关键词： Diamond   Chemical mechanical polishing   Chemical kinetics mechanism   Hard-inert material  

摘要： Hard-inert materials such as diamond, silicon carbide, gallium nitride, and sapphire are difficult to obtain from the smooth and damage-free surfaces efficiently required by semiconductor field. Therefore, this study proposed a chemical kinetics model to evaluate the material removal rate of diamond in chemical mechanical polishing process and to investigate the material removal mechanism by examining the surface information with optical microscopy, surface profilometry, and atomic force microscopy as well as X-ray photoelectron spectroscopy. The theoretical and experimental results show that chemical and mechanical synergic effect may promote the diamond oxidation reaction in chemical kinetics. The material removal rate is acceptable when the mechanical activation coefficient is smaller than 0.48. The 2.5 mu m B4C abrasives, the polishing temperature of 50 A degrees C, and the polishing pressure of 266.7 MPa are optimal parameters for diamond polishing with potassium ferrate slurry. It provides the highest material removal rate of 0.055 mg/h, the best surface finish (about Ra 0.5 nm) and surface quality (no surface scratches or pits). It then discusses how mechanical stress may promote the chemical oxidation of oxidant and diamond by forming "C-O," "C=O," and "O=C-OH" on diamond surface. The study concludes that chemical kinetics mechanism is effective for the investigation of the synergic effect in chemical mechanical polishing hard-inert materials.

关键词： Astroglia   animal model   cell transplantation   experimental   Parkinson's disease  

摘要： Background: Transplantation of fetal mesencephalic tissue is a well-established concept for functional reinnervation of the dopamine-depleted rat striatum. However, there is no extensive description of the glial response of the host brain following this procedure. Aims: The present study aimed to quantitatively and qualitatively analyse astrogliosis surrounding intrastriatal grafts and compare it to the reaction to mechanical injury with the transplantation instrument only. Study Design: Animal experimentation. Methods: The standard 6-hydroxydopamine-induced unilateral model of Parkinson's disease was used. The experimental animals received transplantation of a single-cell suspension of E14 ventral mesencephalic tissue. Control animals (sham-transplanted) were subjected to injury by the transplantation cannula, without injection of a cell suspension. Histological analyses were carried out 7 and 28 days following the procedure by immunohistochemistry assays for tyrosine hydroxylase and glial fibrillary acidic protein. To evaluate astrogliosis, the cell density and immunopositive area were measured in distinct zones within and surrounding the grafts or the cannula tract. Results: Statistical analysis revealed that astrogliosis in the grafted striatum increased from day 7 to day 28, as shown by a significant change in both cell density and the immunopositive area. The cell density increased from 816.7 +/- 370.6 to 1403 +/- 272.1 cells/mm(2) (p<0.0001) and from 523 +/- 245.9 to 1164 +/- 304.8 cells/mm(2) (p<0.0001) in the two zones in the graft core, and from 1151 +/- 218.6 to 1485 +/- 210.6 cells/mm(2)(p<0.05) for the zone in the striatum immediately adjacent to the graft. The glial fibrillary acidic protein-expressing area increased from 0.3109 +/- 0.1843 to 0.7949 +/- 0.1910 (p<0.0001) and from 0.1449 +/- 0.1240 to 0.702 +/- 0.2558 (p<0.0001) for the same zones in the graft core, and from 0.5277 +/- 0.1502 to 0.6969 +/- 0.1223 (p<0.0001) for the same area adjacent to

关键词： climate change   hybrid ecological niche model   independent model validation   land use   mechanistic model   metapopulation and dispersal dynamics   species distribution model   transferability  

