• The Korean Journal of Rheology
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• v.11 no.2
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• pp.105-111
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• 1999

Dampers have been used to dissipate energy in mechanical systems. There are several types of dampers such as passive, active, and semi-active damper. Semi-active dampers have higher performance than passive ones and require less power to operate than active ones. Their damping characteristics can be changed properly for varying conditions. In this paper, we investigated the semi-active damper using Magneto-Rheological fluid. Magneto-Rheological fluid, which is one of controllable fluids, changes its damping and rheological characteristics from Newtonian fluid to Bingham fluid as the magnetic field is applied. It has several advantages such as high yield strength, low viscosity, robustness to impurities and wide temperature range of stability. If we designe a semi-active damper by using this material, we can not only design a simply structured damper but also expect rapid response. In this study, we propose several types of semi-active dampers which are designed and manufactured using Magneto-Rheological fluid and some problems encountered during their applications.

• Journal of the Korean Magnetics Society
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• v.10 no.3
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• pp.133-138
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• 2000

We have investigated some crystallographic, magnetic, and transport properties of the first colossal magnetoresistive compounds $La_{1-x}Ba_{x}MnO_3(0\leq\chi\leq$1)$(5\;K\leqT\leq360K,-5T\leqH\leq5T$ and resistivity $(100K\leqT\leq350K$measurements. $La_{1-x}Ba_{x}MnO_3$ were found to be ferromagnetic for all x.The $La_{1-x}Ba_{x}MnO_3$were found to be insulating for x< 0.2, metallic for 0.20.5. The magnitude of saturation magnetization (Ms) increased until x=1/8 and had theoretical maximum Ms for 0.13$\sfrac{3}{8}$ and had a constant value of 335~340 K for x>$\sfrac{3}{8}$. For $x\geq0.5$ the $La_{1-x}Ba_{x}MnO_3$ samples showed a percolation-type conduction behavior and enhanced low field magnetoresistance caused by simultaneous occurrence of the chemical/magnetic phase separation.

• Journal of the Korean Society of Radiology
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• v.82 no.1
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• pp.99-115
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• 2021

Various sequences have been developed for MRI to aid in the radiologic diagnosis. Among the various MR sequences, susceptibility-weighted imaging (SWI) is a high-spatial-resolution, three-dimensional gradient-echo MR sequence, which is very sensitive in detecting deoxyhemoglobin, ferritin, hemosiderin, and bone minerals through local magnetic field distortion. In this regard, SWI has been used for the diagnosis and treatment of various neurologic disorders, and the improved image quality has enabled to acquire more useful information for radiologists. Here, we explain the principle of various signals on SWI arising in neurological disorders and provide a retrospective review of many cases of clinically or pathologically proven disease or components with distinctive imaging features of various neurological diseases. Additionally, we outline a short and condensed overview of principles of SWI in relation to neurological disorders and describe various cases with characteristic imaging features on SWI. There are many different types diseases involving the brain parenchyma, and they have distinct SWI features. SWI is an effective imaging tool that provides complementary information for the diagnosis of various diseases.

• Investigative Magnetic Resonance Imaging
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• v.12 no.2
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• pp.142-147
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• 2008

Purpose : By using the micro-imaging unit modified from NMR spectrometer, the high resolution MRI protocols of finer than 100 micron in 5 minutes, is sought for mouse, which plays a central role in animal studies Materials and Methods : C57BL/6 mouse, lighter than 50 gram, is used for the experiments. The superconducting magnet is vertical type with 89 mm inner diameter at 4.9 Tesla. The diameter of rf-coil is 30 mm. Mostly used techniques are the fast spin echo and the gradient echo pulse sequence. Results : For 2D images, proton density and T2 weighted images are obtained and their optimum experimental variables were sought. Minute structure of mouse brain can be recognized and 3D brain image is also obtained additionally. 3D image will be useful particularly for the dynamic contrast study using various contrast agents. Conclusion : Like the case of human and other small animals, the high resolution of mouse brain is enough to recognize the minute structure of it. Recently, similar studies are reported domestically, but it seems only a beginning stage. Due to easiness of breeding/control, mouse MRI study will soon play a vital part in brain study.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.106-106
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• 2014

