Investigação de Er3+ nos dois sítios cristalográficos de Gd2SiO5 através da fotoluminescência resolvida no tempo

Gadolinium oxyortho-silicate, Gd2SiO5, presents a monoclinic structure with two crystallographic sites in which Gd3+ ions are equally distributed with coordination numbers CN, 7 and 9, respectively. By doping this host with Er3+ it is possible to distinguish and attribute the two sites by means of lifetime determination of the 4S3/2 state, (in this case, Er3+ substitutes Gd3+ ions). Samples doped with 0.1 and 5.0% molar Er3+ were prepared by solid state reaction and characterized by X-ray Diffractometry, Vibrational and Electronic Absorption Spectroscopies, and Time Resolved Photoluminescence. Based on the experimental results, it is possible to verify that, for the 5,0% doped sample, the lifetime value of the 4S3/2 state of the erbium ion inserted in site 1, (CN = 9), is 2.7 ± 0.1 mus, and for the one inserted in site 2, (CN = 7), it is 1.5 ± 0.1 mus.

Um espectômetro de massas de tempo-de-vôo para o estudo da ionização de amostras gasosas por elétrons rápidos (0,5 - 1,0 keV)

A simple and inexpensive time-of-flight mass spectrometer, dedicated to the study of gas-phase ionization processes induced by high energy electrons (0.5 - 3.0 keV), is described. The spectrometer design is based on the Wiley-McLaren principle, with a total length of about 18 cm. As a demonstration of the performance of the apparatus, mass spectra for Ar, CH4, CO2, and SF6, obtained at 1 keV electron energy, are presented.

Roma al tempo di Caravaggio.1600-1630

Quan l’any 1602 el pintor i tractadista Federico Zuccari publicà L’Ideade’pittori, scultori et architetti, Caravaggio ja havia radicalitzat el seu llenguatge versun fort naturalisme, al qual afegia un tractament de forts contrastos lumínics patent enl’obra, dos anys més tardana, que inaugura la mostra: La verge de Loreto, tambéconeguda com la Verge del peregrins. Davant el procés creatiu de Zuccari basat en laIdea, es a dir el disegno interno de bellesa, Caravaggio pren la realitat com a modeltrencant així amb el manierisme reformat que, a la Roma papal, te la seva plasmació al’Oratori dels Gonfalone on el citat tractadista hi va participar. D’altra banda la novamanera caravaggesca es contraria a la proposada per Annibale Carracci al programa dela Galeria Farnese i, alhora, per la defensada per tota la tractadística italiana del segleXVII, des de Giovanni Battista Agucchi, en el seu Tractat de la pintura(1607-1615),fins a Giovan Pietro Bellori en el seu discurs L’Idea del pittore, dello scultore edell’architetto, scelta dalle bellezze naturali superiore alla natura que seguint els vellsprincipis de la Poètica defensen que l’obra d’art ha de tenir versemblança, ha d’imitar els millors i pot corregir la realitat. No es estrany, doncs, que Agucchi posi comexemple a seguir l’art d’Annibale Carracci i que compari a Caravaggio amb l’escultorgrec Demetri, que va seguir tant al peu de la lletra la semblança que no va tenirconsideració per la bellesa.

Cálculo ab initio de intensidades Raman dinâmicas utilizando a teoria da resposta linear

In this paper a methodology for the computation of Raman scattering cross-sections and depolarization ratios within the Placzek Polarizability Theory is described. The polarizability gradients are derived from the values of the dynamic polarizabilities computed at the excitation frequencies using ab initio Linear Response Theory. A sample application of the computational program, at the HF, MP2 and CCSD levels of theory, is presented for H2O and NH3. The results show that high correlated levels of theory are needed to achieve good agreement with experimental data.

Control of permanent magnet linear synchronous motor in motion control applications

The aim of the thesis is to study the principles of the permanent magnet linear synchronous motor (PMLSM) and to develop a simulator model of direct force controlled PMLSM. The basic motor model is described by the traditional two-axis equations. The end effects, cogging force and friction model are also included into the final motor model. Direct thrust force control of PMLSM is described and modelled. The full system model is proven by comparison with the data provided by the motor manufacturer.

Caracterização de amostras comerciais de vermicomposto de esterco bovino e avaliação da influência do pH e do tempo na adsorção de Co(II), Zn(II) and Cu(II)

Some commercial samples of vermicompost from bovine manure (humus) were characterized by thermogravimetry with respect to humidity, organic matter and ash contents, the percentages of which range from 6.55 to 5.35%, 53.01 to 69.96% and 46.44 to 66,14%, respectively. The capacity of adsorption of Cu2+, Zn2+ and Co2+ ions by these samples has been evaluated as a function of pH and time. The contents of several metal ions in the original vermicompost samples have been determined by flame atomic absorption spectrometry after digestion in a microwave oven. The high nitrogen content suggests that the earthworms used in the maturation procedure lead to an efficient degradation of organic matter. The metal retention was affected by both pH and adsorption time. The results also show that adsorption follows the order Cu2+ > Zn2+ > Co2+.

Irradiação de polímeros com feixe de elétrons: caracterização de íons positivos através da técnica de tempo-de-vôo

With the aim of studying the interaction of fast electrons with solid surfaces we have developed an experimental set-up based on electron stimulated desorption (ESD) coupled to time-of-flight (TOF) mass spectrometry. Poly(methyl methacrylate) and poly(vynil chloride) samples have been irradiated by a pulsed electron beam of 1.2 keV and 0.18 µs FWHM. The results show that H+ is the main ionic species to desorb after electron bombardment. In addition, other ionic fragments were also observed and assigned. These results show the potentiality of this technique in the study of ESD of polymers.

