Buoyancy versus shear forces in building orogenic wedges

International audienceThe dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. Hyperextension generates a basin with exhumed continental mantle bounded by asymmetric passive margins. Before convergence, we replace the top few kilometres of the exhumed mantle with serpentinite to investigate its role during subduction and collision.We study the impact of three parameters: (1) shear resistance, or strength, of serpentinites, controlling the strength of the evolving subduction interface; (2) strength of the continental upper crust; and (3) density structure of the subducted material. Densities are determined by linearized equations of state or by petrological-phase equilibria calculations. The three parameters control the evolution of the ratio of upward-directed buoyancy force to horizontal driving force, FB/FD=ArF, which controls the mode of orogenic wedge formation: ArF≈0.5 causes thrust-sheet-dominated wedges, ArF≈0.75 causes minor wedge formation due to relamination of subducted crust below the upper plate, and ArF≈1 causes buoyancy-flow- or diapir-dominated wedges involving exhumation of crustal material from great depth (>80 km). Furthermore, employing phase equilibria density models reduces the average topography of wedges by several kilometres.We suggest that during the formation of the Pyrenees ArF⪅0.5 due to the absence of high-grade metamorphic rocks, whereas for the Alps ArF≈1 during exhumation of high-grade rocks and ArF⪅0.5 during the post-collisional stage. In the models, FD increases during wedge growth and subduction and eventually reaches magnitudes (≈18 TN m−1) which are required to initiate subduction. Such an increase in the horizontal force, required to continue driving subduction, might have “choked” the subduction of the European plate below the Adriatic one between 35 and 25 Ma and could have caused the reorganization of plate motion and subduction initiation of the Adriatic plate

Effects of Systemic Pesticides Imidacloprid and Metalaxyl on the Phyllosphere of Pepper Plants

Microbes inhabiting the phyllosphere of crops are exposed to pesticides applied either directly onto plant foliage or indirectly through soil. Although, phyllosphere microbiology has been rapidly evolving, little is still known regarding the impact of pesticides on the epiphytic microbial community and especially on fungi. We determined the impact of two systemic pesticides (metalaxyl and imidacloprid), applied either on foliage or through soil, on the epiphytic fungal and bacterial communities via DGGE and cloning. Both pesticides induced mild effects on the fungal and the bacterial communities. The only exception was the foliage application of imidacloprid which showed a more prominent effect on the fungal community. Cloning showed that the fungal community was dominated by putative plant pathogenic ascomycetes (Erysiphaceae and Cladosporium), while a few basidiomycetes were also present. The former ribotypes were not affected by pesticides application, while selected yeasts (Cryptococcus) were stimulated by the application of imidacloprid suggesting a potential role in its degradation. A less diverse bacterial community was identified in pepper plants. Metalaxyl stimulated an Enterobacteriaceae clone which is an indication of the involvement of members of this family in fungicide degradation. Further studies will focus on the isolation of epiphytic microbes which appear to be stimulated by pesticides application

Magnetization reversal mechanism of ramified and compact Co islands on Pt(111)

We report on the magnetization reversal mechanism of Co islands on Pt(111) as a function of their size and shape. We measure the zero-field susceptibility chi(T) and low-temperature magnetization curves M(H) with in situ magneto-optical Kerr effect. Together with the island morphology deduced from scanning tunneling microscopy, this creates sufficient information to determine both the magnetization reversal mechanism and the distribution of anisotropy energies between perimeter and surface atoms. We find a transition from quasicoherent rotation to domain wall nucleation and propagation with a critical size of 350 atoms for ramified, and of 600 atoms for compact islands

Atomic-scale engineering of magnetic anisotropy of nanostructures through interfaces and interlines

The central goals of nanoscale magnetic materials science are the self-assembly of the smallest structure exhibiting ferromagnetic hysteresis at room temperature, and the assembly of these structures into the highest density patterns. The focus has been on chemically ordered alloys combining magnetic 3d elements with polarizable 5d elements having high spin-orbit coupling and thus yielding the desired large magneto-crystalline anisotropy. The chemical synthesis of nanoparticles of these alloys yields disordered phases requiring annealing to transform them to the high-anisotropy L10 structure. Despite considerable efforts, so far only part of the nanoparticles can be transformed without coalescence. Here we present an alternative approach to homogeneous alloys, namely the creation of nanostructures with atomically sharp bimetallic interfaces and interlines. They exhibit unexpectedly high magnetization reversal energy with values and directions of the easy magnetization axes strongly depending on chemistry and texture. We find significant deviations from the expected behaviour for commonly used element combinations. Ab-initio calculations reproduce these results and unravel their origin

