Bidirectional Drift Research Articles

A new ship tracing technology from oil spills based on multi-source data

Oil spill from ship can cause serious pollution to the Marine environment, but it is very difficult to find and confirm the troublemaker. In order to determine the oil spill ship, this paper proposes a new method to trace the source of ship oil spills and find the suspected ship that spills oil based on SAR imagery, AIS data and related marine environment data. First, we filter AIS data based on position of oil spill areas on remote sensing imagery and convert oil spill areas into trajectory points. Secondly, based on the Lagrangian particle motion model, a bidirectional drift model is proposed to calculate the average similarity between the forward and backward drift results. Finally, the most likely oil spill ship is determined according to the average similarity results. The results of the case study show that the method is effective and practical.

Vibro-impact dynamics of an experimental rig with two-sided constraint and bidirectional drift

This paper demonstrates a theoretical and experimental study on a universal vibro-impact system with bidirectional drift. With a dedicated experimental rig that is able to verify numerical simulations, the system has revealed various bifurcations from a piecewise-smooth dynamical model involving impact and dry friction. This experimental rig with a two-sided constraint is designed with adjustable configurations which can be used for experimental testing of versatile piecewise-smooth dynamical systems, e.g., the impact oscillator, the drifting oscillator and the capsule system. It is able to be customised to alter different system parameters, such as friction, number of constraints, mass ratio, impact gap and constraint stiffness, for developing and testing various control strategies. In this paper we particularly studied several types of bifurcations from our preliminary experimental results and discussed the dynamical responses of the system under different excitation frequencies and amplitudes. It was found that with a higher excitation frequency and amplitude, the vibro-impact dynamics on both ends of the constraints could result in a large amount of uncertainties, thus bi-stable and chaotic motions are likely to be observed. While being unstable, the system runs with a relatively high energy efficiency in this configuration.

Drift of suspended ferromagnetic particles due to the Magnus effect

A minimal system of equations is introduced and applied to study the drift motion of ferromagnetic particles suspended in a viscous fluid and subjected to a time-periodic driving force and a nonuniformly rotating magnetic field. It is demonstrated that the synchronized translational and rotational oscillations of these particles are accompanied by their drift in a preferred direction, which occurs under the action of the Magnus force. We calculate both analytically and numerically the drift velocity of particles characterized by single-domain cores and nonmagnetic shells and show that there are two types of drift, unidirectional and bidirectional, which can be realized in suspensions composed of particles with different core-shell ratios. The possibility of using the phenomenon of bidirectional drift for the separation of core-shell particles in suspensions is also discussed.

Firing rate and pattern heterogeneity in the globus pallidus arise from a single neuronal population

Intrinsic heterogeneity in networks of interconnected cells has profound effects on synchrony and spike-time reliability of network responses. Projection neurons of the globus pallidus (GPe) are interconnected by GABAergic inhibitory synapses and in vivo fire continuously but display significant rate and firing pattern heterogeneity. Despite being deprived of most of their synaptic inputs, GPe neurons in slices also fire continuously and vary greatly in their firing rate (1-70 spikes/s) and in regularity of their firing. We asked if this rate and pattern heterogeneity arises from separate cell types differing in rate, local synaptic interconnections, or variability of intrinsic properties. We recorded the resting discharge of GPe neurons using extracellular methods both in vivo and in vitro. Spike-to-spike variability (jitter) was measured as the standard deviation of interspike intervals. Firing rate and jitter covaried continuously, with slow firing being associated with higher variability than faster firing, as would be expected from heterogeneity arising from a single physiologically distinct cell type. The relationship between rate and jitter was unaffected by blockade of GABA and glutamate receptors. When the firing rate of individual neurons was altered with constant current, jitter changed to maintain the rate-jitter relationship seen across neurons. Long duration (30-60 min) recordings showed slow and spontaneous bidirectional drift in rate similar to the across-cell heterogeneity. Paired recordings in vivo and in vitro showed that individual cells wandered in rate independently of each other. Input conductance and rate wandered together, in a manner suggestive that both were due to fluctuations of an inward current.

