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The nature of the influence of thermionic emission from a condensed phase on the concentration of ions in equilibrium thermal plasma has been studied using an analytical model. Spherical tungsten nanoparticles have been considered as a dust subsystem. It has been revealed that depending on the effective ionization potential of background gas atoms, two regimes of the charge state of the system are realized: with a positively and negatively charged dust component. It has been established that the size of nanoparticles affects the concentration of background gas ions in different ways under these regimes. [ABSTRACT FROM AUTHOR]

We contrast Dirac's theory of transition probabilities and the theory of nonadiabatic transition probabilities, applied to a perturbed system that is coupled to a bath. In Dirac's analysis, the presence of an excited state |k0⟩ in the time-dependent wave function constitutes a transition. In the nonadiabatic theory, a transition occurs when the wave function develops a term that is not adiabatically connected to the initial state. Landau and Lifshitz separated Dirac's excited-state coefficients into a term that follows the adiabatic theorem of Born and Fock and a nonadiabatic term that represents excitation across an energy gap. If the system remains coherent, the two approaches are equivalent. However, differences between the two approaches arise when coupling to a bath causes dephasing, a situation that was not treated by Dirac. For two-level model systems in static electric fields, we add relaxation terms to the Liouville equation for the time derivative of the density matrix. We contrast the results obtained from the two theories. In the analysis based on Dirac's transition probabilities, the steady state of the system is not an equilibrium state; also, the steady-state population ρkk,s increases with increasing strength of the perturbation and its value depends on the dephasing time T2. In the nonadiabatic theory, the system evolves to the thermal equilibrium with the bath. The difference is not simply due to the choice of basis because the difference remains when the results are transformed to a common basis. [ABSTRACT FROM AUTHOR]

Trajectory-based methods that propagate classical nuclei on multiple quantum electronic states are often used to simulate nonadiabatic processes in the condensed phase. A long-standing problem of these methods is their lack of detailed balance, meaning that they do not conserve the equilibrium distribution. In this article, we investigate ideas for restoring detailed balance in mixed quantum–classical systems by tailoring the previously proposed spin-mapping approach to thermal equilibrium. We find that adapting the spin magnitude can recover the correct long-time populations but is insufficient to conserve the full equilibrium distribution. The latter can however be achieved by a more flexible mapping of the spin onto an ellipsoid, which is constructed to fulfill detailed balance for arbitrary potentials. This ellipsoid approach solves the problem of negative populations that has plagued previous mapping approaches and can therefore be applied also to strongly asymmetric and anharmonic systems. Because it conserves the thermal distribution, the method can also exploit efficient sampling schemes used in standard molecular dynamics, which drastically reduces the number of trajectories needed for convergence. The dynamics does however still have mean-field character, as is observed most clearly by evaluating reaction rates in the golden-rule limit. This implies that although the ellipsoid mapping provides a rigorous framework, further work is required to find an accurate classical-trajectory approximation that captures more properties of the true quantum dynamics. [ABSTRACT FROM AUTHOR]

A hallmark of meso-scale interfacial fluids is the multi-faceted, scale-dependent interfacial energy, which often manifests different characteristics across the molecular and continuum scale. The multi-scale nature imposes a challenge to construct reliable coarse-grained (CG) models, where the CG potential function needs to faithfully encode the many-body interactions arising from the unresolved atomistic interactions and account for the heterogeneous density distributions across the interface. We construct the CG models of both single- and two-component polymeric fluid systems based on the recently developed deep coarse-grained potential [Zhang et al., J. Chem. Phys. 149, 034101 (2018)] scheme, where each polymer molecule is modeled as a CG particle. By only using the training samples of the instantaneous force under the thermal equilibrium state, the constructed CG models can accurately reproduce both the probability density function of the void formation in bulk and the spectrum of the capillary wave across the fluid interface. More importantly, the CG models accurately predict the volume-to-area scaling transition for the apolar solvation energy, illustrating the effectiveness to probe the meso-scale collective behaviors encoded with molecular-level fidelity. [ABSTRACT FROM AUTHOR]

The Soret effect is the tendency of fluid mixtures to exhibit concentration gradients in the presence of a temperature gradient. Using molecular-dynamics simulation of two-component Lennard-Jones liquids, it is demonstrated that spatially sinusoidal heat pulses generate both temperature and pressure gradients. Over short timescales, the dominant effect is the generation of compressional waves, which dissipate over time as the system approaches mechanical equilibrium. The approach to mechanical equilibrium is also characterized by a decrease in particle density in the high-temperature region and an increase in particle density in the low-temperature region. It is demonstrated that concentration gradients develop rapidly during the propagation of compressional waves through the liquid. Over longer timescales, heat conduction occurs to return the system to thermal equilibrium, with the particle current acting to restore a more uniform particle density. It is shown that the Soret effect arises due to the fact that the two components of the fluid exhibit different responses to pressure gradients. First, the so-called isotope effect occurs because light atoms tend to respond more rapidly to evolving conditions. In this case, there appears to be a connection to previous observations of "fast sound" in binary fluids. Second, it is shown that the partial pressures of the two components in equilibrium, and more directly, the relative magnitudes of their derivatives with respect to temperature and density, determine which species accumulate in the high- and low-temperature regions. In the conditions simulated here, the dependence of the partial pressure on density gradients is larger than the dependence on temperature gradients. This is directly connected to the accumulation of the species with the largest partial pressure in the high-temperature region and the accumulation of the species with the smallest partial pressure in the low-temperature region. The results suggest that further development of theoretical descriptions of the Soret effect might begin with hydrodynamical equations in two-component liquids. Finally, it is suggested that the recently proposed concept of "thermophobicity" may be related to the sensitivity of partial pressures in a multicomponent fluid to changes in temperature and density. [ABSTRACT FROM AUTHOR]

The surface erosion of polyethylene is interrogated using pulsed x rays at the Z Machine (Sandia National Laboratories) and with proton beams at the Gamble II generator (Naval Research Laboratory) to validate a coupled model for volumetric thermal ablation, photoionization, finite-rate decomposition, and molecular recombination of radicals. The intense radiation pulses (up to ∼ 10 14 W / m 2 over tens of nanoseconds) are used to generate one-dimensional vapor flows with low ionization fractions and a simplified geometry compared to typical laser ablation, allowing for evaluation of the model under local thermal equilibrium conditions. Areal momentum carried by the ensuing uniaxial hydrodynamic shock is used to indicate the extent of ablation. The threshold fluence for ablation is found to be in close correspondence with the bulk melt transition, and reasonable agreement with the model is obtained for peak temperatures in polyethylene up to 5500 K and heating rates up to 10 11 K / s where thermal decomposition reactions are also active. [ABSTRACT FROM AUTHOR]

