Repulsive Term Research Articles

Isothermal compressibility of saturated refrigerants: Chlorodifluoromethane and 1,1,1,2-tetrafluoroethane

A new five-parameter generalized van der Waals equation of state is employed for calculating the isothermal compressibility of saturated refrigerants such as chlorodifluoromethane and 1,1,1,2-tetrafluoroethane in the liquid and vapor states over a temperature range from the boiling point to the critical point. This generalized van der Waals equation of state differs from the known van der Waals equation by the modified repulsive and attractive terms. The parameters of the equation of state are determined through the characteristic thermodynamic parameters of the refrigerants. The generalized van der Waals equation-of-state parameters are compared with the known van der Waals equation-of-state parameters.

Electronic Phase Switching in the Negative Charge Transfer Energy SrCoOx Thin Films with the Mottronic Relevancies

The metal–insulator transition in the negative charge transfer energy (Δ) materials is at the cutting edge for the transition-metal oxide community owing to their tremendous prospects in the Mottronic applications. We demonstrate the underlying mechanism for the Mott-switching in the thin films of negative Δ insulator SrCoO2.5 and negative Δ metal SrCoO3 systems. The control on the lowest energy charge fluctuation energetics in terms of the Coulomb repulsion U and Δ for the electronic phase switching is realized, and a comprehensive picture of the opening and closing of the band gap has been drawn experimentally in the negative Δ regime. The charge disproportionation is observed in the insulating regime, which is melted in the metallic regime of negative Δ in the SrCoOx films. From the electronic structure investigation, we have established the positions of the SrCoOx thin films in the U–Δ phase space and identified the tunable parameters for the electronic phase switching in the films. This study is fundamentally important for understanding the electronic correlation parameters controlling the lowest energy charge fluctuation energetics for the Mott-switching in the negative Δ regime, making SrCoOx thin films a promising candidate for the future Mottronic applications.

Unpolarizable molecular model describing electron distribution for treating halogen bonds

This paper proposes an unpolarizable molecular model for treating halogen bonds that explicitly describes electron distributions. The orbital-like functions are defined as a linear combination of the primitive Gaussian functions for each atom that constitutes the molecule. The electron density of the entire molecule is described as a sum of the squares of these functions. The model evaluates the electrostatic and exchange repulsion terms based on the electron distribution, and thus, both these terms depend on the distribution. This model accurately describes the σ-hole of halogens and the total interaction energy of the halogen bonds in halogen/H2O systems.

Black hole singularity resolution via the modified Raychaudhuri equation in loop quantum gravity

We derive loop quantum gravity corrections to the Raychaudhuri equation in the interior of a Schwarzschild black hole and near the classical singularity. We show that the resulting effective equation implies defocusing of geodesics due to the appearance of repulsive terms. This prevents the formation of conjugate points, renders the singularity theorems inapplicable, and leads to the resolution of the singularity for this spacetime.

Spatiotemporal patterns in a 2D lattice with linear repulsive and nonlinear attractive coupling.

We explore the emergence of a variety of different spatiotemporal patterns in a 2D lattice of self-sustained oscillators, which interact nonlocally through an active nonlinear element. A basic element is a van der Pol oscillator in a regime of relaxation oscillations. The active nonlinear coupling can be implemented by a radiophysical element with negative resistance in its current-voltage curve taking into account nonlinear characteristics (for example, a tunnel diode). We show that such coupling consists of two parts, namely, a repulsive linear term and an attractive nonlinear term. This interaction leads to the emergence of only standing waves with periodic dynamics in time and absence of any propagating wave processes. At the same time, many different spatiotemporal patterns occur when the coupling parameters are varied, namely, regular and complex cluster structures, such as chimera states. This effect is associated with the appearance of new periodic states of individual oscillators by the repulsive part of coupling, while the attractive term attenuates this effect. We also show influence of the coupling nonlinearity on the spatiotemporal dynamics.

