Simulating galactic outflows with kinetic supernova feedback

Feedback from star formation is thought to play a key role in the formation and evolution of galaxies, but its implementation in cosmological simulations is currently hampered by a lack of numerical resolution. We present and test a subgrid recipe to model feedback from massive stars in cosmological smoothed particle hydrodynamics simulations. The energy is distributed in kinetic form among the gas particles surrounding recently formed stars. The impact of the feedback is studied using a suite of high-resolution simulations of isolated disc galaxies embedded in dark haloes with total mass 10¹⁰ and  10¹²  h ⁻¹ M_⊙  . We focus, in particular, on the effect of pressure forces on wind particles within the disc, which we turn off temporarily in some of our runs to mimic a recipe that has been widely used in the literature. We find that this popular recipe gives dramatically different results because (ram) pressure forces on expanding superbubbles determine both the structure of the disc and the development of large-scale outflows. Pressure forces exerted by expanding superbubbles puff up the disc, giving the dwarf galaxy an irregular morphology and creating a galactic fountain in the massive galaxy. Hydrodynamic drag within the disc results in a strong increase in the effective mass loading of the wind for the dwarf galaxy, but quenches much of the outflow in the case of the high-mass galaxy.     

Single-crystal polarized FTIR spectroscopy and neutron diffraction refinement of cancrinite

We relate a single-crystal FTIR (Fourier transform infrared) and neutron diffraction study of two natural cancrinites. The structural refinements show that the oxygen site of the H₂O molecule lies off the triad axis. The water molecule is almost symmetric and slightly tilted from the (0001) plane. It is involved in bifurcated hydrogen bridges, with Ow···O donor–acceptor distances >2.7 Å. The FTIR spectra show two main absorptions. The first at 3,602 cm^?1 is polarized for E ⊥ c and is assigned to the ν₃ mode. The second, at 3,531 cm^?1, is also polarized for E ⊥ c and is assigned to ν₁ mode. A weak component at 4,108 cm^?1 could possibly indicate the presence of additional OH groups in the structure of cancrinite. Several overlapping bands in the 1,300–1,500 cm^?1 range are strongly polarized for E ⊥ c, and are assigned to the vibrations of the CO₃ group.     

Rock slope response to strong earthquake shaking

The 2010–2011 Canterbury earthquakes triggered many mass movements in the Port Hills including rockfalls, debris avalanches, slides and slumps, and associated cliff-top cracking. The most abundant mass movements with the highest risk to people and buildings were rockfalls and debris avalanches sourced from up to 100 m high cliffs inclined at angles >65°. Cliffs lower than 10 m in height generally remained stable during the strong shaking, with only isolated release of a few individual boulders. We used site-specific data to investigate the factors that controlled the response of the cliffs to the main earthquakes of the Canterbury sequence, adopting two-dimensional finite element seismic site response and stability modeling that was calibrated using the field observations and measurements. Observations from the assessed cliffs in response to the earthquakes show the taller cliffs experienced larger amounts of permanent cliff-top displacement and produced larger volumes of debris than the smaller cliffs. Results indicated a mean K_MAX amplification ratio for all sites under study of 1.6 (range of 1.1–3.8). Field data and numerical modeling results, however, show that amplification of shaking does not necessarily increase linearly with increasing cliff height. Instead, our results show that accelerations are amplified mainly due to the impedance contrasts between the geological materials, corresponding to where strong differences in rock mass shear wave velocity exist. The resulting acceleration contrasts and rock mass strength control cliff stability. However, the amount of permanent slope displacement and volume of debris leaving the cliffs varied between the sites, due to site-specific geometry and rock mass strength.     

Depositional facies and stratal geometry of an Upper Carboniferous prograding and aggrading high-relief carbonate platform (Cantabrian Mountains, N Spain)

Seismic‐scale continuous exposures of an Upper Carboniferous (Bashkirian–Moscovian) carbonate platform (N Spain) provide detailed information about the lithofacies and stratal geometries (quantified with differential global positioning system measurements) of microbial boundstone‐dominated, steep prograding and aggrading platform margins. Progradational and aggradational platform‐to‐slope transects are characterized by distinct lithological features and stratal patterns that can be applied to the understanding of geometrically comparable, high‐relief depositional systems. The Bashkirian is characterized by rapid progradation at rates of 415–970 m My^?1. Characteristic outer‐platform facies are high‐energy grainstones with coated intraclasts, ooids and pisoids, moderate‐energy algal‐skeletal grainstones to packstones and lower energy algal packstone and boundstone units. The Moscovian aggradational phase is characterized by aggradation rates of 108 m My^?1. Coated‐grain shoals are less common, whereas crinoidal bars nucleated in well‐circulated settings below wave‐base. Boundstones form a belt (30–300 m wide) at the platform break and interfinger inwards with massive algal‐skeletal wackestones (mud‐rich banks). The progradational phase has divergent outer‐platform strata with basinward dips of 12° to 2°. Steep clinoforms with dips of 20–28° are 650–750 m in relief and possibly sigmoidal to concave in the lower part. The basinward‐dipping outer‐platform strata might be depositional for less than 6°, consistent with lithofacies deepening seaward. The basinward dip is attributed to the downward shift of upper‐slope boundstone, forced by late highstand and relative sea‐level fall, and to compaction‐induced differential subsidence during progradation. The aggradational phase is characterized by horizontally layered platform strata. Clinoforms steepen to 30–45° reaching heights of 850 m and are planar to concave. The evolution from progradation to aggradation, at the Bashkirian–Moscovian boundary, is attributed to increased foreland‐basin subsidence and decreased boundstone accumulation rates. Progradation was primarily controlled by boundstone growth rather than by highstand shedding from the platform top. Within the major phases, aggradational–progradational increments are produced by third‐ to fourth‐order relative sea‐level fluctuations.     

