1,721,035 research outputs found
A novel mechanism for delay-insensitive data transfer based on current-mode multiple valued logic
No full textBy conventional delay-insensitive data encodings, the number of required wires for transferring N-bit data is 2N+1. To reduce the required number of wires to N+1, and thus, reducing complexity in designing a large scaled chip, a novel data transfer mechanism based on current-mode multiple valued logic is proposed. Effectiveness of proposed data transfer mechanism is validated by comparisons with conventional data transfer mechanisms using dual-rail and 1-of-4 encodings at the 0.25-mum CMOS technology. Simulation results of 32-bit data transfer with 10 rum wire length demonstrate that proposed data transfer mechanism reduces the time-power product values of dual-rail and 1-of-4 encoding by 55.5% and 8.5%, respectively, in addition to the reduction of the number of wire by about half
Low delay-power product current-mode multiple valued logic for delay-insensitive data transfer mechanism
No full textConventional delay-in sensitive (DI) data encodings require 2N+1 wires for transferring N-bit. To reduce complexity and power dissipation of wires in designing a large scaled chip, a DI data transfer mechanism based on current-mode multiple valued logic (CMMVL), where N-bit data transfer can be performed with only N+1 wires, is proposed. The effectiveness of the proposed data transfer mechanism is validated by comparisons with conventional data transfer mechanisms using dual-rail and 1-of-4 encodings through simulation at the 0.25-mu m CMOS technology. Simulation results with wire lengths of 4 mm or larger demonstrate that the CMMVL scheme significantly reduces delay-power product values of the dual-rail encoding with data rate of 5 MHz or more and the 1-of-4 encoding with data rate of 18 MHz or more
Microstructure control of DS NiAl/Ni3Al alloy by fabrication of columnar-grained NiAl martensite
No full textWe have reported that the various microstructures of polycrystalline NiAl/Ni3Al alloys can be obtained by heat-treatment using the M-s temperature control of NiAl martensite, and that the mechanical properties are considerably dependent on their microstructures. In this study, we tried to align the grain boundaries by directional solidification to suppress the intergranular fracture at room temperature or grain boundary sliding at high temperature or both. To effectively maintain the grain boundary alignment in the course of the heat-treatment. of a DS ingot, suppressing recrystallization during solutionizing treatment, which is the preceding process of martensitic transformation of a DS alloy, is very important. Based on the orientation relationship between parent beta-NiAl (the B2 structure) and product beta'-martensite (the L1(0) structure), we determined the heat-treatment condition for the DS ingot. Consequently, columnar-grained NiAl/Ni3Al alloys could be achieved after additional aging treatment, and they could show a higher yield strength than the polycrystalline alloys at high temperature
Rheological evidence for the silica-mediated gelation of xanthan gum
No full textIn the present study, the conformational effects of the adsorbed polyelectrolyte xanthan gum on the stability of colloidal silica suspensions were investigated by monitoring the rheological responses. The conformational transition of xanthan molecules was induced by changes in pH, added salts, and annealing temperature. The suspension stability was probed by examining the rheological behavior such as shear viscosity versus shear rate and shear moduli versus oscillatory frequency. The oscillatory shear measurements provided useful information on the structural change in the suspension. The results showed that the silica particles dispersed in the xanthan solution remained stable at pH 9 for a long period, whereas at pH 2, the gel network structure formed within a few days. When the gel structure formed, the storage modulus was larger than the loss modulus over the entire frequency range considered here and exhibited a thixotropic behavior. The heat treatment temperature best for stabilizing the silica suspension was shown about 60 degrees C and the silica sol treated at this temperature sustained its stability for more than 6 weeks. (C) 1999 Academic Press.This work was supported partly by a grant from KOSEF (971-1109-058-2).
