Determination of the oxidative stability of perfluoropolyalkyl ethers and correlation with chemical structure

The oxidative stabilities of several perfluoropolyalkyl ethers (PFPAE) with related chemical structures were determined by thermal gravimetric analysis and correlated with their chemical structures. These results show that oxidative stability increases as the number of difluoroformal groups decreases and as trifluoromethyl substituents are added. They are also consistent with a recently proposed intramolecular disproportionation reaction mechanism involving coordination of successive ether oxygens to a Lewis acid. Since polytetrafluoroethylene contains no oxygen, it provides an indication of the upper limit to oxidative stability of PFPAE fluids. These results also show that oxidative decomposition of PFPAE fluids requires the presence of an active metal as well as air. Consequently, it may be possible to minimize decomposition and thus improve oxidative stability by passivating reactive metal surfaces

Determination of the thermal stability of perfluoroalkylethers

The thermal decomposition temperatures of several commercial and custom synthesized perfluoroalkylether fluids were determined with a computerized tensimeter. In general, the decomposition temperatures of the commercial fluids were all similar and significantly higher than those for custom synthesized fluids. Correlation of the decomposition temperatures with the molecular structures of the primary components of the commercial fluids revealed that the stability of the fluids is not affected by intrinsic factors such as carbon chain length, branching, or cumulated difluoroformal groups. Instead, correlation with extrinsic factors revealed that the stability may be limited by the presence of small quantities of thermally unstable material and/or chlorine-containing material arising from the use of chlorine-containing solvents during synthesis. Finally, correlation of decomposition temperatures with molecular weights for Demnum and Krytox fluids supports a chain cleavage reaction mechanism for Demnum fluids and an unzipping reaction mechanism for Krytox fluids

A Model for Academic Planning

Under conditions of limited and selective growth, institutions propose resource allocation changes which are not strictly related to overall institutional enrollment levels. These proposals often focus attention on the resource impact of internal shifts in student demand and the desirability of maintaining minimum or "critical mass "levels of academic program breadth and quality. This paper addresses the academic planning procedures needed to advance non-enrollment driven resource maintenance and acquisition proposals at institutional and state levels. The purpose of critical mass modeling for academic planning is to facilitate analysis, prioritization and negotiation of academic program alternatives and resources. The critical mass approach to academic planning would establish a campus-wide process and informa- tion base for prioritization of academic program development through (a) analysis of existing breadth and depth of faculty expertise in instruction and research at the sub- disciplinary level, (b) identification of subdisciplinary areas in which academic units would like to provide instruction and research in the future. Critical mass denotes the level of course offerings and research which academic units could not reduce and still maintain programs which fulfill their own objectives compatible with the overall mission of their institution. Critical mass program size and "core" resource requirements would be established by academic unit faculty and then would be negotiated with committees of academic senates and with institutional administrations. The planning process described is designed for application in medium and large sized institutions in which formal, comprehensive and integrated academic ¡resource planning systems do not operate presently.Dans une conjoncture de croissance limitée et sélective, les institutions projètent, dans l'allocation des ressources, des modifications qui ne se rapportent pas nécessairement aux niveaux globaux des effectifs de l'institution. Ces propositions répondent souvent à l'impact sur les ressources des changements internes des demandes de la part des étudiants et au caractère désirable de maintenir des niveaux minimums ou de "masse critique"dans la gamme et dans la qualité du programme académique. Cette étude s'adresse aux pro-cédures de planification académique qui sont nécessitées pour permettre le maintien des ressources provenant des sources autres que les effectifs inscrits ainsi que des propositions pour des acquisitions provenant des institutions ou de l'état. L'objectif de modèles basés sur la "masse critique" en vue de la planification académi-que est de faciliter l'analyse, la sélection des priorités et la négociation des alternatives au programme académique et aux ressources. L'approche de la "masse critique"à la planifi-cation académique verrait la mise sur pied d'une base de renseignements et d'un processus touchant la cité universitaire entière en vue de la sélection des priorités dans le développe-ment des programmes académiques. Ceci comprendrait ¡a) une analyse de l'envergure et de la profondeur existantes des expertises du corps enseignant dans les domaines de l'enseignement et des recherches au niveau sous-disciplinaire, (b) l'identification des domaines sous-disciplinaires dans lesquels des unités académiques voudraient, à l'avenir, fournir des cours et entreprendre des recherches. La "masse critique"signifie le niveau des cours offerts et des recherches entreprises que le corps enseignant ne pourrait pas réduire tout en maintenant encore des programmes remplissant leurs propres objectifs compatibles avec la mission globale de leur institution. L'importance du programme de "masse critique" et les exigences centrales en termes de ressources seraient établies par les unités du corps enseignant et seraient, par la suite, négociées avec des comités choisis par des sénats académiques et avec des administrations institutionnelles. Le modèle du processus de planification décrit s'appliquerait aux grandes institutions ainsi qu 'à celles de taille moyenne qui ne possèdent pas actuellement des systèmes de planification des ressources et du programme académique explicites, compréhensifs et intégrés

