1,648 research outputs found
Determination of Solidification of Rigidity Point Temperature Using a New Method
This work aims to calculate the rigidity point temperature of aluminum alloys by three new methods and compare them with currently employed methods. The influence of major and minor alloying elements over the rigidity point temperature is also discussed. Until now it has been difficult to determine the exact temperature of the rigidity point, since small variations in the data obtained give variable results, making it difficult to automate the process with high accuracy. In this work we suggested three new mathematic methods based on the calculation of higher order derivatives of (dT/dt) with respect to time or temperature compared to those currently employed. A design of experiments based on the Taguchi method was employed to compare the effect of the major and minor alloying elements for the AlSi10Mg alloy, and to evaluate the accuracy of each developed method. Therefore, these systems will allow better automation of rigidity point temperature (RPT) determination, which is one of the most important solidification parameters for solidification simulators. The importance of the correct determination of this parameter lies in its relation to quality problems related to solidification, such as hot tearing. If the RPT presents very low-temperature values, the aluminum casting will be more sensitive to hot tearing, promoting the presence of cracks during the solidification process. This is why it is so important to correctly determine the temperature of the RPT. An adequate design of chemical composition by applying the methodology and the novel methods proposed in this work, and also the optimization of process parameters of the whole casting process with the help of the integrated computational modeling, will certainly help to decrease any internal defective by predicting one of the most important defects present in the aluminum industry.This research was partially funded by the Basque Government through the Etorgai Programme 2016, under the Filing Identification Number ZE-2016/00018 and the Elkartek Programme 2020, KK-2020-00047 for research, technological development and demonstration
Hausdorff dimension in -analytic profinite groups
We study the Hausdorff dimension of R-analytic subgroups in an R-analytic
profinite group, where R is a pro-p ring whose asso- ciated graded ring is an
integral domain. In particular, we prove that the set of such Hausdorff
dimensions is a finite subset of the rational numbers.Comment: 7 page
Solutions for New Terrestrial Broadcasting Systems Offering Simultaneously Stationary and Mobile Services
221 p.[EN]Since the first broadcasted TV signal was transmitted in the early decades of
the past century, the television broadcasting industry has experienced a series of
dramatic changes. Most recently, following the evolution from analogue to digital
systems, the digital dividend has become one of the main concerns of the
broadcasting industry. In fact, there are many international spectrum authorities
reclaiming part of the broadcasting spectrum to satisfy the growing demand of
other services, such as broadband wireless services, arguing that the TV services
are not very spectrum-efficient.
Apart from that, it must be taken into account that, even if up to now the
mobile broadcasting has not been considered a major requirement, this will
probably change in the near future. In fact, it is expected that the global mobile
data traffic will increase 11-fold between 2014 and 2018, and what is more, over
two thirds of the data traffic will be video stream by the end of that period.
Therefore, the capability to receive HD services anywhere with a mobile device is
going to be a mandatory requirement for any new generation broadcasting system.
The main objective of this work is to present several technical solutions that
answer to these challenges. In particular, the main questions to be solved are the
spectrum efficiency issue and the increasing user expectations of receiving high
quality mobile services. In other words, the main objective is to provide technical
solutions for an efficient and flexible usage of the terrestrial broadcasting spectrum
for both stationary and mobile services.
The first contributions of this scientific work are closely related to the study of
the mobile broadcast reception. Firstly, a comprehensive mathematical analysis of
the OFDM signal behaviour over time-varying channels is presented. In order to
maximize the channel capacity in mobile environments, channel estimation and
equalization are studied in depth. First, the most implemented equalization
solutions in time-varying scenarios are analyzed, and then, based on these existing
techniques, a new equalization algorithm is proposed for enhancing the receivers’
performance.
An alternative solution for improving the efficiency under mobile channel
conditions is treating the Inter Carrier Interference as another noise source.
Specifically, after analyzing the ICI impact and the existing solutions for reducing
the ICI penalty, a new approach based on the robustness of FEC codes is
presented. This new approach employs one dimensional algorithms at the receiver
and entrusts the ICI removing task to the robust forward error correction codes.
Finally, another major contribution of this work is the presentation of the
Layer Division Multiplexing (LDM) as a spectrum-efficient and flexible solution
for offering stationary and mobile services simultaneously. The comprehensive
theoretical study developed here verifies the improved spectrum efficiency,
whereas the included practical validation confirms the feasibility of the system and
presents it as a very promising multiplexing technique, which will surely be a strong
candidate for the next generation broadcasting services.[ES]Desde el comienzo de la transmisión de las primeras señales de televisión a
principios del siglo pasado, la radiodifusión digital ha evolucionado gracias a una
serie de cambios relevantes. Recientemente, como consecuencia directa de la
digitalización del servicio, el dividendo digital se ha convertido en uno de los
caballos de batalla de la industria de la radiodifusión. De hecho, no son pocos los
consorcios internacionales que abogan por asignar parte del espectro de
radiodifusión a otros servicios como, por ejemplo, la telefonía móvil, argumentado
la poca eficiencia espectral de la tecnología de radiodifusión actual.
