6,673 research outputs found
POINTS CLASSIFICATION BY A SEQUENTIAL HIGHER - ORDER MOMENTS STATISTICAL ANALYSIS OF LIDAR DATA
The paper deals with a new sequential procedure to perform unsupervised LIDAR points classification by iteratively studying skewness and kurtosis for elevation and intensity point distribution values. After a preliminary local shape analysis of elevation and intensity point distributions, carried out from the original discrete frequencies by a non parametric estimation of the density functions, the procedure starts by choosing the category of data (elevation or intensity) to analyse at first: the choice falls on the category better showing by a testing procedure a bi or a multi clustering distribution. The first point cluster is identified by studying the distribution skewness and kurtosis variations, after removing at each step the largest data values. The selected cluster is furthermore analysed by studying higher order moments behaviour of the complementary data category. This makes possible to find out potential sub clusters of the original selected one, permitting, in this way, a more effective point classification. Successive clusters are identified by applying the same iterative procedure to the still unclassified LIDAR points. For complex point distribution shapes or for the classification of large areas, a progressive analysis method, based on the partition of the entire data set into regular subsets, is proposed. Some real numerical experiments confirm the capability of the method proposed. The classification total errors in the experiments range from a minimum value of 1,2% to a maximum value of 8,9%
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Shake table testing of a tuned mass damper inerter (Tmdi)-equipped structure and nonlinear dynamic modeling under harmonic excitations
This paper presents preliminary experimental results from a novel shaking table testing campaign investigating the dynamic response of a two-degree-of-freedom (2DOF) physical specimen with a grounded inerter under harmonic base excitation and contributes a nonlinear dynamic model capturing the behavior of the test specimen. The latter consists of a primary mass connected to the ground through a high damping rubber isolator (HDRI) and a secondary mass connected to the primary mass through a second HDRI. Further, a flywheel-based rack-and-pinion inerter prototype device is used to connect the secondary mass to the ground. The resulting specimen resembles the tuned mass damper inerter (TMDI) configuration with grounded inerter analytically defined and numerically assessed by the authors in a number of previous publications. Physical specimens with three different inerter coefficients are tested on the shake table under sine-sweep excitation with three different amplitudes. Experimental frequency response functions (FRFs) are derived manifesting a softening nonlinear behavior of the specimens and enhanced vibration suppression with increased inerter coefficient. Further, a 2DOF parametric nonlinear model of the specimen is established accounting for non-ideal inerter device behavior and its potential to characterize experimental response time-histories, FRFs, and force-displacement relationships of the HDRIs and of the inerter is verified
Hidden geometric correlations in real multiplex networks
Real networks often form interacting parts of larger and more complex
systems. Examples can be found in different domains, ranging from the Internet
to structural and functional brain networks. Here, we show that these multiplex
systems are not random combinations of single network layers. Instead, they are
organized in specific ways dictated by hidden geometric correlations between
the individual layers. We find that these correlations are strong in different
real multiplexes, and form a key framework for answering many important
questions. Specifically, we show that these geometric correlations facilitate:
(i) the definition and detection of multidimensional communities, which are
sets of nodes that are simultaneously similar in multiple layers; (ii) accurate
trans-layer link prediction, where connections in one layer can be predicted by
observing the hidden geometric space of another layer; and (iii) efficient
targeted navigation in the multilayer system using only local knowledge, which
outperforms navigation in the single layers only if the geometric correlations
are sufficiently strong. Our findings uncover fundamental organizing principles
behind real multiplexes and can have important applications in diverse domains.Comment: Supplementary Materials available at
http://www.nature.com/nphys/journal/v12/n11/extref/nphys3812-s1.pd
Variation of DNA methylation and phenotypic traits following unilateral sexual polyploidization in Medicago
Sexual hybridization is an important generator of biodiversity and a powerful breeding tool. Hybridization can also overcome ploidy barriers when it involves 2n gametes, as in the case of unilateral sexual polyploidization (USP) that has been utilized in several crops, among which alfalfa. This research was aimed at gaining insights into the effects of USP on genome methylation and on phenotypic traits in alfalfa, an important forage species. The Methylation-Sensi- tive Amplified Polymorphism technique was used to estimate the cytosine methylation changes occurring in a tetraploid (2n = 4x = 32) USP progeny from crosses between a diploid Medicago sativa subsp. falcata genotype that produces 2n eggs and a cultivated tetraploid Medicago sativa subsp. sativa variety. De novo methylation or demethylation in the USP progeny were observed for 13% of the detected genomic sites, indicating that methylation changes can be relevant. USP plants showed larger surface area of the leaf epidermis cells than both parents, but this did not result in larger leaf size or higher plant biomass. They displayed significant higher ovule sterility than the tetraploid parent, but normal fertility was observed in crosses with unrelated male testers. We conclude that hybridization and sexual polyploidization resulted in novel variation in terms of remodeling of the methylation landscape as well as changes in phenotypic traits in alfalfa
Spin Needlets for Cosmic Microwave Background Polarization Data Analysis
Scalar wavelets have been used extensively in the analysis of Cosmic
Microwave Background (CMB) temperature maps. Spin needlets are a new form of
(spin) wavelets which were introduced in the mathematical literature by Geller
and Marinucci (2008) as a tool for the analysis of spin random fields. Here we
adopt the spin needlet approach for the analysis of CMB polarization
measurements. The outcome of experiments measuring the polarization of the CMB
are maps of the Stokes Q and U parameters which are spin 2 quantities. Here we
discuss how to transform these spin 2 maps into spin 2 needlet coefficients and
outline briefly how these coefficients can be used in the analysis of CMB
polarization data. We review the most important properties of spin needlets,
such as localization in pixel and harmonic space and asymptotic uncorrelation.
