Analysis Of Particle Trajectories Research Articles

Experimental analysis of spallation particle trajectories in an arc-jet environment

Spallation is a phenomenon in which solid particles are ejected off the surface of an ablative material in a high-enthalpy, high-shear flow field. The main contributor to this phenomenon in carbon-based heat shields is the mechanical erosion of carbon fibers weakened by oxidation decomposition. The dynamics of this phenomenon, which are poorly characterized in the literature, strongly affect the ablation rate of the material. In state-of-the-art codes, ablation by spallation is modeled using a “failure” ablation rate that is empirically determined. The present study aims at understanding the rate of ablation of low-density carbon materials. Results from a test campaign at the NASA Langley Hypersonic Materials Environmental Test System (HYMETS) arc jet facility are used to examine spallation. High-speed multi-camera imagery at 44,000 fps is used to generate velocity vectors of spalled particles emitted from carbon-fiber samples exposed to an arc jet airflow. The imagery recorded approximately 4×106 unique particles, indicating that spallation is a potentially non-trivial process. The velocities of the particles ejected from the surface were found to be between 10 m/s and 20 m/s, accelerating to velocities as high as 250 m/s further away from the sample surface. Although the particle diameters were not directly observable, estimates suggest anywhere from 0.06% to 5.6% of the mass loss from the sample occurred due to spallation.

Macroscopic equivalence for microscopic motion in a turbulence driven three-dimensional self-assembly reactor

We built and characterised a macroscopic self-assembly reactor that agitates magnetic, centimeter-sized particles with a turbulent water flow. By scaling up the self-assembly processes to the centimeter-scale, the characteristic time constants also drastically increase. This makes the system a physical simulator of microscopic self-assembly, where the interaction of inserted particles is easily observable. Trajectory analysis of single particles reveals their velocity to be a Maxwell-Boltzmann distribution and it shows that their average squared displacement over time can be modelled by a confined random walk model, demonstrating a high level of similarity to the Brownian motion. The interaction of two particles has been modelled and verified experimentally by observing the distance between two particles over time. The disturbing energy (analogue to temperature) that was obtained experimentally increases with sphere size and differs by an order of magnitude between single-sphere and two-sphere systems (approximately 80 µJ versus 6.5 µJ, respectively).

Development of models relating charge shape and power draw to SAG mill operating parameters and their use in devising mill operating strategies to account for liner wear

A set of 22 three-dimensional DEM simulations are used to understand and quantify the relationship between key charge locations and three important operating parameters – fill level, lifter height and mill speed for a generic SAG mill. The charge shape and location are characterised by the shoulder, head, bulk and impact toe positions and are assessed by analysis of particle trajectories and the spatial variation of the pressure on the liner. Parametric models, created as a best fit to the DEM mill data, are used to relate these charge shape characteristics and the power draw to these operating parameters. They also allow inverse prediction of the fill level and lifter height (or wear state) from measurements of the charge structure and the mill speed. Such models can then be used to interpret experimental measurement data for SAG mills and to infer charge structure. The paper will also explore how such parametric models can be used to create operational management strategies (in terms of how to vary control variables such as target mill fill level and mill speed) in order to maintain chosen performance attributes over the wear life cycle of the liner. Examples of development of strategies that preserve for example, the bulk toe or the power draw of the mill are demonstrated.

Analysis of particle trajectories in a quick-contact cyclone reactor using a discrete phase model

ABSTRACTThe Eulerian–Lagrangian approach with a discrete phase model (DPM) is used to investigate the motion trajectories of the particles at the range of 1–50 μm in the quick-contact cyclone reactor, in which the cracking reactions and the separations of catalysts and products can occur respectively and simultaneously. The results show that the typical motion trajectories of the particles in the quick-contact cyclone reactor can be described as three types: trapping, escaping and dust ring. The first typical motion of particles corresponds to the particles successfully separated from the gas flow, while the other two types can lead to more coking and erosion in the reactor. Moreover, a pre-vortex flow is observed in the mixing-reaction chamber. Additionally, the grade separation efficiency of each particle size is also obtained by counting the numbers of escaping and capturing particles. The particles with diameter larger than 10 μm are separated completely from the gas. The reactor also has a strong capability to trap the particles of small diameters (5 μm <dp<10 μm). Both results indicate that the separation efficiency of the reactor has met the requirement as a primary separator. Compared with the experimental results, the separation efficiency in the simulated method is higher than 98% with errors of no more than 1.31%. It is illustrated that separation efficiency of the reactor can be predicted by CFD simulation.

