Results 1 - 10 of 326
Results 1 - 10 of 326. Search took: 0.024 seconds
|Sort by: date | relevance|
[en] In this paper the authors study the conformal integrable models obtained from conformal reductions of WZNW theory associated with second order constraints. These models are called bosonic superconformal Toda models due to their conformal spectra and their resemblance to the usual Toda theories. From the reduction procedure they get the equations of motion and the linearized Lax equations in a generic Z gradation of the underlying Lie algebra. Then, in the special case of principal gradation, they derive the classical r matrix, fundamental Poisson relation, exchange algebra of chiral operators and find out the classical vertex operators. The result shows that their model is very similar to the ordinary Toda theories in that one can obtain various conformal properties of the model from its integrability
[en] The condition, for determining the Hill stability of a coplanar four-body system, is analyzed for the particular situation where the mass of a body is much greater than the other three. In this case, the criterion can be expressed in a closed form, which makes it easier to judge the stability of a system or predict the stable regions described by physical and orbital parameters. The criterion is applied to nine known four-body systems in our Solar System. Besides, the situations where a passing star moving on a parabolic or hyperbolic orbit encounters a triple system are considered. The Hill stability of all extrasolar triple systems are investigated during encounters of a passing star.
[en] Effects of surface roughness on the optical scattering properties of ice crystals are investigated using a random wave superposition model of roughness that is a simplification of models used in studies of scattering by surface water waves. Unlike previous work with models of rough surfaces applicable only in limited size ranges, such as surface perturbation methods in the small particle regime or the tilted-facet (TF) method in the large particle regime, ours uses a single roughness model to cover a range in sizes extending from the Rayleigh to the geometric optics regimes. The basic crystal shape we examine is the hexagonal column but our roughening model can be used for a wide variety of particle geometries. To compute scattering properties over the range of sizes we use the pseudo-spectral time domain method (PSTD) for small to moderate sized particles and the improved geometric optics method (IGOM) for large ones. Use of the PSTD with our roughness model is straightforward. By discretizing the roughened surface with triangular sub-elements, we adapt the IGOM to give full consideration of shadow effects, multiple reflections/refractions at the surface, and possible reentrance of the scattered beams. We measure the degree of roughness of a surface by the variance (σ2) of surface slopes occurring on the surfaces. For moderately roughened surfaces (σ2≤0.1) in the large particle regime, the scattering properties given by the TF and IGOM agree well, but differences in results obtained with the two methods become noticeable as the surface becomes increasingly roughened. Having a definite, albeit idealized, roughness model we are able to use the combination of the PSTD and IGOM to examine how a fixed degree of surface roughness affects the scattering properties of a particle as the size parameter of the particle changes. We find that for moderately rough surfaces in our model, as particle size parameter increases beyond about 20 the influence of surface roughness on the scattering properties of randomly oriented hexagonal particles starts to become evident. Somewhat surprisingly, in calculations using the IGOM certain qualitatively clear differences in patterns of roughness that have the same σ2 result in negligible difference in scattering effects. The phase matrix elements given by the IGOM for smooth and roughened hexagonal columns with the “large” size parameter 100 agree very well with the PSTD results, and the integral scattering properties given by the PSTD for small-to-moderate sized particles are shown to merge smoothly with those given by the IGOM for moderate-to-large sizes. -- Highlights: •We compute scattering properties of roughened particles over the entire size range. •Our roughness model is based on a random surface wave representation. •We use a combination of IGOM and PSTD methods to cover the range. •We evaluate strengths and weaknesses of the tilted facet ray tracing method
