scholarly journals Assessment of structural sediment connectivity within catchments: insights from graph theory

2016 ◽  
Author(s):  
Étienne Cossart ◽  
Mathieu Fressard
Keyword(s):  
Graph Theory ◽  
Network Structure ◽  
Small Scale ◽  
Potential Contribution ◽  
Sediment Sources ◽  
Sediment Delivery ◽  
Field Reconstruction ◽  
Black Boxes ◽  
Sediment Connectivity ◽  
Broad Scale

Abstract. To understand the sedimentary signal delivered at catchment outlets, many authors now refer to the concept of connectivity. In this framework, the sedimentary signal is seen as an emergent organization of local filiations and interactions. The challenge is then to open black boxes that remain within a sediment cascade, that requires both accurate geomorphic investigations in the field (reconstruction of sequences of geomorphic evolution, description of sediment pathways) but also the development of tools dedicated to sediment cascades modelling. More precisely the development of tools dedicated to the study of connectivity in geomorphology is still in progress, even if the graph theory offers promising perspectives (Heckmann and Schwanghart, 2013). In this paper, graph theory is applied to abstract the network structure of sediment cascades, keeping only nodes (sediment sources, sediment stores, outlet) and links (linkage by a transportation agent), represented as vertices and edges. From the description of the assemblages of sedimentary flows, we provide three main indices to explore how small-scale processes may result in significant broad-scale geomorphic patterns. First, we assess the potential contribution of each node to the sediment delivery at the outlet. Second, we measure the influence of each node regarding how this node is accessible from both sediment sources and outlet. Third, we calculate a connectivity index to reveal whether the potential contribution of a node is lower or higher than expected from its location within the network. These indices are calculated in the case of a virtual sediment cascade, but are also applied to a catchment located in southern french alps. We demonstrate that these indices are robust, and may lead to simulations. In the present case, we try to predict how a sediment cascade may be impacted by a node disruption or by a reconnection.

scholarly journals Assessment of structural sediment connectivity within catchments: insights from graph theory

2017 ◽  
Vol 5 (2) ◽  
pp. 253-268 ◽  
Author(s):  
Étienne Cossart ◽  
Mathieu Fressard
Keyword(s):  
Graph Theory ◽  
Network Structure ◽  
Structural Connectivity ◽  
Connectivity Index ◽  
Flow Index ◽  
Small Scale ◽  
Potential Contribution ◽  
Sediment Sources ◽  
Sediment Delivery ◽  
Main Hypothesis

Abstract. To describe the sedimentary signal delivered at catchment outlets, many authors now refer to the concept of connectivity. In this framework, the sedimentary signal is seen as an emergent organization of local links and interactions. The challenge is thus to open the black boxes that remain within a sediment cascade, which requires both accurate geomorphic investigations in the field (reconstruction of sequences of geomorphic evolution, description of sediment pathways) and the development of tools dedicated to sediment cascade modeling. More precisely, the development of tools devoted to the study of connectivity in geomorphology is still in progress, although graph theory offers promising perspectives (Heckmann and Schwanghart, 2013). In this paper, graph theory is applied to abstract the network structure of sediment cascades, keeping only the nodes (sediment sources, sediment stores, outlet) and links (linkage by a transportation agent), represented as vertices and edges. From the description of the assemblages of sedimentary flows, we provide three main indices to explore how small-scale processes may result in significant broad-scale geomorphic patterns. The main hypothesis guiding this work is that the network structure dictates how sediment inputs from various sources interact at tributary junctions and finally at the outlet of a cascading system. First, we use the flow index to assess the potential contribution of each node to the sediment delivery at the outlet. Second, we measure the influence of each node regarding how it is accessible from both sediment sources and the outlet (using the Shimbel index). Third, we propose a new connectivity index named Network Structural Connectivity index (NSC) revealing whether the potential contribution of a node is lower or higher than expected from its location within the network. These indices are first computed for a conceptual sediment cascade network and then applied to a catchment located in the southern French Alps. We demonstrate that this index may be used to simulate sediment transfer and help in identifying the hotspots of geomorphic change. In the present case, we try to predict how a sediment cascade may be impacted by an edge disruption or a reconnection.

