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

Horizontal Inequity in Access to Healthcare Services and Educational Level in Spain

The aim of this study is to measure horizontal equity in the use of healthcare services in Spain, proposing two methodological innovations. First by defending it as equality of access for equal need, irrespective of educational level, unlike the prevailing methodological approach to horizontal equity which relates it to income. Second, by estimating it by means of the slope index of the inequality of characteristics, analagous to the inequity index proposed by Kakwani, Wagstaff and van Doorslaer (1997; HIWV) but presenting some methodological advantages, the greater robustness of the data available on educational level than of those on income, and the possibility of isolating the net effect of the educational level on the use of healthcare by controlling for other variables. The methodology is designed in three parts: (1) estimation of the relationship between the educational level and the use of healthcare services by means of a model of the likelihood of demand for healthcare services, commonly used in the literature; (2) estimation of the relationship between educational level and health by approximating a production function of individuals' health according to their personal characteristics and other factors conditioning health; and (3) estimation of the slope index of inequality as a measure of horizontal inequity, using educational level instead of income as the criterion for ranking individuals. The data base used was a sample of 55,598 observations from the Survey of disabilities, handicaps and state of health of 1999, carried out in Spain. No significant statistical association was found between educational level and use of healthcare services. On the other hand, the relationship between educational level and health, with the three proxy variables used (perception of health, days of limitation and number of chronic illnesses) shows a positive correlation, i.e. an increase in educational level is associated with a greater probability of enjoying better health. Horizontal inequity, measured by the proposed slope index of inequality, gives a range of statistically significant values between 13.91% and 9.40%, depending on cases, i.e. the significant inverse relationship between state of health and educational level is not reflected proportionally in healthcare use, implying that, with greater need, the access of individuals with a lower educational level to public healthcare services is the same as for the rest. These results suggest that the educational level may be a variable to consider when characterizing the healthcare needs of a population in a defined geographical area, at least from the normative characterization of horizontal equity proposedEducation and health; Healthcare needs; Horizontal Inequity; Logistic regression ; Ordinal regression; Regional funding

The temporal evolution of the energy flux across scales in homogeneous turbulence

A temporal study of energy transfer across length scales is performed in 3D numerical simulations of homogeneous shear flow and isotropic turbulence. The average time taken by perturbations in the energy flux to travel between scales is measured and shown to be additive. Our data suggests that the propagation of disturbances in the energy flux is independent of the forcing and that it defines a `velocity' that determines the energy flux itself. These results support that the cascade is, on average, a scale-local process where energy is continuously transmitted from one scale to the next in order of decreasing size.Comment: Accepted for publication as a Letter in Physics of Fluid

Dominance Measuring Method Performance under Incomplete Information about Weights.

In multi-attribute utility theory, it is often not easy to elicit precise values for the scaling weights representing the relative importance of criteria. A very widespread approach is to gather incomplete information. A recent approach for dealing with such situations is to use information about each alternative?s intensity of dominance, known as dominance measuring methods. Different dominancemeasuring methods have been proposed, and simulation studies have been carried out to compare these methods with each other and with other approaches but only when ordinal information about weights is available. In this paper, we useMonte Carlo simulation techniques to analyse the performance of and adapt such methods to deal with weight intervals, weights fitting independent normal probability distributions orweights represented by fuzzy numbers.Moreover, dominance measuringmethod performance is also compared with a widely used methodology dealing with incomplete information on weights, the stochastic multicriteria acceptability analysis (SMAA). SMAA is based on exploring the weight space to describe the evaluations that would make each alternative the preferred one

Health status and retirement decisions for older European couples

In this paper we use data the European Community Household Panel (ECHP) to describe and analyse the dynamics of joint labour force behaviour of older couples for the EU12 countries. We focus on three main issues: the relevance of joint retirement across EU12 countries, the existence of complementarities in leisure and/or assortative matting and the effects of health variables. Concerning the evidence, we first find that a working spouse is more likely to retire the more recently the other spouse has retired; this effect is stronger if the wife is the working spouse. Second, there is evidence of assortative mating and/or complementarities in leisure; the effects of all relevant factors on the retirement decision of one spouse depend strongly on whether the other one is working, unemployed, or retired. Third, besides the standard evidence that poor health increases the retirement probability, we find that the husband's health affects the couple's retirement decisions much more strongly than the wife's health does. Additional asymmetric effects are detected with respect to income related variables.joint retirement decisions ; labour force transitions ; health variables ; asymmetric effects

Health status and retirement decisison for older european couples.

