18,188 research outputs found
The formation of spiral arms and rings in barred galaxies
In this and in a previous paper (Romero-Gomez et al. 2006) we propose a
theory to explain the formation of both spirals and rings in barred galaxies
using a common dynamical framework. It is based on the orbital motion driven by
the unstable equilibrium points of the rotating bar potential. Thus, spirals,
rings and pseudo-rings are related to the invariant manifolds associated to the
periodic orbits around these equilibrium points. We examine the parameter space
of three barred galaxy models and discuss the formation of the different
morphological structures according to the properties of the bar model. We also
study the influence of the shape of the rotation curve in the outer parts, by
making families of models with rising, flat, or falling rotation curves in the
outer parts. The differences between spiral and ringed structures arise from
differences in the dynamical parameters of the host galaxies. The results
presented here will be discussed and compared with observations in a
forthcoming paper.Comment: 16 pages, 13 figures, accepted in A&A. High resolution version
available at http://www.oamp.fr/dynamique/pap/merce.htm
Biodiversity study of Southern Biscayne Bay and Card Sound 1968-1973
A multi-disciplinary investigation was conducted in southern Biscayne Bay and Card Sound from 1968 to 1973. The purpose of the investigation was to conduct an integrated study of the ecology of southern Biscayne Bay with special emphasis on the effects of the heated effluent from the Turkey Point fossil fuel power plant, and to predict the impact of additional effluent from the planned conversion of the plant to nuclear fuel. The results of this investigation have been discussed in numerous publications. This report contains the unpublished biology data that resulted from the investigation. (PDF contains 44 pages
Neutrinoless double-beta decay. A brief review
In this brief review we discuss the generation of Majorana neutrino masses
through the see-saw mechanism, the theory of neutrinoless double-beta decay,
the implications of neutrino oscillation data for the effective Majorana mass,
taking into account the recent Daya Bay measurement of theta_13, and the
interpretation of the results of neutrinoless double-beta decay experiments.Comment: 22 page
On SIR epidemic models with generally distributed infectious periods: number of secondary cases and probability of infection
Recently, Clancy [SIR epidemic models with general infectious period distribution, Statist. Prob. Lett. 85 (2014) 1–5] has shown how SIR epidemics in which individuals’ infection periods are not necessarily exponentially distributed may be modeled in terms of a piecewise-deterministic Markov process (PDMP). In this paper, we present a more detailed description of the underlying PDMP, from which we analyze the population transmission number and the infection probability of a certain susceptible individual
Kinematics of Big Biomedical Data to characterize temporal variability and seasonality of data repositories: Functional Data Analysis of data temporal evolution over non-parametric statistical manifolds
[EN] Aim: The increasing availability of Big Biomedical Data is leading to large research data samples collected over long periods of time. We propose the analysis of the kinematics of data probability distributions over time towards the characterization of data temporal variability.
Methods: First, we propose a kinematic model based on the estimation of a continuous data temporal trajectory, using Functional Data Analysis over the embedding of a non-parametric statistical manifold which points represent data temporal batches, the Information Geometric Temporal (IGT) plot. This model allows measuring the velocity and acceleration of data changes. Next, we propose a coordinate-free method to characterize the oriented seasonality of data based on the parallelism of lagged velocity vectors of the data trajectory throughout the IGT space, the Auto-Parallelism of Velocity Vectors (APVV) and APVVmap. Finally, we automatically explain the maximum variance components of the IGT space coordinates by means of correlating data points with known temporal factors from the domain application.
Materials: Methods are evaluated on the US National Hospital Discharge Survey open dataset, consisting of 3,25M hospital discharges between 2000 and 2010.
Results: Seasonal and abrupt behaviours were present on the estimated multivariate and univariate data trajectories. The kinematic analysis revealed seasonal effects and punctual increments in data celerity, the latter mainly related to abrupt changes in coding. The APVV and APVVmap revealed oriented seasonal changes on data trajectories. For most variables, their distributions tended to change to the same direction at a 12-month period, with a peak of change of directionality at mid and end of the year. Diagnosis and Procedure codes also included a 9-month periodic component. Kinematics and APVV methods were able to detect seasonal effects on extreme temporal subgrouped data, such as in Procedure code, where Fourier and autocorrelation methods were not able to. The automated explanation of IGT space coordinates was consistent with the results provided by the kinematic and seasonal analysis. Coordinates received different meanings according to the trajectory trend, seasonality and abrupt changes.
