Topological phase transitions between chiral and helical spin textures in a lattice with spin-orbit coupling and a magnetic field

We consider the combined effects of large spin-orbit couplings and a perpendicular magnetic field in a 2D honeycomb fermionic lattice. This system provides an elegant setup to generate versatile spin textures propagating along the edge of a sample. The spin-orbit coupling is shown to induce topological phase transitions between a helical quantum spin Hall phase and a chiral spin-imbalanced quantum Hall state. Besides, we find that the spin orientation of a single topological edge state can be tuned by a Rashba spin-orbit coupling, opening an interesting route towards quantum spin manipulation. We discuss the possible realization of our results using cold atoms trapped in optical lattices, where large synthetic magnetic fields and spin-orbit couplings can be engineered and finely tuned. In particular, this system would lead to the observation of a time-reversal-symmetry-broken quantum spin Hall phase.Comment: 8 pages, 3 figures, Accepted in Europhys. Lett. (Dec 2011

Optical conductivity of charge carriers interacting with a two-level systems reservoir

Using the functional-integral method we investigate the effective dynamics of a charged particle coupled to a set of two-level systems as a function of temperature and external electric field. The optical conductivity and the direct current (dc) resistivity induced by the reservoir are computed. Three different regimes are found depending on the two-level system spectral function, which may lead to a non-Drude optical conductivity in a certain range of parameters. Our results contrast to the behavior found when considering the usual bath of harmonic oscillators which we are able to recover in the limit of very low temperatures.Comment: 13 pages, 7 figure

Quantum dots and spin qubits in graphene

This is a review on graphene quantum dots and their use as a host for spin qubits. We discuss the advantages but also the challenges to use graphene quantum dots for spin qubits as compared to the more standard materials like GaAs. We start with an overview of this young and fascinating field and will then discuss gate-tunable quantum dots in detail. We calculate the bound states for three different quantum dot architectures where a bulk gap allows for confinement via electrostatic fields: (i) graphene nanoribbons with armchair boundary, (ii) a disc in single-layer graphene, and (iii) a disc in bilayer graphene. In order for graphene quantum dots to be useful in the context of spin qubits, one needs to find reliable ways to break the valley-degeneracy. This is achieved here, either by a specific termination of graphene in (i) or in (ii) and (iii) by a magnetic field, without the need of a specific boundary. We further discuss how to manipulate spin in these quantum dots and explain the mechanism of spin decoherence and relaxation caused by spin-orbit interaction in combination with electron-phonon coupling, and by hyperfine interaction with the nuclear spin system.Comment: 23 pages, 10 figures, topical review prepared for Nanotechnolog

Dominance and G×E interaction effects improvegenomic prediction and genetic gain inintermediate wheatgrass (Thinopyrumintermedium)

Genomic selection (GS) based recurrent selection methods were developed to accelerate the domestication of intermediate wheatgrass [IWG, Thinopyrum intermedium (Host) Barkworth & D.R. Dewey]. A subset of the breeding population phenotyped at multiple environments is used to train GS models and then predict trait values of the breeding population. In this study, we implemented several GS models that investigated the use of additive and dominance effects and G×E interaction effects to understand how they affected trait predictions in intermediate wheatgrass. We evaluated 451 genotypes from the University of Minnesota IWG breeding program for nine agronomic and domestication traits at two Minnesota locations during 2017–2018. Genet-mean based heritabilities for these traits ranged from 0.34 to 0.77. Using fourfold cross validation, we observed the highest predictive abilities (correlation of 0.67) in models that considered G×E effects. When G×E effects were fitted in GS models, trait predictions improved by 18%, 15%, 20%, and 23% for yield, spike weight, spike length, and free threshing, respectively. Genomic selection models with dominance effects showed only modest increases of up to 3% and were trait-dependent. Crossenvironment predictions were better for high heritability traits such as spike length, shatter resistance, free threshing, grain weight, and seed length than traits with low heritability and large environmental variance such as spike weight, grain yield, and seed width. Our results confirm that GS can accelerate IWG domestication by increasing genetic gain per breeding cycle and assist in selection of genotypes with promise of better performance in diverse environments

Enquitreídeos como indicadores de qualidade do solo em sistemas integrados de produção nos Campos Gerais, Paraná.

