Magnetohydrodynamic normal mode analysis of plasma with equilibrium pressure anisotropy

In this work, we generalise linear magnetohydrodynamic (MHD) stability theory to include equilibrium pressure anisotropy in the fluid part of the analysis. A novel 'single-adiabatic' (SA) fluid closure is presented which is complementary to the usual 'double-adiabatic' (CGL) model and has the advantage of naturally reproducing exactly the MHD spectrum in the isotropic limit. As with MHD and CGL, the SA model neglects the anisotropic perturbed pressure and thus loses non-local fast-particle stabilisation present in the kinetic approach. Another interesting aspect of this new approach is that the stabilising terms appear naturally as separate viscous corrections leaving the isotropic SA closure unchanged. After verifying the self-consistency of the SA model, we re-derive the projected linear MHD set of equations required for stability analysis of tokamaks in the MISHKA code. The cylindrical wave equation is derived analytically as done previously in the spectral theory of MHD and clear predictions are made for the modification to fast-magnetosonic and slow ion sound speeds due to equilibrium anisotropy.Comment: 19 pages. This is an author-created, un-copyedited version of an article submitted for publication in Plasma Physics and Controlled Fusion. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Topological nature of in-gap bound states in disordered large-gap monolayer transition metal dichalcogenides

We propose a physical model based on disordered (a hole punched inside a material) monolayer transition metal dichalcogenides (TMDs) to demonstrate a large-gap quantum valley Hall insulator. We find an emergence of bound states lying inside the bulk gap of the TMDs. They are strongly affected by spin-valley coupling, rest- and kinetic- mass terms and the hole size. In addition, in the whole range of the hole size, at least two in-gap bound states with opposite angular momentum, circulating around the edge of the hole, exist. Their topological insulator (TI) feature is analyzed by the Chern number, characterized by spacial distribution of their probabilities and confirmed by energy dispersion curves (Energy vs. angular momentum). It not only sheds light on overcoming low-temperature operating limitation of existing narrow-gap TIs, but also opens an opportunity to realize valley- and spin- qubits.Comment: 5 pages, 5 figures. Feedback is welcome

Generating quadrature squeezed light with dissipative optomechanical coupling

The recent demonstration of cooling of a macroscopic silicon nitride membrane based on dissipative coupling makes dissipatively coupled optomechanical systems as promising candidates for squeezing. We theoretically show that such a system in a cavity on resonance can yield good squeezing which is comparable to that produced by dispersive coupling. We also report the squeezing resulting from the combined effects of dispersive and dissipative couplings and thus the device can be operated in one regime or the other. We derive the maximal frequency and quadrature angles to observe squeezing for given optomechanical coupling strengths. We also discuss the effects of temperature on squeezing

Spontaneous Generation of Photons in Transmission of Quantum Fields in PT Symmetric Optical Systems

We develop a rigorous mathematically consistent description of PT symmetric optical systems by using second quantization. We demonstrate the possibility of significant spontaneous generation of photons in PT symmetric systems. Further we show the emergence of Hanbury-Brown Twiss (HBT) correlations in spontaneous generation. We show that the spontaneous generation determines decisively the nonclassical nature of fields in PT symmetric systems. Our work can be applied to other systems like plasmonic structure where losses are compensated by gain mechanisms.Comment: 4 pages, 5 figure

Fabrication and mechanical properties of chitosan composite membrane containing hydroxyapatite particles

This paper described the development of chitosan composites containing precipitated hydroxyapatite particles for potential applications in orthopaedic surgery or waste water treatment. The synthetic process and morphology of hydroxyapatite were reported. The effects of hydroxyapatite content on the microstructure and mechanical properties of composites were investigated. It was found that the Young’s Modulus of the composites decreases with hydroxyapatite content while the failure strength and strain increase with the hydroxyapatite content