Arecibo timing and single-pulse observations of 17 pulsars

We have analysed the soft X-ray emission in a wide area of the Sculptor supercluster by using overlapping ROSAT Position Sensitive Proportional Counter pointings. After subtraction of the point sources, we have found evidence for extended, diffuse soft X-ray emission. We have investigated the nature of such extended emission through the cross-correlation with the density of galaxies as inferred from the Münster Redshift Survey. In particular, we have analysed the correlation as a function of the temperature of the X-ray emitting gas. We have found a significant correlation of the galaxy distribution only with the softest X-ray emission (0.1 – 0.3 keV) and only for gas temperatures   kT < 0.5 keV  . We have excluded the fact that this soft X-ray diffuse emission, and its correlation with the galaxy distribution, is significantly contributed by unresolved active galactic nuclei, groups of galaxies or individual galaxies. The most likely explanation is that the soft, diffuse X-ray emission is tracing warm–hot intergalactic medium, with temperatures below 0.5 keV, associated with the large-scale structures in the Sculptor supercluster.     

Highly localised distribution patterns of juvenile sea cucumber Australostichopus mollis

Information on the environmental characteristics of the juvenile habitat of many deposit-feeding sea cucumber species is limited, despite most fished species exhibiting rapid localised depletion. The current study combined large and small scale surveying techniques within a New Zealand harbour to identify areas with high densities of juvenile Australostichopus mollis, a commercially valuable aspidochirote holothurian. Data from detailed surveys were used to relate densities of juveniles and adults with measures of physical habitat characteristics including depth, sediment facies type, grain size range, as well as measures of chlorophyll-a, phaeopigment, carbon and nitrogen content of surface sediment. Results revealed a highly localised distribution of juvenile A. mollis focused on one site associated with an area of high adult density. Sites of high juvenile A. mollis density were characterised by sediment qualities favouring epibenthic detritivorous deposit feeding, including high nitrogen content, high phaeopigment:chlorophyll-a ratio and small grain size. The high-density juvenile site had facies that were further characterised by the presence of large shell fragments (>10 cm length) of the horse mussel (Atrina zelandica), which may provide a unique settlement microhabitat for early juveniles. Unlike some other sea cucumber species, juvenile A. mollis shows no distinct spatial separation from adult sea cucumbers, no association with dense macroalgae and no clear preference for shallower depths than adults. Overall, the results illustrate the highly localised pattern of recruitment of this species to a widely distributed adult population, which may help to explain the lack of previous observations of juveniles in this species. These results indicate the importance of identifying and protecting what appear to be very specific juvenile habitats in deposit-feeding sea cucumbers to ensure continuing recruitment to exploited populations.     

La déformation post-Miocène en Provence occidentale

Résumé

Le but de la présente étude est de caractériser la déformation récente subie par la Provence occidentale, située entre la nappe de Digne à l’est et la faille de Nîmes à l’ouest. Dans un premier temps, la déformation subie par un marqueur sédimentaire qui est à la fois le plus récent possible et le plus uniformément représenté dans la zone étudiée est considérée. Ce marqueur sédimentaire est le Miocène. La caractérisation de la déformation passe par l’étude de la localisation de celle-ci et donc par l’identification des structures actives responsables de la déformation du Miocène. Ces caractéristiques permettent d’estimer la quantité de raccourcissement total accumulé lors des derniers 20 millions d’années. Dans un deuxième temps, on distingue la part de la déformation postMiocène de cette déformation totale. Les marqueurs utilisés sont des surfaces et des objets géomorphologiques repères. Dans ce travail, nous montrons que la déformation en Provence a été de faible importance entre le Miocène et factuel et qu’elle est surtout produite au cours du Miocène. En conséquence, la déformation récente à actuelle est très difficile à localiser et à caractériser. 11 n’y a pas eu de déplacements post Miocène importants de part et d’autre de la faille de la Durance, pas plus d’ailleurs que le long de toutes les discontinuités majeures du domaine étudié. © 2000 Éditions scientifiques et médicales Elsevier SAS     

DNA identification of the phyllosoma diet of Jasus edwardsii and Scyllarus sp. Z

The development of an effective artificial larval diet has been a major stumbling block for advancing the aquaculture of spiny lobsters internationally. Attempts to determine the natural diet of spiny lobster larvae have been impeded by their small size and sparse distribution in the open ocean, making these larvae difficult to study using conventional methods. Recent advances in molecular genetic techniques have provided a novel route for identifying the natural prey of spiny lobster larvae (phyllosoma). In this study, sequences from zooplankton found associated with phyllosomas, along with sequences from GenBank, were used to design a suite of group-specific primers. These primers were able to amplify via the polymerase chain reaction (PCR) a short (100–200 base pair) DNA fragment from the 16S or COI locus of potential prey but not from lobster. These methods were applied to four wild-caught phyllosomas of Jasus edwardsii and two phyllosomas of Scyllarus sp. Z. Gadiforme, Cnidaria, Gastropoda and Decapoda crustacean (non-lobster) DNA sequences were obtained from the gut contents of these lobster larvae and inferred as prey. These initial results confirm previous studies using other less definitive methods which have indicated that phyllosomas are opportunistic predators of a wide range of zooplankton taxa.     

