Search results for " mechanism"
showing 10 items of 1091 documents
The filter and calibration wheel for the ATHENA wide field imager
2016
The planned filter and calibration wheel for the Wide Field Imager (WFI) instrument on Athena is presented. With four selectable positions it provides the necessary functions, in particular an UV/VIS blocking filter for the WFI detectors and a calibration source. Challenges for the filter wheel design are the large volume and mass of the subsystem, the implementation of a robust mechanism and the protection of the ultra-thin filter with an area of 160 mm square. This paper describes performed trade-offs based on simulation results and describes the baseline design in detail. Reliable solutions are envisaged for the conceptual design of the filter and calibration wheel. Four different varian…
Fundamentals on the Molecular Mechanism of Action of Antimicrobial Peptides
2019
Abstract Antimicrobial peptides (AMPs) are produced by several organisms as their first line of defense. Constituted by amino acids, they may present different mechanisms of action. The antimicrobial activity can be used by the peptide-producing organism itself, as innate immune strategy, or in the industry, applying as natural source preservatives. Understanding the possibilities of the operation of these compounds is a prerequisite for the development of effective uses, as well as for the establishment of combinations, which can even expand their applications considering the possibilities of genetic manipulations. Thus, the objective of this article is to review the basic principles of AM…
Nanoscale Etching of GaAs and InP in Acidic H<sub>2</sub>O<sub>2</sub> Solution: A Striking Contrast in Kinetics and Surface …
2018
In this study of nanoscale etching for state-of-the-art device technology the importance of the nature of the surface oxide, is demonstrated for two III-V materials. Etching kinetics for GaAs and InP in acidic solutions of hydrogen peroxide are strikingly different. GaAs etches much faster, while the dependence of the etch rate on the H+ concentration differs markedly for the two semiconductors. Surface analysis techniques provided information on the surface composition after etching: strongly non-stoichiometric porous (hydr)oxides on GaAs and a thin stoichiometric oxide that forms a blocking layer on InP. Reaction schemes are provided that allow one to understand the results, in particular…
Aqueous Corrosion of the GeSe4 Chalcogenide Glass: Surface Properties and Corrosion Mechanism
2009
International audience; The aqueous corrosion behavior of the GeSe4 glass composition has been studied over time under various conditions (temperature and pH). The evolution of the surface topography by atomic force microscopy and properties such as surface hardness and reduced modulus, as well as the optical transmission in the 1-16 μm window, have been measured as a function of time spent in the corrosive solution. It was found that even if the glass reacts at room temperature, its optical transparency was barely affected. Nevertheless, the durability of GeSe4 was found to be drastically affected by an increase of both temperature and pH. Furthermore, pure selenium nanoparticles were form…
Unexpected Substituent Effects in the Iso-Heterocyclic Boulton-Katritzky Rearrangement of 3-Aroylamino-5-methyl-1,2,4-oxadiazoles: A Mechanistic Stud…
2019
The kinetics of the iso-heterocyclic mononuclear rearrangement of some 3-aroylamino-5-methyl-1,2,4-ozadiazoles was carefully examined under largely variable acidic or alkaline conditions. This reaction may proceed via two different mechanistic pathways (an uncatalyzed and a base-catalyzed one), as accounted for also by the evaluation of the relevant activation parameters. Substituent effects, as quantified by means of the Hammett’s equation, appear relatively modest; however, they reveal some interesting anomalies, which enabled us to draw a very precise picture of the intimate reaction course.
Intermediate-depth earthquake generation and shear zone formation caused by grain size reduction and shear heating
2015
cited By 23; The underlying physics of intermediate-depth earthquakes have been an enigmatic topic; several studies support either thermal runaway or dehydration reactions as viable mechanisms for their generation. Here we present fully coupled thermomechanical models that investigate the impact of grain size evolution and energy feedbacks on shear zone and pseudotachylite formation. Our results indicate that grain size reduction weakens the rock prior to thermal runaway and significantly decreases the critical stress needed for thermal runaway, making it more likely to result in intermediate-depth earthquakes at shallower depths. Furthermore, grain size is reduced in and around the shear z…
Allelopathy and the role of allelochemicals in plant defence
2017
International audience; Allelopathy is described as the interference to plant growth resulting from chemical interactions among plants and other organisms mediated through release of plant-produced bioactive secondary metabolites referred to as allelochemicals. A number of mechanisms have been studied for the release of allelochemicals from various plant tissues including volatilization or leaching from aerial parts, exudation from roots and decomposition of plant residues in soil. Despite differences in biological activity and mode of action, related compounds commonly share similar biosynthetic pathways while some classes of metabolites can be produced using diverse biosynthetic pathways.…
Vertebrate defense against parasites: Interactions between avoidance, resistance, and tolerance
2017
Hosts can utilize different types of defense against the effects of parasitism, including avoidance, resistance, and tolerance. Typically, there is tremendous heterogeneity among hosts in these defense mechanisms that may be rooted in the costs associated with defense and lead to trade‐offs with other life‐history traits. Trade‐offs may also exist between the defense mechanisms, but the relationships between avoidance, resistance, and tolerance have rarely been studied. Here, we assessed these three defense traits under common garden conditions in a natural host–parasite system, the trematode eye‐fluke Diplostomum pseudospathaceum and its second intermediate fish host. We looked at host ind…
Divergent parasite infections in sympatric cichlid species in Lake Victoria
2018
Parasitism has been proposed as a factor in host speciation, as an agent affecting coexistence of host species in species-rich communities and as a driver of post-speciation diversification. Young adaptive radiations of closely related host species of varying ecological and genomic differentiation provide interesting opportunities to explore interactions between patterns of parasitism, divergence and coexistence of sympatric host species. Here, we explored patterns in ectoparasitism in a community of 16 fully sympatric cichlid species at Makobe Island in Lake Victoria, a model system of vertebrate adaptive radiation. We asked whether host niche, host abundance or host genetic differentiatio…
Repeated switches from cooperative to selfish worker oviposition during stingless bee evolution
2018
Reproductive division of labour is a defining feature of insect societies. Stingless bees (Meliponini) are an interesting exception among the highly eusocial insects in that workers of many species contribute significantly to the production of males. Since workers remain sterile in other species of this large tropical tribe, it has been hypothesized that, in the latter species, ancestral queens have won the conflict over who produces the males. The fact that sterile workers of some species lay trophic eggs to feed the queen and display ritualized behaviours towards her during oviposition has been interpreted as an evolutionary relic of this ancient conflict. Here, I used ancestral state est…