1,282 research outputs found
Preparation and characterization of electrocatalysts for high temperature polymer electrolyte fuel cells
Get PDFE’ noto che per una effettiva immissione nel settore automotive delle celle a combustibile ad elettrolita polimerico (PEFCs) alimentate a idrogeno, una delle principali barriere da superare è legata durata dei materiali adoperati. Il fenomeno di sintering del platino e la corrosione che quest’ultimo assieme al supporto, subiscono operando alle alte temperature richieste dal settore automotive (120 ÷ 130 °C), si traduce in una riduzione del tempo di vita del catalizzatore nel suo complesso. Gli effetti del sintering e della corrosione del catalizzatore si traducono in una perdita di area superficiale attiva del platino e di conseguenza una diminuzione della potenza erogata dal sistema.
Un’altra problematica da superare, per una diffusione concorrenziale nel settore automotive delle PEFCs rispetto ai classici motori a combustione interna, è il carico totale di platino. Ad oggi, le potenze erogate da questi apparati (ca. 100 kW) richiedono, soprattutto nel comparto catodico, una quantità notevole di metallo prezioso che, di riflesso, causa un aumento del costo complessivo del prodotto finito. Risulta ovvio che l’abbassamento del tenore di platino nel catalizzatore catodico gioca un ruolo determinante per una effettiva ed efficace immissione delle celle a combustibile all’interno di questo vasto mercato.
Scopo di questo dottorato di ricerca è stato lo sviluppo di nuovi elettrocatalizzatori supportati in grado resistere al sintering ed alla corrosione. Per ridurre il carico di platino questi materiali devono anche essere caratterizzati da una maggiore efficienza. Si è deciso, quindi, di sviluppare catalizzatori a base di platino e di leghe platino-cobalto con caratteristiche chimico-fisiche ben definite. La scelta del cobalto deriva dalle numerose indagini effettuate su questi catalizzatori; queste hanno mostrato che alcuni catalizzatori di leghe binarie di Pt-M (dove M = Co, Fe, Ni, Cu, ecc) presentano una maggiore attività elettrocatalitica per la reazione di riduzione dell’ossigeno rispetto ai catalizzatori di solo Pt. Tra queste la lega PtCo sembra risultare quella più promettente.
Ancora, vari studi hanno indicato che per i catalizzatori supportati Pt/C si ha un’attività massima a circa 3 nm come compromesso adatto tra il numero di siti e la fase cristallografica con basso indice di Miller caratterizzata da alta attività intrinseca. Obiettivo di questa attività è stato, quindi, quello di sintetizzare catalizzatori supportati a base di Pt e leghe PtCo con dimensione di particelle minore di 3 nm e contraddistinti da un adeguato grado di lega.
I catalizzatori sviluppati sono stati infine caratterizzati dal punto di vista chimico-fisico ed elettrochimico (in semicella ed in cella singola) ad elevate temperature (75 °C ÷ 130 °C) con lo scopo di analizzarne il comportamento e approfondire le cause della loro degradazione.Large scale application of polymer electrolyte fuel cell (PEFC) system technology requires a reduction of its high cost as well as improvement of performance and stability. The catalysts employed for operation in the present PEMFC are nanosized platinum particles supported on carbon. The reduction of the noble metal content and enhancement of catalytic stability are significant challenges for this fuel cell technology on the way to become cost competitive. High temperature PEFC operation (130°C) requires the development of catalyst with proper resistance to sintering and corrosion under working conditions.
In order to reach these goals, the aim of this research was the development of practical carbon supported Pt anode and cathode catalysts with high metal surface area capable of operation at high temperature (130°C) with suitable resistance to corrosion, Pt dissolution, thermal and electrochemical sintering. Another aspect was the development of new alloyed electrocatalysts. Several papers in the current literature address to the development of binary and ternary Pt-alloys. In fact, results show more active and less expensive Pt-alloy for oxygen reduction reaction (ORR) catalysts with better stability than pure Pt based catalysts. Accordingly, the work was focused on the development of practical carbon supported Pt-Co alloyed catalysts. The choice of cobalt as a transition metal in alloy with platinum was derived from literature, as many of investigations shown that it is the most promising catalyst for high temperature PEFC operation.
