Multibody Interactions Research Articles

Binary collisions of dark matter blobs

We describe the model-independent mechanism by which dark matter and dark matter structures heavier than ~ 8 × 1011 GeV form binary pairs in the early Universe that spin down and merge both in the present and throughout the Universe’s history, producing potentially observable signals. Sufficiently dense dark objects will dominantly collide through binary mergers instead of random collisions. We detail how one would estimate the merger rate accounting for finite size effects, multibody interactions, and friction with the thermal bath. We predict how mergers of dark dense objects could be detected through gravitational and electromagnetic signals, noting that such mergers could be a unique source of high frequency gravitational waves. We rule out objects whose presence would contradict observations of the CMB and diffuse gamma-rays.

DEM-enriched contact approach for material point method

A major challenge for material point method (MPM) is to model multi-body and multi-material interactions. Prevailing contact schemes developed for MPM suffer from numerical instabilities, especially for the coexistence of multiple material boundary conditions. This study proposes a generalized contact scheme based on a hybrid scheme of MPM and discrete element method (DEM) to tackle such issues. The new scheme contains two novel features of particle–particle and particle–structure contact schemes guided by a DEM contact model to handle multi-material interactions. It leverages the advantages of both MPM and DEM, offering a unified way to flexibly handle either the boundary–particle or particle–particle multi-material interactions. Several typical physical processes are simulated to showcase the versatility of the proposed approach, including interface rotation and sliding, penetration, and granular material impact. It demonstrates that the generalized contact scheme can flexibly capture the mechanical responses of multi-body and multi-material systems in MPM.

A constant parameter time domain model for dynamic modelling of multi-body system with strong hydrodynamic interactions

It is well known that direct evaluation of the wave-induced dynamics of floating structures by Cummins equation is time-consuming due to the convolution integrals. Particularly, for a multi-body system, a complete matrix of the impulse response functions, namely the kernel of the convolution integral in Cummins equation, is required as the cross-coupling terms in the hydrodynamic matrices are important in accurately evaluating the dynamic responses, resulting in increased computation time. Rather than solving the convolution kernel, state-space models have been adopted as an alternative, working well for single body cases. However, it has the disadvantage of numerical instability, which may cause significant errors for strongly resonant phenomena, e.g. in the multi-body interactions. To overcome this issue, the practise is to introduce a damping lid to the free surface in the gap between multiple bodies in frequency domain. Based on the hydrodynamic coefficients obtained in the frequency domain, this study presents a time domain model that combines the damping lid method and state-space model, resulting in a Constant Parameter Time Domain Model (CPTDM). Due to the nature of the time domain model, it is possible to account for nonlinear viscous damping, wherever it is appropriate. The finding shows that the damping lid method helps to stabilize the numerical simulation of the multi-body system which undergoes gap resonances. It is found that a larger damping lid factor favors the decaying of the impulse response functions and the development of lower-order state-space models. The developed CPTDM is found to work well for different wave frequencies and wave headings, with better accuracy and higher efficiency than AQWA's time-domain simulations. Particularly, at the resonant frequency, the developed CPTDM still retains good accuracy as compared with the RAO-based responses.

Isothermal compressibility and effects of multibody molecular interactions in a strongly interacting ultracold Fermi gas

We theoretically investigate the isothermal compressibility $\kappa_{T}$ in the normal state of an ultracold Fermi gas. Including pairing fluctuations, as well as preformed-pair formations, within the framework of the self-consistent $T$-matrix approximation (SCTMA), we evaluate the temperature dependence of this thermodynamic quantity over the entire BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region. While $\kappa_T$ in the weak-coupling BCS regime is dominated by Fermi atoms near the Fermi surface, correlations between tightly bound Cooper-pair molecules are found to play crucial roles in the strong-coupling BEC regime. In the latter region, besides a two-body molecular interaction, a three-body one is shown to sizably affect $\kappa_T$ near the superfluid phase transition temperature. Our results indicate that the strong-coupling BEC regime of an ultracold Fermi gas would provide a unique opportunity to study multi-body correlations between Cooper-pair molecules.

