• 한국세라믹학회지
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• 제37권3호
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• pp.219-226
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• 2000

Amorphous Ge20As20Se60 chalcogenide thin films were prepared by spin coating technique from mixed solutions of As40Se60 and Ge40Se60 dissolved in ethylenediamine. Films were prepared at a roating speed of 3500 rpm and spinning time was 10 second and heat-treateed at 27$0^{\circ}C$ for 1 hour. The resulting film thickness and RMS roughness were approximately 340 nm and 15$\AA$. Photostructure changes were investigated with 514.5nm Ar+ laser irradiation and heat-treatment. After Ar+ laser irradiation, transmittance and transmission efficiency decreased respectively up to 24.9% at 2.43 eV and 67.5% at 3.27 eV, and absorption edge shifted toward long wavelength. Optical bandgap changed from 2.03 to 1.83 eV, and absoprtion coefficient and absorption efficiency increased up to 0.33$\times$105cm-1 at 3.37eV and 88.3% at 1.31 eV, respectively. These photodarkening state were recovered reversibly by heat-treatment at 27$0^{\circ}C$ for 1 hour. Photodarkening and thermal bleaching effects by laser irradiation and heat-treatment revealed reversible amorphous-to-amorphous transition varying only coordination number.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.148-151
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• 2003

The spin density of ${\beta}-MnO_2$ structure was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}O_{56}]^{-52}$. The ${\beta}-MnO_2$ is a paramagnetic oxide semiconductor material having the energy band gap of 0.18 eV and an 3 loan-pair electrons in the 3d orbital of an cation. This material exhibits spin-only magnetism and has the magnetic ordering temperature of 94 K. Below this temperature its magnetism appears as antiferromagnetism. The calculations of electronic state showed that if the initial spin condition of input parameters changed, the magnetic state changed from paramagnetic to antiferromagnetic. When d orbital of all Mn atoms in cluster had same initial spin state as only up spin, paramagnetic spin density distribution appeared by the calculation. On the other way, d orbital had alternately changed spin state along special direction the resulted spin distribution showed antiferromagnetism.

• 한국해양학회지:바다
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• 제5권3호
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• pp.186-194
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• 2000

본 연구에서는 중규모 해양모형을 이용하여 주어진 한반도 주변 대기경계조건에 대한 해양모형의 반응을 연구하였다. 연구는 크게 스핀업(spin-up) 실험과 재현(reproduction) 실험으로 나뉘는데, 스핀업 실험은 해양모형을 스핀업시켜 기후학적 월평균 해양상태로 유도하는 실험으로 월평균 대기상태를 경계조건으로 하여 해양모형을 장기적분하였다. 재현 실험은 1980년${\sim}$1998년 동안(19년)의 한반도 주변 해역의 해양변동을 재현하고자 한 실험으로 이를 위하여 스핀업 마지막 해의 해양상태를 모형의 초기상태로 하고 그 기간 동안의 월평균 기상 자료를 경계조건으로 해양모형에 적용하여 19년간 적분하였다. 스핀업 실험에서 모형은 동해지역에서의 동한 해류의 이안, 극전선대(polar front)형성 그리고 소규모 에디들에 의한 냉수대의 형성과 황해지역에서의 연안역과 중앙부 사이에 남북으로 형성되는 수온전선 대 그리고 역풍류(Upwind Current)의 변화에 기인한 순환 구조의 계절적인 변동 등 한반도 주변해역에서 나타나는 특징적인 순환들을 잘 모사하였다. 또한 1982${\sim}$98년까지에 대한 재현 실험에서는 주어진 대기 경계조건에 따른 해면온도의 변동성과 기간동안 약 0.5$^{\circ}$C의 해면온도 아노말리의 상승을 관측과 유사하게 모사하였다. 따라서 실험은 모형이 주어진 경계조건에 대하여 해양의 평균적인 상태 뿐만 아니라 변동성도 잘 모사하고 있음을 보여주었다.

• 대한기계학회논문집B
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• 제30권1호
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• pp.67-73
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• 2006

This investigation deals with the spin-up flows in a circular container of aspect ratio, 2.0. Shear front is generated in the transient spin-up process and propagating from the side wall to the central axis in a rotating container. Propagation of the shear front to the axis in a rotating container means the region acquires an angular momentum transfer from the solid walls. Propagating speed of the shear front depends on the apparent viscosity of polymer solution. Two kinds of polymer solutions are considered as a working fluid: one is CMC and the other is CTAB solution. CMC solution has larger apparent viscosity than that of water, and CTAB shows varying apparent viscosities depending on the applied shear rates. Transient and spatial variations of the apparent viscosities of the present polymer solutions (CTAB and CMC) cause different speeds of the propagating shear front. In practice, CMC solution that has larger values of apparent viscosity than that of water always shows rapid approach to the steady state in comparison of the behavior of the flows with water. However, for the CTAB solution, the speed of the propagating of the shear front changes with the local magnitude of its apparent viscosity. Consequently, the prediction of Wedemeyer's model quantitatively agrees with the present experimental results.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.145.1-145.1
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• 2016

Binding and unbinding between molecular oxygen and metallo-porphyrin is a key process for oxygen delivery in respiration. It can be also used to control spin state of magnetic metallo-porphyrin molecules. Controlling and sensing spin states of magnetic molecules in such reactions at the single molecule level is essential for spintronic molecular device applications. Here, we demonstrate that spin states of metallo-porphyrin on surfaces can be controlled over by binding and unbinding of oxygen molecule, and be sensed using scanning tunneling microscopy and spectroscopy. Kondo localized state of metallo-porphyrin showed significant modification by the binding of oxygen molecule, implying that the spin state was changed. Our density functional theory calculation results explain the observations with the hybridization of unpaired spins in d and ${\pi}^*$ orbitals of metallo-porphyrin and oxygen, respectively. Our study opens up ways to control molecular spin state and Kondo effect by means of molecular binding and unbinding reactions on surfaces.

