Graphene-MoS2 Hybrid Technology for Large-Scale Two-Dimensional Electronics

Two-dimensional (2D) materials have generated great interest in the last few years as a new toolbox for electronics. This family of materials includes, among others, metallic graphene, semiconducting transition metal dichalcogenides (such as MoS2) and insulating Boron Nitride. These materials and their heterostructures offer excellent mechanical flexibility, optical transparency and favorable transport properties for realizing electronic, sensing and optical systems on arbitrary surfaces. In this work, we develop several etch stop layer technologies that allow the fabrication of complex 2D devices and present for the first time the large scale integration of graphene with molybdenum disulfide (MoS2) , both grown using the fully scalable CVD technique. Transistor devices and logic circuits with MoS2 channel and graphene as contacts and interconnects are constructed and show high performances. In addition, the graphene/MoS2 heterojunction contact has been systematically compared with MoS2-metal junctions experimentally and studied using density functional theory. The tunability of the graphene work function significantly improves the ohmic contact to MoS2. These high-performance large-scale devices and circuits based on 2D heterostructure pave the way for practical flexible transparent electronics in the future. The authors acknowledge financial support from the Office of Naval Research (ONR) Young Investigator Program, the ONR GATE MURI program, and the Army Research Laboratory. This research has made use of the MI.

Fabrication, Optical Analysis and Photonic Applications of Certain Metallic Nanostructure-Integrated Dye Doped Polymer Optical Fibers” submitted by Ms. Suneetha Sebastian

Polymer Optical Fibers have occupied historically a place for large core flexible fibers operating in short distances. In addition to their practical passive application in short-haul communication they constitute a potential research field as active devices with organic dopants. Organic dyes are preferred as dopants over organic semiconductors due to their higher optical cross section. Thus organic dyes as gain media in a polymer fiber is used to develop efficient and narrow laser sources with a tunability throughout the visible region or optical amplifier with high gain. Dyes incorporated in fiber form has added advantage over other solid state forms such as films since the pump power required to excite the molecules in the core of the fiber is less thereby utilising the pump power effectively. In 1987, Muto et.al investigated a dye doped step index polymer fiber laser. Afterwards, numerous researches have been carried out in this area demonstrating laser emission from step index, graded index and hollow optical fibers incorporating various dyes. Among various dyes, Rhodamine6G is the most widely and commonly used laser dye for the last four decades. Rhodamine6G has many desirable optical properties which make it preferable over other organic dyes such as Coumarin, Nile Blue, Curcumin etc. The research focus on the implementation of efficient fiber lasers and amplifiers for short fiber distances. Developing efficient plastic lasers with electrical pumping can be a new proposal in this field which demands lowest possible threshold pump energy of the gain medium in the cavity as an important parameter. One way of improving the efficiency of the lasers, through low threshold pump energy, is by modifying the gain of the amplifiers in the resonator/cavity. Success in the field of Radiative Decay Engineering can pave way to this problem. Laser gain media consisting of dye-nanoparticle composites can improve the efficiency by lowering the lasing threshold and enhancing the photostability. The electric field confined near the surface of metal nanoparticles due to Localized Surface Plasmon Resonance can be very effective for the excitation of active centers to impart high optical gain for lasing. Since the Surface Plasmon Resonance of nanoparticles of gold and silver lies in the visible range, it can affect the spectral emission characteristics of organic dyes such as Rhodamine6G through plasmon field generated by the particles. The change in emission of the dye placed near metal nanoparticles depend on plasmon field strength which in turn depends on the type of metal, size of nanoparticle, surface modification of the particle and the wavelength of incident light. Progress in fabrication of different types of nanostructures lead to the advent of nanospheres, nanoalloys, core-shell and nanowires to name a few. The thesis deals with the fabrication and characterisation of polymer optical fibers with various metallic and bimetallic nanostructures incorporated in the gain media for efficient fiber lasers with low threshold and improved photostability.

