A Stress/Displacement Virtual Element Method for Plane Elasticity Problems

The numerical approximation of 2D elasticity problems is considered, in the framework of the small strain theory and in connection with the mixed Hellinger-Reissner variational formulation. A low-order Virtual Element Method (VEM) with a-priori symmetric stresses is proposed. Several numerical tests are provided, along with a rigorous stability and convergence analysis

Who Creates Jobs? Small vs. Large vs. Young

The view that small businesses create the most jobs remains appealing to policymakers and small business advocates. Using data from the Census Bureau Business Dynamics Statistics and Longitudinal Business Database, we explore the many issues at the core of this ongoing debate. We find that the relationship between firm size and employment growth is sensitive to these issues. However, our main finding is that once we control for firm age there is no systematic relationship between firm size and growth. Our findings highlight the important role of business startups and young businesses in U.S. job creation.

Signals of high cognitive abilities by teachers: structural validaty of the Scale of Cognitive Ability and of Learning

As nomeações pelos professores são muitas vezes utilizadas na sinalização das crianças sobredotadas complementando as avaliações realizadas através dos testes psicológicos de inteligência. Contudo nem sempre essa identificação é isenta de viés, melhorando a qualidade quando os instrumentos de identificação usados pelos professores apresentam boas características métricas de validade e fiabilidade. O objetivo deste estudo foi testar a estrutura empírica da Escala de Habilidades Cognitivas e de Aprendizagem (EHC/A) pertencente à BISAS-T (Bateria de Instrumentos para a Sinalização de Alunos Sobredotados e Talentosos; Almeida, Oliveira, & Melo, 2000), ou seja, procurou-se avaliar a qualidade do ajustamento da sua estrutura fatorial numa amostra de alunos do 6º ano de escolaridade. Esta escala foi construída com base no modelo teórico de Renzulli (1976) sendo formada por 16 itens respondidos numa escala de tipo likert de 6 pontos. A amostra contou com 132 alunos do 6º ano de escolaridade, com idade em torno de 11 anos. Os resultados das qualidades psicométricas da EHC/A são considerados satisfatórios para a amostra em estudo sugerindo a sua utilização em futuras pesquisas com amostras mais alargadas e com o objetivo de sinalização de alunos mais capazes.Screening by teachers is often used in the identification of gifted children and complement assessments through psychological tests of intelligence. However this identification is not always free from bias, improving its quality when identification instruments used by teachers have good metric characteristics of validity and reliability. With this work we intend to test the empirical structure of the Scale of Cognitive Abilities and Learning (EHC/A) included in the BISAS-T (Almeida, Oliveira, & Melo, 2000) or, in other words, to assess the quality of the adjustment of its factor structure in a sample of 6th grade students. This scale was constructed based on Renzulli´s theoretical model (1976) and consisted of 16 items answered on a Likert type scale of 6 points. The sample consisted of 132 students from 6th grade, aged around 11 years. Results of the psychometric qualities of EHC/A are satisfactory for this sample, suggesting its use in future research with broader samples and aiming to identify the most able students

Collapse of Primordial Clouds

We present here studies of collapse of purely baryonic Population III objects with masses ranging from $10M_\odot$ to $10^6M_\odot$. A spherical Lagrangian hydrodynamic code has been written to study the formation and evolution of the primordial clouds, from the beginning of the recombination era ($z_{rec} \sim 1500$) until the redshift when the collapse occurs. All the relevant processes are included in the calculations, as well as, the expansion of the Universe. As initial condition we take different values for the Hubble constant and for the baryonic density parameter (considering however a purely baryonic Universe), as well as different density perturbation spectra, in order to see their influence on the behavior of the Population III objects evolution. We find, for example, that the first mass that collapses is $8.5\times10^4M_\odot$ for $h=1$, $\Omega=0.1$ and $\delta_i={\delta\rho / \rho}=(M / M_o)^{-1/3}(1+z_{rec})^{-1}$ with the mass scale $M_o=10^{15}M_\odot$. For $M_o=4\times10^{17}M_\odot$ we obtain $4.4\times10^{4}M_\odot$ for the first mass that collapses. The cooling-heating and photon drag processes have a key role in the collapse of the clouds and in their thermal history. Our results show, for example, that when we disregard the Compton cooling-heating, the collapse of the objects with masses $>8.5\times10^4M_\odot$ occurs earlier. On the other hand, disregarding the photon drag process, the collapse occurs at a higher redshift.Comment: 10 pages, MN plain TeX macros v1.6 file, 9 PS figures. Also available at http://www.iagusp.usp.br/~oswaldo (click "OPTIONS" and then "ARTICLES"). MNRAS in pres

Relations between creativity and academic performance: study of gender differences in a group of students from 6th grade

