Nuevas técnicas de generación de señal para sistemas radar de alta resolución y baja probabilidad de interceptación

Los sistemas radar actuales deben combatir, entre otros, contra dos enemigos principales: el clutter y los sistemas de interceptación y guerra electrónica. Una forma muy efectiva de luchar contra el clutter es el empleo de celdas de resolución de pequeño tamaño. Esto a su vez se traduce en la posibilidad de identificación de blancos. De esta manera, los radares de alta resolución ganan popularidad día a día. Estos sistemas requieren el empleo de formas de onda con grandes anchos de banda. Por otro lado, la forma de combatir contra los equipos de interceptación es la utilización de técnicas de baja probabilidad de interceptación (LPI). Una opción habitual en este caso es nuevamente el empleo de señales de gran ancho de banda. Un tipo de radar que está ganando mucha aceptación en los últimos tiempos es el radar de onda continua modulado linealmente en frecuencia (LFMCW). Este tipo de radar combina de forma natural características de alta resolución junto con propiedades LPI. Sin embargo, hay dos grandes problemas con este tipo de forma de onda. El primero es la pérdida de resolución debida a la no linealidad de la señal LFM, y el segundo la degradación de la sensibilidad debida al ruido de fase de la señal transmitida. Es necesario, por lo tanto, disponer de un generador de señal de alta linealidad y con muy bajo nivel de ruido de fase para permitir un funcionamiento óptimo de este tipo de radar. El objetivo propuesto en esta Tesis se resume en el análisis de la problemática asociada a la señal LFMCW aplicada a radares de alta resolución con propiedades LPI, abordando tanto la vertiente tecnológica como la analítica del problema. Asimismo, también se aborda el estudio, diseño, simulación, construcción y caracterización experimental de un sistema generador de señales chirp con pendientes de 4.5 THz/seg en banda X, que permita la comprobación experimental de las soluciones propuestas en la mejora de la linealidad y ruido de fase de la señal LFMCW. El sistema generador de señales chirp que se propone en la Tesis esta formado por tres elementos principales: un sintetizador digital directo (DDS), un lazo de enganche en fase (PLL), que actúa como multiplicador de frecuencia, y un oscilador enganchado en fase (PLO) que permite obtener la banda de frecuencia final. Se presentan sus técnicas de diseño y se estudia el impacto de cada uno de los elementos sobre el ruido de fase y las espurias del generador. También, se muestran las técnicas de diseño de los PLOs necesarios para un receptor heterodino en este tipo de radar. Una vez que se dispone del generador de señal, y de los PLOs para los receptores, se estudia el impacto del ruido de fase de los mismos sobre la sensibilidad de dos tipos de sistemas: homodinos y heterodinos. Se compara la sensibilidad del receptor en función del ruido térmico y el ruido de fase. Se identifican los rangos de funcionamiento de ambos tipos de receptores, para el generador propuesto, y se proponen soluciones en aquellos casos en que son necesarias. La realización de la Tesis ha permitido mejorar el conocimiento sobre la degradación de la sensibilidad de los radares LFMCW a consecuencia del ruido de fase de las fuentes de señal, así como establecer metodologías de diseño para la realización de sistemas de generación de señales chirp de altas prestaciones

Challenges And Opportunities In Analytic-Predictive Environments Of Big Data And Natural Language Processing For Social Network Rating Systems

Social Media is playing a key role in today's society. Many of the events that are taking place in diverse human activities could be explained by the study of these data. Big Data is a relatively new parading in Computer Science that is gaining increasing interest by the scientific community. Big Data Predictive Analytics is a Big Data discipline that is mostly used to analyze what is in the huge amounts of data and then perform predictions based on such analysis using advanced mathematics and computing techniques. The study of Social Media Data involves disciplines like Natural Language Processing, by the integration of this area to academic studies, useful findings have been achieved. Social Network Rating Systems are online platforms that allow users to know about goods and services, the way in how users review and rate their experience is a field of evolving research. This paper presents a deep investigation in the state of the art of these areas to discover and analyze the current status of the research that has been developed so far by academics of diverse background

Reacción de diels-alder con ciclopentadieno y derivados sustituidos del diacetato de naftazarina

Tesis - Universidad Complutense de Madrid, 1982.ProQuestDepto. de Química OrgánicaFac. de Ciencias QuímicasTRUEpu

Correlation between the Need for Cognitive Closure and Narrative Creativity in Secondary Education