Hypersonic vehicles and aircraft engine blades face complex and harsh environments such as high heat flow density and high temperature, and they are generally narrow curved spaces, making it impossible to actually install them for testing. Thin-film heat flux sensors (HFSs) have the advantages of small size, fast response, and in-situ fabrication, but they are prone to reach thermal equilibrium and thus fail during testing. In our manuscript, an ITO–In2O3 thick film heat flux sensor (HFS) is designed, and a high-temperature heat flux test system is built to simulate the working condition of a blade subjected to heat flow impact. The simulation and test results show that the test performance of the thick-film HFS is improved by optimizing the structure and parameters. Under the condition of no water cooling, the designed HFS can realize short-time heat flux monitoring at 1450 °C and long-term stable monitoring at 1300 °C and below. With a maximum output thermopotential of 17.8 mV and an average test sensitivity of 0.035 mV/(kW/m2), the designed HFS has superior high-temperature resistance that cannot be achieved by other existing thin (thick) film HFSs. Therefore, the designed HFS has great potential for application in harsh environments such as aerospace, weaponry, and industrial metallurgy. [ABSTRACT FROM AUTHOR]

Context. 46P/Wirtanen is a near-Earth comet (NEC) and several previous modeling works had predicted it would produce a meteor shower for the first time on December 12, 2023. Aims. We report the most comprehensive meteor radar observations of the λ-Sculptorid meteor shower produced by comet 46P/Wirtanen. These measurements are critical to constrain the mass distribution of the particles released by the comet as radars generally detect the smaller particle population of the shower. Methods. We utilized observations with the Southern Argentina Agile Meteor Radar-Orbital System (SAAMER-OS) ideally located in the southern hemisphere to detect this shower. Since the shower was predicted to produce very slow meteors, we used the same methodology applied for the Arid meteor shower. Results. As predicted, the shower peak was observed by SAAMER-OS on December 12, 2023 (λ0 = 259.73°) at 0900 UTC, with a Zenithal Hourly Rate (ZHR) peak value of ~2.5 m h−1. Most of the activity of the shower was observed during 2 h between 0730-0930 UTC. The observed mean radiant of the shower in Sun-centered ecliptic coordinates is located at λ − λ0 = 88.9° and β = −36.6°. Our results suggest that the particles detected by SAAMER-OS are in general larger than those for which thermal equilibrium can be assumed (>3 mg) in agreement with the conclusions of previous reports using video observations. [ABSTRACT FROM AUTHOR]

This study presents calculations for cross sections of the vibrational excitation of H2O(X1A1) via electron impact. The theoretical approach employed here is based on first principles only, combining electron-scattering calculations performed using the UK R-matrix codes for several geometries of the target molecule, three-dimensional (3D) vibrational states of H2O, and 3D vibrational frame transformation. The aim is to represent the scattering matrix for the electron incident of the molecule. The vibrational wave functions were obtained numerically, without the normal-mode approximation, so that the interactions and transitions between vibrational states assigned to different normal modes could be accounted for. The thermally averaged rate coefficients were derived from the calculated cross sections for temperatures in the 10–10 000 K interval and analytical fits for rate coefficients were also provided. We assessed the uncertainty estimations of the obtained data for subsequent applications of the rate coefficients in modelling the non-local thermal equilibrium (non-LTE) spectra of water in various astrophysical environments. [ABSTRACT FROM AUTHOR]

The thermal water deposit in Lądek-Zdrój (SW Poland) occurs in fractured reservoir rocks, and its hydrogeological regime is controlled by the features of the local geology and lithology of the hosting crystalline complexes, mainly impermeable high-grade metamorphosed mica schists and gneisses. The fractured thermal water aquifer is confined by a thrust fault-type aquitard that creates artesian pressure and, therefore, the water intakes and natural springs in Lądek Zdrój provide spontaneous outflow. Classical geothermometers yield an estimation of reservoir temperatures that ranges from 50 to 70 °C, with a maximum of 88 °C. The heat flux (HF) value of the Lądek-Zdrój region is 64 mW/m2. The new borehole, LZT-1, is in the border zone of a local thermal anomaly with a geothermal degree of 25–27 m/°C. The estimated temperature at the bottom of the LZT-1 borehole, under thermal equilibrium conditions, ranges between 70 °C and 80 °C. A stream of heated waters from the deep system flows from the recharge areas, shaping the local geothermal anomaly and thus influencing the thermal conditions in the Lądek-Zdrój area. The activation of this water circulation system occurred in the Pleistocene. [ABSTRACT FROM AUTHOR]

Convective heat transport in permeable media has been widely modeled using the local thermal non-equilibrium (LTNE) model. The majority of earlier LTNE-based models take temperature interactions between the fluid and solid phases into consideration. The present investigation delves into the intricate dynamics of Darcy–Rayleigh–Bènard (DRB) convection occurring within a liquid layer situated above a porous layer, wherein thermal gradients and heat generation play a pivotal role. This research examines the effects of many types of thermal gradients, including parabolic, step function (SF), linear, piecewise linear heated from below (PLHB), inverted parabolic, and piecewise linear cooled from above (PLCA). A fluid layer sits on top of a porous layer in the composite layer that makes up the system. The porous medium has achieved complete saturation with the identical fluid. The observed system demonstrates the manifestation of LTNE phenomena. Furthermore, the composite layer is constrained horizontally due to the presence of adiabatic stiff peripheries. The explanation to the aforementioned issue is obtained by employing the perturbation approach via analytical methodologies. The ongoing research is focused on exploring various physical parameters in order to examine the underlying physical implications that uphold the phenomenon of LTNE, employing the utilization of diagrammatic representation. A juxtaposition is drawn between the results derived from manipulating various constraints, including the temperature expansion ratio of the liquid phase, the corrected internal Rayleigh numbers, the thermal ratio, the diffusivity ratio of the liquid layer, and the permeable layer, within the framework of the LTNE configuration, and those obtained within the Local Thermal Equilibrium (LTE) regime. The depth ratio is a key factor in the onset of DRB convection, and higher depth ratio values which indicate porous layers that predominate in composite layered systems have a noticeable impact on all variables under investigation. [ABSTRACT FROM AUTHOR]

Abstract\nHIGHLIGHTSThe single-phase approach, in which nanofluids are treated as pure fluids assuming that the solid and liquid phases are in local thermal and hydrodynamic equilibrium, has been used with good results to simulate forced convection flows. Conversely, its extension to natural convection has revealed to be more problematic, as the obtained numerical results are substantially different from the experimental data, mainly due to the effects of the slip motion occurring between the suspended nanoparticles and the base liquid, whose consequent nonuniform distribution of the solid phase concentration can significantly affect both heat and momentum transfer. In the present article, a two-phase model based on a double-diffusive approach is proposed to study the natural convection flows of water-based metal oxide nanofluids inside cylindrical and rectangular enclosures heated and cooled at their opposite sides with the scope to reproduce a number of experimental data-sets available in the literature. Given the assumption of local thermal equilibrium between nanoparticles and host liquid, and considering the Brownian and thermophoretic diffusion as responsible for causing significant relative velocity between the solid and liquid phases, the governing equations are solved by a control-volume numerical method implemented using the open-source platform OpenFOAM (Open Field Operation and Manipulation). It has been found that the nanoparticle diffusion gives the major contribution to the decrease of the heat transfer rate red usually observed experimentally in natural convection flows of nanofluids inside differentially-heated enclosures. This means that a two-phase model, in conjunction with proper correlations for the evaluation of the nanofluid effective physical properties, must be necessarily enforced to obtain reliable results for many engineering applications.A two-phase model has been tested and validated reproducing different sets of experimental data available in the literature for natural convection flows of nanofluids inside differentially-heated enclosures.A description of the nanoparticle diffusion is given with the scope to point out the two-phase behavior of nanofluids.Optimal values of both the nanoparticle volume fraction and average nanofluid temperature are found to be imposed to enhance the heat transfer rate.A two-phase model has been tested and validated reproducing different sets of experimental data available in the literature for natural convection flows of nanofluids inside differentially-heated enclosures.A description of the nanoparticle diffusion is given with the scope to point out the two-phase behavior of nanofluids.Optimal values of both the nanoparticle volume fraction and average nanofluid temperature are found to be imposed to enhance the heat transfer rate. [ABSTRACT FROM AUTHOR]

