Giant cationic polyelectrolytes generated via electrochemical oxidation of single-walled carbon nanotubes

Previously, reduced single-walled carbon nanotube anions have been used for effective processing and functionalization. Here we report individually separate and distinct (that is, discrete) single-walled carbon nanotube cations, directly generated from a pure anode using a non-aqueous electrochemical technique. Cyclic voltammetry provides evidence for the reversibility of this nanoion electrochemisty, and can be related to the complex electronic density of states of the single-walled carbon nanotubes. Fixed potentiostatic oxidation allows spontaneous dissolution of nanotube cations ('nanotubium'); Raman spectroscopy and transmission electron microscopy show that sequential fractions are purified, separating amorphous carbon and short, defective single-walled carbon nanotubes, initially. The preparation of nanotubium, in principle, enables a new family of nucleophilic grafting reactions for single-walled carbon nanotubes, exploited here, to assemble nanotubes on amine-modified Si surfaces. Other nanoparticle polyelectrolyte cations may be anticipated

Matched ligands for small, stable colloidal nanoparticles of copper, cuprous oxide and cuprous sulfide

This work applies organometallic routes to copper(0/I) nanoparticles and describes how to match ligand chemistries with different material compositions. The syntheses involve reacting an organo-copper precursor, mesitylcopper(I) [CuMes]z (z=4, 5), at low temperatures and in organic solvents, with hydrogen, air or hydrogen sulfide to deliver Cu, Cu2 O or Cu2 S nanoparticles. Use of sub-stoichiometric quantities of protonated ligand (pro-ligand; 0.1-0.2 equivalents vs. [CuMes]z ) allows saturation of surface coordination sites but avoids excess pro-ligand contaminating the nanoparticle solutions. The pro-ligands are nonanoic acid (HO2 CR1 ), 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (HO2 CR2 ) or di(thio)nonanoic acid, (HS2 CR1 ), and are matched to the metallic, oxide or sulfide nanoparticles. Ligand exchange reactions reveal that copper(0) nanoparticles may be coordinated by carboxylate or di(thio)carboxylate ligands, but Cu2 O is preferentially coordinated by carboxylate ligands and Cu2 S by di(thio)carboxylate ligands. This work highlights the opportunities for organometallic routes to well-defined nanoparticles and the need for appropriate ligand selection

Matched Ligands for Small, Stable Colloidal Nanoparticles of Copper, Cuprous Oxide and Cuprous Sulfide

This work applies organometallic routes to copper(0/I) nanoparticles and describes how to match ligand chemistries with different material compositions. The syntheses involve reacting an organo-copper precursor, mesitylcopper(I) [CuMes]z (z=4, 5), at low temperatures and in organic solvents, with hydrogen, air or hydrogen sulfide to deliver Cu, Cu2O or Cu2S nanoparticles. Use of sub-stoichiometric quantities of protonated ligand (pro-ligand; 0.1–0.2 equivalents vs. [CuMes]z) allows saturation of surface coordination sites but avoids excess pro-ligand contaminating the nanoparticle solutions. The pro-ligands are nonanoic acid (HO2CR1), 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (HO2CR2) or di(thio)nonanoic acid, (HS2CR1), and are matched to the metallic, oxide or sulfide nanoparticles. Ligand exchange reactions reveal that copper(0) nanoparticles may be coordinated by carboxylate or di(thio)carboxylate ligands, but Cu2O is preferentially coordinated by carboxylate ligands and Cu2S by di(thio)carboxylate ligands. This work highlights the opportunities for organometallic routes to well-defined nanoparticles and the need for appropriate ligand selection

Cross-linked single-walled carbon nanotube aerogel electrodes via reductive coupling chemistry

Single-walled carbon nanotube (SWCNT) anions can be cross-linked by a dielectrophile to form covalent, carbon-bonded organogels. Freeze-drying produces cryogels with low density (2.3 mg cm−3), high surface area (766 m2 g−1), and high conductivity (9.4 S m−1), showing promise as supercapacitor electrodes. Counterion concentration controls debundling, grafting ratio, as well as all the resulting properties

Charged Carbon Nanomaterials: Redox Chemistries of Fullerenes, Carbon Nanotubes, and Graphenes

