Electron image series reconstruction of twin interfaces in InP superlattice nanowires

The twin interface structure in twinning superlattice InP nanowires with zincblende structure has been investigated using electron exit wavefunction restoration from focal series images recorded on an aberration-corrected transmission electron microscope. By comparing the exit wavefunction phase with simulations from model structures, it was possible to determine the twin structure to be the ortho type with preserved In-P bonding order across the interface. The bending of the thin nanowires away from the intended 110 axis could be estimated locally from the calculated diffraction pattern, and this parameter was successfully taken into account in the simulations.     

Simulation of photoelectron spectra using the reflection principle in combination with unrestricted excitation ADC2 to assess the accuracy of excited-state calculations

The gas-phase photoelectron spectra of ethene, formaldehyde, formic acid and difluoromethane are simulated using the reflection principle and the unrestricted second-order algebraic diagrammatic construction [UADC(2)] scheme of the polarization propagator for the computation of the vertical-excited states of the cations at the equilibrium geometry of the parent neutral molecule. Comparison is made with experimental spectra and the established highly accurate ionization IP-ADC(3) theory to gain insight into the accuracy and applicability of recently developed excitation UADC schemes. Within UADC(2), we distinguish between the strict and extended schemes UADC(2)-s and UADC(2)-x. While the latter approach is found to slightly underestimate the experimental photoelectron spectra by 0.3 eV and can thus be regarded as a reliable scheme within the limits of the applied reflection principle and the underlying approximations, the UADC(2)-s scheme tends to overestimate the excitation energies by about 0.5 eV. Time-dependent density functional theory is also applied in combination with the standard B3LYP xc functional and turns out to be a useful computational tool for the simulation of the photoelectron spectra of the studied species.     

Novel covalent bond in proteins: calculations on model systems question the bond stability

We have investigated the sulfilimine covalent link between methionine (Met) and lysine (Lys), recently identified in collagen IV (R. Vanacore, A.-J. L. Ham, M. Voehler, C. R. Sanders, T. P. Conrads, T. D. Veenstra, K. B. Sharpless, P. E. Dawson, B. G. Hudson, Science 2009, 325, 1230), and have explored its stability with respect to both the redox processes and UV radiation by means of advanced computational methods. We have concluded that the bond should be present in a protonated state, (-NH=S-)(+). The bond is characterized by a relatively high standard reduction potential, that is, the bond should not be stable in a typical cell environment; if the sulfilimine bond exists (as suggested by the experiment) then the bond has to be supported by the protein environment. The sulfilimine bond then destabilizes the protein structure with respect to the alternative tertiary structure. We discuss conditions under which the bond could be formed as well as other possible structural arrangements consistent with the Met-Lys stoichiometry; some of the alternative bond motifs are more thermodynamically stable than the sulfilimine bond. We suggest that the character of the Met-Lys contact could be approached via NEXAFS spectroscopy. Finally, we show that the protonation brings photostability to the sulfilimine bond.     

基于LC串联型储能变换器的 状态反馈控制策略研究

为了满足新能源电站的无功需求,提出了一种LC串联滤波型变换器.以三相380 V/30 kW并网变换器为例,相比传统的L和LC型滤波器结构,所提变换器结构能够在保持变换器输出无功功率能力的同时,降低系统直流工作电压约为原变换器的71％,释放了系统12％的有源容量,同时效率相比原滤波结构有6％的提升.此外,基于LC变换器的离散状态模型,提出了一种基于LC串联滤波器型变换器的状态控制方法,有效地提升了LC串联滤波器在谐振频率处的系统阻尼.最后在PSIM中搭建了LC型变换器的仿真模型,验证了LC滤波型变换器的优势和状态反馈控制策略的可行性.     

钢纤维混凝土的本构模型及力学性能分析

为充分研究钢纤维混凝土的力学性能,基于混凝土的弥散开裂模型,并考虑纤维与混凝土之间的黏结作用,建立了新的钢纤维混凝土本构模型.在模型中分两种情况考虑纤维作用,混凝土开裂前,纤维与混凝土完全黏结,服从复合材料理论;混凝土开裂后,将分别考虑混凝土和钢纤维的贡献.通过黏结滑移模型,计算钢纤维在混凝土中脱黏和拔出过程中,纤维对开裂后混凝土的增强作用.采用Fortran编程,利用有限元软件ABAQUS中提供的子程序Umat,将提出的本构模型引入ABAQUS,并用于有限元模型去模拟钢纤维混凝土的拉伸和四点弯曲试验.通过数值模拟结果和试验数据的对比,充分验证了所提出的钢纤维混凝土本构模型的准确性.并对钢纤维混凝土的受拉强度、残余强度、受弯强度以及韧性等力学性能进行详细的分析.     

