High-field instability of field-induced triplon Bose-Einstein condensate (2009)
Rakhimov, Abdulla, Sherman, E. Ya., Kim, Chul Koo
We study properties of magnetic field-induced Bose-Einstein condensate of triplons as a function of temperature and the field within the Hartree-Fock-Bogoliubov approach including the anomalous...
Reverse Doppler Effect of Sound (2009)
Lee, Sam Hyeon, Park, Choon Mahn, Seo, Yong Mun, Wang, Zhi Guo, Kim, Chul Koo
We report observation of reverse Doppler effect in a double negative acoustic metamaterial. The metamaterial exhibited negative phase velocity and positive group velocity. The dispersion relation is...
Acoustic Metameterial with Negative Modulus (2008)
Lee, Sam Hyeon, Park, Choon Mahn, Seo, Yong Mun, Wang, Zhi Guo, Kim, Chul Koo
We present experimental and theoretical results on an acoustic metamaterial that exhibits negative effective modulus in a frequency range from 0 to 450 Hz. One-dimensional acoustic metamaterial with...
Negative Effective Density in An Acoustic Metamaterial (2008)
Lee, Sam Hyeon, Park, Choon Mahn, Seo, Yong Mun, Wang, Zhi Guo, Kim, Chul Koo
We report theoretical and experimental results for a new type of homogenized acoustic metamaterials with negative effective mass density. We constructed one-dimensional metamaterial, which is a tube...
A Brownian Energy Depot Model of the Basilar Membrane Oscillation with a Braking Mechanism (2008)
Zhang, Yong, Kim, Chul Koo, Lee, Kong-Ju-Bock, Park, Youngah
High auditory sensitivity, sharp frequency selectivity, and otoacoustic emissions are signatures of active amplification of the cochlea. The human ear can also detect very large amplitude sound...
Active motions of Brownian particles in a generalized energy-depot model (2008)
Zhang, Yong, Kim, Chul Koo, Lee, Kong-Ju-Bock
We present a generalized energy-depot model in which the conversion rate of the internal energy into motion can be dependent on the position and the velocity of a particle. When the conversion rate...
Zhang, Yong, Kim, Chul Koo, Lee, Kong-Ju-Bock, Park, Youngah
Cochlea is an important auditory organ in the inner ear. In most mammals, it is coiled as a spiral. Whether this specific shape influences hearing is still an open problem. By employing a three...
Stability of the homogeneous Bose-Einstein condensate at large gas parameter (2008)
Rakhimov, Abdulla, Kim, Chul Koo, Kim, Sang-Hoon, Yee, Jae Hyung
The properties of the uniform Bose gas is studied within the optimized variational perturbation theory (Gaussian approximation) in a self-consistent way. It is shown that the atomic BEC with a...
Ground state energy density of a dilute Bose gas in the canonical transformation (2006)
Kim, Sang-Hoon, Kim, Chul Koo, Das, Mukunda P.
A ground state energy density of an interacting dilute Bose gas system is studied in the canonical transformation scheme. It is shown that the transformation scheme enables us to calculate a higher...
Electromagnetically induced transparency in an atom-molecule Bose-Einstein condensate (2006)
Jin, Guang-Ri, Kim, Chul Koo, Nahm, Kyun
We propose a new measurement scheme for the atom-molecule dark state by using electromagnetically induced transparency (EIT) technique. Based on a density-matrix formalism, we calculate the...
Quantum Dynamics and Statistics Properties of Atom-Molecule Bose-Einstein Condensate (2005)
Jin, Guang-Ri, Kim, Chul Koo, Nahm, Kyun
Based on a two-mode boson model, we study nonclassical properties of the atom-molecule Bose-Einstein condensate. The effects of nonlinear collisions on the dynamics of the molecular formation is...
Modulational instability of two-component Bose-Einstein condensates in an optical lattice (2004)
Jin, Guang-Ri, Kim, Chul Koo, Nahm, Kyun
We study modulational instability of two-component Bose-Einstein condensates in an optical lattice, which is modelled as a coupled discrete nonlinear Schr \"{o}dinger equation. The excitation...
Diamagnetic response of Aharonov-Bohm rings: Impurity backward scatterings (2004)
Kim, Mun Dae, Kim, Chul Koo, Nahm, Kyun
We report a theoretical calculation on the persistent currents of disordered normal-metal rings. It is shown that the diamagnetic responses of the rings in the vicinity of the zero magnetic field are...
