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  • Articles  (16)
  • 550 - Earth sciences
  • Electronic structure and strongly correlated systems
  • uncertainty
  • Biology  (12)
  • Chemistry and Pharmacology  (4)
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  • Articles  (16)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biology and philosophy 15 (2000), S. 493-508 
    ISSN: 1572-8404
    Keywords: complexity ; entropy balance ; environment independence ; evolution ; information fundamental identity ; uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Philosophy
    Notes: Abstract Some real objects show a very particular tendency: that of becomingindependent with regard to the uncertainty of their surroundings. This isachieved by the exchange of three quantities: matter, energy andinformation. A conceptual framework, based on both Non-equilibriumThermodynamic and the Mathematical Theory of Communication is proposedin order to review the concept of change in living individuals. Three mainsituations are discussed in this context: passive independence inconnection with resistant living forms (such as seeds, spores, hibernation,...), active independence in connection with the life span of aliving individual (whether an ant or an ant farm), and the newindependence in connection with the general debate of biological evolution.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Quantitative microbiology 1 (1999), S. 63-88 
    ISSN: 1572-9923
    Keywords: binomial fractions ; microbial counts ; variability ; uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In microbiological studies various methods are employed to estimate fractions from paired counts of organisms. When the fraction (second count divided by first count) is constant among the paired counts, the maximum likelihood estimate is the ratio of the arithmetic means. In many practical applications this fraction may however not be constant, but vary substantially between pairs of counts. We discuss a statistical method that estimates the distribution of the fraction from pairs of counts, to allow for this variation. Four real data sets (concerning viability for growth and infection, recovery of a detection method, and removal in a treatment process) are analyzed by this method. Often, pairs of counts are not determined in the same physical sample, but the first count is made in one sample, and the second count in a second sample. We provide parametric models to deal with such a situation: the desired fraction is still estimated as a binomial probability, but the model includes sampling effects. This approach also allows for analysis of two distinct cases: paired observations, where the counts “before” and “after” are related in some way to each other, and unpaired observations, where they are not. The four models for separate samples: paired or unpaired observations, and binomial probability fixed or variable, are used to analyze the removal data. It is concluded that this approach of statistical analysis of fractions is more appropriate than often used calculations based on the ratio between the (geometric) means “before” and “after”. The implications for risk analysis are briefly discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Biodiversity and conservation 7 (1998), S. 875-894 
    ISSN: 1572-9710
    Keywords: uncertainty ; population viability analysis ; metapopulation model ; human impact
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We demonstrate the effect of uncertainty (resulting from lack of information or measurement error) on the assessment of human impact, with an analysis of the viability of the northern spotted owl throughout its range in the United States. We developed a spatially-explicit, stage-structured, stochastic metapopulation model of the northern spotted owl throughout its range in the United States. We evaluated the viability of the metapopulation using measures such as risk of decline and time to extinction. We incorporated uncertainty in the form of parameter ranges, and used them to estimate upper and lower bounds on the estimated viability of the species. We analysed the effect of this type of uncertainty on the assessment of human impact by comparing the species' viability under current conditions and under an assumed loss of spotted owl habitat in the next 100 years. The ranges of parameters were quite large and resulted in a wide range of risks of extinction. Despite this uncertainty, the results were sensitive to parameters related to habitat loss: under all assumptions and combinations of parameters, the model predicted that habitat loss results in substantially higher risks of metapopulation decline. This result demonstrated that even with relatively large uncertainties, risk-based model results can be used to assess human impact reliably.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Evolutionary ecology 12 (1998), S. 535-541 
    ISSN: 1573-8477
