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Examining the mass transport resistance of porous transport layers at the rib/channel scale in polymer electrolyte membrane water electrolyzers: Modeling and design
Full text linkThe porous transport layer (PTL) plays a relevant role in the efficiency of polymer electrolyte membrane water electrolyzers (PEMWE). Extraction of good design guidelines for this porous component is necessary for efficient water/oxygen transport. In this regard, numerical modeling provides a versatile tool to examine large parameter set and determine optimal PTL conditions to be verified experimentally. Here, a hybrid model is presented to analyze two-phase transport of oxygen and water in the anode PTL of a PEMWE. Oxygen capillary transport is modeled with a multi-cluster invasion-percolation algorithm, while water convective transport is modeled with a continuum formulation that incorporates the blockage of gas saturation. The model is validated against in-operando X-ray computed tomography data of the oxygen saturation distribution at the rib/channel scale. Subsequently, a comprehensive parametric analysis is presented, considering the following variables: () PTL slenderness ratio, () flow-field open area fraction, () PTL isotropy, () PTL average pore radius, and () PTL pore-size heterogeneity. Among other conclusions, the results show that the water transport resistance under the rib can lead to non-negligible mass transport losses at high current density. Water transport from the channel to the catalyst layer can be promoted by: () the use of PTLs with a slenderness ratio, defined as the PTL thickness to rib half-width ratio, around 0.5, () the increase of the flow-field open area fraction, () the design of highly anisotropic PTLs with a relatively large pore radius between ∼ 10 − 40 μm, and () increasing the homogeneity of the PTL microstructure.This work was supported by project TED2021-131620B-C21 of the Spanish Agencia Estatal de Investigación. X-ray computed tomography experiments were performed at the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231
Los registros de ensayos clínicos como elemento de valoración de la investigación: el caso de los registros de ensayos clínicos oncológicos (RECO) en España
No full textPrograma de Doctorado en Documentación: Archivos y Bibliotecas en el Entorno Digital por la Universidad Carlos III de MadridPresidenta: María Fernanda Peset Mancebo.- Secretario: Antonio Perianes Rodríguez.- Vocal: Martín Martín, Albert
Beyond GARCH: Bayesian Neural Stochastic Volatility
Full text linkAccurately forecasting volatility is central to risk management, portfolio allocation, and asset pricing. While high-frequency realised measures have been shown to improve predictive accuracy, their value is not uniform across markets or horizons. This paper introduces a class of Bayesian neural network stochastic volatility (NN-SV) models that combine the flexibility of machine learning with the structure of stochastic volatility models. The specifications incorporate realised variance, jump variation, and semivariance from daily and intraday data, and model uncertainty is addressed through a Bayesian stacking ensemble that adaptively aggregates predictive distributions. Using data from the DAX, FTSE 100, and S&P 500 indices, the models are evaluated against classical GARCH and parametric SV benchmarks. The results show that the predictive content of high-frequency measures is horizon- and market-specific. The Bayesian ensemble further enhances robustness by exploiting complementary model strengths. Overall, NN-SV models not only outperform established benchmarks in many settings but also provide new insights into market-specific drivers of volatility dynamics.This work was supported by the Agencia Estatal de Investigación under Grants PID2019-108079GB-C21/AIE/10.13039/501100011033, PID2021-122919NB-I00; PID2024-157527OB-I00; Fundação para a Ciência e a Tecnologia under Grant UIDB/00315/2020; and Universidad Carlos III de Madrid Grant 2024/00002/006/002/026
The Occupational Roots of Political Preferences: The role of specific skills and labor market context
Full text linkUnderstanding who and when supports income redistribution or holds anti-immigration attitudes is at the core of political economy literature. Nevertheless, even though social stratification literature understands skill specificity as a key element of social class, there are contradictory views on the role they play in shaping political preferences. I elaborate a framework that allows understanding these contradictions. This dissertation contends that the effects of occupation-specific skills (OSS) on political preferences is moderated by the occupational context.
In a first step, Chapter 2 explores how OSS and occupational labor market context interact in shaping various dimensions of labor market risk, that is, perceived probability of job loss and the associated consequences. It shows that higher unemployment rates are associated with higher levels of risk, specially for individuals holding higher OSS. Chapter 3 turns to explores how this mechanism may explain redistribution preferences. Specifically, it shows how holding more OSS are associated with lower redistribution preferences, but only for sufficiently low levels of occupational unemployment rates. Chapter 4 moves from first-dimension politics and explores cultural anti-immigration backlash, highlighting the role of perceived social status. OSS provide individuals with social recognition, but less so when the occupational labor market deteriorates. This chapter shows how higher occupation unemployment rates translate into higher concerns about immigration, specially for those individuals holding more OSS — that is, Professionals and Managers.
