• Journal of Dental Rehabilitation and Applied Science
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• v.30 no.2
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• pp.131-137
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• 2014

Purpose: This study examined the efficiency and wear of periodontal instrument sharpening using aluminum oxide stones with different levels of roughness. Materials and Methods: Thirty new No. 9-10 Gracey curets were used in this study. All curets had become dull after scaling and root planing. After similar blunting, the instruments were divided randomly into three groups (240, 600, 800 grit) containing 10 curets each. The stones were applied correctly to the lateral surface of each curet to maintain the $70-80^{\circ}$ angle. After resharpening, sharpness of the curets was examined by an optical microscope. After 20, 40, 60, and 80 strokes, the wear was measured at 1 mm and 2 mm from the tip of the cutting edge using a digital caliper. The data was analyzed statistically using analysis of variance (ANOVA) with repeated measures, 2-way ANOVA, and a Fisher's exact test. Results: The degree of sharpness increased significantly (P < 0.001) as the number of sharpening strokes grew for all stones. A comparison of the degree of sharpness on the same number of strokes showed that the 240 grit group significantly excelled the other groups on 5 and 10 strokes, respectively (P < 0.001). The mean wear showed no statistically significant difference among the groups (P > 0.05). Conclusion: The efficiency of Gracey curet resharpening was enhanced with more coarse stones, though we should consider the wear of the instrument during resharpening.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.60-68
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• 1991

The updated Lagrangian Finite Element Method is introduced to analyse rigid body-fluid impact problem which is characterized by incompressible Navier-Stokes equations and impact-contact conditions between free surface and rigid body. For the convenience of numerical computation, velocity fields are splinted into vicous and pressure parts, and then the governing equations and boundary conditions are decomposed in accordance with the decomposition. However, Viscous stresses acting an the solid boundaries are neglected on the assumption that very small velocity gradients may occur during extremely small time interval of the impact. Four coded quadrilateral elements are used to discretize the space domain and the fully explicit time-marching algorithm is employed with a reasonably small time step. At the beginning of each time step, contact velocity of the rigid body is computed from the momentum balance between the body and the fluid. The velocity field is then computed to satisfy the discretized equations of motions and incompressibility and contact constraints as well as an exact free surface boundary condition. At the end of each time step, the fluid domain is updated from the velocity field. In the present time stepping numerical analysis, behaviour of the free surface near the body can be observed without any difficulty which is very important in the water impact problem. The applicability of the algorithm is illustrated by a wedge type falling body problem. The numerical solutions for time-varying pressure distributions and impact loadings acting ion the surface are obtained.

• Journal of the Korean Wood Science and Technology
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• v.41 no.4
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• pp.318-326
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• 2013

The effect of finger joint location and distance from joint to joint one another on 3 point mid-concentration bending strength properties was investigated in this experiment. Resorcinol-phenol formaldehyde (RPF) and aqueous vinyl urethane (AVU) was used to domestic Pinus densiflora Sieb. et Zucc and imported Picea sitchensis Carr. that have been cut to different width of 0.15 mm between finger tip and root width and the distance from loading point to finger joint was 0, 30, 40, 50, 60 mm. The effect was not found on the location and distance of finger joint for bending modulus of elasticity, while the efficiency of bending strength property increased proportionally as the location of finger joint from the load point and the distance between finger joint increased. No influence was shown by finger joint location and distance beyond 3 times of specimen thickness, since similar values were shown between the solid wood and no destruction occurred materials.

• Journal of Periodontal and Implant Science
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• v.35 no.3
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• pp.563-575
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• 2005

