bluuebunny/crossref_metadata_2025 huggingface dataset:
Three-dimensional transition in the wake of bluff elongated cylinders
Authors: RYAN K. , THOMPSON M. C. , HOURIGAN K.
Published: August 2005

Despite little supporting evidence, there appears to be an implicit assumption that the wakes of two-dimensional bluff bodies undergo transition to three-dimensional flow and eventually turbulence, through the same sequence of transitions as observed for a circular cylinder wake. Previous studies of a square cylinder wake support this assumption. In this paper, the transition to three-dimensional wake flow is examined for an elongated cylinder with an aerodynamic leading edge and square trailing edge. The three-dimensional instability modes are determined as a function of aspect ratio ($\hbox{\it AR}\,{=}\,$length to width). Floquet analysis reveals that three distinct instabilities occur. These are referred to as Modes A, B$^\prime$ and S$^\prime$ through analogy with the modes for circular and square cylinders. For aspect ratios less than approximately 7.5, Mode A is the most unstable mode. For aspect ratios greater than this, the most unstable mode switches to Mode B$^\prime$. This has the same spatio-temporal symmetry as Mode B for a circular cylinder, but a spanwise wavelength and near-wake features more in common with Mode S for a square cylinder. The dominant wavelength for this mode is approximately two cylinder thicknesses, much longer than for Mode B for a circular cylinder. It is found that the critical Reynolds number for the onset of the Mode A instability varies approximately with the square root of the aspect ratio. On the other hand, the critical Reynolds number for Mode B$^\prime$ is almost independent of aspect ratio. For large aspect ratios, the separation in Reynolds number between the critical Reynolds numbers is substantial; for instance, for $\hbox{\it AR}\,{=}\,17.5$, these values are approximately 450 and 700. In fact, for this aspect ratio, the third instability mode, Mode S$^\prime$, is more unstable than Mode A. These results suggest that the transition scenario for elongated bluff bodies may be distinctly different to short bodies such as circular or square cylinders. At the very least, the dominant spanwise wavelength in the turbulent wake is likely to be much longer than that for a circular cylinder wake. In addition, the reversal of the ordering of occurrence of the two modes with the different spatial symmetries is likely to affect the development of spatio-temporal chaos as a precursor to fully turbulent flow.

In conjunction with prior work, the current results indicate that nearly all three-dimensional instabilities of the vortex street can be identified as one of only a handful of transition modes.
Starting flow through nozzles with temporally variable exit diameter
Authors: DABIRI JOHN O. , GHARIB MORTEZA
Published: August 2005

Starting flow through a nozzle or orifice typically results in the transient formation of a leading vortex ring and trailing jet. Experiments are conducted to investigate the dynamics of this process in the case of a temporally variable nozzle exit diameter, with the aim of understanding these flows as they occur in Nature and emerging technologies. By kinematically decoupling the source flow from the nozzle motion, comparison across several classes of exit diameter temporal variation is facilitated. Kinematic models of the starting flows are used to accurately predict the fluid circulation produced by the vortex generators, and to emphasize the special role of the nozzle boundary layer in dictating the nature of the global flow patterns. A dimensionless temporal parameter is derived in order to track the vortex formation process for the various classes of nozzle motion. Dynamics of vortex ring disconnection from the source flow are studied in this new dimensionless framework. We show that temporally increasing the nozzle exit diameter as the starting flow develops results in higher-energy vortex ring structures with peak vorticity located further from the axis of symmetry relative to a static nozzle case. In addition, the normalized energy supplied by the vortex generator is increased in this process. We do not observe a delay in the onset of vortex ring disconnection from the trailing jet, as predicted by previous numerical simulations. In contrast, growth of the leading vortex ring is substantially augmented by temporally decreasing the nozzle exit diameter during fluid ejection, as noted in a previous experiment. Normalized vortex ring circulation is increased 35% in these cases, and the normalized energy of the generated vortex rings is equivalent to that of Hill's spherical vortex. These observed effects are explained by considering the measured vorticity distribution and energy of the starting flows. Strategies are suggested to exploit the discovered dynamics for various pulsed-jet applications.
Controlled oscillations of a cylinder: forces and wake modes
Authors: CARBERRY J. , SHERIDAN J. , ROCKWELL D.
Published: August 2005

The wake states from a circular cylinder undergoing controlled sinusoidal oscillation transverse to the free stream are examined. As the frequency of oscillation passes through the natural Kármán frequency there is a transition between two distinctly different wake states: the low- and high-frequency states. The transition corresponds to a change in the structure of the near wake and is also characterized by a jump in the phase and amplitude of both the total and vortex lift. Over the range of flow and oscillation parameters studied the wake states exhibit a number of universal features. The phases of the vortex lift and drag forces have characteristic values for the low- and high-frequency states, which appear to be directly related to the phase of vortex shedding. A split force concept is employed, whereby instantaneous force traces and images allow discrimination between the actual loading and the physics, and their conventional time-averaged representations. The wake states for the forced oscillations show some remarkable similarities to the response branches of elastically mounted cylinders. The equivalence between forced and self-excited oscillations is addressed in detail using concepts of energy transfer.
The effect of bubbles on developed turbulence
Authors: RENSEN JUDITH , LUTHER STEFAN , LOHSE DETLEF
Published: August 2005

