Blog posts

I like to keep the mindset of being a student, learning from all sources on all topics I am interested. Recently I have learned quite a lot about mechanics and mechanicians from Applied Mechanics News and its sister blogs and now iMechanica.

With a job as an assistant professor, I always try to motivate my students to become future mechanicians. For this reason, I started Modeling Place as a group blog in January and gently forced my students to participate. Out of the five students I have, two actively participate by posting frequently, two occasionally post, and one dropped out quickly after one post. Together, the blog has been doing reasonably well, in terms of both quantity and quality of posts.

I learned a few tricks in handling images and got to know some interesting works in the general area of mechanics. How about the students? What benefits have they received? I have to ask them. For one, I awarded one student with a little gift as the best post of the semester. More importantly, I believe that they are reading more than they used to do, thus gaining broader knowledge and interest in mechanics and related science. They not only read the posts in the blog but also read from other sources (online or not) to find something to post. Furthermore, they have a place to practice writing. It is a big step from reading to writing, not only for foreign students I think.

It may be still too soon to tell how well this works, but the students themselves should be able to tell us more. If you are a student, I encourage you to comment on this to tell the professors what you like or don't like about iMechanica. At this stage of development, much more features and benefits can be accomodated. Your ideas could shape the future of iMechanica and benefit all students and those considering themselves as students of life.

Nanocomposite performance fundamentally relies on reproducible dispersion and arrangement of nanoparticles, such that the dominate morphology across macroscopic dimensions is also nanoscopic. To facilitate dispersion, chemical approaches, including surfactant or macromolecular stabilization are usually employed to modify the surface of nanoparticles. However, the approach depends on the material system and usually involves trial-and-error to identify the best practice. Much less quantitative information is available on the coupling between the surface modification and external processing factors, including shear, electric or magnetic fields. In a recent work, we considered electric field on the interaction of nano-plates. For ideal dielectrics an electric field may assist (or retard) exfoliation depending on the angle between a collection of plates and the field. A critical electric field strength to promote exfoliation is predicted when the field is parallel to the surface of the plates. Structural refinement is predicted to occur by cleavage through the center of the stack. For lossy dielectrics, frequency can be tuned to cause exfoliation in all plate orientations.

Here is the website for the 2006 ASME Congress. For the applied mechanics program, click "Program Overview", then choose "Applied Mechanics" from the list of topics.

Professor Rodney Ruoff and colleagues at Northwestern University and Purdue University have developed a process that promises to lead to the creation of a new class of composite materials - graphene-based materials. They reported the results of their research in Nature, 442 (2006) 282-286. This team has overcome the difficulties of yielding a uniform distribution of graphene-based sheets in a polymer matrix. Such composites can be readily processed using standard industrial technologies such as moulding and hot-pressing. The technique should be applicable to a wide variety of polymers. The graphene composites may compete with carbon nanotube-based materials in terms of mechanical properties. This new class of composites may stimulate the applied mechanics community to study the fundamental reinforcing mechanisms of graphene sheets from both experimental and theoretical approaches.

You are cordially invited to participate in the Symposium on the Mechanics of Electromagnetic Materials and Structures, the 5th International Conference on Nonlinear Mechanics (ICNM-V), to be held in Shanghai, China, June 11-14, 2007.  You may find more information at the website of the conference.

The symposium topics include piezoelectricity, ferroelectricity, magnetoelasticity, electromagnetic fluids and various applications in engineering and technology, but are not limited to the above. Experimental, theoretical, and computational studies are all welcome.

Please e-mail your one-page abstract(s) to any of us listed below. We look forward to hearing from you. If you have any questions, please do not hesitate to contact us at

Professor Ji Wang, Ningbo University, wangji [at] nbu.edu.cn (wangji[at]nbu[dot]edu[dot]cn)

Professor Yuantai Hu, Central South University, hudeng [at] 263.net (hudeng[at]263[dot]net)

Professor Jiashi Yang, University of Nebraska, jyang1 [at] unl.edu (jyang1[at]unl[dot]edu)

Professor Daining Fang, Tsinghua University, fangdn [at] tsinghua.edu.cn (fangdn[at]tsinghua[dot]edu[dot]cn)

Submission of abstract: as soon as possible.

Notification of acceptance: Nov. 1, 2006

Submission of final paper(s) for the conference proceedings: Jan. 1, 2007

A vicinal Si (001) surface may form stripes of terraces, separated by monatomic-layer-high steps of two kinds, S_A and S_B. As adatoms diffuse on the terraces and attach to or detach from the steps, the steps move. In equilibrium, the steps are equally spaced due to elastic interaction. During deposition, however, S_A is less mobile than S_B. We model the interplay between the elastic and kinetic effects that drives step motion, and show that during homoepitaxy all the steps may move in a steady state, such that alternating terraces have time-independent, but unequal, widths. The ratio between the widths of neighboring terraces is tunable by the deposition flux and substrate temperature. We study the stability of the steady state mode of growth using both linear perturbation analysis and numerical simulations. We elucidate the delicate roles played by the standard Ehrlich-Schwoebel (ES) barriers and inverse ES barriers in influencing growth stability in the complex system containing (S_A+S_B) step pairs.

Preprint available in the attachment.