70 research outputs found

    Electronic Structure of Calcium Hexaboride within the Weighted Density Approximation

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    We report calculations of the electronic structure of CaB6_6 using the weighted density approximation (WDA) to density functional theory. We find a semiconducting band structure with a sizable gap, in contrast to local density approximation (LDA) results, but in accord with recent experimental data. In particular, we find an XX-point band gap of 0.8 eV. The WDA correction of the LDA error in describing the electronic structure of CaB6_6 is discussed in terms of the orbital character of the bands and the better cancelation of self-interactions within the WDA.Comment: 1 figur

    URBAN CENTER. Una casa di vetro per le politiche urbane.

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    Nella cultura di governo della città, il termine "Urban Center" (o "Casa della città") designa una serie di strutture il cui denominatore comune risiede nello svolgimento di attività di servizio per le comunità urbane ai fini di soddisfare la crescente domenda di democrazia partecipativa e deliberativa nei processi di trasformazione degli insediamenti. Traendo spunto dalla storicizzazione del fenomeno e dal confronto tra i consolidati modelli statunitensi e le recenti esperienze in Italia, il volume si interroga sulla maturazione delle missioni dell' "Urban Center" nel passaggio da asettico spazio di informazione a luogo provilegiato per la costruzione trasparente di politiche urbane condivise. Il percorso logico del volume si sviluppa seguendo un fil rouge articolato in quattro parti. Il primo blocco si apre con due tematiche che costituiscono dialetticamente la cornice di riferimento entro cui può essere correttamente collocata la questione degli UC: l’urbanistica partecipata e il marketing urbano. Nella seconda parte attraverso lo studio di casi si ricostruisce il quadro delle articolate declinazioni statunitensi di Urban Center, consolidatesi in diversi decenni di storia. Sono strutture fortemente caratterizzate e autonome per stile, missioni, obiettivi, priorità, modalità operative, ma allo stesso tempo accomunate da un equilibrato mix di passione civile e pragmatismo professionale. Il terzo gruppo di saggi è dedicato alla condizione attuale e di prospettiva degli UC in Italia, delineando criticamente una sorta di “mappa dinamica” delle diverse strutture attivate e in divenire, caratterizzate per soggetti ispiratori, missioni “stili” e protagonismo degli attori coinvolti. Il cerchio delle riflessioni si chiude nella quarta parte discutendo la questione dell’innovazione di metodo per la costruzione di un UC sia attraverso la dimensione teoretica che le potenzialità operative. Testi in italiano e inglese di B. Monardo (curatore), M.C. Bizzarri, E. Carmagnani, M. Carta, F. Ceci, P. Colarossi, L. De Bonis, A. Dina, A. De Rossi, D. Filippi, A. Giorgi, P. Laconte, F. Lovato, L. J. Osmond, R. Shiffman, O Tommasi, A. Uttaro; postfazione di M. Ricci

    Colossal dielectric constants in transition-metal oxides

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    Many transition-metal oxides show very large ("colossal") magnitudes of the dielectric constant and thus have immense potential for applications in modern microelectronics and for the development of new capacitance-based energy-storage devices. In the present work, we thoroughly discuss the mechanisms that can lead to colossal values of the dielectric constant, especially emphasising effects generated by external and internal interfaces, including electronic phase separation. In addition, we provide a detailed overview and discussion of the dielectric properties of CaCu3Ti4O12 and related systems, which is today's most investigated material with colossal dielectric constant. Also a variety of further transition-metal oxides with large dielectric constants are treated in detail, among them the system La2-xSrxNiO4 where electronic phase separation may play a role in the generation of a colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom

    Hot spots for diversity of Magnaporthe oryzae physiological races in irrigated rice fields in Brazil

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    The objective of this work was to evaluate the Magnaporthe oryzae pathotype diversity in new commercial irrigated rice fields in the Araguaia River Valley, state of Tocantins, Brazil. The causal agent of rice blast has heavily affected rice production in the region. Despite the efforts of breeding programs, blast resistance breakdown has been recorded shortly after the release of new resistant cultivars developed for the region. Among the causes of resistance breakage is the capacity of the fungus to rapidly develop new pathotypes. A sample of 479 M. oryzae monosporic isolates was obtained and tested using the international rice blast differential set. Isolate collections were made in small areas designed as trap nurseries and in scattered sites in their vicinity. Analysis of 250 M. oryzae isolates from three trap nurseries indicated the presence of 45 international M. oryzae races belonging to seven pathotype groups (IA-IG). In the isolates tested, 61 M. oryzae pathotypes belonging to all but the IH group were detected. The new areas of irrigated rice in the Araguaia River Valley have the highest diversity of M. oryzae pathotypes reported so far in Brazil

    ENIGMA and global neuroscience: A decade of large-scale studies of the brain in health and disease across more than 40 countries

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    This review summarizes the last decade of work by the ENIGMA (Enhancing NeuroImaging Genetics through Meta Analysis) Consortium, a global alliance of over 1400 scientists across 43 countries, studying the human brain in health and disease. Building on large-scale genetic studies that discovered the first robustly replicated genetic loci associated with brain metrics, ENIGMA has diversified into over 50 working groups (WGs), pooling worldwide data and expertise to answer fundamental questions in neuroscience, psychiatry, neurology, and genetics. Most ENIGMA WGs focus on specific psychiatric and neurological conditions, other WGs study normal variation due to sex and gender differences, or development and aging; still other WGs develop methodological pipelines and tools to facilitate harmonized analyses of "big data" (i.e., genetic and epigenetic data, multimodal MRI, and electroencephalography data). These international efforts have yielded the largest neuroimaging studies to date in schizophrenia, bipolar disorder, major depressive disorder, post-traumatic stress disorder, substance use disorders, obsessive-compulsive disorder, attention-deficit/hyperactivity disorder, autism spectrum disorders, epilepsy, and 22q11.2 deletion syndrome. More recent ENIGMA WGs have formed to study anxiety disorders, suicidal thoughts and behavior, sleep and insomnia, eating disorders, irritability, brain injury, antisocial personality and conduct disorder, and dissociative identity disorder. Here, we summarize the first decade of ENIGMA's activities and ongoing projects, and describe the successes and challenges encountered along the way. We highlight the advantages of collaborative large-scale coordinated data analyses for testing reproducibility and robustness of findings, offering the opportunity to identify brain systems involved in clinical syndromes across diverse samples and associated genetic, environmental, demographic, cognitive, and psychosocial factors

    Study of doubly strange systems using stored antiprotons

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    Bound nuclear systems with two units of strangeness are still poorly known despite their importance for many strong interaction phenomena. Stored antiprotons beams in the GeV range represent an unparalleled factory for various hyperon-antihyperon pairs. Their outstanding large production probability in antiproton collisions will open the floodgates for a series of new studies of systems which contain two or even more units of strangeness at the P‾ANDA experiment at FAIR. For the first time, high resolution γ-spectroscopy of doubly strange ΛΛ-hypernuclei will be performed, thus complementing measurements of ground state decays of ΛΛ-hypernuclei at J-PARC or possible decays of particle unstable hypernuclei in heavy ion reactions. High resolution spectroscopy of multistrange Ξ−-atoms will be feasible and even the production of Ω−-atoms will be within reach. The latter might open the door to the |S|=3 world in strangeness nuclear physics, by the study of the hadronic Ω−-nucleus interaction. For the first time it will be possible to study the behavior of Ξ‾+ in nuclear systems under well controlled conditions
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