p型掺杂1.3μm InAs/GaAs量子点激光器的最大模式增益特性的研究

对p型掺杂13 μm InAs/GaAs量子点激光器的最大模式增益进行了实验和理论分析.实验上,测量了不同腔长激光器阈值电流密度与总损耗的对应关系,拟合出的最大模式增益为175 cm^-1,与相同结构非掺杂量子点激光器的最大模式增益一致.同时理论分析表明,p型掺杂对InAs/GaAs量子点激光器的最大模式增益并无影响,并且最大模式增益的计算结果与实验值相符.具有较小高度或高宽比的量子点能达到更高的最大模式增益,而较高的最大模式增益对p型掺杂13 μm InAs/GaAs自组织量子点激光器在光通信系统中的应用具有重要意义. 关键词： 最大模式增益 p型掺杂 InAs/GaAs量子点激光器     

电光双稳态系统的混沌控制与同步

根据长延时状态下电光双稳系统的特点,提出了实现其混沌控制与同步的具体方案.数值模拟的结果表明：适当选取驱动强度及驱动系统的状态,不仅可以实现对响应系统不同周期状态的稳定控制,还可以实现驱动系统与响应系统间的广义混沌同步.以最大李雅普诺夫指数为标准,给出了实现混沌同步的参数范围.     

质子数Z 分别位于Ru 之上和之下的A~(100~126) 丰中子原子核三轴形变在原子核形状变迁和共存中的重要作用(英文)

