Twenty five years ago, close to the northern Peruvian town of Lambayeque (Huaca Rajada) beneath two large and eroded pyramids, built of adobe mud bricks, Professor Alva discovered the world-famous ...unlooted pre-Columbian burial chambers of the Royal Tombs of Sipan. The tombs contained a large amount of objects of exceptional artistic and historical value including the greatest intact number of gold and silver artefacts in the Americas to be considered one of the most important archaeological discoveries of the last century. Some copper based objects coated with thin layers of gold have been studied by means of the combined use of analytical techniques such as optical microscopy (OM), scanning electron microscopy coupled with energy dispersive X-ray micro-analysis (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) in order to identify the chemical composition and the manufacturing processes of the gold layer as well as the corrosion products formed during the long-term burial. The micro-chemical and structural results give useful information about the manufacturing techniques used by the Moche metalsmiths to modify the surface chemical composition of the coated artefacts likely based on the depletion gilding process carried out by oxidising the surface copper containing the noble metal and etching away the copper oxides. Furthermore, the results reveal that the main degradation agent is the ubiquitous chlorine and that copper has been almost completely transformed during the burial into mineral species giving rise to the formation of stratified structures constituted by different mineral phases such as cuprous oxide (Cu2O) and copper carbonates azurite (Cu3(CO3)2(OH)2 and malachite (CuCO3Cu(OH)2) as well as dangerous chlorine-based compounds such as nantokite (CuCl) and atacamite (Cu2(OH)3Cl) polymorphs. These information evidence the strict interaction of the alloying elements with the soil components as well as the occurrence of the copper cyclic corrosion as post-burial degradation phenomenon. The present study confirms that the combined use of micro-chemical and micro-structural investigation techniques such as SEM-EDS, XPS, XRD, and OM can be successfully used to investigate the technological manufacturing processes of the ancient coated artefacts and to achieve information about degradation agents and mechanisms useful to define tailored conservation strategies possibly including new, more reliable, and safer materials.
Information systems (IS) use, the dominant theoretical paradigm for explaining how users apply IS artifacts toward goal attainment, gives primacy to human agency in the user–IS artifact relationship. ...Models and theorizing in the IS use research stream tend to treat the IS artifact as a passive tool; lacking in the ability to initiate action and accept rights and responsibilities for achieving optimal outcomes under uncertainty. We argue that a new generation of "agentic" IS artifacts requires revisiting the human agency primacy assumption. Agentic IS artifacts are no longer passive tools waiting to be used, are no longer always subordinate to the human agent, and can now assume responsibility for tasks with ambiguous requirements and for seeking optimal outcomes under uncertainty. To move our theorizing forward, we introduce delegation, based on agent interaction theories, as a foundational and powerful lens through which to understand and explain the human– agentic IS artifact relationship. While delegation has always been central to human–IS artifact interactions, it has yet to be explicitly recognized in IS use theorizing. We explicitly theorize IS delegation by developing an IS delegation theoretical framework. This framework provides a scaffolding which can guide future IS delegation theorizing and focuses on the human–agentic IS artifact dyad as the elemental unit of analysis. The framework specifically reveals the importance of agent attributes relevant to delegation (endowments, preferences, and roles) as well as foundational mechanisms of delegation (appraisal, distribution, and coordination). Guidelines are proposed to demonstrate how this theoretical framework can be applied toward generation of testable models. We conclude by outlining a roadmap for mobilizing future research.
Purpose: While modern clinical CT scanners under normal circumstances produce high quality images, severe artifacts degrade the image quality and the diagnostic value if metal prostheses or other ...metal objects are present in the field of measurement. Standard methods for metal artifact reduction (MAR) replace those parts of the projection data that are affected by metal (the so-called metal trace or metal shadow) by interpolation. However, while sinogram interpolation methods efficiently remove metal artifacts, new artifacts are often introduced, as interpolation cannot completely recover the information from the metal trace. The purpose of this work is to introduce a generalized normalization technique for MAR, allowing for efficient reduction of metal artifacts while adding almost no new ones. The method presented is compared to a standard MAR method, as well as MAR using simple length normalization.
Methods: In the first step, metal is segmented in the image domain by thresholding. A 3D forward projection identifies the metal trace in the original projections. Before interpolation, the projections are normalized based on a 3D forward projection of a prior image. This prior image is obtained, for example, by a multithreshold segmentation of the initial image. The original rawdata are divided by the projection data of the prior image and, after interpolation, denormalized again. Simulations and measurements are performed to compare normalized metal artifact reduction (NMAR) to standard MAR with linear interpolation and MAR based on simple length normalization.
Results: Promising results for clinical spiral cone-beam data are presented in this work. Included are patients with hip prostheses, dental fillings, and spine fixation, which were scanned at pitch values ranging from 0.9 to 3.2. Image quality is improved considerably, particularly for metal implants within bone structures or in their proximity. The improvements are evaluated by comparing profiles through images and sinograms for the different methods and by inspecting ROIs. NMAR outperforms both other methods in all cases. It reduces metal artifacts to a minimum, even close to metal regions. Even for patients with dental fillings, which cause most severe artifacts, satisfactory results are obtained with NMAR. In contrast to other methods, NMAR prevents the usual blurring of structures close to metal implants if the metal artifacts are moderate.
Conclusions: NMAR clearly outperforms the other methods for both moderate and severe artifacts. The proposed method reliably reduces metal artifacts from simulated as well as from clinical CT data. Computationally efficient and inexpensive compared to iterative methods, NMAR can be used as an additional step in any conventional sinogram inpainting-based MAR method.
