Dynamic safety assessment of a nonlinear pumped-storage generating system in a transient process

This paper focuses on a pumped-storage generating system with a reversible Francis turbine and presents an innovative framework for safety assessment in an attempt to overcome their limitations. Thus the aim is to analyze the dynamic safety process and risk probability of the above nonlinear generating system. This study is carried out based on an existing pumped-storage power station. In this paper we show the dynamic safety evaluation process and risk probability of the nonlinear generating system using Fisher discriminant method. A comparison analysis for the safety assessment is performed between two different closing laws, namely the separate mode only to include a guide vane and the linkage mode that includes a guide vane and a ball valve. We find that the most unfavorable condition of the generating system occurs in the final stage of the load rejection transient process. It is also demonstrated that there is no risk to the generating system with the linkage mode but the risk probability of the separate mode is 6 percent. The results obtained are in good agreement with the actual operation of hydropower stations. The developed framework may not only be adopted for the applications of the pumped-storage generating system with a reversible Francis turbine but serves as the basis for the safety assessment of various engineering applications.National Natural Science Foundation of ChinaFundamental Research Funds for the Central UniversitiesScientific research funds of Northwest A&F UniversityScience Fund for Excellent Young Scholars from Northwest A&F University and Shaanxi Nova progra

Economic Factors Underlying the Unbundling of Advertising Agency Services

This paper addresses a longstanding puzzle involving the unbundling of services that has occurred over more than two decades in the U.S. advertising agency industry: How can the shift from the bundling to the unbundling of services be explained and what accounts for the slow pace of change? Using a cost-based theoretical framework of bundling due to Evans and Salinger (2005, 2008), we develop a simple model of an advertising agency's decision to unbundle its services as a tradeoff between the fixed cost to the advertiser of establishing and maintaining a relationship with an advertising agency and pecuniary economies of scale available in providing media services. The results from an econometric analysis of cross-sectional and pooled data collected by the U.S. Census Bureau for quinquennial censuses conducted between 1982 and 2002 support the key predictions of the model. We find that advertising agency establishments are more likely to unbundle if they are large and diversified in their service offerings and are less likely to do so with increasing age and greater geographical scope. We also find a strong trend toward unbundling over time, a result that is partially explained by increases in media prices over time.

Contribution du glissement non octaédrique à l'évolution de texture des polycristaux CFC sous cisaillement simple

La contribution du glissement non octaédrique (NOC) à l'évolution de la texture sous cisaillement simple pour les métaux à structure cubique à faces centrées a été étudiée. Les orientations idéales produites par la famille octaédrique {111} ne changent pas après l’ajout de glissement NOC. Toutefois, la stabilité des orientations idéales, le champ de rotation et la vitesse d'évolution de la fonction de densité des orientations ont été affectés. L’impact du glissement NOC sur la forme des équipotentiels, l'état de contrainte ainsi que la distribution de glissement ont été examinés

The Effects of Macular Photocoagulation on Visual Field

Purpose: To evaluate visual field and nerve fiber layer thickness changes after Macular photocoagulation for treatment of diabetic macular edema. Setting: Rassoul Akram Hospital, Tehran, Iran. Material and method: Twenty six eyes with history of diabetes and clinically significant macular edema candidate for Macular photocoagulation were included in this prospective interventional case series. All patients underwent 10-2 and 24-2 Humphrey Visual Field Test with Swedish Interactive Thresholding Algorithm (SITA) standard strategy and also optic nerve and macular optical coherence tomography (OCT), before and 6 months after macular laser photocoagulation. Then visual field, peripapillary and macular nerve fiber layer thickness of each eye were compared before and after photocoagulation. Results: The mean age of patients was 57.60 ± 8.99 (range 33-73) years. There was no statistically significant change after photocoagulation compared to before the procedure regarding the mean deviation, pattern standard deviation and foveal threshold in visual field 10-2 and 24-2 tests except for pattern standard deviation in 10-2 test. Conclusion: Based on our results it seems that visual field is not affected by macular laser photocoagulation

