• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.293-298
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• 2005

We calculate the coordinates of an axisymmetric nozzle with a central body. This nozzle ensures a transonic flow with a plane sound surface, which is orthogonal to the symmetry axis and has a wall kink at the sonic point, The Chaplygin transformation in the subsonic part of the flow leads the Dirichlet problem for a system of nonlinear equations. The definition domain of the solution in the velocity-hodograph plane is taken as a rectangle. This enables one to obtain the nozzle with a monotonic distribution of velocity along its subsonic part. In the nonlinear differential equation, the linear Chaplygin operator for plane flows is separated, which allows the iterative calculation of the solution. The supersonic part of the nozzle is calculated under the assumption that the flow at the nozzle exit is uniform and parallel to the symmetry axis; i.e., the supersonic jet outflows to the submerged space with the same pressure. The calculation is performed by the characteristic method. The exact solution of Tricomi equation for near-sonic flows with the straight sonic line is used to 'move away' the sound plane. The velocity distribution alone the supersonic part of the nozzle is also monotonic, which ensures the absence of the boundary-layer separation and, therefore, the adequacy of the ideal-gas model. calculations show that the flow in the supersonic part of the nozzle is continuous (compression shocks are absent)

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.67.1-67.1
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• 2017

구리는 탄성이방성이 큰 재료로 Si 박막상에 성장시키면 (111) 방향으로 우선 배향된 박막을 얻을 수 있다. 본 연구는 이러한 (111) 우선 방위를 갖는 Cu 박막의 전기도금층의 재결정 후의 매우 평탄한 표면을 갖는 박막에서 에칭에 따른 박막의 단차와 표면형상을 통해 결정방위별 에칭 특성을 비교 분석한 결과이다. 10 vol% 질산용액에서 에칭한 결과는 구리의 용해에 따라 각 결정면에 대한 고유의 facetted surface morphology를 나타내며, 대표적인 결정 방위인 (111), (110), (100)에 대해 triangular flake, ridge and rectangular pyramidal shapes을 나타내는 것을 알 수 있었다. 에칭속도의 정량적 측정을 위해 120초간 2.2M 농도의 질산용액으로 에칭을 실시하였고, nanosize의 as-plated initial region, (111), (110), (100) oriented regions의 각각에서 383, 270, 276, 317 nm/min의 에칭속도를 갖는 것을 확인하였다. Facet surface의 관찰을 통해 에칭반응이 (111) front surface를 갖는 열역학적 평형상태에서 일어나며, 이러한 결정방위별 에칭속도 차이는 각 결정S면이 갖는 Kink or ledge의 밀도의 차이에 기인할 것으로 판단된다. 즉, 에칭이 평형상태에서 step flow mechanism에 의해 열역학적 평형상태를 유지하면서 진행이 된다. 본 연구는 향후 다양한 에칭관련 용액 효과, 구리 박막의 응력 및 불순물에 의한 효과를 볼 수 있는 기본 방법을 제공해 줄 것으로 기대한다.

• Journal of the Korean Society of Industry Convergence
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• v.2 no.2
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• pp.115-124
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• 1999

The interaction of weak normal shock wave with turbulent boundary layer in a supersonic nozzle was investigated experimentally by wall static pressure measurements and by schlieren optical observations. The lime-mean flow in the interaction region was classified into four patterns according to the ratio of the pressure $p_k$ at the first kink point in the pressure distribution of the interaction region to the pressure $p_1$ just upstream of the shock. It is shown for any flow pattern that the wall static pressure rise near the shock foot can be described by the "free interaction" which is defined by Chapman et al. The ratio of the triple point height $h_t$ of the bifurcated shock to the undisturbed boundary layer thickness ${\delta}_1$ upstream of the interaction increases with the upstream Mach number $M_1$, and for a fixed $M_1$, the normalized triple point height $h_t/{\delta}_1$ decreases with increasing ${\delta}_1/h$, where h is the duct half-height.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.109-109
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• 2011

