Large eddy simulation of hot and cold fluids mixing in a T-junction for predicting thermal fluctuations

Temperature fluctuations in a mixing T-junction have been simulated on the FLUENT platform using the large eddy simulation （LES） turbulent flow model and a sub-grid scale Smagorinsky-Lilly model. The normalized mean and root mean square temperatures for describing time-averaged temperature and temperature fluctuation intensity, and the velocity are obtained. The power spectrum densities of temperature fluctuations, which are key parameters for thermal fatigue analysis and lifetime evaluation, are analyzed. Simulation results are consistent with experimental data published in the literature, showing that the LES is reliable. Several mixing processes under different conditions are simulated in order to analyze the effects of varying Reynolds number and Richardson number on the mixing course and thermal fluctuations.

Thermodynamics under the impact of thermal fluctuations and quasi-normal modes of Euler-Heisenberg AdS BH in the framework of NLED

We study the impact of thermal fluctuations on the thermodynamics,quasi-normal modes,and phase transitions of an anti-de Sitter Euler-Heisenberg black hole(BH)with a nonlinear electrodynamic field.An anti-de Sitter Euler-Heisenberg BH with a nonlinear electrodynamic field is composed of four parameters:the mass,electric charge,cosmological constant,and Euler-Heisenberg parameter.We calculate thermodynamic variables such as Hawking temperature,entropy,volume,and specific heat,which comply with the first law of thermodynamics.First,we use this BH to determine the thermodynamics and thermal fluctuations with the Euler-Heisenberg parameter to distinguish their effect on uncorrected and corrected thermodynamical quantities.We derive the expression for corrected entropy to study the impact of thermal fluctuation with simple logarithmic corrections on unmodified thermodynamical potentials,including Helmholtz energy,pressure,Gibbs free energy,and enthalpy.The Euler-Heisenberg parameter improves BH stability at large radii.Second,we analyze the local stability of the proposed BH,and the phase shifts of the BH are also investigated using temperature and specific heat.When there is a decrease in charge and an increase in r_(+)andα,the temperature shifts from an unstable region to a stable one.Similarly,increases in local stability are observed with each of these parameters.Third,we use null geodesics to deal with the effects of nonlinear electrodynamics on the quasi-normal modes of the Euler-Heisenberg anti-de Sitter BH.The null geodesics provide the angular velocity and Lyapunov exponent of the photon sphere,which are the same as the real and imaginary parts of the quasi-normal modes in the eikonal limit.

Effect of thermal fluctuations on homogeneous compressible turbulence

For more than a century,it has been widely believed that there is a clear gap between molecular motions at the microscopic level and turbulent fluctuations at the mac-roscopic level.However,recent studies have demonstrated that the thermal fluctua-tions resulted from molecular motions have nonnegligible effects on the dissipation range of turbulence.To further clarify the reviving debate on this topic,we employ the molecular-level direct simulation Monte Carlo(DSMC)method to simulate homogene-ous turbulence with different turbulent Mach numbers,extending the previous studies by considering the effect of compressibility.Our results show that,for both one-dimensional(1D)stationary turbulence and two-dimensional(2D)decaying isotropic turbulence,the turbulent energy spectra are significantly changed due to thermal fluctuations below the spatial scale comparable to the turbulent dissipation length scale.The energy spectra caused by thermal fluctuations for different spatial dimen-sions d present different scaling laws of the wavenumber k as k(d^(−1)).For 2D cases,we show that the effect of thermal fluctuations on the spectrum of compressible velocity component is greatly affected by the change of compressibility.The 2D spectra of density,temperature and pressure are also obtained,showing the same scaling law at large wavenumbers as found for the energy spectra.Moreover,it is found that the effects of thermal fluctuations on the thermodynamic spectra are the same as those on the spectra of compressible velocity component.

Effects of thermal fluctuations on the Kerr–Newman–NUT–AdS black hole

This paper is devoted to studying the impact of thermal fluctuations on thermodynamics of rotating as well as charged anti-de Sitter black holes with the Newman–Unti–Tamburino(NUT)parameter.To this end,we derive the analytic expression of thermodynamic variables,namely the Hawking temperature,volume,angular velocity,and entropy within the limits of extended phase space.These variables meet the first law of thermodynamics as well as the Smarr relation in the presence of new NUT charge.To analyze the effects of quantum fluctuations,we derive the exact expression of corrected entropy,which yields modification in other thermodynamical equations of state.The local stability and phase transition of the considered black hole are also examined through specific heat.It is found that the NUT parameter increases the stability of small black holes,while the logarithmic corrections induce instability in the system.

