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Teng Li's picture

Video Demo: How to make hyperlinks in your post?

In a recent post, Zhigang Suo explains how to add hyperlinks in your post. We all understand how hard to write an instruction for a simple operation, so we should appreciate Dr. Suo's every effort trying to be elucidative.

If you prefer a visualized instruction, click here to watch a video demonstration on how to make a post in your blog at iMechanica, and how to add a hyperlink in your post.

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.

Teng Li's picture

nanoHUB: online simulations and more

The nanoHUB is a web-based initiative spearheaded by the NSF-funded Network for Computational Nanotechnology (NCN). Based at Purdue University and partnered by eight other universities, nanoHUB provides a web interface to numerous resources relevant to students and practitioners in nanotechnology. The cyber environment includes online courses and tutorials, proceedings of seminars, collaborative tools, and an interface for online simulation.

For example, you can view research seminars on nanoHUB through online slideshow with audio, powered by Breeze technology. You can go over the outline of the seminar, choose thumbnail views of the slides and even search text within the titles of the slides, then locate the content of interest and save some time. Another type of resource on nanoHUB is the online simulation tools, which run realtime on nanoHUB. No installation is needed.

The nanoHUB resources are open to public for free. You just need to register to use. In the last eight months, nanoHUB has served more than 10,000 users, with about 60,000 simulation jobs run and more than 10,000 videos viewed. The web server hits of nanoHUB reach 1 million in May 2006.

Teng Li's picture

MRS Bulletin features Macroelectronics

The June 2006 issue of MRS Bulletin features Macroelectronics.

The guest editor of this issue include Robert H. Reuss (program manager of DARPA's macroelectronics program), Darrel G. Hopper (principal electronics engineer at US ARFL), and Jae-Geun Park (Materials Center at Samsung Advanced Institute of Technology)

The issue include a theme review article by the guest editors and four theme technical articles covering various topics related to macroelectronics.

(via www.macroelectronics.org)

Teng Li's picture

Strength map of carbon nanotube

 

 

In theory, carbon nanotubes are 100 times stronger than steel at one-sixth the weight, but in practice, scientists have struggled make nanotubes that live up to those predictions. This is partly because there are still many unanswered questions about how nanotubes break and under what conditions.

Recently, Prof. Boris I. Yakobson at Rice University, his former postdoc Traian Dumitrica (now assistant professor at University of Minnesota), and his doctoral student Ming Hua, have developed a new computer modeling approach to create a “strength map” that plots the likelihood or probability that a carbon nanotube will break—and how it’s likely to break. Four critical variables are considered in the model: load level, load duration, temperature, and chirality. This work was published in the Proceedings of the National Adacemy of Sciences (Apr. 18, 2006 Cover feature). Full text pdf file of this paper is available here.

Teng Li's picture

Whence the Force of F=ma?

This is the title of a three-part series published in Physics Today by Frank Wilczek, the Herman Feshbach Professor of Physics at MIT. Prof. Wilczek is considered one of the world's most eminent theoretical physicists, and is the 2004 Nobel laureate in Physics for work he did as a graduate student at Princeton University, when he was only 21 years old.

Prof. Wilczek contributes regularly to Physics Today and to Nature, explaining topics at the frontiers of physics to wider scientific audiences. The following series of his "musing on mechanics" won the Best American Science Writing in 2005:
Whence the Force of F=ma? 1: Culture Shock
Whence the Force of F=ma? II: Rationalizations
Whence the Force of F= ma ? III: Cultural Diversity

Prof. Wilczek recently published a book named Fantastic Realities, in which 49 inspiring pieces, including the above three, of "mind journeys" are included. This book also includes contribution from his wife Betsy Devine's blog on what winning a Nobel Prize looks like from inside prizewinner's family.
You may also enjoy a recent podcast of Scientific American, in which Prof. Wilczek and his wife talk about their new book
.

