• Journal of Powder Materials
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• v.22 no.1
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• pp.6-9
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• 2015

In this study, the behavior of densification of copper powders during high-pressure torsion (HPT) at room temperature is investigated using the finite element method. The simulation results show that the center of the workpiece is the first to reach the true density of copper during the compressive stage because the pressure is higher at the center than the periphery. Subsequently, whole workpiece reaches true density after compression due to the high pressure. In addition, the effective strain is increased along the radius during torsional stage. After one rotation, the periphery shows that the effective strain is increased up to 25, which is extensive deformation. These high pressure and severe strain do not only play a key role in consolidation of copper powders but also make the matrix harder by grain refinement.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1071-1080
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• 2018

The study of behavior and values of deformations in the geological medium makes the scientific basis of the methodology of synthesis of true values of parameters of its physico-mechanical and density properties taking into account the influence of geodynamic impacts. The segments of continuous variation of homogeneous elastic uniform deformations are determined under overall compression of the medium. The limits of these segments are defined according to the criteria of instability (on geometric form changes and on "internal" instability). Analytical formulae are obtained to calculate current and limiting (critical) values of deformations within the framework of various variants of small and large initial deformations of the non-classically linearized approach of non-linear elastodynamics. The distribution of deformation becomes non-uniform in the medium while the limiting values of deformations are achieved. The proposed analytical formulae are applicable only within homogeneous distribution of deformations. Numerical experiments are carried out for various elastic potentials. It is found that various forms of instability can precede phase transitions and destruction. The influence of these deformation phenomena should be removed while the physico-mechanical and density parameters of the deformed media are determined. In particular, it is necessary to use the formulae proposed in this paper for this purpose.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.848-859
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• 2004

Mechanical testing methods to determine the material constants for large deformation nonlinear finite element analysis were demonstrated for natural rubber. Uniaxial tension, uniaxial compression, equi-biaxial tension and pure shear tests of rubber specimens are performed to achieve the stress-strain curves. The stress-strain curves are obtained after between 5 and 10 cycles to consider the Mullins effect. Mooney and Ogden strain-energy density functions, which are typical form of the hyperelastic material, are determined and compared with each other. The material constants using only uniaxial tension data are about 20% higher than those obtained by any other test data set. The experimental equations of shear elastic modulus on the hardness and maximum strain are presented using multiple regression method. Large deformation finite element analysis of automotive transmission mount using different material constants is performed and the load-displacement curves are compared with experiments. The selection of material constant in large deformation finite element analysis depend on the strain level of component in service.

• 전자공학회논문지 IE
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• v.47 no.2
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• pp.21-26
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• 2010

This paper proposed an efficient algorithm to reduce the amount of calculation for Scalability Extension which takes a great deal of the operational time in H.264/AVC. This algorithm decides a search range according to the direction of predicted motion vector, and then performs an adaptive spiral search for the candidates with JM(Joint Model) FME(Fast Motion Estimation) which employs the rate-distortion optimization(RDO) method. Experimental results by applying the proposed method to various video sequences showed that the process time was decreased up to 80% comparing to the previous prediction methods. The degradation of video Quality was only from 0.05dB to 0.19dB and the compression ratio decreased as small as 0.58% in average. Therefore, we are sure that the proposed method is an efficient method for the fast inter prediction.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.5
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• pp.474-485
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• 2001

This paper proposes a user-key-based fragile watermarking for detecting image modification. The embedding data in a form of binary image for authentication are inserted to the DCT coefficients of each block of the given image. To minimize possible exposure of being watermarked and the location of insertion, it is proposed to utilize a user-specific key in randomizing those information. Each DCT block hides one bit of data, all of which represent the user-specific authentication data. Experiments with 5 real images demonstrate that the proposed method not only detects whether there is modification or not, but also the actual location of modification with minimal visual deterioration. However, the proposed method has room for improvement against its loss of watermark by an attack of compression by more than 50%.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.7
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• pp.498-509
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• 1988

