Partial L-moments for the analysis of censored flood samples / Utilisation des L-moments partiels pour l’analyse d’échantillons tronqués de crues     

《水文科学杂志》2013,58(5)

Abstract

Abstract A parameter estimation method is proposed for fitting the generalized extreme value (GEV) distribution to censored flood samples. Partial L-moments (PL-moments), which are variants of L-moments and analogous to ?partial probability weighted moments?, are defined for the analysis of such flood samples. Expressions are derived to calculate PL-moments directly from uncensored annual floods, and to fit the parameters of the GEV distribution using PL-moments. Results of Monte Carlo simulation study show that sampling properties of PL-moments, with censoring flood samples of up to 30% are similar to those of simple L-moments, and also that both PL-moment and LH-moments (higher-order L-moments) have similar sampling properties. Finally, simple L-moments, LH-moments, and PL-moments are used to fit the GEV distribution to 75 annual maximum flow series of Nepalese and Irish catchments, and it is found that, in some situations, both LH- and PL-moments can produce a better fit to the larger flow values than simple L-moments.  相似文献   

Assessing uncertainties in a conceptual water balance model using Bayesian methodology / Estimation bayésienne des incertitudes au sein d’une modélisation conceptuelle de bilan hydrologique     

《水文科学杂志》2013,58(1)

Abstract

Abstract The aim of this study was to estimate the uncertainties in the streamflow simulated by a rainfall–runoff model. Two sources of uncertainties in hydrological modelling were considered: the uncertainties in model parameters and those in model structure. The uncertainties were calculated by Bayesian statistics, and the Metropolis-Hastings algorithm was used to simulate the posterior parameter distribution. The parameter uncertainty calculated by the Metropolis-Hastings algorithm was compared to maximum likelihood estimates which assume that both the parameters and model residuals are normally distributed. The study was performed using the model WASMOD on 25 basins in central Sweden. Confidence intervals in the simulated discharge due to the parameter uncertainty and the total uncertainty were calculated. The results indicate that (a) the Metropolis-Hastings algorithm and the maximum likelihood method give almost identical estimates concerning the parameter uncertainty, and (b) the uncertainties in the simulated streamflow due to the parameter uncertainty are less important than uncertainties originating from other sources for this simple model with fewer parameters.  相似文献   

Further Studies Of Atmospheric Turbulence In Layers Near The Surface: Scaling The Tke Budget Above The Roughness Sublayer   总被引：2，自引：0，他引：2  

Paul Frenzen  Christoph A. Vogel 《Boundary-Layer Meteorology》2001,99(2):173-206

The second of two experimental studies of the TKE budget conducted on sites of different roughness is described, and results are compared. The first took place within a shallow layer above a small field of mostly bare, cultivated soil; the second was carried out above a roughness sublayer of significant depth on an extensive plain of tall dry grass. Budget terms observed in the second study were scaled with a modified u which compensated for effects of an unusually large stress gradient and ensured that the _m functions would be collinear. By showing that the modification becomes negligible in smaller gradients, it is demonstrated that in normal conditions, budgets observed above significant roughness sublayers should be normalized by scaling in terms of the unreduced Reynolds stress at the sublayer's upper surface. This procedure is shown to be consistent with the expectation that TKE budgets in layers near the surface all scale in fundamentally the same way.Other findings include: (1) the fact that most _m functions previously reported are not quite collinear is attributed to a type of overspeeding known to affect three-cup anemometers; (2) revised _m functions, collinear and largely free of the effects of overspeeding, are determined from a well-established characteristic of the linear _m relation for the stable case; (3) data that define collinear _m functions can also be represented with single hyperbolic curves; (4) dissipation is found to be 10 to 15% too small to balance total TKE production in unstable and neutral conditions and to decrease with increasing z/L in thestable regime; and (5) new relations for based on the observed behaviour of the dissipation deficit provide an improved closure for the set of equations that express the budget terms as functions of _m and z/L.  相似文献   

