Kullback--Leibler Divergence of a Freely Cooling Granular Gas

Finding the proper entropy-like Lyapunov functional associated with the inelastic Boltzmann equation for an isolated freely cooling granular gas is a still unsolved challenge. The original $H$-theorem hypotheses do not fit here and the $H$-functional presents some additional measure problems that are solved by the Kullback--Leibler divergence (KLD) of a reference velocity distribution function from the actual distribution. The right choice of the reference distribution in the KLD is crucial for the latter to qualify or not as a Lyapunov functional, the asymptotic "homogeneous cooling state" (HCS) distribution being a potential candidate. Due to the lack of a formal proof far from the quasielastic limit, the aim of this work is to support this conjecture aided by molecular dynamics simulations of inelastic hard disks and spheres in a wide range of values for the coefficient of restitution ($\alpha$) and for different initial conditions. Our results reject the Maxwellian distribution as a possible reference, whereas they reinforce the HCS one. Moreover, the KLD is used to measure the amount of information lost on using the former rather than the latter, revealing a non-monotonic dependence with $\alpha$.Comment: 22 pages, 10 figures; v2: old Sec. 4 removed, two new figures added, plus some text change

Relative entropy of freely cooling granular gases. A molecular dynamics study

Whereas the original Boltzmann's $H$-theorem applies to elastic collisions, its rigorous generalization to the inelastic case is still lacking. Nonetheless, it has been conjectured in the literature that the relative entropy of the velocity distribution function with respect to the homogeneous cooling state (HCS) represents an adequate nonequilibrium entropy-like functional for an isolated freely cooling granular gas. In this work, we present molecular dynamics results reinforcing this conjecture and rejecting the choice of the Maxwellian over the HCS as a reference distribution. These results are qualitatively predicted by a simplified theoretical toy model. Additionally, a Maxwell-demon-like velocity-inversion simulation experiment highlights the microscopic irreversibility of the granular gas dynamics, monitored by the relative entropy, where a short ``anti-kinetic'' transient regime appears for nearly elastic collisions only.Comment: 4 pages, 2 figures. v2: Some changes in text and new references added. arXiv admin note: text overlap with arXiv:2010.0335

Translational and rotational non-Gaussianities in homogeneous freely evolving granular gases

The importance of roughness in the modeling of granular gases has been increasingly considered in recent years. In this paper, a freely evolving homogeneous granular gas of inelastic and rough hard disks or spheres is studied under the assumptions of the Boltzmann kinetic equation. The homogeneous base state reached by the system is studied from a theoretical point of view using a Sonine approximation, in contrast to a previous Maxwellian approach. A general theoretical description is done in terms of $d_t$ translational and $d_r$ rotational degrees of freedom, which accounts for the cases of spheres ($d_t=d_r=3$) and disks ($d_t=2$, $d_r=1$) within a unified framework. The non-Gaussianities of the velocity distribution function of this state are determined by means of the first nontrivial cumulants and by the derivation of non-Maxwellian high-velocity tails. The results are validated by computer simulations using direct simulation Monte Carlo and event-driven molecular dynamics algorithms.Comment: 34 pages (including two appendices with 2 pages, and supplementary material with 17 pages), 13 figures (including 4 figures in the supplementary material

Caracterización de sistemas exoplanetarios mediante el ajuste de series temporales fotométricas y de velocidad radial

