Mindlin second-gradient elastic properties from dilute two-phase Cauchy-elastic composites. Part I: Closed form expression for the effective higher-order constitutive tensor

It is shown that second-order homogenization of a Cauchy-elastic dilute suspension of randomly distributed inclusions yields an equivalent second gradient (Mindlin) elastic material. This result is valid for both plane and three-dimensional problems and extends earlier findings by Bigoni and Drugan [Bigoni, D., Drugan, W.J., 2007. Analytical derivation of Cosserat moduli via homogenization of heterogeneous elastic materials. J. Appl. Mech. 74, 741–753] from several points of view: (i) the result holds for anisotropic phases with spherical or circular ellipsoid of inertia; (ii) the displacement boundary conditions considered in the homogenization procedure is independent of the characteristics of the material; (iii) a perfect energy match is found between heterogeneous and equivalent materials (instead of an optimal bound). The constitutive higher-order tensor defining the equivalent Mindlin solid is given in a surprisingly simple formula. Applications, treatment of material symmetries and positive definiteness of the effective higher-order constitutive tensor are deferred to Part II of the present article.     

Formation of single layer h-BN on Pd(1 1 1)

The structure of hexagonal boron nitride (h-BN) on Pd(1 1 1) was studied with low energy electron diffraction (LEED), photoelectron spectroscopy and scanning tunnelling microscopy (STM). h-BN forms flat monolayers on the Pd(1 1 1) surface in contrast to Rh(1 1 1) where a complex self-assembled double layer structure, the nanomesh [M. Corso, W. Auwärter, M. Muntwiler, A. Tamai, T. Greber, J. Osterwalder, Science 303 (2004) 217], appears. The LEED patterns reveal a dominating 10 × 10 h-BN superstructure, with a second, distinct structure rotated by 30° and further azimuthally randomly oriented h-BN overlayers. This is consistent with STM images which show several different Moiré patterns associated with different rotation angles of the overlayer. Additionally the use of thin Pd(1 1 1) films instead of single crystal substrates was studied. No significant differences in the h-BN film quality were found.     

Electric fields with ultrasoft pseudo-potentials: applications to benzene and anthracene

We present density-functional perturbation theory for electric field perturbations and ultra-soft pseudopotentials. Applications to benzene and anthracene molecules and surfaces are reported as examples. We point out several issues concerning the evaluation of the polarizability of molecules and slabs with periodic boundary conditions.     

A Nontraditional Laboratory Proposal: Investigating the Kinetics of a Chemical Reaction

This paper presents an unstructured laboratory in which students determine the rate law for a reaction. We have selected for this investigation the reaction between magnesium and hydrochloric acid. The general goal of the proposal is threefold: (1) to increase students interest in science during first-year chemistry; (2) to create a more active learning environment where students can learn and do science as scientists; and (3) to develop and promote critical thinking, analytical reasoning, collaboration, and interactive discussion based on a scientific problem. This laboratory has proven to be effective because the students, with some guidance from the instructor, were able to (1) state one or more hypotheses related to the problem under study (chemical kinetics); (2) design procedures and strategies to answer specific questions; and (3) establish methods to manipulate and interpret the data. Finally, the students were required to write a report. In this way, the laboratory promotes creativity and improves students critical thinking in an introductory course of university general chemistry.     

Fast Cyclization of a Proline-Derived Self-Immolative Spacer Improves the Efficacy of Carbamate Prodrugs

Self-immolative (SI) spacers are sophisticated chemical constructs designed for molecular delivery or material degradation. We describe herein a (S)-2-(aminomethyl)pyrrolidine SI spacer that is able to release different types of anticancer drugs (possessing either a phenolic or secondary and tertiary hydroxyl groups) through a fast cyclization mechanism involving carbamate cleavage. The high efficiency of drug release obtained with this spacer was found to be beneficial for the in vitro cytotoxic activity of protease-sensitive prodrugs, compared with a commonly used spacer of the same class. These findings expand the repertoire of degradation machineries and are instrumental for the future development of highly efficient delivery platforms.     

Lifshitz transition across the Ag/Cu(111) superlattice band gap tuned by interface doping

The two-dimensional, free-electron-like band structure of noble metal surfaces can be radically transformed by appropriate nanostructuration. A case example is the triangular dislocation network that characterizes the epitaxial Ag/Cu(111) system, which exhibits a highly featured band topology with a full band gap above E(F) and a hole-pocket-like Fermi surface. Here we show that controlled doping of the Ag/Cu(111) interface with Au allows one to observe a complete Lifshitz transition at 300 K; i.e., the hole pockets fill up, the band gap entirely shifts across E(F), and the Fermi surface becomes electron-pocket-like.     

An analytic approach to the measurement of nestedness in bipartite networks

We present an index that measures the nestedness pattern of bipartite networks, a problem that arises in theoretical ecology. Our measure is derived using the sum of distances of the occupied elements in the incidence matrix of the network. This index quantifies directly the deviation of a given matrix from the nested pattern. In the simplest case the distance of the matrix element a_i,j is d_i,j=i+j, the Manhattan distance. A generic distance is obtained as d_i,j=(i^χ+j^χ)^1/χ. The nestedness index is defined by ν=1−τ, where τ is the “temperature” of the matrix. We construct the temperature index using two benchmarks: the distance of the complete nested matrix that corresponds to zero temperature and the distance of the average random matrix where the temperature is defined as one. We discuss an important feature of the problem: matrix occupancy ρ. We address this question using a metric index χ that adjusts for matrix occupancy.     

On the electrophysiology of the atrial fast conduction system: an uncertain quantification study

Acta Mechanica Sinica - Cardiac modeling entails the epistemic uncertainty of the input parameters, such as bundles and chambers geometry, electrical conductivities and cell parameters, thus...