• Journal of Periodontal and Implant Science
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• 제50권4호
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• pp.238-250
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• 2020

Purpose: This study aimed to evaluate the biocompatibility and the mechanical properties of ultraviolet (UV) cross-linked and biphasic calcium phosphate (BCP)-added collagen membranes and to compare the clinical results of ridge preservation to those obtained using chemically cross-linked collagen membranes. Methods: The study comprised an in vitro test and a clinical trial for membrane evaluation. BCP-added collagen membranes with UV cross-linking were prepared. In the in vitro test, scanning electron microscopy, a collagenase assay, and a tensile strength test were performed. The clinical trial involved 14 patients undergoing a ridge preservation procedure. All participants were randomly divided into the test group, which received UV cross-linked membranes (n=7), and the control group, which received chemically cross-linked membranes (n=7). BCP bone substitutes were used for both the test group and the control group. Cone-beam computed tomography (CBCT) scans were performed and alginate impressions were taken 1 week and 3 months after surgery. The casts were scanned via an optical scanner to measure the volumetric changes. The results were analyzed using the nonparametric Mann-Whitney U test. Results: The fastest degradation rate was found in the collagen membranes without the addition of BCP. The highest enzyme resistance and the highest tensile strength were found when the collagen-to-BCP ratio was 1:1. There was no significant difference in dimensional changes in the 3-dimensional modeling or CBCT scans between the test and control groups in the clinical trial (P>0.05). Conclusions: The addition of BCP and UV cross-linking improved the biocompatibility and the mechanical strength of the membranes. Within the limits of the clinical trial, the sites grafted using BCP in combination with UV cross-linked and BCP-added collagen membranes (test group) did not show any statistically significant difference in terms of dimensional change compared with the control group.

• 한국기계가공학회지
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• 제13권3호
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• pp.35-41
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• 2014

Poly(g-glutamic acid) (g-PGA) is a very promising biodegradable polymer that is produced by microorganism of Bacillus subtilis. Because g-PGA is water-soluble, anionic, biodegradable, and even edible, its potential applications have been studied from an industrial standpoint. In this study, we fabricated porous g-PGA foams by means of a freeze-solvent extraction method for tissue-engineering applications. Porous g-PGA foams were chemically cross-linked using a hexamethylene diisocyanate solution. An aqueous basic solution was used to neutralize g-PGA foam for cell culturing. During an in vitro cell culture study, it was observed that primary rabbit ear chondrocytes were well at tached and spread over the surface oft hree-dimensional cross-linkedg-PGA foam. From these results, it is concluded that cross-linkedg-PGA foam is aprom is in gmaterial for tissue-engineering applications, especially those pertaining to the regeneration of human cartilage.

• 한국환경과학회지
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• 제21권3호
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• pp.267-276
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• 2012

Spaceflights results in the reduction of immune status of human beings and increase in the virulence of microorganisms, especially gram negative bacteria. The growth of Klebsiella pneumoniae is enhanced by catecholamines and during spaceflight, elevation in the levels of cortisols occurs. So it is necessary to know the changes in physiology, virulence, antibiotic resistance and gene expression of K. pneumoniae under microgravity conditions. The present study was undertaken to study effect of simulated microgravity on growth, morphology, antibiotic resistance and cross stress resistance of K. pneumoniae to various stresses. The susceptibility of simulated microgravity grown K. pneumoniae to ampicillin, penicillin, streptomycin, kanamycin, hygromycin and rifampicin were evaluated. The growth of bacteria was found to be fast compared with normal gravity grown bacteria and no significant changes in the antibiotic resistance were found. The bacteria cultured under microgravity conferred cross stress resistance to acid, temperature and osmotic stress higher than the normal gravity cultured bacteria but the vice versa was found in case of oxidative stress.

• 한국초등과학교육학회지:초등과학교육
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• 제38권1호
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• pp.116-129
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• 2019

This study investigated elementary students' spatial thinking and visualization when they learned the shape of volcanoes. For this purpose we used GeoMapApp to design instruction program and assessment items. In the instruction, students were asked to connect the floor plan view of Jeju island with the cross-sectional view of the same figure producted by GeoMapApp. Then they were asked to classify four sets of pictures of volcanoes based on the similarities of figures, that is, dome-shaped and shield volcanoes. In the assessment students solved three questions which examined how they connected the plan view and cross-sectional profile of Kilauea, draw cross-sectional profile of Mt. Fuji, and distinguished a shield volcano and dome-shaped one. Students' discourse data during the class were analyzed according to the amount to showing their spatial thinking and visualization. The instruction program using GeoMapApp assisted students to facilitate their spatial thinking for understanding of volcanoes. The outcomes of assessment showed even elementary students had good spatial thinking and visualization. Therefore, we argued spatial thinking and visualization for geoscientific understanding need to be included in the national science curriculum for elementary students.

• 한국의류학회지
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• 제47권4호
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• pp.609-624
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• 2023

This study aimed to explore the effects of perceived benefits on consumers' attitudes towards cross-border online shopping websites. We also explore whether and how consumers' COVID-19 anxiety and brand familiarity weaken or strengthen the relationship between these perceived benefits and consumer attitudes. A total 319 items of data were used for the final analysis. The perceived benefits of a website were found to have only an indirect effect on purchase intentions by mediating consumers' attitudes toward the site. Competitive pricing of fashion products directly affected purchase intentions. COVID-19 anxiety was found to have a negative moderating influence on the relationship between perceived enjoyment and consumer attitudes, whereas brand familiarity had a positive moderating effect on both the relationships between perceived usefulness and consumers' attitudes toward the site and between perceived ease of use and their site attitude. This study provides useful insights for international e-tailers in developing marketing strategies that attract international consumers. Academically, we have contributed to the existing literature on the perceived benefits of global online shopping and the moderators of consumers' attitudes towards e-commerce sites.

