Treatment of external events in the linked event tree methodology NPP Goesgen - Daeniken example

International Nuclear Information System (INIS)

Kozlik, Thomas

2014-01-01

The NPP Goesgen-Daeniken uses a combined level 1 / level 2 PSA model for its event analyses. The model uses a linked event tree approach, using the software RISKMAN R . Each initiating event passes through a modularized event tree structure, consisting of external events pre-trees, alignment and support systems trees and front-line and containment response trees. This paper explains the structure of the linked event trees. Switches are used to bypass certain trees for specific initiating events. The screening process applied to possible external events is explained. The final scope of considered natural external events in the Goesgen PSA consists of earthquakes, seasonal events causing cooling water intake plugging or external floods. The structure of the natural external events pre-trees is explained. The treatment of external floods is explained in more detail. Floods at the Goesgen site are caused by extreme river flows into the old branch of the Aare river. A new model has been developed to analyse the probabilistic flood hazard using a bivariate distribution (water level and flood duration). Analysing the statistical data, the time trend had to be considered. The Goesgen PSA models 7 external flood initiating events, considering different water levels and durations at the flooded plant site. The building fragilities were developed in terms of resistance times. The RISKMAN R external flood pre-tree consists of top events for operator actions and failure of the building functions, which leads to the functional failure of equipment located at the lower elevation of the building. (author)

Arenal-type pyroclastic flows: A probabilistic event tree risk analysis

Science.gov (United States)

Meloy, Anthony F.

2006-09-01

A quantitative hazard-specific scenario-modelling risk analysis is performed at Arenal volcano, Costa Rica for the newly recognised Arenal-type pyroclastic flow (ATPF) phenomenon using an event tree framework. These flows are generated by the sudden depressurisation and fragmentation of an active basaltic andesite lava pool as a result of a partial collapse of the crater wall. The deposits of this type of flow include angular blocks and juvenile clasts, which are rarely found in other types of pyroclastic flow. An event tree analysis (ETA) is a useful tool and framework in which to analyse and graphically present the probabilities of the occurrence of many possible events in a complex system. Four event trees are created in the analysis, three of which are extended to investigate the varying individual risk faced by three generic representatives of the surrounding community: a resident, a worker, and a tourist. The raw numerical risk estimates determined by the ETA are converted into a set of linguistic expressions (i.e. VERY HIGH, HIGH, MODERATE etc.) using an established risk classification scale. Three individually tailored semi-quantitative risk maps are then created from a set of risk conversion tables to show how the risk varies for each individual in different areas around the volcano. In some cases, by relocating from the north to the south, the level of risk can be reduced by up to three classes. While the individual risk maps may be broadly applicable, and therefore of interest to the general community, the risk maps and associated probability values generated in the ETA are intended to be used by trained professionals and government agencies to evaluate the risk and effectively manage the long-term development of infrastructure and habitation. With the addition of fresh monitoring data, the combination of both long- and short-term event trees would provide a comprehensive and consistent method of risk analysis (both during and pre-crisis), and as such

Reconciliation of Gene and Species Trees

Directory of Open Access Journals (Sweden)

L. Y. Rusin

2014-01-01

Full Text Available The first part of the paper briefly overviews the problem of gene and species trees reconciliation with the focus on defining and algorithmic construction of the evolutionary scenario. Basic ideas are discussed for the aspects of mapping definitions, costs of the mapping and evolutionary scenario, imposing time scales on a scenario, incorporating horizontal gene transfers, binarization and reconciliation of polytomous trees, and construction of species trees and scenarios. The review does not intend to cover the vast diversity of literature published on these subjects. Instead, the authors strived to overview the problem of the evolutionary scenario as a central concept in many areas of evolutionary research. The second part provides detailed mathematical proofs for the solutions of two problems: (i inferring a gene evolution along a species tree accounting for various types of evolutionary events and (ii trees reconciliation into a single species tree when only gene duplications and losses are allowed. All proposed algorithms have a cubic time complexity and are mathematically proved to find exact solutions. Solving algorithms for problem (ii can be naturally extended to incorporate horizontal transfers, other evolutionary events, and time scales on the species tree.

Use of fault and decision tree analyses to protect against industrial sabotage

International Nuclear Information System (INIS)

Fullwood, R.R.; Erdmann, R.C.

1975-01-01

Fault tree and decision tree analyses provide systematic bases for evaluation of safety systems and procedures. Heuristically, this paper shows applications of these methods for industrial sabotage analysis at a reprocessing plant. Fault trees constructed by ''leak path'' analysis for completeness through path inventory. The escape fault tree is readily developed by this method and using the reciprocal character of the trees, the attack fault tree is constructed. After construction, the events on the fault tree are corrected for their nonreciprocal character. The fault trees are algebraically solved and the protection that is afforded is ranked by the number of barriers that must be penetrated. No attempt is made to assess the barrier penetration probabilities or penetration time duration. Event trees are useful for dynamic plant protection analysis through their time-sequencing character. To illustrate their usefulness, a simple attack scenario is devised and event-tree analyzed. Two saboteur success paths and 21 failure paths are found. This example clearly shows the event tree usefulness for concisely presenting the time sequencing of key decision points. However, event trees have the disadvantage of being scenario dependent, therefore requiring a separate event tree for each scenario

RAVEN. Dynamic Event Tree Approach Level III Milestone

Energy Technology Data Exchange (ETDEWEB)

Alfonsi, Andrea [Idaho National Lab. (INL), Idaho Falls, ID (United States); Rabiti, Cristian [Idaho National Lab. (INL), Idaho Falls, ID (United States); Mandelli, Diego [Idaho National Lab. (INL), Idaho Falls, ID (United States); Cogliati, Joshua [Idaho National Lab. (INL), Idaho Falls, ID (United States); Kinoshita, Robert [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2014-07-01

Conventional Event-Tree (ET) based methodologies are extensively used as tools to perform reliability and safety assessment of complex and critical engineering systems. One of the disadvantages of these methods is that timing/sequencing of events and system dynamics are not explicitly accounted for in the analysis. In order to overcome these limitations several techniques, also know as Dynamic Probabilistic Risk Assessment (DPRA), have been developed. Monte-Carlo (MC) and Dynamic Event Tree (DET) are two of the most widely used D-PRA methodologies to perform safety assessment of Nuclear Power Plants (NPP). In the past two years, the Idaho National Laboratory (INL) has developed its own tool to perform Dynamic PRA: RAVEN (Reactor Analysis and Virtual control ENvironment). RAVEN has been designed to perform two main tasks: 1) control logic driver for the new Thermo-Hydraulic code RELAP-7 and 2) post-processing tool. In the first task, RAVEN acts as a deterministic controller in which the set of control logic laws (user defined) monitors the RELAP-7 simulation and controls the activation of specific systems. Moreover, the control logic infrastructure is used to model stochastic events, such as components failures, and perform uncertainty propagation. Such stochastic modeling is deployed using both MC and DET algorithms. In the second task, RAVEN processes the large amount of data generated by RELAP-7 using data-mining based algorithms. This report focuses on the analysis of dynamic stochastic systems using the newly developed RAVEN DET capability. As an example, a DPRA analysis, using DET, of a simplified pressurized water reactor for a Station Black-Out (SBO) scenario is presented.

RAVEN: Dynamic Event Tree Approach Level III Milestone

Energy Technology Data Exchange (ETDEWEB)

Andrea Alfonsi; Cristian Rabiti; Diego Mandelli; Joshua Cogliati; Robert Kinoshita

2013-07-01

Conventional Event-Tree (ET) based methodologies are extensively used as tools to perform reliability and safety assessment of complex and critical engineering systems. One of the disadvantages of these methods is that timing/sequencing of events and system dynamics are not explicitly accounted for in the analysis. In order to overcome these limitations several techniques, also know as Dynamic Probabilistic Risk Assessment (DPRA), have been developed. Monte-Carlo (MC) and Dynamic Event Tree (DET) are two of the most widely used D-PRA methodologies to perform safety assessment of Nuclear Power Plants (NPP). In the past two years, the Idaho National Laboratory (INL) has developed its own tool to perform Dynamic PRA: RAVEN (Reactor Analysis and Virtual control ENvironment). RAVEN has been designed to perform two main tasks: 1) control logic driver for the new Thermo-Hydraulic code RELAP-7 and 2) post-processing tool. In the first task, RAVEN acts as a deterministic controller in which the set of control logic laws (user defined) monitors the RELAP-7 simulation and controls the activation of specific systems. Moreover, the control logic infrastructure is used to model stochastic events, such as components failures, and perform uncertainty propagation. Such stochastic modeling is deployed using both MC and DET algorithms. In the second task, RAVEN processes the large amount of data generated by RELAP-7 using data-mining based algorithms. This report focuses on the analysis of dynamic stochastic systems using the newly developed RAVEN DET capability. As an example, a DPRA analysis, using DET, of a simplified pressurized water reactor for a Station Black-Out (SBO) scenario is presented.

Using fuzzy arithmetic in containment event trees

International Nuclear Information System (INIS)

Rivera, S.S.; Baron, Jorge H.

2000-01-01

The use of fuzzy arithmetic is proposed for the evaluation of containment event trees. Concepts such as improbable, very improbable, and so on, which are subjective by nature, are represented by fuzzy numbers. The quantitative evaluation of containment event trees is based on the extension principle, by which operations on real numbers are extended to operations on fuzzy numbers. Expert knowledge is considered as state of the base variable with a normal distribution, which is considered to represent the membership function. Finally, this paper presents results of an example calculation of a containment event tree for the CAREM-25 nuclear power plant, presently under detailed design stage at Argentina. (author)

Dynamic Event Tree advancements and control logic improvements

International Nuclear Information System (INIS)

Alfonsi, Andrea; Rabiti, Cristian; Mandelli, Diego; Sen, Ramazan Sonat; Cogliati, Joshua Joseph

2015-01-01

The RAVEN code has been under development at the Idaho National Laboratory since 2012. Its main goal is to create a multi-purpose platform for the deploying of all the capabilities needed for Probabilistic Risk Assessment, uncertainty quantification, data mining analysis and optimization studies. RAVEN is currently equipped with three different sampling categories: Forward samplers (Monte Carlo, Latin Hyper Cube, Stratified, Grid Sampler, Factorials, etc.), Adaptive Samplers (Limit Surface search, Adaptive Polynomial Chaos, etc.) and Dynamic Event Tree (DET) samplers (Deterministic and Adaptive Dynamic Event Trees). The main subject of this document is to report the activities that have been done in order to: start the migration of the RAVEN/RELAP-7 control logic system into MOOSE, and develop advanced dynamic sampling capabilities based on the Dynamic Event Tree approach. In order to provide to all MOOSE-based applications a control logic capability, in this Fiscal Year an initial migration activity has been initiated, moving the control logic system, designed for RELAP-7 by the RAVEN team, into the MOOSE framework. In this document, a brief explanation of what has been done is going to be reported. The second and most important subject of this report is about the development of a Dynamic Event Tree (DET) sampler named 'Hybrid Dynamic Event Tree' (HDET) and its Adaptive variant 'Adaptive Hybrid Dynamic Event Tree' (AHDET). As other authors have already reported, among the different types of uncertainties, it is possible to discern two principle types: aleatory and epistemic uncertainties. The classical Dynamic Event Tree is in charge of treating the first class (aleatory) uncertainties; the dependence of the probabilistic risk assessment and analysis on the epistemic uncertainties are treated by an initial Monte Carlo sampling (MCDET). From each Monte Carlo sample, a DET analysis is run (in total, N trees). The Monte Carlo employs a pre

LOSP-initiated event tree analysis for BWR

International Nuclear Information System (INIS)

Watanabe, Norio; Kondo, Masaaki; Uno, Kiyotaka; Chigusa, Takeshi; Harami, Taikan

1989-03-01

As a preliminary study of 'Japanese Model Plant PSA', a LOSP (loss of off-site power)-initiated Event Tree Analysis for a Japanese typical BWR was carried out solely based on the open documents such as 'Safety Analysis Report'. The objectives of this analysis are as follows; - to delineate core-melt accident sequences initiated by LOSP, - to evaluate the importance of core-melt accident sequences in terms of occurrence frequency, and - to develop a foundation of plant information and analytical procedures for efficiently performing further 'Japanese Model Plant PSA'. This report describes the procedure and results of the LOSP-initiated Event Tree Analysis. In this analysis, two types of event trees, Functional Event Tree and Systemic Event Tree, were developed to delineate core-melt accident sequences and to quantify their frequencies. Front-line System Event Tree was prepared as well to provide core-melt sequence delineation for accident progression analysis of Level 2 PSA which will be followed in a future. Applying U.S. operational experience data such as component failure rates and a LOSP frequency, we obtained the following results; - The total frequency of core-melt accident sequences initiated by LOSP is estimated at 5 x 10 -4 per reactor-year. - The dominant sequences are 'Loss of Decay Heat Removal' and 'Loss of Emergency Electric Power Supply', which account for more than 90% of the total core-melt frequency. In this analysis, a higher value of 0.13/R·Y was used for the LOSP frequency than experiences in Japan and any recovery action was not considered. In fact, however, there has been no experience of LOSP event in Japanese nuclear power plants so far and it is also expected that offsite power and/or PCS would be recovered before core melt. Considering Japanese operating experience and recovery factors will reduce the total core-melt frequency to less than 10 -6 per reactor-year. (J.P.N.)

Development of Accident Scenarios and Quantification Methodology for RAON Accelerator

International Nuclear Information System (INIS)

Lee, Yongjin; Jae, Moosung

2014-01-01

The RIsp (Rare Isotope Science Project) plans to provide neutron-rich isotopes (RIs) and stable heavy ion beams. The accelerator is defined as radiation production system according to Nuclear Safety Law. Therefore, it needs strict operate procedures and safety assurance to prevent radiation exposure. In order to satisfy this condition, there is a need for evaluating potential risk of accelerator from the design stage itself. Though some of PSA researches have been conducted for accelerator, most of them focus on not general accident sequence but simple explanation of accident. In this paper, general accident scenarios are developed by Event Tree and deduce new quantification methodology of Event Tree. In this study, some initial events, which may occur in the accelerator, are selected. Using selected initial events, the accident scenarios of accelerator facility are developed with Event Tree. These results can be used as basic data of the accelerator for future risk assessments. After analyzing the probability of each heading, it is possible to conduct quantification and evaluate the significance of the accident result. If there is a development of the accident scenario for external events, risk assessment of entire accelerator facility will be completed. To reduce the uncertainty of the Event Tree, it is possible to produce a reliable data via the presented quantification techniques

A fast method for calculating reliable event supports in tree reconciliations via Pareto optimality.

Science.gov (United States)

To, Thu-Hien; Jacox, Edwin; Ranwez, Vincent; Scornavacca, Celine

2015-11-14

Given a gene and a species tree, reconciliation methods attempt to retrieve the macro-evolutionary events that best explain the discrepancies between the two tree topologies. The DTL parsimonious approach searches for a most parsimonious reconciliation between a gene tree and a (dated) species tree, considering four possible macro-evolutionary events (speciation, duplication, transfer, and loss) with specific costs. Unfortunately, many events are erroneously predicted due to errors in the input trees, inappropriate input cost values or because of the existence of several equally parsimonious scenarios. It is thus crucial to provide a measure of the reliability for predicted events. It has been recently proposed that the reliability of an event can be estimated via its frequency in the set of most parsimonious reconciliations obtained using a variety of reasonable input cost vectors. To compute such a support, a straightforward but time-consuming approach is to generate the costs slightly departing from the original ones, independently compute the set of all most parsimonious reconciliations for each vector, and combine these sets a posteriori. Another proposed approach uses Pareto-optimality to partition cost values into regions which induce reconciliations with the same number of DTL events. The support of an event is then defined as its frequency in the set of regions. However, often, the number of regions is not large enough to provide reliable supports. We present here a method to compute efficiently event supports via a polynomial-sized graph, which can represent all reconciliations for several different costs. Moreover, two methods are proposed to take into account alternative input costs: either explicitly providing an input cost range or allowing a tolerance for the over cost of a reconciliation. Our methods are faster than the region based method, substantially faster than the sampling-costs approach, and have a higher event-prediction accuracy on

Dynamic Event Tree advancements and control logic improvements

Energy Technology Data Exchange (ETDEWEB)

Alfonsi, Andrea [Idaho National Lab. (INL), Idaho Falls, ID (United States); Rabiti, Cristian [Idaho National Lab. (INL), Idaho Falls, ID (United States); Mandelli, Diego [Idaho National Lab. (INL), Idaho Falls, ID (United States); Sen, Ramazan Sonat [Idaho National Lab. (INL), Idaho Falls, ID (United States); Cogliati, Joshua Joseph [Idaho National Lab. (INL), Idaho Falls, ID (United States)

2015-09-01

The RAVEN code has been under development at the Idaho National Laboratory since 2012. Its main goal is to create a multi-purpose platform for the deploying of all the capabilities needed for Probabilistic Risk Assessment, uncertainty quantification, data mining analysis and optimization studies. RAVEN is currently equipped with three different sampling categories: Forward samplers (Monte Carlo, Latin Hyper Cube, Stratified, Grid Sampler, Factorials, etc.), Adaptive Samplers (Limit Surface search, Adaptive Polynomial Chaos, etc.) and Dynamic Event Tree (DET) samplers (Deterministic and Adaptive Dynamic Event Trees). The main subject of this document is to report the activities that have been done in order to: start the migration of the RAVEN/RELAP-7 control logic system into MOOSE, and develop advanced dynamic sampling capabilities based on the Dynamic Event Tree approach. In order to provide to all MOOSE-based applications a control logic capability, in this Fiscal Year an initial migration activity has been initiated, moving the control logic system, designed for RELAP-7 by the RAVEN team, into the MOOSE framework. In this document, a brief explanation of what has been done is going to be reported. The second and most important subject of this report is about the development of a Dynamic Event Tree (DET) sampler named “Hybrid Dynamic Event Tree” (HDET) and its Adaptive variant “Adaptive Hybrid Dynamic Event Tree” (AHDET). As other authors have already reported, among the different types of uncertainties, it is possible to discern two principle types: aleatory and epistemic uncertainties. The classical Dynamic Event Tree is in charge of treating the first class (aleatory) uncertainties; the dependence of the probabilistic risk assessment and analysis on the epistemic uncertainties are treated by an initial Monte Carlo sampling (MCDET). From each Monte Carlo sample, a DET analysis is run (in total, N trees). The Monte Carlo employs a pre-sampling of the

Credibilistic multi-period portfolio optimization based on scenario tree

Science.gov (United States)

Mohebbi, Negin; Najafi, Amir Abbas

2018-02-01

In this paper, we consider a multi-period fuzzy portfolio optimization model with considering transaction costs and the possibility of risk-free investment. We formulate a bi-objective mean-VaR portfolio selection model based on the integration of fuzzy credibility theory and scenario tree in order to dealing with the markets uncertainty. The scenario tree is also a proper method for modeling multi-period portfolio problems since the length and continuity of their horizon. We take the return and risk as well cardinality, threshold, class, and liquidity constraints into consideration for further compliance of the model with reality. Then, an interactive dynamic programming method, which is based on a two-phase fuzzy interactive approach, is employed to solve the proposed model. In order to verify the proposed model, we present an empirical application in NYSE under different circumstances. The results show that the consideration of data uncertainty and other real-world assumptions lead to more practical and efficient solutions.

Accident scenarios triggered by lightning strike on atmospheric storage tanks

International Nuclear Information System (INIS)

Necci, Amos; Argenti, Francesca; Landucci, Gabriele; Cozzani, Valerio

2014-01-01

Severe Natech accidents may be triggered by lightning strike affecting storage tanks containing relevant inventories of hazardous materials. The present study focused on the identification of event sequences and accident scenarios following lightning impact on atmospheric tanks. Reference event trees, validated using past accident analysis, are provided to describe the specific accident chains identified, accounting for reference protection and mitigation safety barriers usually adopted in current industrial practice. An overall methodology was outlined to allow the calculation of the expected frequencies of final scenarios following lightning impact on atmospheric storage tanks, taking into account the expected performance of available safety barriers. The methodology was applied to a case study in order to better understand the data that may be obtained and their importance in the framework of quantitative risk assessment (QRA) and of the risk management of industrial facilities with respect to external hazards due to natural events. - Highlights: • Event sequences following lightning impact on atmospheric tanks were identified. • Reference event trees including standard safety barriers were obtained. • Safety barriers applied in industrial practice were assessed to quantify event trees. • Frequencies of final scenarios following lightning impact on tanks were calculated. • Natech scenarios caused by lightning have an important influence on risk profiles

Computer-aided event tree analysis by the impact vector method

International Nuclear Information System (INIS)

Lima, J.E.P.

1984-01-01

In the development of the Probabilistic Risk Analysis of Angra I, the ' large event tree/small fault tree' approach was adopted for the analysis of the plant behavior in an emergency situation. In this work, the event tree methodology is presented along with the adaptations which had to be made in order to attain a correct description of the safety system performances according to the selected analysis method. The problems appearing in the application of the methodology and their respective solutions are presented and discussed, with special emphasis to the impact vector technique. A description of the ETAP code ('Event Tree Analysis Program') developed for constructing and quantifying event trees is also given in this work. A preliminary version of the small-break LOCA analysis for Angra 1 is presented as an example of application of the methodology and of the code. It is shown that the use of the ETAP code sigmnificantly contributes to decreasing the time spent in event tree analyses, making it viable the practical application of the analysis approach referred above. (author) [pt

STRIDE: Species Tree Root Inference from Gene Duplication Events.

Science.gov (United States)

Emms, David M; Kelly, Steven

2017-12-01

The correct interpretation of any phylogenetic tree is dependent on that tree being correctly rooted. We present STRIDE, a fast, effective, and outgroup-free method for identification of gene duplication events and species tree root inference in large-scale molecular phylogenetic analyses. STRIDE identifies sets of well-supported in-group gene duplication events from a set of unrooted gene trees, and analyses these events to infer a probability distribution over an unrooted species tree for the location of its root. We show that STRIDE correctly identifies the root of the species tree in multiple large-scale molecular phylogenetic data sets spanning a wide range of timescales and taxonomic groups. We demonstrate that the novel probability model implemented in STRIDE can accurately represent the ambiguity in species tree root assignment for data sets where information is limited. Furthermore, application of STRIDE to outgroup-free inference of the origin of the eukaryotic tree resulted in a root probability distribution that provides additional support for leading hypotheses for the origin of the eukaryotes. © The Author 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

Alternative measures of risk of extreme events in decision trees

International Nuclear Information System (INIS)

Frohwein, H.I.; Lambert, J.H.; Haimes, Y.Y.

1999-01-01

A need for a methodology to control the extreme events, defined as low-probability, high-consequence incidents, in sequential decisions is identified. A variety of alternative and complementary measures of the risk of extreme events are examined for their usability as objective functions in sequential decisions, represented as single- or multiple-objective decision trees. Earlier work had addressed difficulties, related to non-separability, with the minimization of some measures of the risk of extreme events in sequential decisions. In an extension of these results, it is shown how some non-separable measures of the risk of extreme events can be interpreted in terms of separable constituents of risk, thereby enabling a wider class of measures of the risk of extreme events to be handled in a straightforward manner in a decision tree. Also for extreme events, results are given to enable minimax- and Hurwicz-criterion analyses in decision trees. An example demonstrates the incorporation of different measures of the risk of extreme events in a multi-objective decision tree. Conceptual formulations for optimizing non-separable measures of the risk of extreme events are identified as an important area for future investigation

Gene-Tree Reconciliation with MUL-Trees to Resolve Polyploidy Events.

Science.gov (United States)

Gregg, W C Thomas; Ather, S Hussain; Hahn, Matthew W

2017-11-01

Polyploidy can have a huge impact on the evolution of species, and it is a common occurrence, especially in plants. The two types of polyploids-autopolyploids and allopolyploids-differ in the level of divergence between the genes that are brought together in the new polyploid lineage. Because allopolyploids are formed via hybridization, the homoeologous copies of genes within them are at least as divergent as orthologs in the parental species that came together to form them. This means that common methods for estimating the parental lineages of allopolyploidy events are not accurate, and can lead to incorrect inferences about the number of gene duplications and losses. Here, we have adapted an algorithm for topology-based gene-tree reconciliation to work with multi-labeled trees (MUL-trees). By definition, MUL-trees have some tips with identical labels, which makes them a natural representation of the genomes of polyploids. Using this new reconciliation algorithm we can: accurately place allopolyploidy events on a phylogeny, identify the parental lineages that hybridized to form allopolyploids, distinguish between allo-, auto-, and (in most cases) no polyploidy, and correctly count the number of duplications and losses in a set of gene trees. We validate our method using gene trees simulated with and without polyploidy, and revisit the history of polyploidy in data from the clades including both baker's yeast and bread wheat. Our re-analysis of the yeast data confirms the allopolyploid origin and parental lineages previously identified for this group. The method presented here should find wide use in the growing number of genomes from species with a history of polyploidy. [Polyploidy; reconciliation; whole-genome duplication.]. © The Author(s) 2017. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Tree cover in Central Africa: determinants and sensitivity under contrasted scenarios of global change.

Science.gov (United States)

Aleman, Julie C; Blarquez, Olivier; Gourlet-Fleury, Sylvie; Bremond, Laurent; Favier, Charly

2017-01-30

Tree cover is a key variable for ecosystem functioning, and is widely used to study tropical ecosystems. But its determinants and their relative importance are still a matter of debate, especially because most regional and global analyses have not considered the influence of agricultural practices. More information is urgently needed regarding how human practices influence vegetation structure. Here we focused in Central Africa, a region still subjected to traditional agricultural practices with a clear vegetation gradient. Using remote sensing data and global databases, we calibrated a Random Forest model to correlatively link tree cover with climatic, edaphic, fire and agricultural practices data. We showed that annual rainfall and accumulated water deficit were the main drivers of the distribution of tree cover and vegetation classes (defined by the modes of tree cover density), but agricultural practices, especially pastoralism, were also important in determining tree cover. We simulated future tree cover with our model using different scenarios of climate and land-use (agriculture and population) changes. Our simulations suggest that tree cover may respond differently regarding the type of scenarios, but land-use change was an important driver of vegetation change even able to counterbalance the effect of climate change in Central Africa.

Analysis of event tree with imprecise inputs by fuzzy set theory

International Nuclear Information System (INIS)

Ahn, Kwang Il; Chun, Moon Hyun

1990-01-01

Fuzzy set theory approach is proposed as a method to analyze event trees with imprecise or linguistic input variables such as 'likely' or 'improbable' instead of the numerical probability. In this paper, it is shown how the fuzzy set theory can be applied to the event tree analysis. The result of this study shows that the fuzzy set theory approach can be applied as an acceptable and effective tool for analysis of the event tree with fuzzy type of inputs. Comparisons of the fuzzy theory approach with the probabilistic approach of computing probabilities of final states of the event tree through subjective weighting factors and LHS technique show that the two approaches have common factors and give reasonable results

Attack Trees for Practical Security Assessment: Ranking of Attack Scenarios with ADTool 2.0

NARCIS (Netherlands)

Gadyatskaya, Olga; Jhawar, Ravi; Kordy, P.T.; Lounis, Karim; Mauw, Sjouke; Trujillo-Rasua, Rolando

2016-01-01

In this tool demonstration paper we present the ADTool2.0: an open-source software tool for design, manipulation and analysis of attack trees. The tool supports ranking of attack scenarios based on quantitative attributes entered by the user; it is scriptable; and it incorporates attack trees with

Scenario Modeling of Thermal Influence from Forest Fire Front on a Coniferous Tree Trunk

Directory of Open Access Journals (Sweden)

Baranovskiy Nikolay V.

2016-01-01

Full Text Available Scenario research results of heat transfer and tissue damage in three-layered tree trunk influenced by heat flux from forest fire are presented. The problem is solved in two-dimensional statement in polar coordinates. The typical range of influence parameters (heat flux from forest fire front, trunk radius, coniferous species, air temperature, duration of exposure and distance from fire line is considered. Temperature distributions in different moments of time are obtained. Condition of tree damage by forest fire influence is under consideration in this research. Information summarized using tables with scenario and fire consequences results.

Comparison of event tree, fault tree and Markov methods for probabilistic safety assessment and application to accident mitigation

International Nuclear Information System (INIS)

James, H.; Harris, M.J.; Hall, S.F.

1992-01-01

Probabilistic safety assessment (PSA) is used extensively in the nuclear industry. The main stages of PSA and the traditional event tree method are described. Focussing on hydrogen explosions, an event tree model is compared to a novel Markov model and a fault tree, and unexpected implication for accident mitigation is revealed. (author)

Process Risk Assessment using Dynamic Simulation of Scenarios

DEFF Research Database (Denmark)

Markert, Frank; Kozin, Igor; Duijm, Nijs Jan

2016-01-01

identification, description of accident scenarios and using the conventional approach to develop static event trees for events following a loss of containment. Modelling the impacts and consequences needs models to describe the release, dispersion and effect of the hazardous material, as well as models...

Event tree analysis for the system of hybrid reactor

International Nuclear Information System (INIS)

Yang Yongwei; Qiu Lijian

1993-01-01

The application of probabilistic risk assessment for fusion-fission hybrid reactor is introduced. A hybrid reactor system has been analysed using event trees. According to the character of the conceptual design of Hefei Fusion-fission Experimental Hybrid Breeding Reactor, the probabilities of the event tree series induced by 4 typical initiating events were calculated. The results showed that the conceptual design is safe and reasonable. through this paper, the safety character of hybrid reactor system has been understood more deeply. Some suggestions valuable to safety design for hybrid reactor have been proposed

Inferring phylogenetic trees from the knowledge of rare evolutionary events.

Science.gov (United States)

Hellmuth, Marc; Hernandez-Rosales, Maribel; Long, Yangjing; Stadler, Peter F

2018-06-01

Rare events have played an increasing role in molecular phylogenetics as potentially homoplasy-poor characters. In this contribution we analyze the phylogenetic information content from a combinatorial point of view by considering the binary relation on the set of taxa defined by the existence of a single event separating two taxa. We show that the graph-representation of this relation must be a tree. Moreover, we characterize completely the relationship between the tree of such relations and the underlying phylogenetic tree. With directed operations such as tandem-duplication-random-loss events in mind we demonstrate how non-symmetric information constrains the position of the root in the partially reconstructed phylogeny.

Probabilistic risk assessment course documentation. Volume 4. System reliability and analysis techniques sessions B/C - event trees/fault trees

International Nuclear Information System (INIS)

Haasl, D.; Young, J.

1985-08-01

This course will employ a combination of lecture material and practical problem solving in order to develop competence and understanding of th principles and techniques of event tree and fault tree analysis. The role of these techniques in the overall context of PRA will be described. The emphasis of this course will be on the basic, traditional methods of event tree and fault tree analysis

Contrasting safety assessments of a runway incursion scenario: Event sequence analysis versus multi-agent dynamic risk modelling

International Nuclear Information System (INIS)

Stroeve, Sybert H.; Blom, Henk A.P.; Bakker, G.J.

2013-01-01

In the safety literature it has been argued, that in a complex socio-technical system safety cannot be well analysed by event sequence based approaches, but requires to capture the complex interactions and performance variability of the socio-technical system. In order to evaluate the quantitative and practical consequences of these arguments, this study compares two approaches to assess accident risk of an example safety critical sociotechnical system. It contrasts an event sequence based assessment with a multi-agent dynamic risk model (MA-DRM) based assessment, both of which are performed for a particular runway incursion scenario. The event sequence analysis uses the well-known event tree modelling formalism and the MA-DRM based approach combines agent based modelling, hybrid Petri nets and rare event Monte Carlo simulation. The comparison addresses qualitative and quantitative differences in the methods, attained risk levels, and in the prime factors influencing the safety of the operation. The assessments show considerable differences in the accident risk implications of the performance of human operators and technical systems in the runway incursion scenario. In contrast with the event sequence based results, the MA-DRM based results show that the accident risk is not manifest from the performance of and relations between individual human operators and technical systems. Instead, the safety risk emerges from the totality of the performance and interactions in the agent based model of the safety critical operation considered, which coincides very well with the argumentation in the safety literature.

Yield curve event tree construction for multi stage stochastic programming models

DEFF Research Database (Denmark)

Rasmussen, Kourosh Marjani; Poulsen, Rolf

Dynamic stochastic programming (DSP) provides an intuitive framework for modelling of financial portfolio choice problems where market frictions are present and dynamic re--balancing has a significant effect on initial decisions. The application of these models in practice, however, is limited....... Indeed defining a universal and tractable framework for fully ``appropriate'' event trees is in our opinion an impossible task. A problem specific approach to designing such event trees is the way ahead. In this paper we propose a number of desirable properties which should be present in an event tree...

Treatment of complementary events in constructing the linked Level 1 and Level 2 fault trees

International Nuclear Information System (INIS)

Jo, Young G.; Ahn, Kwang-Il

2009-01-01

Complementary events in the event trees for a PRA model should be treated properly in order to evaluate plant risk correctly. In this paper, the characteristics of the following three different cutset generation methods were investigated first in order to find the best practical way for treating complementary events: (1) exact method which treats complementary events logically, (2) no-delete term method which does not treat complementary events at all, and (3) delete term method which treats complementary events by deleting nonsense cutsets which are generated as a result of ignoring complementary events. Then, practical methods for treating complementary events in constructing linked fault trees for Level 1 and Level 2 PRA were suggested and demonstrated. The suggested methods deal with the following selected four typical cases: (1) Case 1-an event tree event (E) is represented by a fault tree gate whose inputs consist of only fault tree gates, (2) Case 2-E is represented by a single basic event, (3) Case 3-E is represented by an OR fault tree gate which has a single basic event and a fault tree gate as inputs, and (4) Case 4-E is represented by an AND fault tree gate which has a single basic event and a fault tree gate as inputs. In the suggested methods, first the high level logic structures of event tree events are examined and restructured, if needed. Then, the delete term method, the exact method, and the combination of the two methods are applied to through Case 1 to Case 4, respectively. As a result, it is recommended to treat complementary events, using the suggested methods, before Level 1 and Level 2 PRA fault trees are coupled

SCENARIO OF AN ACCIDENT OF SOIL DAMS IN CASE OF WATER SPILL OVER A DAM CREST BY USING FAULT TREE ANALYSIS

Directory of Open Access Journals (Sweden)

Kuznetsov Dmitriy Viktorovich

2016-04-01

Full Text Available The scenario of a hydrodynamic accident of water flow over a crest of a soil dam is considered by the method of fault tree analysis, for which the basic reasons and controlled diagnostic indicators of an accident have been defined. Logical operators “AND”/”OR” were used for creation of a sequence of logically connected events, leading to an undesired event in the scenario of accident. The scenario of the accident was plotted in case of three basic reasons - an excessive settling of a dam crest, an excess flood, an inoperable spillway, taking into account the sequence of the events’ development and with observance of the necessary conditions leading to an accident. “Technical” reasons were observed in the present scenario, force majeure events were not considered. The provided scenario of the accident consists of two branches of events’ development: the left one that depends on an upstream level, and the right one that depends on settling of a dam crest. In each of the considered events an accident “the water spill over a crest of a soil dam” is possible only in case of execution of two different conditions at the same time, i.e. in case of an appropriate upstream level and the appropriate mark of a crest of a soil dam. The conditions of the accident are defined by diagnostic indices - the upstream level and settling of a dam crest, which at the same time are safety criteria of the hydraulic structure for soil dams. They allow defining the technical condition of the construction. Four possible technical conditions are suggested for the definition of technical statuses - normative, operable, limited operable, abnormal. Criteria of safety are the boundaries of the state: for loading and impact - it is the upstream level, for geometrical compliance of the construction - it is a dam crest mark.

Review of the severe accident risk reduction program (SARRP) containment event trees

International Nuclear Information System (INIS)

1986-05-01

A part of the Severe Accident Risk Reduction Program, researchers at Sandia National Laboratories have constructed a group of containment event trees to be used in the analysis of key accident sequences for light water reactors (LWR) during postulated severe accidents. The ultimate goal of the program is to provide to the NRC staff a current assessment of the risk from severe reactor accidents for a group of five light water reactors. This review specifically focuses on the development and construction of the containment event trees and the results for containment failure probability, modes and timing. The report first gives the background on the program, the review criteria, and a summary of the observations, findings and recommendations. secondly, the individual reviews of each committee member on the event trees is presented. Finally, a review is provided on the computer model used to construct and evaluate the event trees

Automated reasoning with dynamic event trees: a real-time, knowledge-based decision aide

International Nuclear Information System (INIS)

Touchton, R.A.; Gunter, A.D.; Subramanyan, N.

1988-01-01

The models and data contained in a probabilistic risk assessment (PRA) Event Sequence Analysis represent a wealth of information that can be used for dynamic calculation of event sequence likelihood. In this paper we report a new and unique computerization methodology which utilizes these data. This sub-system (referred to as PREDICTOR) has been developed and tested as part of a larger system. PREDICTOR performs a real-time (re)calculation of the estimated likelihood of core-melt as a function of plant status. This methodology uses object-oriented programming techniques from the artificial intelligence discipline that enable one to codify event tree and fault tree logic models and associated probabilities developed in a PRA study. Existence of off-normal conditions is reported to PREDICTOR, which then updates the relevant failure probabilities throughout the event tree and fault tree models by dynamically replacing the off-the-shelf (or prior) probabilities with new probabilities based on the current situation. The new event probabilities are immediately propagated through the models (using 'demons') and an updated core-melt probability is calculated. Along the way, the dominant non-success path of each event tree is determined and highlighted. (author)

Introduction of operator actions in the event trees

International Nuclear Information System (INIS)

Bars, G.; Lanore, J.M.; Villeroux, C.

1984-11-01

In the PRA in progress in France for a 900 MW PWR plant, an effort is done for introducing operator actions during accident sequences. A first approach of this complex problem relies on an extensive use of existing methods an knowledge in diverse fields. Identification of actions is based on the operating procedures, and in particular on the existence of special emergency procedures which define the optimal actions during severe accidents. This approach implies the introduction in the event trees of the notion of procedure failure. Quantification of the corresponding probabilities leads to several problems including physics of the sequences, systems availability and human behaviour for decision making and actions. This treatment is illustrated by the example of the small break event tree

A review for identification of initiating events in event tree development process on nuclear power plants

International Nuclear Information System (INIS)

Riyadi, Eko H.

2014-01-01

Initiating event is defined as any event either internal or external to the nuclear power plants (NPPs) that perturbs the steady state operation of the plant, if operating, thereby initiating an abnormal event such as transient or loss of coolant accident (LOCA) within the NPPs. These initiating events trigger sequences of events that challenge plant control and safety systems whose failure could potentially lead to core damage or large early release. Selection for initiating events consists of two steps i.e. first step, definition of possible events, such as by evaluating a comprehensive engineering, and by constructing a top level logic model. Then the second step, grouping of identified initiating event's by the safety function to be performed or combinations of systems responses. Therefore, the purpose of this paper is to discuss initiating events identification in event tree development process and to reviews other probabilistic safety assessments (PSA). The identification of initiating events also involves the past operating experience, review of other PSA, failure mode and effect analysis (FMEA), feedback from system modeling, and master logic diagram (special type of fault tree). By using the method of study for the condition of the traditional US PSA categorization in detail, could be obtained the important initiating events that are categorized into LOCA, transients and external events

Event and fault tree model for reliability analysis of the greek research reactor

International Nuclear Information System (INIS)

Albuquerque, Tob R.; Guimaraes, Antonio C.F.; Moreira, Maria de Lourdes

2013-01-01

Fault trees and event trees are widely used in industry to model and to evaluate the reliability of safety systems. Detailed analyzes in nuclear installations require the combination of these two techniques. This work uses the methods of fault tree (FT) and event tree (ET) to perform the Probabilistic Safety Assessment (PSA) in research reactors. The PSA according to IAEA (International Atomic Energy Agency) is divided into Level 1, Level 2 and level 3. At Level 1, conceptually safety systems act to prevent the accident, at Level 2, the accident occurred and seeks to minimize the consequences, known as stage management of the accident, and at Level 3 are determined consequences. This paper focuses on Level 1 studies, and searches through the acquisition of knowledge consolidation of methodologies for future reliability studies. The Greek Research Reactor, GRR - 1, was used as a case example. The LOCA (Loss of Coolant Accident) was chosen as the initiating event and from there were developed the possible accident sequences, using event tree, which could lead damage to the core. Furthermore, for each of the affected systems, the possible accidents sequences were made fault tree and evaluated the probability of each event top of the FT. The studies were conducted using a commercial computational tool SAPHIRE. The results thus obtained, performance or failure to act of the systems analyzed were considered satisfactory. This work is directed to the Greek Research Reactor due to data availability. (author)

Event and fault tree model for reliability analysis of the greek research reactor

Energy Technology Data Exchange (ETDEWEB)

Albuquerque, Tob R.; Guimaraes, Antonio C.F.; Moreira, Maria de Lourdes, E-mail: atalbuquerque@ien.gov.br, E-mail: btony@ien.gov.br, E-mail: malu@ien.gov.br [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

2013-07-01

Fault trees and event trees are widely used in industry to model and to evaluate the reliability of safety systems. Detailed analyzes in nuclear installations require the combination of these two techniques. This work uses the methods of fault tree (FT) and event tree (ET) to perform the Probabilistic Safety Assessment (PSA) in research reactors. The PSA according to IAEA (International Atomic Energy Agency) is divided into Level 1, Level 2 and level 3. At Level 1, conceptually safety systems act to prevent the accident, at Level 2, the accident occurred and seeks to minimize the consequences, known as stage management of the accident, and at Level 3 are determined consequences. This paper focuses on Level 1 studies, and searches through the acquisition of knowledge consolidation of methodologies for future reliability studies. The Greek Research Reactor, GRR - 1, was used as a case example. The LOCA (Loss of Coolant Accident) was chosen as the initiating event and from there were developed the possible accident sequences, using event tree, which could lead damage to the core. Furthermore, for each of the affected systems, the possible accidents sequences were made fault tree and evaluated the probability of each event top of the FT. The studies were conducted using a commercial computational tool SAPHIRE. The results thus obtained, performance or failure to act of the systems analyzed were considered satisfactory. This work is directed to the Greek Research Reactor due to data availability. (author)

Online scenario labeling using a hidden Markov model for assessment of nuclear plant state

International Nuclear Information System (INIS)

Zamalieva, Daniya; Yilmaz, Alper; Aldemir, Tunc

2013-01-01

By taking into account both aleatory and epistemic uncertainties within the same probabilistic framework, dynamic event trees (DETs) provide more comprehensive and systematic coverage of possible scenarios following an initiating event compared to conventional event trees. When DET generation algorithms are applied to complex realistic systems, extremely large amounts of data can be produced due to both the large number of scenarios generated following a single initiating event and the large number of data channels that represent these scenarios. In addition, the computational time required for the simulation of each scenario can be very large (e.g. about 24 h of serial run simulation time for a 4 h station blackout scenario). Since scenarios leading to system failure are more of interest, a method is proposed for online labeling of scenarios as failure or non-failure. The algorithm first trains a Hidden Markov Model, which represents the behavior of non-failure scenarios, using a training set from previous simulations. Then, the maximum likelihoods of sample failure and non-failure scenarios fitting this model are computed. These values are used to determine the timestamp at which the labeling of a certain scenario should be performed. Finally, during the succeeding timestamps, the likelihood of each scenario fitting the learned model is computed, and a dynamic thresholding based on the previously calculated likelihood values is applied. The scenarios whose likelihood is higher than the threshold are labeled as non-failure. The proposed algorithm can further delay the non-failure scenarios or discontinue them in order to redirect the computational resources toward the failure scenarios, and reduce computational time and complexity. Experiments using RELAP5/3D model of a fast reactor utilizing an Reactor Vessel Auxiliary Cooling System (RVACS) passive decay heat removal system and dynamic analysis of a station blackout (SBO) event show that the proposed method is

Generic physical protection logic trees

International Nuclear Information System (INIS)

Paulus, W.K.

1981-10-01

Generic physical protection logic trees, designed for application to nuclear facilities and materials, are presented together with a method of qualitative evaluation of the trees for design and analysis of physical protection systems. One or more defense zones are defined where adversaries interact with the physical protection system. Logic trees that are needed to describe the possible scenarios within a defense zone are selected. Elements of a postulated or existing physical protection system are tagged to the primary events of the logic tree. The likelihood of adversary success in overcoming these elements is evaluated on a binary, yes/no basis. The effect of these evaluations is propagated through the logic of each tree to determine whether the adversary is likely to accomplish the end event of the tree. The physical protection system must be highly likely to overcome the adversary before he accomplishes his objective. The evaluation must be conducted for all significant states of the site. Deficiencies uncovered become inputs to redesign and further analysis, closing the loop on the design/analysis cycle

Generic physical protection logic trees

Energy Technology Data Exchange (ETDEWEB)

Paulus, W.K.

1981-10-01

Generic physical protection logic trees, designed for application to nuclear facilities and materials, are presented together with a method of qualitative evaluation of the trees for design and analysis of physical protection systems. One or more defense zones are defined where adversaries interact with the physical protection system. Logic trees that are needed to describe the possible scenarios within a defense zone are selected. Elements of a postulated or existing physical protection system are tagged to the primary events of the logic tree. The likelihood of adversary success in overcoming these elements is evaluated on a binary, yes/no basis. The effect of these evaluations is propagated through the logic of each tree to determine whether the adversary is likely to accomplish the end event of the tree. The physical protection system must be highly likely to overcome the adversary before he accomplishes his objective. The evaluation must be conducted for all significant states of the site. Deficiencies uncovered become inputs to redesign and further analysis, closing the loop on the design/analysis cycle.

A review for identification of initiating events in event tree development process on nuclear power plants

Energy Technology Data Exchange (ETDEWEB)

Riyadi, Eko H., E-mail: e.riyadi@bapeten.go.id [Center for Regulatory Assessment of Nuclear Installation and Materials, Nuclear Energy Regulatory Agency (BAPETEN), Jl. Gajah Mada 8 Jakarta 10120 (Indonesia)

2014-09-30

Initiating event is defined as any event either internal or external to the nuclear power plants (NPPs) that perturbs the steady state operation of the plant, if operating, thereby initiating an abnormal event such as transient or loss of coolant accident (LOCA) within the NPPs. These initiating events trigger sequences of events that challenge plant control and safety systems whose failure could potentially lead to core damage or large early release. Selection for initiating events consists of two steps i.e. first step, definition of possible events, such as by evaluating a comprehensive engineering, and by constructing a top level logic model. Then the second step, grouping of identified initiating event's by the safety function to be performed or combinations of systems responses. Therefore, the purpose of this paper is to discuss initiating events identification in event tree development process and to reviews other probabilistic safety assessments (PSA). The identification of initiating events also involves the past operating experience, review of other PSA, failure mode and effect analysis (FMEA), feedback from system modeling, and master logic diagram (special type of fault tree). By using the method of study for the condition of the traditional US PSA categorization in detail, could be obtained the important initiating events that are categorized into LOCA, transients and external events.

Stochastic Unit Commitment Based on Multi-Scenario Tree Method Considering Uncertainty

Directory of Open Access Journals (Sweden)

Kyu-Hyung Jo

2018-03-01

Full Text Available With the increasing penetration of renewable energy, it is difficult to schedule unit commitment (UC in a power system because of the uncertainty associated with various factors. In this paper, a new solution procedure based on a multi-scenario tree method (MSTM is presented and applied to the proposed stochastic UC problem. In this process, the initial input data of load and wind power are modeled as different levels using the mean absolute percentage error (MAPE. The load and wind scenarios are generated using Monte Carlo simulation (MCS that considers forecasting errors. These multiple scenarios are applied in the MSTM for solving the stochastic UC problem, including not only the load and wind power uncertainties, but also sudden outages of the thermal unit. When the UC problem has been formulated, the simulation is conducted for 24-h period by using the short-term UC model, and the operating costs and additional reserve requirements are thus obtained. The effectiveness of the proposed solution approach is demonstrated through a case study based on a modified IEEE-118 bus test system.

Study on probability distribution of fire scenarios in risk assessment to emergency evacuation

International Nuclear Information System (INIS)

Chu Guanquan; Wang Jinhui

2012-01-01

Event tree analysis (ETA) is a frequently-used technique to analyze the probability of probable fire scenario. The event probability is usually characterized by definite value. It is not appropriate to use definite value as these estimates may be the result of poor quality statistics and limited knowledge. Without addressing uncertainties, ETA will give imprecise results. The credibility of risk assessment will be undermined. This paper presents an approach to address event probability uncertainties and analyze probability distribution of probable fire scenario. ETA is performed to construct probable fire scenarios. The activation time of every event is characterized as stochastic variable by considering uncertainties of fire growth rate and other input variables. To obtain probability distribution of probable fire scenario, Markov Chain is proposed to combine with ETA. To demonstrate the approach, a case study is presented.

Event tree analysis using artificial intelligence techniques

International Nuclear Information System (INIS)

Dixon, B.W.; Hinton, M.F.

1985-01-01

Artificial Intelligence (AI) techniques used in Expert Systems and Object Oriented Programming are discussed as they apply to Event Tree Analysis. A SeQUence IMPortance calculator, SQUIMP, is presented to demonstrate the implementation of these techniques. Benefits of using AI methods include ease of programming, efficiency of execution, and flexibility of application. The importance of an appropriate user interface is stressed. 5 figs

EVNTRE, Code System for Event Progression Analysis for PRA

International Nuclear Information System (INIS)

2002-01-01

1 - Description of program or function: EVNTRE is a generalized event tree processor that was developed for use in probabilistic risk analysis of severe accident progressions for nuclear power plants. The general nature of EVNTRE makes it applicable to a wide variety of analyses that involve the investigation of a progression of events which lead to a large number of sets of conditions or scenarios. EVNTRE efficiently processes large, complex event trees. It can assign probabilities to event tree branch points in several different ways, classify pathways or outcomes into user-specified groupings, and sample input distributions of probabilities and parameters. PSTEVNT, a post-processor program used to sort and reclassify the 'binned' data output from EVNTRE and generate summary tables, is included. 2 - Methods: EVNTRE processes event trees that are cast in the form of questions or events, with multiple choice answers for each question. Split fractions (probabilities or frequencies that sum to unity) are either supplied or calculated for the branches of each question in a path-dependent manner. EVNTRE traverses the tree, enumerating the leaves of the tree and calculating their probabilities or frequencies based upon the initial probability or frequency and the split fractions for the branches taken along the corresponding path to an individual leaf. The questions in the event tree are usually grouped to address specific phases of time regimes in the progression of the scenario or severe accident. Grouping or binning of each path through the event tree in terms of a small number of characteristics or attributes is allowed. Boolean expressions of the branches taken are used to select the appropriate values of the characteristics of interest for the given path. Typically, the user specifies a cutoff tolerance for the frequency of a pathway to terminate further exploration. Multiple sets of input to an event tree can be processed by using Monte Carlo sampling to generate

Discrete dynamic event tree modeling and analysis of nuclear power plant crews for safety assessment

International Nuclear Information System (INIS)

Mercurio, D.

2011-01-01

Current Probabilistic Risk Assessment (PRA) and Human Reliability Analysis (HRA) methodologies model the evolution of accident sequences in Nuclear Power Plants (NPPs) mainly based on Logic Trees. The evolution of these sequences is a result of the interactions between the crew and plant; in current PRA methodologies, simplified models of these complex interactions are used. In this study, the Accident Dynamic Simulator (ADS), a modeling framework based on the Discrete Dynamic Event Tree (DDET), has been used for the simulation of crew-plant interactions during potential accident scenarios in NPPs. In addition, an operator/crew model has been developed to treat the response of the crew to the plant. The 'crew model' is made up of three operators whose behavior is guided by a set of rules-of-behavior (which represents the knowledge and training of the operators) coupled with written and mental procedures. In addition, an approach for addressing the crew timing variability in DDETs has been developed and implemented based on a set of HRA data from a simulator study. Finally, grouping techniques were developed and applied to the analysis of the scenarios generated by the crew-plant simulation. These techniques support the post-simulation analysis by grouping similar accident sequences, identifying the key contributing events, and quantifying the conditional probability of the groups. These techniques are used to characterize the context of the crew actions in order to obtain insights for HRA. The model has been applied for the analysis of a Small Loss Of Coolant Accident (SLOCA) event for a Pressurized Water Reactor (PWR). The simulation results support an improved characterization of the performance conditions or context of operator actions, which can be used in an HRA, in the analysis of the reliability of the actions. By providing information on the evolution of system indications, dynamic of cues, crew timing in performing procedure steps, situation

Extreme Drought Events Revealed in Amazon Tree Ring Records

Science.gov (United States)

Jenkins, H. S.; Baker, P. A.; Guilderson, T. P.

2010-12-01

The Amazon basin is a center of deep atmospheric convection and thus acts as a major engine for global hydrologic circulation. Yet despite its significance, a full understanding of Amazon rainfall variability remains elusive due to a poor historical record of climate. Temperate tree rings have been used extensively to reconstruct climate over the last thousand years, however less attention has been given to the application of dendrochronology in tropical regions, in large part due to a lower frequency of tree species known to produce annual rings. Here we present a tree ring record of drought extremes from the Madre de Dios region of southeastern Peru over the last 190 years. We confirm that tree ring growth in species Cedrela odorata is annual and show it to be well correlated with wet season precipitation. This correlation is used to identify extreme dry (and wet) events that have occurred in the past. We focus on drought events identified in the record as drought frequency is expected to increase over the Amazon in a warming climate. The Cedrela chronology records historic Amazon droughts of the 20th century previously identified in the literature and extends the record of drought for this region to the year 1816. Our analysis shows that there has been an increase in the frequency of extreme drought (mean recurrence interval = 5-6 years) since the turn of the 20th century and both Atlantic and Pacific sea surface temperature (SST) forcing mechanisms are implicated.