Extension of a coupled mooring–viscous flow solver to account for mooring–joint–multibody interaction in waves

To account for nonlinear wave–structure interaction, mooring dynamics and the associated viscous flow effects, a coupled mooring–viscous flow solver was formerly developed and validated (Jiang et al. in Mar Struct 72:783, 2020a, Validation of a dynamic mooring model coupled with a RANS solver). This paper presents an extension of the coupled mooring–viscous flow solver to solve mooring dynamics interacting with an articulated multibody offshore system. The presently extended solver is verified by comparing the predicted motions of and loads on a moored floating box to those obtained from the formerly validated solver, which was aimed for solving mooring dynamics interacting with a single floating body. The almost identical results obtained from both solvers verify the presently developed multi-module coupling technique for solving the mooring dynamics and articulated multibody dynamics in a coupled manner. Apart from the code comparison and verification, the numerical predictions are also validated against experimental tank measurements both for a single body and an articulated multibody. The good agreements between the numerical predictions and the experimental measurements validate the presently extended solver, where wave-induced body motions together with loads acting on mooring lines and joint connections were examined. Developed as an open-source tool, the extended solver shows a potential of the coupled methodology for analyzing an articulated multibody offshore system, moored with various mooring configurations in extreme sea states, which goes beyond the state of the art.

Control of the Drying Patterns for Complex Colloidal Solutions and Their Applications.

The uneven deposition at the edges of an evaporating droplet, termed the coffee-ring effect, has been extensively studied during the past few decades to better understand the underlying cause, namely the flow dynamics, and the subsequent patterns formed after drying. The non-uniform evaporation rate across the colloidal droplet hampers the formation of a uniform and homogeneous film in printed electronics, rechargeable batteries, etc., and often causes device failures. This review aims to highlight the diverse range of techniques used to alleviate the coffee-ring effect, from classic methods such as adding chemical additives, applying external sources, and manipulating geometrical configurations to recently developed advancements, specifically using bubbles, humidity, confined systems, etc., which do not involve modification of surface, particle or liquid properties. Each of these methodologies mitigates the edge deposition via multi-body interactions, for example, particle–liquid, particle-particle, particle–solid interfaces and particle–flow interactions. The mechanisms behind each of these approaches help to find methods to inhibit the non-uniform film formation, and the corresponding applications have been discussed together with a critical comparison in detail. This review could pave the way for developing inks and processes to apply in functional coatings and printed electronic devices with improved efficiency and device yield.

A discrete particle model study of the effect of temperature and geometry on the pseudoelastic response of shape memory alloys

In this paper, the effects of temperature and geometry on the hysteresis behavior of shape memory alloy (SMA) under stress induced transformations are studied. We used a discrete model referred to as the constitutively informed particle dynamics (CPD), for the analysis. The CPD approach uses a multibody interaction derived from a polyconvex free energy appropriate for phase transforming materials. This approach is able to describe evolution of the phases in a sharp interface paradigm. Using such an approach allows discrete element models to describe complex material behavior such as phase transformations which were hitherto not possible. The temperature dependent pseudoelastic response is studied under uniaxial tension. The effect of temperature on this stress induced transformation is studied at four different temperatures. The results show an increase in hysteresis at higher temperatures. Next, the effect of geometry on hysteresis is studied in a tapered bar geometry. Tapered bars show hardening in the stress–strain curve. The influence of temperature and specimen geometry on the pseudoelastic stress–strain response would be essential to design and develop MEMS (Micro-Electro-Mechanical Systems) applications using these classes of smart materials.

Multimode photon blockade

Interactions are essential for the creation of correlated quantum many-body states. Although two-body interactions underlie most natural phenomena, three- and four-body interactions are important for the physics of nuclei1, exotic few-body states in ultracold quantum gases2, the fractional quantum Hall effect3, quantum error correction4 and holography5,6. Recently, a number of artificial quantum systems have emerged as simulators for many-body physics, featuring the ability to engineer strong interactions. However, the interactions in these systems have largely been limited to the two-body paradigm and require building up multibody interactions by combining two-body forces. Here we implement a scheme to create a higher-order interaction between photons stored in multiple electromagnetic modes of a microwave cavity. The system is dressed such that there is collectively no interaction until a target total photon number is reached across multiple distinct modes, at which point the photons interact strongly. In our demonstration, we create interactions involving up to three bodies and across up to five modes. We harness the interaction to prepare single-mode Fock states and multimode W states, which we verify by introducing a multimode Wigner tomography method. A method to engineer higher-order interactions between photons provides a route to create non-classical and entangled states across multiple modes.

Seismic response analysis of concrete-faced rockfill dams with dual mortar contact method

Many high concrete-faced rockfill dams (CFRD) are constructed or planned with high seismic intensity. It is challenging to evaluate the resultant seismic response involving multi-body interactions. In this paper, a dual mortar contact method for multi-process sequential analysis accounting for staged construction, water storage, creep effects and seismic loading is presented. A complete derivation of the strong and weak forms, spatial and temporal discretizations, material and contact non-linearity treatments is provided as a solid basis to incorporate the rockfill constitutive behavior and stable algorithm for thin-walled inter-slab interfaces. The present method based on using nonconforming meshes is validated by the comparisons with conforming meshes and then applied to an ideal CFRD. The issues of post-earthquake extrusion damage, slab–slab separation and slab–cushion separation, which are major concerns in CFRDs, are discussed in detail. The additional extrusion stress of the concrete face during an earthquake can be up to 20 MPa and therefore calls for considerations in the design and safety assessment.

