Repulsive Components Research Articles

Electrostatically embedded symmetry-adapted perturbation theory.

Symmetry-adapted perturbation theory (SAPT) is an abinitio approach that directly computes noncovalent interaction energies in terms of electrostatics, exchange repulsion, induction/polarization, and London dispersion components. Due to its high computational scaling, routine applications of even the lowest order of SAPT are typically limited to a few hundred atoms. To address this limitation, we report here the addition of electrostatic embedding to the SAPT (EE-SAPT) and ISAPT (EE-ISAPT) methods. We illustrate the embedding scheme using water trimer as a prototype example. Then, we show that EE-SAPT/EE-ISAPT can be applied for efficiently and accurately computing noncovalent interactions in large systems, including solvated dimers and protein-ligand systems. In the latter application, particular care must be taken to properly handle the quantum mechanics/molecular mechanics boundary when it cuts covalent bonds. We investigate various schemes for handling charges near this boundary and demonstrate which are most effective in the context of charge-embedded SAPT.

Effective mechanical potential of cell-cell interaction in tissues harboring cavity and in cell sheet toward morphogenesis.

Measuring mechanical forces of cell-cell interactions is important for studying morphogenesis in multicellular organisms. We previously reported an image-based statistical method for inferring effective mechanical potentials of pairwise cell-cell interactions by fitting cell tracking data with a theoretical model. However, whether this method is applicable to tissues with non-cellular components such as cavities remains elusive. Here we evaluated the applicability of the method to cavity-harboring tissues. Using synthetic data generated by simulations, we found that the effect of expanding cavities was added to the pregiven potentials used in the simulations, resulting in the inferred effective potentials having an additional repulsive component derived from the expanding cavities. Interestingly, simulations by using the effective potentials reproduced the cavity-harboring structures. Then, we applied our method to the mouse blastocysts, and found that the inferred effective potentials can reproduce the cavity-harboring structures. Pairwise potentials with additional repulsive components were also detected in two-dimensional cell sheets, by which curved sheets including tubes and cups were simulated. We conclude that our inference method is applicable to tissues harboring cavities and cell sheets, and the resultant effective potentials are useful to simulate the morphologies.

Evaluation and improvement of Gay-Berne interaction potential to simulate 3D DLVO interaction of clay particles

This paper first presents a set of DLVO-based energy-separation functions for a pair of finite uniformly charged square platelets of infinitesimal thickness in three elementary configurations: face-to-face, edge-to-edge, and edge-to-face. The novel dataset was generated by summing the electrostatic interaction energy computed numerically by solving the non-linear 3D Poisson-Boltzmann equation and the van der Waals interaction energy calculated analytically. The dataset aims to inform qualitatively and quantitatively the energy/force separation functions used in the Discrete Element Method (DEM) and Coarse-Grained Molecular Dynamics (CGMD) modelling of clays. The same dataset was then used to calibrate and evaluate two Gay-Berne (GB)-type potentials: i) a DLVO-adapted Gay-Berne potential, where the Born-van der Waals branches of the underlying Lennard-Jones (LJ) potential are replaced with van der Waals-Columbic branches to represent DLVO interactions; ii) the Mie potential, where the exponents of the two energy terms are ‘unlocked’ instead of being set equal to 12 and 6 as per the original LJ potential. It is shown that the orientation parameter, µ, and the anisotropy parameter, ν, need to be different from µ = 2 and ν = 1 as adopted in CGMD clay modelling to capture the progression of the shape of the pair energy-separation function from face-to-face to edge-to-face and edge-to-edge configuration. It is also shown that the MIE potential (with exponents m = 3 and n = 1.5) better captures the slow decay of the electrostatic repulsive energy component of the DLVO potential energy Coulombic branch of the interaction potential compared to the DLVO-adapted GB potential, which embeds the Lennard-Jones (LJ) exponents m = 12 and n = 6.

