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신영진,신현길,김택성,유기수,정태수,유평열,정철훈,이훈,신영신,홍관준 한국센서학회 1993 센서학회지 Vol.2 No.1
A CdS single crystal was grown by using sublimation method. Lattice constants, a_o and c_o, obtained by using extrapolation were 4.1318 Å and 6.7122 Å, respectively. The carrier density was ∼10^(23) m^(-3) and the mobility was 2.93X10^(-2) ㎡/V-sec from measured Hall data at room temperature. The mobility has a increasing tendency in proportion to T^½ from 33 K to 150 K and a decreasing tendency in proportion to T^(-2) from 180 K to room temperature. The short wavelength band peak measured from photocurrent was due to intrinsic transition, and the energy value of this peak was equal to the energy band gap of CdS photoconductor.
김용태,이기업,박건춘,송영기,이문호,유은실,이준호,진태선 대한내과학회 1991 대한내과학회지 Vol.40 No.5
Phenochromocytoma is a catecholamine-secreting tumor, most of which grow at the adrenal gland. About 109p Of pheochromocytomas are detected at the extra-adrenal chromaffine tissues and are called paraganglioma. The main symptoms of pheochromacytoma include hypertension, headache, palpitation, and sweating. Gastrointestinal symptoms such as abdominal pain, constipation, and vomiting are found in 20∼40% of patients with pheochromocytoma, but these are usually overlooked because of the severe, prominant cardiovascular symptoms. Intestinal pseudo-obstruction without hypertension in pheochromocytoma is very rarely found. It is caused by the decreased motility of the intestine and the over-contraction of the intestinal sphincter, which are caused by the unbalanced activation of α-and β-adrenal receptors. It can be hypothesized that catecholamine receptors in the cardiovascular system are down-regulated or desensitized, but those in the intestine remain intact. We report herein a case of pheochromocytoma in which intestinal pseudo-obstruction was the main presenting clinical manifestation. Symptoms of intestinal pseudo-obstruction were completely relieved by administration of phenoxybenzamine, an α-receptor blocker, and excisional surgery.
반용융 성형된 A357 합금 성형품의 부식 및 기계적 특성에 관한 연구
김상식,이명호,이정환,유영빈,이재식,이한중 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.8
The mechanical and corrosion properties of thixoformed A357 alloys were examined with different reheating temperatures, and the results were compared with those of permanent mold cast A357 alloys. It was found that the thixoforming process significantly improved the mechanical properties (i.e., tensile elongation, impact energy and resistance to fatigue crack propagation) and the corrosion resistance of A357 alloys. A 380% increase in tensile elongation and a 120% increase in impact energy were, for example, observed with thixoforming process of A357 alloy in the as-fabricated condition, as compared to the PMC counterparts. The impact energy was extremely sensitive to reheating temperature due to the coarsening of eutectic Si particles. The resistance to fatigue crack propagation for the thixoformed alloy was also much higher than that of permanent mold cast counterpart in the as-fabricated condition. The resistance to both general corrosion and stress corrosion cracking was also greatly improved with thixoforming process. The present observations strongly suggest that the enhancement with thixoforming A357 alloy is largely associated with the size and shape of eutectic Si particles.
이택동,유지형,신제식,배준수,이진형,이혁모 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.4
The ordered phase was tried to disappear in 6.5% Si steel to reduce the power loss and enhance the economic interests. They were prepared by the conventional casting or spray forming method, and they were investigated using the transmission electron microscopy(TEM). The variation in the methods of preparing the specimen did not result in any difference in suppressing the ordered B2 phase in the Fe-Si binary system. It was almost impossible to suppress this ordered phase keeping the silicon level as high as 6.5% even after the heat treatment at 1000℃ for 24 hr or after hot rolling. It was necessary to change the silicon level and control the cooling rate to prevent the ordering reaction, especially, in cooling after heat treatments. The silicon level of 5.8% was obtained as a maximum desirable value.
기계적 합금법으로 제조된 Al-Nb 합금 및 Al-Al3Nb 복합재료 압출재의 인장 특성
김상식,박민우,정광철,안인섭,류영빈,이광민 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.12
Tensile behavior of mechanically alloyed(MA) Al-5 wt.%Nb alloy extrusion was examined at various temperatures and strain rates. The tensile ductility of MA Al-5wt.%Nb alloy extrusion was greatly reduced with increasing temperature and/or decreasing strain rate. The SEM observations of side and fracture surfaces of tensile fractured specimens demonstrated that the overall void density formed during deformation was considerably reduced, along with the sign of decreased plasticity around the dimples on the fracture surface. To understand the effect of grain size on the deformation behavior of submicron grain sized alloys, Al-5 vol. %Al₃Nb composite extrusions with different grain sizes were fabricated and tensile tested at different temperatures. The present study confirms that the reduction in tensile ductility of submicron grain sized alloys at elevated temperatures are undoubtedly related to the grain size. Fast dynamic recovery rates, due to the lack of dislocation substructures, in submicron grain sized alloys appears to be responsible for the elevated temperature reduction in tensile ductility.
