Mesoscopic Particles Research Articles

Looking for intermediate statistics

Mesoscopic Physics Elementary particles in three dimensions are either bosons or fermions, depending on their spin. In two dimensions, it is in principle possible to have particles that lie somewhere in between, but detecting the statistics of these so-called anyons directly is tricky. Bartolomei et al. built a collider of anyons in a two-dimensional electron gas of GaAs/AlGaAs (see the Perspective by Feldman). Two beams of anyons collided at a beam splitter and then exited the device at two outputs. The researchers studied the correlations of current fluctuations at the outputs, which revealed signatures of anyonic statistics. Science , this issue p. [173][1]; see also p. [131][2] [1]: /lookup/doi/10.1126/science.aaz5601 [2]: /lookup/doi/10.1126/science.abb3552

Stokes and anti-Stokes quantum fields from a mesoscopic microparticle with cylindrical geometry: Orientation, size and angular-dependence of spectra

We present a semi-analytical theory to describe the nonlinear scattering of Raman photon pairs from a cylindrical microparticle comprising of quantum particles in double Raman configuration. The normally ordered Stokes and anti-Stokes spectra are computed to gain insights into the quantum optical properties of the system and the variation of the spectra with microparticle’s size, orientation as well as observation angles are also analyzed and compared with the results obtained in our previous work involving mesoscopic spherical particle. Our results show several features in the spectra that are unique to the case of cylindrical microparticle and not found in the spherical particle case, such as the shifting of the side peaks originally formed due to ac Stark shifts towards the center at certain range of particle radius values, occurrence of side peaks with magnitudes comparable to that of the central peak, formation of additional peaks at certain observation angles and strong dependence of the spectra on the microparticle’s cylinder axis orientation. Most of these effects are either caused by the inhomogeneity of the incident pump and control laser fields within the volume of the cylindrical microparticle or simply due to the lack of three-dimensional symmetry of cylindrical geometry.

(py)LIon: A package for simulating trapped ion trajectories

The (py)LIon package is a set of tools to simulate the classical trajectories of ensembles of ions in electrodynamic traps. Molecular dynamics simulations are performed using LAMMPS, an efficient and feature-rich program. (py)LIon has been validated by comparison with the analytic theory describing ion trap dynamics. Notable features include GPU-accelerated force calculations, and treating collections of ions as rigid bodies to enable investigations of the rotational dynamics of large, mesoscopic charged particles. Programme summaryProgram Title: (py)LIonProgram Files doi:http://dx.doi.org/10.17632/ywwd9nnxjh.1Licencing provisions: MITProgramming language: Matlab, PythonSubprograms used: LAMMPSNature of problem: Simulating the dynamics of ions and mesoscopic charged particles confined in an electrodynamic trap using molecular dynamics methodsSolution method: Provide a tested, feature-rich API to configure molecular dynamics calculations in LAMMPSUnusual features: (py)LIon can treat collections of ions as rigid bodies to simulate larger objects confined in electrodynamic traps. GPU acceleration is provided through the LAMMPS ▪ package.

Brownian motion and Edagawa phasons

The so far most direct observation of phasons was reported in the year 2000 by Edagawa et al. In HRTEM images of decagonal Al-Cu-Co they detected white spots which formed vertices of a quasiperiodic tiling. Some spots vanished and reappeared in phason flipped positions within seconds to minutes. Already at ICQ13 we had applied a structure model of Zeger and Trebin of the year 1996 to explain the physical origin of the spots and the time scale of the flips. We found that the spots are columns of ten-rings of atoms which change positions by fluctuations of atomistic phason flips. Thus they resemble Brownian motion of mesoscopic particles, which are pushed by fluctuating knocks of fluid molecules. Whereas Brownian motion is described by a random walk in continuous space, Edagawa phasons can be conceived as a random walk on a quasilattice.