The aim of present study is to evaluate the influence of adjacent tooth to the microbiology of clinically healthy implant. Control group included patients who had clinically healthy implant and tooth with healthy $periodontium(PD{\leq}3mm)$, test group was composed of patients who had clinically healthy implant and tooth with periodontal pocket(PD>3mm). The criteria of clinically health implant are no pain or discomfort, the restorative suprastructure provide satisfactory fit and function, and the tissue around the fixtures were firm and probing with standard periodontal probe with a rounded tip 0.5mm in diameter resulted in penetration of no more than 5mm when using a force of 0.5N at any location. 38 patients, partially edentulous subjects with endosseous root-form implants were selected. All subjects were medically healthy and had not taken systemic antibiotics and professional plaque control 3 months before sampling. Number of control group is 25(mean age $52{\pm}13$, 26 teeth, 34 implants) and test group is 13(mean age $60{\pm}13$, 13 teeth, 17 implants). All teeth and implants of each patient were examined probing depth(PD), bleeding on probing(BOP), and plaque index(PI), and samples of subgingival plaque were obtained at each site with sterile curet or fine paper points, then the plaque transferred to PBS. Obtained samples were examined for the presence of P. gingivalis, T. forsythensis, and T. denticola by the polymerase chain reaction(PCR). The relationship among clinical parameters and the colonizations by the 3 bacterial species from natural teeth and implants region were analyzed by student t-test. The results of this study were as follows: 1. PD was different in teeth between 2 groups(p<0.05), but the other parameters were not. 2. Statistically significant difference was not found in clinical parameters of implants between 2 groups. 3. All bacterial prevalences of teeth were higher in test group than in control group, and prevalence of T. forsythensis had statistically significant difference between 2 groups(p<0.05). 4. Prevalences of P. gingivalis and T. forsythensis are higher in test group than control group, and that of T. denticola is higher in control group than in test group. But there were no statistically significant differences between 2 groups. In conclusion, there is no statistically significant difference in prevalence of implant microbiology between 2 groups. But if the number of samples increased, it will be possible to find out statistical significance in prevalence of P. gingivalis. It seems that pocket of adjacent tooth influences prevalence of P. gingivalis. These results mean that improvement of the periodontal condition before implantation is very important.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.31.1-31.1
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• 2009

Carbon nanotubes (CNTs) are attractive material because of their superior electrical, mechanical, and chemical properties. Furthermore, their geometric features such as a large aspect ratio and a small radius of curvature at tip make them ideal for low-voltage field emission devices including backlight units of liquid crystal display, lighting lamps, X-ray source, microwave amplifiers, electron microscopes, etc. In field emission devices for display applications, the phosphor anode is positioned against the CNT emitters. In most case, light generated from the phosphor by electron bombardment passes through the anode front plate to reach observers. However, light is produced in a narrow depth of the surface of the phosphor layer because phosphor particles are big as much as several micrometers, which means that it is necessary to transmit through the phosphor layer. Hence, a drop of light intensity is unavoidable during this process. In this study, we fabricated a transparent cathode back plate by depositing an ultra-thin film of single walled CNTs (SWCNTs) on an indium tin oxide (ITO)-coated glass substrate. Two types of phosphor anode plates were employed to our transparent cathode back plate: One is an ITO glass substrate with a phosphor layer and the other is a Cr-coated glass substrate with phosphor layer. For the former case, light was radiated from both the front and the back sides, where luminance on the back was ~30% higher than that on the front in our experiments. For the other case, however, light was emitted only from the cathode back side as the Cr layer on the anode glass rolled as a reflecting mirror, improving the light luminance as much as ~60% compared with that on the front of one. This study seems to be discussed about the morphologies and field emission characteristics of CNT emitters according to the experimental parameters in fabricating the lamps emitting light on the both sides or only on the cathode back side. The experimental procedures are as follows. First, a CNT aqueous solution was prepared by ultrasonically dispersing purified SWCNTs in deionized water with sodium dodecyl sulfate (SDS). A milliliter or even several tens of micro-liters of CNT solution was deposited onto a porous alumina membrane through vacuum filtration. Thereafter, the alumina membrane was solvated with the 3 M NaOH solution and the floating CNT film was easily transferred to an ITO glass substrate. It is required for CNT film to make standing CNTs up to serve as electron emitter through an adhesive roller activation.

• The Korean Journal of Pain
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• v.20 no.2
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• pp.116-122
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• 2007

