Atomistic spin dynamics of the CuMn spin glass alloy

We demonstrate the use of Langevin spin dynamics for studying dynamical properties of an archetypical spin glass system. Simulations are performed on CuMn (20% Mn) where we study the relaxation that follows a sudden quench of the system to the low temperature phase. The system is modeled by a Heisenberg Hamiltonian where the Heisenberg interaction parameters are calculated by means of first-principles density functional theory. Simulations are performed by numerically solving the Langevin equations of motion for the atomic spins. It is shown that dynamics is governed, to a large degree, by the damping parameter in the equations of motion and the system size. For large damping and large system sizes we observe the typical aging regime.Comment: 18 pages, 9 figure

Optical spectroscopy and the nature of the insulating state of rare-earth nickelates

Using a combination of spectroscopic ellipsometry and DC transport measurements, we determine the temperature dependence of the optical conductivity of NdNiO$_3$ and SmNiO$_{3}$ films. The optical spectra show the appearance of a characteristic two-peak structure in the near-infrared when the material passes from the metal to the insulator phase. Dynamical mean-field theory calculations confirm this two-peak structure, and allow to identify these spectral changes and the associated changes in the electronic structure. We demonstrate that the insulating phase in these compounds and the associated characteristic two-peak structure are due to the combined effect of bond-disproportionation and Mott physics associated with half of the disproportionated sites. We also provide insights into the structure of excited states above the gap.Comment: 12 pages, 13 figure

Cultivo e uso de abóboras ornamentais.

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Cultivo orgânico do morangueiro: densidade de plantio, crescimento e produtividade de cultivares de ?dia neutro?

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Planting density and number of stems for ecological crop determinate growth tomato.

Tomato growers adopting an ecologically based system have opted for determinate growth varieties due to their ease of staking and sprouting, and due to the fact that they have a shorter cycle, which reduces phytosanitary problems that usually occur towards the end of the growing season. This study aimed to evaluate yield components and fruit quality of ‘Floradade’ determinate growth tomato in an ecologically based production system with regard to plant density and number of stems per plant in two growing seasons, spring-summer (SS) and summer-fall (SF). Two experiments were conducted in Pelotas in the years 2010/2011 under open field conditions. Plants were trained with two or four stems and four plant densities were evaluated: 2.0; 2.5; 3.0 and 3.6 plants m-2in SS, and 1.5; 2.0; 2.5 and 3.0 plants m-2 in SF. The fruit number, fruit average weight, fruit yield, ascorbic acid content, total soluble solids and fruit pH were evaluated. The average fruit yield obtained in SF was on average 80% lower than that in SS. The increase of plant density and number of stems per plant led to an increase in fruit number and fruit yield in the two crop seasons. There was an increase in total soluble solids and reduction in the ascorbic acid content of the fruit. Two stemsper plant and plant density of 3.0 plants m-2 are recommended for the ‘Floradade’ tomato crop under an ecological production system and SS crop conditions

Zeros of Rydberg-Rydberg Foster Interactions

Rydberg states of atoms are of great current interest for quantum manipulation of mesoscopic samples of atoms. Long-range Rydberg-Rydberg interactions can inhibit multiple excitations of atoms under the appropriate conditions. These interactions are strongest when resonant collisional processes give rise to long-range C_3/R^3 interactions. We show in this paper that even under resonant conditions C_3 often vanishes so that care is required to realize full dipole blockade in micron-sized atom samples.Comment: 10 pages, 4 figures, submitted to J. Phys.

Desempenho de cultivares de tomateiro em diferentes ambientes de cultivo e sistema ecológico de produção.

O tomate é uma hortaliça de grande importância na mesa dos brasileiros, sendo que frutos produzidos de forma ecológica são preferidos e mais saudáveis. Para a produção exitosa de tomate neste sistema é necessária a utilização de cultivares adaptadas, dando-se preferência por aquelas de polinização aberta. A utilização de ambiente protegido tem viabilizado o cultivo do tomateiro em muitas regiões, com possibilidade de estender o período produtivo. O objetivo deste trabalho foi avaliar a produtividade e a duração do ciclo de duas cultivares de tomateiro produzidas a campo e em ambiente protegido em sistema de produção de base ecológica. O experimento foi realizado na Estação Experimental Cascata (Embrapa Clima Temperado), Pelotas, Rio Grande do Sul. Foram avaliados dois genótipos ?Rose de Berne? e ?Maçã?. O controle de insetos e doenças foi baseado na legislação brasileira de orgânicos. Após cada colheita, os frutos foram pesados e classificados, e ao final do período experimental foi determinada a produção de frutos por planta, número e massa média de frutos, e duração total do ciclo. ?Maçã? produziu mais frutos que ?Rose de Berne? por ser do tipo cereja, porém a produtividade das duas não diferiu entre si nem entre ambientes, mantendo em média 6,5 kg m-2. O descarte foi maior para ?Rose de Berne?. A massa média dos frutos a campo foi maior que na estufa. O ciclo de cultivo no ambiente protegido foi de 126 dias para ambas cultivares, sendo que a campo, ?Maçã? teve ciclo de apenas 109 dias e ?Rose de Berne? de 130 dias. A produtividade de ambas cultivares e ambientes foi satisfatória. O ambiente protegido não diferiu em produtividade com o campo, porém permitiu prolongar o ciclo de produção da cultivar ?Maçã?. Perdas podem ser reduzidas se forem realizadas colheitas mais frequentes

Lag time and parameter mismatches in synchronization of unidirectionally coupled chaotic external cavity semiconductor lasers

We report an analysis of synchronization between two unidirectionally coupled chaotic external cavity master/slave semiconductor lasers with two characteristic delay times, where the delay time in the coupling is different from the delay time in the coupled systems themselves. We demonstrate for the first time that parameter mismatches in photon decay rates for the master and slave lasers can explain the experimental observation that the lag time is equal to the coupling delay time.Comment: LaTex, 5 pages, submitted to PRE(R