139,651 research outputs found
Luján y Avellaneda: ¿impostores o creadores?
No full textEl Guzmán y el Quijote tienen la peculiaridad de haber dado lugar, en la primera mitad del siglo xvii, a una multiplicidad de prolongaciones literarias, ora alógrafas, ora autógrafas. De hecho, estas dos obras seminales han sido el punto de partida de una auténtica sucesión de «continuaciones encadenadas». No cabe duda de que habría mucho que decir acerca de las influencias mutuas entre las Segundas partes alógrafas y autógrafas de ambas obras; pero en el marco de este artículo me centraré en..
Bancos de prueba para la caracterización de dispositivos no lineales de una y dos entradas utilizando multitonos y señales moduladas
No full textIn a mobile communication system, the RF amplifier is the element with the highest power consumption and which introduces unwanted spectral components in the signal to be transmitted. Its design must provide the highest possible efficiency, and reduce non-linearities to guarantee power levels in adjacent channels that do not generate interference and loss of information. In this work a test bench is proposed to evaluate the linearity of them and transistors using continuous and multitone signals. A radio frequency daughter card and universal radio software peripheral are used to generate the baseband tones, and the vector network analyzer is used to measure incident and reflected waves at the input and output of the device under test. Their linearity are inspected under different load and source impedances. The measurement system is a calibrated real-time load-pull capable of obtaining the phase and amplitude of the device’s gain in large signal for any impedance. A graphical interface was created in Matlab for the control and programming of the test bench instruments, facilitating the characterization of these devices. Dissimilar power amplifier configurations have been proposed in the literature to provide high efficiency between backoff and peak powers. Essential in modern transmission systems, which work with modulated signals that have a high value of the peak to average power ratio. For the rapid characterization of baseband signals and the linearization of non-linear multiport devices, a calibrated test bench based on a commercial vector network analyzer is proposed for the first time. This allows the acquisition of continuous and periodic wideband modulated signals without breaking contact with the device, in up to five channels. Time domain measurements are possible by calibrating all receivers in the frequency domain. This calibration provides amplitude and phase corrections for the modulation tones of all incident and reflected waves in the acquisition bandwidth. An orthogonal frequency division multiplexing signal known, is used as phase standard. The IQ constellation is recovered from a signal of 500 MHz bandwidth, 100 000 tones and modulated with a 64 QAM OFDM scheme, with an error vector magnitude of 0.48%. As application, a two-input, one-output power amplifier in a hybrid Doherty-Chireix configuration is characterized at 2.08 GHz. A continuous wave signal is used to determine the phase difference between the input ports and the power levelEn un sistema de comunicaciones móviles, el amplificador de RF es el elemento de mayor consumo de potencia y el cual introduce componentes espectrales no deseadas en la señal a transmitir. Su diseño debe proveer la mayor eficiencia posible, y disminuir las no linealidades para garantizar niveles de potencia en canales adyacentes que no generen interferencia y pérdidas de la información. En este trabajo se propone un banco de pruebas para evaluar la linealidad del mismo y de transistores utilizando señales continuas y multitono. Se utiliza una tarjeta secundaria de radiofrecuencia y un periférico universal de software de radio, para generar los tonos en banda base, y el analizador de redes vectoriales para medir las ondas incidentes y reflejadas en la entrada y salida del dispositivo bajo prueba. Se inspecciona la linealidad de los mismos bajo distintas impedancias de carga y fuente. El sistema de medición es un load-pull en tiempo real calibrado y capaz de obtener la fase y amplitud de la ganancia del dispositivo en gran señal para cualquier impedancia. Se realizó una interfaz gráfica en Matlab para el control y programación de los instrumentos del banco de prueba, facilitando la caracterización de estos dispositivos. Dísimiles configuraciones de amplificadores de potencia han sido propuestos en la literatura para proveer una alta eficiencia entre potencias de backoff y pico. Esencial en los sistemas de transmisión modernos, que trabajan con señales moduladas que presentan un valor elevado de relación de potencia pico a potencia promedio. Para la caracterización rápida de señales en banda base y la linealización de dispositivos multipuerto no lineales se propone por primera vez un banco de pruebas calibrado basado en un analizador de redes vectorial comercial. Este, permite adquirir señales continuas y periódicas moduladas de banda ancha sin romper contacto con el dispositivo, en hasta cinco canales. Las mediciones en el dominio del tiempo son posibles calibrando todos los receptores en el dominio de la frecuencia. Esta calibración proporciona una corrección de fase y amplitud para los tonos de modulación de todas las ondas incidentes y reflejadas en el ancho de banda de adquisición. Se emplea una señal de multiplexación por división de frecuencia ortogonal conocida como estándar de fase. Se recupera la constelación IQ de una señal de 500 MHz de ancho de banda, 100 000 tonos y modulada con un esquema 64 QAM OFDM, obteniendo una magnitud de vector de erro
La escritura inacabada. Continuaciones literarias y creación en España. Siglos XIII a XVII.
