Thin Water Layer Research Articles

Diffusion of PAH in Potato and Carrot Slices and Application for a Potato Model

A method for quantifying the effect of medium composition on the diffusive mass transfer of hydrophobic organic chemicals through thin layers was applied to plant tissue. The method employs two silicone disks, one serving as source and one as sink for a series of PAHs diffusing through thin layers of water, potato tissue, and carrot tissue. Naphthalene, phenanthrene, anthracene, and fluoranthene served as model substances. Their transfer from source to sink disk was measured by HPLC to determine a velocity rate constant proportional to the diffusive conductivity. The diffusive flux through the plant tissue was modeled using Fick's first law of diffusion. Both the experimental results and the model suggest that mass transfer through plant tissue occurs predominantly through pore water and that, therefore, the mass transfer ratio between plant tissue and water is independent of the hydrophobicity of the chemical. The findings of this study provide a convenient method to estimate the diffusion of nonvolatile organic chemicals through various plant materials. The application to a radial diffusion model suggests that "growth dilution" rendersthe concentration of highly hydrophobic chemicals in potatoes below their equilibrium partitioning level. This is in agreement with field results for the bioconcentration of PAHs in potatoes.

Characterization of thin water layers in pulp by tritium exchange. Part 2: Effect of refining on water absorption

Abstract The surface area of pulp increases upon refining, which also increases the quantity of bound water. The subfraction of water attached to the surface as a monolayer can be determined by adding tritiated water to a pulp/water suspension and measuring the distribution of tritium between the pulp and bulk water. For bleached kraft pulp the tightly bound water slowly increases with progressive refining, increases sharply at 360 ml Canadian Standard Freeness (CSF), and then falls below CSF 220 ml. The fiber saturation point displays a similar profile, although the changes are much less pronounced. It is proposed that refining occurs in three discrete stages. First, refining down to CSF 360 ml removes the primary cell wall and S1 layer, while the S2 layer begins to swell. Next, internal delamination occurs within the S2 layer between CSF 360 and 220 ml, as confirmed by scanning electron microscopy. The onset of delamination is sudden: dramatic changes in fiber structure occur at CSF 360 ml, at which point the tightly bound water content rapidly increases. Finally, fiber destruction occurs below CSF 220 ml.

Characterization of thin water layers in pulp by tritium exchange. Part 1: Methods development

Abstract A new technique for measuring the monolayer water content of fiber is presented. Tritiated water is added to a pulp/water suspension, whereupon the tritium partitions between the bulk water and the pulp. In the pulp phase the tritium can exchange with free water, bound water, and with hydroxyl and other protons present in the pulp matrix. The free water in the pulp is then removed by displacement with acetone. The tritium remaining in the pulp is mostly associated with tightly bound water, with a small fraction being tied up with the exchangeable hydrogen in pulp. The procedure provides a value of 10% for the tightly bound water content of hardwood or softwood fiber, either bleached or unbleached. If this water is assumed to cover the fiber surface as a monolayer, then an estimate of the wet surface area of the fiber can be obtained. This estimate compares well with independent measurements of surface area.

The electro-osmotically driven flow near an earthworm's body surface and the inspired bionic design in engineering

The electro-osmotically driven flow near an earthworm’s body surface is a basic electrokinetic phenomenon that takes place when the earthworm moves in moist soil. The flow in a micro thin layer of water is formed in the vicinity of the earthworm’s body surface as a result of the electric double layer interaction. Such a micro scale electro-osmotically driven flow plays the role of lubrication between the earthworm’s body surface and the surrounding medium of moist soil and reduces the surface adhesion. The examples of bionic design in engineering inspired by such natural phenomena of the earthworm in soil are reported.

