Explicit Temperature Dependence Research Articles

Thermal behavior of effective UA(1) anomaly couplings in reflection of higher topological sectors

Thermal behavior of effective, chiral condensate-dependent UA(1) anomaly couplings is investigated using the functional renormalization group approach in the Nf=3 flavor meson model. We derive flow equations for anomaly couplings that arise from instantons of higher topological charge, dependent also on the chiral condensate. These flow equations are solved numerically for the |Q|=1, 2 topological sectors at finite temperature. Assuming that the anomaly couplings at the ultraviolet scale may also exhibit explicit temperature dependence, we calculate the thermal behavior of the effective potential. In accordance with our earlier study, [G. Fejos and A. Patkos, ], we find that for increasing temperatures, the anomalous breaking of chiral symmetry tends to strengthen toward the pseudocritical temperature (TC) of chiral symmetry breaking. It is revealed that below TC, around ∼10% of the UA(1) breaking arises from the |Q|=2 topological sector. Correspondingly, a detailed analysis on the thermal behavior of the mass spectrum is also presented. Published by the American Physical Society 2024

Temperature-dependent dispersal and ectotherm species' distributions in a warming world.

Dispersal is a crucial component of species' responses to climate warming. Warming-induced changes in species' distributions are the outcome of how temperature affects dispersal at the individual level. Yet, there is little or no theory that considers the temperature dependence of dispersal when investigating the impacts of warming on species' distributions. Here I take a first step towards filling this key gap in our knowledge. I focus on ectotherms, species whose body temperature depends on the environmental temperature, not least because they constitute the majority of biodiversity on the planet. I develop a mathematical model of spatial population dynamics that explicitly incorporates mechanistic descriptions of ectotherm life history trait responses to temperature. A novel feature of this framework is the explicit temperature dependence of all phases of dispersal: emigration, transfer and settlement. I report three key findings. First, dispersal, regardless of whether it is random or temperature-dependent, allows both tropical and temperate ectotherms to track warming-induced changes in their thermal environments and to expand their distributions beyond the lower and upper thermal limits of their respective climate envelopes. In the absence of dispersal mortality, warming does not alter these new distributional limits. Second, an analysis based solely on trait response data predicts that tropical ectotherms should be able to expand their distributions polewards to a greater degree than temperate ectotherms. Analysis of the dynamical model confirms this prediction. Tropical ectotherms have an advantage when moving to cooler climates because they experience lower within-patch and dispersal mortality, and their higher thermal optima and maximal birth rates allow them to take advantage of the warmer parts of the year. Previous theory has shown that tropical ectotherms are more successful in invading and adapting the temperate climates than vice versa. This study provides the key missing piece, by showing how temperature-dependent dispersal could facilitate both invasion and adaptation. Third, dispersal mortality does not affect the poleward expansion of ectotherm distributions. But, it prevents both tropical and temperate ectotherms from maintaining sink populations in localities that are too warm to be viable in the absence of dispersal. Dispersal mortality also affects species' abundance patterns, causing a larger decline in abundance throughout the range when species disperse randomly rather than in response to thermal habitat suitability. In this way, dispersal mortality can facilitate the evolution of dispersal modes that maximize fitness in warmer thermal environments.

Backreaction of mesonic fluctuations on the axial anomaly at finite temperature

The impact of mesonic fluctuations on the restoration of the ${U}_{A}(1)$ anomaly is investigated nonperturbatively for three flavors at finite temperature in an effective model setting. Using the functional renormalization group, the dressed, fully field-dependent Kobayashi-Maskawa-'t Hooft (KMT) anomaly coupling is computed. It is found that mesonic fluctuations strengthen this signature of the ${U}_{A}(1)$ breaking as the temperature increases. On the other hand, when instanton effects are included by parametrizing the explicit temperature dependence of the bare anomaly parameter in consistency with the semiclassical result for the tunneling amplitude, a natural tendency appears, diminishing the anomaly at high temperatures. As a result of the two competing effects, the dressed KMT coupling shows a well-defined intermediate strengthening behavior around the chiral (pseudo)transition temperature before the axial anomaly gets fully suppressed at high temperature. As a consequence, we conclude that below $T\ensuremath{\sim}200\text{ }\text{ }\mathrm{MeV}$ the ${U}_{A}(1)$ anomaly is unlikely to be effectively restored. Robustness of the conclusions against different assumptions for the temperature dependence of the bare anomaly coefficient is investigated in detail.

