• Journal of Magnetics
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• 제14권2호
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• pp.53-61
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• 2009

Herein, different concepts for domain wall propagation based on currents and fields that could potentially be used in magnetic data storage devices based on domains and domain walls are reviewed. By direct imaging, we show that vortex and transverse walls can be displaced using currents due to the spin transfer torque effect. For the case of field-induced wall motion, particular attention is paid to the influence of localized fields and local heating on the depinning and propagation of domain walls. Using an Au nanowire adjacent to a permalloy structure with a domain wall, the depinning field of the wall, when current pulses are injected into the Au nanowire, was studied. The current pulse drastically modified the depinning field, which depended on the interplay between the externally applied field direction and polarity of the current, leading subsequently to an Oersted field and heating of the permalloy at the interface with the Au wire. Placing the domain wall at various distances from the Au wire and studying different wall propagation directions, the range of Joule heating and Oersted field was determined; both effects could be separated. Approaches beyond conventional field- and current-induced wall displacement are briefly discussed.

• Journal of Magnetics
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• 제7권2호
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• pp.29-39
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• 2002

The initial NiCuZn synthetic ferrite were acquired from thermally decomposing the metal nitrates $Fe(NO_3)_39H_2O, Zn(NO_3)_26H_2O, Ni(NO_3)_26H_2O, and Cu(NO_3)_23H_2O$ at $150^circ{C}$ for 24 hours, and then we calcined the synthetic powder at $500^circ{C}$, pulverized each of those for 3, 6, 9, 12, and 15 hours in a steel ball mill, sintered each at $700^circ{C}$ to $1,000^circ{C}$ for 1 hour, and thus studied their microstructures and electromagnetic properties. We could make the initial specimens chemically bonded in liquidity at a low-temperature $150^circ{C}$, by using the low melting points less than $200^circ{C}$ of the metal nitrates instead of the mechanical ball-mill pulverization, then narrow a distance between the particles into a molecular one, and thus lower the reaction point of sintering by at least $200^circ{C}$ to $300^circ{C}$. Their initial permeability was 50 to 400 and their maximum magnetic induction density and coercive force, 2,400 G and 0.3 Oe to 0.5 Oe respectively, which was similar to those of NiZnCu ferrite synthesized in the conventional process. In the graph of initial permeability by frequencies, a $180^circ{C}$ rotation of the magnetic domains which appears in a broad band of micro-wave before and after the resonance frequency, could be perceived.

• 한국자기공명학회논문지
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• 제9권2호
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• pp.110-121
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• 2005

E.coli methionyl tRNA synthetase consist of 676 amino acids and plays a key role in initiation of protein synthesis. The native form of this enzyme is a homodimer, but the monomeric enzyme truncated approximately C-terminal 120 amino acids retains the full enzymatic activities. X-ray crystal structure of the active monomeric enzyme shows that it has two domains. The N-terminal domain is thought to be a binding site for acceptor stem of tRNA, ATP, and methionine. The C-terminal domain is mainly a-helical and makes an interaction with the anticodon of $tRNA^{Met}$. Especially it is suggested that the region of helix-loop-helix including the tryptophan residue at the position 461 may be the essential for the interaction with anticodon of $tRNA^{Met}$. In this work the structure and function of E. coli methionyl-tRNA synthetase was studied by spectroscopic method (NMR, CD, Fluorescence). The importance of tryptophan residue at the position 461 was investigated by fluorescence spectroscopy. Tryptophan 461 is expected to be an essential site for the interaction between E. coli methionyl-tRNA synthetase and E. coli $tRNA^{Met}$. Proton and heteonuclear 2-dimensional NMR spectroscopy were also used to elucidate the protein-tRNA interaction.

