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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.
U(1) Chiral Symmetry in a One-Dimensional Interacting Electron System with Spin
Taejin Lee 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.9
We study a spin-dependent Tomonaga-Luttinger model in one dimension, which describes electron transport through a single barrier. Using the Fermi-Bose equivalence in one dimension, we map the model onto a massless Thirring model with a boundary interaction. A field theoretical perturbation theory for the model has been developed, and the chiral symmetry is found to play an important role. The classical bulk action possesses a global UA(1)4 chiral symmetry because the fermion fields are massless. This global chiral symmetry is broken by the boundary interaction, and the bosonic degrees of freedom, corresponding to a chiral phase transformation, become dynamical. They acquire an additional kinetic action from the fermion path-integral measure and govern the critical behaviors of the physical operators. On the critical line where the boundary interaction becomes marginal, they decouple from the fermi fields. Consequently, the action reduces to the free-field action, which contains only a fermion bilinear boundary mass term as an interaction term. By using a renormalization group analysis, we obtain a new critical line, which differs from the previously known critical lines in the literature. The result of this work implies that the phase diagram of the one-dimensional electron system may have a richer structure than previously thought.
Klein Factors and Fermi-Bose Equivalence
Taejin LEE 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.11
Generalizing the kink operator of the Heisenberg spin 1/2 model, we construct a set of Klein factors explicitly such that (1+1)-dimensional fermion theories with an arbitrary number of species are mapped onto the corresponding boson theories with the same number of species and vice versa. The actions for the resultant theories do not possess a nontrivial Klein factor. With this set of Klein factors, we are also able to map the simple boundary states, such as the Neumann and the Dirichlet boundary states, of the fermion (boson) theory onto those of the boson (fermion) theory. Applications of the Fermi-Bose equivalence with the constructed Klein factors to well-known (1+1)- dimensional theories have been discussed.
Witten’s cubic open string field theory on multiple Dp-branes
Lee Taejin 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.2
We study Witten’s cubic open string feld theory on multiple Dp-branes. On multiple Dp-branes the string felds carry U(N) group indices. Mapping the string world-sheet onto the upper half complex plane and evaluating the Polyakov string path integral of Witten’s cubic open string, we obtain a Fock space representation of one, two and three-string vertex operators. In the low energy region, the system is described by massless gauge felds and massless scalar felds, carrying U(N) group indices. The two-string vertex induces mass terms for the gauge felds and the scalar felds. The cubic interaction reduces correctly to the cubic term of the non-Abelian gauge felds, cubic interaction terms of the gauge felds, and the scalar felds on (p + 1) dimensional space. Thus, Witten’s string feld theory may be a useful tool to study the quantum dynamics of open strings on multiple Dp-branes.
Adaptive TCX Windowing Technology for Unified Structure MPEG-D USAC
Taejin Lee,Seungkwon Beack,강경옥,김환우 한국전자통신연구원 2012 ETRI Journal Vol.34 No.3
The MPEG-D unified speech and audio coding (USAC)standardization process was initiated by MPEG to develop an audio codec that is able to provide consistent quality for mixed speech and music contents. The current USAC reference model structure consists of frequency domain (FD) and linear prediction domain (LPD) core modules and is controlled using a signal classifier tool. In this letter, we propose an LPD singlemode USAC structure using an adaptive widowing-based transform-coded excitation module. We tested our system using official test items for all mono-evaluation modes. The results of the experiment show that the objective and subjective performances of the proposed single-mode USAC system are better than those of the FD/LPD dual-mode USAC system.
A Spatial Audio System Using Multiple Microphones on a Rigid Sphere
Taejin Lee,강경옥,김진웅,정대권,Daeyoung Jang,Hareo Hamada 한국전자통신연구원 2005 ETRI Journal Vol.27 No.2
The main purpose of a spatial audio system is to give a listener the same impression as if he/she were present in a recorded environment. A dummy head microphone is generally used for such purposes. Because of its humanlike shape, we can obtain good spatial sound images. However, its shape is a restriction on its public use and it is difficult to convert a 2-channel recording into multichannel signals for an efficient rendering over a multispeaker arrangement. In order to solve the problems mentioned above, a spatial audio system is proposed that uses multiple microphones on a rigid sphere. The system has five microphones placed on special points of the rigid sphere, and it generates audio signals for headphone, stereo, stereo dipole, 4-channel, and 5-channel reproduction environments. Subjective localization experiments show that front/back confusion, which is a common limitation of spatial audio systems using the dummy head microphone, can be reduced dramatically in 4-channel and 5-channel reproduction environments and can be reduced slightly in a headphone reproduction