Program to Optimize Simulated Trajectories (POST). Volume 1: Formulation manual

A general purpose FORTRAN program for simulating and optimizing point mass trajectories (POST) of aerospace vehicles is described. The equations and the numerical techniques used in the program are documented. Topics discussed include: coordinate systems, planet model, trajectory simulation, auxiliary calculations, and targeting and optimization

Development of thin-film based sensors for temperature and tool wear monitoring during machining = [Entwicklung von Dünnschichtsensoren zur Überwachung von Temperatur und Werkzeugverschleiß während der Zerspanung]

Die Entwicklung von Dünnschichtsensoren zur Temperatur- und Verschleißmessung in der Zerspanung wird in diesem Artikel präsentiert. Ein funktionales Dünnschichtsystem, bestehend aus einer Al$_{2}$O$_{3}$-Isolationsschicht, einer mittels Photolithographie strukturierten Chrom-Sensorschicht sowie einer Al$_{2}$O$_{3}$-Verschleiß- und Isolationsschutzschicht, wird per physikalischer Gasphasenabscheidung (engl. physical vapor deposition, PVD) auf der Oberfläche von Hartmetall-Wendeschneidplatten abgeschieden. Erste Proben konnten mit Sensoren gefertigt werden und in Labor- sowie Zerspanversuchen hinsichtlich ihrer Funktionalität getestet werden. Die werkzeugintegrierten Sensoren können zur In-process Messung der Temperaturen auf der Spanfläche im oder in der Nähe des Werkzeug-Span-Kontakts sowie zur Bestimmung der Verschleißmarkenbreite eingesetzt werden. Die Kenntnis dieser wichtigen Prozesskenngrößen bietet die Möglichkeit neuartige In-Process-Regelungsmechanismen zu entwickeln, welche eine gezielte Einstellung der Surface Integrity und damit eine Verbesserung der Leistungsfähigkeit und der Lebensdauer des Bauteils ermöglichen

First-principles calculation of positron lifetimes and affinities in perfect and imperfect transition-metal carbides and nitrides

First-principles electronic structure and positron-state calculations for transition-metal carbides and nitrides are performed. Perfect NaCl structures as well as structures with metal or carbon/nitrogen vacancies are considered. The positron affinities and lifetimes are determined. The trends are discussed and the results are compared with recent positron lifetime measurements for group-IV and -V refractory metal carbides. The present analysis suggests, contradictory to an earlier interpretation, that positrons are trapped and annihilated at both carbon and metal vacancies. The concentration of metal vacancies detected by positron annihilation methods is probably very low, below the sensitivity limit of other experimental methods.Peer reviewe

Global existence and asymptotic behaviour in the future for the Einstein-Vlasov system with positive cosmological constant

The behaviour of expanding cosmological models with collisionless matter and a positive cosmological constant is analysed. It is shown that under the assumption of plane or hyperbolic symmetry the area radius goes to infinity, the spacetimes are future geodesically complete, and the expansion becomes isotropic and exponential at late times. This proves a form of the cosmic no hair theorem in this class of spacetimes

Gallium implantation induced deep levels in n-type 6H-SIC

Two Ga-acceptor levels, located at EV+0.31eV and EV+0.37eV, respectively, have been observed in the gallium implantation manufactured p+n diodes using deep level transient spectroscopy. The behavior of the implanted gallium is very similar to that of implanted aluminum, except that the positions of the introduced levels are different. This result strongly supports the recent model, which was used to explain the discrepant results between boron and aluminum implantation induced deep levels. Besides the two acceptor levels, a thermally stable electron trap is also observed and has been tentatively attributed to a Ga-related complex. © 1999 American Institute of Physics.published_or_final_versio

