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1.
《Journal of Great Lakes research》2022,48(3):707-716
Rapid quantitative PCR-based methods for enterococci monitoring can allow public health authorities to make more timely beach posting decisions. However, qPCR methods must be assessed for proposed sites as locale-specific factors may affect DNA recovery or qPCR inhibition. We assessed the feasibility of the USEPA 1609.1 qPCR-based (Enterococcus) method at two urban Toronto beaches and three recreational areas at nearby river mouths in parallel with culture-based methods on the same water samples. A strong positive correlation was observed between the Enterococcus qPCR method and culturing-based quantification methods for E. coli and enterococci at both beaches and two river mouth areas. One river, known to be highly sewage-impacted, did not yield DNA suitable for qPCR analyses. qPCR results from biological replicates were strongly correlated and showed coefficients of variation as low as or lower than culture-based methods. With respect to Beach Action Value exceedances, the USEPA 1609.1 qPCR method provided an 80–90% level of agreement with E. coli enumeration results and >90% with enterococci enumeration. Results indicated that if recreational water locations and sampling conditions met the requirements of the USEPA 1609.1 qPCR method, the method can meet or exceed all quality control requirements and provide water quality results within 3.5 h for diverse recreational water settings around the City of Toronto. 相似文献
2.
研究强分类器ELM-Adaboost模型在滚动轴承故障诊断中的运用。首先,从滚动轴承故障振动信号中提取时域特征参数,并采用因子分析法对变量进行降维处理;其次,对ELM-Adaboost模型中的关键参数进行详细分析,并选择最优的参数对ELM-Adaboost模型进行优化;最后,将ELM-Adaboost模型用于滚动轴承故障诊断中。实验研究结果表明:神经元数量和激活函数都能明显的影响到故障诊断准确率;激活函数采用Hardlim()函数的诊断效果比其它函数要好;ELM-Adaboost模型对神经元数量引起的诊断准确率波动性较小;在重复30次实验中,ELM-Adaboost模型对不同类型的轴承故障诊断准确率均在84%以上,而ELM模型则在78%以上,且ELM-Adaboost模型对重复诊断导致的结果波动性相比较低。 相似文献
3.
《Advanced Powder Technology》2022,33(1):103371
Black phosphorus (BP), as a new 2D material, is normally synthesized by a high-pressure and high-temperature (HPHT) method from white and red phosphorus, which severely hinders the further development of BP for any potential applications and leads to search for other potential applications of BP with big challenge. Herein, we develop a facile and efficient Thermal-Vaporization-Transformation (TVT) approach to prepare a highly active BP directly grown on carbon paper as the electrode for Oxygen evolution reaction (OER), showing a low onset potential of 1.45 V versus RHE. Simultaneously, the current density of BP-CP illustrates the excellent electro-catalysis stability only decreases by 3.4% after continuous operation for 10000 s. Meanwhile, the density functional theory (DFT) calculations further illustrates the P-doped carbon layer in the upper side of BP layer is actually responsible for its enhanced OER property, and the adjacent carbon atoms of the embedded P atoms are actually the active sites due to the induced local change distribution by intramolecular change transfer. Considering the facile, but efficient and scalable, TVT approach can directly synthesize BP-CP with excellent OER performance, which is promising for BP electrocatalysts used for OER in metal-air batteries, fuel cells, water-splitting devices, even other key renewable energy. 相似文献
4.
《Soils and Foundations》2022,62(6):101222
This work addresses the problem of the loading capacity of an anchor plate coupled with a steel wire mesh in soil retaining applications. The interaction mechanism between the flexible mesh facing, the underlying soil layer and the plate is studied starting from the results of several laboratory punch tests involving both the plate and the mesh only, and the whole soil-mesh-plate system. The experimental tests have been reproduced by adopting a 3D discrete element model where also the wire mesh is discretized as an assembly of interconnected nodal particles. The interaction between these particles is ruled by elasto-plastic tensile force–displacement laws in which a distortion is introduced in a stochastic manner to account for the wires’ geometrical irregularities. The mesh model is then validated with reference to a set of punch tests in which the shape and size of the punching element as well as the nominal wire diameter were varied. Subsequently, the model is extended to a punch against soil test configuration permitting an insight into the nontrivial local mechanism between the mesh facing and the underlying granular layer. The good agreement between the numerical predictions and the experimental observations at the laboratory scale allowed us to extend the model towards more realistic field conditions for which the role of the mesh panel boundary conditions, the mesh mechanical properties, the soil mechanical properties and the anchor plate geometry is investigated. 相似文献
5.
