• 대한치과보철학회지
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• 제41권5호
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• pp.582-595
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• 2003

Statement of problem : Most posts are metallic, but in response to the need for a post that possesses optical properties compatible with an all-ceramic crown. an esthetic post has been developed. Although there have been many studies about the esthetic post materials, 3-dimensional finite element studies about the stress distribution of them are in rare. Purpose : The purpose of this study is to investigate comparatively the distribution of stresses of the restored, endodontically treated maxillary incisors with the esthetic post materials and the displacement on the cement layer on simulated occlusal loading by using a 3-dimensional finite element analysis model. Material and method : Four 3-dimensional finite element models were constructed in a view of a maxillary central incisor, a post, a core, and the supporting tissues to investigate the stresses in various esthetic posts and cores and the displacement on the cement layer (Model 1 ; Cast gold post and core, Model 2 ; Glass fiber post with composite core, Model 3 ; Zirconia post with composite core. Model 4 ; Zirconia post with ceramic core). Force of 300N was applied to the incisal edge and the cingulum (centric stop point) with the angle of 135-degree to the long axis of the tooth. Results : 1. The stresses and displacement on the incisal edge were higher than on the cingulum 2. The stresses in dentin were the highest in Model 2 (Glass fiber post with composite core), and the second was Model 3, the third Model 1, and the lowest Model 4. 3. The stresses in post and core were the highest in Model 4 (Zirconia post with ceramic core), and the second was Model 1, the third Model 3, and the lowest Model 2. 4. The displacement on the cement layer was the highest in Model 2 (Glass fiber post with composite core), and the second was Model 3, the third Model 1, and the lowest Model 4. Conclusion : When a functional maximum bite force was applied, the distribution of stresses or the esthetic post and core materials and the displacement on the cement layer were a little different. It seems that restoring extensively damaged incisors with esthetic post and core materials would be decided according to the remaining tooth structure.

• 대한치과기공학회지
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• 제31권1호
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• pp.55-61
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• 2009

Passive fitting of meso-structure and super-structures is a predominant requirement for the longevity and clinical success of osseointegrated dental implants. However, precision and passive fitting has been unpredictable with conventional methods of casting as well as for corrective techniques. Alternative to conventional techniques, electro discharge machining(EDM) is an advanced method introduced to dental technology to improve the passive fitting of implant prosthesis. In this technique material is removed by melting and vaporization in electric sparks. Regarding the efficacy of EDM, the application of this technique induces severe surface morphological and elemental alterations due to the high temperatures developed during machining, which vary between $10,000{\sim}20,000^{\circ}C$. The aim of this study was to investigate the morphological and elemental alterations induced by EDM process of casting dental gold alloy and non-precious alloy used for the production of implant-supported prosthesis. A conventional clinical dental casting alloys were used for experimental specimens patterns, which were divided in three groups, high fineness gold alloy(Au 75%, HG group), low fineness gold alloy(Au 55%, LG group) and nonprecious metal alloy(Ni-Cr, NP group). The UCLA type plastic abutment patterns were invested with conventional investment material and were cast in a centrifugal casting machine. Castings were sandblasted with $50{\mu}m\;Al_2O_3$. One casting specimen of each group was polished by conventional finishing(HGCON, LGCON, NPCON) and one specimen of each group was subjected to EDM in a system using Cu electrodes, kerosene as dielectric fluid in 10 min for gold alloy and 20 min for Ni-Cr alloy(HGEDM. LGEDM, NOEDM). The surface morphology of all specimens was studied under an energy dispersive X-ray spectrometer (EDS). The quantitative results from EDS analysis are presented on the HGEDM and LGEDM specimens a significant increase in C and Cu concentrations was found after EDM finishing. The different result was documented for C on the NPEDM with a significant uptake of O after EDM finishing, whereas Al, Si showed a significant decrease in their concentrations. EDS analysis showed a serious uptake of C and Cu after the EDM procedure in the alloys studied. The C uptake after the EDM process is a common finding and it is attributed to the decomposition of the dielectric fluid in the plasma column, probably due to the development of extremely high temperatures. The Cu uptake is readily explained from the decomposition of Cu electrodes, something which is also a common finding after the EDM procedure. However, all the aforementioned mechanisms require further research. The clinical implication of these findings is related with the biological and corrosion resistance of surfaces prepared by the EDM process.

