Structural Phase Transition Studies on PMN-0.35PT using Infrared Spectroscopy

The purpose of the present work is to report studies on structural phase transition for PMN-xPT ferroelectric, with melt PbTiO3 composition around the MPB (x = 0.35 mol %), using infrared spectroscopy technique. The study was centered on monitoring the behavior of the 1-(NbO), 1-(TiO) and 1-(MgO) stretching modes as a function of temperature. The increasing as a function of temperature for 1-(TiO) and 1-(MgO) modes, observed between 230 and 300 K, can be related to the monoclinic (MC) + tetragonal (T) phase coexistence in the PMN-PT.

Investigation on dielectric response of PMN ceramics around paraelectric-ferroelectric diffuse phase transition

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

Estimativa da vulnerabilidade natural de aqüíferos: uma contribuição a partir da resistividade e condutância longitudinal

Este trabalho descreve os resultados obtidos com o método da eletrorresistividade usando a técnica da sondagem elétrica vertical (arranjo Schlumberger) aplicada em estudos ambientais envolvendo as águas subterrâneas. A vulnerabilidade natural de aqüíferos, importante ferramenta em estudos ambientais, pode ser estimada a partir de métodos geoelétricos, cujos parâmetros resistividade e condutância longitudinal, aliados ao tipo de ocorrência dos aqüíferos (livre a confinado) e profundidade do nível d'água, permitiram obter um índice de vulnerabilidade natural correspondente ao normalmente utilizado. Os resultados, aplicados em uma fase preliminar de estudos, são bons, permitindo um melhor direcionamento e programação das fases posteriores.

Nitrification processes in groundwaters evidenced by modification on the U contents and U-234/U-238 activity ratios

Groundwaters from the Botucatu-Piramboia aquifer system located at the Parana sedimentary basin in Brazil and sampled at Ribeirao Preto city, São Paulo State, were chemically and isotopically analysed, with the aim of evaluating how uranium isotopes U-234 and U-238 can be utilized to monitor the progress of nitrate, the main indicator of agrichemical pollution into an aquifer. Based on the isotope dilution analysis, the U-234/U-238 activity ratio and U content data in the groundwaters were utilized to deduce their proportions in a mixture, suggesting that the water not affected significantly by nitrification still dominates the exploitation system involving the studied wells.

U-ages in soils and groundwater evidencing wet periods 400-600 kyr ago in southeast Brazil

U-238 and its radiogenic daughter U-234 have been utilized for dating soil formation and groundwater residence time during the last 1.5 million years, in this case based on the U-clissolution/precipitation occurring during modifications of the oxidation-reduction conditions. In this paper, we report a 400-600 kyr proxy of wet periods from sediments occurring in a soil profile developed over rocks outcropping at the Parana sedimentary basin in Brazil, and from groundwater exploited of Guarani aquifer at the same basin. The approaches indicated successful use of the U-modeled ages for suggesting wet periods exceeding the past 116-210 kyr from previous studies. (C) 2007 Elsevier Ltd. All rights reserved.

Radon and progeny (Pb-214 and Bi-214) in urban water-supply systems of São Paulo State, Brazil

Many water-supply systems in South America utilize the waters of the Guarani aquifer at least as part of their networks. However, there is little present knowledge in Brazil of the factors affecting Rn presence in the water supplied for end-users, despite the economic importance of Guarani aquifer. Rn-222 analyzes of 162 water samples were performed at 8 municipalities in São Paulo State, Brazil, with the aim of investigating the major factors affecting its presence in solution. The Rn-222 activity concentration ranged from 0.04 up to 204.9 Bq/L, with three samples exceeding the World Health Organization maximum limit of 100Bq/L. Aeration was confirmed as the most important factor for Rn release, as expected due to its gaseous nature. Accumulation in pipes and stratification in the water column were other significant factors explaining the data obtained in some circumstances. The Rn daughters Ph-214 and Bi-214 were also determined in a set of selected samples and their presence was directly related to the occurrence of Rn dissolved in water. (c) 2008 Elsevier Ltd. All rights reserved.

