Role Of Brownian Motion Research Articles

Role of Brownian motion and Néel relaxations in Mössbauer spectra of magnetic liquids

The absorption cross-section of Mössbauer radiation in magnetic liquids is calculated, taking into consideration both translational and rotational Brownian motion of magnetic nanoparticles as well as stochastic reversals of their magnetization in the absence of an external magnetic field. The role of Brownian motion in ferrofluids is considered in the framework of the diffusion theory, while for the magnetorheological fluids with large nanoparticles, it is done with the aid of Langevin's approach. For stochastic rotation, we derived the equation analogous to Langevin's one and found the corresponding correlation function. In both cases, simple rotational correlation functions are obtained in the approximation of small rotations during the lifetime of the excited Mossbauer nuclei. Influence of the Néel's relaxations is considered in the framework of the Blume - Tjon model.

Fractional order reaction diffusion of calcium regulating NFAT production in T Lymphocyte

[Formula: see text] signals have a crucial role in the immune system for cell functions such as proliferation, differentiation, apoptosis and gene transcription as well as the activation of Nuclear factor of activated T Cell (NFAT) which modulates the immune response of the cells. In this study, a fractional order spatiotemporal calcium dynamics model is formulated using the reaction-diffusion equation incorporating parameters like buffers, source influx, [Formula: see text] and [Formula: see text]. Grünwald estimation is employed to obtain the solution and stability analysis has been performed. The analysis of numerical results provides novel insights about the role of Brownian motion, super diffusion, source influx, buffers, etc., in the regulation of calcium and NFAT concentration levels in T cell and the conditions which might lead to disordered immune responses causing diseases such as HINI, HIV and HBV.

The difference of aggregation mechanism between microplastics and nanoplastics: Role of Brownian motion and structural layer force.

In recent years, microplastics (MPs) and nanoplastics (NPs) have attracted worldwide attention because of the potential risks they pose to aquatic environments, but there are few studies on the difference of aggregation mechanism between MPs and NPs. In this study, 100nm and 1μm polystyrene plastics were selected as models to explore the aggregation mechanism of MPs/NPs under different aquatic environments. The influence of ion species and concentrations on the aggregation behaviors and kinetics were systematically investigated to predict the effects of water quality on the occurrence form of MPs and NPs based on DLVO theory and revised modified Smoluchowski theory. Results showed concentration, valence and hydrated ability of cations jointly affected the aggregation behavior of NPs. The critical coagulation concentration ratio of cations were consistent with Schulze-Hardy rules. But the different aggregation rate coefficients of same valent cations were ascribed to the structural layer force. Anion species played a role in the reaction-controlled regime by producing hydrogen ions to neutralize negative charges on NPs surfaces. Due to the strong Brownian motion and structural layer force, NPs would be stable in freshwater but preferentially aggregated when transport through brackish water, estuaries, eutrophication and high hardness areas and sea water, forming the accumulation hot spots of NPs in the sediment. While for MPs, physical process controlled the aggregation mechanism of them, leading to high stability in natural water and eventually transporting into marine environments. This study provided a theoretical foundation for assessing the transport, distribution, fate and ecological risks of MPs and NPs in realistic aquatic environments.

Role of Brownian Motion and Thermophoresis Effects on Hydromagnetic Flow of Nanofluid Over a Nonlinearly Stretching Sheet with Slip Effects and Solar Radiation

Hydromagnetic flow of water based nanofluids over a nonlinearly stretching sheet in the presence of velocity slip, temperature jump, magnetic field, nonlinear thermal radiation, thermophoresis and Brownian motion has been studied. The article focuses on Cu water nanofluid and Ag water nanofluid. The similarity transformation technique is adopted to reduce the governing nonlinear partial differential equations into nonlinear ordinary differential equations and then they are solved numerically utilizing the Nachistem – Swigert shooting method along with the fourth order Runge Kutta integration technique. The influence of physical parameters on the flow, temperature and nanoparticle volume fraction are presented through graphs. Also the values of the skin friction coefficient at the wall and nondimensional rate of heat transfer are given in a tabular form. A comparative study with previous published results is also made.

