Boundary Structure Research Articles

Image-guided structure-constrained inversion of electrical resistivity data for improving contaminations characterization

Electrical resistivity tomography often has high uncertainty in contamination characterization due to the complex subsurface structure. Utilizing available prior information is crucial for enhancing geological plausibility. We propose an improved structure-constrained method that updates the smooth weights of all eight elements surrounding a boundary element using three different magnitudes. The methodology is tested on seven synthetic models and a field case covering four different types of structural boundaries. Structural constraints are vital to increasing boundary contrast, and the improvement is more significant with increasing depth. With the increase of data points from an optimized array, the influence of structural constraint is reduced. The implementation of accurate structural constraints can enhance the characterization of contamination anomaly zones. However, misplaced structural constraints in the proximity of the contamination can lead to worse depiction. Without knowing the boundary exactly, we propose a method to obtain local constraints from borehole logs, which is verified by both numerical and field data. This method reduces the interference from uncertain structural boundaries and enhances the robustness of the image-guided structure-constrained inversion. In the end, we conclude that correct boundary information even with scattered constraints from borehole logs can increase the identification of the abnormal contamination resistivity.

Grain boundaries in polycrystalline materials for energy applications: First principles modeling and electron microscopy

Polycrystalline materials are ubiquitous in technology, and grain boundaries have long been known to affect materials properties and performance. First principles materials modeling and electron microscopy methods are powerful and highly complementary for investigating the atomic scale structure and properties of grain boundaries. In this review, we provide an introduction to key concepts and approaches for investigating grain boundaries using these methods. We also provide a number of case studies providing examples of their application to understand the impact of grain boundaries for a range of energy materials. Most of the materials presented are of interest for photovoltaic and photoelectrochemical applications and so we include a more in depth discussion of how modeling and electron microscopy can be employed to understand the impact of grain boundaries on the behavior of photoexcited electrons and holes (including carrier transport and recombination). However, we also include discussion of materials relevant to rechargeable batteries as another important class of materials for energy applications. We conclude the review with a discussion of outstanding challenges in the field and the exciting prospects for progress in the coming years.

Exploring the thermal behavior and diffusive functionality of structural defects and phase boundaries in near-stoichiometric chromium diborides by in situ scanning transmission electron microscopy

Exploring the thermal behavior and diffusive functionality of structural defects and phase boundaries in near-stoichiometric chromium diborides by <i>in situ</i> scanning transmission electron microscopy

Combined Experimental and Computational Insight into the Role of Substrate in the Synthesis of Two-Dimensional WSe2.

Synthesis of large-area transition-metal dichalcogenides (TMDs) with controlled orientation is a significant challenge to their industrial applications. Substrate plays a vital role in determining the final quality of monolayer materials grown via the chemical vapor deposition process by controlling their orientation, crystal structure, and grain boundary. This study determined the binding energy and equilibrium distance for tungsten diselenide (WSe2) monolayers on crystalline and amorphous silicon dioxide and aluminum dioxide substrates. Differently oriented WSe2 monolayers are considered to investigate the role of the substrate in the orientation, binding strength, and equilibrium distance. This study can pave the way to synthesizing high-quality two-dimensional (2D) materials for electronic and chemical applications.

Tuning the atomic and electronic structures of mirror twin boundaries in molecular beam epitaxy grown MoSe2 monolayers via rhenium doping

Interplay between defects like mirror twin boundaries (MTBs) and dopants may provide additional opportunities for furthering the research on two-dimensional monolayer (ML) transition metal dichalcogenides. In this work, we successfully dope rhenium (Re) into molecular beam epitaxy grown ML MoSe2 and confirm the formation of a new type of MTBs, named 4|4E-M (M represents metal, Mo/Re) according to the configuration. Data from statistic atomic resolution scanning transmission electron microscopy also reveals a preferable MTB enrichment of Re dopants, rather than intra-domain. In conjunction with density functional theory calculation results, we propose the possible routes for Re doping induced formation of 4|4E-M MTBs. Electronic structures of Re doped MTBs in ML MoSe2 are also predicted theoretically and then preliminarily tested by scanning tunneling microscopy and spectroscopy.