• Journal of Pharmaceutical Investigation
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• 제35권6호
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• pp.417-422
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• 2005

This study was aimed to design and formulate the moisture-activated patches containing ofloxacin and lidocaine for antibacterial and local anesthetic action. The solubility of lidocaine at $32^{\circ}C$ in various vehicles decreased in the rank order of PG $759.5{\pm}44.5\;mg/mL$ > PGL > IPM > PEG 300 > PEG 400 > Ethanol > PGMC > DGME > PGML > OA > $Captex^{\circledR}\;300$ > $Captex^{\circledR}\;200$ > water $(4.0{\pm}0.1\;mg/mL)$. Ofloxacin revealed very low solubility, which the highest solubility was obtained from PEG 400 $(18.7{\pm}6.3\;mg/mL)$ among the vehicles used. The addition of lactic acid increased the solubility of ofloxacin dramatically; the solubility at 5% lactic acid was $133.7{\pm}9.7\;mg/mL$. As $2-hydroxypropyl-{\beta}-cyclodextrin$ was added at the concentrations of 40, 80, 120, 160 and 200 mM, the solubilities of lidocaine and ofloxacin were enhanced up to three and two times, respectively, with concentration-dependent pattern. Gel intermediates for filmtype patches were prepared with mucoadhesive polymer, viscosity builders, lidocaine or ofloxacin at pH values from 5 to 7. Gels were cast onto a release liner and dried at room temperature. Dried patch was attached onto an adhesive backing layer, thus forming a patch system. Patches containing a single drug component were characterized by in vitro measurement of drug release rates through a cellulose barrier membrane. The release study was carried out at $37^{\circ}C$ using a Franz-type cell. Receptor solutions were isotonic phosphate buffers (pH 7.4). Samples $(100\;{\mu}L)$ were taken over 24 hours and quantitated by a verified HPLC method. The releases from all tested were proportional to the square root of time. The release rates were 0.9, 157.3 and $281.7\;{\mu}g/cm^{2}/min^{1/2}$ for the lidocaine patches and 19.8,37.2 and $50.7\;{\mu}g/cm^{2}/min^{1/2}$ for the ofloxacin patches at the concentrations of 0.3, 0.5 and 1 %, respectively. The release rates were dose dependent in both drug patches $(R^{2}\;=\;0.9077\;for\;lidocaine;\;R^{2}\;=\;0.9949\;for\;ofloxacin)$ and those were also thickness-dependent $(R^{2}\;=\;0.9246\;for\;lidocaine;\;R^{2}\;=\;0.9512\;for\;ofloxacin)$.

• Fisheries and Aquatic Sciences
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• 제22권12호
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• pp.31.1-31.12
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• 2019

Background: The black-chinned tilapia, Sarotherodon melanotheron, is the most abundant fish species in the Nakwa (an open lagoon) and Brenu (a closed lagoon) in the Central Region of Ghana. Aspects of the life history characteristics and the ecology of the fish populations in both lagoons were studied to assess the bio-ecological status of this important resource. Methods: Fish samples were obtained from fishermen that fish on the Nakwa and Brenu lagoons using cast, drag and gill nets. The age of the fish was assessed from otoliths analysis and its growth modelled following the von Bertalanffy growth function. Morphometric characteristics of the fish populations were analysed using power regression and ANOVA for parameters comparisons, and Student's t test to determine whether species grew isometrically. The percentage occurrence method was used to analyse the stomach contents of the fish. Results: A total of 382 fish samples from both lagoons were measured, comprising 209 from Nakwa lagoon and 176 from Brenu lagoon. The size and weight of fish samples ranged between 3.9-11.5 cm total length and 1.0-27.3 g for Nakwa Lagoon and 5.6-12.8 cm total length and 3.2-29.8 g for the Brenu Lagoon. The estimated von Bertalanffy growth parameters were L∞ = 12.04 cm and K = 2.76/year for the Nakwa Lagoon samples and L∞ = 13.44 cm and K = 3.27/year for Brenu Lagoon samples. Daily otolith incremental rate ranged from 0.01-0.03 mm per day to 0.01-0.02 mm per day for Nakwa and Brenu lagoons, respectively. Stomach content analysis of the fish samples revealed that the species are planktivorous and the range of food varied between the lagoons. Green algae were the most prevalent food item in the stomachs of the fish samples from Nakwa with the frequency of 69% whilst diatoms (80.5%) were most prevalent phytoplanktonic food item for the fish in Brenu lagoon. Conclusions: The estimates of asymptotic length for the species in both lagoons are close to known values of the species length at first sexual maturity and points to intensive fishing pressure. As a consequence, a comprehensive sample-based survey is required in both lagoons to derive estimates of management reference points. The results of the stomach content analysis are beneficial to the construction of diet matrix for ecosystem models of the two systems.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.54-63
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• 2018

