Bath Of Particles Research Articles

Contrastive factors of activity and crowding on conformational properties of a flexible polymer

Activity and crowding effect is crucial in conformational change and relevant dynamics of biomolecules in complex environment, which remains a challenging problem. We perform a systematic Langevin simulation to investigate the conformational properties of a flexible polymer in an active bath. Firstly, we modulate both active force and bath particle size to probe the activity-induced polymer swelling. Results indicate a significant crowder size effect. Moreover, polymer conformational change shows a monotonic scaling on dynamical persistence length of active particles. Secondly, activity-crowding competition effect is rationalized. An intriguing shrinkage-expansion crossover of polymer dimension is observed with increasing activity.

Preparation and characterization of Ni-Cu dual coated ZTA particles by ionic liquid-assisted electroless plating as reinforcement of metal-based composites

An ionic liquid assisted electroless plating is adopted to prepare continuous and dense Ni-Cu dual coatings on the surface of ZTA particles. The effects of l-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) additive, NiSO4 and CuSO4 concentrations on the surface morphologies, coating thickness, and element content of Ni-Cu dual coated ZrO2-toughened Al2O3 (ZTA@Ni-Cu) particles have been characterized systematically. Results show that with incremental addition of [bmim]BF4, suspended Ni-Cu particles in plating bath can be diminished but the incubation period and plating time of Ni-Cu coatings are prolonged significantly. The addition of 20 g·L−1 [bmim]BF4 is optimum for the preparation of uniform and compact ZTA@Ni-Cu particles. Besides, the thickness of Ni-Cu coating is about 20–30 μm and the Cu element content can be controlled in the range of 14.10–60.76 at.% through adjusting Cu(II) ions concentration. Furthermore, the possible reactions and deposition sequences for the preparation of Ni-Cu coatings on ZTA surfaces are analyzed and an empirical model of the deposition process assisted with [bmim]BF4 additive is also proposed to expound the function mechanism of [bmim]BF4 additive and the formation process of Ni-Cu coatings on ZTA surfaces.

The electrodeposition of composite coatings: Diversity, applications and challenges

Abstract A wide range of coatings can be produced by incorporating particles into an electrodeposit. The matrix may be a metal, conductive polymer or conductive ceramic, whereas the particle can be metallic, polymeric, ceramic or combinations of spheroidal, irregular or layered inclusions. Nanostructured, gradient, multilayer and sandwich layer deposit further widen possibilities. Electrochemical approaches to the deposition of composite coatings offer the benefits of good control over deposition rate (hence thickness), coating composition and deposit properties. Both faradaic electrodeposition and electrophoresis are usually involved. This review focuses on nanosized inclusions in a metal matrix over the last two decades. Interactions between bath composition, particle dispersion, operational variables and resultant deposit properties are poorly documented in the literature. Our understanding of the mechanism of composite deposition remains patchy, despite progress and computer models are scarce. Electrode geometry, electrolyte hydrodynamics and current distribution remain poorly treated. Markets in electronics, surface engineering, aerospace, corrosion protection and electrochemical energy conversion have been stimulated by newer uses for self-cleaning, superhydrophobic and biocompatible surfaces. Challenges to be met by further research and development are prioritised.

Enhanced Orientational Ordering Induced by an Active yet Isotropic Bath.

Can a bath of isotropic but active particles promote ordering of anisotropic but passive particles? In this Letter, we uncover a fluctuation-driven mechanism by which this is possible. Somewhat counterintuitively, we show that the passive particles tend to be more ordered upon increasing the noise strength of the active isotropic bath. We first demonstrate this in a general dynamical model for a nonconserved order parameter (model A) coupled to an active isotropic field and then concentrate on two examples: (i)a collection of polar rods on a substrate in an active isotropic bath and (ii)a passive apolar suspension in a momentum conserved, actively forced but isotropic fluid, which are relevant for current research in active systems. Our theory, which is relevant for understanding ordering transitions in out-of-equilibrium systems can be tested in experiments, for instance, by introducing a low concentration of passive rodlike objects in active isotropic fluids and, since it is applicable to any nonconserved dynamical field, may have applications far beyond active matter.

