arXiv subjects

Celia Anteneodo

Publications and source records attributed to Celia Anteneodo.

At least 37 records · Page 2Linked to original sources

arXiv2021

Analytical results for a minimalist thermal diode

We consider a system consisting of two interacting classical particles, each one subject to an on-site potential and to a Langevin thermal bath. We analytically calculate the heat current that can be established through the system when the bath temperatures are different, for weak nonlinear forces. We explore the conditions under which the diode effect emerges when inverting the temperature difference. Despite the simplicity of this two-particle diode, an intricate dependence on the system parameters is put in evidence. Moreover, behaviors reported for long chains of particles can be extracted, for instance, the dependence of the flux with the interfacial stiffness and type of forces present, as well as the dependencies on the temperature required for rectification. These analytical results can be a tool to foresee the distinct role that diverse types of nonlinearity and asymmetry play in thermal conduction and rectification.

cond-mat.stat-mech↗

arXiv2021

Non-normalizable quasi-equilibrium solution of the Fokker-Planck equation for nonconfining fields

We investigate the overdamped Langevin motion for particles in a potential well that is asymptotically flat. When the potential well is deep compared to temperature, physical observables like the mean square displacement are essentially time-independent over a long time interval, the stagnation epoch. However the standard Boltzmann-Gibbs (BG) distribution is non-normalizable, given that the usual partition function is divergent. For this regime, we have previously shown that a regularization of BG statistics allows the prediction of the values of dynamical and thermodynamical observables in the non-normalizable quasi-equilibrium state. In this work, based on the eigenfunction expansion of the time-dependent solution of the associated Fokker-Planck equation with free boundary conditions, we obtain an approximate time-independent solution of the BG form, valid for times which are long, but still short compared to the exponentially large escape time. The escaped particles follow a general free-particle statistics, where the solution is a an error function, shifted due to the initial struggle to overcome the potential well. With the eigenfunction solution of the Fokker-Planck equation in hand, we show the validity of the regularized BG statistics and how it perfectly describes the time-independent regime though the quasi-stationary state is non-normalizable.

cond-mat.stat-mech↗

arXiv2020

Regularized Boltzmann-Gibbs statistics for a Brownian particle in a non-confining field

We consider an overdamped Brownian particle subject to an asymptotically flat potential with a trap of depth $U_0$ around the origin. When the temperature is small compared to the trap depth ($ξ=k_B T/U_0 \ll 1$), there exists a range of timescales over which physical observables remain practically constant. This range can be very long, of the order of the Arrhenius factor ${\rm e}^{1/ξ}$. For these quasi-equilibrium states, the usual Boltzmann-Gibbs recipe does not work, since the partition function is divergent due to the flatness of the potential at long distances. However, we show that the standard Boltzmann-Gibbs (BG) statistical framework and thermodynamic relations can still be applied through proper regularization. This can be a valuable tool for the analysis of metastability in the non-confining potential fields that characterize a vast number of systems.

cond-mat.stat-mech↗

arXiv2020

Brazilian physicists community diversity, equity and inclusion: a first diagnostic

We report the results of a survey applied to students and professionals in the area of physics in Brazil, pursuing to draw a portrait of the composition of this community in terms of the social markers age, race, ethnicity, geographical origin, sex, gender, sexual orientation, and disabilities. The main goal was to quantify the representativeness of different groups in the community and to detect motivations and difficulties encountered by each group throughout their studies and career. This survey was open to the members of the Brazilian Physics Society (SBF) from July to September 2018. Our outcomes reveal that (i) the Brazilian physicists community is poorly diverse even in comparison with the population composition, (ii) the main obstacle to pursue the career is socioeconomic vulnerability and (iii) harassment is high in our society, being more pronounced among women. We hope that these results will be useful to scientific and educational institutions to develop different strategies and policies to change this current situation.

physics.ed-ph↗

arXiv2019

Imperfect bifurcations in opinion dynamics under external fields

We investigate, through a kinetic-exchange model, the impact that an external field, like advertising and propaganda, has on opinion dynamics. We address the situations where two opposite alternatives can be selected but the possibility of indecision also exists. In this model, individuals influence each other through pairwise interactions, which can be of agreement or disagreement, and there are also external fields that can skew decision making. Two parameters are used to model the interactions with the field: one measures the sensitivity of the individuals to be influenced, another quantifies in which direction. We study this model in a fully connected social network scenario, by means of numerical simulations of the kinetic exchange dynamics and analytical results derived from the mean-field rate equations. We show how the external bias gives rise to imperfect bifurcations, and cusp catastrophes, allowing abrupt changes and hysteresis depending on the level of disagreement in interpersonal interactions and on the strength of the external influence.

