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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

A cumulative effect assessment using scenario analysis methodology to assess future Cowichan River Chinook and Coho salmon survival

Ospan, Arman K 03 May 2021 (has links)
This dissertation describes a proposed methodology for Cumulative Effects Assessment (CEA) with the purpose of improving the process by making it both more substantive and quantitative. The general principles of the approach include the following: use of effect-based analyses where selected Valued Component (VC) sensitivities are identified first and then effect pathways are determined building bottom-up linkages from VC sensitivities to potential stressors or combinations of stressors to effect drivers and forces behind the drivers. Models were developed based on statistical or historic trend analysis or literature review that predicted the responses of the VCs to changes in effect drivers. Further, scenarios of divergent futures were created that involved different developments of each effect driver or force, and finally the models were applied to each scenario to project the state of the studied VCs. A practical implementation was conducted to demonstrate the use of the proposed methods on future population trends of two anadromous salmon species from the Cowichan River, British Columbia, Chinook and Coho. The assessment was conducted for both early freshwater and marine phases of their life. For the freshwater phase, the assessment focused on two main factors affecting salmon survival, streamflow and stream temperature and established two main drivers affecting these stressors, land use and climate change, and two main forces behind these drivers, Local and Global human development driven change, respectively. Effects of stream temperature and streamflow on salmon freshwater survival were simulated using two models; one was based on Chinook freshwater survival correlations with stream temperature and was developed only for Chinook, and the other was based on literature-derived temperature and streamflow thresholds and was developed for both species. Connections between the stressors (stream temperature and streamflow) and drivers (land use and climate change) were established through a hydrologic model and stream temperature regression model. For the marine environment, models were created using Pearson correlation and stepwise regression analysis examining links between survival of Cowichan River Chinook and Strait of Georgia hatchery-raised and wild Coho and various environmental variables of the nearshore zone of Strait of Georgia and Juan de Fuca Strait. The models were applied to project future salmon survival under four future scenarios for 2050 that were created by combining two opposite scenarios of land use in the watershed, forest conservation and development, and two climate change scenarios, extreme and moderate. Scenario projections showed a decrease in overall (combined early freshwater marine) survival by 2050 for all three studied salmon populations. None of them are likely to survive in scenarios with extreme climate change, while scenarios with moderate climate change showed positive survival rates although lower than present-day baseline levels. Analysis also showed that land use management within the Cowichan River watershed can also affect freshwater survival of both Chinook and Coho and marine survival of Chinook through influence of river discharge on nearshore processes. However, our land-use management scenarios have considerably weaker effect than climate change on salmon survival. Therefore, we conclude that land use management alone is not sufficient to offset effects of climate change on salmon survival. / Graduate
82

Quality Assurance of Exposure Models for Environmental Risk Assessment of Substances / Qualitätssicherung von Expositionsmodellen zur Umweltrisikoabschätzung von Substanzen

Schwartz, Stefan 04 September 2000 (has links)
Environmental risk assessment of chemical substances in the European Union is based on a harmonised scheme. The required models and parameters are laid down in the Technical Guidance Document (TGD) and are implemented in the EUSES software. An evaluation study of the TGD exposure models was carried out. In particular, the models for estimating chemical intake by humans were investigated. The objective of this study was two-fold: firstly, to develop an evaluation methodology, since no appropriate approach is available in the scientific literature. Secondly, to elaborate applicability and limitations of the models and to provide proposals for their improvement. The principles of model evaluation in terms of quality assurance, model validation and software evaluation were elaborated and a suitable evaluation protocol for chemical risk assessment models was developed. Quality assurance of a model includes internal (e.g. an investigation of the underlying theory) and external (e.g. a comparison of the results with experimental data) validation, and addresses the evaluation of the respective software. It should focus not only on the predictive capability of a model, but also on the strength of the theoretical underpinnings, evidence supporting the model?s conceptualisation, the database and the software. The external validation was performed using a set of reference substances with different physico-chemical properties and use patterns. Additionally, sensitivity and uncertainty analyses were carried out, and alternative models were discussed. Recommendations for improvements and maintenance of the risk assessment methodology were presented. To perform the software evaluation quality criteria for risk assessment software were developed. From a theoretical point of view, it was shown that the models strongly depend on the lipophilicity of the substance, that the underlying assumptions drastically limit the applicability, and that realistic concentrations may seldom be expected. If the models are applied without adjustment, high uncertainties must inevitably be expected. However, many cases were found in which the models deliver highly valuable results. The overall system was classified as a good compromise between complexity and practicability. But several chemicals and classes of chemicals, respectively, with several restrictions were revealed: The investigated models used to assess indirect exposure to humans are in parts currently not applicable for dissociating compounds, very polar compounds, very lipophilic compounds, ions, some surfactants, and compounds in which metabolites provide the problems and mixtures. In a strict sense, the method is only applicable for persistent, non-dissociating chemicals of intermediate lipophilicity. Further limitations may exist. Regarding the software, it was found that EUSES basically fulfils the postulated criteria but is highly complex and non-transparent. To overcome the inadequacies a more modular design is proposed.
83

