5,501 research outputs found
An internal mechanism for the anti-glitch observed in AXP 1E 2259+586
Magnetars are fascinating objects that are thought to be neutron stars
powered by their strong internal magnetic fields. Clear evidence of a sudden
spin-down was detected in the Anomalous X-ray Pulsar AXP 1E 2259+586, an object
cataloged as a magnetar. This event received the name "anti-glitch". In this
work we present a simple internal mechanism which could account for the
observed sudden spin-down of the star.Comment: Presented in the "Compact Stars in the QCD Phase Diagram IV"
conference. September 26-30, 2014, Prerow, German
Evaluating the more suitable ISM frequency band for iot-based smart grids: a quantitative study of 915 MHz vs. 2400 MHz
IoT has begun to be employed pervasively in industrial environments and critical infrastructures thanks to its positive impact on performance and efficiency. Among these environments, the Smart Grid (SG) excels as the perfect host for this technology, mainly due to its potential to become the motor of the rest of electrically-dependent infrastructures. To make this SG-oriented IoT cost-effective, most deployments employ unlicensed ISM bands, specifically the 2400 MHz one, due to its extended communication bandwidth in comparison with lower bands. This band has been extensively used for years by Wireless Sensor Networks (WSN) and Mobile Ad-hoc Networks (MANET), from which the IoT technologically inherits. However, this work questions and evaluates the suitability of such a "default" communication band in SG environments, compared with the 915 MHz ISM band. A comprehensive quantitative comparison of these bands has been accomplished in terms of: power consumption, average network delay, and packet reception rate. To allow such a study, a dual-band propagation model specifically designed for the SG has been derived, tested, and incorporated into the well-known TOSSIM simulator. Simulation results reveal that only in the absence of other 2400 MHz interfering devices (such as WiFi or Bluetooth) or in small networks, is the 2400 MHz band the best option. In any other case, SG-oriented IoT quantitatively perform better if operating in the 915 MHz band.This research was supported by the MINECO/FEDER project grants TEC2013-47016-C2-2-R (COINS) and TEC2016-76465-C2-1-R (AIM). The authors would like to thank Juan Salvador Perez Madrid nd Domingo Meca (part of the Iberdrola staff) for the support provided during the realization of this work. Ruben M. Sandoval also thanks the Spanish MICINN for an FPU (REF FPU14/03424) pre-doctoral fellowship
Magnetised Accretion Discs in Kerr Spacetimes II: Hot Spots
Context. Quasi-periodic variability has been observed in a number of X-ray
binaries harboring black hole candidates. In general relativity, black holes
are uniquely described by the Kerr metric and, according to the cosmic
censorship conjecture, curvature singularities always have to be clothed by an
event horizon. Aims. In this paper, we study the effect of an external magnetic
field on the observed light curves of orbiting hot spots in thin accretion
discs around Kerr black holes and naked singularities. Methods. We employ a
ray-tracing algorithm to calculate the light curves and power spectra of such
hot spots as seen by a distant observer for uniform and dipolar magnetic field
configurations assuming a weak coupling between the magnetic field and the disc
matter. Results. We show that the presence of an external dipolar magnetic
field leads to potentially observable modifications of these signals for both
Kerr black holes and naked singularities, while an external uniform magnetic
field has practically no effect. In particular, we demonstrate that the
emission from a hot spot orbiting near the innermost stable circular orbit of a
naked singularity in a dipolar magnetic field can be significantly harder than
the emission of the same hot spot in the absence of such a magnetic field.
Conclusions. The comparison of our model with observational data may allow us
study the geometry of magnetic fields around compact objects and to test the
cosmic censorship conjecture in conjunction with other observables such as
thermal continuum spectra and iron line profiles.Comment: 7 pages, 3 figures, submitted to Astronomy and Astrophysic
Jeans instability in the linearized Burnett regime
Jeans instability is derived for the case of a low density self-gravitating
gas beyond the Navier-Stokes equations. The Jeans instability criterium is
shown to depend on a Burnett coefficient if the formalism is taken up to fourth
order in the wave number. It is also shown that previously known viscosity
corrections to the Jeans wave-number are enhanced if the full fourth order
formalism is applied to the stability analysis.Comment: 8 pages, no figures. Submitted to Physica
Dos artistas de apellido Rulfo
En el presente ensayo se da cuenta de la relaciĂłn artistica entre padre e hijo, Juan Rulfo y Juan Carlos Rulfo, a partir de un hecho real que lle llevĂł, tal vez sin querer, a la creaciĂłn artĂstica. Lo real y lo ficticio se emparentan de tal modo que es difĂcil establecer una lĂnea que los divida
Recommended from our members
Electronic properties of SnO2-based ceramics with double function of varistor and humidity sensor
This is the post-print version of the article. The official published version can be obtained from the link below - Copyright @ 2010 AD-Tech.Tin dioxide based varistor ceramics SnO2-Co3O4-Nb2O5-Cr2O3-xCuO (x=0; 0.05; 0.1 and 0.5) were made and their electrical properties were studied. The highest nonlinearity coefficient and electric field (at current density 10-3 A cm-2) were obtained for 0.1 mol.% CuO addition. It was observed that low-field electrical conductivity is increased with relative humidity, therefore, materials obtained exhibit double function of varistor and humidity sensor. The highest humidity sensitivity coefficient is found for SnO2-Co3O4-Nb2O5-Cr2O3 ceramics (without CuO). Observed varistor and humidity-sensitive properties are explained in the frames of grain-boundary double Schottky barrier concept as a decrease of the barrier height with electric field or relative humidity. Using suggested simple theory and data obtained on isothermal capacitance relaxation, the energy of the grain-boundary monoenergetic trapping states were estimated. These values are less than found for activation energy of electrical conduction (as a measure of the barrier height). These observations confirm the barrier concept.This work is funded by the Royal Society, United Kingdom (2007R1/R26999)
- …