Optimal association of mobile users to multi-access edge computing resources

Multi-access edge computing (MEC) plays a key role in fifth-generation (5G) networks in bringing cloud functionalities at the edge of the radio access network, in close proximity to mobile users. In this paper we focus on mobile-edge computation offloading, a way to transfer heavy demanding, and latency-critical applications from mobile handsets to close-located MEC servers, in order to reduce latency and/or energy consumption. Our goal is to provide an optimal strategy to associate mobile users to access points (AP) and MEC hosts, while contextually optimizing the allocation of radio and computational resources to each user, with the objective of minimizing the overall user transmit power under latency constraints incorporating both communication and computation times. The overall problem is a mixed-binary problem. To overcome its inherent computational complexity, we propose two alternative strategies: i) a method based on successive convex approximation (SCA) techniques, proven to converge to local optimal solutions; ii) an approach hinging on matching theory, based on formulating the assignment problem as a matching game

The edge cloud: A holistic view of communication, computation and caching

The evolution of communication networks shows a clear shift of focus from just improving the communications aspects to enabling new important services, from Industry 4.0 to automated driving, virtual/augmented reality, Internet of Things (IoT), and so on. This trend is evident in the roadmap planned for the deployment of the fifth generation (5G) communication networks. This ambitious goal requires a paradigm shift towards a vision that looks at communication, computation and caching (3C) resources as three components of a single holistic system. The further step is to bring these 3C resources closer to the mobile user, at the edge of the network, to enable very low latency and high reliability services. The scope of this chapter is to show that signal processing techniques can play a key role in this new vision. In particular, we motivate the joint optimization of 3C resources. Then we show how graph-based representations can play a key role in building effective learning methods and devising innovative resource allocation techniques.Comment: to appear in the book "Cooperative and Graph Signal Pocessing: Principles and Applications", P. Djuric and C. Richard Eds., Academic Press, Elsevier, 201

The SDSS-GALEX viewpoint of the truncated red sequence in field environments at z~0

We combine GALEX near-UV photometry with a volume-limited sample of local (0.005<z<0.037) SDSS DR4 galaxies to examine the composition and the environmental dependencies of the optical and UV-optical colour-magnitude (C-M) diagrams. We find that ~30% of red sequence galaxies in the optical C-M diagram show signs of ongoing star-formation from their spectra having EW(Halpha)>2A. This contamination is greatest at faint magnitudes (Mr>-19) and in field regions where as many as three-quarters of red sequence galaxies are star-forming, and as such has important consequences for following the build-up of the red sequence. We find that the NUV-r colour instead allows a much more robust separation of passively-evolving and star-forming galaxies, which allows the build-up of the UV-selected red sequence with redshift and environment to be directly interpreted in terms of the assembly of stellar mass in passively-evolving galaxies. We find that in isolated field regions the number density of UV-optical red sequence galaxies declines rapidly at magnitudes fainter than Mr~-19 and appears completely truncated at Mr~-18. This confirms the findings of Haines et al. (2007) that no passively-evolving dwarf galaxies are found more than two virial radii from a massive halo, whether that be a group, cluster or massive galaxy. These results support the downsizing paradigm whereby the red sequence is assembled from the top down, being already largely in place at the bright end by z~1, and the faint end filled in at later epochs in clusters and groups through environment-related processes such as ram-pressure stripping or galaxy harassment.Comment: 12 pages, 7 figures, MNRAS submitte

La monarquía española y los últimos incas ¿una frontera interior?

