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  • 1
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    Stochastic environmental research and risk assessment 1 (1987), S. 1-2 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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  • 2
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    Stochastic environmental research and risk assessment 1 (1987), S. 3-16 
    ISSN: 1436-3259
    Keywords: Annual maximum ; partial duration series ; T-year estimate ; marshall-Olkin bivariate distribution ; Morgenstern bivariate distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract As a basis for development of the annual maximum distribution the so-called partial duration series with Poissonian occurrence times and exponentially distributed peak exceedance values has been selected. The model is generalized by allowing for a Markov dependence between succeeding peak values. Correlation values from p=0 to p=1 can be accounted for by introducing the Marshall-Olkin bivariate exponential distribution, which is presented in detail. The developed distribution function for the annual maximum is throughly analysed and a variety of distribution forms depending on the value of the correlation coefficient and the intensity in the Poisson process is hereby recognized. To a certain extent this might be considered as parallel to the scattering of hydrological regions with different generating mechanisms for the annual maxima.
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  • 3
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    Stochastic environmental research and risk assessment 1 (1987), S. 37-52 
    ISSN: 1436-3259
    Keywords: Cyclonic precipitation ; mathematical modeling ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A stochastic description is developed for extratropical cyclonic precipitation fields at synoptic and meso scales as they are typically observed by radars over the Earth. This description attempts to account I) for the synoptic scale behavior of a cyclonic storm (its birth, its synoptic scale motion trajectory, and its dissipation) II) for the synoptic-scale organizational structure of subsynoptic precipitation areas (rainbands, precipitation cores and raincells) within a cyclonic storm; and III) for the behavior of subsynoptic precipitation areas, in terms of their births, their spatial configuration evolutions, their motions, and their deaths (dissipation). The precipitation cores and the raincells are taken as the building blocks of the subsynoptic precipitation, areas within a cyclonic rainfield.
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  • 4
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    Stochastic environmental research and risk assessment 1 (1987), S. 81-100 
    ISSN: 1436-3259
    Keywords: Stochastic differential equations ; Itô calculus ; Stratovovich integrals ; Jump integrals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Fundamentals of the theory of stochastic calculus and stochastic differential equations (SDE's) which are finding increasing application in water resources engineering are reviewed. The basics of probability theory, mean square calculus and the Wiener, white Gaussian and compound Poisson processes are given in preparation for a discussion of the general Itô SDE with drift, diffusion and jump discontinuity terms driven by Gaussian white noise and compound Poissionian impulses. Also discussed are stochastic integration and the derivation of moment equations via the Itô differential rule. The lierature of SDE's is reviewed with an emphasis on the more accessible sources.
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  • 5
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    Stochastic environmental research and risk assessment 1 (1987), S. 53-66 
    ISSN: 1436-3259
    Keywords: Hurst range ; conditioned exchangeable, variables
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A new theoretical interpretation is proposed for Hurst's empirical law which is applicable to discrete-valued inflows and is consistent with the existing interpretation for continuous-valued inflows. This is applied to independent net inflows {X r} having values +1 and −1 with unequal probabilities. With the aid of a new result on the exchangeability of symmetrically conditioned exchangeable variables, values of the resulting range are obtained and tabulated. It is found that the effect of skewness is very slight for skewness values between (about) 3 and −3, and that Hurst's own approximation, the “conditioned range”, is remarkably accurate.
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  • 6
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    Stochastic environmental research and risk assessment 1 (1987), S. 67-80 
    ISSN: 1436-3259
    Keywords: pattern analysis ; mixed-mode data ; event-covering ; discretization ; hydrometric data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper presents a pattern analysis technique that has been successfully applied to a set of hydrometric network data collected in British Columbia, Canada. This technique can extract information from a set of observed heterogeneous multivariate data. The data are represented as n-tuples of mixed discrete and continuous values. The technique is capable of screening out statistically irrelevant information. It is also able to detect inherent subgroups in the data through adopting an event-covering approach. The subgroup characteristics represent important empirical understanding even though there may be considerable probabilistic variation within each individual subgroup.
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  • 7
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    Stochastic environmental research and risk assessment 1 (1987), S. 17-36 
    ISSN: 1436-3259
    Keywords: Stochastic hydrology ; multivariate analysis ; information extraction ; information transfer ; structure of time series ; time series analysis ; spatial characteristics ; simulation of processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A stochastic approach to the analysis of hydrologic processes is defined along with a discussion of causes of tendency, periodicity and stochasticity in hydrologic series. Sources of temporal non-stationarity are described along with objectives and methods of analysis of processes and, in general, of information extraction from data. Transferred information as measured by correlation coefficients is compared with the transferable information as measured by entropy coefficients. Various multivariate approaches to hydrologic stochastic modeling are classified in light of complexities of spatial/temporal hydrologic processes. Alternatives of time series structural decomposition and modeling are compared. A special approach to modeling of space properties further contributes to approximate simulations of spatial/temporal processes over large areas. Several aspects of stochastic models in hydrology are concisely reviewed.
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  • 8
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    Stochastic environmental research and risk assessment 1 (1987), S. 101-116 
    ISSN: 1436-3259
    Keywords: Soil moisture ; stochastic processes ; stochastic differential equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The dynamics of water within the unsaturated root zone of the soil are represented by a pair of stochastic differential equations (SDE's), one representing the so-called “surplus” state of the moisture and the other the “deficit” condition. The inputs to the model are the climatically controlled random infiltration events and evapotranspiration which are modeled as a compound Poisson process and a Wiener (Brownian motion) process, respectively. The solutions to these SDE's are not in “close-form” but sample functions are obtained by numerical integration. The moment properties of the soil moisture evolution process have also been derived analytically including the mean, variance, covariance and autocorrelation functions. To illustrate the model, climatic parameters representing the “surplus” and “deficit” cases and properties of clay loam soil have been used to numerically derived the corresponding sample functions. With proper selection of all the parameters, physically realistic sample trajectories can be obtained for the model.
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  • 9
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    Stochastic environmental research and risk assessment 1 (1987), S. 127-134 
    ISSN: 1436-3259
    Keywords: Upland erosion ; annual erosion losses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Point rainfall triggers the complex processes of overland flow and surface erosion. The probability density functions of rainfall duration and intensity are coupled with a physically based dynamic formulation of rainfall-runoff-sediment transport relationships for upland areas. When considering a single storm, rainfall depth alone is a poor predictor of sediment transport because of the dispersion introduced by the effect of rainfall intensity. On a long terms basis, however, the total amount of rainfall can be used to predict total erosion losses.
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  • 10
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    Stochastic environmental research and risk assessment 1 (1987), S. 117-126 
    ISSN: 1436-3259
    Keywords: equi-risk line ; detention pond ; urban runoff ; frequency analysis ; flood risk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The expression of equi-risk line derived by the authors represents the relationship between discharge capacityy 0 u and storage capacityz 0 u to keep flood frequency under a certain risk level represented by the return periodT, i.e.,z 0/z 0 u ={(y 0 u −y 0 u )/y 0 u } S , wherey 0 u andz 0 u areT-year probability peak discharge and total volume of a hydrograph. The shape parametersS is evaluated in this paper for various release rules of the storage facilities and correlations of durations and peaks of hydrographs. The expression forS is: $$S = S_\infty + (S_0 - S_\infty )\exp ( - \sqrt p )$$ , whereS 0 andS ∞ are the values ofS forp=0 and ∞, andp is the exponent of a general storage-release relation,q=az' p, wherea is the storage constant, andz' andq are the volume of stored water and the corresponding release. The values ofS 0 andS ∞ are expressed in terms of the correlation coefficient ρ of durations and peaks of inflow hydrographs.
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  • 11
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    Stochastic environmental research and risk assessment 1 (1987), S. 135-140 
    ISSN: 1436-3259
    Keywords: Upland erosion ; annual soil losses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Annual erosion losses from 135 experimental plots under a variety of soil types, vegetation cover densities and conservation practices in Iraq have been measured over a period of four years. The first three years of this data set demonstrate that annual erosion losses can be predicted from annual rainfall depths. The results obtained from regression analysis were then validated with the fourth year of soil erosion data. These results corroborate the theoretical findings of the companion paper in that long term erosion losses can be predicted from the total amount of rainfall.
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  • 12
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    Stochastic environmental research and risk assessment 1 (1987), S. 141-154 
    ISSN: 1436-3259
    Keywords: Contemporaneous ARMA models ; maximum likelihood estimation ; multivariate modelling ; stochastic hydrology ; time series analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In order to allow contemporaneous autoregressive moving average (CARMA) models to be properly applied to hydrological time series, important statistical properties of the CARMA family of models are developed. For calibrating the model parameters, efficient joint estimation procedures are investigated and compared to a set of uivariate estimation procedures. It is shown that joint estimation procedures improve the efficiency of the autoregressive and moving average parameter estimates, but no improvements are expected on the estimation of the mean vector and the variance covariance matrix of the model. The effects of the different estimation procedures on the asymptotic prediction error are also considered. Finally, hydrological applications demonstrate the usefulness of the CARMA models in the field of water resources.
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  • 13
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    Stochastic environmental research and risk assessment 1 (1987), S. 155-160 
    ISSN: 1436-3259
    Keywords: Gamma Markov ; estimation ; maximum likelihood estimates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The linearly regressive Gamma Markov sequence is being increasingly used as a model for geophysical phenomena, one of the reasons being that it is possible to determine the distribution of (weighted or otherwise) cumulative sums of such a sequence. In this paper we show briefly how to simulate such a sequence and its seasonal extension; we also show how to estimate its parameters. It is shown that the estimates obtained by the method of moments do not have a high efficiency, whereas those obtained by a modified maximum likelihood method have an efficiency close to unity.
