Influence of the minimum particle size in the study of shape parameters by digital image analysis

Este trabajo estudia la influencia que el tamaño de partícula (en píxeles) ejerce en los valores de sus parámetros de forma obtenidos mediante técnicas de análisis de imagen, y establece los tamaños mínimos óptimos que generan resultados fiables. La población estudiada correspondió a granos basálticos presentes en una arena volcánica. Los parámetros de forma evaluados fueron solidez (So), esfericidad (S), circularidad (Ci) y dimensión fractal (DF). La caracterización de las partículas se realizó mediante técnicas de análisis de imagen. El trabajo abordó la siguiente metodología: adquisición y segmentación de partículas minerales; cuantificación de parámetros de forma en partículas; aplicación de los tamaños mínimos de partículas descritos en la literatura sobre las muestras estudiadas y estimación de sus parámetros de forma; representación e interpretación de los cambios en las medidas de forma. Los procedimientos aplicados permitieron identificar y cuantificar 71 partículas mediante segmentación por umbrales. La utilización de tres tamaños mínimos de partícula (130, 150 y 200 píxeles) mostró que los cambios en los valores de los parámetros pueden alcanzar hasta un 2,80 % de variación. La utilización del tamaño mínimo de partículas para análisis de forma garantiza que no se incluyan valores numéricos incorrectos debido a limitaciones digitalesThis work addresses the influence of the size (in pixels) of digitized particles on the values of their shape parameters obtained using image analysis techniques, and considers the minimum sizes that provide reliable results. The population studied corresponded to basaltic grains from a volcanic sand. The shape parameters evaluated were solidity (So), sphericity (S), circularity (Ci) and fractal dimension (FD). The particle characterization was carried out by digital image analysis. The methodology was: acquisition and segmentation of mineral particles; quantification of particle shape parameters; application of the minimum particle sizes described in the literature to the studied samples and estimation of their shape parameters; representation and interpretation of changes in shape measures. The procedures applied allowed 71 particles to be identified and quantified using threshold segmentation. The use of three minimum particle sizes (130, 150 and 200 pixels) showed that changes in the shape parameter values can be as high as 2.80 % variation. The use of a minimum particle size for shape analysis ensures that incorrect numerical values produced by digital limitations are not include

Gain in Stochastic Resonance: Precise Numerics versus Linear Response Theory beyond the Two-Mode Approximation

In the context of the phenomenon of Stochastic Resonance (SR) we study the correlation function, the signal-to-noise ratio (SNR) and the ratio of output over input SNR, i.e. the gain, which is associated to the nonlinear response of a bistable system driven by time-periodic forces and white Gaussian noise. These quantifiers for SR are evaluated using the techniques of Linear Response Theory (LRT) beyond the usually employed two-mode approximation scheme. We analytically demonstrate within such an extended LRT description that the gain can indeed not exceed unity. We implement an efficient algorithm, based on work by Greenside and Helfand (detailed in the Appendix), to integrate the driven Langevin equation over a wide range of parameter values. The predictions of LRT are carefully tested against the results obtained from numerical solutions of the corresponding Langevin equation over a wide range of parameter values. We further present an accurate procedure to evaluate the distinct contributions of the coherent and incoherent parts of the correlation function to the SNR and the gain. As a main result we show for subthreshold driving that both, the correlation function and the SNR can deviate substantially from the predictions of LRT and yet, the gain can be either larger or smaller than unity. In particular, we find that the gain can exceed unity in the strongly nonlinear regime which is characterized by weak noise and very slow multifrequency subthreshold input signals with a small duty cycle. This latter result is in agreement with recent analogue simulation results by Gingl et al. in Refs. [18, 19].Comment: 22 pages, 5 eps figures, submitted to PR

Particle quantification from image analysis: application to a quartz-rich sand injection sample at the basal shear zone of the Esla Nappe (Cantabrian Zone, Variscan orogen)

