Thermal Agitation Research Articles

Take time to look at the fish: Behavioral response to acute thermal challenge in two Amazonian cichlids.

Critical thermal maximum (CTmax ) is often used as an index of upper thermal tolerance in fishes; however, recent studies have shown that some fishes exhibit agitation or avoidance behavior well before the CTmax is reached. In this study, we quantified behavioral changes during CTmax trials in two Amazonian cichlids, Apistogramma agassizii and Mesonauta insignis. The thermal agitation temperature (Tag ) was recorded as the temperature at which fish left cover and began swimming in an agitated manner, and four behaviors (duration of sheltering, digging, activity, and aquatic surface respiration [ASR]) were compared before and after Tag . Both A. agassizii and M. insignis exhibited high critical thermal maxima, 40.8°C and 41.3°C, respectively. Agitation temperature was higher in M. insignis (37.3°C) than in A. agassizii (35.4°C), indicating that A. agassizii has a lower temperature threshold at which avoidance behavior is initiated. Activity level increased and shelter use decreased with increased temperatures, and patterns were similar between the two species. Digging behavior increased after Tag in both species, but was higher in A. agassazii and may reflect its substrate-oriented ecology. ASR (ventilating water at the surface film) was extremely rare before Tag , but increased in both cichlid species after Tag and was greater in M. insignis than in A. agassizii. This suggests that fish were experiencing physiological hypoxia at water temperatures approaching CTmax . These results demonstrate that acute thermal challenge can induce a suite of behavioral changes in fishes that may provide additional, ecologically relevant information on thermal tolerance.

Emergent electromagnetic induction beyond room temperature

Emergent electromagnetic induction based on electrodynamics of noncollinear spin states may enable dramatic miniaturization of inductor elements widely used in electric circuits, yet the research is still in its infancy and many issues must be resolved toward its application. One such problem is how to increase working temperature to room temperature, and possible thermal agitation effects on the quantum process of the emergent induction are unknown. We report here large emergent electromagnetic induction achieved around and above room temperature, making use of a few tens of micrometer-sized devices based on the high-temperature (up to 330 K) and short-period (≤ 3 nm) spin-spiral states of a metallic helimagnet. The observed inductance value L and its sign are observed to vary to a large extent, depending not only on the spin-helix structure controlled by temperature and applied magnetic field but also on the applied current density. The present finding on room-temperature operation and possible sign control of L may provide a step toward realizing microscale quantum inductors on the basis of emergent electromagnetism in spin-helix states.

The coupled heat Maxwell equations with temperature-dependent permittivity

We consider the heat equation coupled with the Maxwell system, the Ampère-Maxwell equation being coupled to the heat equation by the permittivity, which depends on the temperature due to thermal agitation, and the heat equation being coupled to the Maxwell system by the volumic heat source term. Our purpose is to establish the existence of a local-in-time solution to this coupled problem. Firstly, fixing the temperature distribution, we study the resulting Maxwell system, a nonautonomous system due to the dependence of the permittivity on the temperature and consequently on time, by using the theory of evolution systems. Next, we return to our coupled problem, introducing a fixed-point problem in the closed convex set K(0;R):={z∈B¯(0;R);z(0)=0} of the Banach space C1([0,T];C1(Ω¯)) and proving that the hypotheses of Schauder's theorem are verified for R sufficiently large. The construction of the fixed-point problem is nontrivial as we need K(0;R) to be stable.

A novel method for removing Rician noise from MRI based on variational mode decomposition

MRI is a highly efficient medical imaging modality that captures all the delicate structural features of human tissues and organs enabling accurate clinical diagnosis. The noise occurred during image acquisition and transmission degrades these structural features and misleads the clinical diagnosis. Rician is the thermal noise found in MRI due to the thermal agitation of electrons. The main objective of the proposed work is to eliminate the Rician noise characteristics from the MRI. The proposed method effectively utilizes the properties of an efficient decomposition technique called variational mode decomposition (VMD). The proposed denoising method is performed in two stages. The high-frequency modes from the decomposed image are discarded and the denoised image is reconstructed from the low-frequency modes. The total variation (TV) image smoothing based on non-convex optimization is performed in the second stage for removing the remnant noise details from the first stage. The effectiveness of the proposed work is confirmed based on the improved peak signal to noise ratio (PSNR), stuctural similarity index measure (SSIM), quality index based on local variance (QILV) and Bhattacharrya coefficient (BC) scores. The proposed method is compared with different existing denoising methods. The experiment is conducted on two different datasets such as simulated Brainweb database and clinical dataset. Based on the comparative experimental analysis, the effectiveness of the proposed VMD-TV is confirmed by the improved objective performance metrics. In addition to objective quality assessments, the subjective evaluations carried out by radiologist and neurologists show the relatively better visual quality of the proposed method compared to the methods such as linear minimum mean square error (LMMSE) and bilateral filtering (BF).

