A method for determining an optimum shape of a class of thin shells of revolution

Optimum shape of convex thin shell of revolution with respect to volume, weight and length - mathematical functio

Staggered Fermion, its Symmetry and Ichimatsu-Patterned Lattice

We investigate exact symmetries of a staggered fermion in D dimensions. The Dirac operator is reformulated by SO(2D) Clifford algebra. The chiral symmetry, rotational invariance and parity symmetries are clarified in any dimension. Local scalar and pseudo-scalar modes are definitely determined, in which we find non-standard modes. The relation to Ichimatsu-patterned lattice approach is discussed.Comment: 3 pages, 1 figure, "Talk at Lattice2004(theory), Fermilab, June 21-26, 2004

Space station integrated wall design and penetration damage control

A methodology was developed to allow a designer to optimize the pressure wall, insulation, and meteoroid/debris shield system of a manned spacecraft for a given spacecraft configuration and threat environment. The threat environment consists of meteoroids and orbital debris, as specified for an arbitrary orbit and expected lifetime. An overall probability of no penetration is calculated, as well as contours of equal threat that take into account spacecraft geometry and orientation. Techniques, tools, and procedures for repairing an impacted and penetrated pressure wall were developed and tested. These techniques are applied from the spacecraft interior and account for the possibility of performing the repair in a vacuum. Hypervelocity impact testing was conducted to: (1) develop and refine appropriate penetration functions, and (2) determine the internal effects of a penetration on personnel and equipment

Space station integrated wall design and penetration damage control

The analysis code BUMPER executes a numerical solution to the problem of calculating the probability of no penetration (PNP) of a spacecraft subject to man-made orbital debris or meteoroid impact. The codes were developed on a DEC VAX 11/780 computer that uses the Virtual Memory System (VMS) operating system, which is written in FORTRAN 77 with no VAX extensions. To help illustrate the steps involved, a single sample analysis is performed. The example used is the space station reference configuration. The finite element model (FEM) of this configuration is relatively complex but demonstrates many BUMPER features. The computer tools and guidelines are described for constructing a FEM for the space station under consideration. The methods used to analyze the sensitivity of PNP to variations in design, are described. Ways are suggested for developing contour plots of the sensitivity study data. Additional BUMPER analysis examples are provided, including FEMs, command inputs, and data outputs. The mathematical theory used as the basis for the code is described, and illustrates the data flow within the analysis

Characterization of submillimetre quasi-optical twin-slot double-junction SIS mixers

We report on the continuing development of submillimetre quasi-optical slot antenna SIS mixers, which use two-junction tuning circuits. Direct and heterodyne Fourier transform spectrometer measurements have been performed to compare device performance with predictions. Demonstrated double-sideband receiver noise temperatures of better than 540 K at 808 GHz make these SIS mixers substantially better than GaAs Schottky receivers for the astronomically important CI and CO transitions near 810 GHz

Interaction Effects in Conductivity of Si Inversion Layers at Intermediate Temperatures

We compare the temperature dependence of resistivity \rho(T) of Si MOSFETs with the recent theory by Zala et al. This comparison does not involve any fitting parameters: the effective mass m* and g*-factor for mobile electrons have been found independently. An anomalous increase of \rho with temperature, which has been considered a signature of the "metallic" state, can be described quantitatively by the interaction effects in the ballistic regime. The in-plane magnetoresistance \rho(B) is qualitatively consistent with the theory; however, the lack of quantitative agreement indicates that the magnetoresistance is more susceptible to the sample-specific effects than \rho(T).Comment: 4 pages, 5 figures. References update

Forecasting U.S. Trade in Services

This paper provides a set of forecasts of United States international trade in services, both at the aggregate level and for four subcategories. These sectors are: travel, which is mostly tourist expenditures; passenger fares, which is mostly passenger air transportation; transportation, other than passenger transportation; and other private services, including education, financial services, insurance, telecommunications, and business, professional and technical services. A forecasting model is constructed and estimated, based on conventional economic forces of supply and demand, dependent on cost variables and income variables as well as relative prices. For forecasting purposes, these variables are taken from the Michigan Quarterly Econometric Model of the U.S. Economy, a macroeconomic forecasting model with forecasts provided regularly by the University of Michigan Research Seminar in Quantitative Economics. The equations of the services trade model are reported and discussed, and the performance of the estimated equations is evaluated. The quarterly forecast paths are provided for both aggregate and sectoral services trade, including exports and imports, through the end of 2001. Results indicate that imports will continue to rise over the forecast period, while exports, after remaining nearly stationary for several quarters in some sectors in 1999, will resume their rise thereafter. This forecasting work is to be continued, and it is suggested, in addition, that future research would be useful to explore the determinants of the production and sales of foreign services affiliates of U.S. parent companies.Services, International Trade