A sintering model for SiC(sub)w/Si3N4 composites

Presented is a model which suggests that it should be possible to pressureless sinter a SiC(sub w)/ Si3N4 composite to theoretical density. Prior failure to achieve complete densification by sintering is attributed to the use of compositions which result in a glass deficit. There is one basic premise for this model. The ratio of glass amount to surface area of nonglass constituents must be the same for both composite and sinterable monolithic Si3N4. This model suggests that whisker and grain sizes and whisker loading influence the glass amount necessary for successful sintering of composites. According to the model, a large glass amount will be necessary for successful sintering of these composites. However, grain boundary thicknesses in the composite will be less than those in the analogous monolithic materials. This suggests that good high temperature strength may still be attained. A recent report supports the predictions of the model

Slurry-pressing consolidation of silicon nitride

A baseline slurry-pressing method for a silicon nitride material is developed. The Si3N4 composition contained 5.8 wt percent SiO2 and 6.4 wt percent Y2O3. Slurry-pressing variables included volume percent solids, application of ultrasonic energy, and pH. Twenty vol percent slurry-pressed material was approximately 11 percent stronger than both 30 vol percent slurry-pressed and dry-pressed materials. The Student's t-test showed the difference to be significant at the 99 percent confidence level. Twenty volume percent (300 h) slurry-pressed test bars exhibited strengths as high as 980 MPa. Large, columnar beta-Si3N4 grains caused failure in the highest strength specimens. The improved strength correlated with better structural uniformity as determined by radiography, optical microscopy, and image analysis

Geometric phase for an adiabatically evolving open quantum system

We derive an elegant solution for a two-level system evolving adiabatically under the influence of a driving field with a time-dependent phase, which includes open system effects such as dephasing and spontaneous emission. This solution, which is obtained by working in the representation corresponding to the eigenstates of the time-dependent Hermitian Hamiltonian, enables the dynamic and geometric phases of the evolving density matrix to be separated and relatively easily calculated.Comment: 10 pages, 0 figure

Needs assessment of Wisconsin primary care residents and faculty regarding interest in global health training

<p>Abstract</p> <p>Background</p> <p>The primary objectives of this study were to assess Wisconsin's primary care residents' attitudes toward international health training, the interest among faculty to provide IH training, and the preferred modality of IH training.</p> <p>Methods</p> <p>Surveys were administered using 505 residents and 413 medical faculty in primary care residencies in Wisconsin. Results from 128 residents and 118 medical school faculty members were collected during the spring of 2007 and analyzed.</p> <p>Results</p> <p>In total, 25% of residents (128/505) and 28% of faculty (118/413) responded to the survey. A majority of residents (58%) and faculty (63%) were interested in global health issues. Among residents, 63% planned on spending professional time working abroad. Few residents (9%) and faculty (11%) assess their residencies as preparing residents well to address topics relating to international health. The survey indicates that adequate faculty in Wisconsin could provide mentorship in international health as 47% (55) of faculty had experience working as a physician internationally, 49% (58) of faculty spend more than 25% clinical time caring for patient from underserved communities and 39% (46) would be willing to be involved with developing curriculum, lecturing and/or mentoring residents in international health.</p> <p>Conclusion</p> <p>Overall, the majority of the respondents expressed high interest in IH and few felt prepared to address IH issues indicating a need for increased training in this area. The findings of this survey are likely relevant as a prototype for other primary care residencies.</p

ECONOMICS OF SWINE CROSSBREEDING SYSTEMS

Livestock Production/Industries,

Soil survey series 25

UNITED STATES DEPARTMENT OF AGRICULTURE Soil Conservation Service In cooperation with ALASKA AGRICULTURAL EXPERIMENT STATIO

Materials for engine applications above 3000 deg F: An overview

Materials for future generations of aeropropulsion systems will be required to perform at ever-increasing temperatures and have properties superior to the current state of the art. Improved engine efficiency can reduce specific fuel consumption and thus increase range and reduce operating costs. The ultimate payoff gain is expected to come when materials are developed which can perform without cooling at gas temperatures to 2200 C (4000 F). An overview is presented of materials for applications above 1650 C (3000 F), some pertinent physical property data, and the rationale used: (1) to arrive at recommendations of material systems that qualify for further investigation, and (2) to develop a proposed plan of research. From an analysis of available thermochemical data it was included that such materials systems must be composed of oxide ceramics. The required structural integrity will be achieved by developing these materials into fiber-reinforced ceramic composites

A CSO Search for ll-C3_3H+^+: Detection in the Orion Bar PDR

The results of a Caltech Submillimeter Observatory (CSO) search for $l$-C$_3$H$^+$, first detected by Pety et al. (2012) in observations toward the Horsehead photodissociation region (PDR), are presented. A total of 39 sources were observed in the 1 mm window. Evidence of emission from $l$-C$_3$H$^+$ is found in only a single source - the Orion Bar PDR region, which shows a rotational temperature of 178(13) K and a column density of 7(2) x $10^{11}$ cm$^{-2}$. In the remaining sources, upper limits of ~10$^{11} - 10^{13}$ cm$^{-2}$ are found. These results are discussed in the context of guiding future observational searches for this species.Comment: 9 pages, 8 figures, 4 table