Molecular Theory of Plastic Deformation (Ⅲ)$^*$

Kim, Jae-Hyun,Ree, Tai-Kyue,Kim, Chang-Hong Korean Chemical Society 1981 Bulletin of the Korean Chemical Society Vol.2 No.3

(1) The flow data of f (stress) and ${\dot{s}$ (strain rate) for Fe and Ti alloys were plotted in the form of f vs. -ln ${\dot{s}$ by using the literature values. (2) The plot showed two distinct patterns A and B; Pattern A is a straight line with a negative slope, and Pattern B is a curve of concave upward. (3) According to Kim and Ree's generalized theory of plastic deformation, pattern A & B belong to Case 1 and 2, respectively; in Case 1, only one kind of flow units acts in the deformation, and in Case 2, two kinds flow units act, and stress is expressed by $f={X_1f_1}+{X_2f_2}$where $f_1\;and\;f_2$ are the stresses acting on the flow units of kind 1 and 2, respectively, and $X_1,\;X_2$ are the fractions of the surface area occupied by the two kinds of flow units; $f_j=(1/{\alpha}_j) sinh^{-1}\;{\beta}_j{{\dot{s}}\;(j=1\;or\;2)$, where $1/{\alpha}_j\;and\;{\beta}_j$ are proportional to the shear modulus and relaxation time, respectively. (4) We found that grain-boundary flow units only act in the deformation of Fe and Ti alloys whereas dislocation flow units do not show any appreciable contribution. (5) The deformations of Fe and Ti alloys belong generally to pattern A (Case 1) and B (Case 2), respectively. (6) By applying the equations, f=$(1/{\alpha}_{g1}) sinh^-1({\beta}_{g1}{\dot{s}}$) and $f=(X_{g1}/{\alpha}_{g1})sinh^{-1}({\beta}_{g1}{\dot{s}})+ (X_{g2}/{\alpha}_{g2})\;shih^{-1}({\beta}_{g2}{\dot{s}})$ to the flow data of Fe and Ti alloys, the parametric values of $x_{gj}/{\alpha}_{gj}\;and\;{\beta}_{gs}(j=1\;or\;2)$ were determined, here the subscript g signifies a grain-boundary flow unit. (7) From the values of ($({\beta}_gj)^{-1}$) at different temperatures, the activation enthalpy ${\Delta}H_{gj}^{\neq}$ of deformation due to flow unit gj was determined, ($({\beta}_gj)^{-1}$) being proportional to .$k_{gj}$, the jumping frequency (the rate constant) of flow unit gj. The ${\Delta}H_{gj}\;^{\neq}$ agreed very well with ${\Delta}H_{gj}\;^{\neq}$ (self-diff) of the element j whose diffusion in the sample is a critical step for the deformation as proposed by Kim-Ree's theory (Refer to Tables 3 and 4). (8) The fact, ${\Delta}H_{gj}\;^{\neq}={\Delta}H_{j}\;^{\neq}$ (self-diff), justifies the Kim-Ree theory and their method for determining activation enthalpies for deformation. (9) A linear relation between ${\beta}^{-1}$ and carbon content [C] in hot-rolled steel was observed, i.e., In ${\beta}^{-1}$ = -50.2 [C] - 40.3. This equation explains very well the experimental facts observed with regard to the deformation of hot-rolled steel..

