Relativistic dispersion effects on SS433 jets

We here investigate the dispersion properties of radiation in the SS433 relativistic jets. We assume that the jet is composed of cold electron-proton plasma immersed in a predominantly parallel magnetic field to the jet axis. We find that for the mildly relativistic source SS433 (for which 〈ψ〉≃79°), the bulk velocity is too small (v≃0.26c) to produce significant changes in the dispersion properties of the medium. Nonetheless, in the rarefied outer regions of the jets, where radio emission dominates, even a weak magnetic field has some influence on the dispersion properties and there appear two different electromagnetic branches that are slightly sensitive to the bulk relativistic motion. In the inner, X-ray region, the magnetic field is much stronger, but in this region the high electron density preserves the isotropic character of the local plasma and no branch separation occurs. In the region of the jet where the IR and optical emission dominates, the cold plasma may be also considered isotropic, i.e., neither the magnetic field nor the bulk velocity is able to affect the propagation of the radiation. Finally, we find that the Doppler line displacement in SS433 is affected by plasma dispersion only in a narrow frequency range in the far IR. As a consequence, although the shift (z) modulation due to precession of the SS433 jets is well described by previous work, it has to be corrected by plasma dispersion effects in the far-IR range.     

The growth and contamination mechanism of the Cana Brava layered mafic-ultramafic complex: new field and geochemical evidences

Mineralogy and Petrology - The Cana Brava complex is the northernmost of three layered complexes outcropping in the Goiás state (central Brasil). New field and geochemical evidences suggest...     

Microwave observations of the 4 January, 1973 solar eclipse

The eclipse was observed at two microwave frequencies, 7 GHz and 22.2 GHz, and has shown the presence of polarized regions, suggesting also excess of left-handed polarized radiation from the solar northern hemisphere. Difference in eclipsing times at the two frequencies for an active center near the limb is discussed.     

Distinctive crystal chemistry and site configuration of the clinopyroxene from alkali basaltic rocks

A crystal chemical investigation of clinopyroxenes from a suite of nepheline-bearing lavas located in the Nyambeni Range of Kenya has delineated the polyhedral site configurations and related intracrystalline relationships. These are distinct from those determined for the clinopyroxene in an analogous suite of leucite-bearing lavas from the Sabatini volcanoes in the Roman Region of Italy (Dal Negro et al. 1985).The Nyambeni clinopyroxene, varying from salite to hedenbergite, preferentially accepts Na in the M2 site to balance increasing Fe²⁺ and Si, respectively, whereas the Sabatini clinopyroxene is confined within the salite field and preferentially accepts Al^iv to balance the effect of increasing (Fe³⁺+Ti⁴⁺+Al^vi+Cr³⁺)_M1.The Fe²⁺/Fe³⁺ and K/Na ratios of the host rocks emerge as significant factors in determining the different polyhedral configurations and evolutions of the clinopyroxene from the two lava suites, respectively. The resulting Mg-Fe²⁺ order-disorder relationships in M1–M2 are also distinct in the two clinopyroxenes. A high degree of MgFe²⁺ order in M1–M2 corresponds to the largest configurational, hence energetic, difference between M1 and M2 in the Nyambeni clinopyroxene, whereas the converse applies to the Sabatini clinopyroxene.In view of the significant crystal chemical differences and distinct evolution trends, it is proposed that salites from alkali volcanic rocks may be referred to as Nyambeni-type or Sabatini-type, respectively.     

Rainfall as a trigger of shallow mass movements. A case study in the Dolomites, Italy

 The article presents results of regional analysis on a historical basis correlating the occurrence of shallow mass movements and disruptive events in time with precipitation trends. For the latter, different time-spans have been considered in an attempt to find the most typical ones which might have triggered landslides. Research was carried out in the 850 km² wide basin of the River Cordevole in the Dolomites (NE Italy). Data concerning slope movements and floods, which have affected the area since the last century, were collected. Events which took place after 1920 have been correlated with the significant pluviometric events recorded. In spite of the regionally high variability of both geological conditions and spatial distribution of precipitation, three types of typical pluviometric trends related to an effective rainfall period of 15 days and to a peak rainfall of 24–48 h preceding the onset of the movements were identified. Received: 1 November 1996 · Accepted: 25 June 1997     

Laboratory tests on soil conditioning of clayey soil

Tunnelling in difficult and challenging conditions such as soft soils in urban areas is increasing. In this condition, it is important to minimise the possible negative effect of the tunnel excavation, such as settlement or, in the worst case, collapses. To achieve this result, earth pressure balance machines are commonly used. One of the key parameters that must be considered for an optimal management of the EPB-TBM excavation is soil conditioning since the excavated muck must properly transmit the pressure to the tunnel face. Soil conditioning is also necessary to reduce the effect of the problems, such as clogging in clay layers, that can occur during the excavation and that can affect the performance of the tools and of the entire tunnelling process. For this reason, in the last decade, much research has been carried out to understand how to deal with and reduce the effects of clogging and stickiness, using different conditioning additives. These studies have proposed several different test procedures to evaluate the effect of the conditioning on the adhesion of the soil on the metallic parts of the machines. The present research has been carried out with the aim of proposing a new approach and new devices to study clay conditioning with laboratory tests, and the results of many tests carried out with the proposed device are presented and discussed.     

The Impact of Human Recreational Activities in Marine Protected Areas: What Lessons Should Be Learnt in the Mediterranean Sea?

Abstract. The aesthetic appeal of marine reserves and the facilities provided, together with the increased public awareness of nature, all contribute to creating massive tourism in MPAs. Human activities are being changed inside MPAs in two ways: humans as top predators are generally being removed, but in turn they could come back at great numbers as visitors.
Many authors have studied the impact of visitors, and the results highlight that the consequences can be very substantial and may represent a severe threat to the overall diversity of marine communities. To date, the documented effects of human recreational activities on natural communities are restricted to assessing the consequences of trampling over intertidal and upper infralittoral areas, boat anchoring in seagrass meadows and tropical reefs, or SCUB A-diving.
In this paper we review the available literature world-wide on the effects of human recreational activities in marine communities. The objective is to address the extent of these impacts and to highlight the gaps of knowledge to be filled in order to optimise decision making on research, monitoring, and management of Mediterranean MPAs. A specific plan for managing tourism use in each Mediterranean MPA should be designated. These strategies should be implemented through education, training, and changes in legislation and policy.     

Benthic Community and Sediment Types: A Structural Analysis

Abstract. The distribution of the macrobenthic community, in relation to various physical and chemical characteristics of the sediment, was studied along the coast of Southern Tuscany (Central Tyrrhenian) in an area under the influence of the Ombrone River outflow.
The zonation of the benthos was found to be primarily under the control of a gradient of water movement, as is reflected by variations in the sediment structure from the coast to the open sea. This correlation is somehow influenced by secondary gradients such as the degree of mixing of the sediment and the deposition of terrigenous materials along the river plume.     

Mechanical Behavior of Clayey Soil Reinforced with Recycled Tire Rubber Using Chips and Fibers

Geotechnical and Geological Engineering - The volume of discarded tires continues to increase each year, becoming a major topic of concern for society. Motivated by this environmental issue, this...