Average Transport Velocity Research Articles

Flood-induced buttertub spill reveals riverine macroplastic transport dynamics

During the July 2021 European floods approximately eight million empty dairy packaging (buttertubs) were flushed from a dairy processing facility in Belgium into the Vesdre river. Some were transported further downstream, into the Ourthe river and eventually the Meuse river. There are many unknowns when it comes to plastic transport in rivers, especially in response to floods. We therefore used this incident as an unique opportunity to study these buttertubs as a tracer for plastic transport dynamics in a riverine environment in response to an extreme flood event. Normally, it is unknown when and where individual plastic items found on riverbanks entered the environment. In this case, however, the ID stamps on the buttertups allowed for them to be traced back to the flooding of the factory. We studied the transport and deposition of these buttertubs in the Dutch Meuse over 2 years following the flood. We also collected buttertubs at different points in time to investigate their fragmentation and mass loss. Within 3 weeks of the flood, the buttertubs were transported up to 328 km from the spilling location. Overall, the majority (78%) of buttertubs we found within the first 3 weeks were deposited within less than 100 km of the point of emission. Over the following 2 years, the mean transport distance of the found buttertubs moved downstream from 100 km in July/August 2021, to 153 km in July 2023. The buttertubs average transport velocity decreased from 11.7 km/d within the first 3 weeks, to 0.2 km/d by July 2023. Based on the 89 buttertubs we collected and analyzed in detail over the 2 years, we did not find a significant mass loss. Of all 89 buttertubs found, 47 showed cracks and only 12 appeared to have pieces missing. This study shows that even during extreme flood events, the majority of spilled plastic litter is retained within a limited distance after being emitted into the river. The findings of this study can be utilized to improve plastic transport modelling, and overall better understand plastic transport in the freshwater environment.

Material Transport Characteristics in Planetary Roller Melt Granulation.

Melt granulation for improving material handling by modifying particle size distribution offers significant advantages compared to the standard methods of dry and wet granulation in dust reduction, obviating a subsequent drying step. Furthermore, current research in pharmaceutical technology aims for continuous methods, as these have an enhanced potential to reduce product quality fluctuations. Concerning both aspects, the use of a planetary roller granulator is consequential. The process control with these machines benefits from the enhanced ratio of heated surface to processed volume, compared to the usually-applied twin-screw systems. This is related to the unique concept of planetary spindles flowing around a central spindle in a roller cylinder. Herein, the movement pattern defines the transport characteristics, which determine the energy input and overall processing conditions. The aim of this study is to investigate the residence time distribution in planetary roller melt granulation (PRMG) as an indicator for the material transport. By altering feed rate and rotation speed, the fill level in the granulator is adjusted, which directly affects the average transport velocity and mixing volume. The two-compartment model was utilized to reflect these coherences, as the model parameters symbolize the sub-processes of axial material transport and mixing.

Spontaneous Transport Mechanics of Water Droplets under a Synergistic Action of Designed Pattern and Non-Wetting Gradient.

The controllable spontaneous transport of water droplets on solid surfaces has a broad application background in daily life. Herein, a patterned surface with two different non-wetting characteristics was developed to control the droplet transport behavior. Consequently, the patterned surface exhibited great water-repellant properties in the superhydrophobic region, and the water contact angle reached 160° ± 0.2°. Meanwhile, the water contact angle on the wedge-shaped hydrophilic region dropped to 22° after UV irradiation treatment. On this basis, the maximum transport distance of water droplets could be observed on the sample surface with a small wedge angle of 5° (10.62 mm), and the maximum average transport velocity of droplets was obtained on the sample surface with a large wedge angle of 10° (218.01 mm/s). In terms of spontaneous droplet transport on an inclined surface (4°), both the 8 μL droplet and 50 μL droplet could move upward against gravity, which showed that the sample surface possessed an obvious driving force for droplet transport. Surface non-wetting gradient and the wedge-shaped pattern provided unbalanced surface tension to produce the driving forces in the process of droplet transport, and the Laplace pressure as well is produced inside the water droplet during this process. This work provides a new strategy to develop a patterned superhydrophobic surface for droplet transport.

