Magnetic properties of acicular ultrafine iron particles

Magnetic properties of acicular (similar to60 and similar to200 nm) iron particles, obtained by reduction of alumina-coated goethite particles, are reported. X-ray diffraction and Mossbauer spectroscopy showed that the particles consist of a alpha-Fe core and a thin surface layer of maghemite. Magnetization data indicated an improvement of similar to28% in the saturation magnetization, coercive field, and squareness for particles with similar to60 nm. This magnetic property enhancement of the present particles, whose size is 40% smaller than those commercially available, could result in a similar decrease of the bit-size for higher density of magnetic media.

Correlation of properties of Brazilian Haplustalfs with magnetic susceptibility measurements

Magnetic susceptibility (chi, mass specific) is useful for easy indirect estimation of other soil properties at a low cost. The aim of this study was to assess the use of chi as measured with an analytical balance for predicting properties with a substantial influence on the management of Typic Haplustalfs in southern Brazil. To achieve this 48 topsoil samples were taken at the intersection points in a rectangular grid of 20 m x 20 m cells, with 38 of these used for calibration and 10 for validation in regression analyses. The obtained chi values were slightly higher than, and highly correlated (r = 0.970; P < 0.001) with those measured with a susceptibility meter. Highly significant (P < 0.001) correlations were also found between chi and other soil properties relevant to soil classification and management such as clay content (r = 0.68), cation exchange capacity (r = 0.62), P sorption capacity (r = 0.76) and haematite content (r = 0.82). Results from a principal component analysis of eight properties important for soil classification explained 11% of the variance in the data set. The good predictive ability of chi was consistent with current knowledge on the formation pathways for pedogenic ferrimagnets. In summary, chi, which can be readily measured with an analytical balance, has the potential for quantifying soil attributes and may therefore be used in pedotransfer functions.

Occupational exposure of physical therapists to electric and magnetic fields and the efficacy of Faraday cages

Objective. Measure physical therapists' exposure to the electric and magnetic fields produced by 17 shortwave diathermy devices in physical therapy clinics in the city of Presidente Prudente, São Paulo State, Brazil. Compare the observed values with the exposure levels recommended by the International Commission on Non-ionizing Radiation Protection (ICNIRP). Observe the efficacy of Faraday cages as a means of protecting physical therapists from exposure to oscillating electric and magnetic fields.Methods. Electric and magnetic field measurements were taken at four points during actual physical therapy sessions: in proximity to the operator's pelvis and head, the devices' electrical cables, and the electrodes. The measuring equipment was a Wandel & Goltermann EMR-200.Results. The values obtained in proximity to the electrodes and cables were 10 to 30 times higher than ICNIRP's recommended occupational reference levels. In the shortwave diathermy treatment rooms with Faraday cages, the fields were even higher than in treatment rooms not so equipped-principally the magnetic field, where the values were more than 100 times higher than the ICNIRP exposure limit.Conclusions. The electric and magnetic field intensities obtained in this study are generally above the exposure levels recommend in ICNIRP standards. It was also observed that the Faraday cage offers physical therapists no protection, and instead, increases their level of exposure.

Relaxor behavior in multiferroic BiMn2O5 ceramics

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

Synthesis and characterization of Li2ZnTi3O8 spinel using the modified polymeric precursor method

In this work we report the synthesis procedure, crystallographic, structural and magnetic properties of the Li2ZnTi3O8 spinel obtained using a modified polymeric precursor method. This synthesis method generates very reactive and property-controlled nanoparticles. The samples were characterized using X-ray powder diffraction (XRD) associated to the Rietveld refinement method, thermogravimetric analysis (TG), specific surface area, scanning electron microscopy (SEM) and magnetic susceptibility measurements.The phase formation temperature of the lithium zinc titanate spinel was observed to decrease due to the homogeneity and highly controlled nanometric particle size. (C) 2003 Elsevier B.V. All rights reserved.

