Fermionic van Hemmen Spin Glass Model with a Transverse Field

In the present work it is studied the fermionic van Hemmen model for the spin glass (SG) with a transverse magnetic field $\Gamma$. In this model, the spin operators are written as a bilinear combination of fermionic operators, which allows the analysis of the interplay between charge and spin fluctuations in the presence of a quantum spin flipping mechanism given by $\Gamma$. The problem is expressed in the fermionic path integral formalism. As results, magnetic phase diagrams of temperature versus the ferromagnetic interaction are obtained for several values of chemical potential $\mu$ and $\Gamma$. The $\Gamma$ field suppresses the magnetic orders. The increase of $\mu$ alters the average occupation per site that affects the magnetic phases. For instance, the SG and the mixed SG+ferromagnetic phases are also suppressed by $\mu$. In addition, $\mu$ can change the nature of the phase boundaries introducing a first order transition.Comment: 9 pages, 4 figures, accepted for publication in Phys. Lett.

Stability conditions for fermionic Ising spin-glass models in the presence of a transverse field

The stability of spin-glass (SG) phase is analyzed in detail for a fermionic Ising SG (FISG) model in the presence of a magnetic transverse field $\Gamma$. The fermionic path integral formalism, replica method and static approach have been used to obtain the thermodynamic potential within one step replica symmetry breaking ansatz. The replica symmetry (RS) results show that the SG phase is always unstable against the replicon. Moreover, the two other eigenvalues $\lambda_{\pm}$ of the Hessian matrix (related to the diagonal elements of the replica matrix) can indicate an additional instability to the SG phase, which enhances when $\Gamma$ is increased. Therefore, this result suggests that the study of the replicon can not be enough to guarantee the RS stability in the present quantum FISG model, especially near the quantum critical point. In particular, the FISG model allows changing the occupation number of sites, so one can get a first order transition when the chemical potential exceeds a certain value. In this region, the replicon and the $\lambda_{\pm}$ indicate instability problems for the SG solution close to all range of first order boundary.Comment: 15 pages, 4 figures, accepted in Physica

Spatial dynamics of labor markets in Brazil

There was substantial spatial variation in labor market outcomes in Brazil over the 1990s. In 2000, about one-fifth of workers lived in apparently economically stagnant municipios where real wages declined but employment increased faster than the national population growth rate. More than one-third lived in apparently dynamic municipios, experiencing both real wage growth and faster-than-average employment growth. These areas absorbed more than half of net employment growth over the period. To elucidate this spatial variation, the authors estimate spatial labor supply and demand equations describing wage and employment changes of Brazilian municipios. They use Conley's spatial GMM technique to allow for instrumental variable estimation in the presence of spatially autocorrelated errors. The main findings include: (1) a very strong influence of initial workforce educational levels on subsequent wage growth (controlling for possibly confounding variables such as remoteness and climate); (2) evidence of positive spillover effects of own-municipio growth onto neighbors'wage and employment levels; (3) an exodus from farming areas; (4) relatively elastic response of wages to an increase in labor supply; and (5) evidence of a local multiplier effect from government transfers.Labor Markets,Economic Theory&Research,Economic Growth,Municipal Financial Management,Achieving Shared Growth

Effect of the North Equatorial Counter Current on the generation and propagation of internal solitary waves off the Amazon shelf (SAR observations)

Synthetic aperture radar (SAR) imagery from the Amazon shelf break region in the tropical west Atlantic reveals for the first time the two-dimensional horizontal structure of an intense Internal Solitary Wave (ISW) field, whose first surface manifestations are detected several hundred kilometres away from the nearest forcing bathymetry. Composite maps and an energy budget analysis (provided from the Hybrid Coordinate Ocean Model - HYCOM) help to identify two major ISW pathways emanating from the steep slopes of a small promontory (or headland) near 44 degrees W and 0 degrees N, which are seen to extend for over 500 km into the open ocean. Further analysis in the SAR reveals propagation speeds above 3 ms(-1), which are amongst the fastest ever recorded. The main characteristics of the ISWs are further discussed based on a statistical analysis, and seasonal variability is found for one of the ISW sources. This seasonal variability is discussed in light of the North Equatorial Counter Current. The remote appearance of the ISW sea surface manifestations is explained by a late disintegration of the internal tide (IT), which is further investigated based on the SAR data and climatological monthly means (for stratification and currents). Acknowledging the possibility of a late disintegration of the IT may help explain the remote-sensing views of other ISWs in the world's oceans

Fitotoxidade de herbicidas aplicados em pós-emergência na fase inicial da cultura do milho.

A aplicacao de herbicidas em pos-emergencia dirigida pode causar injurias as plantas de milho, quando estas sao atingidas por produtos nao totalmente seletivos. Como esses herbicidas sao basicamente bloqueados de processos metabolicos, surge a duvida de quais serao os efeitos dessas injurias na producao final de graos de milho. Assim, o objetivo deste trabalho foi estudar o efeito da fitotoxidade causada pela aplicacao de herbicidas na fase inicial e na pos-emergencia tardia da cultura e o seu efeito na producao de graos. Foi utilizado o hibrido BRS 3123, em 12 tratamentos repetidos 4 vezes. Esses tratamentos consistiram da aplicacao dos seguintes herbicidas: cyanazine + simazine + assist, aplicados nos estadios de crescimentos de 4 e 6 folhas e paraquat + extravon e ametryn + assist, aplicados no estadio de 12 folhas, em jato dirigido. Foram incluidos tambem testemunhas com e sem capinas, alem dos tratamentos com retirada mecanica das folhas do 1 e do 3 pares de folha. Foram avaliados: area foliar, materia seca, teor de clorofila nas folhas, altura da planta e da insercao de espigas, diametro do colmo, indice de espigas, peso de 1000 graos e producao de graos. Observou-se que no primeiro ano agricola (94/95), as variaveis de crescimento nao foram afetadas pelos tratamentos, ao passo que no ano seguinte, o melhor desenvolvimento das plantas foi obtido com a aplicacao de cyanazine + simazine, enquanto que paraquat + extravon, ametryn + assist e testemunha sem capina, (devido ao efeito de matocompeticao), resultaram nos piores tratamentos ate a floracao do milho. A maior producao de espigas e graos no primeiro ano foi obtida com o tratamento cyanazine + simazine + assist, enquanto que, no segundo ano, paraquat + extravon e ametryn + assist proporcionaram as maiores producoes, apesar das injurias observadas na area foliar