Raymond Chastain - Academia.edu (original) (raw)
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University of Engineering and Technology Lahore
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Papers by Raymond Chastain
Astronomy & Astrophysics, 2006
Aims. We present an analysis of the exceptionally turbulent velocity field in the high Galactic l... more Aims. We present an analysis of the exceptionally turbulent velocity field in the high Galactic latitude cirrus cloud MBM 3. As in the other translucent clouds in our study (MBM 16 and MBM 40), there is no evidence for internal star formation. However, the large scale velocity variation in this cloud is more pronounced. Methods. We have mapped the cloud in 12 CO and 13 CO (1−0) at high spatial (0.03 pc) and velocity (0.06 km s −1) resolution. We constructed several velocity probability density functions (PDFs), estimated the turbulent transfer rate, and analyzed the linewidths as a function of the size of randomly chosen regions within the cloud. Results. We find strong shear flows throughout the cloud that can easily power the turbulent motions. The wings of the PDFs are well approximated by a lorentzian distribution. Such distributions, related to Levy processes that are well known to be produced by correlated processes, are an unambiguous diagnostic of the turbulent intermittency. Conclusions. We find that the linewidth-size relation frequently used to indicate the role of turbulence in molecular clouds is not an unambiguous signature of its presence.
A B S T R A C T STEM undergraduate classrooms are increasingly adopting instructional methods to ... more A B S T R A C T STEM undergraduate classrooms are increasingly adopting instructional methods to enhance student engagement and improve learning outcomes. For example, in exploratory learning, students explore novel problems before they are taught the underlying concepts and procedures. The current studies examined the benefits of exploratory learning in undergraduate physics instruction. In Studies 1 and 2, students worked collaboratively in groups to complete a learning activity before lecture (explore-first condition) or after (instruct-first condition). The two studies were conducted in different semesters, with different physics courses and instructors of record. Students' conceptual understanding and procedural knowledge (problem-solving accuracy) were assessed using an instructor-created quiz. Performance on the learning activity indicated that students in the explore-first condition struggled as much as (Study 2) or more than (Study 1) students in the instruct-first condition. However, on the quiz, students in the explore-first condition exhibited better conceptual understanding and equal procedural knowledge, compared to students in the instruct-first condition. In addition, self-reported interest and enjoyment were either equal (Study 1) or greater (Study 2) in the explore-first condition. Study 3 tested the effects of exploring alone versus in a collaborative group. Learning outcomes were equal across conditions, suggesting that there is no added learning benefit of exploring collaboratively compared to individually. However, interest and enjoyment were higher when students explored collaboratively, which may have long-term educational benefits. Exploratory learning, with or without collaboration, offers a useful method to improve student engagement and performance in essential undergraduate STEM courses.
Astronomy & Astrophysics, 2006
Aims. We present an analysis of the exceptionally turbulent velocity field in the high Galactic l... more Aims. We present an analysis of the exceptionally turbulent velocity field in the high Galactic latitude cirrus cloud MBM 3. As in the other translucent clouds in our study (MBM 16 and MBM 40), there is no evidence for internal star formation. However, the large scale velocity variation in this cloud is more pronounced. Methods. We have mapped the cloud in 12 CO and 13 CO (1−0) at high spatial (0.03 pc) and velocity (0.06 km s −1) resolution. We constructed several velocity probability density functions (PDFs), estimated the turbulent transfer rate, and analyzed the linewidths as a function of the size of randomly chosen regions within the cloud. Results. We find strong shear flows throughout the cloud that can easily power the turbulent motions. The wings of the PDFs are well approximated by a lorentzian distribution. Such distributions, related to Levy processes that are well known to be produced by correlated processes, are an unambiguous diagnostic of the turbulent intermittency. Conclusions. We find that the linewidth-size relation frequently used to indicate the role of turbulence in molecular clouds is not an unambiguous signature of its presence.
A B S T R A C T STEM undergraduate classrooms are increasingly adopting instructional methods to ... more A B S T R A C T STEM undergraduate classrooms are increasingly adopting instructional methods to enhance student engagement and improve learning outcomes. For example, in exploratory learning, students explore novel problems before they are taught the underlying concepts and procedures. The current studies examined the benefits of exploratory learning in undergraduate physics instruction. In Studies 1 and 2, students worked collaboratively in groups to complete a learning activity before lecture (explore-first condition) or after (instruct-first condition). The two studies were conducted in different semesters, with different physics courses and instructors of record. Students' conceptual understanding and procedural knowledge (problem-solving accuracy) were assessed using an instructor-created quiz. Performance on the learning activity indicated that students in the explore-first condition struggled as much as (Study 2) or more than (Study 1) students in the instruct-first condition. However, on the quiz, students in the explore-first condition exhibited better conceptual understanding and equal procedural knowledge, compared to students in the instruct-first condition. In addition, self-reported interest and enjoyment were either equal (Study 1) or greater (Study 2) in the explore-first condition. Study 3 tested the effects of exploring alone versus in a collaborative group. Learning outcomes were equal across conditions, suggesting that there is no added learning benefit of exploring collaboratively compared to individually. However, interest and enjoyment were higher when students explored collaboratively, which may have long-term educational benefits. Exploratory learning, with or without collaboration, offers a useful method to improve student engagement and performance in essential undergraduate STEM courses.