Nonequilibrium Research Articles

Redshifting the Study of Cold Brown Dwarfs and Exoplanets: The Mid-infrared Wavelength Region as an Indicator of Surface Gravity and Mass

JWST is opening many avenues for exploration. For cold brown dwarfs and exoplanets, JWST has opened the door to the mid-infrared wavelength region, where such objects emit significant energy. For the first time, astronomers have access to mid-infrared spectroscopy for objects colder than 600 K. The first spectra appear to validate the model suite known as ATMO 2020++: atmospheres that include disequilibrium chemistry and have a nonadiabatic pressure–temperature relationship. Preliminary fits to JWST spectroscopy of Y dwarfs show that the slope of the energy distribution from λ ≈ 4.5 μm to λ ≈ 10 μm is very sensitive to gravity. We explore this phenomenon using PH3-free ATMO 2020++ models and updated Wide-field Infrared Survey Explorer W2−W3 colors. We find that an absolute 4.5 μm flux measurement constrains temperature, and the ratio of the 4.5 μm flux to the 10–15 μm flux is sensitive to gravity and less sensitive to metallicity. We identify 10 T dwarfs with red W2−W3 colors that are likely to be very-low-gravity, young, few-Jupiter-mass objects; one of these is the previously known COCONUTS-2b. The unusual Y dwarf WISEPA J182831.08+265037.8 is blue in W2−W3, and we find that the 4–18 μm JWST spectrum is well reproduced if the system is a pair of high-gravity 400 K dwarfs. Recently published JWST colors and luminosity-based effective temperatures for late-T and -Y dwarfs further corroborate the ATMO 2020++ models, demonstrating the potential for significant improvement in our understanding of cold, very-low-mass bodies in the solar neighborhood.

Influence of phase difference and amplitude ratio on Kelvin–Helmholtz instability with dual-mode interface perturbations

A two-component discrete Boltzmann method (DBM) is employed to study the compressible Kelvin–Helmholtz (KH) instability with dual-mode interface perturbations, consisting of a fundamental wave and a second harmonic. The phase difference is analyzed in two distinct ranges, and the amplitude ratio is studied by varying the amplitude of either the first or second harmonic. The global average density gradient and the global mixing degree are analyzed from a hydrodynamic non-equilibrium perspective. The thermodynamic non-equilibrium (TNE) intensity is probed as a thermodynamic non-equilibrium variable. The system is also explored from a geometric perspective, with a focus on the rotation of two vortices, the mixing layer width, and the non-equilibrium area. Physically, under the influence of shear velocity, the fluid interface becomes distorted and progressively elongated, resulting in the formation of two small vortex structures and an enhancement of the physical gradient. The two vortices then begin to interact and merge into a single large vortex with complex fluid structures. Consequently, the physical gradient decreases, and the local TNE intensity weakens. Subsequently, the material interface elongates further, increasing the non-equilibrium region and enhancing the local TNE intensity. Finally, the physical gradient decreases due to dissipation and/or diffusion, weakening the local TNE intensity.

"Assembly Theory" in life-origin models: A critical review.

Any homeostatic protometabolism would have required orchestration of disparate biochemical pathways into integrated circuits. Extraordinarily specific molecular assemblies were also required at the right time and place. Assembly Theory conflated with its cousins-Complexity Theory, Chaos theory, Quantum Mechanics, Irreversible Nonequilibrium Thermodynamics and Molecular Evolution theory- collectively have great naturalistic appeal in hopes of their providing the needed exquisite steering and controls. They collectively offer the best hope of circumventing the need for active selection required to formally orchestrate bona fide formal organization (as opposed to the mere self-ordering of chaos theory) (Abel and Trevors, 2006b). This paper focuses specifically on AT's contribution to naturalistic life-origin models.

Stochastic thermodynamics for biological functions

AbstractLiving systems operate within physical constraints imposed by nonequilibrium thermodynamics. This review explores recent advancements in applying these principles to understand the fundamental limits of biological functions. We introduce the framework of stochastic thermodynamics and its recent developments, followed by its application to various biological systems. We emphasize the interconnectedness of kinetics and energetics within this framework, focusing on how network topology, kinetics, and energetics influence functions in thermodynamically consistent models. We discuss examples in the areas of molecular machine, error correction, biological sensing, and collective behaviors. This review aims to bridge physics and biology by fostering a quantitative understanding of biological functions.

Why Does the Biosphere Interact with Earth's Climate, and How Do the Two-Way Interactions Work?

