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A study was conducted to show that the emission wavelength of (InP)2/(GaP)2 short-period superlattice quantum wells can be changed by altering the tilt angle of the substrate or by adjusting the interruption time during switching. Variable temperature photoluminescence spectroscopy was carried out to characterize the samples. Results indicated that the growth mechanism can be determined through the bonding preference between the group III adatoms on the surface.

Purpose: The objective of this study was to determine the cytocompatibility of three different extracts of denture base resins and to compare the cytotoxic effect of these materials on a human oral epithelial KB cell line and primary human oral fibroblasts derived from buccal mucosa.Materials and Methods: Set specimens from a heat-cured resin, a self-cured resin, and a light-cured resin were eluted with culture medium for 1, 3, and 5 days. Cytotoxicity was judged using tetrazolium bromide reduction assay.Results: The eluates from self-cured, heat-cured, and light-cured denture base resins were cytotoxic to primary human buccal fibroblast cultures and KB cells. Self-cured resin was the most toxic denture base material among the chemicals tested in all cultures. The cytotoxicity decreased in the order of self-cured resin > heat-cured resin > light-cured resin for KB cells. The rank for buccal fibroblast cells was self-cured resin > heat-cured resin > light-cured resin.Conclusion: The influence of the cytotoxicity depended on the materials tested and the cell culture system used. The use of both permanent and primary cells is recommended for a better screening of the cytotoxic effects of denture base resins. [ABSTRACT FROM AUTHOR]

A dynamic focusing method, which used an analog FIFO for signal sampling and storage, decreased the sampling rate and hardware complexity for dynamic focusing. The nonuniform sampling process was used to achieve delay control on the ultrasound pulse echo at each array element for focusing delay compensation. The FIFO sampled and stored pulse echo values as it arrived from each imaging point at each array element.

Recently, there has been great interest in a new class of solutions to the isotropic/homogeneous scalar wave equation which represents localized waves or limited diffraction beams in electromagnetics, optics, and acoustics. Applications of these solutions to ultrasonic medical imaging, tissue characterization, and nondestructive evaluation of materials have also been reported. This paper reports a real-time medical imager which uses limited diffraction Bessel beams, X waves, Axicons, or conventional beams. Results (in vitro and in vivo) show that the images obtained with limited diffraction beams have higher resolution and good contrast over larger depth of field compared to images obtained with conventional focused beams. These results suggest the potential clinical usefulness of limited diffraction beams.

Instability due to an external cavity effect in the output of dc-biased surface emitting lasers was investigated. The results showed that the output power spectrum had multiple peaks with spacing corresponding to the round-trip delay in silica fibers. Peak magnitude was enhanced in the spectral region centered at the laser relaxation frequency. Increased feedback resulted in a corresponding increase in the output spectrum.

Transmission electron microscopy was used to explore the microstructural characteristics of C49-TiSi2 in narrow lines. With preamorphization implantation, defects that have highly circular distribution around a less-defective region were only seen for C49-TiSi2. Results showed that C49 grains were formed with the mosaic structure in these regions. It indicated a two-dimensional growth of C49-TiSi2 from the less-defective regions toward the defective region.

With the aid of ab initio calculations, an n-body Fe–Nb embedded-atom potential is first constructed and then applied to study the crystal-to-amorphous phase transition through molecular dynamic simulations. The simulations determine that the glass-forming range of the Fe–Nb system is 18–83 at. % of Nb. In ion beam mixing experiments, five Fe–Nb multilayered films with overall compositions of Fe85Nb15, Fe75Nb25, Fe55Nb45, Fe25Nb75, and Fe15Nb85, respectively, are irradiated by 200 keV xenon ions to doses in the range of (1–7)×1015Xe+/cm2. The result shows that the Fe–Nb metallic glasses can be synthesized within a composition range of 25–75 at. % of Nb, matching reasonably well the theoretical prediction. Moreover, in the Fe55Nb45 sample, a fcc-structured alloy phase with a large lattice constant of a≈0.408 nm was obtained at a dose of 3×1015 Xe+/cm2 and the associated magnetic moment per Fe atom was measured to be 2.41μB. The observed magnetic moment is much greater than the initial value of 1.42μB in the bcc-Fe lattice and can thus serve as evidence confirming the high-spin ferromagnetic state of fcc Fe predicted by ab initio calculations. Interestingly, further irradiation induced phase separation in the Fe55Nb45 sample, i.e., irradiation to a dose of 5×1015 Xe+/cm2 results in the growth of a fractal pattern consisting of Fe72Nb28 nanoclusters embedded in Fe35Nb65 matrix. The formation mechanism of the metastable phases as well as that of the fractal pattern observed in the Fe–Nb system was discussed in terms of the atomic collision theory and the well-known cluster-diffusion-limited-aggregation model. [ABSTRACT FROM AUTHOR]

