4,038 research outputs found
Flat 3-webs of degree one on the projective plane
The aim of this work is to study global -webs with vanishing curvature. We
wish to investigate degree foliations for which their dual web is flat. The
main ingredient is the Legendre transform, which is an avatar of classical
projective duality in the realm of differential equations. We find a
characterization of degree foliations whose Legendre transform are webs
with zero curvature.Comment: 14 page
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
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
- …