Juan Carlos Losada

Efficiency of human activity on information spreading on Twitter

Understanding the collective reaction to individual actions is key to effectively spread information in social media. In this work we define efficiency on Twitter, as the ratio between the emergent spreading process and the activity employed by the user. We characterize this property by means of a quantitative analysis of the structural and dynamical patterns emergent from human interactions, and show it to be universal across several Twitter conversations. We found that some influential users efficiently cause remarkable collective reactions by each message sent, while the majority of users must employ extremely larger efforts to reach similar effects. Next we propose a model that reproduces the retweet cascades occurring on Twitter to explain the emergent distribution of the user efficiency. The model shows that the dynamical patterns of the conversations are strongly conditioned by the topology of the underlying network. We conclude that the appearance of a small fraction of extremely efficient users results from the heterogeneity of the followers network and independently of the individual user behavior.

Measuring political polarization: Twitter shows the two sides of Venezuela

We say that a population is perfectly polarized when divided in two groups of the same size and opposite opinions. In this paper, we propose a methodology to study and measure the emergence of polarization from social interactions. We begin by proposing a model to estimate opinions in which a minority of influential individuals propagate their opinions through a social network. The result of the model is an opinion probability density function. Next, we propose an index to quantify the extent to which the resulting distribution is polarized. Finally, we apply the proposed methodology to a Twitter conversation about the late Venezuelan president, Hugo Chávez, finding a good agreement between our results and offline data. Hence, we show that our methodology can detect different degrees of polarization, depending on the structure of the network.

Local frequency analysis and the structure of classical phase space of the LiNC/LiCN molecular system

The phase space structure of a generic Hamiltonian model, describing the vibrational dynamics of the LiNC/LiCN molecular system, is studied using a frequency analysis method. The results obtained for the regular region constitute a true parametrization of the corresponding invariant tori on which the trajectories are located. By performing the frequency analysis locally, much richer information about chaotic trajectories is obtained, since it clearly reveals the dynamical characteristics of trajectory fragments hidden behind the t→∞ ergodic property.

Underlying conservation and stability laws in nonlinear propagation of axicon-generated Bessel beams

The propagation dynamics of Bessel beams, nondiffracting light beams that play an important role in the creation of plasma channels, is unraveled. This study shows a unifying picture in which different dynamical regimes are explained by the properties of an attractor.

Adapting physics courses in an engineering school to the b-learning philosophy

In this paper we introduce the methodology that we have followed to convert traditional notes into interactive online materials. The idea behind this has been to make self-consistent and interactive online materials capable of motivating the students to get involved in the learning process. For this purpose, we have used the e-learning environment Moodle, which is a platform with a high interactivity potential. We conclude that the academic performance reaches its maximum when correctly combining self-organising with minimum teacher guidance.

Community Structure in a Soil Porous System

Abstract Soil is well recognized as a highly complex system. The interaction and coupled physical, chemical, and biological processes and phenomena occurring in the soil environment at different spatial and temporal scales are the main reasons for such complexity. There is a need for appropriate methodologies to characterize soil porous systems with an interdisciplinary character. Four different real soil samples, presenting different textures, have been modeled as heterogeneous complex networks, applying a model known as the heterogeneous preferential attachment. An analytical study of the degree distributions in the soil model shows a multiscaling behavior in the connectivity degrees, leaving an empirically testable signature of heterogeneity in the topology of soil pore networks. We also show that the power-law scaling in the degree distribution is a robust trait of the soil model. Last, the detection of spatial pore communities, as densely connected groups with only sparser connections between them, has been studied for the first time in these soil networks. Our results show that the presence of these communities depends on the parameter values used to construct the network. These findings could contribute to understanding the mechanisms of the diffusion phenomena in soils, such as gas and water diffusion, development and dynamics of microorganisms, among others.

Serendipity in social networks

Serendipity is defined as fortunate discoveries made by chance. In this work we explore the idea that topological measures of a persons social network could be an indicator about how likely that person is to experience fortunate discoveries.

Scaling Characteristics of Soil Structure

As previously discussed in Chap. 5, soil structure is defined by the spatial arrangement of soil primary particles and aggregates. There is increasing evidence that quantitative characterization of the soil structure and of its heterogeneity and complexity holds the key to a deeper understanding on physical, chemical, and biological processes that take place within them (Vogel 2000; Rockhold et al. 2004; Young et al. 2008; Blair et al. 2007; Pajor et al. 2010; Kravchenko et al. 2010; Dullien 2012).Therefore, it is very important to obtain an accurate description of it which best approximates to reality. Although many parameters may be used to attempt to describe irregular morphology, the spatial arrangement of the most prominent features is a challenging problem across a wide range of disciplines (Ripley 1988; Griffith 1988; Baveye and Boast 1988).

Frequency analysis of the laser driven nonlinear dynamics of HCN

We study the vibrational dynamics of a model for the HCN molecule in the presence of a monochromatic laser field. The variation of the structural behavior of the system as a function of the laser frequency is analyzed in detail using the smaller alignment index, frequency maps, and diffusion coefficients. It is observed that the ergodicity of the system depends on the frequency of the excitation field, especially in its transitions from and into chaos. This provides a roadmap for the possibility of bond excitation and dissociation in this molecule.

Agricultural activity shapes the communication and migration patterns in Senegal

The communication and migration patterns of a country are shaped by its socioeconomic processes. The economy of Senegal is predominantly rural, as agriculture employs over 70% of the labor force. In this paper, we use mobile phone records to explore the impact of agricultural activity on the communication and mobility patterns of the inhabitants of Senegal. We find two peaks of phone calls activity emerging during the growing season. Moreover, during the harvest period, we detect an increase in the migration flows throughout the country. However, religious holidays also shape the mobility patterns of the Senegalese people. Hence, in the light of our results, agricultural activity and religious holidays are the primary drivers of mobility inside the country.