Configuration-Dependent Diffusion Dynamics of Downhill and Two-State Protein Folding

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Interaction of amphiphilic derivatives of chitosan with DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Cooper pair dispersion relation for weak to strong coupling

Cooper pairing in two dimensions is analyzed with a set of renormalized equations to determine its binding energy for any fermion number density and all coupling assuming a,generic pairwise residual interfermion interaction. Also considered are Cooper pairs (CP's) with nonzero center-of-mass momentum (CMM) and their binding energy is expanded analytically in powers of the CMM up to quadratic terms. A Fermi-sea-dependent linear term in the CMM dominates the pair excitation energy in weak coupling (also called the BCS regime) while the more familiar quadratic term prevails in strong coupling (the Bose regime). The crossover, though strictly unrelated to BCS theory per se, is studied numerically as it is expected to play a central role in a model of superconductivity as a Bose-Einstein condensation of CPs where the transition temperature vanishes for all dimensionality d less than or equal to 2 for quadratic dispersion, but is nonzero for all d greater than or equal to 1 for linear dispersion.

Partículas nanométricas de ferritas de ítrio

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of the Al content on the phase transformations in Cu-Al-Ag alloys

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural investigations of tungsten silver phosphate glasses by solid state NMR, vibrational and X-ray absorption near edge spectroscopies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Preparation and characterization of new glassy system As2P2S8-Ga2S3

Glasses having the composition (100 - x)As2P2S8-xGa(2)S(3) with x ranging from 0 to 50% were investigated to determine the compositional effect on properties and local structure. The glass transition temperature (T-g) and the stability parameter against crystallization (T-x - T-g) increased with the addition of Ga2S3. The structure of these glasses was probed by Raman scattering, Fourier transform infrared (FT-IR) and P-31 nuclear magnetic resonance. on the basis of the observed vibrations and the strength of the P-31-P-31 homonuclear magnetic dipolar coupling, two scenarios can be proposed for the structural evolution induced by the addition of Ga2S3. For x <= 20% we may have the formation of GaS4E- groups (E = nonbonding electron), and for x >= 30% we have depolymerization of the As2P2S8 units and the formation of a network of GaPS4 units with each PS4/2 unit (Q(4)) species carrying a single positive formal charge.

Thermal, structural and optical properties of new tungsten lead-pyrophosphate glasses

Crystalline lead-pyrophosphate precursor was prepared in aqueous solution from lead nitrate and phosphoric acid and characterized by X-ray diffraction, thermogravimetry and Raman scattering. This crystalline lead-phosphate was then used to prepare glass samples in the binary system Pb(2)P(2)O(7)-WO(3). Dependence of WO(3) content on thermal, structural and optical properties were investigated by thermal analysis (DSC), Raman spectroscopy, UV-visible and near-infrared absorption and M-Line technique to access refractive index values. Incorporation of WO(3) in the lead-pyrophosphate matrix enhances the glass transition temperature and thermal stability against devitrification, favors formation of P-O-W bonds and WO(6) clusters. In addition, optical properties are strongly modified with a redshift of the optical bandgap with WO(3) incorporation as well as an increase of the refractive index from 1.89 to 2.05 in the visible. (C) 2011 Elsevier B.V. All rights reserved.

Crystallization of monoclinic WO3 in tungstate fluorophosphate glasses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Glass transitions and state diagram for freeze-dried pineapple

Glass transition temperature of freeze-dried pineapple conditioned by adsorption at various water activities at 25 degreesC was determined by differential scanning calorimetry (DSC). High moisture content samples corresponding to water activities higher than 0.9, obtained by liquid water addition, were also analysed. The DSC traces showed a well-visible shift in baseline at the glass transition temperature (T(g)). Besides, no ice formation was observed until water activity was equal to 0.75. For water activities lower than 0.88, the glass transition curve showed that T(g) decreased with increasing moisture content and the experimental data could be well-correlated by the Gordon-Taylor equation. For higher water activities, this curve exhibited a discontinuity, with suddenly increasing glass transition temperatures approaching a constant value that corresponds to the T(g) of the maximally freeze-concentrated amorphous matrix. The unfreezable water content was determined through melting enthalpy dependence on the sample moisture content.