Development and application of a multi-criteria decision-support framework for planning rural energy supply interventions in low-income households in South Africa

Dzenga, Bruce 25 August 2022 (has links) (PDF)
Problems in the public policy decision-making environments are typically complex and continuously evolve. In a resource-constrained environment, several alternatives, criteria, and conflicting objectives must be considered. As a result, solutions to these types of problems cannot be modelled solely using single-criteria techniques. It has been observed that most techniques used to shape energy policy and planning either produce sub-optimal solutions or use strong assumptions about the preferences of decision-maker(s). This difficulty creates a compelling need to develop novel techniques that can handle several alternatives, multiple criteria and conflicting objectives to support public sector decision-making processes. First, the study presents a novel scenario-based multi-objective optimisation framework based on the augmented Chebychev goal programming (GP) technique linked to a value function for analysing a decision environment underlying energy choice among low-income households in isolated rural areas and informal urban settlements in South Africa. The framework developed includes a multi-objective optimisation technique that produced an approximation of a Pareto front linked to an a priori aggregation function and a value function to select the best alternatives. Second, the study used this model to demonstrate the benefits of applying the framework to a previously unknown subject in public policy: a dynamic multi-technology decision problem under uncertainty involving multiple stakeholders and conflicting objectives. The results obtained suggest that while it is cost-optimal to pursue electrification in conjunction with other short-term augmentation solutions to meet South Africa's universal electrification target, sustainable energy access rates among low-income households can be achieved by increasing the share of clean energy generation technologies in the energy mix. This study, therefore, challenges the South African government's position on pro-poor energy policies and an emphasis on grid-based electrification to increase energy access. Instead, the study calls for a portfolio-based intervention. The study advances interventions based on micro-grid electrification made up of solar photovoltaics (PV), solar with storage, combined cycle gas turbine (CCGT) and wind technologies combined with either bioethanol fuel or liquid petroleum gas (LPG). The study has demonstrated that the framework developed can benefit public sector decision-makers in providing a balanced regime of technical, financial, social, environmental, public health, political and economic aspects in the decision-making process for planning energy supply interventions for low-income households. The framework can be adapted to a wide range of energy access combinatorial problems and in countries grappling with similar energy access challenges.
84

Analysis of Flash Flood Routing by Means of 1D - Hydraulic Modelling

Tesfay Abraha, Zerisenay 17 September 2010 (has links)
This study was conducted at the mountainous catchment part of Batinah Region of the Sultanate of Oman called Al-Awabi watershed which is about 260km2 in area with about 40 Km long Wadi main channel. The study paper presents a proposed modeling approach and possible scenario analysis which uses 1D - hydraulic modeling for flood routing analysis; and the main tasks of this study work are (1) Model setup for Al-Awabi watershed area, (2) Sensitivity Analysis, and (3) Scenario Analysis on impacts of rainfall characteristics and transmission losses. The model was set for the lower 24 Km long of Al-Awabi main channel (Figure 13). Channel cross-sections were the main input to the 1D-Hydraulic Model used for the analysis of flash flood routing of the Al-Awabi watershed. As field measurements of the Wadi channel cross-sections are labor intensive and expensive activities, availability of measured channel cross-sections is barely found in this study area region of Batinah, Oman; thereby making it difficult to simulate the flood water level and discharge using MIKE 11 HD. Hence, a methodology for extracting the channel cross-sections from ASTER DEM (27mX27m) and Google Earth map were used in this study area. The performance of the model setup was assessed so as to simulate the flash flood routing analysis at different cross-sections of the modeled reach. And from this study, although there were major gap and problems in data as well as in the prevailing topography, slope and other Hydro Dynamic parameters, it was concluded that the 1D-Hydraulic Modelling utilized for flood routing analysis work can be applied for the Al-Awabi watershed. And from the simulated model results, it was observed that the model was sensitive to the type of Boundary Condition chosen and taken, channel cross sections and its roughness coefficient utilized throughout the model reach.
85

