Total Mass Transport Research Articles

Flow modeling and structural characterization in fungal pellets

Fungal pellets are hierarchical systems that can be found in an ample variety of applications. Modeling transport phenomena in this type of systems is a challenging but necessary task to provide knowledge-based processes that improve the outcome of their biotechnological applications. In this work, an upscaled model for total mass and momentum transport in fungal pellets is implemented and analyzed, using elements of the volume averaging and adjoint homogenization methods departing from the governing equations at the microscale in the intracellular and extracellular phases. The biomass is assumed to be composed of a non-Newtonian fluid and the organelles impervious to momentum transport are modeled as a rigid solid phase. The upscaled equations contain effective-medium coefficients, which are predicted from the solution of adjoint closure problems in a three-dimensional periodic domains representative of the microstructure. The construction of these domains was performed for Laccaria trichodermophora based on observations of actual biological structures. The upscaled model was validated with direct numerical simulations in homogeneous portions of the pellets core. It is shown that no significant differences are observed when the dolipores are open or closed to fluid flow. By comparing the predictions of the average velocity in the extracellular phase resulting from the upscaled model with those from the classical Darcy equation (i.e., assuming that the biomass is a solid phase) the contribution of the intracellular fluid phase was evidenced. This work sets the foundations for further studies dedicated to transport phenomena in this type of systems.

Upscaling mass adsorption and momentum transport in the crown of trees

Airborne chemical species transport and adsorption in the crown of trees are relevant processes with many crucial environmental consequences. This multiphase and multiscale process requires incorporation of momentum transport both in the air and in the solid phases composing the biomass (leaves and branches) and coupling with species mass transport. In this work, an upscaled model for momentum transport and adsorption of chemical species in tree crowns is derived using the method of volume averaging. The model comprises four effective-medium equations, namely: the macroscopic balance equation for momentum transport in the air, which has a Darcy-like structure; the macroscopic equations for total mass and momentum transport, considering the air and deformable leaves and branches; and an unsteady upscaled equation for species mass (diffusive and convective) transport and adsorption at the surface of leaves and branches. These equations are written in terms of effective-medium coefficients that capture the essential microscale information by solving ancillary closure problems in periodic unit cells in the Laplace domain. This allowed evaluating the dynamic functionality of the unsteady adsorption and dispersion coefficients in terms of the Reynolds number, the solid velocity and the adsorption rate. The macroscopic model predictions of the average chemical species concentration were found to be in excellent agreement with direct numerical simulations (i.e., with a relative percent difference smaller than 1%), thus providing a first validation of the upscaled model. Extensions to other systems are briefly discussed.

(Invited) Voltammetric Examination of Carbon Nanoelectrodes Under Mixed Diffusion - Migration Mass Transport Conditions

