No abstract

We present calculations for a magnetized hybrid wind model for asymptotic giant branch (AGB) stars. The model incorporates a canonical Weber–Davis (WD) stellar wind with dust grains in the envelope of an AGB star. The resulting hybrid picture preserves traits of both types of winds. It is seen that this combination requires that the dust parameter (Γd) be less than unity in order to achieve an outflow. The emergence of critical points in the wind changes the nature of the dust‐driven outflow; simultaneously, the presence of a dust condensation radius changes the morphology of the magnetohydrodynamic (MHD) solutions for the wind. In this context, we additionally investigate the effect of having magnetic‐cold spots on the equator of an AGB star and its implications for dust formation, which are seen to be consistent with previous findings.

The energy levels of the first few low-lying states of helium and lithium atoms in intense magnetic fields up to ≈ 10 8 − 10 9 T are calculated in this study. A pseudospectral method is employed for the computational procedure. The methodology involves computing the eigenvalues and eigenvectors of the generalized two-dimensional Hartree-Fock partial differential equations for these two-and three-electron systems in a self-consistent manner. The method exploits the natural symmetries of the problem without assumptions of any basis functions for expressing the wave functions of the electrons or the commonly employed adiabatic approximation. It is seen that the results obtained here for a few of the most tightly bound states of each of the atoms, helium and lithium, are in good agreement with findings elsewhere. In this regard, we report new data for two new states of lithium that have not been studied thus far in the literature. It is also seen that the pseudospectral method employed here is considerably more economical, from a computational point of view, than previously employed methods such as a finite-element based approach. The key enabling advantage of the method described here is the short computational times which are on the order of seconds for obtaining accurate results for heliumlike systems.

We present a new pseudo‐spectral algorithm for the calculation of the structure of atoms in strong magnetic fields. We have verified this technique for one‐, two‐ and three‐electron atoms in zero magnetic fields against laboratory results and find typically better than 1 per cent accuracy. We further verify this technique against the state‐of‐the‐art calculations of hydrogen, helium and lithium in strong magnetic fields (up to about 2 × 106 T) and find a similar level of agreement. The key enabling advantages of the algorithm are its simplicity (about 130 lines of commented code) and its speed (about 102–105 times faster than finite‐element methods to achieve similar accuracy).

The microsegregation inherited from the directional solidification and quenching (DSQ) of an experimental third generation single crystal superalloy is characterised using electron probe microanalysis (EPMA). A statistical treatment of the data is used to estimate the composition of the solid in the mushy zone. Comparison of the experimental data with the predictions from a numerical model indicates that the results cannot be rationalised without acknowledging that back diffusion is occurring; it is demonstrated that the magnitudes of the diffusion coefficients which need to be invoked are consistent with recent experimental measurements of the coefficients deduced from diffusion couples.