1T-1C로 구성되는 기존의 DRAM(Dynamic Random Access Memory)은 데이터를 저장하기 위한 적절한 capacitance를 확보해야 한다. 따라서 캐패시터 면적으로 인한 집적도에 한계에 직면해있다. 따라서 이를 대체하기 위한 새로운 DRAM인 1T (Transistor) DRAM이 각광받고 있다. 기존의 DRAM과 달리 SOI (Silicon On Insulator)기술을 이용한 1T-DRAM은 데이터 저장을 위한 캐패시터가 필요없다. Impact Ionization 또는 GIDL을 이용해 발생한 정공을 채널영역에 가둠으로 서 발생하는 포텐셜 변화를 이용한다. 이로서 드레인 전류가 변화하며, 이를 이용해 '0'과 '1'을 구분한다. 기존의 1T-DRAM은 단결정 실리콘을 이용하여 개발되었으나 좀더 광범위한 디바이스로의 적용을 위해서는 다결정 실리콘 박막의 형태로 제작이 필수적이다. 단결정 실리콘을 이용할 경우 3차원 집적이나 기판재료선택에 제한적이지만 다결정 실리콘을 이용할 경우, 기판결정이 자유로우며 실리콘 박막이나 매몰 산화층의 형성 및 두께 조절이 용이하다. 때문에 3차원 적층에 유리하여 다결정 실리콘 박막 형태의 1T-DRAM 제작이 요구되고 있다. 따라서 이번연구에서는 엑시머 레이저 어닐링 및 고상결정화 방법을 이용하여 결정화 시킨 다결정 실리콘을 이용하여 1T-DRAM을 제작하였으며 메모리 특성을 확인하였다. 기판은 상부실리콘 100 nm, buried oxide 200 nm로 구성된 SOI구조의 기판을 사용하였다. 엑시머 레이저 어닐링의 경우 400 mJ/cm2의 에너지를 가지는 KrF 248 nm 엑시머 레이저 이용하여 결정화시켰으며, 고상결정화 방법은 $400^{\circ}C$ 질소 분위기에서 24시간 열처리하여 결정화 시켰다. 두가지 결정화 방법을 사용하여 제작되어진 박막트랜지스터 1T-DRAM 모두 kink 현상을 확인할 수 있었으며 메모리 특성 역시 확인할 수 있었다.

• Economic and Environmental Geology
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• v.31 no.5
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• pp.447-458
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• 1998

The spinel Ihelzolite of ultramafic xenoliths are found in the alkali basalt from eastern part of the Cheju island, Korea. The xenolith is are mainly composed of olivine, orthopyroxene, clinopyroxene and spinel. Based on the chemical compositions of the constituent minerals, the ultramafic xenolith belong to upper mantle peridotite. Each minerals have a protogranular texture. Olivine with kink band texture partly shows undulatory extinction. Some clinopyroxenes have spongy textured rims. Brown spinels occur in the interstices between olivine and pyroxene grains. Olivine is mostly forsterite $(Fo_{89-90})$. Orthopyroxene is enstatite $(Wo_{1.3}En_{88.4}Fs_{10.3})$ with 3.87~5.25 wt% $Al_{2}O_{3}$. Clinopyroxene is diopside $(Wo_{48.0}En_{46.2}Fs_{5.8})$ with 6.75~5.03 wt% $Al_{2}O_{3}$. Spinel has the Mg value of 75.9 and its Cr-number is 10.2. According to the PoT estimations for the mantle xenoliths, equilibrium temperatures of the xenoliths range from 1023 to $1038^{\circ}C$ and pressure is 18 kbar. Spinellhelzolite from this area, which is characterized by lower Cr-number (10.2) and homogeneous chemical compositions, supports that these ultramafic xenoliths are derived from the upper mantle.

• Electrical & Electronic Materials
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• v.7 no.4
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• pp.331-340
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• 1994

Polysilicon on insulator has been recrystallized by zone melting recrystallization method with graphite strip heaters. Experiments are performed with non-seed SOI structures. When the capping layer thickness of Si$\_$3/N$\_$4//SiO$\_$2/ is 2.0.mu.m, grain boundaries are about 120.mu.m spacing and protrusions reduced. After the seed SOI films are annealed at 1100.deg. C in NH$\_$3/ ambient for 3 hours, the recrystallized silicon surface has convex shape. After ZMR process, the tensile stress is 2.49*10$\^$9/dyn/cm$\^$2/ and 3.74*10$\^$9/dyn/cm$\^$2/ in the seed edge and seed center regions. The phenomenon of convex shape and tensile stress difference are completely eliminated by using the PSG/SiO$\_$2/ capping layer. The characterization of SOI films are showed that the SOI films are improved in wetting properties. N channel SOI MOSFET has been fabricated to investigate the electrical characteristics of the recrystallized SOI films. In the 0.7.mu.m thickness SOI MOSFET, kink effects due to the floating substrate occur and the electron mobility was calculated from the measured g$\_$m/ characteristics, which is about 589cm$\^$2//V.s. The recrystallized SOI films are shown to be a good single crystal silicon.

