A thermodynamically consistent Markovian master equation beyond the secular approximation

Markovian master equations provide a versatile tool for describing open quantum systems when memory effects of the environment may be neglected. As these equations are of an approximate nature, they often do not respect the laws of thermodynamics when no secular approximation is performed in their derivation. Here we introduce a Markovian master equation that is thermodynamically consistent and provides an accurate description whenever memory effects can be neglected. The thermodynamic consistency is obtained through a rescaled Hamiltonian for the thermodynamic bookkeeping, exploiting the fact that a Markovian description implies a limited resolution for heat. Our results enable a thermodynamically consistent description of a variety of systems where the secular approximation breaks down.

Regenerative food systems and the conservation of change

In recent years, interest has increased in regenerative practices as a strategy for transforming food systems and solving major environmental problems such as biodiversity loss and climate change. However, debates persist regarding these practices and how they ought to be defined. This paper presents a framework for exploring the regenerative potential of food systems, focusing on how food systems activities and technologies are organized rather than the specific technologies or practices being employed. The paper begins with a brief review of debates over sustainable food systems and the varying ways that regenerative food systems have been defined and theorized. Then, it provides the theoretical backing of the framework—the conservation of change principle—which is an interpretation of the laws of thermodynamics and theories of adaptive change as relevant to the regenerative capacity of living systems. Next, the paper introduces the framework itself, which comprises two independent but intersecting dimensions of food systems organization: resource diversity and livelihood flexibility. These two dimensions result in four archetypical regimes for food systems: degenerative, regenerative, impoverished, and coerced. The paper defines each and offers real-world examples. Finally, the paper concludes with a discussion of pathways for transforming food systems and opportunities for additional research.

Experimental Energy and Exergy Analysis of an Automotive Turbocharger Using a Novel Power-Based Approach

The performance of turbochargers is heavily influenced by heat transfer. Conventional investigations are commonly performed under adiabatic assumptions and are based on the first law of thermodynamics, which is insufficient for perceiving the aerothermodynamic performance of turbochargers. This study aims to experimentally investigate the non-adiabatic performance of an automotive turbocharger turbine through energy and exergy analysis, considering heat transfer impacts. It is achieved based on experimental measurements and by implementing a novel innovative power-based approach to extract the amount of heat transfer. The turbocharger is measured on a hot gas test bench in both diabatic and adiabatic conditions. Consequently, by carrying out energy and exergy balances, the amount of lost available work due to heat transfer and internal irreversibilities within the turbine is quantified. The study allows researchers to achieve a deep understanding of the impacts of heat transfer on the aerothermodynamic performance of turbochargers, considering both the first and second laws of thermodynamics.

Chemical Thermodynamics

Chemical Thermodynamics discusses the fundamental laws of thermodynamics along with their relationships to heat, work, enthalpy, entropy, and temperature. Predicting the direction of a spontaneous change and calculating the change in entropy of a reaction are core concepts. The relationship between entropy, free energy and work is covered. The Gibbs free energy is used quantitatively to predict if reactions or processes are going to be exothermic and spontaneous or endothermic under the stated conditions. Also explored are the enthalpy and entropy changes during a phase change. Finally the Gibbs free energy of a chemical reaction is related to its equilibrium constant and the temperature.

CASCADE REFRIGERATION SYSTEM FOR LOW TEMPERATURES USING NATURAL FLUIDS

Cascade refrigeration systems work with two or more serial disposed cycles and can obtain internal temperatures below -60°C, which is necessary for several activities in medicine and scientific research. This paper presents a thermodynamic analysis of cascade system refrigeration using natural refrigerant fluids for ultra-low temperatures. These fluids are environmentally friendly refrigerant and are an alternative to hydro chlorofluorocarbons (HCFCs) and to hydrofluorocarbons (HFCs). Energy and exergy analyses were performed using a thermodynamic model based on the law of conservation of mass and also on the first and second laws of thermodynamics. A simulator was developed to assess the technical practicability of this system, considering it running as a real refrigeration cycle. Natural fluids have best performance energetically and environmentally.