(1) Background: The present study analyzed the need for cognitive closure and narrative creativity in adolescents. The aim was to demonstrate a strong relationship between narrative creativity and the need for cognitive closure. We analyzed a group of participants by applying a lie scale integrated with the Need for Closure Scale to detect potential relationships between students that entered the lie scale group (discarded) and those that were not discarded by exploring the following variables: gender, school type, group condition, and narrative creativity. (2) Methods: The instruments used were the Need for Closure Scale and the Test of Creative Imagination for Young People, PIC-J. Students of English as a foreign language in the 3rd year of secondary education from two schools were selected based on their availability to participate in the project. The students were aged 14 to 16 with a non-probabilistic sampling value of N = 117. (3) Results: Results show a negative correlation between narrative creativity and the need for cognitive closure. The need for cognitive closure is mainly manifested in two of its five dimensions: order and predictability. In addition, the group analysis of the lie scale revealed a higher tendency of male students to be less likely to respond truthfully. Meanwhile, the percentage of participants in the lie scale group was higher in rural schools. (4) Conclusions: In conclusion, students who do not belong to the lie scale group seem to have more creativity than students in the lie scale group, while students in the lie scale group have a lower final course grade than students in the non lie scale group

The interplay between academic performance, emotional intelligence, and self-concept as predictors of violent behavior in higher education: a multi-group structural equation modeling

Higher education is a focus of increasing violent behavior. The evidence suggests an obsession to achieve the best academic performance in order to access working life. This research aims to develop an explanatory model of violent behavior and its relationship with self-concept and emotional intelligence according to in relation to their academic performance. A sample of 932 Spanish undergraduate students participated in the multi-group structural equation modeling. Findings revealed that students who have a higher academic performance have problems to control and regulate their emotions, showing signs of direct and indirect violence. Moreover, it was found that that emotional intelligence and self-concept have a direct influence on episodes of violent behavior, with academic performance being a key component affecting each variable. The present study provides some implications and suggests some avenues for future research

Lumped-Element Balun for UHF UWB Printed Balanced Antennas

A semi-lumped balun transformer for UHF and ultrawideband (UWB) dipole antennas is presented in this paper. The proposed structure is based on two asymmetric filters that also transform the variable antenna impedance into the desired source impedance. These asymmetric filters make use of a binomial impedance transformer in each filter section. The asymmetric filters (one low pass filter, LPF, and other high pass filter, HPF) allow the balun bandwidth to be increased while the binomial transformer matches the variable balanced dipole impedance. In this way the ripple in the balun response due to the variation of the UWB dipole impedance is reduced. A balun for a UHF and UWB dipole antenna working from 220 to 820 MHz (bandwidth of 4:1) has been achieved with losses lower than 1 dB. These types of baluns are particularly useful in the low microwave frequency band

Enabling Cross Constraint Satisfaction in RDF-Based Heterogeneous Database Integration

Abstract The problem of database integration has been widely tackled through different approaches. While data transformation based systems, such as Data Warehouses, reached the acceptation of the industry during the 80's, in the last decade query translation based approaches have gained popularity given their adequacy to dynamic domains

Moderate-Vigorous Physical Activity, Family Support, Peer Support, and Screen Time: An Explanatory Model

It is important to investigate how the different factors of physical activity and screen time influence each population group in order to design effective proposals for health promotion. This study aims to: (1) create an explanatory model to establish the relationships between moderatevigorous physical activity time, screen time, family support, and peer support of adolescents in the region of Soria (Spain); (2) contrast the explanatory structural model according to the intensity of physical activity. A representative sample of 694 adolescents, aged 12–17 years, from the region of Soria was selected. The Four by One-Day Physical Activity Questionnaire, the Parent Support Scale, and the Peer Support Scale were administered. The data were treated according to a structural equation model to demonstrate the relationships between the study variables. The Chi-square pvalues and standardised fit indices (CFI, NFI, IFI, TLI, and RMSEA) were appropriate. Moreover, acceptable parameters were obtained in the general equations. The theoretical model is useful to explain the relationships between moderate-vigorous physical activity, family support, peer support, and screen time. In addition, models that differentiate between moderate and vigorous physical activity independently are also useful. Peer support plays a particular role relative to physical activity time, and family support plays a specific role regarding screen time

An Explanatory Model of the Relationships between Physical Activity, Social Support and Screen Time among Adolescents

Effective physical activity studies are necessary to understand how factors involved in physical activity mediate behaviour. Therefore, more reliable explanatory models can be generated in order to design effective actions to promote physical activity. The study had two aims: (1) to develop an explanatory model to identify and establish the relationships between physical activity, social support and screen time among adolescents; and (2) to contrast the explanatory structural model by means of a multi-group analysis according to sex. The study design was cross-sectional with descriptive and correlational analysis. The research was carried out with a representative sample of adolescents from the province of Soria (mean age 14.06 +/- 1.27 years). The instruments used were: Four by One-Day Physical Activity Questionnaire, Parent Support Scale and Peer Support Scale. The results show that social support had a negative relationship with screen time (r = -0.178; p <= 0.001); males had a positive relationship between physical activity and screen time (r = 0.118; p <= 0.05); and peer support had more influence on social support than parental support. In conclusion, the proposed model was effective in triangulating the relationships between physical activity, social support and screen time in a novel way, while allowing us to discriminate these results according to participants' sex