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  • 1
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    The Science of Computing: Expert Systems (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: The creative urge of human beings is coupled with tremendous reverence for logic. The idea that the ability to reason logically--to be rational--is closely tied to intelligence was clear in the writings of Plato. The search for greater understanding of human intelligence led to the development of mathematical logic, the study of methods of proving the truth of statements by manipulating the symbols in which they are written without regard to the meanings of those symbols. By the nineteenth century a search was under way for a universal system of logic, one capable of proving anything provable in any other system.
    Keywords: Computer Programming and Software
    Type: American Scientist; Volume 74; No. 1; 18-20
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  • 2
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    The Science of Computing: Virtual Memory (1986)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: In the March-April issue, I described how a computer's storage system is organized as a hierarchy consisting of cache, main memory, and secondary memory (e.g., disk). The cache and main memory form a subsystem that functions like main memory but attains speeds approaching cache. What happens if a program and its data are too large for the main memory? This is not a frivolous question. Every generation of computer users has been frustrated by insufficient memory. A new line of computers may have sufficient storage for the computations of its predecessor, but new programs will soon exhaust its capacity. In 1960, a longrange planning committee at MIT dared to dream of a computer with 1 million words of main memory. In 1985, the Cray-2 was delivered with 256 million words. Computational physicists dream of computers with 1 billion words. Computer architects have done an outstanding job of enlarging main memories yet they have never kept up with demand. Only the shortsighted believe they can.
    Keywords: Computer Programming and Software
    Type: American Scientist; Volume 74; No. 3; 227-229
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  • 3
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    Benchmark Full Configuration-Interaction Calculations on HF and NH2 (1986)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Full configuration-interaction (FCI) calculations are performed at selected geometries for the (sup 1)Sigma(+) state of HCF and the (sup 2)B(sub 1) and (sup 3)A(sub 1) states NH2 using both DZ and DZP Gaussian basis sets. Higher excitations become more important when the bonds are stretched and the SCF reference becomes a poorer zeroth-order description of the wave function. The CASSCF-MRCI procedure gives excellent agreement with the FCI potentials, especially when corrected with a multireference analog of the Davidson correction.
    Keywords: Atomic and Molecular Physics
    Type: Journal of Chemical Physics (ISSN 0021-9606); Volume 85; No. 3; 1469-1474
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  • 4
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    The effect of local advection on the inference of soil moisture from thermal infrared radiances (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The degree to which the GOES-VISSR infrared data can be used to infer area-averaged soil moisture is explored for a five-day case study period. Chosen variables are transformed and incorporated into a multiple linear regression. The actual observations, rather than a simplified model, are used to determine the relationship between soil moisture and GOES-IR radiance. It is shown that a depletion coefficient of 0.92 produces an index of ground truth which is best correlated with soil moisture as inferred from GOES thermal infrared data. When all individual daily soil estimates during the case study period are averaged at each point and compared to the average observed soil moisture, the data correlate at 0.85. This implies that the algorithm can distinguish at least four categories of soil moisture.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
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  • 5
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    Conical foil X-ray mirrors - Performance and projections (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The design, fabrication, and performance of conical grazing incidence mirrors designed to increase the sensitivity and resolution of observations in the iron K spectral band around 7 KeV are discussed. The present mirrors consist of two adjacent, coaxial and confocal arrays of tightly packed fixed-length cones. Heat treatment is used to minimize distortions in forming the cones. Reflector assembly is simplified by changing from rectangular reflector support slots to tapered ones. An image-blur of only 1.3 arcmin half-power radius has been achieved, in addition to X-ray reflectivity in the 1.5-10 keV range at about the 90 percent level of theoretical values.
