沿面闪络流体模型电离参数粒子模拟确定方法

介绍了粒子模拟确定高功率微波介质沿面闪络击穿流体模型相关电离参数的方法.对粒子模拟方法 (包括带电粒子动力学方程、次级电子发射以及蒙特卡罗碰撞模型)和流体整体模型方法 (包括连续性方程和能量守恒方程)做了简介.基于自编的1D3V粒子模拟-蒙特卡罗碰撞程序给出了在高(低)气压、不同气体种类以及不同微波场强和微波频率下流体模型电离参数的粒子模拟结果,包括电离频率、击穿时间、平均电子能量、电子能量分布函数类型.研究结果表明:平均电子能量与电子能量分布函数类型关系不大;中低气压下,电子能量接近Maxwell分布,电子能量分布函数类型对电离参数几乎没有影响;中高气压下,电子能量分布函数类型对电离参数有重要影响,其依赖系数X趋于高阶形式.不同气体的电子能量分布函数类型不同,需要利用粒子模拟对电子能量分布函数类型进行标定.同时,电子能量分布函数依赖系数与微波场强和频率也有关系,其随微波场强增加而增大,随微波频率增加而减小.在给定考察范围(微波场强在7 MV/m以下,微波频率在40 GHz以内),中低气压下,平均电子能量随微波场强增加而迅速增大,电离频率随微波场强增加先增大后降低,平均电子能量随微波频率增加而降低,电离频率随微波频率增加先增加后降低;高气压下,平均电子能量随微波场强增加而缓慢增大,电离频率随微波场强增加而增大,微波频率对平均电子能量和电离频率影响不大.     

(2+1)维Konopelchenko-Dubrovsky方程新的多孤子解

利用齐次平衡方法,将(2+1)维Konopelchenko-Dubrovsky方程转化为两个变量分离的线性偏微分方程,然后采用三种不同的函数假设,得到相应的常系数微分方程,通过求解特征方程,方便地构造出Konopelchenko-Dubrovsky方程新的多孤子解.     

Magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys near Martensitic transformation

This paper studies the magnetic hysteresis and refrigeration capacity of Ni-Mn-Ga alloys in detail during heating and cooling isothermal magnetisation processes. The Ni-Mn-Ga alloys show larger magnetic hysteresis when they transform from austenite to martensite, but smaller magnetic hysteresis when they transform from martensite to austenite. This behaviour is independent of either the pure Ni-Mn-Ga alloys or the alloys doped with other elements. Because of the existence of the magnetic hysteresis, the relation between the magnetic entropy change and refrigeration capacity is not simply linear. For practical consideration, magnetocaloric effect of Ni-Mn-Ga alloys should be investigated both on cooling and heating processes.     

GeFe2O4晶体的基态能级和零场分裂参量

GeFe₂O₄是一种单晶化合物，考虑到由3个〈111〉方向之一的一个 轴，从一个中心位置 到另一个中心位置之间，以Fe²⁺离子为中心离子和O^2-为配体构 成了三角（C 3v）对称体系.利用不可约张量理论，建立了3d⁴/3d⁶离子三角（C3 v）对称的晶体场和 自旋相互作用哈密顿矩阵，因此，由完全对角化的晶体场和自旋-轨道相互作用哈密顿矩阵 和电子顺磁共振理论公式求出单晶GeFe₂O₄中Fe²⁺离子 的电子顺磁共振零场分 裂参量D和F-a.并研究了自旋三重态对电子顺磁共振（EPR）零场分裂的贡献.结果显示自旋 三重态对基态零场分裂的贡献是较强的，理论计算结果与实验值相符. 关键词： 自旋三重态 晶体场 低自旋态 高自旋态 零场分裂     

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在本文中, 令为一列行为混合随机变量阵列. 本文研究了行为混合随机变量阵列加权和的极限行为, 并且一些新的完全收敛性结果被取得, 这些结果推广和改进了相应的已有定理.     

The Synthesis and 31P NMR Spectral Studies of Cyclophosphazenes

A modified method for preparing large-scale quantities of pure hexachlorocyclophosphazene (N₃P₃Cl₆) and octachlorocyclotetraphosphazene (N₄P₄Cl₈), phosphorus pentachloride with ammonium chloride, in the presence of zinc chloride, has been developed. The time of the reaction and the quantities of the catalyst are also studied. It is found that the optimum reaction time is 1.5 h and by-products are remarkably reduced by addition of 10% zinc chloride. As indicated by the ³¹ P NMR spectra, the synthesis and separation of cyclophosphazenes can be accomplished in moderate yield of tetramer (39%) and good yield of trimer (83%).     

