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Search Results: 1 - 10 of 44218 matches for " Yong-Hoon Kim "
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Weather Radar Network with Pulse Compression of Arbitrary Nonlinear Waveforms: Ka-Band Test-Bed and Initial Observations
Hoon Lee;Yong-Hoon Kim
PIER B , 2010, DOI: 10.2528/PIERB10071402
Abstract: Short-wavelength radar networks are expected to complement current long-range weather radar systems. Accordingly, we proposed a configuration for such a network constituting pulse compression radars in order to use frequency resources efficiently and obtain multi-static information. We developed high resolution Ka-band pulse compression weather radar system as a test-bed. Using a commercial direct digital synthesizer (DDS) and field programmable gate array (FPGA) control, we generated linear and arbitrary nonlinear frequency modulated waveforms for low range sidelobes. Further, we completed a high duty factor system with a solid-state power amplifier. In a vertical-pointing mode, we were able to employ the developed radar to detect moderate rainfall up to 15 km. Details of the system design, hardware structure, data acquisition and processing algorithms were described. To validate the performance of the proposed radar system, we conducted several experiments by measuring cloud, snow and rain.
Recent progress in atomistic simulation of electrical current DNA sequencing
Han Seul Kim,Yong-Hoon Kim
Physics , 2014, DOI: 10.1016/j.bios.2015.02.020
Abstract: We review recent advances in the DNA sequencing based on the measurement of transverse electrical currents. Device configurations proposed in the literature are classified according to whether the molecular fingerprints appear as the major (Mode I) or perturbing (Mode II) current signals. Scanning tunneling microscope and tunneling electrode gap configurations belong to the former category, while the nanochannels with or without an embedded nanopore belong to the latter. The molecular sensing mechanisms of Modes I and II roughly correspond to the electron tunneling and electrochemical gating, respectively. Special emphasis will be given on the computer simulation studies, which have been playing a critical role in the initiation and development of the field. We also highlight low-dimensional nanomaterials such as carbon nanotubes, graphene, and graphene nanoribbons that allow the novel Mode II approach. Finally, several issues in previous computational studies are discussed, which points to future research directions toward more reliable simulation of electrical current DNA sequencing devices.
Excitonic optical spectrum of semiconductors obtained by time-dependent density-functional theory with the exact-exchange kernel
Yong-Hoon Kim,Andreas Goerling
Physics , 2002, DOI: 10.1103/PhysRevLett.89.096402
Abstract: Applying the novel exact-exchange (EXX) Kohn-Sham method within time-dependent density-functional theory, we obtained the optical absorption spectrum of bulk silicon in good agreement with experiments including excitonic features. Analysis of the EXX kernel shows that inclusion of the Coulomb coupling of electron-hole pairs and the correct long-wavelength behavior in the kernel is crucial for the proper description of excitonic effects in semiconductors.
Exact Kohn-Sham exchange kernel for insulators and its long-wavelength behavior
Yong-Hoon Kim,Andreas Goerling
Physics , 2002, DOI: 10.1103/PhysRevB.66.035114
Abstract: We present an exact expression for the frequency-dependent Kohn-Sham exact-exchange (EXX) kernel for periodic insulators, which can be employed for the calculation of electronic response properties within time-dependent (TD) density-functional theory. It is shown that the EXX kernel has a long-wavelength divergence behavior of the exact full exchange-correlation kernel and thus rectifies one serious shortcoming of the adiabatic local-density approximation and generalized-gradient approximations kernels. A comparison between the TDEXX and the GW-approximation-Bethe-Salpeter-equation approach is also made.
Prediction of ultra-high ON/OFF ratio nanoelectromechanical switching from covalently-bound C60 chains
Han Seul Kim,Jhinhwan Lee,Yong-Hoon Kim
Physics , 2013, DOI: 10.1016/j.carbon.2013.09.054
Abstract: Applying a first-principles computational approach, we have systematically analyzed the effects of [2+2] cycloaddition oligomerization of fullerene C60 chains on their junction electronic and charge transport properties. For hypothetical infinite C60 chains, we first establish that the polymerization can in principle increase conductance by several orders of magnitude due to the strong orbital hybridizations and band formation. On the other hand, our simulations of the constant-height scanning tunneling microscope (STM) configuration shows that, in agreement with the recent experimental conclusion, the junction electronic structure and device characteristics are virtually unaffected by the C60 chain oligomerization. We further predict that the switching characteristics including even the ON/OFF-state assignment will sensitively depend on the substrate metal species due to the Fermi-level pinning at the substrate-side contact and the subsequent energy level bending toward the STM tip-side contact. We finally demonstrate that a force-feedbacked nanoelectromechanical approach in which both of the C60-electrode distances are kept at short distances before and after switching operations can achieve a metal-independent and significantly improved switching performance due to the Fermi-level pinning in both contacts and the large intrinsic conductance switching capacity of the C60 chain oligomerization.
