Alternating,gradient, block,and block–gradient copolymers of ethylene and norbornene by Pd–Diimine‐Catalyzed “living” copolymerization

We demonstrate, in this article, the facile synthesis of a broad class of low‐polydispersity ethylene–norbornene (E–NB) copolymers having various controllable comonomer composition distributions, including gradient, alternating, diblock, triblock, and block–gradient, through “living”/quasiliving E–NB copolymerization facilitated with a single Pd – diimine catalyst ( 1 ). This synthesis benefits from two remarkable features of catalyst 1 , its high capability in NB incorporation and high versatility in rendering E–NB “living” copolymerization at various NB feed concentrations ([NB]₀) while under an ethylene pressure of 1 atm and at 15 °C. At higher [NB]₀ values between 0.42 and 0.64 M, E–NB copolymerization with 1 renders nearly perfect alternating copolymers. At lower [NB]₀ values (0.11–0.22 M), gradient copolymers yield due to gradual reduction in NB concentration, with the starting chain end containing primarily alternating segments and the finishing end being hyperbranched polyethylene segments. Through two‐stage or three‐stage “living” copolymerization with sequential NB feeding, diblock or triblock copolymers containing gradient block(s) have been designed. This work thus greatly expands the family of E–NB copolymers. All the copolymers have controllable molecular weight and relatively low polydispersity (with polydispersity index below 1.20). Most notably, some of the gradient and block–gradient copolymers have been found to exhibit the characteristic broad glass transitions as a result of their possession of broad composition distribution. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Effect of moisture on the viscoelastic properties of an epoxy-clay nanocomposite

The results of a complex study on the viscoelastic behavior of an epoxy-clay nanocomposite after a long-term exposure to moisture are presented. The main laws of variation in the glass-transition temperature of the nanocomposite in relation to the different content of filler and absorbed moisture were determined by using a thermomechanical analysis. The loading levels in creep experiments were chosen according to the results of quasi-static tensile tests. The sets of creep and creep recovery curves obtained were approximated by the Boltzmann–Volterra linear integral equation with account of the principle of moisture-time analogy. The variation in the spectrum of retardation time of the epoxy resin with introduction of the nanofiller was estimated. It is shown that the moisture-time reduction function correlates with changes in the forced rubber-like elasticity and the volume of nanocomposite specimens upon their moistening.     

$nhbox{-ZnO}/nhbox{-GaAs}$ Heterostructured White Light-Emitting Diode: Nanoscale Interface Analysis and Electroluminescence Studies

n-ZnO/n-GaAs heterostructured light-emitting diodes have been fabricated by a low-cost ultrasonic spray pyrolysis technique. Nanoscale interface analysis was carried out with scanning transmission electron microscopy. An ~ 8.6-nm-thick amorphous GaAsZnInO was found in the n -ZnO/n-GaAs interface. A strong and broad white electroluminescence band centered at ~ 525 nm and a weak near-infrared emission peaked at ~ 815 nm were observed when n-GaAs was positively biased. The 815-nm emission is believed to be related to the interface layer, and the 525-nm emission is assigned to the recombination of electrons from conduction band to deep-level holes in the ZnO layer.     

Second-order nonlinearities of lead borate glasses poled with different electrodes

The second-order nonlinearities in thermally poled lead borate glasses were studied. After poling with different electrodes, both bulk and near surface second-order nonlinearities were obtained. The second harmonic generation signal from near surface effect was two orders of magnitude larger than the bulk effect. By simulating the poling process with a multiple carrier model, we concluded that the bulk second-order nonlinearity was caused by the deficiency of Pb²⁺ in a thick layer after poling, and the near surface second-order nonlinearity was caused by the depletion of H⁺ in a thin layer when H⁺ injection from the atmosphere was blocked.     

