4,884 research outputs found
Methods of Hierarchical Clustering
We survey agglomerative hierarchical clustering algorithms and discuss
efficient implementations that are available in R and other software
environments. We look at hierarchical self-organizing maps, and mixture models.
We review grid-based clustering, focusing on hierarchical density-based
approaches. Finally we describe a recently developed very efficient (linear
time) hierarchical clustering algorithm, which can also be viewed as a
hierarchical grid-based algorithm.Comment: 21 pages, 2 figures, 1 table, 69 reference
Minimal geometric deformation decoupling in dimensional space-times
We study the minimal geometric deformation decoupling in dimensional
space--times and implement it as a tool for obtaining anisotropic solutions
from isotropic geometries. Interestingly, both the isotropic and the
anisotropic sector fulfill Einstein field equations in contrast to the cases
studied in dimensions. In particular, new anisotropic solutions are
obtained from the well known static BTZ solution.Comment: Figure and some comments added. Accepted in EPJ
Fast redshift clustering with the Baire (ultra) metric
The Baire metric induces an ultrametric on a dataset and is of linear
computational complexity, contrasted with the standard quadratic time
agglomerative hierarchical clustering algorithm. We apply the Baire distance to
spectrometric and photometric redshifts from the Sloan Digital Sky Survey
using, in this work, about half a million astronomical objects. We want to know
how well the (more cos\ tly to determine) spectrometric redshifts can predict
the (more easily obtained) photometric redshifts, i.e. we seek to regress the
spectrometric on the photometric redshifts, and we develop a clusterwise
nearest neighbor regression procedure for this.Comment: 14 pages, 6 figure
Minimal Geometric Deformation in asymptotically (A-)dS space-times and the isotropic sector for a polytropic black hole
In the context of the Minimal Geometric Deformation method, in this paper we
implement the inverse problem in a black hole scenario. In order to deal with
an anisotropic polytropic black hole solution of the Einstein field equations
with cosmological constant, the deformation method is slightly extended. After
obtaining the isotropic sector and the decoupler for an anisotropic (A-)dS
polytropic black hole solution, we emphasize a possible relation between
anisotropization/isotropization and the violation of the energy conditions.Comment: 5 pages, typos corrected, references adde
Ring Resonators with Sagnac Loops for Photonic Processing in DWDM Backbone Networks
In this paper, optical configurations based on ring resonators (RR) with an internal Sagnac (SG) loop in the feedback path, are analyzed in terms of their amplitude response and dispersive properties for filtering and chromatic dispersion managing in digital transmission systems over amplified single- mode fiber (SMF) spans in DWDM backbone networks. Design issues for the architecture as regards quadratic dispersion and magnitude distortion are provided. The RR+SG compound filter provides frequency tunability of the amplitude and dispersion peaks by adjusting a coupling coefficient of an optical coupler, with no need for using integrated thermo-optic nor current- injection based phase shifters. The configuration can be employed as an additional structure for a general RR-based design and synthesis architecture, allowing bandwidth increase of dispersion compensators and flexibility. The performance of a compound filter consisting of a two RR in series stage and a RR+SG filter are reported as a more compact and effective solution for existing multi-channel SMF backbone links operating at high bit rates. Design guidelines of an integrated ring resonator based on polymer technology for showing feasibility of the proposal is reported.This work was partially supported by Spanish CICYT (TEC2006-13273-C03-03-MIC), European project NoE
EPhoton/One+, CAM (FACTOTEM-CM:S-0505/ESP/000417), FENIS-CCG06-UC3MITIC-0619.Publicad
Radio-frequency ring resonators for self-referencing fiber-optic intensity sensors
A theoretical and experimental study of radiofrequency ring resonators (RR) for referencing and improving the sensitivity of fiber-optic intensity sensors (FOS) is
reported. The separation between lead and transducer losses in the FOS is solved by converting the light intensity fluctuations to be measured into RR losses that produce
high amplitude variations in the proximity of the RR resonance frequencies. Two different self-referencing techniques are developed. Via the definition of the measurement parameter RM , sensor linearity and sensitivity are analyzed. A calibration
using an optical attenuator is reported to validate the model.Publicad
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