Genera of the bee tribe Reedapini (Hymenoptera: Colletidae)

Those bees classified in the genera Reedapis Michener and Cephalocolletes Michener are discussed and organized into a new tribe, Reedapini Engel. In addition, three species formerly classified in Cephalocolletes are removed to two new genera: Lonchopriscus Engel, new genus, with the species Lonchopriscus crassipunctatus (Urban), new combination, and Cactocolletes Engel, new genus, for Cactocolletes isabelae (Urban), new combination, and C. rugatus (Urban), new combination. The tribe and its constituent genera are diagnosed, and a key is provided for the identification of the latter along with their included species

Stability of the decagonal quasicrystal in the Lennard-Jones-Gauss system

Although quasicrystals have been studied for 25 years, there are many open questions concerning their stability: What is the role of phason fluctuations? Do quasicrystals transform into periodic crystals at low temperature? If yes, by what mechanisms? We address these questions here for a simple two-dimensional model system, a monatomic decagonal quasicrystal, which is stabilized by the Lennard-Jones-Gauss potential in thermodynamic equilibrium. It is known to transform to the approximant Xi, when cooled below a critical temperature. We show that the decagonal phase is an entropically stabilized random tiling. By determining the average particle energy for a series of approximants, it is found that the approximant Xi is the one with lowest potential energy.Comment: 7 pages, 2 figures, Proceedings of Quasicrystals - The Silver Jubile

A new species of Ptiloglossa from Mexico, with new records of Ptiloglossa cyaniventris from Panama and Costa Rica (Hymenoptera: Colletidae)

A new bee species of the genus Ptiloglossa Smith (Colletidae: Diphaglossinae: Caupolicanini) is described and figured from Jalisco, Mexico, while new records are provided for Ptiloglossa cyaniventris Friese from Panama and a single locality in Costa Rica.  Ptiloglossa chamelensis Ayala & Engel, new species, is endemic to Mexico and is close to P. rugata Moure, both sharing a similar shape in the fused metatibial spur, but in the new species the metatibia is widest at the level of the spur, and the female has black integument with dense yellow pubescence on metasomal terga I–IV.  Ptiloglossa cyaniventris is newly recorded from males collected in Panama and Costa Rica and is characteristic for its dark integument, with intense metallic blue highlights on the metasomal terga, the narrow and long metatibia, and elongate metabasitarsus with an anterior, longitudinal ridge and slightly depressed outer surface

Controlled self-assembly of periodic and aperiodic cluster crystals

Soft particles are known to overlap and form stable clusters that self-assemble into periodic crystalline phases with density-independent lattice constants. We use molecular dynamics simulations in two dimensions to demonstrate that, through a judicious design of an isotropic pair potential, one can control the ordering of the clusters and generate a variety of phases, including decagonal and dodecagonal quasicrystals. Our results confirm analytical predictions based on a mean-field approximation, providing insight into the stabilization of quasicrystals in soft macromolecular systems, and suggesting a practical approach for their controlled self-assembly in laboratory realizations using synthesized soft-matter particles.Comment: Supplemental Material can be obtained through the author's website at: http://www.tau.ac.il/~ronlif/pubs/ClusterCrystals-Supp.pd