Online social networks are ubiquitous, have billions of users, and produce large amounts of data.... more Online social networks are ubiquitous, have billions of users, and produce large amounts of data. While platforms like Reddit are based on a forum-like organization where users gather around topics, Facebook and Twitter implement a concept in which individuals represent the primary entity of interest. This makes them natural testbeds for exploring individual behavior in large social networks. Underlying these individual-based platforms is a network whose “friend” or “follower” edges are of binary nature only and therefore do not necessarily reflect the level of acquaintance between pairs of users. In this paper,we present the network of acquaintance “strengths” underlying the German Twittersphere. To that end, we make use of the full non-verbal information contained in tweet–retweet actions to uncover the graph of social acquaintances among users, beyond pure binary edges. The social connectivity between pairs of users is weighted by keeping track of the frequency of shared content ...
Dependence of the coefficients (a) <i>C</i><sub>0</sub>, (b) <i>C</i><sub>1</sub>, and (c) <i>C</i><sub>2</sub> in Eq (4) on the activation frequency <i>f</i>; (d) the <i>R</i><sup>2</sup> values of the corresponding fits
Dependence of the coefficients in Eq (5) on the activation frequency <i>f</i>, where the symbol assignment refers to the different APD<sub><i>n</i></sub> as given in the inset of the last graph, which shows the <i>R</i><sup>2</sup> values of the corresponding fits [Eq (5)]
De tudo houve um começo... e tudo errou... in «Quase», Mário de Sá Carneiro Porque eu sou do tama... more De tudo houve um começo... e tudo errou... in «Quase», Mário de Sá Carneiro Porque eu sou do tamanho do que vejo. in «Guardador de Rebanhos», Alberto Caeiro * Poderá estranhar-se que esta revista insira no seu conteúdo um artigo de um ateu confesso. No entanto, não nos parece descabido nem inconveniente. Primeiro, porque o autor, materialista confesso e assumido, defende, coerente e honestamente, o seu modo de ver o problema do além da morte de modo totalmente respeitoso em relação aos crentes que defendem a existência de uma vida eterna. Segundo, porque as ideias expostas se inscrevem na dinâmica do diálogo com os não crentes, diálogo que hoje a Igreja propõe aos seus filhos, sendo que a estes pode e deve interessar conhecerem o ponto de vista de quem pensa diferentemente deles. Foi aliás nesta perspectiva perspectiva típica de um «átrio dos gentios» que o autor participou, a convite, na XXI Semana de Estudos Teológicos da Faculdade de Teologia-Braga, fazendo, em mesa redonda e com vista ao diálogo, o contraponto do ponto de vista do crente, apresentado pelo Prof. João Duque. Nota da Direcção.
We introduce two improvements in the numerical scheme to simulate collision and slow shearing of ... more We introduce two improvements in the numerical scheme to simulate collision and slow shearing of irregular particles. First, we propose an alternative approach based on simple relations to compute the frictional contact forces. The approach improves efficiency and accuracy of the Discrete Element Method (DEM) when modeling the dynamics of the granular packing. We determine the proper upper limit for the integration step in the standard numerical scheme using a wide range of material parameters. To this end, we study the kinetic energy decay in a stress controlled test between two particles. Second, we show that the usual way of defining the contact plane between two polygonal particles is, in general, not unique which leads to discontinuities in the direction of the contact plane while particles move. To solve this drawback, we introduce an accurate definition for the contact plane based on the shape of the overlap area between touching particles, which evolves continuously in time.
We study the influence of particle shape anisotropy on the occurrence of avalanches in sheared gr... more We study the influence of particle shape anisotropy on the occurrence of avalanches in sheared granular media. We use molecular dynamic simulations to calculate the relative movement of two tectonic plates. Our model considers irregular polygonal particles constituting the material within the shear zone. We find that the magnitude of the avalanches is approximately independent on particle shape and in good agreement with the Gutenberg-Richter law, but the aftershock sequences are strongly influenced by the particle anisotropy yielding variations on the exponent characterizing the empirical Omori's law. Our findings enable one to identify the presence of anisotropic particles at the macromechanical level only by observing the avalanche sequences of real faults. In addition, we calculate the probability of occurrence of an avalanche for given values of stiffness or frictional strength and observe also a significant influence of the particle anisotropy.
