1,721,194 research outputs found
BOUNDARY-LAYERS IN WEDGES OF LAMINATED COMPOSITE STRIPS UNDER GENERALIZED PLANE DEFORMATION .1. ASYMPTOTIC SOLUTIONS
No full textBased upon Lekhnitskii's formulation and the Stroh formalism, the structure of the asymptotic solutions has been examined for the boundary layer on the wedge type cross section of a laminated composite strip. The composite strip is assumed under the so-called generalized plane deformation, which includes tension, bending and/or torsion by the terminal tractions as well as the generalized plane strain problem. The solution structures are obtained, with the aid of numerical calculation, for various kinds of wedge geometry including the free edge and the delamination cracks with the crack faces opened or closed. Finally the nature of the asymptotic solutions is discussed, including the mode mixity of singular stress field ahead of the wedge tip, it is found that for a free edge problem the mode mixity of the singular asymptotic traction vector on the interfacial plane near the free edge remains invariant under varying types of remote loadings once a pair of adjacent materials (or ply orientations) is given and that accordingly one single scaling parameter governs the near field response.The present work has been supported by the Agency for Defence Development (ADD) under the Grant No. ADD-92-5-004
Highly linear receiver front-end adopting MOSFET transconductance linearization by multiple gated transistors
No full textHighly linear receiver RF front-end adopting MOSFET transconductance linearization by linearly superposing several common-source FET transistors in parallel (multiple gated transistor, or MGTR), combined with some additional circuit techniques are reported. In MGTR circuitry, linearity is improved, by using transconductance linearization which can be achieved by canceling the negative peak value of g''(m) of the main transistor with the positive one in the auxiliary transistor having a different size and gate drive combined in parallel. This enhancement, however, is limited by the distortion originated from the combined influence of g'(m) and harmonic feedback, which can greatly be reduced by the cascoding MGTR output for the amplifier and by the tuned load for the mixer. Experimental results designed using the above techniques show IIP3 improvements at given power consumption by as much as, 10 dB for CMOS low-noise amplifier at 900 MHz and 7 dB for Gilbert cell mixer at 2.4 GHz without sacrificing other features such as gain and noise figure.The authors would like to thank Dr. B. K. Ko of Integrant
Technologies for his continuous support
Design of mesoporous silica at low acid concentrations in triblock copolymer-butanol-water systems
No full textAssembly of hybrid mesophases through the combination of amphiphilic block copolymers, acting as structure-directing agents, and silicon sources using low acid catalyst concentration regimes is a versatile strategy to produce large quantities of high-quality ordered large-pore mesoporous silicas in a very reproducible manner. Controlling structural and textural properties is proven to be straightforward at low HCl concentrations with the adjustment of synthesis gel composition and the option of adding co-structure-directing molecules. In this account, we illustrate how various types of large-pore mesoporous silica can easily be prepared in high phase purity with tailored pore dimensions and tailored level of framework interconnectivity. Silica mesophases with two-dimensional hexagonal (p6mm) and three-dimensional cubic (Fm (3) over barm, Im (3) over barm and la (3) over bard) symmetries are generated in aqueous solution by employing HCl concentrations in the range of 0.1-0.5 M and polyalkylene oxide-based triblock copolymers such as Pluronic P123 (EO20-PO70-EO20) and Pluronic F127 (EO106-PO70EO106). Characterizations by powder X-ray diffraction, nitrogen physisorption, and transmission electron microscopy show that the mesoporous materials all possess high specific surface areas, high pore volumes and readily tunable pore diameters in narrow distribution of sizes ranging from 4 to 12 nm. Furthermore, we discuss our recent advances achieved in order to extend widely the phase domains in which single mesostructures are formed. Emphasis is put on the first synthetic product phase diagrams obtained in SiO2-triblock copolymerBuOH-H2O systems, with tuning amounts of butanol and silica source correspondingly. It is expected that the extended phase domains will allow designed synthesis of mesoporous silicas with targeted characteristics, offering vast prospects for future applications.The work was supported by the Korea Ministry of Science and Technology and the School
of Molecular Science through the Brain Korea 21 project. F. Kleitz thanks the Canadian Government for the Canada Research Chair in Functional Nanostructured Materials.