Occurrence of bidirectional type III bursts in solar flares

The 13 pairs of type III bursts with the bidirectional drift structures recorded with the spectrograph in the frequency ranges of 230-300 MHz and 625-1500 MHz at the Yunnan Observatory and 2600-3800 MHz at the Beijing National Astronomical Observatories are analyzed in this present article and the outstanding characteristics of these events are obtained. These bursts respectively reveal that the separatrix frequency between the bursts with positive and negative drifts comes between 250 MHz and 3420 MHz, with a gap being between 0.6 MHz and 110 MHz; the duration is 53 ms-1880 ms and the frequency drift rate is between 45 MHz/s and 56000 MHz/s. The drift rate at metric wavelengths is relatively low, only a few decades of MHz while it is comparatively high at microwave wavelengths, reaching 56000 MHz/s. The qualitative explanation of these events is given in this paper.

Numerical simulation of net longshore sediment transport and granulometry of surficial sediments along Chandeleur Island, Louisiana, USA

The formation and spatial evolution of Chandeleur Island, Louisiana, has been investigated extensively during the past several decades. No significant evaluation of the longshore sediment system, which is instrumental in the island's evolution and morphodynamic maintenance, has been completed. This paper provides the first quantitative description of the longshore transport system that operates along this transgressive, overwash-dominated barrier island system. The net longshore sediment transport system was investigated via the wave refraction model, WAVENRG, which provided estimates of the transport volumes and drift directions alongshore. Surficial samples were collected from the foredune, midtide and step environments in an effort to characterize the sediments along the island and determine if textural or compositional trends have developed in response to a predicted longshore sediment transport system. Data obtained during this research indicate that the longshore transport system along Chandeleur Island is characterized by a bi-directional drift system, with drift directed both north and south from a nodal point located in the south-central portion of the barrier island. Analysis of the predicted transport volumes indicates that the degree of wave refraction, and therefore the breaker angle, is more instrumental in controlling the alongshore volume rate of sediment transport than the breaker wave heights. Additionally, a larger magnitude of sediment transport is predicted in the southern portion of the barrier, which is in a greater state of deterioration than the north and central portion of the island. This apparent contradiction indicates that factors such as a variable subsidence rate along the island are contributing to the alongshore geomorphology. No significant textural or compositional trends were identified alongshore. This absence of granulometric trends is attributed to the lack of variability of the sediments that comprise the barrier and the frequency of overwash events which occur on this low-profile island.

A Quasi-Periodic Solar Radio Fluctuation at Microwave Band

A rare but interesting solar radio fine structure, quasi-periodicfluctuations, on 25 August 1999 was observed at microwave band for thefirst time. They fluctuated initially at a nearly stable frequencylevel then at a reverse drift component up to 5.49 GHz. The individualfluctuation consists of a bi-directional drift component. The featuresare characterized by narrow bandwidth of Δf/f⩽3%,quasi-periodicity of ~100 ms as well as a slowly reverse and a rapidlynormal drift rates on the bi-directional drift component. Theassociated data of the Yohkoh soft and hard x-ray telescope andNobeyama radio heliograph at 17 GHz showed that there are severalbright spots (i.e. inhomogeneities) along the soft x-ray loop, and thelocations of both radio and soft x-ray sources are closely consistent.Therefore, the fluctuations are most likely caused by theinhomogeneities within a flare loop. Based on the two-componentatmospheric model, we suggest a three-component atmospheric model withlarge scale length λ and small scale lengths λ1and λ2 to describe equilibrium atmosphere andinhomogeneity. With the beam model, the characters of fluctuations maybe interpreted reasonably by the quasi-equidistant inhomogeneity alonga flare loop.

Evidence of coronal loop interaction in a flare-CME event

The radio and multi-wavelength signature of coronal loop interaction is discussed in the event on November 28, 1998 with X-class flares and CMEs, observed by Nobeyama Radioheliograph (NoRH), YOHKOH/SXT/HXT, SOHO/EIT/LASCO, and Chinese radio spectrometers (2.6-3.8 GHz). The fluctuations at rising phase with bi-directional drift rates may show the signature of magnetic reconnection caused by loop interaction. There are two or three peaks in radio time profiles and spectra, which show that two or three flares are triggered in the process of loop interaction. The 17 GHz sources are composed of three parts with different time profiles and polarization feature. The formation of twisted loops in post-flare phase may indicate the start time of the CMEs in this event.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Radio and multiwavelength evidence of coronal loop eruption in a flare–coronal mass ejection event on 15 April 1998

