Lyα absorption in the nearby Universe: the sightline to Q1821+643

We present the first results of a survey designed to understand the origin of Lyα-forest absorption systems at low redshift. Using the WYFFOS and HYDRA multifibre spectrographs on the William Herschel and Wisconsin Indiana Yale NOAO (WIYN) telescopes, we have identified 51 galaxies brighter than b _j := :18.5 within 30 arcmin of the sightline of the QSO 1821+643. We find three galaxies within 500 h ⁻¹ kpc of the QSO sightline; the nearest galaxy is 104 h ⁻¹ kpc away from the line of sight, and is at the same redshift as a strong ( W _r :=:0.63Å) Lyα absorption line. The remaining two galaxies have no corresponding absorption to extremely low equivalent width limits (< 0.05 Å). Beyond 500 h ⁻¹ kpc, Lyα absorption lines are found at redshifts similar to those of several galaxies, but we show that these coincidences are likely to be accidental.   Half of the Lyα systems for which we could have found at least an L ^* galaxy have no galaxies at the redshifts of the absorbers. For the majority of the remainder, we show that any apparent association with galaxies is probably coincidental. These Lyα systems are characterized by their weak equivalent widths ( W _r :<:0.2Å), and we conclude that this population of absorbers is uncorrelated, or at best weakly correlated, with galaxies.     

Solar flare hard X-ray observations

Recent hard X-ray observations of solar flares are reviewed with emphasis on results obtained with instruments on the Solar Maximum Mission satellite. Flares with three different sets of characteristics, designated as Type A, Type B, and Type C, are discussed and hard X-ray temporal, spatial, spectral, and polarization measurements are reviewed in this framework. Coincident observations are reviewed at other wavelengths including the UV, microwaves, and soft X-rays, with discussions of their interpretations. In conclusion, a brief outline is presented of the potential of future hard X-ray observations with sub-second time resolution, arcsecond spatial resolution, and keV energy resolution, and polarization measurements at the few percent level up to 100 keV.     

A finite element–based approach for predictions of rigid pile group stiffness efficiency in clays

This paper presents a finite element parametric study of several variables that affect the stiffness efficiency of rigidly capped pile groups with a view to developing a solution for preliminary design purposes. Previous empirical solutions from linear elastic work had identified a significant dependence of stiffness efficiency on pile group size and group spacing, and in this study, the effect of the pile length-to-diameter ratio, the compressibility of a stiff bearing stratum beneath the pile group and the depth below ground level to the stiff bearing stratum are also considered. Pile groups in a soft clay/silt are modelled using PLAXIS 3D Foundation in conjunction with a soil model that captures the stress dependency of soil stiffness. The trends from the soft soil study have been formulated into a set of equations which can be used to predict the stiffness efficiency of pile groups. This new approach captures more variables than previous simpler empirical prediction methods and performs better when applied to a database of 29 published pile group case histories.     

Rivers in Australia

As a continent, Australia is unusual. It has a long history of habitation by a relatively small population of Aboriginals with a low technology culture. Just over 200 years ago, in 1788, it was invaded by a technological society from the UK, and the settlers brought with them an understanding of rivers and the landscapes in which they were situated which was quite at odds with the reality of the Australian continent. Australia is a piece of old continental crust derived from the break-up of Gondwana that, unlike other Gondwana continents, has experienced little tectonic modification since the break-up. It is a low relief continent dominated by arid and semi arid climates. Australian river systems have poor slope-channel coupling and poor hydrological connectivity and are characterized by low rates of sediment delivery. The flow of Australian rivers has high interannual variability, two to three times that of comparable rivers elsewhere, and highly variable flood behavior. In this paper, examples are given of particular Australian rivers to illustrate the manner in which the morphological and climatic characteristics of the continent combine to produce some distinctive river systems.     

