关键词： Lipid oxidation   Membrane rupture   Pore formation   Domain interfaces  

摘要： Biomembranes are under constant attack of free radicals that may lead to lipid oxidation in conditions of oxidative stress. The products generated during lipid oxidation are responsible for structural and dynamical changes which may jeopardize the membrane function. For instance, the local rearrangements of oxidized lipid molecules may induce membrane rupture. In this study, we investigated the effects of mechanical stress on oxidized phospholipid bilayers (PLBs). Model bilayers were stretched until pore formation (or poration) using non-equilibrium molecular dynamics simulations. We studied single-component homogeneous membranes composed of lipid oxidation products, as well as two-component heterogeneous membranes with coexisting native and oxidized domains. In homogeneous membranes, the oxidation products with -OH and -OOH groups reduced the areal strain required for pore formation, whereas the oxidation product with =O group behaved similarly to the native membrane. In heterogeneous membranes composed of oxidized and non-oxidized domains, we tested the hypothesis according to which poration may be facilitated at the domain interface region. However, results were inconclusive due to their large statistical variance and sensitivity to simulation setup parameters. We pointed out important technical issues that need to be considered in future simulations of mechanically-induced poration of heterogeneous membranes. This research is of interest for photodynamic therapy and plasma medicine, because ruptured and intact plasma membranes are experimentally considered hallmarks of necrotic and apoptotic cell death.

关键词： biodegradable bicomponent fibers   polyoxymethylene   poly(l-lactic acid) blends   melt spinning   post drawing   tensile properties   crystalline orientation   hydration behavior   thermal degradation kinetics  

摘要： A series of polyoxymethylene (POM)/poly(l-lactic acid) (PLLA) blends were prepared by melt extrusion, and their spinnability was confirmed by rheological characterizations, successive self-nucleation, and annealing thermal fractionation analysis. The bicomponent fibers were prepared by means of the melt-spinning and post-drawing technologies using the above-obtained blends, and their morphology, crystalline orientation characteristics, mechanical performance, hydration behavior, and thermal degradation kinetics were studied extensively. The bicomponent fibers exhibited a uniform diameter distribution and compact texture at the ultimate draw ratio. Although the presence of PLLA reduced the crystallinity of the POM domain in the bicomponent fibers, the post-drawing process promoted the crystalline orientation of lamellar folded-chain crystallites due to the stress-induced crystallization effect and enhanced the crystallinity of the POM domain accordingly. As a result, the bicomponent fibers achieved the relatively high tensile strength of 791 MPa. The bicomponent fibers exhibited a partial hydration capability in both acid and alkali media and therefore could meet the requirement for serving as a type of biodegradable fibers. The introduction of PLLA slightly reduced the thermo-oxidative aging property and thermal stability of the bicomponent fibers. Such a combination of two polymers shortened the thermal lifetime of the bicomponent fibers, which could facilitate their natural degradation for ecological and sustainable applications.

关键词： Interfaces   Dissociation   Adsorption   Silica   Molecules  

摘要： To clarify the chemical mechanical polishing (CMP) mechanism of Cu in aqueous hydrogen peroxide and glycine, we developed a ReaxFF reactive force field to describe the interaction between Cu, slurry (H2O, H2O2, and glycine), and the silica abrasive. Based on this force field, we used molecular dynamics simulations to illustrate the chemistry at the Cu/silica abrasive interface and Cu atom removal mechanism during the Cu CMP process. Our results indicate that H2O easily chemically adsorbs on the Cu surface, and H2O2 can dissociate into hydroxyl radicals, forming Cu-OH. Besides, the OH-terminated silica surface can chemically interact with the Cu substrate, leading to the formation of Cu OH on the Cu substrate. During the CMP process, Cu atoms on the substrate are effectively removed due to the mechanical sliding process-induced chemical reactions, including mainly three removal pathways: shear-induced glycine-adsorbed Cu atom removal process, shear-induced OH-adsorbed Cu atom removal process, and shear-induced Cu atom removal process due to the formation of interfacial Cu-O-Si bridge bonds. These results provide atomistic insights into the chemical reactions under mechanical effects in the Cu CMP process, thus helping the slurry design and process parameter optimization.

