La gestione del patrimonio culturale di libero accesso delle pubbliche amministrazioni emiliano-romagnole

Le pubbliche amministrazioni detengono un consistente numero di materiali digitali, un vero e proprio patrimonio culturale che spesso però non riesce a raggiungere un numero consistente di utilizzatori. La gestione disaggregata e disgiunta è uno dei principali fattori che frenano la diffusione e la condivisione di tali contenuti. Nell’ambito del Piano telematico dell’Emilia-Romagna (PITER) ci si propone di valorizzare la rete a banda larga delle PA emilia-romagnole LEPIDA creando una piattaforma di gestione di documenti digitali e di erogazione multicanale e multimediale a disposizione degli EELL della regione. Questo intervento mira a sviluppare, con adeguati strumenti tecnologici comuni, la società dell’informazione regionale.2008-04-17Sardegna Ricerche, Edificio 2, Località Piscinamanna 09010 Pula (CA) - ItaliaPAAL 2008 - Pubblica Amministrazione Aperta e Libera: dalle tecnologie aperte alla libera circolazione dei contenuti digital

Technology and reliability of normally-off GaN HEMTs with p-type gate

GaN-based transistors with p-GaN gate are commonly accepted as promising devices for application in power converters, thanks to the positive and stable threshold voltage, the low on-resistance and the high breakdown field. This paper reviews the most recent results on the technology and reliability of these devices by presenting original data. The first part of the paper describes the technological issues related to the development of a p-GaN gate, and the most promising solutions for minimizing the gate leakage current. In the second part of the paper, we describe the most relevant mechanisms that limit the dynamic performance and the reliability of GaN-based normally-off transistors. More specifically, we discuss the following aspects: (i) the trapping effects specific for the p-GaN gate; (ii) the time-dependent breakdown of the p-GaN gate during positive gate stress and the related physics of failure; (iii) the stability of the electrical parameters during operation at high drain voltages. The results presented within this paper provide information on the current status of the performance and reliability of GaN-based E-mode transistors, and on the related technological issues

