Effect Of Repulsive Interactions Research Articles

Effect of repulsive interaction and initial velocity on collective motion process.

Self-propelled collective motion is a highly complex phenomenon, necessitating advanced practical and theoretical tools for comprehension. The significance of studying collective motion becomes apparent in its diverse applications. For instance, addressing evacuation challenges in scenarios with multiple agents can be achieved through an examination of collective motion. Research indicates that the transition of individuals (such as birds, fish, etc.) from a state of rest to equilibrium constitutes a phase transition. Our interest of the issue is to delve into the nature of this transitional phase and elucidate the parameters that shape it. Hence, the primary aim of this paper is to grasp the kinetic phase transition by examining how initial velocity and repulsive interactions impact the dynamics of the system. To gain insight into the complex behavior of multi-agent systems, we apply an extended version of the classical Vicsek model. This extension includes an additional interaction zone, the repulsive zone, where particles repel each other at close range to avoid collisions. Our study uses numerical simulations to explore the system's behavior under various conditions. The focus of this study is the impact of initial velocity on the collective movement of particles. The importance of this research lies in comprehending how velocity affects the overall movement. The conclusion we can draw from these results is that the initial velocity affects both the noise and the density. The novelty of the work is the transition phase, yet it lacks universal characteristics because the critical noise depends on the initial velocity system and the repulsion radius zone. Notably, the repulsion radius and particle density play pivotal roles in achieving a phase transition from one equilibrium state to another aligned equilibrium state.

Mechanically-driven stem cell separation in tissues caused by proliferating daughter cells

The homeostasis of epithelial tissue relies on a balance between the self-renewal of stem cell populations, cellular differentiation, and loss. Although this balance needs to be tightly regulated to avoid pathologies, such as tumor growth, the regulatory mechanisms, both cell-intrinsic and collective, which ensure tissue steady-state are still poorly understood. Here, we develop a computational model that incorporates basic assumptions of stem cell renewal into distinct populations and mechanical interactions between cells. We find that the model generates unexpected dynamic features: stem cells repel each other in the bulk tissue and are thus found rather isolated, as in a number of in vivo contexts. By mapping the system onto a gas of passive Brownian particles with effective repulsive interactions, that arise from the generated flows of differentiated cells, we show that we can quantitatively describe such stem cell distribution in tissues. The interaction potential between a pair of stem cells decays exponentially with a characteristic length that spans several cell sizes, corresponding to the volume of cells generated per stem cell division. Our findings may help understanding the dynamics of normal and cancerous epithelial tissues.

Overcrowding induces fast colloidal solitons in a slowly rotating potential landscape

Collective particle transport across periodic energy landscapes is ubiquitously present in many condensed matter systems spanning from vortices in high-temperature superconductors, frictional atomic sliding, driven skyrmions to biological and active matter. Here we report the emergence of fast solitons propagating against a rotating optical landscape. These experimentally observed solitons are stable cluster waves that originate from a coordinated particle exchange process which occurs when the number of trapped microparticles exceeds the number of potential wells. The size and speed of individual solitons rapidly increase with the particle diameter as predicted by theory and confirmed by numerical simulations. We show that when several solitons coexist, an effective repulsive interaction can stabilize their propagation along the periodic potential. Our experiments demonstrate a generic mechanism for cluster-mediated transport with potential applications to condensed matter systems on different length scales.

Curvature tensor and collective behavior in a population of bacteria

In this work, from a geometric point of view, we analyze the SET model (Schweitzer, Ebeling and Tilch) of the mobility of a bacterium. Biological systems are out of thermodynamic equilibrium and they are subject to complex external or internal influences that can be modeled in the form of noise or fluctuations. In this sense, due to the stochasticity of the variables, we study the probability of finding a bacteria with a speed v in the interval (v, v + dv) or, from a population point of view, we can interpret the probability density function as associated with finding a bacterium with a speed v in the interval (v, v + dv). We carry out this study from the stationary probability density solution of the Fokker-Planck equation and using the structure of the statistical manifold related with the stationary probability density, we study the curvature tensor in terms of two coordinates associated with the state of mobility of the bacteria and the environmental conditions. Taking as reference the geometric interpretations found in the framework of equilibrium thermodynamics, our results suggest that bacteria have an effective repulsive interaction that increases with mobility. These results are compatible with the behavior of populations of bacteria that form biofilms when their mobility decreases.

