Conductivity Gradient Research Articles

Random finite element analysis of backward erosion piping

Backward erosion piping (BEP) is a type of internal erosion that threatens the integrity of dams and levees. BEP has been shown to be highly sensitive to spatial variations in soil properties; however, there are presently no assessment methods that permit incorporating spatial variation in soil properties into BEP analysis. The Random Finite Element Method (RFEM) is a numerical approach for incorporating spatially variable properties into finite element analysis. In this study, an RFEM approach to simulating BEP was developed to assess pipe progression through variable soils. The soil hydraulic conductivity and critical hydraulic gradient for pipe progression were treated as log-normal random variables. Analyses were conducted for a range of hydraulic conductivity and critical gradient random fields with varied spatial correlation lengths, distribution parameters, and field correlations. Results indicate that the probability of failure increases with increasing spatial correlation length. Additionally, increased variance in soil permeability was shown to increase the probability of failure for large correlation lengths and decrease the probability of failure for short correlation lengths. Regardless of correlation length, increasing values of the mean critical hydraulic gradient led to decreased failure probabilities, and increasing values of critical hydraulic gradient variance led to increased failure probabilities.

A preliminary assessment of the sensitivity of uniaxially driven fusion targets to flux-limited thermal conduction modeling

The role of flux-limited thermal conduction on the fusion performance of the uniaxially driven targets studied by Derentowicz et al. [J. Tech. Phys. 18, 465 (1977) and J. Tech. Phys. 25, 135 (1977)] is explored as part of a wider effort to understand and quantify uncertainties in inertial confinement fusion (ICF) systems sharing similarities with First Light Fusion's projectile-driven concept. We examine the role of uncertainties in plasma microphysics and different choices for the numerical implementation of the conduction operator on simple metrics encapsulating the target performance. The results indicate that choices that affect the description of ionic heat flow between the heated fusion fuel and the gold anvil used to contain it are the most important. The electronic contribution is found to be robustly described by local diffusion. The sensitivities found suggest a prevalent role for quasi-nonlocal ionic transport, especially in the treatment of conduction across material interfaces with strong gradients in temperature and conductivity. We note that none of the simulations produce neutron yields that substantiate those reported by Derentowicz et al. [J. Tech. Phys. 25, 135 (1977)], leaving open future studies aimed at more fully understanding this class of ICF systems.

Electrically conductive gradient structure design of thermoplastic polyurethane composite foams for efficient electromagnetic interference shielding and ultra-low microwave reflectivity

Lightweight and compressible composite foams consisting of silver fractal dendrites (AgFDs), carbon nanotubes (CNTs) and thermoplastic polyurethane (TPU) are developed through layer-by-layer construction, followed by freeze-drying. The construction of AgFD/TPU layers through depositing AgFD layers followed by low-temperature sintering and incorporating of TPU endows the AgFD/TPU layers with excellent electrical conductivity. Meanwhile, the electrically conductive gradient CNT/TPU layers constructed by layer-by-layer method greatly decrease the reflection of the electromagnetic (EM) waves and prolong the EM wave dissipation paths. The unique low reflection–absorption-high reflection-reabsorption paths of the EM wave dissipation mechanism facilitates the composite foams with thickness of 3.4 mm to obtain an excellent EMI SE of 88.5 dB and an ultra-low SER of 0.29 dB at an extreme low AgFD loading of 0.103 vol%. Additionally, benefitting from direction freezing, the composite foams exhibit good cyclic compression recovery. This work puts forward a new insight for designing and constructing ultra-efficient absorption-dominated EMI shielding materials with electrically conductive gradient layers, and the prepared shielding materials are highly promising for applications in the EMI protection of modern electronic products.

Hybrid polyion complex micelles enabling high-performance lithium-metal batteries with universal carbonates

