Archive for February 23rd, 2011

The teaching triangle or pyramid?

February 23, 2011

Jay Parini, in his Art of teaching, says, that for instruction, all you need is a student, a teacher and some log to sit on. Generalizing the log, and calling it the tools, one sees that the teaching triangle has for its vertices the tools, the teacher and the student. All three are essential for teaching to happen. However, what ties together all these three vertices is the subject of discussion. Thus, it is more of a pyramid with the subject of discussion forming the fourth vertex.

So, what happens, if any of the vertices disentangle from any other? Obviously, the pyramid collapses. When I am teaching and/or preparing to teach, I continuously worry about my holding on to the vertices of students, subject and tools. While I have control (or, at least I tend to think that I have control) over the subject end and tools end, sometimes, I tend to lose the students — individually or, worse still, as a group. Of course, this might be due to the fact that I have not yet mastered the tools and the subject well enough to make students stick to the task of instruction and sharing. But, the feeling that in spite of your best efforts students get disentangled from the process for reasons outside of your purview and control does pop up occasionally; and, it is quite frustrating when I get such a feeling.

ArunN points to a piece in Chronicle which talks about the problem of students disentangling from the other vertices, the possible reasons and causes for this disentanglement (some of which do lie outside the college campus) and some hints as to what helps in preventing such disentanglement:

Arum and Roksa point out that students in math, science, humanities, and social sciences—rather than those in more directly career-oriented fields—tend to show the most growth in the areas measured by the Collegiate Learning Assessment, the primary tool used in their study. Also, students learn more from professors with high expectations who interact with them outside of the classroom. If you do more reading, writing, and thinking, you tend to get better at those things, particularly if you have a lot of support from your teachers.

The piece seems to be the first in a series; may be it is worth while to follow it up and think on some of the issues discussed!

Update: Another piece about teaching; I can see one difference though; unlike patients who do want to be cured of their current ailments, students might be happy with their current status, or, might want something else which is not part of the mandate!

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Ultrafast nanodiffraction and detection of nanoscale propagating waves

February 23, 2011

Electron microscopes are the eyes of a materials engineer and physical metallurgist; and, the interpretation of an electron microscopic image is not straight-forward, making this process of looking at structures at the atomic and meso-scale levels both exciting and challenging. This is the reason why, even though I never looked at any structure under the microscope, I still am excited about advances in microscopy — my more knowledgeable colleagues will then be able look at things and tell us what they find, which, in turn might give us some ideas and understanding of structures and hence their properties.

Here is a paper in the latest PNAS on nanodiffraction to study wave propagation at the nanoscale:

Coherent atomic motions in materials can be revealed using time-resolved X-ray and electron Bragg diffraction. Because of the size of the beam used, typically on the micron scale, the detection of nanoscale propagating waves in extended structures hitherto has not been reported. For elastic waves of complex motions, Bragg intensities contain all polarizations and they are not straightforward to disentangle. Here, we introduce Kikuchi diffraction dynamics, using convergent-beam geometry in an ultrafast electron microscope, to selectively probe propagating transverse elastic waves with nanoscale resolution. It is shown that Kikuchi band shifts, which are sensitive only to the tilting of atomic planes, reveal the resonance oscillations, unit cell angular amplitudes, and the polarization directions. For silicon, the observed wave packet temporal envelope (resonance frequency of 33 GHz), the out-of-phase temporal behavior of Kikuchi’s edges, and the magnitude of angular amplitude (0.3 mrad) and polarization Graphic elucidate the nature of the motion: one that preserves the mass density (i.e., no compression or expansion) but leads to sliding of planes in the antisymmetric shear eigenmode of the elastic waveguide. As such, the method of Kikuchi diffraction dynamics, which is unique to electron imaging, can be used to characterize the atomic motions of propagating waves and their interactions with interfaces, defects, and grain boundaries at the nanoscale.

Have fun!