摘要： Criticism has been levelled at climate-change-induced forecasts of species range shifts that do not account explicitly for complex population dynamics. The relative importance of such dynamics under climate change is, however, undetermined because direct tests comparing the performance of demographic models vs. simpler ecological niche models are still lacking owing to difficulties in evaluating forecasts using real-world data. We provide the first comparison of the skill of coupled ecological-niche-population models and ecological niche models in predicting documented shifts in the ranges of 20 British breeding bird species across a 40-year period. Forecasts from models calibrated with data centred on 1970 were evaluated using data centred on 2010. We found that more complex coupled ecological-niche-population models (that account for dispersal and metapopulation dynamics) tend to have higher predictive accuracy in forecasting species range shifts than structurally simpler models that only account for variation in climate. However, these better forecasts are achieved only if ecological responses to climate change are simulated without static snapshots of historic land use, taken at a single point in time. In contrast, including both static land use and dynamic climate variables in simpler ecological niche models improve forecasts of observed range shifts. Despite being less skilful at predicting range changes at the grid-cell level, ecological niche models do as well, or better, than more complex models at predicting the magnitude of relative change in range size. Therefore, ecological niche models can provide a reasonable first approximation of the magnitude of species' potential range shifts, especially when more detailed data are lacking on dispersal dynamics, demographic processes underpinning population performance, and change in land cover.

关键词： Metals   Molecules   Ions   Solvents   Extraction  

摘要： The current work reports the experimental and predicted interfacial behavior of metal ion extraction from aqueous phase-diluent system using a newly synthesized calix-benzo-crown-6 (CBCBGA) ionophore. Conductor-like screening model for real solvents was used to predict the selectivity at infinite dilution for the metal ion complexes in both aqueous and diluent phases. The selectivity for Cs+-CBCBGA extraction was found to be higher than that of other metal ions, namely, K+, Na+, and Rb+. This was confirmed by the experimental distribution coefficients obtained in the diluents system at 3 M HNO3 along with 0.01 M CBCBGA/organic solvents. The high selectivity of Cs+-CBCBGA complex over other complexes (K+, Rb+, and Na+) in nitrobenzene was also confirmed and validated by the highest occupied molecular orbital lowest unoccupied molecular orbital energy gap (i.e., 0.13114 > 0.12411 > 0.11719 > 0.11561 eV) and interaction energy (i.e., -68.25 > -57.11 > -55.52 > -52.37 kcal/mol). The interaction and free energies of the extraction were found to increase with the dielectric constant of the organic solvents, namely, nitrobenzene > onitrophenyl hexyl ether > 1-octanol > chloroform. Overall, a higher selectivity of Cs+ ion over that of other metal ions (KE, and Rb+) was obtained for the newly synthesized CBCBGA ionophore in a radioactive waste solution.

关键词： Infinite string   Viscoelastic   Dynamic system   Contact force  

摘要： The mutual interaction between a number of multi degrees of freedom mechanical systems moving with uniform speed along an infinite taut string supported by a viscoelastic layer has been studied using the substructure synthesis method when base excitations of a common frequency are given to the mechanical systems. The mobility or impedance matrices of the string have been calculated analytically by Fourier transform method as well as wave propagation technique. The above matrices are used to calculate the response of the discrete mechanical systems. Special attention is paid to the contact forces between the discrete and the continuous systems which are estimated by numerical simulation. The effects of phase difference, the distance between the systems and different base excitation amplitudes on the collective behaviour of the mechanical systems are also studied. The present study has relevance to the coupled dynamic problem of more than one railway pantographs and an overhead catenary system where the pantographs are modelled as discrete systems and the catenary is modelled as a taut string supported by continuous viscoelastic layer. (C) 2017 Elsevier Ltd. All rights reserved.

