School of Physics - Research Publications
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ItemNo Preview AvailableImpact of Surface Functionalization on the Quantum Coherence of Nitrogen-Vacancy Centers in Nanodiamonds(AMER CHEMICAL SOC, 2018-04-18)Nanoscale quantum probes such as the nitrogen-vacancy (NV) center in diamonds have demonstrated remarkable sensing capabilities over the past decade as control over fabrication and manipulation of these systems has evolved. The biocompatibility and rich surface chemistry of diamonds has added to the utility of these probes but, as the size of these nanoscale systems is reduced, the surface chemistry of diamond begins to impact the quantum properties of the NV center. In this work, we systematically study the effect of the diamond surface chemistry on the quantum coherence of the NV center in nanodiamonds (NDs) 50 nm in size. Our results show that a borane-reduced diamond surface can on average double the spin relaxation time of individual NV centers in nanodiamonds when compared to thermally oxidized surfaces. Using a combination of infrared and X-ray absorption spectroscopy techniques, we correlate the changes in quantum relaxation rates with the conversion of sp2 carbon to C-O and C-H bonds on the diamond surface. These findings implicate double-bonded carbon species as a dominant source of spin noise for near surface NV centers. The link between the surface chemistry and quantum coherence indicates that through tailored engineering of the surface, the quantum properties and magnetic sensitivity of these nanoscale systems may approach that observed in bulk diamond.
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ItemNo Preview AvailableSpeckle and Conservation(International Seminars, 2008)The aim of this research is to demonstrate the usefulness of speckle, a trait of an expanded laser beam, for the non-destructive testing of artwork in both the imaging of subsurface structure and the quantitative detection of physical movement of canvas. Laser Speckle Contrast Method (LSCI) is a useful method for the viewing of subsurface layers and movement. By investigating the statistical properties of dynamic speckle it is possible to reveal drawings that are hidden beneath scattering layers such as the primary layer of paint or adhered paper. This is achieved by taking a series of speckle images captured in a short time frame and applying one of a number of post processing algorithms. We explore the limitations of this method when applied to various paper samples that have a sketch executed in various media beneath the top layer. The ability to resolve gray scale images was examined as well as looking at the dependence of the contrast of the revealed drawings to the temperature of the surface. Current work is being done on using LSCI to reveal indentations in artwork caused by the application process. The successful use of Electronic Speckle Pattern Interferometry (ESPI) both in the laboratory and in-situ for the detection of in-plane movement of painted canvas due to humidity fluctuations and the out-of-plane movement of paint as it dries has also been demonstrated. Canvas paintings can be very susceptible to movement due to changes of the environment. ESPI is a non-destructive technique yielding sensitive results that can detect displacement on a surface of less than the wavelength of the illuminating coherent light source. While ESPI has been successfully applied to the in-situ study of painted frescoes, previous studies have employed tensile testers as a support for painted canvas. We have shown a portable version of ESPI to be of use in tropical environment in the Philippines, Malaysia and Singapore with original artworks where variations in humidity occur and the samples have not undergone special preparation before analysis, revealing significant directional movements. Furthermore, a simple variation in the direction of beams paths permits the characterisation of out-of-plane movement, specifically as the height of paint shrinks due to the drying process. We have used ESPI to view the drying process of alkyd resin paints over the time period of 24 hours.
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ItemNanoscale magnetometry through quantum control of nitrogen-vacancy centres in rotationally diffusing nanodiamonds(IOP Publishing, 2013)The confluence of quantum physics and biology is driving a new generation of quantum-based sensing and imaging technology capable of harnessing the power of quantum effects to provide tools to understand the fundamental processes of life. One of the most promising systems in this area is the nitrogen–vacancy centre in diamond—a natural spin qubit which remarkably has all the right attributes for nanoscale sensing in ambient biological conditions. Typically the nitrogen–vacancy qubits are fixed in tightly controlled/isolated experimental conditions. In this work quantum control principles of nitrogen–vacancy magnetometry are developed for a randomly diffusing diamond nanocrystal. We find that the accumulation of geometric phases, due to the rotation of the nanodiamond plays a crucial role in the application of a diffusing nanodiamond as a bio-label and magnetometer. Specifically, we show that a freely diffusing nanodiamond can offer real-time information about local magnetic fields and its own rotational behaviour, beyond continuous optically detected magnetic resonance monitoring, in parallel with operation as a fluorescent biomarker.
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ItemVortex lattice formation in dipolar Bose-Einstein condensates via rotation of the polarization(AMER PHYSICAL SOC, 2019-08-26)The behavior of a harmonically trapped dipolar Bose-Einstein condensate with its dipole moments rotating at angular frequencies lower than the transverse harmonic trapping frequency is explored in the co-rotating frame. We obtain semi-analytical solutions for the stationary states in the Thomas-Fermi limit of the corresponding dipolar Gross-Pitaevskii equation and utilize linear stability analysis to elucidate a phase diagram for the dynamical stability of these stationary solutions with respect to collective modes. These results are verified via direct numerical simulations of the dipolar Gross-Pitaevskii equation, which demonstrate that dynamical instabilities of the co-rotating stationary solutions lead to the seeding of vortices that eventually relax into a triangular lattice configuration. Our results illustrate that rotation of the dipole polarization represents a new route to vortex formation in dipolar Bose-Einstein condensates.
