Mean Transport Velocity Research Articles

Estimating a mean transport velocity in the marginal ice zone using ice–ocean prediction systems

Abstract. Understanding the transport of objects and material in the marginal ice zone (MIZ) is critical for human operations in polar regions. This can be the transport of pollutants, such as spilled oil, or the transport of objects, such as drifting ships and search and rescue operations. For emergency response, the use of environmental prediction systems are required which predict ice and ocean parameters and are run operationally by many centres in the world. As these prediction systems predict both ice and ocean velocities, as well as ice concentration, it must be chosen how to combine these data to best predict the mean transport velocities. In this paper we present a case study of four drifting buoys in the MIZ deployed at four distinct ice concentrations. We compare short-term trajectories, i.e. up to 48 h lead times, with standard transport models using ice and ocean velocities from two operational prediction systems. A new transport model for the MIZ is developed with two key features aimed to help mitigate uncertainties in ice–ocean prediction systems: first, including both ice and ocean velocities and linearly weighting them by ice concentration, and second, allowing for a non-zero leeway to be added to the ice velocity component. This new transport model is found to reduce the error by a factor of 2 to 3 for drifters furthest in the MIZ using ice-based transport models in trajectory location after 48 h.

Simulation Study on the Mass Transport Based on the Ciliated Dynamic System of the Respiratory Tract

To study the mass transport of mucociliary clearance of the human upper respiratory tract, a two-dimensional mass transport model based on the ciliated movement was established by using the immersed boundary-lattice Boltzmann method (IB-LBM). In this model, different characteristics of the mucus layer (ML) and the periciliary liquid (PCL) were taken into account. A virtual elastic membrane was introduced to divide the two layers dynamically. All moving boundaries that were involved in the present simulation were modeled with the immersed boundary. The Newtonian fluid was used to model the flow in PCL, and the viscoelastic fluid based on the Oldroyd-B model was used for the flow in ML; the two types of flow were both solved by the LBM framework. Based on the model, the ML thickness, the cilia density, and the phase difference of adjacent cilia were regulated, respectively, to study the transport velocity of the ML. In addition, the motion law of solid particles in PCL was also studied. According to the results, four primary conclusions were drawn. (1) At a given beating pattern, the increase of the ML thickness will decrease its transport velocity. (2) Increasing the cilia density can promote the mean transport velocity of the ML. (3) By raising the phase difference of adjacent cilia to a certain scope, the transport of ML can be accelerated. (4) In PCL, particles initially located on the upper part of the cilia tend to migrate upward and then get close to the ML. The above study can provide some reasonable explanations for the mechanism of the mucociliary clearance system, which is also helpful to the further understanding of the mass transport principle of the human upper respiratory tract.

Investigation of the Effect of Geometric Parameters on EWOD Actuation in Rectangular Microchannels

Efficient actuation of liquid slugs in microfluidic circuits is a matter of interest in droplet-based microfluidic (DMF) applications. In this paper, the electrowetting on dielectric (EWOD) actuation of a liquid slug fully confined in a microchannel is studied. A set of experiments are conducted in which the mean transport velocity of a liquid slug enclosed in a microchannel of rectangular cross section and actuated by EWOD method is measured. A printed circuit board-based (PCB-based) microfluidic chip is used as the platform, and the transport velocity of the slug is measured by processing the images recorded by a high-speed camera while the slug moves in the channel. To investigate the effect of microchannel geometry on the mean transport velocity of the slugs, different channel heights and widths (ranging between 250−440μm and 1–2 mm, respectively) as well as different liquid volumes (ranging between 2.94and5.15μL) are tested and slug velocities up to 14.9 mm/s are achieved. A theoretical model is also developed to analyze the effect of involved parameters on the transport velocity. The results show that, within the range of design parameters considered in this study, for a constant slug volume and channel width, increasing the channel height enhances the velocity. Moreover, keeping the slug volume and channel height fixed, the transport velocity is increased by enlarging the channel width. An inverse proportionality between the slug length and velocity is also observed. These results are also shown to agree with the theoretical model developed.

