bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of Coulomb interactions on acoustic oscillations in the outer layers of low-mass stars
Authors: Brito Ana , Lopes Fuentes Ilídio 
Published: December 2024

AbstractAs is well known, low-mass stars constitute the most abundant class of stars in our galaxy. In stars less massive than the Sun, the density within stellar interiors increases as the stellar mass decreases. Therefore, for low-mass stars, the significance of electrostatic effects in stellar interiors cannot be neglected, as these interactions can alter the properties of matter.In our study, we focus on exploring the outer layers of stars less massive than the Sun. We have computed a range of stellar models, ranging from 0.4 to 0.9 solar masses, to investigate the effects of two physical processes on the acoustic oscillations in the envelopes of these stars: partial ionization of chemical elements and electrostatic interactions between particles in the outer layers. In addition to partial ionization, we demonstrate that Coulomb effects also influence the acoustic oscillation spectrum. Our investigation reveals the following findings:1. Coulomb effects can indeed influence the acoustic oscillations in low-mass stars.2. The model with a mass of inline1 serves as a transition point. For models less massive than inline1, their acoustic spectrum is more affected by electrostatic interactions, whereas models more massive than inline1 have their acoustic spectrum more impacted by partial ionization processes.Our work unveils the promising possibilities that future discoveries related to the detection of solar-like oscillations in stars less massive than the Sun could offer in terms of understanding the connections between the internal structure of low-mass stars and their observable characteristics.
Chromosphere activity: relations with Solar cycles (SC)
Authors: Koutchmy S. , Tavabi E. 
Published: December 2024

AbstractThe study’s focus on the modulation of geomagnetism by low latitude solar magnetically activity, including coronal mass ejections (CMEs), solar flares, and solar energetic particles (SEPs). It mentions the Babcock–Leighton (B-L) dynamo model used to predict sunspot numbers in Solar Cycle 25 (SC25) and highlights the challenges in understanding aspects such as the regeneration of the poloidal field and the occurrence of magnetic regions, active longitudes, and coronal holes. The abstract introduces the study’s concentration on the activity of polar regions using chromosphere jets activity proxies and other parameters like polar faculae density and cool ejection events. It also mentions the observation of chromospheric prolateness during the minimum solar activity periods.
Near-surface shear layer of solar rotation: origin and significance
Authors: Kitchatinov Leonid L. 
Published: December 2024

AbstractHelioseismology has discovered a thin layer beneath the solar surface where the rotation rate increases rapidly with depth. The normalized rotational shear in the upper 10 Mm of the layer is constant with latitude. Differential rotation theory explains such a rotational state by a radial-type anisotropy of the near-surface convection and a short correlation time of convective turbulence compared to the rotation period. The shear layer is the main driver of the global meridional circulation.
The near-surface shear layer (NSSL) of the Sun: a theoretical model
Authors: Choudhuri Arnab Rai , Jha Bibhuti Kumar 
Published: December 2024

AbstractWe present a theoretical model of the near-surface shear layer (NSSL) of the Sun. Convection cells deeper down are affected by the Sun’s rotation, but this is not the case in a layer just below the solar surface due to the smallness of the convection cells there. Based on this idea, we show that the thermal wind balance equation (the basic equation in the theory of the meridional circulation which holds inside the convection zone) can be solved to obtain the structure of the NSSL, matching observational data remarkably well.
Recent Developments in the Babcock–Leighton Solar Dynamo Theory
Authors: Karak Bidya Binay 
Published: December 2024

AbstractBabcock–Leighton process, in which the poloidal field is generated through the decay and dispersal of tilted bipolar magnetic regions (BMRs), is observed to be the major process behind the generating poloidal field in the Sun. Based on this process, the Babcock–Leighton dynamo models have been a promising tool for explaining various aspects of solar and stellar magnetic cycles. In recent years, in the toroidal to poloidal part of this dynamo loop, various nonlinear mechanisms, namely the flux loss through the magnetic buoyancy in the formation of BMRs, latitude quenching, tilt quenching, and inflows around BMRs, have been identified. While these nonlinearities tend to produce a stable magnetic cycle, the irregular properties of BMR, mainly the scatter around Joy’s law tilt, make a considerable variation in the solar cycle, including grand minima and maxima. After reviewing recent developments in these topics, I end the presentation by discussing the recent progress in making the early prediction of the solar cycle.
Modelling the rotation dependence of cycle variability in sun-like stars: Answering why only slowly rotating stars produce grand minima
Authors: Vashishth Vindya 
Published: December 2024

