604 research outputs found
The Concept of the Universe in Physical Cosmology
The concept of the universe is used in physical cosmology diferently from the usual meaning of the term, naively considered as the entire reality. Traditionally, thinking about the whole led to logical contradictions. Taking as reference the Kantian antecedent, diferent contemporary philosophical notions of the universe are analysed in the frst part of this paper, including realist and constructivist approaches, as well as a notion of the universe as a physical object. In the second part, the specifc notion from the standard physical cosmology is discussed. Although modelling the universe as a physical system provides a specifc way to defne some global properties, the universe as a whole remains empirically inaccessible. Hence, the discussion about the under-determined global properties depends ultimately on philosophical preferences. Under these circumstances, it is argued that the realist interpretation of such properties becomes problematic because it leads to unstable conclusions. Finally, it is argued that the notion of the universe as conceived in standard cosmology is not necessarily consistent with an approach that considers it to be a physical object.Partial fnancial support for this study was provided by the Spanish Agencia Estatal de Investigación (AEI, MICIU) under the Project with Reference ESP2017-83921-C2-1-R, co-funded with EU FEDER funds
On the void explanation of the Cold Spot
The integrated Sachs-Wolfe (ISW) contribution induced on the cosmic microwave
background by the presence of a supervoid as the one detected by Szapudi et al.
(2015) is reviewed in this letter in order to check whether it could explain
the Cold Spot (CS) anomaly. Two different models, previously used for the same
purpose, are considered to describe the matter density profile of the void: a
top hat function and a compensated profile produced by a Gaussian potential.
The analysis shows that, even enabling ellipticity changes or different values
for the dark-energy equation of state parameter , the ISW contribution
due to the presence of the void does not reproduce the properties of the CS.
Finally, the probability of alignment between the void and the CS is also
questioned as an argument in favor of a physical connection between these two
phenomena
Notas corológicas de la provincia de Jaén. III. "Juncaceae"
Se presenta un catálogo de las especies de la familia Juncaceae existentes en la provincia de Jaén (España), que incluye 21 táxones, 6 de los cuales son primera cita provincial.In this paper we present a catalogue of Juncaceae species from the province of Jaén (S. E. Spain) wich includes 21 taxa, 6 are new in the zone
Graphene Based Poly(Vinyl Alcohol) Nanocomposites Prepared by In Situ Green Reduction of Graphene Oxide by Ascorbic Acid: Influence of Graphene Content and Glycerol Plasticizer on Properties
The enhanced properties of polymer nanocomposites as compared with pure polymers are only achieved in the presence of well-dispersed nanofillers and strong interfacial adhesion. In this study, we report the preparation of nanocomposite films based on poly(vinyl alcohol) (PVA) filled with well dispersed graphene sheets (GS) by in situ reduction of graphene oxide (GO) dispersed in PVA solution using ascorbic acid (L-AA) as environmentally friendly reductant. The combined effect of GS content and glycerol as plasticizer on the structure, thermal, mechanical, water absorption, and water barrier properties of PVA/GS nanocomposite films is studied for the first time. Higher glass transition temperature, lower crystallinity, melting, and crystallization temperature, higher mechanical properties, and remarkable improvement in the thermal stability compared to neat PVA are obtained as a result of strong interfacial interactions between GS and PVA by hydrogen bonding. PVA/GS composite film prepared by ex situ process is more brittle than its in situ prepared counterpart. The presence of GS improves the water barrier and water resistance properties of nanocomposite films by decreasing water vapor permeability and water absorption of PVA. This work demonstrates that the tailoring of PVA/GS nanocomposite properties is enabled by controlling GS and glycerol content. The new developed materials, particularly those containing plasticizer, could be potential carriers for transdermal drug delivery.SAIOTEK 2013 S-PE13UN004 Basque Governmen
Aprendizaje, simulación y desarrollo sobre las tecnologÃas de voz y datos
El objetivo del Proyecto Fin de Carrera (PFC) es el de conocer, simular y crear una red VoIP sobre una red de datos en un entorno docente, más concretamente, en la asignatura Redes y Servicios de telecomunicación en Grado en IngenierÃa de Telecomunicaciones en la Universidad Politécnica de Madrid (UPM). Una vez se adquieran los conocimientos necesarios, se propondrán una serie de prácticas para que los alumnos se vayan familiarizando con el software y hardware utilizados, de manera que, se irá subiendo el grado de dificultad hasta que puedan realizar una auténtica red VoIP por sà mismos. A parte de la realización de las prácticas, los alumnos deberán pasar una prueba de los conocimientos adquiridos al final de cada práctica mediante preguntas tipo test.