Computational investigation of the effect of reduced dynein velocity and reduced cargo diffusivity on slow axonal transport

Contributions of three components of slow axonal transport (SAT) were studied using a computational model: the anterograde motor (kinesin)-driven component, the retrograde motor (dynein)-driven component and the diffusion-driven component. The contribution of these three components of SAT was investigated in three different segments of the axon: the proximal portion, the central portion, and the distal portion of the axon. MAP1B protein was used as a model system to study SAT because there are published experimental data reporting MAP1B distribution along the axon length and average velocity of MAP1B transport in the axon. This allows the optimization approach to be used to find values of model kinetic constants that give the best fit with published experimental data. The effects of decreasing the value of cargo diffusivity on the diffusion-driven component of SAT and decreasing the value of dynein velocity on the retrograde motor-driven component of SAT were investigated. We found that for the case when protein diffusivity and dynein velocity are very small, it is possible to obtain an analytical solution to model equations. We found that, in this case, the protein concentration in the axon is uniform. This shows that anterograde motor-driven transport alone cannot simulate a variation of cargo concentration in the axon. Most proteins are non-uniformly distributed in axons. They may exhibit, for example, an increased concentration closer to the synapse. The need to reproduce a non-uniform distribution of protein concentration may explain why SAT is bidirectional (in addition to an anterograde component, it also contains a retrograde component).

On photonic tunnelling and the possibility of superluminal transport of electromagnetic energy

Motivated by the increased interest in experiments in which light appears to propagate by tunnelling at superluminal velocity, the Lorentz invariant theory proposed by Partha Ghose to explain these surprising effects is revisited. This theory is based on the Harish-Chandra formalism, which describes the relativistic dynamics of a massless spin-1 boson, like a photon. By this formalism, the Bohmian average transport velocity of the electromagnetic energy is formulated. It is proved that this velocity can be superluminal if the dielectric making the waveguide is non-absorptive and non-dispersive. This result is validated in the framework of quantum electrodynamics, demonstrating that the average velocity of the photon inside the waveguide is given by the contribution of instantaneous superluminal velocities. This theory, therefore, suggests the optimal conditions for designing the optical devices capable of locally transporting electromagnetic energy at superluminal velocities mitigating signal attenuation.

Simulation of solute transport behaviors in saturated karst aquifer system

The karst development makes aquifer have strong anisotropy and heterogeneity. In order to reveal the characteristics of solute transport in the karst fissure–conduit aquifer system, this study presents a physical model of fissure–conduit in laboratory experiments to carry out the solute transport simulation. In this paper, the tracer tests of fissure–conduit combination, fissure, and conduit solute transport process in saturated flow are designed. We found that different aquifer structures and tracer injection points have an influence on the shape of the breakthrough curve. Besides, the two-dimensional dispersion model of tracer injection of the instantaneous point was used to calculate the dispersion parameters of each group of experiments. Then, the dynamic responses of the linear distance (x) between the injection point and the receiving point, initial time (t0), peak time (tm), peak concentration (cm), average tracer transport velocity (V), and porosity (p) of aqueous media to the longitudinal dispersion coefficient are discussed. In addition, according to the measured data, Gaussian multi-peak fitting can be used to reflect the overall shape and change trend of the multi-peak BTC. These results demonstrate the solute transport behaviors in the saturated karst aquifer system, which have important reference significance for solving the engineering environmental problems in the karst area.

External-field-induced dynamics of a charged particle on a closed helix.

We investigate the dynamics of a charged particle confined to move on a toroidal helix while being driven by an external time-dependent electric field. The underlying phase space is analyzed for linearly and circularly polarized fields. For small driving amplitudes and a linearly polarized field, we find a split up of the chaotic part of the phase space, which prevents the particle from inverting its direction of motion. This allows for a nonzero average velocity of chaotic trajectories without breaking the well-known symmetries commonly responsible for directed transport. Within our chosen normalized units, the resulting average transport velocity is constant and does not change significantly with the driving amplitude. A very similar effect is found in case of the circularly polarized field and low driving amplitudes. Furthermore, when driving with a circularly polarized field, we unravel a second mechanism of the split up of the chaotic phase space region for very large driving amplitudes. There exists a wide range of parameter values for which trajectories may travel between the two chaotic regions by crossing a permeable cantorus. The limitations of these phenomena, as well as their implication on manipulating directed transport in helical geometries are discussed.

