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37 results on '"CHOO, K. Y."'

1. Fractal Analysis On Internet Traffic Time Series

Author

Chong, K. B. and Choo, K. Y.

Subjects
Physics - Computational Physics, Physics - Data Analysis, Statistics and Probability
Abstract

Fractal behavior and long-range dependence have been observed in tele-traffic measurement and characterization. In this paper we show results of application of the fractal analysis to internet traffic via various methods. Our result demonstrate that the internet traffic exhibits self-similarity. Time-scale analysis show to be an effective way to characterize the local irregularity. Based on the result of this study, these two Internet time series exhibit fractal characteristic with long-range dependence., Comment: 10 pages, 6 figures

Published
2002

5. Positive and negative temperature dependences of electron-impact ionization in In0.53Ga0.47As.

Author

Choo, K. Y. and Ong, D. S.

Subjects
*ELECTRON impact ionization, *ELECTRON temperature, *ELECTRIC fields, *ELECTRONIC excitation, *TEMPERATURE, *IONIZATION (Atomic physics), *FIELD theory (Physics)
Abstract

The electron-impact ionization coefficient (α) in In0.53Ga0.47As increases with temperature at electric fields below 200 kV/cm, in contrast to most crystalline semiconductors. It exhibits conventional negative temperature dependence at higher fields. A four-valley analytical band Monte Carlo model is used to study this anomalous behavior. The simulations show that both alloy scattering and the temperature dependence of the impact ionization threshold energy contribute to the temperature dependence of α. At low fields, we find that most ionization events occur in the first conduction band causing an increase of α with temperature in In0.53Ga0.47As. At high fields, α decreases with temperature again because of the reduced hot-electron population in the second conduction band. [ABSTRACT FROM AUTHOR]

Published
2005
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6. Fermentation of red dragon fruit (Hylocereus polyrhizus) for betalains concentration.

Author

Choo, K. Y., Kho, C., Ong, Y. Y., Thoo, Y. Y., Lim, L. H., Tan, C. P., and Ho, C. W.

Subjects
FERMENTATION, BETALAINS, BETANIN, FLAVONOIDS, BIOACTIVE compounds
Abstract

Red dragon fruits (RDF) contain high levels of health-promoting betalains but its bioavailability in plasma is low (<1.0%). Therefore, fermentation technique was adopted to improve the yield of betalains presenting in fermented red dragon fruit drink (FRDFD) via concentration. Fermentation of RDF was carried out with autochthonous strains. The objectives of present study were to evaluate 1) the effects of fermentation duration 2) white refined cane sugar to flesh ratio and 3) types of sugar on betalainic (betanin, isobetanin) and non-betalainic phenolic compounds in FRDFD using HPLC-DAD, total phenolic content (TPC) and total flavonoid content (TFC) assay. Results indicated that all fermentation parameters showed a significant effect (p<0.05) on the yields of betalainic (betanin, isobetanin) and non-betalainic phenolic compounds in FRDFD. The best fermentation parameters were 7 days fermentation at 10% white refined cane sugar to flesh ratio. The highest concentration of betanin, TPC and TFC achieved were 131.68 g/L, 1136.85 mg GAE/100mL and 10.39 mg CE/100mL respectively. The concentration of betanin obtained through best fermentation parameters (131.68 g/L) in present study has increased nine-fold compared to non-optimized fermentation (14.23 g/L). This indicated that fermentation is a potential economic processing technique to concentrate bioactive compounds present in functional drinks. [ABSTRACT FROM AUTHOR]

Published
2018

11. Yields of O2(b 1 Sigma g +) from reactions of HO2

Author

Keyser, L. F, Choo, K. Y, and Leu, M. T

Subjects
Inorganic And Physical Chemistry
Abstract

The production of O2(b 1 Sigma g +) has been monitored for several reactions of the HO2 radical at 300 K using a discharge-flow apparatus with resonance fluorescence and chemiluminescence detection. In all cases, the resulting quantum efficiencies were found to be less than 0.03. O2(b) was observed when F atoms were added to H2O2 in the gas phase. The signal strengths of O2(b) were proportional to initial concentrations of HO2 formed by the F + H2O2 reaction. Observed /O2(b)/, /HO2/, and /OH/ vs /F/0 were analyzed using a simple three-step mechanism and a more complete computer simulation with 22 reaction steps. The results indicate that the F + HO2 reaction yields O2(b) with an efficiency of (3.6 + or - 1.4) x 10 to the -3rd. Yields from the O + OH2 reaction were less than 0.02, indicating that this reaction cannot be a major source of the O2(b) emission observed in the earth's nightglow.