Radiometric methods in the measurement of particle-laden flows

The article discusses a study on hydrotransport of solid particles (ceramic models of polymetallic nodules) in a vertical pipeline using two different radioisotope methods: tracer and gamma-ray absorption. The radiotracer method makes it possible to determine the velocity of selected solid particles representing specified size fractions while the absorption method enables measurement of mean transport velocity of the entire dispersed phase. The measurements were performed with the use of NaI(Tl) scintillation detectors, sealed linear sources of radiation Am-241 with the energy of 59.54keV and isotope Tc-99m with gamma radiation energy of 140.51keV. The experiments were carried out in a pipeline with an internal diameter of 150mm, for three different water velocities in the range of 1.5–3.6m/s and three different sizes of ceramic models with size up to 60mm. Analyses of the detector signals, in measurements based on both tracer and absorption technique, applied cross-correlation function (CCF). It was shown that with the same water velocity different fractions of solid particles have moved with different velocities and the lowest velocities were obtained for the particles with the largest diameters. This enabled interpretation of the CCF in absorption measurements as a distribution of possible interval times for the specific fractions of conveyed particles.

Factors controlling temporal variability of near-ground atmospheric <sup>222</sup>Rn concentration over central Europe

Abstract. Concentration of radon (222Rn) in the near-ground atmosphere has been measured quasi-continuously from January 2005 to December 2009 at two continental sites in Europe: Heidelberg (south-west Germany) and Krakow (southern Poland). The atmosphere was sampled at ca. 30 and 20 m above the local ground. Both stations were equipped with identical instruments. Regular observations of 222Rn were supplemented by measurements of surface fluxes of this gas in the Krakow urban area, using two different approaches. The measured concentrations of 222Rn varied at both sites in a wide range, from less than 2.0 Bq m−3 to approximately 40 Bq m−3 in Krakow and 35 Bq m−3 in Heidelberg. The mean 222Rn content in Krakow, when averaged over the entire observation period, was 30% higher than in Heidelberg (5.86 ± 0.09 and 4.50 ± 0.07 Bq m−3, respectively). Distinct seasonality of 222Rn signal is visible in the obtained time series of 222Rn concentration, with higher values recorded generally during late summer and autumn. The surface 222Rn fluxes measured in Krakow also revealed a distinct seasonality, with broad maximum observed during summer and early autumn and minimum during the winter. When averaged over a 5-year observation period, the night-time surface 222Rn flux was equal to 46.8 ± 2.4 Bq m−2 h−1. Although the atmospheric 222Rn levels at Heidelberg and Krakow appeared to be controlled primarily by local factors, it was possible to evaluate the "continental effect" in atmospheric 222Rn content between both sites, related to gradual build-up of 222Rn concentration in the air masses travelling between Heidelberg and Krakow. The mean value of this build-up was equal to 0.78 ± 0.12 Bq m−3. The measured minimum 222Rn concentrations at both sites and the difference between them was interpreted in the framework of a simple box model coupled with HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) analysis of air mass trajectories. The best fit of experimental data was obtained for the mean 222Rn flux over the European continent equal to 52 Bq m−2 h−1, the mean transport velocity of the air masses within the convective mixed layer of the planetary boundary layer (PBL) on their route from the Atlantic coast to Heidelberg and Krakow equal to 3.5 m s−1, the mean rate constant of 222Rn removal across the top of the PBL equal to the 222Rn decay constant and the mean height of the convective mixed layer equal to 1600 m.

Transport properties of fractional coupled Brownian motors in flash ratchet potential

Based on the fractional calculus theory, the transport model of fractional coupled Brownian motors in flashing ratchet potential is established. Using the fractional difference, the numerical solution of the model is obtained, and the directional transport properties at various parameters are investigated. Numerical results show that in fractional ratchet system, the fractional order and spring constant not only affect the transport velocity of the particles, but also reverse the current direction. Moreover, when the fractional order is fixed, the generalized stochastic resonance phenomena are observed in the mean transport velocity as the noise density, spring constant or the depth of the ratchet potential varies.

Evaluation of Nonparametric Shape Measures for Solute Breakthrough Curves

A better understanding of the relationships among preferential solute transport, hydrologic boundary conditions, and site properties will help to improve predictions of the fate of contaminants in the vadose zone. The diversity of mechanisms underlying preferential transport, together with problems of nonuniqueness in fitting models to experimental data, suggests that model‐independent (nonparametric) indicators of solute transport may help to establish such relationships. We therefore investigated 17 distinct nonparametric measures of solute breakthrough curve (BTC) shape using a data set of 115 tracer BTCs sampled from the literature. We tested the shape measures for sensitivity to deconvolution approaches based on Gaussian, lognormal, and gamma probability density functions and the mobile–immobile model. Furthermore, we evaluated collinearities among the 17 shape measures. Most deconvolution approaches gave very good fits to the data, with coefficients of determination larger than 0.98. Dual‐domain transfer functions were superior to single‐domain ones, even after accounting for measures of parsimony. The least sensitive shape measures were the normalized first temporal moment, the mean transport velocity, the apparent dispersion coefficient, and the relative arrival time of the first 5 and 85% of the tracer mass. In contrast, the skewness and kurtosis were most sensitive to the choice of deconvolution approach, even for BTC experiments with very long data series of more than eight water‐filled pore volumes. The relative arrival time of the first 5% of the tracer mass was identified as the most robust shape parameter that could serve as an indicator of preferential flow and transport.

