Different crystal structures and luminescent properties of zinc and cadmium coordination polymers constructed from two flexible thioether ligands with different alkyl chains

Treatments of nitrogen-containing heterocyclic dithioether ligands, 1,2-bis(4-(pyridin-3-yl) pyrimidin-2-ylthio) ethane (L¹) and 1,3-bis (4-(pyridin-3-yl) pyrimidin-2-ylthio) propane (L²), with zinc or cadmium salts have resulted in the interesting frameworks with structural motifs from a mononuclear macrocycle or a dinuclear macrocycle to an one-dimensional structure. A small difference of the alkyl length between L¹ and L² led to conspicuous changes of the fluorescent properties of both ligands and their complexes. Mainly due to the size of metal atoms, structures of [ZnL²I₂] (1) and [CdL²I₂] (2) are varied from a mononuclear macrocycle to a 1D framework, while {[ZnL²(H₂O)₄](ClO₄)₂}₂ (3) and {[CdL²(H₂O)₄](ClO₄)₂}₂ (4) are dinuclear macrocycles in which perchlorate anions may play an important template role. As for complexes 5–8 ([ZnL¹I₂]_n (5), [CdL¹I₂]_n (6), {{[ZnL¹₂(H₂O)₄](ClO₄)₂}_0.5 · L¹_0.5 · CH₃OH} (7), {{[Cd_0.5L¹(H₂O)₂](ClO₄)}₂ · CH₃OH · L¹} (8)), the self-assemble processes were mainly directed by the organic ligand in the reactions of L¹ with metal salts. Complexes 1–4 exhibit blue fluorescence emissions, among which 1 and 2 may be suitable as candidates for blue fluorescent materials.     

气液混输悬链线立管系统两相流特性实验

严重段塞流是海洋工程气液混输管线--立管系统中常见的一种特殊有害流动现象, 采用水平--下倾--悬链线立管气液混输组合管道系统, 通过系列实验在悬链线立管中获得了严重段塞流、间歇流和震荡流等流型, 阐述了这些流动现象的形成机理, 提出了能够产生严重段塞流的判定准则. 结果表明, 悬链线立管严重段塞流具有明显周期性, 在一个周期内的流动特征可分为液塞形成、液体出流、液气喷发及液体回流等4个阶段, 进而给出了各阶段中相关流动参数的变化规律. 在实验中同时还对悬链线与垂直立管中严重段塞流形成机理进行了比较分析, 发现两者在液塞形成阶段有显著差别. 其中, 在悬链线立管中液塞形成之前首先需要经历一个气液混合液塞形成过程, 而垂直立管则没有这个过程.      

深水环境下隔水管的横向自由振动分析

隔水管是海洋钻井工程中的必要设备。在深水环境下,隔水管的疲劳失效问题普遍存在,隔水管的强烈振动是导致其失效的主要原因之一。本文采用微元法,得到了隔水管在各种载荷作用下的横向振动规律及其横向振动的固有频率的分布规律,进一步分析了各种因素对隔水管横向振动固有频率的影响。结果表明:隔水管的长度增加时,固有频率减小;随着顶部张力比的增加,隔水管的横向振动的固有频率也增加;随着壁厚的增加,隔水管横向振动的固有频率逐渐降低;而随着钻井液密度的增加,隔水管横向振动的固有频率增加;海水的存在使隔水管的横向振动固有频率降低。该研究有利于避免隔水管在使用过程中出现强烈的共振现象,为减小隔水管的失效提供了理论依据。     

Natural frequencies and mode shapes of statically deformed inclined risers

We investigate numerically the linear vibrations of inclined risers using the Galerkin approach. The riser is modeled as an Euler–Bernoulli beam accounting for the nonlinear mid-plane stretching and self-weight. After solving for the initial deflection of the riser due to self-weight, we use a Galerkin expansion employing 15 axially loaded beam mode shapes to solve the eigenvalue problem of the riser around the static equilibrium configuration. This yields the riser natural frequencies and corresponding exact mode shapes for various values of inclination angles and tension. The obtained results are validated against a boundary-layer analytical solution and are found to be in good agreement. This constitutes a basis to study the nonlinear forced vibrations of inclined risers.     

海洋柔性结构涡激振动的流固耦合机理和响应

对近几十年来国内外在涡激振动的基础研究包括机理认识和动响应分析等方面的进展进行了论述,尤其针对海洋油气平台中的立管、隔水管等细长柔性结构的涡激振动.描述了涡激振动这种典型的非线性流固耦合现象所具有的特征,包括自激、自限制、展向相关、尾迹水动力与结构动力的流固耦合等及其主要影响参数.介绍了目前常用的结构响应预测方法和相关实验.通过讨论当前理论研究和实际工程中的热点问题,诸如多模态宽带振动、浮体运动与水下立管的耦合、响应抑制措施、双向振动、高雷诺数下的大尺度物理实验等,对今后该领域的研究方向进行了力所能及的展望.     

