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431.
MARTÍN H. FÉLIX-MEDINA 《Environmental and Ecological Statistics》2003,10(1):61-82
In this article we consider asymptotic properties of the Horvitz-Thompson and Hansen-Hurwitz types of estimators under the adaptive cluster sampling variants obtained by selecting the initial sample by simple random sampling without replacement and by unequal probability sampling with replacement. We develop an asymptotic framework, which basically assumes that the number of units in the initial sample, as well as the number of units and networks in the population tend to infinity, but that the network sizes are bounded. Using this framework we prove that under each of the two variants of adaptive sampling above mentioned, both the Horvitz-Thompson and Hansen-Hurwitz types of estimators are design-consistent and asymptotically normally distributed. In addition we show that the ordinary estimators of their variances are also design-consistent estimators. 相似文献
432.
This study investigates energy dissipation due to air bubble entrainment for three typical phenomena; a hydraulic jump, a
2-D vertical plunging jet and a vertical circular plunging jet into water. A simple model is presented here which enables
to estimate the energy transformation and dissipation achieved by air bubbles quantitatively for three above phenomena. The
average rate of energy dissipation by air bubbles obtained from the experimental data are 25%, 1.4%, and 2.15% with respect
to total energy loss for the hydraulic jump, 2-D vertical plunging jet and vertical circular plunging jet, respectively. 相似文献
433.
Mingbo Ma Suozhuai Dong Wanhui Jin Chongqi Zhang 《Journal of environmental science and health. Part. B》2019,54(1):70-75
Pesticides carried by cotton fiber are potential risk for production workers and consumers. Dissipation behaviour of a commonly used cotton pesticide profenofos in cotton fiber during growing period and scouring treatment was investigated. The results showed that profenofos in the fiber from the pre-opened and post-opened bolls both decreased to undetectable amounts 21?days after pesticide application. However, a minority of profenofos was converted to a strongly irritant compound, 4-bromo-2-chlorophenol and retained a non-negligible amount in cotton fiber even after 28?days. Profenofos and its degradation product could be completely removed during the conventional cotton scouring process. The degradation half-time of profenofos in scouring bath was only 3.0?min, and the degradation product was also 4-bromo-2-chlorophenol. Cotton products made of profenofos-carrying fiber are safe; however, the scouring waste should be detoxicated before discharge due to the accumulation of 4-bromo-2-chlorophenol in the scouring bath. These results could be useful for evaluating the risk of cotton fiber from the profenofos applied fields. 相似文献
434.
Lena Partzsch 《环境政策》2017,26(2):193-211
Scholars of environmental politics demand serious reform of international governance and institutions to protect planet Earth. There is therefore an urgent need to discuss what causes change and gridlock in environmental politics. Serious reform is inextricably tied up with questions of power. The diversity with which studies on environmental politics understand power is exposed through three ideal type concepts: power with (learning and cooperation), power to (resistance and empowerment) and power over (coercion and manipulation). So far, scholars have mainly used analysis of coercive power (over) to explain gridlock in environmental politics; also needed is explicit acknowledgement of coaction and individual agency that can enable transition to more sustainable societies. 相似文献
435.
在教育体系中,多媒体技术的运用已经成为必然的趋势。多媒体技术应用在中文教学过程中具有丰富教学的形式与内容、提高教学效率、促进教师综合素质增长等优点,但同时也存在着忽略学生主体性、重形式而轻内容、“贪多嚼不烂”等误区,针对以上问题,应端正观念、抓好重点、扬长避短。 相似文献
436.
本文介绍CAE(Computer Aided Engineering)仿真软件在提高遥控器液晶显示屏跌落保护中的应用,阐述CAE在产品设计上的重要性,使CAE仿真软件能得到广泛的应用。 相似文献
437.
438.
采用低温急速冷冻-真空干燥技术制备了PFC-HA絮体的粉末样品,研究了这些样品的物理与分形特征.结果表明,PFC-HA絮体具有晶体结构,SEM图象中有方块状形体;絮体主要组成元素为C、O、Fe,所含的特征官能团保留了絮体组成原料的一些特征;絮体的干燥样品的BET比表面积为51~92 m2·g-1,BJH累积吸附孔体积为0.0638~0.108 cm3·g-1,BJH脱附平均孔径为3.53~4.60nm,PSD峰值对应孔径3.9nm(4#样品还有另外一个PSD峰值53.2nm).PFC-HA絮体的干燥样品具有自相似性的粗糙表面,呈现多尺度分形特征;图象法确定的表面分形维数Ds值远低于N2吸附/脱附等温线法确定的结果,分别为2.14~2.22、2.90~2.96;前者的分形尺度大约处于23~390nm之间,主要属于絮体干燥样品的外表面尺度,后者的分形特征尺度区间的下限大约为0.2nm,属于孔表面尺度,因此,PFC-HA絮体干燥样品的表面粗糙度主要集中于孔表面.另外,对同一絮体,N2吸附法和脱附法确定的孔表面分形维数基本相同.通过热力学模型计算出的4#样品的Ds值接近于FHH理论计算出的结果,但分形尺度的区间变小了. 相似文献
439.
Shuangshuang Xue Hongbo He Qizhe Fan Changlin Yu Kai Yang Weiya Huang Yang Zhou Yu Xie 《环境科学学报(英文版)》2017,29(10):70-77
A series of La/Ce-codoped Bi_2O_3 composite photocatalysts were fabricated via hydrothermal–calcination process. The as-prepared products were intensively characterized by some physicochemical characterizations like N_2 physical adsorption, X-ray powder diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), UV–Vis diffuse reflectance(UV–Vis DRS), Fourier transform infrared spectroscopy(FT-IR),photoelectrochemical measurements, and photoluminescence(PL) spectroscopy. The characterization results indicated that La and Ce doping induced obvious crystal phase transformation in Bi_2O_3, from monoclinic to tetragonal phase. La and Ce codoping also gave rise to the obvious synergetic effects, e.g., the lattice contraction of Bi_2O_3, the decrease of crystal size and the increase of surface area. The photocatalytic performance of the prepared catalysts was evaluated by removal of dye acid orange II with high concentration under visible light irradiation. Results showed that La/Ce-codoped Bi_2O_3 displayed much higher photocatalytic performance than that of bare Bi_2O_3, single La or Ce doped Bi_2O_3 samples. The superior photocatalytic activity was mainly attributed to the improved texture and surface properties and the synergistic effects of La and Ce codoping on suppressing the recombination of photo-generated electrons(e~-) and holes(h~+). 相似文献
440.