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Wei Hong's picture

Interplay between elastic interactions and kinetic processes in stepped Si (001) homoepitaxy

A vicinal Si (001) surface may form stripes of terraces, separated by monatomic-layer-high steps of two kinds, SA and SB. 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, SA is less mobile than SB. 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 (SA+SB) step pairs.

Preprint available in the attachment.

Ting Zhu's picture

Linking Interfacial Plasticity to Ductility: A Modeling Framework for Nanostructured Metals

Ting Zhu, Ju Li, Amit Samanta, Hyoung Gyu Kim and Subra Suresh

Nano-twinned copper exhibits an unusual combination of ultrahigh strength and high ductility, along with increased strain-rate sensitivity. We develop a mechanistic framework for predicting the rate sensitivity and elucidating the origin of ductility in terms of the interactions of dislocations with interfaces. Using atomistic reaction pathway calculations, we show that twin boundary (TB) mediated slip transfer reactions are the rate-controlling mechanisms of plastic flow. We attribute the relatively high ductility of nano-twinned copper to the hardenability of TBs as they gradually lose coherency during deformation. These results offer new avenues for tailoring material interfaces for optimized properties.

see the attached pdf file

Zhigang Suo's picture

How does iMechanica relate to Applied Mechanics Blogs?

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In January 2006, with the encouragement of the Executive Committee of the ASME Applied Mechanics Division, several volunteers initialed Applied Mechanics News (AMN), a blog of news and views of interest to the international community of Applied Mechanics, accompanied by sister blogs covering research and researchers, conferences, and jobs. Within weeks, AMN topped the list on Google, Yahoo and MSN for the query of applied mechanics news. By late August 2006, the four sister blogs had a total of over 65,000 page loads, and on average over hundred unique visitors every day, from all over the world.

The Internet has enabled AMN to be international and inter-organizational. The news can be updated continuously by many volunteers. Some of the initial thoughts of AMN was collected in the entry Applied Mechanics in the Age of Web 2.0.

Teng Li's picture

Why should you post in iMechanica?

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Because you love mechanics and because you want to help others to learn mechanics. Well, these may be part of the reason. Perhaps more importantly, you would like to help yourself by helping others to discover you and your research.

Xi Chen's picture

A molecular dynamics-decorated finite element framework for simulating the mechanical behaviors of biomolecules

Cover of Biophysical JournalOur first paper in biomechanics is featured as the cover of the Biophysical Journal. The paper is attached. Several freelance writers in biophysics have reported this paper in magazines and websites/blogs. This framework is very versatile and powerful, and we are now implementing more details/atomistic features into this phenomenological approach, and the follow-up paper will be submitted soon.

Abstract: The gating pathways of mechanosensitive channels of large conductance (MscL) in two bacteria (Mycobacterium tuberculosis and Escherichia coli) are studied using the finite element method. The phenomenological model treats transmembrane helices as elastic rods and the lipid membrane as an elastic sheet of finite thickness; the model is inspired by the crystal structure of MscL. The interactions between various continuum components are derived from molecular-mechanics energy calculations using the CHARMM all-atom force field. Both bacterial MscLs open fully upon in-plane tension in the membrane and the variation of pore diameter with membrane tension is found to be essentially linear. The estimated gating tension is close to the experimental value. The structural variations along the gating pathway are consistent with previous analyses based on structural models with experimental constraints and biased atomistic molecular-dynamics simulations. Upon membrane bending, neither MscL opens substantially, although there is notable and nonmonotonic variation in the pore radius. This emphasizes that the gating behavior of MscL depends critically on the form of the mechanical perturbation and reinforces the idea that the crucial gating parameter is lateral tension in the membrane rather than the curvature of the

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Mission. The mission of iMechanica is

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See evolving history and recent numbers of iMechanica.

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Zhigang Suo's picture

Plan activities of the Applied Mechanics Division at 2007 ASME Congress

The ASME International Mechanical Engineering Congress and Exposition (IMECE) will be held in 11-16 November 2007, in Seattle, Washington. As the 2007 Program Chair of the Applied Mechanics Division (AMD), I hope to get you involved in planning activities at the Congress.

IMECE is a place where you can meet people and attend talks in Applied Mechanics, as well as in other fields, such as Materials, Electronic Packaging, Tribology, and Heat Transfer. For many mechanicians, a highlight of the Congress is the Applied Mechanics Annual Dinner, where old acquaintances are resumed, new friends made, awards announced, and the Timoshenko lectures delivered.

Teng Li's picture

Review Articles on Flexible Electronics

[img_assist|nid=46|title=|desc=|link=url,http://www.materialstoday.com/2006_issues/april.htm|align=right|width=75|height=100]The cover story of the April 2006 issue of Materials Today features Flexible Electronics. This issue also includes two review articles in this emerging field of research. Access to full text articles is free of charge at http://www.materialstoday.com.

Review Article:

Material challenge for flexible organic devices, by Jay Lewis

Review Article:

Organic and polymer transistors for electronics, by Ananth Dodabalapur

Cover Story:

Jet printing flexible displays, by R.A. Street et al.

Zhigang Suo's picture

Let us seize the greatest opportunity of our time

We've been hearing rumors that print is dead, killed by the Internet. What is the reality then? For example, how are newspapers doing? Not too badly, according to the numbers cited by James Surowiecki, of The New Yorker. He also made the following remarks, however.

"The popular conviction that papers are doomed may cause owners and shareholders to prefer the cash-cow approach, accepting eventual oblivion while continuing to harvest billions of dollars in profits. Settling for a tolerable short-term future, newspapers could end up writing themselves out of the long-term one. Yet it’s also clear that this moment of supposed doom represents a sizable opportunity for newspapers, a chance to reinvigorate their product and, eventually, improve the economics of their business."

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