Transition Region Research Articles

Prediction of fracture toughness of a reactor pressure vessel steel in the ductile-to-brittle transition region based on a probabilistic cohesive zone model approach

The availability of irradiated material for the fracture-mechanical characterization of reactor pressure vessel steels in the context of surveillance programs is severely limited. Additional efforts are necessary to reduce the amount of material required for the determination of the reference temperature based on the Master Curve methodology. The objective of this study is the further development of a method for identifying the parameters of a cohesive zone model to simulate the fracture-mechanical behavior within the ductile-to-brittle transition region. A novel approach is proposed where statistically distributed numerical fracture toughness values are obtained by means of random spatial distributions of cohesive elements with either brittle or ductile fracture properties throughout the cohesive zone. Thereby, a numerical reference temperature is determined based on the ASTM E1921 standard and compared to the reference temperature obtained from tests on miniaturized CT specimens. It is shown that with the presented approach the reference temperature of a reactor pressure vessel steel can be predicted with high accuracy. Less material is required for the calibration of the model parameters than for an experimental determination of the reference temperature. Further development of the model is required to accurately predict the experimentally observed fracture toughness scatter within the transition region.

Critical comparison of different expressions for predicting the effect of loading rate on the ductile-to-brittle transition region

Critical comparison of different expressions for predicting the effect of loading rate on the ductile-to-brittle transition region

IoT based Predictive Modeling Techniques for Cancer Detection in Healthcare Systems

Background: The main objective of the Internet of Things (IoT) has significantly influenced and altered technology, such as interconnection, interoperability, and sensor devices. To ensure seamless healthcare facilities, it's essential to use the benefits of ubiquitous IoT services to assist patients by monitoring vital signs and automating functions. In healthcare, the current stateof-the-art equipment cannot detect many cancers early, and almost all humans have lost their lives due to this lethal sickness. Hence, early diagnosis of cancer is a significant difficulty for medical experts and researchers. Methods: The method for identifying cancer, together with machine learning and IOT, yield reliable results. In the Proposed model FCM system, the SVM methodology is reviewed to classify either benign or malignant disease. In addition, we applied a recursive feature selection to identify characteristics from the cancer dataset to boost the classifier system's capabilities. Results: This method is being applied in conjunction with fuzzy cluster-based augmentation, and classification can employ continuous monitoring to forecast lung cancer to improve patient care. In the process of effective image segmentation, the fuzzy-clustering methodology is implemented, which is used for the goal of obtaining transition region data. Conclusion: The Otsu thresholding method is applied to help recover the transition region from a lung cancer image. Furthermore, morphological thinning on the right edge and the segmentationimproving pictures are employed to increase segmentation performance. In future work, we intend to design a prototype to ensure real-time analysis to provide enhanced results. Thus, this work may open doors to carry patent-based outcomes.

Post-spawning migration and habitat use of adult Pacific bluefin tuna (Thunnus orientalis) in the western North Pacific

Pacific bluefin tuna (PBF, Thunnus orientalis), migrate widely throughout the north Pacific Ocean during all life stages. However, studies on the migration of adult fish in the northwestern Pacific Ocean, where spawning occurs, are limited. This study investigated the post-spawning migration and habitat use of PBF from the major spawning grounds of the Nansei Islands (approximately 23–31° N), Japan, using pop-up satellite archival transmission (PAT) tags. The PAT tags were deployed on 15 PBF individuals (estimated fork lengths: 170–260 cm) in the late spawning season (May–June) of 2021, and tracking data were collected for 3–103 days. Four tagged PBF individuals moved > 2,500 km north to the Kuroshio-Oyashio transition region at high latitudes (40° N) in July–September, immediately after the spawning season. During this northward movement, these PBF showed a spatiotemporal change in their vertical behavior, adapting to regional thermal habitat differences. At low latitudes near the spawning grounds (23.6–29.6° N), the PBF dived to deep depths (mean: 162.8 m) to avoid the warm surface layer (mean: 28.6 °C); however, once they reached higher latitudes (36.6–44.9° N), they spent most of their time in the cool surface layer (mean: 18.5 °C; 22.3 m). Our findings suggest that adult PBF move from spawning grounds to physiologically suitable low-temperature, food-rich waters through long-distance movements, and then exhibit a habitat preference behavior characterized by repeated short-distance movements in response to the feeding environments at high latitudes.

