关键词： 并联机械手   简化刚体动力学模型   组合分配系数  

摘要： 基于虚功原理建立了机械手的完备刚体动力学模型,并对机械手动力学模型的各组成部分(惯性力矩项、惯性力项和重力项)进行了分类;在分析从动臂的运动对机械手力矩各组成部分贡献的基础上,提出了一种基于组合分配系数的刚体动力学模型简化策略;以简化刚体动力学模型与完备刚体动力学模型逼近度为优化目标,提出一种基于运动过程力矩偏差最小的优化指标,从而确定组合分配系数;基于以上刚体动力学简化方法,从机械手尺度参数与运动轨迹参数两方面因素出发,结合机械手典型运动轨迹,采用多因素分析方法,通过仿真分析了各因素对简化刚体动力学模型准确性的影响,结果表明该刚体动力学模型简化方法针对不同机械手尺度参数与运动轨迹参数均具有较高的计算速度和精度。

关键词： Molecular dynamics simulations   Multi-layered graphyne-n   Elastic properties   Fracture properties  

摘要： This paper aims to study the mechanical properties of the multi-layered graphyne and other members of the graphyne family under the uniaxial tensile loading. For this purpose, molecular dynamics simulations are used. The effects of the size and number of layers on the fracture and elastic properties are studied. It is shown that Young's modulus of the zigzag multi-layered graphyne is slightly larger than armchair one. Comparing the stress-strain curves of the multi-layered graphynes with different number of layers, it is observed that the fracture stress and strain of the nanosheets are inversely related to the number of layers. Investigating the influence of the number of acetylene linkage in the structure of the graphyne-n family on their mechanical properties, it is shown increasing the number of triple bonds leads to weakening the fracture stress and Young's modulus of the nanosheet. (C) 2017 Published by Elsevier Inc.

关键词： Forecasting   Real-time modelling   Infectious disease dynamics   Outbreak  

摘要： Real-time forecasts of infectious diseases can help public health planning, especially during outbreaks. If forecasts are generated from mechanistic models, they can be further used to target resources or to compare the impact of possible interventions. However, paremeterising such models is often difficult in real time, when information on behavioural changes, interventions and routes of transmission are not readily available. Here, we present a semi-mechanistic model of infectious disease dynamics that was used in real time during the 2013-2016 West African Ebola epidemic, and show fits to a Ebola Forecasting Challenge conducted in late 2015 with simulated data mimicking the true epidemic. We assess the performance of the model in different situations and identify strengths and shortcomings of our approach. Models such as the one presented here which combine the power of mechanistic models with the flexibility to include uncertainty about the precise outbreak dynamics may be an important tool in combating future outbreaks. (c) 2016 The Author(s). Published by Elsevier B.V.

关键词： Mechanical activation   Carbothermic reduction   Non-isothermal kinetics   Isoconversional models   Model-fitting methods   Coats-Redfern  

摘要： Effect of mechanical activation on carbothermic reduction kinetics and mechanism of ilmenite concentrate containing self-reducing mixture has been investigated using a combination of thermogravimetry and X-ray diffraction. Thermogravimetric comparative study of mechanically activated and non-activated ilmenite concentrate containing self-reducing mixtures with C/O molar ratio of 1.5 was conducted non-isothermally. The samples were heated up to 1573 K at three different heating rates (10, 15, and 20 K min(-1)) under controlled atmosphere. The reduction mechanism of mechanically activated mixture was followed by X-ray diffraction analysis of arrested samples at different reduction extents. In addition, reaction kinetics was further investigated and corresponding kinetic parameters were estimated using isoconversional (model-free) and model-fitting (Coats-Redfern) methods.

关键词： Silica   Silicon carbide   Kinetic   Carbothermic synthesis  

摘要： The effect of mechanical activation on the synthesis temperature decreasing of silicon carbide was investigated and a kinetic model of a carbothermic reduction of silicon carbide was obtained. Silicon carbide was synthesized using silica activated in a planetary mill at different times up to 40 h under an argon atmosphere. Structural changes due to the milling and the reduction of the activated silica were studied by the X-Ray diffraction (XRD) method and non-isothermal TGA with a heating rate of 10(ay)C min(-1) respectively. The kinetic model obtained by the fitting technique for an unmilled sample was found to be chemically controlled of the second order with E = 138.92 ***(-1) and A =3.92x10(15) s(-1). For the sample milled up to 20 h, according to the Avrami-Erofeev3 equation;A = 1465633 s(-1) and E = 66.71 ***(-1).

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.