52,697 research outputs found

    The Generalized Gutzwiller Method for n=>2 Correlated Orbitals: Itinerant Ferromagnetism in eg-bands

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    Using the generalized Gutzwiller method we present results on the ferromagnetic behavior of extended Hubbard models with two degenerate eg orbitals. We find significant differences to results obtained from Hartree-Fock theory.Comment: 7 pages in Latex, 3 figures. Accepted for publication in Physica

    NASA Research in aeropropulsion

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    Selected examples of recent accomplishments and current activities that are relevant to the principal classes of civil and military vehicles: subsonic transports, commuters, supersonic transports, general aviation, rotorcraft, V/STOL, and high performance. Some instances of emerging technologies with potential high impact on further progress are discussed

    Application of NASAP to the design of communication circuits

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    Modifications to CDC 3600 NASAP for design of linear communication circuit

    The interaction between stray electrostatic fields and a charged free-falling test mass

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    We present an experimental analysis of force noise caused by stray electrostatic fields acting on a charged test mass inside a conducting enclosure, a key problem for precise gravitational experiments. Measurement of the average field that couples to test mass charge, and its fluctuations, is performed with two independent torsion pendulum techniques, including direct measurement of the forces caused by a change in electrostatic charge. We analyze the problem with an improved electrostatic model that, coupled with the experimental data, also indicates how to correctly measure and null the stray field that interacts with test mass charge. Our measurements allow a conservative upper limit on acceleration noise, of 2 fm/s2^2\rthz\ for frequencies above 0.1 mHz, for the interaction between stray fields and charge in the LISA gravitational wave mission.Comment: Minor edits in PRL publication proces

    A review of NASA's propulsion programs for aviation

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    A review of five NASA engine-oriented propulsion programs of major importance to civil aviation are presented and discussed. Included are programs directed at exploring propulsion system concepts for (1) energy conservation subsonic aircraft (improved current turbofans, advanced turbofans, and advanced turboprops); (2) supersonic cruise aircraft (variable cycle engines); (3) general aviation aircraft (improved reciprocating engines and small gas turbines); (4) powered lift aircraft (advanced turbofans); and (5) advanced rotorcraft

    COPTRAN - A method of optimum communication systems design

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    Single set of mathematical expressions describes system cost and probability of error of data transmission in terms of four basic parameters in the link equation. A Lagrange multiplier sets up equations whose solutions yield the optimum values for system design considerations and weight and cost values

    Solid state crystal physics at very low temperatures

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    The properties of nearly perfect crystals was studied at cryogenic temperatures. A large Helium 3 and Helium 4 dilution refrigerator has been assembled, and is described. A cryostat suitable for cooling a 35 liter volume to .020 Kelvin was designed and constructed, together with instrumentation to observe the properties of nearly perfect crystals
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