Dirac point resonances due to atoms and molecules adsorbed on graphene and transport gaps and conductance quantization in graphene nanoribbons with covalently bonded adsorbates

We present a tight binding theory of the Dirac point resonances due to adsorbed atoms and molecules on an infinite 2D graphene sheet based on the standard tight binding model of the graphene p-band electronic structure and the extended Huckel model of the adsorbate and nearby graphene carbon atoms. The relaxed atomic geometries of the adsorbates and graphene are calculated using density functional theory. Our model includes the effects of the local rehybridization of the graphene from the sp^2 to sp^3 electronic structure that occurs when adsorbed atoms or molecules bond covalently to the graphene. Unlike in previous tight-binding models of Dirac point resonances, adsorbed species with multiple extended molecular orbitals and bonding to more than one graphene carbon atom are treated. More accurate and more general analytic expressions for the Green's function matrix elements that enter the T-matrix theory of Dirac point resonances than have been available previously are obtained. We study H, F, OH and O adsorbates on graphene and for each we find a strong scattering resonance (two resonances for O) near the Dirac point of graphene, by far the strongest and closest to the Dirac point being the resonance for H. We extract a minimal set of tight binding parameters that can be used to model resonant electron scattering and electron transport in graphene and graphene nanostructures with adsorbed H, F, OH and O accurately and efficiently. We also compare our results for the properties of Dirac point resonances due to adsorbates on graphene with those obtained by others using density functional theory-based electronic structure calculations, and discuss their relative merits. We then present calculations of electronic quantum transport in graphene nanoribbons with these adsorbed species...Comment: 21 pages, 9 figure

Fast ground-state cooling of mechanical resonator with time-dependent optical cavities

We propose a feasible scheme to cool down a mechanical resonator (MR) in a three-mirror cavity optomechanical system with controllable external optical drives. Under the Born-Oppenheimer (BO) approximation, the whole dynamics of the mechanical resonator and cavities is reduced to that of a time-dependent harmonic oscillator, whose effective frequency can be controlled through the optical driving fields. The fast cooling of the MR can be realized by controlling the amplitude of the optical drives. Significantly, we further show that the ground-state cooling may be achieved via the three-mirror cavity optomechanical system without the resolved sideband condition.Comment: Some references including our previous works on cooling of mechanical resonators are added, and some typos are corrected in this new version. Comments are welcom

Electric field manipulated reversible hydrogen storage in graphene studied by DFT calculations

Enhancement of hydrogen storage capacity is a great challenge that the research community is facing. The challenge lies on the fact of interdependence of hydrogen storage and release processes. It presents that the hydrogen release would be difficult if the hydrogen can be stored easily or vice versa. This work strategically tackles this critical issue through density functional theory (DFT) calculations by applying defect engineering on graphene, and also changing the hydrogenation/dehydrogenation and hydrogen diffusion chemical potentials via applying electric field. It is found that hydrogen molecules are dissociatively adsorbed on N-doped graphene spontaneously in the presence of a perpendicular electric field F. After adsorption, H atoms diffuse on N-doped graphene surface with low energy barrier and the graphene can be fully hydrogenated. By removing the electric filed, the stored hydrogen can be released efficiently under ambient conditions. It demonstrates that the N-doped graphene is a promising hydrogen storage material with the storage capacity up to 6.73 wt%. The electric field can act as a switch for hydrogen uptake/release processes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Enhanced stability of hydrogen atoms at the graphene/graphane interface of nanoribbons

The thermal stability of graphene/graphane nanoribbons (GGNRs) is investigated using density functional theory. It is found that the energy barriers for the diffusion of hydrogen atoms on the zigzag and armchair interfaces of GGNRs are 2.86 and 3.17 eV, respectively, while the diffusion barrier of an isolated H atom on pristine graphene was only ~0.3 eV. These results unambiguously demonstrate that the thermal stability of GGNRs can be enhanced significantly by increasing the hydrogen diffusion barriers through graphene/graphane interface engineering. This may provide new insights for viable applications of GGNRs.Comment: 13 pages, 1 figure, 2 tables to appear in Appl. Phys. Let

Perfect Function Transfer in two- and three- dimensions without initialization

We find analytic models that can perfectly transfer, without state initializati$ or remote collaboration, arbitrary functions in two- and three-dimensional interacting bosonic and fermionic networks. We elaborate on a possible implementation of state transfer through bosonic or fermionic atoms trapped in optical lattices. A significant finding is that the state of a spin qubit can be perfectly transferred through a fermionic system. Families of Hamiltonians, both linear and nonlinear, are described which are related to the linear Boson model and that enable the perfect transfer of arbitrary functions. This includes entangled states such as decoherence-free subsystems enabling noise protection of the transferred state.Comment: 4 pages, no figur

Clash detection or clash avoidance? An investigation into coordination problems in 3D BIM

