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  • Articles  (43,332)
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  • 1
    Electronic Resource
    Electronic Resource
    Cost-effective network design for groundwater flow monitoring (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 27-41 
    Details
    ISSN: 1436-3259
    Keywords: Groundwater monitoring networks ; Information reliability ; Information scales ; Kalman filtering in groundwater
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The extensive use of groundwater resources has increased the need for developing cost-effective monitoring networks to provide an indication of the degree to which the subsurface environment has been affected by human activities. This study presents a cost-effective approach to the design of groundwater flow monitoring networks. The groundwater network design is formulated with two problem formats: maximizing the statistical monitoring power for specified budget constraint and minimizing monitoring cost for statistical power requirement. The statistical monitoring power constraint is introduced with an information reliability threshold value. A branch and bound technique is employed to select the optimal solution from a discrete set of possible network alternatives. The method is tested to the design of groundwater flow monitoring problem in the Pomona County, California.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01547730
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  • 2
    Electronic Resource
    Electronic Resource
    Probabilistic modeling of aerated lagoons: A comparison of methodologies (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 65-81 
    Details
    ISSN: 1436-3259
    Keywords: Lagoons ; Ponds ; Facultative ; First-order kinetics ; Complete mixing ; Probabilistic ; Uncertainty ; Environmental ; 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 Two stochastic models are developed to describe the BOD output (i.e. effluent) variation of facultative aerated lagoons in series. One of the models uses the uncertainty analysis (UA) technique and the other is based on the moment equation solution methodology of stochastic differential equations (SDE's). The former considers a second-order approximation of the expectation (SOAE) and a first-order approximation of the variance (FOAV). The SDE model considers that output variability is accounted for by random variations in the rate coefficient. Comparisons are provided. Calibration and verification of the two models are aciieved by using field observations from two different lagoon systems in series. The predictive performances of the two models are compared with each other and with another SDE model, presented in a previous paper, that considers input randomness. The three methods show similar predictive performances and provide good predictions of the mean and standard deviation of the lagoon effluent BOD concentrations and thus are considered as appropriate methodologies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01547733
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  • 3
    Electronic Resource
    Electronic Resource
    Estimation of the annual maximum distribution from samples of maxima in separate seasons (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 89-103 
    Details
    ISSN: 1436-3259
    Keywords: maximum precipitation depths ; extreme-value distributions ; seasonal variation ; partial duration series ; model misspecification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Quantile estimates of the annual maximum distribution can be obtained by fitting theoretical distributions to the maxima in separate seasons, e.g. to the monthly maxima. In this paper, asymptotic expressions for the bias and the variance of such estimates are derived for the case that the seasonal maxima follow a Gumbel distribution. Results from these expressions are presented for a situation with no seasonal variation and for maximum precipitation depths at Uccle/Ukkel (Belgium). It is shown that the bias is often negligible and that the variance reduction by using seasonal maxima instead of just the annual maxima strongly depends on the seasonal variation in the data. A comparison is made between the asymptotic standard error of quantile estimates from monthlymaxima with those from a partial duration series. Much attention is paid to the effect of model misspecification on the resulting quantile estimates of the annual maximum distribution. The use of seasonal maxima should be viewed with caution when the upper tail of this distribution is of interest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543284
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  • 4
    Electronic Resource
    Electronic Resource
    Parameter identification in tidal models with uncertain boundary conditions (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 193-208 
    Details
    ISSN: 1436-3259
    Keywords: Stochastic tidal modeling ; parameter identification ; model calibration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In this paper a parameter estimation algorithm is developed to estimate uncertain parameters in two dimensional shallow water flow models. Since in practice the open boundary conditions of these models are usually not known accurately, the uncertainty of these boundary conditions has to be taken into account to prevent that boundary errors are interpreted by the estimation procedure as parameter fluctuations. Therefore the open boundary conditions are embedded into a stochastic environment and a constant gain extended Kalman filter is employed to identify the state of the system. Defining a error functional that measures the differences between the filtered state of the system and the measurements, a quasi Newton method is employed to determine the minimum of this functional. To reduce the computational burden, the gradient of the criterium that is required using the quasi Newton method is determined by solving the adjoint system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543083
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  • 5
    Electronic Resource
    Electronic Resource
    On the distribution of flood volume in partial duration series analysis of flood phenomena (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 217-226 
    Details
    ISSN: 1436-3259
    Keywords: Exponential distribution ; bivariate exponential distribution ; distribution of flood volume ; partial duration series
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A methodology based on the theory of stochastic processes is applied to the analysis of floods. The approach will be based on some results of the theory of extreme values over a threshold. In this paper, we focus on the estimation of the distribution of the flood volume in partial duration series analysis of flood phenomena, by using a bivariate exponential distribution of discharge exceedances and durations over a base level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543085
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  • 6
    Electronic Resource
    Electronic Resource
    Editorial note (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 254-254 
    Details
    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544080
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  • 7
    Electronic Resource
    Electronic Resource
    Rehabilitation and replacement of water distribution system components considering uncertainties (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 277-294 
    Details
    ISSN: 1436-3259
    Keywords: Water distribution ; optimization ; nonlinear programming ; integer programming ; chance constraints ; rehabilation
    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 the mathematical development of an integer — nonlinear programming chance — constrained optimization model for the minimum cost rehabilitation/replacement of water distribution system components. Particular attention is given to the handling of uncertainties in the roughness factors and the loading conditions including both the random demand and preassure head requirements. The advantages of the proposed model include the ability to: 1) handle the optimal timing of rehabilitation/replacement for water distribution system components; 2) link a mixed-integer linear program solver, a nonlinear program solver, and a hydraulic simulator into an optimization framework; 3) handle the uncertainties of some of the variables; 4) incorporate various kinds of cost functions; and 5) handle multiple loading conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544082
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  • 8
    Electronic Resource
    Electronic Resource
    Assessment of reliability in water distribution networks using entropy based measures (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 309-320 
    Details
    ISSN: 1436-3259
    Keywords: Entropy ; reliability ; redundancy ; water distribution networks ; nodal pair reliability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Entropy based expressions for measurement of reliability and redundancy have recently been reported. These measures approach assessment of the reliability of the distribution network from the intrinsic redundancy of the network layout. The paper extends earlier work on entropy functions by including a more explicit statement of the alternate paths available in the network and by recognizing that under certain circumstances, e.g., failure of some part of the network work, an outflow link from a node under normal working condition may become an inflow link to the same node. The measures are assessed by comparison with parameters measuring Nodal Pair Reliability and percentage of flow supplied at adequate pressure for a range of networks and link failure conditions in this networks. The entropy measures are shown to reflect changes in the network reliability, as measured by these two comparative parameters, very well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544084
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  • 9
    Electronic Resource
    Electronic Resource
    Evaluation of risk concepts in partial duration series (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 1-16 
    Details
    ISSN: 1436-3259
    Keywords: Partial duration series ; unbiased risk ; Bayesian risk
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Conventional design practice aims at obtaining optimal estimates of floods with specified exceedance probabilities. Such estimates are, however, known on the average to be exceeded more frequently than expected. Alternatively, methods focusing on the expected exceedance probability can be used. Two different methods are considered here; the first is based on the sample distribution of true exceedance probabilities. The second is a Bayesian analogue using the likelihood function and a noninformative prior to describe the variability of exceedance probabilities. Appropriate analytical solutions are presented in both cases using the partial duration series approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544174
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  • 10
    Electronic Resource
    Electronic Resource
    Derivation of bivariate probability density functions with exponential marginals (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 55-68 
    Details
    ISSN: 1436-3259
    Keywords: Bivariate probability distribution ; random variables ; zero marginals ; Finch-Groblicki method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A vivariate probability density function (pdf),f(x 1,x 2), admissible for two random variables (X 1,X 2), is of the form $$f(x_1 x_2 ) = f_1 (x_1 )f_2 (x_2 )[1 + \rho \{ F_1 (x_1 ),F_2 (x_2 )\} ]$$ where ρ(u, v) (u=F 1(x 1),v=F 2(x 2)) is any function on the unit square that is 0-marginal and bounded below by−1 andF 1(x 1) andF 2(x 2) are cumulative distribution functions (cdf) of marginal probability density functionsf 1(x 1) andf 2(x 2). The purpose of this study is to determinef(x 1,x 2) for different forms of ρ(u,v). By considering the rainfall intensity and the corresponding depths as dependent random variables, observed and computed probability distributionsF 1(x 1),F(x 1/x 2),F 2(x 2), andF(x 2/x 1) are compared for various forms of ρ(u,v). Subsequently, the best form of ρ(u,v) is specified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544178
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  • 11
    Electronic Resource
    Electronic Resource
    Entropy estimation of hydrological extremes (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 77-87 
    Details
    ISSN: 1436-3259
    Keywords: Flood ; random ; distribution ; estimation ; probability ; entropy ; fractile constraints
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The method of Relative Entropy with Fractile constraints (REF method) is explained and applied to model extreme compound hydrological phenomena, such as extreme sea levels under storm conditions. Also presented is a simple method of Tail Entropy Approximation (TEA), which amounts to a correction of traditional statistical estimates for extreme observations. Distribution assumptions are necessary but downplayed in the REF method, relegating the prior distribution to the role of an extrapolation function. The estimates are objective in an information-theoretical sense. They also satisfy a strict requirement of self-consistency that is generally not satisfied by standard statistical methods: invariance under monotonic transformations of the random variable. Historical records of storm surge levels in the Netherlands and annual maximum tidal heights for Sheerness, UK, are used as examples. Comparison is made with distributions obtained using other methods. It is concluded that the tail entropy approximation provides simple, objective estimates of extremes in the tail beyond the range of observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544180
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  • 12
    Electronic Resource
    Electronic Resource
    On the use of Empirical Orthogonal Function (EOF) analysis in the simulation of random fields (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 125-134 
    Details
    ISSN: 1436-3259
    Keywords: Empirical Orthogonal Function analysis ; random fields ; simulation ; non-homogeneous fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In several fields of Geophysics, such as Hydrology, Meteorology or Oceanography, it is often useful to generate random fields, displaying the same variabilitity as the observed variables. Usually, these synthetic data are used as forcing fields into numerical models, to test the sensitivity of their outputs to the variability of the inputs. Examples can be found in subsurface or surface Hydrology and in Meteorology with General Circulation Models (GCM). Different techniques have already been proposed, often based on the spectral representation of the random process, with, usually, assumptions of stationarity. This paper suggests that Empirical Orthogonal Function (EOF) analysis, which leads to the decomposition of the covariance kernel on the set of its eigen-functions, is a possible answer to this problem. The convergence and accuracy of the method are shown to depend mainly on the number of EOFs retained in the expansion of the covariance kemel. This result is confirmed by a comparison with the turning band method and a matrix technique. Furthermore, a synthetic example of non-homogencous fields shows the interest of EOF analysis in the direct simulation of such fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543054
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  • 13
    Electronic Resource
    Electronic Resource
    A univariate model for long-term streamflow forecasting (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 173-188 
    Details
    ISSN: 1436-3259
    Keywords: Entropy ; spectral analysis ; streamflow forecasting ; univariate model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This paper, the first in a series of two, employs the principle of maximum entropy (POME) via maximum entropy spectral analysis (MESA) to develop a univariate model for long-term streamflow forecasting. Three cases of streamflow forecasting are investigated: forward forecasting, backward forecasting (or reconstruction) and intermittent forecasting (or filling in missing records). Application of the model is discussed in the second paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544056
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  • 14
    Electronic Resource
    Electronic Resource
    Modeling kinetic non-equilibrium using the first two moments of the residence time distribution (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 155-171 
    Details
    ISSN: 1436-3259
