Interactions between Octet Baryons in the SU_6 Quark model

The baryon-baryon interactions for the complete baryon octet (B_8) are investigated in a unified framework of the resonating-group method, in which the spin-flavor SU_6 quark-model wave functions are employed. Model parameters are determined to reproduce properties of the nucleon-nucleon system and the low-energy cross section data for the hyperon-nucleon interaction. We then proceed to explore B_8 B_8 interactions in the strangeness S=-2, -3 and -4 sectors. The S-wave phase-shift behavior and total cross sections are systematically understood by 1) the spin-flavor SU_6 symmetry, 2) the special role of the pion exchange, and 3) the flavor symmetry breaking.Comment: 11 pages, 6 figures, submitted to Phys. Rev. C (Rapid Communication

Quark-Model Baryon-Baryon Interaction and its Applications to Hypernuclei

The quark-model baryon-baryon interaction fss2, proposed by the Kyoto-Niigata group, is a unified model for the complete baryon octet (B_8=N, Lambda, Sigma and Xi), which is formulated in a framework of the (3q)-(3q) resonating-group method (RGM) using the spin-flavor SU_6 quark-model wave functions and effective meson-exchange potentials at the quark level. Model parameters are determined to reproduce properties of the nucleon-nucleon system and the low-energy cross section data for the hyperon-nucleon scattering. Due to the several improvements including the introduction of vector-meson exchange potentials, fss2 has achieved very accurate description of the NN and YN interactions, comparable to various one-boson exchange potentials. We review the essential features of fss2 and our previous model FSS, and their predictions to few-body systems in confrontation with the available experimental data. Some characteristic features of the B_8 B_8 interactions with the higher strangeness, S=-2, -3, -4, predicted by fss2 are discussed. These quark-model interactions are now applied to realistic calculations of few-body systems in a new three-cluster Faddeev formalism which uses two-cluster RGM kernels. As for the few-body systems, we discuss the three-nucleon bound states, the Lambda NN-Sigma NN system for the hypertriton, the alpha alpha Lambda system for 9Be Lambda, and the Lambda Lambda alpha system for 6He Lambda Lambda.Comment: 20 pages, 12 figures, 18th Nishinomiya Yukawa Memorial Symposium on Strangeness in Nuclear Matter, 4 - 5 December 2003, Nishinomiya, Japan. (to be published in Prog. Theor. Phys. Suppl.

Negative thermal expansion in the Prussian Blue analog Zn3[Fe(CN)6]2: X-ray diffraction and neutron vibrational studies

The cubic Prussian Blue (PB) analog, Zn3 [Fe(CN)6]2, has been studied by X-ray powder diffraction and inelastic neutron scattering (INS). X-ray data collected at 300 and 84 K revealed negative thermal expansion (NTE) behaviour for this material. The NTE coefficient was found to be -31.1 x 10-6 K-1. The neutron vibrational spectrum for Zn3[Fe(CN)6]2.xH2O, was studied in detail. The INS spectrum showed well-defined, well-separated bands corresponding to the stretching of and deformation modes of the Fe and Zn octahedra, all below 800 cm-1.Comment: 4 pages, 3 figure

Single-Particle Spin-Orbit Strengths of the Nucleon and Hyperons by SU6 Quark-Model

The quark-model hyperon-nucleon interaction suggests an important antisymmetric spin-orbit component. It is generated from a color analogue of the Fermi-Breit interaction dominating in the one-gluon exchange process between quarks. We discuss the strength S_B of the single-particle spin-orbit potential, following the Scheerbaum's prescription. Using the SU6 quark-model baryon-baryon interaction which was recently developed by the Kyoto-Niigata group, we calculate NN, Lambda N and Sigma N G-matrices in symmetric nuclear matter and apply them to estimate the strength S_B. The ratio of S_B to the nucleon strength S_N =~ -40 MeV*fm^5 is (S_Lambda)/(S_N) =~ 1/5 and (S_Sigma)/(S_N) =~ 1/2 in the Born approximation. The G-matrix calculation of the model FSS modifies S_Lambda to (S_Lambda)/(S_N) =~ 1/12. For S_N and S_Sigma, the effect of the short-range correlation is comparatively weak against meson-exchange potentials with a short-range repulsive core. The significant reduction of the Lambda single-particle potential arises from the combined effect of the antisymmetric LS force, the flavor-symmetry breaking originating from the strange to up-down quark-mass difference, as well as the effect of the short-range correlation. The density dependence of S_B is also examined.Comment: 26 page

Effect of higher orbital angular momenta in the baryon spectrum

We have performed a Faddeev calculation of the baryon spectrum for the chiral constituent quark model including higher orbital angular momentum states. We have found that the effect of these states is important, although a description of the baryon spectrum of the same quality as the one given by including only the lowest-order configurations can be obtained. We have studied the effect of the pseudoscalar quark-quark interaction on the relative position of the positive- and negative-parity excitations of the nucleon as well as the effect of varying the strength of the color-magnetic interaction.Comment: 7 pages, 4 figures. To be published in Phys. Rev. C (November 2001

Hyperon Single-Particle Potentials Calculated from SU6 Quark-Model Baryon-Baryon Interactions

Using the SU6 quark-model baryon-baryon interaction recently developed by the Kyoto-Niigata group, we calculate NN, Lambda N and Sigma N G-matrices in ordinary nuclear matter. This is the first attempt to discuss the Lambda and Sigma single-particle potentials in nuclear medium, based on the realistic quark-model potential. The Lambda potential has the depth of more than 40 MeV, which is more attractive than the value expected from the experimental data of Lambda-hypernuclei. The Sigma potential turns out to be repulsive, the origin of which is traced back to the strong Pauli repulsion in the Sigma N (I=3/2) ^3S_1 state.Comment: 20 pages, 5 figure

Construção de modelo ecofisiologico de simulação para estimar a produtividade potencial de cana de açucar no Brasil e Australia.

Resumo: Neste artigo apresenta-se a construção de um modelo ecofisiológico-matemático (BrCane) para predizer a produtividade potencial - sem restrições nutricionais ou de água, a fim de analisar a sustentabilidade da expansão do cultivo de cana-de-açúcar em novas áreas para produção de etanol. A arquitetura do modelo BRCANE foi concebida para uma planta tipo C4, onde a evolução mensal da biomassa foi estimada em função da temperatura do ar e da radiação incidente. Nas simulações apresentadas a produção de biomassa levou em conta a taxa bruta de fotossíntese subtraída às perdas para respiração de manutenção, senescência de folhas e morte de perfilhos durante o ciclo da cultura. O modelo BRCANE também foi usado para descrever o comportamento fisiológico em função das condições ambientais relacionadas ao tempo termal. A implementação de tais condições permitiu ajustar os resultados das simulações a resultados experimentais disponíveis na literatura. As estimativas de biomassa foram comparadas com dados obtidos durante o ciclo da cultura em experimentos de campo com irrigação (Cultivares RB72 454, NA 56-79, CB 41-76, CB47-355, CP51-22, Q138 e Q141) no Estado de São Paulo (Brasil) e em Bundaberg e Queensland (Austrália) e os resultados foram expressos em toneladas de colmo por hectare (Mg.ha-1), por meio de uma relação linear para cada variedade (R2 = 0,89**) e superiores aos obtidos pelos modelos APSIM (R2=0,78*) e CANEGRO (R2=0,71*). O modelo apresentou resultados consistentes com dados experimentais para crescimento de biomassa no ciclo da cultura da cana-de-açúcar, oriundo de canaviais paulistas e de Bundaberg (Austrália).SIAGRO 2014