高分子量的枝状聚硅烷的合成与表征

根据硅氢加成反应机理设计了“顺点滴式”工艺 ,高效、低耗地合成了甲基苯乙基二氯硅烷和甲基正己基二氯硅烷 .根据Wurtz还原偶联反应原理 ,采用“预聚”和“混聚”两种工艺分别合成枝状共聚硅烷 ,发现运用“预聚”工艺可以合成分子量很高的枝状聚硅烷 .     

Energy transfer rates and impact sensitivities of two classes nitramine explosives molecules

Some explosives are stable molecules with large energy barriers to chemical reaction, and in shock or impact initiation, a sizable amount of phonon energy must be converted to the molecular internal higher vibrations by multiphonon up pumping. To investigate the relationship between impact sensitivities and energy transfer rates, the number of doorway modes of explosive molecules is estimated by a simple theory in which the rate is proportional to the number of normal mode vibrations. We evaluated frequencies of normal mode vibrations of 13 explosive molecules which are CHNO nitramine-contained and have not been analyzed previously. The number of doorway modes in the regions of 200–700 cm⁻¹ was evaluated by the direct counting method. For more clear investigation of the relationship we have classified these 13 nitramine explosive molecules, by the number of nitramine group they contained, into two groups. There are eight molecules that contained one nitramine group and five molecules that contained poly-nitramine groups. It is found that the number of doorway modes shows a linearly correlation to the impact sensitivities derived from drop hammer tests. This result is in agreement with that of several previous works. Besides, it is also noted in our study that in those nitramine explosives molecules with similar molecular structure (similar number nitramine group they contained) and similar molecular weight, the correlation between the sensitivity and the number of doorway modes is higher. We found that the vibrational frequency of ω corresponds to nitro group motions of every molecule is contributed to the number of doorway modes in the regions of 200–700 cm⁻¹.     

Probing buried carbon nanotubes within polymer-nanotube composite matrices by atomic force microscopy

Multi-walled carbon nanotubes (MW-CNT) inside a polyamide-6 (PA6)-MW-CNT composite were visualized by atomic force microscopy (i) in a field-assisted intermittent contact and (ii) in the tunneling (TUNA) mode. Individual buried MW-CNTs were clearly discerned within the PA6 matrix. An average diameter of 33 ± 5 nm of the MW-CNTs was determined based on field-assisted intermittent contact mode AFM images, which is consistent with the expected size of PA6-coated MW-CNTs. Single well dispersed MW-CNTs that are located in the sub-surface region of the composite were also observed in the TUNA mode. These new AFM approaches circumvent the tedious sample preparation based on ultramicrotoming required for high resolution electron microscopy studies to obtain “in-depth” morphological information and hence are expected to facilitate the analysis of CNT-based and other nanocomposites in the future.     

Fast spatially localised electrooptical mode in vertically aligned nematic LCs with negative dielectric anisotropy

ABSTRACT

Electro-optical switching and the liquid crystal (LC) director distribution are studied in spatially periodic electric field for vertically aligned LC with negative dielectric anisotropy. Two electro-optical switching modes characterised by different switching times are observed. These modes are well distinguished optically by choosing proper geometry for the polarisers axes orientation. One of these modes is significantly faster as compared to the other. The fast switching is explained in terms of localised near-to-surface director reorientation. The 3D-numerical simulation shows very good agreement with the experiment: it points out the existence of the disclination lines and field-stabilised walls responsible for the localised director field switching and its relaxation. Possibilities of enhancing the fast mode for high-speed light modulators are discussed.     

旋转输液管动力稳定性理论分析北大核心CSCD

基于Lagrange原理和假设模态法建立了旋转输液管的动力学模型.通过降阶升维的方法求解系统的特征值问题,并分析了旋转输液管自由振动特性.得到了不同端部集中质量和转速下,系统特征值随流速升高的演变轨迹.揭示了临界流速随系统参数的变化规律.研究发现,内部流体的流动对旋转输液管动力学特性存在显著影响.在某些参数组合下,系统低阶模态能够形成不同形式的内共振关系.预示了旋转输液管模型蕴含丰富的动力学现象.     

我国区域绿色技术创新效率的分类测度和提升模式研究——基于非期望产出的SBM-SupSBM模型

本文首先运用考虑非期望产出的SBM-SupSBM模型估计我国各省市绿色技术创新效率并进行分类:稳定上升类、平稳类、大幅度波动类以及下降类。之后从企业内部和外部两方面对绿色技术创新效率提升的影响因素提出假设,着重考虑大幅度波动类别省份的效率提升。运用面板数据模型各影响因素进行验证,结论显示:企业规模对绿色技术创新效率波动较大的省份起到显著的抑制作用,环境规制和技术进步对绿色技术创新效率波动较大的省份作用不明显。针对分析结果,提出结论:在提升绿色技术创新效率的过程中,应注重企业规模和技术进步的协同作用,以及技术的开放程度。     

Event-triggered sliding mode control for switched genetic regulatory networks with persistent dwell time

This paper focus on the event-triggered sliding mode controller design for discrete-time switched genetic regulatory networks (GRNs) with persistent dwell time (PDT) switching. Firstly, the observation error dynamics of switched GRNs with PDT is constructed in the light of event-triggered sliding mode control (SMC) scheme. Next, sufficient conditions are derived to ensure the exponential stability of the augmented plant. Moreover, an event-triggered SMC law is synthesized to impel the system trajectories onto the sliding surface in a finite time. Finally, a verification example is provided to illustrate the effectiveness and potential of the proposed method.     

Laser Raman spectroscopic study of photoreaction dynamics in p -chloro cinnamic acid crystal

Raman phonon spectroscopy has been used to study photodimerization reaction inp-chloro cinnamic acid (pCCA) crystal. The β-form of the crystal yields the 4,4′-dichloro-β-truxinic acid dimer. Six distinct low frequency phonon bands are observed in thepCCA monomer crystal. On reaction progress, these bands show a monotonic shift to lower frequencies and broaden out. Finally, in the dimer crystal the phonon spectrum shows two weak broad bands. These results suggest that the reaction is homogeneous in the initial stages and, as the product concentration increases, the lattice becomes highly disordered. The reactant and the product were characterised by infrared and Raman spectroscopy. The disappearance of aliphatic C=C bond stretching vibration and appearance of cyclobutane ring deformation and cyclobutane ring-breathing vibrations on reaction confirm photodimerization by cyclobutane ring formation. The large Stoke's shift between the absorption and emission band suggest strong exciton-phonon coupling in the monomer lattice. This reaction seems to be phonon-mediated.     

Purification by solid layer melt crystallization

The application of solid layer crystallization techniques in industry is arousing ever more interest. One reason is the increasing demand for ultrapure products, and another is the energysaving potential of this separation technology.This article examines solid layer melt crystallization as concerns its purification efficiency. The crystallization process was carried out in two different modes, whereby the process parameters were varied and post-crystallization treatments were additionally applied. The experimental results were used as the basis for a mathematical fit of a semi-empirical expression which predicts the purification efficiency. It was used for a design of different multistage plants, which operate with different crystallization strategies. One result is that a comparable product quality is attainable with a simple process technique in combination with post-crystallization treatments, instead of a more complicated and therefore more expensive process technique.The authors wish to acknowledge support by the EU (JOULE program), which helped attainment of some results presented here.