Effect Of Thermal Fluctuations Research Articles

General Relations between Stress Fluctuations and Viscoelasticity in Amorphous Polymer and Glass-Forming Systems.

Mechanical stress governs the dynamics of viscoelastic polymer systems and supercooled glass-forming fluids. It was recently established that liquids with long terminal relaxation times are characterized by transiently frozen stress fields, which, moreover, exhibit long-range correlations contributing to the dynamically heterogeneous nature of such systems. Recent studies show that stress correlations and relaxation elastic moduli are intimately related in isotropic viscoelastic systems. However, the origin of these relations (involving spatially resolved material relaxation functions) is non-trivial: some relations are based on the fluctuation-dissipation theorem (FDT), while others involve approximations. Generalizing our recent results on 2D systems, we here rigorously derive three exact FDT relations (already established in our recent investigations and, partially, in classical studies) between spatio-temporal stress correlations and generalized relaxation moduli, and a couple of new exact relations. We also derive several new approximate relations valid in the hydrodynamic regime, taking into account the effects of thermal conductivity and composition fluctuations for arbitrary space dimension. One approximate relation was heuristically obtained in our previous studies and verified using our extended simulation data on two-dimensional (2D) glass-forming systems. As a result, we provide the means to obtain, in any spatial dimension, all stress-correlation functions in terms of relaxation moduli and vice versa. The new approximate relations are tested using simulation data on 2D systems of polydisperse Lennard-Jones particles.

Effect of thermal fluctuations on the nontrivial topology of thed + idsuperconducting phase.

The behavior of the topological index (TI), characterizing the properties of superconducting phases of quasi-two-dimensional systems with nontrivial topology, is investigated depending on the temperature and system parameters. For this purpose, a method of calculating the TI, based on a self-consistent functional-integral theory, is proposed. The chirald + idsuperconducting phase of a quasi-two-dimensional model with effective attraction between the electrons located at the nearest sites of a triangular lattice is considered. It is shown that the structure of the energy dependence of the self-energy function, which occurs when taking into account thermal fluctuations, does not lead to a change in the topological properties of the system. It is found that taking into account thermal fluctuations with an increase in the effective attraction between electrons expands the temperature range in which the value of the TI is close to the integerC1≃-2.

Effects of thermal fluctuations on the evaporation of AdS Schwarzschild scalar tensor vector gravity black hole

The Hawking evaporation process has important implications for our understanding of the universe, as it suggests that black holes are not eternal and can eventually evaporate away completely. We evaluate the Hawking evaporation process of AdS Schwarzschild scalar-tensor-vector gravity black hole by using Stefan-Boltzmann law and find out that Hawking evaporation rate depends on the AdS radius l and deviation parameter α of the scalar-tensor-vector gravity. We analyze that for small values of AdS radius l and positive deviation parameter α black hole evaporates quickly. While there is exponential increase in lifetime of the black hole for large AdS radius l and negative deviation parameter α. Moreover, we find out thermodynamical quantities like Helmholtz free energy, internal energy, pressure, enthalpy, Gibbs free energy and specific heat and show that how deviation parameter α and the correction parameter ζ of the first order corrected entropy play vital role on the stability and phase transitions of the black holes.

Phenotypic plasticity and the effects of thermal fluctuations on specialists and generalists.

Classical theories predict that relatively constant environments should generally favour specialists, while fluctuating environments should be selected for generalists. However, theoretical and empirical results have pointed out that generalist organisms might, on the contrary, perform poorly under fluctuations. In particular, if generalism is underlaid by phenotypic plasticity, performance of generalists should be modulated by the temporal characteristics of environmental fluctuations. Here, we used experiments in microcosms of Tetrahymena thermophila ciliates and a mathematical model to test whether the period or autocorrelation of thermal fluctuations mediate links between the level of generalism and the performance of organisms under fluctuations. In the experiment, thermal fluctuations consistently impeded performance compared with constant conditions. However, the intensity of this effect depended on the level of generalism: while the more specialist strains performed better under fast or negatively autocorrelated fluctuations, plastic generalists performed better under slow or positively autocorrelated fluctuations. Our model suggests that these effects of fluctuations on organisms' performance may result from a time delay in the expression of plasticity, restricting its benefits to slow enough fluctuations. This study points out the need to further investigate the temporal dynamics of phenotypic plasticity to better predict its fitness consequences under environmental fluctuations.

