Simple algorithm for isothermal-isobaric molecular dynamics

We review principles of non-Hamiltonian statistical mechanics and present a new set of equations and integration algorithm for isothermal-isobaric dynamics. The chief advantage of the present scheme is that it is somewhat simpler than previous methods. We perform numerical simulations to test the accuracy of the algorithm and compare its stability to that of a "gold standard," a symplectic integrator for Hamiltonian dynamics of the same system. The stability of the isothermal-isobaric algorithm is comparable to the stability of the symplectic integrator.     

气相色谱过程的计算机模拟及操作条件的优化

建立了气相色谱过程的动态数学模型,给出了模型的实用算法,并据此对各种操作条件下的色谱流出曲线进行了动态模拟计算。模拟计算结果表明该模型是有效的,能够用于各种程序控制的色谱过程,可得到色谱分离的优化条件。     

聚酯-聚酯多嵌段共聚物的合成及其动态力学性能

聚酯-聚醚多嵌段共聚物的动态力学性能谱上有两个T_8,不宜做阻尼材料。本文报道聚对苯二甲酸乙二醇酯(PET)-端羟基聚己二酸乙二醇酯(PEA)共聚物(简称嵌段共聚酯),比聚醚-聚酯多嵌段共聚物有更好的相容性。我们研究了PEA的分子量,间苯二甲酸的用量对嵌段共聚酯的结晶度,以及结晶度对嵌段共聚酯的动态力学性能的影响。     

Thermal techniques to study complex elastomer/filler systems

The transfer of heat through an elastomeric matrix is important for both the processing of the material and its subsequent lifetime. Thermal conductivity can be used to evaluate the influence of different polymers and fillers on heat transfer. Additionally, the dispersion of the filler has an effect on heat transfer and thermal conductivity measurements can be used to provide semi-quantitative estimations of filler dispersion. The degradation of sulfur-crosslinked elastomer systems has been studied for many years. The degradation of the crosslinks (changes in sulfur rank) and degradation of the polymer backbone by thermal and/or oxidative processes have been studied extensively using many techniques including thermal analysis (references). However, the degradation of the crosslinked-polymer 'network' is less well understood. The relationship of the crosslink network to this degradation process is a key to both the long term and higher temperature performance of the sulfur-crosslinked elastomer. The changes in physical properties observed upon exposure of sulfur-crosslinked elastomers can be monitored using dynamic mechanical analysis. Subsequently, other thermal techniques can be used to monitor the chemistry that is occurring during these degradations. Thermal desorption/mass spectroscopy and dynamic scanning calorimetry are used to complete the picture of the degradation processes taking place. Examples of these techniques will be provided to illustrate the utility of the analytical approach, the chemistry involved in these degradation processes and the effect of changes in the polymer, cure package and other ingredients. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanical properties and transition temperatures of crosslinked-oriented gelatin

 This second part of a systematic study of the properties of crosslinked-oriented gelatin involves the effects of orientation and water content on the glass transition temperature T _g and on the melting behavior. The samples were the same as those in the preceding study, and their transition temperatures were determined by both differential scanning calorimetry and dynamic mechanical thermal analysis. The crosslinked gelatin which had been room-conditioned showed two transition temperatures: the lower one was attributed to T _g of the water-plasticized gelatin, and the higher one was interpreted as T _g of dried gelatin superimposed by melting. A rather unusual situation arose because of the fact that the T _g and melting temperatures T _m (217 and 230 ^°C, respectively) are so similar. Using water as plasticizer not only decreases T _g but produces imperfect crystallites which melt below the T _g of the system. The presence of the amorphous phase in the glassy state would presumably make it essentially impossible to define a melting point or crystallization temperature in the normal manner, as an equilibrium between crystalline and amorphous phases. Received: 8 October 1996 Accepted: 2 November 1995     

Nuclear‐Spin Polarization in Electron‐Transfer Reactions of Amines

Chemically induced dynamic nuclear polarization (CIDNP) observed during electron transfer (ET) reactions of tertiary amines such as DABCO ( 1 ) or Et₃N ( 2 ) with a wide range of electron acceptors support the involvement of amine radical‐cations (e.g., 1^{. +} or 2^{. +} ) as key intermediates. Radical ions such as 2^{. +} may be deprotonated, generating neutral aminoalkyl radicals (e.g., 2^. ). When generated by reaction with an electron acceptor of energetically low triplet state such as naphthalene (¹Naph*), the resulting pair 2^{. +} /Naph^.? reacts mostly by reverse electron transfer (RET) from triplet pairs populating the naphthalene triplet state.     

