Articles publicats en revistes (Física de la Matèria Condensada)

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Analyzing user activity on Twitter during long-lasting crisis events: a case study of the Covid-19 crisis in Spain
(Springer Nature, 2024-03-29) Esquirol Juanola, Bernat; Prignano, Luce; Díaz Guilera, Albert; Cozzo, Emanuele
A pandemic crisis like the Covid-19 outbreak is a complex event, involving numerous aspects of the social life on multiple temporal scales. Focusing on the Spanish Twittersphere, we characterized users' activity behavior across the diferent phases of the Covid-19 frst wave. Firstly, we analyzed a sample of timelines of diferent classes of users from the Spanish Twittersphere in terms of their propensity to produce new information or to amplify information produced by others. Secondly, by performing stepwise segmented regression analysis and Bayesian switchpoint analysis, we looked for a possible behavioral footprint of the crisis in the statistics of users’ activity. We observed that generic Spanish Twitter users and journalists experienced an abrupt increment of their tweeting activity between March 9 and 14, in coincidence with control measures being announced by regional and state-level authorities. However, they displayed a stable proportion of retweets before and after the switching point. On the contrary, politicians represented an exception, being the only class of users not experimenting this abrupt change and following a completely endogenous dynamics determined by institutional agenda. On the one hand, they did not increment their overall activity, displaying instead a slight decrease. On the other hand, in times of crisis, politicians tended to strengthen their propensity to amplify information rather than produce it.
Explorative pedestrian mobility geolocated data from a citizen science experiment in a neighbourhood
(Springer Nature, 2025-06-19) Larroya, Ferran; Perelló, Josep, 1974-; Paez i Blanch, Roger; Valtchanova, Manuela Mihailova
Pedestrian geolocated data are key to a better understanding of micro-mobility within a neighbourhood. These data can bring new insights into walkability and livability in the context of urban sustainability. However, pedestrian open data are scarce and often lack a context for their transformation into actionable knowledge in a neighbourhood. Citizen science and public involvement practices are powerful instruments for obtaining these data and take a community-centred placemaking approach. The study shares some 3 000 geolocated records corresponding to 19 unique trajectories made and recorded by groups of participants from three distinct communities (72 participants and 19 groups) in a relatively small neighbourhood. The groups explored the neighbourhood through a number of actions and chose different places to stop and perform various social and festive activities. The study shares not only raw data but also processed records with specific filtering and processing to facilitate and accelerate data usage. Citizen science practices and the data-collection protocols involved are reported in order to offer a complete perspective of the research undertaken jointly with an assessment of how community-centred placemaking and operative mapping are incorporated into local urban transformation actions.
Emergence of dissipation and hysteresis form interactions among reversible, nondissipative units: The case of fluid-fluid interfaces.
(American Physical Society, 2024-06-03) Holtzman, Ran; Dentz, Marco; Moura, Marcel; Chubynsky, Mykyta; Planet Latorre, Ramon; Ortín, Jordi, 1959-
We examine the nonequilibrium nature of two-phase fluid displacements in a quasi-twodimensional medium (a model open fracture) in the presence of localized constrictions (“defects”) from a theoretical and numerical standpoint. Our analysis predicts the capillary energy dissipated in abrupt interfacial displacements (jumps) across defects, and relates it to the corresponding hysteresis cycle, e.g., in pressure-saturation. We distinguish between “weak” (reversible interface displacement, exhibiting no hysteresis and dissipation) and “strong” (irreversible) defects. We expose the emergence of dissipation and irreversibility caused by spatial interactions, mediated by interfacial tension, among otherwise weak defects. We exemplify this cooperative behavior for a pair of weak defects and establish a critical separation distance, analytically and numerically, verified by a proof-of-concept experiment.
