Blog posts

Dr George Rankine Irwin (26 February 1907 - 9 October 1998) was an American scientist in the field of fracture mechanics and strength of materials. He was internationally known for his study of fracture of materials. Read more...

Also see his acceptance speech upon receiving the Timoshenko Medal.

Innovation Hall of Fame, University of Maryland.

Last year, I attended the course ES139/239 in Division of Engineering and Applied Sciences, Harvard University, the innovation in science and technology. The final project of my group was about carbon nanotube (CNT). In the stage of popping up ideas, we did not consider any feasibility issues, and just used our imagination to create fancy ideas. I was inspired by other guys a lot, felt too excited after the evening brainstorm session, and wrote down the ideas I coined up. Some of them are not nonsense, e.g. replacing Cu by CNT as conductor in integrated circuit (IC). Later on, I find a piece of news in nanotoday (Dec. 2005) that the company Arrowhead Research was to provide $680,000 over two years to Duke University to develop technology for IC based on CNTs. Of course, I am not the first one to come up with this idea. But this means the random imaginative idea is very helpful and sometimes feasible. Another point I learned from this course is to write down at least one idea per day. Keep doing this, then you have a large pool of ideas. One year later, you have 365 ideas. Don’t expect every idea to be useful. Even if just one or two of them are great, it is worthy doing. Imagine that if the future technology originated from one of your ideas, you will contribute the society and feel fullness of ecstasy. If you can realize your idea, you can be a millionaire or billionaire, and then lie on the beach of Caribbean to enjoy the sunshine.

(Initially posted in Applied Mechanics News on 25 July 2006)

In an entry on pay per paper, I alluded to Chris Anderson's new book, The Long Tail. It should be straightforward to collect page views or down loads or citations of individual papers in a journal. You can plot the numbers of hits of individual papers against the rankings of the papers. Here is the curve for articles in Slate. (Not sure why data stopped at top 500 hits. Why not go further to see a really long tail?) Hope someone in Applied Mechanics will show the same data for JMPS, IJSS, MOM, etc. It will be fun.

Here is the gist of Anderson's observation: If you care about the total sale, as a publisher might, then what matters is the area under the curve; the contribution of the tail may rival that of the head. This much is objective, and should not be controversial.

Now allow me to play a variation of the theme, which is admittedly subjective and possibly controversial. Let's say the net contribution of a journal to new knowledge is proportional to the area under the curve (the subjective part). Then numerous less cited papers may make a significant contribution comparable to the contribution made by the best cited papers.

If you are interested in this argument, you might as well generalize the analysis from a single journal to all journals in a field, or to all journals in science, engineering and medicine. I'm not sure if such a curve has ever been plotted, but the job should not be too hard.

Now, if you are an individual author, surely you'd like to have a lot of hits for your own papers, just as Anderson is celebrating his book becoming a best seller. However, if your job is to increase the total knowledge, as the NSF is set up to do, then you might as well pay as much attention to the long tail as to the tall head.

Carbon nanotube has been widely investigated and perceived as having great potential in nanomechanical and nanoelectronic devices due to uniqe combination of mechanical, electrical and chemical properties. The carbon nanotubes may be applied (a) as light-weight structural materials with extraordinary mechanical properties such as stiffness and strength; (b) in nano-electronic components as the next-generation of semi-conductors and nanowires; (c) as probes in scanning probe microscopy and atomic force microscopy with the added advantage of a chemically-functionalized tip; (d) as high-sensitivity microbalances; (e) as gas and molecule sensors; (f) in hydrogen storage devices thanks to its high surface-volume ratio; (g) as field-emission type displays; (h) as electrodes in organic light-emitting diodes and (i) as tiny tweezers for nanoscale manipulation, to name a few.

As a postdoc in Xi Chen's group, my current research in the mechanics of carbon nanotubes concentrates in the following areas: a) thermal vibration and application as strain/mass/specie sensors; b) buckling of nanotubes caused by compression, bending, torsion, and indentation; c) mechanical properties of carbon nanotubes in axial and radial directions, and effective continuum modeling; d) fluid conduction in nanotubes. I have published 14 journal papers since 2005 in these areas. I will introduce more details in my blog later.

One possible design of stretchable integrated circuits consists of functional islands of stiff thin films on a polymer substrate. When such a structure is stretched, the substrate carries most of the deformation while the islands experience little strain. However, in practice, the island/substrate interface can never cohere perfectly. Existing experiments suggest that, interface debonding occurs if the island is larger than a certain size. I am now studying the critical size of stiff islands on stretchable polymer substrates due to thin film delamination, using finite element simulations. We show that the maximum energy release rate of interfacial cracking goes down as island size or substrate stiffness decreases. As a result, the critical island size can be enhanced if the substrate is chosen to be more compliant. An approximate formula is given to predict the energy release rate for the configuration of stiff islands on very compliant substrate.