On the Zitterbewegung Transient Regime in a Coarse-Grained Space-Time

In the present contribution, by studying a fractional version of Dirac's equation for the electron, we show that the phenomenon of Zitterbewegung in a coarse-grained medium exhibits a transient oscillatory behavior, rather than a purely oscillatory regime, as it occurs in the integer case, $\alpha=1$. Our result suggests that, in such systems, the Zitterbewegung-type term related to a trembling motion of a quasiparticle is tamed by its complex interactions with other particles and the medium. This can justify the difficulties in the observation of this interesting phenomenon. The possibility that the Zitterbewegung be accompanied by a damping factor supports the viewpoint of particle substructures in Quantum Mechanics.Comment: 11 pages, 1 figure. This paper has been published in J. Adv. Phys. 7 (2015) 144

Modified plasma waves described by a logarithmic electrodynamics

The propagation of plasma waves in a new non-linear, logarithmic electrodynamics model is performed. A cold, uniform, collisionless fluid plasma model is applied. Electrostatic waves in magnetized plasma are shown to correspond to modified Trivelpiece-Gould modes, together with changes of the plasma and upper-hybrid frequencies, driven by the logarithmic electrodynamics effects. Electromagnetic waves are described by a generalized Appleton-Hartree dispersion relation. The cases of propagation parallel or perpendicular to the equilibrium magnetic field are analyzed in detail. In particular, generalized ordinary and extraordinary modes are obtained. We determine the changes, due to logarithmic electrodynamics, in the allowable and forbidden frequency bands of the new extraordinary mode. Estimates are provided about the strength of the ambient magnetic field, so that the non-linear electrodynamics effects become decisive

Do éter questionado por Dirac ao Modelo-Padrão: a diacronia da violação da simetria de Lorentz

Este texto tem como eixo central uma abordagem diacrônica de uma atividade bastante central na multiplicidade de caminhos que se vislumbram quando são investigados possíveis cenários físicos além do Modelo-Padrão das Interações Fundamentais e da Física de Partículas. Pequeníssimos efeitos que podem sinalizar algum desvio da simetria de Lorentz, invariância fundamental na formulação das teorias quânticas relativísticas, ocupam significativo espaço na literatura da Física de Partículas e Campos. Visando um público-alvo de estudantes de Graduação, o presente trabalho propõe-se a apresentar o percurso histórico de desenvolvimento do tópico, permitindo aos principiantes e não-praticantes do tema a percepção de como a investigação de efeitos advindos da violação da simetria de Lorentz se contextualizou em diferentes momentos e atingiu o seu presente status de intensas atividades teóricas e experimentais. Mais recentemente a área tem caminhado na direção de se investigar efeitos da violação da simetria de Lorentz em sistemas de Física da Matéria Condensada, mais especificadamente na direção dos semi-metais de Dirac e Weyl; também, no campo dos efeitos óticos na Astrofísica a atividade de violação da simetria de Lorentz vem recebendo crescente atenção

The axion-photon mixing in non-linear electrodynamic scenarios

In this contribution, we re-assess some aspects of axionic electrodynamics by coupling non-linear electromagnetic effects to axion physics. We present a number of motivations to justify the coupling of the axion to the photon in terms of a general nonlinear extension of the electromagnetic sector. Our emphasis in the paper relies on the investigation of the constitutive permittivity and permeability tensors, for which the axion contributes by introducing dependence on the frequency and wave vector of the propagating radiation. Also, we point out how the axion mass and the axion-photon-photon coupling constant contribute to a dispersive behavior of the electromagnetic waves, in contrast to what happens in the case of non-linear extensions, when effective refractive indices appear which depend only on the direction of the propagation with respect to the external fields. The axion changes this picture by yielding refractive indices with dependence on the wavelength. We apply our results to the special case of the (non-birefringent) Born-Infeld Electrodynamics and we show that it becomes birefringent whenever the axion is coupled. The paper is supplemented by an appendix, where we follow our own path to approach the recent discussion on a controversy in the definition of the Poynting vector of axionic electrodynamics