In the equilibrium immiscible Hf–Nb system characterized by a positive heat of formation, five Hf–Nb metallic glasses with overall compositions of Hf84Nb16, Hf65Nb35, Hf45Nb55, Hf38Nb62, and Hf20Nb80 are obtained by ion beam mixing with properly designed Hf–Nb multilayered films, suggesting a glass-forming composition range of 16–80 at. % of Nb. For the special case of Hf45Nb55 located at the ridge point on the convex free energy curve, dual-glass phases are formed at a dose of 2×1015 Xe+/cm2, which results from a spinodal decomposition of the expected Hf45Nb55 amorphous phase. With increasing irradiation dose, fractal growth of nanocrystals (around 20 nm) appears in the major glass phase and the dimension is determined to be from 1.70 to 1.84 within a dose range of (4–7)×1015 Xe+/cm2. In atomistic modeling, a n-body Hf–Nb potential is first constructed with the aid of ab initio calculations. Applying the constructed potential, molecular dynamics simulations using the hcp and bcc solid solution models, reveals an intrinsic glass-forming range to be within 15–83 at. % of Nb, which is compatible with the ion beam mixing experiments. Moreover, the formation of the metallic glasses and the fractal growth in association with the amorphous spinodal decomposition are also discussed in terms of the atomic collision theory and cluster-diffusion-limited-aggregation model. [ABSTRACT FROM AUTHOR]

Four Ni-Nb metallic glasses are obtained by ion beam mixing and their compositions are measured to be Ni77Nb23, Ni55Nb45, Ni31Nb69, and Ni15Nb85, respectively, suggesting that a composition range of 23–85 at. % of Nb is favored for metallic glass formation in the Ni-Nb system. Interestingly, diffraction analyses show that the structure of the Nb-based Ni31Nb69 metallic glass is distinctly different from the structure of the Nb-based Ni15Nb85 metallic glass, as the respective amorphous halos are located at 2θ≈38 and 39 deg. To explore an atomic scale description of the Ni-Nb metallic glasses, an n-body Ni-Nb potential is first constructed with an aid of the ab initio calculations and then applied to perform the molecular dynamics simulation. Simulation results determine not only the intrinsic glass forming range of the Ni-Nb system to be within 20–85 at. % of Nb, but also the exact atomic positions in the Ni-Nb metallic glasses. Through a statistical analysis of the determined atomic positions, a new dominant local packing unit is found in the Ni15Nb85 metallic glass, i.e., an icositetrahedron with a coordination number to be around 14, while in Ni31Nb69 metallic glasses, the dominant local packing unit is an icosahedron with a coordination number to be around 12, which has been reported for the other metallic glasses. In fact, with increasing the irradiation dose, the Ni31Nb69 metallic glasses are formed through an intermediate state of face-centered-cubic-solid solution, whereas the Ni15Nb85 metallic glass is through an intermediate state of body-centered-cubic-solid solution, suggesting that the structures of the constituent metals play an important role in governing the structural characteristics of the resultant metallic glasses. [ABSTRACT FROM AUTHOR]

Metallic glasses are obtained in an immiscible Ag–Nb system with overall composition ranging from 25 to 90 at. % of Nb by ion beam mixing. Interestingly, the diffraction analysis shows that the formed Nb-rich metallic glass features are two distinct atomic configurations. In atomistic modeling, an n-body Ag–Nb potential is derived, under the assistance of ab initio calculation, and then applied in molecular dynamics simulations. An atomic configuration is discovered, i.e., an icositetrahedral ordering, and as well as an icosahedral ordering observed in the Ag–Nb metallic glasses and in some previously reported systems. Simulations confirm that the two dominate local atomic packing units are formed through a structural phase transition from the Nb-based bcc and fcc solid solutions, respectively, suggesting a concept of structural heredity that the crystalline structure of the constituent metals play a decisive role in determining the atomic structure of the resultant metallic glasses. [ABSTRACT FROM AUTHOR]

The cooling process is of great importance in plastic injection moulding as it has a direct impact on both productivity and product quality. Cooling process optimization is a sophisticated task which includes not only the design of cooling channels but also the selection of process parameters. Most existing optimization systems focus on either cooling channel design or process parameter selection but not both. This paper explores an approach to optimize both cooling channel design and process condition selection simultaneously through an evolutionary algorithm. The prototype system proposed in this paper is an integration of the genetic algorithm and CAE (Computer-Aided Engineering) technology. The aim is to launch a computerized system that can guide the optimization of the cooling process in plastic injection moulding. The objective is to achieve the most uniform cavity surface temperature to assure product quality. [ABSTRACT FROM AUTHOR]