Effects of Short-Term Intercropping of Forage Crops on Soil Microbial Communities in Ziziphus jujuba cv. “Lingwuchangzao” Orchards in Northwest China

In the transitional region between agriculture and livestock rearing in northern China, planting forage crops in rows among fruit trees as feed in orchards represents an effective strategy for enhancing the ecological environment while addressing the increasing demand for livestock feed. Nonetheless, the impact of short-term mowing of cover forage crops for livestock feed on the quality of soil remains unclear. A two-year field experiment was conducted in Ziziphus jujuba cv. “Lingwuchangzao” orchards located in Lingwu County, Ningxia Hui Autonomous Region, in arid and semi-arid Northwest China. The experiment consisted of four treatments: (A) clean tillage (CK), (B) plantation with Lolium perenne (LP), (C) plantation with Trifolium repens (TR), and (D) plantation with Vicia villosa (VV).The results showed that short-term intercropping of forage crops may lead to a reduction in most soil nutrients in Z. jujuba cv. “Lingwuchangzao” orchards, particularly in the 0–20 cm soil layer. However, intercropping with TR can mitigate this declining trend and may even enhance nutrient levels within the 0–40 cm depth. Furthermore, intercropping of forage crops had a more pronounced effect on the α-diversity of fungal communities than on bacterial communities. This practice also altered the relative abundance of bacterial genera such as Sphingomonas, Bacillus, and Flavobacterium in the 20–40 cm depth and dominant fungal genera Fusarium and Mortierella in the 0–20 cm soil layer. The effects of soil physicochemical properties on bacterial communities were more significant than those on fungal communities.These results indicate that the short-term intercropping of forage crops in Z. jujuba cv. “Lingwuchangzao” orchards in arid and semi-arid Northwest China have varying impacts depending on the type of forage crop used.

Theoretical tools for neutrino scattering: interplay between lattice QCD, EFTs, nuclear physics, phenomenology, and neutrino event generators

Abstract Maximizing the discovery potential of increasingly precise neutrino experiments will require an improved theoretical understanding of neutrino-nucleus cross sections over a wide range of energies. Low-energy interactions are needed to reconstruct the energies of astrophysical neutrinos from supernovae bursts and search for new physics using increasingly precise measurement of coherent elastic neutrino scattering. Higher-energy interactions involve a variety of reaction mechanisms including quasi-elastic scattering, resonance production, and deep inelastic scattering that must all be included to reliably predict cross sections for energies relevant to DUNE and other accelerator neutrino experiments. Refined nuclear interaction models in these energy regimes will also be valuable for other applications, such as measurements of reactor, solar, and atmospheric neutrinos. This manuscript discusses the theoretical status, challenges, required resources, and path forward for achieving precise predictions of neutrino-nucleus scattering and emphasizes the need for a coordinated theoretical effort involved lattice QCD, nuclear effective theories, phenomenological models of the transition region, and event generators.

Ultra-miniaturized Bloch mode metasplitters for one-dimensional grating waveguides.

We present, for the first time, to our knowledge, power splitters with multiple channel configurations in one-dimensional grating waveguides (1DGWs) that maintain crystal lattice-sensitive Bloch mode profiles without perturbation across all output channels, all within an ultra-miniaturized footprint of just 2.1 × 2.2 μm2. This novel capability reduces the need for transition regions, simplifies multi-channel configurations of 1DGWs, and maximizes the effective use of chip area. The pixelated metamaterial approach, integrated with a time-domain heuristic algorithm, is utilized to concurrently achieve broadband operation, optimized dispersion control, and minimal loss. We experimentally demonstrate that the 1 × 2 and 1 × 3 metasplitters achieve average minimum losses per channel of 3.80 dB and 5.36 dB, respectively, which are just 0.80 dB and 0.59 dB above ideal splitting. The measurements for both designs demonstrate a 1 dB bandwidth of 15 nm, with excellent uniformity across all output channels. These versatile metasplitter designs can serve as fundamental building blocks for ultrahigh-bandwidth, densely integrated photonic circuits and in scenarios where slow light is essential.

