关键词： abrasion   chemical mechanical polishing   elemental semiconductors   molecular dynamics method   silicon   silicon compounds   surface finishing  

摘要： In an abrasive chemical mechanical polishing (CMP) process, materials were considered to be removed by abrasive sliding and rolling. Abrasive sliding has been investigated by many molecular dynamics (MD) studies;while abrasive rolling was usually considered to be negligible and therefore was rarely investigated. In this paper, an MD simulation was used to study the effects of abrasive rolling on material removal and surface finish in the CMP process. As the silica particle rolled across the silicon substrate, some atoms of the substrate were dragged out from their original positions and adhered to the silica particle, leaving some atomic vacancies on the substrate surface. Meanwhile, a high quality surface could be obtained. During the abrasive rolling process, the influencing factors of material removal, e. g., external down force and driving force, were also discussed. Finally, MD simulations were carried out to examine the effects of abrasive sliding on material removal under the same external down force as abrasive rolling. The results showed that the ability of abrasive rolling to remove material on the atomic scale was not notably inferior to that of abrasive sliding. Therefore, it can be proposed that both abrasive sliding and rolling play important roles in material removal in the abrasive CMP of the silicon substrate. (C) 2011 American Institute of Physics. [doi:10.1063/1.3575177]

关键词： Absorption   Monomers   Hydrolysis   Polymerization   Polymers  

摘要： The temperature dependence of photopolymerization kinetics of tetrakis[(methacryloyloxy)ethoxy]silane (TetMESi) was compared with an analogue, diethylene glycol dimethacrylate and their copolymers. In all cases, the kinetics are controlled by the temperature dependence of the propagation step, the effect of diffusion on radical termination, the effect of rising glass transition during cure, and topological restraint on complete conversion. The glass transition regions of these polymers were very broad, suggesting their use in high temperature applications. NMR of the TetMESi monomer, and FTIR and water sorption measurements during exposure to water of the TetMESi-based polymers showed that the Si-O-C bond was slowly hydrolyzed, resulting in water-swollen polymers containing poly(hydroxyethyl methacrylate) which reduced the glass transition temperature and narrowed the glass transition region. UV-vis spectroscopic studies showed that during exposure to water, SiO2 nanoparticles or nanostructures were formed from the condensation of the silanol groups formed during the hydrolysis of TetMESi.

关键词： dissociation   hydrogen bonds   organic compounds   photon echo  

摘要： We have investigated the dynamics of the hydrogen bonds that connect the components of a [2]rotaxane in solution. In this rotaxane, the amide groups in the benzylic-amide macrocycle and the succinamide thread are connected by four equivalent N-H center dot center dot center dot O=C hydrogen bonds. The fluctuations of these hydrogen bonds are mirrored by the frequency fluctuations of the NH-stretch modes, which are probed by means of three-pulse photon-echo peak shift spectroscopy. The hydrogen-bond fluctuations occur on three different time scales, with time constants of 0.1, 0.6, and >= 200 ps. Comparing these three time scales to the ones found in liquid formamide, which contains the same hydrogen-bonded amide motif but without mechanical constraints, we find that the faster two components, which are associated with small-amplitude fluctuations in the strength of the N-H center dot center dot center dot O=C hydrogen bonds, are very similar in the liquid and the rotaxane. However, the third component, which is associated with the breaking and subsequent reformation of hydrogen bonds, is found to be much slower in the rotaxane than in the liquid. It can be concluded that the mechanical bonding in a rotaxane does not influence the amplitude and time scale of the small-amplitude fluctuations of the hydrogen bonds, but strongly slows down the complete dissociation of these hydrogen bonds. This is probably because in a rotaxane breaking of the macrocycle-axle contacts is severely hindered by the mechanical constraints. The hydrogen-bond dynamics in rotaxane-based molecular machines can therefore be regarded as liquidlike on a time scale 1 ps and less, but structurally frozen on longer (up to at least 200 ps) time scales. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3569761]

关键词： mechanical heart valve   hemodynamics   cardiac catheterization   pressure wire  

摘要： Objectives: Accurate assessment of prosthetic mechanical valve malfunction is challenging for non-invasive and invasive techniques. We evaluated a 0.014-inch pressure-sensing coronary guidewire to assess mechanical valve dysfunction. Background: Several case reports have shown that transaortic pressure gradients can be recorded using a 0.014-inch guidewire during cardiac catheterization. Methods: We performed an ex vivo study measuring the effects of sequentially crossing the center of each valve with a 6 French coronary angiographic catheter, a 0.035-inch guidewire, and a 0.014-inch pressure-sensing guidewire on valve dysfunction using the following 23 mm bileaflet and tilting-disc aortic valves: St. Jude Regent (TM), CarboMedics, Medtronic Hall (TM), and Bjork-Shiley Monostut. A left heart model pulse duplicator recorded 10 consecutive cycles. Results: For all valves, the greatest increase in valve regurgitation occurred with the 6 French catheter, causing a reduction in aortic valve back pressure and cardiac output, with an increase in leakage rate, regurgitant fraction, and energy loss. In comparison to the 0.035-inch guidewire, the 0.014-inch guidewire had greater regurgitation for St. Jude, lower for Medtronic Hall, and equivalent for CarboMedics and Bjork-Shiley valves. For the CarboMedics valve, the 0.035-inch guidewire caused a significant increase in regurgitant fraction and energy loss, while the pressure wire had no change compared to baseline. Conclusions: The degree of regurgitation caused by the 0.014-inch guidewire varies with the type of mechanical aortic valve. While prior case reports have shown that valve hemodynamics may be measured using a pressure-sensing guidewire, valve regurgitation occurs when crossing a St. Jude, Medtronic Hall, or Bjork-Shiley aortic valve. (C) 2011 Wiley-Liss, Inc.

