Cosmo-SkyMed X-band SAR data for classification of ice-free areas and glacier facies on Potter Peninsula,King George Island Antarctica

The climate change phenomena have been influencing terrestrial and glacial ecosystems around the planet. Maritime Antarctica is especially sensitive to these climate variations and over the last 50 years increasing global air temperatures have caused extensive glacial retreat. The objective of this study is to evaluate the potential use of the SAR technology in monitoring the surface dynamics of the Potter Peninsula, King George Island, maritime Antarctica. An image generated by the SAR satellite COSMO-SkyMed, obtained on 2 February 2011, was used to extract the backscattering values of targets on the surface for further processing and classification, using a supervised statistic classifier of maximum likelihood for the determination of the surface classes. The average backscattering of water bodies presented high similarity, which made its separation unattainable. On the other hand, the surface classes’ bare ice and wet snow over the glacier presented distinct average backscattering values, which allowed an efficient and precise classification using only this parameter. The classification process showed satisfactory results for periglacial environments, presenting high fidelity to the field data.     

Observations Towards Star Formation Regions: H2 Near-Infrared Emission Lines

We present near-infrared images of HH93 and L1251. The detection of H₂ emission allows us to study deeply embedded shocks, produced by the strong winds of young stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

CCD images and long-slit spectroscopy of the ring nebula around θ Mus

We present the first digital CCD images and long-slit spectroscopy of the optical ring nebula around the Wolf–Rayet star θ Mus. The CCD images obtained through narrow-band filters centred at [O  iii ] and Hα show that the nebula has a filamentary structure, similar to supernova remnants, mainly seen in [O  iii ]. A spatial detachment between [O  iii ] and Hα images suggests excitation stratification, or multiple rings. An analysis of the physical conditions in the nebula was performed by means of long-slit CCD spectra. The spectral images show that the nebula is of low density and medium excitation. By means of quotients of recombination and collisional spectral line fluxes we determine that the principal excitation mechanism is photoionization. We have determined the electronic temperature and density, and chemical abundances for the oxygen at different sites within the nebula. Nebular chemical abundances are found to be similar to the Galactic ISM, indicating that the nebula is mainly composed of swept up material.     

The structure of galaxy clusters in various cosmologies

We investigate the internal structure of clusters of galaxies in high-resolution N -body simulations of four different cosmologies. There is a higher proportion of disordered clusters in critical-density than in low-density universes, although the structure of relaxed clusters is very similar in each case. Crude measures of substructure, such as the shift in the position of the centre-of-mass as the density threshold is varied, can distinguish the two in a sample of just 20 or so clusters; it is harder to differentiate between clusters in open and flat models with the same density parameter. Most clusters are in a quasi-steady state within the virial radius and are well-described by the density profile of Navarro, Frenk & White.     

Geomorphological and sedimentological analysis of a catastrophic flash flood in the Arás drainage basin (Central Pyrenees, Spain)

On August 7th, 1996, an intense and short-duration convective storm occurred over the 18.6-km² Arás drainage basin (Central Pyrenees, Spain). This high relief basin is composed of three subbasins, Aso, Betés and La Selva, and feeds the Arás alluvial fan, in the Gállego river valley. This alluvial fan had been drained by an artificial channel (about 125 m³/s at bank-full capacity). More than 30 check dams in its feeder channel, the Arás barranco, had been previously filled by earlier sediments. The heaviest rain was over the Betés subbasin (total rainfall 178.4 mm; maximum rainfall intensity of 153 mm/h for a 10-min time interval was estimated). Most of the rainfall fell in a 70-min period. This storm resulted in high runoff, causing catastrophic damage and significant geomorphic changes in the drainage basin, especially in the Betés subbasin. The high discharge, concentrated in the Arás barranco, destroyed most of the check dams, flushing out a great amount of debris. Major channel trenching and widening occurred in this barranco. When the confined sediment-laden flash flood reached the basin mouth, it sheet-flooded the southern sector of the Arás fan depositing a massive amount of debris. On this fan 87 people lost their lives and the direct physical damage has been estimated at 55 million dollars. Two stages in the development of the flood have been differentiated from the sedimentological and morphological analysis of the flooded fan lobe. A first stage (peak discharge) of sheet-flooding deposited a coarse boulder lobe, burying the artificial channel at the fan head and causing a darnming effect on the water flood. During the second stage (discharge decline) the flood made its way through the fan head, incising the previous debris accumulation and splitting into two main flow paths.     

If Quebec Goes . . . The ‘Exodus' Impact?

In this paper, we explore migration aspects of the 1995 Quebec Sovereignty Referendum with data from a survey administered to non-francophones in Montreal two weeks prior to the Referendum. While the Quebec sovereignty issue has been around for some time and earlier exodus from the province, particularly among anglophones, is largely regarded as “forced” in some way, this study neither confirms the 1995 Sovereignty Referendum as a paramount factor in explaining outmigration from Quebec nor points to a real reluctance to leave Montreal. The decision to move is influenced by the interplay of a multitude of factors. The political influence is only an added factor to longstanding economic decline and cultural clash. Moreover, if there is any impulsion, the degree varies among different cultural and socioeconomic groups.     

Advances in discrete element modelling of underground excavations

The paper presents advances in the discrete element modelling of underground excavation processes extending modelling possibilities as well as increasing computational efficiency. Efficient numerical models have been obtained using techniques of parallel computing and coupling the discrete element method with finite element method. The discrete element algorithm has been applied to simulation of different excavation processes, using different tools, TBMs and roadheaders. Numerical examples of tunnelling process are included in the paper, showing results in the form of rock failure, damage in the material, cutting forces and tool wear. Efficiency of the code for solving large scale geomechanical problems is also shown.