Gyoungho Lee

Effectiveness of slow freezing and vitrification for long-term preservation of mouse ovarian tissue.

This study was conducted to evaluate the interaction between cryo-damage and ART outcome after cryopreservation of mouse ovarian tissues with different methods. Either a vitrification or a slow freezing was employed for the cryopreservation of B6CBAF1 mouse ovaries and follicle growth and the preimplantation development of intrafollicular oocytes following parthenogenesis or IVF were monitored. Both cryopreservation protocols caused significant damage to follicle components, including vacuole formation and mitochondrial deformities. Regardless of the cryopreservation protocols employed, a sharp (P < 0.0001) decrease in follicle viability and post-thaw growth was detected. When IVF program was employed, significant (P < 0.05) decrease in cleavage and blastocyst formation was notable in both modes of cryopreservation. However, such retardation was not found when oocytes were parthenogenetically activated. In the IVF oocytes, slow freezing led to better development than vitrification. In conclusion, a close relationship between cryopreservation and ART methods should be considered for the selection of cryopreservation program.

Evaluation of Anti-SE Bacteriophage as Feed Additives to Prevent Salmonella enteritidis (SE) in Broiler

This experiment was conducted to evaluate anti-Salmonella enteritidis (anti-SE) bacteriophage as feed additives to prevent Salmonella enteritidis in broilers. The experimental diets were formulated for 2 phases feeding trial, and 3 different levels (0.05, 0.1 and 0.2%) of anti-SE bacteriophage were supplemented in basal diet. The basal diet was regarded as the control treatment. A total of 320 1-d-old male broilers (Ross 308) were allotted by randomized complete block (RCB) design in 8 replicates with 10 chicks per pen. All birds were raised on rice hull bedding in ambient controlled environment and free access to feed and water. There were no significant differences in body weight gain, feed intake and feed conversion ratio (FCR) at terminal period among treatments (p>0.05). Relative weights of liver, spleen, abdominal fat and tissue muscle of breast obtained from each anti-SE bacteriophage treatment were similar to control, with a slightly higher value in anti-SE bacteriophage 0.2%. In addition, a numerical difference of glutamic-oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT) and LDL cholesterol level was observed in the 0.2% anti-SE bacteriophage application even though blood profiles were not significantly affected by supplemented levels of anti-SE bacteriophage (p>0.05). In the result of a 14 d record after Salmonella enteritidis challenge of 160 birds from 4 previous treatments, mortality was linearly decreased with increasing anti-SE bacteriophage level (p<0.05), and Salmonella enteritidis concentration in the cecum was decreased with increasing levels of anti-SE bacteriophage (p<0.05). Based on the results of this study, it is considered that supplementation of 0.2% anti-SE bacteriophage may not cause any negative effect on growth, meat production, and it reduces mortality after Salmonella enteritidis challenge. These results imply to a possible use of anti-SE bacteriophage as an alternative feed additive instead of antibiotics in broilers diet.

Identifying student difficulty in problem solving process via the framework of the House Model (HM)

Recently, many students have been losing their interest in physics. One of the essential reasons why students look away from physics is the fact that they face difficulty in solving physics problems. Since mechanics is a fundamental subject in physics, many researchers have studied how students learn mechanics and solve problems related to mechanics. However, there is little research on the students’ specific difficulties in the process of problem solving. This study investigated degree of students’ difficulties in process and the core sources of these difficulties. 24 university students who majored in physics education participated in this study. We have developed a framework, House Model (HM), for helping and analyzing students’ problem solving. We found that students felt greater difficulty in planning and executing steps than in visualizing, knowing and finding steps. As the problems grew in difficulty, this pattern became more distinct. We also found the sources of the students’ difficulties and dis...

Alternative conceptions, memory, & mental models in physics education

There are two somewhat independent research traditions, which converge to suggest a form of students’ knowledge: alternative conceptions and mental models. However we have little literature that explains what they are different from each other and from memory. This study tried to describe these issues with some thoughts about how cognitive psychology and science education approaches can be best synthesized in order to approach these questions.

Do general physics textbooks discuss scientists’ ideas about atomic structure? A case in Korea

Research in science education has recognized the importance of teaching atomic structure within a history and philosophy of science perspective. The objective of this study is to evaluate general physics textbooks published in Korea based on the eight criteria developed in previous research. The result of this study shows that Korean general physics textbooks often lack detail about the history and philosophy of science. This result is quite similar to those published for the USA. Furthermore, chemistry textbooks published in the USA, Turkey and Venezuela are quite similar to the physics textbooks. This is a cause for concern as textbooks present theories as facts and ignore the historical reconstructions based on the development of scientific theories that frequently involve controversies and conflicts among scientists. The inclusion of historical reconstructions of ideas about atomic structure can provide students with a better appreciation of the dynamics of scientific progress.

In vitro-growth and Gene Expression of Porcine Preantral Follicles Retrieved by Different Protocols

This study was conducted to determine how the isolation method of the porcine preantral follicles influenced the following follicular growth in vitro. Mechanical and enzymatical isolations were used for retrieving the follicles from prepubertal porcine ovaries, and in vitro-growth of the follicles and the expression of folliculogenesis-related genes were subsequently monitored. The enzymatic retrieval with collagenase treatment returned more follicles than the mechanical retrieval, while the percentage of morphologically normal follicles was higher with mechanical retrieval than with enzymatic retrieval. After 4 days of culture, mechanically retrieved, preantral follicles yielded more follicles with normal morphology than enzymatically retrieved follicles, which resulted in improved follicular growth. The mRNA expression of FSHR, LHR Cx43, DNMT1 and FGFR2 genes was significantly higher after culture of the follicles retrieved mechanically. These results suggest that mechanical isolation is a better method of isolating porcine preantral follicles that will develop into competent oocytes in in vitro culture.

Resolving Dilemmas in Acquiring Knowledge of Newton’s First Law: Is the History of Science Helpful?

A historical approach has been regarded as one of the most useful ways of teaching science. Many studies in science education have in fact recognized the importance of the history of science (Niaz, 1998). For instance, Solomon (1989) argued that the teaching of the history of science would be useful in the following ways: displaying science as culture; illustrating the nature of scientific knowledge; showing the human face of science; and understanding the social relations of science. Matthews (1994) discussed the role of history of science in promoting science teaching. He saw it enhancing better comprehension of scientific concepts and methods, and aiding in connecting the development of an individual’s thinking with scientific ideas. The history of science is intrinsically worthwhile, being necessary for an understanding of the nature of science and counteracting the influence of scientism and dogmatism. It also humanizes the subject matter and allows connections to be made among different topics and disciplines of science.

Addressing Students’ Difficulties in Understanding Two Different Expressions of Gravitational Potential Energy (I): mgh & −GMm/r

During our investigation of students’ understanding of gravitational potential energy, we found some difficulties that students have with this topic. Many students who took upper‐level mechanics courses had difficulties in understanding why there are two different expressions of gravitational potential energy. These students said they had some difficulties in understanding why there should be two different signs (+ & −) and two different forms (g & 1/r) even though these expressions were considered as representing the same gravitational potential energy. To gain understanding of the sources of student difficulties, we used weekly reports and individual interviews. We analyzed student difficulties in terms of conceptual knowledge, procedural knowledge, and contextual knowledge. The results of these research have guided the development of teaching material that addresses students’ difficulties in understanding gravitational potential energy. We will show the development process and contents of the material ...