Planet-disc interaction on a freely moving mesh

General-purpose, moving-mesh schemes for hydrodynamics have opened the possibility of combining the accuracy of grid-based numerical methods with the flexibility and automatic resolution adaptivity of particle-based methods. Due to their supersonic nature, Keplerian accretion discs are in principle a very attractive system for applying such freely moving mesh techniques. However, the high degree of symmetry of simple accretion disc models can be difficult to capture accurately by these methods, due to the generation of geometric grid noise and associated numerical diffusion, which is absent in polar grids. To explore these and other issues, in this work we study the idealized problem of two-dimensional planet-disc interaction with the moving-mesh code AREPO. We explore the hydrodynamic evolution of discs with planets through a series of numerical experiments that vary the planet mass, the disc viscosity and the mesh resolution, and compare the resulting surface density, vortensity field and tidal torque with results from the literature. We find that the performance of the moving-mesh code in this problem is in accordance with published results, showing good consistency with grid codes written in polar coordinates. We also conclude that grid noise and mesh distortions do not introduce excessive numerical diffusion. Finally, we show how the moving-mesh approach can naturally increase resolution in regions of high densityaround planets and planetary wakes, while retaining the background flow at low resolution. This provides an alternative to the difficult task of implementing adaptive mesh refinement in conventional polar-coordinate codes.Comment: 21 pages, 15 figures, 2 tables. Updated to match version published by MNRA

Automated Network Service Scaling in NFV: Concepts, Mechanisms and Scaling Workflow

Next-generation systems are anticipated to be digital platforms supporting innovative services with rapidly changing traffic patterns. To cope with this dynamicity in a cost-efficient manner, operators need advanced service management capabilities such as those provided by NFV. NFV enables operators to scale network services with higher granularity and agility than today. For this end, automation is key. In search of this automation, the European Telecommunications Standards Institute (ETSI) has defined a reference NFV framework that make use of model-driven templates called Network Service Descriptors (NSDs) to operate network services through their lifecycle. For the scaling operation, an NSD defines a discrete set of instantiation levels among which a network service instance can be resized throughout its lifecycle. Thus, the design of these levels is key for ensuring an effective scaling. In this article, we provide an overview of the automation of the network service scaling operation in NFV, addressing the options and boundaries introduced by ETSI normative specifications. We start by providing a description of the NSD structure, focusing on how instantiation levels are constructed. For illustrative purposes, we propose an NSD for a representative NS. This NSD includes different instantiation levels that enable different ways to automatically scale this NS. Then, we show the different scaling procedures the NFV framework has available, and how it may automate their triggering. Finally, we propose an ETSI-compliant workflow to describe in detail a representative scaling procedure. This workflow clarifies the interactions and information exchanges between the functional blocks in the NFV framework when performing the scaling operation.Comment: This work has been accepted for publication in the IEEE Communications Magazin

Purely Flavored Leptogenesis

peer reviewedWe study a model for leptogenesis in which the total CP asymmetries in the decays and scatterings involving the SU(2) singlet seesaw neutrinos Nα vanish (ϵNα=0). Leptogenesis is possible due to nonvanishing CP violating lepton flavor asymmetries, realizing a situation in which the baryon asymmetry is due exclusively to flavor effects. We study the production of a net lepton asymmetry by solving the Boltzmann equations specific to this model, and we show that successful leptogenesis can be obtained at a scale as low as the TeV. We also discuss constraints on the model parameter space arising from current experimental upper limits on lepton flavor violating decays

A reexamination of the effective fine structure constant of graphene, as measured in graphite

We present a refined and improved study of the influence of screening on the effective fine structure constant of graphene, $\alpha^*$, as measured in graphite using inelastic x-ray scattering. This follow-up to our previous study [J. P. Reed, et al., Science 330, 805 (2010)] was carried out with two times better energy resolution, five times better momentum resolution, and improved experimental setup with lower background. We compare our results to RPA calculations and evaluate the relative importance of interlayer hopping, excitonic corrections, and screening from high energy excitations involving the $\sigma$ bands. We find that the static, limiting value of $\alpha^*$ falls in the range 0.25 to 0.35, which is higher than our previous result of 0.14, but still below the value expected from RPA. We show the reduced value is not a consequence of interlayer hopping effects, which were ignored in our previous analysis, but of a combination of excitonic effects in the $\pi \rightarrow \pi^*$ particle-hole continuum, and background screening from the $\sigma$-bonded electrons. We find that $\sigma$-band screening is extremely strong at distances of the order of a few nm, and should be highly effective at screening out short-distance, Hubbard-like interactions in graphene, as well as other carbon allotropes.Comment: 23 pages, 5 figure

Modeling and Simulation of Circumstellar Disks with the Next Generation of Hydrodynamic Solvers

