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High-Temperature Firing Effect on the Structure and Dielectric Properties of (0.5) La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSMO) + (0.5) Ba{sub 0.5}K{sub 0.5}TiO{sub 3} (BKT) Composite
A composite of two perovskite materials namely Ba{sub 0.5}K{sub 0.5}TiO{sub 3}[BKT] and La{sub 0.8}Sr{sub 0.2}MnO{sub 3} [LSMO] was prepared via solid state reaction route. Analysis of the XRD data confirmed the single-phased crystalline cubic structure with assigned space group Pm-3m though parent compounds, i.e., BKT and LSMO, were cubic and rhombohedral structured, respectively, having space groups Pm-3m and R3c. The single phase of the composite is found to occur due to higher heat treatment. Retvield refinement of the XRD data confirmed the structure and other essential parameters regarding cubic structure. The Raman studies displayed active modes corresponding to the BKT (Pm-3m) phase. The surface morphology studies confirmed an increase in average particle size, and the energy dispersive analysis of X-ray (EDAX) technique revealed the presence of all the constituents of the material under investigation. The dielectric studies were carried out, and the sample was found to exhibit appreciable dielectric behaviour with a lower loss value. Impedance analysis revealed the non-Debye behaviour of the resultant composite and distribution of relaxation throughout the material. Resistivity measurement conveyed that incorporation of the BKT phase in the metallic phase of LSMO leads the composite to exhibit an insulating nature.
The Influence of Warm abc-Pressing on the Structure and Mechanical Properties of Stable Chromium-Nickel-Molybdenum Steel
The structure and properties of the 17Cr13Ni3Mo0.01C stable austenitic steel subjected to high-temperature plastic deformation by the abc-pressing (multiaxial forging) are investigated in the temperature range from 800 to 600°С. The results of investigations demonstrate that after the abc-pressing the steel has a single-phase austenitic ultrafine-grained structure with the size of its elements (grains and subgrains) of (200 ± 140) nm. The formation of the ultrafine-grained state increases the strength properties (0.2 proof stress increases threefold) and decreases the elongation value of the steel at room temperature compared to the coarse-grained specimens. An analysis of the contributions from hardening during abc-pressing evidences in favor of the strength improvement being primarily due to the grain refinement; it is well described by the Hall–Petch relationship. In this case steel with ultrafine-grained austenitic structure exhibits an effect of structural superplasticity at the temperatures T > 750°С: the elongation value at Т = 800°С is found to be 180%.
Effect of Network Structure on Characterization and Flow Modeling Using X-ray Micro-Tomography Images of Granular and Fibrous Porous Media
Image-based network modeling has become a powerful tool for modeling transport in real materials that have been imaged using X-ray computed micro-tomography (XCT) or other three-dimensional imaging techniques. Network generation is an essential part of image-based network modeling, but little quantitative work has been done to understand the influence of different network structures on modeling. We use XCT images of three different porous materials (disordered packings of spheres, sand, and cylinders) to create a series of four networks for each material. Despite originating from the same data, the networks can be made to vary over two orders of magnitude in pore density, which in turn affects network properties such as pore-size distribution and pore connectivity. Despite the orders-of-magnitude difference in pore density, single-phase permeability predictions remain remarkably consistent for a given material, even for the simplest throat conductance formulas. Detailed explanations for this beneficial attribute are given in the article; in general, it is a consequence of using physically representative network models. The capillary pressure curve generated from quasi-static drainage is more sensitive to network structure than permeability. However, using the capillary pressure curve to extract pore-size distributions gives reasonably consistent results even though the networks vary significantly. These results provide encouraging evidence that robust network modeling algorithms are not overly sensitive to the specific structure of the underlying physically representative network, which is important given the variety image-based network-generation strategies that have been developed in recent years.
Effects on Lignin Structure of Coumarate 3-Hydroxylase Downregulation in Poplar
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Activation of PI3K[alpha] by physiological effectors and by oncogenic mutations: structural and dynamic effects
Abstract not provided
Approximate methodology to account for effects of coherent structures on sediment entrainment in RANS simulations with a movable bed and applications to pier scour
Not Available
Morphing Mn core @Pt shell nanoparticles: Effects of core structure on the ORR performance of Pt shell
Currently, the catalysts performance for the oxygen reduction reaction (ORR) is limited by two major factors, their price and the scaling relationship, i.e. constant offset, between the binding energy of reactants and reaction intermediates. Here we show that both limitations may be eased by using nanoparticle catalysts composed of a core of earth-abundant Mn and Pt shell of two atomic layers. We report the unusual atomic-structure of Mn core renders the distribution of coordination numbers and related atomic-level stresses on the Pt shell very broad in com- parison to pure Pt particles. This increases the chances of nearby sites on the shell to affect each other’s activity such that the dissociative absorption of molecular oxygen is facilitated without correspondingly increasing the binding strength of reaction intermediates, thereby promoting the ORR kinetics. Our findings introduce the concept of structural flexibility of the 3d-metal core and 5d-Pt shell as a strategy for catalysis performance.
Atomistic modeling of tensile deformation and fracture of carbon fibers: Nanoscale stress redistribution, effect of local structural characteristics and nanovoids
The mechanisms of tensile deformation and fracture of carbon fibers are investigated in large-scale molecular dynamics simulations. The simulations performed for computational samples with different structural characteristics enable analysis of the structural sensitivity of the mechanical properties. It is found that the carbon fiber nanostructure can be represented by a fine (nanoscale) mixture of stiff and soft regions. Despite the nanoscale structural heterogeneity of the computational fibers, their fracture strain and tensile strength exceed the experimental values by almost an order of magnitude. Here, this observation is explained by the ability of the carbon fiber nanostructure, largely consisting of curved and folded layers of turbostratic carbon, to exhibit continuous nanoscale load redistribution during the deformation. The transient, fluid nature of a percolating cluster of stress-holding structural elements prevents stress localization at the early stage of the deformation and enables the fiber nanostructure to adapt to the increasing load. Overall, the results of the simulations suggest that the design of advanced carbon fiber manufacturing and post-processing methods focused on the elimination of critical mesoscopic structural defects (internal voids, foreign inclusions, and surface flaws) can yield a substantial increase in the strength and fracture strain of carbon fibers.
The effect of pore structure in ethane-selective metal-organic frameworks for ethylene purification
Separation of ethylene from ethane is of great importance in petrochemical industry. Adsorptive separation making use of porous materials such as metal-organic frameworks (MOFs) is an energy efficient technology compared to the conventional cryogenic distillation. However, preferential adsorption of ethylene over ethane represents the major current challenge. Here we demonstrate how pore structure can significantly alter the adsorption selectivity in two isoreticular Zr-MOFs. A simple ligand functionalization in UiO-66 yields smaller/better matching pore for ethane, and weaker interaction with ethylene, greatly enhancing ethane/ethylene selectivity in MOF-801. Ab initio calculations combined with in situ infrared spectroscopic analysis unveil the nature of host-guest interactions and differences in the overall binding energies. Polymer-grade ethylene (99.9%) can be produced directly from ethane/ethylene mixture in a single step. Having well-balanced adsorption capacity and selectivity, low-cost synthesis and easy scalability MOF-801 stands out as a promising ethane-selective adsorbent for one-step ethylene purification under ambient conditions.
Effect of pressure on crystal structure and superconductivity of NbSexTe2−x (x = 2, 1.5)
Not Available
Disturbance has variable effects on the structural complexity of a temperate forest landscape
Not Available
Effect of Vertically Structured Porosity on Electrochemical Performance of FeF2 Films for Lithium Batteries
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