Boundary Structure Research Articles

Magnetotelluric sampling theorem

We consider a general case of a magnetotelluric (MT) study to reveal three-dimensional (3D) distribution of the electrical conductivity within the Earth based on measurements of electromagnetic (EM) fields by a two-dimensional (2D) array. Such an MT array observation can be regarded as a spatially discrete sampling of the MT responses (impedances), and each observation site can be regarded as a sampling point. This means that MT array measurements must follow the Nyquist–Shannon sampling theorem. This paper discusses how the sampling theorem is applied to MT array studies and what kind of consideration is required in the application on the basis of synthetic model calculations, with special attention to spatial resolutions. With an aid of the EM scattering theory and the sampling theorem, we can show that an observation array resolves some features of the MT impedance but does not others. We call the resolvable and unresolvable features the MT signal and noise, respectively. This study introduces the spatial Fourier transform of array MT data (impedances) which helps us investigating sampling effects of lateral heterogeneity from a different angle (in the wavenumber domain). Shallow heterogeneities cause a sharp spatial change of impedance elements near structural boundaries. High wavenumber Fourier components are required to describe such a feature, which means the site spacing must be sufficiently short to be able to resolve such features. Otherwise, a set of array MT data will suffer from aliasing, which is one of the typical causes of MT distortion (MT geologic noise). Conversely, a signal due to a deep-seated conductivity anomaly will have more reduced amplitude at higher wavenumbers, which means focused imaging of such an anomaly is generally difficult. Finally, it is suggested to properly consider the sampling theorem in an observation array design, so as to have best performance in resolving MT signals.Graphical abstract

How are microstructural defect interactions linked to simultaneous intergranular and transgranular fracture modes in polycrystalline systems?

The major objective of this investigation is to fundamentally understand and predict how intergranular (IG) and transgranular (TG) fracture modes nucleate and propagate in f.c.c. polycrystalline systems due to defects, such as total and partial dislocation densities and grain boundary (GB) structures and misorientations. A dislocation density crystalline plasticity (DCP) formulation based on the evolution and interaction of total and partial dislocation densities was integrated with a recently developed fracture approach to investigate the fracture nucleation and propagation of simultaneous multiple fracture events, including both IG and TG fracture events. The aggregate grains and GB orientations and morphologies are based on EBSD measurements that are representative of polycrystalline copper aggregates with a broad range of random high angle and low angle GBs. The predictions indicate that dislocation density pileups induce IG fracture due to interrelated stress, slip, and total and partial dislocation density accumulations and interactions for both high angle GBs (HAGBs) and low angle GBs (LAGBs). TG fracture nucleation and propagation occurred due to normal stress accumulations, which exceeds the fracture stress, along cleavage planes. Furthermore, it is shown how IG cracks transition from the GB plane to the cleavage planes as cracks nucleate and propagate. Accumulated plastic zones due to different slip system activities can impede and blunt crack propagation and fronts. These plastic zones form due to high Lomer and Shockley partial dislocation densities. These predictions, which are consistent with experimental observations, provide a fundamental understanding of how simultaneous failure modes initiate and propagate for physically representative microstructures.

Remote sensing image semantic segmentation via class-guided structural interaction and boundary perception

Existing remote sensing semantic segmentation methods generally ignore the structural information of objects that is vital in the human visual recognition system. The absence of overall structural information often results in weak perceptions of subtle textures and fragmented predictions, especially for complex and variable ground object scenarios. Besides, they still suffer from the semantic ambiguity caused by the unclear object boundary features in remote sensing images. In this paper, we propose a novel remote sensing semantic segmentation framework, called CSBNet, which aims to enhance the capacity of class-guided structural interaction and boundary perception simultaneously. It consists of a class-guided structure interaction module (CSIM), a Transformer-based context aggregation module (TCAM) and a class-guided boundary supervision module (CBSM). The CSIM has the ability to progressively extract the class-specific structural features, i.e., refining the structural information of each class by iteratively exchanging information between initial coarse class tokens and contexts. Meanwhile, the TCAM is constructed to provide CSIM with more discriminative multi-scale contexts without losing spatial features. In particular, the CBSM plays an auxiliary role, which applies the boundary information obtained from the class tokens to supervise the segmentation of boundary regions. When tested on the ISPRS dataset, LoveDA dataset, UAVid dataset, our method significantly outperforms the state-of-the-art remote sensing semantic segmentation approaches.