    Keywords: life histories ; scaling ; uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many life-history parameters have condition-dependent optima, but individuals are often required to set the values of such parameters relatively early in development, before the relevant conditions can be assessed with full accuracy. If cues are available that predict such future conditions, then the condition-dependent parameter should evolve to assume values that deviate from the mean in the direction implied by the cues, but these deviations should regress towards the mean to the degree that the cues are less than fully reliable. Under mild assumptions, the slopes of the resulting relationships between condition-dependent life-history parameters and the variable conditions on which their optima depend will be the ‘ideal’ slopes (those that would maximize fitness if the parameter could be chosen on the basis of full information) devalued by the squared correlation between the condition and the parameter.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-5184
    Keywords: anchovy ; decision rule ; management ; objectives ; sardine ; uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The pelagic fishery in South Africa targets mainly anchovy, Engraulis capensis, and sardine, Sardinops sagax, both of which have varied substantially in abundance during the history of the fishery. Since 1988, there has been progress in this fishery towards the use of management procedures as the basis for determination of management regulations, where a management procedure is defined as a set of rules, derived by simulation and normally implemented for three to five years, specifying how the regulatory mechanism is set, the data collected for this purpose and how these data are to be analysed and used. Advantages of management procedures include formal consideration of uncertainty, the ability to choose decision rules based on their predicted medium-term consequences and a saving in workload compared with annual assessments. This paper discusses the lessons learned in application of management procedures and their precursors in this fishery. The high variability in abundance of the two stocks, the trend in their relative abundance, the substantial uncertainties in information, strong pressure to meet socio-economic goals and the conflicting objectives which arose between the directed anchovy and directed sardine fishery are identified as major problems in implementation of procedures and management of the resources. However, the use of management procedures is considered to have led to greatly improved communication with the industry and to substantial input by them into the management process. The procedures and the simulations upon which they were based also enabled consideration of the major sources of uncertainty in understanding of the resource dynamics and facilitated the development of procedures that were robust to them. It is argued that biological uncertainty greatly exacerbated the problems in application of the procedures but probably cannot be markedly reduced in the near future. Management procedures must be robust to likely variability and uncertainty. Of equal importance are identification and selection of achievable objectives, and allocation to the political decision makers and not to the scientists, of responsibility for determining acceptable trade-offs between conservation and socio-economic goals. Other issues, including the importance of long-term rights and allowance for flexibility in fishing practice, are also highlighted
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Landscape ecology 12 (1997), S. 309-320 
    ISSN: 1572-9761
    Keywords: landscape indexes ; landscape diversity ; accuracy assessment ; uncertainty ; classification error ; error matrixes ; bootstrapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many landscape indexes with ecological relevance have been proposed, including diversity indexes, dominance, fractal dimension, and patch size distribution. Classified land cover data in a geographic information system (GIS) are frequently used to calculate these indexes. However, a lack of methods for quantifying uncertainty in these measures makes it difficult to test hypothesized relations among landscape indexes and ecological processes. One source of uncertainty in landscape indexes is classification error in land cover data, which can be reported in the form of an error matrix. Some researchers have used error matrices to adjust extent estimates derived from classified land cover data. Because landscape diversity indexes depend only on landscape composition – the extent of each cover in a landscape – adjusted extent estimates may be used to calculate diversity indexes. We used a bootstrap procedure to extend this approach and generate confidence intervals for diversity indexes. Bootstrapping is a technique that allows one to estimate sample variability by resampling from the empirical probability distribution defined by a single sample. Using the empirical distribution defined by an error matrix, we generated a bootstrap sample of error matrixes. The sample of error matrixes was used to generate a sample of adjusted diversity indexes from which estimated confidence intervals for the diversity indexes were calculated. We also note that present methods for accuracy assessment are not sufficient for quantifying the uncertainty in landscape indexes that are sensitive to the size, shape, and spatial arrangement of patches. More information about the spatial structure of error is needed to calculate uncertainty for these indexes. Alternative approaches should be considered, including combining traditional accuracy assessments with other probability data generated during the classification procedure.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Accreditation and quality assurance 2 (1997), S. 186-192 
