1,886 research outputs found
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Non-invasive imaging of subsurface paint layers with optical coherence tomography
Optical coherence tomography (OCT) systems are fast scanning infrared Michelson interferometers designed for the non-invasive examination of the interiors of the eye and subsurface structures of biological tissues. OCT has recently been applied to the non-invasive examinations of the stratigraphy of paintings and museum artefacts. So far this is the only technique capable of imaging non-invasively the subsurface structure of paintings and painted objects. Unlike the traditional method of paint cross-section examination where sampling is required, the non-invasive and non-contact nature of the technique enables the examination of the paint cross-section anywhere on a painting, as there is no longer an issue with conservation ethics regarding the taking of samples from historical artefacts. A range of applications of the technique including the imaging of stratigraphy of paintings and painted artefacts, the imaging of underdrawings to the analysis of the optical properties of paint and varnish layers is presented. Future projects on the application of OCT to art conservation are discussed
The Large Scale Curvature of Networks
Understanding key structural properties of large scale networks are crucial
for analyzing and optimizing their performance, and improving their reliability
and security. Here we show that these networks possess a previously unnoticed
feature, global curvature, which we argue has a major impact on core
congestion: the load at the core of a network with N nodes scales as N^2 as
compared to N^1.5 for a flat network. We substantiate this claim through
analysis of a collection of real data networks across the globe as measured and
documented by previous researchers.Comment: 4 pages, 5 figure
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Optical coherence tomography - a tool for high resolution non-invasive 3D-imaging of the subsurface structure of paintings
Optical Coherence Tomography (OCT) is an imaging technique originally developed for high-resolution 3D imaging of the human eye. In 2004, Targowski et al. and Liang et al. first reported its application to paintings, demonstrating that it was possible to produce cross-section images noninvasively with this technique. In 2005 Liang et al. explored further applications such as imaging of underdrawing at a resolution and contrast greater than that achievable with infrared reflectography Since then the authors have been conducting a project to investigate systematically the potential of O C T as a new tool in the non-invasive examination of paintings and to design an O C T optimised for use in museums. This paper discusses recent developments in this work and presents examples of the use of O CT on paintings undergoing conservation treatment in the National Gallery, London
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Optical coherence tomography for art conservation and archaeology
Optical coherence tomography (OCT) is a fast scanning Michelson interferometer originally designed for in vivo imaging of the eye. In 2004, our group along with two other groups first reported the application of OCT to art conservation and archaeology. Since that time we have been conducting a project to investigate systematically the potential of OCT as a new tool for non-invasive examinations of a wide range of museum objects and to design an OCT optimised for in situ use in museums. Here we present the latest results from this ongoing project, which include the determination of the optimum spectral windows for OCT imaging of paintings and painted objects executed using traditional techniques, and non-invasive imaging of the subsurface stratigraphy of painted layers at multiple wavelengths. OCT imaging in assisting spectral pigment identification and in measuring refractive indices of paint will also be presented to illustrate the potential of the technique
Discovery of an inhibitor of the production of the Pseudomonas aeruginosa virulence factor pyocyanin in wild-type cells.
Pyocyanin is a small molecule produced by Pseudomonas aeruginosa that plays a crucial role in the pathogenesis of infections by this notorious opportunistic pathogen. The inhibition of pyocyanin production has been identified as an attractive antivirulence strategy for the treatment of P. aeruginosa infections. Herein, we report the discovery of an inhibitor of pyocyanin production in cultures of wild-type P. aeruginosa which is based around a 4-alkylquinolin-2(1H)-one scaffold. To the best of our knowledge, this is the first reported example of pyocyanin inhibition by a compound based around this molecular framework. The compound may therefore be representative of a new structural sub-class of pyocyanin inhibitors, which could potentially be exploited in in a therapeutic context for the development of critically needed new antipseudomonal agents. In this context, the use of wild-type cells in this study is notable, since the data obtained are of direct relevance to native situations. The compound could also be of value in better elucidating the role of pyocyanin in P. aeruginosa infections. Evidence suggests that the active compound reduces the level of pyocyanin production by inhibiting the cell-cell signalling mechanism known as quorum sensing. This could have interesting implications; quorum sensing regulates a range of additional elements associated with the pathogenicity of P. aeruginosa and there is a wide range of other potential applications where the inhibition of quorum sensing is desirable.The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no [279337/DOS]. In addition, the group research was supported by grants from the Engineering and Physical Sciences Research Council, Biotechnology and Biological Sciences Research Council, Medical Research Council and Welcome Trust. Y.S.T. was supported by an A*STAR Graduate Scholarship
Quantum teleportation on a photonic chip
Quantum teleportation is a fundamental concept in quantum physics which now
finds important applications at the heart of quantum technology including
quantum relays, quantum repeaters and linear optics quantum computing (LOQC).
Photonic implementations have largely focussed on achieving long distance
teleportation due to its suitability for decoherence-free communication.
Teleportation also plays a vital role in the scalability of photonic quantum
computing, for which large linear optical networks will likely require an
integrated architecture. Here we report the first demonstration of quantum
teleportation in which all key parts - entanglement preparation, Bell-state
analysis and quantum state tomography - are performed on a reconfigurable
integrated photonic chip. We also show that a novel element-wise
characterisation method is critical to mitigate component errors, a key
technique which will become increasingly important as integrated circuits reach
higher complexities necessary for quantum enhanced operation.Comment: Originally submitted version - refer to online journal for accepted
manuscript; Nature Photonics (2014
Quantum protocols for anonymous voting and surveying
We describe quantum protocols for voting and surveying. A key feature of our
schemes is the use of entangled states to ensure that the votes are anonymous
and to allow the votes to be tallied. The entanglement is distributed over
separated sites; the physical inaccessibility of any one site is sufficient to
guarantee the anonymity of the votes. The security of these protocols with
respect to various kinds of attack is discussed. We also discuss classical
schemes and show that our quantum voting protocol represents a N-fold reduction
in computational complexity, where N is the number of voters.Comment: 8 pages. V2 includes the modifications made for the published versio
Integrated Photonic Sensing
Loss is a critical roadblock to achieving photonic quantum-enhanced
technologies. We explore a modular platform for implementing integrated
photonics experiments and consider the effects of loss at different stages of
these experiments, including state preparation, manipulation and measurement.
We frame our discussion mainly in the context of quantum sensing and focus
particularly on the use of loss-tolerant Holland-Burnett states for optical
phase estimation. In particular, we discuss spontaneous four-wave mixing in
standard birefringent fibre as a source of pure, heralded single photons and
present methods of optimising such sources. We also outline a route to
programmable circuits which allow the control of photonic interactions even in
the presence of fabrication imperfections and describe a ratiometric
characterisation method for beam splitters which allows the characterisation of
complex circuits without the need for full process tomography. Finally, we
present a framework for performing state tomography on heralded states using
lossy measurement devices. This is motivated by a calculation of the effects of
fabrication imperfections on precision measurement using Holland-Burnett
states.Comment: 19 pages, 7 figure
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