Solid state NMR characterisation of crystalline Na2OZrO2SiO2 phases

The NMR interactions of crystalline phases in the system Na₂O-ZrO₂-SiO₂ have been studied by a combination of static and magic angle spinning NMR methods for the first time. A full multinuclear (¹⁷O, ²³Na, ²⁹Si and ⁹¹Zr) approach has been employed that allows the phases to be clearly identified. NMR interactions such as ²⁹Si isotropic chemical shift correlate with the known structural units present. For ²³Na the different sites can often be distinguished on the basis of differing quadrupolar interactions.     

Electroluminescence from a current-emitting nanostructured silicon device

A three-dimensional silicon based nanodevice mainly consisting of two conductive silicon cantilevers was fabricated out of silicon-on-insulator material by electron beam lithography, reactive ion etching, and fluoride based wet chemical etching. One of the cantilevers is bent and sticks to the silicon substrate while the other one is freely suspended. We observed electroluminescence in the visible range when a voltage of any polarity is dropped across both levers. The measured spectra covered the range 400–950 nm peaking at about 650 nm. The current applied to the device could tune the intensity of the electroluminescence spectrum. Light powers ranging from 160 fW to some pW were measured at frequencies up to 17 kHz. The origin of the electroluminescence is discussed in comparison to porous silicon and spark-processed silicon.     

Spatiotemporal complexity of the cubic Ginzburg-Landau equation

The linear dispersive relation of the travelling-wave solution is investigated for cubic G-L equation. Moreover, the relation among the parameter c₀, the amplitude |μ_o| and the most unstable wave number q is discussed. Then convergence of an unconditionally stable, explicit pseudo-spectral scheme is proved by energy estimates. Finally, by using the proposed scheme, the chaotic attractor, bifurcation structure and asymptotic dynamics are obtained. The results show there exist two different types of chaotic attractors for the most unstable wave number q_o and was fixed the amplitude |μ_o| in the same one system.     

应用电化学方法研究α和βi(I=1,2,3)-K5SiAl(OH2)W11O39·nH2O的氧化还原性质

本文系统地研究了α和βi(i=1,2 ,3) - K5Si Al(OH2 ) W11O3 9· n H2 O的氧化还原性质 ,通过导数脉冲伏安、常规脉冲伏安确定了其氧化还原机理 ,并比较了其氧化还原性质的强弱。     

Nano- and Pico-Scale Transport Phenomena in Fluids

A new theoretical approach to describe pre-hydrodynamic stages of evolution in nonequilibrium fluids is presented. The local density, velocity, and temperature fields are expressed as integrals over Green's functions that depend on initial-state ensemble averages of dynamical quantities. For systems in which the initial states are nonuniform in only one spatial direction, explicit expressions for the Green's functions are derived in terms of initial-state ensemble averages of moments of particle displacements and products of particle velocities and particle displacements.     

Effect of surfactants in the electrochemical preparation of porous silicon

Summary Porous-silicon layers were prepared by anodic oxidation of mono- and multi-crystalline Si substrates,n ⁺ andp-doped, in aqueous HF solutions containing surfactants. The resulting samples show a bright red-orange photoluminescence: PL spectra and uniformity are analysed as a function of surfactants kind and concentration. Moreover, the results of Raman spectroscopy are discussed in terms of current theories. Paper presented at the III INSEL (Incontro Nazionale sul Silicio Emettitore di Luce), Torino, 12–13 October 1995.     

具有磁场效应的非线性Schrdinger方程组的拟谱方法

考察一类具有磁场效应的非线性Ｓｃｈｒｏｄｉｎｇｅｒ方程组的周期初值问题，构造了全离散的Ｆｏｕｒｉｅｒ拟谱格式，利用有界延拓法，证明了其格式的收敛性与稳定性，并给出了误差估计及其算法分析，为对此模型的数值分析提供了理论基础和一个有效的算法．最后，通过数值例子，检验了理论结果的可信性．     

Dealing with degeneracy in reduced gradient algorithms

Many algorithms for linearly constrained optimization problems proceed by solving a sequence of subproblems. In these subproblems, the number of variables is implicitly reduced by using the linear constraints to express certain ‘basic’ variables in terms of other variables. Difficulties may arise, however, if degeneracy is present; that is, if one or more basic variables are at lower or upper bounds. In this situation, arbitrarily small movements along a feasible search direction in the reduced problem may result in infeasibilities for basic variables in the original problem. For such cases, the search direction is typically discarded, a new reduced problem is formed and a new search direction is computed. Such a process may be extremely costly, particularly in large-scale optimization where degeneracy is likely and good search directions can be expensive to compute. This paper is concerned with a practical method for ensuring that directions that are computed in the reduced space are actually feasible in the original problem. It is based on a generalization of the ‘maximal basis’ result first introduced by Dembo and Klincewicz for large nonlinear network optimization problems. Research supported in part by NSF Grant ECS-8119513 and DOT Research Grant CT-06-0011.     

Asymmetric variational inequality problems over product sets: Applications and iterative methods

In this paper, we (i) describe how several equilibrium problems can be uniformly modelled by a finite-dimensional asymmetric variational inequality defined over a Cartesian product of sets, and (ii) investigate the local and global convergence of various iterative methods for solving such a variational inequality problem. Because of the special Cartesian product structure, these iterative methods decompose the original variational inequality problem into a sequence of simpler variational inequality subproblems in lower dimensions. The resulting decomposition schemes often have a natural interpretation as some adjustment processes. This research was based on work supported by the National Science Foundation under grant ECS 811–4571.     

Effect of ordering transformation rate on the magnetic properties of Fe–Pt-based bulk alloys

We have investigated the ordering transformation and magnetic properties of Fe_59.75Pt_39.5Nb_0.75 bulk alloys in detail by using different high-temperature homogenization treatments, different cooling rates and different low-temperature annealing treatments to obtain samples with different microstructure and different atomically ordered states. The quenching rate after the high-temperature homogenization treatment was chosen much lower than in previous investigations. In this way, we were able to obtain nanostructured bulk alloys consisting exclusively of the hard-magnetic face-centered-tetragonal phase. A high remanence ratio was obtained by profiting from the nanocomposite exchange coupling between nearest-neighbor-ordered regions. The present results are compared with results of previous investigations in which much higher cooling rates were applied. We also discussed why the present alloy systems are less suitable for the attainment of exchange spring behavior.