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[en] The development of microsatellites requires the development of engines to modify their orbit. It is natural to use solar energy to drive such engines. For an unlimited energy source the optimal thruster must use a minimal amount of expendable material to minimize launch costs. This requires the ejected material to have the maximal velocity and, hence, the ejected atoms must be as light as possible and be ejected by as high an energy density source as possible. Such a propulsion can be induced by pulses from an ultra-short laser. The ultra-short laser provides the high-energy concentration and high-ejected velocity. We suggest a microthruster system comprised of an inflatable solar concentrator, a solar panel, and a diode-pumped fiber laser. We will describe the system design and give weight estimates.
[en] Energy in nuclear matter is, in practice, completely characterized at different densities and asymmetries, when the density dependencies of symmetry energy and of energy of symmetric matter are specified. The density dependence of the symmetry energy at subnormal densities produces mass dependence of nuclear symmetry coefficient and, thus, can be constrained by that latter dependence. We deduce values of the mass dependent symmetry coefficients, by using excitation energies to isobaric analog states. The coefficient systematic, for intermediate and high masses, is well described in terms of the symmetry coefficient values of aaV = (31.5-33.5) MeV for the volume coefficient and aaS = (9-12) MeV for the surface coefficient. These two further correspond to the parameter values describing density dependence of symmetry energy, of L∼95 MeV and Ksym∼25 MeV
[en] The Utility PhotoVoltaic Group (UPVG) is a nonprofit association of over 100 energy service providers (electric utilities and energy service companies) cooperating to develop photovoltaic power as a thriving commercial energy option for the benefit of its members and their customers. The U. S. Department of Energy (DOE) and UPVG are sponsoring an initiative named TEAM-UP that has co-funded 37 business ventures since 1995 that are resulting in more than 2,500 PV installations, totaling more than 7.5 megawatts of power in 30 states. The TEAM-UP1 ventures are significantly leveraging the federal funds. Under TEAM-UP, venture teams are investing four dollars for every dollar invested by the U. S. taxpayer. The UPVG programs are increasing the experience of electric utilities and their customers with photovoltaics and are stimulating growth in the demand for solar power. This paper describes these efforts and outlines the current status of the TEAM-UP program. copyright 1999 American Institute of Physics
[en] The nature of the heat flux in special relativistic kinetic theory is discussed to some detail emphasizing the need to explicitly include the chaotic velocity in order to correctly define dissipative fluxes while retaining both their physical meaning and the Lorentz covariance of the theory.
[en] Hydrogen is a high quality, low polluting fuel, which could replace oil and natural gas for transportation, heating, and power generation. If hydrogen is generated via solar photovoltaic (PV) powered water electrolysis, it would be possible to produce and use energy on a large scale with essentially no greenhouse gas emission and very little local pollution. In previous studies, we investigated some of the implications of projected advances in thin film PV technologies for PV hydrogen production. Here we summarize our findings on the design and economics of PV hydrogen systems, and discuss potential long term applications of PV hydrogen as a transportation fuel for ''zero emissions'' fuel cell vehicles
[en] Partial shading conditions are among the most important problems in large photovoltaic array. Many works of literature are interested in modeling, control and optimization of photovoltaic conversion of solar energy under partial shading conditions, The aim of this study is to build a software simulator similar to hard simulator and to produce a shading pattern of the proposed photovoltaic array in order to use the delivered information to obtain an optimal configuration of the PV array and construct MPPT algorithm. Graphical user interfaces (Matlab GUI) are built using a developed script, this tool is easy to use, simple, and has a rapid of responsiveness, the simulator supports large array simulations that can be interfaced with MPPT and power electronic converters.
[en] This article is concerned with natural convective heat transfer from square cylinder mounted on a plane adiabatic base, the cylinders having an exposed cylinder surface according to different horizontal angle. The cylinder receives heat from a radiating heater which results in a buoyant flow. There are many industrial applications, including refrigeration, ventilation and the cooling of electrical components, for which the present study may be applicable
[en] We investigated the evolution of experimental two-neutron separation energies (S2n) along the isotopic chains for the even-even nuclei. In order to enhance the sensitivity of our search, differential variation of the S2n has been investigated. The emphasis is on finding nonmonotonic behaviors which can be correlated with phase/shape transition. Correlations of the ground state S2n values with the excited states energies R4/2 ratio are also discussed.