MESSENGER observations of the plasma environment near Mercury

The MESSENGER Fast Imaging Plasma Spectrometer (FIPS) measured the bulk plasma characteristics of Mercury's magnetosphere and solar wind environment during the spacecraft's first two flybys of the planet on 14 January 2008 (M1) and 6 October 2008 (M2), producing the first measurements of thermal ions in Mercury's magnetosphere. In this work, we identify major features of the Mercury magnetosphere in the FIPS proton data and describe the data analysis process used for recovery of proton density (n_p) and temperature (T_p) with a forward modeling technique, required because of limitations in measurement geometry. We focus on three regions where the magnetospheric flow speed is likely to be low and meets our criteria for the recovery process: the M1 plasma sheet and the M1 and M2 dayside and nightside boundary-layer regions. Interplanetary magnetic field (IMF) conditions were substantially different between the two flybys, with intense reconnection signatures observed by the Magnetometer during M2 versus a relatively quiet magnetosphere during M1. The recovered ion density and temperature values for the M1 quiet-time plasma sheet yielded n_p∼1–10 cm⁻³, T_p∼2×10⁶ K, and plasma β∼2. The nightside boundary-layer proton densities during M1 and M2 were similar, at n_p∼4–5 cm⁻³, but the temperature during M1 (T_p∼4–8×10⁶ K) was 50% less than during M2 (T_p∼8×10⁶ K), presumably due to reconnection in the tail. The dayside boundary layer observed during M1 had a density of ∼16 cm⁻³ and temperature of 2×10⁶ K, whereas during M2 this region was less dense and hotter (n_p∼8 cm⁻³ and T_p∼10×10⁶ K), again, most likely due to magnetopause reconnection. Overall, the southward interplanetary magnetic field during M2 clearly produced higher T_p in the dayside and nightside magnetosphere, as well as higher plasma β in the nightside boundary, ∼20 during M2 compared with ∼2 during M1. The proton plasma pressure accounts for only a fraction (24% for M1 and 64% for M2) of the drop in magnetic pressure upon entry into the dayside boundary layer. This result suggests that heavy ions of planetary origin, not considered in this analysis, may provide the “missing” pressure. If these planetary ions were hot due to “pickup” in the magnetosheath, the required density for pressure balance would be an ion density of ∼1 cm⁻³ for an ion temperature of ∼10⁸ K.     

Imaging X-ray Polarimeter for Solar Flares (IXPS)

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IXPS). This novel instrument, a Time Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level in the 20?C50 keV energy range during an M- or X-class flare, and will provide imaging information at the ??10 arcsec level. The primary objective of such observations is to determine the directivity of nonthermal high-energy electrons producing solar hard X-rays, and hence to learn about the particle acceleration and energy release processes in solar flares. Secondary objectives include the separation of the thermal and nonthermal components of the flare X-ray emissions and the separation of photospheric albedo fluxes from direct emissions.     

Distribution of high field strength elements (Y, Zr, REE, Hf, Ta, Th, U) in adjacent magnetite and chert bands and in reference standards FeR-3 and FeR-4 from the Temagami iron-formation, Canada, and the redox level of the Neoarchean ocean

Adjacent magnetite and chert bands and reference standards FeR-3 and FeR-4 from the Neoarchean Temagami iron-formation (IF) show shale-normalized rare earth and yttrium (REY) patterns with low Nd/Yb ratios and positive Eu, Gd and Y anomalies, indicating that they formed as marine chemical sediments. In contrast to previous claims, none of the samples shows any Ce anomaly, indicating the absence of oxidative Ce-REY decoupling and arguing against oxic conditions in the wider vicinity of the Neoarchean “Temagami seabasin”. The distribution of Zr, Hf and Ta yields Zr/Hf and Hf/Ta ratios that differ from those of chondrites, average upper continental crust and local shales, suggesting that the Temagami IF is the only case observed so far in which a significant fraction of these elements is non-detrital but sourced from seawater. If Neoarchean seawater was characterized by Zr/Hf and Hf/Ta ratios similar to those of modern seawater these ratios point towards preferential scavenging of Hf over Zr and Ta, as is typical of the modern ocean. Similar to the 2.9 Ga old Mozaan IF in the Pongola Supergroup, South Africa, the Temagami IF shows low Th/U ratios that differ from those of the respective local shales and from that of average upper continental crust. Decoupling of U and Th results from U⁴⁺ oxidation in the Earth's surface system and fractionated Th/U ratios in these marine chemical sediments are, therefore, at odds with the lack of Ce anomalies. This suggests a different redox-sensitivity of the two paleo-redox-proxies Th–U and Ce-REY and demonstrates that the Temagami IF and the Mozaan IF warrant further study of other paleo-redox-proxies.     