Active fluids composed of constituents that are constantly driven away from thermal equilibrium can support spontaneous currents and can be engineered to have unconventional transport properties. Here, we report the emergence of (meta)stable traveling bands in computer simulations of aligning circle swimmers. These bands are different from polar flocks and, through coupling phase with mass transport, induce a bulk particle current with a component perpendicular to the propagation direction, thus giving rise to a collective Hall (or Magnus) effect. Traveling bands require sufficiently small orbits and undergo a discontinuous transition into a synchronized state with transient polar clusters for large orbital radii. Within a minimal hydrodynamic theory, we show that the bands can be understood as nondispersive soliton solutions fully accounting for the numerically observed properties. [ABSTRACT FROM AUTHOR]

Conceptually, the Matsubara formalism (MF), using imaginary frequencies, and the Keldysh formalism (KF), formulated in real frequencies, give equivalent results for systems in thermal equilibrium. The MF has less complexity and is thus more convenient than the KF. However, computing dynamical observables in the MF requires the analytic continuation from imaginary to real frequencies. The analytic continuation is well‐known for two‐point correlation functions (having one frequency argument), but, for multipoint correlators, a straightforward recipe for deducing all Keldysh components from the MF correlator had not been formulated yet. Recently, a representation of MF and KF correlators in terms of formalism‐independent partial spectral functions and formalism‐specific kernels was introduced by Kugler, Lee, and von Delft [Phys. Rev. X 11, 041006 (2021)]. This representation is used to formally elucidate the connection between both formalisms. How a multipoint MF correlator can be analytically continued to recover all partial spectral functions and yield all Keldysh components of its KF counterpart is shown. The procedure is illustrated for various correlators of the Hubbard atom. [ABSTRACT FROM AUTHOR]

In this paper, we examine how finite time disentanglement can be manipulated for the quantum system out of thermal equilibrium. To this aim, we employ the Markovian master equation approach to find the rate equations and Wootter's concurrence to analyze out of thermal equilibrium entanglement dynamics for Dicke bases. The effect of super- and sub-radiant rates on entanglement sudden death is examined for different classes of X-states. It is found that the shorter dark period is achieved at a higher transition rate of a super-radiant state. This approach allows us to analyze the further applications of quantum information technologies. [ABSTRACT FROM AUTHOR]

An ultranarrow‐band ultraviolet (UV) GaN detector with a simple device architecture is presented. The device displays an ultranarrow band response centred at 366 nm with only ≈5 nm width, a UV–visible rejection ratio of >2 × 103, and detectivity of 1.3 × 1010 Jones at room temperature. The device is tested over a wide temperature range where the maximum response is recorded at 200 K. Temperature dependence of device response is explained by considering the thermal activation of shallow donors in low‐temperature regime and the establishment of thermal equilibrium of the donor level with conduction band at elevated temperatures. Moreover, the device displays three orders UV‐to‐visible rejection ratio over a wide temperature range of 150–350 K, showing great potential for narrowband UV detection even at elevated temperatures. Conventional and pump‐probe surface photovoltage spectroscopy measurements are performed with UV and infrared lasers to identify the electronic transitions associated with the narrowband response. It is understood that carrier excitation from valance band to shallow donor level in the interfacial depletion region is responsible for the observed behavior. The results presented here demonstrate an innovative methodology for achieving a stable and high spectrum‐selective UV photodetection without involving complex device architecture. [ABSTRACT FROM AUTHOR]

In this study, we revisit the oxidation reactions of a single-crystal silicon wafer and compare the reported crystal structures of the formed oxides with the original diamond structure of single-crystal silicon. It is commonly assumed that interstitial silicon atoms are always emitted during oxidation at the reactive interface between silicon and the formed oxide due to volume differences. However, it is important to acknowledge that this phenomenon may not always be observed. Thermal equilibrium studies have revealed that a certain percentage of silicon atoms in the diamond structure remains even after surface oxidation [Kamiyama and Sueoka, J. Appl. Phys. 134, 115301 (2023)]. These retained silicon atoms undergo a transformation into a different crystal structure, presenting as β-cristobalite (space group: P41212) rather than the anticipated non-ideal cristobalite (space group: Fd-3m). Our ab initio calculations indicated that the latter remains stable next to a quartz-based structure, exhibiting optimal compatibility with the Si (001) surface. This quartz-based structure is formed through the emission of a Si atom during the oxidation of single-crystal silicon, finally forming a quartz/Si (001) interface. Therefore, we propose a coexisting model involving an alternative β-cristobalite and a quartz crystal structure originating from the surface oxidation of single-crystal silicon. This model offers an explanation for why thermally oxidized films derived from single-crystal silicon exhibit an amorphous nature. In addition, studies have revealed that the oxide precipitates observed in Si crystals are cristobalite and coesite. Hence, the qualitative differences in SiO2/Si interfaces between surface and internal oxidations in metal-gettering effectivity shown in experimental literature require clarification. We also discuss the conditions that prevent the emission of Si atoms. [ABSTRACT FROM AUTHOR]