Utilização do TEMPO (N-oxil-2,2,6,6-tetrametilpiperidina) na oxidação de álcoois primários e secundários

The oxidation of alcohols to obtain ketones, aldehydes or carboxylic acids is a fundamental transformation in organic synthesis and many reagents are known for these conversions. However, there is still a demand for mild and selective reagents for the oxidation of alcohols in the presence of other functional groups. As an alternative, the nitroxyl radical TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) has been demonstrated to be a useful reagent for the transformation of alcohols. The oxidation of alcohols using TEMPO is often efficient, fast, selective, made in mild conditions and can tolerate sensitive functional groups. In this article we report different methodologies using TEMPO in the oxidation of alcohols.

Alquilbenzeno sulfonato linear: uma abordagem ambiental e analítica

The environmental impact of detergents and other consumer products is behind the continued interest in the chemistry of the surfactants used. Of these, linear alkylbenzene sulfonates (LASs) are most widely employed in detergent formulations. The precursors to LASs are linear alkylbenzenes (LABs). There is also interest in the chemistry of these hydrocarbons, because they are usually present in commercial LASs (due to incomplete sulfonation), or form as one of their degradation products. Additionally, they may be employed as molecular tracers of domestic waste in the aquatic environment. The following aspects are covered in the present review: The chemistry of surfactants, in particular LAS; environmental impact of the production of LAS; environmental and toxicological effects of LAS; mechanisms of removal of LAS in the environment, and methods for monitoring LAS and LAB, the latter in domestic wastes. Classical and novel analytical methods employed for the determination of LAS and LAB are discussed in detail, and a brief comment on detergents in Brazil is given.

Utilização do índice de retenção linear para caracterização de compostos voláteis em café solúvel utilizando GC-MS e coluna HP-Innowax

Gas chromatography coupled with mass spectrometry (GC-MS) is widely used for the characterization of volatile compounds. However, due to the complexity of the soluble coffee matrix, a complete identification of the components should not be based on mass spectra interpretation only. The linear index of retention (LRI) is frequently used to give support to mass spectra. The aim of this work is to investigate the characterization of the volatile compounds in soluble coffee samples by GC-MS using LRI values found with a HP-INNOWAX column. The method used allows a significant increase of the reliability of identifying compounds.

Tempo de vida útil de propelentes base-simples

The purpose of this work was to determine the safe shelf life of single-base propellants. The kinetic parameters relative to the consumption of the stabilizer diphenylamine (DPA) added to the propellant were determined as a function of the storage and ageing time. High Performance Liquid Chromatography (HPLC) with spectrophotometric detection was used to determine the DPA percentage before and after the artificial ageing at 60, 70 and 80 ºC. The experimental data were very well adjusted to a pseudo-first order kinetic model and the respective kinetic constants are 8.0-10-3 day-1 (60 ºC); 1.9-10-2 day-1 (70 ºC); 1.2-10-1 day-1 (80 ºC). The activation energy was calculated as 130 kJ mol-1 and the half-time for depletion of the DPA at the hypothetical temperature of 40 ºC of storage was estimated as being 6 years.

Readout electronics for low dark count pixel detectors based on geiger mode avalanche photodiodes fabricated in conventional CMOS technologies for future linear colliders

The high sensitivity and excellent timing accuracy of Geiger mode avalanche photodiodes makes them ideal sensors as pixel detectors for particle tracking in high energy physics experiments to be performed in future linear colliders. Nevertheless, it is well known that these sensors suffer from dark counts and afterpulsing noise, which induce false hits (indistinguishable from event detection) as well as an increase of the necessary area of the readout system. In this work, we present a comparison between APDs fabricated in a high voltage 0.35 µm and a high integration 0.13 µm commercially available CMOS technologies that has been performed to determine which of them best fits the particle collider requirements. In addition, a readout circuit that allows low noise operation is introduced. Experimental characterization of the proposed pixel is also presented in this work.

Interesterificação química de óleo de soja e óleo de soja totalmente hidrogenado: influência do tempo de reação

Chemical interesterification is an important alternative to produce zero trans fats. In practice, however, excessive reaction times are used to ensure complete randomization. This work evaluated the influence of the reaction time on the interesterification of soybean oil/fully hydrogenated soybean oil blend, carried out in the following conditions: 100 ºC, 500 rpm stirring speed, 0.4% (w/w) sodium methoxide catalyst. The triacylglycerol composition, solid fat content and melting point analysis showed that the reaction was very fast, reaching the equilibrium within 5 min. This result suggests the interesterification can be performed in substantially lower times, with reduction in process costs.

Influência do tipo de ácido e tempo de envelhecimento na atividade fotocatalítica de filmes finos de TiO2

TiO2 thin films were prepared by the sol-gel method using different acids (HCl and HAc), with a parallel evaluation of the gel ageing effects on the film properties. After the thermal treatments, the resulting materials were characterized through gravimetric analysis, UV-VIS spectrophotometry (from which optical parameters such as band gap was derived), XRD, morphological surface analysis (AFM) and photocatalytic activity. The majority of the obtained thin films parameters were similar independent of the acid type and the ageing time of the gel. Nevertheless, a visible effect of the surface morphology properties on the films and their photocatalytic activity was observed.