Block Boundaries Research Articles

New Insights Into Crustal Deformation of the Indonesia–Australia–New Guinea Collision Zone From a Broad‐Scale Kinematic Model

AbstractThe Indonesia‐Australia‐New Guinea collision zone comprises a complex system of tectonic blocks whose relative motion accommodates convergence of the Sunda Block, Pacific, Australian, and Philippine Sea plates. Previous studies have considered either the western or eastern ends of this system, in eastern Indonesia and Papua New Guinea, respectively. However, these studies had limited ability to characterize either the kinematics of the central part of the system or transitions in tectonic regime across it. In this study, we perform a simultaneous inversion of 492 earthquake slip vectors and 267 GPS velocities to quantify the block movement spanning the Sunda‐Banda Arc, Western New Guinea, and Papua New Guinea. Our best‐fitting kinematic block model comprises 23 elastic blocks, for which we estimate the rotation rates and block boundary slip rates. We show how the Cenderawasih Bay sphenochasm was likely formed by a combination of both rotations (2.82 ± 0.11°/Myr anticlockwise) of the Bird's Head Block and southwest‐directed convergence (39.9 ± 1.7 mm/yr) along the Lowlands fault. Our estimated relative slip vectors across the New Guinea Fold‐and‐Thrust Belt indicate a transition in the tectonic regime of the block boundary from predominately thrust faulting at its western segment, with a convergence rate up to 19.5 ± 0.6 mm/yr, to predominately sinistral motion in the center segment with slip rate ∼7 mm/yr, and returning to thrust in the eastern segment with a convergence rate up to 9.0 ± 0.5 mm/yr, implying the combined effect of multiple driving mechanisms.

Relationship between hydrogeochemical characteristics of hot springs and seismic activity in the Jinshajiang fault zone, Southeast Tibetan Plateau

Significant anomalous hydrogeochemical changes in hot spring water are detected during strong seismic cycles. It is now necessary to clarify the relationship between tectonic movements, earthquakes and the evolution of hot springs. In this paper, laboratory analyses of major, trace elements, δD, δ18O and 87Sr/86Sr values of 28 hot spring waters in the Jinshajiang fault zone (JSJFZ) in the northwestern boundary of the Sichuan-Yunnan block were conducted. The results showed that the primary source of water for JSJFZ hot springs was atmospheric precipitation. The geothermal reservoir temperature variation based on the silicon enthalpy mixing model ranged from 73 to 272°C. And the circulation depth range was 1.2–5.4 km. The segmentation characteristics of the 87Sr/86Sr values were related to the influence of source rocks on groundwater cycle processes. A conceptual model of the hydrologic cycle of hot springs explained the spatial distribution of earthquakes associated with tectonic movements. The Batang segment had the strongest water-rock reaction, the highest reservoir temperature and the deepest circulation depth; meanwhile, it was also an earthquake prone area. The fluid circulation of the JSJFZ corresponds well with the seismicity, which indicates that the hydrological characteristics of the hot spring water in a fracture zone play a crucial role in receiving information on seismic activity.

Substructure and crystallography of lath martensite in as-quenched interstitial-free steel and low-carbon steel

In this study, the substructures and crystallographic features of as-quenched lath martensite in interstitial-free (IF) steel and low-carbon steel (0.2C steel) were investigated using focused ion beam-scanning electron microscopy serial sectioning and advanced transmission electron microscopy. A three-dimensional analysis revealed that the morphology of the so-called lath, the smallest structural unit, exhibited a wedge-shaped plate instead of the ideal lath shape. The habit plane orientations were distributed from (5 7 5)A to (1 1 1)A in the IF steel, whereas they were near to that predicted based on the phenomenological theory of martensite crystallography in the 0.2C steel. In the IF steel, well-developed dislocation cells, tangled dislocations, and curved dislocations could be observed. Conversely, straight dislocations and cementite formation were observed in the 0.2C steel. Moreover, the orientation changed significantly inside a given lath in both steels. The lath boundary comprised regularly spaced steps with (0 1 1)M atomistic terrace planes. Interfacial dislocations corresponding to the discontinuity of the (0 1 1)M lattice planes could be observed at steps, and these dislocations were introduced to compensate for the misorientation between adjacent laths. Additionally, carbon segregations were observed at the lath and block boundaries in the 0.2C steel. Our observation results on the dislocation structures, cementite formation, and segregation of carbon atoms on the lath and block boundaries indicated that the substructure changed significantly during quenching. Based on our experimental results, we discuss the origin of the substructures and crystallographic features of lath martensite.