cond-mat.stat-mech↗

arXiv2019

Women in Physics: Scissors Effect from the Brazilian Olympiad of Physics to Professional Life

Despite the legislation in force in most countries and the discourse on gender equality, the observed reality, still today, shows a clear picture of inequality and restrictions for women, particularly when the issue is the choice of a career and the subsequent promotions. In many professions, although women represent the majority in the entrance to undergraduate courses, their participation is dramatically reduced as the career progresses to the highest levels. While the participation of men increases, that of women decreases as the academic levels move towards the top ranks. This kind of evolution of two groups in opposed directions is usually referred as the "scissors effect". This effect with respect to sexes also occurs in the area of physics, both in Brazil and in the rest of the world. But at what age does this effect begin? What is its intensity in the different stages of women's lives? In this article we aim to shed some light on these questions by analyzing data of the Brazilian Olympiad of Physics and of fellowships for physicists in Brazil. We observe the systematic occurrence of scissors effect throughout the full studied data, ranging from the first years of participation in the Olympiads (13 years old) to the highest stages of the scientific career.

physics.ed-ph↗

arXiv2018

Threshold $q$-voter model

We introduce the threshold $q$-voter opinion dynamics where an agent, facing a binary choice, can change its mind when at least $q_0$ amongst $q$ neighbors share the opposite opinion. Otherwise, the agent can still change its mind with a certain probability $\varepsilon$. This threshold dynamics contemplates the possibility of persuasion by an influence group even when there is not full agreement among its members. In fact, individuals can follow their peers not only when there is unanimity ($q_0=q$) in the lobby group, as assumed in the $q$-voter model, but, depending on the circumstances, also when there is simple majority ($q_0>q/2$), Byzantine consensus ($q_0>2q/3$), or any minimal number $q_0$ amongst $q$. This realistic threshold gives place to emerging collective states and phase transitions which are not observed in the standard $q$-voter. The threshold $q_0$, together with the stochasticity introduced by $\varepsilon$, yields a phenomenology that mimics as particular cases the $q$-voter with stochastic drivings such as nonconformity and independence. In particular, nonconsensus majority states are possible, as well as mixed phases. Continuous and discontinuous phase transitions can occur, but also transitions from fluctuating phases into absorbing states.

physics.soc-ph↗

arXiv2018

From synchronous to one-time delayed dynamics in coupled maps

We study the completely synchronized states (CSSs) of a system of coupled logistic maps as a function of three parameters: interaction strength ($\varepsilon$), range of the interaction ($α$), that can vary from first-neighbors to global coupling, and a parameter ($β$) that allows to scan continuously from non-delayed to one-time delayed dynamics. % We identify in the plane $α$-$\varepsilon$ periodic orbits, limit cycles and chaotic trajectories, and describe how these structures change with the delay. These features can be explained by studying the bifurcation diagrams of a two-dimensional non-delayed map. This allows us to understand the effects of one-time delays on CSSs, e.g, regularization of chaotic orbits and synchronization of short-range coupled maps, observed when the dynamics is moderately delayed. Finally, we substitute the logistic map by cubic and logarithmic maps, in order to test the robustness of our findings.

nlin.CD↗

arXiv2018

Importance sampling with imperfect cloning for the computation of generalized Lyapunov exponents

We revisit the numerical calculation of generalized Lyapunov exponents, $L$($q$), in deterministic dynamical systems. The standard method consists of adding noise to the dynamics in order to use importance sampling algorithms. Then $L$($q$) is obtained by taking the limit noise-amplitude $\to$0 after the calculation. We focus on a particular method that involves periodic cloning and pruning of a set of trajectories. However, instead of considering a noisy dynamics, we implement an imperfect (noisy) cloning. This alternative method is compared with the standard one and, when possible, with analytical results. As a workbench, we use the asymmetric tent map, the standard map, and a system of coupled symplectic maps. The general conclusion of this study is that the imperfect-cloning method performs as well as the standard one, with the advantage of preserving the deterministic dynamics.

