Abstract Thermodynamic cycles are idealized processes that can convert heat into work or produce heat flow against a temperature gradient with the input of work. They remain an active area of research in modern stochastic thermodynamics. In particular, cyclic active heat engines have been shown to display a rich phenomenology, such as "violations" of the Carnot bound on efficiency and an improved performance in comparison to their passive counterparts. We introduce the concept of cyclic active refrigerators using a previously derived second law for cyclic active systems. We show that for cyclic active refrigerators, a naive definition of the coefficient of performance can exceed the bound set by the standard second law for passive refrigerators. We also show that cyclic active systems can behave like a Maxwell's demon, with heat flowing from the cold to the hot reservoir without any work input. Beyond this phase, cyclic active systems can enter a hybrid phase, functioning as both a heat engine and a refrigerator simultaneously. Our results are obtained with two models that involve active Brownian particles, a simpler one that allows for analytical results and a more realistic one that is analyzed through numerical simulations.

We investigate a two-qubit SWAP thermal machine—a streamlined analog of the four-stroke Otto cycle—whose working medium comprises inertially moving Unruh-DeWitt qubit detectors, each coupled to a thermal quantum field bath prepared at a different temperature. In the presence of relative motion between the working medium and the thermal baths, we derive thermodynamic uncertainty relations (TURs) that quantify the trade-off between performance, entropy production, and power fluctuations. Our analysis identifies regimes where relativistic motion leads to stronger violation of classical TURs, previously observed in static quantum setups. In addition, we establish generalized performance bounds for the thermal machine operating as either a heat engine or a refrigerator, and discuss how relativistic motion can enhance their performances beyond the standard Carnot limits defined by rest-frame temperatures.

Excessive heat generation during bone drilling causes thermal osteonecrosis, posing a significant risk in orthopedic and dental procedures. While various aspects of drill design have been studied, the specific influence of margin geometry remains underexplored in the context of thermal engineering. This study integrates drilling simulation, experimental validation, and statistical optimization to evaluate the thermal impact of drill margin width ( M w ) and height ( M h ) during cortical bone drilling. A validated thermo-mechanical model was developed using commercial software DEFORM-3D. The simulation results were validated with experimental bone drilling with small temperature prediction errors (2.4% and 8.0%). Key thermal metrics (maximum temperature ( T max ), osteonecrosis diameter (OD), and osteonecrosis depth (OH)) were optimized using a central composite design (CCD) of response surface methodology (RSM) and desirability-based multi-objective optimization. Results revealed that M w had the most significant second-order influence on T max (47.2%), while M h dominated OD (41.1%) and OH (47.8%). The optimal drill margins ( M h = 0.05 mm and M w = 0.22 mm), which achieved a desirability score of 0.985, could reduce T max by up to 44.8°C, which is below the osteonecrosis threshold. This work highlights drill margins as a critical yet previously underutilized design variable, offering an alternative pathway for the thermally optimized development of surgical tools and next-generation robotic-assisted drilling systems.

Tesla valves are passive flow-control devices that enables asymmetry without moving parts. In recent years, they have attracted renewed interest due to their wide range of applications, spanning from biomedical and agricultural systems to thermal and marine engineering. The performance of a 3D-printed double Tesla valve is experimentally investigated using an integrated low-cost Internet of Things (IoT) measurement system. The valve performance is evaluated for inlet volumetric flow rates ranging from 5 to 20 L/min. The results demonstrate a clear asymmetry between forward and reverse flow, with a maximum diodicity of 1.96 observed at the lowest (5–6 L/min) flow rate. The proposed low-cost experimental framework combines additive manufacturing and real-time IoT-based monitoring, offering a reproducible and accessible approach for investigating passive flow-control devices at flow-rate regimes beyond typical microfluidic applications.

