Interactive mixture of inhomogeneous dark fluids driven by dark energy: a dynamical systems analysis

We examine the evolution of an inhomogeneous mixture of non-relativistic pressureless cold dark matter (CDM), coupled to dark energy (DE) characterised by the equation of state parameter $w<-1/3$, with the interaction term proportional to the DE density. This coupled mixture is the source of a spherically symmetric Lema\^\ itre-Tolman-Bondi (LTB) metric admitting an asymptotic Friedman-Lema\^\ itre-Robertson-Walker (FLRW) background. Einstein's equations reduce to a 5-dimensional autonomous dynamical system involving quasi--local variables related to suitable averages of covariant scalars and their fluctuations. The phase space evolution around the critical points (past/future attractors and five saddles) is examined in detail. For all parameter values and both directions of energy flow (CDM to DE and DE to CDM) the phase space trajectories are compatible with a physically plausible early cosmic times behaviour near the past attractor. This result compares favourably with mixtures with the interaction driven by the CDM density in which conditions for a physically plausible past evolution are more restrictive. Numerical examples are provided describing the evolution of an initial profile that can be associated with idealised structure formation scenariosComment: 23 pages, IOP format, 8 figure

La motivación de los estudiantes de término de Ingeniería Industrial en la asignatura Tópicos Especiales de Ingeniería Industrial

Este es un estudio de caso sobre la motivación en los estudiantes universitarios de República Dominicana. Circunscribiéndose —por un período de clases específico— a la asignatura Tópicos Especiales de Ingeniería Industrial (carrera de Ingeniería Industrial), se interrogó y encuestó a sus estudiantes y a los profesores con el propósito de determinar el tipo de motivación que primaba en los alumnos, así como las estrategias y técnicas que más podrían influir en la orientación de su atención al aprendizaje de las enseñanzas y conocimientos que brinda la señalada asignatura. Los resultados apuntan a que prima la motivación extrínseca, esto es, que se estudia la materia más por los resultados o recompensas que de ello se puedan desprender que por la vivencia misma del proceso. Los datos de que solo el 42% de los estudiantes participantes en el estudio disfrutaba la asignatura y de que el 88% de los que participaban en clases lo hacían para sumar puntos en la calificación acumulada reflejarían tal situación. Ahora bien, habría otros factores de importancia que incidirían en la poca motivación estudiantil. Entre ellos estaría la realidad de que son pocos los estudiantes que poseen experiencia laboral en el área de estudio, algo que les dificultaría su capacidad de conectar las enseñanzas con sus realidades vividas y así poder trascender el conocimiento teórico o meramente nominal. Entre las conclusiones a las que el presente estudio llegó, cabe citar el papel que el maestro debe desempeñar en el proceso: despertar a los estudiantes a los nuevos conocimientos a través de un plan o estrategia que tome en cuenta sus condicionamientos particulares, puesto que son múltiples y distintos los factores que influyen en el grado de motivación del estudiantado

Two successive partial mini-filament confined ejections

Active region (AR) NOAA 11476 produced a series of confined plasma ejections, mostly accompanied by flares of X-ray class M, from 08 to 10 May 2012. The structure and evolution of the confined ejections resemble that of EUV surges; however, their origin is associated to the destabilization and eruption of a mini-filament, which lay along the photospheric inversion line (PIL) of a large rotating bipole. Our analysis indicate that the bipole rotation and flux cancellation along the PIL have a main role in destabilizing the structure and triggering the ejections. The observed bipole emerged within the main following AR polarity. Previous studies have analyzed and discussed in detail two events of this series in which the mini-filament erupted as a whole, one at 12:23 UT on 09 May and the other at 04:18 UT on 10 May. In this article we present the observations of the confined eruption and M4.1 flare on 09 May 2012 at 21:01 UT (SOL2012-05-09T21:01:00) and the previous activity in which the mini-filament was involved. For the analysis we use data in multiple wavelengths (UV, EUV, X-rays, and magnetograms) from space instruments. In this particular case, the mini-filament is seen to erupt in two different sections. The northern section erupted accompanied by a C1.6 flare and the southern section did it in association with the M4.1 flare. The global structure and direction of both confined ejections and the location of a far flare kernel, to where the plasma is seen to flow, suggest that both ejections and flares follow a similar underlying mechanism.Fil: Poisson, Mariano. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Bustos, C.. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Lopez Fuentes, Marcelo Claudio. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Cristiani, Germán Diego. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Hadron plus photon production in polarized hadronic collisions at next-to-leading order accuracy

