Diffusion Region Research Articles

Secondary Reconnection Between Interlinked Flux Tubes Driven by Magnetic Reconnection With a Short X‐Line

AbstractA three‐dimensional particle‐in‐cell simulation is performed to study secondary reconnection between two interlinked flux tubes produced by neighboring guide field reconnection x‐lines. The reconnecting magnetic fields of this secondary reconnection is enhanced toward the diffusion region, agree well with that in observations. The magnetic field pileup is attributed to the upstream magnetic tension force, that smashes the flux tubes into each other. We propose that the primary reconnection x‐line length is a key parameter to determine the formation of interlinked flux tubes and secondary reconnection therein. Interlinked flux tubes will form only if the x‐line is short; when the x‐line is long enough, the regular flux ropes are formed instead. The critical x‐line length to form interlinked flux tubes is determined by the distance between two neighbor x‐lines and the magnetic shear angle of the primary reconnection. The results provide a novel scenario of secondary reconnection generation during three‐dimensional reconnection.

A consistent diffuse-interface model for two-phase flow problems with rapid evaporation

We present accurate and mathematically consistent formulations of a diffuse-interface model for two-phase flow problems involving rapid evaporation. The model addresses challenges including discontinuities in the density field by several orders of magnitude, leading to high velocity and pressure jumps across the liquid–vapor interface, along with dynamically changing interface topologies. To this end, we integrate an incompressible Navier–Stokes solver combined with a conservative level-set formulation and a regularized, i.e., diffuse, representation of discontinuities into a matrix-free adaptive finite element framework. The achievements are three-fold: First, we propose mathematically consistent definitions for the level-set transport velocity in the diffuse interface region by extrapolating the velocity from the liquid or gas phase. They exhibit superior prediction accuracy for the evaporated mass and the resulting interface dynamics compared to a local velocity evaluation, especially for strongly curved interfaces.Second, we show that accurate prediction of the evaporation-induced pressure jump requires a consistent, namely a reciprocal, density interpolation across the interface, which satisfies local mass conservation. Third, the combination of diffuse interface models for evaporation with standard Stokes-type constitutive relations for viscous flows leads to significant pressure artifacts in the diffuse interface region. To mitigate these, we propose to introduce a correction term for such constitutive model types. Through selected analytical and numerical examples, the aforementioned properties are validated. The presented model promises new insights in simulation-based prediction of melt–vapor interactions in thermal multiphase flows such as in laser-based powder bed fusion of metals.

NIMG-44. ELEVATED TRANSLOCATOR PROTEIN 18KDA BINDING IN LOW MEAN DIFFUSIVITY CLUSTERS IS A FEATURE OF THE TRANSFORMING GLIOMA AND IDH MUTANT GLIOMA MICROENVIRONMENT

Abstract Around 95% of low-grade gliomas undergo anaplastic de-differentiation into high-grade gliomas, a process only partially understood from in vivo clinical imaging. 11 patients with suspected transforming gliomas underwent a combined magnetic resonance imaging (MRI) and positron emission tomography (PET) protocol, incorporating post-contrast T1-weighted/FLAIR acquisition for tumour delineation and diffusion tensor imaging. The PET radiotracer [11C]-(R)-PK11195 assessed translocator protein 18kDa (TSPO) distribution, whose upregulation is associated with inflammation/glioma progression. [11C]-(R)-PK11195 binding potential (BPND) maps were generated using the simplified reference tissue model, with the grey-matter cerebellar time-activity curve serving as the reference tissue input function. KMeans clustering of mean diffusivity (MD) intensity values defined spatially distinct “habitats” of high/low MD voxels within the glioma microenvironment. BPND values within high/low MD clustering habitats were evaluated, across glioma grades and isocitrate dehydrogenase (IDH) mutational status. Across all grade 2 and 3 gliomas (n= 6), mean TSPO BPND values in low MD habitats (0.0383 ±0.102) were significantly greater than high MD habitats (-0.045 ±0.142) (p= 0.003). In grade 4 gliomas (n= 5), no significant difference was observed in mean BPND values between low (0.514 ±0.176) and high (0.465 ±0.296) MD habitats (p= 0.543). IDH mutant gliomas (n= 7) exhibited significantly higher mean BPND in low MD habitats (0.116 ±0.225), relative to high habitats (0.052 ±0.287) (p= 0.021). IDH wildtype gliomas (n= 4) showed no significant differences between BPND values in low (0.498 ±0.199) and high MD habitats (0.424 ±0.325) (p= 0.467). Our novel findings demonstrate spatial heterogeneity in TSPO expression within 2/3/IDH mutant gliomas, a characteristic absent from grade 4/IDH wildtype varieties. Regions of restricted diffusion with high TSPO signal in grade 2/3/IDH mutant tumours indicate the heterogenous distribution of active TSPO-expressing immune/neoplastic cell populations, contrasting the homogenous distribution in grade 4/IDH wildtype gliomas, highlighting differences between their inflammatory profile and pathological features.

