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Rui Huang's picture

Nanoscience Initiative Workshop

The Air Force Office of Scientific Research (AFOSR) of the U.S. Air Force Research Laboratory (AFRL) and National Science Council (NSC) in Taiwan are pleased to announce that the 4th U.S. Air Force/Taiwan Nanoscience and Nanotechnology workshop will be held on February 8-9, 2007 at the main campus of the University of Houston. We invite you to join us at the workshop.

Tienchong Chang's picture

Nonlinear stick-spiral model for predicting mechanical behavior of single-walled carbon nanotubes

(PRB,74,245428,2006)  Based on a molecular mechanics concept, a nonlinear stick-spiral model is developed to investigate the mechanical behavior of single walled carbon nanotubes (SWCNTs). The model is capable of predicting not only the initial elastic properties (e.g., Young’s modulus) but also the stress-strain relations of a SWCNT under axial, radial, and torsion conditions. The elastic properties, ultimate stress, and failure strain under various loading conditions are discussed and special attentions have been paid to the effects of the tube chirality and tube size. Some unique mechanical behaviors of chiral SWCNTs, such as axial strain-induced torsion, circumferential strain-induced torsion, and shear strain-induced extension are also studied. The predicted results from the present model are in good agreement with existing data, but very little computational cost is needed to yield them.

A "cool" way to remove hydrogen...and possibly a faster way to grow better crystals?

In growth of essentially every compound material such as GaN, one element always diffuses faster than the other(s) at the growth front. To grow good-quality materials, even the most sluggish element has to be sufficiently mobile, forcing materials growers to go to higher growth temperatures.

Multi-phase hyperelasticity with interface energy effect

Recently, J. Wang, L. Sun and I have formulated some ideas about the effective properties of heterogeneous materials with surface/interface energy effect, which are shown in the attached file.

Papers in the attached file can be viewed as a two-part paper, called “Multi-phase hyperelasticity with interface energy effect” if it is standalone. Part one of this topic is covered in “A theory of hyperelasticity of multi-phase media with surface/interface energy effect”, which provides theoretical background. Part two is covered in “Size-dependent effective properties of a heterogeneous material with interface energy effect: from finite deformation theory to infinitesimal strain analysis”, with more emphasis on application.

Young's modulus of single-walled carbon nanotubes

We report in detail that unlike other materials, carbon nanotubes are so small that changes in structure can affect the Young's modulus. The variation in modulus is attributed to differences in torsional strain, which is the dominant component of the total strain energy. Torsional strain, and correspondingly Young's modulus, increases significantly with decreasing tube diameter and increases slightly with decreasing tube helicity.  Journal of Applied Physics 84, 1939 (1998).

Force response and actin remodeling (agglomeration) in fibroblasts due to lateral indentation

We report the loading and unloading force response of single living adherent fibroblasts due to large lateral indentation obtained by a two-component microelectromechanical systems (MEMS) force sensor. Strong hysteretic force response is observed for all the tested cells. For the loading process, the force response is linear (often with small initial non-linearity) to a deformation scale comparable to the undeformed cell size, followed by plastic yielding. In situ visualization of actin fibers (GFP) reveals that during the indentation process, actin network depolymerizes irreversibly at discrete locations to form well-defined circular actin agglomerates all over the cell, which explains the irreversibility of the force response. Similar agglomeration is observed when the cell is compressed laterally by a micro plate. The distribution pattern of the agglomerates strongly correlates with the arrangement of the actin fibers of the pre-indented cell. The size of the agglomerates increases with time as ta  with a= 2~3 initially,   followed by a=.5~1. The higher growth rate suggests influx of actin into the agglomerates. The slower rate suggests a diffusive spreading, but the diffusion constant is two orders of magnitude lower than that of an actin monomer through the cytoplasm. Actin agglomeration has previously been observed due to biochemical treatment, gamma-radiation, and ischemic injury, and has been identified as a precursor to cell death. We believe, this is the first evidence of actin agglomeration due to mechanical stimuli. The study demonstrates that living cells may initiate similar functionalities in response to dissimilar mechanical and biochemical stimuli.

Axial-Strain-Induced Torsion in Single-Walled Carbon Nanotubes

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Using classical molecular dynamics and empirical potentials, we show that the axial deformation of single-walled carbon nanotubes is coupled to their torsion. The axial-strain-induced torsion is limited to chiral nanotubes—graphite sheets rolled around an axis that breaks its symmetry. Small strain behavior is consistent with chirality and curvature-induced elastic anisotropy (CCIEA)—carbon nanotube rotation is equal and opposite in tension and compression, and decreases with curvature and chirality. The largestrain compressive response is remarkably different.

MichelleLOyen's picture

New Book "Tissue Mechanics"

A new book, "Tissue Mechanics" by SC Cowin and SB Doty is of potential interest to those from a classical mechanics background considering work in biomechanics. Downloadable versions of the first two chapters are available at the book's website along with a full table of contents and other supplemental information.

Xiaodong Li's picture

Experimental Nanomechanics

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Colleagues and friends,

DEPARTMENT CHAIR: San Diego State University, Department of Mechanical Engineering

The Department of Mechanical Engineering invites applications and nominations for the position of Department Chairperson to begin in Fall 2007.

Applicants must hold an earned PhD in Mechanical Engineering or closely related discipline. A record of leadership showing interpersonal skills and organizational ability, strong research background and funding records with recognized professional accomplishments in mechanical engineering, demonstrated ability to interact with industry, and a commitment to excellence in teaching at both undergraduate and graduate levels are required. Mechanical Engineering is one of four departments in the College of Engineering at San Diego State University with an EAC, ABET-accredited B.S. degree program in Mechanical Engineering, as well as M.S. and Ph.D. programs involving students in leading edge research.

