From C58 to C62 and back: Stability,structural similarity,and ring current

An increasing number of observations show that non‐classical isomers may play an important role in the formation of fullerenes and their exo‐ and endo‐derivatives. A quantum‐mechanical study of all classical isomers of C₅₈, C₆₀, and C₆₂, and all non‐classical isomers with at most one square or heptagonal face, was carried out. Calculations at the B3LYP/6‐31G* level show that the favored isomers of C₅₈, C₆₀, and C₆₂ have closely related structures and suggest plausible inter‐conversion and growth pathways among low‐energy isomers. Similarity of the favored structures is reinforced by comparison of calculated ring currents induced on faces of these polyhedral cages by radial external magnetic fields, implying patterns of magnetic response similar to those of the stable, isolated‐pentagon C₆₀ molecule. © 2016 Wiley Periodicals, Inc.     

Analysis of interfacial thermal stresses for damaged structures: new theoretical model

The use of the composites for the reinforcement of the beams and structures metallic and non-metallic, is one of the recent methods of the rehabilitation by composites, what permits to replace the classic techniques of the assembly based on soldering, bonding, etc. But this technique gives stresses concentrations to the level of the zone of the assembly. The methods of rehabilitation by composites permit to prolong the life span of these structures under a reduced exploitation cost and with less pollution to the environment. In this article, an original survey on the stresses between the structure and the composite (fiber reinforced polymer [FRP]) was finalized, taking account, as well, of the mechanical and thermal loadings, as well as the effects of deformation shear lag. This originality puts in evidence a new theoretical model which takes into account the thermal effect of the stresses concentration that has not been treated seriously by the previous studies.     

Theoretical Study on Hydrogen Bonding of Mono‐ and Dihydrated Complexes of 7‐(3′‐Pyridyl)indole in Excited States

The intermolecular hydrogen bonds of mono‐ and dihydrated complexes of 7‐(3′‐Pyridyl)indole (7‐3′PI) have been investigated using the time‐dependent density functional theory (TD‐DFT) method. The electrostatic potential analysis of monomer 7‐3′PI and 7‐(3′‐Pyridyl)indole‐water (7‐3′PI‐W) indicates that an intermolecular hydrogen bond between two waters can be formed for 7‐(3′‐Pyridyl)indole‐2water (7‐3′PI‐2W) complex. The calculated bond lengths of the intermolecular hydrogen bonds of 7‐3′PI‐W and 7‐3′PI‐2W in the S₁ state (the first excited singlet state) are all shortened compared to the ground state. By the analysis of bond length, charge population and infrared spectra, it is demonstrated that the intermolecular hydrogen bonds of 7‐3′PI‐W and 7‐3′PI‐2W are all strengthened upon electronic excitation to the S1 state. Moreover, the fluorescence of 7‐3′PI‐W and 7‐3′PI‐2W are all red‐shifted to larger wavelength compared to monomer 7‐3′PI. The red‐shift of fluorescence peak of 7‐3′PI‐W and 7‐3′PI‐2W should be attributed to the change of hydrogen bond interaction before and after photoexcitation. Therefore, it can be concluded that the intermolecular hydrogen bonding strengthening in the excited S₁ state induces the fluorescence weakening of 7‐3′PI.     

K9光学玻璃化学钢化技术研究

为提高K9光学玻璃在一些特殊应用领域（如高压、温度变化剧烈等）的力学性能,并保证其光学性能符合精密光学仪器要求,对K9光学玻璃进行了化学钢化技术研究。以脆性材料断裂过程微裂纹扩展理论为基础,导出化学钢化玻璃强度应力因子计算模型,分析化学钢化表面应力与表面微裂纹深度、韧性之间的关系,指出化学钢化工艺应注意的事项。通过实验研究,分析化学钢化温度和钢化时间对K9光学玻璃抗弯强度、表面应力及应力层厚度的影响,优化得出K9光学玻璃化学钢化温度为400 ℃、钢化时间为40 h。采用优化工艺,获得了表面应力为500 MPa、应力层厚度为50 μm量级及规格为220 mm×110 mm×22 mm的化学钢化K9光学玻璃样件。钢化后,样件抗弯强度提高了3.5倍以上,且表面疵病、光学鉴别率、透过率等光学性能指标未见明显变化。     

