Generation of bismuthane in non-aqueous media

The generation of BiH₃ in non-aqueous media in an MHS-10 Perkin-Elmer hydride generator is studied. Optimal conditions for generation of BiH₃ inN,N-dimethylformamide, dimethylsulfoxide and formamide (concentration of NaBH₄, acidic medium, optimum volume, characteristic concentration and detection limit) are studied. The results obtained are compared with those corresponding to hydride generation in aqueous medium.     

本征态的局域化与增益介质中局域态的放大

用时域有限差分方法(FDTD)模拟了二维增益、非增益随机介质中的光学现象。在非增益介质中，观察到了局域态空间分布及其频率特征。在增益介质中，观察到局域态的放大过程。模拟结果显示非增益介质中的局域态相当于传统激光腔的腔模，随机激光是由局域态谐振产生的。     

Statistical topography. I. Fractal dimension of coastlines and number-area rule for Islands

Summary Statistical topography involves the study of the geometrical properties of the iso-sets (contour lines or surfaces) of a random potential (r). Previous work [1,2] has addressed coastlines on a random relief (x, y) that possess a single characteristic spatial scale with topography belonging to the universality class of the random percolation problem. In the present paper this previous analytical approach is extended to the case of a multiscale random function with a power spectrum of scales, ^H , in a wide range of wavelengths, ₀ < < _m . It is found that the pattern of the coastline differs significantly from that of a monoscale landscape provided that –3/4 <H < 1, with the case –3/4 <H < 0 corresponding to the long-range correlated percolation and 0 <H < 1 to the fractional Brownian relief. The expression for the fractal dimension of an individual coastline is derived,D _h = (10 – 3H)/7, the maximum value of whichD _h = 7/4, corresponds to the monoscale relief. The distribution functionF(a) of level lines over their sizea is calculated:F(a) a ^–4(1-H)/7, for ₀ a _m . A comparison of the theoretical results with geographical data is presented.     

Calculation of the permeability of porous media using hydrodynamic cellular automata

The permeability of two-dimensional porous media is calculated numerically as a function of porosity using the hydrodynamic cellular automata (lattice gas) approach. Results are presented for systems with up to 22 million sites (8192×2688). For randomly distributed solid obstacles whose macroscopic dimensions are much longer than the mean free path of particles in the fluid, the permeability varies with porosity as (–0.6)/(1–) for>0.7. When the solid obstacles are much smaller than the mean free path of particles in the fluid, i.e., when they form a dust of point objects, then such a relationship no longer holds and the permeability is more than an order of magnitude smaller than for the former case. The program used for the simulations is discussed and a listing is presented in the Appendix which achieved a sustained speed of 185 million sites updated per second on a single processor of the Cray-YMP. (On a Sun Sparc Workstation, the same program ran about 100 times slower.)     

