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    ABSTRACT: Using positron emission particle tracking (PEPT), the influence of system geometry on the dynamical and segregative properties of a three dimensional, vibrofluidised granular system is explored. A relationship between the aspect ratio of a system and the degree of segregation observed is established, demonstrating the ability to adjust segregation intensity within a system simply by modifying its aspect ratio without altering any other parameters, including the number of particles within the system, its volume and the manner in which it is driven. Such a relationship is potentially of value in future research, as well as in industrial settings. The range over which this relationship is valid is determined in terms of the quantity q, the ratio of heating to cooling events within an excited granular system. Within this range, a relationship between self-diffusion, D, and aspect ratio, A, of the form D = alpha exp (beta A(gamma)) is also proposed. Finally, this study presents what is believed to be the first experimental evidence of sudden chain energy transfer events, a phenomenon recently discovered in two-dimensional granular beds, in a three-dimensional system.
    Powder Technology 07/2014; 261:133–142. DOI:10.1016/j.powtec.2014.04.009
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    ABSTRACT: We report the size-dependent propagation of gold nanoclusters through few-layer graphene (FLG). We employ aberration-corrected scanning transmission electron microscopy (STEM) to track the fate of Au55 and Au923 clusters that have been deposited, independently and isoenergetically, onto suspended FLG films using cluster beam deposition. We demonstrate that Au55 clusters penetrate through the FLG, whereas the monodisperse Au923 clusters reside at the surface. Our approach offers a route to the controlled incorporation of dopant nanoparticles and the generation of nanoscale defects in graphene.
    Nanoscale 11/2013; 6(3). DOI:10.1039/c3nr04770a
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    ABSTRACT: We report the assembly of magic number (C_{60})_{m}-(Au)_{n} complexes on the Au(111) surface. These complexes have a unique structure consisting of a single atomic layer Au island wrapped by a self-selected number (seven, ten, or twelve) of C_{60} molecules. The smallest structure consisting of 7 C_{60} molecules and 19 Au atoms, stable up to 400 K, has a preferred orientation on the surface. We propose a globalized metal-organic coordination mechanism for the stability of the (C_{60})_{m}-(Au)_{n} complexes.
    Physical Review Letters 11/2013; 111(18):186101. DOI:10.1103/PhysRevLett.111.186101
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    ABSTRACT: Leigh Canham received his BSc degree in physics from University College London (London, UK) in 1979 and his PhD in solid state physics from King's College London (London, UK). He now has over 30 years of experience conducting research on widely differing aspects of silicon technology. Two key personal discoveries - that nanostructured silicon can emit visible light efficiently (1990) and can be rendered medically biodegradable (1995) - have had significant academic (>15,000 citations) and commercial (multiple companies created) impact. Professor Canham is a scientist who is devoted to finding novel properties and uses for semiconductors that already pervade our everyday lives. He has 13 years of experience of start up company management, right through from cofounding with seed venture capital finance to NASDAQ listing. He has served on the board of two companies based in England, UK, one in Singapore and one in Australia. Since 1999, he has held an Honorary Professorship at the School of Physics, University of Birmingham (Birmingham, UK) for his work on luminescent silicon. In 2011, Leigh was a shortlisted finalist for the European Inventor of the Year Award from the European Patent Office for his work on biodegradable silicon. In 2012, he became a Thomson Reuters Citation Laureate for his work on luminescent silicon. Professor Canham has authored over 150 peer-reviewed papers and has more than 100 granted patents worldwide.
    Nanomedicine 10/2013; 8(10):1573-6. DOI:10.2217/nnm.13.134
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    ABSTRACT: A search for excited electrons is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb−1. The electroweak decays of excited electrons e∗→eγ, e∗→eZ and e∗→νW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e∗ production cross sections and on the ratio f/Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e∗ production via contact interactions is also addressed for the first time in ep collisions.