A fundamental assumption in numerous studies of heat transfer in porous media is local thermal equilibrium (LTE), which assumes that the temperature of the porous media at the fluid and solid interface is in instantaneous equilibrium. Although significant efforts have been made to quantify the occurrence and consequences of local thermal nonequilibrium (LTNE), where the temperatures of the fluid and adjacent solid phases differ, there is no simple expression for quantifying the occurrence and effects of local thermal disequilibrium. Using a numerical model combining LTE and LTNE models, we develop here two simple general criteria based on Darcian velocities (q) and particle sizes (dp) of porous media for determining when LTNE effects occur (denoted as g(dp, q)) and when they become significant (denoted as f(dp, q)). Results show that using an LTE model can result in an underestimation of effective thermal diffusivity and the unaffected Darcian velocities when g(dp, q) > 0. It is possible that using the LTE model can result in an underestimation of the effective thermal diffusivity by more than 200 times within Darcian velocities ranging from 0 to 60 m/d. In the case of g(dp, q) < 0, the use of the LTE model can result in an overestimation of effective thermal diffusivity and Darcian velocities. The performances of the newly developed general criteria are demonstrated using three typical data sets and corresponding numerical models. These data sets include new heat tracer tests conducted in the laboratory and the field, as well as temperature‐time series collected in streambed sediments from a previous study by Shanafield et al. (2012, https://doi.org/10.5194/hessd‐9‐4305‐2012). The potential LTNE effects should be considered when using heat as a tracer to characterize flow and heat transport in porous media in the presence of Darcian velocities less than 2 m/d and particle sizes larger than 10 mm. Plain Language Summary: This study explores heat transport in saturated porous media and in particularly potential temperature differences between water and solid phases, a phenomenon called local thermal nonequilibrium (LTNE). While typically neglected, we demonstrate that under some hydraulic conditions LTNE effects should be addressed in more accurate modeling of heat transport in natural porous media. We presented two new criteria on the occurrence and becoming significant of LTNE effects and validated them using three case studies, including both laboratory and field experiments. These findings provide new insights into flow and heat transport processes controlling a range of applications, such as hydrogeological investigations, and subsurface energy storage and extraction. Key Points: New general criteria are developed for determining when LTNE effects occur and when they become significantThree case studies involving different particle sizes and Darcian velocities are used to verify the reliability of the proposed criteriaLocal thermal nonequilibrium effects can result in an increase in effective thermal diffusivity by more than 200 times at Darcian velocities ranging from 0 to 60 m/d [ABSTRACT FROM AUTHOR]

This study designs a differential dual-drive micro-feed mechanism, superposing the two "macro feed motions" ("motor drive screw" and "motor drive nut") using the same transmission of "the nut rotary ball screw pair" structure. These two motions are almost equal in terms of speed and turning direction, thus the "micro feed" can be obtained. (1) Background: Thermal deformation is the primary factor that can restrict the high-precision micro-feed mechanism and the distribution of heat sources differs from that of the conventional screw single-drive system owing to the structure and motion features of the transmission components. (2) Discussion: This study explores the thermal field distribution and thermal deformation of the differentially driven micro-feed mechanism when two driving motors are combined at different speeds. (3) Methods: Based on the theory of heat transfer, the differential dual-drive system can be used as the research object. The thermal equilibrium equations of the micro-feed transmission system are established using the thermal resistance network method, and a thermal field distribution model is obtained. (4) Results: Combined with the mechanism of thermal deformation theory, the established thermal field model is used to predict the axial thermal deformation of the differential dual-drive ball screw. (5) Conclusions: Under the dual-drive condition, the steady-state thermal error of the nut-rotating ball screw transmission mechanism increases with the increase in nut speed and composite speed and is greater than the steady-state thermal error under the single screw drive condition. After reaching the thermal steady state, the measured thermal elongation at the end of the screw in the experiment is approximately 10.5 μm and the simulation result is 11.98 μm. The experimental measurement result demonstrates the accuracy of the theoretical analysis model for thermal error at the end of the screw. [ABSTRACT FROM AUTHOR]

In this study, we revisit the oxidation reactions of a single-crystal silicon wafer and compare the reported crystal structures of the formed oxides with the original diamond structure of single-crystal silicon. It is commonly assumed that interstitial silicon atoms are always emitted during oxidation at the reactive interface between silicon and the formed oxide due to volume differences. However, it is important to acknowledge that this phenomenon may not always be observed. Thermal equilibrium studies have revealed that a certain percentage of silicon atoms in the diamond structure remains even after surface oxidation [Kamiyama and Sueoka, J. Appl. Phys. 134, 115301 (2023)]. These retained silicon atoms undergo a transformation into a different crystal structure, presenting as β-cristobalite (space group: P41212) rather than the anticipated non-ideal cristobalite (space group: Fd-3m). Our ab initio calculations indicated that the latter remains stable next to a quartz-based structure, exhibiting optimal compatibility with the Si (001) surface. This quartz-based structure is formed through the emission of a Si atom during the oxidation of single-crystal silicon, finally forming a quartz/Si (001) interface. Therefore, we propose a coexisting model involving an alternative β-cristobalite and a quartz crystal structure originating from the surface oxidation of single-crystal silicon. This model offers an explanation for why thermally oxidized films derived from single-crystal silicon exhibit an amorphous nature. In addition, studies have revealed that the oxide precipitates observed in Si crystals are cristobalite and coesite. Hence, the qualitative differences in SiO2/Si interfaces between surface and internal oxidations in metal-gettering effectivity shown in experimental literature require clarification. We also discuss the conditions that prevent the emission of Si atoms. [ABSTRACT FROM AUTHOR]

We propose a toy model of a spherical universe made up of an exotic dark gas with temperature T in thermal equilibrium with a black-body in adiabatic expansion. Each particle of this exotic gas mimics a kind of particle of dark energy. So, each dark particle occupies a very small area of space so-called Planck area L p 2 , which represents the minimum area of the whole space-time given by the spherical surface with area 4 π R H 2 , where R H is the Hubble radius. We realize that such spherical surface is the surface of the black-body for representing the dark universe as if it were the surface of an expanding balloon. Thus, we are able to derive the law of universal gravitation, thus leading us to understand the cosmological anti-gravity. We estimate the tiny order of magnitude of the cosmological constant and the acceleration of expansion of the dark sphere. In this toy model, as the dark universe can be thought of as a large black body, when we obtain its power and frequency of emission of radiation, we find very low values. We conclude that such radiation and frequency of the black body made up of dark energy is a background gravitational wave with very low frequency in the order of 1 0 − 1 7 Hz due to the slight stretching of the fabric of space-time. [ABSTRACT FROM AUTHOR]

Upon dibenzo annulation on Thiele's hydrocarbon (tetraphenyl‐p‐quinodimethane), the quinoid form and the biradical form adopt quite different geometries, and thus are no longer resonance structures. When these two forms can interconvert rapidly due to the small energy barrier (ΔG≠), the equilibrated mixture contains both forms in a ratio that is determined by the energy difference (ΔGo) between the two forms. For a series of tetrakis[5‐(4‐methoxyphenyl)‐2‐thienyl]‐substituted derivatives, the more stable quinoid form and the metastable biradical form coexist in solution as an equilibrated mixture due to small ΔG≠ (<15 kcal mol−1) and ΔGo (1–4 kcal mol−1), in which the proportion of the two forms can be regulated by temperature. Since the biradical form can undergo easy two‐electron (2e) oxidation to the corresponding dications as well as easy 2e‐reduction to the dianions, it exhibits very high electrochemical amphotericity. This character with a record‐small span for not only the first oxidation and reduction potentials but also the second those, [E1sum≈E2sum=E2ox−E2red=ca. 1.4 V], is attained through thermally enhanced conversion to the biradical form from the corresponding quinoid form, the latter of which is less amphoteric due to higher Eox and lower Ered values. [ABSTRACT FROM AUTHOR]

