1,721,000 research outputs found
Fuusiomateriaalitutkimuslaitoksen turvallisuustavoitteiden täyttymisen varmistaminen käyttäen suunnitteluvaiheen PRA-mallinnusta
No full textThe design of nuclear facilities is tightly regulated to ensure the safety of people and environment. Safety analysis is performed to prove that the design reaches safety objectives set by the regulator. The aim of this work is to develop a process to verify the fulfillment of safety objectives using design phase probabilistic risk analysis, PRA.
In this work, safety objectives are defined for non-reactor nuclear facilities, one of which is IFMIF-DONES fusion materials irradiation facility. The fulfillment of the safety objective is studied using a PRA model of the facility. Based on the results reliability allocation to safety systems is discussed. An example of studying the effect of design changes to safety is performed by modelling an accident sequence due to a trip of an electromagnetic pump.
Using design phase PRA is found to be beneficial in the early phase of the design. Probabilistic analysis effectively finds the weak links between systems and levels of defence in depth, and is a useful tool in comparison of different design choices and their impact on the risk estimate of the facility.Ydinlaitosten suunnittelua ohjaa tiukka säätely, jotta ihmisten ja ympäristön turvallisuus voidaan taata. Turvallisuusanalyyseillä osoitetaan valvovalle osapuolelle, että laitoksen suunnittelu täyttää turvallisuustavoitteet. Tämän työn tavoite on kehittää suunnitteluvaiheen todennäköisyyspohjaista riskianalyysiä, PRA:ta, hyödyntävä prosessi, jolla voidaan varmistaa turvallisuusvaatimusten täyttyminen.
Tässä työssä määritetään turvallisuustavoitteet ydinlaitoksille, jotka eivät ole ydinvoimalaitoksia. Esimerkkinä käytetään IFMIF-DONES materiaalitutkimuslaitosta. Turvallisuusvaatimusten täyttyminen varmistetaan laitoksen PRA-mallin avulla. Tulosten perusteella pohditaan vaatimustavoitteiden määrittämistä turvajärjestelmille. Esimerkkinä suunnittelumuutoksen analysoinnin vaikutuksesta turvallisuuteen mallinnetaan onnettomuusketju, joka alkaa sähkömagneettisen pumpun vikaantumisesta.
Suunnitteluvaiheen PRA:n hyödyntäminen suunnittelun aikasessa vaiheessa todetaan hyödylliseksi. Todennäköisyyspohjaisella mallinnuksella voi tunnistaa haavoittuvaisuuksia systeemien ja syvyyssuuntaisen puolustuksen tasojen välillä. PRA-mallilla voi myös verrata eri suunnitteluratkaisuja ja niiden vaikutusta laitoksen riskiarvioon
Reliability estimation of safety-critical software-based systems using bayesian networks
No full textDue to the nature of software faults and the way they cause system failures new methods are needed for the safety and reliability evaluation of software-based safety-critical automation systems in nuclear power plants. In the research project "Programmable automation system safety integrity assessment (PASSI)", belonging to the Finnish Nuclear Safety Research Programme (FINNUS, 1999-2002), various safety assessment methods and tools for software based systems are developed and evaluated. The project is financed together by the Radiation and Nuclear Safety Authority (STUK), the Ministry of Trade and Industry (KTM) and the Technical Research Centre of Finland (VTT). In this report the applicability of Bayesian networks to the reliability estimation of software-based systems is studied. The applicability is evaluated by building Bayesian network models for the systems of interest and performing simulations for these models. In the simulations hypothetical evidence is used for defining the parameter relations and for determining the ability to compensate disparate evidence in the models. Based on the experiences from modelling and simulations we are able to conclude that Bayesian networks provide a good method for the reliability estimation of software-based systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
PASSI special report:Bayes networks in reliability analysis of software-based automation systems
No full textQuantitative reliability models of programmable systems are presented. The models are based on Bayes network approach. The models are applied to a simple example case where data from different operational profiles are combined. In addition, the approach is applied to determine the amount of data from another operational profile needed to compensate the lack of data from the operational profile under consideration
Practical modelling approach for assessing cascading effects of critical infrastructures
No full textA practical modelling approach for assessing cascading effects of critical infrastructures (CIs) is presented. The overall objective in the modelling is to specify threats and dependencies leading to the cascading effects of identified CIs. The threats are presented as threat functions describing the expected level of intensity of threats at a certain time and location. The dependencies are presented in interdependency tables stating the rules of CI dependencies. The predicted cascading effects are set on a timeline in order to create a common picture of the situation. The timeline can be used to understand the incident evolution and to mitigate the consequences. For the modelling approach two initial requirements were set. The modelling approach should be versatile to be used in different accident scenarios implementing information from different kinds of threat functions. It should be scalable in the level of detail so that the spatial modelling of the accident scenario concurs with the overall assessment objectives. In an accident scenario, the overall assessment objective is often two-fold. It can be the crisis management during the accident, or it can be the accident recovery to normal life with functioning CIs. In the crisis management during the accident, the main focus is in the short-term operations trying to minimize the injury of people and the damage to the environment and property. In the accident recovery, the focus is more in the long-term operations trying to repair the subsequent damages. The two overall objectives are of course overlapping and their actual difference is in the time span of the operations. The modelling approach was developed using a flooding scenario in a densely populated area as an example. The crisis management during the accident was chosen as the overall assessment objective. An accident scenario map, locating the initiating events and CIs, was defined and a hexagonal grid was laid on the map. The relevant CIs for each hex were identified, and their interdependencies and vulnerabilities were defined in the model. A reference point was chosen for each hex. The threat function results on the reference point were then applied to all CIs in the hex. The threat function describing the expected level of water in the different locations of the polder area at a certain time was provided by a separate modelling tool. The initial failure times (i.e. not considering the interdependencies) of the CIs were determined. The final failure times were determined taking into account the interdependencies between the CIs, and the cascading effects were assessed. The modelling approach results are best utilized in the preparedness and training phase of crisis management. It gives guidance for the planning of emergency response by revealing the CIs that are important to protect in order to prevent or mitigate the escalation of the accident. The failure times can be compared with the estimated response times to evaluate the feasibility of different accident responses and what kind of impact the responses can have to the overall accident sequence
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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