Mechanisms of interface jumps, pinning and hysteresis during cyclic fluid displacements in an isolated pore
(Elsevier, 2025-10-15) Nepal, Animesh; Hidalgo, Juan J.; Ortín, Jordi, 1959-; Lunati, Ivan; Dentz, Marco
Hypothesis Quasi-static displacements of one immiscible fluid by another in a single pore can lead to interface jumps, pinning and capillary hysteresis, depending on the pore dimensions. It is expected that there is a critical pore configuration for which the interface becomes unstable and an interface jump is triggered. These processes are at the origin of hysteresis in porous media and control macroscopic two-phase fluid displacements. Experiments and theory We conduct quasi-static imbibition and drainage experiments and detailed numerical simulations in three and two-dimensional pores, represented by capillaries of different radii that are joined by a conical section (ink-bottle). A theoretical model for the interface is derived based on pressure balance that captures the full spectrum of possible interface behaviors. Findings Depending on the slope of the conical section, we observe a range of interfacial behaviors, including capillary jumps and interface pinning during both imbibition and drainage, which give rise to capillary hysteresis, that is, history dependence of the interface position. We identify a critical pore configuration for the occurrence of interface jumps and hysteresis, which depends on surface tension and contact angle.
Multicaloric effects and magnetostructural coupling in the Cr2Ge2Te6 van der Waals crystal
(Elsevier, 2025-04-22) Abadia-Huguet, Aleix; Mendive Tapia, Eduardo; Stern Taulats, Enric; Planes Vila, Antoni; Eggert, Benedikt; Wende, Heiko; Acet, Mehmet; Sturza, Mihai-Ionut; Kohlmann, Holger; Costache, Marius V.; Mañosa, Lluís
Materials with significant coupling between magnetism and their crystal structure are prone to exhibit multicaloric effects, which offer a novel approach to addressing the bottlenecks of ecologic solid-state refrigeration by optimizing the interplay of multiple driving fields. Here we uncover the multicaloric properties of CrGeTe, establishing ferromagnetic van der Waals (vdW) crystals, famous for their spintronics applications, as a previously unrecognized class of multicaloric materials. By combining magnetization measurements with an ab initio disordered local moment theory, we report, for the first time, pronounced barocaloric and multicaloric effects induced by the application of magnetic fields and hydrostatic pressure around CrGeTe’s ferromagnetic phase transition. Our experimental and ab initio analysis quantifies the underlying magnetostructural coupling in this material, which accounts for approximately 25% of the total multicaloric entropy change. Significant multicaloric effects are expected to be found in other vdW ferromagnets with strong magnetostructural coupling.
First Order Alignment Transition in an Interfaced Active Nematic
(American Physical Society, 2024-06-15) Bantysh, Olga; Martinez-Prat, Berta; Nambisan, Jyothishraj; Fernandez de las Nieves, Alberto; Sagués i Mestre, Francesc; Ignés i Mullol, Jordi
We investigate experimentally the dynamic phase transition of a two-dimensional active nematic layer interfaced with a passive liquid crystal. Under a temperature ramp that leads to the transition of the passive liquid into a highly anisotropic lamellar smectic-A phase, and in the presence of a magnetic field, the coupled active nematic reorganizes its flow and orientational patterns from the turbulent into a quasilaminar regime aligned perpendicularly to the field. Remarkably, while the phase transition of the passive fluid is known to be continuous, or second order, our observations reveal intermittent dynamics of the order parameter and the coexistence of aligned and turbulent regions in the active nematic, a signature of discontinuous, or first order, phase transitions, similar to what is known to occur in relation to flocking in dry active matter. Our results suggest that alignment transitions in active systems are intrinsically discontinuous, regardless of the symmetry and momentum-damping mechanisms.
A new era in brain drug delivery: Integrating multivalency and computational optimisation for blood–brain barrier permeation
(Elsevier, 2025-06-14) Porro, Giulia Maria; Basile, Marco; Xie, Zhendong; Tuveri, Gianmarco; Battaglia, Giuseppe; Carvalho Ferreira Lopes, Cátia Daniela
Efficient drug delivery across the blood–brain barrier (BBB) remains a significant obstacle in treating central nervous system (CNS) disorders. This review provides an in-depth analysis of the structural and molecular mechanisms underlying BBB integrity and its functional properties. We detail the role of key cellular and molecular components that regulate selective molecular transport across the barrier, alongside a description of the current therapeutic approaches for brain drug delivery, including those leveraging receptor-mediated transcytosis. Emphasis is placed on multivalency-based strategies that enhance the specificity of nanoparticle targeting and improve transport efficacy across the BBB. Additionally, we discuss the added value of integrating mathematical and computational models with experimental validation for accelerating BBB-targeted delivery systems optimisation.
