Space power systems technology enablement study

The power system technologies which enable or enhance future space missions requiring a few kilowatts or less and using the space shuttle were assessed. The advances in space power systems necessary for supporting the capabilities of the space transportation system were systematically determined and benefit/cost/risk analyses were used to identify high payoff technologies and technological priorities. The missions that are enhanced by each development are discussed

The Economics of Exporting North Dakota Beef to Asian Pacific Markets

International Relations/Trade,

Combustion system processes leading to corrosive deposits

Degradation of turbine engine hot gas path components by high temperature corrosion can usually be associated with deposits even though other factors may also play a significant role. The origins of the corrosive deposits are traceable to chemical reactions which take place during the combustion process. In the case of hot corrosion/sulfidation, sodium sulfate was established as the deposited corrosive agent even when none of this salt enters the engine directly. The sodium sulfate is formed during the combustion and deposition processes from compounds of sulfur contained in the fuel as low level impurities and sodium compounds, such as sodium chloride, ingested with intake air. In other turbine and power generation situations, corrosive and/or fouling deposits can result from such metals as potassium, iron, calcium, vanadium, magnesium, and silicon

Thermochemical analyses of the oxidative vaporization of metals and oxides by oxygen molecules and atoms

Equilibrium thermochemical analyses are employed to describe the vaporization processes of metals and metal oxides upon exposure to molecular and atomic oxygen. Specific analytic results for the chromium-, platinum-, aluminum-, and silicon-oxygen systems are presented. Maximum rates of oxidative vaporization predicted from the thermochemical considerations are compared with experimental results for chromium and platinum. The oxidative vaporization rates of chromium and platinum are considerably enhanced by oxygen atoms

Theoretical and experimental studies of the deposition of Na2So4 from seeded combustion gases

Flames in a Mach 0.3 atmospheric pressure laboratory burner rig were doped with sea salt, NaS04, and NaCl, respectively, in an effort to validate theoretical dew point predictions made by a local thermochemical equilibrium (LTCE) method of predicting condensation temperatures of sodium sulfate in flame environments. Deposits were collected on cylindrical platinum targets placed in the combustion products, and the deposition was studied as a function of collector temperature. Experimental deposition onset temperatures checked within experimental error with LTCE-predicted temperatures. A multicomponent mass transfer equation was developed to predict the rate of deposition of Na2SO4(c) via vapor transport at temperatures below the deposition onset temperature. Agreement between maximum deposition rates predicted by this chemically frozen boundary layer (CFBL) theory and those obtained in the seeded laboratory burner experiments is good

Risk-bounded formation of fuzzy coalitions among service agents.

Cooperative autonomous agents form coalitions in order ro share and combine resources and services to efficiently respond to market demands. With the variety of resources and services provided online today, there is a need for stable and flexible techniques to support the automation of agent coalition formation in this context. This paper describes an approach to the problem based on fuzzy coalitions. Compared with a classic cooperative game with crisp coalitions (where each agent is a full member of exactly one coalition), an agent can participate in multiple coalitions with varying degrees of involvement. This gives the agent more freedom and flexibility, allowing them to make full use of their resources, thus maximising utility, even if only comparatively small coalitions are formed. An important aspect of our approach is that the agents can control and bound the risk caused by the possible failure or default of some partner agents by spreading their involvement in diverse coalitions

Prospect for room temperature tunneling anisotropic magnetoresistance effect: density of states anisotropies in CoPt systems

Tunneling anisotropic magnetoresistance (TAMR) effect, discovered recently in (Ga,Mn)As ferromagnetic semiconductors, arises from spin-orbit coupling and reflects the dependence of the tunneling density of states in a ferromagnetic layer on orientation of the magnetic moment. Based on ab initio relativistic calculations of the anisotropy in the density of states we predict sizable TAMR effects in room-temperature metallic ferromagnets. This opens prospect for new spintronic devices with a simpler geometry as these do not require antiferromagnetically coupled contacts on either side of the tunnel junction. We focus on several model systems ranging from simple hcp-Co to more complex ferromagnetic structures with enhanced spin-orbit coupling, namely bulk and thin film L1$_0$-CoPt ordered alloys and a monatomic-Co chain at a Pt surface step edge. Reliability of the predicted density of states anisotropies is confirmed by comparing quantitatively our ab initio results for the magnetocrystalline anisotropies in these systems with experimental data.Comment: 4 pages, 2 figure

An interstellar precursor mission

A mission out of the planetary system, with launch about the year 2000, could provide valuable scientific data as well as test some of the technology for a later mission to another star. Primary scientific objectives for the precursor mission concern characteristics of the heliopause, the interstellar medium, stellar distances (by parallax measurements), low energy cosmic rays, interplanetary gas distribution, and mass of the solar system. Secondary objectives include investigation of Pluto. Candidate science instruments are suggested. Individual spacecraft systems for the mission were considered, technology requirements and problem areas noted, and a number of recommendations made for technology study and advanced development. The most critical technology needs include attainment of 50-yr spacecraft lifetime and development of a long-life NEP system

Magnetic friction in Ising spin systems

A new contribution to friction is predicted to occur in systems with magnetic correlations: Tangential relative motion of two Ising spin systems pumps energy into the magnetic degrees of freedom. This leads to a friction force proportional to the area of contact. The velocity and temperature dependence of this force are investigated. Magnetic friction is strongest near the critical temperature, below which the spin systems order spontaneously. Antiferromagnetic coupling leads to stronger friction than ferromagnetic coupling with the same exchange constant. The basic dissipation mechanism is explained. If the coupling of the spin system to the heat bath is weak, a surprising effect is observed in the ordered phase: The relative motion acts like a heat pump cooling the spins in the vicinity of the friction surface.Comment: 4 pages, 4 figure

Experimental application of sum rules for electron energy loss magnetic chiral dichroism

We present a derivation of the orbital and spin sum rules for magnetic circular dichroic spectra measured by electron energy loss spectroscopy in a transmission electron microscope. These sum rules are obtained from the differential cross section calculated for symmetric positions in the diffraction pattern. Orbital and spin magnetic moments are expressed explicitly in terms of experimental spectra and dynamical diffraction coefficients. We estimate the ratio of spin to orbital magnetic moments and discuss first experimental results for the Fe L_{2,3} edge.Comment: 11 pages, 2 figure