Decrease In Anisotropy Research Articles

Shear-Induced Anisotropy Analysis of Rock-like Specimens Containing Different Inclination Angles of Non-Persistent Joints

Discontinuities in rock mass are usually considered to be important influencing factors for shear failure. As a type of granular material, the macroscopic mechanical behavior of rock masses is closely related to the anisotropy of the contact network. This paper uses the discrete element method (DEM) to simulate direct shear tests of specimens with different joint inclinations and analyzes the evolution of shear-induced fabric anisotropy and contact force anisotropy during the shear process. Three anisotropic tensors aijc, aijn and aijt are defined to characterize the anisotropic behavior of granular materials. The macroscopic mechanical behavior of the specimens is explained from the micromechanical level combined with the evolution laws of the microcracks and energy of the specimens. The research results indicate that, after the appearance of microcracks in the specimens, the joint inclination leads to changes in their macroscopic mechanical behavior such as peak shear stress, peak displacement and failure mode by affecting the development of the fabric and contact anisotropy of the specimens. Meanwhile, a decrease in fabric and contact anisotropy often indicates specimen failure.

First Principle Analysis on Elastic and Mechanical Behavior of High-Pressure Hexagonal MgZn2 Phase

There is a paucity of previous related studies exploring hexagonal MgZn2 in high-pressure environments. This study systematically analyzes the mechanical behavior of MgZn2 hexagonal alloys under high-pressure conditions using first principle calculations, bridging the gap in research in this area in the field. The results reveal that, with increasing pressure, the crystallite spacing (a/a0,c/c0) and ratio of volumes (V/V0) decrease significantly, indicating the structural condensation of the material under high pressure. Elastic constant analysis showed a notable enhancement in all constants, except for C13. Among them, C11 increased from 87.399 GPa to 311.45 GPa, and C33 increased from 135.279 GPa to 341.739 GPa, showing a faster growth rate, suggesting improved tensile strength in the material along the tensile direction. Mechanical stability assessments confirmed that the alloy remains stable over the 0 to 30 GPa pressure range. Further material characterization indicated that Poisson’s ratio remained above 0.26 at pressures from 0 to 30 GPa, suggesting excellent ductility and agreeing with the ratio of the shear modulus to the bulk modulus. As the pressure increases, both the hardness and sound velocity of MgZn2 increase, while the degree of anisotropy decreases. The present work gives important insights on the mechanical behavior of MgZn2 under high pressure, contributing to its application and property optimization.

Anisotropic Wetting and Diffusion Behavior of Water Droplets on Biphenylene Compared to Graphene.

We comparatively studied the wetting behavior of water droplets on graphene and biphenylene using molecular dynamics simulations. The research showed that pristine biphenylene (BPN), unlike graphene, exhibits greater hydrophobicity and anisotropic wettability. This specific anisotropy can be tuned by the layer number and vacancy concentration. Particularly, there was a decrease in the water contact angle with increasing BPN layer number, highlighting the importance of water-BPN interactions. As the concentration of vacancies increases, the contact angle increases both along the zigzag direction and the armchair direction, while the anisotropy decreases. In planar defective biphenylene heterojunctions, water droplets spontaneously move from the defective area to the pristine area, where the zigzag direction exhibits a larger energy gradient compared to the armchair direction, leading to a faster movement of water droplets in the zigzag direction. The energy factor plays an important role in the directional movement of the water droplets. Our study explores new 2D materials with strong hydrophobicity and highlights the direction-dependent wetting behavior of biphenylene.

INVESTIGATING LARGE-SCALE STRUCTURES IN TURBULENT MIXING LAYERS USING TWO-POINT CORRELATION

The formation and development of large-scale structures are primary research subjects in the study of turbulent mixing layers. Visualizing these structures based on published experimental data enhances the understanding of complex flow behaviors, which is the main objective of this article. The authors employed a two-point statistical correlation method to evaluate the size of large vortex structures along the interaction region. Additionally, the article provides a guide for analyzing the turbulent energy spectrum at selected fixed points. The calculations were performed using MATLAB software. The results indicate that at the beginning of the mixing layer, the vortices are small and highly anisotropic, with large-scale structures stretching in irregular directions. Further downstream, the vortices increase in size in all directions, and the degree of anisotropy decreases. In the self-similar region, isotropic states are almost achieved. The energy spectrum analysis findings align with Kolmogorov's theory of energy cascade in turbulent flow. The two-point statistical correlation method proves to be highly effective for analyzing structures within turbulent flows.

