Papers by Keyword: Mechanism

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Authors: Zeng Ming Li, Bin Bin Peng, Bao Gang Yang, Hao Yuan Chen
Abstract: In the paper, a novel 2-DOF (degree of freedom) plane translational parallel manipulator with passive universal joints and three legs is presented. Firstly, the 2-DOF translational parallel manipulator which has the spatial structure and high bearing capacity in the direction perpendicular to the kinematics plane is described. Then, the kinematics analysis of the 2-DOF parallel manipulator, which include inverse and forward solutions, are studied in detail, and the Jacobian matrix of the parallel manipulator is also derived based on it. Lastly, to improve the stability and bearing capacity further, the symmetric mechanisms with four legs and passive universal joints are constructed by adding a leg in parallel. The proposed 2-DOF parallel manipulator not only has the simple structure, but high stiffness especially in the direction perpendicular to kinematics plane for its spatial arrangment and passive universal joints.
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Authors: Lin Cheng, Nian Hong, Xiang Qun Xu, Jie Yang, You Quan Zhong
Abstract: In this work, a series of theoretical methods were employed to investigate the reaction mechanisms of ribosomal peptide bond formation catalyzed by peptidyl transferase. For the studies described in this paper, reaction pathways and free energy barriers for the model reaction of the peptide bond synthesis were studied by performing Ab initio calculation. Two self-consistent reaction field (SCRF) methods were used to calculate of the whole reaction pathway. These results show that the present theoretical reaction mechanism is a potential and competitive one for the reaction modeling of the ribosomal peptide synthesis.
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Authors: Cheng Wen Wang, Rui He Wang, Rong Chao Cheng, Er Ding Chen
Abstract: A study on a new lithium salt accelerator was conducted in this paper aiming at the low temperature environment in deepwater cementing. The acceleration mechanism and comprehensive performance of the lithium salt accelerator were thoroughly discussed. Results show that the lithium salt accelerator can accelerate the low-temperature hydration rate of C3S and C2S by speeding up the rupture of protective hydration film and shortening the hydration induction period, and thereby significantly shortens the low-temperature thickening time and the 48-240 Pa transition time for the static gel strength of oil well cement slurry, dramatically improves the compressive strength at low temperatures and shows no effect on the initial consistency of cement slurry. The lithium salt accelerator shows favorable low-temperature early strength accelerating property and has no effect on the types of hydration product, which still remains the same with that of conventional oil well cement, namely the calcium silicate gel, Ca(OH)2 crystal and a small amount of ettringite AFt crystal. But the micro-structure of the system with the lithium salt accelerator is more compact than that of conventional set cement.
1174
Authors: Anna Zymla, Victor Zymla, Jean-Bernard Guillot
844
Authors: Dong Ming Zhang, Zheng Yi Fu, Jing Kun Guo
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Authors: John F. Humphreys
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Authors: T.A. Parthasarathy, Robert A. Rapp, Mark Opeka, Ronald J. Kerans
Abstract: A mechanistic model that interprets the transition in oxidation behavior of zirconium diboride as the temperature is varied from 600°C to 2500°C is presented. Available thermodynamic data and literature data for vapor pressures, oxygen permeability in boria, and viscosity of boria were used to evaluate the model. Three regimes and the temperatures of transition between them were identified. In the intermediate temperature regime, viz., 1000°C to 1800°C, good correspondence was obtained between theory and experiments for weight gain, recession, and scale thickness as functions of temperature and oxygen partial pressure. In this regime, the rate-limiting step is the diffusion of dissolved oxygen through a film of liquid boria in capillaries at the base of the oxidation product. At lower temperatures, an external boria scale forms, but it was not found to contribute significantly to oxidation resistance. Comparison with literature data on recession is very good, but weight gain is predicted to be higher than experimentally observed unless flow of viscous boria is included. At higher temperatures, the boria is lost by evaporation, and the oxidation rate is limited by diffusion of molecular oxygen through the capillaries between nearly columnar blocks of the oxide MO2.; this regime is soon followed by a rapid acceleration of recession due to vaporization of the oxide MO2 itself.
823
Authors: Jian Yi Lv, Xu Dan Ren, Jie Gao
Abstract: Soot, a crucial component of PM2.5 in the ambient air, is a prime product of incomplete combustion of fule. The present paper uses a series of models, including nucleation of soot precursors, surface growth of soot particles as well as particles coagulation, to do numerical simulation of soot particles formation mechanism over time in combustion flame, with the aid of MATLAB platform by C language. Simulation results indicate that the concentration distribution of soot precursors like polycyclic aromatic hydrocarbons (PAHs) have direct effect on the concentration distribution of soot nuclei. Mass addition rate on soot particles surface rises over time since the enlargement of the surface area. In coagulation process, the number of small diameter particles decreases, while that of large diameter particles increases.
1167
Authors: Dong Shin Yun, Hyun Jung Kim, Hyun Chang Shin, Venkatathri Narayanan, Jung Whan Yoo, Seong Ho Lee, Dong Jin Lee, Nam Hoon Kim
Abstract: The physicochemical characteristics (SEM, N2 adsorption, FT-IR, MASNMR) of samples from kinetics (10 min, 20 min, 30 min, 1 h and 3h) of hydrolysis of tetraethyl orthosilicate (TEOS) gives new insight into the synthesis of nanosphere. The particle sizes are increased with time, however, the surface areas decreased. FT-IR investigation reveals the presence of high intensed silanol groups of 960 cm-1 at 10 min, which reduced on progress of the reaction time. This suggests the partial hydrolysis and condensation of alkoxy groups in TEOS. 29Si MASNMR analysis shows the presence three different silica species(Q4, Q3 and Q2) in 10 and 20 min samples. The intensity of Q2 species decreases with time and other species concentration were increased.
1249
Authors: Pei Wen An, Zhong Liang Lv
Abstract: Epicyclic gear trains have been broadly applied in engineering practice. In this paper, kinematic chains (K.C.) with single-joint (S.J.) were applied to innovative synthesis of the epicyclic gear trains. The method of the innovative synthesis of the epicyclic gear trains was presented. Not only the epicyclic gear trains in common uses were obtained, but some new types of epicyclic gear trains that are got difficultly by means of conventional combination method were gained. Thereby, a new way has been offered for the innovative synthesis of the epicyclic gear trains, at the same time, a way has also been offered for practical application of some multi-link kinematic chains gained by using the theory of type-number synthesis of the K.C. with S.J.. Examples show that the method presented in this paper is right and feasible, and the method is efficient and practical for the innovative synthesis of the epicyclic gear trains.
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