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  • 14
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    Stochastic environmental research and risk assessment 1 (1987), S. 161-168 
    ISSN: 1436-3259
    Keywords: Inverse problem ; groundwater management ; groundwater response function ; stochastic control ; consistent parameter estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The response of groundwater basins to natural and anthropogenic inputs depends on many interrelated factors such as the values of groundwater flow and mass transport parameters. This work presents a theoretical analysis of the impact of parameter uncertainty on groundwater management decisions. It is shown that under classical, Bayesian, and deterministic assumptions about the parameter structure, the resulting management decisions could be very different. This underscores the importance of adopting the proper parameter structure and the need for using consistent methods to solve the inverse problem.
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  • 15
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    Stochastic environmental research and risk assessment 1 (1987), S. 185-198 
    ISSN: 1436-3259
    Keywords: Pattern matching ; tracking ; rainfall ; mesoscale ; radar
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper presents a new feature-based matching algorithm for tracking mesoscale precipitation phenomena in radar image sequences. Distinct rainfall areas are identified in each image and characterized by a feature vector of shape descriptors, which provide a mathematical representation of the spatial characteristics of each identified area. Rainfall areas observed in consecutive images are matched by comparing the relative values of the features. Two match scoring algorithms are developed to generate the initial estimates of correct matches, which are then updated by likelihood measures based on relative location. The method is applied to mesoscale rainfall areas observed in sequences of radar-derived images of rainfall activity over Southwestern Ontario during the summers of 1980 and 1981.
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  • 16
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    Stochastic environmental research and risk assessment 1 (1987), S. 199-208 
    ISSN: 1436-3259
    Keywords: Extreme value distribution ; two-component distribution ; maximum entropy principle ; parameter estimation ; regional estimation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The two component extreme value (TCEV) distribution has recently been shown to account for most of the characteristics of the real flood experience. A new method of parameter estimation for this distribution is derived using the principle of maximum entropy (POME). This method of parameter estimation is suitable for application in both the site-specific and regional cases and appears simpler than the maximum likelihood estimation method. Statistical properties of the regionalized estimation were evaluated using a Monte Carlo approach and compared with those of the maximum likelihood regional estimators.
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  • 17
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    Stochastic environmental research and risk assessment 1 (1987), S. 169-184 
    ISSN: 1436-3259
    Keywords: Stochastic control and programming ; real-time hydrologic forecasting ; reservoir theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A new approximate method of solution for stochastic optimal control problems with many state and control variables is introduced. The method is based on the expansion of the optimal control into the deterministic feedback control plus a caution term. The analytic, small-perturbation calculation of the caution term is at the heart of the new method. The developed approximation depends only on the first two statistical moments of the random inputs and up to the third derivatives of the cost functions. Its computational requirements do not exhibit the exponential growth exhibited by discrete stochastic DP and can be used as a suboptimal solution to problems for which application of stochastic DP is not feasible. The method is accurate when the cost-to-go functions are approximately cubic in a neighbourhood around the deterministic trajectory whose size depends on forecasting uncertainty. Furthermore, the method elucidates the stochastic optimization problem yielding insights which cannot be easily obtained from the numerical application of discrete DP.
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  • 18
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    Stochastic environmental research and risk assessment 1 (1987), S. 209-216 
    ISSN: 1436-3259
    Keywords: Transport ; sedimentation ; random walk ; Markov chain in continuous time ; distribution of maximum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A simple two-dimensional random walk model is developed for the motion of a particle in a fluid flow. Some earlier results for the persistent injection of particles into the flow are extended, and the distribution of the maximum number of particles in suspension over the period (0,t) is derived.
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  • 19
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    Stochastic environmental research and risk assessment 1 (1987), S. 217-240 
    ISSN: 1436-3259
    Keywords: Transport of fluid ; random network ; macro-permeability ; micro-geometry ; statistical mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper presents a detailed statistical analysis of Hagen-Poiseuille flow in plane random isotropic networks of interconnected channels. The emphasis is on statistico-geometrical features of networks that affect macroscopic permeability. It is shown that permeability of a network depends on its average co-ordination number, the first two moments of the channel length distribution and other explicitly identifiable geometrical features. Distributions of flow rates in channels and average flow rates are established by minimization of the rate of energy dissipation. Theoretical developments are interpreted in the context of classical statistical mechanics. Analytical results are illustrated and verified using numerical analysis of flow in a simulated random network.
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  • 20
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    Stochastic environmental research and risk assessment 1 (1987), S. 280-280 
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
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  • 21
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    Stochastic environmental research and risk assessment 1 (1987), S. 241-262 
    ISSN: 1436-3259
    Keywords: Martingale ; stochastic-convective ; stochastic-relativist ; spectral-integral ; perturbative ; statistical-mechanical
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The use of stochastic models in subsurface hydrology is growing at a logistic pace. To tie together a number of different stochastic methodologies for deriving subsurface transport equations, we have put together a brief review of some of the more common techniques. Our attention is confined to a few select methodologies so that we might delve in detail into assumptions required by the various approaches and their strengths and weaknesses. The methods reviewed include: Martingale, stochastic-convective, stochastic-relativist, spectral-integral, perturbative, statistical-mechanical, and generalized hydrodynamics. Within this list, we also have included a few stochastic methodologies which have been used solely to develop expressions for the dispersion tensor.
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  • 22
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    Stochastic environmental research and risk assessment 1 (1987), S. 297-302 
    ISSN: 1436-3259
    Keywords: Stochastic PDE ; Zakai equation ; nonlinear filtering ; distributed systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract We shall consider in this article a general class of stochastic PDE which in particular covers the Zakai equation of nonlinear filtering and natural formulations of distributed systems involving control variables. We use only fixed point arguments, hence we get uniqueness results. In the case of the Zakai equation, Galerkin approximations have been considered by Pardoux (1979) to derive the existence of the solution
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  • 23
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    Stochastic environmental research and risk assessment 1 (1987), S. 281-296 
    ISSN: 1436-3259
    Keywords: Stochastic groundwater flow ; semigroups ; random in time Gaussian process ; random physical parameters ; stochastic partial differential equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Two methods for the solution of partial differential equations (PDE) for the general case of random in time physical parameters are presented and their application to the solution of unsteady regional groundwater flow equations are illustrated. The first method is the semigroup approach which directly offers a solution without resorting to “closure approximations” (hierarchy techniques), perturbation techniques, or Montecarlo simulation techniques. The semigroup approach can also handle the general stochastic problem when randomness also appears as initial conditions, boundary conditions or forcing terms. The second method is an approximation scheme to obtain the semigroup solution in complex cases and permits the solution of equations with more than one random coefficient.
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  • 24
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    Stochastic environmental research and risk assessment 1 (1987), S. 303-318 
    ISSN: 1436-3259
    Keywords: Rainfall-runoff models ; forecasting ; unit hydrograph
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Here we review the main thrusts of rainfall-runoff modelling with an eye toward the advantageous use of the massive date sets being accumulated and the modern computers capable of dealing effectively with such sets. More than a tutorial, this study is aimed at providing a unifying structure for analyzing available techniques. The closing section draws attention to the existence of an alternative methodology.
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  • 25
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    Stochastic environmental research and risk assessment 1 (1987), S. 263-279 
    ISSN: 1436-3259
    Keywords: Porous media ; heterogeneity ; groundwater ; dispersion ; stochastic theory ; plume evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The migration of contaminants in heterogeneous aquifers involves dispersive processes that act at different scales. The interaction of these processes as a plume evolves can be studied by micro-scale modelling whereby two scales, a local- or micro-scale and an aquifer- or macro-scale, are covered simultaneously. Local-scale dispersive processes are represented through the local dispersion coefficient in the transport equation, while large-scale dispersion due to heterogeneities is represented through the resolution of the flow field and the diffusive exchange between streamtubes. The micro-scale model provides both the high degree of resolution compatible with local-scale processes, and the extent required for the approach to asymptotic conditions, using grids of up to a million nodal points. The model is based on the dual potential-streamfunction formulation for flow, and the transport problem is formulated in a natural coordinate system provided by the flownet. Simulations can be used to verify stochastic theories of dispersion, without the restrictive assumptions inherent in the theory. For the two-dimensional case, results indicate convergence of the effective dispersivity to the theoretical macrodispersivity value. Convergence takes place within a travel distance of about 50 correlation lengths of the hydraulic conductivity field. However, the approach taken to asymptotic conditions, as well as the macrodispersivity value, may differ for different realizations of the same medium. The influence of early-time events such as plume splitting on the asymptotic convergence remains to be investigated.
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  • 26
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    Stochastic environmental research and risk assessment 2 (1988), S. 17-33 
    ISSN: 1436-3259
    Keywords: River flow forecasting ; discrete linear cascade model ; ARMAX ; coupled models ; Kalman filtering ; Danube
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The objective of the paper is to compare three recursive linear state space models used to forecast river flow. The three models are as follows: (i) Purely deterministic discrete linear cascade model (DLCM); (ii) Purely stochastic autoregressive moving average (ARMAX) time series model; and (iii) Coupled deterministic (DLCM) — stochastic (ARMA) model. Description of DLCM is given shortly. The state space formulation of the ARMAX model enables the recursive estimation of random walk parameters and the forecast of flows by linear Kalman filtering. The correlated error sequence of DLCM is described by an ARMA model. The DLCM and ARMA models are put together in a coupled deterministic-stochastic model. The recursive conditional forecasting of the augmented state vector is performed by the linear Kalman-filter. The conditional output forecast is given by linear projection of thea priori state vector. Numerical investigations on River Danube data lead to the conclusion that the coupled deterministic-stochastic model is the most efficient forecasting model of all the three recursive techniques compared.
