垒层温度对InGaN量子点/量子阱复合结构内量子效率的影响

使用金属有机化学气相沉积(metal organic chemical vapor deposition, MOCVD)方法生长了三个具有不同垒层温度的InGaN/GaN量子阱。由于高密度V型坑的形成,完整的量子阱结构被破坏,转变成了InGaN量子点(quantum dots, QDs)/量子阱(quantum well, QW)复合结构。通过变功率光致发光谱和变温光致发光谱,分析了在不同的垒层温度下量子限制斯塔克效应(quantum confined Stark effect, QCSE)、非辐射复合中心密度和载流子局域化效应的变化。结果表明:在较低的垒层温度下,QCSE较弱,因为在较低的温度下,V型坑的深度较深,应力释放较明显,残余应变较低;非辐射复合中心密度也随着温度的升高而逐渐增大;样品的内量子效率(internal quantum efficiency, IQE)随着垒层生长温度的升高而降低。QCSE的增强和非辐射复合中心密度的增大是垒层生长温度升高时内量子效率下降的主要因素。     

超前/延误排序问题的进展(英文)

近年来对超前／延误（Ｅ／Ｔ）排序问题进行了广泛的研究．本文总结了对Ｅ／Ｔ排序问题的各种研究中的一些特别领域,虽然没有覆盖所有的新成果,但对该课题有兴趣的读者提供了指导．     

两例弯曲型二酸Zn(Ⅱ)、Cd(Ⅱ)配合物的合成，结构与荧光性质

本文以弯曲型二酸2,2′-azanediyldibenzoic acid(H₂L)为配体，溶液法合成了2个新的配合物[Zn₂(L)₂(H₂O)₂]·H₂O (1)和[(NH₄)₂ Cd(L)₂]·C₂H₅OH (2)。通过X射线单晶衍射分别测定了他们的结构：配合物1属于单斜晶系，空间群为P2₁/c，a=1.487 9(2) nm，b=0.898 9(1) nm，c=1.210 0(2) nm，β=99.211(2)°，V=1.597 3(3) nm³。配体L的羧酸根均为单齿配位，桥连2个锌离子，形成一个零维的[2+2]扭曲环状结构，并由氢键作用连接成二维结构。配合物2属于正交晶系，空间群为Pbcn，a=2.060 2(2) nm，b=1.281 9(1) nm，c=2.246 1(1) nm，V=5.931 9(6) nm³。Cd(Ⅱ)取较少见的羧酸根螯合八配位结构，L与Cd(Ⅱ)也形成了二核环状结构，并通过共用1个镉离子而形成一维的阴离子链，抗衡阳离子为NH₄⁺。链间通过π…π作用堆积成三维结构。此外，还并测定了配体及配合物的荧光性质。     

To be or not to be – nematic liquid crystals from shape-persistent V-shaped nematogens with the ‘magic angle’

The tetrahedral bending angle in V-shaped nematogens was claimed to be the optimum for finding a biaxial nematic liquid crystal phase. The benzo[1,2-b:4,3-b’]dithiophene core, recently successfully applied as a tetrahedral bending unit in mesogens with lateral flexible chains, is here embedded in a scaffold with only terminal chains, which conventionally promotes the formation of nematic phases at low temperature. A series of new mesogens has been successfully prepared, realising hockey-stick, hockey-stick dimer and V-shaped molecular topologies. Only the hockey-stick mesogens assemble in uniaxial nematic phases over a broad temperature range. Single crystal structure analysis of a hockey-stick and V-shaped compound reveal remarkable similarities with the benzodithiophene core wrapped by aliphatic chains. A model explaining the absence of nematic mesophases in the family of V-shaped, shape-persistent mesogens with terminal aliphatic chains is presented and results in the proposal of a new design for biaxial nematogens.     

