Archive for January 3rd, 2008

How anthropologists differ from bench scientists

January 3, 2008

Rex at Savage Minds ponders the question and comes up with at least two important differences:

… what really makes scientists ‘scientists’ is the distinct form of knowledge and practice that crystallizes around a lab, which creates a sort of sandbox for experimentation for some variables. At first I thought the anthropological equivalent would be our fieldnotes, since these are purified, recontextualized bits of life that can be manipulated, sorted, and searched through in a way that creates an ‘archive’ whose affordances have a scarily large effect on what sort of research results we produce.

Then it struck me—maybe it seems stupid to you that it took me this long—that the equivalent for anthropologists really is the field site. A lot of doing fieldwork means transforming your situation in your fieldsite from just ‘being in the field’ to ‘doing fieldwork’ which means creating routines, instruments, methods, and relationships which allow you to do things (like census, interviews, transcription, etc.) which are more or less like embryonic experimental systems.

If this is true, then it seems to me that anthropologists differ from bench scientists in two important ways. First, we do a lot more ‘being in the field’ and a lot less ‘fieldwork’ than most of us would care to admit—and that includes the people who see ‘fieldwork’ as alienatingly objectivistic, scientistic, obsessed with a false standards of neutrality and objectivity etc. etc. I have the idea—totally unbased on any actual evidence—that through the past couple of decades the ratio of being to doing has grown greatly. This has implications.

Second, anthropologists rarely spend much time in the field. Even ones at ‘research universities’ like me are really paid to teach, and must show tremendous amounts of hustle to get the funding together for major time in the field. This has to do with lots of things (and of course bench science in unis involves juggling teaching duties too) but key among them is that for most of us the field is just not that easy to get to, and it takes time to get things set up when you arrive.

An interesting piece!

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What is CAVE?

January 3, 2008

Victor Keegan explains in the Hindu:

The most memorable moment for me personally in 2007 was walking into an engineering laboratory at University College London, where a team led by Anthony Steed has constructed a CAVE (Cave Automatic Virtual Environment). This is a trademark of the University of Illinois, which pioneered this sort of thing years ago, based on Plato’s allegory about a cave (tinyurl.com/yq7a98). It is one of about 200 around the world, half of them run by corporations.

It is an ordinary-sized room with three walls, the fourth being left open. After putting on special spectacles (wired to a computer) I entered the room and saw a statue that might have been in the British Museum. But it wasn’t a real statue, nor a hologram, but a three-dimensional recreation of one that really did look real. I could walk most, but not all the way, around it as if it were in real life. The only thing that gave it away was that if I touched it with my finger there was nothing there, though apparently they may soon be able to programme the computer so it prompts a reaction in you as if you had touched a hard surface.

Take a look!PS: The wiki page on CAVE is very informative too, and is full of links.

Small is not just beautiful but strong too

January 3, 2008

Sometime back, while writing about studies on flow in glass, I also wrote about flow in crystals and the role in dislocations in flow; however, I did not write a detailed explanation of how dislocations help in flow.

A Science Blog post on deformation studies of nickel pillars of size between 150 and 400 nanometres gives the explanation in a rather nice manner:

“What controls the deformation of a metal object is the way that defects, called dislocations, move along planes in its crystal structure,” Minor says. “The result of dislocation slip is plastic deformation. For example, bending a paper clip causes its trillions of dislocations per square centimeter to tangle up and multiply as they run into one another and slide along numerous slip planes.”

In general, mechanical deformation tends to increase the number of dislocations in a material.

As the post goes on to explain, this explanation fails for very small crystals. How small is too small? When the the surface area of the crystal (which goes as the square of the size of the crystal) becomes larger than the volume of the crystal (which goes as the cube of the size of the crystal) by several factors,  that size is small enough.

What happens at small sizes?

“Essentially all the dislocations escape from the crystal at the surface, and you do not get storage of dislocations like you would in larger crystals,” Minor says. “What results is a process called ‘dislocation starvation,’ recently proposed by William D. Nix of Stanford, among others, which has quickly became one of the leading theories of why smaller structures are stronger.”

Minor explains, “The idea is that if dislocations escape the material before they can interact and multiply, there are not enough active dislocations to enable the imposed deformation. The structure can only deform after new dislocations are created.” This is precisely the process he and his colleagues observed with NCEM’s In Situ Microscope, strong evidence that “dislocation starvation” is the correct explanation for the increased strength of small structures.

The report is based on a paper of Shan et al, published in Nature Materials titled Mechanical annealing and source-limited deformation in submicrometre-diameter Ni crystals:

The fundamental processes that govern plasticity and determine strength in crystalline materials at small length scales have been studied for over fifty years. Recent studies of single-crystal metallic pillars with diameters of a few tens of micrometres or less have clearly demonstrated that the strengths of these pillars increase as their diameters decrease, leading to attempts to augment existing ideas about pronounced size effects with new models and simulations. Through in situ nanocompression experiments inside a transmission electron microscope we can directly observe the deformation of these pillar structures and correlate the measured stress values with discrete plastic events. Our experiments show that submicrometre nickel crystals microfabricated into pillar structures contain a high density of initial defects after processing but can be made dislocation free by applying purely mechanical stress. This phenomenon, termed ‘mechanical annealing’, leads to clear evidence of source-limited deformation where atypical hardening occurs through the progressive activation and exhaustion of dislocation sources.

Take a look!