Édgar Roldán

Stochastic thermodynamics is a framework for describing non-equilibrium processes at the level of fluctuating trajectories, where the state of a system evolves as a stochastic time series, allowing thermodynamic quantities such as work, heat, and entropy production to be defined along individual realizations rather than at the ensemble level only. Over the past three decades, the field has yielded fundamental results, including fluctuation theorems and several universal bounds, such as thermodynamic uncertainty relations, speed limit theorems, and many others. Many of them have been tested on a range of experimental platforms. This Perspective reviews recent developments in stochastic thermodynamics that extend its scope beyond its traditional domains, including systems with memory and hidden degrees of freedom, microscopic approaches to interacting and active matter, and geometric formulations based on optimal transport. Next, the Perspective surveys the challenges that arise when applying these ideas to macroscopic and complex systems, where the link between statistical irreversibility and thermodynamic dissipation becomes less direct. Finally, emerging applications in non-physical contexts are highlighted, including computation, biological systems, and social dynamics. Transcending the traditional boundaries of physics, these developments catalyze an unorthodox framework to tackle the thermodynamics of complex systems.

Se evaluó la variabilidad morfológica de cinco especies de Agave salmiana en el Rancho Agrosilvicultores de Hidalgo (RAH). Mediante métricas específicas y análisis discriminante, se determinó que las variedades locales y comúnmente conocidas por los productores, difieren de otras registradas en la misma área. Los resultados indicaron que variables como la longitud de la planta, el diámetro de la roseta, el número de hojas y la longitud foliar explican la mayor parte de la variabilidad observada, lo que permite una clara diferenciación estadística entre las especies analizadas. Asimismo, se confirmó que las variedades locales presentan características distintas en comparación con otras poblaciones reportadas en Hidalgo. Este estudio aporta evidencia científica que respalda el conocimiento empírico de los productores y fortalece la conservación del maguey. Además, la investigación incluye cartografía y análisis de ADN (en curso), con el objetivo de validar científicamente estos recursos y promover su conservación y certificación sustentable.

Hair cells actively drive oscillations of their mechanosensitive organelles—the hair bundles that enable hearing and balance sensing in vertebrates. Why and how some hair cells expend energy by sustaining this oscillatory motion in order to fulfill their function as sensors and amplifiers remains unknown. Here, we develop a stochastic thermodynamic theory to describe flows of energy in a periodically driven hair bundle. Our analysis of thermodynamic fluxes associated with hair-bundle motion and external sinusoidal stimulus reveals that these organelles function as thermodynamic work-to-work machines under different operational modes. One mode allows the cell to harvest energy of the external signal, whereas another channels the power supplied by the cell into the signal. These two regimes might represent thermodynamic signatures of signal sensing and amplification, respectively, which we further connect to the receptor currents through ion channels controlled by the hair bundles. In addition to energy harvesting and work transduction, our model also substantiates the capability of hair cells to operate as heaters and, at the expense of external driving, as active feedback refrigerators. We quantify the performance and robustness of the mechanical work-to-work conversion by hair bundles, whose thermodynamic efficiency in some conditions exceeds 80% of the applied power.

Cerebral aneurysms and arteriovenous malformations are life-threatening hemodynamic pathologies of the brain. While surgical intervention is often essential to prevent fatal outcomes, it carries significant risks both during the procedure and in the postoperative period, making the management of these conditions highly challenging. Parameters of cerebral blood flow, routinely monitored during medical interventions or with modern noninvasive high-resolution imaging methods, could potentially be utilized in machine-learning-assisted protocols for risk assessment and therapeutic prognosis. To this end, we developed a linear oscillatory model of blood velocity and pressure for clinical data acquired from neurosurgical operations. Using the method of Sparse Identification of Nonlinear Dynamics (SINDy), the parameters of our model can be reconstructed online within milliseconds from a short time series of the hemodynamic variables. The identified parameter values enable automated classification of the blood-flow pathologies by means of logistic regression, achieving a balanced accuracy of 74%. Our results demonstrate the potential of this model for both diagnostic and prognostic applications, providing a robust and interpretable framework for assessing cerebral blood vessel conditions.

Micro-calorimetry offers significant potential as a quantitative method for studying the structure and function of biological systems, for instance, by probing the excess heat released by cellular or sub-cellular structures, isothermal or not, when external parameters change. We present the conceptual framework of nonequilibrium calorimetry, and as illustrations, we compute the heat capacity of biophysical models with few degrees of freedom related to ciliar motion (rowing model) and molecular motor motion (flashing ratchets). Our quantitative predictions reveal intriguing dependencies of the (nonequilibrium) heat capacity as a function of relevant biophysical parameters, which can even take negative values as a result of biological activity.

