关键词： H-abstraction   fluoroesters   potential energy surface   G2(MP2)   canonical transition state theory  

摘要： Theoretical investigations are carried out on the title reactions by means of ab initio and DFT methods. The optimized geometries, frequencies and minimum energy path are obtained at MPWB1K/6-31+G(d,p) level. Single point energy calculations are performed at MP2 and QCISD(T) levels of theory. Energetics were further refined by calculating the energy of the species with a high level G2(MP2) method. The rate constant of the two reactions are calculated at 298K and 1atm using Canonical Transition State Theory (CTST) utilizing the ab initio data obtained during the present study. The rate constant values are found to be 5.5x10(-14) and 5.9x10(-14)cm(3) molecule(-1) s(-1), respectively which are in good agreement with the experimental data.

关键词： 动力学方程   机械臂   质心   符号表达式  

摘要： 由于机械臂大部分为不规则、不均匀的连杆构成,所以在计算过程中使用质心法推导,简化了运算过程,降低了运算复杂度,仿真结果表明,使用质心法能正确推导出多自由度机械臂动力学方程,为以后在不规则连杆构成的机械臂上使用质心法推导动力学方程提供了依据。

关键词： 空间机械臂   冲击动力学   滑模控制   神经网络  

摘要： 通过对漂浮基空间机械臂冲击动力学的建模,计算出完成抓取操作后空间机械臂各关节的运动速度,从而为数值仿真计算提供初始条件.针对目标物体及空间机械臂系统惯性参数存在未知的情况,设计了冲击后空间机械臂及目标物体组合系统的载体姿态及关节运动滑模神经网络控制,并对平面自由漂浮空间机械臂系统抓取目标物体的操作及冲击后控制进行了数值仿真.仿真结果表明,空间机械臂抓取目标物体时的冲击对系统有重大的影响,所设计的控制方案可保证系统对期望运动的追踪.

关键词： 柔性空间机械臂   谐波传动   运动滞后   动力学特性  

摘要： 空间机械臂是在轨航天器重要维护工具,其动力学特性的优劣直接关系到航天任务的成败。现有空间机械臂多采用谐波传动作为减速机构,该减速机构对空间机械臂的动力学特性有较大影响。基于Euler-Bernoulli梁模型,结合谐波传动误差模型,建立了考虑臂杆柔性与谐波传动运动滞后的动力学方程,通过数值模拟分析了臂杆刚性、臂杆刚性与谐波滞后、臂杆柔性,以及臂杆柔性与谐波滞后等4种模型对应的空间机械臂动力学特性。仿真结果表明:与刚性空间机械臂相比,臂杆柔性使得输出的角度曲线包含明显高频成分,考虑谐波传动的柔性空间机械臂输出特性存在明显滞后。

关键词： ABS-g-MAH   blend   effective activation energy   mechanical properties   nonisothermal crystallization kinetics   poly(trimethylene terephthalate)  

摘要： The mechanical properties, morphology, crystallization, and melting behaviors and nonisothermal crystallization kinetics of poly (trimethylene terephthalate)(PTT)/maleinized acrylonitrile-butadiene-styrene (ABS-g-MAH) blends were investigated by an impact tester, polarized optical microscopy, and differential scanning calorimetry (DSC). The results suggested that the ABS-g-MAH component served as both a nucleating agent for increasing the crystallization rate and as a toughening agent for improving the impact strength of PTT. When the ABS-g-MAH content was 5wt.%, the blend had the best toughness and a high crystallization rate. The blends showed different crystallization rates and subsequent melting behaviors due to their different ABS-g-MAH contents. The Ozawa theory and the method developed by Mo and coworkers were used to study the nonisothermal crystallization kinetics of the blends. The kinetic crystallization rate parameters suggested that the proper contents of ABS-g-MAH can highly accelerate the crystallization rate of PTT, but this effect nearly reaches saturation for ABS-g-MAH contents over 5%. The Ozawa exponents calculated from the DSC data suggested that the PTT crystals in the blends have similar growth dimensions as those in neat PTT, although they are smaller and/or imperfect. The effective activation energy calculated by the method developed by Kissinger also indicates that the blends with higher ABS-g-MAH content were easier to crystallize.

关键词： 产学研合作   地方院校   机械动力类   培养模式  

摘要： 对目前产学研合作中机械类应用型人才培养的现状进行了分析,论述了地方院校机械动力类专业在人才培养中建立产学研模式的必要性,对机械动力类专业的产学研培育模式进行了初步探索,构建了地方院校机械类应用型人才培养质量的新模式。实践表明,地方院校机械动力类专业产学研模式切实可行,为今后地方院校的教学改革提供了示范作用。

关键词： healthy lung   lung strain   lung stress   mechanical ventilation   positive end-expiratory pressure   transpulmonary pressure   ventilator-induced lung injury  

