• Restorative Dentistry and Endodontics
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• 제45권4호
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• pp.50.1-50.11
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• 2020

Objectives: In this study, we investigated the potential of amoxicillin-loaded polymeric microspheres to be delivered to tooth root infection sites via a bioactive reparative cement. Materials and Methods: Amoxicillin-loaded microspheres were synthesized by a spray-dray method and incorporated at 2.5% and 5% into a mineral trioxide aggregate cement clinically used to induce a mineralized barrier at the root tip of young permanent teeth with incomplete root development and necrotic pulp. The formulations were modified in liquid:powder ratios and in composition by the microspheres. The optimized formulations were evaluated in vitro for physical and mechanical eligibility. The morphology of microspheres was observed under scanning electron microscopy. Results: The optimized cement formulation containing microspheres at 5% exhibited a delayed-release response and maintained its fundamental functional properties. When mixed with amoxicillin-loaded microspheres, the setting times of both test materials significantly increased. The diametral tensile strength of cement containing microspheres at 5% was similar to control. However, phytic acid had no effect on this outcome (p > 0.05). When mixed with modified liquid:powder ratio, the setting time was significantly longer than that original liquid:powder ratio (p < 0.05). Conclusions: Lack of optimal concentrations of antibiotics at anatomical sites of the dental tissues is a hallmark of recurrent endodontic infections. Therefore, targeting the controlled release of broad-spectrum antibiotics may improve the therapeutic outcomes of current treatments. Overall, these results indicate that the carry of amoxicillin by microspheres could provide an alternative strategy for the local delivery of antibiotics for the management of tooth infections.

• Restorative Dentistry and Endodontics
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• 제28권1호
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• pp.89-99
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• 2003

The purpose of this study was to investigate the bonding of resin- based root canal sealer, AH26 when the sealer was applied as a thin layer between dentine and gutta-percha surface. In this study forty non-caries extracted human molars and resin-based root canal sealer(AH 26, DeTrey/Dentsply, Germany) were used. Disks of gutta-percha, 6mm in diameter.6mm thick (Diadent/Dentsply, Korea) for thermoplastic obturation were used and dentin surfaces were treated with 2% NaOCl(Group 1) or 2%NaOCl+17% EDTA(Group 3). Disks of gutta-Percha, 6mm in diameter.6mm thick (Diadent/Dentsply, Korea) for conventional obturation were used and dentin surface were treated with 2% NaOCl(Group 2) or 2%NaOCl+17% EDTA(Group 4). Enamel was removed by a horizontal section 1mm below the deepest portion of the central occlusal groove by using a watercooled low speed diamond saw. A second horizontal section was done around cementoenamel junction. Exposed dentin surface was cut to approximately $8{\times}8{\;}mm$ rectangular shape and was ground against 320, 400, 600 grade silicon carbide abrasive paper serially. After grinding, the dentine surface were soaked in a solution of 2% NaOCl for 30 minutes and twenty of specimens were treated with 17% EDTA solution for 1 minute. The treated specimens were washed and dried, Root canal sealer, AH26 was prepared according to the manufacture's instructions The Gutta-percha and dentin surface were coated with a thin layer of the freshly mixed seal or. The specimens were left overnight at room temperature. After their initial set, they were transferred to an incubator at $37$^{\circ}C$ for 72 h. After 72 hours, resin blocks were made. The resin block was serially sectioned vertically into stick of $1{\cdot}1mm$. Twenty sticks were prepared from each group. After that, tensile bond strength f3r each stick was measured with Microtensile Tester Failure patterns of the specimens at the interface between gutta-percha and dentin were observed under the SEM(x1000) and Stereomicroscope (LEICA M42O, Meyer Inst., TX U.S.A) at 1.25 x25 magnification. The results were statistically analysed by using a One-way ANOVA and Tukey's test. The results were as follows; 1. Tensile bond strengths($mean{\pm}SD$) were expressed with ascending order as follows: Group 1, $3.09{\pm}$ 1.05Mpa : Group 2, $6.23{\pm}1.16MPa$ : Group 3, $7.12{\pm}1.07MPa$ : Group 4, $10.32{\pm}2.06MPa$. 2. Tensile bond strengths of the group 2 and 4 used disks of gutta-percha for conventional obturation were significantly higher than that of the group 1 and 3 used fir thermoplastic obturation. (p < 0.05). 3. Tensile bond strengths of the group 3 and 4 treated with 2% NaOC1+17% EDTA were significantly higher than that of the group 1 and 2 treated with 2% NaOCl. (p < 0.05). 4. In analysis of failure patterns at the interface between sealer and gutta-percha, there were observed 49 (61%)cases of adhesive failure patterns and 31 (39%) cases of mixed failures patterns.