Colloquium : Ice rule and emergent frustration in particle ice and beyond

Geometric frustration and the ice rule are two concepts that are intimately connected and widespread across condensed matter. The first refers to the inability of a system to satisfy competing interactions in the presence of spatial constraints. The second, in its more general sense, represents a prescription for the minimization of the topological charges in a constrained system. Both can lead to manifolds of high susceptibility and non-trivial, constrained disorder where exotic behaviors can appear and even be designed deliberately. In this Colloquium, we describe the emergence of geometric frustration and the ice rule in soft condensed matter. This Review excludes the extensive developments of mathematical physics within the field of geometric frustration, but rather focuses on systems of confined micro- or mesoscopic particles that emerge as a novel paradigm exhibiting spin degrees of freedom. In such systems, geometric frustration can be engineered artificially by controlling the spatial topology and geometry of the lattice, the position of the individual particle units, or their relative filling fraction. These capabilities enable the creation of novel and exotic phases of matter, and also potentially lead towards technological applications related to memory and logic devices that are based on the motion of topological defects. We review the rapid progress in theory and experiments and discuss the intimate physical connections with other frustrated systems at different length scales.

Calibration of linear contact stiffnesses in discrete element models using a hybrid analytical-computational framework

Efficient selections of particle-scale contact parameters in discrete element modelling remain an open question. The aim of this study is to provide a hybrid calibration framework to estimate linear contact stiffnesses (normal and tangential) for both two-dimensional and three-dimensional simulations. Analytical formulas linking macroscopic parameters (Young's modulus, Poisson's ratio) to mesoscopic particle parameters for granular systems are derived based on statistically isotropic packings under small-strain isotropic stress conditions. By taking the derived analytical solutions as initial approximations, the gradient descent algorithm automatically obtains a reliable numerical estimation. The proposed framework is validated with several numerical cases including randomly distributed monodisperse and polydisperse packings. The results show that this hybrid method practically reduces the time for artificial trials and errors to obtain reasonable stiffness parameters. The proposed framework can also be extended to other parameter calibration problems in DEM.

Tunable Sorting of Mesoscopic Chiral Structures by External Noise in Achiral Periodic Potentials

Efficient chirality sorting is now highly in demand to separate assembled mesoscopic chiral structures which are of very special physical properties rather than their achiral counterparts or those at the single-particle level. However, the efficiency of conventional methods usually suffers from the thermal or external noise. Here, we propose a mechanism utilizing external noise to attain a tunable sorting of mesoscopic chiral particles in an achiral periodic potential. The complete chirality separation stems from the path selection by a noise-induced biased flux in a nonequilibrium landscape. Such a mechanism provides a practical way to control the motion of chiral particles by simply adjusting the noise intensity, which is demonstrated by simultaneous separation of several kinds of enantiomorphs with different degrees of chirality. The robustness and generalizability of noise-tuned chirality sorting is further verified in systems with other types of periodic potentials or spatially/temporally correlated noise.

Mesoscale modelling of miscible and immiscible multicomponent fluids

A mesoscopic simulation method based on the integration of dissipative particle dynamics (DPD), smoothed particle hydrodynamics (SPH) and computational thermodynamics (CT) has been developed. The kinetic behaviours of miscible and immiscible fluids were investigated. The interaction force between multicomponent mesoscopic particles is derived from the system free energy. The diffusivity of the components in non-ideal solution is determined by the chemical potential. The proposed method provides convincing predictions to the effects of convection, diffusion and microscopic interaction on the non-equilibrium evolution of engineering fluids, and demonstrates a potential to simulate more complicated phenomena in materials processing.