基于Ru (Z = 44) 丰中子同位素中存在最大三轴形变的理论预言和实验证据,综述了近年来Rh (Z = 45),Pd (Z =46), Ag (Z =47), Cd (Z =48)(质子数Z 位于Ru,Z =44 之上)及Zr (Z =40), Nb (Z =41), Mo (Z =42),Tc (Z =43)(质子数Z 位于Ru,Z =44 之下) 的A~ (100~126) 丰中子同位素中关于三轴形变的形状变迁和形状共存系统性研究的重要进展。252Cf 自发裂变瞬发 射线-- 三重符合、特别是新建立的--- 四重符合数据的系统观测和研究,在Ru, Pd, Cd 和Nb 丰中子同位素中显著扩展或首次观测到了一系列能带,为这个核区原子核形状的研究提供了新的、重要的实验数据。联系此前报道的有关进展,使用PES, TRS, PSM, CCCSM 和SCTAC 理论模型计算拟合新的实验数据,在该核区沿同中素和同位素链,并随自旋和激发能变化各自由度,跟踪原子核形状渐进变化,获得了新的系统性研究成果,显著扩展和深化了人们对原子核形状变迁和形状共存的认知。对于Ru 及其上的Rh (Z = 45), Pd (Z = 46), Ag (Z = 47) 和Cd (Z = 48) 丰中子同位素的研究表明:Rh 丰中子核具有比最大值稍小的三轴形变,γ = 28°,并在103{106Rh 同位素链上鉴别出了手征对称破缺;在三轴形变核112Ru和114Pd(N = 68)中发现了三轴原子核的摆动运动,该摆动运动也可能在114Ru (N = 70)中存在;观察到了从具有最大三轴形变的110,112Ru 中手征破缺到稍小三轴形变的112,114,116Pd 中扰动的手征破缺的过渡;在较软的Ag 核中观察到了丰富的谱学结构,在104,105Ag 中鉴别出了可能的手征对称破缺,在较重的115,117Ag 中提出了趋于三轴形变的软度;具有小形变的Cd核的能级结构被解释为准粒子耦合、准转动和软三轴形变;最近的库伦激发的研究提供了Z = 50, N = 82满壳附近122,124,126Cd 核中出现核集体性的实验和理论证据;上述研究成果展现出从Ru中的最大三轴形变(γ=30°,三轴形变极小增益为0.67 MeV), 经具有大三轴形变的Rh核γ=28°),到Pd核中的稍小、但稳定于中等自旋到高自旋区的三轴形变(γ~41°,三轴形变极小增益为0.32 MeV),再经Ag核中的软度,最后到具有很小形变、但仍出现集体性质、包括软三轴形变的Cd核的过渡。对于Pd核转动带交叉系统性的研究揭示了其第一带交叉(νh_11/2)2 中子转动顺排的上行驱动,和第二带交叉(πg_9/2)2质子转动顺排的下行驱动效应,成功地解释了114Pd 中的三轴摆动运动,并给出了110-118Pd同位素链中理论早已预言、而比早期理论预言更为完整准确的形状渐进变迁和形状共存的图像。根据该核区的系统研究,发现最大三轴形变出现在112Ru,而在相邻的偶Z(Pd)同位素链,三轴形变极小的中心在114Pd, 两者均为N = 68。上述系统性研究沿相邻的Ru和Pd偶Z同位素链,在N =68同中素中鉴别出最大三轴形变,均比理论预言的108Ru 和110Pd 多4个中子。在Z值位于Ru (Z = 44) 之下的Zr (Z = 40), Nb (Z = 41), Mo (Z = 42) and Tc (Z = 43) 丰中子同位素中,Y和Zr核具有很强的轴对称四极形变,而在较重的Zr同位素中出现了自由度;较重的Nb核(A = 104~106) 基态具有中等程度的软三轴形变和强四极形变,随着自旋和激发能的增加,过渡到接近于轴对称的强四极形变;而较轻的Nb核(A≤103) 基态均接近轴对称形状;在Nb同位素链上基态由球形到强四极形变的形状突变发生在100Nb(N = 59),在100-106Nb同位素链中基态的软三轴形变随中子数增加而增加;在Nb核中还观察到关于软三轴形变的形状共存;Mo核具有大的三轴形变,观察到了振动和手征对称破缺;Tc核具有比最大值稍小的三轴形变,γ=26°,并观察到了手征对称破缺。质子数Z从41到48的A~(100~126)丰中子同位素,特别是Pd和Nb 同位素,呈现出关于三轴形变的过渡特征。This paper reviews the systematic investigations and understanding for the shape transitions and coexistence with regard to triaxial deformations in A s 100 to 126 neutron-rich Rh (Z = 45), Pd (Z = 46), Ag (Z = 47), Cd (Z = 48) and Zr (Z = 40), Nb (Z = 41), Mo (Z = 42), Tc (Z = 43) isotopes with Z beyond and below Ru (Z = 44), respectively, in Ru the maximal triaxial deformation having been predicted and deduced. The recent measurements and studies of prompt triple- and four-fold, γ-γ-γ and γ-γ-γ-γ, coincidence data from the spontaneous fission of 252Cf using Gammasphere have yielded considerable expansion and extension or first observation of the bands in Ru, Pd, Cd, and Nb isotopes,which provided important data for the studies of nuclear shapes in this region. Combined with previous investigations, recent systematic studies of the new data well reproduced by PES, TRS, PSM, CCCSM and SCTAC model calculations have traced shape changes along the isotonic and isotopic chains, respectively,and with changing excitations/spins as well, significantly expanding our knowledge of shape transitions/coexistence in nuclei.For the neutron-rich Ru and beyond, Rh, Pd, Ag and Cd isotopes, triaxial deformations γ= 28°,slightly smaller than the maximal value, were deduced in Rh (Z = 45) isotopes, with chiral symmetry breaking proposed in 103-106Rh; onset of wobbling motions were identified in 112Ru and 114Pd (N =68),and probably also in 114Ru (N =70); evolution from chiral symmetry breaking in 110,112Ru with maximal triaxial deformations to disturbed chirality in 112,114,116Pd with less pronounced triaxial deformations was proposed; rich nuclear structure was proposed in soft Ag isotopes with possible chiral doubling structure suggested in 104,105Ag, and softness towards triaxial deformation proposed in heavier 115,117Ag;quasi-particle couplings, quasi-rotations and soft triaxiality were suggested in Cd (Z =48) isotopes with small deformations; onset of collectivity was recently suggested in 122,124,126Cd in the vicinity of Z =50 and N = 82 closed shells by studies of Coulomb excitations; shape evolutions from maximal triaxial deformations in Ru (γ=30°, with triaxial minimum energy gain of 0.67 MeV), through Rh with large triaxial deformations ( γ=28°), to less pronounced triaxiality in Pd (with triaxial minimum energy gain of 0.32 MeV), then soft triaxiality in Ag, and finally to slightly deformed Cd isotopes but with emergence of collectivity and soft triaxiality were proposed. The systematic studies of the band crossings in Pd revealed up-rising drivings of the first band crossings caused by (νh_11/2)2 and down-sloping drivings of the second band crossings by (πg_9/2)2, explained the onset of wobbling motions in 114Pd,and showed a long-sought picture of shape evolution and coexistence in the Pd isotopic chain which is more complete but complex than earlier predictions. Based on the systematic studies in the mass region,maximal triaxial deformation is found to be reached in 112Ru and less-pronounced triaxiality centered at 114Pd, both for N =68, four neutrons more than predicted in earlier theoretical calculations.In the neutron-rich Zr (Z =40), Nb (Z =41), Mo (Z =42) and Tc (Z =43) isotopes with Z just below Ru, large quadrupole deformations of axially symmetric shapes were deduced in Y and Zr isotopes, with emergence of the degree of freedom having been suggested for heavier Zr isotopes; medium triaxial deformations were deduced for the ground states of heavier (A > 104) Nb isotopes, and, with increasing excitations and spins, evolution from medium triaxial deformations with strong quadrupole deformations at ground states to nearly axially-symmetric shapes were deduced; light Nb isotopes (A6103) have near axially-symmetric shapes with strong quadrupole deformations; combining with the identification of onset of strong quadrupole deformation at 100Nb in the Nb isotopic chain, an increase of soft triaxiality with increasing neutron number was proposed in 100-106Nb. Shape coexistence with regard to soft triaxiality is also proposed in Nb isotopes; large triaxial deformations, vibrations and chiral doublets were proposed in Mo isotopes; chiral doubling and large triaxial deformations (γ ~26°) slightly smaller than the maximal triaxiality were suggested in Tc isotopes.The neutron-rich nuclei with Z ranging from 41 through 48 and A ~100 to 126, especially the Pd and Nb isotopes are thus found to be transitional nuclei with regard to triaxiality.     