• 대한치과보철학회지
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• 제37권4호
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• pp.506-515
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• 1999

Dental practice can produce and spread some infectious diseases from patients to dentist, dental assistant, and dental labors. One possible method for preventing these cross-contamination is to immerse dental impression in chemical disinfectants. So for many investigators studied on the dimensional changes of dental impressions and on the surface qualities of stone casts made from impression following immersion in disinfectants. This study was proposed to evaluate some popular impression disinfectant combination from the point of dimensional stability. Impression was taken from dental arch-shaped metal model. Irreversible hydrocolloid and 3 elastomers(polyvinyl siloxane, polysulfide, polyether) were immersed in 3 disinfectants (2% glutaraldehyde, 1% povidone-iodine, 0.5% sodium hypochlorite) for 10 minutes and measured both cross-arch and anterior-posterior distance under stereo microscope to evaluate dimensional change. The results obtained were as follows: 1. Dimensional changes of irreversible hydrocolloid impression was statistically different in cross-arch and anterior-posterior distance when immersed in 2% glutaraldehyde solution and in anterior-posterior distance when immersed in 0.5% sodium hypochlorite solution from control group (p<0.05). 2. Dimensional changes of polyvinyl siloxane and polysulfide impression were not statistically different from control group (p>0.05). 3. Dimensional changes of polyether impression was statistically different in cross-arch distance when immersed in 0.5% sodium hypochlorite solution and in anterior-posterior distance when immersed in 1% povidone-iodine solution from control group (p<0.05). 4. In all cases, dimensional changes were less than 0.1% from the original dimension and concluded clinically acceptable.

• 한국추진공학회지
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• 제25권1호
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• pp.19-28
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• 2021

회전 데토네이션 엔진(Rotating Detonation Engine, RDE)은 기계 장치나 유동이 아닌 데토네이션 파만이 연소실 벽을 따라 회전한다. 따라서 RDE 단면이 원형이어야 할 필요가 없으며 임의 단면의 닫힌 형상이 가능하다. 본 연구에서는 임의의 단면을 가지는 RDE의 한 가지 예로써 tri-arc 단면 형상의 RDE를 설계하였으며, 실험적으로 작동 및 성능 특성을 살펴보았다. 동압 센서와 고속카메라를 통하여 데토네이션 파의 회전을 확인하였으며, 오목 면과 볼록 면에서 질량 유량에 따른 데토네이션파의 특징을 알아보았다. 본 연구에서는 유량 조건에 따라 17.0 N에서 96.0 N의 추력 수준을 얻을 수 있었다.

• 한국동물학회:학술대회논문집
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• 한국동물학회 1996년도 한국생물과학협회 국제학술대회
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• pp.273.1-273
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• 1996

No Abstract, See Full Text

• 한국수자원학회논문집
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• 제42권4호
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• pp.271-279
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• 2009

본 연구는 단순한 직사각형 하도에서 발생한 댐 붕괴 및 홍수전파 등에서 만족스러운 결과를 보였던 Riemann 근사해법을 이용한 1차원 유한체적기법을 불규칙한 하도형상의 자연하도에 적용하기 위하여 새로운 기법을 개발하는 것이 목적이다. 이를 위하여 자연하천 단면을 등가의 직사각형 단면으로 변환하는 개념을 도입하였으며, 그 결과, 운동량방정식이 수정되었다. 새롭게 개발된 기법을 정확해가 존재하는 삼각형 단면하도의 댐 붕괴 흐름에 적용하고 그 결과를 비교함으로써, 기법의 정확성 및 적용성이 검증되었다. 단면의 형상 및 단면간 거리가 균일하지 않는 자연하도에 적용한 결과는 실측수위와 비교하여 홍수파의 전파 양상, 도수의 발생 위치 및 크기, 그리고 전 구간에서의 최대 수위가 잘 일치함을 나타낸다. 본 연구결과로부터 기존의 균일한 단면을 사용하여 개발된 기법들을 복잡한 수치처리과정 없이 자연하천 단면에 직접 적용할 수 있을 것으로 판단된다.

• 한국가금학회지
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• 제7권2호
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• pp.28-36
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• 1980

This study was carried out to estimate combining abilitie or economic traits in layer chickens. The data used in this study were the record of 10 single crosses produced by half diallel cross of 5 lines of Single Comb White Leghorns, such as A, B, C, K and S lines. Total 720 progenies of the crosses were reared at the Poultry Breeding Farm, College of Agriculture, Seoul National University from Feb. 1979 to August, 1980. Combining abilities were estimated by Grilling's mathematical model for the traits; age the first egg, total egg number, egg weight and body weight. The results attained from the studies were summarized as follows; In estimate of combining ability, an age at first egg of BS cross was largely due to significiantly higher general combining ability (G. C. A.) effect of B and S strains than Cand K strains in G. C. A. effect, and to specific combining ability (S. C. A) effect of B and S-trains. AB and BS crosses showed the highest egg Production. AB cross performance was result from high G.C.A. effect of A ana B strains. BS cross performance was result from high G. C. A. effect of B and high S. C. A. effect of BS cross. Specific combining ability effect in egg. weight was not statiscally significiant, but S strain showed high G. C. A. effect. A and B strains in body weight showed significantly low C. C. A. effect. From the above results, BS cross in an age at first egg, AB and BS crosses in egg Production, S strain in egg weight and AB cross in body weight were superior to other strains or crosses.