Optimizing impact toughness of Zr-based bulk metallic glasses via cryogenic thermal cycling-induced free volume engineering

Abstract Open quantum systems play a central role in current nanoscale technologies, such as molecular electronics, quantum heat engines, quantum computation and information processing. A major theoretical challenge is to construct dynamical models that are simultaneously consistent with classical thermodynamics and with the requirement of complete positivity of quantum evolution. In this work we develop a framework that addresses this issue by systematically extending classical stochastic dynamics to the quantum domain. We begin by formulating a generalized Langevin equation in which both friction and noise act symmetrically on the two Hamiltonian equations. From this, we derive a generalized Klein–Kramers equation expressed in terms of Poisson brackets, and we show that it admits the Boltzmann distribution as its stationary solution while fulfilling the first and second laws of thermodynamics along individual trajectories. Applying canonical quantization to this classical framework yields two distinct quantum master equations, depending on whether the friction operators are taken to be Hermitian or non-Hermitian. By analyzing the dynamics of a harmonic oscillator, we determine the conditions under which these equations reduce to a Lindblad-type generator. Our results demonstrate that complete positivity is ensured only when friction and noise are included in both Hamiltonian equations, fully justifying the classical construction. Moreover, we find that the friction coefficients must adhere to the same positivity condition in both the Hermitian and non-Hermitian formulations, revealing a form of universality that transcends the specific operator representation. The formalism developed here presents a thermodynamically consistent and completely positive quantum extension of classical stochastic mechanics. It offers a versatile tool for deriving quantum versions of thermodynamic laws and is directly applicable to a broad class of non-equilibrium nanoscale systems of current theoretical and technological interest.

The development of low-cost and high-performance noble-metal-free catalysts for the oxygen evolution reaction (OER) is central to advancing alkaline water electrolysis. This work introduces a novel "composition-thermal history" design strategy, synergistically combining controlled A-site Sr2+ doping with optimized high-temperature sintering (950°C) in Pr-based perovskite. The resulting Pr0.75Sr0.25Ni0.7Co0.3O3 (PSNC-25) exhibits unprecedented nanostructuring and a maximized concentration of oxygen vacancies, unlocking efficient OER via lattice oxygen-mediated mechanism. Sr-induced lattice distortion drastically reduces oxygen vacancy formation energy from 2.06 to 1.14eV, promoting facile lattice oxygen participation. Thermal engineering stabilizes high-valence Co4+/Ni3+ states and enhances M─O covalency. Electrochemically, PSNC-25 achieves exceptional activity in 1M KOH: a low overpotential of 389mV at 10mA cm-2 and a Tafel slope of 83mV dec-1, significantly surpassing undoped PrNi0.7Co0.3O3 (η10 ＞ 570 mV). It also exhibits robust durability, by > 120 h chronopotentiometry at 10mA cm-2 with only ∼45mV potential drift. This work establishes a rational framework for activating LOM in cost-effective perovskites through dopant-induced electronic modulation and nano-structural control, advancing scalable green hydrogen production.

Quantum heat engines, compared to their classical counterparts, offer many advantages due to quantum effects. The study of different cycle modes contributes to the improvement of heat engine efficiency. In this paper, based on a quantum hybrid heat engine, we compare three cycle modes involving Bell-type quantum weak measurement (without observing the results) and two heat baths at different temperatures, where quantum weak measurements play the role of heat source. Thus, there are two types of heat sources and three processes involving heat absorption or release in our model. In other words, we study a multi-stroke quantum hybrid heat engine. Moreover, we further investigate three types of cycle modes using a working substance composed of a three-particle XXZ spin chain. In the adiabatic stroke, we select three Hamiltonian parameters and vary them adiabatically from their initial to final values, comparing their effects on engine efficiency. In particular, we examine how the ordering of the weak-measurement stroke and the adiabatic stroke influences heat absorption, heat release, and engine efficiency. Additionally, we analyze the impact of the high-temperature bath’s temperature and the weak-measurement strength on the engine efficiency.

The Indosinian granitoids of Guangdong Province, South China, record a complex history of crust–mantle interactions during the Triassic assembly of the South China Block (SCB) and Indochina Block (ICB). Integrated zircon U–Pb geochronology, geochemistry, and Sr–Nd–Hf isotopes from these plutons reveal two magmatic episodes: an Early Indosinian phase (253–230 Ma) of large, west-to-east younging batholiths, and a later scattered phase (230–200 Ma). While most granitoids are peraluminous S-types formed by the melting of the Paleoproterozoic crust with limited mantle input (0–30%), the Taibao pluton and its enclaves are anomalous. They are more mafic and record a substantial mantle contribution (40–65%), pointing to focused, high-heat flux magmatism. This spatial and petrogenetic heterogeneity, coupled with the granitoids’ NE–SW trend orthogonal to the collisional zone, cannot be explained by simple crustal thickening. We propose that these features are the direct result of the slab tearing of the subducting Paleo-Tethys oceanic plate, triggered by an oblique collision between the SCB and ICB. This tearing induced asthenospheric upwelling, providing the thermal engine for widespread crustal anatexis and localized mantle melting. Our findings establish slab tearing as a key catalyst for syn-collisional, high-temperature magmatism, offering a unified framework for interpreting lithospheric processes during continental collisions.