We analyze the empirical series of malaria incidence, using the concepts of autocorrelation, Hurs... more We analyze the empirical series of malaria incidence, using the concepts of autocorrelation, Hurst exponent and Shannon entropy with the aim of uncovering hidden variables in those series. From the simulations of an agent model for malaria spreading, we first derive models of the malaria incidence, the Hurst exponent and the entropy as functions of gametocytemia, measuring the infectious power of a mosquito to a human host. Second, upon estimating the values of three observables—incidence, Hurst exponent and entropy—from the data set of different malaria empirical series we predict a value of the gametocytemia for each observable. Finally, we show that the independent predictions show considerable consistency with only a few exceptions which are discussed in further detail.
With the aim of improving the reconstruction of stochastic evolution equations from empirical tim... more With the aim of improving the reconstruction of stochastic evolution equations from empirical time-series data, we derive a full representation of the generator of the Kramers–Moyal operator via a power-series expansion of the exponential operator. This expansion is necessary for deriving the different terms in a stochastic differential equation. With the full representation of this operator, we are able to separate finite-time corrections of the power-series expansion of arbitrary order into terms with and without derivatives of the Kramers–Moyal coefficients. We arrive at a closed-form solution expressed through conditional moments, which can be extracted directly from time-series data with a finite sampling intervals. We provide all finite-time correction terms for parametric and non-parametric estimation of the Kramers–Moyal coefficients for discontinuous processes which can be easily implemented—employing Bell polynomials—in time-series analyses of stochastic processes. With ex...
Coherence in Complex Networks of Oscillators; ; ; The logistic map and the route to chaos : from the beginnings to modern applications
We study fully synchronized (coherent) states in complex networks of chaotic oscillators, reviewi... more We study fully synchronized (coherent) states in complex networks of chaotic oscillators, reviewing the analytical approach of determining the stability conditions for synchronizability and comparing them with numerical criteria. As an example, we present detailed results for networks of chaotic logistic maps having three different scale-free topologies: random scale-free topology, deterministic pseudo-fractal scale-free network and Apollonian network. For random scale-free topology we find that the lower boundary of the synchronizability region scales approximately as k−μ, where k is the outgoing connectivity and μ depends on the local nonlinearity. For deterministic scale-free networks coherence is observed only when the coupling is heterogeneous, namely when it is proportional to some power of the neighbour connectivity. In all cases, stability conditions are determined from the eigenvalue spectrum of the Laplacian matrix and agree well with numerical results based on histograms ...
Preference aggregation in Group Decision Making (GDM) is a substantial problem that has received ... more Preference aggregation in Group Decision Making (GDM) is a substantial problem that has received a lot of research attention. Decision problems involving fuzzy preference relations constitute an important class within GDM. Legacy approaches dealing with the latter type of problems can be classified into indirect approaches, which involve deriving a group preference matrix as an intermediate step, and direct approaches, which deduce a group preference ranking based on individual preference rankings. Although the work on indirect approaches has been extensive in the literature, there is still a scarcity of research dealing with the direct approaches. In this paper we present a direct approach towards aggregating several fuzzy preference relations on a set of alternatives into a single weighted ranking of the alternatives. By mapping the pairwise preferences into transitions probabilities, we are able to derive a preference ranking from the stationary distribution of a stochastic matrix. Interestingly, the ranking of the alternatives obtained with our method corresponds to the optimizer of the Maximum Likelihood Estimation of a particular Bradley-Terry-Luce model. Furthermore, we perform a theoretical sensitivity analysis of the proposed method supported by experimental results and illustrate our approach towards GDM with a concrete numerical example. This work opens avenues for solving GDM problems using elements of probability theory, and thus, provides a sound theoretical fundament as well as plausible statistical interpretation for the aggregation of expert opinions in GDM.