Different intra- and interspecific facilitation mechanisms between two Mediterranean trees under a climate change scenario.

Science.gov (United States)

Gimeno, Teresa E; Escudero, Adrián; Valladares, Fernando

2015-01-01

In harsh environments facilitation alleviates biotic and abiotic constraints on tree recruitment. Under ongoing drier climate change, we expect facilitation to increase as a driver of coexistence. However, this might not hold under extreme abiotic stress and when the outcome depends on the interaction with other drivers such as altered herbivore pressure due to land use change. We performed a field water-manipulation experiment to quantify the importance of facilitation in two coexisting Mediterranean trees (dominant Juniperus thurifera and coexisting Quercus ilex subsp. ballota) under a climate change scenario. Shifts in canopy dominance favouring Q. ilex could be based on the extension of heterospecific facilitation to the detriment of conspecific alleviation. We found that saplings of both species transplanted under the canopy of nurse trees had greater survival probability, growth and photochemical efficiency. Intra- and interspecific facilitation mechanisms differed: alleviation of abiotic stress benefited both species during summer and J. thurifera during winter, whereas browsing protection was relevant only for Q. ilex. Facilitation was greater under the dry treatment only for Q. ilex, which partially agreed with the predictions of the stress gradient hypothesis. We conclude that present rainfall availability limits neither J. thurifera nor Q. ilex establishment. Nevertheless, under current global change scenarios, imposing increasing abiotic stress together with altered herbivore browsing, nurse trees could differentially facilitate the establishment of Q. ilex due to species-specific traits, i.e. palatability; drought, heat and cold tolerance, underlying species differences in the facilitation mechanisms and eventually triggering a change from pure juniper woodlands to mixed formations.

Analytic expressions for the construction of a fire event PSA model

International Nuclear Information System (INIS)

Kang, Dae Il; Kim, Kil Yoo; Kim, Dong San; Hwang, Mee Jeong; Yang, Joon Eon

2016-01-01

In this study, the changing process of an internal event PSA model to a fire event PSA model is analytically presented and discussed. Many fire PSA models have fire induced initiating event fault trees not shown in an internal event PSA model. Fire-induced initiating fault tree models are developed for addressing multiple initiating event issues. A single fire event within a fire compartment or fire scenario can cause multiple initiating events. As an example, a fire in a turbine building area can cause a loss of the main feed-water and loss of off-site power initiating events. Up to now, there has been no analytic study on the construction of a fire event PSA model using an internal event PSA model with fault trees of initiating events. In this paper, the changing process of an internal event PSA model to a fire event PSA model was analytically presented and discussed. This study results show that additional cutsets can be obtained if the fault trees of initiating events for a fire event PSA model are not exactly developed.

Analytic expressions for the construction of a fire event PSA model

Energy Technology Data Exchange (ETDEWEB)

Kang, Dae Il; Kim, Kil Yoo; Kim, Dong San; Hwang, Mee Jeong; Yang, Joon Eon [KAERI, Daejeon (Korea, Republic of)

2016-05-15

In this study, the changing process of an internal event PSA model to a fire event PSA model is analytically presented and discussed. Many fire PSA models have fire induced initiating event fault trees not shown in an internal event PSA model. Fire-induced initiating fault tree models are developed for addressing multiple initiating event issues. A single fire event within a fire compartment or fire scenario can cause multiple initiating events. As an example, a fire in a turbine building area can cause a loss of the main feed-water and loss of off-site power initiating events. Up to now, there has been no analytic study on the construction of a fire event PSA model using an internal event PSA model with fault trees of initiating events. In this paper, the changing process of an internal event PSA model to a fire event PSA model was analytically presented and discussed. This study results show that additional cutsets can be obtained if the fault trees of initiating events for a fire event PSA model are not exactly developed.

AUTOET code (a code for automatically constructing event trees and displaying subsystem interdependencies)

International Nuclear Information System (INIS)

Wilson, J.R.; Burdick, G.R.

1977-06-01

This is a user's manual for AUTOET I and II. AUTOET I is a computer code for automatic event tree construction. It is designed to incorporate and display subsystem interdependencies and common or key component dependencies in the event tree format. The code is written in FORTRAN IV for the CDC Cyber 76 using the Integrated Graphics System (IGS). AUTOET II incorporates consequence and risk calculations, in addition to some other refinements. 5 figures

Development of nuclear spent fuel Maritime transportation scenario

International Nuclear Information System (INIS)

Yoo, Min; Kang, Hyun Gook

2014-01-01

Spent fuel transportation of South Korea is to be conducted through near sea because it is able to ship a large amount of the spent fuel far from the public comparing to overland transportation. The maritime transportation is expected to be increased and its risk has to be assessed. For the risk assessment, this study utilizes the probabilistic safety assessment (PSA) method and the notions of the combined event. Risk assessment of maritime transportation of spent fuel is not well developed in comparison with overland transportation. For the assessment, first, the transportation scenario should be developed and categorized. Categories are assorted into the locations, release aspects and exposure aspects. This study deals with accident that happens on voyage and concentrated on ship-ship collision. The collision accident scenario is generated with event tree analysis. The scenario will be exploited for the maritime transportation risk model which includes consequence and accident probability

Development of nuclear spent fuel Maritime transportation scenario

Energy Technology Data Exchange (ETDEWEB)

Yoo, Min; Kang, Hyun Gook [KAIST, Daejeon (Korea, Republic of)

2014-08-15

Spent fuel transportation of South Korea is to be conducted through near sea because it is able to ship a large amount of the spent fuel far from the public comparing to overland transportation. The maritime transportation is expected to be increased and its risk has to be assessed. For the risk assessment, this study utilizes the probabilistic safety assessment (PSA) method and the notions of the combined event. Risk assessment of maritime transportation of spent fuel is not well developed in comparison with overland transportation. For the assessment, first, the transportation scenario should be developed and categorized. Categories are assorted into the locations, release aspects and exposure aspects. This study deals with accident that happens on voyage and concentrated on ship-ship collision. The collision accident scenario is generated with event tree analysis. The scenario will be exploited for the maritime transportation risk model which includes consequence and accident probability.

AUTOMATIC TREE-CROWN DETECTION IN CHALLENGING SCENARIOS

Directory of Open Access Journals (Sweden)

D. Bulatov

2016-06-01

Full Text Available In this paper, a new procedure for individual tree detection and modeling is presented. The input of this procedure consists of a normalized digital surface model NDSM, and a possibly error-prone classification result. The procedure is modular so that the functionality, the advantages and the disadvantages for every single module will be explained. The most important technical contributions of the paper are: Employing watershed transformation combined with classification results, applying hotspots detectors for identifying treetops in groups of trees, and correcting NDSM by detecting and geometric reconstruction of small anomalies, such as earth walls. Two minor contributions are made up by a detailed literature research on available methods for individual tree detection and estimation of tree-crowns for clearly identified trees in order to reduce arbitrariness by assigning trees to one of the few types in the output model.

Systems analysis programs for hands-on integrated reliability evaluations (SAPHIRE) Version 5.0. Fault tree, event tree, and piping ampersand instrumentation diagram (FEP) editors reference manual: Volume 7

International Nuclear Information System (INIS)

McKay, M.K.; Skinner, N.L.; Wood, S.T.

1994-07-01

The Systems Analysis Programs for Hands-on Integrated Reliability Evaluations (SAPHIRE) refers to a set of several microcomputer programs that were developed to create and analyze probabilistic risk assessments (PRAs), primarily for nuclear power plants. The Fault Tree, Event Tree, and Piping and Instrumentation Diagram (FEP) editors allow the user to graphically build and edit fault trees, and event trees, and piping and instrumentation diagrams (P and IDs). The software is designed to enable the independent use of the graphical-based editors found in the Integrated Reliability and Risk Assessment System (IRRAS). FEP is comprised of three separate editors (Fault Tree, Event Tree, and Piping and Instrumentation Diagram) and a utility module. This reference manual provides a screen-by-screen guide of the entire FEP System

A Method of Fire Scenarios Identification in a Consolidated Fire Risk Analysis

International Nuclear Information System (INIS)

Lim, Ho Gon; Han, Sang Hoon; Yang, Joon Eon

2010-01-01

Conventional fire PSA consider only two cases of fire scenarios, that is one for fire without propagation and the other for single propagation to neighboring compartment. Recently, a consolidated fire risk analysis using single fault tree (FT) was developed. However, the fire scenario identification in the new method is similar to conventional fire analysis method. The present study develops a new method of fire scenario identification in a consolidated fire risk analysis method. An equation for fire propagation is developed to identify fire scenario and a mapping method of fire scenarios into internal event risk model is discussed. Finally, an algorithm for automatic program is suggested

Fault trees based on past accidents. Factorial analysis of events

International Nuclear Information System (INIS)

Vaillant, M.

1977-01-01

The method of the fault tree is already useful in the qualitative step before any reliability calculation. The construction of the tree becomes even simpler when we just want to describe how the events happened. Differently from screenplays that introduce several possibilities by means of the conjunction OR, you only have here the conjunction AND, which will not be written at all. This method is presented by INRS (1) for the study of industrial injuries; it may also be applied to material damages. (orig.) [de

Effects of climate change adaptation scenarios on perceived spatio-temporal characteristics of drought events

Science.gov (United States)

Vidal, J.-P.; Martin, E.; Kitova, N.; Najac, J.; Soubeyroux, J.-M.

2012-04-01

Drought events develop in both space and time and they are therefore best described through summary joint spatio-temporal characteristics, like mean duration, mean affected area and total magnitude. This study addresses the issue of future projections of such characteristics of drought events over France through three main research questions: (1) Are downscaled climate projections able to reproduce spatio-temporal characteristics of meteorological and agricultural droughts in France over a present-day period? (2) How such characteristics will evolve over the 21st century under different emissions scenarios? (3) How would perceived drought characteristics evolve under theoretical adaptation scenarios? These questions are addressed using the Isba land surface model, downscaled climate projections from the ARPEGE General Circulation Model under three emissions scenarios, as well as results from a previously performed 50-year multilevel and multiscale drought reanalysis over France (Vidal et al., 2010). Spatio-temporal characteristics of meteorological and agricultural drought events are computed using the Standardized Precipitation Index (SPI) and the Standardized Soil Wetness Index (SSWI), respectively, and for time scales of 3 and 12 months. Results first show that the distributions of joint spatio-temporal characteristics of observed events are well reproduced by the downscaled hydroclimate projections over a present-day period. All spatio-temporal characteristics of drought events are then found to dramatically increase over the 21st century under all considered emissions scenarios, with stronger changes for agricultural droughts. Two theoretical adaptation scenarios are eventually built based on hypotheses of adaptation to evolving climate and hydrological normals. The two scenarios differ by the way the transient adaptation is performed for a given date in the future, with reference to the normals over either the previous 30-year window ("retrospective

A Two-Account Life Insurance Model for Scenario-Based Valuation Including Event Risk

Directory of Open Access Journals (Sweden)

Ninna Reitzel Jensen

2015-06-01

Full Text Available Using a two-account model with event risk, we model life insurance contracts taking into account both guaranteed and non-guaranteed payments in participating life insurance as well as in unit-linked insurance. Here, event risk is used as a generic term for life insurance events, such as death, disability, etc. In our treatment of participating life insurance, we have special focus on the bonus schemes “consolidation” and “additional benefits”, and one goal is to formalize how these work and interact. Another goal is to describe similarities and differences between participating life insurance and unit-linked insurance. By use of a two-account model, we are able to illustrate general concepts without making the model too abstract. To allow for complicated financial markets without dramatically increasing the mathematical complexity, we focus on economic scenarios. We illustrate the use of our model by conducting scenario analysis based on Monte Carlo simulation, but the model applies to scenarios in general and to worst-case and best-estimate scenarios in particular. In addition to easy computations, our model offers a common framework for the valuation of life insurance payments across product types. This enables comparison of participating life insurance products and unit-linked insurance products, thus building a bridge between the two different ways of formalizing life insurance products. Finally, our model distinguishes itself from the existing literature by taking into account the Markov model for the state of the policyholder and, hereby, facilitating event risk.

Scenario development methodologies

International Nuclear Information System (INIS)

Eng, T.; Hudson, J.; Stephansson, O.

1994-11-01

In the period 1981-1994, SKB has studied several methodologies to systematize and visualize all the features, events and processes (FEPs) that can influence a repository for radioactive waste in the future. All the work performed is based on the terminology and basic findings in the joint SKI/SKB work on scenario development presented in the SKB Technical Report 89-35. The methodologies studied are a) Event tree analysis, b) Influence diagrams and c) Rock Engineering Systems (RES) matrices. Each one of the methodologies is explained in this report as well as examples of applications. One chapter is devoted to a comparison between the two most promising methodologies, namely: Influence diagrams and the RES methodology. In conclusion a combination of parts of the Influence diagram and the RES methodology is likely to be a promising approach. 26 refs

Simplified containment event tree analysis for the Sequoyah Ice Condenser containment

International Nuclear Information System (INIS)

Galyean, W.J.; Schroeder, J.A.; Pafford, D.J.

1990-12-01

An evaluation of a Pressurized Water Reactor (PER) ice condenser containment was performed. In this evaluation, simplified containment event trees (SCETs) were developed that utilized the vast storehouse of information generated by the NRC's Draft NUREG-1150 effort. Specifically, the computer programs and data files produced by the NUREG-1150 analysis of Sequoyah were used to electronically generate SCETs, as opposed to the NUREG-1150 accident progression event trees (APETs). This simplification was performed to allow graphic depiction of the SCETs in typical event tree format, which facilitates their understanding and use. SCETs were developed for five of the seven plant damage state groups (PDSGs) identified by the NUREG-1150 analyses, which includes: both short- and long-term station blackout sequences (SBOs), transients, loss-of-coolant accidents (LOCAs), and anticipated transient without scram (ATWS). Steam generator tube rupture (SGTR) and event-V PDSGs were not analyzed because of their containment bypass nature. After being benchmarked with the APETs, in terms of containment failure mode and risk, the SCETs were used to evaluate a number of potential containment modifications. The modifications were examined for their potential to mitigate or prevent containment failure from hydrogen burns or direct impingement on the containment by the core, (both factors identified as significant contributors to risk in the NUREG-1150 Sequoyah analysis). However, because of the relatively low baseline risk postulated for Sequoyah (i.e., 12 person-rems per reactor year), none of the potential modifications appear to be cost effective. 15 refs., 10 figs. , 17 tabs

Probabilistic risk assessment using event tables and the BNL [Brookhaven National Laboratory] event-tree analyzer

International Nuclear Information System (INIS)

Fullwood, R.R.; Shier, W.G.

1989-01-01

Probabilistic risk analysis (PRA) is being used to study design alternatives for the advanced neutron source research reactor being designed at Oak Ridge National Laboratory for operation in the 1990s. Major communication paths between the designers and the safety analysts are accident discussions supported by event tables, event-tree graphics, and accident sequence probabilities. The BETA code used in conjunction with a word processor provides this linkage. This paper describes the process, features of the BETA, how it works, and some examples of usage

Identification of independent modules in fault trees which contain dependent basic events

International Nuclear Information System (INIS)

Sun, H.; Andrews, J.D.

2004-01-01

The reliability performance of a system is frequently a function of component failures of which some are independent whilst others are interdependent. It is possible to represent the system failure logic in a fault tree diagram, however only the sections containing independent events can be assessed using the conventional fault tree analysis methodology. The analysis of the dependent sections will require a Markov analysis. Since the efficiency of the Markov analysis largely depends on the size of the established Markov model, the key is to extract from the fault tree the smallest sections which contain dependencies. This paper proposes a method aimed at establishing the smallest Markov model for the dependencies contained within the fault tree

Waste Isolation Safety Assessment Program scenario analysis methods for use in assessing the safety of the geologic isolation of nuclear waste

International Nuclear Information System (INIS)

Greenborg, J.; Winegardner, W.K.; Pelto, P.J.; Voss, J.W.; Stottlemyre, J.A.; Forbes, I.A.; Fussell, J.B.; Burkholder, H.C.

1978-11-01

The relative utility of the various safety analysis methods to scenario analysis for a repository system was evaluated by judging the degree to which certain criteria are satisfied by use of the method. Six safety analysis methods were reviewed in this report for possible use in scenario analysis of nuclear waste repositories: expert opinion, perspectives analysis, fault trees/event trees, Monte Carlo simulation, Markov chains, and classical systems analysis. Four criteria have been selected. The criteria suggest that the methods: (1) be quantitative and scientifically based; (2) model the potential disruptive events and processes, (3) model the system before and after failure (sufficiently detailed to provide for subsequent consequence analysis); and (4) be compatible with the level of available system knowledge and data. Expert opinion, fault trees/event trees, Monte Carlo simulation and classical systems analysis were judged to have the greatest potential appliation to the problem of scenario analysis. The methods were found to be constrained by limited data and by knowledge of the processes governing the system. It was determined that no single method is clearly superior to others when measured against all the criteria. Therefore, to get the best understanding of system behavior, a combination of the methods is recommended. Monte Carlo simulation was judged to be the most suitable matrix in which to incorporate a combination of methods

Modeling time-to-event (survival) data using classification tree analysis.

Science.gov (United States)

Linden, Ariel; Yarnold, Paul R

2017-12-01

Time to the occurrence of an event is often studied in health research. Survival analysis differs from other designs in that follow-up times for individuals who do not experience the event by the end of the study (called censored) are accounted for in the analysis. Cox regression is the standard method for analysing censored data, but the assumptions required of these models are easily violated. In this paper, we introduce classification tree analysis (CTA) as a flexible alternative for modelling censored data. Classification tree analysis is a "decision-tree"-like classification model that provides parsimonious, transparent (ie, easy to visually display and interpret) decision rules that maximize predictive accuracy, derives exact P values via permutation tests, and evaluates model cross-generalizability. Using empirical data, we identify all statistically valid, reproducible, longitudinally consistent, and cross-generalizable CTA survival models and then compare their predictive accuracy to estimates derived via Cox regression and an unadjusted naïve model. Model performance is assessed using integrated Brier scores and a comparison between estimated survival curves. The Cox regression model best predicts average incidence of the outcome over time, whereas CTA survival models best predict either relatively high, or low, incidence of the outcome over time. Classification tree analysis survival models offer many advantages over Cox regression, such as explicit maximization of predictive accuracy, parsimony, statistical robustness, and transparency. Therefore, researchers interested in accurate prognoses and clear decision rules should consider developing models using the CTA-survival framework. © 2017 John Wiley & Sons, Ltd.

Widespread Amazon forest tree mortality from a single cross-basin squall line event

Science.gov (United States)

Negrón-Juárez, Robinson I.; Chambers, Jeffrey Q.; Guimaraes, Giuliano; Zeng, Hongcheng; Raupp, Carlos F. M.; Marra, Daniel M.; Ribeiro, Gabriel H. P. M.; Saatchi, Sassan S.; Nelson, Bruce W.; Higuchi, Niro

2010-08-01

Climate change is expected to increase the intensity of extreme precipitation events in Amazonia that in turn might produce more forest blowdowns associated with convective storms. Yet quantitative tree mortality associated with convective storms has never been reported across Amazonia, representing an important additional source of carbon to the atmosphere. Here we demonstrate that a single squall line (aligned cluster of convective storm cells) propagating across Amazonia in January, 2005, caused widespread forest tree mortality and may have contributed to the elevated mortality observed that year. Forest plot data demonstrated that the same year represented the second highest mortality rate over a 15-year annual monitoring interval. Over the Manaus region, disturbed forest patches generated by the squall followed a power-law distribution (scaling exponent α = 1.48) and produced a mortality of 0.3-0.5 million trees, equivalent to 30% of the observed annual deforestation reported in 2005 over the same area. Basin-wide, potential tree mortality from this one event was estimated at 542 ± 121 million trees, equivalent to 23% of the mean annual biomass accumulation estimated for these forests. Our results highlight the vulnerability of Amazon trees to wind-driven mortality associated with convective storms. Storm intensity is expected to increase with a warming climate, which would result in additional tree mortality and carbon release to the atmosphere, with the potential to further warm the climate system.

Risk assessment of mitigated domino scenarios in process facilities

International Nuclear Information System (INIS)

Landucci, Gabriele; Necci, Amos; Antonioni, Giacomo; Argenti, Francesca; Cozzani, Valerio

2017-01-01

The propagation of accidents among process units may lead to severe cascading events or domino effects with catastrophic consequences. Prevention, mitigation and management of domino scenarios is of utmost importance and may be achieved in industrial facilities through the adoption of multiple safety layers. The present study was aimed at developing an innovative methodology to address the quantitative risk assessment (QRA) of domino scenarios accounting for the presence and role of safety barriers. Based on the expected performance of safety barriers, a dedicated event tree analysis allowed the identification and the assessment of the frequencies of the different end-point events deriving from unmitigated and partially mitigated domino chains. Specific criteria were introduced in consequence analysis to consider the mitigation effects of end-point scenarios deriving from safety barriers. Individual and societal risk indexes were calculated accounting for safety barriers and the mitigated scenarios that may result from their actions. The application of the methodology to case-studies of industrial interest proved the importance of introducing a specific systematic and quantitative analysis of safety barrier performance when addressing escalation leading to domino effect. - Highlights: • A methodology was developed to account for safety barrier performance in escalation prevention. • The methodology allows quantitative assessment accounting for safety barrier performance. • A detailed analysis of transient mitigated scenarios is allowed by the developed procedure. • The procedure allows accounting for safety barrier performance in QRA of domino scenarios. • An important reduction in the risk due to domino scenarios is evidenced when considering safety barriers.

Event-based scenario manager for multibody dynamics simulation of heavy load lifting operations in shipyards

Directory of Open Access Journals (Sweden)

Sol Ha

2016-01-01

Full Text Available This paper suggests an event-based scenario manager capable of creating and editing a scenario for shipbuilding process simulation based on multibody dynamics. To configure various situation in shipyards and easily connect with multibody dynamics, the proposed method has two main concepts: an Actor and an Action List. The Actor represents the anatomic unit of action in the multibody dynamics and can be connected to a specific component of the dynamics kernel such as the body and joint. The user can make a scenario up by combining the actors. The Action List contains information for arranging and executing the actors. Since the shipbuilding process is a kind of event-based sequence, all simulation models were configured using Discrete EVent System Specification (DEVS formalism. The proposed method was applied to simulations of various operations in shipyards such as lifting and erection of a block and heavy load lifting operation using multiple cranes.

Intensity earthquake scenario (scenario event - a damaging earthquake with higher probability of occurrence) for the city of Sofia

Science.gov (United States)

Aleksandrova, Irena; Simeonova, Stela; Solakov, Dimcho; Popova, Maria

2014-05-01

Among the many kinds of natural and man-made disasters, earthquakes dominate with regard to their social and economical impact on the urban environment. Global seismic risk to earthquakes are increasing steadily as urbanization and development occupy more areas that a prone to effects of strong earthquakes. Additionally, the uncontrolled growth of mega cities in highly seismic areas around the world is often associated with the construction of seismically unsafe buildings and infrastructures, and undertaken with an insufficient knowledge of the regional seismicity peculiarities and seismic hazard. The assessment of seismic hazard and generation of earthquake scenarios is the first link in the prevention chain and the first step in the evaluation of the seismic risk. The earthquake scenarios are intended as a basic input for developing detailed earthquake damage scenarios for the cities and can be used in earthquake-safe town and infrastructure planning. The city of Sofia is the capital of Bulgaria. It is situated in the centre of the Sofia area that is the most populated (the population is of more than 1.2 mil. inhabitants), industrial and cultural region of Bulgaria that faces considerable earthquake risk. The available historical documents prove the occurrence of destructive earthquakes during the 15th-18th centuries in the Sofia zone. In 19th century the city of Sofia has experienced two strong earthquakes: the 1818 earthquake with epicentral intensity I0=8-9 MSK and the 1858 earthquake with I0=9-10 MSK. During the 20th century the strongest event occurred in the vicinity of the city of Sofia is the 1917 earthquake with MS=5.3 (I0=7-8 MSK). Almost a century later (95 years) an earthquake of moment magnitude 5.6 (I0=7-8 MSK) hit the city of Sofia, on May 22nd, 2012. In the present study as a deterministic scenario event is considered a damaging earthquake with higher probability of occurrence that could affect the city with intensity less than or equal to VIII

Protective Alternatives of SMR against Extreme Threat Scenario – A Preliminary Risk Analysis

International Nuclear Information System (INIS)

Shohet, I.M.; Ornai, D.; Gal, E.; Ronen, Y.; Vidra, M.

2014-01-01

The article presents a preliminary risk analysis of the main features in NPP (Nuclear Power Plant) that includes SMR - Small and Modular Reactors, given an extreme threat scenario. A review of the structure and systems of the SMR is followed by systematic definitions and analysis of the threat scenario to which a preliminary risk analysis was carried out. The article outlines the basic events caused by the referred threat scenario, which had led to possible failure mechanisms according to FTA (Fault-Tree-Analysis),critical protective circuits, and todetecting critical topics for the protection and safety of the reactor

Making systems with mutually exclusive events analysable by standard fault tree analysis tools

International Nuclear Information System (INIS)

Vaurio, J.K.

2001-01-01

Methods are developed for analysing systems that comprise mutually exclusive events by fault tree techniques that accept only statistically independent basic events. Techniques based on equivalent models and numerical transformations are presented for phased missions and for systems with component-caused system-level common cause failures. Numerical examples illustrate the methods

The fuzzy set theory application to the analysis of accident progression event trees with phenomenological uncertainty issues

International Nuclear Information System (INIS)

Chun, Moon-Hyun; Ahn, Kwang-Il

1991-01-01

Fuzzy set theory provides a formal framework for dealing with the imprecision and vagueness inherent in the expert judgement, and therefore it can be used for more effective analysis of accident progression of PRA where experts opinion is a major means for quantifying some event probabilities and uncertainties. In this paper, an example application of the fuzzy set theory is first made to a simple portion of a given accident progression event tree with typical qualitative fuzzy input data, and thereby computational algorithms suitable for application of the fuzzy set theory to the accident progression event tree analysis are identified and illustrated with example applications. Then the procedure used in the simple example is extended to extremely complex accident progression event trees with a number of phenomenological uncertainty issues, i.e., a typical plant damage state 'SEC' of the Zion Nuclear Power Plant risk assessment. The results show that the fuzzy averages of the fuzzy outcomes are very close to the mean values obtained by current methods. The main purpose of this paper is to provide a formal procedure for application of the fuzzy set theory to accident progression event trees with imprecise and qualitative branch probabilities and/or with a number of phenomenological uncertainty issues. (author)

Identification of reference accident scenarios in SEVESO establishments

International Nuclear Information System (INIS)

Delvosalle, C.; Fievez, C.; Pipart, A.; Fabrega, J. Casal; Planas, E.; Christou, M.; Mushtaq, F.

2005-01-01

In the frame of the ESREL special session on ARAMIS project, this paper aims at presenting the work carried out in the first Work Package, devoted to the definition of accident scenarios. This topic is a key-point in risk assessment, and serves as basis for the whole risk quantification. A first part of the work aims at building a Methodology for the Identification of Major Accident Hazards (MIMAH), which is carried out with the development of generic fault and event trees based on a typology of equipment and substances. This work is coupled with an historical analysis of accidents. In a second part, influence of safety devices and policies will be considered, in order to build a Methodology for the Identification of Reference Accident Scenarios (MIRAS). This last one will take into account safety systems and lead to obtain more realistic scenarios

Application of accident progression event tree technology to the Savannah River Site Defense Waste Processing Facility SAR analysis

International Nuclear Information System (INIS)

Brandyberry, M.D.; Baker, W.H.; Wittman, R.S.; Amos, C.N.

1993-01-01

The Accident Analysis in the Safety Analysis Report (SAR) for the Savannah River Site (SRS) Defense Waste Processing Facility (DWPF) has recently undergone an upgrade. Non-reactor SARs at SRS (and other Department of Energy (DOE) sites) use probabilistic techniques to assess the frequency of accidents at their facilities. This paper describes the application of an extension of the Accident Progression Event Tree (APET) approach to accidents at the SRS DWPF. The APET technique allows an integrated model of the facility risk to be developed, where previous probabilistic accident analyses have been limited to the quantification of the frequency and consequences of individual accident scenarios treated independently. Use of an APET allows a more structured approach, incorporating both the treatment of initiators that are common to more than one accident, and of accident progression at the facility

Study of 'inadvertent human intrusion or rare natural event scenarios' for sub-surface disposal of radioactive waste

International Nuclear Information System (INIS)

Nakatani, Takayoshi; Ishitoya, Kimihide; Funabashi, Hideyuki; Sugaya, Toshikatsu; Sone, Tomoyuki; Shimada, Hidemitsu; Nakai, Kunihiro

2010-03-01

Japan Atomic Energy Agency (JAEA) is making preparations for the sub-surface disposal of radioactive wastes, in an integrated fashion according to the properties of the waste material regardless of the generators or waste sources. In this study, 'Inadvertent Human Intrusion or Rare Natural Event Scenarios' of 'Three Types scenarios' was considered according to the standard of the Atomic Energy Society of Japan (AESJ) on the sub-surface disposal system that was based on 'Basic Policy for Safety Regulation Concerning Land Disposal of Low-Level Radioactive Waste (Interim Report)' by Nuclear Safety Commission of Japan (NSC). Selection of the assessed scenarios, development of the assessment tool and preliminary exposure dose assessment for general public were conducted. Among the assessed scenarios, the exposure dose of 'well water drinking scenario' was the highest under the very conservative assessment condition. This scenario assumed that the groundwater in Excavation Disturbed Zone (EDZ) was directly used as drinking water without any dilution. Although this was very conservative condition and the result exceeded 10 mSv/y, it stayed under the upper limit of standard dose value for 'Inadvertent Human Intrusion or Rare Natural Event Scenarios' (10 - 100 mSv/y). (author)

Post-event human decision errors: operator action tree/time reliability correlation

International Nuclear Information System (INIS)

Hall, R.E.; Fragola, J.; Wreathall, J.

1982-11-01

This report documents an interim framework for the quantification of the probability of errors of decision on the part of nuclear power plant operators after the initiation of an accident. The framework can easily be incorporated into an event tree/fault tree analysis. The method presented consists of a structure called the operator action tree and a time reliability correlation which assumes the time available for making a decision to be the dominating factor in situations requiring cognitive human response. This limited approach decreases the magnitude and complexity of the decision modeling task. Specifically, in the past, some human performance models have attempted prediction by trying to emulate sequences of human actions, or by identifying and modeling the information processing approach applicable to the task. The model developed here is directed at describing the statistical performance of a representative group of hypothetical individuals responding to generalized situations

Post-event human decision errors: operator action tree/time reliability correlation

Energy Technology Data Exchange (ETDEWEB)

Hall, R E; Fragola, J; Wreathall, J

1982-11-01

This report documents an interim framework for the quantification of the probability of errors of decision on the part of nuclear power plant operators after the initiation of an accident. The framework can easily be incorporated into an event tree/fault tree analysis. The method presented consists of a structure called the operator action tree and a time reliability correlation which assumes the time available for making a decision to be the dominating factor in situations requiring cognitive human response. This limited approach decreases the magnitude and complexity of the decision modeling task. Specifically, in the past, some human performance models have attempted prediction by trying to emulate sequences of human actions, or by identifying and modeling the information processing approach applicable to the task. The model developed here is directed at describing the statistical performance of a representative group of hypothetical individuals responding to generalized situations.

Using Binary Trees to Synchronize Events in Heterogeneous Datastreams

Directory of Open Access Journals (Sweden)

Stefan-Szalai Dragos

2012-06-01

Full Text Available In the context of growing ubiquity of sensors, surveillance equipment and other mobile devices, a shift in the data processing paradigm was necessary. New systems are required to be capable of processing data streams of infinite length, having a high throughput, that cannot be stored and processed using classical Database Management Systems (DBMSs. These are called Data Stream Management Systems (DSMSs within the scientific community. A first step performed by them is time synchronization between events arriving on different timestamped data streams. Within this paper an event synchronization method that makes use of binary trees to achieve its task is introduced and compared with other approaches in order to emphasize its strengths. Furthermore the integration with DSCPE (our Data Stream Continuous Processing Engine is proposed.

Vulnerability Analysis of Urban Drainage Systems: Tree vs. Loop Networks

Directory of Open Access Journals (Sweden)

Chi Zhang

2017-03-01

Full Text Available Vulnerability analysis of urban drainage networks plays an important role in urban flood management. This study analyzes and compares the vulnerability of tree and loop systems under various rainfall events to structural failure represented by pipe blockage. Different pipe blockage scenarios, in which one of the pipes in an urban drainage network is assumed to be blocked individually, are constructed and their impacts on the network are simulated under different storm events. Furthermore, a vulnerability index is defined to measure the vulnerability of the drainage systems before and after the implementation of adaptation measures. The results obtained indicate that the tree systems have a relatively larger proportion of critical hydraulic pipes than the loop systems, thus the vulnerability of tree systems is substantially greater than that of the loop systems. Furthermore, the vulnerability index of tree systems is reduced after they are converted into a loop system with the implementation of adaptation measures. This paper provides an insight into the differences in the vulnerability of tree and loop systems, and provides more evidence for development of adaptation measures (e.g., tanks to reduce urban flooding.

Development of the public exercise system for an emergency using response action applied with the event tree approach

Energy Technology Data Exchange (ETDEWEB)

Lee, De Whey; Lee, Byung Il; Park, Youn Won [BEES Inc., Rm No. L507, KAIST Munji Campus, Daejeon (Korea, Republic of)

2016-12-15

According to APPRE (Act on Physical Protection and Radiological Emergency), Korea Nuclear Safety and Security Committee (NSSC) jointly with other central government ministries shall conduct a unified radiological exercise once every year while a local government conduct an integrated exercise once every two-year period. What we experience up to date there are several limitations in the emergency exercises such as low public acceptance, poor enthusiasm in the exercise participation, not very attracting exercise scenarios, low efficiency in conducting an exercise, and so on. In order to overcome the limitations of the current exercise system, we have endeavored to develop an emergency exercise system using the VR (virtual reality) method based on a radioactive material release accident from the nuclear power plant. In this paper, we aim to introduce some basic development methods and emergency response action event tree for the public based on the exercise scenario as a beginning stage. We introduce a VR based emergency exercise system, which is expected to overcome some difficulties in the current exercise system. After developing this system properly and by testing it, we shall expect to deduce the weak points identified in the current emergency arrangements and emergency response strategy we now have.

Event-based knowledge elicitation of operating room management decision-making using scenarios adapted from information systems data.

Science.gov (United States)

Dexter, Franklin; Wachtel, Ruth E; Epstein, Richard H

2011-01-07

No systematic process has previously been described for a needs assessment that identifies the operating room (OR) management decisions made by the anesthesiologists and nurse managers at a facility that do not maximize the efficiency of use of OR time. We evaluated whether event-based knowledge elicitation can be used practically for rapid assessment of OR management decision-making at facilities, whether scenarios can be adapted automatically from information systems data, and the usefulness of the approach. A process of event-based knowledge elicitation was developed to assess OR management decision-making that may reduce the efficiency of use of OR time. Hypothetical scenarios addressing every OR management decision influencing OR efficiency were created from published examples. Scenarios are adapted, so that cues about conditions are accurate and appropriate for each facility (e.g., if OR 1 is used as an example in a scenario, the listed procedure is a type of procedure performed at the facility in OR 1). Adaptation is performed automatically using the facility's OR information system or anesthesia information management system (AIMS) data for most scenarios (43 of 45). Performing the needs assessment takes approximately 1 hour of local managers' time while they decide if their decisions are consistent with the described scenarios. A table of contents of the indexed scenarios is created automatically, providing a simple version of problem solving using case-based reasoning. For example, a new OR manager wanting to know the best way to decide whether to move a case can look in the chapter on "Moving Cases on the Day of Surgery" to find a scenario that describes the situation being encountered. Scenarios have been adapted and used at 22 hospitals. Few changes in decisions were needed to increase the efficiency of use of OR time. The few changes were heterogeneous among hospitals, showing the usefulness of individualized assessments. Our technical advance is the

Event-based knowledge elicitation of operating room management decision-making using scenarios adapted from information systems data

Directory of Open Access Journals (Sweden)

Epstein Richard H

2011-01-01

Full Text Available Abstract Background No systematic process has previously been described for a needs assessment that identifies the operating room (OR management decisions made by the anesthesiologists and nurse managers at a facility that do not maximize the efficiency of use of OR time. We evaluated whether event-based knowledge elicitation can be used practically for rapid assessment of OR management decision-making at facilities, whether scenarios can be adapted automatically from information systems data, and the usefulness of the approach. Methods A process of event-based knowledge elicitation was developed to assess OR management decision-making that may reduce the efficiency of use of OR time. Hypothetical scenarios addressing every OR management decision influencing OR efficiency were created from published examples. Scenarios are adapted, so that cues about conditions are accurate and appropriate for each facility (e.g., if OR 1 is used as an example in a scenario, the listed procedure is a type of procedure performed at the facility in OR 1. Adaptation is performed automatically using the facility's OR information system or anesthesia information management system (AIMS data for most scenarios (43 of 45. Performing the needs assessment takes approximately 1 hour of local managers' time while they decide if their decisions are consistent with the described scenarios. A table of contents of the indexed scenarios is created automatically, providing a simple version of problem solving using case-based reasoning. For example, a new OR manager wanting to know the best way to decide whether to move a case can look in the chapter on "Moving Cases on the Day of Surgery" to find a scenario that describes the situation being encountered. Results Scenarios have been adapted and used at 22 hospitals. Few changes in decisions were needed to increase the efficiency of use of OR time. The few changes were heterogeneous among hospitals, showing the usefulness of

Biogeochemical hotspots following a simulated tree mortality event of southern pine beetle

Science.gov (United States)

Siegert, C. M.; Renninger, H. J.; Karunarathna, S.; Hornslein, N.; Riggins, J. J.; Clay, N. A.; Tang, J. D.; Chaney, B.; Drotar, N.

2017-12-01

Disturbances in forest ecosystems can alter functions like productivity, respiration, and nutrient cycling through the creation of biogeochemical hotspots. These events occur sporadically across the landscape, leading to uncertainty in terrestrial biosphere carbon models, which have yet to capture the full complexity of biotic and abiotic factors driving ecological processes in the terrestrial environment. Given the widespread impact of southern pine beetle on forest ecosystems throughout the southeastern United States, it is critical to management and planning activities to understand the role of these disturbances. As such, we hypothesize that bark beetle killed trees create biogeochemical hotspots in the soils surrounding their trunk as they undergo mortality due to (1) increased soil moisture from reductions in plant water uptake and increased stemflow production, (2) enhanced canopy-derived inputs of carbon and nitrogen, and (3) increased microbial activity and root mortality. In 2015, a field experiment to mimic a southern pine beetle attack was established by girdling loblolly pine trees. Subsequent measurements of throughfall and stemflow for water quantity and quality, transpiration, stem respiration, soil respiration, and soil chemistry were used to quantify the extent of spatial and temporal impacts of tree mortality on carbon budgets. Compared to control trees, girdled trees exhibited reduced water uptake within the first 6 months of the study and succumbed to mortality within 18 months. Over two years, the girdled trees generated 33% more stemflow than control trees (7836 vs. 5882 L m-2). Preliminary analysis of carbon and nitrogen concentrations and dissolved organic matter quality are still pending. In the surrounding soils, C:N ratios were greater under control trees (12.8) than under girdled trees (12.1), which was driven by an increase in carbon around control trees (+0.13 mg C mg-1 soil) and not a decrease around girdled trees (-0.01 mg C mg-1

Sequence Tree Modeling for Combined Accident and Feed-and-Bleed Operation

International Nuclear Information System (INIS)

Kim, Bo Gyung; Kang Hyun Gook; Yoon, Ho Joon

2016-01-01

In order to address this issue, this study suggests the sequence tree model to analyze accident sequence systematically. Using the sequence tree model, all possible scenarios which need a specific safety action to prevent the core damage can be identified and success conditions of safety action under complicated situation such as combined accident will be also identified. Sequence tree is branch model to divide plant condition considering the plant dynamics. Since sequence tree model can reflect the plant dynamics, arising from interaction of different accident timing and plant condition and from the interaction between the operator action, mitigation system, and the indicators for operation, sequence tree model can be used to develop the dynamic event tree model easily. Target safety action for this study is a feed-and-bleed (F and B) operation. A F and B operation directly cools down the reactor cooling system (RCS) using the primary cooling system when residual heat removal by the secondary cooling system is not available. In this study, a TLOFW accident and a TLOFW accident with LOCA were the target accidents. Based on the conventional PSA model and indicators, the sequence tree model for a TLOFW accident was developed. If sampling analysis is performed, practical accident sequences can be identified based on the sequence analysis. If a realistic distribution for the variables can be obtained for sampling analysis, much more realistic accident sequences can be described. Moreover, if the initiating event frequency under a combined accident can be quantified, the sequence tree model can translate into a dynamic event tree model based on the sampling analysis results

Sequence Tree Modeling for Combined Accident and Feed-and-Bleed Operation

Energy Technology Data Exchange (ETDEWEB)

Kim, Bo Gyung; Kang Hyun Gook [KAIST, Daejeon (Korea, Republic of); Yoon, Ho Joon [Khalifa University of Science, Abu Dhabi (United Arab Emirates)

2016-05-15

In order to address this issue, this study suggests the sequence tree model to analyze accident sequence systematically. Using the sequence tree model, all possible scenarios which need a specific safety action to prevent the core damage can be identified and success conditions of safety action under complicated situation such as combined accident will be also identified. Sequence tree is branch model to divide plant condition considering the plant dynamics. Since sequence tree model can reflect the plant dynamics, arising from interaction of different accident timing and plant condition and from the interaction between the operator action, mitigation system, and the indicators for operation, sequence tree model can be used to develop the dynamic event tree model easily. Target safety action for this study is a feed-and-bleed (F and B) operation. A F and B operation directly cools down the reactor cooling system (RCS) using the primary cooling system when residual heat removal by the secondary cooling system is not available. In this study, a TLOFW accident and a TLOFW accident with LOCA were the target accidents. Based on the conventional PSA model and indicators, the sequence tree model for a TLOFW accident was developed. If sampling analysis is performed, practical accident sequences can be identified based on the sequence analysis. If a realistic distribution for the variables can be obtained for sampling analysis, much more realistic accident sequences can be described. Moreover, if the initiating event frequency under a combined accident can be quantified, the sequence tree model can translate into a dynamic event tree model based on the sampling analysis results.

Probabilistic construction of inflow scenarios at a reservoir; Construction probabiliste de scenarios d'apports a un reservoir

Energy Technology Data Exchange (ETDEWEB)

Seidou, O.; Robert, B.; Marche, C.; Rousselle, J. [Ecole Polytechnique de Montreal, Departement des Genies Civil, Geologique et des Mines, Montreal, PQ (Canada); Lefebvre, M. [Ecole Polytechnique de Montreal, Departement de Mathematiques et de Genie Industriel, Montreal, PQ (Canada)

2004-02-01

Development of risk indicators to aid in decisions affecting the operation of hydric systems is described. The significant part of the risk affecting hydric systems is the uncertainty surrounding future inflows. A method to construct inflow scenarios starting from an arbitrary date 'y' of the year is developed using a Markovian process which also has been used to model short-term uncertainty in stream flow. The text is divided in five parts: (1) methodology, (2) terminology, (3) theory, (4) application, and (5) results. The scenarios are built to reproduce the statistical behaviour of the river or reservoir and have the shape of an event tree whose structure is defined by the user before application of the method. Application of the method is illustrated by two examples, one involving the Harricana River, the other the Cabonga Reservoir, both situated in the province of Quebec. 11 refs., 4 tabs., 4 figs.

A fuzzy-based reliability approach to evaluate basic events of fault tree analysis for nuclear power plant probabilistic safety assessment

International Nuclear Information System (INIS)

Purba, Julwan Hendry

2014-01-01

Highlights: • We propose a fuzzy-based reliability approach to evaluate basic event reliabilities. • It implements the concepts of failure possibilities and fuzzy sets. • Experts evaluate basic event failure possibilities using qualitative words. • Triangular fuzzy numbers mathematically represent qualitative failure possibilities. • It is a very good alternative for conventional reliability approach. - Abstract: Fault tree analysis has been widely utilized as a tool for nuclear power plant probabilistic safety assessment. This analysis can be completed only if all basic events of the system fault tree have their quantitative failure rates or failure probabilities. However, it is difficult to obtain those failure data due to insufficient data, environment changing or new components. This study proposes a fuzzy-based reliability approach to evaluate basic events of system fault trees whose failure precise probability distributions of their lifetime to failures are not available. It applies the concept of failure possibilities to qualitatively evaluate basic events and the concept of fuzzy sets to quantitatively represent the corresponding failure possibilities. To demonstrate the feasibility and the effectiveness of the proposed approach, the actual basic event failure probabilities collected from the operational experiences of the David–Besse design of the Babcock and Wilcox reactor protection system fault tree are used to benchmark the failure probabilities generated by the proposed approach. The results confirm that the proposed fuzzy-based reliability approach arises as a suitable alternative for the conventional probabilistic reliability approach when basic events do not have the corresponding quantitative historical failure data for determining their reliability characteristics. Hence, it overcomes the limitation of the conventional fault tree analysis for nuclear power plant probabilistic safety assessment

Probability intervals for the top event unavailability of fault trees

International Nuclear Information System (INIS)

Lee, Y.T.; Apostolakis, G.E.

1976-06-01

The evaluation of probabilities of rare events is of major importance in the quantitative assessment of the risk from large technological systems. In particular, for nuclear power plants the complexity of the systems, their high reliability and the lack of significant statistical records have led to the extensive use of logic diagrams in the estimation of low probabilities. The estimation of probability intervals for the probability of existence of the top event of a fault tree is examined. Given the uncertainties of the primary input data, a method is described for the evaluation of the first four moments of the top event occurrence probability. These moments are then used to estimate confidence bounds by several approaches which are based on standard inequalities (e.g., Tchebycheff, Cantelli, etc.) or on empirical distributions (the Johnson family). Several examples indicate that the Johnson family of distributions yields results which are in good agreement with those produced by Monte Carlo simulation

Algorithms for computing parsimonious evolutionary scenarios for genome evolution, the last universal common ancestor and dominance of horizontal gene transfer in the evolution of prokaryotes

Directory of Open Access Journals (Sweden)

Galperin Michael Y

2003-01-01

Full Text Available Abstract Background Comparative analysis of sequenced genomes reveals numerous instances of apparent horizontal gene transfer (HGT, at least in prokaryotes, and indicates that lineage-specific gene loss might have been even more common in evolution. This complicates the notion of a species tree, which needs to be re-interpreted as a prevailing evolutionary trend, rather than the full depiction of evolution, and makes reconstruction of ancestral genomes a non-trivial task. Results We addressed the problem of constructing parsimonious scenarios for individual sets of orthologous genes given a species tree. The orthologous sets were taken from the database of Clusters of Orthologous Groups of proteins (COGs. We show that the phyletic patterns (patterns of presence-absence in completely sequenced genomes of almost 90% of the COGs are inconsistent with the hypothetical species tree. Algorithms were developed to reconcile the phyletic patterns with the species tree by postulating gene loss, COG emergence and HGT (the latter two classes of events were collectively treated as gene gains. We prove that each of these algorithms produces a parsimonious evolutionary scenario, which can be represented as mapping of loss and gain events on the species tree. The distribution of the evolutionary events among the tree nodes substantially depends on the underlying assumptions of the reconciliation algorithm, e.g. whether or not independent gene gains (gain after loss after gain are permitted. Biological considerations suggest that, on average, gene loss might be a more likely event than gene gain. Therefore different gain penalties were used and the resulting series of reconstructed gene sets for the last universal common ancestor (LUCA of the extant life forms were analysed. The number of genes in the reconstructed LUCA gene sets grows as the gain penalty increases. However, qualitative examination of the LUCA versions reconstructed with different gain penalties

The Attentional Demand of Automobile Driving Revisited: Occlusion Distance as a Function of Task-Relevant Event Density in Realistic Driving Scenarios.

Science.gov (United States)

Kujala, Tuomo; Mäkelä, Jakke; Kotilainen, Ilkka; Tokkonen, Timo

2016-02-01

We studied the utility of occlusion distance as a function of task-relevant event density in realistic traffic scenarios with self-controlled speed. The visual occlusion technique is an established method for assessing visual demands of driving. However, occlusion time is not a highly informative measure of environmental task-relevant event density in self-paced driving scenarios because it partials out the effects of changes in driving speed. Self-determined occlusion times and distances of 97 drivers with varying backgrounds were analyzed in driving scenarios simulating real Finnish suburban and highway traffic environments with self-determined vehicle speed. Occlusion distances varied systematically with the expected environmental demands of the manipulated driving scenarios whereas the distributions of occlusion times remained more static across the scenarios. Systematic individual differences in the preferred occlusion distances were observed. More experienced drivers achieved better lane-keeping accuracy than inexperienced drivers with similar occlusion distances; however, driving experience was unexpectedly not a major factor for the preferred occlusion distances. Occlusion distance seems to be an informative measure for assessing task-relevant event density in realistic traffic scenarios with self-controlled speed. Occlusion time measures the visual demand of driving as the task-relevant event rate in time intervals, whereas occlusion distance measures the experienced task-relevant event density in distance intervals. The findings can be utilized in context-aware distraction mitigation systems, human-automated vehicle interaction, road speed prediction and design, as well as in the testing of visual in-vehicle tasks for inappropriate in-vehicle glancing behaviors in any dynamic traffic scenario for which appropriate individual occlusion distances can be defined. © 2015, Human Factors and Ergonomics Society.

Fire propagation equation for the explicit identification of fire scenarios in a fire PSA

International Nuclear Information System (INIS)

Lim, Ho Gon; Han, Sang Hoon; Moon, Joo Hyun

2011-01-01

When performing fire PSA in a nuclear power plant, an event mapping method, using an internal event PSA model, is widely used to reduce the resources used by fire PSA model development. Feasible initiating events and component failure events due to fire are identified to transform the fault tree (FT) for an internal event PSA into one for a fire PSA using the event mapping method. A surrogate event or damage term method is used to condition the FT of the internal PSA. The surrogate event or the damage term plays the role of flagging whether the system/component in a fire compartment is damaged or not, depending on the fire being initiated from a specified compartment. These methods usually require explicit states of all compartments to be modeled in a fire area. Fire event scenarios, when using explicit identification, such as surrogate or damage terms, have two problems: there is no consideration of multiple fire propagation beyond a single propagation to an adjacent compartment, and there is no consideration of simultaneous fire propagations in which an initiating fire event is propagated to multiple paths simultaneously. The present paper suggests a fire propagation equation to identify all possible fire event scenarios for an explicitly treated fire event scenario in the fire PSA. Also, a method for separating fire events was developed to make all fire events a set of mutually exclusive events, which can facilitate arithmetic summation in fire risk quantification. A simple example is given to confirm the applicability of the present method for a 2x3 rectangular fire area. Also, a feasible asymptotic approach is discussed to reduce the computational burden for fire risk quantification

Proposal for the classification of scenarios for deep geological repositories in probability classes

International Nuclear Information System (INIS)

Beuth, Thomas

2013-03-01

The provided report was elaborated in the framework of the project 3609R03210 ''Research and Development for Proof of the long-term Safety of Deep Geological Repositories''. It contains a proposal for a methodology that enables the assignment of developed scenarios in the frame of Safety Cases to defined probability classes. The assignment takes place indirectly through the categorization of the defining relevant factors (so-called FEP: Features, Events and Processes) of the respective scenarios also in probability classes. Therefore, decision trees and criteria were developed for the categorization of relevant factors in classes. Besides the description of the methodology another focal point of the work was the application of the method taking into account a defined scenario. By means of the scenario the different steps of the method and the decision criteria were documented, respectively. In addition, potential subjective influences along the path of decisions regarding the assignment of scenarios in probability classes were identified.

Temporal aspects in the development of a cascading-event crisis scenario: A pilot demonstration of the CRISMA project

Science.gov (United States)

Aubrecht, Christoph; Almeida, Miguel; Polese, Maria; Reva, Valeria; Steinnocher, Klaus; Zuccaro, Giulio

2013-04-01

In this abstract we illustrate the various temporal aspects to be considered in a multi-hazard crisis scenario set up as pilot study in the EU-FP7 Integrated Project CRISMA. In the framework of CRISMA a simulation-based decision support system for crisis management is developed facilitating the modeling of realistic crisis scenarios, related pre-event vulnerabilities, as well as possible response actions and associated varying potential impacts on society. Both external factors driving crisis development and actions of the involved crisis management team are considered in the system setup. The presented case is a complex cascading-event crisis scenario that is initiated by an earthquake causing building collapse and a consequent gas pipeline failure that triggers a follow-up fire in a nearby forest with potential to spread and endangering a village of the neighborhood. In terms of the hazard components, major earthquakes are rapid-onset events that can occur at any time without warning while fires are rather slow-progressing hazards usually allowing a certain lead time for preparations. In our scenario, which is based on the 2009 L'Aquila earthquake in Italy, a series of low-magnitude events preceding the main shock over a few months increases population awareness and at the same time brings disaster managers to assess risks and evaluate evacuation options already in the pre-disaster phase. This seismic swarm and the associated period of increased general awareness thus add an additional temporal component to the scenario, initiating response considerations earlier as when compared to a single shock scenario. In addition, the seismic vulnerability of buildings may increase due to damage accumulation, with higher probability of collapse at a given earthquake intensity. With regard to best possible impact mitigation, detailed spatio-temporal exposure and vulnerability characteristics of population and associated assets have to be analyzed for all crisis stages

Analysis of unintended events in hospitals: inter-rater reliability of constructing causal trees and classifying root causes

NARCIS (Netherlands)

Smits, M.; Janssen, J.; Vet, de H.C.W.; Zwaan, L.; Timmermans, D.R.M.; Groenewegen, P.P.; Wagner, C.