Los sistemas elegidos para la implantación de una red VoIP en los módulos de laboratorio son: 3CX System Phone y Asteisk-Trixbox. Los cuales, son capaces de trabajar mediante gestores gráficos para simplificar el nivel de dificultad de la configuración.
3CX es una PBX que trabaja sobre Windows y se basa exclusivamente en el protocolo SIP. Esto facilita el manejo para usuarios que solo han usado Windows sin quitar funcionalidades que tienen otras centralitas en otros sistemas operativos. La versión demo activa todas las opciones para poder familiarizarse con este sistema.
Por otro lado, Asterisk trabaja en todas las plataformas, aunque se ha seleccionado trabajar sobre Linux. Esta selección se ha realizado porque el resto de plataformas limitan la configuración de la IP PBX, esta es de código abierto y permite realizar todo tipo de configuraciones. Además, es un software gratuito, esto es una ventaja a la hora de configurar novedades o resolver problemas, ya que hay muchos especialistas que dan soporte y ayudan de forma gratuita.
La voz sobre Internet es habitualmente conocida como VoIP (Voice Over IP), debido a que IP (Internet Protocol) es el protocolo de red de Internet. Como tecnologÃa, la VoIP no es solo un paso más en el crecimiento de las comunicaciones por voz, sino que supone integrar las comunicaciones de datos y las de voz en una misma red, y en concreto, en la red con mayor cobertura mundial: Internet.
La mayor importancia y motivación de este Proyecto Fin de Carrera es que el alumno sea capaz de llegar a un entorno laboral y pueda tener unos conocimientos capaces de afrontar esta tecnologÃa que esta tan a la orden del dÃa. La importancia que estas redes tienen y tendrán en un futuro muy próximo en el mundo de la informática y las comunicaciones. Cabe decir, que se observa que estas disciplinas tecnológicas evolucionan a pasos agigantados y se requieren conocimientos más sólidos.
ABSTRACT.
The objective of my final project during my studies in university was, to simulate and create a VoIP network over a data network in a teaching environment, more specifically on the subject of telecommunications networks and services in Telecommunication Engineering Degree in Polytechnic University of Madrid (UPM). Once acquiring the necessary knowledge a number of practices were proposed to the students to become familiar with the software and hardware used, so that it would rise to the level of difficulty that they could make a real VoIP network for themselves. Parts of the experimental practices were that students must pass a test of knowledge acquired at the end of each practice by choice questions.
The systems chosen for the implementation of a VoIP network in the laboratory modules are: 3CX Phone System and Asteisk - Trixbox. Which were able to work with graphics operators to simplify the difficulty level of the configuration.
3CX is a PBX that works on Windows and is based solely on the SIP protocol. This facilitates handling for users who have only used Windows without removing functionality with other exchanges in other operating systems. Active demo version all options to get to grips with this system.
Moreover, Asterisk works on all platforms, but has been selected to work on Linux. This selection was made because other platforms limit the IP PBX configuration, as this is open source and allows all kinds of configurations. Also, Linux is a free software and an advantage when configuring new or solve problems, as there are many specialists that support and help for free.
Voice over Internet is commonly known as VoIP (Voice Over IP), because IP (Internet Protocol) is the Internet protocol network. As technology, VoIP is not just another step in the growth of voice communications, but communications of integrating data and voice on a single network, and in particular, in the network with the largest global coverage: Internet.
