Mazurka Italienne

https://digitalcommons.library.umaine.edu/mmb-ps/2238/thumbnail.jp

H2O2 adsorption and dissociation on various CeO2(111) surface models: a first-principles study

Periodic density functional theory (DFT) calculations using the hybrid PBE0 functional and atom-centered Gaussian functions as basis sets were carried out to investigate the absorption and the first steps involved in the decomposition of hydrogen peroxide (H2O2) on three different models of the ceria (111) surface. One of the models is a clean surface, and the others are defective and partially hydroxylated ceria surfaces. On the clean surface, we found that the minimum energy path of hydrogen peroxide decomposition involves a three-step process, i.e., adsorption, deprotonation, and formation of the peroxide anion, stabilized through its interaction with the surface at a Ce (IV) site, with activation barriers of less than about 0.5 eV. The subsequent formation of superoxide anions and molecular oxygen species is attributed to electron transfer from the reactants to the Ce (IV) ions underneath. On the defective surface, H2O2dissociation is an energetically downhill reaction thermodynamically driven by the healing of the O vacancies, after the reduction and decomposition of H2O2into oxygen and water. On the hydroxylated surface, H2O2is first adsorbed by forming a favorable H-bond and then undergoes heterolytic dissociation, forming two hydroxyl groups at two vicinal Ce sites

Recursive patterns in online echo chambers

Despite their entertainment oriented purpose, social media changed the way users access information, debate, and form their opinions. Recent studies, indeed, showed that users online tend to promote their favored narratives and thus to form polarized groups around a common system of beliefs. Confirmation bias helps to account for users’ decisions about whether to spread content, thus creating informational cascades within identifiable communities. At the same time, aggregation of favored information within those communities reinforces selective exposure and group polarization. Along this path, through a thorough quantitative analysis we approach connectivity patterns of 1.2 M Facebook users engaged with two very conflicting narratives: scientific and conspiracy news. Analyzing such data, we quantitatively investigate the effect of two mechanisms (namely challenge avoidance and reinforcement seeking) behind confirmation bias, one of the major drivers of human behavior in social media. We find that challenge avoidance mechanism triggers the emergence of two distinct and polarized groups of users (i.e., echo chambers) who also tend to be surrounded by friends having similar systems of beliefs. Through a network based approach, we show how the reinforcement seeking mechanism limits the influence of neighbors and primarily drives the selection and diffusion of contents even among like-minded users, thus fostering the formation of highly polarized sub-clusters within the same echo chamber. Finally, we show that polarized users reinforce their preexisting beliefs by leveraging the activity of their like-minded neighbors, and this trend grows with the user engagement suggesting how peer influence acts as a support for reinforcement seeking

Carbon isotope discrimination and water use efficiency in interspecific Prunus hybrids subjected to drought stress

In C3 plants, carbon isotope composition (δ13C) is influenced by isotopic effects during diffusion from the atmosphere to the chloroplasts and carboxylation reactions. This work aimed to demonstrate if δ13C of leaf soluble carbohydrates (δ13Cleaves) and of dry matter from new-growth shoots (δ13Cshoots) of Prunus plants subjected to a period of water deficit was related to water use efficiency (WUE). For this purpose, three interspecific Prunus hybrids rootstocks (6–5, 7-7 and G × N) were gradually subjected to drought and then rewatered. Soil water content (SWC) decreased from 26.1 to 9.4% after 70 days of water shortage, when plants reached values of predawn leaf water potential (LWP) ranging from −3.12 to −4.00 MPa. Gas exchange, particularly net photosynthetic and transpiration rates, differed among the three hybrids, leading to different values of WUE. After 70 days of drought, a significant δ13C increase of 5.86, 4.28 and 4.99‰ was observed in 6–5, 7-7 and G × N, respectively. Significant correlations between δ13C and other parameters (substomatal CO2/atmospheric CO2 ratio, stomatal conductance and stem water potential) were found in all hybrids. The rewatering phase caused a recovery of the physiological status of the plants. The isotope composition of δ13Cshoots was correlated with the average WUE measured during the whole experiment. δ13Cleaves and δ13Cshoots were positively related (r = 0.87; p < 0.001). The isotopic signature was a reliable screening tool to identify Prunus genotypes tolerant to drought stress. The results suggest the possibility of using δ13C as an integrated indicator of level of drought stress in plants subjected to prolonged stress conditions

