Photolithotrophic cultivation of <Emphasis Type="Italic">Laminaria japonica</Emphasis> gametophyte cells in a silicone tubular membrane-aerated photobioreactor

Gametophyte cells of brown algae Laminaria japonica were employed both in a modified silicone tubular membrane-aerated photobioreactor (bubble-less cultivation mode) and a bubble-column photobioreactor (bubbling cultivation mode), to study different gas–liquid mixing modes on cell growth rate and cell physiological status. With an inoculum density of 50 mg DCW l⁻¹, in modified artificial Pacific seawater (APSW) medium at 13°C, light intensity of 60 μE m⁻² s⁻¹, light cycle of 16/8 h L/D, and aeration rate of 60 ml min⁻¹, the specific growth rates were 0.082 d⁻¹ for bubble-less mode and 0.070 d⁻¹ for bubbling mode with biomass, in the form of dry cell density, increasing 10.9 and 6.8 times, respectively, during the 36 days’ photolithotrophic cultivation. The specific oxygen evolution rate under bubble-less mode was 39.6% higher than under bubbling mode on the 18th day. The gametophyte cells grew in cell aggregates with clump sizes, at day 36, of 1.5 mm and 0.5 mm diameter under bubble-less and bubbling mode respectively and cell injury percentages of 5.1% and 21.1%, respectively. The silicone tubular membrane-aerated photobioreactor was better suited for the cultivation of fragile macroalgal gametophyte cells due to the absence of hydrodynamic shear stress caused by fluid turbulence and the presence of a bubble-less gas supply.     

Protein denaturation by combined effect of shear and air-liquid interface

The effect of shear alone on the aggregation of recombinant human growth hormone (rhGH) and recombinant human deoxyribonuclease (rhDNase) has been found to be insignificant. This study focused on the synergetic effect of shear and gas-liquid interface on these two model proteins. Two shearing systems, the concentric-cylinder shear device (CCSD) and the rotor/stator homogenizer, were used to generate high shear (> 10(6)) in aqueous solutions in the presence of air. High shear in the presence of an air-liquid interface had no major effect on rhDNase but caused rhGH to form noncovalent aggregates. rhGH aggregation was induced by the air-liquid interface and was found to increase with increasing protein concentration and the air-liquid interfacial area. The aggregation was irreversible and exhibited a first-order kinetics with respect to the protein concentration and air-liquid interfacial area. Shear and shear rate enhanced the interaction because of its continuous generation of new air-liquid interfaces. In the presence of a surfactant, aggregation could be delayed or prevented depending upon the type and the concentration of the surfactant. The effect of air-liquid interface on proteins at low shear was examined using a nitrogen bubbling method. We found that foaming is very detrimental to rhGH even though the shear involved is low. The use of anti-foaming materials could prevent rhGH aggregation during bubbling. The superior stability exhibited by rhDNase may be linked to the higher surface tension and lower foaming tendency of its aqueous solution. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 503-512, 1997.     

Vortex behavior in the waldhof fermentor

This is the first part of a systematic study on the mechanisms of the Waldhof fermentor. When an agitator is rotating in a liquid, a vortex will develop on the surface. Air is dispersed into the liquid when the vortex is deep enough to reach the agitator. This is the basic mechanism of air dispersion in a Waldhof fermentor. In this work, experimental results, empirical correlations, and theoretical equations were obtained to relate the vortex depth to a number of physical factors including agitator diameter, agitator speed, tank diameter, liquid depth, liquid viscosity, and so on. The vortex depth was found a function of both Reynolds number and Froude Number.     