Sound transmission loss optimization of clamped double-panels

The panel cavity structure is one of the key components of the aircraft (vehicle) body and is among the main noise transmission pathways. Based on the modal superposition and Galerkin method, this paper realizes the theoretical model of sound insulation of the clamped, double-panel structure. The non-dominated sorting genetic algorithm-II (NSGA-II) is used to realize the sound insulation of the clamped double-panel structure. Through optimization, the fitting function and law of structural surface density and the optimized normal weighted sound insulation Pareto fronts were obtained. The results show that among the optimization, for the Pareto front cases, their double-panel thickness ratio h1/ h2 is relatively far away from 1, and the corresponding cavity thickness H is relatively large. The influence of boundary conditions and size effects of lightweight sound insulation optimization are also discussed. The research on the influence of boundary and size indicates that the difference in the optimal weighted sound insulation Pareto fronts corresponding to the same surface density is mostly within the 1 dB range. Both the boundary and thickness of the panel will affect the frequency STL, while the boundary conditions or structure size changed, even the total thickness of panels needs to be the same, and the structure can also have similar weighted sound transmission loss ( Rw) when the thickness ratio of the double-panel structure is chosen properly. The difference of material effects is also discussed. This research provides a method for the sound insulation optimization of clamped double-panel structures concerning the boundary and size effect.

Magnetogravimetric study on the Scotia Plate, in the South Atlantic Ocean for the characterization of tsunamis

The marine and coastal environments of the Scotia Sea regions in the Southern Atlantic Ocean and Antarctica are vulnerable to the potentially disastrous effects of seismic activity along the Scotia Arc. This paper presents a magnetogravimetric study of the Scotia Plate for tsunami characterization. The influence of earthquakes on the Geomagnetic Field (GMF) is investigated using data from INTERMAGNET network observatories. A tectonic model is evaluated using gravity data from NOAA and seismic refraction data from Lamont-Doherty Earth Observatory. The study also assesses the impact on water level (WL) measured at Intergovernmental Oceanographic Commission (IOC) tide gauge stations. Cross Wavelet Transform (XWT) is applied, and a frequency analysis of the GMF is conducted to identify specific frequencies during seismic events. A 2D tectonic model is constructed for the North Scotia Ridge using gravimetric and seismic data to characterize structural boundaries that may be activated during seismic events. Water level records collected from 6 tide gauge stations in the region are filtered and analyzed to identify tsunamis at each station. The results reveal anomalous frequencies in the frequency analysis of the horizontal component of the GMF during the November 25, 2013 earthquake, with high data correlation from different observatories in the study area for periods of 0.5 and 1 hour. Gravimetric modeling delineates faults activated during seismic activity and edges of structures potentially activated due to the transcurrent and compressional nature of the margin. WL anomalies up to 1.30 m are obtained following earthquakes with a magnitude greater than 8. The propagation speed in the study area averaged 460 km/h, consistent with the expected speed for those depths, except for Puerto Argentino, which exceeded them in 50%.

Coercivity enhancement and microstructure optimization of Nd-Fe-Co-B magnets by Dy70Al10Cu20 grain boundary diffusion

The effect of grain boundary diffusion on the magnetic properties and microstructure of Nd-Fe-Co-B sintered magnets is investigated using Dy70Al10Cu20 alloy as the diffusion source. After the secondary annealing of the Nd-Fe-Co-B sintered magnet (Hcj = 7.94 kOe), its coercivity is substantially increased to 13.10 kOe. Following post-diffusion annealing, the coercivity of the sintered magnet significantly increased to 20.86 kOe. Microstructure analysis revealed that after the second annealing, the main phase grains in the magnet were connected but lacked thin intergranular phases. The distribution of Co was uneven, with an abundance of soft magnetic phases rich in Co, which was not conducive to improving coercivity. After diffusion, Dy formed a shell structure with high magnetic crystal anisotropy on the outer side of the main phase grains, leading to a significant increase in coercivity. Al and Cu entered the interior of the magnet, reducing the melting point of the grain boundary phase and promoting the uniform distribution of Co through the flow of the liquid phase. A large amount of thin continuous intergranular phase is generated inside the magnet, which helps reduce the exchange coupling between hard magnetic grains. The experimental results indicate that the Dy-Al-Cu alloy can effectively enhance the grain boundary structure of Nd-Fe-Co-B magnets, reduce the abundance of Co-rich phases, and improve the coercivity of the magnet.