Formulation of electro-chemico-osmotic processes in soils

Electrokinetic techniques have been used for various purposes including consolidation of soils, dewatering of sludges, and hazardous waste remediation among others. Estimating the feasibility of employing electro-osmosis in a particular operation depends on the ability to predict the outcome under a variety of conditions. Predictions of this type are frequently facilitated by the use of a mathematical model designed to represent the physical system under consideration in a rigorous fashion. First, a review of fundamental aspects of electro-chemico-osmotic flow in soils is presented. Following a brief outline of previous studies, identification and quantification of the significant processes, and the construction of mathematical representations are given. This is achieved using an approach based on the macroscopic conservation of mass equations and the principle of a continuum, in contrast to an approach based on the irreversible thermodynamics of coupled flows. Special emphasis is given to coupling effects on transport processes. A complete model and associated boundary conditions are then obtained for electrokinetic processes in a compressible porous medium. The proposed model takes into consideration the migration of a contaminant plume in a flow field generated by an applied electric potential.Symbols a _v soil compressibility - A an entity - C _w mass fraction of water component in the water phase - C _s mass fraction of chemical component in the water phase - C ^* capacitance of the porous medium per unit volume of porous volume - D mechanical dispersion coefficient - D _fw ^ps hydrodynamic diffusion tensor for the chemical component in the water phase - D _fw ^pw hydrodynamic dispersion coefficient for the water component in the water phase - D _f( )/Dt material derivative with respect to an observer moving at the water phase velocity V _f - D _s( )/Dt material derivative with respect to moving solids - e void ratio - f a function - F = 0 equation of a moving boundary - g gravitational acceleration - k permeability tensor of the porous medium - k _e coefficient of electro-osmotic permeability - k _ec coefficient of migration potential - k _hc chemico-osmotic coupling coefficient - m _i number of moles of the ith component - m _i0 number of moles of the ith component at a reference level - n porosity - p pore pressure - p _oi pore pressure at a reverence level - q specific discharge of water phase - q _e current density - q _fe ^p0 constant current density applied at a boundary - q ₀ constant flow rate - q _r specific discharge of the water phase relative to the moving solid matrix - R net mass transfer rate of the chemical component in the water phase - t time - u velocity of a moving surface - _i partial molar density of ith component - V _f velocity of the water phase - V _s velocity of the solid (rate of deformation) - x vertical coordinate - coefficient of matrix compressibility - _p compressibility of water phase in motion - total (overburden) stress tensor - effective stress tensor - _h streaming current conductivity - _e electrical conductivity - electrical potential - _f viscosity of the water phase - _hf density of the water phase     

Microscopic-based fluid flow invasion simulations

A microscopic method for the generation of invasion percolation structures using armies of interacting random walkers is presented. Two distinct species are used to simulate the invading and defending fluids of a fluid invasion process. Trapping of the defending species is accomplished purely by local rules, without the need to repetitively check the connection between the to be displaced defender phase and the sink.     

Ni和P微量掺杂的Pd基催化剂对碱性介质中乙醇电氧化性能的增强效应研究

保证催化剂质量活性（通常以贵金属质量为计量）的基础上,减小催化剂中助催化剂的用量可有效降低燃料电池膜电极组（MEA）催化剂层的厚度,从而提高贵金属利用率和增大放电电压.于此,本文以微量NaH₂PO₂作为还原剂,适当调节合成溶液的碱度,成功制备了助催化剂Ni和P的掺杂量分别低至0.2%（w）和0.05%（w）的三元碳载Pd-Ni-P纳米合金催化剂.所得催化剂在0.5 mol/L CH₃CH₂OH＋1 mol/L NaOH溶液中的循环伏安表征显示,质量活性最高可达到2466 mA•mg^-1 Pd,是商业化Pd/C催化剂的2.7倍;同时,计时电流法测试表明,该催化剂的稳定性相对于商业化催化剂提升了2.8倍.这说明所得低掺杂型Pd-Ni-P催化剂达到了上述设计要求.本工作可能为燃料电池高效低成本阳极催化剂设计制备提供新的思路.     

Ergodic theorems arising in correlation dimension estimation

The Grassberger-Procaccia (GP) empirical spatial correlation integral, which plays an important role in dimension estimation, is the proportion of pairs of points in a segment of an orbit of lengthn, of a dynamical system defined on a metric space, which are no more than a distancer apart. It is used as an estimator of the GP spatial correlation integral, which is the probability that two points sampled independently from an invariant measure of the system are no more than a distancer apart. It has recently been proven, for the case of an ergodic dynamical system defined on a separable metric spaceythat the GP empirical correlation integral converges a.s. to the GP correlation integral at continuity points of the latter asn. It is shown here that for ergodic systems defined on ^d with the max metric the convergence is uniform inr. Further, a simplified proof based on weak convergence arguments of the result in separable spaces is given. Finally, the Glivenko-Cantelli theorem is used to obtain ergodic theorems for both the moment estimators and least square estimators of correlation dimension.