Hydration of Oligo(ethylene glycol) Self-Assembled Monolayers Studied Using Polarization Modulation Infrared Spectroscopy

The interaction with water of protein-resistant monolayers (SAMs), self-assembled from (triethylene glycol) terminated thiol HS(CH2)11(OCH2CH2)3OMe solutions, was studied using in and ex situ polarization-modulated Fourier transform infrared spectroscopy. In particular, shifts in the position of the characteristic C-O-C stretching vibration were observed after the monolayers had been exposed to water. The shift in frequency increased when the SAM was observed in direct contact with a thin layer of water. It was found that the magnitude of the shift also depended on the surface coverage of the SAM. These findings suggest a rather strong interaction of oligo(ethylene glycol) SAMs with water and indicate the penetration of water into the upper region of the monolayer.

Convection driven by collective buoyancy of microbubbles

Characteristics of convective flows produced by buoyancy of small bubbles rising from the horizontal bottom of a thin water layer are investigated with laboratory experiments, numerical experiments and theoretical analysis for steady convection cells. Immediately after the production of bubbles, small plumes of bubble-contained fluid are produced by Rayleigh–Taylor instability. The laboratory experiment suggests that the convective pattern is modified from plumes to cellular convection when the plumes reach the top of the fluid layer. There is a tendency for the aspect ratio of the cell to increase with the bubble flux, and this tendency was confirmed by numerical simulations. The analysis for steady convection cells also derived consistent solutions: a convection cell with too large a horizontal scale cannot be sustained, and the critical scale increases with the flux of the bubbles. The convective patterns in the final stage depend mainly upon the volume flux ( F ) of the bubbles and the rising velocity ( w b ) of a bubble in a still fluid. According to the numerical simulation, the steady cellular pattern is obtained only in limited combinations of F and w b . It is also found that the steady organized cellular convection is only sustained in a system without diffusion of the buoyancy. If the buoyancy diffuses across the trajectories of bubbles, the cellular convection eventually disappears. In the final steady state the buoyancy is transported only by the rising velocity of bubbles. In this respect, this convective motion is quite different from Bénard convection where the steady cellular convection is maintained in a diffusive system.

Submicrosecond dynamics of water explosive boiling and lift-off from laser-heated silicon surfaces

Explosive boiling and lift-off of a thin layer of micron-sized transparent water droplets from an absorbing Si substrate heated by a nanosecond KrF laser were studied using a contact photoacoustic technique. The compressive photoacoustic response increases steeply to an asymptotic value on the order of the water critical pressure starting at a threshold laser fluence of 0.20J∕cm2, where lift-off of the water layer also occurs. Above this threshold, several reproducible discrete multimegahertz components are revealed in Fourier spectra of the acoustic transients, corresponding to nanosecond oscillations of steam bubbles inside the water droplets on the microsecond time scale of the lift-off process. The acoustic pressure buildup, bubble dynamics, and the subsequent lift-off of the thin water layer are interpreted as relaxation stages after near-spinodal explosive boiling of the superheated interfacial water.

Electrochemically and catalytically active layer-by-layer films of myoglobin with zirconia formed by vapor-surface sol–gel deposition

Abstract A myoglobin (Mb) film was successfully assembled layer-by-layer with zirconia formed by vapor-surface sol–gel deposition on solid surfaces. The method involved vaporization of zirconium butoxide (Zr(OBu) 4 ) into thin layers of water, forming ZrO 2 sol–gel layers after hydrolysis of Zr(OBu) 4 . Mb was assembled by adsorption alternated with the ZrO 2 layers. The {ZrO 2 /Mb} n layer-by-layer films at pyrolytic graphite electrodes demonstrated a pair of well-defined and nearly reversible CV peaks at about −0.34 V vs SCE, characteristic of Mb Fe(III)/Fe(II) redox couple, and used to catalyze reduction of oxygen and hydrogen peroxide. FTIR spectroscopy and comparison studies with {ZrO 2 /catalase} n films suggest that Mb in the zirconia sol–gel films essentially retains its native structure. Compared with Mb layer-by-layer films assembled with ZrO 2 nanoparticles, {ZrO 2 /Mb} n films showed larger numbers of electroactive bilayers and higher maximum surface concentration of electroactive Mb, which may be related to the unique structure of ZrO 2 sol–gel with higher porosity.

