Korea Institute of Advanced Study

Seoul, South Korea

Korea Institute of Advanced Study

Seoul, South Korea
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He M.,Shanghai JiaoTong University | He X.-G.,Shanghai JiaoTong University | He X.-G.,National Taiwan University | He X.-G.,National Center for Theoretical science | Tang Y.,Korea Institute of Advanced Study
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2016

Recent data collected by ATLAS and CMS at 13 TeV collision energy of the LHC indicate the existence of a new resonant state φ with a mass of 750 GeV decaying into two photons γγ. The properties of φ should be studied further at the LHC and also future colliders. Since only φ→γγ decay channel has been measured, one of the best ways to extract more information about φ is to use a γγ collider to produce φ at the resonant energy. In this work we show how a γγ collider helps to verify the existence of φ and to provide some of the most important information about the properties of φ, such as branching fractions of φ→V1V2. Here Vi can be γ, Z, or W±. We also show that by studying angular distributions of the final γ's in γγ→φ→γγ, one can obtain crucial information about whether this state is a spin-0 or a spin-2 state. © 2016 The Author(s).

Baek S.K.,Sungkyunkwan University | Baek S.K.,Umeå University | Um J.,Korea Institute of Advanced Study | Yi S.D.,Sungkyunkwan University | Kim B.J.,Sungkyunkwan University
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

In a number of classical statistical-physical models, there exists a characteristic dimensionality called the upper critical dimension above which one observes the mean-field critical behavior. Instead of constructing high-dimensional lattices, however, one can also consider infinite-dimensional structures, and the question is whether this mean-field character extends to quantum-mechanical cases as well. We therefore investigate the transverse-field quantum Ising model on the globally coupled network and on the Watts-Strogatz small-world network by means of quantum Monte Carlo simulations and the finite-size scaling analysis. We confirm that both of the structures exhibit critical behavior consistent with the mean-field description. In particular, we show that the existing cumulant method has difficulty in estimating the correct dynamic critical exponent and suggest that an order parameter based on the quantum-mechanical expectation value can be a practically useful numerical observable to determine critical behavior when there is no well-defined dimensionality. © 2011 American Physical Society.

Seo J.-H.,Seoul National University | Kyung D.,Seoul National University | Kyung D.,SK Holdings Co. | Joo K.,Korea Institute of Advanced Study | And 2 more authors.
Biotechnology and Bioengineering | Year: 2011

The half reactions of ω-aminotransferase (ω-AT) from Vibrio fluvialis JS17 (ω-ATVf) were carried out using purified pyridoxal 5'-phosphate-enzyme (PLP-Enz) and pyridoxamine 5'-phosphate-enzyme (PMP-Enz) complexes to investigate the relative activities of substrates. In the reaction generating PMP-Enz from PLP-Enz using L-alanine as an amine donor, L-alanine showed about 70% of the initial reaction rate of (S)-α-methylbenzylamine ((S)-α-MBA). However, in the subsequent half reaction recycling PLP-Enz from PMP-Enz using acetophenone as an amine acceptor, acetophenone showed nearly negligible reactivity compared to pyruvate. These results indicate that the main bottleneck in the asymmetric synthesis of (S)-α-MBA lies not in the amination of PLP by alanine, but in the amination of acetophenone by PMP-Enz, where conformational restraints of the enzyme structure is likely to be the main reason for limiting the amine group transfer from PMP-Enz to acetophenone. Based upon those half reaction experiments using the two amino acceptors of different activity, it appears that the relative activities of the two amine donors and the two acceptors involved in the ω-AT reactions can roughly determine the asymmetric synthesis yield of the target chiral amine compound. Predicted conversion yields of several target chiral amines were calculated and compared with the experimental conversion yields. Approximately, a positive linear correlation (Pearson's correlation coefficient = 0.92) was observed between the calculated values and the experimental conversion yields. To overcome the low (S)-α-MBA productivity of ω-ATVf caused by the possible disadvantageous structural constraints for acetophenone, new ω-ATs showing higher affinity to benzene ring of acetophenone than ω-ATVf were computationally screened using comparative modeling and protein-ligand docking. ω-ATs from Streptomyces avermitilis MA-4680 (SAV2612) and Agrobacterium tumefaciens str. C58 (Atu4761) were selected, and the two screened ω-ATs showed higher asymmetric synthesis reaction rate of (S)-α-MBA and lower (S)-α-MBA degradation reaction rate than ω-ATVf. To verify the higher conversion yield of the variants of ω-ATs, the reaction with 50 mM acetophenone and 50 mM alanine was performed with coupling of lactate dehydrogenase and two-phase reaction system. SAV2612 and Atu4761 showed 70% and 59% enhanced yield in the synthesis of (S)-α-MBA compared to that of ω-ATVf, respectively. © 2010 Wiley Periodicals, Inc.

Milburn T.J.,Vienna University of Technology | Kim M.S.,Imperial College London | Kim M.S.,Korea Institute of Advanced Study | Vanner M.R.,University of Queensland | Vanner M.R.,University of Oxford
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

Nonclassical-state generation is an important component throughout experimental quantum science for quantum information applications and probing the fundamentals of physics. Here, we investigate permutations of quantum nondemolition quadrature measurements and single quanta addition or subtraction to prepare quantum superposition states in bosonic systems. The performance of each permutation is quantified and compared using several different nonclassicality criteria including Wigner negativity, nonclassical depth, and optimal fidelity with a coherent-state superposition. We also compare the performance of our protocol using squeezing instead of a quadrature measurement and find that the purification provided by the quadrature measurement can significantly increase the nonclassicality generated. Our approach is ideally suited for implementation in light-matter systems such as quantum optomechanics and atomic spin ensembles, and offers considerable robustness to initial thermal occupation. © 2016 American Physical Society.

