Study of Ge-As-Se system with high refractive index for infrared glass molded lens

For chalcogenide-based infrared glass materials, the need was emphasized along with the spread of thermal imaging cameras in COVID 19 environment. Commercial Ge-As-Se glass system exhibits a dispersion value of 100 similar to 180 and a refractive index of 2.5 or more, and is suitable for the glass molding process, so it is used as an aspherical infrared lens for various thermal imaging cameras. However, some compositions are not suitable for glass molding process. In this study, the composition of the long wavelength infrared glass melting was designed based on the Ge-As-Se system with a Ge composition range of 0 similar to 35 at%, As composition range of 20 similar to 40 at%, and Se composition range of 25 similar to 60 at%. As a result of XRD analysis for each Ge-As-Se-based composition, it was confirmed that all amorphous grains were obtained in the developed composition area. For the Ge-As-Se glass-forming composition region, the glass transition temperature ranged from 180 to 425 degrees C. The refractive index was measured using the prism method in the 3 to 12 mu m wavelength band. The refractive index (lambda=10 mu m) of Ge5As40Se55 and Ge5As35Se60 was 2.6913 and 2.6538, respectively. Moldability test was performed using a glass molding press. As a result of observing whether the lens has internal defects and microcracks after molding, it was confirmed that there was no abnormality and that it was suitable for glass molding process.

Perception of instructor presence and its effects on learning experience in online classes

Aim/Purpose One of the most critical challenges to the student learning experience in online classes would be providing interactions between students and instruc-tors as effective as in face-to-face learning. This study introduces perceived instructor presence as a way to promote such interactions and investigates its effects on student learning experience in online learning. Background Drawing upon theories of constructivism and social presence, this study pro-poses a research model to explore the causal relationships from the interac-tivity of a communication tool to the perception of instructor presence and to student learning experiences such as engagement and satisfaction. Methodology The survey method was used to collect data from online business classes where an interactive communication tool was required to use for class com-munication and collaboration. Partial Least Squares analysis was used as the primary data analysis tool. Contribution This study introduces perceived instructor presence in the online learning context and empirically tests its effects on the online learning experience. This study also contributes to the online learning literature by confirming the constructivist's point of view on learning that interactions lead to better learning experiences, in the online learning environment. Findings The study results show that the use of an interactive communication tool in online learning fosters strong student-instructor interactions and promotes students' perceptions of instructor presence, which eventually enhances stu-dent engagement and satisfaction in online classes. Recommendations for Practitioners This study recommends practitioners (e.g., teachers and professors) to use more interactive communication tools such as Microsoft Teams and Slack to promote the instructor presence in their online classes, which ultimately in-crease student engagement and satisfaction. Practitioners are also recom-mended to develop and use any other teaching methods or activities that can increase perceived instructor presence, which has a direct impact on student engagement in online learning. Recommendations for Researchers While the fellow researchers can take one of the future research directions in this paper, it is recommended to consider more fundamental approaches to the study of online learning. For example, the concept of presence is a radical difference when courses are moved from face-to-face to online learning. Fu-ture research could investigate how various types of presence can play differ-ently in online learning. Impact on Society Better learning experiences are likely to have a significant impact on society's well-being, and the findings of this study suggest how student learning expe-riences can be improved in online classes. Furthermore, this is particularly useful when many face-to-face classes were forced to switch to online classes abruptly during the COVID-19 pandemic as many students, parents, and ed-ucators were concerned with online learning experiences. Future Research A replication study with different communication tools in various courses would be good future research to support the generalizability of the findings. Another interesting future research is to employ other types of dependent variables, such as tool adoption and academic performance. It would be worth investigating how different types of learning experiences can be associ-ated with various learning tools. As this study finds that an interactive com-munication tool is associated with student engagement, gamification can be associated with student enjoyment in online learning. © 2020.