Multimass spherical structure models for N-body simulations

We present a simple and efficient method to set up spherical structure models for N -body simulations with a multimass technique. This technique reduces by a substantial factor the computer run time needed in order to resolve a given scale as compared to single-mass models. It therefore allows to resolve smaller scales in N -body simulations for a given computer run time. Here, we present several models with an effective resolution of up to  1.68 × 10⁹  particles within their virial radius which are stable over cosmologically relevant time-scales. As an application, we confirm the theoretical prediction by Dehnen that in mergers of collisionless structures like dark matter haloes always the cusp of the steepest progenitor is preserved. We model each merger progenitor with an effective number of particles of approximately 10⁸ particles. We also find that in a core–core merger the central density approximately doubles whereas in the cusp–cusp case the central density only increases by approximately 50 per cent. This may suggest that the central regions of flat structures are better protected and get less energy input through the merger process.     

Dynamics and mass balance of the 2007 Cima Una rockfall (Eastern Alps, Italy)

On October 12th, 2007 about 40,000 m³ of dolomitic rock detached from the northern wall of the peak known as “Cima Una” (Val Fiscalina, Sesto Dolomites, Bolzano, Italy), and fell 900 m to Fiscalina Valley below. The event generated a dense dust cloud, which traveled up to 4 km from the source area. The failure surface was formed by two near-vertical surfaces, almost perpendicular to each other. The orientation of these surfaces is consistent with two of the main regional tectonic sets. Only a small portion of the fallen material appeared to be preserved as blocks deposited at the base of the rock wall. About a fifth of the fallen mass was deposited on a colluvial cone. The missing mass, estimated to be about 80 %, may be represented by highly fragmented rock in part deposited as sand on the valley floor and in part dispersed as a dense dust cloud generated during the rockfall. There appears to be a deficit of deposited material, which could lead underestimation in the calculation of rock–cliff recession rates. The dynamics of the rockfall, strongly conditioned by the local topography, partially explains the intense rock breakage and the generation of the dust cloud. The rockfall was not caused by an external trigger, such as an earthquake or heavy rainfall; the failure was most likely progressive due to mechanical and physical degradation along highly stressed failure surfaces, possibly promoted by permafrost degradation and freeze and thaw processes.     

Sediment accumulation rates in European lakes since AD 1850: trends,reference conditions and exceedence

Sediment accumulation rate (SAR) is an important physical parameter in all lakes and increases have been observed in many over the last c.100 years. This has been ascribed to changes in land-use and land-management causing accelerated catchment soil erosion and an increase in autochthonous organic matter production. The EU Water Framework Directive requires that assessment of biological, hydromorphological and chemical elements of water quality should be based on the degree to which present day conditions deviate from those expected in the absence of significant anthropogenic influence, termed reference conditions. Currently however, the reference condition for sediment accumulation rate for lakes of different types is undefined. To improve our understanding of the controls on SARs we compiled SAR and lake typology data for 207 European lakes derived from ²¹⁰Pb dated cores to assess how rates have changed through time (in 25 year classes) both overall and for lakes of different types. Seventy-one percent of these sediment cores showed surface SARs higher than “basal” (mainly nineteenth century) rates, 11% showed no change while 18% showed a decline. Lakes were then classified into lake-types using four variables: alkalinity (3 classes), altitude (3 classes), maximum depth (2 classes) and lake area (2 classes). This generated a possible 36 lake classes of which 25 were represented in the dataset. Nine lake-types contained >10 lakes. Little change in SAR occurred prior to 1900 and most increases occurred in more recent periods, in particular 1950–1975 and post-1975. This indicates a general acceleration in SAR in European lakes during the second half of the twentieth century. Reference SARs were estimated for six lake-types with the highest number of sites. European mountain lakes had the lowest reference SAR (0.005 ± 0.003 g cm⁻² yr⁻¹) while lowland, high alkalinity sites had the highest (0.03–0.04 g cm⁻² yr⁻¹). SARs for other lake-types ranged between 0.012 and 0.024 g cm⁻² yr⁻¹. Using the mountain lake-type as an example, the 1850 reference SAR appears to show good agreement with available data for lakes beyond Europe indicating these values may be more broadly applicable. Contemporary SARs in lakes of all classes showed exceedence over their defined reference SAR. This may be partly due to diagenetic processes. Greatest exceedences were found in shallow, low altitude lakes and these are considered to be the ones under the greatest threat from continued elevation of SAR. It is considered that climate change may play a progressively more important role in driving SAR in the future.     