Graph theory-based sediment connectivity analysis of a glacierised Alpine basin for different event scenarios

2020 ◽  
Author(s):  
Anuschka Buter ◽  
Tobias Heckmann ◽  
Lorenzo Fillisetti ◽  
Antonia Spitzer ◽  
Luca Mao ◽  
...  
Keyword(s):  
Graph Theory ◽  
Sediment Transport ◽  
Hot Spot ◽  
Specific Area ◽  
Transport Processes ◽  
Transport Network ◽  
Connectivity Analysis ◽  
Sediment Sources ◽  
Sediment Connectivity ◽  
Talus Deposits

<p>Sediment connectivity has been receiving increased attention in the last years. Several approaches have been applied to analyse where and to what extent sediment sources are connected to the main fluvial network and/or to depositional areas. Especially in mountain environments, sediment transport is temporally and spatially variable, and thus assessing sediment connectivity is challenging. Within this work, a graph theory-based approach is presented, with the aim to identify changes in space and time within the sediment transport network during the main sediment transport periods of the year.</p><p>A network, built up by nodes and directed edges, was manually digitized for the Sulden/Solda river basin (Vinschgau/Venosta valley, Italian Alps). The nodes represent landforms delineated within a previously developed geomorphological map, which features 32 different landform categories and seamlessly covers the entire basin (~130 km²). The directed edges are connecting nodes if sediment transport is (potentially) occurring from one to the subsequent geomorphological unit. This evaluation was made based on visual evidences from orthophotos and geomorphological as well as topographical characteristics of the respective landforms. Furthermore, a sediment transport process type was assigned to each edge.</p><p>Snow and glacier melt scenarios are defined by the occurrence of specific sediment transport processes, hence activation or deactivation of the related edges. Scenarios representing potential sediment transport networks during intensive heat periods and intense rain storms are included for both melt seasons, taking into consideration the expected higher frequency of these meteorological conditions in the future decades. For example, rain storm scenarios include edges showing potential debris flow trajectories, whereas these connections are not present in scenarios representing just snow- and ice-melt events. Therefore, functional connectivity changes within the proposed sediment transport network scenarios. For all the events, graph theory measures are calculated, as e.g. the betweenness centrality index to identify “hot-spot” nodes of the sediment cascades. Furthermore, the quantity and the composition of the sediment cascades reaching the catchment outlet can be identified in order to highlight the most relevant transport processes as well as to derive the most typical sediment cascades for a specific area.</p><p>The study basin is characterized by a high sediment availability due to large glacio-fluvial deposits present at the glaciers forefield and to the wide areas covered with talus deposits. However, the connectivity analysis demonstrates that a vast portion of these sediment sources is not connected to the main channel under the modelled melt runoff scenarios. Only in case of intense rainstorms talus deposits might become a coupled sediment source due to the potential occurrence of debris flows. Hence, areas connected only occasionally due to the (re-)activation of specific sediment cascades can be mapped. Additionally, a relative connectivity degree is calculated for every scenario, introducing a better comparability.</p>

scholarly journals Formation of raiding parties for intergroup violence is mediated by social network structure

2016 ◽  
Vol 113 (43) ◽  
pp. 12114-12119 ◽  
Author(s):  
Luke Glowacki ◽  
Alexander Isakov ◽  
Richard W. Wrangham ◽  
Rose McDermott ◽  
James H. Fowler ◽  
...  
Keyword(s):  
Social Network ◽  
Network Structure ◽  
Social Dynamics ◽  
Small Scale ◽  
East African ◽  
Nomadic Pastoralists ◽  
Social Network Structure ◽  
The Social ◽  
Total Impact ◽  
Social Network Position

