Galaxy threshing and the formation of ultracompact dwarf galaxies

Recent spectroscopic and morphological observational studies of galaxies around NGC 1399 in the Fornax Cluster have discovered several ultracompact dwarf galaxies with intrinsic sizes of similar to 100 pc and absolute B-band magnitudes ranging from -13 to -11 mag. In order to elucidate the origin of these enigmatic objects, we perform numerical simulations on the dynamical evolution of nucleated dwarf galaxies orbiting NGC 1399 and suffering from its strong tidal gravitational field. Adopting a plausible scaling relation for dwarf galaxies, we find that the outer stellar components of a nucleated dwarf are totally removed. This is due to them being tidally stripped over the course of several passages past the central region of NGC 1399. The nucleus, however, manages to survive. We also find that the size and luminosity of the remnant are similar to those observed for ultracompact dwarf galaxies, if the simulated precursor nucleated dwarf has a mass of similar to 10(8) M.. These results suggest that ultracompact dwarf galaxies could have previously been more luminous dwarf spheroidal or elliptical galaxies with rather compact nuclei.

A new formation model for M32: a threshed early-type spiral galaxy?

The origin of M32, the closest compact elliptical galaxy (cE), is a long-standing puzzle of galaxy fort-nation in the Local Group. Our N-body/smoothed particle hydrodynamics simulations suggest a new scenario in which the strong tidal field of M31 can transform a spiral galaxy into a compact elliptical galaxy. As a low-luminosity spiral galaxy plunges into the central region of M31, most of the outer stellar and gaseous components of its disk are dramatically stripped as a result of M31's tidal field. The central bulge component, on the other hand, is just weakly influenced by the tidal field, owing to its compact configuration, and retains its morphology. M31's strong tidal field also induces rapid gas transfer to the central region, triggers a nuclear starburst, and consequently forms the central high-density and more metal-rich stellar populations with relatively young ages. Thus, in this scenario, M32 was previously the bulge of a spiral galaxy tidally interacting with M31 several gigayears ago. Furthermore, we suggest that cE's like M32 are rare, the result of both the rather narrow parameter space for tidal interactions that morphologically transform spiral galaxies into cE's and the very short timescale (less than a few times 10(9) yr) for cE's to be swallowed by their giant host galaxies (via dynamical friction) after their formation.

Postural activity of the diaphragm is reduced in humans when respiratory demand increases

1. Respiratory activity of the diaphragm and other respiratory muscles is normally co-ordinated with their other functions, such as for postural control of the trunk when the limbs move. The integration may occur by summation of two inputs at the respiratory motoneurons. The present study investigated whether postural activity of the diaphragm changed when respiratory drive increased with hypercapnoea. 2. Electromyographic (EMG) recordings of the diaphragm and other trunk muscles were made with intramuscular electrodes in 13 healthy volunteers. Under control conditions and while breathing through increased dead-space,subjects made rapid repetitive arm movements to disturb the stability of the spine for four periods each lasting 10 s, separated by 50 s. 3. End-tidal CO2, and ventilation increased for the first 60-120 s of the trial then reached a plateau. During rapid arm movement at the start of dead-space breathing, diaphragm EMG became tonic with superimposed modulation at the frequencies of respiration and arm movement. However, when the arm was moved after 60 s of hypercapnoea, the tonic diaphragm EMG during expiration and the phasic activity with arm movement were reduced or absent. Similar changes occurred for the expiratory muscle transversus abdominis, but not for the erector spinae. The mean amplitude of intra-abdominal pressure and the phasic changes with arm movement were reduced after 60 s of hypercapnoea. 4. The present data suggest that increased central respiratory drive may attenuate the postural commands reaching motoneurons. This attenuation can affect the key inspiratory and expiratory muscles and is likely to be co-ordinated at a pre-motoneuronal site.

Does habitat modification affect oviposition by the salt marsh mosquito, Ochlerotatus vigilax (Skuse) (Diptera : Culicidae)?

Studies were conducted at sites in south-cast Queensland, Australia, to investigate the effect of habitat modification for mosquito control on the distribution of eggshells of the salt marsh mosquito, Ochlerotatus vigilax (Skuse). Modifications were mainly tunnelling, but an Open Marsh Water Management (OMWM) site and a grid-ditched site were also included. There were two separate experimental designs: one was data collected Before and After (BA) modification and the other was for other sites with a Treatment and Control (TC) experimental design. For the BA data, there were significant reductions in eggshells after modification. Eggshells were generally fewer after modification in areas which were close to unrestricted tidal flushing. A sandy substrate and vegetation changes which resulted in reduced Sporobolus virginicus or mixed Sporobolus and Sarcocornia quinqueflora also contributed to the effect. In the TC experiment, there was no effect of modification at the tunnelled site, eggshells were fewer at the OMWM site, but there were more eggshells at the grid-ditched site. There was some general indication that recent oviposition activity was reduced in sites that had been modified, evidenced by a relatively small proportion of young (dark coloured) eggshells.