Published
1985

14. Anomalous Charge Transport in Disordered Organic Semiconductors.

Author

Muniandy, S. V., Woon, K. L., and Choo, K. Y.

Subjects
ORGANIC semiconductors, SEMICONDUCTOR defects, ELECTRON transport, FOKKER-Planck equation, DIFFERENTIAL equations, FRACTIONAL calculus, RANDOM walks
Abstract

Anomalous charge carrier transport in disordered organic semiconductors is studied using fractional differential equations. The connection between index of fractional derivative and dispersion exponent is examined from the perspective of fractional Fokker-Planck equation and its link to the continuous time random walk formalism. The fractional model is used to describe the bi-scaling power-laws observed in the time-of flight photo-current transient data for two different types of organic semiconductors. [ABSTRACT FROM AUTHOR]

Published
2011
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17. The Absolute Measurement of Rate Constants for Some Key Reactions Involving Free Radicals.

Author

STANFORD RESEARCH INST MENLO PARK CALIF PHYSICAL SCIENCES DIV, Alfassi,Z. B., Beadle,P. C., Benson,S. W., Choo,K. Y., Golden,D. M., STANFORD RESEARCH INST MENLO PARK CALIF PHYSICAL SCIENCES DIV, Alfassi,Z. B., Beadle,P. C., Benson,S. W., Choo,K. Y., and Golden,D. M.

Abstract

Absolute values of the rate constant for isopropyl radical combination have been determined over the temperature range 683-808K. It was found that isopropyl radicals react heterogeneously in a first-order manner with fused silica, probably to produce propylene. The four species (n-butane, 2,3-dimethylbutane, 2,2',3,3',-tetramethylbutane, and isobutane) were decomposed under (VLPP) very low-pressure conditions at temperatures in the vicinity of 1100K. Three model transition states were constructed that fit the low-pressure data thus obtained. Study of the pyrolysis, tBu-NO to tBu+ NO by VLPP yielded the Arrhenius parameters. A new free-volume model for the transition state for dissociation is shown to fit the data.

Published
1973

37. Estrogen attenuates cell death induced by carboxy-terminal fragment of amyloid precursor protein in PC12 through a receptor-dependent pathway.

Author

Chae HS, Bach JH, Lee MW, Kim HS, Kim YS, Kim KY, Choo KY, Choi SH, Park CH, Lee SH, Suh YH, Kim SS, and Lee WB

Subjects
Alzheimer Disease metabolism, Alzheimer Disease pathology, Alzheimer Disease physiopathology, Animals, Carbon Dioxide antagonists & inhibitors, Cell Death physiology, Estrogen Antagonists pharmacology, Nerve Degeneration metabolism, Nerve Degeneration pathology, Nerve Degeneration physiopathology, PC12 Cells drug effects, PC12 Cells metabolism, PC12 Cells pathology, Peptide Fragments antagonists & inhibitors, Protein Structure, Tertiary drug effects, Protein Structure, Tertiary physiology, Rats, Receptors, Estrogen drug effects, Tamoxifen pharmacology, Amyloid beta-Protein Precursor metabolism, Carbon Dioxide toxicity, Cell Death drug effects, Estradiol pharmacology, Neuroprotective Agents pharmacology, Peptide Fragments toxicity, Receptors, Estrogen metabolism
Abstract

In the present study, we investigated effects of estrogen on cell death induced by carboxy-terminal fragment of amyloid precursor protein (CT), a candidate causative substance in the pathogenesis of Alzheimer's disease. 17 beta-Estradiol attenuated CT-induced cell death in PC12 cells, whereas 17 alpha-estradiol, nonestrogenic stereoisomer, did not exert any significant protective effect on CT-induced cell death. These results suggest that protective effects of estrogen may be mediated by estrogen receptor (ER) in PC12 cells. To confirm the results, we determined the effects of tamoxifen, an estrogen receptor antagonist. Tamoxifen blocked the protective effects of 17 beta-estradiol, although it did not affect those of 17 alpha-estradiol. Overall, it might be thought that the protective effect of estradiol on CT-induced cell death is achieved by hormonal properties mediated through the estrogen receptor rather than the structural properties as a reducing agent., (Copyright 2001 Wiley-Liss, Inc.)

Published
2001
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