$(Ru_{1-x}Ta_x)Sr_2(Gd_{1.4}Ce_{0.6})Cu_2O_z$ 계의 초전도 및 자기적 특성

이호근,Lee, H.K. 한국초전도학회 2012 Progress in superconductivity Vol.13 No.3

The effects of Ta substitution on the superconducting and magnetic properties of the $(Ru_{1-x}Ta_x)Sr_2(Gd_{1.4}Ce_{0.6})Cu_2O_z(0{\leq}x{\leq}0.5)$ system have been investigated. The X-ray diffraction measurements indicate that the Ta ion replaces Ru sites up to x = 0.4. It is found that the Ta substitution for Ru significantly reduces the weak-ferromagnetic component of the field-cooled magnetic susceptibility without an appreciable change of room temperature thermopower at lower Ta doping level below x = 0.2. The resistive transition temperature tends to decrease monotonically from 27 K for the x = 0 sample to 16 K (9 K) for the x = 0.4 (x = 0.5) sample. These results suggest that superconductivity of the $(Ru_{1-x}Ta_x)Sr_2(Gd_{1.4}Ce_{0.6})Cu_2O_z$ compound is not significantly affected by the magnetic state of the Ru sublattice. The experimental results are discussed in connection with previous reports on the effects of Nb substitution.

품질위험 지각 정도에 따른 인터넷 중고차 사이트의 신뢰형성 요인과 구매의도에 미치는 영향에 관한 연구

이호근,이승창,성대원,Lee, Ho-Geun,Lee, Seung-Chang,Seong, Dae-Won 한국경영정보학회 2003 Asia Pacific Journal of Information Systems Vol.13 No.2

Trust has been identified as a key component in many e-Commerce studies. The purpose of this study is to find out which factors play a major role in building trust and how the built-up trust affect consumer's purchase intention in Internet used-car transactions. Based on the information asymmetry, TAM(Technology Acceptance Model), and the trust theory, our research model includes factors such as a buyer's propensity-to-trust, institutional characteristics(inspection and warranty policy), word-of-mouth referral, perceived size, and perceived benefits as independent variables. The model also includes trust as a mediate variable, intention to purchase as a dependent variable and perceived quality risk as a moderate variable. The research model is tested by analyzing 787 sample data gathered from Internet used-car transaction sites. The result shows that the trust has significant effects on the online purchase intention, and institutional characteristics has been identified as the most significant factor for the trust of Internet used-car sites. The independent factors influencing trust vary depending on the level of perceived quality risk. For users who perceive the quality risk low, the perceived benefits explain a little portion of the purchase intention. However, those who perceive quality risk high would purchase used-cars only when they have trust on the Internet sites, indicating that trust play an important role as a mediate variable. This study suggests that enhancing the trust in Internet used-car sites is important to increase online transactions.

불순물 치환을 통한 Ru$Sr_2$EuCe$Cu_2$$O_z$ 계의 강자성 천이온도의 조절특성

이호근,김영호,권오현,Lee H. K,Kim Y. H,Kwon O. H 한국초전도학회 2004 Progress in superconductivity Vol.6 No.1

We investigated the effects of impurity doping on the electrical transport and magnetic properties of $(Ru, Sn)(Sr, La)<_2$$EuCeCu_2$$O_{z}$ samples. We found that Sn substitution fur Ru causes a significant decrease of the volume fraction of ferromagnetic phase, as well as a decrease of the temperature where the ferromagnetic component is observed. La substitution for Sr leads to an increase of the magnetic ordering temperature with a moderate change of ferromagnetic component. The experimental results are discussed in conjunction with the structural data, transport properties and a possible change of oxygen content.

