Hybrid nanomaterial flow and heat transport in a stretchable convergent/divergent channel:a Darcy-Forchheimer model

The flow behavior in non-parallel walls is an important factor of any physical model including cavity flow and canals, which is applicable for diverging/converging channel. The present communication explains that the flow of the hybrid nanomaterial subjected to the convergent/divergent channel has non-parallel walls. It is assumed that the hybrid nanomaterial movement is in the porous region. A Darcy-Forchheimer medium of porosity is considered to interpret the porosity features. A useful similarity function is adopted to get the strong ordinary coupled equations. Numerical solutions are achieved through the Runge-Kutta-Fehlberg(RKF) fourth-fifth order method, and they are validated with the existing results. Physical nature of the involving constraints is reported with the help of plots. It is explored that the velocity of divergent channel decreases, and convergent channel enhances for the higher solid volume faction. Further, the presence of inertia coefficient and porosity parameter amplifies the velocity at the wall.     

An embedded boundary framework for compressible turbulent flow and fluid–structure computations on structured and unstructured grids

The finite volume method with exact two‐phase Riemann problems (FIVER) is a two‐faceted computational method for compressible multi‐material (fluid–fluid, fluid–structure, and multi‐fluid–structure) problems characterized by large density jumps, and/or highly nonlinear structural motions and deformations. For compressible multi‐phase flow problems, FIVER is a Godunov‐type discretization scheme characterized by the construction and solution at the material interfaces of local, exact, two‐phase Riemann problems. For compressible fluid–structure interaction (FSI) problems, it is an embedded boundary method for computational fluid dynamics (CFD) capable of handling large structural deformations and topological changes. Originally developed for inviscid multi‐material computations on nonbody‐fitted structured and unstructured grids, FIVER is extended in this paper to laminar and turbulent viscous flow and FSI problems. To this effect, it is equipped with carefully designed extrapolation schemes for populating the ghost fluid values needed for the construction, in the vicinity of the fluid–structure interface, of second‐order spatial approximations of the viscous fluxes and source terms associated with Reynolds averaged Navier–Stokes (RANS)‐based turbulence models and large eddy simulation (LES). Two support algorithms, which pertain to the application of any embedded boundary method for CFD to the robust, accurate, and fast solution of FSI problems, are also presented in this paper. The first one focuses on the fast computation of the time‐dependent distance to the wall because it is required by many RANS‐based turbulence models. The second algorithm addresses the robust and accurate computation of the flow‐induced forces and moments on embedded discrete surfaces, and their finite element representations when these surfaces are flexible. Equipped with these two auxiliary algorithms, the extension of FIVER to viscous flow and FSI problems is first verified with the LES of a turbulent flow past an immobile prolate spheroid, and the computation of a series of unsteady laminar flows past two counter‐rotating cylinders. Then, its potential for the solution of complex, turbulent, and flexible FSI problems is also demonstrated with the simulation, using the Spalart–Allmaras turbulence model, of the vertical tail buffeting of an F/A‐18 aircraft configuration and the comparison of the obtained numerical results with flight test data. Copyright © 2014 John Wiley & Sons, Ltd.     

Role of dicumyl peroxide on the morphology and mechanical performance of polypropylene random copolymer in microinjection molding

The purpose of this work is to systematically investigate the effects of dicumyl peroxide (DCP) on the microstructural evolution and mechanical properties of polypropylene random copolymers (PPRs) during the microinjection process. Polarized light microscopy, differential scanning calorimetry, X‐ray diffraction, and scanning electronic microscopy measurements were employed to characterize the morphology evolution of the PPR microparts with DCP. A hierarchical structure was found in the PPR microparts with DCP. Specifically, with the individual addition of organic peroxide, the orientation parameter of the PPR microparts decreased pronouncedly and the formation of skin layer was suppressed, while the formation of core layer was promoted. This was ascribed to the distribution of shear rate in the microchannel, which was determined by the wall ship effect in the filling stage and the relaxation behavior in the cooling stage. A mechanism was proposed to explain the distinctive filling behavior and molding characteristics of PPR with DCP in microinjection molding.     

