Magnetoresistance studies on barium doped nanocrystalline manganite

An energetically attractive, simple, fast and a novel low temperature (300 °C) solution combustion route for the synthesis of crystalline and homogeneous nanoparticles of lanthanum barium manganese oxide La_0.9Ba_0.1MnO_3+δ (LBMO) is reported. Formation and homogeneity of the solid solutions have been confirmed by powder X-ray diffraction (PXRD) and energy dispersive X-ray analysis (EDS) respectively. The Rietveld analysis shows both as-formed as well as calcined samples are in cubic phase with space group pm3m. The microstructure and agglomerated particle size of the compounds are examined by scanning electron microscope. Infrared spectroscopy revealed that both MnOMn bending mode and MnO stretching mode are influenced by calcination temperature. The magnetoresistance measurement on sintered LBMO pellet exhibits a broad metal–insulator transition (T_M-I) at around 228 K. At 1 T applied magnetic field, LBMO shows magnetoresistance (MR) of 10%, whereas for 4 and 7 T, the negative magnetoresistance values are in the range 51 and 59% respectively at T_M-I. The experimental resistivity data of the present investigation are fitted to a simple empirical equation in order to understand conduction mechanism in this compound.     

Impedance spectroscopy and conductivity studies on B site modified (Na0.5Bi0.5)(Nd x Ti1 − 2x Nb x )O3 ceramics

Nd and Nb doped sodium bismuth titanate ceramics have been synthesized and characterized. Structural properties were obtained based on the XRD pattern analysis, indicating rhombohedral symmetry at room temperature. Impedance and conductivity (DC and AC) studies were done on polycrystalline samples. The results indicate that DC and AC conduction occurs by different mechanism in each case. The possible mechanism in the present case is discussed.     

Radiation and mass transfer effects on two-dimensional flow past an impulsively started infinite vertical plate

The interaction of free convection with thermal radiation of a viscous incompressible unsteady flow past an impulsively started vertical plate with heat and mass transfer is analyzed. The fluid is gray, absorbing-emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative flux in the energy equation. The dimensionless governing equations are solved using an implicit finite-difference method of Crank–Nicolson type. Numerical results for the velocity, the temperature, the concentration, the local and average skin-friction, the Nusselt number and Sherwood number are shown graphically. It is observed that, when the radiation parameter increases, the velocity and temperature decrease in the boundary layer. The local and average skin-friction increases with the increase in radiation parameter. For increasing values of radiation parameter the local as well as average Nusselt number increases.     

Chemical mechanical planarization of copper in alkaline slurry with uric acid as inhibitor

Chemical mechanical planarization of copper disks in hydrogen peroxide and l-arginine based alkaline slurry was investigated. Various commonly proposed inhibitors were screened by static etch rate experiments and only BTA and uric acid were found to be effective in the alkaline pH range, while potassium sorbate was moderately effective. The combination of arginine, hydrogen peroxide and uric acid leads to a more robust polish rate than can be achieved with glycine, hydrogen peroxide and BTA based slurries. The dissolution in presence of uric acid was further studied by potentiodynamic and cyclic polarization experiments which indicate formation of a passivation layer on the copper surface. Silicon dioxide wafers were polished to determine the Cu/silicon dioxide polish rate selectivity in alkaline pH range and a high selectivity (>100) was observed. These results indicate that it is possible to conduct a robust copper CMP with alkaline slurries while maintaining an excellent Cu/silicon dioxide polish rate selectivity.     

Energy sector reform,energy transitions and the poor in Africa

There is little systematic information about the impact of energy sector reform on all sources and methods of energy utilised or potentially utilised by the poor. It is not sufficiently known what fuels the poor use, if a larger range of fuels becomes available and affordable and if barriers to access and consumption are reduced. A detailed assessment is presented for four countries, three in Africa (Botswana, Ghana and Senegal) and for comparison one in Latin America (Honduras), of steps taken to reform the energy sector and their effect on various groups of poor households. The paper analyses the pattern of energy supply to, and use by, poor households and explores the link—or its absence—to energy policy. We investigate what works for the poor and which type of reforms and implementation are effective and lead to a transition to more efficient and clean fuels from which the poor benefit.     

