Localized Flow Research Articles

MCMS submersibles: A safe undersea adventure

Abstract. Maritime Cruises Mini-Submarines (MCMS), a company based in Greece, aims to offer safe and deep-sea exploratory experiences to tourists. This paper discusses the primary challenges involved in ensuring tourist safety, particularly focusing on maintaining security in scenarios of mechanical failures or lost communication with the main vessel. We propose comprehensive safety protocols and technological solutions tailored for deep-sea tourist submersibles. The analysis begins with a detailed study of the forces acting on a submersible, considering both operational modes and the impact of ocean currents, utilizing a rigid-body coordinate system and Eulerian angular coordinate transformations to describe the submersibles motion comprehensively. We derive motion and safety parameters by solving the force differential equations, allowing the host ship to predict the submersibles position accurately. In addressing the recovery of lost submersibles, our approach evaluates power loss scenarios and search efficiency, recommending an optimal combination of hydroacoustic and frequency-hopping communication technologies for reliable, low-loss data transmission. We further enhance search methodologies by integrating motion parameters and ocean current dynamics to pinpoint probable locations, adjusting search strategies dynamically based on real-time data, and employing probabilistic models to optimize resource allocation during search operations. A case study in the Caribbean Sea exemplifies applying these methodologies, incorporating localized flow regimes and cooperative communication strategies among multiple submersibles to improve operational efficiency and safety.

A comparative study of friction stir welding and friction stir scribe technique for dissimilar metal joining

Abstract Friction stir welding (FSW) has emerged as a novel method for joining similar and dissimilar ferrous and non-ferrous materials. This solid-state welding process utilizes frictional heat generated between a tool shoulder and the base material. The stirring action facilitates the movement and consolidation of the material, resulting in localized fusion and the formation of a joint. This review examines their effectiveness in joining various material combinations, with particular focus on automotive and aerospace applications. FSW utilizes frictional heat and stirring action to create localized plasticity and material flow, while FSS incorporates a cutting feature to mechanically interlock dissimilar materials. The review paper shows comparison of various experimental investigations considering variables such as tool geometry, welding parameters, and material combinations. FSW has some significant parameters to enhance weld quality such as traverse speed, plunge depth, and tool design. These techniques show promising applications for multi-material integration, offering advantages over conventional fusion welding methods. Future research directions include expanding material combinations, developing automated systems, and exploring hybrid joining approaches.

Multi-channeled halloysite nanotube-blended polybenzimidazole separators for enhancing lithium-ion battery performance

The microscopic transport mode of lithium ions in the separator is crucial for solving the problem of irregular lithium dendrite growth, thereby enhancing the safety of battery operation, and it also has a positive impact on the electrochemical performance of the battery. Furthermore, the heat resistance of the separator is an important indicator for measuring the performance of the separator and the safety of battery usage. In this work, we have introduced sulfonated and lithiated halloysite nanotubes into a high-temperature-resistant OPBI matrix through an easily implementable NIPS, resulting in a high-temperature-resistant separator with multiple lithium-ion micro-transport morphologies. Lithium ions can shuttle through the halloysite nanotube pores, negatively charged sulfonate groups on the surface, and larger finger-like pores formed by NIPS within the separator, creating a high and uniform lithium-ion flux that prevents excessive localized ion flow leading to the aggressive growth of lithium dendrites. According to the characterization data, this separator exhibits relatively satisfactory performance, such as an ionic conductivity of 1.82 mS cm−1, a porosity of 82 %, an electrolyte uptake of 397 %, and no significant physical shrinkage at 200 °C. Additionally, the cells assembled using the OPBI@sHNT-Li20 separator delivers higher discharge capacity (164.92 mAh·g−1), more stable cycle, superior rate performance. So the OPBI@sHNT-Li separator is expected to play an active role in improving the safety and electrochemical performance of lithium-ion batteries.

