Experimental Velocity Distributions Research Articles

Filamentary velocity scaling validation and spin dynamics in the DIII-D tokamak

Measured filament velocities in the DIII-D tokamak are compared against theoretical scalings, finding that the latter often represents an upper limit on experimental velocity distributions with most filaments possessing lower velocity. Filament spin from internal E × B drift is experimentally demonstrated to alter filament radial velocity. A critical spin velocity, where filament radial velocity peaks, is observed and corresponds to approximately 5 km/s. This transition is corroborated using a less direct measure of filament spin in the form of a temperature ratio. These techniques are combined to find that the critical spin velocity closely aligns with transport times along and across filaments becoming comparable. The normalized filament size distribution is consistent with the most stable size as dictated by Kelvin–Helmholtz and curvature-driven instabilities. Overall, the findings suggest filament stability and spin alter filamentary transport that may threaten the integrity of first walls in fusion devices.

Structure and principle of operation of the apparatus for introducing chlorine into the process pipeline

The article discusses the study of swirling flow in technological pipelines. It examines the nature of the swirling flow, presenting the experimental velocity distribution and pressure inside the pipe in graphical and tabular form. The scope of the study includes the displacement of liquid and gas, as well as the purification of natural waters using ozone and chlorine. The article analyzes the existing technological processes for the preparation of drinking water from surface water sources in Uzbekistan. Due to the significant volumes of water consumption for economic activities, the issue of drinking water disinfection is crucial. In addition to traditional disinfection methods, modern researchers are focusing on developing innovative technologies for this process. The article also studies the features of water formation and its qualitative composition, with an analysis of the reliability of the existing drinking water treatment technology.

Simulations suggest robust microtubule attachment of kinesin and dynein in antagonistic pairs

Intracellular transport is propelled by kinesin and cytoplasmic dynein motors that carry membrane-bound vesicles and organelles bidirectionally along microtubule tracks. Much is known about these motors at the molecular scale, but many questions remain regarding how kinesin and dynein cooperate and compete during bidirectional cargo transport at the cellular level. The goal of the present study was to use a stochastic stepping model constructed by using published load-dependent properties of kinesin-1 and dynein-dynactin-BicD2 (DDB) to identify specific motor properties that determine the speed, directionality, and transport dynamics of a cargo carried by one kinesin and one dynein motor. Model performance was evaluated by comparing simulations to recently published experiments of kinesin-DDB pairs connected by complementary oligonucleotide linkers. Plotting the instantaneous velocity distributions from kinesin-DDB experiments revealed a single peak centered around zero velocity. In contrast, velocity distributions from simulations displayed a central peak around 100 nm/s, along with two side peaks corresponding to the unloaded kinesin and DDB velocities. We hypothesized that frequent motor detachment events and relatively slow motor reattachment rates resulted in periods in which only one motor is attached. To investigate this hypothesis, we varied specific model parameters and compared the resulting instantaneous velocity distributions, and we confirmed this systematic investigation using a machine-learning approach that minimized the residual sum of squares between the experimental and simulation velocity distributions. The experimental data were best recapitulated by a model in which the kinesin and dynein stall forces are matched, the motor detachment rates are independent of load, and the kinesin-1 reattachment rate is 50 s−1. These results provide new insights into motor dynamics during bidirectional transport and put forth hypotheses that can be tested by future experiments.

Role of Low Energy Resonances in the Stereodynamics of Cold He + D2 Collisions.

In recent experiments using the Stark-induced adiabatic Raman passage technique, Zhou et al. ( J. Chem. Phys. 2021, 154, 104309; Science 2021, 374, 960-964) measured the product's angular distribution for the collisions between He and aligned D2 molecules at cold collision energies. The signatures of the angular distributions were attributed to an [Formula: see text] = 2 resonance that governs scattering at low energies. A first-principles quantum mechanical treatment of this problem is presented here using a highly accurate interaction potential for the He-H2 system. Our results predict a very intense [Formula: see text] = 1 resonance at low energies, leading to angular distributions that differ from those measured in the experiment. A good agreement with the experiment is achieved only when the [Formula: see text] = 1 resonance is artificially removed, for example, by excluding the lowest energies present in the experimental velocity distribution. Our analysis revealed that neither the position nor the intensity of the [Formula: see text] = 1 resonance significantly changes when the interaction potential is modified within its predicted uncertainties. Energy-resolved measurements may help to resolve the discrepancy.