Erosion, transport and deposition of a sediment replenishment under flood conditions

AbstractRiver reaches downstream of dams with constant residual discharge often lack sediment supply and periodic high flows due to dam sediment retention and flow regulation, respectively. To test a novel multi‐deposit methodology for defining environmental flows for activating the dynamics of the river morphology downstream of dams, a flood was released from Rossens Dam in Switzerland. This event was combined for the first time with a multi‐deposit configuration of sediment replenishment consisting of four artificial deposits allocated as alternate bars along the riverbanks as a restoration measure. To validate the sediment transport behaviour observed in laboratory tests, stones were equipped with radiofrequency identification (RFID) passive integrated transponder (PIT) tags, a fixed antenna was installed at the river bed and a mobile antenna was used to enable the investigation of the erosion, transport and deposition of replenished sediments. The duration of the erosion period was determined for the tracked stones, and average transport velocities were found to be on the order of 10–3 m/s. To estimate the erosion efficiency of the flood, defined as the eroded tagged stones compared with the released water volume, the hydrograph was divided into different periods: rising limb, constant peak discharge, decreasing limb. During the rising limb of the flood, which lasted for 20% of the total flood duration, more than 40% of the PIT tags were transported. The defined erosion efficiency is a measure to support the hydrographic design of artificial flood releases from dams. The deposition of tagged stones resulted in a repeating cluster formation, as expected from previous laboratory experiments, creating an increase in hydraulic habitat diversity. Comparison of the results obtained in the field and from laboratory experiments confirmed the robustness of the multi‐deposit sediment replenishment method. Combined with the knowledge gained on the erosion efficiency, these results could motivate further applications and research into multi‐deposit sediment replenishment techniques as a habitat‐oriented river restoration measure. © 2020 John Wiley & Sons, Ltd.

Transport behavior of pressure-driven electrolyte solution through a surface-charged nanochannel

The transport behavior of a pressure-driven electrolyte solution through a surface-charged nanochannel is investigated using molecular dynamics (MD) simulations. Similar to pure water, the relationship between the applied pressure (P) and the average transport velocity () of the electrolyte solution is roughly linear, which matches with the theoretical solution very well. The friction coefficient λ is used to describe the transport behavior (a higher λ leads to a lower ), which scales with the slope of the P- relationship and increases with the increases of both the charge density of the channel wall σ and the electrolyte concentration n. The physical mechanism is found as follows: the solid–liquid interaction energy between the channel wall and the liquid inside the channel decreases with both σ and n (being more negative), which makes it more difficult for the liquid boundary layer to slide against the channel wall, leading to a higher λ. In addition, the increase of σ also causes a significant decrease of the liquid–liquid interaction energy but the opposite effect is found with the increase of n. However, λ increases with the increase of both σ and n, suggesting that the relationship between λ and the liquid–liquid interaction energy is more complicated for an electrolyte solution, different from the corresponding result of pure water.

Characterization of ancestral myosin XI from Marchantia polymorpha by heterologous expression in Arabidopsis thaliana.

SummaryPrevious studies have revealed duplications and diversification of myosin XI genes between angiosperms and bryophytes; however, the functional differentiation and conservation of myosin XI between them remain unclear. Here, we identified a single myosin XI gene from the liverwort Marchantia polymorpha (Mp). The molecular properties of Mp myosin XI are similar to those of Arabidopsis myosin XIs responsible for cytoplasmic streaming, suggesting that the motor function of myosin XI is able to generate cytoplasmic streaming. In cultured Arabidopsis cells, transiently expressed green fluorescent protein (GFP)‐fused Mp myosin XI was observed as some intracellular structures moving along the F‐actin. These intracellular structures were co‐localized with motile endoplasmic reticulum (ER) strands, suggesting that Mp myosin XI binds to the ER and generates intracellular transport in Arabidopsis cells. The tail domain of Mp myosin XI was co‐localized with that of Arabidopsis myosin XI‐2 and XI‐K, suggesting that all these myosin XIs bind to common cargoes. Furthermore, expression of GFP‐fused Mp myosin XI rescued the defects of growth, cytoplasmic streaming and actin organization in Arabidopsis multiple myosin XI knockout mutants. The heterologous expression experiments demonstrated the cellular and physiological competence of Mp myosin XI in Arabidopsis. However, the average velocity of organelle transport in Marchantia rhizoids was 0.04 ± 0.01 μm s−1, which is approximately one‐hundredth of that in Arabidopsis cells. Taken together, our results suggest that the molecular properties of myosin XI are conserved, but myosin XI‐driven intracellular transport in vivo would be differentiated from bryophytes to angiosperms.