본 연구에서는 고속도로 도로부의 표준단면을 대상으로 패널식 보강토 옹벽의 높이별 안전율과 경제성에 대해 비교 검토하였다. 설계기준에 따라 하중조건은 고속도로의 단면 및 형상조건을 고려하여 콘크리트 포장의 사하중과 차량하중을 재하하고 최상단 보강재의 경우 방호벽의 충돌하중을 고려하였다. 보강재의 길이는 보강토 옹벽의 높이에 따라 0.9H로 배치하였기 때문에, 보강토체의 형상에 따라 지배되는 외적 안정성에 대해 높이의 증가에 따른 영향은 거의 없는 것으로 나타났다. 지지력에 대한 안전율은 보강토 옹벽의 높이에 따라 자중이 증가되기 때문에 급격히 감소되었다. 복합중력식 설계법에 따른 내적 안정성을 검토한 결과, 인발 안전율은 증가되고 파단 안전율은 감소되었다. 보강토 옹벽의 높이가 증가될수록 활동력으로 작용되는 수평토압과 저항력으로 작용되는 수직토압이 함께 증가되기 때문에 인발의 안전율은 증가되었다. 돌기형 강재 보강재의 장기 허용인장력은 상수이기 때문에, 높이에 따라 활동력에 대한 안전율은 수평토압이 증가되어 감소되었다. 블록식 보강토 옹벽보다는 패널식 보강토 옹벽의 경제성이 우수한 것으로 나타났고, 기존 옹벽과 비교하면 5.0 m이상의 높이에서 패널식 보강토 옹벽의 경제성이 가장 우수한 것으로 나타났다.

• 노동경제논집
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• 제30권2호
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• pp.1-31
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• 2007

본 연구는, 비정규 근로에 대한 차별처우의 문제를 실증적으로 분석하여, 고용형태에 따른 임금격차에 대한 객관적 사실들을 제시함으로써, 비정규 근로에 대한 논의를 보다 생산적이게 하는 데에 기여하고자 한다. 비정규 근로의 임금수준은 2005년에 정규 근로의 63%에 불과하여 37%의 임금격차가 존재한다. 그러나 이는 근로시간, 인적자본의 양, 직무의 성격, 그리고 개인의 능력 등을 전혀 고려하지 않은 것이다. 근로시간만 추가로 감안하더라도 임금격차는 29%로 감소한다. 근로자들의 인적특성, 인적자본, 사업체 규모, 노동조합 등 분석에 전통적으로 사용되는 변수들 대부분을 통제하면 임금격차는 2.7%로 급감한다. 직무까지 추가로 통제할 경우, 임금격차는 다시 2.2%로 줄어든다. 이 가운데 생산성에 의한 임금격차가, Oaxaca 방법으로 분해하면, 91%를 차지한다. 이는 차별처우의 최대치가 정규 근로 시간당 임금의 0.2%에 불과함을 의미한다. 나아가 개개인의 능력을 비롯한 미관측 이질성까지도 추가로 통제하기 위해 패널자료를 구축하고 고정효과 모형을 사용하여 추정 할 경우, 비정규 근로의 시간당 임금은 정규 근로의 경우와 의미 있는 차이를 보이지 않거나 오히려 다소 높게 나타난다. 이러한 결과는 경제이론으로 쉽게 설명된다. 다른 상황이 동일하다면 근로자들은 고용이 보다 불안한 비정규 근로로 노동을 공급할 경우 이에 대한 보상으로 보다 높은 임금을 받으려 할 것이다. 기업들은 추가로 고용유연성을 확보할 경우 보다 높은 임금을 지급할 용의가 있다. 따라서 비정규 근로가 정규 근로에 비해 보다 불안한 고용과 보다 높은 임금을 가지는 균형이 성립될 수 있다. 이상의 결과는 비정규 근로 문제를 차별처우의 차원에서 접근하는 시각에 매우 회의적이며, 비정규 근로에 대한 논의의 방향을 수정할 것을 함축하고 있다.

