Flow of magnetic repelling grains in a two-dimensional silo

During a typical silo discharge, the material flow rate is determined by the contact forces between the grains. Here, we report an original study concerning the discharge of a two-dimensional silo filled with repelling magnetic grains. This non-contact interaction leads to a different dynamics from the one observed with conventional granular materials. We found that, although the flow rate dependence on the aperture size follows roughly the power-law with an exponent $3/2$ found in non-repulsive systems, the density and velocity profiles during the discharge are totally different. New phenomena must be taken into account. Despite the absence of contacts, clogging and intermittence were also observed for apertures smaller than a critical size determined by the effective radius of the repulsive grains.Comment: 6 pages, 8 figure

Importância da distribuição de chuvas para o cultivo de milho no agreste sergipano.

O Agreste Sergipano é uma das mesorregiões onde a cultura do milho é cultivada com alta tecnologia. Nesse contexto, os efeitos relacionados ao déficit hídrico podem trazer perdas significativas à produtividade. O objetivo desse trabalho foi avaliar o possível efeito da distribuição de chuvas sobre o comportamento produtivo do milho em um experimento de campo em dois anos agrícolas. O estudo foi realizado na Estação Experimental Jorge Sobral da Embrapa Tabuleiros Costeiros, localizada no município de Nossa Senhora das Dores (SE), por meio da execução de um experimento de campo, conduzido nas safras de 2012 e 2013. Concluiu-se que a safra de 2012, mesmo com precipitações abaixo da média dos últimos 10 anos, teve uma produtividade absoluta maior quando comparada com a safra de 2013

Avaliação da cobertura do solo em sistemas de produção de milho e soja em Sergipe utilizando imagens aéreas.

O sistema de monocultivo empregado nas regiões produtoras de milho no Estado de Sergipe, associado ao preparo do solo com grades pesadas e utilização dos restos culturais como pastagens, pode num futuro próximo resultar na degradação dos solos destinados a essa atividade agrícola, resultando na queda de produtividade das lavouras, e consequentemente, na redução dos lucros obtidos pelos rodutores. Uma técnica já consagrada em outras regiões do Brasil é a semeadura simultânea de milho com espécies de capim Brachiaria, que após a colheita do milho desenvolve formando boa cobertura do solo, que pode ser usada com dupla fi nalidade: a) pastagem no sistema integração lavoura pecuária; b) formação de cobertura morta no sistema plantio direto, que proporciona efi ciente proteção do solo contra erosão, além de diminuir a evaporação da água, contribuindo para menor estres hídrico das lavouras na ocasião de veranicos, muito comuns na região. Portanto, esse trabalho teve como objetivo avaliar a cobertura do solo em sistemas de produção de milho e soja na transição dos Tabuleiros Costeiros e Agreste de Sergipe, por meio de imagens aéreas digitais. O estudo foi realizado por meio da execução de um experimento de campo, conduzido na safra 2013 em um Argissolo da Estação Experimental Jorge Sobral da Embrapa Tabuleiros Costeiros localizada no município de Nossa Senhora das Dores, SE. O delineamento experimental foi em blocos ao acaso, com quatro repetições, e cinco tratamentos: 1) milho monocultivo em preparo do solo convencional (MMPC); 2) soja monocultivo em preparo do solo convencional (SMPC); 3) milho monocultivo em plantio direto (MMPD); 4) soja monocultivo em plantio direto (SMPD); 5) milho consorcio com Brachiaria decumbens em plantio direto (MBDPD) e 6) milho consórcio com Brachiaria ruziziensis em plantio direto (MBRPD). Após a colheita do milho a cobertura do solo foi avaliada por meio da interpretação de imagens digitais obtidas por uma câmera Gopro estabilizada por um gimbal instalado em um Drone rádio controlado do tipo quadricóptero, utilizado para sobrevoar as parcelas experimentais. Conforme resultados obtidos, concluímos que o cultivo de milho consorciado com braquiárias contribui signifi ativamente para formação de cobertura do solo, para adoção de sistema integração lavoura/pecuária e do sistema plantio direto em Sergipe. A utilização de Drones para obtenção de imagens aéreas é viável para avaliação de cobertura do solo em sistemas de produção de grãos e pastagens. Palavras-chave: Drone, SisCob, plantio simultâneo, plantio direto, braquiária

Double fermiophobic Higgs boson production at the LHC and LC

We consider the phenomenology of a fermiophobic Higgs boson (h_f) at the Large Hadron Collider (LHC) and a e+e- Linear Collider (LC). At both machines the standard production mechanisms which rely on the coupling h_fVV (V=W,Z) can be very suppressed at large tan beta. In such cases the complementary channels pp to H^\pm h_f, A^0 h_f and e+e- to A^0 h_f offer promising cross-sections. Together with the potentially large branching ratios for H^\pm to h_fW* and A^0 to h_fZ*, these mechanisms would give rise to double h_f production, leading to signatures of gamma gamma gamma gamma, gamma gamma VV and VVVV.Comment: 19 pages, 9 figures, expanded discussion, fig.1 changed slightly, version to appear in Phys.Rev.

