A Multi-Channel Packet Scheduling Approach to Improving Video Delivery Performance in Vehicular Networks †

When working with the Wireless Access in Vehicular Environment (WAVE) protocol stack, the multi-channel operation mechanism of the IEEE 1609.4 protocol may impact the overall network performance, especially when using video streaming applications. In general, packets delivered from the application layer during a Control Channel (CCH) time slot have to wait for transmission until the next Service Channel (SCH) time slot arrives. The accumulation of packets at the beginning of the latter time slot may introduce additional delays and higher contention when all the network nodes try, at the same time, to obtain access to the shared channel in order to send the delayed packets as soon as possible. In this work, we have analyzed these performance issues and proposed a new method, which we call SkipCCH, that helps the MAC layer to overcome the high contention produced by the packet transmission bursts at the beginning of every SCH slot. This high contention implies an increase in the number of packet losses, which directly impacts the overall network performance. With our proposal, streaming video in vehicular networks will provide a better quality of reconstructed video at the receiver side under the same network conditions. Furthermore, this method has particularly proven its benefits when working with Quality of Service (QoS) techniques, not only by increasing the received video quality but also because it avoids starvation of the lowerpriority traffic

Sistema de evaluación automatizada de prácticas para Tecnología de Computadores

Se presenta un sistema automatizado de evaluación de prácticas de la asignatura de Tecnología de Computadores de primer curso de Ingeniería Técnica en Informática de Gestión (ITIG), aunque es perfectamente aplicable a asignaturas similares de otras titulaciones. Se basa en el uso combinado de dos herramientas software: Simulín y SimulínEval, las cuales permiten la realización de prácticas, y su posterior corrección de forma automatizada, respectivamente. El sistema también detecta los casos de plagio entre alumnos de forma sistemática, y proporciona estadísticas sobre la eficacia de las prácticas y el sistema de enseñanza del profesor. Ello se traducirá en una mayor calidad en la enseñanza y evaluación del alumnado, así como en una reducción del esfuerzo realizado por parte del profesor

Filter Response of Resonant Waveguide Dielectric Gratings at Plane-Wave Conical Incidence

An accurate and efficient formulation is presented for the electromagnetic analysis of dielectric waveguide gratings under plane-wave conical incidence. An arbitrary number of dielectric bars can be placed inside each one-dimension periodic cell, including the effect of dielectric losses. The reflectance of a dielectric waveguide grating under conical incidence is compared with theoretical results presented by other authors, finding a very good agreement. A single-layer reflection filter has been designed centered at λ0=1.5 μm whose spectral and angular responses are shown. For this structure, the effect of the asymmetry of the distribution of the refraction index in the reflectance has been analyzed, observing a splitting of the reflection peak around the design wavelength. Finally it is discussed the equivalence between a volume grating and a shallow surface-relief grating, providing two examples of designing prescriptions

Is true friendship possible on Facebook? A study from the psychological perspective of Laín Entralgo

The present work aims to analyse the meaning of the concept of friendship through the study of the work of the doctor and philosopher Pedro Laín Entralgo. The initial hypothesis of the study is that the concept of friendship has been used instrumentally by social media networks, and that these do not offer the conditions necessary to fully experience true friendship. To verify this, we focused on the study of the psychological dimensions of friendship proposed by the author, identifying a series of variables and conducting an analysis by means of a survey of university students who are active users of the platform. With these results the descriptive statistics were extracted and a nonparametric analysis was performed of the variables to determine if Facebook does in fact offer the conditions necessary for to experience true friendship in its psychological dimensions. As the results show, to experience true friendship on social networks is difficult, given that the nature of the interactions between users of the platform are not appropriate for this experience. In calling this different type of relationship friendship Facebook benefits from an attractive hook which leads users to generate contacts as a form of currency which benefits the business model of the social media platform. The concept of true friendship is altered, deformed and displaced in favour of other types of relationships.El presente trabajo tiene como objetivo analizar el significado del concepto de amistad a través del estudio de la obra del médico y filósofo Pedro Laín Entralgo. La hipótesis inicial del estudio es que el concepto de amistad ha sido utilizado instrumentalmente por las redes sociales, y que estas no ofrecen las condiciones necesarias para la vivencia plena de la verdadera amistad. Para comprobarlo, nos centramos en el estudio de las dimensiones psicológicas de la amistad que propone el autor, identificando una serie de variables y realizando un análisis mediante una encuesta a estudiantes universitarios que son usuarios activos de la plataforma. Con estos resultados se extrajo la estadística descriptiva y se realizó un análisis no paramétrico de las variables para determinar si Facebook efectivamente ofrece las condiciones necesarias para la vivencia de la verdadera amistad en sus dimensiones psicológicas. Como muestran los resultados, la experiencia de la verdadera amistad en las redes sociales es difícil, dado que la naturaleza de las interacciones entre los usuarios de la plataforma no son las adecuadas para esta experiencia. Al llamar amistad a este tipo diferente de relación, Facebook se beneficia de un atractivo gancho que lleva a los usuarios a generar contactos como moneda de cambio que favorece el modelo de negocio de la plataforma de redes sociales. El concepto de verdadera amistad se altera, deforma y desplaza a favor de otro tipo de relaciones

On the combination of multi-cloud and network coding for cost-efficient storage in industrial applications

The adoption of both Cyber–Physical Systems (CPSs) and the Internet-of-Things (IoT) has enabled the evolution towards the so-called Industry 4.0. These technologies, together with cloud computing and artificial intelligence, foster new business opportunities. Besides, several industrial applications need immediate decision making and fog computing is emerging as a promising solution to address such requirement. In order to achieve a cost-efficient system, we propose taking advantage from spot instances, a new service offered by cloud providers, which provide resources at lower prices. The main downside of these instances is that they do not ensure service continuity and they might suffer from interruptions. An architecture that combines fog and multi-cloud deployments along with Network Coding (NC) techniques, guarantees the needed fault-tolerance for the cloud environment, and also reduces the required amount of redundant data to provide reliable services. In this paper we analyze how NC can actually help to reduce the storage cost and improve the resource efficiency for industrial applications, based on a multi-cloud infrastructure. The cost analysis has been carried out using both real AWS EC2 spot instance prices and, to complement them, prices obtained from a model based on a finite Markov chain, derived from real measurements. We have analyzed the overall system cost, depending on different parameters, showing that configurations that seek to minimize the storage yield a higher cost reduction, due to the strong impact of storage cost

Static and dynamic properties of a reversible gel

We study a microscopically realistic model of a physical gel and use computer simulations to investigate its static and dynamic properties at thermal equilibrium. The phase diagram comprises a sol phase, a coexistence region ending at a critical point, a gelation line, and an equilibrium gel phase unrelated to phase separation. The global structure of the gel is homogeneous, but the stress is supported by a fractal network. Gelation results in a dramatic slowing down of the dynamics, which can be used to locate the transition, which otherwise shows no structural signatures. Moreover, the equilibrium gel dynamics is highly heterogeneous as a result of the presence of particle families with different mobilities. An analysis of gel dynamics in terms of mobile and arrested particles allows us to elucidate several differences between the dynamics of equilibrium gels and that of glass-formers.Comment: 9 pages, 7 figures, paper presented at the 10th Granada Seminar on Computational and Statistical Physic

Investigation of consistency of juvenile surveys (e.g. JUVESAR, JUVENA, ECOCADIZ RECLUTAS) for potential future incorporation in the assessments

Evaluación de recursos marinos vivos en el área del ICESEVALICE