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ItemComparative Mapping of Seed Dormancy Loci Between Tropical and Temperate Ecotypes of Weedy Rice (Oryza sativa L.)(OXFORD UNIV PRESS INC, 2017-08)Genotypic variation at multiple loci for seed dormancy (SD) contributes to plant adaptation to diverse ecosystems. Weedy rice (Oryza sativa) was used as a model to address the similarity of SD genes between distinct ecotypes. A total of 12 quantitative trait loci (QTL) for SD were identified in one primary and two advanced backcross (BC) populations derived from a temperate ecotype of weedy rice (34.3°N Lat.). Nine (75%) of the 12 loci were mapped to the same positions as those identified from a tropical ecotype of weedy rice (7.1°N Lat.). The high similarity suggested that the majority of SD genes were conserved during the ecotype differentiation. These common loci are largely those collocated/linked with the awn, hull color, pericarp color, or plant height loci. Phenotypic correlations observed in the populations support the notion that indirect selections for the wild-type morphological characteristics, together with direct selections for germination time, were major factors influencing allelic distributions of SD genes across ecotypes. Indirect selections for crop-mimic traits (e.g., plant height and flowering time) could also alter allelic frequencies for some SD genes in agroecosystems. In addition, 3 of the 12 loci were collocated with segregation distortion loci, indicating that some gametophyte development genes could also influence the genetic equilibria of SD loci in hybrid populations. The SD genes with a major effect on germination across ecotypes could be used as silencing targets to develop transgene mitigation (TM) strategies to reduce the risk of gene flow from genetically modified crops into weed/wild relatives.
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ItemMeasurement of the Bc+ meson lifetime using Bc+ → J/ψ μ+νμX decays(SPRINGER, 2014-05-01)The lifetime of the [Formula: see text] meson is measured using semileptonic decays having a [Formula: see text] meson and a muon in the final state. The data, corresponding to an integrated luminosity of [Formula: see text], are collected by the LHCb detector in [Formula: see text] collisions at a centre-of-mass energy of 8 TeV. The measured lifetime is [Formula: see text]where the first uncertainty is statistical and the second is systematic.
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ItemDiscovery of processive catalysis by an exo-hydrolase with a pocket-shaped active site.(Springer Science and Business Media LLC, 2019-05-20)Substrates associate and products dissociate from enzyme catalytic sites rapidly, which hampers investigations of their trajectories. The high-resolution structure of the native Hordeum exo-hydrolase HvExoI isolated from seedlings reveals that non-covalently trapped glucose forms a stable enzyme-product complex. Here, we report that the alkyl β-D-glucoside and methyl 6-thio-β-gentiobioside substrate analogues perfused in crystalline HvExoI bind across the catalytic site after they displace glucose, while methyl 2-thio-β-sophoroside attaches nearby. Structural analyses and multi-scale molecular modelling of nanoscale reactant movements in HvExoI reveal that upon productive binding of incoming substrates, the glucose product modifies its binding patterns and evokes the formation of a transient lateral cavity, which serves as a conduit for glucose departure to allow for the next catalytic round. This path enables substrate-product assisted processive catalysis through multiple hydrolytic events without HvExoI losing contact with oligo- or polymeric substrates. We anticipate that such enzyme plasticity could be prevalent among exo-hydrolases.
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ItemAngular-momentum nanometrology in an ultrathin plasmonic topological insulator film.(Springer Science and Business Media LLC, 2018-10-24)Complementary metal-oxide-semiconductor (CMOS) technology has provided a highly sensitive detection platform for high-resolution optical imaging, sensing and metrology. Although the detection of optical beams carrying angular momentum have been explored with nanophotonic methods, the metrology of optical angular momentum has been limited to bulk optics. We demonstrate angular-momentum nanometrology through the spatial displacement engineering of plasmonic angular momentum modes in a CMOS-compatible plasmonic topological insulator material. The generation and propagation of surface plasmon polaritons on the surface of an ultrathin topological insulator Sb2Te3 film with a thickness of 100 nm is confirmed, exhibiting plasmonic figures of merit superior to noble metal plasmonics in the ultraviolet-visible frequency range. Angular-momentum nanometrology with a low crosstalk of less than -20 dB is achieved. This compact high-precision angular-momentum nanometrology opens an unprecedented opportunity for on-chip manipulation of optical angular momentum for high-capacity information processing, ultrasensitive molecular sensing, and ultracompact multi-functional optoelectronic devices.
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ItemToward broadband, dynamic structuring of a complex plasmonic field(AMER ASSOC ADVANCEMENT SCIENCE, 2018-06)The ability to tailor a coherent surface plasmon polariton (SPP) field is an important step toward many new opportunities for a broad range of nanophotonic applications. Previously, both scanning a converging SPP spot and designing SPP profiles using an ensemble of spots have been demonstrated. SPPs, however, are normally excited by intense, coherent light sources, that is, lasers. Hence, interference between adjacent spots is inevitable and will affect the overall SPP field distributions. We report a reconfigurable and wavelength-independent platform for generating a tailored two-dimensional (2D) SPP field distribution by considering the coherent field as a whole rather than as individual spots. With this new approach, the inherent constraints in a 2D coherent field distribution are revealed. Our design approach works not only for SPP waves but also for other 2D wave systems such as surface acoustic waves.
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ItemSuperTranscripts: a data driven reference for analysis and visualisation of transcriptomes (vol 18, pg 148, 2017)(BIOMED CENTRAL LTD, 2017-08-24)