Pairing effects on pure rotational energy of nuclei

By applying the angular-momentum projection to the self-consistent axial mean-field solutions with the semi-realistic effective Hamiltonian M3Y-P6, the pairing effects on the pure rotational energy of nuclei, i.e. the rotational energy at a fixed intrinsic state, have been investigated. While it was shown at the Hartree–Fock (HF) level that the individual terms of the Hamiltonian contribute to the rotational energy with ratios insensitive to nuclides except for light or weakly-deformed nuclei, the pair correlations significantly change the contributions, even for the well-deformed heavy nuclei. The contribution of the interaction to the rotational energy is found to correlate well with the degree of proximity between nucleons, which is measured via the expectation value that two nucleons exist at the same position. While the nucleons slightly spread as the angular momentum increases at the HF level, accounting for the positive (negative) contribution of the attractive (repulsive) components of the interaction, the pair correlations reduce or invert the effect.

Harmonic models and molecular dynamics simulations of isomorph behavior of Lennard-Jones fluids: Excess entropy and high temperature limiting behavior

Henchman’s approximate harmonic model of liquids is extended to predict the thermodynamic behavior along lines of constant excess entropy (“isomorphs”) in the liquid and supercritical fluid regimes of the Lennard-Jones (LJ) potential phase diagram. Simple analytic expressions based on harmonic cell models of fluids are derived for the isomorph lines, one accurate version of which only requires as input parameters the average repulsive and attractive parts of the potential energy per particle at a single reference state point on the isomorph. The new harmonic cell routes for generating the isomorph lines are compared with those predicted by the literature molecular dynamics (MD) methods, the small step MD method giving typically the best agreement over a wide density and temperature range. Four routes to calculate the excess entropy in the MD simulations are compared, which includes employing Henchman’s formulation, Widom’s particle insertion method, thermodynamic integration, and parameterized LJ equations of state. The thermodynamic integration method proves to be the most computationally efficient. The excess entropy is resolved into contributions from the repulsive and attractive parts of the potential. The repulsive and attractive components of the potential energy, excess Helmholtz free energy, and excess entropy along a fluid isomorph are predicted to vary as ∼T−1/2 in the high temperature limit by an extension of classical inverse power potential perturbation theory statistical mechanics, trends that are confirmed by the MD simulations.

Probing nuclear equation of state with the cdm3y version of B3y-fetal effective interaction

This paper is a study of the nuclear Equation of State (EOS) of cold nuclear matter with the B3Y-Fetal effective interaction in its CDM3Y density-dependent version within the framework of Hartree-Fock approximation. The well-known saturation properties of both symmetric and asymmetric nuclear matter are well-reproduced in this work. Using the CDM3Y-K approach, this study has evolved a new set of user interactions, some of which are CDB3Y1-, CDB3Y2-, CDB3Y3-, CDB3Y4-, CDB3Y5-, CDB3Y6-Fetal interactions with corresponding incompressibilities K0 = 188, 204, 217,228, 241 and 252 MeV respectively, in excellent agreement with those of the M3Y-Paris and M3Y-Reid effective interactions. For asymmetric nuclear matter, the new set of interactions has produced the symmetry energy Esym = 32.00 MeV with an associated slope parameter L = 55 MeV at a saturation density ρ = 0.17fm−3 and asymmetry parameter δ = 1.00 (pure neutron matter) in good agreement with the standard values obtained from coupled channel analysis of charge exchange reactions, statistical multifragmentation model and terrestrial Nuclear Physics experimental analyses. Furthermore, the new set of interactions has been found to have bright prospects in a nuclear reaction as the real folded potential computed with the CDB3Y6-Fetal interaction within the framework of double folding potential has been found to be good and similar to that of CDB3Y6-Paris whose optical potential has a repulsive direct component.

