关键词： nanocomposites   PMMA   zirconia   morphology   dynamic mechanical analysis   thermal degradation  

摘要： Zirconia nanoparticles were synthesized by means of a sol-gel method and embedded in poly(methyl methacrylate) (PMMA) by melt compounding. The zirconia was well dispersed in the PMMA matrix, with only a few clusters, especially for the highest investigated zirconia content. NMR results showed heteronuclear dipolar interactions involving the carbons and the surrounding hydrogen nuclei. The effect of the amount of zirconia, in the range of 1-5 wt%, on the thermo-mechanical properties and thermal degradation kinetics of PMMA was also investigated by means of dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), and Fourier-transform infrared spectroscopy (FTIR). The presence of zirconia showed a decrease in the storage and loss moduli at lower temperatures, probably due to a plasticization effect. The presence of zirconia in PMMA slightly increased its thermal stability, but the activation energies of thermal degradation for the nanocomposites were significantly lower, at degrees of conversion higher than 0.3, than those of pure PMMA.

关键词： Crystals   Crystallinity   Crystallization   Fibers   Composites  

摘要： The biocomposites of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3,4HB)] and recycled carbon fiber (RCF) were prepared via a melting extrusion. The crystallization behaviors and kinetics of the P(3,4HB) matrix in composites were exclusively studied under both nonisothermal and isothermal conditions. The corresponding results indicated that the P(3,4HB) either neat or compositing with RCF had a dual-peak cold crystallization behavior in the nonisothermal condition, and the isothermal crystallization rate of P(3,4HB) in composites was jointly determined by the rates of the nucleation and the crystal growth and integrity. However, it was reduced with the incorporation of RCF. Wide-angle X-ray scattering investigation demonstrated that the presence of RCF did not change the crystallization mechanism and crystalline structure of the P(3,4HB) matrix, but the crystallinity of the P(3,4HB) either neat or compositing with RCF was enhanced with an increase of crystallization temperature. Dynamic mechanical analysis revealed that the storage moduli of P(3,4HB)-based composites were significantly improved with increasing the RCF loadings, and the dual internal friction peaks corresponding to the thermal motion of surface molecule of crystalline zone and the glass transfer of whole macromolecules were observed on the thermograms of the P(3,4HB) either neat or compositing with RCF. The mechanical properties including tensile, flexural, and notched Izod impact strength were significantly improved in the presence of RCF, and such reinforcing and toughening effects were due to the good interfacial adhesion between RCF and P(3,4HB) as a result of bonding effect of silane coupling agent. Scanning electronic microscopy further confirmed a good dispersion of RCF in P(3,4HB) matrix and a strong interfacial interaction between fibers and matrix.

关键词： compressive strength   electromechanical effects   electromigration   failure (mechanical)   metallic thin films   surface diffusion   surface morphology   tensile strength   tensors   voids (solid)  

摘要： We report results of a systematic computational study of the electromigration-driven complex surface dynamics of voids in mechanically stressed thin films of face-centered cubic metals with < 100 >-oriented film planes. The films are subjected to an external electric field simultaneously with biaxial mechanical loading, which can be either purely compressive, ranging from purely isotropic to strongly anisotropic including uniaxial, or a mixed type of loading with both tensile and compressive stress components in the applied stress tensor. Our analysis is based on self-consistent dynamical simulations of driven void surface morphological evolution following a well validated, two-dimensional, and fully nonlinear model. We find that depending on the electromechanical conditions, void size, and surface diffusional anisotropy, two types of asymptotic states can be stabilized in the void surface dynamical response, namely, morphologically steady or time-periodic traveling voids, and film failure can be caused by void tip extension. The loading mode as well as the loading anisotropy are found to be the significant factors in determining the void morphological stability domains and can be tailored to stabilize steady or time-periodic states and to increase the film's resistance to failure. Under a mixed (tensile+compressive) loading mode, we find that it is impossible to stabilize steady states in the void morphological response and that the stress levels that the film can sustain prior to failure are much lower than those under purely tensile or purely compressive biaxial loading. (C) 2012 American Institute of Physics. [http://***/10.1063/1.4759451]