Background: Lumbar zygapophysial joints are a common source of chronic lower back pain and radiofrequency thermocoagulation (RF) of the medial branches (MB) has been shown to be effective at providing substantial pain relief for chronic low back pain. Therefore, we carried out this study to determine the short term outcomes and prognostic factors of RF on the MB of patients with lumbar facet syndrome. Methods: We performed RF in fourteen patients who showed greater than 80% pain relief up to three times after a diagnostic MB block was conducted using 0.3 ml of 0.5% bupivacaine. Using 10 cm curved electrodes with 10-mm active tip, a 60 second, $80^{\circ}C$ lesion was made after electrical stimulation at 50 Hz for sensory and 2 Hz for motor nerve testing. The degree of pain relief was then assessed after 2 weeks, and again after 3 months using a visual analog scale (VAS) and a four point Likert scale. The outcome was regarded as 'success' if at least a 50% reduction in the VAS was observed. Possible prognostic factors between the two groups were also evaluated Results: The success rate was 71.4% (10/14) after three months of follow-up. However, there were transient complications, such as neuritis like syndrome, in 4 patients. In addition, short symptom duration and low minimal voltage (< 0.4 V) for sensory stimulation were shown to be the relevant prognostic factors for a successful outcome. Conclusions: RF may be an alternative to repeated MB block or intraarticular injection for palliation of lumbar facet syndrome. For better outcomes, early diagnosis and strict patient selection should be coupled with efforts to avoid anatomically incorrect RF.

• Journal of radiological science and technology
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• v.45 no.4
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• pp.299-304
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• 2022

This study uses the 'S-align' function to present a reference value of the X-ray tube angle for the realization of an image similar to that of the chest PA image during chest AP radiography. This study targeted dummy phantom and used a 17"×17" DR image receptor. The irradiation conditions were 110 kVp, 160 mA, 50 ms, and the distance between the central X-ray and the image receptor was set to 180 cm and 110 cm, respectively. The end of the catheter was placed at the 11th thoracic height to indicate the nasogastric tube. In the case of lung apex length measurement, the mean value of measurement was 30.53±0.47 in PA. T 0°, TCA 5~25°, TCE 5~15° were 21.07±0.29, 27.60±0.21, 34.13±0.44, 39.86±0.31, 45.96±0.61 mm, 54.13±0.37 mm, 16.16±0.46 mm, 9.81±0.35 mm, 2.75±0.30 mm, respectively. For the depth of the catheter end, the average value measured at PA was 6.70±0.31 mm. T 0°, TCA 5~25°, TCE 5~15° were 15.72±0.38 mm, 24.10±0.50 mm, 29.24±0.86 mm, 34.35±0.35 mm, 41.06±1.08 mm, 48.07±0.38 mm, 12.85±0.25 mm, 7.92±0.36 mm, 3.01±0.39 mm, respectively. The length of the lung apex was similar to that of chest PA when the angle of incidence was adjusted from 5° to 10° in the leg direction, and the depth of the catheter tip was most similar when the X-ray tube angle was incident at 10° in the head direction. Therefore, To change the X-ray tube angle according to the purpose of the examination during the chest AP radiography using 'S-align' function is considered necessary.

• Journal of Hydrogen and New Energy
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• v.33 no.1
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• pp.95-104
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• 2022

Micro hydropower is a readily available renewable energy source that can be harvested utilizing hydrokinetic turbines from shallow water canals, irrigation and industrial channel flows, and run-off river stream flows. These sources generally have low head (<1 m) and low velocity which makes it difficult to harvest energy using conventional turbines. A horizontal-axis screw turbine was designed and numerically tested to extract power from such low-head water sources. The 3-bladed screw-type turbine is placed horizontally perpendicular to the incoming flow, partially submerged in a narrow water channel at no-head condition. The turbine hydraulic performances were studied using Computational Fluid Dynamics models. Turbine design parameters such as the shroud diameter, the hub-to-shroud ratios, and the submerged depths were obtained through a steady-state parametric study. The resulting turbine configuration was then tested by solving the unsteady multiphase free-surface equations mimicking an actual open channel flow scenario. The turbine performance in the shallow channel were studied for various Tip Speed Ratios (TSR). The highest power coefficient was obtained at a TSR of 0.3. The turbine was then scaled-up to test its performance on a real site condition at a head of 0.3 m. The highest power coefficient obtained was 0.18. Several losses were observed in the 3-bladed turbine design and to minimize losses, the number of blades were increased to five. The power coefficient improved by 236% for a 5-bladed screw turbine. The fluid losses were minimized by increasing the blade surface area submerged in water. The turbine performance was increased by 74.4% after dipping the turbine to a bottom wall clearance of 30 cm from 60 cm. The final output of the novel horizontal-axis screw turbine showed a 2.83 kW power output at a power coefficient of 0.63. The turbine is expected to produce 18,744 kWh/year of electricity. The design feasibility test of the turbine showed promising results to harvest energy from small hydropower sources.