Abstract In a recent analysis (Misra et al. in npj Quantum Inf 10:34, 2024. 10.1038/s41534-024-00817-w), it has been shown that Hawking radiation is the main source of energy to empower a coherent signal pulse. In this work, we have explored the same effect for a case where the time derivative of the scalar field mode of the redirected Hawking radiation appears explicitly in the interaction Hamiltonian. We have considered a stream of two-level atoms falling freely towards the event horizon of a black hole. The Hawking radiation redirected from an orbiting mirror interacts with the atoms which make a transition between the ground state and the excited state through the emission of a signal photon. The signal pulse is amplified by the mechanical work done by the redirected Hawking mode. The whole set up works as a black hole powered quantum heat engine. We have shown that this amplification depends on the frequency of both the signal mode and the Hawking mode, the flux of the redirected Hawking mode and the lapse function of the black hole. In contrast to the result obtained in Misra et al. (npj Quantum Inf 10:34, 2024. 10.1038/s41534-024-00817-w), we observe in our analysis, that due to the coupling of the momentum degrees of freedom of the Hawking radiation modes with the freely falling detector, the power output depends inversely with the lapse function of the black hole and is proportional to the frequency of the emitted Hawking radiation. As a result the maximum output power enhances significantly if the atom is very close to the event horizon of the black hole. We have analyzed this effect for two types of detectors attached to the cavity. At first we considered a point-like detector and then we have done the analysis from the perspective of a detector with smearing.

Abstract Black holes are some of the most interesting objects in the universe. While they first arise in the complicated behavior of general relativity, the physical laws ruling their behavior are surprisingly simple. For example, one of the core facts about black holes is that their area never decreases, much alike the entropy in thermodynamics. In this note directed at introductory physics students and their instructors, we use this similarly to understand properties of black hole physics using standard techniques from an undergraduate course in thermal physics. We explore the never-decreasing nature of black hole area to obtain bounds on the energy emitted in a black hole merger (a calculation originally done by Hawking). We show how this allows us to think of black holes in manners very similar to heat engines, and how these ideas have been used in modern gravitational wave observatories to test general relativity. This allows a research-level topic to be discussed in introductory physics lectures.

Quantum heat engine based on a three-spin-½ XX model with DM interaction and magnetic field

Lightweight polymer-based composites with high thermal conductivity and mechanical robustness are highly desirable for high-efficiency thermal management in electronics. Herein, a thermal annealing-directed molecular engineering strategy is developed to precisely reconfigure the chain conformation and reconstruct the hydrogen-bonding network in aramid nanofiber (ANF) films. Moderate annealing at 200 °C induces the generation of ordered molecular structures and the reconstruction of hydrogen-bonding networks in the ANF film, leading to a substantial increase in its intrinsic thermal conductivity up to 6.16 W m-1 K-1 (a 45.3% enhancement relative to the unannealed film), along with an improved tensile strength of 262.9 MPa. On this basis, highly oriented graphite microplatelets (GMPs) with a large aspect ratio are incorporated to form a synergistic thermally conductive architecture. The improved π-π interactions between the matrix with ordered molecular chain conformation and GMPs significantly contribute to enhancing interfacial phonon coupling and constructing continuous thermal transfer pathways. Thus, the annealed ANF/GMP composite film delivers an exceptional in-plane thermal conductivity of 68.06 W m-1 K-1 while maintaining a mechanical strength of 165.0 MPa. By integrating molecular-scale structural regulation with multiscale synergistic design, this study offers a new avenue for the development of high-performance intrinsically thermally conductive polymers and their composites.

This paper builds upon a 2024 IJMEE paper, which formally established the logical equivalence of the first and second laws of thermodynamics. Logical equivalence means that both laws are either true or false together; however, this does not imply that the laws are identical or necessarily derivable from one another. As stated in the 2024 paper, “… if we can know that the first and second laws are equivalent, then we should know.” Accordingly, the present work investigates how this equivalence informs our understanding of heat engine cycles. Through a truth table analysis and application to real and hypothetical heat engine cycles , this paper shows that a violation of one law necessitates the violation of the other, even if numerical calculations appear to suggest otherwise. Understanding this relationship not only clarifies the interconnectedness of the two laws but also provides students and educators with a valuable conceptual framework for analyzing thermodynamic systems. This insight enriches problem-solving strategies and reinforces the critical role of equilibrium and energy conservation in determining the feasibility of thermodynamic processes.

