• Smart Structures and Systems
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• v.22 no.6
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• pp.643-662
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• 2018

One of the methods for investigation of mechanical behavior of materials is numerical simulation. For simulation, its need to model behavior is close to real condition. PFC is one of the rock mechanics software that needs calibration for models simulation. The calibration was performed based on simulation of unconfined compression test and Brazilian test. Indeed the micro parameter of models change so that the UCS and Brazilian test results in numerical simulation be close to experimental one. In this paper, the effect of four micro parameters has been investigated on the uniaxial compression test and Brazilian test. These micro parameters are friction angle, Accumulation factor, expansion coefficient and disc distance. The results show that these micro parameters affect the failure pattern in UCS and Brazilian test. Also compressive strength and tensile strength are controlled by failure pattern.

• Journal of the Semiconductor & Display Technology
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• v.16 no.3
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• pp.25-30
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• 2017

Arago's disk system consists of a speed controller of the DC motor (inner loop controller) and a position controller of the magnetic bar angle (main controller), which are implemented by the design of the PI and PID controller, respectively. First, we analyzed the nonlinear characteristics of the Arago disk system and found the operating point range of three locations as a result. In this paper, a gain scheduler method was applied to guarantee a constant control performance in the range of $0{\sim}130^{\circ}C$, and a structure to change the controller according to the control reference value based on the previously obtained operating points was experimentally implemented. The Distributed Control Systems (DCS) configuration using the Controller Area Network (CAN) was used to verify the proposed method by improving the operational efficiency of the entire experimental system. So, simplicity of the circuit and easy diagnosis were achieved through a single CAN bus communication.

• Journal of Korean Neurosurgical Society
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• v.30 no.2
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• pp.144-149
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• 2001

Objective : Spinal nerve root compression occurs commonly in conditions, such as herniated nucleus pulposus, spinal stenosis, intervertebral foraminal stenosis, and trauma. However, the pathophysiolosy of the symptoms and signs related to spinal nerve root compression is poorly understood. The purpose of the present study was to assess and compare the changes of various pressures of intervertebral foraminal pressure before and after decompression. Method : After laminetomy without foraminotomy was performed, pressure sensor tip of Camino parenchymal type was located at the middle-central portion of the intervertebral foramen and anterior portion of nerve root for the foraminal pressure before decompression of the intervertebral foramen. After laminectomy with foraminotomy, the same method was used for the foraminal pressure after decompression. The authors studied 40 consecutive patients (57 disc spaces) with severe constant root pain to the lower leg, pain unrelived by bed rest, and minimal tension signs, diagnosed by MRI. Results : In patients with intervertebral foraminal stenosis, the intraforaminal pressure was decreased from $86{\pm}2.23mmHg$ to $17.1{\pm}1.51mmHg$ and in patients without stenosis, from $55.9{\pm}1.08mmHg$ to $11.9{\pm}1.25mmHg$. All patients below 20mmHg after decompression showed good outcome, but 4 cases who showed poor outcome had foraminal stenosis, posterolateral type of the herniated disc, and above 30mmHg of foraminal pressure after decompression. Conclusion : These findings suggest that if the foraminal pressure falls below 20mmHg after decompression, good outcome can be anticipated. Central type of the herniated disc shows better outcome compared to the posterolateral type.

• Journal of Veterinary Science
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• v.22 no.5
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• pp.65.1-65.12
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• 2021

Background: To assess the normal retina of the pigeon eye using spectral domain optical coherence tomography (SD-OCT) and establish a normative reference. Methods: Twelve eyes of six ophthalmologically normal pigeons (Columba livia) were included. SD-OCT images were taken with dilated pupils under sedation. Four meridians, including the fovea, optic disc, red field, and yellow field, were obtained in each eye. The layers, including full thickness (FT), ganglion cell complex (GCC), thickness from the retinal pigmented epithelium to the outer nuclear layer (RPE-ONL), and from the retinal pigmented epithelium to the inner nuclear layer (RPE-INL), were manually measured. Results: The average FT values were significantly different among the four meridians (p < 0.05), with the optic disc meridian being the thickest (294.0 ± 13.9 ㎛). The average GCC was thickest in the optic disc (105.3 ± 27.1 ㎛) and thinnest in the fovea meridian (42.8 ± 15.3 ㎛). The average RPE-INL of the fovea meridian (165.5 ± 18.3 ㎛) was significantly thicker than that of the other meridians (p < 0.05). The average RPE-ONL of the fovea, optic disc, yellow field, and red field were 91.2 ± 5.2 ㎛, 87.7 ± 5.3 ㎛, 87.6 ± 6.5 ㎛, and 91.4 ± 3.9 ㎛, respectively. RPE-INL and RPE-ONL thickness of the red field meridian did not change significantly with measurement location (p > 0.05). Conclusions: Measured data could be used as normative references for diagnosing pigeon retinopathies and further research on avian fundus structure.

• The Journal of Advanced Prosthodontics
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• v.6 no.4
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• pp.309-316
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• 2014

PURPOSE. The color of the ceramic restorations is affected by various factors such as brand, thickness of the layered the ceramic, condensation techniques, smoothness of surface, number of firings, firing temperature and thickness of dentin. The aim of this study was to evaluate the color change and surface roughness in dental porcelain with different thicknesses during repeated firings. MATERIALS AND METHODS. Disc-shaped (N=21) metal-ceramic samples (IPS Classic; Ivoclar Vivadent; Shaar, Liechtenstein) with different thickness were exposed to repeated firings. Color measurement of the samples was made using a colorimeter and profilometer was used to determine surface roughness. ANOVA and Tukey tests with repeated measurements were used for statistical analysis. RESULTS. The total thickness of the ceramics which is less than 2 mm significantly have detrimental effect on the surface properties and color of porcelains during firings (P<.05). CONCLUSION. Repeated firings have effects on the color change and surface roughness of the dental ceramics and should be avoided.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.1
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• pp.29-35
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• 2012

