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40 GHz 대역에서 프라임 부호를 이용한 RoF 시스템용 DOS-CDMA 실험적 연구
崔宰源,全榮民,朴鐘大,徐東善 明知大學校 産業技術硏究所 2004 産業技術硏究所論文集 Vol.23 No.-
In this paper, we propose and demonstrate a future wide band mobile communication technology based on millimeter-wave Direct Optical Switching CDMA (MMW DOS-CDMA) in Radio-over-Fiber system. This DOS-CDMA system uses millimeter waves in 40 GHz bands as its carrier waves, which is much higher than the frequencies of several GHz used in the existing mobile communication technology. Orthogonal codes used in the encoding and decoding in CDMA have two types: prime code and unipolar code. Unipolar orthogonal code is used to eliminate padding chip. The code lengths and chip rates of the two orthogonal codes were 16 chips and 2.5 Gchip/sec, respectively. We selected code sequences with cross-correlation less than 2. Pulse-amplitude-equalized 40 GHz laser pulses were provided by rational-harmonically mode locked a 10 GHz fiber ring laser. By experiments, the RF spectra of the decoded optical signals and the optical interference noises showed noise suppression of 20 dB. However, CIR (Carrier-to-Interference power Ratio) raised to 45 dB after 40 GHz filtering of the decoded optical signals. Moreover, since the code frequency was 156MHz (2.5 Gcps/16), MMW signal bandwidth was as large as 78 MHz without spectral aliasing canceling.
Hierarchical Multiscale Modeling Method for Head/Disk Interface
Jhon, M S,Smith, R,Vemuri, S H,Pil Seung Chung,Dehee Kim,Biegler, L T IEEE 2011 IEEE transactions on magnetics Vol.47 No.1
<P>Multiscale modeling opens a new paradigm by providing a novel methodology of establishing molecular design criteria and potentially gives several orders of magnitude advances in nanotechnology. The head/disk interface (HDI) in the hard disk drive system investigated here can be used as a benchmark for multiscale modeling. Our approach, stemmed from the novel middle-out approach in modern multiscale modeling using the lattice Boltzmann method (LBM) as the centerpiece formulation, marches towards continuum level (top) and molecular level (bottom). This approach will become an extremely valuable tool in generating design criteria of HDI.</P>
The mechanical responses of tilted and non-tilted grain boundaries in graphene
Jhon, Y.I.,Zhu, S.E.,Ahn, J.H.,Jhon, M.S. Pergamon Press ; Elsevier Science Ltd 2012 Carbon Vol.50 No.10
Various mechanical characteristics of tilted and non-tilted grain boundaries in graphene were investigated under tension and compression in directions perpendicular and parallel to the grain boundaries using molecular dynamics simulation. In contrast to the non-tilted grain boundary and the pristine graphene, the mechanical response of tilted grain boundary was observed to be quite unique under perpendicular tension, exhibiting distinct crack propagation prior to tensile failure and the subsequent pattern of incomplete fracture. These features are manifested as a remarkable decrease in the slope and a rugged pattern in the stress-strain curves. The characteristic of incomplete fracture was striking especially for large misorientation angles with formation of long monoatomic carbon chains, suggesting a methodology for feasible production of the monoatomic carbon chains that have been difficult to synthesize and extract. Under perpendicular compression, the folding of the sheet occurred consistently along grain boundaries during the entire process, indicating a tunable folding, while the folding line wandered extensively for pristine graphene. Under parallel compression, we found that folding along grain boundaries disturbed the bending of the graphene substantially for intrinsic reinforcement.