Совершенствование риск-ориентированного подхода к управлению энергоремонтами на примере ОАО «УРАЛТУРБО» : магистерская диссертация / Improvement of the risk-oriented approach to energy repair management on the example of JSC “URALTURBO”

Тушов, П. А., Tushov, P.A. January 2019 (has links)
Энергоремонтный бизнес занимает важное место в энергетическом секторе России. Без его успешного функционирования энергокомпании не смогут эффективно осуществлять свою операционную деятельность. Тем не менее большинство энергоремонтных компаний не могут подстроиться под быстроменяющиеся условия внешней среды: актуальным трендом данного бизнеса является активное внедрение системы риск-менеджмента на предприятиях. Цель работы – совершенствование риск-ориентированного подхода к управлению энергоремонтами. Научная новизна заключается в разработке рекомендаций по управлению рисками на энергоремонтных предприятиях. Они направлены на снижение потерь от воздействий факторов внешней среды и повышение эффективности деятельности бизнеса. Практическая значимость состоит во внедрении нового для сектора инструмента стресс-тестирования в процессе управления рисками. Это позволит повысить эффективность операционной деятельности энергоремонтных предприятий: сценарно выявить чрезвычайные ситуации, которые приведут к критическим последствиям для компаний; оценить способность организации противостоять таким рискам; составить план мероприятий по их нейтрализации. / Energy repair business occupies an important place in the Russian energy sector. Without its successful operation, energy companies will not be able to effectively carry out their operations. However, the majority of the energy repair companies cannot adapt to the rapidly changing conditions of the external environment: the current trend of this business is the active implementation of the risk management system at enterprises. The aim is to improve the risk- oriented approach to energy repair management. The scientific novelty is to develop recommendations for risk management at energy repair enterprises. They are aimed at reducing losses from external factors and improving the efficiency of business. The practical significance is to introduce a new sector tool for the stress testing in the process of risk management. This will improve the efficiency of the operating activities of energy repair enterprises: scenario to identify emergencies that will lead to critical consequences for companies; assess the ability of the organization to withstand such risks; make a plan of measures to neutralize them.
86

Spatial and Temporal Dynamics of  Carbon Sequestration in Stockholm  County's Green areas : A GIS-based Analysis / Kolbindningsdynamiken i Stockholm Läns Grönområden genom Tid : En GIS-baserad Analys

