics in curvilinear geometries. A suitable discrete Boltzmann equation is solved in contravariant coordinates, and the equilibrium distribution function is obtained by a Hermite polynomials expansion of the Maxwell-Boltzmann distribution, expressed in terms of the contravariant coordinates and the metric tensor. To validate the model, we calculate the critical Reynolds number for the onset of the Taylor-Couette instability between two concentric cylinders, obtaining excellent agreement with the theory. In order to extend this study to more general geometries, we also calculate the critical Reynolds number for the case of two concentric spheres, finding good agreement with experimental data. In the case of two concentric tori, we have found that the critical Reynolds is about 10% larger than the respective value for the two concentric cylinders., Comment: This paper has been withdrawn by the authors due to the fact that new very interesting results have come out

In this paper, we investigate the recently developed lattice Boltzmann model for relativistic hydrodynamics. To this purpose, we perform simulations of shock waves in quark-gluon plasma in the low and high viscosities regime, using three different computational models, the relativistic lattice Boltzmann (RLB), the Boltzmann Approach Multi-Parton Scattering (BAMPS), and the viscous sharp and smooth transport algorithm (vSHASTA). From the results, we conclude that the RLB model departs from BAMPS in the case of high speeds and high temperature(viscosities), the departure being due to the fact that the RLB is based on a quadratic approximation of the Maxwell-J\"uttner distribution, which is only valid for sufficiently low temperature and velocity. Furthermore, we have investigated the influence of the lattice speed on the results, and shown that inclusion of quadratic terms in the equilibrium distribution improves the stability of the method within its domain of applicability. Finally, we assess the viability of the RLB model in the various parameter regimes relevant to ultra-relativistic fluid dynamics., Comment: 10 pages, 16 Figures

Starting from the Maxwell-Juettner equilibrium distribution, we develop a relativistic lattice Boltzmann (LB) algorithm capable of handling ultrarelativistic systems with flat, but expanding, spacetimes. The algorithm is validated through simulations of quark-gluon plasma, yielding excellent agreement with hydrodynamic simulations. The present scheme opens the possibility of transferring the recognized computational advantages of lattice kinetic theory to the context of both weakly and ultra-relativistic systems., Comment: 12 pages, 8 figures

Microcrystals of diaquocobalt(II) oxalate have been synthesized by the coprecipitation reaction of aqueous solutions of Cobalt (II) bromide and oxalic acid. Chemical analysis and thermal experiments revealed that there is only one phase present. X-ray powder diffraction studies show that this compound is orthorhombic with space group Cccm. Molar susceptibility versus temperature measurements show the existence of an antiferromagnetic ordering, however, the hysteresis measured in magnetization measurements as a function of magnetic field reveals a weak ferromagnetic behavior., Comment: 7 pages, 11 figures

Large parity violating longitudinal single spin asymmetries A^{e^-}_L= -0.86^{+0.14}_{-0.30} and A^{e^+}_L= 0.88^{+0.12}_{-0.71} are observed for inclusive high transverse momentum electrons and positrons in polarized pp collisions at a center of mass energy of \sqrt{s}=500\ GeV with the PHENIX detector at RHIC. These e^{+/-} come mainly from the decay of W^{+/-} and Z^0 bosons, and the asymmetries directly demonstrate parity violation in the couplings of the W^{\pm} to the light quarks. The observed electron and positron yields were used to estimate W^\pm boson production cross sections equal to \sigma(pp \to W^+ X) \times BR(W^ \to \nu_e)= 144.1+/-21.2(stat)^{+3.4}_{-10.3}(syst) +/- 15%(norm) pb, and \sigma(pp \to W^{-}X) \times BR(W^\to e^-\bar{\nu_e}) = 31.7+/-12.1(stat)^{+10.1}_{-8.2}(syst)+/-15%(norm) pb., Comment: PHENIX Collaboration - 376 authors, 6 pages text, 4 figures, 2 tables. Submitted to Phys. Rev. Lett. v2 has minor changes to match PRL submission. Plain text data tables for the points plotted in figures are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html

A detailed derivation of the Lattice Boltzmann (LB) scheme for relativistic fluids recently proposed in Ref. [1], is presented. The method is numerically validated and applied to the case of two quite different relativistic fluid dynamic problems, namely shock-wave propagation in quark-gluon plasmas and the impact of a supernova blast-wave on massive interstellar clouds. Close to second order convergence with the grid resolution, as well as linear dependence of computational time on the number of grid points and time-steps, are reported.

We propose an analytical model to predict the adhesives penetration into hard wood. Penetration of hard wood is dominated by the vessel network which prohibits porous medium approximations. Our model considers two scales: a one dimensional capillary fluid transport of a hardening adhesive through a single, straight vessel with diffusion of solvent through its walls and a mesoscopic scale based on topological characteristics of the vessel network, where results from the single vessel scale are mapped onto a periodic network. Given an initial amount of adhesive and applied bonding pressure, we calculate the portion of the filled structure. The model is applied to beech wood samples joined with three different types of adhesive (PUR, UF, PVAC) under various growth ring angles. We evaluate adhesive properties and bond line morphologies described in part I of this work. The model contains one free parameter that can be adjusted in order to fit the experimental data., Comment: 17 pages

A study with synchrotron radiation X-ray tomographic microscopy (SRXTM) of PUR, PVAC, and UF adhesive bond lines in beech wood, bonded under various growth ring angles is presented. After determining the hardening characteristics of the adhesives, we evaluate the bond line morphologies, and the adhesive penetration into the wood structure. We find distinct bond line imperfections for the different adhesive systems. To describe the adhesive distribution inside the bond line we propose the saturation of the pore space instead of the commonly used maximum penetration depth. The results are the basis for a penetration model of hardening fluids into hardwood (part II)., Comment: 22 pages