Este trabalho analisa as relações entre criatividade e o rendimento escolar tomando em atenção o género dos alunos. A amostra é constituída por de 240 alunos do 6º ano de escolaridade, 124 rapazes (52%) e 116 raparigas (48%) com média de idades de 11,6. Aplicaram-se seis subtestes do Teste de Pensamento Criativo de Torrance, repartidos por tarefas verbais e figurativas, orientando-nos pelos critérios de cotação da versão brasileira (Wechsler, 2002). O rendimento escolar foi obtido tomando as classificações dos alunos no final do 3º trimestre escolar. Este estudo sugere uma relação positiva e estatisticamente significativa entre a criatividade e o desempenho escolar dos alunos, explicando a criatividade cerca de 20% da variância no rendimento escolar. Não se verificaram diferenças de género nos critérios da criatividade, mas registaram-se resultados superiores nas alunas no rendimento escolar.Este trabajo analiza la relación entre la creatividad y el rendimiento escolar teniendo en cuenta el género de los estudiantes. La muestra se compone de 240 estudiantes de 6 to grado, 124 varones (52%) y 116 mujeres (48%) con una edad media de 11,6. Se aplicaron seis subtests del Test de Pensamiento Creativo de Torrance, dividido en tareas verbales y figurativos, nos guiamos por los criterios de inclusión de la versión brasileña (Wechsler, 2002). El rendimiento académico se obtuvo mediante la adopción de las calificaciones de los estudiantes al final del tercer trimestre escolar. Este estudio sugiere una relación positiva y estadísticamente significativa entre la creatividad y el rendimiento académico de los estudiantes. La creatividad explica alrededor del 20% de la varianza en el rendimiento escolar. No hubo diferencias de género en los criterios de creatividad, pero hubo mejores resultados en las niñas en el rendimiento escolar.This paper analyzes the relationship between creativity and school performance in to account the gender of the students. The sample consists of 240 students from the 6th grade, 124 boys (52%) and 116 girls (48%) with mean age of 11.6. Were applied six subtests of the Test of Creative Thinking of Torrance, divided into verbal and figurative tasks, guiding us by listing criteria of the Brazilian version (Wechsler, 2002). The academic achievement students was obtained by taking the ratings of the at the end of the 3rd school term. This study suggests a positive and statistically significant relationship between creativity and academic performance of the students, explaining creativity about 20% of the variance in school performance. There were no gender differences in the creativity criteria, but there were better results than in girls in school performance

Diferenças de género no raciocínio e no autoconceito em alunos com talento académico

Na literatura constata-se que não são conclusivos os estudos efetuados acerca das diferenças entre rapazes e raparigas na realização de provas que avaliam as diversas variáveis psicológicas. Para além de eventuais dificuldades resultantes do tipo de testes utilizados, é também questionado as amostras consideradas nos estudos. No caso concreto deste estudo, a amostra é constituída por um grupo de 135 alunos academicamente talentosos do 5º ano de escolaridade (71 rapazes e 64 raparigas), com um rendimento académico situado no percentil 80, e analisam-se eventuais diferenças de género em provas de raciocínio e autoconceito. Nas provas de raciocínio, nenhuma diferença tem significado estatístico, sendo na prova de raciocínio numérico que ocorre a diferença mais elevada e é favorável às alunas. Nas dimensões do auto conceito observa-se uma diferença com significado estatístico na dimensão de ansiedade, mostrando as alunas níveis mais moderados de ansiedade ou a sua melhor gestão. Sendo frequentes tais diferenças quando se consideram amostras heterogéneas de alunos, os resultados deste estudo apontam para uma não diferenciação dos desempenhos e das autoavaliações dos alunos segundo o género quando se consideram os alunos com elevado rendimento académico.In the literature it appears that are not conclusive studies about the differences between boys and girls in tests scores that assess the various psychological variables. In addition to any difficulties arising from the type of tests used, is also questioned the samples considered in the studies. In the case of this study, the sample consists of a group of 135 academic talented students from 5th grade (71 boys and 64 girls) with an academic achievement located in the 80th percentile, and it will be analyzed possible gender differences in reasoning and self-concept tests. In the reasoning tests, no difference has statistical significance, being the numerical reasoning test that is the highest difference and is favorable to girls. The dimensions of the self-concept present a statistically significant difference in the level of anxiety, showing more moderate levels of anxiety or better management in girls. Being frequent such differences when considering heterogeneous samples of students, the results of this study point to a lack of gender differentiation of students performances and self-assessments when considering students with high academic performance

Scalar Spectrum from a Dynamical Gravity/Gauge model

We show that a Dynamical AdS/QCD model is able to reproduce the linear Regge trajectories for the light-flavor sector of mesons with high spin and also for the scalar and pseudoscalar ones. In addition the model has confinement by the Wilson loop criteria and a mass gap. We also calculate the decay amplitude of scalars into two pion in good agreement to the available experimental data.Comment: Presented in the 4th International Workshop on Astronomy and Relativistic Astrophysic