The Effect of Different Cathode Configurations of the Plasma Cell on the Ion Velocity Distribution Function

The ion velocity distribution in a plasma source was investigated through a comparison between two different configurations of the cathode of the plasma cell, namely, the one mesh system electrodes (OMSE), and the one mesh and three system electrodes (OMTSE). The velocity ranged from 1 to 3.5 km/s for OMSE and from 4 to 22 km/s for OMTSE. The comparison between the experimental and theoretical ion velocity distribution function (IVDF) of OMSE and OMTSE under the same applied conditions shows a better agreement for OMSE than for OMTSE due to the difference in plasma cell construction, cathode mesh wire configuration, and cathode edge. Even though the velocity and density of ions for the OMTSE reactor are higher than those for the OMSE reactor, the OMSE reactor was found to be the best system to avoid dusty plasma defects through the etching process.

Numerical and experimental investigations of instability in a spouted bed with non-spherical particles

A spouted bed containing non-spherical particles was investigated numerically using the non-spherical discrete hard-sphere method, and experimentally using particle image velocimetry. The experimental and simulated particle velocity distributions were in agreement. Different operating conditions were used to investigate the instability of the spouted bed. Certain conditions created an S-shaped gas channel in the center of the bed, which proved the instability of non-spherical particles. The motion of micro-scale particles and bubbles was studied to determine their potential relationship with instability. It was found that the granular temperature distribution of the particles and bubbles was associated with the gas channel region. The behaviors of bubbles differed from those of particles. These results contribute to an understanding of instability mechanisms in spouted beds.

Buffer-gas cooling of molecules in the low-density regime: comparison between simulation and experiment

Cryogenic buffer gas cells have been a workhorse for the cooling of molecules in the last few decades. The straightforward sympathetic cooling principle makes them applicable to a huge variety of different species. Notwithstanding this success, detailed simulations of buffer gas cells are rare, and have never been compared to experimental data in the regime of low to intermediate buffer gas densities. Here, we present a numerical approach based on a trajectory analysis, with molecules performing a random walk in the cell due to collisions with a homogeneous buffer gas. This method can reproduce experimental flux and velocity distributions of molecules emerging from the buffer gas cell for varying buffer gas densities. This includes the strong decrease in molecule output from the cell for increasing buffer gas density and the so-called boosting effect, when molecules are accelerated by buffer-gas atoms after leaving the cell. The simulations provide various insights which could substantially improve buffer-gas cell design.

An improved model for the tangential velocity distribution in strong free-surface vortices: an experimental and theoretical study

ABSTRACTA study of the tangential velocity field in a strong free-surface vortex is presented. Experiments were conducted on an open channel scroll type vortex chamber by investigating the tangential velocity for three approach flow conditions. The tangential velocity and circulation fields were ascertained at various sub-surface depths using particle tracking techniques. The results revealed that the experimental tangential velocity distribution is dependent on the initial circulation but is largely independent of the vertical axis. The theoretical tangential velocity profile was found to diverge from the experimental data in the near-field close to the core. It was concluded that the tangential velocity field in this region is strongly dependent on the axial flow conditions. Consequently, an alternative tangential velocity model was developed which models the near-field axial flow effects using the inverse circulation number and an empirical coefficient. Application of a nonlinear least squares multiple regression analysis identified values for the empirical coefficient to obtain a good solution.

Dynamic Behavior of Polydisperse Dust System in Cryogenic Gas Discharge Complex Plasmas

AbstractComplex (dusty) plasmas of micron‐sized CeO2 polydisperse particles in dc glow discharges at 77 and ∼ 10 K were experimentally investigated. It was obtained that dust structure in cryogenic gas discharge plasma can be a mixture of two fractions (components) with completely different dust ordering and dynamics. We observed under some specific conditions that fast‐moving particles of one component diffuse through another component consisted of dust particles arranged in linear chains (strings). From experimental data analysis particle velocity distribution functions for each dust component were obtained. The possible nature of two‐component dust structure formation was discussed. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of particle dynamics in a rotary drum by means of experiments and numerical simulations using DEM

The present paper describes an experimental and numerical study conducted to investigate the particle movement inside an unbaffled rotary drum under different operating conditions and using particles of different shapes. The Discrete Element Method (DEM) was used in order to describe the granular flow pattern properly, along with the clumping method which enables the creation of particles of different shapes. A calibration and subsequent verification of the DEM calibrated model were performed. Experimental particle velocity distributions were determined by means of a high-speed video camera in order to validate the model in a scaled-up rotary drum. The drum length effect on the particle dynamics was also analyzed. It was observed that, besides the model parameter values, the particle shape plays an important role in particle motion and DEM granular flow prediction. The drum geometry also exhibited a major and nontrivial influence on particle dynamics since the greater the distance between front and back wall, the lower the dynamic angle of repose and the lower the particle velocity values in the active region.