Comparison between Pollutant Concentration in the Samples of Fog and Rime Water Collected at Mt. Milešovka     

Fišák  Jaroslav  Řezáčová  Daniela 《Studia Geophysica et Geodaetica》2001,45(3):319-324

The article aims at showing the differences in concentration of pollutants that are contained in the samples of fog and/or low cloud water in comparison with the water from rime. The results follow from the fog and rime measurements made at Mt. Mileovka (eské Stedohoí Mountains). They are compared with the results of other studies that also report the differences in fog and rime chemistry.  相似文献   

p—范分布的近似表示   总被引：8，自引：0，他引：8  

孙海燕 《武汉大学学报(信息科学版)》2001,26(3):222-225

p-范分布是一个包含拉普拉斯分布、正态分析、均匀分布等常见分布的分布族。用p-范分布描述观测误差的统计特性，只需假定误差的分布为单峰、对称，因此、p-范分布似然平差可以避免事先假定误差的具体分布模式，而在平差过程中确定未知参数及误差的分布具有自适应的特点。但是p-范分布的密度函数比较复杂，不利于理论分析和实际应用。 的研究表明，p-范分布可以近似地表示为拉普拉斯分布与正态分析或正态分布均均匀分布的线性组全。p-范分布与本文给出的近似分布具有相的前四阶矩。由于拉普拉斯分布。正态分布。均匀分布的密度函数都比较简单，用近似分布代替p-范分布会使相关的问题得到简化。  相似文献   

Gas and Particulate Products Distribution from the Photooxidation of α-Humulene in the Presence of NOx, Natural Atmospheric Air and Sunlight     

M. Jaoui  R. M. Kamens 《Journal of Atmospheric Chemistry》2003,46(1):29-54

The photooxidation of -humulene in the presence of NO_x, natural sunlight, and rural background air was investigated using a combination of gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). Identification and quantification of gas and particulate reaction products were reported over the course of the reaction. The daytime photooxidation was carried out in a large outdoor smog chamber (190 m³). A wide range of ring retaining and ring opening products in the gas and particle phase are reported. On average, measured gas and particle phase products accounted for 44% of the reacted -humulene carbon. Measurements show that a number of reaction products with low vapor pressures (e.g. 3-seco--humulone aldehyde, 7-seco--humulone aldehyde, -humulal aldehyde, -humulene 3-oxide or -humulene 7-oxide, -humulaic/alic acid isomers, and 3-seco--14-hydroxyhumulone aldehyde) were found in the early stage of the reaction and may play an important role in the early formation of secondary organic aerosol. A detailed mechanism is proposed to account for most products observed in this investigation.  相似文献   

不同温压下岩石弹性波速度、衰减及各向异性与组构的关系   总被引：16，自引：0，他引：16  

刘斌 《地学前缘》2000,7(1):247-257

结合岩石组构分析 ,阐述了岩石弹性波传播速度和衰减以及它们的各向异性与岩石组构之间的关系。在不同温压条件下对具有很强晶格优选方位的岩石样品的研究表明 ,随着围压的增加 ,波速和Q值均增大 ,但是在相互正交的 3个方向上 (垂直或平行于层理面及线理方向 )增大的速度并不相同 ,这与微裂隙的逐渐闭合密切相关。观测到的波速和Q值的各向异性具有不同的形成机理 ,波速各向异性主要与定向分布的微裂隙和主要矿物的晶格优选方位等构造因素有关 ;高围压下Q值各向异性与速度各向异性正好相反 ,可能是由于定向排列的矿物晶体沿不同方向其边界之间接触程度不同造成的。对岩石组构的研究不仅可以揭示岩体的变形机制、变形的动力学过程及其有关的热力学信息 ,还可以对宏观岩石的各种物理性质 ,尤其是力学特性 ,从微观机理上加以解释。文中特别强调了岩石组构分析对研究岩石物理性质的各向异性具有十分重要的意义。  相似文献   

