Short-range Forces Research Articles

Thermocapillary migration of droplets under molecular and gravitational forces

We study the thermocapillary migration of two-dimensional droplets of partially wetting liquids on a non-uniformly heated surface. The effect of a non-zero contact angle is imposed through a disjoining–conjoining pressure term. The numerical results for two different molecular interactions are compared: on the one hand, London–van der Waals and ionic–electrostatics molecular interactions that account for polar liquids; on the other hand, long- and short-range molecular forces that model molecular interactions of non-polar fluids. In addition, the effect of gravity on the velocity of the drop is analysed. We find that for small contact angles, the long-time dynamics is independent of the molecular potential, and the footprint of the droplet increases with the square root of time. For intermediate contact angles we observe that polar droplets are more likely to break up into smaller volumes than non-polar ones. A linear stability analysis allows us to predict the number of droplets after breakup occurs. In this regime, the effect of gravity is stabilizing: it reduces the growth rates of the unstable modes and increases the shortest unstable wavelength. When breakup is not observed, the droplet moves steadily with a profile that consists in a capillary ridge followed by a film of constant thickness, for which we find power law dependencies with the cross-sectional area of the droplet, the contact angle and the temperature gradients. For large contact angles, non-polar liquids move faster than polar ones, and the velocity is proportional to the Marangoni stress. We find power law dependencies for the velocity for the different regimes of flow. The numerical results allow us to shed light on experimental facts such as the origin of the elongation of droplets and the existence of saturation velocity.

Diversiform electrical and thermal expansion properties of (1 − x)Ba0.95Ca0.05Ti0.94Zr0.06O3–(x)Dy lead-free piezoelectric ceramics influenced by defect complexes

(1 − x)Ba0.95Ca0.05Ti0.94Zr0.06O3–(x)Dy (x = 0–0.90 mol%) lead-free ceramics were prepared at 1190 °C with as-synthesized nanoparticles via a modified Pechini polymeric precursor method. X-ray powder diffraction, Raman spectrometer, and X-ray photoelectron spectroscopy were used to investigate the phase, symmetry, and valence state, respectively. The results indicated dysprosium could induce the phase transformation from O to R. The mechanism of defect complexes and oxygen vacancies that influenced by various dysprosium contents were discussed in detail. The results of dielectric, ferroelectric, and piezoelectric characteristics suggested the electrical properties were initially elevated with a trifling addition of dysprosium contents, and then decreased with further increased x. Moreover, reasons for diversified electrical properties, i.e., imbalanced long-range and short-range forces, changed octahedron structure, defect dipole, pinching effects of domain wall and element electronegative, were all stated in detail. The optimal physical properties, d33 = 371 pC/N, Qm = 87, and CTE2 = 1.23 × 10−5 K−1, were detected at x = 0.60 mol%, and those findings were regarded as prospect in the development of lead-free ferroelectric ceramic materials.

Incorporating electrostatic effects into the effective stress relation — Insights from chalk experiments

Which forces are responsible for holding highly porous chalks together? We use the effective stress to quantify the electrostatic effects around particle contacts originating from the adsorption of ions onto charged mineral surfaces. The induration of chalk indicates that it is held together by contact cement, where planar crystal contacts allow the action of short-ranged adhesive Van der Waals forces. At particle distances exceeding a few nanometers, recent studies have indicated electrostatic repulsion between water-embedded adjacent particles. The magnitude of the repelling force depends, among other parameters, upon temperature and brine composition. Our premise is that by perturbing the electrostatic forces at the particle level, we can control the mechanical behavior of chalk samples tested in triaxial cells. We report the results of an experimental series, investigating how the mechanical strength and stiffness varied among samples saturated with four different brines, tested at two temperatures, and tested directly or after aging for three weeks at high temperature. We associate stiffness with bulk modulus and strength with the stress at yield. Systematic softening and weakening is observed, especially when the pore fluid is sulfate bearing, as well as for some high-temperature experiments and for aged samples. However, softening and weakening are not totally correlated, and neither brine composition, temperature, nor aging can alone dictate the mechanical behavior of the chalk — a combination is required to predict the chalk stiffness and strength. To obtain a coherent description of our experimental results, we estimated the electrostatic stress arising from ion adsorption and found it unnecessary for these experiments to postulate significant dissolution or precipitation-related changes to the rock frame.