SIGMA (Scientific cubesat with Instrument for Global Magnetic field and rAdiation)는 근 지구공간에서 우주방사선량 측정과 자기장 변화 검출의 과학적 목적과 교육적 목적을 가지고 개발하고 있는 초소형 큐브위성이다. $100mm{\times}100mm{\times}340.5mm$의 크기로 약 3.6 kg의 무게를 가지며, 탑재체는 방사선에 대하여 인체와 동일한 산란 흡수 특성을 가진 Tissue Equivalent Proportional Counter (TEPC)와 자기장 측정을 위한 Magnetometer (Mag)이다. 위성체는 구조계, 자세제어계, 전력계, 명령 및 데이터처리계, 통신계로 구성되어있다. 구조계는 위성의 뼈대인 Chassis와 Mag deployer로 이루어져있고, 위성의 안정적인 자세유지를 목적으로 Attitude Control System (ACS) Board와 Torque Coil이 자세제어계로 구성된다. 전력의 생산과 공급 및 충전은 태양전지판과 Electrical Power System (EPS), 리튬 배터리로 구성된 전력계에서 이뤄지며, 명령 및 데이터처리계는 On Board Computer (OBC)와 Instrument Interface board (IIB)를 중심으로 서브시스템의 명령체계와 데이터처리를 다룬다. 통신계는 Uplink인 VHF 안테나와 Downlink인 UHF, S-band 안테나로 구성되며 지상과 명령을 송수신한다. SIGMA는 타임인터럽트 기능을 활용한 Flight Software (FSW)로 운용되며 임무에 따른 6가지 모드의 시나리오로 위성을 운용한다. 이에 SIGMA의 개발과 테스트 결과를 소개한다. 본 큐브위성 개발기술을 바탕으로 향후 천문관측용 위성에도 활용할 예정이다.

• Journal of Korean Philosophical Society
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• v.117
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• pp.327-354
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• 2011

This study has a key assumption that 'characteristics of discouse can be found in not its inside, but its outside'. The prism through which we can see those characteristics was provided by Foucault and Bakhtin who were introduced in the study. As an effort co probe the outside of discourse, the study is briefed 'the three attributes of discourse' that were suggested by Foucault First, discourse has the principle of selection and exclusion, which is based on power relations. Second, discourse is not transparent at all since it is always offensive towards other discourses and defensive against selected ones Third, discourse which is naturally accepted because of its dailiness had a deep structure secretly hidden in it. Based on the above attributes, Foucault and Bakhtin paid their attention to the outside of discourse. Specifically, they considered discourse fundamentally and went beyond it, and reflected the procedures of discourse. This study focused on 'Socrates', something common in the two scholars' works with discourse. In dealing with discourse, Bakhtin started with 'Socratic dialogue' that is based on the dialogic nature of human thoughts which purse the truth. For Foucault, it was Socrates who had the 'courage to cell the truth' and practiced 'self-consideration'. According to Foucault, the ethics of self-practice originated from the philosopher. The ethics is neither the precise representation of individual life that is withdrawn towards the inner self, nor the skills of happiness. It is just relational and cross-sectional. For a better understanding, this study pointed out that Kafka created a variety of 'dialogic voices' focusing on the outside of discourse. Dialogues found in his writings are 'interminable dialogues' that truly 'communicate with different times and different spaces'. For example, his novel, 'Der Prozess' opens the possibility of discussing in various ways the court which is look beyond conventions and extraordinary. Kafka's novels have a structure that their starting point found at the introduction reappears at the termination, presenting multi-vocal dialogues.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.297-297
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• 2010

