Mesoscale modeling of amorphous metals by shear transformation zone dynamics

A new mesoscale modeling technique for the thermo-mechanical behavior of metallic glasses is proposed. The modeling framework considers the shear transformation zone (STZ) as the fundamental unit of deformation, and coarse-grains an amorphous collection of atoms into an ensemble of STZs on a mesh. By employing finite element analysis and a kinetic Monte Carlo algorithm, the modeling technique is capable of simulating glass processing and deformation on time and length scales greater than those usually attainable by atomistic modeling. A thorough explanation of the framework is presented, along with a specific two-dimensional implementation for a model metallic glass. The model is shown to capture the basic behaviors of metallic glasses, including high-temperature homogeneous flow following the expected constitutive law, and low-temperature strain localization into shear bands. Details of the effects of processing and thermal history on the glass structure and properties are also discussed.     

Critical issues in the formation of quantum computer test structures by ion implantation

The formation of quantum computer test structures in silicon by ion implantation enables the characterization of spin readout mechanisms with ensembles of dopant atoms and the development of single atom devices. We briefly review recent results in the characterization of spin dependent transport and single ion doping and then discuss the diffusion and segregation behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy implantations as characterized through depth profiling by secondary ion mass spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the SiO₂/Si interface during activation anneals, while antimony diffusion is found to be minimal. An effect of the ion charge state on the range of antimony ions, ¹²¹Sb²⁵⁺, in SiO₂/Si is also discussed.     

Kinetics of biaxial dome formation by transformation superplasticity of titanium alloys and composites

By thermally cycling through their transformation temperature range, coarse-grained polymorphic materials can be deformed superplastically, owing to the emergence of transformation mismatch plasticity (or transformation superplasticity) as a deformation mechanism. This mechanism is presently investigated under biaxial stress conditions during thermal cycling of unalloyed titanium, Ti-6Al-4V, and their composites (Ti/10 vol. pct TiC _p , Ti-6Al-4V/10 vol. pct TiC _p , and Ti-6Al-4V/5 vol. pct TiB _w ). During gas-pressure dome bulging experiments, the dome height was measured as a function of forming time. Adapting existing models of biaxial doming to the case of transformation superplasticity where the strain-rate sensitivity is unity, we verify the operation of this deformation mechanism in all experimental materials and compare the biaxial results directly to new uniaxial thermal cycling results on the same materials. Finally, existing thickness distribution models are compared with experimentally measured profiles.     

Disposal of aerobic treated swine waste by refeeding to finishing swine (author's transl)

Simple aerobic treatment of swine waste did not increase the production of microorganismprotein (pure protein). Addition of available energy resulted in a small increase of pure protein: During continuous aerobic treatment 20 g pure protein were produced by 100 g starch, during discontinuous aerobic treatment 10 g pure protein by 100 g organic matter from molasses (mean values). Comparative feeding trials with 90% resp. 80% feed restricted finishing swine without and with added swine waste (continuous treated without supplements resp. discontinuous treated with addition of yeasts and molasses) had as results no improvement in body-weight-gain but a 12% resp. 17% deterioration in feed conversion with 13% less bodyfat formation. Weight gains of both groups with restricted feed (without and with added swine waste) was 22% less in comparison to full fed swine. Losses at slaughter of swine in the group with feed restriction and added swine waste were partly due to higher intestine contents higher than that of swine with feed restriction and without added swine waste. Higher weights of livers and kidneys in swine of the "waste group" counts for a possibly higher metabolism-stress.     

Laterally defined freely suspended quantum dots in GaAs/AlGaAs heterostructures

Free-standing beams containing a two-dimensional electron system are shaped from a GaAs/AlGaAs heterostructure. Quantum point contacts and (double) quantum dots are laterally defined using metal top gates. We investigate the electronic properties of these nanostructures by transport spectroscopy. Tunable localized electron states in freely suspended nanostructures are a promising tool to investigate the electron-phonon interaction.     

Aluminiumnitrid als Festelektrolyt in Hochtemperatur-Meßzellen

Beschreibung der Meßzelle mit AIN als Festelektrolyt zur elektrochemischen Ermittlung der in Metallschmelzen gelösten Gehalte an Stickstoff. EMK-Messungen in Eisenschmelzen bei 1640 °C und Stickstoffgehalten zwischen 30 und 480 ppm. Vergleich der Meßwerte mit den theoretisch errechneten Werten. Schlußfolgerungen über die lonenleitung im Festelektrolyten AIN.     

Characterization of poly(glycolide-co-D,L-lactide)/poly(D,L-lactide) microspheres for controlled release of GM-CSF

PURPOSE: This study describes the preparation and characterization of a controlled release formulation of granulocyte-macrophage colony-stimulating factor (GM-CSF) encapsulated in poly(glycolide-co-D,L-lactide) (PLGA) and poly(D,L-lactide) (PLA) microspheres. METHODS: GM-CSF was encapsulated in PLGA/PLA microspheres by a novel silicone oil based phase separation process. Several different blends of PLGA and low molecular weight PLA were used to prepare the microspheres. The microspheres and the encapsulated GM-CSF were extensively characterized both in vitro and in vivo. RESULTS: Steady release of GM-CSF was achieved over a period of about one week without significant "burst" of protein from the microspheres. Analysis of microsphere degradation kinetics by gel permeation chromatography (GPC) indicated that low molecular weight PLA enhanced the degradation of the PLGA and thereby affected release kinetics. GM-CSF released from the microspheres was found to be biologically active and physically intact by bioassay and chromatographic analysis. Analysis of serum from mice receiving huGM-CSF indicated that the GM-CSF was biologically active and that a concentration of greater than 10 ng/mL was maintained for a period lasting at least nine days. MuGM-CSF was not detected following in vivo administration of muGM-CSF microspheres. The tissues of mice receiving muGM-CSF microspheres were characterized by infiltration of neutrophils, and macrophages which were in significant excess of those found in mice administered with placebo controls (i.e. microspheres without GM-CSF). CONCLUSIONS: This study demonstrates the influence of formulation parameters on the encapsulation of GM-CSF in PLGA/PLA microspheres and its controlled release in biologically active form. The intense local tissue reaction in mice to muGM-CSF microspheres demonstrates the importance of the mode of delivery on the pharmacologic activity of GM-CSF.