Effect of thermal fluctuations on mold coating delamination during continuous casting of high-alloy (Mn, Al) steel

During the continuous casting of high-alloy (Mn, Al) steels, mold coating delamination occurs specifically at the narrow face (NF) mold corner immediately below the meniscus, different from where mold surface problems are generally known to occur. Most mechanical analyses have been performed assuming negligible thermal fluctuations and steady state interfacial heat fluxes. However, high-alloy steels exhibit larger thermal fluctuations than general steels during continuous casting, attributable to the reaction between the high-alloy steels and mold flux. Therefore, in this study, thermo-mechanical analyses are performed under both steady and fluctuating interfacial heat fluxes to compare the effects of thermal fluctuations on the continuous casting mold, with the results indicating that monotonic stresses are generated under steady interfacial heat fluxes at the corner of the NF mold, whereas cyclic stresses are induced by thermal fluctuations under fluctuating interfacial heat fluxes. Accordingly, the cyclic stresses at the corner of the NF mold, induced by thermal fluctuations, are determined as the major cause of mold coating delamination. These results can be applied to develop methods to reduce mold coating delamination, prevent the degradation of strand quality, and improve mold life.

Effect of thermal fluctuations on spectra and predictability in compressible decaying isotropic turbulence

This study investigates the impact of molecular thermal fluctuations on compressible decaying isotropic turbulence using the unified stochastic particle (USP) method, encompassing both two-dimensional (2-D) and three-dimensional (3-D) scenarios. The findings reveal that the turbulent spectra of velocity and thermodynamic variables follow the wavenumber (k) scaling law of ${k}^{(d-1)}$ for different spatial dimensions $d$ within the high wavenumber range, indicating the impact of thermal fluctuations on small-scale turbulent statistics. With the application of Helmholtz decomposition, it is found that the thermal fluctuation spectra of solenoidal and compressible velocity components ( ${\boldsymbol {u}}_{s}$ and ${\boldsymbol {u}}_{c}$ ) follow an energy ratio of 1 : 1 for 2-D cases, while the ratio changes to 2 : 1 for 3-D cases. Comparisons between 3-D turbulent spectra obtained through USP simulations and direct numerical simulations of the Navier–Stokes equations demonstrate that thermal fluctuations dominate the spectra at length scales comparable to the Kolmogorov length scale. Additionally, the effect of thermal fluctuations on the spectrum of ${\boldsymbol {u}}_{c}$ is significantly influenced by variations in the turbulent Mach number. We further study the impact of thermal fluctuations on the predictability of turbulence. With initial differences caused by thermal fluctuations, different flow realizations display significant disparities in velocity and thermodynamic fields at larger scales after a certain period of time, which can be characterized by ‘inverse error cascades’. Moreover, the results suggest a strong correlation between the predictabilities of thermodynamic fields and the predictability of ${\boldsymbol {u}}_{c}$ .

Symmetry breaking charge transfer and control of the transition dipole moment in excited octupolar molecules.

The structure of the energy levels of excited symmetric donor-acceptor octupolar molecules suggests a completely symmetric state and a degenerate doublet. For most molecules, the doublet is the first excited state, which is called the normal level order, but there are molecules with the reverse level order. Symmetry breaking charge transfer (SBCT) and its effect on the transient dipole moment in these structures are studied. It has been established that for reverse level order, SBCT is possible only if the reorganization energy exceeds a certain threshold, whereas for the normal level order, there is no such threshold. The lowest completely symmetric excited state is shown to become bright after SBCT. The dependence of the fluorescence transition dipole moment on the SBCT extent is calculated. It was established that the direction and magnitude of the transition dipole moment change similarly to the change in the dipole moment for the reverse level order, whereas for the normal level order, the changes are opposite. The effect of solvent thermal fluctuations on the transition dipole moment is simulated and discussed. A way for controlling the direction of the transition dipole moment by an external electric field is suggested.

