Search results for "Axia"
showing 10 items of 638 documents
Thickness sensitivity of ultrasound velocity in long bone phantoms
2004
One approach to bone disease diagnosis such as osteoporosis is to measure the velocity of ultrasound propagating axially along long bones. In this study, the variation in velocity as a function of radial position was assessed using two polyvinyl chloride (PVC) bone phantoms with cross-sectional geometry similar to the human tibia but differing in medullary cavity diameter. Two ultrasonometers were used: these were a commercial device operating at a relatively high frequency (HF) of 1.25 MHz and a prototype low frequency (LF) device operating at approximately 200 kHz. The LF measurements showed a larger variation with radial position, with changes in velocity of up to 20% occurring around th…
Gradient-enhanced model and its micromorphic regularization for simulation of Lüders-like bands in shape memory alloys
2018
Abstract Shape memory alloys, notably NiTi, often exhibit softening pseudoelastic response that results in formation and propagation of Luders-like bands upon loading, for instance, in uniaxial tension. A common approach to modelling softening and strain localization is to resort to gradient-enhanced formulations that are capable of restoring well-posedness of the boundary-value problem. This approach is also followed in the present paper by introducing a gradient-enhancement into a simple one-dimensional model of pseudoelasticity. In order to facilitate computational treatment, a micromorphic-type regularization of the gradient-enhanced model is subsequently performed. The formulation empl…
Influence of Axial Pressure on the Electrical Properties of Li0.06Na0.94NbO3 Ceramic
2011
Lead-free ceramic Li0.06Na0.94NbO3 was synthesized using a conventional solid-state processing. The single-phase perovskite structure was identified by X-ray powder diffraction technique. The values of lattice parameters of Li0.06Na0.94NbO3 are lower than those for pure NaNbO3. The EDS analysis shows the fairly homogeneous distribution of all elements throughout the grains. An axial pressure significantly influences electric properties. With increasing pressure the peak intensity in the ϵ(T) curve decreases, the peak becomes diffused and shifts to a lower temperature. The value of tanδ increases with increasing axial pressure and its local maximum shifts towards lower temperatures.
Optical and photovoltaic properties of indium selenide thin films prepared by van der Waals epitaxy
2001
Indium selenide thin films have been grown on p-type gallium selenide single crystal substrates by van der Waals epitaxy. The use of two crucibles in the growth process has resulted in indium selenide films with physical properties closer to these of bulk indium selenide than those prepared by other techniques. The optical properties of the films have been studied by electroabsorption measurements. The band gap and its temperature dependence are very close to those of indium selenide single crystals. The width of the fundamental transition, even if larger than that of the pure single crystal material, decreases monotonously with temperature. Exciton peaks are not observed even at low temper…
Moment-axial force domain of corroded R.C. columns
2016
In the present paper, a simple model to determine the moment-axial force domain of the cross-section of reinforced concrete (R.C.) columns subjected to corrosion process is presented. The model considers members with square and rectangular cross-sections and it accounts for—cover spalling; buckling of longitudinal reinforcing bars; loss of bond of bar in tension; reduction of confinement pressures (due to the reduction of the area of stirrups and cracking of concrete induced by rust formation). The analytical expressions for prediction of the area reduction of steel, bond strength and critical load of longitudinal bars utilized were verified against experimental data available in the litera…
Shape-persistent V-shaped mesogens—formation of nematic phases with biaxial order
2006
A homologous series of shape-persistent V-shaped molecules has been designed to form the biaxial nematic phase. Phenyleneethynylene moieties are attached to a bent fluorenone unit to create an apex angle of about 90°, which is determined from the single crystal structure. Two mesogens, one symmetric and another unsymmetric, have been synthesized by attaching a cyano group to one or both of the peripheral phenyl units, respectively. These groups introduce local dipoles essential for the formation of the nematic phases. The tendency to form a crystalline phase is reduced by laterally substituted hexyloxy chains which allow the nematic phase to be supercooled to a glassy state. Two of the thre…
Applicability Range of the One-Parameter Ply Plasticity Model for Prediction of the Nonlinear Response of Laminates
2005
A one-parameter lamina plasticity model is applied to predict the nonlinear deformation of an E-glass / epoxy cross-ply composite laminate under quasi-static uniaxial tensile loading at different angles to the material orthotropy axes. It is shown that the laminate theory yields accurate results within the plastic strain range covered in unidirectional continuous-fibre reinforced composite tests that are used to determine the plasticity model parameters.
Behavior of fiber-reinforced concrete columns under axially and eccentrically compressive loads
2010
An experimental investigation into the behavior of 16 short, confined, reinforced concrete columns with and without steel fibers was carried out. The columns with square sections had a concrete core 165 x 165 mm (6.49 x 6.49 in.) at the midsection and were hunched at the ends to apply eccentric loading and prevent boundary effects. The specimens were tested to failure at different strain rates under two loading schemes: concentric compression and eccentric compression with a constant eccentricity. The axial load and axial strains were obtained to evaluate the effects of the presence of steel fibers, the thickness of the cover concrete, and the eccentricity of the applied axial load. The com…
Progress in Violet Light-Emitting Diodes Based on ZnO/GaN Heterojunction
2020
Progress in light-emitting diodes (LEDs) based on ZnO/GaN heterojunctions has run into several obstacles during the last twenty years. While both the energy bandgap and lattice parameter of the two semiconductors are favorable to the development of such devices, other features related to the electrical and structural properties of the GaN layer prevent an efficient radiative recombination. This work illustrates some advances made on ZnO/GaN-based LEDs, by using high-thickness GaN layers for the p-region of the device and an ad hoc device topology. Heterojunction LEDs consist of a quasicoalesced non-intentionally doped ZnO nanorod layer deposited by chemical bath deposition onto a metal&ndash
Elastic and piezoelectric properties of BaTiO3 at room temperature
1999
Abstract We have calculated the phonon dispersion curves of barium titanate (BaTiO 3 ) at room temperature. A lattice dynamical formalism using the shell model is used. This microscopic model includes the short-range interactions of axially symmetric type and the long-range Coulomb interactions and taking into account the electronic polarizability of constituent ions. Zone center phonon and a few phonons in the first Brillouin zone are used for fitting. The values of relevant parameters are critically analyzed. A calculation of the elastic and piezoelectric properties is presented and compared with the available experimental data.