Effect of reaction time on the particle size of ZnO and ZnO : Ce obtained by a sol-gel method

In this work particles of ZnO of size range 33-56 Angstrom were prepared by a sol-gel method. The effect of reaction time on the particle size of ZnO or ZnO:Ce was investigated by transmission electron microscopy measurements, UV-vis absorption and luminescence spectroscopy. A linear increase of the mean particle size is observed as a function of reaction time. The cerium-doped particles are bigger than the pure ZnO ones obtained at the same reaction time. A shift to lower energy at the maximum of the bands is observed in all absorption, emission and excitation spectra as a function of particle growth. From the absorption spectra the optical energy gap values (Eg) for these particles were determined. In the quantum size regime, Eg was found to decrease with particle growth.

Structural refinement and photoluminescence properties of irregular cube-like (Ca-1_Cu-x(x))TiO3 microcrystals synthesized by the microwave-hydrothermal method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Tm and Tm-Tb-doped germanate glasses for S-band amplifiers

The mechanism involved in the Tm(3+)((3)F(4)) -> Tb(3+)((7)F(0,1,2)) energy transfer as a function of the Tb concentration was investigated in Tm:Tb-doped germanate (GLKZ) glass. The experimental transfer rate was determined from the best fit of the (3)F(4) luminescence decay due to the Tm -> Tb energy transfer using the Burshtein model. The result showed that the 1700 nm emission from (3)F(4) can be completely quenched by 0.8 mol% of Tb(3+). As a consequence, the (7)F(3) state of Tb(3+) interacts with the (3)H(4) upper excited state of TM(3+) slighting decreasing its population. The effective amplification coefficient beta(cm(-1)) that depends on the population density difference Delta n = n((3)H(4))-n((3)F(4)) involved in the optical transition of Tm(3+) (S-band) was calculated by solving the rate equations of the system for continuous pumping with laser at 792 nm, using the Runge-Kutta numerical method including terms of fourth order. The population density inversion An as a function of Tb(3+) concentration was calculated by computational simulation for three pumping intensities, 0.2, 2.2 and 4.4 kWcm(-2). These calculations were performed using the experimental Tm -> Tb transfer rates and the optical constants of the Tm (0.1 mol%) system. It was demonstrated that 0.2 mol% of Tb(3+) propitiates best population density inversion of Tin(3+) maximizing the amplification coefficient of Tm-doped (0.1 mol%) GLKZ glass when operating as laser intensity amplification at 1.47 mu m. (C) 2007 Elsevier B.V. All rights reserved.

Alternatives Panels from Waste Plastics Reinforced With Fibers of Pupunha Palm for Use in Civil Construction and Furniture Industry

In order to cooperate in minimizing the problems of the current and growing volume of waste, this work aims at the production of panels made from industrial waste -thermoplastic (Polypropylene - PP; Polyethylene - PE and Acrylonitrile Butadiene Styrene - ABS) reinforced with agro-industrial waste - pupunha palm waste (shells and sheaths). The properties of the panels were evaluated: density, thickness swelling, water absorption and moisture content. It was used the ASTM D1037; EN 317; and ANSI A208.1 standards regarding particle boards. The best results in physical tests were treatments 1 (100% waste plastic), 6 (60% plastic waste and 40% waste of pupunha) and 7 (70% waste plastic and 30% waste of pupunha). The best results in the mechanical tests were treatments 3 (30% de residuos plasticos e 70% de residuos da pupunha), 4 (40% de residuos plasticos c 60% de residuos da pupunha) and 5 (50% de residuos plasticos e 50% de residuos da pupunha). For mechanical tests it was concluded that the results of modulus of rupture and of modulus of elasticity the best treatments were those with more fibers. In the tensile tests perpendicular to the surface, it is clear that using more waste plastics leads to the best results. It was concluded that the waste can be used as raw material for the production of alternative materials mainly in civil construction and furniture industries, and it can be employed in urban or rural environment, given the concept of eco-efficient products.

