地聚物砂浆高温后抗拉和粘结性能及退化机理

为考察地聚物砂浆在有耐高温要求的混凝土结构加固领域的应用可行性,开展了常温下和高温后地聚物砂浆的抗拉强度试验以及地聚物砂浆与普通水泥砂浆及普通混凝土基体的粘结性能试验,并与普通水泥砂浆的抗拉及粘结性能进行试验比较;通过热重分析-差示扫描量热分析(TG-DSC),探究了地聚物砂浆的高温强度退化机理.试验结果表明:地聚物砂浆与水泥砂浆及混凝土之间的常温粘结强度分别达2.15 MPa及1.7 MPa,经300℃高温后残余粘结强度仍有1.5 MPa左右,远高于普通水泥砂浆的粘结强度;超过300℃以后地聚物砂浆的强度急剧退化,这主要是因地聚物砂浆高温脱水、微观结构遭受破坏引起.基于上述试验结果,可将地聚物砂浆用于300℃以下高温环境的混凝土结构修补加固.     

Rheological behaviors of fresh cement pastes with polycarboxylate superplasticizer

The rheologicalbehaviors of fresh cement paste with polycarboxylate superplasticizer were systematically investigated.Influentialfactors including superplasticizer to cement ratio(Sp/C),water to cement ratio(w/c),temperature,and time were discussed.Fresh cement pastes with Sp/Cs in the range of 0 to 2.0% and varied W/Cs from 0.25 to 0.5 were prepared and tested at 0,20 and 40 °C,respectively.Flowability and rheologicaltests on cement pastes were conducted to characterize the development of the rheologicalbehavior of fresh cement pastes over time.The exprimentalresults indicate that the initialflowability and flowability retention over shelf time increase with the growth in superplasticizer dosage due to the plasticizing effect and retardation effect of superplasticizer.Higher temperature usually leads to a sharper drop in initialflowability and flowability retention.However,for the cement paste with high Sp/C or w/c,the flowability is slightly affected by temperature.Yield stress and plastic viscosity show similar variation trends to the flowability under the abovementioned influentialfactors at low Sp/C.In the case of high Sp/C,yield stress and plastic viscosity start to decline over shelf time and the decreasing rate descends at elevated temperature.Moreover,two equations to roughly predict yield stress and plastic viscosity of the fresh cement pastes incorporating Sp/C,w/c,temperature and time are developed on the basis of the existing models,in which experimentalconstants can be extracted from a database created by the rheologicaltest results.     

Controllable preparation and superior rate performance of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> hollow microspheres as cathode material for lithium-ion batteries

Spinel LiMn₂O₄ microspheres and hollow microspheres with adjustable wall thickness have been prepared using controllable oxidation of MnCO₃ microspheres precursors and following solid reactions with lithium salts. Scanning electron microscopy (SEM) investigations demonstrate that the microsphere morphology and hollow structure of precursors are inherited. The effect of hollow structure properties of as-prepared LiMn₂O₄ on their performance as cathode materials for lithium-ion batteries has been studied. Electrochemical performance tests show that LiMn₂O₄ hollow microspheres with small wall thickness exhibit both superior rate capability and better cycle performance than LiMn₂O₄ solid microspheres and LiMn₂O₄ hollow microspheres with thick wall. The LiMn₂O₄ hollow microspheres with thin wall have discharge capacity of 132.7 mA·h·g^-1 at C/10 (14.8 mA·g^-1) in the first cycle, 94.1% capacity retention at C/10 after 40 cycles and discharge capacity of 116.5 mAh·g^-1 at a high rate of 5C. The apparent lithium-ion diffusion coefficient (D _app) of as-prepared LiMn₂O₄ determined by capacity intermittent titration technique (CITT) varies from 10^-11 to 10^-8.5 cm²·s^-1 showing a regular “W” shape curve plotted with test voltages. The Dapp of LiMn₂O₄ hollow microspheres with thin wall has the largest value among all the prepared samples. Both the superior rate capability and cycle stability of LiMn₂O₄ hollow microspheres with thin wall can be ascribed to the facile ion diffusion in the hollow structures and the robust of hollow structures during repeated cycling.     

