Pulsar slow glitches in a solid quark star model

A series of five unusual slow glitches of the radio pulsar B1822-09 (PSR J1825-0935) were observed over the 1995-2005 interval. This phenomenon is understood in a solid quark star model, where the reasonable parameters for slow glitches are presented in the paper. It is proposed that, because of increasing shear stress as a pulsar spins down, a slow glitch may occur, beginning with a collapse of a superficial layer of the quark star. This layer of material turns equivalently to viscous fluid at first, the viscosity of which helps deplete the energy released from both the accumulated elastic energy and the gravitation potential. This performs then a process of slow glitch. Numerical calculations show that the observed slow glitches could be reproduced if the effective coefficient of viscosity is ~10^2 cm^{2}/s and the initial velocity of the superficial layer is order of 10^{-10} cm/s in the coordinate rotating frame of the star.Comment: 5 pages, 5 figures, accepted for publication in MNRAS (Main Journal

3D quantum Hall effect of Fermi arcs in topological semimetals

The quantum Hall effect is usually observed in 2D systems. We show that the Fermi arcs can give rise to a distinctive 3D quantum Hall effect in topological semimetals. Because of the topological constraint, the Fermi arc at a single surface has an open Fermi surface, which cannot host the quantum Hall effect. Via a "wormhole" tunneling assisted by the Weyl nodes, the Fermi arcs at opposite surfaces can form a complete Fermi loop and support the quantum Hall effect. The edge states of the Fermi arcs show a unique 3D distribution, giving an example of (d-2)-dimensional boundary states. This is distinctly different from the surface-state quantum Hall effect from a single surface of topological insulator. As the Fermi energy sweeps through the Weyl nodes, the sheet Hall conductivity evolves from the 1/B dependence to quantized plateaus at the Weyl nodes. This behavior can be realized by tuning gate voltages in a slab of topological semimetal, such as the TaAs family, Cd$_3$As$_2$, or Na$_3$Bi. This work will be instructive not only for searching transport signatures of the Fermi arcs but also for exploring novel electron gases in other topological phases of matter.Comment: 5 pages, 3 figure

An extended finite element method with smooth nodal stress

The enrichment formulation of double-interpolation finite element method (DFEM) is developed in this paper. DFEM is first proposed by Zheng \emph{et al} (2011) and it requires two stages of interpolation to construct the trial function. The first stage of interpolation is the same as the standard finite element interpolation. Then the interpolation is reproduced by an additional procedure using the nodal values and nodal gradients which are derived from the first stage as interpolants. The re-constructed trial functions are now able to produce continuous nodal gradients, smooth nodal stress without post-processing and higher order basis without increasing the total degrees of freedom. Several benchmark numerical examples are performed to investigate accuracy and efficiency of DFEM and enriched DFEM. When compared with standard FEM, super-convergence rate and better accuracy are obtained by DFEM. For the numerical simulation of crack propagation, better accuracy is obtained in the evaluation of displacement norm, energy norm and the stress intensity factor

In-medium Properties of Θ+\Theta^{+} as a Kπ\piN structure in Relativistic Mean Field Theory

The properties of nuclear matter are discussed with the relativistic mean-field theory (RMF).Then, we use two models in studying the in-medium properties of $\Theta^+$: one is the point-like $\Theta^*$ in the usual RMF and the other is a K$\pi$N structure for the pentaquark. It is found that the in-medium properties of $\Theta^+$ are dramatically modified by its internal structure. The effective mass of $\Theta^+$ in medium is, at normal nuclear density, about 1030 MeV in the point-like model, while it is about 1120 MeV in the model of K$\pi$N pentaquark. The nuclear potential depth of $\Theta^+$ in the K$\pi$N model is approximately -37.5 MeV, much shallower than -90 MeV in the usual point-like RMF model.Comment: 8 pages, 5 figure