Hot-film anemometry measurements are performed in a fully developed turbulent bubbly flow. For the bubble detection in the signal, both a threshold method and a new pattern recognition algorithm are employed. The measurements are carried out with gas fractions up to 3% and a mean water velocity of 0.20 m s$^{-1}$, corresponding to a Reynolds number of about $9\,{\times}\,10^4$. The typical bubble radius is 1–2 mm, corresponding to 10–20 Kolmogorov length scales. In this regime, a ‘bubblance’ parameter $b$ which compares the kinetic energy originating from the rising bubbles with that of the turbulence fluctuations is smaller than 1. Probability distribution functions, structure functions (with and without the extended self-similarity (ESS) method), and spectra of the water velocity time series are calculated. Both our results for the turbulent energy spectra and the second-order structure functions show qualitative agreement with numerical results by Massitelli, Lohse & Toschi (Phys. Fluids, vol. 15 (2003), p. L5), i.e. a more pronounced energy enhancement on small scales than on large scales owing to the presence of bubbles, leading to a less steep slope in the spectrum as compared to the Kolmogorov $-5/3$ law. These results are robust, i.e. do not depend on details of the bubble detection scheme.
Low-dimensional models for turbulent plane Couette flow in a minimal flow unit
Authors: SMITH T. R. , MOEHLIS J. , HOLMES P.
Published: August 2005

We model turbulent plane Couette flow in the minimal flow unit (MFU) – a domain whose spanwise and streamwise extent is just sufficient to maintain turbulence – by expanding the velocity field as a sum of optimal modes calculated via proper orthogonal decomposition from numerical data. Ordinary differential equations are obtained by Galerkin projection of the Navier–Stokes equations onto these modes. We first consider a 6-mode (11-dimensional) model and study the effects of including losses to neglected modes. Ignoring these, the model reproduces turbulent statistics acceptably, but fails to reproduce dynamics; including them, we find a stable periodic orbit that captures the regeneration cycle dynamics and agrees well with direct numerical simulations. However, restriction to as few as six modes artificially constrains the relative magnitudes of streamwise vortices and streaks and so cannot reproduce stability of the laminar state or properly account for bifurcations to turbulence as Reynolds number increases. To address this issue, we develop a second class of models based on ‘uncoupled’ eigenfunctions that allow independence among streamwise and cross-stream velocity components. A 9-mode (31-dimensional) model produces bifurcation diagrams for steady and periodic states in qualitative agreement with numerical Navier–Stokes solutions, while preserving the regeneration cycle dynamics. Together, the models provide empirical evidence that the ‘backbone’ for MFU turbulence is a periodic orbit, and support the roll–streak–breakdown–roll reformation picture of shear-driven turbulence.
Time singularities in conjugated thermo-fluid-dynamic phenomena
Authors: POZZI AMILCARE , TOGNACCINI RENATO
Published: August 2005

The thermo-fluid-dynamic field that arises when an infinite thick plate is impulsively accelerated to a constant speed in a laminar regime is studied, taking into account the coupling of the convection and conduction in the fluid with the conduction in the solid. Two significant cases are discussed depending on the boundary condition imposed on the unwetted side of the plate: constant temperature or adiabatic wall. The work is particularly focused on analysing the singularities arising in the field at the initial time. For this purpose an exact analytical solution of the problem governed by the Navier–Stokes equations with constant properties and by the energy equations in the fluid and in the solid is proposed and discussed. The non-dimensional parameter governing the conjugated effects is shown to be the ratio between the thermal effusivities in the fluid and in the solid. The results have also been extended to the analysis of compressible flows by the Stewartson–Dorodnitsin transformation.
Unsteady hydrodynamic effect of rotation on steady rigid-body motion
Authors: BHATTACHARYA S.
Published: August 2005

Owing to the inertial effect of the flow, an unsteady hydrodynamic force will act on a particle of arbitrary shape undergoing a steady rigid-body motion with small but finite Reynolds number if the axis of rotation of the particle is not its axis of rotational symmetry. Unsteady flow field is generated owing to such rotation of the body and as a result the particle experiences a time-dependent translational resistance. In this paper, we analyse this time-dependent hydrodynamic force and obtain its higher-order correction by systematically expanding the Navier–Stokes equation in small Reynolds number.
On the development of singularities in linear dispersive systems
Authors: CRAIK ALEX D. D.
Published: August 2005

Benilov, O'Brien & Sazonov (2003) and Benilov (2004) describe “a new type of instability” in a liquid film inside a rotating cylinder. Though their linear systems support only neutrally stable modes, they find explosive disturbances which become singular after a finite time. They suggest that this result casts doubt on the reliability of modal analysis for prediction of instability; and they claim that “Such cases have never been described in the literature, and they are probably extremely rare”. Here, other examples are given, some of which have been known (though not well-known) for many years. A common feature of all these singularities is a local phase synchronization of short-wave modes; but the configuration of Benilov et al. has the additional feature of eigenfunctions that exhibit very large changes in amplitude within the spatial domain. The relevance, or not, of such singularities to real physical systems is discussed.
Effects of an opening on pressure wave propagation in a tube
Authors: AUVITY B. , BELLENOUE M.
Published: August 2005