Resumo. FERTBIO 2014

MATURIDADE NA GERÊNCIA DE PROJETOS DE EMPRESAS DE TECNOLOGIA DA INFORMAÇÃO: UM ESTUDO ANALÍTICO E EXPLORATÓRIO

Project management is basic requirement to meet new markets and to search for continuous growth of the companies. This paper presents an evaluation of the maturity level of the processes for managing projects portfolio of three IT companies. These companies were evaluated on five levels of P3M3 maturity model. At each level, criteria were identified according to model structure. At the end of the study, there was low adherence of companies to P3M3, resulting in suggesting improvements to companies.A necessidade em atender novos clientes e a busca por crescimento contínuo das empresas tornou a gerência de projetos requisito básico. Neste trabalho, o objetivo é apresentar uma avaliação realizada em três empresas de TI quanto ao nível de maturidade em gerenciar portfólio de projetos. Essas empresas foram avaliadas nos cinco níveis do modelo de maturidade P3M3. Em cada nível, foram identificados critérios de acordo com a estrutura do modelo. Ao finalizar o estudo, verificou-se baixa aderência das empresas ao P3M3, resultando em sugestões de melhorias às empresas

Crossover from thermal hopping to quantum tunneling in Mn_{12}Ac

The crossover from thermal hopping to quantum tunneling is studied. We show that the decay rate $\Gamma$ with dissipation can accurately be determined near the crossover temperature. Besides considering the Wentzel-Kramers-Brillouin (WKB) exponent, we also calculate contribution of the fluctuation modes around the saddle point and give an extended account of a previous study of crossover region. We deal with two dangerous fluctuation modes whose contribution can't be calculated by the steepest descent method and show that higher order couplings between the two dangerous modes need to be taken into considerations. At last the crossover from thermal hopping to quantum tunneling in the molecular magnet Mn_{12}Ac is studied.Comment: 10 pages, 3 figure

Simulation of Flow of Mixtures Through Anisotropic Porous Media using a Lattice Boltzmann Model

We propose a description for transient penetration simulations of miscible and immiscible fluid mixtures into anisotropic porous media, using the lattice Boltzmann (LB) method. Our model incorporates hydrodynamic flow, diffusion, surface tension, and the possibility for global and local viscosity variations to consider various types of hardening fluids. The miscible mixture consists of two fluids, one governed by the hydrodynamic equations and one by diffusion equations. We validate our model on standard problems like Poiseuille flow, the collision of a drop with an impermeable, hydrophobic interface and the deformation of the fluid due to surface tension forces. To demonstrate the applicability to complex geometries, we simulate the invasion process of mixtures into wood spruce samples.Comment: Submitted to EPJ

Comparative evaluation between the extenders TES-TRIS and ACP-112® and the association of Sálva Marajó oil (Lippia origanoides) in the quality of cryopreserved buffalo sperm.

For artificial insemination, it is essential to use frozen semen, however the freezing process causes deleterious changes to the structure and integrity of sperm membranes that compromise the function of sperm. To avoid this cellular damage, extenders and suitable substrates must be used to recover the highest possible number of viable cells post-thaw. To this end, in the first experiment, we evaluated three different extenders: TES-TRIS, which is widely used for buffaloes; and an extender composed of powdered coconut water-based (ACP-112®) with or without milk (ACP-112®-milk) for buffalo semen freezing. In the second experiment, we evaluated the effect of Lippia origanoides oil extract on protecting buffalo sperm against cryoinjury arising from freezing semen. Semen was collected from ten buffalo bulls (10 ejaculates/bull) and diluted in TES-TRIS (control), ACP-112® or ACP-112®-Milk in the first experiment. In the second experiment, the samples were diluted in the diluent with the best results for sperm quality obtained in experiment I, and 2.5 µg mL-1, 5 µg mL-1 or 10 µg mL-1 of the plant extract was added to treatments; and a control group containing only the diluent was also included. The fresh semen was analyzed for conventional features such as motility, concentration, morphology and viability. After thawing, the samples were evaluated again for motility, vigor and supra-vital staining, and then, were performed the of thermal-resistance test, hypoosmotic test and evaluated sperm membrane integrity with the fluorescent probes PI, FITC-PSA and JC-1 using flow cytometry. The data were submitted to ANOVA, and the results were compared by Tukey?s test at a significance of 5%. In the first experiment, the extender TES-TRIS showed better results for the various characteristics evaluated compared to ACP-112® and ACP-112®-Milk (P 0.05). Based on these data, we demonstrated the beneficial effects of TES-TRIS for post-thaw buffalo sperm quality; however, no protective effect was observed for buffalo sperm cryopreserved with the different tested concentrations of Lippia origanoides extract oil