4,893 research outputs found

    SPS structures and control: A perspective

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    The characteristics and design requirements for the structure and control systems for a solar power satellite were evaluated. A simplistic, indicative analysis on a representative configuration was developed. Representative configuration masses and dimensions are given in convenient approximate magnitudes. The significance of structure control interaction and the significance of stiffness to the minimization of dynamic energy was demonstrated. It was found that the thermal environment for the SPS was dominated by solar radiation and waste heat rejection by the antenna. A more in-depth assessment of the control system design and associated system performance is still needed, specifically the inter-relatonships between control sensors, actuators, and structural response

    Orbiter entry aerothermodynamics

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    The challenge in the definition of the entry aerothermodynamic environment arising from the challenge of a reliable and reusable Orbiter is reviewed in light of the existing technology. Select problems pertinent to the orbiter development are discussed with reference to comprehensive treatments. These problems include boundary layer transition, leeward-side heating, shock/shock interaction scaling, tile gap heating, and nonequilibrium effects such as surface catalysis. Sample measurements obtained from test flights of the Orbiter are presented with comparison to preflight expectations. Numerical and wind tunnel simulations gave efficient information for defining the entry environment and an adequate level of preflight confidence. The high quality flight data provide an opportunity to refine the operational capability of the orbiter and serve as a benchmark both for the development of aerothermodynamic technology and for use in meeting future entry heating challenges

    On the relationship between aging, edical progress and age-specific health care expenditures

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    This paper investigates the impact of population aging, driven by medical progress, upon agespecific expenditure on health care. In a model set up in discrete time, individuals at each age may catch a lethal disease which, upon receiving appropriate medical treatment, nevertheless involves a mortality risk such that length of life is stochastic. The incidence of lethal diseases, the associated survival probability conditional upon treatment, and health care expenditure conditional upon health status may all depend on an individual´s history. For a given age, the history of an individual contains information on her health status in the past. Medical progress is taken to involve an increase in the survival probability of a specified lethal disease. On the one hand, this produces a direct effect on age-specific health care expenditure to the extent that progress affects the cost of treatment of the disease. On the other hand, indirect effects may also arise. These effects are caused by individuals who, having survived the disease at some prior age due to progress, change the structure of individuals alive at current age. Specifically, the new survivors may have an influence on age-specific expenditure either through changes in the incidence of lethal diseases or in the associated treatment cost. The sign of an indirect effect crucially depends on health care expenditure for new survivors relative to their peers. The analysis yields a number of general results which are important for the discussion of the impact of medical progress on the age profile of health care expenditure. Compression of morbidity, to the extent that it involves a reduction in age-specific expenditure, is neither necessary nor sufficient for medical progress to produce a downward shift of the profile. A similar observation applies to an expansion of morbidity. Both concepts relate to new survivors and, thus, take into account only indirect effects of progress. --aging,medical progress,age-specific expenditure on health care

    Achievable flatness in a large microwave power transmitting antenna

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    A dual reference SPS system with pseudoisotropic graphite composite as a representative dimensionally stable composite was studied. The loads, accelerations, thermal environments, temperatures and distortions were calculated for a variety of operational SPS conditions along with statistical considerations of material properties, manufacturing tolerances, measurement accuracy and the resulting loss of sight (LOS) and local slope distributions. A LOS error and a subarray rms slope error of two arc minutes can be achieved with a passive system. Results show that existing materials measurement, manufacturing, assembly and alignment techniques can be used to build the microwave power transmission system antenna structure. Manufacturing tolerance can be critical to rms slope error. The slope error budget can be met with a passive system. Structural joints without free play are essential in the assembly of the large truss structure. Variations in material properties, particularly for coefficient of thermal expansion from part to part, is more significant than actual value

    Macroeconomic Policy in a Heterogeneous Monetary Union

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    We use a two-country model with a central bank maximizing union-wide welfare and two fiscal authorities minimizing comparable, but slightly different country-wide losses. We analyze the rivalry between the three authorities in seven static games. Comparing a homogeneous with a heterogeneous monetary union, we find welfare losses to be significantly larger in the heterogeneous union. The best-performing scenarios are cooperation between all authorities and monetary leadership. Cooperation between the fiscal authorities is harmful to both the whole union’s and the country-specific welfare.monetary union, heterogeneities, policy game, simultaneous policy, sequential policy, coordination, discretionary policies.

    SPS structural dynamics and control workshop: Findings and recommendations

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    The structural dynamics and control of the Solar Power Satellite (SPS), a concept which holds promise for meeting a portion of the energy needs of the United States beyond the year 2000 are examined. The assumptions, methodologies and conclusions of existing SPS studies in the areas of structural dynamics and control (with structural design and materials also being considered) are assessed

    Macroeconomic Policy in a Heterogeneous Monetary Union

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    We use a two-country model with a central bank maximizing union-wide welfare and two fiscal authorities minimizing comparable, but slightly different country-wide losses. We analyze the rivalry between the three authorities in seven static games. Comparing a homogeneous with a heterogeneous monetary union, we find welfare losses to be significantly larger in the heterogeneous union. The best-performing scenarios are cooperation between all authorities and monetary leadership. Cooperation between the fiscal authorities is harmful to both the whole union’s and the country-specific welfare.monetary union, heterogeneities, policy game, simultaneous policy, sequential policy, coordination, discretionary policies

    Cwikel's bound reloaded

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    There are a couple of proofs by now for the famous Cwikel--Lieb--Rozenblum (CLR) bound, which is a semiclassical bound on the number of bound states for a Schr\"odinger operator, proven in the 1970s. Of the rather distinct proofs by Cwikel, Lieb, and Rozenblum, the one by Lieb gives the best constant, the one by Rozenblum does not seem to yield any reasonable estimate for the constants, and Cwikel's proof is said to give a constant which is at least about 2 orders of magnitude off the truth. This situation did not change much during the last 40+ years. It turns out that this common belief, i.e, Cwikel's approach yields bad constants, is not set in stone: We give a drastic simplification of Cwikel's original approach which leads to an astonishingly good bound for the constant in the CLR inequality. Our proof is also quite flexible and leads to rather precise bounds for a large class of Schr\"odinger-type operators with generalized kinetic energies. Moreover, it highlights a natural but overlooked connection of the CLR bound with bounds for maximal Fourier multipliers from harmonic analysis.Comment: 30 page
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