Role of Brownian Motion and Nonlinear Thermal Radiation on Heat Transfer of a Casson Nanofluid Over Stretching Sheet with Slip Velocity and Non-Uniform Heat Source/Sink

Role of Brownian Motion and Nonlinear Thermal Radiation on Heat Transfer of a Casson Nanofluid Over Stretching Sheet with Slip Velocity and Non-Uniform Heat Source/Sink

On the assessment of modeling combined convection heat transfer in nanofluids using dissipative particle dynamics

The effect of nanoparticles on mixed convection heat transfer mechanisms in a vertical lid-driven cavity using dissipative particle dynamics method is addressed. The effect of nanoparticle concentration on the random heat flux and the total heat flux is assessed via simulating the opposing buoyancy mechanism in a lid-driven cavity filled with Al2O3-water nanofluids. The study covered a wide range of nanoparticles volume fraction (1% ≤ φ ≤ 5%), and three Richardson numbers were considered, Ri = 0.1, 1, and 10. The results were verified via comparing the temperatures and the streamlines contours with the ones obtained using finite-volume method over the same range of Richardson number and nanoparticles concentration. The effect of the compressibility of the system for natural convection dominated flows has been noted in the results as a deviation from the finite-volume results. The results reveal that the enhancement in the convection heat transfer is directly connected to the nanoparticles concentration, though the effect of the convection mechanism is more dominant. Also, it is found that the role of Brownian motion in the vicinity of hot and cold walls are negligible, where the ratio of random heat flux to the total heat flux is below 5%. For low nanoparticle concentration the enhancement of the total heat transfer is disperse, however for high nanoparticle concentration it is more localized to certain region depending on the Richardson number.

Time dependent conduction heat transfer during solidification in a storage system using nanoparticles

In this research, nanofluid thermal behavior in an energy storage system is illustrated by means of FEM. CuO nanoparticles have been dispersed into the water to overcome the poor thermal conductivity. Role of Brownian motion is included for estimating characteristics of nanofluid. Results are shown as solid fraction, isotherm contours, average temperature and total energy profiles. Results showed that dispersing nanoparticles to pure PCM have important impact on heat transfer rate. As A and N enhances, total energy and solidification time decrease. Furthermore, in order to reach greatest solidification rate, nanoparticles with dp = 40 nm should be used.

Effect of nanoparticles Brownian motion and uniform sinusoidal roughness elements on natural convection in an enclosure

The aim of the present study is to examine natural convection heat transfer in a square cavity filled with Al2O3–water nanofluid using lattice Boltzmann method. Right and left walls are kept at hot and cold constant temperatures, respectively, while uniform sinusoidal roughness elements are placed on both walls. Effective viscosity and thermal conductivity of nanofluid are obtained using Koo–Kleinstreuer model implementing Brownian motion of nanoparticles. The influence of pertinent parameters, such as Rayleigh number, solid volume fraction of nanoparticles, frequency and dimensionless amplitude of uniform sinusoidal roughness elements, on flow and heat transfer fields is investigated in the present paper. Results show an increase in Nusselt number with increasing nanoparticles volume fraction for various Rayleigh numbers with their most prominent effect at φ = 0.04 for Ra = 103. Moreover, it was observed that mean Nusselt number decreases by increasing frequency and dimensionless amplitude of roughness elements for the whole range of Rayleigh numbers. In general, effect of nanoparticles on heat transfer enhancement is more highlighted by considering the role of Brownian motion.

Dissipative particle dynamics investigation of heat transfer mechanisms in Al2O3-water nanofluid

The current paper applied dissipative particle dynamics (DPD) approach to investigate the effect of nanoparticles on the heat transfer mechanisms in natural convection using Al2O3-water nanofluids. The study investigated in detail the effect of nanoparticle concentration on the random heat flux (i.e., Brownian motion) and the total heat flux. The DPD model considered the viscosity and the thermal conductivity of the Al2O3-water nanofluid to be dual function of temperature and volume fraction of nanoparticles. The study covered a wide range of nanoparticles (1% ≤ φ ≤ 7%) and three Rayleigh numbers were considered, which are Ra = 104, Ra = 5 × 104, and Ra = 105. The DPD results predicted an enhancement in heat transfer due to the addition of nanoparticles. However, the results revealed that the relative of enhancement of the total heat flux in the cavity is more effective at low Rayleigh numbers than at high Rayleigh numbers. The regions around the hot wall of the cavity are found to experience the maximum enhancement in heat transfer in the cavity whereas the region adjacent to the cold wall experienced a deterioration in heat transfer due to the addition of nanoparticles. Also, the DPD results revealed that the role of Brownian motion in the vicinity of hot and cold walls was negligible where the ratio of random heat flux to the total heat flux was below 5%. However, this ratio reached a very large value around the center of the cavity and the bottom wall of the cavity, where this value at low Rayleigh number and high volume fraction of nanoparticles exceeded 65%. Moreover, the study revealed that the random heat flux enhances with increase of volume fraction of nanoparticles.

