Magnetic behavior of a spin-1 Blume-Emery-Griffiths model

I study the one-dimensional spin-1 Blume-Emery-Griffiths model with bilinear and biquadratic exchange interactions and single-ion crystal field under an applied magnetic field. This model can be exactly mapped into a tight-binding Hubbard model - extended to include intersite interactions - provided one renormalizes the chemical and the on-site potentials, which become temperature dependent. After this transformation, I provide the exact solution of the Blume-Emery-Griffiths model in one dimension by means of the Green's functions and equations of motion formalism. I investigate the magnetic variations of physical quantities - such as magnetization, quadrupolar moment, susceptibility - for different values of the interaction parameters and of the applied field, focusing on the role played by the biquadratic interaction in the breakdown of the magnetization plateaus.Comment: 4 pages, 5 figures. ICM 2009 (Karlsruhe) Conference proceeding

The N-Chain Hubbard model in the Composite Operator Method

We propose a theoretical framework to describe the ladder systems. The N-chain Hubbard model has been studied within the Composite Operator Method. In this scheme of calculations the single-particle Green's function for any number of coupled chains is obtained by solving self-consistently a system of integral equations.Comment: 6 pages, 1 embedded Postscript figure, LaTeX, to be published in Physica

Equations of motion approach to the spin-1/2 Ising model on the Bethe lattice

We exactly solve the ferromagnetic spin-1/2 Ising model on the Bethe lattice in the presence of an external magnetic field by means of the equations of motion method within the Green's function formalism. In particular, such an approach is applied to an isomorphic model of localized Fermi particles interacting via an intersite Coulomb interaction. A complete set of eigenoperators is found together with the corresponding eigenvalues. The Green's functions and the correlation functions are written in terms of a finite set of parameters to be self-consistently determined. A procedure is developed, that allows us to exactly fix the unknown parameters in the case of a Bethe lattice with any coordination number z. Non-local correlation functions up to four points are also provided together with a study of the relevant thermodynamic quantities.Comment: RevTex, 29 pages, 13 figure

Bosonic sector of the two-dimensional Hubbard model studied within a two-pole approximation

The charge and spin dynamics of the two-dimensional Hubbard model in the paramagnetic phase is first studied by means of the two-pole approximation within the framework of the Composite Operator Method. The fully self-consistent scheme requires: no decoupling, the fulfillment of both Pauli principle and hydrodynamics constraints, the simultaneous solution of fermionic and bosonic sectors and a very rich momentum dependence of the response functions. The temperature and momentum dependencies, as well as the dependency on the Coulomb repulsion strength and the filling, of the calculated charge and spin susceptibilities and correlation functions are in very good agreement with the numerical calculations present in the literature

A Study of the Antiferromagnetic Phase in the Hubbard Model by means of the Composite Operator Method

We have investigated the antiferromagnetic phase of the 2D, the 3D and the extended Hubbard models on a bipartite cubic lattice by means of the Composite Operator Method within a two-pole approximation. This approach yields a fully self-consistent treatment of the antiferromagnetic state that respects the symmetry properties of both the model and the algebra. The complete phase diagram, as regards the antiferromagnetic and the paramagnetic phases, has been drawn. We firstly reported, within a pole approximation, three kinds of transitions at half-filling: Mott-Hubbard, Mott-Heisenberg and Heisenberg. We have also found a metal-insulator transition, driven by doping, within the antiferromagnetic phase. This latter is restricted to a very small region near half filling and has, in contrast to what has been found by similar approaches, a finite critical Coulomb interaction as lower bound at half filling. Finally, it is worth noting that our antiferromagnetic gap has two independent components: one due to the antiferromagnetic correlations and another coming from the Mott-Hubbard mechanism.Comment: 20 pages, 37 figures, RevTeX, submitted to Phys. Rev.

Exploring the acceptance of entomophagy: A survey of italian consumers

Insect-based food is not common in Europe, because most people do not consider insects to be edible, but rather a threat and a health risk. Fear and refusal to eat a new food product introduced into a culture is called food neophobia, which results in a hesitation to trying and experimenting with new foods. Although there is significant interest in this novel sector, there is a lack of research on the link between rejection, the level of food neophobia, and consumer behavior related to the introduction of insects into the diet. In this study, through 420 questionnaires, a specific experimental scale of insects was introduced which, together with a neophobia scale, analyzed the probability and the intention of respondents to consume insects. Another issue tested has been their intention to eat food containing insects. We observed that the analyses of the two scales produced different results, confirming the need for a specific scale to measure “insect phobia”. This is important, since knowledge about consumer preferences for and barriers to using insects as human food sources is limited but necessary in order to set up commercialization strategies. The development of insect-based food offers physical health benefits and also improves the sustainability of the food industry

Reconhecimento de padrões de pontes de hidrogênio – preliminares do desenvolvimento de uma metodologia baseada em TI para a predição da posição de átomos de hidrogênio em proteínas.

Os primeiros resultados do desenvolvimento de um novo método para a localização do átomo de hidrogênio contido em grupos hidroxila da cadeia lateral dos aminoácidos é apresentado neste artigo. Os métodos existentes utilizam campos de força para esse problema de localização. Os autores propõem uma abordagem computacional para esse problema, pelo reconhecimento de padrões de pontes de hidrogênio agrupados por similaridade em clusters.bitstream/item/11853/1/bp20.pd

Spin and charge orderings in the atomic limit of the U-V-J model

In this paper we study a generalization of the 1D Hubbard model by considering density-density and Ising-type spin-spin nearest neighbor (NN) interactions, parameterized by $V$ and $J$, respectively. We present the T=0 phase diagram for both ferro ($J>0$) and anti-ferro ($J<0$) coupling obtained in the narrow-band limit by means of an extension to zero-temperature of the transfer-matrix method. Based on the values of the Hamiltonian parameters, we identify a number of phases that involve orderings of the double occupancy, NN density and spin correlations, being these latter very fragile.Comment: 4 pages, 2 figures, SCES2011 Proceeding

Koagulacija krvi i lipidi u serumu (Studija stanovništva)

Two population groups differing in dietary habits and physical activity were examined on blood lipids and blood coagulability. The results showed a higher lipid concentration and shorter clotting time in the physically less active group, having a higher fat and caloric intake.Dvije populacione grupe, koje se razlikuju po svojoj prehrani, a osobito po povećanoj potrošnji masnoća i smanjenom fizičkom aktivitetu, ispitivane su s obzirom na nivo krvnih lipida i na koagulabilitet krvi. Rezultati pokazuju, da prehrana, osobito povećana potrošnja animalnih masnoća, te smanjena psihička aktivnost utječu na povećanje nivoa krvnih lipida i bržeg koagulabiliteta krvi mjerenog kao vrijeme zgrušavanja i protrombinsko vrijeme. Ti rezultati potvrđuju već ranija zapažanja autora o povećanom koagulabilitetu krvi u populacionim grupama, koje se istovremeno razlikuju i u koncentraciji krvnih lipida i u učestalosti koronarnih bolesti