Drop Trap Research Articles

Effect of ash-bridge deposition in asymmetric diesel particulate filter channels on the pressure drop and particulate matter trapping characteristics

A diesel particulate filter (DPF) is commonly used to trap particulate matter (PM). The collapse and sintering of carbon and ash deposits during exhaust gas flow and DPF regeneration frequently result in the formation of ash bridges, which are buildups of ash and PM that clog the filter channels. To investigate the impact of an ash bridge formed by accumulated ash on the pressure drop and PM trapping characteristics of asymmetric DPFs, an asymmetric DPF channel with an ash bridge was constructed. The analysis employed computational fluid dynamics to examine how the ash bridge affects the pressure drop and PM trapping characteristics in an asymmetric DPF. This study reveals that the asymmetric DPF design effectively enhances the ash-holding capacity, thereby mitigating the risk of channel blockage. The presence of ash bridges in DPF channels has a more substantial impact on the pressure drop through radial congestion than through axial congestion. The application of asymmetric thin-wall DPFs can counteract the increase in exhaust backpressure caused by ash bridges. An ash bridge located in the middle of a DPF channel intensifies the uneven deposition of PM. However, implementing an asymmetric DPF structure enhances the uniformity of PM deposition.

Culicoides Species of the Rain Forest Belt of the Littoral Region of Cameroon: Their Incrimination in the Transmission of Mansonella perstans.

Biting midges belonging to the genus Culicoides are tiny stout-shaped hematophagous insects and are thought to transmit the filarial nematode Mansonella perstans. Little is known about the Culicoides fauna in the rain forest belt of the Littoral Region of Cameroon. This study was designed to investigate the diversity, abundance and distribution of Culicoides spp. and their role as the purported vector(s) of M. perstans. Overnight light trap collections and human landing catches (HLCs) revealed eight species of Culicoides with C. grahamii being the most abundant species followed by C. milnei. Four anthropophilic species (C. inornatipennis, C. grahamii, C. fulvithorax and C. milnei) were determined by the HLCs with a higher abundance in the 4-6 p.m. collections. The drop trap technique and Mp419 LAMP assay confirmed C. milnei to be the most efficient vector in enabling the development of the microfilarial stage to the infective larval form of M. perstans. The LAMP assay also revealed that natural transmission of this nematode is fostered by C. milnei and C. grahamii in the wild. In conclusion, C. milnei was shown to be the main vector of M. perstans in the rain forest belt of the Littoral Region of Cameroon.

Evaporation-driven Supraparticle Synthesis by Self-Lubricating Colloidal Dispersion Microdrops.

The surface-templated evaporation-driven (S-TED) method that uses liquid-repellent surfaces has attracted considerable attention for its use in fabricating supraparticles of defined shape, size, and porosity. However, challenges in achieving mass production have impeded the widespread adoption of the S-TED method. To overcome this limit, we introduce an evaporation-driven "multiple supraparticle" synthesis by drying arrays of self-lubricating colloidal dispersion microdrops. To facilitate this synthetic method, a hydrophilic micropattern is prepared on a hydrophobic substrate as a template. During the removal of the substrate out of a dispersion, liquid drops are trapped and generate a microdrop array. To produce supraparticles, the contact lines of the trapped drops must be able to recede freely during evaporation. However, hydrophilic micropatterns induce strong contact line pinning for microdrops that hinders supraparticle formation. Herein, we solve this contradiction by employing an Ouzo-like colloidal dispersion, where we can control the wettability of the drop trapping domain. The self-lubrication effect provided by the Ouzo-like solution enables smooth movement of the drops' contact lines during evaporation, thereby resulting in the successful fabrication of supraparticle arrays even within the trapping domain. This strategy offers a promising and scalable approach for large-scale evaporation-driven supraparticle synthesis with a potential for extension to various primary colloidal particles, further broadening its applicability.