A BF(breadth-first) linear quadtree as a new data structure for image data is suggested, which enables us to compress the image data efficiently and to make operations of the compressed data easily. It is a list of path names for black nodes as the linear quadtree is. The path name for each black node of a BF linear quadtree is represented as a sequence of path codes from the root node to itself, whereas that of linear quadtree as a sequence of path codes from the root node to itself and fill characters for cut-offed path from it to any n-level node which corresponds to a pixel of an image. The BF linear quadtree provides a more efficent compression ratio than the linear quadtree does, because the former does not require redundant characters, fill characters, for the cut-offed paths. Several operations for image processing can be also implemented on this hierarchical structure efficiently, because it is composed of only the black nodes ad the linear quadtree is . In this paper, algorithms for several operations on the BF linear quadtree are defined and analyzed. Experimental results for forur image data are also given and discussed.

• Journal of Biomedical Engineering Research
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• v.28 no.6
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• pp.732-743
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• 2007

Background noise is one of the major complaints of not only hearing impaired persons but also normal listeners. This paper describes the results of two experiments in which speech recognition performance was determined for listeners with normal hearing and sensorineural hearing loss in noise environment. First, we compared speech enhancement algorithms by evaluation speech recognition ability in various speech-to-noise ratios and types of noise. Next, speech enhancement algorithms by reducing background noise were presented and evaluated to improve speech intelligibility for sensorineural hearing impairment listeners. We tested three noise reduction methods using single-microphone, such as spectrum subtraction and companding, Wiener filter method, and maximum likelihood envelop estimation. Their responses in background noise were investigated and compared with those by the speech enhancement algorithm that presented in this paper. The methods improved speech recognition test score for the sensorineural hearing impaired listeners, but not for normal listeners. The results suggest the speech enhancement algorithm with the loudness compression can improve speech intelligibility for listeners with sensorineural hearing loss.

• Transactions of the Korean hydrogen and new energy society
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• v.13 no.4
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• pp.313-320
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• 2002

The characteristics of the AISI bipolar plates have been investigated to replace the expensive graphite bipolar plates. It was found from the contact resistance evaluation of graphites, composites, and AISI that the contact resistance of AISI was the lowest, but it could approach to that of composites at higher compression forces. The single cell operation using the AISI bipolar plates revealed that the lower performance of the AISI single cell compared to the graphite one was due to not only the higher contact resistance but the flooding effect caused by high wettability of AISI. The performance of the AISI single cell could be improved if the channels were modified appropriately. The large size AISI single cell was operated to investigated the size effect on the performance.

• Journal of Korean Clinical Health Science
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• v.2 no.2
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• pp.133-147
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• 2014

Purpose. Radiation therapy for oncologic emergencies is an important modality in the management of cancer patients. The aim of the present study was to review the roles of RT in oncologic emergencies based on literature review. Methods. The oncologic emergencies requiring rapid treatment include superior vena cava syndrome, spinal cord compression, brain metastasis, and bone metastasis. We reviewed the literatures on the pathophysiology, diagnosis, and treatment of oncologic emergencies. Results. In this literature review, radiation therapy among treatment modalities for oncologic emergencies has been shown to be fast and very effective treatment modality for oncologic emergencies. Conclusions. Based on this review, we conclude that the literature provides support for the role of radiation therapy in the situation of oncologic emergencies. As the number of cancer patients increase, the prevalence of oncologic emergencies will increase. In the future, the development of RT techniques will provide the improvement of not only patient's quality of life but also the survival.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.59-63
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• 2005

Compression tests were performed for six types of hat stiffened composite panels with different bonding methods and stiffener section shapes. Six panels showed similar behaviors in buckling and post-buckling region before a skin-stiffener separation failure occurred. The skin-stiffener separation failures occurred in the panels with closed type stiffeners regardless of bonding methods, but not in the panels with open type stiffeners. The separation failures not only reduced the postbuckling strength but also changed buckling mode and postbuckling stiffness. All the separation failures were initiated at the stiffener flange edges closest to skin buckling crests. The co-cured or secondary bonded panels with open type stiffeners had the largest structural performance. Because the post-buckling strength and performance of the composite stiffened panels are reduced by the separation failure, it is important to find bonding methods, stiffener types and manufacturing parameters for preventing of the separation failure.