Narrow Results

We review the topic of quantized vortices in multicomponent Bose–Einstein condensates of dilute atomic gases, with an emphasis on the two-component condensates. First, we review the fundamental structure, stability and dynamics of a single vortex state in a slowly rotating two-component condensates. To understand recent experimental results, we use the coupled Gross–Pitaevskii equations and the generalized nonlinear sigma model. An axisymmetric vortex state, which was observed by the JILA group, can be regarded as a topologically trivial skyrmion in the pseudospin representation. The internal, coherent coupling between the two components breaks the axisymmetry of the vortex state, resulting in a stable vortex molecule (a meron pair). We also mention unconventional vortex states and monopole excitations in a spin-1 Bose–Einstein condensate. Next, we discuss a rich variety of vortex states realized in rapidly rotating two-component Bose–Einstein condensates. We introduce a phase diagram with axes of rotation frequency and the intercomponent coupling strength. This phase diagram reveals unconventional vortex states such as a square lattice, a double-core lattice, vortex stripes and vortex sheets, all of which are in an experimentally accessible parameter regime. The coherent coupling leads to an effective attractive interaction between two components, providing not only a promising candidate to tune the intercomponent interaction to study the rich vortex phases but also a new regime to explore vortex states consisting of vortex molecules characterized by anisotropic vorticity. A recent experiment by the JILA group vindicated the formation of a square vortex lattice in this system.

In this paper, the effect of dissipative energy arising from bulk-viscosity on the collapse of a self-gravitating viscoelastic medium permeated with a nonuniform magnetic field and rotation is analyzed using the standard Jeans mechanism. A local solution of the system of nondimensional linearized perturbation equations, having variable coefficients, is obtained using the normal modes analysis method. The Jeans instability criteria are derived from the characteristic equation (valid under the kinetic and hydrodynamic limits) for parallel and perpendicular wave propagation, modified due to bulk viscosity and Alfvén wave velocity. From the calculated critical values of Jeans wavenumber, it is found that the bulk-viscosity and magnetic field have stabilizing influence on the onset of gravitational instability for each mode of wave propagation. It is observed that the nonuniform rotation does not affect the instability criterion, however, the rotation strongly suppresses the growth rate of the Jeans instability in both the hydrodynamic and kinetic limits. Also, a comparison of the impact of various rotational and magnetic field orientations on the growth rate in viscoelastic fluid is also presented. From the analysis, it is also observed that the presence of dissipative energy reduces the growth rate, in both modes of wave propagation.

The vibrations of rotating joined conical–conical shells with classical supported conditions have been studied extensively. As a matter of fact, in some cases, these classical boundary conditions cannot exactly model actual situations. Moreover, theoretical frameworks on them are still limited. This research aims to investigate the fundamental frequencies and dynamic mode shapes of the traveling wave of the rotating porous metal material joined conical–conical thin shells (PJCS) with elastic supports. By utilizing artificial spring technology, arbitrary elastic supported boundary conditions and classical boundary conditions are achieved efficiently. A new dynamic model has been formulated with the help of the first-order shear deformation theory (FSDT) and Hamilton’s principle. By employing the generalized differential quadrature (GDQ) method along with stress boundary conditions and generalized eigenvalues, various factors such as porosity, semi-vertex angles and stiffness are analyzed for their impact on the fundamental frequencies of forward wave (FW), backward wave (BW) and mode shapes. The presented results are validated through the convergence and comparison studies from literatures. The interesting and novel results indicate that the in-plane displacement constraints have the most significant impact on the critical speed, while the lateral displacement constraint has the least effect. The vibrations are more easily excited for the part with a larger half vertex angle. Rotating PJCS with Type 1 has the biggest critical rotating speed.

We summarize properties of the Kerr–NUT–(A)dS spacetime in a general dimension. We also investigate a limit when several rotational parameters in the metric are set equal and study geometry of the resulting spacetime. In dimension D = 6, we found a suitable Killing vector basis, whose algebraic structure proves that symmetries of the spacetime after the limit are further enhanced.

The persistent emission of the anomalous X-ray pulsar 4U 0142+61 extends over a broad range of energy, from mid-infrared up to hard X-rays. In particular, this object is unique among soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) in presenting simultaneously mid-infrared emission and also pulsed optical emission. In spite of having many propositions to explain this wide range of emission, it is still lacking one that reproduces simultaneously all the observations. Filling this gap, we present a model that is able, for the first time, to reproduce simultaneously the entire spectral energy distribution of 4U 0142+61 using plausible physical components and parameters. We propose that the persistent emission comes from an accreting white dwarf (WD) surrounded by a debris disk. This model is thoroughly discussed at Ref. 2 and assumes that: (i) the hard X-rays are due to the bremsstrahlung emission from the post-shock region of the accretion column; (ii) the soft X-rays are originated by hot spots on the WD surface; and (iii) the optical and infrared emissions are caused by an optically thick dusty disk, the WD photosphere, and the tail of the post-shock region emission. In this scenario, 4U 0142+61 harbors a fast-rotator near-Chandrasekhar WD, which is highly magnetized. Such a WD can be formed by a merger of two less massive WDs.

We study the occurrence of delayed Type Ia supernovae in the single degenerate (SD) scenario. We assume that a massive carbon-oxygen (CO) white dwarf (WD) accretes matter coming from a companion star, making it to spin at the critical rate. We assume uniform rotation due to magnetic field coupling. The carbon ignition mass for nonrotating WDs is $M_{\text{ig}}^{\text{NR}}\approx \text{1}\text{.38 }{M}_{\odot }$; while for the case of uniformly rotating WDs it is few percents larger $\left(M_{\text{ig}}^{\text{R}}\approx \text{1}\text{.43 }{M}_{\odot }\right)$. When accretion rate decreases, the WD begins to lose angular momentum, shrinks and spins up; however it does not overflow its critical rotation rate, avoiding mass shedding. Thus, angular momentum losses can lead the CO WD interior to compression and carbon ignition, which would induce a Type Ia supernova. The delay, largely due to angular momentum losses timescale, may be large enough to allow the companion star to evolve to a He WD, becoming undetectable at the moment of explosion. This scenario supports the occurrence of delayed SNe Ia if the final COWD mass is 1.38 M_⊙ < M < 1.43 M_⊙. We also find that if the delay is longer than ∼ 3 Gyr, the WD would become too cold to explode, rather undergo collapse.

We construct mass-radius relations of white dwarfs taking into account the effects of rotation and finite temperatures. We compare and contrast the theoretical mass-radius relations with observational data.