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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.
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.
Topological Insulators for Mode-Locking of 2-μm Fiber Lasers
Jhon, Young In,Lee, Jinho,Jhon, Young Min,Lee, Ju Han IEEE 2018 IEEE journal of selected topics in quantum electro Vol.24 No.5
<P>We performed density functional theory calculations for the topological insulators (TIs) of Bi<SUB>2</SUB>Se<SUB>3 </SUB> and CoSb<SUB>3</SUB> (skutterudite) in a comparison with Bi<SUB>2</SUB>Te<SUB>3</SUB> and In<SUB>2</SUB>Co<SUB>4 </SUB>Sb<SUB>12</SUB> (filled skutterudite) to explore whether the former TIs can serve as saturable-absorption materials for laser mode-locking at the wavelengths of 2 μm and beyond. The calculated electronic-band structures and optical-absorption spectra indicate the potential of these TIs in terms of midinfrared saturable-absorption applications. Especially, in consideration of the film and bulk forms of Bi<SUB>2</SUB>Se<SUB>3 </SUB> and Bi<SUB>2</SUB>Te<SUB>3</SUB>, we investigated the electronic and/or optical properties of the metallic surface states and the semiconducting interior states, respectively. They exhibited an excellent broadband operability regardless of the state, and particularly, we noted a linearly dispersive relation around the Fermi levels of all of the electrons of the Bi<SUB>2</SUB>Se<SUB>3</SUB> surface in both the conduction and valence bands, whereas this is not evident for Bi<SUB>2</SUB>Te<SUB>3</SUB>. Assuming the importance of linear dispersion for a fast electronic relaxation, and considering the decent oxidation resistance of the Bi<SUB>2</SUB>Se<SUB>3</SUB> surface, we suggest that Bi<SUB>2</SUB>Se<SUB>3</SUB> is superior to Bi<SUB>2</SUB>Te<SUB>3</SUB> for midinfrared mode-locking. A review of the experimental studies regarding TI-based 2-μm saturable absorbers that have been performed so far is presented, and the discussion and rationalization of the possible universality of TIs regarding mid- to far-infrared passive mode lockers results in the suggestion of a new CoSb<SUB>3</SUB>-TI-based saturable absorber.</P>
Thermodynamic Properties of Aliphatic and Aromatic Hydrocarbons in Liquid Water
성용길,김은식,전무식,Sung Yong Kiel,Kim Un Shik,Jhon Mu Shik Korean Chemical Society 1972 대한화학회지 Vol.16 No.5
지방족 및 방향족 탄화수소의 수용액을 Jhon 등이 제창한 liquid water의 significant structure theory 를 이용하여 연구하였으며 Helmholtz free energy, internal energy, entropy, heat capacity 등의 열역학적 성질을 계산하였다. 계산결과는 문헌에 발표된 실험치와 잘 일치됨을 볼 수 있다 The aqueous solutions of aliphatic and aromatic hydrocarbons have been studied on the basis of the significant structure theory of liquid water proposed by Jhon, et al. The thermodynamic properties such as Helmholtz free energy, internal energy entropy, and heat capacity have been calculated. The results show good agreements with the experiments in the literature.
성용길,전무식,Yong Kil Sung,Mu Shik Jhon Korean Chemical Society 1970 대한화학회지 Vol.14 No.2
The extension of the theory of the electrolyte solution to the calculation of the hydration number and the mean activity coefficient of some 1:1 electrolytes in the concentrated solutions has been made. In this derivation, the hydration number has been calculated from the equation of the dielectric constant proposed by Hobbs, Jhon, and Eyring, and the mean activity coefficient from the theoretical formula developed by Jhon and Eyring. The agreement between theory and experiment over a.wide concentration range is quite satisfactory.
JHON, DEOK-YOUNG,LEE, SUN-HO 한국미생물 · 생명공학회 2003 Journal of microbiology and biotechnology Vol.13 No.6
The complete 1,486 nucleotide sequence of a cryptic plasmid separated from Lactobacillus bifermentans strain A02 isolated from Kimchi has been determined. The plasmid, designated as pA021, encodes a 33,488 Da putative Rep protein. Based on the sequence similarity, the protein shows homology with coding protein of pRS I , a previously reported plasmid of 0enncoccus oeni and the replication initiation protein (Rep) of the Staphylococcal pT181 plasmid family.
RF protection technique of antenna tuning switch in all-off condition
Jhon, Heesauk,Lee, Sanghun The Korea Institute of Information and Commucation 2022 한국정보통신학회논문지 Vol.26 No.10
This paper, we presents a RF protection technique of antenna switch by improving the power handling capability in worst case environment mode for mobile phone applications without critical payment of circuit performances such as insertion loss, isolation and ACBV (AC breakdown voltage). By applying a additional capacitive path located in front of the antenna in cell-phone, it performs the effective reduction of input power in high voltage standing wave ratio (VSWR) condition. Under the all-path off condition which causes a high VSWR, it achieved 37.7dBm power handling level as high as 5.7dB compared to that of conventional one at 2GHz. In addition, insertion loss and isolation performances were 0.31dB and 42.72dB at 2 GHz, respectively which were almost similar to that of the conventional circuit. The proposed antenna switch was fabricated in 130nm CMOS SOI technology.