改进BP神经网络的再生粗骨料混凝土强度预测*

抗压强度作为评价再生混凝土主要性能指标之一,从四篇文献中搜集了43个抗压强度样本。基于改进的BP神经网络理论,建立了以再生粗骨料取代率、水灰比、龄期为输入,抗压强度为输出的神经网络模型,其结构形式为3-7-9-1。对该网络进行训练和学习,对并测试样本进行检测,结果表明,训练效率不仅大大提高,且而误差较小,并结合回归拟合系数,进一步表明该模型能够有效的的预测再生混凝土抗压强度值,能满足工程需要。     

高效液相色谱法测定保健食品中磷脂酰丝氨酸含量

摘 要: 目的 建立高效液相色谱法测定磷脂酰丝氨酸。方法 样品经过正己烷：异丙醇（25：75, V:V）溶解, 以正己烷：异丙醇：1%磷酸水溶液=（25:70:5, V:V:V）为流动相, 等度洗脱, 经SIL 色谱柱（4.6 mm×250 mm，5 μm）分离, 并于205 nm波长检测。结果 磷脂酰丝氨酸在浓度0.13504~0.67520 mg/mL之间呈现良好的线性关系, r=0.9993, 平均回收率为96.16%~99.60%, 相对标准偏差为1.1%。结论 该方法测定保健食品中磷脂酰丝氨酸含量具专属性强, 耗时短、操作简便、准确、重现性好，可在实验室推广。     

利用非糖物质快速鉴别单花蜂蜜

本文利用非糖物质快速鉴别四种常见的单花蜂蜜(枸杞蜂蜜、荆条蜂蜜、枣花蜂蜜和洋槐蜂蜜)。利用固相萃取除糖提取蜂蜜非糖物质,并用高效液相色谱(HPLC)结合化学计量学进行蜂蜜花源的判定。发现了四种单花蜂蜜的非糖特征标志物。芦丁、丁香酸甲酯、阿魏酸的含量在四种蜂蜜中差异最大。对羟基苯甲酸和脱落酸在枸杞蜂蜜中平均含量分别为0.59μg/g和0.42μg/g,可作为枸杞蜂蜜的花源标志物;对香豆酸和肉桂酸在荆条蜂蜜中平均含量为0.08μg/g和0.05μg/g,可作为荆条蜂蜜的潜在花源标志物;阿魏酸、异阿魏酸是枣花蜂蜜的特征标志物,平均含量分别为0.40μg/g和0.76μg/g;洋槐蜂蜜的特征标志物是芦丁和丁香酸甲酯,平均含量为0.08μg/g和0.14μg/g。利用高效液相色谱指纹图谱结合化学计量学方法(主成分分析和判别分析),四种单花蜂蜜依据其花源被成功区分。本研究对蜂蜜真实性判定有重要参考价值,为后续蜂蜜真伪鉴别奠定基础。     

采用绝热式自燃测试方法分析煤的自燃倾向

对煤的自燃倾向进行快速有效鉴别,有助于对煤的自燃倾向采取分级分类管理从而有效防治煤矿火灾,因而采用绝热式自燃测试方法对煤的自燃倾向进行准确分析很有必要。简要介绍绝热式自燃测试方法的测试原理及其仪器结构,模拟煤炭自燃的物理过程,通过采用包括反应器、气体预热铜管和跟踪温度控制方式等综合绝热措施以实现300 g煤样的自然发火实验,记录煤样从40℃上升到70℃的升温速率(或前30 h的升温速率),测试煤样的自燃特性曲线并分析曲线特征。即建立煤绝热氧化产热速率计算模型,结合实验数据计算所得的煤在绝热氧化条件下的升温速率和产热速率可鉴定煤自燃倾向性的强弱。采用绝热式自燃测试方法对不同煤的自燃倾向分析后表明,无烟煤和部分烟煤的自燃倾向较低,褐煤的自燃倾向较高,故而在煤矿开采时需特别注意褐煤的自燃倾向。     

基于密闭爆发器试验的发射装药内弹道性能预估

为了预估发射装药的内弹道性能,建立了一种基于密闭爆发器试验检测发射药的静态燃烧性能参数进而预测其装药内弹道性能的方法,采用不同批次的单樟-5/7发射药进行了装药性能预估计算,并基于30 mm火炮对内弹道性能预估精度进行了试验验证。结果表明,采用所建立的基于密闭爆发器试验的发射装药内弹道性能预估方法计算获得的最大膛压为376.0 MPa,与试验测试的膛压平均值388.7 MPa的计算误差为3.27%;计算的炮口初速为1143.5 m/s,与试验测试的炮口初速平均值1156.3 m/s的计算误差为1.11%。所建立的基于密闭爆发器试验的发射装药内弹道性能预估方法具有较高的精度,可对发射药样品不同批次间的内弹道性能进行高效精确的预估,为长期贮存发射药使用寿命的判定及发射药产品的出厂校验提供了一种高效低成本的弹道性能评价方法。     

