38,243 research outputs found
Phase space solutions in scalar-tensor cosmological models
An analysis of the solutions for the field equations of generalized
scalar-tensor theories of gravitation is performed through the study of the
geometry of the phase space and the stability of the solutions, with special
interest in the Brans-Dicke model. Particularly, we believe to be possible to
find suitable forms of the Brans-Dicke parameter omega and potential V of the
scalar field, using the dynamical systems approach, in such a way that they can
be fitted in the present observed scenario of the Universe.Comment: revtex, 2 pages, 4 eps figures, to appear in Brazilian Journal of
Physics (proceedings of the Conference 100 Years of Relativity, Sao Paulo,
Brazil, August 2005
Parametric Competition in non-autonomous Hamiltonian Systems
In this work we use the formalism of chord functions (\emph{i.e.}
characteristic functions) to analytically solve quadratic non-autonomous
Hamiltonians coupled to a reservoir composed by an infinity set of oscillators,
with Gaussian initial state. We analytically obtain a solution for the
characteristic function under dissipation, and therefore for the determinant of
the covariance matrix and the von Neumann entropy, where the latter is the
physical quantity of interest. We study in details two examples that are known
to show dynamical squeezing and instability effects: the inverted harmonic
oscillator and an oscillator with time dependent frequency. We show that it
will appear in both cases a clear competition between instability and
dissipation. If the dissipation is small when compared to the instability, the
squeezing generation is dominant and one can see an increasing in the von
Neumann entropy. When the dissipation is large enough, the dynamical squeezing
generation in one of the quadratures is retained, thence the growth in the von
Neumann entropy is contained
Crystallization, data collection and data processing of maltose-binding protein (MalE) from the phytopathogen Xanthomonas axonopodis pv. citri
Maltose-binding protein is the periplasmic component of the ABC transporter
responsible for the uptake of maltose/maltodextrins. The Xanthomonas axonopodis
pv. citri maltose-binding protein MalE has been crystallized at 293 Kusing
the hanging-drop vapour-diffusion method. The crystal belonged to the
primitive hexagonal space group P6_122, with unit-cell parameters a = 123.59,
b = 123.59, c = 304.20 Ã…, and contained two molecules in the asymetric unit. It
diffracted to 2.24 Ã… resolution
- …