An Optimal Trade-off between Content Freshness and Refresh Cost

Caching is an effective mechanism for reducing bandwidth usage and alleviating server load. However, the use of caching entails a compromise between content freshness and refresh cost. An excessive refresh allows a high degree of content freshness at a greater cost of system resource. Conversely, a deficient refresh inhibits content freshness but saves the cost of resource usages. To address the freshness-cost problem, we formulate the refresh scheduling problem with a generic cost model and use this cost model to determine an optimal refresh frequency that gives the best tradeoff between refresh cost and content freshness. We prove the existence and uniqueness of an optimal refresh frequency under the assumptions that the arrival of content update is Poisson and the age-related cost monotonically increases with decreasing freshness. In addition, we provide an analytic comparison of system performance under fixed refresh scheduling and random refresh scheduling, showing that with the same average refresh frequency two refresh schedulings are mathematically equivalent in terms of the long-run average cost

The geography of simply-connected symplectic manifolds

summary:By using the Seiberg-Witten invariant we show that the region under the Noether line in the lattice domain $\mathbb{Z}\times \mathbb{Z}$ is covered by minimal, simply connected, symplectic 4-manifolds

Guided instruction with Logo programming and the development of cognitive monitoring strategies among college students

As our society changes and becomes more complex, and as new knowledge and technology emerge, the need for teaching students to be independent thinkers and problem solvers increases more rapidly than ever before. Responding to the ever increasing societal demands, educators have sought for proper learning tools and methodologies to improve students\u27 higher-order thinking and problem solving skills. In particular, cognitive monitoring has been a primary concern of educators and cognitive psychologists. Cognitive monitoring has been regarded as one of the most important strategies in efficient thinking and problem solving. Logo programming has been considered a powerful tool to help students develop higher order thinking, an awareness of their thinking processes, and problem solving skills. Unfortunately, little evidence has been collected for the development of cognitive monitoring and problem solving through Logo programming;This research examined the effects of guided instruction with Logo programming on the development of cognitive monitoring strategies among college students. Guided instruction in this study involved three pedagogical elements. First, Logo programming was selected as a particular learning tool to teach cognitive monitoring strategies. Second, an explicit instructional model of cognitive monitoring processes was included in the process of solving Logo problems: decomposing, planning, executing, identifying errors, and debugging. Third, teacher mediated practice of cognitive monitoring activities was facilitated in a Logo programming environment as well as outside of the programming domain;The results of this study demonstrated positive effects of guided instruction with Logo programming on both near transfer and far transfer of cognitive monitoring strategies. The result also indicated that guided instruction contributed most significantly to the development of Logo error identification and debugging skills

Intercultural competence for future leaders of educational technology and its evaluation

Demands of globalization today continue to increase pressure for the education of global citizens who preserve the variety and vitality of life. Our transatlantic project has been developing a shared community of graduate students and faculty experts in educational technology across six universities. Evidence of the development of intercultural competence was analyzed from artifacts, self-report, interviews, and surveys. The findings showed that students gained intercultural competence in professional and personal spheres, with openness and flexibility that include acceptance, adaptability, and multiple perspectives. Applications of educational technology served as a bridge to introduce new cultures, knowledge and people to students.Demands of globalization today continue to increase pressure for the education of global citizens who preserve the variety and vitality of life. Our transatlantic project has been developing a shared community of graduate students and faculty experts in educational technology across six universities. Evidence of the development of intercultural competence was analyzed from artifacts, self-report, interviews, and surveys. The findings showed that students gained intercultural competence in professional and personal spheres, with openness and flexibility that include acceptance, adaptability, and multiple perspectives. Applications of educational technology served as a bridge to introduce new cultures, knowledge and people to students

Intercultural competence for future leaders of educational technology and its evaluation

Demands of globalization today continue to increase pressure for the education of global citizens who preserve the variety and vitality of life. Our transatlantic project has been developing a shared community of graduate students and faculty experts in educational technology across six universities. Evidence of the development of intercultural competence was analyzed from artifacts, self-report, interviews, and surveys. The findings showed that students gained intercultural competence in professional and personal spheres, with openness and flexibility that include acceptance, adaptability, and multiple perspectives. Applications of educational technology served as a bridge to introduce new cultures, knowledge and people to students.Demands of globalization today continue to increase pressure for the education of global citizens who preserve the variety and vitality of life. Our transatlantic project has been developing a shared community of graduate students and faculty experts in educational technology across six universities. Evidence of the development of intercultural competence was analyzed from artifacts, self-report, interviews, and surveys. The findings showed that students gained intercultural competence in professional and personal spheres, with openness and flexibility that include acceptance, adaptability, and multiple perspectives. Applications of educational technology served as a bridge to introduce new cultures, knowledge and people to students

Cultural Foundations of Contentious Democracy in South Korea

This study takes a cultural approach to examine the unstable and contentious nature of Korean democracy. Analyzing an original nationwide survey conducted in 2015, we find that the democratic and participatory culture of the Korean people underlies Korean democracy. This finding suggests substantial tension between the participatory orientation of the public and Korean representative democracy

Development of a high yield purification process for the production of influenza virus vaccines

Production of influenza virus in animal cells has emerged as an alternative to conventional platforms such as egg-based production system. Animal cells, especially MDCK and VERO cell lines, are widely used as the primary production cell for influenza virus vaccine because of their high susceptibility to infection with various influenza viruses. Recently, a robust and reliable purification process was successfully developed for the production of quadri-valent HA proteins (from two strains of the type A virus and two strains of the type B virus) by using animal cell-based production system in Green Cross Corp., Korea. The UF/DF process, Benzonase treatment at high temperature as well as column chromatography strategy was optimized to maximize the final HA production yields. Benzonase treatment was conducted to reduce in hcDNA (host cell DNA) because hcDNA was main impurity for cell-based influenza virus vaccine. A simple and stable UF/DF process has been tested with membrane molecular weight cutoffs of 100 and 300 kDa as well as 0.2 and 0.45 um microfiltration membrane. Anion exchange chromatography (AEC) and size exclusion chromatography (SEC) were selected for acceptable reduction in hcDNA and HCP. AEC was used to separate hcDNA from virus at a salt concentration of 0.5 M sodium chloride. The HA yield through AEC & SEC combination process was sufficiently achieved under specific purification process condition. Overall, the amount of residual hcDNA was reduced to an acceptable level (10ng/dose) and the increased HA yield was maintained throughout the whole process. The performance, productivity and scalability of the purification process were successfully demonstrated in over 30 GMP batches using 4 different influenza virus strains