Perspective distortion in craniofacial superimposition: Logarithmic decay curves mapped mathematically and by practical experiment
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Stephan, Carl N. (ORCID:0000000186963809)↗
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Discorpy : algorithms and software for camera calibration and correction
Camera or lens-based detector calibration is essential for spatial accuracy in applications like dimensional tomography, optical metrology, and computer vision. Many methods and software exist yet there is still a lack of approaches that achieve both high accuracy and robustness while being easy to use and capable of handling a wide range of distortions. Radial lens distortion is common in high-resolution X-ray detector optics used in parallel-beam tomography at synchrotrons. Achieving sub-pixel accuracy requires calibrating with an optical target image. Although methods for characterizing radial distortion are well established, acquired images often also include perspective distortion and optical center offset. Here, we present our approaches to individually characterize and correct both types of distortion using a single calibration image, implemented in the Discorpy software.
36 MATERIALS SCIENCE↗
Quantitative Electroluminescence Imaging Analysis for Performance Estimation of PID-Influenced PV Modules
An empirical method for estimating relative power losses caused by potential-induced degradation (PID) for p-type solar cells and modules using quantitative electroluminescence (EL) analysis (QELA) is presented. First, EL images are corrected for camera- and perspective distortion. The relative power loss map is then calculated from the logarithmic ratio of two EL images, taken either before and after PID degradation or at different applied currents. Only the cell average of the resulting power loss map is evaluated. The highest power loss across each string is averaged to obtain the overall power loss. Consequently, for modules with three strings, three cells are averaged. The resulting power loss depends on the current applied. The conversion to equivalent irradiance allows for comparison of measured and estimated device performance. The analysis of roughly 2000 EL images and related current-voltage (I-V) curves indicates a good agreement between flash-test-measured and performance estimated using QELA. A relative root mean square error of 1-3% can be achieved.
14 SOLAR ENERGY↗
Challenges and prospects for better measurements of the CMB intensity spectrum
Spectral distortions of the Cosmic Microwave Background (CMB) offer the possibility of probing processes which occurred during the evolution of our Universe going back up to Z≅ 10{sup 7}. Unfortunately all the attempts so far carried out for detecting distortions failed. All of them were based on comparisons among absolute measurements of the CMB temperature at different frequencies. We suggest a different approach: measurements of the frequency derivative of the CMB temperature over large frequency intervals instead of observations of the absolute temperature at few, well separated, frequencies as frequently done in the past, and, direct measurements of the foregrounds which hinder observations, at the same site and with the same radiometer prepared for the search of CMB distortions. We discuss therefore the perspectives of new observations in the next years from the ground, at very special sites, or in space as independent missions or part of other CMB projects.
79 ASTRONOMY AND ASTROPHYSICS↗
Comprehending the occupying preference of manganese substitution in crystalline cement clinker phases: A theoretical study
Highlights: • The element distributions of manganese in clinker are successfully predicted by atomic simulations. • Occupying preference of Mn in clinker follows the ''electronic properties matching'' principle. - Abstract: Understanding the dopant behavior in cement clinker has been an important issue due to the increasing use of alternative fuels and secondary raw materials for cement manufacturing following the rising demand for reduction of CO{sub 2} emissions and energy consumption. In this work, state-of-the-art ab initio calculations have been employed to systematically investigate manganese (Mn) doping mechanism in four dominant clinker phases. Corresponding experimental studies are incorporated to verify simulated results. A conspicuous preference of Mn for occupying the Fe site in ferrite is found based on formation energy analyses, which is in accord with our experiments and vast literatures. More in-depth analyses indicate the Mn doping mechanism follows the ''electronic structure matching'' principle, which influences the stability of doped structures by inducing localized coordination distortions. The work provides a fundamental perspective to investigate doped clinker, which facilitates the searching for other doping species, thereby designing steerable doping-enhanced cement.