Study of the trapping mechanism of merging drops moving under thermocapillary migration on a surface with wettability contrast

Trapping of drops due to wettability contrast in porous materials emerges in a variety of subsurface and manufacturing applications. In carbon capture and storage, carbon dioxide must be trapped in order to avoid its release into the atmosphere, while trapped oil must be displaced. Both carbon dioxide and oil can exist as drops in porous media. The migration of a single drop attached to a wall can be hindered if the wall surface has a different wettability. However, the trapping condition becomes more complicated in the presence of two or more drops. In this work, we aim to study the trapping mechanism during thermocapillary migration of a merging drop on a heterogeneous surface. To do so, numerical simulations have been performed using the Front-Tracking/Finite Volume Method, where the Navier-Stokes equations are coupled with the conservation equations. The generalized Navier boundary condition (GNBC) has been used as the slip model to remove the viscous singularity. The combined finite-volume and tracking method is able to deal with different types of discontinuities in compressible or incompressible fluid flows, as e.g., interfaces. The material properties of the drop and the ambient fluid are different, and surface tension depends on the temperature. The results have shown that there exist three regimes characterizing the motion of merging drops, including the passage of the leading drop, the trapping of the merging drop, and the partial trapping, which correspond to the trapping of the leading drop but the passage of the merging drop. We show that there is a critical wettability contrast at which the merging drop gets trapped. The effects of Marangoni number (Ma) and viscosity ratio are investigated. The critical wettability contrast decreases with the increase of Ma number and the regime shift as a function of the viscosity and Marangoni number. These findings have implications for the design of geological carbon dioxide storage, improvement of oil recovery and microfluidic device development.

High Hysteresis Suspended Wetting State: A Wetting Regime for Controlled Trapping of Drops on Micro‐Trench Covered Surfaces

AbstractWetting of simple liquids on rough surfaces is usually described either by the Cassie–Baxter model where drops are suspended over the roughness features with air trapped below, or by the Wenzel model where the drops are impaled on the roughness features. According to the Wenzel model, drops can be trapped on the surfaces, whereas in the Cassie–Baxter model, the drops can be easily released upon adding a small tilt. Surfaces with very regular surface pattern, such as closely spaced micro‐trenches, can exhibit the so‐called High Hysteresis Suspended State (HySS). In this state the drops assume a spherical shape with air trapped below them, a characteristic feature of the Cassie–Baxter state, but show a very high contact angle hysteresis (up to >70°), typical for the Wenzel regime. The HySS regime is studied as a function of the surface geometry, applied pressure and the mass of the drop. Through roll‐off measurements it is shown that surfaces with controlled trapping conditions can be generated, where drops can be captured, however, upon addition of a small amount of energy (e.g., induced by tilt) can be released. The parameters that can be used to control the “depth” of the trap are elucidated.

Update on the biology and ecology of Culicoides species in the South-West region of Cameroon with implications on the transmission of Mansonella perstans

BackgroundCulicoides (Diptera; Ceratoponidae) are tiny, stout, blood-sucking flies with a near worldwide distribution. When present, they are often considered a biting nuisance but in addition, they are involved in the transmission of pathogens to humans, domestic and wild animals. Data on Culicoides species in the South-West region of Cameroon dates back to the 1950s. Over the decades, ecological transformation due to agriculture and deforestation may have affected the population dynamics of Culicoides and therefore our study provides an update of their bio-ecology in the region. Furthermore, the role of various Culicoides species in the transmission of parasitic filariae of the genus Mansonella remains inconclusive in this region. This study was designed to address these unknown issues and expand on current scientific knowledge.ResultsEight species of Culicoides (C. bedfordi, C. inornatipennis, C. fulvithorax, C. grahamii, C. imicola, C. milnei, C. neavei and C. kumbaensis) were collected using light traps and human baits. Culicoides grahamii was the most abundant species, followed closely by C. milnei. Three species (C. milnei, C. grahamii and C. inornatipennis) were common in all observed larval development sites. Only four species (C. inornatipennis, C. fulvithorax, C. grahamii and C. milnei) were collected on humans. Anthropophilic species were more abundant (P < 0.001) in the evening (4–7 pm) when compared to the morning collections (6–9 am). After overnight fly collections using a drop trap with a human microfilaremic donor, C. milnei emerged as the potential host for transmitting Mansonella perstans. Substantial heterogeneity was observed between the trap visiting cycles of the various species (P < 0.001). The biting cycle of the main vector, C. milnei, showed two peaks (10–11 pm and 4–5 am), the highest being 10–11 pm.ConclusionsThe Culicoides fauna of the South-West region of Cameroon has not changed significantly since the 1950s. Culicoides milnei was demonstrated to be the major vector of M. perstans in this part of Cameroon. It is essentially a nocturnal species which peaks in abundance between 10 and 11 pm.