    Keywords: Kinetic non-equilibrium ; residence time ; spatially variable chemical reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A method for simulating field scale transport of kinetically adsorbing solutes is described. The non-equilibrium adsorption is modeled as a birth and death process and is coupled with the particle tracking approach using the first two moments of the distribution of the particle residence time, i.e., the time that a solute particle stays in the liquid phase. A single residence time distribution, regardless of the initial and final phase, is demonstrated to yield an accurate description of chemical kinetics in the vast majority of field scale problems. The first two moments of the residence time distribution are derived as a function of chemical reaction rates and the transport time interval Δt. It is shown that the first moment of the residence time represents a measure of the speed of the chemical reaction relative to the transport time scale Δt which is chosen depending on the velocity field. The second moment of the residence time reflects the relative importance of the chemical kinetics versus local equilibrium conditions for the given transport time step Δt. The simulated spatial moments of the contaminant plume are compared in the one-dimensional case with available analytical solutions to demonstrate the accuracy of the proposed technique. A two-dimensional case for stratified formations is presented to study the transport behavior for heterogeneous velocity fields and variable distribution coefficient, hypothesized as being negatively correlated with hydraulic conductivity. The results show that the enhanced plume spreading and the statistics of the arrival time distribution appear to be more sensitive to the spatially variable distribution coefficient than to the kinetics alone. In fact, the second spatial moment was almost doubled in the case of spatially variable distribution coefficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543057
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  • 15
    Electronic Resource
    Electronic Resource
    Stochastic partial differential equations in groundwater hydrology (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 239-251 
    Details
    ISSN: 1436-3259
    Keywords: Parameter estimation ; maximum likelihood estimation ; stochastic partial differential equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Part I of this series of two papers (Unny, 1989) dealt with the theoretical derivation of the moment equations for the stochastic partial differential equation in the water table depth forced by stochastic rainfall input. Part I also developed a maximum likelihood estimation procedure for parameter determination. The primary aim of the present manuscript is the application of the parameter estimation procedure to the Borden aquifer, an aquifer designated as an experimental site, where extensive field measurements have been carried out. Estimates of hydraulic conductivity and transmissivity for the Borden aquifer, derived from the maximum likelihood algorithm, have been compared with estimates obtained by “traditional” procedures. The paper also presents the simulated solution of the governing differential equation in the one dimensional problem applied to the Borden aquifer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01544060
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  • 16
    Electronic Resource
    Electronic Resource
    Technical reports (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 280-294 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543136
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  • 17
    Electronic Resource
    Electronic Resource
    Drought monitoring (1991)
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 261-266 
    Details
    ISSN: 1436-3259
    Keywords: Drought ; drought indices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Drought detection, monitoring and indices are closely related to its definition. The specific definition chosen for a particular drought analysis will affect the procedures one uses in drought detection and monitoring. The traditional Palmer Drought Severity Index (PDSI) has been proven to be ineffective in regions of predominantly irrigated agriculture. The recently developed ALERT (Automated Local Evaluation in Real Time) system is proposed for use in monitoring the spatial and temporal variations of drought in real time. The ALERT system uses standardized instruments, radio frequencies, software and hardware. It was originally developed as a flash flood waming system by local flood control districts and the National Weather Service. However, now it has expanded to over 100 other uses in the areas of natural and man-made disaster detection and warning. The successful ALERT system indicates the need for the continued development of a national drought monitoring index that is applicable to a wide range of climate, hydrologic and water resource environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543134
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  • 18
    Electronic Resource
    Electronic Resource
    In memory of Professor T. E. Unny (1992)
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 1-2 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581670
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  • 19
    Electronic Resource
    Electronic Resource
    On the control of an infinite capacity storage system (1993)
    Springer
    Stochastic environmental research and risk assessment 7 (1993), S. 195-204 
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    ISSN: 1436-3259
    Keywords: Infinite dam ; resolvent operator ; Lévy process ; integrated Markov chain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract We consider an infinite-capacity storage system. The cumulative input to the system is assumed to be either (a) a non-decreasing Lévy process or (b) an integrated continuous-time Markov chain. Reward accumulates at a rate depending on the instantaneous release rate. The objective is to choose the release rule in such a way as to maximize the expected total discounted return. In this note we show how to determine the expected discounted return when the release rate is either constant or a linear function of the content.
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    URL: http://dx.doi.org/10.1007/BF01585598
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  • 20
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    Stochastic perturbation analysis of groundwater flow. Spatially variable soils, semi-infinite domains and large fluctuations (1993)
    Springer
    Stochastic environmental research and risk assessment 7 (1993), S. 213-239 
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    ISSN: 1436-3259
    Keywords: Stochastic hydrology ; perturbation ; random fields ; graph theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract As is well known, a complete stochastic solution of the stochastic differential equation governing saturated groundwater flow leads to an infinite hierarchy of equations in terms of higher-order moments. Perturbation techniques are commonly used to close this hierarchy, using power-series expansions. These methods are applied by truncating the series after a finite number of terms, and products of random gradients of conductivity and head potential are neglected. Uncertainty regarding the number or terms required to yield a sufficiently accurate result is a significant drawback with the application of power series-based perturbation methods for such problems. Low-order series truncation may be incapable of representing fundamental characteristics of flow and can lead to physically unreasonable and inaccurate solutions of the stochastic flow equation. To support this argument, one-dimensional, steady-state, saturated groundwater flow is examined, for the case of a spatially distributed hydraulic conductivity field. An ordinary power-series perturbation method is used to approximate the mean head, using second-order statistics to characterize the conductivity field. Then an interactive perturbation approach is introduced, which yields improved results compared to low-order, power-series perturbation methods for situations where strong interactions exist between terms in such approximations. The interactive perturbation concept is further developed using Feynman-type diagrams and graph theory, which reduce the original stochastic flow problem to a closed set of equations for the mean and the covariance functions. Both theoretical and practical advantages of diagrammatic solutions are discussed; these include the study of bounded domains and large fluctuations.
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    URL: http://dx.doi.org/10.1007/BF01585600
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  • 21
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    Operator and integro-differential representations of conditional and unconditional stochastic subsurface flow (1994)
    Springer
    Stochastic environmental research and risk assessment 8 (1994), S. 157-172 
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    ISSN: 1436-3259
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Operator representations of stochastic subsurface flow equations allow writing their solutions implicitly or explicitly in terms of integro-differential expressions. Most of these representations involve Neumann series that must be truncated or otherwise approximated to become operational. It is often claimed that truncated Neumann series allow solving groundwater flow problems in the presence of arbitrarily large heterogeneities. Such claims have so far not been backed by convincing computational examples, and we present an analysis which suggests that they may not be justified on theoretical grounds. We describe an alternative operator representation due to Neuman and Orr (1993) which avoids the use of Neumann series yet accomplishes a similar purpose. It leads to a compact integro-differential form which provides considerable new insight into the nature of the solution. When written in terms of conditional moments, our new representation contains local and nonlocal effective parameters that depend on scale and information. As such, these parameters are not unique material properties but may change as more is learned about the flow system.
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    URL: http://dx.doi.org/10.1007/BF01589896
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  • 22
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    Groundwater contaminant transport including adsorption and first order decay (1994)
    Springer
    Stochastic environmental research and risk assessment 8 (1994), S. 185-205 
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    ISSN: 1436-3259
    Keywords: Contaminant transport ; adsorption ; decay ; random walk ; killing ; Kolmogorov equations ; contamination of a well
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This study deals with the transport of a contaminant in groundwater. The contaminant is subject to first order decay or linear adsorption. Its displacement can be modeled by a random walk process in which particles are killed at exponentially distributed times. Dirichlet problems are derived for the rate and mean time at which contaminated particles reach a particular part of the boundary of a certain domain. These Dirichlet problems are solved asymptotically for two types of 2D-flow patterns: flow parallel to the boundary of a domain and arbitrary flow towards a well in an aquifer.
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    URL: http://dx.doi.org/10.1007/BF01587234
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  • 23
    Electronic Resource
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    Nonequilibrium statistical mechanical derivation of a nonlocal Darcy's Law for unsaturated/saturated flow (1994)
    Springer
    Stochastic environmental research and risk assessment 8 (1994), S. 109-116 
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    ISSN: 1436-3259
    Keywords: Unsaturated ; nonlocal ; memory ; statistical physics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract As illustrated variously by wetting and drying scanning curves, flow in unsaturated porous media is inherently nonlocal. This nonlocality is also manifest in hysteresis in the classical Darcy conductivity. It is the authors' belief that most current theories of unsaturated/saturated flow are often inadequate, as they do not account for spatial nonlocality and memory. Here we provide a fundamental theory in which nonlocality of the flow constitutive theory is a natural consequence of force balances. The results are derived from general principles in statistical physics and under appropriate limiting conditions, the classical Darcy's Law is recovered for saturated flow. A notable departure in this theory from other nonlocal flow theories is that a classical Darcy type equation on a small scale need not exist.
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    URL: http://dx.doi.org/10.1007/BF01589892
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    Inverse methods for subsurface flow: A critical review of stochastic techniques (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 1-26 
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    ISSN: 1436-3259
    Keywords: Inverse ; calibration ; estimation ; groundwater flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The development of stochastic methods for groundwater flow representation has undergone enormous expansion in recent years. The calibration of groundwater models, the inverse problem, has lately received comparable attention especially and almost exclusively from the stochastic perspective. In this review we trace the evolution of the methods to date with a specific view toward identifying the most important issues involved in the usefulness of the approaches. The methods are critiqued regarding practical usefulness, and future directions for requisite study are discussed.
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    URL: http://dx.doi.org/10.1007/BF01547729
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    Bayes estimate of the probability of exceedance of annual floods (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 55-64 
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    ISSN: 1436-3259
    Keywords: Predictive distribution ; Bayesian approximation ; parameter uncertainty ; non-informative prior ; method of moments ; Gumbel distribution ; 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 In this paper Lindley's Bayesian approximation procedure is used to obtain the Bayes estimate of the probability of exceedence of a flood discharge. The Bayes estimates of the probability of exceedence has been shown by S.K. Sinha to be equivalent to the estimate of the probability of exceedence from the predictive or Bayesian disribution, of a future flood discharge. The evaluation of complex ratios of multiple integrals common in a Bayesian analysis is not necessary using Lindley's procedure. The Bayes estimates are compared to those obtained by the method of maximum likelihood and the method of moments. The results show that Bayes estimates of the probability of exceedence are larger as expected, but have smaller posterior standard deviations.
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    URL: http://dx.doi.org/10.1007/BF01547732
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    Identification of wind stress on shallow water surfaces by optimal smoothing (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 105-119 
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    ISSN: 1436-3259
    Keywords: Kalman filtering ; Optimal smoothing ; Shallow water equations ; Wind stress ; On-line prediction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Using the state space approach, an on-line filter procedure for combined wind stress identification and tidal flow forecasting is developed. The stochastic dynamic approach is based on the linear twodimensional shallow water equations. Using a finite difference scheme, a system representation of the model is obtained. To account for uncertainties, the system is embedded into a stochastic environment. By employing a Kalman filter, the on-line measurements of the water-level available can be used to identify and predict the shallow water flow. Because it takes a certain time before a fluctuation in the wind stress can be noticed in the water-level measurements, an optimal fixed-lag smoother is used to identify the stress.
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    URL: http://dx.doi.org/10.1007/BF01543285
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    Advanced use into rainfall prediction of three-dimensionally scanning radar (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 135-150 
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    ISSN: 1436-3259
    Keywords: Radar ; rainfall prediction ; real-time prediction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A computational method for the determination of rainfall distribution for applications in short term rainfall prediction is presented here. The method is strongly influenced by the experience gained from the observation and analysis of data gathered on a heavy rainfall event in 1986 that occurred during the Baiu Season in Japan. The method is based on the concept that rainfall occurs as an interaction between an instability field, appropriately modeled, and a field of water vapor under the influence of topography. The results from this computational method showed good agreement with the temporal variation in the rainband that moved across the observation field in 1986. Towards determination of the parameters in the computational model, another method for the determination of the rainfield is also developed. This second method determines the rainfall distribution from estimation of the conversion rate of water vapor to liquid water through use of data from a three dimensional scanning radar. The results are consistent with those obtained from the first method.
