• Journal of Dental Rehabilitation and Applied Science
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• v.25 no.2
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• pp.95-107
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• 2009

The purpose of this research was to examine the fitness of zirconia cores that were made by different sintering methods; generic electricity furnace and microwave furnace. Firstly, 12 cores for each group were made by using each different sintering process and attached them to a metal die with silicon. The internal and marginal gap of sintered zirconia was measured by using Skyscan 1076 micro-CT, then it was reorganized by CT-An software. To each samples, we extracted B-L image, M-D image of cutting side, and cross-sectional side of tooth long axis and calculated the mean value of marginal, axial, and occlusal gap each side. Results: 1. The mean marginal gap of sintered zirconia was $36.20{\mu}m$ for EVE, $47.67{\mu}m$ for LAV, $52.47{\mu}m$ for DEN, and $54.63{\mu}m$ for CER. 2. For the axial wall, the research showed the largest value of $63.49{\mu}m$ for EVE, but there were no statistical significance. 3. In related to the occlusal internal measurement, DEN showed the smallest value ($77.06{\mu}m$), EVE and CER showed significantly high value. From this study, it is suggested that CAD/CAM zirconia core which was made in the process of microwave sintering has clinically acceptable values in marginal and internal gap.

• Sleep Medicine and Psychophysiology
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• v.20 no.2
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• pp.82-87
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• 2013

Objectives: Previous studies have reported an association between circadian preference and personality. Defense mechanism is unconscious ego process which deals with an individual's anxiety and is closely associated with one's personality. Our aim is to investigate the association between defense mechanism and circadian preference in medical students. Methods: One hundred forty eight medical students (70 males, 78 females), aged 22 to 30, answered the Beck Depression Inventory-II, Morningness-eveningness Questionnaire, and Korean version of Defense Style Questinnaire. Results: Consumption (beta=-0.262, p=0.001) and being a male (beta=0.175, p=0.031) were significant positive predictors of eveningness, while sublimation (beta=0.185, p=0.023) was a significant negative predictor of eveningness. Conclusion: Our study showed a relationship between specific defense mechanisms (i.e., consumption and sublimation) and eveningness in medical students, but it did not address whether the relationship is a causal one.

• Polymer(Korea)
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• v.31 no.5
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• pp.447-453
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• 2007

In this study, we fabricated recrystallized PLGA (rPLGA) particles using the vacuum drying method. In order to investigate an applicability of the rPLGA particles for controlled release system of 5-fluorouracil (5-FU) loaded PLGA wafer, we prepared three different wafers using; 1) untreated PLGA (uPLGA), 2) rPLGA, and 3) uPLGA and rPLGA (4 : 1, 1 : 1 or 1 : 4). The rPLGA particles were characterized using NMR, IR and GPC to compare with uPLGA particles. The surface and cross section morphology of the prepared wafers were observed by the scanning electron microscope. The release profile of the 5-FU loaded wafer was measured by HPLC. The 5-FU/rPLGA wafer released the incorporated 5-FU in a sustained manner with low initial burst compared to 5-FU/uPLGA. These results showed that the ratio of pure PLGA/recrystallized PLGA can affect the release behaviors.

• Korean Journal of Optics and Photonics
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• v.30 no.6
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• pp.243-248
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• 2019

The respiratory tract is an essential part of the respiratory system involved in the process of respiration. However, if stenosis occurs, it interferes with breathing and can even lead to death. Asthma is a typical example of a reversible cause of airway narrowing, and the number of patients suffering from acute exacerbation is steadily increasing. Therefore, it is important to detect airway narrowing early and prevent the patient's condition from worsening. Optical coherence tomography (OCT), which has high resolution, is suitable for observing the microstructure of tissues. In this study we developed an endoscopic OCT system. We combined a 1300-nm OCT system with a servo motor, which can rotate at a high speed. A catheter was pulled back using a linear stage while imaging with 360° rotation by the motor. The motor was selected considering various requirements, such as torque, rotational speed, and gear ratio of pulleys. An ex vivo rabbit tracheal model was used as a sample, and the sample and catheter were immobilized by acrylic structures. The OCT images provided information about the structures of the mucosa and submucosa. The difference between normal and stenosed parts in the trachea was confirmed by OCT. Furthermore, through a three-dimensional (3-D) reconstruction process, it was possible to identify and diagnose the stenosis in the 3-D image of the airway, as well as the cross-sectional image. This study would be useful not only for diagnosing airway stenosis, but also for realizing 3-D imaging.

• Journal of Korean Society of Forest Science
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• v.99 no.3
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• pp.397-403
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• 2010

This study was conducted to investigate the changes in soil temperature, soil moisture content, light availability (photosynthetically active radiation, PAR) and diameter growth in 46-year-old Korean pine (Pinus koraiensis Siebold et Zuccarini) plantation located in Gwangneung experimental forest after 4 years from thinning. Three different thinning intensities [control, 45%(T45), and 60%(T60) basal area reduction] were applied in 2004. Mean soil temperature and soil water content were $8.9^{\circ}C$ and 14.3% for control, $10^{\circ}C$ and 16.1% for T45 and $10.2^{\circ}C$ and 16.1% for T60, respectively. Mean soil temperature and moisture content were significantly different among the treatment plots (p<0.05). Mean PAR in control, T45 and T60 was 44, 143 and178 ${\mu}mol/m^2$/sec, respectively and the differences were also statistically significant among the treatment plots (p<0.05). Mean annual diameter growth in control, T45 and T60 was 0.4, 1.5 and 1.2 mm, respectively. Diameter growth of Pinus koraiensis was steadily increased after thinning in comparison to control. Consequently, the results suggested that soil temperature, soil moisture content and light availability were likely to last beyond the 4 years after thinning in this Korean pine plantation.

