Properties of a genetic algorithm extended by a random self-learning operator and asymmetric mutations: A convergence study for a task of powder-pattern indexing

Genetic algorithms represent a powerful global-optimisation tool applicable in solving tasks of high complexity in science, technology, medicine, communication, etc. The usual genetic-algorithm calculation scheme is extended here by introduction of a quadratic self-learning operator, which performs a partial local search for randomly selected representatives of the population. This operator is aimed as a minor deterministic contribution to the (stochastic) genetic search. The population representing the trial solutions is split into two equal subpopulations allowed to exhibit different mutation rates (so called asymmetric mutation). The convergence is studied in detail exploiting a crystallographic-test example of indexing of powder diffraction data of orthorhombic lithium copper oxide, varying such parameters as mutation rates and the learning rate. It is shown through the averaged (over the subpopulation) fitness behaviour, how the genetic diversity in the population depends on the mutation rate of the given subpopulation. Conditions and algorithm parameter values favourable for convergence in the framework of proposed approach are discussed using the results for the mentioned example. Further data are studied with a somewhat modified algorithm using periodically varying mutation rates and a problem-specific operator. The chance of finding the global optimum and the convergence speed are observed to be strongly influenced by the effective mutation level and on the self-learning level. The optimal values of these two parameters are about 6 and 5%, respectively. The periodic changes of mutation rate are found to improve the explorative abilities of the algorithm. The results of the study confirm that the applied methodology leads to improvement of the classical genetic algorithm and, therefore, it is expected to be helpful in constructing of algorithms permitting to solve similar tasks of higher complexity.     

Age-dependent variations of cell response to oxidative stress: proteomic approach to protein expression and phosphorylation

We investigated the protein profiles of variously aged rat astrocytes in response to oxidative stress. After H2O2-exposure of cells at 100 microM for 30 min, the relative intensity of ten protein spots changed on two-dimensional (2-D) gels compared with control gels after silver staining. Matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) analysis after in-gel digestion revealed that six of these spots corresponded to three kinds of proteins, each of which was composed of a protein and its modified form with a different isoelectric point (pI). These three proteins were identified as peroxiredoxins (PRDXs) II and III, and calpactin I light chain (p11). H2O2-exposure increased the intensity of the spot with lower pI and simultaneously decreased that of the spot with higher pI for both PRDXs II and III. In addition, the expression of annexin VII, S-adenosyl-L-homocysteine hydrolase, elongation factor II fragment (EF-II), and adenosine deaminase was increased by H2O2-exposure in astrocytes from variously aged rats. Using the Pro-Q Diamond staining, heat shock protein 60 kDa (Hsp 60) and alpha-tubulin were observed to be phosphorylated upon H2O2-exposure. While phosphorylation of alpha-tubulin was correlated positively with age, the changes in abundance of ten protein spots as described above were independent of age. These results suggest that aging does not suppress the responses aimed at limiting injury and promoting repair brought about by severe oxidative stress, and might affect cell dynamics including the formation of microtubules.     

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     

PbO2阳极在硫酸溶液中的析氧失活行为

采用热分解鄄电镀法制备了以Sb 掺杂SnO₂(Sb-SnO₂)为底层的Ti 基PbO₂阳极(Ti/PbO₂). 采用加速电解寿命测试、电化学阻抗谱、XRD、SEM-EDX 等技术, 研究了Ti/PbO₂阳极在硫酸溶液中的电解失效行为和机制.结果表明,在新制备的PbO₂镀层中, 由于氧空位的存在, PbO₂镀层的内应力表现为拉应力, 随着电解的进行, 阳极表面生成的活性氧原子在向基底扩散的过程中, 将Pb³⁺态氧化为Pb⁴⁺态, 逐渐占据镀层内作为自由电子施主的氧空位, 这不仅导致镀层的导电性能下降, 同时使镀层的应力逐渐由拉应力转变为压应力, 镀层性质逐渐劣化. 这一过程基本结束时,活性氧原子才大量扩散至Ti基底导致基底的钝化, 在Ti 基底和镀层界面出现显著的界面应力, 在界面应力和镀层内压应力的共同作用下, 阳极出现鼓泡、脱落, 迅速进入失活阶段.     

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．