In general, experiments carried out with nanoelectrodes are similar to those with microelectrodes. However, the extremely increased efficiency of the mass transport to nanoelectrodes results in steady-state current conditions in ultra-short times and high current densities. The transport of electroactive species to the working electrode surface is mainly realized by diffusion. The contribution of migration to the total mass transport is usually eliminated by shortening the thickness of the electrical double layer (EDL) achieved by the addition of supporting electrolyte excess. This simplifies the theoretical description of mass transport to pure diffusion but on the other hand, modifies physicochemical properties, including transport parameters of the analyzed environment. In systems containing a deficiency of supporting electrolyte, migration contributes to mass transport. The transport studies in these systems require the employment of small-sized electrodes (micro- / nanoelectrodes) and potentiostats capable of measuring ultralow currents.Migration introduces an additional variable (electrostatic potential) to the transport expressed by the Nernst-Planck equation. Under the low ionic strength conditions, the transport dynamics depends on the concentration profiles of a substrate, product, cations and anions of supporting electrolyte, and an uncompensated electrostatic potential gradient. In practice, the contribution of migration can be quantitatively related to the support ratio parameter (ξ), defined as the ratio of the concentrations of electroinactive charge carriers (i.e. not involved in the electrode reaction) to the concentration of the electrode reaction substrate. In terms of the ξ parameter, migration has a negligible effect on mass transport under the conditions of high values of the support ratio (ξ > 100). As the support ratio decreases (ξ < 1) the potential gradient occurs due to increased resistivity of the system and, consequently, the total mass transport is affected by the migrational contribution.The problem of diffusion-migration transport in voltammetric experiments involving microelectrodes was treated theoretically and the derived models allow one to predict the voltammograms for various types of electrode processes carried out under the conditions of various concentration of supporting electrolyte. The major factor complicating the theoretical description of mass transport induced by migration is the influence of an EDL. In the system containing a deficiency of supporting electrolyte, EDL may occupy a significant part of the diffusion layers of the substrate and the product of the electrode process. With the decrease of the electrode radius (below 100 nm), the EDL start to overlap with the diffusion layer and significantly affects the transport even in the system containing substantial concentrations of supporting electrolyte.To explore new research domains for nanoelectrodes, the procedures for the fabrication of nanoelectrodes of reproducible parameters and the theoretical description of the mass transport to nanoelectrodes under mixed diffusion-migration transport conditions have to be developed.The ultrasmall electrodes are highly susceptible to electrostatic mechanical and electrochemical damage, leading to the formation of recessed or protruding electrodes with altered current response, which is an additional impediment in the studies with their use. As a result of the damage causing recession, the electrodes lose their current response and give low feedback in their use as probes in scanning electrochemical microscopy (SECM). The damage caused by electrostatic discharging can be avoided by handling and storing the electrodes grounded together with objects in the vicinity.This work demonstrates the voltammetric behavior of the fabricated carbon nanoelectrodes in the presence and absence of supporting electrolyte. The ferrocene derivatives of various charges served as redox probes for the studies of diffusion-migration transport to nanoelectrodes. The obtained results are confronted to the theoretical predictions derived for microelectrodes. They revealed that migration of electroactive species to nanoelectrodes does not introduce significant changes to voltammetric signal as much as for bigger microelectrodes. Moreover, the elimination of supporting electrolyte in most cases led to the poor development of the voltammetric waves at nanoelectrodes. The possible reason may be related to the breakdown of the electroneutrality in the region adjacent to the nanoelectrode, since the electrical double layer for nanoelectrodes may occupy a significant fraction of the transport depletion layer. The uncertainty in the concentrations of ionic impurities (that determine the actual support ratio) in the layer adjacent to the electrode is another factor that may produce unpredictable and, to some extent, random voltammetric behavior of charged redox probes at nanoelectrodes in the absence of supporting electrolyte.

Surface Diffusion in Nanopores and Its Effects on Total Mass Transport in Shale Gas Reservoirs

Surface Diffusion in Nanopores and Its Effects on Total Mass Transport in Shale Gas Reservoirs

Exploring plastic transport dynamics in the Odaw river, Ghana

Plastic pollution in rivers threatens ecosystems, increases flood risk due to its accumulations at hydraulic structures and its final emissions into the ocean threaten aquatic life, especially and probably most in coastal urbanized areas. Previous work suggests that plastic pollution in these urban rivers is influenced by hydrometeorological and anthropogenic factors. However, the transport dynamics of the plastics in such rivers are non-linear and complex and remain largely unresolved. Here, we show that tidal dynamics can be the main driver of plastic transport closest to the river mouth. Outside the tidal zone, rainfall and river discharge were identified to be more important drivers. We monitored plastic transport in the Odaw river, Ghana during the dry season. The Odaw drains the densely populated city of Accra and discharges into the Gulf of Guinea. Data were collected between March and May 2021 (dry season), using visual counting at four bridges along the river, of which two were located within the tidal zone. We explored the correlations between river plastic transport, and rainfall, tidal dynamics, and river discharge. Finally, we estimated the total plastic mass transport by using item-to-mass conversion data from previously published literature. We observed a peak in plastic transport at the upstream bridge within the tidal zone after an increase in rainfall (7.3 times larger). We found a gradient of the hydrometeorological factors driving plastic transport. Closer to the river mouth, tidal dynamics were more strongly correlated with plastic transport than upstream. The daily mass transport was estimated to be between 1.4–3.8 × 102 kg/d, which is lower than previous model estimates. These results add to the evidence of inconsistent correlations between plastic transport and hydrometeorological variables. Long-term monitoring data is required to further investigate this. The results also support the hypothesis that tidal dynamics are a crucial factor in controlling the emissions of plastics from rivers into the ocean. The findings provide a baseline for the Odaw river during the dry season and allow for comparison with the wet season. The approach adopted here also serves as a blueprint for similar urban river systems, regionally and globally.