Discounting the Distant Future: What Do Historical Bond Prices Imply about the Long-Term Discount Rate?
(MDPI, 2024-03-01) Farmer, J. Doyne; Geanakoplos, John; Richiardi, Matteo G.; Montero Matellanes, M. Mikel; Perelló, Josep, 1974-; Masoliver, Jaume, 1951-
We present a thorough empirical study on real interest rates by also including risk aversion through the introduction of the market price of risk. From the viewpoint of complex systems science and its multidisciplinary approach, we use the theory of bond pricing to study the long-term discount rate to estimate the rate when taking historical US and UK data, and to further contribute to the discussion about the urgency of climate action in the context of environmental economics and stochastic methods. Century-long historical records of 3-month bonds, 10-year bonds, and inflation allow us to estimate real interest rates for the UK and the US. Real interest rates are negative about a third of the time and the real yield curves are inverted more than a third of the time, sometimes by substantial amounts. This rules out most of the standard bond-pricing models, which are designed for nominal rates that are assumed to be positive. We, therefore, use the Ornstein–Uhlenbeck model, which allows negative rates and gives a good match to inversions of the yield curve. We derive the discount function using the method of Fourier transforms and fit it to the historical data. The estimated long-term discount rate is 1.7% for the UK and 2.2% for the US. The value of 1.4% used by Stern is less than a standard deviation from our estimated long-run return rate for the UK, and less than two standard deviations of the estimated value for the US. All of this once more reinforces the need for immediate and substantial spending to combat climate change.
Characterizing the Hard and Soft Nanoparticle-Protein Corona with Multilayer Adsorption
(Frontiers Media, 2025-01-17) Vilanova, O.; Martinez-Serra, Alberto; Monopoli, Marco P.; Franzese, Giancarlo
Nanoparticles (NPs) in contact with biological fluid adsorb biomolecules into a corona. This corona comprises proteins that strongly bind to the NP (hard corona) and loosely bound proteins (soft corona) that dynamically exchange with the surrounding solution. While the kinetics of hard corona formation is relatively well understood, thanks to experiments and robust simulation models, the experimental characterization and simulation of the soft corona present a more significant challenge. Here, we review the current state of the art in soft corona characterization and introduce a novel open-source computational model to simulate its dynamic behavior, for which we provide the documentation. We focus on the case of transferrin (Tf) interacting with polystyrene NPs as an illustrative example, demonstrating how this model captures the complexities of the soft corona and offers deeper insights into its structure and behavior. We show that the soft corona is dominated by a glassy evolution that we relate to crowding effects. This work advances our understanding of the soft corona, bridging experimental limitations with improved simulation techniques.
Integrated information decomposition unveils major structural traits of in silico and in vitro neuronal networks
(American Institute of Physics (AIP), 2024-05-01) Menesse, Gustavo; Houben, Akke Mats; Soriano i Fradera, Jordi; Torres, Joaquín J.
The properties of complex networked systems arise from the interplay between the dynamics of their elements and the underlying topology. Thus, to understand their behavior, it is crucial to convene as much information as possible about their topological organization. However, in large systems, such as neuronal networks, the reconstruction of such topology is usually carried out from the information encoded in the dynamics on the network, such as spike train time series, and by measuring the transfer entropy between system elements. The topological information recovered by these methods does not necessarily capture the connectivity layout, but rather the causal flow of information between elements. New theoretical frameworks, such as Integrated Information Decomposition (Phi-ID), allow one to explore the modes in which information can flow between parts of a system, opening a rich landscape of interactions between network topology, dynamics, and information. Here, we apply Phi-ID on in silico and in vitro data to decompose the usual transfer entropy measure into different modes of information transfer, namely, synergistic, redundant, or unique. We demonstrate that the unique information transfer is the most relevant measure to uncover structural topological details from network activity data, while redundant information only introduces residual information for this application. Although the retrieved network connectivity is still functional, it captures more details of the underlying structural topology by avoiding to take into account emergent high-order interactions and information redundancy between elements, which are important for the functional behavior, but mask the detection of direct simple interactions between elements constituted by the structural network topology.
