Evaluation of proficiency testing results taking into account their uncertainties

A new composite score for the evaluation of performance of proficiency testing participants is proposed. The score is based on a combination of the z-score, uncertainty of a participant’s measurement result and uncertainty of the proficiency testing scheme’s assigned value. The use of such a composite score will allow evaluation not only of the participant’s ability to determine an analyte in corresponding matrix, but also their understanding of the uncertainty in the obtained analytical result. The score may be helpful for the laboratory’s quality system and for laboratory accreditation according to ISO 17025.     

High critical oxygen concentration in microcrystalline silicon solar cells

For microcrystalline silicon based p–i–n solar cells the effect of deposition conditions on the critical oxygen concentration was investigated. All solar cells were prepared by 13.56 MHz plasma‐enhanced chemical vapour deposition. The critical oxygen concentration defines the lowest oxygen concentration in the intrinsic absorber layer causing a deterioration of the solar cell performance. For intentional contamination of ～1.2–1.3 µm thick i‐layers, the oxygen was inserted by a controllable leak at the process gases supply line, i.e. by a gas pipe leak. For µc‐Si:H deposited at a discharge power of 0.53 W/cm² we find a critical oxygen concentration of 1–2 × 10¹⁹ cm^–3 in agreement with values commonly reported in literature. However, changing the deposition conditions, we find that the critical oxygen concentration in µc‐Si:H cells is not fixed. At reduced power of 0.20 W/cm² a much higher value for the critical oxygen concentration of 1 × 10²⁰ cm^–3 is observed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermodynamics of lattice heteropolymers

We calculate thermodynamic quantities of hydrophobic-polar (HP) lattice proteins by means of a multicanonical chain-growth algorithm that connects the new variants of the Pruned-Enriched Rosenbluth Method and flat histogram sampling of the entire energy space. Since our method directly simulates the density of states, we obtain results for thermodynamic quantities of the system for all temperatures. In particular, this algorithm enables us to accurately simulate the usually difficult accessible low-temperature region. Therefore, it becomes possible to perform detailed analyses of the low-temperature transition between ground states and compact globules.     

Kertész line in the three-dimensional compact U(1) lattice Higgs model

The three-dimensional lattice Higgs model with compact U(1) gauge symmetry and unit charge is investigated by means of Monte Carlo simulations. The full model with fluctuating Higgs amplitude is simulated, and both energy as well as topological observables are measured. The data show a Higgs and a confined phase separated by a well-defined phase boundary, which is argued to be caused by proliferating vortices. For fixed gauge coupling, the phase boundary consists of a line of first-order phase transitions at small Higgs self-coupling, ending at a critical point. The phase boundary then continues as a Kertész line across which thermodynamic quantities are non-singular. Symmetry arguments are given to support these findings.     

Conformational transitions of nongrafted polymers near an absorbing substrate

We have performed multi-canonical chain-growth simulations of a polymer interacting with an adsorbing surface. The polymer, which is not explicitly anchored at the surface, experiences a hierarchy of phase transitions between conformations binding and nonbinding with the substrate. We discuss the phase diagram in the temperature-solubility plane and highlight the transition path through the free-energy landscape.     

Phase transition in complex /psi/(4) theory

Motivated by recent claims for rather unconventional first-order phase transitions in the two- and three-dimensional complex /psi/(4) theory in certain parameter ranges we performed Monte Carlo simulation studies of this model. From our results in two and three dimensions we can unambiguously conclude that there is no evidence for a first-order transition, provided the measure of field fluctuations is treated properly. The origin of the discrepancy is traced by comparative simulations reproducing the erroneous results and by a transfer-matrix study of the one-dimensional case.