Political participation as public pedagogy : The Educational Situation in Young People´s Political Conversations in Social Media

In this article we argue that young people’s political participation in the social media can be considered ‘public pedagogy’. The argument builds on a previous empirical analysis of a Swedish net community called Black Heart. Theoretically, the article is based on a particular notion of public pedagogy, education and Hannah Arendt’s expressive agonism. The political participation that takes place in the net community builds up an educational situation that involves central characteristics: communication, community building, a strong content focus and content production, argumentation and rule following. These characteristics pave the way for young people’s public voicing, experiencing, preferences and political interests that guide their everyday political life and learning – a phenomenon that we understand as a form of public pedagogy. 

Global Trade Governance and ASEAN: Studies of Trade-Related Aspects of Labor, Environment and Culture in Southeast Asia

Thesis (Ph.D.)--University of Washington, 2016-08

L'intégration des femmes sur le marché du travail et les différentes problématiques: réflexion appliquée à la clientèle du Centre Le Pont

L'intégration des femmes sur le marché du travail n'est pas un phénomène nouveau. Toutefois, pour chacune des femmes qui cherche à réaliser cette importante transition, bien des inquiétudes et des besoins se font présents. L'objectif principal de cet essai consiste à réaliser un relevé historique de l'intégration des femmes sur le marché du travail et à présenter une application concrète d'intervention et de soutien. La pertinence et l'originalité de l'essai repose sur un réel souci de faire des liens entre l'histoire des femmes, les obstacles qu'elles rencontrent et des activités de soutien susceptibles de faciliter leur intégration. Les préoccupations théoriques et pratiques sont toutes deux de première importance. L'essai s'amorce par une présentation historique visant à décrire le processus par lequel les femmes se sont progressivement intégrées sur le marché du travail. Cette présentation met en évidence que le phénomène de l'implication des femmes sur le marché du travail est largement soumis aux variations économiques et socio-culturelles de chacune des époques. C'est ainsi qu'il est possible d'observer des cycles où s'accroît massivement la participation des femmes et des cycles de "ressac" où elles sont invitées à retourner dans les responsabilités familiales, sociales et traditionnelles. Des événements tels les guerres et l'essor industriel ont favorisé l'entrée massive des femmes sur le marché du travail. A ce moment plusieurs parmi elles ont occupé des postes de responsabilité et des emplois du type non traditionnel. Même leurs nombreuses grossesses ne posaient pas d'obstacle à cette venue sur le marché du travail puisque des religieuses veillaient à la bonne éducation des petits. Le clergé, avec réserve, encourageait le mouvement des femmes à condition, bien sûr, qu'elles ne négligent pas la famille. La mécanisation et la fin de la guerre ont fait en sorte qu'il y a eu un surplus de main d'œuvre. Les femmes ont été les plus pénalisées. Elles se retrouvent dans le secteur tertiaire à occuper des emplois mal rémunérés et précaires. Cette perspective historique pave la voie à une présentation de la situation actuelle des femmes. Dans cette partie, nous nous attardons spécifiquement au taux de participation des femmes aux types d'emplois qu'elles occupent, aux conditions dans lesquelles elles exercent ces emplois et aux défis qu'elles relèvent en voulant concilier travail et responsabilités familiales. Bien des études, commissions et lois veulent rendre équitable l'accès à l'emploi. Malgré tout l'accès demeure toujours difficile. Même si le niveau de scolarité augmente, les femmes se confinent encore en 1990 dans les mêmes secteurs d'emploi. Il en origine un surplus de main-d’œuvre féminine. En somme, l'ensemble du premier chapitre vise essentiellement décrire l'évolution du processus d'intégration des femmes sur le marché du travail et des conditions dans lesquelles elles exercent leur emploi. Cette réflexion historique nous semble pertinente puisqu'elle permet une compréhension plus juste des difficultés et des défis rencontrés par les femmes qui cherchent à s'intégrer sur le marché du travail. Nous avons réalisé ce relevé de documentation en référant principalement aux divers rapports gouvernementaux et à d'autres sources spécifiques d'information concernant la situation des femmes. Le second chapitre de l'essai présente d'abord un organisme visant à soutenir les femmes dans une démarche d'intégration : le Centre Le Pont. Nous nous attardons particulièrement au profil des participantes, aux difficultés qu'elles rencontrent et à leurs inquiétudes. Pour cette dernière dimension, nous avons choisi d'utiliser des témoignages provenant de participantes impliquées dans la démarche de formation. Nous présenterons même en appendice certains dessins réalisés par ces femmes et qui illustrent de belle façon quelques unes des inquiétudes les plus vives. Le dernier chapitre vise la présentation des objectifs principaux de l'intervention au Centre le Pont et la description de cinq types d'intervention soit : l'aide individuelle, le groupe d'entraide, le jeux de rôle, la démarche autonome et le suivi. Ces interventions nous invitent à proposer quelques innovations.