Aplicação de ensaios de resistividade na caracterização do Sistema Aquífero Barreiras / Marituba em Maceió - AL

A caracterização do Sistema Aquífero Barreiras / Marituba, maior fonte de abastecimento de água da cidade de Maceió, capital de Alagoas, Brasil, é importante para fornecer subsídios para uma utilização racional e sustentável desse recurso. O arcabouço tectônico e estratigráfico da área construído por meio de perfis de poços, análise de elementos estruturais e mapeamento geológico propõe um modelo com uma série de grabens e horsts. Com o objetivo de confirmar a presença de estruturas delimitando blocos estruturais e refinar o modelo foram realizados ensaios de sondagem elétrica vertical e caminhamento elétrico dipolo-dipolo. Os resultados dos ensaios geofísicos confirmaram a existência de zonas mais condutoras, que caracterizam as zonas de falhas normais que delimitam os blocos estruturais. A integração dos dados geológicos e estruturais aos resultados geofísicos confirmaram a existência de um modelo estrutural com blocos escalonados, que influenciam fortemente o comportamento do sistema águas subterrâneas.

Avaliação de parâmetros indicadores de poluição por efluente líquido de um aterro sanitário

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Hyperfine interaction measurements on ceramics: PZT revisited

The solid solution of PbZr1-xTixO3, known as lead-zirconate titanate (PZT), was probably one of the most studied ferroelectric materials, especially due to its excellent dielectric, ferroelectric and piezoelectric properties. The highest piezoelectric coefficients of the PZT are found near the morphotropic phase boundary (MPB) (0.46 <= x <= 0.49), between the tetragonal and rhombohedral regions of the composition-temperature phase diagram. Recently, a new monoclinic phase near the MPB was observed, which can be considered as a bridge between PZT's tetragonal and rhombohedral phases. This work is concerned with the study of the structural properties of the ferroelectric PZT (Zr/Ti = 52/48, 53/47) by hypertine interaction (HI) measurements obtained from experiments performed by using the nuclear spectroscopy time differential perturbed angular correlation (TDPAC) in a wide temperature range. (c) 2006 Elsevier B.V. All rights reserved.

Uranium speciation in groundwaters from Parana basin, Brazil

This paper describes the results of a regional study involving the sampling of 60 pumped tubular wells drilled at the Parana sedimentary basin, Brazil, which was carried out with the purpose of evaluating the U speciation in the Botucatu-Piramboia aquifer. Uranium proved to be intensively dissolved even under the enhanced reducing conditions occurring at the most confined zones of the aquifer, and Eh-pH diagrams were utilized to evaluate the influence of temperature and pressure on the migration of the U-species within the aquifer.

Evaluating the residual stress in PbTiO3 thin films prepared by a polymeric chemical method

We report a study of residual stress in PbTiO3 (PT) thin films prepared on Si substrates by a polymeric chemical method. The E(1TO) frequency was used to evaluate the residual stress through an empirical equation available for bulk PT. We find that the residual stress in PT films increases as the film thickness decreases and conclude that it originates essentially from the contributions of extrinsic and intrinsic factors. Polarized Raman experiments showed that the PT films prepared by a polymeric chemical method are somewhat a-domain (polar axis c parallel to the substrate) oriented.

Well productivity controlling factors in crystalline terrains of southeastern Brazil

Over the last decades, increasing water demands have fostered research to obtain high well yields in crystalline terrains where, besides the intrinsic properties of rocks, the groundwater flow depends on several factors. The depth of the wells, the lithotypes, the presence and thickness of sedimentary coverings and weathered layers, the landforms, the geological structures, and the effects of tectonic stresses are among the most investigated factors considered as determinant of well productivity. The influence of these factors on productivity of wells that exploit the Crystalline Aquifer System in the Jundiai-River Catchment, southeastern Brazil, is investigated in this work. The largest region of the studied area is located on the Precambrian Basement, partially covered by sedimentary deposits. The results show that the sedimentary deposits and the weathered layer are important for high well yield, but it also depends on the existence of a net of open fractures, in order to maintain high productivity. The sites that have more possibility of occurrence of such structures are the regional shear and fault zones and other minor structures with NW-SE and E-W directions, which characterize areas subjected to transtensional stress related to the neotectonics.

