Periodic density functional study of Rh and Pd interaction with the (100)MgO surface

The adsorption geometry and electronic properties of palladium and rhodium atoms deposited on the regular (100)MgO surface were analyzed by means of periodic DFT calculations using local, gradient-corrected and hybrid (B3LYP) functionals. Spin-polarized computations revealed doublet spin state of Rh atom to be the most stable electronic state for the adsorbed rhodium atom on (100)MgO. The preferred adsorption site of the metal (Pd and Rh) atoms was found to be the site on top of the surface oxygen atoms. A relatively stable geometry for the adsorption of the Pd and Rh in a bridge position above the two surface oxygens was found as well. The electronic structures suggested partly covalent bonding with contribution from electrostatic attraction between the metal and the oxygen atoms for both optimized structures. Small charge transfer was obtained from the support to the Pd and Rh metal atoms. The calculations showed that rhodium was bound stronger to the substrate probably due to stronger polarization effects

A DFT study of the NO adsorption on Pdn (n = 1–4) clusters

We report a density-functional study of some properties of the adsorption process of the NO molecule on small palladium clusters (n = 1–4). The interaction between NO and the Pdn clusters is studied on various adsorption sites. Both, NO and Pdn geometrical relaxations are taken into account. The significant conformational reconstruction of the metallic cluster upon NO adsorption induces a large decrease of the NO adsorption energy. Nevertheless, the N–O binding energy is strongly weakened when the molecule is adsorbed on the small Pdn clusters due essentially to an electrostatic repulsion between both N and O atoms. The possible dissociation process of NO on Pd4 cluster is then investigated within two processes: the NO molecule does not dissociate on Pd4 with process (i) (dissociation of the isolated gas phase NO molecule followed by the adsorption of both nitrogen and oxygen atoms on the cluster). Process (ii)which presents three successive steps (adsorption of the NO molecule, dissociation of the NO molecule adsorbed on Pd4, adsorption of the O atom on the cluster) is studied in details and we propose a reaction pathway locating transition states and intermediate species. The activation energy for process (ii) is high and the dissociation of the NO molecule on the Pd4 cluster is thus highly improbable

The adiabatic invariant of any harmonic oscillator : an unexpected application of Glauber's formalism

In this theoretical paper, we propose a general derivation of the adiabatic invariant of the n-degree-of-freedom harmonic oscillator, available whichever the physical nature of the oscillator and of the parametrical excitation it undergoes. This derivation is founded on the use of the classical Glauber variables and ends up with this simplest result: the oscillator's adiabatic invariant is just the sum of all the semiclassical quanta numbers associated with its different eigenmodes

De Nabucodonosor a Hadriano: respigaduras midráxias sobre o Livro de Lamentações

Resumo: este artigo pretende ilustrar como o livro de Lamentações, composto depois da destruição do primeiro Templo de Jerusalém em 587 a.C. e lido na sinagoga a cada ano na festa do dia 9 de Av, foi relido à luz das sucessivas experiências traumáticas coletivas do povo judeu ao longo da história. Para tanto, apresenta traduções de trechos extensos do seu comentário rabínico tradicional, o Lamentações Rabbah, que relatam vários episódios da primeira guerra judaico-romana que culminou na destruição do segundo Templo em 70 d.C. e da revolta de Simão Bar Kokhba (132-136 d.C.). Palavras-chave: Livro de Lamentações. Releituras bíblicas. Lamentações Rabba

The ash mass load of volcanic plumes: retrievals from a new millimeter-wave radar at Stromboli and Sabancaya volcanoes

In the framework of the French Government Laboratory of Excellence ClerVolc initiative, two experiments using a new millimeter-wave radar were carried out to retrieve various physical properties of the ash plumes, especially the mass loading parameters which are critical for the modelling of ash dispersal, as well as to study the internal dynamics of the plumes and their fallout. First measurements at Stromboli in 2015 using a 95 GHz cloud radar prototype with a fixed beam pointing above the crater characterized the distribution of plume internal reflectivities, plume widths and durations at unprecedented space-time resolutions. Combining radar in situ measurements with data modelling from a disdrometer and ash sampling on the ground further allowed the retrieval of ash concentration and gradients inside the plumes, and sometimes proximal fallout. Plume maximum ash concentration range from 1 mg/m3 to about 1 g/m3. Structuration of ash concentration with variations by a factor of 3 was also found to occur inside the falling ash in correlation with variations in the sedimentation rate measured on the ground by the disdrometer. New results from radar measurements inside stronger plumes and fallout at Sabancaya volcano (Peru, May 2018) using volume scans will also be presented

Surveillance des flux d’azote en zone de captage : Premières avancées du projet RIVE

L’azote est un des éléments nutritifs les plus utilisé en agriculture. L’impact d’un excès d’azote sur la qualité des eaux est bien connu. Cela provoque notamment la pollution en nitrate des eaux souterraines. Par ailleurs, lors de l’applicationde ces fertilisants azotés, une quantité non négligeable de l’azote est perdue par volatilisation sous forme d’ammoniac. Ces émissions engendrent des nuisances olfactives et sont également responsables de la formation de particules fines. Ces pollutions peuvent être réduites en améliorant les pratiques culturales et plus particulièrement la fertilisation. Le projet de recherche RIVE (Ruissellement, Infiltration, Volatilisation, Erosion) financé par la SPGE (Société Publique de la Gestion de l'Eau, BE) est basé sur la surveillance d'une prairie permanente entourant une zone de captage dont les concentrations en nitrate sont trop importantes. Ce projet, de deux ans, vise à développer un outil d’aideà la décision concernant les pratiques agricoles dans les zones de captage d’eaude distribution, affectées notamment par l’agriculture. L’ensembledes données récoltées permettra de déterminer un bilan azote complet en zones agricoles et d'adapter les pratiques agricoles afin de réaliser des apports azotés optimaux

Ash concentration of Sabancaya volcanic plumes retrieved from a 95 GHz radar and a disdrometer

We have carried out an experiment using a 3.2 mm-wavelength scanning Doppler radar and a laser disdrometer to investigate ash plumes of Sabancaya volcano (Peru) in May 2018. Our main objectives were to retrieve the mass loading parameters (concentration, mass flux) which are critical for the modelling of ash dispersal, as well as to study the dimensions and internal dynamics of the eruptive columns, plumes and fallout. The radar and the disdrometer were respectively located at 4.5 km NNE and 4.5 km E from the vent. Multiple radar sounding configurations were tested either in fixed-pointing mode, generally close to the source, or using scans across various regions of the plumes. Particle Size Distribution, shapes and density were characterized from microphysical analyses, sieving and water pycnometry of ash samples collected on the ground. A Parsivel2 disdrometer also recorded the sizes, and settling velocities of fallout, allowing us to estimate sedimentation rates on the ground and to derive an empirical law relating calculated ash concentrations and reflectivities. Comparing the latter with reflectivities measured by the radar at unprecedented space-time resolutions (down to 12.5 m and 0.25 s) allowed us to obtain the internal mass distribution of eruptive columns, plumes, and fallout at various distances from the emission source

S’engager résolument vers une gestion améliorée des ressources en eau au Burkina Faso

Department for International Development (DFID