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Numerical simulations have consistently shown that the reconnection rate in certain collisionless regimes can be fast, of the order of $0.1v_{A}B_{u}$ , where $v_{A}$ and $B_{u}$ are the Alfvén speed and the reconnecting magnetic field upstream of the ion diffusion region. This particular value has been reported in myriad numerical simulations under disparate conditions. However, despite decades of research, the reasons underpinning this specific value remain mysterious. Here, we present an overview of this problem and discuss the conditions under which the ‘0.1 value’ is attained. Furthermore, we explain why this problem should be interpreted in terms of the ion diffusion region length.

The linear collisionless plasma response to a zonal-density perturbation in quasisymmetric stellarators is studied, including the geodesic-acoustic-mode oscillations and the Rosenbluth–Hinton residual flow. While the geodesic-acoustic-mode oscillations in quasiaxisymmetric configurations are similar to tokamaks, they become non-existent in quasi-helically symmetric configurations when the effective safety factor in helical-angle coordinates is small. Compared with concentric-circular tokamaks, the Rosenbluth–Hinton residual is also found to be multiplied by a geometric factor $\\mathcal {C}$ that arises from the flux-surface-averaged classical polarization. Using the near-axis-expansion framework, we derive an analytic expression for $\\mathcal {C}$, which varies significantly among different configurations. These analytic results are compared with numerical simulation results from the global gyrokinetic particle-in-cell code GTC, and good agreement with the theoretical Rosenbluth–Hinton residual level is achieved when the quasisymmetry error is small enough.

The paper describes the physical characterization of CdS nanoparticles, green synthesized using Termitomyces heimii mushroom extract. The CdS samples obtained are wurtzite type. The amount of extract used for synthesis affects the particle size. FT-IR spectra confirmed the presence of proteins as well as the formation of CdS. A blue shift of the absorption maximum based on particle size was observed in the UV–Vis spectra. The size of the nanocrystallites estimated from the XRD and UV–Vis studies were in 3–5 nm range which is in conformity with the results obtained from the SEM and TEM studies. Electronic polarizability of the CdS samples has been estimated. The study presents a simple, cost effective and eco-friendly method of CdS nanoparticle (size < 5 nm) synthesis suitable for large scale production.

Quasisymmetric stellarators are an attractive class of optimised magnetic confinement configurations. The property of quasisymmetry (QS) is in practice limited to be approximate, and thus the construction requires measures that quantify the deviation from the exact property. In this paper we study three measure candidates used in the literature, placing the focus on their origin and a comparison of their forms. The analysis shows clearly the lack of universality in these measures. As these metrics do not directly correspond to any physical property (except when exactly quasisymmetric), optimisation should employ additional physical metrics for guidance. It is suggested that close to QS minima, one should treat QS metrics through inequality constraints so that additional physics metrics dominate optimisation. The impact of different quasisymmetric measures on optimisation is presented through an example, for which the standard metric that weights the asymmetric Fourier modes of the field magnitude appears to perform best.

▪ Abstract  Impulsive reconnection dynamics is characterized not only by fast growth but also by a sudden change in the time derivative of the growth rate. I review recent developments in the theory and simulation of forced impulsive reconnection based on the equations of resistive and Hall magnetohydrodynamics (MHD). Impulsive reconnection can be realized in resistive as well as Hall MHD by the imposition of suitable boundary conditions. However, compared with resistive MHD, Hall MHD reconnection is distinguished by qualitatively different magnetic field and electron and ion signatures in the reconnection layer. Furthermore, nonlinear reconnection rates in Hall MHD are weakly dependent on the Lundquist number. I discuss applications of the physics of impulsive reconnection to substorms in the Earth's magnetotail and solar flares.

The present research focuses on proposing a novel theoretical micromechanical model (TMM) designed to derive the frequency-dependent storage and loss moduli of woven fabric (WF)-matrix composites, as well as WF-particulate matrix (Hybrid) composites, based on their constituent properties. The TMM serves as a higher-order modulus operator, accounting for the composite woven fabric unit cell geometry and the effective modulus of both the fabric and matrix using equivalent modulus theory. This model also incorporates viscoelastic parameters obtained from literature and experiments for each constituent, namely woven glass fabric and SiC particles embedded in an epoxy matrix. The proposed TMM is validated by comparing its predictions of the frequency-dependent storage modulus and loss factor with experimental data acquired through dynamic mechanical analyzer tests on samples with varying fiber and particulate volume fractions. To address the inherent complexities of the higher-order modulus operator, the model is streamlined into a lower-order form expressed as a function of two separate variables: volume fraction and a differential time operator. This advancement enhances the applicability and usability of the model for predicting the mechanical behaviour of these complex composite materials. This novel mathematical model eliminates the cost and time for conducting the explicit experiments as well as can be applied to different range of similar hybrid composites considering the fact that the constituent properties are known.