Generation of nonreciprocal single photons in the chiral waveguide-cavity-emitter system

We investigate the generation of nonreciprocal single photons in the chiral waveguide-cavity-emitter system. Due to the chirality of light-emitter interactions, photons in the left direction couple to a cavity which induces only linear optical effects, while photons in the right direction couple to a cavity-emitter system which can generate optical nonlinearity. In the regime of single-photon transmission, photons in the left direction are absorbed by the cavity at the resonance frequency, while photons in the right direction are transmitted due to the Rabi splitting. In the regime of two-photon transmission, optical linearity in the left direction cannot produce photon-photon interactions and does not change the statistics of photons. However, the effective repulsive interaction between photons can be produced by the optical nonlinearity in the right direction, suppressing two-photon transmission (photon blockade). Physically, the photon-photon bound state, which emerges due to the strong-photon-photon correlation mediated by the cavity-emitter system, plays a key role in generation of photon blockade at the resonance frequency. As a result, nonreciprocal single photons can be realized in the combination of single-photon transmission and photon blockade at the resonance frequency. Additionally, photon-photon interactions are sensitive to the width of the wave packet since photons should coincide at the interaction site.

Triblock copolymer micelle model of spherical paraspeckles.

Paraspeckles are nuclear bodies scaffolded by RNP complexes of NEAT1_2 RNA transcripts and multiple RNA-binding proteins. The assembly of paraspeckles is coupled with the transcription of NEAT1_2. Paraspeckles form the core-shell structure, where the two terminal regions of NEAT1_2 RNP complexes compose the shell of the paraspeckle and the middle regions of these complexes compose the core. We here construct a theoretical model of paraspeckles by taking into account the transcription of NEAT1_2 in an extension of the theory of block copolymer micelles. This theory predicts that the core-shell structure of a paraspeckle is assembled by the association of the middle region of NEAT1_2 RNP complexes due to the multivalent interactions between RBPs bound to these regions and by the relative affinity of the terminal regions of the complexes to the nucleoplasm. The latter affinity results in the effective repulsive interactions between terminal regions of the RNA complexes and limits the number of complexes composing the paraspeckle. In the wild type, the repulsive interaction between the middle and terminal block dominates the thermal fluctuation. However, the thermal fluctuation can be significant in a mutant, where a part of the terminal regions of NEAT1_2 is deleted, and distributes the shortened terminal regions randomly between the shell and the core, consistent with our recent experiments. With the upregulated transcription, the shortened terminal regions of NEAT1_2 in a deletion mutant is localized to the core to decrease the repulsive interaction between the terminal regions, while the structure does not change with the upregulation in the wild type. The robustness of the structure of paraspeckles in the wild type results from the polymeric nature of NEAT1_2 complexes.

PH‐Dependent Behavior of Ionizable Cationic Lipids in mRNA‐Carrying Lipoplexes Investigated by Molecular Dynamics Simulations

RNA Delivery In article number 2100683, Giovanni Settanni, Friederike Schmid, and co-workers present molecular dynamics simulations of a lipoplex composed of RNA (yellow) helper DOPC lipids (gray) and ionizable cationic lipids DODMA (protonated: red, neutral: cyan). Protonated DODMA and RNA attract each other, whereas neutral DODMA and RNA experience an effective repulsive interaction. As a result, the structure of the lipoplex becomes pH dependent.