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  • 27
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    Stochastic environmental research and risk assessment 2 (1988), S. 61-72 
    ISSN: 1436-3259
    Keywords: Binary data ; censored observations ; autocorrelations ; acid rain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The properties of the well known estimator of the transition probabilities in a binary time series are investigated. A formula for the variance is obtained, which generally involves a double integral. However, in the case when the binary series is obtained by hard clipping of an AR(1) process, a good and fairly simple approximation is derived. In the MA(1) or MA(2) case exact formulae for the variance is given. In the appendix an excellent approximation to the fourth order cumulant of a clipped AR(1) process is derived, which may be of interest in other applications as well.
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  • 28
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    Stochastic environmental research and risk assessment 2 (1988), S. 175-188 
    ISSN: 1436-3259
    Keywords: Reservoir storage ; range ; adjusted range
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract It was remarked by Hurst in 1951 that the adjusted range gives the size of the smallest reservoir capable of providing a constant discharge equal to the mean inflow. Since that time this range and its rescaled modification, the Hurst range, have been widely discussed, not however primarily with a view to applying them to reservoir design problems, but rather on account of their possible relevance to the simulation of geophysical time series. Acknowledging the well-known conceptual weaknesses of adjusted ranges and the theoretical difficulties that inhibit their direct utilisation in the design and operation of real reservoirs, the authors argue that the interest displayed on ranges during the past few decades justifies the effort of eliminating one in particular of these weakness, namely their non-implementability as operating policies, a consequence of the fact that they can only be retrospectively evaluated. The paper proposes modifications in which the unknowable mean and standard deviation of future samples are replaced by the known mean and sample standard deviation of historical data, leading to the historically adjusted range and the historically rescaled and adjusted range. The latter is produced as an implementable approximation to Hurst's (1951) solution to the optimal reservoir problem. The expected values of the new ranges are evaluated and numerically tabulated.
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  • 29
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    Stochastic environmental research and risk assessment 2 (1988), S. 245-261 
    ISSN: 1436-3259
    Keywords: Geostatistics ; areal rainfall distribution ; areal reduction factor ; Gumbel distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Areal rainfall statistics are more relevant in flood hydrology and water resources management than point rainfall statistics when it comes to help designing dams or hydraulic structures. This paper presents a geostatistically based method to derive the areal statistics from point statistics. Assuming that the distribution models of point rainfall and areal belong to the same class of models and that the rainfall process is stationary, it is shown how the parameters of the areal distribution model can directly be computed from the parameters of the point distribution models in case of a non stationary process, an approximation is derived that yielded good results when applied to a mountainous region in Southern France. The method also allows the computation of the areal reduction factors in a very general form.
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    Stochastic environmental research and risk assessment 2 (1988), S. 303-315 
    ISSN: 1436-3259
    Keywords: Physically based stochastic models ; stochastic dynamic models ; statistical predictability ; internannual variability ; ARMA models ; water level variations
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Several physically based stochastic dynamic models (SDM) are described including year-to-year variations of water volume in terminal and non-terminal lakes, streamflow of lake-fed rivers, and salinity of an inland sea (the Sea of Azov). All of these models are based upon the SDM of water volume of terminal lakes developed by Kritzky and Menkel in 1946 in co-operation with Kolomogorov. Explicit formulae are derived for second order statistical moments of the output processes, including variance, correlation function, spectra, etc., under the assumption that the forcing functions from stationary random sequences. The least-squares prediction problem is solved for both stationary and non-stationary cases. Some of the processes are shown to possess high statistical predictability. Actual predictions are compared with independent observations. Problems for further study are stated.
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    Stochastic environmental research and risk assessment 3 (1989), S. 1-16 
    ISSN: 1436-3259
    Keywords: Width function ; instantaneous unit hydrograph ; peak ; regression ; birth-death process
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    Notes: Abstract We investigate optimal predictors of the peak (S) and distance to peak (T) of the width function of drainage networks under the assumption that the networks are topologically random with independent and exponentially distributed link lengths. Analytical results are derived using the fact that, under these assumptions, the width function is a homogeneous Markov birth-death process. In particular, exact expressions are derived for the asymptotic conditional expectations ofS andT given network magnitudeN and given mainstream lengthH. In addition, a simulation study is performed to examine various predictors ofS andT, includingN, H, and basin morphometric properties; non-asymptotic conditional expectations and variances are estimated. The best single predictor ofS isN, ofT isH, and of the scaled peak (S divided by the area under the width function) isH. Finally, expressions tested on a set of drainage basins from the state of Wyoming perform reasonably well in predictingS andT despite probable violations of the original assumptions.
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    Stochastic environmental research and risk assessment 3 (1989), S. 68-69 
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    Stochastic environmental research and risk assessment 3 (1989), S. 281-292 
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    Keywords: Generalised Pareto distribution ; Peaks over threshold ; Probability weighted moments ; Regionalisation
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    Notes: Abstract A peaks over threshold (POT) method of analysing daily rainfall values is developed using a Poisson process of occurrences and a generalised Pareto distribution (GPD) for the exceedances. The parameters of the GPD are estimated by the method of probability weighted moments (PWM) and a method of combining the individual estimates to define a regional curve is proposed.
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    Stochastic environmental research and risk assessment 2 (1988), S. 155-160 
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    Stochastic environmental research and risk assessment 2 (1988), S. 161-174 
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    Keywords: Floods ; estimation ; quantiles ; generalized gamma ; generalized moments ; standard error
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    Notes: Abstract The generalized gamma (GG) distribution has a density function that can take on many possible forms commonly encountered in hydrologic applications. This fact has led many authors to study the properties of the distribution and to propose various estimation techniques (method of moments, mixed moments, maximum likelihood etc.). We discuss some of the most important properties of this flexible distribution and present a flexible method of parameter estimation, called the “generalized method of moments” (GMM) which combines any three moments of the GG distribution. The main advantage of this general method is that it has many of the previously proposed methods of estimation as special cases. We also give a general formula for the variance of theT-year eventX T obtained by the GMM along with a general formula for the parameter estimates and also for the covariances and correlation coefficients between any pair of such estimates. By applying the GMM and carefully choosing the order of the moments that are used in the estimation one can significantly reduce the variance ofT-year events for the range of return periods that are of interest.
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    Stochastic environmental research and risk assessment 2 (1988), S. 239-244 
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    Stochastic environmental research and risk assessment 2 (1988), S. 201-212 
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    Keywords: Flood risk ; flood frequency analysis ; generalised extreme value distributions
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    Notes: Abstract Conventional flood frequency analysis is concerned with providing an unbiased estimate of the magnitude of the design flow exceeded with the probabilityp, but sampling uncertainties imply that such estimates will, on average, be exceeded more frequently. An alternative approach is therefore, to derive an estimator which gives an unbiased estimate of flow risk: the difference between the two magnitudes reflects uncertainties in parameter estimation. An empirical procedure has been developed to estimate the mean true exceedance probabilities of conventional estimates made using a GEV distribution fitted by probability weighted moments, and adjustment factors have been determined to enable the estimation of flood magnitudes exceeded with, on average, the desired probability.
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    Stochastic environmental research and risk assessment 2 (1988), S. 263-279 
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    Keywords: Cyclonic rain fields ; cyclone center behavior ; stochastic model
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    Notes: Abstract Earlier the authors have developed a stochastic geometric model for extratropical cyclonic precipitation fields at synoptic and meso scales as they are typically observed by weather radars over the mainland U S A (see Kavvas and Puri 1983; Kavvas et al. 1987). Here the earlier mathematical development of the model is further extended by incorporating the stochastic description of cyclone center births and their evolutions over U S A into the model.
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    Stochastic environmental research and risk assessment 2 (1988), S. 315-316 
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    Stochastic environmental research and risk assessment 3 (1989), S. 31-49 
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    Keywords: Reservoir operation ; prediction ; Kalman filtering ; flood prevention ; fuzzy control
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    Notes: Abstract Japan has traditionally performed flood prevention through the construction and use of dikes, storage reservoirs, and basins which are costly and time consuming options. Another non-structural option is to operate the flood control system appropriately with a view to reducing flood damage. In this paper, a flood control system combining the runoff prediction model in the whole river basin with the reservoir operation is discussed. Different models of the runoff process are introduced in order to compare their accuracies and the computational time for the flood forecasting system. The reservoir operational rule is formulated in terms of fuzzy inference theory. Historical data are applied in a case study for verification of the proposed theories.
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    Stochastic environmental research and risk assessment 3 (1989), S. 69-69 
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    Stochastic environmental research and risk assessment 3 (1989), S. 154-154 
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    Stochastic environmental research and risk assessment 3 (1989), S. 155-178 
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    Keywords: Stochastic differential equations ; Stochastic Taylor formula ; Numerical methods ; Simulations ; Strong convergence ; Weak convergence
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    Notes: Abstract The development of numerical methods for stochastic differential equations has intensified over the past decade. The earliest methods were usually heuristic adaptations of deterministic methods, but were found to have limited accuracy regardless of the order of the original scheme. A stochastic counterpart of the Taylor formula now provides a framework for the systematic investigation of numerical methods for stochastic differential equations. It suggests numerical schemes, which involve multiple stochastic integrals, of higher order of convergence. We shall survey the literature on these and on the earlier schemes in this paper. Our discussion will focus on diffusion processes, but we shall also indicate the extensions needed to handle processes with jump components. In particular, we shall classify the schemes according to strong or weak convergence criteria, depending on whether the approximation of the sample paths or of the probability distribution is of main interest.
