Browsing by Author "Briceno, Matias"

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    Hydroclimate variations over the last 17,000 years as estimated by leaf waxes in rodent middens from the south-central Atacama Desert, Chile
    (2023) Frugone-Alvarez, Matias; Contreras, Sergio; Meseguer-Ruiz, Oliver; Tejos, Eduardo; Delgado-Huertas, Antonio; Valero-Garces, Blas; Diaz, Francisca P.; Briceno, Matias; Bustos-Morales, Manuel; Latorre, Claudio
    Leaf cuticular waxes are one of the most important environment-plant interaction structural systems that enable desert plants to withstand extreme climatic conditions. We present a long chain n-alkyl lipids study in fresh plant leaves and rodent palaeomiddens collected along an elevational gradient in the south-central Atacama Desert of Chile, covering six different vegetation belts: Steppe (4500-4000 m asl), Puna (4000-3300 m asl), pre-Puna (3300-2400 m asl), Absolute Desert (2400-1000 m asl) and Coastal Desert (1000-0 m asl). The 28 rodent palaeomiddens analyzed from Quebrada Incahuasi (25.6 & DEG;S, 3600 m asl) span the last 17,000 years. Modern-day distribution of long-chain n-alkanes and n-alkanoic acids varies among the dominant plant associations of the Atacama Desert. These plants show a species -specific chemotaxonomy linked to the climatic conditions. Furthermore, differences in average chain length (ACL) and carbon preference index (CPI) suggest that these plant communities are highly adapted to extreme environmental conditions. The sum of leaf wax n-alkanes was highest under wet conditions, while n-alkanoic acids (between n -C24 and n -C28) increased with hyperaridity. Similarly, analysis of n- alkane time series from palaeomiddens showed that the greatest changes in leaf wax n-alkane distri-butions (ACL and CPI) corresponded to the greatest increases in moisture during the Central Andean Pluvial Event (CAPE; between 18 and 9 ka cal BP) and the Late Holocene. The shift in the palaeomidden n- alkane distributions is corroborated by the relative abundance of rainfall-dependent extra-local taxa. This is the first study to report leaf wax content obtained from ancient rodent middens, and shows promising results as a robust hydroclimate proxy for the Atacama Desert region. & COPY; 2023 Published by Elsevier Ltd.
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    Overspinning naked singularities in AdS3 spacetime
    (2021) Briceno, Matias; Martinez, Cristian; Zanelli, Jorge
    The Banados-Teitelboim-Zanelli (BTZ) black hole belongs to a family of locally three-dimensional antide Sitter (AdS(3)) spacetimes labeled by their mass M and angular momentum J. The case Ml >= vertical bar J vertical bar, where l is the anti-de Sitter radius, provides the black hole. Extending the metric to other values of M and J leads to geometries with the same asymptotic behavior and global symmetries but containing a naked singularity at the origin. The case Ml <= -vertical bar J vertical bar corresponds to spinning conical singularities that are reasonably well understood. Here, we examine the remaining case, which is -vertical bar J vertical bar < Ml < vertical bar J vertical bar. These naked singularities are mathematically acceptable solutions describing classical spacetimes. They are obtained by identifications of the covering pseudosphere in R-2,R-2 and are free of closed timelike curves. Here, we study the causal structure and geodesics around these overspinning geometries. We present a review of the geodesics for the entire BTZ family. The geodesic equations are completely integrated, and the solutions are expressed in terms of elementary functions. Special attention is given to the determination of circular geodesics, where new results are found. According to the radial bounds, eight types of noncircular geodesics appear in the BTZ spacetimes. For the case of overspinning naked singularity, null, and spacelike geodesics can reach infinity passing by a point nearest to the singularity, others extend from the central singularity to infinity, and others still have a radial upper bound and terminate at the singularity. As expected for an anti-de Sitter spacetime, timelike geodesics cannot reach infinity; they either loop around the singularity or fall into it. The spatial projections of the geodesics (orbits) exhibit self-intersections, whose number is determined for null and spacelike geodesics, and it is found a special class of timelike geodesics whose spatial projections are closed.