Survey of reliability and availability prediction methods from the viewpoint of software architecture

Many future software systems will be distributed across a network, extensively providing different kinds of services for their users. These systems must be highly reliable and provide services when required. Reliability and availability must be engineered into software from the onset of its development, and potential problems must be detected in the early stages, when it is easier and less expensive to implement modifications. The software architecture design phase is the first stage of software development in which it is possible to evaluate how well the quality requirements are being met. For this reason, a method is needed for analyzing software architecture with respect to reliability and availability. In this paper, we define a framework for comparing reliability and availability analysis methods from the viewpoint of software architecture. Our contribution is the comparison of the existing analysis methods and techniques that can be used for reliability and availability prediction at the architectural level. The objective is to discover which methods are suitable for the reliability and availability prediction of today’s complex systems, what are the shortcomings of the methods, and which research activities need to be conducted in order to overcome these identified shortcomings. The comparison reveals that none of the existing methods entirely fulfill the requirements that are defined in the framework. The comparison framework also defines the characteristics required of new reliability and availability analysis methods. Additionally, the framework is a valuable tool for selecting the best suitable method for architecture analysis. Furthermore, the framework can be extended and used for other evaluation methods as well.     

Latency and mode of error detection in a process industry

Licensee event reports (LERs) from an industry provide important information feedback about safety to the industry itself, the regulators and to the public. LERs from four nuclear power reactors were analyzed to find out about detection times, mode of detection and qualitative differences in reports from different reactors. The reliability of the codings was satisfactory and measured as the covariance between the ratings from two independent judges. The results showed differences in detection time across the reactors. On the average about 10% of the errors remained undetected for 100 weeks or more, but the great majority of errors were detected soon after their first appearance in the plant. On the average 40% of the errors were detected in regular tests and 40% through alarms. Operators found about 16% of the errors through noticing something abnormal in the plant. The remaining errors were detected in other ways. There were qualitative differences between the LERs from the different reactors reflecting the different conditions in the plants. The number of reports differed by a magnitude 1:2 between the different plants. However, a greater number of LERs can indicate both higher safety standards (e.g. a greater willingness to report all possible events to be able to learn from them) and lower safety standards (e.g. reporting as few events as possible to make a good impression). It was pointed out that LERs are indispensable in order to maintain safety of an industry and that the differences between plants found in the analyses of this study indicate how error reports can be used to initiate further investigations for improved safety.     

Thermal tuning of laser pulse parameters in passively Q-switched Nd:YAG lasers

Modifying the output pulses of a passively Q-switched Nd:YAG laser, operating at 1064 nm, was realized by heating the laser crystal. With the demonstrated laser setups, a 100 K temperature rise led to a more than 50% increase in the pulse energy and a more than 10% decrease in the pulse length. This method offers an effective way to tune the output of the laser without mechanical adjustment or a change of components.     

Countable Sofic Shifts with a Periodic Direction

Theory of Computing Systems - As a variant of the equal entropy cover problem, we ask whether all multidimensional sofic shifts with countably many configurations have SFT covers with countably...     

Iron overload in the rat pancreas following portacaval shunting and dietary iron supplementation

Reproduction of pancreatic iron overload in an animal model has been difficult to achieve primarily because of the first-pass extraction of iron by the liver. We hypothesized that portacaval shunting would avoid this hepatic phenomenon and increase pancreatic iron deposition. An end-to-side portacaval shunt was surgically created in male Sprague-Dawley rats, and they were subsequently fed a carbonyl iron-supplemented diet for 17 weeks. This resulted in marked iron accumulation in the pancreas (1621 +/- 188 micrograms/g) compared to minimal deposition in sham-operated rats fed the same diet (138 +/- 53 micrograms/g). Iron deposition in the acinar and centroacinar cells was confirmed histologically by Gomori staining, as well as by ultrastructural examination. Iron overloading was associated with enhanced oxidative stress evidenced by a twofold increase in the levels of glutathione disulfide and thiobarbituric acid-reactive substances. Also, adducts of proteins with malondialdehyde and 4-hydroxynonenal were demonstrated in acinar and ductal cells. Other apparent consequences of iron overload were a 50% reduction in pancreatic amylase content and a decrease in pancreatic protein concentration. These hypotrophic changes were associated with a reduced mass of zymogen granules in the acinar cells noted histologically. Our results show that a combination of portacaval shunting and carbonyl iron feeding achieve pancreatic iron overload and support the role of oxidative stress in the pathogenesis of iron-induced damage in the pancreas.     