Intergroup violence is common among humans worldwide. To assess how within-group social dynamics contribute to risky, between-group conflict, we conducted a 3-y longitudinal study of the formation of raiding parties among the Nyangatom, a group of East African nomadic pastoralists currently engaged in small-scale warfare. We also mapped the social network structure of potential male raiders. Here, we show that the initiation of raids depends on the presence of specific leaders who tend to participate in many raids, to have more friends, and to occupy more central positions in the network. However, despite the different structural position of raid leaders, raid participants are recruited from the whole population, not just from the direct friends of leaders. An individual’s decision to participate in a raid is strongly associated with the individual’s social network position in relation to other participants. Moreover, nonleaders have a larger total impact on raid participation than leaders, despite leaders’ greater connectivity. Thus, we find that leaders matter more for raid initiation than participant mobilization. Social networks may play a role in supporting risky collective action, amplify the emergence of raiding parties, and hence facilitate intergroup violence in small-scale societies.

scholarly journals SE-IYOLOV3: An Accurate Small Scale Face Detector for Outdoor Security

Mathematics ◽  
2020 ◽  
Vol 8 (1) ◽  
pp. 93 ◽  
Author(s):  
Zhenrong Deng ◽  
Rui Yang ◽  
Rushi Lan ◽  
Zhenbing Liu ◽  
Xiaonan Luo
Keyword(s):  
Receptive Field ◽  
Face Detection ◽  
Network Structure ◽  
Difficult Problem ◽  
Detection Performance ◽  
Experimental Results ◽  
Small Scale ◽  
Detection Accuracy ◽  
Novel Method ◽  
Face Detector

Small scale face detection is a very difficult problem. In order to achieve a higher detection accuracy, we propose a novel method, termed SE-IYOLOV3, for small scale face in this work. In SE-IYOLOV3, we improve the YOLOV3 first, in which the anchorage box with a higher average intersection ratio is obtained by combining niche technology on the basis of the k-means algorithm. An upsampling scale is added to form a face network structure that is suitable for detecting dense small scale faces. The number of prediction boxes is five times more than the YOLOV3 network. To further improve the detection performance, we adopt the SENet structure to enhance the global receptive field of the network. The experimental results on the WIDERFACEdataset show that the IYOLOV3 network embedded in the SENet structure can significantly improve the detection accuracy of dense small scale faces.

Modelling multi-topic information propagation in online social networks based on resource competition

2016 ◽  
Vol 43 (3) ◽  
pp. 342-355 ◽  
Author(s):  
Liyuan Sun ◽  
Yadong Zhou ◽  
Xiaohong Guan
Keyword(s):  
Social Networks ◽  
Network Structure ◽  
Online Social Networks ◽  
Resource Competition ◽  
Propagation Model ◽  
Small Scale ◽  
Model Parameters ◽  
Information Propagation ◽  
Practical Applications ◽  
The Impact

Understanding information propagation in online social networks is important in many practical applications and is of great interest to many researchers. The challenge with the existing propagation models lies in the requirement of complete network structure, topic-dependent model parameters and topic isolated spread assumption, etc. In this paper, we study the characteristics of multi-topic information propagation based on the data collected from Sina Weibo, one of the most popular microblogging services in China. We find that the daily total amount of user resources is finite and users’ attention transfers from one topic to another. This shows evidence on the competitions between multiple dynamical topics. According to these empirical observations, we develop a competition-based multi-topic information propagation model without social network structure. This model is built based on general mechanisms of resource competitions, i.e. attracting and distracting users’ attention, and considers the interactions of multiple topics. Simulation results show that the model can effectively produce topics with temporal popularity similar to the real data. The impact of model parameters is also analysed. It is found that topic arrival rate reflects the strength of competitions, and topic fitness is significant in modelling the small scale topic propagation.

scholarly journals Representation of Graph Theory in Students’ Communication Network at Female Students’ Dormitory of State Islamic Institute of Palopo

CAUCHY ◽  
2016 ◽  
Vol 4 (2) ◽  
pp. 95
Author(s):  
Muhammad Hajarul Aswad ◽  
Wahyuni Husain
Keyword(s):  
Communication Network ◽  
Graph Theory ◽  
Network Analysis ◽  
Network Structure ◽  
Significant Influence ◽  
Female Students ◽  
Path Distance

