9,849 research outputs found
Ventilatory function in young adults and dietary antioxidant intake
ArtĂculo de publicaciĂłn 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
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
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
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
String propagation in four-dimensional dyonic black hole background
We study string propagation in an exact, four-dimensional dyonic black hole
background. The general solutions describing string configurations are obtained
by solving the string equations of motion and constraints. By using the
covariant formalism, we also investigate the propagation of physical
perturbations along the string in the given curved background.Comment: 19 pages, Tex (macro phyzzx is needed
Planetoid String Solutions in 3 + 1 Axisymmetric Spacetimes
The string propagation equations in axisymmetric spacetimes are exactly
solved by quadratures for a planetoid Ansatz. This is a straight
non-oscillating string, radially disposed, which rotates uniformly around the
symmetry axis of the spacetime. In Schwarzschild black holes, the string stays
outside the horizon pointing towards the origin. In de Sitter spacetime the
planetoid rotates around its center. We quantize semiclassically these
solutions and analyze the spin/(mass) (Regge) relation for the planetoids,
which turns out to be non-linear.Comment: Latex file, 14 pages, two figures in .ps files available from the
author
A theoretical analysis of the resolution due to diffusion and size-dispersion of particles in deterministic lateral displacement devices
We present a model including diffusion and particle-size dispersion for
separation of particles in deterministic lateral displacement devices also
known as bumper arrays. We determine the upper critical diameter for
diffusion-dominated motion and the lower critical diameter for pure
convection-induced displacement. Our model explains the systematic deviation,
observed for small particles in several experiments, from the critical diameter
for separation given by simple laminar flow considerations.Comment: 5 pages, 3 eps figures, revtex
Quantum String Dynamics in the conformal invariant SL(2,R) WZWN Background: Anti-de Sitter Space with Torsion
We consider classical and quantum strings in the conformally invariant
background corresponding to the SL(2,R) WZWN model. This background is locally
anti-de Sitter spacetime with non-vanishing torsion. Conformal invariance is
expressed as the torsion being parallelized. The precise effect of the
conformal invariance on the dynamics of both circular and generic classical
strings is extracted. In particular, the conformal invariance gives rise to a
repulsive interaction of the string with the background which precisely cancels
the dominant attractive term arising from gravity. We perform both
semi-classical and canonical string-quantization, in order to see the effect of
the conformal invariance of the background on the string mass spectrum. Both
approaches yield that the high-mass states are governed by m sim HN (N,`large
integer'), where m is the string mass and H is the Hubble constant. It follows
that the level spacing grows proportionally to N: d(m^2 alpha')/dN sim N, while
the entropy goes like: S sim sqrt{m}. Moreover, it follows that there is no
Hagedorn temperature,so that the partition function is well defined at any
positive temperature. All results are compared with the analogue results in
Anti- de Sitter spacetime, which is a non conformal invariant background.
Conformal invariance simplifies the mathematics of the problem but the physics
remains mainly unchanged. Differences between conformal and non-conformal
backgrounds only appear in the intermediate region of the string spectrum, but
these differences are minor. For low and high masses, the string mass spectra
in conformal and non-conformal backgrounds are identical. Interestingly enough,
conformal invariance fixes the value of the spacetime curvature to be -69/(26
alpha').Comment: Latex file, 23 pages, no figure
Quantum Coherent String States in AdS_3 and SL(2,R) WZWN Model
In this paper we make the connection between semi-classical string
quantization and exact conformal field theory quantization of strings in 2+1
Anti de Sitter spacetime. More precisely, considering the WZWN model
corresponding to SL(2,R) and its covering group, we construct quantum {\it
coherent} string states, which generalize the ordinary coherent states of
quantum mechanics, and show that in the classical limit they correspond to
oscillating circular strings. After quantization, the spectrum is found to
consist of two parts: A continuous spectrum of low mass states (partly
tachyonic) fulfilling the standard spin-level condition necessary for unitarity
|j|< k/2, and a discrete spectrum of high mass states with asymptotic behaviour
m^2\alpha'\propto N^2 (N positive integer). The quantization condition for the
high mass states arises from the condition of finite positive norm of the
coherent string states, and the result agrees with our previous results
obtained using semi-classical quantization. In the k\to\infty limit, all the
usual properties of coherent or {\it quasi-classical} states are recovered. It
should be stressed that we consider the circular strings only for simplicity
and clarity, and that our construction can easily be used for other string
configurations too. We also compare our results with those obtained in the
recent preprint hep-th/0001053 by Maldacena and Ooguri.Comment: Misprints corrected. Final version to appear in Phys. Rev.
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