• Proceedings of the KSME Conference
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• 2000.11a
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• pp.135-140
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• 2000

The characteristics of mechanical behavior were estimated for Ti-6Al-4V alloy with four kinds of microstructure prepared with heat treatments. For this study, impact test, tensile test and fatigue crack growth test were performed, and then compared mechanical properties on the four microstructures. Furthermore, for quantitative evaluation, fractal dimensions of crack pass were obtained using the box counting method. The main results obtained are summarized as follows. (1) The microstructures exhibited equiaxed microstructure, bimodal-microstructure and lamellar microstructure by heat treatment. (2) The impact absorbed energy and elongation is superior in the bimodal-microstructure, and the hardness and tensile strength are superior in the lamellar microstructure. (3) The fatigue crack growth rate is similar to all microstructures in the low ${\Delta}K$ region. The fatigue crack growth rate of equiaxed microstructure is fastest, and that of lamellar microstructure is lowest in the high ${\Delta}K$ region. (4) The fractal dimension D of lamellar microstructure is higher then that of the equiaxed microstructure and bimodal microstructure.

• Imaging Science in Dentistry
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• v.36 no.2
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• pp.69-72
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• 2006

Purpose : We evaluated the fractal dimension changes on bovine rib radiographs according to the decalcification degree and the exposure time in the bovine rib. Materials and Methods : Twenty 5 mm thick cross-sectional blocks from bovine rib bone were progressively decalcified in 30 mL 0.1 N hydrochloric acid for 5, 30, and 90 minutes. They were radiographed at three exposure time settings (0.22, 0.36, 0.43 mAs) before and after each decalcification stage. We selected $100{\times}100$ pixel-sized regions of interests (ROIs) on trabecular bone and calculated fractal dimensions by box-counting method. Results : Repeated measures ANOVA showed that fractal dimensions gradually decreased after acid-induced demineralization and with more exposure (P<0.001). Conclusion : The fact that fractal dimensions decrease after decalcification might support the hypothesis that patients with osteoporosis have decreased radiographic fractal dimension in trabecular bone in comparison to normal subjects.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.38 no.2
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• pp.96-100
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• 2012

Objectives: This study sought to evaluate trabecular changes in the mandible using fractal analysis and to explain the transient osteopenia related to rapid orthodontic tooth movement after orthognathic surgery. Materials and Methods: Panoramic radiographs were taken of 26 patients who underwent bilateral sagittal split ramus osteotomy. Radiographs taken before the surgery and 1 month after surgery were overlapped, and $40{\times}40$ pixel square regions of interest were selected near the mandibular canines and 1st molars. After the image processing procedure, the fractal dimension was calculated using the box-counting method. Results: Fractal dimension after orthognathic surgery decreased in a statistically significant manner (P<0.05). The change in fractal dimension on the canine side had greater statistical significance as compared to that seen on the 1st molar side. Conclusion: This study found that bone density decreases after orthognathic surgery due to transient osteopenia related to the regional acceleratory phenomenon. This result can provide a guide to evaluating orthodontic tooth movement after orthognathic surgery.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.33 no.5
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• pp.494-498
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• 2007

Purpose: This study was done to know the usefulness of fractal analysis when evaluating the radiologic changes after decompression on jaw bone cystic lesions using fractal analysis. Materials and methods: 30cases of cystic lesions were followed up after decompression. Panoramic image was used to observe radiologic changes around the cystic lesion. The part of the panoramic image which showed radiologic change was defined as region of interest(ROI); The fractal dimension of the ROI was calculated using box-counting method. Results: Using sign-rank test, there was a statistically significant difference in fractal dimensions after decompression therapy(P<0.0001). The fractal dimensions statistically increased after decompression(the median of D:0.12). Conclusions: The ROI after decompression showed higher fractal dimensions which offer the objective proof of the bone healing around cystic lesions after decompression treatment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.609-616
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• 2002

The characteristics of mechanical behavior are investigated for Ti-6Al-4V alloy. Four kinds of the specimens are prepared under different heat treatments in order to produce different microstructures. In the present investigations, impact, tensile and fatigue crack growth tests are performed for each test specimen. The results obtained through the investigations are compared. Additionally fr actal dimensions of crack pass are obtained using the box counting method. The results are, 1) the microstructures shows as equiaxed, bimodal and Widmanstatten microstructures respectively, 2) the impact energy and elongation are superior fur the bimodal microstructure, and the hardness and tensile strength are superior fur the Widmanstatten microstructure, 3) the fatigue crack growth rate is similar to all microstructures in low ΔK region while that of equiaxed microstructure is the largest, and that of Widmanstatten microstructure is the lowest in high ΔK region respectively, 4) the fractal dimension D of Widmanstatten microstructure shows higher value than that of the equiaxed and bimodal microstructures under 200 magnification view of the SEM micrographs.

• Journal of Electrochemical Science and Technology
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• v.14 no.2
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• pp.194-204
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• 2023

Models based on diffusion-limited aggregation (DLA) have been extensively used to explore the mechanisms of dendritic particle aggregation phenomena. The physical and chemical properties of systems in which DLA aggregates emerge are given in their fractal. In this paper, we present a comprehensive study of the growth of electrodeposited copper dendrites in flat plate electrochemical cells from a fractal perspective. The effects of growth time, applied voltage, copper ion concentration, and electrolyte acidity on the morphology and fractal dimension of deposited copper were examined. 'Phase diagram' set out the variety of electrodeposited copper fractal morphology analysed by metallographic microscopy. The box counting method confirms that the electrodeposited dendritic structures manifestly exhibit fractal character. It was found that with the increase of the voltage and copper ion concentration. The fractal copper size becomes larger and its morphology shifts towards a dendritic structure, with the fractal dimension fluctuating around 1.60-1.70. In addition, the morphology of the deposited copper is significantly affected by the acidity of the electrolyte. The increase in acidity from 0.01 to 1.00 mol/L intensifies the hydrogen precipitation side reactions and the overflow path of hydrogen bubbles affects the fractal growth of copper dendrites.

