• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.4
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• pp.353-360
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• 2010

In this paper, an efficient algorithm is established in order to estimate the plastic properties of power-law hardening bulk specimen materials with one simple spherical indentation impression test. This work is based on a new formulation of representative strain and, therefore, compare to the preceding approaches the fitting parameters are significantly reduced. Moreover, the new definition of representative strain endowed more physical meaning to the representative strain. In order to verify the reliability of the reverse analysis, we have studied a broad set of materials whose property ranges cover essentially all engineering metals and alloys. Based on the indentation force-displacement P-${\delta}$ curves obtained from numerical simulations, the characteristics of the indentation response and material elastoplastic properties are bridged via explicit functions. Next, through the procedure of reverse analysis the yield stress and power-law hardening exponent of bulk specimen materials can be determined. Finally, good agreement between the result from reverse analysis and initial input data from experiment can be observed.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.125-130
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• 2008

A spherical indentation has been proposed as a nondestructive method of measuring local residual stress field in laser-voided joints. The apparent yield strengths interpreted from the spherical indentation data of as-welded cutting wheel were compared with the intrinsic yield strengths measured at nearly equivalent locations in annealed wheel. Their difference along the distance from the welding line is welding stress distribution because the intrinsic yield strength is invariant regardless of the elastic residual stress. The spherical indentations show that the laser-welded diamond cutting wheel displays a 10 min-wide distribution of the welding residual stress and has peak compressive and tensile stresses in the shank and tip regions, respectively.

• Journal of Aerospace System Engineering
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• v.11 no.6
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• pp.26-33
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• 2017

We propose a variable frame structure connected with telescopic mast-shaped shaft for a robot displaying outstanding ability to cross obstacles, and for effective traction control. The wireless control system was built to extend and contract a deployable mechanism, which is shaped into a hoberman sphere assembled with frame structures. In order to develop important parameters for efficient locomotion, we derived an Euler-Lagrange equation for the spherical robot. According to the equation, the DC motor was selected. A prototype mechanism was tested and a Finite-Element Analysis (FEA) was conducted in parallel. Using these data, we constructed a deployable spherical robot with structural stability. The deployable robot moved at a speed of 0.85 m/s from 520 mm to 650 mm.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.3
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• pp.61-64
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• 2008

Purpose: The analysis of individual eye model designed from clinical demonstration about emmetropia shows that the aberration would be changed by the wave change. Method: The model on the basis of clinical demonstration of eye ball is designed in a form of having 4 refraction surfaces and a constant refractive index. We analyzed designed twelve individual eye model into aberrations changes, as giving changes Fraunhofer lines's six wavelengths. Result: About individual eye model, change in the wavelength of the wavefront aberrations analysis using the Zernike coefficient. This data indicate that the shorter wave is, the more defocus increases and the deviation value of spherical aberration and RMS are widened. Conclusion: As quantity of defocus according to result wavelength change is shorter and shorter, inclination which is similar twelve individual eye model is bigger and bigger and individual eye model majority of cases, little change, and change is shown in part individual eye model is a significant performance degradation can be raised.

• Journal of the Korean Data and Information Science Society
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• v.3 no.1
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• pp.33-46
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• 1992

The set of eigenvectors of the second moment matrix and the mean vector are the measures of orientation for a distribution supported on the unit sphere. Bootstrap confidence cone for the eigenvector is constructed and the consistency of this method is discussed. The performance of our bootstrap cone for the eigenvector is compared with that of the asymptotic confidence cones for two measures under the parametric assumptions for the underlying distributions and that of the bootstrap cone for the mean vector by Monte Carlo simulation.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.5
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• pp.516-522
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• 2002

For the experimental study of rotor steel, seven kind of specimens with different degradation levels were prepared by isothermal heat treatment at $630^{\circ}C$. Spherical indentation technique was developed to evaluate the flow properties of metallic materials in carbon steel, stainless steel, and alloys, etc. Through the spherical indentation test, differently degraded 1Cr-1Mo-0.25V steel's mechanical properties were observed and compared with conventional standard test data. The flow properties of 1Cr-1Mo-0.25V steel's were estimated by analyzing the indentation load-depth curve. To characterize the flow property, we used material yield slope and constraint factor index rather than strain-hardening exponent because the variation of strain-hardening exponent was very little and the data showed irregularly. And the constraint factor's effect was small when the material yield slope was taken into account.

