Lie-group interpolation and variational recovery for internal variables

We propose a variational procedure for the recovery of internal variables, in effect extending them from integration points to the entire domain. The objective is to perform the recovery with minimum error and at the same time guarantee that the internal variables remain in their admissible spaces. The minimization of the error is achieved by a three-field finite element formulation. The fields in the formulation are the deformation mapping, the target or mapped internal variables and a Lagrange multiplier that enforces the equality between the source and target internal variables. This formulation leads to an $L_2$ projection that minimizes the distance between the source and target internal variables as measured in the $L_2$ norm of the internal variable space. To ensure that the target internal variables remain in their original space, their interpolation is performed by recourse to Lie groups, which allows for direct polynomial interpolation of the corresponding Lie algebras by means of the logarithmic map. Once the Lie algebras are interpolated, the mapped variables are recovered by the exponential map, thus guaranteeing that they remain in the appropriate space.     

Chlor-alkali electrolysis with oxygen depolarized cathodes: history,present status and future prospects

The historical development, current status and future prospects of chlor-alkali electrolysis with oxygen depolarized cathodes (ODCs) are summarized. Over the last decades, membrane chlor-alkali technology has been optimized to such an extent that no substantial reduction of the energy demand can be expected from further process modifications. However, replacement of the hydrogen evolving cathodes in the classical membrane cells by ODCs allows for reduction of the cell voltage and correspondingly the energy consumption of up to 30%. This replacement requires the development of appropriate cathode materials and novel electrolysis cell designs. Due to their superior long-term stability, ODCs based on silver catalysts are very promising for oxygen reduction in concentrated NaOH solutions. Finite-gap falling film cells appear to be the technically most mature design among the several ODC electrolysis cells that have been investigated.

Particle formation and characteristics of Celecoxib-loaded poly(lactic-co-glycolic acid) microparticles prepared in different solvents using electrospraying

Microparticles were fabricated for pharmaceutical purposes using electrospraying with the aim to determine the effect of the solvent(s) used. Particles of poly(lactic-co-glycolic acid) (PLGA) and the drug Celecoxib were prepared from acetone, acetonitrile and acetone:methanol with different polymer and drug concentrations. The solvent power, evaporation rate and electrical conductivity of the solvents all had a significant effect on the particle formation process as well as the particle characteristics and drug release profile. Particles were near-spherical and between 2 and 7 μm in diameter with smooth or corrugated surfaces. The drug release rate was mainly dependent on particle size, with larger particles showing slower release. The solvent in which PLGA was poorly soluble resulted in small grainy particles that disintegrated instantaneously with full drug release. It may be concluded that the selection of an appropriate solvent may be a useful way to control particle characteristics and drug release profiles when using electrospraying.     

Photoinduced electron transfer reactions: from the elucidation of old problems in bulk solutions towards the exploration of interfaces

The activities of our research group in the field of photoinduced electron transfer reactions are discussed and illustrated by several examples.     

Diagnostics of low pressure microplasmas for surface modification

We investigated low pressure microplasmas for surface modification. The aim of this work was to functionalize only the inner surface of a porous polymeric hollow fiber membrane with amino groups. For the surface functionalization with amino groups, especially the concentrations of NH and NH₂ in the plasma gas-phase are of relevance. They can be generated for example from ammonia with admixtures of helium. A limitation is that all plasmas should have a gas temperature below the melting temperature of thermoplastic polymers.The temperature was measured in two ways; one was a fiber optical temperature sensor attached on the outside of a glass capillary, used as plasma chamber, the other one was carried out by estimation of the rotational temperature with optical emission spectroscopy from the distribution of the rotational transitions of the first negative system N₂⁺(B² ∑ _u⁺→X² ∑ _g⁺). By using plasma excitation in the kHz range, temperatures below 50 °C were measured with the temperature sensor. With MHz-excitation, however, the temperature raised up to 200 °C. With optical emission spectroscopy, the products of decomposition of ammonia were investigated. A gas mixture with a high amount of NH molecules in the gas phase was found. By means of the investigated microplasmas, we were able to functionalize the inner surface of a porous hollow fiber with amino-groups.     

A Content Analysis of Print News Coverage of Media Violence and Aggression Research

We conducted a content analysis of news articles (N = 540) to examine whether news coverage of media violence accurately reflects scientific knowledge about exposure to media violence and its effects on viewer aggression. The analysis revealed that over the past 30 years, news articles generally suggested that a link between media violence and aggression exists. However, the tone shifted sharply back toward a neutral conclusion since 2000. This shift may be attributable to the type of medium discussed (e.g., television vs. video games), the number of unaffiliated sources that are cited in the news article, and the sex of the journalist. Implications for how this news coverage may influence news readers are discussed.     

Poly(3-hexylthiophene)/C60 heterojunction solar cells: Implication of morphology on performance and ambipolar charge collection

The performance of heterojunction organic solar cells is critically dependent on the morphology of the donor and acceptor components in the active film. We report results of photovoltaic devices consisting of bilayers and bulk heterojunctions using poly(3-hexylthiophene) (P3HT) and Buckminsterfullerene C₆₀. White light power efficiencies of η2.2% (bulk heterojunction) and 2.6% (bilayer) were measured after a thermal annealing step on completed devices. Optical and structural investigations on non-annealed bilayer thin films indicated a distinct porosity of the spin-coated polymer, which allows C₆₀ to penetrate the P3HT layer and to touch the anode. This resulted for these bilayer solar cells in the experimental observation that electrons were collected predominantly at the cathode after photo-excitation of P3HT, but predominantly at the anode after C₆₀ excitation. A morphological model to explain the ambipolar charge collection phenomenon is proposed.     

Mechanical properties and features of erosion of cermets

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It has been shown that cermets erosive wear resistance cannot be estimated only by hardness, characterised by resistance to penetration. The differences in wear resistance between cermet materials with equal hardness level can be attributed to differences in their resistance to fracture. The present paper discusses some features of the material removal process during the particle–wall collision. Solid particle erosion tests on eight materials have been performed using silicon carbide and silica abrasive particles within a range of erodent size of 0.1–0.3 mm, impact angles from 30 to 90° and particle velocity from 30 to 80 m s⁻¹. In order to clarify the details of the impact, the process of interaction of solid particles with cermet targets was studied using a laser Doppler anemometer (LDA) measuring technique. Systematic studies of the influence of the impact variables on the collision process have been carried out.