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    Stochastic environmental research and risk assessment 3 (1989), S. 217-226 
    ISSN: 1436-3259
    Keywords: Stochastic integral equation method ; rainfall-runoff models ; confidence interval
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    Notes: Abstract The stochastic integral equation method (S.I.E.M.) is used to evaluate the relative performance of a set of both calibrated and uncalibrated rainfall-runoff models with respect to prediction errors. The S.I.E.M. is also used to estimate confidence (prediction) interval values of a runoff criterion variable, given a prescribed rainfall-runoff model, and a similarity measure used to condition the storms that are utilized for model calibration purposes. Because of the increasing attention given to the issue of uncertainty in rainfall-runoff modeling estimates, the S.I.E.M. provides a promising tool for the hydrologist to consider in both research and design.
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    Stochastic environmental research and risk assessment 3 (1989), S. 241-260 
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    Keywords: Hat matrix ; Mahalanobis distance ; Additive outliers ; Innovation outliers ; Influential data ; Autoregressive models ; Threshold autoregression ; Lake Huron
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    Notes: Abstract A practical method is developed for outlier detection in autoregressive modelling. It has the interpretation of a Mahalanobis distance function and requires minimal additional computation once a model is fitted. It can be of use to detect both innovation outliers and additive outliers. Both simulated data and real data re used for illustration, including one data set from water resources.
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    Stochastic environmental research and risk assessment 3 (1989), S. 293-316 
    ISSN: 1436-3259
    Keywords: Confined aquifer ; Transmissivity identification ; Geostatistics ; Inverse problem ; Ill-posedness ; Ill-conditioning ; Stability analysis ; Regularization
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    Notes: Abstract In recent years, geostatistical concepts have been applied to the inverse problem of transmissivity estimation from piezometric head data. It has been claimed that such methods overcome various difficulties encountered in other approaches. However, the reconstruction of transmissivity from head measurements is ill-posed as it depends on derivatives of the head field. Consequently, any accurate method for its solution is likely to encounter numerically ill-conditioned systems. This paper reviews the geostatistical approach, and uses the stability analyses of linear algebra to show that, as the amount of available data increases and the discretization of the system is refined, both a numerically ill-conditioned parameter estimation problem and ill-conditioned cokriging equations may appear. Therefore, while the geostatistical approach does have conceptual appeal, it does not avoid the fundamental difficulties arising out of the ill-posed nature of transmissivity identification. Instead, the method is likely to be quite sensitive to these difficulties, so care must be taken in its formulation to minimize their effects. A means to stabilize the geostatistical method is suggested and numerical experiments that highlight key points of our analysis are given.
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    Stochastic environmental research and risk assessment 2 (1988), S. 34-34 
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    Stochastic environmental research and risk assessment 3 (1989), S. 85-96 
    ISSN: 1436-3259
    Keywords: Stochastic equations ; irregularly spaced observations ; prediction, interpolation ; random fields
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    Notes: Abstract The steady state two dimensional groundwater flow equation with constant transmissivities was studied by Whittle in 1954 as a stochastic Laplace equation. He showed that the correlation function consisted of a modified Bessel function of the second kind, order 1, multiplied by its argument. This paper uses this pioneering work of Whittle to fit an aquifer head field to unequally spaced observations by maximum likelihood. Observational error is also included in the model. Both the isotropic and anisotropic cases are considered. The fitted field is then calculated on a two dimensional grid together with its standard deviation. The method is closely related to the use of two-dimensional splines for fitting surfaces to irregularly spaced observations.
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    Stochastic environmental research and risk assessment 3 (1989), S. 71-84 
    ISSN: 1436-3259
    Keywords: Hydraulics ; quasilinearization ; simulation ; stochastic ; estuarine system ; Monte Carlo methods ; random differential equations ; parameter uncertainty
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    Notes: Abstract A new methodology is presented for the solution of the stochastic hydraulic equations characterizing steady, one-dimensional estuarine flow. The methodology is predicated on quasi-linearization, perturbation methods, and the finite difference approximation of the stochastic differential operators. Assuming Manning's roughness coefficient is the principal source of uncertainty in the model, stochastic equations are presented for the water depths and flow rates in the estuarine system. Moment equations are developed for the mean and variance of the water depths. The moment equations are compared with the results of Monte Carlo simulation experiments. The results confirm that for any spatial location in the estuary that (1) as the uncertainty in the channel roughness increases, the uncertainty in mean depth increases, and (2) the predicted mean depth will decrease with increasing uncertainty in Manning'sn. The quasi-analytical approach requires significantly less computer time than Monte Carlo simulations and provides explicit
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    Stochastic environmental research and risk assessment 3 (1989), S. 135-153 
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    Keywords: Stochastic partial differential equations ; maximum likelihood estimation ; parameter estimation ; moment equations ; stodhastic contaminant transport
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    Notes: Abstract Many problems in hydraulics and hydrology are described by linear, time dependent partial differential equations, linearity being, of course, an assumption based on necessity. Solutions to such equations have been obtained in the past based purely on deterministic consideration. The derivation of such a solution requires that the initial conditions, the boundary conditions, and the parameters contained within the equations be stipulated in exact terms. It is obvious that the solution so derived is a function of these specified, values. There are at least four ways in which randomness enters the problem. i) the random initial value problem; ii) the random boundary value problem; iii) the random forcing problem when the non-homogeneous part becomes random and iv) the random parameter problem. Such randomness is inherent in the environment surrounding the system, the environment being endowed with a large number of degrees of freedom. This paper considers the problem of groundwater flow in a phreatic aquifer fed by rainfall. The goveming equations are linear second order partial differential equations. Explicit form solutions to this randomly forced equation have been derived in well defined regular boundaries. The paper also provides a derivation of low order moment equations. It contains a discussion on the parameter estimation problem for stochastic partial differential equations.
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    Stochastic environmental research and risk assessment 3 (1989), S. 179-190 
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    Keywords: Groundwater ; Stochastic ; Monte Carlo simulation ; First order Taylor series approximation
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    Notes: Abstract The expected head and standard deviation of the head from the first order Taylor series approximation is compared to Monte Carlo simulation, for steady flow in a confined aquifer with transmissivity as a random variable. Emphasis is on the effect of changes in the covariance structure of the transmissivity, and pumping rates, on the errors in the first order Taylor series approximation. The accuracy of the first order Taylor series approximation is found to be particularly sensitive to pumping rates. With significant pumping the approximation is found to under estimate both the expected drawdown and head variance, and the error increases as the pumping rate increases. This can lead to large errors in probability constraints based on moments from the first order Taylor series approximation.
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    Stochastic environmental research and risk assessment 3 (1989), S. 227-240 
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    Keywords: Kalman filter ; Maximum likelihood estimation ; Periodic models ; Stochastic hydrology ; Time series analysis
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    Notes: Abstract An exact maximum likelihood procedure is presented for estimating the parameters of a periodic autogressive-moving average (PARMA) model. To develop an estimator which is both statistically and computationally efficient, the PARMA class of models is written using a state-space representation and a Kalman filtering algorithm is used to estimate the parameters. In order to demonstrate how to fit PARMA models in practice, the most appropriate types of PARMA models are identified for fitting to two average monthly riverflow time series and the new estimator is employed for estimating the model parameters.
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    Stochastic environmental research and risk assessment 2 (1988), S. 51-59 
    ISSN: 1436-3259
    Keywords: Soil moisture ; stochastic modelling ; shot noise models ; infiltrated rainfall ; evapotranspiration ; water balance ; root zone
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    Notes: Abstract An attempt is made to estimate the expected contribution of rainfall to soil moisture during the irrigation season. Effective rainfall and evapotranspiration are the parameters considered in the water balance carried out in the root zone. Rainfall occurrence is simulated by a Poisson process whereas evapotranspiration is described by a simple deterministic function of potential evapotranspiration and soil moisture in the root zone. Using the theory of shot noise models a closed form solution is derived from the expected soil moisture in the root zone at the end of the time interval (0,t]. For illustration purposes the proposed model is applied to a series of data from Mikra meteorological station in Greece.
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    Stochastic environmental research and risk assessment 2 (1988), S. 35-50 
    ISSN: 1436-3259
    Keywords: Stochastic models ; spectral analysis
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    Notes: Abstract Autoregressive (AR) and Autoregressive-moving average (ARMA) methods of spectral analysis have been developed and are being increasingly used as alternatives to traditional methods of spectral analysis. Two of these methods developed by Marple and Friedlander are tested in this study by using generated data from models with known spectra. The Blackman-Tukey spectral estimates are also compared to the Marple and Friedlander estimates. The variability of the Marple and Friedlander estimates with sample sizes is investigated. Although both Marple's and Friedlander's methods are satisfactory, Friedlander's method is preferred because of its ability to handle a wider class of models.
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    Stochastic environmental research and risk assessment 2 (1988), S. 73-78 
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    Keywords: Instantaneous unit hydrograph ; channel networks ; linear channel routing ; topological randomness
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    Notes: Abstract The instantaneous unit hydrograph for a channel network under general linear routing and conditioned on the network magnitude,N, tends asymptotically, asN grows large, to a Rayleigh probability density function. This behavior is identical to that of the width function of the network, and is proven under the assumption that the network link configuration is topologically random and the link hydraulic and geometric properties are independent and identically distributed random variables. The asymptotic distribution depends only on a scale factor, $$\xi \sqrt n$$ , where ξ is a mean link wave travel time.
