10,074 research outputs found
Ventilatory function in young adults and dietary antioxidant intake
Artículo de publicación ISIDietary antioxidants may protect against poor ventilatory function. We assessed the relation between ventilatory function and antioxidant components of diet in young Chileans. Forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), and the ratio FEV1/FVC were measured in 1232 adults aged 22-28 years, using a Vitalograph device. Dietary intake was ascertained with a food frequency questionnaire (FFQ) designed for this study, from which nutrient and flavonoid intakes were estimated. Dietary patterns were derived with Principal Component Analysis (PCA). After controlling for potential confounders, dietary intake of total catechins was positively associated with FVC (Regression coefficient (RC) of highest vs. lowest quintile of intake 0.07; 95% CI 0.01 to 0.15; p per trend 0.006). Total fruit intake was related to FVC (RC of highest vs. lowest quintile 0.08; 95% CI 0.003 to 0.15; p per trend 0.02). Intake of omega 3 fatty acids was associated with a higher FEV1 (RC for highest vs. lowest quintile 0.08; 95% CI 0.01 to 0.15 L; p per trend 0.02) and with FVC 0.08 (RC in highest vs. lowest quintile of intake 0.08, 95% CI 0.001 to 0.16; p per trend 0.04). Our results show that fresh fruits, flavonoids, and omega 3 fatty acids may contribute to maintain ventilatory function.Wellcome Trust 059448Z
Bubble generation in a twisted and bent DNA-like model
The DNA molecule is modeled by a parabola embedded chain with long-range
interactions between twisted base pair dipoles. A mechanism for bubble
generation is presented and investigated in two different configurations. Using
random normally distributed initial conditions to simulate thermal
fluctuations, a relationship between bubble generation, twist and curvature is
established. An analytical approach supports the numerical results.Comment: 7 pages, 8 figures. Accepted for Phys. Rev. E (in press
Null Strings in Schwarzschild Spacetime
The null string equations of motion and constraints in the Schwarzschild
spacetime are given. The solutions are those of the null geodesics of General
Relativity appended by a null string constraint in which the "constants of
motion" depend on the world-sheet spatial coordinate. Because of the extended
nature of a string, the physical interpretation of the solutions is completely
different from the point particle case. In particular, a null string is
generally not propagating in a plane through the origin, although each of its
individual points is. Some special solutions are obtained and their physical
interpretation is given. Especially, the solution for a null string with a
constant radial coordinate moving vertically from the south pole to the
north pole around the photon sphere, is presented. A general discussion of
classical null/tensile strings as compared to massless/massive particles is
given. For instance, tensile circular solutions with a constant radial
coordinate do not exist at all. The results are discussed in relation to
the previous literature on the subject.Comment: 16 pages, REVTEX, no figure
From the WZWN Model to the Liouville Equation: Exact String Dynamics in Conformally Invariant AdS Background
It has been known for some time that the SL(2,R) WZWN model reduces to
Liouville theory. Here we give a direct and physical derivation of this result
based on the classical string equations of motion and the proper string size.
This allows us to extract precisely the physical effects of the metric and
antisymmetric tensor, respectively, on the {\it exact} string dynamics in the
SL(2,R) background. The general solution to the proper string size is also
found. We show that the antisymmetric tensor (corresponding to conformal
invariance) generally gives rise to repulsion, and it precisely cancels the
dominant attractive term arising from the metric.
Both the sinh-Gordon and the cosh-Gordon sectors of the string dynamics in
non-conformally invariant AdS spacetime reduce here to the Liouville equation
(with different signs of the potential), while the original Liouville sector
reduces to the free wave equation. Only the very large classical string size is
affected by the torsion. Medium and small size string behaviours are unchanged.
We also find illustrative classes of string solutions in the SL(2,R)
background: dynamical closed as well as stationary open spiralling strings, for
which the effect of torsion is somewhat like the effect of rotation in the
metric. Similarly, the string solutions in the 2+1 BH-AdS background with
torsion and angular momentum are fully analyzed.Comment: 24 pages including 4 postscript figures. Enlarged version including a
section on string solutions in 2+1 black hole background. To be published in
Phys. Rev. D., December 199
Breather trapping and breather transmission in a DNA model with an interface
We study the dynamics of moving discrete breathers in an interfaced piecewise
DNA molecule.
