533 research outputs found
Graphical and Kinematical Approach to Cosmological Horizons
We study the apparition of event horizons in accelerated expanding
cosmologies. We give a graphical and analytical representation of the horizons
using proper distances to coordinate the events. Our analysis is mainly
kinematical. We show that, independently of the dynamical equations, all the
event horizons tend in the future infinity to a given expression depending on
the scale factor that we call asymptotic horizon. We also encounter a subclass
of accelerating models without horizon. When the ingoing null geodesics do not
change concavity in its cosmic evolution we recover the de Sitter and
quintessence-Friedmann-Robertson-Walker models.Comment: Latex2e, 27 pages, 4 figures, submitted to Class. Quantum Gra
Brane Realizations of Quantum Hall Solitons and Kac-Moody Lie Algebras
Using quiver gauge theories in (1+2)-dimensions, we give brane realizations
of a class of Quantum Hall Solitons (QHS) embedded in Type IIA superstring on
the ALE spaces with exotic singularities. These systems are obtained by
considering two sets of wrapped D4-branes on 2-spheres. The space-time on which
the QHS live is identified with the world-volume of D4-branes wrapped on a
collection of intersecting 2-spheres arranged as extended Dynkin diagrams of
Kac-Moody Lie algebras. The magnetic source is given by an extra orthogonal
D4-brane wrapping a generic 2-cycle in the ALE spaces. It is shown as well that
data on the representations of Kac-Moody Lie algebras fix the filling factor of
the QHS. In case of finite Dynkin diagrams, we recover results on QHS with
integer and fractional filling factors known in the literature. In case of
hyperbolic bilayer models, we obtain amongst others filling factors describing
holes in the graphene.Comment: Lqtex; 15 page
Motion and Trajectories of Particles Around Three-Dimensional Black Holes
The motion of relativistic particles around three dimensional black holes
following the Hamilton-Jacobi formalism is studied. It follows that the
Hamilton-Jacobi equation can be separated and reduced to quadratures in analogy
with the four dimensional case. It is shown that: a) particles are trapped by
the black hole independently of their energy and angular momentum, b) matter
alway falls to the centre of the black hole and cannot understake a motion with
stables orbits as in four dimensions. For the extreme values of the angular
momentum of the black hole, we were able to find exact solutions of the
equations of motion and trajectories of a test particle.Comment: Plain TeX, 9pp, IPNO-TH 93/06, DFTUZ 93/0
On F-theory Quiver Models and Kac-Moody Algebras
We discuss quiver gauge models with bi-fundamental and fundamental matter
obtained from F-theory compactified on ALE spaces over a four dimensional base
space. We focus on the base geometry which consists of intersecting F0=CP1xCP1
Hirzebruch complex surfaces arranged as Dynkin graphs classified by three kinds
of Kac-Moody (KM) algebras: ordinary, i.e finite dimensional, affine and
indefinite, in particular hyperbolic. We interpret the equations defining these
three classes of generalized Lie algebras as the anomaly cancelation condition
of the corresponding N =1 F-theory quivers in four dimensions. We analyze in
some detail hyperbolic geometries obtained from the affine A base geometry by
adding a node, and we find that it can be used to incorporate fundamental
fields to a product of SU-type gauge groups and fields.Comment: 13 pages; new equations added in section 3, one reference added and
typos correcte
Situation, challenges, and SEOM recommendations for the future of undergraduate education in Oncology in Spain
Purpose The Spanish Society of Medical Oncology (SEOM, for its Spanish acronym) would like to attest to the relevance
of training in Oncology as part of the undergraduate education in Medicine program and issue recommendations to improve
said training, with the aim of responding better to the challenges that cancer poses to our society.
Materials and methods The curricula of 42 schools of medicine were reviewed with interviews with at least one teaching
medical oncologist from each faculty. The qualitative and opinion analysis was completed by means of an online questionnaire
targeting lecturers, resident tutors, and residents in Medical Oncology (MO), enabling the detection of needs and areas
for improvement at an organizational level and in terms of skill acquisition.
Results While the number of medical schools with a specific, mandatory program in MO has grown by up to 90%, it has
not been accompanied by an increase in independent programs. Instead, they largely consist of programs shared with other
specialties (61% of the medical faculties). In most of the undergraduate education programs, Oncology contents are fragmented
and approached from the perspective of each organ system.
Conclusions Despite the positive evolution in recent years, the heterogeneity in Oncology contents during undergraduate
education training continues to be remarkable. Cross-sectional programs with an integral vision, taught in the final years of
undergraduate medical education would be desirable. Among the recommendations for improvement of training in Medical
Oncology, the SEOM proposes that updated, theoretical content be incorporated and clinical practice in Medical Oncology departments be promotedThis study was funded as an unrestricted grant by Jansse
Lessons from the operation of the "Penning-Fluorescent" TPC and prospects
We have recently reported the development of a new type of high-pressure
Xenon time projection chamber operated with an ultra-low diffusion mixture and
that simultaneously displays Penning effect and fluorescence in the
near-visible region (300 nm). The concept, dubbed `Penning-Fluorescent' TPC,
allows the simultaneous reconstruction of primary charge and scintillation with
high topological and calorimetric fidelity
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