Monopole Percolation in the Compact Abelian Higgs Model

We have studied the monopole-percolation phenomenon in the four dimensional Abelian theory that contains compact U(1) gauge fields coupled to unitary norm Higgs fields. We have determined the location of the percolation transition line in the plane $(\beta_g, \beta_H)$. This line overlaps the confined-Coulomb and the confined-Higgs phase transition lines, originated by a monopole-condensation mechanism, but continues away from the end-point where this phase transition line stops. In addition, we have determined the critical exponents of the monopole percolation transition away from the phase transition lines. We have performed the finite size scaling in terms of the monopole density instead of the coupling, because the density seems to be the natural parameter when dealing with percolation phenomena.Comment: 13 pages. REVTeX. 16 figs. included using eps

Monopole Percolation in pure gauge compact QED

The role of monopoles in quenched compact QED has been studied by measuring the cluster susceptibility and the order parameter $n_{max}/n_{tot}$ previously introduced by Hands and Wensley in the study of the percolation transition observed in non-compact QED. A correlation between these parameters and the energy (action) at the phase transition has been observed. We conclude that the order parameter $n_{max}/n_{tot}$ is a sensitive probe for studying the phase transition of pure gauge compact QED.Comment: LaTeX file + 4 PS figures, 12 pag., Pre-UAB-FT-308 ILL-(TH)-94-1

The Phases and Triviality of Scalar Quantum Electrodynamics

The phase diagram and critical behavior of scalar quantum electrodynamics are investigated using lattice gauge theory techniques. The lattice action fixes the length of the scalar (``Higgs'') field and treats the gauge field as non-compact. The phase diagram is two dimensional. No fine tuning or extrapolations are needed to study the theory's critical behovior. Two lines of second order phase transitions are discovered and the scaling laws for each are studied by finite size scaling methods on lattices ranging from $6^4$ through $24^4$. One line corresponds to monopole percolation and the other to a transition between a ``Higgs'' and a ``Coulomb'' phase, labelled by divergent specific heats. The lines of transitions cross in the interior of the phase diagram and appear to be unrelated. The monopole percolation transition has critical indices which are compatible with ordinary four dimensional percolation uneffected by interactions. Finite size scaling and histogram methods reveal that the specific heats on the ``Higgs-Coulomb'' transition line are well-fit by the hypothesis that scalar quantum electrodynamics is logarithmically trivial. The logarithms are measured in both finite size scaling of the specific heat peaks as a function of volume as well as in the coupling constant dependence of the specific heats measured on fixed but large lattices. The theory is seen to be qualitatively similar to $\lambda\phi^{4}$. The standard CRAY random number generator RANF proved to be inadequateComment: 25pages,26figures;revtex;ILL-(TH)-94-#12; only hardcopy of figures availabl

Chiral transition and monopole percolation in lattice scalar QED with quenched fermions

We study the interplay between topological observables and chiral and Higgs transitions in lattice scalar QED with quenched fermions. Emphasis is put on the chiral transition line and magnetic monopole percolation at strong gauge coupling. We confirm that at infinite gauge coupling the chiral transition is described by mean field exponents. We find a rich and complicated behaviour at the endpoint of the Higgs transition line which hampers a satisfactory analysis of the chiral transition. We study in detail an intermediate coupling, where the data are consistent both with a trivial chiral transition clearly separated from monopole percolation and with a chiral transition coincident with monopole percolation, and characterized by the same critical exponent $\nu \simeq 0.65$. We discuss the relevance (or lack thereof) of these quenched results to our understanding of the \chupiv\ model. We comment on the interplay of magnetic monopoles and fermion dynamics in more general contexts.Comment: 29 pages, 13 figures included, LaTeX2e (elsart

Thermal performance of two heat exchangers for thermoelectric generators

Thermal performance of heat exchanger is important for potential application in integrated solar cell/module and thermoelectric generator (TEG) system. Usually, thermal performance of a heat exchanger for TEGs is analysed by using a 1D heat conduction theory which ignores the detailed phenomena associated with thermo-hydraulics. In this paper, thermal and mass transports in two different exchangers are simulated by means of a steady-state, 3D turbulent flow k -e model with a heat conduction module under various flow rates. In order to simulate an actual working situation of the heat exchangers, hot block with an electric heater is included in the model. TEG model is simplified by using a 1D heat conduction theory, so its thermal performance is equivalent to a real TEG. Natural convection effect on the outside surfaces of the computational model is considered. Computational models and methods used are validated under transient thermal and electrical experimental conditions of a TEG. It is turned out that the two heat exchangers designed have a better thermal performance compared with an existing heat exchanger for TEGs, and more importantly, the fin heat exchanger is more compact and has nearly half temperature rise compared with the tube heat exchanger

Structure formation under steady-state isothermal planar elongational flow of n-eicosane: A comparison between simulation and experiment

We use nonequilibrium molecular dynamics simulations to investigate the structural properties of an oriented melt of n-eicosane under steady-state planar elongational flow. The flow-induced structure was evaluated using the structure factor sk taken as the Fourier transform of the total pair correlation function gr. We found that the equilibrium liquid structure factor is in excellent agreement with the one determined via x-ray diffraction. Moreover, a new x-ray diffraction experiment has been performed on a crystalline n-eicosane sample. The resulting intramolecular contribution to the structure factor was found to be in very good agreement with the simulated one at a high elongation rate, indicating the existence of a possible crystalline precursor structure.open11

First-order transition of tethered membranes in 3d space

We study a model of phantom tethered membranes, embedded in three-dimensional space, by extensive Monte Carlo simulations. The membranes have hexagonal lattice structure where each monomer is interacting with six nearest-neighbors (NN). Tethering interaction between NN, as well as curvature penalty between NN triangles are taken into account. This model is new in the sense that NN interactions are taken into account by a truncated Lennard-Jones potential including both repulsive and attractive parts. The main result of our study is that the system undergoes a first-order crumpling transition from low temperature flat phase to high temperature crumpled phase, in contrast with early numerical results on models of tethered membranes.Comment: 5 pages, 6 figure

Indoor characterization of a reflective type 3D LCPV system

This is the final version of the article. Available from AIP Publishing via the DOI in this record.Low concentrating photovoltaic (LCPV) systems produces higher electrical output per unit solar cell compared to typical PV systems. The high efficiency Si solar cells can be utilized with little design and manufacturing changes for these applications. However, a key barrier towards achieving economic viability and the widespread adoption of LCPV technologies is the losses related to high operating temperature. In the present study, we evaluate the performance 3D low concentration system designed for 3.6x, using a reflective Cross compound parabolic concentrator (CCPC) and a Laser Grooved Buried Contact solar cell having an area of 50∗50mm 2 . Results demonstrate the losses occurring due to the temperature rise of the solar cell under concentration and we analyze the potential which could be utilized for low grade heating applications.The authors gratefully acknowledge financial support received from the EPSRC through Solar Challenge project SUNTRAP (EP/K022156/1). We would also like to thank the Super Solar Hub for providing us with the travel grant for this conference