Les plasmocytes et leur niche: Étude de la génération de plasmocytes humains in vitro

Chez l’humain, les lymphocytes B mémoires IgG+ et IgA+ sont des cellules clés de l’immunité humorale. Ces cellules mémoires sont maintenues à long-terme dans notre organisme. Elles représentent une défense rapide et efficace contre toutes les infections que nous avons déjà vaincues pendant notre vie. Ces cellules mémoires qui rencontrent à nouveau leur antigène se différencient rapidement en plasmocytes à courte vie, et permettent la sécrétion massive d’immunoglobuline (Ig). La contrepartie mémoire de ces cellules sont les plasmocytes à longue vie qui sont présents dans les niches de la moelle osseuse et y sécrètent en permanence des anticorps protecteurs qui circulent dans le sang. Ces cellules sécrétrices peuvent avoir une durée de vie allant de dizaines d’années à la vie entière de l’individu. Les patients qui reçoivent des traitements de chimiothérapie ou de radiothérapie sont privés de ces cellules mémoires détruites par ces traitements au même titre que les cellules cancéreuses. Ces patients deviennent vulnérables aux infections et leur survie dépend de la régénération rapide de leur système hématopoïétique. Notre équipe a déjà mis au point une méthode pour préparer de grandes quantités des cellules mémoires capables de sécréter des IgG et des IgA. Les présents travaux visent à générer des plasmocytes fonctionnels et capables de survivre à long terme in vitro. La stratégie expérimentale visait à établir des conditions permettant de se rapprocher de l’environnement de la moelle osseuse. Dans un premier temps, nous avons étudié les paramètres permettant la différenciation des lymphocytes B mémoires en plasmocytes. Étant donné l’importance du potentiel redox dans l’environnement de la moelle osseuse, nous avons d’abord tenté d’en contrôler l’impact avec un antioxydant, le N-acétyle cystéine (NAC). Nos résultats ont démontré que le NAC avait un effet significatif et diminuait la phosphorylation de la protéine STAT3 en raison d’une inhibition des kinases JAK2 et JAK3. Étonnamment, cet antioxydant retardait la différenciation de nos lymphocytes B qui étaient stimulés avec une forte interaction CD40-CD154. Par la suite, la comparaison des interactions CD40-CD154 et CD27-CD70 a permis de conclure qu’il était essentiel de réduire à son minimum l’interaction CD40-CD154 et qu’il fallait ajouter les cytokines IL-6 et IL-10. Les cellules CD31+CD38+CD138+ générées présentaient un phénotype similaire à celui des plasmocytes de la moelle osseuse. Malheureusement la fréquence de ces cellules était faible et leur viabilité insuffisante. Afin d’augmenter la survie de ces cellules le dernier volet de nos travaux visait à se rapprocher des niches de la moelle osseuse. Notre but a été atteint en ajoutant des cellules mésenchymateuses issues de la moelle osseuse en présence de 8% de dioxygène (O2). Les cellules CD31+CD38+CD138+ générées ont une excellente viabilité et représentent plus de 50% des cellules totales en culture. De plus, le modèle de culture est maintenant établi dans un milieu exempt de sérum et de protéines animales. Dans l’ensemble, nos résultats permettent de proposer la production ex vivo de plasmocytes autologues avec une perspective thérapeutique pour réduire les risques d’infections des patients devenues immunodéficients, suite à un traitement de radiothérapie ou de chimiothérapie.

Proof theory for hybrid(ised) logics

Hybridisation is a systematic process along which the characteristic features of hybrid logic, both at the syntactic and the semantic levels, are developed on top of an arbitrary logic framed as an institution. In a series of papers this process has been detailed and taken as a basis for a speci cation methodology for recon gurable systems. The present paper extends this work by showing how a proof calculus (in both a Hilbert and a tableau based format) for the hybridised version of a logic can be systematically generated from a proof calculus for the latter. Such developments provide the basis for a complete proof theory for hybrid(ised) logics, and thus pave the way to the development of (dedicated) proof support.