Superplastic Deformation in the Low Stress Region

Jang, Chun-Hag,Kim, Chang-Hong,Ree, Tai-Kyue Korean Chemical Society 1984 Bulletin of the Korean Chemical Society Vol.5 No.2

Superplastic alloys generally exhibit a three-stage sigmoidal variation of stress (f) with strain rate (s), the stages being named region 1, 2 and 3 according to the increasing order of stress or strain rate. In the recent years, two different types of papers have been published on the plastic deformation of Zn-22% Al eutectoid in region Ⅰ differing in strain-rate sensitivity m (= dln f/dln s). In this paper, the data of the two groups have been analysed by applying Kim and Ree's theory of superplastic deformation. (1) We obtained the parametric values of $X_{gj}/{\alpha}_{gj}\;and\;{\beta)_{gj}$ (g: grain boundary, j = 1,2 indicating flow units) appearing in Kim and Ree's theory [Eq. (2a)]. (2) It was found that the value of $X_{g^2}/{\alpha}_{g^2}$ is small for the group data with small m, i.e., ${\alpha}_{g^2}$, which is proportional to the size of flow unit g2, is large whereas ${\alpha}_{g^2}$ is small for the groups data with large m, i.e., the size of the flow unit g2 is small. In other words, the two types of behavior occur by the size difference in the flow units. (3) From the ${\beta}_{gj}$ value, which is proportional to the relaxation time of flow unit gj, the ${\Delta}H_{gj}^{\neq}$ for the flow process was calculated, and found that ${\Delta}H_{g^2}^{\neq}$ is large for the group data with small m whereas it is small for the group data with large m. (4) The flow-unit growth was studied, but it was concluded that this effect is not so important for differentiating the two groups. (5) The difference in ${\alpha}_{g^2}$ and in the growth rate of flow units is caused by minute impurities, crystal faults, etc., introduced in the sample preparation.

톨루엔 취급 근로자의 ALDH2 Genetic Polymorphism에 따른 뇨중 마뇨산 배설량

김창윤,정종학,권오춘,김성용,이중정,주리 大韓産業醫學會 1997 대한직업환경의학회지 Vol.9 No.2

In this study we evaluated the effects of the genetic polymorphism of aldehyde dehydrogenase2 (ALDH2) on the toluene metabolism and determined biological exposure indices(BEIs) for toluene by the genotypes of ALDH2. The study subject were 77 men workers who are handling toluene in a video tape manufacturing factory and a textile company. Through the face-to-face interview, the information about smoking and drinking behavior was obtained. For determination of ALDH2 polymorphism, 5ml of venous blood sample was obtained from each subject after informed consent. DNA was extracted from the buffy coat and ALDH2 genotyping were performed using a polymerase chain reaction(PCR) method. The genotype of ALDH2 was classified into the homozygous genotype of normal ALDH2(NN), and the heterozygous genotype of normal and inactive ALDH2(ND), and homozygous genotype of an inactive ALDH2(DD). The concentration of hippuric acid (HA), the main metabolite of toluene, was determined in urine specimens collected at the end of shift, corrected with creatinine(HA/C), and compared with BEI for toluene, which is 2.5 g/g creatinine. The personal exposure level of toluene were monitored, using personal air sampler and analyzed by gas chromatography. The frequencies of the three genotypes in this study subject were, NN : 45 (58.4%), ND : 26 (33.8%) and DD : 6 (7.8%), and frequencies of the genotypes in the middle or heavy toluene exposure workers were not significantly different from those in the mild toluene exposure workers. The frequencies of the DD type of ALDH2 was lower among alcohol drinkers than among non-drinkers. The urinary HA concentration of DD group was significantly lower than that of the NN or ND group, which suggests that the HA formation from toluene decreased in DD group. Regression lines were used to estimate the BEIs of the NN, ND, and DD groups. NN : y = 0.0085x + 0.23, r = 0.90 ND : y = 0.0074x + 0.21, r = 0.85 DD : y = 0.0041x + 0.82, r = 0.83 The three regression lines revealed that the estimated urinary HA concentration of NN, ND, and DD groups at 377 mg/㎥ toluene (TLV-TWA) exposure were 3.43, 3.00, and 2.37g/g than that of the ACGIH BEI (2.5 g/g creatinine) ; however, the HA level of DD group was lower than the BEI. These results suggest that the ACGIH BEI is not adequate to estimate the toluene exposure of the NN, ND and DD groups at the same time. Based upon these results, a new BEI for ALDH2 deficient workers may be necessary.

