389 research outputs found
Women in Transition – Menopause and Body Composition in Different Populations
Human biology has provided valuable and applicable points of view to contribute towards
human welfare, when it has analyzed changes in the transitional phases of the
ontogenetic process. The purpose of this presentation coincides with WHO recommendations
to study the modifications suffered by the female body during her stage of reproductive
aging in different environments. We study and compared three different groups
of women living in the cities of Madrid (Spain), Havana (Cuba) and in Tuxpan, a village
in the State of Michoacán (Mexico). Three groups differed with respect to their socio-economic
levels, food habits, social organization and culture. We used the same anthropometric
techniques, recommended by the IBP, and same tools to assess the women\u27s reproductive
life, demography and socio-economic condition. All three groups coincidences
regarding the remodelation of their thorax, so after 55 years of age their waist-hip ratio
surpassed the cut point of 0.80, associated whit higher risk for chronic cardiovascular
disorders. However, examined groups differed, for instance, the rural Mexican women
altered their bone density earlier, five years before the urban samples. Next, Mexican
women of younger ages maintained high levels of their body mass index above the cut
point for overweight
On the stability and spectral radius of a finite set of matrices
This paper studies some problems related to the stability and the spectral radius of a finite set of matrices. A seasonal epidemic model is given to illustrate the use of the obtained results. In this example, the relationship between the obtained results and the stability of a discrete time periodic linear system is obtained.This work has been partially supported by Spanish [grant number MTM2013-43678-P].Cantó Colomina, B.; Coll, C.; Sánchez, E. (2016). On the stability and spectral radius of a finite set of matrices. Linear and Multilinear Algebra. 64(3):353-361. https://doi.org/10.1080/03081087.2015.1040404S35336164
Statistical Analysis of Water Masers in Star-Forming Regions: Cepheus A and W75 N
We have done a statistical analysis of Very Long Baseline Array (VLBA) data
of water masers in the star-forming regions (SFRs) Cepheus A and W75 N, using
correlation functions to study the spatial clustering and Doppler-velocity
distribution of these masers. Two-point spatial correlation functions show a
characteristic scale size for clusters of water maser spots < or ~1 AU, similar
to the values found in other SFRs. This suggests that the scale for water maser
excitation tends to be < or ~1 AU. Velocity correlation functions show
power-law dependences with indices that can be explained by regular velocity
fields, such as expansion and/or rotation. These velocity fields are similar to
those indicated by the water maser proper-motion measurements; therefore, the
velocity correlation functions appear to reveal the organized motion of water
maser spots on scales larger than 1 AU.Comment: 16 pages, 8 figures, and 3 tables. Accepted by The Astrophysical
Journa
Winds from clu\sters with non-uniform stellar distributions
We present analytic and numerical models of the `cluster wind' resulting from
the multiple interactions of the winds ejected by the stars of a dense cluster
of massive stars. We consider the case in which the distribution of stars
(i.e., the number of stars per unit volume) within the cluster is spherically
symmetric, has a power-law radial dependence, and drops discontinuously to zero
at the outer radius of the cluster. We carry out comparisons between an
analytic model (in which the stars are considered in terms of a spatially
continuous injection of mass and energy) and 3D gasdynamic simulations (in
which we include 100 stars with identical winds, located in 3D space by
statistically sampling the stellar distribution function). From the analytic
model, we find that for stellar distributions with steep enough radial
dependencies the cluster wind flow develops a very high central density and a
non-zero central velocity, and for steeper dependencies it becomes fully
supersonic throughout the volume of the cluster (these properties are partially
reproduced by the 3D numerical simulations). Therefore, the wind solutions
obtained for stratified clusters can differ dramatically from the case of a
homogeneous stellar distribution (which produces a cluster wind with zero
central velocity, and a fully subsonic flow within the cluster radius).
Finally, from our numerical simulations we compute predictions of X-ray
emission maps and luminosities, which can be directly compared with
observations of cluster wind flows.Comment: 10 pages, 11 figures. MNRAS - Accepted 2007 June 29. Received 2007
June 28; in original form 2007 May 2
Side-entrainment in a jet embedded in a sidewind
Numerical simulations of HH jets never show side-entrainment of environmental
material into the jet beam. This is because the bow shock associated with the
jet head pushes the surrounding environment into a dense shell, which is never
in direct contact with the sides of the jet beam. We present 3D simulations in
which a side-streaming motion (representing the motion of the outflow source
through the surrounding medium) pushes the post-bow shock shell into direct
contact with the jet beam. This is a possible mechanism for modelling well
collimated "molecular jets" as an atomic/ionic flow which entrains molecules
initially present only in the surrounding environment.Comment: 8 pages, 12 figures, 1 table, accepted for publication in Ap
Revisiting 2D Numerical Models for the 19th century outbursts of Carinae
We present here new results of two-dimensional hydrodynamical simulations of
the eruptive events of the 1840s (the great) and the 1890s (the minor)
eruptions suffered by the massive star Car. The two bipolar nebulae
commonly known as the Homunculus and the little Homunculus were formed from the
interaction of these eruptive events with the underlying stellar wind. As in
previous work (Gonzalez et al. 2004a, 2004b), we assume here an interacting,
nonspherical multiple-phase wind scenario to explain the shape and the
kinematics of both Homunculi, but adopt a more realistic parametrization of the
phases of the wind. During the 1890s eruptive event, the outflow speed {\it
decreased} for a short period of time. This fact suggests that the little
Homunculus is formed when the eruption ends, from the impact of the
post-outburst Car wind (that follows the 1890s event) with the eruptive
flow (rather than by the collision of the eruptive flow with the pre-outburst
wind, as claimed in previous models; Gonzalez et al. 2004a, 2004b). Our
simulations reproduce quite well the shape and the observed expansion speed of
the large Homunculus. The little Homunculus (which is embedded within the large
Homunculus) becomes Rayleigh-Taylor unstable and develop filamentary structures
that resembles the spatial features observed in the polar caps. In addition, we
find that the interior cavity between the two Homunculi is partially filled by
material that is expelled during the decades following the great eruption. This
result may be connected with the observed double-shell structure in the polar
lobes of the Car nebula. Finally, as in previous work, we find the
formation of tenuous, equatorial, high-speed features that seem to be related
to the observed equatorial skirt of Car.Comment: accepted for publication in MNRA
- …