Simple Temperature Dependence Research Articles

Analytic models for organic field-effect transistors based on exponential and power mobility models

The fundamental I–V formula of an organic field effect transistor (OFET) is improved to overcome the divergence of the integrand, so it is very convenient for both numerical calculations and analytic derivations. The analytic I–V formulae are derived based on the exponential mobility model and power-function mobility model, respectively, and the derived analytic formulae are applied to three OFET devices. The results calculated from the reformulated analytic I–V formulae taking in exponential and power function mobility models are all in good agreement with the experimental I–V data. The parameters μ 0 and γ that are extracted from the mobility model and fitted by experimental data show simple Arrhenius temperature dependence and inverse linear relationship with temperature, respectively. These findings are very useful for practical applications and device simulations.

ON THE PHYSICAL NATURE OF SUBJECTIVE PSYCHOLOGICAL TIME

A simple temperature dependence of rate changing a psychological time tps(tС) in human was suggested: (∂tps/∂Sps)=Dps·δТ, where Dps is some cоnstant, Sps is the psychological entropy, characterizing current human physical/mental state; δТ is the normalized body temperature δТ=(tС – tСn), tС – the now temperature and tСn – the normal temperature. This dependence as an empirical result of personal experience in “perception” of time intervals (~10 min) at high body temperature (tС ≥38.20С) was ascertained. It has been shown the determining factor to successfully finding the task of quantitatively estimating a duration and changing rate of the psychological time there is cooperation of two thinking components – consciousness and subconsciousness. The optimal physical conditions for involving the subconscious results in significant strengthening of the brain capacity (synergy effect) were found out. The possible application of the formulas obtained for analyzing the changes of psychological time with temperature and entropy was suggested. Using on the calculations performed the graphical temperature dependences δТ, δtps (Dps ·∆Sps) were plotted, that confirmed the expected growth of these parameters.

Long Wavelength Thermal Density Fluctuations in Molecular and Polymer Glass-Forming Liquids: Experimental and Theoretical Analysis under Isobaric Conditions.

We establish via an in-depth analysis of experimental data that the dimensionless compressibility (proportional to the dimensionless amplitude of long wavelength thermal density fluctuations) of one-component normal and supercooled liquids of chemically complex nonpolar and weakly polar molecules and polymers follows extremely well a surprisingly simple and general temperature dependence over an exceptionally wide range of pressures and temperatures. A theoretical basis for this behavior is shown to exist in the venerable van der Waals model and its more modern interpretations. Although associated hydrogen-bonding (and to a lesser degree strongly polar) liquids display modestly more complex behavior, rather simple temperature and pressure dependences are also discovered. A new approach to collapse the temperature- and pressure-dependent dimensionless compressibility data onto a master curve is formulated that differs from the empirical thermodynamic scaling approach. As a practical matter, we also find that the dimensionless compressibility scales well as an inverse power law with temperature with an exponent that is system dependent and decreases with pressure. At very high pressures and low temperatures, the thermal liquid behavior appears to approach (but not reach) a repulsion-dominated random close packing limit. All these findings are relevant to our recent theoretical work on the problem of activated relaxation and vitrification of supercooled molecular and polymeric liquids.

Surviving winter: Physiological regulation of energy balance in a temperate ectotherm entering and exiting brumation