Etude de l'interaction entre les mastocytes et les lymphocytes T helper

Les mastocytes ont longtemps été associés aux réponses allergiques, néanmoins de nombreuses études les décrivent comme des acteurs de la réponse inflammatoire. Les mastocytes sont souvent retrouvés en étroite apposition au sein des tissus avec les lymphocytes T Helper (TH). L'objet de ma thèse est de caractériser la nature de l'interaction mastocyte/TH et notamment la capacité des mastocytes à jouer le rôle de cellules présentatrices d'antigène. Dans une première étude, nous avons démontré que des lignées primaires de mastocytes murins (PCMC) peuvent acquérir un phénotype de cellules présentatrices d'antigènes, lorsqu'elles sont traitées en présence d'IFN-gamma pendant 72 heures. Ainsi conditionnés, les PCMC capturent, apprêtent et présentent l'antigène à des lymphocytes T CD4+ activés, mais restent incapables d'activer leurs homologues naïfs. Durant ce phénomène, une véritable synapse immunologique est mise en place où le lymphocyte TH polarise son TCR et toute sa machinerie sécrétoire vers l'aire de contact intercellulaire. En retour, le mastocyte s'active et baisse significativement le seuil d'activation des récepteurs FcepsilonRI en réponse à une stimulation par des IgE. Ces résultats indiquent que les mastocytes peuvent établir une coopération spécifique avec les lymphocytes TH. Dans une seconde étude, nous avons déterminé les conséquences fonctionnelles d'une telle coopération sur la biologie des lymphocytes TH humains. In vitro les mastocytes humains forment des synapses immunologiques fonctionnelles avec des lymphocytes T CD4+ activés. Ces interactions productives favorisent la génération de lymphocytes TH produisant de grandes quantités d'IL-22 (à la fois de purs TH22 et des TH produisant simultanément de l'IL-22 et de l'IFN-gamma) à partir d'un pool de lymphocytes TH mémoires. Cette différenciation vers un tel profil de TH est dépendante de l'action de deux cytokines que sont l'IL-6 et le TNF-alpha. L'analyse microscopique détaillée d'échantillons de peaux psoriasiques révèle un enrichissement en lymphocytes TH produisant simultanément de l'IL-22 et de l'IFN-gamma, lors qu'ils sont au contact des mastocytes. Ces résultats indiquent que les mastocytes peuvent être de véritables partenaires fonctionnels pour les lymphocytes TH au sein des tissus, leur fournissant des signaux d'activation et les orientant vers la production d'une cytokine supplémentaire l'IL-22.Mast cells have been classically associated to allergic disorders, however several studies describe their involvement in the inflammatory response. Mast cells are often observed in tissues in close apposition with CD4 T cells (TH). The aim of my thesis is to better characterize the nature of mast cell/TH interaction and in particular the mast cell capacity to act as antigen presenting cell and the consequences for the TH cell response. We first addressed this question using mouse primary mast cell lines derived from peritoneal progenitors (PCMC) used as antigen presenting cell to activate cognate OTii T cells with OVA peptide. Our results show that in vitro treatment of PCMC with IFN-gamma and IL-4 induced surface expression of mature MHC class II and costimulatory molecules. When IFN-gamma primed PCMC were used as antigen presenting cells for Helper T (TH) cells, they induced activation of effector T cells but not of their naive counterparts. Confocal laser scanning microscopy showed that TH cells formed immunological synapses and polarized their secretory machinery towards antigen-loaded PCMC. Finally, upon cognate interaction with TH cells, mast cells lowered their threshold of activation via FcepsilonRI. These results show that mast cells can specifically cooperate with class II restricted TH cells. In a second part, we investigated the functional impact of mast cell antigen presentation on human T cell-mediated responses. In vitro, human mast cells form productive immunological synapses with antigen-experienced TH cells. These interactions promote the generation of interleukin 22 (IL-22) producing TH cells (either pure TH22 or IL-22 plus IFN-gamma-producing TH cells) from the circulating CD4+ memory T cell pool via a tumor necrosis factor (TNF-alpha) - and IL-6-dependent mechanism. Three-color immunohistochemistry and confocal laser scanning microscopy reveal a rich infiltrate of IL-22+ TH cells in psoriatic skin biopsies. Most of the IL-22+ TH cells are found in contact with mast cells and co-express IFN-gamma, suggesting that IFN-gamma+IL-22+ TH cells are generated in vivo upon interaction with mast cells. Our results reveal a novel functional trait of mast cells by showing that they can shape the inflammatory potential of human TH lymphocytes in tissues, by providing activating signals and skewing the TH cell response toward the production of IL-22

François-René de Chateaubriand, Viaggio in America

Il Viaggio in America (del Nord) costituì il coronamento di un suo antico sogno; partì da Saint-Malo il 6 Maggio 1791 e fu di ritorno in Francia nel Gennaio 1792: il suo soggiorno nel Nuovo Mondo durò, effettivamente, dal 10 Iuglio al 10 Dicembre del 1791. Questo Diario di Viaggio da lui ripreso, in vari modi, in molte delle sue opere successive, quando fu dato alle stampe, provocò forti impressioni ed alimentò anche precise contestazioni e numerose osservazioni critiche. Infatti, fin dalla s..