KSTAR 토카막의 두번째 실험 캠페인 동안 고속파 전자가열 (FWEH)을 위한 ICRF 고주파입사 실험을 실시하였다. 토로이달 자기장은 2 T, 플라즈마 전류는 200-300 kA, 주반경은 1.8 m, 부반경은 0.5 m의 원형 플라즈마가 가열 대상이 되었으며, 네개의 ICRF 안테나 전류띠 가운데 중심부의 두개의 전류띠를 최대 300 kW로 구동하기 위한 운전 주파수는 44.2 MHz가 선택 되었다. 이 주파수는 플라즈마의 모든 영역에서 이온 사이클로트론 공명을 일으키지 않으므로 플라즈마에 흡수되는 대부분의 출력은 전자에게 전달될 것으로 기대되었다. 낮은 고주파-플라즈마 결합으로 인하여 전송선의 최대 고주파 전압이 허용치를 초과하기 때문에 비교적 낮은 최대 출력만이 허용 되었으나, ECE에 의해 관측된 전자의 온도는 국지적으로 최대 150 % 까지 증가하는 것을 확인 할 수 있었다. 낮은 고주파-플라즈마 결합의 첫번째 원인은 FWEH의 효율이 이온을 가열할 때 보다 상대적으로 낮기 때문이다. 플라즈마 내에 이온 사이클로트론 공명층이 형성되면 높은 효율로 고주파를 입사 할 수 있다는 것은 잘 알려진 사실이다. 또다른 원인은 D 형상의 플라즈마에 맞도록 만들어진 안테나와, 원형 플라즈마간의 부조화로 인하여 고속파 차단층이 (Fast Wave Cutt-off Layer) 평균적으로 넓게 형성되기 때문이다. 플라즈마 외곽에 반드시 존재하는 낮은 플라즈마 밀도의 고속파 차단층 내부에서, 중심부로 향하는 고주파의 진폭은 지수함수로 감쇠하므로 가능하면 플라즈마 밀도를 높여 차단층 자체의 폭을 줄이거나, 안테나 전류띠를 플라즈마에 바짝 접근시켜야만 한다. 고주파 진단 장치로는 송출기의 출력과 반사파 측정 장치, 공명루프의 전압 측정 장치가 있는데, 이것들을 이용하여 안테나에 전달되는 출력 및 고주파-플라즈마 결합 효율을 나타내는 플라즈마에 대한 고주파 부하 저항을 구할 수 있다. 측정 결과, 부하 저항의 최소값은 진공시 또는 ICRF만의 방전시의 값 0.25 Ohm 보다 큰 0.5 Ohm을 나타냈으며, 최대값은 플라즈마의 상태에 따라 1 Ohm에서 2 Ohm 사이에서 매우 빠르게 요동하는 것을 확인했다. Mm 파 반사계의 측정에 의하면 플라즈마 언저리의 위치가 약 3 cm 정도의 크기로 요동하는 것으로 나타났는데, 부하 저항과 언저리 위치의 파형이 정확하게 일치하지 않지만 유사한 경향성을 가진 것으로 보인다. 따라서 플라즈마 언저리 위치의 제어를 통하여 가열 효율을 높게 유지할 수 있음을 알 수 있다. 본 발표에서는 실험의 소개와 함께 부하 저항의 관점에서 가열 효율을 높일 방안을 토론하도록 한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.214-214
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• 2022

감포댐은 2006년 준공하여 각종 시설 및 설비의 노후화가 진행중에 있으며, 최근 감포댐 인근 지역에서 발생한 경주지진(규모 5.8) 및 포항지진(규모 5.4)이 발생하여 지진시 시설물의 안전성에 대해 중요성이 대두되고 있었다. 이에 감포댐 안전성강화 사업을 추진하게 되었고, 주요 사업내용은 취수탑 관리교 내진보강, 댐체 심벽보강을 통한 댐체 안전성확보, 비상방류시설 개선이다. 취수탑 관리교는 교각단면의 변위연성도 및 교량받침에 의한 구조물 안전성 평가를 시행하였고, 단면강도는 모멘트-곡률해석법에서 탄성영역의 단면강도 대비 탄성지진력을 비교하여 안전성을 검토하였다. 검토결과 교량받침의 내진성능은 부족한 것으로 검토되어 유량제어형 멀티펌프와 안전잭을 이용한 변위제어 방식의 교량동시 인상공법이 가능하고 인상정밀도 ±0.5mm이내의 성능을 가진 교량인상공법 적용하여 보강을 하는 것으로 계획하였다. 댐체 심벽보강을 위해 먼저 전기비저항탐사를 수행하여 전기비저항대를 탐사하여 심벽부에서 포화대가 형성된 부위를 조사하였다. 그리고 댐 상·하류에 전극을 설치하고 전류를 발생시켜 측정 지점별 자기장을 측정을 통하여 댐체내 침투에 따른 유로 형성여부 파악을 위한 전자기장탐사를 시행하였다. 마지막으로 심벽 시추조사를 시행하여 공내수를 조사하였다. 조사결과 포화대의 위치 및 이상대가 다양한 것으로 나타났으며, 이는 불특정 지점에 연약대가 존재한다 판단하여 심벽부 보강계획을 전반적으로 적용하는 것으로 결정하였다. 비상방류시설은 최근 15년 실측자료의 홍수기(6~9월) 평균유입량을 적용하여 검토하였으며 검토결과 배제대상 높이 75%까지는 3.7일, 완전배제까지는 11.2일이 걸려 댐설계기준을 충족하는 것으로 검토되다. 다만 감포댐 비상방류시설이 하천제방과 직각방향으로 형성되어 있고, 하천의 폭이 좁아 과거 방류시에도 제방을 월류하는 것으로 조사되어 하천의 세굴을 방지하고 제방 안전성을 확보하기 위하여 비상방류시설에 감세공을 설치하고, 제방에 디플렉터 옹벽을 설치하는 것으로 계획하였다. 감세공은 2번에 걸친 감세효과로 방류시 하류바닥 및 옹벽 보호 효과가 큰 미국 USBR의 TypeVI를 적용하였으며, Flow-3D 모델링을 통하여 제방에 월류가 발생하지 않는 최적의 대안 옹벽규모를 산정하였다.