A Bifurcated Reconnecting Current Sheet in the Turbulent Magnetosheath

We report the Magnetospheric Multiscale (MMS) observation of a bifurcated reconnecting current sheet in Earth’s dayside magnetosheath. Typical signatures of the ion diffusion region, including sub-Alfvénic demagnetized ion outflow, super-Alfvénic electron flows, Hall magnetic fields, electron heating, and energy dissipation, were found when MMS traversed the current sheet. The weak ion exhaust at the current sheet center was bounded by two current peaks in which super-Alfvénic electron flow directed toward and away from the X line were observed, respectively. Both off-center current peaks were primarily carried by electrons, one of which was supported by field-aligned current, while the other was mainly supported by current driven by electric field drift. The two current peaks also exhibit other differences, including electron heating, electron pitch angle distributions, electron nongyrotropy, energy dissipation, and magnetic field curvature. An ion-scale magnetic flux rope was detected between the two current peaks where electrons showed field-aligned bidirectional distribution, in contrast to field-aligned distribution parallel to the magnetic field in two current peaks. The observed current sheet was embedded in a background shear flow. This shear flow worked together with the guide field and asymmetric field and density to affect the electron dynamics. Our results reveal the reconnection properties in this special plasma and field regime which may be common in turbulent environments.

Superconductivity at Pd/Bi2Se3 Interfaces Due to Self-Formed PdBiSe Interlayers.

Understanding the physical and chemical processes at the interfaces of metals and topological insulators is crucial for the development of the next generation of topological quantum devices. Here, we report the discovery of robust superconductivity in Pd/Bi2Se3 bilayers fabricated by sputtering Pd on the surface of Bi2Se3. Through transmission electron microscopy measurements, we identify that the observed interfacial superconductivity originates from the diffusion of Pd into Bi2Se3. In the diffusion region, Pd chemically reacts with Bi2Se3 and forms a layer of PdBiSe, a known superconductor with a bulk transition temperature of 1.5 K. Our work provides a method for the introduction of superconductivity into Bi2Se3, laying the foundation for the development of sophisticated Bi2Se3-based topological devices.

Probing Three-dimensional Magnetic Fields. III. Synchrotron Emission and Machine Learning

Synchrotron observation serves as a tool for studying magnetic fields in the interstellar medium and intracluster medium, yet its ability to unveil three-dimensional (3D) magnetic fields, meaning probing the field’s plane-of-the-sky (POS) orientation, inclination angle relative to the line of sight, and magnetization from one observational data, remains largely underexplored. Inspired by the latest insights into anisotropic magnetohydrodynamic (MHD) turbulence, we found that synchrotron emission’s intensity structures inherently reflect this anisotropy, providing crucial information to aid in 3D magnetic field studies: (i) the structure’s elongation gives the magnetic field’s POS orientation and (ii) the structure’s anisotropy degree and topology reveal the inclination angle and magnetization. Capitalizing on this foundation, we integrate a machine learning approach—convolutional neural network (CNN)—to extract this latent information, thereby facilitating the exploration of 3D magnetic fields. The model is trained on synthetic synchrotron emission maps, derived from 3D MHD turbulence simulations encompassing a range of sub-Alfvénic to super-Alfvénic conditions. We show that the CNN is physically interpretable and the CNN is capable of obtaining the POS orientation, inclination angle, and magnetization. Additionally, we test the CNN against the noise effect and the missing low-spatial frequency. We show that this CNN-based approach maintains a high degree of robustness even when only high-spatial frequencies are maintained. This renders the method particularly suitable for application to interferometric data lacking single-dish measurements. We applied this trained CNN to the synchrotron observations of a diffuse region. The CNN-predicted POS magnetic field orientation shows a statistical agreement with that derived from synchrotron polarization.

