Anisotropic Thermal Diffusivity Research Articles

Decrypting Allostery in Membrane-Bound K-Ras4B Using Complementary In Silico Approaches Based on Unbiased Molecular Dynamics Simulations.

Protein functions are dynamically regulated by allostery, which enables conformational communication even between faraway residues, and expresses itself in many forms, akin to different "languages": allosteric control pathways predominating in an unperturbed protein are often unintuitively reshaped whenever biochemical perturbations arise (e.g., mutations). To accurately model allostery, unbiased molecular dynamics (MD) simulations require integration with a reliable method able to, e.g., detect incipient allosteric changes or likely perturbation pathways; this is because allostery can operate at longer time scales than those accessible by plain MD. Such methods are typically applied singularly, but we here argue their joint application─as a "multilingual" approach─could work significantly better. We successfully prove this through unbiased MD simulations (∼100 μs) of the widely studied, allosterically active oncotarget K-Ras4B, solvated and embedded in a phospholipid membrane, from which we decrypt allostery using four showcase "languages": Distance Fluctuation analysis and the Shortest Path Map capture allosteric hotspots at equilibrium; Anisotropic Thermal Diffusion and Dynamical Non-Equilibrium MD simulations assess perturbations upon, respectively, either superheating or hydrolyzing the GTP that oncogenically activates K-Ras4B. Chosen "languages" work synergistically, providing an articulate, mutually coherent, experimentally consistent picture of K-Ras4B allostery, whereby distinct traits emerge at equilibrium and upon GTP cleavage. At equilibrium, combined evidence confirms prominent allosteric communication from the membrane-embedded hypervariable region, through a hub comprising helix α5 and sheet β5, and up to the active site, encompassing allosteric "switches" I and II (marginally), and two proposed pockets. Upon GTP cleavage, allosteric perturbations mostly accumulate on the switches and documented interfaces.

Darcy–Benard–Oldroyd convection in anisotropic porous layer subject to internal heat generation

An anisotropic horizontal porous layer saturated with viscoelastic liquids of the Oldroyd-B type is explored to determine how the internal heat source affects thermal convection. As a momentum equation, a modified Darcy–Oldroyd model is used that takes into account the anisotropy of the porous layer. The energy equation is formulated in such a way that the influence of internal heat sources and anisotropy in thermal diffusivity on the stability criterion may be easily identified. The effects of anisotropy, viscoelasticity, and internal heat generation on the onset of thermal convection are investigated using linear stability analysis. It is understood that convection begins via an oscillatory mode instead of a stationary mode because viscous relaxation, thermal diffusions, and internal heat generation mechanisms compete with one another. Both steady and unsteady finite-amplitude convections are studied using nonlinear stability analysis with the truncated Fourier series method. The effect of different governing parameters on the system’s stability and on convective heat transfer is studied. The present investigation has been significantly validated by the recovery of several prior results as special situations. The findings presented in this work are anticipated to have significant implications for a number of real-world applications, including modeling of oil reservoirs, crude oil extraction, crystal growth, the pharmaceutical and medical industries, and the use of geothermal energy, among others.

Apparent anisotropic thermal diffusivity measured in cubic single crystals by transient grating spectroscopy

The effect of elastic anisotropy on thermal diffusivity determination by transient grating spectroscopy (TGS) was studied. In experiments performed on a set of cubic single crystals, it was observed that TGS measurements may indicate anisotropy of thermal diffusivity in otherwise thermally isotropic materials, and that the strength of this apparent anisotropy is correlated with the strength of the elastic anisotropy. To find a source of the observed phenomenon, finite-element simulations of the TGS measurements were carried out. Time-domain TGS signals were generated from the simulations and processed identically to the experimental data. The simulation results revealed that the elastic anisotropy affects the detected time-domain signals. Consequently, the thermal diffusivity coefficients determined from them showed the artificial directional dependence. For the chosen set of cubic crystals, ranging from nearly isotropic to strongly anisotropic in terms of elastic constants, this simulated directional dependence was in full agreement with the one observed in the experiments.

