2,590 research outputs found
Cosmic magnetic fields and dark energy in extended electromagnetism
We discuss an extended version of electromagnetism in which the usual gauge
fixing term is promoted into a physical contribution that introduces a new
scalar state in the theory. This new state can be generated from vacuum quantum
fluctuations during an inflationary era and, on super-Hubble scales, gives rise
to an effective cosmological constant. The value of such a cosmological
constant coincides with the one inferred from observations as long as inflation
took place at the electroweak scale. On the other hand, the new state also
generates an effective electric charge density on sub-Hubble scales that
produces both vorticity and magnetic fields with coherent lengths as large as
the present Hubble horizon.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish
Relativity Meeting 2010, Granada, Spain, 6-10 September 201
A Structural Comparison of Ordered and Non-Ordered Ion Doped Silicate Bioactive Glasses
One of the key benefits of sol-gel-derived glasses is the presence of a mesoporous structure
and the resulting increase in surface area. This enhancement in textural properties has a significant
e ect on the physicochemical properties of the materials. In this context the aim of this study was to
investigate how sol-gel synthesis parameters can influence the textural and structural properties of
mesoporous silicate glasses. We report the synthesis and characterization of metal ion doped sol-gel
derived glasses with di erent dopants in the presence or absence of a surfactant (Pluronic P123)
used as structure-directing templating agent. Characterization was done by several methods. Using
a structure directing agent led to larger surface areas and highly ordered mesoporous structures.
The chemical structure of the non-ordered glasses was modified to a larger extent than the one
of the ordered glasses due to increased incorporation of dopant ions into the glass network. The
results will help to further understand how the properties of sol-gel glasses can be controlled by
incorporation of metal dopants, in conjunction with control over the textural properties, and will be
important to optimize the properties of sol-gel glasses for specific applications, e.g., drug delivery,
bone regeneration, wound healing, and antibacterial materials.European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 643050, project “HyMedPoly
Metastability of non-reversible mean-field Potts model with three spins
We examine a non-reversible, mean-field Potts model with three spins on a set
with points. Without an external field, there are three
critical temperatures and five different metastable regimes. The analysis can
be extended by a perturbative argument to the case of small external fields. We
illustrate the case of large external fields with some phenomena which are not
present in the absence of external field.Comment: 34 pages, 12 figure
Educación intercultural en los centros de personas adultas en Huelva
El trabajo que se presenta comienza realizando una reflexión sobe la interdependencia de las relaciones socioeconómicas y culturales en un mundo global. A continuación se realiza una breve reseña histórica sobre la evolución de la Educación de Personas Adultas hasta llegar al concepto de educación permanente y formación a lo largo de toda la vida de acuerdo con la actual Ley Orgánica de Ordenación General del Sistema educativo LOGSE. De esta manera, los Centros de Educación de Personas Adultas ofrecen una respuesta formativa y educativa a la población adulta en el seno de una sociedad multicultural como la que vivimos. Se dedica un amplio apartado al reto que tiene ante sí la Administración Educativa en la formación de los Equipos Docentes para abordar la interculturalidad. Se hace amplia referencia al Plan Andaluz de Educación de Inmigrantes como pieza clave para la intervención, reconociendo que es un instrumento fundamental para abordar la labor educativa desde una perspectiva intercultural y de género. Teniendo en cuenta que cada día es más numerosa y diversa la población inmigrante que acude a los Centros de Personas Adultas, se expone la preocupación que el profesorado ha puesto de manifiesto y el proceso de formación que se viene realizando desde el curso 1995/96 en esta línea, donde la labor de la intervención pedagógica, se considera imprescindible para abordar con calidad la complejidad de la educación intercultural.This work begins making a reflexion about the interdependence of the socioeconomic and cultural relations in a global world. Then, a brief historical outline about the evolution of the adult people´s education is made in order to arrive to the concept of permanent education and the training during all the life from in accordance with the current Organic Law of General Ordinaion of the Educational System L.O.G.S.E. In this way, the adult people´s educational centres offer a formative and educative answer to the adult population of a multicultural society like this where we are living.
A wide section is dedicated to the challenge that the educative administration has in training the teaching staff to tackle the interculture. A large reference is dedicated to the Andaluz Plan of the Inmigrants´Education as a key piece for the intervention, recognizing that it´s an essential instrument to face the educative labour from an intercultural perspective which also takes into account the genre.
