Albert Solé-Ribalta’s research while affiliated with Universitat Oberta de Catalunya and other places

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Publications (60)


City-scale assessment of pedestrian exposure to air pollution: A case study in Barcelona
  • Article

November 2024

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11 Reads

Urban Climate

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Cristina Carnerero

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Clément Rames

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[...]

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Albert Solé-Ribalta

City-Scale Assessment of Pedestrian Exposure to Air Pollution: A Case Study in Barcelona
  • Preprint
  • File available

October 2024

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28 Reads

Air pollution is a pressing environmental risk to public health, particularly in cities where population density and pollution levels are high. Traditional methods for exposure analysis often rely on census data, but recent studies highlight the impact of daily mobility on individuals' exposure. Here, we develop a methodology to determine unprecedented pedestrian exposure estimates at the city scale by combining sidewalk pedestrian flows with high-resolution (25 m x 25 m) NO2 data from bias-corrected predictions of the air quality system CALIOPE-Urban. Applied to Barcelona (Spain) for the year 2019, we show that pedestrian flow and NO2 levels exhibit negligible temporal correlation. While short-term (hourly) exposure is driven by pedestrian mobility, long-term (monthly) exposure is dominated by NO2 patterns. We identify strong spatial gradients of exposure, highlighting the importance for high-resolution solutions at the sidewalks scale. Finally, we determine that exposure mitigation strategies should consider different citizen subgroups based on their mobility and preferred routes, as significant differences were found between residential and pedestrian exposure. Our results provide exposure indicators designed for city planners and policymakers, helping to prioritize mitigation measures where and when they are most needed.

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Network- and role-view of the countries in Folder A*
a Graph representing the pruned network Folder A*. Community labels are represented by colour, and node size is proportional to its strength (sent-received correspondence). Some communities reflect historical or geographical affinities, but these alone do not explain the emergence of the structure. b Functional role of countries according to their position in the (p, z) plane for Folder A*. Labels denote the countries’ ISO 3166-1 alpha-3 codes. The colour of points is consistent with community membership in (a). Nodes in the structurally more relevant roles (R3, R5, R6) display a fair amount of diversity (North and Latin America, Western and Central Europe), but Africa and Asia are mostly relegated to peripheral roles (R1, R2).
Network- and role-view of the countries in Folder F*
a Graph representing the pruned network Folder F*. Colour represents community membership, and node size is proportional to strength. As with Folder A*, some communities reflect historical or geographical affinities (Table 2), but that is not the dominant pattern. b Functional role of countries according to their position in the (p, z) plane for Folder F*. The colour of points is consistent with community membership in (a). Nodes in R6 are scarce and geographically homogeneous (in contrast with Folder A*, Fig. 1b). Also in Folder F*, Africa and Asia are mostly relegated to peripheral roles (R1, R2).
Analysing inter-state communication dynamics and roles in the networks of the International Institute of Intellectual Cooperation

October 2024

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17 Reads

Humanities and Social Sciences Communications

The International Institute of Intellectual Cooperation (IIIC) was an international organisation established post-World War I, aimed to foster intellectual relations for global peace. As this institution becomes centenary, the digitisation of archival records has democratised access, sparking renewed scholar interest and eventually enabling new research avenues. Here, we examine two letter collections from IIIC’s digitised funds, focusing on administrative and artistic/literary matters. By analysing recognisable sender-receiver pairs and their geographical origins, we construct networks revealing intricate international relationships. Notably, the community structures and roles differ between administrative and literary exchanges, suggesting distinct communication dynamics. Administrative matters depict a more egalitarian distribution. In contrast, relevant literary correspondents include Western European countries exclusively, reflecting the prominence of certain geocultural areas as well as potential geopolitical influence attempts, challenging the established historical narratives on centres and peripheries, inviting a revaluation of the IIIC’s geographical organisation and intellectual cooperation during the interwar period.