Lithium (Li) metal emerges as an anode for high-energy-density Li metal batteries due to their high theoretical capacity (3860 mAh g−1) and low electrochemical potential (−3.04V versus standard hydrogen electrodes). Nonetheless, the inherent instability of Li metal against conventional carbonate-based electrolytes (denoted as carbonates), causing unpredictable reactions and unstable interphase layers, precludes the commercialization of Li metal batteries. Herein, an innovative strategy-hybrid polyion complex micelle to enable high-performance Li metal anodes in carbonates is reported. Ionized LiNO3 cooperates with block copolymer (polystyrene-block-poly(2-vinyl pyridine) (S2VP)) micelles via electrostatic interaction and plants on the Li metal surface together. The union with S2VP and ionized LiNO3 can shut off from contact with the Li surface and carbonates, construct the unique solid electrolyte interface layers with a Li-ion conductivity gradient, and control Li morphology. S2VP/LiNO3-Li metal electrodes enable high-efficiencies over 100 cycles and even at high-temperature with universal carbonates. S2VP/LiNO3-Li//LiNi0.8Co0.1Mn0.1O2 full cells achieve long-stable cycling over 300 cycles under harsh test conditions: limited-excess Li (thickness of 40 and 100 μm), high-areal capacity (4.0 mAh cm−2), and high-current density (4.0 mA cm−2). Moreover, a pouch-type full cell demonstrates commercial viability. This work provides new insights into enabling Li metal batteries with high-energy-density to adopt conventional carbonates.Data Availability: Data will be made available on request.

Development and Testing of a Methodology for Assessing of the Correlation Velocity Measurements’ Accuracy for the Hydrodynamic Investigations of the Turbulent Coolant Flow in Nuclear Reactor Elements

The correlation method of the coolant flow measuring is widely used in research practice including for studying of turbulent coolant flows in scale models of elements of nuclear power plants. The aim of this work was to develop a technique for assessing the effect of noise recorded by a measuring system on the flow rate readings obtained using the correlation method.A technique to assess the effect of noise as well as the relative position and acquisition period of sensors is presented. An insignificant concentration of a salt solution (NaCl or Na2SO4 ) is used as a passive impurity which creates a conductivity gradient of the medium recorded by a conductometric system. Turbulent pulsations at the interface between two concurrent isokinetic flows in a channel with a square cross section are used as the signal source for the correlational algorithm.Paper presents the values of the turbulence′s transport time between spatial conductometers, the results of estimating the spectral power density and band of the recorded signal and also the signalto-noise ratios of the measuring system obtained on their basis which are subsequently used to estimate the confidence interval of the transport time.As a result of measurements the relationship between the confidence interval value and the signal length were obtained. The measurements which were carried out at different relative positions of conductometers make it possible to make a conclusion about an increase in the spectral width of the signal and, as a consequence, a decrease in the length of the confidence interval with increasing of distance between sensors.The presented work is an approbation of this approach for its application as part of an experimental model of a nuclear reactor in order to determine per-channel flow rates in the channels of the core simulator using mesh conductometric sensors taking into account the effect of noise.

Sensing mechanism of a carbon nanocomposite-printed fabric as a strain sensor

Conductive fabrics have gained widespread attention all around the electro-textile areas, owing to ease of fabrication and large freedom of design. In this paper, printed conductive knitted fabric was fabricated, which revealed favorable merits as a strain sensor such as large strain measurement range, good repeatability, good sensitivity to strain, high resistance to fatigue and low Young’s modulus. The electro-mechanical behavior as well as sensing mechanism of the conductive fabric was further elaborated, based on tunneling conductive mechanism of conductive composites and gradient strain distribution of the sensing area. An electromechanical model of the conductive fabric was established and verified as effective, with maximum averaged error observed only 5.51%. The printed fabric and its model of sensing mechanism not only lay the foundation for further design, analysis and optimizations of textile-based conductive fabrics, but also reveal interesting material phenomena with a rather broad scope in the area of electronic textiles.

Phase transitions for a class of gradient fields

We consider gradient fields on {mathbb {Z}}^d for potentials V that can be expressed as e-V(x)=pe-qx22+(1-p)e-x22.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$\\begin{aligned} e^{-V(x)}=pe^{-\\frac{qx^2}{2}}+(1-p)e^{-\\frac{x^2}{2}}. \\end{aligned}$$\\end{document}This representation allows us to associate a random conductance type model to the gradient fields with zero tilt. We investigate this random conductance model and prove correlation inequalities, duality properties, and uniqueness of the Gibbs measure in certain regimes. We then show that there is a close relation between Gibbs measures of the random conductance model and gradient Gibbs measures with zero tilt for the potential V. Based on these results we can give a new proof for the non-uniqueness of ergodic zero-tilt gradient Gibbs measures in dimension 2. In contrast to the first proof of this result we rely on planar duality and do not use reflection positivity. Moreover, we show uniqueness of ergodic zero tilt gradient Gibbs measures for almost all values of p and q and, in dimension dge 4, for q close to one or for p(1-p) sufficiently small.