Superfluid-supersolid phase transition of elongated dipolar Bose-Einstein condensates at finite temperatures

We analyze the finite-temperature phase diagram of a dipolar Bose-Einstein condensate confined in a tubular geometry. The effect of thermal fluctuations is accounted for by means of Bogoliubov theory employing the local density approximation. In the considered geometry, the superfluid-supersolid phase transition can be of first and second order. We discuss how the corresponding transition point is affected by the finite temperature of the system. Published by the American Physical Society 2024

Temperature and immune challenges modulate the transcription of genes of the ubiquitin and apoptosis pathways in two high-latitude Notothenioid fish across the Antarctic Polar Front.

Thermal variations due to global climate change are expected to modify the distributions of marine ectotherms, with potential pathogen translocations. This is of particular concern at high latitudes where cold-adapted stenothermal fish such as the Notothenioids occur. However, little is known about the combined effects of thermal fluctuations and immune challenges on the balance between cell damage and repair processes in these fish. The aim of this study was to determine the effect of thermal variation on specific genes involved in the ubiquitination and apoptosis pathways in two congeneric Notothenioid species, subjected to simulated bacterial and viral infections. Adult fish of Harpagifer bispinis and Harpagifer antarcticus were collected from Punta Arenas (Chile) and King George Island (Antarctica), respectively, and distributed as follows: injected with PBS (control), LPS (2.5mg/kg) or Poly I:C (2mg/kg) and then submitted to 2, 5 and 8°C. After 1week, samples of gills, liver and spleen were taken to evaluate the expression by real-time PCR of specific genes involved in ubiquitination (E3-ligase enzyme) and apoptosis (BAX and SMAC/DIABLO). Gene expression was tissue-dependent and increased with increasing temperature in the gills and liver while showing an opposite pattern in the spleen. Studying a pair of sister species that occur across the Antarctic Polar Front can help us understand the particular pressures of intertidal lifestyles and the effect of temperature in combination with biological stressors on cell damage and repair capacity in a changing environment.

Magnetic properties of the spin-1 J 1 − J 3 Heisenberg model on a triangular lattice

We study the spin-1 J 1 − J 3 Heisenberg model with antiferromagnetic nearest neighbors J 1 > 0 and the ferromagnetic third nearest neighbor J 3 < 0 for a triangular lattice. The ground-state and thermodynamic properties are evaluated under the Popov-Fedotov functional integral method and the Luttinger-Tisza procedure. Perturbation expansion of the auxiliary field around mean-field theory was carried out to investigate the effect of thermal fluctuations on ground state energy and sublattice magnetization. The results are compared with those of the spin wave approximation and other methods.

Effect of thermal fluctuations on the flux motion and vortex dynamic in (Li0.8Fe0.2)OHFeSe single crystals

We present a qualitatively investigation on the influence of thermal fluctuation on flux motion and vortex dynamic of (Li0.8Fe0.2)OHFeSe single crystals. The importance of thermal fluctuations has been assessed through the Ginzburg number Gi. The resistivity in the mixed state for (Li0.8Fe0.2)OHFeSe exhibits a thermally activated behavior investigated by TAFF theory. The field-dependent activation energy follows the relation U0 (H) ∼ H-α. The appearance of crossover at 2 T is related to the different pinning mechanisms. Single-vortex pinning occurs in the low fields range at H < 2 T, and collective pinning dominates in the region of field higher than 2 T. The vortex phase diagram from glass state to liquid state has been discussed based on the vortex-glass theory. Due to the influence of thermal fluctuations, there is a broad vortex liquid regime in the vortex phase diagram.

Quantum thermodynamics of the charged AdS black hole with nonlinear electrodynamics field

In this paper, we investigate the thermodynamic properties of an AdS-charged black hole coupled with a nonlinear electrodynamic field, taking into account the effects of thermal fluctuations. Our analysis focuses on how thermal fluctuations impact the entropy of the black hole. It is known that at the quantum level, thermal fluctuations bring about changes in the entropy of a black hole in both exponential and logarithmic ways. We present the logarithmic and exponentially corrected thermodynamic characteristics of the black hole, such as Helmholtz free energy, pressure, enthalpy, Gibbs free energy, and specific heat. A comparative analysis of equilibrium states with corrected thermodynamic potentials is conducted to observe the significant influence of the black hole under consideration. Additionally, we examine a second-order phase transition in the case of non-perturbed correction.

