3,875 research outputs found
Topological Point Cloud Clustering
We present Topological Point Cloud Clustering (TPCC), a new method to cluster
points in an arbitrary point cloud based on their contribution to global
topological features. TPCC synthesizes desirable features from spectral
clustering and topological data analysis and is based on considering the
spectral properties of a simplicial complex associated to the considered point
cloud. As it is based on considering sparse eigenvector computations, TPCC is
similarly easy to interpret and implement as spectral clustering. However, by
focusing not just on a single matrix associated to a graph created from the
point cloud data, but on a whole set of Hodge-Laplacians associated to an
appropriately constructed simplicial complex, we can leverage a far richer set
of topological features to characterize the data points within the point cloud
and benefit from the relative robustness of topological techniques against
noise. We test the performance of TPCC on both synthetic and real-world data
and compare it with classical spectral clustering
Non-isotropic Persistent Homology: Leveraging the Metric Dependency of PH
Persistent Homology is a widely used topological data analysis tool that
creates a concise description of the topological properties of a point cloud
based on a specified filtration. Most filtrations used for persistent homology
depend (implicitly) on a chosen metric, which is typically agnostically chosen
as the standard Euclidean metric on . Recent work has tried to
uncover the 'true' metric on the point cloud using distance-to-measure
functions, in order to obtain more meaningful persistent homology results. Here
we propose an alternative look at this problem: we posit that information on
the point cloud is lost when restricting persistent homology to a single
(correct) distance function. Instead, we show how by varying the distance
function on the underlying space and analysing the corresponding shifts in the
persistence diagrams, we can extract additional topological and geometrical
information. Finally, we numerically show that non-isotropic persistent
homology can extract information on orientation, orientational variance, and
scaling of randomly generated point clouds with good accuracy and conduct some
experiments on real-world data.Comment: 30 pages, 17 figures, comments welcome
Dilution versus pollution in watercourses affected by acid mine drainage: a graphic model for the Iberian Pyrite Belt (SW Spain)
The aim of this study was to chemically characterize
the water quality impacts of the 88 acid mine drainage
(AMD) generating mines in the Spanish sector of the Iberian
Pyrite Belt (IPB). This was necessary because the Water
Framework Directive of the European Union and the hydrological
plans of the Tinto, Odiel, and Piedras river basins
require that water quality be improved enough to allow at
least some of the rivers in the IPB to sustain healthy fish
populations by 2027. The results indicate a clear decrease in
metals, arsenic, and sulfate concentrations and increased pH
between the AMD-sources and the river channels.info:eu-repo/semantics/publishedVersio
Effective growth of matter density fluctuations in the running LCDM and LXCDM models
We investigate the matter density fluctuations \delta\rho/\rho for two dark
energy (DE) models in the literature in which the cosmological term \Lambda is
a running parameter. In the first model, the running LCDM model, matter and DE
exchange energy, whereas in the second model, the LXCDM model, the total DE and
matter components are conserved separately. The LXCDM model was proposed as an
interesting solution to the cosmic coincidence problem. It includes an extra
dynamical component, the "cosmon" X, which interacts with the running \Lambda,
but not with matter. In our analysis we make use of the current value of the
linear bias parameter, b^2(0)= P_{GG}/P_{MM}, where P_{MM} ~
(\delta\rho/\rho)^2 is the present matter power spectrum and P_{GG} is the
galaxy fluctuation power spectrum. The former can be computed within a given
model, and the latter is found from the observed LSS data (at small z) obtained
by the 2dF galaxy redshift survey. It is found that b^2(0)=1 within a 10%
accuracy for the standard LCDM model. Adopting this limit for any DE model and
using a method based on the effective equation of state for the DE, we can set
a limit on the growth of matter density perturbations for the running LCDM
model, the solution of which is known. This provides a good test of the
procedure, which we then apply to the LXCDM model in order to determine the
physical region of parameter space, compatible with the LSS data. In this
region, the LXCDM model is consistent with known observations and provides at
the same time a viable solution to the cosmic coincidence problem.Comment: LaTeX, 38 pages, 8 figures. Version accepted in JCA
Perturbations in the relaxation mechanism for a large cosmological constant