Atmospheric densities from satellites and rocket observation

Atmospheric densities deduced from high altitude rocket nights have a large variability of which a large percentage is undoubtedly due to measurement errors. Prior to the IGY, the available density data gave reasonable support to the ARDC Model Atmosphere. Satellite data which at first appeared to be inconsistent with rocket data are now seen to be continuous with the average of presently available rocket derived densities. The current data suggest the revision of the 1956 ARDC Model to lower densities near 100 km altitude and demand higher densities above 160 km (a twenty fold increase at 500 km). The revised altitude distribution of density implies (1) lower temperatures at 90 km and (2) temperature-altitude gradients between 105 and 160 km (two times the molecular-scale-temperature gradient of the 1956 ARDC Model). Density-altitude and temperature-altitude profiles for a revised model atmosphere are discussed.     

Characteristics of Stable Flows over Southern Greenland

The main characteristic features of stable atmospheric flows over a large mountain plateau are summarised and then compared with mesoscale and synoptic scale numerical simulation, meteorological analysis, satellite imagery, and surface observations for the cases of flows over Southern Greenland for four wind directions. The detailed features are identified using the concepts and scaling of stably stratified flow over large mountains with variations in surface roughness, elevation, and heating. For westerly and easterly winds detached jets form at the southern tip, where coastal jets converge, which propagate large distances across the ocean. Near coasts katabatic winds can combine with barrier jets and wake flows generated by synoptic winds. Note how the approach flow rises/falls over southern Greenland for easterly/westerly winds, leading in both cases to more cloud on the western side. Some conclusions are drawn about the large-scale influences of these flows; detached jets in the atmosphere; air-sea interaction; formation of low pressure systems. For accurate simulations of these flows, mesoscale models are necessary with resolutions of order of 20 km or less.     

流体——重力式锥状单腿平台结构——土相互作用体系的地震动力响应

本文用配点法对流体——重力式锥状单腿平台结构——土相互作用体系在地震作用下的动力响应问题进行了研究。采用频域分析法，将锥柱体Ｎ等分，利用运动方程和边界条件联立解方程组，继而求出平台结构顶端弹性位移和腿柱所受的动水压力、基础平移和基础转角的频响函数。分析不同锥角下体系的动力响应的影响，并分析研究了刚性地基和考虑土——结构相互作用时结构体系的动力响应情况，得到一些很有益的结果。     

Determining the correct identity of South African Marthasterias (Echinodermata: Asteroidea)

Marthasterias glacialis are found in the cool-temperate waters of the north-eastern Atlantic Ocean, in the subtropical waters of the Mediterranean Sea and along the south-western tip of Africa. The South African Marthasterias population includes two morphotypes, a smooth, spineless rarispina form and a spiny africana form, that have been described as separate species, subspecies, or forma by various authors over the past century. To test whether these two morphotypes represent separate species, and whether either, or both, are conspecific with the North-East Atlantic species, 78 Marthasterias were collected from the Cape Peninsula of South Africa. Morphological comparisons between individuals of the two forms showed no significant clustering of samples, indicating that there is no morphological separation of the two South African forms into distinct groupings. The africana and rarispina forms were also shown to be genetically indistinguishable, using a fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene and the nuclear internal transcribed spacer 1 (ITS1). In addition, the COI sequences were also compared to those from European specimens, and phylogenetic reconstruction and intra- and interspecific levels of divergence suggested that the South African specimens form a single group that is genetically distinct from the European M. glacialis. Although the allopatric distribution, high genetic divergence (more than 3% for the COI fragment) and morphological differences suggest that the South African form should be raised to species status under the name Marthasterias africana, further work must assess an independent genetic marker (nuclear) to support raising the COI clade to species level. True M. glacialis have a spine-armament pattern of a series of three or more regular spine rows down the length of each arm, whereas M. africana are either covered in many irregularly spaced spines, or have an extraordinarily bare surface with only two spine rows per arm. Marthasterias africana may also have an actinal spine simulating the presence of a third inferomarginal spine. This work tentatively resolves the taxonomic dispute, elucidates the separation and amalgamation of the two African forms and suggests a single, uniquely South African Marthasterias species that might be distinct from the north Atlantic M. glacialis, although further analyses to test reproductive isolation between the North-East Atlantic and South African forms are required.     

The effect of near-fault directivity on building seismic collapse risk

Forward directivity may cause large velocity pulses in ground motion time histories that are damaging to buildings at sites close to faults, potentially increasing seismic collapse risk. This study quantifies the effects of forward directivity on collapse risk through incremental dynamic analysis of building simulation models that are capable of capturing the key aspects of strength and stiffness degradation associated with structural collapse. The paper also describes a method for incorporating the effects of near-fault directivity in probabilistic assessment of seismic collapse risk. The analysis is based on a suite of RC frame models that represent both past and present building code provisions, subjected to a database of near-fault, pulse-like ground motions with varying pulse periods. Results show that the predicted collapse capacity is strongly influenced by variations in pulse period and building ductility; pulse periods that are longer than the first-mode elastic building period tend to be the most damaging. A detailed assessment of seismic collapse risk shows that the predicted probability of collapse in 50 years for modern concrete buildings at a representative near-fault site is approximately 6%, which is significantly higher than the 1% probability in the far-field region targeted by current seismic design maps in the US. Copyright © 2012 John Wiley & Sons, Ltd.