Research on solute transport behaviors in the lacunar-canalicular system using numerical simulation in microgravity

BackgroundThe lack of mass transfer in microgravity might be the underlying cause of disuse osteoporosis in astronauts after long-term space flights. The osteons are cylindrical structures and are the main structural units of the diaphysis in long bones. MethodsA multi-scale 3D fluid-solid coupled finite element model of osteon with a two-stage pore structure was developed using COMSOL software in order to investigate solute transport behaviors in the lacunar-canalicular system (LCS) induced by physiological strain loading. Certain small molecules that are necessary as solutes in tissue fluid for osteocyte metabolism were simplified to micro-particles. A comparative analysis of solute transport behaviors in the LCS induced by physiological strain loading was conducted with a frequency of 0.2–2.5 Hz in microgravity and the Earth's gravitational fields. ResultsThe average velocity of solute transport in lacunae in microgravity was 2–3 orders of magnitude lower than in Earth's gravitational field. The number of particles that represented solute transport quantity in the middle and deep lacunae increased steadily with a load frequency within the Earth's gravitational field. However, it differed based on the load frequency in microgravity, with the number of particles increasing with frequencies in the range of 0.2–0.5 Hz and 0.8–2 Hz, and decreasing with frequencies in the range of 0.5–0.8 Hz. ConclusionsA moving load with appropriate frequency could promote solute transport to the middle and deep lacunae, effectively preventing apoptosis of deep osteocytes due to a lack of nutrients. The results of this study provided theoretical guidance for preventing bone loss in astronauts during long-term space flights.

Development of a quantitative transport-time-based groundwater vulnerability model for non-point-source pollution in karst aquifers: a conceptual approach and example from the Tanour and Rasoun spring catchment, north-western Jordan

A quantitative transport-time-based vulnerability assessment approach for non-point-source pollution using a spatially distributed geographic information system (GIS)-generated topographic model was developed for the karst aquifer system feeding the Tanour and Rasoun springs in NW Jordan. The approach implies the assessment of the groundwater residence times in different compartments of the karst system, i.e. the epikarst, the vadose zone and the phreatic system. Groundwater transport times within the epikarst zone were determined by employing two main variables: (1) the length of the flow path, and (2) the transport velocity between the assumed point of subsurface infiltration into the soil and the location for the actual groundwater recharge at the ephemeral streams. Sub-horizontal lateral flow is assumed for the epikarst. The base-flow recession curve method was employed to estimate the effective, average and catchment-wide transmissivity of the epikarst. Based on the calculated transmissivity, three different hydraulic conductivity values were assumed to assess the effect of the unknown average saturated thickness of the epikarst. The developed method was validated by independent measurements of the transport-time-based on the δ18O breakthrough signal in the spring catchment discharge, following a recharge event. The transport-time distribution map, calculated based on flow-path length towards the streams and average solute transport velocity, shows high correlation with the catchment-averaged stable isotopes’ breakthrough curves. Because of the intensive karstification below the stream bed, residence times in the vadose and the phreatic zones can be assumed to be negligible compared to the transport times in the epikarst.

Directed transport properties of double-headed molecular motors with balanced cargo

Under the background of subdiffusion in cytosol, the nonlinear-coupling fractional Langevin equations is proposed to model the stepping modes of the double-headed molecular motor: inchworm and hand-over-hand mechanisms, and the transport properties in flashing asymmetrical periodic potential are investigated. By numerical simulations, the influences of noise intensity, height of potential barriers, and external load force on the average velocity of coupled particles current in the overdamped limit are assessed. With the exception of conventional directed transport, we observe some anomalous phenomena, including inverse transport and cooperative transport, which cannot be described by the integral-order models. Moreover, the average transport velocity varies non-monotonously with the noise intensity and the height of potential barrier, which shows there exists generalized stochastic resonance (GSR) phenomenon in proposed coupled fractional systems. The results also indicate that the damping force involving the weighted sum of historical velocity leads to the nonlocal memory property and blocks the traditional dissipative behaviors, and it even plays a cooperative role of the driving force in drift motion.