2009-01-01

BACKGROUND: Root cause analysis is a method to examine causes of unintended events. PRISMA (Prevention and Recovery Information System for Monitoring and Analysis: is a root cause analysis tool. With PRISMA, events are described in causal trees and root causes are subsequently classified with the

Analysis of unintended events in hospitals : inter-rater reliability of constructing causal trees and classifying root causes

NARCIS (Netherlands)

Smits, M.; Janssen, J.; Vet, R. de; Zwaan, L.; Groenewegen, P.P.; Timmermans, D.

2009-01-01

Background. Root cause analysis is a method to examine causes of unintended events. PRISMA (Prevention and Recovery Information System for Monitoring and Analysis) is a root cause analysis tool. With PRISMA, events are described in causal trees and root causes are subsequently classified with the

Analysis of unintended events in hospitals: inter-rater reliability of constructing causal trees and classifying root causes.

NARCIS (Netherlands)

Smits, M.; Janssen, J.; Vet, R. de; Zwaan, L.; Timmermans, D.; Groenewegen, P.; Wagner, C.

2009-01-01

Background: Root cause analysis is a method to examine causes of unintended events. PRISMA (Prevention and Recovery Information System for Monitoring and Analysis) is a root cause analysis tool. With PRISMA, events are described in causal trees and root causes are subsequently classified with the

An application of the explicit method for analysing intersystem dependencies in the evaluation of event trees

International Nuclear Information System (INIS)

Oliveira, L.F.S.; Frutuoso e Melo, P.F.; Lima, J.E.P.; Stal, I.L.

1985-01-01

We discuss in this paper a computational application of the explicit method for analyzing event trees in the context of probabilistic risk assessments. A detailed analysis of the explicit method is presented, including the train level analysis (TLA) of safety systems and the impact vector method. It is shown that the penalty for not adopting TLA is that in some cases non-conservative results may be reached. The impact vector method can significantly reduce the number of sequences to be considered, and its use has inspired the definition of a dependency matrix, which enables the proper running of a computer code especially developed for analysing event trees. This code constructs and quantifies the event trees in the fashion just discussed, by receiving as input the construction and quantification dependencies defined in the dependency matrix. The code has been extensively used in the Angra 1 PRA currently underway. In its present version it gives as output the dominant sequences for each given initiator, properly classifying them in core-degradation classes as specified by the user. This calculation is made in a pointwise fashion. Extensions of this code are being developed in order to perform uncertainty analyses on the dominant sequences and also risk importance measures of the safety systems envolved. (orig.)

Quantitative assessment of consequences of natural events for the performance of waste disposal isolation system. On consequences of natural events in groundwater scenario

International Nuclear Information System (INIS)

Ohkubo, Hiroo

1999-02-01

This year, first, on seismicity and faulting, uplift and erosion, climate change and human activity (intrusion) scenarios, while effects of those scenarios were primarily evaluated in reference cases last year, variant cases with another kind of patterns of models and parameters compared to reference cases, have been studied and set, and their effects have been analyzed and evaluated. Secondly, referring to the results of the above discussions, a preliminary study was made to evaluate the complex effect caused by combining natural events such as volcanism, seismicity and faulting, uplift and erosion and climate change, where discussions have been made on which combined scenario was more important and how to set the analysis framework. (author)

On the use of non-coherent fault trees in safety and security studies

International Nuclear Information System (INIS)

Contini, S.; Cojazzi, G.G.M.; Renda, G.

2008-01-01

This paper gives some insights on the usefulness of non-coherent fault trees in system modelling from both the point of view of safety and security. A safety-related system can evolve from the working states to failed states through degraded states, i.e. working state, but in a degraded mode. In practical applications the degraded states may be of particular interest due e.g. to the associated risk increase or the different types of consequent actions. The top events definitions of such states contain the working conditions of some sub-systems/components. How the use of non-coherent fault trees can greatly simplify both the modelling and quantification of these states is shown in this paper. Some considerations about the interpretation of the importance indexes of negated basic events are also briefly described. When dealing with security applications, there is a need to cope not only with stochastic events, such as component failures and human errors, but also with deliberate intentional actions, whose successes might be characterised by high probability values. Different mutually exclusive attack scenarios may be envisaged for a given system. Hence, the essential feature of a fault tree analyser is the capability to determine the exact value of the top event probability containing mutually exclusive events. It is also shown that in these cases the use of non-coherent fault trees allows solving the problem with limited effort

On epistemic uncertainties in event tree success criteria

International Nuclear Information System (INIS)

Jordan Cizelj, R.; Parzer, I.

2003-01-01

Uncertainty analysis of parameters, which are used as success criteria in PSA event trees, is presented in the paper. The influence of parameters on PSA model is indirect, and they are rather subject to epistemic uncertainties. Consequently, point estimates of these parameters cannot be automatically exchanged with probability distributions. For each PSA parameter, the analysis of several influencing factors is performed. As a result, recommended parameters' values for sensitivity analysis of the influence of these parameters on PSA results are given. In particular, the parameters related to exposure times were investigated. The values of the exposure times are assessed using different methodologies. The analysis of three parameters is presented in the paper, based on the comparison between the results of MAAP 3.0B and RELAP5/MOD2 codes. (author)

Postprocessing of Accidental Scenarios by Semi-Supervised Self-Organizing Maps

Directory of Open Access Journals (Sweden)

Francesco Di Maio

2017-01-01

Full Text Available Integrated Deterministic and Probabilistic Safety Analysis (IDPSA of dynamic systems calls for the development of efficient methods for accidental scenarios generation. The necessary consideration of failure events timing and sequencing along the scenarios requires the number of scenarios to be generated to increase with respect to conventional PSA. Consequently, their postprocessing for retrieving safety relevant information regarding the system behavior is challenged because of the large amount of generated scenarios that makes the computational cost for scenario postprocessing enormous and the retrieved information difficult to interpret. In the context of IDPSA, the interpretation consists in the classification of the generated scenarios as safe, failed, Near Misses (NMs, and Prime Implicants (PIs. To address this issue, in this paper we propose the use of an ensemble of Semi-Supervised Self-Organizing Maps (SSSOMs whose outcomes are combined by a locally weighted aggregation according to two strategies: a locally weighted aggregation and a decision tree based aggregation. In the former, we resort to the Local Fusion (LF principle for accounting the classification reliability of the different SSSOM classifiers, whereas in the latter we build a classification scheme to select the appropriate classifier (or ensemble of classifiers, for the type of scenario to be classified. The two strategies are applied for the postprocessing of the accidental scenarios of a dynamic U-Tube Steam Generator (UTSG.

Mistletoe infection alters the transpiration flow path and suppresses water regulation of host trees during extreme events

Science.gov (United States)

Griebel, A.; Maier, C.; Barton, C. V.; Metzen, D.; Renchon, A.; Boer, M. M.; Pendall, E.

2017-12-01

Mistletoe is a globally distributed group of parasitic plants that infiltrates the vascular tissue of its host trees to acquire water, carbon and nutrients, making it a leading agent of biotic disturbance. Many mistletoes occur in water-limited ecosystems, thus mistletoe infection in combination with increased climatic stress may exacerbate water stress and potentially accelerate mortality rates of infected trees during extreme events. This is an emerging problem in Australia, as mistletoe distribution is increasing and clear links between mistletoe infection and mortality have been established. However, direct observations about how mistletoes alter host physiological processes during extreme events are rare, which impedes our understanding of mechanisms underlying increased tree mortality rates. We addressed this gap by continuously monitoring stem and branch sap flow and a range of leaf traits of infected and uninfected trees of two co-occurring eucalypt species during a severe heatwave in south-eastern Australia. We demonstrate that mistletoes' leaf water potentials were maintained 30% lower than hosts' to redirect the trees' transpiration flow path towards mistletoe leaves. Eucalypt leaves reduced water loss through stomatal regulation when atmospheric dryness exceeded 2 kPa, but the magnitude of stomatal regulation in non-infected eucalypts differed by species (between 40-80%). Remarkably, when infected, sap flow rates of stems and branches of both eucalypt species remained unregulated even under extreme atmospheric dryness (>8 kPa). Our observations indicate that excessive water use of mistletoes likely increases xylem cavitation rates in hosts during prolonged droughts and supports that hydraulic failure contributes to increased mortality of infected trees. Hence, in order to accurately model the contribution of biotic disturbances to tree mortality under a changing climate, it will be crucial to increase our process-based understanding of the interaction

Reactor safety study. An assessment of accident risks in U.S. commercial nuclear power plants. Appendix I. Accident definition and use of event trees

International Nuclear Information System (INIS)

1975-10-01

Information is presented concerning accident definition and use of event trees, event tree methodology, potential accidents covered by the reactor safety study, analysis of potential accidents involving the reactor core, and analysis of potential accidents not involving the core

Tasting the Tree of Life: Development of a Collaborative, Cross-Campus, Science Outreach Meal Event.

Science.gov (United States)

Clement, Wendy L; Elliott, Kathryn T; Cordova-Hoyos, Okxana; Distefano, Isabel; Kearns, Kate; Kumar, Raagni; Leto, Ashley; Tumaliuan, Janis; Franchetti, Lauren; Kulesza, Evelyn; Tineo, Nicole; Mendes, Patrice; Roth, Karen; Osborn, Jeffrey M

2018-01-01

Communicating about science with the public can present a number of challenges, from participation to engagement to impact. In an effort to broadly communicate messages regarding biodiversity, evolution, and tree-thinking with the campus community at The College of New Jersey (TCNJ), a public, primarily undergraduate institution, we created a campus-wide, science-themed meal, "Tasting the Tree of Life: Exploring Biodiversity through Cuisine." We created nine meals that incorporated 149 species/ingredients across the Tree of Life. Each meal illustrated a scientific message communicated through interactions with undergraduate biology students, informational signs, and an interactive website. To promote tree-thinking, we reconstructed a phylogeny of all 149 ingredients. In total, 3,262 people attended the meal, and evaluations indicated that participants left with greater appreciation for the biodiversity and evolutionary relatedness of their food. A keynote lecture and a coordinated social media campaign enhanced the scientific messages, and media coverage extended the reach of this event. "Tasting the Tree of Life" highlights the potential of cuisine as a valuable science communication tool.

Relating phylogenetic trees to transmission trees of infectious disease outbreaks.

Science.gov (United States)

Ypma, Rolf J F; van Ballegooijen, W Marijn; Wallinga, Jacco

2013-11-01

Transmission events are the fundamental building blocks of the dynamics of any infectious disease. Much about the epidemiology of a disease can be learned when these individual transmission events are known or can be estimated. Such estimations are difficult and generally feasible only when detailed epidemiological data are available. The genealogy estimated from genetic sequences of sampled pathogens is another rich source of information on transmission history. Optimal inference of transmission events calls for the combination of genetic data and epidemiological data into one joint analysis. A key difficulty is that the transmission tree, which describes the transmission events between infected hosts, differs from the phylogenetic tree, which describes the ancestral relationships between pathogens sampled from these hosts. The trees differ both in timing of the internal nodes and in topology. These differences become more pronounced when a higher fraction of infected hosts is sampled. We show how the phylogenetic tree of sampled pathogens is related to the transmission tree of an outbreak of an infectious disease, by the within-host dynamics of pathogens. We provide a statistical framework to infer key epidemiological and mutational parameters by simultaneously estimating the phylogenetic tree and the transmission tree. We test the approach using simulations and illustrate its use on an outbreak of foot-and-mouth disease. The approach unifies existing methods in the emerging field of phylodynamics with transmission tree reconstruction methods that are used in infectious disease epidemiology.

FB-Tree: A B+-Tree for Flash-Based SSDs

DEFF Research Database (Denmark)

Jørgensen, Martin V.; Rasmussen, René B.; Saltenis, Simonas

2011-01-01

Due to their many advantages, flash-based SSDs (Solid-State Drives) have become a mainstream alternative to magnetic disks for database servers. Nevertheless, database systems, designed and optimized for magnetic disks, still do not fully exploit all the benefits of the new technology. We propose....... As a consequence, the FB-tree outperforms a regular B+-tree in all scenarios tested. For instance, the throughput of a random workload of 75% updates increases by a factor of three using only two times the space of the B+-tree....

Safety analyses of potential exposure in medical irradiation plants by Fuzzy Fault Tree

International Nuclear Information System (INIS)

Casamirra, Maddalena; Castiglia, Francesco; Giardina, Mariarosa; Tomarchio, Elio

2008-01-01

The results of Fuzzy Fault Tree (FFT) analyses of various accidental scenarios, which involve the operators in potential exposures inside an High Dose Rate (HDR) remote after-loading systems for use in brachytherapy, are reported. To carry out fault tree analyses by means of fuzzy probabilities, the TREEZZY2 computer code is used. Moreover, the HEART (Human Error Assessment and Reduction Technique) model, properly modified on the basis of the fuzzy approach, has been employed to assess the impact of performances haping and error-promoting factors in the context of the accidental events. The assessment of potential dose values for some identified accidental scenarios allows to consider, for a particular event, a fuzzy uncertainty range in potential dose estimate. The availability of lower and upper limits allows evaluating the possibility of optimization of the installation from the point of view of radiation protection. The adequacy of the training and information program for staff and patients (and their family members) and the effectiveness of behavioural rules and safety procedures were tested. Some recommendations on procedures and equipment to reduce the risk of radiological exposure are also provided. (author)

Risk assessment of complex accident scenarios

International Nuclear Information System (INIS)

Kluegel, Jens-Uwe

2012-01-01

The use of methods of risk assessment in accidents in nuclear plants is based on an old tradition. The first consistent systematic study is considered to be the Rasmussen Study of the U.S. Nuclear Regulatory Commission, NRC, WASH-1400. Above and beyond the realm of nuclear technology, there is an extensive range of accident, risk and reliability research into technical-administrative systems. In the past, it has been this area of research which has led to the development of concepts of safety precautions of the type also introduced into nuclear technology (barrier concept, defense in depth, single-failure criterion), where they are now taken for granted as trivial concepts. Also for risk analysis, nuclear technology made use of methods (such as event and fault tree analyses) whose origins were outside the nuclear field. One area in which the use of traditional methods of probabilistic safety analysis is encountering practical problems is risk assessment of complex accident scenarios in nuclear technology. A definition is offered of the term 'complex accident scenarios' in nuclear technology. A number of problems are addressed which arise in the use of traditional PSA procedures in risk assessment of complex accident scenarios. Cases of complex accident scenarios are presented to demonstrate methods of risk assessment which allow robust results to be obtained even when traditional techniques of risk analysis are maintained as a matter of principle. These methods are based on the use of conditional risk metrics. (orig.)

Use of the event tree method for evaluate the safety of radioactive facilities

International Nuclear Information System (INIS)

Hernandez S, A.; Cornejo D, N.; Callis F, E.

2006-01-01

The work shows the validity of the use of Trees of Events like a quantitative method appropriate to carry out evaluations of radiological safety. Its were took like base the evaluations of safety of five Radiotherapy Departments, carried out in the mark of the process of authorization of these facilities. The risk values were obtained by means of the combination of the probabilities of occurrence of the events with its consequences. The use of the method allowed to suggest improvements to the existent safety systems, as well as to confirm that the current regulator requirements for this type of facilities to lead to practices with acceptable risk levels. (Author)

A scenario tree model for the Canadian Notifiable Avian Influenza Surveillance System and its application to estimation of probability of freedom and sample size determination.

Science.gov (United States)

Christensen, Jette; Stryhn, Henrik; Vallières, André; El Allaki, Farouk

2011-05-01

In 2008, Canada designed and implemented the Canadian Notifiable Avian Influenza Surveillance System (CanNAISS) with six surveillance activities in a phased-in approach. CanNAISS was a surveillance system because it had more than one surveillance activity or component in 2008: passive surveillance; pre-slaughter surveillance; and voluntary enhanced notifiable avian influenza surveillance. Our objectives were to give a short overview of two active surveillance components in CanNAISS; describe the CanNAISS scenario tree model and its application to estimation of probability of populations being free of NAI virus infection and sample size determination. Our data from the pre-slaughter surveillance component included diagnostic test results from 6296 serum samples representing 601 commercial chicken and turkey farms collected from 25 August 2008 to 29 January 2009. In addition, we included data from a sub-population of farms with high biosecurity standards: 36,164 samples from 55 farms sampled repeatedly over the 24 months study period from January 2007 to December 2008. All submissions were negative for Notifiable Avian Influenza (NAI) virus infection. We developed the CanNAISS scenario tree model, so that it will estimate the surveillance component sensitivity and the probability of a population being free of NAI at the 0.01 farm-level and 0.3 within-farm-level prevalences. We propose that a general model, such as the CanNAISS scenario tree model, may have a broader application than more detailed models that require disease specific input parameters, such as relative risk estimates. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

Introduction of accidental procedures in the event trees of the 900MW PWR PRA

International Nuclear Information System (INIS)

Bars, G.; Champ, M.; Lanore, J.M.; Pochard, R.

1985-02-01

This paper presents the example of the small LOCA Event Trees and the studies related to the introduction of procedure actions is case of HPSI failure. The results illustrate the interest of the approach and its significant impact on the PRA. The present studies are related to the Y actions in case of small LOCAs without HPIS

Missing rings in Pinus halepensis – the missing link to relate the tree-ring record to extreme climatic events

Science.gov (United States)

Klemen Novak; Martin de Luis; Miguel A. Saz; Luis A. Longares; Roberto Serrano-Notivoli; Josep Raventos; Katarina Cufar; Jozica Gricar; Alfredo Di Filippo; Gianluca Piovesan; Cyrille B.K. Rathgeber; Andreas Papadopoulos; Kevin T. Smith

2016-01-01

Climate predictions for the Mediterranean Basin include increased temperatures, decreased precipitation, and increased frequency of extreme climatic events (ECE). These conditions are associated with decreased tree growth and increased vulnerability to pests and diseases. The anatomy of tree rings responds to these environmental conditions. Quantitatively, the width of...

A new Bayesian Event Tree tool to track and quantify volcanic unrest and its application to Kawah Ijen volcano

Science.gov (United States)

Tonini, Roberto; Sandri, Laura; Rouwet, Dmitri; Caudron, Corentin; Marzocchi, Warner; Suparjan

2016-07-01

Although most of volcanic hazard studies focus on magmatic eruptions, volcanic hazardous events can also occur when no migration of magma can be recognized. Examples are tectonic and hydrothermal unrest that may lead to phreatic eruptions. Recent events (e.g., Ontake eruption on September 2014) have demonstrated that phreatic eruptions are still hard to forecast, despite being potentially very hazardous. For these reasons, it is of paramount importance to identify indicators that define the condition of nonmagmatic unrest, in particular for hydrothermal systems. Often, this type of unrest is driven by movement of fluids, requiring alternative monitoring setups, beyond the classical seismic-geodetic-geochemical architectures. Here we present a new version of the probabilistic BET (Bayesian Event Tree) model, specifically developed to include the forecasting of nonmagmatic unrest and related hazards. The structure of the new event tree differs from the previous schemes by adding a specific branch to detail nonmagmatic unrest outcomes. A further goal of this work consists in providing a user-friendly, open-access, and straightforward tool to handle the probabilistic forecast and visualize the results as possible support during a volcanic crisis. The new event tree and tool are here applied to Kawah Ijen stratovolcano, Indonesia, as exemplificative application. In particular, the tool is set on the basis of monitoring data for the learning period 2000-2010, and is then blindly applied to the test period 2010-2012, during which significant unrest phases occurred.

Epistemic-based investigation of the probability of hazard scenarios using Bayesian network for the lifting operation of floating objects

Science.gov (United States)

Toroody, Ahmad Bahoo; Abaiee, Mohammad Mahdi; Gholamnia, Reza; Ketabdari, Mohammad Javad

2016-09-01

Owing to the increase in unprecedented accidents with new root causes in almost all operational areas, the importance of risk management has dramatically risen. Risk assessment, one of the most significant aspects of risk management, has a substantial impact on the system-safety level of organizations, industries, and operations. If the causes of all kinds of failure and the interactions between them are considered, effective risk assessment can be highly accurate. A combination of traditional risk assessment approaches and modern scientific probability methods can help in realizing better quantitative risk assessment methods. Most researchers face the problem of minimal field data with respect to the probability and frequency of each failure. Because of this limitation in the availability of epistemic knowledge, it is important to conduct epistemic estimations by applying the Bayesian theory for identifying plausible outcomes. In this paper, we propose an algorithm and demonstrate its application in a case study for a light-weight lifting operation in the Persian Gulf of Iran. First, we identify potential accident scenarios and present them in an event tree format. Next, excluding human error, we use the event tree to roughly estimate the prior probability of other hazard-promoting factors using a minimal amount of field data. We then use the Success Likelihood Index Method (SLIM) to calculate the probability of human error. On the basis of the proposed event tree, we use the Bayesian network of the provided scenarios to compensate for the lack of data. Finally, we determine the resulting probability of each event based on its evidence in the epistemic estimation format by building on two Bayesian network types: the probability of hazard promotion factors and the Bayesian theory. The study results indicate that despite the lack of available information on the operation of floating objects, a satisfactory result can be achieved using epistemic data.

基于情景的突发事件链构建方法*%A Scenario-based Construction Method of Emergency Event Chain

Institute of Scientific and Technical Information of China (English)

马骁霏; 仲秋雁; 曲毅; 王宁; 王延章

2013-01-01

突发事件前兆缺失，危害巨大，其次生、衍生事件构成的事件链给人类造成严重的影响。针对突发事件演变路径不明，形成的链式结构复杂多变的特点，借鉴共性知识模型，利用知识元刻画情景与事件，通过知识元间的关联，分析情景与事件相互作用关系，事件间的演变规律；以数据和规则为驱动，提出了一种基于情景的突发事件链构建方法，该方法可为“情景-应对”决策提供了支持，最后给出案例分析。%Lacking of precursor, emergency events do harm to human society greatly. Emergency event chain, constituted by secondary e-vents, has severe negative effects on human race. The chain structure of emergency event is complex and varies frequently, and it is diffi-cult to judge the evolution path for emergency events. Drawing on the common knowledge model, using knowledge element to express scenario and events, the paper analyzes the interaction between scenario and events and the evolution of events based on the relationship of knowledge element. Using data and rule as drive, a scenario-based construction method of emergency event chain is proposed. The meth-od supports“scenario-response” policy decision-making. At last, a case study is presented.

An application of the explicit method for analysing intersystem dependencies in the evaluation of event trees

International Nuclear Information System (INIS)

Oliveira, L.F.S. de; Frutuoso e Melo, P.F.F.; Lima, J.E.P.; Stal, I.L.

1985-01-01

A computacional application of the explicit method for analyzing event trees in the context of probabilistic risk assessments is discussed. A detailed analysis of the explicit method is presented, including the train level analysis (TLA) of safety systems and the impact vector method. It is shown that the penalty for not adopting TLA is that in some cases non-conservative results may be reached. The impact vector method can significantly reduce the number of sequences to be considered, and its use has inspired the definition of a dependency matrix, which enables the proper running of a computer code especially developed for analysing event trees. The code has been extensively used in the Angra 1 PRA currently underway. In its present version it gives as output the dominant sequences for each given initiator, properly classiying them in core-degradation classes as specified by the user. (Author) [pt

Phylogenetic framework for coevolutionary studies: a compass for exploring jungles of tangled trees.

Science.gov (United States)

Martínez-Aquino, Andrés

2016-08-01

Phylogenetics is used to detect past evolutionary events, from how species originated to how their ecological interactions with other species arose, which can mirror cophylogenetic patterns. Cophylogenetic reconstructions uncover past ecological relationships between taxa through inferred coevolutionary events on trees, for example, codivergence, duplication, host-switching, and loss. These events can be detected by cophylogenetic analyses based on nodes and the length and branching pattern of the phylogenetic trees of symbiotic associations, for example, host-parasite. In the past 2 decades, algorithms have been developed for cophylogetenic analyses and implemented in different software, for example, statistical congruence index and event-based methods. Based on the combination of these approaches, it is possible to integrate temporal information into cophylogenetical inference, such as estimates of lineage divergence times between 2 taxa, for example, hosts and parasites. Additionally, the advances in phylogenetic biogeography applying methods based on parametric process models and combined Bayesian approaches, can be useful for interpreting coevolutionary histories in a scenario of biogeographical area connectivity through time. This article briefly reviews the basics of parasitology and provides an overview of software packages in cophylogenetic methods. Thus, the objective here is to present a phylogenetic framework for coevolutionary studies, with special emphasis on groups of parasitic organisms. Researchers wishing to undertake phylogeny-based coevolutionary studies can use this review as a "compass" when "walking" through jungles of tangled phylogenetic trees.

Extended tree-level gauge mediation

DEFF Research Database (Denmark)

Monaco, M.; Nardecchia, M.; Romanino, A.

2011-01-01

Tree-level gauge mediation (TGM) is a scenario of SUSY breaking in which the tree-level exchange of heavy (possibly GUT) vector fields generates flavor-universal sfermion masses. In this work we extend this framework to the case of E(6) that is the natural extension of the minimal case studied so...... if the gauge group does not contain SU(5). If SUSY breaking is mediated purely by the U(1) generator that commutes with SO(10) we obtain universal sfermion masses and thus can derive the CMSSM boundary conditions in a novel scenario....

Human decision error (HUMDEE) trees

International Nuclear Information System (INIS)

Ostrom, L.T.

1993-01-01

Graphical presentations of human actions in incident and accident sequences have been used for many years. However, for the most part, human decision making has been underrepresented in these trees. This paper presents a method of incorporating the human decision process into graphical presentations of incident/accident sequences. This presentation is in the form of logic trees. These trees are called Human Decision Error Trees or HUMDEE for short. The primary benefit of HUMDEE trees is that they graphically illustrate what else the individuals involved in the event could have done to prevent either the initiation or continuation of the event. HUMDEE trees also present the alternate paths available at the operator decision points in the incident/accident sequence. This is different from the Technique for Human Error Rate Prediction (THERP) event trees. There are many uses of these trees. They can be used for incident/accident investigations to show what other courses of actions were available and for training operators. The trees also have a consequence component so that not only the decision can be explored, also the consequence of that decision

Automated Generation of Attack Trees

DEFF Research Database (Denmark)

Vigo, Roberto; Nielson, Flemming; Nielson, Hanne Riis

2014-01-01

Attack trees are widely used to represent threat scenarios in a succinct and intuitive manner, suitable for conveying security information to non-experts. The manual construction of such objects relies on the creativity and experience of specialists, and therefore it is error-prone and impractica......Attack trees are widely used to represent threat scenarios in a succinct and intuitive manner, suitable for conveying security information to non-experts. The manual construction of such objects relies on the creativity and experience of specialists, and therefore it is error......-prone and impracticable for large systems. Nonetheless, the automated generation of attack trees has only been explored in connection to computer networks and levering rich models, whose analysis typically leads to an exponential blow-up of the state space. We propose a static analysis approach where attack trees...... are automatically inferred from a process algebraic specification in a syntax-directed fashion, encompassing a great many application domains and avoiding incurring systematically an exponential explosion. Moreover, we show how the standard propositional denotation of an attack tree can be used to phrase...

Scenario aggregation and analysis via Mean-Shift Methodology

International Nuclear Information System (INIS)

Mandelli, D.; Yilmaz, A.; Metzroth, K.; Aldemir, T.; Denning, R.

2010-01-01

A new generation of dynamic methodologies is being developed for nuclear reactor probabilistic risk assessment (PRA) which explicitly account for the time element in modeling the probabilistic system evolution and use numerical simulation tools to account for possible dependencies between failure events. The dynamic event tree (DET) approach is one of these methodologies. One challenge with dynamic PRA methodologies is the large amount of data they produce which may be difficult to analyze without appropriate software tools. The concept of 'data mining' is well known in the computer science community and several methodologies have been developed in order to extract useful information from a dataset with a large number of records. Using the dataset generated by the DET analysis of the reactor vessel auxiliary cooling system (RVACS) of an ABR-1000 for an aircraft crash recovery scenario and the Mean-Shift Methodology for data mining, it is shown how clusters of transients with common characteristics can be identified and classified. (authors)

THE 'TWIN-CME' SCENARIO AND LARGE SOLAR ENERGETIC PARTICLE EVENTS IN SOLAR CYCLE 23

International Nuclear Information System (INIS)

Ding, Liuguan; Jiang, Yong; Zhao, Lulu; Li, Gang

2013-01-01

Energetic particles in large solar energetic particle (SEP) events are a major concern for space weather. Recently, Li et al. proposed a 'twin-CME' scenario for ground-level events. Here we extend that study to large SEP events in solar cycle 23. Depending on whether preceding coronal mass ejections (CMEs) within 9 hr exist and whether ions >10 MeV nucleon –1 exceed 10 pfu, we categorize fast CMEs with speed >900 km s –1 and width >60° from the western hemisphere source regions into four groups: groups I and II are 'twin' and single CMEs that lead to large SEPs; groups III and IV are 'twin' and single CMEs that do not lead to large SEPs. The major findings of this paper are: first, large SEP events tend to be 'twin-CME' events. Of 59 western large SEP events in solar cycle 23, 43 are 'twin-CME' (group I) events and 16 are single-CME (group II) events. Second, not all 'twin CMEs' produced large SEPs: 28 twin CMEs did not produce large SEPs (group III events). Some of them produced excesses of particles up to a few MeV nucleon –1 . Third, there were 39 single fast CMEs that did not produce SEPs (group IV events). Some of these also showed an excess of particles up to a few MeV nucleon –1 . For all four groups of events, we perform statistical analyses on properties such as the angular width, the speed, the existence of accompanying metric type II radio bursts, and the associated flare class for the main CMEs and the preceding CMEs.

Simple street tree sampling

Science.gov (United States)

David J. Nowak; Jeffrey T. Walton; James Baldwin; Jerry. Bond

2015-01-01

Information on street trees is critical for management of this important resource. Sampling of street tree populations provides an efficient means to obtain street tree population information. Long-term repeat measures of street tree samples supply additional information on street tree changes and can be used to report damages from catastrophic events. Analyses of...

Consequence Assessment for Potential Scenarios of Radiological Terrorists Events

International Nuclear Information System (INIS)

Shin, Hyeongki; Kim, Juyoul

2007-01-01

Radiological dispersal device (RDD) means any method used to deliberately disperse radioactive material to create terror or harm. Dirty bomb is an example of RDD, which usually consists of radioactive material and unconventional explosive. Dirty bomb was a problem long before September 11, 2001. In 1987, the Iraqi government tested a one-ton radiological bomb. The Iraqi tests confirmed that a dirty bomb is not effective as weapons of mass destruction (WMD) and that its main value is as a psychological weapon. In 1995, Chechen rebels buried a dirty bomb in a park in Moscow threatening to detonate one in the future if their demands were not met. Another good example of potential dirty bomb effects was an incident in Goiania, Brazil on September 18, 1987, where an orphaned medical source containing 1,375 Ci of Cs-137 resulted the death of four people and extensive environmental contamination. The purposes of radiological terrorists events are not to destroy or damage the target but to disperse radioactivity in the environment. They inflict panic on a public and economic damage by disruption of business. They also have influence on enormous clean-up costs by spreading radioactive contamination including secondary impacts on water supply reservoirs. Generally, two major long-term concerns following a RDD are human health and economic impacts. In this study, we developed potential scenarios of radiological terrorists events and performed their radiological consequence assessments in terms of total effective dose equivalent (TEDE), projected cumulative external and internal dose, and ground deposition of radioactivity

Consequence Assessment for Potential Scenarios of Radiological Terrorists Events

Energy Technology Data Exchange (ETDEWEB)

Shin, Hyeongki [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of); Kim, Juyoul [Seoul National University, Seoul (Korea, Republic of)

2007-07-01

Radiological dispersal device (RDD) means any method used to deliberately disperse radioactive material to create terror or harm. Dirty bomb is an example of RDD, which usually consists of radioactive material and unconventional explosive. Dirty bomb was a problem long before September 11, 2001. In 1987, the Iraqi government tested a one-ton radiological bomb. The Iraqi tests confirmed that a dirty bomb is not effective as weapons of mass destruction (WMD) and that its main value is as a psychological weapon. In 1995, Chechen rebels buried a dirty bomb in a park in Moscow threatening to detonate one in the future if their demands were not met. Another good example of potential dirty bomb effects was an incident in Goiania, Brazil on September 18, 1987, where an orphaned medical source containing 1,375 Ci of Cs-137 resulted the death of four people and extensive environmental contamination. The purposes of radiological terrorists events are not to destroy or damage the target but to disperse radioactivity in the environment. They inflict panic on a public and economic damage by disruption of business. They also have influence on enormous clean-up costs by spreading radioactive contamination including secondary impacts on water supply reservoirs. Generally, two major long-term concerns following a RDD are human health and economic impacts. In this study, we developed potential scenarios of radiological terrorists events and performed their radiological consequence assessments in terms of total effective dose equivalent (TEDE), projected cumulative external and internal dose, and ground deposition of radioactivity.

Tracing footprints of environmental events in tree ring chemistry using neutron activation analysis

Science.gov (United States)

Sahin, Dagistan

The aim of this study is to identify environmental effects on tree-ring chemistry. It is known that industrial pollution, volcanic eruptions, dust storms, acid rain and similar events can cause substantial changes in soil chemistry. Establishing whether a particular group of trees is sensitive to these changes in soil environment and registers them in the elemental chemistry of contemporary growth rings is the over-riding goal of any Dendrochemistry research. In this study, elemental concentrations were measured in tree-ring samples of absolutely dated eleven modern forest trees, grown in the Mediterranean region, Turkey, collected and dated by the Malcolm and Carolyn Wiener Laboratory for Aegean and Near Eastern Dendrochronology laboratory at Cornell University. Correlations between measured elemental concentrations in the tree-ring samples were analyzed using statistical tests to answer two questions. Does the current concentration of a particular element depend on any other element within the tree? And, are there any elements showing correlated abnormal concentration changes across the majority of the trees? Based on the detailed analysis results, the low mobility of sodium and bromine, positive correlations between calcium, zinc and manganese, positive correlations between trace elements lanthanum, samarium, antimony, and gold within tree-rings were recognized. Moreover, zinc, lanthanum, samarium and bromine showed strong, positive correlations among the trees and were identified as possible environmental signature elements. New Dendrochemistry information found in this study would be also useful in explaining tree physiology and elemental chemistry in Pinus nigra species grown in Turkey. Elemental concentrations in tree-ring samples were measured using Neutron Activation Analysis (NAA) at the Pennsylvania State University Radiation Science and Engineering Center (RSEC). Through this study, advanced methodologies for methodological, computational and

Model checking exact cost for attack scenarios

DEFF Research Database (Denmark)

Aslanyan, Zaruhi; Nielson, Flemming

2017-01-01

Attack trees constitute a powerful tool for modelling security threats. Many security analyses of attack trees can be seamlessly expressed as model checking of Markov Decision Processes obtained from the attack trees, thus reaping the benefits of a coherent framework and a mature tool support....... However, current model checking does not encompass the exact cost analysis of an attack, which is standard for attack trees. Our first contribution is the logic erPCTL with cost-related operators. The extended logic allows to analyse the probability of an event satisfying given cost bounds and to compute...... the exact cost of an event. Our second contribution is the model checking algorithm for erPCTL. Finally, we apply our framework to the analysis of attack trees....

Are trees long-lived?

Science.gov (United States)

Kevin T. Smith

2009-01-01

Trees and tree care can capture the best of people's motivations and intentions. Trees are living memorials that help communities heal at sites of national tragedy, such as Oklahoma City and the World Trade Center. We mark the places of important historical events by the trees that grew nearby even if the original tree, such as the Charter Oak in Connecticut or...

Development of accident event trees and evaluation of safety system failure modes for the nuclear ultra large crude carrier

International Nuclear Information System (INIS)

Lewe, C.K.; Coffey, R.S.; Goodwin, E.F.; Maltese, J.G.; Pyatt, D.W.

1978-01-01

A method of applying the probabilistic accident event tree methodology to safety assessments of a nuclear powered Ultra Large Crude Carrier is presented. Also presented are the procedures by which an external accident initiating event, such as a ship collision, may be correlated with the probabilities of damage to the ship's safety systems and to their ultimate availabilities to perform required safety functions

Applicability of PRISM PRA Methodology to the Level II Probabilistic Safety Analysis of KALIMER-600 (I) (Core Damage Event Tree Analysis Part)

International Nuclear Information System (INIS)

Park, S. Y.; Kim, T. W.; Ha, K. S.; Lee, B. Y.

2009-03-01

The Korea Atomic Energy Research Institute (KAERI) has been developing liquid metal reactor (LMR) design technologies under a National Nuclear R and D Program. Nevertheless, there is no experience of the PSA domestically for a fast reactor with the metal fuel. Therefore, the objective of this study is to establish the methodologies of risk assessment for the reference design of KALIMER-600 reactor. An applicability of the PSA of the PRISM plant to the KALIMER-600 has been studied. The study is confined to a core damage event tree analysis which is a part of a level 2 PSA. Assuming that the accident types, which can be developed from level 1 PSA, are same as the PRISM PRA, core damage categories are defined and core damage event trees are developed for the KALIMER-600 reactor. Fission product release fractions of the core damage categories and branch probabilities of the core damage event trees are referred from the PRISM PRA temporarily. Plant specific data will be used during the detail analysis

Generic event trees and the treatment of dependencies and non-proceduralized actions in a low power and shutdown Probabilistic Risk Assessment

International Nuclear Information System (INIS)

Forester, J.; Yakle, J.; Whitehead, D.; Darby, J.

1993-01-01

Sandia National Laboratories was tasked by the US Nuclear Regulatory Commission to perform a Probabilistic Risk Assessment (PRA) of a boiling water reactor (BWR) during low power and shutdown (LP ampersand S) conditions. The plant chosen for the study was Grand Gulf Nuclear Station (GGNS), a BWR 6. In performing the analysis, it was found that in comparison with full-power PRAs, the low decay heat levels present during LP ampersand S conditions result in a relatively large number of ways by which cooling can be provided to the core. In addition, because of the less stringent requirements imposed on system configurations possible is large and the availability of plant systems is more difficult to specify. These aspects of the LP ampersand S environment led to the development and use of ''generic'' event trees in performing the analysis. The use of ''generic'' event trees, in turn, had a significant impact on the nature of the human reliability analysis (HRA) that was performed. This paper describes the development of the event trees for the LP ampersand S PRA and important aspects of the resulting HRA

Potential off-normal events and associated radiological source terms for the compact ignition tokamak: Fusion Safety Program

International Nuclear Information System (INIS)

Holland, D.F.; Lyon, R.E.

1987-10-01

The Compact Ignition Tokamak (CIT), the latest step in the United States program to develop the commercial application of fusion power, is designed as the first fusion device to achieve ignition conditions. It is to be constructed near Princeton, New Jersey on the site of the existing Tokamak Fusion Test Reactor (TFTR). To address the environmental impact and public safety concerns, a preliminary analysis was performed of potential off-normal radiological releases. Operational occurrences, natural phenomena, accidents with external origins, and accidents external to the PPPL site were considered as potential sources for off-normal events. Based on an initial screening, events were selected for preliminary analysis. Included in these events were tritium releases from the tritium delivery and recovery system, tritium releases from the torus, releases of activated nitrogen from the test cell or cryostat, seismic events, and shipping accidents. In each case, the design considerations related to the event were reviewed and the release scenarios discussed. Because of the complexity of some of the proposed safety systems, in some cases event trees were used to describe the accident scenarios. For each scenario, the probability was estimated as well as the release magnitude, isotope, chemical form, and release mode. 10 refs., 17 figs., 5 tabs

Use of a scenario-development procedure to identify potentially disruptive scenarios, Greater Confinement Disposal facility, Area 5, Nevada Test Site

International Nuclear Information System (INIS)

Guzowski, R.V.; Sandia National Labs., Albuquerque, NM

1994-01-01

The Greater Confinement Disposal (GCD) facility includes four boreholes that contain transuranic (TRLT) waste. Presence of the TRU waste means that this facility must comply with the US Environmental Protection Agency's Environmental Radiation Protection Standards for Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Waste-Final Rule 40 CFR Part 191. To comply with the Containment Requirements of this rule, all potentially disruptive events and processes, and by implication all potentially disruptive combinations of events and processes (scenarios), must be identified for possible inclusion in performance assessments. Screening of the FEPs identified four events for scenario development: exploratory drilling for natural resources, drilling withdrawal wells, irrigation, and subsidence. Recent environmental-isotope analyses of the vadose zone suggest that radionuclide transport from the boreholes to the water table by infiltration is not a feasible transport mechanism within the time frame of regulatory concern. For this reason, the event of drilling withdrawal wells was merged with exploratory drilling for resources. The descriptions of the remaining three events were modified slightly to aid in estimation of event probabilities and consequence analyses. The three events are: exploratory drilling for resources penetrates a TRU borehole, irrigation occurs at the Radioactive Waste Management Site (RWMS), and subsidence occurs at the RWMS. Use of a logic diagram with these three events resulted in the construction of eight scenarios, including base-case (undisturbed) conditions. Screening these scenarios at this stage of scenario development was beyond the scope of this task. Based on the implementation assumptions, this scenario-development procedure produced a comprehensive set of mutually exclusive scenarios that are reproducible and auditable for use in GCD performance assessments

Learning in data-limited multimodal scenarios: Scandent decision forests and tree-based features.

Science.gov (United States)

Hor, Soheil; Moradi, Mehdi

2016-12-01

Incomplete and inconsistent datasets often pose difficulties in multimodal studies. We introduce the concept of scandent decision trees to tackle these difficulties. Scandent trees are decision trees that optimally mimic the partitioning of the data determined by another decision tree, and crucially, use only a subset of the feature set. We show how scandent trees can be used to enhance the performance of decision forests trained on a small number of multimodal samples when we have access to larger datasets with vastly incomplete feature sets. Additionally, we introduce the concept of tree-based feature transforms in the decision forest paradigm. When combined with scandent trees, the tree-based feature transforms enable us to train a classifier on a rich multimodal dataset, and use it to classify samples with only a subset of features of the training data. Using this methodology, we build a model trained on MRI and PET images of the ADNI dataset, and then test it on cases with only MRI data. We show that this is significantly more effective in staging of cognitive impairments compared to a similar decision forest model trained and tested on MRI only, or one that uses other kinds of feature transform applied to the MRI data. Copyright © 2016. Published by Elsevier B.V.

Present diversity of Galápagos leaf-toed geckos (Phyllodactylidae: Phyllodactylus) stems from three independent colonization events.

Science.gov (United States)

Torres-Carvajal, Omar; Rodríguez-Guerra, Andrea; Chaves, Jaime A

2016-10-01

We re-examined the biogeography of the leaf-toed geckos (Phyllodactylus) endemic to the Galápagos Islands by analyzing for the first time samples of P. gilberti, a species endemic to Wolf island, in a phylogenetic framework. Our aim was to test the three-colonizations scenario previously proposed for these lizards and estimate the age of each colonization event. To achieve this we estimated simultaneously a species tree and divergence times with Bayesian methods. Our results supported the three-colonizations scenario. Similar to a previous hypothesis, the species tree obtained here showed that most species of Phyllodactylus are nested in a single clade with an age between 5.49 and 13.8Ma, whereas a second independent colonization corresponding to P. darwini from San Cristóbal island occurred 3.03Ma ago. The species from Wolf island, P. gilberti, stems from a more recent colonization event (0.69Ma). Thus, present diversity of Galápagos leaf-toed geckos stems from three independent, asynchronous colonization events. As with other Galápagos organisms, the Pacific coast of South America seems to be the source for the founders of P. gilberti. Copyright © 2016 Elsevier Inc. All rights reserved.

Nonbinary tree-based phylogenetic networks

OpenAIRE

Jetten, Laura; van Iersel, Leo

2016-01-01

Rooted phylogenetic networks are used to describe evolutionary histories that contain non-treelike evolutionary events such as hybridization and horizontal gene transfer. In some cases, such histories can be described by a phylogenetic base-tree with additional linking arcs, which can for example represent gene transfer events. Such phylogenetic networks are called tree-based. Here, we consider two possible generalizations of this concept to nonbinary networks, which we call tree-based and st...

TREE SELECTING AND TREE RING MEASURING IN DENDROCHRONOLOGICAL INVESTIGATIONS

Directory of Open Access Journals (Sweden)

Sefa Akbulut

2004-04-01

Full Text Available Dendrochronology is a method of dating which makes use of the annual nature of tree growth. Dendrochronology may be divided into a number of subfields, each of which covers one or more aspects of the use of tree ring data: dendroclimatology, dendrogeomorphology, dendrohydrology, dendroecology, dendroarchaelogy, and dendrogylaciology. Basic of all form the analysis of the tree rings. The wood or tree rings can aid to dating past events about climatology, ecology, geology, hydrology. Dendrochronological studies are conducted either on increment cores or on discs. It may be seen abnormalities on tree rings during the measurement like that false rings, missing rings, reaction wood. Like that situation, increment cores must be extracted from four different sides of each tree and be studied as more as on tree.

Application of the Integrated Safety Assessment methodology to safety margins. Dynamic Event Trees, Damage Domains and Risk Assessment

International Nuclear Information System (INIS)

Ibánez, L.; Hortal, J.; Queral, C.; Gómez-Magán, J.; Sánchez-Perea, M.; Fernández, I.; Meléndez, E.; Expósito, A.; Izquierdo, J.M.; Gil, J.; Marrao, H.; Villalba-Jabonero, E.

2016-01-01

The Integrated Safety Assessment (ISA) methodology, developed by the Consejo de Seguridad Nuclear, has been applied to an analysis of Zion NPP for sequences with Loss of the Component Cooling Water System (CCWS). The ISA methodology proposal starts from the unfolding of the Dynamic Event Tree (DET). Results from this first step allow assessing the sequence delineation of standard Probabilistic Safety Analysis results. For some sequences of interest of the outlined DET, ISA then identifies the Damage Domain (DD). This is the region of uncertain times and/or parameters where a safety limit is exceeded, which indicates the occurrence of certain damage situation. This paper illustrates application of this concept obtained simulating sequences with MAAP and with TRACE. From information of simulation results of sequence transients belonging to the DD and the time-density probability distributions of the manual actions and of occurrence of stochastic phenomena, ISA integrates the dynamic reliability equations proposed to obtain the sequence contribution to the global Damage Exceedance Frequency (DEF). Reported results show a slight increase in the DEF for sequences investigated following a power uprate from 100% to 110%. This demonstrates the potential use of the method to help in the assessment of design modifications. - Highlights: • This paper illustrates an application of the ISA methodology to safety margins. • Dynamic Event Trees are useful tool for verifying the standard PSA Event Trees. • The ISA methodology takes into account the uncertainties in human action times. • The ISA methodology shows the Damage Exceedance Frequency increase in power uprates.

Modeling the Effects of Drought Events on Forest Ecosystem Functioning Historically and Under Scenarios of Climate Change

Science.gov (United States)

Ren, J.; Hanan, E. J.; Kolden, C.; Abatzoglou, J. T.; Tague, C.; Liu, M.; Adam, J. C.

2017-12-01

Drought events have been increasing across the western United States in recent years. Many studies have shown that, in the context of climate change, droughts will continue to be stronger, more frequent, and prolonged in the future. However, the response of forest ecosystems to droughts, particularly multi-year droughts, is not well understood. The objectives of this study are to examine how drought events of varying characteristics (e.g. intensity, duration, frequency, etc.) have affected the functioning of forest ecosystems historically, and how changing drought characteristics (including multi-year droughts) may affect forest functioning in a future climate. We utilize the Regional Hydro-Ecological Simulation System (RHESSys) to simulate impacts of both historical droughts and scenarios of future droughts on forest ecosystems. RHESSys is a spatially-distributed and process-based model that captures the interactions between coupled biogeochemical and hydrologic cycles at catchment scales. Here our case study is the Trail Creek catchment of the Big Wood River basin in Idaho, the Northwestern USA. For historical simulations, we use the gridded meteorological data of 1979 to 2016; for future climate scenarios, we utilize downscaled data from GCMs that have been demonstrated to capture drought events in the Northwest of the USA. From these climate projections, we identify various types of drought in intensity and duration, including multi-year drought events. We evaluate the following responses of ecosystems to these events: 1) evapotranspiration and streamflow; 2) gross primary productivity; 3) the post-drought recovery of plant biomass; and 4) the forest functioning and recovery after multi-year droughts. This research is part of an integration project to examine the roles of drought, insect outbreak, and forest management activities on wildfire activity and its impacts. This project will provide improved information for forest managers and communities in the wild

Unified framework for triaxial accelerometer-based fall event detection and classification using cumulants and hierarchical decision tree classifier.

Science.gov (United States)

Kambhampati, Satya Samyukta; Singh, Vishal; Manikandan, M Sabarimalai; Ramkumar, Barathram

2015-08-01

In this Letter, the authors present a unified framework for fall event detection and classification using the cumulants extracted from the acceleration (ACC) signals acquired using a single waist-mounted triaxial accelerometer. The main objective of this Letter is to find suitable representative cumulants and classifiers in effectively detecting and classifying different types of fall and non-fall events. It was discovered that the first level of the proposed hierarchical decision tree algorithm implements fall detection using fifth-order cumulants and support vector machine (SVM) classifier. In the second level, the fall event classification algorithm uses the fifth-order cumulants and SVM. Finally, human activity classification is performed using the second-order cumulants and SVM. The detection and classification results are compared with those of the decision tree, naive Bayes, multilayer perceptron and SVM classifiers with different types of time-domain features including the second-, third-, fourth- and fifth-order cumulants and the signal magnitude vector and signal magnitude area. The experimental results demonstrate that the second- and fifth-order cumulant features and SVM classifier can achieve optimal detection and classification rates of above 95%, as well as the lowest false alarm rate of 1.03%.

Pareto Efficient Solution of Attack-Defence Trees

NARCIS (Netherlands)

Aslanyan, Zaruhi; Nielson, Flemming

Attack-defence trees are a promising approach for representing threat scenarios and possible countermeasures in a concise and intuitive manner. An attack-defence tree describes the interaction between an attacker and a defender, and is evaluated by assigning parameters to the nodes, such as

Development and application of a tree-code in simulation scenarios of the plasma-wall interaction

International Nuclear Information System (INIS)

Berberich, Benjamin

2012-03-01

Processes in the plasma edge layer of magnetic fusion devices occur on widely disparate length- and time-scales. Also recently developed features in this particular region, such as stochastic magnetic fields, underline the necessity for three dimensional, full-kinetic simulation tools. Contemporary programs often deploy ad hoc assumptions and approximations for microscopic phenomena for which self-consistent ab initio models in principle exist, but are still computationally too expensive or complex to implement. Recently, mesh-free methods have matured into a new class of tools for such first-principles computations which thanks to their geometric flexibility are highly promising for tackling complicated TOKAMAK regions. In this work we have develop the massively parallel Tree-Code PEPC-B (Pretty Efficient Parallel Coulomb solver) into a new tool for plasma material interaction studies. After a brief overview of the working principles of Tree-Codes two main topic groups are addressed: First the leap-frog Boris integration scheme is discussed and its numerical limitations are pointed out. To overcome these limitations the method is enhanced to a guiding-center integrator. As a proof of principal, numerical experiments are conducted reproducing the anticipated drift kinetic aspects of particle orbits. It turns out that this new technique is much less sensitive to large time steps than the original concept was. One major drawback of mesh-free methods which hinders their direct use for plasma-edge simulations is the difficulty in representing solid structures and associated boundary conditions. Therefore, an alternative concept is proposed using charge carrying Wall-Particles, which fits naturally in the mesh-free doctrine. These developments incorporate the second main topic group of this report. To prove the physical correctness of this new idea, a quasi one dimensional plasma-wall interface scenario is chosen. By studying the system with great detail, good agreement

[Effects of sampling plot number on tree species distribution prediction under climate change].

Science.gov (United States)

Liang, Yu; He, Hong-Shi; Wu, Zhi-Wei; Li, Xiao-Na; Luo, Xu

2013-05-01

Based on the neutral landscapes under different degrees of landscape fragmentation, this paper studied the effects of sampling plot number on the prediction of tree species distribution at landscape scale under climate change. The tree species distribution was predicted by the coupled modeling approach which linked an ecosystem process model with a forest landscape model, and three contingent scenarios and one reference scenario of sampling plot numbers were assumed. The differences between the three scenarios and the reference scenario under different degrees of landscape fragmentation were tested. The results indicated that the effects of sampling plot number on the prediction of tree species distribution depended on the tree species life history attributes. For the generalist species, the prediction of their distribution at landscape scale needed more plots. Except for the extreme specialist, landscape fragmentation degree also affected the effects of sampling plot number on the prediction. With the increase of simulation period, the effects of sampling plot number on the prediction of tree species distribution at landscape scale could be changed. For generalist species, more plots are needed for the long-term simulation.