Kyung-Suk Kim's picture

Heritage for Experimental Mechanicians

On July 16, 1976, when I was writing my very first paper in U.S. with my lab senior Dr. Prashant Kumar and thesis advisor Professor Rodney J. Clifton to the Journal of Applied Physics, Professor Clifton put a copy of an article on my desk while I was away. The article was "Advice to Young Physicists" by Walther Bothe. It was translated from German to English in Physics Today, September, 1958. I do not know whether this advice still holds for the whole; however, I believe that most of the advice is still valuable for anyone, in particular, an experimentalist, who undertakes a piece of scientific work. Therefore, I would like to share his advice with the society of iMechanica by recollecting it here. - K.-S. Kim

Non linear cell mechanics

Ex-vivo measure of stress-strain relationships in populations of living adherent cells by means of ligand-coated ferromagnetic microbeads (mean diameter: 4.5 µm) attached to the transmembrane mechanoreceptors which are linked to the cytoskeleton (CSK), reveal non linear cell mechanical behavior. However, this non linear cell mechanical behaviour is subjected to controversy for various reasons. First, it has not been systematically found. Results seem to depend on the micromanipulation method used and/or the cell type.

Zhigang Suo's picture

What is Grid Computing? How can it be important to mechanicians? When?

At the suggestion of Joy Sircar, the Chief Technology Officer at the School of Engineering and Applied Sciences, of Harvard University, iMechanica has just added a forum called Technology Corner. As Joy has framed it, this new forum intends to host conversations on software and hardware technologies that might be relevant to mechanicians.

Here is a question I have. Lately I've heard the phrase Grid Computing a number of times. It is about networking lots of computers and other electronic devices, and supply users with computing power like supplying electricity. That is, computing power will become a utility. One might even hope software will also become utilities. Some people say that Grid Computing will happen in just a few years, or may be already here. Here is a collection of essays in Nature on 2020 Future of Computing.

Weixu Zhang's picture

Effect of surface energy on the yield strength of nanoporous materials

This is a very rough manuscript but including the original material we used. Any criticism or suggestion is welcome. The only aim of this letter is to reflect the multi-effect of surface energy on material or structure in nanosize scale. Here we report the effect of surface energy on the yield strength of nanoporous materials. The conventional micromechanics method is extended to consider the surface effect and expression of effective yield surface of nanoporous materials in complex stress state is derived.

Northwestern University: Faculty Position in Mechanical Engineering

The Department of Mechanical Engineering at Northwestern University invites applications for a tenure track faculty position in the area of micro- and nano-scale devices, systems and related phenomena, though outstanding candidates in other research areas will be considered. The candidate should have a PhD in engineering or science, demonstrated excellence in research, and will be expected to develop innovative research and teaching programs in an interdisciplinary environment.

Pradeep Sharma's picture

Call for Future Monthly Themes for the J-Club

Everyone,

As you may have already gathered from previous posts, J-club is set to launch on January 2007. Michelle Oyen has agreed to be the first guest editor/host (----does anyone remeber what nomenclature we decided on?). Her selected theme is "Biomechanics" followed by John Dolbow who will design the February issue on "Computational mechanics".

Nanshu Lu's picture

TWELVE STEPS TO A WINNING RESEARCH PROPOSAL

By George A. Hazelrigg, National Science Foundation

I have been an NSF program director for 18 years. During this time, I have personally administered the review of some 3,000 proposals and been involved in the review of perhaps another 10,000. Through this experience, I have come to see that often there are real differences between winning proposals and losing proposals. The differences are clear. Largely, they are not subjective differences or differences of quality; to a large extent, losing proposals are just plain missing elements that are found in winning proposals. Although I have known this for some time, a recent experience reinforced it.

THE MOST CITED SCIENTIFIC PAPERS IN SOLID AND COMPUTATIONAL MECHANICS

I posted this survey in Applied Mechanics Research and Researchers on 16 April 2006, based on a survey of Web of Science. A paper making the list satisfied the following conditions:

  • It is in the areas of solid mechanics, mechanics of materials, or computational mechanics, and
  • It has at least 1000 citations.

This list may not be complete. If anyone finds a missing entry, please leave a comment below.

The cited number has been updated up to 18 Dec. 2006.

Biomaterials faculty position at Lehigh University

I am chairing the search for a new faculty member in the Materials Science and Engineering Department at Lehigh. As you will see in the ad below, the position is in the Biomaterials area. I would like to encourage more applications from candidates with interests in biomechanics (so I will have good opportunities to collaborate), and would like to invite applicants from this forum. If you are not personally in a position to apply, please pass the announcement along to anyone you know who might be suitable.

Xiaodong Li's picture

Nanostructured Metals Reveal Their Secret Strengthening Mechanisms

It is well known that metals are hardened by deformation and soften by annealing. How about nanostructured metals? Can we reply on conventional metal-working lore?

Nicolas Cordero's picture

Max Planck Society: Independent Junior Research Group Leader positions

The Max Planck Society (MPS) aims at promoting young international scientists by enabling them to perform their research (in all fields pursued by the MPS) at a Max Planck Institute of their choice.

The MPS offers Independent Junior Research Group Leader positions (W2; equivalent to associate professor level without tenure) granted for a period of 5 years with the option for prolonging twice for 2 years. The deadline for application is January 10, 2007.

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