Thermal Agitation Research Articles

Soft Ca2+-induced pea protein gels through mild heating: Controlling elasticity and fracturing behavior

With the rising demand for plant-based protein, understanding the formation of pea protein gels induced by calcium is important for manufacturing of food products with appealing textural properties. Moreover, the moderate temperature processing is becoming of greater and greater interest, based on conditions used for food fermentation. The objective of this study is to understand the structural and rheology behaviour of calcium-induced pea protein aggregates at moderate plateau temperatures i.e. in the range 30–45 °C with holding times from 0 to 60,000s. Based on the combination of confocal fluorescence microscopy (CLSM) imaging, rheology and IR spectroscopy, our results show that despite the relatively low temperature range, thermal agitation not only allows for partial protein particle dissolution, but also induces interactions leading to soft gel formation. Within a shorter holding time (0–600s) range, higher Gʹ/Gʹ0 (t) were observed at 40 °C and 45 °C, the end elastic modulus reaching for any parameters tested at least 1000 Pa. As the holding time was extended to 60,000s, the effect of temperature became less pronounced, i.e., all gels reached similar high values of Gʹ even for the low temperature of 30 °C, which is nearly 3–4 times higher than that formed at 600s holding time (at the temperature plateau). IR spectroscopy measurements showed that the protein secondary structure remained stable within the holding time ranging from 0s to 6,000s, while significant but moderate changes were monitored when extending the holding time to 60,000s, which correlated with a more progressive yielding observed in rheology, pointing to the formation of apparently more fragile physical gels. The combination of the techniques shows that the gel formation and strengthening mainly originated from rearrangements at the colloidal level leading to a denser network, while molecular rearrangements only intervened at the longest holding times (i.e, 60,000s).

Thermal effects on damping determination of perpendicular MRAM devices by spin-torque ferromagnetic resonance

We report device-level damping measurements using spin-torque driven ferromagnetic resonance on perpendicular magnetic random-access memory cells. It is shown that thermal agitation enhances the apparent damping for cells smaller than about 55 nm. The effect is fundamental and does not reflect a true damping increase. In addition to the thermal effect, it is still found that device-level damping is higher than film-level damping and increases with decreasing cell size. This is attributed to edge damage caused by device patterning.

Understanding the transport properties of perovskite compounds as a function of temperature, frequency and DC-bias voltage using experimental measurements and appropriate theoretical models.

The present paper provides interesting measurements and methodologies to investigate the key factors controlling the electrical response of perovskite systems. The studied system was successfully prepared using a solid-state route. The chemical analysis and the X-ray diffraction results confirm the formation of the desired perovskite phase. As a result, the DC-resistivity analysis shows that the transport properties are governed by hopping mechanisms above the transition temperature. In this case, thermal agitation allows the charge-carriers to hop across the insulating barrier in the form of grain boundaries. Then, the dominance of the grain boundary contribution is proved. AC-resistivity spectra are investigated in terms of numerous power laws (UDR, SPL and NCL). Accordingly, the decrease in the resistivity values at high frequencies is explained through hopping and tunneling processes. Indeed, it is proved that the electrical transport phenomena are governed by QMT and CBH models. The coexistence of direct (C-C) and indirect (C-A-C) interactions explains the multi-behavior of the AC-resistivity. The scaling representation displays a single muster curve describing the universal dynamic response (UDR). Thus, it reveals the universality of the electrical resistivity of the system. However, the double Schottky barrier model is used to explain the grain boundary effects. A critical frequency "νc" is detected under temperature and DC-bias voltage effects. These observations disclose, in a different way, the separate contributions of the electro-active regions of the sample in the conduction phenomenon.

Generalized energy-conserving dissipative particle dynamics with mass transfer: coupling between energy and mass exchange

Abstract The complete description of energy and material transport within the Generalized energy-conserving dissipative particle dynamics with mass transfer (GenDPDE-M) methodology is presented. In particular, the dynamic coupling between mass and energy is incorporated into the GenDPDE-M, which was previously introduced with dynamically decoupled fluxes (J. Bonet Avalos et al., J. Chem. Theory Comput., 18 (12): 7639–7652, 2022). From a theoretical perspective, we have derived the appropriate Fluctuation-Dissipation theorems along with Onsager’s reciprocal relations, suitable for mesoscale models featuring this coupling. Equilibrium and non-equilibrium simulations are performed to demonstrate the internal thermodynamic consistency of the method, as well as the ability to capture the Ludwig–Soret effect, and tune its strength through the mesoscopic parameters. In view of the completeness of the presented approach, GenDPDE-M is the most general Lagrangian method to deal with complex fluids and systems at the mesoscale, where thermal agitation is relevant.