Deposition dynamics and analysis of polyurethane foam structure boundaries for aerial additive manufacturing

Deposition dynamics and analysis of polyurethane foam structure boundaries for aerial additive manufacturing

Dynamic reliability calculation of random structures by conditional probability method

For the composite random reliability problem, based on the Markov hypothesis of the dynamic response spanning action, two procedures of conditional probability explanation are accomplished: to derive the 2nd-order approximate expression for the calculation of the dynamic reliability of the random structure based on Taylor expansion method; secondly is to determine a mathematical sampling technique based on the Kriging model derive from the statistical analysis. Between them, the sampling procedure by the Kriging interpolation model meets the nonlinear correlation among dynamic reliability and structural random boundaries. Consequently, the finite element results can be used instantly to anatomize the significance of random structural parameters on dynamic reliability, avoiding the tedious and cumbersome theoretical derivation. The numerical example outcomes demonstrate that the numerical sampling method established upon the Kriging model is inconsiderate to the ratio to represent the dispersion and has additional benefits in computational verisimilitude and calculation productivity

Atomic-scale observation of nucleation- and growth-controlled deformation twinning in body-centered cubic nanocrystals

Twinning is an essential mode of plastic deformation for achieving superior strength and ductility in metallic nanostructures. It has been generally believed that twinning-induced plasticity in body-centered cubic (BCC) metals is controlled by twin nucleation, but facilitated by rapid twin growth once the nucleation energy barrier is overcome. By performing in situ atomic-scale transmission electron microscopy straining experiments and atomistic simulations, we find that deformation twinning in BCC Ta nanocrystals larger than 15 nm in diameter proceeds by reluctant twin growth, resulting from slow advancement of twinning partials along the boundaries of finite-sized twin structures. In contrast, reluctant twin growth can be obviated by reducing the nanocrystal diameter to below 15 nm. As a result, the nucleated twin structure penetrates quickly through the cross section of nanocrystals, enabling fast twin growth via facile migration of twin boundaries leading to large uniform plastic deformation. The present work reveals a size-dependent transition in the nucleation- and growth-controlled twinning mechanism in BCC metals, and provides insights for exploiting twinning-induced plasticity and breaking strength-ductility limits in nanostructured BCC metals.

Mobility of screw dislocations absorbed in symmetric tilt grain boundaries in Al

ABSTRACT The strength and ductility of polycrystalline metals are influenced by the interactions between dislocations and grain boundaries, particularly when the grain size is small. One possible reaction is the absorption of dislocations into the grain boundary structure; however, the mobility of the resulting grain boundary dislocations (GBDs) remains largely unexplored. Thus, the objective of this work is to determine the mobility of GBDs arising from the absorption of lattice screw dislocations into Σ3{111} and Σ11{113} <110> symmetric tilt grain boundaries (STGBs) in Al. Atomistic simulations reveal a reduction in Peierls stress of ∼80% and phonon damping coefficient of ∼65% for GBDs in the {111}<110> STGB compared to lattice screw dislocations. This significant mobility increase is caused by the complete dissociation of the absorbed dislocation. The Peierls stress of GBDs in the {113}<110> STGB is increased to almost 8 times that of the lattice screw dislocation due to the smaller interplanar spacing between slip planes. This work provides a structural justification for the absorption reactions and demonstrates that the mobility of an absorbed dislocation is highly sensitive to the structure of the host grain boundary. Ultimately, mobility laws are provided which can be used to model GBD motion in mesoscale simulations.

