量子点的尺寸效应及声子对激子基态结合能的影响

利用变分法研究了有很小厚度圆盘形GaAs量子点模型中激子的基态结合能,及电子-空穴间距随量子点尺寸变化的规律．考察了电子-空穴的关联明显加强时及完全束缚发生时量子点的横向尺度,初步考虑了体纵光学声子对量子点中激子基态结合能的影响,得出一些定性的结论。     

Emergent reduction of electronic state dimensionality in dense ordered Li-Be alloys

High pressure is known to influence electronic structure and crystal packing, and can in some cases even induce compound formation between elements that do not bond under ambient conditions. Here we present a computational study showing that high pressure fundamentally alters the reactivity of the light elements lithium (Li) and beryllium (Be), which are the first of the metals in the condensed state and immiscible under normal conditions. We identify four stoichiometric Li(x)Be(1-x) compounds that are stable over a range of pressures, and find that the electronic density of states of one of them displays a remarkable step-like feature near the bottom of the valence band and then remains almost constant with increasing energy. These characteristics are typical of a quasi-two-dimensional electronic structure, the emergence of which in a three-dimensional environment is rather unexpected. We attribute this observation to large size differences between the ionic cores of Li and Be: as the density increases, the Li cores start to overlap and thereby expel valence electrons into quasi-two-dimensional layers characterized by delocalized free-particle-like states in the vicinity of Be ions.     

半导体纳米环中激子的磁场效应

在有效质量近似下,采用矩阵对角化方法,研究了半导体纳米环中激子的磁场效应.研究发现半导体纳米环中激子的谐振子强度随磁通变化呈现Aharonov-Bohm振荡,振子强度的振幅随纳米环的半径增加而减少.讨论了线性、三阶非线性和总光学吸收系数随环半径和磁通的变化关系,结果表示半导体纳米环中激子的光吸收随磁通的变化显示Aharonov-Bohm效应.     

改革我国高职教育宏观管理体制的若干思考

当前我国高职教育在宏观管理体制方面还存在一些难以适应高职教育快速发展的问题,对此,必须进一步深化管理体制改革,转变职能简政放权、建立健全教育法律法规、构建现代职教体系、多渠道筹集高职教育经费、加强多元互动和有效制衡机制的建设以及提高技能人才的地位,才能使高职教育的发展迈上一个新的台阶.     

光学微腔中WSe2激子与光子耦合效应的研究

研究了300 K下,自制的法布里-珀罗(Fabry-P6rot,F-P)半导体微腔中,光场与WSe2单分子薄膜激子之间的强弱耦合作用.利用集成角分辨功能的显微荧光/白光反射光谱系统研究了样品的光学性质,并在强耦合区间内看到了激子极化激元的形成,对应的拉比分裂能量为46.7 meV.理论拟合结果跟实验现象吻合,为激子极化...     

分数阶Lorenz系统的混沌控制方法

分数阶混沌系统已经引起了人们的广泛关注,论文研究了分数阶Lorenz系统的混沌控制方法,基于分数阶线性系统平衡点渐近稳定性理论,利用反馈控制方法得到了分数阶Lorenz系统混沌控制器设计方案,结合预估校正方法设计算法进行数值仿真,验证了所得方案的有效性.     

对一个农业系统三年运行状态的剖析

本文对一个用系统工程方法建立起来的农业系统生产结构模型进行了分析和研究。文中简述了三年来系统运行的状况。模型方案经过了三年以上的实践考验并获得了经济效益,为垦区的决策者提供了决策的科学依据。凡系统必有结构。文章研究了处于系统结构中的系统各元素之间的协调的定量关系。系统结构决定了功能。系统结构愈合理,系统的总体功能就越优良。这些系统科学的概念已在石河子垦区的生产实践中得到了初步的证实.     

