Andres R. R. Papa

Advantage of wavelet technique to highlight the observed geomagnetic perturbations linked to the Chilean tsunami (2010)

The vertical component (Z) of the geomagnetic field observed by ground-based observatories of the International Real-Time Magnetic Observatory Network has been used to analyze the induced magnetic fields produced by the movement of a tsunami, electrically conducting sea water through the geomagnetic field. We focus on the survey of minutely sampled geomagnetic variations induced by the tsunami of 27 February 2010 at Easter Island (IPM) and Papeete (PPT) observatories. In order to detect the tsunami disturbances in the geomagnetic data, we used wavelet techniques. We have observed an 85% correlation between the Z component variation and the tide gauge measurements in period range of 10 to 30 min which may be due to two physical mechanisms: gravity waves and the electric currents in the sea. As an auxiliary tool to verify the disturbed magnetic fields, we used the maximum variance analysis (MVA). At PPT, the analyses show local magnetic variations associated with the tsunami arriving in advance of sea surface fluctuations by about 2 h. The first interpretation of the results suggests that wavelet techniques and MVA can be effectively used to characterize the tsunami contributions to the geomagnetic field and further used to calibrate tsunami models and implemented to real-time analysis for forecast tsunami scenarios.

Criticality in a simple model for brain functioning

Abstract We introduce a simple model for a set of interacting idealized neurons. The model presents a self-organized state in which avalanches of all sizes are observed and activity is detected in the whole extension of the simulated system without a typical length scale. The basic elements of the model are endowed with the main features of a neuron function. On this basis it is speculated that the collective system that they form, i.e., the brain, could display self-organized criticality in some situations.

Study of local regularities in solar wind data and ground magnetograms

Abstract Interplanetary coronal mass ejections (ICMEs) can reach the Earth׳s magnetosphere causing magnetic disturbances. For monitoring purposes, some satellites measure the interplanetary parameters which are related to energy transfer from solar wind into magnetosphere, while ground-based magnetometers measure the geomagnetic disturbance effects. Data from the ACE satellite and from some representative magnetometers were examined here via discrete wavelet transform (DWT). The increase in the amplitude of wavelet coefficients of solar wind parameters and geomagnetic field data is well-correlated with the arrival of the shock and sheath regions, and the sudden storm commencement and main phase, respectively. As an auxiliary tool to verify the disturbed magnetic fields identified by the DWT, we developed a new approach called effectiveness wavelet coefficient (EWC) methodology. The first interpretation of the results suggests that DWT and EWC can be effectively used to characterize the fluctuations on the solar wind parameters and their contributions to the geomagnetic field. Further, this kind of technique could be implemented in quasi real-time to facilitate the identification of the shock and the passage of the sheath region which sometimes can be followed by geoeffective magnetic clouds. Also, the technique shows to be very useful for the identification of time intervals in the dataset during geomagnetic storms which are associated to interplanetary parameters under very well defined conditions. It allows selecting ideal events for investigation of magnetic reconnection in order to highlight in a more precise manner the mechanisms existing in the electrodynamical coupling between the solar wind and the magnetosphere.

Similarities between the dynamics of geomagnetic signal and of heartbeat intervals

We analyze the dynamics of a widely used measure of geomagnetic activity —the Dst index— and compare our findings with those found in healthy human heartbeat dynamics. We show that the Dst index belongs to a special class of complex signals, exhibiting long-range temporal correlations, multifractality and scale-invariant distribution. Specifically, we find that i) Dst series and magnitude series of Dst increments are long-range correlated while the sign series of Dst increments is anti-correlated; ii) the scaling exponents that govern these temporal correlations increase with geomagnetic activity; iii) Dst series exhibit multifractal behavior; iv) the multifractal spectra that characterize Dst series are practically independent of the geomagnetic activity; and v) the distribution of Dst increments exhibits scale invariance at a wide range of time scales. These results are in surprising agreement with those found in the study of heartbeat intervals. Our findings are consistent with the concept of universality in complex systems and may contribute to a better understanding of the mechanisms that govern geomagnetic activity.

