Synthesis and Characterization of Monodispersed Copper Colloids in Polar Solvents

A chemical reduction method for preparing monodispersed pure-phase copper colloids in water and ethylene glycol has been reported. Owing to the reduction property of ethylene glycol, the reaction rate in ethylene glycol is higher than that in water. In addition, the amount of reducing agent can be reduced largely. Ascorbic acid plays roles as reducing agent and antioxidant of colloidal copper, due to its ability to scavenge free radicals and reactive oxygen molecules. Thermogravimetric results reveal that the as-prepared copper nanoparticles have good stability, and they begin to be oxidized at above 210 °C. Polyvinyl pyrrolidone works both as size controller and polymeric capping agents, because it hinders the nuclei from aggregation through the polar groups, which strongly absorb the copper particles on the surface with coordination bonds

Les fromages de la Slovaquie dans la république Tchéquo-Slovaque

O artigo propõe-se a uma reflexão acerca da luta ao direito de cidadania pelas pessoas que vivem com HIV/Aids em uma sociedade onde a esfera pública moderna é baseada na Imprensa. De que forma se constitui o espaço público no Brasil contemporâneo e qual a postura dos meios de comunicação em relação à epidemia da Aids nas duas últimas décadas. Concluiu-se que apesar da contribuição da Imprensa para dar visibilidade e pautar a questão da Aids na sociedade, os meios de comunicação ainda não contribuem de forma efetiva para que as pessoas que vivem com HIV/Aids possam gozar de seus direitos de cidadania plena sem o fantasma do preconceito e da discriminação

Electron Absorption and Emission Spectra of Eu3+\text{}^{3+} in KEu(WO4\text{}_{4})2\text{}_{2}

Electron absorption and emission spectra of Eu$\text{}^{3+}$ ion in stoichiometric KEu(WO$\text{}_{4}$)$\text{}_{2}$ were measured at the temperature range 15-300 K. The oscillator strengths of f-f transitions and the Judd-Ofelt parameters were evaluated. The assignment of vibronic transitions is given and mechanism of emission decay is discussed

Spectroscopic ProPerties of Eu3+\text{}^{3+} Ion in KEu(MoO4\text{}_{4})2\text{}_{2} Crystal

IR, Raman, electron absorption and emission spectra of KEu(MoO$\text{}_{4}$)$\text{}_{2}$ crystal were measured at the temperature range 8-300 K. The oscillator strengths of f-f transitions were evaluated

Structural and Optical Characterisation of Hydrogenated Soda-Lime Silicate Glasses Doped with Silver and Copper

The results of comparative studies of the effect of hydrogenation upon structural and optical properties of the commercial soda-lime silicate glasses doped either with monovalent silver or copper have been presented. The samples were characterised by means of the scanning and transmission electron microscopy and the UV-VIS-IR absorption spectroscopy. It has been shown that the annealing of suitably ion-exchanged specimens in gaseous hydrogen atmosphere could be considered as an effective procedure for obtaining composite materials of expected properties correlated with the induced changes of the morphology of both the glassy matrix and the dopant

Polarizing-field orientation and thermal treatment effects on the dielectric behavior of fluorapatite

A thermally stimulated depolarization currents (TSDC) study in natural fluorapatite single crystals has established different relaxation mechanisms for two polarization orientations (E-p parallel and perpendicular to the crystallographic c axis), which are discussed in relation to the defect chemistry and the specific columnar structure in apatite. The intensities of the thermostimulated current signals between the two poling field orientations demonstrate a difference of at least one order of magnitude, with the higher one recorded for the electric field parallel to the c axis. The TSDC thermogram appearing with the electric field parallel to c axis, in the 10-320 K range, consists of a broad and complex band (HT), with a maximum around 300 K. The relative intensity of associated current signals is indicative of extensive dipole-like ionic motions along c axis with a distribution in their activation energies ranging between 0.14 and 0.85 eV. The microdomain structure of fluorapatite along c axis permits the formation of charge layers at the interfaces. After annealing, the induced changes of size and/or shape of the interfaces could explain the observed changes of band intensity and location. With the electric field perpendicular to c axis, the spectrum consists of at least five well-defined relaxation bands, the high temperature ones (HT1, HT2, HT3) decreasing after heating at 673-873 K. The most dramatic change was recorded for an intermediate LT2 single-relaxation band located around 185 K, with a high activation energy of 1.06 eV, which manifested a significant growth after annealing. Rietvelt analysis of the x-ray diffraction patterns of the original and annealed apatite powders, indicates change in the unit cell parameters of the hexagonal structure (i.e., a increases from 9.3921 to 9.3940 Angstrom after annealing), which can be related to the establishment of a new equilibrium distribution of the abundant trivalent rare-earth (Ce, La, Nd, Pr,...) impurity ions. The origin of the TSDC bands is discussed and tentative correlations are suggested, in terms of substitute aliovalent ions-vacancy dipoles. The thermal response of the high temperature relaxation bands in the case of E-p perpendicular to c axis, is characteristic of dipole clustering phenomena - although an explanation based on localized changes in the structural environment of the pertinent dipoles/ions cannot be disregarded. (C) 1999 American Institute of Physics. [S00218979(99)10001- X]