A model for twinning

The modelling of twins in crystals with strain gradient theories provides interesting problems both in thermodynamics and in the calculus of variations. Here, Dunn and Serrin's thermomechanical theory of interstitial working is used to obtain a variational principle that governs the equilibria of materials with non-convex Helmholtz free energy. In some geometries, this principle reduces to a novel calculus of variations problem; an example is described in which symmetry-related uniform equilibrium states can be connected by nonconstant extremals which realiselocal minima of the free energy. Certain implications of different definitions of local minima are also discussed.     

Analyse von Preussisch-Blau

Ohne Zusammenfassung     

A new application of neutron activation analysis with239U to determine uranium in groundwaters

A rapid neutron activation method was developed to determine very low levels of uranium (gl^–1) in groundwater from the Palmyrides region, Central Syria. The²³⁹U -ray at 74.7 keV energy was used in the measurements. Results of this technique were compared against the conventional neutron activation analysis (INAA) with²³⁹Np and the laser-induced fluoremetry (LIF). In general, the three data sets showed a very good agreement. The described method provides good accuracy, precision and low detection limit, particularly when the total dissolved solids (TDS) of the samples is low.     

Rotational Symmetries of Crystals with Defects

I use the theory of Lie groups/algebras to discuss the symmetries of crystals with uniform distributions of defects.      

Electric Field Induced Changes of Spin Lattice Relaxation Time T1 in Polar Liquids

T ₁ was found to change linearly with applied electric field for the liquids nitrobenzene, chlorobenzene, ether and dioxane: no change was observed in hexane and cyclohexane. These substantial reductions in T ₁ are explained in terms of quasi-crystalline structures in the liquid.