Tracking the Light-Induced Excited-State Dynamics and Structural Configurations of an Extraordinarily Long-Lived Metastable State at Room Temperature

Time-resolved X-ray (Tr-XAS) and optical transient absorption (OTA) spectroscopy on the pico-microsecond timescale coupled with density functional theory calculations are applied to study the light-induced spin crossover processes of a Fe-based macrocyclic complex in solution. Tr-XAS analysis after light illumination shows the formation of a seven-coordinated high-spin quintet metastable state, which relaxes to a six-coordinated high-spin configuration before decaying to the ground state. Kinetic analysis of the macrocyclic complex reveals an unprecedented long-lived decay lifetime of approximately 42.6 μs. Comparative studies with a non-macrocyclic counterpart illustrate a significantly shortened approximately 568-fold decay lifetime of about 75 ns, and highlight the importance of the ligand arrangement in stabilizing the reactivity of the excited state. Lastly, OTA analysis shows the seven-coordinated high-spin state to be formed within approximately 6.2 ps. These findings provide a complete understanding of the spin crossover reaction and relaxation pathways of the macrocyclic complex, and reveal the importance of a flexible coordination environment for their rational design.     

某发动机喷管内流动与换热的瞬态模拟

为准确预测发动机喷管内部的流动及传热特性,以Navier-Stokes方程、重整化群(RNG)k-ε湍流模型为基础,借助计算流体力学软件Fluent对喷管内流场及温度场进行了瞬态数值模拟。计算结果表明:发动机燃烧初期,喷管内燃气呈亚音速状态流动,喷管整体温度还比较低;随着时间的推移,喷管内开始出现激波,燃气的速度突然降低,温度突然上升,由于激波的影响,气流在激波下游形成低速高温区域;随着燃气的膨胀,激波逐渐移出喷管,喷管内燃气呈超音速状态流动,喷管整体温度较高。研究结果可为喷管的设计及优化提供一定的参考。     

Small and moderate Vadasz number chaotic convection in porous media in the presence of non-Boussinesq effects and feedback control

Feedback control on thermal convection in a fluid-saturated porous medium is investigated based on the approach of dynamical systems. A low dimensional Lorenz-like model was obtained using the Galerkin truncated approximation. The possible suppression or enhancement of chaotic convection is demonstrated.     

Thermal degradation behaviour of radiation grafted FEP-g-polystyrene sulfonic acid membranes

The thermal degradation behaviour and the gaseous products of FEP-g-polystyrene sulfonic acid membranes prepared by radiation-induced grafting of styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films and the subsequent sulfonation were studied using thermal gravimetric analysis coupled with Fourier transform infrared spectrometry (TGA/FTIR). The membranes were found to have a three-step degradation behaviour due to water removal, elimination of sulfonic acid groups and decomposition of the FEP matrix. The evolving gaseous products were identified using FTIR analysis. The degree of grafting was found to have a strong effect on the weight loss in the membranes, whilst the degradation temperatures of the individual membrane components were shown to be independent of the degree of grafting.     

Hard mode Raman spectroscopy and its application to ferroelastic and ferroelectric phase transitions

The application of Raman spectroscopy for the investigation of phase transitions focused traditionally on the observation of soft modes in displacive systems. The present furthergoing study on displacive and order-disorder systems is based on the observation of systematic changes of the scattering profiles of hard modes during the phase transition. It reveals the temperature evolution of the order parameters, the role of order-parameter fluctuations and phonon density of states effects in model systems like improper ferroelastic Pb₃(P_1-x As _x O₄)₂, lead diluted ferroelastic (Pb_1-x Ba _x )₃(PO₄)₂, pure ferroelastic As₂O₅ and the relaxor ferroelectric Pb(Sc_0.5Ta_0.5)O₃. Allied with supplementary experimental techniques hard-mode Raman spectroscopy (HMRS) is an ideal method for the investigation of order-parameter coupling effects and the characterization of structural phase transitions.     

新型超塑化剂Supercizer—6工程效果的试验研究

超塑化剂是配制高性能砼不可缺少的组合。通过与ＦＤＮ的对比试验， 新型超塑化剂Ｓｕｐｅｒｃｉｚｅｒ－６的工程效果。结果表明：Ｓ－６基本不含Ｃｌ＾－，ＳＯ＾２－４等有害成分，掺少量Ｓ－６可有效提高水泥净浆、砂浆，砼的流动性，且各龄期的抗折，抗压强度及其发展规律基本不变；     

阶跃过渡应答法研究甲醇完全氧化反应动力学──反应机理及动力学参数的求取

在第一部分基础上，进一步研究了甲醇完全氧化反应过程中某些物种的行为，证实了甲醇在ＰｄＡｇ／Ａｌ２Ｏ３催化剂上的吸附是该反应的慢步骤，并提出了反应机理，用ＲｕｎｇｅＫｕｔａ法和修正的ＧａｕｓＮｅｗｔｏｎ法求取了各基元步骤的速率常数、活化能和指前因子等动力学参数。     

HT-7U装置纵场线圈的稳态及瞬态传热分析

文章分析了 TH- 7U托卡马克核聚变装置在正常和非正常运行情况下产生的各种热负荷在纵场磁体上的热行为 ,给出了纵场线圈盒最严重部位上的温度分布云图 ,计算过程考虑了核热沉积、各种热传导、热辐射、涡流损耗热和迫流式超临界氦进行对流换热等过程。针对等离子体快速破裂时 ,在极短的时间内 ,其纵场磁体中产生的较大涡流损耗而引起的焦耳热对纵场线圈盒与超导磁体之间的热传递过程加以研究。该文采用国际上较为流行的有限元分析软件 COSMOS/ M进行计算 ,由于简化了纵场线圈有限元分析模型及真实情况下部分热流量的不确定性 ,所得结果较为乐观 ,但这些结果对 HT- 7U装置的工程设计仍具有重要意义。     

A new material model for concrete in high-dynamic hydrocode simulations

Summary  The development of material laws for concrete subjected to highly dynamic loadings is a topic of current research. Explosive charges or high-velocity impacts produce high pressures in the kilobar region within microseconds. Hydrocode simulations by coupling of Lagrangian with Eulerian grids have been carried out, considering the interaction between explosive loading and the structure. Concrete is a composite material with a variety of inhomogenities. By homogenization of the microstructure, a macroscopic approach in the framework of continuum mechanics has been adopted. Appropriate constitutive laws that enable the nonlinear rate-dependent as well as the local damage behaviour to be modelled had to be introduced. A new damage law that describes void compaction as well as the classical theory of plasticity had been taken into account. An equation of state had to be provided to ensure the compliance with conservation laws on which hydrocodes are based. To obtain the necessary material data, experimental investigations were indispensable. Therefore, a series of field tests with specimens which were concrete slabs exposed to explosive contact charges has been conducted. Received 19 March 1999; accepted for publication 9 December 1999