Sheep breed and shearing influences attraction and blood-feeding behaviour of Culicoides (Diptera: Ceratopogonidae) on a UK farm

BackgroundCulicoides biting midges (Diptera: Ceratopogonidae) are responsible for the biological transmission of arboviruses of international importance between ruminant livestock. These arboviruses include bluetongue virus (BTV) and Schmallenberg virus (SBV), which have emerged in unprecedented outbreaks in northern Europe. The impact of breed and shearing of sheep on Culicoides: host contact rates has not been investigated in detail and has the potential to influence arbovirus transmission and control measures employed to limit spread.MethodsAttraction of Culicoides to Hartline and Hartline/Suffolk cross-breed sheep was compared using 224 drop trap collections over 22 nights and 181 catches from sheared or unsheared Hartline/Suffolk ewes were made over 17 nights to compare Culicoides activity and rates of blood engorgement.ResultsA total of 31,314 Culicoides was collected in the two trials and females of the subgenus Avaritia represented over 96.9% of individuals collected. Attraction to breed was dependent upon species of Culicoides and physiological status, with a significantly greater number of individuals collected on the cross-breed sheep. Shearing of sheep did not significantly increase or decrease the number of Culicoides attracted but increased the rate of successful engorgement.ConclusionsBoth breed and shearing were shown to influence Culicoides biting rate on sheep. These data are useful in a direct context in understanding the likely impact of control measures against arboviruses including BTV and SBV and additionally in providing data from field-based studies to enable modelling exercises of arbovirus transmission and spread.

Numerical Analysis of Gas-Solid Behavior in a Cyclone Separator for Circulating Fluidized Bed System

Cyclones are one of the most widely used gas-solid separators in circulating fluidized bed (CFB) systems. This paper focuses on numerical study of the gas-solid flow in a cyclone attached to the CFB system. The objective was to understand the flow pattern in the cyclone in order to run the CFB setup problem free. The previous works on cyclone separators do not include critical parameter such as coefficient of restitution which is responsible for swirling effect and increase in efficiency. Reynolds stress model (RSM) is used to obtain the gas flow characteristics. The resulting flow and pressure fields are verified by comparing with the measured experimental results and then used in the determination of solids flow that is simulated by the use of a discrete phase model. The simulation results show how the particle trajectories and cyclone efficiency change with varying coefficient of restitution and particle size keeping inlet velocity of gas and mean particle diameter constant. The separation efficiency, pressure drop and particle trapping time from the numerical analysis are shown to be comparable to those observed experimentally. The velocity distribution pattern obtained from the analysis exhibits strong flow recirculation with large turbulent eddies in the cyclone separator. The particle trajectories depend upon relative velocity of fluid/particles and concentration of particles. Efficiency of the cyclone is found to be dependent on particle size and coefficient of restitution. The results obtained are further utilized to optimize the velocity range of gas flow in the loop seal and riser for stable operation of CFB setup.

Foamed emulsion drainage: flow and trapping of drops.