Abstract The ternary hybrid nanofluids are in high demand in the context of engineering systems such as compact heat exchangers, rotating chemical reactors, and high-performance cooling of electronics engineering devices, which are seeking far more advanced thermal management solutions. This research provides an extensive computational model of a ternary hybrid nanofluid flow (molybdenum disulfide (MoS 2 ), graphene oxide (GO) and copper (Cu) in acetic acid–water base) between two turns comprising of concentric cylinders. The model has a unique combination of the influence of chemical reaction, thermal radiation, and the shape fracture of nanoparticles (spherical, cylindrical, platelet) to fill a considerable gap in the literature. The main aim is to create a strong mathematical model of this complicated system, define the heat generated in the system, and determine the effect of shape fracture on the thermal conductivity and fluid dynamics. The resulting governing nonlinear partial differential equations are then reduced to ordinary differential equations and solved through the use of the Adomian Decomposition Method (ADM) with the validation of the results by the Homotopy Analysis Method (HAM)-package, which reveals very good agreement (e.g., velocity profiles within 3% of benchmark studies). The most important quantitative results are that the flow velocity is increased with an increase in the Grashof number by half, and the radiation parameter may drop the temperature of the fluid by 20%. Moreover, nanoparticles in the form of plates produce approximately 8% more entropy than the spheres. These outcome proves that the forces of buoyancy, Brownian motion, and thermo-phoresis severely affect the flow and heat transfer. The findings present the critical information toward the optimisation of the thermal efficiency and design of advanced energy systems, which have a great contribution to the thermal engineering and sustainable energy technology.

Mode coupling offers a degree of freedom for tailoring optical responses in plasmonic nanostructures, which is beneficial for both fundamental and applied studies in optoelectronics. While a wealth of mode hybridization phenomena were reported for interactions between two bright modes or a bright mode and a dark mode, the coupling between dark modes remains underexplored. Here, we report on the coupling properties of two dark modes in plasmonic metamaterials. In our fabricated dual-stripe resonators made of metal–insulator–metal (MIM) layers, the coupling of dark second-order magnetic resonances leads to both hybridized bright mode and dark mode, whose quality (Q) factors are improved by a factor of approximately 2 compared to the uncoupled mode in single-stripe resonators in measurement. Polarization-selective excitations of the hybridized bright mode and dark mode are also demonstrated and are explained with both near-field and far-field mode properties. By varying the coupling strength of the MIM resonators, critical coupling of the hybridized mode can be achievable, allowing a flexible control over the absorption efficiency and the Q factor. Our findings provide new insights into dark mode coupling properties, which laid a foundation for hybridized mode applications in sensing, thermal engineering, and nanophotonic devices.

Introduction The specific geological bedrock in the Czech Republic causes one of the highest levels of radon exposure in the world. The current Czech National Action Plan, based on the WHO 2005 directive on the reduction of radon exposure in workplaces and homes, covers the monitoring of the non-exceedance of the reference level of 300 Bq m −3 in relevant buildings, including the determination of the average air exchange rate (AER). Methods A dual-tracer source–sorbent tube system was designed to determine the average AER over the measurement period, ranging from a few days up to 1 month. This system aims to create a cost-effective method for application in houses on a national level. AER assessment and simultaneous radon gas measurements enable the estimation of the behavior of radon entry rate into the buildings. The system based on the use of multiple tracer gases also allows the estimation of inter-compartment airflows between individual floors of measured multi-story buildings. The average AER in a building is calculated from the known weight difference of the container filled with suitable volatile organic compounds (VOCs), the amount of the tracer adsorbed on a tube determined by a gas chromatography system, the temperature, time exposure in a dwelling, and the uptake rate for specific sorbent and VOC tracer. Results The total uncertainties of the AER measured in the field were around 15%, and the inter-compartment airflows, which were typically of the order of units of m 3 h −1 , ranged from 30% to 60%, with a coverage factor of k = 1. The exposure time influence in correlation with temperatureinfluence of the uptake rates for a PFT—Carbopack B™ systemwas assessed during measurement in the radon chamber. Discussion The main outcome of the method developed is to provide customers, from the relevant field of building and thermal engineering or indoor air and radiation hygiene, an independent result of the measurement of the AER which has a key influence on heat loss in buildings and the behavior of all indoor pollutants in gaseous and aerosol form.

