Theoretical study of p-d hybridization in Co perovskite

The real-space recursion method and unrestricted Hartree-Fock approximation have been applied to calculate the density of states of various Co perovskite, CeCoO3, SrCoO3 and Sr1-xCexCoO3. We have studied the magnetically ordered states of these Co perovskites in an enlarged double cell, and find its various magnetic structures due to the occupancy of 3d band and its interaction with neighboring Co ions. In this study, we have studied the p-d hybridization of the three Co perovskites, we find t(2g) electrons are localized and the flat e(g) band is responsible for the itinerant behavior, and although the rare earth elements itself contribute little to the DOS at the Fermi energy, the DOS at Fermi energy and the magnetic moment changed consequently because of different valence of Co ions in these compounds and p-d hybridization effect is very important. (C) 2009 Elsevier B.V. All rights reserved.

Highly ordered mesoporous carbons as electrode material for the construction of electrochemical dehydrogenase- and oxidase-based biosensors

In this work, the excel lent catalytic activity of highly ordered mesoporous carbons (OMCs) to the electrooxidation of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H2O2) was described for the construction of electrochemical alcohol dehydrogenase (ADH) and glucose oxidase (GOD)-based biosensors.

The characteristics of highly ordered mesoporous carbons as electrode material for electrochemical sensing as compared with carbon nanotubes

In this paper, the unique properties of highly ordered mesoporous carbons modified glassy carbon electrode (OMCs/GE) are illustrated from comparison with carbon nanotubes modified glassy carbon electrode (CNTs/GE) for the electrochemical sensing applications.

Growth of Space Ordered on GaAs（100） Vicinal 1.3μm InAs Quantum Dots Substrates by MOCVD

Space ordered 1.3μm self-assembled InAs QDs are grown on GaAs（100） vicinal substrates by MOCVD. Photoluminescence measurements show that the dots on vicinal substrates have a much higher PL intensity and a narrower FWHM than those of dots on exact substrates, which indicates better material quality. To obtain 1.3μm emissions of InAs QDs, the role of the so called InGaAs strain cap layer （SCL） and the strain buffer layer （SBL） in the strain relaxation process in quantum dots is studied. While the use of SBL results only in a small change of emission wavelength,SCL can extend the QD＇s emission over 1.3μm due to the effective strain reducing effect of SCL.

A magnetic, luminescent and mesoporous core-shell structured composite material as drug carrier

In this paper, hydrothermal synthesized Fe3O4 microspheres have been encapsulated with nonporous silica and a further layer of ordered mesoporous silica through a simple sol-gel process. The surface of the outer silica shell was further functionalized by the deposition of YVO4:Eu3+ phosphors, realizing a sandwich structured material with mesoporous, magnetic and luminescent properties. The multifunctional system was used as drug carrier to investigate the storage and release properties using ibuprofen (IBU) as model drug by the surface modification. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), N-2 adsorption/desorption, photoluminescence (PL) spectra, and superconducting quantum interference device (SQUID) were used to characterized the samples.

High-density gold nanoparticles supported on a [Ru(bpy)(3)](2+)-doped silica/Fe3O4 nanocomposite: Facile preparation, magnetically induced immobilization, and applications in ECL detection

A large-scale process combined sonication with self-assembly techniques for the preparation of high-density gold nanoparticles supported on a [Ru(bpy)(3)](2+)-doped silica/Fe3O4 nanocomposite (GNRSF) is provided. The obtained hybrid nanomaterials containing Fe3O4 spheres have high saturation magnetization, which leads to their effective immobilization on the surface of an ITO electrode through simple manipulation by an external magnetic field (without the need of a special immobilization apparatus). Furthermore, this hybrid nanomaterial film exhibits a good and very stable electrochemiluminescence (ECL) behavior, which gives a linear response for tripropylamine (TPA) concentrations between 5 mu m and 0.21 mM, with a detection limit in the micromolar range. The sensitivity of this ECL sensor can be easily controlled by the amount of [Ru(bpy)(3)](2+) immobilized on the hybrid nanomaterials (that is, varying the amount of [Ru(bpy)(3)](2+) during GNRSF synthesis).

