15,673 research outputs found
The snail lemma for internal groupoids
We establish a generalized form both of the Gabriel-Zisman exact sequence associated with a pointed functor between pointed groupoids, and of the Brown exact sequence associated with a fibration of pointed groupoids. Our generalization consists in replacing pointed groupoids with groupoids internal to a pointed regular category with reflexive coequalizer
Role of heat generation and thermal diffusion during frontal photopolymerization
Frontal photopolymerization (FPP) is a rapid and versatile solidification process that can be used to fabricate complex three-dimensional structures by selectively exposing a photosensitive monomer-rich bath to light. A characteristic feature of FPP is the appearance of a sharp polymerization front that propagates into the bath as a planar traveling wave. In this paper, we introduce a theoretical model to determine how heat generation during photopolymerization influences the kinetics of wave propagation as well as the monomer-to-polymer conversion profile, both of which are relevant for FPP applications and experimentally measurable. When thermal diffusion is sufficiently fast relative to the rate of polymerization, the system evolves as if it were isothermal. However, when thermal diffusion is slow, a thermal wavefront develops and propagates at the same rate as the polymerization front. This leads to an accumulation of heat behind the polymerization front which can result in a significant sharpening of the conversion profile and acceleration of the growth of the solid. Our results also suggest that a novel way to tailor the dynamics of FPP is by imposing a temperature gradient along the growth directio
Mesothelioma and thymic tumors: Treatment challenges in (outside) a network setting
The management of patients with mesothelioma and thymic malignancy requires continuous multidisciplinary expertise at any step of the disease. A dramatic improvement in our knowledge has occurred in the last few years, through the development of databases, translational research programs, and clinical trials. Access to innovative strategies represents a major challenge, as there is a lack of funding for clinical research in rare cancers and their rarity precludes the design of robust clinical trials that could lead to specific approval of drugs. In this context, patient-centered initiatives, such as the establishment of dedicated networks, are warranted. International societies, such as IMIG (International Mesothelioma Interest Group) and ITMIG (International Thymic Malignancy Interest Group) provide infrastructure for global collaboration, and there are many advantages to having strong regional groups working on the same issues. There may be regional differences in risk factors, susceptibility, management and outcomes. The ability to address questions both regionally as well as globally is ideal to develop a full understanding of mesothelioma and thymic malignancies. In Europe, through the integration of national networks with EURACAN, the collaboration with academic societies and international groups, the development of networks in thoracic oncology provides multiplex integration of clinical care and research, ultimately ensuring equal access to high quality care to all patients, with the opportunity of conducting high level clinical and translational research projects
Fisher Metric, Geometric Entanglement and Spin Networks
Starting from recent results on the geometric formulation of quantum
mechanics, we propose a new information geometric characterization of
entanglement for spin network states in the context of quantum gravity. For the
simple case of a single-link fixed graph (Wilson line), we detail the
construction of a Riemannian Fisher metric tensor and a symplectic structure on
the graph Hilbert space, showing how these encode the whole information about
separability and entanglement. In particular, the Fisher metric defines an
entanglement monotone which provides a notion of distance among states in the
Hilbert space. In the maximally entangled gauge-invariant case, the
entanglement monotone is proportional to a power of the area of the surface
dual to the link thus supporting a connection between entanglement and the
(simplicial) geometric properties of spin network states. We further extend
such analysis to the study of non-local correlations between two non-adjacent
regions of a generic spin network graph characterized by the bipartite
unfolding of an Intertwiner state. Our analysis confirms the interpretation of
spin network bonds as a result of entanglement and to regard the same spin
network graph as an information graph, whose connectivity encodes, both at the
local and non-local level, the quantum correlations among its parts. This gives
a further connection between entanglement and geometry.Comment: 29 pages, 3 figures, revised version accepted for publicatio
Galaxy evolution across the optical emission-line diagnostic diagrams?
The discovery of the M-sigma relation, the local galaxy bimodality, and the
link between black-hole and host-galaxy properties, have raised the question
whether AGN play a role in galaxy evolution. Several theoretical models
implement AGN feedback to explain the observed galaxy luminosity function, and
possibly the color and morphological transformation of spiral galaxies into
passive ellipticals. To understand the importance of AGN feedback, a study of
the AGN populations in the radio-optical domain is crucial. A mass sequence
linking star-forming galaxies and AGN has been already noted in previous works,
and it is now investigated as possible evolutionary sequence. We observed a
sample of 119 intermediate-redshift (0.04<z<0.4) SDSS-FIRST radio emitters with
the Effelsberg 100-m telescope at 4.85 and 10.45 GHz and obtained spectral
indices. We find indications of spectral index flattening in high-metallicity
star-forming galaxies, composite galaxies, and Seyferts. This "flattening
sequence" along the [NII]-based emission-line diagnostic diagram is consistent
with the hardening of galaxy ionizing field, due to nuclear activity. After
combining our data with FIRST measurements at 1.4 GHz, we find that the
three-point radio spectra of Seyferts and LINERs show substantial differences,
attributable to small radio core components and larger (arcsecond sized)
jet/lobe components, respectively. A visual inspection of FIRST images seems to
confirm this hypothesis. Galaxies along this sequence are hypothesized to be
transitioning from the active star-forming galaxies (blue cloud) to the passive
elliptical galaxies (red sequence). This supports the suggestion that AGN play
a role in shutting down star-formation, and allow the transition from one
galaxy class to the other.Comment: 20 pages, 19 figures, accepted for publication in A&
Measuring the star formation rate with gravitational waves from binary black holes
A measurement of the history of cosmic star formation is central to
understand the origin and evolution of galaxies. The measurement is extremely
challenging using electromagnetic radiation: significant modeling is required
to convert luminosity to mass, and to properly account for dust attenuation,
for example. Here we show how detections of gravitational waves from
inspiraling binary black holes made by proposed third-generation detectors can
be used to measure the star formation rate of massive stars with high precision
up to redshifts of ~10. Depending on the time-delay model, the predicted
detection rates ranges from ~1400 to ~16000 per month with the current
measurement of local merger rate density. With three months of observations,
parameters describing the volumetric star formation rate can be constrained at
the few percent level, and the volumetric merger rate can be directly measured
to 3% at z~2. Given a parameterized star formation rate, the characteristic
delay time between binary formation and merger can be measured to ~60%.Comment: 7 pages, 1 table, 4 fig
The Kirillov picture for the Wigner particle
We discuss the Kirillov method for massless Wigner particles, usually
(mis)named "continuous spin" or "infinite spin" particles. These appear in
Wigner's classification of the unitary representations of the Poincar\'e group,
labelled by elements of the enveloping algebra of the Poincar\'e Lie algebra.
Now, the coadjoint orbit procedure introduced by Kirillov is a prelude to
quantization. Here we exhibit for those particles the classical Casimir
functions on phase space, in parallel to quantum representation theory. A good
set of position coordinates are identified on the coadjoint orbits of the
Wigner particles; the stabilizer subgroups and the symplectic structures of
these orbits are also described.Comment: 19 pages; v2: updated to coincide with published versio
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