3D Segmentation Method for Natural Environments based on a Geometric-Featured Voxel Map

This work proposes a new segmentation algorithm for three-dimensional dense point clouds and has been specially designed for natural environments where the ground is unstructured and may include big slopes, non-flat areas and isolated areas. This technique is based on a Geometric-Featured Voxel map (GFV) where the scene is discretized in constant size cubes or voxels which are classified in flat surface, linear or tubular structures and scattered or undefined shapes, usually corresponding to vegetation. Since this is not a point-based technique the computational cost is significantly reduced, hence it may be compatible with Real-Time applications. The ground is extracted in order to obtain more accurate results in the posterior segmentation process. The scene is split into objects and a second segmentation in regions inside each object is performed based on the voxel’s geometric class. The work here evaluates the proposed algorithm in various versions and several voxel sizes and compares the results with other methods from the literature. For the segmentation evaluation the algorithms are tested on several differently challenging hand-labeled data sets using two metrics, one of which is novel.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The properties of penumbral microjets inclination

We investigate the dependence of penumbral microjets inclination on the position within penumbra. The high cadence observations taken on 10 November 2006 with the Hinode satellite through the \ion{Ca}{ii} H and G--band filters were analysed to determine the inclination of penumbral microjets. The results were then compared with the inclination of the magnetic field determined through the inversion of the spectropolarimetric observations of the same region. The penumbral microjet inclination is increasing towards the outer edge of the penumbra. The results suggest that the penumbral microjet follows the opening magnetic field lines of a vertical flux tube that creates the sunspot.Comment: 4 pages, 4 figures, A&A Letter in pres

Reliability of the Star Excursion Balance Test and Two New Similar Protocols to Measure Trunk Postural Control

Background: Although the Star Excursion Balance test (SEBT) has shown a good intrasession reliability, the intersession reliability of this test has not been deeply studied. Furthermore, there is an evident high influence of the lower limbs in the performance of the SEBT, so even if it has been used to measure core stability, it is possibly not the most suitable measurement. Objective: (1) To assess the absolute and relative between-session reliability of the SEBT and 2 novel variations of this test to assess trunk postural control while sitting, ie, the Star Excursion Sitting Test (SEST) and the Star Excursion Timing Test (SETT); and (2) to analyze the relationships between these 3 test scores. Design: Correlational and reliability testeretest study. Setting: Controlled laboratory environment. Participants: Twenty-seven physically active men (age: 24.54 3.05 years). Method: Relative and absolute reliability of the SEBT, SEST, and SETT were calculated through the intraclass correlation coefficient (ICC) and standard error of measurement (SEM), respectively. A Pearson correlation analysis was carried out between the variables of the 3 tests. Main Outcome Measures: Maximum normalized reach distances were assessed for different SEBT and SEST directions. In addition, composite indexes were calculated for SEBT, SEST, and SETT. Results: The SEBT (dominant leg: ICC ¼ 0.87 [0.73-0.94], SEM ¼ 2.12 [1.66-2.93]; nondominant leg: ICC ¼ 0.74 [0.50-0.87], SEM ¼ 3.23 [2.54-4.45]), SEST (ICC ¼ 0.85 [0.68-0.92], SEM ¼ 1.27 [1.03-1.80]), and SETT (ICC ¼ 0.61 [0.30-0.80], SEM ¼ 2.31 [1.82-3.17]) composite indexes showed moderate-to-high 1-month reliability. A learning effect was detected for some SEBT and SEST directions and for SEST and SETT composite indexes. No significant correlations were found between SEBT and its 2 variations (r .366; P > .05). A significant correlation was found between the SEST and SETT composite indexes (r ¼ .520; P > .01). Conclusions: SEBT, SEST, and SETT are reliable field protocols to measure postural control. However, whereas the SEBT assesses postural control in single-leg stance, SEST and SETT provide trunk postural control measures with lower influence of the lowerlimbs