The single-crystal,polarized-light,FTIR spectrum of stoppaniite,the Fe analogue of beryl

We report here a single-crystal polarized-light study of stoppaniite, ideally (Fe,Al,Mg)₄(Be₆Si₁₂O₃₆)(H₂O)₂(Na,□), from Capranica (Viterbo). Polarized-light FTIR spectra were collected on an oriented (hk0) section, doubly polished to 15 μm. The spectrum shows two main bands at 3,660 and 3,595 cm⁻¹; the former is strongly polarized for E ⊥c, while the latter is polarized for E //c. A sharp and very intense band at 1,620 cm⁻¹, plus minor features at 4,000 and 3,228 cm⁻¹ are also polarized for E //c. On the basis of literature data and considering the pleochroic behavior of the absorptions, the 3,660 cm⁻¹ band is assigned to the ν₃ stretching mode and the 1,620 cm⁻¹ (associated with an overtone 2*ν₂ at 3,230 cm⁻¹) band to the ν₂ bending mode of “type II” water molecules within the structural channels of the studied beryl. The sharp band at 3,595 cm⁻¹ is not associated with a corresponding ν₂ bending mode; thus it is assigned to the stretching vibration of O–H groups in the sample. The minor 4,000 cm⁻¹ feature can be assigned to the combination of the O–H bond parallel to c with a low-frequency metal-oxygen mode such as the Na–O stretching mode. The present results suggest that the interpretation of the FTIR spectrum of Na-rich beryl needs to be carefully reconsidered.     

Experimental investigation on the effect of the mode of deposition on the pore-access size distribution of sand

It is well known that the specimen preparation method and the resulting sand fabric significantly affect sand behaviour and sand liquefaction resistance. In this study, a simple experimental method namely tensiometric method is presented for evaluation of the effect of the samples reconstituting methods on microstructure and the pore-access size distribution of sands. Specimens were prepared using dry funnel pluviation (DFP) and wet deposition (WD) at two densities Dr = 40% (loose state) and Dr = 80% (dense state). The water-retention curve of a sand specimen is evaluated using a technique similar to the hanging column method by application of a step-by-step variation of suction and measure of the corresponding changes in water content. The pore-access size distribution is then evaluated from the water-retention curve. In this experimental study the effects of the mode of deposition and the uniformity coefficient on the pore-access size distribution are investigated. It was found that the specimen generated by the WD method contained a higher percentage of pore size, contrary to the specimen prepared by the DFP which contained a limited percentage of pore size, causing a great influence on the mechanical behaviour of the specimens.     

A re-evaluation of Late Devensian glacial Lake Humber levels in the Vale of York,UK

Proglacial Lake Humber formed in the Vale of York and Ancholme Valley during the Late Devensian (Weichselian) glaciation, but its lake levels and their precise ages are uncertain. Three-dimensional geological modelling, based on 193 borehole sediment logs from the eastern part of the Vale of York, indicates that glaciolacustrine sediments extend no higher than 10?m O.D. By contrast, recent palaeoenvironmental reconstructions for the region that suggest Lake Humber had eight recessional shorelines, extending from 42?m to 5?m O.D. Above 10?m O.D., the sediments become more discontinuous, and comprise clay with occasional chalk and flint gravel, and matrix-rich diamicton interdigitated with sands and gravels. Sedimentary and geochemical analyses of sands and gravels from one of the putative shorelines, at 25?m O.D., indicate an easterly provenance for these sediments. They are interpreted here as colluvial deposits, sourced largely by periglacial weathering of Jurassic and chalk bedrock. Collectively, the geological evidence suggests that the highest level of Lake Humber during the Late Devensian did not exceed 10?m O.D., and therefore reconstructions invoking higher lake levels are thought to be unlikely.     

The Experience of Realizing a Semantic Web Urban Computing Application

Urban Computing is a branch of Pervasive Computing that investigates urban settings and everyday lifestyles. A large quantity of information to develop pervasive applications for urban environments is often already available, even if scattered and not integrated: maps, points of interest, user locations, traffic, pollution, and events are just a few examples of the digitalized information which we can access on the Web. Applications for mobile users that leverage such information are rapidly growing. In this article, we report our experience in addressing practical computational issues influencing the use of Geographic Information Systems and geospatial data from the standpoint of semantics and pervasive computing. We refer to the early achievements of the LarKC project, in which we developed an Urban Computing demonstrator. We highlight the positive sides of our experience and we discuss open issues and possible advances.