Results 1 - 10 of 15490
Results 1 - 10 of 15490. Search took: 0.042 seconds
|Sort by: date | relevance|
[en] We have studied several decay processes of potassium clusters and found that a dimer-decay mechanism can explain the observed lowest abundance of K10 in the Kn mass spectra. Total-energy curves for decay processes are calculated using a jellium-background model for positive-ion cores and the local-spin-density-functional approximation for valence electrons. The energy-barrier height for a dimer decay of K10 from the energy-minimum point is found to be 0.18 eV, which is a reasonable magnitude for the decay to take place thermally in the experiment. The monomer decay of K9 and the dimer decay of K11, which are expected to be the most favorable decays of K9 and K11, are found to have high barriers. Monomer and dimer decays of K8 are also studied and the monomer decay is found to be more favorable, in accord with the high-nozzle-temperature mass spectrum. (orig.)
[en] Volume decomposition methods are one type of feature recognition method. They decompose a solid model into simple volumes which are mostly overlapped by each other. However, the overlap of decomposed volumes leads to unnatural results in the recognition of design features. In order to address this problem, we suggest a novel method called non-overlapping volume decomposition in which the overlap of volumes decomposed from a solid model is minimized; the overlap is only allowed when it is desirable from the viewpoint of feature-based 3D modeling practice. After introducing the concept of non-overlapping volume decomposition, we discuss technical issues and their solutions. Non-overlapping volume decomposition was also verified by experiments using a prototype system.
[en] We discuss the recent report of a roaming type mechanism for the decomposition of the Criegee intermediate. We show that the predicted barrier height for this new pathway is too low by ∼30 kcal/mol owing to an inconsistent use of spin-restricted and spin-unrestricted calculations. As a result, this new pathway is not expected to compete significantly with the well-known dioxirane pathways for the decomposition of the Criegee intermediate
[en] We find general formulas for Thévenin equivalents (equivalent voltage and equivalent impedance) for inhomogeneous ladder networks of generators defined as a voltage source and an impedance in series. In the projective matrix representation, this is accomplished by adopting a special decomposition of a 3 × 3 transfer matrix which transforms a product of transfer matrices to a product of diagonal matrices up to a prefactor and a postfactor. In particular, we calculate Thévenin equivalents in a closed form for two ladder networks of generators with a periodic transfer matrix of period 1 (tapered ladder network) and period 2. (paper)
[en] Complete text of publication follows. High precision measurements of the geomagnetic field have been and are essential to provide insight into the internal structure of the Earth and the solar interaction with the Earth's magnetic field. These measurements reveal the resulting magnetic field that stems from the superposition of three sources: the core field, the crustal field and the current driven field. The spatial and temporal structure of these sources are very different from each other, and therefore not only signal extraction methods and modelling but also measurement strategies have to be taken into account in order to successfully separate these signal contributors. Furthermore, this decomposition process requires that the global field is known at any given time with a relatively high accuracy, wherefore accurate magnetic field mapping is only viable using spaceborne observations. The data obtained from one single spacecraft is extremely valuable. The first mission to ever map the Earth's magnetic field vector at LEO was the NASA MAGSAT (1978-9). Twenty years later, the Danish Orsted micro satellite (1999-), the German CHAMP (2000-), the Argentine SAC-C (2000-5) have been designed specifically for mapping the LEO magnetic field. Common to these resent missions is the magnetometry package, which utilizes a vector field magnetometer co-mounted with a star tracker (2 in the case of CHAMP) on an optical bench. As the accuracy of the instrument package has constantly increased, as well as the modelling methods have been improved towards optimized signal decomposition, it has been realized that simultaneous data from several points in space is needed, if the ultimate modelling barrier, the spatial-temporal ambiguity, has to be broken. The ESA Swarm mission under the Living Planet Programme consists of three identical spacecraft orbiting in near polar orbits with altitudes varying between 400km to 550km. This constellation is to map the magnetic field of the Earth with unprecedented spatial and temporal accuracy. For this purpose, each spacecraft will be equipped with a vector field magnetometer and three star trackers co-mounted in an optical bench, which will ensure 100% data coverage over the orbit with arcsecond accuracy. This accuracy of the magnetometry package is essential for fulfilling the mission objectives. This paper describes the basic design characteristics and the performance potentials of the Swarm Magnetometry Package. The key performance parameter is an absolute attitude recovery accuracy in the arcsecond range over time, temperature and aging. The methods used to achieve and validate this accuracy are discussed, as well as the potential for using this methodology on other future missions with extreme stability and accuracy demands.
[en] We present a self-contained proof of Rivière’s theorem on the existence of Uhlenbeck’s decomposition for for , with Sobolev type estimates in the case and Morrey–Sobolev type estimates in the case . We also prove an analogous theorem in the case when , which corresponds to Uhlenbeck’s decomposition with conformal gauge group.
[en] In the fuel cycle system of a fusion reactor, tritium is extracted from exhaust gas and reused. When graphite materials are used in a part of plasma facing components, tritiated methane is contained in exhaust gas. Plasma decomposition is one of the techniques for extracting hydrogen from hydrocarbon. In order to evaluate direct decomposition of methane using helium RF plasma, a flow-type plasma reactor utilizing capacitively coupled plasma was developed and direct decomposition of methane was demonstrated. The decomposition rate of methane by helium plasma was proportional to the supplied RF power. However, it became small when total pressure of gas was high. A part of hydrogen generated from methane was retained in carbon deposits on the electrode. However, the accumulated hydrogen and carbon were effectively removed by the discharge-cleaning with oxygen plasma.
[en] The trends of realization of cyclic reactions of water decomposition into hydrogen and oxygen are considered and, in particular, so-called combined cycles of reactions, for example, thermoelectrical ones. Such cycles can have only two reactions: thermal and electrochemical. These combined cycles make it possible to use existing nuclear reactors with their temperature limits without recourse to designing and development of special high-temperature apparatuses. Preliminary calculations show that 20.4-244 Kcal is required to obtain oxygen in the thermoelectrochemical cycle (corresponding to 1-3 mole hydrogen). This value is acceptable for practical realization
[en] The liquid wastes generated by the reprocessing of spent fuel can be converted into solid form by using several known processes. When the wastes contain nitrates and nitrites large quantities of noxious nitrogen oxide gases are formed, which are at present released to the atmosphere. Their evolution may be suppressed by adding urea to the waste solution before the solution is heated, so that upon heating the urea reacts wth the nitrates and nitrites to evolve elemental nitrogen, carbon dioxide and ammonia. The addition of urea does not add any additional materials to the solids being formed from the waste solution. A slight excess of a stoichiometric amount of urea relative to the nitrates and nitrites present is added to the liquid waste, and the solution is heated to at least 1300 C while bubbling carbon dioxide through the solution. This method can be used with the pot calcination process of waste solidification, or in the fluidized bed calcination process. (LL)
[en] Sample preparation of soil samples (reference material) in a microwave oven using the EPA - 3051 methods showed that, with microwave decomposition, the extraction coefficient of metals from the soil improved and sample preparation time is drastically reduced.