Temperature-dependent Regimes Research Articles

Constraints on the scalar-field potential in warm inflation

We quantify the degree of fine-tuning required to achieve an observationally viable period of inflation in the strongly dissipative regime of warm inflation. The ``fine-tuning'' parameter $\ensuremath{\lambda}$ is taken to be the ratio of the change in the height of the potential $\mathrm{\ensuremath{\Delta}}V$ to the change in the scalar field $(\mathrm{\ensuremath{\Delta}}\ensuremath{\phi}{)}^{4}$, i.e., the width of the potential, and therefore measures the requisite degree of flatness in the potential. The best motivated warm inflationary scenarios involve a dissipation rate of the kind $\mathrm{\ensuremath{\Gamma}}\ensuremath{\propto}{T}^{c}$ with $c\ensuremath{\ge}0$, and for all such cases, the bounds on $\ensuremath{\lambda}$ are tighter than those for standard cold inflation by at least 3 orders of magnitude. In other words, these models require an even flatter potential than standard inflation. On the other hand for the case of warm inflation with $c<0$, we find that in a strongly dissipative regime the bound on $\ensuremath{\lambda}$ can significantly weaken with respect to cold inflation. Thus, if a warm inflation model can be constructed in a strongly dissipative, negatively temperature-dependent regime, it accommodates steeper potentials otherwise ruled out in standard inflation.

Experimental evidence for dissipationless transport of the chiral edge state of the high-field Chern insulator in MnBi2Te4 nanodevices

We demonstrate the dissipationless transport of the chiral edge state (CES) in the nanodevices of quantum anomalous Hall insulator candidate MnBi2Te4. The device presents a near-zero longitudinal resistance together with a quantized Hall plateau in excess of 0.97 h/e2 over a range of temperatures from very low up to the Neel temperature of 22 K. Each of four-probe nonlocal measurements gives near-zero resistance and two-probe measurements exhibit a plateau of +1 h/e2, while the results of three-probe nonlocal measurements depend on the magnetic field. This indicates non-dissipation as well as the chirality of the edge state. The CES shows three regimes of temperature dependence, i.e., well-preserved dissipationless transport below 6 K, variable range hopping while increasing the temperature and thermal activation at higher than 22 K. Even at the lowest temperature, a current of over 1.4 {\mu}A breaks the dissipationless transport. These form a complete set of evidences of the Chern insulator state in the MnBi2Te4 systems.

Relevance of weak and strong classical scattering for the giant negative magnetoresistance in two-dimensional electron gases

The giant negative magnetoresistance (GNMR), observed in two-dimensional electron gases of high mobility, is studied by controlled definition of additional short-range scatterers in form of two-dimensional Lorentz arrays of varying obstacle density, as well as in the presence of edge scattering. The results support models, which ascribe the temperature-independent regime of the GNMR to strong, classical scattering and the temperature-dependent regime to electron-electron interactions under the influence of mixed disorder. The threshold magnetic field, which separates the two regimes, is in rough agreement with the lower percolation transition of the Lorentz array. At large obstacle densities, interaction corrections are suppressed and memory effects become more relevant. Shape, amplitude, and width of the GNMR depend sensitively on the time scales of the contributing scattering mechanisms. This can lead to qualitatively similar shapes for quite different parameter values.

Temperature-Dependent Tunneling in Furan Oligomer Single-Molecule Junctions.

Two commonly observed charge transport mechanisms in single-molecule junctions are coherent tunneling and incoherent hopping. It has been generally believed that tunneling processes yield temperature-independent conductance behavior and hopping processes exhibit increasing conductance with increasing temperature. However, it has recently been proposed that tunneling can also yield temperature-dependent transport due to the thermal broadening of the Fermi energy of the contacts. In this work, we examine a series of rigid, planar furan oligomers that are free from a rotational internal degree of freedom to examine the temperature dependence of tunneling transport directly over a wide temperature range (78-300 K). Our results demonstrate conductance transition from a temperature-independent regime to a temperature-dependent regime. By examining various hopping and tunneling models and the correlation between the temperature dependence of conductance and molecular orbital energy offset from the Fermi level, we conclude thermally assisted tunneling is the dominant cause for the onset of temperature-dependent conductance in these systems.

Mechanical response of a metastable austenitic stainless steel under different deformation modes

The deformation behaviour of AISI 304L stainless steel was examined under uniaxial tension and shear deformation modes in the temperature range of 0–500°C. A linear relationship between the tensile and shear yield stresses was observed over the whole temperature range, which was in a good agreement with the predictions of the von-Mises criterion. The relationship between the ultimate shear and tensile strength values, however, showed three distinct temperature-dependent regimes. In the temperature ranges corresponding to the transformation-induced plasticity effect and the dynamic strain aging phenomenon, a deviation from the expected behaviour was observed, which was related to the dependency of these phenomena on the loading mode.