The purpose of this work was addressed on the achievement of a proper crystalline structure with face-centered-cubic phase and a high degree of alloying for the catalysts with small mean particle size (< 3 nm). The synthesis method was optimized to obtain a suitable dispersion of the metal particles on the support for high metal concentration catalysts (50 wt.%) with a mean particle size smaller than 3 nm for both Pt and Pt-Co alloyed electrocatalysts. Moreover, further studied were addressed to different pre-leaching methods on the performance and stability of synthesized Pt-Co alloy catalysts supported on carbon. These treatments were adopted to reduce the dissolution of cobalt from the particle surface in PEFCs.
To understand catalysts behaviour in terms of resistance to corrosion and electrochemical sintering, different analyses (XRD, cycling voltammetry and polarization) were carried out before and after various accelerated degradation tests (ADTs) performed in a gas-fed sulphuric acid electrolyte half cell at 75°C and in a PEM single cell in a temperature range of 80 – 130°C.
In conclusion, an appropriate synthesis method was developed to obtain Pt and PtCo electrocatalysts with a small particle size (< 3 nm) and suitable degree of alloying in the bimetallic electrocatalysts. Pre-leaching treatments were adopted to improve the catalytic activity and the resistance towards sintering and degradation. Accelerated degradation tests in sulphuric acid gas-fed half cell were carried out in order to investigate the influence of different pre-leaching treatments on the electrochemical behaviour. These analyses showed that the particle size of all catalysts increased after the tests. It was observed that after the Pt degradation test, the HClO4 pre-leached catalyst showed the best performance in terms of electrochemical activity and resistance to sintering
SOLUBILITY OF VEGETABLE CUTICULAR WAXES IN SUPERCRITICAL CO2 ISOTHERMAL CALORIMETRY INVESTIGATIONS
No full textVegetable cuticular waxes have to be separated from the more valuable essential oils in extraction processes carried out with supercritical fluids (namely CO2), allowing a solvent selectivity by modification of temperature and pressure. The solubility of these waxes in supercritical CO2 can be adequately represented by that of solid n-octacosane. The present work shows that isothermal investigations, carried out with a differential flux calorimeter with adequate cells, allow the solubility and solubilization enthalpy of n-octacosane to be determined. The results concern investigations either at constant pressure and variable supercritical CO2 flow-rate, or at zero flow-rate and increasing pressure. The latter conditions allow the solubility-pressure trend to be obtained, in satisfactory agreement with literature data derived from standard dynamic methods
Crystallization of TiO2 Nanotubes by In Situ Heating TEM
Get PDFThe thermally-induced crystallization of anodically grown TiO2 amorphous nanotubes has been studied so far under ambient pressure conditions by techniques such as differential scanning calorimetry and in situ X-ray diffraction, then looking at the overall response of several thousands of nanotubes in a carpet arrangement. Here we report a study of this phenomenon based on an in situ transmission electron microscopy approach that uses a twofold strategy. First, a group of some tens of TiO2 amorphous nanotubes was heated looking at their electron diffraction pattern change versus temperature, in order to determine both the initial temperature of crystallization and the corresponding crystalline phases. Second, the experiment was repeated on groups of few nanotubes, imaging their structural evolution in the direct space by spherical aberration-corrected high resolution transmission electron microscopy. These studies showed that, differently from what happens under ambient pressure conditions, under the microscope’s high vacuum (p < 10−5 Pa) the crystallization of TiO2 amorphous nanotubes starts from local small seeds of rutile and brookite, which then grow up with the increasing temperature. Besides, the crystallization started at different temperatures, namely 450 and 380 °C, when the in situ heating was performed irradiating the sample with electron beam energy of 120 or 300 keV, respectively. This difference is due to atomic knock-on effects induced by the electron beam with diverse energy
"La presenza del sacro nel territorio albano" in Res Sacrae, Atti del XXXI Corso di Archeologia e Storia antica del Museo Civico Albano
