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Hydrogen and hydroxide ion transport in narrow carbon nanotubes (CNTs) of diameter 8.1 Å and lengths up to 582 Å are investigated by molecular dynamics simulations using a dissociating water model. The diffusion coefficients of the free ions in an open chain are significantly larger than in periodically replicated wires that necessarily contain D or L end defects, and both are higher than they are in bulk water. The free hydroxide ion diffuses faster than the free hydronium ion in short CNTs, unlike diffusion in liquid water, and both coefficients increase and converge to nearly the same value with increasing tube length. The diffusion coefficients of the two ions increase further when the tubes are immersed in a water reservoir and they move easily out of the tube, suggesting an additional pathway for proton transport via OH- ions in biological channels. [ABSTRACT FROM AUTHOR]

We introduce a sparse-matrix algorithm that allows for the simulation of two-dimensional infrared (2DIR) spectra in systems with many coupled chromophores. We apply the method to bulk water, and our results are based on the recently developed ab initio maps for the vibrational Hamiltonian. Qualitative agreement between theory and experiment is found for the 2DIR spectra without the use of any fitting or scaling parameters in the Hamiltonian. The calculated spectra for bulk water are not so different from those for HOD in D2O, which we can understand by considering the spectral diffusion time-correlation functions in both cases. We also calculate the ultrafast anisotropy decay, which is dominated by population transfer, finding very good agreement with experiment. Finally, we determine the vibrational excitation diffusion rate, which is more than two orders of magnitude faster than the diffusion of the water molecules themselves. [ABSTRACT FROM AUTHOR]

Using simple theoretical arguments and exact numerical lattice calculations, Hickey et al. [J. Chem. Phys. 124, 204903 (2006)] derived and tested an expression for the effective diffusion coefficient of a probe molecule in a two-phase medium consisting of a hydrogel with large gel-free inclusions. Although providing accurate predictions, this expression neglects important characteristics that such two-phase systems can present. In this article, we extend the previously derived expression in order to include local interactions between the gel and the analyte, interfacial effects between the main phase and the inclusions, and finally a possible incomplete separation between the two phases. We test our new, generalized expressions using exact numerical calculations. These generalized equations should be a useful tool for the development of novel multiphase systems for specific applications, such as drug-delivery platforms. [ABSTRACT FROM AUTHOR]

Interactions of thin water films with surfaces of graphite and vitrified room-temperature ionic liquid [1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6])] were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature and annealing time to elucidate the glass-liquid transition of water at the molecular level. Surface diffusion of water occurs at temperatures higher than 120 K, thereby forming three-dimensional clusters (a two-dimensional layer) on the [bmim][PF6] (graphite) surface. The hydrophobic effect of the surface decreases with increasing coverage of water; the bulklike properties evolve up to 40 ML, as evidenced by the occurrence of film dewetting at around the conventional glass transition temperature (140 K). Results also showed that aging is necessary for the water monolayer (a 40 ML water film) to dewet the graphite ([bmim][PF6]) surface. The occurrence of aging is explainable by the successive evolution of two distinct liquids during the glass-liquid transition: low density liquid is followed by supercooled liquid water. The water monolayer on graphite is characterized by the preferred orientation of unpaired OH groups toward the surface; this structure is arrested during the aging time despite the occurrence of surface diffusion. However, the water monolayer formed on the [bmim][PF6] surface agglomerates immediately after the commencement of surface diffusion. The structure of low density liquid tends to be arrested by the attractive interaction with the neighbors. [ABSTRACT FROM AUTHOR]

Fluid flow exerts a critical impact on the convection of thermal energy in geological media, whereas heat transport in turn affects fluid properties, including fluid dynamic viscosity and density. The interplay of flow and heat transport also affects solute transport. To unravel these complex coupled flow, heat, and solute transport processes, here, we present a theory for the idealized scale‐dependent Poiseuille flow model considering a constant temperature gradient (∇T) along a single fracture, where fluid dynamic viscosity connects with temperature via an exponential function. The idealized scale‐dependent model is validated based on the solutions from direct numerical simulations. We find that the hydraulic conductivity (K) of the Poiseuille flow either increases or decreases with scales depending on ∇T > 0°C/m or ∇T < 0°C/m, respectively. Indeed, the degree of changes in K depends on the magnitude of ∇T and fracture length. The scale‐dependent model provides an alternative explanation for the well‐known scale‐dependent transport problem, for example, the dispersion coefficient increases with travel distance when ∇T > 0°C/m according to the Taylor dispersion theory, because K (or equivalently flux through fractures) scales with fracture length. The proposed theory unravels intertwined interactions between flow and transport processes, which might shed light on understanding many practical geophysical problems, for example, geothermal energy exploration. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Proposed two process intensified designs viz., symmetrical and asymmetrical CCFI. • Evaluated RTD and pressure drop experimentally and numerically over 10 ⩽ N R e ⩽ 145. • An evolution of narrower RTD with increasing tube length is computed numerically. • Revealed superiority of symmetrical CCFI over asymmetrical CCFI and CFI. Abstract The present study focuses on the intensification of flow and mixing in coiled flow inverter (CFI) geometries in order to achieve higher mixing efficiency with a lower base footprint. For this, two designs of "compact coiled flow inverter (CCFI)", namely, symmetrical compact coiled flow inverter and asymmetrical compact coiled flow inverter, are proposed within the same floor area as covered by a standard design of a conventional CFI. The design of the symmetrical CCFI is based on incorporating as many as possible 90° bends, whereas the asymmetrical CCFI is based on incorporating as much as possible mixing volume. In order to quantify the improvements caused by proposed designs, all three geometries (two CCFIs and one standard CFI) are compared (experimentally and numerically) with each other in terms of dimensionless dispersion number (D / UL) and mixing efficiency (that measures induced radial mixing by incorporating pressure drop penalty), over laminar flow regime (10 ⩽ N R e ⩽ 145). After validation of the numerical model (CFD) with experimental data, the RTD at different cross-sectional planes along the length of coiled tube is investigated. Such a study provides the relative contribution of helical turns and 90° bends in reducing axial dispersion, and also provides an insight of the required length of coiled tube that is sufficient to achieve a desired reduction in the axial dispersion. The present study reveals that the symmetrical compact coiled flow inverter has the highest mixing efficiency per unit occupied floor area, and requires the least length of coiled tube in order to reduce the axial dispersion at same extent. Thus, the symmetrical CCFI has potential to save significant material and operational energy cost in the Industry. [ABSTRACT FROM AUTHOR]