On solving the unrelated parallel machine scheduling problem: active microrheology as a case study

Modern computational platforms are characterized by the heterogeneity of their processing elements. Additionally, there are many algorithms which can be structured as a set of procedures or tasks with different computational cost. Balancing the computational load among the available processing elements is one of the main keys for the optimal exploitation of such heterogeneous platforms. When the processing time of any procedure executed on any of the available processing elements is known, this workload-balancing problem can be modeled as the well-known scheduling on unrelated parallel machines problem. Solving this type of problems is a big challenge due to the high heterogeneity on both, the tasks and the machines. In this paper, the balancing problem has been formally defined as a global optimization problem which minimizes the makespan (parallel runtime) and a heuristic based on a Genetic Algorithm, called Genetic Scheduler (GenS), has been developed to solve it. In order to analyze the behavior of GenS for several heterogeneous clusters, an example taken from the field of statistical mechanics has been considered as a case study: an active microrheology model. Given this type of problem and a heterogeneous cluster, we seek to minimize the total runtime to extend and analyze in depth the case of study. In such context, a task consists of the simulation of a tracer particle pulled into a cubic box with smaller bath particles. The computational load depends on the total number of the bath particles. Moreover, GenS has been compared to other dynamic and static scheduling approaches. The experimental results of such a comparison show that GenS outperforms the rest of the tested alternatives achieving a better distribution of the computational workload on a heterogeneous cluster. So, the scheduling strategy developed in this paper is of potential interest for any application which requires the execution of many tasks of different duration (a priori known) on a heterogeneous cluster.

Nonlinear microrheology of active Brownian suspensions.

The rheological properties of active suspensions are studied via microrheology: tracking the motion of a colloidal probe particle in order to measure the viscoelastic response of the embedding material. The passive probe particle with size R is pulled through the suspension by an external force Fext, which causes it to translate at some speed Uprobe. The bath is comprised of a Newtonian solvent with viscosity ηs and a dilute dispersion of active Brownian particles (ABPs) with size a, characteristic swim speed U0, and a reorientation time τR. The motion of the probe distorts the suspension microstructure, so the bath exerts a reactive force on the probe. In a passive suspension, the degree of distortion is governed by the Péclet number, Pe = Fext/(kBT/a), the ratio of the external force to the thermodynamic restoring force of the suspension. In active suspensions, however, the relevant parameter is Ladv/l = UprobeτR/U0τR∼Fext/Fswim, where Fswim = ζU0 is the swim force that propels the ABPs (ζ is the Stokes drag on a swimmer). When the external forces are weak, Ladv≪l, the autonomous motion of the bath particles leads to "swim-thinning," though the effective suspension viscosity is always greater than ηs. When advection dominates, Ladv≫l, we recover the familiar behavior of the microrheology of passive suspensions. The non-Newtonian behavior for intermediate values of Ladv/l is determined by l/Rc = U0τR/Rc-the ratio of the swimmer's run length l to the geometric length scale associated with interparticle interactions Rc = R + a. The results in this manuscript are approximate as they are based on numerical solutions to mean-field equations that describe the motion of the active bath particles.

Sticky-probe active microrheology: Part 2. The influence of attractions on non-Newtonian flow

We derive a theoretical framework for the non-Newtonian viscosity of a sticky, attractive colloidal dispersion via active microrheology by modeling detailed microscopic attractive and Brownian forces between particles. Actively forcing a probe distorts the surrounding arrangement of particles from equilibrium; the degree of this distortion is characterized by the Péclet number, Pe≡Fext/(2kT/a), where kT is the thermal energy and a the probe size. Similarly, the strength of attractive interactions relative to Brownian motion is captured by the second virial coefficient, B2. We formulate a Smoluchowski equation governing the pair configuration as it evolves with external and attractive forces. The microviscosity is then computed via non-equilibrium statistical mechanics. For active probe forcing, the familiar hard-sphere boundary-layer and wake structures emerge as Pe grows strong, but attractions alter its shape: changes in relative probe motion arising from its attraction to the bath particles can lead to a high-Pe, strong-attraction flipping of the microstructure, where an upstream depletion boundary layer forms, along with a downstream accumulation wake. This highly distorted structure is analyzed at the micro-mechanical level, where changes in the time spent upstream or downstream from a bath particle lead to hypo- and hyper-viscosity. When attractions are strong, separating the interparticle microviscosity into contributions from attractions and repulsions reveals an attractive undershoot and a repulsive overshoot, as advection grows strong enough to break interparticle bonds downstream and drain the wake. In contrast to linear-response rheology that is predictable entirely by B2 for short-ranged attractions, here the non-Newtonian viscosity is not, owing to the additional length scale introduced by the boundary layer. The ratio of external to attractive forces eventually supersedes B2 as the relevant predictor of structure and rheology. This behavior may provide interesting connections to active motion in biological systems where attractive forces are present.

