Soft Spheres Research Articles

Active control of the sound power scattered by a locally-reacting sphere.

Active control of the sound power scattered by a sphere is theoretically investigated using spherical harmonic expansions of the primary and secondary fields. The sphere has a surface impedance that is uniform, real, and locally reacting while being subjected to an incident monochromatic plane wave. The scattered power is controlled with a number of monopole sources, initially on the surface of the sphere, and is expressed as the sum of squared amplitudes of the spherical harmonics due to both the scattered and control fields. This quadratic function is minimized to identify the optimal strengths for different numbers of control sources. At low frequencies, the scattered field is dominated by the first few spherical harmonic terms, and its power can be significantly reduced with a single controlling monopole for a soft or absorbent sphere and with two monopoles for a hard sphere. The number of secondary sources required to significantly attenuate the scattered field at higher frequencies is found to be proportional to the square of the frequency, and the attenuation also falls off rapidly if the secondary sources are moved away from the surface of the sphere, no matter what its surface impedance.

Particles’ flow characteristics in a drum cooler with heat exchanger tubes: Simulation and comparison with traditional solution

In order to improve the waste heat recovery efficiency of metallized pellets, a new drum cooler with heat exchanger tubes was creatively proposed, and the flow characteristics of metallized pellets were investigated. The soft sphere model and discrete element method were used to investigate the axial velocity, the total velocity, the mixed standard deviation and the contact number of particles. The calculated values of the motion of particles showed good agreement with the corresponding available experimental data. The results show that, the flow characteristics of particles in the drum cooler with heat exchanger tubes are quite different from that in the drum cooler without heat exchanger tubes. The heat exchanger tubes can prevent the axial velocity, and promote the radial velocity and the mixing effect of particles. The ratio of the contact number between particles in the new drum cooler to the contact number between particles in the traditional drum cooler is 25.8%, and the heat exchanger tubes can make the bed of particles becomes loose. The violent motion of particles in the new drum cooler must be better for the cooling of particles and waste heat recovery.

Electrical double layer in molten salts taking into account Lennard-Jones potential

Results are presented of canonical ensemble Monte Carlo simulations of molten salt electrical double layers. Electrode surface atoms and ions are modelled as soft spheres with the use of the Lennard-Jones potential. Ions and electrode atoms have the same diameter but differ in the applied energetic Lennard-Jones parameter values. The electrode surface consists of C (graphite), Hg or Pb atoms. The values of the applied parameters allow a comparison of the results obtained with those of real systems. The paper presents such results as: ion distributions, the mean electrostatic potential and differential capacitance. The differential capacitance values are collated with theoretical and experimental results. The capacitance curves obtained by simulations are flatter than experimental ones. The theoretical capacitance values, in contrast to the experimental ones, are smaller at the positive electrode potentials and this difference is due to the occurrence of chemical bonding between anions and electrode surface in experimental systems.

Numerical investigation into the low-pressure detection sensor performance of hydrogen gas with variable soft sphere molecular model

Direct Simulation Monte Carlo (DSMC) method is used to simulate the hydrogen detection process with Microscale In-Plane Knudsen Radiometric Actuator (MIKRA). The variable soft sphere (VSS) model is applied to depict molecular diffusion in the gas mixtures that its results are compared with variable soft sphere (VSS) in literature. On the right side of the shuttle arm, the influence of molecular model (VSS and VHS) on the simulation results is small. And the temperature ratio, heat transfer ratio and pressure ratio are highly close to 1. But on the left side of the shuttle arm, the differences are significant resulting from molecular models. Especially, for the heat transfer on the left side of the shuttle arm, heat transfer ratio of VHS model to VSS model is maximally about 4.3. The influence of gas pressures and hydrogen concentrations on the detection performance of MIKRA is also discussed. The decrease of hydrogen concentration and the increase of gas pressure cause the center of the main vortex to move towards the heater arm, and the influence of the gas pressure is more significant. On the other hand, Knudsen force increases with the increase of the hydrogen concentration and its peak value is obtained in a higher gas pressure. For example, the peak value of Knudsen force can be attained for the gas pressure of about 387 Pa in the pure hydrogen domain while in the pure nitrogen domain, the gas pressure of about 260 Pa. Simultaneously, the relation of the linear dependence of Knudsen force on the hydrogen concentration is proposed to detect hydrogen concentration in N2–H2 mixtures.