Forestry: Prospective Scenarios for Generating Eletricity

Directory of Open Access Journals (Sweden)

Henrique Dias Blois

2017-05-01

Full Text Available Forestry generates in all production segments a lot of waste which is a potential power source and an opportunity for electricity generation by the use of this material. Therefore, this study represents the construction of future scenarios for the power generation sector from alternative and renewable sources in the region of Vale do Taquari and Alto da Serra do Botucaraí, in the Northern-Central region of the Stat of Rio Grande do Sul, aiming for the application of waste and by-products from forestry present in a intensive and tendentious way in economic activities within the region. By way of prospective scenarios, one will be able to observe which events are impactful on the viability of an environmental project for recovery of forestry waste to generate electricity in the region. Thereby, we used the method described by Grumbach (2000, a methodology that prospects scenarios from the participation of experts, who collaborated analyzing and proposing events that impact as strengths and weaknesses, opportunities and threats and their interrelationships. Also, it was evident the degree of influence and dependence between the events, which create a matrix of cross impacts. Moreover, possible future scenarios have been constructed and analyzed for demonstrating that the study area has potential events that could serve as alternatives to the sector. However, no ideal scenario has been identified for the next five years, a fact that is due to the large amount of adverse events in six out of the ten final events.

Evaluation of temporal surveillance system sensitivity and freedom from bovine viral diarrhea in Danish dairy herds using scenario tree modelling.

Science.gov (United States)

Foddai, Alessandro; Stockmarr, Anders; Boklund, Anette

2016-06-21

The temporal sensitivity of the surveillance system (TemSSe) for Bovine Viral Diarrhea (BVD) in Danish dairy herds was evaluated. Currently, the Danish antibody blocking ELISA is used to test quarterly bulk tank milk (BTM). To optimize the surveillance system as an early warning system, we considered the possibility of using the SVANOVIR ELISA, as this test has been shown to detect BVD-positive herds earlier than the blocking ELISA in BTM tests. Information from data (2010) and outputs from two published stochastic models were fed into a stochastic scenario tree to estimate the TemSSe. For that purpose we considered: the risk of BVD introduction into the dairy population, the ELISA used and the high risk period (HRP) from BVD introduction to testing (at 90 or 365 days). The effect of introducing one persistently infected (PI) calf or one transiently infected (TI) milking cow into 1 (or 8) dairy herd(s) was investigated. Additionally we estimated the confidence in low (PLow) herd prevalence (tree methodology, could be applied to optimize early warning surveillance systems of different animal diseases.

Human factors analysis and design methods for nuclear waste retrieval systems. Volume III. User's guide for the computerized event-tree analysis technique

International Nuclear Information System (INIS)

Casey, S.M.; Deretsky, Z.

1980-08-01

This document provides detailed instructions for using the Computerized Event-Tree Analysis Technique (CETAT), a program designed to assist a human factors analyst in predicting event probabilities in complex man-machine configurations found in waste retrieval systems. The instructions contained herein describe how to (a) identify the scope of a CETAT analysis, (b) develop operator performance data, (c) enter an event-tree structure, (d) modify a data base, and (e) analyze event paths and man-machine system configurations. Designed to serve as a tool for developing, organizing, and analyzing operator-initiated event probabilities, CETAT simplifies the tasks of the experienced systems analyst by organizing large amounts of data and performing cumbersome and time consuming arithmetic calculations. The principal uses of CETAT in the waste retrieval development project will be to develop models of system reliability and evaluate alternative equipment designs and operator tasks. As with any automated technique, however, the value of the output will be a function of the knowledge and skill of the analyst using the program

Calculating Nuclear Power Plant Vulnerability Using Integrated Geometry and Event/Fault-Tree Models

International Nuclear Information System (INIS)

Peplow, Douglas E.; Sulfredge, C. David; Sanders, Robert L.; Morris, Robert H.; Hann, Todd A.

2004-01-01

Since the events of September 11, 2001, the vulnerability of nuclear power plants to terrorist attacks has become a national concern. The results of vulnerability analysis are greatly influenced by the computational approaches used. Standard approximations used in fault-tree analysis are not applicable for attacks, where high component failure probabilities are expected; two methods that do work with high failure probabilities are presented. Different blast modeling approaches can also affect the end results. Modeling the structural details of facility buildings and the geometric layout of components within the buildings is required to yield meaningful results

Nonbinary Tree-Based Phylogenetic Networks.

Science.gov (United States)

Jetten, Laura; van Iersel, Leo

2018-01-01

Rooted phylogenetic networks are used to describe evolutionary histories that contain non-treelike evolutionary events such as hybridization and horizontal gene transfer. In some cases, such histories can be described by a phylogenetic base-tree with additional linking arcs, which can, for example, represent gene transfer events. Such phylogenetic networks are called tree-based. Here, we consider two possible generalizations of this concept to nonbinary networks, which we call tree-based and strictly-tree-based nonbinary phylogenetic networks. We give simple graph-theoretic characterizations of tree-based and strictly-tree-based nonbinary phylogenetic networks. Moreover, we show for each of these two classes that it can be decided in polynomial time whether a given network is contained in the class. Our approach also provides a new view on tree-based binary phylogenetic networks. Finally, we discuss two examples of nonbinary phylogenetic networks in biology and show how our results can be applied to them.

Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern piñon-juniper woodland, USA

Science.gov (United States)

2014-01-01

This study documents tree mortality in Big Bend National Park in Texas in response to the most acute one-year drought on record, which occurred following a five-day winter freeze. I estimated changes in forest stand structure and species composition due to freezing and drought in the Chisos Mountains of Big Bend National Park using permanent monitoring plot data. The drought killed over half (63%) of the sampled trees over the entire elevation gradient. Significant mortality occurred in trees up to 20 cm diameter (P Pinus cembroides Zucc. experienced the highest seedling and tree mortality (P droughts under climate change will likely cause even greater damage to trees that survived this record drought, especially if such events follow freezes. The results from this study highlight the vulnerability of trees in the Southwest to climatic change and that future shifts in forest structure can have large-scale community consequences. PMID:24949231

An integrated pipeline to create and experience compelling scenarios in virtual reality

Science.gov (United States)

Springer, Jan P.; Neumann, Carsten; Reiners, Dirk; Cruz-Neira, Carolina

2011-03-01

One of the main barriers to create and use compelling scenarios in virtual reality is the complexity and time-consuming efforts for modeling, element integration, and the software development to properly display and interact with the content in the available systems. Still today, most virtual reality applications are tedious to create and they are hard-wired to the specific display and interaction system available to the developers when creating the application. Furthermore, it is not possible to alter the content or the dynamics of the content once the application has been created. We present our research on designing a software pipeline that enables the creation of compelling scenarios with a fair degree of visual and interaction complexity in a semi-automated way. Specifically, we are targeting drivable urban scenarios, ranging from large cities to sparsely populated rural areas that incorporate both static components (e. g., houses, trees) and dynamic components (e. g., people, vehicles) as well as events, such as explosions or ambient noise. Our pipeline has four basic components. First, an environment designer, where users sketch the overall layout of the scenario, and an automated method constructs the 3D environment from the information in the sketch. Second, a scenario editor used for authoring the complete scenario, incorporate the dynamic elements and events, fine tune the automatically generated environment, define the execution conditions of the scenario, and set up any data gathering that may be necessary during the execution of the scenario. Third, a run-time environment for different virtual-reality systems provides users with the interactive experience as designed with the designer and the editor. And fourth, a bi-directional monitoring system that allows for capturing and modification of information from the virtual environment. One of the interesting capabilities of our pipeline is that scenarios can be built and modified on-the-fly as they are

Material control study: a directed graph and fault tree procedure for adversary event set generation

International Nuclear Information System (INIS)

Lambert, H.E.; Lim, J.J.; Gilman, F.M.

1978-01-01

In work for the United States Nuclear Regulatory Commission, Lawrence Livermore Laboratory is developing an assessment procedure to evaluate the effectiveness of a potential nuclear facility licensee's material control (MC) system. The purpose of an MC system is to prevent the theft of special nuclear material such as plutonium and highly enriched uranium. The key in the assessment procedure is the generation and analysis of the adversary event sets by a directed graph and fault-tree methodology

TREDRA, Minimal Cut Sets Fault Tree Plot Program

International Nuclear Information System (INIS)

Fussell, J.B.

1983-01-01

1 - Description of problem or function: TREDRA is a computer program for drafting report-quality fault trees. The input to TREDRA is similar to input for standard computer programs that find minimal cut sets from fault trees. Output includes fault tree plots containing all standard fault tree logic and event symbols, gate and event labels, and an output description for each event in the fault tree. TREDRA contains the following features: a variety of program options that allow flexibility in the program output; capability for automatic pagination of the output fault tree, when necessary; input groups which allow labeling of gates, events, and their output descriptions; a symbol library which includes standard fault tree symbols plus several less frequently used symbols; user control of character size and overall plot size; and extensive input error checking and diagnostic oriented output. 2 - Method of solution: Fault trees are generated by user-supplied control parameters and a coded description of the fault tree structure consisting of the name of each gate, the gate type, the number of inputs to the gate, and the names of these inputs. 3 - Restrictions on the complexity of the problem: TREDRA can produce fault trees with a minimum of 3 and a maximum of 56 levels. The width of each level may range from 3 to 37. A total of 50 transfers is allowed during pagination

ARAMIS project: A comprehensive methodology for the identification of reference accident scenarios in process industries

International Nuclear Information System (INIS)

Delvosalle, Christian; Fievez, Cecile; Pipart, Aurore; Debray, Bruno

2006-01-01

In the frame of the Accidental Risk Assessment Methodology for Industries (ARAMIS) project, this paper aims at presenting the work carried out in the part of the project devoted to the definition of accident scenarios. This topic is a key-point in risk assessment and serves as basis for the whole risk quantification. The first result of the work is the building of a methodology for the identification of major accident hazards (MIMAH), which is carried out with the development of generic fault and event trees based on a typology of equipment and substances. The term 'major accidents' must be understood as the worst accidents likely to occur on the equipment, assuming that no safety systems are installed. A second methodology, called methodology for the identification of reference accident scenarios (MIRAS) takes into account the influence of safety systems on both the frequencies and possible consequences of accidents. This methodology leads to identify more realistic accident scenarios. The reference accident scenarios are chosen with the help of a tool called 'risk matrix', crossing the frequency and the consequences of accidents. This paper presents both methodologies and an application on an ethylene oxide storage

Direct evaluation of fault trees using object-oriented programming techniques

Science.gov (United States)

Patterson-Hine, F. A.; Koen, B. V.

1989-01-01

Object-oriented programming techniques are used in an algorithm for the direct evaluation of fault trees. The algorithm combines a simple bottom-up procedure for trees without repeated events with a top-down recursive procedure for trees with repeated events. The object-oriented approach results in a dynamic modularization of the tree at each step in the reduction process. The algorithm reduces the number of recursive calls required to solve trees with repeated events and calculates intermediate results as well as the solution of the top event. The intermediate results can be reused if part of the tree is modified. An example is presented in which the results of the algorithm implemented with conventional techniques are compared to those of the object-oriented approach.

Deduction of probable events of lateral gene transfer through comparison of phylogenetic trees by recursive consolidation and rearrangement

Directory of Open Access Journals (Sweden)

Charlebois Robert L

2005-04-01

Full Text Available Abstract Background When organismal phylogenies based on sequences of single marker genes are poorly resolved, a logical approach is to add more markers, on the assumption that weak but congruent phylogenetic signal will be reinforced in such multigene trees. Such approaches are valid only when the several markers indeed have identical phylogenies, an issue which many multigene methods (such as the use of concatenated gene sequences or the assembly of supertrees do not directly address. Indeed, even when the true history is a mixture of vertical descent for some genes and lateral gene transfer (LGT for others, such methods produce unique topologies. Results We have developed software that aims to extract evidence for vertical and lateral inheritance from a set of gene trees compared against an arbitrary reference tree. This evidence is then displayed as a synthesis showing support over the tree for vertical inheritance, overlaid with explicit lateral gene transfer (LGT events inferred to have occurred over the history of the tree. Like splits-tree methods, one can thus identify nodes at which conflict occurs. Additionally one can make reasonable inferences about vertical and lateral signal, assigning putative donors and recipients. Conclusion A tool such as ours can serve to explore the reticulated dimensionality of molecular evolution, by dissecting vertical and lateral inheritance at high resolution. By this, we mean that individual nodes can be examined not only for congruence, but also for coherence in light of LGT. We assert that our tools will facilitate the comparison of phylogenetic trees, and the interpretation of conflicting data.

Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern piñon-juniper woodland, USA.

Science.gov (United States)

Poulos, Helen M

2014-01-01

This study documents tree mortality in Big Bend National Park in Texas in response to the most acute one-year drought on record, which occurred following a five-day winter freeze. I estimated changes in forest stand structure and species composition due to freezing and drought in the Chisos Mountains of Big Bend National Park using permanent monitoring plot data. The drought killed over half (63%) of the sampled trees over the entire elevation gradient. Significant mortality occurred in trees up to 20 cm diameter (P Quercus emoryi Leibmann also experienced significant declines in tree density (P < 0.02) (30.9% and 20.7%, respectively). Subsequent droughts under climate change will likely cause even greater damage to trees that survived this record drought, especially if such events follow freezes. The results from this study highlight the vulnerability of trees in the Southwest to climatic change and that future shifts in forest structure can have large-scale community consequences.

Simulating phenological shifts in French temperate forests under two climatic change scenarios and four driving global circulation models

Science.gov (United States)

Lebourgeois, François; Pierrat, Jean-Claude; Perez, Vincent; Piedallu, Christian; Cecchini, Sébastien; Ulrich, Erwin

2010-09-01

After modeling the large-scale climate response patterns of leaf unfolding, leaf coloring and growing season length of evergreen and deciduous French temperate trees, we predicted the effects of eight future climate scenarios on phenological events. We used the ground observations from 103 temperate forests (10 species and 3,708 trees) from the French Renecofor Network and for the period 1997-2006. We applied RandomForest algorithms to predict phenological events from climatic and ecological variables. With the resulting models, we drew maps of phenological events throughout France under present climate and under two climatic change scenarios (A2, B2) and four global circulation models (HadCM3, CGCM2, CSIRO2 and PCM). We compared current observations and predicted values for the periods 2041-2070 and 2071-2100. On average, spring development of oaks precedes that of beech, which precedes that of conifers. Annual cycles in budburst and leaf coloring are highly correlated with January, March-April and October-November weather conditions through temperature, global solar radiation or potential evapotranspiration depending on species. At the end of the twenty-first century, each model predicts earlier budburst (mean: 7 days) and later leaf coloring (mean: 13 days) leading to an average increase in the growing season of about 20 days (for oaks and beech stands). The A2-HadCM3 hypothesis leads to an increase of up to 30 days in many areas. As a consequence of higher predicted warming during autumn than during winter or spring, shifts in leaf coloring dates appear greater than trends in leaf unfolding. At a regional scale, highly differing climatic response patterns were observed.

Representing cognitive activities and errors in HRA trees

International Nuclear Information System (INIS)

Gertman, D.I.

1992-01-01

A graphic representation method is presented herein for adapting an existing technology--human reliability analysis (HRA) event trees, used to support event sequence logic structures and calculations--to include a representation of the underlying cognitive activity and corresponding errors associated with human performance. The analyst is presented with three potential means of representing human activity: the NUREG/CR-1278 HRA event tree approach; the skill-, rule- and knowledge-based paradigm; and the slips, lapses, and mistakes paradigm. The above approaches for representing human activity are integrated in order to produce an enriched HRA event tree -- the cognitive event tree system (COGENT)-- which, in turn, can be used to increase the analyst's understanding of the basic behavioral mechanisms underlying human error and the representation of that error in probabilistic risk assessment. Issues pertaining to the implementation of COGENT are also discussed

Multilocus inference of species trees and DNA barcoding.

Science.gov (United States)

Mallo, Diego; Posada, David

2016-09-05

The unprecedented amount of data resulting from next-generation sequencing has opened a new era in phylogenetic estimation. Although large datasets should, in theory, increase phylogenetic resolution, massive, multilocus datasets have uncovered a great deal of phylogenetic incongruence among different genomic regions, due both to stochastic error and to the action of different evolutionary process such as incomplete lineage sorting, gene duplication and loss and horizontal gene transfer. This incongruence violates one of the fundamental assumptions of the DNA barcoding approach, which assumes that gene history and species history are identical. In this review, we explain some of the most important challenges we will have to face to reconstruct the history of species, and the advantages and disadvantages of different strategies for the phylogenetic analysis of multilocus data. In particular, we describe the evolutionary events that can generate species tree-gene tree discordance, compare the most popular methods for species tree reconstruction, highlight the challenges we need to face when using them and discuss their potential utility in barcoding. Current barcoding methods sacrifice a great amount of statistical power by only considering one locus, and a transition to multilocus barcodes would not only improve current barcoding methods, but also facilitate an eventual transition to species-tree-based barcoding strategies, which could better accommodate scenarios where the barcode gap is too small or inexistent.This article is part of the themed issue 'From DNA barcodes to biomes'. © 2016 The Authors.

Pareto Efficient Solutions of Attack-Defence Trees

DEFF Research Database (Denmark)

Aslanyan, Zaruhi; Nielson, Flemming

2015-01-01

Attack-defence trees are a promising approach for representing threat scenarios and possible countermeasures in a concise and intuitive manner. An attack-defence tree describes the interaction between an attacker and a defender, and is evaluated by assigning parameters to the nodes, such as proba......Attack-defence trees are a promising approach for representing threat scenarios and possible countermeasures in a concise and intuitive manner. An attack-defence tree describes the interaction between an attacker and a defender, and is evaluated by assigning parameters to the nodes......, such as probability or cost of attacks and defences. In case of multiple parameters most analytical methods optimise one parameter at a time, e.g., minimise cost or maximise probability of an attack. Such methods may lead to sub-optimal solutions when optimising conflicting parameters, e.g., minimising cost while...... maximising probability. In order to tackle this challenge, we devise automated techniques that optimise all parameters at once. Moreover, in the case of conflicting parameters our techniques compute the set of all optimal solutions, defined in terms of Pareto efficiency. The developments are carried out...

THE 'TWIN-CME' SCENARIO AND LARGE SOLAR ENERGETIC PARTICLE EVENTS IN SOLAR CYCLE 23

Energy Technology Data Exchange (ETDEWEB)

Ding, Liuguan; Jiang, Yong [College of Math and Physics, Nanjing University of Information Science and Technology, Nanjing, Jiangsu 210044 (China); Zhao, Lulu; Li, Gang, E-mail: gang.li@uah.edu [Department of Physics and CSPAR, University of Alabama in Huntsville, AL 35899 (United States)

2013-01-20

Energetic particles in large solar energetic particle (SEP) events are a major concern for space weather. Recently, Li et al. proposed a 'twin-CME' scenario for ground-level events. Here we extend that study to large SEP events in solar cycle 23. Depending on whether preceding coronal mass ejections (CMEs) within 9 hr exist and whether ions >10 MeV nucleon{sup -1} exceed 10 pfu, we categorize fast CMEs with speed >900 km s{sup -1} and width >60 Degree-Sign from the western hemisphere source regions into four groups: groups I and II are 'twin' and single CMEs that lead to large SEPs; groups III and IV are 'twin' and single CMEs that do not lead to large SEPs. The major findings of this paper are: first, large SEP events tend to be 'twin-CME' events. Of 59 western large SEP events in solar cycle 23, 43 are 'twin-CME' (group I) events and 16 are single-CME (group II) events. Second, not all 'twin CMEs' produced large SEPs: 28 twin CMEs did not produce large SEPs (group III events). Some of them produced excesses of particles up to a few MeV nucleon{sup -1}. Third, there were 39 single fast CMEs that did not produce SEPs (group IV events). Some of these also showed an excess of particles up to a few MeV nucleon{sup -1}. For all four groups of events, we perform statistical analyses on properties such as the angular width, the speed, the existence of accompanying metric type II radio bursts, and the associated flare class for the main CMEs and the preceding CMEs.

Proposal for the classification of scenarios for deep geological repositories in probability classes; Vorschlag zur Einordnung von Szenarien fuer tiefe geologische Endlager in Wahrscheinlichkeitsklassen

Energy Technology Data Exchange (ETDEWEB)

Beuth, Thomas

2013-03-15

The provided report was elaborated in the framework of the project 3609R03210 ''Research and Development for Proof of the long-term Safety of Deep Geological Repositories''. It contains a proposal for a methodology that enables the assignment of developed scenarios in the frame of Safety Cases to defined probability classes. The assignment takes place indirectly through the categorization of the defining relevant factors (so-called FEP: Features, Events and Processes) of the respective scenarios also in probability classes. Therefore, decision trees and criteria were developed for the categorization of relevant factors in classes. Besides the description of the methodology another focal point of the work was the application of the method taking into account a defined scenario. By means of the scenario the different steps of the method and the decision criteria were documented, respectively. In addition, potential subjective influences along the path of decisions regarding the assignment of scenarios in probability classes were identified.

Hydroclimate variability: comparing dendroclimatic records and future GCM scenarios

International Nuclear Information System (INIS)

Lapp, S.

2008-01-01

Drought events of the 20th Century in western North America have been linked to teleconnections that influence climate variability on inter-annual and decadal to multi-decadal time scales. These teleconnections represent the changes sea surface temperatures (SSTs) in the tropical and extra-tropical regions of the Pacific Ocean, ENSO (El-Nino Southern Oscillation) and PDO (Pacific Decadal Oscillation), respectively, and the Atlantic Ocean, AMO (Atlantic Multidecadal Oscillation), and also to atmospheric circulation patterns (PNA: Pacific-North American). A network of precipitation sensitive tree-ring chronologies from Montana, Alberta, Saskatchewan and NWT highly correlate to the climate moisture index (CMI) of precipitation potential evapotranspiration (P-PET), thus, capturing the long-term hydroclimatic variability of the region. Reconstructions of annual and seasonal CMI identify drought events in previous centuries that are more extreme in magnitude, frequency and duration than recorded during the instrumental period. Variability in the future climate will include these natural climate cycles as well as modulations of these cycles affected by human induced global warming. The proxy hydroclimate records derived from tree-rings present information on decadal and multi-decadal hydroclimatic variability for the past millennium; therefore, providing a unique opportunity to validate the climate variability simulated by GCMs (Global Climate Models) on longer time scales otherwise constrained by the shorter observation records. Developing scenarios of future variability depends: 1) on our understanding of the interaction of these teleconnection; and, 2) to identify climate models that are able to accurately simulate the hydroclimatic variability as detected in the instrumental and proxy records. (author)

Restructuring of an Event Tree for a Loss of Coolant Accident in a PSA model

International Nuclear Information System (INIS)

Lim, Ho-Gon; Han, Sang-Hoon; Park, Jin-Hee; Jang, Seong-Chul

2015-01-01

Conventional risk model using PSA (probabilistic Safety Assessment) for a NPP considers two types of accident initiators for internal events, LOCA (Loss of Coolant Accident) and transient event such as Loss of electric power, Loss of cooling, and so on. Traditionally, a LOCA is divided into three initiating event (IE) categories depending on the break size, small, medium, and large LOCA. In each IE group, safety functions or systems modeled in the accident sequences are considered to be applicable regardless of the break size. However, since the safety system or functions are not designed based on a break size, there exist lots of mismatch between safety system/function and an IE, which may make the risk model conservative or in some case optimistic. Present paper proposes new methodology for accident sequence analysis for LOCA. We suggest an integrated single ET construction for LOCA by incorporating a safety system/function and its applicable break spectrum into the ET. Integrated accident sequence analysis in terms of ET for LOCA was proposed in the present paper. Safety function/system can be properly assigned if its applicable range is given by break set point. Also, using simple Boolean algebra with the subset of the break spectrum, final accident sequences are expressed properly in terms of the Boolean multiplication, the occurrence frequency and the success/failure of safety system. The accident sequence results show that the accident sequence is described more detailed compared with the conventional results. Unfortunately, the quantitative results in terms of MCS (minimal Cut-Set) was not given because system fault tree was not constructed for this analysis and the break set points for all 7 point were not given as a specified numerical quantity. Further study may be needed to fix the break set point and to develop system fault tree

Restructuring of an Event Tree for a Loss of Coolant Accident in a PSA model

Energy Technology Data Exchange (ETDEWEB)

Lim, Ho-Gon; Han, Sang-Hoon; Park, Jin-Hee; Jang, Seong-Chul [KAERI, Daejeon (Korea, Republic of)

2015-05-15

Conventional risk model using PSA (probabilistic Safety Assessment) for a NPP considers two types of accident initiators for internal events, LOCA (Loss of Coolant Accident) and transient event such as Loss of electric power, Loss of cooling, and so on. Traditionally, a LOCA is divided into three initiating event (IE) categories depending on the break size, small, medium, and large LOCA. In each IE group, safety functions or systems modeled in the accident sequences are considered to be applicable regardless of the break size. However, since the safety system or functions are not designed based on a break size, there exist lots of mismatch between safety system/function and an IE, which may make the risk model conservative or in some case optimistic. Present paper proposes new methodology for accident sequence analysis for LOCA. We suggest an integrated single ET construction for LOCA by incorporating a safety system/function and its applicable break spectrum into the ET. Integrated accident sequence analysis in terms of ET for LOCA was proposed in the present paper. Safety function/system can be properly assigned if its applicable range is given by break set point. Also, using simple Boolean algebra with the subset of the break spectrum, final accident sequences are expressed properly in terms of the Boolean multiplication, the occurrence frequency and the success/failure of safety system. The accident sequence results show that the accident sequence is described more detailed compared with the conventional results. Unfortunately, the quantitative results in terms of MCS (minimal Cut-Set) was not given because system fault tree was not constructed for this analysis and the break set points for all 7 point were not given as a specified numerical quantity. Further study may be needed to fix the break set point and to develop system fault tree.

PL-MOD: a computer code for modular fault tree analysis and evaluation

International Nuclear Information System (INIS)

Olmos, J.; Wolf, L.

1978-01-01

The computer code PL-MOD has been developed to implement the modular methodology to fault tree analysis. In the modular approach, fault tree structures are characterized by recursively relating the top tree event to all basic event inputs through a set of equations, each defining an independent modular event for the tree. The advantages of tree modularization lie in that it is a more compact representation than the minimal cut-set description and in that it is well suited for fault tree quantification because of its recursive form. In its present version, PL-MOD modularizes fault trees and evaluates top and intermediate event failure probabilities, as well as basic component and modular event importance measures, in a very efficient way. Thus, its execution time for the modularization and quantification of a PWR High Pressure Injection System reduced fault tree was 25 times faster than that necessary to generate its equivalent minimal cut-set description using the computer code MOCUS

Current and Future Distribution of the Tropical Tree Cedrela odorata L. in Mexico under Climate Change Scenarios Using MaxLike

Science.gov (United States)

Martínez Meyer, Enrique; Sánchez-Velásquez, Lázaro R.

2016-01-01

Climate change is recognized as an important threat to global biodiversity because it increases the risk of extinction of many species on the planet. Mexico is a megadiverse country and native tree species such as red cedar (Cedrela odorata) can be used to maintain forests while helping mitigate climate change, because it is considered a fast growing pioneer species with great economic potential in the forestry industry. In order to assess possible shifts in areas suitable for C. odorata plantations in Mexico with ecological niche models, we used the MaxLike algorithm, climate variables, the geo-referenced records of this species, three general circulation models and three scenarios of future emissions. Results show a current potential distribution of 573,079 km2 with an average probability of occurrence of 0.93 (± 0.13). The potential distribution area could increase up to 650,356 km2 by 2060 according to the general circulation model HADCM3 B2, with an average probability of occurrence of 0.86 (± 0.14). Finally, we delimited an area of 35,377 km2 that has a high potential for the establishment of C. odorata plantations, by selecting those sites with optimal conditions for its growth that are outside protected areas and are currently devoid of trees. C. odorata has a significant potential to help in the mitigation of the effects of climate change. Using MaxLike we identified extense areas in Mexico suitable to increase carbon sequestration through plantations of this highly valued native tree species. PMID:27732622

Current and Future Distribution of the Tropical Tree Cedrela odorata L. in Mexico under Climate Change Scenarios Using MaxLike.

Science.gov (United States)

Estrada-Contreras, Israel; Equihua, Miguel; Laborde, Javier; Martínez Meyer, Enrique; Sánchez-Velásquez, Lázaro R

2016-01-01

Climate change is recognized as an important threat to global biodiversity because it increases the risk of extinction of many species on the planet. Mexico is a megadiverse country and native tree species such as red cedar (Cedrela odorata) can be used to maintain forests while helping mitigate climate change, because it is considered a fast growing pioneer species with great economic potential in the forestry industry. In order to assess possible shifts in areas suitable for C. odorata plantations in Mexico with ecological niche models, we used the MaxLike algorithm, climate variables, the geo-referenced records of this species, three general circulation models and three scenarios of future emissions. Results show a current potential distribution of 573,079 km2 with an average probability of occurrence of 0.93 (± 0.13). The potential distribution area could increase up to 650,356 km2 by 2060 according to the general circulation model HADCM3 B2, with an average probability of occurrence of 0.86 (± 0.14). Finally, we delimited an area of 35,377 km2 that has a high potential for the establishment of C. odorata plantations, by selecting those sites with optimal conditions for its growth that are outside protected areas and are currently devoid of trees. C. odorata has a significant potential to help in the mitigation of the effects of climate change. Using MaxLike we identified extense areas in Mexico suitable to increase carbon sequestration through plantations of this highly valued native tree species.

Current and Future Distribution of the Tropical Tree Cedrela odorata L. in Mexico under Climate Change Scenarios Using MaxLike.

Directory of Open Access Journals (Sweden)

Israel Estrada-Contreras

Full Text Available Climate change is recognized as an important threat to global biodiversity because it increases the risk of extinction of many species on the planet. Mexico is a megadiverse country and native tree species such as red cedar (Cedrela odorata can be used to maintain forests while helping mitigate climate change, because it is considered a fast growing pioneer species with great economic potential in the forestry industry. In order to assess possible shifts in areas suitable for C. odorata plantations in Mexico with ecological niche models, we used the MaxLike algorithm, climate variables, the geo-referenced records of this species, three general circulation models and three scenarios of future emissions. Results show a current potential distribution of 573,079 km2 with an average probability of occurrence of 0.93 (± 0.13. The potential distribution area could increase up to 650,356 km2 by 2060 according to the general circulation model HADCM3 B2, with an average probability of occurrence of 0.86 (± 0.14. Finally, we delimited an area of 35,377 km2 that has a high potential for the establishment of C. odorata plantations, by selecting those sites with optimal conditions for its growth that are outside protected areas and are currently devoid of trees. C. odorata has a significant potential to help in the mitigation of the effects of climate change. Using MaxLike we identified extense areas in Mexico suitable to increase carbon sequestration through plantations of this highly valued native tree species.

Increased accumulation of cuticular wax and expression of lipid transfer protein in response to periodic drying events in leaves of tree tobacco.

Science.gov (United States)

Cameron, Kimberly D; Teece, Mark A; Smart, Lawrence B

2006-01-01

Cuticular wax deposition and composition affects drought tolerance and yield in plants. We examined the relationship between wax and dehydration stress by characterizing the leaf cuticular wax of tree tobacco (Nicotiana glauca L. Graham) grown under periodic dehydration stress. Total leaf cuticular wax load increased after each of three periods of dehydration stress using a CH2Cl2 extraction process. Overall, total wax load increased 1.5- to 2.5-fold, but composition of the wax was not altered. Homologous series of wax components were classified into organic groups; n-hentriacontane was the largest component (>75%) with alcohols and fatty acids representing drying event. Leaves excised from plants subjected to multiple drying events were more resistant to water loss compared to leaves excised from well-watered plants, indicating that there is a negative relationship between total wax load and epidermal conductance. Lipid transfer proteins (LTPs) are thought to be involved in the transfer of lipids through the extracellular matrix for the formation of cuticular wax. Using northern analysis, a 6-fold increase of tree tobacco LTP gene transcripts was observed after three drying events, providing further evidence that LTP is involved in cuticle deposition. The simplicity of wax composition and the dramatic wax bloom displayed by tree tobacco make this an excellent species in which to study the relationship between leaf wax deposition and drought tolerance.

Missing rings in Pinus halepensis – the missing link to relate the tree-ring record to extreme climatic events

Directory of Open Access Journals (Sweden)

Klemen eNovak

2016-05-01

Full Text Available Climate predictions for the Mediterranean Basin include increased temperatures, decreased precipitation, and increased frequency of extreme climatic events (ECE. These conditions are associated with decreased growth of trees and their increased vulnerability to pests and diseases. The anatomy of tree rings is responsive to these environmental conditions. Quantitatively, the width of a tree ring is largely determined by the rate and duration of cell division by the vascular cambium. In the Mediterranean climate, cambial cell division may occur throughout almost the entire year. Alternatively, cell division may stop during relatively cool and dry winters, only to resume in the same year with milder temperatures and increased availability of water. Under particularly adverse conditions, no xylem may be produced in parts of the stem, resulting in a missing ring (MR, which can link tree-ring anatomy to the occurrence of extreme events. A dendrochronological network of Pinus halepensis, a widespread tree species in the Mediterranean basin, was used to determine the relationship of MR to ECE. The network consisted of 113 sites throughout its distribution range. Binomial logistic regression analysis of 2595 MR series determined that MR increased in frequency with increased cambial age. Spatial analysis indicated that the geographic areas of southeastern Spain and northern Algeria contained the greatest frequency of MR. Further regression analysis indicated that the relationship of MR to total monthly precipitation and mean temperature was non-linear. In this first determination of climatic influences on MR, the formation of MR was most strongly associated with the combination of monthly mean temperature above 10°C from previous October till current February and total precipitation below 50 mm from previous September till current May. This conclusion is global and can be applied to every site across the distribution area. Rather than simply being a

Selection the Optimum Suppliers Compound Using a Mixed Model of MADM and Fault Tree Analysis

Directory of Open Access Journals (Sweden)

Meysam Azimian

2017-03-01

Full Text Available In this paper, an integrated approach of MADM and fault tree analysis (FTA is provided for determining the most reliable combination of suppliers for a strategic product in IUT University. At first, risks of suppliers is estimated by defining the indices for evaluating them, determining their relative status indices and using satisfying and SAW methods. Then, intrinsic risks of utilized equipments in the products are qualified and the final integrated risk for equipments is determined. Finally, through all the different scenarios, the best composition of equipment suppliers is selected by defining the palpable top events and fault tree analysis. The contribution of this paper is about proposing an integrated method of MADM and FTA to determine the most reliable suppliers in order to minimize the final risk of providing a product.

Paleo-event data standards for dendrochronology

Science.gov (United States)

Elaine Kennedy Sutherland; P. Brewer; W. Gross

2017-01-01

Extreme environmental events, such as storm winds, landslides, insect infestations, and wildfire, cause loss of life, resources, and human infrastructure. Disaster riskreduction analysis can be improved with information about past frequency, intensity, and spatial patterns of extreme events. Tree-ring analyses can provide such information: tree rings reflect events as...

Nervous systems and scenarios for the invertebrate-to-vertebrate transition.

Science.gov (United States)

Holland, Nicholas D

2016-01-05

Older evolutionary scenarios for the origin of vertebrates often gave nervous systems top billing in accordance with the notion that a big-brained Homo sapiens crowned a tree of life shaped mainly by progressive evolution. Now, however, tree thinking positions all extant organisms equidistant from the tree's root, and molecular phylogenies indicate that regressive evolution is more common than previously suspected. Even so, contemporary theories of vertebrate origin still focus on the nervous system because of its functional importance, its richness in characters for comparative biology, and its central position in the two currently prominent scenarios for the invertebrate-to-vertebrate transition, which grew out of the markedly neurocentric annelid and enteropneust theories of the nineteenth century. Both these scenarios compare phyla with diverse overall body plans. This diversity, exacerbated by the scarcity of relevant fossil data, makes it challenging to establish plausible homologies between component parts (e.g. nervous system regions). In addition, our current understanding of the relation between genotype and phenotype is too preliminary to permit us to convert gene network data into structural features in any simple way. These issues are discussed here with special reference to the evolution of nervous systems during proposed transitions from invertebrates to vertebrates. © 2015 The Author(s).

Rare event simulation for dynamic fault trees

NARCIS (Netherlands)

Ruijters, Enno Jozef Johannes; Reijsbergen, D.P.; de Boer, Pieter-Tjerk; Stoelinga, Mariëlle Ida Antoinette

2017-01-01

Fault trees (FT) are a popular industrial method for reliability engineering, for which Monte Carlo simulation is an important technique to estimate common dependability metrics, such as the system reliability and availability. A severe drawback of Monte Carlo simulation is that the number of

Rare Event Simulation for Dynamic Fault Trees

NARCIS (Netherlands)

Ruijters, Enno Jozef Johannes; Reijsbergen, D.P.; de Boer, Pieter-Tjerk; Stoelinga, Mariëlle Ida Antoinette; Tonetta, Stefano; Schoitsch, Erwin; Bitsch, Friedemann

2017-01-01

Fault trees (FT) are a popular industrial method for reliability engineering, for which Monte Carlo simulation is an important technique to estimate common dependability metrics, such as the system reliability and availability. A severe drawback of Monte Carlo simulation is that the number of

Representing cognitive activities and errors in HRA trees

International Nuclear Information System (INIS)

Gertman, D.I.

1992-01-01

This paper discusses development of a means by which to present cognitive information in human reliability assessment (HRA) event trees. The descriptions found in probabilistic risk assessments (PRAs) regarding the demands on, and the resulting performance of, nuclear power plant (NPP) crews often make use of the technique for human error rate prediction (THERP), which provides a mechanism, the HRA event tree, for presenting the analyst's conceptualization of the activities underlying performance and the errors associated with that performance. When using THERP, analysts have often omitted the more complex elements of human cognition from these trees. There has yet to be a concerted effort to take theory, principles, and data from cognitive psychology and wed it to the logic structure of the HRA event tree. This paper attempts to do so. The COGENT modeling scheme (cognitively based HRA event trees) adds two taxonomies to the HRA event tree proposed by Swain and Guttman. The first taxonomy, the one proposed by Norman and Reason, describes the type of error committed and implies something about the underlying cognition as well. The second of these, the Rasmussen taxonomy, provides description regarding the skill-based, rule-based, or knowledge-based behavior underlying the execution of tasks. It is not apparent and must be deduced from the pattern of errors exhibited by personnel

TSkim: A tool for skimming ROOT trees

International Nuclear Information System (INIS)

Chamont, David

2010-01-01

Like many HEP researchers, the members of the Fermi collaboration have chosen to store their experiment data within ROOT trees. A frequent activity of such physicists is the tuning of selection criteria which define the events of interest, thus cutting and pruning the ROOT trees so to extract all the data linked to those specific physical events. It is rather straightforward to write a ROOT script to skim a single kind of data, for example the raw measurements of Fermi LAT detector. This proves to be trickier if one wants to process also some simulated or analysis data at the same time, because each kind of data is structured with its own rules for what concerns file names and sizes, tree names, identification of events, etc. TSkim has been designed to facilitate this task. Thanks to a user-defined configuration file which says where to find the run and event identifications in the different kind of trees, TSkim is able to collect all the tree elements which match a given ROOT cut. The tool will also help when loading the shared libraries which describe the experiment data, or when pruning the tree branches. Initially a pair of PERL and ROOT scripts, TSkim is today a fully compiled C++ application, enclosing our ROOT know-how and offering a panel of features going far beyond the original Fermi requirements. In this manuscript, we present TSkim concepts and key features, including a new kind of event list. Any collaboration using ROOT IO could profit from the use of this tool.

Optimizing Decision Preparedness by Adapting Scenario Complexity and Automating Scenario Generation

Science.gov (United States)

Dunne, Rob; Schatz, Sae; Flore, Stephen M.; Nicholson, Denise

2011-01-01

Klein's recognition-primed decision (RPD) framework proposes that experts make decisions by recognizing similarities between current decision situations and previous decision experiences. Unfortunately, military personnel arQ often presented with situations that they have not experienced before. Scenario-based training (S8T) can help mitigate this gap. However, SBT remains a challenging and inefficient training approach. To address these limitations, the authors present an innovative formulation of scenario complexity that contributes to the larger research goal of developing an automated scenario generation system. This system will enable trainees to effectively advance through a variety of increasingly complex decision situations and experiences. By adapting scenario complexities and automating generation, trainees will be provided with a greater variety of appropriately calibrated training events, thus broadening their repositories of experience. Preliminary results from empirical testing (N=24) of the proof-of-concept formula are presented, and future avenues of scenario complexity research are also discussed.

Naive Fault Tree : formulation of the approach

NARCIS (Netherlands)

Rajabalinejad, M

2017-01-01

Naive Fault Tree (NFT) accepts a single value or a range of values for each basic event and returns values for the top event. This accommodates the need of commonly used Fault Trees (FT) for precise data making them prone to data concerns and limiting their area of application. This paper extends

Realistic modelling of external flooding scenarios - A multi-disciplinary approach

International Nuclear Information System (INIS)

Brinkman, J.L.

2014-01-01

against flooding and timing of the events into account as basis for the development and screening of flooding scenarios. Realistic modelling of external flooding scenarios in a PSA requires a multi-disciplinary approach. Next to being thoroughly familiar with the design features of the plant against flooding, like its critical elevations for safety (related) equipment and the strength of buildings, additional knowledge is necessary on design of flood protection measures as dikes and dunes, their failure behaviour and modelling. The approach does not change the basic flooding scenarios - the event tree structure - itself, but impacts the initiating event of the specific flooding scenarios. (authors)

Analyses of robot systems using fault and event trees: case studies

International Nuclear Information System (INIS)

Khodabandehloo, Koorosh

1996-01-01

Safety in the use of robotics outside factories or processing plants has become a matter of great international concern. Domestic robots and those intended to assist nurses and surgeons in hospitals are examples of cases where safety and reliability are considered critical. The safe performance of robot systems depends on many factors, including the integrity of the robot's hardware and software, the way it communicates with sensory and other production equipment, the reliable function of the safety features present and the way the robot interacts with its environment. The use of systematic techniques such as Fault and Event Tree analysis to examine the safety and reliability of a given robotic system is presented. Considerable knowledge is needed before the application of such analysis techniques can be translated into safety specifications or indeed 'fail-safe' design features of robotic systems. The skill and understanding required for the formulation of such specifications is demonstrated here based on a number of case studies

Decision tree analysis of treatment strategies for mild and moderate cases of clinical mastitis occurring in early lactation.

Science.gov (United States)

Pinzón-Sánchez, C; Cabrera, V E; Ruegg, P L

2011-04-01

The objective of this study was to develop a decision tree to evaluate the economic impact of different durations of intramammary treatment for the first case of mild or moderate clinical mastitis (CM) occurring in early lactation with various scenarios of pathogen distributions and use of on-farm culture. The tree included 2 decision and 3 probability events. The first decision evaluated use of on-farm culture (OFC; 2 programs using OFC and 1 not using OFC) and the second decision evaluated treatment strategies (no intramammary antimicrobials or antimicrobials administered for 2, 5, or 8 d). The tree included probabilities for the distribution of etiologies (gram-positive, gram-negative, or no growth), bacteriological cure, and recurrence. The economic consequences of mastitis included costs of diagnosis and initial treatment, additional treatments, labor, discarded milk, milk production losses due to clinical and subclinical mastitis, culling, and transmission of infection to other cows (only for CM caused by Staphylococcus aureus). Pathogen-specific estimates for bacteriological cure and milk losses were used. The economically optimal path for several scenarios was determined by comparison of expected monetary values. For most scenarios, the optimal economic strategy was to treat CM caused by gram-positive pathogens for 2 d and to avoid antimicrobials for CM cases caused by gram-negative pathogens or when no pathogen was recovered. Use of extended intramammary antimicrobial therapy (5 or 8 d) resulted in the least expected monetary values. Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

Selective Tree-ring Models: A Novel Method for Reconstructing Streamflow Using Tree Rings

Science.gov (United States)

Foard, M. B.; Nelson, A. S.; Harley, G. L.

2017-12-01

Surface water is among the most instrumental and vulnerable resources in the Northwest United States (NW). Recent observations show that overall water quantity is declining in streams across the region, while extreme flooding events occur more frequently. Historical streamflow models inform probabilities of extreme flow events (flood or drought) by describing frequency and duration of past events. There are numerous examples of tree-rings being utilized to reconstruct streamflow in the NW. These models confirm that tree-rings are highly accurate at predicting streamflow, however there are many nuances that limit their applicability through time and space. For example, most models predict streamflow from hydrologically altered rivers (e.g. dammed, channelized) which may hinder our ability to predict natural prehistoric flow. They also have a tendency to over/under-predict extreme flow events. Moreover, they often neglect to capture the changing relationships between tree-growth and streamflow over time and space. To address these limitations, we utilized national tree-ring and streamflow archives to investigate the relationships between the growth of multiple coniferous species and free-flowing streams across the NW using novel species-and site-specific streamflow models - a term we coined"selective tree-ring models." Correlation function analysis and regression modeling were used to evaluate the strengths and directions of the flow-growth relationships. Species with significant relationships in the same direction were identified as strong candidates for selective models. Temporal and spatial patterns of these relationships were examined using running correlations and inverse distance weighting interpolation, respectively. Our early results indicate that (1) species adapted to extreme climates (e.g. hot-dry, cold-wet) exhibit the most consistent relationships across space, (2) these relationships weaken in locations with mild climatic variability, and (3) some

Tree mortality from a short-duration freezing event and global-change-type drought in a Southwestern piñon-juniper woodland, USA

Directory of Open Access Journals (Sweden)

Helen M. Poulos

2014-06-01

Full Text Available This study documents tree mortality in Big Bend National Park in Texas in response to the most acute one-year drought on record, which occurred following a five-day winter freeze. I estimated changes in forest stand structure and species composition due to freezing and drought in the Chisos Mountains of Big Bend National Park using permanent monitoring plot data. The drought killed over half (63% of the sampled trees over the entire elevation gradient. Significant mortality occurred in trees up to 20 cm diameter (P < 0.05. Pinus cembroides Zucc. experienced the highest seedling and tree mortality (P < 0.0001 (55% of piñon pines died, and over five times as many standing dead pines were observed in 2012 than in 2009. Juniperus deppeana vonSteudal and Quercus emoryi Leibmann also experienced significant declines in tree density (P < 0.02 (30.9% and 20.7%, respectively. Subsequent droughts under climate change will likely cause even greater damage to trees that survived this record drought, especially if such events follow freezes. The results from this study highlight the vulnerability of trees in the Southwest to climatic change and that future shifts in forest structure can have large-scale community consequences.

Advanced features of the fault tree solver FTREX

International Nuclear Information System (INIS)

Jung, Woo Sik; Han, Sang Hoon; Ha, Jae Joo

2005-01-01

This paper presents advanced features of a fault tree solver FTREX (Fault Tree Reliability Evaluation eXpert). Fault tree analysis is one of the most commonly used methods for the safety analysis of industrial systems especially for the probabilistic safety analysis (PSA) of nuclear power plants. Fault trees are solved by the classical Boolean algebra, conventional Binary Decision Diagram (BDD) algorithm, coherent BDD algorithm, and Bayesian networks. FTREX could optionally solve fault trees by the conventional BDD algorithm or the coherent BDD algorithm and could convert the fault trees into the form of the Bayesian networks. The algorithm based on the classical Boolean algebra solves a fault tree and generates MCSs. The conventional BDD algorithm generates a BDD structure of the top event and calculates the exact top event probability. The BDD structure is a factorized form of the prime implicants. The MCSs of the top event could be extracted by reducing the prime implicants in the BDD structure. The coherent BDD algorithm is developed to overcome the shortcomings of the conventional BDD algorithm such as the huge memory requirements and a long run time

Scenarios for the assessment of urban exposures after radioactive contamination

International Nuclear Information System (INIS)

Silva, D.N.G.; Guimarães, J.R.D.; Rochedo, E.R.R.

2015-01-01

Accidents involving radioactive material are not frequent but may include releases of radionuclides to the air, land or waterways. These releases are usually uncontrollable and may lead to doses in the public in excess of the reference levels established by regulations defined by the national regulatory agencies of each country. Although they had occurred sporadically since the last century, it was observed that, after the emergency phase, the public concern is enhanced when they feel that there is an unpreparedness of authorities responsible for remediation actions, due to the lack of definition of strategies to be adopted in the long term after such events. The aim of this work is to describe reference urban scenarios, considering the characteristics observed in residential and free access areas of urban centers. These scenarios were developed based on the counties surrounding the Brazilian nuclear power plant. Considering the counties within 50 km from the nuclear power plant, nine belong to the state of Rio de Janeiro and seven belong to São Paulo state; the highest population densities were observed in five counties of Rio de Janeiro. Based on the different types of residences and outdoor areas observed in these 16 counties, six reference scenarios for urban areas were developed including areas comprised by four types of residential houses (with low, medium and high shielding building material and houses in a row), apartments in buildings, and park areas with lawn and trees. The characteristics of each of these scenarios were raised through Google Earth images considering 1 km 2 of different locations comprised by each type of area defined. In a next step, the information obtained in each scenario shall be used in computer simulations to characterize the effects and consequences on public exposure of the application of decontamination procedures. (authors)

Fault tree analysis of loss of cooling to a HALW storage tank

International Nuclear Information System (INIS)

Nomura, Yasushi

1992-01-01

Results of a scenario identification, a fault tree construction and an analysis for a loss of cooling accident in a High Activity Liquid Waste (HALW) tank of a typical model of reprocessing facility, is rendered together with considerations of the system reliability improvement by changing the model design. Model plant data, basic failure frequency data and a fault tree analysis named FTL have been introduced from NUKEM GmbH, Germany. They are throughly reviewed and reevaluated at JAERI, and improved to apply to Japanese facilities. A general systematic method for constructing fault trees is used to avoid missing scenarios, thus all of the 10 conceivable accident scenarios for 'HALW storage tank without cooling, HALW boiling' are identified, and a total failure frequency are calculated to be in the 90 % confidence interval of (1.1 ∼ 5.8) x 10 -6 /yr for the German model plant. (author)

Scenario group summary

International Nuclear Information System (INIS)

Thorndike, A.

1976-01-01

A scenario is given for ISABELLE which provides a plausible sequence of events from FY 1980 to 1990. No doubt reality will be quite different. The scenario is based on the construction schedule of the 1976 proposal. Assembly and testing of the accelerator will occur until the end of FY 1983, and the next six years will provide pp interactions for the initial high energy physics research. By 1990 any temporary conditions associated with start-up of ISABELLE should be a thing of the past and all experimental capabilities fully utilized

Scenario group summary

International Nuclear Information System (INIS)

Thorndike, A.

1976-01-01

The scenario is given which provides a plausible sequence of events for ISABELLE from FY 1980 to 1990. No doubt reality will be quite different. The scenario is based on the construction schedule of the 1976 proposal. Assembly and testing of the accelerator will occur until the end of FY 1983, and the next six years will provide pp interactions for the initial high energy physics research. By 1990 any temporary conditions associated with start-up of ISABELLE should be a thing of the past and all experimental capabilities fully utilized

Evaluation of the cost-effectiveness of bovine brucellosis surveillance in a disease-free country using stochastic scenario tree modelling.

Directory of Open Access Journals (Sweden)

Viviane Hénaux

Full Text Available Surveillance systems of exotic infectious diseases aim to ensure transparency about the country-specific animal disease situation (i.e. demonstrate disease freedom and to identify any introductions. In a context of decreasing resources, evaluation of surveillance efficiency is essential to help stakeholders make relevant decisions about prioritization of measures and funding allocation. This study evaluated the efficiency (sensitivity related to cost of the French bovine brucellosis surveillance system using stochastic scenario tree models. Cattle herds were categorized into three risk groups based on the annual number of purchases, given that trading is considered as the main route of brucellosis introduction in cattle herds. The sensitivity in detecting the disease and the costs of the current surveillance system, which includes clinical (abortion surveillance, programmed serological testing and introduction controls, were compared to those of 19 alternative surveillance scenarios. Surveillance costs included veterinary fees and laboratory analyses. The sensitivity over a year of the current surveillance system was predicted to be 91±7% at a design prevalence of 0.01% for a total cost of 14.9±1.8 million €. Several alternative surveillance scenarios, based on clinical surveillance and random or risk-based serological screening in a sample (20% of the population, were predicted to be at least as sensitive but for a lower cost. Such changes would reduce whole surveillance costs by 20 to 61% annually, and the costs for farmers only would be decreased from about 12.0 million € presently to 5.3-9.0 million € (i.e. 25-56% decrease. Besides, fostering the evolution of the surveillance system in one of these directions would be in agreement with the European regulations and farmers perceptions on brucellosis risk and surveillance.

Evaluation of the cost-effectiveness of bovine brucellosis surveillance in a disease-free country using stochastic scenario tree modelling.