Teng Li's picture

A Virtual Tour of the 1906 Great Earthquake in Google Earth

The California earthquake of April 18, 1906 (one century ago today) ranks as one of the most significant earthquakes of all time. Today, its importance comes more from the wealth of scientific knowledge derived from it than from its sheer size --it marked the dawn of modern science of earthquakes.

U.S. Geological Survey (USGS) recently provides a virtual tour utilizing the geographic interactive software Google Earth to explain the scientific, engineering, and human dimensions of this earthquake. This virtual tour can help you visualize and understand the causes and effects of this and future earthquakes.

Enjoy this virtual tour to explore how Google Earth (and other new softwares...) can facilitate and improve the way we teach and conduct research.

Teng Li's picture

Organic LED could replace light bulb?

Lighting accounts for about 22% of the electricity consumed in buildings in the United States, and 40% of that amount is eaten up by inefficient incandescent light bulbs. The search for economical light sources has been a hot topic.

Recently, scientists have made important progress towards making white organic light-emitting diodes (OLEDs) commercially viable as light source. As reported in a latest Nature article, even at an early stage of development this new source is up to 75% more fficient than today's incandescent sources at similar brightnesses. The traditional light bulb's days could be numbered.

Read media report here.

(Via www.macroelectronics.org)

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

Bring researchers from industries to iMechanica

Posts on mechanics in industries may attract considerable interest. The audience will be mechanicians working in industries, students planning industrial careers, and academics looking for industrial collaborations.

Juil Yoon's picture

THE UNIVERSITY OF BRITISH COLUMBIA, Assistant/Associate Professor

THE UNIVERSITY OF BRITISH COLUMBIA, Assistant/Associate Professor

The Department of Mechanical Engineering at the University of British Columbia invites applications for a tenure-track faculty position at the Assistant or Associate Professor level in CAD/CAM. The starting date will be July 1, 2007, or as soon as possible thereafter.

The successful candidate will hold a Ph.D. degree or equivalent in Mechanical Engineering or a closely related field and will be expected to register as a Professional Engineer in British Columbia. The Department has an Industrial Research Chair (IRC) in High Performance Virtual Machining supported by NSERC and Pratt & Whitney Canada. In addition to the regular faculty appointment, the successful candidate will be appointed as NSERC-Pratt & Whitney Canada Associate Industrial Research Chair for a five-year period following the successful renewal of the IRC. He/She will be expected to participate in virtual machining research. We are particularly interested in candidates who have strong practical engineering skills and experience, and who are keen to teach Engineering Design courses at the undergraduate level and CAD/CAM courses at the graduate level. Further information on the department is available at www.mech.ubc.ca, and information on the employment environment in the Faculty of Applied Science is available at www.apsc.ubc.ca/careers.

The University of British Columbia hires on the basis of merit and is committed to employment equity. All qualified persons are encouraged to apply; however, Canadian citizens and permanent residents will be given priority. The position is subject to final budgetary approval. Applicants should submit a detailed resume, a statement (1-2 pages) of research and teaching interests, and names and addresses (fax/email included) of four referees to Professor Nimal Rajapakse, P.Eng., Head, Department of Mechanical Engineering, The University of British Columbia, Vancouver, B.C., Canada V6T 1Z4. The deadline for receipt of applications is November 30, 2006. Please do not forward applications by email.

Teng Li's picture

Google Scholar can localize your search to library links

Search globally, go locally. Starting from Feb. 2006, Google Scholar offers links to find papers in your local library. See here for details.

Teng Li's picture

Online Journal Club on Flexible Electronics

For many years, people accumulate personal collections of academic publications of interest in paper form. As such collections grow with time, more file cabinets and book shelves are needed for storage. First, space becomes a problem. Second, finding a specific paper could be a headache, even if the collections are well categorized.

As more and more publications become available online in recent years, people gradually switch to collect electronic versions, e.g. PDF files of papers. These files are often stored in local hard drives. Space is not an issue anymore. But again, locating a paper from hundreds of files in tens of folders still might be a heck of efforts.

