• Journal of Environmental Health Sciences
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• v.25 no.3
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• pp.64-69
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• 1999

This study was carried out the removal of Cr(VI) which was known to the toxic pollutant in industry using the process of UV and TiO$_2$ photocatalyst in a circular type reactor. In this experiment, the series of photocatalytic process for the removal of Cr(VI) has been selected as a model reaction in a circular type reactor in order to obtain the basic data on the influence of various experimental parameters such as circulation flow rate, pH of solution, initial Cr(VI) light illumination and TiO$_2$ dosage, and salicylic acid concentration. The results of this study were as follows; 1. With both UV light illumination and TiO$_2$ present, Cr(VI) was more effectively eliminated than with either UV or TiO$_2$ alone. 2. As the circulation flow rate of solution increased, the removal efficiency of Cr(VI) was increased. However, over 2.4 l/min of circulation flow rate, the efficiency wa limited. 3. A increase in the photocatalytic removal of Cr(VI) was noticed with decreasing pH. 4. An increase in the photocatalytic removal of Cr(VI) was noticed with decreasing Initial Cr(VI) concentration and first order kinetics was observed from the result at different initial concentration of Cr(VI). 5. Photocatalytic removal efficiency of Cr(VI) increased with increasing TiO$_2$ dosage. However, over 1.0 g/l of TiO$_2$ dosage, the efficiency reached a plateau. 6. As low concentration of saliculic acid were added, there was an increase in the removal efficiency of Cr(VI). However, over 300 mg/l of salicylic acid, the efficiecy was decreased. It eas found that application of photocatalysis to water treatment that contains both Cr(VI) and salicylic acid was possible.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.6000-6007
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• 2013

Cr(VI)-heterocyclic complex[Cr(VI)-isoquinoline] was synthesized by the reaction between of heterocyclic compound(isoquinoline) and chromium trioxide, and characterized by IR and ICP analysis. The oxidation of benzyl alcohol using Cr(VI)-isoquinoline in various solvents showed that the reactivity increased with the increase of the dielectric constant(${\varepsilon}$), in the order : cyclohexene$CH_3$, m-Br, m-$NO_2$). Electron- donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.69(308K). The observed experimental data have been ratiolized. The hydride ion transfer causes the prior formation of a chromate ester in the rate-determining step.

• Korean Journal of Radiology
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• v.25 no.4
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• pp.351-362
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• 2024

Objective: To measure inter-reader agreement and identify associated factors in interpreting complete response (CR) on magnetic resonance imaging (MRI) following chemoradiotherapy (CRT) for rectal cancer. Materials and Methods: This retrospective study involved 10 readers from seven hospitals with experience of 80-10210 cases, and 149 patients who underwent surgery after CRT for rectal cancer. Using MRI-based tumor regression grading (mrTRG) and methods employed in daily practice, the readers independently assessed mrTRG, CR on T2-weighted images (T2WI) denoted as mrCR_T2W, and CR on all images including diffusion-weighted images (DWI) denoted as mrCR_overall. The readers described their interpretation patterns and how they utilized DWI. Inter-reader agreement was measured using multi-rater kappa, and associated factors were analyzed using multivariable regression. Correlation between sensitivity and specificity of each reader was analyzed using Spearman coefficient. Results: The mrCR_T2W and mrCR_overall rates varied widely among the readers, ranging 18.8%-40.3% and 18.1%-34.9%, respectively. Nine readers used DWI as a supplement sequence, which modified interpretations on T2WI in 2.7% of cases (36/1341 [149 patients × 9 readers]) and mostly (33/36) changed mrCR_T2W to non-mrCR_overall. The kappa values for mrTRG, mrCR_T2W, and mrCR_overall were 0.56 (95% confidence interval: 0.49, 0.62), 0.55 (0.52, 0.57), and 0.54 (0.51, 0.57), respectively. No use of rectal gel, larger initial tumor size, and higher initial cT stage exhibited significant association with a higher interreader agreement for assessing mrCR_overall (P ≤ 0.042). Strong negative correlations were observed between the sensitivity and specificity of individual readers (coefficient, -0.718 to -0.963; P ≤ 0.019). Conclusion: Inter-reader agreement was moderate for assessing CR on post-CRT MRI. Readers' varying standards on MRI interpretation (i.e., threshold effect), along with the use of rectal gel, initial tumor size, and initial cT stage, were significant factors associated with inter-reader agreement.