36 MATERIALS SCIENCE↗
The heterogeneous nature of mechanically accelerated grain growth
Abstract While grain growth is traditionally viewed as a purely thermally driven process, nanocrystalline metals can undergo grain growth under mechanical loads, even at room temperature. We performed a detailed atomistic study of the heterogeneous nature of mechanically accelerated grain growth in a polycrystalline Pt nanowire. Using molecular dynamics simulations, we compared the grain-growth behavior of individual grains during tensile and shear cyclic loading, for three different equivalent strain levels, and at two temperatures. Pure thermal grain growth with no mechanical loading provided a baseline reference case. On average, grains that were already susceptible to thermal grain growth were stimulated to grow faster with mechanical loading, as expected. However, when analyzed on a grain-by-grain basis, the results were far more complex: grains that grew fastest under one stimuli were less accelerated under other stimuli. Even when the magnitude of loading changed, the relative growth of individual grains was distorted. We interpret this complexity from the perspective of superimposed growth mechanisms.
Chen, Elton Y.↗
The electron-transfer intermediates of the oxygen evolution reaction (OER) as polarons by in situ spectroscopy
The conversion of diffusive forms of energy (electrical and light) into short, compact chemical bonds by catalytic reactions regularly involves moving a carrier from an environment that favors delocalization to one that favors localization. While delocalization lowers the energy of the carrier through its kinetic energy, localization creates a polarization around the carrier that traps it in a potential energy minimum. The trapped carrier and its local distortion—termed a polaron in solids—can play a role as a highly reactive intermediate within energy-storing catalytic reactions but is rarely discussed as such. Here, we present this perspective of the polaron as a catalytic intermediate through recent in situ and time-resolved spectroscopic investigations of photo-triggered electrochemical reactions at material surfaces. The focus is on hole-trapping at metal–oxygen bonds, denoted M–OH*, in the context of the oxygen evolution reaction (OER) from water. The potential energy surface for the hole-polaron defines the structural distortions from the periodic lattice and the resulting “active” site of catalysis. This perspective will highlight how current and future time-resolved, multi-modal probes can use spectroscopic signatures of M–OH* polarons to obtain kinetic and structural information on the individual reaction steps of OER. A particular motivation is to provide the background needed for eventually relating this information to relevant catalytic descriptors by free energies. Lastly, the formation of the O–O chemical bond from the consumption of M–OH*, required to release O 2 and store energy in H 2 , will be discussed as the next target for experimental investigations.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Tuning From Half-Metallic to Semiconducting Behavior in SiC Nanoribbons
Half-metallic nanoscale conductors, highly sought after for spintronic applications, are usually realized through metal elements, chemical doping, or external electric fields. By means of local and hybrid density functional theory calculations, we identify pristine zigzag silicon carbide nanoribbons (zSiC-NRs) with bare edges as a metal-free monolayered material that exhibits intrinsic half-metallic behavior without chemical doping or external electric field. Ab initio molecular dynamics simulations indicate that the half-metallicity is robust at room temperature. We also demonstrate that edge termination with O and S atoms transforms the zSiC-NRs into a full metal or a semiconducting material, respectively, due to the presence of O dimerization only on the Si edge and of S trimerization on both Si and C edges, the latter being driven by an unusual Peierls-like distortion along the functionalizing S atoms. The rich electronic properties displayed by zSiC-NRs may open new perspectives for spintronic applications using layered, metal-free, and light atom material.
Lopez-Benzanilla, Alejandro↗
Progressive collapse analysis of stiffened panel structure with consideration of actual welding distortion and residual stresses
To date, inclusion of welding distortion and residual stresses in determining the strength of marine structures is based on empirical formulations due to welding complexity. In this study, a more feasible numerical model was developed from the perspective of inherent strain theory. The accuracy of this simplified numerical model was confirmed by transient thermo-elastic–plastic finite element analysis using a novel dynamic mesh refining and iterative substructure method which is 50 times faster than conventional finite element method. Welding distortion by the two numerical approaches was validated with experimental measurement. The collapse analyses indicated that the inherent strain model predicted a compressive strength and load-displacement curve with high accuracy, as validated by the transient thermo-mechanical model. The global stiffness and the ultimate strength of the welded structure would be overestimated by about 22% if no welding effects were considered. The proposed computation procedure for determining the ultimate strength of welded structures is accurate, simple, and practical and enables improvement of ultimate strength through optimization of welding joint design to reduce the welding residual stress and distortion.
