The Pseudo-continuum Bound-free Opacity of Hydrogen and its Importance in Cool White Dwarf Atmospheres

We investigate the importance of the pseudo-continuum bound-free opacity from hydrogen atoms in the atmospheres of cool white dwarfs. This source of absorption, when calculated by the occupation probability formalism applied in the modeling of white dwarf atmospheres with $T_{\rm eff}\rm <17000 K$, dominates all other sources of opacity at optical wavelengths. This is unrealistic and not observed. On the other hand, a significant flux suppression in the blue part of the spectra of cool white dwarfs has been reported, and mainly interpreted as a result of the pseudo-continuum absorption from atomic hydrogen. We investigate this problem by proposing a new, more realistic approach to calculating this source of opacity. We show that this absorption is orders of magnitude smaller than that predicted by current methods. Therefore, we rule out the pseudo-continuum opacity as a source of the flux deficiency observed in the spectra of cool white dwarfs.Comment: 11 pages, 5 gigures, accepted for publication in the Astrophysical Journa

The glory of God is humanity fully alive: exploring Eastern Orthodoxy as a resource for human development in conversation with the capability approach

This dissertation argues that Eastern Orthodox theology is a framework for multidimensional social change or improvement and can inform, and be informed by the multi-disciplinary social science field of development studies. This claim will be examined by analyzing the Trinitarian theology of the Orthodox theologian Dumitru Staniloae in relation to the writings of Nobel Economist Amartya Sen and his ‘capability approach’. The argument begins by justifying EO’s interaction with development studies based on her anthropological optimism. Critical is that supernatural revelation stands very close to and builds on natural revelation. A Trinitarian theological anthropology then provides a rationale for, and integration of, three key concepts in the social sciences: agency, solidarity, and structures. This analytical framework is then used to assess the challenges of post-Communist contexts, where most Orthodox live. The Communist downfall, it is argued, involved a failure to incorporate each of these dimensions in human development. This analysis then serves to test the adequacy of, and reveal weaknesses in, Amartya Sen’s freedom-focused social evaluation framework known as the capability approach. The dissertation proceeds with examining Orthodox salvation as movement from Being, to Well-being, to Eternal-being where Well-being is, notably, the exercise of agency to develop the potentials given in Being. Agency is not individualistic, but is structured into the virtues of solidarity and incorporates the related notion of phronesis (practical reason). The virtue tradition is then postulated as a promising link between theology and development studies. The virtue tradition is analyzed in its classical background, modern human development, as well as both Protestantism and Catholicism to facilitate a comparison with Eastern Orthodoxy. This analysis shows that Orthodoxy offers a theological framework for human development in that she gives priority of practical reason to contemplation, makes virtually no separation between grace and nature, and provides a relevant method for synergizing salvation history with action on behalf of human development

A note on commuting graphs for symmetric groups

The commuting graph C(G;X) , where G is a group and X a subset of G, has X as its vertex set with two distinct elements of X joined by an edge when they commute in G. Here the diameter and disc structure of C(G;X) is investigated when G is the symmetric group and X a conjugacy class of G

Low cost solar array project 1: Silicon material

The low cost production of silicon by deposition of silicon from a hydrogen/chlorosilane mixture is described. Reactor design, reaction vessel support systems (physical support, power control and heaters, and temperature monitoring systems) and operation of the system are reviewed. Testing of four silicon deposition reactors is described, and test data and consequently derived data are given. An 18% conversion of trichlorosilane to silicon was achieved, but average conversion rates were lower than predicted due to incomplete removal of byproduct gases for recycling and silicon oxide/silicon polymer plugging of the gas outlet. Increasing the number of baffles inside the reaction vessel improved the conversion rate. Plans for further design and process improvements to correct the problems encountered are outlined