Thermal Dependence Research Articles

Correction: Investigation of thermal dependence of phonon frequencies, sound velocity, mechanical and optical characteristics of the $$\beta $$-GaN semiconductor compound

Correction: Investigation of thermal dependence of phonon frequencies, sound velocity, mechanical and optical characteristics of the $$\beta $$-GaN semiconductor compound

Electro-Elastic Modeling of Multi-Step Transitions in Two Elastically Coupled and Sterically Frustrated 1D Spin Crossover Chains

One-dimensional spin crossover (SCO) solids that convert between the low spin (LS) and the high spin (HS) states are widely studied in the literature due to their diverse thermal and optical characteristics which allow obtaining many original behaviors, such as large thermal hysteresis, incomplete spin transitions, as multi-step spin transitions with self-organized states. In the present work, we investigate the thermal behaviors of a system of two elastically coupled 1D mononuclear chains, using the electro-elastic model, by including an elastic frustration in the nearest neighbors (nn) bond length distances of each chain. The chains are made of SCO sites that are coupled elastically through springs with their nn and next-nearest neighbors. The elastic interchain coupling includes diagonal springs, while the nn inter-chain distance is fixed to that of the high spin state. The model is solved using MC simulations, performed on the spin states and the lattice distortions. When we only frustrate the first chain, we found a strong effect on the thermal dependence of the HS fraction of the second chain, which displays an incomplete spin transition with a significantly lowered transition temperature. In the second step, we frustrate both chains by imposing different frustration rates. Here, we demonstrate that for high frustration values, the thermal dependence of the total HS fraction exhibits multi-step spin transitions. The careful examination of the spin state structures in the plateau regions showed the coexistence of special dimerized ferro–antiferro patterns of type LL-HH-LL-HH along the first chain and HH-LL-HH-LL (H=HS and L=LS) along the second one, revealing that the two chains are antiferro-elastically coupled. This type of spatial modulation of the spin state and bond length distances is very attractive because it anticipates the possible existence of periodic structures in 2D lattices, made of alternate 1D SCO strings with HLHLHL structures, coupled in the ferro-like fashion along the interchain direction.

Shifts in the Thermal Dependence of Locomotor Performance across an Altitudinal Gradient in Native Populations of Xenopus laevis.

AbstractEctothermic species are dependent on temperature, which drives many aspects of their physiology, including locomotion. The distribution of the native populations of Xenopus laevis is characterized by an exceptional range in latitude and altitude. Along altitudinal gradients, thermal environments change, and populations experience different temperatures. In this study, we compared critical thermal limits and thermal performance curves of populations from the native range across an altitudinal gradient to test whether optimal temperatures for exertion differ depending on altitude. Data on exertion capacity were collected at six different temperatures (8°C, 12°C, 16°C, 19°C, 23°C, and 27°C) for four populations spanning an altitudinal gradient (60, 1,016, 1,948, and 3,197 m asl). Results show that the thermal performance optimum differs among populations. Populations from cold environments at high altitudes exhibit a lower optimal performance temperature than populations from warmer environments at lower altitudes. The ability of this species to change its optimal temperature for locomotor exertion across extremely different climatic environments within the native range may help explain its exceptional invasive potential. These results suggest that ectothermic species capable of adapting to broad altitudinal ranges may be particularly good at invading novel climatic areas, given their ability to cope with a wide range of variation in environmental temperatures.

Flow Activation Energy Estimation by Thermo‐Rheological Method

AbstractPolymer and many other flows exhibit non‐Newtonian rheological behavior. For some materials, the thermal dependence of viscosity is also essential to be established. It can be described by considering an activation energy, estimated by using the viscosity measurements at different temperatures. Nevertheless, the test temperatures must be reliable and accurate. An annular measuring device (TRAC: Thermo‐Rheo Annular Cell) is previously proposed for highly robust temperature measurement and viscosity identification by inverse method, which exploits the viscous dissipation in the flow. This work explains how critical viscosity points, identified thanks to the TRAC, can be used to estimate the activation energy with different approaches involving the principle of time‐temperature superposition. Thanks to the thermal characteristics of the annular flow, the thermal dependence of viscosity can also be estimated from direct temperature measurements to perform fast analysis, without using inverse method.

