1,721,026 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Hybrid Inorganic-organic Ion Conducting Polymer Electrolytes: Synthesis, Structure and Conductivity Mechanism
No full textPolymer Electrolytes are competing for a place in the future energy generation, Storage and distribution markets and they are promising for the development of new devices like sensors and actuators. In this context Mie report an overview on the synthesis, Structure, physical and electrical properties of three classes of new electroactive inorganic-organic hybrid materials.
Theflrst class is due to the ORMOCERS-APE (Organically Modified Ceramics As Polymer Electrolytes or ORMOCERS-APE). These materials are three-dimensional networks composed by organic macromolecules linked together by inorganic atoms like Si, Ti, Zr, Al. Inorganic salts can be dissolved in these materials to determine a tailored conductivity. Taking into account, the recent increased interest in the development of Polymer Electrolyte Membrane Fuel Cells (PEMFCs), we include in the present overview the description of two groups of membranes. In the first group we present membranes based on Nafion and inorganic nano-powders.
These materials can be considered as subgroup of the more general class of the (nano) composite polymer electrolytes. In the second group we describe siloxanic proton-conducting membranes that can be considered as an upgrade version of the ORMOCERS-APE.
The second class is that of the Z-lOPEs (Zeolitic Inorganic-Organic Polymer Electrolytes). These materials are three-dimensional networks composed by organic macromolecules linked together by bridging inorganic clusters. The inorganic clusters are formed by the aggregation of two or more inorganic coordination complexes and are positively or negatively charged.
The third class of materials is that of the HGEs (Hybrid inorganic-organic GEls).
These materials can be considered as an upgrade version ofZ-lOPEs in which the organic component instead of being due to macromolecules is based on organic multi-functional molecules
New inorganic-organic proton conducting membranes based on Nafion and hydrophobic fluoroalkylated silica nanoparticles
No full textIn this report, a new nanofiller consisting of silica "cores" bearing fluoroalkyl surface functionalities is synthesized and adopted in the preparation of a series of hybrid inorganic-organic proton conducting membranes based on Nation. The hybrid materials are obtained by a solvent-casting procedure and include between 0 and 10 wt.% of nanofiller. The resulting systems are extensively characterized by Thermogravimetry (TG), Modulated Differential Scanning Calorimetry (MDSC) and Dynamic Mechanical Analysis (DMA), showing that the hybrid materials are stable up to 240°C and that their overall thermal and mechanical properties are affected both by the polar groups on the surface of the silica "cores" and by the fluoroalkyl surface functionalities of the nanofiller. The electric properties of the hybrid materials are investigated by broadband dielectric spectroscopy (BDS). It is shown that proton conductivity of the materials is not compromised by the lower water uptake arising from the hydrophobic character of the nanofiller. With respect to a pristine Nation recast membrane, the hybrid material characterized by 5 wt.% of nanofiller, [Nafion/(Si80F)0.7], shows the highest conductivity in all the investigated temperature range (5 <= T <= 155°C). Indeed, [Nafion/(Si80F)0.7] features the lowest water uptake and presents a conductivity of 0.083 S/cm at 135°C. This result is consistent with the good performance of the membrane in single fuel cell tests
Identificazione di molecole segnale mediante cromatografia liquida e spettrometria di massa in trasformata di Fourier (LC-ESI-FTMS) ed implicazioni del quorum sensing in batteri gram-negativi coinvolti nei processi di biorisanamento ambientale.
