Magnetocaloric and transport study of poly- and nanocrystalline composite manganites La 0.7Ca 0.3MnO 3/La 0.8Sr 0.2MnO 3

Magnetocaloric and transport properties are reported for novel poly- and nanocrystalline double composite manganites, La 0.8Sr 0.2MnO 3/La 0.7Ca 0.3MnO 3, prepared by the sol-gel method. Magnetic field dependence of magnetic entropy change is found to be stronger for the nano- than the polycrystalline composite. The remarkable broadening of the temperature interval, where the magnetocaloric effect occurs in poly- and nanocrystalline composites, causes the relative cooling power (RCP(S)) of the nanocrystalline composite to be reduced by only 10 compared to the Sr based polycrystalline phase. The RCP(S) of the polycrystalline composite becomes remarkably enhanced. The low temperature magnetoresistance is enhanced by 5 for the nanostructured composite. © 2012 American Institute of Physics.

Intergranular and intragranular properties of superconducting multifilamentary Bi 2223 Ag tapes : comparison of electrical transport and magnetic measurement methods

Several experimental techniques have been used in order to characterize the properties of multifilamentary Bi-2223 / Ag tapes. Pristine samples were investigated by electrical resistivity, current-voltage characteristics and DC magnetic moment measurements. Much emphasis is placed on comparing transport (direct) and magnetic (indirect) methods for determining the critical current density as well as the irreversibility line and resolving usual lacks of consistency due to the difference in measurement techniques and data analysis. The effect of an applied magnetic field, with various strengths and directions, is also studied and discussed. Next, the same combination of experiments was performed on bent tapes in order to bring out relevant information regarding the intergranular coupling. A modified Brandt model taking into account different types of defects within the superconducting filaments is proposed to reconciliate magnetic and transport data.

A simple prediction model for asphalt surface texture incorporating mix gradation and air voids

This paper presents the results of a preliminary study that seeks to show how asphalt grading and air voids are related to the texture depth of asphalt. The fiftieth percentile particle size (D50) is shown to be a good predictor of texture depth measurements from a collected database of field and laboratory studies. The D50 is used to normalise collected texture data and this 'relative texture' is shown to correlate with air voids. Regression analyses confirm that air voids should be included along with a measure of gradation in the interpretation of asphalt surface texture.The derived formulae are used to develop correlation charts.

Experimental and numerical study of a YBCO pancake coil with a magnetic substrate

A finite element model for a YBCO pancake coil with a magnetic substrate is developed in this paper. An axial symmetrical H formulation and the E-J power law are used to construct the model, with the magnetic substrate considered by introducing an extra time-dependent term in the formula. A pancake coil is made and tested. The measurement of critical current and transport loss is compared to the model result, showing good consistency. The influence of magnetic substrate in the condition of AC and DC current is studied. The AC loss decreases without a magnetic substrate. It is observed that when the applied DC current approaches the critical current the coil turn loss profile changes completely in the presence of magnetic substrate due to the change of magnetic field distribution. © 2012 IOP Publishing Ltd.

Model development & application for inland navigational canals

Several agencies in the United Kingdom have interest in the water quality of old navigational canals that have fallen into disuse after the decline of commercial canal transportation. The interested agencies desired a model to predict the water quantity and quality of inland navigational canals in order to evaluate management options to address the issues in the natural streams to which they discharge. Inland navigational canals have unique drivers of their hydrology and water quality compared to either natural streams, irrigation canals, or larger navigational canals connected to seas or oceans. Water in an inland canal is typically sourced from a reservoir and artificially pumped to a summit reach; its movement downhill is controlled by the activity of boats and overflow weirs. Stagnant impoundments between locks, which might normally be expected to result in a decrease in the concentration of sediment-associated pollutants, actually have surprisingly high levels of sediment due to boat traffic. Algal growth in the stagnant reach can be high. This paper describes a canal model developed to simulate hydrology and water quality in inland navigational canals. This model was successfully applied to the Kennet and Avon Canal to predict hydrology, sediment generation and transport, and algal growth and transport. The model is responsive to external influences such as sunlight, temperature, nutrient concentrations, boat traffic, and runoff from the contributing catchment area.

Spin glass behaviour and spin-dependent scattering in la 0.7Ca 0.3Mn 0.9Cr 0.1O 3 perovskites

The magnetic, electrical and thermal transport properties of the perovskite La 0.7Ca 0.3Mn 0.9Cr 0.1O 3 have been investigated by measuring dc magnetization, ac susceptibility, the magnetoresistance and thermal conductivity in the temperature range of 5-300K. The spin glass behaviour with a spin freezing temperature of 70 K has been well confirmed for this compound, which demonstrates the coexistence and competition between ferromagnetic and antiferromagnetic clusters by the introduction of Cr. Colossal magnetoresistance has been observed over the temperature range investigated. The introduction of Cr causes the "double-bump" feature in electrical resistivity ρ(T). Anomalies on the susceptibility and the thermal conductivity associated with the double-bumps in ρ(T) are observed simultaneously. The imaginary part of ac susceptibility shows a sharp peak at the temperature of insulating-metallic transition where the first resistivity bump was observed, but it is a deep-set valley near the temperature where the second bump in ρ(T) emerges. The thermal conductivity shows an increase below the temperature of the insulating-metallic transition, but the phonon scattering is enhanced accompanying the appearance of the second peak of double-bumps in ρ(T). We relate those observed in magnetic and transport properties of La 0.7Ca 0.3Mn 0.9Cr 0.1O 3 to the spin-dependent scattering. The results reveal that the spin-phonon interaction may be of more significance than the electron (charge)-phonon interaction in the mixed perovskite system. © 2005 Chinese Physical Society and IOP Publishing Ltd.