Kinetic energy driven superconductivity in doped cuprates

Within the t-J model, the mechanism of superconductivity in doped cuprates is studied based on the partial charge-spin separation fermion-spin theory. It is shown that dressed holons interact occurring directly through the kinetic energy by exchanging dressed spinon excitations, leading to a net attractive force between dressed holons, then the electron Cooper pairs originating from the dressed holon pairing state are due to the charge-spin recombination, and their condensation reveals the superconducting ground-state. The electron superconducting transition temperature is determined by the dressed holon pair transition temperature, and is proportional to the concentration of doped holes in the underdoped regime. With the common form of the electron Cooper pair, we also show that there is a coexistence of the electron Cooper pair and antiferromagnetic short-range correlation, and hence the antiferromagnetic short-range fluctuation can persist into the superconducting state. Our results are qualitatively consistent with experiments.Comment: 6 pages, Revtex, two figures are included, corrected typo

Raman study of carrier-overdoping effects on the gap in high-Tc superconducting cuprates

Raman scattering in the heavily overdoped (Y,Ca)Ba_2Cu_3O_{7-d} (T_c = 65 K) and Bi_2Sr_2CaCu_2O_{8+d} (T_c = 55 K) crystals has been investigated. For the both crystals, the electronic pair-breaking peaks in the A_{1g} and B_{1g} polarizations were largely shifted to the low energies close to a half of 2Delta_0, Delta_0 being the maximum gap. It strongly suggests s-wave mixing into the d-wave superconducting order parameter and the consequent manifestation of the Coulomb screening effect in the B_{1g}-channel. Gradual mixing of s-wave component with overdoping is not due to the change of crystal structure symmetry but a generic feature in all high-T_c superconducting cuprates.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B, Rapid communicaito

Controle massal da broca‑do‑café com armadilhas de garrafa Pet vermelha em cafeeiro

The objective of this work was to evaluate the efficacy of red PET‑bottle traps, containing attractive alcoholic volatile compounds, in the mass control of coffee berry borer (Hypothenemus hampei). The evaluations were carried out in four coffee crops, during two years. Nine hundred PET‑bottle traps, painted red, were distributed in three of the four coffee crops; one crop without traps was used as a control. Holes drilled into berries (%) were determined in these crops. There was a reduction in drilled berries in crops with traps, from the 2007/2008 harvest to the 2008/2009 harvest. The highest coffee berry borer densities in traps was observed in the flowering and small‑green berries stages. The red PET‑bottle trap is efficient in the mass control of the coffee berry borer population, since it reduces the percentage of drilled berries in 57%; however, this reduction is not enough to keep borer densities below the control level.O objetivo deste trabalho foi avaliar a eficácia de armadilha de garrafa Pet vermelha contendo compostos voláteis alcoólicos atrativos, no controle massal da broca‑do‑café (Hypothenemus hampei). As avaliações foram realizadas em quatro lavouras de café, durante dois anos. Foram distribuídas 900 armadilhas de garrafa Pet, pintadas de vermelho, em três das quatro lavouras; uma lavoura sem armadilhas foi usada como controle. O broqueamento dos frutos (%) foi determinado nessas lavouras. Houve redução do broqueamento de frutos nas lavouras com armadilhas, da safra 2007/2008 para a safra 2008/2009. As maiores densidades da broca‑do‑café nas armadilhas foram observadas nos estádios de floração e de frutos chumbinho. A armadilha de garrafa Pet vermelha é eficaz no controle massal da população da broca‑do‑café, por reduzir a percentagem de frutos broqueados em 57%; entretanto, essa redução não é suficiente para manter as densidades da broca abaixo do nível de controle

Complexity of pseudoknot prediction in simple models

Abstract. Efficient exact algorithms for finding optimal secondary structures of RNA sequences have been known for a quarter of a century. However, these algorithms are restricted to structures without overlapping base pairs, or pseudoknots. The ability to include pseudoknots has gained increased attention over the last five years, but three recent publications indicate that this might leave the problem intractable. In this paper we further investigate the complexity of the pseudoknot prediction problem in two simple models based on base pair stacking. We confirm the intractability of pseudoknot prediction by proving it  ¢¡ hard for binary strings in one model, and for strings over an unbounded alphabet in the other model. Conversely, we are also able to present a polynomial time algorithm for pseudoknot prediction for strings over a fixed size alphabet in the second model and a polynomial time approximation scheme for pseudoknot prediction for strings over a fixed size alphabet in the first model.