Transition Region Research Articles

Thermo-mechanical fatigue crack growth in a nickel-based powder metallurgy superalloy

Fatigue crack growth is studied in a nickel-based powder metallurgy (PM) superalloy (FGH4099) subjected to in-phase (IP) and out-of-phase (OP) thermo-mechanical fatigue (TMF), as well as isothermal fatigue (IF) at peak temperature. The crack growth rate and path are evaluated for both coarse grain (CG) and fine grain (FG) FGH4099, especially the effects of phase angle and polycrystalline microstructure. The results show that the TMF crack propagation is mainly transgranular in OP condition; while in IP condition, fatigue crack propagates intergranularly at low ΔK and transforms to transgranular after passing the transition region. The crack propagation resistance for FG microstructure is lower than that for CG microstructure at elevated temperature, as a result of secondary cracks and grain boundary weakening effect. Crystallographic slip controls the crack propagation process, while the twin boundaries (TB) and special grain boundaries also exert a significant influence on crack deflection. The formation of secondary cracks is closely related to local misorientation and crystallographic deformation during TMF crack propagation. The crack deflection in a single grain reveals a competition mechanism between crystallographic slip and grain boundary effect, which explains the lower crack growth rate for OP when compared to IP or IF.

The Activation Energy Temperature Dependence for Viscous Flow of Chalcogenides

For some chalcogenide glasses, the temperature dependence of the activation energy E(T) of viscous flow in the glass transition region was calculated using the Williams–Landel–Ferry (WLF) equation. A method for determining the activation energy of viscous flow as a function of temperature is proposed using the Taylor expansion of the function E(T) using the example of chalcogenide glasses As-Se, Ge-Se, Sb-Ge-Se, P-Se, and AsSe-TlSe. The calculation results showed that the temperature dependence of the activation energy for the Ge-Se, As-Se, P-Se, AsSe-TlSe, and AsSe systems is satisfactorily described by a polynomial of the second degree, and for Sb-Ge-Se glass by a polynomial of the third degree. The purpose of this work is to compare the values of the coefficients obtained from the Taylor series expansion of E(T) with the characteristics of the E(T) versus (T − Tg) curves obtained directly from the experimental temperature dependence of viscosity. The nature of the dependence E(T) is briefly discussed.

Improved Prediction of the Flow in Cylindrical Critical Flow Venturi Nozzles Using a Transitional Model

Critical flow Venturi nozzles (CFVNs) are a state-of-the-art secondary standard widely used for gas flow measurements with high precision. The flow rate correlates with the type and thickness of the boundary layer (BL) inside the nozzle throat. In the cylindrical type—one of the two standard designs of CFVNs—the nozzle throat encompasses a defined axial length in which the BL develops. This numerical study is concerned with the BL effects in a cylindrical CFVN by means of two turbulence models. Compared to experimental data, the k-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega$$\\end{document} SST model predicts the discharge coefficient well for high and low Reynolds numbers, but not in the intermediate regime. The γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma$$\\end{document}-Reθ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Re_{\ heta }$$\\end{document} model, on the contrary, agrees well with experimental data in the entire flow range. Relevant quantities and profiles of the BL are separately investigated in the laminar, turbulent, and transitional region. The calculated laminar and turbulent BL thicknesses correspond to predictions based on integral methods for solving the BL equations. Simple representations are proposed for the Zagarola-Smits scaled laminar and turbulent deficit BL profiles removing the effects of axial position, Reynolds number, and pressure gradient. Furthermore, the shape factor is investigated as a characteristic parameter for determining the transitional region.

Ni-rich LiNi0.905Co0.043Al0.052O2 cathode material for high-energy density Li-ion cells: Tuning lithium content, structural evolution, and full-cell performance

Ni-rich LiNi0.905Co0.043Al0.052O2 oxides with the Li excess (x) up to 7 mol.% used in the synthesis are prepared by a facile dry-mixing method. It is shown that the Li/Ni mixing level and crystallite size are dependent on the Li amount, while Al from the precursor acts as a scavenger of the excessive Li. Operando X-ray diffraction (XRD) studies enable explaining differences in the structural evolution of materials exhibiting high and low Li/Ni mixing, especially in the H2↔H3 transition region. Soft X-ray absorption spectroscopy (XAS) studies show differences in the charge state evolution of the surface and bulk Ni. The optimized oxide with the Li excess x = 2 mol.% delivers excellent electrochemical performance, with an initial discharge capacity of 205.5 mAh g−1 at 0.1C, and 91.4 % capacity retention after 100 cycles at 1C. The unmodified in any other way cathode material allows achieving the discharge capacity of 178.5 mAh g−1 at the high rate of 5C, and works well in the full-cells.

