Worth reading

 http://www.dpmms.cam.ac.uk/~wtg10/continuity.html

in case you need to explain the epsilon-delta  definition of continuity to an engineering student.

-- Biswajit 

I came upon a recent paper called "Deformation gradients for continuum mechanical analysis of atomistic simulations" by Jonathan A. Zimmerman , Douglas J. Bammann,  and Huajian Gao, International Journal of Solids and Structures 46 (2009) 238–253 where the authors conclude with

Two new papers grabbed my attention on my long unread list of journal tables of contents in Google Reader. 

1) The first was

Ideomechanics of transitory and dissipative systems associated with length, velocity, mass and energy by G.C. Sih

where it is stated that

" One of the rules of the development of IDM is that the “flow of nature” takes precedent when deducting and/or constructing quantitative results. It is hoped that

From PhDComics via Entertaining Research :

Check out the talk by Dr. Arden L. Bement, Jr., Director , National Science Foundation 
on TAM 

at  http://www.nsf.gov/news/speeches/bement/09/alb090424_tamsymp.jsp?govDel=USNSF_51

For the proceedings of the 2008 SBE&S workshop go to

 http://www.wtec.org/sbes/workshop/FinalWS-20080425/SBES-allpresentations-30Apr08-lowres.pdf

From PhDcomics

From Prof. John Nairn:

Via Physical Review Focus:

What you see is an optical fiber recoiling due to pulse of light flowing through it.  The abstract:

Phys. Rev. Lett. 101, 243601 (2008)

Observation of a Push Force on the End Face of a Nanometer Silica Filament Exerted by Outgoing Light

POSITION: POSTDOCTORAL RESEARCH FELLOW AT THE UNIVERSITY
OF AUCKLAND, NEW ZEALAND
Project Title: Advanced Modelling and Simulation of Closed Mould
Composite Manufacturing Processes
Applications are invited for a postdoctoral research position on composite manufacturing processes with the Liquid Composite Moulding (LCM) Group at the University of Auckland. The successful candidate will play a major role in developing the LCM group’s research into advanced composites manufacturing processes (including I/CM, Resin Infusion, VARTM, and RTMLight).

There are several exact relations from the theory of composites that can be used to determine whether a new numerical or analytical approach gives reasonable answers. Here's a paper on some exact relations that I wrote up a long time ago and just recently posted on Scribd. 

Most of you have heard about the commissioning of the Large Hadron Colider (LHC) by CERN and then the explosion of Helium followed by a postponement of operation until spring next year.  One of the worries some people had was that a mini black hole would be created by the collsions.  Also, the anthropic principle in one of its forms suggests that every possible universe exists but we see only our universe because it's the one in which intelligent observers exist.

Following the shutdown of the LHC comes one of the best comments on the matter that I've seen.  From Peter Woit's "Not Even Wrong" blog on the shutdown of the LHC:

I've mostly had quite helpful responses from iMechanica participants whenever I've asked questions on this forum.  However, I've noticed that questions from several posters have gone unanswered.  I feel that there are two main reasons for that lack of response:

1) The questioner has not provided an adequate details by which they can be identified.  I generally don't like responding to a question posed by someone called xyz1983. 

2) The question itself is vague or too general to be answered in anything short of a book length discussion. An example may be "I want to do FEM on RF-EMW.  Can someone help?" 

I was browsing the discussion page for Stress in Wikipedia when I came upon this interesting comment:

"

Refutation of Cauchy stress

The theory of stress based on Euler & Cauchy is now refuted. The profound incompatibility of this theory with the rest of physics, especially the theory of potentials and the theory of thermodynamics, has been documented in

Here's a puzzle for our readers.  The following image is of the surface of a failed joint followed by a picture of the joint (not the same one but a similar one) before joining.  What material is it? What caused the failure?  All manner of speculation is welcome.

Modern composite structures have a wide spread in their failure stress.  Advanced multiphysics codes can have a wide range of predicted behavior for nominally the same inputs.  How do we certify the design of such structures or the accuracy of such codes?