Thermal Aging Effect on In-Plane and Cross-Plane Thermal Diffusivities of Plasma-Sprayed Thermal Barrier Coating

Thermal barrier coatings (TBCs) are used to shield from heat and wear of components which are used at high temperature situation, for example, the blades of gas turbines. There is a pressing need to evaluate the thermal conductivity of TBCs in the thermal design of advanced gas turbines with high energy efficiency. In the case of gas turbines, these TBCs consist of a ceramic-based top-coat (TC) and a bond-coat (BC) on a superalloy substrate. TBCs are commonly prepared by plasma spraying process. The TC is expected to play the role of a thermal shield. Thus, thermal conductivity of thickness direction of TBC has been investigated. However, plasma-sprayed TCs were known that they have anisotropic microstructure. We have been investigating in-plane and cross-plane thermal diffusivities of plasma-sprayed Yttria-stabilized zirconia (YSZ) TCs at 300 K in detail in a previous study. From the results of thermal diffusivity measurements for four kinds of TCs, it was found that plasma-sprayed TCs had significantly anisotropic thermal diffusivity depending on their microstructures. In this study, we measured in-plane and cross-plane thermal diffusivities of typical two plasma-sprayed TCs from 300 K to 1200 K in vacuum. And we also measured in-plane and cross-plane thermal diffusivities of annealed TC with different aging time. It was found that anisotropy estimated from in-plane and cross-plane thermal diffusivities did not change from 300 K to 1200 K. There was a tendency that thermal diffusivity value and anisotropy slightly increased by thermal aging effects.

Advances in thermal‐related analysis techniques for solid‐state lithium batteries

AbstractSolid‐state lithium batteries (SSLBs) have been broadly accepted as a promising candidate for the next generation lithium‐ion batteries (LIBs) with high energy density, long duration, and high safety. The intrinsic non‐flammable nature and electrochemical/thermal/mechanical stability of solid electrolytes are expected to fundamentally solve the safety problems of conventional LIBs. However, thermal degradation and thermal runaway could also happen in SSLBs. For example, the large interfacial resistance between solid electrolytes and electrodes could aggravate the joule heat generation; the anisotropic thermal diffusion could trigger the uneven temperature distribution and formation of hotspots further leading to lithium dendrite growth. Considerable research efforts have been devoted to exploring solid electrolytes with outstanding performance and harmonizing interfacial incompatibility in the past decades. There have been fewer comprehensive reports investigating the thermal reaction process, thermal degradation, and thermal runaway of SSLBs. This review seeks to highlight advanced thermal‐related analysis techniques for SSLBs, by focusing particularly on multiscale and multidimensional thermal‐related characterization, thermal monitoring techniques such as sensors, thermal experimental techniques imitating the abuse operating condition, and thermal‐related advanced simulations. Insightful perspectives are proposed to bridge fundamental studies to technological relevance for better understanding and performance optimization of SSLBs.image

Transformed differential quadrature solution to the coupled thermal–mechanical problem in transversely isotropic media

This study provides a novel solution to the coupled thermal–mechanical problem in transversely isotropic (TI) media by using the transformed differential quadrature method (TDQM). The governing equations are transformed and then discretized by the proposed TDQM. After introducing the internal and boundary conditions, we obtain the thermal–mechanical solution of a medium with various heat sources. Several examples are set up to verify the proposed solution and to discuss the convergence of the method. Also, key parameters including the transverse isotropy of skeleton, the linear expansion coefficients and the anisotropic thermal diffusivity are investigated. Compared with the traditional differential quadrature method (DQM), the TDQM introduces the integral transform theorem to simplify the derivation process and reduce the number of algebraic equations. Consequently, it avoids the exponential increase in the number of algebraic equations when solving multi-dimensional problems.

Morphology of Columnar Defects Dependent on Irradiation Direction in High-T c Superconductors

The morphologies of ion tracks tilted at different angles were systematically investigated by TEM observations on GdBCO coated conductors irradiated with 80 MeV Xe ions. The 80 MeV Xe ion beam along the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis produced shortly segmented (discontinuous) columnar defects (CDs) along the ion path throughout the sample. When the ion beam was tilted at slight angle of 20° from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis, by contrast, not discontinuous CDs but thick and elongated (continuous) ones were formed in the irradiation direction. The formation of continuous CDs was observed to a deeper depth from the surface for the irradiation tilted at larger angle from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis. The variation of the microstructures against the irradiation angles was caused by the anisotropic temperature spread during the formation of CDs, which was attributed to the anisotropic thermal diffusivity in high- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductors. We also demonstrated that discontinuous CDs could be formed at the irradiation angle of ±45° relative to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -axis into YBCO thin films by using 50 MeV Kr ions, which was the irradiation condition estimated backwards from the directional dependent morphology of CDs.

