• Progress in Superconductivity
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• 제9권2호
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• pp.127-135
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• 2008

We study the effects of phonon interaction on the superconducting pairing in the high $T_c$ superconductors (HTSC). Using coupled BCS gap equations, we found that phonon interaction can induce a s-wave component to the d-wave gap, mediated by Antiferromagnetic (AFM) spin fluctuations, in the (D+iS) form. However, $T_c$ is not enhanced compared to the pure d-wave pairing without phonon interaction. On the other hand, anisotropic phonon interaction can dramatically enhance the d-wave pairing and $T_c$ itself, together with the AFM spin fluctuation interaction. This ($D_{AFM}+D_{ph}$) type pairing exhibits strongly reduced isotope coefficient despite the large enhancement of $T_c$ by phonon interaction.

• Journal of Magnetics
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• 제13권4호
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• pp.132-135
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• 2008

The authors studied the conduction mechanism in an uranium doped low dimensional magnetic system $Ca_2CuO_3$. This system exhibits the S=1/2 quasi 1D antiferromagnetic chains of -Cu-O- with strong magnetic coupling, and demonstrates continuous semiconductor-like behavior with constant covalent insulator character. This paper identifies the conduction is due to thermally activated phonon-assisted electron hopping between dopant uranium sites. The parameter a, the characteristic for hopping probability, was determined to be 0.18 ${\AA}^{-1}$. This value manifests a relatively stronger hopping probability for $Ca_2CuO_3$ as compared with other uranium doped ceramics.

• 한국초전도ㆍ저온공학회논문지
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• 제15권1호
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• pp.6-10
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• 2013

We investigate the electrical and thermal transport properties of a sesquicarbide superconductor $La_2C_3$, including electrical resistivity, thermoelectric power, and thermal conductivity. The electrical resistivity exhibits a typical metallic character with a saturation behavior at high temperatures. The thermoelectric power shows a metallic behavior with pronounced phonon-drag effect, comparable with pure metals. The broad peak of the thermal conductivity is observed in the superconducting state, which is rapidly suppressed by magnetic fields. These observations suggest that the electron-phonon scattering is significant in $La_2C_3$, which is relevant with the relatively high-$T_c$ in $La_2C_3$ through strong electron-phonon coupling with low frequency phonon modes.

• ETRI Journal
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• 제18권3호
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• pp.161-170
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• 1996

We show that the electrically coupled Hindmarsh-Rose neuronal model exhibits various patterns of phase locking at fixed parameter value. Through the analysis of the effective coupling, the system is shown to be stabilized in one of these patterns according to the initial conditions. This corresponds to the parameter-tuning independent mode-switching mechanism that changes the electrical output of neuronal systems. It is also presented how the stable fixed points of the effective coupling which characterize the phase locking patterns depend on the external current.

• Current Applied Physics
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• 제18권11호
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• pp.1345-1351
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• 2018

To allow stable cycling of layered nickel-rich cathode material at high voltage, silyl-functionalized dimethoxydimethylsilane is proposed as a multi-functional additive. In contrast to typical functional additive, dimethoxydimethylsilane does not make artificial cathode-electrolyte interfaces by electrochemical oxidation because it is quite stable under anodic polarization. We find that dimethoxydimethylsilane mainly focuses on scavenging nucleophilic fluoride species that can be produced by electrolyte decomposition during cycling, leading to improving interfacial stability of both nickel-rich cathode and graphite anode. As a result, the cell cycled with dimethoxydimethylsilane-controlled electrolyte exhibits 65.7% of retention after 100 cycle, which is identified by systematic spectroscopic analyses for the cycled cell.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.100-105
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• 2024

In this study, we propose an alternative approach using Artificial Neural Networks (ANN) for determining Mass Attenuation Coefficients (MAC) in various glass systems. This method takes into account the weights of glass compositions, density, and photon energy as input features. The ANN model was trained and tested on a dataset consisting of 650 data points and subsequently validated through a K-fold cross-validation procedure. Our findings demonstrate a high level of accuracy, with R² values ranging from 0.90 to 0.99. Additionally, the model exhibits robust extrapolation capabilities with an R² score of 0.87 for predicting MAC values in a new glass system. Furthermore, this approach significantly reduces the need for costly and time-consuming computations and experiments, making it a potential tool for selecting materials for effective radiation protection.

