Transient conduction and radiation in a semi-transparent phase change medium in an annulus

The effect of thermal radiation on the solidification of an absorbing, emitting, isotropically scattering infinite and finite, semi-transparent gray medium bounded between two concentric cylinders is investigated. The conservation of energy principle employing enthalpy and temperature as dependent variables is coupled with a set of moment equations which are derived from the radiative transfer equations and Marshak type boundary conditions by applying P-1 differential approximations. The transient temperature distribution, interface location of a semi-transparent phase change medium, and the local radiative radial and axial heat flux has been obtained by using a Gauss-Seidel iterative numerical scheme for some typical geometric dimensions and parameters. The numerical results for the one-dimensional axisymmetric case of pure conduction are verified by comparison with an analytical approximation where the change in the internal energy in the solid phase is neglected. The results for an optically thick cylindrical medium are obtained, analyzed, and displayed in graphs

Computational Analysis for Time Dependent Two Dimensional Flow of Incompressible Homogeneous Newtonian Fluid (Spin Up Problem)

A digital computer method and a program which employs optimized successive overrelaxation were developed to solve certain problems involving time-dependent two-dimensional flow of an incompressible homogeneous Newtonian fluid. Bubble sort techniques were used in a boundary field and a vectorization of the inner-most Do-loops of the program was carried out using a CRAY-1 computer. A polygon region was selected for analysis purposes. As a test program, "Spin-up problem" for a circular region with rotating solid boundary conditions was analyzed. The results of computations using a fine mesh were in good agreement with analytical results. Finally, a flow contained in an infinite cylinder with part-moving boundarie-s is examined. It is to be applied to an analysis of a flow in a circular cavity

Direct solar-pumped iodine laser amplifier

In order to evaluate the feasibility of the solar pumped dye laser, the parametric study of a dye laser amplifier pumped by a solar simulator and flashlamp was carried out, and the amplifier gains were measured at various pump beam irradiances on the dye cell. Rhodamine 6G was considered as a candidate for the solar pumped laser because of its good utilization of the solar spectrum and high quantum efficiency. The measurement shows that a solar concentration of 20,000 is required to reach the threshold of the dye. The work to construct a kinetic model algorithm which predicts the output parameter of laser was progressed. The kinetic model was improved such that there is good agreement between the theoretical model and experimental data for the systems defined previously as flashlamp pumped laser oscillator, and the long path length solar pumped laser

Direct solar-pumped iodine laser amplifier

The improvement on the collection system of the Tarmarack Solar Simulator beam was attemped. The basic study of evaluating the solid state laser materials for the solar pumping and also the work to construct a kinetic model algorithm for the flashlamp pumped iodine lasers were carried out. It was observed that the collector cone worked better than the lens assembly in order to collect the solar simulator beam and to focus it down to a strong power density. The study on the various laser materials and their lasing characteristics shows that the neodymium and chromium co-doped gadolinium scandium gallium garnet (Nr:Cr:GSGG) may be a strong candidate for the high power solar pumped solid state laser crystal. On the other hand the improved kinetic modeling for the flashlamp pumped iodine laser provides a good agreement between the theoretical model and the experimental data on the laser power output, and predicts the output parameters of a solar pumped iodine laser

Electron Transport in Graphene Nanoribbon Field-Effect Transistor under Bias and Gate Voltages: Isochemical Potential Approach

Zigzag graphene nanoribbon (zGNR) of narrow width has a moderate energy gap in its antiferromagnetic ground state. So far, first-principles electron transport calculations have been performed using nonequilibrium Green function (NEGF) method combined with density functional theory (DFT). However, the commonly practiced bottom-gate control has not been studied computationally due to the need to simulate an electron reservoir that fixes the chemical potential of electrons in the zGNR and electrodes. Here, we present the isochemical potential scheme to describe the top/back-gate effect using external potential. Then, we examine the change in electronic state under the modulation of chemical potential and the subsequent electron transport phenomena in zGNR transistor under substantial top-/back-gate and bias voltages. The gate potential can activate the device states resulting in a boosted current. This gate-controlled current-boosting could be utilized for designing novel zGNR field effect transistors (FETs).ope

Orbital selective Fermi surface shifts and mechanism of high Tc_c superconductivity in correlated AFeAs (A=Li,Na)

Based on the dynamical mean field theory (DMFT) and angle resolved photoemission spectroscopy (ARPES), we have investigated the mechanism of high $T_c$ superconductivity in stoichiometric LiFeAs. The calculated spectrum is in excellent agreement with the observed ARPES measurement. The Fermi surface (FS) nesting, which is predicted in the conventional density functional theory method, is suppressed due to the orbital-dependent correlation effect with the DMFT method. We have shown that such marginal breakdown of the FS nesting is an essential condition to the spin-fluctuation mediated superconductivity, while the good FS nesting in NaFeAs induces a spin density wave ground state. Our results indicate that fully charge self-consistent description of the correlation effect is crucial in the description of the FS nesting-driven instabilities.Comment: 5 pages, 4 figures, supporting informatio