This thesis is a computational study of circumstellar gas disks, with a special focus on modeling techniques and on numerical methods not only as scientific tools but also as a target of study. In particular, in-depth discussions are included on the main numerical strategy used, namely the moving-mesh method for astrophysical hydrodynamics. In this work, the moving-mesh approach is used to simulate circumstellar disks for the first time.Astronom

DIPLOMADO DE PROFUNDIZACION CISCO CCNP SOLUCIÓN DE DOS ESCENARIOS PRESENTES EN ENTORNOS CORPORATIVOS BAJO EL USO DE TECNOLOGÍA CISCO

En el primer escenario se usan dos tipos de enrutamiento que permiten convivir dos protocolos como son OSPF Y EIGRP, esto con el fin que se aprendan las rutas de los dos protocolos y puedan compartir recursos, además de admitirla conexión entre áreas con sistemas autónomos, igual mente de permitir la redistribución de los protocolos usando técnicas donde se aplican las mediciones de ancho de banda, demora, confiabilidad, carga y MTU, el único problema es que consume recursos. En el segundo escenario aplicamos las configuraciones de etherchannel donde LACP Y PAGP se pueden agrupar, los enlaces ethernetchannel y porttrunkinglogran combinarlas interfaces de forma múltiple, permitiendo así un ancho de banda disponible y proporciona una medida de la redundancia física.The first scenario uses two types of routing that allow two protocols such as OSPF and EIGRP to coexist, this in order to learn the routes of the two protocols and share resources, as well as to support the connection between areas with autonomous systems, as well as to allow the redistribution of protocols using techniques where bandwidth measurements are applied, delay, reliability, load and MTU, the only problem is that it consumes resources. in the second scenario we apply etherchannel configurations where LACP and PAGP can be grouped, ethernetchannel and port trunking links manage to combine the interfaces multiplely, thus allowing an available bandwidth and provides a measure of physical redundancy

An approach to Prognosis-Decision-Making for route calculation of an electric vehicle considering stochastic traffic information

International audienceWe present a Prognosis-Decision-Making (PDM) methodology to calculate the best route for an Electric Vehicle (EV) in a street network when incorporating stochastic traffic information. To achieve this objective, we formulate an optimization problem that aims at minimizing the expectation of an objective function that incorporates information about the time and energy spent to complete the route. The proposed method uses standard path optimization algorithms to generate a set of initial candidates for the solution of this routing problem. We evaluate all possible paths by incorporating information about the traffic, elevation and distance profiles, as well as the battery State-of-Charge (SOC), in a prognostic algorithm that computes the SOC at the end of the route. In this regard, the solution of the optimization problem provides a balance between time an energy consumption in the EV. The method is verified in simulation using an artificial street network

An approach to Prognosis-Decision-Making for route calculation of an electric vehicle considering stochastic traffic information

We present a Prognosis-Decision-Making (PDM) methodology to calculate the best route for an Electric Vehicle (EV) in a street network when incorporating stochastic traffic information. To achieve this objective, we formulate an optimization problem that aims at minimizing the expectation of an objective function that incorporates information about the time and energy spent to complete the route. The proposed method uses standard path optimization algorithms to generate a set of initial candidates for the solution of this routing problem. We evaluate all possible paths by incorporating information about the traffic, elevation and distance profiles, as well as the battery State-of-Charge (SOC), in a prognostic algorithm that computes the SOC at the end of the route. In this regard, the solution of the optimization problem provides a balance between time an energy consumption in the EV. The method is verified in simulation using an artificial street network

Massive Clumps in the NGC 6334 Star Forming Region

We report observations of dust continuum emission at 1.2 mm toward the star forming region NGC 6334 made with the SEST SIMBA bolometer array. The observations cover an area of $\sim 2$ square degrees with approximately uniform noise. We detected 181 clumps spanning almost three orders of magnitude in mass (3\Msun$-6\times10^3$ \Msun) and with sizes in the range 0.1--1.0 pc. We find that the clump mass function $dN/d\log M$ is well fit with a power law of the mass with exponent -0.6 (or equivalently $dN/dM \propto M^{-1.6}$). The derived exponent is similar to those obtained from molecular line emission surveys and is significantly different from that of the stellar initial mass function. We investigated changes in the mass spectrum by changing the assumptions on the temperature distribution of the clumps and on the contribution of free-free emission to the 1.2 mm emission, and found little changes on the exponent. The Cumulative Mass Distribution Function is also analyzed giving consistent results in a mass range excluding the high-mass end where a power-law fit is no longer valid. The masses and sizes of the clumps observed in NGC 6334 indicate that they are not direct progenitors of stars and that the process of fragmentation determines the distribution of masses later on or occurs at smaller spatial scales. The spatial distribution of the clumps in NGC 6334 reveals clustering which is strikingly similar to that exhibited by young stars in other star forming regions. A power law fit to the surface density of companions gives $\Sigma\propto \theta^{-0.62}$.Comment: 16 pages, 11 figures, 4 tables. To appear in the Astrophysical Journa