M-SrFe12O19 and ferrihydrite-like ultrathin nanoplatelets as building blocks for permanent magnets: HAADF-STEM study and magnetic properties

Mixtures of M-type strontium hexaferrite (M-SrFe12O19) and ferrihydrite-like particles were prepared by a microwave-assisted hydrothermal process at 200 °C with heating rates in the range 40–50 °C min-1. The particles exhibited a platelet shape with a diameter comprised between 20 and 200 nm and a thickness between 2 and 5 nm. HAADF-STEM observations and EDS analysis were carried out for a better understanding of nucleation and growth process. EDS showed that most of the particles contained Sr and HAADF-STEM revealed that very thin particles with a hexaferrite core extending over less than a unit cell and with surface disorder crystallized along with well crystallized hexaferrite and defect free ferrihydrite particles. The symmetric multilayer structures (SRS) of the ultrathin particles suggested that the nucleation step of the hexaferrite particles involved clusters containing Sr atoms. In comparison with the M-SrFe12O19 micrometer sized platelets prepared with heating rate of 25 °C min-1, the mixtures of ultrathin hexaferrite- and ferrihydrite-like particles combined after annealing a higher coercivity reaching 465 kA m-1 thanks to the smaller initial particle size and a high magnetization reaching 65 A m2 kg-1 thanks to a limited amount of hematite

Very-high-resolution mapping of river-immersed topography by remote sensing

Remote sensing has been used to map river bathymetry for several decades. Non-contact methods are necessary in several cases: inaccessible rivers, large-scale depth mapping, very shallow rivers. The remote sensing techniques used for river bathymetry are reviewed. Frequently, these techniques have been developed for marine environment and have then been transposed to riverine environments. These techniques can be divided into two types: active remote sensing, such as ground penetrating radar and bathymetric lidar; or passive remote sensing, such as through-water photogrammetry and radiometric models. This last technique which consists of finding a logarithmic relationship between river depth and image values appears to be the most used. Fewer references exist for the other techniques, but lidar is an emerging technique. For each depth measurement method, we detail the physical principles and then a review of the results obtained in the field. This review shows a lack of data for very shallow rivers, where a very high spatial resolution is needed. Moreover, the cost related to aerial image acquisition is often huge. Hence we propose an application of two techniques, radiometric models and through-water photogrammetry, with very high-resolution passive optical imagery, light platforms, and off-the-shelf cameras. We show that, in the case of the radiometric models, measurement is possible with a spatial filtering of about 1 m and a homogeneous river bottom. In contrast, with through-water photogrammetry, fine ground resolution and bottom textures are necessary

An implicit method for radiative transfer with the diffusion approximation in SPH

An implicit method for radiative transfer in SPH is described. The diffusion approximation is used, and the hydrodynamic calculations are performed by a fully three--dimensional SPH code. Instead of the energy equation of state for an ideal gas, various energy states and the dissociation of hydrogen molecules are considered in the energy calculation for a more realistic temperature and pressure determination. In order to test the implicit code, we have performed non--isothermal collapse simulations of a centrally condensed cloud, and have compared our results with those of finite difference calculations performed by MB93. The results produced by the two completely different numerical methods agree well with each other.Comment: 25 pages, 9 figure

Impact behavior of injected PP/nanoclay parts

This work attempts to contribute to bridge the gap between scientific challenges and industrial stakes regarding PP/nanoclay composites. Pieces of nanocomposites were obtained by direct injection of commercial PP mixed with a commercial MB of PP with 50% of organoclay, with a double-gated hot runner mould, which produced mouldings with a weld line. The moulding microstructure was assessed by POM and XRD, while the distribution and exfoliation grade of clay was evaluated by TEM and XRD. The typical skin-core structure was found, with a skin thickness wider in bulk than in weld line zones. Regarding clay platelets mostly intercalated structures were seen. The impact properties at room temperature were assessed by means of tensile and biaxial tests. Properties were monitored at different sites of the mouldings. At the weld line zone less energy was consumed under tensile conditions and exhibited higher apparent impact toughness under biaxial conditions than the bulk zone. Visual inspection of biaxially impacted samples showed that the orientation of polymer molecules and clay platelets induced by melt flow prevailed, and the weld line was not the determinant of the toughness of the mouldings. An optimum in impact performance was found for moulding with 3% of clay, since at larger clay contents platelets agglomerated and acted as stress raisers

Uni- and biaxial impact behavior of double-gated nanoclay-reinforced polypropylene injection moldings

Polypopylene/nanoclay three-dimensional parts were produced without intermediate steps by direct injection molding to explore the influence of flow features and nanoclay incorporation in their impact performance. The nanocomposite was obtained by direct compounding of commercial PP with nanoclay masterbatch. The as-molded morphology was analyzed by X-ray and TEM analyses in terms of skin-core structure and nanoclay particle dispersion. The nanoclay particles induced the reduction of b-form spherulites, a known toughener. The impact behavior was assessed in tensile and biaxial modes. The PP nanocomposite molding toughness was practically unaffected by the processing melt temperature and flow rate. Conversely the nanoclay presence is influent in the impact performance. Under biaxial stress impact, the regions close to weld lines are tougher than the bulk and the fracture develops with main crack paths along the flow direction and the weld line. Cracking along the weld line results from less macromolecular interpenetration and chain entanglement, and unfavorable nanoparticle orientation. It seems that a failure mechanism which involves nanoclay delamination and multiple matrix crazing explains the toughening of PP in the directions where the nanoparticle orientation with respect to loading is adequate.Contract grant sponsors: CONICET, ANPCyT from Argentina, MINCyT (Argentina) - FCT (Portugal), Universities Nacional de Mar del Plata and Minho

Characterization of cadmium proteinuria in man and rat.

In workers chronically exposed to cadmium and without signs of renal insufficiency, plasma proteins with molecular weight ranging from 11,800 to 450,000 are excreted in greater amount in urine. Increased urinary excretion of low and high molecular weight proteins can occur independently. Because of its greater stability in urine and provided a sensitive immunological technique is used, the determination of retinol-binding protein is a more practical and reliable test of proximal tubular function than beta 2-microglobulin. The evaluation of renal function of workers removed from cadmium exposure indicates that cadmium-induced renal lesions, albeit of slow progression, are not reversible when exposures ceases. In workers chronically exposed to cadmium or removed from cadmium exposure, metallothionein in urine is directly correlated with cadmium in urine but not with cadmium in blood or years of cadmium exposure. The association between cadmium in urine and metallothionein in urine is independent of the status of renal function and the intensity of current exposure to cadmium. Whereas the repeated IP injection of high doses of cadmium to rat gives rise to a mixed or tubular type proteinuria, the prolonged oral administration of cadmium results mainly in the development of a glomerular type proteinuria. The former is usually reversible after cessation of treatment whereas the latter is not. Circulating antiglomerular basement membrane antibodies have been found in man and in rat chronically exposed to cadmium. The pathogenic significance of this finding deserves further investigation

Tuning complex shapes in Pt(0) nanoparticles : from cubic dendrites to five-fold stars

A platinum star performance: Quasi-single-crystalline Pt nanoparticles with peculiar morphologies—cubic dendrites, planar tripods, and fivefold stars—were synthesized in high yield. Shape selectivity was achieved by finely tuning the growth kinetics under a dihydrogen atmosphere