40,347 research outputs found

    New england and the space program

    Get PDF
    Competing for space program business - marketing facto

    Determing the Proper Scope of Section 2113(b) of the Federal Bank Robbery Act

    Get PDF

    Cerenkov Radiation in a Lorentz-Violating and Birefringent Vacuum

    Get PDF
    We calculate the emission spectrum for vacuum Cerenkov radiation in Lorentz-violating extensions of electrodynamics. We develop an approach that works equally well if the presence or the absence of birefringence. In addition to confirming earlier work, we present the first calculation relevant to Cerenkov radiation in the presence of a birefringent photon k_F term, calculating the lower-energy part of the spectrum for that case.Comment: 17 pages, version to appear in Phys. Rev.

    Nuclear thermionic converter

    Get PDF
    Efficient nuclear reactor thermionic converter units are described which can be constructed at low cost and assembled in a reactor which requires a minimum of fuel. Each converter unit utilizes an emitter rod with a fluted exterior, several fuel passages located in the bulges that are formed in the rod between the flutes, and a collector receiving passage formed through the center of the rod. An array of rods is closely packed in an interfitting arrangement, with the bulges of the rods received in the recesses formed between the bulges of other rods, thereby closely packing the nuclear fuel. The rods are constructed of a mixture of tungsten and thorium oxide to provide high power output, high efficiency, high strength, and good machinability

    Diapause in the Boll Weevil, Anthonontus grandis Boheman, As Related to Fruiting Activity in the Cotton Plant

    Get PDF
    Studies in Arkansas show that boll weevil diapause is related to changes in fruiting activity of the cotton plant. Generally, when larval development took place while fruiting levels were increasing or being held at a high level, diapause in resulting adults was low (0-20%). Diapause was approximately 20-50% when larval development coincided with decreasing fruiting levels, and was 50-100% as true cut-out approached. Regrowth cotton generally lowered diapause incidence and as fruiting levels decreased, diapause increased. Therefore, the boll weevil not only responds to short photoperiods that are characteristic during the fall in the temperate zone, but also may respond throughout the season to changes in fruiting activity of the cotton plant

    Minimal Model for Disorder-induced Missing Moment of Inertia in Solid 4^4He

    Full text link
    The absence of a missing moment inertia in clean solid 4^4He suggests that the minimal experimentally relevant model is one in which disorder induces superfluidity in a bosonic lattice. To this end, we explore the relevance of the disordered Bose-Hubbard model in this context. We posit that a clean array 4^4He atoms is a self-generated Mott insulator, that is, the 4^4He atoms constitute the lattice as well as the `charge carriers'. With this assumption, we are able to interpret the textbook defect-driven supersolids as excitations of either the lower or upper Hubbard bands. In the experiments at hand, disorder induces a closing of the Mott gap through the generation of mid-gap localized states at the chemical potential. Depending on the magnitude of the disorder, we find that the destruction of the Mott state takes place for d+z>4d+z>4 either through a Bose glass phase (strong disorder) or through a direct transition to a superfluid (weak disorder). For d+z<4d+z<4, disorder is always relevant. The critical value of the disorder that separates these two regimes is shown to be a function of the boson filling, interaction and the momentum cut off. We apply our work to the experimentally observed enhancement 3^3He impurities has on the onset temperature for the missing moment of inertia. We find quantitative agreement with experimental trends.Comment: 9 pages, 5 figures: Extended version of previous paper in which the pase diagram for the disordered Bose-Hubbard model is computed using mean-field theory and one-loop RG. The criterion for the Bose glass is derived explicitly. (a few typos are corrected

    A computational method to model radar return range in a polygonally based, computer-generated-imagery simulation

    Get PDF
    Described is a method for modeling a ground-mapping radar system for use in simulations where the terrain is in a polygonal form commonly used with computer generated imagery (CGI). The method employs a unique approach for rapidly rejecting polygons not visible to the radar to facilitate the real-time simulation of the radar return. This rapid rejection of the nonvisible polygons requires the precalculation and storage of a set of parameters that do not vary during the simulation. The calculation of a radar range as a function of the radar forward-looking angle to the CGI terrain is carried out only for the visible polygons. This method was used as part of a simulation for terrain-following helicopter operations on the vertical motion simulator at the NASA Ames Research Center. It proved to be an efficient means for returning real-time simulated radar range data
    • …
    corecore