高层建筑形状及布局对城市街区 行人风环境影响研究

基于风洞试验和计算流体动力学方法(Computational Fluids Dynamics,CFD)研究高层建筑形状及布局对城市街区行人风环境的影响.采用最大风速比和归一化加速面积比,定量研究五种高层建筑形状及四类建筑布局对城市街区行人风环境的影响,确定全风向下的最优建筑形状以及布局,结合CFD数值模拟获得的全域流场信息,揭示建筑形状和布局对于城市街区行人风环境的影响机理.结果表明:在保持建筑高度和街区容积率一致的情况下,高层建筑群周边最大风速比不会随着建筑形状和建筑布局的改变而发生明显变化.但建筑形状和建筑布局会改变建筑群周边高风速区域的面积大小,全风向下的最优建筑形状和布局分别是Y字形和错列式布局,而最不利形状和布局分别是H字形和围合式布局.不同布局下的方形、H字形及X字形高层建筑群的最不利风向均位于斜风向,而十字形及Y字形则为正风向.高层建筑群在行人高度处的风加速现象主要是由狭管效应和角部分离效应造成的.     

基于动态燃料成本双层优化的 燃煤发电企业管控模型

为使燃煤发电企业降低燃料成本,实现燃料科学管控,提出一种综合考虑发电可靠性和生产经济性的燃料成本双层优化模型,上层为电煤采购库存混合整数规划模型,下层为混煤掺烧非线性优化模型,双层模型交替迭代协调优化,实现燃料管控动态决策.针对优化模型高维多约束情况,提出一种混沌映射初始化和高斯变异结合的改进灰狼优化算法.以某燃煤电厂模拟运营进行算例验证分析,结果表明,所提模型可以降低燃煤电厂7.80％的燃煤成本,证明了所提模型与求解算法的有效性和可行性.     

FOXM1688-748结构域相互作用蛋白的鉴定

为了鉴定转录因子FOXM1转录激活结构域(C-端第688位到748位氨基酸序列)的互作蛋白,以FOXM1的cDNA为模板,采用聚合酶链式反应(Polymerase Chain Reaction,PCR)方法扩增获得其转录激活结构域序列,克隆进入原核表达载体pGEX-4T2;利用大肠杆菌原核表达获得融合谷胱甘肽S-转移酶(Glutathione S-Transferase,GST)标签的重组蛋白GST-FOXM1688-748;通过GST-pulldown结合质谱方法鉴定FOXM1688-748的互作蛋白,成功构建了原核表达质粒pGEX-4T2-FOXM1688-748,获得了原核表达的重组蛋白GST-FOXM1688-748.将质谱鉴定获得的互作蛋白进行分析和归类,预示一些互作蛋白可以参与激活FOXM1的转录活性,如RPN2、MISP、MCM7蛋白,一些互作蛋白可以参与调控FOXM1蛋白的稳定性,如USP9Y、CUL4A、HSPB1、BAG2蛋白.FOXM1蛋白的转录激活结构域与许多不同功能的蛋白发生相互作用,暗示该结构域具有重要的分子生物学作用,期望为以FOXM1为靶点的临床药物研发提供实验依据.     

功能梯度仿生头盔防护性能与头部损伤分析

为了提高摩托车头盔防护性能降低头部损伤风险,本文引入功能梯度仿生泡沫结构替代传统头盔的均匀密度泡沫衬垫.通过头盔耦合生物力学头部有限元模型,获取撞击过程中头部质心加速度、生物力学响应和头盔结构响应,综合分析不同密度梯度方案对头盔防护能力的影响.结果表明,功能梯度泡沫结构在中高速冲击下有更明显的优势.相比传统头盔吸能缓冲层的均匀泡沫密度方案和新型头盔的正/负密度梯度方案,最大密度为80 kg/m3的负密度梯度泡沫设计方案可以更有效改善头盔结构碰撞响应并降低碰撞过程中头部损伤,且随着密度差的增大,负密度梯度头盔的防护性能得到了进一步提高.     

基于液冷的锂离子动力电池散热结构优化设计

针对锂离子电池单体成组后温度场的非均匀性导致的热不一致性问题,以及高温下电池单体间的热交互引发的热安全性问题,采用仿真与试验相结合的方式,基于锂离子电池生-传热机理,设计了电池单体单独成组、电池单体之间夹隔泡沫棉、电池模组底部布置液冷板3种递进式散热方案,并对液冷板进行了优化设计.采用有限元软件STAR-CCM+,仿真分析了3种方案下电池模组在不同放电倍率时的温度分布.结果表明:增加泡沫棉可减少电池间的热交互,进而提高电池单体间的热均衡性.在结合泡沫棉、导热板以及优化后(采用液冷管道串-并联组合方式)的液冷系统散热条件下,电池模组以2C倍率放电时最高温度为35.08℃,最大温差仅为4.85℃.研究结果可为电池热管理散热系统结构设计提供一定的理论基础.