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    Stochastic environmental research and risk assessment 2 (1988), S. 113-136 
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    Keywords: spatial statistics ; hydrogeologic mapping ; trend analysis ; groundwater hydrology
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    Notes: Abstract The properties of linear spatial interpolators of single realizations and trend components of regionalized variables are examined in this work. In the case of the single realization estimator explicit and exact expressions for the weighting vector and the variances of estimator and estimation error were obtained from a closed-form expression for the inverse of the Lagrangian matrix. The properties of the trend estimator followed directly from the Gauss-Markoff theorem. It was shown that the single realization estimator can be decomposed into two mutually orthogonal random functions of the data, one of which is the trend estimator. The implementation of liear spatial estimation was illustrated with three different methods, i.e., full information maximum likelihood (FIML), restricted maximum likelihood (RML), and Rao's minimum norm invariant quadratic unbiased estimation (MINQUE) for the single realization case and via generalized least squares (GLS) for the trend. The case study involved large correlation length-scale in the covariance of specific yield producing a nested covariance structure that was nearly positive semidefinite. The sensitivity of model parameters, i.e., drift and variance components (local and structured) to the correlation length-scale, choice of covariance model (i.e., exponential and spherical), and estimation method was examined. the same type of sensitivity analysis was conducted for the spatial interpolators. It is interesting that for this case study, characterized by a large correlation length-scale of about 50 mi (80 km), both parameter estimates and linear spatial interpolators were rather insensitive to the choice of covariance model and estimation method within the range of credible values obtained for the correlation length-scale, i.e., 40–60 mi (64–96 km), with alternative estimates falling within ±5% of each other.
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    Stochastic environmental research and risk assessment 2 (1988), S. 189-200 
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    Keywords: Point process ; rainfall model ; renewal Cox process
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    Notes: Abstract A probabilistic model for the temporal description of daily rainfall at a fixed point is presented. The model is a member of the family of point process models. Model development is based on statistics estimated from rainfall data in Lebanon. Scale considerations for Markovian models and a theory of projection are used to determine the continuous process of alternation between dry and wet periods. The wet spells are defined by a number of storms each of which is associated with a storm depthY i and an interstorm time intervalT i. Computational results are presented for data from Lebanon. The model is successful in preserving the structure of the occurrence process, as well as the distributional properties of the rainfall amount.
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    Stochastic environmental research and risk assessment 2 (1988), S. 213-239 
    ISSN: 1436-3259
    Keywords: Unit hydrograph ; effective rainfall ; linear routing ; link-node model ; probabilistic model
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    Notes: Abstract The design storm approach, where the subject criterion variable is evaluated by using a synthetic storm pattern composed of identical return frequencies of storm pattern input, is shown to be an effective approximation to a considerably more complex probabilistic model. The single area unit hydrograph technique is shown to be an accurate mathematical model of a highly discretized catchment with linear routing for channel flow approximation, and effective rainfalls in subareas which are linear with respect to effective rainfall output for a selected “loss” function. The use of a simple “loss” function which directly equates to the distribution of rainfall depth-duration statistics (such as a constant fraction of rainfall, or a ϕ-index model) is shown to allow the pooling of data and thereby provide a higher level of statistical significance (in estimating T-year outputs for a hydrologic criterion variable) than use of an arbitrary “loss” function. The above design storm unit hydrograph approach is shown to provide the T-year estimate of a criterion variable when using rainfall data to estimate runoff.
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    Stochastic environmental research and risk assessment 2 (1988), S. 295-302 
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    Keywords: Nonlinear structures ; skewed distribution ; Markov chain ; annual data
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    Notes: Abstract Nonlinear serial dependence and skewness of annual hydrologic time series {X t } have been challenging the classical theory of Gaussian stochastic processes, particularly if the study of extremes (dry or wet years) is required as it is often the case. In this paper, a new and general model is proposed assuming that the geophysical system which is responsible forX t can take different states and that this state process is modeled by a Markov chain. At each time,X t is generated from a statistical distribution which depends on the state that has occurred. This model can preserve non-linear structures of serial dependence and it can produce a skewed marginal distribution ofX t without any transformation. A successful application of this model to the study of annual rainfall at Fortaleza (Northeast of Brazil) is also presented.
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    Stochastic environmental research and risk assessment 2 (1988), S. 281-294 
    ISSN: 1436-3259
    Keywords: precipitation field ; stochastic time-space evolution ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The time-space evolution of an extratropical cyclonic precipitation field over U S A is simulated in a stochastic setting as outlined in Kavvas et al. (1988). The birth of a cyclonic storm is characterized by the simultaneous birth of a cyclone center and births of subsynoptic precipitation areas (SPA) at preferred locations around the cyclone center. The precipitation cores and cells which are used as the fundamental building blocks of the SPAs are approximated by circular precipitation areas (CPA) of different sizes. The time space evolution of the precipitation field after the birth is governed by (1) the movement of the synoptic cyclone described by the cyclone center trajectory, (2) independent nonidentically distributed random velocities of the individual CPAs relative to the cyclone center, (3) the births of new CPAs in time and space relative to the cyclone center, (4) the independent evolution in time of the individual spatially uniform intensities of the existing CPAs, (5) the expansion and shrinkage of the existing CPAs in the course of movement and (6) the dissipation (death) of a random number of existing CPAs within the cyclonic system. The computer simulation, the results of which are presented in this paper, successfully reproduced the general mesoscale and synoptic scale features of the radar detected cyclonic rain fields as observed by Austin and Houze (1972), Houze et al. (1976), Hobbs (1978), Hobbs and Locatelli (1978), Houze (1981), Houze and Hobbs (1982) and others.
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    Stochastic environmental research and risk assessment 3 (1989), S. 17-29 
    ISSN: 1436-3259
    Keywords: Stochastic optimization ; linear programming ; simplex method ; Karmarkar's method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Optimization of multi-reservoir systems operations is typically a very large scale optimization problem. The following are the three types of optimization problems solved using linear programming (LP): (i) deterministic optimization for multiple periods involving fine stage intervals, for example, from an hour to a week (ii) implicit stochastic optimization using multiple years of inflow data, and (iii) explicit stochastic optimization using probability distributions of inflow data. Until recently, the revised simplex method has been the most efficient solution method available for solving large scale LP problems. In this paper, we show that an implementation of the Karmarkar's interior-point LP algorithm with a newly developed stopping criterion solves optimization problems of large multi-reservoir operations more efficiently than the simplex method. For example, using a Micro VAX II minicomputer, a 40 year, monthly stage, two-reservoir system optimization problem is solved 7.8 times faster than the advanced simplex code in MINOS 5.0. The advantage of this method is expected to be greater as the size of the problem grows from two reservoirs to multiples of reservoirs. This paper presents the details of the implementation and testing and in addition, some other features of the Karmarkar's algorithm which makes it a valuable optimization tool are illuminated.
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    Stochastic environmental research and risk assessment 3 (1989), S. 51-67 
    ISSN: 1436-3259
    Keywords: Spatial rainfall estimation ; kriging ; ordinary co-kriging ; disjunctive co-kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The feasibility of linear and nonlinear geostatistical estimation techniques for optimal merging of rainfall data from raingage and radar observations is investigated in this study by use of controlled numerical experiments. Synthetic radar and raingage data are generated with their hypothetical error structures that explicitly account for sampling characteristics of the two sensors. Numerically simulated rainfall fields considered to be ground-truth fields on 4×4 km grids are used in the generation of radar and raingage observations. Ground-truth rainfall fields consist of generated rainfall fields with various climatic characteristics that preserve the space-time covariance function of rainfall events in extratropical cyclonic storms. Optimal mean areal precipitation estimates are obtained based on the minimum variance, unbiased property of kriging techniques under the second order homogeneity assumption of rainfall fields. The evaluation of estimated rainfall fields is done based on the refinement of spatial predictability over what would be provided from each sensor individually. Attention is mainly given to removal of measurement error and bias that are synthetically introduced to radar measurements. The influence of raingage network density on estimated rainfall fields is also examined.
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  • 63
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    Stochastic environmental research and risk assessment 3 (1989), S. 97-110 
    ISSN: 1436-3259
    Keywords: ARMA processes ; fractionally differencedARMA processes ; long memory ; spectral density ; maximum likelihood estimates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A class of regression type estimators of the parameterd in a fractionally differencedARMA (p, q) process is introduced. This class is an extension of the estimator considered by Geweke and Porter-Hudak. In a simulation study, we compared three estimators from this class together with two approximate maximum likelihood estimators which are based on two separate approximations to the likelihood. One approximation ignores the determinant term in the likelihood and the other includes a compensating factor for the determinant. When the determinant term is included, the estimate tends to be much less biased and is in general superior to the other estimate. The approximate maximum likelihood estimator out performed, by a large margin, the regression type estimators for pureARIMA (0,d,0) processes. However, forARIMA (1,d,1) processes, a regression type estimator turned out to be the best for realizations of length 400 in 3 out of the 5 cases we tried.
