Energy of \u3cem\u3eK\u3c/em\u3e-Momentum Dark Excitons in Carbon Nanotubes by Optical Spectroscopy

Phonon sideband optical spectroscopy determines the energy of the dark K-momentum exciton for (6,5) carbon nanotubes. One-phonon sidebands appear in absorption and emission, split by two zone-boundary (K-point) phonons. Their average energy locates the E11 K-momentum exciton 36 meV above the E11 bright level, higher than available theoretical estimates. A model for exciton-phonon coupling shows the absorbance sideband depends sensitively on the K-momentum exciton effective mass and has minimal contributions from zone-center phonons, which dominate the Raman spectra of carbon nanotubes

A Complete Electron Microscopy Volume of the Brain of Adult Drosophila melanogaster.

Drosophila melanogaster has a rich repertoire of innate and learned behaviors. Its 100,000-neuron brain is a large but tractable target for comprehensive neural circuit mapping. Only electron microscopy (EM) enables complete, unbiased mapping of synaptic connectivity; however, the fly brain is too large for conventional EM. We developed a custom high-throughput EM platform and imaged the entire brain of an adult female fly at synaptic resolution. To validate the dataset, we traced brain-spanning circuitry involving the mushroom body (MB), which has been extensively studied for its role in learning. All inputs to Kenyon cells (KCs), the intrinsic neurons of the MB, were mapped, revealing a previously unknown cell type, postsynaptic partners of KC dendrites, and unexpected clustering of olfactory projection neurons. These reconstructions show that this freely available EM volume supports mapping of brain-spanning circuits, which will significantly accelerate Drosophila neuroscience. VIDEO ABSTRACT

Optical and magnetic properties of carbon nanotube ensembles

In this work we use optical spectroscopy as a tool to probe the basic properties of carbon nanotubes (CNTs), which include structure-dependent magnetic susceptibility anisotropies Δχ, optical energy transfer between bundled semiconducting CNTs, the energy level splitting between bright singlets and dark K-momentum singlets in (6,5) CNTs, and surfactant-induced photoluminescence (PL) brightening in CNTs. Our polarized and unpolarized measurements of visible and near-infrared Raman scattering, absorbance, and PL are performed on ensembles of CNTs suspended in water, which allows for the high signal-to-noise spectra necessary for detecting weak signals. Additionally, optical techniques are well-suited for ( n, m)-selectivity in heterogeneous samples, since each ( n, m) species has a distinct series of optical resonances. We combine our experimental results with quantum and classical theories to model the response of CNT band structure in a magnetic field, quantify uniaxial and biaxial ordering, predict exciton-phonon coupling, and connect our experimental Δχ values to published calculations within a symmetry-expansion framework

Optical and magnetic properties of carbon nanotube ensembles

In this work we use optical spectroscopy as a tool to probe the basic properties of carbon nanotubes (CNTs), which include structure-dependent magnetic susceptibility anisotropies Δχ, optical energy transfer between bundled semiconducting CNTs, the energy level splitting between bright singlets and dark K-momentum singlets in (6,5) CNTs, and surfactant-induced photoluminescence (PL) brightening in CNTs. Our polarized and unpolarized measurements of visible and near-infrared Raman scattering, absorbance, and PL are performed on ensembles of CNTs suspended in water, which allows for the high signal-to-noise spectra necessary for detecting weak signals. Additionally, optical techniques are well-suited for ( n, m)-selectivity in heterogeneous samples, since each ( n, m) species has a distinct series of optical resonances. We combine our experimental results with quantum and classical theories to model the response of CNT band structure in a magnetic field, quantify uniaxial and biaxial ordering, predict exciton-phonon coupling, and connect our experimental Δχ values to published calculations within a symmetry-expansion framework

High-purity diamagnetic single-wall carbon nanotube buckypaper

0897-4756We describe a novel purification process for single-wall carbon nanotube (SWNT) materials that removes non-nanotube carbon and reduces ferromagnetic impurities to levels at which native SWNT magnetic properties predominate. Ferromagnetism is reduced from 1.04 to less than 0.013 emu/g by magnetic gradient filtration. This procedure creates samples of sufficient quality for spectroscopies such as nuclear magnetic resonance (NMR). The overall cleanliness and purity of the material is confirmed through NIR absorption spectroscopy, X-ray diffraction, C-60 filling experiments with yields exceeding 90%, and high-resolution C-13 NMR