In-situ rapid nondestructive characterization of multiple irregular three-dimensional grain boundary structures and electrical properties by nanorobot with SEM in ZnO

To address the problem of spatial quantification of irregular grain boundaries, a unique approach for the nondestructive characterization of multiple irregular three-dimensional grain boundaries is proposed using nanorobots with scanning electron microscopy (SEM) to accomplish in-situ rapid synchronized quantification of structures and electrical properties. By constructing a three-dimensional trigonometric geometric mapping relationship, multiple irregular three-dimensional grain boundary structures and electrical properties can be rapidly quantified. Experimental results demonstrate that it is feasible to accomplish in-situ rapid nondestructive characterizations. The two-dimensional profile shapes of the targeted grain boundaries at each layer exhibit irregular and non-uniform features in the Y-Z plane. The hypotenuse length between the virtual space tilting lines presents a three-dimensional characteristic in the X-Z plane. The spatial tilt angle of the virtual space tilting line can be calculated using the right-triangle relation. The unequal numbers of grains along the same tilted hypotenuse direction with equal lengths directly illustrate the existence of irregular and nonlinear grain boundaries in bulk ZnO ceramics. The relatively uniform spatial sizes of the grain boundary illustrate the coupled spatial characteristics existing in the irregular micro-structures. The relatively uniform equivalent circuit fitting parameters confirm the existence of relatively uniform doping components in bulk ZnO ceramics. Furthermore, this method provides a unique approach for the rapid nondestructive quantitative analysis of multiple three-dimensional irregular grain boundaries in bulk polycrystalline materials.

Phase Pattern Formation in Grain Boundaries.

In this Letter we derive conditions that predict the existence of two-phase periodic-pattern grain boundary structures that are stable against coarsening. While previous research has established that elastic effects can lead to phase pattern formation on crystal surfaces, the possibility of stable grain boundary structures composed of alternating grain boundary phases has not been previously analyzed. Our theory identifies the specific combination of grain boundary and materials properties that enable the emergence of patterned grain boundary states and shows that the dislocation content of grain boundary phase junctions, absent in surface phenomena, weakens the stability of the patterned structures. The predictions of the theory are tested using a model copper grain boundary that exhibits multiple phases and two-phase pattern formation. We discuss how, similarly to surfaces, elastic effects associated with grain boundary phase junctions have profound implications for how grain boundary phases transform.

Modulation of phase boundary and domain structures to engineer strain properties in BNT-based ferroelectrics

Modulation of phase boundary and domain structures to engineer strain properties in BNT-based ferroelectrics

The effects of polycrystalline 3 C-SiC with different roughness coefficients on the crystal structure of nano-grin ding based on molecular dynamics

To investigate the effect of different roughness subsurface on the crystal structure and grain boundary changes during polycrystalline 3 C-SiC nanocrystalline grinding. Polycrystalline 3 C-SiC with different roughness subsurface is constructed by Voronoi method, the stress, crystal structure change and grain boundary crossing mechanism of polycrystalline 3 C-SiC are analyzed by molecular dynamics method. Three different roughness surfaces (Ry=0.02 um, Ry=0.04 um and Ry=0.045 um) are selected for analysis, before the nano-grinding process, the polycrystalline 3 C-SiC is first annealed to make the atoms closely arranged and eliminate the vacancy defects inside the grains. Different roughness affects the friction force of polycrystalline 3 C-SiC and changes the deformation of its subsurface. Consequently, affecting the elastoplastic properties of polycrystalline 3 C-SiC. Different roughness will affect the shear force on the polycrystalline 3 C-SiC subsurface, the smaller the roughness, the greater the shear stress on the subsurface. The polycrystalline 3 C-SiC crystal structure with a roughness of Ry=0.04um is most obviously affected, the length of the dislocations it produces is relatively small, and the situation is more obvious at the boundary, fewer internal dislocations indicating internal dislocation slip phenomenon is less and more favorable for processing.