[en] FePt nanoparticles coated with 2 nm thick films of surfactant have been studied as candidates for magnetic recording media. The self-assembly of these nanoparticles is influenced by the properties of their surfaces which are coated with a layer of mixed oleic acid and oleyl amine. These surfactant coated FePt nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIR). The observation of both ν(COO) and ν(C=O) vibrational modes indicates that oleic acid bonds to the FePt nanoparticles in both monodentate and bidentate forms. The oleylamine bonds to the FePt nanoparticles through electron donation from the nitrogen atom of the NH2 group. The FTIR spectra indicate that there is a conversion of the alkyl chains from the oleyl form (cis-9-octadecenyl) to the elaidyl form (trans-9-octadecenyl) during the synthesis of the FePt nanoparticles. This is revealed by the presence of several vibrational absorption bands in the region of the olefinic C-H stretching modes. The presence of elaidyl groups on the FePt surfaces is very important because the structures of the oleyl groups and the elaidyl groups are quite different and are expected to pack differently around the FePt nanoparticles. This in turn will influence the self-assembly of nanoparticles on substrates
[en] A conceptual design of a ventilation system for elimination of high radioactivity concentration radon gas from a decommisioning underground storeroom is described in this paper. A mathmatical model is constructed for predition of the variation of radon radioactivity concentration upon time in the storeroom during ventilation. The model is further improved by introduction of a modification factor M whose value is determined by fitting to the experimental data. The final model is Ct = C0 e-(MN)t + E/V + Cair·(MN)/MN - λ [e-λt - e-(MN)t]. The modified model can satisfactorily predict the radon radioactivity concentration in the storeroom at any time, and precisely calculate the ventilation time needed for decrease the radon radioactivity concentration to an acceptable level to avoid harmful inner irradiation by inhalation. (authors)
[en] CdS/Cd1−xZnxS sandwich-structured quantum dots (QDs) were precipitated in silicate glasses with high quantum efficiency up to 53%. The QDs were composed by a CdS core with a Cd1−xZnxS shell of about 1–3 nm in thickness through heat-treatment at 550 °C for 10 h. With the increased heat-treatment temperature, the intensity ratio between the intrinsic emission and the defects emission increased and the Stokes shift decreased from 84 to 4 meV, which was caused by both the increased size and passivated surface defects of the QDs.
[en] The effect of irradiation on permeation and diffusion of hydrogen in low-activation martensitic stainless steel, F82H-mod, was investigated in three experiments: - Permeation and diffusion of H2 in pre-irradiated specimens, showing decrease of both the properties with increasing dose. The diffusion results were evaluated in terms of a saturable-trap-model. - Permeation of deuterium under simultaneous proton irradiation, showing enhancement of permeation by irradiation. - Diffusion of protons which were implanted to various depths in a 800 μm foil. These results were compared to H2 gas diffusion in virgin and pre-irradiated material
[en] Highlights: • Domperidone has good inhibition effect for copper in 3.5 wt.% NaCl solution. • Domperidone acts as an anodic type inhibitor. • The SEM and AFM analyses support the weight loss, polarization, and EIS data. • Molecular dynamics (MD) method simulates the adsorption model of domperidone on Cu surface. • The adsorption of domperidone on copper surface obeys Langmuir adsorption isotherm. - Abstract: Inhibition of copper corrosion in 3.5 wt.% NaCl solution by domperidone was investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The experimental results revealed that domperidone was an anodic inhibitor with a maximum achievable inhibition efficiency of 94.2%. The results of SEM and AFM studies further confirmed the inhibition action of domperidone. Quantum chemical calculation and the molecular dynamics (MD) simulation showed that the domperidone molecule could be adsorbed on copper surface through the imidazolidinone ring, benzene ring and N atom of hexaheterocyclic. Adsorption of domperidone was found to follow the Langmuir adsorption isotherm
[en] A quantitative measurement method determining the diameter, density, sphericity of the fuel kernel and the thickness, density of the coated fuel particles for the High Temperature Gas-Cooled reactor by the image analysis technique is described. The determination of this method is rapid and high precision, its relative standard deviation is 1%
[en] Highlights: • The ultrafine WC–(micron WC–Co) cemented carbides were fabricated. • The addition of micron-sized WC particles can generate the deflection of crack in the extension process. • The addition of micron-sized WC particles can improve the fracture toughness obviously. - Abstract: In this work, the effects of micron grained WC additions on the microstructure and properties of ultrafine WC–(micron WC–Co) cemented carbides produced through low pressure sintering processes were investigated by scanning electron microscope and mechanical properties tests. The results show that the obvious crack deflection and transgranular fracture phenomenon could be observed with the addition of micron WC, which can resist the crack propagation and improve the toughness of cemented carbides. The sintered ultrafine WC–(micron WC–Co) hardmetals demonstrate excellent hardness and fracture toughness values (HV30: 1700 kg/mm2, KIC: 13.82 MPa m1/2). These inhomogeneous ultrafine WC–(micron WC–Co) cemented carbides have considerable potential for use in structural applications