Meta-GGA exchange-correlation free energy density functional to increase the accuracy of warm dense matter simulations

We discuss strategies for thermalization of the ground-state meta-generalized gradient approximation (meta-GGA) exchange-correlation (XC) functionals. A simple but accurate scheme is implemented via universal additive thermal correction to XC using a perturbativelike self-consistent approach. The additive correction with explicit temperature dependence is applied to the ground-state deorbitalized, strongly constrained, and appropriately normed (SCAN-L) meta-GGA XC leading to a thermal XC functional denoted here as T-SCAN-L. The thermal T-SCAN-L meta-GGA functional shows significant improvement in density functional theory calculation accuracy for warm dense matter by a factor of 3 to 10, achieving an accuracy of total pressure between a few tenths and $\ensuremath{\sim}1$% when compared to traditional XC functionals, as demonstrated by the comparison to path-integral Monte Carlo simulations for helium equation of state. The T-SCAN-L calculations of dc conductivity of warm dense aluminum also give better agreement with experiments over other XC functionals such as PBE and SCAN-L.

Phonon Drag Thermopower in Silicene in Equipartition Regime at Room Temperature

Abstract: Similar to graphene, zero band gap limits the application of Silicene in nanoelectronics despite of its high carrier mobility. In this article we calculate the contribution of electron-phonon interaction to thermoelectric effects in silicene. One considers the case of free standing silicene taking into account interaction with intrinsic acoustic phonons. The temperature considered here is at room temperature. We noticed that the contribution to thermoelectromotive force due to electron drag by phonons is determined by the Fermi energy. The explicit temperature dependence of the contribution to thermoelectromotive force deriving from by phonons is weak in contrast to that due to diffusion, which is directly proportional to temperature. Thus a theoretical limit has been established for a possible increase of the thermoelectromotive force through electron drag by the intrinsic phonons of silicene. Keywords: Phonon-drag thermopower, electron-diffusion thermopower, silicene, fermi energy, zero band gap

Improved first-principles equation-of-state table of deuterium for high-energy-density applications

We present a first-principles equation-of-state (EOS) table of deuterium aimed at improving the previously established first-principles equation-of-state table (FPEOS) [S. X. Hu et al., Phys. Rev. B 84, 224109 (2011); S. X. Hu et al., Phys. Plasmas 22, 056304 (2015)]. The EOS table presented here, referred to as iFPEOS, introduces (1) a universal density functional theory (DFT) treatment of all density and temperature conditions, (2) a fully consistent treatment of exchange-correlation (XC) thermal effects across the entire range of temperatures covered, and (3) quantum treatment of ions. Based on ab initio molecular dynamics driven by thermal density functional theory, iFPEOS includes density points in the range $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\ensuremath{\le}\ensuremath{\rho}\ensuremath{\le}1.6\ifmmode\times\else\texttimes\fi{}{10}^{3}$ $\mathrm{g}/{\mathrm{cm}}^{3}$ and temperature points in the range 800 K $\ensuremath{\le}T\ensuremath{\le}256$ MK, thus covering the challenging warm dense matter (WDM) regime. For an improved description of the electronic structure, iFPEOS employs an advanced free-energy XC density functional with explicit temperature dependence, which is at the metageneralized gradient approximation level of DFT. We use the latest orbital-free free-energy density functional for the high-temperature regime where it shows excellent agreement with standard Mermin-Kohn-Sham DFT. For quantum treatment of ions we use path-integral molecular dynamics in order to take into account nuclear quantum effects. Results are compared to other EOS models and most recent experimental measurements of deuterium properties such as the molecular-to-atomic fluid transition, the principal and reshock Hugoniot, and sound speed. We find that iFPEOS provides an improved agreement with experimental data compared to other first-principles EOS models in the WDM regime for pressures up to 200 GPa and temperatures up to $60\phantom{\rule{0.16em}{0ex}}000$ K. For higher pressures and temperatures, however, iFPEOS is in agreement with other models in predicting lower compressibility and higher sound speed along the Hugoniot, compared to experiment.

Thermal relaxation in a disordered one-dimensional array of interacting magnetic nanoparticles

We consider a system of single-domain magnetic nanoparticles placed along a linear chain and address the effect of the distance between them on the magnetic and thermal relaxation properties of the system. The nanoparticles interact with each other through the dipolar interaction and we introduce disorder into the system by allowing random sizes of the nanoparticles and random directions of their uniaxial anisotropy axes. In particular, the radius of the spherical nanoparticles are drawn from a log-normal distribution. The dynamical behavior of the magnetic moments of the system is studied through numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation, taking into account explicit temperature dependence of the saturation magnetization and uniaxial anisotropy energy density to describe the magnetic properties of perovskite manganite oxide nanoparticles. Hysteresis, zero-field-cooled and field-cooled curves are measured, from which we can find the coercive field and the blocking temperature as a function of the magnitude of the dipolar coupling, controlled by the distance between the particles. We show that both the coercive field and blocking temperature decrease as a function of the separation between the nanoparticles. The magnetic relaxation is measured as a function of both temperature and time, from which we estimate the effective energy barrier distribution of the system. We show that the peak of the energy barrier distribution moves to lower energies as the separation between neighboring particles increases, or equivalently, as the dipolar interaction is reduced.