Design and simulation of an efficient gas-liquid separation device for component regulation of zeotropic mixtures

ABSTRACT Improving the overall energy efficiency of thermodynamic cycles relies heavily on the replacement of traditional pure fluids with zeotropic mixtures. The selection of the optimal components within the zeotropic mixture depends on the specific operating conditions of the thermodynamic cycle. Therefore, significant enhancements in performance can be achieved across varying operating conditions by effectively controlling the composition of zeotropic mixtures in the cycle. According to the gas-liquid equilibrium characteristics of the zeotropic mixtures, the adjustment of the medium components and the boundary conditions can be realized if the components can be adjusted through the gas-liquid separation. In this study, a novel device is proposed for automatically regulating the speed of gas-liquid separation in order to separate the components of the zeotropic mixtures. The CFD simulation was utilized to analyze the structural parameters and boundary conditions that impact the efficiency of gas-liquid separation. The results indicate that the adjustable mass flow range of the optimal structure is broadened by 5.5 times compared to conventional gas-liquid separation devices, ranging from 0 kg/s to 0.15 kg/s. Additionally, within this range, the gas-liquid separation efficiency exceeds 95%, representing a 10% improvement over traditional phase separators.

Observations of the 2022 September 5 Solar Energetic Particle Event at 15 Solar Radii

On 2022 September 5, Parker Solar Probe (Parker) observed a large solar energetic particle (SEP) event at the unprecedented distance of only 15 R S from the Sun. The observations from the Integrated Science Investigation of the Sun (IS⊙IS) obtained over the course of this event are remarkably rich, and an overview is presented here. IS⊙IS is capable of measuring ions from 20 keV to over 100 MeV nuc−1 and electrons from 30 keV to 6 MeV; here, we primarily focus on the proton and helium measurements above 80 keV. Among the surprising results are evidence of inverse velocity dispersion at energies above 1 MeV during the onset of the event, a sharp decrease in the energetic particle intensities at all energies at the interplanetary shock crossing, and repeated short durations of highly anisotropic sunward flow. Many changes in the SEP intensities, anisotropy, and spectral steepness are coincident with solar wind structure boundaries identified using the Parker solar wind magnetic field and plasma data. However, there are significant changes that are not correlated with any clearly visible solar wind variation. The observations presented here serve as an introduction to a complex event with numerous opportunities for future, more in-depth studies.

An analytical study on generation of waves due to the rolling of flexible porous barriers

Complete analytical solution for generation of waves due to rolling of a partially immersed vertical elastic porous plate or a tensioned membrane is obtained. The originally defined boundary value problem in the half-plane has been decomposed first into a couple of flexible porous wave potential problems in the quarter-plane. Then, a pair of integral relations are introduced to establish a connection among the flexible porous wave potentials, solid wave potentials, and auxiliary wave potentials. By utilizing the connection, the flexible porous wave potentials can be determined in terms of the solid and the auxiliary wave potentials. The problems for the latter two types of potentials are easier to handle mathematically than the problems for the flexible porous wave potentials because of the involved structural boundary condition. Thus, the solid and the auxiliary wave potentials have been obtained analytically by the existing methods of solutions. Explicit analytical expressions are derived for the radiated wave amplitudes and velocity potentials. These radiated wave amplitudes are numerically computed and analyzed for different parameters involved. The results are validated with those derived for the problem involving a solid plate.

