• Advances in aircraft and spacecraft science
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• 제11권1호
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• pp.55-81
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• 2024

This paper presents the exact solutions and closed forms for of nonlinear stability and vibration behaviors of straight and curved beams with nonlinear viscoelastic boundary conditions, for the first time. The mathematical formulations of the beam are expressed based on Euler-Bernoulli beam theory with the von Karman nonlinearity to include the mid-plane stretching. The classical boundary conditions are replaced by nonlinear viscoelastic boundary conditions on both sides, that are presented by three elements (i.e., linear spring, nonlinear spring, and nonlinear damper). The nonlinear integro-differential equation of buckling problem subjected to nonlinear nonhomogeneous boundary conditions is derived and exactly solved to compute nonlinear static response and critical buckling load. The vibration problem is converted to nonlinear eigenvalue problem and solved analytically to calculate the natural frequencies and to predict the corresponding mode shapes. Parametric studies are carried out to depict the effects of nonlinear boundary conditions and amplitude of initial curvature on nonlinear static response and vibration behaviors of curved beam. Numerical results show that the nonlinear boundary conditions have significant effects on the critical buckling load, nonlinear buckling response and natural frequencies of the curved beam. The proposed model can be exploited in analysis of macrosystem (airfoil, flappers and wings) and microsystem (MEMS, nanosensor and nanoactuators).

• Genomics & Informatics
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• 제5권2호
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• pp.46-55
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• 2007

The convergence of molecular and genetic disciplines with non-invasive imaging technologies has provided an opportunity for earlier detection of disease processes which begin with molecular and cellular abnormalities. This emerging field, known as molecular imaging, is a relatively new discipline that has been rapidly developed over the past decade. It endeavors to construct a visual representation, characterization, and quantification of biological processes at the molecular and cellular level within living organisms. One of the goals of molecular imaging is to translate our expanding knowledge of molecular biology and genomic sciences into good patient care. The practice of molecular imaging is still largely experimental, and only limited clinical success has been achieved. However, it is anticipated that molecular imaging will move increasingly out of the research laboratory and into the clinic over the next decade. Non-invasive in vivo molecular imaging makes use of nuclear, magnetic resonance, and in vivo optical imaging systems. Recently, an interest in Positron Emission Tomography (PET) has been revived, and along with optical imaging systems PET is assuming new, important roles in molecular genetic imaging studies. Current PET molecular imaging strategies mostly rely on the detection of probe accumulation directly related to the physiology or the level of reporter gene expression. PET imaging of both endogenous and exogenous gene expression can be achieved in animals using reporter constructs and radio-labeled probes. As increasing numbers of genetic markers become available for imaging targets, it is anticipated that a better understanding of genomics will contribute to the advancement of the molecular genetic imaging field. In this report, the principles of non-invasive molecular genetic imaging, its applications and future directions are discussed.

• 생명과학회지
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• 제16권5호
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• pp.859-865
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• 2006

옥수수(Zea mays) 자엽초 박편을 분리하여 완충용액에 띄워 배양하면 조직 내부와 외부 사이의 장력 차이에 의하여 밖으로 굽어진다. 그러나 외부에서 옥신을 처리하면 안으로 굽어지는 반응이 나타나는데, 그 반응 정도는 옥신 농도에 따라 변화하였다. 본 연구에서는 옥신에 의하여 자엽초 박편이 안으로 굽어지는 현상을 옥신과 함께 작용하는 물질들을 선별하기 위한 실험에 이용하였다. 옥수수 자엽초의 메탄올 추출물로부터, 옥신에 의해 안으로 굽어지는 자엽초 박편의 반응을 촉진하는 활성을 발견하였다. 이러한 촉진 활성은 에너지원과 관련된 현상은 아니었다. 활성물질은 pH 10과 같은 높은 pH에서도 $C_{18}$ 컬럼에 흡착되어 메탄올로 용리되었으며, 50% 메탄올과 80% 메탄올에 의하여 용리되는 두 가지 물질을 발견하고 각각 Curvature-Enhancing Factor-1 (CEF-1)과 Curvature-Enhancing Factor-2 (CEF-2)라 명명하였다. 그중 CEF-2의 HPLC를 이용한 분리 조건이 확립되었다.