俄罗斯商用压水堆VVER和大多数实验堆均采用了六角形紧凑型栅格布置,为了实现VVER和六角形实验堆的高保真数值模拟分析,本文基于数值反应堆物理计算程序(NECP-X)开展了六角形堆芯高保真计算方法研究和程序开发。首先,将全局-局部耦合共振自屏计算方法拓展至六角形堆芯,实现六角形堆芯燃料棒的全堆芯高精度共振计算;其次,基于2D/1D耦合输运计算方法研究了六角形堆芯的高保真计算方法;最后,为了提高全堆芯计算的计算效率,研究了基于区域分解松耦合的非结构网格的粗网有限差分(CMFD)加速方法,可以实现以矩形、六角形和其他多边形栅元为基础的pin-by-pin CMFD 加速。为了验证六角形堆芯高保真计算方法的精度和效率,计算了六角形C5G7基准问题,并分析了六角形输运计算方法的计算精度和CMFD方法的加速效果;将NECP-X程序应用于西安脉冲堆的2D全堆芯计算,与蒙特卡罗程序的结果对比表明NECP-X程序计算得到的特征值和功率分布均具有较高精度。因此,本文建立的六角形堆芯高保真计算方法可以应用于六角形堆芯的分析计算。 相似文献
6.
在极度不平衡分类问题中,球形分类器将分类正确样本的损失计为零,仅使用误分样本构造决策函数.文中提出光滑有下界的奖惩结合损失函数,将分类正确样本的损失计为负,实现对目标函数的奖励,避免边界附近噪声的干扰.基于最大间隔双球面支持向量机,利用损失函数,建立奖惩结合的最大间隔双球模型.通过牛顿法构造两个同心球.小球体在覆盖多数类样本的同时抛弃多余的空隙.大球通过增加两个同心球之间的间隔,排除少数类.实验表明,文中模型分类效果较优. 相似文献
7.
针对高维度数据集特征之间的复杂性,而传统的L1惩罚项不满足Oracle性质的无偏性,将逻辑回归弹性网(LR-Elastic Net)中的L1惩罚项替换为SCAD(Smoothly Clipped Absolute Deviation)和MCP(Minimax Concave Penalty)惩罚项,分别构建了LR-SCAD和LR-MCP模型,在保留稀疏性的同时满足了无偏性,并利用ADMM(Alternating Direction Method of Multipliers)算法进行求解。通过模拟实验发现,LR-Elastic Net模型能很好地处理特征存在相关性的小样本数据,而LR-SCAD和LR-MCP模型在特征存在相关性的大样本数据中表现较好;建立LR-Elastic Net、LR-SCAD和LR-MCP策略,并应用于沪深300指数成分股数据。回测结果显示,LR-SCAD和LR-MCP策略在股票相关性很强的数据中比LR-Elastic Net策略表现更好。 相似文献
8.
基于Kriging元模型的优化方法通常存在优化效率较低、收敛速度较慢、昂贵估值次数较多且难以有效平衡Kriging模型的局部与全局搜索行为等弊端。为此,提出一种序列Kriging和距离因子辅助的全局优化方法。其实现过程主要包含两个阶段:一是利用Kriging模型近似复杂昂贵的黑箱函数;二是利用Kriging模型与距离因子的乘积构造加点采样法则,并通过免于求导的DIRECT算法优化该法则,以获取新的昂贵估值点。六个数值函数测试和一个摆线泵仿真实例验证所提出方法的有效性。 相似文献
9.
人本主义视角下,量化商业街道空
间使用者的视觉体验进而理解空间要素如何
影响视觉行为与主观感知,对文化遗产地的
可持续发展具有重要作用。本文结合眼动实
验和语义差异法问卷调研测度街道空间主体
的客观视觉行为与主观心理感受,并采用
ANOVA单因素方差分析解析不同商业街道
空间对视觉吸引力及其感知的影响。研究发
现:第一,街道空间的视觉吸引力与主观感
知情况存在一定联系但不完全趋同;第二,
绿化景观的视觉吸引力较弱,但能够降低街道的负面感知;第三,商业门店、招牌广告具有较高的吸引力,但易产生失调、粗糙、狭
窄等负面感知;第四,龙头路的历史风貌建筑并未产生较强的视觉吸引力;第五,部分非
历史风貌建筑产生了较强的视觉吸引力,但可能增强现代感而削弱历史文化氛围;第六,
铺地作为商业街道底界面,是易被忽视的街道空间要素。总体上,本文从主体行为的角度
分析了客体环境的视觉品质,结合主客观感知为街道空间设计提供数据支持。 相似文献
10.
When we speak about capacitance moisture meters for bulk materials we have to face with different values of dielectric permittivity for different bulk materials in dehydrated state, what causes a method error that can be named ‘type uncertainty’. Besides, different varieties of the same material have different values of dielectric permittivity, which depend from geographical origin, processing conditions etc. It can be hardly predicted automatically and type uncertainty can be compensated only in separate situations with the help of preliminary calibration. Main tasks of the research are to develop new comparison principle of moisture measurement with better accuracy due to effective compensation of physical, chemical and granulometric composition influence on the result of moisture measurement, develop new primary and secondary instrument transducers. Moisture sensor consists of four measuring capacitors. Two of them should be filled with a sample, which moisture content should be determined, and other pair of measuring capacitors should be filled with a same substance, but previously dehydrated. Mathematical models, developed to take into account granulometric composition of a bulk material were used to carry out a comparison analysis for three types of instrument measuring transducers. Obtained results proved that suggested principle of moisture measurement provides effective compensation of granulometric composition influence. Developed measuring principle had been experimentally tested what helped to confirm that it provides two times better compensation of different physical and chemical composition for different materials in comparison with the direct comparison method. 相似文献