White matter correlates of gait and balance dysfunction in essential tremor patients

BackgroundEssential tremor (ET) is a syndrome characterized by both motor (tremor, gait, and balance dysfunction) and non-motor features like cognitive deficits, depression, sleep, mood, and anxiety disorders. The present study was conducted to characterize the clinical dysfunction and brain localization of gait and balance disturbances in ET patients. Methods174 ET patients and 150 matched healthy controls were evaluated. ET was diagnosed using the Consensus Statement on the Classification of Tremors, from the Task Force on Tremors of the Movement Disorder Society criteria. Participants were assessed by using a structured neuropsychological battery and validated gait scores. Diffusion tensor imaging (DTI) data comprising mean diffusivity, radial diffusivity, axial diffusivity, and fractional anisotropy were analyzed for all subjects. ResultsThe mean age of essential tremor cases was 45.1 ± 14.08 years. Male: female ratio in ET cases was 2.5:1. Cognitive impairment was observed in a quarter of ET patients. A significant difference was observed in Berg balance scale scores, tandem gait missteps, and tandem stance time between ET cases and controls (p-value < 0.0001). ET patients with higher tremor scores and head tremors were more aged and had poor gait and cognitive scores (p < 0.0001). In our study, we observed poor gait scores significantly correlated with an increase in mean, radial, and axial diffusivities as well as a decrease in fractional anisotropy over various white matter clusters in the brain. No such correlation was observed among the controls. ConclusionThe present study demonstrates a correlation between gait scores and DTI metrics suggesting a neuroanatomic basis for gait impairment in ET patients.

First-principles calculation of the effects of In doping on η-Cu6Sn5 structure, elastic anisotropy, electronic properties and fracture toughness

During the welding and service stages, the anisotropy of Cu6Sn5 between tin solder / Cu solder joints will lead to abnormal grain growth and fracture of Cu6Sn5, which will eventually lead to solder joint failure, so it is very important to study the alloying element indium (In) to reduce the anisotropy of Cu6Sn5. The effects of indium doping on the crystal structure, electronic structure and mechanical properties of η-Cu6Sn5 have been studied systematically by means of first-principles density functional theory. Through calculation, it is found that with the change of indium doping position, the crystal structure is slightly deformed, but remains stable. Indium doping changes the electronic structure of η-Cu6Sn5, and a new bonding peak is formed by the hybridization of Cu-d and In-s around −5.9 eV. In addition, indium doping can significantly increase the mechanical properties of η-Cu6Sn5, including elastic modulus and hardness. Indium significantly reduces the anisotropy of η-Cu6Sn5, and the anisotropy decreases by nearly 80 % at most. At the same time, the addition of indium can increase the fracture toughness of η-Cu6Sn5.

Soft-gluon exchange matters: Isotropic screening in QCD kinetic theory

QCD kinetic theory simulations are a prominent tool for studying the nonequilibrium initial stages in heavy-ion collisions. Despite their success, all implementations rely on approximations of the hard thermal loop (HTL) screened matrix elements in the collision terms. In this paper, we present our results for different isotropic screening prescriptions in the elastic collision term for gluons. In particular, we go beyond the simple Debye-like screening form that is used in all current implementations and apply the isotropic HTL matrix element instead. For isotropic systems, the evolution is nearly unchanged, but when studying the equilibration process in a Bjorken expanding plasma, we find qualitative and quantitative differences in a range of moments of the distribution function, such as a decrease in the maximum pressure anisotropy by up to 50%. In contrast, we find no significant qualitative impact on the jet quenching parameter or on the late-time hydrodynamization dynamics of anisotropic plasmas, but observe systematically smaller values of η/s by about 10% that coincide with perturbative calculations at small couplings. Our study reveals that the choice of the screening prescription can lead to large corrections at early times, but is less important close to equilibrium. Published by the American Physical Society 2024

Cross-rolling induced texture randomization and structural evolution for improved plastic isotropy in Al-Mg alloys with high Mg content