Science.gov (United States)

Hénaux, Viviane; Calavas, Didier

2017-01-01

Surveillance systems of exotic infectious diseases aim to ensure transparency about the country-specific animal disease situation (i.e. demonstrate disease freedom) and to identify any introductions. In a context of decreasing resources, evaluation of surveillance efficiency is essential to help stakeholders make relevant decisions about prioritization of measures and funding allocation. This study evaluated the efficiency (sensitivity related to cost) of the French bovine brucellosis surveillance system using stochastic scenario tree models. Cattle herds were categorized into three risk groups based on the annual number of purchases, given that trading is considered as the main route of brucellosis introduction in cattle herds. The sensitivity in detecting the disease and the costs of the current surveillance system, which includes clinical (abortion) surveillance, programmed serological testing and introduction controls, were compared to those of 19 alternative surveillance scenarios. Surveillance costs included veterinary fees and laboratory analyses. The sensitivity over a year of the current surveillance system was predicted to be 91±7% at a design prevalence of 0.01% for a total cost of 14.9±1.8 million €. Several alternative surveillance scenarios, based on clinical surveillance and random or risk-based serological screening in a sample (20%) of the population, were predicted to be at least as sensitive but for a lower cost. Such changes would reduce whole surveillance costs by 20 to 61% annually, and the costs for farmers only would be decreased from about 12.0 million € presently to 5.3-9.0 million € (i.e. 25-56% decrease). Besides, fostering the evolution of the surveillance system in one of these directions would be in agreement with the European regulations and farmers perceptions on brucellosis risk and surveillance.

Paleoflood Data, Extreme Floods and Frequency: Data and Models for Dam Safety Risk Scenarios

Science.gov (United States)

England, J. F.; Godaire, J.; Klinger, R.

2007-12-01

Extreme floods and probability estimates are crucial components in dam safety risk analysis and scenarios for water-resources decision making. The field-based collection of paleoflood data provides needed information on the magnitude and probability of extreme floods at locations of interest in a watershed or region. The stratigraphic record present along streams in the form of terrace and floodplain deposits represent direct indicators of the magnitude of large floods on a river, and may provide 10 to 100 times longer records than conventional stream gaging records of large floods. Paleoflood data is combined with gage and historical streamflow estimates to gain insights to flood frequency scaling, model extrapolations and uncertainty, and provide input scenarios to risk analysis event trees. We illustrate current data collection and flood frequency modeling approaches via case studies in the western United States, including the American River in California and the Arkansas River in Colorado. These studies demonstrate the integration of applied field geology, hydraulics, and surface-water hydrology. Results from these studies illustrate the gains in information content on extreme floods, provide data- based means to separate flood generation processes, guide flood frequency model extrapolations, and reduce uncertainties. These data and scenarios strongly influence water resources management decisions.

Meteorological Factors and Tree Characteristics Influencing the Initiation and Rate of Stemflow from Deciduous Trees in an Urban Park

Science.gov (United States)

Schooling, J. T.; Carlyle-Moses, D. E.

2013-12-01

Stemflow, SF, represents that portion of precipitation that is intercepted by a tree's canopy and diverted to the ground at the tree base by flowing along branches and down the bole. The focused input of water and nutrients associated with SF have been shown to be of hydrological and biogeochemical importance in a number of plant communities and forest environments. Although the concentrated water volume and the nutrient / pollutant fluxes associated with SF in urban areas may be highly relevant for stormwater quantity and quality management, they have received only minor study in built environments. In an urban park in Kamloops, British Columbia, Canada, SF volumes generated from 40 deciduous trees representing 22 species were sampled on a precipitation event basis over a period of 16 months. Using this data, we derived the threshold rainfall depth required for SF initiation from each tree by taking the absolute value of the y-intercept of the linear regression of SF volume versus rainfall depth divided by the slope of that regression. The SF discharge rate once the threshold rainfall depth had been reached was taken as the slope of the linear regression equation. Thus, a simplified SF equation was developed: SFv = QSF x (Pg = Pg''), where SFv is stemflow volume (litres), QSF is the discharge rate (litres / mm), and Pg and Pg' represent the precipitation depth and the threshold precipitation depth, respectively. We then examined the influence of meteorological factors (precipitation type [rain / snow / rain + snow], precipitation depth, rainfall intensity, wind speed and direction, and vapour pressure deficit), and tree characteristics (tree diameter at breast height, tree height, leaf size and orientation, bark roughness, crown projection area, leaf area index, canopy cover fraction, branching angle, the proportion of the crown that was comprised of branches, and overlap with other tree canopies) on QSF and Pg' in order to expand on the simplified model and

Functional Traits and Water Transport Strategies in Lowland Tropical Rainforest Trees

Science.gov (United States)

Apgaua, Deborah M. G.; Ishida, Françoise Y.; Tng, David Y. P.; Laidlaw, Melinda J.; Santos, Rubens M.; Rumman, Rizwana; Eamus, Derek; Holtum, Joseph A. M.; Laurance, Susan G. W.

2015-01-01

Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species’ hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios. PMID:26087009

Functional Traits and Water Transport Strategies in Lowland Tropical Rainforest Trees.

Directory of Open Access Journals (Sweden)

Deborah M G Apgaua

Full Text Available Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees. We characterised the species' hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios.

Functional Traits and Water Transport Strategies in Lowland Tropical Rainforest Trees.

Science.gov (United States)

Apgaua, Deborah M G; Ishida, Françoise Y; Tng, David Y P; Laidlaw, Melinda J; Santos, Rubens M; Rumman, Rizwana; Eamus, Derek; Holtum, Joseph A M; Laurance, Susan G W

2015-01-01

Understanding how tropical rainforest trees may respond to the precipitation extremes predicted in future climate change scenarios is paramount for their conservation and management. Tree species clearly differ in drought susceptibility, suggesting that variable water transport strategies exist. Using a multi-disciplinary approach, we examined the hydraulic variability in trees in a lowland tropical rainforest in north-eastern Australia. We studied eight tree species representing broad plant functional groups (one palm and seven eudicot mature-phase, and early-successional trees). We characterised the species' hydraulic system through maximum rates of volumetric sap flow and velocities using the heat ratio method, and measured rates of tree growth and several stem, vessel, and leaf traits. Sap flow measures exhibited limited variability across species, although early-successional species and palms had high mean sap velocities relative to most mature-phase species. Stem, vessel, and leaf traits were poor predictors of sap flow measures. However, these traits exhibited different associations in multivariate analysis, revealing gradients in some traits across species and alternative hydraulic strategies in others. Trait differences across and within tree functional groups reflect variation in water transport and drought resistance strategies. These varying strategies will help in our understanding of changing species distributions under predicted drought scenarios.

Development and application of a tree-code in simulation scenarios of the plasma-wall interaction; Entwicklung und Anwendung eines Tree-Codes in Simulationsszenarios der Plasma-Wand-Wechselwirkung

Energy Technology Data Exchange (ETDEWEB)

Berberich, Benjamin

2012-03-15

Processes in the plasma edge layer of magnetic fusion devices occur on widely disparate length- and time-scales. Also recently developed features in this particular region, such as stochastic magnetic fields, underline the necessity for three dimensional, full-kinetic simulation tools. Contemporary programs often deploy ad hoc assumptions and approximations for microscopic phenomena for which self-consistent ab initio models in principle exist, but are still computationally too expensive or complex to implement. Recently, mesh-free methods have matured into a new class of tools for such first-principles computations which thanks to their geometric flexibility are highly promising for tackling complicated TOKAMAK regions. In this work we have develop the massively parallel Tree-Code PEPC-B (Pretty Efficient Parallel Coulomb solver) into a new tool for plasma material interaction studies. After a brief overview of the working principles of Tree-Codes two main topic groups are addressed: First the leap-frog Boris integration scheme is discussed and its numerical limitations are pointed out. To overcome these limitations the method is enhanced to a guiding-center integrator. As a proof of principal, numerical experiments are conducted reproducing the anticipated drift kinetic aspects of particle orbits. It turns out that this new technique is much less sensitive to large time steps than the original concept was. One major drawback of mesh-free methods which hinders their direct use for plasma-edge simulations is the difficulty in representing solid structures and associated boundary conditions. Therefore, an alternative concept is proposed using charge carrying Wall-Particles, which fits naturally in the mesh-free doctrine. These developments incorporate the second main topic group of this report. To prove the physical correctness of this new idea, a quasi one dimensional plasma-wall interface scenario is chosen. By studying the system with great detail, good agreement

Implementation of Tree and Butterfly Barriers with Optimistic Time Management Algorithms for Discrete Event Simulation

Science.gov (United States)

Rizvi, Syed S.; Shah, Dipali; Riasat, Aasia

The Time Wrap algorithm [3] offers a run time recovery mechanism that deals with the causality errors. These run time recovery mechanisms consists of rollback, anti-message, and Global Virtual Time (GVT) techniques. For rollback, there is a need to compute GVT which is used in discrete-event simulation to reclaim the memory, commit the output, detect the termination, and handle the errors. However, the computation of GVT requires dealing with transient message problem and the simultaneous reporting problem. These problems can be dealt in an efficient manner by the Samadi's algorithm [8] which works fine in the presence of causality errors. However, the performance of both Time Wrap and Samadi's algorithms depends on the latency involve in GVT computation. Both algorithms give poor latency for large simulation systems especially in the presence of causality errors. To improve the latency and reduce the processor ideal time, we implement tree and butterflies barriers with the optimistic algorithm. Our analysis shows that the use of synchronous barriers such as tree and butterfly with the optimistic algorithm not only minimizes the GVT latency but also minimizes the processor idle time.

Lognormal Approximations of Fault Tree Uncertainty Distributions.

Science.gov (United States)

El-Shanawany, Ashraf Ben; Ardron, Keith H; Walker, Simon P

2018-01-26

Fault trees are used in reliability modeling to create logical models of fault combinations that can lead to undesirable events. The output of a fault tree analysis (the top event probability) is expressed in terms of the failure probabilities of basic events that are input to the model. Typically, the basic event probabilities are not known exactly, but are modeled as probability distributions: therefore, the top event probability is also represented as an uncertainty distribution. Monte Carlo methods are generally used for evaluating the uncertainty distribution, but such calculations are computationally intensive and do not readily reveal the dominant contributors to the uncertainty. In this article, a closed-form approximation for the fault tree top event uncertainty distribution is developed, which is applicable when the uncertainties in the basic events of the model are lognormally distributed. The results of the approximate method are compared with results from two sampling-based methods: namely, the Monte Carlo method and the Wilks method based on order statistics. It is shown that the closed-form expression can provide a reasonable approximation to results obtained by Monte Carlo sampling, without incurring the computational expense. The Wilks method is found to be a useful means of providing an upper bound for the percentiles of the uncertainty distribution while being computationally inexpensive compared with full Monte Carlo sampling. The lognormal approximation method and Wilks's method appear attractive, practical alternatives for the evaluation of uncertainty in the output of fault trees and similar multilinear models. © 2018 Society for Risk Analysis.

Tree-ring based reconstruction of the seasonal timing, major events and origin of rockfall on a case-study slope in the Swiss Alps

Directory of Open Access Journals (Sweden)

D. M. Schneuwly

2008-03-01

Full Text Available Tree-ring analysis has been used to reconstruct 22 years of rockfall behavior on an active rockfall slope near Saas Balen (Swiss Alps. We analyzed 32 severely injured trees (L. decidua, P. abies and P. cembra and investigated cross-sections of 154 wounds.

The intra-annual position of callus tissue and of tangential rows of traumatic resin ducts was determined in order to reconstruct the seasonality of past rockfall events. Results indicate strong intra- and inter-annual variations of rockfall activity, with a peak (76% observed in the dormant season (early October – end of May. Within the growth season, rockfall regularly occurs between the end of May and mid July (21.4%, whereas events later in the season appear to be quite rare (2.6%. Findings suggest that rockfall activity at the study site is driven by annual thawing processes and the circulation of melt water in preexisting fissures. Data also indicate that 43% of all rockfall events occurred in 1995, when two major precipitation events are recorded in nearby meteorological stations. Finally, data on impact angles are in very good agreement with the geomorphic situation in the field.

Quantitative Verification and Synthesis of Attack-Defence Scenarios Conference

NARCIS (Netherlands)

Aslanyan, Zaruhi; Nielson, Flemming; Parker, David

Attack-defence trees are a powerful technique for formally evaluating attack-defence scenarios. They represent in an intuitive, graphical way the interaction between an attacker and a defender who compete in order to achieve conflicting objectives. We propose a novel framework for the formal

Developing an event-tree probabilistic tsunami inundation model for NE Atlantic coasts: Application to case studies

Science.gov (United States)

Omira, Rachid; Baptista, Maria Ana; Matias, Luis

2015-04-01

This study constitutes the first assessment of probabilistic tsunami inundation in the NE Atlantic region, using an event-tree approach. It aims to develop a probabilistic tsunami inundation approach for the NE Atlantic coast with an application to two test sites of ASTARTE project, Tangier-Morocco and Sines-Portugal. Only tsunamis of tectonic origin are considered here, taking into account near-, regional- and far-filed sources. The multidisciplinary approach, proposed here, consists of an event-tree method that gathers seismic hazard assessment, tsunami numerical modelling, and statistical methods. It presents also a treatment of uncertainties related to source location and tidal stage in order to derive the likelihood of tsunami flood occurrence and exceedance of a specific near-shore wave height during a given return period. We derive high-resolution probabilistic maximum wave heights and flood distributions for both test-sites Tangier and Sines considering 100-, 500-, and 1000-year return periods. We find that the probability that a maximum wave height exceeds 1 m somewhere along the Sines coasts reaches about 55% for 100-year return period, and is up to 100% for 1000-year return period. Along Tangier coast, the probability of inundation occurrence (flow depth > 0m) is up to 45% for 100-year return period and reaches 96% in some near-shore costal location for 500-year return period. Acknowledgements: This work is funded by project ASTARTE - Assessment, STrategy And Risk Reduction for Tsunamis in Europe. Grant 603839, 7th FP (ENV.2013.6.4-3 ENV.2013.6.4-3).

Adaptation of Chain Event Graphs for use with Case-Control Studies in Epidemiology.

Science.gov (United States)

Keeble, Claire; Thwaites, Peter Adam; Barber, Stuart; Law, Graham Richard; Baxter, Paul David

2017-09-26

Case-control studies are used in epidemiology to try to uncover the causes of diseases, but are a retrospective study design known to suffer from non-participation and recall bias, which may explain their decreased popularity in recent years. Traditional analyses report usually only the odds ratio for given exposures and the binary disease status. Chain event graphs are a graphical representation of a statistical model derived from event trees which have been developed in artificial intelligence and statistics, and only recently introduced to the epidemiology literature. They are a modern Bayesian technique which enable prior knowledge to be incorporated into the data analysis using the agglomerative hierarchical clustering algorithm, used to form a suitable chain event graph. Additionally, they can account for missing data and be used to explore missingness mechanisms. Here we adapt the chain event graph framework to suit scenarios often encountered in case-control studies, to strengthen this study design which is time and financially efficient. We demonstrate eight adaptations to the graphs, which consist of two suitable for full case-control study analysis, four which can be used in interim analyses to explore biases, and two which aim to improve the ease and accuracy of analyses. The adaptations are illustrated with complete, reproducible, fully-interpreted examples, including the event tree and chain event graph. Chain event graphs are used here for the first time to summarise non-participation, data collection techniques, data reliability, and disease severity in case-control studies. We demonstrate how these features of a case-control study can be incorporated into the analysis to provide further insight, which can help to identify potential biases and lead to more accurate study results.

Multi scenario seismic hazard assessment for Egypt

Science.gov (United States)

Mostafa, Shaimaa Ismail; Abd el-aal, Abd el-aziz Khairy; El-Eraki, Mohamed Ahmed

2018-05-01

Egypt is located in the northeastern corner of Africa within a sensitive seismotectonic location. Earthquakes are concentrated along the active tectonic boundaries of African, Eurasian, and Arabian plates. The study area is characterized by northward increasing sediment thickness leading to more damage to structures in the north due to multiple reflections of seismic waves. Unfortunately, man-made constructions in Egypt were not designed to resist earthquake ground motions. So, it is important to evaluate the seismic hazard to reduce social and economic losses and preserve lives. The probabilistic seismic hazard assessment is used to evaluate the hazard using alternative seismotectonic models within a logic tree framework. Alternate seismotectonic models, magnitude-frequency relations, and various indigenous attenuation relationships were amended within a logic tree formulation to compute and develop the regional exposure on a set of hazard maps. Hazard contour maps are constructed for peak ground acceleration as well as 0.1-, 0.2-, 0.5-, 1-, and 2-s spectral periods for 100 and 475 years return periods for ground motion on rock. The results illustrate that Egypt is characterized by very low to high seismic activity grading from the west to the eastern part of the country. The uniform hazard spectra are estimated at some important cities distributed allover Egypt. The deaggregation of seismic hazard is estimated at some cities to identify the scenario events that contribute to a selected seismic hazard level. The results of this study can be used in seismic microzonation, risk mitigation, and earthquake engineering purposes.

Development of a parametric containment event tree model for a severe BWR accident

Energy Technology Data Exchange (ETDEWEB)

Okkonen, T [OTO-Consulting Ay, Helsinki (Finland)

1995-04-01

A containment event tree (CET) is built for analysis of severe accidents at the TVO boiling water reactor (BWR) units. Parametric models of severe accident progression and fission product behaviour are developed and integrated in order to construct a compact and self-contained Level 2 PSA model. The model can be easily updated to correspond to new research results. The analyses of the study are limited to severe accidents starting from full-power operation and leading to core melting, and are focused mainly on the use and effects of the dedicated severe accident management (SAM) systems. Severe accident progression from eight plant damage states (PDS), involving different pre-core-damage accident evolution, is examined, but the inclusion of their relative or absolute probabilities, by integration with Level 1, is deferred to integral safety assessments. (33 refs., 5 figs., 7 tabs.).

Developing an Event-Tree Probabilistic Tsunami Inundation Model for NE Atlantic Coasts: Application to a Case Study

Science.gov (United States)

Omira, R.; Matias, L.; Baptista, M. A.

2016-12-01

This study constitutes a preliminary assessment of probabilistic tsunami inundation in the NE Atlantic region. We developed an event-tree approach to calculate the likelihood of tsunami flood occurrence and exceedance of a specific near-shore wave height for a given exposure time. Only tsunamis of tectonic origin are considered here, taking into account local, regional, and far-field sources. The approach used here consists of an event-tree method that gathers probability models for seismic sources, tsunami numerical modeling, and statistical methods. It also includes a treatment of aleatoric uncertainties related to source location and tidal stage. Epistemic uncertainties are not addressed in this study. The methodology is applied to the coastal test-site of Sines located in the NE Atlantic coast of Portugal. We derive probabilistic high-resolution maximum wave amplitudes and flood distributions for the study test-site considering 100- and 500-year exposure times. We find that the probability that maximum wave amplitude exceeds 1 m somewhere along the Sines coasts reaches about 60 % for an exposure time of 100 years and is up to 97 % for an exposure time of 500 years. The probability of inundation occurrence (flow depth >0 m) varies between 10 % and 57 %, and from 20 % up to 95 % for 100- and 500-year exposure times, respectively. No validation has been performed here with historical tsunamis. This paper illustrates a methodology through a case study, which is not an operational assessment.

FTREX Testing Report (Fault Tree Reliability Evaluation eXpert) Version 1.5

International Nuclear Information System (INIS)

Jung, Woo Sik

2009-07-01

In order to verify FTREX functions and to confirm the correctness of FTREX 1.5, various tests were performed 1.fault trees with negates 2.fault trees with house events 3.fault trees with multiple tops 4.fault trees with logical loops 5.fault trees with initiators, house events, negates, logical loops, and flag events By using the automated cutest propagation test, the FTREX 1.5 functions are verified. FTREX version 1.3 and later versions have capability to perform bottom-up cutset-propagation test in order check cutest status. FTREX 1.5 always generates the proper minimal cut sets. All the output cutsets of the tested problems are MCSs (Minimal Cut Sets) and have no non-minimal cutsets and improper cutsets. The improper cutsets are those that have no effect to top, have multiple initiators, or have disjoint events A * -A

Fast admixture analysis and population tree estimation for SNP and NGS data

DEFF Research Database (Denmark)

Cheng, Jade Yu; Mailund, Thomas; Nielsen, Rasmus

2017-01-01

assumption for identifying ancestry components correctly and for inferring the correct tree. In most cases, ancestry components are inferred correctly, although sample sizes and times since admixture can influence the results. We show that the popular Gaussian approximation tends to perform poorly under......-calling associated with Next Generation Sequencing (NGS) data. We also present a new method for estimating population trees from ancestry components using a Gaussian approximation. Using coalescence simulations of diverging populations, we explore the adequacy of the STRUCTURE-style models and the Gaussian...... extreme divergence scenarios e.g. with very long branch lengths, but the topologies of the population trees are accurately inferred in all scenarios explored. The new methods are implemented together with appropriate visualization tools in the software package Ohana....

Neoendemism in Madagascan scaly tree ferns results from recent, coincident diversification bursts.

Science.gov (United States)

Janssen, Thomas; Bystriakova, Nadia; Rakotondrainibe, France; Coomes, David; Labat, Jean-Noël; Schneider, Harald

2008-08-01

More than 80% of Madagascar's 12,000 plant species are endemic with the degree of endemism reaching as much as 95% in the scaly tree ferns, an important species rich component of Madagascar's evergreen rainforests. Predominantly African or Asian ancestry and divergence times usually postdating the separation of Madagascar from the Gondwanan landmasses have been demonstrated for several Madagascan animal and angiosperm groups. However, evolutionary studies of rainforest-specific lineages are scarce and the ecological context of radiation events has rarely been investigated. Here, we examine the evolution of Madagascan tree ferns as a rainforest-specific model family, integrate results from bioclimatic niche analysis with a dated phylogenetic framework, and propose an evolutionary scenario casting new light on our knowledge of the evolution of large island endemic clades. We show that Madagascar's extant tree fern diversity springs from three distinct ancestors independently colonizing Madagascar in the Miocene and that these three monophyletic clades diversified in three coincident radiation bursts during the Pliocene, reaching exceptionally high diversification rates and most likely responding to a common climatic trigger. Recent diversification bursts may thus have played a major role in the evolution of the extant Madagascan rainforest biome, which hence contains a significant number of young, neoendemic taxa.

The Studies of Decision Tree in Estimation of Breast Cancer Risk by Using Polymorphism Nucleotide

Directory of Open Access Journals (Sweden)

Frida Seyedmir

2017-07-01

Full Text Available Abstract Introduction:   Decision tree is the data mining tools to collect, accurate prediction and sift information from massive amounts of data that are used widely in the field of computational biology and bioinformatics. In bioinformatics can be predict on diseases, including breast cancer. The use of genomic data including single nucleotide polymorphisms is a very important factor in predicting the risk of diseases. The number of seven important SNP among hundreds of thousands genetic markers were identified as factors associated with breast cancer. The objective of this study is to evaluate the training data on decision tree predictor error of the risk of breast cancer by using single nucleotide polymorphism genotype. Methods: The risk of breast cancer were calculated associated with the use of SNP formula:xj = fo * In human,  The decision tree can be used To predict the probability of disease using single nucleotide polymorphisms .Seven SNP with different odds ratio associated with breast cancer considered and coding and design of decision tree model, C4.5, by  Csharp2013 programming language were done. In the decision tree created with the coding, the four important associated SNP was considered. The decision tree error in two case of coding and using WEKA were assessment and percentage of decision tree accuracy in prediction of breast cancer were calculated. The number of trained samples was obtained with systematic sampling. With coding, two scenarios as well as software WEKA, three scenarios with different sets of data and the number of different learning and testing, were evaluated. Results: In both scenarios of coding, by increasing the training percentage from 66/66 to 86/42, the error reduced from 55/56 to 9/09. Also by running of WEKA on three scenarios with different sets of data, the number of different education, and different tests by increasing records number from 81 to 2187, the error rate decreased from 48/15 to 13

Analysis of the Steam Generator Tubes Rupture Initiating Event

International Nuclear Information System (INIS)

Trillo, A.; Minguez, E.; Munoz, R.; Melendez, E.; Sanchez-Perea, M.; Izquierd, J.M.

1998-01-01

In PSA studies, Event Tree-Fault Tree techniques are used to analyse to consequences associated with the evolution of an initiating event. The Event Tree is built in the sequence identification stage, following the expected behaviour of the plant in a qualitative way. Computer simulation of the sequences is performed mainly to determine the allowed time for operator actions, and do not play a central role in ET validation. The simulation of the sequence evolution can instead be performed by using standard tools, helping the analyst obtain a more realistic ET. Long existing methods and tools can be used to automatism the construction of the event tree associated to a given initiator. These methods automatically construct the ET by simulating the plant behaviour following the initiator, allowing some of the systems to fail during the sequence evolution. Then, the sequences with and without the failure are followed. The outcome of all this is a Dynamic Event Tree. The work described here is the application of one such method to the particular case of the SGTR initiating event. The DYLAM scheduler, designed at the Ispra (Italy) JRC of the European Communities, is used to automatically drive the simulation of all the sequences constituting the Event Tree. Similarly to the static Event Tree, each time a system is demanded, two branches are open: one corresponding to the success and the other to the failure of the system. Both branches are followed by the plant simulator until a new system is demanded, and the process repeats. The plant simulation modelling allows the treatment of degraded sequences that enter into the severe accident domain as well as of success sequences in which long-term cooling is started. (Author)

Pull-Based Distributed Event-Triggered Consensus for Multiagent Systems With Directed Topologies.

Science.gov (United States)

Yi, Xinlei; Lu, Wenlian; Chen, Tianping

2017-01-01

This paper mainly investigates consensus problem with a pull-based event-triggered feedback control. For each agent, the diffusion coupling feedbacks are based on the states of its in-neighbors at its latest triggering time, and the next triggering time of this agent is determined by its in-neighbors' information. The general directed topologies, including irreducible and reducible cases, are investigated. The scenario of distributed continuous communication is considered first. It is proved that if the network topology has a spanning tree, then the event-triggered coupling algorithm can realize the consensus for the multiagent system. Then, the results are extended to discontinuous communication, i.e., self-triggered control, where each agent computes its next triggering time in advance without having to observe the system's states continuously. The effectiveness of the theoretical results is illustrated by a numerical example finally.

The importance of scenario development in meeting 40 CFR part 191

International Nuclear Information System (INIS)

Hunter, R.L.

1988-01-01

Scenario development and screening is a fundamental part of performance assessment, but its importance in satisfying 40 CFR Part 191 (the standard) is sometimes underestimated. The first step in scenario development in support of performance assessment for the standard's containment requirements is to identify a set of potentially disruptive events and processes. This set must be broad enough to allow the identification, as required by the standard, of those processes and events that might affect the disposal system; data can then be collected on the scenarios identified in this step. The standard also requires that releases be estimated for all significant processes and events; thus the final step in scenario development is systematically screening the scenarios, on the basis of their probabilities and consequences, to select those that are important enough to be modeled in detail. In general, a few hundred scenarios for the release of radionuclides from a nuclear-waste repository can be identified, but only a few of these can or should be modeled in detail

Tree Mortality Undercuts Ability of Tree-Planting Programs to Provide Benefits: Results of a Three-City Study

Directory of Open Access Journals (Sweden)

Sarah Widney

2016-03-01

Full Text Available Trees provide numerous benefits for urban residents, including reduced energy usage, improved air quality, stormwater management, carbon sequestration, and increased property values. Quantifying these benefits can help justify the costs of planting trees. In this paper, we use i-Tree Streets to quantify the benefits of street trees planted by nonprofits in three U.S. cities (Detroit, Michigan; Indianapolis, Indiana, and Philadelphia, Pennsylvania from 2009 to 2011. We also use both measured and modeled survival and growth rates to “grow” the tree populations 5 and 10 years into the future to project the future benefits of the trees under different survival and growth scenarios. The 4059 re-inventoried trees (2864 of which are living currently provide almost $40,000 (USD in estimated annual benefits ($9–$20/tree depending on the city, the majority (75% of which are increased property values. The trees can be expected to provide increasing annual benefits during the 10 years after planting if the annual survival rate is higher than the 93% annual survival measured during the establishment period. However, our projections show that with continued 93% or lower annual survival, the increase in annual benefits from tree growth will not be able to make up for the loss of benefits as trees die. This means that estimated total annual benefits from a cohort of planted trees will decrease between the 5-year projection and the 10-year projection. The results of this study indicate that without early intervention to ensure survival of planted street trees, tree mortality may be significantly undercutting the ability of tree-planting programs to provide benefits to neighborhood residents.

Rare event techniques applied in the Rasmussen study

International Nuclear Information System (INIS)

Vesely, W.E.

1977-01-01

The Rasmussen Study estimated public risks from commercial nuclear power plant accidents, and therefore the statistics of rare events had to be treated. Two types of rare events were specifically handled, those rare events which were probabilistically rare events and those which were statistically rare events. Four techniques were used to estimate probabilities of rare events. These techniques were aggregating data samples, discretizing ''continuous'' events, extrapolating from minor to catastrophic severities, and decomposing events using event trees and fault trees. In aggregating or combining data the goal was to enlarge the data sample so that the rare event was no longer rare, i.e., so that the enlarged data sample contained one or more occurrences of the event of interest. This aggregation gave rise to random variable treatments of failure rates, occurrence frequencies, and other characteristics estimated from data. This random variable treatment can be interpreted as being comparable to an empirical Bayes technique or a Bayesian technique. In the discretizing event technique, events of a detailed nature were grouped together into a grosser event for purposes of analysis as well as for data collection. The treatment of data characteristics as random variables helped to account for the uncertainties arising from this discretizing. In the severity extrapolation technique a severity variable was associated with each event occurrence for the purpose of predicting probabilities of catastrophic occurrences. Tail behaviors of distributions therefore needed to be considered. Finally, event trees and fault trees were used to express accident occurrences and system failures in terms of more basic events for which data existed. Common mode failures and general dependencies therefore needed to be treated. 2 figures

Sequence Algebra, Sequence Decision Diagrams and Dynamic Fault Trees

International Nuclear Information System (INIS)

Rauzy, Antoine B.

2011-01-01

A large attention has been focused on the Dynamic Fault Trees in the past few years. By adding new gates to static (regular) Fault Trees, Dynamic Fault Trees aim to take into account dependencies among events. Merle et al. proposed recently an algebraic framework to give a formal interpretation to these gates. In this article, we extend Merle et al.'s work by adopting a slightly different perspective. We introduce Sequence Algebras that can be seen as Algebras of Basic Events, representing failures of non-repairable components. We show how to interpret Dynamic Fault Trees within this framework. Finally, we propose a new data structure to encode sets of sequences of Basic Events: Sequence Decision Diagrams. Sequence Decision Diagrams are very much inspired from Minato's Zero-Suppressed Binary Decision Diagrams. We show that all operations of Sequence Algebras can be performed on this data structure.

An Event-Based Approach to Design a Teamwork Training Scenario and Assessment Tool in Surgery.

Science.gov (United States)

Nguyen, Ngan; Watson, William D; Dominguez, Edward

2016-01-01

Simulation is a technique recommended for teaching and measuring teamwork, but few published methodologies are available on how best to design simulation for teamwork training in surgery and health care in general. The purpose of this article is to describe a general methodology, called event-based approach to training (EBAT), to guide the design of simulation for teamwork training and discuss its application to surgery. The EBAT methodology draws on the science of training by systematically introducing training exercise events that are linked to training requirements (i.e., competencies being trained and learning objectives) and performance assessment. The EBAT process involves: Of the 4 teamwork competencies endorsed by the Agency for Healthcare Research Quality and Department of Defense, "communication" was chosen to be the focus of our training efforts. A total of 5 learning objectives were defined based on 5 validated teamwork and communication techniques. Diagnostic laparoscopy was chosen as the clinical context to frame the training scenario, and 29 KSAs were defined based on review of published literature on patient safety and input from subject matter experts. Critical events included those that correspond to a specific phase in the normal flow of a surgical procedure as well as clinical events that may occur when performing the operation. Similar to the targeted KSAs, targeted responses to the critical events were developed based on existing literature and gathering input from content experts. Finally, a 29-item EBAT-derived checklist was created to assess communication performance. Like any instructional tool, simulation is only effective if it is designed and implemented appropriately. It is recognized that the effectiveness of simulation depends on whether (1) it is built upon a theoretical framework, (2) it uses preplanned structured exercises or events to allow learners the opportunity to exhibit the targeted KSAs, (3) it assesses performance, and (4

Analysis of large fault trees based on functional decomposition

International Nuclear Information System (INIS)

Contini, Sergio; Matuzas, Vaidas

2011-01-01

With the advent of the Binary Decision Diagrams (BDD) approach in fault tree analysis, a significant enhancement has been achieved with respect to previous approaches, both in terms of efficiency and accuracy of the overall outcome of the analysis. However, the exponential increase of the number of nodes with the complexity of the fault tree may prevent the construction of the BDD. In these cases, the only way to complete the analysis is to reduce the complexity of the BDD by applying the truncation technique, which nevertheless implies the problem of estimating the truncation error or upper and lower bounds of the top-event unavailability. This paper describes a new method to analyze large coherent fault trees which can be advantageously applied when the working memory is not sufficient to construct the BDD. It is based on the decomposition of the fault tree into simpler disjoint fault trees containing a lower number of variables. The analysis of each simple fault tree is performed by using all the computational resources. The results from the analysis of all simpler fault trees are re-combined to obtain the results for the original fault tree. Two decomposition methods are herewith described: the first aims at determining the minimal cut sets (MCS) and the upper and lower bounds of the top-event unavailability; the second can be applied to determine the exact value of the top-event unavailability. Potentialities, limitations and possible variations of these methods will be discussed with reference to the results of their application to some complex fault trees.

Analysis of large fault trees based on functional decomposition

Energy Technology Data Exchange (ETDEWEB)

Contini, Sergio, E-mail: sergio.contini@jrc.i [European Commission, Joint Research Centre, Institute for the Protection and Security of the Citizen, 21020 Ispra (Italy); Matuzas, Vaidas [European Commission, Joint Research Centre, Institute for the Protection and Security of the Citizen, 21020 Ispra (Italy)

2011-03-15

With the advent of the Binary Decision Diagrams (BDD) approach in fault tree analysis, a significant enhancement has been achieved with respect to previous approaches, both in terms of efficiency and accuracy of the overall outcome of the analysis. However, the exponential increase of the number of nodes with the complexity of the fault tree may prevent the construction of the BDD. In these cases, the only way to complete the analysis is to reduce the complexity of the BDD by applying the truncation technique, which nevertheless implies the problem of estimating the truncation error or upper and lower bounds of the top-event unavailability. This paper describes a new method to analyze large coherent fault trees which can be advantageously applied when the working memory is not sufficient to construct the BDD. It is based on the decomposition of the fault tree into simpler disjoint fault trees containing a lower number of variables. The analysis of each simple fault tree is performed by using all the computational resources. The results from the analysis of all simpler fault trees are re-combined to obtain the results for the original fault tree. Two decomposition methods are herewith described: the first aims at determining the minimal cut sets (MCS) and the upper and lower bounds of the top-event unavailability; the second can be applied to determine the exact value of the top-event unavailability. Potentialities, limitations and possible variations of these methods will be discussed with reference to the results of their application to some complex fault trees.

Helping Moroccan women preserve the argan tree at the gateway to ...

International Development Research Centre (IDRC) Digital Library (Canada)

2010-11-01

Nov 1, 2010 ... ... Charrouf of the Faculté des sciences at the Université Mohammed V of Rabat, and Professor ... Therefore, the project aims not only to help prevent further ... the development of argan tree management scenarios; the selection of trees ... on the French networks (France 2 and FR3), and on Radio-Canada.

Use of tree-ring chemistry to document historical ground-water contamination events

Science.gov (United States)

Vroblesky, Don A.; Yanosky, Thomas M.

1990-01-01

The annual growth rings of tulip trees (Liriodendron tulipifera L.) appear to preserve a chemical record of ground-water contamination at a landfill in Maryland. Zones of elevated iron and chlorine concentrations in growth rings from trees immediately downgradient from the landfill are closely correlated temporally with activities in the landfill expected to generate iron and chloride contamination in the ground water. Successively later iron peaks in trees increasingly distant from the landfill along the general direction of ground-water flow imply movement of iron-contaminated ground water away from the landfill. The historical velocity of iron movement (2 to 9 m/yr) and chloride movement (at least 40 m/yr) in ground water at the site was estimated from element-concentration trends of trees at successive distances from the landfill. The tree-ring-derived chloride-transport velocity approximates the known ground-water velocity (30 to 80 m/yr). A minimum horizontal hydraulic conductivity (0.01 to .02 cm/s) calculated from chloride velocity agrees well with values derived from aquifer tests (about 0.07 cm/s) and from ground-water modeling results (0.009 to 0.04 cm/s).

MFAULT: a computer program for analyzing fault trees

International Nuclear Information System (INIS)

Pelto, P.J.; Purcell, W.L.

1977-11-01

A description and user instructions are presented for MFAULT, a FORTRAN computer program for fault tree analysis. MFAULT identifies the cut sets of a fault tree, calculates their probabilities, and screens the cut sets on the basis of specified cut-offs on probability and/or cut set length. MFAULT is based on an efficient upward-working algorithm for cut set identification. The probability calculations are based on the assumption of small probabilities and constant hazard rates (i.e., exponential failure distributions). Cut sets consisting of repairable components (basic events) only, non-repairable components only, or mixtures of both types can be evaluated. Components can be on-line or standby. Unavailability contributions from pre-existing failures, failures on demand, and testing and maintenance down-time can be handled. MFAULT can analyze fault trees with AND gates, OR gates, inhibit gates, on switches (houses) and off switches. The code is presently capable of finding up to ten event cut sets from a fault tree with up to 512 basic events and 400 gates. It is operational on the CONTROL DATA CYBER 74 computer. 11 figures

A support vector machine based test for incongruence between sets of trees in tree space

Science.gov (United States)

2012-01-01

Background The increased use of multi-locus data sets for phylogenetic reconstruction has increased the need to determine whether a set of gene trees significantly deviate from the phylogenetic patterns of other genes. Such unusual gene trees may have been influenced by other evolutionary processes such as selection, gene duplication, or horizontal gene transfer. Results Motivated by this problem we propose a nonparametric goodness-of-fit test for two empirical distributions of gene trees, and we developed the software GeneOut to estimate a p-value for the test. Our approach maps trees into a multi-dimensional vector space and then applies support vector machines (SVMs) to measure the separation between two sets of pre-defined trees. We use a permutation test to assess the significance of the SVM separation. To demonstrate the performance of GeneOut, we applied it to the comparison of gene trees simulated within different species trees across a range of species tree depths. Applied directly to sets of simulated gene trees with large sample sizes, GeneOut was able to detect very small differences between two set of gene trees generated under different species trees. Our statistical test can also include tree reconstruction into its test framework through a variety of phylogenetic optimality criteria. When applied to DNA sequence data simulated from different sets of gene trees, results in the form of receiver operating characteristic (ROC) curves indicated that GeneOut performed well in the detection of differences between sets of trees with different distributions in a multi-dimensional space. Furthermore, it controlled false positive and false negative rates very well, indicating a high degree of accuracy. Conclusions The non-parametric nature of our statistical test provides fast and efficient analyses, and makes it an applicable test for any scenario where evolutionary or other factors can lead to trees with different multi-dimensional distributions. The

Scenario-based approach to risk analysis in support of cyber security

Energy Technology Data Exchange (ETDEWEB)

Gertman, D. I.; Folkers, R.; Roberts, J. [Idaho National Laboratory, Roberts and Folkers Associates, LLC, Idaho Falls, ID 83404 (United States)

2006-07-01

The US infrastructure is continually challenged by hostile nation states and others who would do us harm. Cyber vulnerabilities and weaknesses are potential targets and are the result of years of construction and technological improvement in a world less concerned with security than is currently the case. As a result, cyber attack presents a class of challenges for which we are just beginning to prepare. What has been done in the nuclear, chemical and energy sectors as a means of anticipating and preparing for randomly occurring accidents and off-normal events is to develop scenarios as a means by which to prioritize and quantify risk and to take action. However, the number of scenarios risk analysts can develop is almost limitless. How do we ascertain which scenario has the greatest merit? One of the more important contributions of probabilistic risk analysis (PRA) has been to quantify the initiating event probability associated with various classes of accidents; and to quantify the occurrence of various conditions, i.e., end-states, as a function of these important accident sequences. Typically, various classes of conditions are represented by scenarios and are quantified in terms of cut sets and binned into end states. For example, the nuclear industry has a well-defined set of initiating events that are studied in assessing risk. The maturation of risk analysis for cyber security from accounting for barriers or looking at conditions statically to one of ascertaining the probability associated with certain events is, in part, dependent upon the adoption of a scenario-based approach. For example, scenarios take into account threats to personnel and public safety; economic damage, and compromises to major operational and safety functions. Scenarios reflect system, equipment, and component configurations as well as key human-system interactions related to event detection, diagnosis, mitigation and restoration of systems. As part of a cyber attack directed toward

Scenario-based approach to risk analysis in support of cyber security

International Nuclear Information System (INIS)

Gertman, D. I.; Folkers, R.; Roberts, J.

2006-01-01

The US infrastructure is continually challenged by hostile nation states and others who would do us harm. Cyber vulnerabilities and weaknesses are potential targets and are the result of years of construction and technological improvement in a world less concerned with security than is currently the case. As a result, cyber attack presents a class of challenges for which we are just beginning to prepare. What has been done in the nuclear, chemical and energy sectors as a means of anticipating and preparing for randomly occurring accidents and off-normal events is to develop scenarios as a means by which to prioritize and quantify risk and to take action. However, the number of scenarios risk analysts can develop is almost limitless. How do we ascertain which scenario has the greatest merit? One of the more important contributions of probabilistic risk analysis (PRA) has been to quantify the initiating event probability associated with various classes of accidents; and to quantify the occurrence of various conditions, i.e., end-states, as a function of these important accident sequences. Typically, various classes of conditions are represented by scenarios and are quantified in terms of cut sets and binned into end states. For example, the nuclear industry has a well-defined set of initiating events that are studied in assessing risk. The maturation of risk analysis for cyber security from accounting for barriers or looking at conditions statically to one of ascertaining the probability associated with certain events is, in part, dependent upon the adoption of a scenario-based approach. For example, scenarios take into account threats to personnel and public safety; economic damage, and compromises to major operational and safety functions. Scenarios reflect system, equipment, and component configurations as well as key human-system interactions related to event detection, diagnosis, mitigation and restoration of systems. As part of a cyber attack directed toward

Improvement of testing and maintenance based on fault tree analysis

International Nuclear Information System (INIS)

Cepin, M.

2000-01-01

Testing and maintenance of safety equipment is an important issue, which significantly contributes to safe and efficient operation of a nuclear power plant. In this paper a method, which extends the classical fault tree with time, is presented. Its mathematical model is represented by a set of equations, which include time requirements defined in the house event matrix. House events matrix is a representation of house events switched on and off through the discrete points of time. It includes house events, which timely switch on and off parts of the fault tree in accordance with the status of the plant configuration. Time dependent top event probability is calculated by the fault tree evaluations. Arrangement of components outages is determined on base of minimization of mean system unavailability. The results show that application of the method may improve the time placement of testing and maintenance activities of safety equipment. (author)

Climate change affects winter chill for temperate fruit and nut trees.

Science.gov (United States)

Luedeling, Eike; Girvetz, Evan H; Semenov, Mikhail A; Brown, Patrick H

2011-01-01

Temperate fruit and nut trees require adequate winter chill to produce economically viable yields. Global warming has the potential to reduce available winter chill and greatly impact crop yields. We estimated winter chill for two past (1975 and 2000) and 18 future scenarios (mid and end 21st century; 3 Global Climate Models [GCMs]; 3 greenhouse gas emissions [GHG] scenarios). For 4,293 weather stations around the world and GCM projections, Safe Winter Chill (SWC), the amount of winter chill that is exceeded in 90% of all years, was estimated for all scenarios using the "Dynamic Model" and interpolated globally. We found that SWC ranged between 0 and about 170 Chill Portions (CP) for all climate scenarios, but that the global distribution varied across scenarios. Warm regions are likely to experience severe reductions in available winter chill, potentially threatening production there. In contrast, SWC in most temperate growing regions is likely to remain relatively unchanged, and cold regions may even see an increase in SWC. Climate change impacts on SWC differed quantitatively among GCMs and GHG scenarios, with the highest GHG leading to losses up to 40 CP in warm regions, compared to 20 CP for the lowest GHG. The extent of projected changes in winter chill in many major growing regions of fruits and nuts indicates that growers of these commodities will likely experience problems in the future. Mitigation of climate change through reductions in greenhouse gas emissions can help reduce the impacts, however, adaption to changes will have to occur. To better prepare for likely impacts of climate change, efforts should be undertaken to breed tree cultivars for lower chilling requirements, to develop tools to cope with insufficient winter chill, and to better understand the temperature responses of tree crops.

Sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the Laurentian Channel Ice Stream

Science.gov (United States)

Leng, Wei; von Dobeneck, Tilo; Bergmann, Fenna; Just, Janna; Mulitza, Stefan; Chiessi, Cristiano M.; St-Onge, Guillaume; Piper, David J. W.

2018-04-01

Eastern Canadian margin sediments bear testimony to several catastrophic deglacial meltwater discharges from the retreating Laurentide Ice Sheet. The reddish-brown plumite layers deposited on the levees of the Laurentian Fan valleys have been recognized as indications of multiple outburst floods between Heinrich events 2 and 1. Five event layers have been consistently recorded in three new gravity cores retrieved on the SW Grand Banks slope and comply with the previously published Laurentian Fan core MD95-2029. The apparently huge extent of these outburst plumes around the Laurentian Fan as well as their causes and consequences are investigated in this study using physical properties, rock magnetic and grain-size analyses, together with seismoacoustic profiling. We provide the first detailed 14C ages of the outburst event sequence and discuss their recurrence intervals in the context of regional ice retreat. Compared to the hemipelagic interlayers, event layers have overall uniform and systematic changes of rock-magnetic properties. Hematite contents increase over time and proximally while magnetite grain sizes fine upwards and spatially away from the fan. Based on the sediment composition and load, we argue that these plumites were formed by recurrent erosion of glacial mud deposits in the Laurentian Channel by meltwater outbursts. Three alternative glaciological scenarios are evaluated: in each case, the provenance of the transported sediment is not an indicator of the precise source of the meltwater.

Inferring duplications, losses, transfers and incomplete lineage sorting with nonbinary species trees.

Science.gov (United States)

Stolzer, Maureen; Lai, Han; Xu, Minli; Sathaye, Deepa; Vernot, Benjamin; Durand, Dannie

2012-09-15

Gene duplication (D), transfer (T), loss (L) and incomplete lineage sorting (I) are crucial to the evolution of gene families and the emergence of novel functions. The history of these events can be inferred via comparison of gene and species trees, a process called reconciliation, yet current reconciliation algorithms model only a subset of these evolutionary processes. We present an algorithm to reconcile a binary gene tree with a nonbinary species tree under a DTLI parsimony criterion. This is the first reconciliation algorithm to capture all four evolutionary processes driving tree incongruence and the first to reconcile non-binary species trees with a transfer model. Our algorithm infers all optimal solutions and reports complete, temporally feasible event histories, giving the gene and species lineages in which each event occurred. It is fixed-parameter tractable, with polytime complexity when the maximum species outdegree is fixed. Application of our algorithms to prokaryotic and eukaryotic data show that use of an incomplete event model has substantial impact on the events inferred and resulting biological conclusions. Our algorithms have been implemented in Notung, a freely available phylogenetic reconciliation software package, available at http://www.cs.cmu.edu/~durand/Notung. mstolzer@andrew.cmu.edu.

Missing Rings in Pinus halepensis - The Missing Link to Relate the Tree-Ring Record to Extreme Climatic Events.

Science.gov (United States)

Novak, Klemen; de Luis, Martin; Saz, Miguel A; Longares, Luis A; Serrano-Notivoli, Roberto; Raventós, Josep; Čufar, Katarina; Gričar, Jožica; Di Filippo, Alfredo; Piovesan, Gianluca; Rathgeber, Cyrille B K; Papadopoulos, Andreas; Smith, Kevin T

2016-01-01

Climate predictions for the Mediterranean Basin include increased temperatures, decreased precipitation, and increased frequency of extreme climatic events (ECE). These conditions are associated with decreased tree growth and increased vulnerability to pests and diseases. The anatomy of tree rings responds to these environmental conditions. Quantitatively, the width of a tree ring is largely determined by the rate and duration of cell division by the vascular cambium. In the Mediterranean climate, this division may occur throughout almost the entire year. Alternatively, cell division may cease during relatively cool and dry winters, only to resume in the same calendar year with milder temperatures and increased availability of water. Under particularly adverse conditions, no xylem may be produced in parts of the stem, resulting in a missing ring (MR). A dendrochronological network of Pinus halepensis was used to determine the relationship of MR to ECE. The network consisted of 113 sites, 1,509 trees, 2,593 cores, and 225,428 tree rings throughout the distribution range of the species. A total of 4,150 MR were identified. Binomial logistic regression analysis determined that MR frequency increased with increased cambial age. Spatial analysis indicated that the geographic areas of south-eastern Spain and northern Algeria contained the greatest frequency of MR. Dendroclimatic regression analysis indicated a non-linear relationship of MR to total monthly precipitation and mean temperature. MR are strongly associated with the combination of monthly mean temperature from previous October till current February and total precipitation from previous September till current May. They are likely to occur with total precipitation lower than 50 mm and temperatures higher than 5°C. This conclusion is global and can be applied to every site across the distribution area. Rather than simply being a complication for dendrochronology, MR formation is a fundamental response of trees

Regional climate change scenarios

International Nuclear Information System (INIS)

Somot, S.

2005-01-01

Because studies of the regional impact of climate change need higher spatial resolution than that obtained in standard global climate change scenarios, developing regional scenarios from models is a crucial goal for the climate modelling community. The zoom capacity of ARPEGE-Climat, the Meteo-France climate model, allows use of scenarios with a horizontal resolution of about 50 km over France and the Mediterranean basin. An IPCC-A2 scenario for the end of the 21. century in France shows higher temperatures in each season and more winter and less summer precipitation than now. Tuning the modelled statistical distributions to observed temperature and precipitation allows us to study changes in the frequency of extreme events between today's climate and that at the end of century. The frequency of very hot days in summer will increase. In particular, the frequency of days with a maximum temperature above 35 deg C will be multiplied by a factor of 10, on average. In our scenario, the Toulouse area and Provence might see one quarter of their summer days with a maximum temperature above 35 deg C. (author)

Object-oriented fault tree evaluation program for quantitative analyses

Science.gov (United States)

Patterson-Hine, F. A.; Koen, B. V.

1988-01-01

Object-oriented programming can be combined with fault free techniques to give a significantly improved environment for evaluating the safety and reliability of large complex systems for space missions. Deep knowledge about system components and interactions, available from reliability studies and other sources, can be described using objects that make up a knowledge base. This knowledge base can be interrogated throughout the design process, during system testing, and during operation, and can be easily modified to reflect design changes in order to maintain a consistent information source. An object-oriented environment for reliability assessment has been developed on a Texas Instrument (TI) Explorer LISP workstation. The program, which directly evaluates system fault trees, utilizes the object-oriented extension to LISP called Flavors that is available on the Explorer. The object representation of a fault tree facilitates the storage and retrieval of information associated with each event in the tree, including tree structural information and intermediate results obtained during the tree reduction process. Reliability data associated with each basic event are stored in the fault tree objects. The object-oriented environment on the Explorer also includes a graphical tree editor which was modified to display and edit the fault trees.

On the numerical solution of fault trees

International Nuclear Information System (INIS)

Demichela, M.; Piccinini, N.; Ciarambino, I.; Contini, S.

2003-01-01

In this paper an account will be given of the numerical solution of the logic trees directly extracted from the Recursive Operability Analysis. Particular attention will be devoted to the use of the NOT and INH logic gates for correct logical representation of Fault Trees prior to their quantitative resolution. The NOT gate is needed for correct logical representation of events when both non-intervention and correct intervention of a protective system may lead to a Top Event. The INH gate must be used to correctly represent the time link between two events that are both necessary, but must occur in sequence. Some numerical examples will be employed to show both the correct identification of the events entering the INH gates and how use of the AND gate instead of the INH gate leads to overestimation of the probability of occurrence of a Top Event

Breaking the fault tree circular logic

International Nuclear Information System (INIS)

Lankin, M.

2000-01-01

Event tree - fault tree approach to model failures of nuclear plants as well as of other complex facilities is noticeably dominant now. This approach implies modeling an object in form of unidirectional logical graph - tree, i.e. graph without circular logic. However, genuine nuclear plants intrinsically demonstrate quite a few logical loops (circular logic), especially where electrical systems are involved. This paper shows the incorrectness of existing practice of circular logic breaking by elimination of part of logical dependencies and puts forward a formal algorithm, which enables the analyst to correctly model the failure of complex object, which involves logical dependencies between system and components, in form of fault tree. (author)

Tree-growth analyses to estimate tree species' drought tolerance.

