Temperature Dependence Research Articles

Influence of a laser pulse on thermoelasticity with temperature dependence under the dual-phase-lag model using improved modified extended tanh function method

In this paper, the improved modified extended tanh function method (IMETFM) is introduced for analyzing the influence of laser pulse on a thermo-elastic with temperature-dependence under a dual phase lag model (DPL). Nonlinear thermo-elasticity examines cases in which a material’s response to changing thermal loads causes considerable changes in both its geometry and material properties. This field is crucial for effectively describing real-world phenomena, such as thermal stresses in large-scale structures, the behavior of materials at high temperatures, and the intricate interactions between mechanical and thermal fields. The proposed method generated a variety of exact solutions featuring distinct free parameters, including hyperbolic, rational, bright solitons, singular solitons, dark solitons, exponential, polynomial, and Jacobi elliptic solutions. Additionally, some of the results for displacement component, temperature, and stress tensor are presented through graphical illustrations.

Effect of temperature and frequency on the dielectric behaviour of cellulose nanocrystals

Nanocellulose is a promising material for advanced applications due to its renewable nature, non-toxicity, eco-friendliness, mechanical strength and other unique properties. This study investigates the dielectric properties of cellulose nanocrystals (CNCs) derived from wastepaper through acid hydrolysis, across a temperature range of 30°C to 100°C and a frequency range of 1 Hz to 10 MHz. Using theoretical models such as the modified Cole-Cole model, Jonscher's universal dielectric response (UDR) model and modified Kohlrausch-Williams-Watts (KWW) model, a detailed analysis is performed. The results indicate that the dielectric properties depend on temperature, with the frequency dispersion of the real (ε′) and imaginary parts (ε″) of the dielectric permittivity fitting the modified Cole-Cole equation. These values show an initial increase up to 70°C (ε′∼ 6000 and dielectric loss <1) followed by a decrease at higher temperatures, which is linked to the hydroxyl groups. A temperature dependence is also observed in space charge conductivity, free charge conductivity and relaxation time. Non-Debye type behaviour is attributed to asymmetrical features in the electric modulus spectra, as explained by the modified KWW model at various temperatures. The frequency variation of AC conductivity adheres to Jonscher’s power law and the temperature variation of the frequency exponent (0≤ s ≤1) indicates a correlated barrier hopping conduction mechanism for charge carriers. Overall, these findings highlight CNCs as excellent candidate for antistatic applications, demonstrating conductivity ranging from 10−5 to10−9 Scm−1. The results also suggest CNCs can be used in energy storage applications due to their outstanding dielectric properties and low dielectric loss (<1).

Study of PVAc/EVA polymer series: Influence of the inter-/intra-molecular interaction ratio on the molecular mobility at the glass transition.

In this work, the molecular mobility at the glass transition of poly(vinyl acetate) (PVAc) and poly(ethylene-co-vinyl acetate) (EVA) amorphous sample series was investigated. The temperature and pressure dependences of the intermolecular interactions were studied from time-temperature-pressure superpositions and from the relaxation time dispersion of the segmental relaxation. The difference in terms of intermolecular interactions due to the lateral group ratio of vinyl acetate (VAc) was then estimated from the activation volume and related to the cooperative behavior. The isobaric fragility and its two contributions (thermal and volumetric) were estimated through high pressure broadband dielectric spectroscopy measurements. The volumetric and thermal contributions show different behaviors as a function of the VAc ratio and as a function of the pressure. Thus, the study of the PVAc/EVA series has allowed us to emphasize that the intramolecular and intermolecular interactions induced by the dipolar pendant groups directly influence the thermal and volumetric contributions to the isobaric fragility.

Investigation of ferromagnetic resonance heating of isotropic superparamagnetic on the example of biogenic ferrihydrite nanoparticles

Ferrihydrite nanoparticles have been synthesized and characterized. The dependences of the temperature increment of powders in the pumping mode by a high-frequency electromagnetic field in a constant magnetic field are studied. It is shown that the experimental dependence of the particle temperature on the dc magnetic field strength is in good agreement with the theory of ferromagnetic resonance for an isotropic superparamagnetic.

IR magnetotransmission in double NdBaMn&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; manganite with different degrees of ordering in A-position

The structural, magnetic, and optical properties of double manganites NdBaMn2O6 have been studied depending on the degree of ordering of Nd and Ba atoms in the A-position. Analysis of temperature dependences of light transmission shows the changes of charge carrier subsystem in vicinity of structural and magnetic phase transitions. When the metal-insulator transition occurs the effect of light magnetotransmission near Curie temperature was found.