Cross-flow at the anterior communicating artery and its implication in cerebral aneurysm formation

The anterior communicating artery (ACoA) is an important element of the circle of Willis. While the artery itself is short and small, a large number of intracranial aneurysms can be found at the ACoA. Four subject-specific ACoA models are constructed from 3D rotational angiographic images. The ACoA of these models ranged from 1.7 to 2.7 mm in diameter and 1.5 to 5.7 mm in length. Pulsatile flows through these four ACoA models are studied numerically. Blood is found to move in two opposite directions simultaneously within the ACoA, giving a much higher wall shear at the ACoA. These two opposite flow streams produce a cross-flow that is dependent on the flow rates at the anterior cerebral arteries and internal carotid arteries (ICAs). A larger and shorter ACoA allows flow through the ACoA easily, leading to a greater cross-flow and higher hemodynamic forces on the artery. This cross-flow may disappear when there is a sufficient net flow for a smaller and longer ACoA. Wall shear stress can be as high as 185 Pa at smaller ACoAs, but it can be lowered by asymmetric waveforms at the ICAs. A functional circle of Willis also promotes cross-flow at both the ACoA and posterior communicating arteries.     

Improvement of biodegradation in compact co-current biotrickling filter by high recycle liquid flow rate: Performance and biodegradation kinetics of ammonia removal

As a microbial-environmental-control-type deodorizing system, we have developed a compact biotrickling filter system for small-scale livestock farms. The performance of the compact co-current biotrickling filter operated at high recycle liquid flow rates was systematically examined. In particular, we studied improvements in the nitrification ability of the system due to the resultant enhancement of absorption and dissolution of NH₃ and absorption of O₂ with the high flow rates of recycle liquid flowing downward co-currently with gas flow. At the empty bed residence time of 50 s, almost complete removal of NH₃ was obtained with recycle liquid flow rates of 103 and 205 L m⁻³ day⁻¹ for 20 days while the inlet NH₃ concentration was increased from 200 to 500 ppm. With a recycle liquid flow rate of 411 L m⁻³ day⁻¹ the removal efficiency remained above 95% for 57 days while the inlet NH₃ concentration was increased from 200 to 700 ppm. The biodegradation kinetics for NH₃ removal was successfully analyzed using the Haldane substrate inhibition kinetics. The present data and kinetic analyses showed that the substrate inhibition was suppressed and the biodegradation of ammonia in the compact biotrickling filter could be improved by the high recycle liquid flow rate.     

Using clay to control harmful algal blooms: deposition and resuspension of clay/algal flocs

Harmful algal blooms (HABs) may be legitimate targets for direct control or mitigation, due to their impacts on commercial fisheries and public health. One promising control strategy is the rapid sedimentation of HABs through flocculation with clay. The objective of this study was to evaluate flow environments in which such a control strategy might be effective in removing harmful algae from the water column and depositing a layer of clay/algal flocs on the sea floor. We simulated the natural environment in two laboratory flumes: a straight-channel “17 m flume” in which flocs settled in a still-water column and a “racetrack flume” in which flocs settled in flow. The 17 m flume experiments were designed to estimate the critical bed shear stress for resuspension of flocs that had settled for different time periods. The racetrack flume experiments were designed to examine the deposition and repeated resuspension of flocs in a system with tidal increases in flow speed. All flume runs were conducted with the non-toxic dinoflagellate Heterocapsa triquetra and phosphatic clay (IMC-P4). We repeated the experiments with a coagulant, polyaluminum hydroxychloride (PAC), expected to enhance the removal efficiency (RE) of the clay. Our experiments indicated that at low flow speeds (≤10 cm s⁻¹), phosphatic clay was effective at removing algal cells from the water column, even after repeated resuspension. Once a layer of flocs accumulated on the bed, the consolidation, or dewatering, of the layer over time increased the critical shear stress for resuspension (i.e. decreased erodibility). Resuspension of a 2 mm thick layer that settled for 3 h in relatively low flow speeds (≤3 cm s⁻¹) would be expected at bed shear stress of 0.06–0.07 Pa, as compared to up to 0.09 Pa for a layer that was undisturbed for 9 or 24 h. For the same experimental conditions, the addition of PAC decreased the removal efficiency of algal cells in flow and increased the erodibility of flocs from the bottom. By increasing the likelihood that flocs remain in suspension, the addition of PAC in field trials of clay dispersal might have greater impact on sensitive, filter-feeding organisms. Overall, our experiments suggest that the flow environment should be considered before using clay as a control strategy for HABs in coastal waters.     