Strong Two‐Phonon Correlations and Bound States in the Continuum in Phononic Waveguides with Embedded SiV Centers

AbstractQuantum phononic systems have attracted great attention in quantum science and technology. However, it is quite difficult to realize strong phonon–phonon interactions at the few phonon level in phononic systems, since direct interactions between phonons are generally very weak. Here, the phonon transport properties and the phonon–phonon interactions in a 1D phononic waveguide with embedded silicon‐vacancy (SiV) centers are studied. The authors show that, mediated by the SiV centers, strong phonon–phonon interactions can be realized due to coherent interferences of the emitting phonon waves with the incident waves. In particular, the embedded color centers can induce an effective attractive or repulsive interaction in space for phonons, corresponding to phonon bunching or antibunching. Besides, it is found that a single SiV center can capture two resonant phonons simultaneously, forming a phononic bound state in the continuum. Comparing with photon–photon interactions in photonic systems, the phonon–phonon interactions are stronger for relatively slower phonon velocity and the strongly correlated phonon properties are promising for constructing various all‐phonon quantum devices in quantum information processing.

Interplay between chiral dynamics and repulsive interactions in hot hadronic matter

We investigate fluctuations of the net-baryon number density in hot hadronic matter. We discuss the interplay between chiral dynamics and repulsive interactions and their influence on the properties of these fluctuations near the chiral crossover. The chiral dynamics is modeled by the parity doublet Lagrangian that incorporates the attractive and repulsive interactions mediated via the exchange of scalar and vector mesons, respectively. The mean-field approximation is employed to account for chiral criticality. We focus on the properties and systematics of the cumulants of the net-baryon number density up to the sixth order. It is shown that the higher-order cumulants exhibit a substantial suppression in the vicinity of the chiral phase transition due to the presence of repulsive interactions. We find, however, that the characteristic properties of cumulants near the chiral crossover observed in lattice QCD results are entirely linked to the critical chiral dynamics and, in general, cannot be reproduced in phenomenological models, which account only for effective repulsive interactions via excluded-volume corrections or van-der-Waals type interactions. Consequently, a description of the higher-order cumulants of the net-baryon density in the chiral crossover requires a self-consistent treatment of the chiral in-medium effects and repulsive interactions.

Superfluid–Mott insulator quantum phase transition in hybrid cavity optomechanical arrays

A two-dimensional hybrid cavity optomechanical array formed by an optomechanical cavity embedded with a two-level atom in each site is introduced to discuss the superfluid–Mott insulator quantum phase transition of light. On account of the optomechanical coupling effects stemmed from the coupled movable oscillator, the energy spectrum of the system changes, and an effective on-site repulsive interaction is reformed by modulating the optomechanically controlled parameters. By adjusting the detuning, an intersection between different critical chemical potentials can be found together with a disappearance of certain Mott lobes physically. The pronounced optomechanical coupling strength is in favor of the Mott insulator phase due to the enhanced effective on-site interactions. Additionally, the Kerr-nonlinearity reduces the average excitation of the high Mott insulator state and diminishes the superfluid regime. The results obtained here provide a novel image for characterizing the quantum phase transitions in optomechanical array systems, which will offer valuable insight for quantum simulations.

Flat-band ferromagnetism of SU(N) Hubbard model on Tasaki lattices

We investigate the para-ferro magnetic transition of the repulsive SU(N) Hubbard model on a type of one- and two-dimensional decorated cubic lattices, referred as Tasaki lattices, which feature massive single-particle ground state degeneracy. Under certain restrictions for constructing localized many-particle ground states of flat-band ferromagnetism, the quantum model of strongly correlated electrons is mapped to a classical statistical geometric site-percolation problem, where the nontrivial weights of different configurations must be considered. We prove rigorously the existence of para-ferro transition for the SU(N) Hubbard model on one-dimensional Tasaki lattice and determine the critical density by the transfer-matrix method. In two dimensions, we numerically investigate the phase transition of SU(3), SU(4) and SU(10) Hubbard models by Metropolis Monte Carlo simulation. We find that the critical density exceeds that of standard percolation, and increases with spin degrees of freedom, implying that the effective repulsive interaction becomes stronger for larger N. We further rigorously prove the existence of flat-band ferromagnetism of the SU(N) Hubbard model when the number of particles equals to the degeneracy of the lowest band in the single-particle energy spectrum.