This study deals with further and systematic laboratory evaluation of the already known ammonium 12-molybdophosphate (AMP)-diffusive gradient in thin film (DGT) method, which is used for measuring total Cs concentration in environmental waters. This study confirms that the AMP-binding gel is not stable for pH > 6. In order to reveal a potential impact of AMP degradation on DGT application, time-series experiments were performed by deploying AMP-DGT samplers in Cs-doped moderately basic soft and hard water up to total AMP-binding gel degradation (60 and 175 h of deployment time, respectively). Linear accumulation of Cs by AMP-DGT samplers was observed up to 48 and 58 h in hard and soft waters, respectively. For this deployment time range, AMP-DGT measured over 77 ± 10 and 94 ± 16% of total Cs concentration in hard and soft water, respectively. The difference in DGT response was attributed to Ca2+ and Mg2+ competition reducing the uptake of AMP-DGT samplers in hard water. Shrinkage of agarose-polyacrylamide diffusive gel was experimentally observed only in hard water due to more intensive AMP-binding gel degradation in hard water. Even if the AMP-DGT response was not impacted in this study, it is recommended to use agarose hydrogel as standard diffusive gel. Based on the experience obtained from this detailed validation process, the authors propose a number of key requirements that need to be considered when developing DGT devices, with testing the performance over longer deployment times being critical.ᅟ [ABSTRACT FROM AUTHOR]

Highlights • Development of temporal velocity-based random walk model. • Applicable for mildly to highly heterogeneous formations. • Model has a clearly motivated and light-weight formulation. Abstract Recently, we have analytically derived a temporal velocity random-walk model for macrodispersion or transport uncertainty quantification based on velocity statistics from classical first-order perturbation expansions. The applicability of these expansions is limited to mildly heterogeneous formations with log-conductivity variances σ Y 2 < 1. In this work, we reformulate our model in order to account for velocity skewness and inter-component correlation that emerge as key drivers of non-Fickian dispersion at elevated heterogeneity levels σ Y. Eventually, we arrive at a light-weight parametrization of macrodispersion that is consistent with our earlier formulation, but at the same time is applicable for formations with multi-Gaussian log-conductivity characterization of variable heterogeneity, i.e. σ Y from 0 to 1 and beyond. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sticky crude Andrographis paniculata extract was successfully SEDS precipitated into powder. • 2-fold rise of aqueous solubility of andrographolide precipitated from CO 2 -acetone. • Powder with improved aqueous solubility was irregularly shaped and low crystalline. • 100% andrographolide dissolution from powder (high aqueous solubility) in 90 min. • No degradation of chemical composition of extract upon SEDS process. Abstract The objective of study is to improve aqueous solubility of andrographolide through particle engineering using Solution Enhanced Dispersion by Supercritical Fluids (SEDS) approach. The precipitation pattern of sticky crude Andrographis paniculata extract from CO 2 -acetone system and CO 2 -acetone:ethanol (v/v) 1:1 system as well as the aqueous solubility of andrographolide precipitated were first studied at different pressure (100, 150 bar) and temperature (40, 50 °C) combination (full factorial design). The modification of aqueous solubility of andrographolide was then attempted by manipulating its precipitation process from CO 2 -solvent systems consisting of single solvent and solvent mixture at different proportions (v/v) at the appropriate pressure-temperature combination. A. paniculata powder precipitated from CO 2 -acetone system at 150 bar, 40 °C was found to be large, irregularly shaped, less crystalline with the highest andrographolide aqueous solubility (twofold increment compared to crude extract) and recovery compared to those precipitated from CO 2 -ethanol system and other CO 2 -solvent mixture systems. Complete dissolution of andrographolide from A. paniculata powder precipitated from CO 2 -acetone system had been achieved within 90 min. For SEDS precipitation under solvent mixture system, with increment of proportion of ethanol from 25% to 75%, larger particles and change of powder morphology from stripes into plates were resulted. Based on the higher aqueous solubility and dissolution of andrographolide, recovery as well as a different morphology observed from the less crystalline A. paniculata powder precipitated from CO 2 -acetone system, less impurities could have co-precipitated with andrographolide. [ABSTRACT FROM AUTHOR]