Contexto. Durante las últimas décadas, el desarrollo de espectrógrafos de alta resolución y telescopios espaciales hapermitido el descubrimiento de numerosos exoplanetas alrededor de estrellas de distinto tipo espectral. Los métodosmás usuales de detección son el de las velocidades radiales y el de los tránsitos, y cada uno proporciona distintas propiedades del planeta. Objetivos. Estudiar ambos métodos de detección y aplicarlos conjuntamente a casos de exoplanetas transitantes con observaciones tanto fotométricas como de velocidad radial, usando distintos programas informáticos basados en estadística bayesiana y comparando los resultados que ofrecen. Métodos. Las observaciones fotométricas usadas fueron tomadas por los telescopios espaciales Kepler y TESS, y las medidas de velocidad radial, por espectrógrafos de alta resolución como HARPS, HIRES y CARMENES. La visualización de los datos y un análisis preliminar se ha realizado mediante un código propio escrito en Python. El ajuste de las series temporales a modelos y la obtención de los parámetros se ha llevado a cabo mediante los programas pyaneti, juliet y PyORBIT. Resultados. Se han estudiado principalmente tres sistemas exoplanetarios, K2-140, K2-32 y K2-141, obteniendo unos parámetros planetarios acordes a los publicados en artículos científicos. Se han estudiado las ventajas e inconvenientes de los programas empleados. Conclusiones. Los programas mencionados permiten determinar los parámetros planetarios que mejor ajustan las observaciones de manera rigurosa. Además, el ajuste cojunto de datos fotométricos y de velocidad radial permite determinar estos parámetros con mayor precisión que un análisis separado

Differences between risk perception and risk-taking are related to impulsivity levels

Background Although there is broad agreement that perceived risks determine risk-taking behavior, previous research has shown that this association may not be as straightforward as expected. The main objective of this study was to investigate if the levels of impulsivity can explain part of these controversial findings. Method A total of 1579 participants (Mage = 23.06, from 18 to 60 years; 69.4% women) were assessed for levels of risk perception, risk-taking avoidance, and impulsivity. Results The results showed that while impulsivity was significantly and negatively related to both risk perception and risk-taking avoidance, the relationship with risk-taking avoidance was significantly stronger than with risk perception. The levels of impulsivity predicted risk-taking avoidance even when controlling for risk perception. Conclusions These findings indicate that impulsivity can differentially affect risk perception and risk-taking. We propose that the stronger influence of impulsivity on risk-taking is due to the greater reliance of risk-taking, compared with risk perception, on automatic processes guided by impulses and emotions.This research has been funded by the Regional Ministry of Economy and Knowledge, Junta de Andalucía, to Alberto Megías Robles (UMA18-FEDERJA-13 and EMERGIA20_00056)

Risk proneness modulates the impact of impulsivity on brain functional connectivity

Impulsivity and sensation seeking are considered to be among the most important personality traits involved in risk-taking behavior. This study is focused on whether the association of these personality traits and brain functional connectivity depends on individuals' risk proneness. Risk proneness was assessed with the DOSPERT-30 scale and corroborated with performance in a motorcycle simulator. The associations of impulsivity- and sensation seeking-related traits with the between and within coupling of seven major brain functional networks, estimated from electroencefalograma (EEG) recordings, differ according to whether an individual is risk prone or not. In risk-prone individuals, (lack of) premeditation enhanced the coupling of the ventral attention and limbic networks. At the same time, emotion seeking increased the coupling of the frontoparietal network and the default mode networks (DMNs). Finally, (lack of) perseverance had a positive impact on the coupling of anterior temporal nodes of the limbic network whilst having a negative impact on some frontal nodes of the frontoparietal network and the DMNs. In general, the results suggest that the predisposition to behave riskily modulates the way in which impulsivity traits are linked to brain functionality, seemingly making the brain networks prepare for an immediate, automatic, and maladaptive response.Spanish Ministry of Economy, Industry, and Competitiveness, Grant/Award Number: PSI2016-80558-R; Spanish Ministry of Education, Culture and Sports, Grant/Award Number: FPU14/05928; Andalusian Regional Government, Grant/Award Number: SOMM17/6103/UG