Evolutions of mechanical properties of AISI 304L stainless steel under shear loading

The evolutions of microstructure and mechanical properties during shear punch testing (SPT) of an AISI 304L metastable austenitic stainless steel were studied at deformation temperatures ranging from 0 °C to 550 °C and strain rates in the range of 10-3 s-1 to 1 s-1. Based on the X-ray diffraction (XRD) phase analysis and metallographic observations, it was inferred that by increasing the deformation temperature from 0 °C to 200 °C, the amount of transformed strain-induced martensite decreases at all strain rates, leading to the weakening of the transformation-induced plasticity (TRIP) effect. However, depending on the strain rate, at temperatures higher than 200 °C, an anomalous trend in shear strength was observed, i.e. the shear strength rose by increasing the deformation temperature at low strain rates, due to the dynamic strain aging (DSA) phenomenon. Strain rate sensitivity studies in conjunction with the microstructural evolutions revealed four temperature-dependent regimes: 0–200 °C, 200–300 °C, 300–500 °C and higher than 500 °C, where the respective strain rate sensitivity index (m) becomes positive, zero, negative, and then positive again. These regimes were rationalized based on the TRIP effect, DSA phenomenon, and thermally-activated dislocation glide.

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Two temperature regimes of triplet transfer in the dissociation of the correlated triplet pair after singlet fission

The ability to undergo spin-allowed exciton multiplication makes singlet fission materials promising for photovoltaic applications. Here, we examine the separation of correlated triplet pairs, 1(T…T), in polycrystalline pentacene films via temperature-dependent transient absorption spectroscopy. Single wavelength analysis reveals a profound delay in 1(T…T) dynamics. Moreover, the dynamics of 1(T…T) exhibit temperature dependence, whereas other features show no discernable temperature dependence. Previous literatures have suggested that correlated triplet separation is mediated by a thermally activated hopping process. Surprisingly, we found that the time constants governing triplet pair separation display two distinct temperature-dependent regimes of triplet transport. The high temperature regime follows a thermally activated hopping mechanism. The experimentally derived reorganization energy and electronic coupling is verified by density matrix renormalization group quantum chemical calculations. In addition, we evaluated the low temperature regime and show that the trend can be modelled by a Miller–Abrahams-type model that incorporates the effects of energetic disorder. We conclude that the correlated triplet pair separation is mediated by thermally activated hopping or a disorder driven Miller–Abrahams-type mechanism at high and low temperature, respectively. We observe that crossover between two regimes occurs ∼226 K. We find the time constant for triplet–triplet energy transfer to be 1.8 ps at ambient temperature and 21 ps at 77 K.

Downward flame spreading over electric wire under various oxygen concentrations

The downward flame spread over laboratory electric wire under various oxygen concentrations has been investigated experimentally to improve our knowledge of electric-wire combustion. Two kinds of electrical wire (low-density-polyethylene (LDPE)-insulated copper (Cu) and nickel-chrome (NiCr)) are used in this study. The oxygen concentration of the mixture stream (O2 and N2) in the test section is varied between 15 and 41 vol%. Opposed-flow velocity in the test section is fixed at 15 cm/s. For NiCr wire, the flame spread rate (Vf) and flame length (Lf) monotonically increase with oxygen concentration. For Cu wire, both Vf and Lf show non-monotonic behavior against oxygen concentration. Most interestingly, Vf decreases with oxygen concentration increase in the 25–31% range. Theoretical analysis shows two regimes of variation of Vf with oxygen concentration: the “temperature-dependent regime (TDR)” and the “negative-oxygen-dependent regime (NOR)”. The non-monotonic behavior of Vf against oxygen concentration for Cu can be explained by the controlling mechanism behind TDR and NOR. However, experimental results show one more regime above 31% oxygen concentration that cannot be explained by the theory proposed in this work, namely the “soot-generation-dependent regime (SGR)”; here, radiation from the flame and soot deposit plays a dominant role in flame spread.

