GaAs/AlGaAs patterned quantum well lasers were grown by molecular beam epitaxy on grooved substrates. The carrier confinement and the real-index waveguiding in these lasers rely on lateral thickness variations in the quantum well active layer. Very low threshold currents, as low as 1.8 mA for uncoated devices at room temperature, with 63% differential efficiency have been obtained 相似文献
The rheological analysis of epoxy pre-polymer/MWCNT dispersions indicates that a physical network is formed. This is destroyed with an imposed shear, giving a viscoplastic and shear thinning behavior. Such destruction is not reflected in dynamic viscoelastic experiments, due to the very rapid recovery of the MWCNT network in the pre-polymer matrix. This responds to the observed lower electrical than rheological percolation threshold. Electrical conductivity results fulfill electron hopping/tunnelling mechanism, which implies a tube–tube distance close to 5 nm. However, rheological percolation requires nanotubes should touch each other, since no polymer chains are implied in the network. 相似文献
An experimental procedure was developed to obtain an oxide layer formed mainly by spinel on maraging steels. It consists of different stages with specific conditions, such as atmospheres rich in nitrogen and water vapor, and different steps of temperatures and times. Tests were performed on grade 300 and 350 maraging steels. Oxide layer characterization was done using optical and electron microscopy, spectroscopy, X-ray diffraction, and nanoscratch tests in order to determine the adhesion force as well as to observe the main deformation mechanism induced under sliding tests. In both steels, oxide layers are formed by the spinel’s Fe3O4 and CoFe2O4 in amounts close to ca. 85 pct, whereas TiO2 and MoO3 represent the other 15 pct. No hematite was found. The low oxygen availability during the heat treatment was fundamental for avoiding hematite formation. A nickel-rich austenitic phase formed at the metal-oxide interface due the kinetics of the oxidation process of the cobalt, iron, and molybdenum. The particular conditions of the heat treatments induced the formation of a mixture of iron, nickel, and cobalt spinel ferrites, thereby contradicting previous studies that said that only magnetite would be formed. The sliding tests at the nanometric length scale highlight that the layer formed on maraging 300 grade presents a better adhesion than the other investigated material due to the fact that it requires more load in order to induce cracks located at the edge of the sliding track and, subsequently, the chipping of the formed layer.
Perovskites LaNiO3, LaNi1−xMgxO3−δ and LaNi1−xCoxO3−δ were synthesized by auto combustion method. TPR analysis reveled that Mg or Co substituted perovskites were more difficult to reduce. The perovskites were evaluated as catalyst precursors in the dry reforming of methane. Catalysts obtained by reduction of LaNiO3 and LaNi1−xMgxO3−δ perovskite had the highest catalytic activity for CO2 reforming of CH4 at 700 °C using drastic reaction conditions (10 mg of catalyst, a mixture of CH4/CO2 without dilution gas). Methane and carbon dioxide conversions were 57% and 67%, respectively, with a H2/CO ratio equal to 0.47.The presence of cobalt leads to a decrease of the catalytic activity. This decreasing of activity may be attributed to the Co–Ni alloy formation. Computational calculations revealed that Ni atom cleaves the C–H atom while Co is not able to activate the CH4 molecule. The interaction energy of CH4 with the Ni and CO atom was 18 kcal/mol and 0.7 kcal/mol, respectively.The catalysts were characterized by TPR, TEM and in situ XRD. 相似文献
The performance of strained layer InGaAs/GaAs vertical cavity surface emitting lasers defined by ion implantation over a approximately 75 degrees C temperature range is reported on. Maximum CW output levels for the temperature extremes of 10 and 86 degrees C are 7.5 MW and 200 mu W, respectively for 20*20 mu m/sup 2 /devices. The temperature dependence of the CW threshold current exhibits exponential behaviour to 80 degrees C.<> 相似文献
Molecular beam epitaxy (MBE)-grown Lg=1.7-μm pseudomorphic Al0.38Ga0.62As/n+-In0.15Ga 0.85As metal-insulator-doped channel FETs (MIDFETs) are presented that display extremely broad plateaus in both fT and fmax versus VGS, with fT sustaining 90% of its peak over a gate swing of 2.6 V. Drain current is highly linear with VGS over this swing, reaching 514 mA/mm. No frequency dispersion in gm up to 3 GHz was found, indicating the absence of electrically active traps in the undoped AlGaAs pseudoinsulator layer. These properties combine to make the pseudomorphic MIDFET highly suited to linear, large-signal, broadband applications 相似文献
An efficient boundary element solution of the motion of inelastic non-Newtonian fluids at low Reynolds number is presented
in this paper. For the numerical solution all the domain integrals of the boundary element formulation have been transformed
into equivalent boundary integrals by means of the dual reciprocity method (DRM). To achieve an accurate approximation of
the non-linear and non-Newtonian terms two major improvements have been made to the DRM, namely the use of augmented thin
plate splines as interpolation functions, and the partition of the entire domain into smaller subregions or domain decomposition.
In each subregion or domain element the DRM was applied together with some additional equations that ensure continuity on
the interfaces between adjacent subdomains. After applying the boundary conditions the final systems of equations will be
sparse and the approximation of the nonlinear terms will be more localised than in the traditional DRM. This new method known
as multidomain dual reciprocity (MD-DRM) has been used to solve several non-Newtonian problems including the pressure driven
flow of a power law fluid, the Couette flow and two simulations of industrial polymer mixers.
Received 7 February 2001 相似文献