cond-mat.stat-mech↗

arXiv2018

Impact of network randomness on multiple opinion dynamics

People often face the challenge of choosing among different options with similar attractiveness. To study the distribution of preferences that emerge in such situations, a useful approach is to simulate opinion dynamics on top of complex networks, composed by nodes (individuals) and their connections (edges), where the state of each node can be one amongst several opinions including the undecided state. We use two different dynamics rules: the one proposed by Travieso-Fontoura (TF) and the plurality rule (PR), which are paradigmatic of outflow and inflow dynamics, respectively. We are specially interested in the impact of the network randomness on the final distribution of opinions. For that purpose, we consider Watts-Strogatz networks, which possess the small-world property, and where randomness is controlled by a probability $p$ of adding random shortcuts to an initially regular network. Depending on the value of $p$, the average connectivity $\langle k \rangle$, and the initial conditions, the final distribution can be basically (i) consensus, (ii) coexistence of different options, or (iii) predominance of indecision. We find that, in both dynamics, the predominance of a winning opinion is favored by increasing the number of reconnections (shortcuts), promoting consensus. In contrast to the TF case, in the PR dynamics, a fraction of undecided nodes can persist in the final state. In such cases, a maximum number of undecided nodes occurs within the small-world region, due to ties in the decision group.

physics.soc-ph↗

arXiv2017

Physics courses of the Federal University of Santa Catarina : evasion and gender

In this work, we analyse all existing data related to the number of incomers and outcomers (who actually obtain the degree) of the following courses offered at the Federal University of Santa Catarina: physics teaching, bachelor in physics, master of sciences in physics and doctorate in physics, corresponding to the 1998-2017 period, according to their availability. The data point towards a great male predominance (larger than 76%) and a huge evasion of both sexes (in average, less than 20% of the undergraduate incomers obtain the degree), the evasion being lower in the postgraduate courses and always slightly higher for women. The average number of incomers and outcomers per year decreases as the students advance from graduate to postgraduate courses, although many students in the postgraduate courses come from other institutions. The proportion of women decreases as the carrier advances. The results indicate the need of complementary studies that can help the identification of the causes of such a high evasion in order to minimize them.

physics.ed-ph↗

arXiv2017

Symmetry breaking by heating in a continuous opinion model

We study the critical behavior of a continuous opinion model, driven by kinetic exchanges in a fully-connected population. Opinions range in the real interval $[-1,1]$, representing the different shades of opinions against and for an issue under debate. Individual's opinions evolve through pairwise interactions, with couplings that are typically positive, but a fraction $p$ of negative ones is allowed. Moreover, a social temperature parameter $T$ controls the tendency of the individual responses towards neutrality. Depending on $p$ and $T$, different collective states emerge: symmetry broken (one side wins), symmetric (tie of opposite sides) and absorbing neutral (indecision wins). We find the critical points and exponents that characterize the phase transitions between them. The symmetry breaking transition belongs to the usual Ising mean-field universality class, but the absorbing-phase transitions, with $β=0.5$, are out of the paradigmatic directed percolation class. Moreover, ordered phases can emerge by increasing social temperature.

physics.soc-ph↗

arXiv2016

Role of the range of the interactions in thermal conduction

We investigate thermal transport along a one-dimensional lattice of classical inertial rotators, with attractive couplings which decrease with distance as $r^{-α}$ ($α\ge 0$), subject at its ends to Brownian heat reservoirs at different temperatures with average value $T$. By means of numerical integration of the equations of motion, we show the effects of the range of the interactions in the temperature profile and energy transport, and determine the domain of validity of Fourier's law in this context. We find that Fourier's law, as signaled by a finite $κ$ in the thermodynamic limit, holds only for sufficiently short range interactions, with $α>α_c(T)$. For $α<α_c(T)$, a kind of insulator behavior emerges at any $T$.

cond-mat.stat-mech↗

arXiv2016

Complete synchronization equivalence in asynchronous and delayed coupled maps

Coupled map lattices are paradigmatic models of many collective phenomena. However, quite different patterns can emerge depending on the updating scheme. While in early versions, maps were updated synchronously, there has been in recent years a concern to consider more realistic updating schemes where elements do not change all at once. Asynchronous updating schemes and the inclusion of time delays are seen as more realistic than the traditional parallel dynamics, and, in diverse works, either one or the other has been implemented separately. But are they actually distinct cases? For coupled map lattices with adjustable range of interactions, we prove, using both numerical and analytical tools, that an adequate delayed dynamics leads to the same completely synchronized states as an asynchronous update, providing a unified framework to identify the stability conditions for complete synchronization.