Stacking correlation length in single-stranded DNA
(Oxford University Press, 2024-10-29) Viader-Godoy, Xavier; Mañosas Castejón, María; Ritort Farran, Fèlix
Base stacking is crucial in nucleic acid stabilization, from DNA duplex hybridization to single-stranded DNA (ssDNA) protein binding. While stacking energies are tiny in ssDNA, they are inextricably mixed with hydrogen bonding in DNA base pairing, making their measurement challenging. We conduct unzipping experiments with optical tweezers of short poly-purine (dA and alternating dG and dA) sequences of 20–40 bases. We introduce a helix-coil model of the stacking–unstacking transition that includes finite length effects and reproduces the force-extension curves. Fitting the model to the experimental data, we derive the stacking energy per base, finding the salt-independent value kcal/mol for poly-dA and kcal/mol for poly-dGdA. Stacking in these polymeric sequences is predominantly cooperative with a correlation length of ∼4 bases at zero force . The correlation length reaches a maximum of ∼10 and 5 bases at the stacking–unstacking transition force of ∼10 and 20 pN for poly-dA and poly-dGdA, respectively. The salt dependencies of the cooperativity parameter in ssDNA and the energy of DNA hybridization are in agreement, suggesting that double-helix stability is primarily due to stacking. Analysis of poly-rA and poly-rC RNA sequences shows a larger stacking stability but a lower stacking correlation length of ∼2 bases.
Unraveling the magnetic properties of NiO nanoparticles: From synthesis to nanostructure
(MDPI, 2024-08-28) Moya Álvarez, Carlos; Ara Escario, Jorge; Labarta, Amílcar; Batlle Gelabert, Xavier
NiO nanoparticles have garnered significant interest due to their diverse applications and unique properties, which differ markedly from their bulk counterparts. NiO nanoparticles are p-type semiconductors with a wide bandgap, high discharge capacity, and high carrier density, making them ideal for use in batteries, sensors, and catalysts. Their ability to generate reactive oxygen species also imparts disinfectant and antibiotic properties. Additionally, the higher Néel temperature of NiO compared to other antiferromagnetic materials makes it suitable for high-temperature applications in spintronic devices and industrial settings. This review focuses on the critical role of structure and composition in determining the magnetic properties of NiO nanoparticles. It examines how finite-size surface effects, morphology, crystallinity, and nickel distribution influence these properties. Fundamental physical properties and characterization techniques are discussed first. Various synthesis methods and their impact on NiO nanoparticle properties are then explored. Their magnetic phenomenology is examined in detail, highlighting the effects of finite size, particle composition and surface, and crystal quality. The review concludes with a summary of key insights and future research directions for optimizing NiO nanoparticles in technological applications.
Unveiling the crystal and magnetic texture of iron oxide nanoflowers†
(Royal Society of Chemistry, 2024-01-03) Moya Álvarez, Carlos; Escoda I Torroella, Mariona; Rodríguez Álvarez, Javier; Figueroa Garcia, Adriana Isabel; García, Íker; Batalla Ferrer-Vidal, Inés; Gallo Cordova, Álvaro; Morales, Maria del Puerto; Aballe, Lucía; Fraile Rodríguez, Arantxa; Labarta, Amílcar; Batlle Gelabert, Xavier
Iron oxide nanoflowers (IONF) are densely packed multi-core aggregates known for their high saturation magnetization and initial susceptibility, as well as low remanence and coercive field. This study reports on how the local magnetic texture originating at the crystalline correlations among the cores determines the special magnetic properties of individual IONF over a wide size range from 40 to 400 nm. Regardless of this significant size variation in the aggregates, all samples exhibit a consistent crystalline correlation that extends well beyond the IONF cores. Furthermore, a nearly zero remnant magnetization, together with the presence of a persistently blocked state, and almost temperature-independent field-cooled magnetization, support the existence of a 3D magnetic texture throughout the IONF. This is confirmed by magnetic transmission X-ray microscopy images of tens of individual IONF, showing, in all cases, a nearly demagnetized state caused by the vorticity of the magnetic texture. Micromagnetic simulations agree well with these experimental findings, showing that the interplay between the inter-core direct exchange coupling and the demagnetizing field is responsible for the highly vortex-like spin configuration that stabilizes at low magnetic fields and appears to have partial topological protection. Overall, this comprehensive study provides valuable insights into the impact of crystalline texture on the magnetic properties of IONF over a wide size range, offering a deeper understanding of their potential applications in fields such as biomedicine and water remediation