Plastic anisotropy is a key factor that affects the formability and performance of Al-Mg alloys. In this study, the effects of Mg content and strain path shifting from unidirectional rolling (UDR) to cross rolling processes (CR) on plastic anisotropy in Al-Mg alloys were investigated. Al-6 and 9Mg alloys were heat-treated and rolled in two different ways: the first was a UDR process, and the other was a CR process at room temperature. The rolled specimens were analyzed by electron backscattered diffraction method and tensile test. High Mg content suppresses the formation of texture that strengthens the plastic anisotropy in both UDR and CR processes. CR significantly reduces the rolling texture area fraction, leading to greater texture randomness compared to UDR. CR promotes the formation of low-angle deformation bands, which low-angle bands appear to have a weaker impact on deformation resistance and may contribute to the reduced anisotropy in CR-processed materials. CR results in a more uniform distribution of stored energy. R-value which represents plastic anisotropy decreases by shifting from UDR to CR, and by increment of Mg content. Overall, this study demonstrates that CR is a promising approach for improving the formability and performance of Al-Mg alloys by effectively controlling plastic anisotropy.

Machine learning-assisted wire arc additive manufacturing and heat input effect on mechanical and corrosion behaviour of 316 L stainless steels

Predicting the track forming factor or height-to-width ratio (H/W) in wire arc additive manufacturing is crucial for optimal path planning, heat distribution, structural integrity, distortion control, process efficiency, and defect prevention, ensuring high-quality and reliable components. Different analytical and numerical modeling methods have been introduced to predict the H/W ratio. However, the accuracy of these predictions is relatively low due to the challenges associated with handling complex and non-linear regression equations. This study addressed the challenges by implementing data-driven predictive modeling to predict the H/W ratio from the input process parameters. A stacking ensemble learning approach is employed, where a meta-model integrates predictions from multiple base learners to enhance overall performance. The model performance was evaluated by Coefficient of determination (R2), mean squared error (MSE), and mean absolute error (MAE). The model was validated by comparing the experimental and predicted values based on which five thin walls are printed with different heat inputs. The study also explores the impact of heat input on microstructure, mechanical, and corrosion properties. The findings indicate that a significantly low heat input (178 J/mm) and higher heat inputs (> 356 J/mm) decrease the wire utilization. With increasing heat input, ferrite content increases, microstructures become coarser, dendritic spacing increases, and ferrite transitions from lathy to skeletal. Further, lower heat input (235 J/mm) reduces δ-ferrite, suppresses atomic segregation, and increases Cr and Mo in the matrix. YS and UTS decrease with higher heat inputs, anisotropy decreases, and Vickers microhardness drops from 228 (178 J/mm) to 194 Hv (586 J/mm). Additionally, the corrosion resistance deteriorates with increasing heat input, as evidenced by higher pitting potential (Epit: 0.389 V vs. 0.368 V vs. −0.023 V) and lower corrosion current density (Icorr: 6.76 ×10−7 A/cm2 vs. 7.946 ×10−7 A/cm2 vs. 8.91 ×10−7 A/cm2) for heat inputs of 235 J/mm, 281 J/mm, and 356 J/mm, respectively.

Novel strengthening mechanism of laser powder bed fusion-manufactured Inconel 718: Effects of customized hierarchical interfaces

A novel strengthening mechanism involving hierarchical interfaces self-assembled and/or artificially introduced into Inconel 718 (IN718) via laser powder bed fusion (PBF-LB/M) additive manufacturing (AM) has been discovered for the first time. The structures processed by applying two different scanning directions depending on the region have customized hierarchical interfaces that are formed by self-organization of the microscale lamellar structure comprising distinctively different crystal orientations and artificial control of local texture for mesoscale building blocks. The underlying mechanism of strengthening of the structures is clarified using experimental and numerical approaches. Numerical crystal plasticity finite element analysis successfully reproduces the experimental deformation behavior, including the stress-strain curves and anisotropic changes in the shape of the structures, revealing improvements in the mechanical properties by mechanical interaction owing to plastic anisotropy of the lamellar structure. A systematic numerical analysis of the deformation behavior of structures with a higher density of mesoscale interfaces between regions with different local textures suggests possible improvements in the mechanical properties, showing a 13 % increase in 0.2 % proof stress in the optimum structure. Additionally, excellent peak mechanical properties are observed owing to the competition of mechanical interactions between regions with different local textures and a decrease in plastic anisotropy owing to the activation of additional slip modes of the lamellar structure.