Experimental and analytical investigation of the tensile mechanism of textile-reinforced mortar (TRM) composites and fabric grids in elevated temperatures

The textile-reinforced mortar (TRM) combines high-strength fabric textiles with cementitious mortar matrix to enhance mechanical behaviour and durability, especially at high temperatures. The current study investigated how basalt, carbon, and glass textile grids and TRM composites respond under direct tensile and thermal loading up to 800 ℃. Changes in microstructure were analyzed using scan electron microscopy (SEM), thermo-gravimetric analysis (TGA), and ultrasonic pulse velocity (UPV). The results indicated that temperature significantly affected the coating material and cementitious mortar, weakening the grids and composite specimens. Carbon and glass fibre grids proved more resilient, and the carbon and glass TRM reduced 50% of their ultimate stress at 500 ℃, while for basalt TRM is 200 ℃. A slight gain of strength was observed for all TRM specimens at 300 ℃, and SEM analysis revealed critical changes in the mortar matrix and interfacial transition region. The results were further utilized to calibrate the Gibson model considering humidity and early-stage coating material changes, and yielding results consistent with experimental data.

Modelling the Charpy Impact Ductile-Brittle Transition of a Ship Plate Steel with CAFE Modelling

In the present work, a cellular automata finite element model (CAFE) was developed to model the ductile-brittle transition of a Grade A ship plate steel. Therefore, ductile and brittle cellular automata (CA) arrays of cells were created in the model to integrate material data at microstructural level, along with the ductile and brittle fracture processes. Microstructural data was analysed with Weibull distributions and incorporated in CAFE model using random number generators, along with ductile and brittle fracture parameters. Ductile fracture was modelled with Rousselier damage model; hence damage model parameters were calibrated with experimental data. Brittle fracture was modelled with Beremin model, and four different cleavage particles, found in a Grade A ship plate steel, were incorporated in CAFE model in order to model a competition of particles nucleating microcracks of critical size in the damage regions of Impact Charpy tests and four-point double-notch bend tests performed at low temperature. The mechanical properties the plate steel was measured in the transition region and incorporated in CAFE model, along with ductile-brittle transition rules. The present CAFE model was able to simulate distributions of microcracks in the notch region of four-point double-notch bend models (in the transition region), which correlated with experimental data. CAFE model was also able to simulate microvoids in the notch region of Charpy specimens along with the load-displacement Charpy curve for room test temperature, with very good agreement with experimental data. Once CAFE model was validated at micro and structural level, it was applied to model the typical scatter of impact Charpy energy values in the transition region of Grade A ship plate steel with good agreement with the measured ductile-brittle transition curved of the plate steel. Keywords: cellular automata, finite element modelling, ductile-brittle transition, damage modelling.

Thin Clouds Control the Cloud Radiative Effect Along the Sc‐Cu Transition

AbstractIn situ and spaceborne studies reveal the prevalence of thin clouds in the major Stratocumulus‐to‐Cumulus Transition (SCT) regions. Using instantaneous satellite and reanalysis data, this study investigates the properties of thin clouds in the Southeast Pacific Ocean and their impact on the cloud radiative effect (CRE). Our findings demonstrate that thin clouds are intrinsic to the SCT. The overcast stratocumulus‐dominated regime exhibits a minimal presence of thin clouds, which become notably prominent after the clouds breakup into the cumulus‐dominated regime. The regime dependence of the occurrence of thin clouds is also observed in terms of the marine cold‐air outbreak parameter and the sea surface temperature. Thin clouds at a given cloud cover significantly modulate the shortwave (SW) and longwave (LW) components of CRE. SW CRE decreases by 46 %–65 % with increasing thin cloud cover. They account for a larger variance in cloud albedo than the combined influence of the liquid water path and effective radius. Furthermore, LW CRE decreases by about 12 %–52 % with thin cloud cover. An increase in the fraction of thin clouds also leads to a larger fraction of negative SW CRE offset by positive LW CRE at a given cloud cover. This LW compensation ranges from approximately 8 % at overcast cloud cover to as much as 19 % at about 50 % cloud cover. These findings elucidate the crucial role of thin clouds, and thus cloud morphology, in modulating CRE and underscore the necessity of their accurate representation in climate models.

