Pseudospectral methods for atoms in strong magnetic fields

We present a new pseudospectral 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 one-percent 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 $2\times 10^{6}$ 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 $10^2-10^5$ times faster than finite-element methods to achieve similar accuracy).Comment: 10 pages, version accepted to MNRA

Is Mira a magneto-dusty rotator?

We investigate the possibility that a magnetic field may be present in the star $o-$Ceti (hereafter, Mira) and that the field plays a role in the star's mass loss. The model presented here is an application of an earlier derived theory that has been successfully employed for intermediate and high-mass evolved stars, and is now extended to the low-mass end. The modelling shows that it is possible to obtain a hybrid magnetohydrodynamic-dust-driven wind scenario for Mira, in which the role of a magnetic field in the equatorial plane of the star is dynamically important for producing a stellar wind. The wind velocity and the temperatures obtained from the model appear consistent with findings elsewhere.Comment: 5 pages, 2 figure

The Magnetised Bellows of Betelgeuse

We present calculations for a magnetised hybrid wind model for Betelegeuse ($\alpha -$Orionis). The model is a direct application of our previously derived theory, combining a canonical Weber-Davis (WD) stellar wind with dust grains in the envelope of an AGB star \citep[see][]{Thirumalai2010}. The resulting hybrid picture provides a mechanism for solving the problem of lifting stellar material up from the photosphere \citep[e.g.][] {Harper2009,Guandalini2006,Jura1984} and into the circumstellar envelope. It also predicts wind velocities in agreement with current estimates. Our approach reveals that magnetic fields in supergiant stars like Betelgeuse \citep[see][]{Auriere2010}, may play a vital role in determining the nature of the stellar outflow and consequently, opens a new avenue of investigation in the field of hybrid stellar winds.Comment: 13 pages, 4 figure

Hydrogen and Helium atoms in strong magnetic fields

The energy levels of hydrogen and helium atoms in strong magnetic fields are calculated in this study. The current work contains estimates of the binding energies of the first few low-lying states of these systems that are improvements upon previous estimates. The methodology involves computing the eigenvalues and eigenvectors of the generalized two-dimensional Hartree-Fock partial differential equations for these one- and two-electron systems in a self-consistent manner. The method described herein is applicable to calculations of atomic structure in magnetic fields of arbitrary strength as it 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. The method is found to be readily extendable to systems with more than two electrons.Comment: 15 pages, 6 figure

Remote and local drivers of Pleistocene South Asian summer monsoon precipitation: A test for future predictions

South Asian precipitation amount and extreme variability are predicted to increase due to thermodynamic effects of increased 21st-century greenhouse gases, accompanied by an increased supply of moisture from the southern hemisphere Indian Ocean. We reconstructed South Asian summer-monsoon precipitation and runoff into the Bay of Bengal to assess the extent to which these factors also operated in the Pleistocene, a time of large-scale natural changes in carbon dioxide and ice volume. South Asian precipitation and runoff are strongly coherent with, and lag, atmospheric CO2 changes at Earth-orbital eccentricity, obliquity, and precession bands and are closely tied to cross-equatorial wind strength at the precession band. We find that the projected monsoon response to ongoing, rapid high-latitude ice melt and rising CO2 levels is fully consistent with dynamics of the past 0.9 million years

A hybrid steady-state magnetohydrodynamic dust-driven stellar wind model for AGB stars

We present calculations for a magnetised 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 ($\Gamma_{d}$) 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.Comment: 15 pages, 9 figure

Isolation and Characterization of Bacteria from the Gut of Bombyx mori that Degrade Cellulose, Xylan, Pectin and Starch and Their Impact on Digestion