Huang, Hui↗
Impact of Stabilizing Cations on Lithium Intercalation in Tunneled Manganese Oxide Cathodes
Stabilizing cations such as K + , Ba 2+ , and Ag + are known to provide charge neutrality and enhance structural stability in low-cost tunneled manganese dioxide (MnO 2 ) cathodes for Li ion batteries. However, a fundamental understanding of the role of these cations in the electrochemical performance of tunneled MnO 2 cathodes remains unclear, especially at low stabilizing cation concentrations. Here, we employ density functional theory (DFT + U) calculations to reveal the impact of stabilizing potassium cation (K + ) concentration on the structural stability, electronic properties, and kinetics of lithium transport in 2 x 2 tunneled manganese oxide (α-K y Mn 8 O 16 , at y = 0, 1, and 2) battery cathodes during lithium intercalation. Specifically, we provide insights into the effect of K + ions on several critical factors governing the electrochemical storage performance of tunneled MnO2 cathodes, including (a) energetically favorable Li+ host sites, (ii) Li + and electron transport capabilities, (iii) optimal intercalation pathways, crystal distortion, microstructural stability, and tunneled-to-layer phase transformation as a function of lithium content, and (iv) cell output voltage profile. Interestingly, we find that low K + concentrations (y ≤ 1) yield partially cation-deficient tunnels in the MnO 2 cathode. Such unique tunnel structures in the cathode enable (a) low kinetic barriers for Li transport, (b) excellent thermodynamic stability of the tunneled structure even at a high Li + loading (up to ~ 0.625 Li/Mn), and (c) good electronic conductivity facilitated by Jahn-Teller distortions; all of which are critical for achieving high capacity batteries with enhanced rate capability. Additionally, these results provide perspectives to design low-cost transition metal oxide cathodes for high-performance Li-ion batteries with excellent cycle life.
25 ENERGY STORAGE↗
Vacancy-Driven Disorder and Elevated Dielectric Response in the Pyrochlore Pb 1.5 Nb 2 O 6.5
Lone pair-driven distortions are a hallmark of many technologically important lead (Pb)-based materials. Here, the role of Pb 2+ in polar perovskites is well understood and easily manipulated for applications in piezo- and ferroelectricity, but the control of ordered lone pair behavior in Pb-based pyrochlores is less clear. Crystallographically and geometrically more complex than the perovskite structure, the pyrochlore structure is prone to geometric frustration of local dipoles due to a triangular arrangement of cations on a diamond lattice. The role of vacancies on the O' site of the pyrochlore network has been implicated as an important driver for the expression and correlation of stereochemically active lone pairs in pyrochlores such as Pb 2 Ru 2 O 6.5 and Pb 2 Sn 2 O 6 . In this work we report on the structural, dielectric, and heat capacity behavior of the cation- and anion-deficient pyrochlore Pb 1.5 Nb 2 O 6.5 upon cooling. We find that local distortions are present at all temperatures that can be described by cristobalite-type cation ordering, and this ordering persists to longer length scales upon cooling. From a crystallographic perspective, the material remains disordered and does not undergo an observable phase transition. In combination with density function calculations, we propose that the stereochemical activity of the Pb 2+ lone pairs is driven by proximity to O' vacancies, and the crystallographic site disorder of the O' vacancies prohibits long range correlation of lone pair-driven distortions. This in turn prevents a low-temperature phase transition and results in an elevated dielectric permittivity across a broad temperature range.