Natural convection heat transfer with anisotropic thermal diffusion for tilted two-dimensional cavities

The effects of a domain tilt (counterclockwise, γ=00,300and600) and an anisotropic thermal diffusion on the natural convection heat transfer inside a square or rectangular cavity are investigated. The multiple relaxation time Lattice Boltzmann method with a double distribution function is used. The simulations are performed for a range of Rayleigh number (Ra=104to108). It is observed that the number of eddies is reduced due to the counterclockwise inclination of the cavity for a given Rayleigh number. The flow reversal is observed with a change in γ and anisotropic thermal diffusion ratio (β). Further, the stretching and merging of the inner core eddy with changes in γ and β are discussed. The spatially averaged Nusselt number along the hot wall (Nu¯h) is calculated to study the heat transfer rate and characteristics. It shows that the rate of heat transfer increases with an increase in the inclination and the thermal diffusivity ratio. For Ra=107and108 the observed flow structures are unsteady. The heat transfer in this type of unsteady flow and corresponding thermal plume dynamics are studied by computing Nu¯h at each non-dimensional timestep.

Anisotropic thermal diffusivity and conductivity in SiC/SiC tubes studied by infrared imaging and X-ray computed tomography

Traditional flash diffusivity evaluation of thermal diffusivity/conductivity of composite tubes require machining of specimens. For a thin-wall tube, this method can only be used to obtain through-thickness transport property. A novel method to evaluate anisotropic thermal diffusivity in a composite tube has been developed. Braided SiC/SiC composite tubes were subjected to a xenon flash heating pulse. A high-speed, high-sensitivity infrared camera was used to measure surface temperature changes as a function of time and nondestructively detect subsurface defects/damages, such as macroscopic pores. Standard reference material (Pyroceram 9606) and curved SiC/SiC composite tube specimens were used to validate thermal diffusivity obtained from infrared imaging. Unlike the traditional method, there is no need prepare special specimens, and thermal diffusivity values in three orientations are obtained after a single flash. A finite element analysis model based on x-ray computed tomography scans was developed to simulate the heat transfer. This technique is significant in assessing thermal conductivity and inspecting the health of ceramic tubes during and after service.

Thermal diffusivity and its lower bound in orthorhombic SnSe

The orthorhombic monochalcogenide SnSe has attracted much attention in recent years as a promising high-temperature thermoelectric material. We present a study of its thermal conductivity and specific heat of SnSe between 2~K and 300~K and quantify its anisotropic thermal diffusivity, $D$. For both crystallographic orientations, thermal diffusivity remains above the recently identified Planckian limit ($D > v_s^2 \tau_P$, where $v_s$ is the sound velocity and $\tau_P= \hbar/k_BT$) and its anisotropy in $D$ is set by the anisotropy of $v_s$. Comparison with cubic members of the IV-VI family leads to a consistent picture, where the diffusivity in all members of the family is set by the product of v$_s$, $\tau_P$ and the 'melting' velocity derived from the melting temperature.

Axisymmetric lattice Boltzmann formulation for mixed convection with anisotropic thermal diffusion and associated bubble breakdown

The effect of the mixed convection with anisotropic thermal diffusion on the bubble breakdown inside a cylindrical cavity with a rotating top and the stationary bottom is investigated in this article. The lattice Boltzmann multiple relaxation time axisymmetric method with the D2Q9 model is used. The three distribution functions, one for axial and radial components of the velocity field, second for an azimuthal component of the velocity field, and third for the temperature field, are used. The code is validated for the fluid flow inside a lid-driven cylindrical cavity and for hot rotating-top-lid cylindrical cavity. The results are compared with the benchmark data. The effect of mixed convection on the Bödewadt boundary layer thickness and the temperature boundary layer thickness is investigated. The simulations are perfermed for various Reynolds number (Re) from of 990 and 2494, the Richardson number (Ri in 0.01 and 1, and Rayleigh number (Ra from 9801 and 6.22×106). This study concludes that the Bödewadt boundary layer thickness (δB) is ∝ to Ri and the temperature boundary layer thickness (δTc) is ∝ to Ri for 0.01≤ Ri ≤0.1. Further, the δB≈δTc for isotropic thermal diffusion. For an anisotropic thermal diffusion, the δB remains constant and δTc increases at Ri = 0.01 with an increase in the ratio of thermal diffusivity values (n). The bubble breakdown vanishes with an increase in Ri at a constant Re. The main application of this study is in the mixing/blending processes with convection inside cylindrical shaped reactors.