Multiparametric MRI Assessment of Morpho-Functional Muscle Changes Following a 6-Month FES-Cycling Training Program: Pilot Study in People With a Complete Spinal Cord Injury.

Spinal cord injuries (SCIs) cause debilitating secondary conditions such as severe muscle deterioration, cardiovascular, and metabolic dysfunctions, significantly impacting patients' quality of life. Functional electrical stimulation (FES) combined with cycling exercise (FES-cycling) has shown promise in improving muscle function and health in individuals with SCI. This pilot study aimed to investigate the potential role of multiparametric magnetic resonance imaging (MRI) to assess muscle health during and after an FES-cycling rehabilitation program. Four male participants with chronic SCI underwent a 6-month FES-cycling training program, consisting of two 30-minute sessions per week. MRI scans were performed at baseline (T0), after 3 months (T1), at the end of the training (T2), and 1-month posttraining (T3). The MRI protocol included T1-weighted imaging for volume quantification, Dixon imaging for fat fraction, multi-echo spin echo for T2 relaxation times, and diffusion tensor imaging to assess diffusion parameters. Muscle hypertrophy was observed, with an average increase in muscle volume of 22.3% at T1 and 36.7% at T2 compared with baseline. One month posttraining, muscle volume remained 23.2% higher than baseline. Fat fraction decreased from 11.1% at T0 to 9.1% at T2, with a rebound to 10.9% at T3. T2 relaxation times showed a reduction even though this was not consistent among participants. Diffusion tensor imaging parameters revealed subtle changes in muscle tissue microstructure, with a decrease in fractional anisotropy mainly associated to an increase of radial diffusivity. Although preliminary, this study provides evidence that 6 months of low-intensity FES-bike training can increase muscle volume and decrease fat infiltration in individuals with SCI. The study demonstrates that the use of a multiparametric MRI provides comprehensive insights into both macroscopic and microscopic changes within muscle tissues, supporting its integration into clinical practice for assessing the efficacy of rehabilitation interventions.

Sensitivity of Advanced Magnetic Resonance Imaging to Progression over Six Months in Early Spinocerebellar Ataxia.

Clinical trials for upcoming disease-modifying therapies of spinocerebellar ataxias (SCA), a group of rare movement disorders, lack endpoints sensitive to early disease progression, when therapeutics will be most effective. In addition, regulatory agencies emphasize the importance of biological outcomes. READISCA, a transatlantic clinical trial readiness consortium, investigated whether advanced multimodal magnetic resonance imaging (MRI) detects pathology progression over 6 months in preataxic and early ataxic carriers of SCA mutations. A total of 44 participants (10 SCA1, 25 SCA3, and 9 controls) prospectively underwent 3-T MR scanning at baseline and a median [interquartile range] follow-up of 6.2 [5.9-6.7] months; 44% of SCA participants were preataxic. Blinded analyses of annual changes in structural, diffusion MRI, MR spectroscopy, and the Scale for Assessment and Rating of Ataxia (SARA) were compared between groups using nonparametric testing. Sample sizes were estimated for 6-month interventional trials with 50% to 100% treatment effect size, leveraging existing large cohort data (186 SCA1, 272 SCA3) for the SARA estimate. Rate of change in microstructural integrity (decrease in fractional anisotropy, increase in diffusivities) in the middle cerebellar peduncle, corona radiata, and superior longitudinal fasciculus significantly differed in SCAs from controls (P < 0.005), with high effect sizes (Cohen's d = 1-2) and moderate-to-high responsiveness (|standardized response mean| = 0.6-0.9) in SCAs. SARA scores did not change, and their rate of change did not differ between groups. Diffusion MRI is sensitive to disease progression at very early-stage SCA1 and SCA3 and may provide a >5-fold reduction in sample sizes relative to SARA as endpoint for 6-month-long trials. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Evolution of microstructure, texture and formability of Al–Mg–Si alloys at different hot rolling finish temperatures

