1,720,956 research outputs found
Study of the self-healing behaviour of early age cracks in concrete with crystalline admixtures under six environmental exposures
No full textThe search for self-healing materials is justified by the increasing sustainability and safety needs of structures. The presence of small cracks in structural concrete, which could accelerate the degradation process and diminish its service life, is unavoidable due to the heterogeneous nature of the material. A method to enhance self-healing in concrete is the use of crystalline admixtures (CA), which are hydrophilic products formed by chemical active substances, cement and sand.
This research analyzes the self-healing properties of young concrete specimens for autogenous and CA-based healing under different exposure conditions. Two types of concrete were studied: a control mix, and a mix containing the CA (with a dosage of 4% by the weight of cement). Six exposure conditions were studied: water immersion at 15oC, water immersion at 30oC, water contact with a water head of 2 centimeters, wet/dry cycles, humidity chamber, and laboratory conditions.
Self-healing capability was evaluated by measuring the permeability of concrete specimens before and after the healing period. Cylindrical specimens were pre-cracked by means of splitting test at the age of 2 days, and their permeability measured at the age of 3 days and after 42 days in the healing exposure. The range of studied crack widths was limited to 300 micrometers.
From the tests, the self-healing reaction was confirmed for both mixtures for exposures in direct contact with water. Exposing just one surface to water contact increased healing rates, but only the crack in direct contact could be sealed. Finally, slight differences were measured between both mixtures, with a higher stability for concrete with CA.
To sum up, only cracks in direct contact with water could heal, achieving higher healing rates when the specimens were immersed in water. Ambient humidity was not enough to produce healing either for control concrete or concrete with CA
Self healing capability of concrete containing crystalline admixtures in different exposure conditions
No full textSelf-healing materials have the capability of recovering their performance after damage has occurred. In this work, the self-healing effect of a crystalline admixture for concrete is analysed in different environmental exposures. In order to compare healing capacity of the admixture compared with autogenous healing of concrete, two types of concrete were studied: a control concrete (CC) and a mix containing the crystalline admixture (CAC), with a dosage of 4% by the weight of cement. Four exposure conditions were studied: water immersion, water contact with a water layer of two centimetres, humidity chamber and laboratory conditions. Self-sealing/healing was studied by analysing the permeability of the cracked specimens and by observing with a microscope the closing of the crack. As from the obtained results CAC showed better healing behaviour than CC; the healing rates of CC had higher dispersion than those of CAC, which achieved more stable behaviour for all the different exposures and was anyway able to provide some not negligible healing capacity also in open air conditions. Differences between the exposures with direct contact with water were also noticed, indicating the importance of water for the reaction to take place
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
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
Efficacia degli additivi cristallizzanti sulle capacità di autoriparazione di calcestruzzi giovani
Full text linkLAUREA MAGISTRALELa sostenibilità, nell'ambito dell’ingegneria civile e strutturale, è un concetto che sta acquistando una sempre maggiore rilevanza a causa della costante richiesta di strutture capaci di garantire, nel tempo, specifici livelli di prestazione riducendo al tempo stesso i costi relativi al mantenimento di suddette caratteristiche prestazionali. Da ciò nasce la necessità di realizzare opere capaci di svolgere, nel tempo, la funzione per le quali sono state progettate e, quindi, caratterizzate da una vita utile più estesa e con ridotte capacità manutentive. Questa consapevolezza ha portato all'applicazione del concetto di materiali autoriparanti nel campo edilizio e, in particolare, per le strutture in calcestruzzo. È ben noto che la principale causa di degrado degli elementi in calcestruzzo e delle rispettive armature in acciaio è la formazione di fessure, di ampiezza variabile, che consente la penetrazione di agenti dannosi all'interno della matrice cementizia. L’obiettivo di questa ricerca è stato quello di studiare come l’utilizzo di un additivo cristallizzante consenta di migliorare la capacità, intrinseca del calcestruzzo, di sigillare le fessure. Per fare ciò, è stato predisposto un piano sperimentale che ha previsto la generazione di un danno controllato, la valutazione dell’ampiezza di fessura prodotta e la misurazione della permeabilità nei provini danneggiati. Dopo aver sottoposto i campioni a diverse condizioni di cura, si è proceduto nuovamente all'analisi e alla valutazione dei parametri esaminati in fase iniziale, permettendo di trarre le giuste conclusioni.
L’aggiunta dell’additivo cristallino ha permesso di ottenere una capacità di autoguarigione del calcestruzzo danneggiato più che soddisfacente. Infatti tale prodotto ha avuto una notevole influenza sulla variazione di permeabilità nella maggior parte degli ambienti di cura studiati, in particolare in quelli caratterizzati dalla presenza continua di acqua che ha consentito di raggiungere la completa risigillatura delle fessure. Nonostante la presenza dell’additivo garantisca una maggiore efficacia nei processi di autoguarigione e fornisca un grado di affidabilità più elevato, è stato osservato che anche il calcestruzzo ordinario, quando permanentemente a contatto con acqua, è in grado di sviluppare una buona capacità di recupero della permeabilità del materiale e una totale richiusura delle fessure.
Nel caso di strutture immerse e maggiormente soggette al degrado in caso di fessurazione, l’utilizzo degli additivi cristallini può risultare vantaggioso in quanto consente l’aumento della durabilità di tali opere e la diminuzione delle manutenzioni ritenute necessarie, portando ad una riduzione dei costi totali che vanno a compensare il maggior costo iniziale.Sustainability in civil and structural engineering is a concept that is becoming increasingly important because of the constant demand for structures that can guarantee, over time, more and more demanding performance levels while reducing the costs due to maintenance. The need hence arises to build up structures able to perform, over time, the function for which they were designed and, therefore, characterized by a longer and useful lifetime with reduced maintenance. This awareness has led to the application of the concept of self-healing materials in the construction field and, in particular for concrete structures. It is well known that the main cause of degradation of the concrete elements and the respective steel reinforcement is the formation of cracks, of variable width, which allows the penetration of harmful agents within the cement matrix. The objective of this research was to investigate how the use of a crystalline admixture can improve the inherent ability of the concrete to seal cracks. To do so, an experimental plan has been designed that provides for the controlled generation of damage, evaluation of the generated cracks and the measurement of permeability in damaged specimens. After the samples were subjected to different curing conditions, we proceeded again to the analysis and evaluation of the parameters examined in the initial phase, allowing to derive the right conclusions.
The addition of the crystalline admixture has resulted in a self-healing capacity damaged concrete more than satisfactory. Indeed, this product has had a significant influence on the variation of permeability in most of the investigated curing conditions, in particular those characterized by the continued presence of water, allowing to get the complete sealing of cracks. Despite the presence of the admixture provides a greater effectiveness in the healing processes and provides a higher degree of reliability, it has been observed that even the ordinary concrete may be characterized, when permanently in contact with water, by a high recovery of the permeability of the material and a complete healing of cracks.
For submerged structures, which may be more susceptible to degradation in case of cracking, the use of crystalline admixture can be advantageous because it allows an increase of the durability of these structures and a reduction of the necessary maintenance, with a consequent reduction of the total costs that go to make up for the higher initial cost
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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