The application of Graph Theory Concept in Communication Network Analysis is interesting to observe. This research was carried out to learn how Communication Network structure was formed and who had necessary role in the network. It was explorative research and conducted at Female Students’ Dormitory of State Islamic Institute of Palopo (Asrama Putri IAIN Palopo). The results were interpreted by using Microsoft NodeXL Version 1.0.1.113. It was found that the communication network structure of female students’ who stayed at the Dormitory decentralized. It shows that each student had same opportunity to communicate one another directly or indirectly, which 4 to 9 path distance. It was also identified that from 110 people, Suarni was the student who had significant influence in the communication network.

scholarly journals Peace through Tourism: A Critical Look at Nepalese Tourism

2013 ◽  
Vol 1 (1) ◽  
pp. 15-40 ◽  
Author(s):  
Pranil Upadhayaya
Keyword(s):  
Poverty Reduction ◽  
Codes Of Conduct ◽  
Theoretical Models ◽  
Small Scale ◽  
Potential Contribution ◽  
Viable Option ◽  
Economic Sectors ◽  
Community Based ◽  
Transdisciplinary Approach ◽  
Knowledge Based

Tourism, the world’s largest and one of the fastest developing economic sectors, virtually affects every region and nation of the world due to its potential contribution to international understanding and poverty reduction. Nepal is no exception. The remarkable growth of tourism at present (peace time) has been progressing through its four progressive theoretical models/platforms (e.g., advocacy, cautionary, adaptancy and knowledge-based platforms) with each having both peace potential and limitation. In this scenario, there is likely growing attention and look at tourism with a passion for its peace prospective.‘Peace’, a vital and most cherished dream of humanity, is a state that not only indicates the absence of direct violence but also sustains peaceful relationships among all levels and segments of society and between society and nature.Tourism is sensitive to conflict and responsive to peace. There are both opportunities and challenges for the peace responsiveness of tourism in Nepal. Nepalese tourism, which passed through a decade long (1996-2006) armed conflict, serves a concrete illustration of this nexus of tourism and peace with the dual attributes of tourism for conflict and peace. However, this paper envisages that it is a community-based village tourism supported by sustainable structures and actions, backed by proper implementations of tourism regulations, framed with appropriate codes of conduct and materialized by the integrated effort and partnership actions of all (non-scientific and scientific) stakeholders that can be the most viable option for achieving the noble goal of peace through tourism in Nepal. In this context, this paper exemplifies it with an innovative example of a research-linked and empirically executed case of Machhapuchchhre Model Trek (MMT) in Western Nepal. MMT is footed at the knowledgebased platform on transdisciplinary approach in which the scientific (e.g., researchers) and both academic and non-academic (e.g., local communities, local government, tourism practitioners, tourists, etc.) actors approached in an integrated effort to transform local tourism initiatives as peace promoting and conflict mitigating.This paper finally recommends the knowledge-based approach to Nepalese tourism as important not only for bridging the earlier three platforms but also for fulfilling the dual (mass as well as small-scale community-based village tourism) needs of Nepalese tourism at present and thus succeed on peace aspirations through tourism. DOI: http://dx.doi.org/10.3126/ntdr.v1i1.7368 Nepal Tourism and Development Review Vol.1(1) 2011 15-40

scholarly journals Some Aspects of Sedimentology of the Wanganui Basin, North Island, New Zealand

2021 ◽  
Author(s):  
◽  
Diane Seward
Keyword(s):  
New Zealand ◽  
Shallow Water ◽  
Fission Track ◽  
Sediment Accumulation ◽  
Size Analysis ◽  
Small Scale ◽  
Sediment Sources ◽  
Sedimentary Structures ◽  
Volcanic Region ◽  
Carbon And Oxygen Isotope