Dispersion and mixing of fluids during miscible displacement in porous media are known to be strongly affected by heterogeneity and viscous fingering. In this study, direct pore-level numerical simulations are employed to model flow and solute transport during both stable and unstable miscible displacements in two-dimensional packings of circular grains. Longitudinal dispersion coefficients are then computed by fitting the numerically obtained concentration profiles to the analytical solution of the convection-dispersion equation. We observed that diffusive, mixed diffusive-advective, and mechanical dispersion regimes are present during stable displacements whereas the middle diffusive-advective regime is absent in unstable displacements due to the evolution of viscous fingers. Viscous fingering also increases the longitudinal dispersion coefficient several orders of magnitude compared to the stable displacement. The results reveal that the scale-dependency of longitudinal dispersion is a function of layering direction and viscosity contrast. During stable displacement in porous domains with no layering or with the layering perpendicular to the displacement direction, the longitudinal dispersion coefficient increases along the length of flow until it reaches an asymptotic value. When layering is in the direction of displacement, however, the scale-dependency behavior is a function of the layering pattern. In unstable displacements, however, longitudinal dispersion always exhibits an asymptotic behavior. Finally, it is observed that the effect of heterogeneity and layering on the magnitude of the longitudinal dispersion coefficient diminishes as viscosity ratio increases to higher adverse values. [ABSTRACT FROM AUTHOR]

Solute dispersion and mixing in beach aquifers is strongly influenced by highly transient flow induced from wave forcing. While transport at the groundwater-ocean interface has been modelled, little is known about the quantitative effect of wave forcing on solute dispersion and mixing in beach aquifers. We use a prototype-scale laboratory flume experiment to conduct tracer transport experiments at two locations within a wave-forced beach aquifer. For the first time we demonstrate by systematic laboratory experimentation that transient conditions in the re-circulation zone due to run-up and beach face infiltration as well as head oscillations caused by wave forcing strongly disperse and mix subsurface solute plumes. Wave forcing can increase the apparent dispersion by an order of magnitude depending on conditions, compared to solute transport without waves. Our findings illustrate that beach aquifer transport models need to consider the additional dispersion to correctly quantify mixing and biogeochemical processes in this highly dynamic zone. [ABSTRACT FROM AUTHOR]

Interactions between aqueous fluids and rocks occur in a broad range of contexts ranging from hydrothermal alteration veins to regional metamorphism. Tracking these processes and understanding their reaction kinetics require a precise knowledge of the diffusion of water in rocks, and of isotope fractionation in major minerals, such as chlorite. Deuterium‑hydrogen exchange between Mg-rich chlorite and water (D 2 O) was experimentally investigated using a belt press over the temperature range of 315–650 °C at pressures of 1.5 GPa and 3 GPa. Both chloritite chip and chlorite powder were used. D/(D + H) ratios in chlorite grains were mapped using Raman spectroscopy. Deuterium‑hydrogen exchange proceeded by deuterium‑hydrogen inter-diffusion in chlorite (lattice diffusion). As chlorite is a phyllosilicate, i.e. an anisotropic mineral, diffusion coefficients were determined for crystallographic directions parallel and perpendicular to the silicate layers (perpendicular and parallel to the c* axis, respectively). Arrhenius relations for deuterium‑hydrogen inter-diffusion coefficients were derived from the new dataset. Activation energy (E) is comprised between 215 ± 21 (1σ) kJ/mol (perpendicular to the c* axis) and 194 ± 21 kJ/mol (parallel to the c* axis). Log 10 (D 0 ) is −2.2 ± 1.3 m 2 /s for diffusion in the direction perpendicular to the c* axis and −4.5 ± 1.3 m 2 /s for diffusion parallel to it. The bulk diffusion law derived from a combination of our data with data from Graham et al. (1987) yields E = 176 ± 8 kJ/mol and log 10 (D 0 ) = −5.1 ± 0.4 m 2 /s. [ABSTRACT FROM AUTHOR]

A wide range of real-world flood routing problems can be approached using the Parabolic Approximation, widely recognized as a convenient simplification of the Saint Venant equations. From the Parabolic Approximation, head and discharge-based linear and non-linear advection-diffusion models were also derived by merging mass and momentum conservation equations into a single second-order equation to be used for one-dimensional flood routing. Both head and discharge-based advection-diffusion models were originally derived in their linear forms and extensively studied in the literature because they admit analytical solutions. The discharge-based non-linear models have been used as the basis for the derivation of the variable-parameter Muskingum routing method by setting the truncation error at par with the diffusion parameter. Whereas the linear models are mass-conservative, but inadequately reproduce routing in a variety of cases, the non-linear ones have been recently declared to be non-conservative. In the literature it has also been stated that the variable-parameter Muskingum fails to approximate the discharge-based non-linear discharge based advection-diffusion model on mild slopes. This paper aims at providing a systematic overview of all these models, showing that whereas the non-linear head-based advection-diffusion model, an original version of which is derived here, is in fact conservative, also the discharge-based model, which in principle is not, remains de facto conservative if integrated over a space-time grid with sufficiently small spatial cells. To complete the overview, we also demonstrate that in real-world applications the variable parameter Muskingum gives satisfactory results on mild slopes because lowland rivers in nature are essentially prone to slowly rising hydrographs. The results of all models are intercompared by routing different flood waves through prismatic reference channels with slope 10 - 4 and smaller. [ABSTRACT FROM AUTHOR]

Highly organized and highly stable water—hydrocarbon dispersions of liquid pyrolysis products and an ethane fraction were studied. Water evaporation was used as a dehydration method. Mixtures containing a water cut (20-75 mass%) were studied. Feedstock was separated by a thermomechanical method into bottom-product and distillate fractions. The dehydration efficiency was assessed based on the water cut in the bottom products. The water content in all studied mixtures was reduced to trace levels in the bottom products. Increasing the water cut in the emulsions was shown to increase the ratio of recovered hydrocarbon distillate to bottom products whereas diluting the starting emulsion with light pyrolysis resin had the opposite effect on the yield of dehydration products depending on the starting pyrolysis feedstock. [ABSTRACT FROM AUTHOR]

Reports a tracer diffusion coefficients for Kr85 in liquid argon, liquid nitrogen and liquid oxygen near boiling points. Theory for tracer coefficient determination; Description of the diffusion cell; Tables of tracer coefficients and Stokes radii; Implications of results for tracer coefficient measurement.

