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Failure Risk (failure + risk)
Selected AbstractsDetermining arresters best positions in power system for lightning shielding failure protection using simulation optimization approachEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2010B. Vahidi Abstract The lightning stroke to power system structures especially overhead lines makes severe damages and results in less reliable power supply. The invention of surge arresters was a revolution in these systems for protecting the precise equipments from lightning stroke overvoltages. Nowadays, with ever decreasing prices, using arrester not only for protecting certain instruments but also for decreasing total risk of flashover in overall network, is investigated by academic and industrial pioneers in this area. In this paper, our goal is to introduce a heuristic method for determining optimum positions for placing transmission lines surge arresters (TLSAs) with acceptable approximation, to get lowest possible value of shielding failure risk of flashover in a selected set of overhead lines. Simulation optimization based on neural net (i.e. Meta Model) and genetic algorithm (optimization algorithm) is invoked to suggest best positions for placing TLSAs. A case study on Kerman 230,kV network shows good achievement of simulation optimization for finding optimum positions of TLSAs. Comparison is also made with the results of transient simulation to reveal the effectiveness of the method. Copyright © 2008 John Wiley & Sons, Ltd. [source] On the Determinants and Dynamics of Trade Credit Use: Empirical Evidence from Business Start-upsJOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 1-2 2006Nancy Huyghebaert Abstract: Business start-ups provide an excellent opportunity for testing various hypotheses on why firms use trade credit. At the time of start-up, failure risk and financial constraints are typically large. Also, start-ups have no established relationships with banks and suppliers. The literature has related all these features to trade credit use. Moreover, as firms grow older, these characteristics become less pronounced, allowing us to test the dynamics of trade credit use. We find that start-ups use more trade credit when financial constraints are large, when suppliers have a financing advantage over banks in financing high-risk firms, when entrepreneurs value private benefits of control and when transaction costs are important. Furthermore, the dynamic implications of these theories are supported. [source] Breeding habitat selection behaviors in heterogeneous environments: implications for modeling reintroductionOIKOS, Issue 5 2009Jean-Baptiste Mihoub Animal movement and habitat selection behavior are important considerations in ecology, and remain a major issue for successful animal reintroductions. However, simple rules are often used to model movement or focus only on intrinsic environmental cues, neglecting recent insights in behavioral ecology on habitat selection processes. In particular, social information has been proposed as a widespread source of information for habitat evaluation. We investigated the role of explicit breeding habitat selection strategies on the establishment pattern of reintroduced populations and their persistence. We considered local movement at the scale of a single population. We constructed a spatially-implicit demographic model that considered five breeding habitat selection rules: 1) random, 2) intrinsic habitat quality, 3) avoidance of conspecifics, 4) presence of conspecifics and 5) reproductive success of conspecifics. The impact of breeding habitat selection was examined for different release methods under various levels of environmental heterogeneity levels, for both long and short-lived monogamous species. When heterogeneity between intrinsic habitat patch qualities is high, the persistence of reintroduced populations strongly depends on habitat selection strategies. Strategies based on intrinsic quality and conspecific reproductive success lead to a lower reintroduction failure risk than random, conspecific presence or avoidance-based strategies. Conspecific presence or avoidance-based strategies may aggregate individuals in suboptimal habitats. The release of adults seems to be more efficient independent of habitat selection strategy. We emphasize the crucial role of oriented habitat selection behavior and non