This paper focuses on the effects of an opening placed along a tube on the propagation of a pressure wavefront. Such a configuration has been chosen for its relevance to many of the countermeasures envisaged in reducing strong pressure transients in tunnels due to the entry of high-speed trains (this installation includes a perforated entrance hood and ventilation shaft). We will start by establishing that when a compression wavefront passes through an opening, the front is split into an infinite number of smaller pressure steps, with their amplitude expressed as the terms of a mathematical series. The main parameter of the series is a transmission coefficient of the opening. The shape of each of the smaller pressure steps is driven by the transmission–reflection process that takes place at the opening. Both experimental and numerical studies have been carried out to carefully estimate both the transmission coefficient and the shape of the transmitted and reflected pressure waves. Three major parameters are identified: the relative surface area of the opening to the tube cross-section, the ratio of the incident front length to the longitudinal opening length, and the incident front amplitude.

It will be shown that the transmission coefficient decreases exponentially with the relative surface area of the opening and is significantly influenced by the incident front amplitude. Both the length and shape of the transmitted front are similar to those of the incident front. The reflected front length, however, increases linearly with the incident front length as well as with the longitudinal opening length. The shape of the reflected front is greatly influenced by the incident front length. A linear analysis has been conducted and shows that the transmission coefficient can be predicted in a straightforward manner. These results are deemed to be of help not only in the design of countermeasures for the train/tunnel entry problem, but also for technological applications involving transient pressure pulses in branched pipe flows (e.g. pulsed flow in exhaust pipes).
Analytical solutions for turbulent non-Boussinesq plumes
Authors: CARLOTTI PIERRE , HUNT GARY R.
Published: August 2005

Analytical solutions are developed for non-Boussinesq turbulent plumes rising from horizontal area sources in unconfined quiescent environments of uniform density. The approach adopted follows and extends an earlier approach for Boussinesq plumes and replaces the non-Boussinesq area source of interest and located at $z\,{=}\,0$ with an idealized point source located at a virtual origin $z\,{=}\,z_v$ such that the flow above the idealized source approximates that from the actual source. Asymptotic analytical expressions are developed for the location of the virtual source that are valid for large vertical distances above the non-Boussinesq source. The non-Boussinesq source is characterized by a non-dimensional parameter $\Gamma_{\hbox{\scriptsize{\it nb}}}$ which is a measure of the relative strengths of the mass, momentum and density deficit fluxes at, or at a specified height above, the source. The vertical distance between the actual and virtual sources scales on the length scale $\ell$ that characterizes the height over which the flow is non-Boussinesq and expressions for $z_v/\ell$ are developed for lazy ($\Gamma_{\hbox{\scriptsize{\it nb}}}\,{>}\,1$) and forced plume ($\Gamma_{\hbox{\scriptsize{\it nb}}}\,{<}\,1$) sources. For pure-plume source conditions $\Gamma_{\hbox{\scriptsize{\it nb}}}\,{=}\,1$, and the virtual source provides an exact representation of the actual plume above $z\,{=}\,0$. The limiting cases of a nearly pure lazy plume and of a highly lazy plume are also explored analytically. For fire plumes, $\Gamma_{\hbox{\scriptsize{\it nb}}}$ is determined from the balance of fluxes immediately above the combustion region and a procedure for estimating these fluxes is given. Solutions expressing the dependence of the mass flux with height are also developed for the near-field flow regions and thereafter an approximation for the mass and momentum fluxes valid for all heights and for source conditions yielding $0\,{<}\,\Gamma_{\hbox{\scriptsize{\it nb}}}\,{<}\,\infty$ is deduced. Applications of the model may include plumes above fires and forced releases of highly buoyant gas into the atmosphere, for example, following the rupturing of a pressurized container vessel.
Apparent slip at the surface of a ball spinning in a concentrated suspension
Authors: MONDY L. A. , GRILLET A. M. , PACHECO G. , HENFLING J. , INGBER M. S. , GRAHAM A. L. , BRENNER H.
Published: August 2005

The couple on a ball rotating relative to an otherwise quiescent suspension of comparably-sized, neutrally buoyant spheres is studied both experimentally and numerically. Apparent ‘slip’ relative to the analytical solution for a sphere spinning in a Newtonian fluid (based upon the viscosity of the suspension) is determined in suspensions with volume fractions $c$ ranging from 0.03 to 0.50. This apparent slip results in a decrease of the measured torque on the spinning ball when the radius of the ball becomes comparable with that of the suspended spheres. Over the range of our data, the slip becomes more pronounced as the concentration $c$ increases. At $c\,{=}\,$0.25, three-dimensional boundary-element simulations agree well with the experimental data. Moreover, at $c\,{=}\,$0.03, good agreement exists between such calculations and theoretical predictions of rotary slip in dilute suspensions.
Thermocapillary long waves in a liquid film flow. Part 1. Low-dimensional formulation
Authors: RUYER-QUIL C. , SCHEID B. , KALLIADASIS S. , VELARDE M. G. , R. Kh. ZEYTOUNIAN
Published: August 2005

