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Search Results: 1 - 10 of 403006 matches for " J. H. Chae "
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Enzymatic oxidation of aqueous pentachlorophenol
EYKim,HJChae,KHChu,
E. Y. Kim
,H. J. Chae,K. H. Chu

环境科学学报(英文版) , 2007,
Abstract: The influence of the nonionic surfactant Tween 80 on pentachlorophenol (PCP) oxidation catalyzed by horseradish peroxidase was studied.The surfactant was tested at concentrations below and above its critical micelle concentration (CMC).Enhancement of PCP removal was observed at sub-CMCs.The presence of Tween 80 in the reaction mixture reduced enzyme inactivation which occurred through a combination of free radical attack and sorption by precipitated products.A simple first-order model was able to simulate time profiles for enzyme inactivation in the presence or absence of Tween 80.At supra-CMCs,the surfactant caused noticeable reductions in PCP removal.presumably through micelle partitioning of PCP which precluded the hydrophobic PCP molecule from interacting with the enzyme.
A study on the derivation of a mean velocity formula from Chiu's velocity formula and bottom shear stress
T. H. Choo,I. J. Jeong,S. K. Chae,H. C. Yoon
Hydrology and Earth System Sciences Discussions , 2011, DOI: 10.5194/hessd-8-6419-2011
Abstract: This study proposed a new discharge estimation method using a mean velocity formula derived from Chiu's 2D velocity formula of probabilistic entropy concept and the river bed shear stress of channel. In particular, we could calculate the mean velocity, which is hardly measurable in flooding natural rivers, in consideration of several factors reflecting basic hydraulic characteristics such as river bed slope, wetted perimeter, width, and water level that are easily obtainable from rivers. In order to test the proposed method, we used highly reliable flow rate data measured in the field and published in SCI theses, estimated entropy M from the results of the mean velocity formula and, at the same time, calculated the maximum velocity. In particular, we obtained phi(M) expressing the overall equilibrium state of river through regression analysis between the maximum velocity and the mean velocity, and estimated the flow rate from the newly proposed mean velocity formula. The relation between estimated and measured discharge was analyzed through the discrepancy ratio, and the result showed that the estimate value was quite close to the measured data.
Characteristics of CALIOP attenuated backscatter noise: implication for cloud/aerosol detection
D. L. Wu, J. H. Chae, A. Lambert,F. F. Zhang
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011,
Abstract: A research algorithm is developed for noise evaluation and feature detection of the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Level 1 (L1) backscatter data with an emphasis on cloud/aerosol features in the upper troposphere and lower stratosphere (UT/LS). CALIOP measurement noise of the version v2.01 and v2.02 L1 backscatter data aggregated to (5 km) horizontal resolution is analyzed with two approaches in this study. One is to compare the observed and modeled molecular scatter profiles by scaling the modeled profile (with a fitted scaling factor α) to the observed clear-sky backscatter profiles. This scaling α value is sensitive to errors in the calibrated backscatter and the atmospheric model used. Most of the nighttime 532-nm α values are close to unity, as expected, but an abrupt drop occurred in October 2008 in the daytime 532-nm α, which is likely indicative of a problem in the v2.02 daytime calibrated data. The 1064-nm night α is generally close to 2 while its day α is ~3. The other approach to evaluate the lidar measurement noise is to use the calibrated lidar backscatter data at altitudes above 19 km. With this method, the 532-nm and 1064-nm measurement noises are analyzed and characterized individually for each profile in terms of the mean (μ) and standard deviation (σ), showing larger σ values in general over landmasses or bright surfaces during day and in radiation-hard regions during night. A significant increasing trend is evident in the nighttime 1064-nm σ, which is likely responsible for the increasing difference between the feature occurrence frequencies (532-nm vs. 1064-nm) derived from this study. For feature detection with the research algorithm, we apply a σ–based method to the aggregated L1 data. The derived morphology of feature occurrence frequency is in general agreement with that obtained from the Level 2 (L2) 05 km_CLAY+05 km_ALAY products at 5 km horizontal resolution. Finally, a normalized probability density function (PDF) method is employed to evaluate the day-night backscatter data in which noise levels are largely different. CALIOP observations reveal a higher probability of daytime cloud/aerosol occurrence than nighttime in the tropical UT/LS region for 532-nm total backscatters >0.01 km 1 sr 1.