Unraveling the Role of Surface Mucus-Binding Protein and Pili in Muco-Adhesion of Lactococcus lactis

Adhesion of bacteria to mucus may favor their persistence within the gut and their beneficial effects to the host. Interactions between pig gastric mucin (PGM) and a natural isolate of Lactococcus lactis (TIL448) were measured at the single-cell scale and under static conditions, using atomic force microscopy (AFM). In parallel, these interactions were monitored at the bacterial population level and under shear flow. AFM experiments with a L. lactis cell-probe and a PGM-coated surface revealed a high proportion of specific adhesive events (60%) and a low level of non-adhesive ones (2%). The strain muco-adhesive properties were confirmed by the weak detachment of bacteria from the PGM-coated surface under shear flow. In AFM, rupture events were detected at short (100−200 nm) and long distances (up to 600−800 nm). AFM measurements on pili and mucus-binding protein defective mutants demonstrated the comparable role played by these two surface proteinaceous components in adhesion to PGM under static conditions. Under shear flow, a more important contribution of the mucus-binding protein than the pili one was observed. Both methods differ by the way of probing the adhesion force, i.e. negative force contact vs. sedimentation and normal-to-substratum retraction vs. tangential detachment conditions, using AFM and flow chamber, respectively. AFM blocking assays with free PGM or O-glycan fractions purified from PGM demonstrated that neutral oligosaccharides played a major role in adhesion of L. lactis TIL448 to PGM. This study dissects L. lactis muco-adhesive phenotype, in relation with the nature of the bacterial surface determinants.     

Viscoelastic behaviour aids extrusion from and reabsorption of the liquid phase into the digesta plug: creep rheometry of hindgut digesta in the common brushtail possum Trichosurus vulpecula

Temporal variation in the rheometric properties of the proximal and distal colonic digesta of an arboreal marsupial folivore, the common brushtail possum, was examined to assess flow behaviour during peristalsis, segmentation and other aspects of intestinal motility. The time-dependent rheometric characteristics on application of a constant shear stress within the physiological range showed an initial elastic and subsequent viscoelastic phase, which fitted Burger’s model of creep compliance. Similarly, the time-dependent rheometric characteristics on recovery from shear stress fitted with a generalised two-component Maxwell model of elastic and viscoelastic components for creep recovery. Differences in the relative magnitudes of the viscoelastic components during recovery from those during shear indicated that the physical properties of the digesta plug changed with sustained shear stress, a phenomenon, which is likely to result from extrusion of the liquid phase from the solid elements of the digesta plug. There was significant viscoelastic recovery during the initial 4 s following cessation of stress, which would allow for prompt concomitant reabsorption of the liquid phase into the digesta plug. This supports a hypothesis of alternate extrusion and reabsorption of the liquid phase of the digesta plug. This would promote both nutrient absorption across the intestinal wall (from liquid extrusion) and enzyme permeation and digestion (from liquid absorption into the plug). However, the presence of a slower component of viscoelastic recovery indicates that liquid phase reabsorption into the digesta plug is incomplete if the interval before a subsequent contraction is less than 150 s, in which case unreabsorbed liquid may be driven either orally or aborally. This would at least partly account for differences in retention times of liquid and solid phase digesta markers reported for the gastrointestinal tracts of numerous vertebrate species.     