Experimental and theoretical study for the sorption of Ni2+ and Cd2+ onto phosphoryl functionalized aluminum silicate composite

Phosphoryl functionalized Aluminum silicate (ASP) composite sorbent was synthesized using sol–gel technique and characterized with different techniques. The synthesized sorbent was tested for the sorption of Ni2+ and Cd2+ in aqueous solution at both single- and binary-solute systems under simulated conditions using batch technique. Batch experiments were executed as a function of pH, initial metal ion concentration and temperature. Structural and surface morphology of the synthesized sorbent were determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The studied kinetic models suggested that the sorption of Ni2+ and Cd2+ onto ASP was found to follow the pseudo-second order and the Langmuir-Freundlich model was the best model to depict the sorption isotherms. The sorption equilibria of both ions were analyzed using two diverse statistical physics models (homogeneous and heterogeneous monolayer models). A Theoretical scrutiny of statistical physics calculations indicated that Ni2+ and Cd2+ sorption was multi-ionic where two sorption sites were involved but with a diverse contribution degree. The removal nature of Ni2+ and Cd2+ was endothermic and the calculated sorption amounts at saturation implied that Ni2+> Cd2+. Calculated interaction energies indicated the participation of physical forces in the sorption of both ions onto the synthesized sorbent surface and the variation of these sorption energies confirmed that both sorption sites participated in the removal of Ni2+ and Cd2+ but through different interactions type. Ions sorption capacity was increased with the temperature owing to increase in thermal agitation. This study reveals that phosphoryl functionalized aluminum silicate is an efficient sorbent that can be used for the sorption of Ni2+ and Cd2+ from aqueous solutions in both single- and binary -solute systems.

Teaching Biophysics II. Biophysical approach of transport through cellular membranes

Cellular metabolism implies a permanent transport through membranes of a great diversity of particles (e.g., ions, molecules, macromolecules, protein vesicles, etc.) in and out of the cells. The transport phenomena can be classified as passive (down the concentration gradients, driven solely by thermal agitation) or active (against the concentration gradients, driven by an energy supply) and selective (i.e., through specific pathways) or nonselective through membrane lipid bilayers. This paper will describe in an accessible manner all the types of membrane transport from a biophysical point of view along with their crucial roles in normal cellular functioning. This paper is the successor of a previous work (A. I. Popescu, C. G. Chilom, Rom. Rep. Phys. 75, 605 (2023), Ref. [1]) in a series aiming to disseminate Biophysics in an accessible manner.

Abrupt increase of stochastic behavior in domain-wall motion near depinning field

The domain-wall motion in ferromagnetic films exhibits stochastic behavior due to thermal agitation with quenched disorders. The stochasticity is an obstacle in the sense of consistent repeatability of domain-wall position control in magnetic domain-wall devices. In general, the level of stochasticity is expected to decrease as driving force increases. This property suggests that the magnetic domain-wall devices are capable of simultaneously achieving both high operational speed and decrease in the level of stochasticity. However, we report here an observation of stochasticity anomaly, which involves a significant increase in relative speed dispersion near the depinning field. Domain-wall motion measurements were performed in ferromagnetic wires with perpendicular magnetic anisotropy over the same position to measure the relative speed dispersion. The stochasticity in domain-wall motion is intertwined with the number of pinning–depinning events throughout the domain-wall motion. The size of cluster events, which leads to the number of events, reflects the trend in the relative speed dispersion. The observed anomaly is provided by occurrence of large avalanches of cluster events. The anomaly occurs within the tech-relevant speed range of 1–100 m/s, signaling the necessity of material engineering to mitigate its effects.

Doping effects of transition metals and rare earth ions in KMPO4:Ln ceramics: Implications for electrical and microstructural characteristics

A series of ceramic materials with the chemical formula KMPO4 (M = Mg, Mn, Ni, Cu) and KMgPO4:Ln (Ln = Nd, Dy, Er) were obtained by the solid-state reaction method. Analysis via X-ray diffraction (XRD) revealed that these materials exhibited distinct crystal systems, depending on the divalent used metal. Infrared spectroscopy (IR) was employed to characterize the P–O bonds within the coordination polyhedral. Energy-Dispersive X-Ray (EDX) analysis confirmed the presence of the constituent elements and the quantity of dopants incorporated into the crystalline structure. Complex Impedance Spectroscopy (CIS) was utilized to evaluate the conductivity of these compounds. Notably, conduction in these materials is predominantly cationic within the temperature range of 513–653K, occurring as ions migrate due to thermal agitation. Materials doped with rare earth ions demonstrated low activation energy values, making them promising candidates for use[n electrochemical applications, particularly in potassium-based batteries.