• 한국자기공명학회논문지
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• 제22권4호
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• pp.119-124
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• 2018

Although the transcription factor CP2c has been recently validated as a promising target for development of novel anticancer therapy, its structure has not been solved yet. In the present study, the purified recombinant protein corresponding to the tetramerization domain of CP2c appeared to be well folded, whereas the Elf-1 domain showed a largely unfolded conformation. Particularly, the Elf-1 domain, which contains the putative DNA-binding region, showed a conformational equilibrium between relatively less-ordered and well-ordered conformers. Interestingly, addition of zinc shifted the equilibrium to the relatively more structured conformer, whereas zinc binding decreased the overall stability of the protein, leading to a promoted precipitation. Likewise, a dodecapeptide that has been suggested to bind to the Elf-1 domain also appeared to shift the conformational equilibrium and to destabilize the protein. These results constitute the first structural characterization of the CP2c domains and newly suggest that zinc ion might be involved in the conformational regulation of the protein.

• 한국자기학회지
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• 제17권5호
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• pp.188-193
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• 2007

[ $1.00{\times}0.24\;{\mu}m^2$ ] 크기의 $Ni_{80}Fe_{20}$ 박막의 자화 반전 거동을 자화 용이축으로 1 ns 이하의 펄스 자기장의 지속 시간과 세기를 변수로 인가하여 micromagnetics 시뮬레이션으로 관찰하였다. 자성 박막은 직사각형과 타원형의 모양을 가지며, 두께는 2 nm와 4 nm로 설정하였다. 실험 결과 $Ni_{80}Fe_{20}$ 박막의 두께와 모양에 따라 각각 다른 경향을 보이는 것을 확인할 수 있었다. 박막의 두께에 따라 두께 방향으로 형성되는 반자장의 크기 차에 의해 edge domain에서 스핀의 회전속도와 스핀 스위칭의 거동에 차이가 생기며, 박막이 두꺼울수록 자화 반전에 더 긴 펄스 지속 시간과 강한 펄스 자기장이 필요하다는 것을 확인하였다. 한편, 자화 반전이 예상되는 영역에서 자화 반전이 일어나지 않는 비정상적인 자화 반전 영역을 발견할 수 있었는데, 박막의 모양이 타원일 때와 박막의 두께가 얇은 경우에 그 영역이 더욱 불규칙적이고, 넓게 분포하였다. 이러한 현상은 막의 두께가 매우 얇기 때문에 두께 방향으로 형성된 강한 반자장의 영향에 의해 나타나는 것으로 여겨진다. Edge domain이 더 많은 직사각형 모양의 경우 자화반전이 일어나는 동안 자기모멘트의 세차 운동에 의해 생기는 $M_z$ 성분, 즉 두께방향으로 형성된 반자장이 더 작고, 이에 따라 자화 반전이 예상되는 영역에서 자화 반전이 일어나지 않는 비정상적인 자화 반전 영역이 더 적어짐을 확인하였다. 본 시뮬레이션 결과는 자성박막의 안정된 고속 자화반전을 위해서는 반자장의 영향을 최소화하는 것이 중요하다는 것을 보여준다.

• Macromolecular Research
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• 제17권5호
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• pp.301-306
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• 2009

This work has demonstrated that a novel amphiphilic poly(epichlorohydrine)-graft-polystyrene (PECH-g-PS) copolymer at 34:66 wt% was synthesized via atom transfer radical polymerization (ATRP) of styrene using PECH as a macroinitiator. The structure of the graft copolymer was characterized by nuclear magnetic resonance ($^1H$ NMR) and FTIR spectroscopy, demonstrating that the "grafting from" method using ATRP was successful. The self-assembled graft copolymer was used as a template film for the in-situ growth of silver nanoparticles from $AgCF_3SO_3$ precursor under UV irradiation. The in situ formation of silver nanoparticles with 6-8 nm in average size in the solid state template film was confirmed by transmission electron microscopy (TEM), UV-visible spectroscopy and wide angle X-ray scattering (WAXS). Differential scanning calorimetry (DSC) also displayed the selective incorporation and the in situ formation of silver nanoparticles within the hydrophilic PECH domains, probably due to stronger interaction of the silvers with the ether oxygens of PECH backbone than that with hydrophobic PS side chains.