The impact of hot rolling finish temperature (HRFT) on the evolution of microstructure, texture, as well as formability—including deep drawability and bendability—of Al–Mg–Si alloy was studied in present work. The obtained results reveal that HRFT has a notable influence on the dynamic softening and dynamic precipitation behaviors during the hot rolling process of the investigated alloy. This leads to the volume fraction and number density of micro-sized Mg2Si particles increase as the increase of HRFT, those of nano-sized particles decrease, and the dislocation density decrease, in the hot-rolled sheets. These microstructural variations persist in the cold-rolled sheets, subsequently affecting the ultimate microstructure, texture, as well as formability of T4P sheets. The deep drawability improves as the HRFT rises, as indicated by the increase in normal anisotropy (r‾) and decrease in planar anisotropy (Δr). This is attributed to the weakening of texture intensity. The bendability, quantified by the minimum hemming factor (Rmin/t), deteriorates as the HRFT rises from 260 °C to 390 °C, attributed to the strengthening of P component along with the weakening of Cube component. Conversely, with the HRFT rises from 390 °C to 420 °C, the bendability improves dramatically due to the significant reduction in the average grain size. A combination of excellent deep drawability and bendability could be obtained by elevating the HRFT to 420 °C, attributed to the combined effect of weakened texture intensity and fine grains.

Magnetic response of Ho3+ doped Ni0.4Cu0.6HoyFe2-yO4 spinel ferrites and their correlation with crystallite size

This study investigates the magnetic response of Ho3+ doped Ni0.4Cu0.6HoyFe2-yO4 (y = 0.0, 0.02, 0.04, 0.06, and 0.08) spinel ferrites (SFs) and their correlation with crystallite size. The synthesis was achieved using a sol-gel auto-combustion (SGAC) route and performed different characterizations, including X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy dispersive x-ray (EDX), Inductively coupled plasma atomic emission spectroscopy (ICP-AES), and vibrating sample magnetometer (VSM) analysis. The cubic spinel phase was verified via XRD in pure NCF and Ho3+ doped NCF samples. The lattice constant (a) was improved from 8.344 Å to 8.378 Å. The substitution of Ho3+ ions led to a decrease in porosity from 42.22 % to 39.54 %. The introduction of Ho3+ ions also reduced the crystallite size (D) from 37.05 nm to 27.72 nm. The specific surface area (S) was increased from 27.44 g/cm2 to 36.14 g/cm2 with the doping of Ho3+. The average particle size (DS) was decreased from 54 nm to 35 nm. The EDX and ICP-AES analyses confirmed the good agreement with the theoretical composition. The VSM measurements provided insights into their magnetic properties. Furthermore, the doping of Ho3+ ions enhanced coercivity (HC), while reducing saturation magnetization (MS) from 64.35 emu/g to 16.22 emu/g. The decrease in crystalline anisotropy (K) observed at higher concentrations of Ho3+ may result from the increase in coercivity, potentially attributable to the smaller crystallite size of the single-domain SFs particles. The single-phase matrix and their magnetic behaviour showed that the Ho3+ doped Ni–Cu SFs samples are suitable for high-frequency applications.

The effect of elimination of gibbs ringing, noise and systematic errors on the DTI metrics and tractography in a rat brain

Diffusion tensor imaging (DTI) metrics and tractography can be biased due to low signal-to-noise ratio (SNR) and systematic errors resulting from image artifacts and imperfections in magnetic field gradients. The imperfections include non-uniformity and nonlinearity, effects caused by eddy currents, and the influence of background and imaging gradients. We investigated the impact of systematic errors on DTI metrics of an isotropic phantom and DTI metrics and tractography of a rat brain measured at high resolution. We tested denoising and Gibbs ringing removal methods combined with the B matrix spatial distribution (BSD) method for magnetic field gradient calibration. The results showed that the performance of the BSD method depends on whether Gibbs ringing is removed and the effectiveness of stochastic error removal. Region of interest (ROI)-based analysis of the DTI metrics showed that, depending on the size of the ROI and its location in space, correction methods can remove systematic bias to varying degrees. The preprocessing pipeline proposed and dedicated to this type of data together with the BSD method resulted in an even − 90% decrease in fractional anisotropy (FA) (globally and locally) in the isotropic phantom and − 45% in the rat brain. The largest global changes in the rat brain tractogram compared to the standard method without preprocessing (sDTI) were noticed after denoising. The direction of the first eigenvector obtained from DTI after denoising, Gibbs ringing removal and BSD differed by an average of 56 and 10 degrees in the ROI from sDTI and from sDTI after denoising and Gibbs ringing removal, respectively. The latter can be identified with the amount of improvement in tractography due to the elimination of systematic errors related to imperfect magnetic field gradients. Based on the results, the systematic bias for high resolution data mainly depended on SNR, but the influence of non-uniform gradients could also be seen. After denoising, the BSD method was able to further correct both the metrics and tractography of the diffusion tensor in the rat brain by taking into account the actual distribution of magnetic field gradients independent of the examined object and uniquely dependent on the scanner and sequence. This means that in vivo studies are also subject to this type of errors, which should be taken into account when processing such data.