Effect of pH on successive foam and sonic droplet fractionation of a bromelain-invertase mixture

A droplet fractionation method was previously developed to concentrate a dilute nonfoaming protein solution. In that earlier study with invertase, it was demonstrated that droplets created by ultrasonic energy waves could be enriched up to 8 times that of the initial dilute invertase solution. In this study, a mixture of bromelain (a foaming protein) and invertase (a nonfoaming protein) is investigated as a preliminary step to determine if droplet fractionation can also be used to separate a non-foaming protein from foaming proteins. The foaming mixture containing bromelain is first removed by bubbling the binary mixture with air. After the foam is removed, the protein rich air-water interfacial layer is skimmed off (prior to droplet fractionation) so as not to interfere with the subsequent droplet production from the remaining bulk liquid, rich in non-foaming protein. Finally, sonic energy waves are then applied to this residual bulk liquid to recover droplets containing the non-foaming protein, presumed to be invertase. The primary control variable used in this droplet fractionation process is the pH, which ranged for separate experiments between 2 and 9. It was observed that the maximum overall protein partition coefficients of 5 and 4 were achieved at pH 2 and 4, respectively, for the initial foaming experiment followed by the post foaming droplet fractionation experiment.     

Rapid large-scale growth of Helicobacter pylori in flasks and fermentors.

We developed procedures for large-scale cultivation of Helicobacter pylori in flasks and fermentors. Flasks incubated closed under a microaerophilic gas phase with a cotton plug covered by a plastic bag, followed by removal of the bag after 8 h, gave excellent growth. Growth in a 10-liter fermentor led to excessive foaming if the medium was sparged with gas; silicone- or polyglycol-based antifoaming agents were severely inhibitory. Use of fermentor surface gassing, first with a microaerophilic 6% oxygen gas mixture, then with air, and then with 95% oxygen, allowed the culture to grow to an A600 of 2.5 in < 24 h. This method was modified for scale-up to a 100-liter fermentor.     

Collection characteristics of a batch-type wetted wall bioaerosol sampling cyclone

The collection efficiency and sample retention of a batch-type wetted wall bioaerosol sampling cyclone (BWWC) were experimentally characterized. The BWWC is designed to sample air at 400 l/min and concentrate the particles into 12 ml of water. Aerosol is transported into a cylindrically-shaped axial flow cyclone through a tangential slot and the particles are impacted on the inner wall, which is wetted by air shear acting on a liquid pool at the base of the cyclone. The retention of collected particles and the aerosol collection efficiency of the BWWC were evaluated with polystyrene latex beads (PSL), sodium fluorescein/oleic acid droplets, and Bacillus atrophaeus (aka BG) spores. The retention of particles was determined by adding hydrosol directly into the device, running the BWWC for a pre-set period of time, and then determining the amount of particulate matter recovered relative to the initial amount. For 1-μm diameter PSL, 90% of the particles were recoverable from the cyclone body immediately after their introduction; however, only 10% were retained in the collection liquid after 8 h of operation. The aerosol sampling efficiency was determined by comparing the amount of particulate matter collected in the liquid with that collected by a reference filter. The collection efficiency was 50–60% for 1- and 3-μm polystyrene (PSL) particles, and 1.5% for 10-μm oleic acid particles. The efficiency for 3-μm oleic acid droplets was 35%. Explanations are provided for the difference between liquid and solid particle behavior, and for the low efficiency for the large liquid particles. The collection efficiency for single spore BG was slightly lower than that for 1-μm PSL.     

Determination of urban pollution islands by using remote sensing technology in Moscow,Russia