With the use of matter (carbon dioxide, nutrients, and water) and solar energy, phytoplankton produce oxygen and carbohydrates, which are transported to predators through the oceanic food web hierarchy. From the viewpoint of irreversible processes of non-equilibrium thermodynamics, oceanic photosynthesis gives a mechanistic picture of living things characterized by double sets of self-organizations supported by flows of energy and entropy discarded into the ocean environment. This produces biological, ocean circulation, and climate interactions.

Disequilibrium Chemistry, Diabatic Thermal Structure, and Clouds in the Atmosphere of COCONUTS-2b

Located 10.888 pc from Earth, COCONUTS-2b is a planetary-mass companion to a young (150–800 Myr) M3 star, with a wide orbital separation (6471 au) and a low companion-to-host mass ratio (0.021 ± 0.005). We have studied the atmospheric properties of COCONUTS-2b using newly acquired 1.0–2.5 μm spectroscopy from Gemini/Flamingos-2. The spectral type of COCONUTS-2b is refined to T9.5 ± 0.5 based on comparisons with T/Y dwarf spectral templates. We have conducted an extensive forward-modeling analysis, comparing the near-infrared spectrum and mid-infrared broadband photometry of COCONUTS-2b with 16 state-of-the-art atmospheric model grids developed for brown dwarfs and self-luminous exoplanets near the T/Y transition. The PH 3 -free ATMO2020++, ATMO2020++, and Exo-REM models best match the specific observations of COCONUTS-2b, regardless of variations in the input spectrophotometry. This analysis suggests the presence of disequilibrium chemistry, along with a diabatic thermal structure and/or clouds, in the atmosphere of COCONUTS-2b. All models predict fainter Y-band fluxes than observed, highlighting uncertainties in the alkali chemistry models and opacities. We determine a bolometric luminosity of log(Lbol/L⊙)=−6.18 dex, with a 0.5 dex wide range of [−6.43, −5.93] dex that accounts for various assumptions of atmospheric models. Using several thermal evolution models, we derive an effective temperature of Teff=483−53+44 K, a surface gravity of log(g)=4.19−0.13+0.18 dex, a radius of R=1.11−0.04+0.03 R Jup, and a mass of M = 8 ± 2 M Jup. Various atmospheric model grids consistently indicate that COCONUTS-2b’s atmosphere likely has subsolar or near-solar metallicity and C/O. These findings provide valuable insights into COCONUTS-2b’s formation history and the potential outward migration to its current wide orbit.

Theoretical Analysis of Self-Shrinkage Spheroidization of Irregular Degradable Polymer Powder under Thermodynamic Nonequilibrium State

Laser three-dimensional (3D) printing offers significant advantages in integrating the shape and function of regenerative tissues through biomimetic manufacturing. However, its effectiveness is limited by the lack of specialized biopolymer powders—while solvent methods that use residual solvents produce powders with poor biocompatibility, mechanical methods result in irregularly shaped crystals. In this study, a biopolymer powder spheroidization and shaping technology, which utilizes the evolution of irregular powders into spheres with minimal surface free energy in the molten state, is proposed based on the thermodynamic principle of minimum energy. Initially, the motion trajectory and temperature field of the poly(L-lactic acid) (PLLA) powder during spheroidization were quantitatively assessed and optimized using Stokes’ law and Fourier's principle. Subsequently, the cohesive forces and aggregation kinetics of the polymer chains were calculated using molecular dynamics. Finally, based on these calculations, a phase-field model was constructed to simulate the evolution of the spheroidization rate and deduce the optimal parameters for the process. This precise approach enhances PLLA spheroidization control for laser 3D printing, improves part densification and surface quality, and offers a clean and efficient path for preparing high-quality PLLA spheroidized powder for laser 3D printing.

Opportunities and challenges involving repulsive Casimir forces in nanotechnology

The Casimir force, which arises from quantum electrodynamic fluctuations, manifests as an attraction between metallic surfaces spaced mere hundreds of nanometers apart. As contemporary device architectures scale down to the nano- and microscales, quantum phenomena exert increasing influence on their behaviors. Nano- and microelectromechanical systems frequently encounter issues such as components adhering or collapsing due to the typically attractive Casimir interactions. Consequently, significant efforts have been devoted to manipulating Casimir forces, aiming to transition them from attractive to repulsive. This ability holds promise for mitigating component collapse in nanodevices and facilitating the realization of quantum levitation and ultralow friction devices. Four primary strategies have been proposed for engineering repulsive Casimir forces: employing liquid media, magnetic materials, thermodynamic nonequilibrium conditions, and specialized geometries. In this review, we examine these approaches for engineering repulsive Casimir forces, analyzing their experimental feasibility, and discussing potential implementations.