Construction of an Inexpensive Eye Tracker for Social Inclusion and Education
Lecture Notes in Computer Science, 2020
In this paper we described how to build an inexpensive eye-tracker and to apply it to social incl... more In this paper we described how to build an inexpensive eye-tracker and to apply it to social inclusion and educational activities in schools. The building of the device includes both the construction of the eye-tracking headset as well as the implementation of the code for translating eye trajectories into output data which can afterwards be analyzed and modeled. The procedure is cheap and can be easily implemented in high-schools and first-years undergraduate courses, to teach specific matters in computer sciences, physical sciences and mathematics. Moreover, we also discuss up to which extension such a cheap device can substitute commercial solutions for promoting social inclusion, particularly to develop empathy in communities by showing the difficulties behind eye-movement languages used by non-verbal paralyzed individuals.
Using an agent-based model of malaria, we present numerical evidence that in communities of indiv... more Using an agent-based model of malaria, we present numerical evidence that in communities of individuals having an affinity varying within a broad range of values, disease transmission may increase up to 300%. Moreover, our findings provide new insight into how to combine different strategies for the prevention of malaria transmission. In particular, we uncover a relationship between the level of heterogeneity and the level of conventional and unconventional anti-malarial drug administration (ivermectin and gametocidal agents), which, when taken together, will define a control parameter, tuning between disease persistence and elimination. Finally, we also provide evidence that the entomological inoculation rate, as well as the product between parasite and sporozoite rates are both good indicators of malaria incidence in the presence of heterogeneity in disease transmission and may configure a possible improvement in that setting, upon classical standard measures such as the basic rep...
2017 Computing in Cardiology Conference (CinC), Sep 14, 2017
We present a method for modelling case-specific action potentials (APs) based on a simple model f... more We present a method for modelling case-specific action potentials (APs) based on a simple model for electric wave propagation combined with an optimization procedure that searches the best combination of three model parameter values for a given action potential. The method is applied to a set of 70 APs, showing deviations around 10%. This method can be useful for prognosing possible pathological scenarios of a specific patient, based on data from electrocardiagrams.
Online social networks are ubiquitous, have billions of users, and produce large amounts of data.... more Online social networks are ubiquitous, have billions of users, and produce large amounts of data. While platforms like Reddit are based on a forum-like organization where users gather around topics, Facebook and Twitter implement a concept in which individuals represent the primary entity of interest. This makes them natural testbeds for exploring individual behavior in large social networks. Underlying these individual-based platforms is a network whose “friend” or “follower” edges are of binary nature only and therefore do not necessarily reflect the level of acquaintance between pairs of users. In this paper,we present the network of acquaintance “strengths” underlying the German Twittersphere. To that end, we make use of the full non-verbal information contained in tweet–retweet actions to uncover the graph of social acquaintances among users, beyond pure binary edges. The social connectivity between pairs of users is weighted by keeping track of the frequency of shared content ...
Dependence of the coefficients (a) <i>C</i><sub>0</sub>, (b) <i>C</i><sub>1</sub>, and (c) <i>C</i><sub>2</sub> in Eq (4) on the activation frequency <i>f</i>; (d) the <i>R</i><sup>2</sup> values of the corresponding fits
Dependence of the coefficients in Eq (5) on the activation frequency <i>f</i>, where the symbol assignment refers to the different APD<sub><i>n</i></sub> as given in the inset of the last graph, which shows the <i>R</i><sup>2</sup> values of the corresponding fits [Eq (5)]
De tudo houve um começo... e tudo errou... in «Quase», Mário de Sá Carneiro Porque eu sou do tama... more De tudo houve um começo... e tudo errou... in «Quase», Mário de Sá Carneiro Porque eu sou do tamanho do que vejo. in «Guardador de Rebanhos», Alberto Caeiro * Poderá estranhar-se que esta revista insira no seu conteúdo um artigo de um ateu confesso. No entanto, não nos parece descabido nem inconveniente. Primeiro, porque o autor, materialista confesso e assumido, defende, coerente e honestamente, o seu modo de ver o problema do além da morte de modo totalmente respeitoso em relação aos crentes que defendem a existência de uma vida eterna. Segundo, porque as ideias expostas se inscrevem na dinâmica do diálogo com os não crentes, diálogo que hoje a Igreja propõe aos seus filhos, sendo que a estes pode e deve interessar conhecerem o ponto de vista de quem pensa diferentemente deles. Foi aliás nesta perspectiva perspectiva típica de um «átrio dos gentios» que o autor participou, a convite, na XXI Semana de Estudos Teológicos da Faculdade de Teologia-Braga, fazendo, em mesa redonda e com vista ao diálogo, o contraponto do ponto de vista do crente, apresentado pelo Prof. João Duque. Nota da Direcção.