Tetramers of Two Heavy and Two Light Bosons

This article considers the bound states of two heavy and two light bosons, when a short-range force attracts the bosons of different mass, and a short-range force repel the light bosons. The existence of such four-body bound states results from the competition between these two forces. For a given strength of the attraction, the critical strength of the repulsion necessary to unbind the four particles is calculated. This study is motivated by the experimental realisation of impurity atoms immersed in an atomic Bose-Einstein condensate, and aims at determining in which regime only one boson contributes to binding two impurities.

GPU parallel simulation algorithm of Brownian particles with excluded volume using Delaunay triangulations

A novel parallel simulation algorithm on the GPU, implemented in CUDA and C++, is presented for the simulation of Brownian particles that display excluded volume repulsion and interact with long and short range forces. When an explicit Euler–Maruyama integration step is performed to take into account the pairwise forces and Brownian motion, particle overlaps can appear. The excluded volume property brings up the need for correcting these overlaps as they happen, since predicting them is not feasible due to the random displacement of Brownian particles. The proposed solution handles, at each time step, a Delaunay triangulation of the particle positions because it allows us to efficiently solve overlaps between particles by checking just their neighborhood. The algorithm starts by generating a periodic Delaunay triangulation of the particle initial positions on CPU, but after that the triangulation is always kept on GPU memory. We used a parallel edge-flip implementation to keep the triangulation updated during each time step, checking previously that the triangulation was not rendered invalid due to the particle displacements. We designed and implemented an exact long range force simulation with an all-pairs N-body simulation, tiling the particle interaction computations based on the warp size of the target device architecture. The resulting implementation was validated with two models of active colloidal particles, also showing a speedup of up to two orders of magnitude when compared to a sequential implementation. A short range forces simulation using Verlet lists for neighborhood handling was also developed and validated, showing similar performance improvements.

Efimov states near a Feshbach resonance and the limits of van der Waals universality at finite background scattering length

We calculate the spectrum of three-body Efimov bound states near a Feshbach resonance within a model which accounts both for the finite range of interactions and the presence of background scattering. The latter may be due to direct interactions in an open channel or a second overlapping Feshbach resonance. It is found that background scattering gives rise to substantial changes in the trimer spectrum as a function of the detuning away from a Feshbach resonance, in particular in the regime where the background channel supports Efimov states on its own. Compared to the situation with negligible background scattering, the regime where van der Waals universality applies is shifted to larger values of the resonance strength if the background scattering length is positive. For negative background scattering lengths, in turn, van der Waals universality extends to even small values of the resonance strength parameter, consistent with experimental results on Efimov states in $^{39}$K. Within a simple model, we show that short-range three-body forces do not affect van der Waals universality significantly. Repulsive three-body forces may, however, explain the observed variation between around $-8$ and $-10$ of the ratio between the scattering length where the first Efimov trimer appears and the van der Waals length.

Torsion balances with fibres of zero length

Torsion balances have good immunity to tilt and low rotational stiffness. However precise control of the position of the suspended torsion ‘bob’ is difficult in the presence of ground vibrations and tilt and this is a limiting factor in applications where Casimir forces or putative non-Newtonian short-range forces are being measured. We describe how the desirable characteristics of torsion balances can be reproduced in a rigid body that is suspended using applied forces rather than a torsion fibre. The suspension system can then provide a more precise control of the degrees of freedom of the suspended body. We apply these ideas to a superconducting levitated torsion balance, developed by the authors, and a generic electrostatic suspension. We present results of preliminary experiments that provide support for our analyses.

Interstitial Voids and Resultant Density of Liquid Water: A First-Principles Molecular Dynamics Study.

Many anomalous properties of water can be explained on the basis of the coexistence of more than one density states: high-density water (HDW) and low-density water (LDW). We investigated these two phases of water molecules through first-principles molecular dynamics simulations using density functional theory (DFT) in conjunction with various van der Waals-corrected exchange and correlation functionals. Different density regions were found to exist due to the difference in short-range and long-range forces present in DFT potentials. These density regions were identified and analyzed on the basis of the distribution of molecules and voids present. We defined a local structure index to distinguish and find the probability of occurrence of these different states. HDW and LDW arise due to the presence of “interstitial water” molecules in between the first and second coordination shells. The population of interstitial water molecules is found to affect the overall dynamics of the system as they change the hydrogen bond pattern.