ideal habitat selection in movement modeling, particularly for reintroduction. [source] Early Complete Failures of Fixed Implant-Supported Prostheses in the Edentulous Maxilla: A 3-Year Analysis of 17 Consecutive Cluster Failure PatientsCLINICAL IMPLANT DENTISTRY AND RELATED RESEARCH, Issue 2 2006Odont Dr/PhD, Torsten Jemt DDS ABSTRACT Background, Clusters of implant failures in the edentulous maxilla seem to occur in some patients. To create groups for analysis with higher numbers of these patients implies large original groups for inclusion. Purpose, The aim of this study was to retrospectively describe and compare a group of "cluster failure patients" with randomly selected patients treated in the edentulous maxilla. Materials and Methods, From a group of 1,267 consecutively treated patients in one clinic, all patients presenting failing fixed implant-supported prostheses within the first 3 years of follow-up were included. All patients were treated with turned titanium implants using two-stage surgery. A control group of equal number of patients were created for comparison. Data on patients were retrospectively retrieved from their records, and compared. Results, Seventeen patients (1.3%) met the inclusion criteria in the entire group. The bone resorption index revealed less bone quantity in the study group (p < .05) during implant placement, but there was no difference regarding primary implant stability at first-stage surgery. The distribution of short and long implants showed relatively higher number of short implants in the study group (p < .05), and more patients had a presurgical discussion on the risk of implant failure prior to treatment in this group (p < .05). Only 5 out of 102 implants (4.9%) were lost before prosthesis placement as compared to 38 and 25 lost implants during the following two years in the study group. Smoking habits and signs of bone loss related to periodontitis in the lower dentition were more frequent in the study group, but did not reach a significant level (p > .05). Conclusion, The results indicate that bone quantity, reflected in fixture length, has a significant impact on increased implant failure risk. Other factors of interest as predictors for implant failures could be smoking habits and also possibly signs of periodontitis in the opposing dentition. [source] A systematic review of the survival and complication rates of fixed partial dentures (FPDs) after an observation period of at least 5 yearsCLINICAL ORAL IMPLANTS RESEARCH, Issue 6 2004III. Conventional FPDs Abstract: The present study was done to determine the long-term success and survival of fixed partial dentures (FPDs) and to evaluate the risks for failures due to specific biological and technical complications. A MEDLINE search (PubMed) from 1966 up to March 2004 was conducted, as well as hand searching of bibliographies from relevant articles. Nineteen studies from an initial yield of 3658 titles were finally selected and data were extracted independently by three reviewers. Prospective and retrospective cohort studies with a mean follow-up time of at least 5 years in which patients had been examined clinically at the follow-up visits were included in the meta-analysis. Publications only based on patients records, questionnaires or interviews were excluded. Survival of the FPDs was analyzed according to in situ and intact failure risks. Specific biological and technical complications such as caries, loss of vitality and periodontal disease recurrence as well as loss of retention, loss of vitality, tooth and material fractures were also analyzed. The 10-year probability of survival for fixed partial dentures was 89.1% (95% confidence interval (CI): 81,93.8%) while the probability of success was 71.1% (95% CI: 47.7,85.2%). The 10-year risk for caries and periodontitis leading to FPD loss was 2.6% and 0.7%, respectively. The 10-year risk for loss of retention was 6.4%, for abutment fracture 2.1% and for material fractures 3.2%. Résumé L'étude présente a été effectuée pour déterminer le succès à long terme et la survie des prothèses fixées et d'évaluer les risques d'échecs dûà des complications biologiques et techniques. Une recherche Medline de 1966 à mars 2004 a été effectuée ainsi que manuelle pour les bibliographies des articles pouvant répondre à cette question. Dix-neuf études ont été tirées à partir de 3 658 titres et les données ont été extraites indépendamment