Dielectric and fatigue properties of Pb(Zr0.53Ti0.47)O-3 thin films prepared from oxide precursors method

Fatigue is an important problem to be considered if a ferroelectric film is used for non-volatile memory devices. In this phenomena, the remanent polarization and coercive field properties degrades in cycles which increase in hysteresis loops. The reasons have been attributed to different mechanisms such as a large voltage applied on ferroelectric film in every reading process in Ferroelectric Random Access Memory (FeRAM) or memories for digital storage in computer, grain size effects and others. The aim of this work is to investigate the influence of the crystallization kinetics on dielectric and ferroelectric properties of the Pb(Zr0.53Ti0.47)O-3 thin films prepared by an alternative chemical method. Films were crystallized in air on Pt/Ti/SiO2/Si substrates at 700 degrees C for 1 hour, in conventional thermal annealing (CTA), and at 700 degrees C for 1 min and 700 degrees C 5 min, using a rapid thermal annealing (RTA) process. Final films were crack free and presented an average of 750 nm in thickness. Dielectric properties were studied in the frequency range of 100 Hz - 1 MHz. All films showed a dielectric dispersion at low frequency. Ferroelectric properties were measured from hysteresis loops at 10 kHz. The obtained remanent polarization (P-r) and coercive field (E-c) were 3.7 mu C/cm(2) and 71.9 kV/cm respectively for film crystallized by CTA while in films crystallized by RTA these parameters were essentially the same. In the fatigue process, the P, value decreased to 14% from the initial value after 1.3 x 10(9) switching cycles, for film by CTA, while for film crystallized by RTA for 5 min, P, decreased to 47% from initial value after 1.7 x 10(9) switching cycles.

Seletividade e eficácia de herbicidas inibidores da enzima accase na cultura da mamona

This experiment aimed to evaluate the selectivity and efficacy of ACCase-inhibiting herbicides in castor bean crop, at Paraguacu Paulista, São Paulo, during the 2002/03 agricultural season. The experimental design used was randomized complete blocks, with eleven treatments and four replicates, constituted by the following herbicides and adjuvants: fluazifop-p-butyl 313 g ha(-1)) + Agral (TM) 0.2% v/v); sethoxydim 322 g ha(-1)) + Assist (TM) 0.5% v/v); haloxyfop-methyl 120 g ha(-1)) + Assist (TM) 0.5% v/v); clethodim+ fenoxaprop-p-ethyl 75 g ha(-1)) + Assist (TM) 0.5% v/v); quizalofop-pethyl 125 g ha(-1)) + Assist (TM) 0.5% v/v); clethodim 156 g ha(-1)) + Assist (TM) 0.5% v/v); propaquizafop 175 g ha(-1)) + Assist (TM) 0.5% v/v); tepraloxydim 400 g ha(-1)) + Dash (TM) 0.5% v/v); butroxydim 100 g ha(-1)) + Dash (TM) 0.5% v/v); isoxaflutole 60 g ha(-1)) and weed-free check. At the moment of application, castor bean plants presented 4 to 6 leaves and Cenchrus echinatus, 1 to 5 tillers. AL Guarany 2002 cultivar presented high selectivity to ACCase-inhibiting herbicides, without visible symptoms of phytotoxicity in 14 DAA days after application), except for tepraloxydim, whose symptoms persisted until 21 DAA, and isoxaflutole HPPD inhibiting), which showed injuries in older leaves and significant yield reduction. C. echinatus infestation was efficiently controlled by ACCase-inhibiting herbicides between 14 and 21 DAA (>= 95.0%).

Analytic element modelling for strip aquifers

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