Asimismo, se debe tener en cuenta que a pesar de que los servicios móviles no
se han considerado fundamentales en el pasado, esta tendencia probablemente
variará en el futuro cercano. De hecho, se espera que el tráfico derivado de
servicios móviles se multiplique por once entre los años 2014 y 2018; y lo que es
más importante, se pronostica que dos tercios del tráfico móvil sea video streaming
para finales de ese periodo. Por lo tanto, la posibilidad de ofrecer servicios de alta
definición en dispositivos móviles es un requisito fundamental para los sistemas de
radiodifusión de nueva generación.
El principal objetivo de este trabajo es presentar soluciones técnicas que den
respuesta a los retos planteados anteriormente. En particular, las principales
cuestiones a resolver son la ineficiencia espectral y el incremento de usuarios que
demandan mayor calidad en los contenidos para dispositivos móviles. En pocas
palabras, el principal objetivo de este trabajo se basa en ofrecer una solución más
eficiente y flexible para la transmisión simultánea de servicios fijos y móviles.
La primera contribución relevante de este trabajo está relacionada con la
recepción de la señal de televisión en movimiento. En primer lugar, se presenta un
completo análisis matemático del comportamiento de la señal OFDM en canales
variantes con el tiempo. A continuación, con la intención de maximizar la
capacidad del canal, se estudian en profundidad los algoritmos de estimación y
ecualización. Posteriormente, se analizan los algoritmos de ecualización más
implementados, y por último, basándose en estas técnicas, se propone un nuevo
algoritmo de ecualización para aumentar el rendimiento de los receptores en tales
condiciones.
Del mismo modo, se plantea un nuevo enfoque para mejorar la eficiencia de
los servicios móviles basado en tratar la interferencia entre portadoras como una
fuente de ruido. Concretamente, tras analizar el impacto del ICI en los receptores
actuales, se sugiere delegar el trabajo de corrección de dichas distorsiones en
códigos FEC muy robustos.
Finalmente, la última contribución importante de este trabajo es la
presentación de la tecnología LDM como una manera más eficiente y flexible para
la transmisión simultánea de servicios fijos y móviles. El análisis teórico presentado
confirma el incremento en la eficiencia espectral, mientras que el estudio práctico
valida la posible implementación del sistema y presenta la tecnología LDM c
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E-xcellence methodology: lessons learned over ten years of development and implementation
The E xcellence methodology for quality assurance of e learning in higher education has developed into a flexible and effective approach to quality assurance. It has proved suitable to meet the needs of a diverse range of institutions and national quality assurance regimes, and is applicable to both distance and blended modes. The E xcellence resources (http://e-xcellencelabel.eadtu.eu/) include a quality manual, guidance for institutions and assessors, and an online Quick Scan self-evaluation tool. The manual was updated in 2012 and 2016 to reflect evolving changes in practice.
The E-xcellence methodology provides 35 benchmark statements, grouped under six headings: Strategic Management, Curriculum Design, Course Design, Course Delivery, Staff Support and Student Support. Higher education institutions self-assess their capabilities against each of the benchmark statements on a four-point scale. They also prepare a roadmap of future actions which can be mapped to benchmark statements. A visit by external reviewers enriches and complements the self-assessment.
This study is based on an analysis of E xcellence self-evaluations and roadmaps at twenty higher education institutions. Tabulating those benchmarks that are rated as not yet adequate, and those which attract the most planned actions, highlights the aspects that institutions have found most challenging as they develop and implement online and blended learning programmes.
This profiling exercise indicates that institutions regard issues of strategy, curriculum design and staff support as presenting the greatest challenges. Particular problems include staff workload and developing an online academic community for students. In contrast, the provision of reliable IT systems and hardware is unproblematic
Use of the harmonic phase in synthetic speech detection
Special Session paper: recent PhD thesis descriptionThis PhD dissertation was written by Jon Sanchez and supervised by Inma Hernáez and Ibon Saratxaga. It was defended at the University of the Basque Country the 5th of February 2016. The committee members were Dr. Alfonso Ortega Giménez (UniZar), Dr. Daniel Erro Eslava (UPV/EHU) and Dr. Enric Monte Moreno (UPC). The dissertation was awarded a "sobresaliente cum laude” qualification.This work has been partially funded by the Spanish Ministry of Economy and Competitiveness with FEDER support (RESTORE project,TEC2015-67163-C2-1-R) and the Basque Government (ELKAROLA project, KK-2015/00098)
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