• 한국식품과학회지
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• 제24권2호
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• pp.160-164
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• 1992

원료 차이에 의한 당면의 품질특성을 밝히고, 품질의 평가 기준설정을 위한 기초자료를 마련하기 위하여 고구마 당면(100% 고구마 전분), 일반 당면(50% 고구마 전분-50% 옥수수 전분) 및 옥수수 전분(100% 옥수수 전분)을 대상으로 조리특성, 조리된 당면의 텍스쳐와 관능특성을 조사하였다. 조리에 따른 당면의 무게증가율과 고형분 손실량은 일반 당면이 가장 높았다. 조리중 당면의 압축강도와 신장율은 고구마 당면이 가장 켰으며, 신장 탄성율은 고구마 당면이 가장 낮았다. 압축강도와 인장강도는 직선적인 관계를 보였으며, 동일한 압축강도에서의 인장강도는 옥수수 당면이 가장 크고, 고구마 당면이 가장 작았다. 고구마 당면은 모든 관능특성에서 가장 높은 값을 보였고 관능적 특성중 부착성과 일반 당면과 옥수수 당면의 점착성을 제외한 모든 지표들은 시료간에 유의적인 차이(p<0.05)를 보였다. 당면의 전체 바람직한 정도와 같은 경향을 보이는 관능적 특성은 투명도, 광택, 부착성과 신장성이었다.

• Geomechanics and Engineering
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• 제34권6호
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• pp.697-726
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• 2023

Brittleness as an important property of rock plays a crucial role both in the failure process of intact rock and rock mass response to excavation in engineering geological and geotechnical projects. Generally, rock brittleness indices are calculated from the mechanical properties of rocks such as uniaxial compressive strength, tensile strength and modulus of elasticity. These properties are generally determined from complicated, expensive and time-consuming tests in laboratory. For this reason, in the present research, an attempt has been made to predict the rock brittleness indices from simple, inexpensive, and quick laboratory test results namely dry unit weight, porosity, slake-durability index, P-wave velocity, Schmidt rebound hardness, and point load strength index using multiple linear regression, exponential regression, support vector machine (SVM) with various kernels, generating fuzzy inference system, and regression tree ensemble (RTE) with boosting framework. So, this could be considered as an innovation for the present research. For this purpose, the number of 39 rock samples including five igneous, twenty-six sedimentary, and eight metamorphic were collected from different regions of Iran. Mineralogical, physical and mechanical properties as well as five well known rock brittleness indices (i.e., B₁, B₂, B₃, B₄, and B₅) were measured for the selected rock samples before application of the above-mentioned machine learning techniques. The performance of the developed models was evaluated based on several statistical metrics such as mean square error, relative absolute error, root relative absolute error, determination coefficients, variance account for, mean absolute percentage error and standard deviation of the error. The comparison of the obtained results revealed that among the studied methods, SVM is the most suitable one for predicting B₁, B₂ and B₅, while RTE predicts B₃ and B₄ better than other methods.

• 한국작물학회지
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• 제48권3호
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• pp.205-208
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• 2003

본 연구는 벼 생산비중 육묘에 투입되는 비용을 경감시키고 이앙의 효율을 제고하기 위하여 기계이앙용 상자육묘시 상토를 전혀 사용하지 않고 물과 양액만으로 묘를 생산하는 수경육묘법을 개발하고자 하였다. 이를 위해 적절한 양액의 선발과 공급횟수를 구명하고자 시험을 실시하였던 바 그 결과를 요약하면 다음과 같다. 1. Yoshida액과 원시표준액간의 육묘후 묘소질은 두 양액간에 차이가 없었으나, 양액 공급횟수는 1회에서 3회로 증가할수록 초장, 엽수, 건물중이 증가되었다. 2.육묘후 인장강도는 Yoshida액이 원시표준액에 비해 높았고, 양액 공급횟수는 증가할수록 낮아졌다. 3. 경엽의 무기성분 함량은 공급양액 종류에 관계없이 N, P, K 함량은 증가하였으나 Ca와 Mg는 뚜렷한 경향이 없었다. 4. 수경묘에 축적된 무기성분량은 양액종류에 관계없이 공급횟수가 많을수록 N, P와 K의 축적량은 증가되었으며, 그 정도는 N에서 가장 컸다. 5. 수경묘에 축적된 N에 대한 다른 무기성분 비을중 P/N과 Mg/N의 비율은 원시표준액에 비해 Yoshida액에서 놀았고, 공급횟수가 증가할수록 K/N 비율이 증가되었다. 6. 양액의 이용효율은 N의 경우 공급횟수에 관계없이 비슷하였으나, P, K, Ca와 Mg는 파종 5일후 1회 공급 시 높았다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1234-1239
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• 2003