Neoclassical geopolitics: Preliminary theoretical principles and methodological guidelines

The paper is aimed at making geopolitical studies and neoclassical geopolitics equivalent. In this sense, the objectives are conceptual and operational, comprising an original definition of geopolitical studies, and the explanation of the neoclassical geopolitics model and its variables: systemic stimuli, the geopolitical agent?s perceptions and capacities, and foreign policy outcomes (primarily the geopolitical design). Therefore, the problem at stake is to tie up several theoretical and methodological contributions into a solid new geopolitical model, in the limits of the phenomenological and soft positivist sphere. Two sections constituted the structure of this qualitative paper: 1) formulation of a chain of theoretical fundaments in geopolitical studies, and 2) description of a group of methodological steps that a geopolitical study can use. The research advances a) a new definition of geopolitical studies, b) explains the concept of geomisguidance, c) frames and unwraps Ratzel?s concept of Raumsinn, and d) ultimately systematises and assesses geopolitical studies? literature of different languages with respect to theory and methodology. All these findings were oriented to the practical aspect of the operationalisation of geopolitical studies, presenting the compact conclusion that the analysis of location is not enough for a grand vision of geopolitical studies as an international relations approach.

Virus-mimicking mesoporous organosilica nanocapsules with soft framework and rough surface for enhanced cellular uptake and tumor penetration.

An enveloped virus with soft and rough shells has strong penetration ability for cells. Inspired by the unique structure of virus, we successfully constructed virus-mimicking mesoporous organosilica nanocapsules (denoted as VMONs) for the first time by decorating small-sized silica nanoparticles on soft mesoporous organosilica hollow spheres. TEM and SEM images reveal that the prepared VMONs display uniform diameters (240 nm), a soft framework, a rough surface, and excellent dispersity. Quantitative nanomechanical mapping further demonstrates that the VMONs possess an extremely low Young's modulus (36 MPa) and a scraggly surface. In view of the successful construction of the virus-mimicking nanocapsules, the VMONs are further modified with human serum albumin (HSA) and Cy5.5-maleimide (Mal-Cy5.5) to investigate their cell penetration ability. Flow cytometry analysis reveals that the internalization of VMONs@HSA-Cy5.5 increases 2.74-fold compared to that of the conventional mesoporous nanosphere. Confocal laser scanning microscopy images show that the VMONs@HSA-Cy5.5 diffuses deeper for multicellular spheroids compared to both hard and soft mesoporous organosilica nanospheres. The penetration ability of the VMONs and SMONs increases 18.49 and 6.13-fold compared to that of MONs at the depth of 60 μm. Thanks to the excellent cellular penetration ability, the virus-mimicking VMONs@HSA-Cy5.5 can effectively deliver the anticancer drug doxorubicin (Dox) into drug-resistant MCF-7/ADR human breast cancer cells and significantly enhance the chemotherapeutic efficacy. Taken together, the constructed virus-mimicking organosilica nanocapsules with a soft framework and a rough surface possess strong cellular internalization and tumor penetration abilities, providing a unique and effective nanoplatform for biomedical applications.

Intermittent flow and transient congestions of soft spheres passing narrow orifices

Soft, low-friction particles in silos show peculiar features during their discharge. The outflow velocity and the clogging probability both depend upon the momentary silo fill height, in sharp contrast to silos filled with hard particles. The reason is the fill-height dependence of the pressure at the orifice. We study the statistics of silo discharge of soft hydrogel spheres. The outflow is found to become increasingly fluctuating and even intermittent with decreasing orifice size, and with decreasing fill height. In orifices narrower than two particle diameters, outflow can stop completely, but in contrast to clogs formed by rigid particles, these congestions may dissolve spontaneously. We analyze such non-permanent congestions and attribute them to slow reorganization processes in the container, caused by viscoelasticity of the material.

Steady-state rheology and structure of soft hybrid mixtures of liquid crystals and magnetic nanoparticles.