In this paper we use data the European Community Household Panel (ECHP) to describe and analyse the dynamics of joint labour force behaviour of older couples for the EUI2 countries. We focus on three main issues: the relanvance of joint retirement across EUI2 countries, the existence of complementarities in leisure and/or assortative matting and the effects of health variables. Concerning the evidence, we first find that a working spouse is more likely to retire the more recently the other spouse has retired; this effect is stronger if the wife is the working spouse. Second, there is evidence of assortative mating and/or complementarities in leisure; the effects of all relevant factors on the retirement decision of one spouse depend strongly on whether the other one is working, unemployed, or retired. Third, besides the standard evidence that poor health increases the retirement probabiliby, we find that the husband's health affects the couple's retirement decisions much more strongly than the wife's health does. Additional asymmetric effects are detected with respect to income related variables.Joint retirement decisions; Labour force transitions; Health variables; Asymmetric effects;

Killing by lung cancer or by diabetes? The trade-off between smoking and obesity

As the prevalence of smoking has decreased to below 20%, health practitioners interest has shifted towards the prevalence of obesity, and reducing it is one of the major health challenges in decades to come. In this paper we study the impact that the final product of the anti-smoking campaign, that is, smokers quitting the habit, had on average weight in the population. To these ends, we use data from the Behavioral Risk Factors Surveillance System, a large series of independent representative cross-sectional surveys. We construct a synthetic panel that allows us to control for unobserved heterogeneity and we exploit the exogenous changes in taxes and regulations to instrument the endogenous decision to give up the habit of smoking. Our estimates, are very close to estimates issued in the ’90s by the US Department of Health, and indicate that a 10% decrease in the incidence of smoking leads to an average weight increase of 2.2 to 3 pounds, depending on choice of specification. In addition, we find evidence that the effect overshoots in the short run, although a significant part remains even after two years. However, when we split the sample between men and women, we only find a significant effect for men. Finally, the implicit elasticity of quitting smoking to the probability of becoming obese is calculated at 0.58. This implies that the net benefit from reducing the incidence of smoking by 1% is positive even though the cost to society is $0.6 billions.

An Empirical Analysis of the Demand for Physician Services Across the European Union

This paper presents parameter estimates for physician services equations using the European Community Household Panel for 12 countries covering the period 1994-1996. The focus is on two specific points: i) the identification of behavioural similarities and differences in the demand for health across the countries; ii) the variability of the demand for health captured through a joint model for all the countries. We find that there are significant differences across countries, although there are also similarities in the effect of variables such as the health stock, labour situation or family structure. An important fraction of the variability of the demand of health services across countries could be explained from differences in age, income, and the role of General Practitioners (GP) as a gatekeepers in the public health system. We also find some evidence of induced demand effects in both the decision to visit and the number of visits to specialists.count data; demand; physician services; latent class model; two-part model

Award errors and permanent disability benefits in Spain

There is a controversial debate about the effects of permanent disability benefits on labor market behavior. In this paper we estimate equations for deserving and receiving disability benefits to evaluate the award error as the difference in the probability of receiving and deserving using survey data from Spain. Our results indicate that individuals aged between 55 and 59, self-employers or working in an agricultural sector have a probability of receiving a benefit without deserving it significantly higher than the rest of individuals. We also find evidence of gender discrimination since male have a significantly higher probability of receiving a benefit without deserving it. This seems to confirm that disability benefits are being used as an instrument for exiting the labor market for some individuals approaching the early retirement or those who do not have right to retire early. Taking into account that awarding process depends on Social Security Provincial Department, this means that some departments are applying loosely the disability requirements for granting disability benefits.Disability benefits, Award error, Early retirement, Social security