Determining the Electrostatic Contributions of GTPase-GEF Complexes on Interfacial Drug Binding Specificity: A Case Study of a Protein-Drug-Protein Complex.

Understanding the factors that contribute to specificity of protein-protein interactions allows for design of orthosteric small molecules. Within this environment, a small molecule requires both structural and electrostatic complementarity. While the structural contribution to protein-drug-protein specificity is well characterized, electrostatic contributions require more study. To this end, we used a series of protein complexes involving Arf1 bound to guanine nucleotide exchange factors (GEFs) that are sensitive or resistant to the small molecule brefeldin A (BFA). By comparing BFA-sensitive Arf1-Gea1p and Arf1-ARNO with different combinations of four BFA sensitizing ARNO mutations (ARNOwt, ARNO1M, ARNO3M, and ARNO4M), we describe how electrostatic environments at each interface guide BFA binding specificity. We labeled Arf1 with cyanocysteine at several interfacial sites and measured by nitrile adsorption frequencies to map changes in electric field at each interface using the linear Stark equation. Temperature dependence of nitrile vibrational spectra was used to investigate differences in hydrogen bonding environments. These comparisons showed that interfacial electric field at the surface of Arf1 varied substantially depending on the GEF. The greatest differences were seen between Arf1-ARNOwt and Arf1-ARNO4M, suggesting a greater change in electric field is required for BFA binding to Arf1-ARNO. Additionally, rigidity of the interface of the Arf1-ARNO complex correlated strongly with BFA sensitivity, indicating that flexible interfaces are sensitive to disruption upon orthosteric small molecule binding. These findings demonstrate a qualitatively consistent electrostatic environment for Arf1 binding and more subtle differences preventing BFA specificity. We discuss how these results will guide improved design of other small molecules that can target protein-protein interfaces.

Stability of the first-order character of phase transition in HoCo2

HoCo2 exhibits a giant magnetocaloric (MC) effect at its first-order magnetostructural phase transition around 77 K, and understanding the thermodynamic nature of this transition in response to external magnetic fields is crucial for its MC applications. In this study, we present a comprehensive investigation of specific heat and magnetization measurements of HoCo2 under varying magnetic fields. The specific heat measurements qualitatively indicate a transformation from first- to second-order behavior of this phase transition at higher magnetic fields. However, analysis of the power-law dependence of the magnetic entropy change (ΔSM∝Hn) and the breakdown of universal behavior in the temperature dependence of ΔSM suggest that the first-order nature remains intact, even up to 7 T. This stability of the first-order nature is further manifested through the distinctive non-linear behavior of modified Arrott plots, with a negative slope in the 6–7 T range.

Hexagonal ZnO microdisk grown by mist chemical vapor deposition on c-plane sapphire substrate and lasing actions

Abstract Hexagonal ZnO microdisks were grown by mist chemical vapor deposition (mist-CVD) for 6 h. The microdisks when viewed from the top were typically hexagonal with diameters of a few micrometers, and their typical three-dimensional shape was a hexagonal pyramid. Sharp peaks appeared in the room-temperature photoluminescence (PL) spectra observed from a single hexagonal ZnO microdisk under high optically pumped conditions, and they are assumed to correspond to lasing actions. We also examined the temperature dependence of these sharp peaks in the PL spectra.&amp;#xD;&amp;#xD;

Kr Adsorption in Porous Carbons: Temperature-Dependent Experimental and Computational Studies†.

The temperature dependence of the adsorption energy of krypton adsorption on activated carbon materials was studied by experiment and simulation. Adsorption isotherms were measured at temperatures from 250 to 330 K and analyzed with Henry's law. The adsorption energy determined from these measurements was found to weaken by more than 10% in this range. Slit pore widths for simulations in this work were modeled by the removal of integral numbers of planes in graphite. Vibrational dynamics of the krypton adsorbate and the carbon atom adsorbent were calculated with the stochastic temperature-dependent effective potential (sTDEP) method, using energetics from density functional theory (DFT) with the many-body dispersion energy method (MBD). Thermal displacements of carbon atoms had a negligible effect on the adsorption energy. The width of the slit pore had the greatest effect on the surface dynamics and the energies of the adsorbate atoms at different temperatures. Assuming a distribution of pore widths, the Boltzmann distribution of site occupancies causes a large weakening of the thermally averaged adsorption energy at higher temperatures.