Signature of Vertical Mixing in Hydrogen-dominated Exoplanet Atmospheres

Vertical mixing is a crucial disequilibrium process in exoplanet atmospheres, significantly impacting chemical abundance and observed spectra. While current state-of-the-art observations have detected its signatures, the effect of vertical mixing on atmospheric spectra varies widely based on planetary parameters. In this study, we explore the influence of disequilibrium chemistry across a parameter space that includes eddy diffusion, surface gravity, internal and equilibrium temperature, and metallicity. We also assess the effectiveness of retrieval models in constraining the eddy diffusion coefficient. By running numerous 1D chemical kinetics models, we investigate the impact of vertical mixing on the transmission spectrum. We also built a custom fast-forward disequilibrium model, which includes vertical mixing using the quenching approximation and calculates the model abundance orders of magnitude faster than the chemical kinetics model. We coupled this forward model with an open-source atmospheric retrieval code, used it on the JWST simulated output data of our chemical kinetics model, and retrieved eddy diffusion coefficient, internal temperature, and atmospheric metallicity. We find that there is a narrow region in the parameter space in which vertical mixing has a large effect on the atmospheric transmission spectrum. In this region of the parameter space, the retrieval model can put high constraints on the transport strength and provide optimal exoplanets to study vertical mixing. In addition, the NH3 abundance can be used to constrain the internal temperature for equilibrium temperature T equi > 1400 K.

Numerical simulation of low-rank coal drying based on non-equilibrium thermodynamics

ABSTRACT Coal is considered to be one of the most significant energy sources in the world. Dewatering, upgrading, and reutilization of lignite is an essential way for the clean coal utilization. Numerical simulation is a practical method combined experimental data with fundamental theories. In this study, based on the Luikov irreversible thermodynamic model, numerical calculations were carried out using the finite volume method and total Hermite integration. The drying characteristics of lignite at different drying temperatures and airflow velocities were simulated employing the fluid computational software. Initially, in order to verify the reliability of the simulation model, the simulated results were compared and validated with the experimental data. The results indicated that the drying parameters obtained from the simulation were in good agreement with the experimental values, and the correlation coefficients were greater than 0.95. Furthermore, the influence of airflow velocity and temperature on the drying characteristics was analyzed based on the numerical results. The results revealed that the drying temperature had the greatest effect on the drying process, while the airflow velocity had a minor effect. The optimum drying conditions for lignite were in the range of 1.2–1.8 m/s for airflow velocity and in the range of 140–160°C for drying temperature.

Transport Numbers Ion-Exchange Membranes with Mixed Solvent Electrolyte Mixtures Relevant for Electrodialysis and Battery Technology

In this study, we have analysed measurements of the electric potential and permselectivity in concentration cells with Selemion CMVN and AMVN membranes (cation- and anion-exchange membranes respectively) in electrolyte mixtures of KCl and H2O with and without ethanol (EtOH). The presence of EtOH induced a change in the measured electric potential and permselectivity of the Selemion CMVN and AMVN ion-exchange membranes, but the effect was not well explained by transference of EtOH. Instead, the regression analysis indicated that the measured permselectivities were well explained by EtOH transference coefficients of ta = 0. The variation of the permselectivity could be wholly explained by a gradual decrease in the water transference coefficient proportional to the average EtOH activity, tw ∝ aa , with tw ≈ 4 in the absence of EtOH. The analysis also indicated that the CEM and AEM were perfectly selective toward migration of K+ (tK+ = 1) and Cl- (tCl- = 1), respectively. Relations and the analysis method are based on non-equilibrium thermodynamics, and may be extended to other electrochemical systems of interest.

Efficiency Analysis and Optimization of Two-Speed-Region Operation of Permanent Magnet Synchronous Motor Taking into Account Iron Loss Based on Linear Non-Equilibrium Thermodynamics

In this article, the linear non-equilibrium thermodynamic approach is used to mathematically describe the energy regularities of an interior permanent magnet synchronous motor (IPMSM), taking into account iron loss. The IPMSM is considered a linear power converter (PC) that is multiple-linearized at operating points with a given angular velocity and load torque. A universal description of such a PC by a system of dimensionless parameters and characteristics made it possible to analyze the perfection of energy conversion in the object. For IPMSM, taking into account iron loss, a mathematical model of the corresponding PC has been built, and an algorithm and research program have been developed, which is valid in a wide range of machine speed regulations. This allows you to choose the optimal points of PC operation according to the maximum efficiency criteria and obtain the efficiency maps for IPMSM in different speed regions. The results of the studies demonstrate the effectiveness of the proposed method for determining the references of the d and q components of the armature current for both the loss-minimization strategy at the constant torque range of motor speed and the flux-weakening strategy in the constant power range.