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    URL: http://dx.doi.org/10.1007/BF01543287
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    Development of the instantaneous unit hydrograph using stochastic differential equations (1990)
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 151-160 
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    ISSN: 1436-3259
    Keywords: Instantaneous Unit Hydrograph ; Conceptual models ; 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 Recognizing that simple watershed conceptual models such as the Nash cascade ofn equal linear reservoirs continue to be reasonable means to approximate the Instantaneous Unit Hydrograph (IUH), it is natural to accept that random errors generated by climatological variability of data used in fitting an imprecise conceptual model will produce an IUH which is random itself. It is desirable to define the random properties of the IUH in a watershed in order to have a more realistic hydrologic application of this important function. Since in this case the IUH results from a series of differential equations where one or more of the uncertain parameters is treated in stochastic terms, then the statistical properties of the IUH are best described by the solution of the corresponding Stochastic Differential Equations (SDE's). This article attempts to present a methodology to derive the IUH in a small watershed by combining a classical conceptual model with the theory of SDE's. The procedure is illustrated with the application to the Middle Thames River, Ontario, Canada, and the model is verified by the comparison of the simulated statistical measures of the IUH with the corresponding observed ones with good agreement.
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    URL: http://dx.doi.org/10.1007/BF01543288
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    An exact solution of solute transport by one-dimensional random velocity fields (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 45-54 
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    ISSN: 1436-3259
    Keywords: Solute transport ; random velocity ; Lagrangian description ; travel time ; nonlinear effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The problem of one-dimensional transport of passive solute by a random steady velocity field is investigated. This problem is representative of solute movement in porous media, for example, in vertical flow through a horizontally stratified formation of variable porosity with a constant flux at the soil surface. Relating moments of particle travel time and displacement, exact expressions for the advection and dispersion coefficients in the Focker-Planck equation are compared with the perturbation results for large distances. The first- and second-order approximations for the dispersion coefficient are robust for a lognormal velocity field. The mean Lagrangian velocity is the harmonic mean of the Eulerian velocity for large distances. This is an artifact of one-dimensional flow where the continuity equation provides for a divergence free fluid flux, rather than a divergence free fluid velocity.
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    URL: http://dx.doi.org/10.1007/BF01544177
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    Stochastic overland flows (1991)
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    Stochastic environmental research and risk assessment 5 (1991), S. 89-104 
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    ISSN: 1436-3259
    Keywords: Overland flows ; nonlinear SPDE ; evolutionary probability distributions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A theoretical solution framework to the nonlinear stochastic partial differential equations (SPDE) of the kinematic wave and diffusion wave models of overland flows under stochastic inflows/outflows, stochastic surface roughness field and stochastic state of flows was obtained. This development was realized by means of an eigenfunction representation of the time-space overland flow depths, and by transforming the problem into the phase space. By using Van Kampen's lemma and the cumulant expansion theory of Kubo-Van Kampen-Fox, the deterministic partial differential equation (PDE) for the evolutionary probability density function (pdf) of overland flow depths was finally obtained. Once this deterministic PDE is solved for the time-varying pdf of overland flow depths, then the time-space varying pdf of overland flow depths can be obtained by a transformation given in the text. In this solution framework it is possible to incorporate the stochastic dynamic behavior of the parameters and of the forcing functions of the overland flow process. For example, not only the individual rainfall duration and fluctuating rain intensity characteristics but also the sequential behavior of rainfall patterns is incorporated into the evolutionary probability density function of overland flow depths.
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    Analysis of macrodispersion through volume-averaging: Moment equations (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 5-25 
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    ISSN: 1436-3259
    Keywords: Solute transport ; Heterogeneity ; Dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Macrodispersion is spreading of a substance induced by spatial variations in local advective velocity at field scales. Consider the case that the steady-state seepage velocity and the local dispersion coefficients in a heterogeneous formation may be modeled as periodic in all directions in an unbounded domain. The equations satisfied by the first two spatial moments of the concentration are derived for the case of a conservative non-reacting solute. It is shown that the moments can be calculated from the solution of well-defined deterministic boundary value problems. Then, it is described how the rate of increase of the first two moments can be calculated at large times using a Taylor-Aris analysis as generalized by Brenner. It is demonstrated that the second-order tensor of macrodispersion (or effective dispersion) can be computed through the solution of steady-state boundary-value problems followed by the determination of volume averages. The analysis is based solely on volume averaging and is not limited by the assumption that the fluctuations are small. The large-time results are valid when the system is in a form of equilibrium in which a tagged particle samples all locations in an appropriately defined “phase space” with equal probability.
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    A theory of efficiency of storage-treatment systems (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 89-101 
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    ISSN: 1436-3259
    Keywords: Detention storage ; Pollution control ; Non-point pollutant runoff
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A simple expression is presented on the capability of storage-treatment systems to reduce non-point pollutant runoff load to natural waters. Their efficiency depends on the capacities of the facilities and probabilistic properties of runoff, such as interval, duration, volume, and concentration of runoff events. Assuming the compound Poisson process for runoff time series, the exact expressions of the ratio of treated load in terms of storage and treatment capacities are theoretically derived on the neighbourhoods of all boundaries of the domain on which the problem is defined. Then, an approximate expression over the whole domain is presented, of which the value and the first-order derivative coincide with those of the exact derived expressions near the boundaries. Accuracy is checked by Monte Carlo simulations.
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    On the generation of drought events using an alternating renewal-reward model (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 55-68 
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    ISSN: 1436-3259
    Keywords: Drought severity ; Drought duration ; Renewal-reward process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract This research study focused on the hypothesis that extreme drought and high streamflow events come from different independent populations with different probability distributions which need to be studied separately, rather than considering the streamflow population as a whole. The inability of traditional streamflow generator models to consistently reproduce the frequency of occurrence of severe droughts observed in the historical record has been questioned by many researchers. Our study focused on the development of astochastic event generator model which would be capable of doing so. This was accomplished in a two-step process by first generating the drought event, and then deriving the streamflows which comprised that event. The model considered for this analysis was an alternating renewal-reward procedure that cycles between eventon andoff times, and is representative of drought or high streamflow event duration. The reward gained while the event ison oroff represents drought severity or high streamflow surplus. Geometric and gamma distributions were considered for drought duration and deficit respectively. Model validation was performed using calculated required capacities from the sequent peak algorithm.
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    Probabilistic sensitivity and modeling of two-dimensional transport in porous media (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 103-121 
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    ISSN: 1436-3259
    Keywords: Probabilistic model ; Sensitivity ; Contaminant transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A reliability approach is used to develop a probabilistic model of two-dimensional non-reactive and reactive contaminant transport in porous media. The reliability approach provides two important quantitative results: an estimate of the probability that contaminant concentration is exceeded at some location and time, and measures of the sensitivity of the probabilistic outcome to likely changes in the uncertain variables. The method requires that each uncertain variable be assigned at least a mean and variance; in this work we also incorporate and investigate the influence of marginal probability distributions. Uncertain variables includex andy components of average groundwater flow velocity,x andy components of dispersivity, diffusion coefficient, distribution coefficient, porosity and bulk density. The objective is to examine the relative importance of each uncertain variable, the marginal distribution assigned to each variable, and possible correlation between the variables. Results utilizing a two-dimensional analytical solution indicate that the probabilistic outcome is generally very sensitive to likely changes in the uncertain flow velocity. Uncertainty associated with dispersivity and diffusion coefficient is often not a significant issue with respect to the probabilistic analysis; therefore, dispersivity and diffusion coefficient can often be treated for practical analysis as deterministic constants. The probabilistic outcome is sensitive to the uncertainty of the reaction terms for early times in the flow event. At later times, when source contaminants are released at constant rate throughout the study period, the probabilistic outcome may not be sensitive to changes in the reaction terms. These results, although limited at present by assumptions and conceptual restrictions inherent to the closed-form analytical solution, provide insight into the critical issues to consider in a probabilistic analysis of contaminant transport. Such information concerning the most important uncertain parameters can be used to guide field and laboratory investigations.
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    Contamination of a well in a uniform background flow (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 191-207 
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    ISSN: 1436-3259
    Keywords: Hydrodynamic dispersion ; Fokker-Planck equation ; backward equation ; boundary layer ; complex potential function ; fraction of contaminated particles that enter a well
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In this paper we describe the transport of pollution in groundwater in the neighbourhood of a well in a uniform background flow. We compute the rate at which contaminated particles reach the well as a function of the place of the source of pollution. The motion of a particle in a dispersive flow is seen as a random walk process. The Fokker-Planck equation for the random motion of a particle is transformed using the complex potential for the advective flow field. The resulting equation is solved asymptotically after a stretching transformation. Finally, the analytical solution is compared with results from Monte Carlo simulations with the random walk model. The method can be extended to arbitrary flow fields. Then by a numerical coordinate transformation the analytical results can still be employed.
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    Generation of runoff series at ungauged locations using empirical orthogonal functions in combination with kriging (1992)
    Springer
    Stochastic environmental research and risk assessment 6 (1992), S. 255-269 
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    ISSN: 1436-3259
    Keywords: Emprical Orthogonal Functions ; interpolating runoff ; kriging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The method of Empirical Orthogonal Functions (EOF method) is combined with an objective interpolation technique, kriging, to generate runoff series at ungauged locations. In a case study the results are compared to series interpolated by a combination of EOF analysis and regression using catchment characteristics as independent variables. The results are also compared to linear weighting of an existing runoff series, a commonly used method for spatial interpolation. The influence of altitude on the runoff is studied comparing kriging based on 2 and 3 coordinates. The study showed that the capacity of EOF analysis combined with kriging is as good as the traditionally used linear weighting. The results, when altitude is included in the kriging, are improved.
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    Estimation of periodicities in hydrologic data (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 270-288 
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    ISSN: 1436-3259
    Keywords: Periodicities ; hydraulic cycle ; spectral methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Periodicites in hydrologic data are frequently estimated and studied. In some cases the periodic components are subtracted from the data to obtain the stochastic components. In other cases the physical reasons for the occurrence of these periodicities are investigated. Apart from the annual cycle in the hydrologic data, periods corresponding to the 11 year sunspot cycle, the Hale cycle and others have been detected. The conclusions from most of these studies depend on the reliability and robustness of the methods used to detect these periodicities. Several spectral analysis methods have been proposed to investigate periodicities in time series data. Several of these have been compared to each other. The methods by Siddiqui and Wang and by Damsleth and Spjotvoll, which are stepwise procedures of spectrum estimation, have not been evaluated. Two of the methods of spectral analysis proposed by Siddiqui and Wang and by Damsleth and Spjotvoll are investigated in this study by using generated and observed data. Siddiqui and Wang's method is found to be superior to the Damsleth and Spjotvoll's method.
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    On the shot-noise streamflow model and its applications (1992)
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    Stochastic environmental research and risk assessment 6 (1992), S. 289-303 
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    ISSN: 1436-3259
    Keywords: Stream flow series ; shot-noise model ; sadolle-point approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In this paper we consider the shot-noise model of streamflow series. We show how design discharge can be obtained by the stochastic intensity of thinned Poisson processes describing the peaks over a threshold. The main result concerns the stationary distribution of peaks. We derive an explicit expression for this limit distribution in terms of its Laplace transform. Approximation formulas are developed making use of the saddle point method for the asymptotic evaluation of contour integrals and the Post-Widder formula for inversion of Laplace transforms. We illustrate this methods on the case of Gamma-distributed shots. The stationary peak distribution is used to approximate the maximum value distribution for larger time intervals.
