A Model for Structure Formation Seeded by Gravitationally Produced Matter

The Arecibo H i Strip Survey probed the halos of approximately 300 cataloged galaxies and the environments of approximately 14 groups with sensitivity to neutral hydrogen masses >/=107 M middle dot in circle. The survey detected no objects with properties resembling the high-velocity clouds (HVCs) associated with the Milky Way or Local Group. If the HVCs were typically MHi=107.5 M middle dot in circle objects distributed throughout groups and galaxy halos at distances of approximately 1 Mpc, the survey should have made approximately 70 HVC detections in groups and approximately 250 detections around galaxies. The null detection implies that HVCs are deployed at typical distances of 相似文献   

Effects of kelp Ecklonia maxima inclusion in formulated feed on the growth,feed utilisation and gut microbiota of South African abalone Haliotis midae

The effect of kelp Ecklonia maxima inclusion in formulated feeds on abalone growth and gut bacterial communities has not been previously investigated in South Africa. An eight-month on-farm growth trial was conducted with sub-adult Haliotis midae (～43 mm shell length) fed graded levels of kelp in formulated feeds. Kelp inclusion (0.44–3.54% of pellet dry mass) promoted faster growth (65.7–74.5% total mass gain), with better feed and protein conversions (apparent feed conversion ratio [FCR] 1.4–1.8, apparent protein efficiency ratio [PER] 2.3–2.7), as compared with the non-supplemented feed (52.3% total mass gain, FCR 2.1, PER 1.9; p < 0.001). Abalone-gut bacterial DNA was sequenced using 16S rRNA gene pyrosequencing and the sequences were clustered into operational taxonomic units (OTUs) at a 97% similarity level. A supplementary 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) analysis was employed. The dominant OTUs differed in terms of their relative abundances, with an autochthonous Mycoplasma strain being significantly more abundant (p = 0.03) in the gut of abalone fed a kelp-supplemented feed. The DGGE band patterns displayed higher within-group variability for abalone fed the control diet, suggesting that dietary kelp inclusion promotes gut-bacteria homeostasis. This may contribute to better feed utilisation and growth in abalone fed kelp-supplemented feeds.     

Age verification,growth and life history of rubyfish Plagiogeneion rubiginosum

Age verification of rubyfish (Plagiogeneion rubiginosum) was sought using the bomb radiocarbon chronometer procedure. Stable isotopes were investigated for life history characteristics. Radiocarbon (¹⁴C) and stable isotope (δ¹⁸O and δ¹³C) levels were measured in micro-samples from five otoliths that had been aged using a zone count method. All the core ¹⁴C measurements were ‘pre-bomb’ indicating ages of at least 45 years, and the ¹⁴C measurements across the otolith sections suggested that the zone-count ageing method described herein is not biased. Maximum estimated age was 100 years. There was no significant between-sex difference in the von Bertalanffy growth curves. The δ¹⁸O values indicated that rubyfish are near-surface as juveniles, and move deeper with age. Adults appear to reside in 600–1000 m; this is deeper than most trawl-capture data suggest, but not implausible, and has stock assessment implications. The δ¹³C values reflect fish metabolic rates, trophic feeding levels and oceanographic conditions. The stable isotopes record the environmental life history of each fish, and have value in distinguishing stocks and/or indicating vertical and latitudinal migratory patterns.     

A percent-of-flow approach for managing reductions of freshwater inflows from unimpounded rivers to Southwest Florida estuaries

The Southwest Florida Water Management District has implemented a management approach for unimpounded rivers that limits withdrawals to a percentage of streamflow at the time of withdrawal. The natural flow regime of the contributing river is considered to be the baseline for assessing the effects of withdrawals. Development of the percent-of-flow approach has emphasized the interaction of freshwater inflow with the overlap of stationary and dynamic habitat components in tidal river zones of larger estuarine systems. Since the responses of key estuarine characteristics (e.g., isohaline locations, residence times) to freshwater inflow are frequently nonlinear, the approach is designed to prevent impacts to estuarine resources during sensitive low-inflow periods and to allow water supplies to become gradually more uvailable as inflow increases. A high sensitivity to variation at low inflow extends to many invertebrates and fishes that move upstream and downstream in synchrony with inflow. Total numbers of estuarine-resident and estuarine-dependent organisms have been found to decrease during low-inflow periods, including mysids, grass shrimp, and juveniles of the bay anchovy and sand seatrout. The interaction of freshwater inflow with seasonal processes, such as phytoplankton production and the recruitment of fishes to the tidal-river nursery, indicates that withdrawal percentages during the springtime should be most restrictive. Ongoing efforts are oriented toward refining percentage withdrawal limits among seasons and flow ranges to account for shifts in the responsiveness of estuarine processes to reductions in freshwater inflow.     