Effects of pre-natal and early post-natal undernutrition on adult internal thoracic artery function

Objective: Previous studies in humans and animals have suggested that undernutrition in utero and in early post-natal life may lead to altered vascular function in a number of peripheral arteries. We investigated the effect of pre- and post-natal nutrient restriction on the vascular reactivity of the left internal thoracic artery using a sheep model.Methods: Welsh mountain ewes were mated and assigned to three dietary groups: (1) 100% of total nutritional requirements (control, n = 6); (2) 50% of total nutritional requirements during the first 31 days of gestation (n = 6); and (3) 50% nutritional restriction during the first 31 days of gestation, followed by a restriction in the diet of their offspring 12–25 weeks post-natally, designed to produce a 15% reduction in growth trajectory (n = 7). The male offspring were sacrificed at 130 weeks; the left internal thoracic artery was mounted onto a wire myograph and the reactivity of the vessel to various agonists measured.Results: The offspring of animals who underwent an early gestation nutrient restriction had a significantly increased basal tone (0.41 ± 0.25 vs 6.34 ± 1.35, p = 0.015) and sensitivity to phenylephrine (log EC50: ?6.23 ± 0.04 M vs ?5.74 ± 0.17 M, p = 0.036) as compared with control animals. However, this phenomenon was not seen in animals that underwent both pre- and post-natal nutrient restriction. Conclusions: Pre-natal undernutrition increases the basal tone and sensitivity of the left internal thoracic artery to phenylephrine. This effect is significantly attenuated by continued undernutrition in early post-natal life. These experiments suggest that in utero and early post-natal undernutrition may be important determinants of graft function in later life

SLEUTH* : un modèle d’expansion urbaine scénario-dépendant

International audienceProspective modeling helps decision-making of the stakeholders through exploring a range of possible futures and alternatives of urban development. However, the modeler often faces the limitations of existing simulation tools, which are calibrated based on past trends data, and particularly not adapted to project contrasting prospective scenarios. The aim of this paper is to present a non-path dependent model (SLEUTH*) which is derived from the cellular automata-based SLEUTH model in order to be used in a fully controlled forecasting mode. The SLEUTH model was selected thanks to its ability to simulate four urban expansion patterns: spontaneous growth, new spreading centers, edge-growth and road-influenced growth. SLEUTH*, which is a “scenario-based” model, allows users: (i) to define the – exogenous – expected amount of change regardless of past trends; (ii) to specify the contribution of each urban growth patterns with respect to scenario hypothesis; and (iii) to incorporate an additional spatially explicit factor such as the attractiveness map. Furthermore, SLEUTH* is designed to execute automatically predefined prospective scenarios composed by sub-periods that show different spatial dynamics.La modélisation prospective permet d'éclairer les réflexions des acteurs locaux en leur proposant un panel de futurs et d'alternatives possibles en matière de planification et d'aménagement du territoire. Or, le modélisateur est souvent confronté aux limites des outils de simulation existants qui, calibrés à partir de données passées, sont particulièrement non adaptés à la spatialisation de scénarios prospectifs en rupture avec les tendances passées. L'objectif de cet article est de présenter un modèle de simulation spatiale (SLEUTH*) dédié à la projection de scénarios contrastés et prédéfinis d’expansion urbaine. SLEUTH* constitue une version « scénario-dépendante » issue de la modification du modèle SLEUTH. Ce dernier, dont le fonctionnement est basé sur un automate cellulaire, est un modèle empirique, dynamique et spatialement explicite. Le choix du modèle SLEUTH tient à sa capacité à simuler quatre formes d’expansion urbaine : expansion par diffusion, en continuité de l’urbain existant, le long des routes et par création de nouveaux centres. Les améliorations apportées permettent aux utilisateurs : (i) une maîtrise de la quantité de changement de manière exogène au modèle et indépendante des tendances passées ; (ii) une maîtrise des formes urbaines en offrant à l’utilisateur la possibilité de spécifier les pourcentages contributifs de chacune des formes d'urbanisation adaptées à chaque scénario ; et (iii) l’intégration d’un facteur additionnel de localisation des changements, en l’occurrence l’attractivité du territoire ou le prix des loyers. De plus, SLEUTH* est conçu pour exécuter de façon automatique la spatialisation dynamique d'un scénario prospectif décliné en sous- périodes présentant des dynamiques spatiales variables au cours du temps