Mediterranean biodiversity gradient initiated by basin restriction

Physical connectivity between marine basins facilitates population exchange and hence controls biodiversity. The Mediterranean Sea is a semi-restricted basin with only a small two-way connection to the global ocean, and it is a region heavily impacted by climate change and biological invasions today. The massive migration of non-indigenous species into the basin through the Suez Canal, driven and enabled by climate warming, is drastically changing Mediterranean biodiversity. Understanding therefore the origin and cause(s) of pre-existing biodiversity patterns is crucial for predicting future impacts of climate change. Mediterranean biodiversity exhibits a west-to-east decreasing gradient in terms of species richness, but the processes that resulted in this gradient have only been hypothesized. By examining the fossil record, we provide evidence that this gradient developed 5.33 million years ago at the end of the Messinian Salinity Crisis, and it was therefore caused by the re-population of the basin by marine species with a dominating western source at the Mediterranean¿Atlantic gateway

High spatial resolution analysis of ferromanganese concretions by LA-ICP-MS†

A procedure was developed for the determination of element distributions in cross-sections of ferromanganese concretions using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The effects of carrier flow rates, rf forward power, ablation energy, ablation spot size, repetition rate and number of shots per point on analyte intensity were studied. It is shown that different carrier gas flow rates are required in order to obtain maximum sensitivities for different groups of elements, thus complicating the optimisation of ICP parameters. On the contrary, LA parameters have very similar effects on almost all elements studied, thus providing a common optimum parameter set for the entire mass range. However, for selected LA parameters, the use of compromise conditions was necessary in order to compensate for relatively slow data acquisition by ICP-MS and maintain high spatial resolution without sacrificing the multielemental capabilities of the technique. Possible variations in ablation efficiency were corrected for mathematically using the sum of Fe and Mn intensities. Quantification by external calibration against matrix-matched standards was successfully used for more than 50 elements. These standards, in the form of pressed pellets (no binder), were prepared in-house using ferromanganese concentrates from a deep-sea nodule reference material as well as from shallow-marine concretions varying in size and having different proportions of three major phases: aluminosilicates, Fe- and Mn-oxyhydroxides. Element concentrations in each standard were determined by means of conventional solution nebulisation ICP-MS following acid digestion. Examples of selected inter-element correlations in distribution patterns along the cross-section of a concretion are given

A Spectroscopic Study of Tautomeric Equilibrium of Salicylideneaniline in ZSM-5 Zeolites

Salicylideneaniline (SA) sorbed in cation-exchanged M-ZSM-5 (M = H+, Li+, Na+, K+, Rb+, Cs+ and Zn2+) zeolites was studied by spectroscopic techniques assisted by quantum-chemical calculations. The nature of extra-framework cations present in the zeolite void was found to affect the spectral signature of the sorbed SA molecule that points to the shift of tautomeric equilibrium between the enol and keto forms. Small size cations, such as H+ and Li+, stabilize a cis-keto SA tautomer along with a enol one in the zeolite structure. The calculations indicate that the sorbed cis-keto tautomer may have the dipole large enough to be considered as a zwitterion. New features appearing in the spectra with the increase of the cation size were attributed to the presence of trans-keto SA tautomer, which up to now has been observed only in time-resolved spectroscopic experiments. A strong interaction of the molecule with cations in Zn-ZSM-5 zeolite results in the chelation of enol SA with the divalent Zn2+ ions. The results of the study suggest that the tautomeric equilibrium of molecules belonging to the Schiff base family can be tuned by the confinement in the nanoporous materials via a choice of topology of zeolite framework and the nature of extra-framework cations

Spontaneous Ionization and Electron Transfer of Polyaromatics by Sorption in ZSM-5 Zeolites