May future climate change promote the invasion of the marsh frog? An integrative thermo-physiological study.

Climate change and invasive species are two major drivers of biodiversity loss and their interaction may lead to unprecedented further loss. Invasive ectotherms can be expected to tolerate temperature variation because of a broad thermal tolerance and may even benefit from warmer temperatures in their new ranges that better match their thermal preference. Multi-trait studies provide a valuable approach to elucidate the influence of temperature on the invasion process and offer insights into how climatic factors may facilitate or hinder the spread of invasive ectotherms. We here used marsh frogs, Pelophylax ridibundus, a species that is invading large areas of Western Europe but whose invasive potential has been underestimated. We measured the maximal and minimal temperatures to sustain physical activity, the preferred temperature, and the thermal dependence of their stamina and jumping performance in relation to the environmental temperatures observed in their invasive range. Our results showed that marsh frogs can withstand body temperatures that cover 100% of the annual temperature variation in the pond they live in and 77% of the observed current annual air temperature variation. Their preferred body temperature and performance optima were higher than the average temperature in their pond and the average air temperature experienced under the shade. These data suggest that invasive marsh frogs may benefit from a warmer climate. Broad thermal tolerances, combined with high thermal preferences and traits maximised at high temperatures, may allow this species to expand their activity period and colonise underexploited shaded habitat, thereby promoting their invasion success.

Thermal mismatches explain consumer-resource dynamics in response to environmental warming.

Changing temperatures will impact food webs in ways we yet to fully understand. The thermal sensitivities of various physiological and ecological processes differ across organisms and study systems, hindering the generation of accurate predictions. One step towards improving this picture is to acquire a mechanistic understanding of how temperature change impacts trophic interactions before we can scale these insights up to food webs and ecosystems. Here, we implement a mechanistic approach centered on the thermal sensitivity of energetic balances in pairwise consumer-resource interactions, measuring the thermal dependence of energetic gain and loss for two resource and one consumer freshwater species. Quantifying the balance between energy gain and loss, we determined the temperature ranges where the balance decreased for each species in isolation (intraspecific thermal mismatch) and where a mismatch in the balance between consumer and resource species emerged (interspecific thermal mismatch). The latter reveals the temperatures for which consumer and resource energetic balances respond either differently or in the same way, which in turn informs us of the strength of top-down control. We found that warming improved the energetic balance for both resources, but reduces it for the consumer, due to the stronger thermal sensitivity of respiration compared to ingestion. The interspecific thermal mismatch yielded different patterns between the two consumer-resource pairs. In one case, the consumer-resource energetic balance became weaker throughout the temperature gradient, and in the other case it produced a U-shaped response. By also measuring interaction strength for these interaction pairs, we demonstrated the correspondence of interspecific thermal mismatches and interaction strength. Our approach accounts for the energetic traits of both consumer and resource species, which combined produce a good indication of the thermal sensitivity of interaction strength. Thus, this novel approach links thermal ecology with parameters typically explored in food-web studies.

Crystal Structure, Thermal Expansion and Luminescence of Ca10.5−xNix(VO4)7

The structural and luminescence properties of a new material, Ca10.5−xNix(VO4)7, formed by substitution of a fraction of calcium by nickel, are studied as a function of the Ni content (x). The powder X-ray diffraction results for the polycrystals, synthesized using a solid-state reaction method, show that in the studied temperature range (300–1150 K), the structure of the unsubstituted material (space group R3c, whitlockite-β-Ca3(PO4)2 structure type) is conserved up to the solubility limit, x = 0.72(2), determined on the basis of variation of unit cell size with x. The samples of nominal composition exceeding this limit contain a significant amount of the impurity phase.The structural refinements demonstrate that Ni atoms preferentially occupy the M5 site (one of the five independent Ca sites, M1–M5). The unit cell size was equally studied in the range of 300–1150 K, leading to the determination of the thermal expansion coefficients. It was found that with rising Ni content, the room temperature volumetric thermal expansion decreases from 41.80 MK−1 (x = 0.16) to 39.24 MK−1 (x = 0.66) and to 38.92 MK−1 at the solubility limit, this reduction being in line with earlier reported data for x=0. In the unit cell variation, around 800–900 K, a weak anomaly is observed, detectable most clearly for the axial ratio; it is also visible at thermal expansion coefficient temperature dependence. Substitution of Ca by Ni ions reduces the optical band gap of Ca10.5−xNix(VO4)7 from 3.56 (x = 0) to 3.29 and 3.16 eV observed for Ni-containing samples (x = 0.33 and 0.66, respectively). Observed bands in the absorption and photoluminescence spectra are assigned to electronic transitions in both VO43− groups and Ni2+ ions, confirming that Ni mainly occupies the M5 site. The band gap narrowing and decrease in photoluminescence intensity when the Ni concentration increases makes Ni-substituted compounds attractive for application, e.g., as photocatalysts.

