低温冷链物流技术发展的探析

通过对国内外冷链低温物流实际现状的研究,阐述并剖析了目前国内冷链物流领域存在的冷点及原因。从增强国内冷链意识、完善基础设备建设、改进冷冻冷藏技术及发展先进冷藏运输设备等多方面探析如何高效地发展冷链物流技术,给出相应的建议和对策,以提升国内冷链低温物流技术的竞争力。     

印制电路板微孔机械钻削研究

文章介绍广东工业大学印制电路板精密加工实验室对机械钻削PCB微孔的研究工作进展。研究了PCB机械加工的加工过程、钻削力、钻削温度和钻削质量;分析了钻头磨损与断针的主要特征及原因,分析了钻削机床的动态性能,提出了印制电路板高速数控钻床的设计原则,设计制造出了具有钻削力测定、快速更换主轴等功能、主轴最高转速为250 min的印制电路板超高速超微细钻床。     

折臂式随车起重机转台的拓扑优化设计

为了使折臂式随车起重机转台在最大应力不超过材料许用应力的前提下实现轻量化设计的目的,通过ADAMS软件仿真确定其极限工况,对转台进行静力学分析及拓扑优化。通过拓扑优化得到了理想的材料分布。基于优化结果调整转台结构,并对改进后的转台进行静力学分析。结果表明,优化后的转台能够满足实际的使用需求。同时,转台质量降低了12%,证明了优化设计的有效性和可行性,并为折臂式随车起重机的相关设计提供了一定的借鉴。     

基于自适应LS-SVM的柴油机废气再循环冷却控制系统设计

针对当前柴油机废气再循环冷却控制系统受到时滞问题影响,导致系统开度走势与设定走势不一致、废气再循环效果差的问题,提出基于自适应LS-SVM的柴油机废气再循环冷却控制系统;以AT89C51单片机40针作为电控单元核心部件,利用位置传感器向系统发送负载信号,利用温度传感器来传输信号并反馈至D/A转换器;在D/A转换器中,反馈信号以串行或并行方式进入寄存器,并在转换后输出电流电压,控制系统阀门在排气再循环时的开启;伺服泵采用冷却系统,为系统提供液压动力源;利用自适应LS-SVM原理计算柴油机废气再循环冷却控制目标边界值,在最小二乘支持向量机基础上,利用求解线性方程组进行优化,消除了控制误差;根据控制差的大小,调整控制系统的输出值;由试验结果可知,该系统开度走势与设定开度走势一致,且与设定开度误差为1开度,说明使用该系统具有良好稳态特性,有效克服了系统中时滞问题,废气再循环效果较好。     

Phase stability and thermo-physical properties of ZrO2-CeO2-TiO2 ceramics for thermal barrier coatings

The properties of ZrO₂ co-stabilized by CeO₂ and TiO₂ ceramic bulks were investigated for potential thermal barrier coating (TBC) applications. Results showed that the (Ce_0.15Ti_x)Zr_0.85-xO7 (x?=?0.05, 0.10, 0.15) compositions with single tetragonal phase were more stable than the traditional 8YSZ at 1573?K. These compositions also showed a large thermal expansion coefficient (TEC) and a high fracture toughness, which were comparable to those of YSZ. However, the phase stability, fracture toughness and sintering resistance of the CeO₂-TiO₂-ZrO₂ system showed a decline tendency with the increase of TiO₂ content. The TEC of the ceramic bulks decreased with increase of TiO₂ content as well because the crystal energy was enhanced with increasing substitution of Zr⁴⁺ by smaller Ti⁴⁺. The (Ce_0.15Ti_0.05)Zr_0.8O₂ had the best comprehensive properties among the (Ce_0.15Ti_x)Zr_0.85-xO₂ compositions as well as a low thermal conductivity. Therefore, it can be explored as a TBC candidate material for high-temperature applications.     

Polyurethane/doxorubicin nanoparticles based on electrostatic interactions as pH‐sensitive drug delivery carriers

In order to obtain a pH‐sensitive delivery carrier for doxorubicin (DOX), DOX‐loaded polyurethane (PU·DOX) nanoparticles were readily prepared in water by electrostatic interactions between amphiphilic polyurethane with carboxyl pendent groups (PU‐COOH) and doxorubicin hydrochloride (DOX·HCl). The structures of the products obtained were characterized by Fourier transform infrared spectroscopy, ¹H NMR spectroscopy, gel permeation chromatography, UV–visible spectroscopy, dynamic light scattering and transmission electron microscopy. The average hydrodynamic size of the PU·DOX nanoparticles was around 182 nm with negative surface charge (?1.1 mV) and a spherical or rodlike shape. PU·DOX nanoparticles had a higher drug‐loading content of 14.1 wt%. The in vitro drug release properties of PU·DOX nanoparticles were investigated at pH 4.0, 5.0 and 7.4, respectively. PU·DOX nanoparticles exhibited a good pH‐sensitive drug release property, but there was almost no release of DOX from PU·DOX nanoparticles at pH 7.4. The in vitro cellular uptake assay and the Cell Counting Kit‐8 assay demonstrated that PU·DOX nanoparticles had a higher level of cellular internalization and higher inhibitory effects on the proliferation of human breast cancer (MCF‐7) cells than pure DOX. The enhancement of the inhibition effects resulted from increasing apoptosis‐inducing effects on MCF‐7 cells, which was related to the enhancement of Bax expression and the reduction of Bcl‐2 expression confirmed by terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay, real‐time polymerase chain reaction (PCR) assay and western blot assay. © 2018 Society of Chemical Industry     

碳纤维增强环氧树脂复合材料修复N80Q钢管的力学性能

为考察碳纤维增强环氧树脂复合材料对环状腐蚀的N80Q钢管的修复效果,采用数值分析和全尺寸爆破试验对修复后的力学性能进行了研究,分析了缺陷轴向长度、缺陷深度和修复层厚度对修复效果的影响。结果表明:碳纤维增强环氧树脂复合材料对N80Q钢管的修复效果显著,经试验测试, 6 mm深缺陷的N80Q管道由碳纤维增强环氧树脂复合材料修复后爆破压力值提高了0.985倍;缺陷轴向长度对N80Q管道修复后的强度影响较小,随着缺陷轴向长度的增加,管道爆破压力值仅下降了3.5%;而缺陷深度对N80Q管道修复后的强度影响较明显,与无缺陷管道相比, 6 mm深缺陷管道修复后爆破压力值下降了9.9%, 7 mm深缺陷管道修复后爆破压力值下降了20.6%。     

含预制裂隙类岩石裂隙演化与破裂特征的试验研究

裂隙岩体是自然界中普遍存在的工程岩体,在外力作用下易引起岩体结构破坏失稳而诱发工程故事。为此,基于相似理论制作了含十字交叉裂隙的类岩石试样,利用RMT-150B岩石力学试验机,对含有不同裂隙长度和裂隙倾角的类岩石试样进行单轴压缩试验,分析其裂隙演化规律和破裂特征。研究结果表明:含预制裂隙试样的抗压强度明显低于完整试块;当主裂隙长度一定时,裂隙岩样的峰值应力随次裂隙长度的增大而降低;当裂隙倾角为0°和60°时,裂隙岩样表现为拉伸型翼形裂纹的破坏形式;当裂隙倾角为30°和45°时,裂隙岩样表现为拉剪混合型裂纹的破坏形式,既有翼形裂纹,又有次生共面裂纹。