5,351 research outputs found
Prediction of maximum yields of metabolites and optimal pathways for their production by metabolic flux analysis
No full textThe intracellular metabolic fluxes can be calculated by metabolic flux analysis, which uses a stoichiometric model for the intracellular reactions along with mass balances around the intracellular metabolites. In this study, metabolic flux analyses were carried out to estimate flux distributions for the maximum in silico yields of various metabolites in Escherichia coli. The maximum in silico yields of acetic acid and lactic acid were identical to their theoretical yields. On the other hand, the in silico yields of succinic acid and ethanol were only 83% and 6.5% of their theoretical yields, respectively. The lower in silico yield of succinic acid was found to be due to the insufficient reducing power, but this lower yield could be increased to its theoretical yield by supplying more reducing power. The maximum theoretical yield of ethanol could be achieved, when a reaction catalyzed by pyruvate decarboxylase was added in the metabolic network. Furthermore, optimal metabolic pathways for the production of various metabolites could be proposed, based on the results of metabolic flux analyses. In the case of succinic acid production, it was found that the pyruvate carboxylation pathway should be used for its optimal production in E. coli rather than the phosphoenolpyruvate carboxylation pathway
Capacity improvement in CDMA downlink with orthogonal code-hopping multiplexing
No full textOrthogonal code-hopping multiplexing (OCHM) is a statistical multiplexing scheme designed to increase the number of allowable downlink channels in code division multiple access (CDMA) systems. OCHM is expected to compensate for a lack of codewords in future communication systems. In CDMA systems including OCHM, system capacity is limited by the number of codewords and power (or interference), and the maximum system capacity is determined by a stronger limitation between them. Call blockings due to power limitation may occur firstly if downlink channels demand large E-b/I-O values and a high-channel activity. On the other hand, code limitation may occur prior to power limitation in CDMA. The maximum system capacities determined by both code and power limitations must be known, even in OCHM. However, previous studies on OCRM system capacity focused only on increasing the number of multiplexed users with no consideration of the power limitation. In this paper, the overall system capacity of OCHM considering both code and power limitations was evaluated. For this analysis, the transmission chip energy of base station (BS) and inner/outer-cell interference is mathematically derived in a multicell and multiuser environment. The downlink system capacity for OCHM is larger than for orthogonal code division multiplexing (OCDM) as other cell interference (OCI), mean channel activity, and the required E-b/I-O value decrease.This work was supported in part by MIC, Korea, under the BrOMA
Information Technology Research Center (ITRC) support program supervised
by Institute of Information Technology Assessment (IITA)
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
Performance Evaluation of 1X-EV-DO rev.A with a Per-User Throughput Based Scheduling Algorithm
No full textMicrostructure control of DS NiAi/Ni3Al alloy by fabrication of columnar-grained NiAl martensite
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Effects of ternary elements on phase transformation and microstructure of NiAl/Ni3Al two-phase alloys
No full textThe microstructural evolution of the beta-NiAl/gamma'-Ni3Al two-phase was investigated in (Ni66Al34)(100-chi)X-chi (X Ti, Si, Nb; X=0-4 at.%) alloys. Three different microstructures, such as lamellar, mesh and Widmanstatten, were obtained with the phase transformation procedure which depends on the A(s) (austenite start) temperatures and on the ternary elements. In the case of A(s) > 250 degreesC, lamellar microstructure was formed by the phase transformation, beta'-martensite-->Ni5Al3 --> beta + gamma', in all the alloys. In the case of 20 degreesC < A(s) < 250 degreesC, the phase transformation behavior and the microstructure changed with addition of the alloy elements. Mesh type microstructure was formed in the alloys containing Ti or Nb where the beta --> Ni5Al3 transformation occurred quickly, while Widmanstatten structure was formed in the alloys containing Si where the beta-Ni5Al3 transformation occurred very slowly. This phase transformation showed a significant phase transformation procedure in the formation of the mesh type microstructure, which was different from the morphology of the original martensite plates. In the case of A(s) < 20degreesC the beta-NiAl remained unchanged at room temperature because the martensitic temperature decreased below room temperature. Widmanstatten microstructure formed through the single phase transformation, beta --> beta + gamma'. (C) 2004 Elsevier Ltd. All rights reserved
Simulator on the WCDMA High Speed Downlink Packet Access System and Performance Evaluation of a Multiplexing Scheme with Hybrid Schedulers
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