Magnetic Properties of the t-J Model in the Dynamical Mean-Field Theory

We present a theory for the spin correlation function of the t-J model in the framework of the dynamical mean-field theory. Using this mapping between the lattice and a local model we are able to obtain an intuitive expression for the non-local spin susceptibility, with the corresponding local correlation function as input. The latter is calculated by means of local Goldstone diagrams following closely the procedures developed and successfully applied for the (single impurity) Anderson model.We present a systematic study of the magnetic susceptibility and compare our results with those of a Hubbard model at large U. Similarities and differences are pointed out and the magnetic phase diagram of the t-J model is discussed.Comment: 28 pages LaTeX, postscript figures as compressed and uuencoded file included fil

A pro-drug of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) prevents differentiated SH-SY5Y cells from toxicity induced by 6-hydroxydopamine

Regular consumption of green tea benefits people in prevention from cardiovascular disorders, obesity as well as neurodegenerative diseases. (-)-Epigallocatechin-3-gallate (EGCG) is regarded as the most biologically active catechin in green tea. However, the stability and bioavailability of EGCG are restricted. The purpose of the present study was to investigate whether a pro-drug, a fully acetylated EGCG (pEGCG), could be more effective in neuroprotection in Parkinsonism mimic cellular model. Retinoic acid (RA)-differentiated neuroblastoma SH-SY5Y cells were pre-treated with different concentrations of EGCG and pEGCG for 30 min and followed by incubation of 25 μM 6-hydroxydopamine (6-OHDA) for 24 h. We found that a broad dosage range of pEGCG (from 0.1 to 10 μM) could significantly reduce lactate dehydrogenase release. Likewise, 10 μM of pEGCG was effective in reducing caspase-3 activity, while EGCG at all concentrations tested in the model failed to attenuate caspase-3 activity induced by 6-OHDA. Furthermore, Western-blot analysis showed that Akt could be one of the specific signaling pathways stimulated by pEGCG in neuroprotection. It was demonstrated that 25 μM of 6-OHDA significantly suppressed the phosphorylation level of Akt. Only pEGCG at 10 μM markedly increased its phosphorylation level compared to 6-OHDA alone. Taken together, as pEGCG has higher stability and bioavailbility for further investigation, it could be a potential neuroprotective agent and our current findings may offer certain clues for optimizing its application in future. © 2009 Elsevier Ireland Ltd. All rights reserved.postprin

The protective effects of catechin on palmitic acid-induced cytotoxicity in mouse brain endothelial cell

AIMS: The approximate prevalence of the metabolic syndrome (MS) in patients with coronary heart disease (CAD) is 50%, with a prevalence of 37% in patients with premature CAD. Effective prevention or treatment of MS significantly reduces the risk for developing serious complications. Palmitic acid (PA) is a saturated fatty acid, when being excessive, is a significant risk factor for development of MS or cardiovascular accident. Lipotoxicity in endothelial cells (EC) has been well documented but how PA ...postprin

Slave-Boson Functional-Integral Approach to the Hubbard Model with Orbital Degeneracy

A slave-boson functional-integral method has been developed for the Hubbard model with arbitrary, orbital degeneracy $D$. Its saddle-point mean-field theory is equivalent to the Gutzwiller approximation, as in the case of single-band Hubbard model. Our theory is applied to the doubly degenerate ($D = 2$) model, and numerical calculations have been performed for this model in the paramagnetic states. The effect of the exchange interaction on the metal-insulator (MI) transition is discussed. The critical interaction for the MI transition is analytically calculated as functions of orbital degeneracy and electron occupancy.Comment: Latex 20 pages, 9 figures available on request to [email protected] Note: published in J. Physical Society of Japan with some minor modification

The cardioprotective effect of isosteviol on endothelin-1-induced hypertrophy of cultured neonatal rat cardiomyocytes

Poster Session - P307 Molecular and Cellular Cardiology, Basic Research: no. 1525 ; abstract no. 276AIMS: Isosteviol is an active derivative of stevioside and also possessing an anti-hypertensive effect in our previous report. Left ventricular hypertrophy is an independent cardiovascular risk factor related to cardiovascular complications in patients with hypertension. Therefore, a decrease in left ventricular mass is a therapeutic goal in these patients. In the present study, we elucidate the anti-hypertrophy and molecular mechanisms of isosteviol on endothelin-1(ET-1)-induced hyper…postprin