    ISSN: 1432-0517
    Keywords: Key words Traceability ; Quality ; Measurement ; uncertainty ; Clinical reference ; materials ; Clinical photometric ; system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  It is well known that erroneous data reported to a physician may strongly affect medical decision making. For routine clinical chemistry purposes, different instrumentation can be used to compare measurements of unknown samples with standard reference materials. Currently, acceptable limits of accuracy and precision are poorly defined in the field of clinical chemistry laboratories. In this article, problems associated with spectrophotometric measurements, both manual and automated, are discussed. The task of the validation of photometric systems for clinical analyses is currently of considerable interest. Some practical aspects of this validation and the use of reference materials for this activity in the national area are discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 53 (1997), S. 320-331 
    ISSN: 0006-3592
    Keywords: numerical modeling ; uncertainty ; statistics ; cometabolism ; trichloroethylene ; methanotroph ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The rates of methane utilization and trichloroethylene (TCE) cometabolism by a methanotrophic mixed culture were characterized in batch and pseudo-steady-state studies. Procedures for determination of the rate coefficients and their uncertainties by fitting a numerical model to experimental data are described. The model consisted of a system of differential equations for the rates of Monod kinetics, cell growth on methane and inactivation due to TCE transformation product toxicity, gas/liquid mass transfer of methane and TCE, and the rate of passive losses of TCE. The maximum specific rate of methane utilization (kCH4) was determined by fitting the numerical model to batch experimental data, with the initial concentration of active methane-oxidizing cells (X0a) also used as a model fitting parameter. The best estimate of kCH4 was 2.2 g CH4/g cells-d with excess copper available, with a single-parameter 95% confidence interval of 2.0-2.4 mg/mg-d. The joint 95% confidence region for kCH4 and X0a is presented graphically. The half-velocity coefficient (KS,CH4) was 0.07 mg CH4/L with excess copper available and 0.47 mg CH4/L under copper limitation, with 95% confidence intervals of 0.02-0.11 and 0.35-0.59 mg/L, respectively. Unique values of the TCE rate coefficients kTCE and KS,TCE could not be determined because they were found to be highly correlated in the model fitting analysis. However, the ratio kTCE/KS,TCE and the TCE transformation capacity (TC) were well defined, with values of 0.35 L/mg-day and 0.21 g TCE/g active cells, respectively, for cells transforming TCE in the absence of methane or supplemental formate. The single-parameter 95% confidence intervals for kTCE/KS,TCE and TC were 0.27-0.43 L/mg-d and 0.18-0.24 g TCE/g active cells, respectively. The joint 95% confidence regions for kTCE/KS,TCE and TC are presented graphically. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 320-331, 1997.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Microchimica acta 123 (1996), S. 231-240 
    ISSN: 1436-5073
    Keywords: measurement errors ; reference materials ; validation ; uncertainty ; method evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Quality assurance and method validation are needed to reduce false decisions due to measurement errors. In this context accuracy and standard uncertainty for the analytical method need to be considered to ensure that the performance characteristics of the method are understood. Therefore, analytical methods ought to be validated before implementation and controlled on a regular basis during usage. For this purpose reference materials (RMs) are useful to determine the performance characteristics of methods under development. These performance parameters may be documented in the light of a method evaluation study and the documentation related to international standards and guidelines. In a method evaluation study of Pb in blood using reference samples from the Laboratoire Toxicologie du Quèbec, Canada, a difference between the systematic errors was observed using a Perkin-Elmer Model 5100 atomic absorption spectrometer and a Perkin-Elmer Model 4100 atomic absorption spectrometer, both with Zeeman background correction. For measurement of blood samples, the performance parameters obtained in the method evaluation studies, i.e. slopes and intercepts of the method evaluation function (MEF), were intended to be used for correcting the systematic errors. However, the number of MEF samples was insufficient to produce an acceptable SD for the MEF slopes to be used