Side‐chain effects on the morphology and properties of fluorene‐based alternating copolymers

Soluble fluorene‐based alternating copolymers containing benzene as the comonomer were synthesized and characterized, in which three different side chains (hydrogen atom, linear octyloxy and bulky benzyloxy groups) were attached to the phenylene ring. The effect of the side chains with different steric hindrances on the photophysical, thermal and electrochemical properties as well as the morphology were investigated. Moreover, the chain conformation and spectroscopic properties in dilute solution were studied to understand the solvent effect. Aliphatic and aromatic solvents were demonstrated to have different influences on the spectra of the polymers owing to various interaction mechanisms in the excited states. Also, a significant decrease of up to 80 °C in the thermal degradation temperature was observed as a result of the introduction of large benzyloxy units. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the polymers were estimated to be ? 5.76 to ? 5.82 eV and ? 2.19 to ? 2.27 eV, respectively, from cyclic voltammetry measurements. In addition, the electronic structures of the polymers were described via quantum chemical calculations. Copyright © 2007 Society of Chemical Industry     

Markoff chain modelling of NDI techniques

A procedure for non‐destructive inspection by taking into account the effects of stochastic fatigue crack growth is presented. For this purpose a Markoff chain model is used to update the crack statistics, allowing an efficient computational implementation and a clear account of the involved concepts. In this context, perfect and imperfect removal of cracks, respectively, are considered, which represent idealizations defining bounds for actual situations.     

Early Events, Kinetic Intermediates and the Mechanism of Protein Folding in Cytochrome c

Kinetic studies of the early events in cytochrome c folding are reviewed with a focus on the evidence for folding intermediates on the submillisecond timescale. Evidence from time-resolved absorption, circular dichroism, magnetic circular dichroism, fluorescence energy and electron transfer, small-angle X-ray scattering and amide hydrogen exchange studies on the t ≤ 1 ms timescale reveals a picture of cytochrome c folding that starts with the ~ 1-μs conformational diffusion dynamics of the unfolded chains. A fractional population of the unfolded chains collapses on the 1 – 100 μs timescale to a compact intermediate I_C containing some native-like secondary structure. Although the existence and nature of I_C as a discrete folding intermediate remains controversial, there is extensive high time-resolution kinetic evidence for the rapid formation of I_C as a true intermediate, i.e., a metastable state separated from the unfolded state by a discrete free energy barrier. Final folding to the native state takes place on millisecond and longer timescales, depending on the presence of kinetic traps such as heme misligation and proline mis-isomerization. The high folding rates observed in equilibrium molten globule models suggest that I_C may be a productive folding intermediate. Whether it is an obligatory step on the pathway to the high free energy barrier associated with millisecond timescale folding to the native state, however, remains to be determined.     

Certainty equivalence control with forcing: revisited

Certainty equivalence control with forcing has been shown to be optimal for several stochastic adaptive control problems with the average cost per unit time criterion. Recently researchers have started looking at stochastic adaptive control problems with a view to minimizing the rate of increase of the learning loss. This criterion is stronger than the average cost per unit time criterion. Certainty equivalence control with forcing does not usually suffice for the learning loss criterion and one has to develop fairly complicated schemes in order to achieve optimality. The objective of this paper is to see how well one might be able to do with a certainty-equivalence-control-with-forcing type of scheme. In particular we construct a class of such schemes whose learning loss is O((log n)^1+δ) for δ > 0, whereas optimal schemes typically have a O(log n)learning loss.     

Vine Copula Specifications for Stationary Multivariate Markov Chains

Vine copulae provide a graphical framework in which multiple bivariate copulae may be combined in a consistent fashion to yield a more complex multivariate copula. In this article, we discuss the use of vine copulae to build flexible semiparametric models for stationary multivariate higher‐order Markov chains. We propose a new vine structure, the M‐vine, that is particularly well suited to this purpose. Stationarity may be imposed by requiring the equality of certain copulae in the M‐vine, while the Markov property may be imposed by requiring certain copulae to be independence copulae.     

汕头市基于改进Markov链的空气质量预报模型的研究

为了更有效的对汕头市空气质量进行预测,我们将基于Markov链理论的空气质量的统计预报模型进行了改进,加入了气象因素对模型进行修正,并作实例验证其可行性及准确率检验。证明了该模型具有较好的短期预测正确率,有一定的实用价值。     

基于MCFM模型的集贸市场火灾致灾因素分析

为降低大型集贸市场的火灾风险,探究大型集贸市场火灾致灾因素,运用解释结构模型分析各因素间的内在联系。结合交叉影响分析法和马尔可夫链预测构建定量分析模型,获得火灾致灾因素的稳态概率矩阵。研究结果表明：马尔可夫修正概率更加准确,该模型可明确大型集贸市场火灾致灾因素排查和管控的重点。     

面向用户多品种定制的分布式供应链调度

针对云制造面向分布式供应链环境中的多品种定制问题,提出一种多目标生产运输优化调度模型和基于改进混合蛙跳算法的求解方法。该模型考虑供应链中的制造/供应两阶段,以及不同企业间的运输时间和成本,得到成本最小、时间最短、生产空闲率最小、订单延迟最小的调度方案。同时,该算法重新定义原有算法的核心操作算子以适应离散调度问题求解,并结合模拟退火和极值优化算法的特性,进一步改进离散域的混合蛙跳算法的局部搜索性能。通过项目调度标准测试集验证了该改进算法的性能,并以6个品种定制需求为案例,验证了所提模型与算法的有效性。     

Tailoring side chains of low band gap polymers for high efficiency polymer solar cells

High efficiency organic solar cells (OSCs) require conjugated polymers with a low band gap, broad absorption in visible and IR region, high carrier mobility, and relatively high molecular weight as p-type donor materials. Flexible side chains on the rigid polymer backbone are crucial for the solubility of conjugated polymers. In this work, four polymers with the main chain structure of fluorene-thiophene-benzothiadiazole-thiophene and flexible side chains located on fluorene, thiophene, and benzothiadiazole moiety, respectively, have been synthesized by Suzuki-Miyaura-Schlüter polycondensation. Photovoltaic device measurements with a device configuration of ITO/polymer:PC₇₁BM blends/LiF/Al show that P1 carrying octyloxy chains on benzothiadiazole rings gives the best performance, with a power conversion efficiency of 3.1%.     

Integrated multi‐echelon supply chain design with inventories under uncertainty: MINLP models,computational strategies

We address in this article a problem that is of significance to the chemical industry, namely, the optimal design of a multi‐echelon supply chain and the associated inventory systems in the presence of uncertain customer demands. By using the guaranteed service approach to model the multi‐echelon stochastic inventory system, we develop an optimization model to simultaneously determine the transportation, inventory, and network structure of a multi‐echelon supply chain. The model is an MINLP with a nonconvex objective function including bilinear, trilinear, and square root terms. By exploiting the properties of the basic model, we reformulate this problem as a separable concave minimization program. A spatial decomposition algorithm based on the integration of Lagrangean relaxation and piecewise linear approximation is proposed to obtain near global optimal solutions with reasonable computational expense. Examples for specialty chemicals and industrial gas supply chains with up to 15 plants, 100 potential distribution centers, and 200 markets are presented. © 2009 American Institute of Chemical Engineers AIChE J, 2010