Understanding the Variations in Gibrat's Law with a Markov-Perfect Dynamic Industry Model

Gibrat's Law of proportionate effect, as applied to firms, states that the growth rate of a firm is independent of its size. Empirical work on firm dynamics finds crucial deviations from Gibrat's Law such as smaller firms growing faster than larger firms (Evans, 1987, and Hall, 1987), a negative relationship between the variance of growth rates and size (Dunne and Hughes, 1994), and first-order positive autocorrelation in the growth rates (Kumar, 1995). Moreover, the degree of deviation from Gibrat's Law varies across industries. This paper contributes to our understanding of the forces that make Gibrat's Law a close, but imperfect approximation of firm size distributions and seeks to determine potential sources of cross-industry variation. Here, we employ an extension of the Ericson-Pakes (1995) theoretical framework that allows for firm growth developed by Laincz (2004a). By varying key parameters, the simulations demonstrate potential sources for the various, and sometimes conflicting, results on Gibrat's Law uncovered in the empirical literatureGibrat's Law, Firm Size Distribution, Entry, Exit

Transition of athletes in sport career: from theory to evaluation

Este trabalho analisa a transição dos atletas no desporto, propondo um modelo compreensivo da transição desportiva e um instrumento de avaliação para analisar as transições desportivas dos atletas ao longo da carreira desportiva. Assim, do ponto de vista conceptual descreve-se o Modelo Interativo de Adaptação Humana à Transição Desportiva, que entende este fenómeno como um processo constituído pelos seguintes fatores: (a) circunstâncias da transição desportiva, (b) processos de avaliação cognitiva, (c) respostas ocorridas durante a situação de transição, e (d) resultado final da situação de transição. De seguida, é proposto um guião de entrevista para avaliar a transição desportiva, avaliando seis dimensões: (a) situação de transição, (b) recursos externos disponíveis, (c) mudanças enfrentadas, (d) processos de avaliação cognitiva, (e) respostas psicológicas, fisiológicas e comportamentais, e (f) resultado final da adaptação desportiva. A conjugação de modelos teóricos e instrumentos de avaliação acerca da transição desportiva podem ajudar a compreender este fenómeno.This work analyzes the transition of athletes in sports, proposing a comprehensive model about career transition and an instrument to evaluate the transitions of athletes throughout their careers. First, it is described the Interactive Model of Human Adaptation to Career Transition, proposing that transition is a process constituted by the following factors: (a) circumstances of the career transition, (b) cognitive appraisal, (c) responses occurred during the career transition, and (d) final result of the career transition. Second, it is proposed an interview guide that evaluates six dimensions: (a) circumstances of the career transition, (b) available external resources, (c) demands faced during the career transition, (d) processes of cognitive appraisal, (e) psychological, physiological and behavioral responses, and (f) final result of career transition. The combination of theoretical models and evaluation instruments about the career transition may help to understand this phenomenon.(undefined

A Theoretical Foundation for Understanding Firm Size Distributions and Gibrat's Law

This paper presents a dynamic model of the firm size distribution. Empirical studies of the firm size distribution often compare the moments to a log-normal distribution as implied by Gibrat's Law and note important deviations. Thus, the first, and basic questions we ask are how well does the dynamic industry model reproduce Gibrat's Law and how well does it match the deviations uncovered in the literature. We show that the model reproduces these results when testing the simulated output using the techniques of the empirical literature. We then use the model to study how structural parameters affect the firm size distribution. We find that, among other things, fixed and sunk costs increase both the mean and variance of the firm size distribution while generally decreasing the skewness and kurtosis. The rate of growth in an industry also raises the mean and variance, but has non-monotonic effects on the higher moments.Firm size distribution; Gibrat's Law; R&D.

SAMplus: adaptive optics at optical wavelengths for SOAR

Adaptive Optics (AO) is an innovative technique that substantially improves the optical performance of ground-based telescopes. The SOAR Adaptive Module (SAM) is a laser-assisted AO instrument, designed to compensate ground-layer atmospheric turbulence in near-IR and visible wavelengths over a large Field of View. Here we detail our proposal to upgrade SAM, dubbed SAMplus, that is focused on enhancing its performance in visible wavelengths and increasing the instrument reliability. As an illustration, for a seeing of 0.62 arcsec at 500 nm and a typical turbulence profile, current SAM improves the PSF FWHM to 0.40 arcsec, and with the upgrade we expect to deliver images with a FWHM of $\approx0.34$ arcsec -- up to 0.23 arcsec FWHM PSF under good seeing conditions. Such capabilities will be fully integrated with the latest SAM instruments, putting SOAR in an unique position as observatory facility.Comment: To appear in Proc. SPIE 10703 (Ground-based and Airborne Instrumentation for Astronomy VII; SPIEastro18

