scholarly journals Selection Method of Dendritic River Networks Based on Hybrid Coding for Topographic Map Generalization

2020 ◽  
Vol 9 (5) ◽  
pp. 316
Author(s):  
Chengming Li ◽  
Wei Wu ◽  
Pengda Wu ◽  
Yong Yin ◽  
Zhaoxin Dai
Keyword(s):  
River System ◽  
River Network ◽  
River Networks ◽  
Map Generalization ◽  
Topographic Map ◽  
Top Down ◽  
Bottom Up ◽  
Hybrid Coding ◽  
Coding Systems ◽  
Selection Of

As the coding of a dendritic river system can be used to represent the stream order and spatial-structure of a river network, it is always used in river selection, which is a key step in topographic map generalization. There are two categories of conventional hydrological coding systems, one is the top-down approach, and the other is the bottom-up approach. However, the former does not accurately reflect the hierarchies of a dendritic river network, which is produced by catchment relationships, and it is not appropriate for the stream selection of river networks with uniform distributions of tributaries. The latter cannot directly indicate the subtree depth of a stream, and it is not favorable to stream selection of river systems that have topologically deep structures. Therefore, a selection method for dendritic river networks based on hybrid coding is proposed in this paper. First, the dendritic river network is coded through classical top-down Horton coding. Second, directed topology trees are constructed to organize the river network data, and stroke connections are calculated to code the river network in the bottom-up approach. Third, the river network is marked through hybrid usage of the top-down approach and bottom-up approach, and based on the spatial characteristics of the river network, the river network is classified into three kinds of subtrees: deep branch, shallow branch and modest branch. Then, appropriate coding is assigned automatically to different subtrees to achieve river selection. Finally, actual topographic map data of a river system in a region of Hubei Province are used to comparatively validate the hybrid coding system against two existing isolated coding systems. The experimental results demonstrate that the hybrid coding method is very effective for river network selection, not only in highlighting hierarchies formed by catchment relationships but also in the uniform distribution of tributaries.

scholarly journals AN AUTOMATED BOTTOM UP HYDROLOGIC CODING SYSTEM FOR DENDRITIC RIVER SYSTEM

2019 ◽  
Vol XLII-4/W16 ◽  
pp. 169-175 ◽  
Author(s):  
Z. X. Dai ◽  
C. M. Li ◽  
P. D. Wu ◽  
Y. Yin
Keyword(s):  
Source Coding ◽  
River System ◽  
Coding System ◽  
Topographic Map ◽  
Stream Order ◽  
River Systems ◽  
Bottom Up ◽  
Coding Systems ◽  
Definition Of ◽  
Map Data

Abstract. The hydrologic coding of a dendritic river system can be used to indicate the stream order and spatial-structure features of a river system. However, most conventional hydrologic coding systems use a top down (i.e., from the source to the estuary) approach, which does not accurately reflect the hierarchies of a dendritic river system. Based on Gravelius’ definition of stream order, we have proposed an automated bottom up (i.e., traced from the estuary to the source) coding system for dendritic river systems. Firstly, directed topology trees are constructed to organize the data of a river network, followed by the calculation of stroke connections to construct river entities and identify the main stem. Secondly, the river system is then progressively coded from the estuary up to the source according to the definition of stream order in our system. Finally, actual topographic map data of a river system in some regions of Hubei Province are used to comparatively validate our hydrologic coding system against Horton’s coding system. The experimental results demonstrate that our coding system is very effective in highlighting hierarchies formed by catchment relationships. Our method is also found to be suitable for the selection of streams in topologically shallow dendritic river systems with uniformly distributed tributaries.

scholarly journals A new vector-based global river network dataset accounting for variable drainage density

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Peirong Lin ◽  
Ming Pan ◽  
Eric F. Wood ◽  
Dai Yamazaki ◽  
George H. Allen
Keyword(s):  
Spatial Variability ◽  
Flow Direction ◽  
River System ◽  
Drainage Density ◽  
River Network ◽  
River Networks ◽  
Digital Elevation ◽  
Machine Learning Approach ◽  
Elevation Model ◽  
National Hydrography Dataset

AbstractSpatial variability of river network drainage density (Dd) is a key feature of river systems, yet few existing global hydrography datasets have properly accounted for it. Here, we present a new vector-based global hydrography that reasonably estimates the spatial variability of Dd worldwide. It is built by delineating channels from the latest 90-m Multi-Error-Removed Improved Terrain (MERIT) digital elevation model and flow direction/accumulation. A machine learning approach is developed to estimate Dd based on the global watershed-level climatic, topographic, hydrologic, and geologic conditions, where relationships between hydroclimate factors and Dd are trained using the high-quality National Hydrography Dataset Plus (NHDPlusV2) data. By benchmarking our dataset against HydroSHEDS and several regional hydrography datasets, we show the new river flowlines are in much better agreement with Landsat-derived centerlines, and improved Dd patterns of river networks (totaling ~75 million kilometers in length) are obtained. Basins and estimates of intermittent stream fraction are also delineated to support water resources management. This new dataset (MERIT Hydro–Vector) should enable full global modeling of river system processes at fine spatial resolutions.

