Crystallographic disorder and electron scattering on structural two-level systems in ZrAs1.4Se0.5

Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical vapour transport. While their thermodynamic and transport properties are typical for ordinary metals, the electrical resistivity exhibits a shallow minimum at low temperatures. Application of strong magnetic fields does not influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5 apparently originates from interaction between the conduction electrons and structural two-level systems. Significant disorder in the As-Se substructure is inferred from X-ray diffraction and electron microprobe studies

Understanding the toughness mechanism prompted by submicron rigid particles in polylactide/barium sulfate composites

Polylactides are extensively employed as bone-fixation devices, due to their degradability and high tensile modulus. As demonstrated in a previous study, the incorporation of barium sulfate submicron particles impressively enhanced toughness with almost no adverse effect on yield strength. It is therefore a promising strategy in the design of radiopaque materials intended for use in safety-critical systems. In the present study, the mechanism that causes high-level plastic deformation in this system is identified through tensile and fracture tests, together with a thorough analysis of the microstructure via transmission and SEM (Scanning Electron Microscopy). The presence of submicron particles was observed to reduce crystallinity and to increase energy dissipation during the plastic deformation of the polymer matrix, inducing crack widening and fibrillated crazing that propagated around the crack opening. The result is a five-fold increase in the energy that is required to fracture the composite with respect to its neat polymer counterpart.The authors are grateful for funds from POLYMAT Fundazioa, Basque Government (GV/EJ) (IT-927-16, S-PC13UN025) and MINECO (MAT-2016-78527-P).N.S.and I.M. are respectively thankful for the predoctoral and postdoctoral fellowships to POLYMAT and A.L. wishes to acknowledge support from the Basque Government for his postdoctoral fellowship

Nucleation of a sodium droplet on C60

We investigate theoretically the progressive coating of C60 by several sodium atoms. Density functional calculations using a nonlocal functional are performed for NaC60 and Na2C60 in various configurations. These data are used to construct an empirical atomistic model in order to treat larger sizes in a statistical and dynamical context. Fluctuating charges are incorporated to account for charge transfer between sodium and carbon atoms. By performing systematic global optimization in the size range 1<=n<=30, we find that Na_nC60 is homogeneously coated at small sizes, and that a growing droplet is formed above n=>8. The separate effects of single ionization and thermalization are also considered, as well as the changes due to a strong external electric field. The present results are discussed in the light of various experimental data.Comment: 17 pages, 10 figure

Rough Fibrils Provide a Toughening Mechanism in Biological Fibers

Spider silk is a fascinating natural composite material. Its combination of strength and toughness is unrivalled in nature, and as a result, it has gained considerable interest from the medical, physics, and materials communities. Most of this attention has focused on the one to tens of nanometer scale: predominantly the primary (peptide sequences) and secondary (β sheets, helices, and amorphous domains) structure, with some insights into tertiary structure (the arrangement of these secondary structures) to describe the origins of the mechanical and biological performance. Starting with spider silk, and relating our findings to collagen fibrils, we describe toughening mechanisms at the hundreds of nanometer scale, namely, the fibril morphology and its consequences for mechanical behavior and the dissipation of energy. Under normal conditions, this morphology creates a nonslip fibril kinematics, restricting shearing between fibrils, yet allowing controlled local slipping under high shear stress, dissipating energy without bulk fracturing. This mechanism provides a relatively simple target for biomimicry and, thus, can potentially be used to increase fracture resistance in synthetic materials

Fabrication of composites via spouted bed granulation process and simulation of their micromechanical properties

In this contribution numerical simulation of Young’s modulus of copper-polymer composites is presented. For the simulation of the composites the Bonded-Particle-Model was applied. The model allows representing of the structure of composite materials realistically. The polymer matrix, which surrounds the particles, was represented as network of solid bonds connecting copper particles. Simulation results were validated based on mechanical determination of modulus of elasticity. The modulus of elasticity was approximated in experiments as well as in simulation by four-point-bending tests. It was observed, that obtained simulation results are in good agreement with experimental results

The Conservation Status of Marine Bony Shorefishes of the Greater Caribbean

The greater Caribbean biogeographic region covered in this report (representing 38 countries and territories) encompasses an outstanding marine bony shorefish richness of approximately 1,360 species, with many (53%) being endemic. This report provides an overview of the conservation status of greater Caribbean shorefishes, with detailed information available through the IUCN Red List, and gives recommendations

The in-plane elastic properties of hierarchical composite cellular materials: Synergy of hierarchy, material heterogeneity and cell topologies at different levels

FO and EB are supported by the Queen Mary University of London Start-Up grant for new academics. NMP is supported by the European Research Council (ERC StG Ideas 2011 BIHSNAM n. 279985, ERC PoC 2015 SILKENE nr. 693670), by the European Commission under the Graphene Flagship (WP14 Polymer Nanocomposites, n. 696656)

Advances in modelling of biomimetic fluid flow at different scales

The biomimetic flow at different scales has been discussed at length. The need of looking into the biological surfaces and morphologies and both geometrical and physical similarities to imitate the technological products and processes has been emphasized. The complex fluid flow and heat transfer problems, the fluid-interface and the physics involved at multiscale and macro-, meso-, micro- and nano-scales have been discussed. The flow and heat transfer simulation is done by various CFD solvers including Navier-Stokes and energy equations, lattice Boltzmann method and molecular dynamics method. Combined continuum-molecular dynamics method is also reviewed