Besides the difficulty in searching, other common shortcomings include:

  • Locally stored, limited access flexibility.
  • Personally owned, not easy to share with other people. As a result, the scale of personal collections is often limited.
  • Redundently collected. Consider this: a same gem paper is manually archived by thousands of people individually.
  • Statically and passively maintained. Lack of interactions among people sharing common interests.

Any better idea? Here comes Web2.0, which is all about online collaboration. Among the numerous tools enabled by Web2.0, CiteULike could be the one able to solve the above issues for us. A previous post in AMN explored the possibility to form online journal club based on CiteULike. Here is an example.

Teng Li's picture

CiteULike: Your online library of scientific literature, and more...

CiteULike is an online service to help academics to share, store, and organize the scientific literature. When you see a paper or a book on the web that interests you, you can click one button and have it added to your personal library. CiteULike automatically extracts the citation details (e.g., title, authors, abstract, and DOI). Currently, it supports more than 30 pubishing websites, many of which are of interest of mechanics community, e.g., ScienceDirect, AIP Scitation, Science, Nature, SpringerLink and Amazon.

Searching in your CiteULike library can be very easy. The surnames of all authors in your library are automatically tagged. You can also tag the papers and the books in your library as you like. All these tags appear in a tag cloud. Therefore, locating a paper in your library will be only one or two clicks away. Also, because your library is stored on the web server, you can access it from any computer.

You can also form a group, and integrate every member's own library to a group library. CiteULike also allows everyone to add note on papers or books. By combining the group and the note functions, you can easily form an online journal club among colleagues, collabarators, students, or any group with common interests, no matter how far away from each other.

Programmed by Richard Cameron and generously hosted by the University of Manchester in England, CiteULike is a free service to everyone. You just need to register to use its full functions. It all works within your web browser, no extra software is needed. So give it a try and enjoy.

Note: Nature publishing group also provides a similar service named Connotea. After experimenting both of them, I share the same feeling of many other users: while more attractive at the first sight, Connotea currently offer less flexible functions than CiteULike. I personally vote for CiteULike. You may want to share your experience with CiteULike or Connotea by commenting this entry.

Update on 4 July 2006:

Macroelectronics Journal Club, an online journal club focusing on flexible electronics and running on CiteULike platform, has been launched by www.macroelectronics.org. See a brief introduction here and detail announcement here.

Update on 14 July 2006:

By default, CiteULike stores links to papers. To get full access of a paper, you often need to locate the paper within the subscription of your institution, instead of its original link. By using a scalable bookmarklet, now localizing the paper links can be only as easy as one click away. See a recent iMechanica entry for details.

Rui Huang's picture

EPN - E-print Network

I was notified today that my Web site (http://www.ae.utexas.edu/~ruihuang/) has been included in the E-print Network (EPN). EPN is a fast-growing searchable scientific network of over 20,000 Web sites containing research conducted by researchers - from Nobel Laureates to post-doctoral students - who are offering e-prints of their work via the Internet.

Developed by the Office of Scientific and Technical Information (OSTI) to facilitate the needs of the Department of Energy (DOE) research community, E-print Network enhances dissemination of important research and helps to create opportunities for productive professional contacts.

E-print Network indexes over 900,000 e-prints. Most documents included in the network are recent scientific literature. Functions available to users include conducting full-text searches, searching for documents by contributing author, establishing a personalized alert service to keep abreast of new e-prints, and exploring laboratory Web sites for further details about selected research programs.

Once users find a paper of interest, they can download it from the site hosting the paper. This way you control distribution of your e-prints and can more readily track Web interest in your papers.

My page is listed under both Engineering and Materials Science.

Rui Huang's picture

Modeling Place

Starting from January 2006, my group has been posting in Modeling Place as a blogspot to share research experience and ideas. We will gradually migrate to iMechanica for better publicity and more web functions.

Xi Chen's picture

Why is molecular mechanics simulation at 0K useful?

