8 research outputs found
Obtention of Hard Coating Using Electrochemical Process in Aluminum-Silicon Alloys for Automotive Vehicles
Automotive industry is searching for new ways to improve vehicles’ energy efficiency through mass reduction, using aluminum alloys. This change requires a surface protection to extend the life cycle of the components and aluminum anodization is the most used solution. This research is focused on the intake and exhaust ducts’ surfaces of aluminum internal combustion engines cylinder head, which are subject to chemical agents and temperature variation. To extend the working life of this component it is necessary to obtain a covering protective layer. The process targeted the anodization of an internal surface of a much larger part of a cast aluminum-silicon alloy cylinder head. The anodization was obtained using a H2SO4 solution (184 g.L-1) and a DC voltage starting at 20 V. The Al2O3 layer obtained, inside the cylinder head´s ducts, has an average thickness of 120 µm in accordance with the proposal of providing a suitable surface protection
A Description of the Transport Critical Current Behavior of Polycrystalline Superconductors Under the Applied Magnetic Field
A Comment on the Topological Phase for Anti-Particles in a Lorentz-violating environment
Recently, a scheme to analyse topological phases in Quantum Mechanics by
means of the non-relativistic limit of fermions non-minimally coupled to a
Lorentz-breaking background has been proposed. In this letter, we show that the
fixed background, responsible for the Lorentz-symmetry violation, may induce
opposite Aharonov-Casher phases for a particle and its corresponding
antiparticle. We then argue that such a difference may be used to investigate
the asymmetry for particle/anti-particle as well as to propose bounds on the
associated Lorentz-symmetry violating parameters.Comment: 4 pages - A published versio
Pressure Studies on a High- Superconductor Pseudogap and Critical Temperatures
We report simultaneous hydrostatic pressure studies on the critical
temperature and on the pseudogap temperature performed through
resistivity measurements on an optimally doped high- oxide
. The resistivity is measured as
function of the temperature for several different applied pressure below 1GPa.
We find that both and increases linearly with the pressure. This
result demonstrate that the well known intrinsic pressure effect on is
also present at and both temperatures are originated by the same
superconducting mechanism.Comment: 4 pages and 2 figures in eps, final versio
N=1 Supersymetric Quantum Mechanics in a Scenario with Lorentz-Symmetry Violation
We show in this paper that the dynamics of a non-relativistic particle with
spin, coupled to an external electromagnetic field and to a background that
breaks Lorentz symmetry, is naturally endowed with an N=1-supersymmetry. This
result is achieved in a superspace approach where the particle coordinates and
the spin degrees of freedom are components of the same supermultiplet.Comment: 6 pages, no figure
A Theory for High- Superconductors Considering Inhomogeneous Charge Distribution
We propose a general theory for the critical and pseudogap
temperature dependence on the doping concentration for high- oxides,
taking into account the charge inhomogeneities in the planes. The well
measured experimental inhomogeneous charge density in a given compound is
assumed to produce a spatial distribution of local . These differences
in the local charge concentration is assumed to yield insulator and metallic
regions, possibly in a stripe morphology. In the metallic region, the
inhomogeneous charge density yields also spatial distributions of
superconducting critical temperatures and zero temperature gap
. For a given sample, the measured onset of vanishing gap
temperature is identified as the pseudogap temperature, that is, , which
is the maximum of all . Below , due to the distribution of
's, there are some superconducting regions surrounded by insulator or
metallic medium. The transition to a superconducting state corresponds to the
percolation threshold among the superconducting regions with different
's. To model the charge inhomogeneities we use a double branched
Poisson-Gaussian distribution. To make definite calculations and compare with
the experimental results, we derive phase diagrams for the BSCO, LSCO and YBCO
families, with a mean field theory for superconductivity using an extended
Hubbard Hamiltonian. We show also that this novel approach provides new
insights on several experimental features of high- oxides.Comment: 7 pages, 5 eps figures, corrected typo