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    Information frameworks for conceptual engineering design (1994)
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    Engineering with computers 10 (1994), S. 22-32 
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    ISSN: 1435-5663
    Keywords: Conceptual design ; Database ; Frameworks ; Information management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract An information modeling approach is used to gain an understanding of the information and decision content of conceptual engineering design. Information frameworks are presented that attempt to represent the key decisions made during conceptual design. Elements of the frameworks are derived from results from design theory and methodology and decision theory. Using a number of products, the frameworks are demonstrated in simulated design situations. The models provide an explicit, generic and consistent perspective for identifying the information content of conceptual designs.
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    URL: http://dx.doi.org/10.1007/BF01206537
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    Aluminium electrolytic cells: A computer simulator for training and supervision (1994)
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    Engineering with computers 10 (1994), S. 12-21 
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    ISSN: 1435-5663
    Keywords: Aluminium electrolysis ; Expert systems ; Modelling ; Simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A workstation-based simulator of an aluminium electrolytic cell has been constructed. A mathematical model of the cell is integrated with a database and a knowledge base, and the simulator serves as a tool for the training of personnel and for research related to cell dynamics and cell control. When used in conjunction with an expert system, it provides a powerful decision-making tool or an efficient supervisory system. The mathematical model, the simulator itself, the user environment, the interactive simulation procedure as well as examples of the use of the simulator are presented in detail.
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    A review of automatic dimensioning and tolerancing schemes (1994)
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    Engineering with computers 10 (1994), S. 63-80 
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    ISSN: 1435-5663
    Keywords: Dimensioning ; Tolerancing ; Variational geometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Dimensioning and tolerancing are very important issues in product design and manufacture. This paper gives a survey and review of the current state-of-the-art solutions to the problem of finding a meaning for dimensions and tolerances. Dimensioning and tolerancing in current engineering practices and researches in these topics are also discussed.
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    A new programming paradigm for engineering design software (1994)
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    Engineering with computers 10 (1994), S. 95-111 
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    ISSN: 1435-5663
    Keywords: Engineering design ; Formal ; Functional programming ; Object orientation ; Programming language
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Currently available programming and database systems are insufficient for engineering applications. The authors contend that a logical progression from a formal conceptual model of the engineering domain to a computational model will lead to new programming paradigms capable of directly supporting engineering applications in a rigorous, concise manner. A formal domain model devised by the authors, theHybrid Model (HM) of design information, is briefly introduced. It is an extension of axiomatic set theory and is discussed in detail elsewhere. HM forms the basis ofDesigner, a prototype-based object-oriented programming language supporting a signature-based canonical message-passing mechanism and multiple inheritance. Designer is implemented using the Scheme programming language. Because Designer satisfies a formal conceptual model, and because it is based on a formally specified language, its robustness and logical validity are superior to those of other languages not founded on formal principles. Designer combines concepts of functional and object-oriented programming to provide the formal rigor and flexibility to capture the complex and strongly interrelated information that designers use. Examples demonstrate how Designer represents design information. The results of the authors' research indicate that Designer can capture design information (including aspects of functional requirements and design intent) effectively and efficiently.
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    Rule-based design of a material processing component (1994)
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    Engineering with computers 10 (1994), S. 81-94 
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    ISSN: 1435-5663
    Keywords: Design ; Expert system ; Extension ; Material processing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The main thrust of this research is in developing aknowledge-based system for the design of components for a material processing system. In particular, this paper concentrates on developing methodologies forinitial design andredesign in a quantitative and qualitative format. A die for plastic extrusion has been selected as the subject material processing component. A design algorithm using best first heuristic search and expert knowledge, both in procedural and declarative form, is the core of the scheme. Apart from this expert, the suggestedselection procedure for candidate design is also seen to accelerate the design scheme. The methodologies presented enableefficient design of the component. Some generality has been accomplished by the implementation of the techniques to dies of different cross-sectional shapes. The software is written inLisp within an object-oriented software package using analysis modules written in C.
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    Announcement (1994)
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    Engineering with computers 10 (1994), S. 124-124 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    URL: http://dx.doi.org/10.1007/BF01200182
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    A tandem architecture for cooperating knowledge-based concurrent engineering systems (1994)
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    Engineering with computers 10 (1994), S. 112-123 
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    ISSN: 1435-5663
    Keywords: Agent-based framework ; Architecture ; Concurrent engineering ; Cooperating expert systems ; Tandem integration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper proposes a tandem architecture for cooperating heterogeneous expert systems. Two levels of meta and working expert systems are involved. The working-level expert systems (W-ES), which may be implemented in their own computational environments and in private proof languages, are mainly for application computations. The meta-level expert systems (M-ES), using a common argument language, are mainly responsible for cooperation. The prototype AGENTS system is described for constructing M-ES. Interaction among W-ES has been transformed into two forms: communication between M-ES through ordinary AGENTS messages and communication between M-ES and the corresponding W-ES using the Deductive Inference Language (DIL). DIL predicates are provided for defining DIL: messages, actuators and converters for interpreting DIL queries and instantiating variables. By this approach, stand-alone capability of infividual systems is retained at the working-level and cooperation is achieved effectively with minimum embellishment at the meta-level.
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    URL: http://dx.doi.org/10.1007/BF01200181
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    A proposed structure for a rule-based description of parametric forms (1994)
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    Engineering with computers 10 (1994), S. 155-161 
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    ISSN: 1435-5663
    Keywords: Constrains ; Geometric ; Parametric ; Product form
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Much work has been carried out on the creation of protocols for the exchange of data between CAD systems, but very little on the transfer of knowledge. The knowledge behind the development of a product is vital if modifications and adaptations are to be made within a concurrent development environment. Current CAD systems only contain a limited level of product knowledge through user-defined parametric structures. It is the underlying relationships in these programs that need to be communicated between systems, rather than the form of their individual programming languages. A generic structure is proposed that is able to handle both the current level of parametric programming and is suited to the resolution of conflict through the use of constraint modelling procedures. The structure of a parametric description is described and decomposed into its fundamental components. These components are then re-formed within a truth maintenance structure to allow a transfer protocol to be created. The derived protocol structure is then demonstrated on a number of simple examples.
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    URL: http://dx.doi.org/10.1007/BF01198741
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    Concurrent iterative design and the integration of finite element analysis results (1994)
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    Engineering with computers 10 (1994), S. 245-257 
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    ISSN: 1435-5663
    Keywords: Design methodology ; Iterative design ; Concurrent design ; Features ; Form templates ; Finite element analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract To help foster concurrency in engineering design, methodologies are needed to support the interpretation and abstraction of numerical simulation results for design modification purposes. A methodology is presented in this paper for the integration of continuum-based numerical simulations into a computational system for concurrent design of mechanical components. The technique involves conversion of low-level numerical data, such as that obtained by finite element analysis, into high-level symbolic representations calledform templates. The form templates are based onrudimentary features which carry meaningful qualitative descriptions abstracted from either manufacturing and/or functional numerical simulations. The form templates are superimposed on the design's primary representation in the solid modeler to facilitate the cognitive mapping of concurrent destructive or constructive solid modeling features for design modifications. Examples are presented to demonstrate the methodology.
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    URL: http://dx.doi.org/10.1007/BF01202369
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    Symbolic analysis of linear polyhedra (1990)
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    Engineering with computers 6 (1990), S. 17-29 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper concerns several analytical problems related to linear polyhedra in euclidean three-dimensional-space. Symbolic formulas for line, surface, and volume integration are given, and it is shown that domain integrals are computable in polynomial time. In particular, it is shown that mass, first and second moments, and products of inertia are computable inO(E) time, whereE is the number of edges of the boundary. Simple symbolic expressions for the normal derivatives of domain integrals are also derived. In particular, it is shown that they are closely linked to the topology of the integration domain, as well as that they are expressible as combinations of domain integrals over lower-order domains (faces, edges, and vertices). The symbolic results presented in this paper may lead to an easy incorporation of integral constraints, for example, concerning mass and inertia, in the engineering designing process of solid objects.
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    URL: http://dx.doi.org/10.1007/BF01200201
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    Management of complex structural engineering objects in a relational framework (1990)
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    Engineering with computers 6 (1990), S. 81-92 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract To structure the development of an integrated building design environment, the global representation of the design data may best be organized in terms of hierarchies of objects. In structural engineering design we deal with large sets of independent but interrelated objects. These objects are specified by data. For an engineering design data base the system must be able to model the objects composing the design as well as to manage effectively the design data. The data base management system therefore needs to have some knowledge of the intended use of the data, and must provide an abstraction mechanism to represent and manipulate objects. Much recent research in engineering data bases focuses on object management for specific tasks but gives little attention to the shareability of the underlying information. This paper describes an architecture for the management of complex engineering objects in a sharable, relational framework. Potential application of this approach to object management for structural engineering analysis and design is discussed.
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    URL: http://dx.doi.org/10.1007/BF01200240
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    Toward a unified representation of mechanical assemblies (1990)
    Springer
    Engineering with computers 6 (1990), S. 103-112 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Current solid modeling systems are suitable for modeling individual mechanical parts but they do not capture therelationships and/ordependencies among the geometric features of parts in an assembly. Research in the area of “part and assembly modeling” focuses on capturing this missing information. This paper surveys feature-based models for mechanical assemblies and methods for deriving the actual part positions from the part relationships. We have attempted to extract from the literature the essential requirements for a unified feature-based assembly model. Three levels of representation are envisaged—representation of part positions in terms of their spatial coordinates, representation of geometric (feature) relations between individual parts, and representation of the assembly hierarchy. The actual relative positions can be derived from the hierarchical assembly model. Possible areas of application are tolerance analysis and synthesis, automatic generation of assembly sequences, and kinematic analysis and synthesis.
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    URL: http://dx.doi.org/10.1007/BF01200242
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    Representation of assemblies for automatic tolerance chain generation (1990)
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    Engineering with computers 6 (1990), S. 121-126 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A scheme of representing assemblies and an algorithm for the tolerance chain generation are developed so that tolerance chains of assemblies can be generated automatically to accommodate tolerance analysis at the assembly level. In the hierarchical data structure representing an assembly the connectivity information is carried by the instances of components and subassemblies, and the mating relations between each pair of mating entities are described by mating links, mating paths, mating conditions, and mating features. Mating graphs are derived from the mating links before they are searched for the generation of tolerance chains. The scheme has been implemented in a prototype interactive package that allows the user to model assemblies directly without detailed object modeling. Several examples of various complexity have been tested with success.
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    URL: http://dx.doi.org/10.1007/BF01200244
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    Distributed concurrent engineering computation on a network of microcomputers (1990)
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    Engineering with computers 6 (1990), S. 145-152 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A programming method that facilitates interworkstation communications on a local area network (LAN) of microcomputers has been developed. Communications are managed using a set of common access status and data files, which are writen to and read from the file server hard disk. Use of this programming method permits the work load associated with large computational problems to be distributed to various workstations connected to a LAN for concurrent processing, and has resulted in substantial solution time savings in problems that have been run. Test problems have been programmed in IBM Compiled BASIC [1] and are continuing with further programs in BASIC and IBM Professional FORTRAN [2]. Applications to actual computational engineering problems are presently being investigated and are briefly discussed. This paper describes the basic principles underlying the distributed processing technique that was developed and presents several example problems that were run to test the technique and develop benchmark results for a particular LAN configuration.
