• 한국분말재료학회지
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• 제12권4호
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• pp.303-308
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• 2005

Various kinds of Mg-Zn-Ca base alloys were rapidly quenched via melt spinning process. The meltspun ternary and quaternary alloy ribbons were heat-treated, and then the effects of additional elements on age hardening behavior and phase change of precipitates were investigated using Vickers hardness tester, XRD, and TEM equipped with EDS system. In ternary alloys, age hardening was mostly due to the distribution of $Mg_6Ca_2Zn_3$ and $Mg_2Ca$. The stable phases of precipitates were varied according to the aging temperature and the alloy composition. With the increase of Ca content, $Mg_2Ca$ precipitates were detected more than $Mg_6Ca_2Zn_3$ precipitates. In quaternary alloys, the precipitates taken from Mg-Zn-Ca-Co were identified as new quaternary phase, whereas those taken from Mg-Zn-Ca-Zr as MgZnCa containing Zr. In general, the ternary alloy showed higher peak hardness and thermal stability than the quaternary considering the total amounts of the solutes. It implies that the structure of precipitate should be controlled to have the coherent interface with the Mg matrix.

• 대한전자공학회논문지SD
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• 제45권8호
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• pp.11-16
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• 2008

본 논문에서는 먼저 RTP(Rapid Thermal Processor) 장치를 스트레스 측정에 용이한 구조로 제작하고 PC에서 통합 공정관리 시스템을 설계하였다. 다음으로는 Large deformation 이론을 바탕으로 반도체 웨이퍼 표면의 변형검사를 위한 레이져 인터페로미터리를 구성하였다. 궁극적으로 이러한 레이져장치로부터 웨이퍼 표면의 영상을 추출하고 세선화, 블록화 그리고 스트레스 분포도의 순서로 영상처리 하여 스트레스로 인한 웨이퍼 표면의 변형을 검사하였다. 실험을 하기 위해 변형이 이루어지도록 웨이퍼의 후면을 1mm정도 갈아낸 후 약 1000도에서 $3\sim4$회 열처리를 수행하였으며, 열처리를 가한 영상과 가하지 않은 영상을 통하여 웨이퍼 열처리 후 심각한 변형이 이루어졌음을 알 수 있었다.

• 열처리공학회지
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• 제5권4호
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• pp.201-208
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• 1992

An experimental study of the constitutive response of precipitation-strengthened Al-0.55wt% Zr alloy, which consists of an Al matrix precipitation-strengthened by coherent particles, ${\beta}^{\prime}(Al_3Zr)$ with $L1_2$ structure has been performed. The deformation response of the materials has been examined by stress relaxation test at 573K, 623K and 673K. It was found that there exist the threshold stress during stress relaxation and threshold stress results from the presense of ${\beta}^{\prime}(Al_3Zr)$ particles. The ratio of threshold stress and Orowan stress decreased gradually with increasing temperature. The resistance to climb-pass of particles was independent of particles size for a fixed volume fraction although the threshold for bowing and particles cutting are sensitive to the particles dimensions. The smaller particles cutted by dislocations. This behavior of dislocations in this alloy was explained in terms of the small value antiphase boundary energy. The dislocation networks wrere more extensive in spesimens subjected to stress relaxation and there were numerous areas that have a high denstiy of jogged dislocation. This experiment results indicate that the rate controlling stress relaxation process is the climb of edge dislocation over particles.

• 한국전산유체공학회지
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• 제17권3호
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• pp.87-92
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• 2012

The presence of a layer of vegetation which is relevant in river engineering or coastal engineering can modify the overall flow resistance, turbulent characteristics of flow. The patch of vegetation can be modelled and studied in a simple porous cylinder by previous researchers. Fully three dimensional Large Eddy Simulation is conducted in flow past a porous cylinder with a solid volume fraction (SVF) 0f 20%. The porous cylinder of diameter D contains 89 smaller cylinders which diameter is 0.048D in a regular staggered way. Reynolds number based on porous cylinder diameter D and the bulk velocity is 10,000. The large scale shedding is qualitatively similar to the one observed in the non-porous case (SVF=100%). The difference in the dynamics of the separated shear layer and the streamwise flow penetrating through the porous cylinder are compared with those in the non-porous cylinder. In particular, the wake billows form a larger distance from the back of the porous cylinder.

• 대한기계학회논문집B
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• 제25권11호
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• pp.1527-1534
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• 2001

Phase averaged velocity fields in the near wake region behind a square cylinder have been (successfully) obtained using randomly sampled PIV data sets. The Reynolds number based on the flow velocity and the vertex height was 3,900. To identify the phase information, we examined the magnitude of circulation and the center of peak vorticity. The center of vorticity was estimated from lowpass filtered vorticity contours (LES decomposition) adopting a sub-pixel searching algirithm. Due to the sinusoidal nature of firculation which is closely related to the instantaneous vorticity, the location of peak voticity fits well with a sine curve of the circulation magnitude. Conditionally-averaged velocity fields represent the barman vortex shedding phenomenon very well within 5 degrees phase uncertainty. The oscillating nature of the separated shear layer and the separation bubble at the top surface are clearly observed. With the hot-wire measurements of Strouhal frequency, we found thats the convection velocity changes its magnitude very rapidly from 25 to 75 percent of the free stream velocity along the streamwise direction when the flow passes by the recirculation region.