AbstractThe Sun and solar-type stars exhibit irregular cyclic variations in their magnetic activity over long time scales. To understand this irregularity, we employed the flux transport dynamo models to investigate the behavior of one solar mass star at various rotation rates. To achieve this, we have utilized a mean-field hydrodynamic model to specify differential rotation and meridional circulation, and we have incorporated stochastic fluctuations in the Babcock–Leighton source of the poloidal field to capture inherent fluctuations in the stellar convection. Our simulations successfully demonstrated consistency with the observational data, revealing that rapidly rotating stars exhibit highly irregular cycles with strong magnetic fields and no Maunder-like grand minima. On the other hand, slow rotators produce smoother cycles with weaker magnetic fields, long-term amplitude modulation, and occasional extended grand minima. We observed that the frequency and duration of grand minima increase with the decreasing rotation rate. These results can be understood as the tendency of a less supercritical dynamo in slow rotators to be more prone to produce extended grand minima. We further explore the possible existence of the dynamo in the subcritical regime in a Babcock–Leighton-type framework and in the presence of a small-scale dynamo.
Large-scale electric currents in processes in the solar atmosphere
Authors: Fursyak Yu. A. , Abramenko V. I. , Kutsenko A. S. , Plotnikov A. A. 
Published: December 2024

AbstractIn the late 80s of the 20th century, Crimean astronomers, studying the structure of transverse magnetic fields in active regions (ARs), discovered signs of the presence of large-scale vertical electric currents – global electric currents (Abramenko, Gopasyuk 1987). In 2018–2020, we finalized and adapted the method for detecting large-scale electric currents to the data of modern instruments for studying the Sun, and began studying their dynamics on time scales of 3–5 days (Fursyak et. al 2020). Our researches carried out during 2020–2023 showed that: 1) Large-scale electric currents with values of the order of ~ 1013 A exist in ARs with nonzero flare activity. 2) Large-scale electric currents extend to the upper layers of the solar atmosphere in one part of the AR, and close through the chromosphere and corona in the remaining part of the AR. This assumption for the AR NOAA 12192 is confirmed by the results of numerical simulations performed in 2016 (Jiang et al. 2016). 3) The greater the magnitude of the large-scale electric current, the higher the probability of occurrence of M- and X- class solar flares in the AR. 4) At the final stages of AR evolution, a nonzero large-scale electric current can have a stabilizing effect on the sunspot, preventing its decay by its own magnetic field. 5) Large-scale electric currents are involved in coronal heating processes. Ohmic dissipation of a large-scale electric current is one of the mechanisms of quasi-stationary heating of coronal plasma above the AR. Our research on large-scale electric currents and the processes in which they take part continues.
Prognostic opportunity of the shifted correlation between Wolf numbers and their time derivatives
Authors: Starchenko S. V. , Yakovleva S. V. 
Published: December 2024

AbstractWe correlate the annual Wolf numbers W and their time derivatives Wʹ by shifting time fragments of W and Wʹ relative to each other. The most significant (up to 0.874) correlation is with 3 years shifts for fragments covering 14 years. For longer and shorter periods, the correlation coefficients 0.771–0.855 with 2–3 years shift. The most significant 9 years shift corresponds to -0.852/-0.824 anti-correlation coefficient for 14/11 years period. The other periods are less significant. To evaluate predictive estimates, we use the times series fragments of W shifted back into the past. A forecast can be made using the leading graphs based upon the derived calibration factor. Test calculations show that the most effective is the calibration factor calculated for changing the phase of the cycle. The best linear pairwise correlation coefficient of the approximation is 0.94.
On origin of active/inactive branches on moderate rotating solar analogs
Authors: Pipin Valery V. 
Published: December 2024