36 MATERIALS SCIENCE↗
Reconstruction of three-dimensional anisotropic structure from small-angle scattering experiments
When subjected to flow, the structures of many soft-matter systems become anisotropic due to the symmetry breaking of the spatial arrangements of constituent particles at the microscopic level. At present, it is common practice to use various small-angle scattering techniques to explore flow-induced microstructural distortion. However, there has not been a thorough discussion in the literature on how a three-dimensional anisotropic structure can be faithfully reconstructed from two-dimensional small-angle scattering spectra. Here, in this work, we address this issue rigorously from a mathematical perspective by using real spherical harmonic expansion analysis. We first show that, except for cases in which mechanical perturbation is sufficiently small, the existing small-angle scattering techniques generally do not provide complete information on structural distortion. This limitation is caused by the linear dependence of certain real spherical harmonic basis vectors on the flow-vorticity and flow-velocity gradient planes in the Couette shear cell. To circumvent the constraint imposed by this geometry, an alternative approach is proposed in which a parallel sliding plate shear cell is used with a central rotary axis along the flow direction. Finally, from the calculation of rotation of the reference frame, we demonstrate the feasibility of this experimental implementation for a fully resolved three-dimensional anisotropic structure via a case study of sheared polymers.
36 MATERIALS SCIENCE↗
Heterostructure engineering in electrode materials for sodium-ion batteries: Recent progress and perspectives
Sodium-ion batteries (SIBs) have stepped into the spotlight as a promising alternative to lithium-ion batteries for large-scale energy storage systems. However, SIB electrode materials, in general, have inferior performance than their lithium counterparts because Na + is larger and heavier than Li + . Heterostructure engineering is a promising strategy to overcome this intrinsic limitation and achieve practical SIBs. We provide a brief review of recent progress in heterostructure engineering of electrode materials and research on how the phase interface influences Na + storage and transport properties. Efficient strategies for the design and fabrication of heterostructures (in situ methods) are discussed, with a focus on the heterostructure formation mechanism. The heterostructure's influence on Na + storage and transport properties arises primarily from local distortions of the structure and chemomechanical coupling at the phase interface, which may accelerate ion/electron diffusion, create additional active sites, and bolster structural stability. Finally, we offer our perspectives on the existing challenges, knowledge gaps, and opportunities for the advancement of heterostructure engineering as a means to develop practical, high-performance sodium-ion batteries.
25 ENERGY STORAGE↗
Understanding the lattice thermal conductivity of SrTiO 3 from an ab initio perspective
Here, we present a detailed analysis of the structure dependence of the lattice thermal conductivity of SrTiO 3 . We have used both ab initio molecular dynamic simulations and density functional theory calculations to decouple the effect of different structural distortions on the thermal conductivity. We have identified two main mechanisms for tuning the thermal conductivity when a distortion is applied. First, the modification of the acoustic-modes energy dispersion when a change in the lattice parameters is imposed and second, the low energy polar modes. In particular and counterintuitively, we have found that an increase in the angle of the oxygen octahedral rotations increases the thermal conductivity due to its coupling to these polar modes.
36 MATERIALS SCIENCE↗
Two-dimensional spin liquid behaviour in the triangular-honeycomb antiferromagnet TbInO 3
Spin liquid ground states are predicted to arise within several distinct scenarios in condensed matter physics. The observation of these disordered magnetic states is particularly pervasive among a class of materials known as frustrated magnets, in which the competition between various magnetic exchange interactions prevents the system from adopting long-range magnetic order at low temperatures. Spin liquids continue to be of great interest due to their exotic nature and the possibility that they may support fractionalized excitations, such as Majorana fermions. Systems that allow for such phenomena are not only fascinating from a fundamental perspective but may also be practically significant in future technologies based on quantum computation. Here we show that the underlying antiferromagnetic sublattice in TbInO 3 can undergo a crystal field-induced distortion of its buckled triangular arrangement to one based on a honeycomb. The absence of a conventional magnetic ordering transition at the lowest measurable temperatures indicates that another critical mechanism must govern in the ground-state selection of TbInO 3 . Here, we suggest that anisotropic exchange interactions—mediated through strong spin–orbit coupling on the emergent honeycomb lattice of TbInO 3 —give rise to a highly frustrated spin liquid.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Materials engineering tetrahedron economic evaluation tool
A new open-source project evaluation tool, entitle the Materials Engineering Tetrahedron (MET), has been developed to determine the economic viability of materials design, selection, processing, and validation costs associated with any infrastructure-based project. MET improves project design by providing an economic perspective to the traditional materials science tetrahedron, relating microstructure, processing, property, and performance through the introduction of value-based economic costs for each side of the tetrahedron. The resulting size and distortion, from a regular tetrahedron illustrates the balance between the system, component, or material fabrication project detailed. Furthermore, the MET model also allows for increased budget efficiency and the potential for improved identification of cost saving mechanisms.