Preparation and characterization of N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals by physical vapour transport (PVT) technique

Good quality of N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals (space group Pna21, point group mm2) having different morphologies were successfully grown from vapour phase for the first time by physical vapour transport technique under predefined supersaturation conditions. BNA single crystals of different morphologies resulted at different supersaturation conditions: prismatic (σ = 0.0218 to 0.1553), columnar (σ = 0.1553 to 0.4652), needle (σ = 0.4652 to 0.7245), fine-needle (σ = 0.7245 to 0.9166) and dendritic (σ = 0.9166 to 0.9729). The predicted theoretical morphologies using BFDH, and attachment energy models are in line with the experimental morphologies. The slice thickness, slice energy, attachment energy and anisotropic growth factor of different faces were determined which reveals that {020} are the slow-growing and morphologically important facets amongst others present in the grown BNA single crystal. Fast growth along ‘+c’ direction and no growth along ‘-c’ direction was identified due to the supersaturation-dependant anisotropic growth nature of BNA. Crystal purity and quality are confirmed by single crystal X-ray diffraction study. In addition, the role of intermolecular interactions, electrostatic, polarization, repulsion and dispersion energy components involved in the crystal packing to stabilize the BNA single crystal were characterized by the Crystal Explorer 17.5 software. Computed energy frameworks confirm that the dispersion energy component is predominantly contributing to the crystal packing than the Coulombic interaction energies.

Formation Control for Second-Order Multi-Agent Systems with Collision Avoidance

This paper deals with the formation control problem without collisions for second-order multi-agent systems. We propose a control strategy which consists of a bounded attractive component to ensure convergence to a specific geometrical pattern and a complementary repulsive component to guarantee collision-free rearrangement. For convergence purposes, it is assumed that the communication graph contains at least a directed spanning tree. The avoidance complementary component is formed by applying repulsive vector fields with unstable focus structure. Using the well-known input-to-state stability property a control law for second-order agents is derived in a constructive manner starting from the first-order case. We consider that every agent is able to detect the presence of any other agent in the surrounding area and also can measure and share both position and velocity with his predefined set of neighbours. The resulting control law ensures the convergence to the desired geometrical pattern without collisions during the transient behaviour, as well as bounded velocities and accelerations. Numerical simulations are provided to show the performance and effectiveness of the proposed strategy.

EFFECTIVE SOLUTIONS FOR COMMON PROBLEMS OF ARTIFICIAL POTENTIAL FIELD BASED PATH PLANNING ALGORITHMS FOR MOBILE ROBOTS

Abstract
 Autonomous Path Planning (APP) capability is one of the main factors determining the autonomous level of a mobile robot. Although different methods are used for APP in the literature, the path planning approach based on Artificial Potential Fields (APF) has a very common usage area with its modeling ease and computational performance. APF-based APP, which is a grid-based path planning approach, is usually performed by combining a repulsive and attractive component that models many basic motions with a certain equation and calculating the gradient of this potential field to obtain the vector field. In this study, the basic models used for APF-based APP are examined, and how they are realized and how the resultant potential field is produced are mentioned. Although APF-based APP approaches have advantages, they also have problems such as local minimum, obstacles positioned too close, oscillation, and targets positioned too close to obstacles. Within the scope of the study, these problems were defined one by one and the approaches suggested in the literature for the solution of these problems were mentioned in detail. As a result, it has been seen that to obtain an effective APF-based APP solution, it is necessary to generate a convolutional vector field, limit the fundamental potential fields with exponential functions, use virtual potential fields and perform models with harmonic functions.

Reaction channel contributions to the proton +Pb208 optical potential at 40 MeV

Background: Reaction channel coupling substantially modifies the real and imaginary nucleon-nucleus interactions for nuclei of $Z=20$ or less in ways that cannot be represented as uniform renormalizations of folding model potentials. For such nuclei coupling to inelastic channels also contributes. This raises the question of the effect of these couplings for heavier target nuclei.Purpose: To establish and characterize the contribution to the proton-nucleus interaction generated by coupling to neutron pickup (outgoing deuteron) channels for 40 MeV protons on the heavy closed shell nucleus $^{208}\mathrm{Pb}$. To identify and evaluate the consequent dynamical non-locality.Methods: Coupled reaction channel (CRC) calculations provide the elastic channel $S$-matrix ${S}_{lj}$ due to the included processes. Inversion of ${S}_{lj}$ will produce the local potential that would yield, in a single channel calculation, the elastic scattering observables from the CRC calculation. Subtracting the bare potential of the CRC calculations gives a local and $l$-independent representation of the dynamical polarization potential (DPP). From the DPPs due to various combinations of channel couplings, the influence of dynamically generated nonlocality can be identified.Results: Coupling to deuteron channels generates a repulsive component for the real potential and an absorptive component for the imaginary term. The radial shapes of both terms were modified in ways that could not be represented by uniform renormalization; the rms radius of the real part was substantially altered. Evidence of the dynamical nonlocality of the DPP due to pickup is provided by the nonadditivity of contributions of different couplings and other effects. For the doubly closed shell $^{208}\mathrm{Pb}$ coupling to low-lying (nongiant) collective states has a very small effect on elastic scattering, making a negligible contribution compared with pickup, and was not included.Conclusions: The DPPs established here strongly challenge the notion that folding models, in particular local density models, provide a satisfactory description of elastic scattering of protons from heavy nuclei. Coupling to neutron pickup channels induces dynamical nonlocality in the proton optical model potential with implications for direct reactions.

