Results 1 - 10 of 140793
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[en] The efficiency of materials developed for solar energy and technological applications depends on the interplay between molecular architecture and light-induced electronic energy redistribution. The spatial localization of electronic excitations is very sensitive to molecular distortions. Vibrational nuclear motions can couple to electronic dynamics driving changes in localization. The electronic energy transfer among multiple chromophores arises from several distinct mechanisms that can give rise to experimentally measured signals. Atomistic simulations of coupled electron-vibrational dynamics can help uncover the nuclear motions directing energy flow. Through careful analysis of excited state wave function evolution and a useful fragmenting of multichromophore systems, through-bond transport and exciton hopping (through-space) mechanisms can be distinguished. Such insights are crucial in the interpretation of fluorescence anisotropy measurements and can aid materials design. Finally, this Perspective highlights the interconnected vibrational and electronic motions at the foundation of nonadiabatic dynamics where nuclear motions, including torsional rotations and bond vibrations, drive electronic transitions.
[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] Nucleon self-energies from the pion-ring series are studied in the relativistic mean-field theory of linear σ model with the ω meson and the Δ. Near the Fermi surface of nuclear matter, the pion rings generate attractive scalar and vector potentials of 10--15 % of the nucleon mass. These strongly energy-dependent potentials cause the nucleons to have a significant probability to be in a collective N-hole or Δ-hole configuration
[en] The difficulties arising in the calculation of the nuclear curvature energy are analyzed in detail, especially with reference to relativistic models. It is underlined that the implicit dependence on curvature of the quantal wave functions is directly accessible only in a semiclassical framework. It is shown that also in the relativistic models quantal and semiclassical calculations of the curvature energy are in good agreement. copyright 1996 The American Physical Society
[en] A comparison of federal policy to develop and commercialize solar energy technologies with the federal commitment to develop civilian nuclear power from 1947 to the early 1960s examines how internal factors influence the ability of the federal government to bring nonconventional energy technologies to a level of commercial competitiveness. The article notes three policy variables: the organizational format and institutional structure; the operational practice of contracting with non-federal agents for research and management: and the impact of the political environment of federal policies. It concludes that a federal policy designed to deliver a nonconventional energy technology from the laboratory to the marketplace is difficult to implement if policy-making authority is in the hands of too many participants. The nuclear power experience suggests that a sensitive appreciation of the public-private relationship is necessary to identify and resolve obstacles. 129 references
[en] Risk to human health has become one of the prime considerations in choosing energy systems, if it has not already overtaken economic cost. Accidents at reactors and collapses of dams all capture public attention. But are they the total risk of energy systems. Just as the cost of any article is made up of a number of sources, so the total risk of an energy system has many origins. The author lists these as: raw materials and fuel production, transportation (all applications), component fabrication, plant construction, operation and maintenance, waste disposition and deactivation and public health risk. While it is impossible to state with certainty that these sources of risk are the only ones, they are the major considerations in most risk studies. Most of these listed risk sources seem to be of non-catastrophic origin, i.e., accidents or illnesses that occur one at a time. Even for systems like nuclear power and hydroelectricity, which receive considerable publicity about real or potential catastrophies, the proportion of catastrophic (as meaured by historical statistics) to non-catastrophic risk is very small. As a result of the risk analysis philosophy described in this article, the author concludes that the risk in total man-days lost is least for energy from natural gas, next least from nuclear energy, greatest from coal, next greatest from oil, with all other sources between these limits
[en] In the past 5 years the general attitude towards solar energy has turned from negative to positive. This in itself, however, will not accelerate the introduction of solar energy very much. On the contrary, some of the plans and programs following from it are unrealistic and counter-productive. The better way to go is realism and inspiring the best scientists and politicians to take up the vast amount of R and D work and societal restructuring that has still to be done. Energy has become so vital to mankind that solar energy as a substitute for conventional energy sources will be indispensable for maintaining peace. (author)
[en] The paper presents the results of calculated research on determining the thermal technical indicators of a combined solar desalinization and drying plant. The structure of the plant is developed and proposed. A mathematical model is developed that describes the thermal processes occurring in the plant based on heat-balance equations solved using the Laplace method.
[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