Particle Motion Patterns Research Articles

The nature of particle motion in regional seismograms and its utilization for phase identification

SUMMARY The particle motion of regional arrivals is frequently treated in automatic phaserecognition schemes as that appropriate to simple P or S waves incident on an elastic, laterally homogeneous half-space. This model implies that the motion in ‘P-type’ phases can be described in terms of a single, generalized signal process and ‘S-type’ phases in terms of two independent processes (SV and SH) and thus, all regional arrivals could be fully characterized by three components of motion. In this paper, we present anlyses of the particle-motion patterns of various regional arrivals recorded at the ARCESS array from closely spaced events in the Kola Peninsula. We have found that only Pn-particle motion, described in terms of two independent signal processes, can be reliably characterized by three-component recordings. On the other hand, the various regional arrivals following Pn, such as Pg, Sn and Lg, can only be poorly characterized on the basis of three-component recordings alone. The reason is that these arrivals must be described in terms of more than two independent generalized signal processes, at least three for Pg and Sn, and possibly up to five for Lg. Recognition of these phases will thus require the use of more sensors than signal processes in the observing sensor configuration, such as three-component sensors combined with a small tripartite array. We have investigated the feasibility of adaptive, automatic recognition of regional arrivials by a wavefield extrapolation scheme utilizing such a mini-array . The process, which appear to be promising, adaptively learns the particle-motion patterns of individual arrivals, including complex site-response functions, from examples of closely located regional events.

Movement patterns of abrasive particles in three-body abrasion

The movement patterns of abrasive particles in three-body abrasion are very important to the wear of materials. In the present paper, the movement of a single abrasive particle could be observed in detail through new wear apparatus for three-body abrasion. The new apparatus was used to carry out short-travel wear testing for a single particle sandwiched between two metal surfaces and to measure the frictional force at the same time. A number of experiments showed that there were mainly two kinds of movement patterns of the particles, i.e. sliding and rolling. Based on the experimental results, a criterion was proposed for the movement patterns of abrasive particles. The criterion matched with the experiments quite well.

A wear tester capable of monitoring and evaluating the movement pattern of abrasive particles in three-body abrasion

The movement pattern of abrasive particles plays an important role in the three-body abrasion of tribomaterials. If the attack angle of a particle is greater than the critical attack angle, the particle cuts the materials during sliding. However, when the particles are rolling, the materials are no longer subject to cutting, but to plastic deformation. Therefore, an evaluation of the movement pattern of abrasive particles would be very important for both theoretical research and practical use of three-body abrasion. Based on this idea, a new wear tester was developed which could be used to monitor directly and record the state of movement of the particles. At the same time the friction coefficient could be measured. Using this tester the rolling to sliding ratio could be evaluated statistically and the range of probability of cutting wear could be evaluated.

Stability of motion of high energy particles in crystals and random string approximation

The results of a study of the stability of fast charged particle motion in crystals when the transition occurs from the regular plane motion of a particle in the periodic field of crystal atomic strings to the chaotic motion are presented. The manifestations of such a transition in coherent radiation and the cross sections for pair creation in crystals are discussed. The particle motion pattern in crystals is shown to affect substantially the spectral features of ultrahigh energy electron radiation in crystals.

Estimation of particle renewal rates along the wall in a mechanically stirred granular bed

In indirectly heated mechanically stirred vessels for granular solids, the particle flow characteristics, especially in the immediate vicinity of the heated surface, are important in evaluating the surface-to-bed heat transfer rate. This study presents for the first time experimentally observed particle flow patterns along the wall in a vessel stirred by paddle-type blades. The effects of solids flowability, bed height, blade rotational speed, blade height, wall-to-blade clearance, air flow rate and vessel diameter on the particle movement patterns are examined in this paper. Estimation of the particle renewal rates along the heated wall from the measured information on particle movement is discussed.