Paleoceanographic evolution of the SW Svalbard margin (76°N) since 20,000 14C yr BP

Two cores from the southwestern shelf and slope of Storfjorden, Svalbard, taken at 389 m and 1485 m water depth have been analyzed for benthic and planktic foraminifera, oxygen isotopes, and ice-rafted debris. The results show that over the last 20,000 yr, Atlantic water has been continuously present on the southwestern Svalbard shelf. However, from 15,000 to 10,000 14C yr BP, comprising the Heinrich event H1 interval, the Bølling–Allerød interstades and the Younger Dryas stade, it flowed as a subsurface water mass below a layer of polar surface water. In the benthic environment, the shift to interglacial conditions occurred at 10,000 14C yr BP. Due to the presence of a thin upper layer of polar water, surface conditions remained cold until ca. 9000 14C yr BP, when the warm Atlantic water finally appeared at the surface. Neither extensive sea ice cover nor large inputs of meltwater stopped the inflow of Atlantic water. Its warm core was merely submerged below the cold polar surface water.

Appearance and evolution of marine benthic communities in the Early Palaeozoic

The development of marine benthic communities in the Early Palaeozoic occurred mainly in the shallow water epicontinental seas. It included those stages of the Cambrian and Ordovician evolutionary radiations that were dominated by a high rate of morphogenesis, when new food and territory resources were not limited. This provided many opportunities for coadaptation of emerging organisms. At the time of the Cambrian radiation, the body plans of all animals were formed, while in the Ordovician, the maximum rank of emerging taxa did not exceed the level of class. The beginning of each radiation was explosive. Vendian benthic communities developed in cold seas and in the shallowest areas of warm seas, where organic matter from the surface layers was available at the bottom because of the absence of a thermocline. The Cambrian radiation began with the appearance of pelagic suspension feeders, because of which much of the primary production could penetrate the thermocline and settle at the bottom. This allowed the occupation of warmer seas and greater depths. At the same time, the productivity of the pelagic region sharply increased because of the emergence of positive feedback between the producers and consumers in the water, leading to increased water transparency and elongation of trophic chains. Arthropods, the first suspension feeders, were the launch group of the Cambrian radiation. Cambrian benthic suspension feeders could seize only the smallest particles, mostly bacteria, and dissolved organic matter. This food resource was contained in the thin bottom water layer. Therefore, the food grasping structures of all the Cambrian suspension feeders were near the bottom, without forming tiers. The Ordovician evolutionary radiation began with the launch of the Pelmatozoan echinoderms, which were the first benthic suspension feeders to begin feeding on plankton. The exploitation of this resource led to the creation of a 1-m tier above the bottom and an increase in their calcite productivity. Positive feedback emerged between the grounds and the community of its inhabitants and considerably changed the composition and diversity of grounds, which sharply increased the diversity of benthos. The appearance of positive feedback between different components of ecosystems resulted in explosive evolution in both the Cambrian and Ordovician.

One-dimensional dynamics of nano-scale oxidation

A continuum model is proposed to describe the process of scanned probe oxidation in the presence of a thin water layer on the surface of a substrate. The model describes the electric field and ion transport in both the liquid and the oxide layers and incorporates the reaction mechanism at the substrate/oxide interface. Further, the influence of the space charge due to ions trapped near the substrate/oxide interface is taken into account. Separation of time scales for the chemical reactions and ion transport as well as the asymptotic limit in terms of a small aspect ratio of the oxide layer are used to reduce the complex system of partial differential equations to a one-dimensional system of ordinary differential equations. The analytical solution of the reduced system results in the evolution equation for the oxide thickness. Numerical simulations of the evolution equation predict features of oxide growth that qualitatively agree with the experimental observations. A parametric study is conducted to determine the influence of the key operating and material parameters on the thickness of the oxide, the electric field, and ion concentration in the system.

