The return to firm investment in human capital

In this paper we estimate the rate of return to firm investments in human capital in the form of formal job training. We use a panel of large firms with unusually detailed information on the duration of training, the direct costs of training, and several firm characteristics such as their output, workforce characteristics and capital stock. Our estimates of the return to training vary substantially across firms. On average it is -7% for firms not providing training and 24% for those providing training. Formal job training is a good investment for many firms and the economy, possibly yielding higher returns than either investments in physical capital or investments in schooling. In spite of this, observed amounts of formal training are very small

Enforcement of regulation, informal labor and firm performance

This paper investigates how enforcement of labor regulation affects the firm’s use of informal labor and firm performance. Using firm level data on informal employment and firm performance, and administrative data on enforcement of regulation at the city level, we show that in areas where law enforcement is stricter firms employ a smaller amount of informal employment. Furthermore, by reducing the firm’s access to unregulated labor, stricter enforcement is also associated with lower labor productivity. We control for different regional and firm characteristics, and we instrument enforcement with a measure of the access of labor inspectors to firms. Taken together, our findings suggest that increased access to labor flexibility significantly improves firm performance

Trends in quality-adjusted skill premia in the United States, 1960-2000

This paper presents new evidence that increases in college enrollment lead to a decline in the average quality of college graduates between 1960 and 2000, resulting in a decrease of 8 percentage points in the college premium. The standard demand and supply framework (Katz and Murphy, 1992, Card and Lemieux, 2001) can qualitatively account for the trend in the college and age premia over this period, but the quantitative adjustments that need to be made to account for changes in quality are substantial. Furthermore, the standard interpretation of the supply effect can be misleading if the quality of college workers is not controlled for. To illustrate the importance of these adjustments, we reanalyze the problem studied in Card and Lemieux (2001), who observe that the rise in the college premium in the 1980s occurred mainly for young workers, and attribute this to the differential behavior of the supply of skill between the young and the old. Our results show that changes in quality are as important as changes in prices to explain the phenomenon they document

Estimating distributions of potential outcomes using local instrumental variables with an application to changes in college enrollment and wage inequality

This paper extends the method of local instrumental variables developed by Heckman and Vyt- lacil (1999, 2001, 2005) to the estimation of not only means, but also distributions of potential outcomes. The newly developed method is illustrated by applying it to changes in college enroll- ment and wage inequality using data from the National Longitudinal Survey of Youth of 1979. Increases in college enrollment cause changes in the distribution of ability among college and high school graduates. This paper estimates a semiparametric selection model of schooling and wages to show that, for fixed skill prices, a 14% increase in college participation (analogous to the increase observed in the 1980s), reduces the college premium by 12% and increases the 90-10 percentile ratio among college graduates by 2

Carbon line formation and spectroscopy in O-type stars

The determination of chemical abundances constitutes a fundamental requirement for obtaining a complete picture of a star. Particularly in massive stars, CNO abundances are of prime interest, due to the nuclear CNO-cycle and various mixing processes which bring these elements to the surface. We aim at enabling a reliable carbon spectroscopy for our unified NLTE atmosphere code FASTWIND. We develop a new carbon model atom including CII/III/IV/V, and discuss problems related to carbon spectroscopy in O-type stars. We describe different tests to examine the reliability of our implementation, and investigate which mechanisms influence the carbon ionization balance. By comparing with high-resolution spectra from six O-type stars, we check in how far observational constraints can be reproduced by our new carbon line synthesis. Carbon lines are even more sensitive to a variation of temperature, gravity, and mass-loss rate, than hydrogen/helium lines. We are able to reproduce most of the observed lines from our stellar sample, and to estimate those specific carbon abundances which bring the lines from different ions into agreement. For hot dwarfs and supergiants earlier than O7, X-rays from wind-embedded shocks can impact the synthesized line strengths, particularly for CIV, potentially affecting the abundance determination. We have demonstrated our capability to derive realistic carbon abundances by means of FASTWIND, using our recently developed model atom. We found that complex effects can have a strong influence on the carbon ionization balance in hot stars. For a further understanding, the UV range needs to be explored as well. By means of detailed nitrogen and oxygen model atoms available to use, we will be able to perform a complete CNO abundance analysis for larger samples of massive stars, and to provide constraints on corresponding evolutionary models and aspects.Comment: 22 pages, 16 figures, 6 table