Interaction of microstructure evolution mechanism in Ti-0.3Mo-0.8Ni alloy with initial lamellar microstructure during isothermal compression below the β-transus

The flow behavior and interaction of microstructure evolution mechanisms for a near α Ti-0.3Mo-0.8Ni alloy with as-cast lamellar microstructure are investigated at temperatures of 800∼880 °C in the α+β region with wide strain rate range from 0.01s−1 to 30s−1 during isothermal compression. It is demonstrated that the main reasons of flow softening in the true stress-true strain curves are the kinking of lamellar α, dynamic α→β transformation (DT), dynamic spheroidization (DS), and dynamic recovery (DRV) of β grain. The instability phenomena such as adiabatic shear band (ASB) and flow localization (FL) are the main causes of the stress collapse in the curves at higher strain rate. The dislocation density at the kinking position of initial lamellar α is higher. With the increase of strain rate, the mechanism of the DS changes from flat separation to slat shear. The diffusion of the β-stabilizer results in starting the DT, promoted by the thermodynamic coupling. The interactions between different microstructure evolution mechanisms are extremely complex. In the early stage of hot deformation, the DT promotes the kinking of lamellar α. With the increase of deformation amount, the DT inhibits the DS at higher strain rates, and conversely, the DS promotes the DT. At lower strain rates, the DT and DS accelerate each other in the middle and late stages of hot deformation. The DT and DS are restricted by the process of lamellar α kinking in the middle and late stages of hot deformation.

Tectonic Activity Analysis of the Laji-Jishi Shan Fault Zone: Insights from Geomorphic Indices and Crustal Deformation Data

Fault segmentation plays a critical role in assessing seismic hazards, particularly in tectonically complex regions. The Laji-Jishi Shan Fault Zone (LJSFZ), located on the northeastern margin of the Tibetan Plateau, is a key structure that accommodates regional tectonic stress. This study integrates geomorphic indices, cross-fault deformation rate profiles, and 3D crustal electrical structure data to analyze the varying levels of tectonic activity across different segments of the LJSFZ. We extracted 160 drainage basins along the strike of the LJSFZ from a 30 m resolution digital elevation model and calculated geomorphic indices, including the hypsometric integral (HI), stream length-gradient index (SL), and channel steepness index (ksn), to assess the variations in tectonic activity intensity along the strike of the LJSFZ. The basins were categorized based on river flow directions to capture potential differences across the fault zone. Our results show that the eastern basins of the LJSFZ exhibit the strongest tectonic activity, demonstrated by significantly higher SL and ksn values compared to other regions. A detailed segmentation analysis along the northern Laji Shan Fault and eastern Jishi Shan Fault identified distinct fault segments characterized by variations in SL and ksn indices. Segments with high SL values (>500) correspond to higher crustal uplift rates (~3 mm/year), while segments with lower SL values exhibit lower uplift rates (~2 mm/year), as confirmed by cross-fault deformation profiles derived from GNSS and InSAR data. This correlation demonstrates that geomorphic indices effectively reflect fault activity intensity. Additionally, 3D crustal electrical structure data further indicate that highly conductive mid- to lower-crustal materials originating from the interior of the Tibetan Plateau are obstructed at segment L3 of the LJSFZ. This obstruction leads to localized intense uplift and enhanced fault activity. These findings suggest that while the regional stress–strain pattern of the northeastern Tibetan Plateau is the primary driver of the segmented activity along the Laji-Jishi Shan belt, the direction of localized crustal flow is a critical factor influencing fault activity segmentation.

Field-scale gene flow of fungicide resistance in Pyrenophora teres f. teres and the effect of selection pressure on the population structure.

The effectiveness of fungicides to control foliar fungal crop diseases is being diminished by the increasing spread of resistances to fungicides. One approach that may help to maintain efficacy is remediation of resistant populations by sensitive ones. However, the success of such approaches can be compromised by re-incursion of resistance through aerial spore dispersal; although, knowledge of localized gene flow is lacking. Here, we report on a replicated mark-release-recapture field experiment with several treatments set up to study spore-dispersal-mediated gene flow of a mutated allele that confers demethylase inhibitor resistance in Pyrenophora teres f. teres (Ptt). Artificial inoculation of the host, barley (Hordeum vulgare), was successful across the 12-ha trial, where the introduced sensitive- and resistant-populations were, respectively, 6- and 13-fold the DNA concentration of the native Ptt population. Subsequent disease pressure remained low which hampered spread of the epidemic to such extent that gene flow was not detected at, or beyond 2.5 m from source points. In the absence of gene flow, plots were assessed for treatment effects; fungicide applied to populations that contained 14.3% of allele mutation increased in frequency to 24.5%, whereas sensitive populations had no change in structure. Untreated controls of native Ptt population remained genetically stable, yet untreated controls that were inoculated with sensitive Ptt had half the resistance frequency of the native population structure. The trial demonstrates the potential for management to remediate fungicide resistant pathogen populations, where localized gene flow is minimal; to safeguard chemical crop protection into the future.