The Last Inch at 70 Miles Per Hour

More recently, personal area network connectivity in vehicles has evolved, bringing with it a new set of challenges and associated opportunities. Principal among these challenges is the last-inch problem. The telecommunications industry uses the term "last mile" to refer to the challenge of bringing high-bandwidth connectivity to individual homes. We use the term "last inch" to characterize the challenges of delivering computing services through in-vehicle human-machine interfaces (HMIs) to users who are sometimes driving at speeds upwards of 70 miles per hour. We focus on the nonfunctional requirements of security, privacy, usability, and reliability (SPUR)). These attributes both encompass safety concerns and offer insight into the consumer experience. We took the SPUR requirements into account in designing our vehicle consumer services interface (VCSI), a service-oriented middleware architecture that we've implemented in a demonstration vehicle     

Effects of thermo-mechanical treatments on mechanical properties of AA2219 gas tungsten arc welds

Fusion zone of AA2219 alloy gas tungsten arc welds was subjected to compressive deformation by rolling the crown of the weld in the welding direction. Twelve percent compressive deformation improved the as-weld hardness from 75 to 100 VHN. The yield strength increased from 125 to 220 MPa. The welds made by pulsed current technique exhibited better strength and ductility compared to their continuous current weld counterparts, both in the as-welded condition and the deformed condition. The improvement in strength was found to be due to dislocation loops formed near the grain boundaries in the fusion zone. Direct aging of fusion zone at 190 °C, increased the yield strength significantly from 125 to about 200 MPa. Aging of the deformed fusion zone did not improve tensile strength further.     

Performance of a metallic gas diffusion layer for PEM fuel cells

A novel metallic porous medium with improved thermal and electrical conductivities and controllable porosity was developed based on micro/nano technology for its potential application in PEM fuel cells. In this work to demonstrate its applicability, the gas diffusion medium, made of 12.5 μm thick copper foil, was tested in an operational fuel cell. The small thickness and straight-pore feature of this novel material provides improved water management even at low flow rates. The performance does not decline at lower flow rates, unlike conventional gas diffusion layers. It has been shown that the performance can be further enhanced by increasing the in-plane transport. The improvements of such gas diffusion layer, including pore shape, porosity, and surface properties, are fully discussed.     

A hydrodynamic network model for interdigitated flow fields

The flow field is one of the main components of a fuel cell, which distributes the reactants to the active area of the cell and evacuates the products formed. Interdigitated flow field (IFF) is one among the different types of flow field designs that forces the reactants or products to flow through the electrode, thereby increasing the cell performance by decreasing concentration polarization loss, however, at the cost of higher-pressure drop. Prior understanding of the reactant and water vapour distribution in a flow field helps in obtaining the best flow field design. In the present paper, a model for the flow distribution and the pressure drop in an IFF has been developed using the analogy between fluid flow and electrical network in which the pressure is made analogous to the voltage and the flow rate to the current. The model, which ultimately reduces to the solution of a set of simultaneous algebraic equations, is capable of predicting the flow split among a set of inlet and outlet channels of an interdigitated flow field as well as the overall pressure drop for laminar, turbulent and two-phase flow conditions for arbitrary number of parallel channels. The results from the hydrodynamic network model have been validated against CFD simulations. This model can therefore be used for the optimization of interdigitated flow field design.     

Recent progress on synthetic strategies and applications of transition metal phosphides in energy storage and conversion

Continuous advancements in the field of energy conversion and storage, including the development, evaluation of abundant and inexpensive materials with good electrochemical performance, aim to meet the future energy demands. Transition metal phosphides (TMPs) have recently emerged as excellent energy conversion and storage materials due to their highly active surface sites, electrical conductivity, thermal and structural stability. TMPs exhibit numerous other desirable properties, like hardness and chemical stability, which result from the presence of strong M ? P bonds in the molecules. In this work, comprehensive review of recent advancements in research concerning TMPs and their applications in the area of energy conversion and storage was conducted. Additionally, the frequently employed synthetic strategies for the production of TMPs were investigated. Particularly, hydrogen and oxygen evolution reactions (HER and OER), dye-sensitized solar cells for energy conversion and storage, lithium-ion batteries, and supercapacitors were examined. TMPs display remarkable electrochemical behavior due to the synergistic effects of various compositions and surface structures. Moreover, the M-centers and P-sites possess high electrocatalytic activity. The P-sites of phosphides are negatively charged; thus, they attract protons, enhancing the HER/OER activities. Eventhough platinum-based electrocatalysts perform best in HER, their bifunctional properties have not been extensively studied due to poor OER activities. In energy storage, TMPs used as efficient and stable electrodes owing to their low charge-discharge potentials, high theoretical specific capacities, and a decreased ion-diffusion pathway. Finally, the challenges, future perspectives in the area of energy are discussed and several approaches for the improvement of multifunctional TMPs are proposed.