• The Journal of Korean Academy of Prosthodontics
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• v.59 no.1
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• pp.18-26
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• 2021

Purpose: Generally, patients are noticed to store denture in water when removed from the mouth. However, few studies have reported the advantage of volumetric change in underwater storage over dry storage. To be a reference in defining the proper denture storage method, this study aims to evaluate the volumetric change and dimensional deformation in case of underwater and dry storage. Materials and methods: Definitive casts were scanned by a model scanner, and denture bases were designed with computer-aided design (CAD) software. Twelve denture bases (upper 6, lower 6) were printed with 3D printer. Printed denture bases were invested and flasked with heat-curing method. 6 upper and 6 lower dentures were divided into group A and B, and each group contains 3 upper and 3 lower dentures. Group A was stored dry at room temperature, group B was stored underwater. Group B was scanned at every 24 hours for 28 days and scanned data was saved as stereolithography (SLA) file. These SLA files were analyzed to measure the difference in volumetric change of a month and Kruskal-Wallis test were used for statistical analysis. Best-fit algorithm was used to overlap and 3-dimensional color-coded map was used to observe the changing pattern of impression surface. Results: No significant difference was found in volumetric changes regardless of the storage methods. In dry-stored denture base, significant changes were found in the palate of upper jaw and posterior lingual border of lower jaw in direction away from the underlying tissue, maxillary tuberosity of upper jaw and retromolar pad area of lower jaw in direction towards the underlying tissue. Conclusion: Storing the denture underwater shows less volumetric change of impression surface than storing in the dry air.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.413-416
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• 2004

TOC(total organic carbon)분석은 폐수 및 강수의 오염특성을 평가하기 위한 도구로서 BOD(biochemical oxygen demand), COD(chemical oxygen demand) 와 함께 사용되어 왔다. TOC 측정시간은 10분 정도로 BOD(5～6일), COD(2～3시간)에 비해 아주 짧은 시간에 측정할 수가 있으며, 전처리과정이 단순하고 정확도도 높은 것으로 알려져 있다. 본 연구는 지하수의 잠재오염성을 밝혀내기 위한 도구로 TOC를 활용하여 신뢰성 있는 분석 값을 얻기 위해서 시료의 채취, 보관, 측정까지의 최적 조건을 도출하는데 목적을 두었다. 아울러 시료 채취 후 일정 경과 시간에 따른 TOC의 변화를 관찰하였다. 시료채취 용기, 채취 후 산성화, 보관방법 및 기간에 대한 실험 결과, 대상 변수에 따라서 TOC의 농도변화에 커다란 차이점을 볼 수 있었다. TOC 농도가 낮은 지하수시료의 측정에서는 빛을 차단시킨 불투명 유리병을 사용해야만 하고 채취 즉시 산도를 높여(pH<2)주며 4$^{\circ}C$ 이하에서 보관하여야 한다. 지하수중 TOC 측정시료는 가능한 보관 기간에 있어서 채수 후 24시간 이내에 측정하는 것이 좋으나 1) 본 연구에서는 채취현장과의 거리를 고려하면 현실적으로 불가능하므로 기간에 따른 TOC 변화를 30일까지 측정, 조사하였다.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.350-355
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• 1997

가압중수로(PHWR)형 원자력발전소의 저장수조에 보관중인 사용후핵연료를 대상으로 하는 핵물질 보장조치(safeguards) 이행에 필요한 핵연료다발 수중검증장치를 개발하였다. 본 장치는 CdTe 감마선검출기, 차폐체 및 시준기등으로 구성된 검출부와 이를 지지 및 구동하기 위한 구동부로 구성되어 있다. 검출부에 대하여 감마선 표준선원 및 사용후핵연료 시료를 사용하여 성능시험을 수행한 결과 현장검증시의 요건을 만족하였고, 구동부의 경우 건식조(dry pit)에서 수행한 예비실험 결과 검증목적에 적합하였다. 따라서, PHWR형 원자력발전소인 월성 1 호기의 수중저장조에 있는 사용후CANDU핵연료에 대한 현장성능시험을 현재 준비중에 있으며 그 결과를 바탕으로 하여 국가사찰시에 본 장치를 사용할 예정이며, 향후 IAEA의 공인을 획득하여 IAEA 사찰용 장비로도 활용할 계획이다.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.4
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• pp.312-316
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• 2014