Stable ordered mesoporous silica materials templated by high-temperature stable surfactant micelle in alkaline media

Ordered hexagonal mesoporous silica material (JLU-30) has been successfully synthesized in alkaline media at high temperature (> 160 degreesC, using cationic (1,3-dimethyl-2-imidazolidin-2-ylidene)hexadecylmethyl-ammonium bromide (DIHAB) as a template, and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption isotherms, differential thermal analysis (DTA), and thermogravimetric analysis (TG), as well as Al-27 and Si-29 nuclear magnetic resonance (NMR) spectroscopy. Mesoporous JLU-30 shows much higher hydrothermal stability than MCM-41. Si-29 NMR spectra indicate that the pore walls of JLU-30 samples synthesized at high temperature (160 degreesC) are fully condensed, giving a Q(4)/Q(3) ratio as high as 6.2. In contrast, MCM-41 synthesized at relatively low temperature (100 degreesC) shows the Q(4)/Q(3) + Q(2) ratio at 1.1. Such unique structural feature might be responsible for the observed highly hydrothermal stability of the mesoporous silica materials (JLU-30).

Material response and failure mechanism of unidirectional metal matrix composites under impulsive shear loading

The material response and failure mechanism of unidirectional metal matrix composite under impulsive shear loading are investigated in this paper. Both experimental and analytical studies were performed. The shear strength of unidirectional C-f/A356.0 composite and A356.0 aluminum alloy at high strain rate were measured with a modified split Hopkinson torsional bar technique. The results indicated that the carbon fibers did not improve the shear strength of aluminum matrix if the fiber orientation aligned with the shear loading axis. The microscopic inspection of the fractured surface showed a multi-scale zigzag feature which implied a complicated shear failure mechanism in the composite. In addition to testing, the micromechanical stress field in the composite was analyzed by the generalized Eshelby equivalent method (GEEM). The influence of cracking in matrix on the micromechanical stress field was investigated as well. The results showed that the stress distribution in the composite is quite nonhomogeneous and very high shear stress concentrations are found in some regions in the matrix. The high shear stress concentration in the matrix induces tensile cracking at 45 degrees to the shear direction. This in turn aggravates the stress concentration at the fiber/matrix interface and finally leads to a catastrophic failure in the composite. From the correlation between the analysis and experimental results, the shear failure mechanism of unidirectional C-f/A356.0 composite can be elucidated qualitatively.

Experimental Studies of the Material Properties of the Forewing of Cicada (Homoptera, Cicadidae)

Detailed investigations on the structural and mechanical properties of the forewing of the cicada were carried out. Measurement of the structures of the wings showed that the thickness of the membrane of each cell and the diameter of each vein were non-uniform in both the longitudinal and transverse directions, and their means were approximately 12.2 and 133.3 mum, respectively. However, the aspect ratios of the wings and the bodies were quite uniform and were approximately equal to 2.98 and 2.13, respectively. Based on the measured thickness, mass and area of the membranes of the cells, the mean density and the mean area density of the wing were approximately 2.3 g cm(-3) and 2.8 x 10(-3) g cm(-2), respectively. In addition, the diameters of the veins of the wings, including the diameters of the holes in the vein of the leading edge, were examined. The mechanical properties of the wing were investigated separately by nanoindentation and tensile testing. The results indicated that the mean Young's modulus, hardness and yield stress of the membranes of the wings were approximately 3.7 Gpa, 0.2 Gpa and 29 Mpa, respectively, and the mean Young's modulus and strength of the veins along the direction of the venation of wings were approximately 1.9 Gpa and 52 Mpa, respectively. Finally, the relevant results were briefly analyzed and discussed, providing a guideline to the biomimetic design of the aerofoil materials of micro air vehicles.

Determination of Proper Processing Conditions of Material Surface Heat Treatment Through Finite Element Method

A two-dimensional model has been developed based on the experimental results of stainless steel remelting with the laminar plasma technology to investigate the transient thermo-physical characteristics of the melt pool liquids. The influence of the temperature field, temperature gradient, solidification rate and cooling rate on the processing conditions has been investigated numerically. Not only have the appropriate processing conditions been determined according to the calculations, but also they have been predicted with a criterion established based on the concept of equivalent temperature area density (ETAD) that is actually a function of the processing parameters and material properties. The comparison between the resulting conditions shows that the ETAD method can better predict the optimum condition.