Adaptive structure-based full-waveform inversion

In simultaneous-shot full-waveform inversion (FWI), the re-started limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm can be used to suppress crosstalk, but crosstalk cannot be completely eliminated from the inversion results. To further solve the crosstalk problem caused by the interference among individual shots in simultaneous-shot FWI, adaptive structure-based smoothing is applied to the FWI with the restarted L-BFGS algorithm. Structure-based smoothing can mitigate the crosstalk by highlighting structure boundaries. To perform structure-based smoothing, an implicit anisotropic diffusion equation is solved. We carry out a multiscale inversion strategy. Because the FWI results in the low-frequency band contain less structural information and more crosstalk, structure-based smoothing is applied to the frequency band at frequencies higher than the peak frequency to prevent negative effects from the model structure in the low-frequency band. The estimated structural information is iteratively updated during the inversion process. Furthermore, structure-based smoothing is only added to the iterations with invariant encoding to reduce oversmoothing. The invariant encoding means that the shot encoding remains unchanged between iterations. Numerical experiments with an overthrust model indicate that the proposed adaptive structure-based FWI method can effectively suppress artifacts and provide a high-resolution inversion result, even when the encoded data are contaminated with strong noise. Another advantage of the adaptive structure-based FWI method is that no seismic migration needs to be performed, which makes it more efficient for real data.

How secure memorization promotes expression: A longitudinal case study of performing Chopin’s Barcarolle, Op. 60

Experienced musicians can perform reliably from memory because they prepare performance cues (PCs) that allow them to recover when performance is disrupted. We describe a longitudinal case study in which a pianist (the second author) learned and performed Chopin’s Barcarolle, Op. 60, over a 12-year period. The pianist provided PC reports for 28 performances, starting a month before her first public performance. Shortly after each performance, she marked the features of the music that guided her playing (PCs) on a clean copy of the score, distinguishing five types of PC: structural, Schenkerian (tonal elaborations), expressive, interpretive, and basic. Structural PCs predominated at first and were later replaced by expressive and Schenkerian PCs. PCs were more frequent at structural boundaries than at other locations. This boundary effect was larger under typical, compared to atypical performance conditions, and increased over time, suggesting that the main function of PCs was promoting expression rather than guarding against mistakes. Although the pianist’s initial purpose in learning to use PCs was to have a safety net in case of memory failure, she was surprised to find that she enjoyed playing with PCs and believed they helped her to play more expressively.

Atomic‐Scale Study of Intercrystalline (Mg,Fe)O in Planetary Mantles: Mechanics and Thermodynamics of Grain Boundaries Under Pressure

AbstractPolycrystalline (Mg,Fe)O ferropericlase is the second most abundant mantle constituent of the Earth and possibly of super‐Earth exoplanets. Its mechanical behavior is expected to accommodate substantial plastic deformation in Earth's lower mantle. While bulk properties of ferropericlase have been extensively studied, the thermodynamics of grain boundaries and their role on mechanical response remain largely unexplored. Here, we use density functional theory calculations to investigate mechanical behavior and thermodynamics of the {310}[001] grain boundary—a representative proxy for high‐angle {hk0}[001] tilt grain boundaries—at relevant mantle pressures of the Earth and super‐Earth exoplanets. Our results provide evidence that shear‐coupled migration and grain boundary sliding are the dominant mechanisms of (Mg,Fe)O grain boundary mobility. We show that pressure‐induced structural transformations of grain boundaries can trigger a change in the mechanism and direction of grain boundary motion. Significant mechanical weakening of the grain boundary is observed under multi‐megabar pressures, caused by a change in the grain boundary transition state structure during motion. Our results identify grain boundary weakening in periclase as a potential mechanism for viscosity reductions in the mantle of super‐Earths. We further demonstrate that structural grain boundary transitions control the spin crossover of Fe2+ in the grain boundaries. We model iron partitioning behavior between bulk and grain boundaries and predict equipartitioning to occur in μm size ferropericlase grains. Our findings suggest that the iron spin crossover pressure in ferropericlase may increase several tens of GPa by pressure‐induced structural grain boundary transitions in dynamically active fine‐grained lower mantle regions.