Galaxy threshing and the origin of intracluster stellar objects

We numerically investigate the dynamical evolution of non-nucleated dwarf elliptical/spiral galaxies (dE) and nucleated ones (dE,Ns) in clusters of galaxies in order to understand the origin of intracluster stellar objects, such as intracluster stars (ICSs), GCs (ICGCs), and ultracompact dwarfs (UCDs) recently discovered by all-object spectroscopic survey centred on the Fornax cluster of galaxies. We find that the outer stellar components of a nucleated dwarf are removed by the strong tidal field of the cluster, whereas the nucleus manages to survive as a result of its initially compact nature. The developed naked nucleus is found to have physical properties (e.g., size and mass) similar to those observed for UCDs. We also find that the UCD formation process, does depend on the radial density profile of the dark halo in the sense that UCDs are less likely to be formed from dwarfs embedded in dark matter halos with central 'cuspy' density profiles. Our simulations also suggest that very massive and compact stellar systems can be rapidly and efficiently formed in the central regions of dwarfs through the merging of smaller GCs. GCs initially in the outer part of dE and dE,Ns are found to be stripped to form ICGCs.

Galaxy Disruption Caught in the Act

Direct evidence of stellar material from galaxy disruption in the intra-cluster medium (ICM) relies on challenging observations of individual stars, planetary nebulae and diffuse optical light. Here we show that the ultra-compact dwarf galaxies (UCDs) we have discovered in the Fornax Cluster are a new and easy-to-measure probe of disruption in the ICM. We present spectroscopic observations supporting the hypothesis that the UCDs are the remnant nuclei of tidally threshed dwarf galaxies. Deep optical imaging of the cluster has revealed a 43-kpc long arc of tidal debris, flanking a nucleated dwarf elliptical (dE,N) cluster member. We may be witnessing galaxy threshing in action.

Positive end expiratory pressure during resuscitation of premature lambs rapidly improves blood gases without adversely affecting arterial pressure

Positive end expiratory pressure (PEEP) is important for neonatal ventilation but is not considered in guidelines for resuscitation. Our aim was to investigate the effects of PEEP on cardiorespiratory parameters during resuscitation of very premature lambs delivered by hysterotomy at similar to125 d gestation (term similar to147 d). Before delivery, they were intubated and lung fluid was drained. Immediately after delivery, they were ventilated with a Drager Babylog plus ventilator in volume guarantee mode with a tidal volume of 5 mL/kg. Lambs were randomized to receive 0, 4, 8, or 12 cm H2O of PEEP. They were ventilated for a 15-min resuscitation period followed by 2 h of stabilization at the same PEEP. Tidal volume, peak inspiratory pressure, PEEP, arterial pressure, oxygen saturation, and blood gases were measured regularly, and respiratory system compliance and alveolar/ arterial oxygen differences were calculated. Lambs that received 12 cm H2O of PEEP died from pneumothoraces; all others survived without pneumothoraces. Oxygenation was significantly improved by 8 and 12 cm H2O of PEEP compared with 0 and 4 cm H2O of PEEP. Lambs with 0 PEEP did not oxygenate adequately. The compliance of the respiratory system was significantly higher at 4 and 8 cm H2O of PEEP than at 0 PEEP. There were no significant differences in partial pressure of carbon dioxide in arterial blood between groups. Arterial pressure was highest with 8 cm H2O of PEEP, and there was no cardiorespiratory compromise at any level of PEEP. Applying PEEP during resuscitation of very premature infants might be advantageous and merits further investigation.

Quantum phase-space analysis of the pendular cavity

We perform a quantum-mechanical analysis of the pendular cavity, using the positive-P representation, showing that the quantum state of the moving mirror, a macroscopic object, has noticeable effects on the dynamics. This system has previously been proposed as a candidate for the quantum-limited measurement of small displacements of the mirror due to radiation pressure, for the production of states with entanglement between the mirror and the field, and even for superposition states of the mirror. However, when we treat the oscillating mirror quantum mechanically, we find that it always oscillates, has no stationary steady state, and exhibits uncertainties in position and momentum which are typically larger than the mean values. This means that previous linearized fluctuation analyses which have been used to predict these highly quantum states are of limited use. We find that the achievable accuracy in measurement is fat, worse than the standard quantum limit due to thermal noise, which, for typical experimental parameters, is overwhelming even at 2 mK