Pollution of the atmosphere with harmful substances is currently the most dangerous form of degradation of the natural environment in Russia. The peculiarities of the environmental situation and the emerging environmental problems in some areas of the Russian Federation are caused by local natural conditions and the nature of the impacts from industries, transport, utilities, and agriculture (the specifics of enterprises, their capacity, location, technologies used). As a rule, the magnitude of air pollution depends on the degree of urbanization and anthropogenic transformation of the territory and climatic conditions that determine the potential for atmospheric pollution. During high-temperature technological processes, the smallest aerosol particles (0.5..0.10 μm) formed, poorly captured by gas purification plants, and can migrate in the atmosphere for considerable distances. Larger particles (2.5 μm and above) are formed due to the mechanical decomposition of solid particles and enter the atmosphere due to wind erosion, the dusting of dirt roads, the erasure of vehicle tires. The particles suspended with a diameter of not more than 2.5 μm (PMX) are the most destructive to health since they penetrate and get deposited deep into human lungs. These microns, present in a suspended state in the air, consist of a complex mixture of large and small, solid and liquid particles, of both inorganic and organic substances. The boundary between the two fractions is usually particles with a diameter of 2.5 μm (PM2.5). This study sought to build a model for determining fine dust PM2.5 in the Moscow air environment using Landsat 8 OLI satellite image channels and data on the concentrations of fine dust PM2.5 obtained by weather stations in the city. In addition, a correlation analysis was carried out to determine a regression model for studying the dispersion of fine dust in the city. The results obtained are presented on a map of the concentration of fine dust PM2.5 in Moscow, supporting management decisions and decision-making on environmental policy in urban planning.     

Liquid plug flow in straight and bifurcating tubes.

A finite-length liquid plug may be present in an airway due to disease, airway closure, or by direct instillation for medical therapy. Air forced by ventilation propagates the plug through the airways, where it deposits fluid onto the airway walls. The plug may encounter single or bifurcating airways, an airway surface liquid, and other liquid plugs in nearby airways. In order to understand how these flow situations influence plug transport, benchtop experiments are performed for liquid plug flow in: Case (i) straight dry tubes, Case (ii) straight pre-wetted tubes, Case (iii) bifurcating dry tubes, and Case (iv) bifurcating tubes with a liquid blockage in one daughter. Data are obtainedfor the trailing film thickness and plug splitting ratio as a function of capillary number and plug volumes. For Case (i), the finite length plug in a dry tube has similar behavior to a semi-infinite plug. For Case (ii), the trailing film thickness is dependent upon the plug capillary number (Ca) and not the precursor film thickness, although the shortening or lengthening of the liquid plug is influenced by the precursor film. For Case (iii), the plug splits evenly between the two daughters and the deposited film thickness depends on the local plug Ca, except for a small discrepancy that may be due to an entrance effect or from curvature of the tubes. For Case (iv), a plug passing from the parent to daughters will deliver more liquid to the unblocked daughter (nearly double, consistently) and then the plug will then travel at greater Ca in the unblocked daughter as the blocked. The flow asymmetry is enhanced for a larger blockage volume and diminished for a larger parent plug volume and parent-Ca.     

Simultaneous removal of chlorpyrifos and dissolved organic carbon using horizontal sub-surface flow pilot wetlands

Rural areas of developing countries require low-cost treatment systems to purify wastewater which is contaminated with pesticides and organic matter. This work evaluated for six months the simultaneous removal of chlorpyrifos and dissolved organic matter in water using four horizontal sub-surface flow constructed wetlands (SSFCW) at a pilot scale, that were planted with Phragmites australis at 20 ± 2 °C water temperature. In each wetland, three concentrations of chlorpyrifos and three of dissolved organic carbon (DOC) were tested by liquid chromatography and an organic carbon analyzer respectively. The pesticide and DOC were added to the wetlands in synthetic wastewater. For the experiments, four wetlands of equal dimensions were used, with granular material of igneous rocks, 3.9–6.4 mm in diameter and at a depth of 0.3 m with a layer of water 0.2 m deep. For each treatment, regular sampling was carried out for the influent and effluents. As a supporting feature NH₄⁺, NO₃^? and PO₄^3? were quantified and in situ measurements of dissolved oxygen (DO), pH, electrical conductivity, water temperature and redox potential were taken. The overall removal of the chlorpyrifos (92.6%) and DOC (93.2%) was high, as was DOC removal as a function of pesticide concentration in the influent. The minimum magnitude (92.0%) was reached with 425.6 μg L^?1 of chlorpyrifos and, with the highest pesticide removal (96.8%). At lower concentrations of the agrochemical, DOC removal increased. The removals were possibly due to mineralization processes, biological decomposition and sorption in plants. These findings demonstrate that SSFCW are capable of simultaneously removing dissolved organic matter and organophosphate pesticides such as chlorpyrifos, which indicate that chlorpyrifos did not interfere with the removal of organic material.     

