A mechanism for fast radio bursts

Fast radio bursts are mysterious transient sources likely located at cosmological distances. The derived brightness temperatures exceed by many orders of magnitude the self-absorption limit of incoherent synchrotron radiation, implying the operation of a coherent emission process. We propose a radiation mechanism for fast radio bursts where the emission arises from collisionless Bremsstrahlung in strong plasma turbulence excited by relativistic electron beams. We discuss possible astrophysical scenarios in which this process might operate. The emitting region is a turbulent plasma hit by a relativistic jet, where Langmuir plasma waves produce a concentration of intense electrostatic soliton-like regions (cavitons). The resulting radiation is coherent and, under some physical conditions, can be polarised and have a power-law distribution in energy. We obtain radio luminosities in agreement with the inferred values for fast radio bursts. The timescale of the radio flare in some cases can be extremely fast, of the order of $10^{-3}$ s. The mechanism we present here can explain the main features of fast radio bursts and is plausible in different astrophysical sources, such as gamma-ray bursts and some Active Galactic Nuclei.Comment: 6 pages, 1 figure. Accepted for publication in Phys. Rev.

Effective penetration length and interstitial vortex pinning in superconducting films with regular arrays of defects

In order to compare magnetic and non-magnetic pinning we have nanostructured two superconducting films with regular arrays of pinning centers: Cu (non-magnetic) dots in one case, and Py (magnetic) dots in the other. For low applied magnetic fields, when all the vortices are pinned in the artificial inclusions, magnetic dots prove to be better pinning centers, as has been generally accepted. Unexpectedly, when the magnetic field is increased and interstitial vortices appear, the results are very different: we show how the stray field generated by the magnetic dots can produce an effective reduction of the penetration length. This results in strong consequences in the transport properties, which, depending on the dot separation, can lead to an enhancement or worsening of the transport characteristics. Therefore, the election of the magnetic or non-magnetic character of the pinning sites for an effective reduction of dissipation will depend on the range of the applied magnetic field.Comment: 10 pages, 3 figure

"Aproximaciones teóricas desde la situación universitaria para establecer el deber ser"

La necesidad de dirigir la formación de profesionales universitarios y de egresados de los diferentes niveles de educación, en general, constituye un problema que se plantea la Universidad en distintas partes del mundo, independientemente de las condiciones económicas, políticas e ideológicas de determinado país. Sabemos que la sociedad invierte importantes recursos en la formación de profesionales a los cuales exige la idoneidad necesaria para responder a los retos propios del campo en el cual se desempeñan. Puesto que actualmente en el mundo el conocimiento es la principal fuerza productiva, ninguna sociedad puede eximirse de la formación de una masa crítica de intelectuales en los distintos campos.. No se trata sólo de responder a los retos específicos planteados en las distintas áreas de formación profesional; también se requiere un intenso trabajo cultural para promover el análisis informado y crítico de los problemas por parte de la población. El futuro de la sociedad depende de manera sustancial del conocimiento y la responsabilidad de los egresados de la educación superior."Llegado a este punto, conviene reafirmar que la posibilidad de producir cambios en las instituciones universitarias requiere detenerse en la práctica política y en la práctica administrativa. Recuperar la relación entre la política universitaria y cambio deseado, es imprescindible para que la transformación sea el resultado del ethos común de la comunidad universitaria y de la sociedad y no el mero resultado de la tecnoburocracia reformista que la sujeta a un estricto sistema de regulación con respecto al mercado y a esquemas autoritarios de imposición desde el Estado." La cuestión más importante de la Universidad actual es su adaptación a los cambios que la sociedad le exige, tanto en relación a las enseñanzas que imparte como a la investigación que realiza y las acciones de extensión y/o servicios. Una adaptación de este tipo no ha sido nunca fácil para la Universidad y, casi siempre, los cambios en ella se han producido tras un periodo de crisis más o menos profunda de nuestra institución

Superconducting/magnetic three state nanodevice for memory and reading applications

We present a simple nanodevice that can operate in two modes: i) three-state memory and ii) reading device. The nanodevice is fabricated with an array of ordered triangular-shaped nanomagnets embedded in a superconducting thin film. The input signal is ac current and the output signal is dc voltage. Vortex ratchet effect in combination with out of plane magnetic anisotropy of the nanomagnets is the background physics which governs the nanodevice performance.Comment: 10 pages, 4 figure

Evolució de la superfície protegida dels espais Naturals de les Illes Pitiüses (Eivissa i Formentera)