Gelation of siloxane-poly(oxypropylene) composites

The viscoelastic properties of siloxane-poly(oxypropylene) (PPO) nanocomposites prepared by the sol-gel process has been analyzed during gelation by dynamic rheological measurements. The changes of storage and loss moduli, complex viscosity and phase angle has been measured as a function of time showing the newtonian viscosity of the sol in the initial step of gelation, and its progressive transformation to a viscoelastic gel. The rheologic properties have been correlated to mass fractal, nearly linear growth models and percolation theory. This study, completed by quasi-elastic light scattering and Si-29 solid state nuclear magnetic resonance measurements, shows that the mechanisms of gelation of siloxane-PPO hybrids depend on the molecular weight of the polymer and on the pH of the hybrid sol. For hybrids prepared in acid medium, a polymerization involving silicon reactive species located at the extremity of the polymer chains and presenting a functionality f = 2 occurs, forming a fractal structure during the first stage of sol-gel transition. For samples prepared under neutral pH, the fractal growth is only observed for hybrids containing short polymer chains (M-w similar to 130 gmol(-1)). The fractal dimensionality determined from the change in the rheological properties, indicates that the fractal growth mechanism changes from reaction-limited to diffusion-limited aggregation when the molecular weight of the PPO increases from 130 to 4000 gmol(-1) and as catalyst conditions change from acidic to neutral. Near the gel point, these hybrid gels have the typical scaling behavior expected from percolation theory. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Influência da acurácia de instrumentos de medidas na comparação de métodos de estimativa da evapotranspiração de referência

The aim of this investigation was to evaluate four reference methods to estimate evapotranspiration (Makkink, Hargreaves, Class A pan and Radiation), compared tb Penman-Monteith method, that is considered standard by the Food and Agricultural Organization of the United Nations (FAO). Errors due to variable measurements in the reference evapotranspiration estimate were taken into consideration. The research was developed in an experimental area of the Department of Rural Engieering of the School of Agricultural and Veterinarian Sciences, Campus of Jaboticabal, São Paulo State University. An automated weather station was used and it was equipped with sensors to measure global and net radiation, temperature, relative humidity, and wind speed. The aftermath showed a better adjustment to Hargreaves. Makkink, Class A pan and Radiation methods are different from Penman-Monteith, therefore, they cannot be compared. To evaluate methods to estimate evapotranspiration and avoid possible evaluation errors, ETo estimate errors must be considered.

Comportamento dinâmico não linear e controle de sistemas eletromecânicos em macro e micro escalas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Suscetibilidade magnética para a estimativa de atributos do solo e mapeamento de áreas sob cultivo de cana-de-açúcar

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Obtenção de espécies moleculares e supramoleculares a partir de reações de auto-montagem entre íons lantanídeos e moléculas orgânicas multilópicas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Níquel (II) e moléculas orgânicas multidentadas como building blocks na construção de sólidos de coordenação porosos

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Síntese e caracterização de ferritas de manganês e zinco visando aplicação como agente de contraste em diagnóstico médico (biosusceptometria de corrente alternada)

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

Síntese e funcionalização de superfícies de óxido de ferro superparamagnéticos

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Structure and thermal behavior of PMMA-polysilsesquioxane organic-inorganic hybrids

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Magnetoelastic couplings in the distorted diamond-chain compound azurite

We present results of ultrasonic measurements on a single crystal of the distorted diamond-chain compound azurite Cu-3(CO3)(2)(OH)(2). Pronounced elastic anomalies are observed in the temperature dependence of the longitudinal elastic mode c(22) which can be assigned to the relevant magnetic interactions in the system and their couplings to the lattice degrees of freedom. From a semiquantitative analysis of the magnetic contribution to c(22) the magnetoelastic coupling G = partial derivative J(2)/partial derivative epsilon(b) can be estimated, where J(2) is the intradimer coupling constant and epsilon(b) the strain along the intrachain b axis. We find an exceptionally large coupling constant of | G| similar to 3650 K highlighting an extraordinarily strong sensitivity of J(2) against changes of the b-axis lattice parameter. These results are complemented by measurements of the hydrostatic pressure dependence of J2 by means of thermal expansion and magnetic susceptibility measurements performed both at ambient and finite hydrostatic pressure. We propose that a structural peculiarity of this compound, in which Cu2O6 dimer units are incorporated in an unusually stretched manner, is responsible for the anomalously large magnetoelastic coupling.