This article reviews the recent works of the authors about the spontaneous ionization and subsequent electron transfer of polyaromatic molecules upon sorption into ZSM-5 zeolites. The results demonstrate once again that the tight fit between the size of rod shape polyaromatic molecules and the diameter of the straight channel can stabilize radical cation-electron pairs or electron–hole pairs over long periods. Applying diffuse reflectance UV–visible absorption (DRUVv) spectrometry, Raman scattering spectrometry and continuous wave electron paramagnetic resonance (CW-EPR) we were able to monitor with in situ conditions the sorption and ionization of biphenyl (BP), naphthalene (NPH) and anthracene (ANTH) in ZSM-5 zeolite samples with Mn(AlO2)n(SiO2)96–n composition per unit cell (UC) (n = 0–6.6; M = H+, Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+). Particular emphasis was placed on pulsed electron paramagnetic resonance (EPR) spectrometry, which has shown to be a powerful technique for a new insight of the ejected electron. The spontaneous ionization is an intrinsic property of the inner surface of the porous materials, which depends both on the ionization potential of sorbate and the polarization energy of the host at the sorption site. For molecules with relatively low ionization potential such as ANTH (IP 7.44 eV) the ionization can occur in both dehydrated acidic and non acidic MnZSM-5 (n > 2; M = H+, Li+, Na+, Mg2+, Ca2+) zeolites. However, the ionization yield was found to highly depend on the nature of the extraframework cation and was found to decrease from H+ (100%) > Li+ (30%) ~ Mg2+ ~ Ca2+ >> Na+ >> K+, Rb+, Cs+ (0%). It was established that the ejected electron is trapped as isolated electron in the oxygen framework in close proximity of Al atoms and extraframework cations with some pairing electronic effect with the ANTH•+ radical cation. Calcination of acidic HnZSM-5 under molecular oxygen is a prerequisite for the spontaneous ionization of BP (IP 8.16 eV) and NPH (IP 8.14 eV) with higher ionization potential. The spontaneous ionization of molecules with relatively high ionization potential such as NPH and BP was effective upon sorption after generation of electron acceptor Lewis acid sites. The oxidizing power of radical cations BP•+ and NPH•+ initiates at room temperature subsequent electron abstraction from the framework and generates unusual long-lived electron–hole pairs. The oxidizing power of ANTH•+ is inefficient at room temperature but is effective at 450 K. The electron and positive hole are trapped in the oxygen framework in close proximity of Al and proton with electronic interactions with the occluded sorbate before the final charge recombination. To cite this article: S. Marquis et al., C. R. Chimie 8 (2005)

Modelling of Boiling Heat Transfer in a Turbulent Channel Flow

International audienceA numerical study of boiling heat transfer in a turbulent liquid-vapor flow inside a heated channel is carried out for various flow conditions. The model used for the flow simulation is the Volume Of Fluid model (VOF) for liquid-vapor interface tracking coupled with a k−ε low Reynolds model to predict the effect of turbulence. Boiling and condensation phenomena are included in the model based on the general laws of phase change. The obtained results are compared with available experimental measurements in the literature, where the effect of subcooling, channel inclination and flow velocity on the vapor distribution were investigated. The computational predictions of the vapor bubble development along the heated wall are in satisfactory agreement with experimental results

Long-lived spin-correlated pairs generated by photolysis of naphthalene occluded in non-Brønsted acidic ZSM-5 zeolites

Long-lived spin-correlated pairs were generated by laser irradiation of naphthalene (NAP) occluded as intact molecule within non-Brønsted acidic MnZSM-5 zeolites with MnSiO2)96-n(AlO2)n formula per unit cell. The laser UV photoionization generates primary NAP+-electron pair as a fast phenomenon. These charge carriers exhibit lifetimes that extend over less than 1 h at room temperature and disappear according to two parallel competitive ways: direct charge recombination and electron transfer. This subsequent electron transfer takes place between the electron-deficient radical cation (NAP+) and the electron-donor oxygen atom of zeolite framework. The aluminum rich MnZSM-5 zeolites (n = 3.4, 6.6) hinder efficiently the charge recombination and promote the electron transfer to generate a very long electron-hole pair which exceeds several weeks at room temperature in [email protected]. The electron-hole pair exhibits broad visible absorption bands at 482 and 525 nm. The electron-hole distance, 1.3 nm, was deduced from the dipolar interaction term (D) value. The spin density of trapped electron appears spread over 27Al, 29Si, 7Li, and 1H nuclei as deduced by two-dimensional approach of hyperfine sublevel correlation (HYSCORE). The very low recombination rate by tunneling effect was found to be in agreement with the very low value (J 0) of the magnetic exchange. The combined effects of tight fit between NAP size and straight-channel dimension, the high aluminum content of the framework, and the highly polarizing cation Li+ trapped efficiently the ejected electron in the conduction band and the hole in the valence band of the porous materials

