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Significant Uncertainty (significant + uncertainty)
Selected AbstractsOptimal management of the New Zealand longfin eel (Anguilla dieffenbachii),AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 4 2005Graeme J. Doole Annual recruitment of the New Zealand longfin eel (Anguilla dieffenbachii) has decreased by 75 per cent since significant levels of commercial fishing began in the early 1970s. This motivates application of a multiple-cohort bioeconomic model to a New Zealand longfin eel fishery to investigate its optimal management and ascertain the suitability of existing regulatory policy. The use of historical harvest to calculate total allowable catch is asserted to be unsustainable based on recovery dynamics. In addition, individual transferable quota systems are argued to be fundamentally flawed for the protection of longfin fisheries because of high-grading, low-surplus production and a current lack of effective stock-assessment procedures. Area closure and the spatial definition of harvest rights are attractive alternatives given the territoriality of longfins and high larval spillover. The importance of unfished reserves is reinforced when significant uncertainties regarding population strength, harvest intensity and growth dynamics are considered. Restriction of exploitation to older cohorts in fished areas is demonstrated to maximise economic yield. [source] The influence of elevation error on the morphometrics of channel networks extracted from DEMs and the implications for hydrological modellingHYDROLOGICAL PROCESSES, Issue 11 2008John B. Lindsay Abstract Stream network morphometrics have been used frequently in environmental applications and are embedded in several hydrological models. This is because channel network geometry partly controls the runoff response of a basin. Network indices are often measured from channels that are mapped from digital elevation models (DEMs) using automated procedures. Simulations were used in this paper to study the influence of elevation error on the reliability of estimates of several common morphometrics, including stream order, the bifurcation, length, area and slope ratios, stream magnitude, network diameter, the flood magnitude and timing parameters of the geomorphological instantaneous unit hydrograph (GIUH) and the network width function. DEMs of three UK basins, ranging from high to low relief, were used for the analyses. The findings showed that moderate elevation error (RMSE of 1·8 m) can result in significant uncertainty in DEM-mapped network morphometrics and that this uncertainty can be expressed in complex ways. For example, estimates of the bifurcation, length and area ratios and the flood magnitude and timing parameters of the GIUH each displayed multimodal frequency distributions, i.e. two or more estimated values were highly likely. Furthermore, these preferential estimates were wide ranging relative to the ranges typically observed for these indices. The wide-ranging estimates of the two GIUH parameters represented significant uncertainty in the shape of the unit hydrograph. Stream magnitude, network diameter and the network width function were found to be highly sensitive to elevation error because of the difficulty in mapping low-magnitude links. Uncertainties in the width function were found to increase with distance from outlet, implying that hydrological models that use network width contain greater uncertainty in the shape of the falling limb of the hydrograph. In light of these findings, care should be exercised when interpreting the results of analyses based on DEM-mapped stream networks. Copyright © 2007 John Wiley & Sons, Ltd. [source] Future hydroclimatology of the Mekong River basin simulated using the high-resolution Japan Meteorological Agency (JMA) AGCMHYDROLOGICAL PROCESSES, Issue 9 2008Anthony S. Kiem Abstract Analysis of future Japan Meteorological Agency atmospheric general circulation model (JMA AGCM) based climate scenarios for the Mekong River basin (MRB) indicates that annual mean precipitation will increase in the 21st century (2080,2099) by 4·2% averaged across the basin, with the majority of this increase occurring over the northern MRB (i.e. China). Annual mean temperatures are also projected to increase by approximately 2·6 °C (averaged across the MRB). As expected, these changes also lead to significant changes in the hydrology of the MRB. All MRB subbasins will experience an increase in the number of wet days in the ,future' and, importantly for sustainable water resources management and the mitigation of extreme events (e.g. floods and droughts), the magnitude and frequency of what are now considered extreme events are also expected to increase resulting in increased risk of flooding, but a reduction in the likelihood of droughts/low-flow periods,assuming water extraction is kept at a sustainable level. Despite the fact that the climate change impact projections are associated with significant uncertainty, it is important to act now and put in place policies, infrastructure and mitigation strategies to protect against the increased flooding that could occur. In addition, despite this study indicating a decrease in the number of ,low-flow' days, across most of the MRB, further analysis is needed to determine whether the reduction in low-flow days is enough to compensate for (and sustain) the rapidly increasing population and development in the MRB. Copyright © 2008 John Wiley & Sons, Ltd. [source] Non-diagonal controllers in MIMO quantitative feedback designINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 4 2002Edward Boje Abstract This paper discusses multivariable quantitative feedback design through the use of controllers with off-diagonal elements. Controller design for multivariable plants with significant uncertainty is simpler and potentially less conservative if some sort of dominance is achieved (by reducing the interaction effect of off-diagonal plant elements) before a diagonal (decentralized) controller design is attempted. Traditional approaches for achieving dominance are not applicable when plant uncertainty must be considered. This paper discusses parallel and series implementations