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    URL: http://dx.doi.org/10.1007/BF01200312
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    An intelligent specifications extraction interface for structural design (1990)
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    Engineering with computers 6 (1990), S. 153-165 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Many descriptions of the design process do not include the specifications as part of the process, but rather as an input to the design. Once the specifications are considered to be the input, the assumption is made that they are in a form that is suitable for the design process to proceed. The need for a design always starts with ill-defined objectives. The process by which this information is transformed into well-defined design objectives is called the design specification extraction process. An attempt to expose the underlying structure of the first step in the design process—the design specifications—is presented in this paper. The extraction of specifications is divided into four major tasks—diagnosis or information gathering, interpretation and assessment, classification and decomposition, and information patching. The conceptual framework for the design specification extraction and synthesis is implemented in the expert system program SEISD (specification extraction interface for structural design) developed in the LISP programming language. A few examples are presented to demonstrate the implementation strategies. These examples are drawn from the specific problem of a beam design.
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    URL: http://dx.doi.org/10.1007/BF01200313
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    A formal approach to automating conceptual structural design, part II: Application to floor framing generation (1991)
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    Engineering with computers 7 (1991), S. 91-107 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The function of the structural system in a building is to transfer gravity as well as lateral loads from their points of origin to the ground. Floor framing generation involves providing a path to transfer the gravity loads to the ground through various structural elements in an architectural plan while meeting the requirements imposed by other entities, such as the architect, the mechanical engineer, and the contractor, involved in the design/construct process. In this paper a formal approach for generating floor framing plans for steel office buildings is presented. We describe the knowledge and the reasoning behind a computer system, FFG (floor framing generator), which generates floor framing schemes for steel office buildings that are rectangular in plan and have a single service core. Constraints arising from structural as well as exogenous considerations are enumerated and their effect on framing schemes is identified. We also elaborate on the evaluation mechanism for ranking alternative schemes, in addition to providing details of the computer implementation.
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    URL: http://dx.doi.org/10.1007/BF01195563
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    Announcement (1991)
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    Engineering with computers 7 (1991), S. 129-129 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
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    URL: http://dx.doi.org/10.1007/BF01195566
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    Design of an optimal damper to minimize the vibration of machine tool structures subject to random excitation (1991)
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    Engineering with computers 7 (1991), S. 199-208 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The vibration of machine tools during machining adversely affects machining accuracy and tool life, and therefore must be minimized. The cutting forces for stable turning are generally known to be random, and hence excite all the resonance modes. Of all these modes, those that generate relative motions between a cutting tool and a workpiece are of concern. This paper presents a new approach for designing an optimal damper to minimize the relative vibration between the cutting tool and workpiece during stable machining. An approximate normal mode method is employed to calculate the response of a machine tool system with nonproportional damping subject to random excitation. The major advantage of this method is that it reduces the amount of computation greatly for higher-order systems when responses have to be calculated repeatedly in the process of optimization. An optimal design procedure is presented based on a representative lumped parameter model that can be constructed by using existing experimental or analytical techniques. The two-step optimization procedure based on the modified pattern search and univariate search effectively leads the numerical solution to the global minimun irrespectively of initial values even under the existence of many local minima.
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    URL: http://dx.doi.org/10.1007/BF01206362
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    Toward the integration of knowledge for engineering modeling and computation (1991)
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    Engineering with computers 7 (1991), S. 209-224 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Recent developments in computer science, especially in the area of artificial intelligence (AI), have made possible the representation of knowledge in symbolic terms. This, in turn, has made it possible to represent and integrate a broader range of engineering knowledge so as to provide new kinds of computer support for both analysis and design. This paper presents a typology of engineering knowledge to provide a conceptual basis for its computational integration. A review of the roles of numerical, geometric, and symbolic representations is also given within the context of the knowledge typology. Illustrations are provided from the domain of structural engineering.
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    URL: http://dx.doi.org/10.1007/BF01206363
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    Localization of rational B-spline surfaces (1991)
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    Engineering with computers 7 (1991), S. 237-252 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Localization of curved surfaces is an important problem in the manufacturing and inspection of mechanical elements and in the simulation of manufacturing processes. The objective of this paper is to provide an efficient method for accurate localization of a single free-form surface of the rational B-spline form. Our approach is based on the following components—first, representation of position tolerances in terms of a ball offset tolerance region around the ideal rational spline surface; to facilitate interrogation and data exchange, this is followed by approximation of the bounding surfaces of the tolerance region with rational B-splines; next, optimal positioning of the target surface with respect to the ideal surface by minimizing a distance-based norm; finally, verification of compliance with position tolerance constraints. Examples illustrate our technique.
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    Supporting engineering applications by new data base processing concepts—An experience report (1992)
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    Engineering with computers 8 (1992), S. 31-49 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Data base management systems for nonstandard applications (nonstandard data base systems, NDBS), in particular for engineering applications, nowadays constitute one of the most important challenges in the area of data base research. Some major obstacles are concerned with problems of modeling and processing complex engineering objects. Some new system architectures have been proposed, and appropriate concepts for handling the new types of application objects have been developed over the past few years. Based on PRIMA, an NDBS-kernel prototype implementation, we motivate a workstation-oriented architecture for NDBS application systems. We explain a prototypical application system in the environment of VLSI-chip design, which serves as a practical examples in handling complex objects. Analyzing the weaknesses of this initial approach, we derive general concepts for application linkage, discussing, in particular, key issues for an efficient object processing and language binding.
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    URL: http://dx.doi.org/10.1007/BF01206335
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    Feature-based modeling for automatic mesh generation (1992)
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    Engineering with computers 8 (1992), S. 1-12 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Automatic meshing algorithms for finite element analysis are based on a computer understanding of the geometry of the part to be discretized. Current mesh generators understand the part as either a boundary representation, an octree, or a point set. A higher-level understanding of the part can be achieved by associating engineering significance and engineering data, such as loading and boundary conditions, with generic shapes in the part. This technique, called feature-based modeling, is a popular approach to integrating computer-aided design (CAD) and computer-aided manufacturing through the use of machinable shapes in the CAD model. It would seem that feature-based design also could aid in the finite element mesh generation process by making engineering information explicit in the model. This paper describes an approach to feature-based mesh generation. The feature representation of a fully functioning feature-based system that does automatic process planning and inspection was extended to include finite element mesh generation. This approach is based on a single feature representation that can be used for design, finite element analysis, process planning, and inspection of prismatic parts. The paper describes several advantages that features provide to the meshing process, such as improved point sets and a convenient method of simplifying the geometry of the model. Also discussed are possible extensions to features to enhance the finite element meshing process.
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    URL: http://dx.doi.org/10.1007/BF01206333
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    Approaches to AI methodology in reinforced concrete structures: a case study (1992)
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    Engineering with computers 8 (1992), S. 93-100 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract A system developed earlier for reinforced concrete halls layout is studied and justified from different aspects. Also, updates of both capabilities and limitations, which were recently incorporated in the system, are emphasized. Some of the original aspects of the system were reviewed and modified, to overcome some of the drawbacks in the earlier presentation. The system's organization remains almost the same. Some suggestions for further improvements to the system are presented as well. Finally the function of the system is illustrated by a sample run of the system.
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    URL: http://dx.doi.org/10.1007/BF01200105
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    Construction of a hybrid sweep-CSG modeler—The sweep-CSG representation (1992)
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    Engineering with computers 8 (1992), S. 101-119 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Applying sweep operations on 2-D closed contours is a well known method for modelling 3-D solid objects. This paper deals with the implementation of a solid modeler with sweep as the basic representational scheme. In the modeler, a solid is defined by sweeping a planar polygon along a linear or curved trajectory. A sculptured solid may also be defined by using a beta-spline curve for the sweep polygon and a cubic B-spline curve for the sweep trajectory. By incorporating Boolean operations, a hybrid sweep-CSG solid modeler is implemented. The current implementation allows translational, rotational, and twisted sweep operations on a planar polygon composited of lines and arcs. In addition, a solid primitive can also be created by sweeping a planar closed beta-spline curve along a cubic B-spline curve.
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    URL: http://dx.doi.org/10.1007/BF01200106
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    An automatic coarse and fine surface mesh generation scheme based on medial axis transform: Part i algorithms (1992)
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    Engineering with computers 8 (1992), S. 121-137 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract We present an algorithm for the generation of coarse and fine finite element (FE) meshes on multiply connected surfaces, based on the medial axis transform (MAT). The MAT is employed to automatically decompose a complex shape into topologically simple subdomains, and to extract important shape characteristics and their length scales. Using this technique, we can create a coarse subdivision of a complex surface and select local element size to generate fine triangular meshes within those subregions in an automated manner. Therefore, this approach can lead to integration of fully automatic FE mesh generation functionality into FE preprocessing systems.
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    URL: http://dx.doi.org/10.1007/BF01200364
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    The complementary roles of expert systems and database management systems in a design for manufacture environment (1992)
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    Engineering with computers 8 (1992), S. 139-149 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Effective product design that satisfies functional requirements and can be manufactured easily requires vast amounts of knowledge on the part of the design engineer. This paper focuses on the complementary roles of expert systems and database management systems as they relate to the Intelligent Design System (IDS) in a Design for Manufacture (DFM) environment. Each technology complements the other in its strengths and abilities. The database management system provides during the design process. The expert system provides a reasoning mechanism for identifying manufacturing violations and generating meaningful recommendations. These components work cooperatively with a CAD interface to form a unified, intelligent design environment. An information flow analysis of the Intelligent Design System resulted in the development of three distinct classifications of information within the database: CAD data, a design catalog, and a knowledge base. The CAD data tables employ an, object oriented approach to store specific information about the physical contains cost, weight, and strength characteristics of the standard parts and fasteners used within the system. The knowledge base contains rules and heuristics concerning design and manufacturing methodologies. The placement of the expert system rules in the database represents an innovation. As a result, the expansion and updating of the materials, fasteners, standard parts, or manufacturing processes used by the Intelligent Design System is facilitated without increased due to the efficient management of the knowledge base by the database management system. This allows the designer to modify the knowledge and help the system to learn without the need for a knowledge engineer.
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    An axiomatic theory of engineering design information (1992)
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    Engineering with computers 8 (1992), S. 197-211 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Recent research in design theory has sought to formalize the engineering design process without particular concern for the paradigm used to model design information. The authors propose that no correct formalization of the design process can be achieved without first formalizing the semantics of the information used in the process. To this end, the authors present a new formal theory of design information. The theory, called the hybrid model (HM), is an extended form of axiomatic set theory, and relies on it for consistency and logical rigor. The theory is stated as a collection of axioms, using a standard logic notation. Design entities are modeled by formal units calledobjects. Generalized functions and relations are used to formalize important ordering schemes and abstraction mechanisms relevant to design, including classification by structure and by function, aggregation, specialization, and generalization. The hybrid model is meant not only to aid in the study of the design process itself, but also to improve communications between designers, assist standardization of design specifications, and develop new, powerful software tools to aid the designer in his work.
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    URL: http://dx.doi.org/10.1007/BF01194322
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    A transaction management framework for collaborative engineering (1992)
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    Engineering with computers 8 (1992), S. 213-232 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper discusses the various novel functionalities of a transaction management system for collaborative engineering applications. These features include grouped and shared transactions, dynamic database partitioning, communicative locking, dependency maintenance, update notification schemes, and version management of data configurations. It also establishes protocols for data consistency maintenance on the basis of application semantics and encapsulation of nonserializable data sharing in local databases rather than by the notion of global database consistency. Finally, it presents strategies for implementing these features using a commercial object oriented database management system (OODBMS) environment (ONTOS).