Current Sheet Broadening due to Turbulence in Three-dimensional Collisionless Reconnection

The present study has investigated the statistical distribution of the current sheet width across the reconnection diffusion region by means of the 3D particle-in-cell simulations. The 3D reconnection layers are unstable to the flow shear instabilities, which results in electromagnetic (EM) turbulence generating effective magnetic dissipation around the x-line. The simulations are performed for several ion-to-electron mass ratios and computational domain sizes, which determine the fastest-growing mode in each simulation run. When the turbulence is weak, the current sheet width increases with the turbulence intensity, following a theoretical curve independent of the mass ratio and domain size. However, when the turbulence is stronger, the width saturates at a low level around 2 times the local electron inertia length, i.e., much smaller than the ion kinetic scales. It is found that the intense inductive electric field due to the EM turbulence is partly canceled out by the eddy viscous effect. As a result, the reconnection electric field is almost unchanged during the quasi-steady phase, regardless of the turbulence intensity. The result implies that the magnetohydrodynamic turbulence models are unlikely to be applicable to the reconnection diffusion region.

Hypoechoic ultrasonographic findings in the patellar ligaments are common in riding and trotting horses in training (116 cases).

Patellar ligament (PL) injuries are increasingly being reported in horses, but few studies have described the normal PL ultrasonographic appearance in horses. The aims of this prospective observational study were to describe the ultrasonographic appearance of the PLs and infrapatellar fat pad in a population of horses in training and to relate the ultrasonographic findings to objectively measured movement asymmetry. B-mode and color Doppler ultrasonographic examination of the PLs and infrapatellar fat pad in both hind limbs and objective gait analyses were performed on the 116 riding and trotting horses included in the study. The association between ultrasonographic findings, horse age, and movement asymmetry during the trot was then investigated. Distinct or diffuse hypoechoic regions were commonly found in the intermediate PL (24/116; 20.7%), especially in the caudal aspect of the mid-third of the ligament. The infrapatellar fat pad had a hypoechoic striated appearance in all horses except one, in which it was hyperechoic. No association was found between ultrasonographic findings in the PLs and infrapatellar fat pad and lameness. It is important to recognize that there is biological variation in PL appearance, which may or may not be associated with pain in this area, therefore emphasizing the use of local analgesia to determine the location of the lameness.

Impact of the Out‐Of‐Plane Flow Shear on Magnetic Reconnection at the Flanks of Earth's Magnetopause

AbstractMagnetic reconnection changes the magnetic field topology and facilitates the energy and particle exchange at magnetospheric boundaries such as the Earth's magnetopause. The flow shear perpendicular to the reconnecting plane prevails at the flank magnetopause under southward interplanetary magnetic field conditions. However, the effect of the out‐of‐plane flow shear on asymmetric reconnection is an open question. In this study, we utilize kinetic simulations to investigate the impact of the out‐of‐plane flow shear on asymmetric reconnection. By systematically varying the flow shear strength, we analyze the flow shear effects on the reconnection rate, the diffusion region structure, and the energy conversion rate. We find that the reconnection rate increases with the upstream out‐of‐plane flow shear, and for the same upstream conditions, it is higher at the dusk side than at the dawn side. The diffusion region is squeezed in the outflow direction due to magnetic pressure which is proportional to the square of the Alfvén Mach number of the shear flow. The out‐of‐plane flow shear increases the energy conversion rate , and for the same upstream conditions, the magnitude of is larger at the dusk side than at the dawn side. This study reveals that out‐of‐plane flow shear not only enhances the reconnection rate but also significantly boosts energy conversion, with more pronounced effects on the dusk‐side flank than on the dawn‐side flank. These insights pave the way for better understanding the solar wind‐magnetosphere interactions.

