398 research outputs found
SMT-based Model Checking for Recursive Programs
We present an SMT-based symbolic model checking algorithm for safety
verification of recursive programs. The algorithm is modular and analyzes
procedures individually. Unlike other SMT-based approaches, it maintains both
"over-" and "under-approximations" of procedure summaries. Under-approximations
are used to analyze procedure calls without inlining. Over-approximations are
used to block infeasible counterexamples and detect convergence to a proof. We
show that for programs and properties over a decidable theory, the algorithm is
guaranteed to find a counterexample, if one exists. However, efficiency depends
on an oracle for quantifier elimination (QE). For Boolean Programs, the
algorithm is a polynomial decision procedure, matching the worst-case bounds of
the best BDD-based algorithms. For Linear Arithmetic (integers and rationals),
we give an efficient instantiation of the algorithm by applying QE "lazily". We
use existing interpolation techniques to over-approximate QE and introduce
"Model Based Projection" to under-approximate QE. Empirical evaluation on
SV-COMP benchmarks shows that our algorithm improves significantly on the
state-of-the-art.Comment: originally published as part of the proceedings of CAV 2014; fixed
typos, better wording at some place
From Event-B models to Dafny code contracts
International audienceThe constructive approach to software correctness aims at formal modelling and verification of the structure and behaviour of a system in different levels of abstraction. In contrast, the analytical approach to software verification focuses on code level correctness and its verification. Therefore it would seem that the constructive and analytical approaches should complement each other well. To demonstrate this idea we present a case for linking two existing verification methods, Event-B (constructive) and Dafny (analytical). This approach combines the power of Event-B abstraction and its stepwise refinement with the verification capabilities of Dafny. We presented a small case study to demonstrate this approach and outline of the rules for transforming Event-B events to Dafny contracts. Finally, a tool for automatic generation of Dafny contracts from Event-B formal models is presented
l-Leucine supplemented whey protein. Dose–response effect on heart mTOR activation of sedentary and trained rats
AbstractThe aim of the study was to investigate the effect of leucine supplementation combined with exercise and whey protein in cardiac mTOR anabolic pathway. Ninety-six weanling male Wistar rats were divided into eight groups and fed diets containing either casein or WP plus increasing levels (0, 3, 4.5 and 6% of diet) of l-leucine for 30days. A parallel set of eight groups was exercised for comparison. Serum aspartate amino transferase, alanine aminotransferase, creatine kinase, lactate dehydrogenase and branched chain amino acids were determined by standard methods, and mammalian target of rapamycin (mTOR) and p70S6K by the Western blot analysis. Chronic l-leucine supplementation was capable of increasing both mTOR and p70S6K phosphorylation in the heart in a dose-dependent fashion, independent of the type of dietary protein in both groups, sedentary and exercised, but the exercise potentialized the activation of the anabolic pathway. The content of protein in heart increase with l-leucine supplementation and the heart mass relativized by body mass did not change. In conclusion, the combination of l-leucine and milk proteins (casein or whey protein) has the potential to increase the mTOR pathway in the cardiac muscle without increasing the heart mass. The novelty of this study is to show the effectiveness of a blend of leucine and whey protein as a viable alternative to maximize the activation of the anabolic pathway of cardiac muscle and that the exercise can improve this process
Effects of deliberate reflection on students' engagement in learning and learning outcomes
Context
Reflection in practice is assumed to enhance interest in knowing more about a topic, increasing engagement in learning and learning outcomes. However, this claim lacks empirical evidence, particularly in medical education. The authors investigated the effects of deliberate reflection upon clinical cases on medical students’ engagement in a learning activity and learning outcomes.
Methods
A three‐task (diagnostic task; learning activity; test) experiment was conducted in August 2017. Seventy‐two fourth‐year students from UNIFENAS‐BH Medical School, Brazil, diagnosed two clinical cases with jaundice as the chief complaint, either by following a deliberate reflection procedure or making differential diagnosis. Subsequently, all participants received the same study material on the diagnosis of jaundice. Finally, they took a recall test on the study material. Outcome measurements were study time and test scores.
Results
There was a significant effect of experimental condition on students’ engagement in the learning activity and on learning outcomes. Students who deliberately reflected upon the cases invested more time in studying the material than those who made a differential diagnosis (respectively, mean = 254.97, standard deviation = 115.45 versus mean = 194.96, standard deviation = 111.68; p = 0.02; d = 0.53). Deliberate reflection was also related to higher scores in the test relative to differential diagnosis (respectively, mean = 22.08, standard deviation = 14.94 versus mean = 15.75, standard deviation = 9.24; p = 0.03; d = 0.51). Medium effect sizes (Cohen's d) were observed in both measurements.