PH-dependent phase transitions in ferrofluids: A Monte Carlo simulation study using an extended DLVO model

The present survey focuses on the pH-dependent phase behavior of acidic ferrofluids using Monte Carlo simulations. Samples based on CoFe2O4@γ-Fe2O3 core@shell nanoparticles with five different mean sizes were investigated. The interparticle interactions were modeled employing an extended DLVO theory, which includes the anisotropic magnetic dipolar interaction. The electrostatic repulsive component considers the dependence of the surface charge density with pH and nanoparticle mean size. The simulations highlight the effect of pH on the phase behavior of the samples, where the pH increase towards neutral induces an increase in the number of agglomerates, while also reducing first-neighbor distances, especially for samples based on larger nanoparticles. The results obtained in these simulations agree with experimental observations carried out on acidic ferrofluid samples and allow a reliable characterization of the stability domains of these systems. Ultimately, the general pH-dependent phase behavior is confirmed through a detailed analysis of the results of the simulated samples.

Attracting Conductive Nonmagnetic Objects With Rotating Magnetic Dipole Fields

Recent research has shown that eddy currents induced by rotating magnetic dipole fields can produce forces and torques useful for dexterous manipulation of conductive nonmagnetic objects. This control paradigm shows promise for application in the remediation of space debris. However, the resulting force from each field source always includes a repulsive component, suggesting that the object should be surrounded by field sources to some degree to ensure the object does not leave the dexterous workspace during manipulation. In this letter, we describe the ability of multiple field sources working together in a coordinated fashion to attract conductive nonmagnetic objects that are not surrounded, reminiscent of a tractor beam. This enables an object to be pulled into a dexterous manipulation workspace. We explicitly describe the nominal attractive force on spherical objects, serving as an approximation for other object geometries, as a function of the properties of the object and the field-generation system. We perform experimental verification using a water-based microgravity simulator.

Dark energy and dark matter in emergent gravity

Emergent gravity can be applied to a large $N$ matrix model by considering the vacuum of a noncommutative (NC) Coulomb branch that satisfies the Heisenberg algebra. Due to the fact that IR fluctuations in the NC Coulomb branch always pair with UV fluctuations, this UV/IR mixing is extendable to a macroscopic scale. These vacuum fluctuations in the NC Coulomb branch are described by a four-dimensional NC $U(1)$ gauge theory. The order parameter for the vacuum fluctuations is given by random four-vectors that have their own causal structure in the commutative limit unlike the conventional cosmological models based on a scalar field theory coupled to gravity. We show that their causal structure results in the different nature of gravitational interactions so that space-like fluctuations give rise to the repulsive gravitational force while time-like fluctuations generate the attractive gravitational force. Given the fact that the fluctuations are random in nature and we live in a (3+1)-dimensional spacetime, the ratio of the repulsive vs. attractive components ends up being 3:1 = 75:25, which is interestingly consistent with the dark components of the current universe. If we include ordinary matters acting as an attractive gravitational force, the emergent gravity could more accurately explain the dark side of our universe. This work is an expanded version of the conference proceedings (Yang in EPJ Web Conf 168:03006, 2018).