A data-driven framework for developing a unified density-modulus relationship for the human lumbar vertebral body.

Despite the broad agreement that bone stiffness is heavily dependent on the underlying bone density, there is no consensus on a unified relationship that applies to both cancellous and cortical compartments. Bone from the two compartments is generally assessed separately, and few mechanical test data are available for samples from the transitional regions between them. In this study, we present a data-driven framework integrating experimental testing and numerical modeling of the human lumbar vertebra through an energy balance criterion, to develop a unified density-modulus relationship across the entire vertebral body, without the necessity of differentiation between trabecular and cortical regions. A dataset of 25 spinal segments harvested from fresh-frozen human spines consisting of L1 vertebrae with adjacent intervertebral disks and neighboring T12 and L2 endplates was examined through a systematic process. Each specimen was subjected to axial compression using a custom-designed radiolucent device, and the deformation at multiple points during the ramp was quantified using digital volume correlation applied to the time-lapse series of microcomputed tomography images acquired during loading. A finite element model of each specimen was constructed from quantitative computed tomography images, with the experimental displacement fields imposed to replicate the observed deformation. The optimal density-modulus relationship, both in exponential and polynomial forms, was then determined by using data-driven techniques to match the numerical strain energy with the experimental external work. The resulting relationships effectively recovered bone tissue modulus at the microscale. Subsequently, the unified relationships were applied to investigate the vertebral structure-property correlations at the macroscale: as expected, compressive stiffness exhibited a moderate correlation with bone mineral density, whereas bending stiffness was revealed to correlate strongly with bone mineral content. These findings support the accuracy of the developed density-modulus relationships for the vertebral body and indicate the potential of the proposed framework to extend to other properties of interest such as vertebral strength and toughness.

Surface Circular Photogalvanic Effect in Tl-Pb Monolayer Alloys on Si(111) with Giant Rashba Splitting.

We have found that surface superstructures made of "monolayer alloys" of Tl and Pb on Si(111), having giant Rashba effect, produce nonreciprocal spin-polarized photocurrent via circular photogalvanic effect (CPGE) by obliquely shining circularly polarized near-infrared (IR) light. CPGE is here caused by the injection of in-plane spin into spin-split surface-state bands, which is observed only on Tl-Pb alloy layers but not on single-element Tl nor Pb layers. In the Tl-Pb monolayer alloys, despite their monatomic thickness, the magnitude of CPGE is comparable to or even larger than the cases of many other spin-split thin-film materials. A model analysis has provided the relative permittivity ε* of the monolayer alloys to be ∼1.0, which is because the monolayer exists at a transition region between vacuum and the substrate. The present result opens the possibility that we can optically manipulate the spins of electrons even on monolayer materials.

The Long-term Evolution of the Solar Transition Region

The Long-term Evolution of the Solar Transition Region

A Scenario for Origin of Global 4 mHz Oscillations in Solar Corona

We establish a spherically symmetric model of solar atmosphere, which consists of the whole chromosphere and low corona below the 1.25 solar radius. It is a hydrodynamic model with heating in the chromosphere through an artificial energy flux. We performed a series of simulations with our model and found oscillations with a peak frequency of ∼4 mHz in the power spectrum. We confirmed that this resulted from the p-mode excited in the transition region and amplified in a resonant cavity situated in the height range ∼4×103–2×104 km. This result is consistent with global observations of Alfvénic waves in corona and can naturally explain the observational ubiquity of 4mHz without the difficulty of the p-mode passing through the acoustic-damping chromosphere. We also confirmed that acoustic shock waves alone cannot heat the corona to the observed temperature, and found mass upflows in the height range ∼7×103–7×104 km in our model, which pumped the dense and cool plasma into the corona and might be the mass supplier for solar prominences.

Dynamical properties of hydrogen fluid at high pressures.