Unifying temperature definition in atomistic and field representations of conservation laws

In this work, a field representation of the conservation law of linear momentum is derived from the atomistic, using the theory of distributions as the mathematical tool, and expressed in terms of temperature field by defining temperature as a derived quantity as that in molecular kinetic theory and atomistic simulations. The formulation leads to a unified atomistic and continuum description of temperature and a new linear momentum equation that, supplemented by an interatomic potential, completely governs thermal and mechanical processes across scales from the atomic to the continuum. The conservation equation can be used to solve atomistic trajectories for systems at finite temperatures, as well as the evolution of field quantities in space and time, with atomic or multiscale resolution. Four sets of numerical examples are presented to demonstrate the efficacy of the formulation in capturing the effect of temperature and thermal fluctuations, including phonon density of states, thermally activated dislocation motion, dislocation formation during epitaxial processes, and attenuation of longitudinal acoustic waves as a result of their interaction with thermal phonons.

Dynamic response of a ferromagnetic nanofilament under rotating fields: effects of flexibility, thermal fluctuations and hydrodynamics.

Using nonequilibrium computer simulations, we study the response of ferromagnetic nanofilaments, consisting of stabilized one dimensional chains of ferromagnetic nanoparticles, under external rotating magnetic fields. In difference with their analogous microscale and stiff counterparts, which have been actively studied in recent years, nonequilibrium properties of rather flexible nanoparticle filaments remain mostly unexplored. By progressively increasing the modeling details, we are able to evidence the qualitative impact of main interactions that can not be neglected at the nanoscale, showing that filament flexibility, thermal fluctuations and hydrodynamic interactions contribute independently to broaden the range of synchronous frequency response in this system. Furthermore, we also show the existence of a limited set of characteristic dynamic filament configurations and discuss in detail the asynchronous response, which at finite temperature becomes probabilistic.

A computational study of a light-driven artificial device: a third generation rotational photo-molecular motor in dilute solutions.

A third-generation artificial photo-molecular motor, featuring two photo-switchable rotating moieties in connection with a pseudoasymmetric molecular centre, is investigated by combining quantum-mechanics (QM) algorithms with classical molecular dynamics (MD) propagators. In particular, in the present contribution we have addressed such a molecular motor in different rotational isomers following the experimental observations arising from the application of multiple spectroscopic techniques in dilute solutions. At first, we focused our attention on the reproduction of the UV/Vis absorption spectrum in two solvents (acetonitrile and cyclohexane) with different gradient-corrected density functional theory (B3LYP, Cam-B3LYP, PBE, PBE0) functionals in conjunction with the conductor-like and polarizable continuum model (C-PCM). Furthermore, we refined the absorption signals by combining a classical MD sampling at room-temperature with DFT-based electronic degrees of freedom to compute perturbed excitation wavelengths driven by thermal fluctuation and solvation effects. In this respect, we have modelled the investigated artificial motor within solution nanodroplets with solvent molecules treated contextually at atomistic level and via a dielectric and polarizable continuum model.

Pre-fertilization gamete thermal environment influences reproductive success, unmasking opposing sex-specific responses in Atlantic salmon (Salmo salar).

The environment gametes perform in just before fertilization is increasingly recognized to affect offspring fitness, yet the contributions of male and female gametes and their adaptive significance remain largely unexplored. Here, we investigated gametic thermal plasticity and its effects on hatching success and embryo performance in Atlantic salmon (Salmo salar). Eggs and sperm were incubated overnight at 2°C or 8°C, temperatures within the optimal thermal range of this species. Crosses between warm- and cold-incubated gametes were compared using a full-factorial design, with half of each clutch reared in cold temperatures and the other in warm temperatures. This allowed disentangling single-sex interaction effects when pre-fertilization temperature of gametes mismatched embryonic conditions. Pre-fertilization temperature influenced hatch timing and synchrony, and matching sperm and embryo temperatures resulted in earlier hatching. Warm incubation benefited eggs but harmed sperm, reducing the hatching success and, overall, gametic thermal plasticity did not enhance offspring fitness, indicating vulnerability to thermal changes. We highlight the sensitivity of male gametes to higher temperatures, and that gamete acclimation may not effectively buffer against deleterious effects of thermal fluctuations. From an applied angle, we propose the differential storage of male and female gametes as a tool to enhance sustainability within the hatcheries.

