Temperature Dependence Of Potential Research Articles

Temperature-dependent potential in alpha-decay process

Abstract The temperature dependence of the alpha-nucleus potential and the corresponding alpha-decay half-lives are studied with different versions of the proximity potential. The transfer matrix approach is applied to calculate the penetration probability of alpha particle. The barrier heights and widths increase with the excitation energies of the parent nuclei, which results in the increase of the alpha-decay half-lives with increasing of the temperature and decreasing of the surface energy coefficient. Based on the measured alpha-decay half-lives, we find that the temperature of the parent nuclei in decaying process decreases with the mass number of the parent nuclei.

Temperature-dependent interaction potential between NF3 molecules and thermophysical properties of gaseous NF3

A temperature-dependent effective intermolecular interaction potential is applied to describe the interaction between two nitrogen fluoride (NF3) molecules in gas phase. To this end, a spherically-symmetric (n-6) Lennard-Jones temperature-dependent potential (LJTDP) is used. The (n-6) LJTDP takes into account the influence of vibrational excitation of the molecules on the potential parameters, namely, the equilibrium distance rm and the potential well depth ϵ. The potential parameters at T = 0 K were obtained from the very small amount of existing thermophysical equilibrium and transport properties of low-density NF3 gas. Fitting formulae are tabulated for a fast and reliable prediction of the thermophysical properties and potential parameters in the temperature range between 200 K and 1200 K. A comparison is also presented between our estimates for some thermophysical properties of the NF3 gas with the available experimental and calculated data.

A temperature-based phenology model for predicting development, survival and population growth potential of the mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

The temperature-dependent population growth potential of Phenacoccus solenopsis Tinsley, a highly polyphagous and invasive mealybug species, was studied on sprouted potatoes under laboratory conditions at six constant temperatures (15–40 °C). Several non-linear equations were fitted to the obtained data to model temperature-dependent population growth and species life history. The established equations for each life age/stage of the species were compiled to obtain an overall temperature-dependent phenology model. The life table parameters of P. solenopsis were estimated using stochastic simulation centred on a rate summation and cohort up-dating approach. The theoretical lower development threshold temperatures estimated using linear regressions applied to mean development rates were 11.2, 8.9, 9.8 and 12.7 °C, and the thermal constants for development were 93.7, 129.8, 97.1 and 100.0 degree days (DD) for nymph 1, nymph 2, nymph 3 and male pupa stages, respectively. The developed phenology model predicted temperatures between 25 and 35 °C as the favourable range for P. solenopsis development, survival and reproduction. P. solenopsis population attained a maximum net reproductive rate (107–108 females/female/generation) and total fecundity (216.6–226.5 individuals/female/generation) at temperatures between 25 and 30 °C. Mean length of generations decreased from 75.6 days at 15 °C to 21 days at 40 °C. The maximum finite rate of increase (1.12–1.16 females/female/day) and shortest doubling time (4.3–6.1 days) were also observed at temperatures between 25 and 35 °C. The simulation of phenology model at fluctuating temperatures indicated that P. solenopsis populations might potentially increase with a finite rate of 1.06 females/female/day with an average generation time of 58.7 days and a doubling time of 12.1 days. The obtained life table parameters were reasonably similar when compared with literature data. The present model can be simulated spatially for estimating the pest risk and undertaking agro-ecoregion specific pest management strategies.