• 한국자기학회지
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• 제24권2호
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• pp.35-40
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• 2014

본 연구에서는 제일원리계산방법을 이용하여 스핀전달토크(Spin-Transfer Torque: STT) MRAM을 구현하는 데 적합한 물질로 알려진 CoFe 합금 박막의 자성과 자기결정이방성에 대해 계산하였다. CsCl 구조의 CoFe 합금 박막의 자기결정이방성을 계산하기 위해 교환-상관 퍼텐셜은 일반화 물매근사(general gradient approximation: GGA)를 사용하였으며 k-점은 $12{\times}12{\times}1$, 절단 에너지는 400 eV을 사용하였다. CoFe 합금 박막의 층수는 5층으로 하였고 박막 표면이 Co 원자인 경우와 Fe 원자인 경우에 $2.2{\AA}$에서 $3.2{\AA}$까지 범위에서 2차원 격자상수에 따른 박막의 총에너지를 계산하였다. 총에너지 계산 결과에 따르면 Co 표면의 CoFe 5층 박막의 총에너지는 $2.45{\AA}$와 $2.76{\AA}$의 두 2차원 격자상수에서 극소치를 가지는데 fcc 형 결정구조를 가지는 $2.45{\AA}$의 2차원 격자상수 박막이 bcc 형 결정구조를 가지는 $2.76{\AA}$ 2차원 격자상수 박막보다 약 160 meV 차이로 더 안정함을 알 수 있었다. 반면 Fe 표면의 CoFe 5층 박막은 상당히 복잡한 총에너지 계산 결과를 보여 주는데 이는 Fe 표면의 CoFe 5층 박막은 복잡한 자성 구조를 가지기 때문일 것으로 판단된다. $2.45{\AA}$의 Co 표면의 CoFe 5층 박막은 표면에 평행한 자기결정이방성을 가지는 반면, $2.76{\AA}$일 때는 표면에 수직한 자기결정이방성을 가지는 것으로 계산되었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 B
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• pp.843-846
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• 1992

This thesis was investigated on optical-and ion-induced characteristics in positive(a-$Se_{75}Ge_{25}$) and negative (Ag/a-$Se_{75}Ge_{25}$) resists for focused-ion-beam microlithogaphy. The a-$Se_{75}Ge_{25}$ inorganic thin film shows an increase in optical absorption after exposure to$\sim$$10^{16}$ dose(ions/$cm^{2}$) of Ga ions. The observed shift in the absorption edge toward longer wavelengths is consistent with that in films exposed to band-gap photons ($\sim$$10^{20}$ photons/$cm^{2}$). But, ion induced shift is twice as much as that in film exposed to optical radiation. This result may be related with microstructural rearrangements with in the short range of SeGe network. Due to changes in the short range order, the chemical bonding may be affected, which results in increased chemical dissolution in ion-induced film. Also, this resist exhibits good thermal stability because of its high Tg(~220$^{\circ}C$). The composition of deposited film measured by AES is consistent with that of bulk.

• 한국안광학회지
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• 제5권1호
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• pp.49-53
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• 2000

Sodium borate silicate 유리는 $10Na_2O-39B_2O_3-50SiO_2-CoO$ mol%와 $20Na_2O-14B_2O_3-65SiO_2-CoO$ mol%의 조성비로 혼합한 후 전기로에서 $1210^{\circ}C$ 온도로 2시간 동안 용융하여 공기 중에서 급냉 시켜 제작하였다. 급냉한 유리의 유전적 거동을 조사하기 위하여 온도와 주파수 함수로 유전상수와 비저항을 측정하였다. 유전율 스펙트럼에서 유리전이온도는 $Na_2O$ 20 mol%시료가 낮아졌으며 $Na_2O$ 함량이 증가함에 따라 유전상수는 크게 나타났다. 유리의 비저항 주파수 의존성은 non-Debye형 완화를 보였다.

• 천문학논총
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• 제30권2호
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• pp.439-442
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• 2015

We observed multiple CO transition lines and the HCN(1-0) line at ~ 1" (~ 34 pc) or higher resolution toward the Seyfert 2 nucleus of M51 using the IRAM Plateau de Bure Interferometer (PdBI) and the Submillimeter Array (SMA). All the images show very similar overall molecular gas distribution; there are two discrete clouds at the eastern and western sides of the nucleus, and the western cloud exhibits an elongated distribution and velocity gradient along the radio jet. In addition, high HCN(1-0)/CO(1-0) brightness temperature ratios of about unity have been observed, especially along the radio jet, similar to those observed in shocked molecular gas in our Galaxy. This strongly indicates that the molecular gas along the jet is shocked, that the radio jet and the molecular gas are interacting, and the jet is entraining both diffuse (CO) and dense (HCN) molecular gas outwards from the circumnuclear region. This is the first clear imaging of the outflowing molecular gas entrained by the AGN jet, and showing the detailed physical status of outflowing molecular gas. Since a relatively high HCN(1-0)/CO(1-0) ratio has been observed in the high velocity wing of ultraluminous infrared galaxies, it can also be explained by a similar mechanism to those we describe here.