Thermospheric Impact on the Magnetosphere Through Ionospheric Outflow

AbstractWe have taken a key step in evaluating the importance of ionospheric outflows relative to electrodynamic coupling in the thermosphere’s impact on geospace dynamics. We isolated the thermosphere’s material influence and suppressed electrodynamic feedback in whole geospace simulations by imposing a time‐constant ionospheric conductance in the ionospheric Ohm’s law in a coupled model that combines the multifluid Lyon‐Fedder‐Mobarry magnetosphere model with the Thermosphere Ionosphere Electrodynamic General Circulation Model and the Ionosphere Polar Wind Model that includes both polar wind and transversely accelerated ion species. Numerical experiments were conducted for different thermospheric states parameterized by F10.7 for interplanetary driving representative of the stream interaction region that swept past Earth on March 27, 2003. We demonstrate that thermosphere through its regulation of ionospheric outflows influences magnetosphere‐ionosphere (MI) convection and the ion composition, symmetries, x‐line perimeter and magnetic merging of the magnetosphere. Feedback to the ionosphere‐thermosphere from evolving MI convection, and Alfvénic Poynting fluxes and soft (∼few 100 eV) electron precipitation originating in the magnetosphere, in turn, modify the evolving O+ outflow properties. The simulation results identify a variety of observed magnetospheric features that are attributable directly to the thermosphere’s material influence: Asymmetries in O+ outflow fluxes and velocities in the pre/postnoon low‐altitude magnetosphere, dawn/duskside lobes and pre/postmidnight plasmasheet; O+ distribution of the plasmasheet; magnetic x‐line location and reconnection rate along it. O+ outflows during solar maximum conditions (high F10.7) tend to counteract the plasmasheet’s pre/postmidnight asymmetries caused by the night‐to‐day gradient in ionospheric Hall conductance.

Potential impacts of shale and tight gas developments on unconfined aquifers – a chemical screening framework

The Geological and Bioregional Assessment Program examines the potential impacts of shale, tight and deep coal gas development on water and the environment. A key part of the project was quantifying the potential for a decline in the water quality of unconfined aquifers due to unintentional chemical release at the soil surface. To assess this hazard, a quantitative analysis of chemical migration pathways was undertaken, which involved the estimation of contaminant attenuation by dilution and dispersion in soil and groundwater. This provided a conservative screening approach to identify areas for further analysis. Attenuation calculations involved one-dimensional advection-dispersion (AD) simulations through the unsaturated zone, and three-dimensional AD solute transport within the surficial aquifers. Dilution factor (DF) relationships for the combined effect of attenuation in the unsaturated and saturated zone were used to construct spatial maps of the potential for impact on aquifer properties after accidental chemical spills. A higher DF (therefore lower consequence of the surface contamination) was associated with deeper unsaturated zones characterized by heavier soils near the surface, and lower ground water velocities due to lower hydraulic conductivity and/or hydraulic gradient in the saturated zone. The framework was applied across the Cooper Basin and Beetaloo Sub-basin and resulted in two types of maps. The first identified areas being more susceptible to contamination if soil remediation does not occur within a 10-year period. The second map shows the spatially variable combined DFs for a ground water receptor, which may be used to develop site-specific management plans and mitigation measures.

Disruption to Mouse Ventricular Transmural Conduction Gradients in a Setting of High Cardiac Adiposity

Transmural differences in ventricular action potential duration ensure synchronised repolarisation. It is not clear whether similar differences in conduction velocity exist to help define transmural activation patterns, nor the extent to which this changes in pro-arrhythmic disease states. Cardiac adiposity has been linked with atrial conduction slowing and greater arrhythmia vulnerability. We recently showed that factors released from pericardial adipose modulate cardiomyocyte electrophysiology—shortening action potential duration and slowing inter-cardiomyocyte conduction.

Joule heating effects on electrokinetic flows with conductivity gradients.

Instability occurs in the electrokinetic flow of fluids with conductivity and/or permittivity gradients if the applied electric field is beyond a critical value. Understanding such an electrokinetic instability is significant for both improved transport (via the suppressed instability) and enhanced mixing (via the promoted instability) of liquid samples in microfluidic applications. This work presents the first study of Joule heating effects on electrokinetic microchannel flows with conductivity gradients using a combined experimental and numerical method. The experimentally observed flow patterns and measured critical electric fields under Joule heating effects to different extents are reasonably predicted by a depth-averaged numerical model. It is found that Joule heating increases the critical electric field for the onset of electrokinetic instability because the induced fluid temperature rise and in turn the fluid property change (primarily the decreased permittivity) lead to a smaller electric Rayleigh number.

