Orr-Sherby-Dorn creep strengths of the refractory-metal alloys C-103, ASTAR-811C, W-5Re, and W-25Re

Available creep data for the refractory-metal alloys C-103 (Nb/10 percent Hf/1 percent Ti/0.7 percent Zr), ASTAR-811C (Ta/8 percent W/1 percent Re/0.7 percent Hf/0.025 percent C), W-5Re (W/5 percent Re), and W-25Re (W/25 percent Re) were correlated by the Orr-Sherby-Dorn method and extrapolated to 1 percent creep over 10 years. Useful life was specified to be 2 standard estimates of error below the mean surface through the data. Over the temperature range of 1200 to 1800 K, ASTAR-811C was found to be the strongest of these alloys. In particular, ASTAR-811C was found to have at 1800 K the same creep strength as W-25Re at 1420 K. The difference between these results and those of Horak and Booker likely devolves from the comparative lack of long-time data on tungsten alloys

Alternative power-generation systems

The present state of the art of thermal power systems is surveyed. Because of the great potential variety of thermal power systems, the heat sources, the power conversion systems, and the integration of thermal power systems with missions are treated sequentially

Speculations on future opportunities to evolve Brayton powerplants aboard the space station

The Space Station provides a unique, low-risk environment in which to evolve new capabilities. In this way, the Space Station will grow in capacity, in its range of capabilities, and its economy of operation as a laboratory and as a center for space operations. Although both Rankine and Brayton cycles, two concepts for solar dynamic power generation, now compete to power the station, this paper confines its attention to the Brayton cycle using a mixture of He and Xe as its working fluid. Such a Brayton powerplant to supply the station's increasing demands for both electric power and heat has the potential to gradually evolve higher and higher performance by exploiting already-evolved materials (ASTAR-811C and molten-Li heat storage), its peak cycle temperature rising ultimately to 1500 K. Adapting the station to exploit long tethers (200 to 300 km long) could yield increases in payloads to LEO, to GEO, and to distant destinations in the solar system. Such tethering of the Space Station would not only require additional power for electric propulsion but also would so increase nuclear safety that nuclear powerplants might provide this power. From an 8000-kWt SP-100 reactor, thermoelectric power generation could produce 300 kWe, or adapted solar-Brayton cycle, 2400 to 2800 kWe

Goals of thermionic program for space power

The thermionic and Brayton reactor concepts were compared for application to space power. For a turbine inlet temperature of 15000 K the Brayton powerplant weighted 5 to 40% less than the thermionic concept. The out of core concept separates the thermionic converters from their reactor. Technical risks are diminished by: (1) moving the insolator out of the reactor; (2) allowing a higher thermal flux for the thermionic converters than is required of the reactor fuel; and (3) eliminating fuel swelling's threat against lifetime of the thermionic converters. Overall performance can be improved by including power processing in system optimization for design and technology on more efficient, higher temperature power processors. The thermionic reactors will be larger than those for competitive systems with higher conversion efficiency and lower reactor operating temperatures. It is concluded that although the effect of reactor size on shield weight will be modest for unmanned spacecraft, the penalty in shield weight will be large for manned or man-tended spacecraft

Assessment of lunar sources of He-3 for use on earth

As a gross measure of the economics of mining lunar sources of He-3, the energy densities (GJ/ton) of lunar soils were compared with the energy densities of various existing and future terrestrial sources of energy. On this basis, only the very richest lunar ores appear competitive with coal. Future lunar exploration might emphasize identification of lunar soils having higher concentrations of He-3

Technology of nuclear-Brayton space power systems

The present technology of Brayton power systems is reviewed. The potential for even higher system efficiency at the 10 KWe level is assessed as well as the potential for comparable efficiency with an output of 1 or 2 KWe. Systems accommodation of isotope decay is briefly discussed. The salient features are described for a Brayton power system based on this technology and employing the ZrH reactor. Reactor lives for this and competitive systems are compared. Growth capability with an advanced reactor is assessed. A concept for application of this technology to driving a gas-dynamic laser is described

Analysis of air quality management with emphasis on transportation sources

The current environment and practices of air quality management were examined for three regions: Denver, Phoenix, and the South Coast Air Basin of California. These regions were chosen because the majority of their air pollution emissions are related to mobile sources. The impact of auto exhaust on the air quality management process is characterized and assessed. An examination of the uncertainties in air pollutant measurements, emission inventories, meteorological parameters, atmospheric chemistry, and air quality simulation models is performed. The implications of these uncertainties to current air quality management practices is discussed. A set of corrective actions are recommended to reduce these uncertainties

Senegal: A service economy in need of an export boost

This paper first summarizes the macroeconomic and trade performance of Senegal, emphasizing the limits of traditional exports. It then focuses on three export sectors which have had some success in the past and have good potential for future growth: tourism, horticulture and information technology-enabled services. Sector-specific constraints are identified including beach erosion and hotel quality (tourism), access to land (horticulture), and lack of competition and skilled labour (information technology). Common problems include the absence of strategies and reliable data, tax administration, and the need for a stronger dialogue with the private sector

Preliminary assessment of power-generating tethers in space and of propulsion for their orbit maintenance

The concept of generating power in space by means of a conducting tether deployed from a spacecraft was studied. Using hydrogen and oxygen as the rocket propellant to overcome the drag of such a power-generating tether would yield more benefit than if used in a fuel cell. The mass consumption would be 25 percent less than the reactant consumption of fuel cells. Residual hydrogen and oxygen in the external tank and in the orbiter could be used very effectively for this purpose. Many other materials (such as waste from life support) could be used as the propellant. Electrical propulsion using tether generated power can compensate for the drag of a power-generating tether, half the power going to the useful load and the rest for electric propulsion. In addition, the spacecraft's orbital energy is a large energy reservoir that permits load leveling and a ratio of peak to average power equal to 2. Critical technologies to be explored before a power-generating tether can be used in space are delineated

Point-of-care measurement of blood lactate in children admitted with febrile illness to an African District Hospital.

BACKGROUND: Lactic acidosis is a consistent predictor of mortality owing to severe infectious disease, but its detection in low-income settings is limited to the clinical sign of "deep breathing" because of the lack of accessible technology for its measurement. We evaluated the use of a point-of-care (POC) diagnostic device for blood lactate measurement to assess the severity of illness in children admitted to a district hospital in Tanzania. METHODS: Children between the ages of 2 months and 13 years with a history of fever were enrolled in the study during a period of 1 year. A full clinical history and examination were undertaken, and blood was collected for culture, microscopy, complete blood cell count, and POC measurement of blood lactate and glucose. RESULTS: The study included 3248 children, of whom 164 (5.0%) died; 45 (27.4%) of these had raised levels of blood lactate (>5 mmol/L) but no deep breathing. Compared with mortality in children with lactate levels of ≤ 3 mmol/L, the unadjusted odds of dying were 1.6 (95% confidence interval [CI].8-3.0), 3.4 (95% CI, 1.5-7.5), and 8.9 (95% CI, 4.7-16.8) in children with blood lactate levels of 3.1-5.0, 5.1-8.0, or >8.0 mmol/L, respectively. The prevalence of raised lactate levels (>5 mmol/L) was greater in children with malaria than in children with nonmalarial febrile illness (P < .001) although the associated mortality was greater in slide-negative children. CONCLUSIONS: POC lactate measurement can contribute to the assessment of children admitted to hospital with febrile illness and can also create an opportunity for more hospitals in resource-poor settings to participate in clinical trials of interventions to reduce mortality associated with hyperlactatemia