• Steel and Composite Structures
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• v.12 no.1
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• pp.53-72
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• 2012

In this study, the physically-based failure models for matrix and fibers in compression and tension loading are introduced. For the 3D stress based fiber kinking model a modification is proposed for calculation of the fiber misalignment angle. All of these models are implemented into the finite element code by using the advantage of damage variable and the numerical results are discussed. To investigate the matrix failure model, purely in-plane transverse compression experiments are carried out on the specimens made by Glass/Epoxy to obtain the fracture surface angle and then a comparison is made with the calculated numerical results. Furthermore, shear failure of $({\pm}45)_s$ model is investigated and the obtained numerical results are discussed and compared with available experimental results. Some experiments are also carried out on the woven laminated composites to investigate the fracture pattern in the matrix failure mode and shown that the presented matrix failure model can be used for the woven composites. Finally, the obtained numerical results for stress based fiber kinking model and improved ones (strain based model) are discussed and compared with each other and with the available results. The results show that these models can predict the kink band angle approximately.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.398-402
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• 2015

Fundamental studies of microstructural changes and high temperature deformation of titanium aluminide (TiAl) were conducted from the view point of the effect of Al content in order to develop the manufacturing process of TiAl. Microstructures in an as cast state consisted mainly of lamellar structure irrespective of Al content. By homogenization at 1473 K, the microstructures of Ti-49Al and Ti-51Al were transformed into an equiaxial structure which was composed of ${\gamma}$-TiAl, while the lamellar structure that was observed in Ti-46Al and Ti-47Al was much more stable. We found that the reduction of Al content suppressed the formation of equiaxial grains and resulted in a microstructure of only a lamellar structure. On Ti-49Al and Ti-51Al, dynamic recrystallization occurred during high temperature deformation, and the microstructure was transformed into a fine equiaxial one, while the microstructures of Ti-46Al and Ti-47Al contained few recrystallized grains and consisted mainly of a deformed lamellar structure. We observed that on the low-Al alloys the lamellar structure under hard mode deformation conditions deformed as kink observed B2-NiAl. High temperature deformation characteristics of TiAl were strongly affected by Al content. An increase of Al content resulted in a decrease of peak stress and activation energy for plastic deformation and an increase of the recrystallization ratio in TiAl.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.807-812
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• 1998

Mechanical properties of two types of polycrystlline {{{{ { { Ti}_{3 }SiC }_{2 } }} with different grain size were investigated. A fine grain {{{{ { { Ti}_{3 }SiC }_{2 } }} has a higher fracture strength and hardness. Plot of strength versus Vickers indentation load indicated that {{{{ { { Ti}_{3 }SiC }_{2 } }} has a high flaw tolerance. Hertzian indentation test using a spherical indenter was used to study elastic and plastic behavior in {{{{ { { Ti}_{3 }SiC }_{2 } }}. Indentation stress-strain curves of each material are made to evaluate the plasticity of {{{{ { { Ti}_{3 }SiC }_{2 } }} Both find and coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} showed high plasticity. In-dentation stress-strain curve of coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} deviated even more from an ideal elastic limit in-dicating exceptional plasticity in this material. Deformation zones were formed below the contact as well as around the contact area in both materials but the size of deformation zone in coarse grain {{{{ { { Ti}_{3 }SiC }_{2 } }} was much larger than that in fine grain {{{{ { { Ti}_{3 }SiC }_{2 } }} Intragrain slip and kink would account for high plasticity. Plastic behavior of {{{{ { { Ti}_{3 }SiC }_{2 } }} was strongly influenced by grain size.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.33 no.3
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• pp.1-8
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• 2001

Paper consists of fiber network and paper properties were highly affected by fiber characteristics. Many researchers have tried to relate fiber and paper properties. Softwood and hardwood fiber's are quite different in their properties. Generally, softwood fiber's are longer and more flexible than hardwood fibers. At present, many paper mills make mixed paper with softwood and hardwood fibers except for special grade. During fracture some fiber's are broken and others are pulled out. In this paper, the number of broken and pulled out fiber's during fracture is analyzed depending on the mixing ratio of softwood and hardwood fiber's. Fiber length, curl, kink, coarseness, WRV and formation index were measured. Double-edged strength samples were prepared to observe the number of broken and pulled out fiber's. Mixed paper strength was decreased with increasing hardwood fibers ratio. During fracture, softwood fiber's were more likely broken and hardwood fibers were more likely pulled out. The strength of paper which consists of softwood fibers was determined by fiber's broken strength and that of hardwood fibers by fiber's debonding strength. Paper strength was changed depending on the fiber's bonding capability. If the fiber is longer and more flexible, the fiber network becomes stronger and stiffer.