Distribution Of Particles In Space Research Articles

On the Preferential Concentration of Particles in Turbulent Channel Flow: The Effect of the Added-Mass Factor

Preferential concentration, observed in turbulent flows when particle response times are of the same order of the flow’s characteristic timescales, manifests as non-uniform particle distributions in space. Unraveling its governing mechanisms holds crucial implications for both natural and industrial processes reliant on particle-laden flows. Focusing on particles with small inertia, this study employs Direct Numerical Simulations coupled with Lagrangian particle tracking to investigate the influence of the added-mass factor on the preferential concentration of particles denser than the fluid in the one-way coupling regime. It is shown how the added-mass factor β affects particle distribution within the channel through the statistical correlations between particle concentration and typical descriptors of the flow topology. The results suggest that increasing values of β (corresponding to lighter particles) significantly reduce the effectiveness of turbophoresis in producing particle accumulation in the near-wall region. Resulting in a gradual decorrelation between particle concentration and both the strain-rate and the vorticity tensors, higher values of β lead to a more uniform particle distribution, regardless of the Stokes number.

Kinetics of a Reaction-Diffusion Mtb/SARS-CoV-2 Coinfection Model with Immunity

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Mycobacterium tuberculosis (Mtb) coinfection has been observed in a number of nations and it is connected with severe illness and death. The paper studies a reaction–diffusion within-host Mtb/SARS-CoV-2 coinfection model with immunity. This model explores the connections between uninfected epithelial cells, latently Mtb-infected epithelial cells, productively Mtb-infected epithelial cells, SARS-CoV-2-infected epithelial cells, free Mtb particles, free SARS-CoV-2 virions, and CTLs. The basic properties of the model’s solutions are verified. All equilibrium points with the essential conditions for their existence are calculated. The global stability of these equilibria is established by adopting compatible Lyapunov functionals. The theoretical outcomes are enhanced by implementing numerical simulations. It is found that the equilibrium points mirror the single infection and coinfection states of SARS-CoV-2 with Mtb. The threshold conditions that determine the movement from the monoinfection to the coinfection state need to be tested when developing new treatments for coinfected patients. The impact of the diffusion coefficients should be monitored at the beginning of coinfection as it affects the initial distribution of particles in space.

Effect of Aerosol Dispersion on Its Masking Ability

The improvement of camouflage of troops and objects is necessary in all types of military operations. Aerosol masking is an integral part of this task. The special jamming systems decrease the likelihood of the hit and the destruction of military units (their weapons and equipment) and personnel from enemy weapons. The aim of this work is to study the effect of aerosol dispersion on its masking ability. The fraction of the area screened by aerosols relative to the electromagnetic radiation of the optical range was determined on the basis of a random, equal distribution of aerosol particles in space. It has been established that when theoretically evaluating the effectiveness of camouflage (by the length of the blind area or by the area of camouflage), it is necessary to calculate not only the integral concentration of aerosol along the sightline of the object (in the horizontal and vertical planes, G, cm 3 /m 2 or g/m 2 ), but also take into account the dispersion of the aerosol, since at equivalent aerosol concentrations it has a significant effect on the camouflage efficiency. The dispersion of the aerosol formed by means of smoke release (checkers, TDA, etc.) is a necessary component of the tactical and technical characteristics of products, as well as one of the requirements for promising developments and developments of aerosol countermeasures. The article presents the results of computer simulation of the random distribution of aerosol particles in space to assess its screening capacity relative to electromagnetic radiation in the optical range

Inviscid Suspension Flow along a Flat Boundary

A previously developed self-consistent field method is used to study an arbitrary finite set of identical spherical particles of arbitrary density moving in a uniform inviscid incompressible flow specified at infinity in the presence of a flat wall. For a given initial particle distribution in space, expressions for the particle and fluid velocities are derived taking into account the collective hydrodynamic interaction of the particles with each other and the wall. For a statistically uniform particle distribution in a semibounded inviscid fluid, analytical averaged particle and fluid velocity profiles are obtained in the first approximation with respect to the particle volume fraction in the suspension.

Packings of frictionless spherocylinders.

We present simulation results on the properties of packings of frictionless spherocylindrical particles. Starting from a random distribution of particles in space, a packing is produced by minimizing the potential energy of interparticle contacts until a force-equilibrated state is reached. For different particle aspect ratios α=10⋯40, we calculate contacts z, pressure as well as bulk and shear modulus. Most important is the fraction f_{0}(α) of spherocylinders with contacts at both ends, as it governs the jamming threshold z_{c}(α)=8+2f_{0}(α). These results highlight the important role of the axial "sliding" degree of freedom of a spherocylinder, which is a zero-energy mode but only if no end contacts are present.