Quantum vacuum phenomena in various backgrounds

In this paper, we will review, through various examples, some ideas connecting the physics of the quantum vacuum and the Casimir effect with the mechanism of symmetry breaking in different backgrounds. In the first example, we will discuss how the quantum vacuum energy is altered by the presence of nonlinearities in the underlying quantum field theory in a way that depends on the spatial dimensionality, as dictated by the Mermin–Wagner–Hohenberg–Coleman theorem. In the second example, we will explore how the combination of boundary effects and (discrete) chiral symmetry breaking can affect the thermodynamical behavior of a system of interacting fermions, and how this is reflected on the Casimir force. Even in the simplest setup of two parallel plates, two interesting things happen: first, the order of the transition through which discrete chiral symmetry may be broken/restored changes from second-order for infinitely large separation to first-order for a finite separation between the boundaries. Second, a peculiar behavior in the fermion condensate occurs, resulting in the appearance of two different phases (massless and massive) in the Casimir force. In the third example, we will also be concerned with the Casimir effect on an interacting fermion background over a string of finite length. Using a self-consistent method, we will show how a nontrivial behavior in the Casimir force arises, displaying a switch from an attractive to a repulsive regime, as a result of the competing effects due to the usual attractive Casimir force and a repulsive component coming from the condensate.

Thermodynamic Signatures of Structural Transitions and Dissociation of Charged Colloidal Clusters: A Parallel Tempering Monte Carlo Study.

Computational simulation of colloidal systems make use of empirical interaction potentials that are founded in well-established theory. In this work, we have performed parallel tempering Monte Carlo (PTMC) simulations to calculate heat capacity and to assess structural transitions, which may occur in charged colloidal clusters whose effective interactions are described by a sum of pair potentials with attractive short-range and repulsive long-range components. Previous studies on these systems have shown that the global minimum structure varies from spherical-type shapes for small-size clusters to Bernal spiral and “beaded-necklace” shapes at intermediate and larger sizes, respectively. In order to study both structural transitions and dissociation, we have organized the structures appearing in the PTMC calculations by three sets according to their energy: (i) low-energy structures, including the global minimum; (ii) intermediate-energy “beaded-necklace” motifs; (iii) high-energy linear and branched structures that characterize the dissociative clusters. We observe that, depending on the cluster, either peaks or shoulders on the heat–capacity curve constitute thermodynamics signatures of dissociation and structural transitions. The dissociation occurs at for all studied clusters and it is characterized by the appearance of a significant number of linear structures, while the structural transitions corresponding to unrolling the Bernal spiral are quite dependent on the size of the colloidal system.

Structural studies of various olmesartan solvates.

Seven solvates of the angiotensin II receptor blocker agent olmesartan (C24H26N6O3), namely, the methanol (C24H26N6O3·CH4O), ethanol (C24H26N6O3·C2H6O), isopropanol (C24H26N6O3·C3H8O), isobutanol (C24H26N6O3·C4H10O), 2-ethoxyethanol (C24H26N6O3·C4H10O2), chloroform (C24H26N6O3·CHCl3) and acetonitrile (C24H26N6O3·C2H3N) solvates, were successfully obtained. The crystal structures were determined using the single-crystal X-ray diffraction technique and the structural features are described, each solvate containing one molecule of olmesartan and one of solvent in the asymmetric unit. The samples were also analyzed by powder X-ray diffraction. Total lattice energies and binding energies between the olmesartan and solvent molecules were evaluated, which can be partitioned into electrostatic, polarization, dispersion and repulsion components. Hirshfeld and fingerprint plot analysis was performed to highlight the intermolecular contacts. Hydrogen bonding and supramolecular arrangements were comparatively studied for the seven solvates.