Kareflod, Victoria January 2023 (has links)
The human influence of global climate is an issue currently assessed in various mitigation strategies. Stockholm County has committed to becoming carbon neutral by 2040 and negative by 2045 according to the Paris agreement. The strategy includes cutting of various sectors emissions as well as compensating for remaining emissions with carbon sequestration methods. Accounting for ecosystems ability to sequester carbon at local level in green urban areas is an important in carbon offset efforts. It has emerged from previous research that the sequestration rate may differ depending on vegetation age and thus time passing, which is not assessed on a regional level, which is important for carbon offset efforts to accurately account for the sequestration potential in long-term mitigation strategies. This study therefore aims to fill the knowledge gap of how the temporal aspect affects the current sequestration potential and future predictions, as well as assessing how it can aid in reaching carbon neutrality by 2040. The study are thus aiming to answer the research questions (1) how the carbon sequestration potential of the existing green areas change over time in Stockholm County, (2) if additional measures need to be taken to preserve or increase carbon sequestration to maintain carbon neutrality until 2040 and (3) how the knowledge of sequestration dynamics aid in reaching a carbon neutral city by 2040. A weighing of which Corine Land Cover categories was performed and concluded in the including; discontinuous structures, green urban areas, forests and wetlands, due to their contribution to sequestration potential, estimated change through time, and relevance for Stockholm County. The spatial analysis was made based on calculations with information obtained from processing of obtained data on land cover and species distribution as well as scientific literature on sequestration rates of each vegetation across all life stages, where Net Ecosystem Production was the main measurement used. The estimated results were computed in a Geographic Information System to simulate and visualize the sequestration rates of current and future predictions of 2040 sequestration potential as well as locating areas of interest. The findings show that by including temporal aspects to the assessment of carbon sequestration potential in Stockholm County, the current and future sequestration potential increased from previous research estimations. The total current sequestration potential was 2,8 MtCO2-eq annually and the predictions were estimated to 3,3 MtCO2-eq per year in 2040. As the current emissions in Stockholm County are currently 6 MtCO2-eq per year, the natural sequestration potential provided by the green areas is compensating for 46% of the current emissions. As the estimated future emissions are 0,95 MtCO2-eq annually, the natural sequestration potential more than compensates for the emissions in the county, if the predicted emission reductions are realized. Although further measurements are not seemingly required to achieve carbon neutrality in 2040, the findings further locate areas and species where management practices or protection is beneficial to further add to the sequestration potential of Stockholm County. / Den mänskliga påverkan på det globala klimatet är ett problem som för närvarande bedöms i olika klimatåtgärder. Stockholms län har förbundit sig till ett mål att bli koldioxidneutralt till 2040 och koldioxidnegativt till 2045 enligt Parisavtalets överenskommelser. Strategin innefattar att minska utsläppen från olika sektorer samt att kompensera de återstående utsläppen med olika metoder för koldioxidlagring. Ekosystemens förmåga att binda kol på lokal nivå i gröna stadsområden är en viktig del av ansträngningarna för att kompensera för utsläppen. Det har varit uppenbart från tidigare forskning att potentialen av koldioxidlagring kan skilja sig åt beroende på vegetationens ålder samt passerande tid, även om aktuell forskning inte omfattar frågan på regional nivå, vilket är viktigt för insatser som omfattar koldioxidkompensation så att lagringspotentialen kan redovisas korrekt i de långsiktiga klimatåtgärderna. Denna studie syftar därför till att fylla kunskapsluckan gällande hur den tidsmässiga aspekten påverkar den befintliga lagringspotentialen och framtida prognoser samt hur det kan bidra till att nå koldioxidneutralitet fram till 2040. Studien avser därmed till att svara på forskningsfrågorna (1) hur kolbindningspotentialen för de befintliga grönområdena förändras över tid i Stockholms län, (2) ifall ytterligare åtgärder behöver vidtas för att bevara eller öka koldioxidbindningen för att uppnå eller bibehålla koldioxidneutralitet fram till 2040 och (3) hur kunskapen om koldioxidlagringsdynamiken underlättar för att nå en koldioxidneutral region år 2040. En avvägning av vilka Corina marktäckeskategorier utfördes och resulterade i inkludering av; diskontinuerliga strukturer, gröna stadsområden, skogar och våtmarker, där koldynamiken och omfattningen av lagringspotentialen var relevant för Stockholmsregionen. Den rumsliga analysen gjordes baserad på beräkningar med information erhållen genom bearbetning av införskaffad data om marktäcke och artfördelning samt vetenskaplig litteratur om kolbindningshastighet för varje vegetation över alla livsstadier, där Net Ecosystem Production var det huvudsakliga måttet. De uppskattade resultaten beräknades i ett Geografiskt Informationssystem för att simulera och visualisera lagringshastigheten för nuvarande och framtida förutsägelser om sekvestreringspotentialen år 2040 samt att lokalisera intressanta. Resultaten visar att genom att inkludera tidsmässiga aspekter i bedömningen av kolbindningspotentialen i Stockholms län ökade den nuvarande och framtida bindningspotentialen från tidigare forsknings uppskattningar. Den totala nuvarande lagringspotentialen var 2,8 MtCO2-ekv årligen och de framtida prognoserna uppskattades till 3,3 MtCO2-ekv årligen år 2040. Eftersom de nuvarande utsläppen i Stockholms län för närvarande är 6 MtCO2-ekv årligen, kunde man se att den naturliga lagringspotentialen som grönområdena avsåg, kompenserar för 46 % av de nuvarande utsläppen. Eftersom de beräknade framtida utsläppen är 0,95 MtCO2-ekv per år, mer än kompenserar de gröna områdena för de utsläpp som sker i länet, om den förutsedda reduceringen av utsläppen sker. Även om ytterligare mätningar inte tycks behövas för att uppnå koldioxidneutralitet till 2040, lokaliseras ytterligare områden samt arter i resultatet där förvaltning eller skydd är fördelaktiga för att ytterligare förbättra lagringspotentialen i Stockholms län.
87