The properties of the hydrogen fluid at high pressures are still of interest to the scientific community. The experimentally unreachable dynamical properties could provide new insights into this field. In 2020 [Cheng et al., Nature 585, 217-220 (2020)], the machine-learned approach allows the calculation of the self-diffusion coefficient in the warm dense hydrogen with higher precision. After that, the work [van de Bund et al., Phys. Rev. Lett. 126(22), 225701 (2021)] reports the abinitio treatment of isotopic effects on diffusion in H2/D2 and a significant increase in its value in the region of the phase transition. Both works indicate the anomalous growth of diffusion, but the reasons for this phenomenon are unclear. In the present work, we reveal the plasma-like behavior of the diffusion growth. We apply the classical molecular dynamics method using a machine learning potential developed on the abinitio modeling for the prediction of diffusion and shear viscosity coefficients. We consider dependencies of the vibrational spectrum, molecule lifetime, diffusion, and shear viscosity coefficients on density along the isotherms in the temperature range from 600 to 1100K.

Observations of umbral flashes in the resonant sunspot chromosphere

Context. In sunspot umbrae, the core of some chromospheric lines exhibits periodic brightness enhancements known as umbral flashes. The consensus is that they are produced by the upward propagation of shock waves. This view has recently been challenged by the detection of downflowing umbral flashes and the confirmation of a resonant cavity above sunspots. Aims. We aim to determine the propagating or standing nature of the waves in the low umbral chromosphere and confirm or refute the existence of downflowing umbral flashes. Methods. Spectroscopic temporal series of Ca II 8542 Å, Ca II H, and Hα in a sunspot were acquired with the Swedish Solar Telescope. The Hα velocity was inferred using bisectors. Simultaneous inversions of the Ca II 8542 Å line and the Ca II H core were performed using the code NICOLE. The nature of the oscillations were determined and insights into the resonant oscillatory pattern were gained by analyzing the phase shift between the velocity signals and examining the temporal evolution. Results. Propagating waves in the low chromosphere are more common in regions with frequent umbral flashes, where the transition region is shifted upward, making resonant cavity signatures less noticeable. In contrast, areas with fewer umbral flashes show velocity fluctuations that align with standing oscillations. Evidence suggests dynamic changes in the location of velocity-resonant nodes due to variations in the transition region height. Downflowing profiles appear at the onset of some umbral flashes, but upflowing motion dominates during most of the flash. These downflowing flashes are more common in standing umbral flashes. Conclusions. We confirm the existence of a chromospheric resonant cavity above sunspot umbrae. It is produced by wave reflections at the transition region. The oscillatory pattern depends on the transition region height, which exhibits spatial and temporal variations due to the impact of the waves.

Magnetic topology of quiet-Sun Ellerman bombs and associated ultraviolet brightenings

Context. Quiet-Sun Ellerman bombs (QSEBs) are small-scale magnetic reconnection events in the lower atmosphere of the quiet Sun. Recent work has shown that a small percentage of them can occur co-spatially and co-temporally with ultraviolet (UV) brightenings in the transition region. Aims. We aim to understand how the magnetic topologies associated with closely occurring QSEBs and UV brightenings can facilitate energy transport and connect these events. Methods. We used high-resolution Hβ observations from the Swedish 1-m Solar Telescope (SST) and detected QSEBs using k-means clustering. We obtained the magnetic field topology from potential field extrapolations using spectro-polarimetric data in the photospheric Fe I 6173 Å line. To detect UV brightenings, we used coordinated and co-aligned data from the Interface Region Imaging Spectrograph (IRIS) and imposed a threshold of 5σ above the median background on the (IRIS) 1400 Å slit-jaw image channel. Results. We identify four distinct magnetic configurations that associate QSEBs with UV brightenings, including a simple dipole configuration and more complex fan-spine topologies with a 3D magnetic null point. In the fan-spine topology, the UV brightenings occur near the 3D null point, while QSEBs can be found close to the footpoints of the outer spine, the inner spine, and the fan surface. The height of the 3D null varies between 0.2 Mm and 2.6 Mm, depending on the magnetic field strength in the region. Some QSEBs and UV brightenings, though occurring close to each other, are not topologically connected with the same reconnection process. The energy released during QSEBs falls in the range 1023–1024 ergs. Conclusions. This study shows that magnetic connectivity and topological features, such as 3D null points, are crucial in linking QSEBs in the lower atmosphere with UV brightenings in the transition region.