Effect of graded levels of dietary carbohydrate on growth,feed utilisation and intestinal microbial community structure in dusky kob Argyrosomus japonicus fed a pelleted diet

The ability to utilise carbohydrates is limited for many predatory marine fishes. Graded levels of dietary carbohydrate (4.1–24.6%) were formulated using pregelatinised maize starch, to determine optimal levels for dusky kob Argyrosomus japonicus, an emerging mariculture finfish for which pelleted feeds are being developed. Specific growth rate increased with an increase in the carbohydrate level up to 16.72%, after which it declined. Feed utilisation followed a similar trend, with the best feed conversion ratio (1.28) and protein efficiency ratio (1.76) recorded at 16.4% carbohydrate. Lipid vacuolisation of the hepatocytes was evident in all livers examined, with melano-macrophage aggregates in those of fish fed 24.6% carbohydrate suggesting starvation. Gut bacterial community profiles were variable but were not influenced by dietary carbohydrate level and differed mostly between fish fed trout feed prior to the trial and those fed experimental diets containing starch. The dusky kob were able to clear glucose from their blood when fed up to 16.4% carbohydrate, but glucose removal was not achieved at 24.6% carbohydrate. In conclusion, dusky kob has a limited ability to utilise cooked starch as a carbohydrate source, which may be included in pelleted feed at 16.4% without adverse effects. For this species, levels of dietary carbohydrate above this may result in symptoms consistent with physiological breakdown, including reduced growth, reduced feed intake and feed conversion efficiency, prolonged hyperglycaemia, liver pathology and altered microbial communities in the foregut.     

Causes of interestuarine variability in bay anchovy (<Emphasis Type="Italic">Anchoa mitchilli</Emphasis>) salinity at capture

Salinities occupied by different life stages of bay anchovy (Anchoa mitchilli) were compared over annual cycles at 128 stations in 12 Florida estuaries. The comparison included eight stations in an oligotrophic, groundwater-based estuary in which all life stages were rare or absent. At other stations, adults, eggs, and early larvae occurred in intermediate to high salinities (10-30 psu) with no apparent central salinity tendency. The larva-juvenile transition was marked by an upstream shift to lower salinities (0-15 psu), also with no central salinity tendency. Mean salinities of the juvenile catch were strongly dependent on the salinities of the sampling effort. This dependence was strongest in estuaries that had weak horizontal salinity gradients. Weak salinity gradients were either natural or resulted from estuarine dams. After using nonlinear regression to account for the interaction between effort salinity and catch salinity, catch salinities were found to be similar from year to year within estuaries, but widely different among estuaries, with interestuarine differences ranging as high as 10–13 psu. Lower salinities were occupied by juveniles in estuaries that had long freshwater turnover times. Inherent geomorphic and inflow-related effects on the distribution of prey resources, coupled with an ontogenetic diet shift, are proposed as the explanation for both the habitat shift and the strong interestuarine variability in salinity at capture.     

Non-thermal primeval fireball?

The possible significance of a large cosmic sub-millimeter electromagnetic radiation background is considered. It is shown that in some scalar-tensor cosmological models such an effect could be primeval, that is, the result of processes occurring at an epoch earlier than we now can attempt to compute. The radiation background due to electron pair annihilation in a scalar-tensor model also is considered. It is shown that, while this effect could very substantially increase the far infrared background, it cannot make a spectrum that would be consistent with all the available tentative measurements.Research supported in part by the National Science Foundation.     

A model for continuous clustering in the large-scale distribution of matter

A new view of the nature of the large-scale distribution of matter is suggested by the fact that the covariance function for the distribution varies smoothly, like a power law, over a wide range of separations. This leads one to ask whether superclusters are entities distinguishable in some natural and fundamental way from clusters, or from groups, or even from individual galaxies. I discuss here an attempt to find an acceptable model for clustering consistent with the picture of a continous hierarchy.Research supported in part at Princeton by the National Science Foundation.     

A cosmic virial theorem

A new type of cosmic virial theorem is derived, representing a relation among the two-point and three-point galaxy correlation functions and the mean square relative peculiar velocity v ²(r) averaged over pairs of galaxies separated by distancer. The two correlation functions seem to be fairly well known, but v ²(r) at best is only very roughly estimated from available data. It might be possible to improve the estimate through a systematic program of redshift measurements in sample areas. If so, the cosmic virial theorem might yield an interesting measure of the mean mass density due to galaxies.Research supported in part by the National Science Foundation.     

Synthetic shorelines in New Zealand? Quantification and characterisation of microplastic pollution on Canterbury's coastlines

Microplastics are persistent environmental contaminants found in marine environments worldwide. Microplastic particles isolated from coastlines in the Canterbury region of New Zealand were quantified and characterised. Sediment samples were collected from 10 locations representing exposed-beach, estuarine and harbour environments in both urban and non-urban settings. Particles were isolated from sediments using an NaCl density-separation procedure and quantified and characterised with a combination of optical/fluorescence imaging and micro-Raman spectroscopy. Microplastics were detected at eight out of 10 locations, at concentrations ranging from 0–45.4 particles kg^?1 of dry sediment. The majority of microplastics were identified as polystyrene (55%), polyethylene (21%) and polypropylene (11%). Microplastic concentrations in exposed-beach environments were significantly greater than in harbour and estuarine environments.