Nonequilibrium Theory Research Articles

Monitoring the impact of climate change and human activities on grassland vegetation dynamics in the northeastern Qinghai-Tibet Plateau of China during 2000–2015

Climate change and human activities can influence vegetation net primary productivity (NPP), a key component of natural ecosystems. The Qinghai-Tibet Plateau of China, in spite of its significant natural and cultural values, is one of the most susceptible regions to climate change and human disturbances in the world. To assess the impact of climate change and human activities on vegetation dynamics in the grassland ecosystems of the northeastern Qinghai-Tibet Plateau, we applied a time-series trend analysis to normalized difference vegetation index (NDVI) datasets from 2000 to 2015 and compared these spatiotemporal variations with trends in climatic variables over the same time period. The constrained ordination approach (redundancy analysis) was used to determine which climatic variables or human-related factors mostly influenced the variation of NDVI. Furthermore, in order to determine whether current conservation measures and programs are effective in ecological protection and reconstruction, we divided the northeastern Qinghai-Tibet Plateau into two parts: the Three-River Headwater conservation area (TRH zone) in the south and the non-conservation area (NTRH zone) in the north. The results indicated an overall (73.32%) increasing trend of vegetation NPP in grasslands throughout the study area. During the period 2000–2015, NDVI in the TRH and NTRH zones increased at the rates of 0.0015/a and 0.0020/a, respectively. Specifically, precipitation accounted for 9.2% of the total variation in NDVI, while temperature accounted for 13.4%. In addition, variation in vegetation NPP of grasslands responded not only to long- and short-term changes in climate, as conceptualized in non-equilibrium theory, but also to the impact of human activities and their associated perturbations. The redundancy analysis successfully separated the relative contributions of climate change and human activities, of which village population and agricultural gross domestic product were the two most important contributors to the NDVI changes, explaining 17.8% and 17.1% of the total variation of NDVI (with the total contribution >30.0%), respectively. The total contribution percentages of climate change and human activities to the NDVI variation were 27.5% and 34.9%, respectively, in the northeastern Qinghai-Tibet Plateau. Finally, our study shows that the grassland restoration in the study area was enhanced by protection measures and programs in the TRH zone, which explained 7.6% of the total variation in NDVI.

Adaptive Semiglobal Nonlinear Output Regulation: An Extended-State Observer Approach

This paper proposes a new extended-state observer-based framework for adaptive nonlinear regulator design of a class of nonlinear systems, in the general nonequilibrium theory. By augmenting an extended-state observer with an internal model, one is able to obtain an estimate of the term containing uncertain parameters, which then makes it possible to design an adaptive internal model in the presence of a general nonlinearly parameterized immersion condition.

A quantitative nonequilibrium phase transition theory for analyzing the turbulence development process

In this paper, a quantitative nonequilibrium multi-dimensional phase transition theory is proposed for describing the turbulence spectrum (energy E with wave number k and scaling index [Formula: see text]) of the turbulence development process by a fold catastrophe model. Each of the control variables in this catastrophe model is subtly expressed into a relative multi-parameter multiplication, and then the state variable can be quantitatively described by these parameters. By using this nonequilibrium phase transition theory, the quantitative relationship in the process of turbulence formation can be strictly derived through dimensionless analysis. Therefore, the turbulence development process can be described with respect to a scaling index [Formula: see text], in which there exists an energy containing range with −1.12 power law (E [Formula: see text] k[Formula: see text]) when [Formula: see text] varies from −2 to −1.2, and an inertial subrange with −1.69 power law (E [Formula: see text] k[Formula: see text]) that is almost identical with the famous Kolmogorov’s −5/3 power law when [Formula: see text] varies from −1.2 to −0.8, and then the dissipation range with −2.52 power law (E [Formula: see text] k[Formula: see text]) when [Formula: see text] varies from −0.8 to 0. Furthermore, this quantitative nonequilibrium phase transition theory has been verified by the corresponding theoretical comparison and experiment. This theory provides not only a new understanding of turbulence, but also a new perspective for other complex nonequilibrium phase transitions.

Statistical Mechanics: A Tale of Two Theories

AbstractThere are two theoretical approaches in statistical mechanics, one associated with Boltzmann and the other with Gibbs. The theoretical apparatus of the two approaches offer distinct descriptions of the same physical system with no obvious way to translate the concepts of one formalism into those of the other. This raises the question of the status of one approach vis-à-vis the other. We answer this question by arguing that the Boltzmannian approach is a fundamental theory while Gibbsian statistical mechanics (GSM) is an effective theory, and we describe circumstances under which Gibbsian calculations coincide with the Boltzmannian results. We then point out that regarding GSM as an effective theory has important repercussions for a number of projects, in particular attempts to turn GSM into a nonequilibrium theory.

