We use three-dimensional magnetohydrodynamical (MHD) simulations to study the formation of a corona above an initially weakly magnetized, isothermal accretion disk. The simulations are local in the plane of the disk, but extend up to 5 vertical scaleheights above and below it. We describe a modification to time-explicit numerical algorithms for MHD which enables us to evolve such highly stratified disks for many orbital times. We find that for initially toroidal fields, or poloidal fields with a vanishing mean, MHD turbulence driven by the magnetorotational instability (MRI) produces strong amplification of weak fields within two scale heights of the disk midplane in a few orbital times. Although the primary saturation mechanism of the MRI is local dissipation, about 25% of the magnetic energy generated by the MRI within two scale heights escapes due to buoyancy, producing a strongly magnetized corona above the disk. Most of the buoyantly rising magnetic energy is dissipated between 3 and 5 scale heights, suggesting the corona will also be hot. Strong shocks with Mach numbers ∼ > 2 are continuously produced in the corona in response to mass motions deeper in the disk. Only a very weak mass outflow is produced through the outer boundary at 5 scale heights, although this is probably a reflection of our use of the local approximation in the plane of the disk. On long timescales the average vertical disk structure consists of a weakly magnetized (β ∼ 50) turbulent core below two scale heights, and a strongly magnetized (β ∼ < 10 −1 ) corona which is stable to the MRI above. The largescale field structure in both the disk and the coronal regions is predominately toroidal. Equating the volume averaged heating rate to optically thin cooling curves, we estimate the temperature in the corona will be of order 10 4 K for protostellar disks, and 10 8 K for disks around neutron stars. The functional form of the stress with vertical height is best described as flat within ±2H z , but proportional to the density above ±2H z .For initially weak uniform vertical fields, we find the exponential growth of magnetic field via axisymmetric vertical modes of the MRI produces strongly buoyant sheets of magnetic energy which break the disk apart into horizontal channels. These channels rise several scale heights vertically before the onset of the Parker instability distorts the sheets and allows matter to flow back towards the midplane and reform a disk. Thereafter the entire disk is magnetically dominated and not well modeled by the local approximation. We suggest this evolution may be relevant to the dynamical processes which disrupt the inner regions of a disk when it interacts with a strongly magnetized central object.

We analyse the non‐linear, three‐dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M⊕) to 1 Jupiter mass (1 MJ) by using the zeus hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed circular orbit about the central star. It is also assumed to be able to accrete gas without expansion on the scale of its Roche radius. Only planets with masses Mp≳ 0.1 MJ produce significant perturbations in the surface density of the disc. The flow within the Roche lobe of the planet is fully three‐dimensional. Gas streams generally enter the Roche lobe close to the disc mid‐plane, but produce much weaker shocks than the streams in two‐dimensional models. The streams supply material to a circumplanetary disc that rotates in the same sense as the orbit of the planet. Much of the mass supply to the circumplanetary disc comes from non‐coplanar flow. The accretion rate peaks with a planet mass of approximately 0.1 MJ and is highly efficient, occurring at the local viscous rate. The migration time‐scales for planets of mass less than 0.1 MJ, based on torques from disc material outside the Roche lobes of the planets, are in excellent agreement with the linear theory of type I (non‐gap) migration for three‐dimensional discs. The transition from type I to type II (gap) migration is smooth, with changes in migration times of about a factor of 2. Starting with a core which can undergo runaway growth, a planet can gain up to a few MJ with little migration. Planets with final masses of the order of 10 MJ would undergo large migration, which makes formation and survival difficult.

Hexagonal boron nitride (h-BN) has emerged as a strong candidate for twodimensional (2D) material owing to its exciting optoelectrical properties combined with mechanical robustness, thermal stability, and chemical inertness. Super-thin h-BN layers have gained significant attention from the scientific community for many applications, including nanoelectronics, photonics, biomedical, anti-corrosion, and catalysis, among others. This review provides a systematic elaboration of the structural, electrical, mechanical, optical, and thermal properties of h-BN followed by a comprehensive account of stateof-the-art synthesis strategies for 2D h-BN, including chemical exfoliation, chemical, and physical vapor deposition, and other methods that have been successfully developed in recent years. It further elaborates a wide variety of processing routes developed for doping, substitution, functionalization, and combination with other materials to form heterostructures. Based on the extraordinary properties and thermal-mechanical-chemical stability of 2D h-BN, various potential applications of these structures are described.The ORCID identification number(s) for the author(s) of this article can be found under

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A key challenge of harvesting solar energy for chemical transformations is the scarcity of photocatalysts with broad activation wavelength and easily tunable band structures. Here, we introduce lead halide perovskite (CsPbBr 3 ) nanocrystals as band-edge-tunable photocatalysts for efficient photoinduced electron/energy transfer−reversible addition−fragmentation chain transfer (PET-RAFT) polymerization. PET-RAFT polymerization of various functional monomers is successfully conducted using a broad range of irradiation sources ranging from blue to red light (460 to 635 nm), resulting in polymer products with narrow dispersity (Đ = 1.02−1.13) and high degree of chain-end fidelity. Furthermore, the giant two-photon absorption cross-section of CsPbBr 3 enables activation with a light source in the near-infrared region (laser pulses centered at 800 nm) for the PET-RAFT process.