8,822 research outputs found
Evaluating the Differences of Gridding Techniques for Digital Elevation Models Generation and Their Influence on the Modeling of Stony Debris Flows Routing: A Case Study From Rovina di Cancia Basin (North-Eastern Italian Alps)
Debris \ufb02ows are among the most hazardous phenomena in mountain areas. To cope
with debris \ufb02ow hazard, it is common to delineate the risk-prone areas through
routing models. The most important input to debris \ufb02ow routing models are the
topographic data, usually in the form of Digital Elevation Models (DEMs). The quality
of DEMs depends on the accuracy, density, and spatial distribution of the sampled
points; on the characteristics of the surface; and on the applied gridding methodology.
Therefore, the choice of the interpolation method affects the realistic representation
of the channel and fan morphology, and thus potentially the debris \ufb02ow routing
modeling outcomes. In this paper, we initially investigate the performance of common
interpolation methods (i.e., linear triangulation, natural neighbor, nearest neighbor,
Inverse Distance to a Power, ANUDEM, Radial Basis Functions, and ordinary kriging)
in building DEMs with the complex topography of a debris \ufb02ow channel located
in the Venetian Dolomites (North-eastern Italian Alps), by using small footprint full-
waveform Light Detection And Ranging (LiDAR) data. The investigation is carried
out through a combination of statistical analysis of vertical accuracy, algorithm
robustness, and spatial clustering of vertical errors, and multi-criteria shape reliability
assessment. After that, we examine the in\ufb02uence of the tested interpolation algorithms
on the performance of a Geographic Information System (GIS)-based cell model for
simulating stony debris \ufb02ows routing. In detail, we investigate both the correlation
between the DEMs heights uncertainty resulting from the gridding procedure and
that on the corresponding simulated erosion/deposition depths, both the effect of
interpolation algorithms on simulated areas, erosion and deposition volumes, solid-liquid
discharges, and channel morphology after the event. The comparison among the tested
interpolation methods highlights that the ANUDEM and ordinary kriging algorithms
are not suitable for building DEMs with complex topography. Conversely, the linear
triangulation, the natural neighbor algorithm, and the thin-plate spline plus tension and completely regularized spline functions ensure the best trade-off among accuracy
and shape reliability. Anyway, the evaluation of the effects of gridding techniques on
debris \ufb02ow routing modeling reveals that the choice of the interpolation algorithm does
not signi\ufb01cantly affect the model outcomes
What is the dimension of citation space?
© 2016 Published by Elsevier B.V.Citation networks represent the flow of information between agents. They are constrained in time and so form directed acyclic graphs which have a causal structure. Here we provide novel quantitative methods to characterise that structure by adapting methods used in the causal set approach to quantum gravity by considering the networks to be embedded in a Minkowski spacetime and measuring its dimension using Myrheim-Meyer and Midpoint-scaling estimates. We illustrate these methods on citation networks from the arXiv, supreme court judgements from the USA, and patents and find that otherwise similar citation networks have measurably different dimensions. We suggest that these differences can be interpreted in terms of the level of diversity or narrowness in citation behaviour
Attractor reconstruction of an impact oscillator for parameter identification
Peer reviewedPreprin
Quantifying correlations between galaxy emission lines and stellar continua
We analyse the correlations between continuum properties and emission line
equivalent widths of star-forming and active galaxies from the Sloan Digital
Sky Survey. Since upcoming large sky surveys will make broad-band observations
only, including strong emission lines into theoretical modelling of spectra
will be essential to estimate physical properties of photometric galaxies. We
show that emission line equivalent widths can be fairly well reconstructed from
the stellar continuum using local multiple linear regression in the continuum
principal component analysis (PCA) space. Line reconstruction is good for
star-forming galaxies and reasonable for galaxies with active nuclei. We
propose a practical method to combine stellar population synthesis models with
empirical modelling of emission lines. The technique will help generate more
accurate model spectra and mock catalogues of galaxies to fit observations of
the new surveys. More accurate modelling of emission lines is also expected to
improve template-based photometric redshift estimation methods. We also show
that, by combining PCA coefficients from the pure continuum and the emission
lines, automatic distinction between hosts of weak active galactic nuclei
(AGNs) and quiescent star-forming galaxies can be made. The classification
method is based on a training set consisting of high-confidence starburst
galaxies and AGNs, and allows for the similar separation of active and
star-forming galaxies as the empirical curve found by Kauffmann et al. We
demonstrate the use of three important machine learning algorithms in the
paper: k-nearest neighbour finding, k-means clustering and support vector
machines.Comment: 14 pages, 14 figures. Accepted by MNRAS on 2015 December 22. The
paper's website with data and code is at
http://www.vo.elte.hu/papers/2015/emissionlines
A variational method based on weighted graph states
In a recent article [Phys. Rev. Lett. 97 (2006), 107206], we have presented a
class of states which is suitable as a variational set to find ground states in
spin systems of arbitrary spatial dimension and with long-range entanglement.
Here, we continue the exposition of our technique, extend from spin 1/2 to
higher spins and use the boson Hubbard model as a non-trivial example to
demonstrate our scheme.Comment: 36 pages, 13 figure
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