A thermodynamic framework for nonequilibrium self-assembly and force morphology tradeoffs in branched actin networks.

Branched actin networks are involved in a variety of cellular processes, most notably the formation of lamellipodia in the leading edge of the cell. These systems adapt to varying loads through force dependent assembly rates that allow the network density and material properties to be modulated. Recent experimental work has described growth and force feedback mechanisms in these systems. Here, we consider the role played by energy dissipation in determining the kind of growth-force-morphology curves obtained in experiments. We construct a minimal model of the branched actin network self assembly process incorporating some of the established mechanisms. Our minimal analytically tractable model is able to reproduce experimental trends in density and growth rate. Further, we show how these trends depend crucially on entropy dissipation and change quantitatively if the entropy dissipation is parametrically set to values corresponding to a quasistatic state. Finally, we also identify the potential energy costs of adaptive behavior by branched actin networks, using insights from our minimal models. We suggest that the dissipative cost in the system beyond what is necessary to move the load may be necessary to maintain an adaptive steady state. Our results hence show how constraints from stochastic thermodynamics and non-equilibrium thermodynamics may bound or constrain the structures that result in such force generating processes.

Leaning Sideways: VHS 1256−1257 b is a Super-Jupiter with a Uranus-like Obliquity

We constrain the angular momentum architecture of VHS J125601.92-125723.9, a 140 ± 20 Myr old hierarchical triple system composed of a low-mass binary and a widely separated planetary-mass companion, VHS 1256 b. VHS 1256 b has been a prime target for multiple characterization efforts, revealing the highest measured substellar photometric variability to date and the presence of silicate clouds and disequilibrium chemistry. Here we add a key piece to the characterization of this super-Jupiter on a Tatooine-like orbit: we measure its spin-axis tilt relative to its orbit, i.e., the obliquity of VHS 1256 b. We accomplish this by combining three measurements. We find a projected rotation rate vsinip=8.7±0.1kms−1 for VHS 1256 b using near-infrared high-resolution spectra from Gemini/IGRINS. Combining this with a published photometric rotation period indicates that the companion is viewed edge on, with a line-of-sight spin axis inclination of i p = 90° ± 18°. We refit available astrometry measurements to confirm an orbital inclination of io=23−13+10 degrees. Taken together, VHS 1256 b has a large planetary obliquity of ψ = 90° ± 25°. In total, we have three measured angular momentum vectors for the system: the binary orbit normal, companion orbit normal, and companion spin axis. All three are misaligned with respect to each other. Although VHS 1256 b is tilted like Uranus, their origins are distinct. We rule out planet-like scenarios including collisions and spin–orbit resonances, and suggest that top-down formation via core/filament fragmentation is promising.

Nonequilibrium thermodynamics of non-ideal reaction-diffusion systems: Implications for active self-organization.

We develop a framework describing the dynamics and thermodynamics of open non-ideal reaction-diffusion systems, which embodies Flory-Huggins theories of mixtures and chemical reaction network theories. Our theory elucidates the mechanisms underpinning the emergence of self-organized dissipative structures in these systems. It evaluates the dissipation needed to sustain and control them, discriminating the contributions from each reaction and diffusion process with spatial resolution. It also reveals the role of the reaction network in powering and shaping these structures. We identify particular classes of networks in which diffusion processes always equilibrate within the structures, while dissipation occurs solely due to chemical reactions. The spatial configurations resulting from these processes can be derived by minimizing a kinetic potential, contrasting with the minimization of the thermodynamic free energy in passive systems. This framework opens the way to investigating the energetic cost of phenomena, such as liquid-liquid phase separation, coacervation, and the formation of biomolecular condensates.

Playing with active matter

In the past 20 years, active matter has been a very successful research field, bridging the fundamental physics of nonequilibrium thermodynamics with applications in robotics, biology, and medicine. Active particles, contrary to Brownian particles, can harness energy to generate complex motions and emerging behaviors. Most active-matter experiments are performed with microscopic particles and require advanced microfabrication and microscopy techniques. Here, we propose some macroscopic experiments with active matter employing commercially available toy robots (the Hexbugs). We show how they can be easily modified to perform regular and chiral active Brownian motion and demonstrate through experiments fundamental signatures of active systems such as how energy and momentum are harvested from an active bath, how obstacles can sort active particles by chirality, and how active fluctuations induce attraction between planar objects (a Casimir-like effect). These demonstrations enable hands-on experimentation with active matter and showcase widely used analysis methods.