Local laws and rigidity for Coulomb gases at any temperature

We study Coulomb gases in any dimension $\mathsf{d}\geq2$ and in a broad temperature regime. We prove local laws on the energy, separation and number of points down to the microscopic scale. These yield the existence of limiting point processes after extraction, generalizing the Ginibre point process for arbitrary temperature and dimension. The local laws come together with a quantitative expansion of the free energy with a new explicit error rate in the case of a uniform background density. These estimates have explicit temperature dependence, allowing to treat regimes of very large or very small temperature, and exhibit a new minimal lengthscale for rigidity and screening, depending on the temperature. They apply as well to energy minimizers (formally zero temperature). The method is based on a bootstrap on scales and reveals the additivity of the energy modulo surface terms, via the introduction of subadditive and superadditive approximate energies.

Two-temperature warm dense hydrogen as a test of quantum protons driven by orbital-free density functional theory electronic forces

We consider a steady-state (but transient) situation in which a warm dense aggregate is a two-temperature system with equilibrium electrons at temperature Te, ions at Ti, and Te ≠ Ti. Such states are achievable by pump–probe experiments. For warm dense hydrogen in such a two-temperature situation, we investigate nuclear quantum effects (NQEs) on structure and thermodynamic properties, thereby delineating the limitations of ordinary ab initio molecular dynamics. We use path integral molecular dynamics (PIMD) simulations driven by orbital-free density functional theory (OFDFT) calculations with state-of-the-art noninteracting free-energy and exchange-correlation functionals for the explicit temperature dependence. We calibrate the OFDFT calculations against conventional (explicit orbitals) Kohn–Sham DFT. We find that when the ratio of the ionic thermal de Broglie wavelength to the mean interionic distance is larger than about 0.30, the ionic radial distribution function is meaningfully affected by the inclusion of NQEs. Moreover, NQEs induce a substantial increase in both the ionic and electronic pressures. This confirms the importance of NQEs for highly accurate equation-of-state data on highly driven hydrogen. For Te > 20 kK, increasing Te in the warm dense hydrogen has slight effects on the ionic radial distribution function and equation of state in the range of densities considered. In addition, we confirm that compared with thermostatted ring-polymer molecular dynamics, the primitive PIMD algorithm overestimates electronic pressures, a consequence of the overly localized ionic description from the primitive scheme.

Nernst heat theorem for an atom interacting with graphene: Dirac model with nonzero energy gap and chemical potential

We derive the low-temperature behavior of the Casimir-Polder free energy for a polarizable atom interacting with graphene sheet which possesses the nonzero energy gap $\Delta$ and chemical potential $\mu$. The response of graphene to the electromagnetic field is described by means of the polarization tensor in the framework of Dirac model on the basis of first principles of thermal quantum field theory in the Matsubara formulation. It is shown that the thermal correction to the Casimir-Polder energy consists of three contributions. The first of them is determined by the Matsubara summation using the polarization tensor defined at zero temperature, whereas the second and third contributions are caused by an explicit temperature dependence of the polarization tensor and originate from the zero-frequency Matsubara term and the sum of all Matsubara terms with nonzero frequencies, respectively. The asymptotic behavior for each of the three contributions at low temperature is found analytically for any value of the energy gap and chemical potential. According to our results, the Nernst heat theorem for the Casimir-Polder free energy and entropy is satisfied for both $\Delta > 2\mu$ and $\Delta < 2\mu$. We also reveal an entropic anomaly arising in the case $\Delta = 2\mu$. The obtained results are discussed in connection with the long-standing fundamental problem in Casimir physics regarding the proper description of the dielectric response of matter to the electromagnetic field.

Impact of Use Conditions on Dielectric and Conductor Material Models for High-Speed Package Interconnects

Use conditions based on temperature and humidity can have a significant impact on the package material properties and loss, which is required to be included in modeling assumptions to be able to set realistic specifications. The dielectric loss is affected by both temperature and humidity through material properties. The conductor loss, however, is affected by only temperature explicitly through conductivity and implicitly through skin depth and surface roughness modeling. This paper presents a systematic use condition-dependent methodology for package high-speed interconnects including a robust dielectric material characterization metrology. Correlation to high fidelity insertion loss measurements at different temperatures indicates that the roughness correction factor extracted at one temperature does not fit all and leads to underestimating the loss at higher temperatures. Without loss of generality due to a unified form of correction factors of the existing common roughness models, a modified version of Huray’s snowball model with an explicit temperature dependence is proposed to achieve high-quality on-package interconnect loss correlation at different temperatures.

