Use of spectral kurtosis for improving signal to noise ratio of acoustic emission signal from defective bearings

The use of Acoustic Emission (AE) to monitor the condition of roller bearings in rotating machinery is growing in popularity. This investigation is centred on the application of Spectral Kurtosis (SK) as a denoising tool able to enhance the bearing fault features from an AE signal. This methodology was applied to AE signals acquired from an experimental investigation where different size defects were seeded on a roller bearing. The results suggest that the signal to noise ratio can be significantly improved using SK

Axions in gravity with torsion

We study a scenario allowing a solution of the strong charge parity problem via the Peccei-Quinn mechanism, implemented in gravity with torsion. In this framework there appears a torsion-related pseudoscalar field known as Kalb-Ramond axion. We compare it with the so-called Barbero-Immirzi axion recently proposed in the literature also in the context of the gravity with torsion. We show that they are equivalent from the viewpoint of the effective theory. The phenomenology of these torsion-descended axions is completely determined by the Planck scale without any additional model parameters. These axions are very light and very weakly interacting with ordinary matter. We briefly comment on their astrophysical and cosmological implications in view of the recent BICEP2 and Planck data.Comment: 7 pages, no figures, comments and references added, published versio

Lattice points in rational ellipsoids

AbstractWe combine exponential sums, character sums and Fourier coefficients of automorphic forms to improve the best known upper bound for the lattice error term associated to rational ellipsoids

Metrics for Performance Quantification of Adaptive Mesh Refinement

Non-uniform, dynamically adaptive meshes are a useful tool for reducing computational complexities for geophysical simulations that exhibit strongly localised features such as is the case for tsunami, hurricane or typhoon prediction. Using the example of a shallow water solver, this study explores a set of metrics as a tool to distinguish the performance of numerical methods using adaptively refined versus uniform meshes independent of computational architecture or implementation. These metrics allow us to quantify how a numerical simulation benefits from the use of adaptive mesh refinement. The type of meshes we are focusing on are adaptive triangular meshes that are non-uniform and structured. Refinement is controlled by physics-based indicators that capture relevant physical processes and determine the areas of mesh refinement and coarsening. The proposed performance metrics take into account a number of characteristics of numerical simulations such as numerical errors, spatial resolution, as well as computing time. Using a number of test cases we demonstrate that correlating different quantities offers insight into computational overhead, the distribution of numerical error across various mesh resolutions as well as the evolution of numerical error and run-time per degree of freedom

Use of 2% hydroxypropyl methylcellulose to prevent the corneal swelling during the in vitro mechanical characterization

The aim of this study was to assess the use of 2% HPMC during in vitro uniaxial tensile tests, with corneal strips immediately obtained or after storing the eyes for 24¿h in 0.9% NaCl solution at 4¿¿. The purpose was to establish a standardized procedure to prevent phenomena which can modify the mechanical properties of the tissue. Rabbit eyes were divided into four groups. Group A had seven eyes that were preserved in NaCl solution for 24¿h before testing. Group B had seven eyes that were immediately tested. In both groups, to prevent both swelling and dehydration, 2% hydroxypropyl methylcellulose (2% HPMC) was applied. Group C had seven eyes that were preserved in NaCl solution for 24¿h before testing. Group D had seven eyes that were immediately tested. In both groups, HPMC was not applied. Regarding the mechanical response, groups with HPMC showed similar Cauchy stress–stretch curves and there were no statistically significant differences at 5%, 10% and 15% strain between them, which mean that both showed similar mechanical behavior. The same result was obtained between groups without HPMC. However, for coupled groups with and without HPMC, statistically significant differences at 10% and 15% strain were observed. On the other hand, when grouped by storage time, statistically significant differences were found between groups that had eyes preserved for 24¿h with and without HPMC, respectively, as well as between groups immediately tested with and without HPMC, respectively, at 15% strain. Nevertheless, if coupled groups were considered, between groups that were preserved for 24¿h in NaCl before testing and groups that were immediately tested, no statistically significant differences were obtained. In addition, the Cauchy stress–stretch curves of groups without HPMC showed a decreasing slope of the linear part (strain¿>¿8%) of the graph during the experiment. In summary, the use of HPMC during the handling of the tissue from excision to testing seems to prevent both swelling and dehydration

Birth, death and diffusion of interacting particles

Individual-based models of chemical or biological dynamics usually consider individual entities diffusing in space and performing a birth-death type dynamics. In this work we study the properties of a model in this class where the birth dynamics is mediated by the local, within a given distance, density of particles. Groups of individuals are formed in the system and in this paper we concentrate on the study of the properties of these clusters (lifetime, size, and collective diffusion). In particular, in the limit of the interaction distance approaching the system size, a unique cluster appears which helps to understand and characterize the clustering dynamics of the model.Comment: 15 pages, 6 figures, Iop style. To appear in Journal of Physics A: Condensed matte