Synchrotron radiation XRD experiments at PLS were supported in part by MOST and POSTECH
Improvement of the crystallinity of a CdxZn1-xTe epitaxial film grown on a GaAs substrate using a ZnTe buffer layer
No full textThe effects of a ZnTe buffer layer on the structural and the optical properties of the CdxZn1-xTe films were investigated using CdxZn1-xTe epilayers on GaAs (100) substrates with and without ZnTe buffer layers. X-ray diffraction measurements showed that the grown layers were CdxZn1-xTe epitaxial films. Photoluminescence and transmission electron microscopy measurements showed that the crystallinity quality of the CdxZn1-xTe epilayers grown on the GaAs substrates was remarkably improved using the ZnTe buffer. These results suggest that CdxZn1-xTe epitaxial films grown on GaAs substrates with ZnTe buffers by a simple technique can be used for applications as buffer layers for high-quality HgxCd1-xTe layers
The strain relaxation in a lattice-mismatched heterostructure
No full textStrain relaxation phenomena of the heteroepitaxial lattice-mismatched semiconductors have been investigated. The relationship between the residual in-plane strain and the width of the misfit cell was obtained geometrically. The residual in-plane strain was calculated for various film thicknesses by using the energy minimization theory on the misfit cell in the InxGa1-xAs/GaAs(1 0 0) heterostructure system. A generalized strain relaxation model is presented on the basis of the energy minimization theory. (C) 1999 Elsevier Science B.V. All rights reserved
Medium Optimization of Iron Precipitates(Jarosite) Formation in H2S Removal Process Using Ferric Sulfate and Microorganism
No full textStability problems in CdTe/InSb heterointerfaces grown by temperature gradient vapor transport deposition at low temperature
No full textStability problems of the CdTe epitaxial layers grown on p-InSb (111) substrates at relatively low (similar to 180 degrees) temperature were investigated, From the X-ray diffraction measurements, the grown layer was found to be a CdTe epitaxial film. Transmission electron microscopy (TEM) showed that the CdTe/InSb structures measured immediately after the growth at 180 degrees C had good heterointerfaces. Photoluminescence measurements at 15 K for the as-grown CdTe/InSb heterostructures showed that the ratio of the peak intensity of the defect related emission to excitons bound to neutral donors was small. The high-resolution TEM measurements for the CdTe/InSb heterostructures held during three years showed that an U shaped domain appeared at the CdTe/InSb heterointerface and that the CdTe epitaxial layer near the interface changed to the CdTe polycrystalline or amorphous layers, These results indicated that the CdTe films grown on InSb substrates at 180 degrees C should remove a significant stability problem due to interdiffusion at heterointerfaces for applications
Phase domain of the cubic im3m mesoporous silica in the EO106PO70EO106-butanol-H2O system
No full textn-Butanol has been chosen as an organic additive in the SiO2-EO106PO70EO106-H2O system at low HCl concentrations, for the generation of large-pore mesoporous silicas with easily tailored textural and structural properties. As opposed to previous reports on syntheses of cubic mesoporous silica that are usually performed in a very narrow composition range, we report now the possibility of preparing large-pore cagelike mesoporous silicas in a wide range of synthesis mixture compositions. Particularly, the cubic Im3m silica with large interconnected cagelike pores (SBA-16) can easily be synthesized with controlled pore sizes and wall thicknesses, depending upon the synthesis mixture composition. The primary mesopore volume of the SBA-16 cages can be tuned from 0.27 to 0.56 cm(3) g(-1), and the mesopore size is shown to range from 4.7 to 7.2 nm, by performing a simple adjustment of the starting mixture composition. With the synthesis parameters varied, we describe the first complete diagram of the product phase domains obtained for silica mesophases in a SiO2-EO106PO70E106-butanol-H2O system. Other ordered mesophases also observed in this system are the face-centered cubic Fm3m silica mesophase and a 2D hexagonal-like mesostructure. Importantly here, the use of a low acid catalyst concentration regime allowed the preparation of silica mesophases in almost thermodynamically controlled conditions because of slow condensation kinetics of the inorganics. Such conditions enabled the introduction of n-butanol as the phase-controlling agent in the system, providing efficient tuning of the mesophase topology. The description of the phase domains provides a future basis for the design of large-pore mesoporous silicas with tailored textural and structural properties. Mesoporous samples obtained within the composition ranges of the phase domains are characterized by powder X-ray diffraction (PXRD) and nitrogen physisorption measurements.F. K. thanks the Canadian Government
for the Canada Research Chair in Functional Nanostructured Materials (2005-2010). The work was supported by the Korea Ministry of Science and Technology and the School of Molecular Science through the Brain Korea 21 project. Synchrotron radiation XRD experiments at PLS were supported in part by MOST and POSTECH
Polydiacetylene (PDA) sensors for the detection of nucleic acids based on biotin-streptavidin interactions
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