1,404 research outputs found
Remote spectral imaging with simultaneous extraction of 3D topography for historical wall paintings
PRISMS (Portable Remote Imaging System for Multispectral Scanning) is designed for in situ, simultaneous high resolution spectral and 3D topographic imaging of wall paintings and other large surfaces. In particular, it can image at transverse resolutions of tens of microns remotely from distances of tens of metres, making high resolution imaging possible from a fixed position on the ground for areas at heights that is difficult to access. The spectral imaging system is fully automated giving 3D topographic mapping at millimetre accuracy as a by-product of the image focusing process. PRISMS is the first imaging device capable of both 3D mapping and spectral imaging simultaneously without additional distance measuring devices. Examples from applications of PRISMS to wall paintings at a UNESCO site in the Gobi desert are presented to demonstrate the potential of the instrument for large scale 3D spectral imaging, revealing faded writing and material identification
Adatoms and Anderson localization in graphene
We address the nature of the disordered state that results from the
adsorption of adatoms in graphene. For adatoms that sit at the center of the
honeycomb plaquette, as in the case of most transition metals, we show that the
ones that form a zero-energy resonant state lead to Anderson localization in
the vicinity of the Dirac point. Among those, we show that there is a symmetry
class of adatoms where Anderson localization is suppressed, leading to an
exotic metallic state with large and rare charge droplets, that localizes only
at the Dirac point. We identify the experimental conditions for the observation
of the Anderson transition for adatoms in graphene.Comment: 8 pages, 5 figures, 2 appendixes, Final versio
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Development of portable microfading spectrometers for measurement of light sensitivity of materials
Microfading was originally designed for efficiently detecting extremely light-sensitive materials on objects in situ to determine the appropriate exhibition lighting conditions. By focusing an intense beam of light to a tiny submillimetre sized spot and simultaeously monitoring the colour change over time, the fading rate of the material can be measured without producing noticeable damage. The increased intensity of light allows rapid determination of light-fastness of materials. This paper examines an improved design of microfading spectrometer that is easy to assemble, compact, robust, capable of fully automatic acquisition of data with precision control of the fading time to produce higher precision measurements and to allow simultaneous monitoring of colour, spectral reflectance and other changes in real time. The effects of various parameters such as thickness and concentration of paint layer, the binding medium and substrate on the fading rates are examined for selected pigments and found that in certain cases substrates, binding media and thickness can affect the fading rate. Reciprocity in the context of microfading compared with realistic exhibition conditions is examined and found that it breaks down for some pigment
Dimensional crossover of the exchange-correlation energy at the semilocal level
Commonly used semilocal density functional approximations for the
exchange-correlation energy fail badly when the true two dimensional limit is
approached. We show, using a quasi-two-dimensional uniform electron gas in the
infinite barrier model, that the semilocal level can correctly recover the
exchange-correlation energy of the two-dimensional uniform electron gas. We
derive new exact constraints at the semilocal level for the dimensional
crossover of the exchange-correlation energy and we propose a method to
incorporate them in any exchange-correlation density functional approximation.Comment: 6 pages, 5 figure
A holistic multimodal approach to the non-invasive analysis of watercolour paintings
A holistic approach using non-invasive multimodal imaging and spectroscopic techniques to study the materials (pigments, drawing materials and paper) and painting techniques of watercolour paintings is presented. The non-invasive imaging and spectroscopic techniques include VIS-NIR reflectance spectroscopy and multispectral imaging, micro-Raman spectroscopy, X-ray fluorescence spectroscopy (XRF) and optical coherence tomography (OCT). The three spectroscopic techniques complement each other in pigment identification. Multispectral imaging (near infrared bands), OCT and micro-Raman complement each other in the visualisation and identification of the drawing material. OCT probes the microstructure and light scattering properties of the substrate while XRF detects the elemental composition that indicates the sizing methods and the filler content . The multiple techniques were applied in a study of forty six 19th century Chinese export watercolours from the Victoria & Albert Museum (V&A) and the Royal Horticultural Society (RHS) to examine to what extent the non-invasive analysis techniques employed complement each other and how much useful information about the paintings can be extracted to address art conservation and history questions
Real-space calculation of the conductivity tensor for disordered topological matter
We describe an efficient numerical approach to calculate the longitudinal and
transverse Kubo conductivities of large systems using Bastin's formulation. We
expand the Green's functions in terms of Chebyshev polynomials and compute the
conductivity tensor for any temperature and chemical potential in a single
step. To illustrate the power and generality of the approach, we calculate the
conductivity tensor for the quantum Hall effect in disordered graphene and
analyze the effect of the disorder in a Chern insulator in Haldane's model on a
honeycomb lattice.Comment: 5 pages, 3 figures and a supplementary material (3 pages
Valuation of Personal Data in the Age of Data Ownership
In order to tackle uncertainties about data ownership and data misuse, more accessible and competitive data markets are proposed, especially concerning the use and access rights of data generated by the Internet of Things (IoT) devices. Legal proposals suggest that companies and individuals become owners of their self-generated data, enabling new ways of data monetization. Still, individuals are often uncertain about the value and price of their own generated data. This research builds on construal level theory to propose influencing factors fostering an understanding of intraindividual data value. The results of a pilot study survey (n = 104), conducted during the ICIS 2022, show that data proximity and data sensitivity factors significantly influence intraindividual data value. Our research extends the knowledge on data value from individual perspectives and builds the foundation for future work on data valuation and pricing in intraindividual data trading
Polaron formation in the presence of Rashba spin-orbit coupling: implications for spintronics
We study the effects of the Rashba spin-orbit coupling on the polaron
formation, using a suitable generalization of the Momentum Average
approximation. Contrary to previous investigations of this problem, we find
that the spin-orbit interaction decreases the effective electron-phonon
coupling. It is thus possible to lower the effective mass of the polaron by
increasing the spin-orbit coupling. We also show that when the spin-orbit
coupling is large as compared to the phonon energy, the polaron retains only
one of the spin polarized bands in its coherent spectrum. This has major
implications for the propagation of spin-polarized currents in such materials,
and thus for spintronic applications.Comment: 4 pages, 3 figure
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