1,720,973 research outputs found
An Introduction to Ablative Materials and High-Temperature Testing Protocols
No full textAblative materials are at the base of the entire aerospace industry because as sacrificial materials they allow the production of propulsion devices (such as liquid and solid rocket motors [SRMs]) or the protection of vehicles and probes during hypersonic flight through a planetary atmosphere. Some nonpolymeric materials have been successfully used as ablatives but, due to their versatility, polymeric ablative materials represent the widest family of sacrificial thermal protection system (TPS) materials. Thermal analysis such as differential scanning calorimetry, thermogravimetric analysis, thermomechanical analysis, and differential thermal analysis can establish the bases for a proper and comprehensive evaluation of the thermal response of composite TPS materials when exposed to high temperatures, enabling the modeling of the ablation process. However, the aforementioned protocols cannot properly simulate the real conditions of the hyperthermal environment in which TPS materials have to work. Other techniques such as the oxy-acetylene torch test or the simulated solid rocket motor allow to better study the response of ablative materials; these techniques can reproduce in a smaller scale the environmental conditions produced in an SRM. As a result, in light of the specific topic of Section 3 of this book, the purpose of this chapter is to provide readers with relevant generalities on ablative materials and related testing techniques, i.e., to introduce the proper tools to understand the scientific content and uniqueness of the other chapters of this section
Nanofillers in Polymers
No full textIn this chapter the principal nanoparticles and their effects on the properties of polymeric matrix nanocomposites will be reviewed. The development of new production strategies able to guarantee reliable processing routes for nanocomposites with a good dispersion and distribution of nanoparticles are also addressed including investigations on the functionalization of the particles in order to improve the matrix/particle interactions. The chapter also includes a review of the properties and applications of polymer matrix nanocomposites in relevant industrial sectors as aerospace, cosmetics, biomedicine (scaffold for tissue engineering, filling resins for prosthetic dentistry, etc.), and food packaging, considering also safety and environmental concerns on the use of nanoparticles. This review considers a comprehensive combination of the different possible matrices (thermoplastics, thermosets, elastomers) and most of the nanoparticles currently on the market or at experimental level. The use of nanoparticles as additives in long fiber advanced composites is also considered. Research and technological application opportunities for these new advanced materials are continuously analyzed through the chapter
Nanostructured phenolic matrices: Effect of different nanofillers on the thermal degradation properties and reaction to fire of a resol
No full textIn this work, the effect of 6 different fillers as a nanomodifier of phenolic matrix was evaluated in thermal stability and reaction to fire. The chosen nanoparticles were montmorillonite, silica, carbon black, and 3 carbides—boron, silicon, and zirconium carbides. The nanofillers were mechanically dispersed in the matrix, and the dispersion and distribution of the nanosized particles in the matrix was evaluated by transmission electron microscopy. The thermal stability of nanocomposites was investigated by thermogravimetric analysis both in nitrogen and in air while the thermal combustion properties were measured using a microscale combustion calorimeter. The experimental data highlighted the remarkable effects of nanoboron carbide on the thermal properties it can confer to the phenolic matrix. Rheological behavior of the blends was also investigated to evaluate the effect of the different fillers on the viscosity of the nanostructured matrices
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
Microstructure Refinement and mechanical properties improvement of EUROFER97 steel
No full textEUROFER97 steel for nuclear fusion applications are usually manufactured by hot rolling and subsequent heat treatments: austenitization at 980 °C for 30 minutes, rapid cooling and tempering at 760 °C for 90 minutes. The aim of this work is to refine the microstructure of traditional EUROFER97 steel by means of a thermo-mechanical treatment, in order to improve its mechanical properties without losing ductility. Starting from the traditional treatment conditions, the steel has undergone a cold rolling process and an annealing treatment, with the aim of studying its effects on the microstructure and mechanical properties. The experimentation was conducted on 40 samples, combining 5 different cold reduction ratios (CR: 20%, 40%, 50%, 60%, 80%) and 8 different heat treatment temperatures in the range of 400 ° C to 750 ° C (ΔT: 50 ° C) with a soaking time of 1 hour. For each treatment condition, Vickers hardness measurements, X-ray diffraction and microstructural characterization by optical and scanning electron microscopy were performed. Furthermore, the preliminary results of tensile tests on the samples deformed with the highest reduction ratio (CR: 80%) are reported. Following primary recrystallization, a microstructure with equiaxed grains of sub-micrometric size is observed. In particular, for the sample with CR: 80%, after heat treatment at 650 ° C a high microstructural refinement is achieved which guarantees the strengthening with ductility comparable to the traditional condition of steel. The work has shown the possibility of strengthening EUROFER97 steel without compromising its ductility
Development and Characterization of Lignin-Based Hydrogels for Efficient Adsorption of Diclofenac From Aqueous Environment
Full text linkHydrogels are interesting materials with potential applications in the treatment of water contaminated by organic and inorganic toxic compounds. Among the different monomers/polymers commonly used, the natural polymer lignin is undoubtedly an attractive candidate due to its biocompatibility, biodegradability, low toxicity, and availability in high quantities as the main by-product of the pulp industry. In the present work, the synthesis and characterization of a lignin-based hydrogel are described and tested in the adsorption of the nonsteroidal anti-inflammatory drug, diclofenac, one of the so-called emerging contaminants. Due to the anionic nature of diclofenac currently used in pharmaceutical preparations, a cationic functionality is included in the polymeric backbone. The obtained hydrogel is characterized by a porous structure, thermal stability, and an elastic behavior more pronounced than the viscous one. It has a high swelling capacity and is able to efficiently remove diclofenac in batch mode, following a pseudo-second order kinetic, and adsorption could be well described by Langmuir and Sips isothermal models. For the first time, diclofenac removal by a lignin-based hydrogel is also carried out in a packed-bed column with a maximum capacity of ca. 50 mg/g, and different theoretical models are used to fit the experimental data
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
- …
