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Search Results: 1 - 10 of 327814 matches for " Walace S. Elias "
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Thermodynamics of quantum photon spheres
M. C. Baldiotti,Walace S. Elias,C. Molina,Thiago S. Pereira
Physics , 2014, DOI: 10.1103/PhysRevD.90.104025
Abstract: Photon spheres, surfaces where massless particles are confined in closed orbits, are expected to be common astrophysical structures surrounding ultracompact objects. In this paper a semiclassical treatment of a photon sphere is proposed. We consider the quantum Maxwell field and derive its energy spectra. A thermodynamic approach for the quantum photon sphere is developed and explored. Within this treatment, an expression for the spectral energy density of the emitted radiation is presented. Our results suggest that photon spheres, when thermalized with their environment, have nonusual thermodynamic properties, which could lead to distinct observational signatures.
Análise de metodologia baseada no sistema de ensino individualizado de Keller aplicada em um curso introdutório de eletromagnetismo
Alves, Danilo T.;Souza, Sandro A.V. de;Pereira Filho, Sílvio C.F.;Elias, Walace de Sousa;
Revista Brasileira de Ensino de Física , 2011, DOI: 10.1590/S1806-11172011000100014
Abstract: one of individualized teaching methods used and documented in the 70's was fred keller's personalized system of instruction (psi). several papers about this methodology were published, providing an extensive empirical evidence of psi's positive results. nonetheless its employment has declined staring in the 80's. among the reasons for this decline, we may emphasize the greater effort required to the development of such courses using this methodology as compared to other methodologies and the provisioning of a systematic feedback on students' performance, as well as the criticisms on keller's behaviorist approach. despite being critical to learning, the stimulus to student's active posture, respect for individual learning rhythm, the formative assessments and the provisioning of systematic feedback to students still take place outside the classroom. one strategy to counter such deficiencies is individualized instruction. in this paper, we propose several modifications to keller's spi seeking a feasible methodology to be applied in an introductory course of electromagnetism for students of physics of universidade federal do pará. among these modifications, we highlight: (i) the use of weekly assessments, but not in every lecture; (ii) the correction of assessments and feedback providing made by teachers and not teaching assistants; and (iii) the partial maintenance of the expositive classes. despite the modifications inserted, based on an evaluation which included measurable benchmarks, we have indications that the application of this methodology yielded several of those positive results common to the implementation of keller's spi.
Walace Ferreira
Revista Debates , 2009,
Abstract: This article focuses and analysis the possibilities to the South established by the foreign policy of the Lula government, such as the formation of G-20, the arrangement of the IBSA, the meaning of the BRICS, the defense of regionalism and the approximation to African Continent. Now, the objective is to identify these coalitions, at first as a foreign policy strategy of the current government and, secondly, as a result of the current configuration of international relations post-bipolar era. With information about foreign policy's actions I try to show how, in a multilateralism manner what force, new alternatives in proposal by developing countries, to expand their skills in major international forums. In this context, the role played by Brazil has been of fundamental importance.
Rock art in the State of Roraima: theoretical subsidies to an ethically critical art-education
Walace Rodrigues
Cultura Visual , 2011,
Abstract: Este artigo tenta dar subsídios teóricos para uma melhor compreens o de que a arte rupestre brasileira deve ser utilizada no campo da arte-educa o por seu caráter n o somente de produ o cultural nacional, mas também por seu valor ético em rela o às popula es indígenas e seus fazeres estéticos. Aqui busco uma análise pela via da antropologia estética para concluir sobre a importancia critica e pedagógica desta forma de arte ancestral nacional. ///// This article aims to offer theoretical subsidies to a better understanding that Brazilian rock art must be studied in the art-education field not just as a national cultural production, but also because of its ethical value in relation to the indigenous peoples and their aesthetics production. Hereby I look for an analysis via the aesthetic anthropology to conclude about the critical and pedagogic importance of this ancestral form of national art.