Foamed emulsions are ubiquitous in our daily life but the ageing of such systems is still poorly understood. In this study we investigate foam drainage and measure the evolution of the gas, liquid and oil volume fractions inside the foam. We evidence three regimes of ageing. During an initial period of fast drainage, both bubbles and drops are very mobile. As the foam stabilises drainage proceeds leading to a gradual decrease of the liquid fraction and slowing down of drainage. Clusters of oil drops are less sheared, their dynamic viscosity increases and drainage slows down even further, until the drops become blocked. At this point the oil fraction starts to increase in the continuous phase. The foam ageing leads to an increase of the capillary pressure until the oil acts as an antifoaming agent and the foam collapses.

Trapping of Water Drops by Line-Shaped Defects on Superhydrophobic Surfaces.

We have investigated the effect of line-shaped topographical defects on the motion of water drops across superhydrophobic wax surfaces using a high-speed video camera. The defects are introduced onto the superhydrophobic wax surfaces by a scratching procedure. It is demonstrated that the motion of a drop interacting with the defect can be approximated by a damped harmonic oscillator. Whether a drop passes or gets trapped by the defect is determined by the incident speed and the properties of the oscillator, specifically by the damping ratio and a nondimensional forcing constant representing the effects of gravity and pinning forces. We also show that it is possible to predict a critical trapping speed as well as an exit speed in systems with negligible viscous dissipation using a simple work-energy consideration.

Effects of live and post-mortem shell structures of invasive Pacific oysters and native blue mussels on macrofauna and fish

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 518:123-138 (2015) - DOI: https://doi.org/10.3354/meps11044 Effects of live and post-mortem shell structures of invasive Pacific oysters and native blue mussels on macrofauna and fish P. Norling1,3,*, M. Lindegarth2, S. Lindegarth2, Å. Strand2 1Norwegian Institute for Water Research, Gaustadalléen 21, 0349 Oslo, Norway 2Department of Biology and Environmental Sciences - Tjärnö, University of Gothenburg, 452 96 Strömstad, Sweden 3Present address: Swedish Agency for Marine and Water Management, Box 11 930, 404 39 Gothenburg, Sweden *Corresponding author: pia.c.norling@gmail.com ABSTRACT: Blue mussels Mytilus edulis and the invasive Pacific oyster Crassostrea gigas are both ecosystem engineering species which modify the environment, thus having large effects on associated species. With the introduction of the Pacific oyster, a new biogenic structure has been added to subtidal sediment habitats in Scandinavia. By conducting a field experiment, the effects of live and post-mortem shell structures of C. gigas and M. edulis on associated infauna, epibenthic fauna and fish on the Swedish west coast were evaluated. Plots with 5 different treatments (live Pacific oysters, oyster shells, live blue mussels, mussel shells and sand control) were constructed on bare sandy sediment at 2 subtidal localities. Epibenthic macrofauna and fish were sampled with a drop trap, and sediment and infauna samples were collected with sediment cores. Live bivalve treatments had significant effects on organic content of the sediment; however, no treatment effects on infauna were found. In contrast, abundance and biomass of epibenthic fauna increased 4 to 8 times and species richness increased in the presence of the bivalves or their shells, compared to the sand control. Epibenthic fauna abundance and biomass was higher in the oyster shell treatment compared to the live bivalve treatments, which in turn had higher abundance and biomass than the mussel shell treatment. In general, the mussel shell treatment favoured small crustaceans, while the oyster shell and live bivalve treatments favoured fish and larger invertebrate species. Based on these results, we conclude that further establishment of the Pacific oyster in Swedish waters will cause large changes to community structure of benthic macrofauna and fish. KEY WORDS: Non-indigenous species · Ecosystem engineering · Habitat modification · Macroinvertebrates · Infauna · Epibenthic fauna · Sediment community · Crassostrea gigas · Mytilus edulis Full text in pdf format Supplementary material PreviousNextCite this article as: Norling P, Lindegarth M, Lindegarth S, Strand Å (2015) Effects of live and post-mortem shell structures of invasive Pacific oysters and native blue mussels on macrofauna and fish. Mar Ecol Prog Ser 518:123-138. https://doi.org/10.3354/meps11044 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 518. Online publication date: January 07, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Field trials assessing deltamethrin (Butox®) treatments of sheep against Culicoides species