Multi-physical Modeling of Launcher Electromechanical Actuators Accounting for Production Variability and Thermal Effects

Abstract With the trend towards reusable launchers, there is a need to develop health monitoring systems for electromechanical actuators (EMAs) performing nozzle orientation. To tune such a health monitoring system (HMS), data sets reproducing EMA operation in healthy and faulty modes are needed. Besides, effect of production variability and thermal dependency should also be accounted for. In this paper, a systematic approach to determine an EMA model from which appropriate data sets can be generated is presented. The focus is on mechanical faults such as high friction level that may lead to jamming and excessive backlash. From available experimental data sets recorded on a fleet of EMA, grey box identification is used to estimate the friction parameters including their confidence level for the different EMAs. Production variability is then characterized by showing that each parameter estimate is represented by a Gaussian distribution at a given temperature. Next thermal effects are accounted for through a Gaussian Process characterizing parameter variability w.r.t. temperature. Validation of the model is finally performed with EMA healthy operation data.

Development of Salmon Sperm DNA/Regenerated Silk Bio-Based Films for Biomedical Studies on Human Keratinocyte HaCaT Cells under Solar Spectrum.

In this study, we fabricated adhesive patches from silkworm-regenerated silk and DNA to safeguard human skin from the sun's rays. The patches are realized by exploiting the dissolution of silk fibers (e.g., silk fibroin (SF)) and salmon sperm DNA in formic acid and CaCl2 solutions. Infrared spectroscopy is used to investigate the conformational transition of SF when combined with DNA; the results indicated that the addition of DNA provides an increase in the SF crystallinity. UV-Visible absorption and circular dichroism spectroscopy showed strong absorption in the UV region and the presence of B-form of DNA once dispersed in the SF matrix, respectively. Water absorption measurements as well as thermal dependence of water sorption and thermal analysis, suggested the stability of the fabricated patches. Biological results on cellular viability (MTT assay) of keratinocyte HaCaT cells after exposures to the solar spectrum showed that both SF and SF/DNA patches are photo-protective by increasing the cellular viability of keratinocytes after UV component exposure. Overall, these SF/DNA patches promise applications in wound dressing for practical biomedical purposes.

Synthesis, structures and thermal dependence of photoluminescence of copper(I) halide metallacycle and 1-D chain complexes

In this work, we report the synthesis, X-ray crystal structures, and temperature dependence of solid-state photoluminescence properties of two cuprous iodide complexes, namely, [(mpbi)CuI]n (1) and [(bimb)CuI]n (2) (mpbi = 1,1′-(5-methyl-1,3-phenylene)bis (1H-imidazole), bimb = 1,2-bis((imidazole-1-yl)methyl)benzene). The complexes exhibit efficient solid-state emission at room temperature, with peak emission wavelengths at 580 and 650 nm, respectively. Two complexes display outstanding thermal stability. The X-ray diffraction analysis revealed that the structure of 1 is a discrete metallacycle with the copper atom in the structure adopting a less common triangular configuration, while the structure of 2 is a one-dimensional chain structure of Cu2I2 binuclear rhomboid. The temperature dependence of photoluminescence in the wide temperature range is investigated, which demonstrates that the thermal quenching of luminescence of copper complexes can be regulated by cuprophilic interaction.