No full textThe area around Albano Laziale shows the presence of cult places during the republican and
early-imperial periods. These consist mainly of inscriptions with dedications to a deity and of
votive material. Unfortunately, no architectural structures have been found. However, also
with the help of ancient literature, it is possible to imagine the “sacred landscape” of the Roman period: rural cult places scattered all around the Albano lake within country estates of villas,
and near roads, as the Appia Antica or other roads that linked hills to the sea. The main
sanctuary was a temple of Iuppiter Latiaris, in Monte Cavo
The Hippo Show Must Go On: YAP Activation as a Therapeutic Strategy in Colorectal Cancer
No full textThe role of Hippo pathway in colorectal cancer (CRC) initiation and progression has been controversial. In this issue of Cell Stem Cell, Cheung et al. (2020) shed new light on a distinct function of the transcriptional co-activator YAP as a tumor suppressor and Wnt pathway inhibitor in CRC
Suspended Microchannel resonators with integrated electrodes for thermal and electrical characterization of liquids
Get PDFSuspended microchannel resonator (SMR) has been demonstrated as a versatile technique, allowing to measure mechanical, morphological or even optical properties of cells. However, physical properties of cells may substantially change depending on the chemical composition of the suspension medium. Therefore, it is essential developing novel multiparametric techniques able to provide a complete understanding of the biological samples by characterizing also the liquid in which the cells are suspended. In this work we both theoretically and experimentally introduce a novel electro-mechanical sensing technique using SMR devices with integrated electrodes that allow measuring different physicochemical properties of the liquid sample as thermal conductivity, dielectric constant, electrical conductivity or even concentration of ions. These measured liquid properties can ultimately be used to complement other typical SMR measurements, such as mass. Moreover, we show that this electro-mechanical approach can be also used as a transduction method and as a way of tuning the mechanical resonance frequency
Calorimetric investigations on the metabolism of Bacillus strains isolated from artistic stoneworks
No full textIn the study on the deterioration of artistic stoneworks the possibility to relieve the presence of deteriorative microorganisms on the alterations is becoming evermore important. The spore-forming microorganisms belonging to Bacillus genus are often present in the biological alterations; these bacteria are very common and their caracteristic habitat is the soil, but they are also isolated from different other matrices, as the altered stone of monuments. Their role in the biodeterioration is particularly important for the capability to produce resistant forms, the spores, that permit the resistance to stressing envirnmental conditions. The aim of this work is to study the calorimetric behaviour and characterize the various phases of the cellular cycle of different Bacillus strains isolated from stonework alterations (B.cereus, B.subtilis e B. alvei) and verify if it is possible to obtain from the calorimetric signals significant differences that permit the marking of the single specie. Furthermore in every test carried out using spores a fall of the calorimetric signal results more evident, compared to tests performed with vegetative cells
Características de los procesos de virtualización y su impacto en las estructuras de las Organizaciones
Get PDFFil: Stassi, Héctor Martín. Universidad Nacional de Córdoba. Facultad de Ciencias Económicas. Instituto de Administración; Argentina.En el presente trabajo se busca identificar las principales dimensiones del fenómeno de virtualización organizacional que se observa en nuestros días y que generan cambios estructurales en la configuración de las organizaciones tradicionales. El resultado de dicho análisis, permitirá tener una primera apreciación acerca de la magnitud de los impactos en las organizaciones a medida que intensifiquen sus procesos de digitalización y virtualización. Finalmente se concluye en la necesidad de profundizar en el estudio sobre el impacto de los procesos de virtualización sobre los modelos teóricos tradicional de estructura organizacional, a los fines de realizar una primera aproximación sobre aspectos a considerar para el desarrollo de nuevos paradigmas que contengan a las organizaciones virtuales y brinden herramientas para su gestión.https://revistas.unc.edu.ar/index.php/DTI/issue/view/1426publishedVersionFil: Stassi, Héctor Martín. Universidad Nacional de Córdoba. Facultad de Ciencias Económicas. Instituto de Administración; Argentina.Negocios y Administració
