Eulerian polynomials of type DD have only real roots

We give an intrinsic proof of a conjecture of Brenti that all the roots of the Eulerian polynomial of type $D$ are real and a proof of a conjecture of Dilks, Petersen, and Stembridge that all the roots of the affine Eulerian polynomial of type $B$ are real, as well

GOLLUM: a next-generation simulation tool for electron, thermal and spin transport

We have developed an efficient simulation tool 'GOLLUM' for the computation of electrical, spin and thermal transport characteristics of complex nanostructures. The new multi-scale, multi-terminal tool addresses a number of new challenges and functionalities that have emerged in nanoscale-scale transport over the past few years. To illustrate the flexibility and functionality of GOLLUM, we present a range of demonstrator calculations encompassing charge, spin and thermal transport, corrections to density functional theory such as LDA+U and spectral adjustments, transport in the presence of non-collinear magnetism, the quantum-Hall effect, Kondo and Coulomb blockade effects, finite-voltage transport, multi-terminal transport, quantum pumps, superconducting nanostructures, environmental effects and pulling curves and conductance histograms for mechanically-controlled-break-junction experiments.Comment: 66 journal pages, 57 figure

Finite size effects on transport coefficients for models of atomic wires coupled to phonons

We consider models of quasi-1-d, planar atomic wires consisting of several, laterally coupled rows of atoms, with mutually non-interacting electrons. This electronic wire system is coupled to phonons, corresponding, e.g., to some substrate. We aim at computing diffusion coefficients in dependence on the wire widths and the lateral coupling. To this end we firstly construct a numerically manageable linear collision term for the dynamics of the electronic occupation numbers by following a certain projection operator approach. By means of this collision term we set up a linear Boltzmann equation. A formula for extracting diffusion coefficients from such Boltzmann equations is given. We find in the regime of a few atomic rows and intermediate lateral coupling a significant and non-trivial dependence of the diffusion coefficient on both, the width and the lateral coupling. These results, in principle, suggest the possible applicability of such atomic wires as electronic devices, such as, e.g., switches.Comment: 9 pages, 5 figures, accepted for publication in Eur. Phys. J.

The COMPARE Data Hubs

Data sharing enables research communities to exchange findings and build upon the knowledge that arises from their discoveries. Areas of public and animal health as well as food safety would benefit from rapid data sharing when it comes to emergencies. However, ethical, regulatory and institutional challenges, as well as lack of suitable platforms which provide an infrastructure for data sharing in structured formats, often lead to data not being shared or at most shared in form of supplementary materials in journal publications. Here, we describe an informatics platform that includes workflows for structured data storage, managing and pre-publication sharing of pathogen sequencing data and its analysis interpretations with relevant stakeholders

Characteristics of bamboo defects in peapod-grown double-walled carbon nanotubes

Single-walled carbon nanotubes can function as nanoscale reaction chambers for growing smaller nanotubes within the host tube from encapsulated fullerenes by annealing. The diameter of the host outer tube restricts the diameter of the inner tube due to van der Waals interactions but not its chirality: it is possible that inner tubes with different chiralities start to grow in different places at the same time. A straight junction occurs at the connection of these two tubes which we refer to as bamboo defects. We show that localized states appear in the calculated density of states associated with these bamboo defects, some of them close to the Fermi level, and present a detailed theoretical study of ballistic transport through double-walled tubes where the inner shell contains bamboo defects. We find that the presence of bamboo defects should be possible to detect through electronic-transport measurements and the number of bamboo defects per unit length can be extracted from the structure of the resonances appearing in the transmission coefficient

Eulerian polynomials of type DD have only real roots

We give an intrinsic proof of a conjecture of Brenti that all the roots of the Eulerian polynomial of type $D$ are real and a proof of a conjecture of Dilks, Petersen, and Stembridge that all the roots of the affine Eulerian polynomial of type $B$ are real, as well.Nous prouvons, de façon intrinsèque, une conjecture de Brenti affirmant que toutes les racines du polynôme eulérien de type $D$ sont réelles. Nous prouvons également une conjecture de Dilks, Petersen, et Stembridge que toutes les racines du polynôme eulérien affine de type $B$ sont réelles

Electron transport through ribbonlike molecular wires calculated using density-functional theory and Green's function formalism

We study the length dependence of electron transport through three families of rigid, ribbonlike molecular wires. These series of molecules, known as polyacene dithiolates, polyphenanthrene dithiolates, and polyfluorene dithiolates, represent the ultimate graphene nanoribbons. We find that acenes are the most attractive candidates for low-resistance molecular-scale wires because the low-bias conductance of the fluorene- and phenanthrene-based families is shown to decrease exponentially with length, with inverse decay lengths of beta = 0.29 angstrom(-1) and beta = 0.37 angstrom(-1), respectively. In contrast, the conductance of the acene-based series is found to oscillate with length due to quantum interference. The period of oscillation is determined by the Fermi wave vector of an infinite acene chain and is approximately 10 angstrom. Details of the oscillations are sensitive to the position of thiol end groups and in the case of "para" end groups, the conductance is found initially to increase with length

The Eulerian polynomials of type D have only real roots

Abstract. We give an intrinsic proof of a conjecture of Brenti that all the roots of the Eulerian polynomial of type D are real and the first proof of a conjecture of Dilks, Petersen, and Stembridge that all the roots of the affine Eulerian polynomial of type B are real, as well. Résumé. Nous prouvons, de façon intrinsèque, une conjecture de Brenti affirmant que toutes les racines du polynôme eulérien de type D sont réelles. Nous prouvons également une conjecture de Dilks, Petersen, et Stembridge que toutes les racines du polynôme eulérien affine de type B sont réelles

Advanced Simulation of Conductance Histograms Validated through Channel-Sensitive Experiments on Indium Nanojunctions

We demonstrate a self-contained methodology for predicting conductance histograms of atomic and molecular junctions. Fast classical molecular-dynamics simulations are combined with accurate density functional theory calculations predicting both quantum transport properties and molecular-dynamics force field parameters. The methodology is confronted with experiments on atomic-sized indium nanojunctions. Beside conductance histograms the distribution of individual channel transmission eigenvalues is also determined by fitting the superconducting subgap features in the I-V curves. The remarkable agreement in the evolution of the channel transmissions demonstrates that the simulated ruptures are able to reproduce a realistic statistical ensemble of contact configurations, whereas simulations on selected ideal geometries show strong deviations from the experimental observations