Time dependence of AC flashover characteristics for particle-initiated breakdown in GIS

The AC flashover characteristics for wire-particle-initiated breakdown and its time dependence were studied in a realistic 362 kV SF/sub 6/ gas-insulated bus duct. The voltage leading to breakdown after two hours was calculated from studies of the time to breakdown at different voltages. The calculations were made for different pressures and compared with the experimentally obtained two-hour withstand voltage. The influence that the long-term exposure to voltage has on the particle was studied, including both the particle deformation and the impact that the deformation has on the particle movement pattern and the AC flashover characteristic. It was found that the deformation taking place at the ends of the wire, depends on the wire material and diameter and on the duration of the voltage application. In some cases it plays a decisive role in the time dependence of the AC flashover characteristics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Tests of kinematic models for deposit-feeders' guts: patterns of sediment processing by Parastichopus californicus (Stimpson) (Holothuroidea) and Amphicteis scaphobranchiata Moore (Polychaeta)

Gut-reactor models are used to describe patterns of particle movement within the guts of two deposit-feeders, the holothuroid Parastichopus californicus (Stimpson) and the polychaete Amphicteis scaphobranchiata Moore. The plug-flow model, with modifications, is confirmed for P. californicus and can be generalized to all deposit-feeders with simple tubular guts. The modified plug-flow model, in contrast with the ideal plug-flow model first proposed by Penry and Jumars (1986, 1987) is characterized by the absence of radial as well as axial mixing of particles. The degree of particle mixing observed in the gut of A. scaphobranchiata is too great to be incorporated in a modified plug-flow model. Its gut and the guts of other terebellimorph polychaetes must be modeled as a mixing reactor/plug-flow reactor series with a ventral bypass stream that shunts particles from the mixing region through the plug-flow region for elimination in fecal material. Mixing and bypass may be components of an internal sorting process that results in rapid removal of relatively indigestible particles from the gut and increases the proportion of gut volume available for digesting particles of relatively higher qualities.

A continuum approach for modeling mass transport in fractured media

A continuum approach has been developed for modeling mass transport in fractured rocks. It involves a new application of a particle‐tracking method in which physical transport is simulated in terms of velocity and the variations in velocity. Statistics describing the particle motion come from observing the actual pattern of particle motion in a discrete subdomain. This subdomain is a small but representative piece of the much larger continuum. In effect, particle motion in the continuum is forced to mimic that in the discrete subdomain. The model successfully duplicates patterns of anisotropic dispersion predicted by de Josselin de Jong (1972) and breakthrough curves simulated with a discrete fracture model. Applications demonstrate that the de Josselin de Jong approach for estimating dispersivities for idealized networks cannot generally be applied to networks formed from sets of finite, irregularly spaced fractures. In addition, this study reinforces indications from earlier studies about the complexity of dispersion in fractured media. Factors that contribute to spreading in the major and minor principal directions change with the orientation of the network relative to the mean hydraulic gradient.

The elastodynamic near field

Summary. The elastodynamic fields of point forces and shear dislocations of finite source duration are analysed with the aim of establishing the frequency and time-domain characteristics of the field in the near-source region. Criteria are obtained for amplitude dominance in regions where the source -sensor distance is much smaller than the wavelength. It is shown that in the frequency domain, the Green’s tensor (and hence the displacement field of a single point force) attenuates like R-’ in the nearsource region and there exists no region in which the ‘near-field’ term becomes dominant such that the ‘far-field’ term can be neglected. Hence, there is no real ‘near-field’ term for the elastodynamic Green’s tensor. The near-field terms of the displacements, velocities and accelerations excited by a shear dislocation attenuate like R-’, since the R-3 and R-4 terms tend to be eliminated due to mutual cancellation of P and S motions in the near-source region. In the time domain, the corresponding near field of the displacement field is defined for the steady amplitude interval (away from transients) RIP < t < R/a + T by the condition R < PT where is the shear velocity and T is the source’s duration. The relative strengths of all other arrivals will depend on the particular time window under consideration. The particle motion patterns due to a single force in the near-source region are shown to be similar to rotating hyperbolas with an axis along the force direction, which are quite different from the ‘smoke ring’ motion patterns of the so-called ‘near-field’ term itself.