Reflectivity and Angular Anisotropy of Liquid Crystal Microcapsules with Different Particle Sizes by Complex Coalescence.

Cholesteric liquid crystal microcapsules (CLCMs) are used to improve the stability of liquid crystals while ensuring their stimulus response performance and versatility, with representative applications such as sensing, anticounterfeiting, and smart fabrics. However, the reflectivity and angular anisotropy decrease because of the anchoring effect of the polymer shell matrix, and the influence of particle size on this has not been thoroughly studied. In this study, the effect of synthesis technology on microcapsule particle size was investigated using a complex coalescence method, and the effect of particle size on the reflectivity and angular anisotropy of CLCMs was investigated in detail. A particle size of approximately 66 µm with polyvinyl alcohol (PVA, 1:1) exhibited a relative reflectivity of 16.6% and a bandwidth of 20 nm, as well as a narrow particle size distribution of 22 µm. The thermosetting of microcapsules coated with PVA was adjusted and systematically investigated by controlling the mass ratio. The optimized mass ratio of microcapsules (66 µm) to PVA was 2:1, increasing the relative reflectivity from 16.6% (1:1) to 32.0% (2:1) because of both the higher CLCM content and the matching between the birefringence of the gelatin-arabic shell system and PVA. Furthermore, color based on Bragg reflections was observed in the CLCM-coated ortho-axis and blue-shifted off-axis, and this change was correlated with the CLCM particle size. Such materials are promising for anticounterfeiting and color-based applications with bright colors and angular anisotropy in reflection.

Magnetic loss versus temperature and role of doping in Mn-Zn ferrites

We investigate the effect of different doping schemes on the broadband magnetic losses and their temperature dependence in Mn-Zn ferrites. CaO, Nb2O5, ZrO2, and SiO2 are added with increasing proportions to TiO2-doped prefired powders and, after sintering at either 1275 °C or 1300 °C, the obtained ring samples are tested versus frequency f (DC-1 GHz) and peak polarization Jp (2 mT – 200 mT) up to T = 160 °C. Appropriately enhanced impurity contents are shown to induce further decrease of the energy loss in materials already prepared for best performance at high temperatures (140 – 160 °C). This behavior can be hardly ascribed to the impurity-related increase of the electrical resistivity brough about by extra-doping, being it rather connected to a corresponding monotonical decrease of the effective magnetic anisotropy < Keff > with T. The decreasing anisotropy makes the balance between the contributions of domain wall (dw) displacements and reversible rotations to the magnetization process evolving in favor of the latter. The energy loss correspondingly develops with frequency and peak polarization in a complex fashion, according to the specific dissipative mechanisms sustained by the spins precessing either inside the moving walls or in the bulk. A dividing line in the (Jp − f) plane is identified, which separates dominant dw- and rotation-generated losses. It moves downward (i.e. lower f) with increasing temperature, the higher T the lower the frequency at which the rotations, theoretically assessed via the Landau-Lifshitz equation, supersede the domain wall contribution. Once accomplished, however, the transition to rotations can lead, according to the theoretical model, to higher losses when moving to higher temperatures. Following the experimental trend of the complex resistivity versus frequency at different T values, the calculations and the experiments show that eddy currents start to contribute to the energy loss, in the 5 mm thick ring samples, around a few MHz, accounting for about 50 % of measured loss beyond some 50 MHz. The chief dissipative process at applicative frequencies and induction values is therefore identified with spin damping, to which the generalized loss decomposition method can be applied.

