• Smart Structures and Systems
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• v.23 no.2
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• pp.141-153
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• 2019

This research deals with wave propagation of the functionally graded (FG) nano-beams based on the nonlocal elasticity theory considering surface and flexoelectric effects. The FG nano-beam is resting in Winkler-Pasternak foundation. It is assumed that the material properties of the nano-beam changes continuously along the thickness direction according to simple power-law form. In order to include coupling of strain gradients and electrical polarizations in governing equations of motion, the nonlocal non-classical nano-beam model containg flexoelectric effect is used. Also, the effects of surface elasticity, dielectricity and piezoelectricity as well as bulk flexoelectricity are all taken into consideration. The governing equations of motion are derived using Hamilton principle based on first shear deformation beam theory (FSDBT) and also considering residual surface stresses. The analytical method is used to calculate phase velocity of wave propagation in FG nano-beam as well as cut-off frequency. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as flexoelectric coefficients of the surface, bulk and residual surface stresses, Winkler and shear coefficients of foundation, power gradient index of FG material, and geometric dimensions on the wave propagation characteristics of FG nano-beam. The numerical results indicate that considering surface effects/flexoelectric property caused phase velocity increases/decreases in low wave number range, respectively. The influences of aforementioned parameters on the occurrence cut-off frequency point are very small.

• The korean journal of orthodontics
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• v.47 no.1
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• pp.39-49
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• 2017

Objective: This retrospective, cross-sectional study aimed to establish reference data for normal crown and root lengths and the root-crown ratios (R/C ratios) for the mature maxillary and mandibular incisors in a Korean population by using cone-beam computed tomography (CBCT). Methods: We included 672 Korean patients (141 men and 531 women; mean age, $27.2{\pm}7.7years$) who underwent CBCT examinations during various dental treatments. Crown and root lengths and the R/C ratios of the maxillary and mandibular incisors were measured using CBCT data, which were analyzed to detect significant differences between demographic factors as well as sagittal and vertical skeletal or occlusal relationships. Results: Teeth of the same type in each half-arch were symmetrical. The mean R/C ratios varied from 1.1 to 1.2 for the maxillary incisors and from 1.3 to 1.4 for the mandibular incisors. Crown and root lengths were greater in men than in women, regardless of tooth type. Root lengths and R/C ratios for the mandibular incisors were significantly greater in patients with skeletal Class II malocclusion or an excessive overjet than in the other patients. The R/C ratios for the mandibular incisors were lower in patients with an open bite than in those with a normal or deep bite. Moreover, the R/C ratios for the mandibular incisors increased with age. Conclusions: The data obtained in our study can serve as reference values for crown and root lengths and the R/C ratios for the maxillary and mandibular incisors in the Korean population.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.422-429
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• 2002

The identification of ultrasonic flaw signals is a truly difficult task in the angle beam testing of welded joints due to non-relevant signals from the geometric reflectors such as weld roots and counter bores. This paper describes a new approach called "technique for identification of flaw signal using deconvolution(TIFD)" in order to identify the flaw signals in such a problematic situation. The concept of similarity function based on the deconvolution is introduced in the proposed approach. The "reference" signals from both flaws and geometric reflectors and test signals are acquired and normalized. The similarity functions are obtained by deconvolution of test signals with reference signals. The flaw signals could be identified by the patterns of similarity function. The initiative results show great potential of TIFD to distinguish notch comer signals from the geometric reflections.

• Imaging Science in Dentistry
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• v.45 no.1
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• pp.41-47
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• 2015