    Keywords: OPTICS
    Type: Applied Optics (ISSN 0003-6935); 27; 1447-145
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  • 6
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    Loss of Gaussian beams through off-axis circular apertures (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An attempt is made to solve the problem of the loss caused in a Gaussian beam by an off-axis circular aperture. Although in general the problem cannot be solved in closed form, three special cases are considered. If the offset is zero, the limit of the radial integration coincides with the radius of the circular aperture; in this case, the integration over the angular variable can be performed in closed form. In a second special case, an analytical expression can be obtained when the offset is small. A third special case occurs when the offset is large and equals the aperture radius.
    Keywords: OPTICS
    Type: Applied Optics (ISSN 0003-6935); 27; 1230-123
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  • 7
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    Plasma transport in the auroral return current region (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The classical and anomalous transport properties of a multifluid plasma consisting of H(+), O(+), and electron populations in the presence of auroral field-aligned return currents are investigated, using a multimoment fluid model with anomalous transport coefficients. The macroscopic effects of the electrostatic ion cyclotron (EIC) instability and of an EIC-related anomalous resistivity mechanism which heats the electrons are included in the present version of the model. The responses of the outflowing polar wind plasma to the application of current, with and without instabilities, are exhibited. The simulations show that the electron drift velocity corresponding to a return current of 0.65 micro-A/sq m is above the threshold for EIC waves. Downward electron heat flow competes with upward convection and adiabatic effects to determine the direction of the electron temperature anisotropy. Resistive electron heating lowers the critical drift velocity for marginal EIC stability and leads to enhanced ion heating.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 8673-869
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  • 8
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    Numerical simulations of magnetospheric plasmas - Review and quadrennial report to the IUGG (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This article provides a broad survey of U.S. progress during the quadrennium 1983-1986 in the category 'numerical simulations of magnetospheric plasmas'. There has been a substantial increase of activity in this area during this period. Simulations have been instrumental in providing valuable insights into large scale dynamic phenomena, nonlinear effects, and complex kinetic phenomena in a wide variety of subject areas, including shocks and double layers, ionosphere-magnetosphere coupling phenomena, and important microphysical processes such as broadband electrostatic noise. The methodology of computer simulation has also been advanced during this quadrennium. Vlasov algorithms have been improved; hybrid codes in 2 and 3D have been developed and applied to magnetospheric problems; and complex problems have been subjected with increasing frequency to a multipronged attack in which several types of simulation models, each designed to accurately model phenomena within a particular range of temporal or spatial scales, are employed synergistically.
    Keywords: GEOPHYSICS
    Type: Reviews of Geophysics (ISSN 8755-1209); 25; 599-613
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  • 9
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    Application of optimization techniques to spacecaft fuel usage minimization in deep space navigation (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Mathematical analysis of the minimization of spacecraft fuel usage for both impulsive and finite motor burns is presented. A high precision integrated trajectory search program (SEPV) and several optimization software libraries are used to solve minimum fuel usage problems. The SEPV program has the capacity to vary either the initial spacecraft state or the finite burn parameters to acquire a specified set of target values. Several test examples for the Voyager 2 Uranus Encounter and the Galileo Jupiter Orbiter are presented to show that spacecraft fuel consumption can be minimized in targeting maneuver strategies. The fuel savings achieved by the optimum solution can be significant.
    Keywords: ASTRODYNAMICS
    Type: Mathematical Engineering in Industry (ISSN 0169-121X); 1; 2, 19
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  • 10
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    Evapotranspiration from nonuniform surfaces - A first approach for short-term numerical weather prediction (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations of surface heterogeneity of soil moisture from scales of meters to hundreds of kilometers are discussed, and a relationship between grid element size and soil moisture variability is presented. An evapotranspiration model is presented which accounts for the variability of soil moisture, standing surface water, and vegetation internal and stomatal resistance to moisture flow from the soil. The mean values and standard deviations of these parameters are required as input to the model. Tests of this model against field observations are reported, and extensive sensitivity tests are presented which explore the importance of including subgrid-scale variability in an evapotranspiration model.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 116; 600-621
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