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Abstract: We have theoretically studied the electronic stopping cross section and the energy loss straggling of swift light ions (H+ and He+) moving through several compound semiconductors (GaAs, ZnSe, InP and SiC) as a function of the incident projectile energy. The calculations have been done using the dielectric formalism, in which the electronic structure of the projectile is described by the modified Brandt–Kitagawa model and the energy loss function (ELF) of the semiconductors is obtained using a linear combination of Mermin-type ELF to describe the outer electron excitations and generalized oscillator strengths to take into account the excitations of the inner-shell electrons. The different charge states that the projectile can acquire during its travel through the solid, as a result of electronic capture and loss processes, has been also considered. The contributions to the projectile energy loss from both the outer- and the inner-shell electron excitations are analyzed. The comparison of our calculated stopping cross sections with available experimental data shows a good agreement in a wide range of incident projectile energies. [Copyright &y& Elsevier]

Abstract: We present the results of a palaeogenetic analysis of two Late Pleistocene camelids originating in southern Chile. Our analysis of two mitochondrial DNA fragments (control region and cytochrome b gene) reveals that these specimens do not belong to an extinct taxon, but rather to extant vicuña (Vicugna vicugna), whose modern distribution is restricted to the extreme elevations of the Andes, more than 3500km to the north of where these specimens originated. Our results also suggest fossil specimens from Patagonia that are currently assigned to the extinct taxon Lama gracilis, may actually belong to V. vicugna, implying a continuous distribution of the latter from the southern tip of South America to the Andes during the Final Pleistocene. The haplotypes of both specimens are not present in modern populations, suggesting a loss of genetic diversity concomitant with the contraction of the vicuña geographical distribution during the Final Pleistocene or early Holocene. [Copyright &y& Elsevier]