The structure of algebraic covariant derivative curvature tensors

We use the Nash embedding theorem to construct generators for the space of algebraic covariant derivative curvature tensors

Spectral microscopic mechanisms and quantum phase transitions in a 1D correlated problem

In this paper we study the dominant microscopic processes that generate nearly the whole one-electron removal and addition spectral weight of the one-dimensional Hubbard model for all values of the on-site repulsion $U$. We find that for the doped Mott-Hubbard insulator there is a competition between the microscopic processes that generate the one-electron upper-Hubbard band spectral-weight distributions of the Mott-Hubbard insulating phase and finite-doping-concentration metallic phase, respectively. The spectral-weight distributions generated by the non-perturbative processes studied here are shown elsewhere to agree quantitatively for the whole momentum and energy bandwidth with the peak dispersions observed by angle-resolved photoelectron spectroscopy in quasi-one-dimensional compounds.Comment: 18 pages, 2 figure

Correlation length of the 1D Hubbard Model at half-filling : equal-time one-particle Green's function

The asymptotics of the equal-time one-particle Green's function for the half-filled one-dimensional Hubbard model is studied at finite temperature. We calculate its correlation length by evaluating the largest and the second largest eigenvalues of the Quantum Transfer Matrix (QTM). In order to allow for the genuinely fermionic nature of the one-particle Green's function, we employ the fermionic formulation of the QTM based on the fermionic R-operator of the Hubbard model. The purely imaginary value of the second largest eigenvalue reflects the k_F (= pi/2) oscillations of the one-particle Green's function at half-filling. By solving numerically the Bethe Ansatz equations with Trotter numbers up to N=10240, we obtain accurate data for the correlation length at finite temperatures down into the very low temperature region. The correlation length remains finite even at T=0 due to the existence of the charge gap. Our numerical data confirm Stafford and Millis' conjecture regarding an analytic expression for the correlation length at T=0.Comment: 7 pages, 6 figure

Detection of Leishmania infantum by PCR, serology and cellular immune response in a cohort study of Brazilian dogs

The sensitivity and specificity of PCR, serology (ELISA) and lymphoproliferative response to Leishmania antigen for the detection of Leishmania infantum infection were evaluated in a cohort of 126 dogs exposed to natural infection in Brazil. For PCR, Leishmania DNA from bone-marrow was amplified with both minicircle and ribosomal primers. The infection status and time of infection of each dog were estimated from longitudinal data. The sensitivity of PCR in parasite-positive samples was 98%. However, the overall sensitivity of PCR in post-infection samples, from dogs with confirmed infection, was only 68%. The sensitivity of PCR varied during the course of infection, being highest (78–88%) 0–135 days post-infection and declining to around 50% after 300 days. The sensitivity of PCR also varied between dogs, and was highest in sick dogs. The sensitivity of serology was similar in parasite-positive (84%), PCR-positive (86%) and post-infection (88%) samples. The sensitivity of serology varied during the course of infection, being lowest at the time of infection and high (93–100%) thereafter. Problems in determining the specificity of serology are discussed. The sensitivity and specificity of cellular responsiveness were low. These data suggest that PCR is most useful in detecting active or symptomatic infection, and that serology can be a more sensitive technique for the detection of all infected dogs

Ion-beam mixing induced by atomic and cluster bombardment in the electronic stopping-power regime

Single crystals of magnesium oxide containing nanoprecipitates of sodium were bombarded with swift ions (∼GeV-Pb, U) or cluster beams (∼20 MeV-C60) to study the phase change induced by electronic processes at high stopping power (≳10 keV/nm). The sodium precipitates and the defect creation were characterized by optical absorption and transmission electron microscopy. The ion or cluster bombardment leads to an evolution of the Na precipitate concentration but the size distribution remains unchanged. The decrease in Na metallic concentration is attributed to mixing effects at the interfaces between Na clusters and MgO. In addition, optical-absorption measurements show a broadening of the absorption band associated with electron plasma oscillations in Na clusters. This effect is due to a decrease of the electron mean free path, which could be induced by defect creation in the metal. All these results show an influence of high electronic stopping power in materials known to be very resistant to irradiation with weak ionizing projectiles. The dependence of these effects on electronic stopping power and on various solid-state parameters is discussed

Analytic Bethe Ansatz for 1-D Hubbard model and twisted coupled XY model

We found the eigenvalues of the transfer matrices for the 1-D Hubbard model and for the coupled XY model with twisted boundary condition by using the analytic Bethe Ansatz method. Under a particular condition the two models have the same Bethe Ansatz equations. We have also proved that the periodic 1-D Hubbard model is exactly equal to the coupled XY model with nontrivial twisted boundary condition at the level of hamiltonians and transfer matrices.Comment: 22 pages, latex, no figure

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