关键词： Waxy maize   Swelling kinetics   Granule size distribution   Polymer swelling theory   Second virial coefficient   Cryo SEM  

摘要： The evolution of 8% suspension of waxy maize starch granule size distribution when subjected to heating to 65, 70, 75, 80, 85 and 90 degrees C at a heating rate of 15 degrees C/min were measured. Granule swelling was more pronounced at higher temperatures with an increase in the average size from 13 gm to 25-28 mu m, eventually approaching equilibrium. Cryo SEM images revealed porous structure of swollen granule. The proposed model for starch swelling accounts for entropy of mixing, enthalpy of water-starch interaction and elastic restoring force. The second virial coefficient of waxy maize in aqueous medium was characterized by static light scattering. Chemical potential profile as well as the temperature profile within the granule were predicted from the solution of unsteady state diffusion and heat conduction respectively. The granule size was then inferred from the chemical potential profile. The proposed model predicts the evolution of average granule size and granule size distribution accurately. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Thermoresponsive hydrogel   Cryogels   Nanocomposite   N-Isopropyl acrylamide   Superporous  

摘要： The superporous thermosensitive PNIPA/clay hydrogels were prepared by the advanced two-step freezing polymerization. The formation and properties of the cryogels were controlled by freezing conditions, such as time of freezing during the two-step polymerization and the rate of cooling. The freezing of the reaction mixture in different well-defined stages of structure evolution during polymerization made it possible to fine tune the structure, morphology, and properties of cryogels. The development of structure during polymerization was followed by NMR and chemorheology, and moreover, the morphology, porosity, swelling behavior, and mechanical properties of the cryogels were determined. The results contribute to the basic understanding of the structure evolution under freezing conditions and to the knowledge of the mechanism of a cryogel formation. The smart thermoresponsive gels with a wide variety of properties were prepared, ranging from the weak ultrafast responding cryogels (deswelling in 30 s, reswelling in 8 min), prepared by the early freezing, up to the porous gel with extraordinary mechanical properties (sigma (b) = 320 kPa, epsilon (b) = 900%) still displaying a relatively fast thermal volume transition. The advanced two-step freezing polymerization is shown to be a suitable general approach to controlling and tuning porosity, as well as swelling and mechanical properties of porous gels.

关键词： Isomerization   Solvents   Vacuum   Computational chemistry   Computer simulations  

摘要： Azobenzene-based molecular photoswitches are becoming increasingly important for the development of photoresponsive, fast interconversion between a more stable trans and a metastable cis configuration can be established resulting in pronounced changes in functional soft-matter material systems. Upon illumination with light, conformation, dipole moment or hydrophobicity. A rational design of functional photosensitive molecules with embedded azo moieties requires a thorough understanding of isomerization mechanisms and rates, especially the thermally activated relaxation. For small azo derivatives considered in the gas phase or simple solvents, Eyring's classical transition state theory (TST) approach yields useful predictions for trends in activation energies or corresponding half-life times of the cis isomer. However, TST or improved theories cannot easily be applied when the azo moiety is part of a larger molecular complex or embedded into a heterogeneous environment, where a multitude of possible reaction pathways may exist. In these cases, only the sampling of an ensemble of dynamic reactive trajectories (transition path sampling, TPS) with explicit models of the environment may reveal the nature of the processes involved. In the present work we show how a TPS approach can conveniently be implemented for the phenomenon of relaxation isomerization of azobenzenes starting with the simple examples of pure azobenzene and a push pull derivative immersed in a polar (DMSO) and apolar (toluene) solvent. The latter are represented explicitly at a molecular mechanical (MM) and the azo moiety at a quantum mechanical (QM) level. We demonstrate for the push pull azobenzene that path sampling in combination with the chosen QM/MM scheme produces the expected change in isomerization pathway from inversion to rotation in going from a low to a high permittivity (explicit) solvent model. We discuss the potential of the simulation procedure presented for comparative calculation of r

关键词： ATC manipulator   digital prototyping   double-globoid cam   rigid-flexible coupling analysis   刚柔耦合分析   双弧面凸轮   数字化样机   ATC机械手   Language of Keywords: English   Chinese  

