Context. The Sun’s magnetic field exhibits the 11 year solar cycle as well as shorter periodicities, popularly known as the quasi-biennial oscillations (QBOs) and Rieger-type periods. Although several theories have been proposed to explain the origin of QBOs and Rieger-type periods, no single theory has had widespread acceptance. Aims. We explore whether the Babcock–Leighton dynamo can produce Rieger-type periodicity and QBOs and investigate their underlying physical mechanisms. Methods. We used the observationally guided 3D kinematic Babcock–Leighton dynamo model, which has emerged as a successful model for reproducing many characteristic features of the solar cycle. We used Morlet wavelet and global wavelet power spectrum techniques to analyze the data obtained from the model. Results. In our model, we report QBOs and Rieger-type periods for the first time. Further, we investigated the individual Babcock–Leighton parameters (fluctuations in flux, latitude, time delay, and tilt scatter) role in the occurrence of QBOs and Rieger-type periods. We find that while fluctuations in the individual parameters of the Babcock–Leighton process can produce QBOs and Rieger-type periodicity, their occurrence probability is enhanced when considering combined fluctuations of all parameters in the Babcock–Leighton process. Finally, we find that with the increase in dynamo supercriticality, the model tends to suppress the generation of Rieger-type periodicity. Thus, this result supports earlier studies that suggest the solar dynamo is not highly supercritical. Conclusions. The Babcock–Leighton dynamo model successfully reproduces QBOs and Rieger-type periodicities that are observed in various solar activity data.

In this article, we identify the magnetic reconnections at the hyperbolic flux tube (HFT), aided by slipping reconnection at quasi-separatrix layers (QSLs), which are pivotal to the occurrence of a confined M2.1 class flare in NOAA active region 12268. The magnetic field topology before the flare onset is obtained through a non-force-free field extrapolation scheme that accommodates a non-zero Lorentz force. A key aspect is the presence of an HFT in the computational domain above the flaring region, along with two QSLs at the lower boundary. To simulate the dynamics of the active region, we conduct a data-constrained magnetohydrodynamic (MHD) simulation initiated by the extrapolated field. The dynamics captured in the simulation document the formation of a current sheet within the HFT configuration, leading to magnetic reconnection at the HFT. Additionally, we observe the slipping motion of the footpoints of the magnetic field lines in the QSLs at the bottom boundary, which indicates the occurrence of slipping reconnection in the QSLs. Importantly, the magnetic reconnection at the HFT is suggested to be the primary driver in the development of the intricate flare brightenings and the flare ribbons.

Redshift and luminosity distributions are essential for understanding the cosmic evolution of extragalactic objects and phenomena, such as galaxies, gamma-ray bursts, and fast radio bursts (FRBs). For FRBs, these distributions are primarily estimated using the fluence and the dispersion measure (DM). Calibrating their joint distribution has been challenging due to a lack of accurate fluences in the intensity data of the CHIME/FRB survey. Using the baseband update of CHIME/FRB Catalog 1, we calibrate the 2D fluence-DM distribution for the first time. We find the energy distribution is described well by a Schechter function with a power-law slope of -1.94(-0.12)(+0.14) . Testing two types of redshift evolution models suggests a likely combination of young and old formation channels. 31(-21)(+31) % of FRB sources may track star formation, or correspondingly, FRB sources may have delay times of 1.94(-1.31)(+1.54) Gyr. A pure star formation tracking population is excluded by only one model at >2 sigma confidence. An updated cosmic star formation rate density evolution up to redshift 14 is constrained by compiling results from several JWST studies. The furthest FRB detection with planned radio facilities is expected to be at z approximate to 5. A radio telescope operating at 200 MHz with a system-equivalent flux density of <= 0.07 Jy (equivalent to a detection threshold of 1 mJy ms) and instantaneous sky coverage of greater than or similar to 400 deg2 should be able to detect 630(-485)(+730) FRBs yr(-1) at z greater than or similar to 6 and 53(-43)(+83) FRBs yr(-1) at z greater than or similar to 8, which is sufficient to differentiate between reionization histories.

