• Journal of Welding and Joining
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• v.22 no.1
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• pp.58-64
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• 2004

The control of the weld bead shape is important in laser welding of the small parts. The effects of laser welding parameters on the weld bead shape in the pulsed Nd:YAG laser welding of STS 304L material were investigated. Shielding gas type, flow rate, pumping voltage, pulse frequency, pulse width, focal position and overlap distance were selected as laser welding parameters. Experiments were designed and conducted using the Taguchi method which was a statistical experimental method. The weld bead width, penetration, area and aspect ratio were measured and analysed as the weld bead shape properties and the welding parameters were optimized to maximize the weld aspect ratio. Weld aspect ratio were greatly affected by the pulse width, pumping voltage and pulse frequency, and somewhat by the overlap distance, and little by the shielding gas type, flow rate and focal position. A confirmation experiment were conducted using the optimized welding parameters.

• Journal of the Korean Society of Visualization
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• v.5 no.1
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• pp.12-15
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• 2007

Macromolecule diffusion in cells and tissues is important for cell signaling, metabolism and locomotion. Biophysical methods, including non-invasive or minimally invasive in-vivo photobleaching techniques and single quantum-dot tracking, have been used to measure the rates of macromolecule diffusion in living cells and tissues, including central nervous system and tumors. Mathematical modeling and statistical analysis of experimental data revealed various modes of diffusion, which are strongly coupled with spatiotemporal changes in nanoscale structures and material properties.

• Structural Engineering and Mechanics
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• v.41 no.3
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• pp.421-440
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• 2012

In this analytical study numerous prior experimental studies on reinforced concrete beam-to-column connections subjected to cyclic loading are investigated and a database of geometric properties, material strengths, configuration details and test results of subassemblies is established. Considering previous experimental research and employing statistical correlation method, parameters affecting joint shear capacity are determined. Afterwards, an equation to predict the joint shear strength is formed based on the most influential parameters. The developed equation includes parameters that take into account the effect of eccentricity, column axial load, wide beams and transverse beams on the seismic behavior of the beam-to-column connections, besides the key parameters such as concrete compressive strength, reinforcement yield strength, effective joint width and joint transverse reinforcement ratio.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.247-256
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• 1998

To evalutate the change in shear bond strength according to dentin surface treatment, 4 materials were divided into control group(A) and experimental group(B). Group A was treated according to the instruction of manufacture. Group B was treated with 32% phosphoric acid. After dentin surface treatment, each material was bonded and stored in 100% humidity during 7 days, and then, the shear bond strength was evaluated. The results were as follows: 1. In the case of treatment according to the instruction of manufacture, the shear bond strength according to material showed Z-100 to be highest with 12.42 MPa, Compoglass had the lowest shear bond strength with 4.23 MPa and there was significant difference between Compoglass and Z-100, Dyract (p<0.01). 2. The group treated with 32% phosphoric acid showed lower shear bond strength than that of the group treated according to the instruction of manufacture but there was no statistical significance. 3. As a result of observation under SEM, the fracture pattern was a mixture of cohesive and adhesive failure in group 1, and there was more adhesive failure in group 2, and in group 3 and 4 there was cohesive failure of material or tooth structure. From the results above Dyract showed shear bond strength levels between resin and resin -modified glass ionomer but Compoglass showed much lower shear bond strength than that of resin-modified glass ionomer thus indicating that even though they are the same type of material they show evident differences in physical properties. And it is thought that the treatment of dentin surface with phosphoric acid did not increase the shear bond strength, unlike enamel.

• Journal of the Society of Disaster Information
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• v.17 no.4
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• pp.747-754
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• 2021

Purpose: Seismic safety evaluation of a curved bridge must be performed since the curved bridges exhibit the complex behavior rather than the straight bridges, due to geometrical characteristics. In order to conduct the probabilistic seismic assessment of the curved bridge, Seismic fragility evaluation was performed using the uncertainty of the steel material properties of a curved bridge girde, in this study. Method: The finite element (FE) model using ABAQUS platform of the curved bridge girder was constructed, and the statistical parameters of steel materials presented in previous studies were used. 100 steel material models were sampled using the Latin Hypercube Sampling method. As an input ground motion in this study, seismic fragility evaluation was performed by the normalized scale of the Gyeongju earthquake to 0.2g, 0.5g, 0.8g, 1.2g, and 1.5g. Result: As a result of the seismic fragility evaluation of the curved girder, it was found that there was no failure up to 0.03g corresponding to the limit state of allowable stress design, but the failure was started from 0.11g associated with using limit state design. Conclusion: In this study, seismic fragility evaluation was performed considering steel materials uncertainties. Further it must be considered the seismic fragility of the curved bridge using both the uncertainties of input motions and material properties.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.123-132
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• 2000