복합유기용제에 폭로된 근로자들에 대한 신경행동학적 기능의 평가

김창윤,전만중,정종학,성낙정,김상규,사공준,주 리 영남대학교 의과대학 1997 Yeungnam University Journal of Medicine Vol.14 No.2

복합유기용제를 취급하는 근로자들을 대상으로 유기용제의 폭로가 신경행동기능에 미치는 영향을 평가하기 위하여 대구지역의 중소규모 사업장에서 톨루엔, 크실렌, 메틸에틸케톤 및 신나에 만성적으로 폭로되는 유기용제 폭로군 48명과 폭로군과 같은 사업장에 근무하면서 유기용제에 폭로되지 않은 대조군 50명을 대상으로 1996년 8월에서 10월까지 연령, 교육수준, 음주, 흡연량 및 직업관련 변수들을 조사하고 Neurobehavioral Core Test Battery의 검사항목 중 Benton visual retention검사, 숫자부호 짝짓기, 숫자 외우기, 목적점찍기를 시행하였다. Benton visual retention검사는 폭로군이 7.9개, 대조군이 8.2개로 두군에서 유의한 차이가 없었으며, 숫자부호 짝짓기의 경우 폭로군이 55.6개, 대조군이 62.1개로서 폭로군이 유의하게 적었다(p<0.01). 숫자 외우기의 총 점수와 거꾸로 따라외우기의 점수가 폭로군에서 유의하게 적었으며(p<0.05, p<0.01) 목적점찍기의 바르게 찍은 점의 개수가 폭로군에서 유의하게 적었다(p<0.05).연령의 변화에 따른 신경행동기능의 일관성있는 변화는 없었으나 Benton visual retention검사의 경우 젊은 연령군이 고연령군에 비해 대조군에서 유의하게 높은 성적을 보였다(p<0.05). 부호숫자짝짓기의 경우 폭로군과 대조군 모두에서 학력이 높을수록 검사성적이 유의하게 높은 경향을 보였다(p<0.05). 숫자부호짝짓기에서 섭취하는 알콜의 량이 많을수록 폭로군의 부호숫자짝짓기 검사성적이 감소하는 경향을 보였다(p<0.05). 목적점찍기의 경우 폭로군에서 흡연량이 증가할수록 성적이 감소하는 경향을 보였다(p<0.05). 신경행동학적 검사성적을 종속변수로 하고 유기용제의 폭로유무, 나이, 학력수준, 알콜 및 흡연량을 독립변수로 한 다중회귀분석에서 Benton visual relention검사는 연령이 증가할수록 그 성적이 감소하는 경향을 보였으며(p<0.05), 숫자부호짝짓기는 학력이 높을수록 성적이 증가하는 것으로 나타났다(p<0.01). 숫자외우기에서는 유기용제의 폭로가 유의한 변수로 채택되었다(p<0.01). 목적점찍기의 총점수는 흡연량과 교육수준이(p<0.01), 바르게 찍은 개수는 흡연량과 유기용제의 폭로가 유의한 변수로 채택되었다(p<0.05). 유기용제의 폭로에 의해 지각반응(perception response)과 단기기억능력(short-term memory)이 민감하게 영향을 받는 것으로 평가되었으며, 특히 허용농도이하에서도 장기적으로 폭로되는 경우 폭로자의 신경행동기능에 변화를 초래할 수 있음을 확인할 수 있었다. NCTB에 의한 신경행동기능의 평가는 신경독성물질의 폭로이외에도 연령과 교육수준에 영향을 받으며 특히 지속적 운동능력의 경우 흡연에도 다소 영향을 받을 가능성을 제시하였다. A cross-sectional study was performed to evaluate the effects of chronic exposure to low-dose solvent on neurobehavioral performance of 48 male workers exposed to organic solvents. A control group of 50 workers was selected from same factories. Each worker completed a medical and occupational questionnaire and four tests of Neurobehavioral Core Test Bateery. These included Benton visual retention test, digit symbol, digit span,and pursuit aiming. Comparison of mean performance showed a significantly poorer performance on digit symbol, digit span, and pursuit aiming. In univariate analysis, age contributed to poor performance on Benton visual retention test and educational level was found to reduce the performance on symbol digit in both groups. Amount of alcohol intake was found to reduce the perfomance on digit symbol and smoking appeared to slow pursuit aiming in the exposure group. In multiple regression analysis, controlling for age, educational level, alcohol, and smoking, solvent exposure was found to be associated with performance of digit span, and number of correct dot of pursuit aiming. Age on Benton visual retention, educational level on digit symbol, and smoking on pursuit aiming were found to be a siginificant factors on each test items. This study suggest that short-term memory, and perception can be affected easily by chronic exposure of organic solvents which air concentration levels were under the Threshold Limit Value.