Purpose: The aim of this study was to compare the fracture toughness of currently available resin cements for zirconia restorations and evaluate the effect of water storage on fracture toughness of those resin cements. Materials and methods: Single-edge notched specimens ($3mm{\times}6mm{\times}25mm$) were prepared from three currently available dual cure resin cements for zirconia restorations (Panavia F 2.0, Clearfil SA luting and Zirconite). Each resin cement was divided into four groups: immersed in distilled water at $37^{\circ}C$ for 1 (Control group), 30, 90, or 180 days (n=5). Specimens were loaded in three point bending at a cross-head speed of 0.1 mm/s. The maximum load at specimen failure was recorded and the fracture toughness ($K_{IC}$) was calculated. Data were analyzed using one-way ANOVA and multiple comparison $Scheff{\acute{e}}$ test (${\alpha}$=.05). Results: In control group, the mean $K_{IC}$ was $3.41{\pm}0.64MN{\cdot}m^{-1.5}$ for Panavia F, 2.0, $3.07{\pm}0.41MN{\cdot}m^{-1.5}$ for Zirconite, $2.58{\pm}0.30MN{\cdot}m^{-1.5}$ for Clearfil SA luting respectively, but statistical analysis revealed no significant difference between them. Although a gradual decrease of $K_{IC}$ in Panavia F 2.0 and gradual increases of KIC in Clearfil SA luting and Zirconite were observed with storage time, there were no significant differences between immersion time for each cement. Conclusion: The resin cements for zirconia restorations exhibit much higher $K_{IC}$ values than conventional resin cements. The fracture toughness of resin cement for zirconia restoration would not be affected by water storage.

• Journal of the military operations research society of Korea
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• v.33 no.1
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• pp.93-103
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• 2007

Ship identification systems currently employed provide the underwater sound analysis, analyzed data saving and user interface with comparison function. But final analysis and identification depend only on experts. Therefore, the reliability of these identification systems relies on user's ability on information recognition. This paper presents the method of recognition for the purpose of providing the basic data for an automatic ship class identification. we get the underwater sounds using the PC. We use Matlab in order to reduce ambient noises, take out an acoustic characteristics using the pattern recognition, and classify the ships.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.5
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• pp.351-358
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• 2012

Formation of disinfection by-products (DBPs) including trihalomethans (THM), haloacetic acid (HAA) and haloacetonitriles (HAN) from chlorination of extracellular organic matter (EOM) and cells + intracellular organic matter (IOM) of Microcystis sp., a blue-green algae, during decomposed period was investigated. Microcystis sp. cells + IOM and EOM of Microcystis sp. exhibited a high potential for DBP formation. HAAFP (formation potential) was higher than THMFP during decomposed period. In the variations of HAAFP species during decomposed period, the ratio of di-HAAFP species was gradually decreased and the ratio of tri-HAAFP species was gradually increased in the case of EOM during decomposed period, while the opposite result was in the case of cells + IOM during decomposed period. In the variations of HANFP species during decomposed period, the ratio of di-HANFP species was much higher than the ratio of tri-HAAFP species.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.630-635
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• 2003

We propose an encryption method using visual cryptography and virtual phase images. In the encryption process, the original image is shared by virtual images and the decryption key image. We multiply the virtual phase images with each complex image, which has the constant value of its sum after performing the phase modulation of the virtual images and the decryption key. The encryption cards are made by Fourier transforming the multiplied images. It is possible to protect information about the original image because the cards do not have any information from the original image. To reconstruct the original image, all the encryption cards are placed on each path of a Mach-Zehnder interferometer and then the lights passing through them are summed. Since the summed image is inverse Fourier transformed by a Fourier lens, the phase image is multiplied with the decryption key and the output image is obtained in the form of intensity on the CCD plane. Computer simulations show a good performance of the pro-posed optical security system.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.4
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• pp.685-695
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• 2004