Coupled Modeling of Computational Fluid Dynamics and Granular Mechanics of Sand Production in Multiple Fluid Flow

Summary Sand production is a significant issue in oil and gas fields with poorly consolidated formations, often involving the multiphase flow of reservoir fluids and solid particles. The multiscale mechanisms of sand production, particularly fluid flow and particle movement, remain poorly understood. This study investigates these mechanisms using a coupled computational fluid dynamics and discrete element method (CFD-DEM) modeling approach. Single and multiple fluid flows of water and heavy oil were simulated with increasing fluid injection velocities, leading to different sand production patterns. The simulation results were compared with experimental results from a large cylindrical specimen of weak artificial sandstone under similar loading conditions. The multiphase conditions created various localized flow and deformation patterns that influenced both fluid and solid production, resulting in shorter transient sand production periods. Microstructures and phenomena such as fingering and water coning were observed, associated with a critical flow rate below which oil displacement was uniform and no water breakthrough occurred. Higher fluid injection velocities and fluid viscosities resulted in greater drag forces, leading to progressive damage zones and explaining the occurrence of single or multiple staged sand production events. The evolution of the microscopic granular structure was visualized under the effect of transient sand production.

Experimental study of fuel distribution and combustion characteristics under subatmospheric pressure in an afterburner

The fuel distribution and ignition characteristics of an afterburner with typical components under subatmospheric inlet conditions are important references for improving the performance of the afterburner at high flight altitudes. In this work, lean ignition limits, outlet temperature distributions, fuel droplet size distributions and flame propagation processes in the afterburner were obtained experimentally. The results show that with increasing fuel injection angle, the fuel atomization characteristics improve, but the flame intensity fluctuation increases, and the ignition performance deteriorates; thus, a proper ratio of liquid-phase fuel to vapor-phase fuel is one of the key elements for successful ignition. On the one hand, the increased stabilizer blockage ratio results in a localized flow velocity increase near the trailing edge of the stabilizer, which effectively promotes fuel atomization in the shear layer, resulting in a fuel droplet size reduction of 25–30 μm. On the other hand, the extent of the recirculation zone increases, and a large low-pressure and low-turbulence recirculation zone is not conducive to fuel atomization in the flow direction. During the ignition process in an afterburner with all the typical components, the flame kernel first propagates along the flow direction for a certain distance and then propagates and anchors toward the shear layer. At subatmospheric pressures, the decrease in the intensity of the combustion reaction causes a reduction in the heat released by combustion, and the fuel droplet size increases by 10–25 μm, which requires more heat for evaporation. Therefore, the flame propagates an increased distance along the flow as the pressure decreases. Furthermore, the difficulty of ignition increases, and the ignition equivalence ratio increases by 0.1–0.15.

Characterizing and predicting the partial slip subjected to variable gradients of velocity and pressure in eccentric micro-scale Taylor–Couette flows

In the context of eccentric micro-scale Taylor–Couette flow, variations in localized flow scales result in a non-uniform fluid–solid interface slip state, distinct from the typically studied uniform slip velocity distribution. This study introduces a boundary condition definition method aimed at characterizing partial slip states, complemented by a coupled iterative analysis system tailored to address this complexity. Key contributions include the development of a method for calculating the limiting shear stress, which considers local velocity gradients and pressures. Validation demonstrates that the locally derived slip state aligns more closely with Knudsen number distributions of local flow scales compared to traditional uniform slip models, and exhibits greater consistency with experimentally measured pressure distributions. Additionally, the study reveals that eccentric Taylor–Couette flow, characterized by significant variations in local flow scales and strong self-induced pressure effects, leads to complex distributions of local pressure, velocity gradients, and differences in local slip velocities. Specifically, the non-uniform distribution of local pressure gradients due to eccentricity results in partial slip occurring predominantly on the rotor in regions with positive pressure gradients, and on the stator in regions with negative pressure gradients. Furthermore, the variation in gap height exerts a greater influence on local slip compared to rotational speed and eccentricity ratio. Under certain conditions influenced by pressure gradients, the slip velocity on the rotor may exceed its tangential speed.

