467 research outputs found
Probing the interference between non-linear, axionic and space-time-anisotropy effects in the QED vacuum
We pursue the investigation of a generic non-linear extension of axionic
electrodynamics (ED) in a Carroll-Field-Jackiw (CFJ) scenario that implements
Lorentz-symmetry violation (LSV). The model consists of an arbitrary non-linear
ED action coupled to the axion field in presence of an anisotropy four-vector
that realizes the breaking of Lorentz symmetry under the particle point of
view. The non-linear electromagnetic field is expanded around a constant and
uniform magnetic background up to second order in the propagating photon field.
Our attention is the study of the material properties of the vacuum in the
particular case of a space-like CFJ -vector. The dispersion relations
associated to the plane wave solutions are explicitly worked out in two
situations: the magnetic background perpendicular and parallel to the wave
direction. We extend these results to consider the analysis of the
birefringence phenomenon in presence of non-linearity, the axion and the LSV
manifested through the spatial anisotropy. Three specific proposals of
non-linear ED are contemplated: Euler-Heisenberg, Born-Infeld and the Modified
Maxwell ED. Throughout the paper, we shall justify why we follow the unusual
path of connecting, in a single Lagrangian density, three pieces of physics
beyond the Standard Model, namely, non-linearity, axions and LSV. We anticipate
that we shall not be claiming that the simultaneous introduction of these three
topics beyond the Standard Model will bring new insights or clues for the
efforts to detect axions or to constrain parameters associate to both
non-linear ED and LSV physics . Our true goal is to actually inspect and
describe how axionic, non-linear and LSV effects interfere with one another
whenever physical entities like refraction indices and birefringence are
computed in presence of an external constant and homogeneous magnetic
background.Comment: 27 pages, no figure
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 non-linear 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 Born-Infeld Electrodynamics and we show that
it becomes birefringent whenever the axion is coupled. The paper is
supplemented by an Appendix, where we approach the recent discussion on the
controversy in defining the Poynting vector of axionic electrodynamics. We
present our path to tackle the question and give the expressions we work out
for both the Poynting vector and the momentum density transported by the waves.Comment: 30 pages, no figure
Crystallographic and magnetic properties of UFe5.8Al6.2 single crystals
Single crystals of UFe5.8Al6.2 were characterised by X-ray and neutron diffraction, 57Fe Mössbauer spectroscopy and magnetisation. The structure refinement by X-ray and neutron diffraction shows a ThMn12-type structure, the Fe atoms fully occupying the 8f and partially occupying the 8j positions. Mössbauer spectra confirm these occupations and further indicate a magnetic ordering below 293 K. Magnetisation measurements show a ferromagnetic behaviour below 300 K, with a and b as easy directions and a spontaneous magnetisation of 10.4 [mu]B/f.u. at 5 K, due to the Fe occupation of 8j position. These single crystal results significantly differ from those previously obtained in UFe6Al6 polycrystalline samples obtained by melting and annealing.http://www.sciencedirect.com/science/article/B6TJJ-3V7WTYX-N/1/f7893080a7f27a628198f02aeb40fe2
Triple-q octupolar ordering in NpO_2
We report the results of resonant X-ray scattering experiments performed at
the Np M_4,5 edges in NpO_2. Below T_0 = 25 K, the development of long-range
order of Np electric quadrupoles is revealed by the growth of superlattice
Bragg peaks. The electronic transition is not accompanied by any measurable
crystallographic distortion, either internal or external, so the symmetry of
the system remains cubic. The polarization and azimuthal dependence of the
intensity of the resonant peaks is well reproduced assuming Templeton
scattering from a triple-q longitudinal antiferroquadrupolar structure.
Electric quadrupole order in NpO_2 could be driven by the ordering at T_0 of
magnetic octupoles of Gamma_5 symmetry, splitting the Np ground state quartet
and leading to a singlet ground state with zero dipole magnetic moment.Comment: 4 Pages, 3 Figures, submitted to Phys. Rev. Lett. v2: resubmitted
after referee report
Rubella in Sub-Saharan Africa and sensorineural hearing loss: a case control study
Rubella infection can affect several organs and cause birth defects that are responsible for congenital rubella syndrome (CRS). Congenital hearing loss is the most common symptom of this syndrome, occurring in approximately 60% of CRS cases. Worldwide, over 100 000 babies are born with CRS every year. There is no specific treatment for rubella, but the disease is preventable by vaccination. Since 1969, the rubella vaccine has been implemented in many countries, but in Africa, only a few countries routinely immunize against rubella. The aim of this study was to estimate the rate of infection from the wild-type rubella virus in São Tomé and Príncipe by determining rubella seroprevalence with a DBS method. The goal of this study was to reinforce the need for implementation of the rubella vaccine in this country. As secondary objectives, the validation of a DBS method was first attempted and an association between seroprevalence and hearing loss was assessed.info:eu-repo/semantics/publishedVersio
Desilication of MOR zeolite: Conventional versus microwave assisted heating
MOR zeolites were modified via desilication treatments with NaOH, under conventional and microwave heating. The samples were characterized by powder X-ray diffraction, (27)Al and (29)Si NMR spectroscopy. TEM and N(2) adsorption at -196 degrees C. The acidity of the samples and the space available inside the pores were evaluated through a catalytic model reaction, the isomerization of m-xylene, for which the profiles of the coke thermal decomposition were also analyzed. Powder X-ray diffraction and (29)Si and (27)Al MNR results show that in comparison with conventional heating, microwave irradiation (a less time consuming process) leads to identical amount of Si extraction from the zeolite framework. With this treatment. in addition to the customary mesopores development promoted by conventional heating, a partial conversion of the zeolite microporosity into larger micropores, is observed. The microwave irradiated and conventionally heated samples show different catalytic behavior in the m-xylene isomerization model reaction. It was observed that, by controlling the experimental conditions, it is possible to obtain samples with catalytic properties closer to the parent material, which is also confirmed by the respective coke analysis. (C) 2011 Elsevier B.V. All rights reserved
Determinação da produtividade para diferentes épocas de semeadura do milho irrigado em Minas Gerais utilizando modelagem computacional.
CONBEA 2014
Pulmonary rehabilitation in primary health care: an effective intervention even with minimal resources
No abstract available.publishe
- …