Structure-property relationships of isomeric addition polyimides containing nadimide end groups

Addition polyirnide oligomers with nadimide end groups (I) have been synthesized from 4,4′-oxydiphthalic anhydride and 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride with several isomeric diamines and, nadic anhydride. The low molecular weight amic acid? and corresponding imides were isolated and characterized. Solubility and melt-flow properties of the imide prepolymers were studied to determine the applicability of the resins as adhesives and composite matrices. Thermomechanical transitions of the polymers were obtained by torsional braid analysis. Properties were compared with a similar addition polymer, P13N.      

Optimal Hydropower Generation Under Climate Change Conditions for a Northern Water Resources System

This paper examines climate change impacts on the water resources system of the Manicouagan River (Québec, Canada). The objective is to evaluate the performance of existing infrastructures under future climate projections and the associated uncertainties. The main purpose of the water resources system is hydropower production. A reservoir optimization algorithm, Sampling Stochastic Dynamic Programming (SSDP), was used to derive weekly operating decisions for the existing system subject to reservoir inflows reflecting future climate, for optimum hydropower production. These projections are simulations from the SWAT hydrologic model for climate change scenarios for the period from 2010 to 2099. Results show that the climate change will alter the hydrological regime of the study area: earlier timing of the spring flood, reduced spring peak flow, and increased annual inflows volume in the future compared to the historical climate. The SSDP optimization algorithm adapted the operating policy to the future hydrological regime by adjusting water reservoir levels in the winter and spring, and increasing the release through turbines, which in the end increased power generation. However, there could be more unproductive spills for some power plants, which would decrease the overall efficiency of the existing water resources system.     

The effect of cobalt complex addition on the cure and properties of an epoxy matrix resin

The effects of adding various cobalt complexes to a tetraglycidyl methylene dianiline-based epoxy resin were determined. The addition of cobalt(III) acetylacetonate was found to alter the epoxy cure and improve the flexural strength and fracture toughness of the cured resin. These effects were not duplicated by the addition of various other cobalt complexes.     

Radar Altimetry Aids Managing Gauge Networks

The hydrological observation network in the Amazon basin is made of conventional rainfall and water level stations presently maintained by the Agência Nacional de Águas (ANA), the National Agency for Waters. The water level network has long been plagued by difficulties associated with spatial coverage, timely delivery and data errors. Satellite observations are important means for providing hydrologic data with acceptable spatial and temporal resolution, and radar altimeters embarked onboard successive satellites since the early 1970s collect measurements of water level over rivers in a well-defined geodetic reference frame and can be used to address some of these problems. Nowadays, satellite altimetry can be used to collect the time variations of the water levels over many rivers throughout the word, as long as the reach are several hundred meters wide. This ability is particularly interesting in ungauge basins but it can also be used as an independent source of information to cross-check existing gauge series. In the present study, we focus on examples from the Amazon basin where radar altimetry has been used to provide an independent dataset that can be used to support the management of hydrological observation networks by including new data together with conventional field data,     

Thermodynamic computation of phase equilibria in the sodium-carbon-oxygen system

An existing computational technique was adapted for the derivation of ternary constitution diagrams in the sodium-carbon-oxygen system. The method involved the selection of appropriate chemical equations among seven condensed phases including sodium, carbon, Na₂C₂, Na₂CO₃, Na₂O, Na₂O₂, NaO₂ and the three gases CO, CO₂ and sodium vapor. Using available thermochemical data, gas partial pressures were computed and ternary isotherms derived. At temperatures near 750°C and 1 atm pressure, carbon and Na₂CO₃ can coexist with liquid sodium at high carbon-oxygen ratios whereas carbon and Na₂CO₃ can coexist at low carbon-oxygen ratios. At somewhat higher temperatures and pressures, Na₂C₂ may be an important phase. Although solubility effects would alter slightly the computed data, the results of the study generally agree with the experimental observations of others. ANDREW B. WEAVER, formerly Graduate Student, University of Nebraska.     

Plasma testosterone values in transsexual women

Plasma testosterone was determined by radioimmunoassay in 50 transsexual and 50 normal women. The testosterone levels in transsexuals were significantly higher (nearly double) than in normal women. In transsexuals, minor changes in the pattern of the menstrual cycle were also found.