Water Transport in Bio-based Porous Materials A Model of Local Kinetics of Sorption—Application to Three Hemp Concretes

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Effects of Initial Conditions on Simulations of Hygrothermal Transfers Through a Bio-Based Multi-layered Wall Subjected to a Real Climate

International audienceThis modeling study investigates the effects of the initial conditions on a bio-based multi-layered wall by hygrothermal simulations. Such a study cannot be found in the relevant literature. In a first step, the work consists in numerically generating different climate histories for the studied wall, using two different real climates: a winter and a spring climate. Then, the wall preloaded with these two different climate histories and therefore different hygric and thermal initial conditions is subjected to several cycle of 18 days of the spring climate. This study highlights the significant effects of the initial conditions on the subsequent simulations: strong differences are predicted about relative humidity and water content. Many cycles of 18 days of the spring climate have to be applied to obtain a hygric convergence of the two simulations, i.e., to erase the wall hygric history. The analytic analysis of the results leads to define characteristic times of hygric dependency of about 35–40 days. It appears that the hygric predictions of the simulations become independent of the initial conditions after about three times these characteristic times, i.e., about 3.5 months. Comparatively, the thermal history takes only a few days to be erased. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd

A model of local kinetics of sorption to understand the water transport in bio-based materials

International audienceThe classic models describing the hygric mass transfers inside porous materials seem unsuitable in the case of bio-based materials. They are based on the assumption of instantaneous local equilibrium between relative humidity and water content [1]. These two parameters evolve according to the diffusive fluxes following the sorption isotherms. This study shows that it leads to predict much shorter times of stabilization than those experimentally obtained. A new approach is presented here, it frees from the local instantaneous equilibrium introducing a local kinetics to describe the transformation of water from vapor state to liquid state and vice versa. The local kinetics of sorption is coupled with the well-known hysteresis phenomenon. It is adjusted from bibliographic data [2] giving mass evolution of three hemp concretes under adsorption / desorption conditions. 1D cylindrical simulations allows an excellent fitting on the experiments. Finally, a semi-empirical model is proposed, allowing to determine the kinetics parameters more easily. The effect of the local kinetics model on the hygrothermal transfers occurring through a bio-based wall is then studied

Spontaneous ionization of N-alkylphenothiazine molecules adsorbed in channel-type zeolites: effects of alkyl chain length and confinement on electron transfer.

International audienceThe mere mixing of N-alkylphenothiazines with three channel-type acid zeolites with various structures (ferrierite, H-MFI, and mordenite) induces the spontaneous ionization of the heterocyclic molecule in high yield upon adsorption. The diffuse reflectance UV-visible absorption and Raman scattering spectra show that the accessibility of the highly polarizing acid sites is not indispensable to induce the spontaneous ionization process. Due to their particularly low ionization potential values (6.7 eV), the adsorption of the molecules on the external surface or in the inner volume is the key parameter to generate the radical cation. However, the ionization yield and charge stabilization are intimately correlated to the possibility of the zeolites accommodating molecules inside their channels. Moreover, the higher electrostatic field gradient induced by high confinement is required to favor the second ionization and dication formation. The alkyl chain length plays a decisive role by either slowing down the diffusion process or blocking the molecule at the pore entry. Therefore, the efficiency of the ionization process that depends on the number of adsorbed molecules decreases significantly from phenothiazine to the N-alkylphenothiazines. The spectral data demonstrate that deformation of the alkyl group is necessary to allow the diffusion of the molecules into the channels