Preparation of silicon carbide–silicon nitride fibers by the controlled pyrolysis of polycarbosilazane precursors

Experiments to produce polycarbosilazane resin and high-strength silicon carbide–silicon nitride (Si_xN_yC_z) fibers as well as resin/fiber characteristics are reported. Polycarbosilazane resin was drawn into fibers from the melt and subsequently treated and pyrolyzed into Si_xN_yC_z fibers. These materials are characterized by high tensile modulus (29 × 10⁶ psi for 0.4-mil diameter) and high electrical resistivity (6.9 × 10⁸ Ω·cm for 0.6-mil diameter).     

Contraceptive practice after clinic discontinuation

A follow-up study was conducted of clients who stopped attending 4 family planning clinics in Washington County, Oregon, a predominantly white, middle-class suburban community. Clients had enrolled in the program between 1971-74, and dropped out by April 1975. 29% of the women (746) who were overdue for a return visit by more than 3 months (i.e. inactive clients) were contacted by phone and mail. No significant social or demographic differences were found between active and inactive clients or between dropouts who were contacted and those who were not. 71% of all program enrollees dropped out by the end of 3 years. However, 90% of the sample were either using contraception or not at risk of an unwanted pregnancy for a variety of reasons. The remaining 10% were either unprotected or already pregnant with an unplanned pregnancy (2%). The women at risk and not using contraception were more likely to be young, poorly educated, single, and recent enrollees in the family planning program. No other social or economic differences affected the comparison of the 2 groups. Most users continued to use the same method of contraception they had used before. However, a significantly smaller proportion of women were using the pill, a slightly larger proportion were using IUD and 6% more clients were sterilized. The most common reasons for leaving the program were the decision to use a private physician and relocation. Among women at risk, the most common reason was worry about the contraceptive method, especially the pill. New sources of care included private physicians (71%, but 1/3 of these women were disatisfied with their doctors' care or fees), public health clinic not part of the family planning program (21%) and drugstores. A very few women reported no alternate source of care.     

Training in virtual environments: transfer to real world tasks and equivalence to real task training

Virtual environments (VEs) are extensively used in training but there have been few rigorous scientific investigations of whether and how skills learned in a VE are transferred to the real world. This research aimed to measure and evaluate what is transferring from training a simple sensorimotor task in a VE to real world performance. In experiment 1, real world performances after virtual training, real training and no training were compared. Virtual and real training resulted in equivalent levels of post-training performance, both of which significantly exceeded task performance without training. Experiments 2 and 3 investigated whether virtual and real trained real world performances differed in their susceptibility to cognitive and motor interfering tasks (experiment 2) and in terms of spare attentional capacity to respond to stimuli and instructions which were not directly related to the task (experiment 3). The only significant difference found was that real task performance after training in a VE was less affected by concurrently performed interference tasks than was real task performance after training on the real task. This finding is discussed in terms of the cognitive load characteristics of virtual training. Virtual training therefore resulted in equivalent or even better real world performance than real training in this simple sensorimotor task, but this finding may not apply to other training tasks. Future research should be directed towards establishing a comprehensive knowledge of what is being transferred to real world performance in other tasks currently being trained in VEs and investigating the equivalence of virtual and real trained performances in these situations.     

Chemical Identification of MHC-influenced Volatile Compounds in Mouse Urine. I: Quantitative Proportions of Major Chemosignals

The genes of the major histocompatibility complex (MHC) are highly polymorphic loci that encode cell surface proteins, class I and II molecules. They present peptide antigens to T cells and thereby control immunological self/nonself recognition. Increasing evidence indicates that MHC genes also influence odor and mating preferences; however, it is unclear how. Here we report the results of chemical analyses of male mouse urinary odors collected from a variety of mouse strains, including MHC-congenics, recombinants, mutants, and transgenics (i.e., beta2 microglobulin "knockouts," which lack class I expression, and transporters associated with antigen processing (TAP) knock-outs). After the identification of volatile odor components by gas chromatography/mass spectrometry, the odor profiles of urine samples were analyzed quantitatively by using stir bar sorptive extraction and gas chromatography/atomic emission detection. Results showed that MHC genes influenced the amounts of testosterone-mediated pheromones, sulfur-containing compounds, and several carbonyl metabolites. This is the first report to quantitatively link known mouse pheromones to classical, antigen-binding MHC loci. Surprisingly, these compounds were not influenced by TAP genes, even though these loci are MHC-linked and play a role in peptide presentation. Whereas identification of MHC-determined odorants does not reveal their metabolic origin, some constituents were also present in blood serum, and their levels were not altered by antibiotics.