Discussion: Treating data as a particle moving over time through a multidimensional probabilistic space and studying the kinematics of its trajectory has turned out to a new temporal variability methodology. Its results on the NHDS were aligned with the dataset and population descriptions found in the literature, contributing with a novel temporal variability characterization. We have demonstrated that the APVV and APVVmat are an appropriate tool for the coordinate-free and oriented analysis of trajectories or complex multivariate signals.
Conclusion: The proposed methods comprise an exploratory methodology for the characterization of data temporal variability, what may be useful for a reliable reuse of Big Biomedical Data repositories acquired over long periods of time.This work was supported by UPV grant No. PAID-00-17, and projects DPI2016-80054-R and H2020-SC1-2016-CNECT No. 727560.Sáez, C.; Garcia-Gomez, JM. (2018). Kinematics of Big Biomedical Data to characterize temporal variability and seasonality of data repositories: Functional Data Analysis of data temporal evolution over non-parametric statistical manifolds. International Journal of Medical Informatics. 119:109-124. https://doi.org/10.1016/j.ijmedinf.2018.09.015S10912411
Self-sustained spatiotemporal oscillations induced by membrane-bulk coupling
We propose a novel mechanism leading to spatiotemporal oscillations in
extended systems that does not rely on local bulk instabilities. Instead,
oscillations arise from the interaction of two subsystems of different spatial
dimensionality. Specifically, we show that coupling a passive diffusive bulk of
dimension d with an excitable membrane of dimension d-1 produces a
self-sustained oscillatory behavior. An analytical explanation of the
phenomenon is provided for d=1. Moreover, in-phase and anti-phase
synchronization of oscillations are found numerically in one and two
dimensions. This novel dynamic instability could be used by biological systems
such as cells, where the dynamics on the cellular membrane is necessarily
different from that of the cytoplasmic bulk.Comment: Accepted for publication in Physical Review Letter
On the origin of rR_1 ring structures in barred galaxies
We propose a new theory for the formation of rR_1 ring structures, i.e. for
ring structures with both an inner and an outer ring, the latter having the
form of ``8''. We propose that these rings are formed by material from the
stable and unstable invariant manifolds associated with the Lyapunov orbits
around the equilibrium points of a barred galaxy. We discuss the shape and
velocity structure of the rings thus formed and argue that they are in
agreement with the observed properties of rR_1 structures.Comment: 8 pages, 9 figures, accepted in Astronomy and Astrophysics. High
quality figures are available upon reques
Invariant manifolds as building blocks for the formation of spiral arms and rings in barred galaxies
We propose a theory to explain the formation of spiral arms and of all types
of outer rings in barred galaxies, extending and applying the technique used in
celestial mechanics to compute transfer orbits. Thus, our theory is based on
the chaotic orbital motion driven by the invariant manifolds associated to the
periodic orbits around the hyperbolic equilibrium points. In particular, spiral
arms and outer rings are related to the presence of heteroclinic or homoclinic
orbits. Thus, R1 rings are associated to the presence of heteroclinic orbits,
while R1R2 rings are associated to the presence of homoclinic orbits. Spiral
arms and R2 rings, however, appear when there exist neither heteroclinic nor
homoclinic orbits. We examine the parameter space of three realistic, yet
simple, barred galaxy models and discuss the formation of the different
morphologies according to the properties of the galaxy model. The different
morphologies arise from differences in the dynamical parameters of the galaxy.Comment: 8 pages, 4 figures, in the proceedings of the conference: "Chaos in
Astronomy", Athens, September 2007, G. Contopoulos and P.A. Patsis (eds), to
be published by Springe
Thermalization and Cooling of Plasmon-Exciton Polaritons: Towards Quantum Condensation
We present indications of thermalization and cooling of quasi-particles, a
precursor for quantum condensation, in a plasmonic nanoparticle array. We
investigate a periodic array of metallic nanorods covered by a polymer layer
doped with an organic dye at room temperature. Surface lattice resonances of
the array---hybridized plasmonic/photonic modes---couple strongly to excitons
in the dye, and bosonic quasi-particles which we call
plasmon-exciton-polaritons (PEPs) are formed. By increasing the PEP density
through optical pumping, we observe thermalization and cooling of the strongly
coupled PEP band in the light emission dispersion diagram. For increased
pumping, we observe saturation of the strong coupling and emission in a new
weakly coupled band, which again shows signatures of thermalization and
cooling.Comment: 8 pages, 5 figures including supplemental material. The newest
version includes new measurements and corrections to the interpretation of
the result
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