ASTM1045钢活塞销热挤压工艺过程仿真探究

采用刚塑形有限元DEFORM-2D软件,对φ22mm×φ14.60mm×70mm规格的ASTMI045钢活塞销热挤压工艺过程进行了仿真研究,揭示了挤压力随行程的变化规律、应变场和坯料金属损伤的分布规律.为了避免活塞销外侧产生裂纹,提高抗疲劳开裂能力,上、下凸模挤压余量应≥6mm.模拟结果能为优化活塞销的热挤压工艺提供参考.     

汽车发动机用6A02铝合金管材挤压速度仿真优化

如何实现6A02铝合金在汽车发动机上广泛使用对于汽车发动机发展有着重要作用.而合适的挤压速度范围是实现6A02铝合金管材挤压的关键因素之一.以6A02铝合金管材(φ29 mm×4.5 mm)挤压工艺过程为研究对象,基于DEFORM-2D软件模拟研究了挤压速度对载荷及模口坯料金属峰值温度的影响规律.获得了该规格6A02铝合金管材在250 kN挤压机上的合理挤压速度范围约为25～45 mm/s.     

Self-assembly of rod-terminally tethered three-armed star-shaped coil block copolymer: Investigation of the presence of the branching in the coil to the self-assembled behavior

Self-assembled behavior of rod-terminally tethered three-armed star-shaped coil block copolymer melts was studied by applying self-consistent-field lattice techniques in three-dimensional (3D) space. Similar to rod-coil diblock copolymers, five morphologies were observed, i.e., lamellar, perforated lamellar, gyroidlike, cylindrical and sphericallike structures, while the distribution of the morphologies in the phase diagram was dramatically changed with respect to that of rod-coil diblock copolymers. The perforated lamella was replaced by the cylinder when f_rod = 0.45, and the lamella was replaced by the perforated lamella when f_rod = 0.5 when the arms A₁ and A₂ had an equal length and the volume fraction of A₃ arm was low enough. Simulations were also performed when the arms A₁ and A₂ had unequal lengths. These results demonstrate that simple branching in the coil induces interesting microphase transitions.     

Chitosan-functionalized graphene oxide as a nanocarrier for drug and gene delivery

The covalent functionalization of graphene oxide (GO) with chitosan (CS) is successfully accomplished via a facile amidation process. The CS-grafted GO (GO-CS) sheets consist of about 64 wt.% CS, which imparts them with a good aqueous solubility and biocompatibility. Additionally, the physicochemical properties of GO-CS are studied. As a novel nanocarrier, GO-CS is applied to load a water-insoluble anticancer drug, camptothecin (CPT), via π-π stacking and hydrophobic interactions. It is demonstrated that GO-CS possesses a superior loading capacity for CPT, and the GO-CS-CPT complexes show remarkably high cytotoxicity in HepG2 and HeLa cell lines compared to the pure drug. At the same time, GO-CS is also able to condense plasmid DNA into stable, nanosized complexes, and the resulting GO-CS/pDNA nanoparticles exhibit reasonable transfection efficiency in HeLa cells at certain nitrogen/phosphate ratios. Therefore, the GO-CS nanocarrier is able to load and deliver both anticancer drugs and genes.     

基于熵权模糊综合评价模型的电力系统黑启动方案评估

电力系统黑启动方案的合理选择对系统快速恢复供电具有重要意义。提出了基于熵权模糊综合评价模型的电力系统黑启动方案评价方法,实现对黑启动方案的有效评估和排序。该方法采用了更为合理的熵权权重和专家偏好的结合方法,实现了数据信息的客观性与专家偏好主观性的良好结合;进而将黑启动评价指标合理模糊化,利用方案的模糊评价信息,通过模糊综合评价方法,实现了方案的相对优劣排序。该方法计算过程简单,没有特征值及复杂的优化计算等,也不存在无法通过某项限制性校验而导致方法失效的情况。针对天津电网的实际系统黑启动路径评估结果验证了所提方法的有效性。     