Can top-down and bottom-up forces explain phytoplankton structure in a subtropical and shallow groundwater-connected lake?

2015 ◽  
Vol 66 (12) ◽  
pp. 1106 ◽  
Author(s):  
Diego Frau ◽  
Melina Devercelli ◽  
Susana José de Paggi ◽  
Pablo Scarabotti ◽  
Gisela Mayora ◽  
...  
Keyword(s):  
Shallow Groundwater ◽  
Resource Limitation ◽  
River System ◽  
High Water ◽  
Taxonomic Resolution ◽  
Dominant Group ◽  
Top Down ◽  
Bottom Up ◽  
Physico Chemical ◽  
Phytoplankton Structure

Bottom-up and top-down control of phytoplankton is one of the most important hypothesis that explains and predicts the structure of aquatic community. Our aim was to elucidate whether predation and resource limitation can control phytoplankton composition and abundance in a subtropical shallow lake with groundwater connection to the river system. During 12 months, the lake was sampled at three points. Physico-chemical parameters, phytoplankton and zooplankton were sampled fortnightly, whereas fish were sampled every 3 months. The results showed that Euglenophyta dominated the total biovolume, followed by Dinophyta and Cryptophyta. As for the species composition, Chlorophyta was the dominant group (80 species recorded), followed by phylum Cyanobacteria (26 species recorded). Redundancy analysis (RDA) indicated that temperature and nitrate + nitrite concentration mainly explained biovolume changes, with zooplankton predation not having any measurable effect on phytoplankton during the high-water (HW) period. During low-water (LW) period top-down by fish was more important. At higher taxonomic resolution (species biovolume), phosphorus was another controlling factor. We concluded that phytoplankton in this lake is mainly regulated by hydrological changes as a macrofactor that affects nutrient availability and other environmental conditions. Even though bottom-up top-down forces do not have a central effect, we found evidence of positive nutrient influences at the HW period and fish effect at the LW period.

scholarly journals Top-down or bottom-up? The selection of shadow rapporteurs in the European Parliament

2020 ◽  
Vol 21 (4) ◽  
pp. 706-727
Author(s):  
Frank M Häge ◽  
Nils Ringe
Keyword(s):  
European Parliament ◽  
Third Party ◽  
Top Down ◽  
Bottom Up ◽  
Principal Agent Theory ◽  
Policy Positions ◽  
Competing Demands ◽  
Group Members ◽  
Selection Of

Shadow rapporteurs play an important role in developing the European Parliament’s collective policy positions and in defending them in inter-institutional negotiations. This study sheds light on the ‘how’ and ‘why’ of shadow rapporteur selection. Qualitative insights from practitioner interviews and a quantitative analysis of shadow rapporteur data from the 7th European Parliament (2009–2014) indicate that the appointment process is primarily one of bottom-up self-selection by group members based on their policy interests. The party group leadership, in the form of group coordinators, plays an important coordinating role when there is competition for a shadow rapporteurship. However, the role of group coordinators is more akin to a third-party arbiter of competing demands than a mechanism of top-down control by the leadership, as suggested by principal-agent theory.

scholarly journals Prioritizing selection of new elements: Bottom-up versus top-down control

2003 ◽  
Vol 65 (8) ◽  
pp. 1231-1242 ◽  
Author(s):  
Mieke Donk ◽  
Jan Theeuwes
Keyword(s):  
Top Down ◽  
Bottom Up ◽  
Selection Of

Attention

2017 ◽  
Author(s):  
Martin V. Butz ◽  
Esther F. Kutter
Keyword(s):  
Dynamic Control ◽  
Sensory Information ◽  
Control Process ◽  
Focus Of Attention ◽  
Generative Models ◽  
Top Down ◽  
Bottom Up ◽  
Current Task ◽  
Task Oriented ◽  
Selection Of

Cognition does not work without attention. Attention enables us to focus on particular tasks and particular aspects in the environment. Psychological insights show that attention exhibits bottom-up and top-down components. Attention is attracted from the bottom-up towards unusual, exceptional, and unexpected sensory information. Top-down attention, on the other hand, filters information dependent on the current task-oriented expectations, which depend on the available generative models. This computational interpretation enables the explanation of conjunctive and disjunctive search. Different models of attention emphasize the importance of the unfolding interaction processes and a processing bottleneck can be detected. As a result, attention can be viewed as a dynamic control process that unfolds in redundant, neural fields, in which the selection of one interpretation and thus the processing bottleneck is strongest at the current focus of attention. The actual focus of attention itself is determined by the current behavioral and cognitive goals.

scholarly journals A Prediction–Correction Solver for Real-Time Simulation of Free-Surface Flows in River Networks

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2525 ◽  
Author(s):  
Dechao Hu ◽  
Chengwei Lu ◽  
Shiming Yao ◽  
Shuai Yuan ◽  
Yonghui Zhu ◽  
...  
Keyword(s):  
Free Surface ◽  
River System ◽  
Free Surface Flows ◽  
River Network ◽  
Water Levels ◽  
River Networks ◽  
Time Step ◽  
Flow Process ◽  
Surface Flows ◽  
Pcm Model