Effects of radiofrequency electric fields on cytoplasmic streaming in Nitella

Radiofrequency (RF) electric fields of 0.5 Hz-2.5 GHz at field strengths on the order of 10 V/cm have been shown to interact with isolated Nitella internodal cells in two separate and frequency dependeent manners. At frequencies up to ca. 10 kHz, RF fields act directly to excite the cell membrane, eliciting an action potential and halting cytoplasmic streaming. RF-induced action potentials and accompanying streaming cessations appear to occur through mechanisms not unlike those which result from conventionally applied excitatory stimuli. Neither membrane excitation nor streaming cessation results from exposure to RF of 100 kHz-2.5 GHz. Instead, cellular responses to this band of RF included slight increases in streaming velocity, altered patterns of particle movement, and membrane hyperpolarization. Aberrant particle motions, previously undescribed, were seen to occur from exposure to either RF or static electric fields and can serve as a springboard for further investigations into the mechanisms of cytoplasmic streaming.

Studies on the motility of the foraminifera. I. Ultrastructure of the reticulopodial network of Allogromia laticollaris (Arnold).

Allogromia laticollaris, a benthic marine foraminifer, extends numerous trunk filopodia that repeatedly branch, anastomose, and fuse again to form the reticulopodial network (RPN), within which an incessant streaming of cytoplasmic particles occurs. The motion of the particles is saltatory and bidirectional, even in the thinnest filopodia detected by optical microscopy. Fibrils are visible by differential interference microscopy, and the PRN displays positive birefringence in polarized light. These fibrils remain intact after lysis and extraction of the RPN in solutions that stabilize microtubules (MTs). Electron micrographs of thin sections through these lysed and stabilized cytoskeletal models reveal bundles of MTs. The RPNs of living Allogromia may be preserved by standard EM fixatives only after acclimatization to calcium-free seawater, in which the streaming is normal. The MTs in the RPN are typically arranged in bundles that generally lie parallel to the long axis of the trunk and branch filopodia. Stereo electron micrographs of whole-mount, fixed, and critical-point-dried organisms show that the complex pattern of MT deployment reflects the pattern of particle motion in both flattened and highly branched portions of the RPN. Cytoplasmic particles, some of which have a fuzzy coat, are closely associated with, and preferentially oriented along, either single MTs or MT bundles. Thin filaments (approximately 5 nm) are also observed within the network, lying parallel to and interdigitating with the MTs, and in flattened terminal areas of the filopodia. These filaments do not bind skeletal muscle myosin S1 under conditions that heavily decorate actin filaments in controls (human blood platelets), and are approximately 20% too thin to be identified ultrastructurally as F-actin.

Patterns of particle movement in nerve fibres in vitro. An analysis by photokymography and microscopy.

ABSTRACT Tissue-cultured nerve fibres derived from 3 species of amphibian embryos were composed of bundles of neurites, when viewed by electron microscopy, and contained particles moving in both directions by saltations. Photokymographic analysis of ciné microscopy records taken with Zeiss differential interference optics demonstrated instantaneous particle velocities ranging from 0·15 to 1·8 μm s-1 (13–155 mm/day) in Rana pipiens cultures; 0·16–0·8 μm s-1 (14–74 mm/day) in Ambystoma tigrinum cultures and 0·6—2·25 μm s-1 (45—194 mm/day) in Xenopus laevis cultures. Measured pathlengths for particles saltations ranged from 4 to 63 μm. No correlations between particle velocity and pathlength were found.