Paper] Memory Bandwidth Constrained Overlapped Block Motion Compensation for Video Coding

Overlapped block motion compensation (OBMC) is an inter prediction tool that improves coding performance by blending reference samples of the current and neighboring block across the block boundaries. For this mechanism, OBMC increases the reference samples fetched from the external memory on hardware decoders, i.e., memory bandwidth. This is a disadvantage when introducing OBMC to video coding standards such as VVC, especially for mobile devices with limited batteries, because the extended memory bandwidth increases decoders' power consumption. In this paper, we propose a memory bandwidth constrained OBMC method with adaptive number of motion vectors and interpolation filter taps of the neighboring blocks depending on the current block sizes. Simulation results show that the proposed method achieves -0.22 % performance improvements over VVC reference software without exceeding the maximum memory bandwidth of VVC, which is comparable to the full performance of OBMC (-0.33 %), requiring 3.8 times its memory bandwidth.

Suppression of the Block Effect while Enhancing Dark Images Using Asumu Derivative

Image contrast enhancement is one of the most important tasks in the field of image digital processing. With the help of computers and programming languages, many mathematical methods have been implemented to improve the visual quality of an image. However, the majority of these methods have a major drawback: they tend to make the image look blocked. This effect is visually unpleasant and is likely to cause a computer vision system to falsely recognize as edges the boundaries of different blocks that belong to the same smooth area in the original image. To avoid the block effect while enhancing the quality of dark images, we propose a new fractional differential mask based on the Asumu fractional derivative. Experiments with dark natural images show that, even though our method does not have a better performance in statistical quality, it achieves a solution to the problem that was the motivation to write this paper, suppressing efficiently the block effect while improving the visual qualities of dark images.

STATISTICAL ANALYSIS OF GEOLOGICAL AND GEOPHYSICAL PARAMETERS OF THE MONGOLIAN-BAIKAL REGION

The origins and formation mechanisms of neotectonic structures in a part of the Mongolian-Siberian region were identified by geodynamic zoning based on multidimensional statistical analysis of numerical arrays describing geological-geophysical and geological-geomorphological processes. These processes in the regional lithosphere were described by a set of 11 geological and geophysical parameters, divided into three main groups using the hierarchical method of cluster analysis. The first group includes the seismic moment, the density of active faults, the rates of current horizontal deformations, and the magnitude of the deep heat flow. The second group involves the thicknesses of the earth’s crust and exogenous active layer, the velocities of current horizontal movements, and the amplitudes of vertical neotectonic movements. The third group includes gravity anomalies and the lithosphere thickness. The spatial grouping of parameters by cluster analysis (K-means method) yields seven clusters, whose spatial position and composition are determined by the geological history, geological structure, geodynamic evolution of the region, and the current deformation rates. Some clusters characterize large rigid lithospheric blocks, while other clusters describe large active fault systems in the given area. The search for latent factors that make the greatest contribution to the dispersion of the geological and geophysical parameter values was carried out using the principal component method, which makes it possible to minimize the number of factors. Four main factors were identified for areas that differ in the morphology and origin of neotectonic structures: (i) higher horizontal compressive and tensile strains, (ii) dynamic effect of mantle anomalies, manifested in uplifts and arching, (iii) activation of thinned lithosphere within the boundaries of lithospheric plates and large blocks, and (iv) active shear deformation of the earth’s crust. The results of clustering and factor analysis of numerical arrays describing the geological-geophysical and geological-geomorphological processes within the Mongolian-Siberian region can be interpreted in the framework of physical mesomechanics.

Regularities of change in physical-mechanical and corrosion properties of heat-strengthened reinforcing 20GS2 steel

The effect of the regularities in changes of the physical-mechanical and corrosion properties of 20GS2 reinforcing steel subjected to heat treatment is considered. It is found that steel has the highest sensitivity to cracking, regardless of the type of tempering (from electric heating or furnace), in the temperature range of 400...450 °С, and with a subsequent increase in tempering temperature, cracking resistance increases. The electron microscopic studies made it possible to establish that at 450 °С the martensitic orientation of cementite plates completely disappears, coherence is lost, block boundaries disintegrate, sizes and shapes of cementite plates change, and precipitation of carbides along grain boundaries begins. Such an unstable structure has an increased ability to absorb hydrogen (results of gas analysis), which leads to an acceleration of the process of hydrogen cracking. Therefore, electric heating of 20GS2 steel after high-temperature thermomechanical treatment is required to be carried out to temperatures of 500...550 °С.

Solving Nonlinear Delay-Differential-Algebraic Equations with Singular Perturbation via Block Boundary Value Methods

Solving Nonlinear Delay-Differential-Algebraic Equations with Singular Perturbation via Block Boundary Value Methods

Mechanisms of hardening of 12 % chromium ferritic-martensitic steel EP-823

Based on experimental data on microstructure parameters of the reactor high-strength high-chromium (12 % Cr) ferritic-martensitic steel EP-823, the authors identified the main factors responsible for its strength properties. The hardening mechanisms of this steel were analyzed after processing according to the modes that provide different level of steel strength properties. Traditional heat treatment (THT) and promising modifying high-temperature thermomechanical treatment (HTMT) are considered. The main mechanisms of steel hardening, regardless of the processing mode, are: dispersed hardening by nanoscale particles of the MeX type (Me = V, Nb, Mo; X = C, N) by the Orovana mechanism; grain-boundary hardening by high-angle boundaries of martensitic blocks and ferrite grains; substructural hardening by small-angle boundaries of martensitic lamellae; dislocation hardening by increased dislocation density. HTMT mode, which includes hot deformation in the austenitic area, leads to a significant modification of the structural-phase state of steel relative to THT: a decrease in the average size of blocks and lamellae of martensite, as well as ferrite grains, an increase in the density of dislocations and the volume fraction of nanoscale particles of the MeX type. At the same time, the corresponding contributions to value of the steel yield strength from grain boundary, substructural and dispersed hardening increase by 1.2, 1.3 and 1.8 times in comparison with THT. The relative contributions of the considered hardening mechanisms to the yield strength of ferritic-martensitic steel EP-823 were discussed. The values closest to the experimental yield strength after two treatment modes studied are obtained when the Langford-Cohen model is used to estimate the magnitude of substructural hardening.

A Block-Scale FFT Filter Based on Spatial Autocorrelation Features of Speckle Noise in SAR Image

In order to reduce the impact of noise on the accuracy of inversion products based on SAR images, many filtering algorithms have been developed for noise reduction of SAR images. This paper proposes a filtering method based on the spatial autocorrelation feature of the block fast Fourier transform (BFFT). The method statistically analyses the autocorrelation length of speckle noise on Sentinel-1B images for different features and then constructs a relationship between autocorrelation length and noise period. After that, the size of the optimal FFT filtering window radius was determined based on the relationship between the noise period and the components in the image frequency domain. Finally, we filtered the SAR image within the parcels. We compared BFFT with six commonly used filtering methods. The results show that: (1) The noise periods of the soybean, corn, paddy, and water objects on the SAR image have little difference, with noise periods of 3.36, 3.17, 3.13, and 3.14 pixels on the VV polarization and 3.49, 3.17, 2.94, and 2.42 pixels on the VH polarization; (2) after the BFFT filtering in the land parcel area, the mean value of the backscattering coefficient (BC) kept constant, whilst at the same time, the standard deviation (STD) was reduced to half of that before the filtering and (3) the BFFT and NLM filtering methods have a better effect on noise reduction inside the block. The BFFT filtering method retains the variation trend between different regions within the block and preserves the block boundary’s clarity. This study provides a new idea for refined image processing.

Conservative low-pass filter with compact stencils for hierarchical Cartesian mesh

A conservative low-pass explicit filter with compact stencils for hierarchical Cartesian mesh is proposed. The proposed filter has two key features; the primary conservation of the conservative variables (i.e., mass, momentum, and total energy) are satisfied even at non-conforming block boundaries where grid refinement level change, and the compact stencils are achieved by employing the explicit filter while the low-pass characteristic is enhanced by properly controlling the transfer function. The proposed filter is the flux-based filter and introduces the filter flux that satisfies the conservation of the conservative variables at the non-conforming block boundaries, and the appropriate control of the transfer function is achieved by controlling the filter flux. The proposed filter is coupled with the stable and non-dissipative kinetic energy and entropy preserving (KEEP) scheme for the hierarchical Cartesian mesh (Kuya and Kawai 2020) and applied to the numerical experiments of the inviscid vortex advection, Taylor–Green vortex, and turbulent wake behind a sphere. The numerical experiments demonstrate that the proposed filter conserves the conservative variables on the non-conforming mesh and successfully removes the high-wavenumber spurious oscillations while not showing any major detrimental effects on the well-resolved flows.

Effect of Double-Quenching on the Hardness and Toughness of a Wear-Resistant Steel

Martensitic/bainitic wear-resistant steels are widely used in civilian industry, where a good combination of strength and toughness is required. In the present study, a double-quenching process was applied and compared to the conventional single-quenching process. The microhardness and ductile–brittle transition temperature were measured, and the microstructure was characterized with scanning electron microscopy and electron backscatter diffraction (EBSD) technique. It was found that the double-quenching process refined the prior austenite grain size by 43% and simultaneously improved the toughness and hardness. The ductile-to-brittle transition temperature was decreased from −77 °C to −90 °C, and the hardness was increased by 8%. Based on the EBSD data, a detailed analysis of the grain boundary distribution was performed using a recently developed machine learning model. Unlike what was found in previous studies, for the studied wear-resistant steel, the refinement of the prior austenite grain did not increase the block boundary density while increasing the high-angle packet boundary density. As a result, the total density of the high-angle grain boundaries in the double-quenched specimen was not improved compared to the single-quenched specimen. Further inspection suggested that it is the prior austenite grain boundaries and high-angle packet boundaries that contribute to the hardness and toughness, and the key factors that determine their effectiveness are the high misorientation angle between the {110} slip planes and the high slip transmission factor.

Effect of isovalent substitution on structure of the two-slab BaNd2-xSmxIn2O7 indates

The conditions of isovalent substitution of Nd atoms for Sm atoms in A-positions of the BaNd2In2O7 two-slab perovskite-like structure of the BaNd2-xSmxIn2O7 type (0 £ x £ 1.8) have determined by X-ray powder diffraction methods. Tetragonal crystal structure (space group P42/mnm) of the BaNd2-xSmxIn2O7 phases with substitution degree of Nd atoms equal to 0.5, 1.0, 1.5 and 1.8 was determined by the Rietveld method. Crystal structure of BaNd2-xSmxIn2O7 is based on the two-dimensional (infinite in the XY plane) perovskite-like blocks, consisting of two slabs of the deformed InO6 octahedra connected by vertices. Ba atoms are localized only at 4f position inside the perovskite block, while REE atoms are placed only at 8j position at the boundary of the perovskite block. The adjacent perovskite-like blocks are separated by a slab of LnO9 polyhedra and held together by - O - Ln - O - interblock bonds. It is established that the isovalent substitution of Nd atoms by smaller Sm atoms leads to a decrease in the length of the Ln - O2 distance (from 0.230(2) nm to 0.206(2) nm) and to an increase in the degree of deformation of the interblocks of LnO9 polyhedra, the inner block polyhedra BaO12, and the InO6 octahedra as well. Such structural changes destabilize the interblock "stitching" and are one of the main destruction factors of the slab perovskite-like structure of the BaNd2-xSmxIn2O7 phases at x > 1.8. Data obtained could be used for directed regulation of structure-sensitive properties of materials based on the BaNd2In2O7 indate.

A Novel Approach for Hybrid Image Segmentation GCPSO: FCM Techniques for MRI Brain Tumour Identification and Classification.

In recent times, the early detection of brain tumour analysis and classification has become a very vital part of the medical field. The MRI scan image is the most significant tool to study brain tissue for proper diagnosis and efficient treatment planning to detect the early stages. In this research study, the two contributions were executed in the preprocessing mode. (a) Using wavelet transform to apply decomposed sub-bands of a low-frequency signal to control and adapt the spatial and intensity parameters in a bilateral filter and (b) to detect texture regions and block boundary to control and adapt the spatial and intensity parameters in a bilateral filter When compared to other image resolution methods, the adaptive bilateral method restores the original image quality and has a higher accuracy rate. Using the hybrid segmentation method of GCPSO (Guaranteed Convergence Particle Swarm Optimization) -FCM (Fuzzy C-Mean) techniques, the results were compared with various segmentation. The proposed segmentation gives a better accuracy rate of 95.32%.

Ensemble Clustering in GPS Velocities: A Case Study of Turkey

Block modeling is an effective way to understand Earth’s crustal deformation. However, the choice of block boundaries and the number of blocks affect the model results. Therefore, the subjectivity of this analysis should be avoided. Clustering analysis can be used to define the blocks of GPS (Global Positioning System) velocity fields without a priori information. Unfortunately, clustering methods also have unique solutions and differ with various algorithms. Ensemble methods could be an answer to enhance the clustering results for GPS velocities. In this study, we use ensemble clustering to identify block boundaries before block modeling without a priori information about the data. The ensemble clustering method is used for the first time in the clustering of GPS velocities and the case of Turkey is discussed. The published horizontal GPS velocities were first clustered with five different clustering methods and the optimum classes were determined using ensemble clustering methods. It is proven that the Meta-CLustering Algorithm can be used in terms of ensemble clustering for this region.

Global regularity for Nernst–Planck–Navier–Stokes systems with mixed boundary conditions

We consider electrodiffusion of ions in fluids, described by the Nernst–Planck–Navier–Stokes system, in three-dimensional bounded domains, with mixed blocking (no-flux) and selective (Dirichlet) boundary conditions for the ionic concentrations and Robin boundary conditions for the electric potential, representing the presence of an electrical double layer. We prove global existence of strong solutions for large initial data in the case of two oppositely charged ionic species. The result hold unconditionally in the case where fluid flow is described by the Stokes equations. In the case of Navier–Stokes coupling, the result holds conditionally on Navier–Stokes regularity. We use a simplified argument to also establish global regularity for the case of purely blocking boundary conditions for the ionic concentrations for two oppositely charged ionic species and also for more than two species if the diffusivities are equal and the magnitudes of the valences are also equal.

Carbon segregation and cementite precipitation at grain boundaries in quenched and tempered lath martensite

Tempering is widely applied to make carbon atoms beneficially rearrange in high strength steel microstructures after quenching; though the nano-scale interaction of carbon atoms with crystallographic defects is hard to experimentally observe. To improve, we investigate the redistribution of carbon atoms along martensite grain boundaries in a quenched and tempered low carbon steel. We observe the tempering-induced microstructural evolution by in-situ heating in a transmission electron microscope (TEM) and by compositional analysis through atom probe tomography (APT). Probe volumes for APT originate from a single martensite packet but in different tempering conditions, which is achieved via a sequential lift-out with in-between tempering treatments. The complementary use of TEM and APT provides crystallographic as well as chemical information on carbon segregation and subsequent carbide precipitation at martensite grain boundaries. The results show that the amount of carbon segregation to martensite grain boundaries is influenced by the boundary type, e.g. low-angle lath or high-angle block boundaries. Also, the growth behavior of cementite precipitates from grain boundary nucleation sites into neighboring martensite grains differs at low- and high-angle grain boundaries. This is due to the crystallographic constraints arising from the semi-coherent orientation relationship between cementite and adjacent martensite. We also show that slower quenching stabilizes thin retained austenite films between martensite grains because of enhanced carbon segregation during cooling. Finally, we demonstrate the effect of carbon redistribution along martensite grain boundaries on the mechanical properties. Here, we compare micro-scale Vickers hardness results from boundary-containing probe volumes to nanoindentation results from pure bulk martensite (boundary-free) probe volumes.

Strain rate dependence of strengthening mechanisms in ultrahigh strength lath martensite

The strain rate dependent mechanical properties of lath martensite are important for developing ultrahigh strength steels for automobile applications. Here, taken 2 GPa grade press hardening steel as a model material, we explored the strain rate sensitivity of lath martensite and the underlying physics. Uniaxial tensile tests were carried out over a wide range of strain rates from 10−3 to 1450 s−1 to determine the rate dependent mechanical properties. Strain rate exerts minor effect on mechanical properties at strain rates below 102 s−1. In contrast, both yield strength and work-hardening rate substantially increase with strain rate during high-strain-rate deformation. Microstructural evolution was characterized using electron backscatter diffraction and transmission electron microscopy. Particularly, synchrotron X-ray diffraction was used to measure dislocation density. The respective strengthening contributions from the friction stress, dislocations and high-angle block boundaries in lath martensite were evaluated on the basis of the measured microstructural parameters as well as related phenomenological models for predicting their strengthening effects. It is found that the enhanced yield strength during high-strain-rate deformation is due to a larger lattice friction for dislocation slip. The higher work-hardening rate is attributed to the enhanced mechanical heterogeneity within the current lath martensite microstructure at higher strain rates, which leads to larger strain gradient and thus promoted generation of geometrically-necessary dislocations.

SADHANA: A Doubly Linked List-based Multidimensional Adaptive Mesh Refinement Framework for Solving Hyperbolic Conservation Laws with Application to Astrophysical Hydrodynamics and Magnetohydrodynamics

We report the development of a nested block-structured adaptive mesh framework to solve multidimensional, time-dependent hyperbolic equations encountered in astrophysics. An approach based on a tabular list is used to construct variants of Hilbert space-filling curves in an iterative fashion to maintain the connectivity of locally refined mesh configurations using a doubly linked list. Modifications are made to conventional boundaries of computational blocks to aid the adaptive mesh. We also describe a well-defined, computationally efficient data structure to hold self-similar mesh units for this purpose. The flexibility of this code is demonstrated by the performance of various Riemann solvers implemented in this computational framework.

The effect of charging conditions on hydrogen embrittlement behavior of ultra-high-strength steel 22MnB5

The effect of charging conditions on hydrogen embrittlement (HE) of the hot-stamping boron steel was investigated with its hydrogen distributions and reversibility properties. With low hydrogen concentration, no noticeable hydrogen-induced cracking was detected, coupled with the uniform distributed diffusible hydrogen, realizing reversible HE. The quasi-cleavage fracture modes suggested the hydrogen-enhanced localized plasticity (HELP) mechanism. At high hydrogen concentration, the diffusible hydrogen distributed at the martensitic block and prior austenite grain boundaries which facilitated hydrogen-induced cracking initiation and propagated along the {110} M plane, leading to irreversible HE. The intergranular fracture modes suggested the transition of HELP to hydrogen-enhanced decohesion mechanism (HEDE). • The HE mechanism transits from HELP to HEDE as hydrogen concentration increases. • The distribution of hydrogen atoms is visualized by hydrogen microprint technology. • The reversibility of HE depends on the formation of hydrogen-induced cracking.