Targeting cancer stem cells and the tumor microenvironment
No full textCompelling evidence indicates that the survival and behavior of cancer stem cells (CSCs) are positively regulated by specific stimuli received from the tumor microenvironment, which dictates the maintenance of stemness, invasiveness, and protection against drug-induced apoptotic signals. CSCs are per se endowed with multiple treatment resistance capabilities, thus the eradication of CSC pools offers a precious strategy in achieving a long-term cancer remission. Numerous therapies, aimed at eradicating CSCs, have been elaborated such as: (i) selective targeting of CSCs, (ii) modulating their stemness and (iii) influencing the microenvironment. In this context, markers commonly exploited to isolate and identify CSCs are optimal targets for monoclonal antibody-based drugs. Furthermore, the molecules that inhibit detoxifying enzymes and drug-efflux pumps, are able to selectively suppress CSCs. Auspicious outcomes have also been reported either by targeting pathways selectively operating in CSCs (e.g. Hedgehog, Wnt, Notch and FAK) or by using specific CSC cytotoxic agents. Other compounds are able to attenuate the unique stemness properties of CSCs by forcing cell differentiation, and this being the case in ATRA, HDACi, BMPs and Cyclopamine, among others. Targeting the interplay between paracrine signals arising in the tumor stroma and the nearby cancerous cells via the inhibition of VEGF, HIF, CD44v and CXCR4, is increasingly recognized as a significant factor in cancer treatment response and holds alluring prospects for a successful elimination of CSCs. In the present chapter, we discuss the latest findings in the optimization and tailoring of novel strategies that target both CSCs and tumor bulk for the eradication of malignancies
CCT-2019-05-31-Encuentro con los autores Claudio Stassi y Giovanni di Gregorio, charla sobre el talento italiano en el cómic (solo audio)
No full textAudio del encuentro con los autores Claudio Stassi (dibujante) y Giovanni di Gregorio (guionista), charla sobre el talento italiano en el cómic. Presenta Jordi Ojeda.En la charla se hace un recorrido por la historia del fumetti italiano, desde la creación del personaje de Tex en 1948, el más popular del país, publicado por la Editorial Bonnelli, haciendo un recorrido por su impacto en la cultura popular a lo largo del siglo XX, con personajes míticos como Dylan Dog. Además explican sus experiencias personales en la participación de dibujar y guionizar historias de Dylan Dog y, en especial de Dampyr, y, en concreto, de la historia “El verdugo negro” que acontece en la ciudad de Barcelona.Además relatan la génesis de su primer trabajo importante, la novela gráfica Brancaccio, ambientada en los años noventa en el barrio homónimo de Palermo, mostrando por primera vez en la ficción los principales afectados por la mafia siciliana, es decir, los propios ciudadanos y vecinos, lo que conlleva una lacra social frenando la prosperidad del territorio.También se realiza un análisis de autores destacados de la novela gráfica, en especial de Zerolcalcare, que despuntó con su obra “La profecía del armadillo”, y que recientemente acaba de publicar “Olvida mi nombre”, siempre en clave autobiográfica y representando la voz de toda una generación.En la mesa, de izquierda a derecha: Jordi Ojeda, Giovanni di Gregorio y Claudio Stassi. Duración: 67 minutos (idioma: castellano). Viernes 31 de mayo de 2019 a las 19h en la sala Fòrum de FNAC Triangle de Barcelona.Nota de prensa de las editoriales:Dampyr. El verdugo negro (Aleta Ediciones): Álbum especial de Dampyr con una nueva aventura completa que transcurre en Barcelona, en una Barcelona que pensabas conocer pero que descubrirás que todavía guarda muchos secretos.Brancaccio (Norma Editorial): “UN PUEBLO ENTERO QUE PAGA EL PIZZO* ES UN PUEBLO SIN DIGNIDAD” (* Pizzo es el impuesto que exige la mafia).
Nino quiere ser alguien, salir de Brancaccio, olvidarse de los problemas que corrompen su pueblo, que entristecen a su padre Pietro y preocupan a su madre Angelina. Pero Nino, uno más de esos niños con sueños de Brancaccio, tendrá que aprender a asumir la dura realidad de su pueblo...Más información en: http://comiccienciatecnologia.blogspot.com.es
- …
