PURPOSES: Implementation and verification of the simple linear cohesive viscoelastic contact model that can be used to simulate dynamic behavior of sticky aggregates. METHODS: The differential equations were derived and the initial conditions were determined to simulate a free falling ball with a sticky surface from a ground. To describe this behavior, a combination of linear contact model and a cohesive contact model was used. The general solution for the differential equation was used to verify the implemented linear cohesive viscoelastic API model in the DEM. Sensitivity analysis was also performed using the derived analytical solutions for several combinations of damping coefficients and cohesive coefficients. RESULTS : The numerical solution obtained using the DEM showed good agreement with the analytical solution for two extreme conditions. It was observed that the linear cohesive model can be successfully implemented with a linear spring in the DEM API for dynamic analysis of the aggregates. CONCLUSIONS: It can be concluded that the derived closed form solutions are applicable for the analysis of the rebounding behavior of sticky particles, and for verification of the implemented API model in the DEM. The assumption of underdamped condition for the viscous behavior of the particles seems to be reasonable. Several factors have to be additionally identified in order to develop an enhanced contact model for an asphalt mixture.

This study was to evaluate the efficacy of sanitizer concentrations and treatment time against two major food-borne pathogenic microorganisms such as Escherichia coli and Staphylococcus aureus on a stainless steel surface. As a result, stainless steel, treated with 100 ppm of chlorine showed reduction of E. coli(1.56, 1.49, 1.95 log cfu/25 ㎠) and S. aureus(0.49, 0.88, 1.27 log cfu/25 ㎠) after 0, 5 and 10 min, but none was not detected in treatment with 200 ppm. The population of E. coli(0.73, 0.90, 1.55 log cfu/25 ㎠) and S. aureus(0.37, 1.00, 1.45 log cfu/25 ㎠) reduced in 35.5% ethanol treated group, but none was not detected in treatment with 70%. The population was reduced E. coli(0.28, 0.64, 1.07 log cfu/25 ㎠) and S. aureus(0.53, 0.87, 0.99 log cfu/25 ㎠) by treatment with 45.5ppm of hydrogen peroxide, but none was not detected in treatment with 91 ppm. Quarternary ammonium compound with 100 ppm was reduced E. coli(0.82, 1.62, 1.71 log cfu/25 ㎠) and S. aureus(0.46, 0.93, 1.38 log cfu/25 ㎠), but none was not detected in treatment with 200 ppm. Predictive models of sterilization for all 4 disinfectants were suitable to use with r2 value of higher than 0.94. These models may be of use to food services and manufacture of safe products by controlling E. coli and S. aureus without the need for further detection of the organisms.

목적: 콘택트렌즈 착용시 렌즈가 각막에 부착된 상태를 정확하게 파악하기 위해서는 콘택트렌즈 운동에 대한 이해가 필요하다. 이 중 순목에 수반되는 렌즈의 움직임은 각막에 산소 공급 뿐 아니라 안정된 교정시력을 확보할 수 있다는 점에서도 매우 중요하다. 방법: 순목시 콘택트렌즈의 위치 이동은 눈꺼풀이 렌즈를 누르는 압력, 안쪽 눈꺼풀과 콘택트렌즈 사이의 미끄럼 마찰, 순목에 소요되는 시간, 눈꺼풀이 움직이는 최대 수직거리 등에 의해 결정되므로 순목 직후의 콘택트렌즈 위치는 이러한 순목 관련 요소와 함수관계에 있다고 생각할 수 있다. 결과: 눈꺼풀과 렌즈의 마찰력이 관여하는 눈꺼풀의 운동을 설명할 수 있고, 순목시 콘택트렌즈의 직경, 순목시간, 눈꺼풀의 압력 등의 변수에 따른 콘택트렌즈 위치 및 콘택트렌즈 착용시 발생할 수 있는 문제점을 예측할 수 있는 뉴턴의 운동 방정식 모델을 수립하였다. 결론: 본 연구의 운동방정식 모델을 측정 가능한 변수인 순목 속도와 눈꺼풀 두께를 이용한 선행된 임상연구와 비교한 결과 좋은 일치를 보여 타당성을 확인할 수 있었다.