Statistical Study of Energy Transport and Conversion in Electron Diffusion Regions at Earth's Dayside Magnetopause

AbstractThe electron diffusion region (EDR) is a key region for magnetic reconnection, but the typical energy transport and conversion in EDRs is still not well understood. In this work, we perform a statistical study of 80 previously published near X‐line events identified at the dayside magnetopause in Magnetospheric Multiscale data. We find 44 events that clearly present all commonly accepted EDR signatures and use this database to investigate energy flux partition and energy conversion. We find that energy partition is changed inside EDRs, with a 71%–29% allocation of particle energy flux density between electrons and ions respectively. The electron enthalpy flux density is found to dominate locally at all EDRs and is predominantly oriented in the out‐of‐plane direction, perpendicular to the reconnecting magnetic field. We also examine the transition from electron‐ to ion‐dominated energy flux partition further from the EDR, finding this typically occurs at scales of the order of the ion inertial length, larger than the typical EDR size. We then investigate energy conversion and transport and highlight complex processes, with potential non‐steady‐state energy accumulation and release near the EDR. We discuss the implications of our results for reconnection energy conversion, and for magnetopause dynamics in general.

Study of the Ion-Exchange Capacity of Clinoptilolite for Copper Ions under Ideal Displacement Conditions in the Dynamic Mode

The ionic mechanism of copper ion sorption from an aqueous medium has been confirmed. The study has elucidated the regularities of the process within a stirred bed reactor, where kinetics are limited by the internal diffusion region. Initial sorption curves under dynamic conditions have been obtained.

Dynamic behaviors of interfacial oxides and elements during the ultrasonic-assisted diffusion bonding of 6063Al alloys

Efficiently breaking the oxide layer and rapidly diffusing of elements at low-temperature has been a longstanding goal in the diffusion bonding (DB) of Al alloys. To break the interfacial oxide layers and accelerate atomic diffusion, ultrasound energy was introduced during the DB of 6063Al. A full Zn–Al eutectoid joint was manufactured via a pure Zn interlayer at 360 °C in atmospheric by an ultrasonic-assisted diffusion bonding (U-DB) at only an ultrasonic vibration of10 min. During U-DB, brittle cracks were formed in the interfacial oxide layers due to high strain rate induced by ultrasonic action. Zn diffused into Al alloy through the brittle cracks in oxide layers via “subcutaneous diffusion,” forming a Zn–Al eutectoid diffusion region between the Al alloy and oxide layer. The oxide fragments irregularly migrated to the center of the joint due to Kirkendall effect and ultrasonic action, finally dispersed in the bonded metal. The bonded metal finally transformed as a full Zn–Al eutectoid phase after consuming interlayer. The shear strength of the Zn–Al eutectoid joint reached 82.6 MPa. The Zn–Al mutual diffusion coefficient of U-DB at 360 °C was ∼0.6 μm2/s, which was about 20 times higher than the thermal diffusion coefficient under same temperature condition. Additionally, the mechanism of ultrasonic-assisted diffusion based on the strain-driven diffusion mode was discussed in detail.

Characterization of irradiation-induced dislocation loops in Vanadium at 25-500 °C

Vanadium-based alloys have emerged as promising candidates for structural materials in fusion applications. However, as its base metal, the response of V to irradiation has received limited attention in prior studies. To gain a fundamental understanding of the irradiation damage in V, its microstructure evolution under 6 MeV Ti ion irradiation at 25–500 °C is investigated in the present study, with the focus on the detailed and comprehensive characterization of the behavior of the irradiation-introduced dislocation loops. Under room temperature irradiation, the “black dot” dislocation loops agglomerate linearly into rafts, during which their Burgers vectors are well aligned. With the temperature increases to 300 °C, the size of rafts increases and the density decreases, while the size of small loops maintains similar to the room temperature irradiation condition. As the irradiation temperature reaches 500 °C, the defects become highly mobile, resulting in the formation of extended dislocation loops or lines with hundreds of nanometers in size, with the rafts vanishing. All the observable loops under this irradiation temperature range exhibit the Burgers vectors of a/2 < 111>. All the loops observed in the displacement region are identified to be interstitial-type, while a small portion of loops observed in the diffusion region under elevated temperatures are vacancy-type.

