The collision of two-kinks defects

We have investigated the head-on collision of a two-kink and a two-antikink pair that arises as a generalization of the $\phi^4$ model. We have evolved numerically the Klein-Gordon equation with a new spectral algorithm whose accuracy and convergence were attested by the numerical tests. As a general result, the two-kink pair is annihilated radiating away most of the scalar field. It is possible the production of oscillons-like configurations after the collision that bounce and coalesce to form a small amplitude oscillon at the origin. The new feature is the formation of a sequence of quasi-stationary structures that we have identified as lump-like solutions of non-topological nature. The amount of time these structures survives depends on the fine-tuning of the impact velocity.Comment: 14 pages, 9 figure

Manejo de plantas daninhas em pomares de cajueiro anão precoce no litoral do Ceará.

Este estudo tem como objetivo avaliar o comportamento do cajueiro anao precoce, submetido a diferentes sistemas de manejo, bem como as propriedades fisicas, quimicas e biologicas do solo.bitstream/CNPAT-2010/5400/1/Pa-053.pd

Arborização de pastagens: tecnologia para assegurar o bem-estar animal e a sustentabilidade das pastagens.

bitstream/item/107178/1/arborizacao-Tadario.pd

Efficient Formal Verification for the Linux Kernel

Formal verification of the Linux kernel has been receiving increasing attention in recent years, with the development of many models, from memory subsystems to the synchronization primitives of the real-time kernel. The effort in developing formal verification methods is justified considering the large code-base, the complexity in synchronization required in a monolithic kernel and the support for multiple architectures, along with the usage of Linux on critical systems, from high-frequency trading to self-driven cars. Despite recent developments in the area, none of the proposed approaches are suitable and flexible enough to be applied in an efficient way to a running kernel. Aiming to fill such a gap, this paper proposes a formal verification approach for the Linux kernel, based on automata models. It presents a method to auto-generate verification code from an automaton, which can be integrated into a module and dynamically added into the kernel for efficient on-the-fly verification of the system, using in-kernel tracing features. Finally, a set of experiments demonstrate verification of three models, along with performance analysis of the impact of the verification, in terms of latency and throughput of the system, showing the efficiency of the approach

Untangling the intricacies of thread synchronization in the PREEMPT-RT linux kernel

This article proposes an automata-based model for describing and validating the behavior of threads in the Linux PREEMPT-RT kernel, on a single-core system. The automata model defines the events and how they influence the timeline of threads' execution, comprising the preemption control, interrupt handlers, interrupt control, scheduling and locking. This article also presents the extension of the Linux trace features that enable the trace of the kernel events used in the modeling. The model and the tracing tool are used, initially, to validate the model, but preliminary results were enough to point to two problems in the Linux kernel. Finally, the analysis of the events involved in the activation of the highest priority thread is presented in terms of necessary and sufficient conditions, describing the delays occurred in this operation in the same granularity used by kernel developers, showing how it is possible to take advantage of the model for analyzing the thread wake-up latency, without any need for watching the corresponding kernel code