Resummed Kinetic Field Theory: using Mesoscopic Particle Hydrodynamics to describe baryonic matter in a cosmological framework

We present a new analytical description of baryonic matter in a cosmological framework, using the formalism of “Kinetic Field Theory” (KFT)—a statistical field theory approach to structure formation based on the dynamics of classical particles. So far, only the purely gravitational dynamics of dark matter had been considered in KFT, but an accurate description of cosmic structure formation requires to also take into account the baryonic gas dynamics. In this paper, we propose to achieve this by incorporating an effective mesoscopic particle model of hydrodynamics into the recently developed framework of Resummed KFT. Our main result is the baryonic density contrast power spectrum computed to lowest perturbative order, assuming a simplified isothermal fluid model. Compared to the spectrum of dark matter, the baryonic spectrum shows a suppression of power as well as an oscillatory behaviour associated with sound waves on scales smaller than the Jeans length. We further compare our result to the linear spectrum of an isothermal fluid obtained from Eulerian perturbation theory (EPT), finding good quantitative agreement within the approximations we made in the EPT calculation. A subsequent paper will resolve the problem of coupling both dark and baryonic matter, to gain a full model of cosmic matter. Applying the mesoscopic particle approach to more general ideal or viscous fluids will also be subject of upcoming work.

Self-consistent determination of the many-body state of ultracold bosonic atoms in a one-dimensional harmonic trap

We study zero-temperature quantum fluctuations in harmonically trapped one-dimensional interacting Bose gases,using the self-consistent multiconfigurational time-dependent Hartree method. We define phase fluctuations from the full single-particle density matrix by the spatial decay exponent of off-diagonal long-range order. In a regime of mesoscopic particle numbers and moderate contact couplings, we derive the spatial dependence of the amplitude of phase fluctuations, determined from the self-consistently derived shape of the field operator orbitals and Fock space orbital occupation amplitudes. It is shown that the phase fluctuations display a peak, which in turn corresponds to a dip of the first-order correlations in position space, akin to what has previously been obtained in the Tonks–Girardeau limit of very large interactions and low densities.

On the possibility of laboratory evidence for quantum superposition of geometries

We analyse the recent proposal of measuring a quantum gravity phenomenon in the lab by entangling two mesoscopic particles gravitationally. We give a generally covariant description of this phenomenon, where the relevant effect turns out to be a quantum superposition of proper times. We point out that if General Relativity is assumed to hold for masses at this scale, measurement of this effect would count as evidence for quantum superposition of spacetime geometries. This interpretation addresses objections appeared in the literature. We observe that the effect sheds light on the Planck mass, and argue that it is very plausibly a real effect.

Research on Simulation Analysis Method of Microbial Cemented Sand Based on Discrete Element Method

A simulation method for microbial cemented sand (MCS) based on the Two-Dimensional Particle Flow Code (PFC 2D) has been developed in this study. It consists of an identification of mesoscopic contact model for structural mesoscopic particles, development of morphological algorithm for irregular crystal particles, and classification and setting of mesoscopic parameters for compositional materials and particle size distribution simulation. Additionally, an acoustic emission algorithm based on moment tensor theory was developed for discrete element simulation analysis on fracture characteristic of cemented sand under the action of the force. The simulation method proposed in this article/paper may reflect the physical and mechanical characteristics of real microbial cemented sand based on physical experiments. Quantification of the fracture process of microbial cemented sand is possible by introducing a moment magnitude (MW) in discrete element simulation analysis. The material may have greater probability of fracture between the MW ranges of −6.8 and −6.6. The relationship between probability of fracture at different MWs and the MW follows the Gaussian curve. The research results are a new trial for fracture analysis on microbial cemented sand.

Equations of motion for position-dependent coarse-grain mappings obtained with Mori-Zwanzig theory.

