Metals become softer when they are heated up, as their stiffness decreases due to thermally induced expansion. More than a decade ago, Swiss physicist Charles Edourad Guillaume, who received the Nobel Prize in Physics in 1920, discovered a nickel based alloy with temperature insensitive elastic modules, which he named Elinvar. Such Elinvar alloys are very rare and the underlying mechnisms are still under debate. Recently, a research team led by Prof. Yang Yong at CityU together with international collaborators has discoveried a super-elastic high-entropy alloy, which exhibits an extraordinary Elinvar effect, retaining near-constant elastic modulus from room temperature to more than 600 degree Celsius. Furthermore, normal metals unusally have the elastic strain limit less than one percent, except those having pseuado-elasticity associated with phase transformation and large energy dissipation. This newly discovered alloy can attain a high elastic strain limit of two percent. We performed in situ high energy x-ray diffraction studies which demonstrated that the high elastic strain limit is not related to stress-induced phase transformation, but rather arises from the high lattice friction. Such a novel alloy with unprecendented mechanical properties has a great potential for aerospace engineering.

Read more at Nature:
https://www.nature.com/articles/s41586-021-04309-1

The paper was featured in CityU Research Stories:
https://www.cityu.edu.hk/research/stories/2022/02/10/super-elastic-high-entropy-elinvar-alloy-discovered-potential-aerospace-engineering  

DNA deformations upon environmental changes, e.g., salt and temperature, play crucial roles in many biological processes  and  material  applications.  Here,  our  magnetic  tweezers  experiments  observed  that  the  increase  in  NaCl, KCl, or RbCl concentration leads to substantial DNA overwinding. Our simulations and theoretical calcula-tion quantitatively explain the salt-induced twist change through the mechanism: More salt enhances the screening of interstrand electrostatic repulsion and hence reduces DNA diameter, which is transduced to twist increase through twist-diameter coupling. We determined that the coupling constant is 4.5 ±  0.8 kBT/(degrees∙nm) for one base pair. The coupling comes from the restraint of the contour length of DNA backbone. On the basis of this coupling con-stant and diameter-dependent DNA conformational entropy, we predict the temperature dependence of DNA twist ≈ −0.01 degree/°C, which agrees with our and previous experimental results. Our analysis suggests that twist-diameter coupling is a common driving force for salt- and temperature-induced DNA twist changes.

Read more at Science Advances:
https://www.science.org/doi/epdf/10.1126/sciadv.abn1384