Direct evidence of fluid mixing in the formation of stratabound Pb–Zn–Ba–F mineralisation in the Alston Block, North Pennine Orefield (England)

The North Pennine Orefield Alston Block has produced approximately 4 Mt Pb, 0.3 Mt Zn, 2.1 Mt fluorite, 1.5 Mt barite, 1 Mt witherite, plus a substantial amount of iron ore and copper ore from predominantly vein-hosted mineralisation in Carboniferous limestones. However, a significant proportion of this production (ca. 20%) came from stratabound deposits. Though much is known about the vein mineralisation, the relationship between the veins and the stratabound mineralisation is not well-understood. New petrographic, isotopic and fluid inclusion data derived from samples of stratabound mineralisation allow us to present a unified model that addresses the genesis of both the vein and stratabound styles of mineralisation. The mineralisation can be considered in terms of three episodes:

Plio-Pleistocene basanitic and melilititic series of the Bohemian Massif: K-Ar ages,major/trace element and Sr–Nd isotopic data

The Plio-Pleistocene volcanic rocks of the Bohemian Massif comprise a compositional spectrum involving two series: an older basanitic series (6.0–0.8 Ma) and a younger, melilititic series (1.0–0.26 Ma). The former consists of relatively undifferentiated basaltic rocks, slightly silica-undersaturated, with Mg# ranging from 62 to almost primitive mantle-type values of 74. The major and trace element characteristics correspond to those of primitive intra-plate alkaline volcanic rocks from a common sub-lithospheric mantle source (European Asthenospheric Reservoir – EAR) including positive Nb, and negative K and Pb anomalies. ⁸⁷Sr/⁸⁶Sr ratios of 0.7032–0.7034 and ¹⁴³Nd/¹⁴⁴Nd of 0.51285–0.51288 indicate a moderately depleted mantle source as for other mafic rocks of the central European volcanic province with signs of HIMU-like characteristics commonly attributed to recycling of subducted oceanic crust in the upper mantle during the Variscan orogeny. The melilititic series is characterized by higher degrees of silica-undersaturation, and high Mg# of 68–72 values, compatible with primitive-mantle-derived compositions. The high OIB-like Ce/Pb (19–47) and Nb/U (32–53) ratios indicate that assimilation of crustal material was negligible. In both series, concentrations of incompatible elements are mildly elevated and ⁸⁷Sr/⁸⁶Sr ratios (0.7034–0.7036) and ¹⁴³Nd/¹⁴⁴Nd ratios (0.51285–0.51288) overlap. Variations in incompatible element concentrations and isotopic compositions in the basanitic series and melilititic series can be explained by a lower degree of mantle melting for the latter with preferential melting of enriched mantle domains. The Sr and Nd isotopic compositions of both rock series are similar to those of the EAR. Minor differences in geochemical characteristics between the two series may be attributed to: (i) to different settings with respect to crust and lithospheric mantle conditions in (a) Western Bohemia (WB) and (b) Northeastern Bohemia (NEB) and the Northern Moravia and Silesia (NMS) areas, (ii) a modally metasomatized mantle lithosphere in WB in contrast to cryptically metasomatized domains in the NEB and NMS, (iii) different degrees of partial melting with very low degrees in WB but higher degrees in NEB and NMS. The geochemical and isotopic similarity between the Plio-Pleistocene volcanic rocks and those of the late Cretaceous and Cenozoic (79–6 Ma) suggests that their magmas came from compositionally similar mantle sources, that underwent low degrees of melting over an interval of ∼80 Ma. The Oligocene to Miocene basanitic series that accompanied the Plio-Pleistoicene basanitic series in the NMS region indicate that they shared a common mantle source. There is no geochemical evidence for thermal erosion of the lithospheric mantle or significant changes in mantle compositions within the time of a weak thermal perturbation in the asthenospheric mantle. These perturbations were caused by a dispersed mantle plume or passively upwelling asthenosphere in zones of lithospheric thinning.