7,029 research outputs found
Distributed utility-maximization using a resource pricing power control in uplink DS-CDMA
No full textThis letter considers a distributed utility maximization power control scheme in uplink DS-CDMA systems. Maximizing a utility function is solved by Lagrangian dual decomposition, where the Lagrangian multiplier can be considered as a resource price charging to users. By adjusting the price in a distributed fashion, the proposed algorithm results in a bang-bang type power control, 'maximum power transmission' or 'shutdown'. Numerical result shows that the proposed algorithm achieves around 95% of the optimal utility maximization with a modest computational burden
Substructures and fatigue crack growth in HIPing and semi-liquid die casting A356 alloys
No full textAdsorption and stability of phthalic acid on a colloidal silver surface: surface-enhanced Raman scattering study
No full textThe adsorption characteristics of phthalic acid on a silver surface were investigated by means of surface-enhanced Raman scattering (SERS). For a reliable analysis of the SER spectrum, we also performed an ab initio vibrational wavenumber calculation, The SER spectral features dictated that the phthalic acid molecules should be bound to silver as dicarboxylate, but in contrast with earlier reports, with a strongly tilted orientation with respect to the surface normal. The degree of tilt appeared to increase with increase in the bulk pH, Such a tilted orientation was presumed to occur by the simultaneous sigma- and pi-type coordination of carboxylate groups to silver caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups. Probably owing to the latter effects, phthalic acid on silver was easily displaced with aromatic mono-acids that could be bound to silver by forming only sigma-type coordination. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for an aromatic carboxylic acid derivative to assemble a robust monolayer on a silver surface. Copyright (C) 2000 John Whey & Sons, Ltd.This work was supported by the Korea Science and Engineering Foundation(KOSEF) through the Center for Molecular Catalysis at Seoul
National University (SNU) and by the Korea Research Foundation through the Research Institute for Basic Sciences at SNU. S.W.J. thanks the KOSEF for an Intern Research Fellowship
Adsorption characteristics of p-xylene-alpha,alpha -dithol on gold and silver surfaces: Surface-enhanced Raman scattering and ellipsometry study
No full textThe adsorption behavior of p-xylene-alpha, alpha'-dithiol (p-XDT) on colloidal gold and silver surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). p-XDT chemisorbed dissociatively on both the gold and silver surfaces but as mono- and dithiolate, respectively. Regardless of the bulk concentration of p-XDT, only a monolayer was assembled on the silver surface with a flat orientation by forming two Ag-S bonds. On the gold surface, the monothiolate species, p-XDT1-, appeared to assume a rather flat orientation at a very low surface coverage, but as the surface coverage was increased, the adsorbate took a perpendicular orientation. Furthermore, when the bulk concentration of p-XDT was close to that required for a full-monolayer coverage limit, a band assignable to the S-S stretching vibration appeared at similar to 509 cm(-1) in the gold sol SER spectra. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to trilayers could be assembled on gold in 1 mM n-hexane solution of p-XDT while only a monolayer formed in either methanol or ethanol solution. Although the exact causes were uncertain, such a difference in behavior seemed to have nothing to do with the oxygen species present in ethanol or methanol solution
The influence of Mn and Cr on the tensile properties of A356-0.2OFe alloy
No full textIn the present work, Mn and Cr were added to a commercial A356 (Al-7.0Si-0.38Mg-0.12Ti-0.02Sr in wt.%)-0.20Fe cast alloy to control the crystallization of beta-Al5FeSi. The tensile properties are compared in terms of the way the microstructures changed before and after the addition of 0.20Mn and 0.13Mn-0.13Cr. The addition of 0.20Mn causes the acicular P-Al5FeSi to be replaced by granular or skeletal alpha-Al(Mn,Fe)Si in solidification, and the additions of 0.13Mn-0.13Cr acts as an effective replacing element of beta-Al5FeSi. Moreover, the addition of 0.20Mn functionally improves the strength, and the addition of 0.13Mn-0.13Cr improves the strain as well as the strength compared to a commercial A356 cast alloy. (c) 2005 Elsevier B.V. All rights reserved.This work was supported by the Korea Research Foundation
Grant (KRF-2004-050-D0005)
Adsorption characteristics of 1,3-propanedithiol on gold: Surface-enhanced Raman scattering and ellipsometry study
No full textThe adsorption behavior of 1,3-propanedithiol (1,3-PDT) on a colloidal gold surface has been investigated by means of surface-enhanced Raman scattering (SERS). 1,3-PDT chemisorbed dissociatively on gold as a monothiolate. Moreover, we could clearly identify the S-S stretching band that reveals the formation of multilayers of 1,3-PDT on the colloidal gold surface. As for the case of 1,2-ethanedithiol. the intermolecular disulfide bond appeared to form even at a submonolayer coverage limit, implying that the adsorption of alpha,omega-alkanedithiol on gold does not take place homogeneously from the early stages of self-assembly. On the other hand, referring to the ab initio calculated vibrational frequencies of AuSCH2CH2CH2Cl, we could also analyze the concentration-dependent SER spectral features of 1,3-PDT in terms of the conformational isomerism around the two C-S bonds. Upon the increase of the bulk concentration of 1,3-PDT, a transition from a GG to GT conformation appeared to occur on the sol surface near the monolayer coverage limit; herein the first letter designates the conformation with respect to the C-C bond near the gold surface. On the basis of the concentration-dependent SER peak intensities, the 1,3-PDT-derivatized Au particles appeared to consist in nearly contact configurations. A separate ellipsometry measurement performed with vacuum-evaporated gold substrate revealed that at best one and one-half layered film could be assembled on gold in polar and protic solvents while up to three layers were assembled on gold in n-hexane solution of 1,3-PDT
A study on ray tracing method for CFD simulations of laser keyhole welding: Progressive Search Method
No full textAdsorption of 1,4-benzenedithiol on gold and silver surfaces: Surface-enhanced Raman scattering study
No full textThe adsorption behavior of 1,4-benzenedithiol (1,4-BDT) on colloidal gold and silver surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). 1,4-BDT chemisorbed dissociatively on both gold and silver surfaces but as mono- and dithiolate, respectively. Regardless of the bulk concentration of 1,4-BDT, only a monolayer was assembled on the silver surface with a flat orientation by forming two Ag-S bonds. On the gold surface, the monothiolate species, 1,4-BDT-1, appeared to assume a rather flat orientation at a very low surface coverage, but as the surface coverage was increased, the adsorbate took a perpendicular orientation. Furthermore, when the bulk concentration of 1,4-BDT was close to that required for a full-monolayer coverage limit, a band assignable to the S-S stretching vibration appeared at similar to 536 cm(-1) in the gold sol SERS spectra. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to tetralayers could be assembled on gold in 1 mM n-hexane solution of 1,4-BDT while at best a bilayer formed in either methanol or ethanol solution. The different adsorbate structure of 1,4-BDT on gold and silver was overall quite comparable to that of p-xylene-alpha,alpha ' -dithiol. (C) 2001 Academic Press
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