Diagnostic Reasoning in the Use of Travel Management System

We explore the appropriation of a self-management administrative system from the perspective of diagnostic reasoning. The case study, based on documents, ethnography and videotapes, concerns the appropriation of a travel management system in a major university in Finland. To explore this process from a user-centric view, we focus on the diagnostic work required in the appropriation of the new system, analyzing both the generic diagnostic reasoning of how the users navigate in the system and their individual and collaborative problem-solving strategies. This approach reveals the interaction between the users and the technology, which incorporates inbuilt models of users, administrative work and work processes. Our analysis concerns interactive instances which resulted from misdiagnosis of the functions of the system. For example, the orchestration and labeling of items in the application pose diagnostic challenges to end-users and may eventually be resolved in collaboration with administrative personnel. The individual and collaborative diagnostic reasoning sheds light on the hidden organizational embeddedness of self-management solutions, providing suggestions for developing the design and deployment of administrative self-management systems. The appropriated self-management system should finally be based on the end-user’s diagnostic reasoning so that the employees can base their actions on their taken-for-granted competence and the skills gained during the appropriation of the system.     

Enzymatic synthesis of site-specifically (alpha 1-3)-fucosylated polylactosamines containing either a sialyl Lewis (x), a VIM-2, or a sialylated and internally difucosylated sequence

By using two different reaction pathways, we generated enzymatically three sialylated and site-specifically alpha 1-3-fucosylated polylactosamines. Two of these are isomeric hexasaccharides Neu5Ac(alpha 2-3)Gal(beta 1-4)GlcNAc(beta 1-3)Gal(beta 1-4)[Fuc(alpha 1-3)] GlcNAc and Neu5Ac(alpha 2-3)Gal(beta 1-4)[Fuc(alpha 1-3)]GlcNAc(beta 1-3)Gal(beta 1-4) GlcNAc, containing epitopes that correspond to VIM-2 and sialyl Lewis (x), respectively. The third one, nonasaccharide Neu5Ac(alpha 2-3)Gal(beta 1-4)GlcNAc(beta 1-3)Gal(beta 1-4)[Fuc(alpha 1-3)] GlcNAc(beta 1-3)Gal(beta 1-4)[Fuc(alpha 1-3)]GlcNAc, is a sialylated and internally difucosylated derivative of a trimeric N-acetyllactosamine. All three oligosaccharides have one fucose-free N-acetyllactosaminyl unit and can be used as acceptors for recombinant alpha 1-3-fucosyltransferases in determining the biosynthesis pathways leading to polyfucosylated selectin ligands.     

Improving the Accuracy of Structural Hot‐spot Stress Approach

A method for extending the applicability of the structural hot‐spot stress method for fatigue assessment of welded structures is discussed. The structural hot‐spot stress method for plate structures, as currently presented in commonly used design guidance documents, cannot account for the effect of weld size, and load carrying fillet welds are assessed using a different S‐N curve as compared to non‐load carrying fillet welds. This paper presents a proposal to linearize the local stress distribution through the plate thickness in the plane of the weld toe. This proposal considers the forces transmitted by the weld itself. A bilinear stress distribution, which partially captures the local effect of the weld, is derived from the non‐linear stress distribution. The non‐linear distribution is based on equilibrium and the stress in the fillet weld. A simple procedure is presented to determine the bilinear curve from the nominal weld stress. This is a great advantage in finite element analysis when only nominal base plate stress and nominal weld stresses need to be determined. When compared to the more conventional structural stress approach, the new method also has the advantage that extrapolation is not required. The same weld stresses can also be used in the analysis of the root cracks. The proposed method was scaled to correspond to the traditional structural hot‐spot stress method using detailed linear elastic fracture mechanics simulations. The method is only applied to fully load‐carrying welds here but can also be used for partial load‐carrying welds. A symmetric splice plate having a fully loaded fillet weld is presented as an example case. The influence of base plate thickness is studied as well.