• Journal of Korea Multimedia Society
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• v.7 no.2
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• pp.173-186
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• 2004

This paper proposed the content-based retrieval system as a method for performing image retrieval through the effective feature extraction of the object of significant meaning based on the characteristics of man's visual system. To allow the object region of interest to be primarily detected, the region, being comparatively large size, greatly different from the background color and located in the middle of the image, was judged as the major object with a meaning. To get the original features of the image, the cumulative sum of tile declination difference vector the segment of the object contour had and the signature of the bipartite object were extracted and used in the form of being applied to the rotation of the object and the change of the size after partition of the total length of the object contour of the image into the normalized segment. Starting with this form feature, it was possible to make a retrieval robust to any change in translation, rotation and scaling by combining information on the texture sample, color and eccentricity and measuring the degree of similarity. It responded less sensitively to the phenomenon of distortion of the object feature due to the partial change or damage of the region. Also, the method of imposing a different weight of similarity on the image feature based on the relationship of complexity between measured objects using the fractal dimension by the Boxing-Counting Dimension minimized the wrong retrieval and showed more efficient retrieval rate.

• Imaging Science in Dentistry
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• v.35 no.1
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• pp.33-40
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• 2005

Purpose : (1) To analyse the effect of exposure time, ROI size and one impact factor in the image processing procedure on estimates of fractal dimension; and (2) to analyse the correlated relationship between the fractal dimension and the Cu-Eq value (bone density). Materials and Methods : The cylindric bone phantoms of 6 large and 5 small diameter having different bone densities respectively and human dry mandible segment with copper step wedge were radiographed at 1.0 and 1.2 sec esposure (70 kVp, 7 mA) using one occlusal film and digitized. Eleven rectangular ROIs from 11 cylindric bone phantoms and 4 rectan-gular ROIs from cortical, middle, periodontal regions, and socket of bone were selected. Gaussian blurred Image was subtracted from original image of each ROI and multiplied respectively by 1, 0.8, and 0.5, and then the image was made binary, eroded and dilated once, and skeletonized. The fractal dimension was calculated by means of a box counting method in the software ImageJ. Results : The fractal dimension was decreased gradually with continued bone density decrease showing strong correlations (bone phantom; r> 0.87, bone; r> 0.68) under 70 kVp 1.0 sec M = 0.8. Fractal dimensions showed the significant differerence (p < 0.05) between two different exposure times on the same small ROI of bone phantom. Fractal dimensions between two different sizes of ROI on bone phantom showed the significant differerence (p < 0.05) under 1.2 sec exposure, but did not show it (p > 0.05) under 1.0 sec exposure. Conclusions : Exposure time, ROI size, and modifying factor during subtracting could become impacting on the results of fractal dimension. Fractal analysis with thoroughly evaluated method considering the various impacting factors on the results could be useful in assessing the bone density in dental radiography.

• Journal of Oral Medicine and Pain
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• v.41 no.3
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• pp.85-90
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• 2016

Purpose: The aim of this study was to develop an automated software to extract tooth and pulpal area from sectional cone-beam computed tomography (CBCT) images, which can guarantee more reproducible, objective and time-saving way to measure pulp/tooth volume ratio. Methods: The software program was developed using MATLAB (MathWorks). To determine the optimal threshold for the region of interest (ROI) extraction, user interface to adjust the threshold for extraction algorithm was added. Default threshold was determined after several trials to make the outline of extracted ROI fitting to the tooth and pulpal outlines. To test the effect of starting point location selected initially in the pulpal area on the final result, pulp/tooth volume ratio was calculated 5 times with different 5 starting points. Results: Navigation interface is composed of image loading, zoom-in, zoom-out, and move tool. ROI extraction process can be shown by check in the option box. Default threshold is adjusted for the extracted tooth area to cover whole tooth including dentin, cementum, and enamel. Of course, the result can be corrected, if necessary, by the examiner as well as by changing the threshold of density of hard tissue. Extracted tooth and pulp area are reconstructed three-dimensional (3D) and pulp/tooth volume ratio is calculated by voxel counting on reconstructed model. The difference between the pulp/tooth volume ratio results from the 5 different extraction starting points was not significant. Conclusions: In further studies based on a large-scale sample, the most proper threshold to present the most significant relationship between age and pulp/tooth volume ratio and the tooth correlated with age the most will be explored. If the software can be improved to use whole CBCT data set rather than just sectional images and to detect pulp canal in the original 3D images generated by CBCT software itself, it will be more promising in practical uses.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.1
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• pp.124-129
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• 2010

When a phenolic resin is carbonized by the leakage current flowing along its surface, the carbonization pattern is one of the most important factors to determine its carbonization characteristics. However, the typical carbonization pattern of a phenolic resin is too complicated to be analyzed by conventional Euclidean geometry. In most cases, such a complicated shape shows a fractal structure. It is possible, therefore, to examine the characteristics of the carbonization pattern regarding a given phenolic resin. In order to quantitatively investigate the carbonization pattern of the phenolic resin carbonized by a leakage current, in this paper, the fractal dimension of the carbonization pattern has been calculated as a function of the magnitude of a leakage current and the distance between two electrodes. For reliability of calculation, the correlation function as well as the box counting method has been used to calculate the fractal dimension. According to the result of calculation, the fractal dimension increases as the current increases at the constant electrode gap distance. However, there is no significant relation between the fractal dimension and the electrode gap distance at a constant current.