Investigation of the intrinsic magnetic properties of GdCo4B single crystal: determination of the magnetocrystalline anisotropy from the first-order magnetization processes

We report on the intrinsic magnetic properties of a GdCo4B single crystal as derived from magnetization measurements. The occurrence of a first-order magnetization process (FOMP) in a magnetic field applied perpendicularly to the easy magnetization direction provides an opportunity to determine the anisotropy parameters K1 and K2. To this end, the theoretical approach proposed previously for easy-plane magnets has been adapted for the case of easy-axis compounds exhibiting a FOMP. The obtained anisotropy parameters of GdCo4B are compared with the values deduced by other classical techniques. The presence of a compensation point in the thermal dependence of the spontaneous magnetization has enabled the determination of the exchange field on Gd, Bex = 131 T, which is in good agreement with inelastic neutron scattering results published earlier. Influence of the applied pressure on the anisotropy parameters is quantified using the pressure dependence of the FOMP, revealing a significant sensitivity of the anisotropy parameters to pressure.

Thermal behavior of modern and archeological enamel and dentin by in situ temperature‐dependent Raman spectroscopy

AbstractTeeth and bones are important bioarchives, which can be altered because of diagenesis or burning (cooking, funerary cremations, and fires). Though heating and diagenesis are different processes, an experimental heating of modern bioapatite reproduces in a short time effects similar to diagenetic processes occurring over geological time. The thermal behavior of modern and archeological human enamel and dentin using the in situ thermo‐Raman spectroscopy at 83–873 K was investigated to assess the structural changes in organic and mineral components of a tooth and their interrelationship. The ν1(PO4) vibrational mode in apatite is the most anharmonic and responsible for the reaction of the structure to external influences. The γiP isobaric Grüneisen parameters for archeological (0.41) and modern (0.24) enamel are different from those for fluor‐ (0.17) and chlorapatite (0.17), which indicates a stronger reaction of PO bonds in bioapatite PO4 tetrahedra to temperature changes as compared with geologic samples. The anomalies of the thermal dependences of the ν1(PO4) peak position and (T) autocorrelation function are caused by the combined effect of different factors such as breaking of hydroxyl and hydrogen bonds, the loss of adsorbed and structural water, collagen denaturation, organic phase combustion, and removal and relocation of B‐ and A‐type carbonate ions. The thermal (273, 313, 341, and 363 K) and cold (~160 K) denaturation of collagen is reflected in the ν1(PO4) and (T) dependences. The (T) differences between modern and archeological dentin and enamel are contingent on bioapatite composition (proportions of adsorbed and structural water, hydroxyl and carbonate ions, and trace elements as well as different types of organic matter — low‐molecular noncollagen compounds and high‐molecular collagen). The results obtained contribute to the knowledge about the thermal transformations of the mineral and organic phases of modern and archeological tooth tissues and allow their structural alterations to be evaluated.

Thermal conductivity of the Cs-Pb system liquid alloys

ABSTRACT Thermal conductivity of liquid alloys of the caesium-lead system with a Pb content of 40, 50, 60, and 66.7 at. % is measured by the laser flash method in the temperature range from the liquidus line to 1173 K with an error of 4–6%. It is found that the thermal conductivity of the investigated alloys, obtained by mixing liquid metals Cs and Pb, drops by an order of magnitude to values: 0.5–4.0 W/(m K), characteristic of molten salts. It is shown that the thermal conductivity concentration dependence of the Cs-Pb system liquid alloys has a broad minimum near the equiatomic composition. An analysis of the obtained experimental data indicates the formation of a chemical short-range order in the liquid Cs-Pb system in the vicinity of the equiatomic composition, which indirectly confirms the existing ideas about the presence of Zintl complexes Cs4Pb4 in these melts.