Improved Performance of Polymer:Polymer Solar Cells by Doping Electron‐Accepting Polymers with an Organosulfonic Acid

Nam, Sungho,Shin, Minjung,Kim, Hwajeong,Ha, Chang‐,Sik,Ree, Moonhor,Kim, Youngkyoo WILEY‐VCH Verlag 2011 Advanced functional materials Vol.21 No.23

<P><B>Abstract</B></P><P>The performance of polymer:polymer solar cells that are made using blend films of poly(3‐hexylthiophene) (P3HT) and poly(9,9‐dioctylfluorene‐co‐ benzothiadiazole (F8BT) is improved by doping the F8BT polymer with an organosulfonic acid [4‐ethylbezenesulfonic acid (EBSA)]. The EBSA doping of F8BT, to form F8BT‐EBSA, is performed by means of a two‐stage reaction at room temperature and 60°C with various EBSA weight ratios. The X‐ray photoelectron spectroscopy measurement reveals that both sulfur and nitrogen atoms in the F8BT polymer are affected by the EBSA doping. The F8BT‐EBSA films exhibit huge photoluminescence quenching, ionization potential shift toward lower energy, and greatly enhanced electron mobility. The short‐circuit current density of solar cells is improved by ca. twofold (10 wt.% EBSA doping), while the open‐circuit voltage increases by ca. 0.4 V. Consequently, the power conversion efficiency was improved by ca. threefold, even though the optical density of the P3HT:F8BT‐EBSA blend film is reduced by 10 wt.% EBSA doping due to the nanostructure and surface morphology change.</P>

Abrupt Morphology Change upon Thermal Annealing in Poly(3-Hexylthiophene)/Soluble Fullerene Blend Films for Polymer Solar Cells

Shin, Minjung,Kim, Hwajeong,Park, Jiho,Nam, Sungho,Heo, Kyuyoung,Ree, Moonhor,Ha, Chang-Sik,Kim, Youngkyoo WILEY-VCH Verlag 2010 Advanced Functional Materials Vol.20 No.5

<P>The in situ morphology change upon thermal annealing in bulk heterojunction blend films of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C<SUB>61</SUB> (PCBM) is measured by a grazing incidence X-ray diffraction (GIXD) method using a synchrotron radiation source. The results show that the film morphology—including the size and population of P3HT crystallites—abruptly changes at 140 °C between 5 and 30 min and is then stable up to 120 min. This trend is almost in good agreement with the performance change of polymer solar cells fabricated under the same conditions. The certain morphology change after 5 min annealing at 140 °C is assigned to the on-going thermal transition of P3HT molecules in the presence of PCBM transition. Field-emission scanning electron microscopy measurements show that the crack-like surface of blend films becomes smaller after a very short annealing time, but does not change further with increasing annealing time. These findings indicate that the stability of P3HT:PCBM solar cells cannot be secured by short-time annealing owing to the unsettled morphology, even though the resulting efficiency is high.</P> <B>Graphic Abstract</B> <P>The morphology of P3HT:PCBM blend films, one of the most widely used material blends in polymer solar cells, is monitored using in situ grazing angle X-ray diffraction (GIXD). The study reveals abrupt changes in the nanostructure with annealing time (see image, OOP = out-of-plane), which is in good agreement with variations in device performance (PCE = power conversion efficiency; FF = fill factor). <img src='wiley_img_2010/1616301X-2010-20-5-ADFM200901655-content.gif' alt='wiley_img_2010/1616301X-2010-20-5-ADFM200901655-content'> </P>