Culicoides (Diptera: Ceratopogonidae) biting midges may transmit various diseases of economic importance, including bluetongue virus (BTV) and Schmallenberg (SV) virus, which affect ruminants. During the outbreak of BTV in central and northern Europe in 2006, and in the absence of BTV vaccines, many national veterinary services recommended the treatment of susceptible livestock with pyrethroids as a first-line defense against biting midges, although these insecticides were officially not registered and authorized for use against Culicoides midges. The efficacy of Butox® pour on (7.5 mg deltamethrin/mL) against biting midges was therefore evaluated in a double-blinded GCP field trial performed in Brandenburg, Germany. Forty female Merino sheep with an average body weight of 38 kg (±7 kg) were used for the study. Twenty randomly selected sheep were treated with 10 mL Butox® pour on. The remaining 20 sheep were left untreated and served as a control group. Midge collections took place in two separate drop traps covering two crush pens with three confined treated/untreated sheep standing inside, on weekdays at 1, 7, 14, 21, 28, and 35 days post treatment. A total of 19,057 midges were collected during this period. Midges were identified as belonging to the subgenus Avaritia, Fox (84.6%) and subgenus Culicoides, Latreille (15.4%). A total of 12,031 midges were collected inside the drop trap containing untreated sheep, in comparison to 7,026 midges collected from the vicinity of the treated sheep. Significantly, more midges had fed on control compared to treated sheep with 757 and 103 engorged midges, respectively. The results indicate that treatment of sheep with Butox® pour on provided a significant decrease in Culicoides feeding rates under field conditions for at least 35 days.

Trapping of drops by wetting defects.

Controlling the motion of drops on solid surfaces is crucial in many natural phenomena and technological processes including the collection and removal of rain drops, cleaning technology and heat exchangers. Topographic and chemical heterogeneities on solid surfaces give rise to pinning forces that can capture and steer drops in desired directions. Here we determine general physical conditions required for capturing sliding drops on an inclined plane that is equipped with electrically tunable wetting defects. By mapping the drop dynamics on the one-dimensional motion of a point mass, we demonstrate that the trapping process is controlled by two dimensionless parameters, the trapping strength measured in units of the driving force and the ratio between a viscous and an inertial time scale. Complementary experiments involving superhydrophobic surfaces with wetting defects demonstrate the general applicability of the concept. Moreover, we show that electrically tunable defects can be used to guide sliding drops along actively switchable tracks—with potential applications in microfluidics.

Freezing singularities in water drops

In this fluid dynamics video we show how a drop of water freezes into a singular shape when deposited on a cold surface. The process of solidification can be observed very clearly due to the change in refraction when water turns into ice. The drop remains approximately spherical during most of the process, with a freezing front moving upwards and smoothly following the interface. However, at the final stage of freezing, when the last cap of liquid turns into ice, a singular tip develops spontaneously. Interestingly, the sharp tip of the ice drop acts as a preferential site for deposition of water vapour, and a beautiful "tree" of ice crystals develops right at the tip. The tip singularity attracts the vapour in analogy to a sharp lightning rod attracting lightning.

Drop trapping in axisymmetric constrictions with arbitrary contact angle

The differential Young-Laplace equations are solved numerically with an iterative solution using the method of steepest descent to determine the shape of a drop trapped under gravity in an axisymmetric ring constriction. Prior work for non-wetting drops with a contact angle of π is extended to arbitrary values of the contact angle at the three-phase contact lines. The critical Bond number, representing a dimensionless ratio of gravitational and interfacial forces, and separating static trapping at lower Bond numbers from dynamic squeezing at higher Bond numbers, decreases with decreasing contact angle, indicating that drop squeezing occurs more easily at smaller contact angle. Indeed, a critical contact angle, which depends only on the drop-to-hole and ring-cross-section-to-hole size ratios, is found, below which all drops squeeze through the hole.

