EPJ E Highlight - Granular media friction explained: Da Vinci would be proud

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Published on Monday, 26 June 2017 18:10

New study explains how solid friction forces affect granular materials in two or more dimensions

Leonardo Da Vinci had already noticed it. There is a very peculiar dynamics of granular matter, such as dry sand or grains of wheat. When these granular particles are left on a vibrating solid surface, they are not only subject to random vibrations, they are also under the spell of solid friction forces, like the force a dry floor would exert on a brick in contact with that floor. In a study published in EPJ E, Prasenjit Das from the Jawaharlal Nehru University, India, and colleagues extended our understanding of this problem from the well-known, one-dimensional case to multiple dimensions.

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EPJ D Highlight - First aid kit in some living organisms helps fix DNA after lengthy sun exposure

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Published on Monday, 26 June 2017 17:52

New study unveils the binding mechanisms of enzymes capable of repairing DNA damaged by UV light before any risk of cellular malfunction sets in

Sunburn in living organisms is caused by ultraviolet (UV) light from the sun damaging the DNA in the cells. Many organisms, however, have an in-built mechanism for repairing the sun damage. This is possible thanks to an enzyme called DNA photolyase, which is so specialised that cryptochrome, a structurally similar molecule, is unable to do the same job. By comparing both types of molecule, physicists can understand precisely how the ability of our enzymes to repair DNA boils down to the most minute structural details. In a study published in EPJ D, Katrine Aalbæk Jepsen from the University of Southern Denmark, in Odense, and her colleague Ilia Solov'yov pinpoint the mechanism by which repair enzymes bind to the damaged site.

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EPJ A Highlight - Nuclear and Quark Matter at High Temperature

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Published on Wednesday, 14 June 2017 16:12

In high-temperature field theory applied to nuclear physics, in particular to relativistic heavy-ion collisions, it is a longstanding question how hadrons precisely transform into a quark-gluon matter and back. The change in the effective number of degrees of freedom is rather gradual than sudden, despite the identification of a single deconfinement temperature. In order to gain an insight into this issue while considering the structure of the QGP we review the spectral function approach and its main consequences for the medium properties, including the shear viscosity. The figure plots a sample spectral density on the left and the effective number of degrees of freedom (energy density relative to the free Boltzmann gas) to the right. Two thin spectral lines result in a doubled Stefan-Boltzmann limit (SB), while any finite width reduces the result down to a single SB. When spectral lines become wide, their individual contributions to energy density and pressure drops. Continuum parts have negligible contribution. This causes the melting of hadrons like butter melts in the Sun, with no latent heat in this process.

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