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Search Results: 1 - 10 of 25318 matches for " Jaehoon Lee "
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Algebra of Majorana Doubling
Jaehoon Lee,Frank Wilczek
Physics , 2013, DOI: 10.1103/PhysRevLett.111.226402
Abstract: Motivated by the problem of identifying Majorana mode operators at junctions, we analyze a basic algebraic structure leading to a doubled spectrum. For general (nonlinear) interactions the emergent mode creation operator is highly non-linear in the original effective mode operators, and therefore also in the underlying electron creation and destruction operators. This phenomenon could open up new possibilities for controlled dynamical manipulation of the modes. We briefly compare and contrast related issues in the Pfaffian quantum Hall state.
Design of a MIMO Antenna with Improved Isolation Using MNG Metamaterial
Youngki Lee,Deukhyeon Ga,Jaehoon Choi
International Journal of Antennas and Propagation , 2012, DOI: 10.1155/2012/864306
Abstract: A multi-input multi-output (MIMO) antenna with improved isolation using an interdigital split ring resonator (SRR) is proposed. The necessary impedance bandwidth is obtained by utilizing the coupling between the meander strip and an inverted L strip. Using interdigital SRR, a negative permeability was generated, while achieving improved isolation between the two radiating elements. The fabricated antenna satisfies the 10 dB return loss in the long-term evolution (LTE) band 40 from 2.3 GHz to 2.4 GHz. The measured peak gains of the two elements were 2.0 dBi and 1.3 dBi. The measured envelope correlation coefficient was less than 0.16 over the frequency band of interest.
Design of a Compact MIMO Antenna Using Coupled Feed for LTE Mobile Applications
Xing Zhao,Youngki Lee,Jaehoon Choi
International Journal of Antennas and Propagation , 2013, DOI: 10.1155/2013/837643
Abstract:
Critical Exponents for Supercooled Liquids
Ethan Dyer,Jaehoon Lee,Sho Yaida
Physics , 2013,
Abstract: We compute critical exponents governing universal features of supercooled liquids through the effective theory of an overlap field. The correlation length diverges with the Ising exponent; the size of dynamically heterogeneous patches grows more rapidly; and the relaxation time obeys a generalized Vogel-Fulcher-Tammann relation.
Dynamical heterogeneity and dynamic overlap field
Ethan Dyer,Jaehoon Lee,Sho Yaida
Physics , 2013,
Abstract: Glass-forming liquids universally display dramatic dynamical slowdown within a modest temperature range. This staggering slowdown is long thought to be accompanied by growing length scales. We introduce a dynamic overlap field whose two-point correlation length captures one of these length scales, associated with dynamical heterogeneity. The growth of this length is further confirmed through large scale molecular dynamics simulations.
Feasibility Study of Gas Electron Multiplier Detector as an X-Ray Image Sensor
Sukyoung Shin,Jaehoon Jung,Soonhyouk Lee
Physics , 2015,
Abstract: For its ease manufacturing, flexible geometry, and cheap manufacturing cost, the gas electron multiplier (GEM) detector can be used as an x-ray image sensor. For this purpose, we acquired relative detection efficiencies and suggested a method to increase the detection efficiency in order to study the possibility of GEM detector as an x-ray image sensor. The GEM detector system is composed of GEM foils, the instrument system, the gas system, and the negative power supply. The instrument system consists of the A225 charge sensitive preamp, A206 discriminator, and MCA8000D multichannel analyzer. For the gas system, Argon gas was mixed with CO2 to the ratio of 8:2, and for the negative 2,000 volts, the 3106D power supply was used. The CsI-coated GEM foil was used to increase the detection efficiency. Fe-55 was used as an x-ray source and the relative efficiency was acquired by using the ratio of GEM detector to the CdTe detector. The total count method and the energy spectrum method were used to calculate the relative efficiency. The relative detection efficiency of GEM detector for Fe-55 by using total count method was 32 % and by using energy spectrum method, the relative efficiencies were 5, 43, 33, 37, 35, and 36 % respectively according to the energy spectrum of 2, 3, 4, 5, 6, and 7 KeV. In conclusion, we found that the detection efficiency of the two layered GEM detector is insufficient for the x-ray image sensor, so we suggested a CsI coated GEM foil to increase the efficiency rate and the result value was increased to 41 %.
Saturation Power based Simple Energy Efficiency Maximization Schemes for MU-MISO Systems
Jaehoon Jung,Sang-Rim Lee,Inkyu Lee
Mathematics , 2015,
Abstract: In this paper, we investigate an energy efficiency (EE) maximization problem in multi-user multiple input single output downlink channels. The optimization problem in this system model is difficult to solve in general, since it is in non-convex fractional form. Hence, conventional algorithms have addressed the problem in an iterative manner for each channel realization, which leads to high computational complexity. To tackle this complexity issue, we propose a new simple method by utilizing the fact that the EE maximization is identical to the spectral efficiency (SE) maximization for the region of the power below a certain transmit power referred to as saturation power. In order to calculate the saturation power, we first introduce upper and lower bounds of the EE performance by adopting a maximal ratio transmission beamforming strategy. Then, we propose an efficient way to compute the saturation power for the EE maximization problem. Once we determine the saturation power corresponding to the maximum EE in advance, we can solve the EE maximization problem with SE maximization schemes with low complexity. The derived saturation power is parameterized by employing random matrix theory, which relies only on the second order channel statistics. Hence, this approach requires much lower computational complexity compared to a conventional scheme which exploits instantaneous channel state information, and provides insight on the saturation power. Numerical results validate that the proposed algorithm achieves near optimal EE performance with significantly reduced complexity.