We introduce two improvements in the numerical scheme to simulate collision and slow shearing of ... more We introduce two improvements in the numerical scheme to simulate collision and slow shearing of irregular particles. First, we propose an alternative approach based on simple relations to compute the frictional contact forces. The approach improves efficiency and accuracy of the Discrete Element Method (DEM) when modeling the dynamics of the granular packing. We determine the proper upper limit for the integration step in the standard numerical scheme using a wide range of material parameters. To this end, we study the kinetic energy decay in a stress controlled test between two particles. Second, we show that the usual way of defining the contact plane between two polygonal particles is, in general, not unique which leads to discontinuities in the direction of the contact plane while particles move. To solve this drawback, we introduce an accurate definition for the contact plane based on the shape of the overlap area between touching particles, which evolves continuously in time.
We study the influence of particle shape anisotropy on the occurrence of avalanches in sheared gr... more We study the influence of particle shape anisotropy on the occurrence of avalanches in sheared granular media. We use molecular dynamic simulations to calculate the relative movement of two tectonic plates. Our model considers irregular polygonal particles constituting the material within the shear zone. We find that the magnitude of the avalanches is approximately independent on particle shape and in good agreement with the Gutenberg-Richter law, but the aftershock sequences are strongly influenced by the particle anisotropy yielding variations on the exponent characterizing the empirical Omori's law. Our findings enable one to identify the presence of anisotropic particles at the macromechanical level only by observing the avalanche sequences of real faults. In addition, we calculate the probability of occurrence of an avalanche for given values of stiffness or frictional strength and observe also a significant influence of the particle anisotropy.
We analyze the empirical series of malaria incidence, using the concepts of autocorrelation, Hurs... more We analyze the empirical series of malaria incidence, using the concepts of autocorrelation, Hurst exponent and Shannon entropy with the aim of uncovering hidden variables in those series. From the simulations of an agent model for malaria spreading, we first derive models of the malaria incidence, the Hurst exponent and the entropy as functions of gametocytemia, measuring the infectious power of a mosquito to a human host. Second, upon estimating the values of three observables—incidence, Hurst exponent and entropy—from the data set of different malaria empirical series we predict a value of the gametocytemia for each observable. Finally, we show that the independent predictions show considerable consistency with only a few exceptions which are discussed in further detail.
With the aim of improving the reconstruction of stochastic evolution equations from empirical tim... more With the aim of improving the reconstruction of stochastic evolution equations from empirical time-series data, we derive a full representation of the generator of the Kramers–Moyal operator via a power-series expansion of the exponential operator. This expansion is necessary for deriving the different terms in a stochastic differential equation. With the full representation of this operator, we are able to separate finite-time corrections of the power-series expansion of arbitrary order into terms with and without derivatives of the Kramers–Moyal coefficients. We arrive at a closed-form solution expressed through conditional moments, which can be extracted directly from time-series data with a finite sampling intervals. We provide all finite-time correction terms for parametric and non-parametric estimation of the Kramers–Moyal coefficients for discontinuous processes which can be easily implemented—employing Bell polynomials—in time-series analyses of stochastic processes. With ex...