and for the latter, a pseudo-Gauss elimination approach to the design has been developed. The interaction is measured using the Perron,Frobenius root of an interaction matrix. In some applications, it is possible to trade off individual plant cases against each other in order to reduce to the worst-case interaction over the entire plant set. Copyright © 2002 John Wiley & Sons, Ltd. [source] A simulation-optimization framework for research and development pipeline managementAICHE JOURNAL, Issue 10 2001Dharmashankar Subramanian The Research and Development Pipeline management problem has far-reaching economic implications for new-product-development-driven industries, such as pharmaceutical, biotechnology and agrochemical industries. Effective decision-making is required with respect to portfolio selection and project task scheduling in the face of significant uncertainty and an ever-constrained resource pool. The here-and-now stochastic optimization problem inherent to the management of an R&D Pipeline is described in its most general form, as well as a computing architecture, Sim-Opt, that combines mathematical programming and discrete event system simulation to assess the uncertainty and control the risk present in the pipeline. The R&D Pipeline management problem is viewed in Sim-Opt as the control problem of a performance-oriented, resource-constrained, stochastic, discrete-event, dynamic system. The concept of time lines is used to study multiple unique realizations of the controlled evolution of the discrete-event pipeline system. Four approaches using various degrees of rigor were investigated for the optimization module in Sim-Opt, and their relative performance is explored through an industrially motivated case study. Methods are presented to efficiently integrate information across the time lines from this framework. This integration of information demonstrated in a case study was used to infer a creative operational policy for the corresponding here-and-now stochastic optimization problem. [source] Information, Agreement Design, and the Durability of Civil War SettlementsAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 2 2010Michaela Mattes Civil war is usually examined from the perspective of commitment problems. This approach provides considerable insight regarding which civil war agreement provisions reduce the chance of renewed fighting. Yet, additional insight can be gained by examining information asymmetries as a potential cause of civil war recurrence. We argue that significant uncertainty regarding military capabilities may persist after fighting ends and that this uncertainty may lead to the breakdown of peace. However, carefully designed peace agreements can guard against renewed civil war by calling for international monitoring, making the belligerents submit military information to third parties, and providing for verification of this information. Our empirical analysis of 51 civil war settlements between 1945 and 2005 shows that these provisions significantly reduce the risk of new civil war. Encouraging the adoption of these provisions may be a useful policy in the international community's effort to establish peace in civil-war-torn societies. [source] Modelling hydroclimatic uncertainty and short-run irrigator decision making: the Goulburn system,AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 4 2009Marnie Griffith Australia has an incredibly variable and unpredictable hydroclimate, and while irrigation is designed to reduce risk, significant uncertainty remains in both seasonal water availability (,allocations') and irrigation crop water requirements. This paper explores the nature and impacts of seasonal hydroclimatic uncertainty on irrigator decision making and temporary water markets in the Goulburn system in northern Victoria. Irrigation and water trading plans are modelled for the three seasons of the irrigation year (spring, summer and autumn) via discrete stochastic programming, and contrasted against a perfect information base case. In water-scarce environments, hydroclimatic uncertainty is found to be costly, in terms of both the efficiency of irrigation decisions and the allocation of water via the water market. [source] Good modeling practice for PAT applications: Propagation of input uncertainty and sensitivity analysisBIOTECHNOLOGY PROGRESS, Issue 4 2009Gürkan Sin Abstract The uncertainty and sensitivity analysis are evaluated for their usefulness as part of the model-building within Process Analytical Technology applications. A mechanistic model describing a batch cultivation of Streptomyces coelicolor for antibiotic production was used as case study. The input uncertainty resulting from assumptions of the model was propagated using the Monte Carlo procedure to estimate the output uncertainty. The results showed that significant uncertainty exists in the model outputs. Moreover the uncertainty in the biomass, glucose, ammonium and base-consumption were found low compared to the large uncertainty observed in the antibiotic and off-gas CO2 predictions. The output uncertainty was observed to be lower during the exponential growth phase, while higher in the stationary and death phases - meaning the model describes some periods better than others. To understand which input parameters are responsible for the output uncertainty, three sensitivity methods (Standardized Regression Coefficients, Morris and differential analysis) were evaluated and compared. The results from these methods were mostly in agreement with each other and revealed that only few parameters (about 10) out of a total 56 were mainly responsible for the output uncertainty. Among these significant parameters, one finds parameters related to fermentation characteristics such as biomass metabolism, chemical equilibria and mass-transfer. Overall the uncertainty and sensitivity analysis are found promising for helping to build reliable mechanistic models and to interpret the model outputs properly. These tools make part of good modeling practice, which can contribute to successful PAT applications for increased process understanding, operation and control purposes. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] | ||||||||||