关键词： 动力车   机械间   装饰结构   三明治夹芯板  

摘要： 为了打造具有中国特色的动力集中动车组,实现国内铁路进一步提速,降低铁路营运成本,提升中国高端铁路装备技术水平,在研制动力集中动车组动力车的同时,应用新材料、新工艺、新技术的动力车机械间装饰结构应运而生。

关键词： 光动力疗法   马氏硬度   弹性模量   粘接强度   核黄素   亚甲基蓝  

摘要： 目的:评价不同光动力(PDT)对根牙本质的马氏硬度(MH)和弹性模量(Eit*)及与纤维桩粘接强度的影响。方法:100颗单根管前磨牙桩道预备后,随机分成5组,每组20颗,行桩道处理。A组:蒸馏水;B组:2.25%NaCIO+17%EDTA;C组:Er,Cr∶YSGG激光+2.25%NaCIO+17%EDTA;D组:核黄素+17%EDTA;E组:亚甲基蓝+17%EDTA。每组随机选取10颗,使用DUH-211数字超显微硬度计分别测量根颈、根中、根尖切片的MH和Eit*值。剩余每组10颗,粘接纤维桩后,使用万能试验机分别测量根颈、根中、根尖切片的粘接强度值。最后采用方差分析和Tukey检验进行数据分析。结果:(1)MH和Eit*值:A组最高,但组间无差异。根颈、根中、根尖组间无差异。(2)粘接强度值:A组最低,D组最高,均有显著差异(P<0.05),A组

关键词： 柔性关节   移动柔性机械臂   多体系统离散时间传递矩阵法   动力学  

摘要： 开展了含有柔性关节的轮式移动机械臂的动力学特性研究。基于多体系统离散时间传递矩阵法(discrete time transfer matrix method of multibody system, MS-DT-TMM)建立了车轮、车体、柔性关节和机械臂的动力学方程,进而得到平面轮式移动柔性机械臂的整体动力学模型。在不平路面的激励下,分析机器人系统的动力学特性,并讨论柔性关节对系统的影响。数值仿真结果验证了基于MS-DT-TMM模型的可行性和有效性,与刚性结果对比分析表明,由柔性关节引起机械臂的弹性振动,直接影响机器人末端的操作精度,说明考虑关节中柔性因素的必要性。

关键词： 粮食生产   农业劳动力   农业机械化   驱动效应   中国  

摘要： 农业劳动力转移和农业机械化相互影响和关联,两者共同驱动着中国粮食生产变化。为更好地促进中国粮食生产,提升国家粮食安全保障能力,采用Kaya恒等式模型构建了农业劳动力转移和农业机械化联合影响下的粮食产量变化分析框架,运用对数平均迪氏分解法,将它们分解为规模效应、数量效应、装备效应和效率效应,揭示了四大效应对2003—2018年中国及其31个省域(不包括港澳台)粮食生产的影响程度。研究结果表明:(1)无论在时间还是空间变化层面,数量效应都明显抑制了粮食生产,而规模效应和装备效应则显著促进了粮食生产,两者在粮食主产区表现尤为突出;(2)2003—2018年,效率效应对全国层面的粮食生产由负向抑制变为正向驱动,对省域层面的24个省区呈现明显的负向驱动作用。为促进中国粮食产量持续稳定增产,建议持续加大对粮食主产区的政策和资金扶持,稳定其农业生产队伍,进一步强化粮食主销区的粮食安全责任,因地制宜地促进不同区域粮食生产的机械化发展。

关键词： 要素相对价格   机械化发展   机械劳动力替代弹性  

摘要： 农业机械化是通往农业现代化的必经之路。为探究农业机械化发展的深层客观因素,本文以机械化水平最高的粮食作物小麦为例,从要素替代视角出发,基于1998~2018年全国小麦主产省份面板数据,分析要素相对价格变化对小麦生产机械化发展的影响,进一步测算出小麦生产机械劳动力价格替代弹性,并分析不同地形条件下的机械劳动力价格替代弹性。结果表明,劳动力与机械使用的价格之比上升可以显著促进小麦生产机械化程度;机械与劳动之间存在较强的替代关系,且替代弹性大小受到地形条件的调节。最后,本文给出进一步推动中国农产品机械化进展的一些政策意见。

关键词： 装载机   变速箱   V型作业   载荷谱  

摘要： 本文借助AVL-CRUISE软件搭建某型装载机动力传动系统模型,经试验场测试数据验证,模型仿真误差小于8%,满足仿真精度要求;基于装载机的V作业和高速行驶工况仿真分析,获得变速箱仿真载荷谱,并在变速箱机械传动系统MASTA模型进行加载计算,分析变速箱零部件安全系数是否满足要求,以此验证基于工程机械动力系统仿真的变速箱载荷谱编制方法的准确性及实用性,为类似变速箱正向设计的载荷谱获取提供参考依据。