Biomimetic flexible plate actuators are faster and more efficient with a passive attachment

Using three-dimensional computer simulations, we probe biomimetic free swimming of an internally actuated flexible plate in the regime near the first natural frequency. The plate is driven by an oscillating internal moment approx-imating the actuation mechanism of a piezoelectric macro fiber composite (MFC) bimorph. We show in our simulations that the addition of a passive attachment increases both swim-ming velocity and efficiency. Specifically, if the active and passive sections are of similar size, the overall performance is the best. We determine that this optimum is a result of two competing factors. If the passive section is too large, then the actuated portion is unable to generate substantial deflection to create sufficient thrust. On the other hand, a large actu-ated section leads to a bending pattern that is inefficient at generating thrust especially at higher frequencies.     

New method for oblique impact dynamics research of a flexible beam with large overall motion considering impact friction force

A flexible beam with large overall rotating motion impacting with a rigid slope is studied in this paper. The tangential friction force caused by the oblique impact is analyzed. The tangential motion of the system is divided into a stick state and a slip state. The contact constraint model and Coulomb friction model are used respectively to deal with the two states. Based on this hybrid mod-eling method, dynamic equations of the system, which include all states (before, during, and after the collision) are obtained. Simulation results of a concrete example are compared with the results obtained from two other models: a nontangential friction model and a modified Coulomb model. Differences in the results from the three models are discussed. The tangential friction force cannot be ignored when an oblique impact occurs. In addition, the results obtained from the model proposed in this paper are more consistent with real movement.     

Effect of wheelset flexibility on wheel–rail contact behavior and a specific coupling of wheel–rail contact to flexible wheelset

The fexibility of a train's wheelset can have a large effect on vehicle–track dynamic responses in the medium to high frequency range.To investigate the effects of wheelset bending and axial deformation of the wheel web,a specifi coupling of wheel–rail contact with a fexible wheelset is presented and integrated into a conventional vehicle–track dynamic system model.Both conventional and the proposed dynamic system models are used to carry out numerical analyses on the effects of wheelset bending and axial deformation of the wheel web on wheel–rail rolling contact behaviors.Excitations with various irregularities and speeds were considered.The irregularities included measured track irregularity and harmonic irregularities with two different wavelengths.The speeds ranged from 200 to400km/h.The results show that the proposed model can characterize the effects of fexible wheelset deformation on the wheel–rail rolling contact behavior very well.     

Cu(II) Compounds with Pyrimidine-Based Chelating Ligands,Bridged by a Flexible Alkyl Spacer: Synthesis,Characterisation and X-Ray Structures of Methoxide-Bridged Dinuclear-Based Species

Abstract  The synthesis and full structural characterisation is described of 3 dinuclear-based Cu(II) compounds bridged by methoxide anions, and flexible linear bis(pyrimidine)-α,ω-diaminoalkane ligands. The structures are dinuclear based in all cases, in which the bis(pyrimidine)diaminoalkane ligand chelates to 2 Cu(II) ions in the same dinuclear unit (N–C–C–C–C–C–N linker), or to two different dinuclear units (with the short N–C–C–N linker), thereby generating a polymeric chain. The magnetic exchange in the compounds is dominated by the alkoxido-bridged ligands, which generate a very strong antiferromagnetic coupling between the Cu(II) ions, resulting in diamagnetism at room temperature and below, and EPR silent behaviour. Index Abstract  Dinuclear-based Cu(II) compounds with pyrimidine-based chelating ligands flexible linear bis(pyrimidine)-α,ω-diaminoalkane ligands are described, bridged by methoxide anions. The structures are dinuclear based in all cases, with the ligand chelating to 2 Cu(II) ions in the same dinuclear unit (N–C–C–C–C–C–N linker), or to 2 different dinuclear units (with short N–C–C–N linkers). The very strong antiferromagnetic magnetic exchange in all compounds is caused by the alkoxido-bridged ligands. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

基于柔性电路板单纤双向光纤组件的以太无源光网络单元研制(英文)

随着宽带接入技术的发展,以太无源光网络是光纤到户的一种备选方案.而光网络单元数量众多,其成本成为限制以太无源光网络技术实施的重要影响因素.本文提出了一种低成本以太无源光网络单元实现方式:采用带柔性电路板的单纤双向光纤组件直接安装在光网络单元的电路板上.为了验证弯曲柔性电路板的高速性能没有恶化,采用有限元方法仿真了弯曲柔性电路板的小信号响应.由于该方式没有独立的光收发模块,无法采用比特误码分析仪进行测试,因此提出了采用网络测试仪搭建光网络单元的光信号性能测试系统的方案并实现了对光信号的性能测试.结果表明:对于发射机,在0℃~70℃的范围内得到了超过10dB的消光比和1dBm的平均发射功率;对于接收机,估算灵敏度为-27dBm.