可中断的多任务平行机排序问题

Leung等(Preemptive multiprocessor order scheduling to minimize total weighted flowtime [J]. European Journal of Operational Research, 2008, 190: 40-51)研究了如下问题: 有 n 个订单, 其中每个订单 i 含有 n_i 个不同的工件. 所有的订单在零时刻已经到达, 并且工件的加工是可中断的. 每个订单 i有一个权重 \omega_i, 定义订单 i 的完工时间 C_i 为订单 i 最后一个完工工件的完工时间. 目标是找到一个可行排序使得加权总完工时间\sum\limits_{i=1}^n \omega_iC_i 最小. Leung等证明了这个问题是NP-难的, 给出了一个近似算法, 并且分析了该算法的最坏情况界. 但是定理2的证明存在一些错误. 证明了尽管定理2的证明过程存在错误, 但是其结论仍然正确. 另外, 对上述模型的一种特殊情形给出了更好的近似算法.     

基于金刚石氮-空位色心的精密磁测量

磁是一种重要的物理现象,对其进行精密测量推动了许多科技领域的发展.各类测磁技术,包括霍尔传感器、超导量子干涉仪、自旋磁共振等,都致力于提升空间分辨率和灵敏度.近年来,金刚石中的氮-空位色心广受关注.这一固态单自旋体系具有许多优点,例如易于初始化和读出、可操控、具有较长相干时间等,这使得它不仅在量子信息、量子计算等领域崭露头角,而且在量子精密测量上显现出巨大的应用前景.基于氮-空位色心,利用动力学解耦、关联谱等技术,已实现若干高灵敏度、高分辨率的微观磁共振实验,其中包括纳米尺度乃至单分子、单自旋的核磁共振和电子顺磁共振.氮-空位色心也可以用于微波和射频信号的精密测量.本文对围绕上述主题开展的一系列研究工作进行综述.     

