ALBERT

Description: Records of unusual cephalopods, taken as by-catch in Irish and Scottish waters in the years 1985–1995, are presented. Of most interest are three specimens of giant squid (Architeuthis) that were caught in bottom trawls off the west of Ireland between April and June 1995, all were mature males of mantle length ∼1000 mm. Other records include a large mature female Histioteuthis bonnellii from the west of Ireland and three specimens of the gelatinous incirrate octopus, Haliphron atlanticus.

Description: Recent attention to members of the sepiolid squid genus Euprymna and symbiotic associations with luminescent bacteria ( Vibrio fischeri strains) has prompted a review of this poorly-resolved group of squids. Twelve nominal species have been placed in this genus of which the majority are ill-defined, known only from their original descriptions and separated on the basis of inadequate characters. As a first step in resolving this group, a temperate Australian species, the Southern dumpling squid, Euprymna tasmanica , is here redescribed in detail. As the genus Euprymna currently stands, most members are only distinguished on the number and position of enlarged suckers in mature males. No diagnostic characters are available to identify females. All nominal species placed in this genus are reviewed and a key to proposed valid species is presented. Six species are considered here to be valid: Euprymna berryi, E. hoylei, E. morsei, E. scolopes, E. tasmanica and an undescribed species treated here as Euprymna sp. 1. Euprymna similis is a synonym of E. morsei of Japan. Due to inadequate original descriptions, and lost or poor type material, two species are considered here to be nomen dubia ( E. schneehageni and E. pusilla ), while the taxonomic status of four additional species remain unresolved ( E. albatrossae, E. bursa, E. phenax and E. stenodactyla ).

Description: The statolith microstructure was studied in 142 females (mantle length, ML, ranging from 77–402 mm) and 119 males (72–328 mm ML) of Martialia hyadesi caught on the Patagonian and Falkland shelves and at the Antarctic Polar Frontal Zone between 1989–94. The statolith microstructure dark zone in this species, contains narrower and more numerous growth increments than the dark zones of other ommastrephid squids. Assuming daily production of putative growth increments within statoliths males live up to 12 months, and females live up to 13 months. It is likely that the life cycle lasts c. 1 yr, but immature squids with ages 〉330–340 d suggest that a part of M. hyadesi populations could have life span 〉1 yr. Growth in length was best described by the Gompertz function, whereas growth in weight was best described by the logistic function. M. hyadesi is characterized by slow juvenile growth (〈100 mm ML), fast growth of immature squids and a sharp decrease in growth rates during maturation. M. hyadesi mature later (at ages 〉270 d) than other temperate ommastrephids, but maturation is rather rapid (2–3 months). In the south-west Atlantic, M. hyadesi hatch throughout the year.

Description: Changes in the molecular structure of a highly ordered kaolinite, intercalated with urea and potassium acetate, have been studied using Raman microscopy. A new Raman band, attributed to the inner surface hydroxyl groups strongly hydrogen bound to the acetate, is observed at 3605 cm (super -1) for the potassium acetate intercalate with the consequential loss of intensity in the bands at 3652, 3670, 3684 and 3693 cm (super -1) . Remarkable changes in intensity of the Raman spectral bands of the low-frequency region of the kaolinite occurred upon intercalation. In particular, the 144 and 935 cm (super -1) bands increased by an order of magnitude and were found to be polarized. These spectroscopic changes provide evidence for the inner surface hydroxyl group-acetate bond being at an angle approaching 90 degrees to the 001 face. Decreases in intensity of the bands at 243, 271 and 336 cm (super -1) were observed. The urea intercalate shows additional Raman bands at 3387, 3408 and 3500 cm-1 which are attributed to N-H vibrations after formation of the urea-kaolinite complex. Changes in the spectra of the inserting molecules were also observed.