• Investigative Magnetic Resonance Imaging
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• v.9 no.2
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• pp.117-133
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• 2005

For identifying the pathological findings in magnetic resonance images (MRIs), normal anatomical structures in MRIs should be identified in advance. For studying the anatomical structures in MRIs, a learning tool that includes the followings is necessary. First, MRIs of the entire body; second, horizontal, coronal, and sagittal MRIs; third, segmented images corresponding to the MRIs; fourth, three dimensional (3D) images of the anatomical structures in the MRIs; fifth, software incorporating the MRIs, segmented images, and 3D images. Such a learning tool, however, is hard to obtain. Therefore, in this research, such a learning tool which helps medical students and doctors study the normal anatomical structures in MRIs was made as follows. A healthy young Korean male adult with standard body shape was selected. Six hundred thirteen MRIs of the entire body were scanned (slice thickness 3 mm, interslice gap 0 mm, field of view 480 mm${\times}$480 mm, resolution 512${\times}$512, T1 weighted), and transferred to the personal computer. Sixty anatomical structures in the MRIs were segmented to make segmented images. Coronal, sagittal MRIs and coronal, sagittal segmented images were made. On the basis of the segmented images, forty-seven anatomical structures 3D images were made by manual surface reconstruction method. Software incorporating the MRIs, segmented images, and 3D images was composed. This learning tool that includes horizontal, coronal, sagittal MRIs of the entire body, corresponding segmented images, 3D images of the anatomical structures in the MRIs, and software is expected to help medical students and doctors study the normal anatomical structures in MRIs. This learning tool will be presented worldwide through Internet or CD titles.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.11 no.6
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• pp.11-26
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• 2016

Businesses have to survive and thrive in both domestic and international environments. In order to resolve these problems, new alternatives have been presented. These include the importance of women's resources and entrepreneurship of female CEOs. The sensibility, delicacy, creativity as well as the intuitive power of female CEOs, actively enables them to cope with the ever-changing environment. Because of the rapidly changing circumstances, the above mentions women's attributes are highlighted thus, causing women's roles in society to shift from their traditional tendencies to finding careers and their own identities. Due to this change in social roles, social interest and the values of female CEOs are being reevaluated. Accordingly, the conceptual consideration of female entrepreneurship (innovation, enterprise, risk sensitivity) as well as the factors to be considered for the entrepreneurship of female CEOs in order to promote knowledge management performance was derived in this research. The deducted implication of this research is that generally, the enterprise and risk sensitivity of entrepreneurship affect the knowledge management performance of female CEOs. It is therefore proved that in the case of female CEOs, entrepreneurship and self-efficacy are linked, allowing them to achieve the desired outcome for a specific task performance. Female CEOs are capable of company management through the mediating process of their enterprise, risk sensitivity, and self-efficacy and with faith in their knowledge management, will be able to achieve high performance. Therefore, using strengths and nature peculiar to women, women's economic activities derived from knowledge management based on entrepreneurship will not only help overcome the long-term economy crisis but also lead to high economic growth and development. This will be a dynamic force for the nation's new growth with financial means. The comparative study of existing results will also contribute in suggesting the direction of policies that will enable the success of female CEOs in entrepreneurship.