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Incorporation and Compensatory Doping Processes of Cu into ZnO Nanowires Investigated at the Local Scale
No full textInternational audienceThe Cu compensatory doping of ZnO nanowires is of great interest to face the challenge arising from the detrimental screening of the piezoelectric potential generated under mechanical solicitations. However, the incorporation processes of Cu into ZnO nanowires are largely unknown. Here, they are investigated locally by combining mass spectrometry and optical spectroscopy with X‐Ray linear dichroism using synchrotron radiation. By varying the Cu(NO 3 ) 2 /Zn(NO 3 ) 2 concentration ratio from 0 to 10% in a chemical bath kept at high pH, it is shown that the amount of Cu incorporated into ZnO nanowires varies from around 4.5 × 10 16 to 3.6 × 10 18 at cm −3 . However, only 15% of the incorporated Cu forms Cu Zn ‐related defects, while the remaining Cu lies on the surfaces of ZnO nanowires. Importantly, thermal annealing under O 2 atmosphere is found to electrically activate the incorporated Cu, resulting in the formation of Cu Zn ‐related defect complexes involving nearby V Zn , the structured green emission band with a strong phonon coupling, and the increase in the electrical resistivity. These findings shed light on the local environment of Cu incorporated into ZnO nanowires and the required conditions for electrically activating the compensatory doping, as an important outcome for enhanced piezoelectric nanogenerators and stress/strain sensors
Perspectives and challenges of marine carbon dioxide removal
No full textInternational audienceThe Paris Agreement to limit global warming to well below 2°C requires drastic reductions in greenhouse gas emissions and the balancing of any remaining emissions by carbon dioxide removal (CDR). Due to uncertainties about the potential and durability of many land-based approaches to deliver sufficient CDR, marine CDR options are receiving more and more interest. We present the current state of knowledge regarding the potentials, risks, side effects as well as challenges associated with technical feasibility, governance, monitoring, reporting and accounting of marine CDR, covering a range of biotic and geochemical approaches. We specifically discuss to what extent a comparison with direct injection of CO 2 into seawater, which had been proposed decades ago and is now prohibited by international agreements, may provide guidance for evaluating some of the biotic marine CDR approaches
Multi-model assessment of the role of anthropogenic aerosols in summertime climate change in Europe
No full textInternational audience1) The role of anthropogenic aerosols in European summertime climate change is assessed using a set of multi-model regional climate simulations• (2) Reduced concentrations of anthropogenic aerosols in Europe lead to an increase in surface solar radiation and an extra warming near surface • (3) Current differences in aerosol representation explain a part of inconsistencies between global and regional climate projections in Europe</div
Is reducing phosphorus inputs sufficient to reduce hypoxia in estuaries? The example of the Loire estuary
No full textInternational audienceCoastal deoxygenation is mainly attributed to excessive nutrient and organic matter inputs from anthropogenic activities. However, although mitigation strategies have been implemented to reduce nutrient inputs, the recovery of estuarine systems has often been limited. By examining long-term data from the turbid Loire estuary, which is prone to summer hypoxia, we aimed to understand the influence of these initiatives on nutrient and dissolved oxygen levels. The data showed that despite the reduction of dissolved phosphorus in the inner estuary, summer hypoxia persisted. By integrating high spatial resolution datasets, we identified nutrient sources, particularly ammonium, in the estuarine turbidity maximum zone. Nutrient recycling is likely to maintain summer hypoxia and hinder ecosystem recovery from hypoxia. A comprehensive understanding of estuarine geochemistry and internal nutrient cycling is essential to develop targeted remediation strategies and mitigate the ongoing threat of hypoxia
Structure determination of 2,5-difluorophenol by microwave spectroscopy
No full textInternational audienceThe Fourier transform microwave spectrum of 2,5-difluorophenol has been obtained in the centimeter wave range, revealing only one conformer stabilized by an intramolecular interaction where the hydrogen atom of the OH group is in a syn orientation to the fluorine atom at the 2-ring position. The heavy atom backbone structure was obtained from the rotational constants of the 13 C and 18 O isotopologues whose spectra were measured in natural abundance. The spectrum of the OD isotopologue obtained by deuterium enrichment was also measured, and the nuclear quadrupole hyperfine structures arising from deuterium were analyzed. The semi-experimental equilibrium structure ( ) was determined by correcting the experimental rotational constants with the vibration-rotation interaction constants obtained via an anharmonic force field. Quantum chemical calculations at various levels of theory were used to support results from the experiments.</div
An approach for modular environmental life cycle assessment of effluent treatment: Configuration of effluent treatment modules based on decision tree tailored to best available techniques
No full textInternational audienceAn approach was developed to configure treatment scenarios for a given industrial effluent based on pollutant composition, intended end use, available technologies, as well as environmental impact assessments of the scenarios. To overcome the complexity of configuring the industrial effluent treatment chain due to the variety of contaminants and diverse available treatment technologies, a decision tree was developed based on the best available technology tailored to pollutant types. A parametric life cycle inventory was developed for the operation phase of fifteen conventional and advanced treatment technology modules to facilitate a comparative environmental impact assessment, including parametric sensitivity and uncertainty analysis. The comparative modular life cycle assessment revealed the hotspots and contributions of fifteen treatment modules to the environmental impacts of treating of 1m3 effluent, with nanofiltration, reverse osmosis, and ion-exchange having the highest overall impacts, whereas cartilage, sand filtration, and UV have the lowest environmental impacts. Sensitivity analysis unveiled high sensitivity of midpoint and endpoint environmental impacts to energy, resin and chemical consumptions. This approach offers a foundational framework for further decision tree developments as a supporting tool for treatment configuration in the effluent treatment industry, as well as sustainability assessment of treatment scenarios derived from the decision trees. Modular treatment configuration integrated into a decision tree promises more flexibility in setting up fit-for-purpose treatment scenarios and conducting modular life cycle assessments for more sustainable effluent treatment