Pre-conceptual design of the fixed mirrors for the DEMO Electron Cyclotron Heating antenna

The M1 mirrors are part of the in-vessel quasi-optical Electron Cyclotron beam propagation system of the DEMO nuclear fusion reactor. These four mirrors are all non-movable and with a plane reflecting surface. Based on their functionality they are divided into two groups, the Mid-Steering Antenna (MSA) and the Multi-Beam Mirror (MBM) antenna. The MSA is responsible for controlling the neoclassical tearing modes, while the MBM is available for plasma bulk heating, current drive and thermal instability control.These mirrors are designed to withstand the thermal loads generated during operation: neutron heating, ohmic losses and stray radiation caused by the mm-wave beam reflection. To fulfil the design requirements, efficient heat removal strategies based on water cooling principles minimizing pressure drop are implemented.This paper presents the pre-conceptual design of the MBM and MSA M1 mirrors, validating the structural and geometric boundary conditions, as well as the appropriate selection of materials. Using FEA tools, thermal-hydraulic and thermo-mechanical simulations were performed with the available thermal loads to optimize the cooling parameters and perform a first stress assessment on the two M1 mirrors.

Facile Route to Synthesize a Highly Sinterable Li1.3Al0.3Ti1.7(PO4)3 Solid Electrolyte.

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a widely used solid electrolyte in solid-state lithium batteries, owing to its excellent chemical stability against moisture and high total ionic conductivity. However, traditionally, densification of LATP has been achieved through a high-temperature sintering process (approximately 1000 °C) owing to its poor sinterability. Herein, we report a facile synthesis route to obtain highly sinterable LATP solid electrolyte using tetrabutyl titanate (C16H36O4Ti) as the titanium source and incorporating the traditional solid-state reaction method. The synthetic LATP powder mixed with a low ratio of LiTiPO5 exhibited a hybrid crystalline-amorphous phase structure, which facilitated grain fusion, promoted structural homogeneity, and facilitated structural densification under low-temperature sintering. The sintered LATP pellet, which exhibited an interconnected structure and indistinct grain boundaries, achieved a relative density of >90% and an ionic conductivity of 0.667 mS/cm at a sintering temperature of only 750 °C. Additionally, we systematically studied and demonstrated the synthesis reaction mechanism, sintering behavior, and ionic diffusion kinetics of LATP electrolytes. Our study paves the way for synthesizing highly sinterable LATP solid electrolytes using a simple, additive-free, and cost-effective method.

Effect of the grain boundary character distribution on the sulfur corrosion behaviour and mechanisms of copper windings under different high temperatures

AbstractAs a typical failure phenomenon in transformers, sulfur corrosion has garnered significant attention in the field of high‐voltage engineering. Grain boundary character distribution (GBCD) copper windings have been introduced to enhance sulfur corrosion resistance by slowing down intergranular corrosion. In this study, the sulfur corrosion behaviour and mechanisms of the GBCD copper windings under various temperatures were experimentally and theoretically studied. Results show that GBCD can enhance the corrosion resistance of copper in liquid environments. With the increase in temperatures, the insulating properties of oil and papers in traditional copper windings experience notable degradation, while GBCD copper windings show more stable insulating behaviours. In addition, modelling of grain boundary energy indicates that the grain boundary structure of GBCD copper windings has a lower average interface energy of 0.170 eV/Å2. Calculations of reaction thermodynamics show that GBCD copper windings possess a higher failure temperature (135.2°C) and inhibition degree (activation energy) of the sulfur corrosion (32,557.62 J/mol), revealing the stability and enhanced sulfur corrosion resistance at elevated temperatures.