Examines the proton rotating spin-lattice relaxation study of water in hydrated porous silica glass. Detection of the relaxation times in well-defined dispersion; Motion of the molecules between the binding site and pore-core water; Variation of the pore-core water molecule with correlation time.

Effective states arising from variational perturbation calculations in a full configuration interaction basis are used to calculate dynamic multipole polarizabilities for H2 at seven different bond lengths. These are combined with previously calculated dynamic polarizabilities for rare gas atoms to obtain the intramolecular bond length dependence of the anisotropic C6, C8, and C10 dispersion coefficients for H2–X (X=He, Ne, Ar, Kr, Xe) interactions. The results are generally in good agreement with previous semiempirical estimates where available. [ABSTRACT FROM AUTHOR]

An ‘‘optical’’-like collective mode (OM) above 500 cm-1, or ω=100 ps-1, is known on the basis of molecular dynamics (MD) simulation of the TIP4P model for liquid water at T=293 K. Recently we proposed a dielectric theory of the OM for the same water model by applying the reference memory function approximation (RMFA), a theory of the computationally convenient type. It enables us to extend the MD results for the dielectric permittivity εω into the region of finite wave vector k. Thus we calculate the longitudinal dielectric function εL(k,ω) and the corresponding correlation functions for collective fluctuations in local polarization charge densities and currents required to characterize the OM. In the work reported here, we find that the calculated OM and its dispersion relation are relatively insensitive to whether the RMFA is implemented with collective or single particle reference dynamics, the principal difference being a more structured OM in the latter case. This finding provides the justification for applying the RMFA with reference dynamics based on the MD results of Frattini et al. for the single particle dipole reorientation time correlation functions of the same water model at various temperatures. We find that the OM has a definite temperature dependence, but the effect is weak even in the temperature range of real supercooled water. [ABSTRACT FROM AUTHOR]

We analyzed fluid fill height sensing supported by terahertz spoof surface plasmon polaritons (SPPs). The existence of spoof SPPs was proved experimentally and was discussed from perspective of dispersion and field distribution. For the application, we designed a fluid fill height sensor based on spoof SPPs, which is much more sensitive than previous work based on parallel plate waveguide (PPWG). For example, resonant shift of spoof SPPs is almost four times larger than the shift of PPWG at the height of 250 μm. This fluid fill height sensor calibrated the fluid volume in grooves, which contributes to improving the accuracy of high refractive index sensing. The experiment is in good agreement with simulation. Such proposed fluid height sensor has another advantage of being suitable for the fluid with refractive index higher than prism, which further benefits spoof SPPs refractive index sensing, such as blood detection in future. [ABSTRACT FROM AUTHOR]

An algorithm has been developed to track synoptic-scale, westward-traveling mixed Rossby-gravity (MRG) wave-like disturbances with a cross-equatorial component. Applied to space-time-filtered meridional wind data, this algorithm finds locations with Gaussian-shaped wind structures stated in the solutions of shallow-water equations (SWEs). Based on 850-hPa meridional wind from the global National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) dataset, local and instantaneous wave properties including the occurrence time, wavenumber, intrinsic frequency, and magnitude were examined. It was found that these low-level MRG wave-like disturbances can be classified into a longer-wavelength group and a shorter-wavelength group. While most waves identified in the eastern Pacific give longer wavelengths, disturbances in the western Pacific tend to have a wider range of wavenumbers. Composite analysis revealed that east of ~140°E, low-level disturbances are characterized by cross-equatorial wind anomalies with alternating signs, thus consistent with the MRG wave solution. West of ~140°E, they appear as northeast-southwest-tilted eddies that propagate northwestward. Examination of their energetics suggests that such a tilting structure is favorable to the maintenance of these transients because of the meridional shear of background zonal wind west of ~140°E in the off-equatorial Pacific. Farther east, the confluent nature of the low-level background flow plays a dominant role in maintaining the MRG wave-like disturbances because of barotropic conversion. Finally, there is evidence of downward energy dispersion in the mid- to upper levels, suggesting that the upper-level wave activity might be important in triggering these low-level waves in the Pacific basin [ABSTRACT FROM AUTHOR]

Frequent changes between inflow and outflow operations pose significant challenges in the design of bidirectional flow passage components with high efficiency and stability. In this study, hydraulic optimization of the inlet/outlet diffusion segment of a pumped storage power station was performed. First, a 3D-optimization platform was established for the inlet/outlet diffusion segment, and consists of parametric modelling, automatic mesh generation, CFD numerical calculation, and an optimization strategy. Three objective functions; the head loss, velocity uneven distribution, and discharge uneven distribution; were adopted to evaluate the overall performance of the inlet/outlet diffusion segment. Both dual- and triple-objective optimizations were adopted to optimize the shape of the inlet/outlet diffusion segment, the response surface methodology (RSM) was used to generate approximate functions relating to the objectives and design parameters, and the non-dominated sorting genetic algorithm (NSGA-II) was selected to conduct the optimizations. The objective of the present study was to use a numerical optimization method to determine the optimal inlet/outlet structure configurations yielding better hydraulic performance with bidirectional flow conditions. The results show that with triple-objective optimization, the head loss decreased by 2.71%, velocity uneven distribution decreased by 21.05%, and discharge uneven distribution decreased by 2.24%. [ABSTRACT FROM AUTHOR]