Characterizing the physiological response to prolonged cold exposure is essential for understanding the maintenance of long-term energy balance. As part of their natural life cycle, temperate ectotherms are often exposed to seasonal variation in temperatures, including extended periods of cold well below their activity range. Relatively little is known about variation in physiological responses as vertebrate ectotherms enter and exit brumation in response to sustained cold temperatures. We tested the influence of temperature on physiology before, during, and after a simulated brumation in the checkered garter snake (Thamnophis marcianus), a widespread ectothermic vertebrate. We tested for the relative effect of immediate temperature and physiological context (entering or exiting brumation) on hormones regulating energy balance, indicators of energy availability, and resting metabolic rate (V̇O2). Plasma corticosterone, glucose, and insulin, as well as immune cell heterophil: lymphocyte ratios responded to temperature, though they did so with different thermal response curves. Thermal sensitivity varied both among and within physiological measures depending on whether animals were going into or coming out of brumation. Additionally, V̇O2 was regulated beyond simple temperature-dependence, whereby post-brumation measures were depressed relative to pre-brumation measures at the same temperature. This pattern was characterized by a change in the temperature coefficient (Q10), with a larger pre-brumation Q10, suggesting reduced thermal sensitivity of metabolic rate following a period of extended cold exposure. The integrated physiological response presented here demonstrates not only temperature dependence across physiological axes, but seasonal variation in thermal responsiveness. Our results suggest that energy allocation decisions and hormonal regulation of underlying processes promote differing levels of thermal sensitivity when entering or exiting brumation.

Kinetics of first-order phase transitions from microcanonical thermostatistics

More than a century has passed since van’t Hoff and Arrhenius formulated their celebrated rate theories, but there are still elusive aspects in the temperature-dependent phase transition kinetics of molecular systems. Here I present a theory based on microcanonical thermostatistics that establishes a simple and direct temperature dependence for all rate constants, including the forward and the reverse rate constants, the equilibrium constant, and the nucleation rate. By considering a generic model that mimic the microcanonical temperature of molecular systems in a region close to a first-order phase transition, I obtain shape-free relations between kinetics and thermodynamics physical quantities which are validated through stochastic simulations. Additionally, the rate theory is applied to results obtained from protein folding and ice nucleation experiments, demonstrating that the expressions derived here can be used to describe the experimental data of a wide range of molecular systems.

Temperature dependence of double Shockley stacking fault behavior in nitrogen-doped 4H-SiC studied by in-situ synchrotron X-ray topography

We observed the behavior of double Shockley stacking faults (DSFs) in 4H-SiC crystals with nitrogen concentrations of 1.0 × 1019–2.6 × 1019 cm−3 over an extensive temperature range (1380–1910 K) by in-situ synchrotron X-ray topography. For a nitrogen concentration of 2.6 × 1019 cm−3, the expansion velocity of the DSFs exponentially increased with temperature in the range from 1370 to 1650 K. In contrast, at a nitrogen concentration of 1.0 × 1019 cm−3, this velocity decreased above 1610 K and the DSFs shrank above 1730 K. The DSF energy, the magnitude of which is the driving force on partial dislocation (PD) movement, was quantitatively estimated from the radius of the curvature of bowed-out partial PDs pinned by threading screw dislocations (TSDs), showing a positive temperature dependence and lying in the range from −0.6 to 0.8 mJ/m2 for 1630–1910 K at a nitrogen concentration of 1.0 × 1019 cm−3. The DSF expansion and shrinkage behavior can be understood by the simple temperature and nitrogen concentration dependence of the DSF energy.

NMR Shift and Relaxation and the Electronic Spin of Superconducting Cuprates

Very recently, by inspecting large sets of data across all families of superconducting cuprates, it became obvious that the prevailing nuclear magnetic resonance (NMR) interpretation of cuprate properties is not adequate, as it does not account for the differences between the families, as well as common characteristics beyond simple temperature dependence. From the most abundant planar Cu shift data, one concludes readily on two electronic spin components with different doping and temperature dependencies. Their uniform response that causes NMR spin shifts consists of a doping-dependent component due to planar O, and another due to spin in the planar copper 3d(x2 − y2) orbital, where the latter points opposite the field direction. Planar Cu relaxation was found to be rather ubiquitous (except for La2−xSrxCuO4), and Fermi liquid-like, i.e., independent of doping and material, apart from the sudden drop at the superconducting transition temperature, Tc. Only the relaxation anisotropy is doping and material dependent. We showed previously that one can understand the shifts within a two-component scenario, but we failed with a model to account for the relaxation. Here, we suggest a slightly different shift scenario, still based on the two components, by introducing different hyperfine couplings, and, importantly, we are able to account for the Cu nuclear relaxation and its anisotropy for all materials, including also La2−xSrxCuO4. The results represent a solid framework for theory.