Mixed Convection Heat Transfer Characteristics of Al2O3 – MWCNT Hybrid Nanofluid under Thermally Developing Flow; Effects of Particles Percentage Weight Composition

In this research, an experimental investigation of hybrid nanofluid mixed convection heat transfer characteristics is conducted. The research specifically investigates the effects of percentage weight composition (PWC) of nanoparticles in the hybrid nanofluids on mixed convection heat transfer characteristics along the lamina, transition and turbulent regions. Transition boundaries, thermal entrance effects, and the influence of tube axial position were also critically investigated and analysed experimentally. Three hybrid nanofluids of Al2O3 – MWCNT (i.e., Al2O3 (60%) – MWCNT (40%), Al2O3 (50%) – MWCNT (50%) and Al2O3 (40%) – MWCNT (60%)) were prepared using two-step method and then subjected to a constant heat flux through a horizontal circular copper tube with an internal diameter of 8mm. Results show a significant change in heat transfer characteristics with different PWCs. Al2O3 (60%) – MWCNT (40%) have shown a better heat transfer enhancement among the three fluids investigated. Its Nusselt number has an enhancement of more than 5 % better than the other two fluids. Along the transition regime, critical Reynold numbers (Recr) of the three nanofluids were found to have differed slightly, with Recr = 2020, 2000 and 2100 for Al2O3 (60%) – MWCNT (40%), Al2O3 (50%) – MWCNT (50%) and Al2O3 (40%) – MWCNT (60%) respectively. Mixed convection effects were found to be more significant with Al2O3 (60%) – MWCNT (40%) than with the other two fluids. At the axial position of 63.75, its mixed convection strength (Ὠ) was about 41%, which is the highest among the three fluids. Its strength of mixed convection was also found to deteriorate to about 14.75% with an increase in axial distance from the tube inlet. A similar observation was also noticed with other fluids. Thermal entrance effects were only found to be significant at x/d = 15 and 31.25, as their influence diminishes with an increased x/d distance from the tube inlet. It was concluded that both mixed convection and thermal entrance effects resulted in heat transfer enhancement, especially in the lamina region. Their influences decrease with an increase in axial distance from the tube inlet. Mixed convection influences were only present in the lamina and transition region, and their strength was reduced with an increase in Reynold number and axial position.

Simultaneous determination of Young's modulus and residual stress via dynamic analysis of nanobridge exhibiting beam-to-string behaviors using a genetic algorithm

The mechanical properties of nanostructures, particularly Young's modulus and residual stress, exert significant influence on the performance and reliability of nanomechanical devices. However, conventional methods prove inadequate for evaluating these properties due to the impact of fabrication processes on nanostructures. This study addresses this challenge by proposing a dynamic model that considers the transition between “beam-like” and “string-like” characteristics under residual stress, a factor overlooked in previous research. Through analysis of nanobridge vibration modes and utilization of genetic algorithms (GAs) to reverse-engineer Young's modulus and residual stress from resonant frequencies, we introduce a novel and precise methodology. In contrast to the conventional Euler-Bernoulli beam theory, our proposed model integrates the system's kinetic and potential energies for resonant frequency calculation. This energy-based approach, grounded in physical principles, excels at capturing dynamic changes in structural behavior. Particularly in the critical “transition region” where the resonator shifts from “beam-like” to “string-like” behavior, our method adeptly accounts for energy conversion processes, resulting in more accurate resonant frequency estimations. By comparing with existing published data, our proposed method achieves a maximum error of 5.87 % in the determination of Young's modulus and residual stress of nanostructures.

Experimental investigations of effects of nanoparticle size on force convective heat transfer characteristics of Al2O3 - MWCNT hybrid nanofluids in transitional flow regime