Turbulence is a fundamental process that drives mixing and energy redistribution across a wide range of astrophysical systems. For warm (T≈104 K) plasma, the material is partially ionized, consisting of both ionized and neutral species. The interactions between ionized and neutral species are thought to play a key role in heating (or cooling) of partially ionized plasmas. Here, mixing is studied in a two-fluid partially ionized plasma undergoing the shear-driven Kelvin–Helmholtz instability to evaluate the thermal processes within the mixing layer. Two-dimensional numerical simulations are performed using the open-source (PIP) code that solves for a two-fluid plasma consisting of a charge-neutral plasma and multiple excited states of neutral hydrogen. Both collisional and radiative ionization and recombination are included. In the mixing layer, a complex array of ionization and recombination processes occur as the cooler layer joins the hotter layer, and vice versa. In localized areas of the mixing layer, the temperature exceeds the initial temperatures of either layer with heating dominated by collisional recombinations over turbulent dissipation. The mixing layer is in approximate ionization-recombination equilibrium, however the obtained equilibrium is different to the Saha–Boltzmann local thermal equilibrium. The dynamic mixing processes may be important in determining the ionization states, and with that intensities of spectral lines, of observed mixing layers. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'. [ABSTRACT FROM AUTHOR]

Accurately predicting the thermal characteristics and heat transfer distribution of the rotating detonation engine (RDE) and acquiring a clear understanding of the performance and mechanism of the rotating detonation are of great significance for achieving the safe and reliable long-duration operation of RDEs. Using RP-3 as fuel, a long-duration experimental study is performed on a 220 mm-diameter RDC to investigate the details with respect to the thermal environment. The heat flux at the typical location and the average heat flux of both the inner and outer cylinders are measured, respectively. Meanwhile, the peak pressure of the rotating detonation wave (RDW) and specific thrust are analyzed. When the ER is between 0.5 and 1 (oxidizer 2 kg/s), the stable rotating detonation mode is obtained, and the detonation duration is set as 40 s to accurately calculate the heat released by the detonation combustion. The heat flux in the upstream region of the RDW location ranges from 2.40 × 105 W/m2 to 3.17 × 105 W/m2, and the heat flux in the downstream area of the RDW location ranges from 1.05 × 106 W/m2 to 1.28 × 106 W/m2. The results demonstrate the important role of the detonation combustion zone, and the thrust performance of RDC can be improved by making the RDW move forward along the RDC axis, which is the optimal direction of detonation combustion. Through a comparison of average heat flux under different conditions, it is found that the heat released by the RDC is directly related to its thrust. In addition, the average heat flux of the inner cylinder is about three times that of the outer cylinder for the two-phase RDC with a Tesla valve intake structure, indicating that the high-temperature combustion product is closer to the inner wall. Therefore, more thermal protection should be allocated to the inner cylinder, and a more systematic analysis of the two-phase flow field distribution in the annular combustion chamber should be carried out to improve the thrust performance. In this paper, the average heat flux of the inner and outer cylinders of the RDC as well as the typical local heat flux of the outer cylinders is quantitatively measured by means of experiments, which not only deepens the understanding of RDC flow field distribution, but also provides quantitative boundary conditions for the thermal protection design of RDCs. [ABSTRACT FROM AUTHOR]

In our investigation, we delve into the dynamics of thermal entanglement and quantum-memory-assisted entropic uncertainty relation (QMA-EUR) within an XXZ Heisenberg spin-1/2 chain consisting of two qubits. This system is affected by the Herring–Flicker (HF) coupling and exposed to the Dzyaloshinsky–Moriya (DM) interaction, in the presence of an external homogeneous magnetic field. We assume that the system is in thermal equilibrium with a reservoir and examine how various parameters, including the HF coupling distance R, equilibrium temperature, and other system characteristics, affect the logarithmic negativity used to quantify thermal entanglement and QMA-EUR. Our findings reveal intriguing distinctions in the behaviors of QMA-EUR and thermal entanglement. Notably, an increase in temperature is found to effectively reduce thermal entanglement while simultaneously enhancing QMA-EUR. Furthermore, we notice that bipartite entanglement and QMA-EUR exhibit distinct behaviors as we vary the coupling distance, R. Specifically, the logarithmic negativity attains its highest value at a coupling distance of R = 1.25 , which coincides with the lowest QMA-EUR value. Furthermore, we discover that the presence of high-intensity magnetic fields has a detrimental influence on the level of thermal entanglement. However through adjustments in the inter-spins relative distance R, the strength of the DM interaction, temperature T, the anisotropy parameter, and the static magnetic field B, it is possible to suppress the QMA-EUR and enhance bipartite entanglement within the system. These findings suggest encouraging possibilities for advancing quantum technologies that make use of this quantum system. [ABSTRACT FROM AUTHOR]

Robotic Friction Stir Welding (RFSW) technology integrates the advantages of friction stir welding and industrial robots, finding extensive applications and research in aerospace, shipbuilding, and new energy vehicles. However, the high-speed rotational process of friction stir welding combined with the low stiffness characteristics of serial industrial robots inevitably introduces vibrations during the welding process. This paper investigates the vibration patterns and impacts during the RFSW process and proposes an active vibration avoidance control method for variable speed welding based on constant heat input. This method utilizes a vibration feedback strategy that adjusts the spindle speed actively if the end-effector's vibration exceeds a threshold, thereby avoiding the modal frequencies of the robot at its current pose. Concurrently, it calculates and adjusts the welding speed of the robot according to the thermal equilibrium equation to maintain constant heat input. A simplified dynamic model of the RFSW robot was established, and the feasibility of this method was validated through simulation experiments. This study fills the gap in vibration analysis of RFSW and provides new insights into control strategies and process optimization for robotic friction stir welding. [ABSTRACT FROM AUTHOR]

We show that powder pressed specimens of nickel can be sintered to 99.96% density by injecting electrical current, without the use of a furnace. Full sintering could be accomplished in 10 to 52 s by changing the current rate from 5 to 1 A/s. In all instances, the samples sintered abruptly at a current density of ∼20 A mm−2. The grain size of the sintered samples was somewhat larger than the nickel powder particle size (∼60 μm vs. 40 μm). Tensile testing yielded a yield strength of 98 MPa, ultimate tensile stress of 323 MPa, and ductility of ∼17%. Four in‐operando measurements are reported: (i) sintering, (ii) the change in resistance with current density, (iii) the temperature, and (iv) electroluminescence. The change in resistance during flash sintering exhibited a high peak followed by a steep decline in resistance; the transient is attributed to the breakdown of particle–particle interface resistance. The same cycle repeated with the flash‐sintered, dense sample, did not show the spike, and gave reproducible results. The resistance data for these latter cycles, when viewed as a function of temperature exhibited sigmoidal behavior: initially lower, and then higher than the literature values. This unusual behavior reflects the influence of defects generated during flash. We have also measured the endothermic enthalpy, expressed by the difference between the in situ input electrical energy and the radiation, convection, and specific heat losses. Dividing by the formation energy of Frenkel pairs yields the concentration of defects, estimated to be 0.3–0.4 mol %. These concentrations are far above thermal equilibrium; it is concluded that flash of metals is a far from equilibrium phenomenon. [ABSTRACT FROM AUTHOR]

