1,721,543 research outputs found
Ionic Syntax and Equilibrium Approach to Redox Exchanges in Melts
No full textThe properties of melts and glasses are heavily affected by redox equilibria and these are sensitive to changes in temperature, oxygen fugacity and composition. The compositional control includes the amphoteric behaviour of some components such as iron oxides and demands the understanding of the link between redox, acid-base properties and structural coordination. This goes through a precise and coherent chemical "syntax" for redox and more in general chemical exchanges in melts and magmas. This syntax applies also to the understanding of how bulk composition drives the redox evolution via melt and gas speciation from source depths up to surface. Useful shortcuts and rules of thumbs might be adopted, but we must keep in mind that redox is not a Maxwell's demon or an adjustable parameter. Rather, it is the twin-face of acid-base exchanges that occur in chemically complex mixtures and solutions. In this study we show that recognizing chemically reactive entities allows decrypting the effect of composition on redox patterns of iron and sulfur. Besides, this allows proposing a stoichiometry-based methodology to describe in detail the chemical mechanisms that drive the melt system to get rid of sulfur via decompression, degassing, and precipitation of S-bearing phases. These stoichiometric constraints allow exploring the different features of magma degassing in basaltic and andesitic systems, independently of any model of redox state proposed in the literature
Redox equilibria: From basic concepts to the magmatic realm
No full textThe basic aspects of redox geochemistry are reviewed to provide a useful compendium of the redox connection between the aqueous-hydrothermal and igneous realms of Earth. The redox description of a system is intimately coupled to the knowledge of acid-base properties of the solvent in which redox exchanges take place. For magmas, and then silicate melts, approaches reporting the redox state were so far cantered around the sole concept of oxygen fugacity, f O 2 . Mastering the concept of f O 2 in experimental and observational petrology was the key to constrain the processes behind the very large range of relative oxygen fugacity observed on Earth. Although current descriptions of silicate melts and magma thermodynamic properties are mainly based on oxides or mineral-like molecular components, disregarding the actual melt reactivity poses many limits in our understanding of the true chemical exchanges involving oxygen, iron and the other redox-sensitive elements. Because silicate melts, unlike aqueous solutions, lack of a full acid-base description, compositional dependencies are solved by means of empirical treatments based on oxides and their combinations. However, these can bias the interpretation of redox exchanges recorded in analyzed samples and used to identify the several processes (e.g., batch or fractional crystallization, elemental recycling, degassing, deep fluid infiltration) which characterize magma evolution and its geodynamic environment. This short compendium aims at stimulating the quest for a comprehensive and unifying picture of the acid-base and redox properties of melts from which we could extrinsic its reactivity in way similar to aqueous solutions and molten salts
Volcanic and geothermal redox engines
No full textThe redox (reduction-oxidation) potential is an essential variable that controls the chemical reactions of fluids in magmatic and associated geothermal systems. However, the evolution of the redox potential is difficult to trace from a magma's source at depth to the surface. The key is knowing that electron transfer is the twin face of the acid-base exchanges that drive charge transfer in the many reactions that occur in multiphase and chemically complex systems. The deduced redox reactivity can reveal many features about the evolution of a system's composition and the external factors that control it. As such, redox potential analysis is an important geochemical tool by which to monitor volcanoes and to explore geothermal systems
Harnessing mosquito-Wolbachia symbiosis for vector and disease control
No full textMosquito species, members of the genera Aedes, Anopheles and Culex, are the major vectors of human pathogens including protozoa (Plasmodium sp.), filariae and of a variety of viruses (causing dengue, chikungunya, yellow fever, West Nile). There is lack of efficient methods and tools to treat many of the diseases caused by these major human pathogens, since no efficient vaccines or drugs are available; even in malaria where insecticide use and drug therapies have reduced incidence, 219 million cases still occurred in 2010. Therefore efforts are currently focused on the control of vector populations. Insecticides alone are insufficient to control mosquito populations since reduced susceptibility and even resistance is being observed more and more frequently. There is also increased concern about the toxic effects of insecticides on non-target (even beneficial) insect populations, on humans and the environment. During recent years, the role of symbionts in the biology, ecology and evolution of insect species has been well-documented and has led to suggestions that they could potentially be used as tools to control pests and therefore diseases. Wolbachia is perhaps the most renowned insect symbiont, mainly due to its ability to manipulate insect reproduction and to interfere with major human pathogens thus providing new avenues for pest control. We herein present recent achievements in the field of mosquito Wolbachia symbiosis with an emphasis on Aedes albopictus. We also discuss how Wolbachia symbiosis can be harnessed for vector control as well as the potential to combine the sterile insect technique and Wolbachia-based approaches for the enhancement of population suppression programs. © 2013 International Atomic Energy Agency 2013
