Unidentified γ-ray Sources off the Galactic Plane as Low-Mass Microquasars?

A subset of the unidentified EGRET γ-ray sources with no active galactic nucleus or other conspicuous counterpart appears to be concentrated at medium latitudes. Their long-term variability and their spatial distribution indicate that they are distinct from the more persistent sources associated with the nearby Gould Belt. They exhibit a large scale height of 1.3 ± 0.6 kpc above the Galactic plane. Potential counterparts for these sources include microquasars accreting from a low-mass star and spewing a continuous jet. Detailed calculations have been performed of the jet inverse Compton emission in the radiation fields from the star, the accretion disc, and a hot corona. Different jet Lorentz factors, powers, and aspect angles have been explored. The up-scattered emission from the corona predominates below 100 MeV whereas the disc and stellar contributions are preponderant at higher energies for moderate (∼15^∘) and small (∼1^∘) aspect angles, respectively. Yet, unlike in the high-mass, brighter versions of these systems, the external Compton emission largely fails to produce the luminosities required for 5 to 10 kpc distant EGRET sources. Synchrotron-self-Compton emission appears as a promising alternative.     

Typical properties of dynamic systems and the instability of hydrodynamic flows

Summary Based on Peixot's theorem of topological dynamics, the unstable behaviour of hydrodynamic flows on a two-dimensional annuloid T ² is analysed. The generating property is the curvature of the group of S ₀ Diff T ² diffeomorphisms of the (Riemannian) flow region T ² . This group is the configuration space of the ideal fluid flowing on T ² .

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a m ma u mn u ¶rt;uauu ¶rt;am mu n¶rt;uu¶rt;¶rt;uauu nm a ¶rt; m T ² u¶rt; mu. ¶rt;au m m a m uuann S ₀ Diff T ² ¶rt;uu amu mu ( uaa) T ² . manna m uau nmam ¶rt; u¶rt;a u¶rt;mu a T ² .

     

Sublethal effects of contamination on the Mediterranean sponge Crambe crambe: metal accumulation and biological responses

The effect of low levels of pollution on the growth, reproduction output, morphology and survival of adult sponges and settlers of the sponge Crambe crambe were examined. We transplanted sponges from a control area to a contaminated site and measured the main environmental variables (chemical and physical) of both sites during the study period. Except some punctual differences in particulate organic matter, silicates, nitrates, and water motion, most environmental variables in the water were similar at both sites during the study months. Mainly copper, lead and OM concentrations in the sediment, and water motion were significantly higher at the polluted site and may be implicated in the biological effects observed: decrease in the percentage of specimens with embryos, increase in shape irregularity and decrease in growth rate. Individuals naturally occurring at the polluted site and those transplanted there for four months accumulated ten times more copper than either untouched or transplant controls. Although lead concentration in sediment did not differ between sites, native specimens from the contaminated site accumulated this metal more than untouched controls. Vanadium concentration also tended to increase in the sponges living at or transplanted to the contaminated site but this difference was not significant. C. crambe is a reliable indicator of metal contamination since it accumulates copper, lead and vanadium in high amounts. At the contaminated site, sponge growth, fecundity and survival were inhibited, whereas sponge irregularity ending in sponge fission was promoted. All these effects may compromise the structure and dynamics of the sponge populations in sheltered, metal-contaminated habitats.     

No more blind dates with calcite:Fluid-flow vs.fault-slip along the O(c)kov thrust,Prague Basin

Dating of fracture-filling calcite with U-Pb geochronology is becoming a rapidly adopted technique for determin-ing the absolute timing of brittle deformation i...     

Stress field in the earth's crust with curved boundaries

Summary A two-dimensional theory of gravitational stresses in the Earth's crust with curved boundaries is presented. The crust is modelled by an elastic plate lying on an elastic half-space. The solution obtained in the case of periodically varying boundaries is shown to be very sensitive to the ratio of both elastic parameters. Moreover, the geometrical configuration of both boundaries and their phase shift are of great importance for the resulting stress pattern.     