The dynamics of pinned charge density wave in NbSe3 nanoribbons revealed by noise spectroscopy

Abstract Systematic nonlinear transport and broadband noise (BBN) measurements are performed on single nanoribbon devices of the charge density wave (CDW) conductor NbSe$_{3}$ over a wide range of excitation levels and temperatures. The nonlinear voltage-current characteristics elucidate the depinning process of the two CDWs and the temperature dependence of their threshold electric fields. Within the temperature and electric field range where the CDW is anticipated to be entirely pinned by residual impurities, a non-monotonic behavior in the noise magnitude versus electric field is observed. This phenomenon is attributed to the proliferation of thermally activated phase slip events, enhanced by the size effect in nanodevices. The idea is corroborated by the observation of a smeared activated behavior described by the Dutta-Horn relation. Certain aspects of the temperature dependence of the noise magnitude deviate from a simple activated behavior, suggesting a multifaceted origin of the resistance fluctuations in CDW systems at the nanometer scale. These findings provide valuable insights into the dynamics of CDW in nanodevices.

The Electron–Phonon Interaction in Non-Stoichiometric Bi2Sr2CaCu2O8+δ Superconductor Obtained from the Diffuse Elastic Scattering of Helium Atoms

Previously, helium atom scattering (HAS) has been shown to probe the electron–phonon interaction at conducting crystal surfaces via the temperature dependence of the specular peak intensity. This method is now extended to non-stoichiometric superconductors. The electron–phonon interaction, as expressed by the mass-enhancement factor λ, is derived from the temperature dependence of the diffuse elastic scattering intensity, which specifically depends on the non-stoichiometric component responsible for superconductivity. The measured value of the mass-enhancement factor for Bi2Sr2CaCu2O8+δ at the optimal doping δ = 0.16 is λ = 0.55 ± 0.08 is in good agreement with values of λ recently estimated with other methods. This also confirms the relevant role of electron–phonon interaction in high-temperature non-stoichiometric cuprate superconductors.

Internal quantum efficiency of GaAsBi MQW structure for the active region of VECSELs

Internal quantum efficiency of GaAsBi MQW structure for the active region of VECSELs

Li2CO3 as a Modifier for PVA/PVP/PEG Blend Polymer Electrolytes: Effects on Structural Integrity, Electrical Performance, Thermal Behavior and Optical Properties

ABSTRACT The effects of incorporating lithium carbonate (Li2CO3) into a polyvinyl alcohol/polyvinyl pyrrolidone/polyethylene glycol (PVA/PVP/PEG) blend polymer electrolyte were investigated. Electrolytes were prepared via solution casting method, with Li2CO3 added at 10, 20, and 30 wt.% to the PVA/PVP/PEG blend (50/30/20 ratio). Fourier transform infrared spectroscopy analysis revealed interactions between the added salt and the polymer blend. The addition of both PEG and Li2CO3 resulted in increased ionic conductivity, reaching a maximum of 4.51 × 10− 5 S/cm at 30°C with 20 wt.% Li2CO3. Ionic conductivity also exhibited a positive temperature dependence. Optical analysis showed a decrease in the optical energy gap with the addition of PEG and Li2CO3. Differential thermal analysis indicated improved thermal stability with increasing Li2CO3 content, as evidenced by higher onset, endset, and midset temperatures. The enhanced properties of the modified electrolyte suggest its potential applicability in lithium-based electrochemical devices.

3T-VASP: fast ab-initio electrochemical reactor via multi-scale gradient energy minimization

Ab-initio methods such as density functional theory (DFT) is useful for fundamental atomistic-level study and is widely used across many scientific fields, including for the discovery of electrochemical reaction byproducts. However, many DFT steps may be needed to discover rare electrochemical reaction byproducts, which limits DFT’s scalability. In this work, we demonstrate that it is possible to generate many elementary electrochemical reaction byproducts in-silico using just a small number of ab-initio energy minimization steps if it is done in a multi-scale manner, such as via previously reported tiered tensor transform (3T) method. We first demonstrate the algorithm through a simple example of a complex floppy organic molecule passivator binding onto perovskite solar cell surface defect site. We then demonstrate more complex examples by generating hundreds of electrochemical reaction byproducts in lithium-ion battery liquid electrolyte (many are verified in previous experimental studies), with most trajectories completed within 50–100 DFT steps as opposed to more than 10,000 steps typically utilized in an ab-initio molecular dynamics trajectory. This approach requires no machine learning training data generation and can be directly applied on any new chemistries, making it suitable for ab-initio elementary chemical reaction byproduct investigation when temperature dependence is not required.

