Anchoring single Pt atoms on hollow Ag3VO4 spheres for improved activity towards photocatalytic H2 evolution reaction

The high cost of noble metal catalysts has been a great bottleneck for the catalyst industry. Using the noble metal at a single-atom level for catalytic applications could dramatically decrease the cost. The impacts of single Pt atoms on the photocatalytic performance of Ag₃VO₄ have been investigated and reported. In this report, single Pt atoms were anchored on the surface of Ag₃VO₄ (AVO) as a cocatalyst, and the resultant composite photocatalyst has been studied for photocatalytic H₂ production from water driven by visible light. The as-prepared AVO particles are hollow nanospheres in the monoclinic phase with a bandgap of 2.20 eV. The light absorption edge of AVO/Pt is slightly red-shifted compared to that of the pristine AVO, indicating more visible light absorption of AVO/Pt. The XPS peaks of Ag, V, and Pt exhibit a significant shift after AVO and Pt get into contact, suggesting the strong interaction between the surface Ag and V atoms, and single Pt atoms. After 3-h illumination, the photocatalytic H₂ evolution amount from AVO/Pt is improved up to 1400 μmol, which is 2.8 times that on the bare AVO. Such efficient photocatalytic H₂ evolution on AVO/Pt is still maintained after five reaction cycles. The better photocatalytic performance of AVO/Pt has been attributed to the more efficient visible light utilization and the lower interfacial charge transfer resistance, as demonstrated in the DRS and EIS spectra. The presence of the surface Pt atoms also leads to a higher amount of reactive radicals, which could efficiently promote the surface redox reactions.     

Model Selection for Unsupervised Learning of Visual Context

This study addresses the problem of choosing the most suitable probabilistic model selection criterion for unsupervised learning of visual context of a dynamic scene using mixture models. A rectified Bayesian Information Criterion (BICr) and a Completed Likelihood Akaike’s Information Criterion (CL-AIC) are formulated to estimate the optimal model order (complexity) for a given visual scene. Both criteria are designed to overcome poor model selection by existing popular criteria when the data sample size varies from small to large and the true mixture distribution kernel functions differ from the assumed ones. Extensive experiments on learning visual context for dynamic scene modelling are carried out to demonstrate the effectiveness of BICr and CL-AIC, compared to that of existing popular model selection criteria including BIC, AIC and Integrated Completed Likelihood (ICL). Our study suggests that for learning visual context using a mixture model, BICr is the most appropriate criterion given sparse data, while CL-AIC should be chosen given moderate or large data sample sizes.     

变频器调速装置节能浅析

1概述 近十多年来,随着电力电子技术、微电子技术及现代控制理论的发展,变频调速技术已经广泛地用于交流电动机的速度控制,其最主要的特点是具有高效率的驱动性能及良好的控制特性.它是一种高新技术电力节能装置,它通过改变（降低）电源工作频率,来降低动力设备（电机）的转速,减少设备的输出功率,达到输出功率与工作负荷的最佳匹配,实现节能目的,有效地提高了经济效益和产品质量.几乎可以说,有电动机的地方就有变频器,在一切需要进行速度控制的场合,变频器以其操作方便、体积小、控制性能高而获得广泛应用.     

水驱前缘测试技术在复杂砂岩油藏中的应用

对平面剩余油分布的认识，是油田开发后期的一项重要工作，水驱前缘测试是当前平面剩余油监测比较好的方法之一。水驱前缘测试技术是利用注水产生的微地震，通过检测分析微震信号来确定裂缝发育状况、水驱波及范围、优势注水方向，为评价区块水驱状况和平面剩余油分析提供直接依据。因此开展该项技术的现场试验与运用研究，对油田开发和产油增效具有重要意义。文章介绍了该技术方法的原理以及在华北复杂砂岩油藏水驱特征分析中的应用效果。     

多介质立体取样及在北黄海油气化探中的应用

由于不同环境条件下,不同化探测试指标受到不同的因素干扰,所以不同介质样品的应用条件存在一定的差异。针对不同介质样品特点,分别采集海底沉积物、底部海水和低空大气3种介质样品,并采用在海底沉积物柱状样不同深度部位取样的立体取样方法,通过多指标综合分析,对不同介质和深度样品的多项化探指标互相进行了验证和补充,可以抑制干扰因素的影响,为油气资源远景评价提供依据。运用该方法在北黄海盆地油气勘查中进行初步尝试,并据此划分了三级化探异常区,提出了有利的含油气远景区,均与已知油气区和区域地质分析的结果相符合,取得了很好的效果。      

国内外聚乙烯管材树脂生产现状

介绍国内外聚乙烯管材料的开发和生产情况,以及聚乙烯管材树脂的主要生产厂家。     

丙烯腈装置回收塔内聚合物生成原因的分析

针对丙烯腈生产过程中回收塔内聚合物堵塞降液管造成回收塔运行周期短的问题,通过对丙烯腈回收塔内各组分分布的模拟计算,直观显示了回收塔内各组分的浓度分布,发现了回收塔的聚合段与丙烯醛的富集段相吻合的现象,初步得出了回收塔内局部聚合的原因;通过对塔内聚合物的特性分析和评判,进一步证实了“回收塔内局部聚合严重是由于在聚合段丙烯醛聚集引起”这一现象;根据模拟计算结果和实际运行经验,提出了预防聚合物堵塞降液管的措施,并进行了部分生产验证,为丙烯腈生产企业延长装置运行周期提供了理论指导。     

膨胀套管的弹塑性理论分析

分析认为，膨胀套管在膨胀过程中先进入弹性阶段，然后进入弹塑性阶段，最后进入塑性流动阶段。采用弹塑性分析方法，对膨胀套管膨胀过程中套管内壁的受力与变形进行了研究，模拟了其成形的过程，并建立了解析解，为膨胀套管膨胀操作过程中确定关键操作参数提供了理论支持。根据推导出的力学模型，计算出了外径107．9mm、钢级为J55的膨胀套管膨胀到直径139．7mm时膨胀芯头拉头处的轴向力为195．94kN。     

卷积码的线性系统

介绍了卷积码的线性离散时不变系统模型。从建立卷积码的状态变量方程出发,研究了卷积码的代数结构,并详细论述了基于状态变量方程描述的迭代译码算法。     

基于扩展分形和CFAR特征融合的SAR图像目标识别

研究了多信息融合技术在SAR图像目标识别中的应用。将扩展分形特征(Extended Fractal)与双参数恒虚警特征(Double Parameter CFAR)形成的多信息进行融合处理。运用Dempster-Shafer证据理论，在决策层对SAR图像中的像素进行识别分类。实验结果表明通过融合对像素分类的准确性明显好于单特征的检测结果，减少了虚警概率，提高了系统的识别能力。