Orientation dependence of the fracture behavior of graphene
Jhon, Y.I.,Jhon, Y.M.,Yeom, G.Y.,Jhon, M.S. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.66 No.-
Graphene has unique mechanical properties in that it is simultaneously very strong and stretchy, which severely hampers the prediction of its orientation-dependent fracture behavior based on conventional theories used for common brittle or ductile materials. For the first time, by exploring the entire range of available tensile orientations, this study reveals the unique anisotropic fracture response of graphene using molecular dynamics simulations. We found that, as the uniaxial tensile direction rotates from armchair (0<SUP>o</SUP>) to zigzag orientation (30<SUP>o</SUP>), both the tensile strength and strain remain almost constant up to an orientation angle of ~12<SUP>o</SUP>, then they rapidly increase (exponential growth), resulting in a remarkable degradation of the tensile strength compared to brittle fracture counterpart (inverse-sinusoidal growth). This typical fracture pattern holds for 100-700K. We propose a model that can explain its physical origin in good agreement with the simulation results. We also found that the elastic behavior of graphene is quasi-isotropic for all tensile orientations, in contrast to its anisotropic fracture behavior. Using indentation simulations of graphene, we showed that the anisotropic/isotropic features of fracture/elasticity are also well-preserved in the two-dimensional tensile systems but its fracture anisotropicity is greatly attenuated due to the inherent sixfold symmetry of graphene.
Polyaniline and its modification for electroresponsive material under applied electric fields
Cho, M. S.,Kim, J. W.,Choi, H. J.,Jhon, M. S. John Wiley Sons, Ltd. 2005 Polymers for advanced technologies Vol.16 No.4
<P>Polyaniline (PANI) and its various copolymers were synthesized using different monomers such as o-methyl-, o-methoxy-, o-ethyl-, o-ethoxyaniline and sodium diphenylamine sulfonate by the chemical oxidation polymerization as air-stable organic conducting polymers, and adopted as one of the most potential materials of electrorheological (ER) fluids, especially for the anhydrous system. A relatively low density, a controllable conductivity, and thermal stability are advantages of the PANI based ER system compared with other ER materials. An FT-IR analysis was adopted to confirm their synthesis and a scanning electron microscopy (SEM) analysis indicated the shape of PANI derivatives was irregular. The effect of functional group of PANI on electric and electroresponsive properties of poly(aniline-co-ethoxyaniline) (COPA) particles were examined. A universal scaling equation of the yield stress was applied to these ER fluids and it was found that all data were collapsed successfully onto a single curve regardless of monomer type of the polyaniline synthesized. Copyright © 2005 John Wiley & Sons, Ltd.</P>
Perfluoropolyether Lubricant Interactions With Novel Overcoat via Coarse-Grained Molecular Dynamics
Vemuri, S. H.,Pil Seung Chung,Smith, R.,Geun-Young Yeom,Young In Jhon,Nae-Eung Lee,Biegler, L. T.,Jhon, M. S. IEEE 2012 IEEE transactions on magnetics Vol.48 No.11
<P>In this paper, we investigated physiochemical properties of new lubricant candidates for head-disk interface through various perfluoropolyether lubricant films on diamond, diamond-like carbon, and graphene overcoat surfaces via large scale coarse-grained bead-spring molecular dynamics stemming from the atomistic theory. Lubricant film conformations were characterized by investigating perpendicular component of molecular conformation, which determines the thickness of monolayer lubricant film. The distribution of functional endgroups and the mobility were analyzed via self-diffusion process. Here, we illustrate the effects of endgroup structure and carbon-surface structure on the film conformation and the mobility by expanding the multiscale simulation methodology and select candidates for future HDI design.</P>
ELECTRORHEOLOGICAL POLYANILINE DISPERSIONS USING VERTICAL OSCILLATION RHEOMETER
Cho, M.S.,Lee, J.H.,Choi, H.J.,Kim, S.K.,Jhon, M.S. 한국재료학회 1995 Fabrication and Characterization of Advanced Mater Vol.1 No.3
Rheological properties of electrorheological(ER) fluids have been investigated by either steady-shear test or dynamic test. In this work, we studied rheological properties of polyaniline-silicone oil ER system through dynamci mechanical test using vertical oscillation rheometer(VOR) that is designed by our lab. It was then calibrated with Physcia rheometer using corn starch-polybutene(PB)/kerosene system. Data from VOR rwer quite reliable in a wide range of either strain or frequency. For amplitude sweep of polyaniline system, G's in linear region were slightly different with each otehr for the applied electric field, but the linear range was becoming larger as increasing elecric field. From begining of the nonlinear region, the differences were becoming bigger and input strain wave began to distort.