Salt-tolerant Bacillus species as a promising strategy to mitigate the salinity stress in wheat (Triticum turgidum subsp. durum)

Salinity negatively impacts the bacterial diversity associated with crops in commercial fields; however, Bacillus species -due to their great metabolic/genomic background and spore formation-have shown high resilience to this abiotic stress enhancing the tolerance of plants to saline soils. This work aimed to assess the diversity of cultivable salt-tolerant Bacillus species associated with wheat commercial fields in the Yaqui Valley, Mexico, as well as to identify native salt-tolerant Bacillus strains as promising alternatives to mitigate the negative effects of saline soils on wheat. Thus, based on morphological and molecular (sequencing the 16S rRNA gene) traits related to this genus, fifty-one Bacillus strains were isolated from thirty-six 1 ha-wheat commercial fields in the Yaqui Valley, Mexico [soils showed a gradient of electrical conductivity (E.C.) from 0.6 to 6.4 dS m−1]. These strains were grouped into ten Bacillus species: 1) B. subtilis (25.5%), 2) B. megaterium (25.5%), 3) B. cereus (19.6%), 4) B. amyloliquefaciens (7.8%), 5) B. pumilus (5.9), 6) B. licheniformis (5.9%), 7) B. endophyticus (3.92%), 8) B. atrophaeus (1.96%), 9) B. safensis (1.96%), and 10) B. mojavensis (1.96%). The soil salinity in wheat fields (E.C. 0.6–6.4 dS m−1) and the in vitro salt-tolerance assay (E.C. 6.4 dS m−1) negatively impacted the abundance and diversity of Bacillus species; however, B. licheniformis TRQ65 (isolated from soils having 4.1–5.0 dS m−1) showed the highest tolerance to in vitro saline stress (6.4 dS m−1), increasing its growth 223% under saline vs. non-saline conditions. Finally, the inoculation of B. licheniformis TRQ65 was able to mitigate the negative effects of saline soil conditions on wheat (30 days post-inoculation), since the growth promotion of inoculated seedlings under a saline soil condition (6.4 dS m−1) was similar (no significant differences, p > 0.05) to inoculated wheat seedlings under a non-saline soil condition, which was higher (significant differences, p < 0.05) than un-inoculated wheat seedlings under a non-saline and saline soil. Bacillus licheniformis TRQ65 (recently taxonomically affiliated as B. paralicheniformis TRQ65) is a promising native salt-tolerant strain that needs to be studied in the future for improving wheat growth and yield, under saline or non-saline soils.

Creating electronic and ionic conductivity gradients for improving energy storage performance of ruthenium oxide electrodes

Robust Ru-based thin films are successfully fabricated by single- (SA) and multiple-annealing (MA) thermal decomposition methods and are utilized as high-performance electrodes for the supercapacitors. Two critical parameters, the annealing temperature and treatment duration, are engineered for synthesizing stable thin-film electrodes. It is found that the SA thermal decomposition technique at 250 °C for 6 h results in stable RuO2 electrodes with remarkable electrochemical performance. The MA approach consists of 2- and 3-stage thermal treatment steps. The maximal capacitance of MA-treated capacitor reaches as high as 308.8 F g−1. The MA-treated electrodes deliver exceptional rate capability as well as superior cycling stability (93% capacitance retention upon 2000 cycles). The enhanced performance is attributed to the multistep thermal stages along with the layer-by-layer deposition, enabling enhanced heat transfer to individual thin layers. An optimal thermal treatment procedure is assessed empowering enhanced capacitive performance due to high hydrous RuO2·xH2O ratio, reduced crystalline structure, facile electrolyte wetting, and stable adhesion between the deposits and the Ti substrate. The robust design of MA-treated thin film deposits paves the way for synthesizing high-performance electrodes for the supercapacitors.