Effects of Chemical Short-Range Order and Temperature on Basic Structure Parameters and Stacking Fault Energies in Multi-Principal Element Alloys

In the realm of advanced material science, multi-principal element alloys (MPEAs) have emerged as a focal point due to their exceptional mechanical properties and adaptability for high-performance applications. This study embarks on an extensive investigation of four MPEAs—CoCrNi, MoNbTa, HfNbTaTiZr, and HfMoNbTaTi—alongside key pure metals (Mo, Nb, Ta, Ni) to unveil their structural and mechanical characteristics. Utilizing a blend of molecular statics and hybrid molecular dynamics/Monte Carlo simulations, the research delves into the impact of chemical short-range order (CSRO) and thermal effects on the fundamental structural parameters and stacking fault energies in these alloys. The study systematically analyzes quantities such as lattice parameters, elastic constants (C11, C12, and C44), and generalized stacking fault energies (GSFEs) across two distinct structures: random and CSRO. These properties are then evaluated at diverse temperatures (0, 300, 600, 900, 1200 K), offering a comprehensive understanding of temperature’s influence on material behavior. For CSRO, CoCrNi was annealed at 350 K and MoNbTa at 300 K, while both HfMoNbTaTi and HfNbTaTiZr were annealed at 300 K, 600 K, and 900 K, respectively. The results indicate that the lattice parameter increases with temperature, reflecting typical thermal expansion behavior. In contrast, both elastic constants and GSFE decrease with rising temperature, suggesting a reduction in resistance to stability and dislocation motion as thermal agitation intensifies. Notably, MPEAs with CSRO structures exhibit higher stiffness and GSFEs compared to their randomly structured counterparts, demonstrating the significant role of atomic ordering in enhancing material strength.

Formal description of the initial propagation of martensite and the martensitic spread

This article analyses the spread of martensite nucleation in small particles and polycrystalline materials, considering the influence of thermal agitation on the diffusionless aspect of martensitic transformation. Henceforth, we propose a formal description of the initiation of the martensitic transformation supported by experimental data, which emphasises the conditioning of the austenite for martensite transformation and applies to martensitic transformation in general

Suppressing pre-aggregation to increase polymer solar cell ink shelf life

An approach to slow down the polymer solar cell ink aging by employing an additive (i.e., PCBM variants) was developed. It is inferred that PCBMs in the ink act as a co-solvent and slow down the polymer pre-aggregation.

Thermal quantum coherence of two–qutrit Heisenberg XXZ model with Herring-Flicker coupling and Dzyaloshinskii-Moriya interaction under magnetic field

In this study, we use the concept of l 1-norm coherence to characterize the entanglement of a two–qutrit Heisenberg XXZ model for subject to a uniform magnetic field and z–axis Dzyaloshinskii–Moriya interaction with Herring-Flicker coupling. We show that the temperature, magnetic field, DM interaction, and distance of Herring-Flicker coupling can all control the entanglement. However, the state system becomes less entangled at high temperatures or strong magnetic fields and vice versa. Our findings suggest that entanglement rises when the z–axis DM interaction increases. Additionally, we show that plateau behavior in the entanglement between spins (1, 1) occurs in the XXZ Heisenberg spin system and is influenced by the magnetic field, demonstrating that thermal agitation can weaken entanglement plateaus. Moreover, by setting the strengths coupling of the spin, we quickly recover the isotropic XY and XXX Heisenberg models. Finally, Herring-Flicker coupling affects the degree of entanglement. When Herring-Flicker coupling and temperature are at small values, the degree of entanglement is at its highest. Still, when Herring-Flicker coupling is at substantial values, the degree of entanglement tends to stabilize.

Position error-free control of magnetic domain-wall devices via spin-orbit torque modulation

Magnetic domain-wall devices such as racetrack memory and domain-wall shift registers facilitate massive data storage as hard disk drives with low power portability as flash memory devices. The key issue to be addressed is how perfectly the domain-wall motion can be controlled without deformation, as it can replace the mechanical motion of hard disk drives. However, such domain-wall motion in real media is subject to the stochasticity of thermal agitation with quenched disorders, resulting in severe deformations with pinning and tilting. To sort out the problem, we propose and demonstrate a new concept of domain-wall control with a position error-free scheme. The primary idea involves spatial modulation of the spin-orbit torque along nanotrack devices, where the boundary of modulation possesses broken inversion symmetry. In this work, by showing the unidirectional motion of domain wall with position-error free manner, we provide an important missing piece in magnetic domain-wall device development.

