1,720,966 research outputs found
Analytical model for performability evaluation of Practical Byzantine Fault-Tolerant systems
No full textDesigning systems tolerant to faults is crucial to assure continuity of service for mission critical applications. However, their implementation may be costly and challenging. In this study, analytical models are presented for performance evaluation of systems equipped with Practical Byzantine Fault-Tolerant consensus protocols. Byzantine Fault Tolerance is particularly compelling, since it can provide a robust consensus mechanism to implement decentralized platforms, like Decentralized Ledger Technology and, notably, blockchains. The performability model is based on continuous-time Markov chains, in which the processes involved follow the exponential distribution. The numerical results presented report an inverse non-linear relation between number of nodes and performability. Performance decreases also as the ratio between break-down rate and repair rate increases
Derivation of the Linear Landau Equation and Linear Boltzmann Equation from the Lorentz Model with Magnetic Field
No full textWe consider a test particle moving in a random distribution of obstacles in the plane, under the action of a uniform magnetic field, orthogonal to the plane. We show that, in a weak coupling limit, the particle distribution behaves according to the linear Landau equation with a magnetic transport term. Moreover, we show that, in a low density regime, when each obstacle generates an inverse power law potential, the particle distribution behaves according to the linear Boltzmann equation with a magnetic transport term. We provide an explicit control of the error in the kinetic limit by estimating the contributions of the configurations which prevent the Markovianity. We compare these results with those ones obtained for a system of hard disks in Bobylev et al. (Phys Rev Lett 75:2, 1995), which show instead that the memory effects are not negligible in the Boltzmann-Grad limit
Summability of Connected Correlation Functions of Coupled Lattice Fields
No full textWe consider two nonindependent random fields and defined on a countable set . For instance, or , where denotes a finite set of possible ``internal degrees of freedom'' such as spin. We prove that, if the cumulants of and enjoy a certain decay property, then all joint cumulants between and are -summable in the precise sense described in the text. The decay assumption for the cumulants of and is a restricted summability condition called -clustering property. One immediate application of the results is given by a stochastic process whose state is -clustering at any time : then the above estimates can be applied with and and we obtain uniform in estimates for the summability of time-correlations of the field.
The above clustering assumption is obviously satisfied by any -clustering stationary state of
the process, and our original motivation for the control of the summability of time-correlations
comes from a quest for a rigorous control of the Green-Kubo correlation function in such a system.
A key role in the proof is played by the properties of non-Gaussian Wick polynomials and their connection to cumulants
Off-chain trading for micro grid systems
Full text linkAs micro grids and blockchain gained the interest and attention of both academia and the industry, the interaction between the two technologies seems inevitable. However, there are challenges to overcome in order to actually realize the integration between micro grids and blockchains. In this article, we review the solutions proposed to enhance micro grids with blockchains. We discuss the scalability challenges and the opportunities derived from the off-chaining computing techniques. In this context, we draft a design to implement a micro grid-based peer-to-peer local energy market, powered by an off-chain computing protocol called DIVERSITY. DIVERSITY aims to shift the computational burden from a main blockchain to an intermediate layer of nodes, aggregating data and executing smart contracts off-chain. We simulate different data logging approaches, and it is found that DIVERSITY allows an actual saving on fees and power consumption derived from using a public blockchain platform, such as Ethereum, in order to assure a truly decentralized renewable energy distribution at a lower cost
Harmonic Chain with Velocity Flips: Thermalization and Kinetic Theory
No full textWe consider the detailed structure of correlations in harmonic chains with pinning and a bulk velocity flip noise during the heat relaxation phase which occurs on diffusive time scales, for where L is the chain length. It has been shown earlier that for non-degenerate harmonic interactions these systems thermalize, and the dominant part of the correlations is given by local thermal equilibrium determined by a temperature profile which satisfies a linear heat equation. Here we are concerned with two new aspects about the thermalization process: the first order corrections in to the local equilibrium correlations and the applicability of kinetic theory to study the relaxation process. Employing previously derived explicit uniform estimates for the temperature profile, we first derive an explicit form for the first order corrections to the particle position-momentum correlations. By suitably revising the definition of the Wigner transform and the kinetic scaling limit we derive a phonon Boltzmann equation whose predictions agree with the explicit computation. Comparing the two results, the corrections can be understood as arising from two different sources: a current-related term and a correction to the position-position correlations related to spatial changes in the phonon eigenbasis
Availability Model for Byzantine Fault-Tolerant Systems
No full textThe growth in the complexity and extensibility of computer systems have caused vulnerabilities such as exploitable software bugs and configuration flaws. In turn, confirming computer security is becoming an increasingly important task. Byzantine fault-tolerant algorithms are popularly used to allow systems automatically continue operating. In addition, Byzantine Fault-Tolerant Systems are used in blockchain networks, commonly in tandem with other consensus mechanisms. This study proposes an analytical availability model which is critical for the evaluation of fault-tolerant multi-server systems. A model is proposed based on continuous-time Markov chains to analyse the availability of Byzantine Fault-Tolerant systems. Numerical results are presented reporting availability as a function of the number of participants and the relative number of honest actors in the system. It can be concluded from the model that there is a non-linear relationship between the number of servers and availability inversely proportional to the number of nodes in the system. This relationship is further strengthened as the ratio of honest malicious nodes to the total number of nodes increases
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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