原位生成Ni颗粒增韧纳米ZrB2基陶瓷的制备方法与微观结构研究

目的提高Zr B2基防热陶瓷材料的韧性,以满足其高抗热冲击性能的需求。方法采用沉淀-共沉积法在纳米Zr B2粉体中原位生成Ni颗粒作为增韧相,经放电等离子烧结后获得分布均匀的Ni-Zr B2纳米复合材料,通过三点弯曲实验、断裂韧性实验以及硬度测试,分别评价不同Ni含量对Ni-Zr B2纳米复合材料力学性能的影响,并通过SEM,XRD对材料微观组织进行分析。结果 Ni颗粒的引入,可有效提高Zr B2的相对密度,增加韧性,同时强度和硬度有所提高。通过不同Ni含量的对比发现,Zr B2-15%Ni力学性能最优,断裂韧性达到7.8±0.3 MPa·m1/2,相对于原始Zr B2材料提升1倍。从微观组织的电子扫描照片也可以看出,Ni颗粒在Zr B2表面均匀分布,断口表现为穿晶断裂和延晶断裂的复合断裂模式,不同于原始Zr B2材料的穿晶断裂。这也是断裂韧性显著提升的主要原因。结论原位生成Ni颗粒的引入,可有效提高Zr B2材料相对密度、强度、硬度以及断裂韧性。对比不同Ni含量的力学性能,Zr B2-15%Ni组分的力学性能最优,这一方法可有效提高Zr B2材料的断裂韧性,进一步满足其高抗热冲击性能的需求。     

The safety of obstetrical ultrasound: a review

Ultrasound is a commonly employed imaging modality in obstetrics and is generally regarded as safe to the fetus. Current ultrasound technology, however, has significantly higher output potential than older machines used in most clinical studies, and the safety profile for the increasing use of Doppler, 3-dimensional (D) and 4-D ultrasound with modern machines is unknown. This article reviews the current status of ultrasound safety within obstetrics, including proposed mechanisms of harm, existing scientific and clinical evidence regarding those mechanisms, and considerations of safety for the clinical user. Copyright © 2009 John Wiley & Sons, Ltd.     

山西省“三生”功能协同/权衡关系分析

为探究生产—生活—生态（“三生”）功能协调情况,基于综合评价模型和力学平衡模型,选用2005年、2010年和2018年土地利用类型和统计数据,测度山西省“三生”功能时空演变及协同/权衡关系特征。结果表明:（1）2005—2018年“三生”功能时空分异特征明显,生产功能为下降态势,呈现出“平原高,山区低”的分布格局;生活功能持续上升,空间分布与生产功能相似;生态功能呈上升状态,但需注意恶化倾向,空间格局稳定。（2）研究期间,“三生”功能协同性显著提升且趋势合理,空间分布与生产、生活功能趋同。（3）依据“三生”功能协调度偏离情况,划分功能主导区和提升区,明确各县域功能特征。研究结果可为国土空间规划提供依据。     

拱形支架在煤矿巷道中的应用研究

针对目前一些高压力和不宜采用锚杆支护的巷道,为适应其支护的要求,研制开发了拱形支架。对于巷道支护,其着眼点应放在充分利用和发挥岩层的自承能力上。对本文的拱形支架支护,根据力法原理,采用曲梁模型进行了支架系统的力学分析,得出其最大承载能力;通过与直梁支架承载能力相比较,得到了拱形支架承载能力系数与支架半径和巷道跨度的影响关系。同时为了使巷道断面更为合理,对支架构件轮廓曲线进行了优化,以使支架构件的内力和变形最为合理。结果证明：拱形支架承载能力比直梁梯形支架的承载能力有大幅度提高,其半径和跨度直接影响着承载能力,从而有效解决了软岩巷道难以支护的问题。另外,从合理拱轴线的角度,得出在均布等压的巷道中,选用圆弧形支架构件进行支护,能最大程度地发挥支架的力学性能。     

夏季大空间内火灾机械排烟效率的研究

采用全尺寸实验对夏季大空间内火灾机械排烟的效率进行了研究.实验过程中主要测量了火源功率和大空间内的烟气温度两个参数.通过分析大空间内烟气温度的分布规律,得到了机械排烟控制下不同火源功率的大空间内稳定的烟气层高度.根据Heskestad羽流模型计算了烟气生成速率,与机械排烟速率比较得到了夏季大空间内火灾机械排烟的效率.实验结果表明,在夏季大空间中,当火源功率不是很大时,大空间内外的温差使得外界补充进来的空气和火灾生成的烟气更加容易发生掺混,导致机械排烟的效率大大降低;按照规范规定的6次换气率进行排烟,在实验的300～1 000 kW的火源功率范围内,夏季大空间内火灾机械排烟的效率约为30%.火源功率的增大,在一定程度上削弱了空气与烟气的掺混,机械排烟的效率略有提高,但是提高的效果并不是很明显.     

