Dipòsit Digital de la Universitat de Barcelona
El Dipòsit Digital de la Universitat de Barcelona és el repositori institucional que conté en format digital els materials derivats de l'activitat docent, investigadora i institucional de la comunitat universitària.
Enviaments recents
Article3D Printing of Fe27 Al24 Ni22 Cu18 Co9 High-Entropy Alloy Scaffold with Direct Ink Writing for the Degradation of Methyl Red Azo Dye(American Chemical Society, 2015-10-30) Rius Ayra, Oriol; Tahchieva, Alisiya Biserova; Carmona-Ruiz, M.; Llorca i Isern, NúriaDyes are emerging pollutants that can be classified in various ways, with azo dyes being among the most persistent in water. These dyes contain conjugated double bonds and azo groups (R–NN–R’), making their degradation in water a significant challenge. In this study, we demonstrate that a high-entropy alloy (HEA) with the composition Fe27Al24Ni22Cu18Co9 can be synthesized using mechanical alloying and subsequently 3D printed using material-extrusion direct ink writing. X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy confirmed the synthesis of a new HEA with a face-centered cubic crystal structure after 40 h of mechanical alloying. The degradation properties of the 3D-printed HEA were then investigated for the azo dye known as methyl red, revealing its efficiency at 60 °C in the presence of nitric acid (pH = 1.50), with a degradation time of 28 min and an efficiency of 99%. Moreover, according to the results of high-performance liquid chromatography, we propose the degradation mechanism occurring at the surface of the Fe27Al24Ni22Cu18Co9 HEA that effectively degrades methyl red and leading to the cleavage of the azo bond and generating two different products.- ArticleEnergy and Capital Cost Reduction in Ester Transesterification Using an Optimized Reactive Distillation System with Prefractionation(American Chemical Society, 2025-11-11) Troyano Ferré, Carles; Cabello, Rúben; Risco Morillo, Alvaro; Plesu Popescu, Alexandra Elena; Bonet, JordiReactive distillation is a highly efficient process, but its application presents significant challenges in mixtures that have azeotropes, such as in the transesterification of methyl acetate (MeAc) and methanol (MeOH) with n-butanol (BuOH). This paper proposes a reactive distillation with a prefractionation column (RDPFC) system to valorize the waste stream from the poly(vinyl alcohol) industry (30.7 wt % MeAc and 69.3 wt % MeOH) to recover high-purity MeOH and valuable n-butyl acetate (BuAc). The process was modeled and optimized in Aspen Plus version 12.1, with the objective of minimizing the total annual cost (TAC). The proposed system incorporates a prefractionation column (PFC) consisting of 26 stages working under vacuum conditions (0.6 atm) alongside a reactive column (RC) with 38 stages operating at high pressures (8 atm) to improve the conversion of the reaction. The RDPFC process attains a MeAc conversion rate of 99.2 mol %, yielding products that align with commercial specifications, including over 99.85 wt % MeOH and more than 99.5 wt % BuAc. A comparative analysis reveals that the RDPFC configuration utilizes 2.56 GJ/tBuAc, showcasing a significant 67% reduction in energy consumption when compared to the traditional reactive and extractive distillation (RED) process. The removal of the entrainer and its corresponding recovery unit primarily accounts for this improvement. This study suggests that the RDPFC system could be a highly efficient and economically attractive solution for valuing waste streams in the poly(vinyl alcohol) industry.
- ArticleHierarchies of knowledge in responses to messages of newbies in online health support groups(Elsevier, 2025-05-25) Figueras, Carolina; De Cock, BarbaraObjectives: To determine how hierarchies of knowledge are established in two online health forums: one for recovery from eating disorders and the other for diabetes. Methods: 28 threads, with a total of 55,462 words were collected from the eating disorders (ED) forum. From the diabetes (D) forum, 18 threads were extracted, with a total of 51,397 words. We performed a quantitative and a qualitative analysis of the structures and mechanisms to convey experiential knowledge and to deliver advice. Results: The frequency of strategies such as providing facts about the illness, sharing personal stories and using medical terminology was higher in the diabetes forum than in the eating disorder forum. In the category of providing advice, ED and D responders behaved as experts and formulated advice in an authoritative way by resorting to imperatives and deontics of obligation. Conclusion: In both fora, epistemic and emotional experiences are presented. The goal in each site is the creation of shared understanding among their members. Experiential knowledge is highly personal, and it is never depicted as antagonistic to medical expertise. Practice implications: Experiential knowledge is complex and rich and can complement medical expertise in the treatment of long-term and/or chronic health conditions.