We discuss several statistical applications, including the relation of angular
power spectra to the needlet coefficients, testing for non-Gaussianity on
polarization data, and reconstruction of the E and B scalar maps.Comment: Accepted for publication in Phys. Rev.
A General Framework for Recursive Decompositions of Unitary Quantum Evolutions
Decompositions of the unitary group U(n) are useful tools in quantum
information theory as they allow one to decompose unitary evolutions into local
evolutions and evolutions causing entanglement. Several recursive
decompositions have been proposed in the literature to express unitary
operators as products of simple operators with properties relevant in
entanglement dynamics. In this paper, using the concept of grading of a Lie
algebra, we cast these decompositions in a unifying scheme and show how new
recursive decompositions can be obtained. In particular, we propose a new
recursive decomposition of the unitary operator on qubits, and we give a
numerical example.Comment: 17 pages. To appear in J. Phys. A: Math. Theor. This article replaces
our earlier preprint "A Recursive Decomposition of Unitary Operators on N
Qubits." The current version provides a general method to generate recursive
decompositions of unitary evolutions. Several decompositions obtained before
are shown to be as a special case of this general procedur
Limits on isotropic Lorentz violation in QED from collider physics
We consider the possibility that Lorentz violation can generate differences
between the limiting velocities of light and charged matter. Such effects would
lead to efficient vacuum Cherenkov radiation or rapid photon decay. The absence
of such effects for 104.5 GeV electrons at the Large Electron Positron collider
and for 300 GeV photons at the Tevatron therefore constrains this type of
Lorentz breakdown. Within the context of the standard-model extension, these
ideas imply an experimental bound at the level of -5.8 x 10^{-12} <=
\tilde{\kappa}_{tr}-(4/3)c_e^{00} <= 1.2 x 10^{-11} tightening existing
laboratory measurements by 3-4 orders of magnitude. Prospects for further
improvements with terrestrial and astrophysical methods are discussed.Comment: Replaced with final version published in PR
A numerical study of a binary Yukawa model in regimes characteristic of globular proteins in solutions
The main goal of this paper is to assess the limits of validity, in the
regime of low concentration and strong Coulomb coupling (high molecular
charges), for a simple perturbative approximation to the radial distribution
functions (RDF), based upon a low-density expansion of the potential of mean
force and proposed to describe protein-protein interactions in a recent
Small-Angle-Scattering (SAS) experimental study. A highly simplified Yukawa
(screened Coulomb) model of monomers and dimers of a charged globular protein
(-lactoglobulin) in solution is considered. We test the accuracy of the
RDF approximation, as a necessary complementary part of the previous
experimental investigation, by comparison with the fluid structure predicted by
approximate integral equations and exact Monte Carlo (MC) simulations. In the
MC calculations, an Ewald construction for Yukawa potentials has been used to
take into account the long-range part of the interactions in the weakly
screened cases. Our results confirm that the perturbative first-order
approximation is valid for this system even at strong Coulomb coupling,
provided that the screening is not too weak (i.e., for Debye length smaller
than monomer radius). A comparison of the MC results with integral equation
calculations shows that both the hypernetted-chain (HNC) and the Percus-Yevick
(PY) closures have a satisfactory behavior under these regimes, with the HNC
being superior throughout. The relevance of our findings for interpreting SAS
results is also discussed.Comment: Physical Review E, in press (2005
The physics of spreading processes in multilayer networks
The study of networks plays a crucial role in investigating the structure,
dynamics, and function of a wide variety of complex systems in myriad
disciplines. Despite the success of traditional network analysis, standard
networks provide a limited representation of complex systems, which often
include different types of relationships (i.e., "multiplexity") among their
constituent components and/or multiple interacting subsystems. Such structural
complexity has a significant effect on both dynamics and function. Throwing
away or aggregating available structural information can generate misleading
results and be a major obstacle towards attempts to understand complex systems.
The recent "multilayer" approach for modeling networked systems explicitly
allows the incorporation of multiplexity and other features of realistic
systems. On one hand, it allows one to couple different structural
relationships by encoding them in a convenient mathematical object. On the
other hand, it also allows one to couple different dynamical processes on top
of such interconnected structures. The resulting framework plays a crucial role
in helping achieve a thorough, accurate understanding of complex systems. The
study of multilayer networks has also revealed new physical phenomena that
remain hidden when using ordinary graphs, the traditional network
representation. Here we survey progress towards attaining a deeper
understanding of spreading processes on multilayer networks, and we highlight
some of the physical phenomena related to spreading processes that emerge from
multilayer structure.Comment: 25 pages, 4 figure
The defect variance of random spherical harmonics
The defect of a function is defined as the
difference between the measure of the positive and negative regions. In this
paper, we begin the analysis of the distribution of defect of random Gaussian
spherical harmonics. By an easy argument, the defect is non-trivial only for
even degree and the expected value always vanishes. Our principal result is
obtaining the asymptotic shape of the defect variance, in the high frequency
limit. As other geometric functionals of random eigenfunctions, the defect may
be used as a tool to probe the statistical properties of spherical random
fields, a topic of great interest for modern Cosmological data analysis.Comment: 19 page
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