Acoustic Characteristics of a Plate Silencer with a Flexible Back Cavity Under Arbitrary Boundary Conditions

The flexible back cavity (FBC) plate silencer is composed of an FBC and a flexible inner plate. Through the coupling of the sound field with the flexible inner and outer plates, the transmitted sound energy of the downstream is reduced, and it has a good broadband muffling effect at low frequencies. In order to obtain the transmission loss (TL) of the FBC plate silencer under arbitrary boundary conditions, this paper establishes the acoustic-vibration coupling model of the FBC plate silencer based on the energy principle. Translational restraints and rotational restraints are used to simulate the arbitrary boundary conditions of the flexible plate, and then the influence of the boundary conditions of the flexible plate on the TL is analyzed. The results show that the results of the proposed method are in good agreement with the finite element method (FEM) results. The structural boundary restraint has a significant influence on the acoustic characteristics of the system, and the rotational restraints suppress the muffling effect. By appropriately releasing the translational restraints, a better low-frequency broadband muffling effect can be achieved, with the minimum muffling frequency reduced by 44.8% and the muffling bandwidth broadened by 57.4%.

The dilemma of the split between theory and reality as experienced by primary healthcare professionals: a mixed methods study of evidence-based practice in a primary care context

BackgroundPrimary care depends upon a good information flow across professional and structural boundaries to provide the best care for patients. Previous research has mainly focused on Evidence-Based Practice (EBP) within specific professions. Mapping of pan-professional experiences of and attitudes to EBP in publicly funded clinical practice is necessary to deepen the understanding of EBP and its implementation. Thus, this study aimed to investigate healthcare professionals’ experiences of and attitudes towards working in accordance with EBP in primary care.MethodsThe study used a convergent mixed methods design divided into two strands: a quantitative enquiry tool (Evidence-Based Practice Attitude Scale, EBPAS) and a set of qualitative interviews analysed by means of qualitative content analysis. Both strands included all primary care employees with patient interaction in the studied county (n = 625), including doctors, nurses, physiotherapists, psychologists and assistant nurses. Out of the original 625 healthcare professionals, 191 finished the first strand and 8 volunteered for the second strand (2 nurses, 2 physiotherapists, 1 psychiatrist and 3 doctors).ResultsThe EBPAS value of 2.8 (max 4) indicated a generally positive attitude towards EBP amongst the population, which was also evident in the interviews. However, there were additional experiences of not having the ability or resources to engage in EBP. This was illustrated by the theme that emerged from the qualitative content analysis: “The dilemma of the split between theory and reality”. Due to the organisational and managerial focus on efficiency rather than quality of care, there were few or no incentives for promoting individual educational or research development.ConclusionsAlthough the general attitude towards EBP is positive, experiences of practising it differ. There is a need to increase knowledge of EBP concepts, requirements and implementation in the clinical setting. The absence of opportunities to do research and collegial debate about new ways of finding and implementing research-based evidence results might influence the quality of care.

Adapting Crystal Structure and Grain Boundaries through Sm3+ Doping in Na3Zr2Si2PO4 for Boosting Applicability in Sodium Solid-State Batteries.

Solid-state sodium batteries represent a highly promising option for future electrochemical energy storage applications. The ionic conductivity of solid-state electrolytes is one of the significant factors limiting the development of solid-state batteries. In this study, we establish that Sm3+ doping effectively boosts the ionic conductivity of Na3Zr2Si2PO12 (NZSP). The optimal composition, Na3.2Zr1.8Sm0.2Si2-PO12 (NZSP-S20), exhibits a total conductivity of 1.87 mS cm-1 at 23 °C. Structural and microscopic morphology analyses reveal that Sm3+ doping enhances the ionic conductivity of NZSP through structural modulation, phase fraction adjustment, and grain size reduction. High-frequency impedance spectroscopy (40 Hz to 110 MHz) demonstrates that bulk and grain boundaries contribute 49.4 and 50.6%, respectively, to the total conductivity. The structural and microscopic morphology analyses reveal that Sm3+ doping enhances the ionic conductivity of NZSP. Furthermore, the critical current density (CCD) attained in the symmetric cell, assembled by using NZSP-S20 as the solid-state electrolyte and NaSn alloy as the electrode, reaches 2.2 mA cm-1. These results furnish a theoretical foundation for comprehending the modification of solid-state electrolytes.