A-train CALIOP and MLS observations of early winter Antarctic polar stratospheric clouds and nitric acid in 2008
A. Lambert, M. L. Santee, D. L. Wu,J. H. Chae
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: A-train Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Microwave Limb Sounder (MLS) observations are used to investigate the development of polar stratospheric clouds (PSCs) and the gas-phase nitric acid distribution in the early 2008 Antarctic winter. Observational evidence of gravity-wave activity is provided by Atmospheric Infrared Sounder (AIRS) radiances and infrared spectroscopic detection of nitric acid trihydrate (NAT) in PSCs is obtained from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Goddard Earth Observing System Data Assimilation System (GEOS-5 DAS) analyses are used to derive Lagrangian trajectories and to determine temperature-time histories of air parcels. We use CALIOP backscatter and depolarization measurements to classify PSCs and the MLS measurements to determine the corresponding gas-phase HNO3 as a function of temperature. For liquid PSCs the uptake of HNO3 follows the theoretical equilibrium curve for supercooled ternary solutions (STS), but at temperatures about 1 K lower as determined from GEOS-5. In the presence of solid phase PSCs, above the ice frost-point, the HNO3 depletion occurs over a wider range of temperatures (+2 to 7 K) distributed about the NAT equilibrium curve. Rapid gas-phase HNO3 depletion is first seen by MLS from from 23–25 May 2008, consisting of a decrease in the volume mixing ratio from 14 ppbv (parts per billion by volume) to 7 ppbv on the 46–32 hPa (hectopascal) pressure levels and accompanied by a 2–3 ppbv increase by renitrification at the 68 hPa pressure level. The observed region of depleted HNO3 is substantially smaller than the region bounded by the NAT existence temperature threshold. Temperature-time histories of air parcels demonstrate that the depletion is more clearly correlated with prior exposure to temperatures a few kelvin above the frost-point. From the combined data we infer the presence of large-size NAT particles with effective radii >5–7 μm and low NAT number densities <1 × 10 3 cm 3. This denitrification event is observed close to the pole in the Antarctic vortex before synoptic temperatures first fall below the ice frost point and before the widespread occurrence of large-scale NAT PSCs. An episode of mountain wave activity detected by AIRS on 28 May 2008 led to wave-ice formation in the rapid cooling phases over the Antarctic Peninsula and Ellsworth Mountains, seeding an outbreak of NAT PSCs that were detected by CALIOP and MIPAS. The NAT clouds formed at altitudes of 18–26 km in a polar freezing belt and appear to be composed of relatively small particles with estimated effective radii of around 1 μm and high NAT number densities >0.2 cm 3. This NAT outbreak is similar to an event previously reported from MIPAS observations in mid-June 2003.
The role of tropical deep convective clouds on temperature, water vapor, and dehydration in the tropical tropopause layer (TTL)
J. H. Chae, D. L. Wu, W. G. Read,S. C. Sherwood
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011,
Abstract: Temperature and water vapor variations due to clouds in the tropical tropopause layer (TTL) are investigated using co-located MLS, CALIPSO, and CloudSat data. Convective cooling occurs only up to the cloud tops, with warming above these heights in the TTL. Water vapor and ozone anomalies above the cloud tops are consistent with the warming being due to downward motion. Thicker clouds are associated with larger anomalies. Environmental water vapor below cloud tops can be either higher or lower than when clouds are absent, depending on the cloud top height. The critical factor determining the sign of this change appears to be the relative humidity. In general cloud-forming processes hydrate the environment below 16 km, where the air after mixing between cloud and the environmental air does not reach saturation, but clouds dehydrate above 16 km, as the larger temperature drop and the high initial relative humidity cause supersaturation to occur. Negative water vapor anomalies above cloud tops compared to clear skies suggest another dehydration mechanism operating above the detected cloud layers.
The role of tropical deep convective clouds on temperature, water vapor, and dehydration in the tropical tropopause layer (TTL)
J. H. Chae,D. L. Wu,W. G. Read,S. C. Sherwood
Atmospheric Chemistry and Physics Discussions , 2010, DOI: 10.5194/acpd-10-8963-2010
Abstract: Temperature and water vapor variations due to clouds in the TTL have been investigated using co-located MLS, CALISPO, and CloudSat data. Convective cooling occurs only up to cloud top heights, but there is warming above these heights in the TTL. Water vapor and ozone anomalies above cloud top heights support that the warming anomalies occur due to downward motion. Thicker clouds cause a greater magnitude of the temperature anomalies. Water vapor of the environment below cloud tops can either increase or decrease, depending on the cloud top height. The critical factor, which divides these different water vapor variations below cloud tops, is the relative humidity. Clouds hydrate the environment below 16 km, where the air after mixing between cloud and the environmental air does not reach saturation, but clouds dehydrate above 16 km, due to the supersaturation because of the larger temperature drop and the high initial relative humidity. Water vapor above cloud tops has negative anomalies compared to clear skies and suggests another dehydration mechanism.