Coherence in Complex Networks of Oscillators; ; ; The logistic map and the route to chaos : from the beginnings to modern applications
We study fully synchronized (coherent) states in complex networks of chaotic oscillators, reviewi... more We study fully synchronized (coherent) states in complex networks of chaotic oscillators, reviewing the analytical approach of determining the stability conditions for synchronizability and comparing them with numerical criteria. As an example, we present detailed results for networks of chaotic logistic maps having three different scale-free topologies: random scale-free topology, deterministic pseudo-fractal scale-free network and Apollonian network. For random scale-free topology we find that the lower boundary of the synchronizability region scales approximately as k−μ, where k is the outgoing connectivity and μ depends on the local nonlinearity. For deterministic scale-free networks coherence is observed only when the coupling is heterogeneous, namely when it is proportional to some power of the neighbour connectivity. In all cases, stability conditions are determined from the eigenvalue spectrum of the Laplacian matrix and agree well with numerical results based on histograms ...
Preference aggregation in Group Decision Making (GDM) is a substantial problem that has received ... more Preference aggregation in Group Decision Making (GDM) is a substantial problem that has received a lot of research attention. Decision problems involving fuzzy preference relations constitute an important class within GDM. Legacy approaches dealing with the latter type of problems can be classified into indirect approaches, which involve deriving a group preference matrix as an intermediate step, and direct approaches, which deduce a group preference ranking based on individual preference rankings. Although the work on indirect approaches has been extensive in the literature, there is still a scarcity of research dealing with the direct approaches. In this paper we present a direct approach towards aggregating several fuzzy preference relations on a set of alternatives into a single weighted ranking of the alternatives. By mapping the pairwise preferences into transitions probabilities, we are able to derive a preference ranking from the stationary distribution of a stochastic matrix. Interestingly, the ranking of the alternatives obtained with our method corresponds to the optimizer of the Maximum Likelihood Estimation of a particular Bradley-Terry-Luce model. Furthermore, we perform a theoretical sensitivity analysis of the proposed method supported by experimental results and illustrate our approach towards GDM with a concrete numerical example. This work opens avenues for solving GDM problems using elements of probability theory, and thus, provides a sound theoretical fundament as well as plausible statistical interpretation for the aggregation of expert opinions in GDM.
Construction of an Inexpensive Eye Tracker for Social Inclusion and Education
Lecture Notes in Computer Science, 2020
In this paper we described how to build an inexpensive eye-tracker and to apply it to social incl... more In this paper we described how to build an inexpensive eye-tracker and to apply it to social inclusion and educational activities in schools. The building of the device includes both the construction of the eye-tracking headset as well as the implementation of the code for translating eye trajectories into output data which can afterwards be analyzed and modeled. The procedure is cheap and can be easily implemented in high-schools and first-years undergraduate courses, to teach specific matters in computer sciences, physical sciences and mathematics. Moreover, we also discuss up to which extension such a cheap device can substitute commercial solutions for promoting social inclusion, particularly to develop empathy in communities by showing the difficulties behind eye-movement languages used by non-verbal paralyzed individuals.
Using an agent-based model of malaria, we present numerical evidence that in communities of indiv... more Using an agent-based model of malaria, we present numerical evidence that in communities of individuals having an affinity varying within a broad range of values, disease transmission may increase up to 300%. Moreover, our findings provide new insight into how to combine different strategies for the prevention of malaria transmission. In particular, we uncover a relationship between the level of heterogeneity and the level of conventional and unconventional anti-malarial drug administration (ivermectin and gametocidal agents), which, when taken together, will define a control parameter, tuning between disease persistence and elimination. Finally, we also provide evidence that the entomological inoculation rate, as well as the product between parasite and sporozoite rates are both good indicators of malaria incidence in the presence of heterogeneity in disease transmission and may configure a possible improvement in that setting, upon classical standard measures such as the basic rep...
2017 Computing in Cardiology Conference (CinC), Sep 14, 2017
We present a method for modelling case-specific action potentials (APs) based on a simple model f... more We present a method for modelling case-specific action potentials (APs) based on a simple model for electric wave propagation combined with an optimization procedure that searches the best combination of three model parameter values for a given action potential. The method is applied to a set of 70 APs, showing deviations around 10%. This method can be useful for prognosing possible pathological scenarios of a specific patient, based on data from electrocardiagrams.
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Papers by Pedro G. Lind