Particle motion along a kinematic fault model

abstract Particle motion was examined along the following kinematic fault model: the fault plane is a rectangle so elongated that differences in particle motion in the shorter dimension can be neglected and rupture, once initiated, can be considered to propagate only in the longitudinal direction(s) at constant speed; the distribution of particle displacement along the ruptured fault segment maintains the same sinusoidal shape at different times until finally all particles stop simultaneously. It was found that the pattern of particle motion in this model depends on whether the rupture propagates unilaterally or bilaterally. For the bilateral case, particle displacement and velocity are nearly a finite ramp and a box-car function of time, respectively. The maximum particle velocity is the same everywhere along the final ruptured fault segment, but the average velocity is slightly higher for particles closer to the ends. For the unilateral case, particle velocity is approximately an impulse function of time for particles near the starting edge and gradually becomes a box-car function for particles near the ending edge of rupture. The maximum velocity is the same for all particles along the fault segment, but the average velocity is considerably higher for particles closer to the ending edge. It is not a good approximation for either of these cases to assume that all the particles along the fault segment have the same displacement-time function with only a time delay.

Tracing Soil Particle Movement with Fe‐59

AbstractRates and patterns of actual soil particle movement were established by measuring changes in radiation intensity with time on an eroding sandstone soil. Applying 300 µc of Fe59 in a 5‐foot line along the contour gave a better measure of soil erosion pattern than 100 µc applied to a point. More than 70% of the isotope applied moved 3 or more inches downslope from the line of application. Apparently Fe59 forms mainly stable precipitates or reacts with existing ferric compounds on clay and silt particles because it is not found in the soil solution or on the soil base‐exchange capacity. Only 20% of the Fe59 was temoved by 72‐hour treatment with 30% H2O2. Over 90% of the Fe59 was retained in the surface 1 cm of soil.

SURFACE ASSOCIATIONS BETWEEN PARTICLES AND THE ENDOPLASMIC RETICULUM IN PROTOPLASMIC STREAMING

SummaryProtoplasmic streaming was observed in Tradescantia virginiana staminal hair cells using a bright field oil immersion obective and particle movements were followed in the cytoplasm. By recording and plotting particle positions in every fourth frame of a cine film, different velocities were measured for particles which appeared to follow a common pathway in a transvacuolar strand. From the same kind of analysis, various patterns of particle movement were revealed on the surface of the nucleus.Phase contrast observations of leaf hair cells of Primula obconica and Perilla frutescens showed that the endoplasmic reticulum was particularly well developed in regions of active protoplasmic streaming. Tubules of the endoplasmic reticulum were mainly in parallel orientation, with occasional lateral connections and anastomoses. Groups of parallel, endoplasmic reticulum tubules also appeared to be in continuity with the nucleus and, although these elements approached the nucleus at different angles from the parietal cytoplasm, they were more usually orientated with the long axis of the cell. Particles moved along the endoplasmic reticulum surfaces, sometimes in opposite directions on adjacent tubules, and a dynamic association was observed between the endoplasmic reticulum and mobile particles. This association was well illustrated when endoplasmic reticulum developed in a microscopically undifferentiated region of parietal cytoplasm. As the endoplasmic reticulum developed, the undifferentiated region was apparently transformed and became part of the endoplasmic reticulum. Occasionally, a centre of endoplasmic reticulum development was observed as a compact, complex pattern of tubules which gradually became orientated in a more linear manner as it expanded. This differentiation occurred in association with unusual, concentric, particle movement at the development centre. Finally the endoplasmic reticulum elements formed parallel pathways as commonly seen in actively streaming cytoplasm. These observations are incompatible with current theories of protoplasmic streaming which propose that particles are carried along by the fluid endoplasm or the endoplasmic reticulum. An extension of earlier theories has been made to explain the movement of particles in relation to the activities of the endoplasmic reticulum.Associations of particles and membranes were also observed in cytoplasm of cells involved in the synthesis and transport of organic nutrients. This structural association may be part of a common transport mechanism within parenchyma cells and over long distances in the vascular system.