Since the discovery of buckminsterfullerene over 30 years ago, sp2-hybridised carbon nanomaterials (including fullerenes, carbon nanotubes, and graphene) have stimulated new science and technology across a huge range of fields. Despite the impressive intrinsic properties, challenges in processing and chemical modification continue to hinder applications. Charged carbon nanomaterials (CCNs), formed via the reduction or oxidation of these carbon nanomaterials, facilitate dissolution, purification, separation, chemical modification, and assembly. This approach provides a compelling alternative to traditional damaging and restrictive liquid phase exfoliation routes. The broad chemistry of CCNs not only provides a versatile and potent means to modify the properties of the parent nanomaterial but also raises interesting scientific issues. This review focuses on the fundamental structural forms: buckminsterfullerene, single-walled carbon nanotubes, and single-layer graphene, describing the generation of their respective charged nanocarbon species, their interactions with solvents, chemical reactivity, specific (opto)electronic properties, and emerging applications

Sexual Size Dimorphism and Body Condition in the Australasian Gannet

Funding: The research was financially supported by the Holsworth Wildlife Research Endowment. Acknowledgments We thank the Victorian Marine Science Consortium, Sea All Dolphin Swim, Parks Victoria, and the Point Danger Management Committee for logistical support. We are grateful for the assistance of the many field volunteers involved in the study.Peer reviewedPublisher PD

Reflexive learning, socio-cognitive conflict and peer-assessment to improve the quality of feedbacks in online tests

International audienceOur previous works have introduced the Tsaap-notes platform dedicated to the semi automatic generation of multiple choice questionnaire providing feedbacks: it reuses interactive questions asked by teachers during lectures, as well as the notes taken by students after the presentation of the results as feedbacks integrated into the quizzes. In this paper, we introduce a new feature which aims at increasing the number of contributions of students in order to significantly improve the quality of the feedbacks used in the resulting quizzes. This feature splits the submission of an answer into several distinct phases to harvest explanations given by students, and then applies an algorithm to filter the best contributions to be integrated as feedbacks in the tests. Our approach has been validated by a first experimentation involving master students enrolled in a computer science course

Ocean Surface Winds Drive Dynamics of Transoceanic Aerial Movements

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through “wind highways” that do not match the shortest great circle routes. Bird routes closely followed the low-cost “wind-highways” linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns

Ocean Surface Winds Drive Dynamics of Transoceanic Aerial Movements

Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through “wind highways” that do not match the shortest great circle routes. Bird routes closely followed the low-cost “wind-highways” linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns

Wind, Waves, and Wing Loading: Morphological Specialization May Limit Range Expansion of Endangered Albatrosses

Among the varied adaptations for avian flight, the morphological traits allowing large-bodied albatrosses to capitalize on wind and wave energy for efficient long-distance flight are unparalleled. Consequently, the biogeographic distribution of most albatrosses is limited to the windiest oceanic regions on earth; however, exceptions exist. Species breeding in the North and Central Pacific Ocean (Phoebastria spp.) inhabit regions of lower wind speed and wave height than southern hemisphere genera, and have large intrageneric variation in body size and aerodynamic performance. Here, we test the hypothesis that regional wind and wave regimes explain observed differences in Phoebastria albatross morphology and we compare their aerodynamic performance to representatives from the other three genera of this globally distributed avian family. In the North and Central Pacific, two species (short-tailed P. albatrus and waved P. irrorata) are markedly larger, yet have the smallest breeding ranges near highly productive coastal upwelling systems. Short-tailed albatrosses, however, have 60% higher wing loading (weight per area of lift) compared to waved albatrosses. Indeed, calculated aerodynamic performance of waved albatrosses, the only tropical albatross species, is more similar to those of their smaller congeners (black-footed P. nigripes and Laysan P. immutabilis), which have relatively low wing loading and much larger foraging ranges that include central oceanic gyres of relatively low productivity. Globally, the aerodynamic performance of short-tailed and waved albatrosses are most anomalous for their body sizes, yet consistent with wind regimes within their breeding season foraging ranges. Our results are the first to integrate global wind and wave patterns with albatross aerodynamics, thereby identifying morphological specialization that may explain limited breeding ranges of two endangered albatross species. These results are further relevant to understanding past and potentially predicting future distributional limits of albatrosses globally, particularly with respect to climate change effects on basin-scale and regional wind fields