First Principles Calculations of the Energetic, Structural, Electronic, and Magnetic Properties of Fe/Ir(100) System

Although the Fe/Ir(100) system has been extensively investigated, contradictory conclusions were drawn from different experimental and theoretical studies about its magnetic ground state. In this work, density functional theory calculations are performed for the adsorption of Fe on the Ir(100) surface with different coverages to resolve this contradiction. The obtained adsorption energy decreases as the coverage increases, which reflects the effect of repulsive interaction between the adsorbates. Antiferromagnetic (AFM) configuration is found to be more stable than the ferromagnetic (FM) configuration for the 0.50 and 1.00 monolayer (ML) coverages. Fe atoms start to form a body centered cubic (BCC) structure, with the basis of a lattice parameter of Ir and have a pseudomorphic growth. The FM configuration is found to be more stable than the AFM configuration for Fe bilayer on Ir(100) surface with c/a ≈ 0.53, which predicts a BCC Fe precursor due to the small lattice mismatch between Fe and Ir surface. The electronic properties predict that the reactivity of Ir surface decreases beyond Fe coverage of 0.50 ML since the d band center of 5d Ir shifts to the left of Fermi energy as Fe coverage increases.

Modeling the influence of effective oil volume fraction and droplet repulsive interaction on nanoemulsion gelation

The aim of this work was to test the applicability of the Mason-Scheffold model, developed for monodispersed systems, on predicting the storage modulus of sodium dodecyl sulfate-stabilized polydisperse canola oil nanoemulsion gels as a function of oil volume fraction (ϕ) and average droplet size. The storage moduli increased with ϕ, but at a constant ϕ they increased with a decrease in droplet size. An effective oil volume fraction (ϕeff) was calculated by combining the effects of ϕ, average droplet size, their inter-droplet repulsive interaction using the Debye screening length and the counterion dissociation factor (f). With increasing ϕeff, storage modulus rapidly increased at the onset of jamming, followed by a gradual increase at higher ϕeff where gelation is controlled by deformation of droplets and their surrounding charge cloud. The model fits the data well, although, the values of critical volume fraction for jamming (ϕc) did not seem appropriate for the polydisperse nanoemulsions. It was proposed that the influence of f on ϕc could be significant and values lower than 0.1 could be more appropriate for high concentration of ionic emulsifier.

Polymer nanocomposites from natural clay: understanding clay-PEG interactions and their effect on spacing between clay-plates

The interactions between clay-plates and hydrophilic polymer are investigated assuming that the polyethylene glycol (PEG) chains are grafted onto face-to-face clay-plates. Besides the usual van der Waals attractive interaction, the clay-plates experience a repulsive effective interaction, due to the excluded volume force between monomers along the grafted PEG chains. The face-to-face clay-plates then play the role of polymer brushes. The free energy (per unit area) of a clay-plate pair is the sum of these interactions, and from its expression, we determine the minimal inter-sheet distance, after intercalation, which corresponds to a critical percentage of PEG. Finally, our result is in good agreement with some recent experimental work.

Pressure and flow of exponentially self-correlated active particles.

Microscopic swimming particles, which dissipate energy to execute persistent directed motion, are a classic example of a nonequilibrium system. We investigate the noninteracting Ornstein-Uhlenbeck Particle (OUP), which is propelled through a viscous medium by a force which is correlated over a finite time. We obtain an exact expression for the steady-state phase-space density of a single OUP confined by a quadratic potential, and use the result to explore more complex geometries, both through analytical approximations and numerical simulations. In a "Casimir"-style setup involving two narrowly spaced walls, we describe a particle-trapping phenomenon, which leads to a repulsive effective interaction between the walls, while in a two-dimensional annulus geometry, we observe net stresses which resemble the Laplace pressure.

Occurrence of a Mott-like gap in single-particle spectra of electron systems possessing flat bands

An unconventional type of the Mott’s insulators where the gap in the spectrum of single-particle excitations is associated with repulsive effective interactions between quasiparticles is shown to exist in strongly correlated electron systems of solids that possess flat bands. The occurrence of this gap is demonstrated to be the consequence of violation of particle–hole symmetry, inherent in such systems. The results obtained are applied to elucidate the Fermi arc structure observed at temperatures up to 100 K in angle-resolved photoemission spectra of the compound Sr2IrO4, not showing superconductivity down to low T.