Test of the adiabatic nucleation model in SeTe and GeSnSe glasses

Se1-yTey and Ge1-ySnySe2.5 glasses, with compositions Y less than or equal to 0.5 and Y less than or equal to 0.6 respectively, are investigated. These glasses show a glass transition temperature (T-g) above the stability limit, indicated by the Adiabatic Nucleation Model (ANM). This effect has to be so because, other-wise, when cooled, these undercooled liquids would crystallize by generalized nucleation near the stability limit and no T-g could be observed. This shows that Se1-yTey glasses for Y < 0.5 are structurally stable. Limiting cases are pure Te and Se50Te50, which have T'(g)'s on the stability limit. Pure amorphous Te has to be obtained by fast quenching techniques, where the effective (fast quenching) T-g(*) is higher and Se50Te50 tends to crystallize easily. (C) 2004 Elsevier B.V. All rights reserved.

A viscosity model for fluorochloroindate glasses

Viscosity of fluoride glasses is generally Arrhenian between glass transition temperature and crystallization temperature. This dependence on temperature is not observed in some special compositions which have two regions with different activation energies. The viscosity of glasses 40InF(3)-20ZnF(2)-25BaF(2)-10SrF(2)-5LiCl and 40InF(3)-20ZnF(2)-15SrF(2)-20BaF(2)-5NaCl was obtained by the parallel plate method. A theoretical model has been proposed to explain the viscosity data. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Poole-Frenkel effect in amorphous poly(p-phenylene sulfide)

The conductivity of poly(p-phenylene sulfide) (PPS) amorphous samples sandwiched between metallic electrodes has been studied as a function of applied voltage, temperature, and electrode material. The voltage (U) dependence of the currents for electric fields within the range 10(3)-10(6) V/cm exhibits exp beta U-1/2 behavior with beta = beta(Schottky) below the glass transition temperature (T-g congruent to 90 degrees C), and beta = beta(Poole-Frenkel) above T-g. Coordinated temperature measurements of de currents with different metallic contacts and thermally stimulated currents (TSC) indicate, however, that the conductivity at T < T-g is consistent with the so-called ''anomalous'' Poole-Frenkel effect rather than the Schottky effect. Consequently, the p-type conductivity in amorphous PPS is proposed to be a bulk-limited process due to ionization of two different types of acceptor centers in the presence of neutral hole traps. (C) 1996 John Wiley & Sons, Inc.

Photosensitivity in antimony based glasses

New glass forming systems based on Sb2O3-SbPO4 has been explored. These glasses present higher thermal stability against devitrification and higher refractive index than chalcogenide glasses. Under irradiation, using Ar-laser 350nm wavelength and 50 mW power density, change on the coloration is observed. Structural and electronic modifications around Sb cations induced by such treatment have been characterized by XANES measurements at the L-Sb edges. on the one hand, XANES spectra, at the LJ edge, show a decrease of the coordination number for Sb atoms induced by exposure to light indicating a breaking of Sb-O bonds in the glassy network. on the other hand, XANES spectra, at the Lt edge, suggest a change in the oxidation state of Sb atoms. These modifications associated to the photodarkening of the glass is reversible either after a couple of days or after heating the glass at the glass transition temperature, T-g.

Unilamellar vesicles obtained by simply mixing dioctadecyldimethylammonium chloride and bromide with water

Optically clear dispersions of dioctadecyldimethylammonium bromide and chloride (DODAX, X = Br-, Cl-) in water can be obtained by simply mixing the amphiphiles at low concentrations (I mM) and at a temperature safely above the gel to liquid crystalline phase transition temperature (T-m approximate to 45-48 degrees C) of DODAX in water. Under these conditions, dynamic light scattering shows that, at room temperature, the dispersions contain two well-defined populations of large vesicles with average hydrodynamic radii (RH) of 80 and 337 nm for DODAB and of 69 and 247 nm for DODAC. Cryo-transmission electron microscopy (cryo-TEM) micrographs show that DODAX vesicles are unilamellar and polydisperse with apparent radius up to 800 nm. The vesicles are stable for at least I month according to the ageing time-dependence of the turbidity and molar absorption coefficient. (c) 2006 Elsevier B.V.. All rights reserved.