The triangular Ising model with nearest- and next-nearest-neighbor couplings in a field

We study the Ising model on the triangular lattice with nearest-neighbor couplings $K_{\rm nn}$, next-nearest-neighbor couplings $K_{\rm nnn}>0$, and a magnetic field $H$. This work is done by means of finite-size scaling of numerical results of transfer matrix calculations, and Monte Carlo simulations. We determine the phase diagram and confirm the character of the critical manifolds. The emphasis of this work is on the antiferromagnetic case $K_{\rm nn}<0$, but we also explore the ferromagnetic regime $K_{\rm nn}\ge 0$ for H=0. For $K_{\rm nn}<0$ and H=0 we locate a critical phase presumably covering the whole range $-\infty < K_{\rm nn}<0$. For $K_{\rm nn}<0$, $H\neq 0$ we locate a plane of phase transitions containing a line of tricritical three-state Potts transitions. In the limit $H \to \infty$ this line leads to a tricritical model of hard hexagons with an attractive next-nearest-neighbor potential

Thermodynamic relations in a driven lattice gas: numerical exprements

We explore thermodynamic relations in non-equilibrium steady states with numerical experiments on a driven lattice gas. After operationally defining the pressure and chemical potential in the driven lattice gas, we confirm numerically the validity of the integrability condition (the Maxwell relation) for the two quantities whose values differ from those for an equilibrium system. This implies that a free energy function can be constructed for the non-equilibrium steady state that we consider. We also investigate a fluctuation relation associated with this free energy function. Our result suggests that the compressibility can be expressed in terms of density fluctuations even in non-equilibrium steady states.Comment: 4 pages, 4 figure

Colligative properties of solutions: II. Vanishing concentrations

We continue our study of colligative properties of solutions initiated in math-ph/0407034. We focus on the situations where, in a system of linear size $L$, the concentration and the chemical potential scale like $c=\xi/L$ and $h=b/L$, respectively. We find that there exists a critical value \xit such that no phase separation occurs for \xi\le\xit while, for \xi>\xit, the two phases of the solvent coexist for an interval of values of $b$. Moreover, phase separation begins abruptly in the sense that a macroscopic fraction of the system suddenly freezes (or melts) forming a crystal (or droplet) of the complementary phase when $b$ reaches a critical value. For certain values of system parameters, under ``frozen'' boundary conditions, phase separation also ends abruptly in the sense that the equilibrium droplet grows continuously with increasing $b$ and then suddenly jumps in size to subsume the entire system. Our findings indicate that the onset of freezing-point depression is in fact a surface phenomenon.Comment: 27 pages, 1 fig; see also math-ph/0407034 (both to appear in JSP

A two-dimensional finite element model of front surface current flow in cells under non-uniform, concentrated illumination

A two-dimensional finite element model of current flow in the front surface of a PV cell is presented. In order to validate this model we perform an experimental test. Later, particular attention is paid to the effects of non-uniform illumination in the finger direction which is typical in a linear concentrator system. Fill factor, open circuit voltage and efficiency are shown to decrease with increasing degree of non-uniform illumination. It is shown that these detrimental effects can be mitigated significantly by reoptimization of the number of front surface metallization fingers to suit the degree of non-uniformity. The behavior of current flow in the front surface of a cell operating at open circuit voltage under non-uniform illumination is discussed in detail

Leptoquark Single and Pair production at LHC with CalcHEP/CompHEP in the complete model

We study combined leptoquark (LQ) single and pair production at LHC at the level of detector simulation. A set of kinematical cuts has been worked out to maximize significance for combined signal events. It was shown that combination of signatures from LQ single and pair production not only significantly increases the LHC reach, but also allows us to give the correct signal interpretation. In particular, it was found that the LHC has potential to discover LQ with a mass up to 1.2 TeV and 1.5 TeV for the case of scalar and vector LQ, respectively, and LQ single production contributes 30-50% to the total signal rate for LQ-l-q coupling, taken equal to the electromagnetic coupling. This work is based on implementation of the most general form of scalar and vector LQ interactions with quarks and gluons into CalcHEP/CompHEP packages. This implementation, which authors made publicly available, was one the most important aspects of the study.Comment: LaTeX, 27 pages, 15 figure

An integrated approach to modelling the fluid-structure interaction of a collapsible tube

The well known collapsible tube experiment was conducted to obtain flow, pressure and materials property data for steady state conditions. These were then used as the boundary conditions for a fully coupled fluid-structure interaction (FSI) model using a propriety computer code, LS-DYNA. The shape profiles for the tube were also recorded. In order to obtain similar collapse modes to the experiment, it was necessary to model the tube flat, and then inflate it into a circular profile, leaving residual stresses in the walls. The profile shape then agreed well with the experimental ones. Two departures from the physical properties were required to reduce computer time to an acceptable level. One of these was the lowering of the speed of sound by two orders of magnitude which, due to the low velocities involved, still left the mach number below 0.2. The other was to increase the thickness of the tube to prevent the numerical collapse of elements. A compensation for this was made by lowering the Young's modulus for the tube material. Overall the results are qualitatively good. They give an indication of the power of the current FSI algorithms and the need to combine experiment and computer models in order to maximise the information that can be extracted both in terms of quantity and quality

Hybrid R&D

We develop a model of R&D competition and collaboration in which individual firms carry out independent in-house research and also undertake joint research projects with other firms. We examine the impact of collaboration on in-house research and explore the circumstances under which a hybrid organization of R&D which combines the two is optimal for firms and society. We find that investments in independent research and in joint research are complementary. Firm profits are highest under a hybrid organization if the number of firms is small; otherwise they are highest with pure in-house research. However, social welfare is maximized under a hybrid organization of R&D in all cases. Our analysis also yields new results on the role of cooperative R&D. Non-cooperative firm decision making leads to more R&D and higher social welfare than fully cooperative decision making. However, bilateral cooperation in joint projects and non-cooperative decision making in in-house research yields the highest level of welfare in concentrated industries

Transverse instability and its long-term development for solitary waves of the (2+1)-Boussinesq equation

The stability properties of line solitary wave solutions of the (2+1)-dimensional Boussinesq equation with respect to transverse perturbations and their consequences are considered. A geometric condition arising from a multi-symplectic formulation of this equation gives an explicit relation between the parameters for transverse instability when the transverse wavenumber is small. The Evans function is then computed explicitly, giving the eigenvalues for transverse instability for all transverse wavenumbers. To determine the nonlinear and long time implications of transverse instability, numerical simulations are performed using pseudospectral discretization. The numerics confirm the analytic results, and in all cases studied, transverse instability leads to collapse.Comment: 16 pages, 8 figures; submitted to Phys. Rev.

Chair and Bed Rise Performance in ADL‐Impaired Congregate Housing Residents

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111141/1/j.1532-5415.2000.tb04999.x.pd