Computer Sciences Corporation

About: Computer Sciences Corporation is a based out in . It is known for research contribution in the topics: Spacecraft & Software development. The organization has 1916 authors who have published 2389 publications receiving 62729 citations. The organization is also known as: CSC.

Analysis of Phobos mission gamma ray spectra from Mars

Abstract: The determination of the elemental composition of the surface of a planetary body can be achieved, in many cases, by remote-sensing gamma ray spectroscopy. A gamma ray spectrometer was carried on the Soviet spacecraft Phobos-2, and obtained data while in an elliptical orbit around Mars. Results of two independent approaches to data analysis, one by the Soviet group and one by an American group are reported. The results for five elements are given for two different orbits of Mars. Major geologic units that contribute to the signal for each orbit have been identified. The results from the two techniques are in general agreement and there appear to be no geologically significant differences between the results for each orbit.

Preliminary evidence for the influence of physiography and scale upon the autocorrelation function of remotely sensed data

Abstract: Previously established results demonstrate that LANDSAT data are autocorrelated and can be described by a univariate linear stochastic process known as auto-regressive-integrated-moving-average model of degree 1, 0, 1 or ARIMA (1, 0, 1). This model has two coefficients of interest for interpretation phi(1) and theta(1). In a comparison of LANDSAT thematic mapper simulator (TMS) data and LANDSAT MSS data several results were established: (1) The form of the relatedness as described by this model is not dependent upon system look angle or pixel size. (2) The phi(1) coefficient increases with decreasing pixel size and increasing topographic complexity. (3) Changes in topography have a greater influence upon phi(1) than changes in land cover class. (4) The theta(1) seems to vary with the amount of atmospheric haze. These patterns of variation in phi(1) and theta(1) are potentially exploitable by the remote sensing community to yield stochastically independent sets of observations, characterize topography, and reduce the number of bytes needed to store remotely sensed data.

Determination of similarity functions of the resistance laws for the planetary boundary layer using surface-layer similarity functions

Abstract: Functional forms of the universal similarity functions A, B (for wind components parallel and normal to the surface stress), and C (for potential temperature difference) are determined based on the generalized theory of the resistance laws for the Planetary Boundary Layer (PBL). The similarity-profile functions for the surface layer are matched with the velocity and temperature-defect profiles that are assumed to have shapes modified by certain powers of nondimensional height z/h, where h is the PBL height. The powers of the outer-layer profile functions are determined, so that the functions become negligible in the surface layer. To close the temperature defect law, an assumption that the temperature gradient across the top of the PBL is continuous with the stratification of the overlying atmosphere is used. The result of this assumption is that nondimensional momentum and temperature profiles in the PBL can be described in terms of four basic ratios: (1) roughness ratio η= ζ/h (2) scale-height ratio λ=|f|h/u*, (3) ambient stratification parameter κ=γh/θ*, and (4) stability parameter μ=h/L, where L is the Monin-Obukhov length, z0 is the surface roughness, γ is the upper-air stratification, u* is the friction velocity, and θ* is the temperature scale at the surface. For stable conditions, the scale-height ratio can be related to the atmospheric stability and the upperair stratification, and the generalized similarity and Rossby number similarity theories become identical. Under appropriate boundary conditions, function A is explicitly dependent on the stability parameter γ, while B is a function of scale-height ratio λ, which in turn depends on the stability. Function C is shown to be dependent on the stability and the upper-air stratification, due to the closure assumption used for the temperature profile.

NAS Parallel Benchmarks Results 3-95

Abstract: The NAS Parallel Benchmarks (NPB) were developed in 1991 at NASA Ames Research Center to study the performance of parallel supercomputers. The eight benchmark problems are specified in a "pencil and paper" fashion, i.e., the complete details of the problem are given in a NAS technical document. Except for a few restrictions, benchmark implementors are free to select the language constructs and implementation techniques best suited for a particular system. In this paper, we present new NPB performance results for the following systems: (a) Parallel-Vector Processors: CRAY C90, CRAY T90 and Fujitsu VPP500; (b) Highly Parallel Processors: CRAY T3D, IBM SP2-WN (Wide Nodes), and IBM SP2-TN2 (Thin Nodes 2); and (c) Symmetric Multiprocessors: Convex Exemplar SPPIOOO, CRAY J90, DEC Alpha Server 8400 5/300, and SGI Power Challenge XL (75 MHz). We also present sustained performance per dollar for Class B LU, SP and BT benchmarks. We also mention future NAS plans for the NPB.

A General Theory of Intelligible Crosstalk between Frequency-Division Multiplexed Angle-Modulated Carriers

Abstract: A new method for calculating intelligible crosstalk between frequency-division multiplexed (FDM) angle-modulated carriers has been developed and is directly applicable to multicarrier operation in communications satellite systems. The analysis is general in scope and accounts for both the nonlinear amplitude and phase characteristics of the amplifying device by the use of a complex Bessel function expansion. Group delay and amplitude variation preceding the input of the nonlinear device are modeled using a Fourier series expansion. FDM baseband loading is also considered in the analysis. A comparison of theoretical results with measurement shows good agreement.