NEURAL MODELS FOR THE BROADSIDE-COUPLED V-SHAPED MICROSHIELD COPLANAR WAVEGUIDES

This article presents a new approach based on multilayered perceptron neural networks (MLPNNs) to calculate the odd-and even-mode characteristic impedances and effective permittivities of the broadside-coupled V-shaped microshield coplanar waveguides (BC-VSMCPWs). Six learning algorithms, bayesian regulation (BR), Levenberg-Marquardt (LM), quasi-Newton (QN), scaled conjugate gradient (SCG), resilient propagation (RP), and conjugate gradient of Fletcher-Powell (CGF), are used to train the MLPNNs. The neural results are in very good agreement with the results reported elsewhere. When the performances of neural models are compared with each other, the best and worst results are obtained from the MLPNNs trained by the BR and CGF algorithms, respectively.     

Ultrastretchable,Tough, and Notch‐Insensitive Hydrogels Formed with Spherical Polymer Brush Crosslinker

Spherical polymer brushes, poly(acrylic acid) (PAA)‐grafted polystyrene nanoparticle (PAA@PS), are employed as the macro‐crosslinker to prepare PAA hydrogels. Benefitting from the innumerable hydrogen bonds between highly entangled PAA chains both in bulk and on the polymer brush, the PAA/PAA@PS hydrogels combine desirable stretchability, toughness, and notch‐insensitivity. The uniaxial tensile tests show a very high fracture elongation up to 9.1 × 10³% while the fracture toughness reaches 3.0 MJ m⁻³ and the maximum swelling ratio of the hydrogel can be 2.0 × 10³ as well. After being loaded with silver nanoparticles, the PAA/PAA@PS hydrogels are employed as a recyclable catalyst successfully.     

Metal and structure tuned in vitro antitumor activity of benzimidazole-based copper and zinc complexes

Four new complexes, Cu₂(p-2-bmb)₂Cl₄ (1), Cu₂(p-2-bmb)₂Br₄ (2), Zn₂(p-3-bmb)₂Cl₄ (3), and [Cu₃(p-3-bmb)₂Cl₄·(CH₃OH)₂] _n (4), have been synthesized under solvothermal reactions based on V-shaped flexible ligands 1-((2-(pyridin-2-yl)-1H-benzoimidazol-1-yl)methyl)-1Hbenzotriazole (p-2-bmb) and 1-((2-(pyridin-3-yl)-1H-benzoimidazol-1-yl)methyl)-1Hbenzotriazole (p-3-bmb). Complexes 1–3 are binuclear, whereas 4 is an infinite chain with trimetallic units, and then these complexes are further extended into 3D supramolecular architectures by π…π interactions and hydrogen bonds. In vitro antitumor activities of these complexes on four human tumor cell lines (gastric tumor cell line, esophagus tumor cell line, liver tumor cell line, colon tumor cell line) were evaluated by MTT assay. The results exhibit that these complexes inhibit the growth of cancer cells by inducing apoptosis, and the inhibition effect shows time- and dose-effect relationship.     

布氏折射装置的设计

本文介绍了一种利用布儒斯特原理设计的折射装置，该装置具有原理简单、操作方便、对待测物要求低的特点。     

A dominant subset of V-shaped sequences for a class of single machine sequencing problems

In this note we define a subset of V-shaped sequences, ‘V-shaped about T’, which generalize ‘V-shaped about d’ sequences. We derive a condition under which this subset contains an optimal sequence for a class of single machine sequencing problems. Cost functions from the literature are used to illustrate our results.     

Performance limitation of chirped-fiber-Bragg-grating-based photonic microwave notch filter due to group delay and reflectivity ripples

We investigated the performance limitation of a frequency-tunable photonic microwave notch filter incorporating a chirped fiber Bragg grating (FBG) as a group delay line. In particular, we carried out theoretical and experimental studies to analyze the impact of the reflectivity ripple (RR) and group delay ripple (GDR) in the chirped FBG on the output notch performance. The results of experimental and theoretical analyses performed on a photonic microwave notch filter in which an S-bending-based linearly chirped FBG was incorporated, revealed that the notch depth and notch frequency were significantly affected by imperfections in the chirped FBG. The notch depth was found to be decreased by the RRs, whereas significant fluctuations in the notch frequency were caused by the GDRs. On the basis of the obtained results, we conclude that the RR and the GDR are the fundamental factors that degrade the performance of chirped FBG-based photonic microwave filters.