Machine Vision Based Measurement of Dynamic Contact Angles in Microchannel Flows

When characterizing flows in miniaturized channels, the determination of the dynamic contact angle is important. By measuring the dynamic contact angle, the flow properties of the flowing liquid and the effect of material properties on the flow can be characterized. A machine vision based system to measure the contact angle of front or rear menisci of a moving liquid plug is described in this article. In this research, transparent flow channels fabricated on thermoplastic polymer and sealed with an adhesive tape are used. The transparency of the channels enables image based monitoring and measurement of flow variables, including the dynamic contact angle. It is shown that the dynamic angle can be measured from a liquid flow in a channel using the image based measurement system. An image processing algorithm has been developed in a MATLAB environment. Images are taken using a CCD camera and the channels are illuminated using a custom made ring light. Two fitting methods, a circle and two parabolas, are experimented and the results are compared in the measurement of the dynamic contact angles.     

Removal of Selected Metals from Wastewater Using a Constructed Wetland

Removal of selected metals from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied. The objective of the work was to determine the efficiency of Cu, Zn, Ni, Co, Sr, Li, and Rb removal, and to describe the main removal mechanisms. The highest removal efficiencies were attained for zinc and copper (89.8 and 81.5%, respectively). It is apparently due to the precipitation of insoluble sulfides (ZnS, CuS) in the vegetation bed where the sulfate reduction takes place. Significantly lower removal efficiencies (43.9, 27.7, and 21.5%) were observed for Li, Sr, and Rb, respectively. Rather, low removal efficiencies were also attained for Ni and Co (39.8 and 20.9%). However, the concentrations of these metals in treated water were significantly lower compared to Cu and Zn (e.g., 2.8 ± 0.5 and 1.7 ± 0.3 μg/l for Ni at the inflow and outflow from the wetland compared to 27.6 ± 12.0 and 5.1 ± 4.7 μg/l obtained for Cu, respectively). The main perspective of the constructed wetland is the removal of toxic heavy metals forming insoluble compounds depositing in the wetland bed. Metal uptake occurs preferentially in wetland sediments and is closely associated with the chemism of sulfur and iron.     

Wood anatomy and tree growth covary in riparian ash forests along climatic and ecological gradients

Riparian ash forests subjected to seasonal drought are among the most endangered ecosystems in Europe. They are threatened by climate warming causing aridification and by land-use changes modifying river flow. To assess the impacts of these two stress factors on riparian forests, we studied radial growth and xylem anatomical traits in five narrow-leaved ash (Fraxinus angustifolia) stands across wide climatic and ecological gradients from northern Italy to southern Portugal. Radial growth rates and earlywood hydraulic diameter (Dh) were directly correlated, whilst earlywood vessel density and growth rates were inversely associated. Ash growth positively responded to precipitation. Higher and lower rates of growth increase in response to precipitation were found in dry (annual precipitation 357–750 mm, annual water balance −39 to −48 mm) and wet (annual precipitation 1030 mm, annual water balance 27 mm) sites, respectively. Wet conditions in autumn and winter of the year prior to tree-ring formation lead to larger Dh values, except in the wet site where warmer conditions from prior autumn to current spring were positively associated to wider vessels. Growth was also enhanced by a higher river flow, reflecting higher soil moisture due to elevated groundwater table levels. Peaks in river flow from late winter to early spring increased Dh in dry-continental sites. Growth and potential hydraulic conductivity in drought-prone riparian ash forests are differently impacted by climate variability and river flow depending on site and hydrological conditions. Nevertheless, covariation between radial growth and the earlywood vessel diameter was found, regardless of site specific differences. Wood production and hydraulic conductivity are coordinated through the production of large earlywood vessels which may allow reaching higher growth rates.     