From the nonlinear Fokker-Planck equation to the Vlasov description and back: Confined interacting particles with drag.

Nonlinear Fokker-Planck equations endowed with power-law diffusion terms have proven to be valuable tools for the study of diverse complex systems in physics, biology, and other fields. The nonlinearity appearing in these evolution equations can be interpreted as providing an effective description of a system of particles interacting via short-range forces while performing overdamped motion under the effect of an external confining potential. This point of view has been recently applied to the study of thermodynamical features of interacting vortices in type II superconductors. In the present work we explore an embedding of the nonlinear Fokker-Planck equation within a Vlasov equation, thus incorporating inertial effects to the concomitant particle dynamics. Exact time-dependent solutions of the q-Gaussian form (with compact support) are obtained for the Vlasov equation in the case of quadratic confining potentials.

Molecular Modeling Analysis of CO2 Absorption by Glymes.

The properties of diglyme + CO2 systems were analyzed through density functional theory and molecular dynamics methods with the objective of inferring the microscopic properties of CO2 capture by glyme-based solvents and the effect of ether group regarding solvents affinity toward CO2. Calculations of diglyme + CO2 molecular clusters using density functional theory allowed accurate quantification and characterization of short-range intermolecular forces between these molecules, whereas the molecular dynamics simulation of diglyme + CO2 liquid mixtures, for different CO2 contents, were the means to infer the properties and dynamics of bulk liquid phases upon CO2 absorption. Likewise, liquid diglyme + CO2 gas interfaces were also studied using molecular dynamics methods to examine the kinetics of CO2 capture, adsorption at the gas-liquid interface, and the mechanism of interface crossing, which is of pivotal importance for the design of CO2 capturing units.

Dynamic forces between emulsified water drops coated with Poly-Glycerol-Poly-Ricinoleate (PGPR) in canola oil

The dynamic collision of emulsified water drops in the presence of non-ionic surfactants plays a crucial role in many practical applications. Interaction force between water drops coated with non-ionic food grade surfactants is expected to exhibit rich dynamic behavior that is not yet explored. The collision forces between immobilized water drops in canola oil in the presence of a well-known food grade surfactant polyglycerol polyricinoleate (PGPR) are measured at concentrations well below typically used to form stable emulsions. An extension or kink, attributed to a short-range attractive interaction due to PGPR bridging between the drops, was observed in the retract portion of the force curves at higher applied forces or slower collision velocities. The Stokes-Reynolds-Young-Laplace (SRYL) model was used to calculate theoretical force curves. For higher collisions velocities, the agreement between the calculated and experiment data was acceptable, but the SRYL model failed to describe the extension or kink feature observed at slower velocities below. Both the AFM data and the comparison to the model calculation indicated the presence of a short-range attractive force, not of a hydrodynamic origin, attributed to the bridging and extension of PGPR molecules on the surface of water drops below saturation of the interface.

A smoothed particle hydrodynamics framework for modelling multiphase interactions at meso-scale

A smoothed particle hydrodynamics (SPH) framework is developed for modelling multiphase interactions at meso-scale, including the liquid–solid interaction induced deformation of the solid phase. With an inter-particle force formulation that mimics the inter-atomic force in molecular dynamics, the proposed framework includes the long-range attractions between particles, and more importantly, the short-range repulsive forces to avoid particle clustering and instability problems. Three-dimensional numerical studies have been conducted to demonstrate the capabilities of the proposed framework to quantitatively replicate the surface tension of water, to model the interactions between immiscible liquids and solid, and more importantly, to simultaneously model the deformation of solid and liquid induced by the multiphase interaction. By varying inter-particle potential magnitude, the proposed SPH framework has successfully simulated various wetting properties ranging from hydrophobic to hydrophilic surfaces. The simulation results demonstrate the potential of the proposed framework to genuinely study complex multiphase interactions in wet granular media.