The Bunburra Rockhole meteorite fall in SW Australia: fireball trajectory,luminosity, dynamics,orbit, and impact position from photographic and photoelectric records

Abstract– We report an analysis of the first instrumentally observed meteorite fall in Australia, which was recorded photographically and photoelectrically by two eastern stations of the Desert Fireball Network (DFN) on July 20, 2007. The meteoroid with an initial mass of 22 kg entered the atmosphere with a low speed of 13.36 km s^?1 and began a luminous trajectory at an altitude of 62.83 km. In maximum, it reached ?9.6 absolute magnitude and terminated after a 5.7 s and 64.7 km long flight at an altitude of 29.59 km with a speed of 5.8 km s^?1. The angle of the atmospheric trajectory to the Earth’s surface was 30.9°. The first organized search took place in October 2008 and the first meteorite (150 g) was found 97 m southward from the predicted central line at the end of the first day of searching (October 3, 2008). The second stone (174 g) was recovered 39 m northward from the central line, both exactly in the predicted mass limits. During the second expedition in February 2009, a third fragment of 14.9 g was found again very close (～100 m) from the predicted position. Total recovered mass is 339 g. The meteorite was designated Bunburra Rockhole (BR) after a nearby landscape structure. This first DFN sample is an igneous achondrite. Initial petrography indicated that BR was a brecciated eucrite but detailed analyses proved that BR is not a typical eucrite, but an anomalous basaltic meteorite ( Bland et al. 2009 ). BR was delivered from an unusual, Aten type orbit (a < 1 AU) where virtually the entire orbit was contained within Earth’s orbit. BR is the first achondrite fall with a known orbit and it is one of the most precise orbits ever calculated for a meteorite dropping fireball.     

A new proposal for the late Cenozoic geodynamic evolution of the western Mediterranean

A simple mechanism of arcuate fold belt and back-arc basin formation is presented based on the opening of mega-continental tension gashes along pre-existing, deep, parallel and steep faults that separate lithospheric units with different properties. If plate convergence is parallel to these faults, the fault-bounded units open at right angles to the convergence vector, adopting an arcuate shape with thrusting in front of the bowed-out units and extensional basin opening between the separated units. This model is applied to the Cenozoic geodynamic evolution of the western Mediterranean. After the Iberian collision 35–30 Ma, several ellipsoidal basins (Valencia, Alboran, North Algerian and Liguro–Provençal) developed by 10 Ma along the eastern margin of the Iberian plate. The formation of these basins is attributed to an increase in NE–SW horizontal tectonic palaeostress during early–middle Miocene times resulting from the post-subduction collision of the Tethyan oceanic lithosphere.     

Ground fissures within the Main Ethiopian Rift: Tectonic,lithological and piping controls

Ground fissures, especially if they open due to a sudden collapse of the surface, is a serious risk for populated areas. Their common occurrence in unconsolidated sediments of the Main Ethiopian Rift was found to be mostly a result of piping. The fissures start by piping in linear sub-horizontal underground voids, which often propagate upwards resulting in ceiling collapse and formation of deep and long ground fissures with vertical walls. In the southern and central Main Ethiopian Rift the fissures pose a serious risk to infrastructure and settlements. The ground fissures are often linear (up to several kilometres long and often tens of metres deep) and accompanied by sinkholes (along the length). A detailed field mapping of the geological (rock composition, orientation and character of lithological boundaries, primary fabrics and brittle structures) and geomorphological features (especially a length, width and depth of fissures, sinkholes and gullies) followed by in situ seismic anisotropy measurements and a laboratory determination of the geomechanical properties of volcanoclastic deposits was carried out to investigate the ground fissures' origin. The conditions and factors leading to the formation of the ground fissures have been linked to: (a) the presence of regional normal faults and the associated extensional joints and (b) the alternation of lithological units with contrasting hydraulic permeability. The latter corresponds to a sequence of less permeable hard rocks (e.g., rhyolitic ignimbrites) overlain by heterogeneous, soft and permeable, unconsolidated volcaniclastic deposits with a low amount of clay (less than 10%). The ground fissures' occurrence has shown affiliation to areas which have a significantly high seismic anisotropy (more than 20% at the study sites), which can be used as a proxy to map out high risk areas prone to piping and ground fissure formation.     

Exhibitions

In this paper we propose the use of ‘Encountering’ a location-based game (LBG) based on the Wherigo platform to facilitate interdisciplinary student learning about places on field courses. Deploying a mobile, digital map-based platform addresses significant challenges – such as the sacrifice of context specificity and methodological applicability and depth. It also runs the danger of ‘gamifying’ the fieldwork, blinding the participant to their own agency and emergent encounters. Interactive and layered digital map interfaces have affordances that can potentially overcome such challenges. We claim that one such affordance is the ability to play through the map. In other words, maps – and digital maps in particular – offer the possibility of decoupling results-orientated actions from free-form serendipitous engagement with the field. Our argument is two-fold. First, that LBG toolsets such as Wherigo can provide a ‘common ground’ for students engaging in place-based interdisciplinary research, by providing a material, cartographic basis for playful investigation. Second, that they can facilitate the production of ‘spaces of epistemological failure’, allowing students to challenge taken-for-granted conceptual and methodological axioms within and across disciplines.