Computational modelling of an amide functionalized single-walled carbon nanotube based H2S gas sensor

Abstract Due to the importance of detection of hydrogen sulphide in some industries, we are seeking to design a real-time H 2 S gas sensor with high sensitivity and very low detection limit. Here, we have investigated the sensitivity of amido-functionalized semiconducting single-walled carbon nanotube (SWCNT), interconnected between two gold electrodes , in terms of electrical conductance behavior. For this reason, we have used the non-equilibrium Green's function method and density functional theory and compared our results to our previous study (SWCNT functionalized with palladium nanoclusters) to find the best H 2 S gas sensor with high sensitivity. Initially, the optimized structure of the SWCNT functionalized with amide groups with and without H 2S gas is computed. Then, the electrical properties of the sensor prior to and after the exposure to H2S gas are computed and compared at different bias voltages. The highest sensitivity is found to be at 40 mV bias voltage with a current change of 1 order of magnitude in response to H2 S gas which in comparison to SWCNT functionalized with palladium nanoclusters , the current change, and as a result the sensitivity, are more significant. So it is inferred that amido-functionalized SWCNT can act as an effective detector with a considerable current change.

Augmented variational superposed Gaussian approximation for Fokker–Planck equations with rational polynomial functions

Reliable methods for obtaining time-dependent solutions of Fokker–Planck equations are in high demand in the field of non-equilibrium theory. In this paper, we present a new method based on variational superposed Gaussian approximation (VSGA) and Padé approximants. The VSGA obtains time-dependent probability density functions as a superposition of multiple Gaussian distributions. However, a limitation of the VSGA is that the expectation of the drift term with respect to the Gaussian distribution needs to be calculated analytically, which is typically satisfied when the drift term is a polynomial function. When this condition is not met, the VSGA must rely on the numerical integration of the expectation at each step, resulting in huge computational cost. We propose an augmented VSGA (A-VSGA) method that effectively overcomes the limitation of the VSGA by approximating non-linear functions with the Padé approximant. We apply the A-VSGA to two systems driven by chaotic input signals, a stochastic genetic regulatory system and a soft bistable system, whose drift terms are a rational polynomial function and a hyperbolic tangent function, respectively. The numerical calculations show that the proposed method provides accurate results with less computational time than that required for Monte Carlo simulation.

Improved prediction of solubility of gases in polymers using an innovative non-equilibrium lattice fluid/Flory-Huggins model

A combination of Flory-Huggins and non-equilibrium lattice fluid models are utilized for predicting the solubility coefficients of CO2, CH4, N2, n-C4H10 and i-C4H10 in low and high-density polyethylene, polysulfone and polycarbonate. The genetic programming has been used to acquire the appropriate function for this model. The solubility coefficients at infinite dilution are calculated based on non-equilibrium lattice fluid theory and the gas-polymer interaction is expressed by the Flory-Huggins interaction parameter. The solubility coefficients at infinite dilution, Flory-Huggins interaction parameter and pressure were selected as terminal sets and some simple mathematical functions and operators such as multiplication, division, summation, power and absolute value were regarded as mathematical function sets. The adjustable parameters of the proposed function were determined for each gas-polymer system based on nonlinear data fitting. The first adjustable model parameter was in the form of constant power and the second was obtained as a variable coefficient in the form of quadratics function of temperature. The results of the presented model demonstrate improved ability to predict the solubility of investigated gases in the considered polymers at high pressures in comparison to non-equilibrium lattice fluid and Sanchez-Lacombe equation of state models. In some cases, the absolute errors between experimental and predicted values of solubility coefficients were below 1% at the considered conditions.

Analytical model for the condensation heat and mass transfer characteristics of binary zeotropic mixtures

An analytical model was developed to study the condensation heat and mass transfer characteristics of binary zeotropic mixtures for annular flow inside a horizontal tube. The model was based on non-equilibrium film theory including consideration of the surface tension variation in the liquid phase as the concentration changes. The model was validated by comparing the calculated heat transfer coefficient with experimental data from the literature for methane/ethane mixtures with various compositions and mass fluxes. The model was then used to study the effects of composition, mass flux, inlet pressure and tube diameter on the heat and mass transfer resistances in the vapor phase and the heat transfer coefficient during condensation of methane/ethane mixtures. The results showed that the mass transfer resistance in the vapor phase was important in the high vapor quality region with the heat transfer resistance in the liquid phase being more significant in some cases.