Although it is more realistic to study the mechanical properties of nanostructures such as the carbon nanotubes (CNTs) at room temperature, atomistic simulations at finite temperature (such as molecular dynamics, MD) may cause the following problems: (1) Due to the limitation of the time scale achievable in MD (typically at the nanosecond scale), the loading rate in MD simulation at any finite temperature is not realistic. Very often, the loading rate used in MD simulations may well exceed 10m/s at 300K and thus many orders of magnitude higher than the real loading rate used in experiments. (2) A great advantage of simulation is to be able to turn on and turn off certain features and explore their effects, which is otherwise impossible in experiments. For example, the buckling behavior of CNTs is very sensitive to geometrical perturbations, which is prominent at room temperature and such perturbations causes severe uncertainties and makes it difficult to explore the intrinsic buckling behaviors. Therefore, by removing the temperature effect, we could better evaluate other key factors affecting the intrinsic buckling behavior, such as tube chirality, radius, and length, which could be otherwise covered by the thermal fluctuation effect. (3) Due to both time and length scale limitations, the MD simulations of large system are not yet possible, and thus the effective continuum models must be developed which need to be calibrated by atomistic simulations. At present, the temperature factor is still absent in most continuum models. Therefore, atomistic simulations at 0K or near 0K may provide a useful benchmark for the development of parallel continuum models, focusing on the most intrinsic and basic mechanical properties of nanostructures. Based on the above analysis, atomistic simulations at 0K by using the molecular mechanics (MM) method are still very useful, especially to us as mechanicians.

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

Xi Chen's picture

Appropriate range of materials used in indentation analysis

The conventional indentation analysis uses finite element simulations on a wide range of materials and studies their indentation responses, which is known as the forward analysis; then, from the reverse analysis it may be possible to extract material properties from the indentation responses on a particular specimen. In doing so, it is important to selecte a wide yet appropriate range of materials during the forward analysis. Often times when I read or review papers, I found some authors "randomly" select a large range of materials without really knowing what does that mean and whether it is practical; in many cases the materials employed in their forward/reverse analyses do not exist in reality or are actually not suitable for conventional indentation analysis.

In indentation analysis the constitutive elastoplastic properties of the specimen is often expressed by the power-law form. It is important to note that most brittle ceramic or glass materials crack upon indentation, and polymers creep during indentation experiment, moreover the tension and compression behaviors of polymers are often very different; thus, they typically cannot be well-described by the power-law form and their mechanical properties cannot be obtained from the conventional indentation analysis. Thus, ceramics and polymers should be excluded from the present analysis, as well as the highly anisotropic woods. In addition, composite materials, nanocomposites and other nano-structured materials, as well as thin films also need to be excluded from the continuum analysis because the underlying micro/nanostructures play a key role in their mechanical responses. Therefore, only the more ductile and "plastic" polycrystalline bulk metals and alloys are suitable for conventional indentation analysis at room temperature since large strain will occur beneath the indenter during indentation, and also because the conventional plasticity theory is developed for metals which is the foundation of the elastoplastic finite element analysis. The indentation depth also has to be sufficient large on the bulk specimen so as to overcome the strain gradient effect.

The material selection chart taken from page 425 of the famous handbook"Materials selection in mechanical design" by Mike Ashby can be used as a guide. In general, for most engineering metals and alloys suitable for conventional indentation study, the Young's modulus is from about 10 to 600GPa, and the yield strength is from roughly 10MPa to 2GPa, and the inverse of yield strain is in the range roughly from 100 to about 5000 (some pure metals may have even higher inverse yield strain, but should not far exceed such bound). Note that since the specimen must undergo relatively large strain during indentation without cracking, thus the material must be sufficiently ductile (i.e. plastic or soft).

In forward analysis, however, the material range chosen in finite element simulation needs to be moderately larger than the aforementioned bound, so as to avoid possible numerical ill conditions at the boundaries. The reverse analysis, however, should focus on the more practical materials, i.e. the range of metals and alloys listed above.

Xi Chen's picture

use NMA to get the elastic properties of loop

(originally written by Yuye Tang) A key procedure of the molecular-dynamics decorated finite element method (MDeFEM) is to determine the effective properties of components of a macromolecule. Here I illustrate how could one use the NMA computed from MD to estimate the elastic properties of loops in mechanosensitive channels, which is related with my research.