AbstractThe fast rotating solar analogs show a decrease of the dynamo period with an increase of the rotation rate for the moderate stellar rotation periods in the range between 10 and 25 days. Simultaneously, observations indicate two branches: the “in-active” branch stars shows short dynamo cycles and the active branch stars show the relatively long magnetic cycles. We suggest that this phenomenon can be produced by effect of the doubling frequency of the dynamo waves, which is due to excitation of the second harmonic. It is generated because of the nonlinear B2 effects in the large-scale dynamo.
Modeling line-of-sight magnetograms of emerging active regions
Authors: Poisson M. , López–Fuentes M , Mandrini C. H. , Grings F. , Démoulin P. 
Published: December 2024

AbstractActive regions (ARs) appear in the solar atmosphere as a consequence of the emergence of magnetic flux ropes (FRs). Due to the presence of twist, the photospheric line-of-sight (LOS) magnetograms of emerging ARs show an elongation of the polarities known as magnetic tongues. These tongues can affect the estimation of tilt angles during their emergence phase. In this work, we propose a Bayesian method to model LOS magnetograms of emerging ARs using a half-torus twisted FR model. We apply this model to 21 emerging ARs observed during Solar Cycle 23. We find that the Bayesian method corrects the tilt when compared to other methods, removing the spurious rotation of the polarities produced by the retraction of the tongues during the emergence. We find a variation in Joy’s law with the stage of the AR emergence and the method used for its estimation.
Detecting coronal mass ejections with machine learning methods
Authors: Vida K. , Seli B. , Szklenár T. , Kriskovics L. , Görgei A. , Kövári Zs. 
Published: December 2024

AbstractFlares on the Sun are often associated with ejected plasma: these events are known as coronal mass ejections (CMEs). These events, although are studied in detail on the Sun, have only a few dozen known examples on other stars, mainly detected using the Doppler-shifted absorption/emission features in Balmer lines and tedious manual analysis. We present a possibility to find stellar CMEs with the help of high-resolution solar spectra.
Recent Progress in Time–Distance Helioseismology: Meridional Circulation, Far-side Imaging, and Sunquakes
Authors: Chen Ruizhu , Zhao Junwei 
Published: December 2024

AbstractTime–distance helioseismology uses solar surface Doppler observations to measure areas that are not directly observable, such as solar interior, far side, and sunquake sources. In this work, we briefly review recent advancements in time–distance helioseismology, focusing on meridional circulation measurements, far-side imaging, and sunquakes. Solar deep meridional flows are crucial for understanding the dynamics of the solar interior, but precise measurements of these flows are challenging. This review explores recent developments in this area, particularly highlighting new findings related to systematic effects that have long challenged meridional circulation determination. We also review recent progress in solar far-side imaging, which is useful in improving space weather forecasting. Recent developments in far-side imaging using time–distance techniques and Deep Learning are introduced. Additionally, we review a new approach in sunquake reconstruction by incorporating observation-based Green’s functions constructed by time–distance helioseismology.
Stellar activity in open clusters
Authors: Görgei A. , Vida K. , Seli B. , Kriskovics L. 
Published: December 2024

AbstractStellar activity depends on multiple parameters one of which is the age of the star. The members of open clusters are good targets to observe the activity at a given age of the stars since their ages are more precisely determined than that of field stars. Choosing multiple clusters, each with different age, gives us insight to the change in activity during the lifetime of stars. With the analysis of these stars we can also refine the parameters of gyrochronology (Barnes 2003), which is a method for estimating the age of low-mass, main sequence stars from their rotation periods.
Flux emergence simulation and coronal response at ephemeral region scale
Authors: Wang Zi–Fan , Cameron R. H. 
Published: December 2024

AbstractFlux emergence at different spatial scales and with different amounts of flux has been studied using radiative magnetohydrodynamics (rMHD) simulations. We use the radiative MHD code MURaM to simulate the emergence of an untwisted magnetic flux tube of ephemeral region scale with a density nonuniformity into a background atmosphere with a small unipolar open field. We find that the tube rises to the photosphere, forming complex loop structures seen in synthetic Atmospheric Imaging Assembly(AIA) 171 Å images. The atmosphere reaches 105K at 3Mm above the surface. Our simulation provides a reference example of a less twisted ephemeral region emergence and the atmospheric response.
Predicting the Emergence of Solar Active Regions Using Machine Learning
Authors: Kasapis Spiridon , Kitiashvili Irina N. , Kosovichev Alexander G. , Stefan John T. , Apte Bhairavi 
Published: December 2024