Ivanov G.,University of Bergen | Kang N.-G.,Korea Institute of Advanced Study | Vasil'ev A.,University of Bergen
Complex Analysis and Operator Theory | Year: 2016

It was realized recently that the chordal, radial and dipolar Schramm–Löwner evolution (SLEs) are special cases of a general slit holomorphic stochastic flow. We characterize those slit holomorphic stochastic flows which generate level lines of the Gaussian free field. In particular, we describe the modifications of the Gaussian free field (GFF) corresponding to the chordal and dipolar SLE with drifts. Finally, we develop a version of conformal field theory based on the background charge and Dirichlet boundary condition modifications of GFF and present martingale-observables for these types of SLEs. © 2016 Springer International Publishing

Chung H.S.,Korea University | Yu C.,Korea University | Kim S.,Sejong University | Kim S.,Korea Institute of Advanced Study | And 2 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Within the framework of the nonrelativistic QCD (NRQCD) factorization approach, we compute the polarization of prompt J/ψ produced at the Brookhaven's Relativistic Heavy-Ion Collider from proton-proton collisions at the center-of-momentum energy √s=200GeV. The perturbative contributions are computed at leading order in the strong coupling constant. The prediction reveals that the color-singlet contribution severely underestimates the PHENIX preliminary data for the differential cross section integrated over the rapidity range |y|<0.35 and its contribution is strongly transversely polarized, which disagrees with the PHENIX preliminary data. After including the color-octet contributions, we find that the NRQCD predictions for both the cross section and polarization over the transverse-momentum range 1.5GeV

Okur A.,U.S. National Institutes of Health | Miller B.T.,U.S. National Institutes of Health | Joo K.,Korea Institute of Advanced Study | Lee J.,Korea Institute of Advanced Study | Brooks B.R.,U.S. National Institutes of Health
Journal of Chemical Theory and Computation | Year: 2013

Temperature replica exchange molecular dynamics (T-REM) has been successfully used to improve the conformational search for model peptides and small proteins. However, for larger and more complicated systems, the use of T-REM is computationally intensive since the complexity of the free energy landscape and number of required replicas increase with system size. Achieving convergence of systems with slow transition kinetics is often difficult. Several methods have been proposed to overcome the size and convergence speed issues of standard T-REM. One of these is the Reservoir Replica Exchange Method (R-REM), in which the conformational search and temperature equilibration are separated by exchanging with a pre-existing reservoir of structures. This approach allows the integration of computationally efficient search algorithms with replica exchange. The Conformational Space Annealing (CSA) method has been shown to be able to determine the global energy minimum of proteins efficiently and has been used in structure prediction successfully. CSA uses a genetic algorithm to generate a diverse set of conformations to determine the minimum energy structure. We combine these methods by using conformations generated by the CSA method to build a reservoir. R-REM is then used to seed the top replica with the structures from the reservoir; fast convergence at every temperature is observed. The efficiency of this method is then demonstrated with model peptides and small proteins, and significant improvement of efficiency is observed while maintaining the overall shape of the free energy landscape. © 2013 American Chemical Society.

Gupta S.,Yonsei University | Kim C.S.,Yonsei University | Sharma P.,Korea Institute of Advanced Study
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

We systematically analyze the radiative corrections to the S3 symmetric neutrino mass matrix at high energy scale, say the GUT scale, in the charged lepton basis. There are significant corrections to the neutrino parameters both in the Standard Model (SM) and Minimal Supersymmetric Standard Model (MSSM) with large tan<>β, when the renormalization group evolution (RGE) and seesaw threshold effects are taken into consideration. We find that in the SM all three mixing angles and atmospheric mass squared difference are simultaneously obtained in their current 3σ ranges at the electroweak scale. However, the solar mass squared difference is found to be larger than its allowed 3σ range at the low scale in this case. There are significant contributions to neutrino masses and mixing angles in the MSSM with large tan<>β from the RGEs even in the absence of seesaw threshold corrections. However, we find that the mass squared differences and the mixing angles are simultaneously obtained in their current 3σ ranges at low energy when the seesaw threshold effects are also taken into account in the MSSM with large tan<>β. © 2014 The Authors.

Yap C.,Courant Institute of Mathematical Sciences | Yap C.,Korea Institute of Advanced Study
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

The master theorem provides a solution to a well-known divide-and-conquer recurrence, called here the master recurrence. This paper proves two cook-book style generalizations of this master theorem. The first extends the treated class of driving functions to the natural class of exponential-logarithmic (EL) functions. The second extends the result to the multiterm master recurrence. The power and simplicity of our approach comes from re-interpreting integer recurrences as real recurrences, with emphasis on elementary techniques and real induction. © 2011 Springer-Verlag.

Lee J.,Korea Institute of Advanced Study | Gross S.P.,University of California at Irvine
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

We propose a modularity optimization method, Mod-CSA, based on stochastic global optimization algorithm, conformational space annealing (CSA). Our method outperforms simulated annealing in terms of both efficiency and accuracy, finding higher modularity partitions with less computational resources required. The high modularity values found by our method are higher than, or equal to, the largest values previously reported. In addition, the method can be combined with other heuristic methods, and implemented in parallel fashion, allowing it to be applicable to large graphs with more than 10 000 nodes. © 2012 American Physical Society.

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