No full textInternational audiencePropiciadas por el desarrollo de la imprenta, las continuaciones literarias conocen en la España de la Edad Clásica un verdadero auge que afecta a todos los ámbitos de la ficción. Sin embargo, este fenómeno no es totalmente nuevo puesto que durante la Edad Media cualquier elaboración literaria se centraba en la reutilización y continuación de textos ajenos. Sin hacer caso omiso de esta herencia medieval, este libro trata de especificar la noción de continuación para la época moderna considerándola como una modalidad peculiar del préstamo. Situándose por encima de las fronteras genéricas, ofrece un estudio de conjunto de esta práctica proponiendo una arqueología de la misma y tomando en cuenta la dimensión creativa que conllevan las obras correspondientes
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
Characteristics of overlap region in high-Reynolds number turbulent channel flow
No full textDirect numerical simulation of the fully developed turbulent channel flows have been carried out at the Reynolds number based on the friction velocity and the channel half width, 2000, 4000 and 8000. A hybrid 10th order accurate finite difference scheme in the stream and spanwise directions, and a second-order scheme in the wall-normal direction is adapted as the spatial discretization method. We observed the plateau profiles in the indicator function corresponded to the von Karman constant. Furthermore, second peak of streamwise pre-multiplied spectra were appeared in the same wall normal height, 300 < y+ < 600, in case of Re = 4000. Nevertheless, the effects of the lager than the channel half height scale on the streamwise turbulent intensity are fixed contributions without dependence on Reynolds number. These results suggested that the new streamwise vortexes are formed between buffer layer and outer layer with increasing of Reynolds number
La 'circunstancia' de 'Herederos y Pretendientes
No full textIn June 2010, the Ortega y Gasset Foundation hosted a Conference about the “Spanish Philosophical Transition” in order to debate the book of Francisco Vázquez, La filosofía española. Herederos y Pretendientes. Una lectura sociológica (1963-1990), recently published. This paper is the author’s response to criticism raised in the Conference and to published reviews received by this book. First, the author summarized the argument of Herederos y pretendientes. Secondly he responds and takes into account the most important objections against the book’s hypothesis and methodology. Finally the author evaluates the favorable judgments received by the book and suggests the limits of the historian’s task.Fundación Ortega y Gasset-Marañó
Author self-citation in orthodontics is associated with author origin and gender.
No full textBACKGROUND
The aims of this bibliometric study were to determine author self-citation trends in high-impact orthodontic literature and to investigate possible association between self-citation and publication characteristics.
METHODS
Six orthodontic journals with the highest impact factor as ranked by 2017 Journal Citation Reports were screened for a full publication year (2018) for original research articles, reviews, and case reports. Eligible articles were scrutinized for article and author characteristics and citation metrics. Univariable and multivariable negative binomial regression was used to examine associations between self-citation incidence and publication characteristics.
RESULTS
Medians for author self-citation rate of the most self-citing authors and self-citations were 3.03% (range 0-50) and 1 (range 0-19), respectively. In the univariable analysis, there was no association between self-citation counts and study type (P = 0.41), article topic (P = 0.61), number of authors (P = 0.62), and rank of authors (P = 0.56). Author origin (P = 0.001), gender (P = 0.001) and journal (P = 0.05) were associated with self-citation counts and in the multivariable analysis only origin and gender remained strong self-citation predictors. Asian authors and females self-cited significantly less often than all other regions and male authors.
