做优做精钢丝绳问题思考

虽然我国已经成为世界钢丝绳生产第一大国,但从产品实物质量、结构品种和对其制造技术研究深度等方面看,与业界强者相比尚存明显差距.根据数十年技术工作经历、接触企业引进北美与欧洲钢丝绳设计制造技术和日常对国外钢丝绳资料学习,综合分析认为,欲做优做精钢丝绳,应在以下几个方面扣深扣细、补齐短板:对基础理论研究要深;对所需专业构成...     

《液压与气压传动》课程试题库系统的建立

《液压与气压传动》已成为各院校机械类学生的必修课。为了减少该课程的出题工作量,使课程考试规范统一,建立了该课程的试题库系统。该系统不但能完成对试题的添加、删除和编辑的功能,而且能够自动完成试卷题目的抽取和试卷的组织工作,该系统界面友好、操作简便,能大大提高教师的工作效率。     

基于决策树的堆芯物理参数预测研究

反应堆堆芯核设计涉及大量方案的搜索与详细计算,缩短方案搜索时间有利于提高核设计效率。数据挖掘技术通过对大量数据进行学习与模式识别,可实现核设计方案物理参数的快速预测,更快地筛选出可行的备选堆芯方案。本文基于数据挖掘的决策树4种算法：C4.5、RepTree、Random Forest及Random Tree,在计算时以燃料富集度、含可燃毒物燃料棒数量及含量作为自变量,以寿期内k_eff不均匀系数偏差（KUCD）、径向功率不均匀系数偏差（RPNCD）、径向中子通量不均匀系数偏差（RFNCD）、堆芯寿期（CL）作为目标函数,构成目标函数符合度（CPF）,利用大量已知核设计参数的组件及堆芯设计方案作为数据挖掘训练集,构建数据挖掘模型,并用于对未知核设计参数的组件方案集合（测试集）进行CPF快速预测。结果表明,4种算法利用训练集构建数据挖掘模型的时间在0.6 s以内,各算法的交叉验证精度均在0.7以上,其中C4.5算法对CPF预测精度最高;对测试集方案的核设计参数预测中,单个方案的预测时间均在0.9 s以内,而Random Forest算法对CPF等于4的预测效果最好。     

Expansion-Based Clearing of Golgi-Cox-Stained Tissue for Multi-Scale Imaging

Obtaining fine neuron morphology and connections data is extraordinarily useful in understanding the brain’s functionality. Golgi staining is a widely used method for revealing neuronal morphology. However, Golgi-Cox-stained tissue is difficult to image in three dimensions and lacks cell-type specificity, limiting its use in neuronal circuit studies. Here, we describe an expansion-based method for rapidly clearing Golgi-Cox-stained tissue. The results show that 1 mm thick Golgi-Cox-stained tissue can be cleared within 6 hours with a well preserved Golgi-Cox-stained signal. At the same time, we found for the first time that the cleared Golgi-Cox-stained samples were compatible with three-dimensional (3D) immunostaining and multi-round immunostaining. By combining the Golgi-Cox staining with tissue clearing and immunostaining, Golgi-Cox-stained tissue could be used for large-volume 3D imaging, identification of cell types of Golgi-Cox-stained cells, and reconstruction of the neural circuits at dendritic spines level. More importantly, these methods could also be applied to samples from human brains, providing a tool for analyzing the neuronal circuit of the human brain.     

Cobalt-Containing Hyperbranched Poly(silylenearylene)s

A group of hyperbranched poly(silylenearylene)s are synthesized by homopolycyclotrimerizations of A₂-type silylenediynes. The polymers can be readily metallized by complexations of their periphery triple bonds with cobalt octacarbonyls Co₂(CO)₈. Pyrolysis of these organometallic polymers gives magnetic ceramics in good yields. Analyses by SEM, TEM, XPS, EDX, and XRD demonstrate that the ceramics comprise ferromagnetic Co and paramagnetic Co₂Si nanocrystallites wrapped by carboneous shell. The ceramics show high magnetic susceptibilities (M _s up to ~50 emu/g) and near-zero coercivity (H _c down to ~0.14 kOe), suggesting that they are good soft magnetic materials with low hysteresis loss. This article was to be included in the March issue of Volume 19, which was dedicated to Professor Takakazu Yamamoto. The journal editors sincerely apologize for the omission and delay in publication for which the authors and the guest editor bare no responsibility. M. Zeldin and A. S. Abd-El-Aziz, Editors.     

Large-Eddy/Reynolds-averaged Navier–Stokes simulation of combustion oscillations in a cavity-based supersonic combustor

Combustion oscillations in a supersonic combustor with hydrogen injection upstream of a cavity flameholder are investigated numerically using a hybrid RANS/LES (Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation) method acting as a wall-modeled LES. A turbulent boundary layer with thickness of δ_inf = 2.5 mm is considered and a recycling/rescaling method is adopted to treat the unsteady inflow. The results show that combustion oscillations can mainly be attributed to two mechanisms. One is the unsteady flame spreading from the cavity shear layer to the main stream, which is greatly influenced by the interaction of the jet-with-cavity shear layer. This mechanism leads to relatively low-frequency oscillations that correspond to the cavity-shear layer oscillations. The other is the auto-ignition of the combustible fluid packets formed around the fuel jet accompanied by the generation of the hairpin-like vortices, which leads to relatively high-frequency oscillations that correspond to the jet instabilities.     

Pt-Pd催化剂的萘加氢活性和抗氮性能研究

本工作研究了球形硅铝氧化物负载的铂-钯(Pt-Pd)贵金属催化剂的加氢活性和抗氮性能.首先,以过量共浸渍法制成5种不同负载量的Pt-Pd贵金属催化剂,元素分析结果表明浸渍液中Pt的质量分数升高会显著提高催化剂上Pt的负载量并明显降低Pd的负载量,而浸渍液中Pd的质量分数的升高对Pt、Pd的负载量几乎无影响;进一步的分析...     

撞击流反应器撞击区流动特性研究

为研究撞击区的流动特性,在有效容积为160 L的撞击流反应器内,以水为介质,饱和KCl溶液为示踪剂,用电导法测定了不同导流筒出口间距和撞击流速下的示踪剂浓度曲线,并通过多釜串联模型拟合得到了撞击区的平均停留时间及模拟釜数。结果表明:导流筒出口间距减小,撞击流速增大,撞击区平均停留时间减小,釜数减小;撞击流速为2.0 m/s时,撞击区内流型接近于全混流。停留时间分布主要受撞击流速的影响,增大流速有利于促进撞击区中的宏观混合。