Site-occupancy factors in the Debye scattering equation. A theoretical discussion on significance and correctness.

The Debye scattering equation (DSE) [Debye (1915). Ann. Phys. 351, 809-823] is widely used for analyzing total scattering data of nanocrystalline materials in reciprocal space. In its modified form (MDSE) [Cervellino et al. (2010). J. Appl. Cryst. 43, 1543-1547], it includes contributions from uncorrelated thermal agitation terms and, for defective crystalline nanoparticles (NPs), average site-occupancy factors (s.o.f.'s). The s.o.f.'s were introduced heuristically and no theoretical demonstration was provided. This paper presents in detail such a demonstration, corrects a glitch present in the original MDSE, and discusses the s.o.f.'s physical significance. Three new MDSE expressions are given that refer to distinct defective NP ensembles characterized by: (i) vacant sites with uncorrelated constant site-occupancy probability; (ii) vacant sites with a fixed number of randomly distributed atoms; (iii) self-excluding (disordered) positional sites. For all these cases, beneficial aspects and shortcomings of introducing s.o.f.'s as free refinable parameters are demonstrated. The theoretical analysis is supported by numerical simulations performed by comparing the corrected MDSE profiles and the ones based on atomistic modeling of a large number of NPs, satisfying the structural conditions described in (i)-(iii).

Simulation Analysis of Thermal Decay and Read-Write Characteristics Depending on the Structure of Sputtered Tape Media

We developed a magnetic recording simulator that takes into account thermal agitation by employing a probabilistic switching model based on the Arrhenius-Neel equation. Using this simulator, we investigated the impact of Capped and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H_k</i> -Graded media on sputtered perpendicular media for magnetic tape recording. Our simulation results were in good agreement with the experimental data, as evidenced by the consistency of the M-H curves and read-write characteristics. Specifically, we found that the use of Capped media enhances writability, but it also increases the transition noise, while Graded media has no significant effect on writability. Furthermore, our thermal decay simulation showed a correlation between the reproduction output decay and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M_r/M_s</i> decay, and no clear relationship between the media SNR decay over time and the media <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K_uV/k_BT</i> . These findings illustrate the potential of our simulator as a valuable tool for designing magnetic media.

Thermally tunable electromagnetic surface waves supported by graphene loaded indium antimonide (InSb) interface

The thermal agitation plays a vital role in tunability of optoelectronic, structural and chemical characteristics of the temperature sensitive materials. Graphene enables the THz optics, due to its unprecedent controlling characteristics over the traditional materials. The influence of temperature on the monolayer graphene is very negligible due to its low free charge carrier density, to enhance the thermal sensitivity of graphene, the graphene loaded temperature sensitive material interface has been proposed. A theoretical analysis has been carried out on temperature dependent propagation characteristics of electromagnetic surface waves supported by the graphene loaded semi-infinite indium antimonide (InSb). The InSb has been taken as temperature sensitive material. The Drude model has been used for the modeling of InSb in the THz region while the modeling of the graphene has been done by random phase approximation-based Kubo’s formulism. To realize the graphene loaded indium antimonide interface, the impedance boundary conditions (IBCs) have been employed. The numerical analysis has been conducted to analyze the influence of temperature on the characteristics of electromagnetic surface waves i.e., dispersion curve, effective mode index (Neff), penetration depth (δ), propagation length (Lp), phase speed (Vp) and field profile, propagating along the graphene loaded InSb. In all the numerical results, the temperature variation has been considered from 200 to 350 K. It has been concluded that the graphene–InSb interface provides more temperature assisted tunability to the interfacial surface modes, commonly known as surface waves, as compared to monolayer graphene. Further, the graphene parameters can play a vital role in the dynamical tuning of electromagnetic surface waves in THz to IR frequency range. The numerically computed results have potential applications in designing of thermo-optical waveguides, temperature assisted communication devices, thermo-optical sensors and near field thermal imaging platforms.

Oscillations of the Hall Resistivity in Natural Single Crystals of Pyrrhotite Associated with the Orientation of the Elementary Magnetic Moments of Fe Atoms

The Hall resistivity of natural single crystals of pyrrhotite Fe7S8 exhibits oscillations with the inverse external magnetic field 1/B at temperature 77 K and B up to 0.73 Tesla. This resembles phenomena due to Landau quantization of the carriers demanding very pure samples, temperatures near 4 K and magnetic fields of several Tesla. However, none of these requirements is met in the experiments. The oscillations appear only when there is orientation of the elementary magnetic moments of Fe atoms, which happens when B is parallel to the c‐plane at 77 K. At room temperature with the orientation destroyed by the thermal agitation and for B parallel to the c‐axis along which the alignment of the Fe magnetic moments is negligible, the oscillations disappear. According to the s–d model proposed for heavily doped magnetic semiconductors, defects and impurities produce large local fluctuations of carrier concentrations. These through the strong s–d exchange interaction between the carriers and the lattice magnetic moments of Fe establish variations of local magnetization. These constitute scattering centers which are enforced for certain values of B, though for others weaken giving the oscillatory behavior of the Hall resistivity.

