Nearly a century ago it was recognized that radiation absorption by stellar matter controls the internal temperature profiles within stars. Laboratory opacity measurements, however, have never been performed at stellar interior conditions, introducing uncertainties in stellar models. A particular problem arose when refined photosphere spectral analysis led to reductions of 30-50 per cent in the inferred amounts of carbon, nitrogen and oxygen in the Sun. Standard solar models using the revised element abundances disagree with helioseismic observations that determine the internal solar structure using acoustic oscillations. This could be resolved if the true mean opacity for the solar interior matter were roughly 15 per cent higher than predicted, because increased opacity compensates for the decreased element abundances. Iron accounts for a quarter of the total opacity at the solar radiation/convection zone boundary. Here we report measurements of wavelength-resolved iron opacity at electron temperatures of 1.9-2.3 million kelvin and electron densities of (0.7-4.0) × 10(22) per cubic centimetre, conditions very similar to those in the solar region that affects the discrepancy the most: the radiation/convection zone boundary. The measured wavelength-dependent opacity is 30-400 per cent higher than predicted. This represents roughly half the change in the mean opacity needed to resolve the solar discrepancy, even though iron is only one of many elements that contribute to opacity.

We present a new, publicly available set of Los Alamos OPLIB opacity tables for the elements hydrogen through zinc. Our tables are computed using the Los Alamos ATOMIC opacity and plasma modeling code, and make use of atomic structure calculations that use fine-structure detail for all the elements considered. Our equation of state model, known as ChemEOS, is based on the minimization of free energy in a chemical picture and appears to be a reasonable and robust approach to determining atomic state populations over a wide range of temperatures and densities. In this paper we discuss in detail the calculations that we have performed for the 30 elements considered, and present some comparisons of our monochromatic opacities with measurements and other opacity codes. We also use our new opacity tables in solar modeling calculations and compare and contrast such modeling with previous work.

A theoretical approach, based upon the assumption of predominance of solvophobic interactions, was formulated to quantitatively describe the sorption and transport of hydrophohic organic chemicals (HOC) from aqueous and aqueous‐organic‐solvent mixtures. In the theoretical approach, solvent‐sorbate interactions (solubility) are specifically considered in order to predict sorbate‐sorbent interactions (sorption). For HOC sorption from a single solvent, the HOC sorption coefficient was shown to increase loglinearly with the hydrocarbonaceous surface area (HSA) of the sorbate. For HOC sorption from aqueous‐organic binary solvent mixtures, the sorption coefficient is predicted to decrease exponentially as the fraction of organic cosolvent increases. This is a direct consequence of increased HOC solubility in the binary solvent. Because sorption and mobility of HOC are inversely related, a decrease in sorption coefficient leads to an enhanced HOC mobility as the fraction of organic cosolvent is increased. A preliminary verification of the theory was performed by an analysis of published data for (i) HOC sorption by soils and sediments from water, (ii) HOC retention by reversed‐phase chromatographic sorbents during isocratic elution with methanol‐water binary solvent mixture, and (iii) HOC mobility on soil‐TLC plates eluted with ethanol‐water mixtures.

The Los Alamos suite of relativistic atomic physics codes is a robust, mature platform that has been used to model highly charged ions in a variety of ways. The suite includes capabilities for calculating data related to fundamental atomic structure, as well as the processes of photoexcitation, electron-impact excitation and ionization, photoionization and autoionization within a consistent framework. These data can be of a basic nature, such as cross sections and collision strengths, which are useful in making predictions that can be compared with experiments to test fundamental theories of highly charged ions, such as quantum electrodynamics. The suite can also be used to generate detailed models of energy levels and rate coefficients, and to apply them in the collisional-radiative modeling of plasmas over a wide range of conditions. Such modeling is useful, for example, in the interpretation of spectra generated by a variety of plasmas. In this work, we provide a brief overview of the capabilities within the Los Alamos relativistic suite along with some examples of its application to the modeling of highly charged ions.

Diffusion of nonadsorbed solutes (3H2O and 36Cl‐) out of two sizes of porous ceramic spheres (0.55‐ and 0.75‐cm radius) was measured. These data were analyzed to provide independent estimates of the input parameters required in two simulation models for describing solute transport in aggregated porous media with distinct mobile and stagnant pore‐water regions. Tracer‐saturated porous spheres were placed in tracer‐free 0.01N CaCl2 solution and the rate of tracer diffusion out of the porous spheres was measured by monitoring the increase in tracer concentration with time in the external electrolyte solution. Experimental results were analyzed using two mathematical models. Fick's second law, written in spherical coordinates, formed the basis for Model I. In Model II, the time‐rate of solute transfer into or out of the porous spheres was assumed to be proportional to the difference in tracer concentration inside and outside the porous spheres. The analytical solution to Model I for given initial and boundary conditions was substituted into Model II, to derive an explicit expression relating the empirical mass transfer rate coefficient (α) in Model II and known physical constants of the system. This theoretical analysis indicated that the α value is dependent upon the sphere radius, time of diffusion, volumetric water contents inside and outside the sphere, and the molecular diffusion coefficient. Over a range of experimental conditions, excellent agreement was found between measured α values and those calculated using the analytic expression developed here.

a b s t r a c tWe report on the use of the Los Alamos suite of relativistic atomic physics codes to generate radiative opacities for the modeling of astrophysically relevant plasmas under local thermodynamic equilibrium (LTE) conditions. The atomic structure calculations are carried out in fine-structure detail, including full configuration interaction. Three example applications are considered: iron opacities at conditions relevant to the base of the solar convection zone, nickel opacities for the modeling of stellar envelopes, and samarium opacities for the modeling of light curves produced by neutron star mergers. In the first two examples, comparisons are made between opacities that are generated with the fully and semirelativistic capabilities in the Los Alamos suite of codes. As expected for these highly charged, ironpeak ions, the two methods produce reasonably similar results, providing confidence that the numerical methods have been correctly implemented. However, discrepancies greater than 10% are observed for nickel and investigated in detail. In the final application, the relativistic capability is used in a preliminary investigation of the complicated absorption spectrum associated with cold lanthanide elements.

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Using the wave-packet propagation method of Rodberg and Thaler and the density matrix method of Fano and Blum, we have defined by completely quantum-mechanical methods the cross sections for the creation, destruction, and transfer of atomic multipole moments by both elastic and inelastic scattering of electrons by atomic targets. All cross sections obtained quantum mechanically, except for the coherence transfer cross sections, agree in form with those obtained semiclassically by Fujimoto and co-workers. We also used the converged close-coupling ͑CCC͒ method to calculate numerically some of the above cross sections for selected transitions in electron scattering from hydrogen and barium atoms.