Results 1 - 10 of 20273
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[en] A novel nuclear astrophysics facility, CLAIRE (Center for Low Energy Astrophysics and Interdisciplinary REsearch), is being designed at Lawrence Berkeley National Laboratory to address the need for precise fusion cross section measurements at near-solar energies (∼20 keV). At these low energies, fusion cross sections decrease exponentially with energy and are expected to approach femtobarn levels or less. In order to measure such small cross sections, the CLAIRE facility will incorporate a versatile accelerator capable of transporting high current (>100 mA), low energy (50-300 keV) ion beams with a tight focus (<1 cm) to a cooled, dense gas-jet target. The conceptual design for this accelerator is discussed, and simulations of both beam extraction and transport are presented
[en] The large penetration of wind farm into interconnected power systems may cause the severe problem of tie-line power oscillations. To suppress power oscillations, the superconducting magnetic energy storage (SMES) which is able to control active and reactive powers simultaneously, can be applied. On the other hand, several generating and loading conditions, variation of system parameters, etc., cause uncertainties in the system. The SMES controller designed without considering system uncertainties may fail to suppress power oscillations. To enhance the robustness of SMES controller against system uncertainties, this paper proposes a robust control design of SMES by taking system uncertainties into account. The inverse additive perturbation is applied to represent the unstructured system uncertainties and included in power system modeling. The configuration of active and reactive power controllers is the first-order lead-lag compensator with single input feedback. To tune the controller parameters, the optimization problem is formulated based on the enhancement of robust stability margin. The particle swarm optimization is used to solve the problem and achieve the controller parameters. Simulation studies in the six-area interconnected power system with wind farms confirm the robustness of the proposed SMES under various operating conditions
[en] After two years of very strong growth, the solar thermal market (taking all technologies including unglazed flexible collectors into account) marked time in 2007 with 6.9% less collectors being sold with respect to year 2006. In the end, this market reached 2.9 million m2 vs. 3.1 million m2 in 2006, i.e. an equivalent capacity of more than 2000 MWth. This decrease is explained for a large part by a strong decline of the German market, the largest market of the European Union. Conversely, other countries are continuing to develop their markets and are showing double-digit growth rates
[en] This paper proposes the principle of SMES capacity determination for power system stable operation. Adopting the energy function method, the mechanism of SMES damping power oscillation in the classical single-machine infinite-bus (SMIB) system is analyzed. The released kinetic energy during disturbance is the original of power system oscillation, which is taken as the principle of SMES capacity determination. Then, the influence of fault type, fault position, and fault clearing time on the SMES capacity determination are discussed. Using MATLAB simulation, the principle of SMES capacity determination is evaluated.
[en] Symmetry and pairing energies of atomic nuclei are related to the differences between the excitation energies of isobaric analog states in the same nucleus. Numerous such excitation energies are known experimentally. In addition, a comprehensive global set can be deduced from the available experimental masses by applying Coulomb energy corrections. Replacing the experimental mass data by available theoretical mass predictions as basis for this procedure to extract symmetry and pairing energies makes it possible to directly compare theoretical and experimental quantities. These comparisons reflect upon the goodness or possible shortcomings of the respective mass equation since symmetry energies are related to the curvature of the nuclear mass surface. A discussion of eleven selected mass equations or procedures for reproducing experimental masses and extrapolating into regions of unknown nuclei is presented
[en] In this work, we have systemically investigated the ground-state properties of the rare-earth even-even nuclei with the parameter set FSUGold that includes the isoscalar-isovector coupling to soften the symmetry energy. It is the first time that this parameter set is applied to investigate the properties of deformed nuclei. The present study is mainly focused on the nuclei with the known experimental binding energies ranging from Z=58 to Z=70. The calculated binding energies, quadrupole deformations, and charge radii are in good agreement with the available experimental data. It has been shown that the parameter set FSUGold is as successful as the NL3 in reproducing the known ground-state properties of deformed nuclei.
[en] This report provides an overview of the status of the solar electricity market in 2008, both from a national an international perspective. It gives insight in the global solar electricity market and the Dutch market in an international perspective.
[nl]Dit rapport geeft een overzicht van de status van zonnestroommarkt anno 2008, zowel internationaal als nationaal. Het geeft inzicht in de globale zonnestroommarkt en de Nederlandse markt in een internationaal perspectief.
[en] A new model describing the dark sector of the universe is established. The model involves Bose-Einstein condensate (BEC) as dark energy (DE) and an excited state above it as dark matter (DM). The condensate is assumed to have a negative pressure and is embodied as an exotic fluid with Chaplygin equation of state. Excitations are described as a quasiparticle gas. It is shown that the model is not in disagreement with the current observations of the cosmic acceleration. The model predicts increase of the effective cosmological constant and a complete disappearance of the matter at the far future.
[en] We investigate the influence of low-energy recoils with respect to the electronic excitation of solids generated in atomic collision cascades. It is found that the electronic friction experienced by recoil atoms moving with kinetic energies below 10 eV contributes substantially to the total excitation energy dissipated into electronic degrees of freedom. The collision dynamics, on the other hand, remain virtually unchanged if the friction loss of these particles is switched on or off. This is illustrated by looking at the yield, emission sites and energies of sputtered surface atoms
[en] Na, Al and Ar atoms with energies ranging from 3 to 80 keV are scattered from Al(1 1 1) and Al(0 0 1) surfaces under axial surface channeling conditions. Well defined peaks in the angular distributions for scattered projectiles are attributed to 'rainbow-scattering' and are analyzed in terms of the effective scattering potential. Computer trajectory simulation of the rainbow angles with established pair potentials leads to good agreement for potential energies above about 30 eV. At smaller potential energies we observe pronounced deviations for the three different projectile atoms which are attributed to an additional contribution to the overall potential due to the effect of embedding the atoms into the electron gas in front of the metal surface. Taking into account this additional potential leads to a consistent description of data