Microstructure,Tribological Behavior,and Corrosion-Resistant Performance of Bonded MoS2 Solid Lubricating Film Filled with Nano-LaF3

The anti-friction and wear-resistant performances of bonded MoS₂ solid lubricating films filled with nano-LaF₃ filler were investigated under in drying wear conditions, the corrosion-resistant performances of bonded lubricating films was evaluated according to ASTM-B117, and the characteristics of the bonded lubricating films were examined by TEM and elemental x-ray map. The wear-resistant performance of the bonded lubricating films filled with nano-LaF₃ filler increases with increasing content of nano-LaF₃ filler within a content range between 0 and 5 wt%, whereas the bonded lubricating films filled with 0.5–1 wt% micro-LaF₃ filler exhibit the better wear-resistant performances. The incorporation of both nano-LaF₃ and micro-LaF₃ filler leads the increase of the coefficient of friction of the bonded lubricating films. The LaF₃ filler can improve the corrosion-resistant performance of the bonded MoS₂ solid lubricating films, whereas the incorporation of nano-LaF₃ filler is more effective to improve the corrosion-resistant performance of the bonded lubricating films than micro-LaF₃ filler. The improvement in the wear-resistant and corrosion-resistant performances of the bonded lubricating films by the incorporation of the nano-LaF₃ filler is attributed to the strengthened interfacial bonding among the nano-LaF₃ and the MoS₂ lubricant and the polymeric matrix. However, a too high mass fraction of the nano-LaF₃ filler in the bonded lubricating films will increase surface and interface defects, and lead the worsening of corrosion-resistant performance of the bonded lubricating films.     

A quantum mechanics/molecular mechanics study on the hydrolysis mechanism of New Delhi metallo-β-lactamase-1

New Delhi metallo-β-lactamase-1 (NDM-1) has emerged as a major global threat to human health for its rapid rate of dissemination and ability to make pathogenic microbes resistant to almost all known β-lactam antibiotics. In addition, effective NDM-1 inhibitors have not been identified to date. In spite of the plethora of structural and kinetic data available, the accurate molecular characteristics of and details on the enzymatic reaction of NDM-1 hydrolyzing β-lactam antibiotics remain incompletely understood. In this study, a combined computational approach including molecular docking, molecular dynamics simulations and quantum mechanics/molecular mechanics calculations was performed to characterize the catalytic mechanism of meropenem catalyzed by NDM-1. The quantum mechanics/molecular mechanics results indicate that the ionized D124 is beneficial to the cleavage of the C–N bond within the β-lactam ring. Meanwhile, it is energetically favorable to form an intermediate if no water molecule coordinates to Zn2. Moreover, according to the molecular dynamics results, the conserved residue K211 plays a pivotal role in substrate binding and catalysis, which is quite consistent with previous mutagenesis data. Our study provides detailed insights into the catalytic mechanism of NDM-1 hydrolyzing meropenem β-lactam antibiotics and offers clues for the discovery of new antibiotics against NDM-1 positive strains in clinical studies.     

From Nitro‐ to Sulfonyl‐Based Chromophores: Improvement of the Comprehensive Performance of Nonlinear Optical Dendrimers

Through the combination of the divergent and convergent approaches, coupled with the utilization of the powerful Sharpless “click‐chemistry” reaction, two series of sulfonyl‐based high‐generation NLO dendrimers were conveniently prepared with high purity and in satisfactory yields. Thanks to the perfect three‐dimensional (3D) spatial isolation from the highly branched structure and the isolation effect of the exterior benzene moieties and the interior triazole rings, these dendrimers exhibited large second harmonic generation coefficient (d₃₃) values up to 181 pm V^?1, which, to the best of our knowledge, is the highest value so far for polymers containing sulfonyl‐based chromophore moieties. Meanwhile, compared with the nitro‐chromophore‐based analogues, their optical transparency and NLO stability were improved in a large degree, due to the lower dipole moment (μ) and the special main‐chain structure of sulfonyl‐based chromophore in these dendrimers.     

Preparation and characterization of ZrCO/C composite aerogels

Zr-containing organic aerogels were synthesized by ligand substitution reaction of polyzirconoxone and 2, 4-dihydroxybenzoic acid, followed by polymerization with formaldehyde, and then supercritical drying using CO₂. After carbonization and carbothermal reduction under an argon atmosphere, ZrCO/C composite aerogels with controllable zirconium content (47.8–78.6 wt%) were obtained. The carbothermal reduction was substantially completed at 1,500 °C, and the obtained ZrCO/C composite aerogels exhibit low oxygen contents (9.4–6.7 wt%) and high surface areas (589–147 m²/g). Pore morphologies of the ZrCO/C composite aerogels were investigated in detail by nitrogen sorption measurements, scanning electron microscopy and its associated energy-dispersive X-ray microanalysis measurements. The results show that the aerogels are composed of carbon framework and Zr-conglomerations, and the surface area of aerogel is severely affected by its zirconium content. The presence of reductive ZrC crystals can greatly enhance the oxidation resistance ability of amorphous carbon framework and prevent collapse.