No full textComunicazione POSTER
Electrocatalysts based on mono/plurimetallic carbon nitrides for polymer electrolyte membrane fuel cells fuelled with hydrogen (PEFC) and methanol (DMFC) and for H2 electrogenerators
No full textThe invention describes the preparation of electrocatalysts, both anodic (aimed at the oxidation of the fuel) and cathodic (aimed at the reduction of the oxygen), based on mono- and plurimetallic carbon nitrides to be used in PEFC (Polymer electrolyte membrane fuel cells), DMFC (Direct methanol fuel cells) and H2 electrogenerators. The target of the invention is to obtain materials featuring a controlled metal composition based on carbon nitride clusters or on carbon nitride clusters supported on oxide-based ceramic materials. The preparation protocol consists of three steps. In the first the precursor is obtained through reactions of the type: a) sol-gel; b) gel-plastic; c) coagulation-flocculation-precipitation. The second step consists of the thermal treatments to decompose the precursors in an inert atmosphere leading to the production of the carbon nitrides. In the last step the chemical and electro-chemical activation of the electrocatalysts is performed. Precursors are obtained through reactions leading to: a) the complexation of a "soft" transition metal with a coordination complex acting as a ligand to obtain clusters; b) 3-D networking of the resulting clusters through suitable organic molecules and/or macromolecules
Broadband Dielectric Spectroscopy and conductivity mechanism of Nafion and inorganic-organic Nafion/oxoclusters hybrids
No full textPreprints of Symposia - American Chemical Society, Division of Fuel Chemistr
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
New Inorganic-Organic Polymer Electrolytes based on PEG400 and Al[OCH(CH3)2]3 (part II): Morphology, Thermal Stability and Conductivity Mechanism
No full textThis report presents detailed studies on the morphology, thermal stability, and electrical spectroscopy of 11 aluminum-containing hybrid inorganic-organic polymer electrolytes with the general formula {Al[O(CH2CH2O)8.7]r/(LiClO4)z}n , where 1.85 < r< 2.24 and 0 < z < 1.06. Scanning electron microscopy showed a solid-plastic appearance and a smooth texture on the surface of the bulk materials. Thermogravimetric investigations indicated that the hybrid polymer electrolytes are thermally stable up to about 260°C. Furthermore, a detailed study of the mechanism of ion conduction in these systems was carried out by impedance
spectroscopy in the 20 Hz to 1 MHz range and at temperatures varying from 18 to 80°C. It was demonstrated that the {Al[O(CH2CH2O)8.7]r/(LiClO4)z}n materials conduct ionically by a charge-transfer mechanism mainly regulated by segmental motion and fast ion-hopping processes between equivalent coordination sites distributed along polyether chains. The "anion trapping'' ability of the aluminum atoms toward perchlorate contributes greatly to the conductivity performance of the {Al[O(CH2CH2O)8.7]r/(LiClO4)z}n networks. Finally, the best conductivity observed in these materials is 1.66x10-5 S/cm at 25°C
Effect of SiO2 on relaxation phenomena and mechanism of ion conductivity of [Nafion/(SiO2)x] composite membranes
No full textThis report describes a study of the effect of SiO2 nanopowders on the mechanism of ionic motion and interactions taking place in hybrid inorganic-organic membranes based on Nafion. Five nanocomposite membranes of the formula [Nafion/(SiO2)x] with SiO2 ranging from 0 to 15 wt % were prepared by a solvent casting procedure. TG measurements demonstrated that the membranes are thermally stable up to 170 °C but with the loss water it changes the cluster environments and changes the conductivity properties. MDSC investigations in the 90-300°C temperature range revealed the presence of three intense overlapping endothermal peaks indicated as I, II, and III. Peak I measures the order-disorder molecular rearrangement in hydrophilic polar clusters, II corresponds to the endothermic decomposition of -SO3 groups, and III describes the melting process in microcrystalline regions of hydrophobic fluorocarbon domains of the Nafion moiety.
ESEM with EDAX measurements revealed that the membranes are homogeneous materials with smooth surfaces. DMA studies allowed us to measure two relaxation modes. The mechanical relaxation detected at ca. 100°C is attributed to the motion of cluster aggregates of side chains and is diagnostic for R-SO3H---SiO2 nanocluster interactions. DMA disclosed that at SiO2/-SO3H (phi) molar ratios lower than
1.9, the oxoclusters act to restrict chain mobility of hydrophobic domains of Nafion and the dynamics inside
polar cages of [Nafion/(SiO2)x] systems; at phy higher than 1.9, the oxoclusters reduce the cohesiveness of hydrophilic polar domains owing to a reduction in the density of cross-links. FT-IR and FT-Raman studies of the [Nafion/(SiO2)x] membranes indicated that the fluorocarbon chains of Nafion hydrophobic domains assume the typical helical conformation structure with a D(14pigreco/15) symmetry. These analyses revealed four different species of water domains embedded inside polar cages and their interconnecting channels:(a) bulk
water [(H2O)n]; (b) water solvating the oxonium ions directly interacting with sulfonic acid groups [H3O+---SO3
-](H2O)n; (c) water aggregates associated with H3O+ ions [H3O+---(H2O)n]; and (d) low associated water species in dimer form [(H2O)2]. The conductivity mechanism and relaxation events were investigated by broadband dielectric spectroscopy (BDS). [Nafion/(SiO2)x] nanocomposite membranes were found to possess two different molecular relaxation phenomena which are associated with the R-relaxation mode of PTFE-like fluorocarbon domains and the â-relaxation mode of acid side groups of the Nafion component. Owing to their strong coupling, both these relaxation modes are diagnostic for the interactions between the polar groups
of the Nafion host polymer and the (SiO2)x oxoclusters and play a determining role in the conductivity mechanism of the membranes. The studies support the proposal that long-range proton charge transfer in [Nafion/(SiO2)x] composites takes place due to a mechanism involving exchange of the proton between the four water domains. This latter proton transfer occurs owing to a subsequent combination of domain intersections resulting from the water domain fluctuations induced by the molecular relaxation events of host
Nafion polymer
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