POLYMER-NANOPARTICLE COMPOSITES FOR APPLICATIONS IN FLEXIBLE ELECTRONICS

The aim of this dissertation was to investigate flexible polymer-nanoparticle composites with unique magnetic and electrical properties. Toward this goal, two distinct projects were carried out. The first project explored the magneto-dielectric properties and morphology of flexible polymer-nanoparticle composites that possess high permeability (µ), high permittivity (ε) and minimal dielectric, and magnetic loss (tan δε, tan δµ). The main materials challenges were the synthesis of magnetic nanoparticle fillers displaying high saturation magnetization (Ms), limited coercivity, and their homogeneous dispersion in a polymeric matrix. Nanostructured magnetic fillers including polycrystalline iron core-shell nanoparticles, and constructively assembled superparamagnetic iron oxide nanoparticles were synthesized, and dispersed uniformly in an elastomer matrix to minimize conductive losses. The resulting composites have demonstrated promising permittivity (22.3), permeability (3), and sustained low dielectric (0.1), magnetic (0.4) loss for frequencies below 2 GHz. This study demonstrated nanocomposites with tunable magnetic resonance frequency, which can be used to develop compact and flexible radio frequency devices with high efficiency. The second project focused on fundamental research regarding methods for the design of highly conductive polymer-nanoparticle composites that can maintain high electrical conductivity under tensile strain exceeding 100%. We investigated a simple solution spraying method to fabricate stretchable conductors based on elastomeric block copolymer fibers and silver nanoparticles. Silver nanoparticles were assembled both in and around block copolymer fibers forming interconnected dual nanoparticle networks, resulting in both in-fiber conductive pathways and additional conductive pathways on the outer surface of the fibers. Stretchable composites with conductivity values reaching 9000 S/cm maintained 56% of their initial conductivity after 500 cycles at 100% strain. The developed manufacturing method in this research could pave the way towards direct deposition of flexible electronic devices on any shaped substrate. The electrical and electromechanical properties of these dual silver nanoparticle network composites make them promising materials for the future construction of stretchable circuitry for displays, solar cells, antennas, and strain and tactility sensors.

Analysis on the connotation of probability in the artificial intelligence algorithm for economic decision making.

This paper analyzes the inner relations between classical sub-scheme probability and statistic probability, subjective probability and objective probability, prior probability and posterior probability, transition probability and probability of utility, and further analysis the goal, method, and its practical economic purpose which represent by these various probability from the perspective of mathematics, so as to deeply understand there connotation and its relation with economic decision making, thus will pave the route for scientific predication and decision making.

Coupling of magnetic, strain and electric polarization fields in the structure of multiferroic material