Normal fault architecture, evolution, and deformation mechanisms in basalts, Húsavik, Iceland: Impact on fluid flow in geothermal reservoirs and seismicity

Faults within layered basaltic sequences significantly influence hydrothermal fluid flow in shallow geothermal reservoirs and potentially during CO2 sequestration and storage. Nevertheless, their characterization regarding fault zone architecture, fluid flow, deformation mechanisms, and seismic potential remains underdeveloped. This study addresses this gap by integrating structural and microstructural observations with X-ray diffraction analyses of exposed normal-transtensional faults associated with the seismically active Húsavík-Flatey Fault in the Tjörnes Fracture Zone, Northern Iceland. Our findings demonstrate that the evolution of basalt-hosted normal-transtensional faults progresses through distinct stages: (1) low-displacement fault propagation from pre-existing cooling joints; (2) fault linkage via dilational jogs; (3) damage zone/fault core growth through brecciation and cataclastic processes; (4) shear localization along sharp slip surfaces; and (5) smearing of volcaniclastic interbeds along the principal fault plane. Evidence of shear localization, truncated clasts, and hydrothermal breccias/veins suggests repeated seismic slip events facilitated by overpressured fluids. Conversely, the presence of clay-rich foliated cataclasite indicates aseismic slips during interseismic periods. Slip along fault jogs, bends, geometric irregularities, and orientation changes causes the dilatant opening of the fault planes and extensional horsetail fractures at fault tips. These structures create main tabular zones for lateral movement of hydrothermal fluids parallel to the fault strike in shallow geothermal reservoirs situated in active extensional-transtensional tectonic settings. In addition, the dilational jogs and the intersection of horsetail veins with the hosting faults may define linear zones of high structural permeability and intense localized fluid flow parallel to the σ2 paleostress orientation and finally mineral precipitation. The results of this study can be utilized to improve models of geothermal fluid flow for enhanced recovery in basaltic reservoirs and assess seismic risk in basaltic faults.

Comparative effectiveness of open and closed skill exercises on cognitive function in young adults: a fNIRS study

While it is widely acknowledged that exercise has positive effects on cognitive function, the specific impacts of different types of exercises, particularly open and closed skill exercises, on cognitive impairment continue to be a debated topic. In this study, we used fNIRS and cognitive psychology tasks to investigate the effects of different types of exercises on cognitive function and brain activity in young adults. We conducted an observational study to assess the cognitive function of participants who had engaged in these exercises for a long period. Additionally, we examined the effects of open skill exercise (badminton) and closed skill exercise (calisthenics) on localized blood flow in the prefrontal lobe of the brain using an experimental research method. Specifically, during the Stroop task, the badminton group exhibited significantly higher △HbO2 in channel 18, corresponding to the dorsolateral prefrontal cortex, compared to the calisthenics group (F = 4.485, P < 0.05, η2 = 0.074). In the 2-back task, the calisthenics group showed significantly higher △HbO2 in channel 17, corresponding to the frontopolar area, dorsolateral prefrontal cortex and inferior prefrontal gyrus, than the badminton group (F = 8.842, P < 0.01, η2 = 0.136). Our findings reveal that open skill exercises are more effective in enhancing cognitive inhibition, thereby increasing attention capacity, self-regulation, and flexibility in response to environmental changes. Conversely, closed skill exercises demonstrate greater efficacy in improving working memory within cognitive functions, showcasing an enhanced capacity for information processing and storage. These data indicate that while both open and closed skill exercises are beneficial for cognitive function, they exhibit significant distinctions in some aspects.