关键词： Vesicles   Phases of matter   Lipids   Gold   Aggregation  

摘要： In recent years, the underlying mechanism of formation of the lipid corona and its stability have begun to garner interest in the nanoscience community. However, until now, very little is known about the role of different properties of nanoparticles (NPs) (surface charge density, hydrophobicity, and size) in lipid corona formation. Apart from the physicochemical properties of NPs, the different properties of lipids remain elusive in lipid corona formation. In the present contribution, we have investigated the interaction of phenylalanine-functionalized gold NPs (Au-Phe NPs) with different zwitterionic lipid vesicles of different phase states (sol-gel and liquid crystalline at room temperature) as a function of lipid concentration. The main objective of the present work is to understand how the lipid phase affects lipid corona formation and lipid-induced aggregation in various media. Our results establish that the lipid phase state, area per lipid head group, and the buffer medium play important roles in lipid-induced aggregation. The lipid corona occurs for NPs at high lipid concentration, irrespective of the phase states and area per lipid head group of the lipid bilayer. Notably, the lipid corona also forms at a low concentration of lipid vesicles in the liquid crystalline phase (1,2-dioleoyl-sn-glycero-3-phosphocholine). The corona formation brings in remarkable stability to NPs against freeze-thaw cycles. Based on the stability, for the first time, we classify lipid corona as "hard lipid corona" and "soft lipid corona". This distinct classification will help to develop suitable nanomaterials for various biomedical applications.

关键词： curing of PPS   chain extension   mechanical properties   polyphenylene sulfide (PPS)   thermal properties  

摘要： Polyphenylene sulfide (PPS) is a type of thermoplastic that has high thermal and mechanical performances and extensive applications. Before processing, precuring is required to improve its processability and mechanical properties. Here, effects of curing temperature (245 and 260 degrees C) and time (10, 30, 60, and 120 min) on structure and thermal-mechanical behavior of PPS were studied through melt flow index (MFI), rheology, Fourier-transform infrared spectroscopy, and thermal-mechanical characterizations. The MFI was decreased from similar to 700 g/10 min to less than 100 g/10 min (315 degrees C/5.0 kg) after 60 min of curing at two different temperatures, greatly improving the processability of PPS in melt extrusion and injection molding processes. The functional groups remained unchanged after curing, due to the main reactions of chain extension and scission that occurred. For the PPS cured both at 245 and 260 degrees C, the samples cured for 10 min displayed the highest degree of crystallinity and heat deflection temperature but had the lowest glass transition temperatures. The coefficient of linear expansion of PPS cured at 260 degrees C showed anisotropy on flow and normal directions, which greatly differed from the PPS cured at 245 degrees C. This study promotes an improved understanding of the curing process for solid PPS.

关键词： Dissolution  

摘要： Oxide dissolution is important for metal extraction from ores and has become an attractive route for the preparation of inks for thin film solution deposition;however, oxide dissolution is often kinetically challenging. While binary "alkahest" systems comprised of thiols and N-donor species, such as amines, are known to dissolve a wide range of oxides, the mechanism of dissolution and identity of the resulting solute(s) remain unstudied. Here, we demonstrate facile dissolution of both bulk synthetic and natural mineral ZnO samples using an "alkahest" that operates via reaction with thiophenol and 1-methylimidazole (MeIm) to give a single, pseudotetrahedral Zn(SPh)(2)(MeIm)(2) molecular solute identified by X-ray crystallography. The kinetics of ZnO dissolution were measured using solution H-1 NMR, and the reaction was found to be zero-order in the presence of excess ligands, with more electron withdrawing para-substituted thiophenols resulting in faster dissolution. A negative entropy of activation was measured by Eyring analysis, indicating associative ligand binding in, or prior to, the rate determining step. Combined experimental and computational surface binding studies on ZnO reveal stronger, irreversible thiophenol binding compared to MeIm, leading to a proposed dissolution mechanism initiated by thiol binding to the ZnO surface with the liberation of water, followed by alternating MeIm and thiolate ligand additions, and ultimately cleavage of the ligated zinc complex from the ZnO surface. Design rules garnered from the mechanistic insight provided by this study should inform the dissolution of other bulk oxides into inks for solution processed thin films.

关键词： Negative ions  

摘要： In this work, we report the results from molecular dynamics simulations of lithium salt-ionic liquid electrolytes (ILEs) based either on the symmetric bis[(trifluoromethyl)sulfonyl]imide (TFSI-) anion or its asymmetric analogue 2,2,2-(trifluoromethyl)sulfonyl-N-cyanoamide (TFSAM(-)). Relating lithium's coordination environment to anion mean residence times and diffusion constants confirms the remarkable transport behaviour of the TFSAM(-)-based ILEs that has been observed in recent experiments: for increased salt doping, the lithium ions must compete for the more attractive cyano over oxygen coordination and a fragmented landscape of solvation geometries emerges, in which lithium appears to be less strongly bound. We present a novel, yet statistically straightforward methodology to quantify the extent to which lithium and its solvation shell are dynamically coupled. By means of a Lithium Coupling Factor (LCF) we demonstrate that the shell anions do not constitute a stable lithium vehicle, which suggests for this electrolyte material the commonly termed "vehicular" lithium transport mechanism could be more aptly pictured as a correlated, flow-like motion of lithium and its neighbourhood. Our analysis elucidates two separate causes why lithium and shell dynamics progressively decouple with higher salt content: on the one hand, an increased sharing of anions between lithium limits the achievable LCF of individual lithium-anion pairs. On the other hand, weaker binding configurations naturally entail a lower dynamic stability of the lithium-anion complex, which is particularly relevant for the TFSAM(-)-containing ILEs.