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

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.

Ensaio sobre a literatura de análise dos efeitos da educação no crescimento económico

This essay summarizes and analyses the most important theoretical and empirical contributions to assess and understand the effects of education on the performance of countries in terms of economic growth. Two debates are approached: the controversial issue "first differences versus levels" as well as "micro-macro paradox". In this paper are shown the differences that come up when one try to develop models of education benefits, as well as the uncertainty of the empirical results. It is given, however, a clear support to the education effects in terms of economic productiveness and it is also expressed the conviction that the widest benefits of education may be many times underestimated.Este ensaio sumariza e analisa as mais importantes contribuições teóricas e empíricas para a avaliação e o entendimento dos efeitos da educação no desempenho dos países em termos de crescimento económico. São abordados dois debates: a controvérsia "primeiras diferenças versus níveis" e o "paradoxo micro-macro". Neste trabalho são expostas as dificuldades que surgem quando se tenta modelizar os benefícios da educação, assim como a incerteza que rodeia os resultados empíricos. Manifesta-se, no entanto, um claro apoio aos efeitos da educação em termos de produtividade económica e é expressa também a convicção de que os benefícios mais amplos da educação poderão permanecer sempre subestimados

The dynamics of market structure and R&D competition

This thesis investigates the articulation of ~he incentives to perform Research and Development of profit seeking firms. Throughout the thesis, the dynamic evolution of the distribution of these incentives across firms is the engine of industry transformation and growth. Thus, in order to a.'5SesS the impact of different industry characteristics on the market structure, we need a faithful picture of the context where firms make their R&D choices. Chapter.one exposes more in detail the motivation to pursue the analysis developed in each chapter independently, and how they combine to build up' the search for the understanding of the interactions between R&D, appropriability and market structure. Chapter two presents a dynamic model of the firm size distribution. Empirical studies of the firm size distribution often compare its moments to those of a log-normal distribution, as implied by Gibrat's Law, and note important deviations. Thus, the first and basic questions addressed in the first chapter 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. In the third chapter we explore the implications of different degrees of R&D appropriability on market structure and welfare. We propose a framework to -- pursue this analysis by extending the ¥arkov-Perfect dynamic industry model proposed by Ericson and Pakes (E-P, henceforth) (1995) through the introdu~tion of a non-proprietary productivity component to R&D as part of a dynamic, stochastic process. We first assume that spillovers are costlessly absorbed and exploited by firms in the industry, and find that, in this case, a free rider problem arises, thereby decreasing the incentives for investment. This leads to a lower amount of innovations being developed in the industry, which in turn, implies lower consuriier welfare while leaving the degree of concentration in the industry fairly unchanged. We then model a settmg where it is assumed that in order to build its absorptive capacity the firm has to engage in some R&D of its own. In this case, we find that an increase in spillovers will enhance both consumer and producer welfare substantially, and increases the likelihood of neck-and-neck competition, therefore reduciJ;lg the level of concentration in the industry. These results arise from the fact that having absorptive capacity being.built as a byproduct ofR&D enhances the productivity ofR&D investment, compensating for the free rider effect associated with the lack of appropriability. The frameworks used in the two first chapters suffer from the 'curse of dimensionality', such that the industries under analysis are limited in terms of the number of agents simultaneously active. In order to overcome this problem, in chapter four we move away from oligopolistic market structures and propose a model of monopolistic competition, where firms are sufficiently large to generate a firm size distribution with a certain degree of asYIDlIletry, although each firm is too small to affect the industry's outcome. Furthermore, we account for industry growth by having the industry's output increasing over time as a result ofknowledge externalities. The rich micro set-up of this model is analogous to .that of E-P (1995), as it is composed by heterogeneous :firms making their in- .~ vestment decisions in a world of uncertainty, but we abstract from entry and exit and instead of an oligopolistic market structure we model a monopolistic competition environment with many, heterogeneous firms. In thiS setting, :firms are asYmmetric in terms of the technology they use to produce a given commodity, and they are able to increase the likelihood of decreasing their marginal costs of production by investing in Cost Reducing R&D. In order to evaluate their future stream of profits and make their investment decisions :firms only care about the eV9lution of their efficiency and the long-run efficiency index in the industry. Cutting down the oligopolistic interactions present in the E-P framework, and having firms looking at the long-run average industry state, allows us to overcome the curse of dimensionality usually associated with dynamic models with agent heterogeneity. Therefore, we are able to simulate the model with a large number of firms competing in the industry and we show that, contrary to most existing endogenouS growth models, this model is able to deliver a firm size distribution with a substantial degree of heterogeneity. Chapter 6 presents the final remarks to the investigation carried out in this thesis

