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Gravitational Scattering Amplitudes and Closed String Field Theory in the Proper-Time Gauge
Lee, Taejin,Gwak, B.,Kang, G.,Kim, C.,Kim, H.-C.,Lee, C.-H.,Lee, J.,Lee, S.,Lee, W. EDP Sciences 2018 The European Physical Journal Conferences Vol.168 No.-
<P>We construct a covariant closed string field theory by extending recent works on the covariant open string field theory in the proper-time gauge. Rewriting the string scattering amplitudes generated by the closed string field theory in terms of the Polyakov string path integrals, we identify the Fock space representations of the closed string vertices. We show that the Fock space representations of the closed string field theory may be completely factorized into those of the open string field theory. It implies that the well known Kawai-Lewellen-Tye (KLT) relations of the first quantized string theory may be promoted to the second quantized closed string theory. We explicitly calculate the scattering amplitudes of three gravitons by using the closed string field theory in the proper-time gauge.</P>
Stable isotope on the evaluation of water quality in the presence of WWTPs in rivers
Lee, Jaewoong,Park, Taejin,Kim, Min-seob,Kim, Jongmin,Lee, Seunghyun,Lee, Su Kyuong,Lee, Young Sun,Lee, Won-seok,Yu, Soonju,Rhew, Doughee Springer-Verlag 2016 Environmental science and pollution research inter Vol.23 No.18
<P>We investigated the distribution of nitrogen compounds in Han River as well as two tributaries of Tancheon and Jungrangcheon. Particularly, we observed the significant releases of NH4+-N from effluent of wastewater treatment plants (WWTPs) in two tributaries that has resulted in the increases of ammonium nitrogen (NH4+-N) in Han River as well as in Tancheon and Jungrangcheon. Due to the increases of NH4+-N in two tributaries, the larger distribution of delta N-15-NH4+ was observed than those of delta N-15-NO3- in downstream. We calculated the contribution rate of ammonium nitrogen and nitrate nitrogen from effluent to downstream according to the results of stable isotope. The contribution rates of delta N-15-NH4+ from effluent to downstream were significant that ranged between 53 and 100 % in Tancheon and between 27 and 100 % in Jungrangcheon. While the contribution of delta N-15-NO3- was not significant in Tancheon, it was occasionally observed in Jungrangcheon. These results demonstrated that WWTPs are the major sources of NH4+-N in two tributaries, which caused the distinguishable stable isotope of delta N-15-NH4+. Therefore, the stable isotope of delta N-15-NH4+ could be a useful parameter or tracer for the evaluation of NH4-N released from WWTPs in rivers.</P>
차량용 가변사판식 압축기의 흡입체크밸브 최적화에 관한 연구
이봉섭(Bongsub Lee),이용주(Yongju Lee),이태진(Taejin Lee),한준석(Junseok Han),배인표(Inpyo Bae),이건호(Geonho Lee) 대한설비공학회 2016 대한설비공학회 학술발표대회논문집 Vol.2016 No.6
Development of a compressor for vehicle air conditioning system has been focused on high performance and noise reduction. Suction check valve is used to prevent the noise that is caused by the suction pulsation when a clutch-less compressor is operating in an OFF state. However, the suction pressure drop due to the increased flow resistance reduces the cooling capacity of a compressor. The aim at this study is to predict the cooling capacity drop rate and improving the performance with optimized suction check valve shapes. It proposed the theoretical cooling capacity drop rate, and the experimental studies were carried out in order to verify this. But those were not matched each other so that CFD analysis program was used to look for the cause. Results show that the pressure distribution of a valve surfaces affects the suction pressure drop. The cooling capacity was improved by the suction check valve that is modified to increase average pressure on a valve surface.
Lee, Taewoo,Oh, Jeong-Ik,Kim, Taejin,Tsang, Daniel C.W.,Kim, Ki-Hyun,Lee, Jechan,Kwon, Eilhann E. Pergamon 2018 Energy Conversion and Management Vol. No.