Hexagonal boron nitride and alumina dual-layer coating for space solar thermal shielding

Reducing the temperature of a solar probe or an orbital spacecraft has been successful in the spectral selectivity regime by maximizing the sunlight reflection and irradiating heat to the cold universe. Despite the extensive work on the adjustment of the absorbance/emissivity ratio, few efforts have been devoted to the modulation of heat conduction. In fact, the backlit-side of the spacecraft facing the cold universe is ideal for radiative cooling, as long as the sunlight generated heat is transferred effectively to the backlit surface with minimum heating of the interior structures. Here, by using a hexagonal‑boron nitride (h-BN) and Al 2 O 3 dual-layer coating, we demonstrate a strategy for space solar thermal shielding that combines radiative cooling and anisotropic thermal conduction. The in-plane alignment of the top-layer h-BN flakes to the coating surface leads to a highly anisotropic thermal diffusion behavior, enabling rapid in-plane heat transfer and effective out-of-plane thermal insulation. The spectral selectivity optimization allows the dual-layer coating to reflect nearly 89% of solar irradiation while having an emissivity >0.86 across the thermal infrared wavelength. Moreover, the coating exhibits remarkable spectral stability under proton irradiation, showing its great potential in aerospace applications. • An h-BN/Al 2 O 3 dual-layer coating with radiative cooling and anisotropic thermal conduction functions was designed. • The coating was fabricated by a facile one-step LPES method. • The coating cools a spacecraft by conducting heat to the backlit-side and radiates it to the cold universe.

Spatially localized measurement of isotropic and anisotropic thermophysical properties by photothermal radiometry

This work presents the development of a new photothermal radiometry (PTR) setup using a mix between frequency and spatial domain scans, along with a three-dimensional (3D) heat diffusion model. This newly developed PTR system, with a spatial resolution of 33 μm, is used to measure thermophysical properties of several kinds of materials. These properties include the thermal diffusivity, a, of homogeneous semi-infinite materials, thermal boundary resistance, Rth, and thermal anisotropy of membranes. The measured properties for homogeneous semi-infinite materials and two-layered systems are in good agreement with the literature values. In addition, it was possible to obtain an anisotropic factor of 24.6 between the in-plane and cross-plane thermal diffusivity of a 25 μm anisotropic flexible graphite sheet. Furthermore, it was also possible to measure, both directly and independently, the anisotropic thermal diffusivities for a 1 μm titanium membrane. It is suggested that this new hybrid technique can help us to fill the gap between conventional PTR and other photothermal and thermoreflectance techniques. Using this PTR setup, it is possible to experimentally measure isotropic and anisotropic thermophysical properties of bulk and thin materials, including membranes, with high precision through accurate characterization of the pump beam spots size. This is accomplished without the need for an optical transducer layer.

Axisymmetric thermal-lattice Boltzmann method for Rayleigh-Bénard convection with anisotropic thermal diffusion

Rayleigh-Bénard convection (RBC) with anisotropic thermal diffusion inside a cylindrical cavity is investigated using the axisymmetric thermal-lattice Boltzmann method with MRT collisions. The axisymmetric approach for cylindrical geometries reduces the overall computational requirements, however, is valid for a certain range of governing non-dimensional number, here the Rayleigh number. The D2Q9 model is used with two distribution functions one for the flow-field and another for the temperature-field. The new results are presented for RBC in a cylindrical cavity for cavity aspect ratios (ratio of height (H) to the radius (R) of the cylinder Γ=H/R) 1 and 2 up to Rayleigh number 10,000.

Ferroconvection in an Anisotropic Porous Medium with Variable Gravity

A linear stability assessment was performed to study the impact of internal heating and variable gravity in an anisotropic porous medium of a ferrofluid layer system on the onset of Benard-Marangoni convection. The system is heated from below with both the lower and upper limits are considered as completely insulated to the disturbance of the temperature. The eigenvalue problem is solved by using regular perturbation technique to obtain the critical Marangoni number and also the critical thermal Rayleigh number. It is noted that the increase of value anisotropic permeability, Darcy number and also magnetic number will enhance the convection of the system while the increasing values of anisotropic thermal diffusivity will help to stabilize the system.

Heat capacity and thermal diffusivity of heavy oil saturated rock materials at high temperatures

