关键词： 农业机械   劳动力错配   改善  

摘要： 以农业机械化如何改善农业劳动力错配为研究对象,首先提出了一些具体的研究方法,结合研究实际分详细的析了一些计算模型,通过对这些模型进行计算分析,得出了最终结果并进行了探讨。

关键词： 三维结构设计   教学现状   改进措施  

摘要： 作为新工科基础课程与专业课程的桥梁和纽带,“三维结构设计”课程的开设具有重要意义。本文针对该课程授课过程中发现的各种问题,提出了课前认知、小班授课、项目分组及加大实操考核比例等改进措施,旨在有效提升该课程教学效果,培养和提高学生的团队合作能力与综合素质。

关键词： hexagonal boron-nitride   mechanical properties   crack   notch   point defects   molecular dynamics  

摘要： ABSTRACT In this work we conducted classical molecular dynamics(MD)simulation to investigate the mechanical characteristics and failure mechanism of hexagonal boron-nitride(h-BN)*** and defective structure of h-BN nanosheets were considered under the uniaxial tensile loadings at various *** defective structure contains three types of the most common initial defects in engineering materials that are known as cracks,notches(with various length/size),and point vacancy defects(with a wide range of concentration).MD simulation results demonstrate a high load-bearing capacity of extremely defective(amorphized)h-BN *** results also reveal that the tensile strength decline by increasing the defect content and temperature as *** MD results provide a comprehensive and useful vision concerning the mechanical properties ofh-BN nanosheets with/without defects,which is very critical for the designing of nanodevices exploiting the exceptional physics of h-BN.

关键词： Polystyrene nanoparticles   Molecular dynamics simulation   Elastic modulus   Hardness  

摘要： Chemical mechanical planarization (CMP) is an important step in the semiconductor technology. The surface of the wafer after CMP must be defect-free with low roughness. Polymer particles are one of the potential candidates for using as abrasive in CMP. Hence, studying mechanical properties of these abrasives is of great importance. In the current study, the size-dependence elastic modulus and hardness of polystyrene (PS) nanoparticles is investigated via molecular dynamics (MD) simulations. The effect of strain on elastic modulus and hardness is examined and also the impact of strain rate on the mechanical response of PS nanoparticles during compression is studied. Additionally, the pop-in event during loading is precisely examined using volumetric analysis and shear strain distribution inside the nanoparticles is investigated. The results show that the elastic modulus increases linearly by decreasing the particle size while the hardness has a non-linear behavior. The predictions are compared with empirical measurements and good agreement is accomplished.

关键词： Silica aerogel nanocomposites   Molecular dynamics   Mechanical properties   Fracture behavior  

摘要： Silica aerogel is a brittle as well as a low-tensile strength highly porous solid. Therefore, the primary goal of the present work is to incorporate glass fibers, graphene sheets and carbon nanotubes into the silica aerogel matrix using molecular dynamics (MD) simulations to improve not only the mechanical properties, e.g., tensile strength, elastic modulus, and toughness, but also the deformation characteristics due to the pre-existing cracks. This work investigates and compares the mechanical properties obtained from tension and compression tests of native silica aerogels and their nanocomposites. The results show that the axial and lateral direction mechanical properties of carbon-based nanocomposites are significantly higher than the native and glass fibers reinforced silica aerogels. For example, in the axial loading, the elastic modulus of the proposed glass fibers, graphene sheets, and carbon nanotubes reinforced nanocomposites were similar to 3.5, similar to 9.5 and similar to 11.5 times higher than the native silica aerogels, respectively. Moreover, the influence of crack depth has been studied in the tensile fracture simulations, and we found that in nanocomposites, the tensile load bearing candidates are mainly reinforced materials. The outcome of this work is a vital step in the process of designing advanced nanocomposites.

关键词： 逆向工程   挠性机械臂   三维动力模型   机械强度  

摘要： 为深入研究提高挠性机械臂结构强度的方法,进行了基于逆向工程的挠性机械臂三维动力建模研究。基于线性代数中逆向工程的运算理论来设计新型挠性机械臂三维动力建模方法,建立挠性机械臂运动学方程、挠性机械臂拉格朗日动力学方程、挠性机械臂三维动力模型,完成挠性机械臂三维动力模型的构建。通过仿真试验,对比了新型挠性机械臂三维动力建模方法与传统方法所得模型的精确度,证明了新型挠性机械臂三维动力建模方法的使用价值,为提高挠性机械臂的产品质量提供了技术支持。

关键词： High-energy X-ray diffraction   High-resolution electron microscopy   Atomic ordering   Gold and silver alloys   Lattice strain  