摘要： Objective: Tidal volume (V-T) and volume of gas caused by positive end-expiratory pressure (V-PEEP) generate dynamic and static lung strains, respectively. Our aim was to clarify whether different combinations of dynamic and static strains, resulting in the same large global strain, constantly produce lung edema. Design: Laboratory investigation. Setting: Animal unit. Subjects: Twenty-eight healthy pigs. Interventions: After lung computed tomography, 20 animals were ventilated for 54 hours at a global strain of 2.5, either entirely dynamic (V-T 100% and V-PEEP 0%), partly dynamic and partly static (V-T 75-50% and V-PEEP 25-50%), or mainly static (V-T 25% and V-PEEP 75%) and then killed. In eight other pigs (V-T 25% and V-PEEP 75%), V-PEEP was abruptly zeroed after 36-54 hours and ventilation continued for 3 hours. Measurements and Main Results: Edema was diagnosed when final lung weight (balance) exceeded the initial weight (computed tomography). Mortality, lung mechanics, gas exchange, pulmonary histology, and inflammation were evaluated. All animals ventilated with entirely dynamic strain (V-T 825 +/- 424 mL) developed pulmonary edema (lung weight from 334 +/- 38 to 658 +/- 99 g, p < 0.01), whereas none of those ventilated with mainly static strain (V-T 237 +/- 21 mL and V-PEEP 906 +/- 114 mL, corresponding to 19 +/- 1 cm H2O of positive end-expiratory pressure) did (from 314 +/- 55 to 277 +/- 46 g, p = 0.65). Animals ventilated with intermediate combinations finally had normal or largely increased lung weight. Smaller dynamic and larger static strains lowered mortality (p < 0.01), derangement of lung mechanics (p < 0.01), and arterial oxygenation (p < 0.01), histological injury score (p = 0.03), and bronchoalveolar interleukin-6 concentration (p < 0.01). Removal of positive end-expiratory pressure did not result in abrupt increase in lung weight (from 336 +/- 36 to 351 +/- 77 g, p = 0.51). Conclusions: Lung edema forms (possibly as an all-or-none response) depend

关键词： RETINOIC acid receptors   PHOSPHORYLATION   ALLOSTERIC regulation   NUCLEAR receptors (Biochemistry)   TRANSCRIPTION factors   EMBRYOLOGY   CELLULAR growth  

摘要： Nuclear receptor proteins constitute a superfamily of proteins that function as ligand dependent transcription factors. They are implicated in the transcriptional cascades underlying many physiological phenomena, such as embryogenesis, cell growth and differentiation, and apoptosis, making them one of the major signal transduction paradigms in metazoans. Regulation of these receptors occurs through the binding of hormones, and in the case of the retinoic acid receptor (RAR), through the binding of retinoic acid (RA). In addition to this canonical scenario of RAR activity, recent discoveries have shown that RAR regulation also occurs as a result of phosphorylation. In fact, RA induces non-genomic effects, such as the activation of kinase signaling pathways, resulting in the phosphorylation of several targets including RARs themselves. In the case of RAR alpha, phosphorylation of Ser369 located in loop L9-10 of the ligand-binding domain leads to an increase in the affinity for the protein cyclin H, which is part of the Cdk-activating kinase complex of the general transcription factor TFIIH. The cyclin H binding site in RAR alpha is situated more than 40 angstrom from the phosphorylated serine. Using molecular dynamics simulations of the unphosphorylated and phosphorylated forms of the receptor RAR alpha, we analyzed the structural implications of receptor phosphorylation, which led to the identification of a structural mechanism for the allosteric coupling between the two remote sites of interest. The results show that phosphorylation leads to a reorganization of a local salt bridge network, which induces changes in helix extension and orientation that affects the cyclin H binding site. This results in changes in conformation and flexibility of the latter. The high conservation of the residues implicated in this signal transduction suggests a mechanism that could be applied to other nuclear receptor proteins.

关键词： Molecular Dynamics   Nanoscratching   Graphene   Interface Dynamics  

摘要： The interface dynamics and nanoscratched mechanisms of few-layered graphene are investigated using molecular dynamics (MD) simulation. The interface dynamics mainly include the atomic deformations, the nanoscratched layers, and the slip vector. The nanoscratched mechanisms include the nanoscratched shear force, the normal force, the lateral force, and the contact pressure. The simulation results show the graphene atoms easily piled up in front of the nanoindenter and in two sides of the nanoindenter. The disorder and the plastic mobility of atomic structures increased with increasing scratched distance. The sp(2) honeycomb lattice of grapheme changed to sp(3) structures after nanoscratching. The scratched shear force, lateral force, normal force, and contact pressure increased with increasing graphene layers. This can be attributed to the contact area between the grapheme atoms and the nanoindenter increasing with increasing graphene layers. A stress that is normal to the slip plane is greater for homogeneous dislocation nucleation in a single crystal. There have the dislocations of glide and shuffle in the graphene slip vector.

关键词： acoustic wave velocity   Brillouin spectra   elastic moduli   elasticity   liquids   organic compounds   piezoceramics   piezoelectric transducers   piezoelectricity   transparency   viscoelasticity   vitrification  

摘要： This paper presents and discusses the temperature and frequency dependence of the longitudinal and shear viscoelastic response at MHz and GHz frequencies of the intermediate glass former glycerol and the fragile glass former tetramethyl-tetraphenyl-trisiloxane (DC704). Measurements were performed using the recently developed time-domain Brillouin scattering technique, in which acoustic waves are generated optically, propagated through nm thin liquid layers of different thicknesses, and detected optically after transmission into a transparent detection substrate. This allows for a determination of the frequency dependence of the speed of sound and the sound-wave attenuation. When the data are converted into mechanical moduli, a linear relationship between longitudinal and shear acoustic moduli is revealed, which is consistent with the generalized Cauchy relation. In glycerol, the temperature dependence of the shear acoustic relaxation time agrees well with literature data for dielectric measurements. In DC704, combining the new data with data from measurements obtained previously by piezo-ceramic transducers yields figures showing the longitudinal and shear sound velocities at frequencies from mHz to GHz over an extended range of temperatures. The shoving model's prediction for the relaxation time's temperature dependence is fairly well obeyed for both liquids as demonstrated from a plot with no adjustable parameters. Finally, we show that for both liquids the instantaneous shear modulus follows an exponential temperature dependence to a good approximation, as predicted by Granato's interstitialcy model. (C) 2013 American Institute of Physics. [http://***/10.1063/1.4789948]