Decreased production of TNF-alpha by lymph node cells indicates experimental autoimmune encephalomyelitis remission in Lewis rats

Experimental autoimmune encephalomyelitis (EAE) is mediated by CD4+ Th1 cells that mainly secrete IFN-γ and TNF-α, important cytokines in the pathophysiology of the disease. Spontaneous remission is, in part, attributed to the down regulation of IFN-γ and TNF-α by TGF-β. In the current paper, we compared weight, histopathology and immunological parameters during the acute and recovery phases of EAE to establish the best biomarker for clinical remission. Female Lewis rats were immunised with myelin basic protein (MBP) emulsified with complete Freund's adjuvant. Animals were evaluated daily for clinical score and weight prior to euthanisation. All immunised animals developed the expected characteristics of EAE during the acute phase, including significant weight loss and high clinical scores. Disease remission was associated with a significant reduction in clinical scores, although immunised rats did not regain their initial weight values. Brain inflammatory infiltrates were higher during the acute phase. During the remission phase, anti-myelin antibody levels increased, whereas TNF-α and IFN-γ production by lymph node cells cultured with MBP or concanavalin A, respectively, decreased. The most significant difference observed between the acute and recovery phases was in the induction of TNF-α levels in MBP-stimulated cultures. Therefore, the in vitro production of this cytokine could be used as a biomarker for EAE remission

práticas artísticas no ensino básico e secundário

Educação Artística: integrar a inovação. A educação artística apresenta-se como um território a re-cartografar, numa atualização tão rápida quanto aquela que ocorre no campo artístico. As propostas publicadas neste número 11 da Revista Matéria-Prima trazem essa diversidade de abordagens, com novidades conceptuais que estabelecem as devidas relações entre educação e cidadania, participação, sustentabilidade, cultura visual, e também com alguma atenção sobre os debates pós-coloniais e as questões de género. Os 16 artigos reunidos neste 11º número da Revista Matéria-Prima trazem a realidade operativa quer na formação de professores e quer na formulação dos discursos pedagógicos, suas justificações e suas propostas alternativas.As propostas apresentadas devolvem o debate ao terreno, e alargam-no. Provocam as periferias, convocam abordagens diferenciadas sobre o tema da arte e da educação. Em todas elas a proposta de crescimento através da arte, que hoje implica cada vez mais cidadania, crítica, criatividade, interligação, comprometimento, participação.info:eu-repo/semantics/publishedVersio

A search for ultra-high-energy photons at the Pierre Auger Observatory exploiting air-shower universality

The Pierre Auger Observatory is the most sensitive detector to primary photons with energies above ∼0.2 EeV. It measures extensive air showers using a hybrid technique that combines a fluorescence detector (FD) with a ground array of particle detectors (SD). The signatures of a photon-induced air shower are a larger atmospheric depth at the shower maximum (X$_{max}$) and a steeper lateral distribution function, along with a lower number of muons with respect to the bulk of hadron-induced background. Using observables measured by the FD and SD, three photon searches in different energy bands are performed. In particular, between threshold energies of 1-10 EeV, a new analysis technique has been developed by combining the FD-based measurement of X$_{max}$ with the SD signal through a parameter related to its muon content, derived from the universality of the air showers. This technique has led to a better photon/hadron separation and, consequently, to a higher search sensitivity, resulting in a tighter upper limit than before. The outcome of this new analysis is presented here, along with previous results in the energy ranges below 1 EeV and above 10 EeV. From the data collected by the Pierre Auger Observatory in about 15 years of operation, the most stringent constraints on the fraction of photons in the cosmic flux are set over almost three decades in energy

Study on multi-ELVES in the Pierre Auger Observatory

Since 2013, the four sites of the Fluorescence Detector (FD) of the Pierre Auger Observatory record ELVES with a dedicated trigger. These UV light emissions are correlated to distant lightning strikes. The length of recorded traces has been increased from 100 μs (2013), to 300 μs (2014-16), to 900 μs (2017-present), to progressively extend the observation of the light emission towards the vertical of the causative lightning and beyond. A large fraction of the observed events shows double ELVES within the time window, and, in some cases, even more complex structures are observed. The nature of the multi-ELVES is not completely understood but may be related to the different types of lightning in which they are originated. For example, it is known that Narrow Bipolar Events can produce double ELVES, and Energetic In-cloud Pulses, occurring between the main negative and upper positive charge layer of clouds, can induce double and even quadruple ELVES in the ionosphere. This report shows the seasonal and daily dependence of the time gap, amplitude ratio, and correlation between the pulse widths of the peaks in a sample of 1000+ multi-ELVES events recorded during the period 2014-20. The events have been compared with data from other satellite and ground-based sensing devices to study the correlation of their properties with lightning observables such as altitude and polarity