Effect of memory behavior on electric-field-induced phase transition and electrocaloric response in antiferroelectric ceramics

Field-induced phase transition in antiferroelectric (AFE) materials always facilitates giant positive/negative electrocaloric (EC) responses for a promising cooling application, while it is not only associated with external field conditions but also applied field history, i.e., memory behavior. Herein, we demonstrate that memory behavior increases the likelihood of observing an EC response when the operating field is parallel to the pre-poling field, as compared to the antiparallel condition. Additionally, when the temperature is slightly above the AFE-ferroelectric (FE) phase transition temperature, the field-off process induces a two-step microstructure change, characterized by a rapid domain rotation followed by a slow phase transition, which finally produces an abnormal EC heat flow signal. Through a Landau theory analysis, this kinetic behavior is contributed to the competition between the ferroelectric (FE) order pinned by memory behavior and the thermal agitation favored AFE state. This work deepens the understanding of the phase transition in the ferroelectric system.

Temperature variations in caves induced by atmospheric pressure variations—Part 2: Unveiling hidden thermal signals

In underground cavities, temperature variations of the order of 10−3°C are permanently induced by the variations of atmospheric pressure, even at great depths, with couplings of the order of 0.2 to 20 × 10−3°C/hPa depending on frequency. In the first part of this study, we established the atmospheric pressure to temperature transfer function (TF) as a function of frequency from 8 × 10−7 to 8 × 10−4 Hz. Here, we use this TF to calculate the expected PIT variations, which, after being subtracted from the observed time-series, provide residual temperature time-series. We calculated such temperature residuals in four natural caves in France: Esparros, Aven d'Orgnac, Pech Merle and Chauvet-Pont d'Arc Caves, the last two containing unique prehistoric wall paintings. Temperature signals, as small as a few 10−3°C, due to human presence, are then conspicuous, with evidence of relaxation longer than several days and long-term cumulative effects. In addition, we observe temperature signals suggesting non-stationary states characterized by several processes which are not necessarily easy to separate, such as transient air currents, due to barometric winds or locally semi-confined convection cells, transient infiltration, or energy dissipation by evaporation-condensation at the rock surface. This background thermal agitation displays a scale-free amplitude spectrum, from 2 × 10−5 to 4 × 10−4 Hz, of the form f−α, with α varying from 0.1 to 0.6 depending on the site. Furthermore, at the Chauvet Cave, a weak but unambiguous peak emerges during some months at a period of about 82.2 ± 0.8 minutes, suggesting a Helmholtz-type resonance. Small but significant temperature signals are therefore detected in underground cavities once the effect of atmospheric pressure variations is corrected for. These signals reveal subtle coupled processes whose knowledge is essential to evaluate preservation strategies and to establish conditions for resilience of underground systems under artificial or natural influence including climate change.

An Experimental Investigation of the Tribological Performance and Dispersibility of 2D Nanoparticles as Oil Additives

The present study aims to investigate the tribological performance of 2D nanoparticles such as graphene (G), molybdenum disulfide (MoS2), hexagonal boron nitride (hBN), and reduced graphene oxide (rGO) as gear lubricant additives. A new method of additive doping in gear lubricants was proposed and examined in terms of the degradation of lubricants. The additives were energized by ultrasonication, thermal agitation, and mechanical shearing to enhance the dispersibility and stability, which were confirmed using visual and rheological analysis. Further, the tribological performance of the nano-additives was studied by doping them in fresh lubricants, chemically degraded lubricants, and chemically degraded lubricants with surfactants. The results indicate that surface roughness and the method of mixing play a crucial role in reducing wear. The nano-additives exhibit an inverse relationship with the roughness, and their agglomeration results in a decline in performance. To mitigate agglomeration, oleic acid surfactant was employed, which diminished the effects of nano-additives and degraded the lubricant. The attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analysis revealed that the oleic acid and deteriorating reagent work synergistically, leading to enhanced wear volume and reduced friction. The nano-additives were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Overall, the study presents a comprehensive plan for new method of additive mixing, stability, dispersibility and tribological performance of the selected 2D nanoparticles.