We compute the next-to-leading order QCD corrections to the polarized (and unpolarized) cross sections for the production of a hadron accompanied by an opposite-side prompt photon. This process, being studied at RHIC, permits us to reconstruct partonic kinematics using experimentally measurable variables. We study the correlation between the reconstructed momentum fractions and the true partonic ones, which in the polarized case might allow us to reveal the spin-dependent gluon distribution with a higher precision.Comment: 18 figures included. New version, discussion about polarized asymmetries extended, 7 new figures, new reference

A Tractable Model of the LTE Access Reservation Procedure for Machine-Type Communications

A canonical scenario in Machine-Type Communications (MTC) is the one featuring a large number of devices, each of them with sporadic traffic. Hence, the number of served devices in a single LTE cell is not determined by the available aggregate rate, but rather by the limitations of the LTE access reservation protocol. Specifically, the limited number of contention preambles and the limited amount of uplink grants per random access response are crucial to consider when dimensioning LTE networks for MTC. We propose a low-complexity model of LTE's access reservation protocol that encompasses these two limitations and allows us to evaluate the outage probability at click-speed. The model is based chiefly on closed-form expressions, except for the part with the feedback impact of retransmissions, which is determined by solving a fixed point equation. Our model overcomes the incompleteness of the existing models that are focusing solely on the preamble collisions. A comparison with the simulated LTE access reservation procedure that follows the 3GPP specifications, confirms that our model provides an accurate estimation of the system outage event and the number of supported MTC devices.Comment: Submitted, Revised, to be presented in IEEE Globecom 2015; v3: fixed error in eq. (4

Dynamics of Interacting Quintessence Models: Observational Constraints

Interacting quintessence models have been proposed to explain or, at least, alleviate the coincidence problem of late cosmic acceleration. In this paper we are concerned with two aspects of these kind of models: (i) the dynamical evolution of the model of Chimento et al. [L.P. Chimento, A.S. Jakubi, D. Pavon, and W. Zimdahl, Phys. Rev. D 67, 083513 (2003).], i.e., whether its cosmological evolution gives rise to a right sequence of radiation, dark matter and dark energy dominated eras, and (ii) whether the dark matter dark energy ratio asymptotically evolves towards a non-zero constant. After showing that the model correctly reproduces these eras, we correlate three data sets that constrain the interaction at three redshift epochs: $z\le 10^{4}$, $z=10^{3}$, and $z=1$. We discuss the model selection and argue that even if the model under consideration fulfills both requirements, it is heavily constrained by observation. The prospects that the coincidence problem can be explained by the coupling of dark matter to dark energy are not clearly favored by the data.Comment: 16 pages, 7 figures and 3 tables. Modifications introduced to match published versio

What Can Wireless Cellular Technologies Do about the Upcoming Smart Metering Traffic?

The introduction of smart electricity meters with cellular radio interface puts an additional load on the wireless cellular networks. Currently, these meters are designed for low duty cycle billing and occasional system check, which generates a low-rate sporadic traffic. As the number of distributed energy resources increases, the household power will become more variable and thus unpredictable from the viewpoint of the Distribution System Operator (DSO). It is therefore expected, in the near future, to have an increased number of Wide Area Measurement System (WAMS) devices with Phasor Measurement Unit (PMU)-like capabilities in the distribution grid, thus allowing the utilities to monitor the low voltage grid quality while providing information required for tighter grid control. From a communication standpoint, the traffic profile will change drastically towards higher data volumes and higher rates per device. In this paper, we characterize the current traffic generated by smart electricity meters and supplement it with the potential traffic requirements brought by introducing enhanced Smart Meters, i.e., meters with PMU-like capabilities. Our study shows how GSM/GPRS and LTE cellular system performance behaves with the current and next generation smart meters traffic, where it is clearly seen that the PMU data will seriously challenge these wireless systems. We conclude by highlighting the possible solutions for upgrading the cellular standards, in order to cope with the upcoming smart metering traffic.Comment: Submitted; change: corrected location of eSM box in Fig. 1; May 22, 2015: Major revision after review; v4: revised, accepted for publicatio

The H=xp model revisited and the Riemann zeros

Berry and Keating conjectured that the classical Hamiltonian H = xp is related to the Riemann zeros. A regularization of this model yields semiclassical energies that behave, in average, as the non trivial zeros of the Riemann zeta function. However, the classical trajectories are not closed, rendering the model incomplete. In this paper, we show that the Hamiltonian H = x (p + l_p^2/p) contains closed periodic orbits, and that its spectrum coincides with the average Riemann zeros. This result is generalized to Dirichlet L-functions using different self-adjoint extensions of H. We discuss the relation of our work to Polya's fake zeta function and suggest an experimental realization in terms of the Landau model.Comment: 5 pages, 3 figure