Compact QED under scrutiny: it's first order

We report new results from our finite size scaling analysis of 4d compact pure U(1) gauge theory with Wilson action. Investigating several cumulants of the plaquette energy within the Borgs-Kotecky finite size scaling scheme we find strong evidence for a first-order phase transition and present a high precision value for the critical coupling in the thermodynamic limit.Comment: Lattice2002(Spin

A Study of Practical Implementations of the Overlap-Dirac Operator in Four Dimensions

We study three practical implementations of the Overlap-Dirac operator $D_o= (1/2) [1 + \gamma_5\epsilon(H_w)]$ in four dimensions. Two implementations are based on different representations of $\epsilon(H_w)$ as a sum over poles. One of them is a polar decomposition and the other is an optimal fit to a ratio of polynomials. The third one is obtained by representing $\epsilon(H_w)$ using Gegenbauer polynomials and is referred to as the fractional inverse method. After presenting some spectral properties of the Hermitian operator $H_o=\gamma_5 D_o$, we study its spectrum in a smooth SU(2) instanton background with the aim of comparing the three implementations of $D_o$. We also present some results in SU(2) gauge field backgrounds generated at $\beta=2.5$ on an $8^4$ lattice. Chiral properties have been numerically verified.Comment: 23 pages latex with 9 postscript figures included by epsf. Some change in referencing and one figure modifie

Evaluation available encapsulation materials for low-cost long-life silicon photovoltaic arrays

Experimental evaluation of selected encapsulation designs and materials based on an earlier study which have potential for use in low cost, long-life photovoltaic arrays are reported. The performance of candidate materials and encapsulated cells were evaluated principally for three types of encapsulation designs based on their potentially low materials and processing costs: (1) polymeric coatings, transparent conformal coatings over the cell with a structural-support substrate; (2) polymeric film lamination, cells laminated between two films or sheets of polymeric materials; and (3) glass-covered systems, cells adhesively bonded to a glass cover (superstrate) with a polymeric pottant and a glass or other substrate material. Several other design types, including those utilizing polymer sheet and pottant materials, were also included in the investigation

Probing the QCD vacuum with overlap fermions

We use low lying eigenvectors of the overlap-Dirac operator as a probe of the QCD vacuum. If instantons play a significant role one would expect the low lying eigenmodes of the overlap-Dirac operator to consist mainly of the mixed ``would be zero modes''. Then, the eigenmodes should exhibit local chirality. Studying a recently introduced local chirality parameter, we find evidence supporting this picture.Comment: LaTeX, 5 pages, 5 postscript figures. Talk given by U.M. Heller at the Workshop on Lattice Hadron Physics ``LHP2001'', July 9 -- 18, 2001, Cairns, Australi

Overlap Dirac Operator, Eigenvalues and Random Matrix Theory

The properties of the spectrum of the overlap Dirac operator and their relation to random matrix theory are studied. In particular, the predictions from chiral random matrix theory in topologically non-trivial gauge field sectors are tested.Comment: 3 pages latex with 1 postscript figure. Talk presented at LATTICE99(topology

Concentration effects on the dynamics of liquid crystalline self-assembly: Time-resolved X-ray scattering studies.

A manifold of ordering transitions relevant to chemical and biological systems occur at interfaces from liquids to self-assembled soft solids like membranes or liquid crystals. In the present case, we were interested in understanding the phase transition from the microemulsion phase to the liquid crystal phase in terms of their driving forces, i.e., activation energy and entropy. The purpose of this work was to clarify the influence of concentration effects of the amphiphilic molecules on the nature of these self-assembly processes. By photosensitization of the model system (polyalkylglycolether (C(10)E(4)), water, decane, and cyclohexane) with laser dyes, we could effectively induce and control the phase transition through the absorption of optical photons. The photo transformation conditions were chosen in such a way that the system was in thermal equilibrium. By application of time-resolved photo small-angle X-ray scattering we could monitor the conversion process and demonstrate that the surfactant concentration has a direct impact on the activation energy, which is observable through the length of the induction time

Verhalten funktionalisierter Nanopartikel an Grenzschichten mit Polymerbürsten

Die vorliegende Arbeit liefert einen Beitrag zum Verständnis der komplexen Wechselwirkungen zwischen Nanopartikeln und Polymeren in dünnen Schichtsystemen. Dazu wurden in einem geeignetem Modellsystem drei verschiedene Einflussparameter auf die Nanopartikelverteilung im Polymer und zwischen einer hydrophilen und einer hydrophoben Grenzfläche analysiert. Für eine erste Abschätzung der Verträglichkeit der einzelnen Komponenten wurden Wechselwirkungsparameter, binäre und ternäre Phasendiagramme ermittelt. Die experimentelle Charakterisierung der Nanopartikelverteilung erfolgte mittels Rasterkraftmikroskopie, Rasterelektronenmikroskopie und Transmissionselektronenmikroskopie. Die erhaltenen Ergebnisse wurden mit denen der theoretischen Vorbetrachtungen verglichen um herauszufinden, ob Vorhersagen zur Nanopartikelverteilung in einem Polymer möglich sind. In dieser Arbeit konnte gezeigt werden, dass die Nanopartikelverteilung im Polymer mit den untersuchten Parametern gezielt beeinflusst werden kann

The hermitian Wilson-Dirac operator in smooth SU(2) instanton backgrounds

We study the spectral flow of the hermitian Wilson-Dirac operator \ham(m) as a function of $m$ in smooth SU(2) instanton backgrounds on the lattice. For a single instanton background with Dirichlet boundary conditions on \ham(m), we find a level crossing in the spectral flow of \ham(m), and we find the shape of the crossing mode at the crossing point to be in good agreement with the zero mode associated with the single instanton background. With anti-periodic boundary conditions on \ham(m), we find that the instanton background in the singular gauge has the correct spectral flow but the one in regular gauge does not. We also investigate the spectral flows of two instanton and instanton-anti-instanton backgrounds.Comment: 18 pages, Latex file, 12 postscript figure