• Structural Engineering and Mechanics
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• v.12 no.1
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• pp.17-34
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• 2001

The frictionless contact problem for a layered composite which consists of two elastic layers having different elastic constants and heights resting on two simple supports is considered. The external load is applied to the layered composite through a rigid stamp. For values of the resultant compressive force P acting on the stamp vertically which are less than a critical value $P_{cr}$ and for small flexibility of the layered composite, the continuous contact along the layer - the layer and the stamp - the layered composite is maintained. However, if the flexibility of the layered composite increases and if tensile tractions are not allowed on the interface, for P > $P_{cr}$, a separation may be occurred between the stamp and the layered composite or two elastic layers interface along a certain finite region. The problem is formulated and solved for both cases by using Theory of Elasticity and Integral Transform Technique. Numerical results for $P_{cr}$, separation initiation distance, contact stresses, distances determining the separation area, and the vertical displacement in the separation zone between two elastic layers are given.

• Economic and Environmental Geology
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• v.38 no.3 s.172
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• pp.221-236
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• 2005

In order to investigate the contamination levels and dispersion patterns of heavy metals such as Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn by urbanization, soils beneath roadside-trees and leaves of Ginkgo biloba were collected from Seoul area during October to November in 2001. All tree leaves were grouped into washed and unwashed ones. The pH of most soil ranges from 6 to 9 indicating a weak acidic and alkaline. The element couples of Cd-Co, Cr-Ni and Zn-Cu-Pb have good correlation in soils, and contamination sources of Cd-Co, Cr-Ni and Zn-Cu-Pb could be similar. High correlation coefficients among Pb, Cu and Zn in G. biloba indicates that these elements show the similar behavior during the metabolism processes. From the results of pollution index calculation for soils, industrialized and heavy traffic area were severly polluted by heavy metals such as Cd, Cu, Pb and Zn. By the discriminant analysis, industrialized and heavy traffic areas are enriched in the order of Ni> Cr> Pb. Cadmium is useful to discriminate between industrialized and heavy traffic areas, Co and Pb are highly enhanced in heavy traffic area.

• Journal of Magnetics
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• v.7 no.3
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• pp.115-125
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• 2002

We proposed a novel method to evaluate the magnetic properties of the initial layer and the columnar structure separately for CoCr-based perpendicular recording media. We show that the thickness of the initial layer and the intrinsic magnetocrystalline anisotropy of columnar structure can be quantitatively evaluated using the plotted product of perpendicular anisotropy to magnetic film thickness versus magnetic film thickness ($K_{u{\bot}}^{ex{p.}}$ $\times$ d$_{mag.}$ vs. d$_{mag.}$ plot). Based on the analyses, it is found that: (1) compared with CoCrPtTa media, CoCrPtB media have relatively thin initial layer, and have fine grains with homogeneous columnar structure with c-plane crystallographic orientation; (2) CoCrPtB media can be grown epitaxially on Ru or CoCr/C intermediate layer, and as the result, the magnetic properties of the media within thin thickness region of d$_{mag.}$ $\leq$ 20 nm is significantly improved; (3) the key issue of material investigation for CoCr-based perpendicular recording media will be focused on how to fabricate c-plane-oriented columnar grains well isolated with nonmagnetic substance in epitaxial-growth media, while maintaining the thermal stability of the media.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.405-412
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• 2004