Water contents of synthetic sweet and sour natural gas–like mixtures and their constituents for wide ranges of temperature and pressure are studied in this work. The perturbed-chain version of statistical associated fluid theory (PC-SAFT) is used to describe the vapor and aqueous phase. In addition to repulsion and dispersion interactions, the 4C association scheme is used to account for self-association between water molecules. Using the PC-SAFT approach, the water contents of methane, ethane, hydrogen sulfide, carbon dioxide, and certain synthetic sweet and sour natural gas mixtures are predicted satisfactorily. [ABSTRACT FROM AUTHOR]

Usually, during oil production, water and oil flow simultaneously in the wellbore. When water holdup in the borehole is small, water droplets may be dispersed into bulk oil making water breakthrough detection a challenging task. In this paper, a comprehensive engineering model of droplet dispersion is presented. Dispersion of droplets in a long vertical turbulent tubing flow is modeled by an Advection-Diffusion-Population Balance equation. The Prandtl Mixing-Length model of turbulence is used to describe the velocity profile across a tubing. The turbulence energy dissipation rate distribution across a pipe is calculated by an analytical equation. The fixed pivot method is employed for calculation of the population balance term of the governing equation. Droplet fragmentation is modeled using a recently developed droplet breakup model (Eskin et al., 2017). It is assumed that volume concentration of a dispersed phase does not exceed 10%. A computational code developed allows tracking evolution of droplet size distribution along a tubing. Model performance is illustrated by computations of the water in oil dispersion process. Effects of oil/water interfacial tension, well production rate and oil viscosity on dispersion are demonstrated. [ABSTRACT FROM AUTHOR]

This is a historical account on the development of capillary LC from its beginning to the present day. The first investigations into the viability of capillary LC date back to the late 1970s, a decade after the pioneering efforts in HPLC. The drastically reduced column dimensions were required to counter the slow solute diffusion in liquids. There were numerous instrumental difficulties with sample introduction and detection in the picoliter or even femtoliter volumes. High-efficiency separations were needed in the analysis of complex biological mixtures. Miniaturization brought distinct advantages in spectroscopic and electrochemical detection. Since the 1980s, column technologies underwent significant changes: (a) from glass-drawn microcapillaries to slurry-packed, small-diameter fused silica columns; and (b) in microcapillaries packed alternatively with sub-2-μm particles or monoliths. The viability of LC–MS combination has dramatically promoted the use of small-diameter capillaries. Through “omics technologies”, capillary LC/tandem MS accounts for most applications in proteomics, glycomics and metabolomics. [ABSTRACT FROM AUTHOR]

This investigation experimentally examines the role of interface capture on the transport and deposition of colloidal material in evaporating droplets. It finds that deposition patterns cannot be characterized by the ratio of interface velocity to particle diffusion rate alone when the two effects are of the same order. Instead, the ratio of radial velocity to particle diffusion rate should also be considered. Ring depositions are formed when the ratio of radial velocity to the particle diffusion rate is greater than the ratio of interface velocity to diffusion. Conversely, uniform depositions occur when the ratio of radial velocity to diffusion is smaller than the ratio of interface velocity to diffusion. Transitional depositions with a ring structure and nonuniform central deposition are observed when these ratios are similar in magnitude. Since both ratios are scaled by diffusion rate, it is possible to characterize the depositions here using a ratio of interface velocity to radial velocity. Uniform patterns form when interface velocity is greater than radial velocity and ring patterns form when radial velocity is larger. However, Marangoni effects are small and Derjaguin, Landau, Verwey, and Overbeek (DLVO) forces repel particles from the surface in these cases. Further research is required to determine if these conclusions can be extended or modified to describe deposition patterns when particles are subjected to appreciable Marangoni recirculation and attractive DLVO forces. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of hydrodynamic dispersion on the stability of free convection in a saturated horizontal porous layer subject to a transient vertical concentration gradient and a steady horizontal background flow. A linear stability analysis (LSA) was conducted using the quasi-steady-state approximation to obtain neutral stability curves, critical times, and the corresponding wavenumbers as a function of dispersivity ratio (α) and longitudinal dispersion strength (β). The LSA results showed that the dispersive boundary layer becomes less unstable as longitudinal and transverse dispersivity increase. In addition, for the isotropic dispersive system with α = 1, the critical time and its corresponding wavenumber follow τc = 167.6/(1 − β) and κc = 0.0696 (1 − β), respectively. The nonlinear dynamics of the system were studied by examining the interaction of convective fingers, dissolution flux, and the time-dependent Sherwood number. Finally, the results were applied to 24 deep saline aquifers in the Alberta Basin. [ABSTRACT FROM AUTHOR]

Small tide-dominated estuaries are affected by large scale flow structures which combine with the underlying bed generated smaller scale turbulence to significantly increase the magnitude of horizontal diffusivity. Field estimates of horizontal diffusivity and its associated scales are however rare due to limitations in instrumentation. Data from multiple deployments of low and high resolution clusters of GPS-drifters are used to examine the dynamics of a surface flow in a small micro-tidal estuary through relative dispersion analyses. During the field study, cluster diffusivity, which combines both large- and small-scale processes ranged between, 0.01 and 3.01 m 2 /s for spreading clusters and, −0.06 and −4.2 m 2 /s for contracting clusters. Pair-particle dispersion, Dp 2 , was scale dependent and grew as D p 2 ∼ t 1.83 in streamwise and D p 2 ∼ t 0.8 in cross-stream directions. At small separation scale, pair-particle ( d < 0.5 m) relative diffusivity followed the Richardson's 4/3 power law and became weaker as separation scale increases. Pair-particle diffusivity was described as K p ∼ d 1.01 and K p ∼ d 0.85 in the streamwise and cross-stream directions, respectively for separation scales ranging from 0.1 to 10 m. Two methods were used to identify the mechanism responsible for dispersion within the channel. The results clearly revealed the importance of strain fields (stretching and shearing) in the spreading of particles within a small micro-tidal channel. The work provided input for modelling dispersion of passive particle in shallow micro-tidal estuaries where these were not previously experimentally studied. [ABSTRACT FROM AUTHOR]