Abstract 15418: An Arrhythmogenic Isolated Septal Aneurysm

Background: Septal infarct due to isolated occlusion of a perforator branch is extremely rare. Few reported cases only describe either the EKG findings, imaging abnormalities or revascularization techniques. Objective: We report a case of an isolated septal aneurysm (ISA) caused by the acute occlusion of the second septal perforator presenting with recurrent ventricular fibrillation (VF). Results: A 63 year old woman presented to the hospital with chest pain. EKG showed an ST segment elevation localized to lead V3 (Fig1A), troponin 18.23. Angiogram showed an isolated 95% tubular stenosis of large second septal branch of LAD (Fig1B). No revascularization was performed. The patient subsequently had cardiac arrest (VF) requiring cardioversion. Repeat angiogram was unchanged. Echo showed isolated mid septal dyskinetic segment (Fig1C). LVEF was 60%. The patient was discharged with an external defibrillator. Repeat echo showed unchanged EF but presence of the isolated dyskinetic segment. An electrophysiologic study (EPS) showed VF induced with 2 extra stimuli at 250 ms with a drive cycle of 600 ms (Fig1D). An ICD was implanted for prevention of SCD. Conclusion: We describe the first case of an arrhythmogenic ISA in the presence of normal LVEF. The interventricular septum is composed of right and left ventricular endocardium. Experiments have shown that acute septal ischemia produces trans-septal asymmetry in expression of membrane ion channels and action potentials in local conduction velocity and gradients. This results in trans-mural heterogeneity of tissue excitability, a substrate for transmural re-entry and ventricular tachyarrhythmias, in septal infarction. This also explains the persistence of enhanced arrhythmogenicity in our patient during the initial and chronic phases of ischemia. ISA is rare but potentially arrhythmogenic. ISA with preserved LVEF, EPS for arrhythmogenicity and ICD for secondary prevention of SCD should be considered in such cases.

&lt;p&gt;&lt;strong&gt;Diatom genus &lt;em&gt;Planothidium&lt;/em&gt; (Bacillariophyta) from streams and rivers in California, USA: diversity, distribution and autecology&lt;/strong&gt;&lt;/p&gt;

The diatom genus Planothidium from streams and rivers in California was studied by applying the most current species designations. Twenty Planothidium taxa were identified in total, including a previously undescribed species, Planothidium californicum. Extensive light and scanning electron microscopic documentation is provided to support consistent further identification of the taxa for the local stream bioassessment. The most common and abundant species, recorded across the entire state, were P. frequentissimum, P. lanceolatum, P. victorii, P. cryptolanceolatum, P. amphibium, and P. minutissimum. Species ranges and species-weighted averages for the main anthropogenic stressors, i.e. chloride, conductivity, dissolved organic carbon, total nitrogen and total phosphorus were determined for the eleven most common Planothdium taxa. Statistically significant differences among species weighted averages were determined by randomization test. Of these eleven species, P. delicatulum, P. robustum, P. engelbrechtii, P. frequentissimum and P. victorii had the highest weighted averages along the chloride and conductivity gradients. P. potapovae, Planothidium sp. 1, P. amphibium, and P. engelbrechtii had narrow nutrient ranges and lowest weighted averages for total nitrogen and phosphorus, making them significantly different from P. delicatulum which had highest total nitrogen average and from P. minutissimum, associated with highest total phosphorus average level. Given that there were differences in associations with environmental variables between recently described species, it is important to use the new taxonomy when using diatoms in bioassessment work.

Thick Sintered Electrode Lithium-Ion Battery Discharge Simulations: Incorporating Lithiation-Dependent Electronic Conductivity and Lithiation Gradient Due to Charge Cycle

In efforts to increase the energy density of lithium-ion batteries, researchers have attempted to both increase the thickness of battery electrodes and increase the relative fractions of active material. One system that has both of these attributes are sintered thick electrodes comprised of only active material. Such electrodes have high areal capacities, however, detailed understanding is needed of their transport properties, both electronic and ionic, to better quantify their limitations to cycling at higher current densities. In this report, efforts to improve models of the electrochemical cycling of sintered electrodes are described, in particular incorporation of matrix electronic conductivity which is dependent on the extent of lithiation of the active material and accounting for initial gradients in lithiation of active material in the electrode that develop as a consequence of transport limitations during charging cycles. Adding in these additional considerations to a model of sintered electrode discharge resulted in improved matching of experimental cell measurements.

Pore-scale investigation on flow boiling heat transfer mechanisms in gradient open-cell metal foams by LBM

Flow boiling heat transfer mechanisms inside gradient open-cell metal foam are investigated based on the newly proposed metal foam model. This new model considers thermal responses of metal skeletons. The structural effects of gradient metal foam, including porosity gradient, thermal conductivity gradient and wettability gradient, on flow boiling heat transfer performance are studied by pseudopotential lattice Boltzmann method. Reynolds number effect on bubble departure characteristics, such as bubble departure diameter, bubble departure frequency and the corresponding probability density distributions, are investigated based on statistical analysis. The results show that bubble confinement weighs heavily over bubble movement inside pore cell during bubble escaping process in porosity-gradient metal foams. Bubble nucleation is depressed by the highly thermal conductive gradient metal foam at high heat fluxes. The interaction between escaping bubble and pore throat shifts from “complete contact” mode to “thin liquid film” mode in the positive wettability-gradient metal foam. Shear force dominates over buoyant force with increasing Reynolds number, resulting in the sliding motion of premature bubbles.