Shear stress-induced Ca2+ mobilization in MDCK cells is ATP dependent,no matter the primary cilium

Primary cilium has emerged as mechanosensor to subtle flow variations in epithelial cells, but its role in shear stress detection remains controversial. To probe the function of this non-motile organelle in shear stress detection by cells, we compared calcium signalling responses induced by shear stress in ciliated and unciliated MDCK cells. Cytosolic free Ca²⁺ ([Ca²⁺]_i) was measured using Fura-PE3 video imaging fluorescence microscopy in response to shear stress due to laminar flow (385 μl s^?1). Our results show that both unciliated and ciliated MDCK cells are shear stress sensitive via ATP release and autocrine feedback through purinergic receptors. However, purinergic calcium signals differed in response intensity and receptor subtypes. In unciliated cells, shear stress-induced elevation in [Ca²⁺]_i was predominantly mediated through P2X receptors (P2XR). In contrast, calcium mobilization in ciliated MDCK cells resulted from P2YRs and store-operated Ca²⁺-permeable channels besides P2XRs. These findings lend support to the hypothesis that ATP release in response to shear stress is independent of the primary cilium and that transduction of mechanical strain into a specific biochemical responses stems on the mobilization of different sets of purinergic receptors.     

Higher risk of fatality by predatory attacks in earlier ontogenetic stages of modern Nautilus pompilius in the Philippines: evidence from the ontogenetic analyses of shell repairs

The shell repair scars of modern Nautilus pompilius in the Philippines presumably due to sub‐lethal predatory attacks were examined throughout ontogeny ranging from hatching to maturity, revealing the higher risk of fatality in earlier ontogenetic stages. The examinations throughout ontogeny demonstrate that: (1) sub‐lethal predatory attacks by other organisms have no preferred position through ontogeny; (2) the sizes of shell repair scars are similar throughout ontogeny and, therefore, the width and length of shell repair scars relative to shell diameter decrease from hatching towards maturity; and (3) the proportion of sub‐lethal predatory attacks within 10 mm increments of shell diameter are similar irrespective of shell diameter or decrease approaching maturity. The numbers of the irregular, radiating, black shell repair scars, indicating injury to the soft parts at shell breakage, decrease at a diameter >80 mm and none were found at <56 mm in shell diameter. Furthermore, the rarity of juvenile trapping data might be related to the higher fatality from predatory attacks in earlier ontogenetic stages, providing crucial information for the conservation of N. pompilius.     

Computational analysis of confined jet flow and mass transport in a blind tube.

A computational analysis of confined nonimpinging jet flow in a blind tube is performed as an initial investigation of the underlying fluid and mass transport mechanics of tracheal gas insufflation. A two-dimensional axisymmetric model of a laminar steady jet flow into a concentric blind-end tube is put forth and the governing continuity, momentum, and convection-diffusion equations are solved with a finite element code. The effects of the jet diameter based Reynolds number (Re(j)), the ratio of the jet-to-outer tube diameters (epsilon), and the Schmidt number (Sc) are evaluated with the determined velocity and contaminant concentration fields. The normalized penetration depth of the jet is found to increase linearly with increasing Re(j) for epsilon = O(0.1). For a given epsilon, a ring vortex that develops is observed to be displaced downstream and radially outward from the jet tip for increasing Re(j). The axial shear stress profile along the inside wall of the outer tube possesses regions of fixed shear stress in addition to a local minimum and maximum in the vicinity of the jet tip. Corresponding regions of axial shear stress gradients exist between the fixed shear stress regions and the local extrema. Contaminant concentration gradients develop across the ring vortex indicating the inward diffusion of contaminant into the jet flow. For fixed epsilon and Sc and Re(j) approximately 900, normalized contaminant flow rate is observed to be approximately twice that of simple diffusion. This model predicts modest net axial contaminant transport enhancement due to convection-diffusion interaction in the region of the ring vortex.