Simulation of geomagnetic reversals through magnetic critical models

We use numerical simulations of a well-known phase-transition model to study reversals of the geomagnetic field. Each ring current in the geodynamo was supposed to behave as a magnetic spin while the magnetization of the model was supposed to be proportional to the Earths magnetic dipole. We have performed a size-dependence study of the calculated quantities. Power laws were obtained for the distribution of times between reversals. Some of our results are closer to actual ones than the corresponding to previous simulations. For the largest systems that we have simulated the exponent of the power law tends towards values very near -1.5, generally accepted as the right value for this phenomenon. Some possible trends for future works are advanced.

Small world picture of worldwide seismic events

The understanding of long-distance relations between seismic activities has for long been of interest to seismologists and geologists. In this paper we have used data from the worldwide earthquake catalog for the period between 1972 and 2011 to generate a network of sites around the world for earthquakes with magnitude m≥4.5 in the Richter scale. After the network construction, we have analyzed the results under two viewpoints. First, in contrast to previous works, which have considered just small areas, we showed that the best fitting for networks of seismic events is not a pure power law, but a power law with exponential cutoff; we also have found that the global network presents small-world properties. Second, we have found that the time intervals between successive earthquakes have a cumulative probability distribution well fitted by nontraditional functional forms. The implications of our results are significant because they seem to indicate that seisms around the world are not independent. In this paper we provide evidence to support this argument.

Explorando sistemas hamiltonianos: estudo analítico

A double pendulum submitted to external torques is employed to introduce some basic fundamentals of dynamical systems theory to physics undergraduate courses, soon after the student takes the analytical mechanics discipline. This system is a good example for the introduction of such techniques. Hamiltons equations of motion indicate the existence of stationary solutions (equilibrium points) in the phase space of the model. The identification of the nature of these points allows the description of the system dynamics around their linear neighborhood. Moreover, qualitative results obtained in the linear neighborhood of a fixed point are not changed by the introduction of non-vanishing constant external torques. This work emphasizes the analysis of the linear neighborhood of the equilibrium points.

A local-field-type model for immunological systems: time evolution in real and shape spaces

We introduce a new model for the interaction of immunological cells that takes into account their location in real space. Each one of the model cells mimics the real B cells in the sense that they detect antigens and they are also capable of reproducing themselves. We perform computer simulations for the simplest cases. The main differences between the results obtained within this model and those obtained through the usual models, which do not consider a real space, concern the final stationary states. In mean field calculations not only the system as a whole but also each individual cell population reach an equilibrium state. In the present approach the entire system reaches a stationary state, but the individual populations present strong fluctuations, at least for the explored range of parameters. We exhibit that, in spite of the simplicity of the present model, interesting real-space effects can take place.

The Small World of Seismic Events

The understanding of long-distance relations between seismic activities has for long been of interest to seismologists and geologists. In this paper we have used data from the world-wide earthquake catalog for the period between 1972 and 2011, to generate a network of sites around the world for earthquakes with magnitude m ≥ 4.5 on the Richter scale. After the network construction, we have analyzed the results under two viewpoints. Firstly, in contrast to previous works, which have considered just small areas, we showed that the best fitting for networks of seismic events is not a pure power law, but a power law with an exponential cutoff. We also have found that the global network presents small-world properties. The implications of our results are discussed.

Towards evidence of long-range correlations in shallow seismic activities

In this work, we introduce a new methodology to construct a network of epicenters that avoids problems found in well-established methodologies when they are applied to global catalogs of seisms. The new methodology involves essentially the introduction of a time window which works as a temporal filter. Our approach is more generic and for small regions the results coincide with previous findings. The network constructed with that model has small-world properties and the distribution of node connectivity follows a non-traditional