Fast radio bursts (FRBs) are microsecond-to-millisecond-duration radio transients1 that originate mostly from extragalactic distances. The FRB emission mechanism remains debated, with two main competing classes of models: physical processes that occur within close proximity to a central engine2-4; and relativistic shocks that propagate out to large radial distances5-8. The expected emission-region sizes are notably different between these two types of models9. Here we present the measurement of two mutually coherent scintillation scales in the frequency spectrum of FRB 20221022A10: one originating from a scattering screen located within the Milky Way, and the second originating from its host galaxy or local environment. We use the scattering media as an astrophysical lens to constrain the size of the observed FRB lateral emission region9 to ≲3 × 104 kilometres. This emission size is inconsistent with the expectation for the large-radial-distance models5-8, and is more naturally explained by an emission process that operates within or just beyond the magnetosphere of a central compact object. Recently, FRB 20221022A was found to exhibit an S-shaped polarization angle swing10, most likely originating from a magnetospheric emission process. The scintillation results presented in this work independently support this conclusion, while highlighting scintillation as a useful tool in our understanding of FRB emission physics and progenitors.

Redshift and luminosity distributions are essential for understanding the cosmic evolution of extragalactic objects and phenomena, such as galaxies, gamma-ray bursts, and fast radio bursts (FRBs). For FRBs, these distributions are primarily estimated using the fluence and the Dispersion Measure (DM). Calibrating their joint distribution has been challenging due to a lack of accurate fluences in the intensity data of the CHIME/FRB survey. Using the baseband update of CHIME/FRB Catalog 1, we calibrate the 2D fluence-DM distribution for the first time. We find the energy distribution is described well by a Schechter function with power-law slope of $-1.94^{+0.14}_{-0.12}$. Testing two types of redshift evolution models suggests a likely combination of young and old formation channels. $31^{+31}_{-21}$\% of FRB sources may track star formation, or correspondingly, FRB sources may have delay times of $1.94^{+1.54}_{-1.31}$ Gyr. A pure star formation tracking population is excluded by only one model at $> 2\sigma$ confidence. An updated cosmic star formation rate density evolution up to redshift 14 is constrained by compiling results from several JWST studies. Using this information, we expect next-generation radio telescopes to detect a few dozen bursts per year at $z \gtrsim 6$. A radio telescope with a system-equivalent flux density of $\leq 1$ Jy (equivalent to a detection threshold of 14 mJy ms) and instantaneous sky coverage of $\gtrsim 200$ square degrees should be able to detect $1.4^{+1.6}_{-1.0}\times 10^3$ FRBs year$^{-1}$ at $z \gtrsim 6$ and $234^{+250}_{-162}$ FRBs year$^{-1}$ at $z\gtrsim 8$, which is sufficient to differentiate between reionization histories.

We propose different estimators to probe the intergalactic medium (IGM) during the epoch of reionization (EoR) using the dispersion measure (DM) of the fast radio bursts. We consider three different reionization histories, which we can distinguish with a total of ≲1000 DM measurements during EoR if their redshifts are known. We note that the redshift derivatives of DM are also directly sensitive to the reionization history. The major point of this work is to explore the variance in the DM measurements and the information encoded in them. We find that the all-sky average DM ¯ ( z ) gets biased from the line-of-sight fluctuations in the DM measurements introduced by the ionization of the IGM during EoR. We find that the ratio σ DM / DM ¯ depends directly on the ionization bubble sizes as well as the reionization history. On the other hand, we also find that angular variance (coined as structure function ) of DM encodes the information about the duration of reionization and the typical bubble sizes as well. We establish the usefulness of variances in DM using toy models of reionization and later verify it with the realistic reionization simulations.

In this paper, we present a magnetohydrodynamics simulation of NOAA active region 11166 to understand the origin of a confined X-class flare that peaked at 23:23 UT on 2011 March 9. The simulation is initiated with a magnetic field extrapolated from the corresponding photospheric magnetogram, using a non-force-free-field extrapolation technique. Importantly, the initial magnetic configuration identifies three-dimensional (3D) magnetic nulls and quasi-separatrix layers (QSLs), which nearly agree with the bright structures appeared in multi-wavelength observations. The Lorentz force associated with the extrapolated field self-consistently generates the dynamics that leads to the magnetic reconnections at the 3D nulls and the QSLs. These reconnections are found to contribute to the pre-flare activities and, ultimately, lead to the development of the flare ribbons. Notably, the anchored spine of the 3D null and the complete absence of flux rope in the flaring region are congruent with the confined nature of the flare. Furthermore, the simulation also suggests the role of reconnections at the 3D null with an open spine in the onset of a jet away from the flaring site.