Numerical simulation of phase transition with the hyperbolic Godunov-Peshkov-Romenski model

In this paper, a thermodynamically consistent numerical solution of the interfacial Riemann problem for the first-order hyperbolic continuum model of Godunov, Peshkov and Romenski (GPR model) is presented. In the presence of phase transition, interfacial physics are governed by molecular interaction on a microscopic scale, beyond the scope of the macroscopic continuum model in the bulk phases. The developed approximate two-phase Riemann solvers tackle this multi-scale problem, by incorporating a local thermodynamic model to predict the interfacial entropy production. Using phenomenological relations of non-equilibrium thermodynamics, interfacial mass and heat fluxes are derived from the entropy production and provide closure at the phase boundary. We employ the proposed Riemann solvers in an efficient sharp interface level-set Ghost-Fluid framework to provide coupling conditions at phase interfaces under phase transition. As a single-phase benchmark, a Rayleigh-Bénard convection is studied to compare the hyperbolic thermal relaxation formulation of the GPR model against the hyperbolic-parabolic Euler-Fourier system. The novel interfacial Riemann solvers are validated against molecular dynamics simulations of evaporating shock tubes with the Lennard-Jones shifted and truncated potential. On a macroscopic scale, evaporating shock tubes are computed for the material n-Dodecane and compared against Euler-Fourier results. Finally, the efficiency and robustness of the scheme is demonstrated with shock-droplet interaction simulations that involve both phase transfer and surface tension, while featuring severe interface deformations.

Efficient training of energy-based models using Jarzynski equality**This article is an updated version of: Carbone D, Hua M, Coste S and Vanden-Eijnden E 2023 Efficient training of energy-based models using Jarzynski equality Advances in Neural Information Processing Systems vol 36, ed A Oh, T Naumann, A Globerson, K Saenko, M Hardt and S Levine (Curran Associates, Inc.) pp 52583–614.

Abstract Energy-based models (EBMs) are generative models inspired by statistical physics with a wide range of applications in unsupervised learning. Their performance is well measured by the cross-entropy (CE) of the model distribution relative to the data distribution. Using the CE as the objective for training is, however, challenging because the computation of its gradient with respect to the model parameters requires sampling of the model distribution. Here, we show how the results for nonequilibrium thermodynamics based on the Jarzynski equality together with tools from sequential Monte Carlo sampling can be used to perform this computation efficiently and avoid the uncontrolled approximations made using the standard contrastive divergence algorithm. Specifically, we introduce a modification of the unadjusted Langevin algorithm (ULA), in which each walker acquires a weight that enables the estimation of the gradient of the CE at any step during gradient descent, thereby bypassing sampling biases induced by slow mixing of the ULA. We illustrate these results with numerical experiments on Gaussian mixture distributions as well as the MNIST and CIFAR-10 datasets. We show that the proposed approach outperforms methods based on the contrastive divergence algorithm in all the considered situations.

Research on Non-Equilibrium Dynamics Theory in Chemical Thermodynamics

Non-equilibrium dynamics theory is an important branch of chemical thermodynamics, widely applied in describing complex chemical reaction systems far from equilibrium. With the advancement of modern science and technology, an increasing number of chemical reactions exhibit unique behaviors under non-equilibrium conditions, such as self-organization and periodic oscillations—nonlinear phenomena. This paper systematically explores the distinctions between non-equilibrium and equilibrium states, introduces the fundamental principles of non-equilibrium thermodynamics, and analyzes cutting-edge issues such as nonlinear phenomena and multi-scale dynamics. Additionally, it discusses the specific applications of non-equilibrium dynamics in far-from-equilibrium reactions, heterogeneous catalysis, and industrial chemical processes, addressing both theoretical and experimental challenges. Through the combination of theoretical analysis and practical application, this paper aims to provide new insights and methodologies for research on non-equilibrium dynamics in the field of chemistry.

Biothermodynamic analysis of the Dengue virus: Empirical formulas, biosynthesis reactions and thermodynamic properties of antigen-receptor binding and biosynthesis

After the experience with the COVID-19 pandemic, WHO has issued a warning about the possible causes of future pandemics. One such causative agent is the Dengue virus. Until now, we have had information mostly on biological properties of the Dengue virus and very little information about its chemical and thermodynamic properties. To be better prepared for a potential Dengue pandemic, the goal of this paper is to chemically and thermodynamically characterize the Dengue virus, as well as to describe the biophysical basis of the virus-host interactions of the Dengue virus. To that goal, the empirical formula was determined, as well as biosynthesis reactions and thermodynamic properties of antigen-receptor binding and thermodynamic properties of biosynthesis and multiplication of the Dengue virus. A model was developed of virus-host interactions between the Dengue virus and its host tissues, based on nonequilibrium thermodynamics.