Point and Diffuse Loads of Selected Pollutants in the River Rhine and Its Main Tributaries

The research described in this working paper was conducted for the study "Sources of Chemical Pollution in the Rhine Basin," a collaborative effort between IIASA and the Netherlands National Institute for Public Health and Environmental Protection (RIVM). The goal of the study was to determine, by mass balance analysis, the inputs and outputs to the Rhine Basin over the time period 1950-2010. Particular attention was given to "cradle-to-grave" analysis in which the pollutants are traced from their pathways through the industrial economy and into the environment. For the historical analysis, it was necessary to estimate emissions from various industrial sectors (point sources) and runoff from urban, agricultural and forested lands (diffuse sources). The analysis is hindered, however, by the scarcity of historical data on sources of emission. On the other hand, the Rhine River has been intensively monitored for heavy metals since the early 1970s, and for nutrients and other hydrological parameters since the 1950s. These data provide a basis for making reasonable estimates of inputs to the river in previous decades. Prior to the analysis presented herein, no comprehensive investigation of the long-term time series of chemical loads to the river had been undertaken. This working paper not only quantifies the total loads of the various chemicals over time. It also subdivides the loads into the point-source and diffuse fractions, applying a new methodology developed by the senior author of this paper. With the estimates provided here, it is possible to calibrate the emission factors assumed for industrial and diffuse sources. The paper thus makes an invaluable contribution of the major goals of the study

Characterization of Iridium Coated Rhenium Used in High-Temperature, Radiation-Cooled Rocket Thrusters

Materials used for radiation-cooled rocket thrusters must be capable of surviving under extreme conditions of high-temperatures and oxidizing environments. While combustion efficiency is optimized at high temperatures, many refractory metals are unsuitable for thruster applications due to rapid material loss from the formation of volatile oxides. This process occurs during thruster operation by reaction of the combustion products with the material surface. Aerojet Technical Systems has developed a thruster cone chamber constructed of Re coated with Ir on the inside surface where exposure to the rocket exhaust occurs. Re maintains its structural integrity at high temperature and the Ir coating is applied as an oxidation barrier. Ir also forms volatile oxide species (IrO2 and IrO3) but at a considerably slower rate than Re. In order to understand the performance limits of Ir-coated Re thrusters, we are investigating the interdiffusion and oxidation kinetics of Ir/Re. The formation of iridium and rhenium oxides has been monitored in situ by Raman spectroscopy during high temperature exposure to oxygen. For pure Ir, the growth of oxide films as thin as approximately 200 A could be easily detected and the formation of IrO2 was observed at temperatures as low as 600 C. Ir/Re diffusion test specimens were prepared by magnetron sputtering of Ir on Re substrates. Concentration profiles were determined by sputter Auger depth profiles of the heat treated specimens. Significant interdiffusion was observed at temperatures as low as 1000 C. Measurements of the activation energy suggest that below 1350 C, the dominant diffusion path is along defects, most likely grain boundaries, rather than bulk diffusion through the grains. The phases that form during interdiffusion have been examined by x ray diffraction. Analysis of heated test specimens indicates that the Ir-Re reaction produces a solid solution phase of Ir dissolved in the HCP structure of Re

Segregation of Anhydrite in Sintered Naturally Occurring Rock Salt

This study examines the sintering of naturally occurring rock salt in dependence of pressure and temperature as is desired for storage and other applications in saline environments where rock salt is thermodynamically stable and shows a mechanical behavior compatible to the surrounding host material. Rock salt consists mainly of sodium chloride with small impurities of less soluble compounds such as anhydrite, CaSO4 . A special interest in the sintering process of naturally occurring rock salt is the segregation of anhydrite to the grain boundaries between individual sodium chloride crystals. Our study has shown that sintering naturally occurring rock salt at different pressures will influence the segregation of anhydrite. Experiments support a greater segregation of anhydrite resulting from an increased pressure treatment. As the solubility of anhydrite is less than sodium chloride, the sintered samples of naturally occurring rock salt show greater stability towards dissolution than pure sodium chloride

Power systems research at MSFC

Power systems research reviews at Marshall Space Flight Cente

Spin relaxation dynamics of radical-pair processes at low magnetic fields

We report measurements of room-temperature spin-relaxation times $T_1$ and $T_2$ of charge-carrier spins in a $\pi$-conjugated polymer thin film under bipolar injection and low (1\mbox{ mT}\lesssim B_0\lesssim 10\mbox{ mT}) static magnetic fields, using electrically detected magnetic resonant Hahn-echo and inversion-recovery pulse sequences. The experiments confirm the correlation between the magnetic-field sensitive observables of radical-pair processes, which include both the spin-dependent recombination currents in organic semiconductors and the associated spin-relaxation times when random local hyperfine fields and external magnetic fields compete in magnitude. Whereas a striking field dependence of spin-lattice relaxation exists in the low-field regime, the apparent spin decoherence time remains field independent as the distinction between the two is lifted at low fields.Comment: Manuscript: 14 pages, 4 figures; Supplemental Material: 13 pages, 7 figure