Biomimetic flow fields for proton exchange membrane fuel cells: A review of design trends

Bipolar Plate design is one of the most active research fields in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) development. Bipolar Plates are key components for ensuring an appropriate water management within the cell, preventing flooding and enhancing the cell operation at high current densities. This work presents a literature review covering bipolar plate designs based on nature or biological structures such as fractals, leaves or lungs. Biological inspiration comes from the fact that fluid distribution systems found in plants and animals such as leaves, blood vessels, or lungs perform their functions (mostly the same functions that are required for bipolar plates) with a remarkable efficiency, after millions of years of natural evolution. Such biomimetic designs have been explored to date with success, but it is generally acknowledged that biomimetic designs have not yet achieved their full potential. Many biomimetic designs have been derived using computer simulation tools, in particular Computational Fluid Dynamics (CFD) so that the use of CFD is included in the review. A detailed review including performance benchmarking, time line evolution, challenges and proposals, as well as manufacturing issues is discussed.Ministerio de Ciencia, Innovación y Universidades ENE2017-91159-EXPMinisterio de Economía y Competitividad UNSE15-CE296

Environmental and health management in small and medium size enterprises

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2004.Includes bibliographical references (p. 96-100).Workers and employees are increasingly exposed in the workplace to chemical compounds and substances that are potentially toxic; for most of these compounds, no information exist regarding effects on human health. As one of the main employment generation sources, Small and Medium size Enterprises (SMEs) host a significant proportion of the environmental hazards currently present in the workplace. However, only a negligible amount of research or information has been completed and collected concerning SMEs environmental and health performance. SMEs possess environmental perceptions and an environmental and health behavior conditioned by the same qualitative attributes inherent to the small firm, from the kin relationships among the business members to the social role of the small company in a given community. With a prominent economic and social role in the society, SMEs are an important and still underestimated link in the environment-to-health chain. This thesis proposes an Environmental and Health Management model for SMEs. The model considers the convergence of medical, environmental, labor, and safety approaches and explores their interrelationship in three main components: the environmental conditions in the workplace, the (individuals) health conditions in the workplace, and the work-related conditions in the workplace. Nine fields of knowledge (Industrial Safety, Occupational Health, Occupational Medicine, Epidemiology, Industrial Hygiene, Toxicology, Environmental Health, Environmental Management, and Risk assessment) are considered as useful tools and approaches whose interaction may help SMEs to shape or modify their environmental perceptions and behavior, as well as may provide a general framework for the regulations applicable to SMEs.by Juan C. Arredondo.S.M

Estudios de perfiles de profundidad AES y fotoconductividad de películas delgadas de AgInS2 preparadas por co-evaporación

In this study, thin films of AgInS2 with chalcopyrite-type tetragonalstructure were grown by means of a procedure based on the sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process. The effect of the growth temperature and the proportion of the evaporated Ag mass in relation to the evaporated In mass (mAg/mIn) on the phase and homogeneity in the chemical composition were researched through X-ray diffraction measurements and Auger electrons spectroscopy. These measurements evidenced that the conditions for preparing thin films containing only the AgInS2 phase, grown with tetragonal chalcopyrite-type structure and good homogeneity of thechemical composition in the entire volume, are a temperature of 500 ºC and a 0.89 mAg/mIn proportionEn este trabajo se crecieron películas delgadas de AgInS2 con estructura tetragonal tipo calcopirita usando un procedimiento basado en la evaporación secuencial de precursores metálicos en presencia de azufre elemental, en un proceso en dos etapas. Se investigó el efecto de la temperatura de crecimiento y la proporción de la masa de Ag evaporada a la masa de In evaporada (mAg/mIn) sobre la fase y la homogeneidad en la composición química a través de medidas de difracción de rayos X y espectroscopía de electrones Auger. Estas medidas mostraron que las condiciones parapreparar películas delgadas que contengan únicamente la fase AgInS2, crecidas con estructura tipo calcopirita tetragonal y buena homogeneidad de la composición química en todo el volumen son temperatura de 500 °C y proporción mAg/mIn 0.89.  Las medidas de fotocorriente de transiente indicaron que el transporte eléctrico es afectado por procesos de recombinación, vía transiciones banda a banda y transiciones asistidas por trampas

