On the solution of a supersymmetric model of correlated electrons

We consider the exact solution of a model of correlated electrons based on the superalgebra $Osp(2|2)$. The corresponding Bethe ansatz equations have an interesting form. We derive an expression for the ground state energy at half filling. We also present the eigenvalue of the transfer matrix commuting with the Hamiltonian.Comment: Palin latex , 8 page

Exact solution of the lattice vertex model analog of the coupled Bariev XY chains

We present the algebraic Bethe Ansatz solution for the vertex model recently proposed by Zhou as the classical analog of the Bariev interacting XY chains. The relevant commutation rules between the creation fields contain the Hecke symmetry pointed out recently by Hikami and Murakami. The eigenvalues of the corresponding transfer matrix are explicitly given.Comment: Plain latex, 8 pag

The origin of power-law distributions in deterministic walks: the influence of landscape geometry

We investigate the properties of a deterministic walk, whose locomotion rule is always to travel to the nearest site. Initially the sites are randomly distributed in a closed rectangular ($A/L \times L)$ landscape and, once reached, they become unavailable for future visits. As expected, the walker step lengths present characteristic scales in one ($L \to 0$) and two ($A/L \sim L$) dimensions. However, we find scale invariance for an intermediate geometry, when the landscape is a thin strip-like region. This result is induced geometrically by a dynamical trapping mechanism, leading to a power law distribution for the step lengths. The relevance of our findings in broader contexts -- of both deterministic and random walks -- is also briefly discussed.Comment: 7 pages, 11 figures. To appear in Phys. Rev.

Novos marcadores para fins de mapeamento e localização de QTLs a partir de PCR-RFLP de genes de genoma café brasileiro.

O mapeamento genético é uma das estratégias mais visadas para fins de melhoramento genético e ganha maior importância a partir do surgimento de marcadores do tipo SNPs ou INDELs, facilitado pelos projetos genomas, sobretudo de ESTs. Assim, análises in silico de busca de polimorfismo SNPs em seqüências relacionadas com qualidade de bebida e derivadas de C.arabica e C.canephora foram analisadas e o polimorfismo entre as duas espécies validado para seis genes (quatro proteases e dois de sacarose) a partir de estudos de laboratório utilizando a técnica PCR-RFLP. Para tanto, após confirmação do polimorfismo nas duas espécies parentais, foram genotipadas 90 plantas F2 derivadas da autofecundação de um híbrido interespecífico de Coffea arabica e C. canephora 4x. Após a obtenção dos amplificados, estes foram digeridos com diversas enzimas de restrição de quatro bases (Alu I, Dde I, Eco RI, Hae III, Mse I e Msp, Fnu DII, Taq I; Scr FI). Dos seis genes analisados, quatro deles apresentaram segregação do tipo 3:1 na população F2 (Cisteína 8, Cisteína 5, B-Fructosidase e Sacarose Fosfato Síntase), demonstrando a utilização dos mesmos para fins de mapeamento

Eight state supersymmetric UU model of strongly correlated fermions

An integrable eight state supersymmtric $U$ model is proposed, which is a fermion model with correlated single-particle and pair hoppings as well as uncorrelated triple-particle hopping. It has an $gl(3|1)$ supersymmetry and contains one symmetry-preserving free parameter. The model is solved and the Bethe ansatz equations are obtained.Comment: Some cosmetic changes; to appear in Phys. Rev.

On-ground tests of LISA PathFinder thermal diagnostics system

Thermal conditions in the LTP, the LISA Technology Package, are required to be very stable, and in such environment precision temperature measurements are also required for various diagnostics objectives. A sensitive temperature gauging system for the LTP is being developed at IEEC, which includes a set of thermistors and associated electronics. In this paper we discuss the derived requirements applying to the temperature sensing system, and address the problem of how to create in the laboratory a thermally quiet environment, suitable to perform meaningful on-ground tests of the system. The concept is a two layer spherical body, with a central aluminium core for sensor implantation surrounded by a layer of polyurethane. We construct the insulator transfer function, which relates the temperature at the core with the laboratory ambient temperature, and evaluate the losses caused by heat leakage through connecting wires. The results of the analysis indicate that, in spite of the very demanding stability conditions, a sphere of outer diameter of the order one metre is sufficient. We provide experimental evidence confirming the model predictions.Comment: 18 pages, 5 figures, LaTeX2e (compile with pdflatex), sumbitted to CQG. This paper is a significant extension of gr-qc/060109

Algebraic Bethe ansatz approach for the one-dimensional Hubbard model

We formulate in terms of the quantum inverse scattering method the algebraic Bethe ansatz solution of the one-dimensional Hubbard model. The method developed is based on a new set of commutation relations which encodes a hidden symmetry of 6-vertex type.Comment: appendix additioned with Boltzmann weigths and R-matrix. Version to be published in J.Phys.A:math.Gen. (1997

Critical and Tricritical Points for the Massless 2d Gross-Neveu Model Beyond Large N

Using optimized perturbation theory, we evaluate the effective potential for the massless two dimensional Gross-Neveu model at finite temperature and density containing corrections beyond the leading large-N contribution. For large-N, our results exactly reproduce the well known 1/N leading order results for the critical temperature, chemical potential and tricritical points. For finite N, our critical values are smaller than the ones predicted by the large-N approximation and seem to observe Landau's theorem for phase transitions in one space dimension. New analytical results are presented for the tricritical points that include 1/N corrections. The easiness with which the calculations and renormalization are carried out allied to the seemingly convergent optimized results displayed, in this particular application, show the robustness of this method and allows us to obtain neat analytical expressions for the critical as well as tricritical values beyond the results currently known.Comment: 29 pages, 14 figure

Sociology in Portugal: Local, national, and international dialogues

Although the institutionalisation of sociology in Portugal was only possible after the revolution of 1974, it is currently characterised by a remarkable vitality, noticeable for instance in the number and diversity of the members of the Portuguese Sociological Association (Associação Portuguesa de Sociologia), as well as the participants at its national conference. However, significant challenges have also emerged, not only resulting from the expansion and diversification of sociologists, but also from the economic crisis, the austerity policies, the growth of social sciences specialisations, and policies favouring business, law, health and engineering in research and the labour markets.info:eu-repo/semantics/acceptedVersio