par deux personnes. Les études prospectives et rétrospectives avec un temps de suivi de minimum cinq années dans lesquelles les patients avaient été examinés cliniquement lors du suivi ont été incluses dans cette méta-analyse. Les publications uniquement basées sur les dossiers des patients, les questionnaires et les interviews ont été exclues. La survie des prothèses a été analysée suivant les risques d'échec et de succès in situ. Des complications techniques et biologiques spécifiques telle que les caries, la perte de vitalité et la réapparition de la maladie parodontale ainsi que la perte de rétention, la perte de vitalité, les fractures dentaires et de matériaux ont également été analysées. La survie à 10 ans pour les prothèses fixées était de 89,1% (intervalle de confiance de 95% : 81,0 à 93,8%) tandis que le succès était de 71,1% (52,2 à 83,6%). Le risque à dix ans pour des caries ou de la parodontite entraînant la perte de la prothèse était respectivement de 2,6 et 0,7%. Le risque à dix années pour la perte de rétention était de 6,4%, de fracture du pilier de 2,1% et de fracture de matériaux de 3,2%. Zusammenfassung Die vorliegende Studie wurde unternommen, um die Langzeiterfolgs- und Ueberlebensraten von festsitzenden Brückenrekonstruktionen (FPDs) zu bestimmen und die Risiken für Misserfolge aufgrund spezifischer biologischer und technischer Komplikationen auszuwerten. Es wurde eine Medline Suche (PubMed) über einen Zeitraum von 1966 bis März 2004 durchgeführt und die Bibliographien von relevanten Artikeln wurden manuell durchsucht. Von einer anfänglichen Auswahl von 3658 Artikeln wurden schlussendlich 19 ausgewählt und die Daten wurden von drei Rezensenten unabhängig herausgelesen. Es wurden prospektive und retrospektive Kohorten-Studien mit einer mittleren Beobachtungszeit von mindestens 5 Jahren, in welchen Patienten klinisch nachuntersucht worden waren, in die Meta-Analyse einbezogen. Publikationen, welche nur auf Einträgen in Krankengeschichten, Fragebogen oder Interviews basierten, wurden ausgeschlossen. Das Ueberleben der FPDs wurde entsprechend des in situ und intakten Misserfolgsrisikos analysiert. Spezifische biologische und technische Komplikationen wie Karies, Vitalitätsverlust und das Auftreten von Parodontalproblemen sowie Retentionsverlust, Zahn- und Materialfrakturen wurden ebenfalls analysiert. Die Ueberlebensrate von festsitzenden Brückenrekonstruktionen über 10 Jahre betrug 89.1% (95% Vertrauensintervall (CI): 81,93.8%), während die Erfolgsrate 71.1% betrug (95% CI: 52.2,83.6%). Das 10-Jahres Risiko für Karies und Parodontitis, welche zum Verlust der FPD führen, betrug 2.6% bzw. 0.7%. Das 10-Jahres Risiko für Retentionsverlust betrug 6.4%, für die Pfeilerfrakturen 2.1% und für Materialfrakturen 3.2%. Resumen El presente estudio se llevó a cabo para determinar el éxito y supervivencia a largo plazo de dentaduras fijas parciales (FPDs) y evaluar los riesgos de fracasos debido a complicaciones biológicas y técnicas específicas. Se llevó a cabo una búsqueda por Medline (PubMed) desde 1996 hasta Marzo de 2004 al igual que una búsqueda a mano de bibliografías de artículos relevantes. Finalmente se seleccionaron diecinueve artículos de una cantidad inicial de 3,658 títulos y se extrajeron los datos independientemente por tres revisores. Se incluyeron en este meta-análisis estudios cohorte prospectivos y retrospectivos con un tiempo de seguimiento medio de 5 años en los que los pacientes se examinaron clínicamente en las visitas de mantenimiento. Se excluyeron publicaciones basadas solamente en las fichas de los pacientes, cuestionarios o entrevistas. Se analizó la supervivencia de los FPDs de acuerdo con los riesgos de fracaso in situ e intacto. También se analizaron las complicaciones biológicas específicas tales como caries, pérdida de vitalidad y recurrencia de enfermedad periodontal al igual que la pérdida de retención, pérdida de vitalidad, fracturas dentales y del material. La supervivencia a los diez años para las dentaduras parciales fijas fue del 89.1% (95% intervalo de confianza (CI): 81,93.8%) mientras que el éxito fue del 71.1% (95% CI: 52.2,83.6%). El riesgo de caries a los 10 años y periodontitis que condujo a la pérdida del FPD fue del 2.6% y del 0.7% respectivamente. El riesgo de pérdida de retención a los 10 años fue del 6.4%, para la fractura del pilar del 2.1% y para la fractura del material del 3.2%. [source] | ||||||||||