<p>The thesis comprises studies of the marine Pleistocene sediments of the Wanganui Basin, North Island, New Zealand. Part I deals with the chronology of the sediments and correlation of horizons within and outside the basin, by dating glass shards from tephra horizons using the fission-track method. Correlation to similar tephras from Hawke's Bay, to deep-sea cores taken 1000km east of New Zealand and to the central North Island volcanic district is attempted. These fission-track ages fill a dating gap that previously existed in the New Zealand marine Quaternary sequence. Thirteen tephras were examined in the Wanganui Basin and were found to range in age from 1.50 [plus or minus] 0.21m.y.B.P. (Ohingaiti Ash) to 0.28 [plus or minus] 0.05m.y.B.P. (uppermost Finnis Road Ash). These tephras record major rhyolitic eruptive phases in the central volcanic region. The most significant eruptive phase began 1.06 [plus or minus]0.16m.y.B.P. with the deposition of the Makirikiri Tuff sediments, continued to 0.88 [plus or minus]0.13m.y.B.P. and is tentatively associated with the older ignimbrites of the King Country, west of Lake Taupe. A volcanically quiet period followed when no volcanic glass was deposited in the sediments, until 0.74 [plus or minus] 0.09m.y.B.P. Several large eruptions then occurred between 0.74 and 0.28m.y.B.P. The age of the Plio-Pleistocene boundary, at the base of the Hautawan Stage in the Wanganui Basin is 1.87m.y.B.P. The age of the base of the Nukumaruan is 1.55m.y.B.P., the Okehuan, 1.06m.y.B.P., the Castleclifflan 0.45m.y.B.P., and the Hawera Series is less than 0.38m.y.B.P. Palaeomagnetic stratigraphy was determined for the upper Nukumaruan and lower Okehan sequence in the Rangitikei River. Viscous components of magnetism were removed from the samples by thermal demagnetising, extreme care being needed to obtain consistent results. Independent dates from the palaeomagnetic stratigraphy substantially confirm the fission-track dates. The Bruhnes-Matuyama boundary is clearly defined between the Rewa and Potaka Pumice Members (aged 0.74 and 0.61m.y.B.P. respectively) of the Kaimatira Pumice Send Formation. The Jaramillo event was not recognised and is probably represented in part of the sequence where sediments are too coarse and friable to yield palaeomagnetic cores. Part II deals with the detailed sedimentology of the lower Okehuan Stage sequence which is composed of two volcaniclastic formations, the Makirikiri Tuff and Kaimatira Pubmice Sand, separated by a non-volcaniclastic siltstone formation, the Okehu Siltstone. Interpretations of the Sedimentary structures in the Makirikiri Tuff and the Kaimatira Pumice Sand Formation confirm previous conclusions of shallow water deposition based on palaeontological evidence. Some structures also indicate the high rate of sediment accumulation during deposition of the volcancic sediments. Size analysis statistics show influence of source material and processes acting on the sediment during transport and deposition. Rapid sediment accumulation is emphasised by poor sorting, and processed inferred from the sedimentary structures are confirmed by the grain size analyses of the same structures. Analysis of the attitude of large and small scale cross-stratification reveals a complex polymodal palaeocurrent pattern, as might be expected of shallow water to intertidal sequences. Although often bipolar-bimodal, the dominant sediment transport appears to have been from west to east, similar to the direction of current movement along the Wanganui coast today. Size and petrography of clasts from the conglomeratic horizons indicated sediment sources both from the central volcanic region of North Island and from the Mesozoic "greywackes" of the axial mountain ranges which were emergent and probably significantly elevated at the time when the sediments were accumulating. No volcanic debris was deposited with the Okehu Siltstone. The mineralogy of the sands points to the same sediment sources but also indicates that some metamorphic material was being introduced most likely from South Island. Part III of the thesis represents a pilot study undertaken to determine whether isotopic differences in fossil shell composition could be used to distinguish shells that grew in fully marine water from those that grew in less saline conditions. Carbon and oxygen isotope ratios were determined on shells from three formations whose environments had been adequately studied by paleontologists. The horisons chosen were the Waipuru Shellbed, the Tewkesbury Formation and the Tainui Shellbed. Agreement with the palaeontological evidence and thus distinction between the fully marine and the fresh water contaminated marine environments was possible with the technique.</p>

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