Space-time finite elements for a simplified thermo-metallurgical problem relevant to casting

The non-linear thermo-metallurgical problem, relevant for the cooling of a molten metal including the macro-segregation that occurs during the cooling process, is studied here. Due to the strong non-linearities involved in phase transformations, it is necessary to use a fine resolution in space-time in a finite element approximation in order to meet accuracy requirements. We derive space-time FE-methods based on the discontinuous and continuous Galerkin method in time for the energy equation. This formulation integrates the stored energy exactly for a given heat flux. When macro-segregation is incorporated into the model, the problem can be formulated in such a way that the phase-transition drives a flow of species. In addition, diffusion is possible throughout the domain. The model can be further rewritten using a potential approach. By this approach for modelling macro-segregation, we are able to obtain discretizations that guarantee that the balance equations are satisfied, and it is possible to solve the phase-transition problem either as a field problem or as a local problem (defined by a local evolution rule).     

Rapid thermal chemical vapor deposition of in-situ boron doped polycrystalline SIxGe1-x

In-situ doped polycrystalline Si_xGe_1-x (x = 0.7) alloys were deposited by rapid thermal chemical vapor deposition (RTCVD) using the reactive gases SiH₂Cl₂, GeH₄ and B₂H₆ in a H₂ carrier gas. The depositions were performed at a total pressure of 4.0 Torr and at temperatures 600° C, 650° C and 700° C and different B₂H₆ flow rates. The conditions were chosen to achieve high doping levels in the deposited films. Our results indicate negligible effect of B₂H₆ flow on the deposition rate. The depositions follow an Arrhenius type behavior with an activation energy of 25 kcal/mole. Boron incorporation in the films was found to follow a simple kinetic model with higher boron levels at lower deposition rates and higher B₂H₆ flow rates. As-deposited resistivities as low as 2 mΩ-cm were obtained. Rapid thermal annealing (RTA) in the temperature range 800-1000° C was found to reduce the resistivity only marginally due to the high levels of boron activation achieved during the deposition process. The results indicate that polycrystalline Si_xGe_1-x films can be deposited by RTCVD with resistivities comparable to those reported for in-situ doped polysilicon.     

Vergleich der Extrakte und des Lignins aus frischem und gelagertem Kiefernholz (Pinus sylvestris L.)

The degradation processes of the extractives of pine wood caused by aging are only noticeable in the heartwood. In seasoned sapwood the percentages of the water extracts and the cyclohexane-ethanol extract increase compared with the green sample; the alkali extracts, however, do not vary. The contents of acid lignin as well as the UV and IR spectra of MWL do not show differences. The amount of OCH₃/C₉ is in all samples 0.96, but the degree of oxidation is higher in the seasoned wood than in the green one.     

Computer-aided design in mechanisms

The man-machine dialog is very important for the design process. In this paper a program system, based on the minicomputer KRS 4201 (ROBOTRON), is demonstrated by using an interactive graphical screen. This program system provides the opportunity to analyze and synthesize mechanisms up to 16 links. The application is demonstrated by designing a front-loader-system for a truck. Real-time animation of seven-bar linkages and coupler curves, including velocity and acceleration, are shown.     

Structured document storage and refined declarative and navigational access mechanisms in HyperStorM

The combination of SGML and database technology allows to refine both declarative and navigational access mechanisms for structured document collection: with regard to declarative access, the user can formulate complex information needs without knowing a query language, the respective document type definition (DTD) or the underlying modelling. Navigational access is eased by hyperlink-rendition mechanisms going beyond plain link-integrity checking. With our approach, the database-internal representation of documents is configurable. It allows for an efficient implementation of operations, because DTD knowledge is not needed for document structure recognition. We show how the number of method invocations and the cost of parsing can be significantly reduced. Edited by Y.C. Tay. Received April 22, 1996 / Accepted March 16, 1997     

Contribution of beta-lactamase production to the resistance of mycobacteria to beta-lactam antibiotics

Changes in motor function were assessed in male rats after injecting graded doses (100, 200, 400, and 800 mg/kg, IP) of ammonium chloride and ammonium acetate. The effects were correlated with the concentrations of ammonia and glucose in the brain and blood. Spontaneous motor activity and motor coordination were inhibited after injecting 100 and 200 mg/kg, whereas with 400 and 800 mg/kg the animals exhibited convulsive movements. A dose-dependent increase was found in the concentrations of ammonia and glucose in both blood and brain. These were restored, 25 min after treatment, to control levels in the blood and not in the brain. A correlation was found between the time courses of inhibitory motor events and a rise in brain ammonia levels. Convulsant action of ammonium salts was accompanied by a marked elevation of ammonia and glucose concentration in the brain. The findings suggest that detoxication of diffused ammonia is a rate-limiting process in the brain and that ammonia, at toxic concentrations, decreases glucose utilization in the brain, resulting in an inhibition of motor function. A very high concentration of ammonia in the brain, although inhibiting glucose utilization, produces clonic convulsions probably by activating directly the motor neurons.     

Initial Stages in the Metal-dusting Process on Alloy 800

The initial stages of the metal-dusting process on Alloy 800 at 620 °C were investigated by light optical microscopy, RAMAN spectroscopy, atomic-force microscopy, Auger electron spectroscopy, transmission-electron microscopy and electron back-scatter diffraction. As it turned out the incubation period for metal-dusting is characterized by simultaneous formation of a heterogeneously growing oxide scale and deposition of carbon. The material surface shows different tarnish colors depending on the substrate-grain orientation with different susceptibility to the beginning of metal-dusting attack. “Low-index” grains were not attacked within the times investigated while the other grain orientations showed pitting. Carbon is evidently incorporated into the oxide scale from the very beginning of exposure with different intensities depending on the underlying substrate-grain orientation leading to differences in the tarnish colors. As a consequence carbides are formed even underneath “dense” oxide layers. Evidently metal-dusting attack starts at positions of the oxide scale where “higher carbon concentrations” are present.     

Physical degradation of genomic DNA of soybean flours does not impair relative quantification of its transgenic content

In this paper, four different physical treatments (microwaves, heating by conduction, sonication and pressure autoclaving) were performed to degrade a pure DNA extract, and their influence on GMO quantification was studied. The aim was to check the hypothesis that processing of agrofood products results in a similar degradation rate for both the transgenic target and the specific target. Indeed we could observe that even if the used physical treatments could lead to a significant increase of C _t values for both transgenic and specific targets, the resulting ΔC _t remained stable. So, the main conclusion of the study is that the aforementioned hypothesis seems valid and thus a physical degradation of DNA will not affect the relative quantitation of the GMO content, provided that both the specific and transgenic targets have very similar size. A second important issue of the experiments performed was that DNA is a very robust molecule as it is extremely difficult to reach a mean size below 100 bp. The study also gives evidence of the importance of using small targets.