The role of thermal fluctuations in the motion of a free body

The motion of a rigid body is described in Classical Mechanics with the venerable Euler’s equations which are based on the assumption that the relative distances among the constituent particles are fixed in time. Real bodies, however, cannot satisfy this property, as a consequence of thermal fluctuations. We generalize Euler’s equations for a free body in order to describe dissipative and thermal fluctuation effects in a thermodynamically consistent way. The origin of these effects is internal, i.e. not due to an external thermal bath. The stochastic differential equations governing the orientation and central moments of the body are derived from first principles through the theory of coarse-graining. Within this theory, Euler’s equations emerge as the reversible part of the dynamics. For the irreversible part, we identify two distinct dissipative mechanisms; one associated with diffusion of the orientation, whose origin lies in the difference between the spin velocity and the angular velocity, and one associated with the damping of dilations, i.e. inelasticity. We show that a deformable body with zero angular momentum will explore uniformly, through thermal fluctuations, all possible orientations. When the body spins, the equations describe the evolution towards the alignment of the body’s major principal axis with the angular momentum vector. In this alignment process, the body increases its temperature. We demonstrate that the origin of the alignment process is not inelasticity but rather orientational diffusion. The theory also predicts the equilibrium shape of a spinning body.

High-Frequency Magnetic Response of Arrays of Planar Fe65Co35 Nanodots: Effects of Bias Field and Thermal Fluctuations

High-Frequency Magnetic Response of Arrays of Planar Fe₆₅Co₃₅ Nanodots: Effects of Bias Field and Thermal Fluctuations

Effect of thermal fluctuations on the electronic excitation energies of linear polyenes: A combined molecular dynamics and TD‐DFT study

AbstractIn the present study, thermally averaged electronic excitation energies (the so‐called dynamic approach) are quantitatively assessed for a model molecular system composed of a series of increasingly longer chains of simple linear polyenes. The molecular dynamics trajectories are calculated using the semi‐empirical “Geometry, Frequency, Noncovalent, eXtended Tight Binding” (GFN2‐xTB) method, while TD‐DFT vertical excitation energies of selected snapshots are obtained with the spin‐component‐scaled double hybrid density functional SCS‐wPBEPP86. Boltzmann weighted average excitation energies were then calculated in order to take into account the contribution of thermal motions. Excitation energies via the dynamic approach are compared with that of the static approach in which thermal fluctuations are not considered. The differences between the dynamic and the static approaches were found to be around the range to eV for polyenes up to 44 carbon atoms. This range of errors is relatively small in comparison with typical errors produced by using different density functionals and/or basis sets. Therefore, the electronic excited states of small to medium lengths of linear polyenes (less than 50 carbon atoms) can be safely modeled via the static approach. However, extrapolation of the results to longer polyenes indicates that the difference between both approaches is estimated to be 0.05 eV for polyenes containing 100 carbon atoms, which suggests that considering thermal motions in the calculations of excitation energies is recommended for such long conjugated molecular systems.

Thermal stability and effects of thermal fluctuations on the static and spherically symmetric hairy black hole by gravitational decoupling

In this paper, we explore the thermodynamic aspects of the hairy black hole solution developed by gravitational decoupling in the spherical symmetry, considering its energy emission, Gibbs free energy, and thermal fluctuations. Our analysis involves the calculation of various quantities, including the Hawking temperature, geometric mass, and heat capacity to discuss the thermodynamic stability at local and global scales. To determine the temperature of the black hole, we utilize the first law of thermodynamics. Additionally, we evaluate the energy emission rate and establish its proportionality to the decoupling parameter α. By calculating the Gibbs free energy, we investigate the phase transition behavior through the swallowing tails of the hairy black holes. Furthermore, we derive the corrected entropy to examine the impact of thermal fluctuations on small and large black holes. We also calculated horizon radius r0, inner stable circular orbit rISCO , photon sphere radius rph, and shadows radius Rsh. Remarkably, the length scale parameters α (decoupling parameter) and β exhibit substantial influences on the thermodynamic properties of under consideration hairy black holes.