TBM 도로터널의 환기방식에 따른 최적단면 선정에 관한 연구

이호근,강현욱,김현수,김홍문,Lee, Ho-Keun,Kang, Hyun-Wook,Kim, Hyun-Soo,Kim, Hong-Moon 한국터널지하공간학회 2013 한국터널지하공간학회논문집 Vol.15 No.2

최근 도로터널은 장대화되고 있으며 도심지 등의 장대 대심도 도로터널의 계획이 추진되고 있다. 이러한 장대, 대심도 터널 굴착공법은 NATM과 TBM 공법 등이 있으며 유럽에서는 약 80%, 기타 선진국에서도 약 30%의 교통터널에서 Shield TBM 공법을 적용하고 있다. 하지만 국내에서는 대부분의 장비가 외국에서 고가에 수입되고 있어 국내의 TBM 터널 보급률이 상당히 낮아 NATM 굴착방식이 보편적으로 적용되고 있는 실정이다. TBM 터널의 보급을 늘리기 위해서는 TBM 장비의 국내 수급을 통한 경제성의 확보가 필요하며 이를 위해 표준화된 TBM 구경의 선정이 시급한 실정이다. 따라서 본 연구에서는 도로터널의 표준화된 TBM 최적단면 선정을 위해 교통량에 따라 차로수의 규모 및 내부형상(단층 혹은 복층), 환기방식에 따른 TBM 굴착 내공단면을 활용 방안 등을 검토하여 최적 단면의 산출방안을 제시하고자 하였다. Recently, road tunnels have become longer and the plans for long and deep road tunnel have been underway in urban areas. These long and deep tunnel excavations include NATM and TBM. Shield TBM is applied to around 80% of traffic tunnels in Europe, and approximately 30% of them in other developed countries. However, as much of equipment is imported from foreign countries at high prices and distribution rate of TBM tunnel is considerably low in Korea, NATM excavation method is commonly used. To increase TBM tunnel, it is necessary to do assure economic feasibility with the supply-demand of TBM equipment. For this, the selection of standardized TBM diameter is urgently needed. Therefore, the study aims to estimate the standardized optimum section properties of TBM by examining TBM excavation cross section utilization depending on the volume of traffic, the number of lane and its cross-section type(single or double deck), and ventilation system.

Ba 치환에 따른 (Ru,Cu)(Sr,Eu)$_2$(Eu,Ce)$_2Cu_2O_z$ 계의 초전도 특성

이호근,Lee, H.K. 한국초전도학회 2011 Progress in superconductivity Vol.13 No.1

We investigated the effects of Ba and Cu co-substitution on the structural and superconducting properties of ($Ru_{1-y}Cu_y$)($Sr_{1.67-x}Ba_xEu_{0.33}$)($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$ samples. X-ray diffraction(XRD) reveals that single-phase samples can be obtained in the range from x = 0.1 to 0.2 for ($Ru_{0.5}Cu_{0.5}$)($Sr_{1.67-x}Ba_xEu_{0.33}$)($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$ and from y = 0.25 to 0.5 for ($Ru_{1-y}Cu_y$)($Sr_{1.47}Ba_{0.2}Eu_{0.33}$)($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$, respectively. All samples with compositions of ($Ru_{0.5}Cu_{0.5}$)($Sr_{1.67-x}Ba_xEu_{0.33}$) ($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$ (x = 0 - 0.33) show superconducting transition behavior and the onset transition temperature decreases slightly with increasing x in consistent with the change of hole concentration estimated from room temperature thermoelectric power measurements. The XRD and resistivity measurements for the ($Ru_{1-y}Cu_y$)($Sr_{1.47}Ba_{0.2}Eu_{0.33}$)($Eu_{1.34}Ce_{0.66}$) $Cu_2O_z$ system indicate that the partial substitution of Cu for Ru is necessary to form phase pure samples, but result in a small change in transition temperature in the single-phase region from x = 0.25 to 0.5.

Cu 치환에 따른 $(Ru_{1-x}Cu_x)Sr_2(Eu_{1.34}Ce_{0.66})Cu_2O_z$ 계의 초전도 특성

이호근,Lee, H.K. 한국초전도학회 2009 Progress in superconductivity Vol.11 No.1

The effect of Cu substitution on the structural and superconducting properties of the $(Ru_{1-x}Cu_x)Sr_2(Eu_{1.34{\cdot}}Ce_{0.66})Cu_2O_z$ system with x = 0, 0.25 and 0.5 prepared under ambient pressure have been investigated. The X-ray diffraction patterns indicated that the Ru ions are replaced by the Cu ions. It is found that the Cu substitution for Ru significantly reduces the ferromagnetic component of field-cooled magnetic susceptibility, but results in a small change in diamagnetic onset transition temperature of zero-field-cooled magnetic susceptibility. In contrast to the Ru $Sr_2(Eu_{1.34{\cdot}}Ce_{0.66})Cu_2O_z$, bulk Meissner effect is observed in the field-cooled magnetization measurements of the Cu doped samples. The experimental results are discussed in connection with the spontaneous vortex phase interpretation.