Aquifer heterogeneity affects the characteristics of solute breakthrough curves (BTCs). A better understanding of the relationship between aquifer heterogeneity and BTCs will help improve prediction of the fate of contaminants in an aquifer. Previous studies have shown that systematic research of aquifer heterogeneity on solute transport is limited. Therefore, this study investigates the impacts of aquifer heterogeneity on conservative solute BTCs and transport mechanism via experimental and modeling approaches. Tracer experiments are conducted in four flow-through columns exhibiting different patterns of heterogeneities. Furthermore, this study also examines the influence of hydraulic conductivity on transport mechanism. In addition, this paper analyses the correlation between hydraulic conductivity and dispersivity, which are the key parameters of conservative solute transport in an aquifer. Experimental data indicates the impacts of aquifer heterogeneity on transport of tracer. Tracer BTCs in a homogeneous aquifer have the typical sigmoid shape without tailing. In a heterogeneous aquifer, tracer BTCs display a strong and persistent tailing. In a preferential flow aquifer, tracer BTCs have pronounced tailing and early arrival time. The hydraulic conductivity of an aquifer significantly affects the transport mechanism of tracer. When the hydraulic conductivity is higher than 1.53 cm/min, transport of tracer is applicable to the ADE. When the hydraulic conductivity is lower than 1.53 cm/min, transport of tracer is applicable to the TRM. This work offers insight into the correlation between the hydraulic conductivity of an aquifer and the dispersivity of a conservative solute. A critical finding is that hydraulic conductivity K and dispersivity $$\lambda$$ correspond to an exponential regression form $$\lambda = e^{{ - 0.24555 - 4.54413K + 2.27308K^{2} }}$$ ( R = 0.957). [ABSTRACT FROM AUTHOR]

Atlantic Coastal Plain Flora (ACPF) are a group of plants mostly inhabiting lakeshores along the Atlantic coast of the United States, with disjunct populations in Nova Scotia and Ontario. To better define their ecological requirements, the main objective of this study was to determine the factors (biotic and abiotic habitat components) influencing ACPF communities (distribution, species abundance, and richness) at both the landscape and local scales. On 16 lakeshores in southwestern Nova Scotia, we characterized ACPF communities and habitat within 20 cm square contiguous quadrats distributed along 20 m transects (landscape scale) and in 5 m × 5 m grids (local scale). Performing redundancy analysis ( n = 16 transects), we found that at the landscape scale, shoreline slope and shrub species distribution influenced the quantity of suitable habitat available for ACPF, with mineral shorelines supporting higher ACPF richness. Using spatial generalized linear mixed models ( n = 3125 quadrats in five grids), we found that elevation, vegetation elements (shrubs, sundews, graminoids), and substrate type mostly influenced ACPF presence and abundance. ACPF also showed inter-specific differences in habitat preferences. Defining ACPF ecological requirements at both the landscape and local scales is important to guide conservation and management actions in Nova Scotia and throughout their North American range. [ABSTRACT FROM AUTHOR]

In this work, single particle dispersion was analyzed for a bacterial turbulence by retrieving the virtual Lagrangian trajectory via numerical integration of the Lagrangian equation. High-order displacement functions were calculated for cases with and without mean velocity effect. The two-regime power-law behavior for short and long time evolutions was identified experimentally, which was separated by the Lagrangian integral time. For the case with the mean velocity effect, the experimental Hurst numbers were determined to be 0.94 and 0.97 for short and long time evolutions, respectively. For the case without the mean velocity effect, the values were 0.88 and 0.58. Moreover, very weak intermittency correctionwas detected.All measured Hurst numbers were above 1/2, the value of the normal diffusion, which verifies the super-diffusion behavior of living fluid. This behavior increases the efficiency of bacteria to obtain food. [ABSTRACT FROM AUTHOR]

The diffusion of the hydroxide ion in bulk water was examined by linear-scaling divide-and-conquer density-functional tight-binding molecular dynamics (DC-DFTB-MD) simulations using three different-sized unit cells that contained 522, 1050, and 4999 water molecules as well as one hydroxide ion. The repulsive potential for the oxygen-oxygen pair was improved by iterative Boltzmann inversion, which adjusted the radial distribution function of DFTB-MD simulations to that of the reference density functional theory-MD one. The calculated diffusion coefficients and the Arrhenius diffusion barrier were in good agreement with experimental results. The results of the hydroxide ion coordination number distribution and potential of mean force analyses supported a dynamical hypercoordination diffusion mechanism. [ABSTRACT FROM AUTHOR]

This article employs a hydro-economic optimization model to analyze the effects of the Grand Ethiopian Renaissance Dam on the distribution and magnitude of benefits in the Eastern Nile. Scenarios are considered based on plausible institutional arrangements that span varying levels of cooperation, as well as changes in hydrological conditions (water availability). The results show that the dam can increase Ethiopia’s economic benefits by a factor of 5–6, without significantly affecting or compromising irrigation and hydropower production downstream. However, increasing GERD water storage during a drought could lead to high costs not only for Egypt and Sudan, but also for Ethiopia. [ABSTRACT FROM AUTHOR]