We propose a scenario that can describe a broad range of fast radio burst (FRB) phenomenology, from nonrepeating bursts to highly prolific repeaters. Coherent radio waves in these bursts are produced in the polar cap region of a magnetar, where magnetic field lines are open. The angle between the rotation and magnetic axes, relative to the angular size of the polar cap region, partially determines the repetition rate and polarization properties of FRBs. We discuss how many of the properties of repeating FRBs—such as their lack of periodicity, energetics, small polarization angle (PA) swing, spectro–temporal correlation, and inferred low source density— are explained by this scenario. The systematic PA swing and the periodic modulation of long-duration bursts from nonrepeaters are also natural outcomes. We derive a lower limit of about 400 on the Lorentz factor of FRB sources applying this scenario to bursts with a linear polarization degree greater than 95%.

This paper investigates the average bit error rate (BER) of a reconfigurable intelligent surface (RIS)-assisted downlink non-orthogonal multiple access (NOMA) system under Nakagami-m fading. The base station communicates binary phase-shift keying (BPSK) data with the near and far users through an RIS unit enabled with discrete phase shifter elements. The total number of RIS elements is divided into two parts, each supporting an individual user. We use generalized-K and mixture gamma-based approximation to present an accurate analysis for an arbitrary number of RIS elements. We provide upper and lower bounds on the average BER for uniform quantized phase error. The bounds are applicable for 2-bit and higher-level quantization. Both bounds render a better approximation with an increase in the quantization level. Moreover, the lower bound is tighter than the upper bound and, specifically, for 3-bit and higher quantization levels, offers an accurate approximation with the simulation results. We also present the asymptotic average BER to simplify the analysis at high signal-to-noise ratios. Furthermore, we demonstrate some numerical results that may help design similar systems.

Dispersion measures (DM) of fast radio bursts (FRBs) probe the density of electrons in the intergalactic medium (IGM) along their lines-of-sight, including the average density versus distance to the source and its variations in direction. While previous study focused on low-redshift, FRBs are potentially detectable out to high redshift, where their DMs can, in principle, probe the epoch of reionization (EOR) and its patchiness. We present the first predictions from large-scale, radiation-hydrodynamical simulation of fully-coupled galaxy formation and reionization, using Cosmic Dawn (“CoDa") II to model the density and ionization fields of the universe down to redshifts through the end of the EOR at z_re≈6.1. Combining this with an N-body simulation CoDa II–Dark Matter of the fully-ionized epoch from the EOR to the present, we calculate the mean and standard deviation of FRB DMs as functions of their source redshift. The mean and standard deviation of DM increase with redshift, reaching a plateau by z(x_HII≲0.25)≳8, i.e. well above z_re. The mean-DM asymptote 𝒟ℳ_max≈ 5900 pc cm^-3 reflects the end of the EOR and its duration. The standard deviation there is σ_DM, max≈497 pc cm^-3, reflecting inhomogeneities of both patchy reionization and density. Inhomogeneities in ionization during the EOR contribute 𝒪(1 per cent) of this value of σ_DM,max from FRBs at redshifts z≳ 8. Current estimates of FRB rates suggest this may be detectable within a few years of observation.

In this study, various compositions of alpha-Fe2O3, Li3x Fe2-xO3, where x = 0.1, 0.3, and 0.5, along with chitosan (CTS)-coated Li1.5Fe1.5O3 nanomaterials (NMs), were synthesized using a sol-gel method. Rietveld refinement analysis indicated a predominance of the rhombohedral phase for lower Li-doped content (x = 0.1) and a transition to cubic crystal structures at higher Li-doped content (x = 0.3 and 0.5) within the host lattice. Field emission scanning electron microscopy (FE-SEM) images revealed irregular spherical morphologies, while transmission electron microscopy (TEM) images showed average particle sizes ranging from 19 to 40 nm across the various NMs. Superconducting quantum interference device (SQUID) analysis demonstrated a ferromagnetic nature with the highest saturation magnetization measured at 49.84 emu/g for Li1.5Fe1.5O3 NMs. X-ray photoelectron spectra (XPS) exhibited Fe 2p3/2 and Fe 2p1/2 peaks at 712.60 and 726.13 eV, respectively, Li 1s at 57.58 eV, and O 1s at 533.44 eV for the representative samples; these characteristic XPS peaks shifted to a lower binding energy for CTS-coated Li1.5Fe1.5O3 NMs. Hyperthermia studies demonstrated that the Li-doped samples reached a temperature range between 42 and 44 degrees C under an alternating current (AC) magnetic field applied at 167.6 to 335.2 Oe, with a constant frequency of 278 kHz. The specific absorption rate (SAR) was recorded as 265.11 W/g for Li1.5Fe1.5O3 and 153.48 W/g for CTS-coated Li1.5Fe1.5O3 NMs, both surpassing the SAR values of the other samples. Furthermore, various machine learning techniques were utilized to analyze how different synthesis conditions and material properties affected the heating efficiency and SAR values of the synthesized materials. The study also suggests an optimized set of guidelines and heuristics to enhance the heating performance and SAR values of these materials. Finally, magnetic CTS-coated Li1.5Fe1.5O3 NMs exhibited a higher cell viability, as confirmed by MTT assays conducted on the NRK 52 E normal cell line.