Theoretical cosmogenic nuclide concentration in river bed load clasts: Does it depend on clast size?

Terrestrial Cosmogenic Nuclides (TCNs) have been widely used to date the exposure of alluvial surfaces and to estimate catchment-scale erosion rates. However, TCN concentration differences in samples of different grain sizes remain to be fully understood. In order to explore the possibility that river processes generate such differences, we develop a numerical model to calculate along-stream clast-scale TCN concentrations. Using the hillslope model, there is a progressive detachment of successive clasts of specific sizes followed by their instantaneous fall into the river. In the river, transport velocity and TCN concentration evolution in a clast depend 1) on the probability of being trapped in the sediment mixing layer of the river or within an adjacent terrace; 2) on its size which decreases downstream by attrition. The size-dependent transport law corresponds to the partial transport state in a river. We model the distribution of TCN concentrations in different clast size fractions in the 0–5 cm radius range for catchments in steady-state erosion, and for catchments experiencing sedimentation. We propose that clast attrition tends to increase the variance of TCN concentrations of the small clast size fractions because these fractions incorporate initially big clasts that travelled a long distance in addition to small clasts contributed near the outlet. We obtained numerous clast size–TCN concentration correlations, positive or negative, the significance of which depends on the initial clast size distribution, hillslope erosion rate, river length and lithology. For an equilibrium catchment, even large, we found that the addition of TCN concentration acquired during river transport is negligible compared to TCN concentration acquired on a hillslope, although a clast size–TCN concentration relationship can result from or be modified by clast attrition. On the contrary, aggrading catchments may show a significant clast size-dependent TCN concentration increase during river transport. This may introduce a small bias in the TCN-derived catchment erosion rate, but it could be used positively to quantify the mean transport velocity of clasts of different sizes over thousands of years. In addition, the lack of correlation between TCN concentration and clast size does not imply that the mean transport velocity is the same for all clast size fractions. Overall, our study provides an alternative explanation for observed clast size-dependent TCN concentrations and brings to the fore the need for measuring TCN concentration in larger clast size fractions than is usually done. To see if the byproducts of abrasion dilute or increase the TCN concentration of sand, all products should be included in a future study.

A model for biased diffusion of collagenase along collagen fibrils

We present a model to describe the biased diffusion of a collagenase along collagen fibrils. Based on the structures of collagen fibril and collagenase, the interaction is described by a one-dimensional potential that is symmetric in the region of no cleavage and asymmetric in the cleavage region. We show that the mean velocity of the unidirectional diffusion of the collagenase depends on the three parameters: the asymmetric ratio of the local potential in the cleavage region, the chemical reaction rate of proteolysis and the jumping rate of collagenase between two neighboring tracks. We calculate the correlation function and the mean transport velocity for both wild-type and mutant collagenases along collagen fibrils, the results of which are consistent with the previous experiments.

Drag reduction and improvement of material transport in creeping films

It is widely accepted that for bodies in turbulent flows a reduction of skin friction can be reached if the surface of the body is provided with small ridges aligned in the local flow direction. This surprising and counterintuitive phenomenon is called the shark-skin effect, motivated from the dermal surface morphology of sharks. In the present article we examine the possibility of resistance reduction due to a rippled surface topography in Stokes flow. We especially analyse the influence of wall riblets perpendicular to the flow direction on the mean transport velocity in gravity-driven creeping film flows following the idea that eddies generated in the valleys of the riblets act like fluid roller bearings and hence may reduce drag. Using a theoretical treatment of the Stokes equations with complex function theory, parameter studies with varying flow rate, bottom amplitude and bottom shape are presented. For the given bottom shapes the maximum enhancement of transport velocity is found by optimising the film thickness.

Variational inverse parameter estimation in a long‐term tidal transport model

A variational data assimilation scheme for parameter estimation is developed and tested with a long‐term tidal transport model. Long‐term advective transport in a tidal environment is represented by the Lagrangian mean transport velocity that can be decomposed into two parts: the Eulerian transport velocity and the curl of a three‐dimensional vector potential A. In the present study, the vector potential A is treated as a poorly known parameter field, and the optimal long‐term advection transport field is obtained through adjusting the vector potential using a variational inverse data assimilation method to obtain the best fit between the model output and the data. Experiments were performed in an idealized estuary. Results showed that variational inverse data assimilation could successfully retrieve poorly known parameters in a long‐term tidal transport model. The results also showed that the smooth best fit model state could be retrieved using a penalty method even when observed data are too sparse or contain noisy signals.