AbstractTo create early warning capabilities for upcoming Space Weather disturbances, we have selected a dataset of 61 emerging active regions, which allows us to identify characteristic features in the evolution of acoustic power density to predict continuum intensity emergence. For our study, we have utilized Doppler shift and continuum intensity observations from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The local tracking of 30.66 × 30.66-degree patches in the vicinity of active regions allowed us to trace the evolution of active regions starting from the pre-emergence state. We have developed a machine learning model to capture the acoustic power flux density variations associated with upcoming magnetic flux emergence. The trained Long Short-Term Memory (LSTM) model is able to predict 5 hours ahead whether, in a given area of the solar surface, continuum intensity values will decrease. The performed study allows us to investigate the potential of the machine learning approach to predict the emergence of active regions using acoustic power maps as input.
Observational Study of Reynolds Stresses Associated with Solar Inertial Modes
Authors: Mandowara Yash , Bekki Yuto , Bogart Richard S. , Gizon Laurent 
Published: December 2024

AbstractWe study the m = 1 high-latitude inertial mode and its contribution to the latitudinal transport of the Sun’s angular momentum. Ring-diagram helioseismology applied to 5° tiles is used to obtain the horizontal flows near the surface of the Sun. Using 10 years of data from SDO/HMI, we report on the horizontal eigenfunction and Reynolds stress
$\[{Q_{\theta \phi }} = \langle {u&#x0027;_\theta }{u&#x0027;_\phi }\rangle \]$
for the m = 1 high-latitude inertial mode (frequency –86.3 nHz, critical latitudes ±58°). We find that Qθφ takes significant values above the critical latitude and is positive (negative) in the northern (southern) hemisphere, implying equatorward transport of angular momentum. The Qθφ peaks above latitude 70° with a value of 38 m2/s2.
Probing the superadiabaticity of the solar convection zone with inertial modes
Authors: Dey Prithwitosh , Bekki Yuto , Gizon Laurent 
Published: December 2024

AbstractOur understanding of solar convection is incomplete. A crucial gap is the unknown superadiabaticity in the solar convection zone, δ = ▽–▽ad. Global modes of oscillations in the inertial frequency range are sensitive to δ and serve as a novel tool to explore solar convection. Here, we address the forward problem where the superadiabaticity δ(r) varies with radius. We solve the 2.5D eigenvalue problem, considering the linearized equations for momentum, mass and energy conservation with respect to a realistic solar model. We find that the frequency and eigenfunction of the m = 1 high-latitude mode are influenced by δ in the lower convection zone. Our prescribed setup suggests that the superadiabaticity in the lower half of the convection zone is below 2.4×10-7 to reach a qualitative agreement with the observed eigenfunction.
Solar Inertial Modes
Authors: Gizon Laurent , Bekki Yuto , Birch Aaron C. , Cameron Robert H. , Fournier Damien , Philidet Jordan , Lekshmi B. , Liang Zhi–Chao 
Published: December 2024

AbstractThe Sun’s global inertial modes are very sensitive to the solar differential rotation and to properties of the deep solar convection zone which are currently poorly constrained. These properties include the superadiabatic temperature gradient, the latitudinal entropy gradient, and the turbulent viscosity. The inertial modes also play a key role in controlling the Sun’s large-scale structure and dynamics, in particular the solar differential rotation. This paper summarizes recent observations and advances in the (linear and nonlinear) modeling of the solar inertial modes.
Bit efficiency of distributed- and collocated-massive MIMO base station systems in OTA measurement and simulation
Authors: Kaneko Tomoya , Kuwabara Toshihide , Tawa Noriaki , Maruta Yasushi 
Published: December 2024

