InGaAs/GaAs量子链的光学特性研究

研究了InGaAs/GaAs量子链的稳态和瞬态光谱特性,特别是载流子的动力学过程.实验发现荧光寿命有很强的探测能量依赖关系,荧光寿命随发光能量的增加而减小;实验还发现,当激发功率较小时,荧光寿命随激发功率增大而增大,当激发功率足够大时,荧光寿命趋于饱和.这些结果清楚地表明,在量子链结构中,参与发光的载流子之间存在明显的耦合和输运现象,进一步分析表明,这种输运主要是由于载流子沿量子链方向的耦合造成的.发光的偏振特性研究进一步证实了载流子沿量子链方向输运过程. 关键词： InGaAs/GaAs 量子点 量子链     

Kink Pair in Hydrogen Bonded Systems with Symmetric Double-Well Potential

In hydrogen-bonded systems with a symmetric double-well potential, using the variational method, we study the nonlinear excitations and motion of the solitons in the presence of the optical mode of the heavy ion sublattice, based on a new two-component soliton model. We give the equations of motion and soliton-solutions in such a case. Based on these results we calculate further the energy, the momentum and the effective mass of the kink pair.     

单糖化学催化制取运输燃料

农作物秸秆和林业废弃物是资源量大、可再生的非粮生物质。它们由半纤维素、纤维素和木质素组成,源于这些生物质的单糖不仅可以经过生物催化过程制备纤维乙醇,还是化学催化法制备传统烃类运输燃料的重要平台。本文首先介绍了木质生物质酶法和酸催化法水解制备单糖的工艺特点,然后详细介绍了近几年来开发的从单糖出发制取烃类生物燃料的各种新型催化方法,如单糖直接HZSM-5分子筛催化重整制备液体烃类,以及单糖经乙酰丙酸和酯化加氢工艺、经多元醇和水相脱水加氢（APD/H）工艺、经糠醛类化合物和羟醛缩合加氢工艺、经单官能团化合物和催化提质工艺。对这些催化方法的工艺条件、催化剂组成和化学反应进行了总结评述。考虑到由单糖制备C₆以上烃类可以直接或混配为传统的液体燃料,本文对这两条工艺路线进行了重点介绍,总结了过程所发生的反应和脱氧机理,并探讨了工业化过程中需要注意的科学难题。     

On the transition from a Markov chain to a continuous time process

Starting from a real-valued Markov chain X₀,X₁,…,X_n with stationary transition probabilities, a random element {Y(t);t[0, 1]} of the function space D[0, 1] is constructed by letting Y(k/n)=X_k, k= 0,1,…,n, and assuming Y (t) constant in between. Sample tightness criteria for sequences {Y(t);t[0,1]};_n of such random elements in D[0, 1] are then given in terms of the one-step transition probabilities of the underlying Markov chains. Applications are made to Galton-Watson branching processes.     

Effect of surface oxygen complexes of sugar charcoal on the half cell potential of carbon-nickel ferrite electrodes

Carbon-nickel ferrite electrodes were prepared by pressing equal amounts of charcoals and nickel ferrite using ABS polymer (in acetone + benzene) as binder on a steel mesh. The half cell potentials reported were measured with reference to saturated calomel electrode. The electrolyte used was 4-N potassium hydroxide and fuel used was methanol. The surface oxygen complexes on the charcoals were varied (i) by heat-treating the sugar charcoal in vacuum at 400, 750 and 1000° C and (ii) by boiling in 4N.HNO₃ for different intervals of time. Half cell potential measured increases with the increase of oxygen content of the charcoals. The oxygen complex which is disposed off as carbon dioxide imparts polarity to the charcoal surface, and is largely responsible for the increase in potential.     

Sufficient conditions for ergodicity and recurrence of Markov chains on a general state space

Let {X_n} be a ?-irreducible Markov chain on an arbitrary space. Sufficient conditions are given under which the chain is ergodic or recurrent. These extend known results for chains on a countable state space. In particular, it is shown that if the space is a normed topological space, then under some continuity conditions on the transition probabilities of {X_n} the conditions for ergodicity will be met if there is a compact set K and an ? > 0 such that $\text{E}\text{{6X}{}_{\mathrm{n+1}}\text{6 — 6X}{}_{\mathrm{n}}\text{6 ∣ X}{}_{\mathrm{n}}\text{= x} ? ??}$ whenever x lies outside K and $\text{E}\text{{6X}{}_{\mathrm{n+1}}\text{6 ∣ X}{}_{\mathrm{n}}\text{=x}}$ is bounded, x ∈ K; whilst the conditions for recurrence will be met if there exists a compact K with $\text{E}\text{{6X}{}_{\mathrm{n+1}}\text{6 ? 6X}{}_{\mathrm{n}}\text{6 ∣ X}{}_{\mathrm{n}}\text{= x} ? 0}$ for all x outside K. An application to queueing theory is given.     

Adhesion of Thermoplastic Matrices with Different Molecular Weights to Fibers

The dependence of the interfacial strength in polymer-fiber systems on the molecular weight (MW) of the matrix is investigated. Adhesive joints of poly(phenylene-sulfide sulfones) and polysulfones with a steel wire 150 m in diameter and glass fibers 200-300 m in diameter are examined. The MW of both polymers was controlled during the synthesis process. The shear adhesive strength was determined by the pull-out technique. For all the systems investigated, it is shown that the adhesive strength in relation to the duration t _f of their isothermal formation is described by curves with a maximum, whose values depend on the formation temperature T _f. For each polymer with a given MW, the greatest possible of these values, called optimum and denoted by _opt, are determined. It is found that _opt increases with molecular weight. It is speculated that the effect observed stems from the different packing of polymer chains with distinct lengths in the near-surface layers.     

L estimates on functions of Markov operators

We prove L estimates for functions of Markov operators on a discrete measure space of superpolynomial volume growth.

     

Generating Uniform Random Vectors

In this paper, we study the rate of convergence of the Markov chain X _n+1=AX _n +b _n mod p, where A is an integer matrix with nonzero integer eigenvalues and {b _n } _n is a sequence of independent and identically distributed integer vectors. If _i±1 for all eigenvalues _i of A, then n=O((log p)²) steps are sufficient and n=O(log p) steps are necessary to have X _n sampling from a nearly uniform distribution. Conversely, if A has the eigenvalue ₁=±1, and _i±1 for all i1, n=O(p²) steps are necessary and sufficient.