Trajectory Analysis of Copper and Glass Particles in Electrostatic Separation for the Recycling of ASR

Automobile-shredder-residue (ASR) recycling techniques have been widely applied for improving the total recycling rate of end-of-life vehicles. In this study, to obtain useful information for predicting or improving ASR-separation efficiency, trajectory analyses of conductors (copper) and non-conductors (glass) were performed using a lab-scale induction electrostatic separator. The copper-wire trajectories obtained showed a good agreement depending significantly on the electric field strength and particle size. The observed copper-wire trajectories showed consistent congruity with the coarse-particles simulation (0.5 and 0.25 mm). The observed fine-particles (0.06 mm) trajectory was deflected toward the (−) attractive electrode, owing to the charge density effects due to the particle characteristics and relative humidity. This results in superior separation performance because more copper enters the conductor products bin. The actual dielectric-glass trajectory was deflected toward the (−) attractive electrode, thus showing characteristics similar to conductive-particle characteristics. Through analyses conducted using a stereoscopic microscope, scanning electron microscope, and energy dispersive spectroscope, we found heterogeneous materials (fine ferrous particles and conductive organics) on the glass surface. This demonstrates the separation-efficiency decrease for non-ferrous metals during electrostatic separation in the recycling of ASR. Future work should include a pretreatment process for eliminating impurities from the glass and advanced trajectory-simulation processes.

Deposition fraction of ellipsoidal fibers in a model of human nasal cavity for laminar and turbulent flows

In this study, the deposition fraction of ellipsoidal fibers in a realistic model of a human nasal cavity was evaluated for laminar and turbulent airflow conditions. The mean flow field was simulated by solving the discretized continuity and Navier-Stokes equations using the ANSYS-Fluent software. For ellipsoidal particle trajectory analysis, several user defined functions (UDFs) were developed and coupled to the ANSYS-Fluent discrete phase model (DPM). The presented formulation accounted for the coupled translation and rotational motions of ellipsoidal fibers and included the stochastic modeling of turbulence velocity and velocity gradient fluctuations. Particular attention was given to the proper modeling of turbulence fluctuation fields especially in the near wall region for accurate evaluation of fiber deposition rate. The predicted fiber deposition fractions in the nasal passage were compared with the available experimental and numerical results for both laminar and turbulent flows and good agreement was observed.

The Splashback Radius of Halos from Particle Dynamics. I. The SPARTA Algorithm

Abstract Motivated by the recent proposal of the splashback radius as a physical boundary of dark-matter halos, we present a parallel computer code for Subhalo and PARticle Trajectory Analysis (Sparta). The code analyzes the orbits of all simulation particles in all host halos, billions of orbits in the case of typical cosmological N-body simulations. Within this general framework, we develop an algorithm that accurately extracts the location of the first apocenter of particles after infall into a halo, or splashback. We define the splashback radius of a halo as the smoothed average of the apocenter radii of individual particles. This definition allows us to reliably measure the splashback radii of 95% of host halos above a resolution limit of 1000 particles. We show that, on average, the splashback radius and mass are converged to better than 5% accuracy with respect to mass resolution, snapshot spacing, and all free parameters of the method.

Studying Binding, Conformational Transition and Assembly of E. Coli Cytolysin a Pore Forming Toxin by Single Molecule Fluorescence