Bombyx mori L. (Lepidoptera: Bombycidae) have been domesticated and widely used for silk production. It feeds on mulberry leaves. Mulberry leaves are mainly composed of pectin, xylan, cellulose and starch. Some of the digestive enzymes that degrade these carbohydrates might be produced by gut bacteria. Eleven isolates were obtained from the digestive tract of B. mori, including the Gram positive Bacillus circulans and Gram negative Proteus vulgaris, Klebsiella pneumoniae, Escherichia coli, Citrobacter freundii, Serratia liquefaciens, Enterobacter sp., Pseudomonas fluorescens, P. aeruginosa, Aeromonas sp., and Erwinia sp.. Three of these isolates, P. vulgaris, K. pneumoniae, C. freundii, were cellulolytic and xylanolytic, P. fluorescens and Erwinia sp., were pectinolytic and K. pneumoniae degraded starch. Aeromonas sp. was able to utilize the CMcellulose and xylan. S. liquefaciens was able to utilize three polysaccharides including CMcellulose, xylan and pectin. B. circulans was able to utilize all four polysaccharides with different efficacy. The gut of B. mori has an alkaline pH and all of the isolated bacterial strains were found to grow and degrade polysaccharides at alkaline pH. The number of cellulolytic bacteria increases with each instar

Study of back-diffusion in the nickel-base single crystal superalloy RR-2100

Nickel-base superalloys have been an topic of active research for over five decades and the findings from various researchers worldwide have had a direct impact not only on different areas of materials science but also on applications thereof, in particular the aircraft industry, i.e. the aeroengine. One of the primary concerns of aircraft engine manufacturers has been the problem of microsegregation in turbine blade alloys. This phenomenon which is present in almost all cast products occurs due to the partitioning of solute between the solid and the liquid phases during solidification and is ultimately the source of several types of defects such freckling and white spots in castings resulting in rejection of defective products. Since microsegregation results in a heterogeneous distribution of alloying elements in the cast product it is deleterious to the component's thermo-mechanical properties as well as to its resistance to environmental attack. Thus, much of the current work in superalloy technology has been directed towards gaining a better understanding of microsegregation in different alloys through experimentation coupled with efforts leading towards finding a means of satisfactorily predicting its effects and also to a degree controlling it. Over the years efforts have culminated in many models of microsegregation having been developed for different alloy systems with reasonably acceptable predictive capacities. Nearly all of these models consider the phenomenon of back-diffusion in the solid which serves to reduce the degree of microsegregation in the final cast product by redistributing the solute during solidification. In Ni—base superalloys however, evidence for back diffusion is scarce and only a handful of models of microsegregation are available. The work contained in this thesis addresses the issue of obtaining experimental proof for back diffusion in a Ni—base single crystal superalloy. The study was also aimed at developing a suitable model to predict the microsegregation in the alloy. Directional solidification experiments were conducted in a Directional Solidification and Quench (DSQ) furnace for producing cast single crystal specimens of the alloy RR-2100 which were characterized using Differential Scanning Calorimetry (DSC) for the alloy's solidification behaviour and range. Electron—probe microanalysis (EPMA) experiments were conducted on specimens prepared in this way to obtain compositional data in the mushy zone. The raw data from these experiments were sorted and interpreted with the model of microsegregation. The agreement between the model's predictions and the experimental data were found to be reasonably good. The analysis revealed evidence for back diffusion in RR-2100 nickel-base single crystal superalloy and the measures of the diffusivities of the solutes obtained were found to be consistent with previous findings in the literature.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat

Hydrogen and helium atoms in strong magnetic fields

The energy levels of hydrogen and helium atoms in magnetic fields of arbitrary strength are calculated in this study. The current work contains estimates of the ground and first few excited Hartree-Fock states of these systems that are improvements upon previous estimates. The methodology involves computing the eigenvalues and eigenvectors of the generalized Hartree-Fock partial differential equations for these one- and two-electron systems in a self-consistent manner. The method described herein is applicable to calculations of atomic structure in magnetic fields of arbitrary strength as it exploits the natural symmetries of the problem without assumptions of any basis functions.Science, Faculty ofPhysics and Astronomy, Department ofGraduat