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  • 64
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    Stochastic environmental research and risk assessment 3 (1989), S. 111-133 
    ISSN: 1436-3259
    Keywords: Rainfall-runoff models ; random channel network ; regionalization ; flood frequency ; instanteous unit hydrograph
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A rainfall-runoff model is used in conjunction with a probabilistic description of the input to this model to obtain simple regression-like relations for basin runoff in terms of basin and storm characteristics. These relations, similar to those sought in regionalization studies, are computed by evaluating the conditional distribution of model output given basin and storm characteristics. This method of conditioning provides a general way of examining model sensitivity to various components of model input. The resulting relations may be expected to resemble corresponding relations obtained by regionalization using actual runoff to the extent that the rainfall-runoff model and the model input specification are physically realistic. The probabilistic description of model input is an extension of so-called “random-model” of channel networks and involves postulating an ensemble of basins and associated probability distributions that mimic the variability of basin characteristics seen in nature. Application is made to small basins in the State of Wyoming. Parameters of the input variable distribution are estimated using data from Wyoming, and basin-scale relations are estimated both, parametrically and nonparametrically using model-generated runoff from simulated basins. Resulting basin-scale relations involving annual flood quantiles are in reasonable agreement with those presented in a previous regionalization study, but error estimates are smaller than those in the previous study, an artifact of the simplicity of the rainfall-runoff model used in this paper. We also obtain relations for peak of the instantaneous unit hydrograph which agree fairly well with theoretical relations given in the literature. Finally, we explore the issues of sensitivity of basin-scale, relations and error estimates to parameterization of the model input probability distribution and of how this sensitivity is related to making inferences about a particular ungaged basin.
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    Stochastic environmental research and risk assessment 3 (1989), S. 191-202 
    ISSN: 1436-3259
    Keywords: Random variable ; Distribution ; Estimation ; Probability analysis ; Cross-entropy ; Fractile constraints ; Flood
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The cross-entropy method with fractile constraints has been developed to estimate a random variable when the data are a set of independent observations of the variable. The method can claim several advantages over existing methods. It uses a reference distribution like the prior distribution in Bayesian analysis and likewise generates a posterior distribution. The method is of interest, in particular, because it satisfies two fundamental requirements for selfconsistency in the analysis of a probabilistic system based on data: a principle of invariance and a principle of data monotonicity. The method is applied to flood analysis. Robustness of the minimum cross-entropy method is compared with other methods: the methods of moments and the maximum likehood.
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    Stochastic environmental research and risk assessment 3 (1989), S. 203-216 
    ISSN: 1436-3259
    Keywords: Cloud seeding ; Rainfall enhancement ; Regression
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A comparison is carried out between historical records of the flow measured in Kinneret watershed during and prior to the time of cloud seeding for rainfall enhancement. Precipitation series for the control area of the meteorological experimentation serve as a reference for the comparison. The fluctuations of the flow, which would have occurred unless the effect of the seeding, are estimated by a linear regression on the precipitation as the control. The regression parameters are calibrated separately for the unseeded and for the seeded time series. The model with the parameters calibrated for the unseeded series is applied on the rainfall recorded during the seeded time, and vice versa. The difference between the measured and the computed data is attributed to the effect of cloud seeding. Similar comparisons are carried out with respect to rainfall series recorded at the target area and at the edge of the enhanced area. The results indicate that the flow from the affected sector of the watershed has been enhanced, with respect to the control, by 31×106 m 3/year, at a significance level of 31. This enhancement is 5% of the volume which is generated in that area. The rates found with respect to the rainfall at the edge are higher than those found with respect to the control, while those with respect to the rainfall at the center of the target area are lower.
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    Stochastic environmental research and risk assessment 3 (1989), S. 261-280 
    ISSN: 1436-3259
    Keywords: Rain fields ; time-space arrivals ; stochastic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Rainfall in time at any ground location can be described by the rain intensity distribution over the subtrajectories which are drawn by the ground location point on the radar-detected incremental rain fields (IRFs) that pass over this location. Based on this conceptualization, this study develops a stochastic description of the arrivals of IRF subtrajectories (SIRFs) onto any given set of ground locations over a geographical region. The arrivals of SIRFs is described by a multivariate doubly stochastic Poisson process, excited by the time-space arrival process of IRFs onto the designated geographical region. The arrival process of IRFs is described by a 3-level time-space nonhomogeneous Poisson cluster model. At the primary level of this model are the arrivals of synoptic cyclonic systems; at the secondary level are the arrivals of large mesoscale rain areas (LMSAs) and at the tertiary level are the arrivals of IRFs onto the designated geographical region, all detected by the weather radar. The models are substantiated both by the graphical analysis of rain fields, as detected on a radar scope, and by the statistical analysis of the arrivals data at all of the four levels at three different ground locations over a rectangular geographical region in Northern Kentucky. It is pointed out that a doubly stochastic Poisson process is basically a Poisson cluster process. Hence, the final process of SIRF arrivals onto any ground location may be interpreted as a 4-level Poisson cluster process. Finally, heavy tails in the sample covariance density functions of the IRF and SIRF arrivals are detected. This study shows that the appropriate incorporation of clustering at all observable distinct scales of the rain fields models the heavy tail behavior of the covariance density adequately.
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    Stochastic environmental research and risk assessment 2 (1988), S. 1-16 
    ISSN: 1436-3259
    Keywords: Daily rainfall occurrences ; wet and dry sequences length ; distribution of the number of wet days in ℓ-day intervals ; Pascal distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A model for the periodic (annual cycle), discrete rainfall occurrence process is presented. Using this model the probabilistic properties of the process in ℓ-day intervals can be investigated. In such an interval the rainfall occurrence process is approximated by some stationary processa t ,t∃IN. The processa t ,t∃IN is described by the distributions of the lengths of wet and dry sequences. It is assumed that the lengths of successive wet and dry sequences are independent. For this process the distribution of the number of wet days in ℓ-day intervals is calculated. The model is fitted to 50-year rainfall data from Wroclaw, Poland. Rainfall amounts of 0.1, 1.0 and 2.0 mm are considered as thresholds defining a wet day. To estimate the distribution of the length of wet and dry sequences the family of Pascal distribution is chosen.
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    Stochastic environmental research and risk assessment 2 (1988), S. 79-97 
    ISSN: 1436-3259
    Keywords: Stochastic groundwater transport ; semigroups ; stochastic partial differential equations
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This series of articles present general applications of functional-analytic theory to the solution of the partial differential equation describing solid transport in aquifers, when either the evolution of the system, the sources, the parameters and/or the boundary conditions are prescribed as stochastic processes in time or in space. This procedure does not require the restricting assumptions placed upon the current particular solutions on which today's stochastic transport theory is based, such as “small randomness” assumptions (perturbation techniques), Montecarlo simulations, restriction to small spatial stochasticity in the hydraulic conductivity, use of spectral analysis techniques, restriction to asymptotic steady state conditions, and restriction to variance of the concentration as the only model output among others. Functional analysis provides a rigorous tool in which the concentration stochastic properties can be predicted in a natural way based upon the known stochastic properties of the sources, the parameters and/or the boundary conditions. Thus the theory satisfies a more general modeling need by providing, if desired, a systematic global information on the sample functions, the mean, the variance, correlation functions or higher-order moments based on similar information of any “size”, anywhere, of the input functions. Part I of this series of articles presents the main relevant results of functional-analytic theory and individual cases of applications to the solution of distributed sources problems, with time as well as spatial stochasticity, and the solution subject to stochastic boundary conditions. It was found that the stochastically-forced equation may be a promising model for a variety of random source problems. When the differential equation is perturbed by a time and space stochastic process, the output is also a time and space stochastic process, in contrast with most of the existing solutions which ignore the temporal component. Stochastic boundary conditions seems to quickly dissipate as time increases.
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    Stochastic environmental research and risk assessment 2 (1988), S. 99-112 
    ISSN: 1436-3259
    Keywords: Stochastic groundwater transport ; random dispersion coefficient ; semigroups ; stochastic partial differential equations
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This series of articles present general applications of functional-analytic theory to the solution of the partial differential equation describing solid transport in aquifers, when either the evolution of the system, the sources, the parameters and/or the boundary conditions are prescribed as stochastic processes in time or in space. Part II of these series of articles completes the developments of part I by first presenting the semigroup solution of the randomly-forced three-dimensional advective-dispersive equation, and then introducing the semigroup solution for the particular case when the dispersion coefficient or the groundwater velocity are defined as stochastic processes in time or in space. As an illustration, the solution of the advective-dispersive equation subject to a time-stochastic dispersion coefficient is shown in detail. This new solution demonstrates that the time stochasticity in the dispersion coefficient may explain the uncertainly in the concentration distribution.
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    Stochastic environmental research and risk assessment 2 (1988), S. 137-150 
    ISSN: 1436-3259
    Keywords: shallow water equations ; Kalman filtering ; data assimilation ; observability
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    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Kalman filtering for stochastic dynamic tidal models, is a hyperbolic filtering problem. The questions of observability and stability of the filter as well as the effects of the finite difference approximation on the filter performance are studied. The degradation of the performance of the filter, in case an erroneous filter model is used, is investigated. In this paper we discuss these various practical aspects of the application of Kalman filtering for tidal flow identification problems. Filters are derived on the basis of the linear shallow water equations. Analytical methods are used to study the performance of the filters under a variety of circumstances.
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    Stochastic environmental research and risk assessment 2 (1988), S. 151-155 
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    Journal of chemical crystallography 18 (1988), S. I 
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    Journal of chemical crystallography 18 (1988), S. 651-658 
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    Notes: Abstract Acis-Pt(creat)2(NO2)2 complex was synthesized stereoselectively in a high yield (65%) and characterized by IR spectral and X-ray diffraction analysis. Crystal data: Pt(C4H7N3O)2(NO2)2,M r=767.55, monoclinic, space groupP21/n,a=9.736(1),b=13.433(1),c=12.098(1) Å,β=110.55(1)°,V c=1482(1) Å3,Z=2,D x=3.441 g cm−3,λ(MoKα)=0.71073 Å,μ=97.0 cm−1,F(000)=1504,T=292 K,R=0.026 andR w=0.028 for 2061 observed reflections with I〉2σ(I). The structure consists of Pt(creat)2(NO2)2 molecules disposed in general positions and joined by N-H⋯O and N-H⋯N hydrogen bonds. The platinum atom has square-planar PtN4 coordination of twocis disposed pairs of nitro [Pt-Nav 2.023(7) Å] and creatinine [Pt-N(endo)av 1.991(8) Å] ligands. The creatinine moieties are planar and tilted to the equatorial plane by ~80°.