Análise ergonómica da postura e dos movimentos na profissão de médico dentista

Actualmente, as lesões músculo-esqueléticas (LME) afectam milhões de trabalhadores de todo o mundo, pertencentes a todos os sectores de actividade e constituem um dos problemas mais graves de saúde ocupacional da Europa. Se tivermos em consideração a incidência e os custos associados às LME, assim como os principais factores de risco associados já identificados em diversos estudos, a relevância deste tema parece ser significativa para muitas das actividades relacionadas com a saúde, nomeadamente para a Medicina Dentária. Assim, este trabalho consistiu na identificação e na análise dos principais factores de risco relativos ao desenvolvimento de LME nos dentistas. A primeira fase do estudo consistiu no envio de um questionário a um total de cerca de 4200 médicos dentistas distribuídos por todo o território português. Obtivemos uma taxa de resposta de 17%. Os dados recolhidos permitiram caracterizar a amostra de dentistas quanto à idade, ao sexo, à estatura, ao número de horas semanais de trabalho, à antiguidade na profissão, ao tipo e à frequência com que eram desempenhadas as diversas actividades, às condições de trabalho, à posição de trabalho adoptada e, ainda permitiram retirar informações acerca das queixas relativas às LME: quanto à sua causa, à sua localização e também quanto à respectiva intensidade da dor. Numa segunda fase, a análise ergonómica das posturas e dos movimentos de alguns dentistas enquanto operavam, foi realizada por intermédio da técnica RULA, aplicada a um filme previamente feito nos respectivos consultórios. Os resultados mostraram que as tarefas desenvolvidas pelos dentistas envolvem, em geral, um risco elevado de ocorrência de lesões músculo-esqueléticas. Algumas recomendações e sugestões foram tecidas no final do trabalho tentando, deste modo, contribuir para o aumento do bem-estar dos médicos dentistas, nomeadamente no que respeita à diminuição do risco de ocorrência de LME de origem ocupacional.Nowadays musculoskeletal disorders (MSDs) affect millions of workers across the world and constitute one of the most serious occupational health problem in Europe. When considering the incidence, overall costs, and the main risk factors already identified associated with MSDs, the relevance of this issue appears of major importance also for the professionals of Dentistry. Accordingly, this research aimed at identifying and analysing the main risk factors associated with the prevalence of MSDs in dentists. The project started with the development and subsequent distribution of a questionnaire to a sample of 4200 dentists across Portugal main land. A response rate of circa 17% was obtained. Data gathered through the questionnaire enabled the characterization of the dentists’ population regarding age, gender, height, weekly hours of work, number of years in the profession, the type and frequency with which different professional activities are performed, work conditions, work posture adopted and a description of the complaints regarding pains and discomfort (location on the body and intensity). Research proceeded with the ergonomic analysis of the postures and movements of a sample of dentists while treating a patient. Different activities were filmed and the footage was used for subsequent analysis, which was undertaken using RULA. Results gathered show that, in general, there is a high risk of musculoskeletal disorders. A range of recommendations and suggestions is put forward at the end of this document. Then main aim is to contribute to reduce the risk and increase general well-being of the dentists, namely in what concerns the incidence of musculoskeletal disorders

Identificação de proteínas que interagem com o fator de elongação EF1 alfa no endosperma do grão do milho.

bitstream/item/68614/1/ct-193.pd

Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks

X-rays/EUV radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres, and can be the mechanism responsible for the production of highly ionized species. To allow for these processes in the context of spectral analysis, we have implemented such emission into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. The shock structure and corresponding emission is calculated as a function of user-supplied parameters. We account for a temperature and density stratification inside the post-shock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included into the NLTE network. We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of OIV/OV around Teff = 45,000 K. Finally, we investigated the behavior of the mass absorption coefficient, kappa_nu(r), important in the context of X-ray line formation in massive star winds. In almost all considered cases, direct ionization is of major influence, and Auger ionization significantly affects only NVI and OVI. The approximation of a radially constant kappa_nu is justified for r > 1.2 Rstar and lambda < 18 A, and also for many models at longer wavelengths. To estimate the actual value of this quantity, however, the HeII opacities need to be calculated from detailed NLTE modeling, at least for wavelengths longer than 18 to 20 A, and information on the individual CNO abundances has to be present.Comment: accepted by A&