A few weeks ago I had mentioned in one of my comments that

"Almost every object that is used in modern societies contains some
material that has been extracted from the earth.  A huge amount of
energy is used in crushing rocks to a fine enough size that surface
chemistry may then be used to extract a particular metal.  Assuming
that we would like to use energy more efficiently, is there a way our
knowledge of mechanics can be used to minimize the energy used in
crushing rocks?  A huge number of people have worked on this problem -
yet an optimal solution seems as far away as ever. "

A meeting with my ex-classmate Dr. Barun Gorain of Barrick Gold Company  last weekend showed me that there are still quite a few problems of that nature in the mining industry.  In fact, Barrick is willing to spend as much as $10 million to solve one such problem.  The main site is called Unlock the Value and the bit that they are willing to offer cash for is a particular silver recovery operation.  Barun tells me that proposals are already in and are being evaluated - but I'm not sure whether those are for the silver problem or some other issue.   Can mechanicians help solve the problem?  Some of you might want to give it a try.

-- Biswajit 

I'm leaving the US in a couple of days and will probably take a hiatus of a few months from iMechanica.  Before I leave, I want to tell you about a C++ idiom that eases the implementation and use of multiple material models in a computational mechanics code.

The first book on C++ idioms was by Jim Copilien sometime in the late 1990s called "Advanced C++: Programming Styles and Idioms".  The idea of such idioms has become considerably widespread since then - so much so that there is a Wikibook on the subject .

I had promised to talk about subversion in my post on digitizing and editing figures but never quite got around to it. A recent spate of requests about downloading Uintah reminded me of my promise. So here's the story.

From Jim Guilkey: You are invited to attend the Fourth MPM Workshop.  This year workshop will be held in Salt Lake City, Utah on the campus of the University of Utah, on March 17th & 18th, 2008.  The format will be similar to the previous workshops,  held at University of Utah, Oklahoma State University and Sandia National Laboratory, where relaxed environments facilitated understanding and awareness of the MPM's strengths and  weaknesses via informal talks and discussion.  Topics of interest include, but are not limited to, numerical implementation and properties, algorithm properties, variations and additions, and  applications.  Please feel free to pass this announcement along to other potentially interested colleagues.

The following link brightened my day quite a bit.  Wikipedia can now be tasted!

http://ourfounder.typepad.com/leblog/2007/10/jimmy-wales-gro.html 

Metals have a lustre because electromagnetic radiation in the visible range is almost completely absorbed at an exponential rate close to a metal surface and then radiated back.  This effect and other properties of crystalline materials can be explained by their electronic band structure and the associated dispersion relations. In certain materials, notably semiconductors, distinctive band gaps are found indicating that electrons of certain forbidden energies which cannot propagate through the material.  A concise description of the basics can be found here.  

There is a close analogy between the motion of electrons in periodic crystals and electromagnetic waves in periodic dielectric structures. This analogy and the quest for materials with unusual electromagnetic properties has led to exploration of periodic materials with tunable electromagnetic band structures and band gaps.  Such materials are called photonic crystals and photonic composites.  A good review article on the subject is  E. Yablonovitch, 1993, "Photonic band-gap crystals", J. Phys.: Condens. Matter, 5, 2443-2460,   doi:10.1088/0953-8984/5/16/004.

Those of you who are looking for academic jobs and have not heard back from the places that you applied may find the following wiki useful.

http://wikihost.org/wikis/academe/wiki/mechanical_engineering 

The idea is to let people know whether a position has been filled or not.  You can add the positions you have applied to, whether you have been called for an interview, whether references have been requested, or whether you have got a rejection letter.

I just remembered another video that I had seen some time ago.  Many of you have probably seen it but here it is for those who have not. (The original page where I found it is http://www.maniacworld.com/Laminar-Reverse-Flow.html.)

Prof. Pat McMurtry's explanation is:

The following video is a nice depiction of how the eigenmodes of a plate change with increasing forcing frequency.

Following Andy's recommendation I have been reading Ellis Dill's Continuum Mechanics[1]. In page 75 of the book, we find the
well known result that the constitutive equation for an isotropic hypoelastic
material can be derived from a stored energy function only if