Unbiased ‘walk-on-spheres’ Monte Carlo methods for the fractional Laplacian

We consider Monte Carlo methods for simulating solutions to the analogue of the Dirichlet problem in which the Laplacian is replaced by the fractional Laplacian. Specifically we consider the analogue of the so-called `walk-on-spheres' algorithm. In the diffusive setting, this entails sampling the path of Brownian motion as it uniformly exits a sequence of spheres maximally inscribed in the domain on which the Dirichlet problem is defined. As this algorithm would otherwise never end, it is truncated when the `walk-on-spheres' comes within ϵ>0 of the boundary. In the setting of the fractional Laplacian, the role of Brownian motion is replaced by an isotropic α-stable process with α∈(0,2). A significant difference to the Brownian setting is that the stable processes will exit spheres by a jump rather than hitting their boundary. This difference ensures that disconnected domains may be considered and that unlike the diffusive setting, the algorithm ends after an almost surely finite number of steps which does not depend on the point of issue of the stable process.

Three dimensional flow of Maxwell fluid with suspended nanoparticles past a bidirectional porous stretching surface with thermal radiation

This article concerned with the three-dimensional flow fills the porous space bounded by a bidirectional stretching sheet with non-linear thermal radiation and heat source/sink. Maxwell fluid model is accounted as a working liquid. The imposed conditions for temperature and nanoparticle concentration are convective type. The self-similar forms of equations are obtained by the implementation of similarity variables. The solutions are computed via shooting algorithm with fourth-fifth-order Runge-Kutta-Fehlberg procedure. Comparison of obtained results with the known numerical solution is made and examined an excellent agreement. It is noted that the role of Brownian motion in temperature and heat transfer rate is significant. The results reveal that concentration of nanoparticles and temperature are decreased with an enhancement in Deborah number.

Effects of nanoparticles Brownian motion in a linearly/sinusoidally heated cavity with MHD natural convection in the presence of uniform heat generation/absorption

In this numerical work, natural convection of CuO–water nanofluid and pure water in a cavity submitted to different heating modes on its vertical walls, is analyzed using the Lattice Boltzmann Method (LBM). The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. The influence of pertinent parameters such as Rayleigh number (Ra=103–106), Hartmann number (Ha=0–80), heat generation or absorption coefficient (q=−10, −5, 0, 5, 10) and nanoparticle volume concentration (ϕ=0–0.04) on the flow and heat transfer characteristics has been examined. In general, by considering the role of Brownian motion, the enhancement in heat transfer is observed at any Hartman and Rayleigh numbers. In addition, the heat generation or absorption influences the heat transfer in the cavity at Ra=103 more than other Rayleigh numbers as the least effect is observed at Ra=106.

Coupling of lever arm swing and biased Brownian motion in actomyosin.

An important unresolved problem associated with actomyosin motors is the role of Brownian motion in the process of force generation. On the basis of structural observations of myosins and actins, the widely held lever-arm hypothesis has been proposed, in which proteins are assumed to show sequential structural changes among observed and hypothesized structures to exert mechanical force. An alternative hypothesis, the Brownian motion hypothesis, has been supported by single-molecule experiments and emphasizes more on the roles of fluctuating protein movement. In this study, we address the long-standing controversy between the lever-arm hypothesis and the Brownian motion hypothesis through in silico observations of an actomyosin system. We study a system composed of myosin II and actin filament by calculating free-energy landscapes of actin-myosin interactions using the molecular dynamics method and by simulating transitions among dynamically changing free-energy landscapes using the Monte Carlo method. The results obtained by this combined multi-scale calculation show that myosin with inorganic phosphate (Pi) and ADP weakly binds to actin and that after releasing Pi and ADP, myosin moves along the actin filament toward the strong-binding site by exhibiting the biased Brownian motion, a behavior consistent with the observed single-molecular behavior of myosin. Conformational flexibility of loops at the actin-interface of myosin and the N-terminus of actin subunit is necessary for the distinct bias in the Brownian motion. Both the 5.5–11 nm displacement due to the biased Brownian motion and the 3–5 nm displacement due to lever-arm swing contribute to the net displacement of myosin. The calculated results further suggest that the recovery stroke of the lever arm plays an important role in enhancing the displacement of myosin through multiple cycles of ATP hydrolysis, suggesting a unified movement mechanism for various members of the myosin family.