The different parts of the argument are tested using large-scale surveys with quantitative methods. The evidence on perceived labor market risk and political attitudes comes from the European Social Survey, the International Social Survey Programme, and the German Socio-Economic Panel. The data on occupations comes from the Programme for the International Assessment of Adult Competencies and distinct labor force surveys provided by the Eurostat. Methodologically, this dissertation employs regression models that allow for flexible interactive effects.Programa de Doctorado en Ciencias Sociales/ Social Sciences por la Universidad Carlos III de MadridPresidente: Irene Menéndez González.- Secretario: Pablo Beramendi Alvarez.- Vocal: Alexander Ku
A meta-model based cross-sectional shape of a Savonius hydrokinetic turbine for sustainable power generation in remote rural areas
Full text linkEnergy accessibility and transition converge on exploring non-conventional renewable energy sources and the technology to harness them. An interesting and abundant resource is hydrokinetics. This work presents a Savonius cross-sectional blade shape modification that enhances the turbine performance in low-flow speed applications through a metamodel-based process. The blade profile is described by a Bézier curve control point as the parametrization strategy for generating a set of geometries to evaluate with COMSOL CFD. The obtained performance parameter of each geometry is defined as the output, and their control points parameters as inputs. This data set is utilized to train an Artificial Neural Network (ANN) to describe the interaction of blade shape and performance. The ANN is subsequently used as the target function in a Genetic Algorithm, to get the blade shape that best fits the model. A geometry with a power coefficient of 0.2405 results in an operational condition of 0.8 m/s flow speed at 1.1 Tip-Speed-Ratio. It means a performance increase of 8.3% compared with a standard turbine in the same conditions. This achievement leads to the implementation of this technology to supply the base load of rural households with a riverine resource of around 1 m/s flow speed.The Universidad Pontificia Bolivariana, Colombia funded this research through the internal project ““Proyecto Flexibilidad Energética”” code 686C-08/21-19
Residuo acumulativo. La potencialidad del feminismo en la era del #MeToo
Full text linkPrograma de Doctorado en Humanidades por la Universidad Carlos III de MadridPresidenta: Asunción Bernárdez Rodal.- Secretaria: Silvina Verónica Ribotta.- Vocal: Begoña Sáez Tajafuerc
Hedges of the Second Republic: firms, equity investors and political uncertainty in a nascent democracy, 1930&-1936
Full text link[EN] We study how Spanish equity investors assessed firms¿ exposure to political risk during the regime change of the 1930s. We show that shifts in political uncertainty regularly predicted a general deterioration of future investment opportunities in the stock market. However, we also find that firms differed in their sensitivity to uncertainty, reflecting important differences in their perceived exposures to political risk. The negative impact of uncertainty was significantly milder for firms with political connections to republican parties. The price of some stocks increased in periods of heightened uncertainty, thus allowing investors to hedge against reinvestment risk. In the case of firms that became targets of hostile political actions, we observe that investors frequently adjusted their assessment of individual stocks to changes in firm-specific political circumstances. Over the whole period of the Second Republic, investors' systematic preference for safer equity hedges led to a continuous decline in the price of stocks perceived as more exposed to political risk.[ES] Este artículo estudia cómo los inversores españoles en renta variable evaluaron la exposición de las empresas al riesgo político durante el cambio de régimen de los años treinta. Mostramos que repuntes en la incertidumbre política predijeron con regularidad un deterioro general de las oportunidades de inversión futuras en el mercado accionario. Sin embargo, encontramos también que las empresas diferían en su sensibilidad a la incertidumbre, lo que reflejaba diferencias importantes en la percepción de su exposición al riesgo político. El impacto negativo de la incertidumbre fue significativamente menor para las empresas con conexiones políticas con partidos republicanos. El precio de algunas acciones aumentó en periodos de mayor incertidumbre, permitiendo así a los inversores blindarse contra el riesgo de reinversión. En el caso de las empresas que terminaron siendo objetivos de iniciativas políticas hostiles, observamos cómo los inversores ajustaron frecuentemente su evaluación en función de los cambios intervenidos en las circunstancias políticas específicas de las empresas. Durante todo el período de la Segunda República, la preferencia sistemática de los inversores por las acciones más seguras, que garantizaban una mejor capacidad de cobertura, se tradujo en una caída continua del precio de las acciones más expuestas al riesgo político.Battilossi gratefully acknowledges financial support of Universidad Carlos III de Madrid through Strategic Action “Historical Development of Spanish Capital Markets”. The usual disclaimer for remaining errors and omissions applies. Funding for APC: Universidad Carlos III de Madrid (Agreement CRUE-Madroño 2024)
Three Essays on Organizational Responsiveness to Pressures: The Role of Ownership
No full textMención Internacional en el título de doctorOrganizations today face increasing pressure from stakeholders in diverse environmental, social, and governance (ESG) domains, making it essential to understand how they respond to these demands and the factors driving variation in their responsiveness (Durand et al., 2019). This thesis examines the role of ownership, particularly the influence of owners whose priorities extend beyond financial interests and who must navigate tensions between responding to these external pressures and pursuing internal objectives (Miller et al., 2013).