Microscopic theory of ultrafast out-of-equilibrium magnon-phonon dynamics in insulators

The interaction between lattice and spins is at the heart of an extremely intriguing ultrafast dynamics in magnetic materials. In this work we formulate a general non-equilibrium theory that disentangles the complex interplay between them in a THz laser-excited antiferromagnetic insulator. The theory provides a quantitative description of the transient energy flow between the spin and lattice sub-systems, subject to magnon-phonon and phonon-phonon scatterings, giving rise to finite life-times of the quasiparticles and to the equilibration time of the system. We predict a novel kind of scattering process where two magnons of opposite polarizations decay into a phonon, previously omitted in the literature. The theory is combined with first-principle calculations and then applied to simulate a realistic dynamics of NiO. The main relaxation channels and hot spots in the reciprocal space, giving the strongest contribution to the energy transfer between phonons and magnons are identified. The diverse interaction strengths lead to distinct coupled dynamics of the lattice and spin systems and subsequently to different equilibration timescales.

Non-Equilibrium Scaling Applied to the Wake Evolution of a Model Scale Wind Turbine

The present paper addresses the evolution of turbulence characteristics in wind turbine wakes immersed in a turbulent boundary layer. The study thereby focuses on finding physically consistent scaling laws for the wake width, the velocity deficit, and the Reynolds stresses in the far wake region. For this purpose, the concept of an added wake is derived which allows to analyse the self-similarity of the added flow quantities and the applicability of the non-equilibrium dissipation theory. The investigation is based on wind tunnel measurements in the wake of a three-bladed horizontal axis wind turbine model (HAWT) immersed in two neutrally-stratified turbulent boundary layers of different aerodynamic roughness length. The dataset also includes wake measurements for various yaw angles. A high degree of self-similarity is found in the lateral profiles of the velocity deficit and of the added Reynolds stress components. It is shown that these can be described by combined Gaussian shape functions. In the vertical, self-similarity can just be shown in the upper part of the wake. Moreover, it is observed that the degree of self-similarity is affected by the ground roughness. Results suggest an approximately constant anisotropy of the added turbulent stresses in the far wake, and the axial scaling of the added Reynolds stress components is found to be in accordance with non-equilibrium dissipation theory. It predicts a x − 1 decay of the added turbulent intensity I + , and a x − 2 evolution of the added Reynolds shear stresses Δ u i ′ u j ′ ¯ and the velocity deficit Δ u . Based on these findingsa semi-empirical model is proposed for predicting the Reynolds stresses in the far wake region which can easily be coupled with existing analytical wake models. The proposed model is found to be in good agreement with the measurement results.

A New Model for Thermodynamic Characterization of Hemoglobin

In this paper, we formulate a thermodynamic model of hemoglobin that describes, by a physical point of view, phenomena favoring the binding of oxygen to the protein. Our study is based on theoretical methods extrapolated by experimental data. After some remarks on the non-equilibrium thermodynamic theory with internal variables, some thermodynamic functions are determined by the value of the complex dielectric constant. In previous papers, we determined the explicit expression of a dielectric constant as a function of a complex dielectric modulus and frequency. The knowledge of these functions allows a new characterization of the material and leads to the study of new phenomena that has yet to be studied. In detail, we introduce the concept of “hemoglobe”, a model that considers the hemoglobin molecule as a plane capacitor, the dielectric of which is almost entirely constituted by the quaternary structure of the protein. This model is suggested by considering a phenomenological coefficient of the non-equilibrium thermodynamic theory related to the displacement polarization current. The comparison of the capacity determined by the mean of this coefficient, and determined by geometrical considerations, gives similar results; although more thermodynamic information is derived by the capacity determined considering the aforementioned coefficient. This was applied to the normal human hemoglobin, homozygous sickle hemoglobin, and sickle cell hemoglobin C disease. Moreover, the energy of the capacitor of the three hemoglobin was determined. Through the identification of displacement currents, the introduction of this model presents new perspectives and helps to explain hemoglobin functionality through a physical point of view.