The Metal-Insulator Transition in the Doubly Degenerate Hubbard Model

A systematic study has been made on the metal-insulator (MI) transition of the doubly degenerate Hubbard model (DHM) in the paramagnetic ground state, by using the slave-boson mean-field theory which is equivalent to the Gutzwiller approximation (GA). For the case of infinite electron-electron interactions, we obtain the analytic solution, which becomes exact in the limit of infinite spatial dimension. On the contrary, the finite-interaction case is investigated by numerical methods with the use of the simple-cubic model with the nearest-neighbor hopping. The mass-enhancement factor, $Z$, is shown to increase divergently as one approaches the integer fillings ($N = 1, 2, 3$), at which the MI transition takes place, $N$ being the total number of electrons. The calculated $N$ dependence of $Z$ is compared with the observed specific-heat coefficient, $\gamma$, of $Sr_{1-x}La_xTiO_3$ which is reported to significantly increase as $x$ approaches unity.Comment: Latex 16 pages, 10 ps figures included, published in J. Phys. Soc. Jpn. with some minor modifications. ([email protected]

SDSS J143030.22-001115.1: A misclassified narrow-line Seyfert 1 galaxy with flat X-ray spectrum

We used multi-component profiles to model H$\beta$ and [O III]$\lambda \lambda$4959,5007 lines for SDSS J143030.22-001115.1, a narrow-line Seyfert 1 galaxy (NLS1) in a sample of 150 NLS1s candidates selected from the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR). After subtracting the H$\beta$ contribution from narrow line regions (NLRs), we found that its full width half maximum (FWHM) of broad H$\beta$ line is nearly 2900 \kms, significantly larger than the customarily adopted criterion of 2000 \kms. With its weak Fe II multiples, we think that SDSS J143030.22-001115.1 can't be classified as a genuine NLS1. When we calculate the virial black hole masses of NLS1s, we should use the H$\beta$ linewidth after subtracting the H$\beta$ contribution from NLRs.Comment: 7 pages, 1 table, accepted by ChJA

Reexamining radiative decays of 1−−1^{--} quarkonium into η′\eta' and η\eta

Recently CLEO has studied the radiative decay of $\Upsilon$ into $\eta'$ and an upper limit for the decay has been determined. Confronting with this upper limit,most of theoretical predictions for the decay fails. After briefly reviewing these predictions we re-examine the decay by separating nonperturbative effect related to the quarkonium and that related to $\eta'$ or $\eta$, in which the later is parameterized by distribution amplitudes of gluons in $\eta'$. With this factorization approach we obtain theoretical predictions which are in agreement with experiment. Uncertainties in our predictions are discussed. The possibly largest uncertainties are from relativistic corrections for $J/\Psi$ and the value of the charm quark mass. We argue that the effect of these uncertainties can be reduced by using quarkonium masses instead of using quark masses. An example of the reduction is shown with an attempt to explain the violation of the famous 14% rule in radiative decays of charmonia.Comment: 9 Pages, Latex fil

Various Models for Pion Probability Distributions from Heavy-Ion Collisions

Various models for pion multiplicity distributions produced in relativistic heavy ion collisions are discussed. The models include a relativistic hydrodynamic model, a thermodynamic description, an emitting source pion laser model, and a description which generates a negative binomial description. The approach developed can be used to discuss other cases which will be mentioned. The pion probability distributions for these various cases are compared. Comparison of the pion laser model and Bose-Einstein condensation in a laser trap and with the thermal model are made. The thermal model and hydrodynamic model are also used to illustrate why the number of pions never diverges and why the Bose-Einstein correction effects are relatively small. The pion emission strength $\eta$ of a Poisson emitter and a critical density $\eta_c$ are connected in a thermal model by $\eta/n_c = e^{-m/T} < 1$, and this fact reduces any Bose-Einstein correction effects in the number and number fluctuation of pions. Fluctuations can be much larger than Poisson in the pion laser model and for a negative binomial description. The clan representation of the negative binomial distribution due to Van Hove and Giovannini is discussed using the present description. Applications to CERN/NA44 and CERN/NA49 data are discussed in terms of the relativistic hydrodynamic model.Comment: 12 pages, incl. 3 figures and 4 tables. You can also download a PostScript file of the manuscript from http://p2hp2.lanl.gov/people/schlei/eprint.htm

Laser-assisted collision effect on nonsequential double ionization of helium in a few-cycle laser pulse

Nonsequential double ionization (NSDI) of helium in an intense few-cycle laser pulse is investigated by applying the three-dimensional semi-classical re-scattering method. It is found that the momentum distribution of He$^{2+}$ shows a single-double-single peak structure as the pulse intensity increases. According to the different mechanisms dominating the NSDI process, the laser intensity can be classified into three regimes where the momentum distribution of He$^{2+}$ exhibits different characteristics. In the relatively high intensity regime, an NSDI mechanism named the "laser-assisted collision ionization" is found to be dominating the NSDI process and causing the single peak structure. This result can shed light on the study of non-sequential ionization of a highly charged ion in a relatively intense laser pulse