Linking B-factor and temperature-induced conformational transition

The crystallographic B-factor, also called temperature factor or Debye-Waller factor, has long been used as a surrogate for local protein flexibility. However, the use of the absolute B-factor as a probe for protein motion requires reproducible validation against conformational changes against chemical and physical variables. Here we report the investigation of the thermal dependence of the crystallographic B-factor and its correlation with conformational changes of the protein. We obtained the crystal protein structure coordinates and B-factors at high resolution (1.5 Å) over a broad temperature range (100 K to 325 K). The exponential thermal dependence of B-factor as a function of temperature was equal for both the diffraction intensity data (Wilson B-factor) and for all modeled atoms of the system (protein and non-protein atoms), with a thermal diffusion constant of about 0.0045 K−1, similar for all atoms. The extrapolated B-factor at zero Kelvin (or zero-point fluctuation) varies among the atoms, although with no apparent correlation with temperature-dependent protein conformational changes. These data suggest that the thermal vibration of the atom does not necessarily correlate with the conformational dynamics of the protein.

Band structure of a nonparabolic two-dimensional electron gas system

Using angle-resolved photoelectron spectroscopy (ARPES), we study the band structures of two-dimensional electron gases (2DEGs) formed at Te-doped surfaces of InAs(110), as a result of band bending. The selected surface system is very clean and stable; therefore, ARPES spectra may be registered in short times, with minimal adsorption of residual gases and no photon beam-induced damage. We record a set of data that allows for a detailed analysis of the 2DEG band shapes, their thermal dependencies, and for an assessment of the many-body interactions. We find the electron-phonon interaction extremally weak and the electron-electron interactions hidden in dominant electron-donor interactions. While 2DEG band shapes are observed to be variable in correlation with the 2DEG density, this is tracked down to the variability of the band-bending potential and nonparabolicity of the system, and not to the many-body interactions. Thus, many-body renormalization of the 2DEG bands is not required, and the bands are described well by using the one-electron theoretical frame.

Coupling of 3D thermal with 1D thermohydraulic model for single-phase flows of direct steam generation in parabolic-trough solar collectors

Estimating 3D temperature distribution around the heat collector element (HCE) is an essential matter for the safety and efficiency of parabolic-trough solar collectors (PTC) due to non-uniform heat flux distribution (NUHFD). Particularly in 2nd and 3rd generation PTC systems, such as direct steam generation (DSG), because of the higher thermal stress around the absorber. 3D HCE thermal models linked to a 1D approach of fluid flow appear as the fastest alternative to study this phenomenon. However, there are still challenges such as the thermal coupling between HCE and heat transfer fluid (HTF) for accurately estimating the receiver thermal field. In this work, the coupling is studied in depth for single-phase flows of DSG in PTC, with a fast and realistic 3D HCE − 1D HTF model, which is validated with experimental data of the Direct Steam Solar (DISS) facility for heat transfer and absorber thermal field variables. Firstly, the inability of standard heat transfer coefficient (HTC) correlations to predict absorber thermal field is constated, being deviations greater than −36.1% for absorber cross-sections (CS) maximum thermal gradients. Assuming underestimated and constant thermophysical properties of the absorber, as former models did, underestimations of more than −29.6% are reported. Besides, the heat transfer variables are overestimated by around 14.3–15.9% for temperatures above 600 K. Secondly, a new correction factor (CF) for standard HTC is proposed involving the NUHFD. Considering this CF and the thermal dependence of the absorber thermophysical properties, deviations fall below 7.5% for heat transfer variables, whilst the absorber CS maximum thermal gradients are under 6.0%. This approach also improves the results reported by former models around 4.3–7.3% for heat transfer variables, without underestimating absorber CS maximum thermal gradients. These deviations are between 4.9–19.1% guaranteeing the safety of the absorber when the model is used during the design stage.

Copper- and Silver-Containing Heterometallic Iodobismuthates: Features of Thermochromic Behavior.

Nine heterometallic iodobismuthates with the general formula Cat2{[Bi2M2I10}] (M = Cu(I), Ag(I), Cat = organic cation) were synthesized. According to X-ray diffraction data, their crystal structures consisted of {Bi2I10} units interconnected with Cu(I) or Ag(I) atoms through I-bridging ligands, forming one-dimensional polymers. The compounds are thermally stable up to 200 °C. Optical band gaps (Eg), estimated at room temperature via diffuse reflectance measurements, range from 1.81 to 2.03 eV. Thermally induced changes in optical behavior (thermochromism) for compounds 1-9 were recorded, and general correlations were established. The thermal dependence of Eg appears to be close to linear for all studied compounds.