We consider the dynamics of a thin liquid film falling down a uniformly heated wall. The heating sets up surface tension gradients that induce thermocapillary stresses on the free surface, thus affecting the evolution of the film. We model this thermocapillary flow by using a gradient expansion combined with a Galerkin projection with polynomial test functions for both velocity and temperature fields. We obtain equations for the evolution of the velocity and temperature amplitudes at first- and second-order in the expansion parameter. These equations are fully compatible close to criticality with the Benney long-wave expansion. Models of reduced dimensionality for the evolution of the local film thickness, flow rate and interfacial temperature only, are proposed.
Mixing regimes for the flow of dense fluid down slopes into stratified environments
Authors: BAINES PETER G.
Published: August 2005

Downslope flows into density-stratified environments have been observed to have the character of detraining gravity currents on small slopes, and of entraining plumes on steep slopes. In this paper, observations of flows on slopes of intermediate (20$^{\circ}$–30$^{\circ}$) steepness are described, and their mixing properties quantified. Both gravity-current-like and plume-like flows are observed, and an observational boundary between these two types is identified. Theoretical models for the bulk properties of these flows are presented, and their predictions are compared with the observations. A theoretical criterion is derived for the limit of applicability of the gravity-current model in terms of the Buoyancy number, the bottom slope and the bottom drag coefficient. This provides a criterion for the boundary between the plume-like and gravity-current-like flows, which is consistent with the observations. These results have implications for the modelling of downslope flows in nature, and indicate where the appropriate dynamical model may change from one type to the other.
Thermocapillary long waves in a liquid film flow. Part 2. Linear stability and nonlinear waves
Authors: SCHEID B. , RUYER-QUIL C. , KALLIADASIS S. , VELARDE M. G. , ZEYTOUNIAN R. Kh.
Published: August 2005

We analyse the regularized reduced model derived in Part 1 (Ruyer-Quil et al. 2005). Our investigation is two-fold: (i) we demonstrate that the linear stability properties of the model are in good agreement with the Orr–Sommerfeld analysis of the linearized Navier–Stokes/energy equations; (ii) we show the existence of nonlinear solutions, namely single-hump solitary pulses, for the widest possible range of parameters. We also scrutinize the influence of Reynolds, Prandtl and Marangoni numbers on the shape, speed, flow patterns and temperature distributions for the solitary waves obtained from the regularized model. The hydrodynamic and Marangoni instabilities are seen to reinforce each other in a non-trivial manner. The transport of heat by the flow has a stabilizing effect for small-amplitude waves but promotes the instability for large-amplitude waves when a recirculating zone is present. Nevertheless, in this last case, by increasing the shear in the bulk and thus the viscous dissipation, increasing the Prandtl number decreases the amplitude and speed of the waves.
Particle migration and free-surface topography in inclined plane flow of a suspension
Authors: TIMBERLAKE BRIAN D. , MORRIS JEFFREY F.
Published: August 2005

Gravity-driven free-surface flow of a suspension of neutrally buoyant particles down an inclined plane channel of constant width has been studied experimentally and by flow modelling. A uniform suspension of spheres, sieved to radii of $a \,{=}\, 53--125 $\umu$m or 125–150$\,\umu$m, was introduced to create films of initial depth $h_o$. The flow was always at small film-depth-based Reynolds numbers. The film depth and the mixture flow profile were measured at the initial and two locations at least $200 h_o$ and $400 h_o$ downstream. The bulk particle volume fraction, $\phi_{\rm B}$, was varied in the range $0.01\,{\le}\, \phi_{\rm B} \,{\le}\, 0.5$; $h_o\,{\approx}\, 1.8$–3.2 mm and the inclination angle relative to horizontal, $0.1^{\circ} \,{<}\, \alpha\,{\le}\, 90^{\circ}$, were also varied. Analysis of the particle velocity was performed by stereoscopic imaging to determine particle location followed by particle correlation velocimetry. A two-layer Newtonian viscosity model was applied to the velocimetry results in order to infer particle concentration information. Measured velocity profiles and film depth show that film thickness decreases from $h_o$, while the velocity gradient at the wall and the mean velocity increase, as the mixture flows down the plane. The free surface, examined using direct imaging, becomes progressively more deformed as $\alpha$ and $\phi_{\rm B}$ increase, with the onset of observable deformation found at a particle-scale capillary number of $\hbox{\it Ca}_{p} \,{\sim}\, {\rho g_x a^2}/{\sigma}\,{=}\, O(10^{-4})$; $\rho$ is the mixture density, $g_x\,{=}\, g \sin \alpha$ is the axial component of gravitational acceleration and $\sigma$ is the surface tension of the suspending liquid. An existing model for suspension flow which describes phase migration as driven by normal stresses caused by the suspended particles is used to predict the flow, with satisfactory agreement for film depth and development distance for the non-uniform local solid volume fraction, $\phi$. The agreement with the detailed $\phi$ profile is less good, as the model fails to predict the observed $\phi \,{\approx}\, 0$ near the solid boundary while $\phi$ is overpredicted adjacent to the free surface.
A new friction factor relationship for fully developed pipe flow
Authors: McKEON B. J. , ZAGAROLA M. V. , SMITS A. J.
Published: August 2005