A Constru¸c˜ao de um paradigma da f´Ä±sica te´orica: A teoria de Yang-Mills-Shaw

In June 28, 1954, C. N. Yang and R. Mills have published a truly fundamental paper on the Physics of Fundamental Interactions in Physical Review. At the same time, Ronald Shaw, a Salam’s PhD student, develops the same subject in his thesis. In both works, this is the first formulation of a field theory for vector boson mediators with self-interactions, different from the scenario set up by Quantum Electrodynamics (QED). This year, Yang-Mills-Shaw theory is sixty-year old andit sets out as a remarkable contribution to contemporary physics, consolidating the gauge-theory paradigm in many branches of Physics, such as the Electroweak Theory, the Standard Model of Particles Physics, including gravity and other physical landscapes beyond the Standard Model. Our aim in this paper is mainly to present a popularization text, discussing the key contributions of the Yang-Mills set-up, the independent efforts by R. Shaw and the previous works and ideas thatinfluenced the constitution of the gauge-thinking era.Em 28 de junho de 1954, C. N. Yang e R. Mills apresentam um artigo ao peri´odico Physical Review,  uma contribui¸c˜ao estruturante para a F´Ä±sica das Intera¸c˜oes Fundamentais. Paralelamente, R. Shaw, estudante de doutorado de A. Salam, desenvolve o mesmo assunto em sua tese. Trata-se da primeira formula¸c˜ao de uma teoria de campos para mediadores vetoriais em auto-intera¸c˜ao, diferente do que se tinha at´e ent˜ao com a Eletrodinˆamica Quˆantica (QED). No presente ano, comemora-se os 60 anos desse feito importante para a f´Ä±sica contemporˆanea e que consolida uma forma de fazer f´Ä±sica que se estende a v´arias outras teorias modernas, como a Teoria Eletrofraca, o Modelo Padr˜ao da F´Ä±sica de Part´Ä±culas, inclusive abrangendo teorias que envolvem a gravita¸c˜ao e que descrevem f´Ä±sica al´em do Modelo Padr˜ao. Nossa inten¸c˜ao nesse trabalho ´e produzir um texto de divulga¸c˜ao, particularmente voltado para os cursos de Forma¸c˜ao de Professores e, ao mesmo tempo, contribuir para a discuss˜ao dos caminhos de uma f´Ä±sica escolar mais pr´oxima de quest˜oes contemporˆaneas. Nesse texto, pretendemos fazer uma incurs˜ao aos antecedentes do trabalho de Yang-Mills-Shaw (YMS) e que influenciaram os autores: apresentar uma pequena discuss˜ao sobre a QED e a constitui¸c˜ao de seu paradigma, no que for relevante `a discuss˜ao espec´Ä±fica do trabalho de Yang-Mills-Shaw; Introduzir o problema da intera¸c˜ao nuclear forte, que era inicialmente o problema de YMS; e a retomada por Salam da proposta da teoria de YMS para as intera¸c˜oes fracas. Tudo isso, sempre focando nos princ´Ä±pios f´Ä±sicos e matem´aticos importantes contidos em seu bojo, e que possa ser utilizado em cursos de forma¸c˜ao de professores

Phosphorus requirement of Nelore steers

A determinação da absorção real de fósforo (P) em bovinos deve levar em consideração a fração endógena mínina do mineral, que se perde nas fezes. De modo geral esses cálculos são feitos utilizando-se tabelas cujos valores foram obtidos em outros países, com outras raças de animais e em condições bem diferentes das condições brasileiras. O trabalho teve como objetivo determinar a perda endógena de P nas fezes e estimar a exigência mínima de P em novilhos da raça Nelore (Bos indicus). Foram utilizados 18 novilhos castrados, com peso médio de 190,82±27,53 kg e idade aproximada de 12 meses, divididos em três grupos de seis animais, e mantidos em gaiolas metabólicas individuais. Os animais receberam dieta básica constituída de feno de Brachiaria decumbens e uma mistura de concentrados durante os 30 dias de período experimental. Os tratamentos consistiram de diferentes quantidades de fosfato bicálcico em níveis de 0,12, 0,24 e 0,36% de P, com base na dieta total. Foram aplicadas injeções de 32P nos animais para a determinação da perda endógena fecal de P. A perda endógena mínima fecal de P para uma ingestão zero do mineral, calculada por interpolação, foi de 5,72 mg/kg de peso vivo e para um balanço zero, o requerimento mínimo foi de 8,84 mg/kg de peso vivo por dia.The nutritional phosphorus (P) requirement of cattle has to consider the minimum endogenous fecal loss of this element. In general, ration formulation is based on foreign tables, without taking Brazilian conditions in consideration. The aim of this study was to determine the endogenous losses of P and to estimate the minimum P requirement of Nelore cattle. Eighteen castrated steers aged 12 months and weighing 190.82±27.53 kg were housed in metabolism cages. In a 30 day experimental period the animals were fed with hay and a concentrate mixture. Different levels of dicalcium phosphate were added to basal diet as to obtain 0.12, 0.24 and 0.36% of P, based on the total dry matter intake. 32P was intravenously injected and endogenous P losses were determined. The minimum endogenous fecal loss for zero P intake calculated by interpolation was 5.72 mg/kg (LW) per day, and for zero balance, the minimum P requirement was 8.84 mg/kg (LW) per day

Avaliação da aterosclerose subclínica e de níveis plasmáticos de LDL minimamente modificada em pacientes com espondilite anquilosante e sua correlação com a atividade da doença

AbstractIntroductionAccelerated atherosclerosis has been shown in some autoimmune diseases, mainly in Systemic Lupus Erythematosus and Rheumatoid Arthritis. Although high preva- lence of corticosteroids use may be a confounding factor due to their detrimental effects on several risk factors, systemic inflammation per se is supposed to play an important role in atherogenesis in these patients.MethodsWe have evaluated sub-clinical atherosclerosis and plasma levels of circulating electronegative LDL, which represents the fraction of LDL that is minimally modified, in patients with ankylosing spondylitis (AS). Fourteen patients who fulfilled the modified New York criteria for AS were compared with 13 paired controls. Carotid intimal-media thick- ness (IMT) was assessed by ultrasonography bilaterally in common carotid artery, internal carotid artery and in the bifurcation. Groups were homogeneous regarding cardiovascular risk factors. Only a single patient in AS group was in use of corticosteroid.ResultsThe presence of active inflammation was demonstrated by elevated BASDAI and higher CRP levels and in patients versus controls (12.36 vs. 3.45mg/dl, P = 0.002). No dif- ference was found in carotid IMT between both groups, in any site of artery. Averaged IMT (6 measurements, at 3 pre-specified sites bilaterally) was 0.72 ± 0.28 in AS group and 0.70 ± 0.45mm in controls (P = 0.91). Minimally modified LDL did not differ significantly either between patients and controls (14.03 ± 17.40 vs. 13.21 ± 10.21; P = 0.88).ConclusionsPatients with AS did not show increased carotid IMT in comparison to con- trols. In the same way, circulating plasma levels of LDL (-), did not differ significantly in both groups