Home-to-school pedestrian mobility GPS data from a citizen science experiment in the Barcelona area
(Springer Nature, 2023-07-04) Larroya, Ferran; Díaz, Ofelia; Sagarra, Oleguer; Colomer Simón, Pol; Ferré, Salva; Moro, Esteban; Perelló, Josep, 1974-
The analysis of pedestrian GPS datasets is fundamental to further advance on the study and the design of walkable cities. The highest resolution GPS data can characterize micro-mobility patterns and pedestrians’ micro-motives in relation to a small-scale urban context. Purposed-based recurrent mobility data inside people’s neighbourhoods is an important source in these sorts of studies. However, micro-mobility around people’s homes is generally unavailable, and if data exists, it is generally not shareable often due to privacy issues. Citizen science and its public involvement practices in scientific research are valid options to circumvent these challenges and provide meaningful datasets for walkable cities. The study presents GPS records from single-day home-to-school pedestrian mobility of 10 schools in the Barcelona Metropolitan area (Spain). The research provides pedestrian mobility from an age-homogeneous group of people. The study shares processed records with specific filtering, cleaning, and interpolation procedures that can facilitate and accelerate data usage. Citizen science practices during the whole research process are reported to offer a complete perspective of the data collected.
Observation of heterogeneities in elastocaloric natural/wastes rubber composites.
(Budapest University of Technology and Economics, 2022-12) Candau, Nicolas; Vives i Santa-Eulàlia, Eduard; Fernández Renna, Ana Inés; Oguz, Oguzhan; Corvec, Guillaume; Federico, Carlos Eloy; Fernandes, João Paulo Cosas; Stoclet, Gregory; Maspoch, Maria Lluïsa
The strain-induced crystallization and elastocaloric properties of various natural rubber (NR)/ground tire rubber (GTR) blends, comprising waste particles of diverse sizes and contents, were investigated. The decreasing inter-distance between particles in conjunction with their increasing content as studied by micro-computed tomography (μCT) as well as the inter-melling between GTR and NR matrix were observed. It resulted in a strain localization in the NR matrix at the GTR and NR interface at the origin of mechanical reinforcement upon tensile deformation. In addition, GTR particles were found to show a nucleating ability on strain-induced crystallization (SIC) and elastocaloric properties independently of the particle size. The strain localization was found to relate to a localization of the temperature field, suggesting localization of the elastocaloric effect in NR/GTR blends. The evidence of such heterogeneities would be of interest for the proper design of elastocaloric waste-based rubber composites for heating/cooling applications.
Modular architecture facilitates noise-driven control of synchrony in neuronal networks
(American Association for the Advancement of Science, 2023-08-25) Yamamoto, Hideaki; Spitzner, F. Paul; Takemuro, Taiki; Buendía, Victor; Murota, Hakuba; Morante, Carla; Konno, Tomohiro; Sato, Shigeo; Hirano-Iwata, Ayumi; Levina, Anna; Priesemann, Viola; Muñoz Pérez, Miguel Ángel; Zierenberg, Johannes; Soriano i Fradera, Jordi
High-level information processing in the mammalian cortex requires both egregated processing in specialized circuits and integration across multiple circuits. One possible way to implement these seemingly opposing demands is by flexibly switching between states with different levels of synchrony. However, the mechanisms behind the control of complex synchronization patterns in neuronal networks remain elusive. Here, we use precision neuroengineering to manipulate and stimulate networks of cortical neurons in vitro, in combination with an in silico model of spiking neurons and a mesoscopic model of stochastically coupled modules to show that (i) a modular architecture enhances the sensitivity of the network to noise delivered as external asynchronous stimulation and that (ii) the persistent depletion of synaptic resources in stimulated neurons is the underlying mechanism for this effect. Together, our results demonstrate that the inherent dynamical state in structured networks of excitable units is determined by both its modular architecture and the properties of the external inputs.