On optimal energy-extraction performance of arrays of wave-energy converters, with full consideration of wave and multi-body interactions

An array of ocean-wave energy converters, compared to a stand-alone device, provides lower energy-production costs but affects the aggregate power performance. Previous studies suggested that wave-interaction effects within the array could increase energy production by over 15% per device. However, no physical constraints on the WECs were considered in these studies; as a result, the devices can experience unrealistically large motions. A control strategy is thus desirable to coordinate individual WECs and maximize the energy extraction. We apply model-predictive control (MPC) to an array of point-absorber-type WECs by developing a formulation that accommodates hard constraints on the motion of each device and on the Power-takeoff (PTO) forces with excellent computational efficiency. Full multi-body wave-interaction effects are computed by a semi-analytical method within linear-wave theory. This framework enables us to demonstrate results of realistic maximal power production for arrays of two, three, and four devices operating under constraints in sea waves of various incident angles. It is observed that wave–body interactions have actually destructive effects on the array power production for the majority cases in irregular sea waves. Also discussed are effects of the reactive power produced by the PTO unit and the possibility of removing it within the MPC framework.

Hydrodynamic characteristics of a hybrid oscillating water column-oscillating buoy wave energy converter integrated into a π-type floating breakwater

Combining multiple-types of Wave Energy Converters (WECs) and integrating them into in-development or pre-existing marine platforms can reduce the total Levelised Cost of Energy (LCoE) by sharing infrastructures and maintenance costs. The current study proposes an innovative multi-purpose solution by deploying an Oscillating Buoy (OB) device inside the chamber of an Oscillating Water Column (OWC) WEC integrated into a π-type floating breakwater. A fully non-linear time-domain model based on the Higher-Oder Boundary Element Method (HOBEM) is established to investigate the hydrodynamic performance of the proposed concept. The non-linear time-domain model is generalised to incorporate the OWC (aero and hydrodynamics coupling) and multi-body interaction. A series of simulations are performed to examine the hydrodynamic performance of the proposed hybrid concept. Results were compared with an isolated breakwater and an OWC-integrated breakwater, demonstrating that the proposed hybrid concept has a beneficial impact on both wave energy conversion and transmitted wave attenuation. In addition, long-period waves enter into the chamber more easily, which leads to a larger inner water motion and pressure fluctuation in the chamber. Importantly, there exists a coupled resonant motion between the OB device and the water surface in the chamber, which enhances the maximum capture efficiency and the efficiency frequency bandwidth. The asymmetric OB with a triangle-shaped bottom is found to absorb the wave energy along with the water depth more effectively. Despite the better performance, the current design does not increase the characteristic system volume and has no external moving part, making it ideal for array deployment.

Data Mining Meets Machine Learning: A Novel ANN-based Multi-body Interaction Docking Scoring Function (MBI-score) Based on Utilizing Frequent Geometric and Chemical Patterns of Interfacial Atoms in Native Protein-ligand Complexes.

Accurate prediction of binding poses is crucial to structure-based drug design. We employ two powerful artificial intelligence (AI) approaches, data-mining and machine-learning, to design artificial neural network (ANN) based pose-scoring function. It is a simple machine-learning-based statistical function that employs frequent geometric and chemical patterns of interacting atoms at protein-ligand interfaces. The patterns are derived by mining interfaces of "native" protein-ligand complexes. Each interface is represented by a graph where nodes are atoms and edges connect protein-ligand interfacial atoms located within certain cutoff distance of each other. Applying frequent subgraph mining to these interfaces provides "native" frequent patterns of interacting atoms. Subsequently, given a pose for a protein-ligand complex of interest, the pose-scoring function (the information-processing unit or neuron) calculates the degree of matching between the interaction patterns present at the pose's interface and the native frequent patterns. The pose-scoring function takes into account the frequency of occurrence of the matching native patterns, the size of the match, and the degree of geometrical similarity between pose-specific and matching native frequent patterns. This novel "multi-body interaction" pose-scoring function (MBI-Score) was validated using two databases, PDBbind and Astex-85, and it outperformed seven commonly used commercial scoring functions. MBI-Score is available at www.khashanlab.org/mbi-score.

