Hydrothermal alteration of the surface volcanic rocks at the Acoculco geothermal field,Mexico:a multi-parametric approach

The studies on hydrothermal alteration-induced eff ects in surface and subsurface rocks provide useful information in the characterization and exploitation of a geothermal reservoir.Generally,these studies are based on traditional,and reliable methods like petrography(primary and secondary minerals,and grade of alteration),and geochemistry(mobility of elements,changes in mass and concentration of elements,and fluid inclusions).Recently,apart from these established methods,some methods based on the geochemical(Chemical Index of Alteration,CIA;Weathering Index of Parkar,WIP;Loss on Ignition,LOI;and Sulfur,S)and rock magnetic properties(magnetic susceptibility,χlf;and percentage frequency-dependent susceptibility,χfd%)are also being applied in the identification of whether a rock is an altered or a fresh one.The Acoculco Geothermal Field(AGF),Mexico,is characterized by high temperature and very low permeability,and it is considered a promissory Enhanced Geothermal System.The following changes are observed in the rocks as a result of an increase in hydrothermal alteration:(1)an increase in CIA,LOI,and S values,and a decrease in WIP;(2)an increase in quartz and quartz polymorph minerals(silicification),and clay minerals(argillization);and(3)decrease inχlf values.At AGF,the most altered surface acid rocks are characterized by entirely quartz and its polymorphs,and clay minerals.The present study also indicates the applicability of the binary plots of major elements(felsic vs mafic component)and rock magnetic parameters(χlf vs.χfd%).The rock withχfd%value of 2-10 andχlf value<0.5×10^(-6)m^(3) kg^(-1)indicate the presence of single domain and stable single domain grains,which in turn suggests that it is an altered rock.These methods are simple to apply,rapid,reliable,and have the potential to become eff ective tools for the identifi cation of hydrothermally altered rocks during the initial stage of geothermal exploration.

Host-parasite interactions in perpetual darkness:Macroparasite diversity in the cavefish Astyanax mexicanus

Astyanax mexicanus has repeatedly colonized cave environments,displaying evolutionary parallelisms in many troglobitic traits.Despite being a model system for the study of adaptation to life in perpetual darkness,the parasites that infect cavefish are practically unknown.In this study,we investigated the macroparasite communities in 18 cavefish populations from independent lineages and compared them with the parasite diversity found in their sister surface fish populations,with the aim of better understanding the role that parasites play in the colonization of new environments.Within the cavefish populations,we identified 13 parasite taxa,including a subset of 10 of the 27 parasite taxa known for the surface populations.Parasites infecting the cavefish belong to five taxonomic groups,including trematodes,monogeneans,nematodes,copepods,and acari.Monogeneans are the most dominant group,found in 14 caves.The macroparasites include species with direct life cycles and trophic transmission,including invasive species.Surprisingly,paired comparisons indicate higher parasite richness in the cavefish than in the surface fish.Spatial variation in parasite composition across the caves suggests historical and geographical contingencies in the host-parasite colonization process and potential evolution of local adaptations.This base-line data on parasite diversity in cavefish populations of A.mexicanus provides a foundation to explore the role of divergent parasite infections under contrasting ecological pressures(cave vs.surface environments)in the evolution of cave adaptive traits.

Gas Chromatography as an Analytical Monitoring Technique for Hydrogen Production from Spirulina maxima 2342

Hydrogen (H2) production from experiments with Spirulina maxima 2342 is reported in this work. The performance of this photosynthetic microorganism for producing H2 was evaluated for the first time under specific experimental conditions (e.g., a biomass concentration of 0.34 ± 0.02 g, a light intensity of 150 μE.s-1.m-2 and reaction times of 19.3 ± 1.2 h). The performance of this photosynthetic microorganism for producing hydrogen was successfully improved by the addition of sodium dithionite (a reducing agent) as an innovative method for increasing the gas production, and as a main contribution of this work. Quantitative gas chromatography (GC) analyses of H2 to verify the production performance were successfully carried out at low concentration levels. GC analyses were performed by means of a conventional thermal conductivity detector coupled to a separation system of a Molecular Sieve column 500 mm × 3175 mm (L × ID). Low detection limits were consistently obtained with the GC system used. The separation of H2 in culture samples was efficiently achieved in average retention times of 1.47 min. The H2 produced in this process was subsequently used for power generation using a Proton Exchange Membrane Fuel Cell (PEMFC).

Highly graphitized carbon nanosheets with embedded Ni nanocrystals as anode for Li-ion batteries

A C/Ni composite was prepared via thermal decomposition of a nickel oleate complex at 700℃,yielding disperse Ni nanocrystals with an average size of 20 nm,encapsulated by carbon nanosheets as deduced from transmission electron microscopy(TEM)images and confirmed from X-ray photoelectron spectroscopy(XPS).Furthermore,the X-ray diffraction pattern revealed a good ordering of the carbon layers,forced by the Ni encapsulation to adopt a bending structure.Considering the close interaction between the graphitized framework and the metallic nanoparticles we have studied the properties of the composite as an anode for Li-ion batteries.Compared with other nanostructured synthetic carbons,this carbon composite has a low voltage hysteresis and a modest irreversible capacity value,properties that play a significant role in its behaviour as electrodes in full cell configuration.At moderate rate values,0.25 C,the electrode delivers an average capacity value around 723 mAh·g^−1 on cycling,among the highest values so far reported for this carbon type.At higher rate values,1 C,the average capacity values delivered by the cell on cycling decrease,around 205 mAh·g^−1,but it maintains good capacity retention,a coulombic efficiency close to 100%after the first cycles and recovery of the capacity values when the rate is restored from 3 to 0.1 C.

The anthocyanin's role on the food metabolic pathways,color and drying processes:An experimental and theoretical approach

This review is intended to cover the works related to the anthocyanin behavior in food that is subjected to drying.Both experimental and theoretical results available in scientific literature are discussed.An increase in anthocyanin concentration has been observed upon thermal processing.Nevertheless,a conclusive explanation is still unavailable.The accessible studies suggest an increase in concentration during maturations,which could be related to the enzymatic activity.The possible enzymes involved in such a procedure have also been covered,including their role played in the process.The possible activation mechanisms and the related factors such as temperature,pH,oxygen contents and the presence of UV-light irradiation were also considered.Moreover,the metabolic pathways were also explored including experimental evaluation and theoretical models based on atomistic methodologies such as density functional theory(DFT).This review is aimed to provide a comprehensive overview of the probable mechanisms behind the increase of anthocyanin concentration during drying.