The aim of this study was to evaluate the resistance to degradation and to compare the wear resistance characteristics of four composite resins in an alkaline solution. The resistance to degradation was evaluated on the basis of mass loss(%), degradation depth(${\mu}m$), Si loss(ppm) and wear depth. The brands studied were Heliomolar flow, Filtek supreme, Point4, Tetric flow. The results were as follows: 1. The sequence of the mass loss was in descending order by Heliomolar flow, Filtek supreme, Point4, Tetric flow. There was significant differences among the materials except Heliomolar flow and Filtek supreme. 2. The sequence of the degree of degradation layer depth was in descending order by Filtek supreme, Heliomolar flow, Tetric flow, Point4. There were significant differences among the materials except Heliomolar flow and Tetric flow. 3. The sequence of Si loss was in descending order by Filtek supreme, Heliomolar flow, Point4, Tetric flow. There were significant differences among the materials except Point 4 and Tetric flow. 4. The sequence of maximum wear depth was in descending order by Heliomolar flow, Point4, Fillet supreme, Tetric flow and there was increasing wear depth on soaking in 0.1N NaOH solution. 5. When observed with SEM, destruction of bonding between matrix and filler was observed and when observed with CLSM, the depth of degradation layer of specimen surface was observed. There results indicate that wear and hydrolytic degradation could be considered to be evaluation factors of composite resins.

• Korean Chemical Engineering Research
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• v.53 no.5
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• pp.584-589
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• 2015

For effective power generation with fuel cells in low-oxygen environments such as submarines and unmanned underwater vehicles, a hydrogen source which has a high hydrogen storage density is required. Diesel fuel is easy to storage and supply due to its liquid phase and it has a high density per unit volume and unit mass of hydrogen that required for driving the fuel cells. In this paper, diesel fuel was selected as a hydrogen source for driving the fuel cell in oxygen lean environments. In addition, the aqueous hydrogen peroxide solution was suggested as an alternative oxidant for hydrogen production through the diesel reforming reaction because of its high oxygen density and liquid phase which makes it easy to storage. In order to determine the characteristics of hydrogen peroxide as an oxidant of diesel reforming, comparative experiments were conducted and it was found that hydrogen peroxide solution has the same characteristics when reformed with oxidants of both steam and oxygen. Moreover, the commercial diesel reforming performances were analyzed according to the reaction temperature and concentration of aqueous hydrogen peroxide solution. Then, through the 49 hours accelerated degradation tests, the possibility of hydrogen production via diesel and aqueous hydrogen peroxide solution was confirmed.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.2
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• pp.193-202
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• 2006

Objective To evaluate the influence of water storage on the mechanical properties of dental adhesives over 1 and 3 months. Materials and Methods Adhesive resin sheets were prepared by pouring either All-bond 2(AB), Clearfil SE Bond(SE) into a mold measuring $15{\times}15{\times}0.9mm$. After solvent in primer evaporation, the adhesives were light-cured and removed from the mold and divided in two pieces, trimmed to hourglass shape that were used to determine the micro-tensile strength(MTS). Another hourglass shaped metal mold measuring $2.0{\times}1.5mm$ in cross-section area was made to determine the Young's modulus(E). Adhesive specimens for Young's modulus(E) were prepared in the same method. Specimens were stored at $37^{\circ}C$ in distilled water and tested after 1 and 3 months. The data were analyzed by one-way ANOVA and Tukey's test. Results Water storage significantly decreased the micro-tensile strength(MTS) of AB and SE specimens after 1 and 3 months(P<0.05). The Young's modulus(E) were also decreased after water storage for 1 and 3 months, but statistically not significant in each group of AB and SE group respectively. Conclusions Long-term exposure of adhesive resin to water can cause reduction of mechanical properties. It may compromise resin/dentin bonds and affect longevity of restorations.