A model of credit limits and bankruptcy with applications to welfare and indebtedness

This paper presents a macroeconomic model of unsecured consumer debt and default where credit conditions consist of pre-approved interest rates and borrowing limits, a feature of actual credit cards. All loans, irrespective of their size and risk, take place against the same type of credit line, and some borrowers are credit constrained. This type of situation is shown to arise in a free-entry competitive equilibrium if there are fixed costs in banking and the banks' decisions on interest rates and on credit limits are made separately. Numerical experiments are conducted to study, on one hand, the macroeconomic and welfare effects of the consumer bankruptcy code, and on the other hand, the consequences of various factors for both indebtedness and bankruptcy. Restricting bankruptcy filings - be it through a stricter Chapter 7 means testing or a longer period of credit exclusion - leads to sizable welfare loses. The recent rise in filing rates and debt is best explained by a combination of lower intermediation costs and more severe non-discretionary expenditures shocks. The endogenous response ofthe credit limit proves to be crucial for these findings Keywords; bankruptcy, unsecured credit, general equilibrium, default risk, credit limits

Schooling and distortions in a vintage capital model

This paper integrates the analysis of choices on education and on technology adoption to study international economic disparities. Two candidate explanations are considered: di¤erences in distortions that a¤ect the cost of technology adoption and di¤erences in the e¤ectiveness of schools. The implications of these two factors for di¤erences in output per capita, educational attainment, and the age of technologies across-countries are assessed in a vintage capital model with technology-speci…c learning-by-doing. Predictions are obtained for a parameterized economy that matches US aggregate observations and evidence on learning. Di¤erences in investment distortions produce plausible correlations only if the major role of education is to improve the ability to learn technologies. On the other hand, di¤erences in school e¤ectiveness produce plausible results only if the role of education is to provide a productive ability that is independent of learning.

Are changes in education important for the wage premium and unemployment?

A generalized rise in unemployment rates for both college and high-school graduates, a widening education wage premium, and a sharp increase in college education participation are characteristic features of the transformations of the U.S. labor market between 1970 and 1990. This paper investigates the interactions between these changes in the labor market and in educational attainment. First, it develops an equilibrium search and matching model of the labor market where education is endogenously determined. Second, calibrated versions of the model are used to study quantitatively whether either a skill-biased change in technology or a mismatch shock can explain the above facts. The skill-biased shock accounts for a considerable part of the changes but fails to produce the increase in unemployment for the educated labor force. The mismatch shock explains instead much of the change in the four variables, including the wage premium.Education, wage Premium, unemployment

Wage inequality and unemployment with overeducation

A skill-biased change in technology can account at once for the changes observed in a number of important variables of the US labour market between 1970 and 1990. These include the increasing inequality in wages, both between and within education groups, and the increase in unemployment at all levels of education. In contrast, in previous literature this type of technology shock cannot account for all of these changes. The paper uses a matching model with a segmented labour market, an imperfect correlation between individual ability and education, and a fixed cost of setting up a job. The endogenous increase in overeducation is key to understand the response of unemployment to the technology shock.Unemployment, wage premium, overeducation, SBTC

Crystal growth, optical characterisation and laser operation of yb3+ in monoclinic double tungstates