摘要： Precious alloys are subjected to a series of mechanical and thermal operations during manufacturing. For 18 carat gold alloys the processing operations can induce L1(0) ordered nanodomains, known to lead to the buildup of residual stresses, which are the prime cause for shape distortion. Here, in situ high-energy synchrotron X-ray diffraction experiments in combination with electron microscopy observations reveal the influence of the thermo-mechanical history and chemical composition on the ordering kinetics during isochronal heating. Initially, during heating, the elastic lattice strain in the ordered nanodomains increases. The ordering rate and accumulation of lattice strain depend on the cooling rate, predeformation and chemical composition. Above a given temperature, which depends on the deformation state and chemical composition, the lattice strain in the ordered domains relaxes which is ascribed to the formation of a tweed structure. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： myoferlin   mitochondria   mitofusin   pancreas cancer  

摘要： Pancreas ductal adenocarcinoma is one of the deadliest cancers where surgery remains the main survival factor. Mitochondria were described to be involved in tumor aggressiveness in several cancer types including pancreas cancer. We have previously reported that myoferlin controls mitochondrial structure and function, and demonstrated that myoferlin depletion disturbs the mitochondrial dynamics culminating in a mitochondrial fission. In order to unravel the mechanism underlying this observation, we explored the myoferlin localization in pancreatic cancer cells and showed a colocalization with the mitochondrial dynamic machinery element: mitofusin. This colocalization was confirmed in several pancreas cancer cell lines and in normal cell lines as well. Moreover, in pancreas cancer cell lines, it appeared that myoferlin interacted with mitofusin. These discoveries open-up new research avenues aiming at modulating mitofusin function in pancreas cancer.

关键词： Climate models   Reanalysis data   Climate variability   Multidecadal variability  

摘要： This paper addresses the dynamics of internal hemispheric-scale multidecadal climate variability by postulating an energy-balance (EBM) model comprising two deep-ocean oscillators in the Atlantic and Pacific basins, coupled through their surface mixed layers via atmospheric teleconnections. This system is linear and driven by the atmospheric noise. Two sets of the EBM model parameters are developed by fitting the EBM-based mixed-layer temperature covariance structure to best mimic basin-average North Atlantic/Pacific sea surface temperature (SST) covariability in either observations or control simulations of comprehensive climate models within the CMIP5 project. The differences between the dynamics underlying the observed and CMIP5-simulated multidecadal climate variability and predictability are encapsulated in the algebraic structure of the two EBM model versions so obtained: EBMCMIP5 and EBMOBS. The multidecadal variability in EBMCMIP5 is overall weaker and amounts to a smaller fraction of the total SST variability than in EBMOBS, pointing to a lower potential decadal predictability of virtual CMIP5 climates relative to that of the actual climate. The EBMCMIP5 decadal hemispheric teleconnections (and, by inference, those in CMIP5 models) are largely controlled by the variability of the Pacific, in which the ocean, due to its large thermal and dynamical memory, acts as a passive integrator of atmospheric noise. By contrast, EBMOBS features a stronger two-way coupling between the Atlantic and Pacific multidecadal oscillators, thereby suggesting the existence of a hemispheric-scale and, perhaps, global multidecadal mode associated with internal ocean dynamics. The inferred differences between the observed and CMIP5 simulated climate variability stem from a stronger communication between the deep ocean and surface processes implicit in the observational data.

关键词： Actin   Super-resolution microscopy  

摘要： Zhang et al. show that dynamin forms a helical structure with actin and, upon disruption, enhances branched actin polymerization, constituting a dynamic cycle to regulate actin cytoskeleton mechanical strength. The dynamin GTPase is known to bundle actin filaments, but the underlying molecular mechanism and physiological relevance remain unclear. Our genetic analyses revealed a function of dynamin in propelling invasive membrane protrusions during myoblast fusion in vivo. Using biochemistry, total internal reflection fluorescence microscopy, electron microscopy and cryo-electron tomography, we show that dynamin bundles actin while forming a helical structure. At its full capacity, each dynamin helix captures 12-16 actin filaments on the outer rim of the helix. GTP hydrolysis by dynamin triggers disassembly of fully assembled dynamin helices, releasing free dynamin dimers/tetramers and facilitating Arp2/3-mediated branched actin polymerization. The assembly/disassembly cycles of dynamin promote continuous actin bundling to generate mechanically stiff actin super-bundles. Super-resolution and immunogold platinum replica electron microscopy revealed dynamin along actin bundles at the fusogenic synapse. These findings implicate dynamin as a unique multifilament actin-bundling protein that regulates the dynamics and mechanical strength of the actin cytoskeletal network.