Driving mechanisms for groundwater flow and salt transport in a subterranean estuary

This paper presents field measurements and numerical simulations of groundwater dynamics in the intertidal zone of a sandy meso-tidal beach. The study, focusing on vertical hydraulic gradients and pore water salinities, reveals that tides and waves provide important forcing mechanisms for flow and salt transport in the nearshore aquifer. Such forcing, interacting with the beach morphology, enhances the exchange between the aquifer and ocean. The spatial and temporal variations of vertical hydraulic gradients demonstrate the complexity and dynamic nature of the processes and the extent of mixing between fresh groundwater and seawater in a subterranean estuary''. These results provide evidence of a potentially important reaction zone in the nearshore aquifer driven by oceanic oscillations. Land-derived contaminants may undergo important biogeochemical transformations in this zone prior to discharge.

Diel vertical migration: Modelling light-mediated mechanisms

Light is generally regarded as the most likely cue used by zooplankton to regulate their vertical movements through the water column. However, the way in which light is used by zooplankton as a cue is not well understood. In this paper we present a mathematical model of diel vertical migration which produces vertical distributions of zooplankton that vary in space and time. The model is used to predict the patterns of vertical distribution which result when animals are assumed to adopt one of three commonly proposed mechanisms for vertical swimming. First, we assume zooplankton tend to swim towards a preferred intensity of light. We then assume zooplankton swim in response to either the rate of change in light intensity or the relative rate of change in light intensity. The model predicts that for all three mechanisms movement is fastest at sunset and sunrise and populations are primarily influenced by eddy diffusion at night in the absence of a light stimulus. Daytime patterns of vertical distribution differ between the three mechanisms and the reasons for the predicted differences are discussed. Swimming responses to properties of the light field are shown to be adequate for describing diel vertical migration where animals congregate in near surface waters during the evening and reside at deeper depths during the day. However, the model is unable to explain how some populations halt their ascent before reaching surface waters or how populations re-congregate in surface waters a few hours before sunrise, a phenomenon which is sometimes observed in the held. The model results indicate that other exogenous or endogenous factors besides light may play important roles in regulating vertical movement.

Maintaining clearance in peritoneal dialysis

Numerous studies have now established that there is a strong association between small solute clearance and improved outcomes in peritoneal dialysis (PD) patients. Preservation of both renal and peritoneal clearances is therefore of paramount importance, although very few trials have satisfactorily addressed this critical issue. Observational studies have suggested that the groups most at risk of loss of residual renal function are women, non-whites, diabetic patients, patients with congestive cardiac failure, patients who experience frequent episodes of peritonitis and, possibly, patients treated with automated PD (APD). There have been no controlled trials of renoprotective therapies in PD patients, but reasonable strategies for preventing renal functional decline include avoidance of nephrotoxins and infection, maintenance of adequate blood pressure, abstinence from smoking and possibly administration of angiotensin-converting enzyme inhibitors and/or calcium channel blockers. In contrast, peritoneal small solute removal can be maximized by augmenting fill volume, increasing exchange frequency and using either long-dwell continuous ambulatory PD (CAPD) or short-dwell (APD) therapies to suit individual patients' transport characteristics. Tidal PD may additionally increase solute clearance, although studies have reported conflicting findings. Preservation of membrane function may be achieved by minimizing episodes of peritonitis and avoiding hypertonic glucose exchanges. Newer peritoneal dialysates, such as icodextrin, amino acids, bicarbonate-buffered solutions and aldehyde-poor fluids, are more biocompatible in experimental models of PD, but their long-term clinical safety and efficacy have not yet been established by clinical trials. Moreover, no trials have demonstrated an independent effect of peritoneal clearance on patient outcomes. Further studies determining the relative value of renal and peritoneal clearances are therefore urgently required in order to optimize dialytic adequacy for PD patients.

Temperature variation within and between nests of the green sea turtle, Chelonia mydas (Chelonia : Cheloniidae) on Heron Island, Great Barrier Reef

Four temperature data-loggers were placed in each of five green sea turtle nests on Heron Island in the 1998-99 nesting season. Temperatures in all nests increased as incubation progressed due to general sand heating and increased metabolic heat production of the developing embryos. Even at the top of nests no daily diurnal fluctuation in temperature was evident. The temperature of eggs in the middle of the nest increased above those in the nest periphery during the last third of incubation. However, this metabolic nest heating would have little effect on hatchling sex ratio because it occurred after the sex-determining period. Small differences in temperature between regions of a nest persisted throughout incubation and may be important in ensuring the production of at least some individuals of the opposite sex in nests that have temperatures close to either the all-male or all-female determining temperatures. Location and degree of shading of nests had little effect on mean nest temperature, but deeper nests were generally cooler and therefore were predicted to produce a higher proportion of males than were shallower nests. Nest temperature profile data indicated that the 1998-99 nesting season on Heron Island would have produced a strongly female-biased sex ratio amongst hatchlings.