Gas transport in organic-rich nanoporous media with nonequilibrium sorption kinetics

We present a mathematical model for one-dimensional gas transport in organic-rich nanoporous media subject to nonequilibrium sorption. The model is developed from two governing equations to simulate Knudsen diffusion and viscous flow in the free phase, and surface diffusion in the sorbed phase. The pore space is shared between the free and sorbed phases by defining concentration-dependent free- and sorbed-phase volume fractions. The governing equations are coupled through a source/sink term described by a kinetic sorption model. The impact of the reduced effective pore space and sorption on free-phase mass transfer is characterized by defining effective diffusion coefficients. The governing equations are numerically solved based on the finite element method. The model is utilized to analyze the temporal and spatial concentration data obtained using X-ray micro-CT scans from two experiments, including Krypton transport into a coal sample and Xenon uptake into a shale sample. The proposed model closely reproduces total concentration profiles in both experiments, and captures the concentration peak in Xe-shale system due to the significant nonequilibrium sorption and slower process of reaching equilibrium. The modeling results show that surface diffusion dominates the total mass transport in Xe-shale system with higher adsorption affinity. In Kr-coal system with lower adsorption affinity, the sorbed phase contributes significantly to the total mass transport mainly at high pressures. In addition, the sorbed phase can occupy up to 30% of pore space, which reduces the free-phase diffusion coefficient by 40% in Xe-shale and 80% in Kr-coal. Accordingly, neglecting the sorbed-phase volume in nanoporous media may overestimate the effective free-phase diffusion coefficient. This study shows the significance of the nonequilibrium adsorption for gas transport in nanoporous media.

Apparent diffusion coefficient for adsorption-controlled gas transport in nanoporous media

We present an apparent diffusion coefficient derived from a diffusion-based mass conservation equation for single-component gas transport in nanoporous media. Multiple transport and storage mechanisms have been considered, including Knudsen diffusion and viscous flow for the free phase and surface diffusion and multilayer adsorption for the sorbed phase. The real gas effect, confinement effect, and dynamic adsorption layer thickness are also considered. A pore-scale simplified local density method is utilized to obtain sorbed phase properties, such as volume fraction, concentration, and adsorption isotherm. The developed apparent diffusion coefficient is applied to investigate the effects of fluid–solid attraction, fluid–solid species, and pore sizes on the gas diffusion and adsorption in nanoporous media. The results reveal that the sorbed phase occupies a significant volume of nanopores, and the entire pore space becomes sorbed-phase volume in pores with diameters ≤ 2 nm. The total mass transport in these pores is dominated by surface diffusion, and free-phase diffusion contribution increases as the pore size increases. Furthermore, in strong adsorption systems such as CO2-coal, the apparent diffusion coefficient is up to two orders of magnitude smaller than in weak adsorption systems (e.g., N2-coal and CH4-coal). This is attributed to the reduced free-phase volume fraction and increasing adsorption capacity. The proposed apparent diffusion coefficient can be used in the diffusion-based models for gas transport in nanoporous media.

Observations of Drifting Snow Using FlowCapt Sensors in the Southern Altai Mountains, Central Asia