Modélisation et simulation numérique de la propagation de fissure de fatigue assistée par I'hydrogène gazeux à haute pression

Dans le but d'estimer la durabilité des structures en condition de fonctionnement, il est nécessaire de connaître la résistance des matériaux en condition d'usage, en particulier sous chargements cycliques. Dans cette étude on s’intéressera à la fragilisation par l’hydrogène gazeux d'une classe d'aciers inoxydables. L’hydrogène entraîne généralement une dégradation des propriétés mécaniques des aciers. En outre, des études expérimentales ont mis en évidence l’influence néfaste de l’hydrogène sur la résistance à la fissuration en fatigue des métaux. L’objectif de cette étude est la modélisation de la propagation des fissures de fatigue assistée par l’hydrogène, et la comparaison aux résultats expérimentaux. Le modèle numérique a pour but d’aider à la compréhension du rôle de l’hydrogène dans la modification des mécanismes d’endommagement en pointe de fissure de fatigue en comparant les vitesses de propagation simulées à celles relevées au cours des essais. Pour ce faire, un modèle de zone cohésive dédiée à la fissuration sous chargement cyclique a été implanté dans le code de calcul ABAQUS. Le modèle éléments finis est développé dans le cadre de la Thermodynamique des Processus Irréversibles. On formule une loi de traction-séparation spécifique, apte à décrire la dégradation progressive des contraintes cohésives sous chargement cyclique, et sensible à la présence d’hydrogène. Le couplage entre comportement mécanique et diffusion de l’hydrogène peut être modélisé à l’aide d’un calcul couplé température/déplacement, disponible dans ABAQUS. Les simulation sont comparées à des essais de propagation de fissure en fatigue réalisés sur éprouvettes CT sous différentes pressions d’hydrogène sur le banc d’essais Hycomat, à l’Institut PPRIME à Poitiers, sur un acier inoxydable martensitique 15-5PH durci par précipitation. Elles montrent qu’on est capable de prévoir une forte diminution de la résistance à la fissuration en présence d’hydrogène

Effects of predisposing, reinforcing and enabling factors on self-care behaviors of the patients with diabetes mellitus in the Minoodasht city, Iran

Background: To control diabetes mellitus (DM) it is necessary to make overall changes in the life style of the patients. The aim of this study was to determine the effects of predisposing, reinforcing and enabling factors on self-care behaviors of the patients with DM in the Minoodasht city, Iran in 2012.Methods: In this quasi-experimental study, 78 people with DM were selected by convenience sampling method. In the first stage of study, the educational program was compiled and executed on six information sessions. To present the informative content, a video projector and different lecturing methods including questions and answers, dynamic group discussion and different educational materials such as pamphlets and CDs were employed. After one month, the efficiency of the educational program was determined by using the same questioner. Data were analyzed using paired sample T-test and McNemar test. Results: The mean age of participants was 49 (SD: 3.27.) years old, 87.2 were married, and 19.2 were illiterate. The results showed that the enabling factors like adopting to go on a diet and the educational classes facilitated by the staff had significant effects on health care behavior of the patients. Furthermore 69.2 of the participants adopted to go on a diet before the educational sessions; that figure increased to 94.9 after the educational sessions. According to the results the mean scores for the knowledge, attitude, and behavior, reinforcement factors and enabling factors increased significantly after of the educational intervention (p- value >0.001).Conclusion: Predisposing, enabling and reinforcement factors affected in taking self-care behavior in the patient with DM. © 2015 Borhani et al.; licensee BioMed Central

Nouveau procédé d'hyper-déformations de tubes par torsion

Un nouveau procédé est proposé afin de déformer des tubes cylindriques sous de très grandes déformations plastiques sans modifier leurs dimensions. Une pression hydrostatique est obtenue par compression axiale d'un mandrin cylindrique placée dans le tube. Le tube est ainsi déformé par torsion. Cette nouvelle technique de grandes déformations plastiques semble être très prometteuse pour de futures applications industrielles

Prevalence of diabetic peripheral neuropathy in Iran : A systematic review and meta-analysis

Peer reviewedPublisher PD