La conquesta i el control del que va ser denominat Regne del Perú van resultar en un procés més llarg del que habitualment la historiografia considera. La resistència indígena i l’aspror i fragmentació del territori sota el control de diferents agents i grups ètnics van complicar el control exercit per l’administració espanyola. Això va influir en les estratègies polítiques i militars de la corona. Així, entre el 1532 i el 1572 aquest va ser un escenari creuat en el seu interior per una multiplicitat de fronteres ètniques, econòmiques, polítiques, militars, culturals i religioses. Aquest article analitza la presència d’una frontera interior deguda a la resistència dels inques de Vilcabamba. L’existència d’aquesta frontera interior va influir sobre l’actuació de la corona espanyola. Analitzar aquestes circumstàncies d’interacció permet aprofundir en el coneixement de la implantació colonial en aquests escenaris. Aquests entorns configuraven mosaics mòbils de relacions —fronteres interiors— i van trigar dècades a consolidar-se en les estructures que van sorgir després de la conquesta.The conquest and administrative control of the Kingdom of Peru was a longer process than historiography has assumed. The resistance of the indigenous peoples and the ruggedness and fragmentation of the territory under the control of different agents and ethnic groups complicated the Spanish administration and government. These factors had an influence on the political and military strategies of the Crown. As a result, between 1532 and 1572, this was an area crisscrossed by ethnic, economic, political, military, cultural and religious boundaries. This article analyzes the presence of an internal frontier due to the resistance of the Incas of Vilcabamba, which influenced the Spanish colonial government. Analyzing these particular circumstances of interaction provides a deeper understanding of the colonial presence in these lands. These environments formed mobile mosaics of social and political relations — internal borders — in which the consolidation of the Spanish Empire’s control took several decades after the Conquest.La conquista y el control de lo que fue denominado Reino de Perú resultaron en un proceso más largo de lo que comúnmente la historiografía considera. La resistencia indígena y la aspereza y fragmentación del territorio bajo el control de diferentes agentes y grupos étnicos complicaron el control ejercido por la administración española. Esto influyó en las estrategias políticas y militares de la corona. Así, entre 1532 y 1572, este fue un escenario cruzado en su interior por una multiplicidad de fronteras étnicas, económicas, políticas, militares, culturales y religiosas. Este artículo analiza la presencia de una frontera interior debida a la resistencia de los incas de Vilcabamba. La existencia de esta frontera interior influyó sobre la actuación de la corona española. Analizar estas circunstancias de interacción permite profundizar en el conocimiento de la implantación colonial en estos escenarios. Estos entornos configuraban mosaicos móviles de relaciones —fronteras interiores— y tardaron décadas en consolidarse en las estructuras que surgieron después de la conquista

Structure and kinematics of the peculiar galaxy NGC 128

This is a multiband photometric and spectroscopic study of the peculiar S0 galaxy NGC128. We present results from broad (B and R) and narrow band optical CCD photometry, near (NIR) and far (FIR) infrared observations, long slit spectroscopy, and Fabry-Perot interferometry (CIGALE). The peculiar peanut shape morphology of the galaxy is observed both at optical and near-infrared wavelengths. The stellar disk is thick and distorted (arc-bended), with a color asymmetry along the major axis due to the presence of a large amount of dust, estimated through NIR and FIR data of ~6x10^6 M_sun, in the region of interaction with the companion galaxy NGC127. The color maps are nearly uniform over the whole galaxy, but for the major axis asymmetry, and a small gradient toward the center indicating the presence of a redder disk-like component. The H_alpha image indeed reveals the existence of a tilted gaseous ``disk'' around the center, oriented with the major axis toward the companion galaxy NGC127. Long slit and CIGALE data confirm the presence of gas in a disk-like component counter-rotating and inclined approximately of 50 deg. to the line of sight. The mass of the gas disk in the inner region is ~2.7x10^4 M_sun. The stellar velocity field is cylindrical up to the last measured points of the derived rotation curves, while the velocity dispersion profiles are typical for an S0 galaxy, but for an extended constant behaviour along the minor axis.Comment: accepted for pubblication in A&A Supp

Structure and Evolution of Galaxy Clusters: Internal Dynamics of ABCG 209 at z~0.21

We study the internal dynamics of the rich galaxy cluster ABGC 209 on the basis of new spectroscopic and photometric data. The distribution in redshift shows that ABCG 209 is a well isolated peak of 112 detected member galaxies at z=0.209, characterised by a high value of the line-of-sight velocity dispersion, sigma_v=1250-1400 Km/s, on the whole observed area (1 Mpc/h from the cluster center), that leads to a virial mass of M=1.6-2.2x10^15 M_sun within the virial radius, assuming the dynamical equilibrium. The presence of a velocity gradient in the velocity field, the elongation in the spatial distribution of the colour-selected likely cluster members, the elongation of the X-ray contour levels in the Chandra image, and the elongation of cD galaxy show that ABCG 209 is characterised by a preferential NW-SE direction. We also find a significant deviation of the velocity distribution from a Gaussian, and relevant evidence of substructure and dynamical segregation. All these facts show that ABCG 209 is a strongly evolving cluster, possibly in an advanced phase of merging.Comment: 26 pages, 14 figures. A&A in pres

Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal Interactions in the Shapley Supercluster

We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10 Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in ugriK bands and in Halpha narrow-band are used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending respectively 30kpc and 41kpc in projection from their disks. The galaxies' gaseous disks are truncated and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting about 250Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster-cluster interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS-90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster-cluster merger on RPS.Comment: 27 pages, 28 figures, MNRAS accepte