Electromagnetic waves propagation in normal and pathological hemoglobins: Thermodynamic comparative study of the influence of the relative macromolecular variability

In the last decades the exposure to human-made electromagnetic fields is strongly increased. Considering that all biological tissues interact with electromagnetic it is clear that more studies are needed to deepen the knowledge acquired to date on the effects on human health. This paper study the waves propagation on differently substituted hemoglobins, homozygous hemoglobin SS and heterozygous hemoglobin SC comparing with adult normal hemoglobin AA. After recall briefly the non-equilibrium thermodynamic theory with internal variables, we introduce the explicit form of the phenomenological and state coefficients as function of the perturbation frequency by mean of which we determine the real and imaginary part of the wave number K and the phase velocity of the wave for the three solutions. The difference between them suggests the beta 6 amino acid substitution as the main prerequisite for these variations. The results obtained from the application of our mathematical model can contribute to the interpretation of the structural functionality of the different hemoglobins and improve the development of biomedical applications in diagnostic and therapeutic technologies.

Low bias negative differential resistance with dual-peaks based on octacene molecular device

Based on non-equilibrium Green's function and density functional theory, a first-principles study of the transport properties of a molecular device is performed. This device is composed of two octacene molecules separated by a ethyl barrier, which are then linked to Ag leads through thiolates. The device shows low bias negative differential resistance effect with dual-peaks, which may be useful for designing molecular devices with low power-dissipation and multi-function in the future.

Influence of cyclic non-isothermal heat treatment on microstructure, mechanical property and corrosion behavior of Al–Zn–Mg alloy

The influence of cyclic non-isothermal heat treatment times on microstructure, mechanical properties and corrosion behavior of Al–Zn–Mg alloy is investigated. The results show that Mg segregation at grain boundary becomes severer with the increase of non-isothermal heat treatment times, and the tensile strength and elongation of the alloy decrease gradually. The increase of Mg segregation at grain boundary can be interpreted by non-equilibrium segregation theory. The size and quantity of MgZn2 precipitation decrease after one time of non-isothermal heat treatment, but increase significantly after two and three times of non-isothermal heat treatment. The change of MgZn2 precipitation results in slight improvement of corrosion resistance of Al–Zn–Mg alloy after one time of non-isothermal heat treatment, and serious deterioration of corrosion resistance of Al–Zn–Mg alloy after two and three times of non-isothermal heat treatment.

Conservation-Dissipation Formalism for soft matter physics: II. Application to non-isothermal nematic liquid crystals.

For most existing non-equilibrium theories, the modeling of non-isothermal processes is a hard task. Intrinsic difficulties involve the non-equilibrium temperature, the coexistence of conserved energy and dissipative entropy, etc. In this paper, by taking the non-isothermal flow of nematic liquid crystals as a typical example, we illustrate that thermodynamically consistent models in either vectorial or tensorial forms can be constructed within the framework of the Conservation-Dissipation Formalism (CDF). And the classical isothermal Ericksen-Leslie model and Qian-Sheng model are shown to be special cases of our new vectorial and tensorial models in the isothermal, incompressible and stationary limit. Most importantly, from the above examples, it is known that CDF can easily solve the issues relating with non-isothermal situations in a systematic way. The first and second laws of thermodynamics are satisfied simultaneously. The non-equilibrium temperature is defined self-consistently as a partial derivative of the entropy function. Relaxation-type constitutive relations are constructed, which give rise to classical linear constitutive relations, like Newton's law and Fourier's law, in stationary limits. Therefore, CDF is expected to have a broad scope of applications in soft matter physics, especially under complicated situations, such as non-isothermal, compressible and nanoscale systems.