Effective Hamiltonians and empirical fluid equations of state

Hamiltonians with explicit temperature and density dependence are employed in classical and quantized partition functions to derive caloric and thermal equations of state (EoS) for real gases and liquids. To define a fluid equilibrium system, the density- and temperature-dependent Hamiltonian has to satisfy an equilibrium condition derived here, which ensures that the internal-energy derivative of entropy coincides with the reciprocal temperature. The inverse problem to obtain an effective Hamiltonian from a prescribed thermal EoS is discussed, and explicit examples of this reconstruction are given for cubic and non-cubic EoSs. A non-cubic multi-parameter EoS is proposed, a generalization of the Peng-Robinson EoS, which can accurately reproduce the power-law ascent of pressure isotherms in the high-pressure/high-density regime. This EoS is put to test by fitting isothermal data sets of classical and quantum fluids (nitrogen, carbon monoxide, methane, carbon dioxide, methanol, water, hydrogen and helium) over an extended pressure range up to 1 GPa, at critical, super- and subcritical temperatures. The least-squares fits are compared with the cubic Peng-Robinson approximation of the pressure isotherms, which becomes singular at high density. The internal-energy variable derived from the effective Hamiltonian can also be used to discriminate between different EoSs in the high-density regime, as demonstrated with methane isotherms.

Calculations of shear, bulk viscosities and electrical conductivity in the Polyakov-quark–meson model

We have calculated different transport coefficients such as shear, bulk viscosities and electrical conductivity of quark and hadronic matter within the framework of a 2 flavor Polyakov-quark–meson model. For constant thermal widths of quarks and mesons, the temperature dependence of different transport coefficients reveals the thermodynamical phase space structure and their qualitative behavior are quite well in agreement with earlier works, based on other dynamical models. Besides the phase-space structure of quarks and mesons, their thermal width also have explicit temperature dependence. This dependence has been obtained here from the imaginary part of their respective self-energies at finite temperature. Due to the threshold conditions of their self energies, only some limited temperature regions of quark and hadronic phase are relevant for our numerical estimation of transport coefficients, which are grossly in agreement with some of the earlier results. An interesting outcome of the present analysis is that the quark relaxation time due to quark–meson loops can develop perfect fluid nature within a specific temperature range.

Quantum Dynamics of Skyrmions in Chiral Magnets

We study the quantum propagation of a Skyrmion in chiral magnetic insulators by generalizing the micromagnetic equations of motion to a finite-temperature path integral formalism, using field theoretic tools. Promoting the center of the Skyrmion to a dynamic quantity, the fluctuations around the Skyrmionic configuration give rise to a time-dependent damping of the Skyrmion motion. From the frequency dependence of the damping kernel, we are able to identify the Skyrmion mass, thus providing a microscopic description of the kinematic properties of Skyrmions. When defects are present or a magnetic trap is applied, the Skyrmion mass acquires a finite value proportional to the effective spin, even at vanishingly small temperature. We demonstrate that a Skyrmion in a confined geometry provided by a magnetic trap behaves as a massive particle owing to its quasi-one-dimensional confinement. An additional quantum mass term is predicted, independent of the effective spin, with an explicit temperature dependence which remains finite even at zero temperature.

Multi-Objective Path Planning for Single Crystal Size and Shape Modification

The application of consecutive cycles of growth and dissolution during crystallization from solution is a possibility to systematically modify crystal size and shape. Under the assumption that crystal size and shape can be described by two independent dimensions, we propose a derivative-free path planning methodology to compute temperature profiles that induce a desired size and shape modification of a single crystal in a batch crystallization framework. The proposed methodology allows screening of a subset of the crystal size and shape space for possible size and shape changes, thereby quantifying the trade-off between the required path time and the allowed number of growth and dissolution stages. We compare this methodology with an alternative, gradient-based path planning approach and present case studies based on models of the compounds potassium dihydrogen phosphate and β l-glutamic acid. Analyzing the results of these case studies reveals that an explicit temperature dependence of the growth and dissolution rates of the independent crystal dimensions can have a significant impact on the trade-off between the path time and the number of stages.

