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[en] Despite remarkable progress, lithium ion batteries still need higher energy density and better cycle life for consumer electronics, electric drive vehicles and large-scale renewable energy storage applications. Silicon has recently been explored as a promising anode material for high energy batteries; however, attaining long cycle life remains a significant challenge due to materials pulverization during cycling and an unstable solid-electrolyte interphase. Here, we report double-walled silicon nanotube electrodes that can cycle over 6000 times while retaining more than 85% of the initial capacity. This excellent performance is due to the unique double-walled structure in which the outer silicon oxide wall confines the inner silicon wall to expand only inward during lithiation, resulting in a stable solid-electrolyte interphase. This structural concept is general and could be extended to other battery materials that undergo large volume changes.
[en] Precipitation processes were developed to introduce second phases as flux pinning centers in Gd-Ba-Cu-O and Nd-Ba-Cu-O superconductors. In Gd-Ba-Cu-O, precipitation is caused by the decrease of the upper solubility limit of Gd1+xBa2-xCu3O7 solid solution (Gd123ss) in low oxygen partial pressure. Processing of supersaturated Gd1.2Ba1.8Cu3O7 in low oxygen partial pressure can produce dispersed second phases. Gd211 is formed as a separate phase while extensive Gd124 type stacking fault is formed instead of a separate CuO phase. As a result of the precipitation reaction, the transition temperature and critical current density are increased. In Nd-Ba-Cu-O, precipitation is caused by the decrease of the lower solubility limit of Nd1+xBa2-xCu3O7 solid solution (Nd123ss) in oxygen. DTA results reveal the relative stability of Nd123ss in different oxygen partial pressures. In 1 bar oxygen partial pressure, Nd123ss with x = 0.1 is the most stable phase. In lower oxygen partial pressures, the most stable composition shifts towards the stoichiometric composition. The relative stability changes faster with decreasing oxygen partial pressure. Therefore, processing in oxygen and air tends to produce broad superconducting transitions but sharp transitions can be achieved in 0.01 bar and 0.001 bar oxygen partial pressures. While the lower solubility limits in 0.01 bar and 0.001 bar oxygen partial pressures remain at x = 0.00, the solubility limits in oxygen and air show a narrowing with decreasing temperature. Because of the narrowing of the solubility range in oxygen, oxygen annealing of Nd123 initially processed in low oxygen partial pressures will result in precipitation of second phases. The equilibrium second phase is BaCuO2 for temperature above 608 C, and at lower temperatures the equilibrium second phases are Ba2CuO3.3 and Ba2Cu3O5+y. However, annealing at low temperature may produce a fine metastable transition phase. A coherent intermediate perovskite structure with a composition of BaCuO2 is observed along with a high density of dislocations during the precipitation process at 500 C in oxygen. It is believed that oxygen annealing at 900 C produces the equilibrium BaCuO2 phase. These precipitates are responsible for the strong flux pinning in Nd123 melt-textured in low oxygen partial pressure
[en] A uniform and stable relativistic electron sheet can be generated by the two-layer target scheme, where a linearly polarized drive laser is originally employed. The energy and density of the electron layer are found to be sensitive to carrier-envelope phases of few-cycle laser pulses. To circumvent this problem, the present letter proposes to use a circularly polarized laser. The produced electron layer becomes completely independent of the phase of the laser, avoiding the rigorous requirement for phase stabilization in an ultra-intense few-cycle laser system. The improved scheme makes coherent x-ray sources based on relativistic electron sheets more attainable.