Density-induced geometric frustration of ultra-cold bosons in optical lattices

A density-dependent gauge field may induce density-induced geometric frustration, leading to a non-trivial interplay between density modulation and frustration, which we illustrate for the particular case of ultra-cold bosons in zig-zag optical lattices with a density-dependent hopping amplitude. We show that the density-induced frustration leads to a rich landscape of quantum phases, including Mott insulator, bond-order insulator, two-component superfluids, chiral superfluids, and partially paired superfluids. We show as well that the density-dependent hopping results in an effective repulsive or attractive interaction, and that for the latter case the vacuum may be destabilized leading to a strong compressibility. Finally, we discuss the characteristic momentum distribution of the predicted phases, which can be used to detect the phases in time-of-flight measurements.

Small-angle neutron scattering study of the short-range organization of dispersed CsNi[Cr(CN)6] nanoparticles

Prussian blue analogues magnetic nanoparticles (of radius R0 = 2.4–8.6 nm) embedded in PVP (polyvinylpyrrolidone) or CTA+ (cetyltrimethylammonium) matrices have been studied using neutron diffraction and small angle neutron scattering (SANS) at several concentrations. For the most diluted particles in neutral PVP, the SANS signal is fully accounted for by a “single-particle” spherical form factor with no structural correlations between the nanoparticles and with radii comparable to those inferred from neutron diffraction. For higher concentration in PVP, structural correlations modify the SANS signal with the appearance of a structure factor peak, which is described using an effective “mean-field” model. A new length scale R* ≈ 3R0, corresponding to an effective repulsive interaction radius, is evidenced in PVP samples. In CTA+, electrostatic interactions play a crucial role and lead to a dense layer of CTA+ around the nanoparticles, which considerably alter the SANS patterns as compared to PVP. The SANS data of nanoparticles in CTA+ are best described by a core-shell model without visible inter-particle structure factor.

Wetting-Dewetting and Dispersion-Aggregation Transitions Are Distinct for Polymer Grafted Nanoparticles in Chemically Dissimilar Polymer Matrix.

Simulations and experiments are conducted on mixtures containing polymer grafted nanoparticles in a chemically distinct polymer matrix, where the graft and matrix polymers exhibit attractive enthalpic interactions at low temperatures that become progressively repulsive as temperature is increased. Both coarse-grained molecular dynamics simulations, and X-ray scattering and neutron scattering experiments with deuterated polystyrene (dPS) grafted silica and poly(vinyl methyl ether) PVME matrix show that the sharp phase transition from (mixed) dispersed to (demixed) aggregated morphologies due to the increasingly repulsive effective interactions between the blend components is distinct from the continuous wetting-dewetting transition. Strikingly, this is unlike the extensively studied chemically identical graft-matrix composites, where the two transitions have been considered to be synonymous, and is also unlike the free (ungrafted) blends of the same graft and matrix homopolymers, where the wetting-dewetting is a sharp transition coinciding with the macrophase separation.

Self-phoretic active particles interacting by diffusiophoresis: A numerical study of the collapsed state and dynamic clustering.

Self-phoretic active colloids move and orient along self-generated chemical gradients by diffusiophoresis, a mechanism reminiscent of bacterial chemotaxis. In combination with the activity of the colloids, this creates effective repulsive and attractive interactions between particles depending on the sign of the translational and rotational diffusiophoretic parameters. A delicate balance of these interactions causes dynamic clustering and for overall strong effective attraction the particles collapse to one single cluster. Using Langevin dynamics simulations, we extend the state diagram of our earlier work (Phys. Rev. Lett. 112, 238303 (2014)) to regions with translational phoretic repulsion. With increasing repulsive strength, the collapsed cluster first starts to fluctuate strongly, then oscillates between a compact form and a colloidal cloud, and ultimately the colloidal cloud becomes static. The oscillations disappear if the phoretic interactions within compact clusters are not screened. We also study dynamic clustering at larger area fractions by exploiting cluster size distributions and mean cluster sizes. In particular, we identify the dynamic clustering 2 state as a signature of phoretic interactions. We analyze fusion and fission rate functions to quantify the kinetics of cluster formation and identify them as local signatures of phoretic interactions, since they can be measured on single clusters.