Microtextural characteristics of quartz grains transported and deposited by tsunamis and storms

International audienc

Aeolian microtextures in silica spheres induced in a wind tunnel experiment: Comparison with aeolian quartz

Microtextures in quartz attributed to aeolian transport, principally bulbous edges and abrasion fatigue have seldom been tested in the laboratory under controlled conditions. A wind tunnel experiment was conducted, using glass spheres (>70% SiO2) as a proxy for quartz, with the objective of determining the extent of mechanical damage to silica/glass transported in a mixture with quartz beach sand. The microspheres were microscopically imaged prior to transport in a wind tunnel, subjected at velocities ranging from 4 to 13 m/s in sequential runs of 10 min. The range in velocity is capable of lifting grains into the air column or saltating quartz grains and silica/glass spheres to produce mechanical impact, i.e. abrasion commonly experienced in aeolian transport. With increasing velocity silica/glass spheres, which displayed minor imperfections prior to transport, began to show significant grain damage exhibiting increasing depth into the silica/glass fabric – a result of mechanical contact – as well as increasing frequency of craters, dislodged plates and abrasion fatigue. While pits appear earlier in the experiment (8 m/s), dislodged plates and abrasion fatigue need a threshold velocity of near 10 m/s to become more frequent. Bulbous edges on the grain surface, often considered the hallmark of aeolian transport, are not seen in the grain population analyzed, possibly because of the initial near-perfect sphericity of the silica/glass spheres. The experiment proved that aeolian transport throughout short distances and during a relatively short period of time is enough to imprint significant abrasion marks in microspheres. In fact, the microtextures produced were fresh surfaces, fractures and abrasion that imprinted areas of different sizes. A comparison of microtextural imprints on silica/glass spheres relative to coastal dune sands was made to better understand energy thresholds required to achieve grain damage

Genetical genomics of Th1 and Th2 immune response in a baboon model of atherosclerosis risk factors

Objective: CD4+ T-cells mediate inflammation in atherosclerosis, but additive genetic effects on associated pathways of Th1 and Th2 immune response have not been described. We sought to characterize heritability, pleiotropy, and QTL effects on the expression of genes implicated in Th1 and Th2 immune response in a baboon model of risk factors for atherosclerosis. Methods: We employed a maximum likelihood-based variance decomposition approach to estimate additive genetic effects on transcript levels generated from a gene expression profile of lymphocytes in 499 pedigreed baboons maintained on a basal diet. Transcript levels for 57 genes implicated in Th1 and Th2 immune response were selected for analysis based on significant heritability in this profile. Multipoint whole genome scans were conducted on heritable transcript levels to localize QTLs influencing these measures. To evaluate pleiotropic effects on transcript levels, we estimated genetic and phenotypic correlations among transcript measures, and assessed their correspondence using a Mantel test. Network analysis using GeneGo's MetaCore™ software was conducted to characterize known interaction among coded proteins.Results: Heritabilities for candidate gene transcript levels ranged from 0.092–0.786 (median h2 = 0.278, P = 4.72 × 10−4). Linkage analyses yielded significant evidence (LOD ≥ 2.73) for 14 eQTLs (LOD score range 2.76–14.87, genome-wide P = 4.9 × 10−2–1.03 × 10−14). Estimates of genetic correlation supported shared additive genetic effects incorporating all 57 transcripts (null hypothesis of ρG = 0 rejected at FDR ≤ 0.05 for 522 of 1596 estimates), and accounted for most of the observed phenotypic correlation among transcripts (Mantel test, r[ρP],[ρG] = 0.781, P < 0.0001). Network analysis revealed direct interactions among 54 of the 57 coded proteins. Conclusions: We conclude that major genetic effects influence expression levels of multiple genes implicated in Th1 and Th2 immune response. Additionally, we find that expression levels of these candidate genes are characterized by extensive pleiotropy, consistent with known interaction among their coded proteins, many of which are independently associated with atherosclerosis