The effect of seasonal variation in precipitation and evapotranspiration on the transient travel time distributions

Precipitation (P), plant water use, and evaporation from the soil surface control the travel time of streamflow (Q) and evapotranspiration (ET) in a complex way. However, the impact of soil moisture and energy availability on the travel time distribution (TTD) of evaporated and transpired waters are yet less understood. In this study, we investigate how the seasonal variability of P and ET in terms of phase shift and rate influences the temporal dynamics of TTDs. To this end, we choose four contrasting climate types described as in-phase P and ET, out-of-phase P and ET, year-round constant P with seasonal ET, and year-round constant ET with seasonal P. We use a physically-based hydrological model to simulate dominant processes in the water and energy cycles as well as subsurface flow velocity, which are subsequently used in a Lagrangian particle-tracking model to characterize the age distribution of water particles in space and time. The results prove that the soil moisture availability than the ET rate imposes a stronger control on the TTD of transpired water in all climate scenarios. Plants indicate an overall tendency towards younger water particles unless in periods with a pronounced dry condition when old waters are more available in the deeper soil layers. In particular, the climate scenario with out-of-phase P and ET yields the highest percentage of old particles taken up by plants. Furthermore, ET age sampling mechanism shows hysteresis against the ET rate, with an opposite direction in climates with in-phase and out-of-phase P and ET. Our results also suggest that the ratio between the median travel time of Q and the median age of water storage has a dual relationship with the Q rate, indicating the existence of a threshold behavior that distinguishes the direct and inverse storage effects based on the storage volume.

Non-equilibrium statistical mechanical approach to the formation of non-Maxwellian electron distribution in space

Boltzmann-Gibbs (BG) entropy has additive and extensive properties, but for certain physical systems, such as those governed by long-range interactions – plasma or fully ionized gas being an example – it is speculated that the entropy must be non-additive and non-extensive. Because of the fact that Tsallis entropy possesses such characteristics, many spacecraft observations of charged particle distributions in space are interpreted with the conceptual framework based upon Tsallis statistical principles. This paper formulates the non-equilibrium statistical theory of space plasma, and it is shown that the steady state electrostatic turbulence in plasma coincides with the formation of non-Maxwellian electron distribution function known as the kappa distribution. The kappa distribution is equivalent to the q-Gaussian distribution in the Tsallis statistical theory, which represents the most probable state subject to Tsallis entropy. This finding represents an independent confirmation that the space plasma may indeed be governed by the Tsallis statistical principle.

Entanglement content of quantum particle excitations. III. Graph partition functions

We consider two measures of entanglement, the logarithmic negativity, and the entanglement entropy, between regions of space in excited states of many-body systems formed by a finite number of particle excitations. In Papers I and II [O. A. Castro-Alvaredo et al., J. High Energy Phys. 2018(10), 39; ibid., e-print arXiv:1904.01035 (2019)], it has been shown in one-dimensional free-particle models that, in the limit of large system’s and regions’ sizes, the contribution from the particles is given by the entanglement of natural qubit states, representing the uniform distribution of particles in space. We show that the replica logarithmic negativity and Rényi entanglement entropy of such qubit states are equal to the partition functions of certain graphs, formed out of Wick pairings, which encode the topology of the manifold induced by permutation twist fields. Using this new connection, we provide a general proof, in the massive free boson model, which the qubit result holds in any dimensionality and for any regions’ shapes and topology. The proof is based on clustering and the permutation-twist exchange relations and is potentially generalizable to other situations, such as lattice models, particle and hole excitations above generalized Gibbs ensembles, and interacting integrable models.

Numerical Simulation of Penning Gas Discharge in 2D/3D Setting

This work presents a numerical simulation of the Penning discharge in 2D/3D formulation. The simulation is based on the electrostatic particle method in cells using structured rectangular grids and implemented in the VSim software package. To simulate the kinetic processes in a gas-discharge plasma, the Monte-Carlo collision method was used. The calculations were carried out for several sets of chemical kinetics reactions, and their comparison is given. Various characteristics of the Penning discharge in 2D and 3D formulation were calculated, such as anodic/cathodic currents, the distribution of charged particles in space and energies, etc. A comparison of the simulation results with experimental data was observed.

Kappa Distributions: Statistical Physics and Thermodynamics of Space and Astrophysical Plasmas

Kappa distributions received impetus as they provide efficient modelling of the observed particle distributions in space and astrophysical plasmas throughout the heliosphere. This paper presents (i) the connection of kappa distributions with statistical mechanics, by maximizing the associated q-entropy under the constraints of the canonical ensemble within the framework of continuous description; (ii) the derivation of q-entropy from first principles that characterize space plasmas, the additivity of energy, and entropy; and (iii) the derivation of the characteristic first order differential equation, whose solution is the kappa distribution function.