Cosmological shocks form as an inevitable consequence of gravitational collapse during the large scale structure formation and cosmic-rays (CRs) are known to be accelerated at collisionless shocks via diffusive shock acceleration (DSA). We have calculated the evolution of CR modified shocks for a wide range of shock Mach numbers and shock speeds through numerical simulations of DSA in 1D quasi-parallel plane shocks. The simulations include thermal leakage injection of seed CRs, as well as pre-existing, upstream CR populations. Bohm-like diffusion is assumed. We show that CR modified shocks evolve to time-asymptotic states by the time injected particles are accelerated to moderately relativistic energies (p/mc $\ge$ 1), and that two shocks with the same Mach number, but with different shock speeds, evolve qualitatively similarly when the results are presented in terms of a characteristic diffusion length and diffusion time. We find that $10^{-4} - 10^{-3}$ of the particles passed through the shock are accelerated to form the CR population, and the injection rate is higher for shocks with higher Mach number. The CR acceleration efficiency increases with shock Mach number, but it asymptotes to ${\~}50\%$ in high Mach number shocks, regardless of the injection rate and upstream CR pressure. On the other hand, in moderate strength shocks ($M_s {\le} 5$), the pre-existing CRs increase the overall CR energy. We conclude that the CR acceleration at cosmological shocks is efficient enough to lead to significant nonlinear modifications to the shock structures.

• Bulletin of the Korean Chemical Society
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• v.32 no.9
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• pp.3437-3442
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• 2011

An on-line flow injection analysis with dual pre-concentration method was developed to determine the ultra trace tri and hexavalent chromium in water. In this system, the cation and anion pre-concentration columns were combined with a 10-port injection valve and then used to separate and concentrate Cr (III) and Cr (VI) selectively. The two species of concentrated chromium were sequentially eluted and determined by using HCl-KCl buffer of pH 1.8 as an eluent. Cr (III) was oxidized by hydrogen peroxide to Cr (VI). It was detected spectrophotometrically at 548 nm by complexation with DPC (diphenylcarbazide). Several factors such as concentration of $H_2O_2$, DPC and coil length in reaction condition were optimized. The linear range for Cr (III) and Cr (VI) was 0.1-50 ${\mu}g$/L. The limit of detections ($3{\sigma}$) of Cr (III) and Cr (VI) were 52 ng/L and 44 ng/L under the optimized FIA system, and their recoveries 98% and 103%, respectively. This method was applied to analyze contamination level of chromium species in tap water, groundwater and bottled water.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.242-244
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• 1996

The effects of $Co_{67}$C $r_{33}$ underlayer on the crystallographec and magnetic characteristics of the Co-Cr-Ta layer deposited on the underlayer was investigated. The diffraction intensity $I_{p(002)}$ of Co-Cr-Ta layers on the $Co_{67}$C $r_{33}$ layer was stronger than that of single layer and Co-Cr-Ta/Ti double layer. Therefore, the crystallinity of Co-Cr-Ta layer was improved by the $Co_{67}$C $r_{33}$ underlayers rather than Ti ones. However, the coercivity $H_{c}$ of Co-Cr-Ta layers deposited on $Co_{67}$C $r_{33}$ underlayer was as low as 250 Oe even at substrate temperature of 22$0^{\circ}C$. This $H_{c}$ decrease seems to be attributed to the effect of the $Co_{67}$C $r_{33}$ underlayer as well as interval time between deposition of the underlayer and the Co-Cr-Ta layer.yer.layer.yer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.5
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• pp.418-422
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• 1998

The Co-Cr films are one of the most suitable candidates for perpendicular magnetic recording media. The facing targets sputtering(FTS) system has a advantage of preparing films over a wide range of working gas pressure on plasma-free substrate. In this study, we investigated the possibility of employing FTS system for depositing Co-Cr films. The Co-Cr thin films were deposited with various sputter gas pressure($P_Ar$, 0.1~10mTorr) by using FTS apparatus at temperature of $40^{\circ}C and 220^{\circ}C$, respectively. Crystallographic and magnetic characteristics were evaluated by x-ray diffractometry (XRD) and vibrating sample magnetometer(VSM), respectively. Under argon gas pressure at 0.1mTorr, films with morphologically dense microstructure, good c-axis orientation and higher coercivity were obtained. It has been confirmed that the FTS system is very useful for preparing Co-Cr thin film recording media.