Kinematic studies of transport across an island wake, with application to the Canary islands

Transport from nutrient-rich coastal upwellings is a key factor influencing biological activity in surrounding waters and even in the open ocean. The rich upwelling in the North-Western African coast is known to interact strongly with the wake of the Canary islands, giving rise to filaments and other mesoscale structures of increased productivity. Motivated by this scenario, we introduce a simplified two-dimensional kinematic flow describing the wake of an island in a stream, and study the conditions under which there is a net transport of substances across the wake. For small vorticity values in the wake, it acts as a barrier, but there is a transition when increasing vorticity so that for values appropriate to the Canary area, it entrains fluid and enhances cross-wake transport.Comment: 28 pages, 13 figure

Socioeconomic background and academic achievement. The case of an argentine university

El objetivo de la investigación es determinar mediante regresiones estadísticas las relaciones entre las características socioeconómicas de los alumnos de las carreras de grado de la Universidad Nacional del Nordeste (UNNE, Argentina) y sus resultados académicos, y compararlos con los hallazgos de estudios similares efectuados en otras universidades nacionales. Se encuentra evidencia contundente de que las variables de Nivel Socioeconómico (NSE) son significativas para explicar las diferencias de rendimiento académico entre los alumnos de las facultades analizadas. Las variables que se han utilizado como indicadores de NSE elevado han presentado una correlación positiva, y las variables que se emplearon como indicadores de NSE más bajo han presentado una correlación negativa. Las variables sexo femenino, edad, estado civil casado y situación laboral inactiva están asociadas a un mejor rendimiento académico, mientras que las variables cantidad de hijos del estudiante, situación laboral ocupado, situación laboral desocupado, ausencia de cobertura médica y beneficiario de planes sociales están relacionadas a menores desempeños académicos. En materia de género, el hallazgo más relevante se manifiesta en los resultados de las estudiantes mujeres con hijos: su rendimiento es notoriamente inferior al de los estudiantes hombres con hijosThe aim of our research is to assess the relationships between socioeconomic characteristics of students in undergraduate courses of Northeastern University (UNNE, Argentina) and their academic results using statistical regression, and to compare the findings with the ones obtained in similar studies in other national universities. There is strong evidence that variables of Socioeconomic Status (SES) are significant in explaining the differences in academic achievement between students of the several schools. The variables used as indicators of high SES presented a positive correlation, and variables that were used as indicators of lower SES have presented a negative correlation. The variables female sex, age, married marital status and inactive employment status are associated with better academic performance, while the variables number of children of the student, busy employment status, employment status, medical coverage, and beneficiary of social plans are related to lower academic performance. Regarding gender, the most important finding is that female students with children have lower performance than male students with childre

Clustering, advection and patterns in a model of population dynamics with neighborhood-dependent rates

We introduce a simple model of population dynamics which considers birth and death rates for every individual that depend on the number of particles in its neighborhood. The model shows an inhomogeneous quasistationary pattern with many different clusters of particles. We derive the equation for the macroscopic density of particles, perform a linear stability analysis on it, and show that there is a finite-wavelength instability leading to pattern formation. This is the responsible for the approximate periodicity with which the clusters of particles arrange in the microscopic model. In addition, we consider the population when immersed in a fluid medium and analyze the influence of advection on global properties of the model.Comment: Some typos and some problems with the figures correcte

Assessment of corneal biomechanical properties and intraocular pressure in myopic Spanish healthy population

Purpose. To examine biomechanical parameters of the cornea in myopic eyes and their relationship with the degree of myopia in a western healthy population. Methods. Corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intraocular pressure (IOP), and corneal compensated IOP (IOPcc) were measured using the ocular response analyzer (ORA) in 312 eyes of 177 Spanish subjects aged between 20 and 56 years. Refraction was expressed as spherical equivalent (SE), which ranged from 0 to -16.50 diopters (D) (mean: -3.88 ± 2.90 D). Subjects were divided into four groups according to their refractive status: group 1 or control group: emmetropia (-0.50 = SE 0.05); nevertheless, IOPcc was significantly higher in the moderatelymyopic (15.47±2.47mmHg) and highlymyopic (16.14± 2.59mmHg) groups than in the emmetropia (15.15 ± 2.06mmHg) and low myopia groups (14.53 ± 2.37mmHg). No correlation between age and the measured parameters was found. CH and IOPcc were weakly but significantly correlated with SE (¿ = 0.171, ¿ = 0.002 and ¿ = -0.131, ¿ = 0.021, resp.). Conclusions. Present study showed only a very weak, but significant, correlation between CHand refractive error, with CH being lower in both moderately and highlymyopic eyes than that in the emmetropic and low myopic eyes.These changes in biomechanical properties of the cornea may have an impact on IOP measurement, increasing the risk of glaucom