Temperature Dependence of Double Shockley Stacking Fault Behavior in Nitrogen-Doped 4h-Sic Studied by In-Situ Synchrotron X-Ray Topography

We observed the behavior of double Shockley stacking faults (DSFs) in 4H-SiC crystals with nitrogen concentrations of 1.0×1019-2.6×1019 cm−3 over an extensive temperature range (1380-1910 K) by in-situ synchrotron X-ray topography. For a nitrogen concentration of 2.6×1019 cm−3, the expansion velocity of the DSFs exponentially increased with temperature for temperatures in the range from 1370 to 1650 K. In contrast, at a nitrogen concentration of 1.0×1019 cm−3, this velocity decreased above 1610 K and the DSFs shrank above 1730 K. The DSF energy, considered to be the driving force for DSF expansion, was quantitatively estimated from the radius of the curvature of bowed-out partial dislocations (PDs) pinned by threading screw dislocations (TSDs), showing a positive temperature dependence and lying in the range from −0.6 to 0.8 mJ/m2 at a nitrogen concentration of 1.0×1019 cm−3. The DSF expansion and shrinkage behavior can be understood by the simple temperature and nitrogen concentration dependence of the DSF energy.

Conductivity equations of protons transporting through 2D crystals obtained with the rate process theory and free volume concept

The Eyring’s rate process theory and free volume concept are employed to treat protons (or other particles) transporting through a 2D (two dimensional) crystal like graphene and hexagonal boron nitride. The protons are assumed to be activated first in order to participate conduction and the conduction rate is dependent on how much free volume available in the system. The obtained proton conductivity equations show that only the number of conduction protons, proton size and packing structure, and the energy barrier associated with 2D crystals are critical; the quantization conductance is unexpectedly predicted with a simple Arrhenius type temperature dependence. The predictions agree well with experimental observations and clear out many puzzles like much smaller energy barrier determined from experiments than from the density function calculations and isotope separation rate independent of the energy barrier of 2D crystals, etc. Our work may deepen our understandings on how protons transport through a membrane and has direct implications on hydrogen related technology and proton involved bioprocesses.

Continuous liquid level detection based on two parallel plastic optical fibers in a helical structure

A simple and low-cost continuous liquid-level sensor based on two parallel plastic optical fibers (POFs) in a helical structure is presented. The change in the liquid level is determined by measuring the side-coupling power in the passive fiber. The side-coupling ratio is increased by just filling the gap between the two POFs with ultraviolet-curable optical cement, making the proposed sensor competitive. The experimental results show that the side-coupling power declines as the liquid level rises. The sensitivity and the measurement range are flexible and affected by the geometric parameters of the helical structure. A higher sensitivity of 0.0208 μW/mm is acquired for a smaller curvature radius of 5 mm, and the measurement range can be expanded to 120 mm by enlarging the screw pitch to 40 mm. In addition, the reversibility and temperature dependence are studied. The proposed sensor is a cost-effective solution offering the advantages of a simple fabrication process, good reversibility, and compensable temperature dependence.

Isothermal Pearlite Formation Kinetics in High-Chromium Cast Irons without Additional Alloying

A model of isothermal pearlite reaction kinetics in high-carbon ternary Fe–Cr–C alloys (cast irons) containing (Cr, Fe)7C3 carbide phase is presented. The model is based on traditional Avrami approach completed with a simple type temperature dependence of K coefficient. The model parameters for individual alloys were determined from F. Maratray and R. Usseglio-Nanot’s experimental data covering composition range from 2.1 to 4.3 %C and from 12 to 26 %Cr. The dependence of parameters (Avrami exponent n, activation energy U and time-scale constant C) on gamma phase composition by the end of austenitization (calculated with account for kinetics of carbide dissolution) is determined. The model thus permits to calculate the isothermal pearlite Ccurve (TTT diagram) for an alloy of arbitrary composition after given austenitization regime. The comparison of calculation results to experimental data shows their sufficient correlation.