Science.gov (United States)

Eilmann, Britta; Rigling, Andreas

2012-02-01

Climate change is challenging forestry management and practices. Among other things, tree species with the ability to cope with more extreme climate conditions have to be identified. However, while environmental factors may severely limit tree growth or even cause tree death, assessing a tree species' potential for surviving future aggravated environmental conditions is rather demanding. The aim of this study was to find a tree-ring-based method suitable for identifying very drought-tolerant species, particularly potential substitute species for Scots pine (Pinus sylvestris L.) in Valais. In this inner-Alpine valley, Scots pine used to be the dominating species for dry forests, but today it suffers from high drought-induced mortality. We investigate the growth response of two native tree species, Scots pine and European larch (Larix decidua Mill.), and two non-native species, black pine (Pinus nigra Arnold) and Douglas fir (Pseudotsuga menziesii Mirb. var. menziesii), to drought. This involved analysing how the radial increment of these species responded to increasing water shortage (abandonment of irrigation) and to increasingly frequent drought years. Black pine and Douglas fir are able to cope with drought better than Scots pine and larch, as they show relatively high radial growth even after irrigation has been stopped and a plastic growth response to drought years. European larch does not seem to be able to cope with these dry conditions as it lacks the ability to recover from drought years. The analysis of trees' short-term response to extreme climate events seems to be the most promising and suitable method for detecting how tolerant a tree species is towards drought. However, combining all the methods used in this study provides a complete picture of how water shortage could limit species.

(Almost) practical tree codes

KAUST Repository

Khina, Anatoly

2016-08-15

We consider the problem of stabilizing an unstable plant driven by bounded noise over a digital noisy communication link, a scenario at the heart of networked control. To stabilize such a plant, one needs real-time encoding and decoding with an error probability profile that decays exponentially with the decoding delay. The works of Schulman and Sahai over the past two decades have developed the notions of tree codes and anytime capacity, and provided the theoretical framework for studying such problems. Nonetheless, there has been little practical progress in this area due to the absence of explicit constructions of tree codes with efficient encoding and decoding algorithms. Recently, linear time-invariant tree codes were proposed to achieve the desired result under maximum-likelihood decoding. In this work, we take one more step towards practicality, by showing that these codes can be efficiently decoded using sequential decoding algorithms, up to some loss in performance (and with some practical complexity caveats). We supplement our theoretical results with numerical simulations that demonstrate the effectiveness of the decoder in a control system setting.

Key drivers and economic consequences of high-end climate scenarios: uncertainties and risks

DEFF Research Database (Denmark)

Halsnæs, Kirsten; Kaspersen, Per Skougaard; Drews, Martin

2015-01-01

The consequences of high-end climate scenarios and the risks of extreme events involve a number of critical assumptions and methodological challenges related to key uncertainties in climate scenarios and modelling, impact analysis, and economics. A methodological framework for integrated analysis...... of extreme events increase beyond scaling, and in combination with economic assumptions we find a very wide range of risk estimates for urban precipitation events. A sensitivity analysis addresses 32 combinations of climate scenarios, damage cost curve approaches, and economic assumptions, including risk...... aversion and equity represented by discount rates. Major impacts of alternative assumptions are investigated. As a result, this study demonstrates that in terms of decision making the actual expectations concerning future climate scenarios and the economic assumptions applied are very important...

Fuzzy probability based fault tree analysis to propagate and quantify epistemic uncertainty

International Nuclear Information System (INIS)

Purba, Julwan Hendry; Sony Tjahyani, D.T.; Ekariansyah, Andi Sofrany; Tjahjono, Hendro

2015-01-01

Highlights: • Fuzzy probability based fault tree analysis is to evaluate epistemic uncertainty in fuzzy fault tree analysis. • Fuzzy probabilities represent likelihood occurrences of all events in a fault tree. • A fuzzy multiplication rule quantifies epistemic uncertainty of minimal cut sets. • A fuzzy complement rule estimate epistemic uncertainty of the top event. • The proposed FPFTA has successfully evaluated the U.S. Combustion Engineering RPS. - Abstract: A number of fuzzy fault tree analysis approaches, which integrate fuzzy concepts into the quantitative phase of conventional fault tree analysis, have been proposed to study reliabilities of engineering systems. Those new approaches apply expert judgments to overcome the limitation of the conventional fault tree analysis when basic events do not have probability distributions. Since expert judgments might come with epistemic uncertainty, it is important to quantify the overall uncertainties of the fuzzy fault tree analysis. Monte Carlo simulation is commonly used to quantify the overall uncertainties of conventional fault tree analysis. However, since Monte Carlo simulation is based on probability distribution, this technique is not appropriate for fuzzy fault tree analysis, which is based on fuzzy probabilities. The objective of this study is to develop a fuzzy probability based fault tree analysis to overcome the limitation of fuzzy fault tree analysis. To demonstrate the applicability of the proposed approach, a case study is performed and its results are then compared to the results analyzed by a conventional fault tree analysis. The results confirm that the proposed fuzzy probability based fault tree analysis is feasible to propagate and quantify epistemic uncertainties in fault tree analysis

A fault tree analysis strategy using binary decision diagrams

International Nuclear Information System (INIS)

Reay, Karen A.; Andrews, John D.

2002-01-01

The use of binary decision diagrams (BDDs) in fault tree analysis provides both an accurate and efficient means of analysing a system. There is a problem, however, with the conversion process of the fault tree to the BDD. The variable ordering scheme chosen for the construction of the BDD has a crucial effect on its resulting size and previous research has failed to identify any scheme that is capable of producing BDDs for all fault trees. This paper proposes an analysis strategy aimed at increasing the likelihood of obtaining a BDD for any given fault tree, by ensuring the associated calculations are as efficient as possible. The method implements simplification techniques, which are applied to the fault tree to obtain a set of 'minimal' subtrees, equivalent to the original fault tree structure. BDDs are constructed for each, using ordering schemes most suited to their particular characteristics. Quantitative analysis is performed simultaneously on the set of BDDs to obtain the top event probability, the system unconditional failure intensity and the criticality of the basic events

A practical method for accurate quantification of large fault trees

International Nuclear Information System (INIS)

Choi, Jong Soo; Cho, Nam Zin

2007-01-01

This paper describes a practical method to accurately quantify top event probability and importance measures from incomplete minimal cut sets (MCS) of a large fault tree. The MCS-based fault tree method is extensively used in probabilistic safety assessments. Several sources of uncertainties exist in MCS-based fault tree analysis. The paper is focused on quantification of the following two sources of uncertainties: (1) the truncation neglecting low-probability cut sets and (2) the approximation in quantifying MCSs. The method proposed in this paper is based on a Monte Carlo simulation technique to estimate probability of the discarded MCSs and the sum of disjoint products (SDP) approach complemented by the correction factor approach (CFA). The method provides capability to accurately quantify the two uncertainties and estimate the top event probability and importance measures of large coherent fault trees. The proposed fault tree quantification method has been implemented in the CUTREE code package and is tested on the two example fault trees

Scenarios of socio-economic and energy development of the country up to 2010

International Nuclear Information System (INIS)

Tsvetanov, P.

1990-01-01

The scenarios description is given as the first stage of a procedure of an energy-economy interrelations dynamics study, the other two stages being the formulation and the analysis of the development variants. The scenarios reflect quantitatively the policies and the international conditions for the socio-economic, energy demand and energy supply developments of the country. Two economic development scenarios ('high' - official macroeconomic views and 'low' - economic restructuring and decrease of energy intensity) hierarchically preside over the two corresponding energy demand scenarios of different technological evolutions ('traditional' and 'energy efficiency' oriented one) in the industry, the transport and the domestic and services sectors. Four energy supply system scenarios follow, corresponding to different approaches in the development of the energy conversion technologies and energy carriers, thus constituting a scenario tree of the studies. 16 refs., 2 figs., 7 tab., 1 ann. (R.Ts.)

Climatic changes lead to declining winter chill for fruit and nut trees in California during 1950-2099.

Science.gov (United States)

Luedeling, Eike; Zhang, Minghua; Girvetz, Evan H

2009-07-16

Winter chill is one of the defining characteristics of a location's suitability for the production of many tree crops. We mapped and investigated observed historic and projected future changes in winter chill in California, quantified with two different chilling models (Chilling Hours, Dynamic Model). Based on hourly and daily temperature records, winter chill was modeled for two past temperature scenarios (1950 and 2000), and 18 future scenarios (average conditions during 2041-2060 and 2080-2099 under each of the B1, A1B and A2 IPCC greenhouse gas emissions scenarios, for the CSIRO-MK3, HadCM3 and MIROC climate models). For each scenario, 100 replications of the yearly temperature record were produced, using a stochastic weather generator. We then introduced and mapped a novel climatic statistic, "safe winter chill", the 10% quantile of the resulting chilling distributions. This metric can be interpreted as the amount of chilling that growers can safely expect under each scenario. Winter chill declined substantially for all emissions scenarios, with the area of safe winter chill for many tree species or cultivars decreasing 50-75% by mid-21st century, and 90-100% by late century. Both chilling models consistently projected climatic conditions by the middle to end of the 21st century that will no longer support some of the main tree crops currently grown in California, with the Chilling Hours Model projecting greater changes than the Dynamic Model. The tree crop industry in California will likely need to develop agricultural adaptation measures (e.g. low-chill varieties and dormancy-breaking chemicals) to cope with these projected changes. For some crops, production might no longer be possible.

Analysis of internal events for the Unit 1 of the Laguna Verde nuclear power station

International Nuclear Information System (INIS)

Huerta B, A.; Aguilar T, O.; Nunez C, A.; Lopez M, R.

1993-01-01

This volume presents the results of the starter event analysis and the event tree analysis for the Unit 1 of the Laguna Verde nuclear power station. The starter event analysis includes the identification of all those internal events which cause a disturbance to the normal operation of the power station and require mitigation. Those called external events stay beyond the reach of this study. For the analysis of the Laguna Verde power station eight transient categories were identified, three categories of loss of coolant accidents (LOCA) inside the container, a LOCA out of the primary container, as well as the vessel break. The event trees analysis involves the development of the possible accident sequences for each category of starter events. Events trees by systems for the different types of LOCA and for all the transients were constructed. It was constructed the event tree for the total loss of alternating current, which represents an extension of the event tree for the loss of external power transient. Also the event tree by systems for the anticipated transients without scram was developed (ATWS). The events trees for the accident sequences includes the sequences evaluation with vulnerable nucleus, that is to say those sequences in which it is had an adequate cooling of nucleus but the remoting systems of residual heat had failed. In order to model adequately the previous, headings were added to the event tree for developing the sequences until the point where be solved the nucleus state. This process includes: the determination of the failure pressure of the primary container, the evaluation of the environment generated in the reactor building as result of the container failure or cracked of itself, the determination of the localization of the components in the reactor building and the construction of boolean expressions to estimate the failure of the subordinated components to an severe environment. (Author)

Developing future precipitation events from historic events: An Amsterdam case study.

Science.gov (United States)

Manola, Iris; van den Hurk, Bart; de Moel, Hans; Aerts, Jeroen

2016-04-01

Due to climate change, the frequency and intensity of extreme precipitation events is expected to increase. It is therefore of high importance to develop climate change scenarios tailored towards the local and regional needs of policy makers in order to develop efficient adaptation strategies to reduce the risks from extreme weather events. Current approaches to tailor climate scenarios are often not well adopted in hazard management, since average changes in climate are not a main concern to policy makers, and tailoring climate scenarios to simulate future extremes can be complex. Therefore, a new concept has been introduced recently that uses known historic extreme events as a basis, and modifies the observed data for these events so that the outcome shows how the same event would occur in a warmer climate. This concept is introduced as 'Future Weather', and appeals to the experience of stakeholders and users. This research presents a novel method of projecting a future extreme precipitation event, based on a historic event. The selected precipitation event took place over the broader area of Amsterdam, the Netherlands in the summer of 2014, which resulted in blocked highways, disruption of air transportation, flooded buildings and public facilities. An analysis of rain monitoring stations showed that an event of such intensity has a 5 to 15 years return period. The method of projecting a future event follows a non-linear delta transformation that is applied directly on the observed event assuming a warmer climate to produce an "up-scaled" future precipitation event. The delta transformation is based on the observed behaviour of the precipitation intensity as a function of the dew point temperature during summers. The outcome is then compared to a benchmark method using the HARMONIE numerical weather prediction model, where the boundary conditions of the event from the Ensemble Prediction System of ECMWF (ENS) are perturbed to indicate a warmer climate. The two

Success tree method of resources evaluation

International Nuclear Information System (INIS)

Chen Qinglan; Sun Wenpeng

1994-01-01

By applying the reliability theory in system engineering, the success tree method is used to transfer the expert's recognition on metallogenetic regularities into the form of the success tree. The aim of resources evaluation is achieved by means of calculating the metallogenetic probability or favorability of the top event of the success tree. This article introduces in detail, the source, principle of the success tree method and three kinds of calculation methods, expounds concretely how to establish the success tree of comprehensive uranium metallogenesis as well as the procedure from which the resources evaluation is performed. Because this method has not restrictions on the number of known deposits and calculated area, it is applicable to resources evaluation for different mineral species, types and scales and possesses good prospects of development

Breakage or uprooting: How tree death type affects hillslope processes in old-growth temperate forests

Science.gov (United States)

Šamonil, Pavel; Daněk, Pavel; Adam, Dušan; Phillips, Jonathan D.

2017-12-01

Tree breakage and uprooting are two possible scenarios of tree death that have differing effects on hillslope processes. In this study we aimed to (i) reveal the long-term structure of the biomechanical effects of trees (BETs) in relation to their radial growth and tree death types in four old-growth temperate forests in four different elevation settings with an altitudinal gradient of 152-1105 m a.s.l., (ii) quantify affected areas and soil volumes associated with the studied BETs in reserves, and (iii) derive a general model of the role of BETs in hillslope processes in central European temperate forests. We analyzed the individual dynamics of circa 55,000 trees in an area of 161 ha within four old-growth forests over 3-4 decades. Basal tree censuses established in all sites in the 1970s and repeated tree censuses in the 1990s and 2000s provided detailed information about the radial growth of each tree of DBH ≥ 10 cm as well as about types of tree death. We focused on the quantification of: (i) surviving still-living trees, (ii) new recruits, (iii) standing dead trees, (iv) uprooted trees, and (v) broken trees. Frequencies of phenomena were related to affected areas and volumes of soil using individual statistical models. The elevation contrasts were a significant factor in the structure of BETs. Differences between sites increased from frequencies of events through affected areas to volumes of soil associated with BETs. An average 2.7 m3 ha-1 year-1 was associated with all BETs of the living and dying trees in lowlands, while there was an average of 7.8 m3 ha-1 year-1 in the highest mountain site. Differences were caused mainly by the effects of dying trees. BETs associated with dead trees were 7-8 times larger in the mountains. Effects of dying trees and particularly treethrows represented about 70% of all BETs at both mountain sites, while it was 58% at the highland site and only 32% at the lowland site. Our results show a more significant role of BETs in

Missing Rings in Pinus halepensis – The Missing Link to Relate the Tree-Ring Record to Extreme Climatic Events

Science.gov (United States)

Novak, Klemen; de Luis, Martin; Saz, Miguel A.; Longares, Luis A.; Serrano-Notivoli, Roberto; Raventós, Josep; Čufar, Katarina; Gričar, Jožica; Di Filippo, Alfredo; Piovesan, Gianluca; Rathgeber, Cyrille B. K.; Papadopoulos, Andreas; Smith, Kevin T.

2016-01-01

Climate predictions for the Mediterranean Basin include increased temperatures, decreased precipitation, and increased frequency of extreme climatic events (ECE). These conditions are associated with decreased tree growth and increased vulnerability to pests and diseases. The anatomy of tree rings responds to these environmental conditions. Quantitatively, the width of a tree ring is largely determined by the rate and duration of cell division by the vascular cambium. In the Mediterranean climate, this division may occur throughout almost the entire year. Alternatively, cell division may cease during relatively cool and dry winters, only to resume in the same calendar year with milder temperatures and increased availability of water. Under particularly adverse conditions, no xylem may be produced in parts of the stem, resulting in a missing ring (MR). A dendrochronological network of Pinus halepensis was used to determine the relationship of MR to ECE. The network consisted of 113 sites, 1,509 trees, 2,593 cores, and 225,428 tree rings throughout the distribution range of the species. A total of 4,150 MR were identified. Binomial logistic regression analysis determined that MR frequency increased with increased cambial age. Spatial analysis indicated that the geographic areas of south-eastern Spain and northern Algeria contained the greatest frequency of MR. Dendroclimatic regression analysis indicated a non-linear relationship of MR to total monthly precipitation and mean temperature. MR are strongly associated with the combination of monthly mean temperature from previous October till current February and total precipitation from previous September till current May. They are likely to occur with total precipitation lower than 50 mm and temperatures higher than 5°C. This conclusion is global and can be applied to every site across the distribution area. Rather than simply being a complication for dendrochronology, MR formation is a fundamental response of trees

Fuzzy Uncertainty Evaluation for Fault Tree Analysis

Energy Technology Data Exchange (ETDEWEB)

Kim, Ki Beom; Shim, Hyung Jin [Seoul National University, Seoul (Korea, Republic of); Jae, Moo Sung [Hanyang University, Seoul (Korea, Republic of)

2015-05-15

This traditional probabilistic approach can calculate relatively accurate results. However it requires a long time because of repetitive computation due to the MC method. In addition, when informative data for statistical analysis are not sufficient or some events are mainly caused by human error, the probabilistic approach may not be possible because uncertainties of these events are difficult to be expressed by probabilistic distributions. In order to reduce the computation time and quantify uncertainties of top events when basic events whose uncertainties are difficult to be expressed by probabilistic distributions exist, the fuzzy uncertainty propagation based on fuzzy set theory can be applied. In this paper, we develop a fuzzy uncertainty propagation code and apply the fault tree of the core damage accident after the large loss of coolant accident (LLOCA). The fuzzy uncertainty propagation code is implemented and tested for the fault tree of the radiation release accident. We apply this code to the fault tree of the core damage accident after the LLOCA in three cases and compare the results with those computed by the probabilistic uncertainty propagation using the MC method. The results obtained by the fuzzy uncertainty propagation can be calculated in relatively short time, covering the results obtained by the probabilistic uncertainty propagation.

Efficient fault tree handling - the Asea-Atom approach

International Nuclear Information System (INIS)

Ericsson, G.; Knochenhauer, M.; Mills, R.

1985-01-01

In recent years there has been a trend in Swedish Probabilistic Safety Analysis (PSA) work towards coordination of the tools and methods used, in order to facilitate exchange of information and review. Thus, standardized methods for fault tree drawing and basic event coding have been developed as well as a number of computer codes for fault tree handling. The computer code used by Asea-Atom is called SUPER-TREE. As indicated by the name, the key feature is the concept of one super tree containing all the information necessary in the fault tree analysis, i.e. system fault trees, sequence fault trees and component data base. The code has proved to allow great flexibility in the choice of level of detail in the analysis

Testing a distributed hydrological model to predict scenarios of extreme events on a marginal olive orchard microcatchment

Science.gov (United States)

Guzmán, Enrique; Aguilar, Cristina; Taguas, Encarnación V.

2014-05-01

Olive groves constitute a traditional Mediterranean crop and thus, an important source of income to these regions and a crucial landscape component. Despite its importance, most of the olive groves in the region of Andalusia, Southern Spain, are located in sloping areas, which implies a significant risk of erosion. The combination of data and models allow enhancing the knowledge about processes taking place in these areas as well as the prediction of future scenarios. This aspect might be essential to plan soil protection strategies within a context of climate change where the IPCC estimates a significant increase of soil aridity and torrential events by the end of the century. The objective of this study is to estimate the rainfall-runoff-sediment dynamics in a microcatchment olive grove with the aid of a physically-based distributed hydrological model in order to evaluate the effect of extreme events on runoff and erosion. This study will allow to improve land-use and management planning activities in similar areas. In addition, the scale of the study (microcatchment) will allow to contrast the results in larger areas such as catchment regional spatial scales.

Scenario development for the Waste Isolation Pilot Plant compliance certification application

International Nuclear Information System (INIS)

GALSON, D.A.; SWIFT, PETER N.; ANDERSON, D. RICHARD; BENNETT, D.G.

1998-01-01

Demonstrating compliance with the applicable regulations for the Waste Isolation Pilot Plant (WIPP) requires an assessment of the long-term performance of the disposal system. Scenario development is one starting point of this assessment, and generates inquiry about the present state and future evolution of the disposal system. Scenario development consists of four tasks: (1) identifying and classifying features, events and processes (FEPs), (2) screening FEPs according to well-defined criteria, (3) forming scenarios (combinations of FEPs) in the context of regulatory performance criteria and (4) specifying of scenarios for consequence analysis. The development and screening of a comprehensive FEP list provides assurance that the identification of significant processes and events is complete, that potential interactions between FEPs are not overlooked, and that responses to possible questions are available and well documented. Two basic scenarios have been identified for the WIPP: undisturbed performance (UP) and disturbed performance (DP). The UP scenario is used to evaluate compliance with the Environmental Protection Agency's (EPA's) Individual Dose (40 CFR Section 191-15) and Groundwater Protection (40 CFR Section 191-24) standards and accounts for all natural-, waste- and repository-induced FEPs that survive the screening process. The DP scenario is required for assessment calculations for the EPA's cumulative release standard (Containment Requirements, 40 CFR Section 191-13) and accounts for disruptive future human events, which have an uncertain probability of occurrence, in addition to the UP FEPs

When Things Do Not Go as Expected: Scenario Life Savers

DEFF Research Database (Denmark)

Dieckmann, Peter; Lippert, A.; Glavin, R.

2010-01-01

In this paper we discuss scenario life savers - interventions before and during simulation scenarios that allow to create and use relevant learning opportunities, even if unexpected events happen during the conduction of the scenario. Scenario life savers are needed, when the comprehension...... or acceptance of the scenario by the participants is at stake, thus compromising learning opportunities. Scenario life savers can principally work by bringing participants back on track of the planned scenario or by adapting the conduction to their actions on the fly. Interventions can be within the logic...... of the scenario or from the "outside," not being part of the scenario itself. Scenario life savers should be anticipated during the design of scenarios and used carefully during their conduction, aiming to maximize the learning for participants. (Sim Healthcare 5: 219-225, 2010)...

Updated of the events tree of total loss of power at the site, SBO, taking into account the results of stress tests and methodological updates, convolution, and hydraulic power recovery from model RCPs

International Nuclear Information System (INIS)

Lopez Lorenzo, M. A.; Perez Martin, F.

2013-01-01

In this paper, is described a tree of events to an accident loss total power at the site (SBO) considering, first the results of stress tests arising from the Fukushima accident and moreover, various methodological updates related to this initiating event.

DLRS: gene tree evolution in light of a species tree.

Science.gov (United States)

Sjöstrand, Joel; Sennblad, Bengt; Arvestad, Lars; Lagergren, Jens

2012-11-15

PrIME-DLRS (or colloquially: 'Delirious') is a phylogenetic software tool to simultaneously infer and reconcile a gene tree given a species tree. It accounts for duplication and loss events, a relaxed molecular clock and is intended for the study of homologous gene families, for example in a comparative genomics setting involving multiple species. PrIME-DLRS uses a Bayesian MCMC framework, where the input is a known species tree with divergence times and a multiple sequence alignment, and the output is a posterior distribution over gene trees and model parameters. PrIME-DLRS is available for Java SE 6+ under the New BSD License, and JAR files and source code can be downloaded from http://code.google.com/p/jprime/. There is also a slightly older C++ version available as a binary package for Ubuntu, with download instructions at http://prime.sbc.su.se. The C++ source code is available upon request. joel.sjostrand@scilifelab.se or jens.lagergren@scilifelab.se. PrIME-DLRS is based on a sound probabilistic model (Åkerborg et al., 2009) and has been thoroughly validated on synthetic and biological datasets (Supplementary Material online).

Tree Simulation Techniques for Integrated Safety Assessment

International Nuclear Information System (INIS)

Melendez Asensio, E.; Izquierdo Rocha, J.M.; Sanchez Perez, M.; Hortal Reymundo, J.; Perez Mulas, A.

1999-01-01

In the development of a PSA a central role is played by the construction of the event trees that, stemming from each initiating event considered, will finally lead to the calculation of the core damage frequency (CDF). This construction is extensively done by means of expert judgement, performing simulation of the sequences only when some doubt arises (typically for small break LOCAs) using integrated codes. Transient analysis done within the framework of the PSA has important simplifications that affect the transient simulation, specially in relation with the control and protection systems, and may not identify complicated sequences. Specialised simulation tools such as RELAP5 have been used only at very specific points of the PSAs due to time and model complexity constraints. On the other hand, a large amount of work and expertise has been laid in the development of simulation tools, independently of the PSA effort. Tools simplified in the phenomena they consider, but complete in the treatment of automatic and manual control and protection systems are now available for automatic generation and testing of the sequences appearing in the Event Trees. Additionally, an increasing effort and interest has been spent in the development of efficient means for the representation of the Emergency Operating Procedures, which, incorporated into the simulating tool would make a more realistic picture of the real plant performance. At present; both types of analyses - transient and probabilistic - can converge to be able to dynamically generate an Event Tree while taking into account the actual performance of the control and protection systems of the plant and the operator actions. Such a tool would allow for an assessment of the Event Trees, and, if fed with probabilistic data, can provide results of the same nature. Key aspects of this approach that imply new theoretical as well as practical developments in addition to those traditionally covered by classical simulation

Biodiversity and climate change: consequences for upper tree line in Slovakia

Directory of Open Access Journals (Sweden)

Minďaš Jozef

2016-09-01

Full Text Available Study of the effects of climate change on upper tree limit has mainly focused on the diversity of tree species as a result of the ability of species to tolerate temperature and moisture changes as well as some effects of disturbance regime changes. The tree species diversity changes due to climate change has been analysed via gap model and biodiversity indices. Gap models are individually based on simulations of establishment, growth, and mortality of each tree on the forest plot. Input ecological data for model calculations have been taken from the permanent research plots located in primeval forests in mountainous regions in Slovakia. The results of regional scenarios of the climatic change for the territory of Slovakia have been used, from which the values according to the CGCM3.1 (global model, KNMI and MPI (regional models. Model results for conditions of the climate change scenarios suggest a shift of the upper forest limit to the region of the present subalpine zone, in supramontane zone. The most significant tree species diversity changes have been identified for the upper tree line and current belt of dwarf pine (Pinus mugo occurrence. Hill’s index of biodiversity in the upper forest line increased by 30 – 35% for horizon of 2050, resp. by 45 – 50% modeled for the horizon of 2075. Calculated values of Shannon’s index show an even higher increase due to climate change. For horizon 2050 is a roughly of three fold increase and horizon for 2075 by almost fivefold increase in the value of the index. Results from the gap model indicate the increase of tree species diversity 2 – 2,5 times.

The impact of within-herd genetic variation upon inferred transmission trees for foot-and-mouth disease virus.

Science.gov (United States)

Valdazo-González, Begoña; Kim, Jan T; Soubeyrand, Samuel; Wadsworth, Jemma; Knowles, Nick J; Haydon, Daniel T; King, Donald P

2015-06-01

Full-genome sequences have been used to monitor the fine-scale dynamics of epidemics caused by RNA viruses. However, the ability of this approach to confidently reconstruct transmission trees is limited by the knowledge of the genetic diversity of viruses that exist within different epidemiological units. In order to address this question, this study investigated the variability of 45 foot-and-mouth disease virus (FMDV) genome sequences (from 33 animals) that were collected during 2007 from eight premises (10 different herds) in the United Kingdom. Bayesian and statistical parsimony analysis demonstrated that these sequences exhibited clustering which was consistent with a transmission scenario describing herd-to-herd spread of the virus. As an alternative to analysing all of the available samples in future epidemics, the impact of randomly selecting one sequence from each of these herds was used to assess cost-effective methods that might be used to infer transmission trees during FMD outbreaks. Using these approaches, 85% and 91% of the resulting topologies were either identical or differed by only one edge from a reference tree comprising all of the sequences generated within the outbreak. The sequence distances that accrued during sequential transmission events between epidemiological units was estimated to be 4.6 nucleotides, although the genetic variability between viruses recovered from chronic carrier animals was higher than between viruses from animals with acute-stage infection: an observation which poses challenges for the use of simple approaches to infer transmission trees. This study helps to develop strategies for sampling during FMD outbreaks, and provides data that will guide the development of further models to support control policies in the event of virus incursions into FMD free countries. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Uncertainties related to the fault tree reliability data

International Nuclear Information System (INIS)

Apostol, Minodora; Nitoi, Mirela; Farcasiu, M.

2003-01-01

Uncertainty analyses related to the fault trees evaluate the system variability which appears from the uncertainties of the basic events probabilities. Having a logical model which describes a system, to obtain outcomes means to evaluate it, using estimations for each basic event of the model. If the model has basic events that incorporate uncertainties, then the results of the model should incorporate the uncertainties of the events. Uncertainties estimation in the final result of the fault tree means first the uncertainties evaluation for the basic event probabilities and then combination of these uncertainties, to calculate the top event uncertainty. To calculate the propagating uncertainty, a knowledge of the probability density function as well as the range of possible values of the basic event probabilities is required. The following data are defined, using suitable probability density function: the components failure rates; the human error probabilities; the initiating event frequencies. It was supposed that the possible value distribution of the basic event probabilities is given by the lognormal probability density function. To know the range of possible value of the basic event probabilities, the error factor or the uncertainty factor is required. The aim of this paper is to estimate the error factor for the failure rates and for the human errors probabilities from the reliability data base used in Cernavoda Probabilistic Safety Evaluation. The top event chosen as an example is FEED3, from the Pressure and Inventory Control System. The quantitative evaluation of this top event was made by using EDFT code, developed in Institute for Nuclear Research Pitesti (INR). It was supposed that the error factors for the component failures are the same as for the failure rates. Uncertainty analysis was made with INCERT application, which uses the moment method and Monte Carlo method. The reliability data base used at INR Pitesti does not contain the error factors (ef

How much does climate change threaten European forest tree species distributions?

Science.gov (United States)

Dyderski, Marcin K; Paź, Sonia; Frelich, Lee E; Jagodziński, Andrzej M

2018-03-01

Although numerous species distribution models have been developed, most were based on insufficient distribution data or used older climate change scenarios. We aimed to quantify changes in projected ranges and threat level by the years 2061-2080, for 12 European forest tree species under three climate change scenarios. We combined tree distribution data from the Global Biodiversity Information Facility, EUFORGEN, and forest inventories, and we developed species distribution models using MaxEnt and 19 bioclimatic variables. Models were developed for three climate change scenarios-optimistic (RCP2.6), moderate (RCP4.5), and pessimistic (RPC8.5)-using three General Circulation Models, for the period 2061-2080. Our study revealed different responses of tree species to projected climate change. The species may be divided into three groups: "winners"-mostly late-successional species: Abies alba, Fagus sylvatica, Fraxinus excelsior, Quercus robur, and Quercus petraea; "losers"-mostly pioneer species: Betula pendula, Larix decidua, Picea abies, and Pinus sylvestris; and alien species-Pseudotsuga menziesii, Quercus rubra, and Robinia pseudoacacia, which may be also considered as "winners." Assuming limited migration, most of the species studied would face a significant decrease in suitable habitat area. The threat level was highest for species that currently have the northernmost distribution centers. Ecological consequences of the projected range contractions would be serious for both forest management and nature conservation. © 2017 John Wiley & Sons Ltd.

Efficient reduction and modularization for large fault trees stored by pages

International Nuclear Information System (INIS)

Chen, Shanqi; Wang, Jin; Wang, Jiaqun; Wang, Fang; Hu, Liqin

2016-01-01

Highlights: • New fault tree pre-processing methods used in RiskA are presented. • Including the fault tree paging storage, simplification and modularization. • For getting MCS for fault trees containing more than 10,000 gates and events. • Reduce computer resources needs (RAM) and improve computation speed. - Abstract: Fault Tree Analysis (FTA), an indispensable tool used in Probabilistic Risk Assessment (PRA), has been used throughout the commercial nuclear power industry for safety and reliability analyses. However, large fault tree analysis, such as those used in nuclear power plant requires significant computer resources, which makes the analysis of PRA model inefficient and time consuming. This paper describes a fault tree pre-processing method used in the reliability and probabilistic safety assessment program RiskA that is capable of generating minimal cutsets for fault trees containing more than 10,000 gates and basic events. The novel feature of this method is not only that Boolean reduction rules are used but also that a new objective of simplification is proposed. Moreover, since the method aims to find more fault tree modules by the linear-time algorithm, it can optimize fault tree modularization, which further reduces the computational time of large fault tree analysis.

Preliminary hazard analysis using sequence tree method

International Nuclear Information System (INIS)

Huang Huiwen; Shih Chunkuan; Hung Hungchih; Chen Minghuei; Yih Swu; Lin Jiinming

2007-01-01

A system level PHA using sequence tree method was developed to perform Safety Related digital I and C system SSA. The conventional PHA is a brainstorming session among experts on various portions of the system to identify hazards through discussions. However, this conventional PHA is not a systematic technique, the analysis results strongly depend on the experts' subjective opinions. The analysis quality cannot be appropriately controlled. Thereby, this research developed a system level sequence tree based PHA, which can clarify the relationship among the major digital I and C systems. Two major phases are included in this sequence tree based technique. The first phase uses a table to analyze each event in SAR Chapter 15 for a specific safety related I and C system, such as RPS. The second phase uses sequence tree to recognize what I and C systems are involved in the event, how the safety related systems work, and how the backup systems can be activated to mitigate the consequence if the primary safety systems fail. In the sequence tree, the defense-in-depth echelons, including Control echelon, Reactor trip echelon, ESFAS echelon, and Indication and display echelon, are arranged to construct the sequence tree structure. All the related I and C systems, include digital system and the analog back-up systems are allocated in their specific echelon. By this system centric sequence tree based analysis, not only preliminary hazard can be identified systematically, the vulnerability of the nuclear power plant can also be recognized. Therefore, an effective simplified D3 evaluation can be performed as well. (author)

Fault tree analysis. Implementation of the WAM-codes

International Nuclear Information System (INIS)

Bento, J.P.; Poern, K.

1979-07-01

The report describes work going on at Studsvik at the implementation of the WAM code package for fault tree analysis. These codes originally developed under EPRI contract by Sciences Applications Inc, allow, in contrast with other fault tree codes, all Boolean operations, thus allowing modeling of ''NOT'' conditions and dependent components. To concretize the implementation of these codes, the auxiliary feed-water system of the Swedish BWR Oskarshamn 2 was chosen for the reliability analysis. For this system, both the mean unavailability and the probability density function of the top event - undesired event - of the system fault tree were calculated, the latter using a Monte-Carlo simulation technique. The present study is the first part of a work performed under contract with the Swedish Nuclear Power Inspectorate. (author)

Accident Fault Trees for Defense Waste Processing Facility

Energy Technology Data Exchange (ETDEWEB)

Sarrack, A.G.

1999-06-22

The purpose of this report is to document fault tree analyses which have been completed for the Defense Waste Processing Facility (DWPF) safety analysis. Logic models for equipment failures and human error combinations that could lead to flammable gas explosions in various process tanks, or failure of critical support systems were developed for internal initiating events and for earthquakes. These fault trees provide frequency estimates for support systems failures and accidents that could lead to radioactive and hazardous chemical releases both on-site and off-site. Top event frequency results from these fault trees will be used in further APET analyses to calculate accident risk associated with DWPF facility operations. This report lists and explains important underlying assumptions, provides references for failure data sources, and briefly describes the fault tree method used. Specific commitments from DWPF to provide new procedural/administrative controls or system design changes are listed in the ''Facility Commitments'' section. The purpose of the ''Assumptions'' section is to clarify the basis for fault tree modeling, and is not necessarily a list of items required to be protected by Technical Safety Requirements (TSRs).

Topical report on release scenario analysis of long-term management of high-level defense waste at the Hanford Site

International Nuclear Information System (INIS)

Wallace, R.W.; Landstrom, D.K.; Blair, S.C.; Howes, B.W.; Robkin, M.A.; Benson, G.L.; Reisenauer, A.E.; Walters, W.H.; Zimmerman, M.G.

1980-11-01

Potential release scenarios for the defense high-level waste (HLW) on the Hanford Site are presented. Presented in this report are the three components necessary for evaluating the various alternatives under consideration for long-term management of Hanford defense HLW: identification of scenarios and events which might directly or indirectly disrupt radionuclide containment barriers; geotransport calculations of waste migration through the site media; and consequence (dose) analyses based on groundwater and air pathways calculations. The scenarios described in this report provide the necessary parameters for radionuclide transport and consequence analysis. Scenarios are categorized as either bounding or nonbounding. Bounding scenarios consider worst case or what if situations where an actual and significant release of waste material to the environment would happen if the scenario were to occur. Bounding scenarios include both near-term and long-term scenarios. Near-term scenarios are events which occur at 100 years from 1990. Long term scenarios are potential events considered to occur at 1000 and 10,000 years from 1990. Nonbounding scenarios consider events which result in insignificant releases or no release at all to the environment. Three release mechanisms are described in this report: (1) direct exposure of waste to the biosphere by a defined sequence of events (scenario) such as human intrusion by drilling; (2) radionuclides contacting an unconfined aquifer through downward percolation of groundwater or a rising water table; and (3) cataclysmic or explosive release of radionuclides by such mechanisms as meteorite impact, fire and explosion, criticality, or seismic events. Scenarios in this report present ways in which these release mechanisms could occur at a waste management facility. The scenarios are applied to the two in-tank waste management alternatives: in-situ disposal and continued present action

An Integrated Scenario Ensemble-Based Framework for Hurricane Evacuation Modeling: Part 1-Decision Support System.

Science.gov (United States)

Davidson, Rachel A; Nozick, Linda K; Wachtendorf, Tricia; Blanton, Brian; Colle, Brian; Kolar, Randall L; DeYoung, Sarah; Dresback, Kendra M; Yi, Wenqi; Yang, Kun; Leonardo, Nicholas

2018-03-30

This article introduces a new integrated scenario-based evacuation (ISE) framework to support hurricane evacuation decision making. It explicitly captures the dynamics, uncertainty, and human-natural system interactions that are fundamental to the challenge of hurricane evacuation, but have not been fully captured in previous formal evacuation models. The hazard is represented with an ensemble of probabilistic scenarios, population behavior with a dynamic decision model, and traffic with a dynamic user equilibrium model. The components are integrated in a multistage stochastic programming model that minimizes risk and travel times to provide a tree of evacuation order recommendations and an evaluation of the risk and travel time performance for that solution. The ISE framework recommendations offer an advance in the state of the art because they: (1) are based on an integrated hazard assessment (designed to ultimately include inland flooding), (2) explicitly balance the sometimes competing objectives of minimizing risk and minimizing travel time, (3) offer a well-hedged solution that is robust under the range of ways the hurricane might evolve, and (4) leverage the substantial value of increasing information (or decreasing degree of uncertainty) over the course of a hurricane event. A case study for Hurricane Isabel (2003) in eastern North Carolina is presented to demonstrate how the framework is applied, the type of results it can provide, and how it compares to available methods of a single scenario deterministic analysis and a two-stage stochastic program. © 2018 Society for Risk Analysis.

A synthesis of radial growth patterns preceding tree mortality

Science.gov (United States)

Cailleret, Maxime; Jansen, Steven; Robert, Elisabeth M.R.; Desoto, Lucia; Aakala, Tuomas; Antos, Joseph A.; Beikircher, Barbara; Bigler, Christof; Bugmann, Harald; Caccianiga, Marco; Cada, Vojtech; Camarero, Jesus J.; Cherubini, Paolo; Cochard, Herve; Coyea, Marie R.; Cufar, Katarina; Das, Adrian J.; Davi, Hendrik; Delzon, Sylvain; Dorman, Michael; Gea-Izquierdo, Guillermo; Gillner, Sten; Haavik, Laurel J.; Hartmann, Henrik; Heres, Ana-Maria; Hultine, Kevin R.; Janda, Pavel; Kane, Jeffrey M.; Kharuk, Vyacheslav I.; Kitzberger, Thomas; Klein, Tamir; Kramer, Koen; Lens, Frederic; Levanic, Tom; Calderon, Juan C. Linares; Lloret, Francisco; Lobo-Do-Vale, Raquel; Lombardi, Fabio; Lopez Rodriguez, Rosana; Makinen, Harri; Mayr, Stefan; Meszaros, IIona; Metsaranta, Juha M.; Minunno, Francesco; Oberhuber, Walter; Papadopoulos, Andreas; Peltoniemi, Mikko; Petritan, Any M.; Rohner, Brigitte; Sanguesa-Barreda, Gabriel; Sarris, Dimitrios; Smith, Jeremy M.; Stan, Amanda B.; Sterck, Frank; Stojanovic, Dejan B.; Suarez, Maria L.; Svoboda, Miroslav; Tognetti, Roberto; Torres-Ruiz, Jose M.; Trotsiuk, Volodymyr; Villalba, Ricardo; Vodde, Floor; Westwood, Alana R.; Wyckoff, Peter H.; Zafirov, Nikolay; Martinez-Vilalta, Jordi

2017-01-01

Tree mortality is a key factor influencing forest functions and dynamics, but our understanding of the mechanisms leading to mortality and the associated changes in tree growth rates are still limited. We compiled a new pan-continental tree-ring width database from sites where both dead and living trees were sampled (2970 dead and 4224 living trees from 190 sites, including 36 species), and compared early and recent growth rates between trees that died and those that survived a given mortality event. We observed a decrease in radial growth before death in ca. 84% of the mortality events. The extent and duration of these reductions were highly variable (1–100 years in 96% of events) due to the complex interactions among study species and the source(s) of mortality. Strong and long-lasting declines were found for gymnosperms, shade- and drought-tolerant species, and trees that died from competition. Angiosperms and trees that died due to biotic attacks (especially bark-beetles) typically showed relatively small and short-term growth reductions. Our analysis did not highlight any universal trade-off between early growth and tree longevity within a species, although this result may also reflect high variability in sampling design among sites. The intersite and interspecific variability in growth patterns before mortality provides valuable information on the nature of the mortality process, which is consistent with our understanding of the physiological mechanisms leading to mortality. Abrupt changes in growth immediately before death can be associated with generalized hydraulic failure and/or bark-beetle attack, while long-term decrease in growth may be associated with a gradual decline in hydraulic performance coupled with depletion in carbon reserves. Our results imply that growth-based mortality algorithms may be a powerful tool for predicting gymnosperm mortality induced by chronic stress, but not necessarily so for angiosperms and in case of intense drought or

The Prediction of Drought-Related Tree Mortality in Vegetation Models

Science.gov (United States)

Schwinning, S.; Jensen, J.; Lomas, M. R.; Schwartz, B.; Woodward, F. I.

2013-12-01

Drought-related tree die-off events at regional scales have been reported from all wooded continents and it has been suggested that their frequency may be increasing. The prediction of these drought-related die-off events from regional to global scales has been recognized as a critical need for the conservation of forest resources and improving the prediction of climate-vegetation interactions. However, there is no conceptual consensus on how to best approach the quantitative prediction of tree mortality. Current models use a variety of mechanisms to represent demographic events. Mortality is modeled to represent a number of different processes, including death by fire, wind throw, extreme temperatures, and self-thinning, and each vegetation model differs in the emphasis they place on specific mechanisms. Dynamic global vegetation models generally operate on the assumption of incremental vegetation shift due to changes in the carbon economy of plant functional types and proportional effects on recruitment, growth, competition and mortality, but this may not capture sudden and sweeping tree death caused by extreme weather conditions. We tested several different approaches to predicting tree mortality within the framework of the Sheffield Dynamic Global Vegetation Model. We applied the model to the state of Texas, USA, which in 2011 experienced extreme drought conditions, causing the death of an estimated 300 million trees statewide. We then compared predicted to actual mortality to determine which algorithms most accurately predicted geographical variation in tree mortality. We discuss implications regarding the ongoing debate on the causes of tree death.

Single event and TREE latchup mitigation for a star tracker sensor: An innovative approach to system level latchup mitigation

International Nuclear Information System (INIS)

Kimbrough, J.R.; Colella, N.J.; Davis, R.W.; Bruener, D.B.; Coakley, P.G.; Lutjens, S.W.; Mallon, C.E.

1994-08-01

Electronic packages designed for spacecraft should be fault-tolerant and operate without ground control intervention through extremes in the space radiation environment. If designed for military use, the electronics must survive and function in a nuclear radiation environment. This paper presents an innovative ''blink'' approach rather than the typical ''operate through'' approach to achieve system level latchup mitigation on a prototype star tracker camera. Included are circuit designs, flash x-ray test data, and heavy ion data demonstrating latchup mitigation protecting micro-electronics from current latchup and burnout due to Single Event Latchup (SEL) and Transient Radiation Effects on Electronics (TREE)

Probabilistic approach relative to fire scenarios study

International Nuclear Information System (INIS)

Chabot, Jean-Luc

1998-01-01

The main objective of this thesis is to develop a calculation method of the occurring probability of the fire scenarios (detection, setting of the intervention, extinction) taking into account the size and the impact of the fire on the surroundings. This new method is called 'hybrid simulation'. It includes in a unique modelling the processing of continuous and discrete phenomenon. Moreover, to correctly represent fire scenarios, it is necessary not to take only into account the 'continuous' growing of the fire itself but of also 'discrete' events like detection, fire fighting and extinction, human behaviour and related faults. For that purpose we couple a code modelling the physical aspects of the fire to Petri nets which is able to model these 'discrete' events, this coupling consists of driving the 'continuous' model by the occurring of the 'discrete' events. This new technique which can be used to cover 'discrete' and 'continuous' events in a single calculation represents a solution to dynamic reliability calculation problems, for which there is a continuously increasing demand for analysing reliability, availability of production and maintainability of complex industrial systems. (author) [fr

Twisted trees and inconsistency of tree estimation when gaps are treated as missing data - The impact of model mis-specification in distance corrections.

Science.gov (United States)

McTavish, Emily Jane; Steel, Mike; Holder, Mark T

2015-12-01

Statistically consistent estimation of phylogenetic trees or gene trees is possible if pairwise sequence dissimilarities can be converted to a set of distances that are proportional to the true evolutionary distances. Susko et al. (2004) reported some strikingly broad results about the forms of inconsistency in tree estimation that can arise if corrected distances are not proportional to the true distances. They showed that if the corrected distance is a concave function of the true distance, then inconsistency due to long branch attraction will occur. If these functions are convex, then two "long branch repulsion" trees will be preferred over the true tree - though these two incorrect trees are expected to be tied as the preferred true. Here we extend their results, and demonstrate the existence of a tree shape (which we refer to as a "twisted Farris-zone" tree) for which a single incorrect tree topology will be guaranteed to be preferred if the corrected distance function is convex. We also report that the standard practice of treating gaps in sequence alignments as missing data is sufficient to produce non-linear corrected distance functions if the substitution process is not independent of the insertion/deletion process. Taken together, these results imply inconsistent tree inference under mild conditions. For example, if some positions in a sequence are constrained to be free of substitutions and insertion/deletion events while the remaining sites evolve with independent substitutions and insertion/deletion events, then the distances obtained by treating gaps as missing data can support an incorrect tree topology even given an unlimited amount of data. Copyright © 2015 Elsevier Inc. All rights reserved.

Analytical solutions of linked fault tree probabilistic risk assessments using binary decision diagrams with emphasis on nuclear safety applications

International Nuclear Information System (INIS)

Nusbaumer, O. P. M.

2007-01-01

This study is concerned with the quantification of Probabilistic Risk Assessment (PRA) using linked Fault Tree (FT) models. Probabilistic Risk assessment (PRA) of Nuclear Power Plants (NPPs) complements traditional deterministic analysis; it is widely recognized as a comprehensive and structured approach to identify accident scenarios and to derive numerical estimates of the associated risk levels. PRA models as found in the nuclear industry have evolved rapidly. Increasingly, they have been broadly applied to support numerous applications on various operational and regulatory matters. Regulatory bodies in many countries require that a PRA be performed for licensing purposes. PRA has reached the point where it can considerably influence the design and operation of nuclear power plants. However, most of the tools available for quantifying large PRA models are unable to produce analytically correct results. The algorithms of such quantifiers are designed to neglect sequences when their likelihood decreases below a predefined cutoff limit. In addition, the rare event approximation (e.g. Moivre's equation) is typically implemented for the first order, ignoring the success paths and the possibility that two or more events can occur simultaneously. This is only justified in assessments where the probabilities of the basic events are low. When the events in question are failures, the first order rare event approximation is always conservative, resulting in wrong interpretation of risk importance measures. Advanced NPP PRA models typically include human errors, common cause failure groups, seismic and phenomenological basic events, where the failure probabilities may approach unity, leading to questionable results. It is accepted that current quantification tools have reached their limits, and that new quantification techniques should be investigated. A novel approach using the mathematical concept of Binary Decision Diagram (BDD) is proposed to overcome these deficiencies

From Gene Trees to a Dated Allopolyploid Network: Insights from the Angiosperm Genus Viola (Violaceae)

Science.gov (United States)

Marcussen, Thomas; Heier, Lise; Brysting, Anne K.; Oxelman, Bengt; Jakobsen, Kjetill S.

2015-01-01

Allopolyploidization accounts for a significant fraction of speciation events in many eukaryotic lineages. However, existing phylogenetic and dating methods require tree-like topologies and are unable to handle the network-like phylogenetic relationships of lineages containing allopolyploids. No explicit framework has so far been established for evaluating competing network topologies, and few attempts have been made to date phylogenetic networks. We used a four-step approach to generate a dated polyploid species network for the cosmopolitan angiosperm genus Viola L. (Violaceae Batch.). The genus contains ca 600 species and both recent (neo-) and more ancient (meso-) polyploid lineages distributed over 16 sections. First, we obtained DNA sequences of three low-copy nuclear genes and one chloroplast region, from 42 species representing all 16 sections. Second, we obtained fossil-calibrated chronograms for each nuclear gene marker. Third, we determined the most parsimonious multilabeled genome tree and its corresponding network, resolved at the section (not the species) level. Reconstructing the “correct” network for a set of polyploids depends on recovering all homoeologs, i.e., all subgenomes, in these polyploids. Assuming the presence of Viola subgenome lineages that were not detected by the nuclear gene phylogenies (“ghost subgenome lineages”) significantly reduced the number of inferred polyploidization events. We identified the most parsimonious network topology from a set of five competing scenarios differing in the interpretation of homoeolog extinctions and lineage sorting, based on (i) fewest possible ghost subgenome lineages, (ii) fewest possible polyploidization events, and (iii) least possible deviation from expected ploidy as inferred from available chromosome counts of the involved polyploid taxa. Finally, we estimated the homoploid and polyploid speciation times of the most parsimonious network. Homoploid speciation times were estimated by

Drug Adverse Event Detection in Health Plan Data Using the Gamma Poisson Shrinker and Comparison to the Tree-based Scan Statistic

Directory of Open Access Journals (Sweden)

David Smith

2013-03-01

Full Text Available Background: Drug adverse event (AE signal detection using the Gamma Poisson Shrinker (GPS is commonly applied in spontaneous reporting. AE signal detection using large observational health plan databases can expand medication safety surveillance. Methods: Using data from nine health plans, we conducted a pilot study to evaluate the implementation and findings of the GPS approach for two antifungal drugs, terbinafine and itraconazole, and two diabetes drugs, pioglitazone and rosiglitazone. We evaluated 1676 diagnosis codes grouped into 183 different clinical concepts and four levels of granularity. Several signaling thresholds were assessed. GPS results were compared to findings from a companion study using the identical analytic dataset but an alternative statistical method—the tree-based scan statistic (TreeScan. Results: We identified 71 statistical signals across two signaling thresholds and two methods, including closely-related signals of overlapping diagnosis definitions. Initial review found that most signals represented known adverse drug reactions or confounding. About 31% of signals met the highest signaling threshold. Conclusions: The GPS method was successfully applied to observational health plan data in a distributed data environment as a drug safety data mining method. There was substantial concordance between the GPS and TreeScan approaches. Key method implementation decisions relate to defining exposures and outcomes and informed choice of signaling thresholds.

Development and application of a methodology for identifying and characterising scenarios

International Nuclear Information System (INIS)

Billington, D.; Bailey, L.

1998-01-01

This report forms part of a suite of documents describing the Nirex model development programme. The programme is designed to provide a clear audit trail from the identification of significant features, events and processes (FEPs) to the models and modelling processes employed within a detailed performance assessment. A scenario approach to performance assessment has been adopted. It is proposed that potential evolutions of a deep geological radioactive waste repository can be represented by a base scenario and a number of variant scenarios. It is intended that assessment of the base, scenario would form the core of any future performance assessment. The base scenario is chosen to be broad-ranging and to represent the natural evolution of the repository system and its surrounding environment. The base scenario is defined to include all those FEPs which are certain to occur and those which are judged likely to occur for a significant period of the assessment timescale. Variant scenarios are defined by FEPs which represent a significant perturbation to the natural system evolution, for example the occurrence of a large seismic event. A variant scenario defined by a single initiating FEP is characterised by a sequence of events. This is represented as a 'timeline' which forms the basis for modelling that scenario. To generate a variant scenario defined by two initiating FEPs, a methodology is presented for combining the timelines for the two underlying 'single-FEP' variants. The resulting series of event sequences can be generated automatically. These sequences are then reviewed, in order to reduce the number of timelines requiring detailed consideration. This is achieved in two ways: by aggregating sequences which have similar consequence in terms of safety performance; and by combining successive intervals along a timeline where appropriate. In the context of a performance assessment, the aim is to determine the conditional risk and appropriate weight for each

Quantitative analysis of a fault tree with priority AND gates

International Nuclear Information System (INIS)

Yuge, T.; Yanagi, S.

