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점토층위의 모래지반에 위치한 얕은 기초의 지지력에 대한 상한 한계해석
김대현,야마모토켄타로 한국지반공학회 2004 한국지반공학회논문집 Vol.20 No.3
본 연구는 점토층위의 모래지반에 위치하는 표면기초의 극한지지력에 대해 이론적으로 조사하였다. 실용적인 적용을 위하여 표면기초의 지지력에 관한 연구들에 대한 검토와 논의가 제시되며, 한계해석(Limit Analysis)의 운동학적 접근방법을 이용하여 정해의 극한 지지력이 계산되었다. 운동학적 해는 상한값이며 해의 정확성은 파괴메카니즘의 형상에 달려 있다. 이러한 방법은 설계도표를 만드는데 편리할 뿐만 아니라 물성치의 영향을 추정할 수 있다. 본 연구에서는 범용 유한요소해석 프로그램인 ABAQUS를 사용하여 탄소성 이론에 근거하여 극한지지력을 계산하였다. 운동학적 방범으로 계산된 결과와 유한요소 해석, 한계평형론에 근거한 몇몇 알려진 식들(Yamaguchi, Meyerhof와 Okamura 등)에 의한 결과를 비교하였다. 아울러, 운동학적 방법에 의한 제안식과 유한요소해석 결과와 한계평형해석 결과의 유효성에 대하여 검증하였다. The ultimate bearing capacity of surface foundations on a sand layer overlying clay has been theoretically investigated. First, a review of previous studies on the bearing capacity problems for this type of foundation was performed and a discussion was presented concerning the practical application. Second, the kinematic approach of limit analysis was used to calculate the upper bound of the true ultimate bearing capacity. The kinematic solutions are upper bounds and their accuracy depends primarily on the nature of the assumed failure mechanism. This approach makes it convenient to create design charts, and it is possible to trace the influence of parameters. Third, the commercial finite element program ABAQUS was applied to obtain the ultimate bearing capacity based on the elasto-plastic theory. Results obtained from the kinematic approach were compared with those from the program ABAQUS and the limit equilibrium equations proposed by Yamaguchi, Meyerhof and Okamura et al. Finally, the validities of the results from the kinematic approach, the results from the program ABAQUS and the limit equilibrium equations were examined.
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김대현,Ohr Sewon 한국생태학회 2020 Journal of Ecology and Environment Vol.44 No.3
Background : Ecologists have achieved much progress in the study of mechanisms that maintain species coexistence and diversity. In this paper, we reviewed a wide range of past research related to these topics, focusing on five theoretical bodies: (1) coexistence by niche differentiation, (2) coexistence without niche differentiation, (3) coexistence along environmental stress gradients, (4) coexistence under non-equilibrium versus equilibrium conditions, and (5) modern perspectives. Results : From the review, we identified that there are few models that can be generally and confidently applicable to different ecological systems. This problem arises mainly because most theories have not been substantiated by enough empirical research based on field data to test various coexistence hypotheses at different spatial scales. We also found that little is still known about the mechanisms of species coexistence under harsh environmental conditions. This is because most previous models treat disturbance as a key factor shaping community structure, but they do not explicitly deal with stressful systems with non-lethal conditions. We evaluated the mainstream ideas of niche differentiation and stochasticity for the coexistence of plant species across salt marsh creeks in southwestern Denmark. The results showed that diversity indices, such as Shannon–Wiener diversity, richness, and evenness, decreased with increasing surface elevation and increased with increasing niche overlap and niche breadth. The two niche parameters linearly decreased with increasing elevation. These findings imply a substantial influence of an equalizing mechanism that reduces differences in relative fitness among species in the highly stressful environments of the marsh. We propose that species evenness increases under very harsh conditions if the associated stress is not lethal. Finally, we present a conceptual model of patterns related to the level of environmental stress and niche characteristics along a microhabitat gradient (i.e., surface elevation). Conclusions : The ecology of stressful systems with non-lethal conditions will be increasingly important as ongoing global-scale climate change extends the period of chronic stresses that are not necessarily fatal to inhabiting plants. We recommend that more ecologists continue this line of research.
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김대현,배상락,최우석,박형근,백성현,김형곤,노용수 대한비뇨의학회 2014 Investigative and Clinical Urology Vol.55 No.9
Purpose: Transrectal ultrasonography-guided prostate biopsy (TRUS-Bx) is an essentialprocedure for diagnosing prostate cancer. The American Urological Association(AUA) Guideline recommends fluoroquinolone alone for 1 day during TRUS-Bx. However, this recommendation may not be appropriate in regions where the prevalenceof quinolone-resistant Escherichia coli is high. We investigated the real practice of antibioticprophylaxis for TRUS-Bx in Korea. Materials and Methods: A total of 77 hospitals performing TRUS-Bx were identifiedand an e-mail was sent to the Urology Department of those hospitals. The questionsin the e-mail included the choice of antibiotics before and after the procedure and theduration of antibiotic therapy after TRUS-Bx. Results: A total of 54 hospitals (70.0%) responded to the e-mail. Before TRUS-Bx, allhospitals administered intravenous antibiotic prophylaxis. The percentage of hospitalsthat used quinolone, cephalosporin, and aminoglycoside alone was 48.1%, 20.4%, and9.3%, respectively. The percentage of hospitals that used two or more antibiotics was22.2%. After biopsy, all 54 hospitals prescribed oral antibiotics. The percentage of hospitalsthat prescribed quinolone alone, cephalosporin alone, or a combination of two ormore antibiotics was 77.8%, 20.4%, and 1.8%, respectively. The duration of antibioticuse was more than 3 days in most hospitals (79.6%). Only four hospitals (7.4%) followedthe AUA recommendation of a 1-day regimen. Conclusions: The AUA recommendation was not followed by most hospitals in Korea. This clinical behavior might reflect the high quinolone resistance rate in Korea, andfurther studies on the most efficient prophylactic antibiotics after TRUS-Bx in Koreaare warranted.
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