超高性能混凝土国内外研究与应用进展*

介绍了超高性能混凝土（UHPC）的制备原理和性能特点，对UHPC国内外研究和应用情况进行了综述，指出了我国UHPC研究和应用中存在的问题。结果表明：UHPC是一种具有优异的力学性能、耐久性能和环保效益的新型水泥基复合材料。国外在UHPC理论研究和应用研究方面都取得了大量成果，在实际工程中已经获得了广泛的应用；近年来我国在理论研究和应用方面也得到了快速发展；如何简化UHPC制备工艺、降低生产成本、补偿自收缩是今后的主要研究方向，完善相关规范标准以更好地指导UHPC现浇工程应用是目前首要解决的问题。随着环保和可持续发展理念的日益重视，UHPC这种低碳环保材料将有广阔的发展前景。     

Adaptive control of unactuated dynamical systems through interconnections: Stability and performance guarantees

This article studies control and performance enforcement for a class of uncertain dynamical systems that consist of actuated and unactuated portions physically interconnected to each other. The proposed approach stabilizes the overall interconnected system in the presence of unknown physical interconnections as well as system uncertainties. Performance guarantees are enforced, individually, on the actuated as well as unactuated portions of the interconnected system via this approach. For enforcing these performance guarantees, a set-theoretic model reference adaptive control approach is used, in conjunction with linear matrix inequalities, to restrict the respective system error trajectories of the actuated and unactuated dynamics inside a priori, user-defined compact sets. The efficacy of the proposed approach is demonstrated using simulations.     

Semiconductor Fe-doped SrTiO3-δ perovskite electrolyte for low-temperature solid oxide fuel cell (LT-SOFC) operating below 520 °C

High-temperature operation of solid oxide fuel cells causes several degradation and material issues. Lowering the operating temperature results in reduced fuel cell performance primarily due to the limited ionic conductivity of the electrolyte. Here we introduce the Fe-doped SrTiO_3-δ (SFT) pure perovskite material as an electrolyte, which shows good ionic conduction even at lower temperatures, but has low electronic conduction avoiding short-circuiting. Fuel cell fabricated using this electrolyte exhibits a maximum power density of 540 mW/cm² at 520 °C with Ni-NCAL electrodes. It was found that the Fe-doping into the SrTiO_3-δ facilitates the creation of oxygen vacancies enhancing ionic conductivity and transport of oxygen ions. Such high performance can be attributed to band-bending at the interface of electrolyte/electrode, which suppresses electron flow, but enhances ionic flow.     

Investigation of the residual stress in UO2-Mo composites via a neutron diffraction method

UO₂-Mo composites with a core-shell structure have been considered candidates for the thermal conductivity (TC)-enhanced UO₂ pellets and have demonstrated commercial potential for use in novel high-level safety reactors. Nevertheless, UO₂-Mo composites tend to form micro-cracks that are caused by the presence of residual stress (RS) during manufacturing. In this work, neutron diffraction measurements were employed to analyse the RS in UO₂-Mo core-shell structured composites fabricated by spark plasma sintering (SPS) for the first time. It was found that in the UO₂-Mo composites, the RS state present in the UO₂ matrix was tensile in nature. The RS in the UO₂ matrix increased with increaseing Mo content. There was a maximum value of 148 ± 15 MPa in the UO₂-10 vol% Mo composite. The micro-cracks produced in the high-Mo content composites were explained by the results of the neutron diffraction measurements. These results could provide significant guidance for the manufacturing and improvement of the operational performance of UO₂-Mo composites as next-generation fuels.     

Composite fibers of La0.5Sr0.5CoO3-δ-LaSrCoO4±δ with high catalytic activity toward oxygen reduction reaction

To promote catalytic activity toward oxygen-reduction reaction in the intermediate temperature solid-oxide fuel cells, we prepared a dual-phase composite cathode material 75 mol%La0.5Sr0.5CoO_3-δ-LaSrCoO_4±δ with a fibrous structure via one-pot electrospinning of a polymer containing solution. We then investigated the micro-structure and electrochemical performance of this fibrous composite. The results confirm that the fibrous composite is composed of intimately mixed nano-crystalline grains and that the compositional phases are compatible with each other. Compared with the corresponding single-phase fibers, the nano-crystalline size of the composite is more stable, and the fine nano-crystalline grains are more resistant to growth and coarsening, indicating the mutual dispersion and suppression between the constituent phases. Furthermore, compared with the corresponding single-phase fibers, the electrochemical performance of this fibrous composite cathode is more favorable. At 800 °C, its area specific resistance (ASR) is as low as 0.03 Ω cm², and maximum output power density is as high as 960 mW cm⁻², which is achieved from an electrolyte-supported single cell that was developed using this cathode. After aging this cathode for a long time, ASR is less worsened and the output power density decreases only slightly, indicating that the prolonged electrochemical performance in the running cells is more stable.