关键词： magnetic friction   thin films   micromagnetics  

摘要： Magnetic friction is a form of non-contact friction arising from the dissipation of energy in a magnet due to spin reorientation in a magnetic field. In this paper, we study magnetic friction in the context of micromagnetics, using our recent implementation of smooth spring-driven motion (Rissanen and Laurson 2018 Phys. Rev. E 97 053301) to simulate ring-down measurements in two setups where domain wall dynamics is induced by mechanical motion. These include a single thin film with a domain wall in an external field and a setup mimicking a magnetic cantilever tip and substrate, in which the two magnets interact through dipolar interactions. We investigate how various micromagnetic parameters influence the domain wall dynamics actuated by the oscillatory spring-driven mechanical motion and the resulting damping coefficient. Our simulations show that the magnitude of magnetic friction can be comparable to other forms of non-contact friction. For oscillation frequencies lower than those inducing excitations of the internal structure of the domain walls, the damping coefficient is found to be independent of frequency. Hence, our results obtained in the frequency range from 8-112 MHz are expected to be relevant also for typical experimental setups operating in the 100 kHz range.

关键词： Titanium nitride   SPS sintering   Titanium vacancies   Mechanical properties  

摘要： Fully dense titanium nitride polycrystals have been prepared by spark plasma sintering. The kinetics of the sintering process and the optimized conditions for SPS processing have been put forward. Microstructural analyses of the resulting samples have unambiguously shown the coexistence of titanium as Ti2+, Ti3+ and Ti4+, thus driving the presence of cation vacancies. This fact is a new ingredient which is shown to influence the mechanical properties of this strategic ceramic. (C) 2019 Elsevier B.V. All rights reserved.

关键词： Rubber aging   Fourier-transform rheology   H-1 double quantum NMR  

摘要： Nowadays mainly the linear rheological properties of natural rubber (NR) vulcanizate during aging are studied, even though NR is rheologically nonlinear under most application conditions. Here, the nonlinearity was quantified via Fourier transform rheology (FT-Rheology) using I-3/1, the relative intensity of the 3rd harmonic. The crosslink density and the content of defects were investigated by the H-1 double quantum nuclear magnetic resonance (DQ-NMR). For aerobic aging at 120 degrees C, the crosslink density increases, but later turns into a broader mesh size distribution with more defects. Accordingly, the rheological nonlinearity of the material increases in the earlier stage and then decreases. For mechanical aging, the nonlinearity continuously decreases as a function of the fatigue cycle numbers, whereas the local crosslink density of the polymer network remains constant. This behavior can be assigned to the micro-cracks generated along adjacent network defects, which are larger than the detection scale of DQ-NMR. Compared to the linear rheological parameters, storage modulus G' and loss factor tans delta, I-3/1 exhibits higher sensitivity to the aging of crosslinked NR under both high temperature aerobic and mechanical fatigue conditions.

标准号: LY/T 3166-2019

摘要： 本标准规定了以内燃机为动力的山地单轨运输机的术语和定义、型号编制方法、基本参数、技术要求及试验方法、标志、使用说明书、包装、运输和贮存。本标准适用于由内燃机驱动的单轨运行的自行式轨道运输机（以下简称“运输机”）。

标准号: LY/T 3170-2019

摘要： 本标准规定了以锂离子电池为动力源的杆式绿篱修剪机（以下简称“锂电杆式绿篱机”）的术语和定义、型号编制方法、基本参数、技术要求及试验方法、标志、使用说明书、包装、运输、贮存及处理。本标准适用于一般环境条件下，以标称电压不大于直流75V可充电锂离子电池包（电池组）供电的杆式绿篱修剪机。

标准号: LY/T 3168-2019

摘要： 本标准规定了以锂离子电池为动力源的配刚性切割装置的手持式修边机和手推式修边机（以下简称“锂电手持式修边机”和“锂电手推式修边机”）的术语和定义、型号编制方法、基本参数、技术要求及试验方法、标志、使用说明书、包装、运输、贮存和处理。本标准适用于以标称电压不大于直流75 V可充电锂离子电池包（电池组）供电的手持式修边机和手推式修边机。

标准号: LY/T 3167-2019

摘要： 本标准规定了农业、园艺和场地维护(如景观美化)中使用的动力驱动的集料系统设计与结构的安全要求及其检验方法。本标准适用于在其颁布实施后生产的悬挂式、半悬挂式和牵引式机械。本标准给出了按既定用途使用集料系统时消除或减少机械危险的方法。本标准不涉及环境危险、道路安全、电磁兼容性、动力输出装置(PTO)、PTO驱动轴防护及控制要求。本标准不适用于GB/T 38364.2《园林机械 以内燃机为动力的草坪修剪机安全要求 第2部分:步进式草坪修剪机》和GB/T 38364.3《园林机械 以内燃机为动力的草坪修剪机安全要求 第3部分:坐骑式草坪修剪机中规定的机械》。