Image analysis of rock samples in thin sections or polished surfaces allows the characterisation of the sizes and shapes of the particles that conform the rock. In order to test the effectiveness of different parameters in discriminating particles and grains of different origin and evolution within a rock, we use one sample from a quartz grain-rich injection at the base of the Esla Nappe (Cantabrian Zone, Variscan Orogen). We characterise particles using the parameters area (A), perimeter (P), sphericity (Es), solidity (So), normalised perimeter-area (PAn) and fractal dimension (DF). The analysis allows to discern rounded sand grains of detrital sedimentary origin from grains that have been partially or totally fractured. However, the parameters used could not discriminate sufficiently grains partially corroded by fluids during their injection perhaps due to the effect of subsequent overgrowths by cementsEl análisis de imagen en muestras de roca en lámina delgada o superficie pulida permite la caracterización de los tamaños y formas de los granos o partículas que constituyen una roca. Para comprobar la eficacia de diferentes parámetros en la discriminación de granos y partículas con diferente origen y evolución en una misma roca, utilizamos una muestra de una inyección arenosa en la base del manto del Esla (Zona Cantábrica, orógeno Varisco). Caracterizamos las partículas con los parámetros de área (A), perímetro (P), esfericidad (Es), solidez (So), perímetro-área normalizado (PAn) y dimensión fractal (DF). Este análisis permite diferenciar los granos redondeados de origen sedimentario detrítico, de aquellos que han sufrido fracturación parcial o total. Sin embargo, el análisis no permitió discriminar suficientemente los granos parcialmente expuestos a la acción corrosiva de fluidos durante la inyección debido quizá a una posible cementación posterio

U-Pb zircon SHRIMP evidence for Cambrian volcanism in the Schistose Domain within the Galicia-Trás-os.Montes Zone (Variscan Orogen, NW Iberian Peninsula)

SHRIMP U–Pb zircon analyses have shown the complexity of dating volcanic rocks due to the presence of inner cores within zircon crystals. Using the cathodoluminescence studies assisting ion microprobe analyses allow as to conclude that: the two low-grade metavolcanic samples from the Schistose Domain of the Galicia-Trás-os-Montes Zone in the northeast limb of the Verín-Bragança synform (NW Spain and NE Portugal) yield ages of 488.7 ± 3.7Ma and 499.8 ± 3.7Ma (lowermost Ordovician-Upper Cambrian). The Schistose Domain had been traditionally considered as a parautochthonous tectonic unit, i.e. as the stratigraphic continuation of the autochthonous underlying rocks, only locally or moderately detached from them as a result of strong dragging forces from large allochthonous units above it. Current interpretation of the Schistose Domain suggests that this domain formed the outboard edge of the Iberian terrane. Important Arenig, felsic magmatism with similar geochemical signature to the volcanic bodies in the Schistose Domain of the Galicia-Trás-os-Montes Zone (GTMSD) series is present also in the adjacent Ollo de Sapo Domain of the Central Iberian Zone. This contemporary nature of magmatic events provides an additional argument to support the "Iberian" affinity of the Schistose Domain of the Galicia-Trás-os-Montes Zone. However, the Cambro–Ordovician facies are very different in the Schistose Domain with respect to the autochthonous unit, the Central–Iberian Zone, suggesting that the Schistose Domain must be considered as a major allochthonous unit with a displacement of over several tens of kilometers

Un único episodio de subción a ca. 392 Ma para las rocas máficas- ultramáficas de alta P y alta T del Complejo de Cabo Ortegal

SHRIMP-dating of zircons from ultramafic, mafic and metasedimentary high-pressure (HP) rocks of Cabo Ortegal gave the following results: The MORB-type protoliths of the eclogites are Cambrian (507±7 7 Ma). Their transformation into eclogites occurred during a Devonian subduction that was accompanied by partial melting of the mantle wedge, giving rise to the formation of pyroxenites. The lon-microprobe-data suggest a single HP-loop around 392 Ma that involved all analyzed rocksLa datación de zircones, mediante SHRIMP de rocas ultramáficas, máficas y rocas metasedimentarías de alta presión (HP) del complejo de Cabo Ortegal, muestra los siguientes resultados: Los protolitos de tipo MORB de las eclogitas son Cámbricos (507±7 7 Ma). Su transformación a eclogitas tuvo lugar durante una subducción Devónica que estuvo acompañada de una fusión parcial en la cuña mantélica produciendo la formación de piroxenitas. Los datos producidos mediante la microsonda-iónica sugieren un único episodio metamórfico de alta presión alrededor de los 392 Ma para todas las rocas analizada

Arrays of noisy bistable elements with nearest neighbor coupling: equilibrium and stochastic resonance

This work deals with finite arrays of bistable systems with nearest neighbor coupling. We focus on the statistical equilibrium of a collective variable, as well as its response to a weak time periodic perturbation. By means of numerical simulations we demonstrate the sharp contrast between the system behaviors depending on whether the coupling parameter is positive or negative. The stochastic resonance phenomenon is analyzed in terms of the power spectral amplification and the signal-to-noise ratio of the collective variable. Even though those quantifiers show the typical non-monotonic dependence on the noise strength, they lack, for negative coupling, the large enhancement which has been previously observed for arrays with positive coupling