Coupling Eulerian‐Lagrangian method of air‐particle two‐phase flow with population balance equations to simulate the evolution of vehicle exhaust plume

SummaryIn this paper, we present a new numerical scheme to describe the dynamic evolution of multiphase polydisperse systems in terms of time, space, and properties by coupling the Eulerian‐Lagrangian method for air‐particle two‐phase flow and population balance equations to describe particle property evolution due to microbehaviors (eg, aggregation, breakage, and growth). This coupling scheme was used to comprehensively simulate the two‐phase flow structure, particle size spectrum, particle number, and volume concentrations. These were characterized by a high‐resolution particle tracking using the Lagrangian approach and the high precision of moments of the particle size spectrum by solving the population balance equation with the quadrature method of moments. The algorithm of the coupling scheme was incorporated into the open source computational fluid dynamics software OpenFOAM to simulate the dynamic evolution of vehicle exhaust plume. The impacts of vehicle velocity, exhaust temperature, and aggregation efficiency on the distribution of auto exhaust particles in space and changes in their properties were analyzed. The results indicate that the particle number concentration, volume concentration, and average diameter of particles in the vehicle exhaust plume could be strongly affected by the plume structure and flow properties.

Survival of aerosol particles in a puff with spatially inhomogeneous size spectrum

Aerosol particles released from emission sources undergo various atmospheric and aerosol processes before they become a part of the background aerosols. Coagulation and dispersion, the two important processes that governs evolution of particle characteristics in a puff with an inhomogeneous size distribution of particles in space is considered in this study. This specific case consists of an initial Gaussian aerosol packet in which larger particles are preferentially segregated to farther distances from the centre of the packet. The coagulation-dispersion equation is solved using Jaffe approximation technique for obtaining essential results such as survival fraction, that is, fraction of particles surviving due to the simultaneous action of coagulation and dispersion. Analytical results are developed for the temporal variations of the number concentration, mean size and the standard deviation. The asymptotic results yield the final characteristics of the spectra of the particles which form a part of the background aerosols. These quantities are useful for defining the "effective aerosol source terms" in the general dynamic equations for background aerosols, long-range transport of aerosols, and geo-engineering applications. The results are further discussed.

A lattice method for the Eulerian simulation of heavy particle suspensions

Abstract Modeling dispersed solid phases in fluids still represents a computational challenge when considering a small-scale coupling in wide systems, such as the atmosphere or industrial processes at high Reynolds numbers. A numerical method is here introduced for simulating the dynamics of diffusive heavy inertial particles in turbulent flows. The approach is based on the position/velocity phase–space particle distribution. The discretization of velocities is inspired from lattice Boltzmann methods and is chosen to match discrete displacements between two time steps. For each spatial position, the time evolution of particles momentum is approximated by a finite-volume approach. The proposed method is tested for particles experiencing a Stokes viscous drag with a prescribed fluid velocity field in one dimension using a random flow, and in two dimensions with the solution to the forced incompressible Navier–Stokes equations. Results show good agreements between Lagrangian and Eulerian dynamics for both spatial clustering and the dispersion in particle velocities. In particular, the proposed method, in contrast to hydrodynamical Eulerian descriptions of the dispersed phase, is able to reproduce fine particle kinetic phenomena, such as caustic formation or trajectory crossings. This indicates the suitability of this approach at large Stokes numbers for situations where details of collision processes are important.

Inhomogeneous distribution of water droplets in cloud turbulence.

We consider sedimentation of small particles in the turbulent flow where fluid accelerations are much smaller than acceleration of gravity g. The particles are dragged by the flow by linear friction force. We demonstrate that the pair-correlation function of particles' concentration diverges with decreasing separation as a power law with negative exponent. This manifests fractal distribution of particles in space. We find that the exponent is proportional to ratio of integral of energy spectrum of turbulence times the wave number over g. The proportionality coefficient is a universal number independent of particle size. We derive the spectrum of Lyapunov exponents that describes the evolution of small patches of particles. It is demonstrated that particles separate dominantly in the horizontal plane. This provides a theory for the recently observed vertical columns formed by the particles. We confirm the predictions by direct numerical simulations of Navier-Stokes turbulence. The predictions include conditions that hold for water droplets in warm clouds thus providing a tool for the prediction of rain formation.