中红外发光二极管的痕量气体检测系统的研究

在离轴石英增强型光声光谱(OB-QEPAS)技术的基础上,提出了一种以中红外发光二极管(MIR-LED)代替传统方案中的激光作为系统光源来检测痕量气体的方案。搭建了以CO_2为目标气体,以中心波长在4.36μm的MIR-LED为光源的OB-QEPAS平台来检测系统的灵敏度,并对系统的各部分进行了详细介绍。实验得到系统的检测极限达到ppm量级,相应的归一化噪声等效吸收系数(NNEA)达到了10~(-8)量级。基于红外光源的OB-QEPAS技术为发展低成本、操作方便灵敏的痕量气体检测提供了一种新的技术手段。     

塑性铰区采用FRC柱试验研究及正截面承载力分析

采用简化的纤维增强混凝土应力应变关系,根据截面变形的平截面假定和截面力的平衡方程,推导出塑性铰区采用纤维增强混凝土柱在不同极限状态时的曲率。根据各极限状态点曲率,求得截面上各分布力,对截面形心轴取距,到塑性铰区采用FRC柱的开裂、屈服、峰值和极限点的弯矩表达式。与试验结果对比表明,计算值与试验值吻合较好。     

太阳能喷射-压缩复合制冷系统的实验及仿真

建立了太阳能喷射-压缩复合制冷系统的实验研究平台,基于EES软件程序进行系统稳态仿真,实验验证了仿真模拟程序的正确性,分析了不同发生温度、中间温度对系统性能的影响。研究表明,在中间温度和冷凝温度不变的情况下,随着发生温度的升高,总功率先降低后升高,系统EER先升高后降低;同时,系统COP呈先逐渐升高而后降低的趋势。在研究范围内,最优发生温度工作区域为78~80℃,此时,系统的总耗功量最小;最优中间温度工作区域为7~10℃,此时,系统制冷量达2 245 W,EER最高为3.39。     

基于改进的特征图串法识别人体行为

视频的有效表达是识别行为关键与难点。本文提出了一种改进的特征图串的视频表达方法,在动态规划框架下,利用子模优化方法和图匹配技术实现了行为的识别。首先,利用近年来被广泛应用的时空特征点探测器获取视频序列中的关键点;接着引入子模优化方法完成视频在时域上的划分;然后在每个时域区间内以关键点为节点形成图结构,使得行为视频的特征表示转化为有序的特征图串;最后基于重加权随机游走的图匹配方法和动态时间规整实现成对视频的匹配与对齐。通过两组公开数据集（KTH和UT-interaction）上的实验及与其他方法的比较,验证了本文方法是有效的、可行的。     

水电项目监理服务费计价模式的研究与实践

DG公司创造性地提出了按投入费用法进行监理服务费计价,并于2013年11月率先用于DG水电站工程的监理招标和施工管理中。投入费用法有利于督促监理单位保证现场投入、提高监理人员的责任心和监理费用的控制等。DG电站实施的良好效果,使投入费用计价法进行监理招标与管理模式得到了众多水电行业建设单位与知名监理企业的认同。     

高温气候下沥青混凝土心墙连续碾压施工结合面温控试验研究

在夏季高温气候沥青混凝土心墙连续多层施工时,为减少等待结合面温度降至规范要求上限值90℃的时间,通过室内试验模拟结合面温度提高后心墙连续两层铺筑的情况,分别研究了结合面温度在90℃、100℃、110℃情况下沥青混凝土的压实性和变形情况,并进行了现场试验论证。室内试验结果表明:心墙沥青混凝土结合面温度降至100℃时,上层沥青混凝土的孔隙率为2.88%,下层沥青混凝土的最大侧向应变值为2.78%;结合面温度为110℃时,上层沥青混凝土的孔隙率为3.85%,下层沥青混凝土的最大侧向应变值为4.00%。现场试验结果表明:结合面温度为100℃时的上层沥青混凝土孔隙率和渗透系数均满足规范要求。因此,沥青混凝土心墙连续多层碾压时,结合面温度提高至100℃的施工质量可以得到保证。