• 한국강구조학회 논문집
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• 제20권2호
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• pp.227-236
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• 2008

강합성 교량에서 일반적으로 사용되는 콘크리트는 단위질량이 ${2,300kg/m^{3}}$인 일반콘크리트이다. 그러나 강합성 교량에서 경량콘크리트를 사용한다면 바닥판 자중에 의한 단면력을 감소시킬 수 있어 더욱 경제적인 교량설계가 가능할 것이다. 경량콘크리트를 사용한 강합성 거더 교량에서 적용될 수 있는 바닥판 형식은 크게 현장타설 콘크리트 바닥판과 프리캐스트 바닥판으로 구분할 수 있다. 이 두형식의 바닥판은 시공측면이나 구조적 거동 측면에서 다소 차이가 있어, 바닥판과 강거더를 연결하는 전단연결부도 사용되는 바닥판의 형식에 따라 구조적 거동 특성이 위하여 Push-out 실험을 수행하였다. 또한 베딩층이 있는 프리캐스트 부재에 대해서는 강도감소의 주요한 원인이 되는 베딩층의 균열을 방지하기 위하여 프리캐스트 바닥판과 베딩층 사이에 전단키를 설치하고 베딩층을 횡방향으로 구속시킨 실험체에 대해 실험을 수행하여 그 영향을 평가하였다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제30권4호
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• pp.331-338
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• 2004

Stress transfer to the surrounding tissues is one of the factors involved in the design of dental implants. Unfortunately, insufficient data are available for stress transfer within the regenerated bone surrounding dental implants. The purpose of this study was to investigate the concentration of stresses within the regenerated bone surrounding the implant using three-dimensional finite element stress analysis method. Stress magnitude and contours within the regenerated bone were calculated. The $3.75{\times}10-mm$ implant (3i, USA) was used for this study and was assumed to be 100% osseointegrated, and was placed in mandibular bone and restored with a cast gold crown. Using ANSYS software revision 6.0, a program was written to generate a model simulating a cylindrical block section of the mandible 20 mm in height and 10 mm in diameter. The present study used a fine grid model incorporating elements between 165,148 and 253,604 and nodal points between 31,616 and 48,877. This study was simulated loads of 200N at the central fossa (A), at the outside point of the central fossa with resin filling into screw hole (B), and at the buccal cusp (C), in a vertical and $30^{\circ}$ lateral loading, respectively. The results were as follows; 1. In case the regenerated bone (bone quality type IV) was surrounded by bone quality type I and II, stresses were increased from loading point A to C in vertical loading. And stresses according to the depth of regenerated bone were distributed along the implant evenly in loading point A, concentrated on the top of the cylindrical collar loading point B and C in vertical loading. And, In case the regenerated bone (bone quality type IV) was surrounded by bone quality type III, stresses were increase from loading point A to C in vertical loading. And stresses according to the depth of regenerated bone were distributed along the implant evenly in loading point A, B and C in vertical loading. 2. In case the regenerated bone (bone quality type IV) was surrounded by bone quality type I and II, stresses were decreased from loading point A to C in lateral loading. Stresses according to the depth of regenerated bone were concentrated on the top of the cylindrical collar in loading point A and B, distributed along the implant evenly in loading point C in lateral loading. And, In case the regenerated bone (bone quality type IV) was surrounded by bone quality type III, stresses were decreased from loading point A to C in lateral loading. And stresses according to the depth of regenerated bone were distributed along the implant evenly in loading point A, B and C in lateral loading. In summary, these data indicate that both bone quality surrounding the regenerated bone adjacent to implant fixture and load direction applied on the prosthesis could influence concentration of stress within the regenerated bone surrounding the cylindrical type implant fixture.

