Plasmons of a two-dimensional electron gas in the presence of spin orbit interaction

A theoretical study of the collective excitation associated with plasmon modes is presented for a two-dimensional electron gas in the presence of spin orbit (SO) interaction induced by the Rashba effect. In such a case, the plasmon excitation can be achieved via intra- and inter-SO electronic transitions. As a result, three branches of the plasmon oscillations can be observed. It is found that inter-SO plasmons depend strongly on sample parameters and, at a long-wavelength limit, are optic-like, in contrast to intra-SO ones. The interesting features of these plasmon modes are examined.The author is a Research Fellow of the Australian Research Council. Discussions with P. Vasilopoulos (Concordia, Canada) and M. P. Das (ANU, Australia) are gratefully acknowledged

Secure Communication for Spatially Sparse Millimeter-Wave Massive MIMO Channels via Hybrid Precoding

In this paper, we investigate secure communication over sparse millimeter-wave (mm-Wave) massive multiple-input multiple-output (MIMO) channels by exploiting the spatial sparsity of legitimate user's channel. We propose a secure communication scheme in which information data is precoded onto dominant angle components of the sparse channel through a limited number of radio-frequency (RF) chains, while artificial noise (AN) is broadcast over the remaining nondominant angles interfering only with the eavesdropper with a high probability. It is shown that the channel sparsity plays a fundamental role analogous to secret keys in achieving secure communication. Hence, by defining two statistical measures of the channel sparsity, we analytically characterize its impact on secrecy rate. In particular, a substantial improvement on secrecy rate can be obtained by the proposed scheme due to the uncertainty, i.e., 'entropy', introduced by the channel sparsity which is unknown to the eavesdropper. It is revealed that sparsity in the power domain can always contribute to the secrecy rate. In contrast, in the angle domain, there exists an optimal level of sparsity that maximizes the secrecy rate. The effectiveness of the proposed scheme and derived results are verified by numerical simulations

Large scale behaviour of 3D continuous phase coexistence models

We study a class of three dimensional continuous phase coexistence models, and show that, under different symmetry assumptions on the potential, the large-scale behaviour of such models near a bifurcation point is described by the dynamical $\Phi^p_3$ models for $p \in \{2,3,4\}$. This result is specific to space dimension $3$ and does not hold in dimension $2$

Geometric model for the critical-value problem of nucleation phenomena containing the size effect of nucleating agent

Nucleation is of great concern in many cases—for example, the production of artificial rainfall and the synthesis of advanced amorphous alloys. Although exact solutions have been well known to both homogeneous nucleation and heterogeneous nucleation occurring on a large flat container wall, yet in more general situations the actual nucleation takes place around finite-sized heterogeneous particles. The understanding of nucleation in such situations requires a more extended model which considers the size effect of nucleating agents. Partially motivated by our research on bulk metallic glasses, we construct such a geometric model. Also we derive an exact solution to the model and discuss briefly its physical implications. A previously presumed relation between the critical energy barrier (Ec) and the volumetric Gibbs free energy of the critical nucleus (Gc)—i.e., Ec=(1/2)Gc—is found to be not true for general cases, although it is correct for the limiting cases

Experimental and theoretical research on the electrical conductivity of a liquid desiccant for the liquid desiccant air-conditioning system: LiCl aqueous solution

At present, the energy consumption in buildings occupies a large proportion of total energy use, and air-conditionings cost a large proportion of energy in the buildings. The liquid desiccant air-conditioning system has a good energy saving potential and the electrodialysis (ED) regeneration is a reliable choice for the liquid desiccant regeneration. In order to establish the energy consumption model and the performance coefficient model of liquid desiccant air-conditioning system based on ED regeneration using LiCl, experimental and theoretical research on the electrical conductivity of LiCl aqueous solution with a lot of concentrations and temperatures was conducted in this paper. The results show that when polynomial degrees of the mass concentration and the temperature of the LiCl aqueous solution are both 3, the electrical conductivity model for the LiCl aqueous solution is most suitable as its simplicity and high accuracy. Moreover, when the concentration is 36% and the temperature is 22 °C, the liquid desiccant cooling system has the maximum COP of about 5. Finally, a case study of a small office room was conducted, and the result shows that the liquid desiccant cooling system based on electrodialysis regeneration has a good energy-saving potential

Linear Vlasov theory of a magnetised, thermally stratified atmosphere

The stability of a collisionless, magnetised plasma to local convective disturbances is examined, with a focus on kinetic and finite-Larmor-radius effects. Specific application is made to the outskirts of galaxy clusters, which contain hot and tenuous plasma whose temperature increases in the direction of gravity. At long wavelengths (the "drift-kinetic" limit), we obtain the kinetic version of the magnetothermal instability (MTI) and its Alfv\'enic counterpart (Alfv\'enic MTI), which were previously discovered and analysed using a magnetofluid (i.e. Braginskii) description. At sub-ion-Larmor scales, we discover an overstability driven by the electron temperature gradient of kinetic-Alfv\'en drift waves -- the electron MTI (eMTI) -- whose growth rate is even larger than the standard MTI. At intermediate scales, we find that ion finite-Larmor-radius effects tend to stabilise the plasma. We discuss the physical interpretation of these instabilities in detail, and compare them both with previous work on magnetised convection in a collisional plasma and with temperature-gradient-driven drift-wave instabilities well-known to the magnetic-confinement-fusion community. The implications of having both fluid and kinetic scales simultaneously driven unstable by the same temperature gradient are briefly discussed.Comment: 51 pages, 9 figures; to appear in Journal of Plasma Physic

Energy levels of a parabolically confined quantum dot in the presence of spin-orbit interaction

We present a theoretical study of the energy levels in a parabolically confined quantum dot in the presence of the Rashba spin-orbit interaction (SOI). The features of some low-lying states in various strengths of the SOI are examined at finite magnetic fields. The presence of a magnetic field enhances the possibility of the spin polarization and the SOI leads to different energy dependence on magnetic fields applied. Furthermore, in high magnetic fields, the spectra of low-lying states show basic features of Fock-Darwin levels as well as Landau levels.Comment: 6 pages, 4 figures, accepted by J. Appl. Phy

The Extended Regularized Dual Averaging Method for Composite Optimization

We present a new algorithm, extended regularized dual averaging (XRDA), for solving composite optimization problems, which are a generalization of the regularized dual averaging (RDA) method. The main novelty of the method is that it allows more flexible control of the backward step size. For instance, the backward step size for RDA grows without bound, while XRDA the backward step size can be kept bounded