超高层建筑消防给水系统分区的评价方法探讨

针对超高层建筑消防给水系统的不同分区形式,提出了对消防给水系统分区的评估和评价的问题.超高层建筑消防给水系统分区的评价有利于解决系统分区形式,从定性与定量的角度给出评价的结果,建立了基于可靠性为基础的分区形式系统评价方法.消防给水分区的系统评价包括直接评定和综合评定的评定方法.直接评价对存在重大隐患的设计进行对标评定.综合评定可以采用不同的指标进行多因素的评估,提出了评估的指标,并给出了系统组件可靠度的计算方法.     

微型步进马达线架组自动卷线设备设计

微型步进马达线圈组卷线上下料基本靠手动作业,效率低下,同时因工人技术水平的不同造成产品品质不稳定的问题多发.为此专门设计了微型步进马达线圈组自动卷线及上下料设备.通过结合现阶段的先进工业技术,采用振动盘分离区分进料,多机构并联三菱PLC及威纶人机界面触摸屏研发了此微型步进马达线圈组自动上下料及卷线设备.通过该设备实现了微型步进马达因工人不足导致产能减少和品质多发问题,减少企业成本,提升产品品质.     

Microwave synthesis of worm-like SiC nanowires for thin electromagnetic wave absorbing materials

Thin thickness is always the pursuit of excellent electromagnetic wave absorbing materials. Herein, SiC nanowires with worm-like morphology were synthesized by microwave heating the mixture of expanded graphite and silica. The worm-like SiC nanowires exhibit an excellent microwave absorption ability at a thin thickness. With the filling ratio of SiC nanowires increases in the matrix, the dielectric loss and microwave absorbing ability are significantly enhanced; meanwhile the number of absorption peaks is gradually increased, and the absorption peaks also move toward a thinner thickness. When the nanowires filling ratio was 40?wt%, the minimum reflection loss reached down to ?35.2?dB and the effective absorption (RL?<??10?dB) bandwidth was 1.8?GHz?at a thickness of 1.3?mm. The possible growth mechanism of the worm-like SiC nanowires is that the intermediate reaction gas phases, SiO and CO, were confined in the relatively independent tiny pores of expanded graphite. This resulting in an excessive local gas phase pressure, which causes the nanowire growth direction changes randomly.     

基于随机振动仿真分析的阵列天线结构改进

某型阵列天线属于机载设备,在做完随机振动试验后,第2个天线单元的一个辐射板被振裂.为了快速找到断裂原因,改进天线结构,利用有限元仿真软件ANSYS Workbench进行随机振动仿真分析.分析结果表明:原天线单元辐射板根部圆角太小,产生较大应力集中,最大3σ应力为102.74 MPa,超过材料疲劳极限应力87 MPa;改进后的天线结构,最大3σ应力降低24.2％,其数值为77.85 MPa,小于疲劳极限应力,满足设计要求.最终,改进后的天线结构顺利通过振动试验,有效验证了仿真分析与结构改进的合理性.     

Effect of Gd doping on electrical transport properties of La0.8Sr0.2MnO3 polycrystalline ceramics

Gd doped La_0.8Sr_0.2MnO₃ (La_0.8-xGd_xSr_0.2MnO₃, LGSMO) ceramics were prepared by a sol-gel method. X-ray diffraction (XRD) patterns showed that all samples exhibited distorted perovskite structures, R_3c. When the Gd³⁺ content x > 0.03, the crystal structure changed to orthorhombic, Pnma. Scanning electron microscopy (SEM) images showed that the ceramics characterize high density and grain boundary connectivity, and higher Gd³⁺ doping decreased the grain size from 26.72 μm to 7.42 μm. The temperature dependence of resistivity showed a transition from a low-temperature metal to a high-temperature insulator. The resistivity increased with Gd doping content, and the metal-insulator transition temperature, T_P, increased first and then decreased, while the temperature coefficient of resistance (TCR) of the samples first decreased and then increased with Gd³⁺, and the magnetoresistance (MR) increased first and then decreased. The peak TCR at x = 0.06 was 5.18%·K^?1, and MR at 0.04 was 34.57%. The electrical transport properties of the ceramics were explained based on the double exchange (DE) interaction mechanism. The obtained material may have application prospects in magnetic devices and infrared detectors.     

Synthesis of strontium (Sr) doped hydroxyapatite (HAp) nanorods for enhanced adsorption of Cr (VI) ions from wastewater

The development of high-efficiency adsorbents for heavy metal ion removal from wastewater is highly desirable and challenging due to their synthesis complexity and low adsorption capacities. Herein, we reported the synthesis of strontium (Sr) doped hydroxyapatite (HAp) for the increased Cr (VI) adsorption. The effects of pH, temperature, and time on adsorption performances were studied. As a result, the Sr-HAp nanorods can achieve a Cr (VI) adsorption capacity of 443 mg/g, which is significantly higher than that of HAp nanorods (318 mg/g). To better understand the adsorption mechanism, the Langmuir isotherm model was established. The modeling results indicated that Langmuir monolayer chemical adsorption contributed to the efficient Cr (VI) ion removal for Sr-HAp nanorods adsorbents. The surface area and surface functional groups (O–H) contributed to the different Cr (VI) adsorption capacities between HAp and Sr-HAp.     

Fabrication of crescent-shaped ceramic microparticles based on single emulsion microfluidics

Ceramic microparticles have great potentials in various fields such as materials engineering, biotechnology, microelectromechanical systems, etc. Morphology of the microparticle performs an important role on their application. To date, it remains difficult to find an effective and controllable way for fabricating nonspherical ceramic microparticles with 3D features. This work demonstrates a method that combines UV light lithography and single emulsion opaque-droplet-templated microfluidic molding to prepare the crescent-shaped ceramic microparticles. By tailoring the intensity of UV light and flow rate of fluid, the shapes of microparticles are accordingly tuned. Therefore, varieties of crescent-shaped microparticles and their variations have been fabricated. After sintering, the crescent-shaped alumina ceramic microparticles were obtained. Benefitting from the light absorption and scattering behavior of most ceramic nanoparticles, this system can serve as a general platform to produce crescent-shaped microparticles made from different materials, and hold great potentials for applications in microrobotics, structural materials in MEMS, and biotechnology.     

42CrMo钢加热过程中的奥氏体晶粒尺寸演变

通过金相试验方法测定42CrMo钢在890~930 ℃下保温10~240 min后的晶粒尺寸。结果表明,42CrMo钢在加热到试验温度890~930 ℃时已经完全奥氏体化,保温过程中的晶粒生长属于正常生长;加热温度对晶粒尺寸的影响较大,保温时间对晶粒尺寸的影响较小;随保温时间的延长晶粒生长缓慢,晶粒尺寸与保温时间满足指数小于1的函数关系。基于试验数据,通过线性回归得到晶粒长大的Beck模型参数,通过非线性回归得到Sellars和Anelli模型参数,3个模型的预测精度都较好,而Anelli模型的适用性要高于Beck模型和Sellars模型,故在预测42CrMo钢的奥氏体晶粒长大规律时宜使用Anelli模型。