Results 1 - 10 of 366
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[en] The Richtmyer-Meshkov (RM) instability is an interfacial instability between two fluids of different densities driven by shock waves and plays an important role in the studies of inertial confinement fusion and supernova. So far, most of the studies are for RM unstable interfaces driven by weak or intermediate shocks in planar geometry. Some results are given for the weak shock case in cylindrical geometry. For experiments conducted at Nova laser, the unstable material interface is accelerated by very strong shocks. We also present scaling laws for the RM unstable interface driven by strong imploding and exploding shocks. (c) 2000 The American Astronomical Society
[en] The global asymptotic stability of Hopfield neural networks with transmission delays is considered in this Letter. We present a new sufficient condition for the asymptotic stability. This condition is dependent on the size of delays. The result is less conservative than those established in the earlier references. A numerical example is given to illustrate the applicability of this condition
[en] A model of Hopfield neural networks (HNN) with continuously distributed delays is considered. A sufficient condition which guarantees global exponential stability (GES) of an equilibrium point is given based on the method of variation parameter and inequality technique. Compared with the previous methods, our method does not resorting to any Lyapunov functionals
[en] Some new sufficient conditions for the global exponential stability and estimations of bound on the rate of exponential convergence of the neural networks with time-varying delays are obtained by means of an approach based on delay differential inequality. The method, which does not make use of any Lyapunov functionals, is simple and valid for the stability analysis of neural networks with time-varying delays. Some previously established results in the literature are shown to be special cases of the presented results
[en] Based on the Lyapunov-Razumikhin technique as well as linear matrix inequality analysis, two new sufficient conditions are presented for the global asymptotic stability of neural networks with variable delays. The results given here are less conservative than those provided in the earlier references
[en] Highlights: • We built a new falling-film flow model that analyzed the film flow characteristics. • We have obtained a new formula of film thickness over the horizontal tube. • We derived analysis solution to analyze the effect of inertial force to velocity in the entrance region of liquid film. • It described the characters of the ammonia-waterfalling-film film over the horizontal tube. • It is good for falling-film absorption, generation and evaporation to optimizing the design parameters and further improving the capabilities. - Abstract: A new horizontal tube falling film velocity model was built and calculated to analyze the problem of film flow conditions. This model also analyzed the film thickness distribution in horizontal tube falling film flow and considered the effect of the inertial force on velocity. The film thickness and velocity profile can be obtained based on the principle of linear superposition, a method of separation of variables that introduces the effect of variable inertial force on the velocity profile in the process of falling-film absorption. The film flow condition and the film thickness distribution at different fluid Reynolds numbers (Re) and tube diameters were calculated and compared with the results of the Crank–Nicolson numerical solution under the same conditions. The results show that the film flow condition out of a horizontal tube and that the film thickness increases with the fluid Re. At a specific Re and suitable tube diameter, the horizontal tube reaches a more uniform film. Finally, the analysis results have similar trend with the experimental and numerical predicted data in literature.
[en] Highlights: • We synthesized β-Ni(OH)2 nanoflakes through a novel ion diffusion method. • The possible formation mechanism of the Ni(OH)2 nanoflakes was discussed. • The temperature influence on growth of Ni(OH)2 nanocrystals and its subsequent effect on electrochemical supercapacitive properties were examined. • The β-Ni(OH)2 nanoflakes prepared at 50 °C for 12 h exhibits the highest specific capacitance of 2102 F g−1. - Abstract: A novel method, ion diffusion method controlled by ion exchange membrane was reported for the synthesis of Ni(OH)2 nanomaterials in the absence of any template or organic surfactant. The structure and morphology of as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), BET specific surface area and pore size distribution analyzer. It can be observed that β-Ni(OH)2 nanoflake-like structure was obtained, and the sheet size, thickness and pore size of as-prepared samples can be controlled by altering reaction time and reaction temperature. The BET specific surface area of Ni(OH)2 nanomaterials obtained by this method can be up to 280.5 m2/g at 30 °C. The electrochemical supercapacitive properties of Ni(OH)2 nanostructures have been investigated by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy techniques. All these Ni(OH)2 samples exhibit good capacity for electrochemical supercapacitor in KOH electrolyte. The flake nanostructures synthesized at 50 °C for 12 h exhibit a highest specific capacitance of 2102 F g−1 at a current density of 20 mA cm−2 within the potential range of 0.5 V and the Ni(OH)2 sample retains 85.1% of the initial capacitance even after 1000 continuous charge–discharge cycles. The results indicate that ion diffusion method controlled by ion exchange membrane is a useful method for synthesizing inorganic nanomaterials.
[en] Highlights: • The NiO nanocrystals were prepared by calcinating Ni(OH)_2 nanoflakes synthesized via an ion diffusion controlled by ion exchange membrane. • The NiO sample calcinated at 400 °C exhibits the highest specific capacitance of 381 F g"−"1 and specific surface area of 188.4 m"2 g"−"1. • The NiO samples with the lower binding energy are harder to capture OH- than Ni(OH)2, which is disadvantageous to charge storage. • The UV–Vis absorption peak of NiO samples have a red shift with increasing the calcination temperature due to the increase in crystallinity. - Abstract: The NiO nanocrystals were successfully prepared by calcinating Ni(OH)_2 precursor synthesized via a facile ion diffusion controlled by ion exchange membrane without adding any solvent or template. X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) isotherm, X-ray photoelectron spectroscopy (XPS) and Ultraviolet–visible (UV–vis) analysis were used to investigate the crystallinity, morphology, surface and porosity characteristics, chemical composition and optical properties in more detail. The pseudocapacitive behavior of the NiO samples was investigated by cyclic voltammograms (CV) and galvanostatic charge-discharge tests in 2 M KOH. The results analysis reveals that both specific capacitance and surface area decrease with the increase of calcination temperatures. Among the NiO samples, the NiO-400 nanoflakes calcinated at 400 °C possess the highest specific capacitance of 381 F g"−"1 at a current density of 2 A g"−"1, but much lower than the Ni(OH)_2 sample. In addition, the UV–vis analysis shows that there is a red shift of absorption peak for the three NiO samples with the increasing temperature and the NiO-400 has a broad band gap of 3.3 eV, which renders the material highly interesting for application in photocatalyst.