Carbonic anhydrase in leaves during radish plant ontogeny and glucose effect

Radish (Raphanus sativus L.) plants were grown in a greenhouse in soil at natural illumination, temperature, and CO2 concentration. A relationship between the activity of soluble carbonic anhydrase (sCA) and the content of soluble carbohydrates (sCH) was investigated depending on leaf position on the stem during plant development. Indices characterizing leaf ageing during the phase of vegetative growth (PVG) (in lower leaves as compared to upper ones) were a decrease in the rate of photosynthetic release of O2, photosynthetic efficiency, quantum efficiency of photosystem II, and the content of chlorophylls a and b. During PVG and the phase of flower bud formation, the activity of sCA and the contents of sCH, soluble protein, and Glu were the greatest in young (topmost) leaves and declined in the leaves of middle and lower storeys. From the top to the middle leaves, a dependence of sCA activity on the content of Glu or other sCH (without Glu) was direct, whereas, from the middle and the lower leaves, it became inversed. During leaf ageing in vegetatively growing plants and in the phase of budding, the relation between sCA and a relative content of Glu (percent of the rest sCH) was similar to that described above and yielded broken lines, and, during flowering, an inverse relation was observed in the leaves of all three storeys with a low content content of Glu and a low sCA activity. In order to study a dependence of sCA activity on the levels of sCH and Glu during PVG, one half of the leaf was incubated in a thin layer of water at a light schedule: by 12 h of night/day/night + 3-h-long illumination (control material). Within the period of active growth of the hypocotyl up to the storage root formation, the sCA activity and the content of sCH in the leaves incubated in water (control) increased. During a later PVG, both characteristics declined with sCA activity reduced stronger. The rate of the photosynthetic O2 release changed in accordance with the changes in sCA activity. Incubation of the other half of the same leaf in 20 mM Glu during early PVG brought about a considerable increase in sCA activity as compared with control material. During a later PVG and at a much greater Glu concentration (330 mM), its content in the leaves increased manifold; however, there were no significant changes in the activity of sCA, the content of protein or chlorophyll. It was concluded that the activity of sCA in the radish leaves during PVG was not regulated by the absolute content of sCH or Glu in the leaves but depended on endogenous factors associated with plant development.

Evaluation of a large-eddy model simulation of a mixed-phase altocumulus cloud using microwave radiometer, lidar and Doppler radar data

SUMMARY Using the Met Office large-eddy model (LEM) we simulate a mixed-phase altocumulus cloud that was observed from Chilbolton in southern England by a 94 GHz Doppler radar, a 905 nm lidar, a dual-wavelength microwave radiometer and also by four radiosondes. It is important to test and evaluate such simulations with observations, since there are significant differences between results from different cloud-resolving models for ice clouds. Simulating the Doppler radar and lidar data within the LEM allows us to compare observed and modelled quantities directly, and allows us to explore the relationships between observed and unobserved variables. For general-circulation models, which currently tend to give poor representations of mixed-phase clouds, the case shows the importance of using: (i) separate prognostic ice and liquid water, (ii) a vertical resolution that captures the thin layers of liquid water, and (iii) an accurate representation the subgrid vertical velocities that allow liquid water to form. It is shown that large-scale ascents and descents are significant for this case, and so the horizontally averaged LEM profiles are relaxed towards observed profiles to account for these. The LEM simulation then gives a reasonable cloud, with an ice-water path approximately two thirds of that observed, with liquid water at the cloud top, as observed. However, the liquid-water cells that form in the updraughts at cloud top in the LEM have liquid-water paths (LWPs) up to half those observed, and there are too few cells, giving a mean LWP five to ten times smaller than observed. In reality, ice nucleation and fallout may deplete ice-nuclei concentrations at the cloud top, allowing more liquid water to form there, but this process is not represented in the model. Decreasing the heterogeneous nucleation rate in the LEM increased the LWP, which supports this hypothesis. The LEM captures the increase in the standard deviation in Doppler velocities (and so vertical winds) with height, but values are 1.5 to 4 times smaller than observed (although values are larger in an unforced model run, thisonly increases the modelled LWPby a factor of approximately two). The LEM data show that, for values larger than approximately 12 cm s −1 , the standard deviation in Doppler velocities provides an almost unbiased estimate of the standard deviation in vertical winds, but provides an overestimate for smaller values. Time-smoothing the observed Doppler velocities and modelled mass-squared-weighted fallspeeds shows that observed fallspeeds are approximately two-thirds of the modelled values. Decreasing the modelled fallspeeds to those observed increases the modelled IWC, giving an IWP 1.6 times that observed.