[cat] La gran biodiversitat i l'excepcional patrimoni natural de les Pitiüses, fa necessari el seu coneixement i conservació per determinar les necessitats de gestió i protecció, i d'aquesta manera garantir el seu futur. L'objectiu principal d'aquest estudi és l'anàlisi de l'evolució de la superfície protegida dels espais naturals de les illes Pitiüses i les anàlisis dels canvis de l'ocupació del sòl a la franja del primer quilòmetre de costa. El seu coneixement resulta clau per tal de plantejar la planificació i gestió dels espais naturals de les Pitiüses de cara al futur, tot tenint en compte que la pèrdua de biodiversitat és un dels principals problemes ecològics a escala planetària. La superfície inclosa a la Xarxa Natura 2000 (marina i terrestre) era de 32.137,77 ha el 2013 i aquestes augmentaren notablement el 2014 amb la incorporació de l'espai marí de Formentera i del Sud d'Eivissa (47.026,14 ha), de l'espai marí de Ponent i Nord d'Eivissa (47.162,02 ha) i de l'espai marí del Llevant d'Eivissa (19.158,84 ha). Nogensmenys, per a una adequada conservació es fa necessari l’aplicació de plans de gestió a cadascun dels espais naturals protegits i aquest aspecte ha resultat històricament un dels més problemàtics.[eng] The Pityusic Islands host an exceptional natural heritage and biodiversity. Knowledge of biodiversity is crucial in order to determine the management and protection needs and in this way guarantee its future conservation. The main objective of this study is the analysis of the evolution of natural protected areas of Eivissa and Formentera, as well as the analysis of land cover in the coastal strip of the first kilometer. Since biodiversity loss is one of the main global ecological problems, this knowledge is fundamental for future planning and management of the natural areas of the Pityusics. In 2013, the area included in the Natura 2000 Network (marine and terrestrial) was 32,137.77 ha, which increased notably in 2014 with the incorporation of the marine area of Formentera and South of Eivissa (47,026.14 ha), the marine area of West and North of Eivissa (47,162.02 ha) and the marine area of the East of Eivissa (19,158.84 ha). Nonetheless, despite the expansion of protected areas, management plans are essential for their correct conservation and this issue has been historically troublesome

Dynamics of formation and decay of coherence in a polariton condensate

We study the dynamics of formation and decay of a condensate of microcavity polaritons. We investigate the relationship between the number of particles, the emission's linewidth and its degree of linear polarization which serves as the order parameter. Tracking the condensate's formation, we show that, even when interactions are negligible, coherence is not determined only by occupation of the ground state. As a result of the competition between the coherent and thermal fractions of the condensate, the highest coherence is obtained some time after the particle number has reached its maximum

High-energy radiation from collisions of high-velocity clouds and the Galactic disc

High-velocity clouds (HVCs) are interstellar clouds of atomic hydrogen that do not follow normal Galactic rotation and have velocities of a several hundred kilometres per second. A considerable number of these clouds are falling down towards the Galactic disc. HVCs form large and massive complexes, so if they collide with the disc a great amount of energy would be released into the interstellar medium. The cloud-disc interaction produces two shocks: one propagates through the cloud and the other through the disc. The properties of these shocks depend mainly on the cloud velocity and the disc-cloud density ratio. In this work, we study the conditions necessary for these shocks to accelerate particles by diffusive shock acceleration and we study the non-thermal radiation that is produced. We analyse particle acceleration in both the cloud and disc shocks. Solving a time-dependent two-dimensional transport equation for both relativistic electrons and protons, we obtain particle distributions and non-thermal spectral energy distributions. In a shocked cloud, significant synchrotron radio emission is produced along with soft gamma rays. In the case of acceleration in the shocked disc, the non-thermal radiation is stronger; the gamma rays, of leptonic origin, might be detectable with current instruments. A large number of protons are injected into the Galactic interstellar medium, and locally exceed the cosmic ray background. We conclude that under adequate conditions the contribution from HVC-disc collisions to the galactic population of relativistic particles and the associated extended non-thermal radiation might be important.Facultad de Ciencias Astronómicas y Geofísica

Using the strategic relative alignment index for the selection of portfolio projects application to a public Venezuelan Power Corporation