Combined first-principles and Boltzmann transport theory methodology for studying magnetotransport in magnetic materials

Unusual magnetotransport behaviors, such as temperature-dependent negative magnetoresistance (MR) and bowtie-shaped MR, have puzzled us for a long time. Although several mechanisms have been proposed to explain these phenomena, the absence of comprehensive quantitative calculations has made these explanations less convincing. In our work, we introduce a methodology to study magnetotransport behaviors in magnetic materials. This approach integrates the anomalous Hall conductivity induced by the Berry curvature, with a multiband ordinary conductivity tensor, employing a combination of first-principles calculations and semiclassical Boltzmann transport theory. Our method also incorporates the temperature dependence of the relaxation time and the anomalous Hall conductivity, as well as the field dependence of the anomalous Hall conductivity. We initially test this approach on models, obtaining distinct behaviors of magnetoresistance and Hall resistivity across several types of magnetic materials, and then apply it to a Weyl semimetal Co3Sn2S2. The results, which align well with experimental observations in terms of magnetic field and temperature dependencies, demonstrate the efficacy of our approach. This methodology provides a comprehensive and efficient means to understand the underlying mechanisms of the unusual complex behaviors observed in magnetotransport measurements in magnetic materials. Published by the American Physical Society 2024

The impact of tube voltage on the erosion of rotating x-ray anodes.

The permitted input power density of rotating anode x-ray sources is limited by the performance of available target materials. The commonly used simplified formulas for the focal spot surface temperature ignore the tube voltage despite its variation in clinical practice. Improved modeling of electron transport and target erosion, as proposed in this work, improves the prediction of x-ray output degradation by target erosion, the absolute x-ray dose output and the quality of diagnostic imaging and orthovolt cancer therapy for a wide range of technique factors. Improved modeling of electronic power absorption to include volume effects and surface erosion, to improve the understanding of x-ray output degradation, enhance the reliability of x-ray tubes, and safely widen their fields of use. We combine Monte Carlo electron transport simulations, coupled thermoelasticity finite element modelling, erosion-induced surface granularity, and the temperature dependence of thermophysical and thermomechanical target properties. A semi-empirical thermomechanical criterion is proposed to predict the target erosion. We simulate the absorbed electronic power of an eroded tungsten-rhenium target, mimicked by a flat target topped with a monolayer of spheres, and compare with a pristine target. The absorbed electronic power and with it the conversion efficiency varies with tube voltage and the state of erosion. With reference to 80kV (100%), the absorption of a severely eroded relative to a pristine target is 105% (30kV), 99% (100kV), 97% (120kV), 96% (150kV), 93% (200kV), 87% (250kV), and 79% (300kV). We show that, although the simplistic Müller-Oosterkamp model of surface heating underestimates the benefit of higher tube voltages relative to operation at 80kV, the error is limited to below -6% for 30kV (reduction advised) and +13% for 300kV (input power increase permitted). Correcting the x-ray conversion efficiency of eroded target material, that is typically not accessible by measuring the tube current, may imply corrections to existing x-ray dose calculations. The relative increase of the allowable anode input power of rotating anode x-ray tubes with increasing tube voltage is substantially smaller than predicted by volume heating models that only rely on the focal spot surface temperature. The widely used voltage agnostic Müller-Oosterkamp formalism fails to predict the tube voltage dependency of the surface temperature of rotating anode targets, ignores the temperature dependency of the thermal diffusivity of tungsten-rhenium, and the granularity of the material. Nevertheless, we show theoretically why, backed by experience, the practical use of the Müller-Oosterkamp formalism is justified in medical imaging and provides a basis for comparison with new microparticle based targets. The reason for this surprising finding is that voltage dependent material erosion must be primarily considered as a precursor of thermal runaway effects.