This paper reports the study of hydrothermally synthesized coconut charcoal (EDL material) and vanadium-oxide (pseudocapacitive material) based composite material. SEM and TEM studies reveal the formation of embedded V 2 O 5 nanorods (NRs) in the presence of activated charcoal (AC). Whereas, the formation of nanosheet (NSs) morphology of V 2 O 5 was explained based on Ostwald ripening. Embedded V 2 O 5 nanorods (NRs) in AC could be revealed in the form of the blurred dotted electron diffraction pattern of CS-AC/V 2 O 5 NRs, indicating the presence of crystalline and amorphous phases at a point simultaneously in the composite. The V - - O, O-V-O signatures observed in RAMAN and FTIR studies indicate the presence of the alpha phase of V 2 O 5 NSs and NRs. An enhanced diffusion coefficient for CS-AC/V 2 O 5 NRs compared to V 2 O 5 NSs was observed; a decreased total resistance for CS-AC/V 2 O 5 NRs compared to CS-AC was also noted. A characteristic of stable specific capacitance was observed at various current levels of this composite compared to the specific capacitances of coconut shellbased charcoal and vanadium oxide.

Observations find that some fast radio bursts (FRBs) have extremely narrowband spectra, i.e., Δ ν / ν _0 ≪ 1. We show that, when the angular size of the emission region is larger than the Doppler beaming angle, the observed spectral width (Δ ν / ν _0 ) exceeds 0.58 due to the high-latitude effects for a source outside the magnetosphere, even when the spectrum in the source’s comoving frame is monochromatic. The angular size of the source for magnetospheric models of FRBs can be smaller than the Doppler beaming angle, in which case this geometric effect does not influence the observed bandwidth. We discuss various propagation effects to determine if any could transform a broad-spectrum radio pulse into a narrow spectrum signal at the observer’s location. We find that plasma lensing and scintillation can result in a narrow bandwidth in the observed spectrum. However, the likelihood of these phenomena being responsible for the narrow observed spectra with Δ ν / ν _0 < 0.58 in the fairly large observed sample of FRBs is exceedingly small.

This study undertakes a comparative analysis of the structural, morphological, electrical, and magnetic characteristics of Fe-doped LaMnO3 ceramics.

In this article, we consider overlay space-air-ground integrated networks (OSAGINs) where a low earth orbit (LEO) satellite communicates with ground users (GUs) with the assistance of an energy-constrained coexisting air-to-air (A2A) network. Particularly, a non-linear energy harvester with a hybrid SWIPT utilizing both power-splitting and time-switching energy harvesting (EH) techniques is employed at the aerial transmitter. Specifically, we take the random locations of the satellite, ground and aerial receivers to investigate the outage performance of both the satellite-to-ground and aerial networks leveraging the stochastic tools. By taking into account the Shadowed-Rician fading for satellite link, the Nakagami-m for ground link, and the Rician fading for aerial link, we derive analytical expressions for the outage probability of these networks. For a comprehensive analysis of aerial network, we consider both the perfect and imperfect successive interference cancellation (SIC) scenarios. Through our analysis, we illustrate that, unlike linear EH, the implementation of non-linear EH provides accurate figures for any target rate, underscoring the significance of using non-linear EH models. Additionally, the influence of key parameters is emphasized, providing guidelines for the practical design of an energy-efficient as well as spectrum-efficient future non-terrestrial networks. Monte Carlo simulations validate the accuracy of our theoretical developments.