Hydrodynamic Assessment of Increasing the Energy Efficiency of Trawler Propulsion with a Draft Tube  [PDF]
Jonas Eliasson, Elias B. Eliasson, Halldor S. Eliasson
Open Journal of Fluid Dynamics (OJFD) , 2015, DOI: 10.4236/ojfd.2015.52016
Abstract: The economy of the fishing industry is suffering from high fuel prices. Considerable efforts are invested in methods to increase the energy efficiency of fishing vessels and reducing the oil consumption per kilo of catch that may be as high as 0.6 to 0.7 liter oil per kilo catch. It is primarily the fact that sailing and fishing are on two very different speeds that cause these high fuel consumptions. This is called the two-speed problem and it is the trawlers that are hit hardest by it. The essence of the two-speed problem is that a hydraulic efficiency of only 28% can be expected in trawling speed, when it would be 67% if the ship is sailing at optimum speed all the time. Hydrodynamical analysis shows that an average hydraulic efficiency of only 41% can be expected for a trawler. There is no simple remedy for this, but it is possible to use a technology developed in the hydropower industry, i.e. a draft tube, or a diffuser, to recover energy that would otherwise be lost when trawling. A draft of tube the same length as the propellers diameter could mean fuel savings of 10%, a draft tube twice as long 20%. The difficulty is to find a way to get the draft tube out of the water during sailing with a vessel-specific mechanical design that is not a part of the fluid dynamics of the problem and not discussed in the paper.
Cardiovascular responses to passive static flexibility exercises are influenced by the stretched muscle mass and the Valsalva maneuver
Farinatti, Paulo T. V;Soares, Pedro P. S;Monteiro, Walace D;Duarte, Antonio F. A;Castro, Luis A. Viveiros de;
Clinics , 2011, DOI: 10.1590/S1807-59322011000300017
Abstract: background: the respiratory pattern is often modified or even blocked during flexibility exercises, but little is known about the cardiovascular response to concomitant stretching and the valsalva maneuver (vm) in healthy subjects. objectives: this study evaluated the heart rate (hr), systolic blood pressure (sbp), and rate-pressure product (rpp) during and after large and small muscle group flexibility exercises performed simultaneously with the vm. methods: asymptomatic volunteers (n = 22) with the following characteristics were recruited: age, 22 ± 3 years; weight, 73 ± 6 kg; height, 175 ± 5 cm; hr at rest, 66 ± 9 bpm; and sbp at rest, 113 ± 10 mmhg. they performed two exercises: four sets of passive static stretching for 30 s of the dorsi-flexion (df) of the gastrocnemius and the hip flexion (hf) of the ischio-tibialis. the exercises were performed with (v+) or without (v-) the vm in a counterbalanced order. the sbp and hr were measured, and the rpp was calculated before the exercise session, at the end of each set, and during a 30-min post-exercise recovery period. results: the within-group comparisons showed that only the sbp and rpp increased throughout the sets (p<0.05), but no post-exercise hypotension was detected. the between-group comparisons showed that greater sbp increases were related to the vm and to a larger stretched muscle mass. differences for a given set were identified for the hr (the hfv+ and hfv- values were higher than the dfv+ and dfv- values by approximately 12 bpm), sbp (the hfv+ value was higher than the dfv+ and dfv- values by approximately 12 to 15 mmhg), and rpp (the hfv+ value was higher than the hfv- value by approximately 2000 mmhgxbpm, and the hfv+ value was higher than the dfv+ and dfv- values by approximately 4000 mmhgxbpm). conclusion: both the stretched muscle mass and the vm influence acute cardiovascular responses to multiple-set passive stretching exercise sessions.
Upper Cervical Spine Infection. Complication of Hypopharyngeal Injury  [PDF]
Ghassan Skaf, Elias Elias
International Journal of Otolaryngology and Head & Neck Surgery (IJOHNS) , 2016, DOI: 10.4236/ijohns.2016.52016
Abstract: Background: We describe a rare case of Candida albicans retropharyngeal infection with upper cervical spondylodiscitis associated with epidural abscess triggered by ingestion of a chicken bone. Case Description: A 63-year-old woman presented with posterior neck and bilateral shoulders pain three weeks after choking on a 2-centimeter chicken bone. Magnetic resonance imaging (MRI) revealed spondylodiscitis and epidural abscess with significant spinal cord compression at C2 and C3 levels. A Barium swallow showed a focal disruption of the posterior wall of the esophagus. A posterior upper cervical fixation (C2-C5) was initially performed. One week later an anterior decompressive procedure was carried out followed by iliac crest bony fusion, and repair of the esophageal defect. Intra-operative cultures showed heavy growth of Candida albicans. After a transitory post-operative neurologic worsening, and after six weeks of appropriate antifungal therapy, the patient achieved a full clinical and radiologic recovery. Conclusion: Prompt surgical debridement, fusion and stabilization combined with adequate antimicrobial agents are necessary to guarantee a good outcome and reverse the neurological deficits.