- ArticleSuperhydrophobic Materials and Intermolecular Forces for Microplastics Remova(American Chemical Society, 2025-04-02) Rius Ayra, Oriol; Ren, Anhua; Tahchieva, Alisiya BiserovaMicroplastics present a major global environmental issue. The pollution of seas and oceans by microplastics highlights the urgent need to explore sustainable technologies for removing these pollutants from water. Nowadays, various studies are investigating methods to remove microplastics from water, but while these techniques are effective for larger microplastics, they often struggle to capture smaller particles. Recently, to address this challenge, superhydrophobic materials have been explored. These materials can efficiently remove microplastics from water due to their unique wetting properties, achieving removal efficiencies close to 100%. Various types of superhydrophobic materials, such as sponges, meshes, and particulate materials, have been used to remove microplastics under different conditions and environments. This review will highlight the most recent advances in superhydrophobic materials for effectively removing microplastics, as well as review key studies to better understand the microplastic removal mechanism and the intermolecular forces between these solid pollutants and superhydrophobic surfaces.
- Treball de fi de grauA Study of the Kelly Criterion: from Betting to Financial Markets(2026-06-10) Mundet Lopez, Pau; Corcuera Valverde, José Manuel[eng] The Kelly criterion prescribes, at each investment opportunity, the fraction of capital that maximises the long-run exponential growth rate of wealth, equivalently the expected logarithm of wealth. This thesis develops the criterion from first principles and follows it from its origin in games of chance to its place in the continuous-time theory of financial markets. The starting point is the binary gambling model, in which a gambler repeatedly stakes a fixed proportion of current capital on a favourable bet. We show that the Kelly fraction resolves the conflict between maximising expected wealth and minimising the probability of ruin. This fraction is then shown to be asymptotically optimal: almost surely it outgrows any other fixed proportion in the long run, and it minimises the expected time to reach a distant wealth target. Both even and uneven odds are treated. The criterion is then carried into continuous time. A scaling limit of the discrete model yields geometric Brownian motion, and within the one-dimensional Black-Scholes market the long-run growth rate is maximised by the constant fraction $\ell^* = (\mu-r)/\sigma^2$, which a Hamilton-Jacobi-Bellman verification argument proves optimal among all admissible strategies. We conclude by identifying $\ell^*$ as the logarithmic-utility case of Merton’s classical solution to the optimal portfolio problem, so that the Kelly criterion appears as a distinguished member of a one-parameter family of optimal strategies indexed by relative risk aversion. [cat] El criteri de Kelly prescriu, en cada oportunitat d’inversió, la fracció de capital que maximitza la taxa exponencial de creixement de la riquesa a llarg termini, o, equivalentment, l’esperança del logaritme de la riquesa. Aquesta tesi desenvolupa el criteri a partir de primers principis i en segueix l’evolució des del seu origen en els jocs d’atzar fins al seu lloc dins la teoria contínua dels mercats financers. El punt de partida és el model binari d’apostes, en el qual un jugador aposta repetidament una proporció fixa del seu capital actual en una aposta favorable. Mostrem que la fracció de Kelly resol el conflicte entre maximitzar la riquesa esperada i minimitzar la probabilitat de ruïna. A continuació es demostra que aquesta fracció és asimptòticament òptima: gairebé amb certesa supera a llarg termini qualsevol altra proporció fixa, i minimitza el temps esperat necessari per assolir un objectiu llunyà de riquesa. Es tracten tant les apostes amb quotes equitatives com les de quotes desiguals. El criteri es trasllada després al temps continu. Un límit d’escala del model discret condueix al moviment brownià geomètric, i dins del mercat unidimensional de Black-Scholes la taxa de creixement a llarg termini es maximitza amb la fracció constant $\ell^* = (\mu-r)/\sigma^2$, que un argument de verificació basat en l’equació de Hamilton-Jacobi-Bellman demostra òptima entre totes les estratègies admissibles. Finalment, identifiquem $\ell^*$ com el cas d’utilitat logarítmica de la solució clàssica de Merton al problema de cartera òptima, de manera que el criteri de Kelly apareix com un membre distingit d’una família uniparamètrica d’estratègies òptimes indexades pel grau d’aversió relativa al risc.