6,919 research outputs found
BeSpaceD: Towards a Tool Framework and Methodology for the Specification and Verification of Spatial Behavior of Distributed Software Component Systems
In this report, we present work towards a framework for modeling and checking
behavior of spatially distributed component systems. Design goals of our
framework are the ability to model spatial behavior in a component oriented,
simple and intuitive way, the possibility to automatically analyse and verify
systems and integration possibilities with other modeling and verification
tools. We present examples and the verification steps necessary to prove
properties such as range coverage or the absence of collisions between
components and technical details
Modeling the International-Trade Network: A Gravity Approach
This paper investigates whether the gravity model (GM) can explain the
statistical properties of the International Trade Network (ITN). We fit data on
international-trade flows with a GM specification using alternative fitting
techniques and we employ GM estimates to build a weighted predicted ITN, whose
topological properties are compared to observed ones. Furthermore, we propose
an estimation strategy to predict the binary ITN with a GM. We find that the GM
successfully replicates the weighted-network structure of the ITN, only if one
fixes its binary architecture equal to the observed one. Conversely, the GM
performs very badly when asked to predict the presence of a link, or the level
of the trade flow it carries, whenever the binary structure must be
simultaneously estimated
Numerical investigation of the late-time Kerr tails
The late-time behavior of a scalar field on fixed Kerr background is examined
in a numerical framework incorporating the techniques of conformal
compactification and hyperbolic initial value formulation. The applied code is
1+(1+2) as it is based on the use of the spectral method in the angular
directions while in the time-radial section fourth order finite differencing,
along with the method of lines, is applied. The evolution of various types of
stationary and non-stationary pure multipole initial states are investigated.
The asymptotic decay rates are determined not only in the domain of outer
communication but along the event horizon and at future null infinity as well.
The decay rates are found to be different for stationary and non-stationary
initial data, and they also depend on the fall off properties of the initial
data toward future null infinity. The energy and angular momentum transfers are
found to show significantly different behavior in the initial phase of the time
evolution. The quasinormal ringing phase and the tail phase are also
investigated. In the tail phase, the decay exponents for the energy and angular
momentum losses at future null infinity are found to be smaller than at the
horizon which is in accordance with the behavior of the field itself and it
means that at late times the energy and angular momentum falling into the black
hole become negligible in comparison with the energy and angular momentum
radiated toward future null infinity. The energy and angular momentum balances
are used as additional verifications of the reliability of our numerical
method.Comment: 33 pages, 12 figure
Distributed Computability in Byzantine Asynchronous Systems
In this work, we extend the topology-based approach for characterizing
computability in asynchronous crash-failure distributed systems to asynchronous
Byzantine systems. We give the first theorem with necessary and sufficient
conditions to solve arbitrary tasks in asynchronous Byzantine systems where an
adversary chooses faulty processes. In our adversarial formulation, outputs of
non-faulty processes are constrained in terms of inputs of non-faulty processes
only. For colorless tasks, an important subclass of distributed problems, the
general result reduces to an elegant model that effectively captures the
relation between the number of processes, the number of failures, as well as
the topological structure of the task's simplicial complexes.Comment: Will appear at the Proceedings of the 46th Annual Symposium on the
Theory of Computing, STOC 201
A Short Counterexample Property for Safety and Liveness Verification of Fault-tolerant Distributed Algorithms
Distributed algorithms have many mission-critical applications ranging from
embedded systems and replicated databases to cloud computing. Due to
asynchronous communication, process faults, or network failures, these
algorithms are difficult to design and verify. Many algorithms achieve fault
tolerance by using threshold guards that, for instance, ensure that a process
waits until it has received an acknowledgment from a majority of its peers.
Consequently, domain-specific languages for fault-tolerant distributed systems
offer language support for threshold guards.
We introduce an automated method for model checking of safety and liveness of
threshold-guarded distributed algorithms in systems where the number of
processes and the fraction of faulty processes are parameters. Our method is
based on a short counterexample property: if a distributed algorithm violates a
temporal specification (in a fragment of LTL), then there is a counterexample
whose length is bounded and independent of the parameters. We prove this
property by (i) characterizing executions depending on the structure of the
temporal formula, and (ii) using commutativity of transitions to accelerate and
shorten executions. We extended the ByMC toolset (Byzantine Model Checker) with
our technique, and verified liveness and safety of 10 prominent fault-tolerant
distributed algorithms, most of which were out of reach for existing
techniques.Comment: 16 pages, 11 pages appendi
Enhanced Gravity Model of trade: reconciling macroeconomic and network models
The structure of the International Trade Network (ITN), whose nodes and links
represent world countries and their trade relations respectively, affects key
economic processes worldwide, including globalization, economic integration,
industrial production, and the propagation of shocks and instabilities.
Characterizing the ITN via a simple yet accurate model is an open problem. The
traditional Gravity Model (GM) successfully reproduces the volume of trade
between connected countries, using macroeconomic properties such as GDP,
geographic distance, and possibly other factors. However, it predicts a network
with complete or homogeneous topology, thus failing to reproduce the highly
heterogeneous structure of the ITN. On the other hand, recent maximum-entropy
network models successfully reproduce the complex topology of the ITN, but
provide no information about trade volumes. Here we integrate these two
currently incompatible approaches via the introduction of an Enhanced Gravity
Model (EGM) of trade. The EGM is the simplest model combining the GM with the
network approach within a maximum-entropy framework. Via a unified and
principled mechanism that is transparent enough to be generalized to any
economic network, the EGM provides a new econometric framework wherein trade
probabilities and trade volumes can be separately controlled by any combination
of dyadic and country-specific macroeconomic variables. The model successfully
reproduces both the global topology and the local link weights of the ITN,
parsimoniously reconciling the conflicting approaches. It also indicates that
the probability that any two countries trade a certain volume should follow a
geometric or exponential distribution with an additional point mass at zero
volume
The Inhuman Overhang: On Differential Heterogenesis and Multi-Scalar Modeling
As a philosophical paradigm, differential heterogenesis offers us a novel descriptive vantage with which to inscribe Deleuze’s virtuality within the terrain of “differential becoming,” conjugating “pure saliences” so as to parse economies, microhistories, insurgencies, and epistemological evolutionary processes that can be conceived of independently from their representational form. Unlike Gestalt theory’s oppositional constructions, the advantage of this aperture is that it posits a dynamic context to both media and its analysis, rendering them functionally tractable and set in relation to other objects, rather than as sedentary identities. Surveying the genealogy of differential heterogenesis with particular interest in the legacy of Lautman’s dialectic, I make the case for a reading of the Deleuzean virtual that departs from an event-oriented approach, galvanizing Sarti and Citti’s dynamic a priori vis-à -vis Deleuze’s philosophy of difference. Specifically, I posit differential heterogenesis as frame with which to examine our contemporaneous epistemic shift as it relates to multi-scalar computational modeling while paying particular attention to neuro-inferential modes of inductive learning and homologous cognitive architecture. Carving a bricolage between Mark Wilson’s work on the “greediness of scales” and Deleuze’s “scales of reality”, this project threads between static ecologies and active externalism vis-à -vis endocentric frames of reference and syntactical scaffolding
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