Split singularities and the competition between crack penetration and debond at a bimaterial interface

Zhen Zhang and Zhigang Suo

For a crack impinging upon a bimaterial interface at an angle, the singular stress field is a linear superposition of two modes, usually of unequal exponents, either a pair of complex conjugates, or two unequal real numbers. In the latter case, a stronger and a weaker singularity coexist (known as split singularities). We define a dimensionless parameter, called the local mode mixity, to characterize the proportion of the two modes at the length scale where the processes of fracture occur. We show that the weaker singularity can readily affect whether the crack will penetrate, or debond, the interface.

Zhigang Suo's picture

How to make long distance phone calls for free

Like many other communities, we mechanicians are scattered all over the world, often separated from families and colleagues. The Internet has promised for years to make long dstances irrelevant: anybody anywhere is just a click away. While nothing will ever be the same as being together in person, many Internet services can facilitate distant communication and collaboration. For example, Skype, an Internet phone service, allows you make free phone calls around the world. The sound quality is excellent.

Zhigang Suo's picture

Pay per paper (P3)

(Originally published on Applied Mechanics News on 22 July 2006, where many comments provided remarkable insight)

I’ve just stopped subscribing to Science. The magazine is great, but few papers in it interest me. The signal-to-noise ratio of Science, I guess, is just too low to most individuals. Instead, I’ve now subscribed to the RSS feed of Science. If any paper looks interesting, I can access to the full paper online through Harvard Libraries. Outside my office, a color printer is free to use for everyone. A library of an institution seems to be an ideal home for a journal like Science. Nearly every individual paper in Science is of high enough quality to appeal to someone in the institution.

Few journals can make that claim, however. Most journals are only relevant to several people in an institution. Furthermore, few researchers read any scholarly journal from cover to cover. Rather, we all read individual papers. However, libraries subscribe to journals, or even bundles of journals. As a result, the libraries pay for many papers that nobody reads, and miss other papers that someone would like to read.

This business model is bad for authors and readers, and possibly even bad for publishers. Technology now exists to distribute information far more efficiently, in a unit consistent with how people consume the information. For example, many people now prefer buying individual songs to albums. See a recent book, The Long Tail, by Chris Anderson, the editor-in-chief of Wired, for a remarkably perceptive analysis of media industries.

The same business model may apply to scholarly papers. One may argue that journals, like albums, were invented as a packaging technology to suit the old economics of delivery. As scholarly papers are all online, the name of a journal becomes simply a tag to the papers published in that journal. Maybe a powerful tag, but a tag nonetheless. So far as how papers should be distributed, the name of a journal should serve the same function as all other tag-like entities: keywords, names of authors, etc: the tags help readers to sort papers and set priorities. It makes no sense for anyone to insist that papers with any particular tag be delivered as a bundle.

Many publishers already offer individual papers for sale online; for example, the cost is at $30 per paper for many Elsevier journals. Once a reader buys a paper, it seems reasonable to share this paper with his close colleagues, and it also seems reasonable to store the paper for future use. Perhaps we can formalize this practice.

How about we treat a paper just like a book? With one click, a reader will have the paper, and his library will automatically pay for it. Once bought, the paper is accessible to every user of the library. We can also collect statistics. If the users of a library buy many papers in a journal, the library should subscribe to the journal. Libraries will set up an algorithm to minimize the total cost. Publishers will set up their algorithms to maximize profits. However, libraries and publishers do have a common ground: they both want to help people to find papers.

To support such a business model, a third party may provide a web service. It seems to be too wasteful to make every individual library and every individual publisher maintain a separate web service. Something like Amazon.com or Last.fm for papers might do. The service can also be an extension of services like EZproxy or CiteULike.

Zhigang Suo's picture

The LibraryLookup Bookmarklet

(Opriginally posted on Applied Mechanics News on 8 July 2006)

Quick link added on 12 July 2006. Here is a list of LibraryLookup Bookmarklets for many libraries, along with an instruction to use them.

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