The increased importance and motivation of this Thesis is that the student is able to reach a working environment and may have some knowledge to deal with these technologies that is so much the order of the day. The importances of these networks have and will be of essences in the very near future in the world of computing and communications. It must be said it is observed that these technological disciplines evolve by leaps and bounds stronger knowledge required
Exploring two-spin internal linear combinations for the recovery of the CMB polarization
We present a methodology to recover cosmic microwave background (CMB)
polarization in which the quantity is linearly combined at
different frequencies using complex coefficients. This is the most general
linear combination of the and Stokes parameters which preserves the
physical coherence of the residual contribution on the CMB estimation. The
approach is applied to the internal linear combination (ILC) and the internal
template fitting (ITF) methodologies. The variance of of the resulting map
is minimized to compute the coefficients of the linear combination. One of the
key aspects of this procedure is that it serves to account for a global
frequency-dependent shift of the polarization phase. Although in the standard
case, in which no global E-B transference depending on frequency is expected in
the foreground components, minimizing is
similar to minimizing and separately (as previous methodologies proceed), multiplying
and by different coefficients induces arbitrary changes in the
polarization angle and it does not preserve the coherence between the spinorial
components. The approach is tested on simulations, obtaining a similar residual
level with respect to the one obtained with other implementations of the ILC,
and perceiving the polarization rotation of a toy model with the frequency
dependence of the Faraday rotation.Comment: 14 pages, 8 figures, 2 tables. Accepted for publication in MNRA
Using Mobile Devices for Improving Learning Outcomes and Teachers’ Professionalization
Teaching in higher education is changing due to the influence of technology. More and more
technological tools are replacing old teaching methods and strategies. Thus, mobile devices are being
positioned as a key tool for new ways of understanding educational practices. The present paper
responds to a systematic review about the benefits that mobile devices have for university students’
learning. Using inclusion and exclusion criteria in theWeb of Science and Scopus databases, 16 articles
were selected to argue why Mobile learning (Mlearning) has become a modern innovative approach.
The results point to an improvement in students’ learning through Mlearning, factors that encourage
the use of mobile devices in universities have been identified, and e ective mobile applications in
improving teaching and learning processes have been presented. The inclusion of this methodology
requires a new role for teachers, whose characterization is also specified
Searching for a dipole modulation in the large-scale structure of the Universe
Several statistical anomalies in the CMB temperature anisotropies seem to
defy the assumption of a homogeneous and isotropic universe. In particular, a
dipole modulation has been detected both in WMAP and Planck data. We adapt the
methodology proposed by Eriksen et al. (2007) on CMB data to galaxy surveys,
tracing the large-scale structure. We analyse the NRAO VLA Sky Survey (NVSS)
data at a resolution of ~2 degrees for three different flux thresholds: 2.5,
5.0 and 10.0 mJy respectively. No evidence of a dipole modulation is found.
This result suggests that the origin of the dipole asymmetry found in the CMB
cannot be assigned to secondary anisotropies produced at redshifts around z =
1. However, it could still have been generated at redshifts higher or lower,
such as the integrated Sachs-Wolfe effect produced by the local structures.
Other all-sky surveys, like the infrared WISE catalogue, could help to explore
with a high sensitivity a redshift interval closer than the one probed with
NVSS.Comment: 6 pages, 2 figures. Some minor changes have been done from the
original manuscript. This paper is accepted by MNRA
Water as a scarce natural resource and streamlining its use for irrigation
Se hacen algunas reflexiones acerca del agua como recurso escaso que es en el ámbito
planetario, asà como sus principales usos, entre los que destaca el regadÃo.
Tanto en España como en AndalucÃa los usos del agua para riego son los más importantes,
pero lo que se ha pretendido destacar es su irracionalidad, puesto que en un porcentaje
importante de las hectáreas con regadÃo, estas no generan valor añadido para pagar el coste
del agua puesto en la parcela.
Como el agua para riego se subvenciona en general y en un porcentaje muy importante,
se producen problemas, ya sea, de escasez del recurso, de despilfarro por un consumo
mayor al no instalar sistemas de riego que consumen menos agua, y de contaminación de
los acuÃferos.
En el artÃculo se hace finalmente una reflexión acerca del ahorro de este recurso que
se producirÃa si lo gestionamos mejor, y si de verdad acabamos implantando la Directiva
Marco del Agua.This paper offers a critical overview of water, a scarce resource on our planet, and its
main uses, predominantly for agricultural purposes. Both in Spain and in AndalucÃa, the major
part of our water resources are used for irrigation. Yet there are irrational aspects of this use,
as a very considerable proportion of the hectares being irrigated do not yield any additional
value that would compensate the cost of the water destined to that terrain.
Given that irrigation water is subsidized in general, when its use is problematic, we
must address issues such as the scarcity of hydric resources, the wastefulness of excessive
consumption without installing irrigation systems to consume less water, and the contamination
of aquifers.
Some final reflections are concerned with the protection of water resources and their
improved management, including our real adherence to the Water Framework Directive
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