Poly(maleic anhydride) Shell Modified with Negatively and Positively Charged Groups to Control Zeta Potential and Hydrodynamic Size of Encapsulated Quantum Dots at Variable pH

AbstractWe prepared water‐soluble quantum dots (QDs) with tunable ξ‐potential varied from −38 to +20 mV and controlled sensitivity to pH level. Poly(maleic anhydride‐alt‐1‐tetradecene) (PMAT) was modified with bifunctional molecules containing sulfate, sulfonate, phosphate, phosphonate, and quaternary ammonium in different proportions. The sulfonate shell of QDs leads to a stable negative ξ‐potential in the biological pH range from 4.5 to 9.5, while modification with quaternary ammonium groups gives QDs with positive and pH‐independent charge. If nearly half of carboxyl groups of PMAT were modified with quaternary ammonium groups, ξ‐potential begins pH‐dependent with the isoelectric point at pH≈5.5. To obtain pH‐independent, neutrally charged QDs, the rest of carboxyl groups can be converted into sulfonate groups at a 1 : 1 ratio; sulfonate‐quaternary ammonium QDs show high colloidal stability in solutions with high ionic strength. In addition, encapsulated QDs show an unusual correlation between their hydrodynamic size and ζ‐potential: when ζ‐potential approaches zero, the hydrodynamic size markedly increases due to a decrease in the electrostatic repulsion component of the QDs diffusion coefficient.

The hybrid ergodic lattice gas model for critical fluids and the molecular nature of the critical point

This paper introduces the hybrid ergodic lattice gas model as a conceptually simple, computationally cheap, yet accurate model that predicts macroscopic fluid pressure along the critical isotherm of a fluid accurately. A key concept is the hybrid evaluation of the properties: the kinetic and repulsive pressure components are calculated from equations of state, representing the ‘global’ nature of these values, whereas the attractive pressure component is calculated from the ‘local’ particle arrangement, in which particle clusters are identified using unsupervised machine learning. The proposed method captures the fluid pressure of the ideal gas regime and near the critical point, and is much more accurate then the Peng Robinson equation of state for liquid states. The predicted molecular structure is then used to identify three distinct stages of molecular behavior along the isotherm: I. cluster formation, II. cluster consolidation, and III. supercluster growth. Specifically, the critical point is shown to correspond to the state in II. where clusters merge together to form a single supercluster, corresponding to the percolation threshold of a cubic site lattice. The foundation of the model in a lattice gas opens the door for the analytical analysis of near-critical fluids using percolation theory and probabilistic analysis. As an example, a lattice-based derivation of a van der Waals attractive term is given. Finally, the lattice fluid is shown to be related to random networks, but deviates from the classical Erdős and Rényi’s G(N, L) model in that the critical point is found at a degree of 〈k〉 = 2 rather than the classical result of 〈k〉 = 1.

Super-random states in vehicular traffic — Detection & explanation

This article deals with specific states of traffic flow on a two-lane freeway, in which statistical fluctuations of microscopic quantities (inter-vehicle gaps) are significantly higher than in systems with absolutely random events (Poisson systems). These anomalous states (super-random) are detected in empirical traffic data, specifically in the fast lane at traffic densities up to 25 vehicles per kilometer. The origin of these states is then explained mathematically (using the theory of balance particle systems and tools of random matrix theory), physically (by means of an one-dimensional particle gas subjected to local perturbations caused by overtaking cars) and empirically (using an analogy with phenomena observed in photon counting experiments). In the article we show that overtaking maneuvers, when vehicles from a slow lane are injected into a fast-lane stream of faster moving vehicles, disrupt a local balance in microstructure of fast-lane stream and cause atypical arrangement of vehicular positions, that is very rare, generally. With help of original numerical model we demonstrate that the anomalous states detected are identical to equilibrium states formed in a stochastic particle gas with a potential containing, in addition to a repulsive component, also an attractive component.

Boson stars in Palatini gravity

We explore equilibrium solutions of spherically symmetric boson stars in the Palatini formulation of gravity. We account for the modifications introduced in the gravitational sector by using a recently established correspondence between modified gravity with scalar matter and general relativity with modified scalar matter. We focus on the quadratic theory and compare its solutions with those found in general relativity, exploring both positive and negative values of the coupling parameter ξ. As matter source, a complex, massive scalar field with and without self-interaction terms is considered. Our results show that the existence curves of boson stars in Palatini gravity are fairly similar to those found in general relativity. Major differences are observed for negative values of the coupling parameter which results in a repulsive gravitational component for high enough scalar field density distributions. Adding self-interactions makes the degeneracy between and general relativity even more pronounced, leaving very little room for observational discrimination between the two theories.