The friction factor relationship for high-Reynolds-number fully developed turbulent pipe flow is investigated using two sets of data from the Princeton Superpipe in the range $31 \,{\times}\, 10^3 \,{\le}\,\hbox{\it Re}_D \,{\le}\, 35 \,{\times}\, 10^6$. The constants of Prandtl's ‘universal’ friction factor relationship are shown to be accurate over only a limited Reynolds-number range and unsuitable for extrapolation to high Reynolds numbers. New constants, based on a logarithmic overlap in the mean velocity, are found to represent the high-Reynolds-number data to within 0.5%, and yield a value for the von Kármán constant that is consistent with the mean velocity profiles themselves. The use of a generalized logarithmic law in the mean velocity is also examined. A general friction factor relationship is proposed that predicts all the data to within 1.4% and agrees with the Blasius relationship for low Reynolds numbers to within 2.0%.
Granular collapse in two dimensions
Authors: BALMFORTH N. J. , KERSWELL R. R.
Published: August 2005

An experimental investigation is conducted into the collapse of granular columns inside rectangular channels. The final shape is documented for slumps inside relatively wide channels, and for collapses inside much narrower slots. In both cases, the collapse is initiated by withdrawing a swinging gate or sliding door, and the flow remains fairly two-dimensional. Four different granular media are used; the properties of the materials vary significantly, notably in their angles of friction for basal sliding and internal deformation. If $H$ is the initial height of the column, $h_{\infty}$ the maximum final height of the column and $a$ the initial aspect ratio, then the data suggest that $H/h_{\infty} \,{\sim} a^{0.6}$ in wide channels and $H/h_{\infty} \,{\sim}\, a^{0.5}$ for narrow slots. For the runout, we find that $(l_{\infty}\,{-}\,L)/L \,{\sim}\, a^{0.9\pm 0.1}$ for wide channels, and $(l_{\infty}\,{-}\,L)/L \,{\sim}\, a^{0.65\pm0.05}$ or $l_\infty/L \,{\sim}\, a^{0.55\pm0.05}$ for narrow slots, where $l_{\infty}$ is the maximum runout of the material and $L$ the initial length of the column along the channel ($a\,{:=}\,H/L$). In all cases, the numerical constant of proportionality in these scaling relations shows clear material dependence. In wide slots, there is no obvious universal scaling behaviour of the final profile, but such a behaviour is evident in narrow slots. The experimental results are compared with theoretical results based on a shallow granular-flow model. The qualitative behaviour of the slump in the wide slot is reproduced by the theoretical model. However, there is qualitative disagreement between theory and the experiments in the narrow slot because of the occurrence of secondary surface avalanching.
Fluctuating circulation forced by unsteady multidirectional breaking waves
Authors: KENNEDY A. B.
Published: August 2005

In this paper, we consider nearshore rotational currents directly forced by unsteady multidirectional wave breaking. Scaling relationships, simplified analytical solutions, and asymptotic limits are developed for the maximum forced cross-shore and longshore velocities. In all cases, forced longshore velocities are considerably larger than cross-shore velocities. On longshore-uniform beaches, strong fluctuating velocities are found for (i) large waves; (ii) strong directional spreading; and (iii) short peak wave periods. When topographic inhomogeneities control longshore scales of wave breaking, overall scaling changes and the largest fluctuating velocities are found for ($a$) large waves; ($b$) long wave periods; and ($c$) topographic features that vary quickly in the longshore direction. The ratio of fluctuating rotational velocities to mean longshore current does not depend on the wave height or period, but instead on the bottom friction, slope, deep water wave angle, and details of the wave spectrum.
The IPCC and Antarctica
Authors: VAN DEN BROEKE MICHIEL
Published: August 2005

How well is the scientific community doing on providing policy makers with evidence for climate change and predictions for its future trends? The Intergovernmental Panel on Climate Change (IPCC) is one of the flagships of international scientific collaboration. Every five years, IPCC Working Group 1 compiles the state of the art in the science of climate change. The Third Assessment Report was presented in 2001, and writing of the Fourth Assessment Report began in the autumn of 2004. External, invited experts reviewed the initial draft last May and the final report will be made available to governments and public in late 2006. In September 2005 the first draft will even be published on the Internet for an eight-week external review period by anyone interested.
Odyssey of stow-away noctuid moths to southern polar islands
Authors: BARNES DAVID K.A. , CONVEY PETER
Published: August 2005

High southern latitude island environments are unusual in having relatively low or, in some cases, no non-indigenous species (NIS). Here we describe the accidental transport and survivorship of moths (Lepidoptera, Noctuidae) on a research vessel travelling from southern South America (Montevideo, Uruguay) first to the cool temperate Falkland Islands and then onwards to Maritime Antarctic Signy Island (South Orkney Islands). On the vessel's arrival at Stanley, Falkland Islands, from Montevideo we found eight live (and 30 dead) individuals of two species of South American noctuid moth (Pseudaletia adultera Schaus and Peridroma saucia (Hübner)), presumed to have been attracted to the ship's lights while in port. Neither of these is indigenous to the Falkland Islands. Five of the eight living moths (all P. adultera) survived the four days the ship was moored in Stanley and one survived a further four day journey across the Polar Front to Signy Island. Southern oceanic islands are particularly vulnerable to invasion by NIS, with human (shipping) activities being the main route of arrival. With increasing shipping throughout this region some measures have been proposed or adopted to reduce the risk of NIS transfer.
Spawning behaviour and early development in the naked dragonfish Gymnodraco acuticeps
Authors: EVANS CLIVE W. , CZIKO PAUL , CHENG CHI-HING CHRISTINA , DEVRIES ARTHUR L.
Published: August 2005

