Rapid Bursts of Magnetically Gated Accretion in the Intermediate Polar V1025 Cen

Magnetically gated accretion has emerged as a proposed mechanism for producing extremely short, repetitive bursts of accretion onto magnetized white dwarfs in intermediate polars (IPs), but this phenomenon has not been detected previously in a confirmed IP. We report the 27 day TESS light curve of V1025 Cen, an IP that shows a remarkable series of 12 bursts of accretion, each lasting for less than 6 hours. The extreme brevity of the bursts and their short recurrence times (∼1–3 days) are incompatible with the dwarf-nova instability, but they are natural consequences of the magnetic gating mechanism developed by Spruit and Taam to explain the Type II bursts of the accreting neutron star known as the Rapid Burster. In this model, the accretion flow piles up at the magnetospheric boundary and presses inward until it couples with the star’s magnetic field, producing an abrupt burst of accretion. After each burst, the reservoir of matter at the edge of the magnetosphere is replenished, leading to cyclical bursts of accretion. A pair of recent studies applied this instability to the suspected IPs MV Lyr and TW Pic, but the magnetic nature of these two systems has not been independently confirmed. In contrast, previous studies have unambiguously established the white dwarf in V1025 Cen to be significantly magnetized. The detection of magnetically gated bursts in a confirmed IP therefore validates the extension of the Spruit and Taam instability to magnetized white dwarfs.

Direct evidence that twisted flux tube emergence creates solar active regions

The magnetic nature of the formation of solar active regions lies at the heart of understanding solar activity and, in particular, solar eruptions. A widespread model, used in many theoretical studies, simulations and the interpretation of observations, is that the basic structure of an active region is created by the emergence of a large tube of pre-twisted magnetic field. Despite plausible reasons and the availability of various proxies suggesting the accuracy of this model, there has not yet been a methodology that can clearly and directly identify the emergence of large pre-twisted magnetic flux tubes. Here, we present a clear signature of the emergence of pre-twisted magnetic flux tubes by investigating a robust topological quantity, called magnetic winding, in solar observations. This quantity detects the emerging magnetic topology despite the significant deformation experienced by the emerging magnetic field. Magnetic winding complements existing measures, such as magnetic helicity, by providing distinct information about field line topology, thus allowing for the direct identification of emerging twisted magnetic flux tubes.

A new family of copper-based MXenes

In this work, we demonstrate, through first-principles calculations, the existence of a new family of copper-based MXenes. These add up new structures to the previously reported universe and span the interest of such 2D materials for applications in heterogeneous catalysis, ion-based batteries, sensors, biomedical applications, and so on. First, we propose the MXene-like structures: Cu2N, Cu2C, and Cu2O. Phonon spectra calculations confirmed their dynamical stability by showing just positive frequencies all through the 2D Brillouin zone. The new MXenes family displays metallic characteristics, mainly induced by the Cu-3d orbitals. Bader charge analysis and charge density differences depict bonds with ionic character in which Cu is positively charged, and the non-metal atom gets an anionic character. Also, we investigate the functionalization of the proposed structures with Cl, F, O, and OH groups. Results show that the H3 site is the most favorable for functionalization. In all cases, the non-magnetic nature and metallic properties of the pristine MXenes remain. Our results lay the foundations for the experimental realization of a new MXenes family.

Evaluation of microstructural, magnetic properties and surface/near-surface chemical state analysis of Mn-CuFe2O4 nanoparticle

Nanocrystalline Mn substituted CuFe2O4 nanoparticles (MCFNPs) were synthesized using urea and egg white. The effects of heat treatment on crystal structure and magnetic properties have been studied using X-ray diffractometer (XRD) and Vibrating Sample Magnetometer (VSM). The single-phase cubic spinel structure of as synthesized MCFNPs was recognized from XRD profile. There are some impurity peaks in the annealed samples, which are the decomposition of the ferrites at higher annealing temperatures to the α-Fe2O3 phase. The crystallite size and Lattice parameter of the samples increases with annealing temperature. The crystallite sizes of the MCFNPs were found in the range ~10 to 55 nm. The morphology and particle size of the sample (annealed at 900 ℃) have been recorded through SEM and TEM. The secondary non-magnetic impurity phase influences the magnetic nature of the samples. The saturation magnetization (Ms) decreases at a temperature of 600 ℃ due to the presence of non-magnetic α-Fe2O3 phase. The surface / near-surface chemical states of the 900 °C annealed MCFNPs were analyzed using XPS within a range of 0-1000eV binding energies.

Phase, Microstructural Characterization and Beneficiation of Iron Ore by Shaking Table

To know about the nature of gangue associated with the ores, characterization has become an integral part in mineral processing and beneficiation, therefore, the as-mined iron ore collected from Karak region of KP has been characterized for its phase, microstructure and chemical composition via XRD, SEM and EDS respectively. Beneficiation of the iron ore has been carried out by shaking table and magnetic separator. XRD analysis confirmed the presence of iron oxide (Fe203) as the major phase along with quartz (Si02) as the minor phase. Finely grinded iron ore powder of 100 (149 µm) and 200 (74 µm) mesh sizes were passed via shaking table and magnetic separator subsequently. The iron ore was successfully upgraded from 28.27 wt.% to 36.51 wt.% at 100 mesh and 38.70 wt.% at 200 mesh via shaking table, thus achieving a maximum of 10% upgraded iron ore. The magnetic separator did not become so effective due to non- magnetic nature of hematite.

Calculation for High Pressure Behaviour of Potential Solar Cell Materials Cu2FeSnS4 and Cu2MnSnS4

Exploring alternatives to the Cu2ZnSnS4 kesterite solar cell absorber, we have calculated first principle enthalpies of different plausible structural models (kesterite, stannite, P4¯ and GeSb type) for Cu2FeSnS4 and Cu2MnSnS4 to identify low and high pressure phases. Due to the magnetic nature of Fe and Mn atoms we included a ferromagnetic (FM) and anti-ferromagnetic (AM) phase for each structural model. For Cu2FeSnS4 we predict the following transitions: P4¯ (AM) →16.3GPa GeSb type (AM) →23.0GPa GeSb type (FM). At the first transition the electronic structure changes from semi-conducting to metallic and remains metallic throughout the second transition. For Cu2MnSnS4, we predict a direct AM (kesterite) to FM (GeSb-type) transitions at somewhat lower pressure (12.1 GPa). The GeSb-type structure also shows metallic behaviour.