GALEX Observations for the Look-back Time Evolution of Far-UV Flux from Elliptical Galaxies

Ree Chang H.,Lee Young-Wook,Sohn Young-Jong,Rey Soo-Chang,Rhee Jaehyon,Yi Sukyoung K.,Yoon Suk-Jin,Lee Jae-Woo,Kim Sug-Whan 한국우주과학회 2004 한국우주과학회보 Vol.13 No.2

Synthetic Color-Magnitude Diagrams for ω

Chang H. Ree,Suk-Jin Yoon,Soo-Chang Rey,Young-Wook Lee 한국천문학회 2001 天文學會報 Vol.26 No.2

Temperature Dependence of the Vibration-Vibration Energy Transfer in the Deexcitaion of NO(2) by NO(0)

Ree, Jong-Baik,Sohn, Chang-Kook,Lee, Chang-Soon,Kim, Yoo-Hang Korean Chemical Society 1987 Bulletin of the Korean Chemical Society Vol.8 No.6

The temperature dependence of the vibrational relaxation of NO(= 2) by NO(v = 0) has been investigated over the temperature range 100-3000 K. We have assumed that the deexcitation of NO(2) by NO(0) undergoes vibration-to-vibration (VV) energy exchange with the transfer of the energy mismatch ${\Delta}$E through rotation (R) and translation(T). The relaxation rate constants are calculated by solving the time-dependent Schrodinger equation. The sum of V-V, T, and V-V, R contributions shows very weak temperature dependence and is in reasonable agreement with observed data over the temperature range 300-3000 K.

Hydrogen Surface Coverage Dependence of the Reaction between Gaseous and Chemisorbed Hydrogen Atoms on a Silicon Surface

Ree, Jong-Baik,Chang, Kyung-Soon,Kim, Yoo-Hang Korean Chemical Society 2002 Bulletin of the Korean Chemical Society Vol.23 No.2

The reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. Especially, we have focused on the mechanism changes with the hydrogen surface coverage difference. On the sparsely covered surface, the gas atom interacts with the preadsorbed hydrogen atom and adjacent bare surface sites. In this case, it is shown that the chemisorption of H(g) is of major importance. Nearly all of the chemisorption events accompany the desorption of H(ad), i.e., adisplacement reaction. Although much less important than the displacement reaction, the formation of $H_2(g)$ is the second most significant reaction pathway. At gas temperature of 1800 K and surface temperature of 300 K, the probabilities of these two reactions are 0.750 and 0.065, respectively. The adsorption of H(g) without dissociating H(ad) is found to be negligible. In the reaction pathway forming $H_2$, most of the reaction energy is carried by $H_2(g)$. Although the majority of $H_2(g)$ molecules are produced in sub-picosecond, direct-mode collisions, there is a small amount of $H_2(g)$ produced in multiple impact collisions, which is characteristic of complex-mode collisions. On the fully covered surface, it has been shown that the formation of $H_2(g)$ is of major importance. All reactive events occur on a subpicosecond scale, following the Eley-Rideal mechanism. At gas temperature of 1800 K and surface temperature of 300 K, the probability of the $H_2(g)$ formation reaction is 0.082. In this case, neither the gas atom trapping nor the displacement reaction has been found.