Capillary-driven blood separation and in-situ electrochemical detection based on 3D conductive gradient hollow fiber membrane

It is essential to develop portable, versatile, and reliable diagnostic devices in point-of-care testing (POCT). The detection of biomarkers requires selective separation and large specific surface for high sensitivity and accuracy at trace levels in whole blood samples using POCT devices. Herein, a kind of 3D electrochemical biosensors were designed via in-situ synthesizing polyaniline (PANI) and platinum nanoparticles (Pt NPs) on polysulfone hollow fiber membrane (HFM) scaffolds with gradient porous structure. The gradient porous HFMs scaffolds provide uniform capillary flow, self-driven blood separation and sufficient enzyme immobilization sites. Simultaneously, the in-situ deposited materials fulfill interconnected conductive networks, thus ensuring accurate and rapid detection of the sensors without hindering capillary progress. These sensors display ultralow sampling (~3 μL), fast fluid flow (>1 μL/ms), wide linear range (glucose: 0–24 mM, R2=0.992; cholesterol: 0–9 mM, R2=0.999), high sensitivity and accuracy especially under different hematocrits in POCT applications towards glucose and cholesterol. The innovative integration of POCT biosensors with interconnected conductive nanoparticles, selective blood separation and gradient porous structures can find wide application in resource-limited regions, large population screening, and public health emergencies.

Different refuge types dampen exotic invasion and enhance diversity at the whole ecosystem scale in a heterogeneous river system

Refuges that result from environmental heterogeneity within ecosystems have an important yet under-appreciated role in maintaining native community diversity in face of exotic invasion. The objective of our study was to determine if different refuge types constrain invasion impacts on native biodiversity at the whole ecosystem-scale of the Upper St. Lawrence River. We focused on the voracious round goby fish as a sentinel exotic species whose spatial distribution within this ecosystem is also representative of the species distributions of several other Ponto-Caspian invaders. We first explored if wetlands were acting as unknown refuges in reducing the local abundance of the round goby fish. We then tested the relative influence of a known broad-scale conductivity gradient compared with local wetlands on structuring the composition, diversity, and abundance of native macroinvertebrate and fish communities inside and outside each of these refuge types. We found that the two types of refuges, broad-scale conductivity gradient and local wetlands, limited round goby abundances at the whole ecosystem scale, and structured macroinvertebrate and fish community diversity. The broad-scale conductivity refuge was twice stronger than wetlands in limiting round goby abundance. Although wetlands were effective in constraining round goby abundance, the direct effect of wetlands rather than their indirect effects through limiting round goby abundance, were more powerful in explaining maintenance of macroinvertebrate and fish community diversity in invaded high conductivity waters. Our findings underscore the important role of environmental heterogeneity in producing different types of refuges that buffer invasion effects in freshwater ecosystems, and we advocate the preservation of wetlands as a part of this process.

A fully coupled hybrid lattice Boltzmann and finite difference method-based study of transient electrokinetic flows.

Transient electrokinetic (EK) flows involve the transport of conductivity gradients developed as a result of mixing of ionic species in the fluid, which in turn is affected by the electric field applied across the channel. The presence of three different coupled equations with corresponding different time scales makes it difficult to model the problem using the lattice Boltzmann method (LBM). The present work aims to develop a hybrid LBM and finite difference method (FDM)-based model which can be used to study the electro-osmotic flows (EOFs) and the onset of EK instabilities using an Ohmic model, where fluid and conductivity transport are solved using LBM and the electric field is solved using FDM. The model developed will be used to simulate three different problems: (i) EOF with varying zeta-potential on the wall, (ii) similitude in EOF, and (iii) EK instabilities due to the presence of conductivity gradients. Problems (i) and (ii) will be compared with the analytical results and problem (iii) will be compared with the simulations of a spectral method-based numerical model. The results obtained from the present simulations will show that the developed model is capable of studying transient EK flows and of predicting the onset of instability.