Unusual rods get thicker when stretched

[link to www.physorg.com]

Day-to-day experience teaches us that stretching an object makes it thinner; pushing it together makes it thicker. However, there are also materials that behave contrary to our expectations: they get thicker when stretched and thinner when compressed. .......Known as "auxetic" substances, these materials include some foams and special crystals. Researchers at the Bar-Ilan University and the Israel Institute of Technology have now used quantum mechanical calculations to identify the first class of chemical compounds that behave auxetically on a molecular level.