Drifting snow is a significant factor in snow redistribution and cascading snow incidents. However, field observations of drifting snow are relatively difficult due to limitations in observation technology, and drifting snow observation data are scarce. The FlowCapt sensor is a relatively stable sensor that has been widely used in recent years to obtain drifting snow observations. This study presents the results from two FlowCapt sensors that were employed to obtain field observations of drifting snow during the 2017–2018 snow season in the southern Altai Mountains, Central Asia, where the snow cover is widely distributed. The results demonstrate that the FlowCapt sensor can successfully acquire stable field observations of drifting snow. Drifting snow occurs mainly within the height range of 80-cm zone above the snow surface, which accounts for 97.73% of the total snow mass transport. There were three typical snowdrift events during the 2017–2018 observation period, and the total snowdrift flux caused during these key events accounted for 87.5% of the total snow mass transport. Wind speed controls the occurrence of drifting snow, and the threshold wind speed (friction velocity) for drifting snow is approximately 3.0 m/s (0.15 m/s); the potential for drifting snow increases rapidly above 3.0 m/s, with drifting snow essentially being inevitable for wind speeds above 7.0 m/s. Similarly, the snowdrift flux is also controlled by wind speed. The observed maximum snowdrift flux reaches 192.00 g/(m2·s) and the total snow transport is 584.9 kg/m during the snow season. Although drifting snow will lead to a redistribution of the snow mass, any accumulation or loss of the snow mass is also affected synergistically by other factors, such as topography and snow properties. This study provides a paradigm for establishing a field observation network for drifting snow monitoring in the southern Altai Mountains and bridges the gaps toward elucidating the mechanisms of drifting snow in the Altai Mountains of Central Asia. A broader network of drifting snow observations will provide key data for the prevention and control of drifting snow incidents, such as the design height of windbreak fences installed on both sides of highways.

Estimating Water Transport from Short-Term Vessel-Based and Long-Term Bottom-Mounted Acoustic Doppler Current Profiler Measurements in an Arctic Lagoon Connected to the Beaufort Sea.

Acoustic Doppler current profilers (ADCP) are quasi-remote sensing instruments widely used in oceanography to measure velocity profiles continuously. One of the applications is the quantification of land–ocean exchange, which plays a key role in the global cycling of water, heat, and materials. This exchange mostly occurs through estuaries, lagoons, and bays. Studies on the subject thus require that observations of total volume or mass transport can be achieved. Alternatively, numerical modeling is needed for the computation of transport, which, however, also requires that the model is validated properly. Since flows across an estuary, lagoon, or bay are usually non-uniform and point measurements will not be sufficient, continuous measurements across a transect are desired but cannot be performed in the long run due to budget constraints. In this paper, we use a combination of short-term transect-based measurements from a vessel-mounted ADCP and relatively long-term point measurements from a moored ADCP at the bottom to obtain regression coefficients between the transport from the vessel-based observations and the depth-averaged velocity from the bottom-based observations. The method is applied to an Arctic lagoon by using an ADCP mounted on a buoyant platform towed by a small inflatable vessel and another ADCP mounted on a bottom deployed metal frame. The vessel-based measurements were performed continuously for nearly 5 h, which was sufficient to derive a linear regression between the datasets with an R2-value of 0.89. The regression coefficients were in turn applied to the entire time for the moored instrument measurements, which are used in the interpretation of the subtidal transport variations.

Impact of Wind Direction on Erodibility of a Hortic Anthrosol in Southeastern Spain

We tested an efficient, easily and economically manufactured wind-transported particle collector of our own design, called a multidirectional trap (MDt), on fine-tilled Anthrosols. Results from the logs of nine vaned masts, each with four MDt collectors at different heights, showed a clear predominance of northeast and south winds. After analyzing sediment transport rates and their balance, we found that sediments from the south were being deposited rather than lost. A large amount of phyllosilicates, which are highly adhesive sediments, and therefore, increase aggregation, decreasing erodibility, were captured in the upper traps. Moreover, they are rich in calcium carbonate, mainly calcite, which is a powerful aggregate, and therefore, also decreases their wind erodibility. Sediments from the northeast, however, with almost double the total mass transport, contained the largest amount of captured quartz, promoting abrasion and increasing soil erodibility. Nevertheless, large amounts of organic matter found in sediments from the NE led to some aggregation, which balances material lost.