ABSTRACT Most fast radio burst (FRB) models can be divided into two groups based on the distance of the radio emission region from the central engine. The first group of models, the so-called ‘nearby’ or magnetospheric models, invoke FRB emission at distances of 109 cm or less from the central engine, while the second ‘far-away’ models involve emission from distances of 1011 cm or greater. The lateral size for the emission region for the former class of models (≲107 cm) is much smaller than the second class of models (≳109 cm). We propose that an interstellar scattering screen in the host galaxy is well-suited to differentiate between the two classes of models, particularly based on the level of modulations in the observed intensity with frequency, in the regime of strong diffractive scintillation. This is because the diffractive length scale for the host galaxy’s interstellar medium scattering screen is expected to lie between the transverse emission-region sizes for the ‘nearby’ and the ‘far-away’ class of models. Determining the strength of flux modulation caused by scintillation (scintillation modulation index) across the scintillation bandwidth (∼1/2πδts) would provide a strong constraint on the FRB radiation mechanism when the scatter broadening (δts) is shown to be from the FRB host galaxy. The scaling of the scintillation bandwidth as ∼ν4.4 may make it easier to determine the modulation index at ≳ 1 GHz.

Decay and dispersal of the tilted Bipolar Magnetic Regions (BMRs) on the solar surface are observed to produce large-scale poloidal field, which acts as the seed for the toroidal field and, thus, the next sunspot cycle. However, various properties of BMR, namely, the tilt, time delay between successive emergences, location, and flux, all have irregular variations. Previous studies show that these variations can lead to changes in the polar field. In this study, we first demonstrate that our 3D kinematic dynamo model, STABLE, reproduces the robust feature of the surface flux transport (SFT) model, namely the variation of the generated dipole moment with the latitude of the BMR position. Using STABLE in both SFT and dynamo modes, we perform simulations by varying the individual properties of BMR and keeping their distributions the same in all the cycles as inspired by the observations. We find that randomness due to the distribution in either the time delay or the BMR latitude produces negligible variation in the polar field and the solar cycle. However, randomness due to BMR flux distribution produces substantial effects, while the scatter in the tilt around Joy law produces the largest variation. Our comparative analyses suggest that the scatter of BMR tilt around Joy law is the major cause of variation in the solar cycle. Furthermore, our simulations also show that the magnetic field-dependent time delay of BMR emergence produces more realistic features of the magnetic cycle, consistent with observation.

We present the discovery of FRB 20210410D, with the MeerKAT radio interferometer in South Africa, as part of the MeerTRAP commensal project. FRB 20210410D has a dispersion measure DM = 578.78 +/- 2 pc cm-3, and was localised to sub-arcsec precision in the 2s images made from the correlation data products. The localisation enabled the association of the FRB with an optical galaxy at z = 0.1415, which when combined with the DM places it above the 3sigma scatter of the Macquart relation. We attribute the excess DM to the host galaxy after accounting for contributions from the Milky Way's interstellar medium and halo, and the combined effects of the intergalactic medium and intervening galaxies. This is the first FRB that is not associated with a dwarf galaxy, to exhibit a likely large host galaxy DM contribution. We do not detect any continuum radio emission at the FRB position or from the host galaxy down to a 3sigma RMS of 14.4 uJy/beam. The FRB has a scattering delay of 29.4 ms at 1 GHz, and exhibits candidate subpulses in the spectrum, which hint at the possibility of it being a repeating FRB. Although not constraining, we note that this FRB has not been seen to repeat in 7.28h at 1.3 GHz with MeerKAT, 3h at 2.4 GHz with Murriyang and 5.7h at simultaneous 2.3 GHz and 8.4 GHz observations with the Deep Space Network. We encourage further follow-up to establish a possible repeating nature.

Although the observed spectra for gamma-ray burst (GRB) prompt emission is well constrained, the underlying radiation mechanism is still not very well understood. We explore photospheric emission in GRB jets by modelling the Comptonization of fast cooled synchrotron photons whilst the electrons and protons are accelerated to highly relativistic energies by repeated energy dissipation events as well as Coulomb collisions. In contrast to the previous simulations, we implement realistic photon-to-particle number ratios of $N_{\gamma}/N_e \sim 10^{5}$ or higher, that are consistent with the observed radiation efficiency of relativistic jets. Using our Monte Carlo radiation transfer (MCRaT) code, we can successfully model the prompt emission spectra when the electrons are momentarily accelerated to highly relativistic energies (Lorentz factor $\sim 50-100$) after getting powered by $\sim30-50$ episodic dissipation events in addition to their Coulomb coupling with the jet protons, and for baryonic outflows that originate from moderate optical depths $\sim20-30$. We also show that the resultant shape of the photon spectrum is practically independent of the initial photon energy distribution and the jet baryonic energy content, and hence independent of the emission mechanism.