Description: Experiments were conducted to measure the collisional particle pressure in both cocurrent and countercurrent flows of liquid-solid mixtures. The collisional particle pressure, or granular pressure, is the additional pressure exerted on the containing walls of a particulate system due to the particle collisions. The present experiments involve both a liquid-fluidized bed using glass, plastic or steel spheres and a vertical gravity-driven flow using glass spheres. The particle pressure was measured using a high-frequency-response flush-mounted pressure transducer. Detailed recordings were made of many different particle collisions with the active face of this transducer. The solids fraction of the flowing mixtures was measured using an impedance volume fraction meter. Results show that the magnitude of the measured particle pressure increases from low concentrations (〈10% solid volume fraction), reaches a maximum for intermediate values of solid fraction (30-40%), and decreases again for more concentrated mixtures (〉40%). The measured collisional particle pressure appears to scale with the particle dynamic pressure based on the particle density and terminal velocity. Results were obtained and compared for a range of particle sizes, as well as for two different test section diameters. In addition, a detailed analysis of the collisions was performed that included the probability density functions for the collision duration and collision impulse. Two distinct contributions to the collisional particle pressure were identified: one contribution from direct contact of particles with the pressure transducer, and the second one resulting from particle collisions in the bulk that are transmitted through the liquid to the pressure transducer.

Description: We examine the inviscid flow generated around a body moving impulsively from rest with a constant velocity U in a constant density gradient, ∇ρ0, which is assumed to be weak in the sense ε = a|∇ρ0|/ρ0 ≪ 1, where a is the length scale of the body. In the absence of a density gradient (ε = 0), the flow is irrotational and no force acts on the body. When 0 〈 ε ≪ 1, vorticity is generated by a baroclinic torque and vortex stretching, which introduce a rotational component into the flow. The aim is to calculate both the flow around the body and the force acting on it. When a two-dimensional body moves perpendicularly to the density gradient U·∇ρ0 = 0, the density and velocity field are both steady in the body's frame of reference and the vorticity field decays with distance from the body. When a three-dimensional body moves perpendicularly to the density gradient, the vorticity field is regular in the main flow region, script D signM, but is singular in a thin inner region script D signI located adjacent to the body and to the downstream-attached streamline, and the flow is characterized by trailing horseshoe vortices. When the body moves parallel to the density gradient U × ∇ρ0 = 0, the density field is unsteady in the body's frame of reference; however to leading order the flow is steady in the region script D signM moving with the body for Ut/a ≫ 1. In the thin region script D signI of thickness O(aε), the density gradient and vorticity are singular. When U × ∇ρ0 = 0 this singularity leads to a downstream 'jet' with velocities of O(-(U·∇ρ0)U a/(ρ0U)) on the downstream attached streamline(s). In the far field the flow is characterized by a sink of strength CMscript V sign(U·∇ρ0)/2ρ0, located at the origin, where CM is the added-mass coefficient of the body and script V sign is the body's volume. The forces acting on a body moving steadily in a weak density gradient are calculated by considering the steady relative velocity field in region script D signM and evaluating the momentum flux far from the body. When U·∇ρ0 = 0, a lift force, CLscript V sign(U × ∇ρ0) × U, pushes the body towards the denser fluid, where the lift coefficient is CL = CM/2 for a three-dimensional body, that is axisymmetric about U, and is CL = (CM + 1)/2 for a two-dimensional body. The direction of the lift force is unchanged when U is reversed. A general expression for the forces on bodies moving in a weak shear and perpendicularly to a density gradient is calculated. When U × ∇ρ0 = 0, a drag force -CDscript D sign(U·∇ρ0)U retards the body as it moves into denser fluid, where the drag coefficient is CD = CM/2, for both two- and three-dimensional axisymmetric bodies. The direction of the drag force changes sign when U is reversed. There are two contributions to the drag calculation from the far field; the first is from the wake 'jet' on the attached streamline(s) caused by the rotational component of the flow and this leads to an accelerating force. The second and larger contribution arises from a downstream density variation, caused by the distortion of the isopycnal surfaces by the primary irrotational flow, and this leads to a drag force. When cylinders or spheres move with a velocity U at arbitrary orientation to the density gradient, it is shown that they are acted on by a linear combination of lift and drag forces. Calculations of their trajectories show that they initially slow down or accelerate on a length scale of order ρ0/|∇ρ0| (independent of script V sign and U) as they move into regions of increasing or decreasing density, but in general they turn and ultimately move parallel to the density gradient in the direction of increasing density gradient.