Using non-equilibrium molecular dynamics simulations, we study the rheology of a model hybrid mixture of liquid crystals (LCs) and dipolar soft spheres (DSS) representing magnetic nanoparticles. The bulk isotropic LC-DSS mixture is sheared with different shear rates using Lees-Edwards periodic boundary conditions. The steady-state rheological properties and the effect of the shear on the microstructure of the mixture are studied for different strengths of the dipolar coupling, λ, among the DSS. We find that at large shear rates, the mixture shows a shear-thinning behavior for all considered values of λ. At low and intermediate values of λ, a crossover from Newtonian to non-Newtonian behavior is observed as the rate of applied shear is increased. In contrast, for large values of λ, such a crossover is not observed within the range of shear rates considered. Also, the extent of the non-Newtonian regime increases as λ is increased. These features can be understood via the shear-induced changes of the microstructure. In particular, the LCs display a shear-induced isotropic-to-nematic transition at large shear rates with a shear-rate dependent degree of nematic ordering. The DSS show a shear-induced nematic ordering only for large values of λ, where the particles self-assemble into chains. Moreover, at large λ and low shear rates, our simulations indicate that the DSS form ferromagnetic domains.

Clustering and phase separation in mixtures of dipolar and active particles.

The self-assembly of colloidal particles in dynamic environments has become an important field of study because of potential applications in fabricating out-of-equilibrium materials. We investigate the phase behavior of mixtures of passive dipolar colloids and active soft spheres using Brownian dynamics simulations in two dimensions. The phase behaviors exhibited include dipolar percolated network, dipolar string-fluid, isotropic fluid, and a phase-separated state. We find that the clustering of dipolar colloids is enhanced in the presence of slow-moving active particles compared to the clustering of dipolar particles mixed with passive particles. When the active particle motility is high, the chains of dipolar particles are either broken into short chains or pushed into dense clusters. Motility-induced phase separation into dense and dilute phases is also present. The area fraction of particles in the dilute phase increases as the fraction of active particles in the system decreases, while the area fraction of particles in the dense phase remains constant. Our findings are relevant to the development of reconfigurable self-assembled materials.

Applying the soft sphere model to improve the understanding of bonding in transition metals

Development in the understanding of electronic structure and chemical bonding and the importance of metals is outlined. A summary of the main features of the soft sphere model of metallic bonding and structure is provided. The soft sphere model is used to show that there are four main components involved in the bonding of transition metal solids and the enthalpy of atomisation of gaseous transition metal atoms are calculated according to the model and results when compared to literature values give good agreement.

Evidence of Structural Inhomogeneities in Hard-Soft Dimeric Particles without Attractive Interactions.

We perform Monte Carlo simulations of a simple hard-soft dimeric model constituted by two tangent spheres experiencing different interactions. Specifically, two hard spheres belonging to different dimers interact via a bare hard-core repulsion, whereas two soft spheres experience a softly repulsive Hertzian interaction. The cross correlations are soft as well. By exploring a wide range of temperatures and densities we investigate the capability of this model to document the existence of structural inhomogeneities indicating the possible onset of aggregates, even if no attraction is set. The fluid phase behavior is studied by analyzing structural and thermodynamical properties of the observed structures, in particular by computing radial distribution functions, structure factors and cluster size distributions. The numerical results are supported by integral equation theories of molecular liquids which allow for a finer and faster spanning of the temperature-density diagram. Our results may serve as a framework for a more systematic investigation of self-assembled structures of functionalized hard-soft dimers able to aggregate in a variety of structures widely oberved in colloidal dispersion.

The structure of clusters formed by Stockmayer supracolloidal magnetic polymers

.Unlike Stockmayer fluids, that prove to undergo gas-liquid transition on cooling, the system of dipolar hard or soft spheres without any additional central attraction so far has not been shown to have a critical point. Instead, in the latter, one observes diverse self-assembly scenarios. Crosslinking dipolar soft spheres into supracolloidal magnetic polymer-like structures (SMPs) changes the self-assembly behaviour. Moreover, aggregation in systems of SMPs strongly depends on the constituent topology. For Y- and X-shaped SMPs, under the same conditions in which dipolar hard spheres would form chains, the formation of very large loose gel-like clusters was observed (E. Novak et al., J. Mol. Liq. 271, 631 (2018)). In this work, using molecular dynamics simulations, we investigate the self-assembly in suspensions of four topologically different SMPs --chains, rings, X and Y-- whose monomers interact via Stockmayer potential. As expected, compact drop-like clusters are formed by SMPs in all cases if the central isotropic attraction is introduced, however, their shape and internal structure turn out to depend on the SMPs topology.Graphical abstract

