Precautionary control rules in US fisheries management: specification and performance     

Restrepo  V. R.; Powers  J. E. 《ICES Journal of Marine Science》1999,56(6):846-852

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Estimation of covariance matrix from geochemical data with observations below detection limits     

Chang-Jo F. Chung 《Mathematical Geology》1993,25(7):851-865

Multivariate statistical analyses have been extensively applied to geochemical measurements to analyze and aid interpretation of the data. Estimation of the covariance matrix of multivariate observations is the first task in multivariate analysis. However, geochemical data for the rare elements, especially Ag, Au, and platinum-group elements, usually contain observations the below detection limits. In particular, Instrumental Neutron Activation Analysis (INAA) for the rare elements produces multilevel and possibly extremely high detection limits depending on the sample weight. Traditionally, in applying multivariate analysis to such incomplete data, the observations below detection limits are first substituted, for example, each observation below the detection limit is replaced by a certain percentage of that limit, and then the standard statistical computer packages or techniques are used to obtain the analysis of the data. If a number of samples with observations below detection limits is small, or the detection limits are relatively near zero, the results may be reasonable and most geological interpretations or conclusions are probably valid. In this paper, a new method is proposed to estimate the covariance matrix from a dataset containing observations below multilevel detection limits by using the marginal maximum likelihood estimation (MMLE) method. For each pair of variables, sayY andZ whose observations containing below detection limits, the proposed method consists of three steps: (i) for each variable separately obtaining the marginal MLE for the means and the variances, , , , and forY andZ: (ii) defining new variables by and and lettingA=C+D andB=C–D, and obtaining MLE for variances, and forA andB; (iii) estimating the correlation coefficient _YZ by and the covariance _YZ by . The procedure is illustrated by using a precious metal geochemical data set from the Fox River Sill, Manitoba, Canada.  相似文献   

Drought forecasting: Methodological topics from a systems perspective     

R. Krzysztofowicz 《Stochastic Environmental Research and Risk Assessment (SERRA)》1991,5(4):267-279

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Numerical Modeling of the Ston-Slano (Croatia) Aftershock Sequence     

Herak  Marijan  Herak  Davorka  Markušić  Snježana  Ivančić  Ines 《Studia Geophysica et Geodaetica》2001,45(3):251-266

The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (M _L 4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock.  相似文献   

Life-cycle cost analysis of design practices for RC framed structures   总被引：1，自引：1，他引：1  

Nikos D. Lagaros 《Bulletin of Earthquake Engineering》2007,5(3):425-442

The objective of this study is to perform life-cycle cost analysis on three design practices namely weak ground storey, short and floating columns and their combinations. Life-cycle cost analysis is recognized as the only suitable tool for assessing the structural performance when the structure is expected to be functional for a long period of time. Life-cycle cost analysis is considered in this study assessing the behaviour of the three design practices against earthquake hazard. Although, a number of checks are performed in order to reduce the influence of these design practices on the seismic behaviour of reinforced concrete (RC) framed structures, it was found that the total life-cycle cost of partially infilled RC designs is significantly increased compared to that of the fully infilled one. Through the test example examined in the framework of this study general conclusions are obtained regarding the behaviour of the three design practices.  相似文献   

Geotechnical properties of a chemically stabilized soil from Malaysia with rice husk ash as an additive   总被引：1，自引：0，他引：1  

F. Haji Ali  A. Adnan  Chew Kam Choy 《Geotechnical and Geological Engineering》1992,10(2):117-134

Summary The stabilization of Malaysian soil by mixing with rice husk ash, a locally available waste material, to improve its engineering properties is described. Stabilizing agents, i.e. cement and lime, were added to produce the reaction products which are responsible for the enhancement of the engineering properties. Based on the strength development, it seems that lime is the more effective stabilizing agent. However, the cheap waste material can be used as partial replacement for the more expensive cement in the cement-treatment of the soil. A durability study was carried out to evaluate the effectiveness of this stabilization method.  相似文献   

Pumpellyite–actinolite facies of the Sanbagawa metamorphism     

S. BANNO 《Journal of Metamorphic Geology》1998,16(1):117-128

The pumpellyite–actinolite facies proposed by Hashimoto is defined by the common occurrence of the pumpellyite–actinolite assemblage in basic schists. It can help characterize the paragenesis of basic and intermediate bulk compositions, which are common constituents of various low-grade metamorphic areas. The dataset of mutually consistent thermodynamic properties of minerals gives a positive slope for the boundary between the pumpellyite–actinolite and prehnite–pumpellyite facies in P–T space. In the Sanbagawa belt in Japan, the mineral parageneses of hematite-bearing and -free basic schists, as well as pelitic schists have been well documented. The higher temperature limit of this facies is defined by the disappearance of the pumpellyite+epidote+actinolite+chlorite assemblage in hematite-free basic schists with X_Fe3+ of epidote around 0.20–0.25 and the appearance of epidote+actinolite+chlorite assemblage with X^Ep_Fe3+≤0.20. In hematite-bearing basic schists, there is a continuous change of paragenesis to higher grade, epidote–glaucophane or epidote–blueschist facies. In pelitic schists, the albite+lawsonite+chlorite assemblage does occur but only rarely, and its assemblage cannot be used to determine the regional thermal structure. The lower temperature equivalence of the pumpellyite–actinolite assemblage is not observed in the field. The Mikabu Greenstone complex and the northern margin of the Chichibu complex, which are located to the south of the Sanbagawa belt, are characterized by clinopyroxene+chlorite or lawsonite+actinolite assemblages, which are lower temperature assemblages than the pumpellyite+actinolite assemblage. These three metamorphic complexes belong to the same subduction-metamorphic complex. The pumpellyite–actinolite facies or subfacies can be useful to help reveal the field thermal structure of metamorphic complexes  相似文献   

