High-Density Effects on the Exciton Systems and Their Dynamical Behavior in Al x Ga 1− x As/AlAs Quantum Wires

In Al x Ga 1 m x As/AlAs quantum wire (QWR) structures, the lower lying indirect exciton (IE) photoluminescence (PL) peak shows remarkable blue-shift under intense light-excitation contrary to the higher lying direct exciton (DE) PL band with very small blue-shift, although the two kinds of exciton states consist of the common hole state. In time-resolved PL spectra in the type-II QWR of x = 0.4, the DE PL band appears at an earlier stage without peak-shift and the excitons relax to the IE state making the IE PL peak dominant with time evolution. The blue-shift of the IE peak in a quasi equilibrium after the relaxation seriously depends on the excitation density. The origin of the blue-shift is explained in terms of many-body effects including band-bending effect due to the electric field induced by spatially separated electrons and holes in the QWR structures.     

Phase instabilities in small particles

In this review we consider the existing theories for the structure of small particles and the nature of morphological instabilities as the size is reduced. The various electron microscopic observations confirming the stability of a new phase, the so called ‘Multiply twinned structure’, in small particles is discussed. A theoretical model is presented to calculate the free energy surfaces for a series of asymmetric and single crystal structures using a modified Curie-Wulff construction for the surface energy, and a disclination model for the elastic strain energy. Depending on the activation barrier heights and the Boltzmann occupancy factors for the various local minima on the energy surface, the idea of ‘quasi-melting’ is introduced and compared with the structural instabilities in molecular clusters seen recently by various authors using computer simulations. A phase diagram for small particles as a function of size and temperature is presented and the effect of statistical fluctuations on stability is discussed. Finally a phenomenological discussion relating the phase instabilities to various melting and related phase transitions is given.     

Fixed equilibria of point vortices in symmetric multiply connected domains

The paper provides symmetric fixed configurations of point vortices in multiply connected domains in the unit circle with many circular obstacles. When the circular domain is invariant with respect to rotation around the origin by a degree of 2π/M, a regular M-polygonal ring configuration of identical point vortices becomes a fixed equilibrium. On the other hand, when we assume a special symmetry, called the folding symmetry, on the circular domain, we find a fixed equilibrium in which M point vortices with the positive unit strength and M point vortices with the negative unit strength are arranged alternately at the vertices of a 2M-polygon. We also investigate the stability of these fixed equilibria and their bifurcation for a special circular domain with the rotational symmetry as well as the folding symmetry. Furthermore, we discuss fixed equilibria in non-circular multiply connected domains with the same symmetries. We give sufficient conditions for the conformal mappings, by which fixed equilibria in the circular domains are mapped to those in the general multiply connected domains. Some examples of such conformal mappings are also provided.     

Radiative recombination of indirect exciton in type-II ZnSeTe/ZnSe multiple quantum wells

The tunability of the emission energy, oscillator strength and photoluminescence (PL) efficiency by varying the well thickness and excitation density was demonstrated in the ZnSe_0.8Te_0.2/ZnSe multiple quantum wells. A significant blueshift about 260 meV of the PL peak energy was observed as the well width decreased from 5 to 1 nm. An extraordinary long lifetime (300 ns) of the recombination for the widest sample was detected. The binding energy of the indirect excitons is determined as 12 meV for the thinnest sample. The reduction of PL efficiency by thermal energy is greatly suppressed by employing a high excitation power.     

Synthesis and characterization of Zn3P2/ZnS core/shell nanowires

Fully-surrounded Zn₃P₂/ZnS core/shell nanowires (NWs) were synthesized for the first time via a two-step method: a catalyst free chemical vapor deposition followed by a low-pressure vulcanization process. Field emission scanning electron microscopy, high-resolution transmission electron microscopy, and high-angle angular dark field scanning transmission electron microscopy were used to characterize the morphologies, crystal structure, and element composition of the core/shell NWs. The band structure analysis demonstrates that the Zn₃P₂/ZnS core-shell NW type-II heterostructures have bright potential in photovoltaic nanodevice applications. The core/shell NW growth method used here can be extended to other material system.     