High-speed x-ray tomography of silo discharge

The outflow of granular materials from storage containers with narrow outlets is studied by means of ultrafast x-ray computed tomography (UFXCT). The used acquisition speed of this tomograph is high enough to allow high-speed recording of two horizontal cross sections (each of them at a rate of 1000 images per second) of the container during the discharge of material. Analyzing space-time plots that were generated from the tomograms, we retrieve velocity profiles and packing structures in the container. We compare hard spherical grains with soft, low-friction hydrogel spheres. Their flow profiles are qualitatively different. While the hard spheres form stagnant zones at the container side walls, the hydrogel spheres with extremely low friction coefficient flow in all regions of the container. Moreover, a shell-like positional arrangement of the soft spheres induced by the container walls is revealed. The results obtained for the flow field structure confirm earlier conclusions drawn from sequences of x-ray tomograms of clogged states.

Characterizing nonaffinity upon decompression of soft-sphere packings.

Athermal elastic moduli of soft-sphere packings are known to exhibit universal scaling properties near the unjamming point, most notably the vanishing of the shear-to-bulk moduli ratio G/B upon decompression. Interestingly, the smallness of G/B stems from the large nonaffinity of deformation-induced displacements under shear strains, compared to insignificant nonaffinity of displacements under compressive strains. In this work, we show using numerical simulations that the relative weights of the affine and nonaffine contributions to the bulk modulus, and their dependence on the proximity to the unjamming point, can differ qualitatively between different models that feature the same generic unjamming phenomenology. In canonical models of unjamming, we observe that the ratio of the nonaffine to total bulk moduli B_{na}/B approaches a constant upon decompression, while in other, less well-studied models, it vanishes. We show that the vanishing of B_{na}/B in noncanonical models stems from the emergence of an invariance of net (zero) forces on the constituent particles to compressive strains at the onset of unjamming. We provide a theoretical scaling analysis that fully explains our numerical observations, and allows us to predict the scaling behavior of B_{na}/B upon unjamming, given the functional form of the pairwise interaction potential.

Molecular simulation study of the glass transition in a soft primitive model for ionic liquids

In this paper, we present a molecular dynamics study of the glass transition for a soft-core primitive model for ionic liquids, in which cations are fully flexible chains of tangent soft spherical monomers, being the positively charged monomer at one of the ends of the chain, and anions as charged soft spheres. We have monitored transport coefficients such as the self-diffusion coefficients and the shear viscosity, as well as correlation functions such as the mean-square displacement, the self-intermediate scattering function, and probes of heterogeneous dynamics such as the van Hove distribution function and the four-points susceptibility. The analysis of these properties indicates that, for a given pressure, the glass transition shows a weak temperature dependence on the cation length, occurring first for short-chain than for long-chain ionic liquids.

Numerical Investigation of Interaction of Counter Flow Jet and Hypersonic Capsule Flow Via Modified DsmcFoam

Abstract In this work, numerical investigation of interaction of counter flow jet and hypersonic re-entry capsule flow has been carried out through modification of DsmcFoam solver. The DsmcFoam modification includes implementation of variable soft sphere (VSS) collision model for more accurate collision model, adjustment of nonuniform initial condition for faster convergence and nonuniform boundary condition, calculation of local Knudsen number in postprocessing for adaptive grid generation, and implementation of different gas species for multigas flow interaction simulations. Therefore, the modified DsmcFoam can be used for investigation of the effect of counter flow jet on the vehicle aerodynamics and aerothermodynamics. New validation test cases from Von Karman gas dynamics facility (VKF) tunnel data of Apollo and blunt-cone re-entry geometries are studied via DsmcFoam in which a suitable agreement of results is observed compared to experimental data and also MONACO code computations. Also, the influence of counter flow jet has been presented, i.e., changing of bow shock configuration and its distance from the vehicle. Consequently, it is observed that by increasing counter flow jet velocity or density, reduction of the drag coefficient and heat flux on the vehicle will occur. Furthermore, variation of the velocity or density of counter flow jet leads to different jet-flow interaction patterns which are presented evidently.