A prediction–correction solver is presented here for rapid simulation of free-surface flows in dendritic and looped river networks. Rather than solving a large global algebraic system over the entire domain of river networks, the model solves subsystems for subdomains of branches in two steps: prediction and correction. With the help of the prediction–correction method (PCM), the partial linearization technique, the semi-implicit method, and the Eulerian–Lagrangian method (ELM), the model only needs to solve tridiagonal linear systems for branches and is free of any iteration. The new model was tested using a hypothetical looped river network with regular cross sections, the Three Gorges Reservoir (TGR) dendritic river network, and the Jing-south looped river system (with seasonally flooding branches). In the first test, a time-step sensitivity study was conducted and the model was revealed to produce accurate simulations at large time steps when the condition for application of the PCM to river networks was satisfied. In the TGR test, the PCM model provided almost the same histories of water levels and discharges as those simulated by the HEC-RAS model. In the Jing-south test, the mean absolute error in simulated water levels was 0.07–0.24 m, and the relative error in simulated cross-section water flux was 0.5–4.9% compared with field data; the conservation error was generally 2 × 10−4 to 3 × 10−4. The PCM model was revealed to be 2–4 times as fast as a reported model, which solves local nonlinear subsystems using two-layer iterations, and 1.2–1.4 times as fast as the HEC-RAS. Using a time step of 1200 s, it took the sequential code 26.8 and 23.1 s to complete a simulation of a one-year unsteady flow process, respectively, in the TGR river networks (with 588 cells) and the Jing-south river system (with 662 cells).

scholarly journals Towards an Asian Model of Clusters and Cluster Policy: The Super Cluster Strategy

2020 ◽  
Vol 12 (4) ◽  
pp. 74-90
Author(s):  
Arkadiusz Michał Kowalski
Keyword(s):  
Traditional Approach ◽  
Foreign Direct Investments ◽  
Asian Countries ◽  
Cluster Policy ◽  
Top Down ◽  
Bottom Up ◽  
Cluster Strategy ◽  
Support Mechanisms ◽  
Economic Zones ◽  
Selection Of

Clusters are recognized as important drivers of competitiveness and economic development. There are various models of clusters development all over the world, some of which may be initiated bottom-up by private firms, as in most European countries, or top-down by public administrations. In the case of Asian clusters, many are driven by foreign direct investments (FDI), with the most notable example being China. The objective of this study is to examine the Super Cluster strategy introduced in Thailand in 2015, especially in terms of the rationale and mechanism for selecting assisted clusters as well as the instruments used to support them. The goal is to contribute to a more in-depth formulation of the Asian model of clusters and cluster policy. The conducted analysis shows that Thai strategy deviates from traditional bottom-up approaches to cluster policy, veering towards the top-down approach in which government designates targeted regions and industries for the development of clusters. Another finding is that the Super Cluster strategy shares more common characteristics with Special Economic Zones (SEZ) than it does with the traditional approach to cluster policy in terms of its main objective of attracting foreign direct investments (FDI), securing support mechanisms as well as in the selection of target areas and the type of instruments to be implemented. The experience of Thailand is discussed along with that of other Asian countries, most notably China, in order to identify and verify the characteristics of the Asian model of clusters and cluster policy.

scholarly journals Frontal and parietal alpha oscillations reflect attentional modulation of cross-modal matching

2018 ◽  
Author(s):  
Jonas Misselhorn ◽  
Uwe Friese ◽  
Andreas K. Engel
Keyword(s):  
Gamma Activity ◽  
Multisensory Perception ◽  
Top Down ◽  
Bottom Up ◽  
Alpha Oscillations ◽  
Sensory Inputs ◽  
Gamma Power ◽  
Sensory Cortices ◽  
Underlying Mechanisms ◽  
Selection Of

Multisensory perception is shaped by both attentional selection of relevant sensory inputs and exploitation of stimulus-driven factors that promote cross-modal binding. Underlying mechanisms of both top-down and bottom-up modulations have been linked to changes in alpha/gamma dynamics in primary sensory cortices and temporoparietal cortex. Accordingly, it has been proposed that alpha oscillations provide pulsed inhibition for gamma activity and thereby dynamically route cortical information flow. In this study, we employed a recently introduced multisensory paradigm incorporating both bottom-up and top-down aspects of cross-modal attention in an EEG study. The same trimodal stimuli were presented in two distinct attentional conditions, focused on visual-tactile or audio-visual components, for which cross-modal congruence of amplitude changes had to be evaluated. Neither top-down nor bottom-up cross-modal attention modulated alpha or gamma power in primary sensory cortices. Instead, we found alpha band effects in bilateral frontal and right parietal cortex. We propose that frontal alpha oscillations reflect the origin of top-down control regulating perceptual gains and that modulations of parietal alpha oscillations relates to intersensory re-orienting. Taken together, we suggest that the idea of selective cortical routing via alpha oscillations can be extended from sensory cortices to the frontoparietal attention network.

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