Purpose: This study was performed to evaluate the linear distance accuracy and reliability of stitched small field of view (FOV) cone-beam computed tomography (CBCT) reconstructed images for the fabrication of implant surgical guides. Material and Methods: Three gutta percha points were fixed on the inferior border of a cadaveric mandible to serve as control reference points. Ten additional gutta percha points, representing fiduciary markers, were scattered on the buccal and lingual cortices at the level of the proposed complete denture flange. A digital caliper was used to measure the distance between the reference points and fiduciary markers, which represented the anatomic linear dimension. The mandible was scanned using small FOV CBCT, and the images were then reconstructed and stitched using the manufacturer's imaging software. The same measurements were then taken with the CBCT software. Results: The anatomic linear dimension measurements and stitched small FOV CBCT measurements were statistically evaluated for linear accuracy. The mean difference between the anatomic linear dimension measurements and the stitched small FOV CBCT measurements was found to be 0.34 mm with a 95% confidence interval of +0.24 - +0.44 mm and a mean standard deviation of 0.30 mm. The difference between the control and the stitched small FOV CBCT measurements was insignificant within the parameters defined by this study. Conclusion: The proven accuracy of stitched small FOV CBCT data sets may allow image-guided fabrication of implant surgical stents from such data sets.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.10
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• pp.64-74
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• 2007

Because of the size and environment in the shipbuilding process, the portable type robot is required for the automatic seam tracking. For this reason, the structure of laser sensor should be considered in the initial design step and the coordinate transformation between welding robot and laser sensor, which is joint finder, must be identified exactly and the real time tracking algorithm based on these consideration could be developed. In this research, laser displacement sensor in which its structure is laser beam's vertical projection, is developed to recognize the location of weld joint. In practical applications, however, images of weld joints are often degraded because of the surface specularity or spatter. To overcome the problem, the constrained joint finding algorithm is proposed. In the approach of coordinate conversion rule for the visual feedback control among welding torch, robot body and laser sensor is applied by the same reference point method. In the real time seam tracking algorithms we propose constrained sampling method which uses look ahead distance. The RLS(Recursive Least Square) filter is applied to obtain the smooth tracking path from the sensitive edge data. From the experimental results, we could see the possibility that the developed laser sensor with proposed processing algorithm and real time seam tracking method can be used as a welding under the shipbuilding condition.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.37 no.1
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• pp.43-48
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• 2011

Introduction: This study examined the anatomical morphology of the medial surface of the posterior mandible using 3-dimensional cone-beam computed tomography (CT) images to reduce the number of complications related to dental implant placement. Materials and Methods: Fifty patients were enrolled in this study with an average age (${\pm}$standard deviation) of 44.28 (${\pm}13.05$). On the coronal views cone-beam CT of the first molars, the distance between the top of the canal and alveolar crest vertical distance (VD), the distance between the upper-most point of the canal and the point perpendicular to the lingual cortical margin of the mandible lingual distance (LD), the location of the starting point of VD for reducing from the vertical reference line (VD point), and the inclination of the mandibular medial surface (lingual inclination) were measured, and a statistical evaluation was performed using SPSS for Windows version 15.0. Results: The mean VD0 was $16.91{\pm}2.47\;mm$ and VDx decreased with increasing x value. The mean LD was $5.27{\pm}1.36\;mm$. The VD began to decrease at the mean location of $6.12{\pm}0.96\;mm$ from the vertical reference line. The mean lingual inclination was $1.52{\pm}0.72^{\circ}$. Conclusion: These results will assist in the accurate placement of dental implants and the reduction of complications, particularly in the case of preoperative implant planning using only 2-dimensional imaging methods. (ex. panoramic radiography)

• Imaging Science in Dentistry
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• v.49 no.3
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• pp.191-199
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• 2019

Purpose: To compare the diagnostic ability of undergraduate dental students to detect maxillary sinus abnormalities in panoramic radiographs(PR) and cone-beam computed tomography (CBCT). Materials and Methods: This was a retrospective study based on the evaluation of PR and CBCT images. A pilot study was conducted to determine the number of students eligible to participate in the study. The images were evaluated by 2 students, and 280 maxillary sinuses were assessed using the following categories: normal, mucosal thickening, sinus polyp, antral pseudocyst, nonspecific opacification, periostitis, antrolith, and antrolith associated with mucosal thickening. The reference standard was established by the consensus of 2 oral radiologists based on the CBCT images. The kappa test, receiver operating characteristic curves, and 1-way analysis of variance with the Tukey-Kramer post-hoc test were employed. Results: Intraobserver and interobserver reliability showed agreement ranging from substantial (0.809) to almost perfect (0.922). The agreement between the students' evaluations and the reference standard was reasonable (0.258) for PR and substantial(0.692) for CBCT. Comparisons of values of sensitivity, specificity, and accuracy showed that CBCT was significantly better(P<0.05). Conclusion: CBCT was better than PR for the detection of maxillary sinus abnormalities by dental students. However, CBCT should only be requested after a careful analysis of PR by students and more experienced professionals.