Pore forming toxins (PFT) belong to a class of bacterial toxin proteins that form nano-scaled pores on target cell's membrane and cause unregulated efflux of ions and biomolecules leading to cell death. They are released in a water-soluble conformation which upon membrane exposure undergoes large structural rearrangement. This membrane bound monomer further oligomerizes and forms of a complete pore. While high resolution structural information of complete pores are available, our understanding of early events of PFT binding and assembly is incomplete owing to the highly dynamic nature of the aforementioned processes. In this study, we use single molecule tracking and spectroscopy to understand the dynamics of Cytolysin A (ClyA), a prototypical α-PFT from E. coli, on lipid bilayer membranes. Binding of ClyA to PEG-cushioned supported bilayer was rapid and reached saturation within a few seconds. Diffusional analysis of particle trajectories showed existence of two discrete mobility states exhibiting ‘fast’ and ‘slow’ motions. Binding of PFT proteins was invariably in the ‘fast’ mobility state that was followed by transitions of the single monomer between the two states. The slow moving population was significantly enhanced in cholesterol containing bilayers. We argue that the change in mobility is a consequence of structural transition to an assembly competent intermediate, the protomer state. Preliminary analysis indicates that cholesterol enhances conformational transition by direct binding to the N-terminus of ClyA leading to stabilization of the protomer-like state. This stabilization directly translates to increased formation of higher order structures at high concentrations of protein as measured by analysis of single molecule photobleaching trajectories of pre-formed ClyA pores. Therefore, we propose a molecular mechanism for selective pore formation in eukaryotic membranes driven by conformational selectivity in the presence of cholesterol.

Automated Analysis of Intracellular Dynamic Processes.

The study of intracellular dynamic processes is of fundamental importance for understanding a wide variety of diseases and developing effective drugs and therapies. Advanced fluorescence microscopy imaging systems nowadays allow the recording of virtually any type of process in space and time with super-resolved detail and with high sensitivity and specificity. The large volume and high information content of the resulting image data, and the desire to obtain objective, quantitative descriptions and biophysical models of the processes of interest, require a high level of automation in data analysis. Two key tasks in extracting biologically meaningful information about intracellular dynamics from image data are particle tracking and particle trajectory analysis. Here we present state-of-the-art software tools for these tasks and describe how to use them.

DEM Analysis of Particle Trajectory in Circumferential Direction at Bell-less Top

DEM Analysis of Particle Trajectory in Circumferential Direction at Bell-less Top

Geomagnetically trapped, albedo and solar energetic particles: Trajectory analysis and flux reconstruction with PAMELA

The PAMELA satellite experiment is providing comprehensive observations of the interplanetary and magnetospheric radiation in the near-Earth environment. Thanks to its identification capabilities and the semi-polar orbit, PAMELA is able to precisely measure the energetic spectra and the angular distributions of the different cosmic-ray populations over a wide latitude region, including geomagnetically trapped and albedo particles. Its observations comprise the solar energetic particle events between solar cycles 23 and 24, and the geomagnetic cutoff variations during magnetospheric storms. PAMELA’s measurements are supported by an accurate analysis of particle trajectories in the Earth’s magnetosphere based on a realistic geomagnetic field modeling, which allows the classification of particle populations of different origin and the investigation of the asymptotic directions of arrival.

Long-range attraction of particles adhered to lipid vesicles.

Many biological systems fold thin sheets of lipid membrane into complex three-dimensional structures. This microscopic origami is often mediated by the adsorption and self-assembly of proteins on a membrane. As a model system to study adsorption-mediated interactions, we study the collective behavior of micrometric particles adhered to a lipid vesicle. We estimate the colloidal interactions using a maximum likelihood analysis of particle trajectories. When the particles are highly wrapped by a tense membrane, we observe strong long-range attractions with a typical binding energy of 150k_{B}T and significant forces extending a few microns.

Analysis of Abrasive Particle Trajectories during Single-Sided Lapping Process with Driven Conditioning Ring

In this paper new kinematics systems were studied for a single lapping process. In order to ensure the constant profile wear of the tool a standard kinematic system can be changed. Lapping is carried out by applying loose abrasive grains between two surfaces and causes a relative motion between them. The result is a finish of multi-directional lay. During process, the mechanism of surface formation are decisively affected by a pressure force, a process time and a motion type of grains. It has been proven, that providing the additional movements of the conditioning ring affects the profile wear of the lapping plate. First of all, the kinematics equations of the lapping process have been developed and the process has been simulated. A type of the abrasive particle trajectories in standard single-disk lapping depends on rotational speed ratio of a tool and a conditioning ring. In addition, two new kinematic systems were presented: with radial and secant movement of the conditioning ring. Finally, comparison and analysis of abrasive trajectories were carried out.

Relationship between saccadic eye movements and formation of the Krukenberg's spindle-a CFD study.