Nesting sites of the naked dragonfish Gymnodraco acuticeps have been identified in 15–35 m water under fast ice adjacent to McMurdo Station, making it possible to examine embryonic development and early larval growth. Egg-laying (predominantly in October) is preceded by a distinctive whirling behavioural pattern driven by the male prodding the side of the female's abdomen. The eggs (3.42 ± 0.19 mm in diameter) are laid on rocks as a single adherent layer (c. 2500 per patch). Development is unusually protracted, the first cleavage occurring after about 24 hr at about −1.9°C. Hatching occurs about 10 months post-fertilization, beginning soon after the sun rises above the horizon. During this period one of the parents may act as a guard in an attempt to keep predators at bay. Upon hatching, the larvae (12.09 ± 0.36 mm long) swim towards the surface ice where they presumably seek refuge. Yolk absorption is complete in about 15 days. Larvae (grown in aquaria at a density of 0.7 larvae l−1) display an average daily growth rate of 0.42% over nine weeks. Hatching in aquaria can occur up to 100 days in advance of that seen in the field, suggesting that under natural conditions hatching may be delayed until an appropriate stimulus (such as the return of the sun) is received.
Leopard seal predation rates at penguin colonies of different size
Authors: AINLEY DAVID G. , BALLARD GRANT , KARL BRIAN J. , DUGGER KATIE M.
Published: August 2005

In a study designed to elucidate the factors that might differentially affect the well being and biology of Adélie penguins (Pygoscelis adeliae) that breed in colonies of different size, we investigated the predation rates on penguins by leopard seals (Hydrurga leptonyx) over a period of six years. The study colonies varied in size across the full range for this penguin species, contrasting with previous studies in which data were gathered only at very large colonies, and only in single years. The number of seals present varied directly with the amount of penguin traffic in the areas near the beach, where most predation takes place. Seals were present persistently only when penguin traffic exceeded about 250 penguins per hour. Predation rates also varied with penguin traffic in a curvilinear fashion, leveling off where traffic exceeded about 1200 penguins per hour. With respect to predation, it appears to be advantageous for Adélie penguins to nest in very small or very large colonies. At large colonies, the number of penguins moving to and from the colony ‘swamp’ the seals' predatory efforts, thus reducing the chances that an individual penguin will be taken. Small colonies are of little interest to the seals.
Composition and biomass of shallow benthic megafauna during an annual cycle in Admiralty Bay, King George Island, Antarctica
Authors: ECHEVERRÍA CARLOS ALEJANDRO , PAIVA PAULO CESAR , ALVES VINÍCIUS COUTO
Published: August 2005

Composition and biomass of an Antarctic megafauna community were studied during a discontinuous 12 months cycle (March–December 1999 and December 2000–March 2001) at two stations (12 and 25 m depth) in Admiralty Bay, King George Island, Antarctica. During this period iceberg impacts were monitored in order to analyse their role in structuring the community. Organic matter content of the sediment showed a seasonal cycle for both depths, with lower values during winter and higher in summer. Composition and biomass of the megafauna were comparable to those described in previous surveys for the maritime Antarctica. Interannual or summer/winter changes in the density or biomass of the megafauna community were not significant, although significant differences between depths occurred during the whole survey. The observed community composition can be the considered result of a continuous invasion from a deeper fauna, constrained at shallower waters by the effects of ice and storms.
Photosynthetic responses of three common mosses from continental Antarctica
Authors: PANNEWITZ STEFAN , GREEN T.G. ALLAN , MAYSEK KADMIEL , SCHLENSOG MARK , SEPPELT ROD , SANCHO LEOPOLDO G. , TÜRK ROMAN , SCHROETER BURKHARD
Published: August 2005

Predicting the effects of climate change on Antarctic terrestrial vegetation requires a better knowledge of the ecophysiology of common moss species. In this paper we provide a comprehensive matrix for photosynthesis and major environmental parameters for three dominant Antarctic moss species (Bryum subrotundifolium, B. pseudotriquetrum and Ceratodon purpureus). Using locations in southern Victoria Land, (Granite Harbour, 77°S) and northern Victoria Land (Cape Hallett, 72°S) we determined the responses of net photosynthesis and dark respiration to thallus water content, thallus temperature, photosynthetic photon flux densities and CO2 concentration over several summer seasons. The studies also included microclimate recordings at all sites where the research was carried out in field laboratories. Plant temperature was influenced predominantly by the water regime at the site with dry mosses being warmer. Optimal temperatures for net photosynthesis were 13.7°C, 12.0°C and 6.6°C for B. subrotundifolium, B. pseudotriquetrum and C. purpureus, respectively and fall within the known range for Antarctic mosses. Maximal net photosynthesis at 10°C ranked as B. subrotundifolium > B. pseudotriquetrum > C. purpureus. Net photosynthesis was strongly depressed at subzero temperatures but was substantial at 0°C. Net photosynthesis of the mosses was not saturated by light at optimal water content and thallus temperature. Response of net photosynthesis to increase in water content was as expected for mosses although B. subrotundifolium showed a large depression (60%) at the highest hydrations. Net photosynthesis of both B. subrotundifolium and B. pseudotriquetrum showed a large response to increase in CO2 concentration and this rose with increase in temperature; saturation was not reached for B. pseudotriquetrum at 20°C. There was a high level of variability for species at the same sites in different years and between different locations. This was substantial enough to make prediction of the effects of climate change very difficult at the moment.
Location and DGGE methodology can influence interpretation of field experimental studies on the response to hydrocarbons by Antarctic benthic microbial community
Authors: POWELL SHANE M. , RIDDLE MARTIN J. , SNAPE IAN , STARK JONATHAN S.
Published: August 2005

