5,530 research outputs found
A novel approach to model dynamic flow interactions between storm sewer system and overland surface for different land covers in urban areas
In this study, we developed a novel approach to simulate dynamic flow interactions between storm sewers and overland surface for different land covers in urban areas. The proposed approach couples the one-dimensional (1D) sewer flow model (SFM) and the two-dimensional (2D) overland flow model (OFM) with different techniques depending on the land cover type of the study areas. For roads, pavements, plazas, and so forth where rainfall becomes surface runoff before entering the sewer system, the rainfall-runoff process is simulated directly in the 2D OFM, and the runoff is drained to the sewer network via inlets, which is regarded as the input to 1D SFM. For green areas on which rainfall falls into the permeable ground surface and the generated direct runoff traverses terrain, the deduction rate is applied to the rainfall for reflecting the soil infiltration in the 2D OFM. In built-up areas with drainage facilities allowing rainfall to drain directly from the roof to sewer networks, the rainfall-runoff process is simulated using the hydrological module in the 1D SFM where no rainfall is applied to these areas in the 2D OFM. The 1D SFM is used for hydraulic simulations in the sewer network. Where the flow in the drainage network exceeds its capacity, a surcharge occurs and water may spill onto the ground surface if the pressure head in a manhole exceeds the ground elevation. The overflow discharge from the sewer system is calculated by the 1D SFM and considered a point source in the 2D OFM. The overland flow will return into the sewer network when it reaches an inlet that connects to an un-surcharged manhole. In this case, the drainage is considered as a point sink in the 2D OFM and an inflow to a manhole in the 1D SFM. The proposed approach was compared to other five urban flood modelling techniques with four rainfall events that had previously recorded inundation areas. The merits and drawbacks of each modelling technique were compared and discussed. Based on the simulated results, the proposed approach was found to simulate floodings closer to the survey records than other approaches because the physical rainfall-runoff phenomena in urban environment were better reflected.Royal SocietyMinistry of Science and Technology, Taiwa
A Geometric Fractal Growth Model for Scale Free Networks
We introduce a deterministic model for scale-free networks, whose degree
distribution follows a power-law with the exponent . At each time step,
each vertex generates its offsprings, whose number is proportional to the
degree of that vertex with proportionality constant m-1 (m>1). We consider the
two cases: first, each offspring is connected to its parent vertex only,
forming a tree structure, and secondly, it is connected to both its parent and
grandparent vertices, forming a loop structure. We find that both models
exhibit power-law behaviors in their degree distributions with the exponent
. Thus, by tuning m, the degree exponent can be
adjusted in the range, . We also solve analytically a mean
shortest-path distance d between two vertices for the tree structure, showing
the small-world behavior, that is, , where N is
system size, and is the mean degree. Finally, we consider the case
that the number of offsprings is the same for all vertices, and find that the
degree distribution exhibits an exponential-decay behavior
Recursive graphs with small-world scale-free properties
We discuss a category of graphs, recursive clique trees, which have
small-world and scale-free properties and allow a fine tuning of the clustering
and the power-law exponent of their discrete degree distribution. We determine
relevant characteristics of those graphs: the diameter, degree distribution,
and clustering parameter. The graphs have also an interesting recursive
property, and generalize recent constructions with fixed degree distributions.Comment: 4 pages, 2 figure
Hierarchical Organization in Complex Networks
Many real networks in nature and society share two generic properties: they
are scale-free and they display a high degree of clustering. We show that these
two features are the consequence of a hierarchical organization, implying that
small groups of nodes organize in a hierarchical manner into increasingly large
groups, while maintaining a scale-free topology. In hierarchical networks the
degree of clustering characterizing the different groups follows a strict
scaling law, which can be used to identify the presence of a hierarchical
organization in real networks. We find that several real networks, such as the
World Wide Web, actor network, the Internet at the domain level and the
semantic web obey this scaling law, indicating that hierarchy is a fundamental
characteristic of many complex systems
Constrained spin dynamics description of random walks on hierarchical scale-free networks
We study a random walk problem on the hierarchical network which is a
scale-free network grown deterministically. The random walk problem is mapped
onto a dynamical Ising spin chain system in one dimension with a nonlocal spin
update rule, which allows an analytic approach. We show analytically that the