In this research, a series of numerical simulations for evaluating the effects of saccadic eye movement on the aqueous humour (AH) flow field and movement of pigment particles in the anterior chamber (AC) was performed. To predict the flow field of AH in the AC, the unsteady forms of continuity, momentum balance and conservation of energy equations were solved using the dynamic mesh technique for simulating the saccadic motions. Different orientations of the human eye including horizontal, vertical and angles of 10° and 20° were considered. The Lagrangian particle trajectory analysis approach was used to find the trajectories of pigment particles in the eye. Particular attention was given to the relation between the saccadic eye movement and potential formation of Krukenberg's spindle in the eye. The simulation results revealed that the natural convection flow was an effective mechanism for transferring pigment particles from the iris to near the cornea. In addition, the saccadic eye movement was the dominant mechanism for deposition of pigment particles on the cornea, which could lead to the formation of Krukenberg's spindle. The effect of amplitude of saccade motion angle in addition to the orientation of the eye on the formation of Krukenberg's spindle was investigated.

Dynamic drag force based on iterative density mapping: A new numerical tool for three-dimensional analysis of particle trajectories in a dielectrophoretic system.

Dielectrophoresis is a widely used means of manipulating suspended particles within microfluidic systems. In order to efficiently design such systems for a desired application, various numerical methods exist that enable particle trajectory plotting in two or three dimensions based on the interplay of hydrodynamic and dielectrophoretic forces. While various models are described in the literature, few are capable of modeling interactions between particles as well as their surrounding environment as these interactions are complex, multifaceted, and computationally expensive to the point of being prohibitive when considering a large number of particles. In this paper, we present a numerical model designed to enable spatial analysis of the physical effects exerted upon particles within microfluidic systems employing dielectrophoresis. The model presents a means of approximating the effects of the presence of large numbers of particles through dynamically adjusting hydrodynamic drag force based on particle density, thereby introducing a measure of emulated particle-particle and particle-liquid interactions. This model is referred to as "dynamic drag force based on iterative density mapping." The resultant numerical model is used to simulate and predict particle trajectory and velocity profiles within a microfluidic system incorporating curved dielectrophoretic microelectrodes. The simulated data are compared favorably with experimental data gathered using microparticle image velocimetry, and is contrasted against simulated data generated using traditional "effective moment Stokes-drag method," showing more accurate particle velocity profiles for areas of high particle density.

Comparison of the transport of the aggregates of nanoscale zerovalent iron under vertical and horizontal flow.

Direct injection of nanoscale zerovalent iron (NZVI) particles is being considered for remediation of contaminated sites. However, the transport characteristics of NZVI under horizontal flow conditions are not fully understood. In this study, NZVI particles were stabilized with carboxymethyl cellulose (CMC) and injected in vertical and horizontal columns to compare the effects of the flow direction on the transport. Columns were packed with sand of mean grain diameters of 180, 340 or 1140 µm (referred to as fine, intermediate and coarse sand, respectively), and were injected with CMC-NZVI suspensions of 0.3, 1 or 3 g Fe L(-1). Experimental breakthrough curves showed that with the coarse and intermediate sands, the steady-state effluent concentration in the horizontal column were up to 84% lower than those in the vertical column regardless of the initial NZVI concentration. However, in the fine sand the differences were insignificant, except at the highest NZVI particle concentration. Additionally, in the horizontally-oriented columns containing the coarse or intermediated sand, NZVI aggregates particles were non-uniformly distributed in the cross-section of the columns and there higher deposition in the bottom-half of the cross-section due to gravity effects. These deposition patterns can be accounted for, in part, by the gravitational settling of the large aggregates of NZVI, especially at high NZVI concentrations. A particle trajectory analysis in three dimensions demonstrated that under horizontal flow, gravity forces resulted in lower deposition of NZVI on the bottom-half of a single collector, as particles approaching the bottom-half of the collector were deflected by gravity to collectors below.

