166 research outputs found
Exploring cloudy gas accretion as a source of interstellar turbulence in the outskirts of disks
High--resolution 2D--MHD numerical simulations have been carried out to
investigate the effects of continuing infall of clumpy gas in extended HI
galactic disks. Given a certain accretion rate, the response of the disk
depends on its surface gas density and temperature. For Galactic conditions at
a galactocentric distance of ~20 kpc, and for mass accretion rates consistent
with current empirical and theoretical determinations in the Milky Way, the
rain of compact high velocity clouds onto the disk can maintain transonic
turbulent motions in the warm phase (~2500 K) of HI. Hence, the HI line width
is expected to be ~6.5 km/s for a gas layer at 2500 K, if infall were the only
mechanism of driving turbulence. Some statistical properties of the resulting
forcing flow are shown in this Letter. The radial dependence of the gas
velocity dispersion is also discussed.Comment: 13 pages, 3 figures, accepted for publication in ApJ Letter
Bounds on the mass and abundance of dark compact objects and black holes in dwarf spheroidal galaxy halos
We establish new dynamical constraints on the mass and abundance of compact
objects in the halo of dwarf spheroidal galaxies. In order to preserve
kinematically cold the second peak of the Ursa Minor dwarf spheroidal (UMi
dSph) against gravitational scattering, we place upper limits on the density of
compact objects as a function of their assumed mass. The mass of the dark
matter constituents cannot be larger than 1000 solar masses at a halo density
in UMi's core of 0.35 solar masses/pc^3. This constraint rules out a scenario
in which dark halo cores are formed by two-body relaxation processes. Our
bounds on the fraction of dark matter in compact objects with masses >3000
solar masses improve those based on dynamical arguments in the Galactic halo.
In particular, objects with masses solar masses can comprise no
more than a halo mass fraction . Better determinations of the
velocity dispersion of old overdense regions in dSphs may result in more
stringent constraints on the mass of halo objects. For illustration, if the
preliminary value of 0.5 km/s for the secondary peak of UMi is confirmed,
compact objects with masses above solar masses could be excluded
from comprising all its dark matter halo.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
On the fraction of dark matter in charged massive particles (CHAMPs)
From various cosmological, astrophysical and terrestrial requirements, we
derive conservative upper bounds on the present-day fraction of the mass of the
Galactic dark matter (DM) halo in charged massive particles (CHAMPs). If dark
matter particles are neutral but decay lately into CHAMPs, the lack of
detection of heavy hydrogen in sea water and the vertical pressure equilibrium
in the Galactic disc turn out to put the most stringent bounds. Adopting very
conservative assumptions about the recoiling velocity of CHAMPs in the decay
and on the decay energy deposited in baryonic gas, we find that the lifetime
for decaying neutral DM must be > (0.9-3.4)x 10^3 Gyr. Even assuming the
gyroradii of CHAMPs in the Galactic magnetic field are too small for halo
CHAMPs to reach Earth, the present-day fraction of the mass of the Galactic
halo in CHAMPs should be < (0.4-1.4)x 10^{-2}. We show that redistributing the
DM through the coupling between CHAMPs and the ubiquitous magnetic fields
cannot be a solution to the cuspy halo problem in dwarf galaxies.Comment: 21 pages, 2 figures. To appear in JCA
Ordinal and nominal classication of wind speed from synoptic pressure patterns
Wind speed reconstruction is a challenging problem in areas (mainly wind
farms) where there are not direct wind measures available. Di erent approaches
have been applied to this reconstruction, such as measure-correlatepredict
algorithms, approaches based on physical models such as reanalysis
methods, or more recently, indirect measures such as pressure, and its relation
to wind speed. This paper adopts the latter method, and deals with wind
speed estimation in wind farms from pressure measures, but including different
novelties in the problem treatment. Existing synoptic pressure-based
indirect approaches for wind speed estimation are based on considering the
wind speed as a continuous target variable, estimating then the corresponding
wind series of continuous values. However, the exact wind speed is not
always needed by wind farms managers, and a general idea of the level of
speed is, in the majority of cases, enough to set functional operations for the
farm (such as wind turbines stop, for example). Moreover, the accuracy of the models obtained is usually improved for the classi cation task, given that
the problem is simpli ed. Thus, this paper tackles the problem of wind speed
prediction from synoptic pressure patterns by considering wind speed as a
discrete variable and, consequently, wind speed prediction as a classi cation
problem, with four wind level categories: low, moderate, high or very high.