基于SDN架构的电力通信网络质量感知技术研究

电力工业是国民经济的基础支柱,其通信网络是电力生产、经营和管理的一个重要组成部分;针对现通信网中业务流实时监测的难题,提出引入一种基于SDN架构设计的新型流量感知监测技术方案,经实际网络延迟数据与RLI算法、MDI指标中的DF参数、VTD指标互作对比;为此搭建基于NetMag可编程网络设备的实验环境通过验证及建模对比,均达到预期效果;论证该项质量感知技术能为电力通信网提供可视化、实时、智能的运维平台作部署,这将使运维管理工作更加主动、有效,有利于提高网络运行的效率与稳定性。     

热氧化方法制备直径可控的有序硅纳米线阵列

采用金属辅助化学刻蚀方法结合纳米球模板技术制备出了有序硅纳米线阵列.硅纳米线阵列经过高温热氧化形成一定厚度的氧化层,再使用稀释的HF溶液去除表面氧化层得到可控直径/周期比、低孔隙密度的有序纳米线阵列.主要研究了氧化温度、氧化时间对硅纳米线形貌的影响,并根据扩展的Deal-Grove模型计算了硅纳米线氧化层厚度与氧化时间的关系,讨论了氧化过程中应力分布的影响,理论计算结果与实验结果一致.最后,采用两步氧化的方法制备出了低直径/周期比(约0.1)、低孔隙密度的有序硅纳米线阵列.     

Gas Breakdown of Radio Frequency Glow Discharges in Helium at near Atmospheric Pressure

A one-dimensional self-consistent fluid model was developed for radio frequency glow discharge in helium at near atmospheric pressure, and was employed to study the gas breakdown characteristics in terms of breakdown voltage. The effective secondary electron emission coefficient and the effective electric field for ions were demonstrated to be important for determining the breakdown voltage of radio frequency glow discharge at near atmospheric pressure. The constant of A was estimated to be 64±4 cm 1 Torr 1 , which was proportional to the first Townsend coefficient and could be employed to evaluate the gas breakdown voltage. The reduction in the breakdown voltage of radio frequency glow discharge with excitation frequency was studied and attributed to the electron trapping effect in the discharge gap.     

Preparation and characterization of mPEG‐g‐α‐zein biohybrid micelles as a nano‐carrier

A new kind of block copolymer micelles methoxy polyethylene glycol (mPEG) grafted α‐zein protein (mPEG‐g‐α‐zein) was synthesized. The chemical composition of mPEG‐g‐α‐zein was identified with the help of FT‐IR and ¹H‐NMR. The biohybrid polymer can self‐assemble into spherical core–shell nanoparticles in aqueous solution. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to investigate the self‐assembled morphology of mPEG‐g‐α‐zein. Dynamic light scattering (DLS) results showed that the particle size of mPEG‐g‐α‐zein was about 90 nm. Moreover, the nanoparticles had a very low critical micelle concentration value with only 0.02 mg/mL. Then, the anticancer drug curcumin (CUR) was encapsulated into the biohybrid polymer micelles. The in vitro drug release profile showed a zero‐order release of CUR up to 12 h at 37°C. Cell viability studies revealed that the mPEG‐g‐α‐zein polymer exhibited low cytotoxicity for HepG2 cells (human hepatoma cells). Consequently, the mPEG‐g‐α‐zein micelles can be used as a potential nano‐carrier to encapsulate hydrophobic drugs and nutrients. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42555.     

Synthesis and properties of monomer casting polyamide 6/poly(methyl methacrylate) blends

We successfully synthesized monomer casting polyamide 6 (MCPA6)/poly(methyl methacrylate) (PMMA) blends in two steps: (1) radical polymerization of methyl methacrylate in ?‐caprolactam and (2) anionic ring‐opening polymerization of this ?‐caprolactam solution. The influence of PMMA on the crystallization behavior of MCPA6 was studied with differential scanning calorimetry and X‐ray diffraction, which showed that PMMA could act as a heterogeneous nucleation agent and favored the formation of the γ‐crystalline form. The rheological properties were also studied and indicated that PMMA reduced the interaction between MCPA6 chains by lowering the density of hydrogen bonding. This study used a novel and convenient method to prepare microporous MCPA6/PMMA particles that involved removing the continuous phase. Their surface area and thermal stability were characterized by the Brunauer–Emmett–Teller method and thermogravimetric analysis, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009