for correction. In a method evaluation study on valproate in plasma using the SYVA's EMIT assay on COBAS MIRA S a significant systematic error above the concentration 300 mmol dm−3 was demonstrated (slope 0.9541) and consequently the slope was used for correction of results. For analytes, where certified RMs (CRMs) exist, a systematic error of measurements can be reduced by correcting errors by assessment of the trueness as recommended in international guidelines issued by ISO or the National Institute of Standards and Technology (NIST). When possible, the analysis of several RMs, covering the concentration range of interest, is the most useful way to investigate measurement bias. Unfortunately, until recently only few RMs existed and only few had been produced and certified by specialized organizations such as NIST or the Standards, Measurements and Testing (SMT, previously BCR) programme. Due to the lack of such RMs, network organizations are nowadays established with the aim of supporting the correct use and production of high-quality CRMs.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Microchimica acta 123 (1996), S. 303-309 
    ISSN: 1436-5073
    Keywords: accuracy ; quality assessment ; instrumental neutron activation analysis ; uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Neutron activation analysis is one of the analytical techniques often used for certification of reference materials. The k0-based method of instrumental neutron activation analysis can also be applied in intercomparison runs in the certification process and therefore it is desirable to know its accuracy in advance. Possible systematic errors related to the application of nuclear data at given neutron flux rate parameters, that can affect the uncertainties of the results obtained by this specific method, are elucidated and error propagation factors calculated for a typical irradiation position in the TRIGA Mark II reactor of the Jozef Stefan Institute. It was found that these uncertainties are at the level of 1–2% on the average.
    Type of Medium: Electronic Resource
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Biodiversity and conservation 5 (1996), S. 1143-1167 
    ISSN: 1572-9710
    Keywords: uncertainty ; ecology ; policy ; sustainability ; biodiversity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Using an Australian focus to explore theoretical and policy issues of wider concern, this article examines linkages between public policy and the science of ecology. This is done within the broader framework of sustainability, emphasizing the problem of decision making in the face of ‘uncertainty’. Insights from the ecological, risk, sustainability and policy literatures are used. The sustainability-uncertainty problem is characterized, and the adequacy of existing policy support techniques and approaches noted, particularly the precautionary principle. The problem is further defined using the notion of ignorance. The treatment of ignorance and uncertainty in ecology is discussed. We suggest that the science of ecology has had a limited influence on policy formulation and discuss the basis of this using biodiversity conservation and ecosystem management as examples. We conclude by considering challenges for handling risk, uncertainty and ignorance in ecological science for policy formulation. We emphasize the need for improved communication between the science and policy communities, greater recognition of the limits of quantitative techniques in addressing uncertainty, and contingency planning.
    Type of Medium: Electronic Resource
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  • 12
    ISSN: 1572-9761
    Keywords: field survey ; vegetation ; land cover type ; mapping ; uncertainty ; error ; change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Land cover data for landscape ecological studies are frequently obtained by field survey. In the United Kingdom, temporally separated field surveys have been used to identify the locations and magnitudes of recent changes in land cover. However, such map data contain errors which may seriously hinder the identification of land cover change and the extent and locations of rare landscape features. This paper investigates the extent of the differences between two sets of maps derived from field surveys within the Northumberland National Park in 1991 and 1992. The method used in each survey was the ‘Phase 1’ approach of the Nature Conservancy Council of Great Britain. Differences between maps were greatest for the land cover types with the smallest areas. Overall spatial correspondence between maps was found to be only 44.4%. A maximum of 14.4% of the total area surveyed was found to have undergone genuine land cover change. The remaining discrepancies, equivalent to 41.2% of the total survey area, were attributed primarily to differences of land cover interpretation between surveyors (classification error). Differences in boundary locations (positional error) were also noted, but were found to be a relatively minor source of error. The implications for the detection of land cover change and habitat mapping are discussed.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Journal of aquatic ecosystem stress and recovery 4 (1995), S. 151-156 