Interpretation of thermal dependence of magnetic aftereffect for magnetic nanocomposite with slow decay rates

A new experimental characterization is presented of time-, field-, and temperature-dependent dynamic effects in magnetization of a nanocomposite which displays slow decay. Field and temperature variations of irreversible susceptibility, χ irr , decay coefficient, S, fluctuation field, hf , and activation volume, V, have been calculated for the nanocomposite sample (Co80Ni20) using a recently developed modified Preisach–Arrhenius (MPA) model. The sample is composed of non-interacting nanoparticles having negligible reversible magnetization. Non-Arrhenius behavior is observed in both the maximum decay coefficient, S max, and the fluctuation field, hf , as a function of temperature T. The peak of both temperature curves are identical and occur at a critical temperature Tk of ∼50 K, which agrees with our experimental results. Based on the effect of a temperature-dependent chemical potential on energy barrier, hf is studied for T < Tk and T ≥ Tk , respectively. A more complete MPA model that can predict the magnetization as function of time, field and temperature for a magnetic material with slow decay rates is proposed. This model uses a multi-variable analytical formula, , which incorporates the characteristic parameters.

Parametrically Temperature-Dependent Potential for Molecular Dynamics Simulation of Uranium Dioxide Properties

The present paper justifies the application of the temperature-dependent potential to the molecular dynamics method through the example of uranium dioxide. Substantiation of the temperature dependence of interatomic potential is carried out based on the Newton quantum equation. Mean force can be represented as a sum of derivative of potential at the average atomic coordinate and the summand that depends on square dispersion of the coordinate depending on the temperature of the crystal. Temperature dependence of potential is introduced as linear slightly varying functions of the Coulomb plus Buckingham potential. The selection of parameters of potential was done at three temperature values: the initial temperature and temperatures of phase transitions – 2670 and 3120K, parameters of potentials for all other temperatures were found by approximation. We calculated temperature dependencies for the lattice constant, enthalpy, heat capacity under constant pressure and volume. Application of the temperature-dependent potential well complies with experimental data; the difference did not exceed 0.5% in the entire temperature range of 300-3120K.

WORM ALGORITHM PATH INTEGRAL MONTE CARLO APPLIED TO THE 3He–4He II SANDWICH SYSTEM

We present a numerical investigation of the thermal and structural properties of the 3 He –4 He sandwich system adsorbed on a graphite substrate using the worm algorithm path integral Monte Carlo (WAPIMC) method [M. Boninsegni, N. Prokof'ev and B. Svistunov, Phys. Rev. E74, 036701 (2006)]. For this purpose, we have modified a previously written WAPIMC code originally adapted for 4 He on graphite, by including the second 3 He -component. To describe the fermions, a temperature-dependent statistical potential has been used. This has proven very effective. The WAPIMC calculations have been conducted in the millikelvin temperature regime. However, because of the heavy computations involved, only 30, 40 and 50 mK have been considered for the time being. The pair correlations, Matsubara Green's function, structure factor, and density profiles have been explored at these temperatures.

Non-adiabatic effects within a single thermally averaged potential energy surface: Thermal expansion and reaction rates of small molecules

At non-zero temperature and when a system has low-lying excited electronic states, the ground-state Born-Oppenheimer approximation breaks down and the low-lying electronic states are involved in any chemical process. In this work, we use a temperature-dependent effective potential for the nuclei which can accommodate the influence of an arbitrary number of electronic states in a simple way, while at the same time producing the correct Boltzmann equilibrium distribution for the electronic part. With the help of this effective potential, we show that thermally activated low-lying electronic states can have a significant effect in molecular properties for which electronic excitations are oftentimes ignored. We study the thermal expansion of the Manganese dimer, Mn(2), where we find that the average bond length experiences a change larger than the present experimental accuracy upon the inclusion of the excited states into the picture. We also show that, when these states are taken into account, reaction-rate constants are modified. In particular, we study the opening of the ozone molecule, O(3), and show that in this case the rate is modified as much as a 20% with respect to the ground-state Born-Oppenheimer prediction.