Nondestructive testing in human teeth using a leaky Lamb wave device

A Lamb wave interdigital transducer mounted on a layered substrate composed of two plates, a thin piezoelectric ceramic plate and an acrylic plate, operating at a liquid–solid boundary, is investigated for ultrasonic nondestructive testing of the layer thickness in human teeth. A higher-order mode having a phase velocity higher than the longitudinal wave velocity in the human teeth can be used for nondestructive testing. In the combination of the two layers, the fourth mode of leaky Lamb wave is most favorable for a frequency-controllable radiation angle of an ultrasound beam into a water layer as an acoustic coupler. In the configuration of an acoustic delay line, the layer-thickness measurement in vivo, evaluated from the time interval between two reflected ultrasound echoes, is successfully realized under a thin water layer as the acoustic coupler.

Influence of cathodic protection on the lifetime extension of painted steel structures

For corrosion to occur on a coated metal surface, an electrochemical double layer must be established. Hence, the adhesion between the substrate and the coating must be weakened to enable a separate thin layer of water to be formed at the interface from water that has permeated the coating. To prevent the failure of a painted coating, we applied a cathodic protection method. This method has been controversial for a few years because cathodic protection can induce cathodic delamination of the entire surface, especially near the anode, and also because it is not effective on a not-wetted surface from the anode. We therefore evaluated the efficiency of cathodic protection for 700 days in an atmospheric environment and performed surface observation, AC impedance measurements and corrosion tests. In the case of a noncathodic protected painted steel specimen, blisters formed after 100 days and grew in number for the remainder of the test. However, cathodic protection of the painted steel increased the coating resistance and extended the lifetime of the coating. According to our calculation with the BEASY program, the thickness of the water film under a rain condition barely influenced the protection potential. The high voltage of the cathodic protection and the subsequent cathodic delamination caused the paint to peel off near the anode. Hence, the protection voltage should be controlled in accordance with changes to the environmental condition.

Down-mixing of phytoplankton above filter-feeding mussels—interplay between water flow and biomixing

Filter-feeding bivalves may have a pronounced grazing impact on the phytoplankton biomass in many shallow marine areas. The blue mussel Mytilus edulis, which lives in dense beds, can filter more than 100 m 3 m -2 d -1 , but the grazing impact is highly influenced by hydrodynamic pro- cesses. Without externally generated currents or turbulent mixing, only a thin layer of near-bottom water would be subject to the down-mixing that causes an important supply of food to the mussels. Here, food-depleted jets of water expelled through the exhalant opening of a mussel may not only prevent the water, once filtered, from re-entering the animal, but the substantial speed of the jet may also help to mix the near-bottom water. The extent of such biological mixing—'biomixing'—caused by a dense population of M. edulis (200 cm long bed, filtering at 147 m 3 m -2 d -1 ) was studied experi- mentally at 2 flow speeds (4 and 8 cm s -1 ) in a laboratory flume channel at natural (low) algal concen- trations in order to determine its relative importance compared to current-generated turbulence. Dis- tributions of algal cells a distance of 162 cm from the start of the bed showed a near-bottom depletion of about 58 and 45%, respectively, for the 2 flow speeds, which indicate the degree of refiltration. In addition, flow structures were quantified in terms of distributions of velocity, turbulent shear stress and turbulent kinetic energy in the benthic boundary layer at 3 levels of mussel filtration-activity (maximal, reduced and zero). A description is given of this filtration activity of M. edulis with and without added suspensions of algal cells, which influence its valve-opening degree and filtration rate. It is concluded that biomixing enhances the flow-induced down-mixing of phytoplankton and can be identified as peaks in profiles of turbulent kinetic energy and turbulent shear stress. The associated increase in friction velocity over the length of the mussel bed at maximal filtration activity amounted to 56 and 49% for the 2 flow speeds studied. This shows the functionality of biomixing to be most helpful at low speed, where it is most needed due to the low levels of flow induced turbulence con- tributing to down-mixing of phytoplankton.

