Reliability and availability analysis of dependent-dynamic systems with DRBDs

Reliability/availability evaluation is an important, often indispensable, step in designing and analyzing (critical) systems, whose importance is constantly growing. When the complexity of a system is high, dynamic effects can arise or become significant. The system might be affected by dependent, cascade, on-demand and/or common cause failures, its units could interfere (load sharing, inter/sequence-dependency), and so on. It is also of great interest to evaluate redundancy and maintenance policies but, since dynamic behaviors usually do not satisfy the stochastic independence assumption, notations such as reliability block diagrams (RBDs), fault trees (FTs) or reliability graphs (RGs) become approximated/simplified techniques, unable to capture dynamic-dependent behaviors. To overcome such problem we developed a new formalism derived from RBDs: the dynamic RBDs (DRBDs). In this paper we explain how the DRBDs notation is able to adequately model and therefore analyze dynamic-dependent behaviors and complex systems. Particular emphasis is given to the modeling and the analysis phases, from both the theoretical and the practical point of views. Several case studies of dynamic-dependent systems, selected from literature and related to different application fields, are proposed. In this way we also compare the DRBDs approach with other methodologies, demonstrating its effectiveness.     

The influence of the molar ratio of Al2O3 to Y2O3 on sintering behavior and the mechanical properties of a SiC–Al2O3–Y2O3 ceramic composite

The influence of the molar ratio of Al₂O₃ to Y₂O₃ (i.e. M_Al2O3/M_Y2O3) on sintering densification, microstructure and the mechanical properties of a SiC–Al₂O₃–Y₂O₃ ceramic composite were studied. It was shown that the optimal value of M_Al2O3/M_Y2O3 was 3/2, not 5/3, which is customarily considered the optimal molar ratio for the formation of YAG (Y₃Al₅O₁₂) phase. When M_Al2O3/M_Y2O3 is 5/3, materials existed in two phases of YAG and very little YAM phases. The sintering mechanism of the solid phase occurred at 1850 °C. When M_Al2O3/M_Y2O3 was 3/2, materials existed in the two phases YAG (Y₃Al₅O₁₂) and YAM (Y₄Al₂O₉). The formation of the low melting point eutectic liquid phase (YAG + YAM) increased sintering densification. Flexure strength, hardness and relative density were all higher.     

Novel carboxymethyl derivatives of chitin and chitosan materials and their biomedical applications

Chitin and chitosan are natural biopolymers that are non-toxic, biodegradable and biocompatible. In the last decade, chitin and chitosan derivatives have garnered significant interest in the biomedical and biopharmaceutical research fields with applications as biomaterials for tissue engineering and wound healing and as excipients for drug delivery. Introducing small chemical groups to the chitin or chitosan structure, such as alkyl or carboxymethyl groups, can drastically increase the solubility of chitin and chitosan at neutral and alkaline pH values without affecting their characteristics; substitution with carboxyl groups can yield polymers with polyampholytic properties. Carboxymethyl derivatives of chitin and chitosan have shown promise for adsorbing metal ions, as drug delivery systems, in wound healing, as anti-microbial agents, in tissue engineering, as components in cosmetics and food and for anti-tumor activities. This review will focus on the preparative methods and applications of carboxymethyl and succinyl derivatives of chitin and chitosan with particular emphasis on their uses as materials for biomedical applications.