Improved methodology to quantify the temperature sensitivity of the soil heterotrophic respiration in croplands

Soil heterotrophic respiration (RH) is usually modeled using simple temperature dependence equations where the temperature sensitivity of RH could vary for different soils and climate conditions. The temperature sensitivity is expressed as a function of the base rate of heterotrophic respiration (RH−0) and the respiration change rate over a 10°C temperature shift (Q10). A methodology was developed to better quantify these two parameters, and was validated using seven contrasting year-site soil respiration datasets collected in wheat fields. The data were acquired using soil respiration chambers and eddy flux towers in three mid-latitude European sites and one North American site. The first step consisted in parameterizing and initializing a semi-mechanistic process-based model then validating the prediction performance using 2/3 of the datasets. The coefficient of determinations between the predictions and the observations of daily soil respiration (Rs) was 0.71 and was 0.73 for its heterotrophic component (RH). The second step consisted in using the daily semi-mechanistic model predictions of RH for each growing season and site to calibrate a simple empirical model describing RH response to soil temperature and water content. It was shown with the contrasting years-sites that coherent results were only obtained when a common average Q10 value was determined prior to fit the base rate of heterotrophic respiration coefficient. Using a common Q10 value of 2.2 provided more stable RH−0 for each site over time. It reflected the strong relationship between the RH−0 and the slow decomposing C in the first 30-cm soil layer. The simple empirical model, which was validated using 1/3 of the data, explained between 42% and 92% of the variability of RH over the different sites.

Variational approach to renormalized phonon in momentum-nonconserving nonlinear lattices

In this letter, we extend a previously proposed variational approach to systematically investigate general momentum-nonconserving nonlinear lattices. Two intrinsic identities characterizing optimal reference systems are firstly revealed, which enables us to derive explicit expressions for optimal variational parameters. The resulting optimal harmonic reference systems provide information for the band gap as well as the dispersion of renormalized phonons in momentum-nonconserving nonlinear lattices. As a demonstration, we consider the one-dimensional lattice. We show that the phonon band gap endows a simple power-law temperature dependence in the weak stochasticity regime where predicted dispersion is reliable by comparing with numerical results. In addition, an exact relation between ensemble averages of the lattice in the whole temperature range is found, regardless of the existence of the strong stochasticity threshold.

Transitions of Ba0.5Sr0.5Co0.8Fe0.2O3-δ and La0.58Sr0.4Co0.2Fe0.8O3-δ

Mixed ionic–electronic conducting perovskites are promising candidates for use as oxygen separation membrane and cathode of solid oxide fuel cells. In the current study, electrical conductivity, magnetic susceptibility, and linear expansion coefficient of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) are measured in a wide temperature range, including room temperature and below. The properties of BSCF reveal a quite complex behaviour, exhibiting five transitions around 200, 350, 500, 800, and 1050K, which can be related to the respective valence state and the spin-state of B-site cations as well as the oxygen non-stoichiometry, whereas those of LSCF has a simple temperature dependence, exhibiting two transitions around 250 and 800K.

A new aqueous activity model for geothermal brines in the system Na-K-Ca-Mg-H-Cl-SO4-H2O from 25 to 300 °C

A revised formulation (named REUNIQUAC) of the Extended Universal QUAsiChemical (EUNIQUAC) activity model has been developed, which fits excess thermodynamic properties of binary and selected aqueous ternary electrolyte solutions in the system Na-K-Ca-Mg-H-Cl-SO4-H2O over temperatures from 298 to 573K and concentrations to 5 molal (or up to saturation if solubility is below 5 molal) for saturated water vapor conditions. Compared to the original EUNIQUAC model, REUNIQUAC employs an extended version of the Debye–Hückel model using effective ionic radii of solute species, a concentration dependence of a UNIQUAC parameter, an additional empirical term for strongly complexing salts, as well as a simple quadratic temperature dependence of the fitting parameters. REUNIQUAC considers only pairwise interactions between solute species, as opposed to the Pitzer activity model, which additionally needs to account for ternary interactions. Since REUNIQUAC uses also species-specific parameters, extension of the existing parameter set to solutions that are composed of different combinations of the fitted species, is straightforward, and involves only the parameterization of the pairwise interaction terms. All systems could be fitted with accuracy comparable to the Pitzer model or better, although with much fewer parameters.