Transforming dark photons into sustainable energy

To produce energy from dark photons γ−, colliding it with Higgs boson particle BR(H → γγ−) under extreme relativistic conditions (ERCs) has been proposed. The Higgs boson BR(H → γγ−) gets excited at extreme relativistic conditions and its quantum field has an extremely short-range weak force which can create electromagnetic field. Thus, it has been assumed that the induction of an electrically charged particle dark photon γ− (non-energy level photon), into these extreme relativistic conditions will create an energy level photon, here named the Hossain dark photon (HDP). To confirm this HDP formation via a dark photon quantum interaction with a Higgs boson particle BR(H → γγ−), a series of mathematical modeling tests using MATLAB software has been performed. Interestingly, these mathematical models revealed that the presence of extra relativistic conditions does transform the dark photon γ− into an HDP for N_{text{eff}} = 4.08_{ - 0.68}^{ + 0.71} at a 95% confidence limit considering the parameters of c_{text{eff}}^{2} = 0.312 pm 0.026 and c_{text{vis}}^{2} = 0.29 _{ - 0.16}^{ + 0.21}, respectively. Thereafter, the feasible HDP photon dynamics is also modeled using the atomic spectra contour maps of the Hamiltonian (H = mathop sum nolimits omega_{ci} a_{i}^{dag } a_{i} + sumnolimits_{K} {omega_{k } b_{k}^{dag } b_{k} } + sumnolimits_{ik} {(V_{ik} a^{dag } b_{k} + V_{ik}^{*} b_{k}^{dag } a_{i} )}) which suggested that formation of HDP by a Higgs boson [BR(H → γγ−] particle reaction under extreme relativistic conditions does form high energy level particle to produce electricity.

Search for Novel Short-Range Forces between Elementary Particles in Neutron Scattering

The sensitivity of the method of neutron scattering to novel neutron–nucleon interactions is analyzed. Upper limits on the coupling constant of such interactions are imposed using the available data on neutron powder diffraction on polycrystalline silicon. For the forces acting at ranges of λ < 10–11 m, these upper limits are already competitive with the best existing constraints on their coupling constant. A dedicated experiment can help improve the sensitivity to this coupling constant by nearly two orders of magnitude.

Shear thinning in non-Brownian suspensions.

We study the flow of suspensions of non-Brownian particles dispersed into a Newtonian solvent. Combining capillary rheometry and conventional rheometry, we evidence a succession of two shear thinning regimes separated by a shear thickening one. Through X-ray radiography measurements, we show that during each of those regimes, the flow remains homogeneous and does not involve particle migration. Using a quartz-tuning fork based atomic force microscope, we measure the repulsive force profile and the microscopic friction coefficient μ between two particles immersed into the solvent, as a function of normal load. Coupling measurements from those three techniques, we propose that (1) the first shear-thinning regime at low shear rates occurs for a lubricated rheology and can be interpreted as a decrease of the effective volume fraction under increasing particle pressures, due to short-ranged repulsive forces and (2) the second shear thinning regime after the shear-thickening transition occurs for a frictional rheology and can be interpreted as stemming from a decrease of the microscopic friction coefficient at large normal load.

Field Coupling-Based Image Filter for Sand Painting Stylization

Sand painting is a very new and popular performance art technique, and it has important meaning for the artistic creation. Computer-aided sand painting is now in the ascendant, whose fully automated mechanism is still an attractive challenge. Image data field, inspired from short-range nuclear force in physics, is introduced into sand painting stylization. With preserving edges and features, a fully automatic image filter pipeline based on image field coupling is proposed, which consists of three main steps, including image data field generating, multiscale field coupling, and additional details optimizing. The visual comparisons indicate that the proposed pipeline and image filter are feasible and effective, and sand painting-like artistic images can be produced by using multiscale field coupling. The qualities of various rendering images are also investigated from the perspective of feature similarity measures. The quantitative and qualitative results suggest that the field coupling-based filter is appropriate for sand painting stylization, and the time cost is satisfied for practice applications. Generally, the proposed method provides a reference for automatic creation of computer-aided sand painting art.