To overcome problems of conventional glass ionomers, resin components have been added to glass ionomers. On a continuum between glass ionomers and composites are a variety of blends, employing different proportions of acid-base and free radical reactions to bring about cure. Popular groups defined between the ends are resin-modified glass-ionomers(RMGIs), polyacid-modified composite resins(Compomers) and ionomer modified resins. These groups show different clinical properties, and in selecting these materials for a restoration, one should sufficiently understand these different setting properties. In this study, some difference in the setting characteristics of different groups of hybrid ionomers were examined. Two RMGIs (Fuji2 LC,GC / Vitremer, 3M), three Compomers (Dyract AP, Dentsply / F2000, 3M / Elan, Kerr) were involved in this study. The identification of the setting characteristics of different groups was achieved by a two-stage study. First, thermal analysis was performed by a differential scanning calorimeter, and then the hardness of each group at different depth and time were measured by a micro-hardness tester. Thermal analysis was performed to identify the inorganic filler content and to record the heat change during setting process. The setting process was progressed for each material by chemical set mode and light-cured mode. In the hardness test, samples of materials were prepared with a 6mm-diameter metal ring, and the hardness was measured at the top, and 1mm, 2.5mm, 4mm below at just after a 40 second-cure, and after 10 minutes, 24 hours, and 7 days. Statistical analysis was performed by Mann-Whitney rank sum test to assess significant differences between set modes and types of materials, and by ANOVA and T-test to evaluate the statistical meanings of data at different times and depths of each materials. Followings are findings and conclusions derived from this study. Thermal analysis; 1. Compomers show no evidence of chemical setting while RMGIs exhibit heat output during the process of chemical setting. 2. Heat of cure of RMGIs exceed Compomers. 3. The net heat output of RMGIs through light-cured mode is higher than through chemically set mode. Hardness test; 1. Initial hardness of RMGIs immediately after light cure is relatively low, but the hardness increases as time goes by. On the contrary, Comomers do not show evident increase of the hardness following time. 2. Compomers show a marked decrease of setting degree as the depth of the material increases. In RMGIs, the setting degree at different depths does not significantly differ.

• Journal of Biosystems Engineering
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• v.27 no.3
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• pp.259-266
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• 2002

It is crucial to know spatial soil variability for precision farming. However, it is time-consuming, and difficult to measure spatial soil properties. Therefore, there are needs fur sensing technology to estimate spatial soil variability, and for electronic mapping technology to store, manipulate and process the sampled data. This research was conducted to develop a real-time soil organic matter sensor and an electronic mapping system. A soil organic matter sensor was developed with a spectrophotometer in the 900∼1,700 nm range. It was designed in a penetrator type to measure reflectance of soil at 15cm depth. The signal was calibrated with organic matter content (OMC) of the soil which was sampled in the field. The OMC was measured by the Walkeley-Black method. The soil OMCs were ranged from 0.07 to 7.96%. Statistical partial least square and principle component regression analyses were used as calibration methods. Coefficient of determination, standard error prediction and bias were 0.85 0.72 and -0.13, respectively. The electronic mapping system was consisted of the soil OMC sensor, a DGPS, a database and a makeshift vehicle. An algorithm was developed to acquire data on sampling position and its OMC and to store the data in the database. Fifty samples in fields were taken to make an N-fertilizer dosage map. Mean absolute error of these data was 0.59. The Kring method was used to interpolate data between sampling nodes. The interpolated data was used to make a soil OMC map. Also an N-fertilizer dosage map was drawn using the soil OMC map. The N-fertilizer dosage was determined by the fertilizing equation recommended by National Institute of Agricultural Science and Technology in Korea. Use of the N-fertilizer dosage map would increase precision fertilization up to 91% compared with conventional fertilization. Therefore, the developed electronic mapping system was feasible to not only precision determination of N-fertilizer dosage, but also reduction of environmental pollution.

