32,128 research outputs found

    Radar studies of the Martian surface

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    The acquisition, processing, and interpretation of radar from Mars are reported with emphasis on the facilities of the Arecibo observatory. The project is now essentially complete. Results include scattering law studies in the Syrtis Major, Elysium, and Chryse areas of that planet and reflectivity measurements. Software for general use in the radar program at Arecibo was developed. Participation in acquisition and reduction of data from Venus and Mercury is detailed

    The cutoff-dependence of the Casimir force within an inhomogeneous medium

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    We consider the ground state energy of the electromagnetic field in a piston geometry. In the idealised case, where the piston and the walls of the chamber are taken as perfect mirrors, the Casimir pressure on the piston is finite and independent of the small scale physics of the media that compose the mirrors; the Casimir-energy of the system can be regularised and is cutoff-independent. Yet we find that, when the body of the piston is filled with an inhomogeneous dielectric medium, the Casimir energy is cutoff-dependent, and the value of the pressure is thus inextricably dependent on the detailed behaviour of the mirror and the medium at large wave-vectors. This result is inconsistent with recent proposals for regularising Casimir forces in inhomogeneous media.Comment: 6 pages, 2 figure

    The large-scale modulation of cosmic rays in mid-1982: Its dependence on heliospheric longitude and radius

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    Near solar maximum, a series of large radial solar wind shocks in June and July 1982 provided a unique opportunity to study the solar modulation of galactic cosmic rays with an array of spacecraft widely separated both in heliocentric radius and longitude. By eliminating hysteresis effects it is possible to begin to separate radial and azimuthal effects in the outer heliosphere. On the large scale, changes in modulation (both the increasing and recovery phases) propagate outward at close to the solar wind velocity, except for the near-term effects of solar wind shocks, which may propagate at a significantly higher velocity. In the outer heliosphere, azimuthal effects are small in comparison with radial effects for large-scale modulation at solar maximum

    Surface properties of Galilean satellites from bistatic radar experiments

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    The icy moons of Jupiter were the first to show unusual radar backscatter behavior in Earth-based experiments. Studies of Europa, Ganymede, and Callisto revealed strong echoes and a reversed sense of circular polarization. No explanations were entirely satisfactory because of the difficult constraints imposed by the existing data. The (scalar) bidirectional coherence model predicts an opposition effect, or enhancement in the backscatter direction, resulting from coherent addition of backscatter from identical (but oppositely directed) ray paths. The mode decoupling model yields a similar, vector result in which the observed polarization properties of the backscattered wave can also be obtained. The possibilities were considered for conducting such experiments using the Galileo spacecraft. Both conventional oblique-forward bistatic experiments (to determine basic electrical and physical properties of the surface material on centimeter-meter scales) and near-backscatter experiments (to sample the enhanced backscatter lobe) were considered

    Career progress and career barriers: Women MBA graduates in Canada and the UK

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    This article explores the career progress of female MBA graduates in Canada and the UK and the nature of career barriers experienced in each context. Results suggest that while Canadian women have similar career profiles to men, women in the UK lag behind their male counterparts after graduation from the course. At the same time, UK women encounter more intractable career barriers in the form of negative attitudes and prejudice. A model of the ‘MBA effect’ is proposed in terms of how the qualification may impact on career barriers. This incorporates three different types of barriers which are seen to operate at the individual level (person centred barriers) and at the intermediate/organizational level (organizational culture and attitudes, corporate practices) as well as, at the macro level, the impact of legislative frameworks. Results from the UK and Canadian surveys are discussed in relation to this model and in the context of feminist theory and women in management literature

    Galactic cosmic ray radial gradients and the anomalous He component near maximum solar modulation and to radii beyond 34 AU from the Sun

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    Radial gradients for relativistic galactic cosmic rays (E 70 MeV) remained nearly constant at approx. 2.5%/AU from 1978-84, which includes the period of maximum solar modulation in 1981-82. For energies 30-70 MeV/n, gradients decreased at solar maximum to values of 1%/AU (protons) and 4%/AU (helium), and appear to be increasing again in 1983-84 toward the values found for solar minimum. The anomalous helium component has not reappeared, either at 1 AU or at Pioneer 10 at R 34 AU

    Potential impacts of advanced technologies on the ATC capacity of high-density terminal areas

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    Advanced technologies for airborne systems (automatic flight control, flight displays, navigation) and for ground ATC systems (digital communications, improved surveillance and tracking, automated decision-making) create the possibility of advanced ATC operations and procedures which can bring increased capacity for runway systems. A systematic analysis is carried out to identify certain such advanced ATC operations, and then to evaluate the potential benefits occurring over time at typical US high-density airports (Denver and Boston). The study is divided into three parts: (1) A Critical Examination of Factors Which Determine Operational Capacity of Runway Systems at Major Airports, is an intensive review of current US separation criteria and terminal area ATC operations. It identifies 11 new methods to increase the capacity of landings and takeoffs for runway systems; (2) Development of Risk Based Separation Criteria is the development of a rational structure for establishing reduced ATC separation criteria which meet a consistent Target Level of Safety using advanced technology and operational procedures; and (3) Estimation of Capacity Benefits from Advanced Terminal Area Operations - Denver and Boston, provides an estimate of the overall annual improvement in runway capacity which might be expected at Denver and Boston from using some of the advanced ATC procedures developed in Part 1. Whereas Boston achieved a substantial 37% increase, Denver only achieved a 4.7% increase in its overall annual capacity
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