Tellurium transport in the RCS under conditions relevant for severe nuclear accidents

In the case of a severe nuclear power plant accident, tellurium is one of the more problematic and volatile fission products. If released it could become a health issue as it decays to iodine which accumulates in the thyroid gland. Research exists, that indicates tellurium likely interacts with caesium under severe accident conditions, thus it is important to further explore related phenomenon. In this work, tellurium was exposed to high temperature under oxidizing and inert conditions simulating severe accident conditions with and without airborne caesium iodide to determine the effect on the tellurium source term.The effect of caesium iodide was noticeable on tellurium transport behaviour in the gas phase under oxidizing and inert conditions. Under humid oxidizing conditions with caesium iodide, no significant impact on the total aerosol mass transport was noticed. However, less tellurium was transported through the model primary circuit and a potentially new compound was observed on the filter located after this model. Comparing inert dry to humid with caesium iodide showed an increase in the total aerosol mass transport whereas there was a decrease noticed of the tellurium reaching the filter after the model primary circuit. In the latter case, new unidentified compound(s) correlated to caesium, iodine and tellurium were observed on the filter located after the model.In this work, evidence was found that tellurium behaviour will be affected by caesium iodide under the investigated conditions. Moreover, it seems that under inert conditions the formed compounds may be stable at close to ambient temperatures. Unlike under oxidizing conditions, where dissociation likely occurred.

Sliding contact accelerates solute transport into the cartilage surface compared to axial loading

The objectives of this study were: first, to compare solute uptake driven by sliding to cyclic uniaxial compression. And secondly, to evaluate the role of the superficial region on passive diffusion to determine if mechanical action is merely overcoming the low permeability of the superficial region or exceeding equilibrium capacity of the tissue. Tests were performed on osteochondral plugs under two types of conditions: cyclic loading (sliding vs axial compression) and unloaded passive diffusion (intact vs superficial zone removed). The articular surfaces were exposed to a fluorescent bath and uptake was quantified from the surface to the subchondral bone using fluorescent microscopy. Primary outcome measures were total mass transfer, mass transfer rate, and surface partition factor. Mass transfer was 2.1-fold higher at 0.5h for sliding compared to uniaxial compression (p=0.004). This increased to 4.4-fold at 2h (p=0.002). Solute transport for both loading conditions at 2h had reached or exceeded intact passive diffusion at 12h. Total mass transport and mass transport per hour was higher in samples without the superficial region compared to intact samples at equilibrium. Rate of mass transfer was not declining for samples subject to sliding indicating solute uptake induced by sliding would exceed passive tissue capacity. These results are the first to quantify solute uptake between two components of joint articulation. The study demonstrates that sliding is a larger driver of solute transport compared to cyclic uniaxial compression. This has implications for cell nutrition, tissue engineering and biochemical signaling.

Electrochemical advanced oxidation for treating ultrafiltration effluent of a landfill leachate system: Impacts of organics and inorganics and economic evaluation

We treated landfill leachate using electrochemical advanced oxidation processes (EAOPs) with a boron-doped diamond (BDD) anode. Before EAOPs, the leachate was first treated using biological treatment (anoxic–aerobic) and then ultrafiltration (hereafter referred as biopretreated UF landfill leachate). We explored impacts of organics and inorganics (nitrogen – and chloride – species) for various current densities (1–80 mA/cm2). We found that EAOPs enhanced biodegradability (BOD/COD ratio) significantly from < 0.03 to up to 0.78. COD destruction followed a pseudo-first order model, with the rate constant and electric energy per order ranging from 0.91 to 28.29 h−1 and 17.1 to 127.5 kWh m−3, respectively. The current efficiency (CE) was 100% for current density 1 mA/cm2 and CE decreased to 57.8% as the current density increased to 30 mA/cm2. The oxidation priority was in this order: COD > nitrogen – species > chloride – species. The evolution of nitrogen – and chloride – species and their oxidation mechanisms were also investigated. The impact of Fickian diffusion and electrical field driven charged ion transport (EFDCIT) on the total mass transport was examined using the Nernst-Planck equation. We found that the contribution of EFDCIT was similar to diffusion for current densities higher than 64 mA/cm2. Finally, we compared the costs for standalone EAOPs and EAOPs integrated with subsequent biological treatment for biopretreated UF landfill leachate and found that the lowest cost for the latter one that meets the effluent discharge criteria was only 0.76 USD/m3. Our study proved that EAOPs are technically and economically promising technology for leachate treatment.