This is a DNA chain in which all the base pairs are identical and there
exists an interface such that the base pairs dipole moments at each side are
oriented in opposite directions.
The Hamiltonian of the Peyrard--Bishop model is augmented with a term that
includes the dipole--dipole coupling between base pairs. Numerical simulations
show the existence of two dynamical regimes. If the translational kinetic
energy of a moving breather launched towards the interface is below a critical
value, it is trapped in a region around the interface collecting vibrational
energy. For an energy larger than the critical value, the breather is
transmitted and continues travelling along the double strand with lower
velocity. Reflection phenomena never occur.
The same study has been carried out when a single dipole is oriented in
opposite direction to the other ones.
When moving breathers collide with the single inverted dipole, the same
effects appear. These results emphasize the importance of this simple type of
local inhomogeneity as it creates a mechanism for the trapping of energy.
Finally, the simulations show that, under favorable conditions, several
launched moving breathers can be trapped successively at the interface region
producing an accumulation of vibrational energy. Moreover, an additional
colliding moving breather can produce a saturation of energy and a moving
breather with all the accumulated energy is transmitted to the chain.Comment: 15 pages, 11 figure
A G1-like globular cluster in NGC 1023
The structure of a very bright (MV = -10.9) globular cluster in NGC 1023 is
analyzed on two sets of images taken with the Hubble Space Telescope. From
careful modeling of King profile fits to the cluster image, a core radius of
0.55+/-0.1 pc, effective radius 3.7+/-0.3 pc and a central V-band surface
brightness of 12.9+/-0.5 mag / square arcsec are derived. This makes the
cluster much more compact than Omega Cen, but very similar to the brightest
globular cluster in M31, G1 = Mayall II. The cluster in NGC 1023 appears to be
very highly flattened with an ellipticity of about 0.37, even higher than for
Omega Cen and G1, and similar to the most flattened clusters in the Large
Magellanic Cloud.Comment: 14 pages, 3 figures, 1 table. Accepted for AJ, Oct 200
Build it, but will they come? Preliminary findings of refuge limitation bottlenecking in juvenile Menippe adina in the Mississippi Sound
Strings in Kerr-Newmann Black Holes
We study the evolution of strings in the equatorial plane of a Kerr-Newmann
black hole. Writting the equations of motion and the constraints resulting from
Hamilton's principle, three classes of exact solutions are presented, for a
closed string, encircling the black hole. They all depend on two arbitrary
integration functions and two constants. A process of extracting energy is
examined for the case of one of the three families of solutions. This is the
analog of the Penrose process for the case of a particle.Comment: 14 pages, no figures, LaTeX. To appear in Gen. Rel. Gra
Variations in Stellar Clustering with Environment: Dispersed Star Formation and the Origin of Faint Fuzzies
The observed increase in star formation efficiency with average cloud
density, from several percent in whole giant molecular clouds to ~30 or more in
cluster-forming cores, can be understood as the result of hierarchical cloud
structure if there is a characteristic density as which individual stars become
well defined. Also in this case, the efficiency of star formation increases
with the dispersion of the density probability distribution function (pdf).
Models with log-normal pdf's illustrate these effects. The difference between
star formation in bound clusters and star formation in loose groupings is
attributed to a difference in cloud pressure, with higher pressures forming
more tightly bound clusters. This correlation accounts for the observed
increase in clustering fraction with star formation rate and with the
observation of Scaled OB Associations in low pressure environments. ``Faint
fuzzie'' star clusters, which are bound but have low densities, can form in
regions with high Mach numbers and low background tidal forces. The proposal by
Burkert, Brodie & Larsen (2005) that faint fuzzies form at large radii in
galactic collisional rings, satisfies these constraints.Comment: 14 pages, 2 figures, ApJ, 672, January 10th 200
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