This study investigates the genesis of gold mineralization at the Rodruin prospect in the central Eastern Desert (CED) of Egypt, with the aim of constraining the relative contributions of metamorphic and magmatic fluids to ore formation. Gold mineralization at Rodruin is hosted by quartz–carbonate veins emplaced within a shear zone that transects low-grade metasedimentary sequences intruded by Ediacaran post-tectonic granitoids. It exhibits characteristics transitional between orogenic turbidite-hosted and polymetallic vein-type mineralization. Although metamorphic devolatilization is interpreted to have generated the dominant ore-forming fluids, adjacent granitoid intrusions acted primarily as a thermal engine, with only a limited direct input of magmatic-hydrothermal fluids. This interpretation is supported by the occurrence of magmatic-affiliated mineral inclusions (monazite, cassiterite, and zircon) coupled with generally low concentrations of trace elements typically enriched in granitic magmatic-hydrothermal fluids (Sb, Bi, Mo, W, Sn, Nb, and Ta), collectively indicating a subordinate magmatic contribution. Rare earth element (REE) patterns of the ore samples closely resemble those of the nearby granitoids, displaying LREE enrichment; however, a distinct positive Eu anomaly is restricted to the ore assemblages and is attributed to hydrothermal feldspar alteration supporting magmatic involvement in ore formation. Carbon and oxygen isotope compositions (δ13C = −6.6 to −2.36‰; δ18O = +15.7 to +19.7‰), together with REE signatures comparable to primitive mantle values and textural evidence for synchronous sulfide–carbonate precipitation, manifested by rhythmic banding of carbonates and sulfides unequivocally indicate a hydrothermal–metasomatic origin. Collectively, these lines of evidence support a hybrid metamorphic–magmatic model in which gold and associated base metals were predominantly transported by metamorphic fluids, whose mobilization and focusing were enhanced by the thermal influence of Younger granitic intrusions, whereas magmatic-hydrothermal fluids contributed only a minor proportion to the overall metal budget.

Niobium oxide (NbOx)-based threshold switching memristors (TSMs) demonstrate significant promise for hardware implementation of neuromorphic computing, but their threshold stability's susceptibility to external environmental variations remains unclear. This work elucidates the switching mechanism in an NbOx-TSM incorporating a low-thermal-conductivity CdTe2 interlayer, which operates via the Poole-Frenkel (PF) emission model. Our investigation reveals that a double interlayer structure yields the highest effective thermal resistance, thereby most effectively reducing the threshold voltage. By implementing this structure, we enhanced the switching stability by 30.9%. Furthermore, increasing the thickness of the double-sided interlayers from 3 nm to 9 nm improved the stability by an additional 24.7% while simultaneously lowering the threshold voltage. The impact of the interlayer thickness on oscillatory behavior was systematically analyzed within a leaky integrate-and-fire (LIF) neuron circuit, where the observed frequency saturation phenomenon provides critical guidance for thermal engineering design. Capitalizing on these findings, we developed a multimodal, integrated memristor-based system for electrocardiogram (ECG) arrhythmia detection that leverages device thickness and temperature characteristics to achieve a classification accuracy rate of 90.0%. This work underscores the significant value of such physically interpretable devices for the hardware realization of neuromorphic computing.

Abstract We propose a quantum Otto heat engine using a finite-size Dicke-Stark model as the working substance. In the extended coherent state space, the complete energy spectrum and eigenstates are obtained through numerical calculations. Within the infinite-time and finite-time thermodynamics frameworks, we find that the output work, efficiency, and power can be optimized by adjusting the Stark field strength, the qubit-boson coupling strength, stroke times, and number of atoms. Our results reveal that output work and efficiency are maximized near the coupling strength at the superradiant phase transition (SPT). Tuning the Stark field strength modifies the energy level structure and SPT, effectively suppressing entropy generation and quantum friction during nonequilibrium evolution. We also show that asymmetric heat engines-where the two isochoric strokes operate with different Stark field strengths and durations-further improve engine performance. These results may guide future implementations of efficient quantum heat engines.