A typical flare–coronal mass ejection (CME) event is studied at the initial time and position of the flare and CME. The photospheric magnetic configuration consists of two main polarities (dipolar structure) with some emerged new polarities, similar to a quadrupolar structure, during the event. The coronal loops in soft X‐ray and EUV images show the signature of the loop interaction, i.e., the storage of the magnetic energy. The radio bursts at 1–2 GHz were observed with fast frequency drifts with bidirectional drift pairs, which may provide a direct signature of upward and downward particle acceleration from the reconnection site, followed by the bulk energy release of the flare. After that, the soft X‐ray and EUV loops were suddenly opened and closed again in 10 min. The open time is around the maximum phase of the flare as well as the start time of the associated CME. Meanwhile, the polarization sense of the microwave bursts suddenly reversed at 2.6–3.8 GHz, which might have been caused by the fast variation of coronal loops or the magnetic field. The high‐time‐resolution (8 ms) data show the microwave bursts at 2.6–3.8 GHz, with slow frequency drifts and zebra structures in the initial phase of the CMEs or shock formation. Hence it is suggested that flares and CMEs may be triggered simultaneously by some MHD instabilities or by reconnection in a favorable magnetic configuration to release the free magnetic energy in two different ways.

Short‐term changes in the plan shape of a sandy beach in response to sheltering by a nearshore mud bank, Cayenne, French Guiana

AbstractMontjoly is a headland‐bound embayed sandy beach in Cayenne, French Guiana, that shows long‐term plan shape equilibrium in spite of periodic changes in accretion and erosion that alternately affect either end of the beach. These changes are caused by mud banks that move alongshore from the Amazon. The mechanisms involved in changes in the plan shape of the beach in response to the passage of one of these mud banks were monitored between 1997 and 2000 from airborne video imagery and field work. The beach longshore drift to the northwest, driven by the incident easterly to northeasterly swell usually affecting this coast, became temporarily reversed as the mud bank, migrating from east to west, initially sheltered the southeastern end of the beach. The difference in exposure to waves engendered a negative wave height gradient alongshore towards the southeast, resulting in the setting up of a cell circulation and counter‐active longshore drift from the exposed northwestern sector to the southeast. Sand eroded from the exposed sector accumulated first in the southeastern, and then the central sectors of the beach. The effect of increasing beach sheltering by the mudbank moving west is highlighted on the videographs by an ‘arrested’ pattern of beach shoreline development. The videographs show hardly any changes in beach plan shape since January 1999, due to sheltering of the beach from wave attack by the mud bank. It is expected that the eroded sector will recover in the future as the mud bank passes, leading to re‐establishment of the northwesterly sand drift. This temporally phased bi‐directional drift within the confines of the bounding headlands results in a rare example of mud‐bank‐induced beach rotation, and probably explains the long‐term equilibrium plan shape of Montjoly beach. Copyright © 2002 John Wiley & Sons, Ltd.

Development of large linear silicon drift detectors for the STAR experiment at RHIC

Large area linear Silicon Drift Detectors (SDD) are being developed for high energy and relativistic heavy ion collider experiments. SDDs have been proposed for the inner tracking detector in the STAR experiment at the BNL relativistic heavy ion collider to become operational in 1999. The Silicon Vertex Tracker (SVT) will consist of a three layer barrel structure composed of 216 individual detectors, each 6.3 × 6.3 cm 2. Prototypes, including one-way drift detectors (4.5 × 4.5 cm 2) and bi-directional drift detectors (6 × 6 cm 2) have been manufactured,and their properties have been studied. Design considerations, as well as test results, are presented in this article. Recent work has focused on minimizing the inactive guard structure area in order to optimize tracking efficiency. Particular attention is given to discussion of parameters that are sensitive to the reduced guard structure area, such as leakage current, maximum voltage and drift non-linearities.

Particle transport through a hollow canine airway cast by high-frequency oscillatory ventilation.