Correlated interface electron gas in infinite-layer nickelate versus cuprate films on SrTiO3(001)

Based on first-principles calculations including a Coulomb repulsion term, we identify trends in the electronic reconstruction of $A$NiO$_2$/SrTiO$_3$(001) ($A=$ Pr, La) and $A$CuO$_2$/SrTiO$_3$(001) ($A=$ Ca, Sr). Common to all cases is the emergence of a quasi-two-dimensional electron gas (q2DEG) in SrTiO$_3$(001), albeit the higher polarity mismatch at the interface of nickelates vs. cuprates to the nonpolar SrTiO$_3(001)$ substrate (${3+}/0$ vs. ${2+}/0$) results in an enhanced q2DEG carrier density. The simulations reveal a significant dependence of the interfacial Ti $3d_{xy}$ band bending on the rare-earth ion in the nickelate films, being $20$-$30\%$ larger for PrNiO$_2$ and NdNiO$_2$ than for LaNiO$_2$. Contrary to expectations from the formal polarity mismatch, the electrostatic doping in the films is twice as strong in cuprates as in nickelates. We demonstrate that the depletion of the self-doping rare-earth $5d$ states enhances the similarity of nickelate and cuprate Fermi surfaces in film geometry, reflecting a single hole in the Ni and Cu $3d_{x^2-y^2}$ orbitals. Finally, we show that NdNiO$_2$ films grown on a polar NdGaO$_3(001)$ substrate feature a simultaneous suppression of q2DEG formation as well as Nd~$5d$ self-doping.

Regularizing effect and decay results for a parabolic problem with repulsive superlinear first order terms

We want to analyze both regularizing effect and long, short time decay concerning a class of parabolic equations having first order superlinear terms. The model problem is the following: $$\begin{aligned} {\left\{ \begin{array}{ll} \displaystyle u_t-\text {div }(A(t,x)|\nabla u|^{p-2}\nabla u)=\gamma |\nabla u|^q &{} \text {in}\,\,(0,T)\times \Omega ,\\ u=0 &{}\text {on}\,\,(0,T)\times \partial \Omega ,\\ u(0,x)=u_0(x) &{}\text {in}\,\, \Omega , \end{array}\right. } \end{aligned}$$ where $$\Omega $$ is an open bounded subset of $${{\,\mathrm{{{\mathbb {R}}}}\,}}^N$$ , $$N\ge 2$$ , $$0<T\le \infty $$ , $$1<p<N$$ and $$q<p$$ . We assume that A(t, x) is a coercive, bounded and measurable matrix, the growth rate q of the gradient term is superlinear but still subnatural, $$\gamma $$ is a positive constant, and the initial datum $$u_0$$ is an unbounded function belonging to a well precise Lebesgue space $$L^\sigma (\Omega )$$ for $$\sigma =\sigma (q,p,N)$$ .

Sound Velocities of Generalized Lennard-Jones (n - 6) Fluids Near Freezing.

In a recent paper [S. Khrapak, Molecules 25, 3498 (2020)], the longitudinal and transverse sound velocities of a conventional Lennard–Jones system at the liquid–solid coexistence were calculated. It was shown that the sound velocities remain almost invariant along the liquid–solid coexistence boundary lines and that their magnitudes are comparable with those of repulsive soft-sphere and hard-sphere models at the fluid–solid phase transition. This implies that attraction does not considerably affect the magnitude of the sound velocities at the fluid–solid phase transition. This paper provides further evidence to this by examining the generalized Lennard–Jones (n − 6) fluids with n ranging from 12 to 7 and demonstrating that the steepness of the repulsive term has only a minor effect on the magnitude of the sound velocities. Nevertheless, these minor trends are identified and discussed.

The dampening role of large repulsive convection in a chemotaxis system modeling tumor angiogenesis

This paper is concerned with a parabolic–parabolic–elliptic system arising as a simplified model for the initial phase of tumor-related angiogenesis. As essential characteristics, this system contains a cascade-like coupling of two chemotaxis processes involving signal production as in classical Keller–Segel systems, linked to a further repulsive cross-diffusive mechanism. It is shown that in n-dimensional bounded convex domains with n≤3 and for any given suitably regular initial data, a suitable assumption on largeness of the parameter corresponding to the latter repulsion term ensures global existence of a bounded classical solution, and hence rules out the possibility of finite-time explosions which in the absence of any such chemorepulsion are known to occur at least in a certain borderline case.

Atomic Force Extrema Induced by the Bending of a CO-Functionalized Probe.