A model for describing near-resonance oscillations in an elastic layer

One-dimensional transverse oscillations in a layer of a non-linear elastic medium are considered, when one of the boundaries is subjected to external actions, causing periodic changes in both tangential components of the velocity. In a mode close to resonance, the non-linear properties of the medium may lead to a slow change in the form of the oscillations as the number of the reflections from the layer boundaries increases. Differential equations describing this process were previously derived. The equations obtained are hyperbolic and the change in the solution may both keep the functions continuous and lead to the formation of jumps. In this paper a model of the evolution of the wave patterns is constructed as integral equations having the form of conservation laws, which determine the change in the functions describing the oscillations of the layer as “slow” time increases. The system of hyperbolic differential equations previously obtained follows from these conservation laws for continuous motions, in which one of the variables is slow time, for which one period of the actual time serves as an infinitesimal quantity, while the second variable is the real time. For the discontinuous solutions of the same integral equations, conditions on the discontinuity are obtained. An analogy is established between the solutions of the equations obtained and non-linear waves propagating in an unbounded uniform elastic medium with a certain chosen elastic potential. This analogy enable discontinuities which may be physically realised to be distinguished. The problem of steady oscillations of an elastic layer is discussed.     

Mutually pumped phase conjugator using a BaTiO3 crystal having two inclined faces

A pentagon-shaped undoped BaTiO₃ crystal was used to construct a high-quality mutually pumped phase conjugator. It yields two very stable phase-conjugate outputs (ǃ.7% fluctuation in intensity) with high reflectivity (the highest ᅝ%) when the two incident beams are of equal intensities. The response time of the conjugator is rather fast (ƻ s) and the tolerance of the acceptance angle is large too (걄°). Fine structures (35 7m) in an image, after passing through a phase aberrator, can be recovered by the conjugate waves yielded by this conjugator.     

电视谈话节目布光浅析

随着电视事业迅猛发展 ,电视谈话节目作为一种与日常生活息息相关的节目形态异军突起。这类节目因其尊重观众参与意识 ,强化电视“贴近”属性倍受受众青睐而走俏。当谈话节目在荧屏抢滩登陆后 ,它在布光方面的独特方式也随之应运而生。电视谈话节目布光强调真实性与艺术性的统一 ,这就要求灯光师布光时 ,要注重在真实中表现美 ,在美中求真实 ,两者兼而有之 ,才能勾画出一幅幅情感真挚的图像来 ,从而让受众通过审美和光线潜移默化的影响 ,达到陶冶情操的目的。电视谈话节目布光是在全方位空间内进行的 ,是一个立体照明结构形式 ,它要适合多机…     

Detection of the photochemical intermediate processes in phycobiliproteins

The delayed luminescence was applied to detect the intermediate processes of the excitedstate decay in the selectively excited phycobiliproteins. Phosphorescence spectra of the five types of phycobiliproteins, R-PE, CPC, APC, R-PC, PEC were reported in this article. The five phycobiliproteins showed different phosphorescence yields, the sequence of which was the same as that of the singlet oxygen yields. Based on the observation, it can be concluded that each of the chromophores possesses a characteristic phosphorescence emission. The delayed luminescence spectra of APC at different aggregation states (trimer, monomer and denatured APC) are researched. The lower aggregation APC showed less phosphorescence because of relative loose structures and less interaction with the surrounding proteins, while the denatured APC showed delayed fluorescence instead of phosphorescence because of triplet-triplet annihilation.     

流产后宫内胎物组织残留的超声诊断

回顾性分析了４６例临床被证实为宫内胎物组织残留的病例。结果表明，流产后较长时间有不规则阴道流血，而作Ｂ超检查能发现特征性改变。声像图显示，子宫增大，宫内有异常光团和不规则液性暗区或宫腔局部膨隆，周边见很亮光条。认为诊断宫内残留组织，可以结合病只与声像技术较易诊断出来。本组超声诊断符合率达９８％。对减少因宫内残留造成的子宫收缩不良、不规则阴道流血等现象，避免并发感染及导致绒癌发生等不良后果，有重要的