Ginzburg Landau theory of superconductivity at fractal dimensions (2004)
Kim, Chul Koo, Rakhimov, A., Yee, Jae Hyung
The post Gaussian effective potential in $D=2+2\veps$ dimensions is evaluated for the Ginzburg-Landau theory of superconductivity. Two and three loop integrals for the post Gaussian correction terms...
Rayleigh-Schroedinger-Goldstone variational perturbation theory for many fermion systems (2004)
We present a Rayleigh-Schroedinger-Goldstone perturbation formalism for many fermion systems. Based on this formalism, variational perturbation scheme which goes beyond the Gaussian approximation is...
Post Gaussian effective potential in the Ginzburg Landau theory of superconductivity (2003)
Kim, Chul Koo, Rakhimov, A., Yee, Jae Hyung
The post Gaussian effective potential in D=3 dimensions and the Gaussian effective potential in D=2+epsilon are evaluated for the Ginzburg-Landau theory of superconductivity. It is shown that, the...
Kondo lattice model with a direct exchange interaction between localized moments (2003)
Kim, Mun Dae, Kim, Chul Koo, Hong, Jongbae
We study the Kondo lattice model with a direct antiferromagnetic exchange interaction between localized moments. Ferromagnetically long-range ordered state coexisting with the Kondo screening shows a...
Fractional populations in multiple gene inheritance (2003)
Chung, Myung-Hoon, Kim, Chul Koo, Nahm, Kyun
Motivation: With complete knowledge of the human genome sequence, one of the most interesting tasks remaining is to understand the functions of individual genes and how they communicate. Using the...
The Functional Schr\"{o}dinger Picture Approach to Many-Particle Systems (2002)
A self-contained pedagogical introduction to the functional Schr\"{o}dinger picture method of many-body theory is given at a level suitable for graduate students and also for many-body physicists who...
Sine-Gordon Effective Potential beyond Gaussian Approximation (2002)
Lu, Wen-Fa, Kim, Chul Koo, Nahm, Kyun
Combining an optimized expansion scheme in the spirit of the background field method with the Coleman's normal-ordering renormalization prescription, we calculate the effective potential of...
Optimized Rayleigh-Schr\"{o}dinger Expansion of the Effective Potential (2002)
Lu, Wen-Fa, Kim, Chul Koo, Nahm, Kyun
An optimized Rayleigh-Schr\"{o}dinger expansion scheme of solving the functional Schr\"odinger equation with an external source is proposed to calculate the effective potential beyond the Gaussian...
Condensate of a charged boson fluid at non-integer dimensions (2002)
Kim, Sang-Hoon, Kim, Chul Koo, Nahm, Kyun
Condensate of a charged boson fluid at non-integer dimensions between 2 and 3 is studied. Interaction between particles is assumed to be Coulombic, and Bogoliubov approximation is applied for a weak...
Magnetic Polarization Currents in Double Quantum Dot Devices (2002)
Cho, Sam Young, McKenzie, Ross H., Kang, Kicheon, Kim, Chul Koo
We investigate coherent electron transport through a parallel circuit of two quantum dots, each of which has a single tunable energy level. Electrons tunneling via each dot from the left lead...
Impact of optical phonon scattering on magnetotransport in double-barrier heterostructures (2001)
Kim, Dae Kwan, Roblin, Patrick, Soh, Kwang-Sup, Kim, Chul Koo
The transport in double-barrier heterostructures of electrons interacting with longitudinal optical phonons in the presence of parallel electric and magnetic fields is analyzed theoretically with the...
Mesoscopic Luttinger Liquid Theory in an Aharonov-Bohm Ring (2001)
Kim, Mun Dae, Cho, Sam Young, Kim, Chul Koo, Nahm, Kyun
A careful study on the mesoscopic PC in a Luttinger liquid ring is carried out. It is shown that discreteness plays an important role in calculating the PC caused by the magnetic flux. At zero...
Kim, Tae-Suk, Cho, Sam Young, Kim, Chul Koo, Ryu, Chang-Mo
In this paper, we study the behavior of the transmission zeros in the closed Aharonov-Bohm(AB) interferometer with an embedded scattering center in one arm and the corresponding change in the...
For a class of system, the potential of whose Bosonic Hamiltonian has a Fourier representation in the sense of tempered distributions, we calculate the Gaussian effective potential within the...
