Scaling test of fermion actions in the Schwinger model

We discuss the scaling behaviour of different fermion actions in dynamical simulations of the 2-dimensional massive Schwinger model. We have chosen Wilson, hypercube, twisted mass and overlap fermion actions. As physical observables, the pion mass and the scalar condensate are computed for the above mentioned actions at a number of coupling values and fermion masses. We also discuss possibilities to simulate overlap fermions dynamically avoiding problems with low-lying eigenvalues of the overlap kernel

Melting transitions in biomembranes

We investigated melting transitions in biological membranes in their native state that include their membrane proteins. These membranes originated from \textit{E. coli}, \textit{B. subtilis}, lung surfactant and nerve tissue from the spinal cord of several mammals. For some preparations, we studied the pressure, pH and ionic strength dependence of the transition. For porcine spine, we compared the transition of the native membrane to that of the extracted lipids. All preparations displayed melting transitions of 10-20 degrees below physiological or growth temperature, independent of the organism of origin and the respective cell type. The position of transitions in \textit{E. coli} membranes depends on the growth temperature. We discuss these findings in the context of the thermodynamic theory of membrane fluctuations that leads to largely altered elastic constants, an increase in fluctuation lifetime and in membrane permeability associated with the transitions. We also discuss how to distinguish lipid transitions from protein unfolding transitions. Since the feature of a transition slightly below physiological temperature is conserved even when growth conditions change, we conclude that the transitions are likely to be of major biological importance for the survival and the function of the cell.Comment: 12 pages, 6 Figures, 1 supplement with 1 figur

Approaches to calculate the dielectric function of ZnO around the band gap

Being one of the most sensitive methods for optical thin film metrology ellipsometry is widely used for the characterization of zinc oxide (ZnO), a key material for optoelectronics, photovoltaics, and printable electronics and in a range of critical applications. The dielectric function of ZnO has a special feature around the band gap dominated by a relatively sharp absorption feature and an excitonic peak. In this work we summarize and compare direct (point-by-point) and parametric approaches for the description of the dielectric function. We also investigate how the choice of the wavelength range influences the result, the fit quality and the sensitivity. Results on ZnO layers prepared by sputtering are presented

Grazing incidence x ray fluorescence analysis for non destructive determination of In and Ga depth profiles in Cu In,Ga Se2 absorber films

Development of highly efficient thin film solar cells involves band gap engineering by tuning their elemental composition with depth. Here we show that grazing incidence X ray fluorescence GIXRF analysis using monochromatic synchrotron radiation and well characterized instrumentation is suitable for a non destructive and reference free analysis of compositional depth profiles in thin films. Variation of the incidence angle provides quantitative access to the in depth distribution of the elements, which are retrieved from measured fluorescence intensities by modeling parameterized gradients and fitting calculated to measured fluorescence intensities. Our results show that double Ga gradients in Cu In1 x,Gax Se2 can be resolved by GIXR

The influence of anesthetics, neurotransmitters and antibiotics on the relaxation processes in lipid membranes

In the proximity of melting transitions of artificial and biological membranes fluctuations in enthalpy, area, volume and concentration are enhanced. This results in domain formation, changes of the elastic constants, changes in permeability and slowing down of relaxation processes. In this study we used pressure perturbation calorimetry to investigate the relaxation time scale after a jump into the melting transition regime of artificial lipid membranes. This time corresponds to the characteristic rate of domain growth. The studies were performed on single-component large unilamellar and multilamellar vesicle systems with and without the addition of small molecules such as general anesthetics, neurotransmitters and antibiotics. These drugs interact with membranes and affect melting points and profiles. In all systems we found that heat capacity and relaxation times are related to each other in a simple manner. The maximum relaxation time depends on the cooperativity of the heat capacity profile and decreases with a broadening of the transition. For this reason the influence of a drug on the time scale of domain formation processes can be understood on the basis of their influence on the heat capacity profile. This allows estimations of the time scale of domain formation processes in biological membranes.Comment: 12 pages, 6 figure