香豆素类荧光传感器*

荧光传感器能够将分子识别的信息转换成荧光信号,荧光法在灵敏度、选择性和实时原位检测等方面优势突出。实时检测被分析物的水平已引起包括化学家、生物学家、临床生物化学家和环境学家的极大兴趣。以香豆素为基础的荧光传感器近年来已成为一个新兴的研究热点。本文综述了香豆素类荧光传感器在阳离子、阴离子、中性分子识别检测中的分子设计、作用机理和应用效果,展望了该领域的发展方向。     

INFLUENCE OF γ-RADIATION ON THE DIELECTRIC CHARACTERISTICS IN Rb2ZnCl4 SINGLE CRYSTALS AT INCOMMENSURATE-COMMENSURATE PHASE TRANSITION

In this paper the influence of γ-radiation on the dielectric constants of Rb₂ZnCl₄ crystal at incommensurate-commensurate phase transition (hereafter abbreviated as INC-C transition) are studied. The thermal hysteresis occurs upon both cooling and heating runs, irrespective of whether the samples have been treated with γ-radiation or not. For the γ-irradiated sample, its transition point, T_c, between the INC and C phases is not changed, but the peak value of the dielectric constant at T_c increases abruptly, compared with that before γ-irradiation, When this sample is annealed at 40℃, the peak value restores to the incipient value for the sample free from γ-irradiation. The origin of the phenomenon of the thermal hysteresis of the dielectric constant may be due to the pinning effect of dejects or impurities in the samples.     

利用界面调控制备二维有机半导体晶体及其机制研究

二维有机半导体晶体是利用分子间的范德瓦耳斯力进行自组装生长的单晶材料。本质上的单晶属性使其具备优异的电学特性。更重要的是,二维极限下增强的界面特性能够大幅调控器件行为,为构建多功能界面器件提供可能。此外,充分暴露的电荷输运沟道和极少的晶面内缺陷能够为研究本征的有机电子输运特性创造可能。目前,对于二维有机半导体晶体的生长工艺研究已经取得了较大的进展,但是从理论层面上研究二维晶体生长的自组装过程仍然十分匮乏。本工作利用添加剂辅助结晶技术成功制备出二维有机半导体晶体,并通过偏光显微镜和原子力显微镜对二维晶体进行了全面的表面形貌和结构表征。通过SEM结合EDS技术对关键的形核界面进行了结构和组成的表征以研究晶体生长的机制。研究结果表明:在添加剂界面上,生长材料能够稳定形核,并计算出添加剂构建的有利界面能够将形核势垒降低为SiO₂界面上的1/5。这项工作充分展现了生长界面对于晶体生长的关键作用,并从理论上揭示了界面的调控行为,为二维有机半导体晶体的生长工艺设计提供了可靠的思路。     

自适应多分辨率方法在反应多相流数值模拟中的应用

将自适应多分辨率方法应用到刚性气体状态方程CJ模型的数值模拟，采用多相流问题的守恒锐利界面格式，通过level-set方法和虚拟流体方法来追踪和处理界面，能够很好地处理时间尺度较大的界面交互问题.利用金字塔型数据结构和多分辨率自适应方法，提高算法的存储效率和计算效率.给出一维和二维的数值算例，证明该算法在反应多相流数值模拟中的稳定性和高效性.     

高耐压和低暗计数SiC紫外雪崩光电二极管

碳化硅（SiC）雪崩光电二极管（APD）是一种独具优势的微弱紫外光探测器,其过偏压承受能力是确保器件可靠工作的一个重要因素。本工作设计并制备了穿通型SiC吸收层-电荷控制层-雪崩倍增层分离（SACM）APD。基于这种结构,器件电场从雪崩倍增层向吸收层扩展,从而减小了雪崩倍增层内电场强度变化率,最终将器件过偏压承受能力提高到10 V;得益于吸收层的分压,雪崩倍增层的电场强度得到有效降低,载流子隧穿可能性减小,这能够有效降低器件暗计数,从而有利于提高器件探测灵敏度;此外,设计的SiC SACM APD倾斜台面仅刻蚀到雪崩倍增层上表面,这能够让器件填充因子提高至约60%,显著改善了深刻蚀导致的传统SACM结构有效光敏区域减小的问题。