1,720,972 research outputs found
OFET for gas sensing based on SuMBE grown pentacene films
No full textSupersonic molecular beam deposition (SuMBE) is a thin film growth method for organic semiconducting molecules that gives unprecedented control oil morphology and structure by tuning the kinetic energy of the impinging molecules. This is the key factor by which we could control the growth of high quality films showing state of the art electrical properties for pentacene films. We show that exploiting such ability to control structure and morphology of the films one could tailor the gas response of the organic thin film transistors. We envisage the potential of such devices in applications where the transistor configuration offers new strategic opportunities as in gas sensing and in microfluidics. (c) 2007 Elsevier Ltd. All rights reserved
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
Supersonic molecular beams deposition of alpha-quaterthiophene: Enhanced growth control and devices performances
No full textThe alpha-quatertiophene is widely considered an interesting material for the realization of organic electronics and opto-electronics. Compared to other oligothiophenes, the performances of transistors based on this compound are limited by its kind of growth on the typical materials used for device realization. Here we show that via seeded supersonic beams we can lead to a nice improvement of both morphological and electrical properties of the film grown, through a better control of the initial state of the precursor in the vapor phase. Using the high kinetic energy achievable in the supersonic beams, we increase the dimensions of the grains and the coalescence of different islands, limiting the grain boundary formation, As consequence, the performance of the realized field effect transistors is enhanced of one order of magnitude. (C) 2009 Elsevier B.V. All rights reserved
Ion selective textile organic electrochemical transistor for wearable sweat monitoring
Full text linkTextile organic electrochemical transistors (txOECTs) are a new class of wearable biosensors used to monitor physiological parameters in bio fluids of clinical interest. Herein the selectivity of a textile biosensor was improved directly functionalizing the textile device with ion selective membranes. The device was prepared by a series of consecutive functionalization of the textile fiber, first by applying the conductive polymer poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) and subsequently the ion selective membrane based on different ionophores with the aim of measuring electrolytes in sweat. The ion selective membranes were previously tested and optimized by potentiometric measurements. The biosensor devices were studied with different concentration of electrolytes. Membrane selectivity was tested comparing transistor response with interfering ions, proving successfully the selective response to sodium, potassium and calcium ions. The ability of the textile biosensors to discriminate among the cations was demonstrated over the 10−5 - 1 M concentration range, a concentration range found in sweat. The electronic parameters of the txOECTs show differences not only in modulation response but also in time constants of kinetic behavior. The selective determination of potassium and calcium in sweat has a great importance in different applications, for example, in human sweat monitoring, to understand physiological conditions, like dehydration, cardiac bioactivity and hypokalemia
A mathematical model of OECTs with variable internal geometry
No full textOrganic Electrochemical Transistor (OECTs) are devices that can measure the ionic content of liquid samples and biological systems. The response of an OECT can provide information on the physiological conditions and characteristics of a biological system. In a typical OECT configuration, the system or sample is connected to a reference electrode (the gate) and to a semiconducting material, typically PEDOT:PSS, with two other terminals (the drain and the source) for connection to an external circuit. The transistor architecture of OECTs enables signal control and amplification. Upon application of an external electromagnetic field at the electrodes, ions are driven from the liquid sample towards the PEDOT:PSS channel, where they modify the conductivity of the channel and generate a continuous current as a function of time. The intensity of that current and the time to the steady state can be correlated to the characteristics of the ions in solution. In most of the existing theories that model the behavior of OECTs, the internal configuration and geometrical parameters of the device are assumed to be constant over time. This simplifying assumption breaks down in living systems and in all those soft devices with elevated value of compliance and absorption (such as devices on paper, textile or polymeric sponges). Similar simplified models may fail to predict the behavior of real systems within acceptable bounds. Here, we present a mathematical model that describes the behavior of OECTs in which the geometry of the internal fluidic circuits of the system can change over time. These circuits represent the network of chambers and channels through which the liquid solution flows from the gate to the drain-source electrodes, enabling the transport of ions. At a certain time, the liquid solution shall be spread throughout a fraction only of the entire network available for liquid transport, i.e. the wet fraction p. The mathematical model that we have developed in this work uses the data generated by OECTs to determine the wet fraction p and the concentration C of ions of a system. The model enables quantification of a system without calibration of the device, which may be of interest for those working in the fields of bioengineering, biomedical sensors, wearable electronics, flexible electronics. In experiments where the variables of system were varied over large intervals, the model achieved an excellent performance and a precision up to 92%
Solid state dye sensitized solar cells based on supersonic beam deposition of organic, inorganic cluster assembled, and nanohybrid materials
No full textThe growth of nanohybrids synthesized by supersonic beam codeposition of metal oxide clusters, produced by microplasma cluster source, and of aerodynamically accelerated molecules has been explored as a novel approach to the preparation of controlled dye sensitized materials for photovoltaic applications. The hybrid nanostructures are formed through deposition via supersonic expansion processes, controlling the kinetic energy of the precursors. With this approach, we developed prototype dye sensitized solar cells based on nanostructured TiO2 and CuPc with different architectures. To explore the viability of this approach, we compare cells made layer by layer with those where an intermediate codeposited layer is inserted between the two raw materials. This latter type of cells presents an enhancement of the photocurrent of a factor of 45 and of the efficiency of a factor of 40. This work opens a new viable perspective in the growth and in the control of the interfacial properties of nanohybrid materials, by direct codeposition of molecules and oxide nanostructures, with demonstrated useful applications in photovoltaic devices. (C) 2010 American Institute of Physics. [doi:10.1063/1.3501337
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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