Multiscale coupling using a finite element framework at finite temperature

SUMMARY This paper presents the formulation and application of a multiscale methodology that couples three domains using a finite element framework. The proposed method efficiently models atomistic systems by decomposing the system into continuum, bridging, and atomistic domains. The atomistic and bridging domains are solved using a combined finite element–molecular mechanics simulation where the system is discretized into atom/nodal centric elements based on the atomic scale finite element method. Coupling between the atomistic domain and continuum domain is performed through the bridging cells, which contain locally formulated atoms whose displacements are mapped to the nodes of the bridging cell elements. The method implements a temperature-dependent potential for finite temperature simulations. Validation and demonstration of the methodology are provided through three case studies: displacement in a one-dimensional chain, stress around nanoscale voids, and fracture. From these studies differences between multiscale and fully atomistic simulations were very small with the simulation time of the proposed methodology being approximately a tenth of the time of the fully atomistic model. Copyright © 2012 John Wiley & Sons, Ltd.

The effect of germination temperature on seed dormancy in Croatian-grown winter wheats

The expression of seed dormancy related to germination temperature was studied in 25 wheat genotypes grown in the field at two locations near Zagreb and Županja in Croatia during 2008/2009 growing season. Germination tests were conducted at 15, 20 and 25 °C at harvest maturity (Time 1) as well as after 10 days (Time 2) and 15 months (Time 3) of seed after-ripening at room temperature, respectively. Significant (P < 0.05) differences among locations (L), temperatures (T) and genotypes (G) as well as significant L × T, G × L, G × T and G × L × T interactions were observed for weighted germination index (WGI) at both Time 1 and Time 2. At Time 3 significant differences among genotypes for germination percentage were found only at the early stages of germination. The 25 wheat genotypes responded with decreasing WGI mean values (increasing dormancy) as temperature changed from 15 to 25 °C. The rate of dormancy increase with higher germination temperature varied among genotypes. Some genotypes, having similar values of WGI at 15 °C, significantly differed from each other at 25 °C and vice versa. This indicates that the range of germination temperatures included in the present study is useful when testing genotypes for their temperature-dependent dormancy potential. The number of genotypes with WGI values significantly different from the mean, as a measure of the power of germination test to detect differences in dormancy level among genotypes, as well as heritability estimates for WGIs were the highest at Time 1 for 15 °C and at Time 2 for 20 °C.

A modified Morse potential accounting for non-zero temperature in molecular statics for Nickel crystals

A modified Morse interatomic potential, which allows extension of the classical Molecular Statics (MS) to non-zero temperatures, is introduced. Accordingly, the constants defining the traditional interatomic potential become temperature-dependent. In this paper they are determined based on experimentally known coefficients of thermal expansion for Nickel. The stress–strain data for a 3D Nickel crystal at different temperatures is found numerically and the results are compared against known experimental data and similar results obtained by the Molecular Dynamics (MD) method. This comparison confirms the validity of the concept of temperature-dependent interatomic potential in MS simulations.

Thermoresponsive Assembly of Charged Gold Nanoparticles and Their Reversible Tuning of Plasmon Coupling

Charged colloidal gold nanoparticles (AuNPs) can be assembled and disassembled in an aqueous solution in response to temperature change and display reversible thermoresponsive tuning of plasmon coupling. The reversible tuning was made possible by manipulating the electrostatic interaction through the temperature-dependent zeta potential of the charged AuNPs (see the extinction spectra of a typical AuNP dispersion).

Simultaneous effects of pressure and temperature on the binding energy and diamagnetic susceptibility of a laser dressed donor in a spherical quantum dot

Binding energies and diamagnetic susceptibility of an impurity in a spherical GaAs quantum dot under the simultaneous influence of static pressure, temperature and laser radiation are investigated. Pressure- and temperature-dependent dressed potential which is produced by the combined effects of laser radiation and impurity considerably change the energy spectrum and diamagnetic susceptibility of the system. It is shown that binding energies and diamagnetic susceptibility increase with increasing pressure. Moreover, laser radiation effects on the diamagnetic susceptibility are not significant in comparison with its effects on the binding energy.