2008-01-01

A method for calculating the exact top event probability of a fault tree with priority AND gates and repeated basic events is proposed when the minimal cut sets are given. A priority AND gate is an AND gate where the input events must occur in a prescribed order for the occurrence of the output event. It is known that the top event probability of such a dynamic fault tree is obtained by converting the tree into an equivalent Markov model. However, this method is not realistic for a complex system model because the number of states which should be considered in the Markov analysis increases explosively as the number of basic events increases. To overcome the shortcomings of the Markov model, we propose an alternative method to obtain the top event probability in this paper. We assume that the basic events occur independently, exponentially distributed, and the component whose failure corresponds to the occurrence of the basic event is non-repairable. First, we obtain the probability of occurrence of the output event of a single priority AND gate by Markov analysis. Then, the top event probability is given by a cut set approach and the inclusion-exclusion formula. An efficient procedure to obtain the probabilities corresponding to logical products in the inclusion-exclusion formula is proposed. The logical product which is composed of two or more priority AND gates having at least one common basic event as their inputs is transformed into the sum of disjoint events which are equivalent to a priority AND gate in the procedure. Numerical examples show that our method works well for complex systems

Scenarios constructed for basaltic igneous activity at Yucca Mountain and vicinity

International Nuclear Information System (INIS)

Barr, G.E.; Dunn, E.; Dockery, H.; Barnard, R.; Valentine, G.; Crowe, B.

1993-08-01

Basaltic volcanism has been identified as a possible future event initiating a release of radionuclides from a potential repository at the proposed Yucca Mountain high-level waste repository site. The performance assessment method set forth in the Site Characterization Plan (DOE, 1988) requires that a set of scenarios encompassing all significant radionuclide release paths to the accessible environment be described. This report attempts to catalogue the details of the interactions between the features and processes produced by basaltic volcanism in the presence of the presumed groundwater flow system and a repository structure, the engineered barrier system (EBS), and waste. This catalogue is developed in the form of scenarios. We define a scenario as a well-posed problem, starting from an initiating event or process and proceeding through a logically connected and physically possible combination or sequence of features, events, and processes (FEPs) to the release of contaminants

Feature, Event, and Process Screening and Scenario Development for the Yucca Mountain Total System Performance Assessment

International Nuclear Information System (INIS)

Barnard, R.; Barr, G.; Burch, P.; Freeze, G.; Rechard, R.; Schenker, A.; Swift, P.

1999-01-01

Scenario development has two primary purposes in the design and documentation of post-closure performance assessments in a regulatory setting. First, scenario development ensures a sufficiently comprehensive consideration of the possible future states of the system. Second, scenario development identifies the important scenarios that must be considered in quantitative analyses of the total system performance assessment (TSPA). Section 2.0 of this report describes the scenario development process. Steps in the process are described in Section 2.1, and terms introduced in this section are defined in Section 2.2. The electronic database used to document the process is described in Section 3, and Section 4 provides a summary of the current status of the YMP scenario development work. Section 5 contains acknowledgments, and Section 6 contains a list of the references cited

New approaches to evaluating fault trees

International Nuclear Information System (INIS)

Sinnamon, R.M.; Andrews, J.D.

1997-01-01

Fault Tree Analysis is now a widely accepted technique to assess the probability and frequency of system failure in many industries. For complex systems an analysis may produce hundreds of thousands of combinations of events which can cause system failure (minimal cut sets). The determination of these cut sets can be a very time consuming process even on modern high speed digital computers. Computerised methods, such as bottom-up or top-down approaches, to conduct this analysis are now so well developed that further refinement is unlikely to result in vast reductions in computer time. It is felt that substantial improvement in computer utilisation will only result from a completely new approach. This paper describes the use of a Binary Decision Diagram for Fault Tree Analysis and some ways in which it can be efficiently implemented on a computer. In particular, attention is given to the production of a minimum form of the Binary Decision Diagram by considering the ordering that has to be given to the basic events of the fault tree

The role of hybridization in facilitating tree invasion

Science.gov (United States)

Hybridization events can generate additional genetic diversity on which natural selection can act and at times enhance invasiveness of the species. Invasive tree species are a growing ecological concern worldwide, and some of these invasions involve hybridization events pre- or post-introduction. Th...

Event-by-event jet quenching

Energy Technology Data Exchange (ETDEWEB)

Fries, R.J.; Rodriguez, R.; Ramirez, E.

2010-08-14

High momentum jets and hadrons can be used as probes for the quark gluon plasma (QGP) formed in nuclear collisions at high energies. We investigate the influence of fluctuations in the fireball on jet quenching observables by comparing propagation of light quarks and gluons through averaged, smooth QGP fireballs with event-by-event jet quenching using realistic inhomogeneous fireballs. We find that the transverse momentum and impact parameter dependence of the nuclear modification factor R{sub AA} can be fit well in an event-by-event quenching scenario within experimental errors. However the transport coefficient {cflx q} extracted from fits to the measured nuclear modification factor R{sub AA} in averaged fireballs underestimates the value from event-by-event calculations by up to 50%. On the other hand, after adjusting {cflx q} to fit R{sub AA} in the event-by-event analysis we find residual deviations in the azimuthal asymmetry v{sub 2} and in two-particle correlations, that provide a possible faint signature for a spatial tomography of the fireball. We discuss a correlation function that is a measure for spatial inhomogeneities in a collision and can be constrained from data.

Event-by-event jet quenching

Energy Technology Data Exchange (ETDEWEB)

Rodriguez, R. [Cyclotron Institute and Physics Department, Texas A and M University, College Station, TX 77843 (United States); Fries, R.J., E-mail: rjfries@comp.tamu.ed [Cyclotron Institute and Physics Department, Texas A and M University, College Station, TX 77843 (United States); RIKEN/BNL Research Center, Brookhaven National Laboratory, Upton, NY 11973 (United States); Ramirez, E. [Physics Department, University of Texas El Paso, El Paso, TX 79968 (United States)

2010-09-27

High momentum jets and hadrons can be used as probes for the quark gluon plasma (QGP) formed in nuclear collisions at high energies. We investigate the influence of fluctuations in the fireball on jet quenching observables by comparing propagation of light quarks and gluons through averaged, smooth QGP fireballs with event-by-event jet quenching using realistic inhomogeneous fireballs. We find that the transverse momentum and impact parameter dependence of the nuclear modification factor R{sub AA} can be fit well in an event-by-event quenching scenario within experimental errors. However the transport coefficient q extracted from fits to the measured nuclear modification factor R{sub AA} in averaged fireballs underestimates the value from event-by-event calculations by up to 50%. On the other hand, after adjusting q to fit R{sub AA} in the event-by-event analysis we find residual deviations in the azimuthal asymmetry v{sub 2} and in two-particle correlations, that provide a possible faint signature for a spatial tomography of the fireball. We discuss a correlation function that is a measure for spatial inhomogeneities in a collision and can be constrained from data.

Modification of the SAS4A Safety Analysis Code for Integration with the ADAPT Discrete Dynamic Event Tree Framework.

Energy Technology Data Exchange (ETDEWEB)

Jankovsky, Zachary Kyle [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Denman, Matthew R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2017-05-01

It is difficult to assess the consequences of a transient in a sodium-cooled fast reactor (SFR) using traditional probabilistic risk assessment (PRA) methods, as numerous safety-related sys- tems have passive characteristics. Often there is significant dependence on the value of con- tinuous stochastic parameters rather than binary success/failure determinations. One form of dynamic PRA uses a system simulator to represent the progression of a transient, tracking events through time in a discrete dynamic event tree (DDET). In order to function in a DDET environment, a simulator must have characteristics that make it amenable to changing physical parameters midway through the analysis. The SAS4A SFR system analysis code did not have these characteristics as received. This report describes the code modifications made to allow dynamic operation as well as the linking to a Sandia DDET driver code. A test case is briefly described to demonstrate the utility of the changes.

Vulnerability of Amazon forests to storm-driven tree mortality

Science.gov (United States)

Negrón-Juárez, Robinson I.; Holm, Jennifer A.; Magnabosco Marra, Daniel; Rifai, Sami W.; Riley, William J.; Chambers, Jeffrey Q.; Koven, Charles D.; Knox, Ryan G.; McGroddy, Megan E.; Di Vittorio, Alan V.; Urquiza-Muñoz, Jose; Tello-Espinoza, Rodil; Alegria Muñoz, Waldemar; Ribeiro, Gabriel H. P. M.; Higuchi, Niro

2018-05-01

Tree mortality is a key driver of forest community composition and carbon dynamics. Strong winds associated with severe convective storms are dominant natural drivers of tree mortality in the Amazon. Why forests vary with respect to their vulnerability to wind events and how the predicted increase in storm events might affect forest ecosystems within the Amazon are not well understood. We found that windthrows are common in the Amazon region extending from northwest (Peru, Colombia, Venezuela, and west Brazil) to central Brazil, with the highest occurrence of windthrows in the northwest Amazon. More frequent winds, produced by more frequent severe convective systems, in combination with well-known processes that limit the anchoring of trees in the soil, help to explain the higher vulnerability of the northwest Amazon forests to winds. Projected increases in the frequency and intensity of convective storms in the Amazon have the potential to increase wind-related tree mortality. A forest demographic model calibrated for the northwestern and the central Amazon showed that northwestern forests are more resilient to increased wind-related tree mortality than forests in the central Amazon. Our study emphasizes the importance of including wind-related tree mortality in model simulations for reliable predictions of the future of tropical forests and their effects on the Earth’ system.

Klasifikasi Nilai Kelayakan Calon Debitur Baru Menggunakan Decision Tree C4.5

Directory of Open Access Journals (Sweden)

Bambang Hermanto

2017-01-01

Full Text Available In an effort to improve the quality of customer service, especially in terms of feasibility assessment of borrowers due to the increasing number of new prospective borrowers loans financing the purchase of a motor vehicle, then the company needs a decision making tool allowing you to easily and quickly estimate Where the debtor is able to pay off the loans. This study discusses the process generates C4.5 decision tree algorithm and utilizing the learning group of debtor financing dataset motorcycle. The decision tree is then interpreted into the form of decision rules that can be understood and used as a reference in processing the data of borrowers in determining the feasibility of prospective new borrowers. Feasibility value refers to the value of the destination parameter credit status. If the value of the credit is paid off status mean estimated prospective borrower is able to repay the loan in question, but if the credit status parameters estimated worth pull means candidates concerned debtor is unable to pay loans.. System testing is done by comparing the results of the testing data by learning data in three scenarios with the decision that the data is valid at over 70% for all case scenarios. Moreover, in generated tree  and generate rules takes fairly quickly, which is no more than 15 minutes for each test scenario

Minimality of critical scenarios with linear logic and cutsets

African Journals Online (AJOL)

DK

establish the causality between undesirable events and normal operations. The proof trees of ... MS (both continuous and discrete features) leads us to choose a ...... Modeling and simulation of hybrid system through. Differential Predicate ...

Interpretation of ambiguous social scenarios in social phobia and depression: evidence from event-related brain potentials.

Science.gov (United States)

Moser, Jason S; Huppert, Jonathan D; Foa, Edna B; Simons, Robert F

2012-02-01

In the current study, event-related potentials (ERPs) and behavioral responses were measured in individuals meeting diagnostic criteria for social phobia, depression, their combination, or neither in order to examine the unique and combined effects of social phobia and depression on the interpretation of ambiguous social scenarios. ERPs revealed a lack of positive interpretation bias and some suggestion of a negative bias in the semantic expectancy N4 component across all clinical groups. Furthermore, socially phobic and comorbid individuals showed reductions in baseline attention allocation to the task, as indexed by P6 amplitude. RT and accuracy likewise revealed a lack of positive interpretation bias across disordered groups. When considered on a continuum across all samples, social phobia and depression symptoms were related to the N4 interpretation bias effect whereas P6 amplitude reduction and RT interpretation bias appeared uniquely associated with social phobia. Copyright © 2011 Elsevier B.V. All rights reserved.

F-term stabilization of odd axions in LARGE volume scenario

International Nuclear Information System (INIS)

Gao, Xin; Shukla, Pramod

2014-01-01

In the context of the LARGE volume scenario, stabilization of axionic moduli is revisited. This includes both even and odd axions with their scalar potential being generated by F-term contributions via various tree-level and non-perturbative effects like fluxed E3-brane instantons and fluxed poly-instantons. In all the cases, we estimate the decay constants and masses of the axions involved

Moisture availability limits subalpine tree establishment.

Science.gov (United States)

Andrus, Robert A; Harvey, Brian J; Rodman, Kyle C; Hart, Sarah J; Veblen, Thomas T

2018-03-01

In the absence of broad-scale disturbance, many temperate coniferous forests experience successful seedling establishment only when abundant seed production coincides with favorable climate. Identifying the frequency of past establishment events and the climate conditions favorable for seedling establishment is essential to understanding how climate warming could affect the frequency of future tree establishment events and therefore future forest composition or even persistence of a forest cover. In the southern Rocky Mountains, USA, research on the sensitivity of establishment of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa)-two widely distributed, co-occurring conifers in North America-to climate variability has focused on the alpine treeline ecotone, leaving uncertainty about the sensitivity of these species across much of their elevation distribution. We compared annual germination dates for >450 Engelmann spruce and >500 subalpine fir seedlings collected across a complex topographic-moisture gradient to climate variability in the Colorado Front Range. We found that Engelmann spruce and subalpine fir established episodically with strong synchrony in establishment events across the study area. Broad-scale establishment events occurred in years of high soil moisture availability, which were characterized by above-average snowpack and/or cool and wet summer climatic conditions. In the recent half of the study period (1975-2010), a decrease in the number of fir and spruce establishment events across their distribution coincided with declining snowpack and a multi-decadal trend of rising summer temperature and increasing moisture deficits. Counter to expected and observed increases in tree establishment with climate warming in maritime subalpine forests, our results show that recruitment declines will likely occur across the core of moisture-limited subalpine tree ranges as warming drives increased moisture deficits. © 2018 by the

Probabilistic assessment of fire related events in CWPH (Pilot study)

International Nuclear Information System (INIS)

Chatterjee, D.; Maity, S.C.; Guptan, Rajee; Mohan, Nalini; Ghadge, S.G.; Bajaj, S.S.

2006-01-01

As a part of Fire PSA for KAPS, a pilot study has been taken up identifying CWPH as the important zone vulnerable to fire. As the CWPH houses pumps belonging to all important cooling (APWC, FFW, NAHPPW, NALPW, etc.) of both the units, a single fire leads to failure of multiple safety/safety support system cooling affecting the safety of the plant. The objective of this study is as follows: Familiarising with the various published Fire-PSA study, comparing and finalisation of the computer code amongst various codes available with DAE, identifying and sequencing different activities involved for carrying out Fire PSA, i.e. Zoning and Sub-Zoning of Fire Source Area, Fire vulnerability of System and Component surrounding Fire Source, etc., finalization of report format and documentation. Computer Code FDS is used to carry out Fire Hazard Analysis. FDS is the latest state-of the-art software package extensively used for Fire Hazard Analysis. It develops a 3D scenario for any given fire giving credit to actual physical location of fire load and ventilation. It gives the time dependent of any fire in a specific zone crediting the time required by operator to take necessary preventive action which helps in quantifying the probability of error for any particular operator's for PSA study. To identify the most vulnerable sub-zone in CWPH, a walk down was organized and physical location of each load; their separation, fire barrier, ventilator in the room, arrangement of fire protection/fighting system, localized operator's room were reviewed. Fire in the middle diesel tank with pump is considered as initiating event in the sub-zone of CWPH. The Event Tree for this initiating event for CWPH was developed. Event Tree end states are identified as large fire i.e. fire which is failed to be detected by both means, i.e. early and late and failure in fighting by both means i.e. early and late. (author)

The longevity of broadleaf deciduous trees in Northern Hemisphere temperate forests: insights from tree-ring series

Directory of Open Access Journals (Sweden)

Alfredo eDi Filippo

2015-05-01

Full Text Available Understanding the factors controlling the expression of longevity in trees is still an outstanding challenge for tree biologists and forest ecologists. We gathered tree-ring data and literature for broadleaf deciduous (BD temperate trees growing in closed-canopy old-growth forests in the Northern Hemisphere to explore the role of geographic patterns, climate variability, and growth rates on longevity. Our pan-continental analysis, covering 32 species from 12 genera, showed that 300-400 years can be considered a baseline threshold for maximum tree lifespan in many temperate deciduous forests. Maximum age varies greatly in relation to environmental features, even within the same species. Tree longevity is generally promoted by reduced growth rates across large genetic differences and environmental gradients. We argue that slower growth rates, and the associated smaller size, provide trees with an advantage against biotic and abiotic disturbance agents, supporting the idea that size, not age, is the main constraint to tree longevity. The oldest trees were living most of their life in subordinate canopy conditions and/or within primary forests in cool temperate environments and outside major storm tracks. Very old trees are thus characterized by slow growth and often live in forests with harsh site conditions and infrequent disturbance events that kill much of the trees. Temperature inversely controls the expression of longevity in mesophilous species (Fagus spp., but its role in Quercus spp. is more complex and warrants further research in disturbance ecology. Biological, ecological and historical drivers must be considered to understand the constraints imposed to longevity within different forest landscapes.

Method to Find Recovery Event Combinations in Probabilistic Safety Assessment

International Nuclear Information System (INIS)

Jung, Woo Sik; Riley, Jeff

2016-01-01

These research activities may develop mathematical methods, engineering analyses, and business processes. The research activities of the project covered by this scope are directed toward the specific issues of implementing the methods and strategies on a computational platform, identifying the features and enhancements to EPRI tools that would be necessary to realize significant improvements to the risk assessments performed by the end user. Fault tree analysis is extensively and successfully applied to the risk assessment of safety-critical systems such as nuclear, chemical and aerospace systems. The fault tree analysis is being used together with an event tree analysis in PSA of nuclear power plants. Fault tree solvers for a PSA are mostly based on the cutset-based algorithm. They generate minimal cut sets (MCSs) from a fault tree. The most popular fault tree solver in the PSA industry is FTREX. During the course of this project, certain technical issues (see Sections 2 to 5) have been identified that need to be addressed regarding how minimal cut sets are generated and quantified. The objective of this scope of the work was to develop new methods or techniques to address these technical limitations. By turning on all the cutset initiators (%1, %2, %3, %), all the possible minimal cut sets can be calculated easier than with the original fault tree. It is accomplished by the fact that the number of events in the minimal cut sets are significantly reduced by using cutset initiators instead of random failure events. And byy turning on a few chosen cutset initiators and turning off the other cutset initiators, minimal cut sets of the selected cutset initiator(s) can be easily calculated. As explained in the previous Sections, there is no way to calculate these minimal cut sets by turning off/on the random failure events in the original fault tree

Method to Find Recovery Event Combinations in Probabilistic Safety Assessment

Energy Technology Data Exchange (ETDEWEB)

Jung, Woo Sik [Sejong University, Seoul (Korea, Republic of); Riley, Jeff [Electric Power Research, Palo Alto (United States)

2016-05-15

These research activities may develop mathematical methods, engineering analyses, and business processes. The research activities of the project covered by this scope are directed toward the specific issues of implementing the methods and strategies on a computational platform, identifying the features and enhancements to EPRI tools that would be necessary to realize significant improvements to the risk assessments performed by the end user. Fault tree analysis is extensively and successfully applied to the risk assessment of safety-critical systems such as nuclear, chemical and aerospace systems. The fault tree analysis is being used together with an event tree analysis in PSA of nuclear power plants. Fault tree solvers for a PSA are mostly based on the cutset-based algorithm. They generate minimal cut sets (MCSs) from a fault tree. The most popular fault tree solver in the PSA industry is FTREX. During the course of this project, certain technical issues (see Sections 2 to 5) have been identified that need to be addressed regarding how minimal cut sets are generated and quantified. The objective of this scope of the work was to develop new methods or techniques to address these technical limitations. By turning on all the cutset initiators (%1, %2, %3, %), all the possible minimal cut sets can be calculated easier than with the original fault tree. It is accomplished by the fact that the number of events in the minimal cut sets are significantly reduced by using cutset initiators instead of random failure events. And byy turning on a few chosen cutset initiators and turning off the other cutset initiators, minimal cut sets of the selected cutset initiator(s) can be easily calculated. As explained in the previous Sections, there is no way to calculate these minimal cut sets by turning off/on the random failure events in the original fault tree.

Shipping container response to three severe railway accident scenarios

International Nuclear Information System (INIS)

Mok, G.C.; Fischer, L.E.; Murty, S.S.; Witte, M.C.

1998-01-01

The probability of damage and the potential resulting hazards are analyzed for a representative rail shipping container for three severe rail accident scenarios. The scenarios are: (1) the rupture of closure bolts and resulting opening of closure lid due to a severe impact, (2) the puncture of container by an impacting rail-car coupler, and (3) the yielding of container due to side impact on a rigid uneven surface. The analysis results indicate that scenario 2 is a physically unreasonable event while the probabilities of a significant loss of containment in scenarios 1 and 3 are extremely small. Before assessing the potential risk for the last two scenarios, the uncertainties in predicting complex phenomena for rare, high- consequence hazards needs to be addressed using a rigorous methodology

Nonbinary Tree-Based Phylogenetic Networks

NARCIS (Netherlands)

Jetten, L.; van Iersel, L.J.J.

2018-01-01

Rooted phylogenetic networks are used to describe evolutionary histories that contain non-treelike evolutionary events such as hybridization and horizontal gene transfer. In some cases, such histories can be described by a phylogenetic base-tree with additional linking arcs, which can for example

Estimating Coextinction Risks from Epidemic Tree Death: Affiliate Lichen Communities among Diseased Host Tree Populations of Fraxinus excelsior

Science.gov (United States)

Jönsson, Mari T.; Thor, Göran

2012-01-01

At least 10% of the world’s tree species are threatened with extinction and pathogens are increasingly implicated in tree threats. Coextinction and threats to affiliates as a consequence of the loss or decline of their host trees is a poorly understood phenomenon. Ash dieback is an emerging infectious disease causing severe dieback of common ash Fraxinus excelsior throughout Europe. We utilized available empirical data on affiliate epiphytic lichen diversity (174 species and 17,800 observations) among 20 ash dieback infected host tree populations of F. excelsior on the island Gotland in the Baltic Sea, Sweden. From this, we used structured scenario projections scaled with empirical data of ash dieback disease to generate probabilistic models for estimating local and regional lichen coextinction risks. Average coextinction probabilities (Ā) were 0.38 (95% CI ±0.09) for lichens occurring on F. excelsior and 0.14 (95% CI ±0.03) when considering lichen persistence on all tree species. Ā was strongly linked to local disease incidence levels and generally increasing with lichen host specificity to F. excelsior and decreasing population size. Coextinctions reduced affiliate community viability, with significant local reductions in species richness and shifts in lichen species composition. Affiliates were projected to become locally extirpated before their hosts, illuminating the need to also consider host tree declines. Traditionally managed open wooded meadows had the highest incidence of ash dieback disease and significantly higher proportions of affiliate species projected to go extinct, compared with unmanaged closed forests and semi-open grazed sites. Most cothreatened species were not previously red-listed, which suggest that tree epidemics cause many unforeseen threats to species. Our analysis shows that epidemic tree deaths represent an insidious, mostly overlooked, threat to sessile affiliate communities in forested environments. Current conservation and

Thematic and spatial resolutions affect model-based predictions of tree species distribution.

Science.gov (United States)

Liang, Yu; He, Hong S; Fraser, Jacob S; Wu, ZhiWei

2013-01-01

Subjective decisions of thematic and spatial resolutions in characterizing environmental heterogeneity may affect the characterizations of spatial pattern and the simulation of occurrence and rate of ecological processes, and in turn, model-based tree species distribution. Thus, this study quantified the importance of thematic and spatial resolutions, and their interaction in predictions of tree species distribution (quantified by species abundance). We investigated how model-predicted species abundances changed and whether tree species with different ecological traits (e.g., seed dispersal distance, competitive capacity) had different responses to varying thematic and spatial resolutions. We used the LANDIS forest landscape model to predict tree species distribution at the landscape scale and designed a series of scenarios with different thematic (different numbers of land types) and spatial resolutions combinations, and then statistically examined the differences of species abundance among these scenarios. Results showed that both thematic and spatial resolutions affected model-based predictions of species distribution, but thematic resolution had a greater effect. Species ecological traits affected the predictions. For species with moderate dispersal distance and relatively abundant seed sources, predicted abundance increased as thematic resolution increased. However, for species with long seeding distance or high shade tolerance, thematic resolution had an inverse effect on predicted abundance. When seed sources and dispersal distance were not limiting, the predicted species abundance increased with spatial resolution and vice versa. Results from this study may provide insights into the choice of thematic and spatial resolutions for model-based predictions of tree species distribution.

Tree-ring analysis of winter climate variability and ENSO in Mediterranean California

International Nuclear Information System (INIS)

Woodhouse, C.A.; Univ. of Colorado, Boulder

2006-01-01

The feasibility of using tree-ring data as a proxy for regional precipitation and ENSO events in the Mediterranean region of California is explored. A transect of moisture-sensitive tree-ring sites, extending from southwestern to north-central California, documents regional patterns of winter precipitation and replicates the regional response to ENSO events in the 20. century. Proxy records of ENSO were used with the tree-ring data to examine precipitation/ENSO patterns in the 18. and 19. centuries. Results suggest some temporal and spatial variability in the regional precipitation response to ENSO over the last three centuries

The future of large old trees in urban landscapes.

Science.gov (United States)

Le Roux, Darren S; Ikin, Karen; Lindenmayer, David B; Manning, Adrian D; Gibbons, Philip

2014-01-01

Large old trees are disproportionate providers of structural elements (e.g. hollows, coarse woody debris), which are crucial habitat resources for many species. The decline of large old trees in modified landscapes is of global conservation concern. Once large old trees are removed, they are difficult to replace in the short term due to typically prolonged time periods needed for trees to mature (i.e. centuries). Few studies have investigated the decline of large old trees in urban landscapes. Using a simulation model, we predicted the future availability of native hollow-bearing trees (a surrogate for large old trees) in an expanding city in southeastern Australia. In urban greenspace, we predicted that the number of hollow-bearing trees is likely to decline by 87% over 300 years under existing management practices. Under a worst case scenario, hollow-bearing trees may be completely lost within 115 years. Conversely, we predicted that the number of hollow-bearing trees will likely remain stable in semi-natural nature reserves. Sensitivity analysis revealed that the number of hollow-bearing trees perpetuated in urban greenspace over the long term is most sensitive to the: (1) maximum standing life of trees; (2) number of regenerating seedlings ha(-1); and (3) rate of hollow formation. We tested the efficacy of alternative urban management strategies and found that the only way to arrest the decline of large old trees requires a collective management strategy that ensures: (1) trees remain standing for at least 40% longer than currently tolerated lifespans; (2) the number of seedlings established is increased by at least 60%; and (3) the formation of habitat structures provided by large old trees is accelerated by at least 30% (e.g. artificial structures) to compensate for short term deficits in habitat resources. Immediate implementation of these recommendations is needed to avert long term risk to urban biodiversity.

Evolution of spatio-temporal drought characteristics: validation, projections and effect of adaptation scenarios

Science.gov (United States)

Vidal, J.-P.; Martin, E.; Kitova, N.; Najac, J.; Soubeyroux, J.-M.

2012-08-01

Drought events develop in both space and time and they are therefore best described through summary joint spatio-temporal characteristics, such as mean duration, mean affected area and total magnitude. This paper addresses the issue of future projections of such characteristics of drought events over France through three main research questions: (1) Are downscaled climate projections able to simulate spatio-temporal characteristics of meteorological and agricultural droughts in France over a present-day period? (2) How such characteristics will evolve over the 21st century? (3) How to use standardized drought indices to represent theoretical adaptation scenarios? These questions are addressed using the Isba land surface model, downscaled climate projections from the ARPEGE General Circulation Model under three emissions scenarios, as well as results from a previously performed 50-yr multilevel and multiscale drought reanalysis over France. Spatio-temporal characteristics of meteorological and agricultural drought events are computed using the Standardized Precipitation Index and the Standardized Soil Wetness Index, respectively, and for time scales of 3 and 12 months. Results first show that the distributions of joint spatio-temporal characteristics of observed events are well simulated by the downscaled hydroclimate projections over a present-day period. All spatio-temporal characteristics of drought events are then found to dramatically increase over the 21st century, with stronger changes for agricultural droughts. Two theoretical adaptation scenarios are eventually built based on hypotheses of adaptation to evolving climate and hydrological normals, either retrospective or prospective. The perceived spatio-temporal characteristics of drought events derived from these theoretical adaptation scenarios show much reduced changes, but they call for more realistic scenarios at both the catchment and national scale in order to accurately assess the combined effect of

Scenario Development for Trgovska Gora Shallow Land Facility

International Nuclear Information System (INIS)

Skanata, D.; Medakovic, S.; Lokner, V.; Levanat, I.

2002-01-01

Safety assessments, either preliminary or final, consist of a qualitative and a quantitative part. The qualitative part of the assessment implies a selection of relevant scenarios to be analyzed, while the quantitative part of the assessment consists of their mathematical modeling. This work is dealing with the qualitative part of safety assessment concerning a specific radioactive waste disposal system, i.e., the shallow land facility situated on the macrolocation Trgovska gora. This article has as its purpose a brief presentation of the ISAM methodology application results (Improvement of Safety Assessment Methodologies for Near Surface Radioactive Waste Facilities;), a methodology developed within the framework of a project of the same name, organized by the IAEA. The above mentioned methodology is based on the development of the so-called FEP list (Features, Events, Process), on selection procedure of the FEP list, specifically regarding particular criteria defined in advance, and on application of systematic methods of selecting relevant scenarios (in this case the matrix of interactions method has been applied). The main aim and purpose of a methodology based on the analysis of FEPs (identification, classification, selection, construction of the matrix of interactions) consists of observing and documenting all the features, events and processes due to be taken into consideration while assessing safety of a particular radioactive waste disposal system. In this connection, by radioactive waste disposal system we mean a system consisting of radioactive waste and engineer features (barriers), geological environment within which the disposal site is located, surface-environment (soil, sediments, vegetation, etc.) and human population near the disposal site. The final step of the application of this methodology consists of generating the scenario using the matrix of interactions. So, for shallow land facility situated on the macrolocation Trgovska gora, applying

Reconstruction of certain phylogenetic networks from their tree-average distances.

Science.gov (United States)

Willson, Stephen J

2013-10-01

Trees are commonly utilized to describe the evolutionary history of a collection of biological species, in which case the trees are called phylogenetic trees. Often these are reconstructed from data by making use of distances between extant species corresponding to the leaves of the tree. Because of increased recognition of the possibility of hybridization events, more attention is being given to the use of phylogenetic networks that are not necessarily trees. This paper describes the reconstruction of certain such networks from the tree-average distances between the leaves. For a certain class of phylogenetic networks, a polynomial-time method is presented to reconstruct the network from the tree-average distances. The method is proved to work if there is a single reticulation cycle.

Use of casual tree method for investigation of incidents and accidents involving radioactive materials

International Nuclear Information System (INIS)

Vasconcelos, Vanderley de; Senne Junior, Murillo; Marques, Raissa Oliveira

2013-01-01

There are many methodologies used for investigation of accidents to facilitate the search of the factors that cause these events in different areas of industry. These can be called proactive methods, if they are used before the occurrence of the events, or reactive methods that are applied after the occurrence of the incident or accident, and are used as a basis of information to prevent further events. One of these methods is the Causal Tree Method (CTM). The basic idea of this technique is that incidents and accidents result from variations in usual processes. These variations can be related to the individual, the task, the material or the environment. The tree starts with the end event (incident or accident) and works backwards. The facts relating to the end event are used in the construction of the causal tree. The end event is the starting point and only the facts that contributed to the incident or accident should be selected. The analyst has to identify and list the variations and then display them in the analytic tree, showing causal relations. The objective of this paper is to test the application of the CTM method in investigation of incidents and accidents involving radioactive materials, in order to evaluate its efficiency on finding the typical factors causing these events. (author)

FTA, Fault Tree Analysis for Minimal Cut Sets, Graphics for CALCOMP

International Nuclear Information System (INIS)

Van Slyke, W.J.; Griffing, D.E.; Diven, J.

1978-01-01

1 - Description of problem or function: The FTA (Fault Tree Analysis) system was designed to predict probabilities of the modes of failure for complex systems and to graphically present the structure of systems. There are three programs in the system. Program ALLCUTS performs the calculations. Program KILMER constructs a CalComp plot file of the system fault tree. Program BRANCH builds a cross-reference list of the system fault tree. 2 - Method of solution: ALLCUTS employs a top-down set expansion algorithm to find fault tree cut-sets and then optionally calculates their probability using a currently accepted cut-set quantification method. The methodology is adapted from that in WASH-1400 (draft), August 1974. 3 - Restrictions on the complexity of the problem: Maxima of: 175 basic events, 425 rate events. ALLCUTS may be expanded to solve larger problems depending on available core memory

An ontology for automated scenario-based training

NARCIS (Netherlands)

Peeters, M.M.M.; Bosch, K. van den; Neerincx, M.A.; Meyer, J.J.Ch.

2014-01-01

An intelligent system for automated scenario-based training (SBT) needs knowledge about the training domain, events taking place in the simulated environment, the behaviour of the participating characters, and teaching strategies for effective learning. This knowledge base should be theoretically

Analytical solutions of linked fault tree probabilistic risk assessments using binary decision diagrams with emphasis on nuclear safety applications[Dissertation 17286

Energy Technology Data Exchange (ETDEWEB)

Nusbaumer, O. P. M

2007-07-01

This study is concerned with the quantification of Probabilistic Risk Assessment (PRA) using linked Fault Tree (FT) models. Probabilistic Risk assessment (PRA) of Nuclear Power Plants (NPPs) complements traditional deterministic analysis; it is widely recognized as a comprehensive and structured approach to identify accident scenarios and to derive numerical estimates of the associated risk levels. PRA models as found in the nuclear industry have evolved rapidly. Increasingly, they have been broadly applied to support numerous applications on various operational and regulatory matters. Regulatory bodies in many countries require that a PRA be performed for licensing purposes. PRA has reached the point where it can considerably influence the design and operation of nuclear power plants. However, most of the tools available for quantifying large PRA models are unable to produce analytically correct results. The algorithms of such quantifiers are designed to neglect sequences when their likelihood decreases below a predefined cutoff limit. In addition, the rare event approximation (e.g. Moivre's equation) is typically implemented for the first order, ignoring the success paths and the possibility that two or more events can occur simultaneously. This is only justified in assessments where the probabilities of the basic events are low. When the events in question are failures, the first order rare event approximation is always conservative, resulting in wrong interpretation of risk importance measures. Advanced NPP PRA models typically include human errors, common cause failure groups, seismic and phenomenological basic events, where the failure probabilities may approach unity, leading to questionable results. It is accepted that current quantification tools have reached their limits, and that new quantification techniques should be investigated. A novel approach using the mathematical concept of Binary Decision Diagram (BDD) is proposed to overcome these

Selective logging in tropical forests decreases the robustness of liana-tree interaction networks to the loss of host tree species.

Science.gov (United States)

Magrach, Ainhoa; Senior, Rebecca A; Rogers, Andrew; Nurdin, Deddy; Benedick, Suzan; Laurance, William F; Santamaria, Luis; Edwards, David P

2016-03-16

Selective logging is one of the major drivers of tropical forest degradation, causing important shifts in species composition. Whether such changes modify interactions between species and the networks in which they are embedded remain fundamental questions to assess the 'health' and ecosystem functionality of logged forests. We focus on interactions between lianas and their tree hosts within primary and selectively logged forests in the biodiversity hotspot of Malaysian Borneo. We found that lianas were more abundant, had higher species richness, and different species compositions in logged than in primary forests. Logged forests showed heavier liana loads disparately affecting slow-growing tree species, which could exacerbate the loss of timber value and carbon storage already associated with logging. Moreover, simulation scenarios of host tree local species loss indicated that logging might decrease the robustness of liana-tree interaction networks if heavily infested trees (i.e. the most connected ones) were more likely to disappear. This effect is partially mitigated in the short term by the colonization of host trees by a greater diversity of liana species within logged forests, yet this might not compensate for the loss of preferred tree hosts in the long term. As a consequence, species interaction networks may show a lagged response to disturbance, which may trigger sudden collapses in species richness and ecosystem function in response to additional disturbances, representing a new type of 'extinction debt'. © 2016 The Author(s).

Selective logging in tropical forests decreases the robustness of liana–tree interaction networks to the loss of host tree species

Science.gov (United States)

Magrach, Ainhoa; Senior, Rebecca A.; Rogers, Andrew; Nurdin, Deddy; Benedick, Suzan; Laurance, William F.; Santamaria, Luis; Edwards, David P.

2016-01-01

Selective logging is one of the major drivers of tropical forest degradation, causing important shifts in species composition. Whether such changes modify interactions between species and the networks in which they are embedded remain fundamental questions to assess the ‘health’ and ecosystem functionality of logged forests. We focus on interactions between lianas and their tree hosts within primary and selectively logged forests in the biodiversity hotspot of Malaysian Borneo. We found that lianas were more abundant, had higher species richness, and different species compositions in logged than in primary forests. Logged forests showed heavier liana loads disparately affecting slow-growing tree species, which could exacerbate the loss of timber value and carbon storage already associated with logging. Moreover, simulation scenarios of host tree local species loss indicated that logging might decrease the robustness of liana–tree interaction networks if heavily infested trees (i.e. the most connected ones) were more likely to disappear. This effect is partially mitigated in the short term by the colonization of host trees by a greater diversity of liana species within logged forests, yet this might not compensate for the loss of preferred tree hosts in the long term. As a consequence, species interaction networks may show a lagged response to disturbance, which may trigger sudden collapses in species richness and ecosystem function in response to additional disturbances, representing a new type of ‘extinction debt’. PMID:26936241

FTA of loss of cooling to a HALW storage tank

International Nuclear Information System (INIS)

Nomura, Yasushi

1991-10-01

A fault tree analysis consisting of assumption of accident scenarios, construction of fault trees, and performing of analyses is given for a loss of cooling accident in a HALW (High Activity Liquid Waste) tank of a typical reprocessing facility. A systematic method is developed to avoid 'missing scenarios', and 'confused scenarios' which are major problems in these analyses. Model plant data, basic failure frequency data and a fault tree analysis code named FTL have been introduced from NUKEM GmbH, Germany. The analyzed occurrence frequencies for the assumed scenarios of the loss of cooling accident are discussed to show a design improvement measure to attain a more reliable system. These results are compared with general requirements to be selected as DBE (design basis event) used in the safety assessment of the facility design. DBE is an event which is considered to have relatively high occurrence probabilities and considerable effects on environment. (author)

MAPLE-II. A program for plotting fault trees

International Nuclear Information System (INIS)

Poucet, A.; Van Den Muyzenberg, C.L.

1987-01-01

The MAPLE II code is an improved version of the MAPLE program for plotting fault trees. MAPLE II has added features which make it a versatile tool for drawing large and complex logic trees. The code is developed as part of a package for computer aided fault tree construction and analysis in which it is integrated and used as a documentation tool. However the MAPLE II code can be used as a separate program which uses as input a structure function of a tree and a description of the events and gates which make up the tree. This report includes a short description of the code and of its features. Moreover it contains the how-to-use and some indications for implementing the code and for adapting it to different graphics systems

Putative recombination events and evolutionary history of five economically important viruses of fruit trees based on coat protein-encoding gene sequence analysis.

Science.gov (United States)

Boulila, Moncef

2010-06-01

To enhance the knowledge of recombination as an evolutionary process, 267 accessions retrieved from GenBank were investigated, all belonging to five economically important viruses infecting fruit crops (Plum pox, Apple chlorotic leaf spot, Apple mosaic, Prune dwarf, and Prunus necrotic ringspot viruses). Putative recombinational events were detected in the coat protein (CP)-encoding gene using RECCO and RDP version 3.31beta algorithms. Based on RECCO results, all five viruses were shown to contain potential recombination signals in the CP gene. Reconstructed trees with modified topologies were proposed. Furthermore, RECCO performed better than the RDP package in detecting recombination events and exhibiting their evolution rate along the sequences of the five viruses. RDP, however, provided the possible major and minor parents of the recombinants. Thus, the two methods should be considered complementary.

Level 2 probabilistic event analyses and quantification

International Nuclear Information System (INIS)

Boneham, P.

2003-01-01

In this paper an example of quantification of a severe accident phenomenological event is given. The performed analysis for assessment of the probability that the debris released from the reactor vessel was in a coolable configuration in the lower drywell is presented. It is also analysed the assessment of the type of core/concrete attack that would occur. The coolability of the debris ex-vessel evaluation by an event in the Simplified Boiling Water Reactor (SBWR) Containment Event Tree (CET) and a detailed Decomposition Event Tree (DET) developed to aid in the quantification of this CET event are considered. The headings in the DET selected to represent plant physical states (e.g., reactor vessel pressure at the time of vessel failure) and the uncertainties associated with the occurrence of critical physical phenomena (e.g., debris configuration in the lower drywell) considered important to assessing whether the debris was coolable or not coolable ex-vessel are also discussed

Seismic Margin Assessment for Research Reactor using Fragility based Fault Tree Analysis

Energy Technology Data Exchange (ETDEWEB)

Kwag, Shinyoung; Oh, Jinho; Lee, Jong-Min; Ryu, Jeong-Soo [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2016-10-15

The research reactor has been often subjected to external hazards during the design lifetime. Especially, a seismic event can be one of significant threats to the failure of structure system of the research reactor. This failure is possibly extended to the direct core damage of the reactor. For this purpose, the fault tree for structural system failure leading to the core damage under an earthquake accident is developed. The failure probabilities of basic events are evaluated as fragility curves of log-normal distributions. Finally, the plant-level seismic margin is investigated by the fault tree analysis combining with fragility data and the critical path is identified. The plant-level probabilistic seismic margin assessment using the fragility based fault tree analysis was performed for quantifying the safety of research reactor to a seismic hazard. For this, the fault tree for structural system failure leading to the core damage of the reactor under a seismic accident was developed. The failure probabilities of basic events were evaluated as fragility curves of log-normal distributions.

Attack tree based cyber security analysis of nuclear digital instrumentation and control systems

International Nuclear Information System (INIS)

Khand, P.A.

2009-01-01

To maintain the cyber security, nuclear digital Instrumentation and Control (I and C) systems must be analyzed for security risks because a single security breach due to a cyber attack can cause system failure, which can have catastrophic consequences on the environment and staff of a Nuclear Power Plant (NPP). Attack trees have been widely used to analyze the cyber security of digital systems due to their ability to capture system specific as well as attacker specific details. Therefore, a methodology based on attack trees has been proposed to analyze the cyber security of the systems. The methodology has been applied for the Cyber Security Analysis (CSA) of a Bistable Processor (BP) of a Reactor Protection System (RPS). Threats have been described according to their source. Attack scenarios have been generated using the attack tree and possible counter measures according to the Security Risk Level (SRL) of each scenario have been suggested. Moreover, cyber Security Requirements (SRs) have been elicited, and suitability of the requirements has been checked. (author)

Denotational, Causal, and Operational Determinism in Event Structures

NARCIS (Netherlands)

Rensink, Arend; Kirchner, H.

1996-01-01

Determinism of labelled transition systems and trees is a concept of theoretical and practical importance. We study its generalisation to event structures. It turns out that the result depends on what characterising property of tree determinism one sets out to generalise. We present three distinct

Denotational, Causal, and Operational Determinism in Event Structures

NARCIS (Netherlands)

Rensink, Arend

Determinism is a theoretically and practically important concept in labelled transition systems and trees. We study its generalisation to event structures. It turns out that the result depends on what characterising property of tree determinism one sets out to generalise. We present three distinct

Mistletoe effects on Scots pine decline following drought events: insights from within-tree spatial patterns, growth and carbohydrates.

Science.gov (United States)

Sangüesa-Barreda, Gabriel; Linares, Juan Carlos; Camarero, J Julio

2012-05-01

Forest decline has been attributed to the interaction of several stressors including biotic factors such as mistletoes and climate-induced drought stress. However, few data exist on how mistletoes are spatially arranged within trees and how this spatial pattern is related to changes in radial growth, responses to drought stress and carbon use. We used dendrochronology to quantify how mistletoe (Viscum album L.) infestation and drought stress affected long-term growth patterns in Pinus sylvestris L. at different heights. Basal area increment (BAI) trends and comparisons between trees of three different infestation degrees (without mistletoe, ID1; moderately infested trees, ID2; and severely infested trees, ID3) were performed using linear mixed-effects models. To identify the main climatic drivers of tree growth tree-ring widths were converted into indexed chronologies and related to climate data using correlation functions. We performed spatial analyses of the 3D distribution of mistletoe individuals and their ages within the crowns of three severely infested pines to describe their patterns. Lastly, we quantified carbohydrate and nitrogen concentrations in needles and sapwood of branches from severely infested trees and from trees without mistletoe. Mistletoe individuals formed strongly clustered groups of similar age within tree crowns and their age increased towards the crown apex. Mistletoe infestation negatively impacted growth but this effect was stronger near the tree apex than in the rest of sampled heights, causing an average loss of 64% in BAI (loss of BAI was ∼51% at 1.3 m or near the tree base). We found that BAI of severely infested trees and moderately or non-infested trees diverged since 2001 and such divergence was magnified by drought. Infested trees had lower concentrations of soluble sugars in their needles than non-infested ones. We conclude that mistletoe infestation causes growth decline and increases the sensitivity of trees to drought

Preliminary identification of potentially disruptive scenarios at the Greater Confinement Disposal Facility, Area 5 of the Nevada Test Site

International Nuclear Information System (INIS)

Guzowski, R.V.; Newman, G.

1993-12-01

The Greater Confinement Disposal location is being evaluated to determine whether defense-generated transuranic waste buried at this location complies with the Containment Requirements established by the US Environmental Protection Agency. One step in determining compliance is to identify those combinations of events and processes (scenarios) that define possible future states of the disposal system for which performance assessments must be performed. An established scenario-development procedure was used to identify a comprehensive set of mutually exclusive scenarios. To assure completeness, 761 features, events, processes, and other listings (FEPS) were compiled from 11 references. This number was reduced to 205 primarily through the elimination of duplications. The 205 FEPs were screened based on site-specific, goal-specific, and regulatory criteria. Four events survived screening and were used in preliminary scenario development: (1) exploratory drilling penetrates a GCD borehole, (2) drilling of a withdrawal/injection well penetrates a GCD borehole, (3) subsidence occurs at the RWMS, and (4) irrigation occurs at the RWMS. A logic diagram was used to develop 16 scenarios from the four events. No screening of these scenarios was attempted at this time. Additional screening of the currently retained events and processes will be based on additional data and information from site-characterization activities. When screening of the events and processes is completed, a final set of scenarios will be developed and screened based on consequence and probability of occurrence

Fault tree analysis for vital area identification

International Nuclear Information System (INIS)

Varnado, G.B.; Ortiz, N.R.

1978-01-01

The use of fault tree analysis techniques to systematically identify (1) the sabotage events which can lead to release of significant quantities of radioactive materials, (2) the areas of the nuclear power plant in which the sabotage events can be accomplished, and (3) the areas of the plant which must be protected to assure that release does not occur are discussed

A rapid cosmic-ray increase in BC 3372-3371 from ancient buried tree rings in China.

Science.gov (United States)

Wang, F Y; Yu, H; Zou, Y C; Dai, Z G; Cheng, K S

2017-11-14

Cosmic rays interact with the Earth's atmosphere to produce 14 C, which can be absorbed by trees. Therefore, rapid increases of 14 C in tree rings can be used to probe previous cosmic-ray events. By this method, three 14 C rapidly increasing events have been found. Plausible causes of these events include large solar proton events, supernovae, or short gamma-ray bursts. However, due to the lack of measurements of 14 C by year, the occurrence frequency of such 14 C rapidly increasing events is poorly known. In addition, rapid increases may be hidden in the IntCal13 data with five-year resolution. Here we report the result of 14 C measurements using an ancient buried tree during the period between BC 3388 and 3358. We found a rapid increase of about 9‰ in the 14 C content from BC 3372 to BC 3371. We suggest that this event could originate from a large solar proton event.

Overview description of the base scenario derived from FEP analysis

International Nuclear Information System (INIS)

Locke, J.; Bailey, L.

1998-01-01

This report forms part of a suite of documents describing the Nirex model development programme. The programme is designed to provide a clear audit trail from the identification of significant features, events and processes (FEPs) to the models and modelling processes employed within a detailed performance assessment. A scenario approach to performance assessment has been adopted. It is proposed that potential evolutions of a deep geological radioactive waste repository can be represented by a base scenario and a number of variant scenarios. It is intended that assessment of the base scenario would form the core of any future performance assessment. The base scenario is chosen to be broad-ranging and to represent the natural evolution of the repository system and its surrounding environment. The base scenario is defined to include all those FEPs which are certain to occur and those which are judged likely to occur for a significant period of the assessment - timescale. Variant scenarios are defined by FEPs which represent a significant perturbation to the natural system evolution, for example the occurrence of a large seismic event. The structuring of FEPs on a Master Directed Diagram (MDD), provides a systematic framework for identifying those FEPs which form part of the natural evolution of the system and those which may define alternative potential evolutions of the repository system. In order to construct a description of the base scenario, FEPs have been grouped into a series of conceptual models. Conceptual models are groups of FEPs, identified from the MDD, representing a specific component or process within the disposal system. It has been found appropriate to define conceptual models in terms of the three main components of the disposal system: the repository engineered system, the surrounding geosphere and the biosphere. For each of these components, conceptual models provide a description of the relevant subsystem in terms of its initial characteristics

Temporal Dynamics in the Concentration, Flux, and Optical Properties of Tree-derived Dissolved Organic Matter (Tree-DOM) in an Epiphyte-laden Oak-cedar Forest.

Science.gov (United States)

Whitetree, A.; Van Stan, J. T., II; Wagner, S.; Guillemette, F.; Lewis, J.; Silva, L.; Stubbins, A.

2017-12-01

Studies on the fate and transport of dissolved organic matter (DOM) along the rainfall-to-discharge flow pathway typically begin in streams or soils, neglecting the initial enrichment of rainfall with DOM during contact with plant canopies. However, rain water can gather significant amounts of tree-derived DOM (tree-DOM) when it drains from the canopy, as throughfall, and down the stem, as stemflow. We examined the temporal variability of event-scale tree-DOM concentrations, yield, and optical (light absorbance and fluorescence) characteristics from an epiphyte-laden Quercus virginiana-Juniperus virginiana forest on Skidaway Island, Savannah, Georgia (USA). All tree-DOM fluxes were highly enriched compared to rainfall and epiphytes further increased concentrations. Stemflow DOC concentrations were greater than throughfall across study species, yet larger throughfall water yields produced greater DOC yields versus stemflow. Tree-DOM optical characteristics indicate it is aromatic-rich with FDOM dominated by humic-like fluorescence, containing 10-20% protein-like (tryptophan-like) fluorescence. Storm size was the only storm condition that strongly correlated with tree-DOM concentration and flux; however, throughfall and stemflow optical characteristics varied little across a wide range of storm conditions (from low magnitude events to intense tropical storms). Annual tree-DOM yields from the study forest (0.8-46 g-C m-2 yr-1) compared well to other yields along the rainfall-to- discharge flow pathway, exceeding DOM yields from some river watersheds.

Effect of tree logging on reproductive performance in Blue Tits (Cyanistes caeruleus)

OpenAIRE

Amininasab, Seyed Mehdi; Xu, Charles C. Y.; Kingma, Sjouke A.; Komdeur, Jan

2017-01-01

For birds, habitat quality is largely determined by local vegetation, and reproductive performance can therefore be negatively influenced by anthropogenic activities. A tree logging event enabled us to examine the effect of removing trees of different maturities and types on the reproductive performance of Blue Tits (Cyanistes caeruleus). Against expectations, only the logging of small coniferous trees, but not larger and deciduous trees, was associated with a reduction in the number of eggs ...

Research study for extremely unlikely scenario of high level waste disposal: Part 3

International Nuclear Information System (INIS)

Ohkubo, Hiroo

1999-02-01

In this research, first, event and process relevant to the key words (or scenario initiator) such as volcanism have been identified and, especially a middle-scale eruption scenario including pyroclastic flows has been analyzed as the catastrophic scenario, which inspires ordinary people to have tremendous concern. Secondly, based upon the characteristic events and processes of each scenario considered in the above and through the research of existing model of such risk, quantitative concept (release amount magnitude, release mode, release form, frequency of release, probability etc.) and impact on repository system, facility and environment have been analyzed, defended and defined. Model which can assess and analyze such impact has been built. Using these models, risks directly or indirectly caused by HLW repository have been calculated. Finally, the process for assessing the consequence of volcanism scenario and its risk calculated by the model developed in the above have been visualized, and presented by comparing with other risks. (author)

Simulated long-term effects of varying tree retention on wood production, dead wood and carbon stock changes.

