1,720,958 research outputs found
THE CHALLENGE OF MAPPING RIVER NETWORK DYNAMICS IN A SEASONALLY DRY CATCHMENT IN CENTRAL ITALY
Get PDFIntermittent rivers and ephemeral streams, namely IRES, are those watercourses that periodically cease to flow. IRES have a global prevalence, covering the 60% of the world river network and they can be found in a variety of climate settings, from dryland to humid headwater catchments. One of the major issues that prevented the scientific community to get deeper insight on river network dynamics in IRES is represented by the difficulties in the monitoring of the temporal variability of the flowing streams. While in-person inspections through visual surveys represent the common method to map flow intermittency, this method is highly time-consuming. Here, motivated by the latest advancement in computer vision, a novel stage-camera system designed to estimate the space and time variations of the water level along the network was developed. This system comprised a consumer grade wildlife camera with near-Infrared (NIR) night vision capabilities and a white pole set in the thalweg as a reference in the collected images. The efficacy of the system was evaluated through a set of benchmark experiments in natural and complex settings. The maximum mean absolute errors between estimated water level and reference data were approximately equal to 2 cm. Moreover, further experimental tests were carried out to assess the optimal stage-cam setup in terms of bar colour and segmentation. The results indicated that the simplest stage-cam setup, represented by a white pole divided into 2 and 3 segments, is the optimal solutions to monitoring the water level fluctuations in most cases. The data gathered by a stage-camera network composed by 21 cameras distributed along the network was combined with the results of 40 field mapping of the active network to reconstruct the space-time network dynamics in a 3.7 km2 seasonally dry catchment of central Italy from October 2019 to August 2022. The two heterogeneous datasets (the data from the field survey and those derived from the stage camera network) were combined exploiting the hierarchical principle, which postulates that the nodes can be ordered in a Bayesian chain based on their local persistency. This chain dictates the activation/deactivation order of the nodes during the expansion/contraction cycles. The application of the hierarchical model allowed the reconstruction of the temporal evolution of the wet portion of the network during the study period, filling all the relevant data gaps in a robust and efficient manner. The combination of experimental data and modeling results highlighted the complexity of the network dynamics in the study area. The number of active nodes decreased during summer and increased during wet season, as imposed by the mediterranean climate, while their local persistency exhibited non-monotonic and highly heterogenous pattern along the network. As a result, some low order branches were found to be less persistent than some order branches. Despite the complexity of observed stream dynamics, the results shows that the hierarchical model well approximated the expansion/contraction cycle of the network with an accuracy exceeding the 99%. Importantly, the case study presented in this thesis emphasizes how the hierarchical principle allows the reconstruction of the entire active network just by monitoring a few nodes. Cameras and computer vision techniques can provide important quantitative information about the wet dynamics of some nodes in the network and can be used to support traditional monitoring methods, especially if they were combined with robust theoretical and modeling tools.Intermittent rivers and ephemeral streams, namely IRES, are those watercourses that periodically cease to flow. IRES have a global prevalence, covering the 60% of the world river network and they can be found in a variety of climate settings, from dryland to humid headwater catchments. One of the major issues that prevented the scientific community to get deeper insight on river network dynamics in IRES is represented by the difficulties in the monitoring of the temporal variability of the flowing streams. While in-person inspections through visual surveys represent the common method to map flow intermittency, this method is highly time-consuming. Here, motivated by the latest advancement in computer vision, a novel stage-camera system designed to estimate the space and time variations of the water level along the network was developed. This system comprised a consumer grade wildlife camera with near-Infrared (NIR) night vision capabilities and a white pole set in the thalweg as a reference in the collected images. The efficacy of the system was evaluated through a set of benchmark experiments in natural and complex settings. The maximum mean absolute errors between estimated water level and reference data were approximately equal to 2 cm. Moreover, further experimental tests were carried out to assess the optimal stage-cam setup in terms of bar colour and segmentation. The results indicated that the simplest stage-cam setup, represented by a white pole divided into 2 and 3 segments, is the optimal solutions to monitoring