ALBERT

Notes: In this paper we investigate the linear stability of an initially axisymmetric thin drop of Newtonian fluid either on a uniformly rotating substrate (the simplest model for spin coating) or on a stationary substrate under the influence of an axisymmetric jet of air directed normally towards the substrate. Drops both with and without a dry patch at their center are considered. For each problem we examine both the special case of quasistatic motion (corresponding to zero capillary number) analytically and the general case of nonzero capillary number numerically. In all cases the drop is found to be unconditionally unstable, but the growth rate and wavenumber of the most unstable mode depend on the details of the specific problem considered.© 2002 American Institute of Physics.

Notes: In this paper we investigate the linear stability of an initially symmetric two-dimensional thin ridge of Newtonian fluid of finite width on a horizontal planar substrate acting under the influence of a symmetric two-dimensional jet of air normal to the substrate. Ridges both with and without a dry patch at their center are considered. For both problems we examine both the special case of quasistatic motion (corresponding to zero capillary number) analytically and the general case of nonzero capillary number numerically. In all cases the ridge is found to be unconditionally unstable, but the nature and location of the most unstable mode are found to depend on the details of the specific problem considered. © 2001 American Institute of Physics.

Notes: Previous experimental measurements and linear stability analyses of curvilinear shearing flows of viscoelastic fluids have shown that the combination of streamwise curvature and elastic normal stresses can lead to flow destabilization. Torsional shear flows of highly elastic fluids with closed streamlines can also accumulate heat from viscous dissipation resulting in nonuniformity in the temperature profile within the flow and nonlinearity in the viscometric properties of the fluid. Recently, it has been shown by Al-Mubaiyedh et al. [Phys. Fluids 11, 3217 (1999)] that the inclusion of energetics in the linear stability analysis of viscoelastic Taylor–Couette flow can change the dominant mode of the purely elastic instability from a nonaxisymmetric and time-dependent secondary flow to an axisymmetric stationary Taylor-type toroidal vortex that more closely agrees with the stability characteristics observed experimentally. In this work, we present a detailed experimental study of the effect of viscous heating on the torsional steady shearing of elastic fluids between a rotating cone and plate and between two rotating coaxial parallel plates. Elastic effects in the flow are characterized by the Deborah number, De, while the magnitude of the viscous heating is characterized by the Nahme–Griffith number, Na. We show that the relative importance of these two competing effects can be quantified by a new dimensionless thermoelastic parameter, aitch-theta=Na1/2/De, which is a material property of a given viscoelastic fluid independent of the rate of deformation. By utilizing this thermoelastic number, experimental observations of viscoelastic flow stability in three different fluids and two different geometries over a range of temperatures can be rationalized and the critical conditions unified into a single flow stability diagram. The thermoelastic number is a function of the molecular weight of the polymer, the flow geometry, and the temperature of the test fluid. The experiments presented here were performed using test fluids consisting of three different high molecular weight monodisperse polystyrene solutions in various flow geometries and over a large range of temperatures. By systematically varying the temperature of the test fluid or the configuration of the test geometry, the thermoelastic number can be adjusted appreciably. When the characteristic time scale for viscous heating is much longer than the relaxation time of the test fluid (aitch-theta(very-much-less-than)1) the critical conditions for the onset of the elastic instability are in good agreement with the predictions of isothermal linear stability analyses. As the thermoelastic number approaches a critical value, the strong temperature gradients induced by viscous heating reduce the elasticity of the test fluid and delay the onset of the instability. At even larger values of the thermoelastic parameter, viscous heating stabilizes the flow completely. © 2001 American Institute of Physics.

Notes: Exposure of sexually mature pre-spawning Atlantic salmon Salmo salar to Fossbekk water (pH 5·2) for 7 days led to a significant reduction in critical swimming speed (U-crit) in females but not in males. Exposure to Fossbekk water +A1 (as AlCl3) for 24 h led to a significant reduction in U-crit in both males and females. In contrast to fish exposed for 7 days to Fossbekk water, fish exposed to Fossbekk+A1 had accumulated much more aluminium and mucus on their gills. Losses of plasma ions were similar in both groups exposed to acid water. Blood glucose was twice as high in fish exposed to Fossbekk water for 7 days compared with fish exposed to Fossbekk+A1 for 24 h. Plasma cortisol was still elevated compared with controls after exposure to Fossbekk water for 7 days. Possible mechanisms for the observed decrease in U-crit at the different exposures are discussed.

Notes: Swimming speed and average electromyogram (EMG) pulse intervals were highly correlated in individual lake trout Salvelinus namaycush (r2=0·52–0·89) and brown trout Salmo trutta (r2=0·45–0·96). High correlations were found also for pooled data in both lake trout (r2=0·90) and brown trout of the Emå stock (r2=0·96) and Lærdal stock (r2=0·96). The linear relationship between swimming speed and average EMG pulse intervals differed significantly among lake trout and the brown trout stocks. This successful calibration of EMGs to swimming speed opens the possibility of recording swimming speed of free swimming lake trout and brown trout in situ. EMGs can also be calibrated to oxygen consumption to record energy expenditure.