Editorial of virtual special issue EMLG/JMLG 2022: Molecular liquids at interfaces
(Elsevier B.V., 2024-04-01) Franzese, Giancarlo; Tassaing, Thierry; Vega, Lourdes
This virtual special issue (VSI) of the Journal of Molecular Liquids publishes a selection of the contributions to the ”Joint European/Japanese Molecular Liquids Group 2022 Annual Meeting” (EMLG/JMLG 2022) held in Barcelona, Spain from September 12-16, 2022.
Double power-law universal scaling function for the distribution of waiting times in labquake catalogs
(American Physical Society, 2024-12-20) Honglian, Li; Valdés, Emma; Vives i Santa-Eulàlia, Eduard
We postulate that waiting times between avalanches in self-organized critical systems are distributed according to a universal double power-law probability density. This density is defined by two critical exponents and characterizing the distribution of short (∼ − ) and long (∼ − ) waiting times, and a crossover parameter 0 that separates the two behaviors in a sharp shoulder. This crossover parameter depends on the system properties as well as on the observation conditions. It can be used as a scaling factor that transforms the distributions into a universal scaling law as proposed by Per Bak. We use experimental data from labquake catalogs (acoustic emission events) obtained during the uniaxial compression of a number of charcoal samples with different hardnesses and different energy thresholds. To obtain good fits it is essential that the catalogs are long enough to include a representative critical mixture of periods with different avalanche rates. In all the cases studied, individual maximum likelihood analysis allows the exponents and and the crossover parameter 0 to be fitted. This parameter shows a clear dependence with the energy threshold that can be explained from the Gutenberg-Richter law for the avalanche energy distributions. The observed variations of the exponents and fall within the sample-to-sample variability, which suggest that these values could be universal. We estimate mean values =0.9±0.1 and =2.0±0.3 from the full set of recorded experimental data. These values are close to the combination =1, =2, which exhibits a special mathematical cancellation of singularities.
Fostering Interdisciplinarity and Collaboration: The Role of Challenge-Driven Research in European University Alliances through the CHARM-EU Experience
(Springer Nature, 2025-04-03) Royuela Mora, Vicente; Llorca, Jaime; Evans, Cristopher; Díaz Guilera, Albert; Ramos Lobo, Raúl
This paper explores the innovative dynamics established through the European Universities Initiative (EUI) and their role in steering collaborative, challenge-driven research with societal impact. The EUI fosters the creation of university alliances aimed at aligning education and research with societal needs within the European Research Area. These alliances are designed to enhance transnational cooperation, particularly via developing common science agendas that serve as joint research strategies designed to deepen scientific collaboration among alliance partners. These agendas are structured around key priorities such as sustainability, inter- and transdisciplinary research, and adherence to Responsible Research and Innovation principles. Our study focuses on the CHARM-EU Alliance as a case study, presenting a participatory process for building multidisciplinary academic teams to define scientific priorities aligned with sustainable development goals. The process provides a practical tool for fostering new scientific networks to identify and tackle complex global issues, being replicable, inclusive, and adaptable for other alliances. Additionally, the paper discusses the main barriers encountered in developing and implementing a procedure to set up a common science agenda, including the challenges of inter-institutional collaboration and the integration of diverse institutional policies and priorities. Our findings offer insight into the successes and limitations of such initiatives, contributing to a collective learning experience that can inform policy and academic communities on fostering transformative research strategies within university alliances.
Engineering tunable fractional Shapiro steps in colloidal transport
(Nature Publishing Group, 2025-03-12) Maass, Philipp; Stikuts, Andris P.; Mishra, Seemant; Ryabov, Artem; Tierno, Pietro
Shapiro steps are quantized plateaus in the velocity-force or velocity-torque curve of a driven system, when its speed remains constant despite an increase in the driving force. For microscopic particles driven across a sinusoidal potential, integer Shapiro steps have been observed. By driving a single colloidal particle across a time-modulated, non-sinusoidal periodic optical landscape, we here demonstrate that fractional Shapiro steps emerge in addition to integer ones. Measuring the particle position via individual particle tracking, we reveal the underlying microscopic mechanisms that produce integer and fractional steps and demonstrate how these steps can be controlled by tuning the shape and driving protocol of the optical potential. The flexibility offered by optical engineering allows us to generate a wide range of potential shapes and to study, at the single-particle level, synchronization behavior in driven soft condensed matter systems.

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