Science.gov (United States)

Santaniello, Francesca; Djupström, Line B; Ranius, Thomas; Weslien, Jan; Rudolphi, Jörgen; Sonesson, Johan

2017-10-01

Boreal forests are an important source of timber and pulp wood, but provide also other products and services. Utilizing a simulation program and field data from a tree retention experiment in a Scots pine forest in central Sweden, we simulated the consequences during the following 100 years of various levels of retention on production of merchantable wood, dead wood input (as a proxy for biodiversity), and carbon stock changes. At the stand level, wood production decreased with increased retention levels, while dead wood input and carbon stock increased. We also compared 12 scenarios representing a land sharing/land sparing gradient. In each scenario, a constant volume of wood was harvested with a specific level of retention in a 100-ha landscape. The area not needed to reach the defined volume was set-aside during a 100-year rotation period, leading to decreasing area of set-asides with increasing level of retention across the 12 scenarios. Dead wood input was positively affected by the level of tree retention whereas the average carbon stock decreased slightly with increasing level of tree retention. The scenarios will probably vary in how they favor species preferring different substrates. Therefore, we conclude that a larger variation of landscape-level conservation strategies, also including active creation of dead wood, may be an attractive complement to the existing management. Copyright © 2017 Elsevier Ltd. All rights reserved.

Real-Time Flood Control by Tree-Based Model Predictive Control Including Forecast Uncertainty: A Case Study Reservoir in Turkey

Directory of Open Access Journals (Sweden)

Gökçen Uysal

2018-03-01

Full Text Available Optimal control of reservoirs is a challenging task due to conflicting objectives, complex system structure, and uncertainties in the system. Real time control decisions suffer from streamflow forecast uncertainty. This study aims to use Probabilistic Streamflow Forecasts (PSFs having a lead-time up to 48 h as input for the recurrent reservoir operation problem. A related technique for decision making is multi-stage stochastic optimization using scenario trees, referred to as Tree-based Model Predictive Control (TB-MPC. Deterministic Streamflow Forecasts (DSFs are provided by applying random perturbations on perfect data. PSFs are synthetically generated from DSFs by a new approach which explicitly presents dynamic uncertainty evolution. We assessed different variables in the generation of stochasticity and compared the results using different scenarios. The developed real-time hourly flood control was applied to a test case which had limited reservoir storage and restricted downstream condition. According to hindcasting closed-loop experiment results, TB-MPC outperforms the deterministic counterpart in terms of decreased downstream flood risk according to different independent forecast scenarios. TB-MPC was also tested considering different number of tree branches, forecast horizons, and different inflow conditions. We conclude that using synthetic PSFs in TB-MPC can provide more robust solutions against forecast uncertainty by resolution of uncertainty in trees.

Imitation learning of car driving skills with decision trees and random forests

Directory of Open Access Journals (Sweden)

Cichosz Paweł

2014-09-01

Full Text Available Machine learning is an appealing and useful approach to creating vehicle control algorithms, both for simulated and real vehicles. One common learning scenario that is often possible to apply is learning by imitation, in which the behavior of an exemplary driver provides training instances for a supervised learning algorithm. This article follows this approach in the domain of simulated car racing, using the TORCS simulator. In contrast to most prior work on imitation learning, a symbolic decision tree knowledge representation is adopted, which combines potentially high accuracy with human readability, an advantage that can be important in many applications. Decision trees are demonstrated to be capable of representing high quality control models, reaching the performance level of sophisticated pre-designed algorithms. This is achieved by enhancing the basic imitation learning scenario to include active retraining, automatically triggered on control failures. It is also demonstrated how better stability and generalization can be achieved by sacrificing human-readability and using decision tree model ensembles. The methodology for learning control models contributed by this article can be hopefully applied to solve real-world control tasks, as well as to develop video game bots

Sensitivity Analysis for Assessing Effects of Tree Population Dynamics on Soil Bioturbation

Science.gov (United States)

Martin, Y. E.; Johnson, E. A.

2012-12-01

Bioturbation due to tree root throw is thought to be an important process in soil production and soil mixing. Despite progress in our understanding of root throw processes, the tree population dynamics affecting the occurrence and timing of root throw events remain much less well explained. Unfortunately, research about forest dynamics is not always undertaken from the perspective of those interested in tree death, tree topple and associated root throw. As a result, the necessary field data about tree population dynamics is often unavailable for many locations. The acquisition of such data would allow for improved interpretation of root throw observations and for incorporation within numerical models of tree root throw occurrence. The present study uses our earlier tree population dynamics model calibrated for subalpine forests in the Canadian Rockies to test the sensitivity of forest parameters within the model that determine tree death, tree topple, root throw and soil bioturbation. Crown wildfire disturbance is the primary driver of tree population dynamics, with wind throw being mainly of local importance. The recruitment and mortality of trees during multiple generations of forest determine the number of live trees on the landscape at any given time. Tree death may occur due to competition/thinning of trees between wildfire events or as a result of the wildfire itself. Unless trees die due to sudden wind throw events (as mentioned above, this is only of local significance in our study area), they remain standing for some time period after tree death and before tree topple; these trees are referred to as standing dead trees. The duration of this time window and several other factors influence if a tree breaks at its base or upheaves a relatively intact root plate with attached sediment. Our field research has also suggested that a minimum dbh is required before a root plate is large enough to upheave notable amounts of sediment. Modelling results in this study

Tree mortality predicted from drought-induced vascular damage

Science.gov (United States)

Anderegg, William R.L.; Flint, Alan L.; Huang, Cho-ying; Flint, Lorraine E.; Berry, Joseph A.; Davis, Frank W.; Sperry, John S.; Field, Christopher B.

2015-01-01

The projected responses of forest ecosystems to warming and drying associated with twenty-first-century climate change vary widely from resiliency to widespread tree mortality1, 2, 3. Current vegetation models lack the ability to account for mortality of overstorey trees during extreme drought owing to uncertainties in mechanisms and thresholds causing mortality4, 5. Here we assess the causes of tree mortality, using field measurements of branch hydraulic conductivity during ongoing mortality in Populus tremuloides in the southwestern United States and a detailed plant hydraulics model. We identify a lethal plant water stress threshold that corresponds with a loss of vascular transport capacity from air entry into the xylem. We then use this hydraulic-based threshold to simulate forest dieback during historical drought, and compare predictions against three independent mortality data sets. The hydraulic threshold predicted with 75% accuracy regional patterns of tree mortality as found in field plots and mortality maps derived from Landsat imagery. In a high-emissions scenario, climate models project that drought stress will exceed the observed mortality threshold in the southwestern United States by the 2050s. Our approach provides a powerful and tractable way of incorporating tree mortality into vegetation models to resolve uncertainty over the fate of forest ecosystems in a changing climate.

Quantitative Verification and Synthesis of Attack-Defence Scenarios

DEFF Research Database (Denmark)

Aslanyan, Zaruhi; Nielson, Flemming; Parker, David

2016-01-01

analysis of quantitative properties of complex attack-defence scenarios, using an extension of attack-defence trees which models temporal ordering of actions and allows explicit dependencies in the strategies adopted by attackers and defenders. We adopt a game-theoretic approach, translating attack...... which guarantee or optimise some quantitative property, such as the probability of a successful attack, the expected cost incurred, or some multi-objective trade-off between the two. We implement our approach, building upon the PRISM-games model checker, and apply it to a case study of an RFID goods...

Scenario development methods and practice

International Nuclear Information System (INIS)

2001-01-01

The safe management of radioactive waste is an essential aspect of all nuclear power programmes. Although a general consensus has been reached in OECD countries on the use of geological repositories for the disposal of high-level radioactive waste, analysis of the long-term safety of these repositories, using performance assessment and other tools, is required prior to implementation. The initial stage in developing a repository safety assessment is the identification of all factors that may be relevant to the long-term safety of the repository and their combination to form scenarios. This must be done in a systematic and transparent way in order to assure the regulatory authorities that nothing important has been forgotten. Scenario development has become the general term used to describe the collection and organisation of the scientific and technical information necessary to assess the long-term performance or safety of radioactive waste disposal systems. This includes the identification of the relevant features, events and processes (FEPs), the synthesis of broad models of scientific understanding, and the selection of cases to be calculated. Scenario development provides the overall framework in which the cases and their calculated consequences can be discussed, including biases or shortcomings due to omissions or lack of knowledge. The NEA Workshop on Scenario Development was organised in Madrid, in May 1999, with the objective of reviewing developments in scenario methodologies and applications in safety assessments since 1992. The outcome of this workshop is the subject of this book. It is a review of developments in scenario methodologies based on a large body of practical experience in safety assessments. It will be of interest to radioactive waste management experts as well as to other specialists involved in the development of scenario methodologies. (author)

Reconstruction of t anti tH (H → bb) events using deep neural networks with the CMS detector

Energy Technology Data Exchange (ETDEWEB)

Rieger, Marcel; Erdmann, Martin; Fischer, Benjamin; Fischer, Robert; Heidemann, Fabian; Quast, Thorben; Rath, Yannik [III. Physikalisches Institut A, RWTH Aachen University (Germany)

2016-07-01

The measurement of Higgs boson production in association with top-quark pairs (t anti tH) is an important goal of Run 2 of the LHC as it allows for a direct measurement of the underlying Yukawa coupling. Due to the complex final state, however, the analysis of semi-leptonic t anti tH events with the Higgs boson decaying into a pair of bottom-quarks is challenging. A promising method for tackling jet parton associations are Deep Neural Networks (DNN). While being a widely spread machine learning algorithm in modern industry, DNNs are on the way to becoming established in high energy physics. We present a study on the reconstruction of the final state using DNNs, comparing to Boosted Decision Trees (BDT) as benchmark scenario. This is accomplished by generating permutations of simulated events and comparing them with truth information to extract reconstruction efficiencies.

Structural system reliability calculation using a probabilistic fault tree analysis method

Science.gov (United States)

Torng, T. Y.; Wu, Y.-T.; Millwater, H. R.

1992-01-01

The development of a new probabilistic fault tree analysis (PFTA) method for calculating structural system reliability is summarized. The proposed PFTA procedure includes: developing a fault tree to represent the complex structural system, constructing an approximation function for each bottom event, determining a dominant sampling sequence for all bottom events, and calculating the system reliability using an adaptive importance sampling method. PFTA is suitable for complicated structural problems that require computer-intensive computer calculations. A computer program has been developed to implement the PFTA.

The space of ultrametric phylogenetic trees.

Science.gov (United States)

Gavryushkin, Alex; Drummond, Alexei J

2016-08-21

The reliability of a phylogenetic inference method from genomic sequence data is ensured by its statistical consistency. Bayesian inference methods produce a sample of phylogenetic trees from the posterior distribution given sequence data. Hence the question of statistical consistency of such methods is equivalent to the consistency of the summary of the sample. More generally, statistical consistency is ensured by the tree space used to analyse the sample. In this paper, we consider two standard parameterisations of phylogenetic time-trees used in evolutionary models: inter-coalescent interval lengths and absolute times of divergence events. For each of these parameterisations we introduce a natural metric space on ultrametric phylogenetic trees. We compare the introduced spaces with existing models of tree space and formulate several formal requirements that a metric space on phylogenetic trees must possess in order to be a satisfactory space for statistical analysis, and justify them. We show that only a few known constructions of the space of phylogenetic trees satisfy these requirements. However, our results suggest that these basic requirements are not enough to distinguish between the two metric spaces we introduce and that the choice between metric spaces requires additional properties to be considered. Particularly, that the summary tree minimising the square distance to the trees from the sample might be different for different parameterisations. This suggests that further fundamental insight is needed into the problem of statistical consistency of phylogenetic inference methods. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Reliability Analysis of Core Protection Calculator System by Combining Petri Net and Fault Tree

International Nuclear Information System (INIS)

Kim, Hyejin; Kim, Jonghyun

2013-01-01

This paper proposes an approach to analyzing the reliability of digital systems by combining Petri net (PN) and Fault tree. The Petri net allows modeling event dependencies and interaction, to represent the time sequence, and to model assumptions for dynamic events. The Petri net model can be straightforwardly transformed to fault tree using the gate. Then, the FT can be integrated into the existing PSA. This paper applies the approach to the reliability analysis of Core Protection Calculator System (CPCS). Digital technology is replacing the analog instrumentation and control (I and C) systems in both new and upgraded nuclear power plants. As digital systems are introduced to nuclear power plants, issues related with reliability analyses of these digital systems are being raised. One of these issues is that static fault tree (FT) and event tree (ET) approach cannot properly account for dynamic interactions in the digital systems, such as multiple top events, logic loops and time delay. Many methods have been proposed to solve the problems, but there is no single method that is universally accepted for the application to the current generation probabilistic safety analysis (PSA)

Reliability Analysis of Core Protection Calculator System by Combining Petri Net and Fault Tree

Energy Technology Data Exchange (ETDEWEB)

Kim, Hyejin; Kim, Jonghyun [KEPCO International Nuclear Graduate School, Ulsan (Korea, Republic of)

2013-10-15

This paper proposes an approach to analyzing the reliability of digital systems by combining Petri net (PN) and Fault tree. The Petri net allows modeling event dependencies and interaction, to represent the time sequence, and to model assumptions for dynamic events. The Petri net model can be straightforwardly transformed to fault tree using the gate. Then, the FT can be integrated into the existing PSA. This paper applies the approach to the reliability analysis of Core Protection Calculator System (CPCS). Digital technology is replacing the analog instrumentation and control (I and C) systems in both new and upgraded nuclear power plants. As digital systems are introduced to nuclear power plants, issues related with reliability analyses of these digital systems are being raised. One of these issues is that static fault tree (FT) and event tree (ET) approach cannot properly account for dynamic interactions in the digital systems, such as multiple top events, logic loops and time delay. Many methods have been proposed to solve the problems, but there is no single method that is universally accepted for the application to the current generation probabilistic safety analysis (PSA)

Model for the probability of core uncovery in loss of offsite power induced accidents, as applied in the Probabilistic Safety Study for ENEL PWR standard power plant

International Nuclear Information System (INIS)

Silvestri, E.; Serra, S.; Paddleford, D.F.

1985-01-01

This paper discusses one particular aspect of the Probabilistic Safety Study conducted for the Italian reference PWR or Progetto Unificato Nucleare (PUN) design. The event scenario addressed involves the loss of offsite power (LOOSP) initiating event in conjunction with an independent loss of certain support systems (to the exclusion of the total independent loss of on-site power which is treated similarly in a separate event tree). An event tree is developed to address the potential for a consequential small LOCA due to reactor coolant pump (RCP) seal failure under conditions of inadequate seal cooling and the subsequent potential for core uncovery should emergency systems be unavailable and not recovered in adequate time. The event scenario and the quantification methodology used are described. Results and sensitivities are presented

TURVA-2012: Formulation of radionuclide release scenarios

International Nuclear Information System (INIS)

Marcos, Nuria; Hjerpe, Thomas; Snellman, Margit; Ikonen, Ari; Smith, Paul

2014-01-01

TURVA-2012 is Posiva's safety case in support of the Preliminary Safety Analysis Report (PSAR) and application for a construction licence for a repository for disposal of spent nuclear fuel at the Olkiluoto site in south-western Finland. This paper gives a summary of the scenarios and the methodology followed in formulating them as described in TURVA-2012: Formulation of Radionuclide Release Scenarios (Posiva, 2013). The scenarios are further analysed in TURVA-2012: Assessment of Radionuclide Release Scenarios for the Repository System and TURVA-2012: Biosphere Assessment (Posiva, 2012a, 2012b). The formulation of scenarios takes into account the safety functions of the main barriers of the repository system and the uncertainties in the features, events, and processes (FEP) that may affect the entire disposal system (i.e. repository system plus the surface environment) from the emplacement of the first canister until the far future. In the report TURVA-2012: Performance Assessment (2012d), the performance of the engineered and natural barriers has been assessed against the loads expected during the evolution of the repository system and the site. Uncertainties have been identified and these are taken into account in the formulation of radionuclide release scenarios. The uncertainties in the FEP and evolution of the surface environment are taken into account in formulating the surface environment scenarios used ultimately in estimating radiation exposure. Formulating radionuclide release scenarios for the repository system links the reports Performance Assessment and Assessment of Radionuclide Release Scenarios for the Repository System. The formulation of radionuclide release scenarios for the surface environment brings together biosphere description and the surface environment FEP and is the link to the assessment of the surface environment scenarios summarised in TURVA-2012: Biosphere Assessment. (authors)

Dry forest resilience varies under simulated climate‐management scenarios in a central Oregon, USA landscape.

Science.gov (United States)

Halofsky, Joshua S; Halofsky, Jessica E; Burcsu, Theresa; Hemstrom, Miles A

Determining appropriate actions to create or maintain landscapes resilient to climate change is challenging because of uncertainty associated with potential effects of climate change and their interactions with land management. We used a set of climate-informed state-and-transition models to explore the effects of management and natural disturbances on vegetation composition and structure under different future climates. Models were run for dry forests of central Oregon under a fire suppression scenario (i.e., no management other than the continued suppression of wildfires) and an active management scenario characterized by light to moderate thinning from below and some prescribed fire, planting, and salvage logging. Without climate change, area in dry province forest types remained constant. With climate change, dry mixed-conifer forests increased in area (by an average of 21–26% by 2100), and moist mixed-conifer forests decreased in area (by an average of 36–60% by 2100), under both management scenarios. Average area in dry mixed-conifer forests varied little by management scenario, but potential decreases in the moist mixed-conifer forest were lower with active management. With changing climate in the dry province of central Oregon, our results suggest the likelihood of sustaining current levels of dense, moist mixed-conifer forests with large-diameter, old trees is low (less than a 10% chance) irrespective of management scenario; an opposite trend was observed under no climate change simulations. However, results also suggest active management within the dry and moist mixed-conifer forests that creates less dense forest conditions can increase the persistence of larger-diameter, older trees across the landscape. Owing to projected increases in wildfire, our results also suggest future distributions of tree structures will differ from the present. Overall, our projections indicate proactive management can increase forest resilience and sustain some societal

Development of Collision Accident Scenario during Nuclear Spent Fuel Maritime Transportation

International Nuclear Information System (INIS)

Yoo, Min; Kang, Hyun Gook

2015-01-01

Population density of South Korea is much higher than the other countries, and it is peninsula. Therefore, it is expected that major means of transportation of the spent fuel will be maritime transportation rather than overland transportation. Korea Maritime safety Tribunal (KMST) categorized various maritime accident, see table I. Among them, collision accident is one of the most important and complicated accident from Probabilistic Safety Analysis (PSA) point of view. We will show what will happen if the transportation ship is struck by other ship, how to calculate collision energy and probability of the branches on ship-ship collision with Event Tree Analysis (ETA) method. We selected and re-categorized maritime accident that KMST categorized for ship-ship collision analysis of spent fuel transportation ship. Event tree is constructed and collision energy distribution is derived from statistics and equation. And outer and inner hull fracture probabilities are calculated. If outer hull is broken but inner hull is fine, water will be flooded into the space between outer and inner hull. It will decrease mobility of the ship. If inner hull is fractured, water will be flooded into the ship inside. The ship has compartment structure to resist from foundering. Loss of mobility and compartment damage (ultimately it ends with sink) mechanism need to be analyzed to complete transportation ship collision event tree

Divergence in strategies for coping with winter embolism among co-occurring temperate tree species: the role of positive xylem pressure, wood type and tree stature

Science.gov (United States)

Cun-Yang Niu; Frederick C. Meinzer; Guang-You. Hao

2017-01-01

1. In temperate ecosystems, freeze-thaw events are an important environmental stress that can induce severe xylem embolism (i.e. clogging of conduits by air bubbles) in overwintering organs of trees. However, no comparative studies of different adaptive strategies among sympatric tree species for coping with winter embolism have examined the potential role of the...

Why natural disaster planning scenarios are often so disastrously wrong.

Science.gov (United States)

Verosub, K. L.

2017-12-01

Taken together the four hurricanes that impacted the United States in the summer of 2017 demonstrate the difficulties involved in trying to plan for any natural disaster, not simply a major hurricane. They also highlight the extraordinary degree to which small and/or random variations in initial conditions can have enormous consequences on the outcome of an event and on the ability of a society to respond to it. For example, if Harvey had been moving faster, it would have meant less rainfall and hence less flooding in the Houston area whereas a slight change in the path of Irma would have significantly affected which portions of the Florida peninsula would have experienced greater or lesser devastation. In the case of Marie, hurricane intensity and path as well as the terrain in Puerto Rico and the inherent state of its infrastructure greatly complicated relief and recovery efforts there. An additional factor that makes planning scenarios so difficult to develop is that major natural disasters can often be analyzed as a sequence of events. At each juncture in the sequence, the event might evolve along two or more very different pathways, which can lead to different outcomes. Sometimes, as with Nate, an event evolves more or less "as expected" and the planning scenario does what it was supposed to do, namely, help people respond to the event. But to a much greater extent than is usually recognized, small or random variations can drive an event off its expected trajectory and into a response realm that "no one could have foreseen." Even worse is when those small or random variations allow an event to bifurcate and follow two or more different pathways simultaneously, leading to a cascading disaster that totally overwhelms whatever planning and preparation has been put in place. Perhaps the main lessons to be learned from these storms is that planning for any disaster requires greater recognition of the importance of small or random factors and greater appreciation of

ETAP user's manual

International Nuclear Information System (INIS)

Watanabe, Norio; Higuchi, Suminori.

1990-11-01

The event tree analysis technique has been used in Probabilistic Safety Assessment for LWRs to delineate various accident scenarios leading to core melt or containment failure and to evaluate their frequencies. This technique often requires manual preparation of event trees with iterative process and time-consuming work in data handling. For the purpose of reducing manual efforts in event tree analysis, we developed a new software package named ETAP (Event Tree Analysis Supporting Program) for event tree analysis. ETAP is an interactive PC-based program which has the ability to construct, update, document, and quantify event trees. Because of its fast running capability to quantify event trees, use of the EATP program can make it easy to perform the sensitivity studies on a variety of system/containment performance issues. This report provides a user's manual for ETAP, which describes the structure, installation, and use of EATP. This software runs on NEC/PC-9800 or compatible PCs that have a 640 KB memory and MS-DOS 2.11 or higher. (author)

Effect of tree logging on reproductive performance in Blue Tits (Cyanistes caeruleus)

NARCIS (Netherlands)

Amininasab, Seyed Mehdi; Xu, Charles C. Y.; Kingma, Sjouke A.; Komdeur, Jan

For birds, habitat quality is largely determined by local vegetation, and reproductive performance can therefore be negatively influenced by anthropogenic activities. A tree logging event enabled us to examine the effect of removing trees of different maturities and types on the reproductive

Speech Recognition Using Randomized Relational Decision Trees

National Research Council Canada - National Science Library

Amit, Yali

1999-01-01

.... This implies that we recognize words as units, without recognizing their subcomponents. Multiple randomized decision trees are used to access the large pool of acoustic events in a systematic manner and are aggregated to produce the classifier.

Automated fault tree analysis: the GRAFTER system

International Nuclear Information System (INIS)

Sancaktar, S.; Sharp, D.R.

1985-01-01

An inherent part of probabilistic risk assessment (PRA) is the construction and analysis of detailed fault trees. For this purpose, a fault tree computer graphics code named GRAFTER has been developed. The code system centers around the GRAFTER code. This code is used interactively to construct, store, update and print fault trees of small or large sizes. The SIMON code is used to provide data for the basic event probabilities. ENCODE is used to process the GRAFTER files to prepare input for the WAMCUT code. WAMCUT is used to quantify the top event probability and to identify the cutsets. This code system has been extensively used in various PRA projects. It has resulted in reduced manpower costs, increased QA capability, ease of documentation and it has simplified sensitivity analyses. Because of its automated nature, it is also suitable for LIVING PRA Studies which require updating and modifications during the lifetime of the plant. Brief descriptions and capabilities of the GRAFTER, SIMON and ENCODE codes are provided; an application of the GRAFTER system is outlined; and conclusions and comments on the code system are given

Beyond Tree Throw: Wind, Water, Rock and the Mechanics of Tree-Driven Bedrock Physical Weathering

Science.gov (United States)

Marshall, J. A.; Anderson, R. S.; Dawson, T. E.; Dietrich, W. E.; Minear, J. T.

2017-12-01

Tree throw is often invoked as the dominant process in converting bedrock to soil and thus helping to build the Critical Zone (CZ). In addition, observations of tree roots lifting sidewalk slabs, occupying cracks, and prying slabs of rock from cliff faces have led to a general belief in the power of plant growth forces. These common observations have led to conceptual models with trees at the center of the soil genesis process. This is despite the observation that tree throw is rare in many forested settings, and a dearth of field measurements that quantify the magnitude of growth forces. While few trees blow down, every tree grows roots, inserting many tens of percent of its mass below ground. Yet we lack data quantifying the role of trees in both damaging bedrock and detaching it (and thus producing soil). By combing force measurements at the tree-bedrock interface with precipitation, solar radiation, wind speed, and wind-driven tree sway data we quantified the magnitude and frequency of tree-driven soil-production mechanisms from two contrasting climatic and lithologic regimes (Boulder and Eel Creek CZ Observatories). Preliminary data suggests that in settings with relatively thin soils, trees can damage and detach rock due to diurnal fluctuations, wind response and rainfall events. Surprisingly, our data suggests that forces from roots and trunks growing against bedrock are insufficient to pry rock apart or damage bedrock although much more work is needed in this area. The frequency, magnitude and style of wind-driven tree forces at the bedrock interface varies considerably from one to another species. This suggests that tree properties such as mass, elasticity, stiffness and branch structure determine whether trees respond to gusts big or small, move at the same frequency as large wind gusts, or are able to self-dampen near-ground sway response to extended wind forces. Our measurements of precipitation-driven and daily fluctuations in root pressures exerted on

Feature, event, and process screening and scenario development for the yucca mountain total system performance assessment

International Nuclear Information System (INIS)

Swift, P.; Barr, G.; Barnard, R.; Rechard, R.; Schenker, A.; Freeze, G.; Burck, P.

2001-01-01

Scenario development has two primary purposes in the design and documentation of postclosure performance assessments in a regulatory setting. First, scenario development ensures a sufficiently comprehensive consideration of the possible future states of the system. Second, scenario development identifies the important scenarios that must be considered in quantitative analyses of the total system performance assessment (TSPA). To ensure clear documentation of the treatment of potentially relevant future states of the system in the Yucca Mountain license application (LA), the US Department of Energy (DOE) has chosen to adopt a scenario development process based on the methodology developed by Cranwell et al. (1990) for the US Nuclear Regulatory Commission (NRC). Although the process, described below, has been modified somewhat as a result of experience gained in the last decade, the underlying methodology is consistent with that outlined by the DOE in the 1988 Site Characterization Plan for the Yucca Mountain Project (YMP) (U.S. DOE, 1988). The approach is fundamentally the same as that used in many performance assessments, including the most recent analysis of the Yucca Mountain repository by the NRC (Wescott et al., 1995). The approach has also been used by the DOE for the Waste Isolation Pilot Plant (WIPP) (U.S. DOE, 1996), by the Nuclear Energy Agency (NEA) of the Organisation for Economic Co-Operation and Development (OECD), and by other radioactive waste programs internationally. Section 2.0 of this report describes the scenario development process. Steps in the process are described in Section 2.1, and terms introduced in this section are defined in Section 2.2. The electronic database used to document the process is described in Section 3, and Section 4 provides a summary of the current status of the YMP scenario development work. Section 5 contains acknowledgments, and Section 6 contains a list of the references cited. (authors)

Growth and reproduction respond differently to climate in three Neotropical tree species.

Science.gov (United States)

Alfaro-Sánchez, Raquel; Muller-Landau, Helene C; Wright, S Joseph; Camarero, J Julio

2017-06-01

The response of tropical forests to anthropogenic climate change is critically important to future global carbon budgets, yet remains highly uncertain. Here, we investigate how precipitation, temperature, solar radiation and dry- and wet-season lengths are related to annual tree growth, flower production, and fruit production in three moist tropical forest tree species using long-term datasets from tree rings and litter traps in central Panama. We also evaluated how growth, flower, and fruit production were interrelated. We found that growth was positively correlated with wet-season precipitation in all three species: Jacaranda copaia (r = 0.63), Tetragastris panamensis (r = 0.39) and Trichilia tuberculata (r = 0.39). Flowering and fruiting in Jacaranda were negatively related to current-year dry-season rainfall and positively related to prior-year dry-season rainfall. Flowering in Tetragastris was negatively related to current-year annual mean temperature while Trichilia showed no significant relationships of reproduction with climate. Growth was significantly related to reproduction only in Tetragastris, where it was positively related to previous year fruiting. Our results suggest that tree growth in moist tropical forest tree species is generally reduced by drought events such as those associated with strong El Niño events. In contrast, interannual variation in reproduction is not generally associated with growth and has distinct and species-specific climate responses, with positive effects of El Niño events in some species. Understanding these contrasting climate effects on tree growth and reproduction is critical to predicting changes in tropical forest dynamics and species composition under climate change.

Modular representation and analysis of fault trees

Energy Technology Data Exchange (ETDEWEB)

Olmos, J; Wolf, L [Massachusetts Inst. of Tech., Cambridge (USA). Dept. of Nuclear Engineering

1978-08-01

An analytical method to describe fault tree diagrams in terms of their modular compositions is developed. Fault tree structures are characterized by recursively relating the top tree event to all its basic component inputs through a set of equations defining each of the modulus for the fault tree. It is shown that such a modular description is an extremely valuable tool for making a quantitative analysis of fault trees. The modularization methodology has been implemented into the PL-MOD computer code, written in PL/1 language, which is capable of modularizing fault trees containing replicated components and replicated modular gates. PL-MOD in addition can handle mutually exclusive inputs and explicit higher order symmetric (k-out-of-n) gates. The step-by-step modularization of fault trees performed by PL-MOD is demonstrated and it is shown how this procedure is only made possible through an extensive use of the list processing tools available in PL/1. A number of nuclear reactor safety system fault trees were analyzed. PL-MOD performed the modularization and evaluation of the modular occurrence probabilities and Vesely-Fussell importance measures for these systems very efficiently. In particular its execution time for the modularization of a PWR High Pressure Injection System reduced fault tree was 25 times faster than that necessary to generate its equivalent minimal cut-set description using MOCUS, a code considered to be fast by present standards.

Not seeing the forest for the trees: size of the minimum spanning trees (MSTs) forest and branch significance in MST-based phylogenetic analysis.

Science.gov (United States)

Teixeira, Andreia Sofia; Monteiro, Pedro T; Carriço, João A; Ramirez, Mário; Francisco, Alexandre P

2015-01-01

Trees, including minimum spanning trees (MSTs), are commonly used in phylogenetic studies. But, for the research community, it may be unclear that the presented tree is just a hypothesis, chosen from among many possible alternatives. In this scenario, it is important to quantify our confidence in both the trees and the branches/edges included in such trees. In this paper, we address this problem for MSTs by introducing a new edge betweenness metric for undirected and weighted graphs. This spanning edge betweenness metric is defined as the fraction of equivalent MSTs where a given edge is present. The metric provides a per edge statistic that is similar to that of the bootstrap approach frequently used in phylogenetics to support the grouping of taxa. We provide methods for the exact computation of this metric based on the well known Kirchhoff's matrix tree theorem. Moreover, we implement and make available a module for the PHYLOViZ software and evaluate the proposed metric concerning both effectiveness and computational performance. Analysis of trees generated using multilocus sequence typing data (MLST) and the goeBURST algorithm revealed that the space of possible MSTs in real data sets is extremely large. Selection of the edge to be represented using bootstrap could lead to unreliable results since alternative edges are present in the same fraction of equivalent MSTs. The choice of the MST to be presented, results from criteria implemented in the algorithm that must be based in biologically plausible models.

Commercial application of fault tree analysis

International Nuclear Information System (INIS)

Crosetti, P.A.; Bruce, R.A.

1970-01-01

The potential for general application of Fault Tree Analysis to commercial products appears attractive based not only on the successful extension from the aerospace safety technology to the nuclear reactor reliability and availability technology, but also because combinatorial hazards are common to commercial operations and therefore lend themselves readily to evaluation by Fault Tree Analysis. It appears reasonable to conclude that the technique has application within the commercial industrial community where the occurrence of a specified consequence or final event would be of sufficient concern to management to justify such a rigorous analysis as an aid to decision making. (U.S.)

Development Of Dynamic Probabilistic Safety Assessment: The Accident Dynamic Simulator (ADS) Tool

International Nuclear Information System (INIS)

Chang, Y.H.; Mosleh, A.; Dang, V.N.

2003-01-01

The development of a dynamic methodology for Probabilistic Safety Assessment (PSA) addresses the complex interactions between the behaviour of technical systems and personnel response in the evolution of accident scenarios. This paper introduces the discrete dynamic event tree, a framework for dynamic PSA, and its implementation in the Accident Dynamic Simulator (ADS) tool. Dynamic event tree tools generate and quantify accident scenarios through coupled simulation models of the plant physical processes, its automatic systems, the equipment reliability, and the human response. The current research on the framework, the ADS tool, and on Human Reliability Analysis issues within dynamic PSA, is discussed. (author)

Development Of Dynamic Probabilistic Safety Assessment: The Accident Dynamic Simulator (ADS) Tool

Energy Technology Data Exchange (ETDEWEB)

Chang, Y.H.; Mosleh, A.; Dang, V.N

2003-03-01

The development of a dynamic methodology for Probabilistic Safety Assessment (PSA) addresses the complex interactions between the behaviour of technical systems and personnel response in the evolution of accident scenarios. This paper introduces the discrete dynamic event tree, a framework for dynamic PSA, and its implementation in the Accident Dynamic Simulator (ADS) tool. Dynamic event tree tools generate and quantify accident scenarios through coupled simulation models of the plant physical processes, its automatic systems, the equipment reliability, and the human response. The current research on the framework, the ADS tool, and on Human Reliability Analysis issues within dynamic PSA, is discussed. (author)

System-level hazard analysis using the sequence-tree method

International Nuclear Information System (INIS)

Huang, H.-W.; Shih Chunkuan; Yih Swu; Chen, M.-H.

2008-01-01

A system-level PHA using the sequence-tree method is presented to perform safety-related digital I and C system SSA. The conventional PHA involves brainstorming among experts on various portions of the system to identify hazards through discussions. However, since the conventional PHA is not a systematic technique, the analysis results depend strongly on the experts' subjective opinions. The quality of analysis cannot be appropriately controlled. Therefore, this study presents a system-level sequence tree based PHA, which can clarify the relationship among the major digital I and C systems. This sequence-tree-based technique has two major phases. The first phase adopts a table to analyze each event in SAR Chapter 15 for a specific safety-related I and C system, such as RPS. The second phase adopts a sequence tree to recognize the I and C systems involved in the event, the working of the safety-related systems and how the backup systems can be activated to mitigate the consequence if the primary safety systems fail. The defense-in-depth echelons, namely the Control echelon, Reactor trip echelon, ESFAS echelon and Monitoring and indicator echelon, are arranged to build the sequence-tree structure. All the related I and C systems, including the digital systems and the analog back-up systems, are allocated in their specific echelons. This system-centric sequence-tree analysis not only systematically identifies preliminary hazards, but also vulnerabilities in a nuclear power plant. Hence, an effective simplified D3 evaluation can also be conducted

Size-related flowering and fecundity in the tropical canopy tree species, Shorea acuminata (Dipterocarpaceae) during two consecutive general flowerings.

Science.gov (United States)

Naito, Yoko; Kanzaki, Mamoru; Numata, Shinya; Obayashi, Kyoko; Konuma, Akihiro; Nishimura, Sen; Ohta, Seiichi; Tsumura, Yoshihiko; Okuda, Toshinori; Lee, Soon Leong; Muhammad, Norwati

2008-01-01

We monitored the reproductive status of all trees with diameters at breast height (dbh) >30 cm in a 40-ha plot at Pasoh, west Malaysia, and investigated the individual fecundity of 15 Shorea acuminata Dyer (Dipterocarpaceae) trees using seed-trapping methods during two consecutive general flowering periods in 2001 (GF2001) and 2002 (GF2002). The proportion of flowering trees was higher, and not dependent on size, in GF2002 (84.2%), than in GF2001 (54.5%), when flowering mainly occurred in trees with a dbh investment during the two consecutive reproductive events clearly differed between medium-sized and large trees; the former concentrated their reproductive investment in one of the reproductive events whereas the latter allocated their investment more evenly to both reproductive events. Our results suggest size-related differences in the resource allocation pattern for reproduction.

Hanford groundwater scenario studies

International Nuclear Information System (INIS)

Arnett, R.C.; Gephart, R.E.; Deju, R.A.; Cole, C.R.; Ahlstrom, S.W.

1977-05-01

This report documents the results of two Hanford groundwater scenario studies. The first study examines the hydrologic impact of increased groundwater recharge resulting from agricultural development in the Cold Creek Valley located west of the Hanford Reservation. The second study involves recovering liquid radioactive waste which has leaked into the groundwater flow system from a hypothetical buried tank containing high-level radioactive waste. The predictive and control capacity of the onsite Hanford modeling technology is used to evaluate both scenarios. The results of the first study indicate that Cold Creek Valley irrigationis unlikely to cause significant changes in the water table underlying the high-level waste areas or in the movement of radionuclides already in the groundwater. The hypothetical tank leak study showed that an active response (in this case waste recovery) can be modeled and is a possible alternative to passive monitoring of radionuclide movement in the unlikely event that high-level waste is introduced into the groundwater

Scenarios constructed for nominal flow in the presence of a repository at Yucca Mountain and vicinity

International Nuclear Information System (INIS)

Barr, G.E.; Hunter, R.L.; Dunn, E.; Flint, A.

1995-03-01

Scenario development for the system performance assessment of the Yucca Mountain Site Characterization Project defines a scenario as a well-posed problem connecting an initiating event with radionuclide release to the accessible environment by a logical and physically possible combination or sequence of features, events, and processes. Drawing on the advice and assistance of the Project's principal investigators (PIs), a collection of release scenarios initiated by the nominal ground-water flow occurring in the vicinity of the potential Yucca Mountain high-level-waste repository is developed and described in pictorial form. This collection of scenarios is intended to provide a framework to assist PIs in recognizing essential field and calculational analyses, to assist performance assessment in providing guidance to site characterization, and to continue the effort to exhaustively identify all features, events, and processes important to releases. It represents a step in the iterative process of identifying what details of the potential site are important for safe disposal. 67 refs

A Bayesian Supertree Model for Genome-Wide Species Tree Reconstruction

Science.gov (United States)

De Oliveira Martins, Leonardo; Mallo, Diego; Posada, David

2016-01-01

Current phylogenomic data sets highlight the need for species tree methods able to deal with several sources of gene tree/species tree incongruence. At the same time, we need to make most use of all available data. Most species tree methods deal with single processes of phylogenetic discordance, namely, gene duplication and loss, incomplete lineage sorting (ILS) or horizontal gene transfer. In this manuscript, we address the problem of species tree inference from multilocus, genome-wide data sets regardless of the presence of gene duplication and loss and ILS therefore without the need to identify orthologs or to use a single individual per species. We do this by extending the idea of Maximum Likelihood (ML) supertrees to a hierarchical Bayesian model where several sources of gene tree/species tree disagreement can be accounted for in a modular manner. We implemented this model in a computer program called guenomu whose inputs are posterior distributions of unrooted gene tree topologies for multiple gene families, and whose output is the posterior distribution of rooted species tree topologies. We conducted extensive simulations to evaluate the performance of our approach in comparison with other species tree approaches able to deal with more than one leaf from the same species. Our method ranked best under simulated data sets, in spite of ignoring branch lengths, and performed well on empirical data, as well as being fast enough to analyze relatively large data sets. Our Bayesian supertree method was also very successful in obtaining better estimates of gene trees, by reducing the uncertainty in their distributions. In addition, our results show that under complex simulation scenarios, gene tree parsimony is also a competitive approach once we consider its speed, in contrast to more sophisticated models. PMID:25281847

A Bayesian Supertree Model for Genome-Wide Species Tree Reconstruction.

Science.gov (United States)

De Oliveira Martins, Leonardo; Mallo, Diego; Posada, David

2016-05-01

Current phylogenomic data sets highlight the need for species tree methods able to deal with several sources of gene tree/species tree incongruence. At the same time, we need to make most use of all available data. Most species tree methods deal with single processes of phylogenetic discordance, namely, gene duplication and loss, incomplete lineage sorting (ILS) or horizontal gene transfer. In this manuscript, we address the problem of species tree inference from multilocus, genome-wide data sets regardless of the presence of gene duplication and loss and ILS therefore without the need to identify orthologs or to use a single individual per species. We do this by extending the idea of Maximum Likelihood (ML) supertrees to a hierarchical Bayesian model where several sources of gene tree/species tree disagreement can be accounted for in a modular manner. We implemented this model in a computer program called guenomu whose inputs are posterior distributions of unrooted gene tree topologies for multiple gene families, and whose output is the posterior distribution of rooted species tree topologies. We conducted extensive simulations to evaluate the performance of our approach in comparison with other species tree approaches able to deal with more than one leaf from the same species. Our method ranked best under simulated data sets, in spite of ignoring branch lengths, and performed well on empirical data, as well as being fast enough to analyze relatively large data sets. Our Bayesian supertree method was also very successful in obtaining better estimates of gene trees, by reducing the uncertainty in their distributions. In addition, our results show that under complex simulation scenarios, gene tree parsimony is also a competitive approach once we consider its speed, in contrast to more sophisticated models. © The Author(s) 2014. Published by Oxford University Press on behalf of the Society of Systematic Biologists.

Human reliability analysis as part of the Probabilistic Safety Assessment - level 1 for the Kozloduy NPP unit 3

Energy Technology Data Exchange (ETDEWEB)

Ilieva, M [Risk Engineereing Ltd., Sofia (Bulgaria)

1996-12-31

Human errors probabilities have been evaluated using Accident Sequence Evaluation Program (ASEP). The model accounts for dynamic human actions as separate top events in event trees and excludes any `repair` actions and operator actions to backup the failed automatic signals. A small loss of coolant accident (LOCA) is analysed as an example. Full diagram of the event tree and 4 different scenarios of human action are presented. 6 refs., 2 figs., 1 tab.

Human reliability analysis as part of the Probabilistic Safety Assessment - level 1 for the Kozloduy NPP unit 3

International Nuclear Information System (INIS)

Ilieva, M.

1995-01-01

Human errors probabilities have been evaluated using Accident Sequence Evaluation Program (ASEP). The model accounts for dynamic human actions as separate top events in event trees and excludes any 'repair' actions and operator actions to backup the failed automatic signals. A small loss of coolant accident (LOCA) is analysed as an example. Full diagram of the event tree and 4 different scenarios of human action are presented. 6 refs., 2 figs., 1 tab

A method for investigating relative timing information on phylogenetic trees.

Science.gov (United States)

Ford, Daniel; Matsen, Frederick A; Stadler, Tanja

2009-04-01

In this paper, we present a new way to describe the timing of branching events in phylogenetic trees. Our description is in terms of the relative timing of diversification events between sister clades; as such it is complementary to existing methods using lineages-through-time plots which consider diversification in aggregate. The method can be applied to look for evidence of diversification happening in lineage-specific "bursts", or the opposite, where diversification between 2 clades happens in an unusually regular fashion. In order to be able to distinguish interesting events from stochasticity, we discuss 2 classes of neutral models on trees with relative timing information and develop a statistical framework for testing these models. These model classes include both the coalescent with ancestral population size variation and global rate speciation-extinction models. We end the paper with 2 example applications: first, we show that the evolution of the hepatitis C virus deviates from the coalescent with arbitrary population size. Second, we analyze a large tree of ants, demonstrating that a period of elevated diversification rates does not appear to have occurred in a bursting manner.

23 March 2015 - Tree planting ceremony Chemin Auguer, by His Holiness the XIIth Gyalwang Drukpa and CERN Director-General, on the occasion of the event Connecting Worlds: Science Meets Buddhism Great Minds, Great Matters.

CERN Multimedia

Brice, Maximilien

2015-01-01

23 March 2015 - Tree planting ceremony Chemin Auguer, by His Holiness the XIIth Gyalwang Drukpa and CERN Director-General, on the occasion of the event Connecting Worlds: Science Meets Buddhism Great Minds, Great Matters.

Biophysical modelling of intra-ring variations in tracheid features and wood density of Pinus pinaster trees exposed to seasonal droughts

Science.gov (United States)

Sarah Wilkinson; Jerome Ogee; Jean-Christophe Domec; Mark Rayment; Lisa Wingate

2015-01-01

Process-based models that link seasonally varying environmental signals to morphological features within tree rings are essential tools to predict tree growth response and commercially important wood quality traits under future climate scenarios. This study evaluated model portrayal of radial growth and wood anatomy observations within a mature maritime pine (Pinus...

High-resolution gravity and seismic-refraction surveys of the Smoke Tree Wash area, Joshua Tree National Park, California

Science.gov (United States)

Langenheim, Victoria E.; Rymer, Michael J.; Catchings, Rufus D.; Goldman, Mark R.; Watt, Janet T.; Powell, Robert E.; Matti, Jonathan C.

2016-03-02

We describe high-resolution gravity and seismic refraction surveys acquired to determine the thickness of valley-fill deposits and to delineate geologic structures that might influence groundwater flow beneath the Smoke Tree Wash area in Joshua Tree National Park. These surveys identified a sedimentary basin that is fault-controlled. A profile across the Smoke Tree Wash fault zone reveals low gravity values and seismic velocities that coincide with a mapped strand of the Smoke Tree Wash fault. Modeling of the gravity data reveals a basin about 2–2.5 km long and 1 km wide that is roughly centered on this mapped strand, and bounded by inferred faults. According to the gravity model the deepest part of the basin is about 270 m, but this area coincides with low velocities that are not characteristic of typical basement complex rocks. Most likely, the density contrast assumed in the inversion is too high or the uncharacteristically low velocities represent highly fractured or weathered basement rocks, or both. A longer seismic profile extending onto basement outcrops would help differentiate which scenario is more accurate. The seismic velocities also determine the depth to water table along the profile to be about 40–60 m, consistent with water levels measured in water wells near the northern end of the profile.

Research frontiers for improving our understanding of drought‐induced tree and forest mortality

Science.gov (United States)

Hartmann, Henrik; Moura, Catarina; Anderegg, William R. L.; Ruehr, Nadine; Salmon, Yann; Allen, Craig D.; Arndt, Stefan K.; Breshears, David D.; Davi, Hendrik; Galbraith, David; Ruthrof, Katinka X.; Wunder, Jan; Adams, Henry D.; Bloemen, Jasper; Cailleret, Maxime; Cobb, Richard; Gessler, Arthur; Grams, Thorsten E. E.; Jansen, Steven; Kautz, Markus; Lloret, Francisco; O’Brien, Michael

2018-01-01

Accumulating evidence highlights increased mortality risks for trees during severe drought, particularly under warmer temperatures and increasing vapour pressure deficit (VPD). Resulting forest die‐off events have severe consequences for ecosystem services, biophysical and biogeochemical land–atmosphere processes. Despite advances in monitoring, modelling and experimental studies of the causes and consequences of tree death from individual tree to ecosystem and global scale, a general mechanistic understanding and realistic predictions of drought mortality under future climate conditions are still lacking. We update a global tree mortality map and present a roadmap to a more holistic understanding of forest mortality across scales. We highlight priority research frontiers that promote: (1) new avenues for research on key tree ecophysiological responses to drought; (2) scaling from the tree/plot level to the ecosystem and region; (3) improvements of mortality risk predictions based on both empirical and mechanistic insights; and (4) a global monitoring network of forest mortality. In light of recent and anticipated large forest die‐off events such a research agenda is timely and needed to achieve scientific understanding for realistic predictions of drought‐induced tree mortality. The implementation of a sustainable network will require support by stakeholders and political authorities at the international level.

Evaluation of Nuclide Release Scenarios for a Hypothetical LILW Repository

International Nuclear Information System (INIS)

Lee, Youn Myoung; Jeong, Jong Tae

2010-11-01

A program for the safety assessment and performance evaluation of a low- and intermediate-level radioactive waste (LILW) repository system has been developed. Utilizing GoldSim (GoldSim, 2006), the program evaluates nuclide release and transport into the geosphere and biosphere under various disruptive natural and manmade events and scenarios that can occur after a waste package failure. We envisaged and illustrated these events and scenarios as occurring after the closure of a hypothetical LILW repository, and they included the degradation of various manmade barriers, pumping well drilling, and natural disruptions such as the sudden formation of a preferential flow pathway in the far-field area of the repository. Possible enhancement of nuclide transport facilitated by colloids or chelating agents is also dealt with. We used the newly-developed GoldSim template program, which is capable of various nuclide release scenarios and is greatly suited for simulating a potential repository given the geological circumstances in Korea, to create the detailed source term and near-field release scheme, various nuclide transport modes in the far-field geosphere area, and the biosphere transfer. Even though all parameter values applied to the hypothetical repository were assumed, the illustrative results, particularly the probabilistic calculations and sensitivity studies, may be informative under various scenarios

A framework for modeling scenario-based barrier island storm impacts

Science.gov (United States)

Mickey, Rangley; Long, Joseph W.; Dalyander, P. Soupy; Plant, Nathaniel G.; Thompson, David M.

2018-01-01

Methods for investigating the vulnerability of existing or proposed coastal features to storm impacts often rely on simplified parametric models or one-dimensional process-based modeling studies that focus on changes to a profile across a dune or barrier island. These simple studies tend to neglect the impacts to curvilinear or alongshore varying island planforms, influence of non-uniform nearshore hydrodynamics and sediment transport, irregular morphology of the offshore bathymetry, and impacts from low magnitude wave events (e.g. cold fronts). Presented here is a framework for simulating regionally specific, low and high magnitude scenario-based storm impacts to assess the alongshore variable vulnerabilities of a coastal feature. Storm scenarios based on historic hydrodynamic conditions were derived and simulated using the process-based morphologic evolution model XBeach. Model results show that the scenarios predicted similar patterns of erosion and overwash when compared to observed qualitative morphologic changes from recent storm events that were not included in the dataset used to build the scenarios. The framework model simulations were capable of predicting specific areas of vulnerability in the existing feature and the results illustrate how this storm vulnerability simulation framework could be used as a tool to help inform the decision-making process for scientists, engineers, and stakeholders involved in coastal zone management or restoration projects.

Riparian responses to extreme climate and land-use change scenarios.

Science.gov (United States)

Fernandes, Maria Rosário; Segurado, Pedro; Jauch, Eduardo; Ferreira, Maria Teresa

2016-11-01

Climate change will induce alterations in the hydrological and landscape patterns with effects on riparian ecotones. In this study we assess the combined effect of an extreme climate and land-use change scenario on riparian woody structure and how this will translate into a future risk of riparian functionality loss. The study was conducted in the Tâmega catchment of the Douro basin. Boosted Regression Trees (BRTs) were used to model two riparian landscape indicators related with the degree of connectivity (Mean Width) and complexity (Area Weighted Mean Patch Fractal Dimension). Riparian data were extracted by planimetric analysis of high spatial-resolution Word Imagery Layer (ESRI). Hydrological, climatic and land-use variables were obtained from available datasets and generated with process-based modeling using current climate data (2008-2014), while also considering the high-end RCP8.5 climate-change and "Icarus" socio-economic scenarios for the 2046-2065 time slice. Our results show that hydrological and land-use changes strongly influence future projections of riparian connectivity and complexity, albeit to diverse degrees and with differing effects. A harsh reduction in average flows may impair riparian zones while an increase in extreme rain events may benefit connectivity by promoting hydrologic dynamics with the surrounding floodplains. The expected increase in broad-leaved woodlands and mixed forests may enhance the riparian galleries by reducing the agricultural pressure on the area in the vicinity of the river. According to our results, 63% of river segments in the Tâmega basin exhibited a moderate risk of functionality loss, 16% a high risk, and 21% no risk. Weaknesses and strengths of the method are highlighted and results are discussed based on a resilience perspective with regard to riparian ecosystems. Copyright © 2016 Elsevier B.V. All rights reserved.

Multi-hazard Assessment and Scenario Toolbox (MhAST): A Framework for Analyzing Compounding Effects of Multiple Hazards

Science.gov (United States)

Sadegh, M.; Moftakhari, H.; AghaKouchak, A.

2017-12-01

Many natural hazards are driven by multiple forcing variables, and concurrence/consecutive extreme events significantly increases risk of infrastructure/system failure. It is a common practice to use univariate analysis based upon a perceived ruling driver to estimate design quantiles and/or return periods of extreme events. A multivariate analysis, however, permits modeling simultaneous occurrence of multiple forcing variables. In this presentation, we introduce the Multi-hazard Assessment and Scenario Toolbox (MhAST) that comprehensively analyzes marginal and joint probability distributions of natural hazards. MhAST also offers a wide range of scenarios of return period and design levels and their likelihoods. Contribution of this study is four-fold: 1. comprehensive analysis of marginal and joint probability of multiple drivers through 17 continuous distributions and 26 copulas, 2. multiple scenario analysis of concurrent extremes based upon the most likely joint occurrence, one ruling variable, and weighted random sampling of joint occurrences with similar exceedance probabilities, 3. weighted average scenario analysis based on a expected event, and 4. uncertainty analysis of the most likely joint occurrence scenario using a Bayesian framework.

Initiating events and accidental sequences taken into account in the CAREM reactor design

International Nuclear Information System (INIS)

Kay, J.M.; Felizia, E.R.; Navarro, N.R.; Caruso, G.J.

1990-01-01

The advance made in the nuclear security evaluation of the CAREM reactor is presented. It was carried out using the Security Probabilistic Analysis (SPA). The latter takes into account the different phases of identification and solution of initiating events and the qualitative development of event trees. The method of identification of initiating events is the Master Logical Diagram (MLD), whose deductive basis makes it appropriate for a new design like the one described. The qualitative development of the event trees associated to the identified initiating events, allows identification of those accidental sequences which are to have the security systems in the reactor. (Author) [es