Density-ratio effects on the capture of suspended particles in aquatic systems

Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is important in a range of environmental processes, including suspension feeding by corals and ‘filtering’ by aquatic vegetation. Although aquatic particles are often considered as perfect tracers when estimating capture efficiency, the particle density ratio (${\it\rho}^{+}$) – the ratio of the particle density to the fluid density – can significantly affect capture. In this paper, we use a numerical analysis of particle trajectories to quantify the influence of ${\it\rho}^{+}$ on particle capture by circular collectors in a parameter space relevant to aquatic systems. As it is generally believed that inertia augments the capture efficiency when the Stokes number ($\mathit{St}$) of the particles exceeds a critical value, we first estimate the critical Stokes number for aquatic-type particles and demonstrate its dependence on both ${\it\rho}^{+}$ and the Reynolds number ($\mathit{Re}$). Second, we analyse how efficiently circular collectors can capture neutrally buoyant (${\it\rho}^{+}=1$), sediment-type (${\it\rho}^{+}=2.6$) and weakly buoyant (${\it\rho}^{+}=0.9$) aquatic particles. Our analysis shows that, for ${\it\rho}^{+}&gt;1$, inertia can either augment or diminish capture efficiency, and inertial effects appear well before the critical Stokes number is reached. The role of particle inertia is maximised at Stokes numbers above the critical value and, for sediment-type particles, can result in as much as a fourfold increase in the rate of capture relative to perfect tracers of the same size. Similar but opposite effects are observed for weakly buoyant particles, where capture efficiency can decrease by 60 % relative to the capture of perfect tracers.

Laboratory study of diffusion region with electron energization during high guide field reconnection

Floating potential profile was measured around the X-point during high guide field reconnection in UTST merging experiment where the ratio of guide field (Bg) to reconnecting magnetic field (Brec) is Bg/Brec&amp;gt;10. Floating potential measurement revealed that a quadrupole structure of electric potential is formed around the X-point during the fast reconnection phase due to the polarization by inductive electric field. Also, our floating potential measurement revealed the existence of parallel electric field in the vicinity of the X-point. While field-aligned components of inductive electric field (E∥ind) and electrostatic electric field (E∥es) cancel out with each other away from the X-point, E∥ind exceeds E∥es around the X-point, indicating the deviation from ideal MHD criterion within the region. The diffusion region extends in the outflow region and the scale length of region is an order of ion skin depth, which is quite different from the VTF experiment result. Based on the measured magnetic field and electric field profile, our particle trajectory analysis indicates that fast electrons with energies over 300 eV are produced within 1 μs around the X-point in the non-ideal MHD region. These results indicate that production of fast electrons or electron heating are expected to be observed in the vicinity of the X-point.

Extreme air–sea interaction over the North Atlantic subpolar gyre during the winter of 2013–2014 and its sub-surface legacy

Exceptionally low North American temperatures and record-breaking precipitation over the British Isles during winter 2013–2014 were interconnected by anomalous ocean evaporation over the North Atlantic subpolar gyre region (SPG). This evaporation (or oceanic latent heat release) was accompanied by strong sensible heat loss to the atmosphere. The enhanced heat loss over the SPG was caused by a combination of surface westerly winds from the North American continent and northerly winds from the Nordic Seas region that were colder, drier and stronger than normal. A distinctive feature of the air–sea exchange was that the enhanced heat loss spanned the entire width of the SPG, with evaporation anomalies intensifying in the east while sensible heat flux anomalies were slightly stronger upstream in the west. The immediate impact of the strong air–sea fluxes on the ocean–atmosphere system included a reduction in ocean heat content of the SPG and a shift in basin-scale pathways of ocean heat and atmospheric freshwater transport. Atmospheric reanalysis data and the EN4 ocean data set indicate that a longer-term legacy of the winter has been the enhanced formation of a particularly dense mode of Subpolar Mode Water (SPMW)—one of the precursors of North Atlantic Deep Water and thus an important component of the Atlantic Meridional Overturning Circulation. Using particle trajectory analysis, the likely dispersal of newly-formed SPMW is evaluated, providing evidence for the re-emergence of anomalously cold SPMW in early winter 2014/2015.

Numerical analysis of particle trajectories in living cells under uncertainty conditions

We have developed a numerical method for the analysis of particle trajectories in living cells, where a type of movement is determined by Akaike's information criterion, while model parameters are identified by a weighted least squares method. The method is realized in computer software, written in the Java programming language, that enables us to automatically conduct the analysis of trajectories. The method is tested on synthetic trajectories with known parameters, and applied to the analysis of replication complexes in cells, infected with hepatitis C virus. Results of the analysis are in agreement with available data on the movement of biological objects along microtubules.