Heuristic Chemistry—Elimination Reactions

Besides additions and substitutions, elimination reactions play a fundamental role in organic synthesis. However, conceptual reviews of known 1,x‐elimination patterns that go beyond the typical olefin‐forming 1,2‐eliminations are scarce. To develop a broader understanding of elimination reactions, we follow a heuristic approach and deduce recurrent reaction patterns from traditional and specific elimination reactions. Our work demonstrates that 1,x‐elimination reactions and their outcomes can be easily rationalized by defined mnemonic categories.     

Actions for non-abelian twisted self-duality

The dynamics of abelian vector and antisymmetric tensor gauge fields can be described in terms of twisted self-duality equations. These first-order equations relate the p-form fields to their dual forms by demanding that their respective field strengths are dual to each other. It is well known that such equations can be integrated to a local action that carries on equal footing the p-forms together with their duals and is manifestly duality invariant. Space-time covariance is no longer manifest but still present with a non-standard realization of space-time diffeomorphisms on the gauge fields. In this paper, we give a non-abelian generalization of this first-order action by gauging part of its global symmetries. The resulting field equations are non-abelian versions of the twisted self-duality equations. A key element in the construction is the introduction of proper couplings to higher-rank tensor fields. We discuss possible applications (to Yang-Mills and supergravity theories) and comment on the relation to previous no-go theorems.     

EPR Study of the Kinetics of the Formation of Radicals from Dibenzoyl Peroxide on Porous Glass

The kinetics of the formation of radicals from dibenzoyl peroxide supported on porous glass have been determined with EPR techniques over the temperature range of 25-100°C. Values of the activation energy of 18.5 and 25 kcal/mole have been observed for two differently prepared porous glass support materials.     

Generalized balanced power diagrams for 3D representations of polycrystals

Characterizing the grain structure of polycrystalline material is an important task in material science. The present paper introduces the concept of generalized balanced power diagrams as a concise alternative to voxelated mappings. Here, each grain is represented by (measured approximations of) its centre of mass position, its volume and, if available, and by its second-order moments (in the non-equiaxed case). Such parameters may be obtained from 3D X-ray diffraction. As the exact global optimum of our model results from the solution of a suitable linear programme it can be computed quite efficiently. Based on verified real-world measurements, we show that from the few parameters per grain (3, respectively, 6 in 2D and 4, respectively, 10 in 3D) we obtain excellent representations of both equiaxed and non-equiaxed structures. Hence our approach seems to capture the physical principles governing the forming of such polycrystals in the underlying process quite well.