关键词： ab initio calculations   configuration interactions   convergence   free radicals   isomerism   organic compounds   photoelectron spectra   positive ions   SCF calculations   vibronic states   wave functions  

摘要： Full dimensional multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) calculations of the dynamics of the three difluorobenzene cationic isomers in five lowest-lying doublet electronic states using the ab initio multistate multimode vibronic coupling Hamiltonian (MMVCH) model are carried out using the Heidelberg MCTDH package. The same dynamical problems, but treated with the MCTDH scheme and using a reduced dimensional ab initio MMVCH model, have been previously reported [S. Faraji, H.-D. Meyer, and H. Koumlppel, "Multistate vibronic interactions in difluorobenzene radical cations. II Quantum dynamical simulations," J. Chem. Phys. 129, 074311 (2008)]. For easy comparison with the reduced dimensional results, 11D or 10D ML-MCTDH calculations are also performed. Extensive ML-MCTDH test calculations are performed to find appropriate ML-MCTDH wavefunction structures (ML-trees), and the convergence of the ML-MCTDH calculations are carefully checked to ensure accurate results. Based on the appropriate ML-trees, the photoelectron (PE) spectrum and the mass analyzed threshold ionization (MATI) spectrum are simulated, analyzed, and compared with corresponding experimental spectra. Because of its efficient simulation capability for large systems, ML-MCTDH calculations save a considerable amount of central processing unit (CPU)-time, even when a reduced dimensional MMVCH is used, i.e., the same reduced model as in the corresponding MCTDH calculations. Simulations of the experimental PE spectra by full dimensional ML-MCTDH calculations reproduced main peaks, which originate from different electronic states. The agreement is improved as compared to the reduced dimensionality calculations. Unfortunately, the experimental PE spectra are not very well resolved. Therefore, we compare our calculations additionally with highly resolved MATI spectra, which, however, are only available for the (X) over tilde state. Based on a series of ML-MCTDH simulations with longer propag

关键词： 农业机械化水平   农村劳动力   中国工程院院士   农机化管理   进程   农机购置补贴   华南农业大学   农机化水平  

摘要： 农业部农机化管理司司长宗锦耀在日前举办的2012中国农机论坛上透露，2011年全国农作物耕种收综合机械化水平已达到54．8％，比2002年增加22．5个百分点，10年间的增幅相当于前35年的总和。中国粮食生产今年有望实现“九连增”，这其中农机化水平的不断提升显然是一个重要因素。对于中国农业机械化水平近年来大幅提升的原因，中国工程院院士、华南农业大学教授罗锡文将其归结为农村劳动力的不断外流和农机购置补贴力度的逐年加大。

关键词： 基坑支护   机械振动   传播规律   小波/小波包   能量  

摘要： 以上海市某大型基坑内支撑机械拆除为例,在大量振动监测的基础上,研究了基坑内支撑机械拆除过程中产生的振动在基坑内部和基坑边缘挡土墙、高层建筑物竖直方向上的传播规律,监测同时考虑了临近建筑对机械振动的动力响应。研究表明:机械拆除基坑内支撑对周围建筑物所产生的振动速度较小,不足以影响构筑物结构安全,但由于振动信号的主频较低,接近于建筑物的固有频率,地震效应仍应该引起足够重视;利用小波包技术可得到振动信号各频带上的能量分布,从能量角度研究振动信号可以直观地了解信号在传播过程中的衰减特性。

关键词： 化工机械   技术协会   动力技术   论坛   厦门市  

摘要： 中国化工机械动力技术协会定于2012年11月13～15日在厦门市召开协会六届三次理事（扩大）会，同时举办全因化工机械动力技术发展论坛，现将有关事项通知如下：