Fig. 1. The figure illustrates the hypothesized impact of different pressures and parameter variations (network size and connectance) along the pollinator season on the structural arrangement of plant-pollinator networks. The upper part of the figure illustrates different structural transformations that one might find throughout the pollinator season: nested to modular, compound to nested, etc. The lower part of the figure shows a line plot with the average variation in size and connectance of the interaction networks observed in the empirical dataset used in this article.
Fig. 4. Diagram illustrating the evolution of size and connectance in relation to the differences in statistical significance of the analyzed structural arrangements. Each point represents a snapshot of the interaction network from a specific dataset, with consecutive snapshots connected by lines. The color scale indicates the absolute difference between the z-scores obtained for nested-like and modular structures. The inset displays the average displacement of consecutive temporal snapshots over the size-connectance diagram with respect to the fraction of time a modular structure is found to be predominant in the plant-pollinator community. Each point corresponds to a dataset. See Section S3 for the raw values obtained in the analysis.
Fig. 5. Stability and feasibility performance in nested, modular, and in-block structured networks. A) Stability vs. feasibility analysis for an ensemble of synthetic networks with varying levels of in-block nested (B = 2, p ∈ [0, 0.06], μ ∈ [0, 0.06], ξ ∈ [1.2, 1.5]), nested (B = 1, p ∈ [0, 0.1], μ = 0, ξ ∈ [1.85, 2.55]), and modular (B = 2, p = 1, μ ∈ [0, 0.1], ξ ∈ [1.1, 1.5]) features, with S = 20 species (|A| = |P| = S) and connectance C = 0.2. Each point represents a network, with its color indicating the type of structural arrangement it contains: blue for nested networks, green for modular networks, and gray for in-block nested networks. Red crosses are located at the average values of stability and feasibility of the corresponding network clusters. B) Stability and feasibility dependence on connectance C) for nested, in-block and modular networks of size S = 20 (left) and S = 60 (right). For a fixed connectance, the average feasibility and stability on several network realizations are reported (shadowed areas represent the variance). All the experiments are performed with γ = 0.1 and ω = 0.01 parameters of the Lotka-Volterra dynamics. C) Here, the stability-feasibility ordering across architectural patterns is portrayed for different values of connectance, varying in the range [0.07, 0.15] at fixed size. Dot-solid lines depict the average of the related network ensemble with size, while darker colors indicate increasing connectance. Deviation around central values arises because of the noise introduced in the interactions between species (see Materials and methods). D) Along the same line, the information of the previous plot is presented for different values of the size [20, 60] at fixed connectance.
Fig. 6. Validity of the mediating role of IBN as a function of mutualism and competition strength. The green area depicts the parameter regime where Eq. 1 holds, i.e. the mediating role of IBN structures is present. Instead, the blue (grey) area indicates the parameter range where nested (modular) structures are best at balancing stability and feasibility. Experiments were conducted with networks of S = 20 and C = 0.2.
Structural dynamics of plant-pollinator mutualistic networks

June 2024

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165 Reads

PNAS Nexus

The discourse surrounding the structural organization of mutualistic interactions mostly revolves around modularity and nestedness. The former is known to enhance the stability of communities, while the latter is related to their feasibility, albeit compromising the stability. However, it has recently been shown that the joint emergence of these structures poses challenges that can eventually lead to limitations in the dynamic properties of mutualistic communities. We hypothesize that considering compound arrangements –modules with internal nested organization– can offer valuable insights in this debate. We analyze the temporal structural dynamics of 20 plant-pollinator interaction networks and observe large structural variability throughout the year. Compound structures are particularly prevalent during the peak of the pollination season, often coexisting with nested and modular arrangements in varying degrees. Motivated by these empirical findings, we synthetically investigate the dynamics of the structural patterns across two control parameters –community size and connectance levels– mimicking the progression of the pollination season. Our analysis reveals contrasting impacts on the stability and feasibility of these mutualistic communities. We characterize the consistent relationship between network structure and stability, which follows a monotonic pattern. But, in terms of feasibility, we observe non-linear relationships. Compound structures exhibit a favorable balance between stability and feasibility, particularly in mid-sized ecological communities, suggesting they may effectively navigate the simultaneous requirements of stability and feasibility. These findings may indicate that the assembly process of mutualistic communities is driven by a delicate balance among multiple properties, rather than the dominance of a single one.




