• Journal of the Korean Society for Heat Treatment
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• v.10 no.4
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• pp.237-245
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• 1997

A study was conducted to examine the effects of In addition on the precipitation behaviors of Al-2.1Li-2.9Cu alloy by differential scanning calorimetry, transmission electron microscopy and micro-hardness tester. DSC analysis was measured over the temperature range of $25{\sim}550^{\circ}C$ at a heating rate of $2{\sim}20^{\circ}C$/min. The heat evolution peaks due to the formation of GP zone and ${\delta}$'phase shift to higher temperature and the peaks to $T_1$ and ${\theta}$'phases shift to lower temperature by In addition. From this result, it was proved that the formation of GP zone and ${\delta}$'phase is suppresed whereas that of $T_1$ and ${\theta}$'phases are accelerated by the In addition of 0.15wt%. The age hardening curve aged at $190^{\circ}C$ showed that the In bearing alloy(alloy B) has more faster age hardening response and a higher peak hardness than In-free alloy(alloy A), attributed to the fine and homogeneous distribution of $T_1$ and ${\theta}$'phases. The activation energies for the formation of ${\delta}$'phase in In-free and In-bearing alloys are 22.3kcal/mol and 18.6kcal/mol, respectively. Those for $T_1(+{\theta}^{\prime})$ phase of In-free and In-bearing alloys are 24.3 and 37.5kcal/mol, respectively. Quenched-in excess vacancies play an important role to the formation of precipitates.

• International Journal of Control, Automation, and Systems
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• v.2 no.1
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• pp.107-117
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• 2004

A new algorithm for planning a collision-free path based on an algebraic curve as well as the concept of path space is developed. Robot path planning has so far been concerned with generating a single collision-free path connecting two specified points in a given robot workspace with appropriate constraints. In this paper, a novel concept of path space (PS) is introduced. A PS is a set of points that represent a connection between two points in Euclidean metric space. A geometry mapping (GM) for the systematic construction of path space is also developed. A GM based on the 2$^{nd}$ order base curve, specifically Bezier curve of order two is investigated for the construction of PS and for collision-free path planning. The Bezier curve of order two consists of three vertices that are the start, S, the goal, G, and the middle vertex. The middle vertex is used to control the shape of the curve, and the origin of the local coordinate (p, $\theta$) is set at the centre of S and G. The extreme locus of the base curve should cover the entire area of actual workspace (AWS). The area defined by the extreme locus of the path is defined as quadratic workspace (QWS). The interference of the path with obstacles creates images in the PS. The clear areas of the PS that are not mapped by obstacle images identify collision-free paths. Hence, the PS approach converts path planning in Euclidean space into a point selection problem in path space. This also makes it possible to impose additional constraints such as determining the shortest path or the safest path in the search of the collision-free path. The QWS GM algorithm is implemented on various computer systems. Simulations are carried out to measure performance of the algorithm and show the execution time in the range of 0.0008 ~ 0.0014 sec.

• Transactions of Materials Processing
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• v.10 no.1
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• pp.35-41
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• 2001

The high temperature deformation behavior of SCM 440 can be characterized by the hot torsion test in the temperature ranges of $900^{\circ}C$~$1100^{\circ}C$ and strain rate ranges of 0.05/sec~5/sec. The aim of this paper is to establish the quantitative equation of the volume fraction of dynamic recrystallization (DRX) as a function of processing variables, such as strain rate ($\varepsilon$), temperature (T), and strain ('$\varepsilon$). During hot deformation, the evolution of microstructure could be analyzed from work hardening rate ($\theta$). For the exact prediction of dynamic softening mechanism the critical strain ($\varepsilon_c$), the strain for maximum softening rate ($\varepsilon^*$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A, respectively. The transformation-effective strain-temperature curve for DRX could be composed. It was found that the calculated results were agreed with the experimental data for the steel at any deformation conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.33-36
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• 2000

