On the thermal and thermodynamic (In)stability of methylammonium lead halide perovskites

The interest of the scientific community on methylammonium lead halide perovskites (MAPbX3, X = Cl, Br, I) for hybrid organic-inorganic solar cells has grown exponentially since the first report in 2009. This fact is clearly justified by the very high efficiencies attainable (reaching 20% in lab scale devices) at a fraction of the cost of conventional photovoltaics. However, many problems must be solved before a market introduction of these devices can be envisaged. Perhaps the most important to be addressed is the lack of information regarding the thermal and thermodynamic stability of the materials towards decomposition, which are intrinsic properties of them and which can seriously limit or even exclude their use in real devices. In this work we present and discuss the results we obtained using non-ambient X-ray diffraction, Knudsen effusion-mass spectrometry (KEMS) and Knudsen effusion mass loss (KEML) techniques on MAPbCl3, MAPbBr3 and MAPbI3. The measurements demonstrate that all the materials decompose to the corresponding solid lead (II) halide and gaseous methylamine and hydrogen halide, and the decomposition is well detectable even at moderate temperatures (~60 °C). Our results suggest that these materials may be problematic for long term operation of solar devices

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Abstract not availabl

New Techniques in Diagnostic X-ray Imaging: A Simulation Tool and Experimental Findings

Abstract Absorption X-ray imaging is a well-established technique. However it is still a challenging task in its search for a compromise between the need for high spatial resolution and high contrast and the request to keep the dose delivered to the patient within acceptable values. New imaging techniques are under investigation, like the use of new X-ray sources, phase contrast imaging or K-edge imaging. Monte Carlo or analytic simulations are often the best way to test and predict the effectiveness of these techniques. A new simulation tool for X-ray imaging will be presented together with some applications to the characterization of new X-ray sources, in-line phase contrast effect and angiographic K-edge imaging. Simulation results will be compared also with experimental dat

Corrigendum: On the thermal and thermodynamic (in)stability of methylammonium lead halide perovskites

NO ABSTRAC

MOLAB growth, aims and results

MOLAB is a unique collection of integrated mobile instrumentation established in Italy in 2001 and open from 2004 to transnational access within the European projects Eu-ARTECH (FP6) and CHARISMA (FP7). Its application demonstrated in the last decade that satisfactory analytical results can be obtained through in situ studies of a variety of heritage objects without sampling or moving them to a laboratory, achieving significant overviews on nature and behavior of the inorganic and organic materials of the examined object. The MOLAB in situ non-invasive approach produced a significant change in diagnostic practices, an increase of scientific inputs in heritage studies and conservation, and a positive modification in the relationships between curators, conservators, and scientists, permitting a common language to be established and partnership strengthened. The recent introduction of innovative mobile 2D and 3D imaging systems, setup within the CHARISMA joint research project, significantly extended the MOLAB tools available in the current project IPERION CH (Horizon 2020), widening number and interest of potential users from Europe and associated countries.MOLAB est un ensemble unique d’instruments mobiles intégrés créé en Italie en 2001 et disponible à un accès transnational depuis 2004 dans le cadre des programmes européens Eu-ARTECH (6e PC) et CHARISMA (7e PC). Son utilisation a démontré au cours des dix dernières années que l’on peut obtenir des résultats analytiques de qualité par des travaux in situ sur différents types d’objets du patrimoine sans avoir à prélever des échantillons ou à les transporter dans un laboratoire, et recueillir des informations importantes sur la nature et le comportement des matériaux organiques et inorganiques de l’objet examiné. Les méthodes in situ et non invasives du MOLAB ont favorisé une inflexion notable des pratiques diagnostiques, une augmentation de la production scientifique dans les sciences du patrimoine et la conservation-restauration, ainsi qu’une évolution positive des relations entre conservateurs de musées, restaurateurs et chercheurs, contribuant à l’adoption d’un langage commun et au renforcement des collaborations. L’introduction récente de systèmes mobiles d’imagerie en 2D et en 3D, mis au point grâce aux activités conjointes de recherche de CHARISMA, a considérablement élargi la gamme des outils du MOLAB disponibles dans le cadre du projet en cours IPERION CH (horizon 2020), accroissant ici le nombre et les motivations des utilisateurs potentiels en Europe et dans les pays associés