AES depth profile and photoconductive studies of AgInS2 thin films prepared by co-evaporation

In this study, thin films of AgInS2 with chalcopyrite-type tetragonal structure were grown by means of a procedure based on the sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process. The effect of the growth temperature and the proportion of the evaporated Ag mass in relation to the evaporated In mass (mAg/mIn) on the phase and homogeneity in the chemical composition were researched through X-ray diffraction measurements and Auger electrons spectroscopy. These measurements evidenced that the conditions for preparing thin films containing only the AgInS2 phase, grown with tetragonal chalcopyrite-type structure and good homogeneity of the chemical composition in the entire volume, are a temperature of 500 ºC and a 0.89 mAg/mIn proportion.En este trabajo se crecieron películas delgadas de AgInS2 con estructura tetragonal tipo calcopirita usando un procedimiento basado en la evaporación secuencial de precursores metálicos en presencia de azufre elemental, en un proceso en dos etapas. Se investigó el efecto de la temperatura de crecimiento y la proporción de la masa de Ag evaporada a la masa de In evaporada (mAg/mIn) sobre la fase y la homogeneidad en la composición química a través de medidas de difracción de rayos X y espectroscopía de electrones Auger. Estas medidas mostraron que las condiciones para preparar películas delgadas que contengan únicamente la fase AgInS2, crecidas con estructura tipo calcopirita tetragonal y buena homogeneidad de la composición química en todo el volumen son temperatura de 500 °C y proporción mAg/mIn 0.89.  Las medidas de fotocorriente de transiente indicaron que el transporte eléctrico es afectado por procesos de recombinación, vía transiciones banda a banda y transiciones asistidas por trampas

Bioenergy transition as a strategic mechanism to diversify energy sources in rural areas in Colombia

Received: February 1st, 2023 ; Accepted: May 27th, 2023 ; Published: October 14th, 2023 ; Correspondence: [email protected], [email protected] growth in population has resulted in an increase in the consumption of goods and services, which has led to a surge in waste generation and the use of fossil fuels. To mitigate the envi-ronmental issues associated with improper waste management and reduce greenhouse gas emissions from fossil fuels, residual organic matter can be used to produce bioenergy in the form of biogas and biomethane through anaerobic digestion (AD). These biofuels can act as substitutes for liquefied petroleum gas (LPG) and natural gas (NG) and can be utilized for power and heat generation. In Colombia, the current production of biogas is 4 MW, and the government aims to increase its utilization by promoting the inclusion of biogas and biomethane in the energy matrix through a supportive regulatory framework. Studies suggest that the theoretical energy potential of livestock waste in Colombia is estimated to be 2,673 MW, but the current technological conditions allow for the utilization of only 198 MW, with the pork sector contributing 34%. This study examines the legal context and the present state of biogas in the Colombian energy matrix, while exploring the potential of the Colombian pig farming sector for biogas production. The social, economic, and environmental barriers and opportunities faced by this sector in becoming an energy producer during the transition period are also identified. The findings suggest that biogas presents a sustainable energy solution for rural areas of Colombia where pig farming is a prominent economic activity. Biogas can replace traditional fuels like LPG and firewood for cooking purposes or serve as a complementary source for electricity and thermal energy production in non-interconnected zones. This could mitigate environmental issues and reduce the prevalence of respiratory diseases associated with the use of firewood

Motives and social actor positioning: the representation of the Chilean student movement in the national press

