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.

Hibridismo y transnacionalidad en contexto Erasmus : el caso de los estudiantes Erasmus en la Universidad de La Coruña

En el ámbito de la problemática de creación del espacio Europeo de trabajo e investigación se pretende, en este artículo, caracterizar el perfil de la movilidad académica, en el grado de la licenciatura. El estudio se dedica a la creación de perfiles balseados en motivaciones objetivas para realizar el programa Erasmus, en España. La base de nuestra investigación es la comparación de estudiantes de distintas nacionalidades, con el fin de correlacionar perfiles de estudiantes y lugares de procedencia. Elegimos los alumnos referentes a tres nacionalidades: Portuguesa, Italiana e Polaca, en las cuales se plantean varias hipótesis sobre los modelos de movilidad estudiantil y los ritmos de flujos recibidos en España, bien como en sus modos de vivir y concebir la experiencia en la Universidad de La Coruña.Fundação para a Ciência e a Tecnologia (FCT)COMPET

Development of alternative diet for the mass culture of the European cuttlefish Sepia officinalis

O objectivo desta dissertação era o desenvolvimento de dietas económicas que permitissem o cultivo em grande escala do choco, Sepia oficinalis. Esta foi dividida em duas grandes áreas de investigação, referentes aos hábitos alimentares das diversas fases da vida do choco, associados ao tamanho e à idade. A primeira parte focou os aspectos de cultivo de misidáceos para alimentar os juvenis de choco. A segunda parte consistiu em determinar os efeitos de dietas artificiais (em substituição de dietas naturais como camarão ou peixe congelado) no cultivo do choco, e determinar se estas poderiam substituir com sucesso as dietas naturais que são normalmente utilizadas.The objective of this dissertation research was to enable the mass culture of Sepia ofitcinalis through the development of inexpensive diets. It was divided into two major areas concerning the feeding habits of S. officinalis according to their age and size. The first part focused on the culture of mysids to feed hatchling cuttlefish. The second part consisted on testing the effects of artificial surimi diets fed to cuttlefish and deterrnine if they could successfully replace natural food (frozen shrimp or fish) that are nonnally used

Evaluating the performance and intrusiveness of virtual machines for desktop grid computing

Comunicação apresentada no 3rd Workshop on Desktop Grids and Volunteer Computing Systems, Rome, 2009.We experimentally evaluate the performance overhead of the virtual environments VMware Player, QEMU, VirtualPC and VirtualBox on a dual-core machine. Firstly, we assess the performance of a Linux guest OS running on a virtual machine by separately benchmarking the CPU, file I/O and the network bandwidth. These values are compared to the performance achieved when applications are run on a Linux OS directly over the physical machine. Secondly, we measure the impact that a virtual machine running a volunteer @home project worker causes on a host OS. Results show that performance attainable on virtual machines depends simultaneously on the virtual machine software and on the application type, with CPU-bound applications much less impacted than IO-bound ones. Additionally, the performance impact on the host OS caused by a virtual machine using all the virtual CPU, ranges from 10% to 35%, depending on the virtual environment

Ethnopharmacological survey among migrants living in the Southeast Atlantic Forest of Diadema, São Paulo, Brazil

<p>Abstract</p> <p>Background</p> <p>Understanding how people of diverse cultural backgrounds have traditionally used plants and animals as medicinal substances during displacements is one of the most important objectives of ethnopharmacological studies. An ethnopharmacological survey conducted among migrants living in the Southeast Atlantic Forest remnants (Diadema, São Paulo, Brazil) is presented herein.</p> <p>Methods</p> <p>Ethnographical methods were used to select and interview the migrants, and botanical and zoological techniques were employed to collect the indicated resources.</p> <p>Results</p> <p>We interviewed five migrants who described knowledge on 12 animals and 85 plants. Only 78 plants were present in Diadema, they belong to 37 taxonomic families; 68 were used exclusively for medicinal purposes, whereas 10 were reported to be toxic and/or presented some restriction of use. These taxa were grouped into 12 therapeutic categories (e.g., gastrointestinal disturbances, inflammatory processes or respiratory problems) based on the 41 individual complaints cited by the migrants. While the twelve animal species were used by the migrants to treat nine complaints; these were divided into six categories, the largest of which related to respiratory problems. None of the animal species and only 57 of the 78 plant species analysed in the present study were previously reported in the pharmacological literature; the popular knowledge concurred with academic findings for 30 of the plants. The seven plants [<it>Impatiens hawkeri </it>W. Bull., <it>Artemisia canphorata </it>Vill., <it>Equisetum arvensis </it>L., <it>Senna pendula </it>(Humb. & Bonpl. ex Willd.) H.S. Irwin & Barneby, <it>Zea mays </it>L., <it>Fevillea passiflora </it>Vell. and <it>Croton fuscescens </it>Spreng)] and the two animals (<it>Atta sexdens </it>and <it>Periplaneta americana</it>) that showed maintenance of use among migrants during their displacement in Brazilian territory, have not been studied by pharmacologists yet.</p> <p><b>Conclusions</b></p> <p>Thus, they should be highlighted and focused in further pharmacology and phytochemical studies, since the persistence of their uses can be indicative of bioactive potentials.</p