Sustained acoustic medicine treatment of discogenic chronic low back pain: A randomized, multisite, double-blind, placebo-controlled trial.

Sustained acoustic medicine (SAM) is a noninvasive long-term treatment that provides essential mechanical and thermal stimulus to accelerate soft tissue healing, alleviate pain, and improve physical activity. SAM increases localized deep tissue temperature, blood flow, cellular proliferation, migration, and nutrition exchange, resulting in reduced inflammation and an increased rate of tissue regeneration. To assess the efficacy of SAM treatment of discogenic back pain in the lower spinal column to reduce pain, improve quality of life, and lower pharmacotherapy use. Sixty-five subjects with chronic low back pain were randomly assigned to SAM (N= 33) or placebo (N= 32) groups. Subjects self-applied SAM device bilaterality on the lower lumbar region for 4 hours daily for 8 weeks and completed daily pain diaries before, during, and after treatment. Subjects recorded pain reduction using a numeric rating scale (NRS), medication use, and physical activity using the Global Rating of Change (GROC) and Oswestry Disability Index (ODI). SAM treatment significantly reduced chronic lower back pain from baseline relative to placebo treatment (p< 0.0001). SAM treated subjects reported significantly lower back pain at 4 weeks, with the highest pain reduction (-2.58 points NRS, p< 0.0001) reported at 8 weeks. Similar trends were observed in improved physical activity (3.48 GROC, p< 0.0001, 69-88% ODI, p< 0.0001) and 22.5% (15.2 morphine milligram equivalent) reduction in the use of opioid medication from baseline to 8 weeks. Daily, home-use SAM treatment significantly improves the clinical symptoms of chronic lower back pain, improves physical mobility, and reduces daily medication use. SAM treatment is well-tolerated by patients and may be considered a safe, non-invasive treatment option for chronic discogenic, lower back pain.

Robust Long-Nanowire Fabrication by Clean-Phase-Assisted Micro Chemical Pen for Enhanced Bioassay Sensitivity.

Long nanowires offer an increased surface area for biomolecule immobilization, facilitating enhanced binding capacity and sensitivity in the detection of target analytes. However, robust long-nanowire fabrication remains a significant challenge. In this paper, we developed a novel construction of a micro chemical pen (MCP), called a clean-assisted micro chemical pen (CAMCP), for robust long-nanowire fabrication. CAMCP, based on localized hydrodynamic flow confinement, was conducted by incorporating a clean phase to effectively dissolve aggregated silver particles in the aspiration channel's shell, thereby enhancing the MCP's longevity by 60.84%, allowing for an 840 μm extension in nanowire patterning capability. A 4600-aspect ratio (length:1200 μm, width: 260 nm) nanowire was fabricated by CAMCP and utilized as a nanowire sensor, showing a 39.7% increase in IgA detection sensitivity compared to a 3000-aspect ratio sensor. Furthermore, the longer nanowire sensor exhibited enhanced signal responses, a higher signal-to-noise ratio, and a lower limit of detection (LOD). The preponderant bioassay performances of the longer nanowire sensor in bioassays, facilitated by CAMCP, open up its possibilities for chemical-synthesis nanowires (NWs) in ultrasensitive biodetection.

High-speed synchrotron X-ray imaging of melt pool dynamics during ultrasonic melt processing of Al6061

Ultrasonic processing of solidifying metals in additive manufacturing can provide grain refinement and advantageous mechanical properties. However, the specific physical mechanisms of microstructural refinement relevant to laser-based additive manufacturing have not been directly observed because of sub-millimeter length scales and rapid solidification rates associated with melt pools. Here, high-speed synchrotron X-ray imaging is used to observe the effect of ultrasonic vibration directly on melt pool dynamics and solidification of Al6061 alloy. The high temporal and spatial resolution enabled direct observation of cavitation effects driven by a 20.2 kHz ultrasonic source. We utilized multiphysics simulations to validate the postulated connection between ultrasonic treatment and solidification. The X-ray results show a decrease in melt pool and keyhole depth fluctuations during melting and promotion of pore migration toward the melt pool surface with applied sonication. Additionally, the simulation results reveal increased localized melt pool flow velocity, cooling rates, and thermal gradients with applied sonication. This work shows how ultrasonic treatment can impact melt pools and its potential for improving part quality.