CONCLUSIONS
Authors in orthodontics do not self-cite at a frequency that suggests potential citation manipulation. Author origin and gender were the only variables associated with citations counts. More bibliometric research is necessary to draw solid conclusions about author self-citation trends in orthodontic literature
Modeling of microwave transistors using artificial neural networks
No full textExiste un voraz interés en modelos precisos de transistores para el diseño de amplificadores de potencia de RF y microondas. Básicamente los modelos de transistores pueden ser divididos en modelos físicos y empíricos. Los modelos físicos son muy precisos, y como lo indica su nombre, están basados en las características físicas del dispositivo tales como longitud de compuerta, ancho del canal, campo eléctrico, carga y movilidad del electrón, etc. Por otro lado, los modelos empíricos están basados en mediciones, son más sencillos de desarrollar y son computacionalmente eficientes. El HEMT de AlGaN/GaN es un excelente candidato para ser usado como dispositivo activo en amplificadores de potencia (AP). Tiene una alta densidad de carga y alta velocidad de saturación, lo cual produce altos niveles de potencia de salida. Asimismo, tiene alta movilidad del electrón originando una baja resistividad de encendido, por consiguiente, se pueden obtener altos niveles de eficiencia de potencia agregada. Además, se pueden alcanzar altos voltajes de ruptura como resultado de su amplia banda prohibida, con una alta densidad de carga y un muy amplio rango de temperatura de operación. Todos estos factores indirectamente mejoran la linealidad del AlGaN/GaN. Sin embargo, la tecnología HEMT de AlGaN/GaN aún está bajo desarrollo, por lo tanto, se están investigando modelos confiables de pequeña y gran señal. En años recientes, las redes neuronales artificiales (RNA) han probado ser una excelente herramienta en la mejora de la precisión de los modelos basados en mediciones debido a sus excelentes propiedades para la aproximación de funciones, teniendo estos modelos mejor desempeño que los basados en tablas los cuales usan funciones spline para interpolación de datos. Por consiguiente, existe una nueva tendencia por utilizar modelos no lineales de RNA basados en, ya sea mediciones lineales, o no lineales del transistor. Al usar una aproximación basada en redes neuronales la cual toma en cuenta la función original y sus derivadas en el proceso de entrenamiento, un modelo no lineal cuasi-estático del FET de GaN basado en mediciones I-V pulsadas y parámetros S pulsados es presentado. El modelo cuasi-estático basado en mediciones es implementado en ADSTM de Agilent y consiste de tres redes neuronales utilizadas para representar las características de corriente y almacenamiento de carga del transistor.There is a keen interest in accurate transistor models for the design of RF and microwave power amplifiers, oscillators and mixers. Basically transistor models can be divided in physical and empirical models. Physical models are very accurate and, as it is stated in their name, are based on the physical characteristics of the device such as gate length, channel width, electric field, electron charge, electron mobility, etc. On the other hand empirical models are based on measurements of the device, simpler to develop and computationally efficient. The AlGaN/GaN HEMT is an excellent candidate to be used as an active device for power amplifiers (PAs). It has high charge density and a high saturation velocity, which produces high output power levels. Besides, it has high electron mobility, originating a low turn on resistivity, and therefore, high power added efficiency levels can be reached. Furthermore, high breakdown voltage levels can be reached as a result of its prohibited band width, with a high charge density, and a very wide range of high temperature operation. All of these factors indirectly improve AlGaN/GaN linearity. However, AlGaN/GaN HEMT technology is still under development, and therefore, reliable small and large signal models are currently being investigated. In recent years, artificial neural networks (ANNs) have proved to be an excellent aid in improving the accuracy of measurement based models due to their excellent function approximation properties, having these models better performance than table based models that use spline functions for interpolation. Hence, there is a newly born tendency for ANN nonlinear models based on either linear or nonlinear measurements of the transistor. By using a neural network approach that takes into account the original function and its derivatives in the training process, a nonlinear quasi-static model of a GaN FET based on measured pulsed I/V, pulsed S-parameters is introduced. The measurement based quasi-static model is implemented in Agilent's ADSTM and consists of three different neural networks used to represent the current and charge storage characteristics of the transistor
Overview of the Author Profiling Task at PAN 2013
No full text[EN] This overview presents the framework and results for the Author Profiling
task at PAN 2013. We describe in detail the corpus and its characteristics,
and the evaluation framework we used to measure the participants performance to
solve the problem of identifying age and gender from anonymous texts. Finally,
the approaches of the 21 participants and their results are described.The author profiling task @PAN-2013 was an activity of the WIQ-EI IRSES project (Grant No. 269180) within the FP 7 Marie Curie People Framework of the European Commission. We want to thank the Forensic Lab of the Universitat Pompeu Fabra Barcelona for sponsoring the award for the winner team. The work of the first author was partially funded by Autoritas Consulting SA and by Ministerio de Economía y Competitividad de España under grant ECOPORTUNITY IPT-2012-1220-430000. The work of the second author was in the framework the DIANA-APPLICATIONS-Finding Hidden Knowledge in Texts: Applications (TIN2012-38603-C02-01) project, and the VLC/CAMPUS Microcluster on Multimodal Interaction in Intelligent Systems. The work of fifth author was funded in part by the Swiss National Science Foundation (SNF) project "Mining Conversational Content for Topic Modelling and Author Identification (ChatMiner)" under grant number 200021_130208.Rangel, F.; Rosso, P.; Koppel, M.; Stamatatos, E.; Inches, G. (2013). Overview of the Author Profiling Task at PAN 2013. CLEF Conference on Multilingual and Multimodal Information Access Evaluation. 352-365. https://riunet.upv.es/handle/10251/46636S35236
Author Co-Citation Analysis (ACA): a powerful tool for representing implicit knowledge of scholar knowledge workers
No full textIn the last decade, knowledge has emerged as one of the most important and valuable organizational assets. Gradually this importance caused to emergence of new discipline entitled ―knowledge management‖. However one of the major challenges of knowledge management is conversion implicit or tacit knowledge to explicit knowledge. Thus Making knowledge visible so that it can be better accessed, discussed, valued or generally managed is a long-standing objective in knowledge management. Accordingly in this paper author co- citation analysis (ACA) will be proposed as an efficient technique of knowledge visualization in academia (Scholar knowledge workers)
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