1,720,958 research outputs found
Linear ViscoElastic (LVE) Behaviour of Pure Bitumen via Fractional Model
No full textBy fitting experimental data from static creep/recovery carried out on pure bitumen, it is shown that the fractional model
proposed enables the description of both creep and recovery behaviour with fewer parameters than those needed by other
models in the literature. In particular, the model is fitted to experimental data of complex modulus |G*| and phase angle δ°
obtained from Dynamic Mechanical Analysis. Lastly, it is demonstrated that when the fractional model is used, complex
modulus isotherms for a range of frequencies can be created simply starting from isochronals at f = 1Hz
Experimental validation of a fractional model for creep/recovery testing of asphalt mixtures
Full text linkPrediction of asphalt mixtures’ behavior during their service life is a challenge due to its complexity and
sensitivity to environmental and loading conditions. It has been proved that, when subjected to loading
conditions comparable with most pavement operating conditions, asphalt mixtures behave as linear
visco-elastic (LVE) materials. Traditionally the LVE behavior of bituminous material is modeled via
creep/recovery functions. In the past, several rheological models constituted by elastic and viscous elements
arranged in series or in parallel (analogical models) have been proposed and specified for both
bitumen and asphalt mixtures. The corresponding constitutive laws always involve first order derivatives
of time with exponential type solutions but problems in setting parameters arise when both the creep
and recovery behavior have to be modeled. In this paper it is shown that experimental creep data follow
a power decay law, rather than an exponential one. As a consequence, a simple fractional model is here
proposed for predicting creep/recovery behavior of asphalt mixtures with a small number of parameters
and low computational efforts with respect to the classical analogical models. The proposed model is
then calibrated by a best fitting procedure on experimental data from creep and creep/recovery tests carried
out on asphalt mixtures under different load and temperature conditions
New helicoidal spindle for mixing and viscosity measurements of tyre rubber modified binders
No full textThe use of modified bituminous binders, in place of pure bitumen, is a common practice to enhance performance of road pavements. The measurement of rheological properties of the modified binders is often challenging due to presence of suspended solids. Phase separation during the course of measurements makes viscosity of non-homogeneous blends, such as tyre rubber modified bitumens, difficult to ascertain. In this study, a new spindle was designed and manufactured to be used with a rotational viscometer in order to adapt the viscometer as a low shear mixer and to guarantee reliable viscosity measurements of samples which contains suspended particles. This helps optimize the modification process of tyre rubber modified bitumen by having a reliable real-time viscosities measurement. Spindle geometry was optimised to create a convective like flow within the sample and so minimise phase separation. Shear rate constant is geometry dependent and a calibration exercise was carried out to ascertain investigate this. Development of prototype spindles was undertaken using a layer based manufacturing technique which allows the rapid realisation of a design intent which could not be achieved in another fashion. In this case nested features are created in a prototype to verify the design before a fully functional prototype is produced using conventional 4-axis machining. The new spindle allows the Brookfield viscometer to be used as a low shear mixer of small volumes of bitumen-rubber blends while allowing real-time reliable measurements of the viscosity
Toward more realistic viscosity measurements of tyre rubber–bitumen blends
Full text linkThe measurement of rheological properties of the tyre rubber bitumen blends is often challenging due to presence of suspended tyre rubber’s crumbs. Furthermore, the phase separation during the course of measurements makes the viscosity of these non-homogeneous blends difficult to ascertain. In this study, a new dual helical impeller was designed and manufactured to be used with a rotational viscometer in order to have a real-time control of the viscosity while performing a laboratory mixing of the blends. Layer based manufacturing techniques showed to be a convenient method to produce complex shaped impeller prototypes before manufacturing the more expensive stainless steel assembly. Impeller geometry was optimised to create a convective like flow within the sample and so minimise phase separation. Shear rate constant is geometry dependent and a calibration exercise was carried out to ascertain this. Results of both calibration and validation phases showed that the new impeller provides reliable viscosity measurements of homogenous fluids such as neat bitumen. With regards to complex fluids the new impeller showed a more stable and realistic trend than that obtained by using a standard spindle. In fact, it was demonstrated that the new impeller significantly decreases phase separation within the blend and in turns provides a more realistic measurement of the viscosity. This system represents a feasible and improved solution for optimising the laboratory modification process of tyre rubber bitumen blends by adapting the rotational viscometer as a low-shear mixer
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
- …