• Journal of Korean Society of Forest Science
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• v.99 no.3
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• pp.337-343
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• 2010

The purpose of this study was to understand water stress development in pine seedlings inoculated with Bursaphelenchus xylophilus. Leaf water potentials of four years old Pinus densiflora seedlings inoculated with the nematode were measured with a plant moisture system at predawn and midday. The midday leaf water potentials on the 35th day after the inoculation were -1.04 MPa in the infected seedlings, while -0.94 MPa in the non-infected seedlings. The predawn water potentials on the 56th day were -0.71 MPa in the infected, while -0.26 MPa in the non-infected. At this time the leaves of the infected seedlings became yellow and resin did not exude on the cut basal stem. Density of the nematode was maximum on the 28th day, but dropped sharply on the 68th day. The phloem and pith tissues became brown and the resin exudation reduced in the infected seedlings. In conclusion, pinewood nematode inoculation developed water stress in pine seedlings in a month.

• Journal of Adhesion and Interface
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• v.9 no.3
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• pp.7-13
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• 2008

The particulate type silicon carbide (SiC) and fiber type carbon fiber (CF) filler, of similar thermal conductivities, were mixed with polyetheretherketone (PEEK) to investigate the filler effects on the thermal diffusivity. The SiC and CF fillers had a good and uniform dispersion in PEEK matrix. Thermal diffusivities of PEEK composites were measured from ambient temperature up to $200^{\circ}C$ by laser flash method. The diffusivities were decreased as increasing temperature due to the phonon scattering between PEEK-filler and filler-filler interfaces. Thermal diffusivity of PEEK composites was increased with increasing filler content and the thermal conductivities of two-phase system were compared to the experimental results and it gave ideas on the filler dispersion, orientation, aspect ratio, and filler-filler interactions. Nielson equation gave a good prediction to the experimental results of PEEK/SiC. The easy network formation by CF was found to be substantially more effective than SiC and it gave a higher thermal diffusivities of PEEK/CF than PEEK/SiC.

• Journal of the Korea Computer Graphics Society
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• v.22 no.5
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• pp.17-26
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• 2016

This paper presents an adaptive slicing method based on merging vertical layer polylines. Firstly, we slice the input 3D polygon model uniformly with the minimum printable thickness, which results in bounding polylines of the cross section at each layer. Next, we group a set of layer polylines according to vertical connectivity. We then remove polylines in overdense area of each group. The number of layers to merge is determined by the layer thickness computed using the cusp height of the layer. A set of layer polylines are merged into a single polyline by removing the polylines within the layer thickness. The proposed method maintains the shape features as well as reduces the printing time. For evaluation, we sliced ten 3D polygon models using our method and a global adaptive slicing method and measured the total length of polylines which determines the printing time. The result showed that the total length from our method was shorter than the other method for all ten models, which meant that our method achieved less printing time.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.321-330
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• 2011

Recently, the effects of high temperature and fiber content on the residual mechnical properties of high-strength concrete were experimentally investigated. In this paper, residual mechanical properties of concrete with water to cement (w/c) ratios of 0.55, 0.42 and 0.35 exposed to high temperature are compared with those obtained in fiber reinforced concrete with similar characteristics ranging from 0.05% to 0.20% polypropylene (PP) fiber volume percentage. Also, factors including pre-load levels of 20% and 40% of the maximum load at room temperature are considered. Outbreak time, thermal strain, length change, and mass loss were tested to determine compressive strength, modulus of elasticity, and energy absorption capacity. From the results, in order to prevent the explosive spalling of 50 MPa grade concretes exposed to high temperature, more than 0.05 vol. % of PP fibers is needed. Also, the cross-sectional area of PP fiber can influence the residual mechanical properties and spalling tendency of fiber reinforced concrete exposed to high temperature. Especially, the external loading increases not only the residual mechanical properties of concrete but also the risk of spalling and brittle failure tendency.

• The korean journal of orthodontics
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• v.39 no.3
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• pp.136-145
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• 2009

Objective: CBCT has become popular for orthodontic diagnosis and treatment planning in recent times. The 3D pharyngeal airway space needs to be analysed using a 3D diagnostic tool. The aim of this study was to analyse the pharyngeal airway of different craniofacial morphology using CBCT. Methods: The sample compromised 102 subjects divided into 3 groups (Class I, II, III) and 6 subgroups according to normal or vertical craniofacial patterns. All samples had CBCT (VCT, Vatech, Seoul, Korea) taken for orthodontic treatment. The pharyngeal airway was assessed according to the reference planes: aa plane (the most anterior point on the anterior arch of atlas), $CV_2$ plane, and $CV_3$ plane (most infero-anterior point on the body of the second & third cervical vertebra). The intergroup comparison was performed with one-way ANOVA and duncan test as a second step. Results: The results showed the pharyngeal airway and anteroposterior width of group 2 (Class II) in aa plane, $CV_2$ plane, $CV_3$ plane were significant narrower than in group 3 (Class III). There was no significant difference between vertical and normal craniofacial patterns except for the anteroposterior pharyngeal width of Group 1 (Class I) in aa plane. Conclusions: Subjects with Class II patterns have a significantly narrower pharyngeal airway than those with Class III. However there was no difference in pharyngeal airway between vertical and normal craniofacial morphology.