Modeling Coordinated Kinetics in Large Groups of Muscle Myosin Motors

The kinetics of molecular motors are usually assessed for single or a few connected motors, or groups exceeding 100 motors. When we previously investigated coordinated kinetics of groups of 10 to 100 muscle myosin motors, we observed the emergence of group size-dependent patterns at the level of the whole motor group[1]. We used automated video analysis of in vitro motility assays, where fluorescent actin filaments were propelled by a surface coated with muscle myosins[2]. Here, actin motion showed two distinct modes: full arrest and phases of unidirectional sliding with a characteristic velocity[1]. The observation of either mode depended on the number of myosins maximally working as a coupled group on the same actin filament, which we calculated from myosin binding site distance (0.0355 µm) and filament length (L)[1]. Short actin filaments (L 1.0 µm) continuously slid forward[1]. We proposed a mathematical model, which monitors the coupled, load-dependent myosin kinetics at single myosin and single reaction resolution[1]. In the simulated myosin group kinetics, actin sliding and arrest corresponded to attractor-like-patterns “fixed point” and “limit cycle”, respectively; stochastic jumping between attractor-like-patterns explained sliding-arrest alternation[3]. We now extended this mathematical model by a spatial component: actin filament length is one spatial dimension, while myosin-to-myosin coupling is limited to ∼0.2 µm. In model simulations, arrested kinetics originated from both ends of the actin filament and could entrain global kinetics into arrest. Further, experimental velocity distributions recorded after addition of filamin crosslinker were reproduced, and explained by local perturbations by filamin crosslinking that spread to global extent along the filament. [1]Hilbert et al. Biophys J 2013 [2]Hilbert et al. PLoS Comp Biol 2013 [3]Hilbert et al. Biophys J 2015.

Particle deposition modeling in the secondary side of a steam generator bundle model

A steam generator (SG) tube rupture (SGTR) model is studied in this paper. This model based on a experimental facility called Aerosol Trapping In a Steam Generator (ARTIST), which is a model of a scaled steam generator tube bundle consisting of 270 tubes and a guillotine tube to address aerosol deposition phenomena on two different scales: near the tube break, where the gas velocities and turbulence are very intensive, and far away from the break, where the flow velocities are three orders of magnitude lower.Owing to complexity of the flow, 3D simulations with highly resolved computational mesh near the break were done. First, the flow inside an isolated tube with a guillotine tube break has been studied in the framework of Reynolds Averaged Navier Stokes (RANS) approach. The next part is devoted to the simulation of an inclined gas jet entering the SG tube bundle via the guillotine tube breach with more advanced CFD tools. In particular, Detached Eddy Simulation (DES) and RANS are applied to tackle the wide range of flow scales. Flow field velocity comparison showed that DES results are reproducing wavy structure of the flow field in far field from the break observed in experiment.Particle transport and deposition is modelled by Lagrangian continuous random walk (CRW) model, which has been developed and validated previously. It is found that the DES combined with the CRW to supply fluctuating velocity components predicts deposition rates that are generally within the scatter of the measured data. Monodisperse, spherical SiO2 particles with AMMD = 1.4μm were used as aerosol particles in simulations.To be economically feasible, the computations were made with the open source CFD code OpenFOAM. Comparison of the calculated flow with the experimental axial velocity distribution data at different vertical levels has been performed.

Coaxial Circular Jet Flows with Conical Attachments

This study is devoted to experiments on jet ows, which have many application areas. It shows the obtained jet ow structure. The experiments were carried out in a subsonic sucking wind tunnel having cross-section of 32 × 32 cm, length of 75 cm, and turbulence densities of 0.5%. One-channel hot-wire anemometer (HWA) was used in measurements. For circular jet, a steel pipe was used with a length of 120 cm and a diameter of 8 mm. Air generator was used for generating air into the jet ow and measurements were done at di erent jet ow velocities. Moreover, a conical di user with a length of 21 cm and 6◦ slope was attached to the nozzle exit and e ect of this di user on jet ow was examined. Seven types of measurement in three di erent categories were carried out. In experimental studies, velocity and turbulence distribution, axial velocity variation, jet half widths and, using these, jet di usion rates and angles were measured. Moreover, ow analyses were done by drawing moment and frequency distribution for measurement sensitivity. These experimental results were compared with the studies on jet ow.

A CPFD model for a bubbly biomass–sand fluidized bed

This study reports a computational particle fluid dynamics model for the numerical simulation of a sand fluidized bed with 8wt.% and 16wt.% biomass loadings. The proposed CPFD model, based on a Barracuda framework, is validated using experimental data obtained in a 15.2cm diameter bed with a 22.5cm static height. This fluidized bed unit is equipped with a pair of fiber optic sensors allowing one to obtain both the bubble size and bubble velocity frequency distributions in an ample range of experimental conditions. In addition to this, the first-, second-, and third-order statistical moments of the bubble size and the bubble velocity distributions are calculated for each one of the operating conditions studied. On this basis, the present study demonstrates that the proposed CPFD model reproduces the asymmetric character of both bubble size and bubble velocity distributions. In addition, the simulated and experimental bubble size and bubble velocity distributions yield close first-, second-, and third-order statistical moments. Accordingly, one can ascertain that the proposed CPFD model is quite satisfactory for establishing fluid flow patterns in sand–biomass fluidized bed gasifiers.