• Journal of Platform Technology
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• v.11 no.3
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• pp.12-23
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• 2023

In the 2020s, the K-Pop market has been dominated by girl groups over boy groups and the fourth generation over the third generation. This paper presents methods and results on lyric clustering to investigate whether the generation of girl groups has started to change. We collected meta-information data for 1469 songs of 47 groups released from 2013 to 2022 and classified them into lyric information and non-lyric meta-information and quantified them respectively. The lyrics information was preprocessed by applying word-translation frequency vectorization based on previous studies and then selecting only the top vector values. Non-lyric meta-information was preprocessed and applied with One-Hot Encoding to reduce the bias of using only lyric information and show better clustering results. The clustering performance on the preprocessed data is 129%, 45% higher for Spherical K-Means' Silhouette Score and Calinski-Harabasz Score, respectively, compared to Hierarchical Clustering. This paper is expected to contribute to the study of Korean popular song development and girl group lyrics analysis and clustering.

• Korean Journal of Mineralogy and Petrology
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• v.34 no.4
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• pp.241-253
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• 2021

Manganese nodules have been found in the shallow water depth of the Arctic Ocean as well as in the abyssal plains of the Pacific and Indian Oceans, but detailed study for them were rarely investigated. Manganese nodules, collected from the East Siberian Sea through the Arctic Expedition using Araon ice braking vessel, have a high potential for Mn mineral resources because they have high Mn content with high Mn/Fe ratio. This study investigated the external form, size and weight, internal texture for the non-spherical manganese nodule, which has about 7 % of total nodule from the East Siberian Sea. This study also researched the relative Mn-oxide mineral composition using the peak area ratio of X-ray diffraction pattern and their chemical composition. All data obtained from non-spherical nodules were compared with the spherical ones. Ellipsoidal, platy and irregular types are common among 5 groups of non-spherical manganese nodule based on the external form, and major axis and weight have positive relationship. All non-spherical manganese nodules have core mainly composed of mud sediments. The average Mn oxide mineral contents in nodules are birnessite, buserite and todorokite in descending order. Although mineral composition does not show any correlation with the external form, kind of core or internal structure, todorokite and buserite contents tend to increase and birnessite content decrease from the surface to the core in the nodule. Non-spherical manganese nodules have higher Mn content and Mn/Fe ratio than those from the shallow water depth of the Arctic Sea and even in the deep-sea of the Pacific and Indian Ocean. Although non-spherical nodule is larger and heavier, and has lower Mn content and Mn/Fe ratio than spherical nodule, there are not any differences in mineral composition and internal structure between them. Almost all manganese nodules collected from the East Siberian Sea are attributed to diagenetic process, because they are higher than 5 in Mn/Fe ratio.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.9
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• pp.1614-1618
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• 2007

We have demonstrated the experimental results to obtain the immunity of FN (Fowler Nordheim) stress for S-RCAT (Spherical-Recess Cell Array Transistor) which has been employed to meet the requirements of data retention time and propagation delay time for sub-100-nm mobile DRAM (Dynamic Random Access Memory). Despite of the same S-RCAT structure, the immunity of FN stress of S-RCAT depends on the process condition of gate oxidation. The S-RCAT using DPN (decoupled plasma nitridation) process showed the different degradation of device properties after FN stress. This paper gives the mechanism of FN-stress degradation of S-RCAT and introduces the improved process to suppress the FN-stress degradation of mobile DRAM.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.8
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• pp.84-91
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• 2002

This paper analyzes the subsurface stress at the spherical contact using Hamilton equation, and with that data, calculates the fatigue limit under the variations of friction coefficient using fatigue theory. After rough surface being made, this paper figures out the random load generated by contacting to the rough surface, analyzes the stress of its subsurface, and calculates the fatigue limit of the rough surface using fatigue theory. The three parts of the fatigue theory are applied, which are critical plane theory, stress invariant theory and mesoscopic theory.