Peridynamic Model for the Numerical Simulation of Anchor Bolt Pullout in Concrete

Predictive simulation of anchor pullout from concrete structures is not only a serious problem in structural mechanics but also very important in structural design safety. In the finite element method (FEM), the crack paths or the points of crack initiation usually need to be assumed in advance. Otherwise, some special crack growth treatment or adaptive remeshing algorithm is normally used. In this paper, an extended peridynamic method was introduced to avoid the difficulties found in FEM, and its application on anchor bolt pullout in plain concrete is studied. In the analysis, the interaction between the anchor bolt and concrete is represented by a modified short-range force and an extended bond-level model for concrete is developed. Numerical analysis results indicate that the peak pullout load obtained and the crack branching of the anchoring system agreed well with the experimental investigations.

Thermodynamic modelling of liquid-liquid extraction systems involving ionic liquids: A new approach

In this study, a new approach is introduced for the thermodynamic correlation of liquid-liquid extraction (LLE) systems involving ionic liquids (ILs). The model incorporates the effect of local composition and ion solvation in the liquid-liquid equilibrium. Margules excess Gibbs energy model was used to express the short-range molecule-molecule forces whereas the ion solvation theory of modified three characteristic parameter correlation (TCPC) model was employed to characterize the ion-molecule short range forces. With this proposed approach, better results were obtained for the correlation of experimental tie line data and activity coefficients for LLE systems involving ILs. Moreover, the new approach imparted theoretical improvements over previously used thermodynamic models for the correlation of said systems. A wide range of published experimental data for ternary liquid-liquid extraction systems was examined and the new interaction parameters were optimized. A very low root mean square deviation (RMSD) was observed for all the ternary systems, indicating the proficiency of the proposed model.

Heavy molecules and one- σ/ω -exchange model

In the framework of the one-boson-exchange model, we explore whether the intermediate and short-range forces from $\sigma/\omega$-exchange can be strong enough to bind heavy molecular states. $\Lambda_cD(\bar{D})$, and $\Lambda_c\Lambda_c(\bar{\Lambda}_c)$ systems have been studied and compared. We find that the force from $\sigma$-exchange is attractive and dominant, whereas the $\omega$-exchange force not. As a consequence, the S-wave $\Lambda_cD$, $\Lambda_c\Lambda_c$, and $\Lambda_c\bar{\Lambda}_c$ can be possible molecular candidates. We further indicate that one hadron-hadron system with more light quarks $(u,d)$ can be easier to form a bound state. As a byproduct, by studying the heavy-quark mass dependence for the $\Lambda_cD(\bar{D})$-like and $\Lambda_c\Lambda_c(\bar{\Lambda}_c)$-like systems, we find that the charm/bottom sector can easily accommodates molecular states. Finally, the $\Lambda_cN(\bar{N})$ and $\Lambda_bN(\bar{N})$ systems are investigated. Our results indicate that they are also likely to form bound states. By including one-$\pi$-exchange forces providing additional attraction when coupled channels are included, we expect many molecular states in heavy quark sectors.

Chaotic quadruple secular evolution and the production of misaligned exomoons and Warm Jupiters in stellar multiples

We study the chaotic and secular evolution of hierarchical quadruple systems in the $3+1$ configuration, focusing on the evolution of mutual inclination of the inner binaries as the system undergoes coupled Lidov-Kozai (LK) oscillations. We include short-range forces (SRF; such as those due to tidal and rotational distortions) that control the eccentricity excitation of the inner binary. The evolution of mutual inclination is described, a priori, by two dimensionless parameters, $\pazocal{R}_0$, the ratio between the inner and outer LK time-scales and $\epsilon_{SRF}$, the ratio between the SRF precession and the inner LK precession rates. We find that the chaotic zones for the mutual inclination depend mainly on $\pazocal{R}_0$, while $\epsilon_{SRF}$ controls mainly the range of eccentricity excitation. The mutual inclination evolves chaotically for $1\lesssim \pazocal{R}_0\lesssim 10$, leading to large misalignments. For $0.4 \lesssim \pazocal{R}_0 \lesssim 0.8$, the system could be weakly excited and produce bimodal distribution of mutual inclination angles. Our results can be applied to exomoons-planets in stellar binaries and Warm/Hot Jupiters in stellar triples. Such systems could develop large mutual inclination angles if the inner binary is tight enough, and also high eccentricities, depending of the strength of the short-range forces. Future detections of tilted Warm/Hot Jupiters and exomoons could put our mechanism under observational tests.