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991.
A variational principle for magnetohydrodynamic gravitational modes, including isotropic viscosity and the shear of magnetic field lines, is given. It is shown to imply a minimum dissipation requirement for the modes. A sufficient condition for stability given in the literature for the case of ordinary fluids is corrected here. 相似文献
992.
Jaime Keller Alejandro Pisanty Maria Del Carmen de Teresa M. Erbudak 《Physics letters. A》1979,71(1):90-92
The multiple scattering cluster method is used to calculate densities of states for Cu, Ag, and Au. The results compare favorably with experimental photoemission spectra. The method converges rapidly with the cluster size used for the calculation. 相似文献
993.
Trying to combine standard quantum field theories with gravity leads to a breakdown of the usual structure of space time at around the Planck length, 1.6x10(-35) m, with possible violations of Lorentz invariance. Calculations of preferred-frame effects in quantum gravity have further motivated high precision searches for Lorentz violation. Here, we explain that combining known elementary particle interactions with a Planck-scale preferred frame gives rise to Lorentz violation at the percent level, some 20 orders of magnitude higher than earlier estimates, unless the bare parameters of the theory are unnaturally strongly fine tuned. Therefore an important task is not just the improvement of the precision of searches for violations of Lorentz invariance, but also the search for theoretical mechanisms for automatically preserving Lorentz invariance. 相似文献
994.
We study the dynamics of perturbations in time-delay dynamical systems. Using a suitable space-time coordinate transformation, we find that the time evolution of the linearized perturbations (Lyapunov vector) can be described by the linear Zhang surface growth model [J. Phys. (France) 51, 2129 (1990)]], which is known to describe surface roughening driven by power-law distributed noise. As a consequence, Lyapunov vector dynamics is dominated by rare random events that lead to non-Gaussian fluctuations and multiscaling properties. 相似文献
995.
A new, low-temperature sealed tube technique for combustion of organic carbon prior to subsequent off-line isotope analysis is proposed. Complete oxidation is achieved with potassium peroxodisulfate and silver permanganate as oxidants at temperatures not exceeding 500 degrees C. The combustion of gaseous (methane), solid (cane sugar, vanilla, N-thiazolyl-2-sulfamide, ascorbic acid, phenanthrene, thiourea, polyethylenefilm, tetrafluoropolyethylene, polyetheretherketone, graphite, and Suwannee River Fulvic Acid), and liquid (tetrachloroethene, toluene, and oil) model compounds and international standards was tested. A 24 h combustion at 500 degrees C was sufficient for complete oxidation in all cases. The time required for complete oxidation of Suwannee River Fulvic Acid, typical of refractory freshwater dissolved organic carbon, as a function of combustion temperature was 2 h at 500 degrees C, 6 h at 400 degrees C, and 24 h at 300 degrees C. Preparation of saline solution parallels of cane sugar, vanilla, N-thiazolyl-2-sulfanilamide, and ascorbic acid gave consistent results. For reproducible delta13C analyses using a Thermoquest MAT 252 MS, a minimum of 5 microg C had to be combusted. Reliable 14C results, measured at an accelerator mass spectrometer facility, were obtained from coal and from cane sugar combusted for 24 h at 500 degrees C by the proposed method. 相似文献
996.
Enriquez AE Matonic JH Scott BL Neu MP 《Chemical communications (Cambridge, England)》2003,(15):1892-1893
Nine-coordinate homoleptic acetonitrile solvate complexes of Pu(III) and U(III) ions have been prepared through oxidation of Pu metal suspended in acetonitrile with metal-hexafluorophosphate salts and dissolution of UI3(THF)4 in acetonitrile, respectively. 相似文献
997.
Zapata Ballesteros Alejandro De Witte Niels Denayer Joeri F. M. Van Assche Tom R. C. 《Adsorption》2022,28(5-6):197-208
Adsorption - A demand-driven pressure swing adsorption biogas upgrading application is modelled using monolayer and multilayered (bilayer) beds, to gain insight on the impact of the adsorbent... 相似文献
998.
999.
The notion of maximal-spacing in several dimensions was introduced and studied by Deheuvels (Probab. Theory Related Fields 64(4), 411–424, 1983), for data uniformly distributed on the unit cube. Later on, Janson (Ann. Prob. 15, 274–280, 1987) extended the results to data uniformly distributed on any bounded set, and obtained a very fine result, namely, he derived the asymptotic distribution of different maximal-spacings notions. These results have been very useful in many statistical applications. We extend Janson’s results to the case where the data are generated from a Hölder continuous density that is bounded from below and whose support is bounded. As an application, we develop a convexity test for the support of a distribution. 相似文献
1000.
The growth kinetics, shape, interfacial and internal orientation texture of a submicron nematic spherulite arising during
the isotropic-to-nematic liquid crystal phase transformation under shallow thermal quenches is analyzed using theory, scaling,
and numerical simulations based on the Landau – de Gennes model (The Physics of Liquid Crystals, 2nd edn. Clarendon, Oxford).
The numerical computations from this model yield interfacial cusp formation that relaxes through the nucleation of two disclination
lines of topological charge +1/2 and subsequently leads to intra-droplet texturing and a net topological charge within the
spherulite of +1. The timing of these events suggests that cusp formation at the interface is intimately associated with the
interfacial defect shedding mechanism (J. Chem. Phys. 124:244902, 2006) for shallow quenches. These results are different
than predictions for deep quenches (J. Chem. Phys. 124:244902, 2006) where interfacial defect shedding leads to four defects
and a net topological charge of +2. A liquid crystal dynamic shape equation is derived from the Landau – de Gennes model to
account for the interface shape changes in terms of surface viscosity, the driving forces due to the uniaxial nematic-isotropic
free energy difference, capillary forces, and friction forces, and used to semi-quantitatively show that during cusp formation
and defect shedding, gradient elasticity, capillary forces and friction play significant roles in decelerating and accelerating
the surface. An interfacial eigenvalue analysis shows that during the shallow quench, disclination lines nucleate within the
interface itself and then texturize the nematic droplet as they migrate from within the interface to the bulk of the growing
nematic droplet. After defect shedding, the spherulite is nearly circular and grows with constant velocity, in agreement with
experiments. The results shed new light on intra-spherulite texturing mechanisms in phase ordering under weak driving forces.
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