• Journal of Korean Neurosurgical Society
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• v.67 no.1
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• pp.60-72
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• 2024

Objective : Recently, robotic-assisted spine surgery (RASS) has been considered a minimally invasive and relatively accurate method. In total, 495 robotic-assisted pedicle screw fixation (RAPSF) procedures were attempted on 100 patients during a 14-month period. The current study aimed to analyze the accuracy, potential risk factors, and learning curve of RAPSF. Methods : This retrospective study evaluated the position of RAPSF using the Gertzbein and Robbins scale (GRS). The accuracy was analyzed using the ratio of the clinically acceptable group (GRS grades A and B), the dissatisfying group (GRS grades C, D, and E), and the Surgical Evaluation Assistant program. The RAPSF was divided into the no-breached group (GRS grade A) and breached group (GRS grades B, C, D, and E), and the potential risk factors of RAPSF were evaluated. The learning curve was analyzed by changes in robot-used time per screw and the occurrence tendency of breached and failed screws according to case accumulation. Results : The clinically acceptable group in RAPSF was 98.12%. In the analysis using the Surgical Evaluation Assistant program, the tip offset was 2.37±1.89 mm, the tail offset was 3.09±1.90 mm, and the angular offset was 3.72°±2.72°. In the analysis of potential risk factors, the difference in screw fixation level (p=0.009) and segmental distance between the tracker and the instrumented level (p=0.001) between the no-breached and breached group were statistically significant, but not for the other factors. The mean difference between the no-breach and breach groups was statistically significant in terms of pedicle width (p<0.001) and tail offset (p=0.042). In the learning curve analysis, the occurrence of breached and failed screws and the robot-used time per screw screws showed a significant decreasing trend. Conclusion : In the current study, RAPSF was highly accurate and the specific potential risk factors were not identified. However, pedicle width was presumed to be related to breached screw. Meanwhile, the robot-used time per screw and the incidence of breached and failed screws decreased with the learning curve.

• Journal of Radiation Protection and Research
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• v.23 no.4
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• pp.259-266
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• 1998

There are three different types of gynecological applicator sets available in microSelectron-high dose-rate(HDR) System by Nucletron; standard applicator set(SAS), standard shielded applicator set(SSAS), and Fletcher-Williamson applicator set(FWAS). Shielding effect of a SAS without shielding material was compared with that of a SSAS with shielding material made of stainless steel(density ${\varrho}=8,000kg/m^3$) at the top and bottom of each ovoid, and of a FWAS with shielding material made of tungsten alloy(density ${\varrho}=14,000kg/m^3$ at the top and bottom of each ovoid. The shielding effects to the rectum and bladder of these two shielded applicator sets were to be measured at reference points with an ion chamber and specially designed supporting system for applicator ovoids inside of the computerized 3-dimensional water phantom. To determine the middle point of two ovoids the measurement was performed with the reference tip of ion chamber placed at the same level and at the middle point from the two ovoids, while scanning the dose with the ion chamber on each side of ovoids. The doses to the reference points of rectum were measured at 20(Rl), 25(R2), 30(R3), 40(R4), 50(R5), and 60(R6) mm located posteriorly on the vertical line drawn from M5(the middle dwell position of ovoid), and the doses to the bladder were measured at 20(Bl), 30(B2), 40(B3), 50(B4), and 60(B5) mm located anteriorly on the vertical line drawn from M5. The same technique was employed to measure the doses on each reference point of both SSAS and FWAS. The differences of measured rectal doses at 25 mm(R2) and 30 mm(R3) between SAS and SSAS were 8.0 % and 6.0 %: 25.0% and 23.0 % between SAS and FWAS. The differences of measured bladder doses at 20 mm(Bl) and 30 mm(B2) between SAS and SSAS were 8.0 % and 3.0 %: 23.0 % and 17.0 % between SAS and FWAS. The maximum shielding effects to the rectum and bladder of SSAS were 8.0 % and 8.0 %, whereas those of FWAS were 26.0 % and 23.0 %, respectively. These results led to the conclusion that FWAS has much better shielding effect than SSAS does, and when SSAS and FWAS were used for gynecological intracavitary brachytherapy in microSelectron-HDR system, the dose to the rectum and bladder was significantly reduced to optimize the treatment outcome and to lower the complication rates in the rectum and bladder.