1,721,010 research outputs found
Sinkhole susceptibility assessment of underground caves in soft rocks by means of FEM-based charts.
No full textThe presence of man-made underground caves in soft carbonate rocks susceptible to degradation processes due to weathering nowadays induce high risk conditions in the Apulia region (Southern Italy) which is characterised by a huge number of caves spread in the territory. In recent years, several collapses affected some of these cavity systems, involving structures and roads located at the ground surface and, therefore, inducing high risk for human life and properties. In order to comply with this problem at the regional scale, Perrotti et al., 2018, have proposed specific charts aimed at assessing at a preliminary stage the stability conditions of a cave along with a safety margin with respect to the occurrence of failure. The charts have been defined upon the results of a large set of parametric two-dimensional finite-element analyses of ideal cases of underground cavities that account for the typical geometrical features of the caves and the range of mechanical properties of these rocks. The relationships obtained in terms of plots representing the ratio between the strength mobilized at failure and the vertical stress at the cavity roof against the ratio between cave width and roof thickness identify mechanically-based threshold envelopes for stability. In this paper, applications of the stability charts to case studies of man-made underground caves of soft carbonate rocks, either subjected to failure in the past or still stable, are discussed. In the first case the applications proposed show the role of specific structural elements, as pillars and walls, on the general stability of the examined quarry system, while in the second case an indication on the safety factor of the cave with respect to instability has been derived. Therefore, the proposed stability charts have been verified to provide a reliable method to assess in a preliminary way the stability of underground cavities in soft carbonate rocks, so that, for those situations where the safety margin results to be low, more detailed and sophisticated numerical models need to be developed
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
Stability charts based on the finite element method for underground cavities in soft carbonate rocks: validation through case-study applications
No full textThe stability of man-made underground cavities in soft rocks interacting with overlying structures and infrastructures represents a challenging problem to be faced. Based upon the results of a large number of parametric twodimensional (2-D) finite-element analyses of ideal cases of underground cavities, Accounting for the variability both cave geometrical features and rock mechanical properties, specific charts have been recently proposed in the literature to assess at a preliminary stage the stability of the cavities. The purpose of the present paper is to validate the efficacy of the stability charts through the application to several case studies of underground cavities, considering both quarries collapsed in the past and quarries still stable. The stability graphs proposed by Perrotti et al. (2018) can be useful to evaluate, in a preliminary way, a safety margin for cavities that have not reached failure and to detect indications of predisposition to local or general instability phenomena. Alternatively, for sinkholes that already occurred, the graphs may be useful in identifying the conditions that led to the collapse, highlighting the importance of some structural elements (as pillars and internal walls) on the overall stability of the quarry system
Assessing the stability of underground caves through iSUMM (innovative, straightforward, user-friendly, mechanically-based method)
No full textA huge number of sinkhole events has been recorded in different Italian urban areas, with an occurrence frequency largely increasing in the last decades, sometimes even causing loss of human lives. The main reason for such catastrophic events is the presence of man-made underground cavities, excavated within soft rocks, several decades ago and then abandoned, at shallow depths. Here, the possibility of interaction with overlying buildings and infrastructures and the corresponding sinkhole hazard is relatively high. In such contexts, the low mechanical properties of the soft rock formations where the cavities have been excavated, like those formed of calcarenites, which outcrop in large areas of Southern Italy, and their high susceptibility to weathering processes, represent one of the most important predisposing factors for instability. Therefore, assessing the stability of underground cavities is crucial for land management and planning purposes. The mechanically-based stability charts developed by Perrotti et al. (Int J Geomech 18(7):04018071, 2018) have proved to be a valid tool for preliminary stability assessment and, although allow to identify an eventual proneness of the cave to instability, they do not provide quantitative assessment about the safety margin itself. In that regard, this study intends to present the most recent outcomes obtained in the development of the methodology and is aimed at promoting an enhanced way for their application, so that the charts can become an operative tool for preliminary sinkhole hazard assessment in similar regions in the world
Analysis of the Displacement Field of Soft Rock Samples During UCS Tests by Means of a Computer Vision Technique
No full textThe measurement of rock sample displacement during laboratory testing is generally carried out by means of instrumental devices, which are capable of detecting average or local sample displacements, but are subjected to various error measurements; instrumental errors especially increase when localization takes place in the rock sample and macro-cracking develops. Photogrammetric techniques and, more recently, computer vision techniques based on non-contact digital image change detection propose an interesting alternative in this field, since they allow for detecting, with high precision, the visible displacement field of the rock sample external surface. This work is aimed at presenting the results of the application of an advanced computer vision technique to the assessment of the evolving displacement field of soft calcarenite samples subjected to uniaxial compression test. The corresponding results confirm that the technique is capable of detecting, with high level of accuracy, both the pre-failure displacement evolution, when continuity conditions still exist in the sample, and in the post-failure state, when large fissuring occur and a clear failure mechanism develops in the sample. A comparison between the results obtained from the technique here proposed and those resulting from a more conventional digital image correlation technique is also provided, highlighting a clear improvement in terms of accuracy of the images and capability of detecting the failure mechanisms of the samples
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
- …