Collection ofCulicoides(Diptera: Ceratopogonidae) Using CO2and Enantiomers of 1-Octen-3-ol in the United Kingdom

The host kairomones carbon dioxide (CO2) and 1-octen-3-ol elicit a host seeking response in a wide range of haematophagous Diptera. This study investigates the response of Culicoides biting midges (Diptera: Ceratopogonidae) to these cues using field-based experiments at two sites in the United Kingdom with very different species complements. Traps used for surveillance (miniature CDC model 512) and control (Mosquito Magnet Pro) were modified to release ratios of (R)- and (S)-1-octen-3-ol enantiomers in combination with CO2 and, in the case of the latter trap type, a thermal cue. Abundance and species diversity were then compared between these treatments and against collections made using a trap with a CO2 lure only, in a Latin square design. In both habitats, results demonstrated that semiochemical lures containing a high proportion of the (R)-enantiomer consistently attracted a greater abundance of host-seeking Culicoides females than any other treatment. Culicoides collected using an optimal stimulus of 500 ml/min CO2 combined with 4.1 mg/h (R)-1-octen-3-ol were then compared with those collected on sheep through the use of a drop trap. While preliminary in nature, this trial indicated Culicoides species complements are similar between collections made using the drop trap in comparison to the semiochemical-baited CDC trap, and that there are advantages in using (R)-1-octen-3-ol.

Development and test of a new drop trap

The results of tests of a new drop trap (condensation trap) consisting of a bed of irregularly stacked ceramic packing of the trademark N3C at airflow velocities 1, 1.5, and 3.2 m/sec, referred to the full cross section of the empty apparatus, are reported. The results are depicted in the form of dependence of the drop trapping efficiency on the airflow velocities and the packing bed height. The obtained data are compared with those for familiar drop traps.

Assessment of vector/host contact: comparison of animal-baited traps and UV-light/suction trap for collecting Culicoides biting midges (Diptera: Ceratopogonidae), vectors of Orbiviruses.

BackgroundThe emergence and massive spread of bluetongue in Western Europe during 2006-2008 had disastrous consequences for sheep and cattle production and confirmed the ability of Palaearctic Culicoides (Diptera: Ceratopogonidae) to transmit the virus. Some aspects of Culicoides ecology, especially host-seeking and feeding behaviors, remain insufficiently described due to the difficulty of collecting them directly on a bait animal, the most reliable method to evaluate biting rates.Our aim was to compare typical animal-baited traps (drop trap and direct aspiration) to both a new sticky cover trap and a UV-light/suction trap (the most commonly used method to collect Culicoides).Methods/resultsCollections were made from 1.45 hours before sunset to 1.45 hours after sunset in June/July 2009 at an experimental sheep farm (INRA, Nouzilly, Western France), with 3 replicates of a 4 sites × 4 traps randomized Latin square using one sheep per site. Collected Culicoides individuals were sorted morphologically to species, sex and physiological stages for females. Sibling species were identified using a molecular assay. A total of 534 Culicoides belonging to 17 species was collected. Abundance was maximal in the drop trap (232 females and 4 males from 10 species) whereas the diversity was the highest in the UV-light/suction trap (136 females and 5 males from 15 species). Significant between-trap differences abundance and parity rates were observed.ConclusionsOnly the direct aspiration collected exclusively host-seeking females, despite a concern that human manipulation may influence estimation of the biting rate. The sticky cover trap assessed accurately the biting rate of abundant species even if it might act as an interception trap. The drop trap collected the highest abundance of Culicoides and may have caught individuals not attracted by sheep but by its structure. Finally, abundances obtained using the UV-light/suction trap did not estimate accurately Culicoides biting rate.