Quantification of object manipulation in children with cerebral palsy.

A shape-posting task was studied in 30 control, eight hemiplegic and 10 diplegic children, to determine how differences in object manipulation between such children could be quantified. Conical, cylindrical and triangular-shaped objects were posted through a hole in a perspex screen, three times each with both preferred and non-preferred hands. Four variables were defined to describe kinematic aspects of the task: adjustment inefficiency, mean transport velocity, adjustment distance to be completed in the placing phase and adjustment velocity in the placing phase. As expected, total task time was increased in subjects with cerebral palsy and with more complex shapes, and reduced by repetition. The four kinematic variables reduced the variation in task time between individual children by 79%, between sets of like objects by 62%, and the residual variation by 63%. Adjustment inefficiency was increased and mean transport velocity reduced in subjects with cerebral palsy, whereas repetition had the opposite effect. It is suggested that combined alterations in adjustment inefficiency and transport velocity reflect changes in the intrinsic uncertainty of a movement and that this quantity is decreased by repetition and increased in cerebral palsy.

Tracer transport in a stochastic continuum model of fractured media

A stochastic continuum model of a fractured medium conditioned on a specific set of field data is developed. Both the more conductive fractures and the less permeable matrix are generated within the framework of a single‐continuum stochastic model based on nonparametric indicator geostatistics. In the stochastic model the fracture zones are distinguished from the matrix by imposing a long‐range correlation structure for a small fraction (the highest approximately 11%) of the hydraulic conductivity in the preferred planes of fracture zones. Results of flow arid transport simulation in three dimensions (3D) are used to illustrate the large spatial variability of point measurements, but for spatially integrated quantities the variability is reduced and results become less sensitive to correlation structure. Therefore it is suggested that spatially integrated quantities may be a more appropriate choice for predicting flow and transport in a strongly heterogeneous medium in that they are more commensurate with the level of our ignorance of the site. The issue of spatial variability giving rise to uncertainty in the site characterization of a heterogeneous medium and the prediction of transport results is also addressed. Simulations are carried out for 3D transport from point tracer sources at hundreds of locations in the medium. The breakthrough curve from each point source release is characterized by two parameters: the mean transport velocity and the dispersion coefficient. The results are presented as a statistical distribution of the transport parameters, thus quantifying the uncertainty in predicting flow and transport based on a limited amount of site characterization data.

Mobilization of cesium in organic rich soils: Correlation with production of dissolved organic carbon

A study of the downward movement of 137Cs in an undisturbed forest soil is presented. Seasonal variations and depth profiles of 137Cs activities were measured in seepage water, which is the transport medium for the downward movement of anthropogenic substances in soils. Furthermore the correlation of 137Cs mobilization and production of dissolved organic carbon (DOC) was investigated. Seasonal variations of both 137Cs and DOC fluxes in the seepage water in a depth of 5 cm depth were observed, where the maximum fluxes in the summer months were about one order of magnitude higher than the minimum fluxes in the winter months. 137Cs fluxes are found to be correlated with DOC fluxes with a correlation coefficient of r = 0.63, and both are highly correlated with soil temperature. This indicates that cesium is bound to soil organic material. The production of DOC is controlled by microbial decomposition of soil organic matter and we assume that this holds true for the 137Cs release as well. The actual transport velocity (0.2 ± 0.14 mm/a) of 137Cs (calculated by the weighed mean of 137Cs concentration in the seepage water and the total 137Cs content of the soil) is about one order of magnitude less than the mean transport velocity (1.2 ± 0.3 mm/a) over the past 25 years (calculated from the 137Cs depth profile). It is possible that the transport velocity of 137Cs in undisturbed soils decreases with time as it binds to aged organic material which is less easily decomposable than fresh organic material.

Assessment of slow axonal transport in lead-exposed rats

To evaluate the effect of lead on slow axonal transport, mean transport velocity (Vmean) of radiolabeled proteins in the motor fibers of the sciatic nerve was calculated by simulating the distribution of radioactivity along the nerve 2 weeks after intraspinal injection of L-[35S] methionine in eight rats given drinking water containing lead acetate for 13 weeks. The transport of individual radiolabeled proteins was also inspected visually by fluorography. It was observed that the Vmean was significantly slowed in the lead-exposed rats and was correlated with blood lead concentration; fluorography indicated that the transport of neurofilament proteins and of tubulins was mildly retarded in the most severely affected lead-exposed rat. These findings suggest that slow axonal transport was impaired by lead. Further study using a large number of animals will be necessary to confirm the findings of the present study.