An experimentally-achieved information-driven Brownian motor shows maximum power at the relaxation time

We present an experimental realization of an information-driven Brownian motor by periodically cooling a Brownian particle trapped in a harmonic potential connected to a single heat bath, where cooling is carried out by the information process consisting of measurement and feedback control. We show that the random motion of the particle is rectified by symmetry-broken feedback cooling where the particle is cooled only when it resides on the specific side of the potential center at the instant of measurement. Studying how the motor thermodynamics depends on cycle period τ relative to the relaxation time τB of the Brownian particle, we find that the ratcheting of thermal noise produces the maximum work extraction when τ ≥ 5τB, while the extracted power is maximum near τ = τB, implying the optimal operating time for the ratcheting process. In addition, we find that the average transport velocity is monotonically decreased as τ increases and present the upper bound for the velocity.

Fluid Transport in Partially Shielded Electrowetting on Dielectric Digital Microfluidic Devices

Theoretical and experimental approaches verifying the fluidic operation of a partially shielded digital microfluidics device are presented in this paper. This paper is motivated by recent demand from the synthetic biology community for electrowetting on dielectric (EWD) enabled in-droplet electroporation, but is generalizable to a range of EWD applications that require shielding structures to be patterned on the EWD. An electrode patterned in an additional metal layer on the insulator that supports EWD actuation reduces the effective strength of the EW force due to dielectric shielding at the droplet contact line. A numerical model was developed to predict the impact of the partially shielding electrode on threshold voltage, EW force, fluid velocity, and droplet transport time. Compared with a batch of devices lacking the extra electrode, the presence of the added metal layer resulted in a 29% increase in threshold voltage, an 82% increase in transport time, and a 44% decrease in average transport velocity. Each trend agrees with the simulation results obtained from the fluid transport model. These results support the development of design rules for microfluidic devices that require partially shielding metal layers to integrate with EWD device architectures. [2016-0034]

Axonal transport cargo motor count versus average transport velocity: is fast versus slow transport really single versus multiple motor transport?

Cargos have been observed exhibiting a "stop-and-go" behavior (i.e. cargo "pause"), and it has generally been assumed that these multi-second pauses can be attributed to equally long pauses of cargo-bound motors during motor procession. We contend that a careful examination of the isolated microtubule experimental record does not support motor pauses. Rather, we believe that the data suggests that motor cargo complexes encounter an obstruction that prevents procession, eventually detach and reattach, with this obstructed-detach-reattach sequence being observed in axon as a "pause." Based on this, along with our quantitative evidence-based contention that slow and fast axonal transport are actually single and multi-motor transport, we have developed a cargo level motor model capable of exhibiting the full range of slow to fast transport solely by changing the number of motors involved. This computational model derived using first-order kinetics is suitable for both kinesin and dynein and includes load-dependence as well as provision for motors encountering obstacles to procession. The model makes the following specific predictions: average distance from binding to obstruction is about 10 μm; average motor maximum velocity is at least 6 μm/s in axon; a minimum of 10 motors is required for the fastest fast transport while only one motor is required for slow transport; individual in-vivo cargo-attached motors may spend as little as 5% of their time processing along a microtubule with the remainder being spent either obstructed or unbound to a microtubule; and at least in the case of neurofilament transport, kinesin and dynein are largely not being in a "tug-of-war" competition.

Can numerical modeling help understand the fate of tau protein in the axon terminal?

In this paper, we used mathematical modeling to investigate the fate of tau protein in the axon terminal. We developed a comprehensive model of tau transport that accounts for transport of cytosolic tau by diffusion, diffusion transport of microtubule (MT)-bound tau along the MT lattice, active motor-driven transport of MT-bound tau via slow axonal transport mechanism, and degradation of tau in the axon due to tau's finite half-life. We investigated the effect of different assumptions concerning the fate of tau in the terminal on steady-state transport of tau in the axon. In particular, we studied two possible scenarios: (i) tau is destroyed in the terminal and (ii) there is no tau destruction in the terminal, and to avoid tau accumulation we postulated zero flux of tau at the terminal. We found that the tau concentration and percentage of MT-bound tau are not very sensitive to the assumption concerning the fate of tau in the terminal, but the tau's flux and average velocity of tau transport are very sensitive to this assumption. This suggests that measuring the velocity of tau transport and comparing it with the results of mathematical modeling for different assumptions concerning tau's fate in the terminal can provide information concerning what happens to tau in the terminal.