Synthesis and Exciton Dynamics of a One-Dimensional Organic Copper Halide Perovskite

Low-dimensional copper halides have recently received increasing attention, owing to their non-toxicity, low-cost, and efficient broadband emission with large Stokes shift. Herein, we report a novel one-dimensional organic copper halide PEACuI2 (PEA = C6H5CH2CH2NH3+), which exhibits broad green emission originating from self-trapped excitons (STEs) with a peak of 525 nm and large Stokes shifts of 215 nm. The dynamics and multi-body interactions of STEs were investigated using femtosecond transient absorption (fs TA) spectroscopy at different pump intensities. Interestingly, under high STE density, we observed the absorption signals of self-trapped biexcitons (STBs) formed by binding two STEs in the fs TA spectra. The hot STBs undergo cooling process with a rate constant of 3.57 ps, yielding relaxed STBs. Furthermore, a trap-associated recombination of STBs with a time constant of 64.98 ps is unveiled. Our results offer direct evidence of the occurrence of STBs and provide new insights into the many body interactions of STEs.

Thermodynamics, morphology, mechanics, and thermal transport of PMMA-PLA blends

Thermodynamics controls structure, function, stability, and morphology of polymer blends. However, obtaining the precise information about their mixing thermodynamics is a challenging task, especially when dealing with complex macromolecules. This is partially because of a delicate balance between the local concentration/composition fluctuations and the monomer level (multibody) interactions. In this context, the Kirkwood-Buff (KB) theory serves as a useful tool that connects the local pairwise fluid structure to the mixing thermodynamics. Using larger scale molecular dynamics simulations, within the framework of KB theory, we investigate a set of technologically relevant poly(methyl methacrylate)-poly(lactic acid) blends with the aim to elucidate the underlying microscopic picture of their phase behavior. Consistent with the existing experiments, we emphasize the importance of properly accounting for the entropic contribution to the mixing Gibbs free-energy change $\mathrm{\ensuremath{\Delta}}{\mathcal{G}}_{\mathrm{mix}}$ that controls the phase morphology. We further show how the relative microscopic interaction details and the molecular level structures between different mixing species can control the nonlinear mechanics, ductility, and heat flow. Therefore, this study provides a guiding principle for the design of light weight functional materials with extraordinary physical properties.

Numerical and experimental study on absorber-type wave energy converters concentrically arranged on an octagonal platform

Present study considers the performance of a truss-type octagonal platform coupled with multiple wave energy converters (WECs). A numerical model was established to investigate multi-body hydrodynamic interaction between an octagonal platform and absorber-type wave energy converters utilizing CFD tool. Firstly, we analyzed the hydrodynamic performance and absorption power of the isolated WEC under different waves. The numerical results were compared with the physical experimental data to validate the proposed numerical method. Then the effects of the connection type and connection angle between the float arm and float were investigated numerically. Based on the numerical results, the fixed-type WEC with a zero deg connection angle is selected as the final design. Finally, the numerical simulation of multi-point-absorber circularly arranged on the octagonal platform was carried out. The numerical results demonstrated that the multi-body interaction has a remarkable influence on the absorption power and, therefore, it cannot be neglected when evaluate the performance of whole system.

Influential groups for seeding and sustaining nonlinear contagion in heterogeneous hypergraphs

Contagion phenomena are often the results of multibody interactions—such as superspreading events or social reinforcement—describable as hypergraphs. We develop an approximate master equation framework to study contagions on hypergraphs with a heterogeneous structure in terms of group size (hyperedge cardinality) and of node membership (hyperdegree). By mapping multibody interactions to nonlinear infection rates, we demonstrate the influence of large groups in two ways. First, we characterize the phase transition, which can be continuous or discontinuous with a bistable regime. Our analytical expressions for the critical and tricritical points highlight the influence of the first three moments of the membership distribution. We also show that heterogeneous group sizes and nonlinear contagion promote a mesoscopic localization regime where contagion is sustained by the largest groups, thereby inhibiting bistability. Second, we formulate an optimal seeding problem for hypergraph contagion and compare two strategies: allocating seeds according to node or group properties. We find that, when the contagion is sufficiently nonlinear, groups are more effective seeds than individual hubs.