Aluminum-implantation-induced deep levels in n-type 6H–SiC

Deep-level defect centers on the n-side of p+n junction diodes formed by low and elevated temperature aluminum-ion implantation into n-type 6H–SiC have been studied using deep-level transient spectroscopy. Two shallow Al-acceptor levels have been observed in the n region just beyond the implantation depth through their minority-carrier emission signatures. The dominant level is situated at 0.26 eV above the valence band and is accompanied by a shallower level of small intensity. Comparison with photoluminescence results suggests the dominant level (labeled Ak) and the shallower level (labeled Ah), are associated with the cubic and hexagonal lattice sites, respectively. Unlike previously reported results, which show many different implantation-induced donors within the implantation region, only one deep donor level at EC – 0.44 eV is found to occur in the postimplantation region, indicating that the various crystal damage sites occur with different spatial distributions. ©1998 American Institute of Physics.published_or_final_versio

Matrix-free calcium in isolated chromaffin vesicles

Isolated secretory vesicles from bovine adrenal medulla contain 80 nmol of Ca2+ and 25 nmol of Mg2+ per milligram of protein. As determined with a Ca2+-selective electrode, a further accumulation of about 160 nmol of Ca2+/mg of protein can be attained upon addition of the Ca2+ ionophore A23187. During this process protons are released from the vesicles, in exchange for Ca2+ ions, as indicated by the decrease of the pH in the incubation medium or the release of 9-aminoacridine previously taken up by the vesicles. Intravesicular Mg2+ is not released from the vesicles by A23 187, as determined by atomic emission spectroscopy. In the presence of N H Q , which causes the collapse of the secretory vesicle transmembrane proton gradient (ApH), Ca2+ uptake decreases. Under these conditions A23 187-mediated influx of Ca2+ and efflux of H+ cease at Ca2+ concentrations of about 4 pM. Below this concentration Ca2+ is even released from the vesicles. At the Ca2+ concentration at which no net flux of ions occurs the intravesicular matrix free Ca2+ equals the extravesicular free Ca2+. In the absence of NH4C1 we determined an intravesicular pH of 6.2. Under these conditions the Ca2+ influx ceases around 0.15 pM. From this value and the known pH across the vesicular membrane an intravesicular matrix free Ca2+ concentration of about 24 pM was calculated. This is within the same order of magnitude as the concentration of free Ca2+ in the vesicles determined in the presence of NH4C1. Calculation of the total Ca2+ present in the secretory vesicles gives an apparent intravesicular Ca2+ concentration of 40 mM, which is a factor of lo4 higher than the free intravesicular concentration of Ca2+. It can be concluded, therefore, that the concentration gradient of free Ca2+ across the secretory vesicle membrane in the intact chromaffin cells is probably small, which implies that less energy is required to accumulate and maintain Ca2+ within the vesicles than was previously anticipated

Community Walking in People with Parkinson's Disease

People with Parkinson's disease often have walking difficulty, and this is likely to be exacerbated while walking in places in the community, where people are likely to face greater and more varied challenges. This study aims to understand the facilitators and the barriers to walking in the community perceived by people with Parkinson's disease. This qualitative study involved 5 focus groups (n = 34) of people with Parkinson's disease and their partners residing in metropolitan and rural regions in Queensland, Australia. Results found that people with PD reported to use internal personal strategies as facilitators to community walking, but identified primarily external factors, particularly the environmental factors as barriers. The adoption of strategies or the use of facilitators allows people with Parkinson's disease to cope so that participants often did not report disability

Thermal Analysis of EPOS components

We present a simulation study of the thermal behaviour of essential parts of the electron-positron converter of the positron source EPOS at the Research Center Dresden-Rossendorf. The positron moderator foil and the upper tube element of the electrostatic extraction einzellens are directly exposed to the primary electron beam (40 MeV, 40 kW). Thus, it was necessary to prove by sophisticated simulations that the construction can stand the evolving temperatures. It was found that thin moderator foils (< 20...40 µm) will not show a too strong heating. Moreover, the temperature can be varied in a wide range by choosing an appropriate thickness. Thus, the radiation-induced lattice defects can at least partly be annealed during operation. The wall of the extraction lens which is made from a stainless steel tube must be distinctly thinned to avoid damage temperatures. The simulations were performed time dependent. We found that the critical parts reach their final temperature after less than a minute