Methods to tune the electronic states of self-organized InAs/GaAs quantum dots

After capping InAs islands with a thin enough GaAs layer, growth interruption has been introduced. Ejected energy of self-organized InAs/GaAs quantum dots has been successfully tuned in a controlled manner by changing the thickness of GaAs capping layer and the time of growth interruption and InAs layer thickness. The photoluminescence (PL) spectra showing the shift of the peak position reveals the tuning of the electronic states of the QD system. Enhanced uniformity of Quantum dots is observed judging from the decrease of full width at half maximum of FL. Injection InAs/GaAs quantum dot lasers have been fabricated and performed on various frequencies. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Broadly Tunable Grating-Coupled External Cavity Laser With Quantum-Dot Active Region

A broadly tunable and high-power grating-coupled external cavity laser with a tuning range of more than 200 nm and a similar to 200-mW maximum output power was realized, by utilizing a gain device with the chirped multiple quantum-dot (QD) active layers and bent waveguide structure. The chirped QD active medium, which consists of QD layers with InGaAs strain-reducing layers different in thickness, is beneficial to the broadening of the material gain spectrum. The bent waveguide structure and facet antireflection coating are both effective for the suppression of inner-cavity lasing under large injection current.

Structure and properties of InAs/AlAs quantum dots for broadband emission

The InAs quantum dots (QDs) on an AlAs layer are grown on GaAs substrates by molecular beam epitaxy technique. The properties of materials and optics of such QD structures have been investigated by cross sectional transmission electron microscopy and photoluminescence (PL) techniques. It is discovered that the inhomogeneous strain filed mainly exists below InAs QDs layers in the case of no wetting layer. The full width at half maximums (FWHMs) and intensities of PL emission peaks of InAs QDs are found to be closely related to the thickness of the thin AlAs layers. The InAs QDs on an eight monolayer AlAs layer, with wide FWHMs and large integral intensity of PL emission peaks, are favorable for producing broadband QD superluminescent diodes, external-cavity QD laser with large tuning range.

数值计算软件包自适应性能优化若干关键技术及评价标准研究

为了能够充分使用计算机资源，使软件运行能够尽可能地接近计算机峰值性能，研究人员 一直在努力。一个思路是为计算机开发优秀的编译器，并使用编译器相关技术对软件进行 性能优化；作为补充，另一个思路是开发能够共用的核心软件包，通过提高核心软件包中 程序的性能提高调用核心库的软件系能。 但科学计算中针对特定的计算机平台和特定的用户问题进行性能调优仍然是一个困难的问 题。速度和可移植性是数值计算软件开发中的一对矛盾。自适应性能优化技术正是为了 解 决数值计算软件中的可移植性问题和进行自动性能优化而提出的，科学家们希望数值计 算 软件能够动态地获悉计算环境的变化以及待求解问题的特征，根据需要改变自身以适应 这些变化以及多种复杂的问题情况，并且在多种求解方法中进行决策以选择最优的解决方 法来求解问题。 本文调研了使用自适应性能优化技术的几个著名软件包：~ATLAS，~SPARSITY，~OSKI以及数字 信号处理领域的快速傅立叶变换软件包FFTW，在此基础上，重点分析和比较了自适应性能 优化的关键技术，着重介绍了矩阵乘计算、MPI通信操作、快速傅立叶变换中涉及的经验搜 索、算法选择和自动代码生成等技术在这些软件包中的应用。 在深入调研的基础上，结合实际应用需求，本文还提出了自适应性能优化过程的新的评价 指标，试图权衡优化效果和优化时间开销，并在不同的实验平台上针对ATLAS的优化过程进 行的实验和过程评价，实验表明，综合优化效果和优化开销能够有效地发现ATLAS自适应优 化过程的特征。将其应用到实际开发和调优过程中，能够在不损失性能的前提下，节省优化时间。 论文最后对HPCC测试软件包在IBM刀片机群上进行了对比测试，发现了测试平台存在的性能 瓶颈，并消除了该瓶颈。表明HPCC软件包确实可以有效的发现被测平台存在的性能瓶颈问 题。

Tunable and switchable multiwavelength fiber lasers with broadband range based on nonlinear polarization rotation technique

Switchable multiwavelength fiber laser outputs with a wide tuning range are experimentally observed in an ultralong cavity. Because of the long spooled single-mode fiber and filter effect of the cavity, multiwavelength lasers with the spacing of similar to 14.5 nm are obtained. The proposed fiber laser has the capacity of simultaneously emitting the three wavelengths. By means of adjusting the polarization controllers, the arbitrary single- and dual-wavelength operations are achieved in our laser. (C) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3485754]

Timing system of HIRFL-CSR

The national science project HIRFL-CSR has recently been officially accepted. As a cyclotron and synchotron complex, it puts some particularly high demands on the control system. There are hundreds of pieces of equipment that need to be synchronized. An integrated timing control system is built to meet these demands. The output rate and the accuracy of the controller are 16 bit/mu s. The accuracy of the time delay reaches 40 ns. The timing control system is based on a typical event distribution system, which adopts the new event generation and the distribution scheme. The scheme of the tuning control system with innovation points, the architecture and the implemented method are presented in the paper.