Reclamation of thermal power plant waste as a distributed phase in electrodeposited Ni composite coating

ABSTRACTIn the exploration for newer and inexpensive distributed phases that can be used in electrodeposited Ni-composite coatings, cenosphere particles which are one of the constituents of fly ash, the waste product of thermal power plants has been explored as a potential candidate material. An attempt was made to prepare electrodeposited Ni-cenosphere composite coating. The as-received cenosphere particles could be codeposited only after reducing the particle size by ball milling. The loading of cenosphere particles in the Ni-sulphamate bath was varied (25, 75 and 100 g L−1) and a maximum microhardness of 430 HK at 50 gF load was obtained for the coating deposited from 100 g L−1 cenosphere containing bath. The Ni-cenosphere composite coating with higher microhardness exhibited lower wear rate. Thus cenosphere, a waste product from thermal power plants is a potential candidate for a greener surface engineering strategy for improving the wear resistance of electrodeposited Ni composite coating.

Configuration dynamics of a flexible polymer chain in a bath of chiral active particles

We investigate the configuration dynamics of a flexible polymer chain in a bath of active particles with dynamic chirality, i.e., particles rotate with a deterministic angular velocity ω besides self-propulsion, by Langevin dynamics simulations in a two dimensional space. Particular attention is paid to how the radius of gyration Rg changes with the propulsion velocity v0, the angular velocity ω, and the chain length N. We find that in a chiral bath with a typical nonzero ω, the chain first collapses into a small compact cluster and then swells again with increasing v0, in quite contrast to the case for a normal achiral bath (ω = 0) wherein a flexible chain swells with increasing v0. More interestingly, the polymer can even form a closed ring if the chain length N is large enough, which may oscillate with the cluster if v0 is large. Consequently, the gyration radius Rg shows nontrivial nonmonotonic dependences on v0, i.e., it undergoes a minimum for relatively short chains and two minima with a maximum in between for longer chains. Our analysis shows that such interesting phenomena are mainly due to the competition between two roles played by the chiral active bath: while the persistence motion due to particle activity tends to stretch the chain, the circular motion of the particle may lead to an effective osmotic pressure that tends to collapse the chain. In addition, the size of the circular motion R0 = v0/ω plays an important role in that the compact clusters and closed-rings are both observed at nearly the same values of R0 for different ω.

Quantum Rydberg Central Spin Model.

We consider dynamics of a Rydberg impurity in a cloud of ultracold bosonic atoms in which the Rydberg electron undergoes spin-changing collisions with surrounding atoms. This system realizes a new type of quantum impurity problems that compounds essential features of the Kondo model, the Bose polaron, and the central spin model. To capture the interplay of the Rydberg-electron spin dynamics and the orbital motion of atoms, we employ a new variational method that combines an impurity-decoupling transformation with a Gaussian ansatz for the bath particles. We find several unexpected features of this model that are not present in traditional impurity problems, including interaction-induced renormalization of the absorption spectrum that eludes simple explanations from molecular bound states, and long-lasting oscillations of the Rydberg-electron spin. We discuss generalizations of our analysis to other systems in atomic physics and quantum chemistry, where an electron excitation of high orbital quantum number interacts with a spinful quantum bath.