A failure analysis of holddown spring screw was performed using fracture mechanics approach. The spring screw was designed such that it was capable of sustaining the loads imposed by the initial tensile preload and operational loads. In order to investigate the cause of failure, a stress analysis of the top nozzle spring assembly was done using finite element analysis and a life prediction of the screw was made using a fracture mechanics approach. The elastic-plastic finite element analysis showed that the local stresses at the critical regions of head-shank fillet and thread root significantly exceeded than the yield strength of the screw material, resulting in local plastic deformation. Primary water stress corrosion cracking life of the Inconel 600 screw was predicted by using integration of the Scott model and resulted in 1.42 years, which was fairly close to the actual service life of the holddown spring screw.

• Geomechanics and Engineering
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• 제5권5호
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• pp.463-483
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• 2013

Considering the influences of fluid penetration, casing, excavation processes of wellbore and perforation tunnels, the seepage-deformation finite element model of oil and gas well coupled with perforating technique is established using the tensile strength failure criterion, in which the user-defined subroutine is developed to investigate the dynamic evolvement of the reservoir porosity and permeability. The results show that the increases of perforation angle and decreases of perforation density lead to a higher fracture initiation pressure, while the changes of the perforation diameter and length have no evident influences on the fracture initiation pressure. As for initiation location for the fracture in wellbore, it is on the wellbore face while considering the presence of the casing. By contrast, the fractures firstly initiate on the root of the tunnels without considering casing. Besides, the initial fracture position is also related with the perforation angle. The fracture initiation position is located in the point far away from the wellbore face, when the perforation angle is around $30^{\circ}$; however, when the perforation angle is increased to $45^{\circ}$, a plane fracture is initiated from the wellbore face in the maximum horizontal stress direction; no fractures was found around perforation tunnels, when the angel is close to $90^{\circ}$. The results have been successfully applied in an oilfield, with the error of only 1.1% comparing the fracture initiation pressure simulated with the one from on-site experiment.

• 한국환경과학회지
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• 제24권8호
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• pp.1037-1043
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• 2015

Since single-use disposable plastic usage has steadily been increasing, recent trends in polymeric research point to increasing demand for eco-friend materials which reduce plastic waste. A huge amount of non-degradable polypropylene (PP)-based pots for seedling culture are discarded for transplantation. The purpose of this study is to investigate an eco-friendly biodegradable material as a possible substitute for PP pot. The blend of poly(lactic acid) (PLA) with poly(butylene adipate-co-terephthalate) (PBAT) was used because of its good mechanical and flexible properties as well as biodegradation. After landfill, various properties of the blend pot were investigated by UTM, SEM, NMR and TGA. The results showed the tensile strength of the blend film rapidly decreased after 5 weeks of landfill due to degradation. From NMR data after landfill, the composition of PLA in the blend was decreased. These results indicate that the biodegradation of the blend preferentially occurs in PLA component. To investigate the effect of holes in pot bottom and side on root growth, a plant in the pot was grown. Some roots came out through holes as landfill period increases. These results indicate that the eco-friendly pot can be directly planted without the removal of pot.

• 한국결정성장학회지
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• 제10권5호
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• pp.345-349
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• 2000

Micro-pulling down법을 이용하여 $Al_2O_3/ZrO_2$eutectic fiber를 제조하여 그 미세구조 및 기계적 특성과 성장속도의 관계를 조사하였다. 성장속도는 0.1~15 mm/min였으며, 직경 0.2~2 mm, 길이 500 mm의 eutectic fiber를 제조하였다. $Al_2O_3/ZrO_2$eutectic fiber의 미세구조는 성장속도에 따라 rod-shape structure에서 lameller structure를 거쳐 lamellar pattern을 갖는 cellular structure로 변화하였다. lamellar thickness는 성장속도가 1 mm/min에서 15 mm/min로 증가함에 따라 380 nm에서 110 nm로 감소하였다. 이와 같은 성장속도에 따른 lamellar thickness의 감소경향은 inverse-square-root로 나타내면, = 1 -l/2와 같이 표현할 수 있다. 여기서 는 m, 는 m/s의 단위를 갖는다. 13.1 Gpa의 hardness, 900 Mpa의 상온인장강도를 나타냈으며, 성장속도의 증가 즉, interlamellar spacing이 감소함에 따라 증가하는 경향을 나타냈다.