Buoyancy-induced squeezing of a deformable drop through an axisymmetric ring constriction

Axisymmetric boundary-integral (BI) simulations were made for buoyancy-induced squeezing of a deformable drop through a ring constriction. The algorithm uses the Hebeker representation for the solid-particle contribution. A high-order, near-singularity subtraction technique is essential for near-critical squeezing. The drop velocity and minimum drop-solid spacing were determined for different ring and hole sizes, viscosity ratios, and Bond numbers, where the latter is a dimensionless ratio of gravitational to interfacial forces. The drop velocity decelerates typically 100-fold or more, and the drop-solid spacing reduces to typically 0.1%–1% of the nondeformed drop radius as the drop passes through the constriction. The critical Bond number (below which trapping occurs) was determined for different conditions. For supercritical conditions, the nondimensional time required for the drop to pass through the ring increases for a fixed drop-to-hole size with increasing viscosity ratio and decreasing Bond number, but it has a nonmonotonic dependence on the ratio of the radii of the drop and ring cross section. Numerical results indicate that the square of the drop squeezing time is inversely proportional to the Bond number minus the critical Bond number for near-critical squeezing. The critical Bond number, determined from dynamic BI calculations, compares favorably to that obtained precisely from a static algorithm. The static algorithm uses the Young–Laplace equation to calculate the pendant and sessile portions of the drop interface coupled through the conditions of global pressure continuity and total drop volume conservation. Over a limited parameter space, the critical Bond number increases almost linearly with the drop-to-hole ratio and is a weak function of the ratio of the ring cross-sectional radius to the hole radius. Another dynamic phenomenon, in addition to drop squeezing, is a drop “dripping” around the outer edge of the ring constriction, and a critical Bond number maximum versus the drop-to-total ring radius ratio is caused by the transitions from squeezing to dripping for the loss of a drop steady state on a constriction. The initial stages of drop dripping are numerically simulated using a boundary-integral method for slightly supercritical Bond numbers. For very large ratios of the drop-to-hole radii, however, a sharp maximum in the critical Bond number is reached, as there is a transition from the drop passing through the inside hole to dripping over the outside edge of the ring for Bond numbers above the critical line. Drop squeezing and trapping mechanisms are also observed experimentally, and the measured critical Bond numbers and trapped drop shapes compare favorably to theoretical calculations from the Young–Laplace algorithm.

Spatial patterns in community structure of motile epibenthic fauna in coastal habitats along the Skagerrak – Baltic salinity gradient

Patterns in community structure and functioning of motile epibenthic fauna were investigated in shallow (0–1 m) sediment habitats along the Skagerrak–Baltic estuarine gradient (salinity range from 4 to 34). The study area was divided into five regions, reflecting different sea-basins along the 1260 km coastline, and fauna was collected at six sites within each region. Ten replicate samples of motile epibenthic fauna were taken randomly at each site with a portable drop trap (bottom area 1 m 2) in June and September in 2004. All together, 110 taxa were found, of which 45 had a marine and 65 a limnic origin. The marine species decreased along the salinity gradient while the limnic showed the opposite pattern. Number of species and abundance of epibenthic fauna exhibited considerable local and regional variation, with a trend of increase with decreasing salinity. Fauna biomass, on the other hand was significantly higher (six times) in the Skagerrak–Kattegat area compared to the Baltic. There was a significant difference in fauna composition among regions and season, but with high similarity within the five regions, which implies that management of such coastal habitats should preferably be based on scales of a region (ca. 100 km) or smaller. Predators were the dominant functional group in all coastal regions, with a species shift from Crustacea to Insecta along the salinity gradient and with gobid fish occurring in all regions. Grazers were the second most important group in the Skagerrak–Kattegat area, but planktovores were more important in two of the Baltic regions. The importance of shallow sediment bottoms as feeding and nursery grounds for coastal fish assemblages is discussed and compared throughout the investigated area.