Mechanistic studies on the formation of glycosidase-substrate and glycosidase-inhibitor covalent intermediates

Glycoside hydrolases catalyze the breaking of the glycosidic bond. This type of bond fashioned between two monosaccharides is very stable, and the polymers created are involved in multiple cellular processes, being crucial to life. In this article, computational methods were used to study the first step of the mechanism of reaction of retaining glycoside hydrolases in atomic detail. The systems modeled included a simplified reaction center and a small substrate/inhibitor. Using DFT calculations we were able to corroborate and provide molecular-level detail to the dissociative mechanism proposed in the literature. The role of the hydrogen bridge between the nucleophile and the C(2)--OH group of the ring was also investigated. Therefore, we concluded that this bridge is responsible for lowering the activation barrier by 5.1 kcal mol(-1) with functional BB1K/6-311+G(2d,2p), and the absence of the bridge explains, at least in part, the inhibitory effect of fluoro-substituted glycosides in the -2 position. The hydrogen bridge could also be involved in favoring the ring distortion verified in the transition state, and the dissociative character of the reaction mechanism. Using the NBO method, point atomic charges were calculated. In the transition state, the positive charge generated in the sugar ring is distributed nearly equally between the anomeric carbon and the ring oxygen, through a partial double bond involving the two atoms.     

Characterization of nonderivatized plant cell walls using high-resolution solution-state NMR spectroscopy

A recently described plant cell wall dissolution system has been modified to use perdeuterated solvents to allow direct in-NMR-tube dissolution and high-resolution solution-state NMR of the whole cell wall without derivatization. Finely ground cell wall material dissolves in a solvent system containing dimethylsulfoxide-d(6) and 1-methylimidazole-d(6) in a ratio of 4:1 (v/v), keeping wood component structures mainly intact in their near-native state. Two-dimensional NMR experiments, using gradient-HSQC (heteronuclear single quantum coherence) 1-bond (13)C--(1)H correlation spectroscopy, on nonderivatized cell wall material from a representative gymnosperm pinus taeda (loblolly pine), an angiosperm Populus tremuloides (quaking aspen), and a herbaceous plant Hibiscus cannabinus (kenaf) demonstrate the efficacy of the system. We describe a method to synthesize 1-methylimidazole-d(6) with a high degree of perdeuteration, thus allowing cell wall dissolution and NMR characterization of nonderivatized plant cell wall structures.     

Flanking transmission of metal stud walls with different junction details

Measurements of the normalised flanking sound level difference of different gypsum board flanking walls are reported. Results of a “standard” wall construction confirmed some results of the current draft standard of DIN 4109. Different constructions with various junction details and different wall constructions are described and measurement results are presented. By additional measurements on the walls, a prediction model for the weighted flanking level difference is suggested, based on the methodology of EN 12354. For the flanking transmission prediction of path Ff, three transmission paths are proposed. The model gives good agreement between calculated and measured weighted flanking level difference except for the case where the transmission along the inner lining of the flanking wall is dominant. In this case the prediction underestimates measurements by up to 7 dB.     

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针对不同体积分布指数p的W/Cu连续功能梯度材料的偏滤器第一壁结构,采用有限元软件计算了8MW.m?2稳态运行热加载以及等离子体破裂条件下1GW.m?2热流冲击下的力学响应。相同稳态加载条件下,W/Cu连续功能梯度材料的最优分布指数与分层梯度材料存在较大差异,其最优等效应力比分层梯度材料要小26%,表现出更优异的性能。在热冲击响应过程中,连续梯度W/Cu材料塑性损伤随p值不同也存在较大变化,其最优p值与其稳态运行时热应力最优p值存在一定差异,从第一壁应用条件考虑,应综合选取,最佳p值在1.2附近。综合来看,连续梯度W/Cu材料具有更连续变化的热物理属性及力学性能,在聚变堆第一壁结构设计中具有更大的应用潜力。     

