Diseño y construcción de un banco de pruebas para medir pérdidas de potencia por fricción en un motor monocilíndrico de cuatro tiempos

Los procesos naturales en los que se ven involucradas interacciones energéticas son determinadas mediante la aplicación de las leyes de la termodinámica. La primera ley, cuyo enunciado dice: “La energía no se crea ni se destruye en un proceso; sólo puede cambiar de forma.”(Termodinámica. Cenguel 6° ed, pag 70) [1].Se refiere al principio de conservación de la energía, pero el cumplimiento de esta ley no garantiza que un proceso pueda tener lugar, para esto es necesario definir la segunda ley de la termodinámica, la cual permite definir el sentido en el que un intercambio energético puede realizarse, además, la segunda ley también establece que la energía posee cierta calidad y la misma puede degradarse; la segunda ley también brinda las herramientas para mantener la energía de mejor calidad posible

Efficiency of inefficient endoreversible thermal machines

We present a study of the performance of endoreversible thermal machines optimized with respect to the thermodynamic force associated with the cold bath in the regime of small thermodynamic forces. These thermal machines can work either as an engine or as a refrigerator. We analyze how the optimal performances are determined by the dependence of the thermodynamic flux on the forces. The results are motivated and illustrated with a quantum model, the three level maser, and explicit analytical expressions of the engine efficiency as a function of the system parameters are given

Inspiratory resistance decreases limb blood flow in COPD patients with heart failure

Hosp Clin Porto Alegre, Exercise Pathophysiol Res Lab, BR-90035007 Porto Alegre, RS, BrazilHosp Clin Porto Alegre, Div Cardiol, BR-90035007 Porto Alegre, RS, BrazilSerra Gaucha Coll, Phys Therapy Dept, Caxias Do Sul, RS, BrazilHosp Clin Porto Alegre, Pulmonary Div, Porto Alegre, RS, BrazilFed Univ Rio Grande, Fac Med, Dept Med, Porto Alegre, RS, BrazilUniversidade Federal de São Paulo, Dept Med, Div Resp Dis, Pulmonary Funct & Clin Exercise Physiol Unit, São Paulo, BrazilQueens Univ, Dept Med, Div Respirol, LACEP, Kingston, ON, CanadaKingston Gen Hosp, Kingston, ON K7L 2V7, CanadaUniversidade Federal de São Paulo, Dept Med, Div Resp Dis, Pulmonary Funct & Clin Exercise Physiol Unit, São Paulo, BrazilWeb of Scienc

Optimal performance of endoreversible quantum refrigerators

The derivation of general performance benchmarks is important in the design of highly optimized heat engines and refrigerators. To obtain them, one may model phenomenologically the leading sources of irreversibility ending up with results that are model independent, but limited in scope. Alternatively, one can take a simple physical system realizing a thermodynamic cycle and assess its optimal operation from a complete microscopic description. We follow this approach in order to derive the coefficient of performance at maximum cooling rate for any endoreversible quantum refrigerator. At striking variance with the universality of the optimal efficiency of heat engines, we find that the cooling performance at maximum power is crucially determined by the details of the specific system-bath interaction mechanism. A closed analytical benchmark is found for endoreversible refrigerators weakly coupled to unstructured bosonic heat baths: an ubiquitous case study in quantum thermodynamics

Recent Progress in Stimuli-Responsive Antimicrobial Electrospun Nanofibers

Electrospun nanofibrous membranes have garnered significant attention in antimicrobial applications, owing to their intricate three-dimensional network that confers an interconnected porous structure, high specific surface area, and tunable physicochemical properties, as well as their notable capacity for loading and sustained release of antimicrobial agents. Tailoring polymer or hybrid-based nanofibrous membranes with stimuli-responsive characteristics further enhances their versatility, enabling them to exhibit broad-spectrum or specific activity against diverse microorganisms. In this review, we elucidate the pivotal advancements achieved in the realm of stimuli-responsive antimicrobial electrospun nanofibers operating by light, temperature, pH, humidity, and electric field, among others. We provide a concise introduction to the strategies employed to design smart electrospun nanofibers with antimicrobial properties. The core section of our review spotlights recent progress in electrospun nanofiber-based systems triggered by single- and multi-stimuli. Within each stimulus category, we explore recent examples of nanofibers based on different polymers and antimicrobial agents. Finally, we delve into the constraints and future directions of stimuli-responsive nanofibrous materials, paving the way for their wider application spectrum and catalyzing progress toward industrial utilization