Notes: From a total of 174 multi-sea-winter Atlantic salmon radio tagged in the Tanafjord (northern Norway, 70°N) during 1992 and 1993, 48 Atlantic salmon were followed from entering the River Tana until spawning. Three phases were identified: (1) migratory, direct or stepwise migration to, or close to the position held at spawning; (2) search, movements both up and down river at or close to the position held at spawning; (3) holding, a period without movements prior to spawning. During the migratory phase, Atlantic salmon migrated directly to near the spawning area, or stopped between one and nine shorter periods during the upstream migration. Number of stops increased with increasing migratory distance in 1993, but no such correlation was found in 1992. The highest migratory speeds were recorded in the lower parts of the river. A distinct change in migratory pattern was found in 67% of the Atlantic salmon near or at the area held at spawning. Most common was a search phase of erratic movements with more than one down river movement. After the movement terminated, 96% of the Atlantic salmon had a period when no or little movement was recorded until spawning (on average 55 days in 1992 and 51 days in 1993). There was no preference for staying at, up or down river from the spawning area during this holding period. Early ascending Atlantic salmon migrated to spawning areas further from the mouth than the later arriving Atlantic salmon in 1993, but not in 1992. The proportion of time spent on the migratory phase increased, while the proportion of time spent on the holding phase decreased with increasing distance to the spawning area.

Notes: American eels Anguilla rostrata, collected from three distinct locations along the St Lawrence River (Lake St Lawrence, Quebec City and Kamouraska), were thought to consist entirely of out-migrating adults at Quebec City and Kamouraska and of both resident and migrants at Lake St Lawrence. The mean plasma levels of 17β-oestradiol closely paralleled the trend observed with gonadosomatic index (IG) and oocyte development. The highest levels of 17βoestradiol and IG were observed in Quebec City and Kamouraska, while the levels observed in the resident eels from Lake St Lawrence were very low. Generally, the concentration of total plasma non-esterified fatty acids (NEFA) appeared to follow the trend of 17β-oestradiol and IG and increased with sexual maturity. However, the most sexually mature group, eels from Kamouraska, had the lowest total plasma NEFA levels. The reason for the drop is not clear at present. In addition, a number of shifts in the plasma NEFA profiles of American eels did occur during their migration in a downstream direction, with several fatty acids either increasing or decreasing in relative abundance. The ratio of n3: n6 fatty acids declined with increasing sexual maturity as most n3 fatty acids became less abundant. Although the correlation between gonadal development and the relative concentration of individual fatty acids was not always clear, both arachidonic acid (20: 4n6) and docosahexaenoic acid (22: 6n3) were significantly higher in the plasma of out-migrating adults than in resident yellow phase eels.

Notes: Large-scale column experiments were undertaken to evaluate the potential of polymer mats to remove selected volatile organic compounds, polycyclic aromatic hydrocarbons, and pesticides (atrazine and fenamiphos) from ground water and potentially to act as permeable reactive barriers in contaminated ground water environments. The polymer mats, composed of interwoven silicone (dimethylsiloxane) tubes and purged with air, were installed in 2 m long flow-through columns. The polymer mats proved efficient in physically removing (stripping) benzene and naphthalene from contaminated water. Removal efficiencies for both these compounds from an aqueous phase flowing past a polymer mat were 75% or greater. However, for atrazine and fenamiphos, removal efficiencies were 5% or less, probably as a result of their lower Henry's law constants and possibly lower polymer diffusion coefficients.These experiments indicate that, at least for relatively volatile compounds, polymer mats can provide a remediation technique for the removal of organic compounds from contaminated water. Application of this technique may be well suited as a longer-term, semipassive strategy to remediate contaminated ground water, using natural ground water flow to deliver contaminated ground water to polymer mats engineered as sorption-stripping barriers.Additional benefits of this technique may include targeted delivery of gaseous chemical amendments, such as oxygen, to enhance aerobic biodegradation and to further reduce any residual concentrations of contaminants.

Notes: Methanotrophic bacteria play an important role in global cycling of carbon and co-metabolism of contaminants. Methanotrophs from pristine regions of the Snake River Plain Aquifer (SRPA; Idaho, USA) were studied in order to gain insight into the native groundwater communities' genetic potential to carry out TCE co-metabolism. Wells were selected that were proximal to a TCE plume believed to be undergoing natural attenuation. Methane concentrations ranged from 1 to 〉1000 nM. Carbon isotope ratios and diversity data together suggest that the SRPA contains active communities of methanotrophs that oxidize microbially produced methane. Microorganisms removed from groundwater by filtration were used as inocula for enrichments or frozen immediately and DNA was subsequently extracted for molecular characterization. Primers that specifically target methanotroph 16S rRNA genes or genes that code for subunits of soluble or particulate methane monooxygenase, mmoX and pmoA, respectively, were used to characterize the indigenous methanotrophs via PCR, cloning, RFLP analysis, and sequencing. Type I methanotroph clones aligned with Methylomonas, Methylocaldum, and Methylobacter sequences and a distinct 16S rRNA phylogenetic lineage grouped near Methylobacter. The majority of clone sequences in type II methanotroph 16S rRNA, pmoA, and mmoX gene libraries grouped closely with sequences in the Methylocystis genus. A subset of the type II methanotroph clones from the aquifer had sequences that aligned most closely to Methylosinus trichosporium OB3b and Methylocystis spp., known TCE-co-metabolizing methanotrophs.