The control and observation of reactants forming a chemical bond at the single-molecule level is a long-standing challenge in quantum physics and chemistry. Using a single CO molecule adsorbed at the apex of an atomic force microscope tip together with a Cu(111) surface, bending of the molecular probe is induced by torques due to van der Waals attraction and Pauli repulsion. As a result, the vertical force between CO and Cu(111) exhibits a characteristic dip-hump evolution with the molecule-surface separation, which depends sensitively on the initial tilt angle the CO axis encloses with the surface normal. The experimental force data are reproduced by model calculations that consider the CO deflection in a harmonic potential and the molecular orientation in the Pauli repulsion term of the Lennard-Jones potential. The presented findings shed new light on vertical-force extrema that can occur in scanning probe experiments with functionalized tips.

Phase diagram of α matter with a Skyrme-like scalar interaction

The equation of state and phase diagram of strongly interacting matter composed of $\alpha$ particles are studied in the mean-field approximation. The particle interactions are included via a Skyrme-like mean field, containing both attractive and repulsive terms. The model parameters are found by fitting known values of binding energy and baryon density in the ground state of $\alpha$ matter, obtained from microscopic calculations by Clark and Wang. Thermodynamic quantities of $\alpha$ matter are calculated in the broad domains of temperature and baryon density, which can be reached in heavy-ion collisions at intermediate energies. The model predicts both first-order liquid-gas phase transition and Bose-Einstein condensation of $\alpha$ particles. We present the profiles of scaled variance, sound velocity and isochoric heat capacity along the isentropic trajectories of $\alpha$ matter. Strong density fluctuations are predicted in the vicinity of the critical point at temperature $T_c\approx 14~\textrm{MeV}$ and density $n_c\approx 0.012~\textrm{fm}^{-3}$.

Effects of the repulsive and attractive forces on phase equilibrium and critical properties of two-dimensional non-conformal simple fluids

Molecular simulations in the canonical and isothermal-isobaric ensembles were performed for a two-dimensional simple fluid using a set of non conformal molecular interactions. The specific characteristics of this interaction model give it some advantages over other well known interaction potentials employed traditionally in the study of thermodynamic properties of soft matter systems. The functional form employed for modelling the effective potentials is the one proposed by the so-called ANC theory (Approximate Non-Conformal Theory), which allows to modify separately the contributions of the repulsive and attractive terms by means of a molecular parameter called softness. The effect of both, repulsive and attractive softness, on the liquid-vapour coexistence, liquid-solid transition and vaporization curve as well as on the value of the critical properties were explored. In fact, the linear dependence on the softness parameters exhibited by the critical properties, allows to extrapolate the linear correlations presented in this work, to reproduce the critical point of a two-dimensional Lennard-Jones fluid. With the aim of showing how versatile is the interaction model presented in this work, adequate values of the softness parameters were selected to reproduce qualitatively the liquid-vapour coexistence and critical points for both, a two-dimensional model fluid with a double exponential interaction potential, widely employed in molecular simulations of simple fluids; and a thin monolayer of methane molecules adsorbed on a planar graphite substrate, a system that can be considered in good approximation as two-dimensional and that has been studied in a lot of work for four decades. Finally, the effects of the dimensionality of the system was evaluated by quantifying the relative percentage differences exhibited by the thermodynamic properties explored in this paper with respect to its three-dimensional counterpart. The results presented in this work show not only the predictive capacity of the linear correlations mentioned, but the robustness of the ANC interactions to reproduce thermophysical properties and phase equilibria for model and real two-dimensional fluids. Discriminating the influence of repulsive and attractive contributions in molecular interaction models is undoubtedly of great relevance to have a better understanding of thermodynamic properties of simple and complex fluids.

The modified Newton attraction law and its connection with cosmological $$\varLambda $$ term

We consider the possibility of generalizing the Newtonian law of gravity and the transition to a general relativistic model for weak fields with the inclusion of a repulsive term identified as a cosmological constant. The analysis includes that of the test particle's motion in a modified gravitational field of the Hilbert metric and then the problem of the reverse transition from the post-Galilean case to the construction of a modified exact point mass metric which includes the $\Lambda$-term.