Early collaboration is crucial if the final design is to be clash-free, and automation processes through Building Information Modelling (BIM) have the capacity to reduce clashes through 3D design coordination. Yet, current design practices are still dependent on clash detection and contemporary literature presents several reasons for this. This paper investigates the root causes of clashes with respect to achieving “clash avoidance” as proposed in PAS 1192-2 design phase specifications for BIM in the UK. Empirical data from BIM coordinators around the world was collected and analyzed using explanatory sequential mixed-methods. It was found that: (i) isolated working was the prime cause of high occurrences of clashes linked to mechanical, electrical and plumbing (MEP) 3D BIM systems; (ii) there is a link between non-BIM specific training (or the professional qualifications) of design practitioners with the high incidence of clashes; and (iii) the current structure of cloud-based common data environments (CDEs) does not facilitate clash avoidance and in fact, encourages isolated working in the early design stage by creating “digital information silos”. A conceptual framework for an open work in progress (OWIP) has been proposed to address this problem. These findings point to the need for more transparency during collaboration through CDE where designers from multidisciplinary backgrounds can engage in concurrent co-creation. This transparent and inclusive process could have consequences on how future architectural, engineering and construction (AEC) professionals are trained

Micelle-Template Synthesis of Nitrogen-Doped Mesoporous Graphene as an Efficient Metal-Free Electrocatalyst for Hydrogen Production

Synthesis of mesoporous graphene materials by softlate methods remains a great challenge, owing to the poor self-assembly capability of precursors and the severe agglomeration of graphene nanosheets. Herein, a micellelate strategy to prepare porous graphene materials with controllable mesopores, high specific surface areas and large pore volumes is reported. By fine-tuning the synthesis parameters, the pore sizes of mesoporous graphene can be rationally controlled. Nitrogen heteroatom doping is found to remarkably render electrocatalytic properties towards hydrogen evolution reactions as a highly efficient metal-free catalyst. The synthesis strategy and the demonstration of highly efficient catalytic effect provide benchmarks for preparing well-defined mesoporous graphene materials for energy production applications

Effet de la fumure organique sur la croissance et le rendement du riz NERICA 3 (WAB 450 IBP 28HB) à Faranah

Dans le but d’évaluer les effets de la matière organique sur la résistance du riz NERICA (New Rice for Africa) au stress hydrique sur sol ferralitique, un essai est réalisé au champ à Faranah de juillet à novembre 2008. Le dispositif utilisé est le Blocs Complets Randomisés factoriel à trois répétitions. Les traitements comportent: (i) trois dates de semis, à 15 jours d’intervalle, induisant trois niveaux de stress : 25/07/08 (d1), 9/08/08 (d2), 24/08/08 (d3); (ii) deux doses de matière organique D0 (témoin) et D1 (60 tonnes de fumure par hectare). La réponse au stress hydrique est évaluée à travers la croissance (hauteur des plants, longueur de la racine la plus allongée), le nombre de talles fertiles, le rendement et l’indice de sensibilité au stress. Les résultats montrent que quelque soit la date de semis l’apport de fumure augmente les rendements par rapport au témoin soit: 4,06 t/ha à d1, 2,43 t/ha à d2 1,44 t/ha à d3. Ainsi l’utilisation de la matière organique permet-elle de maintenir des niveaux de production plus élevés par rapport au témoin; donc la fertilisation améliore la résistance à l’insuffisance d’eau due à un semis tardif ou semi-tardif

Caractérisation physico-chimique et microbiologique du mulet jaune (Mugil cephalus) séché-pilé « Lekhlia » d’origine Imraguen, Mauritanie

Lekhlia est un produit d’origine Imraguen en Mauritanie, fabriqué à base de poisson (mulet jaune séchépilé). Un totale de 163 échantillons de Lekhlia ont été prélevés à partir de 7 villages imraguen et évalués pour leurs qualités physico-chimiques et microbiologiques. Les résultats obtenus ont montré des teneurs moyennes de 65,33% en protéines, de 12,33% en matière grasse, de 9,21% en cendres, de 9,63% en taux d’humidité et de 1,02 mg/100g en histamine. La valeur moyenne en FMAT est de 17,30 104 ufc/g. Les charges moyennes des germes témoins de la contamination fécale sont de 0,74 102 et 3,66 ufc/g respectivement pour les coliformes totaux et fécaux. La flore fongique est de 1,70 103 ufc/g. Cependant, aucun germe pathogène n’a été détecté dans les produits analysés.Mots-clés : Imraguen, mulet jaune, Lekhlia, qualité, Mauritanie

Electrodeposition of mesoporous Co<inf>3</inf>O<inf>4</inf> nanosheets on carbon foam for high performance supercapacitors

Metal oxide nanosheets have promising potential applications in novel energy storage devices. In this work, Co3O4 nanosheets/carbon foam with excellent supercapacitor characteristics was successfully fabricated, without using metal substrates. The experimental results demonstrate that the electrochemical tests showed that the as-prepared Co3O4 nanosheets exhibited an ideal capacitive behavior with a maximum specific capacitance of 106 F/g in 1 M NaOH solution at a scan rate of 0.1 V s-1. © 2014 Zhemi Xu et al