Experimental and numerical study of gas diffusion and sorption kinetics in ultratight rocks

Mass transport in ultratight rocks is markedly different from that in typical permeable rocks due to the presence of nano-scale pores and a dual-storage mechanism in terms of free and adsorbed gas. This work provides a quantitative analysis of gas transport behavior in ultratight rocks by utilizing X-ray computed micro-computed tomography (micro-CT) imaging and numerical modeling. We conducted X-ray micro-CT core-scale experiments using high-attenuation xenon (Xe) and Marcellus shale sample to obtain temporal and spatial Xe density maps from a series of micro-CT images. We present a dual-mechanism numerical model to analyze the sorption and diffusion phenomena observed in the experiment. The numerical model considers both bulk and surface diffusion by coupling of a diffusion-based equation for free-gas transport with a surface-diffusion equation for the sorbed phase. A sorption kinetic model quantifies mass transfer between the free- and sorbed-phase. The governing equations are solved simultaneously using finite element methods. Comparisons of numerical and experimental results reveal that sorption is a non-equilibrium process in ultratight rocks and surface diffusion significantly contributes to total mass transport through nanopores. Further, results show that sorbed-phase transport a nonlinear phenomenon given the dependence of surface diffusion coefficient on concentration. Resulting transport-related parameters, such as bulk and surface diffusion coefficients and sorption rate constants, which are estimated from history matching, are consistent with literature data.

Development of an Oxygen Mass Transport Coefficient Measurement and Separation Method for Proton Exchange Membrane Fuel Cells

In this work, we use a method to separate the total oxygen mass transport coefficient into molecular, Knudsen, and ionomer contributions. Therefore, limiting current density measurements are carried out as a function of the diluent gas (He, N2, CO2), temperature (30, 50, 80°C), relative humidity (50, 75, 100%), and oxygen concentration (1, 3, 5, 7%) using state of the art membrane electrode assemblies with three platinum loadings (0.05, 0.1, 0.15 mg/cm2). As expected, the molecular diffusion coefficient is independent of the platinum loading, but increases with temperature to a varying degree depending on the humidity level. On the other hand, the Knudsen diffusion coefficient increases with increasing electrochemical active surface area and temperature, and with decreasing relative humidity. The separation procedure includes a novel feature to isolate the ionomer mass transport resistance. Its interpretation as well as the method’s reliability are critically questioned using operating condition dependencies.

Evaluation of mass transfer mechanisms involved during the adsorption of metronidazole on granular activated carbon in fixed bed column

This work is focused on the transient analysis of the different mass transfer mechanisms during the adsorption of metronidazole on activated carbon packed in a fixed-bed column. The analysis was carried out by modeling the breakthrough curves at different operation conditions with a fixed bed general model (FBGM) that considers the mass transport mechanisms of axial dispersion, convective, external and intraparticle (pore volume diffusion and surface diffusion). The results show that the FBGM model adequately simulated the dynamics of the experimental data under all operating conditions. Moreover, it was demonstrated that the convective mass transport governs the mass transport of metronidazole primarily, while the axial dispersion contributes only up to 5–10 % within the interstitial space of the packed column. The external mass transfer can be less than 5 % of the total mass transport of solute in the liquid phase. Regarding the intraparticle mass transport inside the activated carbon, it was found that surface diffusion is more important than the pore volume diffusion in the dynamic adsorption of metronidazole, and represents 80–100 % of the total intraparticle transport.

Mass transfer through a concentric-annulus microchannel driven by an oscillatory electroosmotic flow of a Maxwell fluid

In this work we develop a theoretical analysis for the mass transfer of an electroneutral solute in a concentric-annulus microchannel driven by an oscillatory electroosmotic flow (OEOF) of a fluid whose behavior follows the Maxwell model. The annular microchannel connects two reservoirs that have different concentrations of the solute. For the mathematical modeling of the OEOF, we assume the Debye-Hückel approximation and that the wall zeta potentials of the micro-annulus can be symmetric or asymmetric. The governing equations are nondimensionalized, from which the following dimensionless parameters appear: an angular Reynolds number, the ratio of the wall zeta potentials of the annular microchannel, the electrokinetic parameter, the dimensionless gap between the two cylinders, the Schmidt number and the elasticity number. The results indicate that the velocity and concentration distributions across the annular microchannel become non-uniform as the angular Reynolds number increases, and depend notably on the elasticity number. It is also revealed that with a suitable combination of values of the elasticity number and gap between the two cylinders, together with the angular Reynolds number, the total mass transport rate can be increased and the species separation can be controlled.