关键词： Tires   Pyrolysis   Oxygenation   Kinetic model   Film diffusion  

摘要： The kinetics of copper ion (Cu(II)) removal from aqueous solution by pyrolytic tire char was modeled using five different conventional models. A modification to these models was also developed through a modified equation that accounts for precipitation. Conventional first- and second-order reaction models did not fit the copper sorption kinetics well, indicating a lack of simple rate-order dependency on solute concentration. Instead, a reversible first-order rate reaction showed the best fit to the data, indicating a dependence on surface functional groups. Due to the varying solution pH during the sorption process, modified external and internal mass transfer models were employed. Results showed that the sorption of copper onto oxygenated chars was limited by external mass transfer and internal resistance with and without the modification. However, the modification of the sorption process produced very different results for unoxygenated chars, which showed neither internal nor external limitation to sorption. Instead, its slow sorption rate indicates a lack of surface functional groups. The sorption of Cu(II) by oxygenated and unoxygenated chars was also found to occur via three and two distinct stages, respectively. (C) 2010 Elsevier Inc. All rights reserved.

关键词： 在轨服务飞行器   机械臂   雅可比矩阵   角动量  

摘要： 将带机械臂的在轨服务飞行器（on-orbit service vehicle,OSV）等效为自由漂浮空间机械臂（free-flying space manipulator,FSM）系统,建立系统简化动力学模型。以单臂二关节机械臂平面运动为算例,分析了机械臂运动对OSV整体姿态的影响。该动力学模型既可用于分析OSV机械臂系统的运动规律,又可用于研究机械臂系统的运动规划问题。

关键词： 动力机械   山东   发动机制造商   汽油机   四冲程  

摘要： 山东华盛中天动力机械有限公司（原山东汽油机厂），是山东华盛中天机械集团有限公司的全资子公司，江北最大的四冲程通用发动机制造商，公司占地15万平米，

标准号: NF E90-760-7-2011

摘要： La présente partie de l'ISO 10816 donne des instructions pour l'évaluation des vibrations des pompes rotodynamiques pour applications industrielles d'une puissance nominale supérieure à 1 kW. Elle définit les exigences particulières applicables à l'évaluation des vibrations lorsque les mesurages des vibrations sont effectués sur les parties non tournantes (vibrations du corps de palier). Elle donne des recommandations spécifiques pour l'évaluation de l'intensité des vibrations mesurées in situ sur les corps de palier des pompes rotodynamiques et pour l'essai de réception en usine ou dans les installations d'essai du fabricant. La présente partie de l'ISO 10816 fournit également des informations générales et des lignes directrices pour l'évaluation des vibrations relatives à l'arbre *** présente partie de l'ISO 10816 spécifie les zones et les limites relatives aux vibrations des pompes horizontales et verticales, quelle que soit la flexibilité de leurs supports. Les critères généraux d'évaluation sont valables pour la surveillance en exploitation des pompes rotodynamiques et pour les essais de réceptions) in situ ou dans les installations d'essai du fabricant si cela est spécifié. Des conditions spéciales sont indiquées pour l'essai de réception dans les installations d'essai du *** surveiller les valeurs de vibrations pendant un service de longue durée, deux critères sont fournis pour évaluer les vibrations de la machine. Un critère concerne l'amplitude des vibrations observées et l'autre les variations d'amplitude. Les critères d'évaluation sont applicables aux vibrations produites par la pompe ellemême et non aux vibrations qui lui sont transmises par des sources extérieures.

关键词： Chitosan/chemistry   Magnetic Resonance Spectroscopy/methods   X-Ray Diffraction/methods  

摘要： Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films: Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl-) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, Which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational. distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl- counterions act as a defect and impair the long-range organization by immobilizing hydration water.. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content.

关键词： Nanowire   Molecular dynamics   Simulation   Nickel   Size effect   Embedded atom method   Mechanical properties  

摘要： The mechanisms of deformation and failure in face-centered cubic (FCC) nickel nanowires subjected to uniaxial tensile loading are investigated using molecular dynamics (MD) simulation, and the size effect on mechanical properties of FCC metal nanowires is studied. Simulation reveals that the surface free energy has great influence on the deformation and failure mechanism of metal nanowires. As a result of free surfaces and their reconstruction, the surface atoms depart from the perfect crystal lattice positions, leading to the appearance of nanocavities on the surfaces that are exposed to external load. The deformation process of nanowires undergoes expansion and connection of nanocavities from surface into inner lattices. Slip occurs during the deformation process, which is consistent with experimental phenomena. Elastic stiffness, yield, and fracture strength of nickel nanowires with various cross-sectional sizes are obtained, and the size effect on these mechanical properties is further analyzed. Based on numerical results, a set of quantitative prediction formulas are proposed, and they are capable of explaining the size sensitivity of nickel nanowires on the mechanical properties. Both the elastic modulus and yield strength of nickel nanowires are in a linear relationship with respect to the logarithm of their cross-sectional size, whereas the fracture strength exhibits an inverse relationship to the exponent of cross-sectional size of nickel nanowires. By using the MD simulation, the elastic modulus, yield strength, and fracture strength of a nickel nanowire in relationship to its cross-sectional size are well predicted, and they are in remarkable agreement with experimental and available numerical results. The present study demonstrates that the adopted MD simulation is capable of simulating the mechanical behavior of nanowires with respect to their geometrical size and providing numerical data that can be used to develop the empirical formulas on the effect