The plasma-solid transition:some implications in astrophysics

Using a criterion proposed by Salpeter,and standard solid state physics,we have determined the Debye temperature of a solid in equilibrium with the electron gas surrounding it.The results obtained can have implications in studies of the interstellar medium.Comment: plain LaTeX,9 pages,no figure

On density and temperature-dependent ground-state and continuum effects in the equation of state for stellar interiors -- A Comment on the paper by S. Arndt, W. Dappen and A. Nayfonov 1998, ApJ 498, 349

Misunderstandings have occurred regarding the conclusions of the paper by S. Arndt, W. Dappen and A. Nayfonov 1998, ApJ 498, 349. At occasions, its results were interpreted as if it had shown basic flaws in the general theory of dynamical screening. The aim of this comment is to emphasize in which connection the conclusions of the paper have to be understood in order to avoid misinterpretations.Comment: Astrophysical Journal (to appear 1 May 1999), 5 page

The Solar-Interior Equation of State with the Path-Integral Formalism I. Domain of Validity

This is the first paper in a series that deals with solar-physics applications of the equation-of-state formalism based on the formulation of the so-called "Feynman-Kac (FK) representation". Here, the FK equation of state is presented and adapted for solar applications. Its domain of validity is assessed. The practical application to the Sun will be dealt with in Paper II. Paper III will extend the current FK formalism to a higher order. Use of the FK equation of state is limited to physical conditions for which more than 90% of helium is ionized. This incudes the inner region of the Sun out to about .98 of the solar radius. Despite this limitation, in the parts of the Sun where it is applicable, the FK equation of state has the power to be more accurate than the equations of state currently used in solar modeling. The FK approach is especially suited to study physical effects such as Coulomb screening, bound states, the onset of recombination of fully ionized species, as well as diffraction and exchange effects. The localizing power of helioseismology allows a test of the FK equation of state. Such a test will be beneficial both for better solar models and for tighter solar constraints of the equation of state.Comment: Completely rewritten revised version. Accepted for publication in Astronomy & Astrophysic

A synoptic comparison of the MHD and the OPAL equations of state

A detailed comparison is carried out between two popular equations of state (EOS), the Mihalas-Hummer-Dappen (MHD) and the OPAL equations of state, which have found widespread use in solar and stellar modeling during the past two decades. They are parts of two independent efforts to recalculate stellar opacities; the international Opacity Project (OP) and the Livermore-based OPAL project. We examine the difference between the two equations of state in a broad sense, over the whole applicable rho-T range, and for three different chemical mixtures. Such a global comparison highlights both their differences and their similarities. We find that omitting a questionable hard-sphere correction, tau, to the Coulomb interaction in the MHD formulation, greatly improves the agreement between the MHD and OPAL EOS. We also find signs of differences that could stem from quantum effects not yet included in the MHD EOS, and differences in the ionization zones that are probably caused by differences in the mechanisms for pressure ionization. Our analysis do not only give a clearer perception of the limitations of each equation of state for astrophysical applications, but also serve as guidance for future work on the physical issues behind the differences. The outcome should be an improvement of both equations of state.Comment: 33 pages, 26 figures. Corrected discussion of Basu & Antia, 2004, ApJ, 606, L85-L8

Land Cover Inventory of the Niobrara River Watershed

The Niobrara River watershed covers a large area in northern Nebraska, and neighboring parts of South Dakota and Wyoming, and is an important component of statewide natural resources management. Under ongoing agreements with the U.S. Bureau of Reclamation (BoR), the Nebraska Game and Parks Commission are charged with the development of management plans for various BoR projects in the Niobrara River watershed in Nebraska. A detailed delineation of land use and land cover patterns was needed in order to define and implement effective management strategies