‘We had that abortion together’: abortion networks and access to il/legal abortions in Turkey

Abortion was legalised in Turkey in 1983 with a 10-week limit, restrictions on who could provide abortions, and spousal or parental consent requirements. Currently, although abortion is legal, because of structural barriers, access is restricted (O’Neil, Altuntaş, and Keskin 2020). This study aimed to investigate how women strategically mobilise their social networks to overcome such restrictions to abortion care. Drawing from 25 in-depth interviews with urban-educated cis-women aged 24-30, I identify three groups within abortion networks: included, excluded and ambiguous. While included groups comprised largely of female family and friends, excluded groups were male family members and organisations, and the ambiguous category included health professionals and partners. Supporting findings in other contexts, individuals initially utilise their abortion networks to access the provider, they then build abortion solidarity networks to act as buffers against groups they wish to exclude during the abortion experience. Additionally, I show that excluded and ambiguous networks also impact abortion access, decision-making, and experience, even pushing individuals to follow through with illegal or semi-legal abortion procedures. Findings draw attention to the structural boundaries surrounding abortion laws, how patriarchal institutions make access to abortion care and abortion networks challenging, and how social networks may be utilised to alleviate such obstacles.

Extraction of Building Roof Contours from Airborne LiDAR Point Clouds Based on Multidirectional Bands

Because of the complex structure and different shapes of building contours, the uneven density distribution of airborne LiDAR point clouds, and occlusion, existing building contour extraction algorithms are subject to such problems as poor robustness, difficulty with setting parameters, and low extraction efficiency. To solve these problems, a building contour extraction algorithm based on multidirectional bands was proposed in this study. Firstly, the point clouds were divided into bands with the same width in one direction, the points within each band were vertically projected on the central axis in the band, the two projection points with the farthest distance were determined, and their corresponding original points were regarded as the roof contour points; given that the contour points obtained based on single-direction bands were sparse and discontinuous, different banding directions were selected to repeat the above contour point marking process, and the contour points extracted from the different banding directions were integrated as the initial contour points. Then, the initial contour points were sorted and connected according to the principle of joining the nearest points in the forward direction, and the edges with lengths greater than a given threshold were recognized as long edges, which remained to be further densified. Finally, each long edge was densified by selecting the noninitial contour point closest to the midpoint of the long edge, and the densification process was repeated for the updated long edge. In the end, a building roof contour line with complete details and topological relationships was obtained. In this study, three point cloud datasets of representative building roofs were chosen for experiments. The results show that the proposed algorithm can extract high-quality outer contours from point clouds with various boundary structures, accompanied by strong robustness for point clouds differing in density and density change. Moreover, the proposed algorithm is characterized by easily setting parameters and high efficiency for extracting outer contours. Specific to the experimental data selected for this study, the PoLiS values in the outer contour extraction results were always smaller than 0.2 m, and the RAE values were smaller than 7%. Hence, the proposed algorithm can provide high-precision outer contour information on buildings for applications such as 3D building model reconstruction.

Implication of site-specific segregation on grain boundary structural transition and deformation response in nanocrystalline Ni-Nb alloy