Fig. 3. Population size of the largest (blue) and second largest (red) connected component of Barcelona's sidewalk networks, as sidewalks are removed iteratively according to 3 sidewalk attributes: width W in meters, car-pedestrian accident hazard H, and slope I in degrees. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 4. Panel A: When considering both constraint properties, width and slope, at once, 10s of thousands more residents are disconnected from the largest component G of the sidewalk network. P* is the baseline population of G prior to percolation, and P* P C 1 gives the population loss. Panel B: This map shows the nodes disconnected from the network when τ(W) = 2.5 meters (green), τ(I) = 4.5 ∘ (blue), and when both constraints are applied simultaneously (pink). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. Panel A: as sidewalks are removed from narrowest to widest, the median normalized egohood length falls quickly to less than 50%, with high variance. The insets show the distributions of egohood extent for selected τ(W) in more detail. Panel B: These maps show the geographic spread of the breakdown in egohood extent at τ(W) = 2.5 meters. It is evident that peripheral egohoods suffer more than central ones.
Fig. 6. Panel A: The number of residents (in thousands) without access to a given service in their 15-min egohood rises as sidewalk links are removed from narrowest to widest. Panel B: As sidewalks are made inactive, individual facilities are accessible to smaller and smaller numbers of residents. This loss in service level is mapped here for the case of day centers for the elderly. Panel C: The same information as Panel B, in scatter plot form. While some day centers are disconnected from the network, others remain connected but lose large portions of their serviceable population.
The inclusive 15-minute city: Walkability analysis with sidewalk networks

March 2023

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481 Reads

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32 Citations

Computers Environment and Urban Systems

In recent years, the design (and re-design) of cities to encourage walkability has taken on new urgency as part of a wider campaign for sustainable urban development. Complementary to other approaches like infrastructure improvements, increases in residential density, or traffic calming measures, here, we show how planning for walkability can be augmented by the adaptation of tools and approaches from the study of urban networks, by privileging the pedestrian perspective of short-distance access over the car (and rapid transit) perspective of flow and efficiency. Using a recently developed sidewalk network model that moves towards a more realistic representation of the pedestrian environment, we propose a framework for assessing multi-factor walkability using percolation theory and insights into pedestrian behavior. We apply our framework to the city of Barcelona, and show how it can be used to optimize service location and access for vulnerable populations (the elderly and young).


Figure 1. Multilayer network definition scheme using morphological, structural, and functional brain networks with the same underlying anatomical parcellation.
Figure 2. Multilayer adjacency matrix unfolded to a supra-adjacency matrix, interlinked by structural DTI connectivity.
shows the p values obtained from comparing HVs with people with MS in all deep GM regions. Regions involving left thalamus, left hippocampus, right thalamus, right Table 1. Clinical and demographic data. Continuous variables are given as the mean ± standard deviation. EDSS = Expanded Disability Status Scale; MS = multiple sclerosis. P values obtained from comparing the groups.
Applying multilayer analysis to morphological, structural and functional brain networks to identify relevant dysfunction patterns

June 2022

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237 Reads

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19 Citations

Network Neuroscience

In recent years, research on network analysis applied to MRI data has advanced significantly. However, the majority of the studies are limited to single networks obtained from resting-state fMRI, diffusion MRI, or grey matter probability maps derived from T1 images. Although a limited number of previous studies have combined two of these networks, none have introduced a framework to combine morphological, structural and functional brain connectivity networks. The aim of this study was to combine the morphological, structural and functional information, thus defining a new multilayer network perspective. This has proved advantageous when jointly analysing multiple types of relational data from the same objects simultaneously using graph-mining techniques. The main contribution of this research is the design, development and validation of a framework that merges these three layers of information into one multilayer network that links and relates the integrity of white matter connections with grey matter probability maps and resting-state fMRI. To validate our framework, several metrics from graph theory are expanded and adapted to our specific domain characteristics. This proof of concept was applied to a cohort of people with MS, and results show that several brain regions with a synchronised connectivity deterioration could be identified.