Tribological characteristics of perfluoropolyether liquid lubricants under sliding conditions in high vacuum

Tribological characteristics of three PFPE's (Fomblin Z, Demnum, and Krytox) were studied under high vacuum using a four-ball apparatus with 440C steel specimens. Fomblin Z and Demnum exhibited initial scuffing-like high friction whereas Krytox did not. Steady state friction with Fomblin Z was the lowest among the three oils. Frictional values for Demnum and Krytox were almost the same. The lowest wear rate in air was provided by Krytox regardless of load, and low wear rates in vacuum at high load were achieved with Krytox and Demnum. Results are explained by reactivity and pressure-viscosity characteristics of the oils

Why are married women working so much?

We study the large observed changes in labor supply by married women in the United States over 1950-1990, a period when labor supply by single women has hardly changed at all. We investigate the effects of changes in the gender wage gap, technological improvements in the production of nonmarket goods and potential inferiority of these goods on understanding this change. We find that small decreases in the gender wage gap can explain simultaneously the significant increases in the average hours worked by married women and the relative constancy in the hours worked by single women, and single and married men. We also find that technological improvements in the household have-for realistic values-too small an impact on married female hours and the relative wage of females to males. Some specifications of the inferiority of home goods match the hours patterns, but have counterfactual predictions for wages and expenditure patterns.Labor supply ; Women - Employment

Determination of the Thermal Stability of Perfluoroalkylethers by Tensimetry: Instrumentation and Procedure

A computerized tensimeter and experimental procedure for determination of the thermal decomposition temperature (Td) of perfluoroalkylethers have been developed and tested. Both the I+ m apparatus and the procedure are described in detail. Results of QU) testing with bis(2-ethylhexyl) phthlalate and trimethylolpropane wI triheptanoate demonstrate that the reciprocal of the decomposition temperature is a linear function of the logarithm of the gas volume/heated liquid volume ratio. The Td obtained for each compound at a gas volume/heated liquid volume ratio of one was similar to the value previously reported using an isoteniscope technique. Results of testing with a polymer of hexafluoropropylene oxide demonstate that this instrument and procedure can be used to determine the Td of perfluoroalkylethers

Determination of the Thermal Stability of Perfluoroalkylethers

The thermal decomposition temperatures of several commercial and custom synthesized perfluoroalkylether fluids were determined with a computerized tensimeter. In general, the decomposition temperatures of the commercial fluids were all similar and significantly higher than those for custom synthesized fluids. Correlation of the decomposition temperatures with the molecular structures of the primary components of the commercial fluids revealed that the stability of the fluids is not affected by intrinsic factors such as carbon chain length, branching, or cumulated difluoroformal groups. Instead, correlation with extrinsic factors revealed that the stability may be limited by the presence of small quantities of thermally unstable material and/or chlorine-containing material arising from the use of chlorine-containing solvents during synthesis. Finally, correlation of decomposition temperatures with molecular weights for Demnum and Krytox fluids supports a chain cleavage reaction mechanism for Demnum fluids and an unzipping reaction mechanism for Krytox fluids

Conceptual Framework for the National Pilot Project on Livestock and the Environment

Assessing the effects of alternative policies that regulate nonpoint pollution from concentrated animal feeding operations (CAFOs) requires insight into the interactions of livestock production practices, waste management technologies, and their impacts on the environment. CAFOs have been identified as a source of nutrient loadings that impair ground and surface water quality, and they can emit intense odor that impairs air quality. This report describes the conceptual framework and the integrated modeling system being developed to evaluate the economic and environmental impacts of alternative policies that abate pollution from CAFOs

Tribological Characteristics of Perfluoropolyether Liquid Lubricants Under Sliding Conditions in High Vacuum

Tribological characteristics of three PFPE\u27s (Fomblin Z, Demnum, and Krytox) were studied under high vacuum using a four-ball apparatus with 440C steel specimens. Fomblin Z and Demnum exhibited initial scuffing-like high friction whereas Krytox did not. Steady state friction with Fomblin Z was the lowest among the three oils. Frictional values for Demnum and Krytox were almost the same. The lowest wear rate in air was provided by Krytox regardless of load, and low wear rates in vacuum at high load were achieved with Krytox and Demnum. Results are explained by reactivity and pressure-viscosity characteristics of the oils