• Advances in materials Research
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• 제2권4호
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• pp.181-193
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• 2013

Description and theory of spin coating technique has been elaborately outlined and a spin coating machine designed and fabricated using affordable components. The system was easily built with interdisciplinary knowledge of mechanics, fluid mechanics and electronics. This equipment employs majorly three basic components and two circuit units in its operation. These include a high speed dc motor, a proximity sensor mounted at a distance of about 15 mm from a reflective metal attached to the spindle of the motor to detect every passage of the reflective metal at its front and generate pulses. The pulses are transmitted to a micro-controller which process them into rotational speed (revolution per minute) and displays it on a lead crystal display (LCD) which is also a component of the micro-controller. The circuit units are a dc power supply unit and a PWM motor speed controlling unit. The various components and circuit units of this equipment are housed in a metal casing made of an 18 gauge black metal sheet designed with a total area of 1, $529.2cm^2$. To illustrate the use of the spin-coating system, ZnO sol-gel films were prepared and characterized using SEM, XRD, UV-vis, FT-IR and RBS and the result agrees well with that obtained from standard equipment and a speed of up to 9000 RPM has been achieved.

• 한국자기학회지
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• 제17권2호
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• pp.95-98
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• 2007

본 연구에서는 하지층으로 사용한 Mo(MoN)의 두께 변화에 따른 스핀밸브 구조의 자기적 특성과 열처리 결과를 비교 검토하였다. 사용된 스핀밸브는 Si 기판/Mo(MoN)$(t{\AA})/NiFe(21{\AA})/CoFe(28{\AA})/Cu(22{\AA})/CoFe(18{\AA})/IrMn(65{\AA})/Ta(25{\AA})$ 구조이다. 또한 본 연구에서는 MoN 하지층을 Si 기판에 증착하여 열처리후 특성을 분석하였다. Mo 박막에 비해 MoN 박막의 질소량이 증가할수록 증착률은 감소하였고, 비저항은 증가하였다. MoN 하지층을 사용한 경우 Mo의 경우보다 하지층 두께 변화($51{\AA}$까지)에 따라 자기저항비와 교환결합력의 변화는 소폭이었다. Mo 하지층의 열처리 온도별 자기저항비는 열처리 전 상온에서 2.86% 이었고, $200^{\circ}C$ 열처리 때 2.91 %로 증가하였다. 이후 열처리 온도를 $300^{\circ}C$까지 증가시키면 자기저항비는 2.91 %에서 2.16%로 감소하였다. 질소 유입량이 1 sccm인 MoN의 열처리 온도별 자기저항비는 열처리 전 상온에서 5.27%, $200^{\circ}C$일때 5.56%증가하였다. 이후 열처리 온도를 $300^{\circ}C$까지 증가시키면 자기저항비는 5.56%에서 4.9%로 감소하였다.

• Journal of Astronomy and Space Sciences
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• 제33권3호
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• pp.173-176
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• 2016

We report on a systematic analysis of the spin and superorbital modulations of the high-mass X-ray binary 4U 0114+650, which consists of the slowest spinning neutron star known. Utilizing dynamic power spectra, we found that the spin period varied dramatically during the RXTE ASM and Swift BAT observations. This variation consists of a long-term spin-up trend, and two ~1,000 day and one ~600 day random walk epochs previously, MJD 51,000, ~MJD 51,400-52,000, and ~MJD 55,100-56,100. We further found that the events appear together with depressions of superorbital modulation amplitude. This provides evidence of the existence of an accretion disk, although the physical mechanism of superorbital modulation remains unclear. Furthermore, the decrease of the superorbital modulation amplitude may be associated with the decrease of mass accretion rate from the disk, and may distribute the accretion torque of the neutron star randomly in time.

• Journal of Magnetics
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• 제13권4호
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• pp.153-156
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• 2008

We conducted a micromagnetic modeling study to investigate the spin torque oscillator (STO) using a perpendicular polarizer. We used an additional layer of negative anisotropy constant materials (NAM) on a conventional STO. For the NAM layer, the magnetic easy plane is parallel to the in-plane easy axis of the free layer, and inhibits the development of the out-of-plane component of the magnetization in the free layer. As a result, this new type of STO provides a high frequency limit up to 50 GHz.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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• pp.336-338
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• 2016

Recent multifunctional two-dimensional material research has triggered huge interests in various modifications for substitution of atoms. Instead of novel metals used as the most popular catalysts, nonprecious transition metals are promising candidates for efficient oxidation-reduction transfers. The recent discovery of $Co@C_2N$ has an alternate possiblity as catalysts for the ORR(Oxygen Reduction Reaction) in DSSc(Dye Sensitized Solar Cell) and OER(Oxygen evolution cobalt oxides). Here we report spin-polarized DFT calculations of the structure doped Iron that is one of ferromagnetism atoms like Co to provide a basic desciption of the ferromagnetism of the elemental metals. The spin-density-funtional results present the most stable state energetically is when having pairwise up/down spin.