Spectral Analysis of ATP-Dependent Mechanical Vibrations in T Cells.

Mechanical vibrations affect multiple cell properties, including its diffusivity, entropy, internal content organization, and thus—function. Here, we used Differential Interference Contrast (DIC), confocal, and Total Internal Reflection Fluorescence (TIRF) microscopies to study mechanical vibrations in live (Jurkat) T cells. Vibrations were measured via the motion of intracellular particles and plasma membrane. These vibrations depend on adenosine triphosphate (ATP) consumption and on Myosin II activity. We then used spectral analysis of these vibrations to distinguish the effects of thermal agitation, ATP-dependent mechanical work and cytoskeletal visco-elasticity. Parameters of spectral analyses could be related to mean square displacement (MSD) analyses with specific advantages in characterizing intracellular mechanical work. We identified two spectral ranges where mechanical work dominated vibrations of intracellular components: 0–3 Hz for intracellular particles and the plasma-membrane, and 100–150 Hz for the plasma-membrane. The 0–3 Hz vibrations of the cell membrane that we measured in an experimental model of immune synapse (IS) are expected to affect the IS formation and function in effector cells. It may also facilitate immunological escape of extensively vibrating malignant cells.

Coping with climate change: Phenotypic plasticity in an imperilled freshwater fish in response to elevated water temperature

Abstract Climate change has emerged as an increasingly important threat to freshwater systems. To cope with rapidly changing thermal regimes, freshwater fishes must either relocate or adjust through genetic adaptation and/or phenotypic plasticity. Short‐term responses to elevated water temperature have been well studied in freshwater fishes; however, far less is understood about change induced by long‐term exposure. Furthermore, few studies have investigated the effects of temperature on already imperilled species, which may be more sensitive to environmental change. This study investigated the effects of rearing temperature on critical thermal maximum (CTmax), agitation temperature (Tag, temperature at which fish show behavioural signs of thermal stress) and gill size in pugnose shiner, Notropis anogenus, a threatened species in Canada. Juvenile pugnose shiner were reared for 4 months across five different ecologically relevant temperatures. CTmax and Tag were measured under normoxia and acute exposure to hypoxia to test for oxygen sensitivity of the upper thermal limits in this species. CTmax increased with elevated water temperature. Tag also increased with rearing temperature and occurred, on average, 4.3°C above acclimation temperatures. The CTmax and Tag were lower when fish were exposed acutely to hypoxia. Interestingly, gill size (e.g. total gill filament length) increased with rearing temperature, which may increase oxygen uptake capacity and support increased metabolic demands of warmer waters. Overall, pugnose shiner show plasticity in several traits in response to long‐term exposure to elevated water temperature that may facilitate persistence in warmer waters. However, acute hypoxia exposure reduced thermal tolerance, stressing the importance of evaluating interactive effects of multiple stressors. Identifying source populations of pugnose shiner with greater thermal tolerance or implementing captive breeding under higher temperature regimes may improve the success of re‐introduction efforts in the face of climate change, but the consequences to fitness of increased thermal tolerance should be examined.

Pinning-assisted out-of-plane anisotropy in reverse stack FeCo/FePt intermetallic bilayers for controlled switching in spintronics

We study the implications of FeCo underlayer and overlayer on the static and dynamic magnetic properties of FeCo/FePt exchange spring system along with post-annealing kinetics. Probing of FePt/FeCo/Si and FeCo/FePt/Si bilayers using high energy synchrotron X-ray diffraction by varying glancing angles unveiled structural variations at the interface, where FeCo is observed to inhibit the crystalline growth of FePt. A soft ferromagnetic in-plane behavior and defect-driven hard ferromagnetic properties in the out-plane configuration are established. Besides, the magnetization dynamics studied by Ferromagnetic Resonance depicts an out-plane magnetization component of FePt only in FeCo/FePt/Si. X-ray Absorption Spectroscopy (XAS) in the Fe, Co and Pt L-edge regions reveal dissimilar interfaces in the two series due to thermal agitation effects. XAS spectra at Fe and Co K-edges ensure similar local coordination of Co immaterial of stack order, contrary to altered local geometry of Fe observed in the two series ascribed to varied crystallinity of FePt. Such structures are useful for spin-wave assisted low field magnetization switching in highly coercive FePt by using exchange coupled soft FeCo.

Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators

Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators

Inertial magnetization dynamics of ferromagnetic nanoparticles including thermal agitation

The appropriate magnetic Langevin equation, namely the inertial Landau-Lifshitz-Gilbert equation augmented by thermal noise, is written starting from an analogy with the dynamics of the magnetic dipole moment of a circular current-carrying loop (wire) viewed as a symmetric top. Hence the corresponding Fokker-Planck equation for the evolution of the probability density function in the phase space of angular velocities and orientations and its stationary solution are derived. Moreover, the inertial stochastic magnetization dynamics of ferromagnetic nanoparticles is also seen to be analogous to the stochastic dynamics of the electric dipole moment of a polar molecule visualized as a dipole lying along the axis of symmetry of a symmetric top ignoring friction about that axis--a conclusion reached by replacing electrical parameters with their magnetic analogs in the respective Langevin equations. Therefore, existing results from gyroscopic theory, as applied to dielectric relaxation of polar molecules, may with appropriate modifications be used to study inertial magnetization effects in ferromagnetic nanoparticles.

Corrections to: Heat transfer of dry granular materials in a bladed mixer: Effect of thermal properties and agitation rate

Corrections to: Heat transfer of dry granular materials in a bladed mixer: Effect of thermal properties and agitation rate

Analysis of temperature dependence in ferrofluid optical transmission dynamics after magnetic field commutation

The influence of temperature on the ferrofluid magneto-optical response after magnetic field commutation is studied. Its contribution to the diffusion and mobility of the ferrofluid nanoparticles is considered by means of thermal agitation and the temperature-dependent viscosity of the fluid. Experimental responses after magnetic field switch on and off show a significant dependence on temperature. Taking into account both mentioned thermal influences, a qualitative description is provided, in which viscosity turns out to play an important role. In addition, a model based on an adaptation of a paramagnetic gas theory is used to analyze the transmission relaxation evolution after magnetic field switch off. The results are in good agreement with the experimental measurements, demonstrating the validity of this adaptation to consider the temperature dependence of this response.

Effects of Gd2O3 doping on the structure and the conduction mechanism of K2Mg2(SO4)3 langbeinite ceramics: A comparative study

A Gd2O3 with its ‘x’ doping rate in the langbeinite matrix and denoted as KMgSGd (x = 0.2, 0.5, 1 mol%) was synthesized at high temperature via the solid state reaction method. Pure phases were successfully obtained in their simple cubic system with the P213 space group. Gd3+ can effectively replace Mg2+ in the host matrix of langbeinite without any deformation of the structure. KMgSGd (x = 0.5 mol%) was selected as the best ionic conductor because of its low activation energy which has a value of 0.29 eV. Conduction within these materials is done by migration of mobile cations with thermal agitation and it is explained by the CBH (Correlated Barrier Hopping) model. KMgSGd materials are proposed as being useful in the energy storage field and for optical applications in various devices.

Investigation on the Linear and Nonlinear Properties of Morin in Presence of Reverse Micelle and Different Oil Content in Reverse Micelle.

We investigate the linear and nonlinear optical property of Morin (MN) at different concentration (1 × 10-6 and 5 × 10-6M) within AOT reversed micelle prepared by water-in-decane microemulsion having a constant molar ratio of water-to-surfactant molecules of 40 (W = [H2O]/[AOT] = 40) as well as the function of mass fraction of nano-droplet (MFD) values of 0.01,0.04, 0.07, and 0.1 by using UV-Visible, Fluorescence, FTIR, and Z-scan techniques. The steady-state measurement indicates that the presence of microenvironment can greatly affect the tautomeric structure of morin and also Morin property in microenvironment depends upon the amount of oil and Morin concentration. The increase in dipole moment from the ground state to excited state in microenvironment indicate the change in the molecular structure on morin. Morin does not show any nonlinear absorption property but the nonlinear refractive index is observed as a function of Morin concentration as well as MFD values which are due to the thermal agitation of formed dimers. Morin nonlinearity.

Thermal-induced unfolding-refolding of a nucleocapsid COVN protein

Unfolding of a coarse-grained COVN protein from its native configuration shows a linear response with increasing temperature followed by non-monotonic double peaks in its radius of gyration. The protein conforms to a random coil of folded segments in native state with increasingly tenuous and globular structures in specific temperature regimes where the effective dimensions of corresponding structures D ≈ 1.6–2.4. Thermal agitation alone is not sufficient to fully eradicate its segmental folding as few local folds are found to persist around such residues as 65L, 110Y, 224L, 374P even at high temperatures.