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    URL: http://dx.doi.org/10.1007/BF01194323
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    Engineering materials information systems (1992)
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    Engineering with computers 8 (1992), S. 243-252 
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    ISSN: 1435-5663
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Materials properties information systems are poorly understood. Many databases of materials properties and designations have been produced but, except in the most modest of cases, they have been less successful than their creators had hoped Knowledge based systems (KBS) are subject to exactly the same problems as data based materials information systems and it is important to realize what these are before the special character of KBSs can be used to alleviate them. This paper surveys the unusual and difficult aspects of engineering materials information that must be handled by any organizing methodology, whether manual or computerized, data based or knowledge based, handling information which is stored or inferred.
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    URL: http://dx.doi.org/10.1007/BF01194325
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    A KBES for integrated engineering (1993)
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    Engineering with computers 9 (1993), S. 1-16 
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    ISSN: 1435-5663
    Keywords: Blackboard ; Expert systems ; Industrial structures ; Integrated engineering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The expert process of engineering involves application of knowledge fundamental to the engineering process at one end, and of compiled knowledge in the form of heuristics gained through many years of experience at the other. Developments in Artificial Intelligence have made the process of computer aided engineering richer by enabling the simulation of this human process of engineering, which until now has been difficult to capture. Knowledge Based Expert Systems (KBES) in engineering developed so far have addressed only narrow domains of the entire process of engineering. This paper discusses a KBES shell (IES) that integrates various AI technologies, which makes it possible to implement new problem-solving strategies required for efficient handling of the entire engineering process. Issues in the integrated process of engineering are discussed first, in order to evolve a specification for the shell. The blackboard architecture is shown to be the ideal backbone for such a shell. The details of inference techniques, the knowledge based backtracking mechanism and the DBMS used in the IES are presented. The application of the IES is demonstrated using the domain of integrated engineering of steel industrial structures as an example. This application encompasses the engineering activities of conceptual design, detailed design, documentation and construction planning.
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    URL: http://dx.doi.org/10.1007/BF01198249
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    The use of photodynamic therapy (PDT) for the treatment of superficial tumours on the bladder wall (1990)
    Springer
    Lasers in medical science 5 (1990), S. 5-12 
    Details
    ISSN: 1435-604X
    Keywords: Photodynamic therapy ; Superficial bladder tumours ; Dosimetry ; Isotropic light sensors ; Photosensitizers ; Wavelength of irradiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract The use of photodynamic therapy (PDT) for the treatment of superficial tumours on the bladder wall is described. Details are given on the laser, methods of delivering light into the bladder, suitable commercial dosimetry systems and instrumentation suitable for making light measurements on the bladder wall during therapy. New alternative photosensitizers are discussed in some detail. Some early clinical results are presented and the current problems with this type of therapy are highlighted.
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    URL: http://dx.doi.org/10.1007/BF02032616
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    Copper vapour laser treatment of port wine stains: a patient questionnaire (1990)
    Springer
    Lasers in medical science 5 (1990), S. 43-49 
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    ISSN: 1435-604X
    Keywords: Copper vapour laser ; Argon ion laser ; Port wine stains ; Telangiectasia ; Spider naevi ; Questionnaire
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract A questionnaire was sent to 242 patients who had undergone treatment with yellow light (578 nm) from a copper vapour laser for a port wine stain (PWS), for facial telangiectasia (FT), or for a spider naevus (SN). The questionnaire covered the social implications of the lesion, the physical appearance of the lesion after treatment and the patient's judgement of how the treatment has affected them. Replies were received from 73% of the patients. The replies revealed that 83% PWS, 74% FT, and 81% SN patients felt there had been an improvement in their appearance compared with 2.5% PWS, 14% FT, and 7.5% SN patients who felt that their appearance had changed for the worse. The overall impression of the treatment was also very positive, especially with PWS patients, 91% would recommend the treatment to others, 84% would have the treatment again and 60% indicated their feelings regarding their overall treatment and the effect it had on their lives was very good.
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    URL: http://dx.doi.org/10.1007/BF02032622
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    Laser lithotripsy with a 504 nm pulsed dye laser: in vitro fragmentation related to stone weight and pulse energy (1990)
    Springer
    Lasers in medical science 5 (1990), S. 65-69 
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    ISSN: 1435-604X
    Keywords: Biliary calculi ; Laser lithotripsy ; Pulsed 504 nm dye laser ; Salivary calculi ; Urinary calculi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Biliary, urinary and salivary stones were fragmented in vitro with a flashlamp-pumped dye laser operating at 504 nm. A clinical fragmentation criterion was formulated; fragmentation was continued until all fragments had passed through a sieve with holes of 1.5×1.5 mm2. The number of shots of 50 mJ necessary for total fragmentation appeared to be proportional to the stone mass. The three types of stones showed statistically significant differences in the number of shots per unit mass, necessary for fragmentation. On biliary calculi we investigated the influence of the energy per laser pulse. For pulse energies of 32 mJ and larger, the energy necessary for fragmentation appeared to be proportional to the initial stone mass, but did not depend on the energy per pulse.
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    On the physical rationale of laser induced hyperthermia (1990)
    Springer
    Lasers in medical science 5 (1990), S. 121-128 
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    ISSN: 1435-604X
    Keywords: Hyperthermia ; Tissue optics ; Thermal properties ; Lasers ; Cancer therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract The rationale of hyperthermic treatment of tumours is based on the phenomenon that several tumours have a reduced tolerance for exposure to temperatures in the region 42–47 °C for 20–30 min. Hyperthermia may also be used as an adjunct to other modalities such as chemotherapy, conventional radiation therapy or photodynamic therapy. Methods for introducing hyperthermia include electromagnetic radiation in the radiofrequency and microwave region as well as ultrasonic waves. The use of lasers emitting within the visible and near infrared part of the spectrum has the potential to initiate a local elevation of the temperature. The extension of the heated region will depend on optical wavelength, tissue composition and blood perfusion. Typical linear dimensions of the 42–47 °C temperature region will range from 2–3 mm and up to about 10 mm. Superficial tumours may be heated by direct irradiation whereas deeper lying tumours or lesions of large extent may require light delivered by one or several inserted optical fibres. Laser-induced hyperthermia may be of particular relevance in the treatment of retinal or choroidal tumours. Visible and near infrared radiation can be transmitted through the cornea, the lens and the vitreous with negligible loss. The absorption in the tumour is, however, significantly larger and the main part of the optical power will be absorbed within 0.5–5 mm into the neoplastic tissue. This paper emphasizes a discussion of the basic principles.
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    Laser therapy in eye tumours (1990)
    Springer
    Lasers in medical science 5 (1990), S. 137-141 
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    ISSN: 1435-604X
    Keywords: Retinal epiblastic tumours ; Uveal tumours ; Photocoagulation therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Two kinds of tumours are of particular importance in ophthalmology: the retinal epiblastic tumours, like the retinoblastoma and uveal tumours, like the uveal melanoma and the metastatic tumours. The photocoagulation therapy is sometimes used as a first treatment or as the only treatment, and this kind of therapy is useful according to our experience to complete conservative tumour therapy with radioactivity or cytostatic chemistry. A review of literature is done and we present several clinical examples from our own experience in the Lisbon Institute of ophthalmology and in the University Eye Clinic, Santa Maria Hospital, Lisbon.
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    Fluorescence detection and photodynamic treatment of photosensitized tumours in special consideration of urology (1990)
    Springer
    Lasers in medical science 5 (1990), S. 207-212 
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    ISSN: 1435-604X
    Keywords: Bladder tumour ; Diagnosis ; Fluorescence ; Photodynamic therapy ; Photosensitization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Most methods of modern laser tumour therapy are physically based on the conversion of light to heat. Recently tumours have also been treated using ionizing processes for tissue ablation. Photodynamic laser therapy (PDT), however, involves light-induced non-thermal biochemical processes and the use of a photosensitizer. Several drugs are known to be stored selectively in tumours after systemic application. This transient marking can be used for diagnostic and therapeutic procedures. The marker most commonly used is dihaematoporphyrin ether/ester (DHE) intravenously injected at doses of 0.2–3.0 mg/kg bodyweight for diagnosis and therapy, respectively. The corresponding clearance intervals after injection of DHE range from 3–48 h to 25–75 h. Detection of photosensitized tumours might offer great advantages. The highly sensitive two-wavelength laser excitation method with computerized fluorescence imaging recently has been transferred to the hospital for clinical tests. Photoinduced production of singlet oxygen is claimed to be the initial process which leads to later tumour destruction and therapy. PDT has been applied to 20 patients suffering from superficial tumours (TIS GII–III) recurred after application of other treatments. The results after PDT were evaluated by three-monthly check-ups (endoscopy, cytology, bladder mapping, renal ultrasonography) as well as by computed tomography (CT) examination at 8–13 month intervals. In six patients treated by PDT no tumour recurrence has been found over the whole observation period of up to 5 years. Four patients have remained free of tumour (12 and 14 months) after repeated transurethral resection (TUR) and Nd-YAG laser therapy following PDT. Due to an initial application of insufficient irradiation four patients required a second PDT. In one patient a circumscribed dysplasia appeared at the left ostium 26 months following PDT and was treated successfully by means of thermal Nd-YAG laser irradiation following TUR. In six patients slight mucosal atypia persisted for a period of at least 2.5 years. One cystectomy had to be performed because of bladder shrinkage. The dissected bladder, however, was free of tumour. These preliminary results suggest that PDT is justified in patients who are in a worst-case situation with cystectomy recommended in case of recurrent superficial TIS bladder carcinoma and indicate the future potential of photodynamic therapy of tumours. Homogeneous irradiation of the area to be treated and a reliable light dosimetry are prerequisites for an effective tumour therapy. Standard instruments for a routine application do not exist, but are under development.
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    Laser surgery and gynaecological tumours (1990)
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    Lasers in medical science 5 (1990), S. 213-215 
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    ISSN: 1435-604X
    Keywords: Gynaecological tumours ; Endometriosis ; Haematoporphyrin derivative
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
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    URL: http://dx.doi.org/10.1007/BF02031385
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    Palliative treatment for oesophagogastric cancer by laser photocoagulation (1990)
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    Lasers in medical science 5 (1990), S. 217-221 
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    ISSN: 1435-604X
    Keywords: Oesophageal cancer ; Nd-YAG laser ; Endoscopic treatment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Over a 10 year period, 149 non-surgical patients were treated for palliation of an oesophageal cancer. One hundred and twenty-nine patients had an advanced cancer; 20 had a small cancer. The initial success rate was 81% and the complications rate was 3.1% for advanced cancers. Average duration of improvement after initial improvement was 138 days. Location was the only factor affecting the initial results in advanced cancers. Improvement duration was affected by the reason for treatment and an association of treatments during follow up. A complete local destruction of the small cancers was obtained in 18 patients. Three patients had a local recurrence during follow up.
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    Economic appraisal of laser applications in medicine (1990)
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    Lasers in medical science 5 (1990), S. 253-269 
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    ISSN: 1435-604X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Laser applications are developing rapidly in medicine. Virtually every specialty of surgery, and a number of medical specialties, are using the laser for several conditions, and the number of conditions treated seems to grow every day. This fact is of concern to policy-makers in a time of limited resources for health care. Increasingly, health policy decisions are guided by costeffectiveness studies of medical applications. This paper reviews evidence of cost-effectiveness for a number of relatively mature laser applications. In general, although available studies are suggestive of benefit, effectiveness has been demonstrated for relatively few laser applications. Little reliable cost information has been developed, although out-patient therapy and shortened length of stay in hospital seem to be demonstrated for several conditions.
