Scattering of scalar perturbations with cosmological constant in low-energy and high-energy regimes

We study the absorption and scattering of massless scalar waves propagating in spherically symmetric spacetimes with dynamical cosmological constant both in low-energy and high-energy zones. In the former low-energy regime, we solve analytically the Regge-Wheeler wave equation and obtain an analytic absorption probability expression which varies with $M\sqrt{\Lambda}$, where $M$ is the central mass and $\Lambda$ is cosmological constant. The low-energy absorption probability, which is in the range of $[0, 0.986701]$, increases monotonically with increase in $\Lambda$. In the latter high-energy regime, the scalar particles adopt their geometric optics limit value. The trajectory equation with effective potential emerges and the analytic high-energy greybody factor, which is relevant with the area of classically accessible regime, also increases monotonically with increase in $\Lambda$, as long $\Lambda$ is less than or of the order of $10^4$. In this high-energy case, the null cosmological constant result reduces to the Schwarzschild value $27\pi r_g^2/4$.Comment: 12 pages, 6 figure

5D5D Solutions to Λ\LambdaCDM Universe Derived from Global Brane Model

An exact solution of brane universe is studied and the result indicates that Friedmann equations on the brane are modified with an extra term. This term can play the role of dark energy and make the universe accelerate. In order to derive the $\Lambda$CDM Universe from this global brane model, the new solutions are obtained to describe the $5D$ manifold.Comment: 7 pages, no figure, accepted by MPL

Medida de condutividade elétrica do solo adaptada a uma plantadeira.

bitstream/CNPDIA-2009-09/11888/1/CiT46_2008.pd

Modeling of Ni Diffusion Induced Austenite Formation in Ferritic Stainless Steel Interconnects

Ferritic stainless steel interconnect plates are widely used in planar solid oxide fuel cell (SOFC) or electrolysis cell (SOEC) stacks. During stack production and operation, nickel from the Ni/YSZ fuel electrode or from the Ni contact component diffuses into the IC plate, causing transformation of the ferritic phase into an austenitic phase in the interface region. This is accompanied with changes in volume and in mechanical and corrosion properties of the IC plates. In this work, kinetic modeling of the inter-diffusion between Ni and FeCr based ferritic stainless steel was conducted, using the CALPHAD approach with the DICTRA software. The kinetics of inter-diffusion and austenite formation was explored in full detail, as functions of layer thickness, temperature, time, and steel composition. The simulation was further validated by comparing with experimental results. Growth of the austenite phase in commercial interconnect materials is predicted to take place under practical stack operation conditions.</jats:p