Moreover, taking into account that these four di erent classes are associated
to four values in an ordinal scale, the problem can be considered as an ordinal
regression problem. The performance of several ordinal and nominal classi-
ers and the improvement achieved by considering the ordering information
are evaluated. The results obtained in this paper present the Support Vector
Machine as the best tested classi er for this task. In addition, the use of
the intrinsic ordering information of the problem is shown to signi cantly
improve ranks with respect to nominal classi cation, although di erences in
accuracy are smal
ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect
The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO2–10.3CaO–3.3P2O5–4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN + MSC, 4ZN + OST or 4ZN + MSC + OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological, and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice
Formulation and constraints on decaying dark matter with finite mass daughter particles
Decaying dark matter cosmological models have been proposed to remedy the
overproduction problem at small scales in the standard cold dark matter
paradigm. We consider a decaying dark matter model in which one CDM mother
particle decays into two daughter particles, with arbitrary masses. A complete
set of Boltzmann equations of dark matter particles is derived which is
necessary to calculate the evolutions of their energy densities and their
density perturbations. By comparing the expansion history of the universe in
this model and the free-streaming scale of daughter particles with astronomical
observational data, we give constraints on the lifetime of the mother particle,
, and the mass ratio between the daughter and the mother particles
. From the distance to the last scattering surface of the
cosmic microwave background, we obtain 30 Gyr in the massless
limit of daughter particles and, on the other hand, we obtain
0.97 in the limit . The free-streaming constraint
tightens the bound on the mass ratio as for .Comment: 20 pages, 7 figure
Efecto del estrés osmótico sobre el desarrollo in vitro de plántulas de albahaca Ocimum basilicum L.
Se prepararon medios de cultivo adicionados con Polietilenglicol (PEG) y solución salina (NaCl) correspondientes a los tratamientos de sequia (2%, 4% y 6% PEG 3350) y salinidad (25mM, 50mM y 75mM NaCl), en los cuales se colocaron semillas de albahaca previamente desinfectadas. Se colocaron en una Cámara Bioclimática (Lab-Line) bajo condiciones de 12 h luz y 27oC. A los 30 días de su siembra se evaluó el porcentaje de germinación, altura de plántula, longitud de raíz, número de hojas, tamaño de la hoja, peso fresco, peso seco y contenido de prolina libre como indicador de estrés. El porcentaje de germinación y el número de hojas no presentan diferencia significativa entre los tratamientos de sequía y salinidad. Mientras que en el resto de los parámetros, se presentó diferencia significativa entre los tratamientos. Evidenciando que las plántulas expuestas a deficiencias hídricas responden positivamente en su desarrollo a estas condiciones de estrés
Local Group Dwarf Spheroidals: Correlated Deviations from the Baryonic Tully-Fisher Relation
Local Group dwarf spheroidal satellite galaxies are the faintest
extragalactic stellar systems known. We examine recent data for these objects
in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf
spheroidals adhere to the BTFR, others deviate substantially. We examine the
residuals from the BTFR and find that they are not random. The residuals
correlate with luminosity, size, metallicity, ellipticity, and susceptibility
of the dwarfs to tidal disruption in the sense that fainter, more elliptical,
and tidally more susceptible dwarfs deviate farther from the BTFR. These
correlations disfavor stochastic processes and suggest a role for tidal
effects. We identify a test to distinguish between the {\Lambda}CDM and MOND
based on the orbits of the dwarf satellites of the Milky Way and how stars are
lost from them.Comment: 16 pages, 7 figures. Submitted to ApJ. Revised in response to referee
repor
Understanding local Dwarf Spheroidals and their scaling relations under MOdified Newtonian Dynamics
We use a specific form of the interpolation function in the MOND formalism,
which optimally accounts for the internal structure of dwarf spheroidal (dSph)
galaxies, to explore the consequences it has on the scaling relations seen in
these systems.}} {{The particular form of the interpolation function we used
leads to a law of gravity that does not degrade the good fit of the MOND
proposal on galactic scales, and in fact, slightly improves the accordance with
observations at dSph scales. This formalism yields a good description of
gravitational phenomena without the need of invoking any still undetected and
hypothetically dominant dark matter, in the weak field regime probed by local
dSph galaxies.}} {{Isothermal equilibrium density profiles then yield projected
surface density profiles for the local dSph galaxies in very good agreement
with observational determinations, for values of the relevant parameters as
inferred from recent observations of these Galactic satellites. The observed
scaling relations for these systems are also naturally accounted for within the
proposed scheme, including a previously unrecognised correlation of the
inferred mass-to-light ratios of local dSph's with the ages of their stellar
populations, which is natural in modified gravity schemes in the absence of
dark matter.}} {The results shed some light on the form that the MOND
interpolating function may have in the most challenging regime, which occurs at
moderate accelerations and intermediate mass--weighted lengths.Comment: 8 pages, 4 figures, 1 table, Accepted for publication in Astronomy
and Astrophysics. Copy matches published versio
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