Anchor chains—A simple low‐cost device to assist passage of small‐bodied mass fish

AbstractAttention has been placed on a variety of barriers that hinder fish passage in modern times. The most prevalent fish barriers were culverts which have negatively impacted waterway connectivity and fish habitats. For small‐bodied mass fish, high barrel velocities and turbulence have reduced fish swimming performance because of their weak swimming capabilities. In the present study, physical testing was conducted under controlled flow conditions to assess the extent and magnitude of turbulence characteristics, secondary flow and low‐velocity zones in a 0.5‐m‐wide box culvert barrel. Two cases were investigated; a reference case consisting of a smooth rectangular channel and a low‐cost design solution to improve upstream fish migration consisting of a single galvanized anchor chain fitted within a smooth rectangular channel. The single anchor chain was positioned towards one corner of the channel to induce asymmetric flow, reducing overall energy losses and enhancing the existing low‐velocity zone in the adjacent channel corner. The anchor chain induced a strong turbulent flow motion away from the anchor chain, characterized by higher Reynolds stress and turbulent kinetic energy, along with a distinct channel flow asymmetry. Conversely, the low‐velocity zone, between the anchor chain and the bottom channel corner, was significantly expanded with reduced longitudinal mean velocities and turbulent scales. Whilst the anchor chain link contributed to some complex localized wake flow, the anchor chain also influenced the distributions of normal turbulent stresses (v'z2 – v'y2), which in turn influenced the location of secondary flow cells. This secondary flow redirected low momentum fluid into the low‐velocity zones, setting the conditions for the favorable upstream passage of small‐bodied mass fish species.

Tailored micromixing in chemically patterned microchannels undergoing electromagnetohydrodynamic flow.

The study unveils a simple, non-invasive method to perform micromixing with the help of spatiotemporal variation in the Lorentz force inside a microchannel decorated with chemically heterogeneous walls. Computational fluid dynamics simulations have been utilized to investigate micromixing under the coupled influence of electric and magnetic fields, namely, electromagnetohydrodynamics, to alter the direction of the Lorentz force at the specific locations by creating the reverse flow zones where the pressure gradient, . The study explores the impact of periodicity, distribution, and size of electrodes alongside the magnitude of applied field intensity, the flow rate of the fluid, and the nature of the electric field on the generation of the mixing vortices and their strength inside the microchannels. The results illustrate that the wall heterogeneities can indeed enforce the formation of localized on-demand vortices when the strength of the localized reverse flow overcomes the inertia of the mainstream flow. In such a scenario, while the vortex size and strength are found to increase with the size of the heterogeneous electrodes and field intensities, the number of vortices increases with the number of heterogeneous electrodes decorated on the channel wall. The presence of a non-zero pressure-driven inflow velocity is found to subdue the strength of the vortices to restrict the mixing facilitated by the localized variation of the Lorentz force. Interestingly, the usage of an alternating current (AC) electric field is found to provide an additional non-invasive control on the mixing vortices by enabling periodic changes in their direction of rotation. A case study in this regard discloses the possibility of rapid mixing with the usage of an AC electric field for a pair of miscible fluids inside a microchannel.

Hot deformation behavior and microstructural evolution of dual phase Ni48.6 Al10.3 Co17 Cr7.5 Fe9 Ti5.8 Ta0.6 Mo0.8 W0.4 high entropy alloy