Mapping Carbon Storage and Potential Bioenergy Production in Södertälje Using High-resolution Biotope Database

Åkerström, Lisa January 2022 (has links)
Global warming is caused by the human induced increase of Greenhouse Gases (GHG) in the atmosphere. GHG emissions need to be reduced, and carbon dioxide (CO2) emissions from fossil sources ceased to mitigate global warming. Energy production and use is a main contributor to fossil sourced emissions in Europe. Sweden has a high part renewable power production but not completely, to have a 100% renewable power production by 2040 is a goal set by Swedish government. By 2045 Sweden also plans to have net zero emissions nationwide and afterwards negative emissions of CO2, to reduce global warming and reach the Paris agreement of maximum 1.5°C global warming level it is urgent and vital to create Carbon (C) sinks and to reach neutral and even negative emissions within the energy sector. Negative emissions can be reached in Combined Heat and Power plants (CHP) by Bio Carbon Capture and Storage (Bio-CCS). Demand on wood chips and bio-energy fuel is increasing on the European continent. A local source of biofuel might contribute to shorter transports, a local C-sink, security in supply and a way to meet both the increasing competition of fuel and the environmental political targets. Here we investigate the available land for local production of bioenergy forests in Södertälje and the amount of energy possible to produce from that. Using a detailed biotope database over the municipality, Biotopdatabasen, and a Geographical Information System (GIS) based approach 5 scenarios of potential land areal for planting of energy forests in the municipality have been analysed. Different criteria selections in biotopes, grasslands and historical crop fields, and land use, used or un-used, builds the scenarios; 1. All available grasslands, 1010 ha, 2. All available grasslands on earlier crop fields, 815 ha, 3. Unused available grassland on earlier crop field, 300 ha, 4. Available land on earlier crop fields, including forestry, 1715 ha, 5. Unused available land on earlier crop fields, 366 ha. Gross annual energy yields from energy forest in the scenarios were estimated to; 1. 46,2-65,1 GWh/y, 2. 37,3-52,5 GWh/y, 3. 13,7-19,3 GWh/y, 4. 78,4-110,5 GWh/y, 5. 16,7-23,6 GWh/y. The yield from all these scenarios will, in the expected gross normal yield scenario, match the energy produced today by fossil fuels in the local CHP and heating plant (0.64%, 2020) yields 0.69-3.96% of total energy produced. Scenarios 3 and 5 are considered likely scenarios but the effect on spreading pathways and thereby biodiversity needs to be assessed, using old crop fields lowers the risk of harming important biodiversity and possibly help restore C sink in soils.
88