Local non-equilibrium thermal fluctuation,internal noise and dissipation in gaseous heat conduction systems with high values of Prandtl number

By means of a stochastic model suggested in this paper for the systems with local non-equilibrium excited thermal fluctuations, the famous Shannon entropy is extended to include the heat conduction processes controlled externally by boundary constraints of constant temperature gradients at two sides.Meanwhile,using the description of master equation for the continuous Markov processes a balance equation of stochastic entropy production valid for one dimension gaseous heat conduction systems with high values of Prandtl number has been also established.Based on it,a general expression for both the stochastic entropy production and the entropy production of fluctuations have been further deduced by theΩ-expansions.In this formalism,all kinds of stochastic contributions to the dissipation from the non-equilibrium thermal fluctuation and internal noise turn explicit.

A Hybrid Immersed Boundary/Coarse-Graining Method for Modeling Inextensible Semi-Flexible Filaments in Thermally Fluctuating Fluids Dedicated to Professor Karl Stark Pister for his 95th birthday

A new and computationally efficient version of the immersed boundary method,which is combined with the coarse-graining method,is introduced for modeling inextensible filaments immersed in low-Reynolds number flows.This is used to represent actin biopolymers,which are constituent elements of the cytoskeleton,a complex network-like structure that plays a fundamental role in shape morphology.An extension of the traditional immersed boundary method to include a stochastic stress tensor is also proposed in order to model the thermal fluctuations in the fluid at smaller scales.By way of validation,the response of a single,massless,inextensible semiflexible filament immersed in a thermally fluctuating fluid is obtained using the suggested numerical scheme and the resulting time-averaged contraction of the filament is compared to the theoretical value obtained from the worm-like chain model.

Quantum fluctuations of mesoscopic damped double resonance RLC circuit with mutual capacitance-inductance coupling

Based on the scheme of damped harmonic oscillator quantization and thermo-field dynamics （TFD）, the quantization of mesoscopic damped double resonance RLC circuit with mutual capacitance-inductance coupling is proposed. The quantum fluctuations of charge and current of each loop in a squeezed vacuum state are studied in the thermal excitation case. It is shown that the fluctuations not only depend on circuit inherent parameters, but also rely on excitation quantum number and squeezing parameter. Moreover, due to the finite environmental temperature and damped resistance, the fluctuations increase with the temperature rising, and decay with time.

Thermal analysis of the Rindler-Schwarzschild black hole via corrected entropy

In this study,we investigate the thermodynamic characteristics of the Rindler–Schwarzschild black hole solution.Our analysis encompasses the examination of energy emission,Gibbs free energy,and thermal fluctuations.We calculate various quantities such as the Hawking temperature,geometric mass,and heat capacity to assess the local and global thermodynamic stability.The temperature of the black hole is determined using the first law of thermodynamics,while the energy emission rate is evaluated as well.By computing the Gibbs free energy,we explore the phase transition behavior exhibited by Rindler–Schwarzschild black hole,specifically examining the swallowing tails.Moreover,we derive the corrected entropy to investigate the influence of thermal fluctuations on small and large black holes.Notably,we compare the impact of correction terms on the thermodynamic system by comparing the results obtained for large black holes and small black holes.

On the stochastic dynamics of molecular conformation

An important functioning mechanism of biological macromolecules is the transition between different conformed states due to thermal fluctuation. In the present paper, a biological macromolecule is modeled as two strands with side chains facing each other, and its stochastic dynamics including the statistics of stationary motion and the statistics of conformational transition is studied by using the stochastic averaging method for quasi Hamikonian systems. The theoretical results are confirmed with the results from Monte Carlo simulation.

Theory of specific heat of vortex liquid of high T_c superconductors

Superconducting thermal fluctuation(STF) plays an important role in both thermodynamic and transport properties in the vortex liquid phase of high Tsuperconductors.It was widely observed in the vicinity of the critical transition temperature.In the framework of Ginz burg-Landau-La wrence-Doniach theory in magnetic field,a self-consistent analysis of STF including all Landau levels is given.Besides that,we calculate the contribution of STF to specific heat in vortex liquid phase for high Tcuprate superconductors,and the fitting results are in good agreement with experimental data.

Performance characteristics a nonlinear diode and optimal analysis of refrigerator

This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures. Based on the theory of thermal fluctuations, the expressions of the heat flux absorbed from the heat reservoirs are derived. After the heat leak between the two reservoirs is considered, the cooling rate and the coefficient of performance are obtained analytically. The influence of the heat leak and the temperature ratio on the performance characteristics of the refrigerator is analysed in detail.

Quantum thermal field fluctuation induced corrections to the interaction between two ground-state atoms

We generalize the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji(the DDC formalism) in the fourth order for two atoms in interaction with scalar fields in vacuum to a thermal bath at finite temperature T, and then calculate the interatomic interaction energy of two ground-state atoms separately in terms of the contributions of thermal fluctuations and the radiation reaction of the atoms and analyze in detail the thermal corrections to the van der Waals and Casimir–Polder interactions. We discover a particular region, i.e. 4(λ3β)(1/2) ■ L■λwith L, β and λ denoting the interatomic separation, the wavelength of thermal photons and the transition wavelength of the atoms respectively, where the thermal corrections remarkably render the van der Waals force, which is usually attractive, repulsive, leading to an interesting crossover phenomenon of the interatomic interaction from attractive to repulsive as the temperature increases. We also find that the thermal corrections cause significant changes to the Casimir–Polder force when the temperature is sufficiently high, resulting in an attractive force proportional to TL-3in the λ ■ β ■ L region, and a force that can be either attractive or repulsive and even vanishing in the β ■ λ ■ L region depending on the interatomic separation.