The present study reports the hot deformation behavior, microstructural evolution, and the alloying effects of refractory elements (Ta, Mo, W) in Ni48.6 Al10.3 Co17 Cr7.5 Fe9 Ti5.8 Ta0.6 Mo0.8 W0.4 (at. %) high entropy alloy (HEA). The vacuum arc melted specimens were characterized using a scanning electron microscope, X-ray diffractometer, and Differential scanning calorimetry, which revealed the two-phase structure consisting of γ′ precipitates embedded in the γ matrix. The Energy Dispersive Spectroscopy analysis in a scanning electron microscope revealed that Mo and W partitioned into the dendritic region (KMo = 1.23 and KW = 1.28) while Ta is found to be partitioned in the interdendritic region composed of mostly γ′ precipitates (KTa = 0.67). Further, the specimens were subjected to hot deformation in the 800 °C - 1100 °C temperature range at the strain rate of 0.01s−1. The maximum flow strength was around 278 MPa and 183 MPa at 1050 °C and 1100 °C, respectively. The flow behavior is correlated with the microstructure evolution, which is characterized using electron backscattered diffraction (EBSD). In the cases of hot deformation below 1000 °C, localized plastic flow in the form of shear bands developed in coarse grain microstructure, whereas fine grains evolved due to dynamic recrystallization (DRX) in the sample deformed above 1000 °C. Further, the role of refractory elements in retaining high-temperature flow strength has been discussed.

Heat and particle exhaust in high-performance plasmas in Wendelstein 7-X

The paper reports for the first time the heat and particle exhaust at the plasma boundary through various edge diagnostics for the high-performance plasma obtained after pellet injection on Wendelstein 7-X. The plasma density at the edge is found to be reduced by a factor of 2 in the high-performance phase, supporting the previously reported density peaking at the plasma centre. The plasma beta effect on the magnetic topology is reflected by the appearance of the second strike line, which is well understood with simulation. However, during the rapid decay phase of the enhanced confinement, a transient localized heat flow of up to 16 MW m−2 is observed at the leading edge of a poorly cooled divertor component, which has not been understood but raises concerns about machine safety.

Exploring the stabilization mechanism of NH3/CH4 non-premixed flames under gradient magnetic fields

This study explores the stabilization of non-premixed NH3/CH4 flames using gradient magnetic fields, overcoming challenges like low flame speed and instability inherent in ammonia—a carbon-free fuel and efficient hydrogen carrier. The action of the magnetic field modified the flame flow field, resulting in the suppression of emissions. By applying magnetic fields, the blending ratio of ammonia in the diffusion flame was elevated, resulting in an increase of 69% in the limit concentration to a near-pure level of 0.914. Measurements with Particle Image Velocimetry and schlieren system, alongside computational fluid dynamics, reveal how gradient magnetic fields mitigate flame detachment, lift-off, and blowout by altering flame root stabilization mechanisms. Specifically, gradient magnetic fields reduce localized flow velocity at the flame root and improve mass transfer. This indicates that gradient magnetic fields can significantly enhance the stability of NH3/CH4 flames, suggesting a promising route toward cleaner energy production and environmental sustainability.

Influence of Farallon Slab Loading on Intraplate Stress and Seismicity in Eastern North America in the Presence of Pre‐Existing Weak Zones

AbstractDespite the stability of the continental interior, eastern North America has hosted many significant historical earthquakes. Seismicity concentrates within tectonically inherited structures, which can act as weak zones where stress accumulates. Within these zones, systematic stress rotations may be explained by long‐wavelength sources. We test the hypothesis that mantle‐flow driven by the Farallon slab contributes to intraplate seismicity via the reactivation of pre‐existing faults. We model the stress field using seismically constrained global high‐resolution finite‐element flow models with CitcomS. To isolate the slab's effect, we vary its buoyancy between a case of neutrality and a case with full negative thermal buoyancy derived from tomography. Low‐viscosity lithospheric weak zones located at failed rifts, loaded by a mass anomaly at depth, transmit elevated stresses to the overlying crust. The sinking of the Farallon slab drives localized mantle flow beneath the central‐eastern US, generating a large stress amplification of 100–150 MPa peaking over the New Madrid Seismic Zone (NMSZ). This stress amplification exerts a continent‐wide clockwise rotation on the stress field, which in the presence of weak zones reproduces some observed deviations of the seismically inferred SHmax from the regional borehole SHmax, bringing optimally oriented faults, closer to failure, some of which are associated with major historical earthquakes, including the Reelfoot Fault in the NMSZ and the Timiskaming Fault in Western Quebec. However, stronger lithospheric viscosity gradients, shallower weak zones, or weaker faults are still needed to fully reproduce the observed stress field in some areas.