Natural and artificial envenomation of Ceratitis capitata by Eupelmus urozonus and the search for new bioinsecticides
No full textThis study was designed to indentify novel bioactive molecules in the venom of the parasitoid Eupelmus urozonus Dalman (Hymenoptera: Eupelmidae). Parasitism by E. urozonus induces apparent paralysis in the larvae of the host Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) and it arrests the development of host pupae. Parasitoid eggs were transferred from stung to unparasitized host pupae to determine whether adult female stings or bites from the first instars were responsible for the above effects. The two treatments gave the same results, indicating that both parasitoid adults and larvae produced venoms capable to compromise host development. A protocol was developed to artificially microinject E. urozonus venom into healthy host pupae and adults at known concentrations to study the effects. The microinjection of venom was found to produce the same macroscopic result as natural parasitization, indicating that host developmental arrest was caused by molecules produced by the parasitoid venom glands. One-tenth, one-twentieth, and one-hundredth of the contents of a female venom reservoir was sufficient to compromise the development of 100, 90, and 50% of the microinjected host pupae, respectively. The microinjection of 0.1 female venom equivalents into host adults always caused death within 24 h. Extraction and freezing did not affect the activity of the E. urozonus venom, which facilitates its storage, whereas denaturation treatments demonstrated that the bioactive molecules were proteins. The venom was also found to prevent the hosts from decaying for over 2 weeks and it promoted the accumulation of unknown subspherical granules in the host haemocoel. These results suggest the potential identification of novel molecules with interesting biological activity with various possible applications. © 2014 The Netherlands Entomological Society
Larvicidal activity of steroidal saponins from Dracaena arborea on Aedes albopictus
No full textIntroduction: Development of new and improved mosquito control methods, that are economically sustainable and effective, is a critical requirement in the management of vector-borne epidemic diseases. Aedes albopictus is one of the main vectors of various important pathogens in the tropics, which now have the potential to also spread in temperate regions, owing to the environmental and climate changes in act. Materials and Methods: We report about the isolation of steroidal saponins from Dracaena arborea by fractionation followed by column separation. The obtained fractions and/or pure compounds were tested by biological essays for their insecticidal activity against A. albopictus larvae. Results: Various compounds were found to exert larvicidal effects. In specific, spiroconazole A demonstrated the best insecticidal activity, showing LT50 value of 57.23 hours at 25 ppm. Discussion: We finally discuss about the value of this finding in the context of the present strategies of Integrated Mosquito Management. © 2016 Bentham Science Publishers
Male mating performance and cytoplasmic incompatibility in a wPip Wolbachia trans-infected line of Aedes albopictus (Stegomyia albopicta)
No full textWolbachia pipientis Hertig (Rickettsiales: Rickettsiaceae) is a maternally inherited endosymbiont of a large number of insects and other arthropods that induces various effects on host reproductive biology. Among these, cytoplasmic incompatibility (CI) is a form of sterility induced in eggs produced by mating between infected males and females uninfected or infected by an incompatible Wolbachia strain. This phenomenon has been proposed as a potential way to produce functionally sterile males to be used in genetic control programmes. In this paper, we report on experiments carried out to evaluate the mating performances of males of an Aedes albopictus (Stegomyia albopicta) (Diptera: Culicidae) line (ARwP), harbouring a new Wolbachia infection [the wPip strain from Culex pipiens Linnaeus (Diptera: Culicidae)], in comparison with naturally infected males (SR line). ARwP males did not differ from SR males with regard to insemination capacity. Mating competitiveness did not differ significantly between lines in either laboratory or greenhouse conditions. Moreover, crosses with SR females were characterized by a 100% CI regardless of ARwP male age. All of these findings suggest that ARwP males may represent a very efficient tool for control programmes against Ae. albopictus based on the release of functionally sterile males. © 2012 The Royal Entomological Society
Static Analysis of Current Limiting Techniques for Accurate Memristor Programming
No full textWe discuss a novel investigation approach to study current limiting techniques for accurate memristor programming. In detail, referring to the case of the Stanford memristor model, we propose to analyze its programming dynamics adopting a nonlinear static analysis point of view and considering, for the sake of simplicity, the special case of a linear resistive current limiter
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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