A pesar del diferencial y de la reputación, tanto de la especie agavera utilizada como de su graduación estandarizada, el mezcal y el tequila dominan el mercado de bebidas espirituosas de forma notable por su gran expansión y por la propia lógica de los terceros involucrados. El presente texto, a partir de los aportes inmersos en la ecología territorial, identifica las disímiles formas especiales de anclaje, dependencia y huella que dejan la cobertura de ambos destilados sobre los territorios compartidos; alcance que se introduce al analizar sus respectivas líneas discursivas en los litigios legales de protección. En un segundo momento se visibiliza la construcción territorial del destilado de pulque; su relevancia no es menor, pues este se asienta en espacios desprovistos de protecciones de origen, pero aún con amplia disponibilidad de agaves, derivada de su histórica relevancia magueyera nacional. Las estrategias metodológicas transitaron desde recabar información primaria y secundaria para describir la lógica productiva del tequila y del mezcal, hasta construir entre estos y los destilados de pulque, los diferenciales cuantitativos de tipo fisicoquímico. Así pues, es factible afirmar en demasía la desvinculación virtuosa entre el llamado histórico epicentro del tequila (Jalisco) y los referidos territorios compartidos; es decir, pese a su localización estratégica (Tamaulipas), a la alta disponibilidad de planta con rendimientos crecientes (Guanajuato) y a la proximidad fronteriza en expansión (Michoacán), los beneficios económicos aún son limitados, aunque con altos costos ambientales. Más aún, en todas las interpretaciones positivas de la ampliación, pese a que se fundamentan en la pertinencia histórica y cultural, la realidad es que antes de lograr la ampliación de las declaratorias existía una presencia limitada de factores humanos y técnicos, mucho menos de plantaciones agaveras necesarias para procesos de destilación a proteger. En contraste, dada la condición artesanal de los destilados de pulque, la principal disyuntiva para sobrevivir en el mercado de bebidas espirituosas será optar por alejarse de los modelos certificados hasta ahora existentes en México o asumirlos.

We explore first-passage phenomenology for biased active processes with a renewal-type structure, focusing in particular on paradigmatic run-and-tumble models in both discrete and continuous state spaces. In general, we show there is no equality between distributions of conditional first-passage times to symmetric barriers positioned in and against the bias direction. However, we give conditions for such a duality to be restored asymptotically (in the limit of a large barrier distance) and highlight connections to the Gallavotti-Cohen fluctuation relation and the method of images. Our general trajectory arguments for asymmetric run-and-tumble processes escaping from an interval of arbitrary width are supported by exact analytical results for specific first-passage-time (FPT) distributions, which we derive extending Montroll’s defect technique. Furthermore, we quantify the degree of violation of first-passage duality using Kullback-Leibler divergence and signal-to-noise ratios associated with the first-passage times to the two barriers. We reveal an intriguing dependence of such measures of first-passage asymmetry on the underlying, often hidden, tumbling dynamics which may inspire inference techniques based on FPT statistics in active systems.

Antimicrobial resistance is a threat to public health with millions of deaths linked to drug-resistant infections every year. To mitigate resistance, common strategies that are used are combination therapies and therapy switching. However, the stochastic nature of pathogenic mutation makes the optimization of these strategies challenging. Here, we propose a two-scale stochastic model that considers the effective evolution of therapies in a multidimensional efficacy space, where each dimension represents the efficacy of a specific drug in the therapy. The diffusion of therapies within this space is subject to stochastic resets, representing therapy switches. The boundaries of the space, inferred from coarser pathogen-host dynamics, can be either reflecting or absorbing. Reflecting boundaries impede full recovery of the host, while absorbing boundaries represent the development of antimicrobial resistance, leading to therapy failure. We derive analytical expressions for the average absorption times, accounting for both continuous and discrete genomic changes using the frameworks of Langevin and master equations, respectively. These expressions allow us to evaluate the relevance of times between drug switches and the number of simultaneous drugs in relation to typical timescales for drug resistance development. To study realistic therapy scenarios, we impose constraints on the number of administered therapies and/or their costs, which reveals nontrivial optimal drug-switching protocols that maximize the time before antimicrobial resistance develops while reducing therapy costs. Finally, we extend the model to consider single-cell heterogeneity to accurately capture the effects of individual mutations that result in drug resistance.

We consider a general one-dimensional overdamped diffusion model described by the Itô stochastic differential equation (SDE) d X t = μ ( X t , t ) d t + σ ( X t , t ) d W t , where W_t is the standard Wiener process. We obtain a specific condition that µ and σ must fulfil in order to be able to solve the SDE via mapping the generic process, using a suitable space-time transformation, onto the simpler Wiener process. By taking advantage of this transformation, we obtain the propagator in the case of open, reflecting, and absorbing time-dependent boundary conditions for a large class of diffusion processes. In particular, this allows us to derive the first-passage time statistics of such a large class of models, some of which were so far unknown. While our results are valid for a wide range of non-autonomous, non-linear and non-homogeneous processes, we illustrate applications in stochastic thermodynamics by focusing on the propagator and the first-passage-time statistics of isoentropic processes that were previously realised in the laboratory by Brownian particles trapped with optical tweezers.