Quantum coherent transport in a three-arm beam splitter and a Braess paradox

The Braess paradox encountered in classical networks is a counterintuitive phenomenon when the flow in a road network can be impeded by adding a new road or, more generally, the overall net performance can degrade after addition of an extra available choice. In this work, we discuss the possibility of a similar effect in a phase-coherent quantum transport and demonstrate it by example of a simple Y-shaped metallic fork. To reveal the Braess-like partial suppression of the charge flow in such device, it is proposed to transfer two outgoing arms into a superconducting state. We show that the differential conductance-vs-voltage spectrum of the hybrid fork structure varies considerably when the extra link between the two superconducting leads is added and it can serve as an indicator of quantum correlations which manifest themselves in the quantum Braess paradox.Comment: 9 pages, 3 figures, the author version presented at the Quantum 2017 Workshop (Torino, Italy, 7-13 May 2017) and submitted to the International Journal of Quantum Information; v2: reference 9 added and the introduction extende

Harnessing machine learning potentials to understand the functional properties of phase-change materials

The exploitation of phase-change materials (PCMs) in diverse technological applications can be greatly aided by a better understanding of the microscopic origins of their functional properties. Over the last decade, simulations based on electronic-structure calculations within density functional theory (DFT) have provided useful insights into the properties of PCMs. However, large simulation cells and long simulation times beyond the reach of DFT simulations are needed to address several key issues of relevance for the performance of devices. One way to overcome the limitations of DFT methods is to use machine learning (ML) techniques to build interatomic potentials for fast molecular dynamics simulations that still retain a quasi-ab initio accuracy. Here, we review the insights gained on the functional properties of the prototypical PCM GeTe by harnessing such interatomic potentials. Applications and future challenges of the ML techniques in the study of PCMs are also outlined

Combining high-resolution scanning tunnelling microscopy and first-principles simulations to identify halogen bonding

Scanning tunnelling microscopy (STM) is commonly used to identify on-surface molecular self-assembled structures. However, its limited ability to reveal only the overall shape of molecules and their relative positions is not always enough to fully solve a supramolecular structure. Here, we analyse the assembly of a brominated polycyclic aromatic molecule on Au(111) and demonstrate that standard STM measurements cannot conclusively establish the nature of the intermolecular interactions. By performing high-resolution STM with a CO-functionalised tip, we clearly identify the location of rings and halogen atoms, determining that halogen bonding governs the assemblies. This is supported by density functional theory calculations that predict a stronger interaction energy for halogen rather than hydrogen bonding and by an electron density topology analysis that identifies characteristic features of halogen bonding. A similar approach should be able to solve many complex 2D supramolecular structures, and we predict its increasing use in molecular nanoscience at surfaces

Confection D’une Colostomie De Maydl (Sur Baguette) En Situation De Precarite

Nous avions présenté une procédure simplifiée et reproductible de réalisation d’une colostomie sur baguette de Maydl, en conditions de précarité. Il s’agissait d’utiliser une seringue stérile de 10 cc et un fil à peau

A new Miocene deep-sea chiton and early evidence for Teredinidae-sustained wood-fall communities

Deep-sea wood-falls are important biodiversity hot spots for insights on chemosynthesis-based communities. The study of deep-sea wood-fall-related palaeocommunities from the Neogene of north Italy shed light on interesting associations from the Miocene of Torrente Cinghio (Tortonian) and of Moncasale di Casina (Langhian). The most common components of this association are typical chemosynthetic/wood-fall molluscs, such as the gastropods Homalopoma sp. and Pseudonina bellardii, the bivalves Idas sp. and shipworms, and the chiton Leptochiton lignatilis n. sp., which belongs to a genus typical of recent sunken woods in tropical waters. The new species described is compared with other fossil and recent congeners, especially with those sharing the same kind of tegmental sculpture, fully covered with randomly or quincuncially arranged granules. An overview of the sunken wood-related chitons is provided. Surprisingly no taxa of the boring bivalves of the family Xylophagidae, whose species have been known to be fundamental for sustaining this kind of deep sea chemosynthetic ecosystem, were found in the studied site; however, other boring Teredinidae bivalves have been abundantly recovered. This suggests that, conversely to what has previously been observed on sunken wood communities, Teredinidae may be viewed as a counterpart for the maintenance of deep-sea wood-fall ecosystems

