Capsulation of moldings made from silicon ceramic material

Ceramic articles are potted for hot isostatic pressing by porous glass and/or ceramic coating which is sintered to a pressure-tight coating in vacuo. Thus, a powdered SiO2 glass mixture with saturated alcohol sterin is sprayed on a SI3N4 ceramic, dried, introduced into the press which is evacuated to less than 0.013 mbar and heated to approximately 1200 C to drive off the organic binder and leave a powdered glass coating on the ceramic. The coating is sintered by heating to approximately 1200 C for 0.5 to 2 hours and forms a tight gass-impermeable layer. The press is heated to approximately 1700 C at 1000-300 bar and isostatic pressing is performed in the conventional manner

A Comparison of Learning Outcomes of Mentally Disabled Children Educated in Self-Contained Classrooms and Multicategorical Settings

Following the implementation of Public Law 94-142, The Education for All Handicapped Children Act of 1975, categorizing special needs children was a useful way of grouping students who needed similar treatment. Categories for each disability were viewed as performing an important function

Slow dynamics at the smeared phase transition of randomly layered magnets

We investigate a model for randomly layered magnets, viz. a three-dimensional Ising model with planar defects. The magnetic phase transition in this system is smeared because static long-range order can develop on isolated rare spatial regions. Here, we report large-scale kinetic Monte Carlo simulations of the dynamical behavior close to the smeared phase transition which we characterize by the spin (time) autocorrelation function. In the paramagnetic phase, its behavior is dominated by Griffiths effects similar to those in magnets with point defects. In the tail region of the smeared transition the dynamics is even slower: the autocorrelation function decays like a stretched exponential at intermediate times before approaching the exponentially small asymptotic value following a power law at late times. Our Monte-Carlo results are in good agreement with recent theoretical predictions based on optimal fluctuation theory.Comment: 7 pages, 6 eps figures, final version as publishe

Paper Session II-B - Integrated Factory/Launch Site Processing Concept

Achieving low cost, reliable space transportation is one of the most important space policy challenges facing the United States today. Since launch and mission operations are responsible for up to 45 % of the costs of each launch, lowering these costs is critical to reducing overall costs associated with space flight. To reduce these costs significantly, an innovative alternative approach to vehicle element processing was developed. This concept was born from the fact that present day launch processing system (LPS) is undergoing a major upgrade to implement today\u27s technology. Carrying this one step further, the same upgrade could be implemented at various vehicle element manufacturing sites. This would allow expendable vehicle standalone processing to be accomplished offsite without compromising the integrity of the vehicle thus eliminating horizontal checkout at the launch site. This paper will address vehicle test requirements, timelines and ground checkout concepts to implement this approach

Investigations of the carbon fibre cross-sectional areas and their non-circularities by means of laser diffraction

Laser diffraction is a commonly used tool to measure the fibre diameter of carbon fibres prior to mechanical testing. However, non-circularities of carbon fibres need to be considered in order to minimise measuring errors. As the work at hand demonstrates, using a single measurement of the fibre diameter may cause deviations as high as 30% from a computationally determined value. It appears that the error can be minimised by acquiring a data set of several apparent diameters as a function of the angle around the fibre axis. Based on this data, the cross-sectional area can be calculated as a circle with an averaged diameter or as an ellipse by applying an elliptical fitting procedure

Paper Session III-A - Next Generation Reusable Launch Systems Site Selection Trade Study: An Application of the Analytic Hierarchy Process

This paper focuses on site selection trade studies associated with Next Generation Reusable Launch Vehicle concepts. During site selection trade studies the need to utilize a decision making tool enabling tradeoffs between competing objectives while minimizing intuitive bias was recognized. In order to meet established goals of the next generation reusable launch vehicle concepts, a comprehensive site selection trade study must be performed. Estimates for both non-recurring and recurring costs associated with each candidate site must be evaluated. The systems’ operations concept, environmental constraints, logistics, range support, and weather are other important factors which must also be considered. Based on this, the Analytic Hierarchy Process (AHP) was implemented, allowing for systematic evaluation and measurement of each of the identified criteria in the site selection process. AHP is a multi-criterion decision support methodology allowing study participants (engineers and program management) to deal consistently with comparisons between both tangible and intangible criteria. Using this tool, participants in the site selection process can integrate their collective judgment, experience and understanding concerning the relevant importance of identified criteria as they relate to one another. The resulting process is organized in a logical hierarchical structure which can be easily tested for sensitivities to changes in assumptions and judgments

Fused filament fabrication: Comparison of methods for determining the interfacial strength of single welded tracks

The mechanical properties of plastic-based additively manufactured specimens have been widely discussed. However, there is still no standard that can be used to determine properties such as the interfacial strength of adjacent tracks and also to exclude the influence of varying manufacturing conditions. In this paper, a proposal is made to determine the interfacial strength using specimens with only one track within a layer. For this purpose, so-called single-wall specimens of polylactide were characterised under tensile load and the interfacial area between the adjacent layers was determined using three methods. It turned out that the determination of the interfacial area via the fracture surface is the most accurate method for determining the interfacial strength. The measured interfacial strengths were compared with the bulk material strength and it was found that the bulk material strength can be achieved under optimal conditions in the FFF process. It was also observed that with increasing nozzle temperature, the simultaneous printing of specimens influences the interfacial strength. To conclude, this method allows to measure the interfacial strength without superimposing the influence of voids. However, for example, the interfacial strength within a layer cannot be determined