Occurrence of IRGAROL 1051 in coastal waters from Biscayne Bay,Florida, USA

Surface water samples from marinas, commercial ports and open bay areas collected from Biscayne Bay and the Miami River, Florida, USA, were analyzed for the occurrence of IRGAROL 1051 by GC/MS. The anifouling boosting herbicide was found in 80% (46/57) of the samples collected between March 1999 and September 2000. Concentrations within the bay range between non-detected (<1 ppt) and 61 ppt (ng/L) and were generally low compared with levels reported in European or Japanese waters. Aside from the elevated concentrations observed along the Miami River South Fork (61 ppt), the highest concentrations observed in the bay corresponded to marinas with high density of pleasure craft and restricted water circulation. In contrast, occurrence of IRGAROL 1051 along the commercial port or the cruise line terminal was generally lower (<1-2.2 ppt). Concentrations around Coconut Grove Marina were consistently higher (5-12 ppt) than the rest of the bay waters during the whole period of time surveyed.     

Modelling the merging history of Binary SMBHs in Hierarchical Models of Galaxy Formation

We present a model describing the evolution of a Super Massive Black Holes (SMBHs) population within the framework of hierarchical models of galaxy formation. The occurrence of SMBHs binaries at different redshifts and the influence of the interacting SMBHS on the host galaxies are studied by means of Montecarlo realizations of halo merging histories, coupled with a semi-analytical treatment of the interactions between the systems. We find that the main parameters governing the coalescence timescale, and hence the fraction of binary systems, are the initial mass and the accretion history of the SMBHs. This revised version was published online in September 2006 with corrections to the Cover Date.     

Sedimentary evidence of prehistoric distant-source tsunamis in the Hawaiian Islands

Over the past 200 years of written records, the Hawaiian Islands have experienced tens of tsunamis generated by earthquakes in the subduction zones of the Pacific ‘Ring of Fire’ (for example, Alaska–Aleutian, Kuril–Kamchatka, Chile and Japan). Mapping and dating anomalous beds of sand and silt deposited by tsunamis in low-lying areas along Pacific coasts, even those distant from subduction zones, is critical for assessing tsunami hazard throughout the Pacific basin. This study searched for evidence of tsunami inundation using stratigraphic and sedimentological analyses of potential tsunami deposits beneath present and former Hawaiian wetlands, coastal lagoons, and river floodplains. Coastal wetland sites on the islands of Hawai΄i, Maui, O΄ahu and Kaua΄i were selected based on historical tsunami runup, numerical inundation modelling, proximity to sandy source sediments, degree of historical wetland disturbance, and breadth of prior geological and archaeological investigations. Sand beds containing marine calcareous sediment within peaty and/or muddy wetland deposits on the north and north-eastern shores of Kaua΄i, O΄ahu and Hawai΄i were interpreted as tsunami deposits. At some sites, deposits of the 1946 and 1957 Aleutian tsunamis are analogues for deeper, older probable tsunami deposits. Radiocarbon-based age models date sand beds from three sites to ca 700 to 500 cal yr bp , which overlaps ages for tsunami deposits in the eastern Aleutian Islands that record a local subduction zone earthquake. The overlapping modelled ages for tsunami deposits at the study sites support a plausible correlation with an eastern Aleutian earthquake source for a large prehistoric tsunami in the Hawaiian Islands.     