This study reports an experimental investigation of nanoparticle sizes effects on the heat transfer characteristics of hybrid nanofluids along the transitional flow regime. Four different particle sizes were used to prepare hybrid nanofluids of Al2O3 and MWCNT (i.e., 5 nm and 20 nm for Al2O3 and <7 nm and 30–50 nm for MWCNT nanoparticles). Three hybrid nanofluids with different particle combinations (i.e., Al2O3(5 nm) – MWCNT (<7 nm), Al2O3(20 nm) – MWCNT(<7 nm) and Al2O3(20 nm) – MWCNT (30–50 nm)) at a percentage weight composition (PWC) of 60:40 and 0.3 volume concentration were prepared. Results showed that particle sizes significantly affected the convective heat transfer characteristics of the nanofluids. Along the transition region, all three fluids were found to have different critical Reynold numbers 1152, 1172, and 1898 for Al2O3(20 nm) – MWCNT (<7 nm), Al2O3(5 nm) – MWCNT (<7 nm) and Al2O3(20 nm) – MWCNT (30–50) respectively. Al2O3(20 nm) – MWCNT (<7 nm) have shown better heat transfer performances. Its Nusselt number shows an enhancement of about 48.86 % along the transition region. And its coefficient of thermal performance (COP) was better than that of Al2O3(20 nm) – MWCNT (30–50 nm) and Al2O3(5 nm) – MWCNT (<7 nm) with 43.53 % and 21.89 %, respectively. While its friction factor and pressure drop were lower than that of Al2O3(5 nm) – MWCNT (<7 nm) nanofluid by 5.2 % and 12.78 %. It was concluded that for a 60:40 hybrid nanofluid of Al2O3 and MWCNT, particle sizes have influenced heat transfer characteristics and affected other flow characteristics along the transition regime.

Design methods and recommendations for flexural concrete beams reinforced with steel-fiber composite bars

This study aims to establish a complete theoretical model for the nominal flexural strength of concrete beams reinforced with steel-fiber composite bars (SFCB-RC), and determine an optimized range for the ratio of the diameter of the steel core to the diameter of SFCBs (η). Firstly, flexural failure modes for SFCB-RC beams were determined through theoretical analysis, and two failure modes including concrete crushing (compression failure) and FRP in SFCBs rupturing (tension failure) were recommended. It was confirmed that there exists a transition region between the failure modes of tension and compression, where both modes are possible. By conducting a statistical analysis of a database including 57 SFCB-RC beams, an upper-limit reinforcement ratio was recommended for SFCB-RC beams in the transition region. Simplified equations to predict the nominal flexural strength for compression-controlled SFCB-RC beams were proposed by directly using the constitutive model of SFCBs. The flexural strength equations for tension-controlled concrete beams reinforced with fiber reinforced polymer bars (FRP-RC) were confirmed to be also suitable for SFCB-RC beams. Validation of these equations was conducted using the assembled database. Furthermore, the parametric analysis revealed an optimal range of the ratio η (0.77–0.87). This suggested range can serve as a basis for standardizing the production specifications of SFCBs.

High energy-dissipation PDMS polymer-fluid-gels over an ultra-wide temperature range

Viscoelastic polymers exhibit strong energy dissipation in the glass transition region due to the motion of chain segments. Yet, the damping temperature ranges are pretty narrow, and the damping effect is poor at low frequencies. Here, we report two PDMS polymer-fluid-gels prepared by traditional curing and solvothermal polymerization, both of which exhibit excellent energy-dissipation capacity with loss factor larger than 0.7 at 1 Hz both covering 255 K (−55 °C to 200 °C), and larger than 1.0 at 1 Hz covering 134.7 K and 146.7 K, respectively, exceeding all the literature reports. Furthermore, solvothermal polymerization realizes large cross-linking meshes in which polymer fluids can stretch with less restriction and have longer relaxation time, which is conducive to low-frequency damping. The lower the frequency, the more pronounced the relative increase in damping, with the ratio of the two being greater than 4 times in the measuring low-frequency range. Moreover, the gels can absorb impact in extreme environments and protect raw eggs from breaking at temperatures as low as −50 °C when dropped from a height of 2 m.

Low-power and robust ternary SRAM cell with improved noise margin in CNTFET technology

In this paper, a carbon nanotube field-effect transistor (CNTFET) based low power and robust ternary SRAM (TSRAM) cell with enhanced static noise margin (SNM) has been proposed. The proposed cell uses a low-power cell core and a stack of 2 CNTFETs to discharge the read bit line (RBL) to ground, unlike the previous SRAM designs which use read buffers or transmission gates (TG) to alter the voltage levels on the RBL. The proposed TSRAM cell has been simulated relentlessly, using the Stanford 32 nm CNTFET technology mode file with Synopsis HSPICE tool under various operating conditions. Unlike other designs, the cross-coupled ternary inverters used as the cell core in the proposed TSRAM show higher gain and steep curves in the transition region mitigating the static power of the cell. The simulation results exhibit improvements in performance parameters like power consumption, energy, noise margins, and reliability. At 0.9 V supply voltage, the proposed TSRAM cell offers 52.44% and 43.17% reduction in write and read static power, a PDP reduction of 35.29% in comparison, and a 36.36% improvement in SNM compared to the best designs under investigation. Also, the proposed TSRAM design shows higher robustness compared to other designs.