In this study, atomistic simulation technique is utilized to examine the impact of grain boundary (GB) character (disorientation angle), structure (boundary-free volume) and energy (boundary excess energy) on site-specific Nb solute segregation behaviour and structural transition in nanocrystalline (NC) Ni. Further, the role of site-specific solute segregation on deformation response in NC Ni is also studied. Towards this, hybrid Monte Carlo/molecular dynamics simulations is performed to obtain the equilibrium structure in a Ni-Nb binary alloy at 500 K and 1200 K. The spectral nature of GB atoms is explored in NC Ni, and found that the GBs have a skew-normal distribution for excess atomic volume and excess atomic energy. Furthermore, comprehensive segregation energy calculations are performed for each GB site, revealing the preferential affinity of Nb towards GB sites in NC Ni. The study also examined interfacial solute excess for each boundary as a function of GB energy and Voronoi volume. The findings indicate that the GB energy decreased as the solute excess increased, whereas the Voronoi volume demonstrated an increment in response to the solute excess. Moreover, simulations conducted at 1200 K reveal that not all GBs within the microstructure are transformed to amorphous complexions; rather some GBs remain ordered. The simulated tensile tests conducted at 500 K and 1200 K reveal that the strengthening in Ni-Nb enhances with the increase in dopant concentration. Additionally, the simulated shear test conducted at 1200 K shows that the deformation in Ni-5Nb occurs more uniformly than pure NC Ni due to formation of thicker amorphous GBs in the former one.

Grain boundary plasticity in Mg binary alloys by segregation of p-block element

The effect of p-block elements (Ga, Ge and In) addition on grain boundary structures and room temperature mechanical responses was investigated on extruded Mg binary alloys with fine-grained structures. Grain boundary segregation was confirmed in the Mg–Ga and Mg–In alloys, whereas the Mg–Ge alloy did not show such microstructures associated with solubility. Grain boundary segregation affected the plastic deformation of the Mg–Ga and Mg–In alloys. In particular, the Mg–In alloy had a large strain rate dependency and exhibited good deformability at low strain rate regimens. First-principles calculations indicated that p-block elements produce a bond-weakening effect at grain boundaries, and atomistic distances at grain boundaries varies according to the element. Solute atom which brings about both bond-weakening and bond-expansion effects to Mg atoms is effective in enhancing the contribution of grain boundary sliding in deformation.

The Evolution of Grain Boundary Dislocations in Graphene Induced by Strain: Three-Mode Phase-Field Crystal Method

The evolution and role mechanisms of grain boundary structures during the deformation process of graphene are of great significance for understanding the deformation behavior of graphene and optimizing its mechanical properties. This article takes single-layer graphene as the research object and establishes a double crystal graphene model using the three-mode phase-field crystal method, deeply exploring the evolution mechanisms of dislocations at small-angle symmetrical tilt grain boundaries in graphene under strain. In view of the relaxation and deformation process, the relationship between the number of multiple dislocations and the grain boundary angle of graphene was studied at atomic scale, and the deformation and failure mechanism of double crystal graphene under tensile load was revealed, and it is also discussed from the aspect of the free energy.&lt;br&gt;It is found that, after relaxation, with the increase of grain boundary angle, the density of dislocations at the grain boundary decreases, and the number of specific types of dislocations (5|8|7 and 5|7 dislocations) increases. Under stress loading parallel to the grain boundary, the changes of free energy of the systems containing grain boundaries with different angles show the same trend: At first, they descend to the inflection point and then rise abnormally, and the dislocation behavior can not effectively alleviate the stress concentration caused by continuous loading in the system, leading to failure.&lt;br&gt;Under tensile load, the free energy’s change of the systems is divided into four stages, of which the stage (I): the dislocations at grain boundaries are slightly deformed but does not change its structure. The stage (Ⅱ): dislocations at the grain boundaries are transformed into 5|7 or 5|9 dislocation due to C-C bond fracture or rotation. Dislocations that are "incompatible" have higher energy, making them more conducive to improving the tensile properties of graphene. The stage (Ⅲ): the 5|7 and 5|9 dislocations, begin to fail, and the free energy shows a tendency to decrease significantly. The stage (Ⅳ): the double crystal graphene systems have completely failed. The system with a grain boundary angle of 10° exhibits the most substantial free energy decrease in Stages (Ⅰ), (Ⅱ), and (Ⅲ), and possesses the highest overall tensile strength.&lt;br&gt;This work contributes to understanding the micromechanical behavior of graphene at the atomic scale.