Tb이 치환된 $RuSr_2(Eu_{1.34}Ce_{0.66})Cu_2O_z$ 계의 초전도 및 자기적 특성

이호근,이만석,Lee, H.K.,Lee, M.S. 한국초전도학회 2012 Progress in superconductivity Vol.14 No.2

Samples with nominal compositions of $RuSr_2(Eu_{1.34-x}Tb_xCe_{0.66})Cu_2O_z$ (x = 0, 0.67) were prepared and their superconductivity and magnetic properties were compared to shed light on the effect of Tb substitution for Eu. X-ray diffraction measurements indicate that the Tb substitution resulted in a decrease in both a and c lattice parameters in consistent with ionic size difference between Eu and Tb. Contrary to the Tb-free sample, no superconducting transition behavior is observed in the Tb-sustituted sample. It is also found that the Tb substitution for Eu significantly increases the weak-ferromagnetic component of the field-cooled magnetic susceptibility as well as an increase in the magnetic ordering temperature. These results suggest that the magnetic state of the Ru sublattice is significantly affected by the Tb substitution for Eu.

질소 열처리에 따른 $RuSr_2(EuCe)Cu_2O_z$ 계의 구조 및 자기적 특성

이호근,김용일,김영철,Lee, H.K.,Kim, Y.I.,Kim, Y.C. 한국초전도학회 2012 Progress in superconductivity Vol.13 No.3

Two $RuSr_2(EuCe)Cu_2O_z$ samples (as prepared and after $N_2$ treatment) have been investigated by thermogravimetric (TC) analysis, high-resolution x-ray powder diffraction and magnetization measurements. TG measurements which were carried out in $H_2/Ar$ atmosphere showed that the $N_2$ treatment of the as-prepared sample at $650^{\circ}C$ for 2h leads to a decrease in the oxygen content z by about 0.25. This oxygen depletion was accompanied by an increase in the magnetic transition temperature from 54.0 K to 114.9 K. This magnetic behavior is discussed in connection with the results of Rietveld analysis of the x-ray diffraction data which showed that the $N_2$ treatment resulted in both a significant increase in the rotation angle of the $RuO_6$ octahedra and a decrease in c-lattice parameter of the sample.

$(Ru_{0.8}Nb_{0.2})Sr_2(Gd_{1.5-x}Nd_xCe_{0.5})Cu_2O_z$ 계의 합성 및 초전도 특성

이호근,배수민,Lee, H.K.,Bae, S.M. 한국초전도학회 2009 Progress in superconductivity Vol.10 No.2

Polycrystalline samples of $(Ru_{0.8}Nb_{0.2})Sr_2(Gd_{1.5-x}Nd_xCe_{0.5})Cu_2O_z$($ 0{\leq}x{\leq}1.25$) have been synthesized by a solid-state reaction route. The X-ray diffraction data revealed that the Nd solubility limit can be placed between x=0.5 and x=0.75. The superconducting transition temperature decreased with increasing Nd content, confirming that Nd entered the lattice. Room-temperature thermoelectric power measurements showed that all the samples are in the underdoped state and the partial substitution of Nd for Gd resulted in a decrease in the carrier density on the superconducting layers.

전술용 항공기의 생존성 향상을 위한 소요 핵심기술 (2)

이호근,Lee, Ho-Geun 한국방위산업진흥회 2000 國防과 技術 Vol.- No.251

아무리 스텔스성이 높은 항공기라도 만약 적이 위치를 달리하는 복수의 레이더기지에서 동시에 다른 방향에서 추적할 경우 쉽게 탐지되는 것은 당연한 일이며, 실제로 RCS 0인, 즉 레이더로 탐지 불가능한 스텔스성 100%의 기체가 출현할 경우에는 운용자측에도 많은 문제점이 제기된다는 사실을 명심해야 한다. 즉 적의 레이더로 포착이 불가능한 항공기는 적에게 확실히 위협적인 존재임에는 틀림없으나, 그러한 항공기를 운용하는 입장에서 생각할 경우에는 지극히 위험스럽기 짝이 없다는 사실을 간과해서는 안된다.