• 한국소음진동공학회논문집
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• 제23권5호
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• pp.463-471
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• 2013

This paper presents design and control of electronic control suspension(ECS) equipped with controllable magnetorheological(MR) damper for passenger vehicle. In order to achieve this goal, a cylindrical type MR fluid damper that satisfies design specification of a middle-sized commercial passenger vehicle is proposed. After manufacturing the MR damper with design parameters, their field-dependent damping forces are experimentally evaluated and compared with those of a conventional damper. A quarter-vehicle MR ECS system consisting of sprung mass, spring, tire, controller and the MR damper is established in order to investigate the ride comfort performances. On the basis of the governing equation of motion of the suspension system, five control strategies(soft, hard, comfort, sport and optimal mode) are formulated. The proposed control strategies are then experimentally realized with the quarter-vehicle MR ECS system. Control performances such as vertical acceleration of the car body and tire deflection are evaluated in frequency domains on random road condition. In addition, performance comparison of WRMS(weighted root mean square) of the quarter-vehicle MR ECS system on random road are undertaken in order to investigate ride comfort characteristics.

• Bulletin of the Korean Chemical Society
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• 제29권2호
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• pp.405-407
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• 2008

Functionalized SAB-15 samples by octadecyltrimethoxysilane (OTC) were studied by 13C magic angle spinning (MAS) cross polarization (CP) nuclear magnetic resonance (NMR) spectroscopy. In the SBA-15 sample fully functionalized by 3-aminopropyltrimethoxysilane (APS) and OTC in 1:1 molar ratio, octadecyl chains were observed to have, on average, more trans conformation than those in the SBA-15 samples fully modified by OTC only. Our results confirm that long chain molecules tend to organize themselves better in the co-presence of short chain molecules on the surface of mesoporous materials by packing of the different length chains in an interdigitized fashion even when the short chains are long enough to have three carbons and a functional group at the ends. In addition, our results indicate that solid-state 13C CP MAS NMR spectroscopy is a simple and non-destructive method to probe the molecular structures of the domains composed of long alkyl chains.

• Kyungpook Mathematical Journal
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• 제47권4호
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• pp.455-471
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• 2007

The magnetohydrodynamic axisymmetric instability of a streaming gas jet surrounded by bounded fluid with non-uniform field has been developed. The problem is formulated, solved and the boundary conditions are applied across the interfaces. The eigenvalue relation is derived and discussed analytically and the results are confirmed numerically. Some reported works are recovered as limiting cases from the present general results. The streaming has a destabilizing effect for all short and long wavelengths. The capillary force is stabilizing for short wavelengths but it is destabilizing for long wavelengths. The axial magnetic fields interior the gas and fluid media are stabilizing. The transverse field is destabilizing for all wavelengths. The radii ratio of the gas and fluid cylinders plays an important role for stabilizing the model and made it more realistic one than the full liquid jet or/and the ordinary hollow jet. The numerical analysis clarify the stable and unstable domains based on different values of the various parameters of the problem.

• Bulletin of the Korean Chemical Society
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• 제19권1호
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• pp.57-62
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• 1998

We have synthesized a 17-residue peptide with the amino acid sequence RQMKEDAKGKSEEELAD corresponding to residues 84-100 of chicken skeletal troponin C. This stretch of the protein sequence is in the middle one-third of the 32-residue 9-turn α-helix that connects the two globular domains of the dumbell-shaped molecule and includes the D/E linker helix. We describe here the solution conformation of the helix linker as studied by circular dichroism (CD) and two-dimensional nuclear magnetic resonance (2-D NMR) spectroscopy. The NOE connectivities together with the vicinal $^3J_{N{\alpha}}$ coupling constants suggest that the peptide exists in a fast conformational equilibrium among several secondary structure: a nascent helix near the N-terminus, a helix, and a substational population of extended and random coil forms. In addition, two interresidue α-α NOEs are observed suggesting a bent structure with a bend that includes the single glycine in position 92. These results are consistent with the ideas that in neutral solution the D/E linker region of the central helix in troponin C can adopt a helical conformation and the central helix may have a segmental flexibility around Gly 92.