Vector substrate design for grain boundary engineering: boosting oxygen evolution reaction performance in LaNiO3.

The realization and subsequent control of emerging structural and electronic phases in solid materials has significantly enhanced their functionalities, thereby benefiting both fundamental research and practical applications. The grain boundary (GB), as a transitional region within the crystal lattice, exhibits atomic shifts and distinct energy profiles. These unique characteristics offer a promising avenue for the discovery of advanced active catalytic phases for carbon, oxygen, hydrogen, and nitrogen evolution/reduction reactions. However, the challenge lies in isolating and controlling the quantity of grain boundaries in conventional catalysts, which hinders the identification of their functional attributes. In this study, we successfully engineered the (001)/(110), (001)/(111), and (110)/(111) GBs in LaNiO3 (LNO) using a vector substrate design approach. Subsequent evaluation of these GBs in the oxygen evolution reaction (OER) revealed that LNO (110)/(111) exhibited the fastest surface reconstruction into Ni oxyhydroxide and the most superior OER performance, achieving 2.36 mA cm-2 at η = 400 mV. This outstanding performance is attributed to its strongest Ni-O covalency and the proximity of the O 2p-band center to the Fermi level. This research aims to address the challenges associated with isolating and controlling GBs for optimized OER performance, while also providing comprehensive insights into the relationship between GBs and surface reconstruction behaviors.

Fine structures in interlaced magnetic flux ropes via Hall-MHD simulations

Magnetic flux ropes are a fundamental component in both space and laboratory plasmas. We present a Hall-MHD simulation exploring the interaction between two isolated magnetic flux ropes under mesoscale solar wind conditions. The interaction interface is resolved with a resolution approaching the kinetic scale, to reveal unprecedented details of this process. As we replicate previous findings that such interactions can lead to the formation of two new ropes, we also find that magnetic reconnection occurs in multiple locations inside the central current sheet, leading to transient small flux ropes, which is qualitatively consistent with previous magnetospheric multiscale observations. Consequently, each field line undergoes multiple reconnections that alter its connectivity before it exits the current sheet. Later, each flux rope divides into two branches: the reconnected flux moving away from the current sheet to form the transition regions of the new ropes and the remnant flux sustaining the current sheet. For each magnetic flux rope (MFR), the core field reconnects after most surface fields are reconnected so that the reconnecting MFRs maintain a relatively symmetric shape. These results in unprecedented detail highlight the complex internal dynamics and call for further observational and theoretical studies.

Spatial distribution pattern and long-term trend of atmospheric methane in the Atlantic-Mediterranean transition region based on TROPOMI and GOSAT measurements.

Methane (CH4) spatial distribution and its trends in the Atlantic-Mediterranean transition region of southwestern Europe were studied using TROPOMI and GOSAT observations. TROPOMI XCH4 provided insights into the distribution across the entire Iberian Peninsula, highlighting the high XCH4 mixing ratios in the two main valleys and the southern sub-plateau, characterized by agricultural and livestock activities. The marine-continental region in the southwestern Iberian Peninsula was identified as a major CH4 hot spot. Focusing on this region, the seasonal distribution of CH4 and its trends were studied. The lowest XCH4 levels were recorded in a semi-natural landscape in a mountain range with an average mixing ratio of 1871.9±18.5nmolmol-1, while the highest trend was recorded at 10.9±0.7nmolmol-1year-1 for the period 2019-2023. Conversely, the highest XCH4 levels were obtained over an inland wetland, averaging 1888.7±15.8nmolmol-1; while recording the lowest regional trend, 6.4±0.9nmolmol-1year-1. Aiming to identify potential regional changes in the XCH4 trend, GOSAT observations were used, revealing a long-term trend of 8.7±0.3nmolmol-1year-1 from 2009 to 2023. Focusing on the first and last five years of the series, trends of 6.5±0.9nmolmol-1year-1 and 14.9±1.2nmolmol-1year-1 were detected, indicating a trend acceleration ratio of 2.3. An analogous pattern was found in the Atlantic Ocean and central Mediterranean at the same latitude, with ratios of 2.7 and 2.4 respectively. Furthermore, these outcomes were corroborated by ground-based observations from the Azores and Lampedusa stations, which belong to the NOAA network. Despite CH4 increasing globally and its trend accelerating, this work highlights the complexity of its dynamics, with regional variations in its mixing ratios, horizontal distribution, and temporal trends.

