Thermodynamic Calculations on the Chemical Vapor Deposition of Silicon Nitride and Silicon from Silane and Chlorinated Silanes

After a discussion of the thermochemical values of the Si–H–Cl–N system which occur in the literature, CVD phase diagrams are presented which include contours of constant deposition efficiency. The temperature range considered is from 800 to 2600 K. A number of chlorinated silanes as well as silane can be used as a silicon source, while ammonia is used as the nitrogen source. The effects of pressure variation and dilution by nitrogen and hydrogen are also included. Some initial calculations concerning silicon diimide are made. The CVD phase diagrams are used to describe several mechanisms occurring during the formation of silicon nitride from the gas phase.     

Estimating the crop response to fertilizer nitrogen residues in long-continued field experiments

Knowledge of the cumulated effect of long-continued nitrogen (N) inputs is important for both agronomic and environmental reasons. However, only little attention has been paid to estimate the crop response to mineral fertilizer N residues. Before interpreting estimates for the crop response to previous N input rates, the experimental design for testing needs to be examined. Experimental designs that suspend the customary N inputs, leaving the test crop unfertilized, ignore any interaction between the rate of N applied in the past and the rate applied in the test year. We estimated the interaction using data from five long-continued field experiments on mineral and organic N input rates where the main plots were subdivided for incremental rates of mineral N fertilizer in the test year. The interaction between N applied in the past and in the test year significantly affected grain yield and N offtake when the residual effect originated from organic applications, but the interaction was not significant when mineral N fertilizer had been used in the past, making the residual effect of N applied in the past additive to the effect of N applied in the test year. The dry matter (DM) grain yield of spring barley decreased by an average of 5?kg?DM/ha and the grain N offtake by 46?g?N/ha for a decrease in the annual mineral N rate of 1?kg?N/ha applied for more than three decades. Although statistically significant, the crop response to mineral fertilizer N residues was of minor importance when compared with the residual effect of organic inputs.     

Acid Precipitation of Kraft Lignin from Aqueous Solutions: The Influence of pH,Temperature, and Xylan

In this study, the manners in which temperature (45–77?°C) and the addition of xylan (5?g/95?g lignin) influence the onset of precipitation and evolution of the particle size distribution during acid precipitation of softwood kraft lignin were investigated in situ. No systematic trend between the onset pH of precipitation and the temperature or the addition of xylan could be observed at these conditions: the average onset pH was found to be 9.3. However, the size of the agglomerates increased as the temperature was increased, but added xylan rendered a decrease in agglomerate size. A higher onset pH was measured at increased Na ion concentration. The results indicate that the ionization degree of the phenolic groups influences the precipitation at 1?M Na ions but it is also probable that the degree of ionization of the carboxylic groups (on kraft lignin and xylan) influences precipitation (particle numbers and sizes).     

Rapid disappearance of zinc positive terminals in focal brain ischemia

The study was undertaken to determine if the levels of vesicular zinc in neuronal terminals would decrease in response to focal brain ischemia. The middle cerebral artery was occluded distal to the striatal branches in male spontaneously hypertensive rats. At 7, 15, 30, 45, 60, 90, 120 min; 3, 6, 12, 24, 48 h and 7 days later the animals were sacrificed and the brains were stained for zinc-sulfides, cell bodies and AChE-positive cholinergic fibers. The density of zinc positive terminals significantly decreased in the neocortical ischemic zone 7 min after middle cerebral artery occlusion (MCAO). In the neocortical layers II and III most zinc positive neuronal terminals disappeared at 7 min after MCAO whereas the zinc positive terminals in layers V and VI remained positive at least 2 h. Beginning at 1 h after MCAO and progressing to 24 h a significant decrease in the density of zinc positive terminals was observed in the dorsolateral striatum, and ventrobasal thalamic nucleus, both major projection areas of the sensorimotor cortex. The disappearance of zinc positive neuronal terminals in the ischemic neocortex and related areas, is most likely due to a neuronal release of vesicular zinc in response to hypoxia. The high extracellular concentration of zinc is thought to be both neuroprotective by blocking the NMDA receptor and neurotoxic by activating neuronal influx of Ca2+ through voltage gated calcium channels. It seems evident that the latter effect of zinc is contributing to the neuronal death in focal brain ischemia.     

Acoustic Wave Propagation in Complicated Geometries and Heterogeneous Media

We construct finite difference discretizations of the acoustic wave equation in complicated geometries and heterogeneous media. Particular emphasis is placed on the accurate treatment of interfaces at which the underlying media parameters have jump discontinuities. Discontinuous media is treated by subdividing the domain into blocks with continuous media. The equation on each block is then discretized with finite difference operators satisfying a summation-by-parts property and patched together via the simultaneous approximation term method. The energy method is used to estimate a semi-norm of the numerical solution in terms of data, showing that the discretization is stable. Numerical experiments in two and three spatial dimensions verifies the accuracy and stability properties of the schemes.     

Praxis-related research: serving two masters?

This article elucidates criteria which might be helpful in evaluating praxis-related research. The authors explore both sides of the research and development (R & D) project. They examine different ways of understanding contributions to knowledge through research but more especially exploring ideas about contributions to changing praxis. Changing praxis necessarily involves changing not only each participant as an individual actor, but changing patterns of activity. In most praxis-related research, this is pursued by involving a widening range of participants in a setting. This poses the further problem that the ripple effects of the project are not entirely under the researcher's control. Thus, as the title suggests, praxis-related research serves two masters. Very often, R & D projects aim to make contributions to social science. Generally they also aim to make contributions to the world of human affairs. Different criteria are appropriate for judging each.     

Dielectrophoresis-induced separation of metallic and semiconducting single-wall carbon nanotubes in a continuous flow microfluidic system

The AC dielectrophoresis-induced separation of metallic and semiconducting single-wall carbon nanotubes has been carried out in a continuous flow microfluidic system with isolated electrodes. The separation has been studied for single-wall carbon nanotube aqueous suspensions with ionic (sodium dodecylsulphate) and non-ionic (TritonX-100) surfactants. The efficiency of separation has been determined with the help of resonant Raman spectroscopy using various excitation energies. The prototype microfluidic cell presently shows somewhat inferior separation efficiency with respect to static dielectrophoretic filtering on arrays of microelectrodes but has potential for improvements. Factors influencing the separation efficiency and scaling up of the process are discussed.