A field experiment investigating the effect of oil contamination on benthic microbial communities was conducted near Casey Station, East Antarctica. Defaunated sediment was treated with a mixture of Special Antarctic Blend diesel and lubricating oil and deployed in three different bays for eleven weeks. A molecular fingerprinting technique, denaturing gradient gel electrophoresis (DGGE), was used to investigate the microbial community structure. The variation between replicate samples within treatment groups indicates that the benthic microbial populations are very diverse and evenly distributed. Comparisons to determine the significance of both deployment location and hydrocarbon treatment showed that the greatest effect was from a combination of location and treatment. Detailed analysis suggests that subtle differences may be obscured by variability introduced by PCR and gel stages in DGGE, undermining this experimental approach. It is concluded that both location and hydrocarbon contamination influenced the development of the microbial communities but that the effect of hydrocarbon treatment varied with location. This has important implications for the design of future experiments on the effect of hydrocarbons on benthic communities, especially if it is intended to generalize the conclusions drawn from site specific studies.
Response behaviour of seals and penguins to helicopter surveys over the pack ice off East Antarctica
Authors: SOUTHWELL COLIN
Published: August 2005

Data on the response behaviour of seals (crabeater, leopard and Ross) and penguins (Adélie and emperor) to helicopter surveys over the pack ice off East Antarctica are presented. The surveys involved Sikorsky S76 helicopters flying at altitude 130 m and speed 90 knots along straight-line transects. The relative frequency of alert and movement behaviours by seal and penguin groups decreased with distance out to 800 m from the flight path. Penguin groups were more likely to show a movement response than seals at all distances. The perpendicular distances moved relative to the flight path were small (maximum 20 m, mean ≤ 3 m, for both seal and penguin groups) relative to the width of the area searched (800 m), and there was no evidence that response movement resulted in a spiked detection histogram. Observers were more likely to feel confident in identifying seal and penguin species if the animals responded to the helicopter by changing the body posture or moving. In this application of aerial survey, the response behaviour elicited by the passing helicopter was considered to be beneficial from a technical perspective, and the disturbance caused to the surveyed populations negligible from an ethical perspective.
Evidence of late Quaternary environmental change in a continental east Antarctic lake from lacustrine sedimentary pigment distributions
Authors: SQUIER ANGELA H. , HODGSON DOMINIC A. , KEELY BRENDAN J.
Published: August 2005

A sediment core from Progress Lake, one of the oldest lacustrine sequences in East Antarctica, contains distinct zones dating from a previous interglacial (most likely Marine Isotope Stage 5e, c. 125–115 kyr BP) and the present interglacial (Marine Isotope Stage 1), separated by a transition zone representing when the lake became sub-glacial. Profiles of fossil pigments, determined using high performance liquid chromatography and liquid chromatography-tandem mass spectrometry, show distinct differences in the photoautotrophic community during these two interglacial periods. The first was dominated by algae and purple phototrophic bacteria, with periods of photic zone euxinia indicated by pigments from anoxygenic phototrophic bacteria. Specific chlorophyll a derivatives reveal periods when grazing pressure impacted significantly on the phytoplankton community. The virtual absence of pigments in the transition zone reflects severe restriction of photoautotrophic activity, consistent with the lake having become sub-glacial. Retreat of snow and ice in the late Holocene (3345 14C yr BP) allowed establishment of a less diverse primary producer community, restricted to algae and cyanobacteria. Grazers were severely restricted and oxidative transformation was more important than during the previous interglacial. The pigment data provide a unique and detailed insight in to the evolution of the lake ecology over an interglacial-glacial-interglacial transition and strong evidence that the Marine Isotope Stage 5e interglacial in this region of coastal East Antarctica was several degrees warmer than at present.
DNA sequencing and genetic diversity of the 18S–26S nuclear ribosomal internal transcribed spacers (ITS) in nine Antarctic moss species
Authors: SKOTNICKI M.L. , MACKENZIE A.M. , CLEMENTS M.A. , SELKIRK P.M.
Published: August 2005

We have sequenced the 18S–26S nuclear ribosomal DNA ITS region from the genome of nine different moss species from the Ross Sea region of Antarctica. This relatively quick and simple technique enables these species to be readily distinguished, facilitating their taxonomic identification. Only a single moss shoot is required, and for identification of these bryophytes it is only necessary to determine a few hundred nucleotides of the DNA sequence in a single sequencing reaction. Several previously unidentified Antarctic moss specimens were readily characterized by comparison with ITS sequences of known moss species. The relationships between species and locations previously detected by the RAPD (Random Amplified Polymorphic DNA) technique were confirmed by DNA sequencing, demonstrating that the two techniques can be complementary for molecular analysis of the ecology of mosses in Antarctica.
Killer whale harrassment of Adélie penguins at Ross Island
Authors: BALLARD GRANT , AINLEY DAVID G.
Published: August 2005