热-水-力耦合作用下岩石损伤力学模型与验证

为了探讨高温、高孔隙水压、高围压对岩石损伤破坏的影响,基于损伤力学基本理论,并结合应变等价性原理,建立热-水-力耦合作用下的损伤力学模型,构建表征岩石损伤演化的表达式,通过水-力耦合作用下热损伤花岗岩室内试验验证了该模型的合理性,并根据室内试验确定了模型参数。试验结果表明:提出的模型能较好地反映热-水-力耦合作用下岩石应力-应变过程,且能表征上述作用下岩石损伤演化规律;高温损伤会导致岩石由脆性逐渐向延性转变,而孔隙水压会进一步加剧岩石损伤演化。     

Effect of Nanoscale SiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript> as the Fillers on the Mechanical Properties and Aging Behavior of Linear Low-Density Polyethylene/Low-Density Polyethylene Blends

Linear low-density polyethylene (LLDPE) was blended with low-density polyethylene (LDPE) at a fixed ratio (80 wt LLDPE and 20 wt %LDPE) and filled with nanoparticles of SiO₂ and TiO₂ at a ratio up to wt 5%, so as to develop the polymeric composites suitable to preparing the agricultural micro-irrigation pipes having good environmental adaptability. These compounds were blended using calcium stearate, polyethylene wax, and titanate coupling agent as the auxiliary dispersants, and ethylene-vinyl acetate copolymer (EVA) as the toughness improver. The LLDPE/LDPE composites filled with the nanoparticles were extruded and injected to prepare the composites specimens for the performance evaluations and micro-irrigation pipe field test. The mechanical properties, thermostability, and processibility of the injected composites were investigated. The effect of heating in an oven and irradiating by ultraviolet on the mechanical properties of the composites was explored. The environmental adaptability of the micro-irrigation pipes made of the filled LLDPE/LDPE composites was evaluated making use of long-term outdoor field test in northwest China where the arid and harsh natural conditions are of great concerns. It was found that the LLDPE/LDPE blend with the LLDPE mass fraction fixed as 80% showed balanced mechanical and thermal properties and flexibility, and was suitable to be used as the basic resin matrix. The incorporation of nano-TiO₂ contributed to effectively improving the resistance to heating and ultraviolet irradiation of the composites. The composite made from 91% basic resin matrix, 6% EVA, and 3% mixed nano-SiO₂ and TiO₂, showed balanced comprehensive properties. The micro-irrigation pipes made of this filled LLDPE/LDPE composite had good environmental adaptability and service behavior in a three-year field test and were suitable to be used in arid area.     

Kenaf/Ramie Composite for Automotive Headliner

An increasing industrial interest is applications of kenaf and ramie fiber nonwovens for making automotive interior trim parts because of their excellent strength and renewability. This paper presents a study on the manufacture and evaluation of the kenaf/ramie nonwoven composite for this automotive end use. Carding, needle-punching, and wet bonding were used to fabricate the composite. End-use performance of the composite, in terms of tensile strength, thermal conductivity, dynamic mechanical property, and bonding structure, was tested using a series of instruments in accordance with the ASTM methods. Bonding performance of the polyvinyl alcohol binder and acrylic copolymer binder was also compared. Research results revealed that the acrylic-copolymer bonded composite was significantly anisotropic in both tensile and bending deformation and the polyvinyl-alcohol bonded composite was significantly anisotropic only in bending deformation. For the acrylic-copolymer bonded composite, increase of padding times helped enhance tensile properties. The acrylic-copolymer bonded composite also exhibited a better performance in dynamic thermal mechanical deformation but indicated insignificant difference of thermal conductivity compared to the polyvinyl-alcohol bonded composite.     

Effect of Additives on the Improvement of Mechanical and Degradable Properties of Photografted Jute Yarn with Acrylamide

The jute yarn was grafted with acrylamide monomer (AA) under ultraviolet (UV) radiation to modify its mechanical and degradable properties. A number of AA solutions of different concentrations in methanol (MeOH) along with photoinitiator Irgacure 907 [2-methyl-1-(4-methylthiophenyl)-2-morpholinopropanone-1] were prepared. The monomer concentration and irradiation time were optimized. Jute yarn grafted with 30% AA under UV radiation for 60 min showed of the highest polymer loading (PL) value of 22% with a enhanced tensile strength (TS) value of 195% and elongation at break (Eb) value of 256% compared to untreated jute yarn. To further improve the properties of jute yarn, a number of additives (1%) such as urea, polyvinylpyrrolidone, urethane acrylate, and urethane diacrylate were used in the AA (30%) solution. Among all the additives used, urea significantly influenced the PL (27%), TS (230%), and Eb (264%) values of the treated jute yarns. Water uptake and the degradation properties of treated and untreated jute yarn caused by simulated weathering and in soil (25% water) were also studied. The rate of degradation of grafted sample is lower then that of untreated sample. DSC studies showed the thermal stability of the AA plus urea grafted sample.     

联锁控制阀及其在散料除尘中的应用

介绍一种自行设计，并已实践应用的机械联锁控制阀与电动卸料车、同步开启关闭自动控制技术。它是由控制阀、开启步进器、关闭装置等，与卸料车不可分割的相关组合而成，从而实现了散粒物料的转运卸料与通风除尘联锁同步、协调一致的工作特性。