MOLAB : croissance, objectifs et résultats

MOLAB est un ensemble unique d’instruments mobiles intégrés créé en Italie en 2001 et disponible à un accès transnational depuis 2004 dans le cadre des programmes européens Eu-ARTECH (6e PC) et CHARISMA (7e PC). Son utilisation a démontré au cours des dix dernières années que l’on peut obtenir des résultats analytiques de qualité par des travaux in situ sur différents types d’objets du patrimoine sans avoir à prélever des échantillons ou à les transporter dans un laboratoire, et recueillir des informations importantes sur la nature et le comportement des matériaux organiques et inorganiques de l’objet examiné. Les méthodes in situ et non invasives du MOLAB ont favorisé une inflexion notable des pratiques diagnostiques, une augmentation de la production scientifique dans les sciences du patrimoine et la conservation-restauration, ainsi qu’une évolution positive des relations entre conservateurs de musées, restaurateurs et chercheurs, contribuant à l’adoption d’un langage commun et au renforcement des collaborations. L’introduction récente de systèmes mobiles d’imagerie en 2D et en 3D, mis au point grâce aux activités conjointes de recherche de CHARISMA, a considérablement élargi la gamme des outils du MOLAB disponibles dans le cadre du projet en cours IPERION CH (horizon 2020), accroissant ici le nombre et les motivations des utilisateurs potentiels en Europe et dans les pays associés.MOLAB is a unique collection of integrated mobile instrumentation established in Italy in 2001 and open from 2004 to transnational access within the European projects Eu-ARTECH (FP6) and CHARISMA (FP7). Its application demonstrated in the last decade that satisfactory analytical results can be obtained through in situ studies of a variety of heritage objects without sampling or moving them to a laboratory, achieving significant overviews on nature and behavior of the inorganic and organic materials of the examined object. The MOLAB in situ non-invasive approach produced a significant change in diagnostic practices, an increase of scientific inputs in heritage studies and conservation, and a positive modification in the relationships between curators, conservators, and scientists, permitting a common language to be established and partnership strengthened. The recent introduction of innovative mobile 2D and 3D imaging systems, setup within the CHARISMA joint research project, significantly extended the MOLAB tools available in the current project IPERION CH (Horizon 2020), widening number and interest of potential users from Europe and associated countries

Renormalization as a functor on bialgebras

The Hopf algebra of renormalization in quantum field theory is described at a general level. The products of fields at a point are assumed to form a bialgebra B and renormalization endows T(T(B)^+), the double tensor algebra of B, with the structure of a noncommutative bialgebra. When the bialgebra B is commutative, renormalization turns S(S(B)^+), the double symmetric algebra of B, into a commutative bialgebra. The usual Hopf algebra of renormalization is recovered when the elements of B are not renormalised, i.e. when Feynman diagrams containing one single vertex are not renormalised. When B is the Hopf algebra of a commutative group, a homomorphism is established between the bialgebra S(S(B)^+) and the Faa di Bruno bialgebra of composition of series. The relation with the Connes-Moscovici Hopf algebra of diffeomorphisms is given. Finally, the bialgebra S(S(B)^+) is shown to give the same results as the standard renormalisation procedure for the scalar field.Comment: 24 pages, no figure. Several changes in the connection with standard renormalizatio

Local symmetries in gauge theories in a finite-dimensional setting

It is shown that the correct mathematical implementation of symmetry in the geometric formulation of classical field theory leads naturally beyond the concept of Lie groups and their actions on manifolds, out into the realm of Lie group bundles and, more generally, of Lie groupoids and their actions on fiber bundles. This applies not only to local symmetries, which lie at the heart of gauge theories, but is already true even for global symmetries when one allows for fields that are sections of bundles with (possibly) non-trivial topology or, even when these are topologically trivial, in the absence of a preferred trivialization.Comment: 23 page

The dry grasslands of Abruzzo National Park, the oldest protected area in the Apennines (Central Italy): overview of vegetation composition, syntaxonomy, ecology and diversity