The comprehensive study on the coupling of magnetism, electrical polarization and the crystalline lattice with the off-stoichiometric effects in self-doped multiferroic hexagonal h-LuMnxO3±δ (0.92≤x≤1.12) ceramic oxides was carried out for the PhD work. There is a complex coupling of the three ferroic degrees. The cancelation of the magnetic moments of ions in the antiferromagnetic order, electric polarization with specific vortex/antivortex topology and lattice properties have pushed researchers to find out ways to disclose the underlying physics and chemistry of magneto-electric and magneto-elastic couplings of h-RMnO3 multiferroic materials. In this research work, self-doping of Lu-sites or Mn-sites of h-LuMnxO3±δ ceramics prepared via solid state route was done to pave a way for deeper understanding of the antiferromagnetic transition, the weak ferromagnetism often reported in the same crystalline lattices and the ferroelectric properties coupled to the imposed lattice changes. Accordingly to the aim of the PhD thesis, the objectives set for the sintering study in the first chapter on experimental results were two. First, study of sintering off-stoichiometric samples within conditions reported in the bibliography and also extracted from the phase diagrams of the LuMnxO3±δ, with a multiple firings ending with a last high temperature step at 1300ºC for 24 hours. Second, explore longer annealing times of up to 240 hours at the fixed temperature of 1300 ºC in a search for improving the properties of the solid solution under study. All series of LuMnxO3±δ ceramics for each annealing time were characterized to tentatively build a framework enabling comparison of measured properties with results of others available in literature. XRD and Rietveld refinement of data give the evolution the lattice parameters as a function to x. Shrinkage of the lattice parameters with increasing x values was observed, the stability limit of the solid solution being determined by analysis of lattice parameters. The evolution of grain size and presence of secondary phases have been investigated by means of TEM, SEM, EDS and EBSD techniques. The dependencies of grain growth and regression of secondary phases on composition x and time were further characterized. Magnetic susceptibility of samples and magnetic irreversibility were extensively examined in the present work. The dependency of magnetic susceptibility, Neel ordering transition and important magnetic parameters are determined and compared to observation in other multiferroics in the following chapter of the thesis. As a tool of high sensitivity to detect minor traces of the secondary phase hausmannite, magnetic measurements are suggested for cross-checking of phase diagrams. Difficulty of previous studies on interpreting the magnetic anomaly below 43 K in h-RMnO3 oxides was discussed and assigned to the Mn3O4 phase, with supported of the electron microscopy. Magneto-electric coupling where AFM ordering is coupled to dielectric polarization is investigated as a function of x and of sintering condition via frequency and temperature dependent complex dielectric constant measurements in the final chapter of the thesis. Within the limits of solid solubility, the crystalline lattice of off-stoichiometric ceramics was shown to preserve the magneto-electric coupling at TN. It represents the first research work on magneto-electric coupling modified by vacancy doping to author’s knowledge. Studied lattices would reveal distortions at the atomic scale imposed by local changes of x dependent on sintering conditions which were widely inspected by using TEM/STEM methods, complemented with EDS and EELS spectroscopy all together to provide comprehensive information on cross coupling of distortions, inhomogeneity and electronic structure assembled and discussed in a specific chapter. Internal interfaces inside crystalline grains were examined. Qualitative explanations of the measured magnetic and ferroelectric properties were established in relation to observed nanoscale features of h-LuMnxO3±δ ceramics. Ferroelectric domains and topological defects are displayed both in TEM and AFM/PFM images, the later technique being used to look at size, distribution and switching of ferroelectric domains influenced by vacancy doping at the micron scale bridging to complementary TEM studies on the atomic structure of ferroelectric domains. In support to experimental study, DFT simulations using Wien2K code have been carried out in order to interpret the results of EELS spectra of O K-edge and to obtain information on the cation hybridization to oxygen ions. The L3,2 edges of Mn is used to access the oxidation state of the Mn ions inside crystalline grains. In addition, rehybridization driven ferroelectricity is also evaluated by comparing the partial density of states of the orbitals of all ions of the samples, also the polarization was calculated and correlated to the off-stoichiometric effect.

EXCITON ENGINEERING THROUGH TUNALBLE FLUORESCENT QUANTUM DEFECTS

This thesis demonstrates exciton engineering in semiconducting single-walled carbon nanotubes through tunable fluorescent quantum defects. By introducing different functional moieties on the sp2 lattice of carbon nanotubes, the nanotube photoluminescence is systematically tuned over 68 meV in the second near-infrared window. This new class of quantum emitters is enabled by a new chemistry that allows covalent attachment of alkyl/aryl functional groups from their iodide precursors in aqueous solution. Using aminoaryl quantum defects, we show that the pH and temperature of complex fluids can be optically measured through defect photoluminescence that encodes the local environment information. Furthermore, defect-bound trions, which are electron-hole-electron tri-carrier quasi-particles, are observed in alkylated single-walled carbon nanotubes at room temperature with surprisingly high photoluminescence brightness. Collectively, the emission from defect-bound excitons and trions in (6,5)-single walled carbon nanotubes is 18-fold brighter than that of the native exciton. These findings pave the way to chemical tailoring of the electronic and optical properties of carbon nanostructures with fluorescent quantum defects and may find applications in optoelectronics and bioimaging.