The dynamic recrystallization (DRX) of medium carbon steels (SCM 440 and POSMA45) was studied with torsion test in the temperature range of $900-1100^{\circ}C$ and the strain rate range of $5.0x10^{-2}\;-\;5.0x10^0/sec$. To establish the quantitative equations for DRX, the evolution of flow stress curve with strain was analyzed. The critical strain (${\varepsilon}_c$) and strain for maximum softening rate ( ${\varepsilon}^{*}$) could be confirmed by the analysis of work hardening rate ($d{\sigma}/d{\varepsilon}\;=\; \theta$). The volume fraction of dynamic recrystallization ($X_{DRX}$) as a function of processing variables, such as strain rate ( $\dot{\varepsilon}$ ), temperature (T), and strain ( $\varepsilon$ ) were established using the ${\varepsilon}_c$ and ${\varepsilon}^{*}$. For the exact prediction, the ${\varepsilon}_c$, ${\varepsilon}^{*}$ and Avrami' exponent (m') were quantitatively expressed by dimensionless parameter, Z/A respectively. The transformation-effective strain-temperature curve for DRX could be composed. It was found that the calculated results were agreed with the experimental data for the steels at any deformation conditions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.26-34
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• 2008

This paper summarizes a design procedure of radiated noise from engine blocks of marine engines. This air-borne noise is one of the significant noise contributors including the aeroacoustic noise due to intake and exhaust and the re-radiation due to structure-borne noise. Excitation forces by engine operations are evaluated taking into account the power generation mechanism from the burning process to the subsequence motion of internal parts; piston, connecting rod, and crank shaft. The acoustic transfer vector method is incorporated to effectively simulate the radiated noise field under the various operation conditions. A contribution analysis for the various excitations to the radiated noise is conducted. It is found that the firing pressure is the main source of the radiated noise, and so the structure of the cylinder can be modified to significantly reduce the radiated noise from the engine block.

• Journal of Magnetics
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• v.9 no.2
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• pp.52-59
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• 2004

As deposited and annealed MTJs with the structure of $Ta(5 nm)/Cu(10 nm)/Ta(5 nm)/Ni_{80}Fe_{20}(2 nm)/Cu(5 nm)/ Ir_{25}Mn_{75}(10 nm)/Co_{70}Fe_{30}(2.5 nm)/Al-O/Co_{70}Fe_{30}(2.5nm)/Ni_{80}Fe_{20}(t)/Ta(5nm)/Ni_{80}Fe_{20}(t)/Ta(5 nm)$, where t=10, 30, 60 and 100 nm were characterized by XRD and magnetic hysteresis loops measurements. The XRD measurements were done in grazing incidence $(GID scan-2{\theta})$ and ${\theta}-2{\theta}$ geometry, by rocking curve $(scan-{\omega})$ and pole figures in order to establish correlation between texture and crystallites size and magnetic parameters of exchange biased and interlayer coupling. The variations of shifting and coercivity field of free and pinned layers after annealing in $300^{\circ}C$ correlate with the improvement of ［111］ texture and grains size of $Ni_{80}Fe_{20}$ and $Ir_{25}Mn_{75}$ respectively. The exchange biased and the coercivity fields of the pinned layer linearly increased with increasing grain size of $Ir_{25}Mn_{75}$, The reciprocal proportionality between interlayer coupling and coercivity fields of the free layer and grain size of $Ni_{80}Fe_{20}$ was found. The enhancement of interlayer coupling between pinned and free layers, after annealing treatment, indicates on the correlated in-phase roughness of dipolar interacting interfaces due to increase of crystallites size of $Ni_{80}Fe_{20}$.

• Transactions of Materials Processing
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• v.12 no.6
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• pp.588-596
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• 2003

The relationships between evolution of microstructure and mechanical properties of porous Al-3Si-2Mg-2Cu alloy after the foaming and various heat treating were investigated. The foamed alloy having various densities were manufactured by powder compact foaming and heat treated. Then compression test was performed with deformation rate of 0.5/s. The ultimate compression strength was not changed after solution heat treatment but the flow curve after ultimate strength showed very smooth and uniform plateau region. This change of flow curve means that the deformation mechanism is altered from brittle fracture to ductile deformation and the energy absorption property of Al foam is dramatically improved. The improvement of energy absorption without any detriment of mechanical properties is due to that the very brittle precipitation like Al-Cu and Al-Mg was uniformly dissolved in Al matrix after solution heat treatment. And various mechanical properties of Al alloy porous material were improved by 40% with aging of $200^{\circ}C$ and 50min. These improvements are ascribe to the various fine precipitates like $\Omega$ and $\theta$'.