Détermination indirecte des limites d'Atterberg par gravimétrie dynamique     

Chantal Proust  Agnès Jullien  Lydie Le Forestier 《Comptes Rendus Geoscience》2004,336(14):1233-1238

This study presents a new method for Atterberg limits measurements using dynamic drying. Indeed, for some polluted clays, or clay mixtures, classical methods cannot be used. The principle of liquid $(W_{\mathrm{L}})$ and plasticity $(W_{\mathrm{P}})$ limits determination by this method is presented. Experimental values for classical clays are close to those obtained with Casagrande's methods, allowing for larger physical mud characterisation. To cite this article: C. Proust et al., C. R. Geoscience 336 (2004).  相似文献   

The sensitivity of the next generation of lunar Cherenkov observations to UHE neutrinos and cosmic rays     

C.W. James  R.J. Protheroe   《Astroparticle Physics》2009,30(6):318-332

We present simulation results for the detection of ultra-high energy (UHE) cosmic ray (CR) and neutrino interactions in the Moon by radio-telescopes. We simulate the expected radio signal at Earth from such interactions, expanding on previous work to include interactions in the sub-regolith layer for single dish and multiple telescope systems. For previous experiments at Parkes, Goldstone (GLUE), and Kalyazin we recalculate the sensitivity to an isotropic flux of UHE neutrinos. We find the published sensitivity for the GLUE experiment to be too high (too optimistic) by an order of magnitude, and consequently the GLUE limit to be too low by an order of magnitude. Our predicted sensitivity for future experiments using the Australia Telescope Compact Array (ATCA) and the Australian SKA Pathfinder (ASKAP) indicate these instruments will be able to detect the more optimistic UHE neutrino flux predictions, while the square kilometre array (SKA) will also be sensitive to all bar one prediction of a diffuse ‘cosmogenic’, or ‘GZK’, neutrino flux.Outstanding theoretical uncertainties at both high-frequency and low-frequency limits currently prevent a reliable estimate of the sensitivity of the lunar Cherenkov technique for UHE cosmic ray (CR) astronomy. Here, we place limits on the effects of large-scale surface roughness on UHE CR detection, and find that when near-surface ‘formation-zone’ effects are ignored, the proposed SKA low-frequency aperture array could detect CR events above 56 EeV at a rate between 15 and 40 times that of the current Pierre Auger Observatory. Should further work indicate that formation-zone effects have little impact on UHE CR sensitivity, observations of the Moon with the SKA would allow directional analysis of UHE cosmic rays, and investigation of correlations with putative cosmic ray source populations, to be conducted with very high statistics.  相似文献   

Influence of thawed soil depth on rainfall erosion of frozen bare meadow soil in the Qinghai–Tibet Plateau     

Xiaofeng Gao  Xiaonan Shi  Tingwu Lei 《地球表面变化过程与地形》2021,46(10):1953-1963

The Qinghai–Tibet Plateau has a vast area of approximately 70×10⁴ km² of alpine meadow under the impacts of soil freezing and thawing, thereby inducing intensive water erosion. Quantifying the rainfall erosion process of partially thawed soil provides the basis for model simulation of soil erosion on cold-region hillslopes. In this study, we conducted a laboratory experiment on rainfall-induced erosion of partially thawed soil slope under four slope gradients (5, 10, 15, and 20°), three rainfall intensities (30, 60, and 90 mm h⁻¹), and three thawed soil depths (1, 2, and 10 cm). The results indicated that shallow thawed soil depth aggravated soil erosion of partially thawed soil slopes under low hydrodynamic conditions (rainfall intensity of 30 mm h⁻¹ and slope gradient ≤ 15°), whereas it inhibited erosion under high hydrodynamic conditions (rainfall intensity ≥ 60 mm h⁻¹ or slope gradient > 15°). Soil erosion was controlled by the thawed soil depth and runoff hydrodynamic conditions. When the sediment supply was sufficient, the shallow thawed soil depth had a higher erosion potential and a larger sediment concentration. On the contrary, when the sediment supply was insufficient, the shallow thawed soil depth resulted in lower sediment erosion and a smaller sediment concentration. The hydrodynamic runoff conditions determined whether the sediment supply was sufficient. We propose a model to predict sediment delivery under different slope gradients, rainfall intensities, and thawed soil depths. The model, with a Nash–Sutcliffe efficiency of 0.95, accurately predicted the sediment delivery under different conditions, which was helpful for quantification of the complex feedback of sediment delivery to the factors influencing rainfall erosion of partially thawed soil. This study provides valuable insights into the rainfall erosion mechanism of partially thawed soil slopes in the Qinghai–Tibet Plateau and provides a basis for further studies on soil erosion under different hydrodynamic conditions.  相似文献