In Chapters 1 and 2, co-authored with María José Sánchez-Bueno, Cristina Cruz Serrano, and Luis Rafael Gómez-Mejía, we explore the impact of family ownership. Family firms provide a valuable context for studying how ownership shapes organizational responsiveness. Family firms constitute a significant share of businesses worldwide (Chirico et al., 2025), and pursue distinct objectives rooted in socioemotional wealth (SEW)—non-financial benefits that satisfy a family’s emotional needs, such as control, identity, and legacy (Gomez-Mejia et al., 2007). These priorities influence decision-making processes, shaping how family firms interact with stakeholders (Combs et al., 2023).
Finally, Chapter 3, titled “ Strategic Silence After ESG Wrongdoing? The Role of Psychological Ownership”, co-authored with Jordi Surroca and Josep Tribó, extends the analysis of non-economic ownership goals by examining the link between psychological ownership and response to coverage of organizational ESG wrongdoing. Drawing on psychological ownership theory (Pierce et al., 2001), we argue that the deep emotional connection individuals feel toward their organizations heightens leaders’ resistance to engage in restorative communication. We propose that this behavior stems from the discomfort of acknowledging organizational flaws and the fear of losing “sense of self”. As a result, we hypothesize that psychological ownership drives more strategic silence when the organization is reported for engaging in more controversial ESG situations. We further theorize that this connection motivates leaders to remain silent even in the face of more severe and novel controversies, as the need to protect and defend their emotional bond with the organization intensifies. We examine these ideas using a sample of 2,570 firm-year observations from US public firms. In additional analyses, we also show that internal controversies tend to generate more strategic silence than those of an external nature; and that, whilst these leaders remain more silent, incentives to ensure consistency also push them to be less misleading when they decide to disclose information. Findings from this work advance the understanding of the implications of ownership and behavioral mechanisms underlying organizational responsiveness to misconduct.
In all, this thesis advances academic discussions across multiple domains, including ownership (Federo et al., 2020; Martin et al., 2017; Witt et al., 2022); corporate governance (Aguilera et al., 2018, 2021; Ertimur et al., 2015, 2018; Sauerwald et al., 2016, 2018); and strategy (Carlos & Lewis, 2018; Knippen et al., 2019; Gantchev et al., 2020). It contributes to these research streams by offering a more nuanced understanding of how owners’ priorities shape reactions to external pressures, influencing strategies that concern governance, leadership, and communication with stakeholders. Specifically, the insights obtained highlight the critical tensions that owners with non-financial and financial goals face when strategically balancing distinct types of demands (e.g., shareholder activism, ESG pressures, coverage of wrongdoing) with other organizational interests (e.g., control, emotional connection, identity, long-term concerns). Collectively, the studies suggest that this form of ownership may lead firms to resist (or respond symbolically) when issues threaten internal goals. Yet, they also reveal that aligning external pressures with these priorities often creates incentives to pursue substantive change. This is evidenced, for example, in a pronounced responsiveness to dissent under heightened investor scrutiny; a progressive attitude toward appointing women to the board; and a decreased tendency to be misleading when disclosing information.
