摘要:

AbstractThe problem of developing an approach for modelling the response of an organism to chronic toxicity is discussed in this paper and illustrated by studying the toxic effect of NaBr on the reproduction process of a population ofDaphnia magna. A general model is given which includes both the negative binomial and poisson distributions as special cases depending on the values of a single parameter. The steps involved in estimating the parameters of the model and testing the goodness‐of‐fit are presented. In particular the iterative solution of the estimating equations are described in detail along with the problem of setting confidence limits for model parameters. This approach is useful in the analysis of quantal bioassay d

ISSN:1180-4009    

DOI:10.1002/env.3770020302

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe recently reported tendencies toward decreasing total amounts of silicate in the Baltic Sea are investigated by use of non‐parametric trend analysis. The period 1968‐1986 showed significant falling trends in surface waters from the whole system. The deepest parts of the Baltic proper did in contrast reveal strong increasing trends. These trends are more pronounced during the latter part of the analysis period which is characterized by stagnant conditions in the Baltic proper. These conditions have been prevailing since the major inflow in 1976. The causes of the observed changes are unclear. The increased load of nutrients and accompanying increase in primary production is, however, one factor. Another is coupled to the stagnation conditions of the Baltic Pro

ISSN:1180-4009    

DOI:10.1002/env.3770020303

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper describes the use of both an optimization technique and a simulation technique for assessing the performance of alternative configurations for a water system. This methodology is applied to the Aragón ‐ Gállego system, in Spain. This reservoir system is used primarily to supply water for irrigation. The goal is to get more water in conditions to be used for the irrigation of several new areas in the basins. Given a specific configuration in the optimization step, the out‐of‐kilter algorithm is applied to a specially designed network that models the system in order to know the best way to distribute the water resources in a year. Demands in each period are fixed and cost coefficients of the variables are assigned to reproduce the different priorities of the demands. The simulation technique permits one to compare the different configurations and to assess their performance ov

ISSN:1180-4009    

DOI:10.1002/env.3770020304

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractIn case control studies when the relative risk is very high the expected frequencies of diseased but not exposed and non‐diseased but exposed are generally very low. In such situations inverse sampling can be used. This paper presents the relevant theory of inverse sampling in case control studies. The expressions for bias and Mean Square Error (MSE) have been derived. It has been observed that the estimator under inverse sampling is unbiased and more efficient as compared to the estimator under usual case control studie

ISSN:1180-4009    

DOI:10.1002/env.3770020305

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractWhen statistical hypotheses are tested with large environmental data sets, such as those available for ionic constituents of the Great Lakes, even small differences between means are detectable, and the usual result is that all or nearly all differences tested are statistically significant. In this situation, hypothesis testing is not useful. Differences between means also are not useful for comparisons because of differences in units of measurement and variances. Thet‐statistic is used to determine if two populations are significantly different, but the value oftis not useful for evaluating the degree of separation of two populations because the value oftis influenced by sample size,thas no lower or upper bound, and the value ofthas no meaningful interpretation. A separation coefficient is developed that measures the proportion overlap of two normally distributed populations; it is not influenced by sample size, is easily calculated, and takes values between 0 and 1. The separation coefficient was applied to examine differences in ion concentrations between Lake Superior and Lake Huron. The sample sizes were large and all differences were statistically significant, but the coefficients of separation varied from 0.07 to 1, which indicates that concentrations of some ions in the lakes were more similar than others. The pattern in the coefficients of separation indicate meaningful differences between the lake

ISSN:1180-4009    

DOI:10.1002/env.3770020306

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractModelling is currently used in problems connected with the assessment of environmental impact. This class of problems is generally well defined, in that all the characteristics (such as location, strength, etc.) of potential sources of pollution are known. On the other hand, receptor analysis uses the experimental information available in the environment (such as air or water quality) to identify polluting sources. This is why they are generally called inverse problems.The reasons for the negligible amount of research effort in the application of inverse modelling is due to the ill‐posed character (i.e. lack of continuity) of the operator that describes the problem. Nevertheless, large strides have been made in the so‐called regularization of inverse operators, which makes use of additional available information.The aim of this paper is to explore how the statistical information employed in receptor analysis can be used for regularization purposes in the general inverse modelling of environmental probl

ISSN:1180-4009    

DOI:10.1002/env.3770020307

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractEtezadi‐Amoli and Ciampi (Biometrics 1987) introduced a method to approximate the baseline hazard and to estimate the regression coefficients for covariates simultaneously for the extended hazard regression (EHR) model using a quadratic spline approach. In this paper, an estimate of the baseline hazard function by B‐spline approximation using a minimax criterion is proposed. The nonlinear problem is approximated by a linear programming problem with only linear constraints. The nice features of this approach are: (i) the minimax criterion provides a robust approximation to the hazard function, and (ii) the linearized problem is numerically simple and f

ISSN:1180-4009    

DOI:10.1002/env.3770020308

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe annual discharges of the Nile River at Aswan are examined for change‐points in both mean level and in serial correlation structure. The methodology used identifies 1899 as a change‐point for the mean level; this has been observed by others. Second and third change‐points for the mean level are identified at 1954 and 1965. In addition, a change is observed in the serial correlation structure of the detrended series. For the segment prior to 1907 this structure is compatible with white noise; after 1907 it is characterized by strong serial correlation and is closely modelled by an ARMA(2,2) model. This serial correlation is taken into account when identifying the 1954 and 1965 changes in mean level.The history of the Nile basin is examined for significant hydrological and political events that might be connected with these change‐points. It is speculated that the changes in mean level at 1899 and 1954 and in serial correlation structure are changes in the data due to measurement and hydropolitical issues. A competing hypothesis for the cause of changes in mean level involves long‐term climatic shifts that could be modelled by long‐memory or doubly stocha

ISSN:1180-4009    

DOI:10.1002/env.3770020309

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

ISSN:1180-4009    

DOI:10.1002/env.3770020301

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY