Shear Angle Research Articles

Does Reconnection Only Occur at Points of Maximum Shear on Mercury's Dayside Magnetopause?

AbstractMESSENGER observations of large numbers of flux transfer events (FTEs) during dayside crossings of Mercury's magnetopause have shown that the highly dynamic Hermean magnetosphere is strongly driven by frequent and intense magnetic reconnection. Since FTEs are products of reconnection, study of them can reveal information about whether reconnection sites favor points of maximum shear on the magnetopause. Here, we analyze 201 FTEs formed under relatively stable upstream solar wind conditions as observed by MESSENGER during inbound magnetopause crossings. By modeling paths of these FTEs along the magnetopause, we determine the conditions and locations of the reconnection sites at which these FTEs were likely formed. The majority of these FTE formation paths were found to intersect with high‐magnetic shear regions, defined as shear angles above 135°. Seven FTEs were found where the maximum shear angle possible between the reconnecting magnetic field lines was less than 80° and three of these had shear angles less than 70°, supporting the idea that very low‐shear reconnection could be occurring on Mercury's dayside magnetopause under this global‐scale picture of magnetic reconnection. Additionally, for the FTEs formed under these low‐shear reconnection conditions, tracing a dominant X‐line connecting points of maximum shear along the magnetopause that passes through a region of very low‐shear may be difficult to justify, implying reconnection could be occurring anywhere along Mercury's magnetopause and may not be confined to points of maximum shear.

On the formation of Ti2AlN MAX phase coatings and improvement in tool life by superimposing on tungsten carbide cutting tool for machining Ti-6Al-4V alloys

This paper presents the development of (002) textured Ti2AlN coated wear resistant tool utilizing reactive magnetron co - sputtering. The Ti2AlN coating was developed in two different Argon, Nitrogen ratios such as 64:3 and 64:4, the influence of these parameters was identified using crystallographic, microstructural, mechanical and tribological studies. Experimental studies were performed to compare the cutting force as well as the tool life of superimposed Ti2AlN tool with a commercial tool by turning titanium alloy (Ti-6Al-4V). Results from the experimental analysis revealed an 80–85 % increase in hardness, a 13–20 % decrease in wear rate and a 27 % increase in tool life for Ti2AlN coated cutting tool. According to chip morphology, there is a 12 % increase in shear angle, 43 % and 51 % decrease in friction angle and coefficient of friction respectively. The nanomechanical studies were performed which show a maximum hardness of 29.12 ± 5.4 GPa and minimum wear rate of 10.078 × 10−9 mm3/mN.m−1 for superimposed Ti2AlN.

Model of shear strength of ultra-deep fractured sandstone considering fracture morphology

Ultra-Deep fractured tight sandstone gas reservoir, the hotpot unconventional petroleum resources, has been the subject of investigation recently. Due to the presence of natural fractures, drilling in ultra-deep fractured tight sandstone may cause complicated wellbore instabilities, which resulted in a substantial challenge to the efficient exploitation and production of tight gas resources. In order to understand the rock mechanical properties of the ultra-deep fractured tight sandstone under shear stress, tight sandstone core samples were artificially shear-fractured, the 3D characteristics of the fractures were reconstructed by CT scanning, and the fracture aperture and roughness characteristics were systematically evaluated. Simultaneously, triaxial shear strength tests were conducted to evaluate the mechanical properties of fractured rock subjected to varying confining pressures. Considering the contact relationship of the fracture surface during shearing, two indexes of average effective shear angle and contact area ratio were proposed to correct the fracture roughness, and a new fracture shear strength model was constructed, which served as the failure criterion for the fractured formation. The results show that the intact rock has a high compressive strength and can only collapse under conditions of substantial differential stress. Consequently, shear failure of fracture ought to be the primary source of wellbore instability. The fracture aperture's spatial distribution is irregular and conforms to a Gaussian distribution. A clear anisotropy in the fracture roughness is present, and there is less roughness along the initial shear failure path and more roughness perpendicularly. With an increase in normal stress, the fracture's peak shear strength rises, while the friction angle steadily falls. The innovative model's accuracy in predicting shear strength is higher than that of the weak-surface model and the JRC-JCS model.

Development of the tied butterfly shape for structural fuses

Recently, there has been research and interest in structural fuses as a way to concentrate seismic damage in replaceable elements and protect the rest of the structure from inelastic actions. However, there is no consensus on structural fuse shape, particularly for structural fuses consisting of a steel plate subjected to shear deformations, because studies with different objectives arrive at different shapes. For example, studies seeking to optimize the structural fuse shape to maximize fracture resistance often result in something that looks like the butterfly-shaped link, whereas other studies that optimize the form to maximize buckling resistance result in a shape with links that are tied together. In this study, a new structural fuse shape, named the tied butterfly shape, was developed to integrate the advantages of both the buckling-resistant configuration and the butterfly-shaped link. First, the concepts for the tied butterfly shape are presented along with plastic mechanism analysis to derive an equation for shear strength. Then, an experimental program is described including three tied butterfly shape structural fuses and one straight link structural fuse for comparison. Finite element models are then validated against the experimental results and a parametric computational study is presented that evaluates the effect of key design variables on the structural behavior of this tied butterfly shape. The experimental study revealed that the tied butterfly shape structural fuse was capable of maintaining stable hysteretic behavior up to a shear angle of 23% before fracture or buckling and that multiple tied butterfly shapes can be connected together. Based on the plastic mechanism analysis and parametric study, design equations and recommendations for implementation in practice are provided.

The Intra-Ply Shear Behaviour of Non-Isothermal Thermoplastic Composite Laminates

During the thermoforming of fibre-reinforced thermoplastic (FRTP) organosheets, the desire to minimise tool temperatures leads to non-isothermal temperature profiles through the laminate thickness. The aim of this study was to understand the influence of these non-isothermal conditions on FRTP intra-ply shearing. Novel non-isothermal bias extension tests were conducted, revealing that an average between the isothermal shear curves of both laminate faces approximately represented the respective non-isothermal condition. However, these findings were irrespective of FRTP thickness, and only applied to laminates that wholly remained above the crystallisation onset temperature. Upon the onset of crystallisation in a single ply, the non-isothermal shear resistance skewed heavily towards that (within 5%) of the crystallised ply and inhomogeneous shear angles were observed. Non-isothermal thermoforming validated these findings with the presence of wrinkles on non-isothermal hemispheres in which a single ply had reached crystallisation. This reaffirms the importance of accurate thermal monitoring during FRTP processing.

Relationship of Rock Geomechanics and Coal Mine Slope Safety Factor in South Sumatra Region, Indonesia

The research location is in the coal mine area South Sumatera region, Indonesia. This study aims to determine the geomechanics relationship of the rock which includes the physical properties of the rock: bulk density, and mechanical properties of the rock (shear strength), cohesion and internal shear angle to the safety factor of the coal mine slopes in the study area. Field research is carried out by observing and measuring directly in the field in the following ways: (a) Measuring slope azimuth, slope, dip direction and slope height and width using a measuring tape and geological compass. (b) Rock description based on physical characteristics (megascopic) and rock sampling for testing the physical and mechanical properties of the rock in the laboratory. (c) Observing the general condition of water from rock slopes (dry, moist, watery, wet or flowing) and slope vegetation. 2. Cohesion values and internal shear angles are secondary data obtained from PT. X which has been analyzed in the laboratory. 3. Slope modeling was carried out using Rocscience Slide software. This shows that the smaller the rock density value, the greater the rock cohesion value. The greater the cohesion value of the rock, the smaller the value of the shear angle on the rock. The smaller the value of the shear angle in the rock, the greater the value of the safety factor of the rock slope.

The Shear Strength of Clay Stabilized with Palm Bunch Ash and Cement

Roads with soft subgrade have low bearing capacity. The result is non-uniform soil settlement. One way to overcome this is with soil stabilization. Stabilization of clay soil is done chemically with palm bunch ash and cement. The purpose of this study was to determine the bearing capacity of soil for the shear strength value of clay soil with variations in mixing 5%, 10%, 15%, 20% oil palm bunch ash, and 10% cement with a 7-day curing period, and then the samples were tested using a direct shear test tool SNI 3420: 2016. The results showed that in the addition of a mixture of oil palm bunch ash and cement with levels of 5%, 10%, 15%, 20%, and 10% cement, the cohesion value increased at a percentage of 20% oil palm bunch ash and 10% cement, namely 0.5448 kg/cm2 compared to the cohesion value in the original soil of 0.0081 kg/cm2, an increase of 98.51%, and a shear angle value of 53.12° while the value of the original soil shear angle was 16.93°. This research concludes that the shear strength value of clay soil stabilized with oil palm bunch ash and cement increases.

Overall flexural-shear buckling strength design of built-up radially battened columns

The built-up radially battened columns (RBCs) have a promising prospect in public building engineering due to their aesthetical form and good load-bearing capacity. However, their design methods are not covered in the current design specifications because of their distinctive appearance. This paper aims to present the flexural-shear buckling behavior of built-up RBCs and propose its corresponding strength design recommendations. At first, the finite element model (FEM) of the RBC is established, and a lot of examples are calculated in eigenvalue buckling analysis and elastoplastic analysis by using this FEM. Three kinds of possible first-order buckling modes are observed in the elastic buckling analysis, which are flexural-shear buckling, torsional buckling, and local buckling respectively. Only flexural-shear buckling is involved in this study, and torsional buckling will be investigated in a companion paper. Local buckling (of the chord tube wall) can be prevented by a radius-to-thickness ratio limit. It has been proven that shear deformation plays an essential role in determining the flexural-shear buckling of built-up members, thereby a unit shear angle model is established to study the shear stiffness of RBCs when they buckle overall. Then, the prediction equations for elastic flexural-shear buckling load and its corresponding normalized slenderness ratio are derived. The design curves for the ultimate load-bearing capacity of built-up RBCs are also proposed based on the numerous results from elastoplastic FEMs by changing normalized slenderness ratios. Furthermore, the compound buckling of RBCs is considered by employing a FEM that exerted the individual chord initial imperfection (FEM-c), and accordingly, a strength reduction factor caused by compound buckling is proposed. Finally, the design methods for the individual chords and radial-shaped battens are studied. The internal forces in chords and batten plates are derived and the analysis of the local buckling of batten plates is conducted. It is recommended that chords should be regarded as a member under combined compression and bending, and batten plates can be guaranteed to not lose their stability before the RBC reaches their ultimate load-bearing capacity by adopting the ‘isostable criterion’. In conclusion, these results provide a method for accurately and conservatively predicting the strength of RBCs when overall flexural or compound buckling occurs, which will expand the application of RBCs in engineering and make our public buildings more pleasing.

A sequential inverse approach for draping simulations of woven fabrics with anisotropic hyperelastic behavior laws

Simulations of the draping of woven fabrics for the manufacturing of composite parts with complex geometries rely on either the geometrical method, which does not consider the shearing stresses and the external forces, or incremental finite element analyses, which require substantial CPU times. In this study, the one-step finite element method, also referred as the inverse approach in the literature, commonly used for sheet metal forming, is adapted to the woven fabric draping. The main issue of one-step simulations is the convergence of the Newton–Raphson scheme, which relies on an appropriate initial solution estimation. This problem is addressed by a sequential initial solution estimation, based on successive sub-problems with increasing difficulty up to the actual one. Applications of the proposed method on elementary test cases show fast and robust convergence, with CPU times comparable to those of the geometrical method. The proposed method is able to predict the influence of external forces and material hyperelastic mechanical behavior laws on the strain components of interest of woven fabrics, such as the shearing angles between yarns and the yarn elongations.

Multipoint Observations of the Dynamics at an ICME Sheath–Ejecta Boundary

The radial evolution of interplanetary coronal mass ejections (ICMEs) is dependent on their interaction with the ambient medium, which causes ICME erosion and affects their geoefficiency. Here, an ICME front boundary, which separates the confined ejecta from the mixed, interacted sheath–ejecta plasma upstream, is analyzed in a multipoint study examining the ICME at 1 au on 2020 April 20. A bifurcated current sheet, highly filamented currents, and a two-sided jet were observed at the boundary. The two-sided jet, which was recorded for the first time for a magnetic shear angle <40°, implies multiple (patchy) reconnection sites associated with the ICME erosion. The reconnection exhaust exhibited fine structure, including multistep magnetic field rotation and localized structures that were measured only by separate Cluster spacecraft with the mission inter-spacecraft separation of 0.4–1.6 R E. The mixed plasma upstream of the boundary with a precursor at 0.8 au lacked coherency at 1 au and exhibited substantial variations of southward magnetic fields over radial (transverse) distances of 41–237 R E (114 R E). This incoherence demonstrates the need for continuous (sub)second-resolution plasma and field measurements at multiple locations in the solar wind to adequately address the spatiotemporal structure of ICMEs and to produce accurate space weather predictions.

Unveiling the transformation pathways of hierarchical γ90 – εtwin – α’ triple phase structure formation at ε-ε martensite intersection

Deformation-induced martensitic transformation (γ-austenite → ε-martensite/α’-martensite) in austenitic steels has garnered significant interest owing to its transformation-induced plasticity effect. To elucidate the orientation-dependent intricate γ/ε/α’ phase microstructure at deformation-induced ε-ε intersection, a single crystal of 316 austenitic stainless steel was compressed along the [001]γ axis at a cryogenic temperature (173 K). Electron backscattered diffraction analysis was employed to reveal the deformed microstructure on the (110)γ surface. A hierarchical triple phase structure was discovered at ε–ε intersection, where the γ rotated 90° from the matrix (γ90), {101¯2} ε-twin, and α’ phases coexist. Depending on the operative shear angle with a common intersection axis, either 90° (Type I) or 30° (Type II), three distinct atomic rearrangements of the intersection volume were observed: γ90 was present at Type I intersection, and α’-phase was developed at Type II intersection, respectively. {101¯2} ε-twin also occurred at Type I intersection, serving as an accommodation mechanism alongside the intersection γ90. EBSD results confirm the Shoji–Nishiyama (SN), Kurdjumov–Sachs (KS), and Burgers (B) orientation relationships within the complex γ – ε – α’ triple phase structures at ε–ε intersection. Transformation paths for three intersection products were visualized by the unified tetrahedron model, considering T/2 or T/3 γ-twinning shear as an intermediate state. Moreover, a novel scheme is proposed to index the α’-martensite crystallographic variants at ε-ε intersections by establishing a correlation between the Bain distortion and double shear process.

Numerical simulation study on shear resistance of anchorage joints considering tensile–shear fracture criterion of 2G-NPR bolt

2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has significant effects on improving the shear strength of jointed rock mass and controlling the stability of surrounding rock. To achieve an accurate simulation of bolted joint shear tests, we have studied a numerical simulation method that takes into account the 2G-NPR bolt's tensile–shear fracture criterion. Firstly, the indoor experimental study on the tensile–shear mechanical properties of 2G-NPR bolt is carried out to explore its mechanical properties under different tensile–shear angles, and the fracture criterion of 2G-NPR bolt considering the tensile–shear angle is established. Then, a three-dimensional numerical simulation method considering the tensile–shear mechanical constitutive and fracture criterion of 2G-NPR bolt, the elastoplastic mechanical behavior of surrounding rock and the damage and deterioration of grouting body is proposed. The feasibility and accuracy of the method are verified by comparing with the indoor shear test results of 2G-NPR bolt anchorage joints. Finally, based on the numerical simulation results, the deformation and stress of the bolt, the distribution of the plastic zone of the rock mass, the stress distribution and the damage of the grouting body are analyzed in detail. The research results can provide a good reference value for the practical engineering application and shear mechanical performance analysis of 2G-NPR bolt.

Investigation of mechanical behavior, AE and EMR characteristics of rocks under compression-shear loading via variable-angle shear tests

The surrounding rocks of underground engineering are usually subjected to the coupling of compressive and shear stresses. The mechanical characteristics of underground geomaterials subjected submitted to compression-shear loading have received considerable attention recently. The complex response arises from the microstructure redistribution under high in-situ stress and the resulting fracture behaviors at multiaxial stress states. Understanding the compression-shear behavior and failure mechanism of rocks is of essential importance for mechanical characterization and construction safety in deep underground engineering applications. In this study, variable-angle shear tests are conducted for cubic sandstone samples to investigate damage evolution under compression-shear loading, and the acoustic emission (AE) and electromagnetic radiation (EMR) are simultaneously monitored to record crack development. The mechanical behaviors of rock with AE and EMR responses in variable-angle shear tests with shear angle of 30°, 45° and 60° are analyzed. Then, correlation between AE and EMR is evaluated. Damage evolution of the rock specimen is described based on AE and EMR energy. Fractal dimension and b-value of AE and EMR time series are calculated to further reveal the microscopic crack mechanism of rocks. The results suggest that the continuous decline of fractal dimension and b-value of AE and EMR can act as the precursor of rock failure.

Analysis of force generated in composite egg-box structures during draping as a function of draping angle

To closely investigate the correlation between the structural shape and forces generated along yarns, draping simulation was performed using a non-orthogonal constitutive equation programmed by a VUMAT code and a composite lay-up model considering the draping angle (0°, 15°, 30°, 45°) and the actual thickness of the prepregs. Force generation at seven representative points (RP) along the two major axes (sidewall and saddle) of the unit cell structure was studied during draping. Representative deformations, including wrinkle generation, of the fabric prepregs during draping were correlated to the generated forces. To estimate the onset of wrinkle generation of the draped structure for any draping angle cases, the distortion energy which was calculated using the yarn force and shear angle of a simple square FE model was used. Moreover, draping experiments were conducted to verify the deformation characteristics estimated by finite element analysis.

THEORETICAL AND EXPERIMENTAL JUSTIFICATION OF EFFECTIVE TECHNOLOGIES OF HIGH-SPEED MECHANICAL PROCESSING

A refined mathematical model for determining the conditional cutting stress during blade processing has been developed based on the establishment of an analytical dependence for determining the conditional shear angle of the processed material. It is shown that its formation is dominated by the radial component of the cutting force, which leads to its significant decrease (by 1.5 times) compared to the calculated values obtained according to known similar relationships. This made it possible to clarify the calculation of the parameters of mechanical processing power and thermal stresses and substantiate the conditions for their reduction by reducing the intensity of friction in the cutting zone. On the basis of the conducted experimental studies of the technological operations of mechanical processing of complex-profile forming equipment for the food industry, it was established that in the conditions of blade processing, the energy intensity and the maximum cutting temperature take much lower values than during grinding. Therefore, the possibilities of increasing productivity under the conditions of ensuring high quality processing during grinding are very limited. For this, it is necessary to apply modern technologies of high-speed blade processing on high-speed CNC metal cutting machines of the "machining center" type, which, as established in the robot, are characterized by extremely high technological capabilities.

Bond performance between cementitious grout and normal concrete subjected to freeze–thaw damage

Owing to the increasing application of cementitious grout in strengthening projects in cold regions, the freeze–thaw durability of the bond between cementitious grout and concrete has attracted attention. This study investigates the bond performance of a cementitious grout–normal concrete interface after FTCs through splitting tensile and slant shear tests at different angles. The microstructure of the cementitious grout–concrete interface is observed via backscattered electron (BSE) microscopy. The results show that FTCs rapidly reduce the splitting bond strength and slant shear bond strength of the interface. After 240 FTCs, the splitting and slant shear bond strengths decrease by 40.7%–72.4% and 46.1%–57.3%, respectively. An increase in substrate strength significantly enhances the interfacial bond strength, particularly the slant shear bond strength. Freeze–thaw damage to the substrate reduces the interfacial bond strength and frost resistance. The slant shear strength increases significantly with the slant shear angle. The effects of FTCs on the interfacial shear strength parameters are reflected through a rapid decrease in cohesion, whereas the interface internal friction angle remains relatively unaffected. Empirical formulas for calculating the interface bond strength are obtained from experimental data and validated. The BSE images show that cracks begin to appear at the cementitious grout–normal concrete interface as the number of FTCs increases, thereby decreasing the interfacial bond strength.

Spatiotemporal frequency domain analysis for blood velocity measurement during embolization procedures.

Currently, determining procedural endpoints and treatment efficacy of vascular interventions is largely qualitative and relies on subjective visual assessment of digital subtraction angiography (DSA) images leading to large interobserver variabilities and poor reproducibility. Quantitative metrics such as the residual blood velocity in embolized vessel branches could help establish objective and reproducible endpoints. Recently, velocity quantification techniques based on a contrast enhanced X-ray sequence such as qDSA and 4D DSA have been proposed. These techniques must be robust, and, to avoid radiation dose concerns, they should be compatible with low dose per frame imageacquisition. To develop and evaluate a technique for robust blood velocity quantification from low dose contrast enhanced X-ray image sequences that leverages the oscillating signal created by pulsatile bloodflow. The proposed spatiotemporal frequency domain (STF) approach quantifies velocities from time attenuation maps (TAMs) representing the oscillating signal over time for all points along a vessel centerline. Due to the time it takes a contrast bolus to travel along the vessel centerline, the resulting TAM resembles a sheared sine wave. The shear angle is related to the velocity and can be determined in the spatiotemporal frequency domain after applying the 2D Fourier transform to the TAM. The approach was evaluated in a straight tube phantom using three different radiation dose levels and compared to ultrasound transit-time-based measurements. The STF velocity results were also compared to previously published approaches for the measurement of blood velocity from contrast enhanced X-ray sequences including shifted least squared (SLS) and phase shift (PHS). Additionally, an in vivo porcine study (n = 8) was performed where increasing amounts of embolic particles were injected into a hepatic or splenic artery with intermittent velocity measurements after each injection to monitor the resulting reduction invelocity. At the lowest evaluated dose level (average air kerma rate 1.3 mGy/s at the interventional reference point), the Pearson correlation between ultrasound and STF velocity measurements was . This was significantly higher ( ) than corresponding correlation results between ultrasound and the previously published SLS and PHS approaches ( and , respectively). In the in vivo study, a reduction in velocity was observed in of cases after injection of 1 mL, after 3 mL, and after 4 mL of embolicparticles. The results show good agreement of the spatiotemporal frequency domain approach with ultrasound even in low dose per frame image sequences. Additionally, the in vivo study demonstrates the ability to monitor the physiological changes due to embolization. This could provide quantitative metrics during vascular procedures to establish objective and reproducibleendpoints.

Three-Dimensional, Right Ventricular Surface Strain Computation From Three Dimensional Echocardiographic Images From Patients With Pediatric Pulmonary Hypertension.