Spatial and quantitative assessment of wind erosion from adjacent dunes with different surface cover ratios.

Direct measurements, models, and risk maps play significant roles in assessment and monitoring of wind erosion cases. Although active and passive traps allow researchers to measure point sediment transports directly, it is also possible to make geostatistical analysis of wind erosion with grid and random sampling at multiple points. Geostatistical models can be used in multi-sample eolian researches to improve model success and update model parameters. The present study was conducted for case-based geostatistical analysis of sediment transport rates (STRs) over two adjacent dunes (plot A and B) with different vegetation cover rates between 22 May and 15 June 2011. The plot A has a vegetative cover ratio of 30%, while the plot B has a vegetation cover ratio of 2% and sand content of the plots is 88%. Actual mass transports were measured with BEST sediment traps. A total of 19 BEST sediment trap assemblies were placed randomly over the plot A and 21 were placed over the plot B. A climate station was installed over the research site to record climate data throughout the experimental period. There were two wind erosion cases during the research period. U test indicated that differences in sediment transport rates of the plots for each case were significant (p < 0.00). Spatial analyses of STRs (kgm-1h-1) also exhibited case-based differences. While nugget effect was observed in case 1 of the plot B, the other case in both plots were modeled with spherical model. Maximum likelihood distances in plot A and B were respectively identified as 61m and 1m in the first case and as 13m and 30m in the second case. Total mass transport was measured as 112kgm-1 in plot A and as 2162kgm-1 in plot B. Consequently, it was found that 30% vegetation cover reduced the total mass transport dramatically.

Simulation of the influence of voltage level and pulse spacing on the efficiency, aggressiveness and uniformity of the electroporation process in tissues using meshless techniques.

Electroporation is a widely used method consisting of application of high-voltage, short-duration electric pulses to increase cell membrane permeability, allowing cellular internalization of medications. In this work, the influence of two primary parameters, voltage level (V) and pulse spacing (N), on electroporation efficiency, uniformity and aggressiveness, as quantified by the total mass transport to viable cells, intracellular concentration gradients and an aggressiveness factor introduced here, is studied by means of numerical simulations of drug transport in electroporated tissues. The global method of approximate particular solutions (Global MAPS) is used to solve the governing equations, together with domain scaling, singular value decomposition and smoothing algorithms, to address the ill-conditioning of the final system and suppress small scale oscillations. The accuracy of Global MAPS is evaluated by comparing the initial extracellular concentration, Ce , and final intracellular concentration, Ci , with previous finite volume method results, obtaining similar behavior of Ce and Ci along the tissue domain, with some differences for Ci in high-gradient zones. According to the Global MAPS results, the influence of V and N on Ci is only significant over a certain range, within which the largest drug transport to viable cells occurs. In general, both electroporation efficiency and aggressiveness change in nonuniform manner with V and decrease with N, whereas the electroporation uniformity decreases as V increases and N decreases. The contour plots obtained here can be considered useful tools to compare electroporation-based treatments in terms of their efficiency, aggressiveness and uniformity, assisting in the selection of a suitable treatment plan for cancer.

Northward Transport in a Stress Driven Flow Confined to a Porous Medium (Sverdrup Relation in a Porous Medium)

We obtain an expression for the total northward mass transport in a porous bed of large extant subject to a stress applied at the top free surface using  -plane approximation. It is found that  -effect is found to be responsible for western intensification of ocean currents. The total northward transport of fluid (See Sverdrup [11]) is found to be closed through the western boundary layer (See: Stommel [4]) in the presence of porous medium.