    Physics Letters B 09/2013; 666(2):131-139. DOI:10.1016/j.physletb.2008.07.014
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    ABSTRACT: A search for scalar and vector leptoquarks coupling to first generation fermions is performed using the e+p and e−p scattering data collected by the H1 experiment between 1994 and 2000. The data correspond to a total integrated luminosity of 117 pb−1. No evidence for the direct or indirect production of such particles is found in data samples with a large transverse momentum final state electron or with large missing transverse momentum. Constraints on leptoquark models are established. For leptoquark couplings of electromagnetic strength, leptoquarks with masses up to 275–325 GeV are ruled out at 95% confidence level. These limits improve and supercede earlier H1 limits based on subsamples of the data used here.
    Physics Letters B 09/2013; 629(1):9-19. DOI:10.1016/j.physletb.2005.09.048
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    ABSTRACT: One of the great quests in nanotechnology is to translate nanoprecision materials science into practical manufacturing processes. The paper by Angelova et al. in this issue of ACS Nano, which discusses the production of functional carbon-based membranes with a thickness of 0.5 to 3 nm, provides instructive insight into how researchers are pulling together complementary strands from a quarter century of nanoscience research to develop novel, hybrid processing schemes. In this Perspective, we reflect on the progress that is taking place in the two principal component technologies combined in this scheme, namely, (i) control of self-assembled monolayers, including their detailed atomic structures, and (ii) electron-induced manipulation and processing of molecular layers, as well as considering (iii) remaining challenges for thin membrane production in the future.
    ACS Nano 08/2013; 7(8). DOI:10.1021/nn403955e
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    ABSTRACT: Using a vertically vibrated, fully three-dimensional granular system, we investigate the impact of dissipative interactions between the particles in the system and the vertical sidewalls bounding it. We find that sidewall dissipation influences various properties of the bed including, but not limited to, the spatial distribution of granular temperatures, the functional form of velocity distributions, and the strength of convection. Simple, monotonic relationships are observed for all the aforementioned properties, including a striking linear relationship between convection strength and wall dissipation. We conclude that sidewall effects are not limited to the vicinity of the walls themselves, but extend into the bulk of the system and hence must be considered even in relatively wide, three-dimensional systems. We also propose the possibility of using the alteration of sidewall material as a method of "tuning" certain system parameters in situations where changing the bulk properties or driving parameters of a granular system may be undesirable.
    Physical Review Letters 07/2013; 111(3):038001. DOI:10.1103/PhysRevLett.111.038001
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    ABSTRACT: In this work we address the challenge of furthering our understanding of the driving forces responsible for the metal-metal interactions in industrially relevant bimetallic nanocatalysts, by taking a comparative approach to the atomic scale characterization of two core-shell nanorod systems (AuPd and AuRh). Using aberration-corrected scanning transmission electron microscopy, we show the existence of a randomly mixed alloy layer some 4-5 atomic layers thick between completely bulk immiscible Au and Rh, which facilitates fully epitaxial overgrowth for the first few atomic layers. In marked contrast in AuPd nanorods, we find atomically sharp segregation resulting in a quasi-epitaxial, strained interface between bulk miscible metals. By comparing the two systems, including molecular dynamics simulations, we are able to gain insights into the factors that may have influenced their structure and chemical ordering, which cannot be explained by the key structural and energetic parameters of either system in isolation, thus demonstrating the advantage of taking a comparative approach to the characterization of complex binary systems. This work highlights the importance of achieving a fundamental understanding of reaction kinetics in realizing the atomically controlled synthesis of bimetallic nanocatalysts.
    Nanoscale 07/2013; 5(16):7452-7457. DOI:10.1039/c3nr02560h
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    ABSTRACT: We have investigated the generation of highly pure higher-order Laguerre-Gauss (LG) beams at high laser power of order 100W, the same regime that will be used by 2nd generation gravitational wave interferometers such as Advanced LIGO. We report on the generation of a helical type LG33 mode with a purity of order 97% at a power of 83W, the highest power ever reported in literature for a higher-order LG mode.
    Physical Review Letters 06/2013; 110(25):251101. DOI:10.1103/PhysRevLett.110.251101
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Journal of Alloys and Compounds 01/2012; 521:178-182. DOI:10.1016/j.jallcom.2012.01.115
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Physical Review C 06/2015; 91(6):064905. DOI:10.1103/PhysRevC.91.064905
24 Downloads