nlin.CD↗

arXiv2016

Role of the plurality rule in multiple choices

People are often challenged to select one among several alternatives. This situation is present not only in decisions about complex issues, e.g., political or academic choices, but also about trivial ones, as in daily purchases at a supermarket. We tackle this scenario by means of the tools of statistical mechanics. Following this approach, we introduce and analyze a model of opinion dynamics, using a Potts-like state variable to represent the multiple choices, including the ``undecided state'', that represents the individuals that do not make a choice. We investigate the dynamics over Erdös-Rényi and Barabási-Albert networks, two paradigmatic classes with the small-world property, and we show the impact of the type of network on the opinion dynamics. Depending on the number of available options $q$ and on the degree distribution of the network of contacts, different final steady states are accessible: from a wide distribution of choices to a state where a given option largely dominates. The abrupt transition between them is consistent with the sudden viral dominance of a given option over many similar ones. Moreover, the probability distributions produced by the model are validated by real data. Finally, we show that the model also contemplates the real situation of overchoice, where a large number of similar alternatives makes the choice process harder and indecision prevail.

physics.soc-ph↗

arXiv2016

Consequences of nonconformist behaviors in a continuous opinion model

We investigate opinion formation in a kinetic exchange opinion model, where opinions are represented by numbers in the real interval $[-1,1]$ and agents are typified by the individual degree of conviction about the opinion that they support. Opinions evolve through pairwise interactions governed by competitive positive and negative couplings, that promote imitation and dissent, respectively. The model contemplates also another type of nonconformity such that agents can occasionally choose their opinions independently of the interactions with other agents. The steady states of the model as a function of the parameters that describe conviction, dissent and independence are analyzed, with particular emphasis on the emergence of extreme opinions. Then, we characterize the possible ordered and disordered phases and the occurrence or suppression of phase transitions that arise spontaneously due to the disorder introduced by the heterogeneity of the agents and/or their interactions.

physics.soc-ph↗

arXiv2015

Stylized facts in Brazilian vote distributions

Elections, specially in countries such as Brazil with an electorate of the order of 100 million people, yield large-scale data-sets embodying valuable information on the dynamics through which individuals influence each other and make choices. In this work we perform an extensive analysis of data sets available for Brazilian proportional elections of legislators and city councillors throughout the period 1970-2012, which embraces two distinct political regimes: a military dictatorship and a democratic phase. Through the distribution $P(v)$ of the number of candidates receiving $v$ votes, we perform a comparative analysis of different elections in the same calendar and as a function of time. The distributions $P(v)$ present a scale-free regime with a power-law exponent $α$ which is not universal and appears to be characteristic of the electorate. Moreover, we observe that $α$ typically increases with time. We propose a multi-species model consisting in a system of nonlinear differential equations with stochastic parameters that allows to understand the empirical observations. We conclude that the power-law exponent $α$ constitutes a measure of the degree of feedback of the electorate interactions. To know the interactivity of the population is relevant beyond the context of elections, since a similar feedback may occur in other social contagion processes.

physics.soc-ph↗

arXiv2014

How does public opinion become extreme?

We investigate the emergence of extreme opinion trends in society by employing statistical physics modeling and analysis on polls that inquire about a wide range of issues such as religion, economics, politics, abortion, extramarital sex, books, movies, and electoral vote. The surveys lay out a clear indicator of the rise of extreme views. The precursor is a nonlinear relation between the fraction of individuals holding a certain extreme view and the fraction of individuals that includes also moderates, e.g., in politics, those who are "very conservative" versus "moderate to very conservative" ones. We propose an activation model of opinion dynamics with interaction rules based on the existence of individual "stubbornness" that mimics empirical observations. According to our modeling, the onset of nonlinearity can be associated to an abrupt bootstrap-percolation transition with cascades of extreme views through society. Therefore, it represents an early-warning signal to forecast the transition from moderate to extreme views. Moreover, by means of a phase diagram we can classify societies according to the percolative regime they belong to, in terms of critical fractions of extremists and people's ties.

physics.soc-ph↗