Typomorphic and Technological Characteristics of Quartz of the Mica-Pegmatite Formation on the Example of the Berkutinskaya Vein (South Urals)

Abstract ––Understanding the origin of quartz veins of the mica-pegmatite formation is of great importance for deciphering the emplacement conditions for the of commercially prospective quartz targets. On the example of the Berkutinskaya vein, which is the typical metamorphogenic quartz deposit of the mica-pegmatite formation of the South Urals, we study the source and origin of the mineral-forming fluid, temperatures of quartz formation, the structure of intergranular boundaries, their morphometric feature, the fractal dimension of quartz grains and commercial characteristics of quartz grit. An integrated approach to the study of the typomorphic features of quartz allowed us to assess their impact on the technological characteristics of quartz concentrates. Comparison of data on the content of impurity elements in the Berkutinskaya quartz vein with quartz of the vein No. 175 of OOO Russian Quartz and IOTA-std (Sibelco) showed that the Berkutinskaya quartz vein is promising for commercial development.

Erosion Wear Analysis on Valve Cage of Cage-Typed Sleeve Control Valve for Coal Liquefaction

Abstract Cage-typed sleeve control valve (CSCV) is the key basic equipment in direct coal liquefaction projects. The working condition of CSCV has the characteristics of high-pressure difference, high velocity, and high solid content. There is a general issue of liquid–solid two-phase erosion wear in CSCV, which can easily lead to the failure of the internal structure in the valve cage. Therefore, it is necessary to study erosion wear characteristics of internal structures in the valve cage. Considering the real conditions of erosion wear in the valve cage, a simplified T-shaped flow path is designed, and the precision of both the liquid–solid two-phase flow model and the erosion prediction model is validated. The flow characteristics and erosion wear characteristics in the T-shaped flow path under different working conditions are studied. Based on the simulation results of different structural parameters and boundary conditions, the erosion wear of the T-shaped flow path is predicted and calculated by the response surface method. Subsequently, the prediction formula for the maximum erosion rate is derived. The formula enables the swift determination of optimal structural parameters for the flow path, aiming to mitigate damage to the valve caused by erosion wear. This work can quickly predict the erosion wear rate of the key areas in the valve cage, which can provide a certain reference value for the life prediction and structural optimization of CSCV, and it can also benefit the safety and maintenance of the coal liquefaction system.

Efficient production of kilometer-scale ultrafine aluminum wire with superior strength and electrical conductivity

The rapid development of new energy vehicles has generated considerable interest in the efficient production of ultrafine aluminum electronic wiring harnesses with superior strength and electrical conductivity (EC). However, achieving a balance between strength and EC/ductility remains a challenge. To overcome the trade-off relation, we precisely controlled the grain size and grain boundary structure by using ultrafine aluminum powders (∼1 μm) as the starting material, and introduced dislocations into the as-sintered sample to enhance the strain rate sensitivity via cold deformation. In the cold-deformed sample, a unique mechanical response was observed: the elongation increased with deformation. Meanwhile, the strength and EC maintained to be a high level. Based on the unique properties, we successfully fabricated kilometer-scale ultrafine aluminum wire (0.2 mm in diameter) by cold deformation without any intermediate annealing, realizing high strength (206 MPa) and high EC (59.1%IACS, International Annealed Copper Standard) simultaneously. Our work provides a new concept and a new processing route to efficiently produce ultrafine aluminum electronic wiring harness with excellent properties.

Direct recording and reading of mechanical force by afterglow evaluation of multi-piezo mechanoluminescent material Li0.12Na0.88NbO3 on well-designed morphotropic phase boundary

Mechanoluminescence (ML) refers to the photon emission from materials subjected to mechanical stimuli. A general concept concerning ML materials is that they cannot directly record a stress history (mechanical record; MR). Here, we report an approach that retrieves a quantitative recording of stress history through the afterglow characteristics analysis of a specific multi-piezo ML material Li0.12Na0.88NbO3:Pr (LNNO), which has been designated to exist near the structural phase boundary of rhombohedral R3c and orthorhombic P21ma. Contrary to the general expectation that the afterglow characteristics are irrelevant to mechanical loading history, LNNO was strongly correlated with the stress distribution after UV excitation. This enabled us to read the recorded stress precisely from the afterglow image of the material. Furthermore, the spatial distribution of the MR was also realized, showing the capability of the readout of stress history in both time and space. This unusual MR function is attributed to eliminating shallow trap sites, which affected the afterglow characteristics upon applying mechanical load.