• 콘크리트학회논문집
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• 제28권4호
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• pp.489-496
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• 2016

최근, 건물의 자중을 저감시킴으로서 시공성을 향상시키기 위한 방안으로 중공 PC슬래브에 대한 관심이 높아지고 있다. 국내에서 생산되는 대표적인 중공 PC슬래브인 HCS는 생산방식 특성상 전단보강근의 배근이 어렵기 때문에 안전성 및 사용성 측면에서 문제가 제기되고 있다. 이와 같은 측면에서, 최근 새로운 형태의 부분 PC 슬래브 시스템인 Tripple Ribs Slab (TRS)가 개발되었다. TRS는 전단보강근의 배근이 가능한 하프PC형 중공슬래브이다. 본 연구에서는 TRS의 전단성능을 검토하기 위해 전단실험을 진행하였다. 시공단계별로 형성되는 단면조건에 대하여 비대칭 1점 가력으로 실험하였으며 실험결과 강도를 기준 식들과 비교하였다. 실험에서의 변수는 CIP 유무와 래티스바의 유무 또는 래티스바의 종류이다. 실험으로부터, TRS는 설계하중을 충분히 지지할 수 있는 전단성능을 가지고 있으며 실험체의 강도는 국내콘크리트구조기준에서 제시하는 일반식으로 적절하게 예측될 수 있는 것으로 나타났다. CIP가 타설되지 않은 시공단계에서는 래티스바의 기여도가 현저히 낮기 때문에 래티스바의 전단강도를 제외하고 설계하는 것이 바람직하다고 판단된다.

• 대한치과보철학회지
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• 제42권4호
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• pp.386-396
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• 2004

Statement of problem: It is not clear how to make a stable bonding between zirconia ceramic and resin cement. And the study about surface treatment of zirconia ceramic or bonding resin cement are not enough. Purpose: To measure and compare the shear bond strength of some resin cements on zirconia ceramic after different surface treatments. Material and method: 48 ceramic discs were made of 3 ceramic materials, zirconia ceramics (Zi-Ceram), heat-pressed ceramics (IPS Empress 2) and slip cast alumina ceramics (In-Ceram). According to the surface treatments of ceramic specimens and resin cements, specimens were classified into 6 groups and each group was composed of 8 specimens. For the surface treatment of Zi-Ceram group (test group), sandblasting and diamond bur preparation were applied and Superbond C&B and Panavia F were bonded respectively. For IPS Empress 2 group (control group), Variolink II was bonded after sandblasting, acid etching, silanization and for In-Ceram ALUMINA group (control group), Panavia F was bonded after sandblasting. After storing specimens in distilled water for 24 hours, the shear bond strength was measured by the universal testing machine. Results and conclusion: 1. Zi-Ceram group with Superbond C&B cement showed higher bond strength than with Panavia F cement regardless to the surface treatments (p<0.05). 2. In Zi-Ceram group with Superbond C&B cement, sandblasting treatment group (12.1MPa) showed higher bond strength than diamond bur treatment group (7.7MPa) (p<0.05). In Zi-Ceram group with Panavia F cement, there were no significant differences in the bond strength according to the surface treatments (p>0.05). 3. Zi-Ceram group with sandblasting and Superbond C&B cement (12.1MPa) showed the highest bond strength. The bond strength of this group was not significantly different from In-Ceram ALUMINA group (10.4MPa) (p>0.05) and lower than IPS Empress 2 group (15.9MPa) (p<0.05).