A New Energy Efficient Beamforming Strategy for MISO Interfering Broadcast Channels based on Large Systems Analysis
Sang-Rim Lee,Jaehoon Jung,Haewook Park,Inkyu Lee
Mathematics , 2015,
Abstract: In this paper, we propose a new beamforming design to maximize energy efficiency (EE) for multiple input single output interfering broadcast channels (IFBC). Under this model, the EE problem is non-convex in general due to the coupled interference and its fractional form, and thus it is difficult to solve the problem. Conventional algorithms which address this problem have adopted an iterative method for each channel realization, which requires high computational complexity. In order to reduce the computational complexity, we parameterize the beamforming vector by scalar parameters related to beam direction and power. Then, by employing asymptotic results of random matrix theory with this parametrization, we identify the optimal parameters to maximize the EE in the large system limit assuming that the number of transmit antennas and users are large with a fixed ratio. In the asymptotic regime, our solutions depend only on the second order channel statistics, which yields significantly reduced computational complexity and system overhead compared to the conventional approaches. Hence, the beamforming vector to maximize the EE performance can be determined with local channel state information and the optimized parameters. Based on the asymptotic results, the proposed scheme can provide insights on the average EE performance, and a simple yet efficient beamforming strategy is introduced for the finite system case. Numerical results confirm that the proposed scheme shows a negligible performance loss compared to the best result achieved by the conventional approaches even with small system dimensions, with much reduced system complexity.
Design of a Dual-Band On-Body Antenna for a Wireless Body Area Network Repeater System
Kyeol Kwon,Jaegeun Ha,Soonyong Lee,Jaehoon Choi
International Journal of Antennas and Propagation , 2012, DOI: 10.1155/2012/350797
Abstract: A dual-band on-body antenna for a wireless body area network repeater system is proposed. The designed dual-band antenna has the maximum radiation directed toward the inside of the human body in the medical implantable communication service (MICS) band in order to collect vital information from the human body and directed toward the outside in the industrial, scientific, and medical (ISM) band to transmit that information to a monitoring system. In addition, the return loss property of the antenna is insensitive to human body effects by utilizing the epsilon negative zeroth-order resonance property. 1. Introduction Recently, there has been increasing interest in wireless body area network (WBAN) systems for a variety of applications such as biomedical, military, and commercial services. Especially in biomedical applications, in order to monitor a patient’s health status, an implanted device needs to collect various physiological data and wirelessly transmit the information to external medical devices in real time [1]. However, they have a short transmission range due to the low radiation efficiency and the effective radiated power (ERP) regulation of 25?μW. This limitation demonstrates the necessity of a dual-band on-body repeater antenna to deliver weak signals from implanted devices to external devices. In addition, antenna performance is significantly affected by body tissues due to the high dielectric constant and conductivity at the microwave frequency band. Also, the input impedance and resonance frequency cannot be changed, but the gain and radiation efficiency of an antenna can also be deteriorated when an antenna is operated on or in a body. In order to be insensitive to the human body effect, compact zeroth-order resonance (ZOR) antennas for implantable and wearable WBAN systems were proposed in [2, 3]. Additionally, to protect the human body from radio wave exposure, the structure of the antennas for WBAN must have a low specific absorption rate (SAR) [4]. In this paper, we present a novel on-body antenna for a WBAN repeater system. The proposed antenna has a dual-band property that covers the industrial, scientific, and medical (ISM) bands and the medical implantable communication service (MICS) band. Also, the return loss of the antenna is insensitive to human body effects, and the radiation pattern of the antenna is suitable for a repeater system. The antenna structure is designed and analyzed using FEM-based commercial software ANSYS HFSS v.14.0.0 [5]. A semisolid human body phantom is used for verification of the performance of the
Association between FGFR1OP2/wit3.0 Polymorphisms and Residual Ridge Resorption of Mandible in Korean Population
Jee Hwan Kim, Min Young Oh, Janghyun Paek, Jaehoon Lee
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0042734
Abstract: Background A previous study on the genetic association between single nucleotide polymorphisms in FGFR1OP2/wit3.0 and the long term atrophy of edentulous mandible hypothesized that the excessive jawbone atrophy after dental extraction may be associated with abnormal oral mucosa contraction induced by the FGFR1OP2/wit 3.0 gene. It was reported that the minor allele of rs840869 or rs859024 in FGFR1OP2/wit3.0 was associated with the excessive atrophy of edentulous mandible. The present study represents an attempt to replicate the results of this previous study and to examine the genetic association between polymorphisms in FGFR1OP2 and residual ridge resorption of mandible in a Korean population. Methodology/Principal Findings 134 subjects (70.46±9.02 years) with partially or completely edentulous mandible were recruited. The mandibular bone height was measured following the protocol of the American College of Prosthodontists (ACP). From 24 subjects, seven variants in FGFR1OP2 were discovered and four of them were novel. Selected SNPs that are not in high LD at r2 threshold of 0.8 were genotyped for the remaining population. There was no frequency of the minor allele of SNP rs859024 in Korean population. SNP rs840869 was not associated with residual ridge resorption (p = 0.479). The bone height of the subject with the ss518063493 minor allele (8.52 mm) was shorter than that of those subjects with major alleles (18.96±5.33 mm, p = 0.053). Conclusions/Significance The patient with minor allele of ss518063493 may be associated with excessive atrophy of edentulous mandible whereas the patients with that of rs840869 are not associated in Korean population. The result from this study may assist in developing a novel genetic diagnostic test and be useful in identifying Koreans susceptible to developing excessive jawbone atrophy after dental extraction.
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