Relativistic selfinteracting particle­-antiparticle system of bosons

Thermodynamic properties of a system of an interacting boson particles and antiparticles at high tem­peratures are studied within the framework of the thermodynamically consistent Skyrme-­like mean-­field model. The mean field contains both attractive and repulsive terms. Self­-consistency relations between the mean field and thermodynamic functions are derived. We assume a conservation of the isospin density for all temperatures. It is shown that, independently of the strength of the attractive mean field, at the critical tem­perature Tc the system undergoes the phase transition of second order to the Bose­-Einstein condensate, which exists in the temperature interval 0 ≤ T ≤ Tc . It is obtained that the condensation represents a discontinuity of the derivative of the specific heat at T = Tc .

Combining intermolecular potentials for the prediction of fluid properties: Two-body and three-body interactions.

The ability to combine intermolecular potentials without loss of information is investigated. Molecular simulation results for both vapor-liquid equilibria and supercritical isochoric heat capacities are reported for different combinations of n-m potentials. The role of both additional cohesion and repulsive terms is determined. The 12-8-6 potential obtained by adding an m = 6 contribution to the 12-8 potential significantly broadens the phase envelope, which remains inside of the 12-6 envelope. In contrast, the 12+9-6 potential that involves an additional n = 9 repulsive contribution lifts the phase envelope above the 12-6 values. The 12-8-6 potential significantly reduces the maximum and minimum observed for the isochoric heat capacity at supercritical conditions. In contrast, the additional repulsion of the 12+9-6 potential has a relatively small influence on the supercritical behavior of the isochoric heat capacity. Significantly, a comparison of vapor-liquid equilibria data for two-body only simulations for Ar, Kr, and Xe indicates that there is very good agreement with the 12-8-6 data. This means that the 12-8-6 potential may provide a useful description of two-body only interactions for the noble gases. The 12+9-8 potential at least partially reproduces vapor-liquid properties of noble gases interacting via two-body plus three-body interactions. In general, the combination of potentials provides a mechanism of simplifying the calculation of two-body and two-body plus three-body interactions.

Ionic Transport in Non-Aqueous Electrolyte Solutions - (ii) Monte-Carlo Simulation Based on Lattice Gas Model

Transport phenomena in electrolyte solutions have a century-long history of research. Yet its mechanism is still somewhat unclear at the salt concentration C of ca. 1 mol L−1 or higher, at which many electrochemical devices function, such as Li-ion battery. Behind the difficulty in understanding the phenomena lies a fact that at high concentrations the ionic transport is significantly dominated by the inter-ionic interactions that are trivial in a dilute solution. Taking the specific conductivity σ as an example, it marks a maximum σmax at a certain salt concentration C ∗, at which the positive contribution from the increase in the charge carrier with the increase in C is counter-balanced by the correlation between ions dragging or repulsing each other. Another trade-off situation is that, while one may expect that a higher valence of the charge carrier (e.g., Li+ → Mg2+) would be beneficial in increasing the conductivity, its stronger interaction would at the same time dampen the ionic movement.We have put forward a simple (and hence abstract) lattice gas model to explain the ionic conductivity and viscosity of the electrolyte solution at high concentrations.[1,2] This model successfully describes the maximum in σmax and the steep increase in the viscosity with concentration in terms of the strong repulsion between ions with identical sign. It also explains how the dielectic constant of the solvent plays the role in determining these transport properties.Based on the experimental data for the divalent systems added anew— the preceding presentation by Sano et al., the present paper deals with our model to discuss how σmax is scaled by the valence of the charge carrier z ± and ε. We found that, if other conditions are identical, σ is proportional to the “harmonic mean valence” z h of the salt, where 1/z h ≡ (1/z ++1/|z −|)/2, while at the same time σ and C ∗ are scaled by the factor exp(−az +|z −|u/ε) where a is a constant and u is a parameter that represents the strength of the Coulombic interaction between two single charges. As a result, the fact that despite the higher valence of MgA2 (z h = 4/3) than LiA or NaA (z h = 1), σ max of the divalent system is smaller than the monovalent counterparts(σmax(MgA2) < σmax(LiA) or σmax(NaA)) is explained by the greater argument in the exponentially decaying function (i.e., z +|z −| = 2 for MgA2 while z +|z −| = 1 for LiA or NaA), which significantly attenuates the conductivity. The relation to the viscosity will also be addressed on site.

Joint Person Objectness and Repulsion for Person Search.