时空调制对可激发介质螺旋波波头动力学行为影响及控制研究

本文首先研究了时空调制对可激发介质中周期螺旋波波头动力学行为的影响. 随着时空调制的增大, 螺旋波经历了周期螺旋波、外滚螺旋波、旅行螺旋波和内滚螺旋波的显著变化. 通过定义序参量来定量的描述由时空调制引起的螺旋波在不同态之间非平衡跃迁的临界条件, 及漫游螺旋波波头圆滚圆半径随调制参数的变化情况. 当时空调制增大到某个临界值时, 螺旋波发生了破碎; 再增加时空调制, 螺旋波则发生了衰减, 系统最终演化为空间均匀静息态. 在文中给出了螺旋波发生破碎和衰减的机理和原因. 最后将时空调制方法运用于漫游螺旋波, 实现了将漫游螺旋波控制成周期螺旋波, 或将其控制为空间均匀静息态.     

利用短期心脏记忆消除螺旋波和时空混沌

在Luo-Rudy的心脏模型中引入了记忆效应, 该记忆效应表现为膜间电压的延迟耦合. 研究了记忆效应对螺旋波的影响, 数值模拟结果表明:心脏记忆可导致螺旋波无规则漫游;当延迟时间适当选取时, 增加记忆强度会导致螺旋波的频率减小, 如果记忆强度超过临界值, 心脏记忆效应还可以使螺旋波和时空混沌消失, 因为含时外行钾离子电流被心脏记忆过度抑制.     

The effect of intragranular microstress in Al2O3—SiC nanocomposites

A theoretical model is established to investigate the intragranular particle residual stress in Al2O3-SiC nanocomposites.Using this model,we calculate the average compressive stress on the Al2O3 grain boundary(GB) and the average tensile stress within Al2O3 grains caused by SiC nanoparticles.The normal compressive stress strengthens the GB,and the average tensile stress weakens the grains.The model gives a reasonable interpretation of the strength changes of Al2O3-SiC nanocomposites with the number of SiC particles.     

Influence of the Jahn—Teller distortion on magnetic ordering in TbMn1-xFexO3

The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites.In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3（x = 0,0.02,0.05,0.10,and 0.20） single crystals in the basal MnO2 plane.The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn-Teller distortion,which makes the nearest neighboring（NN） FM interaction dominant over the next nearest neighbor（NNN） AFM interaction.This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering,which collapses when x ≥ 0.05.The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.     

The effect of intragranular microstress in A1203-SiC nanocomposites

A theoretical model is established to investigate the intragranular particle residual stress in A1203-SiC nanocom-posites. Using this model, we calculate the average compressive stress on the A1203 grain boundary （GB） and the average tensile stress within A1203 grains caused by SiC nanoparticles. The normal compressive stress strengthens the GB, and the average tensile stress weakens the grains. The model gives a reasonable interpretation of the strength changes of A1203-SiC nanocomposites with the number of SiC particles.     

Anchorage strength models for end-debonding predictions in RC beams strengthened with FRP composites

The increase in the flexural capacity of RC beams obtained by externally bonding FRP composites to their tension side is often limited by the premature and brittle debonding of the external reinforcement. An in-depth understanding of this complex failure mechanism, however, has not yet been achieved. With specific regard to end-debonding failure modes, extensive experimental observations reported in the literature highlight the important distinction, often neglected in strength models proposed by researchers, between the peel-off and rip-off end-debonding types of failure. The peel-off failure is generally characterized by a failure plane located within the first few millimetres of the concrete cover, whilst the rip-off failure penetrates deeper into the concrete cover and propagates along the tensile steel reinforcement. A new rip-off strength model is described in this paper. The model proposed is based on the Chen and Teng peel-off model and relies upon additional theoretical considerations. The influence of the amount of the internal tensile steel reinforcement and the effective anchorage length of FRP are considered and discussed. The validity of the new model is analyzed further through comparisons with test results, findings of a numerical investigation, and a parametric study. The new rip-off strength model is assessed against a database comprising results from 62 beams tested by various researchers and is shown to yield less conservative results. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 373–388, May–June, 2008.