黄土区金盏菊幼苗根部细胞壁对Pb/Cd复合胁迫响应的FTIR和Raman光谱

植物修复法是新兴的重金属污染土壤修复手段,也是未来极富应用潜力的主流技术之一。植物根部细胞壁作为重金属/土壤/植物相的交界面,天然地成为修复效能调控过程的关键部位和信号通道。植物细胞壁与重金属离子的作用行为具有物理化学和生理生化的双重属性,但以光谱技术为切入点,原位解析植物根部细胞壁对土壤重金属离子的响应关系还不多见。以黄土区修复植物金盏菊幼苗为研究对象,分析Pb/Cd复合胁迫对其根部细胞壁形貌的影响,借助X射线荧光光谱(XRF)、X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)和拉曼光谱(Raman)揭示细胞壁对Pb/Cd胁迫的响应信号。结果发现:Pb/Cd胁迫导致金盏菊根部细胞壁弯曲萎缩,表面分布若干点状深色沉积物颗粒;XRF证实细胞壁Pb/Xd含量增加,但XRD图谱没有发现典型Pb/Xd结晶峰。FTIP图谱中—OH振动峰定位于3 416 cm~(-1)处,表明Pb/Cd离子与—OH间可能存在配位键合;1 701和1 593 cm~(-1)处的特征峰分别移动到1 736和1 618 cm~(-1),说明Pb/Cd胁迫改变了金盏菊根部细胞壁蛋白质结构属性。Raman光谱中2 960 cm~(-1)附近峰强增加,暗示Pb/Cd胁迫影响了细胞壁纤维素分子排列方向。可以认为,细胞壁组分(果胶、蛋白质、纤维素等)和典型官能团(—OH,N—H,C=O等)对于减缓Pb/Cd胁迫引起的金盏菊根部细胞壁毒害效应贡献较大。     

A New Method for Assessment of Performing Mechanical Works of Energetic Compounds by the Cylinder Test

A new method is introduced for assessment of performing mechanical works of energetic compounds by cylinder wall velocities of CHNOFCl energetic compounds on the basis of the cylinder test. Four suitable decomposition paths are used to evaluate the number of moles of gaseous detonation products per gram of explosive, the average molecular weight of these gases, and the heat of detonation in calories per gram by considering different decomposition products HF, HCl, CO, N₂, H₂O, H₂, and CO₂. For CHNO and fluoro energetic compounds, the predicted cylinder wall velocities of these compounds give more reliable results than one of the best available empirical methods. The predicted root mean square (rms) deviations of cylinder wall velocities of the new model for some chloro explosives at actual radial expansions 0.6 and 1.9 mm are 0.010 and 0.062 km · s^–1, which show high reliability of the new method.     

边界层流中当地感受性过程的数值研究

边界层流中当地感受性问题的研究对层流向湍流转捩过程的预测与控制起着非常关键的作用,尤其是对边界层内诱导产生三维Tollmien-Schlichting(T-S)波成因过程的探讨具有更加重要的理论意义.采用高精度、高分辨率变间距的紧致有限差分方法,直接数值模拟了在自由来流湍流与二维壁面局部粗糙相互作用下边界层内的当地感受性问题.数值计算发现,在自由来流湍流与二维壁面局部粗糙作用下,边界层内诱导形成的当地感受性过程是真实存在的;且被激发的一组三维T-S波波包沿流向发展的过程中流向涡结构将逐渐形成,其强度将越演越烈.数值结果还显示,边界层内被诱导产生当地感受性过程的波长转换机制仅使流向波数发生改变,而展向波数保持不变;以及自由来流湍流运动方向的改变将决定三维T-S波波包的传播方向,但其传播速度的大小都近似为无穷远来流速度的1/3.另外,还建立了自由来流湍流的强度和运动方向以及二维壁面局部粗糙的长度和高度与边界层内的当地感受性问题之间的关系等.这一课题的深入研究,将在进一步理解和认识层流向湍流转捩的理论机制,以及湍流的形成机理等方面均起到十分重要的作用.