Effect of Ta/Ni dual-interlayer on the microstructure and properties of high strength titanium alloy and steel composite plate

The combination of ultra-high-strength Ti-6Al-4V (TC4) titanium alloy and 30CrNiMoNb (6211) steel was achieved by adding Ta/Ni dual-interlayer and rolling at 950 °C through welding a symmetrical blank sleeve with a vacuum electron beam. In order to unveil the metallurgical bonding mechanism and the interfacial structure, SEM, XRD, and compression-shear performance tests were used. The results revealed the presence of thin-film brittle TiC, TiFe, and TiFe2 compounds at the TC4/6211 interface, resulting in an increased risk of interface mismatch and brittle fracture along the matrix phase interface, and the average interfacial bonding strength was tested at 323 MPa.In contrast, the TC4-Ta interface and the 6211-Ni interface in the TC4/Ta/Ni/6211 composite plate displayed good solid solution formation. The strengthening mechanism of the Ta/Ni dual-interlayer interfacial bonding was analyzed using selected area electron diffraction (SAED), revealing that the Ta-Ni diffusion region consisted of Ni3Ta and Ni2Ta. The addition of the Ta/Ni dual-interlayer prevented the aggregation of Ti and Fe atoms to form Ti-Fe compounds. The malleable intermetallic compounds of Ni3Ta and Ni2Ta effectively coordinated deformation, leading to an average interfacial bonding strength of 469 MPa, which was 45.2 % higher than the composite plate without Ta/Ni dual-interlayer.

Effect of Mo interlayer on the diffusion behavior and mechanical property of Cr-coated Zr alloy cladding tubes

The study examined the diffusion mitigation effect and mechanical properties of a Mo interlayer, prepared by magnetron sputtering, as a Cr-Zr diffusion barrier through annealing experiments and ring compression tests. The results indicate that the existence of the Mo interlayer significantly alleviates the interdiffusion of Cr-Zr, and this effect increases with a thicker Mo interlayer. After high-temperature diffusion at 1332 ℃, the Cr/Mo-coated sample exhibited the formation of Cr, Cr (Mo) solid solution, Cr2Zr Laves phase, Cr-Mo-Zr diffusion region, and Zr substrate structures. During ring compression tests, the Cr/Mo coating remained firmly bonded to the Zr alloy cladding tubes, even under significant ring deformation. The Mo layer has the mechanical potential to serve as a diffusion barrier for Cr-Zr. The details of Mo as a diffusion barrier are discussed.

Separating Hofmeister Trends in Stern and Diffuse Layers at a Charged Interface.

Understanding the role of pH and ions on the electrical double layer (EDL) at charged mineral oxide/aqueous interfaces remains crucial in modeling environmental and industrial processes. Yet the simultaneous contribution of pH and specific ion effects (SIEs) on the different layers of the EDL remains unknown. Here, we utilize zeta potential measurements, vibrational sum frequency generation, and the maximum entropy method to ascertain the detailed structure of the Stern and diffuse regions of the EDL at the silica/water interface with varying pH values for different alkali chlorides. Both at pH 2, when the surface is nearly neutral, and at pH 12, when the surface is highly charged, we observe that Li+ and Na+ disrupt while Cs+ enhances existing water structures within the Stern layer. Moreover, the SIE trends for the diffuse and Stern layers are opposite to one another at pH 2 (in the amount of ordered water) and at pH 12 (in the amount of net oriented water). Finally, we observe an inversion in Hofmeister (SIE) trends at low and high pH in the zeta that impacts the diffuse layer structure. These results indicate that SIEs play critical yet separable roles in governing both the electrostatic and water-structuring capabilities of the EDL.