Dietary supplementation of oregano essential oil and •-tocopheryl acetate on microbial growth and lipid oxidation of Turkey breast fillets during storage

Twenty four 12-week-old turkeys were divided into four equal groups. One of the groups was given a basal diet containing 30 mg •-tocopheryl acetate/kg feed (CONT), whereas the other groups the basal diet further supplemented with 100 mg •-tocopheryl acetate/kg (TOC), or 100 mg oregano essential oil/kg (OR), or 100 mg oregano essential oil plus 100 mg •-tocopheryl acetate/kg (ORTOC), for 4 weeks prior to slaughter. Lipid oxidation, total viable counts (TVC) and Pseudomonas spp. counts were all assessed in breast fillets stored refrigerated at 4°C for 12 days. Results showed that the OR group was more effective (P0.05) among each other. © Asian Network for Scientific Information, 2005

Oxidative stress and antioxidant status in patients with autoimmune liver diseases

Objective: To estimate oxidative stress and antioxidant components during different stages of autoimmune liver diseases and assess their possible implication on disease progression. Methods: We determined several markers of oxidative injury (isoprostane, aldehydes, protein carbonyls, 3-nitrotyrosine, and myeloperoxidase) and antioxidant components (glutathione, glutathione peroxidase, glutathione reductase, superoxide dismutase, and catalase) in whole blood, serum, and urine in 49 patients with autoimmune cholestatic liver diseases (AC) and 36 patients with autoimmune hepatitis (AIH) and healthy subjects matched for sex and age. Results: Both AC and AIH patients had increased levels of all lipid and protein oxidative injury products and significantly decreased whole blood glutathione levels compared to controls. AIH patients had significantly higher levels of aldehydes and glutathione peroxidase activity and significantly lower protein carbonyl levels compared to AC patients. Protein carbonyl and isoprostane levels increased and glutathione levels decreased gradually with progression from mild fibrosis to severe fibrosis and cirrhosis in both AC and AIH patients. In addition, both cirrhotic AC and AIH patients had significantly higher protein carbonyls compared to non-cirrhotics. Discussion: We provide novel findings in support of a major contribution of oxidant/antioxidant imbalance in the progression of liver injury in AC and AIH

Total antioxidant status and erythrocyte superoxide dismutase activity in patients with chronic hepatitis B and C

Damage of hepatitis B virus (HBV) and hepatitis C virus (HCV)-infected hepatocytes is mediated by both a direct cytopathic effect of the viruses and by immunologic response of T-cells. However, other mechanisms such as oxidative stress, may also be involved in cellular damage. We conducted a study to investigate the status of superoxide dismutase activity (SOD) and the total antioxidant status (TAS) in a consecutive cohort of patients infected with HBV and HCV infections, including HBV patients in the chronic inactive state of the disease. The latter were included in an attempt to determine whether antioxidant status is affected even in cases where an obvious viral activity is absent. TAS and SOD were measured in 55 patients (43 HBV, 12 HCV) and 25 healthy controls. 17 out of 43 patients had chronic inactive HBV state, 15 had chronic hepatitis B and 11 had HBV-related cirrhosis. In the HCV group, 6 patients had chronic hepatitis C and 6 HCV-related cirrhosis. Erythrocyte SOD activity was determined in haemolysate from red blood cells using a kinetic spectrophotometer method. TAS was measured by a colorimetric assay. The mean TAS and SOD values in the total number of patients (1.20±0.12 mmol/L and 1040±255 U/g Hb, respectively) were significantly lower (p<0.001) compared to healthy controls (1.57±0.13 mmol/L and 1491±420 U/g Hb). Comparisons between groups showed significantly lower (p<0.001) TAS and SOD values in each subgroup of patients compared to healthy controls. A significant positive correlation was found between TAS and SOD in the total number of patients (n=55, p<0.01), in the chronic hepatitis group (n=21, p=0.01) and in the total group of HBV patients (n=43, p<0.01). We demonstrated a significant reduced antioxidant capacity in patients with chronic HBV and HCV as indicated by low TAS and SOD. These findings were independent of the virological, biochemical and clinical status of the patients, including those with chronic inactive HBV state. This could suggest that the tissue-related consequences of oxidative stress might start from the inactive stage of liver viral diseases. However, our observations should be viewed with caution and need to be tested in a larger numbers of patients in order to determine prospectively whether these findings have pathophysiological and/or clinical significance. Copyright © by BIOLIFE, s.a.s