四川石棉草科穹状岩浆核杂岩构造特征   总被引：1，自引：0，他引：1  

郭建强  喻安光 《矿物岩石》1998,18(4):90-97

位于扬子陆块西缘的石棉草科穹状变形变质体,据近年来的研究表明,该穹隆体经历了三次变形变质时期：早期为收缩滑脱变形的区域动力变质、中期热隆伸展动热变质和后期岩浆热接触变质。对主期变质划分出黑云母带、石榴石带、红柱石－十字石带和矽线石带,确定为低压相系,利用变质反应、矿物地质温压计及相关的同位素年龄资料,建立了草科穹状变形变质体演化的ｐ－Ｔ－ｔ－Ｄ轨迹。轨迹图呈顺时针形式,具碰撞造山带环境的特点,变形变质过程受变质体前缘西油房韧性剪切带逆冲－推覆作用和后缘碰撞晚期岩浆大规模上侵的双重制约,为深源岩浆热动力变质成因,属穹状岩浆核杂岩构造。  相似文献   

Long-Term Observations of Isotope Ratio Accuracy and Reproducibility Using Quadrupole ICP-MS     

Thomas Ulrich  Balz S. Kamber  Jon D. Woodhead  Lizzy A. Spencer 《Geostandards and Geoanalytical Research》2010,34(2):161-174

High precision isotope ratio and trace element determination can be achieved with modern quadrupole ICP-MS provided that short and long-term instrument performance is accurately monitored. Here we present results for the isotope ratios ⁶Li/⁷Li, ¹⁴⁷Sm/¹⁴⁹Sm, ¹⁶⁰Dy/¹⁶¹Dy, ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb, ²⁰⁶Pb/²⁰⁴Pb and ²³⁵U/²³⁸U with which we determined long-term isotope ratio stability of relevance to both trace element and isotope determination. With respect to trace element determination, we first present long-term observations regarding oxide formation rates of Ba and Nd on light REE and heavy REE, as well as Zr on Ag. These showed good correlations and could be used to correct effectively the interference. The efficacy of this correction was demonstrated with analyses of the rock reference material BHVO-2 at both low and high oxide formation rates. Next, we studied the long-term reproducibility of a Dy isotope ratio that was measured to correct for the isobaric interference on Gd. It was found that, regardless of tuning condition, the ratio reproduced very well (0.58% RSD, 1s) and that the estimate of the Gd concentration did not suffer from the large correction (> 10%) caused by the Dy isobar. Long-term reproducibilities of Li, Sm and U isotope ratios, required for accurate mass bias correction when isotopically enriched internal standards of these elements are employed, were measured in the rock reference materials AGV-2 and JA-3 over a time period of up to 3 years. As expected, the Li isotope ratio showed the largest variability (RSD = 7%), but the other two ratios had relative external reproducibilities of only 1.01% (1s, U) and 0.67% (Sm). The mass bias-induced scatter in measurements for Sm and U was so small that the internal standard correction was effective, even for samples with high concentrations of these elements. With regard to Pb-isotope ratio determination, we also present long-term reproducibility for NIST SRM 982, run as an unknown and two accuracy tests for Pb separated from granitoids and from meteorites. It is demonstrated that the obtained ratios, including those involving ²⁰⁴Pb, are accurate relative to MC-ICP-MS determinations and of comparable precision to conventional TIMS analysis. The excellent agreement between all data sets shows the potential of modern quadrupole ICP-MS instrumentation for Pb-isotope determination, particularly for samples with very low Pb content.  相似文献   

基于τ-p变换的地震道重构     

谢小国 《四川地质学报》2014,(4):625-627

基于τ-p变换原理,研究一种基于τ-p变换的地震数据重构方法,运用该方法对待重构道用零道替代,通过τ-p正反变换及一定的迭代处理实现地震道数据重构。理论模型与实际资料应用表明,基于τ-p变换的地震道重构方法效果明显,重构数据稳健。  相似文献