Canopy elastic turbulence: Insights and analogies to canopy inertial turbulence.

Canopy flows occur when a moving fluid encounters a matrix of free-standing obstacles and are found in diverse systems, from forests and marine ecology to urban landscapes and biology (e.g. cilia arrays). In large-scale systems, involving Newtonian fluids (like water or air), canopy flows typically exhibit inertial turbulence due to high Reynolds numbers (Re). However, in small-scale systems like cilia, where Re is low, but the fluid can be viscoelastic (like mucus), the relevant control parameter is the Weissenberg number (Wi), quantifying elastic stresses in the flow. Here, we investigate the flow of a viscoelastic polymer solution over a microscopic canopy within a microfluidic device. As the Weissenberg number increases, the flow undergoes distinct transitions, eventually becoming unstable beyond a critical Wi. At high Wi, we observe the emergence of elastic turbulence (ET), a chaotic flow regime that, despite differing underlying mechanisms, exhibits striking similarities to large-scale canopy inertial turbulence. Similar to canopy inertial turbulence, ET within the canopy can be spatially divided into distinct regions: a porous layer within the canopy, a mixing layer at the canopy tips, a transitional region just above the canopy, and a Poiseuille-like flow further up. The separation of the flow into different regions reveals a new analogy between inertial turbulence and ET, providing a fresh insight into ET flows and expanding their potential for innovative microfluidic designs and real-world applications.

INTEGRATION OF HIGH-TEMPERATURE SURFACE HEAT EXCHANGE

Despite the discrete nature of the interaction of droplets of sprayed liquid with a high-temperature surface, the inevitable formation of a liquid film leads to the fact that the main qualitative laws of the heat exchange that occurs in this case are characteristic of the known process of heat exchange during boiling. At the same time, the presence of extensive theoretical and experimental studies of “large-volume boiling” and the process of steam generation in channels does not allow us to establish the conditions of heat exchange during the thermal interaction of a dispersed liquid - water with different concentrations of surfactants with a high-temperature surface. We did not find any materials about this process in the scientific literature. With a number of features common to the above two cases of heat exchange (the presence of boiling crises, film and bubble modes, etc.), cooling a high-temperature surface with a droplet medium containing various concentrations of surfactants has significant distinctive features due to the hydrodynamics of the process, which is the subject of further study. To fully explore the above task, the following must be done: Develop a methodology for experimental study of local conditions of non-stationary heat exchange of sprayed water with different concentrations of surfactants. Develop and manufacture an experimental setup on which to conduct research on the effects of irrigation density, surface temperature, degree of liquid underheating, its speed and angle of impingement on the surface. Develop a mathematical model for calculations of heat flows, heat transfer coefficients, dynamics of hydraulic methods of liquid dispersion – water with different concentrations of surfactants, critical heat flows and surface temperatures in the transition region from film to bubble boiling as a function of determining factors. Establish the independent influence of the degree of non-stationarity of the process on the heat exchange conditions.

Thermodynamical topology with multiple defect curves for dyonic AdS black holes

Dyonic black holes with quasitopological electromagnetism exhibit an intriguing phase diagram with two separated first-order coexistence curves. In this paper, we aim to uncover its influence on the black hole thermodynamical topology. At first, we investigate the phase transition and phase diagram of the dyonic black holes. Comparing with previous study that there is no black hole phase transition region for a middle pressure, we find this region can narrow or disappear by fine tuning the coupling parameter. Instead, two first-order phase transitions can be observed. Importantly, we uncover that such novel phase diagram shall lead to a multiple defect curve phenomenon in black hole topology where each dyonic black hole is treated as one defect in the thermodynamical parameter space. By examining the topology, it is shown that there could be one, three, or five black hole states for given pressure and temperature. For each case, the topological number is calculated. Our results show that the topological number always takes value of +1, keeping unchanged even when the multiple defect curves appear. Therefore, our study provides an important ingredient on understanding the black hole thermodynamical topology.