Transport of Neutral Optical Excitations Using Electric Fields

Mobile quantum impurities interacting with a fermionic bath form quasiparticles known as Fermi polarons. We demonstrate that a force applied to the bath particles can generate a drag force of similar magnitude acting on the impurities, realizing a novel, nonperturbative Coulomb drag effect. To prove this, we calculate the fully self-consistent, frequency-dependent transconductivity at zero temperature in the Baym-Kadanoff conserving approximation. We apply our theory to excitons and exciton polaritons interacting with a bath of charge carriers in a doped semiconductor embedded in a microcavity. In external electric and magnetic fields, the drag effect enables electrical control of excitons and may pave the way for the implementation of gauge fields for excitons and polaritons. Moreover, a reciprocal effect may facilitate optical manipulation of electron transport. Our findings establish transport measurements as a novel, powerful tool for probing the many-body physics of mobile quantum impurities.

Conformal vacuum and the fluctuation-dissipation theorem in a de Sitter universe and black hole spacetimes

In the studies of quantum field theory in curved spacetime, the ambiguous concept of vacuum state and the particle content is a long-standing debatable aspect. So far it is well known to us that in the background of the curved spacetime, some privileged class of observers detect particle production in the suitably chosen vacuum states of the quantum matter fields. In this work we aim to study the characteristics behaviour of these produced particles in the background of the de-Sitter (dS) Friedmann-Lama\^{i}tre-Robertson-Walker (FLRW) Universe (both for $(1+1)$ and $(3+1)$ dimensions) and $(1+1)$-dimensional Schwarzschild black hole (BH) spacetime, from the point of view of the respective privileged class of observers. Here the analysis is confined to the observers who perceive particle excitations in the conformal vacuum. We consider some test particles in the thermal bath of the produced particles and calculate the correlation function of the fluctuation of the random force as exerted by the produced quanta on the test particles. We obtain that the correlation function abides by the fluctuation-dissipation theorem, which in turn signifies that the test particles execute Brownian-like motion in the thermal bath of the produced quanta.

Particle production between isometric frames on a Poincaré patch of AdS2

In a recent paper [J. P. M. Pitelli, Phys. Rev. D 99, 108701 (2019)], one of us showed that the vacuum state associated with conformal fields on a Poincaré patch of anti-de Sitter spacetime is not AdS invariant for fields satisfying nontrivial boundary conditions (by nontrivial, we mean neither Dirichlet nor Neumann) at the conformal boundary. In this way, two isometrically related observers in anti-de Sitter space have different notions of no particle content. Therefore, an observer who is suddenly transported to a different (but isometrically related) frame will feel a bath of particles. This process contradicts our intuitive notion based on our experience in Minkowski spacetime, where the vacuum is Lorentz invariant, and no particle is produced between boosted frames. We show that the total number of produced particles is finite but grows without limit when we approach (via isometric transformation) Dirichlet or Neumann boundary conditions since in these cases the vacuum is invariant.

Efficiency of a cyclic quantum heat engine with finite-size baths.

In this paper we investigate the relationship between the efficiency of a cyclic quantum heat engine with the Hilbert space dimension of the thermal baths. By means of a general inequality, we show that the Carnot efficiency can be obtained only when both the hot and cold baths are infinitely large. By further introducing a specific model where the baths are constituted of ensembles of finite-dimensional particles, we further demonstrate the relationship between the engine's power and efficiency, with the dimension of the working substance and the bath particles.

Mean-field properties of impurity in Bose gas with three-body forces

We exactly analyze, on the mean-field level, the low-momentum properties of a single impurity atom loaded in the dilute one-dimensional Bose gas with two- and three-body short-range interactions. Particularly the Bose polaron binding energy and the quasiparticle residue are calculated for the considered system in the broad region of parameters change. We also explore the generic mean-field formula for the polaron effective mass which was shown to depend on the density profile of bath particles with a motionless impurity immersed.

Unruh effect for fermions from the Zubarev density operator

Using the Zubarev quantum-statistical density operator, we calculated the corrections to the energy-momentum tensor of a massless fermion gas associated with acceleration. It is shown that when fourth-order corrections are taken into account, the energy-momentum tensor in the laboratory frame is equal to zero at a proper temperature measured by a comoving observer equal to Unruh temperature. Consequently, the Minkowski vacuum is visible to the accelerated observer as a medium filled with a heat bath of particles with the Unruh temperature, which is the essence of the Unruh effect.

