Modelo de duas bandas e transição metal-não metal em sistemas magnéticos

Using the two band model introduced by Mota and Coutinho-Filho, the metal-nonmetal transition is investigated by taking an approximate model Hamiltonian which takes into accout the hybridization of the bands, not included in the original model. A Green's function technique is used to obtain the hybrid bands inthe Hartree-Fock approximation. Investigating the phenomenon of metal-nonmetal transition, in general, increasing the intra-atomic interaction the tendency of the systems toward nonmetalic behavior increases. But, differently of previous results, for strong hybridization and small intra-atomic interaction, where the Hartree-fock approximation is valid, the opposite is observed. this may help to understand the difficult os observing pressure-induced nonmetal-metal transitions in magnetic systems.A transição metal-não metal é investigada usando o modelo de duas bandas apresentado por Mota e Coutinho -Filho utilizando um Hamiltoniano o qual inclui a hibridização de duas bandas não contida no modelo original. A técnica de funções de Green é utilizada para obter as bandas híbridas na aproximação Hartree-Fock. É mostrado que, em geral, com o aumento da interação intra-atômica a tendência do sistema se tornar metálico cresce. Porém, diferentemente de resultados anteriores, para a regição de hibridização forte e interação intra-atôrnica pequena, onde a aproximação Hartree-Fock é válida, o comportamento oposto é observado. Tal comportamento ajuda a entender a difuldade de observar-se transição metal-não metal em sistemas magnéticos

Determination of the Thermal Diffusivity of Plasmonic Nanofluids Containing PVP-Coated Ag Nanoparticles Using Mode-Mismatched Dual-Beam Thermal Lens Technique

Plasmonic nanofluids have found applications in many fields, for example, coolants, solar collectors, and theranostics agents. For such applications, an important parameter is the thermal diffusivity. In this communication, we present an experimental study concerning the dependence of the thermal diffusivity of highly diluted aqueous plasmonic nanofluids containing PVP-coated silver nanoparticles on the concentration. Measurements were made by employing the time resolved mode-mismatched thermal lens technique and the results show an enhancement of the thermal diffusivity, when compared to that of the carrier fluid, on increasing the number density of the nanoparticles and being rather constant as a function of the power of the pump beam

Characterization of native and oxidized human low-density lipoproteins by the Z-scan technique

The nonlinear optical response of human normal and oxidized by Cu2+ low-density lipoproteins particles (LDL), were investigated by the Z-scan technique as a function of temperature and concentration of LDL particles. the Z-scan signals increase linearly with concentration of normal LDL particles, following the usual Beer-Lambert law in a broad range of concentrations. the oxidized LDL particles do not show nonlinear optical response. On the other hand, normal LDL increases its nonlinear optical response as a function of temperature. These behaviors can be attributed to an absorbing element that is modified by the oxidative process. Contrarily. changes in the physical state of the cores and conformation of the ApoB100 protein due to an increase in temperature seems to enhance their nonlinear optical properties. This tendency is not due to aggregation of particles. the main contribution to the nonlinear optical response of normal LDL particles comes from the phospholipid fraction of the particles. (C) 2004 Elsevier Ireland Ltd. All rights reserved.Univ São Paulo, Inst Phys, Complex Fluids Grp, BR-05315970 São Paulo, SP, BrazilUniv São Paulo, Inst Chem, Fast Kinet & Photothermal Anal Lab, São Paulo, BrazilUniv São Paulo, Inst Biomed Sci, Dept Immunol, Lab Immunophysiopathol, São Paulo, BrazilUnifesp, Dept Biophys, São Paulo, BrazilUnifesp, Dept Biophys, São Paulo, BrazilWeb of Scienc

Characterization of native and oxidized human low-density lipoproteins by the Z-scan technique

Univ Sao Paulo, Inst Fis, BR-01498 Sao Paulo, BrazilUniv Sao Paulo, Inst Quim, BR-01498 Sao Paulo, BrazilUniv Sao Paulo, Inst Biomed Sci, BR-01498 Sao Paulo, BrazilUnifesp, Dept Biophys, Sao Paulo, BrazilUnifesp, Dept Biophys, Sao Paulo, BrazilWeb of Scienc

THE NONLINEAR OPTICAL RESPONSE of HUMAN NATIVE and OXIDIZED LDL: A NEW METHOD TO QUANTIFY THEIR AMOUNT in the PLASMA

Univ São Paulo, Inst Fis, BR-05508 São Paulo, BrazilUniv São Paulo, Inst Quim, BR-05508 São Paulo, BrazilUniv Estadual Ponta Grossa, Dept Fis, Parana, BrazilUniv São Paulo, Inst Ciencias Biomed, BR-05508 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, São Paulo, BrazilWeb of Scienc

Ortho-aminobenzoic acid-labeled bradykinins in interaction with lipid vesicles: Fluorescence study

The peptide hormone bradykinin (BK) (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)) and its shorter homolog BK1-5 (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)) were labeled with the extrinsic fluorescent probe ortho-aminobenzoic acid (Abz) bound to the N-terminal and amidated in the C-terminal carboxyl group (Abz-BK-NH2 and Abz-BK1-5-NH2). the fragment des-Arg(9)-BK was synthesized with the Abz fluorescent probe attached to the 3-amino group of 2,3-amino propionic acid (DAP), which positioned the Abz group at the C-terminal side of BK sequence, constituting the peptide des-Arg(9)-BK-DAP(Abz)-NH2. the spectral characteristics of the probe were similar in the three peptides, and their fluorescent properties were monitored to study the interaction of the peptides with anionic vesicles of dimyristoylphosphatidylglycerol (DMPG). Time-resolved fluorescence experiments showed that the fluorescence decay of the peptides was best described by double-exponential kinetics, with mean lifetimes values around 8.0 ns in buffer pH 7.4 that increased about 10% in the presence of DMPG vesicles. About a 10-fold increase, compared with the values in aqueous solution, was observed in the steady-state anisotropy in the presence of vesicles. A similar increase was also observed for the rotational correlation times obtained from time-resolved anisotropy decay profiles, and related to the overall tumbling of the peptides. Equilibrium binding constants for the peptide-lipid interaction were examined monitoring anisotropy values in titration experiments and the electrostatic effects were evaluated through Gouy-Chapman potential calculations. Without corrections for electrostatic effects, the labeled fragment Abz-BK1-5-NH2 presented the major affinity for DMPG vesicles. Corrections for the changes in peptide concentration due to electrostatic interactions suggested higher affinity of the BK fragments to the hydrophobic phase of the bilayer. (C) 2002 Wiley Periodicals, Inc.Univ São Paulo, Fac Filosofia Ciencias & Letras Ribeirao Pret, Dept Fis & Matemat, BR-14040901 Ribeirao Preto, BrazilUniv São Paulo, Inst Fis, BR-14040901 Ribeirao Preto, BrazilUniversidade Federal de São Paulo, Dept Biofis, São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biofis, São Paulo, BrazilWeb of Scienc