Quasi-equilibrium states that can be prepared in solids through Nuclear Magnetic Resonance (NMR) techniques are out-of-equilibrium states that slowly relax towards thermodynamic equilibrium with the lattice. In this work, we use the quantum discord dynamics as a witness of the quantum correlation in this kind of state. The studied system is a set of dipole interacting spin pairs whose initial state is prepared with the NMR Jeener–Broekaert pulse sequence, starting from equilibrium at high temperature and high external magnetic field. It then evolves as an open quantum system within two consecutive dynamic scenarios: adiabatic decoherence driven by the coupling of the pairs to a common phonon field, described within a non-Markovian approach, and spin–lattice relaxation represented by the high-temperature limit of the Born–Markov master equation, and driven by thermal fluctuations. In this way, the studied model is endowed with the dynamics of a realistic solid sample. The quantum discord rapidly increases during the preparation of the initial state, escalating several orders of magnitude compared with thermal equilibrium at room temperature. During decoherence—despite the decay of coherences—the quantum discord oscillates upon this high value, holding the same value as the initial state. Finally, the quantum discord dissipates within a time scale shorter than but comparable to spin–lattice relaxation. [ABSTRACT FROM AUTHOR]

We explore the relationship between entropy and quantum measurements and present a variational algorithm for preparing statistical ensembles on quantum computers using mid-circuit measurements. This algorithm optimizes both the entropy and variational parameters describing the state to obtain the minimum free energy of quantum systems in thermal equilibrium with some external heat bath. We demonstrate our algorithm on IBM-Q Lagos. [ABSTRACT FROM AUTHOR]

The BBBV theorem is known to largely prohibit exponential speedup of quantum search over classical search, though not entirely, with potential loopholes such as adiabatic quantum computing. Recently, Chen-Huang-Preskill-Zhou (CHPZ) quantum (thermal) gradient descent proposal suggested another potential way to go around the BBBV theorem. We simplify the heavily complicated CHPZ analysis by focusing on the final equilibrium in the quantum thermal operation framework that has already been rigorously formulated in quantum thermodynamics, resulting in quantum thermal search. In particular, repeated applications of an identical quantum mixing thermal operation result in exponential convergence (in the number of repeated applications) of the system state to the equilibrium Gibbs state for the given system Hamiltonian at initial bath temperature. This allows for an efficient computation of the system ground state. Quantum mixing thermal operations evade the BBBV theorem by transferring initial system state information to the bath. Despite computational advantage of CHPZ and quantum thermal search for computing the ground state, it is also noted that some ground state computations corresponding to NP decision problems may require bath states that are exponentially close to the bath ground state, which translates to polynomially-scaling inverse bath temperature, potentially limiting usefulness of quantum thermal search. Potential implications for black hole physics, in light of pure to mixed and back to pure state evolution, are briefly noted. [ABSTRACT FROM AUTHOR]

Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is successfully employed to determine the chemical composition of brass samples using the LIBS technique. The sample is irradiated with a Q-switched Nd: YAG laser with a pulse width of 5 ns to generate laser-induced plasma (LIP) on the sample surface. The time evolution spectra were recorded from the surface of the brass sample only with an accumulation of five laser shots to get one LIP spectrum. Time-resolved LIP spectra have been utilized to identify the most appropriate time window (where the plasma is optically thin and in local thermal equilibrium) suitable for CF-LIBS implementation. Stoichiometric ablation is also demonstrated for metallic brass samples with the aforementioned laser in the present study. To obtain definitive quantitative information from LIP, the characterization of the plasma, i.e., spectral line intensity, spectral line broadening, electron number density, and plasma temperature, has been analyzed in this paper. Based on two different CF-LIBS algorithms, the brass sample composition was determined and found to be in good agreement with the certified results. This paper also compares and contrasts both strategies, as well as discusses their place and importance. The results of the present manuscript illustrate the potential applicability of CF-LIBS for yielding precise and accurate compositions of brass. [ABSTRACT FROM AUTHOR]

During the past few decades, abundant evidence for physics beyond the two standard models of particle physics and cosmology was found. Yet, we are tapping in the dark regarding our understanding of the dark sector. For more than a century, open problems related to the nature of the vacuum remained unresolved. As well as the traditional high-energy frontier and cosmology, technological advancement provides complementary access to new physics via high-precision experiments. Among the latter, the Casimir And Non-Newtonian force EXperiment (Cannex) has successfully completed its proof-of-principle phase and is going to commence operation soon. Benefiting from its plane parallel plate geometry, both interfacial and gravity-like forces are maximized, leading to increased sensitivity. A wide range of dark sector forces, Casimir forces in and out of thermal equilibrium, and gravity can be tested. This paper describes the final experimental design, its sensitivity, and expected results. [ABSTRACT FROM AUTHOR]

This study investigates the quantum heat correlations associated with the quantum Otto machine, considering the discrete sides of the Lipkin-Meshkov-Glick model as the working medium in the presence of a magnetic field and a symmetric cross interaction. The eigenenergy and occupation probabilities of two-sided and three-sided spin interactions are determined at thermal equilibrium. The results reveal symmetrical heat correlations around the coupling of the symmetric cross interaction, regardless of whether the working medium adopts anisotropic XY, Ising model, or mixed ferromagnetism. The work done by two or three sides of the mixed ferromagnetic working substance exhibits symmetry but with different maximum bounds. Furthermore, the efficiency of the two-sided mixed ferromagnetism model improves as the exchange parameter increases, while the maximum efficiency of the anisotropic XY model is lower compared to the efficiency of the Ising model and mixed ferromagnetism. It is also highlighted that a quantum heat engine or refrigerator can be generated by controlling the system's anisotropy parameter using a three-sided spin interaction. [ABSTRACT FROM AUTHOR]

The issue of aircraft icing poses a substantial threat to flight safety. In order to investigate more efficient anti-icing and de-icing technologies, a comparative analysis was conducted on the de-icing characteristics of three types of actuator materials under varying conditions. Initially, experimental research was undertaken to analyze the temperature traits of three actuators under ice-free conditions. Three power densities were chosen for the experiment: 0.170 W/cm2, 0.727 W/cm2, and 1.427 W/cm2. The research findings revealed distinct characteristics: plasma actuators and resistance wire actuators exhibited a strip-like high-temperature region during operation, with well-defined boundaries between the high-temperature and low-temperature zones, whereas ceramic-based semiconductor actuators showcased a uniform high-temperature region. As energy consumption rose, the thermal equilibrium temperatures of all three types tended to converge, with resistance wire actuators operating at 1.427 W/cm2, showing the highest temperature rise rate at that power density. Subsequently, experimental research was carried out on the de-icing performance of three actuators under icing conditions at a specific power density. Following 120 s of de-icing, the ice layer covering the surface of the plasma actuator completely melted, forming a cavity. Conversely, the ice layer on the ceramic-based semiconductor actuator remained partially intact in a strip shape. Ice deposits were still visible on the surface of the resistance wire actuator. This observation highlights the remarkable de-icing speed of the plasma actuator. The propulsive force of plasma generated on the fluid inside the ice layer enhances heat transfer efficiency, thereby accelerating the de-icing process of the plasma actuator at the same power density. The analysis of the de-icing performance of these three novel types of actuators establishes a robust groundwork for exploring more effective aircraft de-icing methods. Furthermore, it furnishes theoretical underpinning for the advancement of composite anti-icing and de-icing strategies. [ABSTRACT FROM AUTHOR]