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    Notes: Abstract The crystal structure of ammonium difluorooxodiperoxomolybdate(VI), (NH4)2[MoF2O(O2)2], has been determined by single-crystal X-ray diffraction methods. The yellow compound crystallizes in the triclinic space groupP¯1 witha=7.752(2),b=7.498(3),c=6.066(2) Å,α=86.37(3),β=109.60(3),γ=94.45(3)°, andZ=2. A total of 3857 reflexion intensities was recorded on a SyntexP21 diffractometer using MoKα radiation at room temperature. The structure was solved by the Patterson method and successive electron density calculations. Full-matrix least-squares refinement yielded a finalR value of 0.027 for 3729 observed [I〉3σ(I)] reflexions. In the complex anion molybdenum is surrounded by a pentagonal-bipyramidal arrangement of ligand atoms. Two side-on bonded peroxo groups and a fluorine atom form the equatorial plane and one fluorine atom and a double-bonded oxygen atom occupy the apical positions. The molybdenum atom is displaced 0.311(1) Å from the equatorial plane in the direction of the double-bonded oxygen atom. Bond distances: Mo-Operoxo 1.931(2)-1.976(2) Å, Mo=Oapical 1.688(2) Å, Mo-Fequatorial 1.979 (1) Å, Mo-Fapical 2.199(1) Å and (O-O)peroxo 1.474(2)-1.480(2) Å.
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    Notes: Abstract N,N′-diphenyl-N-(2-pyridinyl)urea hemihydrate (C18H15N3O·1/2H2O) has been studied by crystallographic and NMR-spectroscopic methods. The crystals are monoclinic,I2/a with unit-cell parameters at 86K,a=17.820(1),b=14.857(1),c=11.299(1) Å,β=99.17(1)° andZ=8. The structure was solved by direct methods which involved the use of seventeenmeasured triplet phases in the starting set. This appears to be the first centrosymmetric structure solution being based extensively on physically acquired X-ray phases. Refinement was by full-matrix least-squares involving 3843F o and yieldedR∼R w=0.042. The shape of the molecules can be described approximately by two, nearly orthogonal planes, one containing pyridine, the urea group and the NH-bonded phenyl ring, the other containing the second phenyl ring. Both the X-ray and the NMR studies show that there is an intramolecular H-bond between the urea N and the pyridine N atoms. When pH is lowered, this H-bond is weakened, and eventually breaks due to protonation of the pyridine ring. The X-ray study indicates that about 20% of the pyridine rings in the crystal are protonated. The structure details of the rings, in particular the valency angles, have been analyzed in relation to the orientation of the rings relative to the main molecular plane, and the electronic effects of the substituants.
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    Notes: Abstract Structural and conformational information obtained from the crystal structure and solution1H nmr investigations of the title compound are compared. The 4-aryltetralone, C24H24O10, crystallizes as a chloroform solvate in the monoclinic space group, P21/n, witha=12.519(4),b=17.938(6),c=12.534(9)Å,β=111.90(5)°, and Dcalc=1.51 g cm−3 forZ=4. The data for this compound were collected at −150°C. Least-squares refinement of 2796 observed [F o≥5σ(F o)] reflections led to the final agreement index ofR=0.062. A threefold static disorder was observed for one of the carboxyl groups. The second carboxyl group participates in an intramolecular hydrogen bond and is thus ordered. The1H nmr spectrum revealed the title compound to exist as a keto-enol tautomeric mixture in solution. Vicinal hydrogen coupling constant analysis proved reliable in ascertaining B-ring stereochemistry of 2,3-disubstituted-4-aryltetralones.
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  • 79
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    Notes: Abstract Ethanolic solutions of tetrapropylammonium bromide and copper(I) bromide, from which bis(tetrapropylammonium) hexa-μ-bromo-tetrahedro-tetracuprate(I), [N(C3H7)4]2[Cu4Br6], a bromocuprate(I) cluster comprised of three-coordinated copper(I), crystallizes have been shown, by means of far i.r. spectroscopy, to contain the centrosymmetric, monomeric [CuBr2]− anion as the major, and probably the sole, bromocuprate(I) species,υ 3=323 cm−1. Crystalline [N(C3H7)4]2[Cu4Br6], [N(CH3)4]3[Cu2Br5] and [P(CH3)4]2[CuBr3], all of which contain anions in which copper(I) is three-coordinated, dissolve in nitro-methane to give solutions of the dibromocuprate(I) monomer. Variation of the coordination number of copper(I) in bromocuprates(I) crystallizing with symmetrically substituted quaternary ammonium and related unipositive cations is discussed in terms of dilution of the bromide ions by the cations, and a tentative mechanism for the formation of such compounds is proposed. Toward the end of the precipitation of [N(C3H7)4]2[Cu4Br6] from the ethanolic solution of tetrapropylammonium bromide and copper(I) bromide, a few crystals of a second bromocuprate(I) phase were obtained. This compound has been identified as tetrapropylammonium dibromocuprate(I), and its crystal structure determined from X-ray diffraction data. [N(C3H7)4][CuBr2] crystallizes in space groupP2/n, witha=13.010(15),b=7.577(5),c=8.858(4) Å,β=91.09(7)° andZ=2. The anion is a monomer in which Cu-Br is 2.194(3) Å and Br-Cu-Br 178.4(1)°, copper(I) being situated on a twofold axis.
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    Journal of chemical crystallography 19 (1989), S. 193-201 
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    Notes: Abstract [C16H27N2O2]+·ClO 4 − ·H2O,M r=396.87, orthorhombicP212121 a=13.708(4),b=16.930(7),c=8.311(3) Å,V=1928.3(13) Å3,Z=4,D x=1.367(2) g cm−3,λ(MoKα)=0.71068 Å,μ(MoKμ)=1.95 cm−1,F(000)=848,T=292 K,R=0.061 for 1324 unique reflections. RingsA,B,C,D have half-chair, chair, chair and chair conformations, respectively; the quinolizidone moietyA/E has a quasi-trans and the quinolizidine moietyC/D has a trans configuration. The cations are connected into chains along the crystallographic direction [001] by strong hydrogen bonds utilizing the water molecule: C(2)=O(5)⋯O(W)⋯O(6)-N(16) of 2.623(7) and 2.574(7) Å, respectively. The water molecule is also hydrogen-bonded to one oxygen atom of the perchlorate anion: O(W)⋯O(2) is 3.106(10) Å. A very short intramolecular distance between N(1) and O(6) of 2.696(7) Å, due to the quasitrans-trans configuration of theα-isolupanine skeleton, is observed.
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    Journal of chemical crystallography 19 (1989), S. 289-298 
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    Notes: Abstract The crystal and molecular structure of 4-aminoacetyl-N-p-nitrophenylsulfanilamide (C14H13N3O5S), a derivative of sulfonamide, has been determined from X-ray diffraction data using Cu-Kα radiation. The compound crystallised in the monoclinic space groupP21/c, witha=12.258(9),b=7.339(5),c=16.359(9) Å,β=98.84(4)°. The structure was solved by direct methods and refined by full-matrix least-squares to a finalR value of 0.047 with 2487 unique reflections. In packing, the molecules are found to be stabilised by N-H⋯ O hydrogen bonds.
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    Journal of chemical crystallography 19 (1989), S. 299-306 
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    Notes: Abstract The complextrans-[PtCl2 (Me2PhP)(cis-2,4-dimethylpyrrolidine)] has been characterized by X-ray crystallography. It crystallizes in the monoclinic space group P 22/c witha=8.762(3),b=16.034(5),c=12.600(4)Å,β=93.43(3)° andZ=4. The structure was solved by heavy atom method and refined toR=0.052 for 3251 observed counter reflections. The coordination sphere of the Pt atom is square-planar with a geometry very similar to that of the studied complexes of the type trans-[PtCl2(R3P)L] whereL is either one of the possible isomers of theC,C′-dimethylpyrrolidine or the unsubstituted pyrrolidine. In the present complex the puckered five-membered ring of the dimethylpyrrolidine ligand assumes an envelope conformation with the maximum puckering at the N atom.
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    Journal of chemical crystallography 19 (1989), S. 671-681 
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    Notes: Abstract The infrared and Raman spectra of 2,4,6-tribromobenzonitrile have been recorded in the solid state and in solutions. Assignments of the fundamental vibrations based on Raman polarization data and comparison with the spectra of benzonitrile and its trichloro derivative are given and discussed. The thermodynamic functions have been evaluated for a rigid-rotor harmonic oscillator approximation at several temperatures.
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  • 84
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    Notes: Abstract Crystals of the title compound are monoclinic, P21/c, a=11.464(14),b=21.027(9),c=12.806(3) Å,β=108.00(6)°,V=2935.85 Å3,Z=8. The structure was solved by direct methods, from data collected at room temperature on an Enraf-Nonius CAD4 diffractometer, and refined by full matrix least squares to a finalR value of 0.089 using 3949 reflections. The two nonequivalent molecules are both disordered to the same extent, the ratio of the two models being 0.8∶0.2. In the minor model the substituent hydrogen atom at the 2-position is exactly eclipsed by a chlorine atom in the 2-CCl3 group whereas in the major model the normal staggered conformation is observed. C-Cl bond lengths and C-C-Cl angles in the major model are normal whereas those in the minor model are C-Cl(A) 1.51(3), C-Cl(B) 1.67(3), C-Cl(C) 1.95(3) Å, where Cl(C) is eclipsed, for one molecule and 1.85(3), 1.67(3), 1.94(2) Å for the other. Corresponding C-C-Cl bond angles (deg) are 115(1), 114(1), 80(1); and 120(1), 126(1), 90(1). A comparison is given with a structure which is not disordered but in which similar changes in the geometry of a∶CCl.CCl3 group are found.