A phenomenological modification of thermohaline mixing in globular cluster red giants

Thermohaline mixing is a favoured mechanism for the so-called "extra mixing" on the red giant branch of low-mass stars. The mixing is triggered by the molecular weight inversion created above the hydrogen shell during first dredge-up when helium-3 burns via 3He(3He,2p)4He. The standard 1D diffusive mixing scheme cannot simultaneously match carbon and lithium abundances to NGC 6397 red giants. We investigate two modifications to the standard scheme: (1) an advective two stream mixing algorithm, and (2) modifications to the standard 1D thermohaline mixing formalism. We cannot simultaneously match carbon and lithium abundances using our two stream mixing approach. However we develop a modified diffusive scheme with an explicit temperature dependence that can simultaneously fit carbon and lithium abundances to NGC 6397 stars. Our modified diffusive scheme induces mixing that is faster than the standard theory predicts in the hotter part of the thermohaline region and mixing that is slower in the cooler part. Our results infer that the extra mixing mechanism needs further investigation and more observations are required, particularly for stars in different clusters spanning a range in metallicity.

Importance of finite-temperature exchange correlation for warm dense matter calculations.

The effects of an explicit temperature dependence in the exchange correlation (XC) free-energy functional upon calculated properties of matter in the warm dense regime are investigated. The comparison is between the Karasiev-Sjostrom-Dufty-Trickey (KSDT) finite-temperature local-density approximation (TLDA) XC functional [Karasiev etal., Phys. Rev. Lett. 112, 076403 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.076403] parametrized from restricted path-integral Monte Carlo data on the homogeneous electron gas (HEG) and the conventional Monte Carlo parametrization ground-state LDA XC [Perdew-Zunger (PZ)] functional evaluated with T-dependent densities. Both Kohn-Sham (KS) and orbital-free density-functional theories are used, depending upon computational resource demands. Compared to the PZ functional, the KSDT functional generally lowers the dc electrical conductivity of low-density Al, yielding improved agreement with experiment. The greatest lowering is about 15% for T=15 kK. Correspondingly, the KS band structure of low-density fcc Al from the KSDT functional exhibits a clear increase in interband separation above the Fermi level compared to the PZ bands. In some density-temperature regimes, the deuterium equations of state obtained from the two XC functionals exhibit pressure differences as large as 4% and a 6% range of differences. However, the hydrogen principal Hugoniot is insensitive to the explicit XC T dependence because of cancellation between the energy and pressure-volume work difference terms in the Rankine-Hugoniot equation. Finally, the temperature at which the HEG becomes unstable is T≥7200 K for the T-dependent XC, a result that the ground-state XC underestimates by about 1000 K.

A unified kinetic model for adsorption and desorption – Applied to water on zeolite

A kinetic model for reversible adsorption and desorption processes under non-isothermal conditions based on reaction kinetics is deduced. This is done by explicit temperature dependence of all equations of the model. However in the performed experiments the coupling with the thermal bath was strong enough to neglect thermal conductivity and set the temperature as a timely-varying and spacial-constant parameter. Furthermore adsorption- and desorption-mechanisms of higher order and diffusion are considered. The formulation with partial differential equations is adaptable to the geometry of the adsorbent. To solve the system of coupled differential equations numerical methods of Wolfram Mathematica® are used. This model is applied to water on zeolite 3A. Beside the non-isothermal thermogravimetric analysis and the differential scanning calorimetry an isothermal experiment for the time-dependent measurement of the adsorption is used to evaluate the model. The sorption isotherms of a commercial zeolite manufacturer serve as a further source of comparison. The parameters are fitted numerically with the χ2 -method to the experimental data. As a result of this paper a unified sorption model is introduced.

Absorption of scalars by nonextremal charged black holes in string theory

We analyze the low frequency absorption cross section of minimally coupled massless scalar fields by different kinds of charged static black holes in string theory, namely the D1-D5 system in d=5 and a four dimensional dyonic four-charged black hole. In each case we show that this cross section always has the form of some parameter of the solution divided by the black hole Hawking temperature. We also verify in each case that, despite its explicit temperature dependence, such quotient is finite in the extremal limit, giving a well defined cross section. We show that this precise explicit temperature dependence also arises in the same cross section for black holes with string alpha' corrections: it is actually induced by them.

Temperature dependence of the propagation vector in Ni3−xCoxV2O8 with x=0.1 and 0.5

We present the susceptibility and neutron diffraction data on multiferroic Ni3−xCoxV2O8 with x=0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order–disorder transition occurs at THTI=8.5K in both samples. Below THTI, the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x=0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x=0.5 exhibits a definite temperature dependence, which differs from the case of the undoped sample (x=0).