Overall, findings provide actionable insights for policymakers, investors, and corporate leaders navigating the evolving landscape of governance challenges and stakeholder pressures. Understanding how ownership structures influence corporate responsiveness can inform regulatory frameworks that promote both accountability and long-term value creation (Iliev et al., 2015). Investors, in turn, can leverage these insights to assess how firms navigate the trade-off between financial returns and broader non-financial responsibilities (Goranova & Ryan, 2014). Finally, leaders can use this knowledge to refine responses that align ownership priorities with external expectations, fostering adaptability in the face of shifting market dynamics, highly interdependent corporate relationships, and increasing stakeholder scrutiny (Durand et al., 2019).I am especially indebted to the Spanish Ministry of Science and Innovation (PRE2020-092732) and María José Montes Sancho for leading the project (PID2019-105616RB-I00) which provided funding for my PhD studies at UC3M and research stay at the University of Liverpool.Programa de Doctorado en Empresa y Finanzas / Business and Finance por la Universidad Carlos III de MadridPresidente: Josip Kotlar.- Secretario: Ignacio Requejo Puerto.- Vocal: Mónica Franco Santo
A macroecological perspective to metagenomics: the role of microbial interactions
No full textMención Internacional en el título de doctorMetagenomics has profoundly changed microbiology by enabling the study of microbial communities directly from their natural environments, bypassing traditional culture methods. While early work focused on the limited 16S rRNA gene for taxonomy, the sheer volume of resulting data has driven the convergence of biology, physics, and mathematics, leading to the adoption of top-down approaches in microbial studies. This research embraces macroecology, a quantitative, large-scale approach, to model these complex systems. Starting from Grilli's macroecological laws and the simpler SLM, the work introduces the SLVM—a Stochastic Lotka-Volterra Model that explicitly includes species interactions—to address the limitations of models that ignore correlations between species abundances. The SLVM successfully explains the high variability in abundance distribution parameters observed in nature, challenging the assumptions of simpler models, and identifies a new macroecological pattern related to Taylor's law. Furthermore, the analysis of the SLVM reveals that microbial interaction networks are sparse, dominated by neutralism, commensalism, and amensalism. The thesis highlights the value of using statistical mechanics to characterize these networks and proposes that the key to unlocking the biotechnological promise of microbiomes lies in adopting an appropriate statistical description that focuses on the relevant macro-scale dynamics rather than attempting to model every microscopic detail.This thesis has been funded through an FPI grant from the project PGC2018-098186- B-I00 (BASIC) financed by the MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe. Additional funds were obtained through the project PID2022- 141802NB-I00 (BASIC), financed by the MICIU/AEI/10.13039/501100011033 and by ERDF A way of making Europe’Programa de Doctorado en Ingeniería Matemática por la Universidad Carlos III de Madrid.Presidenta: Susanna Manrubia Cuevas; Vocal: Samir Simon Suweis; Secretario: Pablo Catalán Fernández
Controlled Drug Release Systems for Cerebrovascular Diseases
Full text linkThis review offers a comprehensive exploration of optimized drug delivery systems tailored for controlled release and their crucial role in addressing cerebrovascular diseases. Through an in-depth analysis, various controlled release methods, including nanoparticles, liposomes, hydrogels, and other emerging technologies are examined. Highlighting the importance of precise drug targeting, it is delved into the underlying mechanisms of these delivery systems and their potential to improve therapeutic outcomes while minimizing adverse effects. Additionally, the specific applications of these optimized drug delivery systems in treating cerebrovascular disorders such as ischemic stroke, cerebral aneurysms, and intracranial hemorrhage are discussed. By shedding light on the advancements in drug delivery techniques and their implications in cerebrovascular medicine, this review offers valuable insights into the future of therapeutic interventions in neurology.C.T.e.S. and M.V.G.-G. contributed equally to this work. This research was funded by the Ministerio de Ciencia, Innovación y Universidades co-financed by the European Regional Development Fund, “A Way of making Europe” initiative. Grant PLEC2022-009235 funded by MICIU /AEI /10.13039/501100011033 and by the “European Union NextGeneration EU/ PRTR. Grant PID2022-141080OB-C21 funded by MICIU/AEI /10.13039/501100011033 and by FEDER, UE. This study has been funded by Instituto de Salud Carlos III (ISCIII) through the project “DTS22/00030” and co-funded by the European Union. This work was partially supported by Comunidad de Madrid, project (S2022/BMD-7403 RENIM-CM). The CNIC is supported by the Ministerio de Ciencia, Innovación y Universidades and the Pro CNIC Foundation and is a Severo Ochoa Centre of Excellence (SEV-2015-0505). CTS acknowledges the program Atraccion de Talento (CAM), ref. 2020-T1/IND-1988. The cover has been supported by Comunidad de Madrid, project (S2022/BMD-7403 RENIM-CM) and by Grant PID2022-141080OB-C21 funded by MICIU/AEI /10.13039/501100011033 and by FEDER, UE.