Theoretical assessment of the adsorption mechanism of ibuprofen, ampicillin, orange G and malachite green on a biomass functionalized with plasma

Theoretical assessment and interpretation of the adsorption mechanisms of pharmaceuticals (ibuprofen and ampicillin) and dyes (orange G and malachite green) on a biomass functionalized with a plasma treatment are reported in this paper. This theoretical study was performed via a double-layer adsorption model that was formulated from statistical physics. Modeling results indicated that the adsorption of tested organic adsorbates was affected by the molecular aggregation in the aqueous solution, which depended on the adsorption temperature. These molecules were adsorbed on the functionalized biomass surface via a non-flat orientation (i.e., they interacted with one functional group) at tested operating conditions where thermal agitation and steric hindrance could play a relevant role during the adsorption. Cocoa shell functionalized with plasma showed the highest adsorption for dyes especially orange G at 298 K. Adsorption capacities ranged from 10.32 to 26.14 mg/g, 10.54–15.55 mg/g, 6.31–13.76 mg/g and 4.2–6.54 mg/g for orange G, malachite green, ibuprofen and ampicillin, respectively. Exothermic adsorption energies were calculated for tested adsorbate molecules, which ranged from −10.17 to −18.11 kJ/mol thus indicating that physical forces were involved in the removal of these water pollutants. This study contributes to understand the physicochemical parameters that governed the adsorption of organic molecules on surface functionalized with plasma, which is an alternative for water treatment and purification.

Two-lattice-vibration theory for proton transfer in cubic perovskites: Barium zirconate versus potassium tantalate

Proton transfer (PT) in proton-conducting oxides is an intrinsically quantum phenomenon, due to the very strong quantization of the OH stretching vibration (ℏω~ 0.4 eV). Up to high temperatures, the proton is frozen in the ground state associated with the OH stretching motion, and thus does not undergo the thermal agitation for this vibration. Therefore, these are the thermal fluctuations of the (heavier) lattice atoms which make PT possible, at least above ~ half the Debye temperature of the lattice. These fluctuations may occasionally and randomly produce specific lattice configurations in which the quantum protonic ground levels in the two wells are equalized (coincidence), making PT possible, however with a certain probability. An analytical expression of this transfer probability may be obtained as the solution of a curve-crossing quantum-mechanical problem, and thus described by the Landau-Zener (LZ) formula. Two lattice vibrations play a fundamental role in intra-octahedral PT: (i) a reorganization of the lattice, that sends the protonated system from its initial self-trapped configuration up to the coincidence manifold, and (ii) a reduction of the (donor) oxygen - (acceptor) oxygen distance Q, which facilitates PT by leading the system to coincidence configurations with smaller proton barrier, and thus larger LZ probability. In cubic perovskites, the set of the coincidence configurations plays the role of the transition state for PT. The implementation of this theory of proton transfer [G. Geneste, Solid State Ionics 323, 172 (2018)] is here strongly improved on several points: description of the coincidence configurations, proton zero-point energies and proton potential at coincidence. It is then re-applied to barium zirconate (BZO), and also to potassium tantalate (KTO), with parameters derived from density-functional theory (DFT) calculations. The theory confirms the adiabatic PT regime in BZO, common to most proton conductors, with a negligible contribution of non-adiabatic tunneling transfers to the transfer rate. In KTO, by contrast, the relative contribution of non-adiabatic tunneling transfers is larger than in BZO, especially below ~ 250–300 K. The present work helps to characterize intrinsic features common to most proton conductors, at least from the point of view of proton mobility within the lattice. The activations energies for proton transfer at high temperature are predicted at 0.11 eV (BZO) and 0.25 eV (KTO).

Numerical modeling and MHD stagnation point flow of ferrofluid (non-Newtonian) with Ohmic heating and viscous dissipation

Ferroliquids are made out of exceptionally tiny nanoscale particles (usually diameter 10 nanometers or less) of hematite, magnetite or some other compound comprising iron and a liquid. This is small enough for thermal agitation to scatter them equally inside a transporter liquid, and for them to contribute to general magnetic response of the liquid. The composition of the typical ferroliquid is about 5% magnetic solids, 10% surfactant and 85% carrier by volume. There are frequent applications of ferrofluids in mechanical and industrial engineering. Ferrofluids have innovative characteristics and their impact in magnetic fields prompts many fascinating applications. Albeit magnetic liquids are already utilized in certain devices they have not yet been abused to any level. It is trusted that this research communication may investigate the analyst to think of considering new uses for this entrancing material. Therefore, modeling is developed for the ferrofluid stagnation flow over a stretched surface with Ohmic heating and dissipation. The Tiwari–Das model is used for mathematical modeling of nanofluid. The nonlinear system of differential equations is first converted into first order and then tackled through the built-in-Shooting method. The impact of the different pertinent flow parameters is discussed on the velocity, temperature, Nusselt number and skin friction coefficient through the various plots and tables.