Optimum Carrier Concentration in n‐Type PbTe Thermoelectrics

Taking La‐ and I‐doped PbTe as an example, the current work shows the effects of optimizing the thermoelectric figure of merit, zT, by controlling the doping level. The high doping effectiveness allows the carrier concentration to be precisely designed and prepared to control the Fermi level. In addition to the Fermi energy tuning, La‐doping modifies the conduction band, leading to an increase in the density of states effective mass that is confirmed by transport, infrared reflectance and hard X‐ray photoelectron spectroscopy measurements. Taking such a band structure modification effect into account, the electrical transport properties can then be well‐described by a self‐consistent single non‐parabolic Kane band model that yields an approximate (m*T)1.5 dependence of the optimal carrier concentration for a peak power factor in both doping cases. Such a simple temperature dependence also provides an effective approximation of carrier concentration for a peak zT and helps to explain, the effects of other strategies such as lowering the lattice thermal conductivity by nanostructuring or alloying in n‐PbTe, which demonstrates a practical guide for fully optimizing thermoelectric materials in the entire temperature range. The principles used here should be equally applicable to other thermoelectric materials.

Magnetic property in the ferromagnetic superconductor UGe2 at pressures above the ferromagnetic critical pressure

We have studied the high-pressure magnetic property in UGe2 where ferromagnetic superconductivity appears under high pressure. In this study, we focus on the magnetic property at pressures above the ferromagnetic critical pressure P c =1.6 GPa. The temperature and magnetic field dependences of the dc-magnetization have been measured under high pressures up to 5.1 GPa by using a ceramic anvil high pressure cell. At pressures above P c , the magnetic susceptibility x shows a broad maximum around T χmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetic transition) at H c . With increasing pressure, the peak structure in x becomes broader, and the peak position T χmax moves to the higher temperature region. The metamagnetic field H c increases rapidly with increasing pressure. At pressures above 4.1 GPa, x shows a simple temperature dependence, and the magnetization increases linearly with increasing field. These phenomena in UGe2 resemble to those in the intermetallic compounds of 3d transition metals such as Co(S1−x Se x ) and YCo2. We discuss the experimental results by using the phenomenological spin-fluctuation theory.

CuIIand CuICoordination Complexes Involving Two Tetrathiafulvalene-1,3-benzothiazole Hybrid Ligands and Their Radical Cation Salts