The student movement has always been at the centre of political change in Chile, which has resulted in tensions with the heavily monopolized media. These tensions have forced the student movement to resort to more alternative media outlets to both disseminate their information and to challenge the criminalization of their movement. In this context, this article sets to explore the attributions of motive in the representation of the Chilean student movement during a three-year period (2011-2013) in the mainstream and alternative press. Throughout this article, motive is understood as the implicit and/or explicit manifestation of an individual and/or collective’s drive or wish to do (or not do) something in a particular context. The corpus comprises over 3,000 news articles, which were analysed in the light of Harré’s (2010, 2015) Social Actor Positioning and van Leeuwen’s (2000, 2008) legitimation and purpose frameworks. Results show the use of specific ideological narratives that legitimize these actors’ motives in the media representation of this conflict. Similarly, the attribution of motives depends on the actors’ role in society and the kind of press analysed. Finally, there are irreconcilable ideological differences in the government’s understanding of the students’ right and duties and vice versa, which are heavily grounded in the aftermath of Augusto Pinochet’s dictatorship

Durability parameters of reinforced recycled aggregate concrete: Case study

Recycled concrete aggregate (RA) from pavement demolition was used to make concrete. Ten concrete mixtures with different replacement percentages of RA (coarse and fine) were made. The corrosion rate of steel and the electrical resistivity of concrete were determined on reinforced concrete specimens subjected to wetting-drying cycles (3.5% solution of NaCl). Corrosion rate was determined using the electrochemical technique of linear polarization resistance, while the electrical resistivity was measured by electrochemical impedance spectroscopy. The results show that the use of RA introduces more interfaces in concrete, which accelerates the steel corrosion process because the porosity increases and the electrical resistivity decreases. However, steel corrosion and the electrical resistivity in concrete are not significantly influenced by replacing a maximum 30% of coarse aggregate or 20% of fine aggregate with RA.Peer ReviewedPreprin

Mode and dynamics of vanA-type vancomycin resistance dissemination in Dutch hospitals

Background Enterococcus faecium is a commensal of the gastrointestinal tract of animals and humans but also a causative agent of hospital-acquired infections. Resistance against glycopeptides and to vancomycin has motivated the inclusion of E. faecium in the WHO global priority list. Vancomycin resistance can be conferred by the vanA gene cluster on the transposon Tn1546, which is frequently present in plasmids. The vanA gene cluster can be disseminated clonally but also horizontally either by plasmid dissemination or by Tn1546 transposition between different genomic locations. Methods We performed a retrospective study of the genomic epidemiology of 309 vancomycin-resistant E. faecium (VRE) isolates across 32 Dutch hospitals (2012-2015). Genomic information regarding clonality and Tn1546 characterization was extracted using hierBAPS sequence clusters (SC) and TETyper, respectively. Plasmids were predicted using gplas in combination with a network approach based on shared k-mer content. Next, we conducted a pairwise comparison between isolates sharing a potential epidemiological link to elucidate whether clonal, plasmid, or Tn1546 spread accounted for vanA-type resistance dissemination. Results On average, we estimated that 59% of VRE cases with a potential epidemiological link were unrelated which was defined as VRE pairs with a distinct Tn1546 variant. Clonal dissemination accounted for 32% cases in which the same SC and Tn1546 variants were identified. Horizontal plasmid dissemination accounted for 7% of VRE cases, in which we observed VRE pairs belonging to a distinct SC but carrying an identical plasmid and Tn1546 variant. In 2% of cases, we observed the same Tn1546 variant in distinct SC and plasmid types which could be explained by mixed and consecutive events of clonal and plasmid dissemination. Conclusions In related VRE cases, the dissemination of the vanA gene cluster in Dutch hospitals between 2012 and 2015 was dominated by clonal spread. However, we also identified outbreak settings with high frequencies of plasmid dissemination in which the spread of resistance was mainly driven by horizontal gene transfer (HGT). This study demonstrates the feasibility of distinguishing between modes of dissemination with short-read data and provides a novel assessment to estimate the relative contribution of nested genomic elements in the dissemination of vanA-type resistance.Peer reviewe