Self-assembly,optical and electrical properties of fork-tailed perylene bisimides

Effect of side-chain length on self-assembly, optical and electrochemical properties of N,N′-di(1-pentylbutyl)perylene-3,4,9,10-tetracarboxylic bisimide and N,N′-di(1-hexylpentyl)perylene-3,4,9,10-tetracarboxylic bisimide has been studied. The photo-physical, thermal and electrochemical properties were studied using UV–Vis and fluorescence, differential scanning calorimetry, and cyclic voltammetry, respectively. The molecules self-assembled as 1D – rods and molecular bundles, self-assembly was studied using SEM, optical and fluorescence microscopic techniques. The results concluded that the compound with short tail exhibits low solubility and self-assembled faster. The photo-physical properties of the compounds were not much affected by varying the alkyl chain length. The compounds geometries were optimized at 6-31G^∗ using DFT and the potentials were correlated with molecular orbitals.     

Electronic structure of asymmetric vertically coupled InAs/GaAs quantum dots

In this paper, the electronic structure of an asymmetric self-assembled vertically coupled quantum dots heterostructure has been investigated. The structure consists of two ellipsoidal quantum dot (QDs) caps made with InAs embedded in a wetting layer InAs and surrounded by GaAs. Using the strain dependent k·p theory, the energy of the two lowest states of a single electron/hole which is confined within the coupled QD structure has been calculated. As a result, it can be estimated the energy gap for different geometry parameters and for tuning the external magnetic field. The numerical results show that the energy gap is very sensitive to the size asymmetry of the structure and to the small separation distance of the dots but less sensitive to the existence of an external magnetic field and large interdot distance.     

The exact ground state and the origin of the spin gap in the distorted mixed spin (1, 1/2) diamond chain

By using the method of exact diagonalization, we investigated the properties of the distorted mixed spin (1, 1/2) diamond chain with antiferromagnetic interactions along the rung and leg. The ground states of this model contain the sawtooth chain state and the rung dimer plus Haldane state. The research on the origin of the spin gap of the model discloses that there are three different types of spin excitations at different parameter regimes due to the competition among the interactions J₁, J₂ and J₃.     

点缺陷扶手型石墨烯量子点的电子性质研究

基于有限差分方法, 数值求解了Dirac方程, 研究了垂直磁场下的点缺陷扶手型 石墨烯 量子点的能谱结构, 分析了尺寸大小对带隙的影响. 与无磁场时具有一定带隙 (带隙的大小与半径成反比) 的量子点相比, 在外加有限磁场下, 能谱中出现朗道能级, 最低朗道能级能量为零并与磁场强度无关, 并且朗道能级的简并度随着磁场的增加而增加. 进一步的计算表明, 最低朗道能级的简并度与磁场成线性关系, 与半径的平方成线性关系. 本文工作对基于石墨烯量子点的器件设计具有一定的指导意义.     

二维正方排列圆柱状亥姆赫兹共振腔阵列局域共振声带隙的研究

通过对二维正方排列圆柱状亥姆赫兹共振腔阵列声性质的研究,指出局域共振型声子晶体中存在两类耦合作用, 即共振单元与基体的弱耦合作用及共振单元间的耦合作用.其中前一种耦合作用可以通过改变共振单元的品质因子而改变, 逐渐减小这种耦合作用可以实现从局域共振到布拉格共振的连续转变;后一种耦合是通过共振单元周围的近场耦合实现的, 通过减小共振单元的间距可以增大其耦合强度,因而增大带隙宽度,但带隙中波的衰减深度却是随这种耦合强度的增大而减小的.     

自同步多开关纳秒脉冲发生器

介绍了一种基于传输线变压器（TLT）的多开关脉冲功率技术。该技术可以像Marx发生器一样实现多个开关的自动同步,而且在输出上更具灵活性:不仅可以通过电压叠加获得高电压输出,而且可以通过电流叠加实现大电流输出,或者用于同时驱动多个独立的负载。基于该技术已成功开发了10火花开关的短脉冲系统。理论设计了带有20开关和20级TLT的脉冲发生器,单脉冲能量140 J,预计峰值功率可达5 GW,可实现多种不同输出方式以满足不同应用需求。     

“闪光二号”加速器运行状态分析及维护

介绍了闪光二号加速器在实验运行过程中,Marx发生器、水介质同轴线和二极管的常见故障。Marx发生器200 kV气体开关、水介质同轴线的主开关和预脉冲开关、二极管阴极表面电场和阴阳极间隙等是各部分出现故障的主要原因,针对故障采取相应的维护措施和注意事项,可实现闪光二号加速器正常稳定的运行。     

Optical properties of one-dimensional soft photonic crystals with ferrofluids

We review the recent theoretical study on the optical properties of one-dimensional soft photonic crystals (1D SPCs) with ferrofluids. The proposed structure is composed of alternating ferrofluid layers and dielectric layers. For the ferrofluid, single domain ferromagnetic nanoparticles can align to a chain under the stimuli of an external magnetic field, thus changing the microstructure of the system. Meanwhile, nonlinear optical responses in ferrofluids are also briefly reviewed.     

向量优化问题有效点集的稳定性

在不需要紧性假设下,利用拟C-凸函数及回收锥的性质,建立了向量优化问题有效点集的稳定性, 获得了一列目标函数和可行集均扰动情形下的向量优化问题与对应的向量优化问题有效点集的Painlevé Kuratowski内收敛性结果．所得结果推广和改进了相关文献(Attouch H, Riahi H. Stability results for Ekeland’s ε-variational principle and cone extremal solution; Huang X X. Stability in vector-valued and set-valued optimization)中的相应结果, 并给出例子说明了所得结果的正确性.     

谱元法研究桁架结构的振动带隙特性

采用谱元法研究了桁架周期结构的带隙特性.从杆和梁的运动方程出发,推导出与频率相关的插值函数,得到了杆单元和梁单元的动力学刚度矩阵.在频域下将铰结构考虑为一个谱单元,并推导出铰单元的动力学刚度矩阵.将杆/梁单元和铰单元加以整合得到整体结构的动力学刚度阵,进而建立整体结构的运动方程.通过求解整体结构的动力学方程,获得结构的频域响应,进而研究结构的带隙特性.本文将谱元法求解得到的固有频率结果与有限元法进行了对比,分析了单胞数量和材料的变化对结构带隙特性的影响,拓展了谱元法的应用领域.