Theoretical and numerical analysis of radiation belt electron precipitation by coherent whistler mode waves

AbstractThe interaction between coherent whistler mode waves and energetic radiation belt electrons can result in pitch angle scattering of electrons into the bounce loss cone and subsequent precipitation. In studying the effects of VLF transmitter signals on particle precipitation, past modeling efforts have focused on the computation of diffusion coefficients for a Fokker‐Planck model. In contrast, to capture the nonlinear effects of large‐amplitude coherent waves, we evaluate particle precipitation using a Vlasov‐Liouville (VL) model which computes the phase space particle distribution function directly using a characteristic‐based solution of the Vlasov equation. Previous work has shown that in the case of large‐amplitude coherent waves, phase trapping can significantly perturb resonant particles from their adiabatic paths. We evaluate the importance of phase trapping over a range of wave amplitudes (up to 200 pT); the percentage of particles that precipitate after being phase trapped is computed over a phase space grid in the loss cone. The results demonstrate that phase trapping contributes significantly to precipitation when a large‐amplitude wave (>100 pT) is present. Additionally, linear theory can be valid over a broad range of amplitudes and the relative accuracy of linear theory in calculating the precipitated flux depends strongly on the initial particle distribution. Additionally, we demonstrate the ability of the VL model to calculate the time evolution of the precipitated flux due to short‐duration whistler mode pulses. The physical parameters used in this study are typical of those associated with the Siple Station wave injection experiment.

Параллельный алгоритм решения задач динамики заряженных частиц с учетом балансировки вычислительной нагрузки

We present new solution methods for dynamics of counter charged beams in accelerators and plasma electrons dynamics in a trap with inverse magnetic mirrors and multipole magnetic walls. The models are based on the particle-in-cell method. These problems require extremely large computations and can be solved by the use of powerful supercomputers only. A modification of the euler-lagrangian decomposition is implemented in order to achieve full and balanced load of computational nodes in case of highly nonuniform particle distribution in space and time.

Topology of collisionless relaxation.

Using extensive molecular dynamics simulations we explore the fine-grained phase space structure of systems with long-range interactions. We find that if the initial phase space particle distribution has no holes, the final stationary distribution will also contain a compact simply connected region. The microscopic holes created by the filamentation of the initial distribution function are always restricted to the outer regions of the phase space. In general, for complex multilevel distributions it is very difficult to a priori predict the final stationary state without solving the full dynamical evolution. However, we show that, for multilevel initial distributions satisfying a generalized virial condition, it is possible to predict the particle distribution in the final stationary state using Casimir invariants of the Vlasov dynamics.

Wavelet analysis of the particle distribution in a down-flow fluidized bed based on electrical capacitance tomography images

In the present paper, the extraction of dominant particle concentration fluctuation at various time–space frequency levels from reconstructed electrical capacitance tomography (ECT) images by means of the discrete wavelet transform has been proposed. Using this concept, three-dimensional images (time and two-dimensional space) obtained by an ECT system are decomposed into different time and space levels to characterize the intrinsic features of the particle distribution in a down-flow fluidized bed with a newly designed distributor using three-dimensional discrete wavelet multiresolution. As a result, the dominant time and space particle distribution characteristics for a specific frequency level can be visualized. On the basis of the wavelet analysis results, the best operation condition, under which the most stable and uniform particle distribution can be obtained, was clarified. This provides a good reference for the optimization of a downer reactor to qualify the refinery process in the petroleum industry.

Analyzing of Functionally Graded Materials by Discrete Element Method

Based on discrete element method, the mechanical responses of a functionally graded cantilever beam are studied by using of two kinds of particle with different properties. The variation of material properties along the thickness direction is simulated by the different distribution of constituent particles in space. The method validity was tested, and the influence of material homogenous on deformation and stiffness of cantilever beam under mechanical load were studied make use of numerical examples. Method in this paper will provide a new way for analyzing of functionally graded materials and its optimizing design from micromechanism.

On mean coordination and structural heterogeneity in model amorphous solids

We propose a simple route to analytically evaluate the average coordination of model disordered solids with maximally homogeneous distribution of the particles in space. The model yields the average number of contacts (z) as a function of volume fraction (phi) of a hard-sphere connected system and recovers the critical jamming point of hard spheres (z=6 at phi=0.64). Numerical simulations of Lennard-Jones glasses with a varying attraction range are used to investigate the volume fraction dependence of the average coordination in the presence of attraction. It is observed that upon decreasing phi below 0.6, structural heterogeneity is reflected in values of the coordination number which are higher than those predicted by the model for a statistically homogeneous distribution of particles in space due to the attraction-induced local aggregation. Thus the model can be usefully employed as a quantitative reference to assess the degree of structural heterogeneity in glasses in terms of a directly accessible structural parameter such as the mean number of contacts.