1,720,966 research outputs found
Sol-gel approach to incorporate millimeter-long carbon nanotubes into fabrics for the development of electrical-conductive textiles
No full textIn this paper, a new and versatile approach to obtain a good dispersion in water-based paste of short (ffi 1.5 mm) and long (ffi 3.0 mm) millimeter-sized carbon nanotubes (CNT) for the fabrication of electroconductive textiles is reported. With this aim, N-[3-(triethoxysilyl)propyl]ethylenediamine (EDAES) was used in combination with a waterborne thermo-degradable surfactant to stabilize the dispersion of two different kinds of carbon nanotubes (CNT) in hydroalcoholic solutions. A polyurethane thickener was added to each CNT dispersion to obtain dense pastes that were deposited onto cotton fabrics using the knife-over-roll technique. High magnification images confirm that the nanotubes are well dispersed in both coatings, furthermore appearing homogeneously distributed on the cotton surface. The conductivity of the long CNT-coated fabrics was confirmed by the electrical resistance of 2.61x 104Ω/sq which decreased to 9.46x102Ω/sq for short CNT size. Moreover, after one washing cycle, the electrical conductivity variations of coating containing the shortest nanotubes retain over 99%, demonstrating its adhesion on the fabric. The increase of the textile stiffness was less than 20% for both treated samples compared to the reference, without affecting significantly the fabric samples comfort. The developed cotton fabrics worked well as wearable conductive materials in heart rate monitoring using photoplethysmography
Wear behavior characterization of hydrogels constructs for cartilage tissue replacement
Get PDFThis paper aims to characterize the wear behavior of hydrogel constructs designed for human articular cartilage replacement. To this purpose, poly (ethylene glycol) diacrylate (PEGDA) 10% w/v and gellan gum (GG) 1.5% w/v were used to reproduce the superior (SUP) cartilage layer and PEGDA 15% w/v and GG 1.5% w/v were used to reproduce the deep (DEEP) cartilage layer, with or without graphene oxide (GO). These materials (SUP and DEEP) were analyzed alone and in combination to mimic the zonal architecture of human articular cartilage. The developed constructs were tested using a four-station displacement control knee joint simulator under bovine calf serum. Roughness and micro-computer tomography (μ-CT) measurements evidenced that the hydrogels with 10% w/v of PEGDA showed a worse behavior both in terms of roughness increase and loss of uniformly distributed density than 15% w/v of PEGDA. The simultaneous presence of GO and 15% w/v PEGDA contributed to keeping the hydrogel construct’s characteristics. The Raman spectra of the control samples showed the presence of unreacted C=C bonds in all the hydrogels. The degree of crosslinking increased along the series SUP < DEEP + SUP < DEEP without GO. The Raman spectra of the tested hydrogels showed the loss of diacrylate groups in all the samples, due to the washout of unreacted PEGDA in bovine calf serum aqueous environment. The loss decreased along the series SUP > DEEP + SUP > DEEP, further confirming that the degree of photo-crosslinking of the starting materials plays a key role in determining their wear behavior. μ-CT and Raman spectroscopy proved to be suitable techniques to characterize the structure and composition of hydrogels
High performance, binder-free electrodes with single atom catalysts on doped nanocarbons for electrochemical water splitting synthesized using one-step thermally controlled delamination of thin films
No full textDeveloping high performance catalysts for electrochemical water splitting is critical for an efficient and sustainable route to hydrogen production. For this, single-atom catalysts (SACs) are the best candidates, as they offer the highest atom efficiency. However, current methods to produce SACs involve a complex synthesis, often requiring multiple lengthy and expensive steps and yielding an insufficient density of single atoms. Here, we report a one-step chemical vapor deposition (CVD) synthesis to produce free-standing (FS) electrodes with Ni SACs on a matrix of sulfur-doped carbon nanofibers (CNFs), referred to as SACs@nanocarbon. The mechanism is based on a temperature-controlled delamination of thin films, with Au in contact with a SiO2 substrate, leading to the nucleation and growth of SACs@nanocarbon. Advanced characterization methods indicate the presence of Ni and Au single atoms and larger gold aggregates on the CNF matrix surface. These non-platinum group metal (non-PGM) electrodes showed exceptional performance for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). They performed for over 20 000 cycles with negligible change in overpotential at higher currents, with low onset overpotentials of 305 mV at 10 mA cm-2 for the OER and 40 mV at 17 mA cm-2 for the HER. The overpotential decreased to 195 mV at a current density of 100 mA cm-2. Remarkably, the electrode performance improved over cycling, while gold was dissolving in the electrolyte. This novel synthesis yielding SACs@nanocarbon could pave the way for the development of non-PGM, high performance electrodes for many other electrocatalytic applications. Additionally, the new paradigm of temperature-controlled delamination of thin films could be used to synthesize new materials.Developing high performance catalysts for electrochemical water splitting is critical for an efficient and sustainable route to hydrogen production
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
CNT synthesis for IC interconnects
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 315-336).Based on their properties, carbon nanotubes (CNTs) have been identified as ideal replacements for copper interconnects in integrated circuits given their higher current density, inertness, and higher resistance to electromigration. Although at the laboratory level CNTs have proven their technical viability as interconnects, fabrication issues such as growing the desired type of CNTs in selected positions, at temperatures compatible with CMOS processing (below 500"C), and with the appropriate electrical connections, remain challenges that are hindering their introduction into industry. The purpose of this study was to develop the processes and understanding needed to establish CNTs as viable replacements for metal-based integrated circuit (IC) interconnects. Through over a thousand synthesis experiments using a dedicated thermal Chemical Vapor Deposition (CVD) system, a systematic approach was developed starting with growth of CNTs on insulating substrates, then moving to conducting substrates, and finally integrating CNT growth into insulating scaffolds with regularly spaced pores. The following results were achieved: Control of the type of carbon nanotubes grown using simple process parameter variations: By focusing on controlling catalyst morphology evolution to obtain dense and tall carpets of vertically-aligned CNTs on insulating substrates, we were able to tune the diameter and number of walls, by simply timing the introduction of a reducing agent (hydrogen) into the thermal process.(cont.) Growth of dense carpets of vertically-aligned CNTs on conductive substrates below 5000C: By focusing on the material properties of the catalyst and underlayer, we discovered important requirements for the underlayer grain structure evolution, as well as by preheating the incoming hydrocarbon gas, growth of dense and vertically aligned carpets of nanotubes on conductive underlayers at growth temperatures below 5000C could be achieved. Electrical characterization showed that we obtained ohmic contact between the CNTs and the substrate. Control of CNT crystallinity via gas preheating : We discovered that the time and temperature of gas preheating was critical for the crystallinity of the resulting CNTs. This was done by comparing the output gases from varying gas preheat treatments to the corresponding CNT structures. This allowed a discussion of the critical gas compounds responsible for growth of crystalline CNTs. Growth of CNTs into periodic insulating scaffolds on conductive substrates: We have grown CNTs on conductive substrates and in regularly-spaced pores of an insulating anodized alumina scaffold. This allowed simulation of an interconnect via system for future measurement of the electrical properties of CNTs. This structure can also serve as a starting point for future development of dense arrays of CNT-based devices.by Gilbert Daniel Nessim.Ph.D
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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