As we know, the inmigrant population who go to the adult people´s centres is more numerous each time so teacher´s preocupations about this have been exposed in this work and the teaching process which has been making from the course 1995/96 in this way where the labour of the pedagogic intervention is considered indispensable to face the complexity of the intercultural education with quality is shown too
Dissecting a hot molecular core: The case of G31.41+0.31
We made a detailed observational analysis of a well known hot molecular core
lying in the high-mass star-forming region G31.41+0.31. This core is believed
to contain deeply embedded massive stars and presents a velocity gradient that
has been interpreted either as rotation or as expansion, depending on the
authors. Our aim was to shed light on this question and possibly prepare the
ground for higher resolution ALMA observations which could directly detect
circumstellar disks around the embedded massive stars. Observations at
sub-arcsecond resolution were performed with the Submillimeter Array in methyl
cyanide, a typical hot molecular core tracer, and 12CO and 13CO, well known
outflow tracers. We also obtained sensitive continuum maps at 1.3 mm. Our
findings confirm the existence of a sharp velocity gradient across the core,
but cannot confirm the existence of a bipolar outflow perpendicular to it. The
improved angular resolution and sampling of the uv plane allow us to attain
higher quality channel maps of the CH3CN lines with respect to previous studies
and thus significantly improve our knowledge of the structure and kinematics of
the hot molecular core. While no conclusive argument can rule out any of the
two interpretations (rotation or expansion) proposed to explain the velocity
gradient observed in the core, in our opinion the observational evidence
collected so far indicates the rotating toroid as the most likely scenario. The
outflow hypothesis appears less plausible, because the dynamical time scale is
too short compared to that needed to form species such as CH3CN, and the mass
loss and momentum rates estimated from our measurements appear too high.Comment: Astronomy and Astrophysics, in pres
Bayesian model selection and isocurvature perturbations
Present cosmological data are well explained assuming purely adiabatic perturbations, but an admixture of isocurvature perturbations is also permitted. We use a Bayesian framework to compare the performance of cosmological models including isocurvature modes with the purely adiabatic case; this framework automatically and consistently penalizes models which use more parameters to fit the data. We compute the Bayesian evidence for fits to a data set comprised of WMAP and other microwave anisotropy data, the galaxy power spectrum from 2dFGRS and SDSS, and Type Ia supernovae luminosity distances. We find that Bayesian model selection favors the purely adiabatic models, but so far only at low significance
On the kinematics of massive star forming regions: the case of IRAS 17233-3606
Direct observations of accretion disks around high-mass young stellar objects
would help to discriminate between different models of formation of massive
stars. However, given the complexity of massive star forming regions, such
studies are still limited in number. Additionally, there is still no general
consensus on the molecular tracers to be used for such investigations. Because
of its close distance and high luminosity, IRAS 17233-3606 is a potential good
laboratory to search for traces of rotation in the inner gas around the
protostar(s). Therefore, we selected the source for a detailed analysis of its
molecular emission at 230 GHz with the SMA. We systematically investigated the
velocity fields of transitions in the SMA spectra which are not affected by
overlap with other transitions, and searched for coherent velocity gradients to
compare them to the distribution of outflows in the region. Beside CO emission
we also used high-angular H2 images to trace the outflow motions driven by the
IRAS 17233-3606 cluster. We find linear velocity gradients in many transitions
of the same molecular species and in several molecules. We report the first
detection of HNCO in molecular outflows from massive YSOs. We discuss the CH3CN
velocity gradient taking into account various scenarios: rotation, presence of
multiple unresolved sources with different velocities, and outflow(s). Although
other interpretations cannot be ruled out, we propose that the CH3CN emission
might be affected by the outflows of the region. Higher angular observations
are needed to discriminate between the different scenarios. The present
observations, with the possible association of CH3CN with outflows in a few
thousands AU around the YSOs' cluster, (i) question the choice of the tracer to
probe rotating structures, and (ii) show the importance of the use of H2 images
for detailed studies of kinematics.Comment: accepted for publication in A&
Effects of biasing on the galaxy power spectrum at large scales
n this paper we study the effect of biasing on the power spectrum at large
scales. We show that even though non-linear biasing does introduce a white
noise contribution on large scales, the behavior of the
matter power spectrum on large scales may still be visible and above the white
noise for about one decade. We show, that the Kaiser biasing scheme which leads
to linear bias of the correlation function on {\em large} scales, also
generates a linear bias of the {\rm power spectrum} on rather small scales.
This is a consequence of the divergence on small scales of the pure
Harrison-Zeldovich spectrum. However, biasing becomes k-dependent when we damp
the underlying power spectrum on small scales. We also discuss the effect of
biasing on the baryon acoustic oscillations.Comment: 9 pages, 4 figures. One figure and comments clarifying the linear
biasing on small scales and references added. V3 version accepted in PR
The hyperyoung HII region in G24.78+0.08 A1
Context. G24.78+0.08 A1 is a 20 Msun star surrounded by a hypercompact (HC)
HII region, driving a CO bipolar outflow, and located at the center of a
massive rotating toroid undergoing infall towards the HC region. Recent water
maser observations suggest that the HC region is expanding and accretion onto
the star is halted. Aims. This study aims to confirm the expansion scenario
proposed for the HC region on the basis of recent H2O maser observations.
Methods. We carried out continuum VLA observations at 1.3cm and 7mm with the A
array plus Pie Town configuration to map the HC region towards G24 A1. Results.
The emission of the HC region has been resolved and shows a ring shape
structure. The profiles of the emission obtained by taking slices at different
angles passing through the barycenter of the HC region confirm the shell
structure of the emission. The ratio between the inner and the outer radius of
the shell, Ri/Ro, derived fitting the normalized brightness temperature profile
passing through the peak of the 7mm emission, is 0.9, which indicates that the
shell is thin. The deconvolved outer radius estimated from the fit is 590 AU.
These results imply that the HC region in G24 A1 cannot be described in terms
of a classical, homogeneous HII region but is instead an ionized shell. This
gives support to the model of an expanding wind-driven, ionized shell suggested
by the kinematics and distribution of the H2O masers associated with the HC
region. According to this model, the HC region is expanding on very short times
scales, 21-66 yr.Comment: 4 pages, 5 figures. Accepted for publication by A&A Lette
- …