17,888 research outputs found
Brane Cosmic String Compactification in Brans-Dicke Theory
We investigate an alternative compactification of extra dimensions using
local cosmic string in the Brans-Dicke gravity framework. In the context of
dynamical systems it is possible to show that there exist a stable field
configuration for the Einstein-Brans-Dicke equations. We explore the analogies
between this particular model and the Randall-Sundrum scenario.Comment: RevTex, 5 pages, no figures. To appear in the Physical Review
Towards an hybrid compactification with a scalar-tensor global cosmic string
We derive a solution of the gravitational equations which leads to a
braneworld scenario in six dimensions using a global cosmic string solution in
a low energy effective string theory framework. The final spacetime is composed
by one warped brane with topology and a power
law warp factor, and one noncompact extra dimension transverse to the brane. By
looking at the current experimental bounds, we find a range of parameters in
which, if the on-brane dimension has an acceptable size, it does not solve the
hierarchy problem. In another example this problem is smoothed by the
Brans-Dicke parameter.Comment: RevTex, 7 pages. New version to be published in the JCAP (2008
On the long-term correlation between the flux in the Ca II H & K and Halpha lines for FGK stars
The re-emission in the cores of the Ca II H & K and H lines, are well
known proxies of stellar activity. However, these activity indices probe
different activity phenomena, the first being more sensitive to plage
variation, while the other one being more sensitive to filaments. In this paper
we study the long-term correlation between and , two indices based on the Ca II H & K and H lines
respectively, for a sample of 271 FGK stars using measurements obtained over a
9 year time span. Because stellar activity is one of the main obstacles
to the detection of low-mass and long-period planets, understanding further
this activity index correlation can give us some hints about the optimal target
to focus on, and ways to correct for these activity effects. We found a great
variety of long-term correlations between and . Around 20% of our sample has strong positive correlation between
the indices while about 3% show strong negative correlation. These fractions
are compatible with those found for the case of early-M dwarfs. Stars
exhibiting a positive correlation have a tendency to be more active when
compared to the median of the sample, while stars showing a negative
correlation are more present among higher metallicity stars. There is also a
tendency for the positively correlated stars to be more present among the
coolest stars, a result which is probably due to the activity level effect on
the correlation. Activity level and metallicity seem therefore to be playing a
role on the correlation between and . Possible
explanations based on the influence of filaments for the diversity in the
correlations between these indices are discussed in this paper.Comment: 18 pages, 13 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
A nearly cylindrically symmetric source in the Brans-Dicke gravity as the generator of the rotational curves of the galaxies
Observation shows that the velocities of stars grow by approximately 2 to 3
orders of magnitude when the distances from the centers of the galaxies are in
the range of kpc to kpc, before they begin to tend to a constant
value. Up to know, the reason for this behavior is still a matter for debate.
In this work, we propose a model which adequately describes this unusual
behavior using a (nearly) cylindrical symmetrical solution in the framework of
a scalar-tensor-like (the Brans-Dicke model) theory of gravity.Comment: 24 pages, 4 figures, accepted for publication in Eur. Phys. J.
Levantamento da ocorrência de camu-camu (Myrciaria dubia) na Amazônia e coleta de germoplasma no Alto Solimões (Amazonas-Brasil).
Characterization of requeijão and technological optimization of its manufacturing process
In attempts to characterize Portuguese whey cheese (Requeijão) and optimize the manufacture thereof I7 whey cheeses were produced according to a factorial design using heating time, heating temperature and fractional addition of ovinelcaprine milk as manipulated technological variables. Chemical
analyses were carried out for the 17 cheeses, whereas sensorial and rheological
analyses were carried out for eight selected whey cheeses and a reference (i.e. a
whey cheese produced locally according to traditional procedures). A true local
maximum exists for moisture content (at a temperature of about 93°C heating time of about 30 min and addition of about 17% ovine milk) which lies well within the range chosen for experimentation. Fat content of Requeijão was positively affected by heating temperature (especially via its quadratic effect) and, to a lesser extent, by heating time (especially via its linear effect); nitrogen content was especially affected by heating temperature (via its quadratic effect); and moisture content was affected especially by heating temperature (via its
quadratic effect). The sensorial analyses showed that the eight whey cheeses
produced were prefered with respect to the reference whey cheese. For rheological analyses the most significant observations pertain to the high strain dependence of the dynamic moduli, absence of a true equilibrium storage modulus, and relatively low difference between the loss and the storage modulus
Propagação vegetativa de camu-camu (myrciaria dúbia (H.B.K.) McVaugh) por meio de estaquia: efeito da consistência, tamanho e fitorregulador.
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