the water level fluctuations in most cases. The data gathered by a stage-camera network composed by 21 cameras distributed along the network was combined with the results of 40 field mapping of the active network to reconstruct the space-time network dynamics in a 3.7 km2 seasonally dry catchment of central Italy from October 2019 to August 2022. The two heterogeneous datasets (the data from the field survey and those derived from the stage camera network) were combined exploiting the hierarchical principle, which postulates that the nodes can be ordered in a Bayesian chain based on their local persistency. This chain dictates the activation/deactivation order of the nodes during the expansion/contraction cycles. The application of the hierarchical model allowed the reconstruction of the temporal evolution of the wet portion of the network during the study period, filling all the relevant data gaps in a robust and efficient manner. The combination of experimental data and modeling results highlighted the complexity of the network dynamics in the study area. The number of active nodes decreased during summer and increased during wet season, as imposed by the mediterranean climate, while their local persistency exhibited non-monotonic and highly heterogenous pattern along the network. As a result, some low order branches were found to be less persistent than some order branches. Despite the complexity of observed stream dynamics, the results shows that the hierarchical model well approximated the expansion/contraction cycle of the network with an accuracy exceeding the 99%. Importantly, the case study presented in this thesis emphasizes how the hierarchical principle allows the reconstruction of the entire active network just by monitoring a few nodes. Cameras and computer vision techniques can provide important quantitative information about the wet dynamics of some nodes in the network and can be used to support traditional monitoring methods, especially if they were combined with robust theoretical and modeling tools
Characterizing Space-Time Channel Network Dynamics in a Mediterranean Intermittent Catchment of Central Italy Combining Visual Surveys and Cameras
Get PDFNon-perennial streams have a global prevalence, but quantitative knowledge of the temporal dynamics of their flowing length—namely the extent of the wet portion of the stream network—remains limited, as the monitoring of the spatiotemporal configuration of wet channels is challenging in most settings. This work combines the high spatial resolution of visual surveys and the high temporal resolution of camera-based approaches to reconstruct the space-time stream network dynamics in a 3.7 km2 Mediterranean catchment of central Italy. Information on the hydrological status of the stream network derived from 40 field surveys and sub-hourly images collected with 21 stage-cameras are combined exploiting the hierarchical principle. The latter postulates the existence of a Bayesian chain, defined from the local persistence of the nodes that dictates their wetting/drying order during expansion/retraction cycles of the flowing stream network. Our results highlight the complexity of network dynamics in the study area: while the number of wet nodes decreases during the dry season and increases during the wet season, the local persistency exhibits a highly heterogeneous non-monotonic spatial pattern, originating a dynamically disconnected network. Despite this heterogeneity, the hierarchical model well approximates the temporal evolution of the state of the network nodes, with an accuracy that exceeds 99%. Crucially, the model allows the reconstruction of the wet portion even in cases in which part of the network was not observed. This work provides a novel conceptual approach for the reconstruction of the wet portion of the network in poorly accessible sites
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
Integrating spatially-and temporally-heterogeneous data on river network dynamics using graph theory
Get PDF: The study of non-perennial streams requires extensive experimental data on the temporal evolution of surface flow presence across different nodes of channel networks. However, the consistency and homogeneity of available datasets is threatened by the empirical burden required to map stream network expansions and contractions. Here, we developed a data-driven, graph-theory framework aimed at representing the hierarchical structuring of channel network dynamics (i.e., the order of node activation/deactivation during network expansion/retraction) through a directed acyclic graph. The method enables the estimation of the configuration of the active portion of the network based on a limited number of observed nodes, and can be utilized to combine datasets with different temporal resolutions and spatial coverage. A proof-of-concept application to a seasonally-dry catchment in central Italy demonstrated the ability of the approach to reduce the empirical effort required for monitoring network dynamics and efficiently extrapolate experimental observations in space and time
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
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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