IMDIS — An integrated approach to Gaussian dispersion modeling

Gaussian dispersion models are well established tools for the estimation of ground level concentrations and regulatory purposes. These models are attractive for microcomputers, since the corresponding programs are fast and the input source and meteorological data are usually available. The purpose of this paper is to present a multisource bi-Gaussian dispersion computer program (IMDIS) applicable to stationary point sources, specifically written for the Apple Macintosh microcomputer. The program takes advantage of a user-friendly graphical interface for interactive data entry and retrieval and for displaying concentration isopleths. The model may be adapted to different situations, since it provides several alternatives for the estimation of plume rise, dispersion coefficients, wind profile power law, mean transport velocity and time averaging methods. Powerful numerical non-linear optimization procedures allow for ‘worst-case’ or actual maxima to be determined, independently of the formulas employed within the different submodels. The program was tested with literature data and compared with some other Gaussian models available, and preliminary results suggest its adequacy as a flexible tool for dispersion modeling.

Nasal mucociliary function in the normal newborn

Nasal mucociliary transport has been studied using the seroalbumin-Tc 99m radioisotope method in 10 adults and 10 normal newborns under 28 days of age. The mean transport velocity was 8 and 6 mm/min for the normal adults and newborns, respectively, with no significant differences between the two ( P = 0.07).

Video observations of marine gravel transport

In an analysis of video observations of gravel transport in the West Slent, UK, collective and individual characteristics of 458 ‘bursts’ of bedload have been examined and the transport velocity and distance of 1680 individual particles in a consecutive succession of ‘burst events” determined. Infrequent, long duration, high stress events account for 60% of total transport in only 24% of the total time with the mean free path and transport velocity for particles being 0.16 m and 0.22 m/s, respectively. Clear links between intense intermittent turbulence and bedload transport revealed in this study, suggest progress in modelling requires a clearer understanding of near bed flow structure.

Investigation of partial sputtering of lithium from a binary Al/Li alloy with laser induced fluorescence

Sputtering investigations of an Al/Li alloy containing 9.1 at-% of lithium have been performed for 6 keV helium ion bombardment. Absolute particle densities and velocity distributions of the sputtered neutral lithium atoms were measured with laserinduced fluorescence. The amount of sputtered lithium was found to be constant for target temperatures ranging from room temperature up to 500° C. The mean transport velocity and the sputtering yield of the Li component have been calculated from the measurements. Thermal evaporation of neutral Li atoms could be measured independently of the presence of the helium beam for target temperatures above 300° C. The experimental results indicate that the surface is covered by lithium with at least several atomic layers even under highcurrent ion irradiation.

Slow Component-a of Axonal Transport, Nerve myo-Inositol, and Aldose Reductase Inhibition in Streptozocin-Diabetic Rats

This study measured sugars and polyols, weight/unit length, and slow component-a of axonal transport (SCa) in dorsal root afferents of the sciatic nerves of control rats and rats with streptozocin (STZ)-induced diabetes of 4-wk duration. The effects of two treatments--aldose reductase inhibition [Statil ("Statil" is a trademark; the property of Imperial Chemical Industries PLC.) ICI 128436 at 25 mg/kg/day, p.o.] and myo-inositol supplementation (650 mg/kg/day, p.o.)--were studied in control and diabetic groups. Inclusion of untreated controls and diabetics gave a total of six groups for the study. The treatments were begun on the day after injection of STZ and were maintained throughout the protocol. The sciatic nerves of the diabetic (untreated) rats showed accumulation of sorbitol and fructose, depletion of myo-inositol, and an 8% increase in weight/unit length. All of these abnormalities were prevented by treatment with Statil. Treatment of diabetic rats with myo-inositol prevented its depletion in the sciatic nerve, but did not affect the accumulation of sorbitol and fructose nor the increase in weight/unit length. Neither treatment exerted any apparent effect on body weight, blood glucose, nerve weight, or nerve sugars and polyols in the control rats. The diabetic rats showed a retardation of the wave of transported-labeled protein (shown as increased leftward skewness of the wave) and a reduction in mean transport velocity (calculated as the mean velocity for all segments contributing to the transport wave: 0.96 +/- 0.09 mm/day in diabetics versus 1.15 +/- 0.07 mm/day in controls).(ABSTRACT TRUNCATED AT 250 WORDS)