Predicting the impact of urban change in pedestrian and road safety

February 2022

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116 Reads

Increased interaction between and among pedestrians and vehicles in the crowded urban environments of today gives rise to a negative side-effect: a growth in traffic accidents, with pedestrians being the most vulnerable elements. Recent work has shown that Convolutional Neural Networks are able to accurately predict accident rates exploiting Street View imagery along urban roads. The promising results point to the plausibility of aided design of safe urban landscapes, for both pedestrians and vehicles. In this paper, by considering historical accident data and Street View images, we detail how to automatically predict the impact (increase or decrease) of urban interventions on accident incidence. The results are positive, rendering an accuracies ranging from 60 to 80%. We additionally provide an interpretability analysis to unveil which specific categories of urban features impact accident rates positively or negatively. Considering the transportation network substrates (sidewalk and road networks) and their demand, we integrate these results to a complex network framework, to estimate the effective impact of urban change on the safety of pedestrians and vehicles. Results show that public authorities may leverage on machine learning tools to prioritize targeted interventions, since our analysis show that limited improvement is obtained with current tools. Further, our findings have a wider application range such as the design of safe urban routes for pedestrians or to the field of driver-assistance technologies.


Quantifying the drivers behind collective attention in information ecosystems

November 2021

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75 Reads

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2 Citations

Understanding human interactions in online communications is of paramount importance for our society. Alarming phenomena such as the spreading of fake news or the formation of echo-chambers can emerge in unhealthy communication environments and, ultimately, undermine the democratic discourse. In this context, unveiling the individual drivers that give rise to collective attention can help to conserve the health of our information ecosystems. Here, following a recently proposed analogy between natural and information ecosystems, we explore how competition for attention in online social networks and the strategies adopted by the users to maximize their visibility shape our communication dynamics. Specifically, by analyzing large-scale datasets from the micro-blogging platform Twitter and performing numerical modeling of the system dynamics, we are able to measure the amount of competition for attention experienced by users and how it changes when exogenous events captivate collective attention. The work relies on topic modeling to extract users' interests and memes context from the data and a framework based on ecological niche theory to quantify the strength of negative (competitive) and positive (mutualistic) interactions for both users and memes. Interestingly, our findings show two different behaviors. While memes undergo a sharp increase in competition during exceptional events that can lead to their extinction, users perceive a decrease in effective competition due to a stronger effect of mutualistic interaction, explaining the focus of collective attention around specific topics. Finally, to confirm our results we reproduce the observed shifts with a data-driven model of species dynamics.


Citations (35)


... On Visual Sentiment Analysis, Bustos et al. [35] took note of CLIP capabilities for fine-grained classification and proposed CLIP-E, an extension that adds non-linear fully-connected layers atop the frozen CLIP vision encoder to capture more useful features for the downstream task of fine-grained emotion classification, employing both traditional cross-entropy and metric learning approaches. Demonstrating a significant reduction in training parameters and computational requirements while maintaining the versatility of having a pre-trained model for quick adaptation to new downstream tasks. ...

Reference:

TinyEmo: Scaling down Emotional Reasoning via Metric Projection
On the use of Vision-Language models for Visual Sentiment Analysis: a study on CLIP
  • Citing Conference Paper
  • September 2023

... For example, macro-or meso-scale walkability (objective) measures adopt a comprehensive approach to the assessment of parameters such as proximity to nearby destinations, population density, public transport, street connectivity, land use diversity, and retail floor area ratio, aiming for a thorough evaluation of walkable neighbourhoods. A commonly utilised index for measuring walkability is the Walk Score ® (Redfin Headquarters at 1099 Stewart Street, Suite 600, Seattle, WA, USA), which offers standardised assessments of walking accessibility for cities across North America [20], along with Frank's research-based walkability framework [21], incorporating factors such as land use entropy To that end, the primary goal of this work is to advocate for a paradigm shift in approaching pedestrian accessibility and networks [44]. Rather than fixating on the central road axis as the sole determinant, such as the popular Walk Score ® index [45] or an X-minute city metric [16,46,47], the paramount importance of constructing more comprehensive sidewalk networks was underscored. ...

Sidewalk networks: Review and outlook

Computers Environment and Urban Systems

... In Lima, Peru, low-income habitation is usually located on hillsides or sloping land, which reveals differentials in what distance '15minutes of walking' approximate to [26]. Even in pedestrian-friendly cities like Barcelona, considering various pedestrian mobility profiles is essential to assess the feasibility of a 15-minute city model, as demonstrated in [27]. Aligning a detailed understanding of built form and topography associated with socio-economic analysis further reinforces the need for more nuanced measures. ...