Investigating the hydrological response of an area to adverse climate changes and extreme rainfall events is crucial for managing land and water resources and mitigating the natural hazards like floods. Limited availability of the in situ data, especially in case of Transboundary Rivers, further highlights the need to develop and evaluate decision support systems which may predict the flows in real time using open source rainfall data. This paper presents the study conducted in Chenab River catchment, Pakistan, to develop and evaluate a hydrologic model using HEC-HMS for predicting flows based on TRMM rainfall data. The catchment was analyzed for hydro-morphological properties using SRTM DEM in HEC-GeoHMS. To rely on open source data as much as possible, digital soil map of the world developed by FAO and global land cover map developed by European Space Agency were utilized to compute Curve Number grid data for the catchment. These preliminary data analyses were employed to set initial values of different parameters to be used for model calibration. The model was calibrated for five rainfall events occurred in the rainy seasons of 2006, 2010 and 2013. The calibrated model was then validated for four other rainfall events of similar type in the same years. Consistency in simulated and observed flows was found with percent difference in volume ranging from −6.17 % to 5.47 % and percent difference in peak flows to be in the range of 6.96 % to 7.28 %. Values of Nash-Sutcliffe Efficiency were ranging from 0.299 to 0.909 with an average value of 0.586 for all flow events. The model was found well capable of capturing the hydrologic response of the catchment due to rainfall events and can be helpful in providing alerts of peak flows in real time based on real time/forecasted rainfall data. [ABSTRACT FROM AUTHOR]

Modeling river mixing mechanism in terms of pollution transmission in rivers is an important subject in environmental studies. Dispersion coefficient is an important parameter in river mixing problem. In this study, to model and predict the longitudinal dispersion coefficient ( D ) in natural streams, two soft computing techniques including multivariate adaptive regression splines (MARS) as a new approach to study hydrologic phenomena and multi-layer perceptron neural network as a common type of neural network model were prepared. To this end, related dataset were collected from literature and used for developing them. Performance of MARS model was compared with MLP and the empirical formula was proposed to calculate D . To define the most effective parameters on D structure of obtained formula from MARS model and more accurate formula was evaluated. Calculation of error indices including coefficient of determination (R) and root mean square error (RMSE) for the results of MARS model showed that MARS model with R = 0.98 and RMSE = 0.89 in testing stage has suitable performance for modeling D . Comparing the performance of empirical formulas, ANN and MARS showed that MARS model is more accurate compared to others. Attention to the structure of developed MARS and the most accurate empirical formulas model showed that flow velocity, depth of flow (H) and shear velocity are the most influential parameters on D . [ABSTRACT FROM AUTHOR]

In the north of the province of Santa Fe, especially in the forest wedge, Lower Submeridionals and Occidental Domo, there are more than three million head of cattle, where one of the main de- terminants of production is the irregular quality of groundwater For the watering of the hacienda. The fl uctuation between dry and wet hydrological scenarios has a direct impact on production, where not only the free water table, which is the only available water, varies, but also the chemical quality of the water. In collaboration with the INA, the Government of Santa Fe and UNL Research Centers, INTA has developed research and transfer demonstration units in the fi elds of producers and experi- mental units of the Institution, designing and proposing different technologies that are consen- sual with the Producers in the management of rainwater supplemented with the underground. 3 water systems were implemented with different ways of using rainwater with ground-water, systematizing terrain to guarantee access and recharge of the free aquifer, with pumping mechanisms using renewable energy and with suction systems that do it in the part Surface of the aquifer, where all converge to a central mixing tank, to ensure that all animals take water with the same chemical quality, whatever the place of grazing. Since 2011 the variables of interest are monitored, where the premise is to have contro- lled the salinity of the water in the central mixing tank and that its variations throughout the year are gradual, since this maximizes livestock production. This is visualized in each of the three systems and, fundamentally in the central mixing tank, where the quantity, quali- ty and opportunity during the year clearly show very positive results in the place studied [ABSTRACT FROM AUTHOR]

The longitudinal dispersion coefficient ( k ) is necessary for a plethora of mass transport applications in fluids, but a general formulation for k remains lacking. In this study, we propose a canonical form for k that reflects the physics of dispersion and suits complex flow conditions encountered in natural streams. This general form is much more concise than previous predictors. A predictor for k of natural streams is also obtained using a genetic programming(GP) without pre-specified correlations among field data or a pre-specified form of the predictor. This predictor is physically sound (i.e. exhibits the aforementioned canonical form) and appears to be commensurate to or better than previous estimates of k . A grey model, which measures the proximity of data to a target shape (i.e. the proposed physically sound form), is also used to verify that the canonical form is appropriate. A formulation for k in natural rivers is obtained by utilising a GP. Its form is consistent with the canonical form. [ABSTRACT FROM AUTHOR]

The concepts of hydrological alteration and the related natural flow paradigm conceive variable environmental flows that preserve as much as possible the natural variability of flows, with a particular focus on a suite of specific characteristics, the so-called indicators of hydrological alteration (IHA). In the paper we propose a simple simulation approach for a preliminary desk-top assessment environmental flows, whose principle is to maximize the possible utilization of water while complying with the alteration targets according to a global alteration metric. We investigate the use of three different alteration metrics, with the aim of measuring the sensitivity of environmental flow assessments respect to the index and the corresponding low and moderate alteration target thresholds. An application of the methodology to a case study area in Sicily, comprising several rivers sections, is carried out. Results show that a significant sensitivity of the optimal environmental flows to the alteration metric, both in the pattern and in the amount. While some metrics privilege environmental flow patterns that follow the natural variability of IHA parameters, other yield to optimal environmental flows that follow the long-term means of the IHA parameters. Results also show that in general the attainment of the low alteration target is quite demanding, since at least the 30 % of natural flows should be addressed to environmental flows, while for a moderate alteration hydrological status this percentage reduces to 15 %. [ABSTRACT FROM AUTHOR]