Galactic Dark Matter: a Dynamical Consequence of Cosmological Expansion
Elias A. S. Mégier
Physics , 2014,
Abstract: This work wants to show how standard General Relativity (GR) is able to explain galactic rotation curves without the need for dark matter, this starting from the idea that when Einstein's equations are applied to the dynamics of a galaxy embedded in an expanding universe they do not reduce to Poisson's equation but a generalisation of it taking cosmological expansion into account. A non-linear scheme to perturb Einstein's field equations around the Robertson-Walker (R-W) metric is devised in order to find their non-relativistic limit without losing their characteristic non-linearities. The resulting equation is used to numerically study the gravitational potential of a cosmological perturbation and applied to a simple galactic model with an exponentially decreasing baryonic matter distribution. The non-relativistic limit of GR in a R-W space-time produces a generalised Poisson equation for the gravitational potential which is non-linear, parabolic and heat-like. It is shown how its non-linearities generate an effective "dark matter" distribution caused by both cosmological expansion and the dynamics of the perturbation's gravitational potential. It is also shown how this dynamical effect gets completely lost during a linearisation of Einstein's equations. The equation is then used to successfully fit real galactic rotation curves numerically using a matter distribution following the shape of a simple S\'ersic luminosity profile, common to most galaxies, thus without recourse to dark matter. A relation for the dark to luminous matter ratio is found, explaining the domination of dark matter in low-mass galaxies. A few rotation curves with a faster than Newtonian decrease are also presented and successfully fitted, opening the way to a new possible interpretation of these phenomena in terms of an effective "anti-gravitational" dark matter distribution, purely geometrical in origin.
Scalable Bayesian reduced-order models for high-dimensional multiscale dynamical systems
P. S. Koutsourelakis,Elias Bilionis
Statistics , 2010,
Abstract: While existing mathematical descriptions can accurately account for phenomena at microscopic scales (e.g. molecular dynamics), these are often high-dimensional, stochastic and their applicability over macroscopic time scales of physical interest is computationally infeasible or impractical. In complex systems, with limited physical insight on the coherent behavior of their constituents, the only available information is data obtained from simulations of the trajectories of huge numbers of degrees of freedom over microscopic time scales. This paper discusses a Bayesian approach to deriving probabilistic coarse-grained models that simultaneously address the problems of identifying appropriate reduced coordinates and the effective dynamics in this lower-dimensional representation. At the core of the models proposed lie simple, low-dimensional dynamical systems which serve as the building blocks of the global model. These approximate the latent, generating sources and parameterize the reduced-order dynamics. We discuss parallelizable, online inference and learning algorithms that employ Sequential Monte Carlo samplers and scale linearly with the dimensionality of the observed dynamics. We propose a Bayesian adaptive time-integration scheme that utilizes probabilistic predictive estimates and enables rigorous concurrent s imulation over macroscopic time scales. The data-driven perspective advocated assimilates computational and experimental data and thus can materialize data-model fusion. It can deal with applications that lack a mathematical description and where only observational data is available. Furthermore, it makes non-intrusive use of existing computational models.
A Conceptual Framework for Threat Assessment Based on Organization’s Information Security Policy  [PDF]
Joseph Elias Mbowe, Irina Zlotnikova, Simon S. Msanjila, George S. Oreku
Journal of Information Security (JIS) , 2014, DOI: 10.4236/jis.2014.54016
Abstract: The security breaches of sensitive information have remained difficult to solve due to increased malware programs and unauthorized access to data stored in critical assets. As risk appetite differ from one organization to another, it prompts the threat analysis tools be integrated with organization’s information security policy so as to ensure security controls at local settings. However, it has been noted that the current tools for threat assessment processes have not encompassed information security policy for effective security management (i.e. confidentiality, integrity and availability) based on organization’s risk appetite and culture. The information security policy serves as a tool to provide guidance on how to manage and secure all business operations including critical assets, infrastructure and people in the organization. This guidance (e.g. usage and controls) facilitates the provisions for threat assessment and compliance based on local context. The lack of effective threat assessment frameworks at local context have promoted the exposure of critical assets such as database servers, mails servers, web servers and user smart-devices at the hand of attackers and thus increase risks and probability to compromise the assets. In this paper we have proposed a conceptual framework for security threat assessment based on organization’s information security policy. Furthermore, the study proposed the policy automation canvas for provision of a methodology to alert the security managers what possible threats found in their organizations for quick security mitigation without depending on security expertise.
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