On Systematic Design of Fast and Perfect Detectors

We present a theory of fast and perfect detector components that extends the theory of detectors and correctors of Arora and Kulkarni, and based on which, we develop an algorithm that automatically transforms a fault-intolerant program into a fail-safe fault-tolerant program. Apart from presenting novel insights into the working principles of detectors, the theory also allows the definition of a detection latency efficiency metric for a fail-safe fault-tolerant program. We prove that in contrast to an earlier algorithm by Kulkarni and Arora, our algorithm produces fail-safe fault-tolerant programs with optimal detection latency. The application area of our results is in the domain of distributed embedded applications

New loci for body fat percentage reveal link between adiposity and cardiometabolic disease risk

To increase our understanding of the genetic basis of adiposity and its links to cardiometabolic disease risk, we conducted a genome-wide association meta-analysis of body fat percentage (BF%) in up to 100,716 individuals. Twelve loci reached genome-wide significance (P<5 × 10−8), of which eight were previously associated with increased overall adiposity (BMI, BF%) and four (in or near COBLL1/GRB14, IGF2BP1, PLA2G6, CRTC1) were novel associations with BF%. Seven loci showed a larger effect on BF% than on BMI, suggestive of a primary association with adiposity, while five loci showed larger effects on BMI than on BF%, suggesting association with both fat and lean mass. In particular, the loci more strongly associated with BF% showed distinct cross-phenotype association signatures with a range of cardiometabolic traits revealing new insights in the link between adiposity and disease risk

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

(Im)Possibilities of Predicate Detection in Crash-Affected Systems

In an asynchronous system, where processes can crash, perfect predicate detection for general predicates is difficult to achieve. A general predicate thereby is of the form # #, where# and # refer to a normal process variable and to the operational state of that process, respectively. Indeed, the accuracy of predicate detection largely depends on the quality of failure detection. In this paper, we investigate the predicate detection semantics that are achievable for general predicates using either failure detector classes ##P , #P, or P. For this purpose, we introduce weaker variants of the predicate detection problem, which we call stabilizing and infinitely often accurate. We show that perfect predicate detection is impossible using the aforementioned failure detectors. Rather, #P and only allow stabilizing predicate detection. Consequently, we explore alternative approaches to perfect predicate detection: introducing a stronger failure detector, called ordered perfect, or restricting the general nature of predicates

Transformational approaches to the specification and verification of fault-tolerant systems: Formal Background and classification

Proving that a program suits its specification and thus can be called correct has been a research subject for many years resulting in a wide range of methods and formalisms. However, it is a common experience that even systems which have been proven correct can fail due to physical faults occurring in the system. As computer programs control an increasing part of todays critical infrastructure, the notion of correctness has been extended to fault tolerance, meaning correctness in the presence of a certain amount of faulty behavior of the environment. Formalisms to verify fault-tolerant systems must model faults and faulty behavior in some form or another. Common ways to do this are based on a notion of transformation either at the program or the specification level. We survey the wide range of formal methods to verify fault-tolerant systems which are based on some form of transformation. Our aim is to classify these methods, relate them to one another and, thus, structure the area. We hope that this might faciliate the involvement of researchers into this interesting field of computer science

Byzantine Failures and Security: Arbitrary is not (always) Random

The Byzantine failure model allows arbitrary behavior of a certain fraction of network nodes in a distributed system. It was introduced to model and analyze the effects of very severe hardware faults in aircraft control systems. Lately, the Byzantine failure model has been used in the area of network security where Byzantine-tolerance is equated with resilience against malicious attackers. We discuss two reasons why one should be careful in doing so. Firstly, Byzantine-tolerance is not concerned with secrecy and so special means have to be employed if secrecy is a desired system property. Secondly, in contrast to the domain of hardware faults, in a security setting it is difficult to compute the assumption coverage of the Byzantine failure model, i.e., the probability that the failure assumption holds in practice. To address this latter point we develop a methodology which allows to estimate the reliability of a Byzantine-tolerant solution exposed to attackers of different strengths

An exercise in systematically deriving fault-tolerance specifications

To rigorously prove that a system is correct under normal system operation requires a formal correctness specification. In the context of fault tolerance, correctness means that a system must be correct even if some specified faults occur. The correctness conditions in the former and in the latter case are however not necessarily the same. This is because correctness specifications for fault tolerance must often take the behavior of faulty components into account. In this paper we perform a case study on the interrelations between problem specifications in ideal environments and in faulty ones. The problem considered is that of consensus and the failure model used is crash. The goal of this research is to uncover the influences that specific failure models have on problem specifications so that fault-tolerance specifications can be systematically derived. As this is work in progress, the ideas herein are partly half-baked and deserve some additional discussion