Influences of strain rate and temperature variation on material intrinsic length of plasticity strain gradient theory

Cowper-Symonds and Johnson-Cook dynamic constitutive relations are used to study the influence of both strain rate effect and temperature variation on the material intrinsic length scale in strain gradient plasticity. The material intrinsic length scale decreases with increasing strain rates, and this length scale increases with temperature.

Three-Dimensional Modeling of Heat Transfer and Fluid Flow in Laminar-Plasma Material Re-Melting Processing

Modeling study is performed concerning the heat transfer and fluid flow for a laminar argon plasma jet impinging normally upon a flat workpiece exposed to the ambient air. The diffusion of the air into the plasma jet is handled by using the combined-diffusion-coefficient approach. The heat flux density and jet shear stress distributions at the workpiece surface obtained from the plasma jet modeling are then used to study the re-melting process of a carbon steel workpiece. Besides the heat conduction within the workpiece, the effects of the plasma-jet inlet parameters (temperature and velocity), workpiece moving speed, Marangoni convection, natural convection etc. on the re-melting process are considered. The modeling results demonstrate that the shapes and sizes of the molten pool in the workpiece are influenced appreciably by the plasma-jet inlet parameters, workpiece moving speed and Marangoni convection. The jet shear stress manifests its effect at higher plasma-jet inlet velocities, while the natural convection effect can be ignored. The modeling results of the molten pool sizes agree reasonably with available experimental data.

Evolution induced catastrophe in a nonlinear dynamical model of material failure

In order to study the failure of disordered materials, the ensemble evolution of a nonlinear chain model was examined by using a stochastic slice sampling method. The following results were obtained. (1) Sample-specific behavior, i.e. evolutions are different from sample to sample in some cases under the same macroscopic conditions, is observed for various load-sharing rules except in the globally mean field theory. The evolution according to the cluster load-sharing rule, which reflects the interaction between broken clusters, cannot be predicted by a simple criterion from the initial damage pattern and even then is most complicated. (2) A binary failure probability, its transitional region, where globally stable (GS) modes and evolution-induced catastrophic (EIC) modes coexist, and the corresponding scaling laws are fundamental to the failure. There is a sensitive zone in the vicinity of the boundary between the GS and EIC regions in phase space, where a slight stochastic increment in damage can trigger a radical transition from GS to EIC. (3) The distribution of strength is obtained from the binary failure probability. This, like sample-specificity, originates from a trans-scale sensitivity linking meso-scopic and macroscopic phenomena. (4) Strong fluctuations in stress distribution different from that of GS modes may be assumed as a precursor of evolution-induced catastrophe (EIC).

The effect of nucleation time on the growth of a microvoid in a viscoelastic material

In this paper, discussions are focused on the growth of a nucleated void in a viscoelastic material. The in situ tensile tests of specimens made of high-density polyethylene, filled with spherical glass beads (HDPE/GB) are carried out under SEM. The experimental result indicates that the microvoid nucleation is induced by the partially interfacial debonding of particles. By means of the Laplace transform and the Eshelby's equivalent inclusion method, a new analytical expression of the void strain at different nucleation times is derived. It can be seen that the strain of the nucleated void depends not only on the remote strain history, but also on the nucleation time. This expression is also illustrated by numerical examples, and is found to be of great usefulness in the study of damage evolution in viscoelastic materials.

Dynamic stress intensity factor of a functionally graded material under antiplane shear loading

The dynamic response of a finite crack in an unbounded Functionally Graded Material (FGM) subjected to an antiplane shear loading is studied in this paper. The variation of the shear modulus of the functionally graded material is modeled by a quadratic increase along the direction perpendicular to the crack surface. The dynamic stress intensity factor is extracted from the asymptotic expansion of the stresses around the crack tip in the Laplace transform plane and obtained in the time domain by a numerical Laplace inversion technique. The influence of graded material property on the dynamic intensity factor is investigated. It is observed that the magnitude of dynamic stress intensity factor for a finite crack in such a functionally graded material is less than in the homogeneous material with a property identical to that of the FGM crack plane.