We propose a description for transient penetration simulations of miscible and immiscible fluid mixtures into anisotropic porous media, using the lattice Boltzmann (LB) method. Our model incorporates hydrodynamic flow, diffusion, surface tension, and the possibility for global and local viscosity variations to consider various types of hardening fluids. The miscible mixture consists of two fluids, one governed by the hydrodynamic equations and one by diffusion equations. We validate our model on standard problems like Poiseuille flow, the collision of a drop with an impermeable, hydrophobic interface and the deformation of the fluid due to surface tension forces. To demonstrate the applicability to complex geometries, we simulate the invasion process of mixtures into wood spruce samples., Comment: Submitted to EPJ E

A Lattice Boltzmann formulation for relativistic fluids is presented and numerically verified through quantitative comparison with recent hydrodynamic simulations of relativistic shock-wave propagation in viscous quark-gluon plasmas. This formulation opens up the possibility of exporting the main advantages of Lattice Boltzmann methods to the relativistic context, which seems particularly useful for the simulation of relativistic fluids in complicated geometries., Comment: Submitted to PRL

In this paper we introduce a novel 3D Lattice-Boltzmann model that recovers in the continuous limit the Maxwell equations in materials. In order to build conservation equations with antisymmetric tensors, like the Faraday law, the model assigns four auxiliary vectors to each velocity vector. These auxiliary vectors, when combined with the distribution functions, give the electromagnetic fields. The evolution is driven by the usual BGK collision rule, but with a different form for the equilibrium distribution functions. This LBGK model allows us to consider for both dielectrics and conductors with realistic parameters, and therefore it is adequate to simulate the most diverse electromagnetic problems, like the propagation of electromagnetic waves (both in dielectric media and in waveguides), the skin effect, the radiation pattern of a small dipole antenna and the natural frequencies of a resonant cavity, all with 2% accuracy. Actually, it shows to be one order of magnitude faster than the original FDTD formulation by Yee to reach the same accuracy. It is, therefore, a valuable alternative to simulate electromagnetic fields and opens lattice Boltzmann for a broad spectrum of new applications in electrodynamics. In this paper we develop a 3D Lattice-Boltzmann model that recovers in the continuous limit the Maxwell equations for macroscopic mediums. The model can sucessfully reproduces the propagation of the electromagnetic waves in dielectric mediums and waveguide, the skin effect, the electrical dipole radiation and the electromagnetic response of a resonant cavity., Comment: Accepted for publication in Phys. Rev. E

In this paper we develop a 3D Lattice-Boltzmann model that recovers in the continuous limit the two-fluids theory for plasmas, and consecuently includes the generalizated Ohm's law. The model reproduces the magnetic reconnection process just by given the right initial equlibrium conditions in the magnetotail, without any assumption on the resistivity in the diffusive region. In this model, the plasma is handled like two fluids with an interaction term, each one with distribution functions associated to a cubic lattice with 19 velocities (D3Q19). The electromagnetic fields are considered like a third fluid with an external force on a cubic lattice with 13 velocities (D3Q13). The model can simulate either viscous fluids in the incompressible limit or non-viscous compressible fluids, and sucessfully reproduces both the Hartmann flow and the magnetic reconnection in the magnetotail. The reconnection rate obtained with this model is R=0.109, which is in excellent agreement with the observations., Comment: Submitted to PRE, Computational Physics. 11 pages and 9 figures

We propose an analytical model based on the solution of the magnetohydrodynamics (MHD) equations for studying the origin of intrinsic magnetospheres. For this purpose, we reveal a new gauge condition for the electromagnetic vector potential, which eases the solution of such complex system of non-linear equations. Using this model, we analyse the deformation of the terrestrial magnetic field due to the presence of the solar wind. By comparing with experimental observations, we have found that the geometrical configuration of the magnetosphere, before, and after the magnetic field of the Earth started to deviate the solar wind, has not changed notably, and that the solar wind should have had a finite conductivity. This model can also be used to perform linear stability analysis of fluid and magnetic instabilities., Comment: 5 pages, 3 figures

We propose a controllable way of tuning Fano resonances in open quantum dots in the absence of magnetic field. A quantum dot can be modified by changing the gate voltages that define the dot itself. An extra degree of freedom can be introduced by means of a controllable repulsive perturbation, such as the one induced by scanning a Atomic Force Microscope tip on a real sample. We numerically investigate the coupling between localized states in the dot and the continuum in the leads. The advantage of such position controllable perturbation is the selective manipulation of the quantum dot states. We show that this could be a feasible alternative to quantum dots in Aharonov-Bohm interferometers as a Fano resonance tuning device., Comment: 10 pages, 3 figures

We discuss the minimal conditions for wave function spectroscopy, in which resonant tunneling is the measurement tool. Two systems are addressed: resonant tunneling diodes, as a toy model, and open quantum dots. The toy model is used to analyze the crucial tunning between the necessary resolution in current-voltage characteristics and the breakdown of the wave functions probing potentials into a level splitting characteristic of double quantum wells. The present results establish a parameter region where the wavefunction spectroscopy by resonant tunneling could be achieved. In the case of open quantum dots, a breakdown of the mapping condition is related to a change into a double quantum dot structure induced by the local probing potential. The analogy between the toy model and open quantum dots show that a precise control over shape and extention of the potential probes is irrelevant for wave function mapping. Moreover, the present system is a realization of a tunable Fano system in the wave function mapping regime., Comment: 6 pages, 6 figures