Preparations, crystal structure analyses, and magnetic property investigations on a new Cu(II)(hfac)2 complex coordinated with two TTF-CH═CH-BTA ligands, where hfac is hexafluoroacetylacetonate, TTF is tetrathiafulvalene, and BTA is 1,3-benzothiazole, are reported together with those of its dicationic AsF6(-) salt, [Cu(hfac)2(TTF-CH═CH-BTA)2](AsF6)2, in which each TTF part is in a radical cation state. In these Cu(II)(hfac)2 complexes, two ligands are bonded to the central Cu atom of the Cu(hfac)2 part through the nitrogen atom of the 1,3-benzothiazole ring and occupy the two apical positions of the Cu(hfac)2 complex with an elongated octahedral geometry. These two ligands are located parallelly in a transverse head-to-tail manner, and the Cu(hfac)2 moiety is closely sandwiched by these two ligands. In the AsF6(-) salt of the Cu(hfac)2 complex, each TTF dimer is separated by the AsF6(-) anions and has no overlap with each other within the one-dimensional arrays, resulting in an insulating behavior. Both Cu(hfac)2 complexes showed the simple Curie-like temperature dependence of paramagnetic susceptibilities (χM), indicating that no interaction exists between the paramagnetic Cu(II) d spins. Furthermore, crystal structure analysis and magnetic/conducting properties of a radical cation ReO4(-) salt of the Cu(I) complex with two TTF-CH═CH-BTA ligands, [Cu(TTF-CH═CH-BTA)2](ReO4)2, are also described. Two nitrogen atoms of the ligands are connected to the central Cu(I) in a linear dicoordination with a Cu-N bond length of 1.879(9) Å. Two TTF parts of the neighboring complexes form a dimerized structure, and such a TTF dimer forms a one-dimensional uniform array along the a direction with a short S-S contact of 3.88 Å. Magnetic property measurement suggested the existence of a strongly antiferromagnetic one-dimensional uniform chain of S = 1/2 spins that originate from the radical cation states of the TTF dimers. Due to the construction of the one-dimensional uniform array of the radical cation state of the TTF dimer along the a axis, a semiconducting behavior is observed with σ(rt) = of 6 × 10(-5) S cm(-1) and an activation energy of E(a) = 0.16 eV.

Exploring the unique electrical properties of metastable BiPO4through switchable phase transitions

Metastable materials usually possess unique properties. How to acquire these properties is still a great challenge. In this work, we explored the electrical properties of metastable BiPO4 through switchable phase transitions. A metastable monoclinic phase (denoted as HTMP) was synthesized by a heat-treatment over a hexagonal phase (HP). It is found that there is a reversible phase transformation between HTMP and a low-temperature monoclinic phase (LTMP). Namely, HTMP gradually transformed to LTMP by a simple hand-grinding or ball milling, while LTMP transformed back to HTMP upon a heat treatment. Accompanying the transformation from HTMP to LTMP, the morphology varied from the cobblestone-like to spherical-like, and particle sizes changed from micrometre scale to several tens of nanometres, as followed by a decrease in the symmetry of tetragonal PO43− groups from Cs to C1. The reversible transformation was understood by taking into account several structural factors like the arrangement of PO4 tetrahedra and BiO8 polyhedra, unit cell volume (V/Z), and the symmetry of PO4. Finally, the electrical properties of the metastable HTMP were successfully acquired through a pellet-pressing technique. The temperature dependence of bulk conductivity indicates that the conductivities deviated from the Arrhenius law, but followed a simple temperature dependence, T−1/4, obeying a Mott variable range hopping conduction mechanism. The corresponding characteristic temperature of the bulk conduction for HTMP is estimated to be 2.3 × 109 K. These findings are fundamentally important, as they enable one to acquire the properties of many other metastable phases, meanwhile they pave a way for solving the controversies presented in metastable systems.

Dynamics in N-Isopropylacrylamide-acrylic Acid Copolymer Aqueous Solution from Mechanical Spectroscopy

Gaining control over precise and predictable structures of colloidal systems and understanding the abundant dynamic behaviors remains a formidable challenge. In this study, low-frequency mechanical spectroscopy was applied to investigate the dynamics of aqueous solutions of N-isopropylacrylamide-acrylic acid (NIPAM-AA) copolymers with three different AA contents. A mechanical loss valley was found for the solution with low molar fraction of AA (f(AA)), f(AA) = 25 and 50 mol %, and a loss peak was shown for the solution with f(AA) = 75 mol %. The former is suggested to be due to the particle glass phase of repulsive micelles above the low critical solution temperature, whereas the latter is associated with the α relaxation behavior of NIPAM-AA/water mixture at high concentrations. The relaxation time of the α relaxation seems to follow a simple Arrhenius temperature dependence. The activation energy H is ∼53 kJ/mol, and the larger H value is suggested to be due to multiple strong hydrogen bonds in the copolymer solution. The present work demonstrates that by controlling the proportion of ingredients in the colloidal systems the systems can exhibit distinct dynamic behaviors, which is helpful in the design and fabrication of colloids.