Right Ventricular (RV) dysfunction is routinely assessed with echocardiographic-derived global longitudinal strain (GLS). GLS is measured from a two-dimensional echo (2DE) image and is increasingly accepted as a means for assessing RV function. However, any 2D analysis cannot visualize the asymmetrical deformation of the RV nor visualize strain over the entire RV surface. We believe 3D surface (3DS) strain, obtained from 3D echo (3DE) will better evaluate myocardial mechanics. Components of 3DS strain (longitudinal, LS; circumferential, CS; longitudinal-circumferential shear, ɣCL; principal strains PSMax and PSMin; max shear, ɣMax; and principal angle θMax) were computed from RV surface meshes obtained with 3DE from 50 children with associated PAH, 43 children with idiopathic PAH, and 50 healthy children by computing strains from a discretized displacement field. All 3DS freewall (FW) normal strain (LS, CS, PSMax, and PSMin) showed significant decline at end-systole in PH groups (p<0.0001 for all), as did FW-ɣMax (p=0.0012). FW-ɣMax also changed in disease (p<0.0001). Limits of agreement analysis suggests that 3DS LS, PSMax, and PSMin are related to GLS. 3DS strains showed significant heterogeneity over the 3D surface of the RV. Components of 3DS strain agree with existing clinical strain measures, well classify normal -vs- PAH subjects, and suggest that strains change direction on the myocardial surface due to disease. This last finding is similar to that of myocardial fiber realignment in disease, but further work is needed to establish true associations.

The Role of Magnetic Shear in Reconnection-driven Flare Energy Release

Using observations from the Solar Dynamics Observatory’s Atmosphere Imaging Assembly and the Ramaty High Energy Solar Spectroscopic Imager, we present novel measurements of the shear of post-reconnection flare loops (PRFLs) in SOL20141218T21:40 and study its evolution with respect to magnetic reconnection and flare emission. Two quasi-parallel ribbons form adjacent to the magnetic polarity inversion line (PIL), spreading in time first parallel to the PIL and then mostly in a perpendicular direction. We measure the magnetic reconnection rate from the ribbon evolution, and also the shear angle of a large number of PRFLs observed in extreme ultraviolet passbands (≲1 MK). For the first time, the shear angle measurements are conducted using several complementary techniques allowing for cross validation of the results. In this flare, the total reconnection rate is much enhanced before a sharp increase in the hard X-ray emission, and the median shear decreases from 60°–70° to 20°, on a timescale of 10 minutes. We find a correlation between the shear-modulated total reconnection rate and the nonthermal electron flux. These results confirm the strong-to-weak shear evolution suggested in previous observational studies and reproduced in numerical models, and also confirm that, in this flare, reconnection is not an efficient producer of energetic nonthermal electrons during the first 10 minutes when the strongly sheared PRFLs are formed. We conclude that an intermediate shear angle, ≤40°, is needed for efficient particle acceleration via reconnection, and we propose a theoretical interpretation.

Analysis of Magnetic Nonpotentiality in the Flaring Active Region NOAA 12887

Solar flares are explosive events resulting from the release of stored magnetic energy in active regions. In this study, the Spaceweather Helioseismic and Magnetic Imager Active Region Patch (SHARP) data is utilized to extract nonpotential magnetic parameters of the NOAA 12887 active region, which produced an X1.0 class flare in October 2021. The analysis revealed that the electric current became non-neutral and unstable before the X-class flare due to an increase in the shear angle, exceeding 90 degrees through a collision of positive and negative polarities. We also assessed the magnetic nonpotentiality parameters, including free energy, vertical current, current helicity, and current neutrality. At the beginning, the parameters exhibited elevated values, reflecting the complex nature of the active region. Subsequently, it became even more complex following the collision event. Flare Ribbons and filaments were also observed by the AIA/SDO 1600 Å and 304Å images on this phase. However, the overall complexity decreased over time, with temporary increases after the collision event and subsequent flares. The development of new complex areas outside the collision zone had a lesser impact on the parameter values. The current neutrality value increased after the collision, implying an increasingly unstable region, but sharply decreased after the X-class flare, indicating a return to a more stable state for the active region.