Influence of seaward boundary condition on contaminant transport in unconfined coastal aquifers

Contaminant transport in coastal aquifers is complicated partly due to the conditions at the seaward boundary including seawater intrusion and tidal variations of sea level. Their inclusion in modelling this system will be computationally expensive. Therefore, it will be instructive to investigate the consequence of simplifying the seaward boundary condition by neglecting the seawater density and tidal variations in numerical predictions of contaminant transport in this zone. This paper presents a comparison of numerical predictions for a simplified seaward boundary condition with experimental results for a corresponding realistic one including a saltwater interface and tidal variations. Different densities for contaminants are considered. The comparison suggests that the neglect of the seawater intrusion and tidal variations does not affect noticeably the overall migration rate of the plume before it reaches the saltwater interface. However, numerical prediction shows that a more dense contaminant travels further seaward and part of the solute mass exits under the sea if the seawater density is not included. This is not consistent with the experimental result, which shows that the contaminant travels upwards to the shoreline along the saltwater interface. Neglect of seawater density, therefore, will result in an underestimation of the exit rate of solute mass around the coastline and fictitious migration paths under the seabed. For a less dense contaminant, neglect of seawater density has little effect on numerical prediction of migration paths. (C) 2001 Elsevier Science B.V. All rights reserved.

HI observations of interacting galaxy pair NGC 4038/9

We present the results of new radio interferometer Hi line observations for the merging galaxy pair NGC 4038/9 ('The Antennae'), obtained using the Australia Telescope Compact Array. The results improve substantially with respect to those of van der Hulst and show in detail the two merging galactic discs and the two tidal tails produced by their interaction. The small edge-on spiral dwarf galaxy ESO 572-G045 is also seen near the tip of the southern tail, but distinct from it. It shows no signs of tidal interaction. The northern tidal tail of the Antennae shows no HI connection to the discs and has an extension towards the west. The southern tidal tail is continuous, with a prominent HI concentration at its tip, roughly at the location of the tidal dwarf galaxy observed optically by Mirabel, Dottori & Lutz. Clear velocity structure is seen along the tidal tails and in the galactic discs. Radio continuum images at 20 and 13 cm are also presented, showing the discs in detail.

Assessing ecological impacts of shrimp and sewage effluent: Biological indicators with standard water quality analyses

Despite evidence linking shrimp farming to several cases of environmental degradation, there remains a lack of ecologically meaningful information about the impacts of effluent on receiving waters. The aim of this study was to determine the biological impact of shrimp farm effluent, and to compare and distinguish its impacts from treated sewage effluent. Analyses included standard water quality/sediment parameters, as well as biological indicators including tissue nitrogen (N) content, stable isotope ratio of nitrogen (delta N-15) and amino acid composition of inhabitant seagrasses, mangroves and macroalgae. The study area consisted of two tidal creeks, one receiving effluent from a sewage treatment plant and the other from an intensive shrimp farm. The creeks discharged into the western side of Moreton Bay, a sub-tropical coastal embayment on the east coast of Australia. Characterization of water quality revealed significant differences between the creeks, and with unimpacted eastern Moreton Bay. The sewage creek had higher concentrations of dissolved nutrients (predominantly NO3-/NO2- and PO43-, compared to NH4+ in the shrimp creek). In contrast, the shrimp creek was more turbid and had higher phytoplankton productivity. Beyond 750 m from the creek mouths, water quality parameters were indistinguishable from eastern Moreton Bay values. Biological indicators detected significant impacts up to 4 km beyond the creek mouths (reference site). Elevated plant delta N-15 values ranged from 10.4-19.6 parts per thousand at the site of sewage discharge to 2.9-4.5 parts per thousand at the reference site. The free amino acid concentration and composition of seagrass and macroalgae was used to distinguish between the uptake of sewage and shrimp derived N. Proline (seagrass) and serine (macroalgae) were high in sewage impacted plants and glutamine (seagrass) and alanine (macroalgae) were high in plants impacted by shrimp effluent. The delta N-15 isotopic signatures and free amino acid composition of inhabitant flora indicated that sewage N extended further from the creek mouths than shrimp N. The combination of physical/chemical and biological indicators used in this study was effective in distinguishing the composition and subsequent impacts of aquaculture and sewage effluent on the receiving waters. (C) 2001 Academic Press.