摘要： The high valent Mn-V(O) (lambda(max) approximate to 407 nm) and Mn-IV(O) (lambda(max) approximate to 421 nm) species of a series of electron-rich and electron-deficient meso-tetra(aryl) porphyrins (aryl = phenyl, 2-chlorophenyl, 2-nitrophenyl, 2-methylphenyl, 2-bromophenyl, 2,6-dichlorophenyl 4-methoxyphenyl, 4-methylphenyl, 4-chlorophenyl and 4-pyridyl) were prepared through the reaction of their corresponding manganese porphyrins with oxone in dichloromethane at a relatively low temperature (273 K). While the high valent Mn(O) intermediates of the para-substituted porphyrins were significantly degraded under reaction conditions, the corresponding species of the ortho substituted porphyrins showed high oxidative stability up to 20 min. Interestingly, the high valent Mn(O) of the mono-ortho-substituted meso-tetra(phenyl) porphyrins were as stable as that of meso-tetra(2,6-dichlorophenyl) porphyrin. The presence of imidazole (ImH) was found to play crucial roles in the formation and reactivity of the high valent Mn(O) species. The kinetics and mechanism of the oxidation of olefins with the high valent Mn-V(O) porphyrin intermediate were studied and the second order rate constants were evaluated under pseudo-first-order conditions. Also, the MnIV(O) species showed a reactivity comparable with that of the corresponding Mn-V(O) species. The observation of a Hammet constant of rho = -0.48 in the oxidation of para-substituted styrenes is in accord with an electrophilic mechanism.

关键词： biosynthesis   enzymes   molecular dynamics   molecular modeling   phosphorylation  

摘要： Human a-phosphoglucomutase 1 (alpha-PGM) catalyzes the isomerization of glucose-1-phosphate into glucose-6-phosphate (G6P) through two sequential phosphoryl transfer steps with a glucose-1,6-bisphosphate (G16P) intermediate. Given that the release of G6P in the gluconeogenesis raises the glucose output levels, alpha-PGM represents a tempting pharmacological target for type 2 diabetes. Here, we provide the first theoretical study of the catalytic mechanism of human a-PGM. We performed transition-path sampling simulations to unveil the atomic details of the two catalytic chemical steps, which could be key for developing transition state (TS) analogue molecules with inhibitory properties. Our calculations revealed that both steps proceed through a concerted SN2-like mechanism, with a loose metaphosphate-like TS. Even though experimental data suggests that the two steps are identical, we observed noticeable differences: 1) the transition state ensemble has a well-defined TS region and a late TS for the second step, and 2) larger coordinated protein motions are required to reach the TS of the second step. We have identified key residues (Arg23, Ser117, His118, Lys389), and the Mg2+ ion that contribute in different ways to the reaction coordinate. Accelerated molecular dynamics simulations suggest that the G16P intermediate may reorient without leaving the enzymatic binding pocket, through significant conformational rearrangements of the G16P and of specific loop regions of the human alpha-PGM.

关键词： 动力学方程   拉格朗日   模型简化   ADAMS  

摘要： 拉格朗日方程是通用六自由度工业机械臂进行动力学分析的常用方法。然而,当关节自由度多于三时,其动力方程的展开式相当复杂,完整地求出其表达式并不现实。考虑到通用工业机械臂的满足Pieper准则的特殊结构,只考虑机械臂的前三关节,并将腕部三个关节看作为动力效应的外部干扰,对其进行动力学分析,并通过ADAMS进行对比验证。结果表明,当只考虑机械臂前三关节时其动力学特性与考虑全部六关节相比不失一般性,且具有较小的误差。

关键词： 机械臂   轮毂打磨   并联机构   动力学分析   Lagrange方程   峰值预估模型  

摘要： 提出了一种基于2-UPS+UPU机构的5-DOF机械臂,建立了机械臂的手腕运动状态与其关节驱动参数之间的传递方程显式表达式,从而得到机械臂的伺服电机驱动参数峰值预估模型,计算出各伺服电机中的驱动转速最大理论值为25.1r/s,驱动力矩最大理论值为6.2N獉m。以一组具体的结构参数作为算例,计算出伺服电机中的驱动转速最大值为18.7r/s,驱动力矩最大值为4.73N獉m,算例伺服电机选型的预估功率为700W,证明了伺服电机峰值驱动参数预估模型的合理性。