Evidence of hetero-epitaxial growth of Pb(Mg1/3Nb2/3)O-3 on the BaTiO3 seed particles of a citrate solution

Citrate solution was employed in preparing Pb(Mg1/3Nb1/3)O-3 (PMN) powder from polymeric precursors. BaTiO3 particles of 600 nm average size were used as seed for growing PMN. X-ray diffraction (XRD) indicated the presence of both, pyrochlore Pb6Nb6MgO22 (P6N) and perovskite phases. Transmission electron microscopy (TEM) observations indicated that only the PMN phase has hetero-epitaxially grown on the BaTiO3 seed particles. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Effect of uroguanylin on potassium and bicarbonate transport in rat renal tubules

The effect of uroguanylin (UGN) oil K(+) and H(+) secretion in the renal tubules of the rat kidney was studied using in vivo stationary microperfusion. For the study of K(+) secretion, a tubule was Punctured to inject a column of FDC-green-colored Ringer's solution with 0.5 mmol KCI/L 10(-6)(mol UGN/L, and oil was Used to block fluid flow. K(+) activity and transepithelial potential differences (PD) were measured with double microelectrodes (K(+) ion-selective resin vs. reference) in the distal tubules of the same nephron. During perfusion, K(+) activity rose exponentially, from 0.5 mmol/L to stationary concentration, allowing for the calculation of K(+) secretion J(K)). JK increased from 0.63 +/- 0.06 nmol.cm(-2).s(-1) in the control croup to 0.85 +/- 0.06 in the UGN group (p < 0.01). PD was -51.0 +/- 5.3 mV in the control group and -50.3 +/- 4.98 mV in the UGN group. In the presence of 10(-7) mol iberiotoxin/L, the UGN effect was abolished: JK was 0.37 +/- 0.038 nmol-cm(-2).s(-1) in the absence of, and 0.38 +/- 0.025 in the presence of, UGN. indicating its action oil rnaxi-K channels. In another series of experiments, renal tubule acidification was studied, using similar method: proximal and distal tubules were perfused with solutions containing 25 mmol NaHCO(3)/L. Acidification half-time was increased both in proximal and distal segments and, as a consequence, bicarbonate reabsorption decreased in the presence of UGN (in proximal tubules, from 2.40 +/- 0.26 to 1.56 +/- 0.21 nmol-cm(-2).s(-1)). When the Na(+)/H(+) exchanger was inhibited by 10(-4) mol hexamethylene amiloride (HMA)/L, the control and UGN groups were not significantly different. In the late distal tubule, after HMA, UGN significantly reduced J(HCO3)(-). indicating all effect of UGN oil H(+)-ATPase. These data show that UGN stimulated J(K)(+) by actin, oil maxi-K channels. and decreased J(HCO3)(-) by acting on NHE3 in proximal and H(+)-ATPase in distal tubules.

Dynamic viscosity of binary and ternary mixtures containing poly(ethylene glycol), potassium phosphate, and water

Dynamic viscosity of binary mixtures of poly(ethylene glycol) molar mass 1500 da + water, potassium phosphate + water, and ternary mixtures of poly(ethylene glycol) molar mass 1500 da + potassium phosphate + water were determined at 303.15 K Binary and ternary mixture viscosities showed a direct logarithm-type relation with the increase of poly(ethylene glycol) and potassium phosphate contents. The models used for viscosity correlation gave a good fit to the experimental data.

Study of potassium additive on the phase formation and ferroelectric properties of 0.9PMN-0.1PT ceramics

A recent and innovative method to include Ti into the columbite precursor has permitted to synthesize 0.9PMN-0.1PT powders with high homogeneity. The present work describes this methodology, named modified columbite method, showing that the reaction between MN(T)and PbO at 800 degrees C for 2 h results in perovskite single-phase. The crystal structure alterations in the columbite and perovskite phases obtained by this methodology and the effects of potassium doping were investigated by the Rietveld method. Changes in the powder morphology, density and weight loss during the sintering process were also studied. Conclusively, potassium does not affect significantly the perovskite amount, but reduces the particle and grain sizes. This dopant also changes the relaxor behavior of 0.9PMN-0.1 PT ceramic, reducing the dielectric loss and enhancing the diffuseness of the phase transition. (C) 2005 Published by Elsevier Ltd and Techna Gronp S.r.l.

Physicochemical properties of sildenafil citrate (Viagra) and sildenafil base

Sildenafil citrate (Viagra) [I] and sildenafil base [II] are easily and unequivocally characterized by a set of physicochemical methods that include X-ray diffractometry, infrared spectroscopy, and thermal analysis. Monoclinic lattice constants: [I]: a = 26.98 Angstrom; b = 11.95 Angstrom; c = 16.68 Angstrom; beta = 106.97degrees. [II]: a = 8.66 Angstrom; b = 34.27 Angstrom; c = 8.93 Angstrom; beta = 96.63'. Both compounds decompose at 189.4degreesC [I] and 251.9degreesC [II]. Densities and refractive indices are given. (C) 2003 Wiley-Liss, Inc.