Recently, a mechanism for relaxing a large cosmological constant (CC) has
been proposed [arxiv:0902.2215], which permits solutions with low Hubble rates
at late times without fine-tuning. The setup is implemented in the LXCDM
framework, and we found a reasonable cosmological background evolution similar
to the LCDM model with a fine-tuned CC. In this work we analyse analytically
the perturbations in this relaxation model, and we show that their evolution is
also similar to the LCDM model, especially in the matter era. Some tracking
properties of the vacuum energy are discussed, too.Comment: 18 pages, LaTeX; discussion improved, accepted by CQ
FRCM-to-masonry bonding behaviour in the case of curved surfaces: Experimental investigation
Fabric-reinforced cementitious matrix (FRCM) are composite materials more and more used for the reinforcement of masonry structures. The combination of high tensile strength fabrics (or meshes) with cementitious matrices, having good thixotropic capabilities and vapour permeability, makes such composites suitable for reinforcing a large number of masonry structures, including the one belonging to the historic heritage. FRCMs are bonded to the outer surfaces of structural masonry elements and, thanks to their adhesive capacity, bear much of the tensile stresses that unreinforced masonry cannot withstand. The effectiveness of such reinforcements, which is highly dependent on their ability to adhere to the masonry substrate, is generally investigated throughout specific experimental investigations (shear tests). Almost all the papers in the literature devoted to bond-slip analysis refer to the case of flat bonding surfaces, although these reinforcements are also widely used on curved structural elements such as arches and vaults. Therefore, this paper reports and examines the results of an extensive experimental program concerning the behavior of FRCM systems applied on curved masonry specimens. The results point out the influence of both curvature and reinforcement position (intrados or extrados) on the response of specimens in terms of bearing capacity, failure mode and post-peak response
Different formation routes of pore structure in aluminum powder metallurgy alloy
In powder metallurgy (PM), severe plastic deformation (SPD) is a well-known technological solution to achieve interesting properties. However, the occurrence of pores in the final product may limit these properties. Also, for a given type of microstructure, the stereometric parameters of the pore structures, such as shape (represented by Aspect and Dcircle) and distribution (fshape, and fcircle), decisively affect the final properties. The influence of different processing routes (pressing, sintering and equal channel angular pressing (ECAP)) on pore structures in an aluminum PMalloy is discussed. The nature of porosity, porosity evolution and its behavior is explored. The correlation between pore size and morphology is also considered. The final pore structure parameters (Aspect, Dcircle, fshape, and fcircle) of studied aluminum alloys produced by different processing routes depends on the different formation routes
The operationalized psychodynamic diagnostics system. Clinical relevance, reliability and validity
In this paper, we present a multiaxial system for psychodynamic diagnosis, which has attained wide usage in Germany in the last 10 years. First we will discuss the 4 operationalized psychodynamic diagnostics (OPD) axes: illness experience and treatment assumptions, relationships, mental conflicts, and structure, then clinical applications will be outlined. Focus psychodynamic formulations can be employed both with inpatients and with outpatients. Studies show good reliability in a research context and acceptable reliability for clinical purposes. Validity will be separately summarized as content, criterion, and construct validity. Validity studies indicate good validity for the individual axes. Numerous studies on the OPD indicate areas of possible improvement, for example for clinical purposes the OPD should be more practically formulated
Signal Processing on Product Spaces
We establish a framework for signal processing on product spaces of
simplicial and cellular complexes. For simplicity, we focus on the product of
two complexes representing time and space, although our results generalize
naturally to products of simplicial complexes of arbitrary dimension. Our
framework leverages the structure of the eigenmodes of the Hodge Laplacian of
the product space to jointly filter along time and space. To this end, we
provide a decomposition theorem of the Hodge Laplacian of the product space,
which highlights how the product structure induces a decomposition of each
eigenmode into a spatial and temporal component. Finally, we apply our method
to real world data, specifically for interpolating trajectories of buoys in the
ocean from a limited set of observed trajectories
- …