Phase-Field Modeling of Kinetics of Diffusive Phase Transformation in Compositionally-Graded Ni-Based Superalloys

AbstractKinetics of the $$\gamma$$ γ /$$\gamma ^{\prime}$$ γ ′ phase transformation and the interdiffusion phenomena in single-crystal Ni-based superalloys, under isothermal annealing and composition gradient, is investigated through the phase-field and continuum diffusion models. The employed models in the present work exploit CALPHAD-based thermodynamics and kinetics databases, in order to perform realistic simulations. We specifically predict the interdiffusion of elements for a hypothetical alloy AlCoCrTaNi/Ni diffusion couple, equivalent to the CMSX-10/Ni diffusion couple, at 1323 K. Accordingly, the phase fraction and morphology of $$\gamma ^{\prime}$$ γ ′ precipitations in the $$\gamma$$ γ matrix is simulated as well. The implemented multi-component diffusion model takes into account vacancies and pore formation, reflecting Kirkendall effect. Furthermore, the time evolution of morphology parameters of the precipitate-depleted zone in the diffusive region (i.e., the position and the size) are estimated.

Fast photodiode arrays for high frequency fluctuation measurements of reconnecting flux ropes.

An array of compact, high-bandwidth (>200MHz) and low-cost optical photodiodes has been developed and implemented on the PHASe MApping (PHASMA) experiment. Using purpose-built electronics, an array of 16 photodetectors was constructed and used to monitor broadband (1-5MHz) fluctuations in light intensity emitted by flux ropes undergoing electron-only magnetic reconnection. These measurements reveal a swath of oscillatory behavior, including wave propagation inward toward the diffusion region at approximately the local electron Alfvén speed. Custom 3D-printed collection optics and mounting hardware allow quick reconfiguration of the array for radial or axial measurements. The electronics design is flexible enough to be used with other current-sourcing transducers, such as avalanche photodiodes; silicon photomultipliers; and infrared, x-ray, and UV photodiodes. A noise-rejecting electrical layout allows for low-noise operation close to pulsed plasma discharges. A 16-channel, 64-pixel tomographic array was constructed and initial reconstructions are presented.

Soliton interaction in a two-temperature electron plasma with trapping and superthermality effects

Head-on collision of the two small-amplitude electron-acoustic (EA) solitons is studied in an unmagnetized collisionless plasma in the presence of superthermal (hot) trapped electrons. For this purpose, using a well-known extended Poincare–Lighthill–Kuo (PLK) method, a pair of the trapped Korteweg–de Vries (tKdV) equations is derived to investigate the soliton trajectories and phase shifts. The latter are found dependent on amplitudes of the interacting solitons, effectively altering with hot-electron superthermality and plasma parameters. Typical parameters for the electron diffusion region (EDR) and day-side auroral zone have been selected to examine the impact of hot-electron superthermality, trapping parameter, hot-to-cold electron number density ratio, and cold-to-hot electron temperature ratio on the profiles of potential excitations and phase shifts of interacting solitons. It is found that phase speed of the EA waves becomes altered by varying the κ–parameter, strongly modifying the nonlinearity and dispersive coefficients in a superthermal trapped plasma. However, particle trapping phenomenon does not affect the linear phase speed but introduces a fractional nonlinearity in the tKdV equations of two interacting solitons. The impact of the adiabatic and isothermal pressures is also highlighted to show new modifications in the propagation characteristics of two interacting solitons.

Comparison of NH3 and 12CO, 13CO, C18O Molecular Lines in the Aquila Rift Cloud Complex

The observations of the Aquila Rift cloud complex at 23.708 and 115.271 GHz made using the Nanshan 26 m radio telescope and the 13.7 m millimeter-wavelength telescope are presented. We find that the CO(1 − 0) gas distribution is similar to the NH3 gas distribution in the Aquila Rift cloud complex. In some diffusion regions characterized by CO, we identified several dense clumps based on the distribution of detected ammonia molecular emission. Through the comparison of spectral line parameters for NH3, 13CO, and C18O, our study reveals that the line center velocities of the NH3, 13CO, and C18O lines are comparable and positively correlated, indicating that they originate from the same emission region. No significant correlation was identified for other parameters, including integrated intensity, line widths, main beam brightness temperature, as well as the column densities of NH3, 13CO, and C18O. The absolute difference in line-center velocities between the 13CO and NH3 lines is less than both the average line width of NH3 and that of 13CO. This suggests that there are no significant movements of NH3 clumps in relation to their envelopes. The velocity deviation is likely due to turbulent activity within the clumps.