A position-dependent transformation is introduced for mapping a system of atomistic particles to a system of coarse-grained (CG) variables, which under some circumstances might be considered particles. This CG mapping allows atomistic particles to simultaneously contribute to more than a single CG particle and to change in time the CG particle they are associated with. That is, the CG mapping is dynamic. Mori-Zwanzig theory is then used to obtain the equations of motion for this CG mapping, resulting in conservative, dissipative, and random force terms in generalized, non-Markovian Langevin equations. In addition to the usual forces arising from the effective CG potential derived from atomistic interactions, new forces arise from the dynamic changes in the CG mapping itself. These new forces effectively account for changes arising from fluxes of atomistic particles into and out of CG ones as time progresses. Several examples are given showing the range of problems that can be addressed with this new CG mapping. These range from the usual case where atomistic particles are grouped into large molecular-like chunks, with mappings that remain fixed in time and for which an atomistic particle is part of only a single CG one, to the case where CG particles resemble fluid elements, containing many hundreds of independent atomistic particles. The new CG mapping also allows for hybrid descriptions, in which a part of the system remains atomistic or molecular-like and a part is highly coarse-grained to mesoscopic fluid element-like particles, for example. In the latter case, the equations of motion then provide the correct formalism for determining the forces, beyond the usual conservative ones. This provides a theoretical foundation upon which approximate equations of motion can be formulated to thus build numerical algorithms for expanded applications of accurate CG molecular dynamics.

Microscope images of strongly scattering objects via vectorial transfer matrices: Modeling and an experimental verification

We present an accurate and efficient method for calculating the image of a mesoscopic particle that is captured using a high-numerical-aperture objective lens. We test various scattering models of silica, plastic, and birefringent vaterite spheres in water. We show that the calculated images accurately replicate experimental observations. This method uses the idea that the optical system can be represented as a product of matrices acting on the electromagnetic field in a truncated Hilbert space representation. A general reusable matrix encapsulating the polarization, limited capture angle, or beam shaping in the microscope can be applied to find the image and not be limited to a particular particle shape or medium. We show that the image obtained from this method can be used to determine and match particle properties. We also use incoherent averaging on multiple T-matrices to produce polychromatic images. Data obtained using this method could be used as an input to track the general behavior of particles in suspension or within an optical trap.

Self-assembly and complex manipulation of colloidal mesoscopic particles by active thermocapillary stress.

We demonstrate that the active thermocapillary stresses induced by multiple microbubbles offer simple routes to directed self-assembly and complex but controllable micromanipulation of mesoscopic colloidal particles embedded in a liquid. The microbubbles are nucleated on a liquid-glass interface using optical tweezers. The flow around a single bubble causes self-assembly of the particles in rings at the bubble-base, while an asymmetric temperature profile generated across the bubble interface breaks the azimuthal symmetry of the flow, and induces simultaneous accumulation and repulsion of particles at different axial planes with respect to the bubble. The flow due to two adjacent bubbles leads to more diverse effects including the sorting of particles, and to local vorticity that causes radial and axial rotation of the particles - the latter being obtained for the first time using optical tweezers. The sorting is enabled by nucleating the bubbles on spatially discrete temperature profiles, while the vorticity is generated by nucleating them in the presence of a temperature gradient which once again causes a strong symmetry-breaking in the azimuthal flow. The flow profiles obtained in the experiments are explained by analytical solutions or qualitative explanations of the associated thermocapillary problem employing the Stokes and heat equations.

Damage mechanism of soil-rock mixture after freeze-thaw cycles

As a widely distributed geological and engineering material, the soil-rock mixture always undergoes frequentative and short-term freeze-thaw cycles in some regions. Its internal structure is destroyed seriously, but the damage mechanism is not clear. Based on the damage factor, the damage research of properties of soil-rock mixture after different times of freeze-thaw cycles is investigated. Firstly, the size-distributed subgrade gravelly soil samples are prepared and undergo different times of freeze-thaw cycles periodically (0, 3, 6, 10), and indoor large-scale triaxial tests are completed. Secondly, the degradation degree of elastic modulus is considered as a damage factor, and applied to macro damage analysis of soil-rock mixture. Finally, the mesoscopic simulation of the experiments is achieved by PFC3D, and the influence on strength between soil-rock particles caused by freeze-thaw cycles is analyzed. The results show that freeze-thaw cycles cause internal damage of samples by weakening the strength between mesoscopic soil-rock particles, and ultimately affect the macro properties. After freeze-thaw cycles, on the macro-scale, elastic modulus and shear strength of soil-rock mixture both decrease, and the decreasing degree is related to the times of cycles with the mathmatical quadratic form; on the meso-scale, freeze-thaw cycles mainly cause the degradation of the strength between soil-rock particles whose properties are different significantly.

