3,755 research outputs found
A thread synchronization model for the PREEMPT_RT Linux kernel
This article proposes an automata-based model for describing and validating sequences of kernel events in Linux PREEMPT_RT and how they influence the timeline of threads’ execution, comprising preemption control, interrupt handling and control, scheduling and locking. This article also presents an extension of the Linux tracing framework that enables the tracing of kernel events to verify the consistency of the kernel execution compared to the event sequences that are legal according to the formal model. This enables cross-checking of a kernel behavior against the formalized one, and in case of inconsistency, it pinpoints possible areas of improvement of the kernel, useful for regression testing. Indeed, we describe in details three problems in the kernel revealed by using the proposed technique, along with a short summary on how we reported and proposed fixes to the Linux kernel community. As an example of the usage of the model, the analysis of the events involved in the activation of the highest priority thread is presented, describing the delays occurred in this operation in the same granularity used by kernel developers. This illustrates how it is possible to take advantage of the model for analyzing the preemption model of Linux
Automata-based modeling of interrupts in the Linux PREEMPT RT kernel
This paper presents a methodology to model and check the behavior of a part of the Linux kernel by applying automaton theory and in-kernel tracing from real execution. It is possible to check that the state transitions of the kernel during a real execution match with the allowed ones, according to the formal model. The scope of the paper is limited to the IRQ/NMI subsystem of the Linux kernel
Granitos de Esmolfe e Antas-Matança (Portugal): petrografia e influência da fracturação no estabelecimento de áreas potenciais para exploração de granito ornamental
Datasets for Portuguese Legal Semantic Textual Similarity: Comparing weak supervision and an annotation process approaches
The Brazilian judiciary has a large workload, resulting in a long time to
finish legal proceedings. Brazilian National Council of Justice has established
in Resolution 469/2022 formal guidance for document and process digitalization
opening up the possibility of using automatic techniques to help with everyday
tasks in the legal field, particularly in a large number of texts yielded on
the routine of law procedures. Notably, Artificial Intelligence (AI) techniques
allow for processing and extracting useful information from textual data,
potentially speeding up the process. However, datasets from the legal domain
required by several AI techniques are scarce and difficult to obtain as they
need labels from experts. To address this challenge, this article contributes
with four datasets from the legal domain, two with documents and metadata but
unlabeled, and another two labeled with a heuristic aiming at its use in
textual semantic similarity tasks. Also, to evaluate the effectiveness of the
proposed heuristic label process, this article presents a small ground truth
dataset generated from domain expert annotations. The analysis of ground truth
labels highlights that semantic analysis of domain text can be challenging even
for domain experts. Also, the comparison between ground truth and heuristic
labels shows that heuristic labels are useful
Limites jurídicos da liberdade de expressão : fake news e desinformação
Quais são os limites quando falamos em liberdade? Tudo é permitido quando falamos em liberdade de expressão? E o que não é dito, ou que é mal dito, ou mentido? Até onde vai a liberdade de expressão? Para responder essas questões, será preciso revisitar todas as formas modernas de expressão e acompanhar todos os movimentos jurídicos que estão sendo feitos para tentar frear o crescimento da desinformação como fenômeno de dominação. Para tanto vamos compreender as diferenças entre expressão, opinião, desinformação e a palavra da moda - “fake news” para ao final perceber que não existe liberdades absolutas e que a sociedade procurar alcançar rapidamente uma legislação capaz de democratizar o acesso a informação, impedindo a infiltração de falsas notícias, pós-verdades e manipulação da sociedade.What are the limits when we talk about freedom? Is everything allowed when we talk about freedom of expression? And what is not said, or what is said badly, or lied to? How far does freedom of expression go? To answer these questions, it will be necessary to revisit all modern forms of expression and follow all the legal movements that are being made to try to curb the growth of disinformation as a phenomenon of domination. To do so, we will understand the differences between expression, opinion, disinformation and the buzzword - "fake news" to finally realize that there are no absolute freedoms and that society seeks to quickly achieve legislation capable of democratizing access to information, preventing the infiltration of false news, post-truths and manipulation of society
Diffusive epidemic process: theory and simulation
We study the continuous absorbing-state phase transition in the
one-dimensional diffusive epidemic process via mean-field theory and Monte
Carlo simulation. In this model, particles of two species (A and B) hop on a
lattice and undergo reactions B -> A and A + B -> 2B; the total particle number
is conserved. We formulate the model as a continuous-time Markov process
described by a master equation. A phase transition between the (absorbing)
B-free state and an active state is observed as the parameters (reaction and
diffusion rates, and total particle density) are varied. Mean-field theory
reveals a surprising, nonmonotonic dependence of the critical recovery rate on
the diffusion rate of B particles. A computational realization of the process
that is faithful to the transition rates defining the model is devised,
allowing for direct comparison with theory. Using the quasi-stationary
simulation method we determine the order parameter and the survival time in
systems of up to 4000 sites. Due to strong finite-size effects, the results
converge only for large system sizes. We find no evidence for a discontinuous
transition. Our results are consistent with the existence of three distinct
universality classes, depending on whether A particles diffusive more rapidly,
less rapidly, or at the same rate as B particles.Comment: 19 pages, 5 figure
Casimir energy in a small volume multiply connected static hyperbolic pre-inflationary Universe
A few years ago, Cornish, Spergel and Starkman (CSS), suggested that a
multiply connected ``small'' Universe could allow for classical chaotic mixing
as a pre-inflationary homogenization process. The smaller the volume, the more
important the process. Also, a smaller Universe has a greater probability of
being spontaneously created. Previously DeWitt, Hart and Isham (DHI) calculated
the Casimir energy for static multiply connected flat space-times. Due to the
interest in small volume hyperbolic Universes (e.g. CSS), we generalize the DHI
calculation by making a a numerical investigation of the Casimir energy for a
conformally coupled, massive scalar field in a static Universe, whose spatial
sections are the Weeks manifold, the smallest Universe of negative curvature
known. In spite of being a numerical calculation, our result is in fact exact.
It is shown that there is spontaneous vacuum excitation of low multipolar
components.Comment: accepted for publication in phys. rev.
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