Person search targets to search the probe person from the unconstrainted scene images, which can be treated as the combination of person detection and person matching. However, the existing methods based on the Detection-Matching framework ignore the person objectness and repulsion (OR) which are both beneficial to reduce the effect of distractor images. In this paper, we propose an OR similarity by jointly considering the objectness and repulsion information. Besides the traditional visual similarity term, the OR similarity also contains an objectness term and a repulsion term. The objectness term can reduce the similarity of distractor images that not contain a person and boost the performance of person search by improving the ranking of positive samples. Because the probe person has a different person ID with its neighbors, the gallery images having a higher similarity with the neighbors of probe should have a lower similarity with the probe person. Based on this repulsion constraint, the repulsion term is proposed to reduce the similarity of distractor images that are not most similar to the probe person. Treating the Faster R-CNN as the person detector, the OR similarity is evaluated on PRW and CUHK-SYSU datasets by the Detection-Matching framework with six description models. The extensive experiments demonstrate that the proposed OR similarity can effectively reduce the similarity of distractor samples and further boost the performance of person search, e.g., improve the mAP from 92.32% to 93.23% for CUHK-SYSY dataset, and from 50.91% to 52.30% for PRW datasets.

Elastic Properties and Nonlinear Elasticity of the Noncarbon Hexagonal Lattice Nanomaterials Based on the Multiscale Modeling

Abstract This study presents the elastic properties and nonlinear elasticity of the two-dimensional noncarbon nanomaterials of hexagonal lattice structures having molecular structure XY. Four nitride-based and two phosphide-based two-dimensional nanomaterials, having graphene-like hexagonal lattice structure, are considered in the present study. The four empirical parameters associated with the attractive and repulsive terms of the Tersoff–Brenner potential are calibrated for noncarbon nanomaterials and tested for elastic properties, nonlinear constitutive behavior, bending modulus, bending and torsional energy. The mathematical identities for the tangent constitutive matrix in terms of the interatomic potential function are derived through an atomistic–continuum coupled multiscale framework of the extended version of Cauchy–Born rule. The results obtained using newly calibrated empirical parameters for cohesive energy, bond length, elastic properties, and bending rigidity are compared with those reported in the literature through experimental investigations and quantum mechanical calculations. The continuum approximation is attained through the finite element method. Multiscale evaluations for elastic properties and nonlinear stretching of the nanosheets under in-plane loads are also compared with those obtained from atomistic simulations.

Monoradicals and Diradicals of Dibenzofluoreno[3,2-b]fluorene Isomers: Mechanisms of Electronic Delocalization.

The preparation of a series of dibenzo- and tetrabenzo-fused fluoreno[3,2-b]fluorenes is disclosed, and the diradicaloid properties of these molecules are compared with those of a similar, previously reported series of anthracene-based diradicaloids. Insights on the diradical mode of delocalization tuning by constitutional isomerism of the external naphthalenes has been explored by means of the physical approach (dissection of the electronic properties in terms of electronic repulsion and transfer integral) of diradicals. This study has also been extended to the redox species of the two series of compounds and found that the radical cations have the same stabilization mode by delocalization that the neutral diradicals while the radical anions, contrarily, are stabilized by aromatization of the central core. The synthesis of the fluorenofluorene series and their characterization by electronic absorption and vibrational Raman spectroscopies, X-ray diffraction, SQUID measurements, electrochemistry, in situ UV-vis-NIR absorption spectroelectrochemistry, and theoretical calculations are presented. This work attempts to unify the properties of different series of diradicaloids in a common argument as well as the properties of the carbocations and carbanions derived from them.

Multipole expansion of integral powers of cosine theta

Legendre polynomials form the basis for multipole expansion of spatially varying functions. The technique allows for decomposition of the function into two separate parts with one depending on the radial coordinates only and the other depending on the angular variables. In this work, the angular function cos ^k theta is expanded in the Legendre polynomial basis and the algorithm for determining the corresponding coefficients of the Legendre polynomials is generated. This expansion together with the algorithm can be generalized to any case in which a dot product of any two vectors appears. Two alternative multipole expansions for the electron–electron Coulomb repulsion term are obtained. It is shown that the conventional multipole expansion of the Coulomb repulsion term is a special case for one of the expansions generated in this work.