Joseph W. Ferguson

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Water is generally considered to be the major limiting factor for perennial shrub growth in the Mojave Desert, USA. However, the responses of active fine roots to soil moisture and microsite differed among Ambrosia dumosa, Ephedra nevadensis, Larrea tridentata, and Lycium pallidum, suggesting differences in root foraging strategies. Ambrosia and Ephedra had(More)
We have measured the absorption, gain and spontaneous emission spectra of GalnNAsSb (3.3%N), GalnNAs (0.5%N) and GalnAs quantum well structures to compare their merits as laser gain media. The parameters describing the relations between peak gain and current provide only limited insight. From the analysis of absorption spectra we have determined the(More)
We present the first models allowing one to explore in a consistent way the influence of changes in the α-element-to-iron abundance ratio on the high-resolution spectral properties of evolving stellar populations. The models cover the wavelength range from 3000 Å to 1.34μm at a constant resolution of FWHM=1 Å and a sampling of 0.2 Å, for overall(More)
Context. Observations suggest that a relationship exists between the driving mechanism of roAp star pulsations and the heavy element distribution in these stars. Aims. We attempt to study the effects of local and global metallicity variations on the excitation mechanism of high order p-modes in A star models. Methods. We developed stellar evolutionary(More)
Context. Calculation of stellar models with varying degrees of α-element enhancement. Aims. We investigate the influence of both a new generation of low-temperature opacities and of various amounts of α-element enhancements on stellar evolution models. Methods. New stellar models with two different α-element mixtures and two sets of appropriate opacity(More)
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