Driven probe under harmonic confinement in a colloidal bath

Colloids held by optical or magnetic tweezers have been used to explore the local rheological properties of a complex medium and to extract work from fluctuations with some appropriate protocols. However, a general theoretical understanding of the interplay between the confinement and the interaction with the environment is still lacking. Here, we explore the statistical properties of the position of a probe confined in a harmonic trap moving at constant velocity and interacting with a bath of colloidal particles maintained at a different temperature. Interactions among particles are accounted for by a systematic perturbation, whose range of validity is tested against direct simulations of the full dynamics. Overall, our results provide a way to predict the effect of the driving and the environment on the probe, and can potentially be used to investigate the properties of colloidal heat engines with many-body interactions.

Preparation and properties of composite electroless Ni-P-ZnO coatings

ABSTRACTElectroless nickel–phosphorus (EN) coatings are extensively used in various industrial applications to improve the mechanical and physical properties such as hardness, wear, and corrosion resistance. Heat treatment process and the addition of nanosized metallic/ceramic particles further improve the properties of the coating. The aim of the current research is to study the influence of heat treatment temperature, the proportion of ZnO nanoparticles on microhardness, and corrosion behaviour of EN coatings. Different amounts of ZnO nanoparticles were added to electroless bath by using Ultrasonicator to develop composite coatings. The microhardness and corrosion resistance of the coatings were further analysed through the experiments. Characterisation of the deposited coatings is carried out by using scanning electron microscopy and X-ray diffraction studies. The combination of heat treatment temperature and concentration of ZnO particles in EN bath to achieve maximum microhardness and corrosion resistance is studied.

Fabrication and nucleation study of β-PbO2–Co3O4 OER energy-saving electrode

In this study, β-PbO2–Co3O4 composite coatings were synthesized on a substrate using the electrodeposition method in an electrolyte containing Pb2+ and Co3O4 particles. The preparation process study shows that the β-PbO2 bath containing Co3O4 particles becomes more stable for an ultrasonic dispersion time within 30 min, with the stability beginning to decrease after the ultrasonic time exceeds 30 min. Co3O4 particles in the β-PbO2 bath are positively charged, with anions being adsorbed onto the particles. The nucleation behavior study shows that the electric field force plays a dominant role in the adsorption process for the Co3O4 particles. The nucleation and growth of β-PbO2 on the Co3O4 particles started for the particles closer to the substrate. In addition, the thickness of the β-PbO2 layer on the Co3O4 particles was inversely proportional to the distance between the Co3O4 particles and the substrate. Compared to the pure PbO2 electrode, the oxygen evolution overpotentials for the β-PbO2–Co3O4 electrode are decreased significantly, which demonstrates an energy-saving effect.

Addition of molybdenum disulfide solid lubricant to WC-12Ni thermal spray cemented carbide powders through electroless Ni-MoS2 co-deposition

Molybdenum disulfide solid lubricant was added to thermal spray WC-12Ni powders through electroless Ni-MoS2 co-deposition. With varying the concentration of WC-12Ni and MoS2 particles in the plating bath, varied concentration of MoS2 can be controlled in the powder surface layer and the incorporation mechanism of MoS2 into the shell was discussed as well. The thickness of the Ni-MoS2 coatings as well as the MoS2 distribution structure were characterized with a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The phase structure of the co-deposited coatings was characterized with X-ray diffraction (XRD). It is found that MoS2 particles can be co-deposited with Ni to form a Ni-MoS2 composite layer on WC-12Ni powders when effective Ni electroless deposition occurs, since Ni or Ni2+ can encapsulate MoS2 particles to facilitate its incorporation. The content of MoS2 in the coating increases with increasing the concentration of MoS2 in the plating bath, or with decreasing the concentration of WC-12Ni powders in the bath which results in increased thickness of deposited Ni- MoS2 layers. The Ni-MoS2 coated WC-12Ni powders obtained with the electroless co-deposition process can be used for high velocity oxy-fuel spraying (HVOF) with a proper size and adequate fluidity, and are expected to suppress desulfurization and decarburization effectively.