The Brain Network of Expectancy and Uncertainty Processing

[Background] The Stimulus Preceding Negativity (SPN) is a non-motor slow cortical potential elicited by temporally predictable stimuli, customarily interpreted as a physiological index of expectancy. Its origin would be the brain activity responsible for generating the anticipatory mental representation of an expected upcoming event. The SPN manifests itself as a slow cortical potential with negative slope, growing in amplitude as the stimulus approximates. The uncertainty hypothesis we present here postulates that the SPN is linked to control-related areas in the prefrontal cortex that become more active before the occurrence of an upcoming outcome perceived as uncertain. [Methods/Findings] We tested the uncertainty hypothesis by using a repeated measures design in a Human Contingency Learning task with two levels of uncertainty. In the high uncertainty condition, the outcome is unpredictable. In the mid uncertainty condition, the outcome can be learnt to be predicted in 75% of the trials. Our experiment shows that the Stimulus Preceding Negativity is larger for probabilistically unpredictable (uncertain) outcomes than for probabilistically predictable ones. sLoreta estimations of the brain activity preceding the outcome suggest that prefrontal and parietal areas can be involved in its generation. Prefrontal sites activation (Anterior Cingulate and Dorsolateral Prefrontal Cortex) seems to be related to the degree of uncertainty. Activation in posterior parietal areas, however, does not correlates with uncertainty. [Conclusions/Significance] We suggest that the Stimulus Preceding Negativity reflects the attempt to predict the outcome, when posterior brain areas fail to generate a stable expectancy. Uncertainty is thus conceptualized, not just as the absence of learned expectancy, but as a state with psychological and physiological entity.Research by A. Catena is funded by CONSOLIDER-INGENIO CSD2007-00012 (http://www.bcbl.eu/consolider/index.php). Research by J.C. Perales is founded by a Spanish Ministry of Science and Innovation (MICINN) grant (Dirección General de Programas y Transferencia de Conocimiento, Ref. PSI2009-13133, http://www.micinn.es/). Research by A. Catena, A. Candido, and A. Maldonado is founded by a Spanish Ministry of Science and Innovation (MICINN) grant (Dirección General de Programas y Transferencia de Conocimiento, Ref. PSI2009-12217, http://www.micinn.es/). Research was also founded by a Junta de Andalucía grant (Reference P09/SEJ-4752, http://www.juntadeandalucia.es/servicios​/ayudas/detalle/69962.html)

Exposure to Feminist Humor and the Proclivity to Collective Action for Gender Equality: The Role of Message Format and Feminist Identification

Previous research has pointed out that feminist humor or subversive humor against sexism is an important precursor to collective action for gender equality. This effect has been found contrasting subversive humor with neutral humor, however, to date, no study has explored the impact of the message format. Thus, we conducted two experiments to analyze the effect of exposure to a subversive humorous vignette against sexism (vs. subversive serious information against sexism and neutral humorous vignette) on involvement in collective action for gender equality, considering participants’ feminist identification. In Study 1 (n = 135 men and n = 198 women), participants with lower feminist identification reported a greater proclivity toward collective action after being exposure to both a subversive humorous vignette and subversive serious vignette (vs. neutral humorous vignette). In Study 2 (n = 157 men and 188 women), we replaced the subversive serious vignette with a subversive serious discourse. The results revealed that exposure to a subversive humorous vignette (vs. subversive serious discourse and neutral humorous vignette) increased participants’ collective action proclivity, but only in participants with weaker feminist identification. Both studies highlight a new pathway to motivate collective action for gender equality, as well as the potential effect of humor to promote a change in attitudes.The present research was financially supported by the Spanish Ministry of Science and Innovation under Grants Ref. Project PID2019-104239 GB-I00 and Ref. PID2022-138665NB-I00

Differences between risk perception and risk-taking are related to impulsivity levels

Background Although there is broad agreement that perceived risks determine risk-taking behavior, previous research has shown that this association may not be as straightforward as expected. The main objective of this study was to investigate if the levels of impulsivity can explain part of these controversial findings. Method A total of 1579 participants (Mage = 23.06, from 18 to 60 years; 69.4% women) were assessed for levels of risk perception, risk-taking avoidance, and impulsivity. Results The results showed that while impulsivity was significantly and negatively related to both risk perception and risk-taking avoidance, the relationship with risk-taking avoidance was significantly stronger than with risk perception. The levels of impulsivity predicted risk-taking avoidance even when controlling for risk perception. Conclusions These findings indicate that impulsivity can differentially affect risk perception and risk-taking. We propose that the stronger influence of impulsivity on risk-taking is due to the greater reliance of risk-taking, compared with risk perception, on automatic processes guided by impulses and emotions.Regional Ministry of Economy and Knowledge, Junta de Andalucia UMA18-FEDERJA-13 EMERGIA20_0005