A novel large-scale dynamo mechanism, the magnetic shear-current effect, is discussed and explored. The effect relies on the interaction of magnetic fluctuations with a mean shear flow, meaning the saturated state of the small-scale dynamo can drive a large-scale dynamo – in some sense the inverse of dynamo quenching. The dynamo is non-helical, with the mean field ${\\it\\alpha}$ coefficient zero, and is caused by the interaction between an off-diagonal component of the turbulent resistivity and the stretching of the large-scale field by shear flow. Following up on previous numerical and analytic work, this paper presents further details of the numerical evidence for the effect, as well as an heuristic description of how magnetic fluctuations can interact with shear flow to produce the required electromotive force. The pressure response of the fluid is fundamental to this mechanism, which helps explain why the magnetic effect is stronger than its kinematic cousin, and the basic idea is related to the well-known lack of turbulent resistivity quenching by magnetic fluctuations. As well as being interesting for its applications to general high Reynolds number astrophysical turbulence, where strong small-scale magnetic fluctuations are expected to be prevalent, the magnetic shear-current effect is a likely candidate for large-scale dynamo in the unstratified regions of ionized accretion disks. Evidence for this is discussed, as well as future research directions and the challenges involved with understanding details of the effect in astrophysically relevant regimes.

Alfvén wave collisions are the primary building blocks of the non-relativistic turbulence that permeates the heliosphere and low- to moderate-energy astrophysical systems. However, many astrophysical systems such as gamma-ray bursts, pulsar and magnetar magnetospheres and active galactic nuclei have relativistic flows or energy densities. To better understand these high-energy systems, we derive reduced relativistic magnetohydrodynamics equations and employ them to examine weak Alfvénic turbulence, dominated by three-wave interactions, in reduced relativistic magnetohydrodynamics, including the force-free, infinitely magnetized limit. We compare both numerical and analytical solutions to demonstrate that many of the findings from non-relativistic weak turbulence are retained in relativistic systems. But, an important distinction in the relativistic limit is the inapplicability of a formally incompressible limit, i.e. there exists finite coupling to the compressible fast mode regardless of the strength of the magnetic field. Since fast modes can propagate across field lines, this mechanism provides a route for energy to escape strongly magnetized systems, e.g. magnetar magnetospheres. However, we find that the fast-Alfvén coupling is diminished in the limit of oblique propagation.

We explore the solventless synthesis of iron oxide nanomaterials obtained on thermal conversion of iron(III)citrate in presence of malonic acid and glucose as co-precursors in varying weight ratios and physical characterization of the materials obtained. Pure phase of hematite was found only for a particular combination of precursor and co-precursor and else a mixture of hematite and magnetite. Significant effect of the co-precursors on the nature and size of the synthesized materials was noticed. Gradual conversion of hematite to magnetite with increasing amount of co-precursor was established. Morin transition was observed in the temperature dependent magnetization study for the hematite materials. Absorption spectroscopy exhibited three different electronic transitions that take place within the 3d 5 shell of the octahedrally coordinated Fe 3+ ions for hematite materials. The optical (direct and indirect) band gaps estimated from the Tauc’s plot showed particle size dependence. From photoluminescence study the transitions of trapped electrons in various defect states of oxygen vacancies were observed which led to the appearance of nonradiative peaks. In the Raman spectra the significant bands of hematite (A 1g and E g bands) were noted. From morphology study the hematite nanomaterials appear as clusters of large irregular shaped particles of various sizes. Formation of hematite nanomaterials as observed by XRD studies was supplemented by the SAED patterns obtained in the HRTEM study. Present study established that nano-sized pure hematite materials can be thermally synthesized at comparatively lower temperature on thermal decomposition of iron(III)citrate by varying the weight ratio of suitable co-precursors.

Background Type 2 diabetes (T2DM) is the leading cause of chronic kidney disease (CKD) worldwide. Identifying clinical and laboratory associations with chronic kidney disease (CKD) in type 2 diabetes (T2DM) can help physicians target modifiable risk factors. In light of limited data from India, the CITE (CKD in Indian T2DM Evaluation) study was conducted. Methods The multicenter, cross-sectional CITE study included 3,325 patients from 28 centres across India over a three-month period. CKD was defined as a persistent decline in kidney function (eGFR < 60 ml/min/1.73 m² for ≥ 3 months) or an elevated urine albumin-to-creatinine ratio (UACR) in at least two samples. Descriptive statistics summarised patient characteristics, while logistic regression analyses identified significant risk factors for CKD. Results The prevalence of CKD in T2DM was 32%, with a median patient age of 59.9 years and 60.72% having a T2DM duration > 10 years. Reduced eGFR (< 60 ml/min/1.73 m²) was associated with older age (OR: 2.47, 95% CI 2.11–2.88, P  < 0.001), longer T2DM duration (OR: 2.28, 95% CI 1.77–2.93, P  < 0.001), higher HbA1c (OR: 1.039, 95% CI 1.001–1.079, P  = 0.046), and elevated SBP (OR: 1.005, 95% CI 1.002–1.009, P  = 0.003). Macroalbuminuria (UACR > 300 mg/g) was linked to non-vegetarian diet (OR: 1.95, 95% CI: 1.59–2.40, P  < 0.001) and tobacco use (OR: 1.42, 95% CI: 1.17–1.73, P  < 0.001). CKD increased comorbidity odds. Conclusion The CITE study highlights the prevalence of CKD (32%) in Indian patients with T2DM and identifies clinical and laboratory factors associated with CKD, including age ≥ 60 years, T2DM duration, SBP, HbA1c, tobacco use, non-vegetarian diet, and comorbidities. Longitudinal studies are needed to confirm these associations and evaluate causality.