• Bulletin of the Korean Chemical Society
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• v.15 no.3
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• pp.221-227
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• 1994

The barrier heights of the internal rotations for ethyl halides calculated by ab initio methods differ from those of experiments by more than 0.2 kcal/mol. The use of basis sets larger than the $6-31G^{\ast}$ set and the inclusion of correlation do not improve the agreement between the calculated and experimental values. The zero-point vibration corrections are substantial in the HF calculations with $6-31G^{\ast}$ basis sets, but become negligible in the MP2 calculations with $6-311G^{{\ast}{\ast}}$ basis sets for $C_2H_5F\;and\;C_2H_5Cl$. It is shown that the rigid rotor approximation and the assumed shape of the potential curve as a cos2${\theta}$ curve could also be the sources of discrepancies between calculated and experimental values. Higher order perturbation corrections narrow the gap between experimental and theoretical values, but there still remains about 10% overestimate of 0.3 kcal/mol. Optimized geometries from the HF and MP2 calculations are in good agreement with those from experiments. Dipole moments calculated from the MP2 densities show slightly better agreement with experiments than those from the HF densities.

• The Korean Journal of Nuclear Medicine
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• v.23 no.2
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• pp.175-181
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• 1989

Visual assessment of regional wall motion abnormality (RWMA) by gated blood pol scan (GBPS) serves as an useful parameter in the diagnosis, functional evaluation, and follow up in various clinical settings, but are still subject to some inherent limitations. On important problem may be the interobserver as well as intraobsever variation that may well be present due to the subjective nature of the interpretations. This study was carried out to determine the reliability and reproducibility of visual assessments made in GBPSs, and to observe the degree to which the results would be influenced by observer variation. Fifty two patients with coronary heart disease had resting GBPS and contrast ventriculography within 4 days appall. Contrast ventriculography-showed normal wall motion in 6 patients and the remaining 46 had RWMA in one or more segments. The anterior and left anterolateral views of all 52 GBPSs were analyzed by three independent observers, who selected from 5 scales, their level of confidence that there was RWMA in that segment. Reciever operating characteristic (ROC) curves for each analysis was plotted and the area under the curve $(\theta)$ was used as a parameter representing each observer's performance in his interpretations. The findings of contrast ventriculographies were used as the standard for RWMA. The apical and inferoapical segments showed the best correlation with contrast ventriculography ($\theta=0.90-0.94$, 0.81-0.94, respectively), and the inferior wall showed the poorest correlation $(\theta=0.70-0.74)$. The interpretations of the inferior, septal, apical, and posteroinferior, segments showed no difference between the observers, but there was significantly better performance in assessment by observer A compared to that by B or C for the anterolateral segments ($\theta=0.87$, 0.78, 0.76, respectively. p<0.01 for A vs B, p<0.05 for A vs C), as well as when all segments were considered altogether ($\theta=0.88$, 0.83, 0.82, respectively. both p<0.05). This was also true for the infero-apical segment between A and C ($\theta=0.09$, 0.81, p<0.05). The intraobserver variation, however, did not appear significant, with only the inferior segment for observer B showing any significant difference when observer A and B repeated the analysis 10 days latter. There was no difference in assessing dyskinesia, with all observers showing a high performance ($\theta=0.98$, 0.87, 0.97, respectively). The visual assessment of left ventricular ejection fraction by all three observers correlated well with the calculated value from a semiautomated method (Spearman's r = 0.91, 0.83, 0.83. p<0.01, p<0.05, p < 0.05). The assessment of LV and RV size also correlated well between the three observers (Kendall's w = 0.80, 0.51, p<0.01 for both left and right ventricles). The above findings suggest that RWMA visually assessed by GBPS correlates well with that done by contrast ventriculography. And although the observer's experience or skill may influence the results in certain segments, visual analysis of GBPS may serve as a reliable and reproducible means for evaluating ventricular function.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.4
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• pp.1-8
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• 1999

This paper presents a new algorithm for surface segmentation and feature description. In the first stage of proposed algorithm, the signature of an edge image of object is extracted. The signature technique represents a surface using the distance from the mass center to the boundary of the image as a function of angle rotating counterclockwise. If there exists a range in the angle axis where more than two signatures form a closed curve, we can conclude there is a surface inside the range. Using this feature of the signature, surface can be segmented. The surface features such as number of vertices, number of edges, convex and type of surface can also be extracted from segmented surfaces. This algorithm has distinguished advantages; it can easily recover the lost part in the edge image using the curve fitting method; it extracts surface features correctly regardless of the rotation of the surface in 3-D space.