Non-equilibrium thermodynamics beyond linearity: sliding friction

Nevertheless, sliding friction is frequent and it was the first irreversible process we were faced in the school, very rare effort has been aimed to develop its non-equilibrium thermodynamic theory if ever. The reason may be guessed as Coulomb’s (Amonton’s 3rd) law is often taught as if it where the final solution, even the velocity dependence of the friction force is rarely mentioned in textbooks or in papers, looking away from its direction. On the other hand, the phenomenon cannot be accounted with a linear theory even in the Onsagerian sense. Coulomb’s law displays a strong singularity at equilibrium, which is, at least, extremely rare in nature. On the ground of the thermodynamic theory of rheology, one can guess, that the singularity is virtual. The friction force does depend on the magnitude of the velocity and the function is continuous but it starts so steeply and falls back at practically very low values that to observe it is really difficult. If the two solids are separated by a thin layer of a non-Newtonian fluid the thermodynamic theory of the latter can be applied. This is not a nonsense; the independence of the friction force on the contact area is explained—by rather widely accepted ideas—with plastic flow of the materials at the surface region. In the last decades, the interest has increased and several theories was published and experimentally verified that explain friction and wear at different circumstances and the results are not like to each other nor to Coulomb’s law. Applying Onsager’s thermodynamics beyond the realm of linearity is more or less like guessing. Not a free brainstorm, but severely limited by observations. Here a germ of a thermodynamic theory is sketched without acquiring generality and restricted to stationary sliding. Here the most simple model is looked for to eliminate the gap between static and kinetic friction. It is not a complete idea at all—the transients have been put aside—but may be a guideline for further modeling. The fork the train of thoughts stops at gives way to several kinds of possibilities, a number of which—by the author's opinion—may have their own realm of application. Finally, an accurately accountable model is given that may be assumed friction if we pretend not knowing its origin and the law differs significantly from the nearly exclusively used Coulomb’s law. This example supports the idea that friction cannot be described in a simple and uniform theory.

Study of the enhanced geothermal system (EGS) heat mining from variably fractured hot dry rock under thermal stress

Formation of enhanced geothermal system provides flow and heat transfer paths for heat extraction in HDR (hot dry rock). Based on the local thermal non-equilibrium theory, the THM(thermal-hydraulic-mechanical) coupling is established to describe the interaction of fluid flow, heat transfer and rock deformation in heat mining process. Besides, the randomly generated fractures are adopted to descript the various fracture network. Firstly, the heat mining processes of variably fractured HDR with different fracture network characteristics are researched. Secondly, heat mining performance of multi-well patterns are compared with that of doublet-well pattern. Finally, effect of the key parameters on heat mining are also investigated. The results indicate that the increase of fracture density enhances flow around and retards thermal drawdown. When the angle between fracture orientation and inlet-outlet connection is 45°, the optimal heat mining performance can be achieved. The addition of inlets in multi-well pattern conduces to large-scale utilization, and a reasonable well arrangement can avoid the thermal breakthrough. This study provides the support for EGS (enhanced geothermal system) stimulation and well arrangement to obtain better heat mining performance.

Microscopic dynamics, chaos and transport in nonequilibrium processes

This EPJ - Special Topics issue is a collection of contributions on theory and the recent developments in nonequilibrium statistical mechanics, fluctuations theory and dynamical systems. The various articles report results on the role of microscopic dynamics in giving rise to complex patterns observed at the macroscopic scale in a variety of physical phenomena.

Contour calculus for many-particle functions

In non-equilibrium many-body perturbation theory, Langreth rules are an efficient way to extract real-time equations from contour ones. However, the standard rules are not applicable in cases that do not reduce to simple convolutions and multiplications. We introduce a procedure for extracting real-time equations from general multi-argument contour functions with an arbitrary number of arguments. This is done for both the standard Keldysh contour, as well as the extended contour with a vertical track that allows for general initial states. This amounts to the generalization of the standard Langreth rules to much more general situations. These rules involve multi-argument retarded functions as key ingredients, for which we derive intuitive graphical rules. We apply our diagrammatic recipe to derive Langreth rules for the so-called double triangle structure and the general vertex function, relevant for the study of vertex corrections beyond the GW approximation.

Parameter optimization of gas–solid heat transfer process in sinter packed bed based on further exergy analysis

Based on the porous media and local non-equilibrium thermodynamics theory, a two-dimensional steady numerical model of the annular cooler was established, in the condition that the moving speed of the bed was defined in the model. The modified Ergun formula and experimental Nusselt number were used to accurately describe the gas flow and gas–solid heat transfer process in the sinter bed. The reliability of the calculation model was verified by comparing with the experimental data. The parameters such as the cooling air volume distributed per kg of sinter, sinter bed height, waste heat recovery sector length and inlet air temperature were discussed. The further exergy which considers the pressure resistance was put forward as an optimization criterion, and the optimal parameter combination was obtained by the orthogonal experiments. The results show that the exergy increased with sinter bed height and inlet air temperature. Meanwhile, there are optimal parameter values for cooling air volume and length of waste heat recovery sector, which are 2.05 m3/kg and 56 m respectively. Finally, according to orthogonal experiment, when the annular cooler is in the optimal working condition, the exergy of the system reaches to 217.57 MJ/h, which is 32.04% higher than the standard condition. The results would provide some guidelines for the designs and optimization of operation parameters for the sinter cooling process.