Impact of Temperature on the Resistive Switching Behavior of Embedded $\hbox{HfO}_{2}$-Based RRAM Devices

Back-end-of-line integrated 1 × μm2 TiN/HfO2/Ti/TiN MIM memory devices in a 0.25- μm complementary metal-oxide-semiconductor technology were built to investigate the conduction mechanism and the resistive switching behavior as a function of temperature. The temperature-dependent I- V characteristics in fresh devices are attributed to the Poole-Frenkel mechanism with an extracted trap energy level at φ ≈ 0.2 eV below the HfO2 conduction band. The trap level is associated with positively charged oxygen vacancies. The electroformed memory cells show a stable bipolar switching behavior in the temperature range from 213-413 K. The off -state current increases with temperature, whereas the on-state current can be described by a weak metallic behavior. Furthermore, the results suggest that the I-V cycling not only induces significant changes in the electrical properties of the MIM memory devices, i.e., the increase in the off-state current, but also stronger temperature dependence. The temperature effect on the on-state and off-state characteristics is modeled within the framework of the quantum point-contact model for dielectric breakdown using an effective temperature-dependent confinement potential.

Vacuum fluctuations and the thermodynamics of chiral models

We consider the thermodynamics of chiral models in the mean-field approximation and discuss the relevance of the (frequently omitted) fermion vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended version, we show that the fermion vacuum fluctuations can change the order of the phase transition in the chiral limit and strongly influence physical observables. We compute the temperature-dependent effective potential and baryon number susceptibilities in these models, with and without the vacuum term, and explore the cutoff and the pion mass dependence of the susceptibilities. Finally, in the renormalized model the divergent vacuum contribution is removed using the dimensional regularization.

Temperature-dependent cross sections for meson–meson nonresonant reactions in hadronic matter

We present a potential of which the short-distance part is given by one gluon exchange plus perturbative one- and two-loop corrections and of which the large-distance part exhibits a temperature-dependent constant value. The Schrödinger equation with this temperature-dependent potential yields a temperature dependence of the mesonic quark–antiquark relative-motion wave function and of meson masses. The temperature dependence of the potential, the wave function and the meson masses brings about temperature dependence of cross sections for the nonresonant reactions π π → ρ ρ for I = 2 , K K → K * K * for I = 1 , K K * → K * K * for I = 1 , π K → ρ K * for I = 3 / 2 , π K * → ρ K * for I = 3 / 2 , ρ K → ρ K * for I = 3 / 2 and π K * → ρ K for I = 3 / 2 . As the temperature increases, the rise or fall of peak cross sections is determined by the increased radii of initial mesons, the loosened bound states of final mesons, and the total-mass difference of the initial and final mesons. The temperature-dependent cross sections and meson masses are parametrized.

Effective Intermolecular Interaction Potentials of Gaseous Fluorine, Chlorine, Bromine, and Iodine

Results are presented for binary intermolecular interactions and thermophysical properties in the temperature range between 70K and 1,000K of gaseous fluorine (F2), and between 200K and 1,000K of chlorine (Cl2), bromine (Br2), and iodine (I2). Our studies are carried out with an (n − 6) Lennard-Jones temperature-dependent potential (LJTDP). The underlying model takes into account the influence of vibrational excitations on the equilibrium distance Rm(T) and potential well depth \({\varepsilon(T)}\) . The potential parameters at T = 0K have been obtained by minimization of the sum of squared deviations between experimentally determined and calculated second pVT- and acoustic virial coefficients, B and β, and viscosities η, normalized to their relative experimental error aexp. The majority of the available experimental data are well reproduced within their experimental errors. Tables and fitting formulae for a fast and reliable prediction of the thermophysical properties and potential parameters are also presented.