Velocity fields and turbulence from cosmic filaments to galaxy clusters
No full textInternational audienceGalaxy clusters are currently the endpoint of the hierarchical structure formation; they form via the accretion of dark matter and cosmic gas from their local environment. In particular, filaments contribute grandly by accreting gas from cosmic matter sheets and underdense regions and feeding it to the galaxy clusters. Along the way, the gas in filaments is shocked and heated, which, together with the velocity structure within the filament, induces swirling and, thus, turbulence. In this work, we study a constrained hydrodynamical simulation replica of the Virgo cluster to characterise the velocity field in the two cosmic filaments connected to the cluster with unprecedented high resolution. First, we conduct a qualitative examination of slices extracted from the simulation. We study the temperature, the velocity field, and derived quantities in longitudinal cuts to study the general structure of the filaments and in transverse cuts to study their inner organisation and connection to cosmic matter sheets and underdense regions. Then, we conduct a quantitative study of velocities in Virgo's filaments by computing the 2D energy spectrum from 1 and 5~Mpc square maps extracted from the slices and centred on the core of the filaments. We show that the velocity field goes from mostly compressive far in the filaments to mostly solenoidal in Virgo's core. Moreover, we observe that the total energy spectrum in the filaments gains in amplitude and steepens towards Virgo
The Use of Fluorescent Organic Matter as a Natural Transit Time Tracer in the Unsaturated Zone of the Fontaine De Vaucluse Karst System
No full textInternational audienceThe fluorescence index called the Transit Time index (TTi) is based on the fluorescence of natural organic matter in order to qualitatively assess the transit time of karst groundwater, using springs affected by human activities. This study aims to further evaluate the potential of fluorescent compounds as a natural tracer of transit time when applied to unsaturated zone flows with natural catchments, in contrast to the first study. For this purpose, a bi-monthly sampling of one year of monitoring for organic matter fluorescence, TOC, major elements and water-stable isotopes was performed. A conceptual model of the sources and fates of fluorescent compounds is built, emphasizing the allochthonous origin of humic-like C compounds, and the autochthonous production of humic-like M and protein-like compounds within the unsaturated zone. Fluorescent compound intensity interpretation according to this model reveals consistent relative transit times with flow behavior and also provides complementary information. The results also show the TTi’s ability to summarize fluorescent compounds, its consistency with relative transit time, and its higher sensitivity as compared to other natural tracers. However, prior to its use, a thorough assessment of soil organic matter, microbial activity, and potential anthropogenic contamination is required, encouraging interdisciplinary collaboration between hydrogeologists, microbiologists and soil scientists
Sensitivity Analysis of Global Kinematics on Mantle Structure Using Automatically Generated Adjoint Thermochemical Convection Codes
No full textInternational audienceWithin the past 30 years, numerical models of mantle convection have been able to predict observations on Earth and planets, and among them tectonics. The possibility of building inverse problems in global geodynamics became concrete, and often involve the development of adjoint codes. Such tools provide efficient ways to estimate sensitivities of misfit functions relative to control parameters, like errors on predicted velocities relative to mantle 3D structure. One issue to build an adjoint code is that such code is problem specific in many cases, while forward codes are versatile. We propose here a way to build adjoint codes that are exact adjoints of forward codes through an automated process. Using the automatic differentiation translator TAF \cite{giering2003} and incorporating specific implementations for MPI communications, we generate two adjoint codes of the 3D spherical thermomechanical mantle convection code StagYY \cite{tackley2008}. We first present a benchmarking example computing the sensitivities of a thermal state to initial conditions with a 3D spherical thermochemical model. We then compute the sensitivities of present-day plate velocities relative to guessed temperature distribution in the mantle. The sensitivities reflect either the intrinsic sensitivity of the problem (sensitivity to upper mantle structure) and the errors made in reconstructing the thermal structure of the mantle (deepest mantle structure). Both codes successfully pass the rigorous and demanding gradient test, also called Taylor test. We show that our workflow for automatic generation of adjoint codes for StagYY provides a sustainable and adaptive method to engage in inverse modelling and sensitivity computations of 3D global geodynamics
Impact of pressure anisotropy on the cascade rate of Hall magnetohydrodynamic turbulence with biadiabatic ions
No full textInternational audienceThe impact of ion pressure anisotropy on the energy cascade rate of Hall-MHD turbulence with biadiabatic ions and isothermal electrons is evaluated in three-dimensional direct numerical simulations, using the exact (or third-order) law derived by Simon and Sahraoui in 2022. It is shown that pressure anisotropy can enhance or reduce the cascade rate, depending on the scales, in comparison with the prediction of the exact law with isotropic pressure, by an amount that correlates well with pressure anisotropy, , that develops in simulations initialized with an isotropic pressure (). A simulation with initial pressure anisotropy confirms this trend, exhibiting a stronger impact on the cascade rate, both in the inertial range and at larger scales, close to the forcing scales. Furthermore, a Fourier-based numerical method, to compute exact laws in numerical simulations in the full () increment plane, is presented