330 research outputs found
Random Primordial Magnetic Fields and the Gas Content of Dark Matter Halos
We recently predicted the existence of random primordial magnetic fields
(RPMF) in the form of randomly oriented cells with dipole-like structure with a
cell size and an average magnetic field . Here we investigate models
for primordial magnetic field with a similar web-like structure, and other
geometries, differing perhaps in and . The effect of RPMF on the
formation of the first galaxies is investigated. The filtering mass, , is
the halo mass below which baryon accretion is severely depressed. We show that
these RPMF could influence the formation of galaxies by altering the filtering
mass and the baryon gas fraction of a halo, . The effect is particularly
strong in small galaxies. We find, for example, for a comoving B_0=0.1\muG,
and a reionization epoch that starts at and ends at , for
at , the becomes severely depressed for
M<10^7\msun, whereas for the becomes severely depressed only
for much smaller masses, M<10^5\msun. We suggest that the observation of
and at high redshifts can give information on the intensity and
structure of primordial magnetic fields.Comment: 7 pages, 10 figures, accepted for publication in MNRAS (several
improvements after suggestions of the referee
A physical approach to modelling large-scale galactic magnetic fields
A convenient representation of the structure of the large-scale galactic
magnetic field is required for the interpretation of polarization data in the
sub-mm and radio ranges, in both the Milky Way and external galaxies. We
develop a simple and flexible approach to construct parametrised models of the
large-scale magnetic field of the Milky Way and other disc galaxies, based on
physically justifiable models of magnetic field structure. The resulting models
are designed to be optimised against available observational data.
Representations for the large-scale magnetic fields in the flared disc and
spherical halo of a disc galaxy were obtained in the form of series expansions
whose coefficients can be calculated from observable or theoretically known
galactic properties. The functional basis for the expansions is derived as
eigenfunctions of the mean-field dynamo equation or of the vectorial magnetic
diffusion equation. The solutions presented are axially symmetric but the
approach can be extended straightforwardly to non-axisymmetric cases. The
magnetic fields are solenoidal by construction, can be helical, and are
parametrised in terms of observable properties of the host object, such as the
rotation curve and the shape of the gaseous disc. The magnetic field in the
disc can have a prescribed number of field reversals at any specified radii.
Both the disc and halo magnetic fields can separately have either dipolar or
quadrupolar symmetry. The model is implemented as a publicly available software
package GalMag which allows, in particular, the computation of the synchrotron
emission and Faraday rotation produced by the model's magnetic field. The model
can be used in interpretations of observations of magnetic fields in the Milky
Way and other spiral galaxies, in particular as a prior in Bayesian analyses.
(Abridged.)Comment: 20 pages, 14 figures. Accepted for publication in A&
Carotenoid composition of Umbu-Cajá fruits from Bahia.
Umbu-cajá (Spondias spp.) is a tropical fruit, native from Brazilian northeastern region, consumed fresh or prepared as ice cream, jelly and juice by the population from small cities
Commonalities and Differences in Carotid Body Dysfunction in Hypertension and Heart Failure
Carotid body pathophysiology is associated with many cardiovascular-respiratory-metabolic diseases. This pathophysiology reflects both hyper-sensitivity and hyper-tonicity. From both animal models and human patients, evidence indicates that amelioration of this pathophysiological signalling improves disease states such as a lowering of blood pressure in hypertension, a reduction of breathing disturbances with improved cardiac function in heart failure (HF) and a re-balancing of autonomic activity with lowered sympathetic discharge. Given this, we have reviewed the mechanisms of carotid body hyper-sensitivity and hyper-tonicity across disease models asking whether there is uniqueness related to specific disease states. Our analysis indicates some commonalities and some potential differences, although not all mechanisms have been fully explored across all disease models. One potential commonality is that of hypoperfusion of the carotid body across hypertension and HF, where the excessive sympathetic drive may reduce blood flow in both models and, in addition, lowered cardiac output in HF may potentiate the hypoperfusion state of the carotid body. Other mechanisms are explored that focus on neurotransmitter and signalling pathways intrinsic to the carotid body (e.g. ATP, carbon monoxide) as well as extrinsic molecules carried in the blood (e.g. leptin); there are also transcription factors found in the carotid body endothelium that modulate its activity (Krüppel-like factor 2). The evidence to date fully supports that a better understanding of the mechanisms of carotid body pathophysiology is a fruitful strategy for informing potential new treatment strategies for many cardiovascular, respiratory and metabolic diseases, and this is highly relevant clinically
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