Piezoelectric resonator and high-frequency admittance study of viscosity and density changes in a thin water layer adjacent to the electrode surface

Analysis of the admittance of quartz resonator in contact with water has shown that the viscosity–density product of water at a metallic electrode surface decreases during the positive potential scan. This decrease is more pronounced when the electrode surface is coated by a thin layer of polymer. Literature data provide evidence that the density of water in the first layer attached to the surface increases when the potential is shifted into the positive direction. It is concluded that during such potential scan the decrease of viscosity is larger than the increase of density.

Numerical simulation of glass doors fogging and defogging in refrigerated display cabinets

A numerical procedure for the simulation of fogging and defogging phenomena is presented and is applied to the prediction of the demisting process on the glass door of a refrigerated closed display cabinet. The physical problem depends on the flow field along the glass, both inside and outside the refrigerated cabinet, on the unsteady conduction through the multi-glazed door and on the heat and mass transfer phenomena within the thin water layer on the fogged surface. Thus a suite of routines for the unsteady simulation of the water layer evolution is coupled with FVM solvers for the Navier Stokes and energy equations inside the cabinet and for the conduction problem in the glass. The convective heat transfer coefficient on the exterior side of the glass door is evaluated through empirical correlations. The codes are iterated simultaneously to reproduce the physical transient, before, during and after the door opening. Simulations are carried out for a frozen food display cabinet with an air curtain flowing along the internal side of the door. Both activated and deactivated configurations of the electric heaters inside the glass are considered. The results show a good agreement with the experimental ones and highlight the importance of taking into account the shape and the distribution of the dew droplets.

A Suction Bailer for Sampling Very Thin Saturated Zones

AbstractA suction bailer is developed for the express purpose of sampling very thin perched water bodies (on the order of 1 cm thick) that may also be ephemeral. This device incorporates a semi‐permeable membrane on the bottom of the bailer that allows water entry, while simultaneously blocking air. This design allows unattended sample collection, which is monitored with a simple pressure transducer. Three prototypes were constructed and tested; one is based on a commercial suction lysimeter, while the other two are fabricated from stainless steel. All three prototypes were shown to be capable of sampling thin layers of water on the order of 1 cm thick and operating unattended for extended periods to capture intermittent events. Sample sizes of 100–1,000 mL are possible depending on fluid availability. The design does not place any constraints on the depth of emplacement.

Corona Above Water Reactor for Systematic Study of Aqueous Phenol Degradation

A small batch reactor is developed to study the removal of phenol from a thin layer of water by creating pulsed corona discharges above the water. Pulses of up to 40 kV are applied with a duration of ~50 ns and an energy of ~60 mJ. In this CAW (Corona Above Water) reactor an ozone yield of upto 90 g/kWh is obtained in ambient air. The phenol degradation is 48 g/kWh, using a 1 mM initial concentration in demineralized water. The degradation yield increases to almost 100 g/kWh by adding to the water either H2O2 or Fe2SO4 or NaOH. The first two additions are considered to increase to amount of OH radicals. In the case of NaOH addition it is observed that much more ozone dissolves in the water. The addition of the OH scavenger t-butanol shows that in most cases the main oxidation route of phenol in the CAW reactor is direct ozone attack.