Greffage d’un film mince de nano-TiO2 sur les fibres naturelles cellulosiques pour le renforcement de biocomposites polymériques

Abstract : Natural materials have received a full attention in many applications because they are degradable and derived directly from earth. In addition to these benefits, natural materials can be obtained from renewable resources such as plants (i.e. cellulosic fibers like flax, hemp, jute, and etc). Being cheap and light in weight, the cellulosic natural fiber is a good candidate for reinforcing bio-based polymer composites. However, the hydrophilic nature -resulted from the presence of hydroxyl groups in the structure of these fibers- restricts the application of these fibers in the polymeric matrices. This is because of weak interfacial adhesion, and difficulties in mixing due to poor wettability of the fibers within the matrices. Many attempts have been done to modify surface properties of natural fibers including physical, chemical, and physico-chemical treatments but on the one hand, these treatments are unable to cure the intrinsic defects of the surface of the fibers and on the other hand they cannot improve moisture, and alkali resistance of the fibers. However, the creation of a thin film on the fibers would achieve the mentioned objectives. This study aims firstly to functionalize the flax fibers by using selective oxidation of hydroxyl groups existed in cellulose structure to pave the way for better adhesion of subsequent amphiphilic TiO[subscript 2] thin films created by Sol-Gel technique. This method is capable of creating a very thin layer of metallic oxide on a substrate. In the next step, the effect of oxidation on the interfacial adhesion between the TiO[subscript 2] film and the fiber and thus on the physical and mechanical properties of the fiber was characterized. Eventually, the TiO[subscript 2] grafted fibers with and without oxidation were used to reinforce poly lactic acid (PLA). Tensile, impact, and short beam shear tests were performed to characterize the mechanical properties while Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic mechanical analysis (DMA), and moisture absorption were used to show the physical properties of the composites. Results showed a significant increase in physical and mechanical properties of flax fibers when the fibers were oxidized prior to TiO[subscript 2] grafting. Moreover, the TiO[subscript 2] grafted oxidized fiber caused significant changes when they were used as reinforcements in PLA. A higher interfacial strength and less amount of water absorption were obtained in comparison with the reference samples.

Balancing Belligerents or Feeding the Beast: Transforming Conflict Traps

Since the end of the Cold War, recurring civil conflicts have been the dominant form of violent armed conflict in the world, accounting for 70% of conflicts active between 2000-2013. Duration and intensity of episodes within recurring conflicts in Africa exhibit four behaviors characteristic of archetypal dynamic system structures. The overarching questions asked in this study are whether these patterns are robustly correlated with fundamental concepts of resiliency in dynamic systems that scale from micro-to macro levels; are they consistent with theoretical risk factors and causal mechanisms; and what are the policy implications. Econometric analysis and dynamic systems modeling of 36 conflicts in Africa between 1989 -2014 are combined with process tracing in a case study of Somalia to evaluate correlations between state characteristics, peace operations and foreign aid on the likelihood of observed conflict patterns, test hypothesized causal mechanisms across scales, and develop policy recommendations for increasing human security while decreasing resiliency of belligerents. Findings are that observed conflict patterns scale from micro to macro levels; are strongly correlated with state characteristics that proxy a mix of cooperative (e.g., gender equality) and coercive (e.g., security forces) conflict-balancing mechanisms; and are weakly correlated with UN and regional peace operations and humanitarian aid. Interactions between peace operations and aid interventions that effect conflict persistence at micro levels are not seen in macro level analysis, due to interdependent, micro-level feedback mechanisms, sequencing, and lagged effects. This study finds that the dynamic system structures associated with observed conflict patterns contain tipping points between balancing mechanisms at the interface of micro-macro level interactions that are determined as much by factors related to how intervention policies are designed and implemented, as what they are. Policy implications are that reducing risk of conflict persistence requires that peace operations and aid interventions (1) simultaneously increase transparency, promote inclusivity (with emphasis on gender equality), and empower local civilian involvement in accountability measures at the local levels; (2) build bridges to horizontally and vertically integrate across levels; and (3) pave pathways towards conflict transformation mechanisms and justice that scale from the individual, to community, regional, and national levels.

The Repellent DEET Potentiates Carbamate Effects via Insect Muscarinic Receptor Interactions: An Alternative Strategy to Control Insect Vector-Borne Diseases.

International audience

Experiências formativas de jovens instrumentistas : um estudo a partir de entrevistas narrativas

Dissertação (mestrado)—Universidade de Brasília, Instituto de Artes, Departamento de Música, Programa de Pós-graduação em Música, 2015.