Concept of finite limit of a function at a point: meanings and specific terms

In this paper, we present some results of an exploratory study performed with students aged 16-17. We investigate the different uses that these students make of terms such as ‘to approach’, ‘to tend’, ‘to reach’, ‘to exceed’ and ‘limit’ that describe the basic notions related to the concept of the finite limit of a function at a point. We use the interpretive framework of conceptual analysis to infer the meanings that students associate with these specific terms in connection with the effective use of terms in their answers.This study was performed with aid and financing from Fellowship FPU AP2010-0906 (MEC-FEDER), Projects EDU2009-11337 and EDU2012-33030 of the National Plan for R&D&R (MICIN), Subprogram EDUC and Group FQM-193 of the 3rd Andalusian Research Plan (PAIDI).This chapter is derived in part from an article published in International Journal of Mathematical Education in Science and Technology 05 Jul 2013, available online: http://www.tandfonline.com/10.1080/0020739X.2013.80588

On the validity of the 630 nm Fe I nm lines for the magnetometry of the internetwork quiet Sun

The purpose of this work is to analyze the reliability of the magnetic field strengths inferred from the 630 nm pair of Fe I lines at internetwork quiet Sun regions. Some numerical experiments have been performed that demonstrate the inability of these lines to recover the magnetic field strength in such low flux solar regions. It is shown how different model atmospheres, with magnetic field strengths ranging from few hundred Gauss to kiloGauss, give rise to Stokes profiles that can not be distinguished. The reasons for this degeneracy are discussed.Comment: Accepted for publication in A&

Strong coupling between mechanical modes in a nanotube resonator

We report on the nonlinear coupling between the mechanical modes of a nanotube resonator. The coupling is revealed in a pump-probe experiment where a mode driven by a pump force is shown to modify the motion of a second mode measured with a probe force. In a second series of experiments, we actuate the resonator with only one oscillating force. Mechanical resonances feature exotic lineshapes with reproducible dips, peaks, and jumps when the measured mode is commensurate with another mode with a frequency ratio of either 2 or 3. Conventional lineshapes are recovered by detuning the frequency ratio using the voltage on a nearby gate electrode. The exotic lineshapes are attributed to strong coupling between the mechanical modes. The possibility to control the strength of the coupling with the gate voltage holds promise for various experiments, such as quantum manipulation, mechanical signal processing, and the study of the quantum-toclassical transition.Comment: manuscript and supporting material, 31 pages, 15 figure

Temporal evolution of the Evershed flow in sunspots. II. Physical properties and nature of Evershed clouds

Context: Evershed clouds (ECs) represent the most conspicuous variation of the Evershed flow in sunspot penumbrae. Aims: We determine the physical properties of ECs from high spatial and temporal resolution spectropolarimetric measurements. Methods: The Stokes profiles of four visible and three infrared spectral lines are subject to inversions based on simple one-component models as well as more sophisticated realizations of penumbral flux tubes embedded in a static ambient field (uncombed models). Results: According to the one-component inversions, the EC phenomenon can be understood as a perturbation of the magnetic and dynamic configuration of the penumbral filaments along which these structures move. The uncombed inversions, on the other hand, suggest that ECs are the result of enhancements in the visibility of penumbral flux tubes. We conjecture that the enhancements are caused by a perturbation of the thermodynamic properties of the tubes, rather than by changes in the vector magnetic field. The feasibility of this mechanism is investigated performing numerical experiments of thick penumbral tubes in mechanical equilibrium with a background field. Conclusions: While the one-component inversions confirm many of the properties indicated by a simple line parameter analysis (Paper I of this series), we tend to give more credit to the results of the uncombed inversions because they take into account, at least in an approximate manner, the fine structure of the penumbra.Comment: Accepted for publication in A&

Resolving the Azimuthal Ambiguity in Vector Magnetogram Data with the Divergence-Free Condition: Application to Discrete Data

We investigate how the divergence-free property of magnetic fields can be exploited to resolve the azimuthal ambiguity present in solar vector magnetogram data, by using line-of-sight and horizontal heliographic derivative information as approximated from discrete measurements. Using synthetic data we test several methods that each make different assumptions about how the divergence-free property can be used to resolve the ambiguity. We find that the most robust algorithm involves the minimisation of the absolute value of the divergence summed over the entire field of view. Away from disk centre this method requires the sign and magnitude of the line-of-sight derivatives of all three components of the magnetic field vector.Comment: Solar Physics, in press, 20 pages, 11 figure