On innumerable occasions, Adélie (Pygoscelis adeliae) and emperor penguins (Aptenodytes forsteri) have been observed in close proximity to killer whales (Orcinus orca), with no whale-penguin interactions reported. On the other hand, killer whales reportedly harass and eat seabirds on occasion (Walker 1968: p. 1122, Stacey et al. 1990, Williams et al. 1990). Killer whales are known to prey on young king penguins (A. patagonica) as they are fledging (Guinet 1992, Guinet & Bouvier 1995) and occasionally take emperor penguins (Mikhalev et al. 1981). Thomas et al. (1981) report killer whales chasing Adélies. Here we report the only observations of Adélie-killer whale interactions observed in nine field seasons on Ross Island.
Phyllolepid placoderm fish remains from the Devonian Aztec Siltstone, southern Victoria Land, Antarctica
Authors: YOUNG GAVIN C. , LONG JOHN A.
Published: August 2005

Phyllolepid placoderm remains from the Aztec Siltstone fish fauna are described as Austrophyllolepis quiltyi sp. nov., Austrophyllolepis cf. A. youngi, Placolepis tingeyi sp. nov., and phyllolepid indet. The new Antarctic species of two genera previously only known from Australia reinforce evidence from other fish taxa of close biogeographic affinity, as part of the eastern margin of Palaeozoic Gondwana. At least three genera and four species gives the Aztec Siltstone fish fauna the most diverse phyllolepid assemblage known, and probably the oldest documented so far (?late Middle Devonian). Specimens of Austrophyllolepis from the type locality at Mount Howitt, Victoria, are refigured for comparison with the Antarctic species. The order Phyllolepida is a key group for understanding Devonian vertebrate biogeography and palaeogeography, with a unique disjunct distribution in both time and space between the Southern and Northern hemispheres. Phyllolepids document one of the major dispersal events in early vertebrate history, which approximately coincided with the Frasnian–Famennian boundary mass extinction during the Late Devonian.
Costa Recta beach, Deception Island, West Antarctica: a retreated scarp of a submarine fault?
Authors: FERNÁNDEZ-IBÁÑEZ FERMÍN , PÉREZ-LÓPEZ RAUL , MARTÍNEZ-DÍAZ JOSÉ J. , PAREDES CARLOS , GINER-ROBLES JORGE L. , CASELLI ALBERTO T. , IBÁÑEZ JESÚS M.
Published: August 2005

Deception Island (South Shetlands, Antarctica) is one of the most active volcanoes in Antarctica, having erupted recently in 1967, 1969 and 1970, damaging scientific stations on the island. It is also seismically very active. The island has attracted the attention of many researchers as it constitutes an undisturbed natural laboratory to study seismo-volcanic events and how they affect landscape modelling and evolution. One of the most remarkable geological and geomorphological features on Deception Island is the linearity of its easternmost coastal landform, the origin of which remains unknown. Some answers, based on presence of strike-slip fault or on the ice cap and beach geomorphological dynamics, have been reported in the literature. Our new work provides several indications of the existence of a dip-slip submarine fault, parallel to the coast (NNW–SSE), which suggests a tectonic origin for this morphological feature. Uplifted marine terraces, incision of a fluvial network over the ice cap, normal faulting parallel to the coast in the north and south rock heads bounding the beach and sharp shelf-break with rather constant slope, constitute some of this evidence. Terrace uplift and fluvial channel incision decreasing southward from Macaroni Point, indicates possible tilt movement across this inferred fault plane.
Palaeomagnetic, 40Ar/39Ar, and stratigraphical correlation of Miocene–Pliocene basalts in the Brandy Bay area, James Ross Island, Antarctica
Authors: KRISTJÁNSSON LEÓ , GUDMUNDSSON MAGNÚS T. , SMELLIE JOHN L. , MCINTOSH WILLIAM C. , ESSER RICHARD
Published: August 2005

A revised stratigraphy of Cenozoic volcanic outcrops in the Brandy Bay area on James Ross Island is obtained by combining palaeomagnetic and stratigraphical anlysis with 40Ar/39Ar dating. The fieldwork was carried out between January and March 2002. Oriented palaeomagnetic samples were obtained from 17 volcanic units, the majority of samples being from lava-fed deltas. Individually the deltas are a few to several hundred metres thick and were formed during voluminous basaltic eruptions within an ice sheet or in a marine setting. Out of the sampled units, 15 carry a stable primary magnetization; six were of normal polarity and nine were reversely magnetized. Our 40Ar/39Ar dating constrains the emplacement of most of the Brandy Bay basalts to the Gilbert chron, with the youngest dated unit having an age of 3.95 Ma and the oldest 6.16 Ma. The mean palaeomagnetic field direction from 14 units has an inclination I = −76° and declination D = 352°, α95 = 7°. The results further suggest that the lava caps on some of the deltas have high remanent intensity and should generate recognizable aeromagnetic anomalies. The combination of palaeomagnetic and isotopic analysis with field mapping methods in a single field area is unique in Antarctica so far and demonstrates that the combination can yield rigorous local stratigraphy in a geographically remote volcanic terrain having discontinuous outcrops.