Description: In Hammerton & Kerschen (1996), the effect of the nose radius of a body on boundary-layer receptivity was analysed for the case of a symmetric mean flow past a two-dimensional body with a parabolic leading edge. A low-Mach-number two-dimensional flow was considered. The radius of curvature of the leading edge, rn, enters the theory through a Strouhal number, S ωrn/U, where ω is the frequency of the unsteady free-stream disturbance and U is the mean flow speed. Numerical results revealed that the variation of receptivity for small S was very different for free-stream acoustic waves propagating parallel to the mean flow and those free-stream waves propagating at an angle to the mean flow. In this paper the small-S asymptotic theory is presented. For free-stream acoustic waves propagating parallel to the symmetric mean flow, the receptivity is found to vary linearly with S, giving a small increase in the amplitude of the receptivity coefficient for small S compared to the flat-plate value. In contrast, for oblique free-stream acoustic waves, the receptivity varies with S1/2, leading to a sharp decrease in the amplitude of the receptivity coefficient relative to the flat-plate value. Comparison of the asymptotic theory with numerical results obtained in the earlier paper confirms the asymptotic results but reveals that the numerical results diverge from the asymptotic result for unexpectedly small values of S.

Description: The so-called Crocco integral establishes a relation between the velocity and temperature distributions in steady boundary layer flow. It corresponds to an exact solution of the flow equations in the case of unity Prandtl number and an adiabatic wall, where it reduces to the condition that the total enthalpy remains constant throughout the boundary layer, irrespective of pressure gradient and compressibility. The effect of Prandtl number is usually incorporated by assuming a constant recovery factor across the entire boundary layer. Strictly, however, this modification is in conflict with the conservation-of-energy principle. In search of a more complete expression for the Crocco integral the present study applies an asymptotic solution approach to the energy equation in constant-property flow. The analysis of self-similar boundary layer solutions results in a formulation of the Crocco integral which correctly incorporates the effect of Prandtl number to first order, and that is complete in the sense that it satisfies the energy conservation requirement. Furthermore, the result is found to be applicable not only to self-similar boundary layers, but also to provide a solution to the laminar flow equations in general as well. The effect of varying properties is considered with regard to the extension of the expression to more general flow conditions. In addition to the asymptotic expression for the Crocco integral, asymptotic solutions are also obtained for the recovery factor for various classes of flows.

Description: The equation relating second- and third-order velocity structure functions was presented by Kolmogorov; Monin attempted to derive that equation on the basis of local isotropy. Recently, concerns have been raised to the effect that Kolmogorov's equation and an ancillary incompressibility condition governing the third-order structure function were proven only on the restrictive basis of isotropy and that the statistic involving pressure that appears in the derivation of Kolmogorov's equation might not vanish on the basis of local isotropy. These concerns are resolved. In so doing, results are obtained for the second- and third-order statistics on the basis of local homogeneity without use of local isotropy. These results are applicable to future studies of the approach toward local isotropy. Accuracy of Kolmogorov's equation is shown to be more sensitive to anisotropy of the third-order structure function than to anisotropy of the second-order structure function. Kolmogorov's 4/5 law for the inertial range of the third-order structure function is obtained without use of the incompressibility conditions on the second- and third-order structure functions. A generalization of Kolmogorov's 4/5 law, which applies to the inertial range of locally homogeneous turbulence at very large Reynolds numbers, is shown to also apply to the energy-containing range for the more restrictive case of stationary, homogeneous turbulence. The variety of derivations of Kolmogorov's and Monin's equations leads to a wide range of applicability to experimental conditions, including, in some cases, turbulence of moderate Reynolds number.