Spontaneous coherence in a cold exciton gas

If bosonic particles are cooled down below the temperature of quantum degeneracy, they can spontaneously form a coherent state in which individual matter waves synchronize and combine. Spontaneous coherence of matter waves forms the basis of a number of fundamental phenomena in physics, including superconductivity, superfluidity and Bose-Einstein condensation. Spontaneous coherence is the key characteristic of condensation in momentum space. Excitons--bound pairs of electrons and holes--form a model system to explore the quantum physics of cold bosons in solids. Cold exciton gases can be realized in a system of indirect excitons, which can cool down below the temperature of quantum degeneracy owing to their long lifetimes. Here we report measurements of spontaneous coherence in a gas of indirect excitons. We found that spontaneous coherence of excitons emerges in the region of the macroscopically ordered exciton state and in the region of vortices of linear polarization. The coherence length in these regions is much larger than in a classical gas, indicating a coherent state with a much narrower than classical exciton distribution in momentum space, characteristic of a condensate. A pattern of extended spontaneous coherence is correlated with a pattern of spontaneous polarization, revealing the properties of a multicomponent coherent state. We also observed phase singularities in the coherent exciton gas. All these phenomena emerge when the exciton gas is cooled below a few kelvin.     

Transition from hyper-chaotic state to quasi-steady state in a spailally distributed nonlinear system

The dynamic characteristic in a spatially distributed nonlinear system, a subset of lasers in an array of coupled lasers, has been studied and analysed numerically. The evolution, with the increasing coupling strength, from stable quiescent state to chaotic state, to hyper-chaotic state and, back to quasi-steady state has been observed in this system. Yao Duanzheng: born in Aug. 1946, Associate professor. Current reseach interest is in mathematical physics and nonlinear optics Supported by the National Natural Science Foundation of China     

Spin-dependent exciton formation in pi-conjugated compounds.

The efficiency of light-emitting diodes (LEDs) made from organic semiconductors is determined by the fraction of injected electrons and holes that recombine to form emissive spin-singlet states rather than non-emissive spin-triplet states. If the process by which these states form is spin-independent, the maximum efficiency of organic LEDs will be limited to 25 per cent. But recent reports have indicated fractions of emissive singlet states ranging from 22 to 63 per cent, and the reason for this variation remains unclear. Here we determine the absolute fraction of singlet states generated in a platinum-containing conjugated polymer and its corresponding monomer. The spin-orbit coupling introduced by the platinum atom allows triplet-state emission, so optically and electrically generated luminescence from both singlet and triplet states can be compared directly. We find an average singlet generation fraction of 22 +/- 1 per cent for the monomer, but 57 +/- 4 per cent for the polymer. This suggests that recombination is spin-independent for the monomer, but that a spin-dependent process, favouring singlet formation, is effective in the polymer. We suggest that this process is a consequence of the exchange interaction, which will operate on overlapping electron and hole wavefunctions on the same polymer chain at their capture radius.     

电力系统发电机电气状态监测与故障诊断系统

主要论述在电力系统中如何实现对发电机定子的在线监测与故障诊断,从而提高整个电力系统的安全性和可靠性。通过把采集到的数据结果实时送入微型计算机,经数据库及专家系统诊断、分析,在出现异常时报警并发出指令,通过执行机构自动校正实现综合性的监测与诊断。系统可以保证发电机的安全、经济运行,提高经济效益和社会效益。     

双层量子点中的带负电荷激子

利用精确对角化方法,研究了抛物势双层量子点中带负电荷激子的1S态和3P态的关联能与量子点的束缚势大小的变化关系,以及1S态对应几个不同的量子点间点与点的距离的束缚能随束缚势大小的变化关系,计算了电子与空穴质量比为σ=0.677和σ=0.197的缚能随束缚势大小的变化关系.     

带有可追加订购和季节性销售的报童问题

商品作为使用价值存在一定的时间限制,尤其是季节性的单周期销售商品,如果在一定时间内第一次订购量不足,应进行追加订购,在一定时期内没有卖掉的商品应进行降价销售,最后没有销售掉的商品,则按残价处理,使零售商获得最大的期望利润.从追加订购和季节性销售两个方面考虑, 求解一个最佳订购量,使新模型的收益达到最大,通过研究,我们发现新模型比经典报童模型、或一次订购二次降价销售的报童模型、或可追加订购的报童模型的收益均有较大的提高,同时还分析了模型的灵敏度及服务水平.     

