José A. Lima

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It is argued that the full Einstien equation has more information than the space component of Einstien equation plus energy conservation equation. Applying the former approach to the D-dimensional decrumpling FRW cosmology leads to a diierent result which suuers from a singularity together with lacking the turning points.
The kinetic foundations of Tsallis' nonextensive thermostatistics are investigated through Boltzmann's transport equation approach. Our analysis follows from a nonextensive generalization of the "molecular chaos hypothesis." For q>0, the q-transport equation satisfies an H theorem based on Tsallis entropy. It is also proved that the collisional equilibrium(More)
The thermodynamic behavior of vacuum decaying cosmologies is investigated within a manifestly covariant formulation. Such a process corresponds to a continuous irreversible energy flow from the vacuum component to the created matter constituents. It is shown that if the specific entropy per particle remains constant during the process, the equilibrium(More)
We consider a nonsingular deflationary cosmological model with decaying vacuum energy density in universes of arbitrary spatial curvature. Irrespective of the value of k, the models are characterized by an arbitrary time scale H −1 I which determines the initial temperature of the universe and the largest value of the vacuum energy density, the slow decay(More)
The ages of two old galaxies (53W091, 53W069) at high redshifts are used to constrain the value of the cosmological constant in a flat universe (ΛCDM) and the density parameter Ω M in Friedmann-Robertson-Walker (FRW) models with no Λ-term. In the case of ΛCDM models, the quoted galaxies yield two lower limits for the vacuum energy density parameter, Ω Λ ≥(More)
This work reports a modified flame-brush technique to fabricate fiber tapers with arbitrary waist profiles. The flame-brush approach is used to produce small step reductions in the fiber diameter, or step-tapers, with a constant speed flame brush sweep, while the fiber is uniformly stretched. Arbitrary waist profiles in tapers are fabricated by(More)
Predictions about the kinematic expansion history of the universe are investigated by using the 307 supernovae type Ia from the Union Compilation set. Three simple model parameterizations for the deceleration parameter (constant, linear and abrupt transition) and two different models that are explicitly parametrized by a jerk parameter (constant and(More)