As well-known the rate of heat extraction depends on the thermal conductivity, $$Q = - \, \lambda \left( T \right){\text{grad }}T$$ , and the fluids flow characteristics, while amounts of heat recovery depends on heat capacity of reservoir rocks, $$Q = \left( {1 - \phi } \right)\rho C_{\text{P}} T$$ , where $$\phi$$ is the porosity. In the present work the laser-flash (LFA 457) and differential scanning calorimeter (DSC 204 F1) techniques were employed on a heavy oil saturated natural rock sample for accurate measurements of the thermal diffusivity and heat capacity over a temperature range from (294 to 1024) K and from (306 to 771) K, respectively. The density of the sample at room temperature was 2300 kg m−3 and the porosity was 17.1%. The sample for the present study comes from Russian Oil Field (Eastern Siberia, Russia). The expanded uncertainty of the thermal diffusivity and heat capacity measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 3% and 1%, respectively. At low temperatures (below approximately 373 K), the sharp increases (up to η = 2.3) of the thermal diffusivity anisotropy was observed. Based on the measured thermal diffusivity and heat-capacity data, thermal conductivity of the same oil saturated rock sample was calculated using the thermodynamic relation $$\lambda = a\rho C_{\text{P}}$$ . The effect of temperature and various physical and chemical processes, such as thermal decomposition (chemical reactions) of pore heavy oil occurred in the sample during the heating in distinct temperature ranges were studied. The effect of pore heavy oil decomposition (under thermal stress) on the measured values of heat capacity and other thermophysical properties of rock sample at high temperatures (around 700 K) was experimentally observed. Also, we experimentally found weak temperature maximum of the heat-capacity of the sample under study in the low temperature range (around 380 K).

On the Striated Regularity for the 2D Anisotropic Boussinesq System

In this paper, we investigate the global existence and uniqueness of strong solutions to 2D Boussinesq system with anisotropic thermal diffusion or anisotropic viscosity and with striated initial data. Using the key idea of Chemin to solve 2-D vortex patch of ideal fluid, namely the striated regularity can help to bound the gradient of the velocity, we can prove the global well-posedness of the Boussinesq system with anisotropic thermal diffusion with initial vorticity being discontinuous across some smooth interface. In the case of an anisotropic horizontal viscosity we can study the propagation of the striated regularity for the smooth temperature patches problem.

Evaluation of debonding in CFRP-epoxy adhesive single-lap joints using eddy current pulse-compression thermography

Contaminations arising during the manufacturing or usage of Carbon Fiber Reinforced Plastic (CFRP)-epoxy adhesive single-lap joints can drastically affect the mechanical performance of the structure and eventually lead to its catastrophic failure. Eddy current stimulated thermography has been recently proposed for detecting and characterizing defects in composite materials. The characterization of debonding in adhesive single-lap joints in composites by eddy current stimulated thermography can be challenging due to the anisotropic thermal diffusion caused by the anisotropic conductivity and multi-layer nature of the composites. This work tackles the challenge of detecting the interface contamination by combining eddy current pulse-compression thermography and image post-processing algorithms. The impulse responses from samples containing either brass, release film or release agent contaminations obtained through pulse-compression combined with Eddy Current Pulsed Thermography (ECPT). Non-uniform heating patterns are removed by partial least square technique. Then, the time instants containing meaningful information about the contaminated interface layer are inferred by comparing each norm of kernel principal component over suitable time windows. The evaluation of contamination depths and properties are conducted in selected time windows by principal component analysis and time-phase analysis. Results proved that release agent contamination plays the minor role in changing the electrical and thermal properties of the single-lap joints compared with brass and release film.

Effect of particle size on mechanical and anisotropic thermal conductivity of copper-reduced graphene oxide composites

Copper-reduced graphene oxide composites having good anisotropic thermal conductivity and hardness values fabricated via flake powder metallurgy route. SEM was performed to examine the microstructure of powders and also different composites. Anisotropic thermal diffusivity and micro-hardness test were performed to examine the different concentrations and particle sizes effect on composites. The best thermal conductivity ratio was obtained at 5 wt% reduced graphene oxide (rGO) at 9.5 μm particle size. Moreover, the extraordinarily high value of hardness (85 HV) copper-reduced graphene oxide composite was acquired at 3 wt% rGO with 9.5 µm particle size.

Anisotropy of Thermal Diffusivity in Lead Halide Perovskite Layers Revealed by Thermal Grating Technique

Heat management of optoelectronic devices is of critical significance in lead halide perovskites due to the intrinsically low thermal conductivity of this material. Despite its importance, thermal conductivity remains understudied, particularly in polycrystalline perovskite layers with different halides. Here, we employ a novel method for investigation of thermal properties in perovskite layers, which is based on a light-induced transient diffraction grating technique. We demonstrate the applicability of thermal grating technique by determining in an all-optical way the thermo-optic coefficient, speed of sound, and thermal conductivity in vapor-deposited polycrystalline layers of MAPbX3 (X = Cl, Br, I), MAPbBr2I, and MAPbCl2Br perovskites. We reveal the spatial anisotropy of thermal conductivity, which is noticeably lower in the direction along the layer surface (0.2–0.5 W/(m K)) if compared to that across the layer (0.3–1.1 W/(m K)). Finally, we demonstrate that for both directions the thermal conductivi...