Analytical forecasting of long-term railway track settlement

Railway tracks undergo plastic settlement when subject to repeated train loading. This occurs differentially along the track rather than in a uniform manner, and the profile is a key parameter when scheduling track maintenance operations. Therefore this paper presents a novel numerical approach to predict track irregularity evolution. The model combines empirical settlement laws with finite element theory, where the track-ground structure is modelled explicitly, and multi-body train-track interaction is considered. The stresses induced by rolling stock are solved using a hybrid frequency-wavenumber and time–space approach, considering non-linear track-soil material behaviour. It has several novelties: 1) after every load passage, the track profile is updated before applying the next load, meaning the train-track interaction is constantly evolving; 2) new empirical settlement laws are derived that account for evolving train-track forces and track profiles; 3) fully 3D stress fields in the track and ground are considered. First the model is described, before validating its prediction of track geometry evolution, captured from track recording vehicles. Next, it’s used to show that modelling error is introduced if the geometry isn’t updated frequently (e.g. after every load passage). Finally, a parametric study shows track subgrade material properties have a marked effect on track settlement.

Field-mediated interactions of passive and conformation-active particles: multibody and retardation effects.

Particles in soft matter interact through the deformation field they create, as in the "cheerios" effect or the curvature-mediated interactions of membrane proteins. Using a simple model for field-mediated interactions between passive particles, or active particles that switch conformation randomly or synchronously, we derive generic results concerning multibody interactions, activity driven patterns, and retardation effects.

Density shift measurement and synchronous frequency comparison based on <i>in situ</i> imaging technique

Precision measurement of the density shift caused by the interaction among neutral atoms trapped in an optical lattice has important applications in the study of multi-body interaction and the realization of high-performance optical lattice clocks. The common methods of measuring the density are the self-comparison technique and frequency comparison between two optical lattice clocks. Both methods are based on the identical density shift coefficient and should interrelatedly operate the clock at high- and low-density state, respectively. The precision of self-comparison method is limited by the Dick effect. The synchronous frequency comparison between two optical lattice clocks can realize the precision beyond the Dick limit. However, both methods can only obtain the average density shift and ignore the fact that the magnitude of the density shift is different over the lattice sites as inhomogeneous density distribution in the lattice. In this paper, the synchronous frequency comparison technique based on in situ imaging is used to accurately measure the density shift coefficient of optical lattice clock. Atoms in the optical lattice are simultaneously and independently excited by the same clock laser beam, and the clock transition probability of 11 uncorrelated regions of the optical lattice is simultaneously detected by in situ imaging. Thus, the clock laser noise, which is the root cause of the Dick effect, is common-mode rejected as the frequency difference between uncorrelated regions is measured by the clock transition spectrum. Beyond the Dick-noise-limited stability, the stability of synchronous frequency comparison between uncorrelated regions is consistent with the limit resulting from the atom detection noise. Between the center and margin of the lattice, the differential shifts of the black-body radiation shift, lattice AC Stark shift, probe Stark shift, DC Stark shift, and quadratic Zeeman shift are all below 5 × 10<sup>–6</sup> Hz, which is three orders of magnitude smaller than the density shift and can be ignored in this experiment. Benefitting from the inhomogeneous distribution of atom number and negligible external field gradient in the optical lattice, the compared frequency shift between uncorrelated regions indicates the density shift. By measuring the relationship between the density shift and atom difference, the density shift coefficient is determined as –0.101(3) Hz/atom/site (with a measurement time of 10<sup>3</sup> s), and the fractional measurement uncertainty of the mean density shift of our system is 1.5 × 10<sup>–17</sup>.

Structures of cationic and anionic polyelectrolytes in aqueous solutions: the sign effect.

In this study, we use molecular dynamics simulation to explore the structures of anionic and cationic polyelectrolytes in aqueous solutions. We first confirm the significantly stronger solvation effects of single anions compared to cations in water at the fixed ion radii, due to the reversal orientations of asymmetric dipolar H2O molecules around the ions. Based on this, we demonstrate that the solvation discrepancy of cations/anions and electrostatic correlations of ionic species can synergistically cause the nontrivial structural difference between single anionic and cationic polyelectrolytes. The cationic polyelectrolyte shows an extended structure whereas the anionic polyelectrolyte exhibits a collapsed structure, and their structural differences decline with increasing the counterion size. Furthermore, we corroborate that multiple cationic polyelectrolytes or multiple anionic polyelectrolytes can exhibit largely differential molecular architectures in aqueous solutions. In the solvation dominant regime, the polyelectrolyte solutions exhibit uniform structures; whereas, in the electrostatic correlation dominant regime, the polyelectrolyte solutions exhibit heterogeneous structures, in which the likely charged chains microscopically aggregate through counterion condensations. Increasing the intrinsic chain rigidity causes polyelectrolyte extension and hence moderately weakens the inter-chain clustering. Our work highlights the various, unique structures and molecular architectures of polyelectrolytes in solutions caused by the multi-body correlations between polyelectrolytes, counterions and asymmetric dipolar solvent molecules, which provides insights into the fundamental understanding of ion-containing polymers.