고주파 마그네트론 스펏터링법으로 제조한 ZnO 박막의 기판에 따른 효과
김영진,김기완,권오준,유상대 한국센서학회 1996 센서학회지 Vol.5 No.6
ZnO thin films were prepared on glass and (012) sapphire substrates by rf magnetron sputtering. Polycrystalline ZnO films with a (002) orientation were obtained on glass substrates. (110) ZnO films were epitaxially grown on the (012) sapphire substrates. Surface acoustic wave properties were also measured for propagating along the c axis of ZnO film on the glass and sapphire substrates. The phase velocities (V_P) on glass and sapphire substrate at center frequency were 2&80 m/sec and 5980 m/sec and the effective coupling coefficient (k²) on the 0th mode were 0.98 % and 1.43 % respectively.
가스 침질탄화처리한 SM35C 강의 기계적 성질에 미치는 고주파�칭의 영향
김학신,이규복,유정희,김형태,장환용 한국열처리공학회 2000 熱處理工學會誌 Vol.13 No.4
Carbon steel(SM35C) was gas nitrocarburized at 580℃ in 55%N₂-40%NH₃-5%CO₂mixed gas atmosphere, and then the steel was induction hardened at 850℃. The microstructure of gas nitrocarburized surface layer was observed by optical microscope and SEM. The phase analysis was carried out by X-ray diffraction method. The mechanical properties of gas nitrocarburized SM35C steel was evaluated by hardness, wear and fatigue test. The thickness of compound and diffusion layer were increased with increasing the gas nitrocarburizing time and the densest compound layer was obtained at 3hours gas nitrocarburizing time. In case of 15sec induction hardening after gas nitrocarburizing, the surface hardness was decreased from 800Hv to 630Hv owing to the decomposition of compound layer, but wear resistance was increased because of increased hardness of diffusion layer. The fatigue strength of induction hardened steel after gas nitrocarburizing, 58㎏f/㎟, was higher than 41.5㎏/㎟ of gas nitrocarburized steel and 45㎏/㎟ of induction hardened steel, respectively.
컴퓨터교육에서 정보교육으로의 전환을 위한 교육과정 모형 개발
김현철,이현옥,정순영,유헌창,이원규 한국컴퓨터교육학회 1999 컴퓨터교육학회 논문지 Vol.2 No.4
이 논문에서는 컴퓨터 교육이 정보 능력을 갖춘 인간을 육성한다는 교육 목표를 강조하기 위해 정보 교육 측면에서의 교육과정을 제안한다. 정보 교육이란, 정보활용능력과 정보처리능력을 배양하여 문제를 스스로 해결하고 정보화 사회에 적응할 수 있는 인재를 양성하는 것이다. 정보화 시대에 살아가기 위해서 정보 교육은 중요하다. 하지만 현재 우리 나라 정보 교육의 실태를 분석해 보면 많은 문제점을 발견할 수 있다. 가장 큰 문제점은 정보 교육을 위한 체계적인 교육과정이 미흡하다는 것이다. 이 때문에 학교급별 컴퓨터 교육의 목표와 내용이 연계가 이루어지지 못하고 교육혜택의 불평등이 나타나고 있다. 따라서 이 연구에서는 제 6차·7차 교육과정의 문제점을 분석하고 해결 방안으로 정보의식과 정보활용능력을 포괄하는 새로운 정보 교육과정 모형을 제안한다.
유진,박영배,박익성 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.2
The interfacial fracture energies, Γ, of the Cu/Cr/polyimide system were deduced using X-ray measurement method and theoretical method with variation of Cu film thickness and pretreatment conditions on polyimide surface. The two methods showed reasonably good agreement for most cases, imparting validity of both approaches. Estimated Γ were quite independent of the metal film thickness and increased with the rf plasma power density of polyimide pretreatment as expected. Estimated values of Γ were 46.8±7.8. 170.3±42.9 and 253.9±44.4 J/㎡ for the rf plasma power density of 0.03. 0.036 and 0.05 W/㎠, respectively.