Aviation-integrated communication equipment is integral to modern aircraft to ensure its performance and safety. The heat dissipation problems of equipment have become increasingly prominent for the high electronic integration and system power consumption. To solve the above problem, the heat dissipation performance of aviation-integrated communication equipment based on graphene films is deeply studied. This paper establishes a three-dimensional model of aviation-integrated communication equipment to simulate the distribution of temperature fields. The influence between aluminum alloy and graphene films on the surface of magnesium alloy on the heat dissipation performance of aviation-integrated communication equipment is studied. The simulation results show that the heat balance time of the equipment using graphene films on the surface of magnesium alloy is reduced from 3600 s to 800 s, representing an approximately 77.78% improvement; the measured equipment exhibited a reduction in its overall thermal equilibrium temperature, decreasing from 68.1 °C to 66.3 °C, representing an improvement of approximately 2.64%. [ABSTRACT FROM AUTHOR]

Considering the influence of thermal stress and material property variations, this study employs the Navier–Stokes equations and Fourier heat conduction law to establish a semi-implicit time-domain numerical analysis method for hypersonic aerothermal-structural coupling. Study the temporal variation pattern of different regions of the composite material wing under aerodynamic heating. Using the obtained transient temperature field of the wing, the thermal modal of the wing at different time points is calculated using the finite element method. Additionally, it conducts an analysis and discussion on the factors influencing the thermal modal. Composites can be effectively utilized as thermal protection materials for aircraft. During the aerodynamic heating process, the leading edge temperature reaches thermal equilibrium first, followed by the trailing edge, and the belly plate experiences a slower thermal response. Temperature rise significantly affects higher-order modes, with the change in material properties during the early stages of heating being the dominant factor. This leads to a faster decrease in natural frequency. As heat conduction progresses, the influencing factors of thermal stresses gradually increase, and the natural frequency decreases slowly or even rises. [ABSTRACT FROM AUTHOR]

A numerical model was used to simulate natural convection heat transfer in a two-dimensional square enclosure filled with nanofluid and saturated with porous media. The enclosure contained three heated tubes with Rayleigh numbers (Ra) ranging from 102 to 3 × 104. The governing equations with Boussinesq approximation for natural convection were solved iteratively using the finite volume technique through ANSYS FLUENT-CFD commercial package. The Darcy–Forchheimer–Brinkman and Local Thermal Equilibrium models were applied for water and nanofluid flow across the porous zone. The numerical analysis was executed systematically for significant parameters that have a substantial impact on natural convection heat transfer, namely, aspect ratio (AR = 1.25 − 3.75), nanoparticle volume fraction (Φ = 0.25%, 0.5%, 0.7% and 1%), and the porosity of metal foam (ε = 0.3, 0.4, 0.5, 0.6 and 0.7). The aspect ratio was found to have a considerable impact on the averaged Nusselt number (Nuave). For AR = 3.75, the value of Nuave for all Rayleigh numbers increased by approximately 5.22 times compared to AR = 1.25. Moreover, Nuave remained approximately constant as the concentration of alumina-water nanofluid increased from 0.25% to 1%. The novelty of this study lies in the multi-objective optimal design approach adopted by adopting DX-12 with the outcomes of ANSYS FLUENT-CFD. The averaged Nusselt number and convection heat transfer rate reached their optimal values by nearly 13 and 9 times, respectively, at the lowest possible porosity (ε = 0.3), the lowest possible nanofluid concentration (Φ = 0), and the highest possible aspect ratio value (AR = 3.75). [ABSTRACT FROM AUTHOR]

Four binary mixtures are isolated from the hydrogen bond liquid crystalline mesogenic complexes comprising methyl malonic acid (MM) and p-n heptyloxy benzoic acid (7BAO) abbreviated as MM + 7BAO & p-n dodecyloxy (12BAO) benzoic acid abbreviated as MM + 12BAO as the precursors exhibit rich phase polymorphism. Variation in the even set of molar proportion in steps of 0.2 leads to the formation of four binary mixtures. Each of the precursors used for the preparation of binary mixtures are treated as X and Y component whose molar ratio varies accordingly. Spectroscopic analysis of the binaries confirms the hydrogen bond existence between the binary mixtures. Phase variance and their textural observations are made through polarizing optical microscopic studies. Thermal properties possessed by these binary mixtures such as phase transition temperatures, enthalpy values, thermal equilibrium, thermal stability, order of phase transition and specific heat capacity are extensively investigated from the differential scanning thermograms obtained for the binaries prepared. These calorimetric investigations suggest the mesophases of the binaries for apt display, thermal and optical applications. [ABSTRACT FROM AUTHOR]

The thermal error in the spindle unit is substantial and necessitates mitigation. Current models, being predominantly static in nature, have limited efficacy in error control. Integrating digital twin technology for modeling and controlling spindle unit thermal error holds promise in enhancing the machining accuracy of machine tools. Yet, the notion of a digital twin system specifically tailored for spindle unit thermal characteristics remains uncharted territory. To navigate these challenges, this study introduces a novel digital twin system tailored for spindle unit thermal characteristics. This system is poised to revolutionize thermal error modeling and compensation by harnessing the capabilities of digital twin technology. Within this digital twin framework, both the thermal error control model and the analytical thermal characteristic model are seamlessly integrated. The control model is devised as an exponential function, utilizing operational time, inherent time constants, and both initial and equilibrium thermal errors as parameters. Delving deeper, the analytical thermal characteristic model for the spindle system is rooted in a thermal resistance network approach. This leads to a closed-loop thermal characteristic modeling process, culminating in the derivation of a steady-state thermal error. Intricate heat transfer dynamics between spindle components are dissected, and a comprehensive thermal equilibrium equation set is formulated for the spindle unit. This equation set comprehensively accounts for dynamic variations in key parameters such as preload, lubricant viscosity, thermal load intensity, thermal contact resistance, and convective coefficients. To ascertain the time constant, a meticulously designed set of thermal characteristic experiments is executed. Subsequently, the digital twin system embarks on predictive modeling of thermal errors across varied operational conditions. This prediction then forms the foundation for thermal error compensation. With the integration of the present model into the digital twin system, the results are impressive: the absolute average and maximum deviations in thermal elongation, post-error control, stand at approximately 0.40 μm and 1.24 μm, respectively. [ABSTRACT FROM AUTHOR]