Interaction between nitroheterocyclic compounds with beta-cyclodextrins: Phase solubility and HPLC studies

Chagas disease is a serious health problem for Latin America. Nitrofurazone (NF) and Hidroxymethylnitrofurazone (NFOH) are active against Trypanosoma cruzi. The effect of beta-cyclodextrin (beta-CD) and dimethyl-beta-cyclodextrin (DM-beta-CD) complexation on the UV absorption and retention time of nitrofurazone (NF) and its hydroxymethylated analog (NFOH) were studied in solution. The retention behavior was analyzed on a reversed phase C(18) column and the mobile phase used was acetonitrile-water (20/80 v/v), in which cyclodextrins (beta-CD or DM-beta-CD) were incorporated as a mobile phase additive. The decrease in the retention times of NF (or NFOH) with increasing concentration of HP-beta-CD enables the cleternnination of the complex stability constants by HPLC. A phase-solubility Study was performed. according to the method reported by Higuchi and Connors, to evaluate the changes of NF/NFOH in the complexation state, and the diagrams obtained suggested that it forms complexes with a stoichiometry of 1 : 1. This is an important Study for the characterization of potential formulations to be used as therapeutic options for the treatment of Chagas disease. (c) 2008 Elsevier B.V. All rights reserved.

Structural refinement, optical and microwave dielectric properties of BaZrO3

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

Photoluminescence of bulks and thin films of Eu3+-doped organic/inorganic hybrids

Organic-inorganic hybrids formed by polyether-based chains grafted to both ends to a siliceous backbone through urea cross-linkages (-NHC=O)NH-), named di-ureasil, have been used as host for incorporation of Eu3+ in the form of EuCl3. The bulks and the thin films, both optically transparent, were characterized by excitation, absorption and emission spectroscopy. Photoluminescence results point out that the Eu3+ ions occupy, at least, two distinct local environments. Besides, the processing method (thin films or bulks) has influence on the energy levels of the hybrid host probably due to the lower degree of organization of the thin films structure. (c) 2007 Elsevier B.V. All rights reserved.

Structural refinement, growth process, photoluminescence and photocatalytic properties of (Ba1-xPr2x/3)WO4 crystals synthesized by the coprecipitation method

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

Experimental investigation of soil and groundwater impacts caused by vinasse disposal

The problems caused by the residual effluents of wine distilleries for alcohol production are well known. The effluent effects in soil and groundwater are being researched in an area with sugar cane culture which receives, yearly, vinasse by dispersion. Samples are being collected from the soil, the groundwater and the existing creeks in the area. Four sub-areas are being monitored separately with a vinasse application of 300 m 3/ha year. Experimentation periods in each area have been 0, 5, 10 and 15 years. In the unsaturated zone, samples are being collected at depths of 25, 75 and 150 cm. The chemical analyses include macro and micro nutrients, organic matter and pH. Physical analyses give the soil water retention, hydraulic conductivity and soil particle distribution. These measurements permit the evaluation of nitrogen absorption and fertility changes of the soil. A tendency for the maintenance of soil fertility can be observed but with an elevation of nitrate concentration in groundwater.

Two thermal methods to measure the energy fluence of a brief exposure of diagnostic x rays

This paper describes two simple thermal methods for measuring the energy fluence in J/cm 2 from a diagnostic x-ray exposure. Both detectors absorb essentially 100% of the radiation and give a signal that is directly proportional to the energy fluence of the x-ray beam. One detector measures the thermal effect when a pulse of x rays is totally absorbed in the pyroelectric detector of lead-zirconium-titanate (PZT). The other detector measures the expansion of a gas surrounding a lead disk detector in a photoacoustic chamber. The increased pressure of the gas is transmitted through a 1-mm duct to a sensitive microphone. Both detectors have previously been used to measure the energy fluence rate of continuous x-ray beams in the same energy region using a chopped beam and a lock-in amplifier. Measurement of the energy fluence of a pulse of radiation eliminates the need for the beam chopper and lock-in amplifier and results in a simple, rugged, and inexpensive dosimeter. Either method can be combined with the area of the beam to give an estimate of the imparted energy to the patient from a diagnostic x-ray exposure.

Structural studies in lead germanate glasses: EXAFS and vibrational spectroscopy

The Raman, IR absorption and EXAFS spectra at the Ge K-edge and Pb LIII-edge of eight lead germanate glasses, with general formula xPbO(1-x)GeO2 with x = 0.20, 0.25, 0.33, 0.40, 0.50, 0.53, 0.56 and 0.60, have been measured. The occurrence of [GeO6] units besides [GeO4] could not be deduced unambiguously from the data. The vibrational and EXAFS data agree with a progressive depolymerization of the network. Starting from all Ge atoms linked to four bridging oxygens in GeO2 (x = 0), the number of tetrahedral units with one or two non-bridging oxygens increases with x. At low content, Pb2+ ions act as modifiers in the germanate structure, but to a lesser extent than an equivalent number of alkaline ions. © 1993.