O2Activation over Ag-Decorated CeO2(111) and TiO2(110) Surfaces: A Theoretical Comparative Investigation

Periodic spin-polarized hybrid density functional theory calculations have been performed to investigate the reactivity of pristine, O-defective, and Ag-decorated CeO2(111) and TiO2(110) surfaces with a small Ag10 cluster toward O2. The adsorption of O2 and its subsequent dissociation have been studied in order to provide a better understanding of the role of the oxide, the metallic nanoparticle, and their interaction in the reactivity of composite metal/metal oxide materials toward O2, as potential catalysts to this reaction. Structural, energetic, electronic, and vibrational properties of all species involved in the different reaction paths considered have been fully characterized. On the stoichiometric surfaces, Ag10 is oxidized and reduces surface Ce4+/Ti4+ ions, while on the O-defective surfaces, the adhesion of silver is promoted only on CeO2 but unfavored on TiO2. On the other hand, on the silver-free supports, O2 strongly adsorbs at vacancies and preferentially reduces to peroxide. When no O vacancies are considered on the Ag10-decorated supports, the net positive charge on Ag10 actually prevents the adsorption and reduction of O2. Instead, when O vacancies are included, two reaction pathways are observed; oxygen molecules can weakly absorb on the silver cluster as a superoxide moiety or strongly adsorb at the vacancy as peroxide. The dissociation of the O-O bond of the peroxide is favored both from the thermodynamic and kinetic points of view in silver-decorated surfaces, in contrast with the silver-free cases. In addition, Ag10/CeO2 shows higher activity toward the O2 adsorption and dissociation than Ag10/TiO2, which can be related both to the higher ionicity and superior electron storage/release ability of ceria with respect to titania, thus leading to the weakening of the O-O bond and providing lower activation barriers for oxygen reduction. These results deepen the current understanding of the reactivity of metal/metal oxide composites toward O2, especially elucidating how the surface stoichiometry affects the charge state of the metal clusters, and hence the reactivity of these interfaces toward O2, with potential important consequences when such composites are considered for catalytic applications

La citt\ue0 come modello bioclimatico ed ambientale nella valutazione del benessere psicofisico. Problematiche e proposte applicative

Soltanto lo 0,2 % della superficie terrestre e coperta da aree urbane ma il 47% della popolazione mondiale ed il 73% di quella europea vive in aree densamente popolate caratterizzate da quadri ambientali generalmente degradati (A. Matzarakis). Lo studio dei contesti urbani trova quindi ampia giustificazione nel quadro attuale e nella tendenza, ormai irreversibile, alla crescente concentrazione delle attivit\ue0 umane in ambiti ad alta densit\ue0 abitativa. La citt\ue0 costituisce quindi un modello di riferimento fondamentale per valutare l\u2019impatto che i disastri naturali possono esercitare su strutture, infrastrutture e sulla popolazione in generale. L\u2019Organizzazione Mondiale della Sanit\ue0 dedica crescente importanza ai disastri naturali con specifica attenzione per gli eventi meteoclimatici a carattere estremo ove si evidenziano precise connessioni con la salute pubblica, sia dirette, sia indirette in quanto espressione di code macro e microepidemiologiche al seguito degli eventi stessi. Su un piano sottostante si colloca il concetto di benessere psico-fisico, anch\u2019esso legato all\u2019estrinsecarsi di eventi meteoclimatici in generale ed estremi in particolare ma che, tuttavia, non esaurisce il molteplice insieme di fattori che concorrono a generarlo. La stessa OMS definisce cosa deve intendersi per salute: \u201clo stato di benessere fisico, mentale e sociale ottimale, e non soltanto l\u2019assenza di malattie o di infermit\ue0\u201d. Il well-being \ue8 quindi una espressione generale che coinvolge la sfera psicologica e quella fisica dell\u2019individuo che va a legarsi con un rilevante numero di profili ambientali, siano essi di derivazione naturale oppure indotti dall\u2019attivit\ue0 antropica, con i quali lo stesso individuo interagisce con diversi gradi di consapevolezza; il benessere \ue8, in ultima analisi, una definizione sufficientemente valida per valutare la concordanza euritmica tra l\u2019ambiente in cui l\u2019individuo vive ed il profilo psico-fisico che ne consegue. Trattasi di un modello che trova massima espressione se applicato alla citt\ue0, una metafora complessa che racchiude qualit\ue0 della vita, benessere e malessere psicofisico, patologia, cio\ue8 le diverse caratterizzazioni della salute umana. In questo contributo saranno messi in luce aspetti, problematiche e proposte applicative per un modello di citt\ue0 finalizzato all\u2019accrescimento del benessere psicofisico in generale