characteristic relaxation time scale grows algebraically with the total number
of nodes as . From a scaling argument, we also show the
power-law decay of the autocorrelation function C_{\bfsigma}(t)\sim
t^{-\alpha}, which is the probability to find the Ising spins in the initial
state {\bfsigma} after time steps, with the state-dependent non-universal
exponent . It turns out that the power-law scaling behavior has its
origin in an quasi-ultrametric structure of the configuration space.Comment: 9 pages, 6 figure
Flood Vulnerability and Risk Maps in Taipei City, Taiwan
This paper presents the process of constructing a flood risk map in Taipei City. The study calculates the social vulnerability index (SVI) for flooding at a district level, based on five factors including (1) female population (2) alone living elderly (3) low-income households (4) household income and (5) house-hold possessions. The index is determined according to the factor ratios in a district comparing to the statistical average across Taipei City. By combining the SVI with spatial varied flood potential information simulated by a hydraulic model, the flood risk index is obtained for district level that has an area of about 0.2 km2. Results show that the flood risk in Taipei City changed from 2002 to 2010 due to changes in the demographic structure. During the period from 2002 to 2004, the most obvious change of flood risk occurred in the Wanhua district due to the increase in the ratio of household possessions, which escalated the vulnerability to flooding. Between 2005 and 2007, the ratio of household possessions dropped in the Nankang district such that the flood risk reduced mostly in the region
Transition from fractal to non-fractal scalings in growing scale-free networks
Real networks can be classified into two categories: fractal networks and
non-fractal networks. Here we introduce a unifying model for the two types of
networks. Our model network is governed by a parameter . We obtain the
topological properties of the network including the degree distribution,
average path length, diameter, fractal dimensions, and betweenness centrality
distribution, which are controlled by parameter . Interestingly, we show
that by adjusting , the networks undergo a transition from fractal to
non-fractal scalings, and exhibit a crossover from `large' to small worlds at
the same time. Our research may shed some light on understanding the evolution
and relationships of fractal and non-fractal networks.Comment: 7 pages, 3 figures, definitive version accepted for publication in
EPJ
Effective dimensions and percolation in hierarchically structured scale-free networks
We introduce appropriate definitions of dimensions in order to characterize
the fractal properties of complex networks. We compute these dimensions in a
hierarchically structured network of particular interest. In spite of the
nontrivial character of this network that displays scale-free connectivity
among other features, it turns out to be approximately one-dimensional. The
dimensional characterization is in agreement with the results on statistics of
site percolation and other dynamical processes implemented on such a network.Comment: 5 pages, 5 figure
COMPUCEA 2nd generation performance evaluation
COMPUCEA (Combined Procedure for Uranium Concentration and Enrichment Assay) is used for on-site analytical measurements in support of joint Euratom-IAEA inspections during physical inventory verification (PIV) campaigns in European Low-Enriched Uranium (LEU) fuel fabrication plants. The analyses provided on site during the PIV involve the accurate determination of the uranium element content and of the U-235 enrichment in verification samples (uranium product samples of solid form , i.e. powders, pellets) selected by the Safeguards inspectors. These samples are dissolved and then measured by energy-dispersive X-ray absorption edge spectrometry (L-edge densitometry) to obtain the uranium elemental content and gamma spectrometry with a Lanthanum-bromide detector for the U-235 abundance determination. The second generation of COMPUCEA equipment is compact, rugged and ready-to use directly after transport, no cooling of the detectors with liquid nitrogen is required. A software package for comfortable instrument control and data handling has been implemented. The paper describes the technique, setup and calibration procedure of the instrument. Results from PIV campaigns and comparisons between COMPUCEA results with data obtained by remote analysis with a qualified primary analytical method are presented, which demonstrate the performance of the technique. The achieved uncertainties are well within the international target values. First results obtained with a sandwich detector configuration for enhanced detection efficiency of the passive gamma spectrometry and a small separate X-ray fluorescence unit for the pre-screening of the samples for their Gd content are discussed.JRC.E.7-Nuclear Safeguards and Forensic
Herwig++ Status Report
Herwig++ is the successor of the event generator HERWIG. In its present version 2.2.1 it provides a program for full LHC event generation which is superior to the previous program in many respects. We briefly summarize its features and describe present work and some future plans
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