Estimating Probability of Failure of a Complex System Based on Inexact Information about Subsystems and Components, with Potential Applications to Aircraft Maintenance

In many real-life applications (e.g., in aircraft maintenance), we need to estimate the probability of failure of a complex system (such as an aircraft as a whole or one of its subsystems). Complex systems are usually built with redundancy allowing them to withstand the failure of a small number of components. In this paper, we assume that we know the structure of the system, and, as a result, for each possible set of failed components, we can tell whether this set will lead to a system failure. For each component A, we know the probability P(A) of its failure with some uncertainty: e.g., we know the lower and upper bounds P(A) and P(A) for this probability. Usually, it is assumed that failures of different components are independent events. Our objective is to use all this information to estimate the probability of failure of the entire the complex system. In this paper, we describe several methods for solving this problem, including a new efficient method for such estimation based on Cauchy deviates

First Dinosaur Tracks from the Arabian Peninsula

Background: The evolutionary history of Mesozoic terrestrial vertebrates from the Arabian Peninsula is virtually unknown. Despite vast exposures of rocky outcrops, only a handful of fossils have yet been described from the region. Here we report a multi-taxon dinosaur track assemblage near Madar village, 47 km north of Sana’a, Republic of Yemen. This represents the first dinosaur tracksite from the Arabian Peninsula, and the only multi-taxon dinosaur ichnosite in the Middle East. Methodology/Findings: Measurements were taken directly from trackway impressions, following standard ichnological conventions. The presence of bipedal trackmakers is evidenced by a long series of pes imprints preserving smoothly rounded posterior margins, no evidence of a hallux, bluntly rounded digit tips and digital divarication angles characteristic of ornithopod dinosaurs. Nearby, eleven parallel quadrupedal trackways document a sauropod herd that included large and small individuals traveling together. Based on the morphology of manus impressions along with a narrow-gauged stance, the quadrupedal trackways were made by non-titanosauriform neosauropods. Additional isolated tracks and trackways of sauropod and ornithopod dinosaurs are preserved nearby. Conclusions/Significance: Taken together, these discoveries present the most evocative window to date into the evolutionary history of dinosaurs of the Arabian Peninsula. Given the limited Mesozoic terrestrial record from the region, this discovery is of both temporal and geographic significance, and massive exposures of similarly-aged outcrops nearby offe

QDB: A new database of plasma chemistries and reactions

One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for some reactions, complete and validated datasets of chemistries are rarely available. This hinders research on plasma processes and curbs development of industrial applications. The QDB project aims to address this problem by providing a platform for provision, exchange, and validation of chemistry datasets. A new data model developed for QDB is presented. QDB collates published data on both electron scattering and heavy-particle reactions. These data are formed into reaction sets, which are then validated against experimental data where possible. This process produces both complete chemistry sets and identifies key reactions that are currently unreported in the literature. Gaps in the datasets can be filled using established theoretical methods. Initial validated chemistry sets for SF 6 /CF 4 /O 2 and SF 6 /CF 4 /N 2 /H 2 are presented as examples

Détermination et calcul de la fréquence d'occurrence d'une coupe minimale -Un bref état de l'art -

International audienceSummary Following a bibliography survey, the authors of this paper have gathered a small sample of five approaches representative of the state of the art related to the determination of the occurrence frequency of a given minimal cut set. Each of these different approaches aims to provide a literal expression to easily calculate this frequency. Then it has been decided to test each of them on a system chosen for its simplicity. In order to analyse the relevance of the formulae the results have been compared first to those given by the Markovian approach taken as reference. It has been shown that the formulae which have proven to be relevant are different formulations of a same explicit and concise expression giving the occurrence frequency of a given minimal cut set. This generic expression has been implemented by using a dedicated algorithm based on binary decision diagrams. This allows to quickly calculate the time dependant results and this is described in the last section of the paper.Un petit échantillon de cinq méthodes représentatives de l'état de l'art concernant la détermination et le calcul de la fréquence d'occurrence d'une coupe minimale a été constitué. Leur finalité étant de proposer une formule donnant l'expression littérale de cette fréquence, et permettant ainsi d'en calculer aisément la valeur, il a été décidé de tester chacune de ces méthodes en appliquant la formule qu'elle propose aux coupes minimales d'un système choisi pour sa simplicité. Les résultats ainsi obtenus ont d'abord été comparés à ceux donnés par une méthode Markovienne de référence et appliquée au même système, puis ont été catégorisés en fonction de leur pertinence. Il a été enfin montré que les formules ayant passé positivement le test ne sont que des formulations différentes d'une même expression littérale, à la fois explicite et concise, de la fréquence d'occurrence d'une coupe minimale. L'implémentation de cette formule au sein d'un algorithme, basé sur les diagrammes binaires de décision, permet d'en calculer rapidement la valeur en fonction du temps et fait l'objet de la dernière section

Time of flight photoelectron spectroscopy using synchrotron radiation study of resonances in O

Photoelectron time of flight spectroscopy using pulsed synchrotron radiation is shown to provide accurate binding energies and reliable intensity measurements. Advantage is taken of the high transmission as well as good resolution for low kinetic energy (0-1 eV) electrons, to measure the variation of vibrational branching ratios for [Math] and [Math] states of [Math] upon excitation of oxygen along selecte resonance profiles. Dramatic deviation from Franck-Condon factors are observed

Titan ionospheric chemistry

A new physical chemistry approach is developed in order to provide information necessary to improve the understanding of processes involved in the ionosphere of Titan. The complexity of the chemical processes occuring in the ionosphere calls for an improved description . (i) The uncertainty associated to laboratory measurements, and their propagation in the model schemes and (ii) the simplification of the chemistry scheme, in order to describe the complex behavior, without losing the physical meaning of results will be handled by means of statistical methods. (iii) From the laboratory measurements point of view, the structure of reactants and product in orders to identify the pathways leading to important process such as cyclisation, functionalization, etc will be described accurately by means of a ultra high resolution mass spectrometer. Historical results of our studies on the effect of internal and kinetic energy on the initial step of the chemical scheme will also be discussed

Uncertainty analysis of bimolecular reactions in Titan ionosphere chemistry model

International audienceWe report about the first detailed uncertainty analysis concerning the kinetics parameters of the ion–molecule reactions included in a Titan's ionospheric chemistry model. Uncertainty propagation has been performed by Monte Carlo sampling. Different possible descriptions of the uncertainties on the rate constants are discussed and compared on the basis of our state of knowledge about ion–molecule reaction rates laboratory measurements. We propose also a new method for the treatment of branching ratios correlated uncertainties. We show that the uncertainty on branching ratios contribute significantly to the uncertainty on ion densities predicted by the chemistry model. Simulation of a mass spectrum for ionic species in Titan ionosphere at 1200 km of altitude and night-time chemistry has been performed and compared to the INMS mass-spectrum available on the website of the NASA left angle brackethttp://photojournal.jpl.nasa.gov/catalog/PIA07865right-pointing angle bracket], corresponding to Cassini's T5 flyby