In this paper a new approach that uses the alignment of projects with corporate strategic objectives to prioritize project portfolio in an efficient and reliable way is presented. For this purpose, corporate strategic objectives will be used as prioritization criteria to obtain the Relative Alignment Index (RAI) of each project which indicates how close or far each project is from the strategic objectives of the company. The approach presented uses the Analytic Network Process. This technique allows considering the influences among all the elements within the network, that means, the strategic objectives, and specially the projects within a portfolio. The proposed RAI index helps to select the best strategically aligned projects for the organization. The proposed RAI index and its form of evaluation have not previously been considered in the project portfolio literature until now. The research methodology for the development of RAI is based on a combination of a synthesis of the literature across the diverse fields of project management, project alignment, multicriteria decision methods and a parallel analysis of an industrial case study. The use of the proposed RAI index is demonstrated using a rigorous methodology with acceptable complexity which seeks to assist managers of the National Electricity Corporation of Venezuela, recently founded and composed by 13 merging old companies, both public and private, in their yearly resources' assignment on their projects portfolio. The aim being to determine a projects 'ranking based on their degree of alignment to corporate strategy and on the judgments of a group of experts, such as the management board. The new corporation assumed the challenge of setting strategic directions (Mission, Vision, Values, Strategic objectives, Plans, Programs, etc.) common to all merging companies. This approach with multi-stakeholders support allows managers to strategically allocate resources to each project in a consensual way.García-Melón, M.; Poveda Bautista, R.; Del Valle, JL. (2015). Using the strategic relative alignment index for the selection of portfolio projects application to a public Venezuelan Power Corporation. International Journal of Production Economics. 170:54-66. doi:10.1016/j.ijpe.2015.08.023S546617

Using alignment with corporate strategy for the selection of a project portfolio based on ANP

Trabajo presentado al 14th International Symposium on the Analytic Hierarchy Process celebrado en Washington (US) del 29 de junio al 2 de julio de 2014.In this paper a new approach to prioritize project portfolio in an efficient and reliable way is presented. The research methodology is based on a combination of a synthesis of the literature across the diverse fields of project management, project alignment, multicriteria decision methods and a parallel analysis of an industrial case study. The paper introduces a rigorous methodology with acceptable complexity which seeks to assist managers of the National Electricity Corporation of Venezuela (Corpoelec) in their yearly resources' assignment on their projects portfolio. The aim being to determine the degree of alignment of each project to corporate strategy based on the judgments of a group of experts on the expected contribution of the projects to the business strategic objectives. The model presented can be used both as a descriptive and a prescriptive model. The approach presented uses project prioritization based on the multi-criteria decisionmaking technique called Analytic Network Process. Thus the corporate strategic objectives will be used as prioritization criteria to obtain the Relative Alignment Index (RAI).Peer Reviewe

The Cambrian-Ordovician siliciclastic platform of the Balcarce Formation (Tandilia System, Argentina) : Facies, trace fossils, palaeoenvironments and sequence stratigraphy

The Lower Palaeozoic sedimentary cover of the Tandilia (Balcarce Formation) is made up of thick quartz arenite beds together with kaolinitic claystones and thin fine-grained conglomerates. The Balcarce Formation was formed in the nearshore and inner shelf environments of a tide-dominated and storm influenced open platform. It shows many features suggesting tidal sedimentation. Coarse-grained facies were formed by sand bar migration and accretion. Heterolithic packages are interpreted as interbar (swale) deposits. Subordinated HCS sandstones indicate storm events. The recognition of thick progradational clinoforms allows to confirm that the Balcarce sea was open to the south, as suggested years ago through palaeocurrent interpretation. The great abundance and variety of trace fossils is among the most outstanding characteristics of this unit. The ichnotaxa that have been recognised so far are: Ancorichnus ancorichnus, Arthrophycus alleghaniensis, Arthrophycus isp., Bergaueria isp., Cochlichnus isp., Conostichus isp., Cruziana furcifera, Cruziana isp., Daedalus labeckei, Didymaulichnus lyelli, Didymaulichnus isp., Diplichnites isp., Diplocraterion isp., Herradurichnus scagliai, ?Monocraterion isp., Monomorphichnus isp., Palaeophycus alternatus, Palaeophycus tubularis, Palaeophycus isp., Phycodes aff. pedum, Phycodes isp., Plagiogmus isp., Planolites isp., Rusophycus isp., Scolicia isp. and Teichichnus isp. Trace fossils have traditionally been used to assign the Balcarce Formation to the Lower Ordovician, due to the presence of Cruziana furcifera. However, Plagiogmus is typical of Cambrian successions world-wide