Optimization of superconducting niobium nitride thin films via high-power impulse magnetron sputtering

Abstract We report a systematic comparison of niobium nitride thin films deposited on oxidized silicon substrates by reactive DC magnetron sputtering and reactive high-power impulse magnetron sputtering (HiPIMS). After determining the nitrogen gas concentration that produces the highest superconducting critical temperature for each process, we characterize the dependence of the critical temperature on film thickness. The optimal nitrogen concentration is higher for HiPIMS than for DC sputtering, and HiPIMS produces higher critical temperatures for all thicknesses studied. We attribute this to the HiPIMS process enabling the films to get closer to optimal stoichiometry before beginning to form a hexagonal crystal phase that reduces the critical temperature, along with the extra kinetic energy in the HiPIMS process improving crystallinity. We also study the ability to increase the critical temperature of the HiPIMS films through the use of an aluminum nitride buffer layer and substrate heating.

In pursuit of precise Ca ii H K chromospheric surface fluxes. A gravity and temperature dependence

The emission lines of the Ca ii H K doublet present one of the most important channels of radiative cooling for the chromospheres of cool stars. Although most other line emissions ( Mg ii h k and numerous iron lines) populate the far-UV and require a very competitive space-born observing time, the Ca ii H K lines in the optical UV are easily accessible by ground-based spectroscopy with relatively cheap instrumentation, and the observational data are plentiful. At the same time, in order to include realistic mechanical and magnetic heating, advanced chromospheric models now require radiative cooling losses in absolute terms and therefore call for a precise surface flux scale, which could be provided by matching a photospheric Ca ii H K line profile computed by photospheric models. However, a major obstacle here is the significant ambiguity in parameter space in the face of a very sensitive dependence of cool stellar optical UV surface fluxes on the effective temperature. Consequently, we have developed a rigorous method by which precise physical parameters, most notably the effective temperature, are first determined by iSpec tools working on high signal-to-noise spectra and based on a suitable line list and reference continuum. However, crosstalk and navigation of multiple local chi-square minima (best solutions) in parameter space must be considered. Only with the optimal set of parameters is a single phoenix model calculated, which defines the spectral surface flux scale in the Ca ii H K line region. In this paper, we discuss the results of the absolute measurements of Ca ii K line fluxes for 32 representative cool stars and the accuracy of this approach. Finally, we show a comparison of the Ca ii K chromospheric fluxes with line widths, and a relation of chromospheric flux with effective temperature and gravity following the logarithmic form $ F_ Ca II prime prime T_ eff + C^ prime

Delayed luminescence and thermoluminescence in laboratory-grown diamonds

The “blue-green” phosphorescence/thermoluminescence is most commonly observed in diamonds following excitation at or above the indirect band gap and has been explained by a substitutional nitrogen-boron donor-acceptor pair recombination model. “Orange” and “red” phosphorescence have also been frequently observed in laboratory-grown near-colorless high-pressure high-temperature diamonds following optical excitation and their luminescence mechanisms are shown to be different from that of the blue-green phosphorescence. The physics of the orange and red luminescence and phosphorescence bands including the optical-excitation dependency (UV-NIR), temperature dependency (20K–573K), and related charge transfer process are investigated by a combination of self-built time-resolved imaging/spectroscopic techniques. In this paper, an alternative model for long-lived phosphorescence based on charge trapping is proposed to explain the orange phosphorescence/thermoluminescence band. Additionally, the red phosphorescence band is attributed to point defect, which possibly has a three-level phosphorescence system. Published by the American Physical Society 2024

The Relationship Between Spin Crossover (SCO) Behaviors, Cation and Ligand Motions, and Intermolecular Interactions in a Series of Anionic SCO Fe(III) Complexes with Halogen-Substituted Azobisphenolate Ligands.

To investigate the halogen substitution effect on the anionic spin crossover (SCO) complexes, azobisphenolate ligands with 5,5'-dihalogen substituents from fluorine to iodine were synthesized, and their anionic FeIII complexes 1F, 1Cl, 1Br, and 1I were isolated. The temperature dependence of magnetic susceptibility and crystal structure revealed that 1F, 1Cl, and 1Br are all isostructural and exhibit SCO with the rotational motion of the cation and ligands, whereas 1I shows incomplete SCO. Note that 1Cl and 1Br showed irreversible and reversible cooperative SCO transitions, respectively. Short intermolecular contacts between the FeIII complex anions were found despite Coulomb repulsions for all the complexes. The topological analysis of the electron density distributions revealed the existence of X···X halogen bonds, C-H···X, C-H···N, and C-H···O hydrogen bonds, and C-H···π interactions are evident. The dimensionality of intermolecular interactions is suggested to be responsible for the cooperative SCO transitions in 1Cl and 1Br, whereas the disorder due to the freezing of ligand rotations in 1Cl is revealed to inhibit the SCO cooperativity.