Effects of Nerve Growth Factor and Nitric Oxide Synthase Inhibitors on Amyloid Precursor Protein mRNA Levels and Protein Stability

We determined previously that nitric oxide (NO) modulates the nerve growth factor (NGF)-mediated increases in amyloid precursor protein (APP) levels in PC12 cells. To elucidate potential mechanisms, the effects of NGF and NO synthase (NOS) inhibitors on APP mRNA levels and protein stability were evaluated. Surprisingly, treatment of PC12 cells with NGF resulted in decreased levels of APP695 and APP751/770 mRNA. Therefore, the effect of NGF on APP protein stability was examined using the translation inhibitor, cycloheximide. Under these conditions, NGF did not alter the rate of APP degradation, suggesting that NGF may be enhancing the translation rate of APP. Since NOS inhibitors attenuate the NGF-mediated increase in APP levels, their effect on APP mRNA levels and protein stability was also assessed. S-methylisothiourea (S-MIU), selective for inducible NOS, decreased both APP695 and APP751/770 mRNA levels while the non-selective NOS inhibitor, Nω-nitro-L-arginine methylester (L-NAME) had no effect. In both control and NGF-treated PC12 cells, S-MIU increased the half-life of APP, with the greatest effect observed with the APP695 isoform. Based on these data we propose that in PC12 cells, NGF increases APP levels through enhanced translation rate and that NO, which modulates the NGF-induced increase in APP protein, also regulates APP mRNA levels and could play a role in APP processing

Cutaneous Blood Flow and Percutaneous Absorption: A Quantitative Analysis Using a Laser Doppler Velocimeter and a Blood Flow Meter

Cutaneous blood flow has been directly quantitated in vivo for the first time without animal death utilizing the rat skin sandwich flap. This was accomplished by conducting experiments that made a direct correlation between two instruments: a laser Doppler velocimeter and an electromagnetic blood flow meter. Data demonstrate that the correlation between these two instruments is high and reproducible (r = 0.96) with a small (1.3%) coefficient of variation. Blood flow to skin in the unmanipulated state varies from 0.7 to 1.2 mls/min in an anesthetized rat. Application of the blood flow correlation to the determination of percutaneous absorption of caffeine across human skin and benzoic acid across rat skin demonstrates that assuming cutaneous blood flow is a particular value day to day in any skin type results in an apparent wide range of total compound absorbed across that skin on independent occasions. Utilizing actual blood flow measurements to calculate the amount of chemical absorbed reduces the range of variability in the total amount of chemical absorbed and provides a more accurate knowledge of events occurring during a particular time of the absorption process. Quantitation of cutaneous blood flow will be useful in physiologic and pharmacologic studies where actual cutaneous blood flow is likely to be important to the processes studied, e.g., delivery of drug to skin, metabolism within the skin, and disposition of drug to blood and skin following topical drug application

Mit of Hybrid Mixtures – Why NO New Standard?

The Nex-Hys Project, funded by the German Federal Ministry of Economy as part of the WIPANO frame program, aimed to develop standards for safety characteristics of hybrid mixtures. These should be designed in a way that the standards are extended and the existing values in the experimental setup still hold true. As part of the project, the Otto-von-Guericke University focused on the Minimum Ignition Temperature. Starting from a comparison of apparatuses for liquids (EN 14522) and dusts (IEC 80079-20-2) the decision to use the Godbert Greenwald Oven was made, as only there the possibility to introduce substances in gaseous and solid phase is given in principle. The standardized setup was extended by a heated chamber to evaporate the liquids to be tested. Burnable gases were introduced into the system by means of mixing according to the partial pressure method in the pressurized air chamber or the evaporation chamber. Thus, it was possible to determine the MIT of the pure gases and vapors in the GG oven. Series of test for different substances under variation of the concentration show comparable values to the standard methods and to values found in literature. A trend to slightly higher temperatures (for gases and vapors) with a deviation close to the measurement uncertainty can be found. All in all, the deviation by different operators seems to be in the same range and cannot be neglected. Following various combinations of dust, vapors and gases were tested. Up to now, no combinatory effect was detected. This seems to be in contradiction to former own publications, but there the setup was different. This could be an explanation for these nonreproducible result. In all combinations, the MIT of the substances that has the lower MIT is dominating the final value. The setup-up generally proved to be able to test for the MIT of hybrid mixtures without violating existing values. Part of the tests were made in a GG oven of double length showing a clear influence on the MIT for some substances, due to the longer residence time. Apart from some rather practical weaknesses of the standardized setup there are general disadvantages that limit its use for a further development. First there is the totally unknow concentration and distribution of fuels in this open setup. Secondly, the subjective detection of the ignition by the operator. Third, the temperature distribution and heat transfer conditions that are not well defined. The original intention behind the experiment is not in line with the scientific intention to create a versatile instrument to determine the ignition temperature for all phases and their mixtures. Therefore, a completely new approach would be necessary. The existing MIT standards for dust and vapor/gases can further exist unchanged and fulfil their purpose