• 한국진공학회지
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• 제18권5호
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• pp.384-389
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• 2009

ZnO는 육방정계결정구조의 물질로서 3.37 eV의 넓은 띠 간격과 60 meV의 큰 exciton 결합에너지에 따른 높은 효율의 자외선발광으로 짧은 파장의 빛 (녹, 청, 자외선)을 내는 LED (Light Emitting Diode) 분야에서 관심을 기울이고 있는 물질이다. LED제작을 위해서는 n형의 ZnO와 p형의 ZnO가 필요하지만 기본적으로 ZnO은 n형이므로 신뢰성 있는 p형 ZnO박막을 제작하기 위한 노력이 기울여지고 있다. 본 연구에서는 ALD (Atomic Layer Deposition)로 제작된 ZnO박막에 20 keV의 에너지를 갖는 질소이온을 $10^{13}{\sim}10^{15}ions/cm^2$로 조사한 후 Hall 효과 측정장치를 이용하여 질소이온 조사에 따른 전기적 특성변화를 조사하였다.

• 미생물학회지
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• 제39권4호
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• pp.235-241
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• 2003

제1형 인간 면역결핍 바이러스 (human immunodeficiency virus type 1, HIV-1)의 Rev 단백질에 대하여 야생형보다 10배 더 잘 결합하도록 시험관에서 선택된 RRE40라 명명된 RNA aptamer가 과연 임상적으로 유용한지 알기 위하여 인체의 CD4^+ peripheral blood lymphocytes 세포에서 레트로바이러스 벡터를 이용하여 RRE40 RNA를 발현한 후에 그 세포에서의 HIV-1 증식 현상을 관찰하였다. 그 결과 대조군인 tRNA를 발현하는 유전자가 전달된 세포에 비해 RRE40 RNA를 발현하는 세포에서 보다 더 효과적으로 HIV-1의 증식이 억제되었다. 그러나 바이러스의 증식이 완전히 억제되지는 못 하였고 일시적 또는 감소된 형태로 바이러스 증식이 억제되었다. 이러한 결과는 RRE40 RNA가 decoy로서 세포에서의 HIV-1 증식 억제에 유용함을 시사하지만 RNA decoy를 HIV-1 감염 환자의 치료에 이용하기 위해선 보다 효과적인 유전자 전달방법 및 보다 개선된 RNA decoy의 개발 등이 필요할 것이다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.44-45
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• 2010

We are currently conducting studies on culturing and biocompatibility assessment of various cells such as neural stem cells and induced pluripotent stem cells(IPS cells) on carbon nanotube (CNT), on nerve regeneration electrodes, and on silicon wafers with a focus on developing nerve integrated CNT based bio devices for interfacing with living organisms, in order to develop brain-machine interfaces (BMI). In addition, we are carried out the chemical modification of carbon nanotube (mainly SWCNTs)-based bio-nanosensors by the plasma ion irradiation (plasma activation) method, and provide a characteristic evaluation of a bio-nanosensor using bovine serum albumin (BSA)/anti-BSA binding and oligonucleotide hybridization. On the other hand, the researches in the case of "novel plasma" have been widely conducted in the fields of chemistry, solid physics, and nanomaterial science. From the above-mentioned background, we are conducting basic experiments on direct irradiation of body tissues and cells using a micro-spot atmospheric pressure plasma source. The device is a coaxial structure having a tungsten wire installed inside a glass capillary, and a grounded ring electrode wrapped on the outside. The conditions of plasma generation are as follows: applied voltage: 5-9 kV, frequency: 1-3 kHz, helium (He) gas flow: 1-1.5 L/min, and plasma irradiation time: 1-300 sec. The experiment was conducted by preparing a culture medium containing mouse fibroblasts (NIH3T3) on a culture dish. A culture dish irradiated with plasma was introduced into a $CO_2$-incubator. The small animals used in the experiment involving plasma irradiation into living tissue were rat, rabbit, and pick and are deeply anesthetized with the gas anesthesia. According to the dependency of cell numbers against the plasma irradiation time, when only He gas was flowed, the growth of cells was inhibited as the floatation of cells caused by gas agitation inside the culture was promoted. On the other hand, there was no floatation of cells and healthy growth was observed when plasma was irradiated. Furthermore, in an experiment testing the effects of plasma irradiation on rats that were artificially given burn wounds, no evidence of electric shock injuries was found in the irradiated areas. In fact, the observed evidence of healing and improvements of the burn wounds suggested the presence of healing effects due to the growth factors in the tissues. Therefore, it appears that the interaction due to ion/radicalcollisions causes a substantial effect on the proliferation of growth factors such as epidermal growth factor (EGF), nerve growth factor (NGF), and transforming growth factor (TGF) that are present in the cells.