The inclusive 15-minute city: Walkability analysis with sidewalk networks

Computers Environment and Urban Systems

... Despite the growing interest in applying graph theory to brain graphs in the context of neuroscience [18,19,20,21], existing approaches often fall short in addressing the unique challenges posed by EEG data. Traditional models lack the structured inductive bias required to capture the connectivity patterns inherent in EEG data [22,23,24,7]. Our approach addresses these limitations and ensures that collaborating institutions maintain data privacy [25,26,27]. ...

Applying multilayer analysis to morphological, structural and functional brain networks to identify relevant dysfunction patterns

Network Neuroscience

... Beyond the practical applications of the researches listed in the Introduction, automated FER was used in a plethora of scenarios, such as for assessing the reaction of humans towards noise in urban centers [5], as well as predicting the self reported stress of a driver [6] (similarly to the previously cited study, which however assessed drowsiness). Moreover, some articles aim to aid in the implementation of these technologies. ...

Predicting Driver Self-Reported Stress by Analyzing the Road Scene
  • Citing Conference Paper
  • September 2021

... As the application of BC in traffic flow estimation attracts much attention, some studies have recognized the important role of the spatial interaction in improving the ability of BC to estimate traffic flow [22][23][24]. In [22,23], the authors verified that considering the actual measured origin-destination (OD) matrix in the conventional BC can get a better correlation between the BC and the traffic flow. ...

Publisher Correction: A sustainable strategy for Open Streets in (post)pandemic cities

... The authors also used this dataset in a recently published work [12], where they estimated GHG emissions due to synthetic N fertilizer manufacture, transportation, and field use in agricultural systems. Most studies have tackled the GHG emission problems; while integrating ML tools basically focus on CO 2 or CH 4 emissions [13], very few papers are based on (N 2 O) emissions. In fact, this gas is 300 times more harmful to the climate than (CO 2 ) and steadily increases in the atmosphere, with agriculture being the largest contributor, and nitrogen the most used synthetic fertilizer [14]. ...

Algorithms Air Quality Estimation: A Comparative Study of Stochastic and Heuristic Predictive Models
  • Citing Chapter
  • September 2021

Lecture Notes in Computer Science

... A recent measurement-based assessment of changes to traffic levels on streets with and without Superblock design in Barcelona revealed traffic evaporation: Superblocks reduced traffic on streets with interventions by 14.8 % whilst resulting in a small traffic increase of 0.7 % on immediately adjacent streets 55 . Such traffic evaporation observation is commonly acknowledged and also observed for other instruments, such as Low Traffic Neighbourhoods 56 .Superblocks not only impact car-based mobility but also affect pedestrians through transforming public space, which in cities typically favours automobiles at the expense of pedestrians57 . Changing the urban form, redesigning the streetscape, or urban density affects how, where and how often people walk58 . ...

A sustainable strategy for Open Streets in (post)pandemic cities

... Evaluation of a significant number of real road networks showed that congestion locations moved farther from the city center when the number of larger metropolitan areas increased, resulting in abrupt spatial transitions (Lampo et al. 2021). Furthermore, network analysis of eight urban road networks worldwide (North America, Europe, Australia, and Asia) showed that the betweenness centrality of nodes (urban intersections) followed power-law distribution, however, the degree distribution for weighted and unweighted road networks showed completely different results (Akbarzadeh et al. 2018). ...

Emergence of spatial transitions in urban congestion dynamics

Applied Network Science

... 17,18 That work found that when companies deviated from the highly nested structure of their global training network, a few years later they had disappeared/were replaced by one that more closely followed the larger network's nested structure. 17 This paper draws inspiration from nature's mutualistic networks (which are modeled as bipartite networks, for example, plant-pollinator and soil networks)-their resistance to disturbances and network stability has been found to relate to the levels of modularity and nestedness in their architectures, [19][20][21] however more recent works have found that the previously held ecological belief that "universal nestedness" existed among mutualistic networks is outdated 22 Due to the nature of ecosystem data collection tracking modularity and nestedness changes during and after a disturbance can be difficult. 49 Modularity and nestedness have primarily been used in the ecological realm and as such this paper presents the first investigation into the ability of nestedness and modularity to measure network health over time. ...

Hybrid structural arrangements mediate stability and feasibility in mutualistic networks