关键词： membrane dynamics   CLIC   GEEC   cell migration   endocytosis   exocytosis  

摘要： The plasma membrane represents a physical inelastic barrier with a given area that adheres to the underlying cytoskeleton. The tension in the membrane physically affects cell functions and recent studies have highlighted that this physical signal orchestrates complex aspects of trafficking and motility. Despite its undeniable importance, little is known about the mechanisms by which membrane tension regulates cell functions or stimulates signals. The maintenance of membrane tension is also a matter of debate, particularly the nature of the membrane reservoir and trafficking pathways that buffer tension. In this review we discuss the importance of membrane area and of tension as a master integrator of cell functions, particularly for membrane traffic.

关键词： aluminium-graphite powder system   mechanical alloying   carbon to Al4C3 transformation   compacting   microstructure parameters   mechanical properties   indentation hardness   creep characteristics  

摘要： A method of mechanical alloying process is described. Carbon transformation to Al4C3 is characterized within the different heat treatment schedules and nine commercial carbon powders are tested. The micromechanism of carbon incorporation into the metallic powder, and its compacting are described. The influence of dispersed carbides on mechanical properties is evaluated together with the influence of deformation on microstructure and properties. It was proved that the transformation efficiency of carbon to Al4C3 by heat treatment of aluminium with the porous furnace black and electrographite is higher than that of the hard cracked graphite. Microstructure changes consisted of the fracture processes and welding of the particles with incorporation of C phase and forming of final granules. The dispersed phase Al4C3 particle size was measured on thin foil structures, and it was constant and as small as 30 nm. The particle size was influenced neither by the carbon type nor by the heat treatment technology applied. Subgrain size measured in the range of 100 grains in thin foils depended on the carbon type, as well. It ranged from 0.3 to 0.7 mu m. Using a DSI (depth sensing indentation technique), the Martens hardness, indentation modulus E and deformation work W for Al matrix and Al4C3 particles have been measured. The temperature dependence of ductility, and reduction of area in the temperature range of 623-723 K and strain rate of 10(-1) s(-1), indicated a considerable increase of these properties. In a case when the volume fraction of Al4C3 changes from lower to higher, the grain rotation mechanism dominates instead of the grain boundary sliding. The comparison of the tensile test results and changes in fracture for the Al-Al4C3 system at two temperatures and two strain rates is summarized. The dependence of the minimum deflection rate on the applied force as well as the dependence of the time to fracture on the applied force for two temperature levels (623 and 723 K) b

关键词： Machinery dynamics   n-DOF global model   Reconfigurable manufacturing systems (RMS)  

摘要： Automated model generation and solution for motion planning and re-planning of automated systems will play an important role in future reconfigurable manufacturing systems (RMS). An n-DOF Global Kinematic Model (n-GKM) was previously developed for any combination of either rotational or translational type of joints. In this paper, the automatic generation of the dynamic equations for the n-GKM is presented. For the symbolic calculation of the n-GKM dynamic equations, the recursive Newton-Euler algorithm is employed using the symbolic algebra package MAPLE 12. The dynamic model is named Global Dynamic Model (n-GDM). The significance of the n-GDM is that it automatically generates each element of the inertia matrix A, Coriolis torque matrix B, centrifugal torque matrix C, and the gravity torque vector G, using Automatic Separation Method (ASM). The n-GDM is a dynamic solver for the n-GKM which includes predefined reconfigurable parameters. These parameters are used to control the joint's positive directions and its type (rotational and/or translational). Instead of solving the dynamics of different kinematic structures, the n-GDM can be used to auto-generate the solution by only defining these reconfigurable parameters. Using n-DOF Global Dynamic Model equations, a 3-DOF Global Dynamic Model (GDM) is derived. The 3-GDM has been validated using five selected cases (RR, RT, TR, TT planar and SCARA configurations). The results show the model ability to automatically generate different dynamic realizations for any required configuration. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.