A usage-based size classification scheme for sedimentary charcoal

Terms referring to charcoal particle size classifications are inconsistent in the paleofire literature. Inconsistencies of terminology prevent effective scientific discourse and research comparability. In this paper, I use the Global Charcoal Database (GCD) to determine the relative usage of sieving size boundaries and use these metadata as a proxy for the consensus of the paleofire community. With consideration of the size classification bounds used in other fields, I propose a standardized size classification system and terminology for charcoal particles. This system consists of macroscopic (>125 μm), mesoscopic (50–125 μm), and microscopic (10–50 μm) charcoal particles and aims to unify paleofire jargon by conforming to the terminology and most commonly used size bounds in the community.

Size-tunable capture of mesoscopic matters using thermocapillary vortex

The hydrodynamics in lab-on-a-chip provides an efficient and tunable platform for manipulating mesoscopic particles. Current capture-tunable technology has been mainly focused on inertial flow with little attention on a thermocapillary vortex. The boundary condition is one of the most important factors on particle manipulation in a microvortex. By integrating a photothermal waveguide with a triangular channel in lab-on-a-chip, we present a tunable microvortex array for achieving size-tunable capture. Ellipticity of the temperature field and intensity of vortices are continuously adjustable by moving the photothermal waveguide along the triangular channel, resulting in tunable particle trajectories. Particles can be trapped in a vortex center and driven out of the vortex along with external flow. The detailed theoretical results reveal that a threshold size of trapped particles can be adjustable by the channel width. We believe that the approach, the thermocapillary vortex on chip, will provide a facile way for seamless connection between photonics and microfluidics.

Optical binding of two cooled micro-gyroscopes levitated in vacuum

Coupling between mesoscopic particles levitated in vacuum is a prerequisite for the realization of a large-scale array of particles in an underdamped environment as well as potential studies at the classical–quantum interface. Here, we demonstrate for the first time, to the best of our knowledge, optical binding between two rotating microparticles mediated by light scattering in vacuum. We investigate autocorrelations between the two normal modes of oscillation determined by the center-of-mass and the relative positions of the two-particle system. The inter-particle coupling, as a consequence of optical binding, removes the degeneracy of the normal mode frequencies, which is in good agreement with theory. We further demonstrate that the optically bound array of rotating microparticles retains their optical coupling during gyroscopic cooling, and exhibits cooperative motion whose center-of-mass is stabilized.

Simulating Kelvin–Helmholtz instability using dissipative particle dynamics

Kelvin–Helmholtz (KH) instability is simulated using dissipative particle dynamics (DPD) at the mesoscopic particle level. To model two-phase flow, the ‘color’ repulsion model is introduced to describe binary fluids according to the Rothman–Keller method. The simulated results are compared with similar experiment and simulation using other techniques, and the work concludes that DPD is a promising method for simulating these systems. Furthermore, through the model and numerical simulation, the effects of intermiscibility, temperature, magnitude of velocity difference, and density ratio on the KH instability are investigated, respectively. It is shown that the poor intermiscibility reduces the mixing of two fluids and weakens the eddy currents. It is also found that as the temperature increases, the turbulence feature, i.e. plume-like structures, is more obvious. It is also revealed that as the initial horizontal velocity difference increases, the interface rolls up faster and higher. And it is also observed that as the density ratio increases, the KH instability becomes more suppressed.