Asymmetric transportation induced by thermal noise at the nanoscale

Based on a simple model, we theoretically show that asymmetric transportation is possible in nanoscale systems experiencing thermal noise without the presence of extemal fluctuations. The key to this theoretical advance is that the correlation lengths of the thermal fluctuations become significantly long for nanoscale systems. This differs from macroscopic systems in which the thermal noises are usually treated as white noise. Our observation does not violate the second law of thermodynamics, since at the nanoscale, extra energy is required to keep the asymmetric structure against thermal fluctuations.

Effects of fluctuating thermal regimes on cold survival and life history traits of the spotted wing Drosophila(Drosophila suzukii)

Drosophila suzukii is an invasive pest causing severe damages to a large panel of cultivated crops.To facili tate its biocontrol with stratcgies such as sterile or incompatible insect techniques,D.suzukid must be mass-produced and then stored and transported under low temperature.Prolonged cold exposure induces chill injuries that can be mitigated if the cold period is interrupted with short warming intervals,referred to as fluctuating thermal regimes(FTR).In this study,we tested how to optimally use FTR to extend the shelf life of D.suzukii under cold storage.Several FTR parameters were asessed:temperature(15,20,25℃),duration(0.5,1,2,3 h),and frequency(every 12,24,36,48 h)of warming intervals,in two wild-type lines and in two developmental stages(pupac and adults).Generally,FTR improved cold storage tolerance with respect to constant low temperatures(CLT).Cold mortality was lower when recovery temperature was 20℃ or higher,when duration was 2 h per day or longer,and when warming interruptions occurred frequently(every 12 or 24 h).Applying an optimized FTR protocol to adults greatly reduced cold mortality over long-term storage(up to 130 d).Consequences of FTR on fitness-related traits were also investigated.For adults,poststorage survival was unaffected by FTR,as was the case for female fecundity and male mating capacity.On the other hand,when cold storage occurred at pupal stage,postorage survival and male mating capacity were altered under CLT,but not under FTR.After storage of pupae,female fecundity was lower under FTR compared to CLT,suggesting an energy trade-off between repair of chill damages and C22 production.This study provides detailed information on the application and optimization of an FTR-based protocol for cold storage of D.suzuki that could be useful for the biocontrol of this pest.

On the origin of intrinsic randomness of Rayleigh-Benard turbulence

It is of broad interest to understand how the evolution of non-equilibrium systems can be triggered and the role played by external perturbations. A famous example is the origin of randomness in the laminar-turbulence transition, which is raised in the pipe flow experiment by Reynolds as a century old unresolved problem. Although there exist different hypotheses, it is widely believed that the randomness is "intrinsic", which, however, remains as an open question to be verified. Simulating the modeled RayleighB′enard convection system by means of the so-called clean numerical simulation(CNS) with negligible numerical noises that are smaller even than thermal fluctuation, we verify that turbulence can be self-excited from the inherent thermal fluctuation without any external disturbances, i.e. out of nothing. This reveals a relationship between microscopic physical uncertainty and macroscopic randomness. It is found that in physics the system nonlinearity functions as a channel for randomness information,and energy as well, to transport microscopic uncertainty toward large scales. Such scenario can generally be helpful to understand the various relevant phenomena. In methodology, compared with direct numerical simulation(DNS), CNS opens a new direction to investigate turbulent flows with largely improved accuracy and reliability.

Entanglement generation and protection for two atoms in the presence of two parallel mirrors

We study,in the framework of open quantum systems,the entanglement generation of two atoms in between two parallel mirrors in a thermal bath of quantum scalar fields.We find that the presence of mirrors plays an important role in entanglement generation and protection.The entanglement dynamics is crucially dependent on the geometric configurations of the two-atom system with respect to the mirrors,and the ranges of temperature and interatomic separation within which entanglement can be generated are significantly changed compared with those in a free space.In particular,when the atomic transition wavelength is larger than twice the distance between the two mirrors,the atoms behave as if they were isolated from the environment and the entanglement can persist in the steady state if the atoms are initially entangled and no entanglement can be created if they are initially separable,no matter how the atoms are placed with respect to the mirrors and to each other.This is in sharp contrast to the fact that in a free space,steady-state entanglement is possible only when the two atoms are placed extremely close to each other,while in the presence of one mirror,it is possible when the two atoms placed extremely close to the mirror.