Nano Brazing of Pt-Ag Nanoparticles under Femtosecond Laser Irradiation

Abstract Nano brazing of Pt-Ag nanoparticles with nano Ag filler metal is reported in this letter, which presents an effective way to join nanoobjects by femtosecond laser irradiation. The nano brazed interface between Pt-Ag and Ag showed good lattice matching along (111)Ag//(111)Ag-Pt. Lattice mismatch can hardly be observed at the interface between the filler metal and Pt-Ag nanoparticle, which is important for the joint strength and normally does not occur during joining. The very low mismatch also suggested that melting and solidification occurred during nano brazing by femtosecond laser. The role of Brownian motion on the nano joining process is also discussed in this paper.

Brownian dynamic simulation for the prediction of effective thermal conductivity of nanofluid

Nanofluid is a colloidal solution of nanosized solid particles in liquids. Nanofluids show anomalously high thermal conductivity in comparison to the base fluid, a fact that has drawn the interest of lots of research groups. Thermal conductivity of nanofluids depends on factors such as the nature of base fluid and nanoparticle, particle concentration, temperature of the fluid and size of the particles. Also, the nanofluids show significant change in properties such as viscosity and specific heat in comparison to the base fluid. Hence, a theoretical model becomes important in order to optimize the nanofluid dispersion (with respect to particle size, volume fraction, temperature, etc.) for its performance. As molecular dynamic simulation is computationally expensive, here the technique of Brownian dynamic simulation coupled with the Green Kubo model has been used in order to compute the thermal conductivity of nanofluids. The simulations were performed for different concentration ranging from 0.5 to 3 vol%, particle size ranging from 15 to 150 nm and temperature ranging from 290 to 320 K. The results were compared with the available experimental data, and they were found to be in close agreement. The model also brings to light important physical aspect like the role of Brownian motion in the thermal conductivity enhancement of nanofluids.

Role of Brownian motion on the thermal conductivity enhancement of nanofluids

This study involves Brownian dynamics simulations of a real nanofluid system in which the interparticle potential is determined based on Debye length and surface interaction of the fluid and the solid. This paper shows that Brownian motion can increase the thermal conductivity of the nanofluid by 6% primarily due to “random walk” motion and not only through diffusion. This increase is limited by the maximum concentration for each particle size and is below that predicted by the effective medium theory. Beyond the maximum limit, particle aggregates begin to form. Brownian motion contribution stays as a constant beyond a certain particle diameter.

Role of Brownian motion in the enhanced thermal conductivity of nanofluids

We have found that the Brownian motion of nanoparticles at the molecular and nanoscale level is a key mechanism governing the thermal behavior of nanoparticle–fluid suspensions (“nanofluids”). We have devised a theoretical model that accounts for the fundamental role of dynamic nanoparticles in nanofluids. The model not only captures the concentration and temperature-dependent conductivity, but also predicts strongly size-dependent conductivity. Furthermore, we have discovered a fundamental difference between solid/solid composites and solid/liquid suspensions in size-dependent conductivity. This understanding could lead to design of nanoengineered next-generation coolants with industrial and biomedical applications in high-heat-flux cooling.

Magnetoviscosity of Colloidal Suspensions

A theoretical description of the effect of an applied magnetic field on the viscosity of a colloidal suspension of single-domain ferromagnetic particles is given from the point of view of linearized hydrodynamics, starting from a microscopic Fokker–Planck equation. Reasonable agreement is found between theoretical results and previous experimental measurements of the effect. A comparison with an earlier theoretical explanation of the effect is given. It is found, in particular, that a consideration of the role of Brownian motion is not only desirable but crucial to a proper explanation of the magnetoviscosity effect.

On the role of Brownian motion in the control of detrital remanent magnetization of sediments

The field dependence of magnetic remanence in laboratory deposited sediments is re-examined in terms of the average orientation of small grains of magnetite subject to the combined effect of an aligning field and thermal agitation. The classical (Langevin) formula for paramagnetic susceptibility is generalized to describe an assembly of grains with magnetic moments having a uniform distribution of values between zero and an upper limit, yielding a simple analytical expression in excellent accord with the pioneering measurements of Johnson, Murphy and Torreson. Comparison of theory and observation shows that the grain moments are intermediate between the values expected for single domains and multidomains, confirming the existence of pseudo-single domain effects, as deduced from observations of thermoremanence.