    ISSN: 1573-5141
    Keywords: sediment ; toxicity ; uncertainty ; integrated ; bioassays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During the past few years there has been a tremendous increase in sediment bioassay and toxicity testing and research. The increased activity has paralleled the development of regulatory interest and realization of the role of contaminated sediments in ecosystem degradation. Many critical issues which affect test responses, data interpretation, and extrapolation to in situ conditions, have not been adequately addressed or recognized by the scientific community. Some of these issues may significantly affect contaminant fate and effects and thereby affect the accuracy of data interpretations. Examples of these interferences are disruptive sample collection, extended sample storage, designs which alter exposure routes, improper spiking conditions and sediment dilution, and inadequate validation of laboratory responses against in situ conditions. Over-simplification of complex sediment interactions may lead to erroneous conclusions concerning the significance of moderate to low levels of contamination.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Aquatic sciences 56 (1994), S. 161-178 
    ISSN: 1420-9055
    Keywords: Global climate change ; modeling ; freshwater watersheds ; uncertainty
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A generalized watershed model was used to evaluate the effects of global climate changes on the hydrologic responses of freshwater ecosystems. The Enhanced Trickle Down (ETD) model was applied to W-3 watershed located near Danville, Vermont. Eight years of field data was used to perform model calibration and verification and the results were presented in Nikolaidis et al., (1993). Results from the Goddard Institute for Space Studies (GISS) and the Geophysical Fluid Dynamics Laboratory (GFDL) general circulation models which simulated the doubling of present day atmospheric CO2 scenarios were used to perform the hydrologic simulations for the W-3 watershed. The results indicate that the W-3 watershed will experience increases in annual evapotranspiration and decreases in annual outflow and soil moisture. Stochastic models that simulate collective statistical properties of meteorological time series were developed to generate data to drive the ETD model in a Monte-Carlo fashion for quantification of the uncertainty in the model predictions due to input time series. This coupled deterministic and stochastic model was used to generate probable scenarios of future hydrology of the W-3 watershed. The predicted evapotranspiration and soil moisture under doubling present day atmospheric CO2 scenarios exceed the present day uncertainty due to input time series by a factor greater than 2. The results indicate that the hydrologic response of the W-3 watershed will be significantly different than its present day response. The Enhanced Trickle Down model can be used to evaluate land surface feedbacks and assessing water quantity management in the event of climate change.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Journal of paleolimnology 3 (1990), S. 253-267 
    ISSN: 1573-0417
    Keywords: paleolimnology ; PIRLA ; 210Pb dating ; error analysis ; uncertainty ; constant-rate-of-supply model ; constant-flux model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Lead-210 assay and dating are subject to several sources of error, including natural variation, the statistical nature of measuring radioactivity, and estimation of the supported fraction. These measurable errors are considered in calculating confidence intervals for 210Pb dates. Several sources of error, including the effect of blunders or misapplication of the mathematical model, are not included in the quantitative analysis. First-order error analysis and Monte Carlo simulation (of cores from Florida PIRLA lakes) are used as independent estimates of dating uncertainty. CRS-model dates average less than 1% older than Monte Carlo median dates, but the difference increases non-linearly with age to a maximum of 11% at 160 years. First-order errors increase exponentially with calculated CRS-model dates, with the largest 95% confidence interval in the bottommost datable section being 155±90 years, and the smallest being 128±8 years. Monte Carlo intervals also increase exponentially with age, but the largest 95% occurrence interval is 152±44 years. Confidence intervals calculated by first-order methods and ranges of Monte Carlo dates agree fairly well until the 210Pb date is about 130 years old. Older dates are unreliable because of this divergence. Ninety-five per cent confidence intervals range from about 1–2 years at 10 years of age, 10–20 at 100 years, and 8–90 at 150 years old.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Radiation Physics and Chemistry 42 (1993), S. 731-738 
    ISSN: 0969-806X
    Keywords: Dosimetry ; radiation ; standards ; sterilization ; traceability ; uncertainty
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Physics
    Type of Medium: Electronic Resource
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