Electronic structure and optical property of semiconductor nanocrystallites

Semiconductor nanostructures show many special physical properties associated with quantum confinement effects, and have many applications in the opto-electronic and microelectronic fields. However, it is difficult to calculate their electronic states by the ordinary plane wave or linear combination of atomic orbital methods. In this paper, we review some of our works in this field, including semiconductor clusters, self-assembled quantum dots, and diluted magnetic semiconductor quantum dots. In semiconductor clusters we introduce energy bands and effective-mass Hamiltonian of wurtzite structure semiconductors, electronic structures and optical properties of spherical clusters, ellipsoidal clusters, and nanowires. In self-assembled quantum dots we introduce electronic structures and transport properties of quantum rings and quantum dots, and resonant tunneling of 3-dimensional quantum dots. In diluted magnetic semiconductor quantum dots we introduce magnetic-optical properties, and magnetic field tuning of the effective g factor in a diluted magnetic semiconductor quantum dot. (C) 2004 Elsevier B.V. All rights reserved.

模型论在代数上的应用

给出了模型论在代数上的两个应用,得到了下列定理:定理A:如环R的任何有限生成子环均是局部环,则R是局部环.定理B:存在自然数的真扩张R使其具有下列特征:(1)虽然R有无限多零因子,但R中有无限多零因子,但R中的首1多项式的根的个数可以得到很好的控制.(2)R不仅将自然数的素数特征保留下来,而且还可在其上定义指数函数。

东北农田生态系统排放CH_4和N_2O的研究

本文首次对我国东北地区稻田和旱田（大豆田）中甲烷（CH_4）和氧化亚氮(N_2O)的排放通量进行观测,研究了环境因素对这两种温室效应气体排放的影响。观测结果表明：稻田在作物生长季节是CH_4的排放源(source)，作物被收割之后则成为甲烷的汇(sink)。在作物生长季，稻田的CH_4排放通量变化在2.41-26.1mgCH_4/m~2·h之间，平均通量为14.82mgCH_4/m~2·h。稻田N_2O通量在-116.89-100.69μgN_2O/m~2·h间变化，平均通量为-6.36 μg/m~2·h。旱田完全是N_2O的排放源，通量在3.99-332.3 μg N_2O/m~2·h之间变化，平均通量是88.54 μgN_2O/m~2·h。旱田主要表现为甲烷的汇。稻田中甲烷主要在0-5cm土层中产生。水稻和大豆分别对CH_4和N_2O的排放起着重要作用。稻田甲烷排放通量与温度(特别是气温)有极显著的正相关性，也与土壤中硝态氮含量呈显著正相关／旱田甲烷排放通量与土壤中铵态氮浓度呈显著负相关，而N_2O通量则与铵态氮浓度呈正相关，但有3-4天的时间滞后现象。旱田甲烷和氧化亚氮的排放受土壤含水量的影响。本文还讨论了实验室条件下施肥对稻田土壤CH_4产生作用的影响。厩肥的施入影响较弱，而稻杆的影响则十分强烈。尿素也促进CH_4的产生。100和200μg/g(土)的尿素加入量增大了产甲烷速率和甲烷产量；300μg/g(土)的尿素加入量没有增大产甲烷速率，却延长产甲烷时间，使甲烷产量增加更多。土壤中CH_4和N_2O的产生过程之间似乎呈相互消长关系。