El interés y la originalidad del trabajo científico de esta tesis se centra en el crecimiento cristalino, el análisis composicional, estructural, morfológico y óptico de la fase monoclínica de los tungstatos dobles que responden a la fórmula K(RE3+)(WO4)2, donde RE3+ denota iones como Y3+, Gd3+, Yb3+, Er3+ y Lu3+. Estos materiales cristalinos se han estudiado sin dopar y dopados con iones Yb3+ y Er3+ para la generación de radiación láser. La obtención de la fase monoclínica de estos tungstatos dobles se ha realizado mediante el método de crecimiento a partir de solución a alta temperatura Top-Seeded Solution Growth (TSSG) utilizando como solvente el pirotungstato de potasio, K2W2O7, debido a las ventajas que ofrece respecto otros solventes. Se han obtenido monocristales con una muy buena calidad óptica y de tamaño adecuado para su posterior caracterización tanto química como física. La caracterización óptica de estos materiales ha sido la parte más extendida en el trabajo y se ha centrado, por una parte, en la matriz (tungstatos dobles sin dopar) y por otra parte en los iones activos generadores de radiación láser. En cuanto a la matriz se ha llevado a cabo la determinación del rango espectral de transparencia óptica (el cual se extiende entre 0.32 y 5.4 micrómetros), la orientación de los ejes principales ópticos respecto a los ejes cristalográficos y en la medida de los índices de refracción a lo largo de las tres direcciones principales ópticas y para un rango de longitudes de onda que se extiende desde los 450 nm hasta los 1500 nm (índice de refracción alrededor de 2).Por otra parte la caracterización óptica de los iones activos se ha centrado en la espectroscopia del yterbio y del erbio y en los experimentos de laseado realizados sobre los iones yterbio. La espectroscopia concierne, en primer lugar, a la absorción óptica polarizada de los dos iones a temperatura ambiente y a temperaturas criogénicas, 6 K (es destacable el valor del coeficiente de absorción del yterbio, que deriva en una longitud de absorción de tansolo 13.3 micrómetros para el caso del KYb(WO4)2 y en una elevada sección eficaz de emisión del orden de 14x10-20 cm2 a una longitud de onda de 980 nm para la polarización etiquetada como Nm). Dicha longitud de absorción permite pensar en la posibilidad de láseres de disco fino (Thin disk lasers) y guías de onda, y debido a la elevada sección eficaz de absorción, se ha utilizado este ión como sensibilizador de las emisiones del erbio. Además, el rango de longitudes de onda de absorción del yterbio permite la posibilidad de excitación mediante diodo con las ventajas que ello supone. En segundo lugar, la espectroscopia concierne a la luminiscencia de dichos iones desde el punto de vista de la emisión óptica también a temperatura ambiente y bajas temperaturas y a la medida de vidas medias. La emisión del yterbio también destaca por su anchura de las líneas de emisión, muy interesantes para la generación de láser pulsados en régimen de pico- y femtosegundos. Las emisiones del erbio que se han estudiado con mayor profundidad han sido las emisiones con máximo de intensidad a 1530 nm y a 550 nm.La generación de radiación láser a partir de iones yterbio se ha realizado en modo continuo para el caso de KLu(WO4)2 dopado con yterbio y en modo pulsado (Quasi-CW) para el caso en que el ión activo no está presente en cantidades dopantes en la estructura sino substituyendo totalmente a la tierra rara (RE), el KYb(WO4)2. La excitación del yterbio se ha realizado mediante un láser de titanio-zafiro y mediante diodo.The interest and originality of the scientific work of this thesis focuse on the crystal growth, the compositional, structural, morphologycal and optical analysis of the monoclinic phase of the double tungstates K(RE3+)(WO4)2, where RE3+ denotes ions like Y3+, Gd3+, Yb3+, Er3+ and Lu3+. These crystalline materials have been studied without doping and doped with Yb3+ and Er3+ ions for the generation of laser radiation. The obtention of the monoclinic phase of these double tungstates has been realized by means of the Top-Seeded Solution Growth (TSSG) method using the potassium pyrotungstate, K2W2O7, as solvent. This was due to the advantages that it offers in front of other solvents. Single crystals with very high optical quality and suitable size for later chemical and physical characterizations have been obtained. The optical characterization of these materials has been the most extended part of this work and focused, on the one hand, on the host (double tungstates without doping) and, on the other hand, on the active ions. Concerning the host, the determination of the optical spectral range of transparency (that extends from 0.32 to 5.1 micrometers), the orientation of the principal optical axes with respect to the crystallographic axes and the measurement of the refractive indices along the three principal optical directions and for a wavelength range from 450 nm to 1500 nm (refractive index around 2) have been determined.On the other hand, the optical characterization of the active ions focused on the ytterbium and erbium spectroscopy and the laser experiments realized on ytterbium ions. The spectroscopy concerns, in first place, in the polarized optical absorption of the two ions at room temperature and cryogenic temperature, 6 K (it is remarkable the absorption coefficient of ytterbium, that derived in an absorption length of only 13.3 micrometers for the case of KYb(WO4)2, and in a very high absorption cross-section of 14x10-20 cm2 at 980 nm for the polarization labelled Nm). This absorption length allows think in the possibility of Thin-Disk laser designs and waveguides, and due to the high absorption cross-section, this ion has been used as sensitizer of the erbium emissions. Moreover, the range of absorption wavelength for ytterbium allows the possibility of exciting by means of diode. In second place, the spectroscopy involved the luminescence of these ions under the point of view of the optical emission also at room temperature and low temperature and the measurement of the lifetime. The emission of ytterbium is interesting also for the broadening of the emission lines, that is very interesting for the generation of laser pulses in the pico- and femtosecond regimes. The erbium emissions that have been studied deeper have been the 1530 and 550 nm emissions.The generation of laser radiation from ytterbium ions has been realized in continuous-wave mode for the case of KLu(WO4)2 doped with ytterbium and in pulsed mode (Quasi-CW) for the case of KYb(WO4)2. Ytterbium ions have been excited by means of a Titanium-Sapphire laser and a diode

Demographics and the politics of capital taxation in a life-cycle economy

This article studies the effects of demographics on the mix of tax rates on labour and capital. It uses a quantitative general-equilibrium overlapping-generations model where tax rates are voted without past commitments in every period and characterized as a Markov equilibrium. In the U.S., the younger voting-age population in 1990 compared to 1965 accounts for the observed decline in the relative capital tax rate between those two years. A younger population rises the net return to capital, leads voters to increase their savings, and results in a preference for lower taxes on capital Conversely, ageing might increase capital taxation. Keywords; markov policies, demographic change, capital and labor taxation

The European demographic transition

This paper investigates the factors that shaped the demographic transition in a number of European countries (Sweden, England, and France) since the mid 18th century. The analytical framework is a version of the neoclassical growth model with dynastic preferences calibrated to match the Swedish experience. This setup is studied quantitatively to asses the contribution of various factors to the explanation of the observed demographic patterns, both over time and across countries. The factors considered are mortality changes, technological progress, and the evolution of the cost of children. The analysis suggests that the contribution of observedmortality rates and technology is only partial. A substantial part of the demographic-transition facts must be attributed to unobservable variation in the cost of children, both over time and across countries Keywords; altruism, growth, demographic transition, mortality, fertility