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  • 85
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    Journal of chemical crystallography 19 (1989), S. 695-700 
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    Notes: Abstract C12H12N2O6 crystallized from methanol in the monoclinic space group P21/c (Z=4) witha=13.333(4),b=10.154(3),c=9.597(2) Å andβ=102.37(2)°.M r=280.24,V=1269.1(6) Å3,D x=1.466 g cm−3,λ(Mo Kα)=0.71069 Å,μ=1.29 cm−1,T=295 K. The structure was solved by direct methods and refined by full-matrix least-squares to a finalR (R w)=0.049 (0.057) for 916 observed reflections. The molecules are linked by strong N-H⋯O(4) hydrogen bonds with N⋯O distance of 2.995(4) Å. The infinite racemic chains run in [001] direction.
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  • 86
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    Journal of chemical crystallography 19 (1989), S. 733-744 
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    Notes: Abstract The crystal structure of the diacetate of (+)-epipinoresinol, C24H26O8, has been determined by single-crystal diffraction methods. The compound crystallizes in the monoclinic space groupP21 witha=7.506(3),b=8.526(4),c=17.746(8) Å,β=97.12(4)° andZ=2. A total of 3504 reflexion intensities were recorded on a Syntex P21 diffractometer (MoKα radiation) at room temperature. The structure was solved by direct methods and electron density calculations. Full-matrix least-squares refinement gaveR=0.056 for 2297 observed [I〉3σ(I] reflexions. The individual central tetrahydrofuran rings have envelope conformations with coplanar carbon atoms and the oxygen atoms as flaps; the carbon atom planes form an angle of 119.9(3)°. Bond distances are C-C (aromatic) 1.386(12) Å, C(sp 3)-O 1.421(12) Å, C(sp 2)-O 1.372(20) Å, and C(sp 2)=O 1.186(9) Å. The influence of molecular structure on the positions of signals in the1H nmr spectrum of the diacetate of (+)-epipinoresinol is discussed.
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    Journal of chemical crystallography 19 (1989), S. 765-773 
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    Journal of chemical crystallography 19 (1989), S. 775-785 
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  • 89
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    Notes: Abstract The structures of 1,1,2,2-tetraphenylethane-1,2-diol and its 1∶2 molecular inclusion complex with dmso have been elucidated by X-ray crystallography from single crystal diffraction data. Crystals of the host, compound I, are monoclinic, space groupP21/n, witha=17.669(6) Å,b=6.144(6) Å,c=17.873(6) Å,β=92.67(3)°,z=4. Crystals of the clathrate, compound II, are triclinic,P¯1, witha=9.138(5) Å,b=18.384(6) Å,c=18.496(3) Å,α=61.16(2)°,β=83.22(3)°, γ=88.06(3)°,Z=4. Both structures were solved by direct methods and refined to finalR values of 0.072 and 0.107, respectively. Compound I is partially disordered and its packing is governed by strong intermolecular hydrogen bonds. Compound II is characterized by crossing channels which accommodate the guest dmso molecules. The thermal properties of the latter compound have been characterized by DTA and TGA thermograms.
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  • 90
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    Notes: Abstract The crystal structure ofN′-phosphonomethyl-l-threonine has been determined from three-dimensional X-ray diffractometer data. The molecule crystallizes in the space groupP212121, witha=5.381(1),b=10.558(2),c=15.542(3)Å andz=4. The structure was solved by direct methods, and refined to anR value of 0.038 for 2477 reflections. The molecule exists as a zwitterion in the crystal, with the amino group portonated and the carboxyl group unionized; the phosphonic acid group is ionized. The molecule is in an extended conformation, with the P-C(1)-N-C(2) and C(1)-N-C(2)-C(4) torsion angles −171.1(2) and 166.7(2)°, respectively. The crystal structure is stabilized by five intermolecular and one intramolecular hydrogen bonds.
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  • 91
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    Notes: Abstract Several optically pure representatives of 2α-hydroxy-3α-[N-alkyl (aryl)] pinanoamines, potential chiral auxiliaries in organic synthesis, were obtained. In addition, a structural examination of 2α-hydroxy-3α-(N-n-butyl)-pinanoamine hydrochloride was conducted. Results of these studies confirm the structure of the amines obtained and the correctness of the proposed reaction pathway.Crystal data: C12H28NOCl,P21/c,a=13.196(1),b=8.562(1),c=14.276(1) Å,β=110.41(3)°,R=0.034 for 2046 reflections.
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  • 92
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    Journal of chemical crystallography 19 (1989), S. 929-931 
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    Notes: Abstract The energy order assignment of the d-orbitals of Mo5+ in Mo[S2CN(C2H5)2]4I3 given by Jasimet al. (1985) is restudied and corrected. It is indicated that, in general, the energy order of the d-orbitals of D2d symmetric complexes is depending on the bond angles and bond lengths of the ligands, thus there cannot be any universal energy order.
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  • 93
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    Journal of chemical crystallography 19 (1989), S. 949-955 
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    Notes: Abstract The X-ray crystal structure of 6β-acetoxyprogesterone, C23H32O4, has been determined. This compound crystallizes in space groupP212121 witha=13.195(3),b=15.035(4),c=10.705(3) Å,V=2139.8(9) Å3,M r=372.5,Z=4,D x=1.156g cm−3; MoKα radiation (λ=0.7107 Å),μ=0.72 cm−1,F(000)=808;R=0.069, andR w=0.052 for 1292 reflections. RingA adopts a normal 1α,2β-half-chair conformation. The side chain is typical for a 20-ketosteroid conformation.
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    Journal of chemical crystallography 15 (1985), S. 1-17 
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    Notes: Abstract Ferrocene and nickelocene have pseudo-isomorphous structures at room temperature but only ferrocene undergoes a second-order phase transformation on cooling. Calculation and analysis of appropriate lattice-energy surfaces as a function of concerted ring rotation showed that ferrocene has a disordered structure at room temperature different from nickelocene which exhibits a single minimum in the lattice-energy function. The results readily suggest a mechanism for the ferrocene phase transformation. The correct low-temperature structure is predicted only after taking intramolecular interactions into account.
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  • 95
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    Notes: Abstract A single crystal X-ray investigation of the purple nickel (II) complex Ni[L(en)](NO3)2, produced by condensation of 1,2-diaminoethane (en) with the thiodiketone S(CH2COCH3)2 in the presence of nickel (II) nitrate (L is NH2(CH2)2N=C(CH3)CH2SCH2COCH3), shows that the metal ions are six coordinate. The new ligand L is tetradentate, with the N,N and S donor atoms arranged meridionally, and the coordination shell completed by the carbonyl oxygen atom of L and the nitrogen atoms of 1,2-diaminoethane. Metal-ligand bond distances are Ni-N: 2.08 av. (en), 2.10 and 2.05 (NH2 and N=C respectively of L); Ni-O, 2.16; Ni-S, 2.45 Å. There is considerable angular distortion from regular octahedral values of the bond angles at nickel. The crystals are monoclinic,P21/c (No. 14),a=12.433(2),b=11.709(1),c=13.150(2) Å,β=103.93(1)°,V c=1858.2(4) Å3. The structure was solved by the heavy-atom method and refined by full-matrix least squares to anR value of 0.055 for 3633 reflections.
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    Journal of chemical crystallography 15 (1985), S. 45-52 
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    Notes: Abstract The crystal structure of bis(potassium hydrogenl-malate)·malic acid, 2[K+(C4H5O5)−]·C4H6O5, has been determined: C12H16K2O15, M r =1913.9, orthorhombic, space groupP212121 a=7.719(5),b=7.916(5),c=29.863(20) Å,V c=1824.7 Å3,Z=4. The structure was determined by a new application of theDirdif procedure using MoKα automatic diffractometer X-ray data, and refined by full-matrix least squares toR=0.059 for 962 reflections. A question on space-group assignment and composition was resolved only after the structure had been determined. The conformation of the central carbon skeleton of all three crystallographic independent malate moieties isanti. The potassium ions are coordinated by eight oxygen atoms, forming face-sharing distorted square antiprisms.
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  • 97
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    Notes: Abstract The crystal structure of metalaxyl (C15H21NO4) was determined by three-dimensional X-ray analysis from diffractometer data. The crystals are monoclinic,P21/c,a=7.851(3) Å,b=13.119(10) Å,c=15.107(7) Å,β=101.71(6)°,Z=4,D x=1.218 g cm−3, μ (MoKa)=0.095 mm−1. FinalR=0.079 for 1203 observed reflections. The dimethylphenyl ring is almost perpendicular to the amidic plane of the molecule.
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  • 98
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    Journal of chemical crystallography 15 (1985), S. 115-131 
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    Notes: Abstract The various conformations of δ-lactone rings are described and parametrized.
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    Journal of chemical crystallography 15 (1985), S. 39-43 
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    Notes: Abstract The structure of MeGeI3 is orthorhombic with space groupPnma,a=6.374(3),b=10.412(4),c=12.683(4) Å, andz=4. It has been solved by direct methods and refined by full-matrix least-squares techniques to a conventionalR factor of 0.0791 for 653 unique reflections. The crystal structure contains discrete molecules with mirror symmetry which are separated by normal van der Waals distances. The mean Ge-I distance is 2.500(2) Å.
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