Mineralogy and forms of potassium in red yellow latosol of a guava (Psidium guajava) tree orchard

A trial was conducted during 1994-95 to study the effect of potassium fertilization on a guava (Psidium guajava L.) culture for 3 years. The control plots (without K) showed fruit production and potassium exportation that did not agree with the levels obtained by chemical analysis of the soil. Physical, chemical, mineralogic and morphologic analyses were performed on the red yellow latosol to identify minerals able to supply potassium, with emphasis on the fact that guava trees have a considerably widespread root system. The results obtained confirmed the presence of minerals in this soil that can supply potassium to the trees through weathering. Feldspars were identified in the silt fraction and micas in the clay fraction by X-ray diffractometry. The determination of total potassium revealed that the silt fraction of the soil had the largest absolute amounts of potassium, followed by clay. However, in view of its greater content, clay was the fraction that contributed most to the total amounts of potassium detected.

POTASSIUM ABSORPTION AND PARTITIONING IN COTTON AS AFFECTED BY PERIODS OF POTASSIUM-DEFICIENCY

Cotton (Gossypium hirsutum var. Latifolium) was grown in nutrient media, at two K levels: 58.5 mg/K and 11.7 mg/K. Potassium deficiency (11.7 mg K/g of K) was imposed upon cotton plants at different stages of plant development. A sequence of increasing sensitivity to K deficiency among cotton plant parts was observed: leaves < bolls < roots < stems. When K deficiency symptoms are clearly visible in the leaves, all the other plant parts are already affected. Bolls are a very important component in K partitioning within the cotton plant, but K is required most by the bur itself and is not translocated to seeds or fibers. Cotton could overcome a 30 day deficiency late in the season without significant losses in lint and seed cotton yields.

Dielectric loss and phase transition of sodium potassium niobate ceramic investigated by impedance spectroscopy

The dielectric permittivity of Na0.80K0.20NbO3 ceramic was investigated by impedance spectroscopy. The dielectric characterization was performed from room temperature to 800 degreesC, in the frequency range 5 Hz-13 MHz. The bulk permittivity was derived by the variation of the imaginary part of the impedance as a function of reciprocal angular frequency. The permittivity values as a function of temperature showed two maxima. The first maximum is very similar at 200degreesC and the second one positioned at around 400degreesC, which was associated to Curie's temperature. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency dispersion was investigated in terms of dielectric loss. The Na0.80K0.20NbO3 showed a dissipation factor between 5 and 40 over a frequency range from 1 to 10(2) kHz. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Optical properties of potassium niobate thin films prepared by the polymeric precursor method

Thin films of potassium niobate were deposited on MgO (100) substrates by the polymeric precursor method and annealing in static air at 600 degreesC for 20 h. The obtained films were characterized by X-ray diffraction, atomic force microscopy (AFM) and the prism coupling method. The phi-scan diffraction evidenced the growth of the films with fourfold symmetry. AFM study shows that the films are homogeneous, dense and present a smooth surface. The refractive index and optical losses were strongly influenced by the degree of crystallinity. (C) 2004 Elsevier B.V. All rights reserved.

Degradation of the herbicide tebuthiuron using solar photo-Fenton process and ferric citrate complex at circumneutral pH

The influence of pH on the degradation of the herbicide tebuthiuron (TBH) was investigated using in situ generated Fe(III)-citrate complexes (Fe:cit) submitted to the photo-Fenton process under solar irradiation. Using Fe:cit in a wide pH range (2.5-7.5), 100-78% TBH oxidation was achieved respectively from a UV dose of 2.0 J cm(-2) (15 min). Moreover, the oxidation of TBH obtained in the presence of Fe:cit at pH 6.0 was higher than that obtained using Fe(NO3)3 at pH 2.5. A similar behavior is observed for the removal of total organic carbon (TOC) in TBH solutions. In the presence of Fe:cit, 20% and 85% of TOC was removed at pH 7.5 and 2.5, respectively, after 7.5 J cm-2 irradiation, while no mineralization was observed employing Fe(NO3)(3) for the same UV dose. Using Fe(NO3)(3), mineralization was observed only after 11 J cm-2 (8%). A higher mineralization rate was obtained with Fe(NO3)(3) only when a concentration three times higher was employed at pH 2.5. Besides the high efficiency of TBH degradation observed using the ferric citrate complex in the solar photo-Fenton process, it also offers the advantage of application at a pH of up to 7.5. (c) 2007 Elsevier B.V. All rights reserved.