An Investigation of the Different Flow Regimes in a Rotating Drum through Experimental and Simulation

This paper aims to investigate the particle dynamic behavior in a rotating drum operating in a rolling regime under different rotating velocity, based on experimental results and simulations. Simple superphosphate fertilizer (SSP) was used as particulate matter in the current study. The Eulerian–Eulerian multiphase model along with the kinetic theory of granular flow was used in the simulations. In order to evaluate the simulation results, velocity distributions of the particulate phase were compared with experimental data. The experimental particle velocity distribution was obtained by using a high speed video camera. The numerical simulation results showed significant insights towards understanding of the particle dynamic in a rotating drum. The simulated results of particle velocity were in good agreement with the experimental data.

Experimental and CFD study of the hydrodynamic behavior in a rotating drum

In this work the particle dynamic behavior in a rotating drum under different operating conditions has been analyzed based on experimental results and simulations. The Eulerian–Eulerian multiphase model with the kinetic theory of granular flow was used in the simulations. In order to evaluate the simulation results, different solid flow regimes and velocity distributions of the particulate phase were compared with experimental data. The experimental particle velocity distribution was obtained by using a high-speed video camera technique. The numerical simulation has contributed to understanding the main particle dynamics phenomenon present in rotating drums.

Non-Gaussian nature of fracture and the survival of fat-tail exponents.

We study the fluctuations of the global velocity V(l)(t), computed at various length scales l, during the intermittent mode-I propagation of a crack front. The statistics converge to a non-Gaussian distribution, with an asymmetric shape and a fat tail. This breakdown of the central limit theorem (CLT) is due to the diverging variance of the underlying local crack front velocity distribution, displaying a power law tail. Indeed, by the application of a generalized CLT, the full shape of our experimental velocity distribution at large scale is shown to follow the stable Levy distribution, which preserves the power law tail exponent under upscaling. This study aims to demonstrate in general for crackling noise systems how one can infer the complete scale dependence of the activity--and extreme event distributions--by measuring only at a global scale.

Granular Brownian motion with dry friction

The interplay between Coulomb friction and random excitations is studied experimentally by means of a rotating probe in contact with a stationary granular gas. The granular material is independently fluidized by a vertical shaker, acting as a “heat bath” for the Brownian-like motion of the probe. Two ball bearings supporting the probe exert nonlinear Coulomb friction upon it. The experimental velocity distribution of the probe, autocorrelation function, and power spectra are compared with the predictions of a linear Boltzmann equation with friction, which is known to simplify in two opposite limits: at high collision frequency, it is mapped to a Fokker-Planck equation with nonlinear friction, whereas at low collision frequency, it is described by a sequence of independent random kicks followed by friction-induced relaxations. Comparison between theory and experiment in these two limits shows good agreement. Deviations are observed at very small velocities, where the real bearings are not well modeled by Coulomb friction.

Induced-Charge Electroosmosis Around Touching Metal Rods

Induced-charge electroosmosis (ICEO) around multiple gold-coated stainless steel rods under different ac electric fields is analyzed using microparticle image velocimetry (micro-PIV) and numerical simulations. In the present investigation, the induced electric double layer (EDL) is in weakly nonlinear limit. The ICEO flow around multiple touching rods exhibits geometry dependent quadrupolar flow structures with four vortices. The velocity magnitude is proportional to the square of the electric field. The ICEO flow velocity also depends on the cylinder orientation. The velocity increases with increased radial distance from the rod’s surface, attains a maximum, and then decays to zero. Experimental and numerical velocity distributions have the same trend beyond 0.2 mm of the rod’s surface.

Open channel flows of magnetic fluid induced by traveling magnetic field

A theoretical analysis is made on laminar open channel flows of magnetic fluid induced by a non uniform traveling magnetic field which is applied with a stator of a single-sided linear induction motor. The induced flows are mainly in the direction opposite to the traveling direction of the magnetic field and in proportion to the phase velocity of the magnetic field. The velocity profiles are greatly affected by dimensionless wave number of the magnetic field. Near the bottom of the channel, the theoretical velocity distributions agree well with experimental ones which are measured with a laser optical fiber velocity sensor. However, the experimental velocity distributions become larger near the free surface.