Distinct mechanisms of DNA sensing based on N-doped carbon nanotubes with enhanced conductance and chemical selectivity
Han Seul Kim,Seung Jin Lee,Yong-Hoon Kim
Physics , 2012, DOI: 10.1002/smll.201301225
Abstract: Carrying out first-principles calculations, we study N-doped capped carbon nanotube (CNT) electrodes applied to DNA sequencing. While we obtain for the face-on nucleobase junction configurations a conventional conductance ordering where the largest signal results from guanine according to its high highest occupied molecular orbital (HOMO) level, we extract for the edge-on counterparts a distinct conductance ordering where the low-HOMO thymine provides the largest signal. The edge-on mode is shown to operate based on a novel molecular sensing mechanism that reflects the chemical connectivity between N-doped CNT caps that can act both as electron donors and electron acceptors and DNA functional groups that include the hyperconjugated thymine methyl group.
An Adaptively Accelerated Bayesian Deblurring Method with Entropy Prior
ManojKumar Singh,Uma Shanker Tiwary,Yong-Hoon Kim
EURASIP Journal on Advances in Signal Processing , 2008, DOI: 10.1155/2008/674038
Abstract: The development of an efficient adaptively accelerated iterative deblurring algorithm based on Bayesian statistical concept has been reported. Entropy of an image has been used as a ¢ € prior ¢ € distribution and instead of additive form, used in conventional acceleration methods an exponent form of relaxation constant has been used for acceleration. Thus the proposed method is called hereafter as adaptively accelerated maximum a posteriori with entropy prior (AAMAPE). Based on empirical observations in different experiments, the exponent is computed adaptively using first-order derivatives of the deblurred image from previous two iterations. This exponent improves speed of the AAMAPE method in early stages and ensures stability at later stages of iteration. In AAMAPE method, we also consider the constraint of the nonnegativity and flux conservation. The paper discusses the fundamental idea of the Bayesian image deblurring with the use of entropy as prior, and the analytical analysis of superresolution and the noise amplification characteristics of the proposed method. The experimental results show that the proposed AAMAPE method gives lower RMSE and higher SNR in 44% lesser iterations as compared to nonaccelerated maximum a posteriori with entropy prior (MAPE) method. Moreover, AAMAPE followed by wavelet wiener filtering gives better result than the state-of-the-art methods.
Multiplicity Results of Positive Radial Solutions for p-Laplacian Problems in Exterior Domains
Chan-Gyun Kim,Yong-Hoon Lee,Inbo Sim
Boundary Value Problems , 2008, DOI: 10.1155/2008/395080
Abstract: We find the second positive radial solution for the following p-Laplacian problem: div(| ¢ u|p ¢ ’2 ¢ u)+K(|x|)uq=0 in , u| ¢ =0, u(x) ¢ ’ >0 as |x| ¢ ’ ¢ , where ={x ¢ ¢ N:|x|>r0}, r0>0, N>p>1, K ¢ C( ,(0, ¢ )) and q>p ¢ ’1. We also give some global existence results with respect to the parameter .
Multiplicity Results of Positive Radial Solutions for -Laplacian Problems in Exterior Domains
Kim Chan-Gyun,Lee Yong-Hoon,Sim Inbo
Boundary Value Problems , 2008,
Abstract: We find the second positive radial solution for the following -Laplacian problem: in , , as , where , , , and . We also give some global existence results with respect to the parameter .
Density-functional Study of Small Molecules within the Krieger-Li-Iafrate Approximation
Yong-Hoon Kim,Martin St?dele,Richard M. Martin
Physics , 1999, DOI: 10.1103/PhysRevA.60.3633
Abstract: We report density-functional studies of several small molecules ($H_{2}, N_{2}, CO, H_{2}O$, and $CH_{4}$) within the Krieger-Li-Iafrate (KLI) approximation to the exact Kohn-Sham local exchange potential, using a three-dimensional real-space finite-difference pseudopotential method. It is found that exchange-only KLI leads to markedly improved eigenvalue spectra compared to those obtained within the standard local-density approximation (LDA), the generalized gradient approximation (GGA), and the Hartree-Fock (HF) method. For structural properties, exchange-only KLI results are close to the corresponding HF values. We find that the addition of LDA or GGA correlation energy functionals to the KLI exact exchange energy functional does not lead to systematic improvements.
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