Boundary versus bulk behavior of time-dependent correlation functions in one-dimensional quantum systems

We study the influence of reflective boundaries on time-dependent responses of one-dimensional quantum fluids at zero temperature beyond the low-energy approximation. Our analysis is based on an extension of effective mobile impurity models for nonlinear Luttinger liquids to the case of open boundary conditions. For integrable models, we show that boundary autocorrelations oscillate as a function of time with the same frequency as the corresponding bulk autocorrelations. This frequency can be identified as the band edge of elementary excitations. The amplitude of the oscillations decays as a power law with distinct exponents at the boundary and in the bulk, but boundary and bulk exponents are determined by the same coupling constant in the mobile impurity model. For nonintegrable models, we argue that the power-law decay of the oscillations is generic for autocorrelations in the bulk, but turns into an exponential decay at the boundary. Moreover, there is in general a nonuniversal shift of the boundary frequency in comparison with the band edge of bulk excitations. The predictions of our effective field theory are compared with numerical results obtained by time-dependent density matrix renormalization group (tDMRG) for both integrable and nonintegrable critical spin-$S$ chains with $S=1/2$, $1$ and $3/2$.Comment: 20 pages, 12 figure

Magnetically-controlled impurities in quantum wires with strong Rashba coupling

We investigate the effect of strong spin-orbit interaction on the electronic transport through non-magnetic impurities in one-dimensional systems. When a perpendicular magnetic field is applied, the electron spin polarization becomes momentum-dependent and spin-flip scattering appears, to first order in the applied field, in addition to the usual potential scattering. We analyze a situation in which, by tuning the Fermi level and the Rashba coupling, the magnetic field can suppress the potential scattering. This mechanism should give rise to a significant negative magnetoresistance in the limit of large barriers.Comment: 4 pages, 2 figure

Consistent Gravitationally-Coupled Spin-2 Field Theory

Inspired by the translational gauge structure of teleparallel gravity, the theory for a fundamental massless spin-2 field is constructed. Accordingly, instead of being represented by a symmetric second-rank tensor, the fundamental spin-2 field is assumed to be represented by a spacetime (world) vector field assuming values in the Lie algebra of the translation group. The flat-space theory naturally emerges in the Fierz formalism and is found to be equivalent to the usual metric-based theory. However, the gravitationally coupled theory, with gravitation itself described by teleparallel gravity, is shown not to present the consistency problems of the spin-2 theory constructed on the basis of general relativity.Comment: 16 pages, no figures. V2: Presentation changes, including addition of a new sub-section, aiming at clarifying the text; version accepted for publication in Class. Quantum Grav

Efeito do tipo de cultivar, despendoamento das plantas e da época de semeadura na produção de minimilho.

Minimilho, também conhecido como "baby corn", é o nome dado à espiga jovem, em desenvolvimento, não fertilizada de uma planta de milho. Com o advento da indústria de conservas, o minimilho passou a ser consumido também na forma de conservas. Assim, houve um crescimento na área cultivada com milho para consumo nessa forma, à semelhança do acontecido com o milho verde. Diferentes tipos de cultivares de milho, como doce, pipoca e mesmo milho normal têm sido utilizados para a produção do minimilho. O cultivo desse tipo de milho é pouco expressivo no Brasil, sendo a produção e o processamento agroindustrial pouco tecnificados, se comparados com outros países, além de existir uma escassez de informações em relação ao manejo da cultura, bem como sobre o desempenho dos cultivares. Avaliou-se o desempenho de cultivares de milho em diferentes épocas de semeadura, associado ao efeito do despendoamento das plantas na produção de minimilho. Os experimentos foram instalados em área experimental da Embrapa Milho e Sorgo, em Sete Lagoas, MG, sendo um experimento no ano de 1999 (semeadura em 23/12), dois no ano de 2000 (semeaduras em 20/01 e 12/10) e um em 2001 (semeadura em 02/02). Para cada experimento, o delineamento experimental empregado foi em blocos casualizados, em esquema fatorial 8 (cultivares) x 2 (com e sem despendoamento), com três repetições. Realizaram-se três colheitas, em intervalos de três dias, sendo a primeira três dias após a emissão dos estilos-estigmas. Foram avaliados o peso de espigas empalhadas, o peso de espigas comerciais e o rendimento de espigas comerciais. Entre as cultivares avaliadas, a DKB 929 se destaca, apresentando o melhor desempenho para peso de espigas empalhadas e peso de espigas comerciais, independente da época de semeadura. O despendoamento proporciona aumento na produtividade de espigas comerciais, independente da época de semeadura. Há necessidade de avaliação das cultivares em diferentes épocas, antes da sua recomendação para a produção de minimilho. Para a produção de espigas empalhadas, o aumento na produção devido ao despendoamento depende da época de semeadura

Effect of Electrolyte Balance in Low-Protein Diets on Broiler Performance and Tibial Dyschondroplasia Incidence

A proper dietary electrolyte balance (DEB) is essential to ensure an optimum acid-base equilibrium and broiler performance. In low-CP diets, this balance can be affected by reduction of soybean meal and inclusion of high levels of synthetic amino acids. Although, some studies have related low-protein diets supplemented with amino acids and DEB, these relations are not well explained, because some research demonstrates confusion about the deficiency and balance of nutrients. The objective of these experiments was to evaluate the DEB effects of diets with low levels of protein supplemented with amino acids on broiler performance and bone development. Results indicated that DEB and CP content influenced broiler chick performance in the starter and growing periods. There was no significant effect due to the interaction between DEB and CP content for tibial dyschondroplasia incidence (TD) or in bone breaking resistance during the growing period of either experiment. The incidence of TD was reduced with 253 mEq/kg DEB in the starter period