Ferromagnetic Fixed Point of the Kondo Model in a Luttinger Liquid (2001)
Kim, Mun Dae, Kim, Chul Koo, Nahm, Kyun, Ryu, Chang-Mo
The Kondo effect in a Luttinger liquid is studied using the renormalization group method. By renormalizing the boson fields, scaling equations to the second order for an arbitrary Luttinger...
Within the sine-Gordon formalism of a two-dimensional neutral classical Coulomb gas, a convergent expansion with non-perturbative nature is performed to calculate the thermodynamic potential and...
Rayleigh-Schr\"{o}dinger Perturbation Theory Based on Gaussian Wavefunctional Approch (2001)
Lu, Wen-Fa, Kim, Chul Koo, Yee, Jae Hyung, Nahm, Kyun
A Rayleigh-Schr\"{o}dinger perturbation theory based on the Gaussian wavefunctional is constructed. The method can be used for calculating the energies of both the vacuum and the excited states. A...
Spin Fluctuation and Persistent Current in a Mesoscopic Ring Coupled to a Quantum Dot (2000)
Cho, Sam Young, Kang, Kicheon, Kim, Chul Koo, Ryu, Chang-Mo
We investigate the persistent current influenced by the spin fluctuations in a mesoscopic ring weakly coupled to a quantum dot. It is shown that the Kondo effect gives rise to some unusual features...
A Variational Expansion for the Free Energy of a Bosonic System (2000)
Lu, Wen-Fa, You, Sang Koo, Bak, Jino, Kim, Chul Koo, Nahm, Kyun
In this paper, a variational perturbation scheme for nonrelativistic many-Fermion systems is generalized to a Bosonic system. By calculating the free energy of an anharmonic oscillator model, we...
You, Sang Koo, Kim, Chul Koo, Nahm, Kyun, Noh, Hyun Sik
A variational Perturbation theory based on the functional integral approach is formulated for many-particle systems. Using the variational action obtained through Jensen-Peierls' inequality, a...
Ideal Bose gas in fractal dimensions and superfluid $^4$He in porous media (1999)
Kim, Sang-Hoon, Kim, Chul Koo, Nahm, Kyun
Physical properties of ideal Bose gas with the fractal dimensionality between D=2 and D=3 are theoretically investigated. Calculation shows that the characteristic features of the specific heat and...
Fractional Populations in Sex-linked Inheritance (1998)
Lee, Seung Pyo, Chung, Myung-Hoon, Kim, Chul Koo, Nahm, Kyun
We study the fractional populations in chromosome inherited diseases. The governing equations for the fractional populations are found and solved in the presence of mutation and selection. The...
Kim, Sang-Hoon, Noh, Hyun Sik, Kim, Dae Kwan, Kim, Chul Koo, Nahm, Kyun
A dilute Bose gas system is studied using the functional Schr\"{o}dinger picture theory. The ground state properties are obtained by solving the infinite dimensional Schr\"{o}dinger equation...
Multi-anyons in the magnetic field (1998)
Choi, Taeseung, Ryu, Chang-Mo, Kim, Chul Koo
We consider the external magnetic field effects on the two types of anyon with fractional statistical parameters $p/q$ with coprimes $p$ and $q$, one with fractional charge $e/q $ and flux $p...
A new approximation scheme in quantum mechanics (1997)
You, Sang Koo, Jeon, Kwang Joe, Kim, Chul Koo, Nahm, Kyun
An approximation method which combines the perturbation theory with the variational calculation is constructed for quantum mechanical problems. Using the anharmonic oscillator and the He atom as...
The O(N) Nonlinear Sigma Model in the Functional Schr\"{o}dinger Picture (1997)
We present a functional Schr\"{o}dinger picture formalism of the (1+1)-dimensional $O(N) $ nonlinear sigma model. The energy density has been calculated to two-loop order using the wave functional of...
Noh, Hyun Sik, You, Sang Koo, Kim, Chul Koo
A finite temperature many-particle theory of condensed matter systems is formulated using the functional Schroedinger picture. Using the interacting electron gas as a model system, we solve the...
The effects of parameter variation on helicopter performance.
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Resultant Pressure Distribution Pattern along the Basilar Membrane in the Spiral Shaped Cochlea
Zhang, Yong, Kim, Chul Koo, Lee, Kong-Ju-Bock, Park, Youngah
The cochlea is an important auditory organ in the inner ear. In most mammals, it is coiled as a spiral. Whether this specific shape influences hearing is still an open problem. By employing a...