Charge diffusion in homogeneous molecular chains based on the analysis of generalized frequency spectra in the framework of the Holstein model

We analyzed numerically computed velocity autocorrelation functions and generalized frequency spectra of charge distribution in homogeneous DNA sequences at finite temperature. The autocorrelation function and generalized frequency spectrum (frequency-dependent diffusion coefficient) are phenomenologically introduced based on the functional of mean-square displacement of the charge in DNA. The charge transfer in DNA was modeled in the framework of the semi-classical Holstein model. In this model, DNA is represented by a chain of oscillators placed into thermostat at a given temperature that is provided by the additional Langevin term. Correspondence to the real DNA is provided by choice of the force parameters, which are calculated with quantum-chemical methods. We computed the diffusion coefficient for all homogenous DNA chains with respect to the temperature and found a special scaling of independent variables that the temperature dependence of the diffusion coefficient for different homogenous DNA is almost similar. Our calculations suggest that for all the sequences, only one parameter of the system is mainly responsible for the charge kinetics. The character of individual motions contributing to the charge mobility and temperature-dependent regimes of charge distribution is determined.

Temperature dependence of capillary dynamics: A multiphase and multicomponent adiabatic approach

We present an analysis of the effect of the temperature on the flow of multiphase systems made of multiple miscible components in uniform cylindrical capillaries in adiabatic conditions. The temperature was explicitly included in the dynamic contact angle, tension at the three-phase contact line, and densities and viscosities of the fluids. The mathematical framework accounted for conservative forces (gravity, inertial, and interfacial tensions), nonconservative forces (viscous dissipation), and fluid retardation effects in the reservoirs at the two capillary ends. Temperature-dependent flow regimes ranged from nonoscillatory to oscillatory in a two-phase binary liquid (water-ethanol) system and in a two-phase pure liquid (ether) system. The Ca-Bo orbits highlighted dynamic attractors that depended on specific system characteristics as well as temperature. We conclude that temperature alone expresses and important role in the dynamical characteristics of capillary rise flow around its equilibrium.

Dy(III) Single-Ion Magnet Showing Extreme Sensitivity to (De)hydration

A new mononuclear dysprosium(III)-cucurbit[6]uril complex has been synthesized and characterized structurally and magnetically. It exhibits single-ion magnet (SIM) behavior with two slow magnetic relaxation processes, which are very sensitive to the solvation degree of the sample. Depending on the amount and type of the solvent in the structure, it is possible to switch the slow magnetic relaxation of this compound between the temperature-independent and temperature-dependent regimes.

Singularities in hydrophobic recovery of plasma treated polydimethylsiloxane surfaces under non-contaminant atmosphere

Herein, the hydrophobic recovery of argon plasma treated polydimethylsiloxane surfaces is explored. In contrast to previous works, environmental contamination is here taken into account. We find that diffusion and reorientation strongly dominate the hydrophobic recovery under high thermal activation (60°C), no matter the surrounding environment during storage. However, at lower temperature (24°C and below), we find that contamination plays a major role in lab atmosphere environment. By working at low temperature and under inert nitrogen atmosphere to slow down the diffusion and reorientation dynamics and to avoid contamination, we identify two different temperature-dependent regimes in the kinetics of the hydrophobic recovery. One is fast and involves exclusively relaxation processes occurring in the surface region. The second, much slower, concerns diffusion phenomena in the sub-surface region. Thereby, the specific impact of bulk diffusion and surface reorientation processes can be distinguished during aging by slowing down the surface dynamics and by eliminating all possible sources of contamination.

New constraints on megathrust slip stability under subduction zone P–T conditions

To understand and model subduction zone seismogenesis, data are needed on the frictional properties of (meta)pelitic subduction zone materials under in situ megathrust conditions. Here, we report the results of rotary shear friction experiments on simulated illite–quartz fault gouge at an effective normal stress of 170MPa, a pore fluid pressure of 100MPa, at 150–500°C and sliding velocities of 1–100μm/s. The results show three temperature-dependent regimes, characterized by velocity-strengthening at 150–250°C, velocity-weakening at 250–400°C and velocity-strengthening at 400–500°C. The regimes are defined by a decrease in the rate and state friction (RSF) parameter (a–b) at 150–300°C followed by an increase at 300–500°C. These trends correlate with systematic changes in other RSF parameters, as well as an increase in friction coefficient above 300°C. We explain the effects of increasing temperature in terms of a transition from frictional granular flow (150–250°C), through granular flow whereby dilatation is balanced by thermally activated compaction involving stress corrosion cracking (SCC) of quartz clasts (250–400°C), to non-dilatant slip on the phyllosilicates with accommodation at quartz clasts by SCC (400–500°C). Taking into account the effects of sliding velocity, the observed velocity-weakening regime broadly explains the extent of the seismogenic zone within subduction megathrusts.