时滞独立状态下离散控制系统的稳定性分析

针对一类系统矩阵中含有不确定性、系统状态中含有时变时滞的时滞奇异摄动不确定性综合控制系统,进行了时滞独立的稳定性分析.通过构造一种含有奇异摄动的双二次型Lyapunov泛函,推出系统渐近稳定性判据,给出鲁棒稳定区间以及奇异摄动的最小上界,继而给出相应推论.最后用数值样例说明所得方法的有效性和可行性,并展示了时滞独立情形...     

Electrophoresis of ribonucleoproteins reveals an ordered assembly pathway of yeast splicing complexes

Three splicing complexes formed with a yeast pre-messenger RNA during in vitro splicing can be resolved by non-denaturing gel electrophoresis after incubation in the presence of non-specific competitor RNA. The time course of the appearance of these complexes and their composition suggest that they represent an ordered pathway of splicing complex assembly.     

广义系统结构稳定状态反馈和极点配置

应用矩阵奇异值分解研究当m相似文献   

基于4粒子纠缠态的未知3粒子态概率量子隐形传态

使用4粒子纠缠态作为量子信道,在对4粒子纠缠态的纠缠系数方面并没有做确切要求的前提下,完成了未知3粒子纠缠态的隐形传态.在传输过程中,发送方对2对粒子进行Bell测量并公布结果,然后再对4粒子中的一个粒子作Hadamard操作之后,也对其进行测量,且将测量结果通过经典信道公布.接收方引进2个辅助粒子并实施一次控制非操作,再进行一组适当的幺正变换,便可实现未知3粒子纠缠态的概率量子隐形传态.     

The proteasome antechamber maintains substrates in an unfolded state

Eukaryotes and archaea use a protease called the proteasome that has an integral role in maintaining cellular function through the selective degradation of proteins. Proteolysis occurs in a barrel-shaped 20S core particle, which in Thermoplasma acidophilum is built from four stacked homoheptameric rings of subunits, α and β, arranged α(7)β(7)β(7)α(7) (ref. 5). These rings form three interconnected cavities, including a pair of antechambers (formed by α(7)β(7)) through which substrates are passed before degradation and a catalytic chamber (β(7)β(7)) where the peptide-bond hydrolysis reaction occurs. Although it is clear that substrates must be unfolded to enter through narrow, gated passageways (13?? in diameter) located on the α-rings, the structural and dynamical properties of substrates inside the proteasome antechamber remain unclear. Confinement in the antechamber might be expected to promote folding and thus impede proteolysis. Here we investigate the folding, stability and dynamics of three small protein substrates in the antechamber by methyl transverse-relaxation-optimized NMR spectroscopy. We show that these substrates interact actively with the antechamber walls and have drastically altered kinetic and equilibrium properties that maintain them in unstructured states so as to be accessible for hydrolysis.     

Adaptive immunity maintains occult cancer in an equilibrium state

The capacity of immunity to control and shape cancer, that is, cancer immunoediting, is the result of three processes that function either independently or in sequence: elimination (cancer immunosurveillance, in which immunity functions as an extrinsic tumour suppressor in naive hosts); equilibrium (expansion of transformed cells is held in check by immunity); and escape (tumour cell variants with dampened immunogenicity or the capacity to attenuate immune responses grow into clinically apparent cancers). Extensive experimental support now exists for the elimination and escape processes because immunodeficient mice develop more carcinogen-induced and spontaneous cancers than wild-type mice, and tumour cells from immunodeficient mice are more immunogenic than those from immunocompetent mice. In contrast, the equilibrium process was inferred largely from clinical observations, including reports of transplantation of undetected (occult) cancer from organ donor into immunosuppressed recipients. Herein we use a mouse model of primary chemical carcinogenesis and demonstrate that equilibrium occurs, is mechanistically distinguishable from elimination and escape, and that neoplastic cells in equilibrium are transformed but proliferate poorly in vivo. We also show that tumour cells in equilibrium are unedited but become edited when they spontaneously escape immune control and grow into clinically apparent tumours. These results reveal that, in addition to destroying tumour cells and sculpting tumour immunogenicity, the immune system of a naive mouse can also restrain cancer growth for extended time periods.