[en] The Bayesian system reliability assessment under fuzzy environments is proposed in this paper. In order to apply the Bayesian approach, the fuzzy parameters are assumed as fuzzy random variables with fuzzy prior distributions. The (conventional) Bayes estimation method will be used to create the fuzzy Bayes point estimator of system reliability by invoking the well-known theorem called 'Resolution Identity' in fuzzy sets theory. On the other hand, we also provide the computational procedures to evaluate the membership degree of any given Bayes point estimate of system reliability. In order to achieve this purpose, we transform the original problem into a nonlinear programming problem. This nonlinear programming problem is then divided into four subproblems for the purpose of simplifying computation. Finally, the subproblems can be solved by using any commercial optimizers, e.g. GAMS or LINGO
[en] The shell-model approach played a fundamental role in our early understanding of atoms and nuclei; in nuclear physics in particular, it has provided us with our best understanding of the sd shell nuclei. As a numerical scheme, it has achieved considerable successes in both nuclear and atomic physics. In nuclear physics, it becomes diffiult to apply for nucleo beyond the sd shell. For these nuclei we may well require a rethinking of the shell-model philosophy in which the collective subspace will be the aim of the calculations. The FDUO code, which we will describe below is representative of this new trend in shell-model studies. It is designed to study nuclear collective behavior in a pair-truncated fermion space and yet it is implemented in a full shell-model-style algorithm. Furthermore it has already been successfully applied to medium and heavy nuclei to fit data. An added virtue for the purpose of this chapter is that the FDUO code is relatively short compared with the usual shell-model codes. We first describe some of the shell-model codes currently used in nuclear physics; we briefly indicate the methodology used in these codes as well a point out some advantages and disadvantages of each. We then describe in some detail the FDUO code finally we give a brief tutorial in the use of this code and provide specific examples. (orig./HSI)
[en] The Hausdorff dimension of closed invariant sets under diffeomorphism is an interesting concept as it is a measure of their complexity. The theory of holomorphic dynamical systems provides us with many examples of fractal sets, and in particular, a theorem of Ruelle [Ru1] shows that the Hausdorff dimension of the Julia set depends real analytically on f if f is a rational function of C and the Julia set of J of f is hyperbolic. In this paper we generalize Ruelle's result for complex dimensional 2 and show the real analytic dependence of the Hausdorff dimension of the corresponding Julia sets of hyperbolic Henon mappings. (author). 22 refs
[en] Time series modelling has been shown to be an effective tool for analyzing data from macroeconomics and finance. There seems to be an increased interest to extend univariate models to multivariate case in various application domains. This paper provides an overview of the most important development in parametric multivariate long memory time series modelling, with estimation mainly based on a Gaussian likelihood. It discusses the model specification and estimation methodology for vector autoregressive fractionally integrated moving average (VARFIMA) model and vector Gegenbauer ARMA (VGARMA) model, in both methodology and empirical applications. It standardizes the state space representation of multivariate time series models and presents the simulation results of quasi-maximum likelihood estimator via Kalman filter. The performance of different estimation methods in both time domain and frequency domain are also compared. Finally, the likely directions of future research are identified.
[en] FeCrAl/Al2O3 and FeCrAlY/Al2O3 interfaces were formed by sputter deposition of alloy thin films on A-plane sapphire substrates. The microstructure of both Y-containing and Y-free films consisted of single-phase BCC columnar grains of fairly uniform composition across the film thickness. Both films exhibited a high degree of <110> texture along the growth direction normal to the interface with no preferred in-plane orientation. In both cases, a thin amorphous layer was observed at the interface in the as-deposited state. Annealing the films for 16 h at 850 deg. C improved the crystalline quality of the film/substrate interface and led to grain growth within the films. The annealing did not lead to any significant changes in the film composition in the Y-free film. In the Y-containing film, yttrium oxide precipitates formed in the near interface region, depleting the adjacent alloy matrix of Y completely; accompanied by a significant enhancement of Al in the film, very close to the interface
[en] The interfacial strengths of the FeCrAl/Al2O3 and FeCrAlY/Al2O3 interfaces in both as-deposited and annealed state were measured quantitatively by the laser spallation technique. The results show that in the as-deposited state, the presence of Y significantly improved the interfacial strength from 330±31 to 686±36 MPa. However, after annealing the films at 850 deg. C for 16 h, the interfacial strength of the Y-free samples increased to 545±68 MPa, while the interfacial strength of Y-containing sample decreased to 599±22 MPa. The increase in the interfacial strength of the Y-free films was attributed to an improvement in the crystalline quality of the interface. The decrease in interfacial strength of the annealed Y-containing film in spite of the improvement in the crystalline quality of the interface was attributed to the depletion of Y at the interface due to formation of yttrium oxide precipitates. This is further proved that the presence of Y improves the strength of FeCrAl/Al2O3 interfaces significantly