Sol-Gel Erbium-Doped Silica-Hafnia Planar and Channel Waveguides

Erbium activated SiO2 -HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol-gel method. The films were deposited on v-SiO2 and silica-on-silicon substrates using dip-coating technique. The waveguides show high densification degree, effective intermingling of the two film components, and uniform surface morphology. The waveguide deposited on silica-on-silicon substrates shows one single propagation mode at 1.5μm, with a confinement coefficient of 0.81 and an attenuation coefficient of 0.8 dB/cm at 632.8nm. Emission in the C-telecommunication band was observed at room temperature for all the samples upon continuouswave excitation at 980 nm or 514.5 nm. The shape of the emission band corresponding to the 4I13/2 → 4I15/2 transition is found to be almost independent both on erbium content and excitation wavelength, with a FWHM between 44 and 48 nm. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1 - 6.6 ms, depending on the erbium concentration. Infrared to visible upconversion luminescence upon continuous-wave excitation at 980 nm was observed for all the samples. Channel waveguide in rib configuration was obtained by etching the active film in order to have a well confined mode at 1.5 μm.

Spectroscopic properties of Tm3+ doped fluoroindate glass

Optical absorption and fluorescence were investigated in Tm3+ doped fluoroindate glass. The spectroscopic parameters for transitions in the 4f11 configuration were determined. The fluorescence study revealed the origin of the frequency upconversion process as well as allowed to quantify the interaction between Tm3+ ions.

Lead-cadmium fluorogermanate glasses and transparent glassceramics. Spectroscopy and structure

In Lead-cadmium fluorogermanate glasses (PbF2-CdF 2-PbGeO3) the addition of metal fluorides to the base PbGeO3 glass leads to a decrease of the glass transition temperature (Tg) and to an enhancement of the ionic conductivity properties. Based on different spectroscopic techniques (19F NMR, Ge K-edge X-ryas absorption and Raman scattering) an heterogeneous glass structure is proposed at the molecular scale, which can be described by fluoride rich regions permeating the metagermanate chains. The temperature dependence of the 19F NMR lineshapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluoride mobility in these systems. Eu 3+ emission and vibronic spectra are used to follow the crystallization process leading to transparent glass ceramics.

Postharvest characteristics and treatments to overcome latex exuded from cut flowers of lotus

Lotus (Nelumbo nucifera Gaertn.) is a perennial herbaceous aquatic ornamental plant with potential to be used as a new cut flower for the Brazilian ornamental market. It shows exotic and attractive flowers and has a strong market appeal, once it is known as a symbol of purity, holiness and immortality. However, flowers have a short-vase life. Lotus flower stem exudes a large quantity of sticky milky sap from the cut surface, which is produced in laticifers, spatially associated with both xylem and phloem. It has been reported that latex coagulates on the cut surface preventing or reducing water absorption and reducing flowers' vaselife, requiring treatments to stop the flow of latex. The objective of this study was to report observations of lotus postharvest characteristics and evaluate treatments to overcome latex flow. The experiment was conducted as a complete randomized design with three replications of four stems in each vase and eight treatments; a control (distilled water), pretreatment of cut stem-ends with hot water (40° C/1 minute), boiling water (3 seconds), isopropyl alcohol 90% (10 minutes) or citric acid (pH = 2.8/1h) and, maintenance of stems in a holding solution of Tween® 20 (0.01%), citric acid (200 mg L-1) or Tween® 20 (0.01%) plus citric acid (200 mg L-1). Treatments had no significant effect on flowers vaselife which was only about three days, although isopropyl alcohol, hot and boiling water completely stopped latex flow. Cut stem-ends pretreated with citric acid (pH = 2.8/1 h) showed a significantly higher relative water content of petals compared to others treatments. The senescence symptom of lotus cut flowers was mainly characterized by abscission of turgid petals and dehiscence of stamens without any visual change of petal color and brightness.