Antimonide Type-II “W” Photodiodes with Long-Wave Infrared <Emphasis Type="Italic">R</Emphasis><Subscript>0</Subscript><Emphasis Type="Italic">A</Emphasis> Comparable to HgCdTe

The recent development of graded-gap W-structured superlattices (GG-Ws) has led to a substantial improvement in the dark current performance of infrared photodiodes implemented with type-II superlattices (T2SLs). A study of ten GG-W photodiode wafers with 50% power responsivity cutoffs from 9 μm to 13.4 μm is presented. Dark current performance has increased by a factor of 10 over that of previous type-II structures, without degrading quantum efficiency. In relation to HgCdTe (MCT) based photodiodes, several samples in the study show effective dynamic-resistance-area products close to the MCT trend line for diffusion-limited R ₀ A.     

Estimation for Entropy and Parameters of Generalized Bilal Distribution under Adaptive Type II Progressive Hybrid Censoring Scheme

Entropy measures the uncertainty associated with a random variable. It has important applications in cybernetics, probability theory, astrophysics, life sciences and other fields. Recently, many authors focused on the estimation of entropy with different life distributions. However, the estimation of entropy for the generalized Bilal (GB) distribution has not yet been involved. In this paper, we consider the estimation of the entropy and the parameters with GB distribution based on adaptive Type-II progressive hybrid censored data. Maximum likelihood estimation of the entropy and the parameters are obtained using the Newton–Raphson iteration method. Bayesian estimations under different loss functions are provided with the help of Lindley’s approximation. The approximate confidence interval and the Bayesian credible interval of the parameters and entropy are obtained by using the delta and Markov chain Monte Carlo (MCMC) methods, respectively. Monte Carlo simulation studies are carried out to observe the performances of the different point and interval estimations. Finally, a real data set has been analyzed for illustrative purposes.     

纳秒激光电离分子团簇产生高价离子实验研究

 利用飞行时间质谱仪，研究了功率密度为10⁹~10¹¹ W/cm²，波长为532 nm 的纳秒激光对苯、呋喃、甲醇及碘甲烷分子团簇的激光电离过程。实验观察到了高平动能的高价离子C^q+(q≤3)，O^q+(q≤3)和I^q+(q≤4)，该过程经历了以“初始的多光子电离引发-逆轫致吸收加热-电子碰撞电离模式”为主的激光团簇作用过程，后期经历了团簇的库仑爆炸过程。实验发现：即使激光能量变化一个量级以上时，主要高价离子的种类及占全部离子产物的比率也没有明显的变化，但是高价离子的初始平动能随激光强度的增大而增加；分子中含有较多个外壳层电子的氧、碘原子更容易电离产生高价离子，而碳离子的价态和强度相对较低。     

一种求解时变双线性系统的新方法

本文给出了移位雅可比多项式的乘积运算矩阵,利用该矩阵,将时变双线性系统的状态方程等效变换成一个矩阵代数方程,使其计算量大为减少.通过对实例的计算,获得了令人满意的结果.     

Matrix-assisted ionization vacuum for protein detection,fragmentation and PTM analysis on a high resolution linear ion trap-orbitrap platform

Matrix-assisted ionization vacuum (MAIV) is a novel ionization technique that generates multiply charged ions in vacuum without the use of laser ablation or high voltage. MAIV can be achieved in intermediate-vacuum and high-vacuum matrix-assisted laser desorption/ionization (MALDI) sources and electrospray ionization (ESI) sources without instrument modification. Herein, we adapt MAIV onto the MALDI-LTQ-Orbitrap XL platform for biomolecule analysis. As an attractive alternative to MALDI for in solution and in situ analysis of biomolecules, MAIV coupling to high resolution and accurate mass (HRAM) MS instrument has successfully expanded the mass detection range and improved the fragmentation efficiency due to the generation of multiply charged ions. Additionally, the softness of MAIV enables potential application in labile post-translational modification (PTM) analysis. In this study, proteins as large as 18.7 kDa were detected with up to 18 charges; intact peptides with labile PTM were well preserved during the ionization process and characterized MS/MS; peptides and proteins in complex tissue samples were detected and identified both in liquid extracts and in situ. Moreover, we demonstrated that this method facilitates MS/MS analysis with improved fragmentation efficiency compared to MALDI-MS/MS.