Analytical solution for estimation of temperature-dependent material properties of metals using modified morse potential

Summary An atomic-level analytical solution, together with a modified Morse potential, has been developed to estimate temperature-dependent thermal expansion coefficients (CTE) and elastic characteristics of bulk metals. In this study, inter-atomic forces are considered as a set of anharmonic oscillator networks which can be described by Morse potential, while the material properties can be defined by these inter-atomic forces; when temperature increases, the vibration of the anharmonic oscillator causes the phenomenon of temperature-dependent material properties. The results of analysis showed that the original Morse potential can give a reasonable prediction of the thermal expansion coefficients and elastic constants of metals at room temperature; however, it has difficulties in giving an accurate result at low and high temperatures. Therefore, to overcome the deficiency, a temperaturedependent modified Morse potential is developed and validated with various metals.

Effective (n-6) Lennard-Jones Potentials with Temperature-Dependent Parameters Introduced for Accurate Calculation of Equilibrium and Transport Properties of Ethene, Propene, Butene, and Cyclopropane

The alkenes and cycloalkanes CmH2m (m = 1 to 4) are important reactants, intermediates, and end products in the chemical industry. Some of them are also widely used in the polymer industry. This paper presents tables with recommended thermophysical data in the temperature range (200 to 1000) K and pressures ≤ 0.1 MPa of ethene, propene, cyclopropane, 1-butene, cis-2-butene, trans-2-butene, and iso-butene. Second pVT virial coefficients B, viscosities η, and diffusion coefficients D are calculated by means of a (n-6) Lennard-Jones temperature-dependent potential. The potential parameters, equilibrium distance Rm(T), and potential well-depth ε(T) are defined as functions of the temperature T by solving an ill-posed problem of minimization of the squared deviations between measured and calculated B, η, and D, normalized to their experimental error. Tables with potential parameters as well as algorithms for calculation of the potential-dependent properties are given in this paper.

Combined Atomistic Simulation and Quasielastic Neutron Scattering Study of the Low-Temperature Dynamics of Hydrogen and Deuterium Confined in NaX Zeolite

A direct comparison of quasielastic neutron scattering experimental measurements and molecular dynamics computer simulations is carried out for the first time for hydrogen and deuterium confined in the nanostructure of faujasite type zeolites at a temperature of 100 K, in order to investigate the dependence of sorption thermodynamics and sorbate dynamics on the sorbed phase concentration. The charged crystal framework of NaX is digitally reconstructed based on X-ray diffraction spectra, with the compensating Na + positions determined by neutron diffraction data. For the quantum statistical mechanical description of the guest-guest and guest-zeolite interactions, the temperature-dependent effective potential of Feynman and Hibbs is employed, resulting from an approximation to the quantum mechanical path integral formulation of the motion. Computer simulation and neutron scattering are found in satisfactory agreement, both exhibiting a slight increase of the self-diffusivity and a maximum in the transport diffusivity as a function of sorbate loading. Our findings are further elaborated on the basis of the quasichemical mean field theory in conjunction with a model for surface transport due to Reed and Ehrlich, through which the computed and measured dynamical behavior can be related to the strength of interactions between the sorbate molecules.

Temperature-dependent parameters of band anticrossing in InGaPN alloys

Temperature-dependent photoreflectance (PR) measurements are employed to characterize the conduction band structure of In0.54Ga0.46P1−yNy (y=0 and 0.02) grown on GaAs substrates. The band gap and the upper subband E+ transition are observed in InGaPN as predicted by the band anticrossing (BAC) model. To investigate the energetic positions of the features in the PR spectra, a Kramers–Kronig analysis is proposed. Based on the PR data and the BAC model, we find that the energy EN of isolated nitrogen states shifts significantly to higher energies with decreasing temperature. Simultaneously, the interaction potential V between the nitrogen states and the unperturbed conduction band also rises to higher values. At 293 K, EN=2.054 eV and V=1.513 eV are determined. The thermal shifts of EN and V are dEN/dT≈−0.43 meV/K and dV/dT≈−0.67 meV/K, respectively. The temperature-dependent EN level and interaction potential V are attributed to the lattice distortions, which can be affected by temperature-induced changes in deformation potential. This information is important for overall validity of the BAC model to dilute nitride InGaPN alloys.