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The aim of the authors is to model the shock response of concrete structures submitted to the effects of projectile penetration or contact detonation, in a range of pressure levels from 0 to 20 GPA. The limitations of current computers imply the need to homogenize the response of the different constituents of concrete into a single macroscopic model. Though concrete is widely used as a construction material, the knowledge concerning its response under shock loading response remains rather modest. An exhaustive review of the research effort in this field shows that the limited available data is affected by an important dispersion. As a consequence, any general rule correlating the composition of concrete to its shock properties have not yet been evidenced. A simple method to predict the shock Hugoniot of concrete based on a mixture theory is developed considering concrete as a mix of cement hydrates, free water, rock and voids. Experimental results obtained on special concrete compositions are presented. They illustrate the relation between the wave structure and the size of the aggregates, and so, the level of heterogeneity of the composition. Numerical simulations demonstrate the ability of a mesoscopic model to describe this phenomenon, and the failure of the homogenized approach to do so. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

At room temperature Li4C60 forms a unique two-dimensional polymer network where the bonding encounters [2+2] cycloaddition along one direction and a single C[Single_Bond]C bond along the perpendicular direction. This structure thus involves both so-far known bonding motifs and is unique among fullerene structures. The structural and electronic properties of this system were investigated by temperature dependent cw-ESR. The ESR signal of the polymer phase has an extremely narrow Lorentzian line with a linewidth of about 0.3 G. On heating, the transition from the low-temperature polymer phase to a metallic monomeric phase occurs above ∼250 °C. The high-temperature ESR signal has a characteristic Dysonian lineshape. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]