No effect of recumbency duration on the occurrence of post-lumbar puncture headache with a 22G cutting needle
Sung R Kim, Hyun S Chae, Mi J Yoon, Jung H Han, Kwang J Cho, Sun J Chung
BMC Neurology , 2012, DOI: 10.1186/1471-2377-12-1
Abstract: A non-equivalent control/experimental pre-/post-test study design was used. Seventy consecutive patients were prospectively enrolled between July 2007 and July 2008. Thirty-five patients underwent supine recumbence for four hours after lumbar puncture (Group 1) and 35 patients underwent supine recumbence for one hour (Group 2).The overall frequency of PLPH was 31.4%. The frequency of PLPH was not significantly different between the Group 1 (28.6%) and Group 2 (34.3%) (P = 0.607). In patients with PLPH, the median severity (P = 0.203) and median onset time of PLPH (P = 0.582) were not significantly different between the two groups. In a logistic regression analysis, the previous history of post-lumbar puncture headache was a significant risk factor for the occurrence of PLPH (OR = 11.250, 95% CI: 1.10-114.369, P = 0.041).Our study suggests that short duration (one hour) of supine recumbence may be as efficient as long duration (four hours) of supine recumbence to prevent PLPH.Lumbar puncture (LP) is an essential medical procedure in many clinical practices. Although LP is relatively safe, several adverse events have been reported, including headache, hemorrhage, local pain, and infections[1]. Among these adverse events, post-lumbar puncture headache (PLPH) is the most frequent and disabling in many patients. The International Headache Society has defined a PLPH as a headache that develops within 5 days of dural puncture and resolves within 1 week spontaneously or within 48 hours after effective treatment of the spinal fluid leak (usually by epidural blood patch)[2]. The headache usually worsens within 15 minutes after sitting or standing, and disappears or improves within 15 minutes after lying down. The headache is generally located in the frontal or occipital areas, or both, but may also involve the neck and upper shoulders. The severe PLPH may be associated with nausea, vomiting, blurred vision, vertigo, hearing alteration, and back pain[3].PLPH has been considere
Room temperature ferromagnetism in chemically synthesized ZnO rods
Shalendra Kumar,Y. J. Kim,B. H. Koo,S. Gautam,K. H. Chae,Ravi Kumar,C. G. Lee
Physics , 2009, DOI: 10.1016/j.matlet.2008.09.057
Abstract: We report structural and magnetic properties of pure ZnO rods using X-ray diffraction (XRD), magnetization hysteresis (M-H) loop and near edge x-ray fine structure spectroscopy (NEXAFS) study at O K edge. Sample of ZnO was prepared by co-precipitation method. XRD and selective area electron diffraction measurements infer that ZnO rods exhibit a single phase polycrystalline nature with wurtzite lattice. Field emission transmission electron microscopy, field emission scanning electron microscopy micrographs infers that ZnO have rod type microstructures with dimension 200 nm in diameter and 550 nm in length. M-H loop studies performed at room temperature display room temperature ferromagnetism in ZnO rods. NEXAFS study reflects absence of the oxygen vacancies in pure ZnO rods.
Optical investigations on electronic structure changes related to the metal-insulator transition in VO2 film
C. H. Koo,J. S. Lee,M. W. Kim,Y. J. Chang,T. W. Noh,J. H. Jung B. G. Chae,H. -T. Kim
Physics , 2005,
Abstract: We investigated optical absorption coefficient spectra of an epitaxial VO2 film in wide photon energy (0.5 - 5.0 eV) and temperature (100 - 380 K) regions. In its insulating phase, we observed two d-d transition peaks around 1.3 eV and 2.7 eV and a charge transfer peak around 4.0 eV. As temperature goes above the metal-insulator transition temperature near 340 K, a large portion of the spectral weight of the peak around 4.0 eV becomes redistributed and a Drude-like peak appears. We initially applied the band picture to explain the details of the spectral weight changes, especially the temperature-dependent shift at 2.7 eV, but failed. To check whether the spectral changes are optical signatures of the electron-electron correlation effects, we applied the Hubbard model which takes into account orbital degeneracy. This orbitally degenerate Hubbard model could explain the details of the temperature-dependent peak shifts quite well. In addition, from the peak assignments based on the orbitally degenerate Hubbard model, we could obtain the values of U + delta(~ 3.4 eV) and JH (~ 0.7 eV), where U, delta, and JH are the on-site Coulomb repulsion energy, the crystal field splitting between the t2g bands, and the Hund's rule exchange energy, respectively. Our spectroscopic studies indicate that the electron-electron correlation could play an important role in the metal-insulator transition of VO2.
Scaling behaviors of RESET voltages and currents in unipolar resistance switching
S. B. Lee,S. C. Chae,S. H. Chang,J. S. Lee,S. Seo,B. Kahng,T. W. Noh
Physics , 2008, DOI: 10.1063/1.3036532
Abstract: Unipolar switching phenomena have attracted a great deal of recent attention, but the wide distributions of switching voltages still pose major obstacles for scientific advancement and practical applications. Using NiO capacitors, we investigated the distributions of the RESET voltage and current. We found that they scaled with the resistance value Ro in the low resistance state, and that the scaling exponents varied at Ro = 30 Ohm. We explain these intriguing scaling behaviors and their crossovers by analogy with percolation theory. We show that the connectivity of conducting filaments plays a crucial role in the RESET process.
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