The authors also appreciate partial support from Clean Creative Co., Ltd
Long-term oxidation properties of Al-Ti-Cr two-phase alloys as coating materials for TiAl alloys
No full textBoth Al-21Ti-23Cr (L1(2)+Cr2Al) and Al-37Ti-12Cr (gamma+TiAlCr) two-phase alloys have been accepted as the most appropriate coating materials in the Al-Ti-Cr alloy system to improve the high-temperature oxidation resistance of TiAl alloy, taking into consideration their oxidation resistance. resistance to thermal stress, and chemical compatibility with TiAl alloys. In this study, thermal stress analyses were performed on the basis of the thermal expansion coefficient and tensile and compressive strength of coating and substrate materials. Also the reaction properties between the alloys of interest in this paper and TiAl substrate were studied by bonding the two materials. This elucidates the long-term oxidation properties in L1(2)-based and gamma-based alloys. There was no significant difference in short-term oxidation resistance between the L1(2)-based and gamma-based alloys because both alloys could form a stable Al2O3 layer. However, although both alloys show similar resistance to thermal stress, it was confirmed that the L1(2)-based two-phase alloy has much better oxidation properties than the gamma-based two-phase alloy in long-term oxidation as it is considering the interface reaction properties with TiAl alloy. (C) 2002 Elsevier Science Ltd. All rights reserved
Microstructure control of DS NiAi/Ni3Al alloy by fabrication of columnar-grained NiAl martensite
No full textEffects of Zr addition on the phase stability of L1(2)-based Al-Ti-Cr alloys
No full textZr was added to the Al-21Ti-23Cr (L1(2)+Cr2Al) alloy to improve the L1(2) phase stability at temperatures around 800 degrees C. It was found that the addition of Zr effectively reduced and delayed the decomposition of the L1(2) matrix into L1(2) and Ti(Cr,Al)(2) phases in the Al-21Ti-23Cr alloy. Furthermore, the temperature range of the L1(2) matrix decomposition was narrowed when Zr was added to. the Al-21Ti-23Cr alloy. It is suggested that improvement of L1(2) phase stability by the addition of Zr could be the result of two factors. First, the movement of the L1(2) single-phase field could be reduced by the addition of Zr, possible decreasing the fraction of L1(2) matrix decomposition. Second, atomic diffusion could be suppressed by the addition of Zr, possible delaying the precipitation of the Ti(Cr,Al)(2) phase in the L1(2) matrix. (C) 2005 Elsevier B.V. All rights reserved
Effects of polyvinyl alcohol on the rheological behavior and phase stability of aqueous silica suspensions
No full textIn this world various silica suspensions mere synthesized by a single step Stober method and by a two-step grow th method using either fumed silica or colloidal silica as a seed. The synthesis proceeded through a controlled hydrolysis and condensation reactions of tetraethylorthosilicate (TEOS). After the reactions were completed, the solvent ethanol of the silica suspension was substituted by water through vacuum evaporation and ultra-centrifugation in order to obtain the aqueous silica suspension. Then, the silica suspension was stabilized by adjusting electrostatic repulsion, and by generating steric repulsion from the adsorbed polyvinyl alcohol (PVA). To elucidate the steric stabilization of colloidal silica by the polymeric surfactant of PVA, the adsorption isotherms of PVA in the aqueous silica suspension are determined. Moreover, the rheological behavior of the silica suspensions stabilized by PVA is investigated to characterize the dispersion stability of the colloidal silica suspensions. The results show that the phase stability of silica suspensions of relatively smaller particles is mainly induced by the electrostatic repulsion compared with steric stabilization contributed from the adsorbed layer of PVA. Meanwhile, for larger particle suspensions, the phase stability is governed predominantly by steric stabilization of the adsorbed PVA
Effect of nitrogen on the mean lamellar thickness of fully lamellar TiAl alloys
No full textThe effect of nitrogen addition in the 0-1.0 at.% range on the mean lamellar thickness of a fully lamellar TiAl alloy (Ti-48.5Al-1.5Mo) has been studied. Mean lamellar thickness first decreases with 0.3 at.% N addition but then increases with further increase in N level in the alloy. The increase in lamellar spacing for N levels between 0.3 and 1.0 at.% is attributed to the formation of Ti2AlN nitrides and the consequent change in Al level in the matrix. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved
Crack propagation behavior in TiAl-Nb single and Bi-PST crystals
No full textThe fracture toughness of directional solidified Ti-(45,47)Al-3Nb, Ti-(45,47)Al-3Nb-0.2Si-0.1C, Ti-(45,47)Al-3Nb-0.3Si-0.2C type I alloys and their contribution to crack growth resistance of TiAl-Nb alloys were studied using PST (polysynthetically twinned) crystals produced by directional solidification in FZ (floating zone) furnace. Lamellar orientations in the individual colonies are described using two angles defined with respect to the notch orientation: an in-plane kink angle and a through-thickness twist angle. Therefore, lamellar misorientation across an individual colony boundary is quantified as differences in these angles across the boundary. Crack growth resistance in colony boundary was identified by three-point bend test and crack advance was monitored by interrupted in situ test. From three-point bend test, it was found that the colony boundary could offer significant resistance to crack growth under large twist angle difference. Fracture toughness of type I specimens (in which crack propagates against lamellae boundaries) of the alloys decreased slightly with increasing Si and C contents and increased rapidly with decreasing Al content. The toughness for type I specimens was controlled by alpha(2)-alpha(2) spacing in which the delamination-type separation occurred. Compared to 47Al alloys, alpha(2)-alpha(2) spacing in 45Al alloys increased by decreasing Al content, therefore, fracture toughness increased rapidly. These results are discussed and the ability to improve toughness by changing Al content, Si and C addition in TiAl-Nb alloys produced by directional solidification is suggested. (C) 2007 Elsevier Ltd. All rights reserved
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