Effect on Risk Based Inspection of spatio-temporal dependence of ROC curves: Study of the corrosion of steel harbour structures
Owners of civil infrastructures base their maintenance decisions schemes mainly both on structural integrity assessment and consequence analysis. Some inputs come from information collected by non-destructive or destructive tools. Uncertainties and noise of measurements can lead to bad decisions but are rarely integrated into the process of decision. Nowadays, Risk Based Inspection (RBI) provides the basic concepts for optimizing the maintenance plans of existing structures while insuring a good safety and availability conditions during service life of structures. In this paper, concepts are applied on a steel sheet pile seawall submitted to uniform corrosion where spatio-temporal dependence of performance of ROC (Receiver Operating Characteristic) curves is studied. Résumé Les gestionnaires d’infrastructures de génie civil basent leurs schémas décisionnels de maintenance essentiellement à partir de l’évaluation de l’intégrité structurale des ouvrages et de l’analyse des conséquences en cas de défaillance. Certaines données d’entrée proviennent de contrôles destructifs ou non destructifs. Les incertitudes et le bruit sur les mesures peuvent conduire à de mauvaises décisions mais sont rarement pris en compte dans les processus de décision. Actuellement, les méthodes RBI (Risk Based Inspection) donnent les fondamentaux pour aboutir à des plans de maintenance optimisés tout en garantissant la sécurité et la disponibilité des ouvrages en service. Dans cet article, ces concepts sont appliqués à un quai constitué par un rideau de palplanches soumis à la corrosion uniforme et la dépendance spatio-temporelle de la performance des courbes ROC (Caractéristique Opérationnelle du Récepteur) est étudiée.
Probabilistic modeling of inspection results for offshore structures
Operators of marine structures have to ensure that structural integrity is maintained at a sufficient level during in-service life or in the case of the structure life prolongation. This can be achieved by Inspection, Maintenance and Repair plans (IMR), as rational aid-tools for decisional purposes. Such plans are complex and can be expensive. This leads to their global optimization, particularly regarding inspections. In this context, original results on inspections data in IMR plans are presented. The approach is based on decision and detection theories and include both the probability of false alarm and the probability of detection. It is shown how to introduce these probabilities in a decision scheme. The effect of false alarms and miss detections on the global cost of inspection planning is underlined through a basic example.
Optimized Delivery System Achieves Enhanced Endomyocardial Stem Cell Retention
Background—Regenerative cell-based therapies are associated with limited myocardial retention of delivered stem cells. The objective of this study is to develop an endocardial delivery system for enhanced cell retention. Methods and Results—Stem cell retention was simulated in silico using 1- and 3-dimensional models of tissue distortion and compliance associated with delivery. Needle designs, predicted to be optimal, were accordingly engineered using nitinol, a nickel and titanium alloy displaying shape memory and superelasticity. Biocompatibility was tested with human mesenchymal stem cells. Experimental validation was performed with species-matched cells directly delivered into Langendorff-perfused porcine hearts or administered percutaneously into the endocardium of infarcted pigs. Cell retention was quantified by flow cytometry and real-time quantitative polymerase chain reaction methodology. Models, computing optimal distribution of distortion calibrated to favor tissue compliance, predicted that a 75°-curved needle featuring small-to-large graded side holes would ensure the highest cell retention profile. In isolated hearts, the nitinol curved needle catheter (C-Cath) design ensured 3-fold superior stem cell retention compared with a standard needle. In the setting of chronic infarction, percutaneous delivery of stem cells with C-Cath yielded a 37.7±7.1% versus 10.0±2.8% retention achieved with a traditional needle without effect on biocompatibility or safety. Conclusions—Modeling-guided development of a nitinol-based curved needle delivery system with incremental side holes achieved enhanced myocardial stem cell retention.