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    Chromophores in tissue for laser medicine and laser surgery (1990)
    Springer
    Lasers in medical science 5 (1990), S. 289-292 
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    ISSN: 1435-604X
    Keywords: Cancer ; Laser ; Chromophores ; Photodynamic therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Chromophores in tissue are of considerable interest for the tissue interactions with lasers in the visible light range. The natural chromophores in man are essentially melanin and red cell haemoglobin. With the development of Photodynamic Therapy (PDT) in the treatment of human cancer, the new technology of exogenous chromophores was developed and continues to expand both in laser medicine and laser surgery. This technology relates specific chromophores to specific wavelengths for the destruction of tumours and has been very effective for PDT in those instances where there is accessibility to the tumour mass by the laser beam. The problems today are concerned with how to mark these malignant foci deep in the tissue, how to detect them, and how to direct selected laser beams to the marked carcinomatous tissue. In laser medicine, the field is expanding especially for tissue and laboratory diagnostics.
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    Quantitative and comparative study of haematoporphyrin-derived photosensitizers on a murine tumour model (1990)
    Springer
    Lasers in medical science 5 (1990), S. 309-316 
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    ISSN: 1435-604X
    Keywords: Photodynamic therapy ; PDT ; Fluorescence ; Haematoporphyrin derivative ; HPD ; Diagnosis ; Murine tumour ; Laser ; Pharmacodynamic ; Pharmacokinetic ; Regrowth delay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Eight commercially available HPD-photosensitizers intended for photodynamic therapy were tested in a murine tumour model with regard to their therapeutic efficacy. The regrowth delay of the fibrosarcoma SSK-2 on the mouse C3H, Neuherberg-line, was determined 3, 24, 48 and 72 h after injection of the drugs (dose: 9 mg kg−1 body weight). The corresponding pharmacodynamics, as measured by regrowth delay, were approximated by an exponential function and the characterizing coefficients derived. These coefficients served to quantify the photodynamic properties of the drugs. The pharmacodynamics of five substances were compared with those obtained fluorometrically. The latter showed shorter decay constants than the therapy-correlated substances which indicates different metabolic behaviour of the therapeutic and diagnostically useful fluorescent components of haematoporphyrin-derived photosensitizers.
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    Meetings announcements (1990)
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    Lasers in medical science 5 (1990), S. 337-337 
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    ISSN: 1435-604X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
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    URL: http://dx.doi.org/10.1007/BF02032666
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    Effect of low energy laser on the growth and regeneration of capillaries (1990)
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    Lasers in medical science 5 (1990), S. 381-386 
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    ISSN: 1435-604X
    Keywords: HeNe laser irradiation ; Biostimulation ; Wound healing ; Capillary regeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Laser light of low energy is discussed to have an accelerating effect on wound healing. The aim of the present study was to proof whether HeNe laser irradiations have a positive effect on regeneration of capillaries. For this purpose aluminium chambers were implanted in the dorsal skin flap of Syrian hamsters. After coagulation of blood vessels by means of an argon laser the tissue was irradiated daily with the low energy light of a HeNe laser. Regeneration of capillaries was studied by means of intravital microscopy. The results of the study revealed a positive effect of low dose HeNe laser irradiation on the regeneration of capillaries at day 5 after the coagulation. The measurable part of the capillaries was about 27% higher for the irradiated animals compared to controls.
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    New laser literature (1990)
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    Lasers in medical science 5 (1990), S. 411-413 
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    ISSN: 1435-604X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
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    In vitro effects of CO2 laser irradiation on platelets: Influence of aspirin (1991)
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    Lasers in medical science 6 (1991), S. 15-21 
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    ISSN: 1435-604X
    Keywords: Laser ; Platelets ; Aspirin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Laser angioplasty involves intravascular laser irradiation which may affect platelets and aggregation. In this study we examined the in vitro effects of different energy doses and modes of CO2 laser irradiation on the platelet number, function and ultrastructure. Since aspirin is used in many patients suffering from coronary artery disease, the consequences of laser irradiation on aspirin-treated platelets were studied as well. We found that CO2 laser irradiation causes a dose-response reduction of the platelet number that is most pronounced with high energy-short duration irradiation, and a dose-response reduction in platelet aggregation which is independent of the mode of irradiation. Pretreatment with aspirin does not change the effects of laser irradiation on platelet number, while aggregation is reduced only at relatively high energy doses. Electron microscopy revealed significant intracellular injury following low energy irradiation, while progressive damage to membranes occurred in a dose-response mode, both in untreated and aspirin-treated platelets. The clinical application of our findings should be done cautiously since important in vivo factors, such as the effect of laser irradiation on the vessel wall and coagulation system, were not studied.
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    Book review (1991)
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    Lasers in medical science 6 (1991), S. 53-53 
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    ISSN: 1435-604X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
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    URL: http://dx.doi.org/10.1007/BF02042647
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    Percutaneous peripheral laser angioplasty with a pulsed Nd-YAG laser and sapphire tips (1991)
    Springer
    Lasers in medical science 6 (1991), S. 43-48 
    Details
    ISSN: 1435-604X
    Keywords: Atherosclerosis ; Peripheral arteries ; Laser angioplasty ; Pulsed Nd-YAG laser ; Sapphire tips
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Percutaneous transluminal laser angioplasty with a pulsed Nd-YAG laser (1064 nm wavelength, 100μs pulse duration, up to 0.4 J per pulse, 10 Hz repetition rate) coupled to optical fibres with sapphire tips of 1.8 and 2.2 mm diameter was performed under experimental conditions and then in 30 chronic occlusions of femoral and popliteal arteries in 22 patients. The experimental study in 11 human cadaverous arteries revealed that this laser system was effective in the recanalization of seven femoropopliteal occlusions, but the relative rigidity of the sapphire-tipped contact probe prevented its access to two infrapopliteal vessels. Two perforations occurred after the recanalization of 18 and 15 cm, respectively. Clinically the procedure was successful in 17 out of 25 sessions (68%). The probe formed a primary channel of at least 2.0 mm width which was further dilated by conventional balloon catheter. Ankle/brachial systolic pressure index (ABPI) increased from 0.43±0.13 to 0.79±0.21 after the procedure. In eight cases complications occurred. Two reocclusions were treated by Streptokinase infusion, two procedures were repeated 2 months later, one patient was referred to elective bypass surgery, and three patients were treated conservatively. Six patients were followed-up for more than 6 months. In one patient claudication of 400 m reappeared. ABPI showed a moderate decrease from 0.84±0.20 to 0.69±0.19. These first results are encouraging and it is likely that this method could become an important adjunct to balloon angioplasty.
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    Improved criteria for the recognition of atherosclerotic plaque using fluorescence spectroscopy (1991)
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    Lasers in medical science 6 (1991), S. 141-146 
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    ISSN: 1435-604X
    Keywords: Laser angioplasty ; Coronary artery disease ; Nitrogen laser ; Tissue fluorescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract To determine the fluorescence pattern for distinguishing normal (N) from calcified and fibrous plaque (P), fluorescence spectra of cadaveric aorta were measured with a spectrofluorometer. Emission (Em) and excitation (Ex) spectra corrected for instrumental response were obtained from 200 to 1000 nm. Specimens from 50 patients were measured less than 24 h after autopsy and then examined histologically. Spectra from 25 specimens demonstrated that the ratio of fluorescence intensity 460 nm/385 nm with Ex=337 nm provided separation of N from P (1.53±29 vs 0.82±0.25,p〈0.01) and that a ratio of 1.25 correctly identified all N and P. A prospective test of this ratio on an additional 25 specimens yielded a significant difference between N and P (1.70±0.37 vs 0.87±0.23,p〈0.0001) with a value of 1.25 correctly identifying all (10/10) N and 93% (14/15) P. Prospective analysis of previously proposed fluorescence ratios (600 nm/580 nm at Ex=480 nm; 530 nm/550 nm at Ex=459 nm; 448 nm/514 nm and 538 nm/514 nm at Ex=337 nm) all resulted in poor separation of N from P. The ratio of 460 nm/385 nm with Ex=337 nm is superior to previously reported criteria for distinguishing N from P and may be useful for guiding laser angioplasty systems.
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    Cutaneous phototoxicity in photodynamic therapy: Clinical experience with and without histamine antagonists (1991)
    Springer
    Lasers in medical science 6 (1991), S. 179-182 
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    ISSN: 1435-604X
    Keywords: Photodynamic therapy ; Skin photosensitivity ; Antihistamines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract We have investigated the incidence of cutaneous phototoxicity in 47 patients who received photodynamic therapy between April 1988 and March 1990. Of these, 15 patients received antihistamines as part of a pilot study to evluate their photoprotective role. Patients were followed-up for a minimum of 8 weeks. One out of the fifteen who received antihistamines and 15 out of the 32 patients who did not (p〈0.005), developed cutaneous phototoxicity. On the basis of these results we have initiated a randomized double-blind trial to evaluate the role of antihistamines in haematoporphyrin derivative-induced cutaneous phototoxicity.
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    In vitro Alexandrite laser angioplasty: A study on fibre conduction and tissue effects (1991)
    Springer
    Lasers in medical science 6 (1991), S. 183-188 
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    ISSN: 1435-604X
    Keywords: Atherosclerosis ; Alexandrite ; Angioplasty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Pulsed ultra-violet excimer laser radiation is capable of tissue ablation with only minimal thermal injury of adjacent tissue structures. Since difficult fibre optic coupling of energy was observed, alternative Q-switched laser sources capable of ablation of atherosclerotic plaque are under current investigation. To evaluate tissue effects of Alexandrite laser radiation, 160 arterial segments with macroscopic evidence of atherosclerotic disease were treated. The laser light was transmitted via silica based quartz fibres with different diameters. Using the Q-switched Alexandrite laser at the fundamental wavelength (748 nm) with a pulse duration of 300 ns the energy density threshold for tissue ablation was found to be in the range of 63 to 126 J cm−2 using a 300μm fibre. On macroscopic examination only limited thermal and acoustic injury was found in crater adjacent tissue structures. Crater edges were even and did not reveal signs of crater charring or debris in the crater lumen. However, the histological cross-sections revealed thermal injury extending from 100 up to 200μm lateral into adjacent tissue. The crater margins revealed fissuring as a result of shock wave injury. Thermal damage was most evident if irradiation of atherosclerotic tissue was performed in blood.
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    Book review (1991)
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    Lasers in medical science 6 (1991), S. 215-215 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
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    URL: http://dx.doi.org/10.1007/BF02032553
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    Laser angioplasty versus balloon angioplasty: The need for imaging (1991)
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    Lasers in medical science 6 (1991), S. 223-233 
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    ISSN: 1435-604X
    Keywords: Angioplasty ; Recanalization ; Laser ; Balloon ; Intravascular ultrasound ; Restenosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract The current state of clinical laser angioplasty is reviewed. Compared to balloon dilation at the beginning of the past decade, both peripheral and coronary laser angioplasty devices produce better results. Compared to current balloon angioplasty techniques, however, laser angioplasty does not seem to offer improved initial or long term results. Intravascular ultrasound imaging may help to improve laser ablation of atherosclerotic plaque. It remains to be established, however, whether precise debulking of the obstruction will result in a reduced restenosis rate compared to balloon angioplasty.