摘要： Aiming at the double-globoid cam-type ATC manipulator, 3D model was completed;the multi-degree ridge-flexible coupling dynamic model of ATC device was established based on the theoretical basis of mechanical system dynamics. And the input shaft, fork shaft,sleeve and fork of ATC manipulator were flexed through ANSYS and established the rigid-flexible coupling digital prototyping; the dynamic performance of ATC arm up, down and rotary motion was analyzed based on ADMAS. The analysis process simulated the actual working situation of ATC manipulator as much as possible. And the result has a reference value to ATC device desigmproduction and rigid-flexible coupling analysis in the future. [ABSTRACT FROM AUTHOR]

关键词： Mechanics on Lie algebroids   Higher order mechanics   Lagrangian mechanics   Lagrangian submanifolds  

摘要： The study of mechanical systems on Lie algebroids permits an understanding of the dynamics described by a Lagrangian or Hamiltonian function for a wide range of mechanical systems in a unified framework. Systems defined in tangent bundles, Lie algebras, principal bundles, reduced systems, and constrained are included in such description. In this paper, we investigate how to derive the dynamics associated with a Lagrangian system defined on the set of admissible elements of a given Lie algebroid using Tulczyjew's triple on Lie algebroids and constructing a Lagrangian Lie subalgebroid of a symplectic Lie algebroid, by building on the geometric formalism for mechanics on Lie algebroids developed by M. de Leon, J.C. Marrero and E. Martinez on "Lagrangian submanifolds and dynamics on Lie algebroids".

关键词： MoS2   phase transition   molecular dynamics   nanoindentation   uniaxial compression  

摘要： The single-layer molybdenum disulfide (SLMoS2) nanosheets have been experimentally discovered to exist in two different polymorphs, which exhibit different electrical properties, metallic or semiconducting. Herein, molecular dynamics (MD) simulations of nanoindentation and uniaxial compression were conducted to investigate the phase transition of SLMoS2 nanosheets. Typical load-deflection curves, stress-strain curves, and local atomic structures were obtained. The loading force decreases sharply and then increases again at a critical deflection under the nanoindentation, which is inferred to the phase transition. In addition to the layer thickness, some related bond lengths and bond angles were also found to suddenly change as the phase transition occurs. A bell-like hollow, so-called residual deformation, was found to form, mainly due to the lattice distortion around the waist of the bell. The effect of indenter size on the residual hollow was also analyzed. Under the uniaxial compression along the armchair direction, a different phase transition, a uniformly quadrilateral structure, was observed when the strain is greater than 27.7%. The quadrilateral structure was found to be stable and exhibit metallic conductivity in view of the first-principle calculation.

关键词： 劳动力契约   技术停滞   治理机制  

摘要： 该文针对近代上海机械缫丝工业长期技术停滞的问题,采用威廉姆森关于劳动力契约关系的理论分析工具,通过对丝厂劳动力契约制度的解析发现：近代上海丝厂所采用的连续现货计时劳动力契约模式所导致的厂商倾向于保持原有生产技术不变,是制约近代上海机械缫丝工业技术进步的主要因素。该文进一步深入解析了丝厂劳动力契约的治理机制变迁的史实,并以此来对研究结果进行验证。该文尝试从劳动力契约的视角解释技术进步的制约因素。

关键词： Molecular dynamics  

摘要： Defects are likely ubiquitous in metal-organic frameworks (MOFs). Investigation of the effect of defects on the mechanical deformation of MOFs remains at a nascent stage. In this study molecular dynamics simulation was adopted to investigate the deformation mechanisms of defected MOF-5. Our results show that the defects reduce the yield strength via inducing the nucleation of dislocations. The type of dislocations depends on the defect structure, presented as a subject increased scientific interest. Also, the defected MOF-5 was deformed under different loading modes (compression, shear and tension) to understand the deformation mechanism. Revealing the mechanical deformation of defected MOFs is expected to yield considerable benefits in both controlling and tailoring the mechanical properties of MOFs.

关键词： 转型发展   机械专业   培养模式   工程   项目  

摘要： 在"新工科"背景下,对于转型发展院校机械类专业学生的培养,提出了以工程为动力、以项目为抓手的人才培养模式,界定这种培养模式的内涵和提出实施方案,并把这种模式应用到机械类专业学生的培养过程中。通过实施这种培养模式,使机械类专业的学生树立了工程意识,具备了工程能力,为毕业后的工作打下了坚实的基础。