Assessing effectiveness of Komagataeibacter strains for producing surface-microstructured cellulose via guided assembly-based biolithography.

In this study, a medical device made of surface microstructured bacterial cellulose was produced using cellulose‑producing acetic acid bacteria wild‑type strains in combination with guided assembly‑based biolithography. The medical device aims at interfering with the cell’s focal adhesion establishment and maturation around implantable devices placed in soft tissues by the symmetrical array on its surface. A total of 25 Komagataeibacter strains was evaluated over a three‑step selection. In the first step, the ability of strains to produce a suitable bacterial cellulose layer with high production yield was examined, then nine strains, with a uniform and smooth layer of bacterial cellulose, were cultured in a custom‑made silicone bioreactor and finally the characteristics of the symmetrical array of topographic features on the surface were analysed. Selected strains showed high inter and intra species variability in bacterial cellulose production. The devices obtained by K2G30, K1G4, DSM 46590 (Komagataeibacter xylinus), K2A8 (Komagataeibacter sp.) and DSM 15973T (Komagataeibacter sucrofermentas) strains were pouched‑formed with hexagonal surface pattern required for reducing the formation of fibrotic tissue around devices, once they are implanted in soft tissues. Our findings revealed the effectiveness of the selected Komagataeibacter wild‑type strains in producing surface microstructured bacterial cellulose pouches for making biomedical devices

Selección de genotipos por comportamiento forrajero a partir de una progenie F2 de stylosanthes guianensis (fabaceae)

Stylosanthes guianensis (Aubl.) Sw. es una especie autógama de gran importancia forrajera en el norte de Argentina, ya que estudios previos han mostrado que se adapta bien a diferentes tipos de suelos y ambientes, siendo poco exigente en requerimientos de fósforo, además, tienen buen valor nutritivo comparado con otras especies tropicales. En Corrientes se han evaluado algunos de los cultivares comerciales, observándose una buena producción media durante 4 años. Sin embargo, la producción en período frío disminuye o se produce la muerte de las plantas debido a las bajas temperaturas. Sería de gran interés incorporar a Stylosanthes guianensis a un programa de mejoramiento genético. Con la finalidad de obtener genotipos que produjeran durante todo el año, sean tolerantes a las heladas y con mayor vigor. Con respecto a este punto, la cátedra de Forrajicultura de FCA UNNE cuenta con germoplasma de cuatro cultivares de S. guianensis (Endavour, Cook, CIAT 184 y Graham), los cuales fueron cultivados y caracterizados previamente. El objetivo del presente trabajo fue identificar y seleccionar genotipos deseables a partir de progenies segregantes (F2), provenientes de la hibridación de cultivares comerciales de Stylosanthes guianensis. Para ello se dispuso de un total de 390 plantas a campo, distribuidas en un diseño en bloques completos al azar con 3 repeticiones. Se realizaron mediciones relativas a la producción primaria, altura de plantas y diámetro, susceptibilidad a las enfermedades, tolerancia al frío y producción de semillas, como así también a observaciones del hábito de crecimiento y porte de la planta. Los resultados permiten identificar genotipos altamente favorables desde el punto de vista de la tolerancia al frío principalmente, logrando sobrevivir al invierno un total de 15 genotipos F2, pertenecientes a 8 familias, pero además 16 genotipos de padres o variedades comerciales. Lo cual daría un indicio de la factibilidad de la técnica de mejoramiento empleadaFil: Winter, Jonatan D.. Universidad Nacional del NordesteFil: Acuña, Carlos A.. Universidad Nacional del NordesteFil: Brugnoli, Elsa A.. Universidad Nacional del Nordest