• Imaging Science in Dentistry
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• v.51 no.1
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• pp.49-54
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• 2021

Purpose: This study was conducted to establish age- and sex-specific reference standards for pterygoid hamulus(PH) dimensions using cone-beam computed tomography (CBCT). Materials and Methods: CBCT scans of 1,000 patients(493 males and 507 females) were retrospectively assessed in coronal sections for length and width measurements of the PH by 3 investigators. The study data were divided into 3 age groups(group 1: <20 years, group 2: 20-50 years, group 3: >50 years). Length and width were compared using one-way analysis of variance and the t-test for age and sex, respectively. Results: The length of the PH on the right side significantly increased from group 1 (6.11±1.47mm), through group 2 (6.65±1.67 mm) to group 3 (6.99±1.79 mm) and on the left side from group 2 (6.58±1.63) to group 3 (6.98±1.70). The width of the PH significantly decreased from group 1 (1.81±0.39 mm) to group 2 (1.61±0.39 mm) on the right side, and similarly from 1.87±0.36mm to 1.67±0.37mm on the left side. PH length (7.18±1.81mm on the right side and 7.10±1.72 mm on the left side) and width (1.68±0.38 mm on the right side and 1.74±0.36 mm on the left side) were significantly greater in males than in females. Conclusion: The length of the PH increased with age, whereas width first decreased and then increased. Length and width measurements were significantly higher in males than in females. These findings will aid in the diagnosis of untraceable pain in the oropharyngeal region related to altered PH morphology.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.5
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• pp.529-537
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• 2001

According to increase of preference to the large display device, demand of a three-tube projection TV increase in the display market. But luminance per unit area of a 3-tube projection TV is less bright than that of original one -tube TV The color gamut of phosphor used in the projection TV is different to standard gamut of phosphor in NTSC. In this paper, we analyze the relationship between coordinates of RGB phosphor and RGB beam currents according to the color temperature in projection HDTV. We also proposed the range of reference white which maximize the luminance that viewer feel based on both Helmholtz-Kohlrausch effect which is visual property and degradation of image according to the change of beam profile by current-ratio.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.4102-4102
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• 2001

In multivariate analysis, absorbance spectrum is measured over a band of wavelengths. One does not often pay attention to the size of this wavelength band. However, it is desirable that spectrum is measured at only necessary wavelengths as long as the acceptable accuracy of prediction can be met. In this paper, the method of selecting an optimal band of wavelengths based on the loading vector analysis was proposed and applied for determining total protein in human serum using near-infrared transmission spectroscopy and PLSR. Loading vectors in the full spectrum PLSR were used as reference in selecting wavelengths, but only the first loading vector was used since it explains the spectrum best. Absorbance spectra of sera from 97 outpatients were measured at 1530∼1850 nm with an interval of 2 nm. Total protein concentrations of sera were ranged from 5.1 to 7.7 g/㎗. Spectra were measured by Cary 5E spectrophotometer (Varian, Australia). Serum in the 5 mm-pathlength cuvette was put in the sample beam and air in the reference beam. Full spectrum PLSR was applied to determine total protein from sera. Next, the wavelength region of 1672∼1754 nm was selected based on the first loading vector analysis. Standard Error of Cross Validation (SECV) of full spectrum (1530∼l850 nm) PLSR and selected wavelength PLSR (1672∼1754 nm) was respectively 0.28 and 0.27 g/㎗. The prediction accuracy between the two bands was equal. Wavelength selection based on loading vector in PLSR seemed to be simple and robust in comparison to other methods based on correlation plot, regression vector and genetic algorithm. As a reference of wavelength selection for PLSR, the loading vector has the advantage over the correlation plot since the former is based on multivariate model whereas the latter, on univariate model. Wavelength selection by the first loading vector analysis requires shorter computation time than that by genetic algorithm and needs not smoothing.