A comparative analysis of the observed white dwarf cooling sequence from globular clusters

We report our study of features at the observed red end of the white dwarf cooling sequences for three Galactic globular clusters: NGC\,6397, 47\,Tucanae and M\,4. We use deep colour-magnitude diagrams constructed from archival Hubble Space Telescope (ACS) to systematically investigate the blue turn at faint magnitudes and the age determinations for each cluster. We find that the age difference between NGC\,6397 and 47\,Tuc is 1.98$^{+0.44}_{-0.26}$\,Gyr, consistent with the picture that metal-rich halo clusters were formed later than metal-poor halo clusters. We self-consistently include the effect of metallicity on the progenitor age and the initial-to-final mass relation. In contrast with previous investigations that invoked a single white dwarf mass for each cluster, the data shows a spread of white dwarf masses that better reproduce the shape and location of the blue turn. This effect alone, however, does not completely reproduce the observational data - the blue turn retains some mystery. In this context, we discuss several other potential problems in the models. These include possible partial mixing of H and He in the atmosphere of white dwarf stars, the lack of a good physical description of the collision-induced absorption process and uncertainties in the opacities at low temperatures. The latter are already known to be significant in the description of the cool main sequence. Additionally, we find that the present day local mass function of NGC\,6397 is consistent with a top-heavy type, while 47\,Tuc presents a bottom-heavy profile.Comment: Accepted for publication in MNRAS (16 pages, 19 figures

Structural Modeling of Straw Bale Loadbearing Wall

In Ecuador, there are qualitative and quantitative housing deficits that must be covered with materials that produce seismic-resistant, energy-efficient buildings that do not require a large amount of energy to be produced. Several studies indicate that the answer lies in straw bale structures. However, for these to be considered by designers, aids are needed to facilitate their structural modeling in specialized computer programs. Through literature reviews, the present research proposes a model that adapts the specific structural considerations of straw bale buildings to the tools available in a design program. Keywords: structure, bales, straw, model, program, design. Resumen En el Ecuador existe un déficit cualitativo y cuantitativo de viviendas que debe ser cubierto con materiales que produzcan edificaciones sismo resistentes, energéticamente eficientes y a la vez que no requieran gran cantidad de energía para ser producidos. Varios estudios señalan que la respuesta está en las estructuras elaboradas con fardos de paja. Sin embargo, para que éstas sean consideradas por los diseñadores son necesarias ayudas para facilitar su modelamiento estructural en programas informáticos especializados. La presente investigación, a través de revisiones bibliográficas, propone un modelo que adapta las consideraciones estructurales específicas de las construcciones con fardos de paja a las herramientas disponibles en un programa de diseño. Palabras Clave: estructura, fardos, paja, modelo, programa, diseñ

Bounds for the time to failure of hierarchical systems of fracture

For years limited Monte Carlo simulations have led to the suspicion that the time to failure of hierarchically organized load-transfer models of fracture is non-zero for sets of infinite size. This fact could have a profound significance in engineering practice and also in geophysics. Here, we develop an exact algebraic iterative method to compute the successive time intervals for individual breaking in systems of height $n$ in terms of the information calculated in the previous height $n-1$. As a byproduct of this method, rigorous lower and higher bounds for the time to failure of very large systems are easily obtained. The asymptotic behavior of the resulting lower bound leads to the evidence that the above mentioned suspicion is actually true.Comment: Final version. To appear in Phys. Rev. E, Feb 199

Proposal for applying combined selection to diallel analysis.

The phylosophy of intrapopulation combined selection is the search for and identification of individuals with superior genotypic behavior, based on their performance compared to the family mean and, at the same time, of their family mean in relation to the population mean, through the weighting of the phenotypic values represented, respectively, by the within and among families heritability coeficient. The objective of this study was to adapt and apply this philosophy ti diallel analysis. The crosses were considered as having fixed effects and selected on the basis of their specific combining ability (SCA), and on the mean performance of the two involved parents, in relation to the general combining ability (GCA). This work was based on Griffing's (Heredity 10; 35-50, 1956) method 2, model 1 which involves p(p+1)/2 treatments. The proposed index result from the weighting of the effects of GCA (gi's) and SCA (sij's) by the respective determination coefficient of additive and dominant genetic determinations, resulting from the partitioning of the total genotypic determination coefficient. An example is given for illustration

The Effective Particle-Hole Interaction and the Optical Response of Simple Metal Clusters

Following Sham and Rice [L. J. Sham, T. M. Rice, Phys. Rev. 144 (1966) 708] the correlated motion of particle-hole pairs is studied, starting from the general two-particle Greens function. In this way we derive a matrix equation for eigenvalues and wave functions, respectively, of the general type of collective excitation of a N-particle system. The interplay between excitons and plasmons is fully described by this new set of equations. As a by-product we obtain - at least a-posteriori - a justification for the use of the TDLDA for simple-metal clusters.Comment: RevTeX, 15 pages, 5 figures in uufiles format, 1 figure avaible from [email protected]