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    Biophysics of the photoablation process (1991)
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    Lasers in medical science 6 (1991), S. 241-254 
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    ISSN: 1435-604X
    Keywords: Laser angioplasty ; Photoablation ; Photohydraulic effect ; Fast thermal explosion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Besides the coagulation, where the body digests the necrotic tissue and direct evaporation of tissue, the photoablation effect turns out to be very important in tissue removal. In the case of high tissue absorption the process channels in photoablation can either be photochemical (bond breaking) or fast thermal. In the case of transparent media, a plasma formation due to high irradiances and an optical breakdown is necessary for ablation or photodisruption. All the process channels lead to a fast microscale explosion and to Shockwaves. For soft tissue the main process channel is the fast thermal explosion. Assuming that tissue will be disintegrated, if the energy deposited within a single laser pulse is larger than a material specific threshold, the thresholds for the radiant exposure and ablation rates respectively can be calculated. There is a large difference, whether the laser radiation is applied to the tissue surface in noncontact or through a fibre in contact. In contact the ‘fast thermal explosion’ happens in a closed chamber and hence the photohydraulic effect will support the photoablation. The thermally damaged zone in the surrounding tissue depends on the optical penetration depth mainly in cases that the pulse duration is shorter than a critical time given by the heat conductivity. Pulsed lasers can be used ‘non-thermally’ only if the average power is less than a tenth of a watt. With a higher amount of average power a pulsed laser will act comparable to a cw laser.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02030877
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  • 92
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    Laser-assisted fluorescence detection of plaque (1991)
    Springer
    Lasers in medical science 6 (1991), S. 289-296 
    Details
    ISSN: 1435-604X
    Keywords: Atherosclerosis ; Dihaematoporphyrin ether/ester, DHE ; Haematoporphyrin derivative, HPD ; Laser angioplasty ; Laser-induced fluorescence ; Plaque
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Selective fluorescence-marking of plaque offers new possibilities in cardiovascular diagnosis and therapy. Angioscopic investigations and spectrometry-assisted laser angioplasty will be simplified and more effective as compared with methods of today. It might help to make laser angioplasty a further promising interventional method to overcome, at least partially, the problems caused by atheromatous or atherosclerotic changes in the cardiovascular system. Fluorescence detection and imaging of markers is usually limited by the intrinsic fluorescence of tissue. Optical differential methods in combination with two-wavelength laser excitation and computer-assisted image processing, however, allow for discrimination of background-related signals and enable plaque detection and imaging at a high contrast. Plaque consists of either fibrotic, lipoid, or calcified depositions and is rather bradytrophic. For that reason in vitro experiments on human specimens post mortem seem to be justified and of clinical evidence. Due to intrinsically different fluorometric properties of plaque and normal vascular tissue imaging of marker-free plaque areas is possible. Additionally the specimens have been incubated with a haematoporphyrin-containing fluorescence marker at concentrations of 10–40μg ml−1 and incubation times of 60 min in order to obtain a corresponding increase in contrast. Lipoid depositions show the highest contrast because of lipophilic properties of the marker, while fibrotic and calcified plaque is slightly less effectively marked. The results, however, so far obtained indicate that fluorescence detection of plaque promises further progress in diagnosis and therapy of cardiovascular diseases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02030882
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  • 93
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    Improved results of coronary excimer laser angioplasty by the use of advanced transmission devices (1991)
    Springer
    Lasers in medical science 6 (1991), S. 317-321 
    Details
    ISSN: 1435-604X
    Keywords: Laser angioplasty ; Coronary artery disease ; PTCA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Excimer laser angioplasty is an alternative method for the treatment of obstructive coronary lesions. Initial clinical results demonstrated the safety and feasibility of the procedure. However, efficacy was limited by low catheter flexibility and unreliable energy transmission. Advanced transmission devices were used in 80 interventions in 79 patients. The catheter diameter is 1.3, 1.5 or 1.8 mm, the catheters consist of 20, 30 or 35 quartz fibres (100 μm) respectively. The mean energy density was 55 ±18 mJ mm−2, mean loss of energy transmission was 20%. The pulse width was 60 ns and 115 ns in 40 interventions each. The target vessel was the LAD in 53, the LCX in 6 and the RCA in 21 interventions. Failure of laser angioplasty occurred in 10 patients due to failed guidewire placement (N=6), failed catheter placement (N=3) or impossibility to cross the lesion with the catheter (N=1). Stand-alone laser angioplasty was performed in 43/70 procedures. Additional balloon angioplasty was necessary due to an unsatisfactory result (N=10) or due to complications (N=17) in 27 patients. Vessel occlusion occurred in 18 patients (25%) and could be successfully resolved by balloon dilatation (N=16) or additional laser angioplasty (N=1) in 17 patients. Two early occlusions were found at the 24-h control angiography. The incidence of myocardial infarction and in-hospital death (N=1) was 1.4%. Conclusion: The use of an advanced energy delivery system with trusted energy transmission and higher energy density increased the primary success rate of stand-alone excimer laser angioplasty. However, further improvement of catheter flexibility and reduction of dead space at the catheter tip is necessary to optimize ablation efficacy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02030887
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  • 94
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    Excimer laser coronary angioplasty: Initial experience at St. Thomas' Hospital (1991)
    Springer
    Lasers in medical science 6 (1991), S. 339-347 
    Details
    ISSN: 1435-604X
    Keywords: Xenon chloride ; Excimer laser ; Coronary angioplasty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Photochemical ablation of coronary artery atheroma using pulsed xenon-chloride excimer laser has, over the past 18 months produced promising results. Worldwide experience amounts to some 2000 cases. In the first 6 months following installation of the Dymer 200+ laser (Advanced Interventional Systems, Irvine, California, USA) at St. Thomas' Hospital, 53 procedures have been performed in 49 patients. Of these, 52.8% were ‘high risk’ (triple vessel disease, unstable angina, LV ejection fraction 〈35%, need to treat sole remaining coronary conduit). Complications were two in hospital deaths (18 and 48 h post-procedure-3.8%); one ELCA related myocardial infarct (1.9%); two haemorrhage requiring transfusion (3.8%); no emergency bypass graft surgery (0%). Current indications for the use of laser include: (1) long-segment diffuse disease; (2) proximal or ostial stenoses in coronary artery or graft; (3) restenosis after balloon angioplasty; (4) total occlusions crossed by a guidewire; (5) severe stenoses crossed by guidewire but not balloon; and (6) bifurcation lesions or stenoses compromising an important side-branch. Potential complications include: arterial perforation; aneurysm formation; peripheral embolization by plaque material; abrupt thrombotic closure; dissection; late sudden occlusion; spasm; and restenosis. Minor problems at the start of the programme involved: modifications to the machine to meet local laser safety requirements; special gases required for the machine; supply and design of fibre optic catheters; guiding catheters; heparin dose; dissection of the coronary artery (major and minor); and selection of patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02030891
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  • 95
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    Has the argon laser ever been used optimally for the treatment of port wine stain birthmarks? (1991)
    Springer
    Lasers in medical science 6 (1991), S. 371-371 
    Details
    ISSN: 1435-604X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042458
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  • 96
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    A study of gelatin ablation induced by a novel design TEA CO2 laser (1991)
    Springer
    Lasers in medical science 6 (1991), S. 429-435 
    Details
    ISSN: 1435-604X
    Keywords: TEA CO2 laser ; Ablation ; Thermal modelling ; Pulse width ; Gelatin ; Absorption coefficient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Ablation of gelatin samples was performed by using a semiconductively preionized TEA CO2 laser, emitting pulses of the lower TEM mode, 100 ns duration, at a repetition rate of 2.4Hz. Ablation rate experiments were performed at a range of fluences from 2J cm−2 to 10J cm−2. Assuming that the absorption coefficient is much larger than the scattering coefficient, experimental data were explained by simple models of ablation. The ablation depth per pulse and the specific absorption depth were calculated from the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042466
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  • 97
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    Activity of haematoporphyrin derivative photoproduct in photodynamic therapy in vivo (1991)
    Springer
    Lasers in medical science 6 (1991), S. 425-428 
    Details
    ISSN: 1435-604X
    Keywords: Photodynamic therapy ; Tumour ; Haematopor-phyrin derivative ; Photoproduct ; Laser illumination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Illumination of haematoporphyrin derivative in phosphate-buffered solutions causes the formation of a stable photoproduct with new absorption and fluorescence bands. We report data showing photodynamic activity of the photoproduct. Praestomic tumour OJ-5, carcinosarcoma W-256 (mice) and adenocarcinoma Akatol of colon (rats) have been used. Dynamics of tumour growth, life span of animals and morphological changes of tumour tissues have been the main criteria used to show the photoproduct activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042465
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  • 98
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    The propagation of optical radiation in tissue. II: Optical properties of tissues and resulting fluence distributions (1991)
    Springer
    Lasers in medical science 6 (1991), S. 379-390 
    Details
    ISSN: 1435-604X
    Keywords: Tissue optics ; Absorption ; Scattering ; Fluence distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract This paper is the second of two reviewing the propagation of electromagnetic radiation of wavelength 0.25–10μm in tissue. This part begins with a discussion of how the fundamental optical interaction coefficients of tissue may be measured. Both direct methods, in which the coefficients are measured for optically thin samples, and indirect methods, in which the coefficients are inferred from measurements on bulk samples are described. The difficulties inherent in both types of measurement are outlined. Next the wavelength dependence of the scattering and absorption coefficient is discussed, both from a heuristic point of view and by illustration from current literature. We illustrate how the optical spectrum can be divided into regions where the propagation of light is dominated by absorption or scattering effects. Finally we show how the distribution of light fluence in these spectral regions is dramatically different and illustrate the important features of these distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042460
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  • 99
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    Preliminary experience with the 1.32 μm neodymium-YAG laser in the treatment of tracheobronchial malignancy (1991)
    Springer
    Lasers in medical science 6 (1991), S. 407-413 
    Details
    ISSN: 1435-604X
    Keywords: Laser bronchoscopy ; 1.32μm Nd-YAG laser
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Endoscopic laser treatment for tracheobronchial malignancy is usually given with the neodymium-YAG laser using the 1.064μm output beam. However, recent experimental work suggests that the 1.32μm output beam of this laser has more desirable tissue effects. We have now treated 55 patients with the 1.32μm Nd-YAG laser (MBB-Medizintechnic) under general anaesthesia, using power settings of 10–20 W and pulse durations of up to 1 s. The indications for treatment were localized airway obstruction in each case. Airway calibre was improved in 46 (84%) patients and this was associated with an improvement in symptoms of cough and breathlessness. Patients with tracheal and carinal obstruction exhibited the most striking clinical improvements with up to four-fold increases in peak expiratory flow. In patients with more peripheral endobronchial obstruction, treatment improved airway calibre less frequently and resulted in a smaller clinical improvement. Of 11 patients with obstruction of a main bronchus and lung collapse, treatment led to partial or complete re-expansion in 10 cases (91%). The 1.32μm wavelength allows treatment to be conducted efficiently and safely but at a considerably lower power than is required for the 1.064μmwavelength. The ability to use low powers has the apparent advantage of generating only negligible quantities of smoke. Our experience with this new laser system demonstrates its considerable potential in the management of tracheobronchial malignancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042463
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  • 100
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    Clinical recording of laser-induced fluorescence spectra for evaluation of tumour demarcation feasibility in selected clinical specialities (1991)
    Springer
    Lasers in medical science 6 (1991), S. 415-424 
    Details
    ISSN: 1435-604X
    Keywords: Autofluorescence ; Fluorescence ; Laser spectroscopy ; Tumour detection ; Tumour diagnosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Physics , Technology
    Notes: Abstract Laser-induced autofluorescence spectra from humans were recorded in vivo at three different clinics in a study aimed at investigating the capability of this method to discriminate between malignant tumours and normal surrounding tissues. For the recordings a mobile trolley with the necessary equipment was constructed for use in an examination room or in an operating theatre environment. Laser light was guided through a 600μm optical fibre to the target tissue. The fluorescence from the excited tissue was collected with the same fibre and was fed to an optical multichannel analyser. Two excitation wavelengths were used (337 and 405 nm) in order to optimize the fluorescence signals in two interesting wavelength regions (380–500 and 550–700 nm). Oral and oropharyngeal tumours excited with 405 nm light contained detectable endogenous porphyrins and were in this way discriminated from the normal mucosa. Astrocytoma grade III–IV fluorescence different from that of normal brain tissue, while tumours in the bronchial tree were not detectable using the spectral shape of the pure tissue autofluorescence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02042464
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