Recovering magnetic domains of nanoscale-mechanically damaged ferromagnetic thin film of information data storage

Combined effects of stress and temperature on magnetic domains and scratch morphology of the ferromagnetic film of a perpendicular magnetic recording media are investigated using nanoscratch, atomic force microscope, and magnetic force microscope. The stored magnetic signals in the non-scratched area become weak with increasing temperature due to the thermal agitation of magnetic spins. The high local stress permanently damages the magnetic signals at the scratch center. However, the weakened magnetic signals at lightly stressed regimes recover significantly with increasing temperature up to 300 °C due to the partial recovery of ferromagnetism. Regarding the nanoscratch morphology, when the temperature increases up to 300 °C, the scratch is healed noticeably due to metal oxides (CoO, Cr2O3, and PtO2) built-up on the scratched surface. Surprisingly, the scratch deepens at 400 - 600 °C. This is attributed to PtO2 evaporation and the phase transition of magnetic grains from HCP to FCC.

Nucleophilic substitution reaction mechanisms: An atomic-molecular perspective on chemical speciation and transport properties in silicate melts

There has been no systematic attempt to determine if nucleophilic substitution (SN) reactions proceed in silicate melts, even though they commonly occur in gaseous and liquid phases containing C, Si, P, and Ge centered tetrahedra. The oversight is here rectified by providing such an analysis. Conditions required for nucleophilic substitution reactions to occur are: (1) the presence of nucleophiles (Lewis bases) which in silicate melts are bridging oxygen (BO), non-bridging oxygen (NBO−) and free oxygen (O2−); (2) the presence of tetrahedra (Q species) with strongly electrophilic centers (i.e., Si atoms); (3) the presence of Si transition species containing pentahedrally coordinated Si (i.e., VSi species); (4) rapid reaction rates among tetrahedral species. All conditions are met for silicate melts. For example, the strong nucleophile, NBO− exists at high temperatures in binary alkali and alkaline earths silicate melts due primarily to thermal agitation whereby some Si-NBO-M bonds are ruptured to produce the nucleophilic Si-NBO− moiety. This nucleophile attacks the Si center of an adjacent tetrahedron to form a SiO bond thereby producing a VSi transition species. The transition species decomposes by rupture of another SiO bond located on the polar opposite side of the transition species. Three types of SN reaction are recognized and all involve VSi transition species. They are NBO-BO exchange reactions (e.g., Q3 + Q4 → Q4 + Q3), disproportionation reactions (e.g., 2Q3 → Q4 + Q2) and polymerization reactions (e.g., Q3 → Q4 + 1/2O2−). H2O and OH− are also nucleophiles and their reaction with Q species proceeds via SN reaction mechanisms, and may cause depolymerization of melts. Hydrogen bonding of H2O to BO and NBO may also occur, as in ice and water, thereby enhancing H2O solubilities in melts. These latter reactions should neither depolymerize melts nor affect NBO/T values.The diffusivity of Si and O in melts, anionic conductivity and chemical speciation (e.g. Q species abundances) proceed via one or other SN reaction, with the transition species assuming a critical role in diffusivity, conductivity and viscosity. The SN reaction mechanism, coupled with transition state theory, provides explanations for: (1) the formation of pentahedrally coordinated Si (VSi) and its apparent restriction to highly siliceous glasses; (2) the remarkably similar diffusivities of Si and O in silicate melts; (3) the ‘jump distance’ (α) of the Eyring equation, which by the SN mechanism is ~3.5 Å (i.e., diameter of the VSi transition species); (4) the minimum number of monomeric units (i.e., Q species) involved in the ‘cooperative region’ of the Adam-Gibbs equation; and (5) the quantitative distribution of Q species in Na silicate glasses up to ~50 mol% Na2O.

Temperature and magnetic field dependent behavior of atomic-scale skyrmions in Pd/Fe/Ir(111) nanoislands

The thermal stability of atomic-scale skyrmions is of high relevance for potential spintronics applications and validation of theoretical models. We investigated Pd/Fe nanoislands on an Ir(111) substrate as a function of temperature and magnetic field. Utilizing noncollinear magnetoresistance contrast in scanning tunneling microscopy, the thermomagnetic phase space is explored up to 3 T within a temperature range between 1 K to 100 K. Evidence is found for the spin spiral, field-polarized, and fluctuating disordered magnetic phases. Evidence for the presence of atomic-scale skyrmions at up to approximately 80 K is found, irrespective of considerable magnetization dynamics arising from thermal agitation.