Neurinomes et neurofibromes spinaux diagnostic et resultats du traitement chirurgical a yaounde

Description les neurinomes et neurofibromes spinaux restent très peu étudiés en Afrique sub-saharienne. Objectif rapporter les résultats du traitement chirurgical des neurinomes et neurofibromes spinaux à Yaoundé. Méthodes étude rétrospective menée à l’Hôpital Général et à l’Hôpital Central de Yaoundé, du 1er Janvier 1995 au 1er Janvier 2005. Critères d’inclusion: dossier médical comprenant les résultats de l’examen clinique pré et post opératoire, ceux des examens neuroradiologiques et histopathologiques, le compte rendu opératoire. Un suivi post-opératoire minimal de six mois. Le résultat fonctionnel été évaluée par l’échelle de Karnofsky. Résultats sur 62 patients opérés d’une tumeur intrarachidiennes, 12 (19,35 %) ont été sélectionnés (neuf neurinomes, deux neurofibromes, un neurofibrosarcome). L’age moyen était de 40,66 ans ±13,20, le sex ratio 0,71. La durée moyenne de symptômes avant le diagnostic était de 17,83 mois ± 5,81, extrêmes 6 et 28 mois ; le signe d’appel le plus fréquent était la radiculalgie (six cas). Cinq patients étaient paraplégiques. Le score deKarnofsky moyen préopératoire était de 50,00 ±12,79 et de 70,83±23,53 en postopératoire. Le siège tumoral était cervical (quatre cas), dorsal (six cas), lombaire (deux cas). La tumeur était extradurale dans six cas, intra durale quatre, intra et extradurale deux cas. L’exérèse était macroscopiquement complète dans neuf cas, partielle dans trois. Cinq patients ont connu une amélioration permettant une réinsertion professionnelle. Conclusion le diagnostic des neurinomes et neurofibromes reste tardif dans notre environnement, ce qui limite lerésultat chirurgical

Modelling the interactions of NO in a-SiO2

Nitric oxide (NO) is often used for the passivation of SiC/SiO2 metal oxide semiconductor (MOS) devices. Although it is established experimentally, using XPS, EELS, and SIMS measurements, that the 4H-SiC/SiO2 interface is extensively nitridated, the mechanisms of NO incorporation and diffusion in amorphous (a)-SiO2 films are still poorly understood. We used Density Functional Theory (DFT) to simulate the diffusion of NO through a-SiO2 and correlate local steric environment in amorphous network to interstitial NO (NOi) incorporation energy and migration barriers. Using an efficient sampling technique we identify the energy minima and transition states for neutral and negatively charged NOi molecules. Neutral NO interacts with the amorphous network only weakly with the smallest incorporation energies in bigger cages. On the other hand NOi -1 binds at the intrinsic precursor sites for electron trapping

Universality of transport properties of ultra-thin oxide films

We report low-temperature measurements of current-voltage characteristics for highly conductive Nb/Al-AlOx-Nb junctions with thicknesses of the Al interlayer ranging from 40 to 150 nm and ultra-thin barriers formed by diffusive oxidation of the Al surface. In the superconducting state these devices have revealed a strong subgap current leakage. Analyzing Cooper-pair and quasiparticle currents across the devices, we conclude that the strong suppression of the subgap resistance comparing with conventional tunnel junctions originates from a universal bimodal distribution of transparencies across the Al-oxide barrier proposed earlier by Schep and Bauer. We suggest a simple physical explanation of its source in the nanometer-thick oxide films relating it to strong local barrier-height fluctuations which are generated by oxygen vacancies in thin aluminum oxide tunnel barriers formed by thermal oxidation.Comment: revised text and a new figur