Efficient heat dissipation and thermal protection present urgent challenges in high-power integrated circuits (ICs). Although applying a coating of highly thermally conductive materials on the surface of ICs is anticipated to mitigate heat concentration issues, ensuring thermal protection for adjacent devices continues to pose a challenge. Inspired by the microstructure of unidirectional nutrient transport in plant roots, this study utilizes magnetic liquid metal droplets to develop a high thermal conductivity network capable of adaptively manipulating the heat transfer path. This approach aims to tackle the challenges of heat concentration, disordered thermal dissipation, and thermal protection for high-power ICs, thereby enhancing thermal management efficiency. By controlling the distribution of the magnetic field, this study orchestrates the structure of the thermal conduction network to ensure rapid and orderly heat dissipation of ICs while simultaneously validating the network's thermal protection performance. The temperature in the IC thermal concentration zone reaches thermal equilibrium at 399.1 K when the ambient temperature is at 295 K. As the ambient temperature rises to 333 K, the temperature in the IC heat concentration zone stabilizes at approximately 400 K. Simultaneously, the temperature at a specific point in the thermal path of the network registers at 341 K, with the temperatures of the devices flanking this point at 314 K. The magnetron thermal conduction network, inspired by the root structure of bionic plants, not only boosts the thermal management efficiency of ICs but also shows promising application prospects in aerospace, electronics, and other related industries. [ABSTRACT FROM AUTHOR]

Sessile water droplet evaporation in varied gravity and electric fields has been experimentally studied. Specifically, the influences of gravity and electric fields are investigated in the context of the heat flux distribution beneath the droplets, as well as the droplet mechanics and resulting shapes. Experimental testing was carried out during a European Space Agency (ESA) Parabolic Flight Campaign (PFC 66). The droplets tested evaporated with a pinned contact line, a single wettability condition, and varied droplet volume and substrate heat flux. The peak heat transfer was located at the contact line for all cases. The peak heat flux, average heat flux, and droplet evaporation rate were shown to vary strongly with gravity, with higher values noted for hypergravity conditions and lower values in microgravity conditions. The droplet thermal inertia was shown to play a significant role, with larger droplets taking more time to reach thermal equilibrium during the parabolic testing period. No significant impact of the electric field on the droplet evaporation was noted for these test conditions. [ABSTRACT FROM AUTHOR]

In this study, three randomly packed beds with varying tube-to-particle diameter ratios (D/d) are constructed using the discrete element method (DEM) and simulated via CFD under low pore Reynolds numbers (Rep < 100). An innovation of this research lies in the application of hydrogen in randomly packed beds, coupled with the consideration of its temperature-dependent thermal properties. The axial analysis of the heat transfer characteristics shows that PB−5 and PB−6 achieve thermal equilibrium 44% and 58% faster than PB−4, respectively, demonstrating enhanced heat transfer efficiency. However, at higher flow rates (0.8 m/s), the large-sized fluid channels in PB−6 severely impact the heat transfer efficiency, slightly reducing it compared to PB−5. Additionally, this study introduces a localized segmentation method for calculating the axial local Nusselt number, showing that the axial local Nusselt number (Nu) not only exhibits an inverse relationship with the axial porosity distribution, but also matches its amplitude fluctuations. The wall effect significantly impacts the flow and temperature distribution in the packed bed, causing notable velocity and temperature oscillations in the near-wall region. In the near-wall region, the average temperature is lower than in the core region, and the axial temperature profile exhibits more intense oscillations. These findings may provide insights into the use of hydrogen in randomly packed beds, which are vital for enhancing industrial applications such as hydrogen storage and utilization. [ABSTRACT FROM AUTHOR]

A relativistic diffusion model with cylindrical symmetry, which propagates an initial state based on quantum chromodynamics in time toward a thermal equilibrium limit, is derived from nonequilibrium–statistical considerations: adapting an existing framework for Markovian stochastic processes representing relativistic phase‐space trajectories, a Fokker–Planck equation is obtained for the time evolution of particle‐number distribution functions with respect to transverse and longitudinal rapidity. The resulting partially‐evolved distribution functions are transformed to transverse‐momentum and pseudorapidity space, and compared with charged‐hadron data from the CERN Large Hadron Collider. [ABSTRACT FROM AUTHOR]

In strongly scattering elastic media without attenuation and dispersion, the wavefield is dominated by shear waves, and in three dimensions, the ratio of the S to P energy is given by E S / E P = 2 (v P / v S) 3 . This study investigates how this ratio is influenced by attenuation. Both the case of the ringdown mode, where the energy evolves from initial values, and the case of energy equilibrium, where the attenuation is balanced by energy injection sources, are treated. It is shown that in ringdown mode, the energy ratio E S / E P satisfies a Ricatti equation in time: hence, the energy ratio is not an exponential function of time. It is also shown that the long-time energy ratio differs from the value in non-attenuating media when the attenuation coefficients for P and S waves are different. In the case of energy equilibrium, the energy ratio only is equal to the value in non-attenuating media when (1) the time scale of P- and S-wave equilibration is much smaller than the attenuation time or (2) the energy injection rate for each wave type is balanced by the dissipation for that wave type. The latter situation happens when the wavefield is excited by thermal fluctuations in thermal equilibrium. [ABSTRACT FROM AUTHOR]

This paper presents a system that is able to detect physical intrusion in a specific space based on temperature and humidity change. This specific space was housing hardware components important for information security management infrastructure. Presented system is able to predict that two spaces are connected and that there is a physical breach in protected space. The presented prediction approach involves identifying patterns in historical data, where the subsequent outcomes are already known in advance, and validating these patterns using more recent data. System is implemented using k-Nearest Neighbours, Random Forest, and Support Vector Machine algorithms in Python programming language on Raspberry Pi. Real observed data to predict if specific temperature and humidity indicates intrusion were used. This approach can be used to detect intrusions in the room or in other closed space. More specifically thermal equilibrium phenomenon between two spaces after barrier between them are opened was monitored. Through process of supervised learning using labelled data, system was able to detect intrusion by using k-nearest neighbours, random forest, and support vector machine with different accuracy. Presented model shows better results using k-nearest neighbours and support vector machine with accuracy of 100% compared to random forest with accuracy of 95%. The system is low cost because of cheap Raspberry Pi controller and sensors. [ABSTRACT FROM AUTHOR]

Granular matter like sand is composed of a large number of interacting grains and is, thus, expected to be amenable to a statistical physics treatment. Yet, the frictional properties of grains make the statistical physics of granular matter significantly different from the equilibrium statistical physics of atomic or molecular systems. We use three simple models to illustrate some of the key concepts of the statistical physics introduced by Edwards and co-workers more than 30 years ago to describe shaken granular piles: non-interacting frictional grains attached to a wall by a spring, a chain of frictional grains connected by springs, and a simplified mean-field model of a granular packing. We observe that a chain of frictional grains connected by springs exhibits a critical point at an infinite effective temperature (i.e., infinitely strong shaking) at odds with the zero-temperature critical point generically found in one-dimensional systems at thermal equilibrium in the presence of local interactions. Since the late 20th century, granular materials have been recognized as forming a distinct state of matter, neither solid nor liquid, but amenable to a statistical description. It turns out that dissipation, through inter-grain friction, governs the large-scale properties of these systems, so that the usual Boltzmann–Gibbs statistics is replaced by the Edwards statistics. These statistics are full of surprises. For instance, model granular systems can exhibit a critical point at infinite-temperature. To know more, you can delve into this paper, which can be used in advanced statistical physics courses, or as a graduate-level introduction to soft matter. [ABSTRACT FROM AUTHOR]