A two-layer model with uniform non-hydrostatic pressure in the bottom produces favorable dispersion properties for coastal wave transformation at the computational requirements of a one-layer model. We derive the nonlinear governing equations and the corresponding dispersion relation, shoaling gradient, and super- and sub-harmonics to understand the theoretical performance of this reduced model. With the layer interface near the bottom, the dispersion relation shows an extended applicable range into deeper water at the expense of a slight overestimation of the celerity in intermediate water depth. The shoaling gradient rapidly converges to the exact solution in the shallow and intermediate depth range. These complementary characteristics allow identification of an optimal interface position for both linear wave properties. The resulting model exhibits good nonlinear performance in shallow and intermediate water depth and produces super- and sub-harmonics comparable to a two-layer model. Numerical tests involving standing waves show the reduced model has smaller discretization errors in the dispersion relation comparing to a one-layer model. Case studies of regular wave transformation over a submerged bar and a uniform slope provide comparison with laboratory data and demonstrate the linear and nonlinear properties derived from the governing equations. The good shoaling and nonlinear properties give rise to accurate waveforms in both cases, while dispersion errors from the governing equations and numerical schemes accumulate over time leading to phase shifts of the modeled waves. [ABSTRACT FROM AUTHOR]

Theoretical methods have been developed to estimate the longitudinal dispersion coefficients (k) in natural rivers. The triple integral expression for longitudinal dispersion caused by the transverse velocity gradient and the solution for the depth-averaged streamwise velocity distribution in the transverse direction in a rectangular flume are used in this study. The longitudinal dispersion coefficient was calculated after changing the nonintegral formula for the velocity distribution into a trigonometric function series by Fourier transformation and then by substituting this series into the triple integral expression. A dimensionless formula for longitudinal dispersion in the flume was then obtained by regression analysis and was consistent with the experimental results obtained in previous studies and this study. By analyzing the measured dispersion coefficients of the natural rivers and the corresponding values obtained from the formula for a flume with the same hydraulic parameters, a formula was derived for the longitudinal dispersion coefficient of natural rivers. The formula provides a suitable method for estimating pollutant transport in natural rivers. [ABSTRACT FROM AUTHOR]

Estimating groundwater recharge is crucial to ensuring the proper management of aquifers. In this study, net regional recharge and spatial potential recharge are estimated at four watersheds within the Charlevoix-Haute-Côte-Nord (CHCN) regions, Quebec Province, Canada. Four methods are applied based on available data. The first two approaches are regional water budget methods. These two methods differ in their estimation of vertical inflow (VI), which is estimated from two hydrological models: GR4J and HYDROTEL. The third method estimates potential recharge spatially over the study area. Finally, the streamflow data are analysed using the Eckhardt baseflow separation method to obtain an estimation of recharge, assuming that discharge is equal to recharge. According to the results of all investigated methods, the mean annual recharge for the CHCN region is approximately 183 mm, which is 18% of the total annual precipitation (P). The discussion section highlights uncertainties due to the assumptions of each method and the reliability of the data. [ABSTRACT FROM AUTHOR]

A new semianalytical solution is developed for the velocity-dependent dispersion Henry problem using the Fourier-Galerkin method (FG). The integral arising from the velocity-dependent dispersion term is evaluated numerically using an accurate technique based on an adaptive scheme. Numerical integration and nonlinear dependence of the dispersion on the velocity render the semianalytical solution impractical. To alleviate this issue and to obtain the solution at affordable computational cost, a robust implementation for solving the nonlinear system arising from the FG method is developed. It allows for reducing the number of attempts of the iterative procedure and the computational cost by iteration. The accuracy of the semianalytical solution is assessed in terms of the truncation orders of the Fourier series. An appropriate algorithm based on the sensitivity of the solution to the number of Fourier modes is used to obtain the required truncation levels. The resulting Fourier series are used to analytically evaluate the position of the principal isochlors and metrics characterizing the saltwater wedge. They are also used to calculate longitudinal and transverse dispersive fluxes and to provide physical insight into the dispersion mechanisms within the mixing zone. The developed semianalytical solutions are compared against numerical solutions obtained using an in house code based on variant techniques for both space and time discretization. The comparison provides better confidence on the accuracy of both numerical and semianalytical results. It shows that the new solutions are highly sensitive to the approximation techniques used in the numerical code which highlights their benefits for code benchmarking. [ABSTRACT FROM AUTHOR]

Background: Produced water from offshore oil and gas platforms is often disposed of directly into the sea, and there has been concern that this discharge might have deleterious effects on the marine environment. To help understand the patterns of dispersion and dilution of produced water discharges, and their potential effects, a combined modeling and monitoring study was conducted. Results: Chemical analysis of representative produced water samples recovered from the Sable Offshore Energy Project (SOEP) Venture platform showed elevated concentrations of several organic and inorganic compounds of environmental concern; however, of the 25 stations sampled within 500 m of the platform, only one station, NE50, located 50 m to the northeast, showed chemicals associated with produced water at levels significantly above background values. The Dose-related Risk and Effect Assessment Model (DREAM) was used to evaluate the fate and transport processes of produced water after discharge. The results revealed that the near background level concentrations detected at the 26 stations were due to sampling outside the narrow plume boundary. This indicated that there was no accumulation of pollutants near the platform except inside the narrow plume. Conclusion: The comparison of modeled and empirical data showed that the DREAM model can effectively predict plume behaviour. The results agreed well with the monitoring data and simulated the location of the plume as it changed continuously with the tidal currents. The model illustrated that elevated concentrations within the produced water plume occur only near the vicinity of the discharge. [ABSTRACT FROM AUTHOR]