The Abruzzo, Lazio and Molise National Park was established in 1923 and is considered a flagship conservation area in Italy. It includes large extensions of semi-natural grasslands, maintained by traditional transhumant grazing for centuries. The patterns and drivers of grassland composition within the Park are still poorly investigated, and the scattered phytosociological data available were often based on relevés with varied and not precisely defined sizes. In order to provide for the first time a general overview of the Park’s dry grasslands, we analysed a dataset of 87 relevés with a fixed size of 2 × 2 m, precisely delimited in the field and GPS-located. Specific research aims were: (1) to classify the vegetation plots into floristic-ecological types, supported by an analysis of mean (Italy-specific) Ellenberg Indicator Values (EIVs); (2) to assign the types to up-to-date phytosociological syntaxa; (3) to identify the main environmental drivers for both composition and richness patterns; (4) to test the degree of correlation between (Italy-specific) EIVs and the measured environmental variables. Environmental predictors included high-resolution climatologies and remote-sensed standing biomass. Main vegetation types were identified using Hierarchical Cluster Analysis (HCA). Distancebased RDA was performed as a constrained ordination method to reveal correlations between floristic composition and environmental variables. Drivers of species richness were explored through partial correlation and Regression Trees. HCA and NMDS revealed four floristically and ecologically well-interpretable groups, in turn well corresponding to the level of phytosociological class (namely Molinio-Arrhenatheretea, Nardetea strictae, Festuco hystricis-Ononidetea striatae and Festuco-Brometea). Constrained ordination showed that most of the floristic variation was explained by biomass, annual precipitation (Pann) and mean annual temperature (Tm). Strong and significant positive correlations were found between biomass and EIV for Nitrogen (EIV-N), and between Tm and EIV for Temperature (EIV-T). Strong and significant negative correlations were found between Pann and EIV-T, EIV for Continentality (EIV-C) and EIV for soil Reaction (EIV-R). Species richness was positively correlated with slope inclination and negatively with elevation; richness was higher in sites with a high rock cover, and on limestone or clayey substrata than on siliceous ones. We conclude that in the study area: a) dry semi-natural grasslands are arranged at least into four distinguishable, high rank floristic-ecological groups; b) a mixture of climatic (especially precipitation) and edaphic (especially bedrock and soil reaction) gradients are the main drivers of such composition patterns; c) species richness is higher in sites more stressed by summer drought and/or nutrient scarcity; d) community-means of Italy’s specific EIVs are well correlated with environmental variables in grasslands, including a good correspondence between EIV-T and mean annual temperature

Cuando la ciencia se encuentra con el arte. La experiencia MOLAB® en el estudio no invasivo in situ

El MOLAB® es un laboratorio móvil dotado de instrumentos para efectuar investigaciones no invasivas in situ en obras de arte mediante técnicas espectroscópicas. El estudio de las pinturas antiguas, modernas y contemporáneas, así como las esculturas antiguas y modernas, y también los manuscritos miniados, son algunos ejemplos de la actividad desarrollada en los últimos diez años por esta infraestructura única en su género. El abordaje multitécnico que caracteriza al MOLAB® permite obtener informaciones sobre los materiales constitutivos, la técnica de ejecución y el estado de conservación del objeto examinado sin necesidad de extracción de muestras y de desplazamiento de la obra. En este trabajo presentamos ejemplos de investigaciones in situ y de integración con investigaciones en el laboratorio: en ellas se pone de manifiesto el grado de compenetración e inseparabilidad que existe entre ciencia y arte en el estudio y en la conservación de patrimonio artístico.MOLAB® is a mobile laboratory equipped with instruments designed to carry out not invasive in situ research in artworks by means of spectroscopic technique. The study of ancient, modern, and contemporary paintings, as well as ancient and modern sculptures, and illuminated manuscripts, are some examples of the activity in the last ten years of this unique infrastructure. The multi-technique approach that characterizes the MOLAB® allows to get information on the constituent materials, the execution technique and the state of conservation of the examined object without the need of sampling and displacement of the artwork. In this work we present examples of research in situ and its integration with investigations in the laboratory: in them it is highlighted the degree of insight and inseparability that exists between science and art in the study and conservation of artistic heritage.El MOLAB® es un laboratorio móvil dotado de instrumentos para efectuar investigaciones no invasivas in situ en obras de arte mediante técnicas espectroscópicas. El estudio de las pinturas antiguas, modernas y contemporáneas, así como las esculturas antiguas y modernas, y también los manuscritos miniados, son algunos ejemplos de la actividad desarrollada en los últimos diez años por esta infraestructura única en su género. El abordaje multitécnico que caracteriza al MOLAB® permite obtener informaciones sobre los materiales constitutivos, la técnica de ejecución y el estado de conservación del objeto examinado sin necesidad de extracción de muestras y de desplazamiento de la obra. En este trabajo presentamos ejemplos de investigaciones in situ y de integración con investigaciones en el laboratorio: en ellas se pone de manifiesto el grado de compenetración e inseparabilidad que existe entre ciencia y arte en el estudio y en la conservación de patrimonio artístico