Low‐dose X‐ray computed tomography (LDCT) imaging is highly recommended for use in the clinic because of growing concerns over excessive radiation exposure. However, the CT images reconstructed by ...the conventional filtered back‐projection (FBP) method from low‐dose acquisitions may be severely degraded with noise and streak artifacts due to excessive X‐ray quantum noise, or with view‐aliasing artifacts due to insufficient angular sampling. In 2005, the nonlocal means (NLM) algorithm was introduced as a non‐iterative edge‐preserving filter to denoise natural images corrupted by additive Gaussian noise, and showed superior performance. It has since been adapted and applied to many other image types and various inverse problems. This paper specifically reviews the applications of the NLM algorithm in LDCT image processing and reconstruction, and explicitly demonstrates its improving effects on the reconstructed CT image quality from low‐dose acquisitions. The effectiveness of these applications on LDCT and their relative performance are described in detail.
To conduct a systematic review of the existing literature with the aim of evaluating and consolidating the present understanding of strategies for mitigating magnetic resonance imaging (MRI) ...artifacts related to cochlear implants in adult and pediatric patients, covering both in-vivo and ex-vivo investigations.
A systematic review of MEDLINE-Ovid, Embase, Google Scholar, The Cochrane Library, and Scopus was performed from inception through April 2022. The protocol was registered with PROSPERO before commencement of data collection (CRD CRD42022319651).
The data were screened and collected by two authors independently, and eligibility was assessed according to Cochrane Handbook and Preferred Reporting Items for Systematic Review and Meta-Analysis recommendations, whereas the quality of the articles was evaluated using the NIH Study Quality Assessment.
The search yielded 2,354 potentially relevant articles, of which 27 studies were included in the final review. Twelve studies looked at 1.5-T MRI, four studies looked at 3-T MRI, eight studies looked at both 1.5 and 3 T, one study looked at 0.2 and 1.5 T, and one study looked at 3- and 7.0-T MRI. Nineteen studies focused on MRI sequences as a means of artifact reduction, nine studies focused on implant magnet positioning, two studies focused on head positioning, and one study focused on both magnet and head positioning. In terms of MRI sequences, diffusion-weighted imaging produced larger artifacts compared with other sequences, whereas fast spin echo/turbo spin echo sequences and fat suppression techniques produced smaller artifacts. The position of the magnet was also found to be important, with a magnet position more than 6.5 cm posterior to the external auditory canal producing the best images with the least distortion. The angle at which the magnet is placed also affects visibility of different brain structures.
Proper head positioning, magnet placement at a distance of over 6.5 cm from the external auditory canal, use of spin echo sequences, and fat suppression techniques reduce the size and shape of MRI artifacts.
The nonplanar shape of a painting as well as practical constraints often result in the painting's surface not being parallel to the plane in that the measurement head of a MA‐XRF scanner is being ...moved. Changing the working distance affects the measurement geometry, so that the sensitivity for the same element may vary throughout the investigated area and induce visible artifacts. These artifacts are especially visible when different scans of the same painting are stitched together. In this article, we present an approach to correct for the variation of the measurement distance. We explored using an intrinsic part of the XRF data set, the Ar signal from the air, to estimate the distance between surface and instrument. The model is developed based on fundamental parameter calculations and a measurement of a NIST 610 standard and is verified on a set of scans of Rembrandt's ‘Portrait of Oopjen Coppit (1611–1689)’.
The theory of electric polarization in crystals defines the dipole moment of an insulator in terms of a Berry phase (geometric phase) associated with its electronic ground state. This concept not ...only solves the long-standing puzzle of how to calculate dipole moments in crystals, but also explains topological band structures in insulators and superconductors, including the quantum anomalous Hall insulator and the quantum spin Hall insulator, as well as quantized adiabatic pumping processes. A recent theoretical study has extended the Berry phase framework to also account for higher electric multipole moments, revealing the existence of higher-order topological phases that have not previously been observed. Here we demonstrate experimentally a member of this predicted class of materials-a quantized quadrupole topological insulator-produced using a gigahertz-frequency reconfigurable microwave circuit. We confirm the non-trivial topological phase using spectroscopic measurements and by identifying corner states that result from the bulk topology. In addition, we test the critical prediction that these corner states are protected by the topology of the bulk, and are not due to surface artefacts, by deforming the edges of the crystal lattice from the topological to the trivial regime. Our results provide conclusive evidence of a unique form of robustness against disorder and deformation, which is characteristic of higher-order topological insulators.
Se expone de manera sintética el proceso de estudio de objetos sin contexto tomando como ejemplo el caso de los cascos celtibéricos dispersos en el mercado anticuario internacional. Partiendo de la ...experiencia personal se presenta el concepto de "descontextualizado" y los distintos grados de descontextualización y se analizan los riesgos o la problemática del estudio de este tipo de piezas. Para ello atenderemos a los principios y reticencias de aquellos planteamientos que rechazan completamente cualquier tipo de contacto con piezas del mercado anticuario, pero también las de aquellos que de manera completamente opuesta han decidido ponerlos en valor y valoraremos los beneficios del estudio puntual de piezas descontextualizadas tanto para el conocimiento específico de esos objetos como para el estudio de la cultura antigua a la que pertenecen y su relevancia en el contexto contemporáneo particular en el que se han comercializado y coleccionado.
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