• Ocean and Polar Research
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• 제30권1호
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• pp.33-46
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• 2008

In order to investigate seasonal variations of the physical environments in the region of Jinhae Bay-Nakdongpo, we carried out hydrographic surveys from November 2000 to November 2001. Horizontal and vertical distribution of salinity and temperature shows large seasonal variations. Water column is well mixed in winter and stratified in summer. Low-salinity water is distributed in the form of patches because of the drainage control at the Nakdong River. Seasonal variations in the sea near Gadeok-Sudo are affected by topography, river discharge and tidal current. Currents have been measured using a bottom mounted ADCP and DCM12 between November 2000 and August 2001 in the Gadeok-Sudo. The current in the Gadeok-Sudo shows a distinct two-layer structure with reversed current. Low-pass filtered time series of wind, sea elevation and current are coherent for the period of 1-2 days and are attributed to Ekman-like dynamics. Spatial and temporal circulation pattern shows a slight different. The subtidal current in Jinhae Bay goes northward, however is reversed in the Gadeok-Sudo mouth.

• 시스템엔지니어링학술지
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• 제2권2호
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• pp.27-32
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• 2006

The emerging standards since 1990's can be classified as 'system standards' (process-oriented standards) and they specify the process of an enterprise and also apply to almost all industries regardless of size, type and products. Notice that the conventional specification-oriented standards present relatively clear criteria even though the structure, performance, and terminology are defined in text-based form. However, the system standards dealing with the processes do not present a coherent guide. Therefore, it is difficult to analyze them with the same viewpoint, thereby resulting in differences in the level of understanding. This study is aimed at graphically modeling the system standards originally described in text-based form. The study has been carried out in the framework of the PMTE (Process, Methods, Tools, and Environment) paradigm. The system standard targeted here is ISO/IEC 15288. Firstly, review of the literature on the systems engineering (SE) standard/process and on the graphic model IDEF0 was done, respectively, for the parts of 'E' and 'M'. Then the SE process of the MIL-STD 499B was applied to ISO/IEC 15288 as 'P'. Finally, the graphical model was generated by AI0Wins as 'T'. As a result, the graphical model-based approach can complement the drawbacks of the text-based form.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1801-1806
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• 2004

Stochastic nature of subgrid-scale stress causes the predictability problem in large eddy simulation (LES) by which the LES solution field decorrelates with field from filtered directnumerical simulation (DNS). In order to evaluate the predictability limit in a priori sense, the information on the interplay between resolved scale and subgrid-scale (SGS) is required. In this study, the analysis on the inter-scale interaction is performed by applying tophat and cutoff filters to DNS database of flow over a circular cylinder at Reynolds number of 3900. The effect of filter shape is investigated on the interpretation of correlation between scales. A critique is given on the use of tophat filter for SGS analysis using DNS database. It is shown that correlations between Karman vortex and SGS kinetic energy drastically decrease when the cutoff filter is used, which implies that the small scale universality holds even in the presence of the large scale coherent structure.

• 반도체디스플레이기술학회지
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• 제15권1호
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• pp.22-26
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• 2016

Extreme ultraviolet (EUV) pellicle is one of the most concerned research in the field of EUV lithography (EUVL). Imaging performance of EUV mask with pellicle should be investigated prior to high volume manufacturing (HVM) of EUVL. In this paper, we analyzed the relationship between standoff distance and imaging performance of EUV mask to verify the influences of relative standoff distance on imaging performance. As a result, standoff distance of EUV pellicle has no effect on imaging performance of EUV mask such as critical dimension (CD), normalized image log slope (NILS) and image contrast. Therefore, pellicle support structure can be flexibly designed and modified in diverse ways to complement the thermal limitation of EUV pellicle membrane.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.319-323
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• 2003

In this paper, we propose a hybrid transceiver for underwater acoustic communication, which allows the system to reduce complexity and increase robustness in time variant underwater channel environments. It is designed in the digital domain except for amplifiers and implemented by using a multiple digital signal processors (DSPs) system. The digital modulation technique is quadrature phase shift keying (QPSK) and frame synchronization is an energy (non-coherent) detection scheme based on the quadrature receiver structure. DSP implementation is based on block data parallel architecture (BDPA). We shaw experimental results in th? underwater anechoic basin at KRISO. The results indicate that the frame synchronization is performed without PLL. Also, we shaw that the adaptive equalizer can compensate frame synchronization error and the correction capability is dependent on the length of equalizer.