Multi-objective optimization strategy for regional multi-energy systems integrated with medium-high temperature solar thermal technology

The high proportion and volatility of renewable energy pose a significant challenge to efficient collaboration between photovoltaic/thermal and wind power in multi-energy systems. Therefore, this paper proposes a Regional Multi-Energy System (RMES) based on Medium-High Temperature Solar Thermal (MHTST) technology. The novelty of the solution integrates dispatchable photovoltaic and photothermal conversion pathways, facilitating flexible and controllable utilization of solar energy via installed Thermal Energy Storage (TES). A multi-objective optimization model is developed to ensure the optimal operation of the proposed system under typical seasonal scenarios. The method that combines Branch-and-Reduce with Multi-Learning-Task is used to handle the formulated Mixed Integer Nonlinear Programming (MINLP) and swiftly identify optimal Pareto solutions. Case studies are performed over the improved united communities of the Test Region for Energy Transition and Comprehensive Reform in Taiyuan, China. Compared with the conventional photovoltaic technology, the simulation results show that the proposed solution has superior performance in both winter-heating and summer-cooling operations across 24-hour scheduling periods: operating costs reduced by 12.5% and 18.7%, carbon emissions decreased by 7.4% and 21.4%, with local solar power accommodation increased by 263.89kW and 487.47kW, respectively.

The applications of GNPs and SNPs in medical implant

Nanomaterials have been widely utilized in medical implant. This review demonstrates a number of applications of GNPs (gold nanoparticles) and SNPs (silver nanoparticles) in medical implants, including three main aspects, which are dentistry, orthopaedics and soft tissue. Nanomaterials are also known as ultrafine particle materials. Nanomaterials are composed of particles with a size range of 1 ~ 100nm. They are usually in the transition region of the interface between atomic clusters and macroscopic objects. Subsequently, the differences and identities between the applications of two sorts of nanoparticles are compared, along with advantages and limits accordingly and respectively. GNPs are more utilized according to their stability, biocompatibility, coordination functions and promotion mechanism in the human body, while SNPs are more used according to, most significantly antibacterial properties, biocompatibility and coordination functions. And this may path pave the way for those who need to generally decide which nanoparticle is more suitable when it comes to a certain field of medical implant.

Fatigue life analysis of scraper conveyor chain ring under different chain speeds and loads

This study aims to explore how different chain speeds and loads impact the fatigue life of the scraper conveyor chain ring. To achieve this, the study validates the reliability of a coupled simulation involving multi-body dynamics and the discrete element method. It also acquires time-varying tension load spectra under various operational conditions. The research evaluates the effects of distinct chain speeds and loads on parameters such as chain tension, vibration acceleration in the Y and Z-directions of the chain ring. Furthermore, finite element simulation is employed to examine stress distribution changes and fatigue life trends within the three-chain ring structure. The findings demonstrate that Y and Z-direction vibration accelerations of the chain ring correlate positively with the load. Additionally, the vibration acceleration in the Y-direction correlates positively with the chain speed. Across different chain speeds and loads, the maximum equivalent stress in the chain ring exhibits dynamic variations mirroring the load spectrum. Within the elastic deformation range of the chain ring, the highest stress within the transition region correlates linearly with chain tension. Load has a greater effect on the fatigue life of chain rings than chain speed. The fatigue life within the transition region of the chain ring decreases exponentially with increasing load at a constant chain speed. Conversely, at a constant load, chain ring life correlates positively with chain speed. Specifically, the fatigue life of the chain ring in LS 22 amounts to 32.64 days. When both chain speed and load are adjusted by 25%, the chain ring's lifespan reduces by 51.66% during simultaneous increments and increases by 39.26% with concurrent reductions in speed and load.