Atividade física de lazer entre as gestantes da coorte de nascimentos de Pelotas de 2004

OBJECTIVE: Physical activity during pregnancy is a poorly investigated subject on population level. The study aimed to describe duration, type and frequency of leisure-time physical activity during pregnancy, and to explore its associated factors. METHODS: A population-based study was carried out during 2004 in Southern Brazil. A total of 4,471 mothers were interviewed soon after delivery. Physical activity was measured using a questionnaire, developed for the study. Results were obtained by Poisson regression. RESULTS: In the sample, 14.8% of women reported to engage in some type of physical activity prior to pregnancy and 12.9% during pregnancy. In the first trimester, 10.4% of all mothers engaged in some type of physical activity; 8.5% in the second trimester and 6.5% in the third trimester. Only 194 mothers (4.3%) were active during the whole pregnancy. In the adjusted analysis, leisure-time physical activity was positively associated with schooling, physical activity advice during prenatal care, and family income (pOBJETIVO: A atividade física durante a gestação é pouco estudada em nível populacional. O objetivo do estudo foi descrever a duração, tipo e freqüência de atividade física de lazer durante a gravidez e explorar fatores associados. MÉTODOS: Estudo de base populacional, realizado durante o ano de 2004 em Pelotas, RS, Brasil. Logo após o parto, 4.471 mães foram entrevistadas. Utilizou-se questionário, desenvolvido para o estudo, para verificar a atividade física de lazer. Os resultados foram obtidos por regressão de Poisson. RESULTADOS: Antes da gravidez, 14,8% das mulheres relataram algum tipo de atividade física de lazer e durante, 12,9%. No primeiro trimestre, 10,4% de todas as mães fizeram alguma atividade física de lazer; no segundo, 8,5% e no terceiro, 6,5%. Apenas 194 mães (4,3%) foram ativas durante toda a gestação. Na análise ajustada, atividade física de lazer esteve positivamente associada com escolaridade, aconselhamento para atividade física durante o pré-natal e renda familiar (

Hiatal hernia recurrence after open surgery - a systematic review regarding risk factors