<P><B>Abstract</B></P> <P>This study emphasizes the control of benzene derivatives and polycyclic aromatic hydrocarbons (PAHs) in thermolysis of polyvinyl chloride (PVC) using CO<SUB>2</SUB>. To this end, the generation of benzenes and PAHs from the thermolysis of PVC in N<SUB>2</SUB> was characterized and all experimental findings from the thermolysis of PVC in N<SUB>2</SUB> were used as the reference value to configure the role of CO<SUB>2</SUB> in the thermolysis of PVC. The formation of hydrogen chloride (HCl) followed by the subsequent dechlorination in the thermolysis of PVC in N<SUB>2</SUB> resulted in the high yield of charring compounds, providing a favorable condition for forming benzene derivatives and PAHs. However, the thermal degradation of PVC in CO<SUB>2</SUB> showed the genuine thermal degradation patterns. For instance, despite the presence of the source for oxygen, the formation of CO at temperatures higher than 600 °C was observed in the thermolysis of PVC in CO<SUB>2</SUB>, suggesting that some unknown reactions between hydrocarbons from the thermolysis of PVC and CO<SUB>2</SUB> are initiated to form CO. In addition to these unknown reactions, the enhanced thermal cracking induced by CO<SUB>2</SUB> was observed. Two identified roles of CO<SUB>2</SUB> during the thermolysis of CO<SUB>2</SUB> was only limited at temperatures higher than 600 °C. However, despite no precise description for the mechanistic role of CO<SUB>2</SUB> at this stage of study, the formation of benzene derivatives and PAHs was effectively controlled in the presence of CO<SUB>2</SUB> at temperatures higher than 480 °C. Thus, these empirical findings in this study are necessary to further be investigated in the future, which offers a great venue offering a new means for modifying and/or controlling the harmful chemical species.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CO<SUB>2</SUB> acts a donor for carbon and oxygen. </LI> <LI> CO<SUB>2</SUB> expedites the thermal cracking of PVC. </LI> <LI> CO<SUB>2</SUB> block a pathway for the generation of benzene derivatives and PAHs. </LI> <LI> CO<SUB>2</SUB> can be used as reaction medium to control the harmful chemical species. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Analysis of Temperature Reduction Effect by Cool Roof
( Taejin Lee ),( Kyoung-sik Choi ) 한국환경기술학회 2019 한국환경기술학회지 Vol.20 No.5
The cool roof measure, is actively being performed to reduce indoor temperature. The study was conducted to establish a monitoring system and to investigate the effects of the cool roof including measuring methods. Six houses were grouped into three groups to compare the rooftop and indoor temperatures of the houses with and without cool roofs. Two groups in Mojeong village of Gimhae city and one in Bansong-dong of Busan were selected. The indoor and outdoor temperatures of the houses selected during the same time period were measured for houses with and without a cool roof. The results showed that the rooftop surface temperatures of three houses with cool roofs decreased in average temperature of at least 4.5 ℃ and up to 7.3 ℃, compared to households without cool roofs. In one group, the average indoor temperature of the house with the cool roof was measured to be 1.0 ℃ lower than that of the house without the roof. However, for the two comparison groups, households without a cool roof were measured to be at least 0.5 ℃, and at most 0.7 ℃, lower than those with cool roofs. The reason for the rapid drop in indoor temperature is considered to be greatly influenced by variables such as the number of people living in the house, the insulating materials and the use of air conditioning equipment.
Lee, Kangeui,Lee, So Hee,Park, Taejin,Lee, Ji-yeon KOREAN ACADEMY OF MEDICAL SCIENCE 2017 JOURNAL OF KOREAN MEDICAL SCIENCE Vol.32 No.3
<P>We conducted in-depth interviews with 11 Korean Disaster Relief Team (KDRT) members about stress related to disaster relief work and analyzed the interview data using the Consensual Qualitative Research (CQR) method in order to evaluate difficulties in disaster relief work and to develop solutions to these problems in cooperation with related organizations. Results showed that members typically experienced stress related to untrained team members, ineffective cooperation, and the shock and aftermath of aftershock experiences. Stress tended to stem from several factors: difficulties related to cooperation with new team members, the frightening disaster experience, and the aftermath of the disaster. Other stressors included conflict with the control tower, diverse problems at the disaster relief work site, and environmental factors. The most common reason that members participated in KDRT work despite all the stressors and difficulties was pride about the kind of work it involved. Many subjects in this study suffered from various stresses after the relief work, but they had no other choice than to attempt to forget about their experiences over time. It is recommended that the mental health of disaster relief workers will improve through the further development of effective treatment and surveillance programs in the future.</P>
Lee, Hyungsoo,Jo, Min Chul,Sohn, Seok Su,Kim, Sang-Heon,Song, Taejin,Kim, Sung-Kyu,Kim, Hyoung Seop,Kim, Nack J.,Lee, Sunghak Elsevier 2019 Materials characterization Vol.147 No.-
<P><B>Abstract</B></P> <P>The weldability is one of the key factors governing applications of TWinning-Induced Plasticity (TWIP) steels to automotive industries demanding high economy, environmental friendliness, and high performance. During spot welding of Zn-coated Al-containing TWIP steel sheets, liquid metal embrittlement (LME) frequently occurs by Zn infiltration into grain boundaries to form cracks, but the direct observation and detailed analysis of LME cracking are quite difficult because it occurs instantaneously within a second. Here in the present study, the LME was investigated by detailed microstructural evolutions of small Zn infiltrations or cracks as well as formation behavior of various intermetallic phases. In the heat-affected zone, the applied tensile stress and spot-welding heat tore down a diffusion-inhibiting Fe<SUB>2</SUB>Al<SUB>5</SUB> layer formed between the Zn-coated layer and the TWIP steel substrate, and formed Zn-containing ferrite (α-Fe(Zn)) particles on the steel surface which provided paths for liquid Zn infiltration. α-Fe(Zn) particles played critical roles in accelerating the LME by reducing the ductility because they were brittle due to high contents of Zn and Al. In the present Al-containing TWIP steels, the increase in welding current generally aggravates the LME.</P>