High-frequency oscillatory ventilation (HFV) of the mammalian respiratory tract can maintain good respiratory ventilation, even with tidal volumes less than half of the anatomic dead space. A steady bidirectional drift is established in airways when the frequency is greater than 2 Hz, resulting in quasi-steady axial streams in the airways. Convective transport from the trachea to peripheral airways takes place in the central core of the bifurcating network of the bronchial tree. It takes place in the opposite direction in the annular regions near the airway walls. In this study, aerosol particle transport was measured in a hollow cast of a canine tracheobronchial tree that extended from the trachea to terminal bronchioles. The 0.5 micron particles, placed in the upper trachea as a bolus, were transported rapidly to the terminal airways of the cast by HFV with tidal volumes of less than one third the volume of the cast. Carrier gases of different kinematic viscosity were used to investigate the fluid dynamics of the transport. Particle transport during HFV was fastest in a gas of high kinematic viscosity (helium), and slowest in a gas of low kinematic viscosity (sulfur hexafluoride). The results are consistent with the application of lubrication theory, improve our understanding of convective processes involved in HFV, and provide new insights into particle penetration in the airways and other aspects of respiratory ventilation.

An experimental investigation of oscillating flow in a tapered channel

Oscillating flow in a tapered channel was studied experimentally by observing the deformation of a dye streak within a Plexiglas channel during piston induced, volume-cycled oscillations. The observed steady streaming was compared to theoretical calculations. Both the theoretical and experimental results show bi-directional drift for all frequencies, with characteristics dependent upon the value of the Womersley parameter, α = b(ω/ν)½. For large values of α, e.g. α > 10, the fluid near the walls and along the centreline drifted towards the narrow end of the channel, while fluid in an intermediate region drifted towards the wide end of the channel. For small values of α, e.g. α < 5, the fluid drifted towards the narrow end at the wall and the wide end of the channel along the centreline. Applications to mass transport in the lung are discussed.

Volume-cycled oscillatory flow in a tapered channel

Oscillatory viscous flow in a tapered channel is analysed under conditions of fixed stroke volume. A lubrication theory is developed for small taper and the general result is steady bidirectional drift and an induced steady pressure gradient. The characteristics of the drift profiles change significantly as the Womersley parameter is increased. For large values difficulties arise in the matched asymptotics method which are resolved by introducing a steady drift layer that is much thicker than the Stokes layer. This double boundary layer does not arise in pressure-cycled oscillations. Both Eulerian and Lagrangian drift are examined. The results are compared qualitatively to experimental observations which primarily focus on the application to ventilation in the lung.

K-type coefficients in the littoral drift system

The quantity q (volume of sand transported past a given point, per unit time; L 3T −1, can be related to P L (the littoral component of wave power, per unit length of coast; MLT −3) by using the expression k γρa (where gamma is the acceleration of gravity, rho is the mass density of sediment, and a is a packing coefficient). In this third expression, three of the values can be taken as constants which provide that the resulting equation will be dimensionally homogeneous: q = kP L/γϱs a The coefficient k is, therefore, dimensionless. Its value, as reported in the literature, ranges from numbers close to (but smaller than) 1.0, down to numbers such as 10 −4 and 10 −5. If one wishes to use P L in order to predict q, and hence dq dx (erosion or deposition, according to the algebraic sign on the derivative), there must be a better assessment of k than a range of four, five, or six orders of magnitude. The coefficient k was originally defined in an instantaneous sense, so it can have values greater than 0.1. For long term calculations, a similar coefficient can be defined as: In K = C t 1P 1 t 2P 2 − 1.0 where C can be taken as −11, and the tP-ratio expresses the extent to which wave power is cancelled in a bidirectional drift system, thus producing values of K in the general range down to 10 −5 or perhaps smaller.

A new mathematical continuum theory of axoplasmic transport

The hypothesis is advanced that successive waves of apparent contraction-relaxation (due perhaps to filament sliding) propagate along the filamentous proteins that pierce axoplasm oriented parallel to the axon length. A mathematical continuum model is developed to characterize the flow that could result in the viscous fluid bathing the moving filamentous proteins. This flow is complicated and oscillatory in time and space, but, on the average, it yields a bi-directional drift of fluid. It would transport various substances riding in the fluid, soluble and particulate, at various distinct speeds both up and down the axon. The model can thus account qualitatively for many observed features of axoplasmic transport.