The effect of medium doses electron irradiation on the scattering of charge carriers in YBa2Cu3O7-δ single crystal

The influence of electron irradiation with energies of 0.5–2.5 MeV with fluences up to 70 × 1018 cm–2 on the electrical resistivity in the basal plane of YBa2Cu3O7–δ single crystals in the temperature range from the superconducting transition, Tc, to 300 K has been studied. Such irradiation leads to the appearance of a significant number of defects that cause a decrease in anisotropy, an appreciable increase in phonon scattering, reduction of Tc, and broadening of the superconducting transition. Under the conditions specified, the temperature dependence of electrical resistivity is approximated with high accuracy by the charge carriers’ scattering on defects and phonons, and fluctuating conductivity in the Lawrence-Doniach (LD) model. The dependences of approximation parameters on fluence are discussed.

Effects of strain rate and bedding on shale fracture mechanisms

Anisotropic shale is commonly distributed in nature and undergoes both dynamic compressive and tensile load in geological engineering. In this article, the coupling effects of strain rate and bedding structures on the fracture mechanisms of shale are investigated using a split Hopkinson pressure bar (SHPB) system. The tension–compression comparative study is conducted. The Brazilian disc method is modified, and a unified strain rate measurement method is established to comprehensively analyze shale’s fracture-related properties, including moduli, strength and energy dissipation. The results indicate that the energy dissipated by shale fracture is strongly related to its strength. The strain rate and bedding affect the anisotropic strength and dissipated energy by changing the crack density and crack propagation mode. At low or medium strain rates, the bedding orientation of shale determines the direction of crack propagation. However, at high strain rates, microcracks in different directions are widely activated in the shale, which increases the fracture degree and decreases the difference in fracture toughness between the shale’s matrix and bedding planes. This also leads to a decrease in anisotropy and causes the bedding planes to lose control over the direction of crack propagation. Additionally, the dynamic tensile strength of shale increases faster than the compressive one with the strain rate, leading to a reduction in the proportion of tensile failure under impact load. Based on the experimental findings, a new anisotropic damage constitutive model is developed to characterize the dynamic properties of shale. This model reflects the anisotropic damage evolution behaviors and aligns well with experimental results, offering a theoretical foundation for predicting shale’s dynamic fracture behavior. In addition to shale, the developed experimental methods and theoretical models can also be applied to the fracture analysis of other brittle transversely isotropic materials.

Effect of rare earth (Ho and Er) co-substitution on the magnetic and dielectric properties of nanocrystalline cobalt ferrites

Nanocrystalline cobalt ferrites co-substituted with rare earth Ho and Er (CoFe2-2xHoxErxO4, 0 ≤x≤0.10) have been synthesized via the sol-gel method. X-ray Diffraction (XRD) confirmed the single-phase spinel structure with reduced crystallite sizes (65 nm–12 nm), micro-strain (ε) and increased lattice constant (a) with Ho–Er co-substitution. Rietveld refinement and theoretical computation revealed Ho and Er occupancy at octahedral sites and Fe and Co ions redistribution between the tetrahedral and octahedral sites. Infrared spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) supported the formation of the desired spinel structure, aggregated spherical morphology, chemical stoichiometry and elemental states. Magnetic measurements showed a systematic decrease in saturation magnetization (Ms), magnetocrystalline anisotropy (K1), coercivity (Hc) and Curie temperature (Tc) with Ho–Er co-substitution. Electron Spin Resonance (ESR) exhibited asymmetric resonance peaks, reduced resonance field (Hr), linewidth (ΔHpp) and deviation in Lande g values. Impedance spectroscopy revealed two conduction mechanisms (holes and electrons) with distinct activation energies (EaI and EaII). Modulus spectrum analysis confirmed the thermally activated sample-electrode effects and the Nyquist plots indicated the dominant contribution of the grain boundary resistance to the conduction process. A notable enhancement in the dielectric constant (ε′) was observed with Ho–Er co-substitution. The ac conductivity (σac) followed the Jonscher Power Law (JPL). The temperature-dependent frequency exponent s(T), suggests the existence of two conduction mechanisms: non-overlapping small polaron tunneling (NSPT) and correlated barrier hopping (CBH).