Abstract
This paper presents the bit efficiency of 28 GHz digital beamforming in over-the-air (OTA) measurements and simulations for distributed massive multiple-input–multiple-output (D-MIMO) and collocated massive multiple-input–multiple-output (C-MIMO) systems, as well as simulations for a 3.75 GHz small-cell scenario. Under the condition that users are randomly located in the line of sight coverage indoor area and spatially selected from each other by the normalized zero-forcing method, the OTA measured D-MIMO system exhibits an average of 4–7 dB better signal-to-noise ratio compared to C-MIMO when the number of simultaneously connected users “K” approaches the number of transceivers “M.” This means that the D-MIMO system provides higher bit efficiency than the C-MIMO system when K/M is large. Furthermore, the D-MIMO 3.75 GHz simulation predicts a relatively approximate 30% higher maximum efficiency than C-MIMO due to the shorter average distances between user equipment and access points in the D-MIMO system. To the best of the author’s knowledge, an earlier version of this paper has been presented at the 53rd European Microwave Conference as a first report on the 28 GHz OTA measured bit efficiency between C-MIMO and D-MIMO, highlighting D-MIMO’s advantage.
Design of polarization reconfigurable Koch fractal antenna for S-and C-band applications
Authors: Patel Khushbu , Behera Santanu Kumar 
Published: December 2024

Abstract
In this research, a novel polarization reconfigurable fractal antenna with high gain is proposed for wideband applications. This antenna consists of a Koch curve based hexagonal ring patch, two Positive-Intrinsic-Negative (PIN) diodes, and partial ground. The patch is positioned on a Rogers RT/Duroid 5880 substrate (ϵr = 2.2) with overall dimensions 33 × 30 × 1.6 mm3. It has three frequency bands with three different cases i.e., case I, 3–7.91 (90%); case II, 3–7.73 (88.16%); and case III, 3.54–6.7 GHz (61.7%). As a result, the proposed antenna’s impedance bandwidth (IBW) offers constant wideband coverage ranging from 3–7.91 GHz (90%). The axial ratio bandwidth (ARBW) is below 3 dB over 3.6–6.9 (62.86%) and 3.33–7.14 GHz (72.78%) for LHCP (Case I) and RHCP modes (Case II), respectively. The value for LP mode (Case III) is 3.54–6.7 GHz (61.7%). A peak realized gains of 4.75, 5.07, and 3.8 dBi are achieved at 6.2, 6.3, and 6 GHz for Case I, Case II, and Case III, respectively. Both linear and circular polarization prototype was developed and the performance was verified through measurements. The design confirms good polarization-reconfigurable characteristics within the band of 3.91 – 7.91 GHz.
Social disconnectedness, subsequent medical conditions, and, the role of pre-existing mental disorders: a population-based cohort study
Authors: Laustsen L. M. , Lasgaard M. , Momen N. C. , Chen D. , Gradus J. L. , Grønkjær M. S. , Jensen M. M. , Plana-Ripoll O. 
Published: December 2024

Abstract

Aims
Individuals with diminished social connections are at higher risk of mental disorders, dementia, circulatory conditions and musculoskeletal conditions. However, evidence is limited by a disease-specific focus and no systematic examination of sex differences or the role of pre-existing mental disorders.

Methods
We conducted a cohort study using data on social disconnectedness (loneliness, social isolation, low social support and a composite measure) from the 2013 and 2017 Danish National Health Survey linked with register data on 11 broad categories of medical conditions through 2021. Poisson regression was applied to estimate incidence rate ratios (IRRs), incidence rate differences (IRDs), and explore sex differences and interaction with pre-existing mental disorders.

Results
Among 162,497 survey participants, 7.6%, 3.5% and 14.8% were classified as lonely, socially isolated and with low social support, respectively. Individuals who were lonely and with low social support had a higher incidence rate in all 11 categories of medical conditions (interquartile range [IQR] of IRRs, respectively 1.26–1.49 and 1.10–1.14), whereas this was the case in nine categories among individuals who were socially isolated (IQR of IRRs, 1.01–1.31). Applying the composite measure, the highest IRR was 2.63 for a mental disorder (95% confidence interval [CI], 2.38–2.91), corresponding to an IRD of 54 (95% CI, 47–61) cases per 10,000 person-years. We found sex and age differences in some relative and absolute estimates, but no substantial deviations from additive interaction with pre-existing mental disorders.

Conclusions
This study advances our knowledge of the risk of medical conditions faced by individuals who are socially disconnected. In addition to the existing evidence, we found higher incidence rates for a broad range of medical condition categories. Contrary to previous evidence, our findings suggest that loneliness is a stronger determinant for subsequent medical conditions than social isolation and low social support.
A preregistered analysis plan and statistical code are available at Open Science Framework (https://osf.io/pycrq).