HIPS／PP熔融反应共混及其动态力学性质

研究了高抗冲聚苯乙烯（HIPS）／聚丙烯（PP）共混物在过氧化二异丙苯（DCP）存在下的熔融反应过程及其动态力学性质．HIPS在DCP存在下以聚苯乙烯（PS）的降解为主，伴随着聚丁二烯（PB）的交联和接枝，PP在DCP存在下以降解为主，HIPS／PP在DCP存在下以PP同HIPS的反应接枝为主，这种原位生成的增容剂显著地改善了HIPS／PP两组份间的相容性，其分子运动特征较前两者发生明显变化，PS的Tg下降，PB和PP的Tg升高．     

Normalized Dynamic Characterization and Application of Multiple Heat Storage Materials Based on Standard Thermal Resistance北大核心CSCD

基于标准热阻和能量流法,推导出储热材料与换热流体的瞬态换热热阻,通过类比电路分析法,获得了储热-换热过程的瞬态热量流模型及动态响应时间常数。进一步引入节点温度,重新定义换热热阻,获得了储热与换热过程耦合的三阶电路瞬态热量流模型,求解得到了加热、储热和释热三类时间常数,可用于协同表征储热材料中储热与释热的快慢程度,从而实现了多类储热材料的归一化动态表征。通过数值模拟验证与应用对比分析,发现基于多时间常数的归一化动态模型用于表征储热材料的动态特性是可行的,可直接对不同换热、储热材料进行对比分析。案例分析发现与固体储热材料换热时,液态金属的动态换热能力优于熔融盐,而相比于水蒸气和CO₂,空气与陶瓷材料换热能更快达到稳态。     

考虑油膜动态过程的海上溢油应急物资调度优化

针对溢油应急响应中海上油膜所具有的动态特性,综合考虑需求点的时变物资需求、运输网络的不确定性以及物资调度决策与外部决策环境之间的相互作用关系之后,构建了效率目标与成本目标相结合的多目标海上溢油应急物资调度优化模型。根据模型的特点,提出了一种基于鲸鱼算法的求解方法。该算法利用非线性收敛因子克服了算法后期易陷入局部最优的不足,同时还引入小生境共享机制以确保解的多样性。最后,通过仿真案例对模型与算法的有效性与可行性进行了验证。结果表明,该方法可以为决策者提供高质量的决策支持。     

Molecular dynamics of cyclic and linear poly(dimethylsiloxanes)

Dielectric spectroscopy (10^–1 Hz to 10⁷ Hz) has been employed to study the molecular dynamics of a series of cyclic and linear polydimethylsiloxanes (PDMS) of various molecular weights ranging from 300 to 10 000 g/mol in the temperature range above the glass transition (from 130 K to 190 K). The observed -relaxation depends strongly on both molecular weight and structure of the samples. For linear PDMS oligomers, the -relaxation shifts towards lower temperatures with decreasing molecular weight in good accordance with the Fox-Flory-model. Cyclic PDMS reveals a qualitatively different molecular weight dependence: for a given temperature the -relaxation time increases with decreasing ring length, but has a maximum for small oligomers (degree of polymerizationn6). The shape of relaxation curves and, with it, the relaxation time distribution is independent from length and architecture of the chains The observed experimental findings are in qualitative agreement with dynamic Monte-Carlo simulations.Dedicated to Prof. E.W. Fischer on the occasion of his 65th birthday Fast macht' das WLF ihn krank, jetzt raucht er wieder, Gott sei Dank! (frei nach Wilhelm Busch)