Dark Energy Survey Year 6 results: Intra-cluster light from redshift 0.2 to 0.5

ABSTRACT Using the full 6 years of imaging data from the Dark Energy Survey, we study the surface brightness profiles of galaxy cluster central galaxies and intra-cluster light. We apply a ‘stacking’ method to over 4000 galaxy clusters identified by the redMaPPer cluster finder in the redshift range of 0.2−0.5. This yields high-signal-to-noise circularly averaged profile measurements of the central galaxy and intra-cluster light out to 1 Mpc from the cluster centre. Using redMaPPer richness as a cluster mass indicator, we find that the brightness of the intra-cluster light has a strong mass dependence throughout the 0.2−0.5 redshift range, and this dependence grows stronger at a larger radius. In terms of redshift evolution, we find some evidence that the central galaxy, as well as the diffuse light within the transition region between the cluster central galaxy and intra-cluster light within 80 kpc from the centre, may be growing over time. At larger radii, more than 80 kpc away from the cluster centre, we do not detect evidence of additional redshift evolution beyond the cluster mass dependence, consistent with the findings from the IllustrisTNG hydrodynamic simulation. We speculate that the major driver of intra-cluster light growth, especially at large radii, is associated with cluster mass growth. Finally, we find that the colour of the cluster central galaxy and intra-cluster light displays a radial gradient that becomes bluer at a larger radius, which is consistent with a stellar stripping and disruption origin of intra-cluster light as suggested by simulation studies.

Return on Investment of Three-Year Accelerated Programs for Students, Medical Schools, Departments, and Community

Building on the initial accelerated pathway programs in the 1970s to increase workforce, nearly 30 schools have launched accelerated 3-year pathways (A3YP) during the past decade. The authors based on their educational roles, experiences, and scholarship with A3YP provide this perspective of the argument for A3YP and potential disadvantages for each group—students, schools, residencies, departments, and community. When schools consider innovations, they might consider A3YPs for multiple reasons; this perspective helps provide justification for the program and broadly considers return on investment (ROI). The ROI for students includes decreased debt, reduced costs and stress associated with the fourth-year residency applications, and a directed pathway with facilitated transition into a residency program with accompanying professional identity development. Disadvantages for students include early specialty commitment, risk of deceleration, and condensed curriculum. The ROI for schools includes recruiting and retaining students, who will then transition more easily into residency and stimulating innovation. Residency programs gain residents with known skills, who have been a part of the department for 3 years. In addition, fewer residency slots for interviewing leads to saving recruitment administrative costs and time. Finally, many programs are intended to increase the workforce, since students who come to the region for medical school and transition directly into residency are likely to stay in the region. Disadvantages include increased curricular complexity for the medical school, increased administrative support, and advising resources. Finally, several of the accelerated programs attract matriculants from diverse backgrounds contributing to the diversity of the medical school, residency program, and community workforce.

Statistical Investigation of Wave Propagation in the Quiet-Sun Using IRIS Spectroscopic Observations

In this analysis, we use spectroscopic observations of the quiet Sun made by the IRIS instrument and investigate wave propagation. We analyze various spectral lines formed in different atmospheric layers, such as the photosphere, chromosphere, and transition region. We examine the Doppler velocity time series at various locations in the quiet Sun to determine the dominant oscillation periods. Our results executing statistical analysis resemble those of the classical physical scenario, indicating that the photosphere is mainly characterized by the dominant 5 minute period, while the chromosphere is primarily associated with the 3 minute oscillation period. In the transition region, we observe a variety of oscillation periods, with dominant periods of 3, 8, and 12 minutes. We estimate the cutoff frequency by deducing the phase difference between two Doppler velocity time series obtained from spectral line pairs in different atmospheric layers formed at different temperatures. This reveals a significant correlation between 3 minute periods in the transition region and photospheric oscillations, suggesting that these oscillations in the transition region might propagate from the photosphere. Additionally, we analyze the phase difference between chromospheric oscillations and photospheric oscillations, demonstrating that only the 3 minute oscillations propagate upward. Based on the statistical analyses, we suggest the presence of magnetoacoustic waves in the solar atmosphere, some of which are propagating from the lower solar atmosphere upward, while some others are propagating downward. The transition region carries both long-period oscillations generated in situ and some photospheric oscillations that are also able to reach there from below.

Maximum open-set entropy optimization via uncertainty measure for universal domain adaptation

Universal Domain Adaptation (UniDA) is a technology that enables the intelligent model to transfer knowledge learned from labeled source domains to related but unlabeled target domains without any prior label set relationship. The key to UniDA lies in rejecting target domain-specific “unknown” samples to achieve domain alignment on shared classes. In this paper, we propose the Maximum Open-set Entropy Optimization via uncertainty measure to adaptively reject “unknown” samples. Specifically, MOEO sets a transition region within the most easily confused class in the open-set space. We optimize the maximum open-set entropy of simple samples outside the transition region to further improve their confidence and separate difficult samples within the transition region by aggregating similar neighbors. Accordingly, a secure boundary is formed between shared samples and “unknown” samples, promoting domain alignment within shared classes. Experiments on four benchmarks show that MOEO outperforms the previous state-of-the-art significantly.