Flounder growth and production as indicators of the nursery value of marsh habitats in a Mediterranean lagoon

Estuarine marshes are known as suitable nursery areas for many marine migrant fishes, such as flounder. The potential nursery value of such habitats was investigated in the Venice lagoon, by using growth and production of 0-group flounder as indicators. Size–frequency distribution analysis was performed on fish samples collected fortnightly, from March 2004 to June 2005, in two marsh sites, Dese and Tessera, differing in their origin and environmental conditions. Samples were mostly composed of juvenile individuals, belonging to 0- and 1-group cohorts (the latter being present in Tessera only). A higher total production, either annual or monthly, and faster growth of 0-group flounder was observed in Dese, associated to a higher ecological performance of 0-group individuals in this site, as indicated by the higher P:B ratio values. Dese is a site located in a marsh complex characterized by the relevant influence of a nearby river, and the observed higher potential nursery value of this marsh area with respect to the other is discussed in the light of the higher trophic status and other environmental conditions in this site. The production results were also compared to those from other estuarine environments commonly acknowledged as important nurseries for European flounder.     

High-resolution spectrometer for atmospheric studies

A high-resolution spectrometer (0.0014 nm at 313 nm) has been developed at the University of L’Aquila (Italy) for atmospheric spectroscopic studies. The layout, optics and software for the instrument control are described. Measurements of the mercury low-pressure lamp lines from 200 to 600 nm show the high performances of the spectrometer. Laboratory measurements of OH and NO₂ spectrums demonstrate that the system could be used for cross-section measurements and to detect these species in the atmosphere. The first atmospheric application of the system was the observation of direct solar and sky spectrums that shows a filling-in of the sky lines due to rotational Raman scattering. The measurements have been done with clear and cloudy sky and in both there was a strong dependence of the filling-in from the solar zenith angle whereas no dependence from the wavelengths was evident at low solar zenith angles (less than 85°).     

The graininess of dark matter haloes

We use the recently completed one billion particle Via Lactea II Λ cold dark matter simulation to investigate local properties like density, mean velocity, velocity dispersion, anisotropy, orientation and shape of the velocity dispersion ellipsoid, as well as the structure in velocity space of dark matter haloes. We show that at the same radial distance from the halo centre, these properties can deviate by orders of magnitude from the canonical, spherically averaged values, a variation that can only be partly explained by triaxiality and the presence of subhaloes. The mass density appears smooth in the central relaxed regions but spans four orders of magnitude in the outskirts, both because of the presence of subhaloes as well as of underdense regions and holes in the matter distribution. In the inner regions, the local velocity dispersion ellipsoid is aligned with the shape ellipsoid of the halo. This is not true in the outer parts where the orientation becomes more isotropic. The clumpy structure in local velocity space of the outer halo cannot be well described by a smooth multivariate normal distribution. Via Lactea II also shows the presence of cold streams made visible by their high 6D phase space density. Generally, the structure of dark matter haloes shows a high degree of graininess in phase space that cannot be described by a smooth distribution function.     

A strategy for finding gravitationally lensed distant supernovae

Distant Type Ia and II supernovae (SNe) can serve as valuable probes of the history of the cosmic expansion and star formation, and provide important information on their progenitor models. At present, however, there are few observational constraints on the abundance of SNe at high redshifts. A major science driver for the Next Generation Space Telescope is the study of such very distant SNe. In this paper we discuss strategies for finding and counting distant SNe by using repeat imaging of supercritical intermediate redshift clusters whose mass distributions are well constrained via modelling of strongly lensed features. For a variety of different models for the star formation history and supernova progenitors, we estimate the likelihood of detecting lensed SNe as a function of their redshift. In the case of a survey conducted with Hubble Space Telescope ( HST ), we predict a high probability of seeing a supernova in a single return visit with either Wide Field Planetary Camera 2 or Advanced Camera for Surveys, and a much higher probability of detecting examples with     in the lensed case. Most events would represent magnified SNe II at     and a fraction will be more distant examples. We discuss various ways to classify such events using ground-based infrared photometry. We demonstrate an application of the method using the HST archival data and discuss the case of a possible event found in the rich cluster AC 114     .