Geographical constraints to range-based attacks on links in complex networks

In this paper, we studied range-based attacks on links in geographically constrained scale-free networks and found that there is a continuous switching of roles of short-and long-range attacks on links when tuning the geographical constraint strength. Our results demonstrate that the geography has a significant impact on the network efficiency and security; thus one can adjust the geographical structure to optimize the robustness and the efficiency of the networks. We introduce a measurement of the impact of links on the efficiency of the network, and an effective attacking strategy is suggested

High sensitivity beam phase measurement system for isochronous cyclotron

The beam phase measurement system in the HIRFL is introduced. Based on the double-balanced mixer principle using rf-signal mixing and filtering techniques, a stable and sensitive phase measurement system has been developed. The phase history of the ion beam is detected by using a set of capacitive pick-up probes installed in the cyclotron. The phase information of the measurement is necessary for tuning to obtain a optimized isochronous magnetic field which induces to maximize the beam intensity and to optimize the beam quality. The result of the phase measurement is reliable and the accurancy reaches +/- 0.5 degrees.

Preliminary study of a niobium quarter-wave prototype cavity for a heavy-ion superconducting linac

Superconducting quarter-wave resonators, due to their compactness and their convenient shape for tuning and coupling, are very attractive for low-beta beam acceleration. In this paper, two types of cavities with different geometry have been numerically simulated: the first type with larger capacitive load in the beam line and the second type of lollipop-shape for 100 MHz, beta=0.06 beams; then the relative electromagnetic parameters and geometric sizes have been compared. It is found that the second type, whose structural design is optimized with the conical stem and shaping drift-tube, can support the better accelerating performance. At the end of the paper, some structural deformation effects on frequency shifts and appropriate solutions have been discussed.

Segmented All-Platinum Nanowires with Controlled Morphology through Manipulation of the Local Electrolyte Distribution in Fluidic Nanochannels during Electrodeposition

Synthesis of segmented all-Pt nanowires is achieved by a template-assisted method. The combination of a suitably chosen electrolyte/template system with pulse-reverse electrodeposition allows the formation of well-defined segments linked to nanowires. Manipulation of the morphology is obtained by controlling the electrokinetie effects on the local electrolyte distribution inside the nanochannels during the nanowire growth process, allowing a deviation from the continuously cylindrical geometry given by the nanoporous template. The length of the segments can be adjusted as a function of the cathodic pulse duration. Applying constant pulses leads to segments with homogeneous shape and dimensions along most of the total wire length. X-ray diffraction demonstrates that the preferred crystallite orientation of the polycrystalline wires varies with the average segment length. The results are explained considering transitions in texture formation with increasing thickness of the electrodeposit. A mechanism of segment formation is proposed based on structural characterizations. Nanowires with controlled segmented morphology are of great technological importance, because of the possibility to precisely control their substructure as a means of tuning their electrical, thermal, and optical properties. The concept we present in this work for electrodeposited platinum and track-etched polycarbonate membranes can be applied to other selected materials as well as templates and constitutes a general method to controlled nanostructuring and synthesis of shape controlled nanostructures.

新型高性能同步加速器无调谐高频腔体

在本论文中，对一种新型高性能同步加速器无调谐高频腔体进行了深入的研究。该高频腔体基于一个T型桥全通域网络，在铁氧体加载的高频谐振腔体上实现宽频带高频功率激励。虽然，新型无调谐高频腔体与常规同调型高频腔体相比，体积更小，结构更加简单。但是通过研究和实验证明，新型无调谐高频腔体可以在很宽频率通带内，激励比常规同调型高频腔体更高的高频电压，因而具有更加良好的性能。加速器高频系统研究通常分为两个领域：从加速器物理观点出发的纵向束流动力学研究和电子工程技术领域的高频电子技术研究。在本论文中，首先介绍了带电粒子高频加速的基本原理。然后，详细研究和阐述了同步加速器新型无调谐型和常规同调型两种高频腔体的性能以及高频腔体加载的铁氧体材料的特性。再次，为了更好地研究高频腔体及其相应的参数，对束流纵向动力学理论进行了详细的阐述。最后，为兰州重离子加速器冷却储存环HIRFL-CSR的实验环CSRe设计了一个新型高性能同步加速器无调谐高频腔体，利用新型无调谐高频腔体作为平顶波腔体使用，实现同步加速器高频平顶波加速技术，并且可以提高HIRFL-CSR的实验环CSRe中的具有大动量散度的次级束流的俘获效率。