The temperature of maximum density of diluted aqueous solutions of non-polar solutes: A molecular simulation study using TIP4P/2005 water and LJ point solutes

The effect of non polar solutes on the temperature of maximum density of water, TMD, is analyzed in detail by means of molecular simulations over an ample pressure interval ranging from negative to very high pressures. Non polar solutes are represented by single Lennard-Jones (LJ) sites, whose non-polar character is tuned with the width and depth of the Lennard-Jones water-solute potential parameters. Our analysis is focused on the behavior of the partial molar volume of the solute at infinite solution, whose thermal dependence is correlated with changes in the TMD. We find that for pressures below −200 bar all possible LJ water-solute potential parameters decrease the TMD, i.e. the solute acts as a “structure breaker”. At higher pressures, it is always possible to find a range of LJ parameters which induce an increase of the TMD, whose magnitude rises gradually with pressure. Our results are consistent with previous simulations of non polar gases in solution and with theoretical studies in the case of small LJ centers. It will be shown that the partial molar volume of an ideal gas at infinite dilution can provide information concerning the existence and size of the LJ parameter space that induces TMD increases for a given water model. Finally, we analyze the changes in the TMD in terms of the competition between low density and high density water states. We find that the temperature dependence of the variation of the low density water mole fraction with the addition of LJ solutes seems to be at the source of the changes in the TMD.

Modelling and Validation of Typical PV Mini-Grids in Kenya: Experience from RESILIENT Project

PV-based mini-grids are identified as a feasible and, often, only economically viable option for the electrification of Kenyan remote and scattered rural areas, where connection to the national grid is challenging, and the related costs are high, if not prohibitive. This paper presents the analysis of typical Kenyan PV mini-grids by using some results of the work in the project “Reliable, Efficient and Sustainable Mini-Grids for Rural Infrastructure Development in Kenya (RESILIENT)”. After presenting average annual and seasonal daily load profiles of residential and small commercial mini-grid customers identified from the measured demands, the paper introduces the main mini-grid components and their models, including a simplified, but reasonably accurate, model of a mini-grid battery storage system based on the manufacturer’s charge–discharge curves. All mini-grid components are assembled in a scalable and easily reconfigurable simulation model of an actual Kenyan PV mini-grid, and they are implemented for the evaluation of PV mini-grid performance and the potential for expansion and connection of additional residential and small commercial customers. During the validation of the developed simulation model using available measurement data, an empirical approach for adjusting the PV system output power is specified for a more accurate match with the measurements. The presented results indicate the importance of the information on the actual control algorithms and control settings of the mini-grid energy management systems, on the thermal dependencies and characteristics of both PV generation system and battery storage system, and on the availability of on-site measurements of temperature and input solar irradiance. The developed PV mini-grid model can be used for further analyses, such as to study the techno-economic performance of different mini-grid configurations, to identify the optimal sizing of mini-grid components, and to specify efficient control and operation schemes based on the locally available resources.

Thermal Effects on Shear Characteristics of Unbound Granular Materials under Drained Conditions

In this study, the thermally induced changes in the shear characteristics of unbound granular materials (UGMs) were investigated. A series of drained shear tests were conducted using a large-scale triaxial apparatus under controlled temperatures. The thermal dependence of the peak strength, critical strength, internal friction angle, and dilatancy of UGMs were investigated under different temperatures, initial mean effective stresses, and relative compaction. Dense UGMs tended to expand during heating and slightly contract during cooling. In the heating and cooling process, a nonlinear relationship was observed between thermal deformation and temperature. Thermal deformation was attributed to the deformation, movement, and rotation of soil particles and closely related to the initial mean effective stress and relative compaction. A thermal softening effect was observed during the shear test, and the peak strength decreased with increasing temperature. However, negligible thermal effects were observed relative to residual strength. The effect of temperature on the shear characteristics of UGMs was primarily related to the thermal expansion of pores in the soil skeleton. The relationship between peak strength and initial thermal volumetric strain was found to be exponential. Considering the thermal effect, a normalized semi-empirical model of the parabolic Hvorslev envelope for dense UGMs was proposed to supply guidelines for road base design.