• The Journal of Advanced Prosthodontics
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• v.11 no.2
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• pp.95-104
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• 2019

PURPOSE. To evaluate the effect of surface treatments and repair materials on the shear bond strength and to measure the fracture toughness of CAD/CAM provisional restoration materials. MATERIALS AND METHODS. Four CAD/CAM (3D printing: Nextdent C&B and ZMD-1000B Temporary, CAD/CAM resin block: Yamahachi PMMA disk and Huge PMMA block) and four conventional (monometacrylate: Jet and Alike, dimetacrylate: Luxatemp and Protemp 4) materials were selected to fabricate disk-shaped specimens and divided into six groups according to surface treatment (n=10). CAD/CAM materials were repaired with Jet or Luxatemp, while conventional materials were repaired with their own materials. The shear bond strength was measured by using universal testing machine. Ten rectangular column-shaped specimens for each material were fabricated to measure the fracture toughness by single edge v notched beam technique. Statistical analysis was performed by one-way ANOVA. RESULTS. The highest shear bond strength of CAD/CAM materials was achieved by SiC paper + sandblasting. It was also accomplished when repairing 3D printing materials with Luxatemp, and repairing CAD/CAM resin blocks with Jet. Yamahachi PMMA disk showed the highest fracture toughness. Nextdent C&B showed the lowest fracture toughness value but no statistically significant difference from Alike and Luxatemp (P>.05). CONCLUSION. In order to successfully repair the CAD/CAM provisional restoration, mechanical surface treatment and appropriate repair material according to the CAD/CAM material type should be selected. The CAD/CAM provisional materials have proper mechanical properties for clinical use as compared to conventional materials.

• Journal of Digital Convergence
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• v.18 no.4
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• pp.309-314
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• 2020

Polymethyl methacrylate (PMMA) is concerned with promoting oral infection due to its low antibacterial activity. To overcome this, the nanoparticles of Ag-MSN, nGO, and CNP were mixed with MMA liquid in a weight ratio of 0, 0.25, 0.5, 1.0, 2.0% compared to resin powder using Orthocryl from Dentarum, a calibration resin, and then instructed by the manufacturer. Accordingly, a specimen for calibration was prepared by mixing PMMA: MMA (1.2: 1) ratio, and physical properties of the calibration resin, antifungal experiments, and statistical analysis were performed. As a result of antibacterial experiments, the antibacterial properties of Ag-MSN increased. In nGO, the antibacterial adhesive effect increased hydrophilicity, not a change in surface roughness. The higher the CNP concentration, the higher the antibacterial activity. This suggests its potential usefulness as an antibacterial dental material for orthodontic devices and temporary restorations.

• ALGAE
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• v.37 no.2
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• pp.175-183
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• 2022

Polar microorganisms produce physiologically active substances to adapt to harsh environments, and these substances can be used as biomedical compounds. The green microalga Micractinium variabile KSF0031, which was isolated from Antarctica, produced phytol, a natural antimicrobial agent. Furthermore, several polyunsaturated fatty acids (PUFAs), including omega-3, exhibit antioxidant properties. Here statistical methods (Plackett-Burman design and Box-Behnken design) were used to optimize the culture medium of KSF0031 to improve biomass production, and K₂HPO₄, MgSO₄·7H ₂O, and ammonium ferric citrate green (AFCg) were selected as significant components of the culture medium. Changes in the concentration of K₂HPO₄ and MgSO₄·7H ₂O as positive factors and AFCg as a negative factor affected cell growth to a remarkable degree. The biomass production in a 100 L culture using the optimized medium for 24 d at 18℃ was improved by 37.5% compared to that obtained using the original BG-11 medium. The quantities of PUFAs and phytol obtained were 13 mg g^-1 dry cell weight (DCW) and 10.98 mg g^-1 DCW, which represent improved yields of 11.70% and 48.78%, respectively. The results of this study could contribute to an improved production of phytol and fatty acids from Antarctic microalgae in the biomedical industry.