分离扇加速器的物理工作—调束效率的提高和等时性优化

本论文详细地介绍了直边分离扇等时性回旋加速器的理论。结合兰州重离子加速器系统的主加速器SSC，介绍了这种加速器的等时场建立及优化的方法。编写了相关的计算程序。分析并解决了长期以来SSC在注入区附近运行调束十分困难的问题。最后进行了等时场优化的实验。第一章概述性地介绍了兰州重离子加速器装置HIRFL和SSC的注入引出系统、磁场系统及高频系统。第二章作为分析分离扇等时性回旋加速器束流轨道动力学的基础知识，介绍了具有周期磁场结构加速器的基本理论。第三章根据分离扇等时性回旋加速器的磁场周期结构还具有反射对称性特点，分析了传输矩阵元关于磁场周期结构对称点的对称性质。在此基础上讨论了束流的包络和散角沿平衡轨道的分布形态及计算方法。讨论了共振线对这种加速器的磁场结构和能量范围的限制。并计算了SSC加速质子的能量上限。第四章介绍用Kb-Kr方法建立SSC理论等时场的过程。给出了计算平衡轨道和Kb、Kr参数及扇中心线上理论等时场的方法，编写了相应的计算程序。详细地介绍了根据线圈效率和扇中心线上的理论等时场面计算SSC各线圈电流值的一种方法，根据这个方法编写了计算SSC各线圈电流值的程序。提高了SSC预置电流的准确度和自动化的程度。为等时场面优化工作做了必要的准备。分析并找出了长期以来SSC在注入区附近运行调束十分困难、花费时间长的原因。采取了解决的方法。经过一年多的运行实践证明，所采用的方法极大地提高了SSC在注入区附近运行调束的效率。最后介绍了SSC等时场优化的原理和方法并做了SSC等时场优化的实验。

Chiral synthesis on catalysts immobilized in microporous and mesoporous materials

This paper reviews the recent progress made in the asymmetric synthesis on chiral catalysts in porous materials and discusses the effects of surface and pores on enantio-selectivity (confinement effect). This paper also summarizes various approaches of immobilization of the chiral catalysts onto surfaces and into pores of solid inorganic supports such as microporous and mesoporous materials. The most important reactions surveyed for the chiral synthesis in porous materials include epoxidation. hydrogenation, hydroformylation, Aldol and Diels-Alder reactions, etc. The confinement effect originated from the surfaces and the pores turns out to be a general phenomenon. which may make the enantioselectivity increase (positive effect) or decrease (negative effect). The confinement effect becomes more pronounced particularly when the bonding between the catalyst and the surface is more rigid and the pore size is tuned to a suitable range. It is proposed that the confinement in chiral synthesis is essentially a consequence of subtle change in transition states induced by weak-interaction in pores or on surfaces. It is also anticipated that the enantioselectivity could be improved by tuning the confinement effect based on the molecular designing of the pore/surface and the immobilized catalysts according to the requirements of chiral reactions.

Separation of peptides by pressurized capillary electrochromatography

A pressurized electrochromatography (pCEC) instrument with gradient capability was used in this work for separation of peptides. Three separation modes, namely, pCEC, high-performance liquid chromatography and capillary electrophoresis can be carried out with the instrument. In pCEC mode, the mobile phase is driven by both electroosmotic flow and pressurized flow, facilitating fine-tuning in selectivity of neutral and charged species. A continuous gradient elution can be carried out conveniently on this instrument, which demonstrates that it is more powerful than isocratic pCEC for separation of complicated samples. The effects of applied voltage, supplementary pressure and ion-pairing agents on separation of peptides in gradient pCEC were investigated. The effects of flow-rate of the pump and the volume of the mixer on resolution were also evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.

Assembly of the highest connectivity Wells-Dawson polyoxometalate coordination polymer: the use of organic ligand flexibility

Through tuning the length of flexible bis(triazole) ligands and different metal ion coordination geometries, four Wells-Dawson polyoxoanion-based hybrid compounds, [Cu-6(btp)(3)(P2W18O62)] center dot 3H(2)O (1) (btp = 1,3-bis(1,2,4-triazol-1-yl)propane), [Cu-6(btb)(3)((P2W18O62) center dot 2H(2)O (2), [Cu-3(btb)(6)(P2W18O62)] center dot 6H(2)O (btb = 1,4-bis(1,2,4-triazol-1-yl)butane) (3), and [Cu-3(btx)(5.5)((P2W18O62) center dot 4H(2)O (btx = 1,6-bis(1,2,4-triazol-1-yl)hexane) (4), were synthesized and structurally characterized. in compound 1, the metal-organic motif exhibits a ladder-like chain, which is further fused by the ennead-dentate [P2W18O62](6-) anions to construct a 3D structure. In compound 2, the metal-organic motif exhibits an interesting Cu-btb grid layer, and the ennead-dentate polyoxoanions are sandwiched by two Cu-btb layers to construct a 3D structure