The treatments for spinal canal stenosis are radicular cyst removal, spine fusion, and implantation of an artificial intervertebral disc. Artificial intervertebral discs have been most widely used since the mid-2000s. The study of artificial intervertebral discs has been focused on the analysis of the axial rotation, lateral bending, the degrees of freedom of the disc, and flexion-extension of the vertebral body. The issue of fatigue failure years after the surgery has arisen as a new problem. Hence, study of artificial intervertebral discs must be focused on the fatigue failure properties and increased durability of the sliding core. A finite element model based on an in the artificial intervertebral disc (SB Charit$\acute{e}$ III) was produced, and the influence of the radius of curvature and the change in the coefficient of friction of the sliding core on the von-Mises stress and contact pressure was evaluated. Based on the results, new artificial intervertebral disc models (Models-I, -II, and -III) were proposed, and the fatigue failure behavior of the sliding core after a certain period of time was compared with the results for SB Charit$\acute{e}$ III.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.203-211
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• 2021

Octacalcium phosphate(OCP, Ca₈H₂(PO₄)₆·5H₂O) is one of biodegradable calcium phosphate materials with osteoconductivity and biocompatibility. It has the advantage of rapid bone formation and resorption due to the property of stimulating stromal cells to differentiate into osteoblasts. However, if OCP is inserted in body, it is immediately decomposed without maintaining of its shape as scaffolds due to their weak cohesive force between powder. On the other hand, hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), which has a crystal structure similar to that of OCP, remains in the body without decomposition until the bone defect is restored. In this study, the degradation behavior of OCP/HA disc with different amount of HA in SBF (simulated body fluid) solution was characterized in terms of the weight loss, pH variation and microstructure change with immersion duration in SBF solution. As a result, the OCP/HA disc was not quickly decomposed and maintained its own shape for 2 weeks regardless of HA content. In particular, the surface of 40HA specimen was uniformly dissolved and then CDHA (calcium deficient hydroxyapatite) phase were formed onto the surface of disc after 7 days in SBF solution. It would be suggested that the 40HA specimen would be suitable candidate material as the scaffolds for the restoration of bone defect.

• Journal of dental hygiene science
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• v.2 no.1
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• pp.31-38
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• 2002

This study was to investigate the antibacterial effect of 63 species herbal medicine extracts on S. mutans growth by paper disc method and then examined the effects of S. mutans growth by some selected herbal medicines. Antibacterial effect of 63 species medicinal herb extracts on S. mutans was superior to Lycopi herba, Scutellariae radix in regular order and antibacterial activity(20 mg/ml concentration) through paper disc method were measured 6.3 mm and 3.5 mm, respectively. The growth of S. mutans in control medium was the highest at 8hrs, while that of medicinal herbs extract added-medium(2 mg/ml) was at 16 hrs. The pH values of the control media and media supplemented with Lycopi herba and Scutellariae radix extract were 5.08, 5.80, and 5.74 at 8 hrs, respectively. In the change of total carbohydrate of the control media and supplemented with Lycopi herba and Scutellariae radix extract were 0.81 mg/ml, 1.70 mg/ml and 1.84 mg/ml at 8 hrs, respectively. In the change of proteins of the control media and supplemented with Lycopi herba and Scutellariae radix extract were 8.39 mg/ml, 9.52 mg/ml and 9.28 mg/ml at 8 hrs, respectively. The polysaccharide contents of the control media and supplemented with Lycopi herba and Scutellariae radix extract were 300 mg/100 ml, 200 mg/100 ml and 220 mg/100 ml at 8hrs, respectively.

• Journal of Korean Medicine Rehabilitation
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• v.20 no.4
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• pp.159-169
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• 2010

Objectives : This study was designed to evaluate the correlation of the cross-sectional areas(CSA) of paraspinalis(iliocostalis lumborum, multifidus, longissimus thoracis parts lumborum) and psoas muscle and sex, age, change of the VAS(visual analogue scale) and past history of chronic low back pain in patients suffering from HIVD(herniation of intervertebral disc). Methods : Medical records of 140 subjects with HIVD were retrospectively reviewed. The MRI(magnetic resonance imaging) findings on the patients were scanned and analyzed by PiView program to find the paraspinal and psoas muscle CSA and were evaluated by the correlation of sex, age, change of the VAS, and past history of chronic low back pain. Results : There was significant difference between groups in male and female, young-adults age and middle age, middle age and old age, young-adults age and old age. But the correlation of the paraspinal and psoas muscle CSA and past history of chronic low back pain were partially significant. On the other hand, the correlation of the paraspinal and psoas muscle CSA and change of the VAS were not significant. Conclusions : These results suggest that the cross-sectional areas(CSA) of paraspinalis and psoas muscle have relevance to sex and age.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.139-142
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• 2004

Nickel base superalloys are widely used for high temperature applications due to heat resisting capability and corrosion resistance at high temperatures. Superalloys with many strengthening alloying elements are frequently used in powder form to alleviate harmful effects of alloy segregation. HIP (hot isostatic pressing) and DB (diffusion bonding) as a form of solid-state bonding process is used to make turbine components, such as integrated turbine rotors. HIP/DB process requires many technical overcomes related to dimensional changes as well as microstructural control. In this research, HIP/DB process for nickel base superalloys, Udimet 720 and MM 247, were investigated with a view to control the dimensional change during the consolidation process. Simple disc-shaped cans were used to select the conceptual die design for the control of the dimensional change especially in radial direction. The change in the shape of consolidated shape was investigated using commercial FE code with constitutive equations fur low temperature plasticity deformation.