36 MATERIALS SCIENCE↗
Workshop Report on Additive Manufacturing for Large-Scale Metal Components - Development and Deployment of Metal Big-Area-Additive-Manufacturing (Large-Scale Metals AM) System
Additive manufacturing (AM) is considered an emerging technology that is expected to transform the way industry can make low-volume, high value complex structures. This disruptive technology promises to replace legacy manufacturing methods for the fabrication of existing components in addition to bringing new innovation for new components with increased functional and mechanical properties. This report outlines the outcome of a workshop on large-scale metal additive manufacturing held at Oak Ridge National Laboratory (ORNL) on March 11, 2016. The charter for the workshop was outlined by the Department of Energy (DOE) Advanced Manufacturing Office program manager. The status and impact of the Big Area Additive Manufacturing (BAAM) for polymer matrix composites was presented as the background motivation for the workshop. Following, the extension of underlying technology to low-cost metals was proposed with the following goals: (i) High deposition rates (approaching 100 lbs/h); (ii) Low cost (<$10/lbs) for steel, iron, aluminum, nickel, as well as, higher cost titanium, (iii) large components (major axis greater than 6 ft) and (iv) compliance of property requirements. The above concept was discussed in depth by representatives from different industrial sectors including welding, metal fabrication machinery, energy, construction, aerospace and heavy manufacturing. In addition, DOE’s newly launched High Performance Computing for Manufacturing (HPC4MFG) program was reviewed. This program will apply thermo-mechanical models to elucidate deeper understanding of the interactions between design, process, and materials during additive manufacturing. Following these presentations, all the attendees took part in a brainstorming session where everyone identified the top 10 challenges in large-scale metal AM from their own perspective. The feedback was analyzed and grouped in different categories including, (i) CAD to PART software, (ii) selection of energy source, (iii) systems development, (iv) material feedstock, (v) process planning, (vi) residual stress & distortion, (vii) post-processing, (viii) qualification of parts, (ix) supply chain and (x) business case. Furthermore, an open innovation network methodology was proposed to accelerate the development and deployment of new large-scale metal additive manufacturing technology with the goal of creating a new generation of high deposition rate equipment, affordable feed stocks, and large metallic components to enhance America’s economic competitiveness.
36 MATERIALS SCIENCE↗
Molecular events in the light of strong fields: A light‐induced potential scenario
A new perspective on how to manipulate molecules by means of very strong laser pulses is emerging with insights from the so‐called light‐induced potentials, which are the adiabatic potential energy surfaces of molecules severely distorted by the effect of the strong field. Different effects appear depending on how the laser frequency is tuned, to a certain electronic transition, creating light‐induced avoided crossings, or very off‐resonant, generating Stark shifts. In the former case it is possible to induce dramatic changes in the geometry and redistribution of charges in the molecule while the lasers are acting and to fully control photodissociation reactions as well as other photochemical processes. Several theoretical proposals taken from the work of the authors are reviewed and analyzed showing the unique features that the strong‐laser chemistry opens to control the transient properties and the dynamics of molecules. © 2016 Wiley Periodicals, Inc.
Chang, Bo Y.↗