Assessing the mixing performance of extruders: indices and scale-up

This work proposes the use of global quantitative dispersive and distributive mixing indices to characterize the performance of a given screw. Calculation of these quantities uses a model of morphology evolution as a function of material and flow characteristics, which was coupled to a description of the flow developing along the screw from hopper to die. Scale-up on the basis of these indices is briefly discussed. Some results are presented in order to illustrate the usefulness of the methodology

Novas metodologias para a fermentação alcoólica do soro de queijo

Em Portugal, são diariamente lançados no meio ambiente cerca de 1 milhão de litros de soro de queijo – fracção líquida resultante do fabrico de queijo. O impacte ambiental ocasionado por tal volume de efluentes, com elevada carga orgânica, é enorme. Recorrendo à tecnologia de DNA recombinante, modificou-se uma estirpe floculante de Saccharomyces cerevisiae sendo-lhe conferida capacidade para fermentar lactose. Com esta estirpe foram realizados ensaios de fermentação em contínuo, utilizando como substrato soro de queijo desproteinizado, possibilitando operar a uma taxa de diluição máxima de 0,45 hˉ¹, correspondente a uma produtividade volumétrica em etanol de cerca de 10 gLˉ¹hˉ¹, cerca de 7 vezes superior aos processos actualmente existentes. O processo integrado de recuperação da proteína e fermentação alcoólica permite uma redução superior a 90 % de CQO do soro, o que, por si só, se traduz numa enorme diminuição do impacte ambiental negativo, e, por outro lado, abre a porta à produção de etanol com viabilidade económica.Instituto de Biotecnologia e Química Fina (IBQF); PROLAC; Agência de Inovação; Fundação para a Ciência e Tecnologia (FCT)

Translocating the blood-brain barrier using electrostatics

Copyright © 2012 Ribeiro,Domingues, Freire,Santos and Castanho. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.Mammalian cell membranes regulate homeostasis, protein activity, and cell signaling. The charge at the membrane surface has been correlated with these key events. Although mammalian cells are known to be slightly anionic, quantitative information on the membrane charge and the importance of electrostatic interactions in pharmacokinetics and pharmacodynamics remain elusive. Recently, we reported for the first time that brain endothelial cells (EC) are more negatively charged than human umbilical cord cells, using zeta-potential measurements by dynamic light scattering. Here, we hypothesize that anionicity is a key feature of the blood-brain barrier (BBB) and contributes to select which compounds cross into the brain. For the sake of comparison, we also studied the membrane surface charge of blood components—red blood cells (RBC), platelets, and peripheral blood mononuclear cells (PBMC).To further quantitatively correlate the negative zeta-potential values with membrane charge density, model membranes with different percentages of anionic lipids were also evaluated. From all the cells tested, brain cell membranes are the most anionic and those having their lipids mostly exposed, which explains why lipophilic cationic compounds are more prone to cross the blood-brain barrier.Fundação para a Ciência e Tecnologia — Ministério da Educação e Ciência (FCT-MEC, Portugal) is acknowledged for funding (including fellowships SFRH/BD/42158/2007 to Marta M.B. Ribeiro, SFRH/BD/41750/2007 to Marco M. Domingues and SFRH/BD/70423/2010 to João M. Freire) and project PTDC/QUI-BIQ/119509/2010. Marie Curie Industry-Academia Partnerships and Pathways (European Commission) is also acknowledged for funding (FP7-PEOPLE-2007-3-1-IAPP, Project 230654)

Comportamento termodinâmico da adsorção dos enantiômeros do omeprazol na fase estacionária quiral TRIS(3,5-Dimetilfenilcarbamato) de amilose.

O objetivo deste trabalho foi avaliar o comportamento termodinâmico da adsorção dos enantiômeros do omeprazol na fase estacionária quiral tris(3,5- dimetilfenilcarbamato) de amilose, sintetizada em larga escala a partir de uma metodologia definida em escala analítica. Para avaliar as constantes de Henry e os parâmetros termodinâmicos foram realizados experimentos de pulsos cromatográficos com soluções do traçador e da mistura racêmica em diferentes temperaturas e vazões da fase móvel. As isotermas de adsorção foram determinadas das curvas de ruptura obtidas com soluções da mistura racêmica em diferentes concentrações. As constantes de Henry diminuíram com a elevação da temperatura devido a uma aproximação dos picos cromatográficos. Valores negativos das variações de entalpia e entropia indicaram que é energeticamente mais favorável o soluto estar na adsorvido na fase estacionária do que em solução e que os enantiômeros encontram-se mais ordenados no estado adsorvido, respectivamente. No intervalo de concentração analisado, o modelo de isoterma de Langmuir foi bem correlacionado aos dados experimentais de equilíbrio. A capacidade de saturação da fase estacionária sintetizada é relativamente inferior à capacidade da mesma fase disponível comercialmente. A diferença está provavelmente relacionada à derivação dos grupos hidroxila da amilose e à obtenção de um derivado de uréia, durante a reação de síntese do carbamato, e ao processo de recobriment

Continuous ethanol production from cheese whey permeate

Praxis XXI - BD/11306/97