Introdução As hérnias do hiato ocorrem principalmente devido a fragilidade da membrana frenoesofágica e de outras estruturas próximas, como os pilares do diafragma. Isto resulta na migração intratorácica através do hiato esofágico de uma porção do tubo digestivo, o que acarreta um risco aumentado de complicações como refluxo, esofagite ou mesmo estrangulamento. A reparação cirúrgica é efetuada tradicionalmente por cirurgia aberta ou, mais recentemente, de forma minimamente invasiva. Os fatores que determinam a recorrência das hérnias do hiato após cirurgia aberta não estão ainda completamente esclarecidos. Métodos Seguindo as guidelines PRISMA, realizou-se uma revisão sistemática da literatura incidindo nos fatores de recorrência da hérnia do hiato após cirurgia aberta. Recorreu-se a duas bases de dados de referências, a Medline e a Scopus. Resultados Identificaram-se um total de 1070 referências. Após exclusão de duplicados, artigos não disponíveis ou irrelevantes, analisaram-se qualitativamente 18 artigos. Discussão Vários estudos consideram o impacto do tipo de apresentação (urgente, não urgente), um maior IMC, idade ou o tipo de cirurgia (com ou sem procedimento antirefluxo associado). Contudo, ainda não foi encontrada uma associação entre estes fatores e o aumento do risco de recorrência. Um estudo descreve uma associação entre complicações graves de refluxo e o maior risco de recorrência. Não existe uniformidade na definição de recorrência nem como a diagnosticar. Conclusão Os determinantes da recorrência após reparação aberta da hérnia do hiato permanecem controversos. Demonstra-se a necessidade de estudos prospetivos que permitam uma compreensão mais aprofundada com melhor evidência sobre as causas de recorrência da hérnia do hiato e como esta pode ser prevenida.Introduction Due to fragility of phrenoesophageal membrane and nearby structures such as diaphragmatic crura (among other causes), hiatal hernias can develop. This results in intrathoracic migration of a portion of the digestive tube through the esophageal hiatus, with added risk of complications such as reflux, esophagitis, or even strangulation. This surgical repair can be performed traditionally with open surgery or, more recently, by minimal invasive surgery. The factors that determine hiatal hernia recurrence after open repair are not yet well understood. Methods Following the PRISMA guidelines, we performed a systematic review of literature regarding risk factors for recurrence after open surgery for hiatal hernia repair. We used both Medline and Scopus libraries. Results We identified a total of 1070 records. After exclusion of duplicates, unavailable and non-relevant articles, we included 18 studies in our qualitative analysis. Discussion Several studies consider the role of acute presentation, higher patient BMI, older age, or the type of surgery with or without a reflux procedure. However, a lack of significant association between these factors and a higher recurrence risk remains. A significant association was found between serious reflux complications the risk of recurrence, in one study. There is also a lack of consensus regarding what constitutes a recurrence, and how to diagnose it. Conclusion The factors related to the recurrence of hiatal hernia after open repair remain controversial. There is a need for prospective studies that allow for a more comprehensive understanding specially with better evidence on why hernias recur and how can this be prevented

Reduced Frequency of Knowledge of Results Enhances Learning in Persons with Parkinson's Disease

Parkinson's disease (PD) is a progressive neurological disorder, known to cause a large number of motor and non-motor limitations. Research related to factors that affect motor control and learning in people with PD is still relatively limited. The purpose of this study was to compare the effects of different frequencies (100 versus 66%) of knowledge of results (KR) on the learning of a motor skill with spatial demands in participants with PD. Twenty individuals with PD were randomly assigned to one of two groups. The 100% group received KR after each trial, while the 66% group received KR on two thirds of the trials. A linear positioning task with a spatial target was used. Participants carried out the task with the dominant hand while blindfolded. In the acquisition and retention phases, the goal was to position the cursor at a distance of 60 cm from the starting point. The hypothesis was that participants with PD, who practiced with a reduced KR frequency, would demonstrate more effective learning than those who practiced with a 100% KR frequency, similar to previous findings with adults without neurological disorders. The results showed differences between the groups in the retention phase (without KR): The 66% KR group was more accurate and less variable in their performance than the 100% KR group. Thus, reducing KR frequency can enhance motor learning in persons with PD, similar to what has previously been found for unimpaired participants

Escherichia coli expression and purification of LL37 fused to a family III carbohydrate-binding module from Clostridium thermocellum

The cathelicidin derived human peptide LL37 has a broad spectrum of antimicrobial and immunomodulatory activities. The large variety of biological activities makes LL37 a very promising candidate for clinical applications. The production of biologically active LL37 in large amounts with reduced costs can only be achieved using recombinant techniques. In this work, LL37 has been cloned to the N- and C-termini of a family III carbohydrate-binding module fused to the linker sequence (LK-CBM3) from Clostridium thermocellum; both constructions (LL37-LK-CBM3 and LK-CBM3-LL37) were cloned into the pET-21a vector. A formic acid recognition site was introduced between the two modules, allowing the isolation of LL37 after chemical cleavage. The recombinant proteins were expressed in Escherichia coli BL21 (DE3) and solubilized with Triton X-100. The purification was achieved using cellulose CF11 fibers, taking advantage of the CBM3 specific affinity for cellulose; after hydrolysis with formic acid, LL37 was further purified by reverse-phase HPLC, as confirmed by MALDI-TOF mass spectrometry. The production and purification methodology developed in this work compares advantageously to other protocols previously described, having fewer purification steps. Only the recombinant LL37 obtained from the C-terminally fused protein (LK-CBM3-LL37) showed antibacterial activity against E. coli K12, with a MIC of 180 μg/ml.University of Porto. Institute of Molecular Pathology and Immunology. Proteomics Unit (IPATIMUP)Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/27404/200