The directional transport phenomenon in fractional logarithm coupled system under a non-periodic external force

Using the fractional calculus theory, we investigate the directional transport phenomenon in a fractional logarithm coupled system under the action of a non-periodic external force. When a Brownian particle moves in the media with memory such as viscoelastic media, the system should be modeled as a nonlinear fractional logarithm coupled one. Using the method of fractional difference, we can solve the model numerically and discuss the influences of the various system parameters on the average transport velocity of the particles. Numerical results show that: 1) The directional transport phenomenon in this fractional logarithmic coupled model appears only when the external force exists, and the value of the average transport velocity of the particles increases with increasing external force. 2) When the fractional order of the system is small enough, the damping memory has a significant impact on the average transport velocity of the particles. Furthermore, the average transport velocity of the particles has an upper bound (although it is very small), no matter how the external force, coupled force and the intensity of noise change, the average transport velocity of the particles is no more than the upper bound. When there is no external force and the damping force is big enough, the directional transport phenomenon disappears. 3) When the fractional order of the system and the external force are big enough, although the directional transport phenomenon appears, the coupled force and the intensity of noise have no impact on the system. 4) Only when the external force is small enough, could the coupled force and noise intensity influence the average transport velocity of the particles. In this situation, the directional transport phenomenon appears when the fractional order of the system is big enough, and the average transport velocity of the particles changes along with the change of the coupled force and the noise intensity.

Velocity measurement of the liquid–solid flow in a vertical pipeline using gamma-ray absorption and weighted cross-correlation

Developing technology for the deep-sea mining of polymetallic nodules requires, theoretical analyses, simulation and numerous experimental studies. In this paper authors focused on nuclear methods adoption to velocity of solid phase measurement in an extremely hard and varying environment. Selected results of the experimental studies of two-phase liquid–solid particles flow in a vertical pipeline obtained by probing with photon beams are presented. With the use of the sealed 241Am isotopes emitting gamma radiation of 59.5keV, and the scintillation probes with NaI(TI) detectors, the average transport velocity for ceramic models representing natural polymetallic nodules were determined. In the paper for analysis of the signals coming from the probes, the cross correlation function (CCF) and its modifications consisting in the combination of the CCF with such procedures as the average square difference function (ASDF) and the average magnitude difference function (AMDF) were used. An example of measurement is presented and its resulting uncertainties determined. In described experiment the relative values of the combined uncertainty of solid particles average velocity estimation are equal to: 3.2% for the CCF, 3.0% for the CCF/AMDF and 2.8% for the CCF/ASDF.

A comparison between the diffusion–reaction and slow axonal transport models for predicting tau distribution along an axon

This paper developed equations describing steady-state tau distributions for three versions of the diffusion-reaction model of tau transport: a model with constant kinetic rates, a model that additionally accounts for tau diffusion along microtubules (MTs) and a model with a modulated rate of tau attachment to MTs. We demonstrated that, for the model with constant kinetic rates, the concentration of free tau in the cytoplasm was determined by a single dimensionless parameter that represents the ratio of the diffusion time (the time it takes tau to diffuse from the axon hillock to the axon tip) to the half-life of tau. We also developed a model based on the hypothesis that tau is actively transported. Analytical solutions for some special situations were obtained. The model predictions were compared with experimentally measured tau distributions in axons reported in Black et al. (1996, J. Neurosc., 16: , 3601-3619), and based on these comparisons, we discussed the performance of various models. We demonstrated the significance of modulation of the tau attachment rate to MTs in the diffusion-reaction model. On the other hand, the active transport model predictions were consistent with experimental data even with constant kinetic rates. For short axons (up to 600 μm in length) the predicted average transport velocity of tau was in the experimentally reported range for both the diffusion-reaction and active transport models, but for the active transport model the average tau velocity was larger.