Lo spettro di un anello e i suoi punti

L'elaborato tratta argomenti di geometria algebrica. Si analizzeranno nel dettaglio lo spettro di un anello commutativo con unità e la sua topologia e si vedrà come cambia la nozione di varietà algebrica con l'introduzione degli schemi. Verranno poi definiti i punti di uno schema (punti chiusi e punti generici) terminando la discussione con l'analisi delle varietà su un campo non algebricamente chiuso e del funtore dei punti associato ad uno schema

Gate stability of GaN-Based HEMTs with P-Type Gate

status: publishe

analysis and reliability study of luminescent materials for white lighting

In this work, we report on the characterization and reliability/stability study of phosphorescent materials for lighting applications. More specifically, we investigated (a) phosphors directly deposited over light-emitting diodes (LED) chip, (b) remote phosphor (RP) solutions encapsulated in plastic medium for LED lighting, and (c) phosphors without binder for extreme high-intensity laser diode white lighting. The optical and thermal properties of phosphors were studied to develop a sample based on a mix of phosphor compounds in order to achieve different correlated color temperatures (CCT) and high color rendering index (CRI) LEDs. Thermal properties of cerium-doped YAG (Yttrium Aluminum Garnet) phosphor materials were evaluated in order to study thermal quenching. A maximum phosphor operating temperature of 190–200 °C was found to cause a sensible efficiency degeneration. Reduced efficiency and Stokes shift also caused a localized temperature increase in the photoluminescent materials. In the case of remote phosphors, heat did not find a low thermal resistance path to the heatsink (as occurred through the GaN LED chip for direct phosphor-converted devices) and thermal analysis indicated that material temperature might therefore increase to values in excess of 60 °C when a radiation of 435 mW/cm2 hit the sample template. Reliability was also investigated for both plastic-encapsulated materials and binder-free depositions. Pure thermal reliability study indicated that phosphors encapsulated in polycarbonate material were stable up to temperature of approximately 100 °C, while binder-free phosphor did not show any sensible degradation up to temperatures of 525 °C

Trapping phenomena and degradation mechanisms in GaN-based power HEMTs

Abstract This paper reports an overview of the most relevant trapping and degradation mechanisms that limit the performance and lifetime of GaN-based transistors for application in power electronics. Results obtained on state-of-the-art devices are described and discussed throughout the paper, with the aim of providing a clear description of the topic. The first part of the paper deals with the issue of dynamic-Ron: after describing a robust test strategy for the analysis of the pulsed characteristics of the devices, we discuss the voltage- and temperature-dependent pulsed I-V characteristics of 650 V-rated transistors, and the physical origin of dynamic Ron in these devices. The results demonstrate that through proper buffer optimization it is possible to reach negligible trapping at high voltage. The properties of the traps responsible for dynamic-Ron are also discussed in detail in the paper, based on drain-current transient data. A specific discussion is devoted to hot-electron trapping processes, that – under hard switching conditions – may lead to significant modifications in the resistance of the 2DEG. The second part of the paper deals with device degradation: based on a wide set of experimental results, we describe the physical mechanisms responsible for the worsening of the properties of the devices. More specifically, we demonstrate that stress in off-state conditions may result in measurable changes in the pinch-off voltage, mostly consisting in a negative-threshold instability (NBTI). The origin of this shift is discussed in detail; we also demonstrate that in a real-life cascode configuration (where a low, subthreshold leakage current flows through the device in the off-state), NBTI effects are mitigated. Finally, we discuss the stability of the gate-stack, induced by the exposure to positive gate bias

Electric Field and Self-Heating Effects on the Emission Time of Iron Traps in GaN HEMTs

In this paper we separately investigate the role of electric field and device self-heating (SHE) in enhancing the charge emission process from Fe-related buffer traps (0.52 eV from Ec) in AlGaN/GaN High Electron Mobility Transistors (HEMTs). The experimental analysis was performed by means of Drain Current Transient (DCT) measurements for either i) different dissipated power (PD,steady) at constant drain-to-source bias (VDS,steady) or ii) constant PD,steady at different VDS,steady. We found that i) an increase in PD,steady yields an acceleration in the thermally activated emission process, consistently with the temperature rise induced by SHE. On the other hand, ii) the field effect turned out to be negligible within the investigated voltage range, indicating the absence of Poole-Frenkel effect (PFE). A qualitative analysis based on the electric field values obtained by numerical simulations is then presented to support the interpretation and conclusions