以SRI情境預測分析法預測台灣細胞分流技術與市場之發展

林建成, Lin, Chien-Chen Unknown Date (has links)
幹細胞在組織器官再造中的價值已成共識,由幹細胞體外培養誘導的細胞、組織和器官,用於移植時可避免免疫排斥。未來,幹細胞將在組織工程領域搶盡頭采,逐步取代傳統的異體移植。因為成體幹細胞在人體內的數目通常不多,骨髓中每1 萬個到1 萬5 千個細胞才有一個造血幹細胞(hematopoietic stem cell),必須要經過特殊的血球分離系統才能取得足夠量,目前醫界與學界所採用的血球分離儀器主要分為螢光細胞免疫分析儀(FACS),另外,有鑑於使用者對於可攜式的需求加上半導體技術的成熟,目前還有一項全新的微導流技術被開發,因此對於幹細胞的研究,無論是胚胎幹細胞或是造血幹細胞,一個良好適用的血液分流系統都是必須而且重要的,我們也可以看見,隨著幹細胞的運用日趨廣泛,血液分流系統技術未來成長潛力更加可以預期。 本研究係採用SRI情境分析方式,透過包含學界及實務界的專家群會議,輔以腦力激盪的方法討論出關鍵決定因素與驅動力量,並以二個不確定軸面形成情境主軸,發展擴充成為情境內涵,再就各選定之情境(微導流領先,技術導向,美麗舊時光)內容進行SWOT及策略發展分析,並發展出細胞分流技術之市場及技術共同發展策略: 1. 積極推動幹細胞研究,增加市場需求。 2. 與國際同步建立儀器的確效與驗證模式,減少法規對於儀器的限制。 3. 積極推動產業的國際化,增加產業範疇 4. 積極發展奈米技術,同步提昇微小化技術與染色技術。 5. 流體與驅動技術的持續開發。 6. 光電偵測系統的研發方向。 7. 國家介入釋放舊的半導體製程技術。 關鍵字:SRI情境分析法,細胞分流技術,微導流技術,螢光細胞分析儀,情境預測,SWOT分析。 / Stem cell's value in the tissue engineering is given a new lease of life to has already become the common understanding, train the cell , tissue and organ from stem cell, can prevent the immunity from repelling when being used for transplanting. In the near future, the stem cell will rob the end to adopt in the field of tissue engineering, will replace traditional allograft to transplant progressively. Because body stem cell usually few figure having in human body, every ten thousand have a hematopoietic stem cell in the bone marrow, must pass the special cell sorting system to make enough quantity. No matter in clinical use or academic research use, fluorescence active cell sorting system is only way to separate stem cells from blood or bone marrow. For adding the maturity of the technology of the semiconductor to with the demand of the type, a brand-new cell sorting technology with micro fluidic system is developed at present, so the research to the stem cell, no matter embryo stem cell or hematopoietic stem cell, one good suitable cell sorting system must and important, we can see with application of stem cell being becoming extensive, cell sorting systematic technology grow up potentiality may it is expected future too. This research adopts SRI scenario analysis, through include academic researchers and expert groups of meeting, commercial end users, it produce the key decisive factor and drive strength to discuss so as to method that mental work agitate to complement, and with form the situation main shaft the 2 uncertain axle, development expands and becomes situation intension, selected situation content analyzed SWOT and tactics development each, erupt simultaneously and exhibit the market that the cell sorting technology and common development tactics of technology. In this research, our conclusions are as follows: 1. Actively prompt nano- technology research. 2. Actively promote stem-cell research. 3. Actively promote the research of cell's mark. 4. Develop monoclonal antibody commercialized channel and research. 5. Develop Micro fluidics and micro pumping system technology. 6. Develop the photo electricity detecting system. Key word: S R I scenario analysis methods, cell sorting system, micro fluidics system, fluorescence active cell sorting system, technology forecasting, scenario forecasting.
89

Development of new scenario decomposition techniques for linear and nonlinear stochastic programming