Section 172 of the Companies Act 2006: Desperate Times Call for Soft Law Measures

Section 172 of the Companies Act 2006 has been afforded much attention during parliamentary discussions on the codification of directors’ duties and has since the enactment of the Companies Act 2006 occupied much space in discussions among scholars who share an academic interest in the shareholder/stakeholder debate, in policy documents on law reforms following a series of corporate failures, as well as in company law lecture notes provided by Law Schools across the UK. With the UK leaving the EU, it is a critical time to discuss enlightened decision-making on boards, considering that, arguably, one of the key benefits of joining the EU with regard to UK company law, was that the UK was prompted to consider incorporating provisions affording a certain level of protection to the interests of other constituencies across a wide range of company and securities law Acts and regulations. What often escapes the attention of participants in discussions surrounding s. 172 CA 2006, is the section’s limitations not so much in terms of it prioritising the interests of shareholders over the interests of other constituencies, but with regard to its enforcement and utility overall. The purpose of this paper is twofold. First it aims to shed some light on the background and function of section 172 CA 2006. Secondly, after considering the challenges, shortcomings and dilemmas surrounding the function of this section, it suggests ways forward by proposing a change in the mode of regulating this aspect of managerial conduct. Ample evidence suggests that section 172 CA 2006 in terms of enlightened decision-making and in its hard law form will not facilitate the goal of promoting the ‘good governance’ of companies that have a high impact on society. Thus, the paper aims to advance an important aspect of UK corporate law in the making: namely suggest the use of alternative means available in the soft law sphere, that could support a more pluralistic and democratic formation of corporate decision-making.

Critical scaling for yield is independent of distance to isostaticity

Using discrete element simulations, we demonstrate that critical behavior for yielding in soft disk and sphere packings is independent of distance to isostaticity over a wide range of dimensionless pressures. Jammed states are explored via quasistatic shear at fixed pressure, and the statistics of the dimensionless shear stress $\mu$ of these states obey a scaling description with diverging length scale $\xi \propto |\mu-\mu_c|^{-\nu}$. The critical scaling functions and values of the scaling exponents are nearly independent of distance to isostaticity despite the large range of pressures studied. Our results demonstrate that yielding of jammed systems represents a distinct nonequilibrium critical transition from the isostatic critical transition which has been demonstrated by previous studies. Our results may also be useful in deriving nonlocal rheological descriptions of granular materials, foams, emulsions, and other soft particulate materials.

Can a Large Packing be Assembled from Smaller Ones?

We consider zero temperature packings of soft spheres that undergo a jamming to unjamming transition as a function of packing fraction. We compare differences in the structure, as measured from the contact statistics, of a finite subsystem of a large packing to a whole packing with periodic boundaries of an equivalent size and pressure. We find that the fluctuations of the ensemble of whole packings are smaller than those of the ensemble of subsystems. Convergence of these two quantities appears to occur at very large systems, which are usually not attainable in numerical simulations. Finding differences between packings in two dimensions and three dimensions, we also consider four dimensions and mean-field models, and find that they show similar system size dependence. Mean-field critical exponents appear to be consistent with the 3D and 4D packings, suggesting they are above the upper critical dimension. We also find that the convergence as a function of system size to the thermodynamic limit is characterized by two different length scales. We argue that this is the result of the system being above the upper critical dimension.

Investigation on the multiphase sink vortex Ekman pumping effects by CFD-DEM coupling method

The gas-liquid-solid multiphase sink vortex is a complex turbulent mechanical phenomenon, in which the pumping effects of Ekman boundary layer involved in the above process has the important scientific value and engineering significance. To address the matter, a coupled Computational Fluid Dynamic and Discrete Element Method (CFD-DEM) method for the simulation of the multiphase sink vortex is proposed based on the realizable k-ε turbulent model and the soft sphere model. The suction and extraction regularities of gas-liquid coupling process are analyzed to reveal the matter transfer mechanism of Ekman boundary layer. Then, the phenomenon for the particle sucked by sink vortex is investigated to obtain the Ekman pumping effects. Finally, the influences of Ekman pumping effects on particles with respect to different densities are studied to verify the validity and reliability of the proposed method. Numerical results demonstrate that the suction and extraction intensities constitute a data set that is dependent on the initial disturbance components; there is an apparent upwelling phenomenon in the liquid boundary layer, which is caused by the spiral coupling structure of Ekman boundary layer. The Ekman pumping process for particles has three typical stage: Ekman suction-extraction state, Ekman horizontal pumping state, and Ekman upwelling state, wherein the flow patterns are dominated by the initial disturbance and appear a complex nonlinear turbulence features; with the particle density increasing, the effects of Ekman suction-extraction state and horizontal pumping state are enhanced, but the Ekman upwelling effect for particle has apparent decreased.