Conclusions
Relative to making differential diagnosis, deliberate reflection while diagnosing cases fostered medical students’ engagement in learning and increased learning outcomes. Teachers can employ this relatively easy procedure, possibly both with simulated and real scenarios, to motivate their students and help them expand their knowledge, an important requirement for their professional development
6Li direct breakup lifetimes
alpha-d coincidence data were studied for the 6Li + 59Co reaction at E(lab) =
29.6 MeV. By using a kinematic analysis, it was possible to identify which
process, leading to the same final state, has the major contribution for each
of the selected angular regions. Contributions of the 6Li sequential and direct
breakup to the incomplete fusion/transfer process were discussed by considering
the lifetimes obtained by using a semiclassical approach, for both breakup
components.Comment: 5 pages, 4 figures, Invited Talk (Parrallel Sessions) of A. Szanto de
Toledo, prepared for the Proccedings of the 10th International Conference on
Nucleus-Nucleus Collisions, August 16-21, 2009, Beijing, China; submitted to
Nucl. Phys. A (Proceedings of NN2009
Study of 9Be+12C elastic scattering at energies near the Coulomb barrier
In this work, angular distribution measurements for the elastic channel were
performed for the 9Be+12C reaction at the energies ELab=13.0, 14.5, 17.3, 19.0
and 21.0 MeV, near the Coulomb barrier. The data have been analyzed in the
framework of the double folding S\~ao Paulo potential. The experimental elastic
scattering angular distributions were well described by the optical potential
at forward angles for all measured energies. However, for the three highest
energies, an enhancement was observed for intermediate and backward angles.
This can be explained by the elastic transfer mechanism.
Keywords: 9Be+12C, Elastic Scattering, S\~aoo Paulo Potential
Reaction mechanisms in the 6Li+59Co system
The reactions induced by the weakly bound 6Li projectile interacting with the
intermediate mass target 59Co were investigated. Light charged particles
singles and - coincidence measurements were performed at the near
barrier energies E_lab = 17.4, 21.5, 25.5 and 29.6 MeV. The main contributions
of the different competing mechanisms are discussed. A statistical model
analysis, Continuum-Discretized Coupled-Channels calculations and two-body
kinematics were used as tools to provide information to disentangle the main
components of these mechanisms. A significant contribution of the direct
breakup was observed through the difference between the experimental sequential
breakup cross section and the CDCC prediction for the non-capture breakup cross
section.Comment: 30 pages, 8 figure
Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets
An experimental overview of reactions induced by the stable, but weakly-bound
nuclei 6Li, 7Li and 9Be, and by the exotic, halo nuclei 6He, 8B, 11Be and 17F
on medium-mass targets, such as 58Ni, 59Co or 64Zn, is presented. Existing data
on elastic scattering, total reaction cross sections, fusion processes, breakup
and transfer channels are discussed in the framework of a CDCC approach taking
into account the breakup degree of freedom.Comment: 7 pages, 6 figures, Invited Talk given by C. Beck to the 10th
International Conference on Nucleus-Nucleus Collisions, August 16-21, 2009
Beijing, China; Paper submitted to the NN2009 Proceedings, Nuclear Physics A
(to be published
Trabalho, terra e geração de renda em três décadas de reflorestamentos no alto Jequitinhonha.
A partir dos anos 1970, as chapadas do Alto Jequitinhonha, localizadas no nordeste de Minas Gerais, até então áreas de uso comum de agricultores familiares, foram plantadas com eucaliptos. O objetivo deste artigo é comparar os efeitos do reflorestamento sobre a estrutura fundiária, valor da produção agrícola e ocupação rural com os efeitos da produção agrícola familiar sobre essas mesmas variáveis na microrregião homogênea de Capelinha, no Alto Jequitinhonha. Tal microrregião foi escolhida para o estudo por ser a área de maior concentração de eucaliptais da região. Foram utilizados dados secundários dos Censos do IBGE para os anos de 1970, 1980, 1985 e 1996, além de dados secundários de pesquisas realizadas sobre a região em questão, incluindo entrevistas com dirigentes de empresas e lideranças sindicais. O artigo conclui que, em trinta anos, o reflorestamento concentrou terras e criou um número reduzido de empregos; a agricultura familiar, ao contrário, teve suas áreas de terras comprimidas e super-exploradas em decorrência da perda das chapadas, mas continuou sendo a principal responsável pela geração de ocupações e rendas na região
Checking bounded reachability in asynchronous systems by symbolic event tracing
This report presents a new symbolic technique for checking reachability properties of asynchronous systems by reducing the problem to satisfiability in restrained difference logic. The analysis is bounded by fixing a finite set of potential events, each of which may occur at most once in any order. The events are specified using high-level Petri nets. The logic encoding describes the space of possible causal links between events rather than possible sequences of states as in Bounded Model Checking. Independence between events is exploited intrinsically without partial order reductions, and the handling of data is symbolic. On a family of benchmarks, the proposed approach is consistently faster than Bounded Model Checking. In addition, this report presents a compact encoding of the restrained subset of difference logic in propositional logic
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