Early stages of surface graphitization on nanodiamond probed by x-ray photoelectron spectroscopy

We have investigated the early stages of graphitization on detonation nanodiamond during sequential annealing treatments under vacuum using x-ray photoelectron spectroscopy. Two different temperature-dependent regimes were observed. Below 900 \ifmmode^\circ\else\textdegree\fi{}C, the nanodiamond surface reconstructs into graphitic domain but does not alter the diamond core. Above 900 \ifmmode^\circ\else\textdegree\fi{}C, graphitization, i.e., carbon hybridization changes from $s{p}^{3}$ to $s{p}^{2}$, occurs from the nanodiamond surface toward the diamond core. Graphitization is observed at much lower temperatures on nanodiamonds than on bulk diamond due to the high concentration of structural defects on their surface. These results indicate that low-temperature annealing under vacuum is an efficient method to uncouple surface and bulk graphitization. Hybrid nanocarbons formed in these conditions, constituted of a diamond core with a thin graphitic outer shell, may have interesting catalytic and chemical properties.

Effect of pH on Hydride Transfer by Escherichia coli Dihydrofolate Reductase

The kinetic isotope effect (KIE) on hydride transfer in the reaction catalysed by dihydrofolate reductase from Escherichia coli (EcDHFR) is known to be temperature dependent at pH 7, but essentially independent of temperature at elevated pH. Here, we show that the transition from the temperature-dependent regime to the temperature-independent regime occurs sharply between pH 7.5 and 8. The activation energy for hydride transfer is independent of pH. The mechanism leading to the change in behaviour of the KIEs is not clear, but probably involves a conformational change in the enzyme brought about by deprotonation of a key residue (or residues) at high pH. The KIE on hydride transfer at low pH suggests that the rate constant for the reaction is not limited by a conformational change to the enzyme under these conditions. The effect of pH on the temperature dependence of the rate constants and KIEs for hydride transfer catalysed by EcDHFR suggests that enzyme motions and conformational changes do not directly influence the chemistry, but that the reaction conditions affect the conformational ensemble of the enzyme prior to reaction and control the reaction though this route.

Post-deformational annealing at the subgrain scale: Temperature dependent behaviour revealed by in-situ heating experiments on deformed single crystal halite

The dynamics of substructures, which encompass all structures present at the subgrain-scale, were investigated by static, in-situ annealing experiments. Deformed, single crystal halite was annealed inside a scanning electron microscope at temperatures between 280 and 470 °C. Electron backscatter diffraction maps provided detailed information about crystallographic orientation changes. Three temperature dependent regimes were distinguished based on boundary misorientation changes. In regime I (280–300 °C) some low angle boundaries (LABs), i.e. with 1°–15° misorientation, increase in misorientation angle, while others decrease. In regime II (∼300 °C) all LABs undergo a decrease in misorientation angle. Regime III (>300 °C) is defined by enhancement of the subgrain structure as remaining LABs increase and some undergo a rotation axis change. Throughout regimes I and II, new LABs develop, subdividing subgrains. LABs could be divided into four categories based on annealing behaviour, orientation and morphology. We suggest that these observations can be directly related to the mobility and activation temperature of climb of two dislocation groups introduced during deformation. Therefore, with in-depth investigation of a substructure with known deformation geometry, we can infer ratios of dislocation types and their post-deformation and post-annealing location. These can potentially be used to estimate the post-deformational annealing temperature in crystalline materials.

Thermodynamics of Adsorption of Imidacloprid at Constant Charge Hydrophobic Surfaces: Physicochemical Aspects of Bioenvironmental Activity

Adsorption of the insecticide 1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine (Imidacloprid) on the hanging mercury drop electrode (HMDE) surface was studied by temperature-dependent stripping voltammetry (TD-SV). At near physiological pH, under reducing conditions, the Gibbs free energy of adsorption, DeltaGADS, shows two distinct temperature-dependent regimes. (a) At 0 degrees < T < 10 degrees C a temperature-independent mechanism occurs with a constant DeltaGADS = -40.5 kJ/mol, resulting in strong chemisorption at high surface coverage. For T < 10 degrees C a considerable enthalpy gain is estimated, and this represents the driving force for the adsorption of Imidacloprid onto the electrode surface. (b) At T > 10 degrees C a temperature-dependent mechanism is operative with DeltaGADS/DeltaT = -91.4 J/K mol, resulting in a rapid weakening of adsorption and low surface coverage. On the basis of the present findings we suggest that the strong chemisorption at T < 10 degrees C at physiological pH under reducing conditions is related to the high specific insecticide activity of Imidacloprid in cool-blooded insects as contrasted to its low efficiency in warm-blooded organisms.