Thermodynamics of the quantum and classical Ising models with skew magnetic field

The thermodynamics of the unitary (normalized spin) quantum and classical Ising models with skew magnetic field, for |J|β?0.9, is derived for the ferromagnetic and antiferromagnetic cases. The high-temperature expansion (β-expansion) of the Helmholtz free energy is calculated up to order β⁷ for the quantum version (spin S≥1/2) and up to order β¹⁹ for the classical version. In contrast to the S=1/2 case, the thermodynamics of the transverse Ising and that of the XY model for S>1/2 are not equivalent. Moreover, the critical line of the T=0 classical antiferromagnetic Ising model with skew magnetic field is absent from this classical model, at least in the temperature range of |J|β?0.9.     

The β-expansion of periodic dressed chain models

We revisit the method of calculating the $\beta$-expansion of the Helmholtz free energy of any one-dimensional (1D) Hamiltonian with invariance under space translations, presented in [O. Rojas, S.M. de Souza, M.T. Thomaz, J. Math. Phys. 43 (2002) 1390], extending this method to 1-D Hamiltonians that are invariant under translations along super-sites (sequences of $l$ sites). The method is applicable, for instance, to spin models and bosonic/fermionic versions of Hubbard models, either quantum or classical. As an example, we focus on the staggered spin-$S$ Ising model in the presence of a longitudinal magnetic field, comparing some of its thermodynamic functions to those of the standard Ising model. We show that for arbitrary values of spin ($S\in \{1,3/2,2,\dots \}$) but distinct values of the coupling constant and the magnetic field, the specific heat and the $z$-component of the staggered and usual magnetizations can be well approximated by their respective thermodynamic function of the spin-$1/2$ models in a suitable interval of temperature. These approximations are valid for the standard Ising model as well as for the staggered model, the thermodynamics of which are known exactly.     

Production and Characterization of the Exopolysaccharides Produced by Agaricus brasiliensis in Submerged Fermentation

The aim of the work was to study the production of the exopolysaccharides by Agaricus brasiliensis and the isolation of exopolysaccharides (EPSs) with biological effects. A brasiliensis LPB03 was cultured in submerged fermentation in a medium containing glucose, yeast extract, hydrolyzed soybean protein, and salts (pH 6.1) at 29 degrees C and 120 rpm for 144 h. The maximum biomass and EPS yield was 7.80 +/- 0.01 and 1,430.70 +/- 26.75 mg/L, respectively. To isolate the produced EPSs, two methods were compared: (1) with alcohol precipitation and (2) treatment with tricloroacetic acid (TCA), followed by alcohol precipitation. The use of TCA facilitated the purification of the EPS, reducing the amount of the contaminant soy proteins. For monosaccharide identification, the EPSs were hydrolyzed, derivatized to alditol acetates, and analyzed by gas chromatography (GC) and GC-mass spectrometry, which showed the presence (in molar percentage) of mannose (58.7), galactose (21.4), and glucose (13.1) as major sugars, with lower amounts of rhamnose (3.9) and xylose (2.8). Scanning electron microscopy was used to observe the morphological structure of the EPS. The experiments in vivo including EPS in the mice diet during 8 weeks indicated the hipocholesteremic and hypoglycemic effects.     

ChemInform Abstract: The Ground-State Potential Energy Surface of Diazene

has been studied by using a complete active space MCSCF wave function generated by distributing eight electrons among eight orbitals.