Hubbard physics in the symmetric half-filled periodic Anderson-Hubbard model

Two very different methods -- exact diagonalization on finite chains and a variational method -- are used to study the possibility of a metal-insulator transition in the symmetric half-filled periodic Anderson-Hubbard model. With this aim we calculate the density of doubly occupied $d$ sites as a function of various parameters. In the absence of on-site Coulomb interaction ($U_f$) between $f$ electrons, the two methods yield similar results. The double occupancy of $d$ levels remains always finite just as in the one-dimensional Hubbard model. Exact diagonalization on finite chains gives the same result for finite $U_f$, while the Gutzwiller method leads to a Brinkman-Rice transition at a critical value ($U_d^c$), which depends on $U_f$ and $V$.Comment: 10 pages, 5 figure

Periodic Anderson model with correlated conduction electrons: Variational and exact diagonalization study

We investigate an extended version of the periodic Anderson model (the so-called periodic Anderson-Hubbard model) with the aim to understand the role of interaction between conduction electrons in the formation of the heavy-fermion and mixed-valence states. Two methods are used: (i) variational calculation with the Gutzwiller wave function optimizing numerically the ground-state energy and (ii) exact diagonalization of the Hamiltonian for short chains. The f-level occupancy and the renormalization factor of the quasiparticles are calculated as a function of the energy of the f orbital for a wide range of the interaction parameters. The results obtained by the two methods are in reasonably good agreement for the periodic Anderson model. The agreement is maintained even when the interaction between band electrons, U d, is taken into account, except for the half-filled case. This discrepancy can be explained by the difference between the physics of the one- and higher-dimensional models. We find that this interaction shifts and widens the energy range of the bare f level, where heavy-fermion behavior can be observed. For large-enough U d this range may lie even above the bare conduction band. The Gutzwiller method indicates a robust transition from Kondo insulator to Mott insulator in the half-filled model, while U d enhances the quasiparticle mass when the filling is close to half filling. © 2012 American Physical Society

Periodic anderson model with d-f interaction

We investigate an extended version of the periodic Anderson model where an interaction is switched on between the doubly occupied d- and f-sites. We perform variational calculations using the Gutzwiller trial wave function. We calculate the f-level occupancy as a function of the f-level energy with different interaction strengths. It is shown that the region of valence transition is sharpened due to the new interaction

Direct effect of bile on colonic mucosa in alimentary induced hyperlipidemy in rats

An experimental surgical model was developed in rats after a short term alimentary induced hyperlipidemy to study the direct effect of bile on the colonic mucosa, with regard to the cancerogenic properties of lipid rich diet. The purpose of this study was to light on the role of fatty acid alteration and lipid peroxidation processes of bile in the epithelial cell damage. Animals were fed with normal (group A) and fat rich diet (group B) for 10 days and then bile samples were collected by the cannulation of the common bile duct in deep anaesthesia. The circulation preserved colons of control rats were treated either with bile from the control or hyperlipidemic rats. The treatment was carried out for 30 minutes. The electronmicroscopic alterations of epithelial cells (both enterocytes and goblet cells) caused by bile from hyperlipidemic rats were significantly greater than that of controls. Unfavourable changes of the redox state of the colonic mucosa were also detected both in the hyperlipidemic and bile treated groups. A significant increase was observed in the free-SH concentration of the two bile treated groups against the untreated animals. The changes could be explained among others by the modified bile fatty acid composition. The present study supports that the alimentary modified bile can influence the structure of the epithelium of colonic mucosa and it can be one of the inducing factor of carcinogenesis

Altered element homeostasis and transmethylation ability in short-term polyphenol rich supplementation in hyperlipidemic animal model

Abstract Non-alcoholic fatty liver disease is one of the most common chronic liver diseases with unclarified pathomechanism and without evidence-proven therapy. Dietary polyphenols, targeting oxidative stress, are at the center of investigations. Our aim was to examine the effects of a polyphenol rich extract on metal element homeostasis and transmethylation ability in non-alcoholic fatty liver model. A ten-day rat model was used (control group, hyperlipidemic group with fat-rich diet, hyperlipidemic group with fat-rich diet and polyphenol supplementation, N = 8 in each group). The hyperlipidemic diet increased the concentration of the majority of the elements with significantly higher contents of B, Co, Cu, Fe, Mg, Mn, Na, Ni, P, Se, Si, and Zn in the liver. Further elevation of Al, Pb, and Sn concentrations could be observed in polyphenol supplemented animals. The polyphenol supplement unexpectedly decreased the transmethylation ability of the liver (132.00 vs. 114.15 vs. 92.25 HCHO μg g−1) further. The results emphasize the possible role of altered metal and non-metal element concentrations and decreased transmethylation ability in the pathomechanism of fatty liver disease. Dietary supplementation with natural compounds may have undesirable effect as well, there is the necessity to improve the efficacy of polyphenol formulations because of their low oral bioavailability

Antioxidant properties of a mixture of Lamiaceaeplants intended to use as a food additive

Culinary herbs and medicinal plants could be used as natural food ingredients to replace synthetic antioxidants. Two natural antioxidant preparations, namely Rosmol (liquid) and Rosmol-P (powder) were produced by extraction from a mixture of medicinal plants belonging to the Lamiaceaefamily, such as rosemary (Rosmarinus officinalis L.),self heal(Prunella vulgaris L.) hyssop(Hyssoppus officinalis L.)and lemon balm (Melissa officinalis L.). The main active compound of the extract is supposed to be a phenolic (caffeic) acid derivative. The total polyphenol content of the preparations is very high, 8.72 g l-1 for Rosmol and 93.7 g kg-1 for Rosmol-P. The products acted as primary and secondary antioxidants, chelating transitional metal ions and inhibiting the autoxidation of linoleic acid. Rosmol and Rosmol-P scavenged free radicals formed during Fenton type reaction measured by chemiluminometry, and also exhibited strong antioxidant property in Randox TAS measurement. The antioxidant activity of the products was unchanged after six months of storage. According to the in vitro studies, the products are suitable to use as antioxidant ingredients instead of synthetic ones in lipid containing food products