Zehtabian, Shohre 08 1900 (has links)
Une approche classique pour traiter les problèmes d’optimisation avec incertitude à deux- et multi-étapes est d’utiliser l’analyse par scénario. Pour ce faire, l’incertitude de certaines données du problème est modélisée par vecteurs aléatoires avec des supports finis spécifiques aux étapes. Chacune de ces réalisations représente un scénario. En utilisant des scénarios, il est possible d’étudier des versions plus simples (sous-problèmes) du problème original. Comme technique de décomposition par scénario, l’algorithme de recouvrement progressif est une des méthodes les plus populaires pour résoudre les problèmes de programmation stochastique multi-étapes. Malgré la décomposition complète par scénario, l’efficacité de la méthode du recouvrement progressif est très sensible à certains aspects pratiques, tels que le choix du paramètre de pénalisation et la manipulation du terme quadratique dans la fonction objectif du lagrangien augmenté. Pour le choix du paramètre de pénalisation, nous examinons quelques-unes des méthodes populaires, et nous proposons une nouvelle stratégie adaptive qui vise à mieux suivre le processus de l’algorithme. Des expériences numériques sur des exemples de problèmes stochastiques linéaires multi-étapes suggèrent que la plupart des techniques existantes peuvent présenter une convergence prématurée à une solution sous-optimale ou converger vers la solution optimale, mais avec un taux très lent. En revanche, la nouvelle stratégie paraît robuste et efficace. Elle a convergé vers l’optimalité dans toutes nos expériences et a été la plus rapide dans la plupart des cas. Pour la question de la manipulation du terme quadratique, nous faisons une revue des techniques existantes et nous proposons l’idée de remplacer le terme quadratique par un terme linéaire. Bien que qu’il nous reste encore à tester notre méthode, nous avons l’intuition qu’elle réduira certaines difficultés numériques et théoriques de la méthode de recouvrement progressif. / In the literature of optimization problems under uncertainty a common approach of dealing with two- and multi-stage problems is to use scenario analysis. To do so, the uncertainty of some data in the problem is modeled by stage specific random vectors with finite supports. Each realization is called a scenario. By using scenarios, it is possible to study smaller versions (subproblems) of the underlying problem. As a scenario decomposition technique, the progressive hedging algorithm is one of the most popular methods in multi-stage stochastic programming problems. In spite of full decomposition over scenarios, progressive hedging efficiency is greatly sensitive to some practical aspects, such as the choice of the penalty parameter and handling the quadratic term in the augmented Lagrangian objective function. For the choice of the penalty parameter, we review some of the popular methods, and design a novel adaptive strategy that aims to better follow the algorithm process. Numerical experiments on linear multistage stochastic test problems suggest that most of the existing techniques may exhibit premature convergence to a sub-optimal solution or converge to the optimal solution, but at a very slow rate. In contrast, the new strategy appears to be robust and efficient, converging to optimality in all our experiments and being the fastest in most of them. For the question of handling the quadratic term, we review some existing techniques and we suggest to replace the quadratic term with a linear one. Although this method has yet to be tested, we have the intuition that it will reduce some numerical and theoretical difficulties of progressive hedging in linear problems.
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風險基礎資本,情境分析及動態模擬破產預測模型之比較 / Regulatory Solvency Prediction: Risk-Based Capital, Scenario analysis and Stochastic Simulation

宋瑞琳, Sung, Jui-Lin Unknown Date (has links)
保險公司清償能力一直是保險監理的重心,在所有現行的制度中風險基礎資本是最重要的,但此項制度仍有其缺點,因此其他動態分析模型被許多學者所提出,如涉險值及情境分析。雖然這些動態分析模型被學者所偏好,但監理機關仍須對這些模型的精確程度加以了解,這也是本篇論文所要研究的目的。 基於此,本篇論文以模擬方式及經濟模型加以分析風險基礎資本、情境分析及涉險值等方法的破產預測的相對精確性。其中風險基礎資本完全採用現有NAIC的年報資料,情境分析及涉險值則採用我們所建立的模型,基於此也可以確認現有監理制度是否有缺失。 我們的結果發現風險基礎資本的預測能力很低,動態模型-情境分析及涉險值皆優於風險基礎資本,且在不同動態模型中涉險值的預測能力較好。因此可知被學者所偏好的動態分析模型應是未來保險監理的方向希望藉由本篇提供監理機關一個參考的依據。 / Solvency prediction of insurers has been the focus of insurance regulation. Among the solvency regulation systems, risked-based capital (RBC) is the most important but RBC still has some drawbacks. Thus, the dynamic financial analyses-scenario analysis and Value at Risk have been developed to be the regulation tool. Although, the scholars prefer the dynamic financial analysis, the regulators still want to make sure the accuracy of dynamic financial analysis. That is the purpose of our paper. Therefore, we use the simulation result and the econometric model to analyze the relative effectiveness of RBC, scenario and Value at Risk (VaR). The RBC is from the annual statement and the scenario and VaR come from our simulation model. Our result shows that the RBC has very low explanatory power, the dynamic financial analysis is better than RBC, and VaR outperform scenario analysis. Thus, we conclude that VaR is the way to go for property-casualty insurance regulators.

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