Polarization of individual pulses of radio pulsars at the low frequencies 40, 60, and 103 MHz

Measurements of the linear polarization of individual pulses at 40, 60, and 103 MHz are presented for ten pulsars. The degree and position angle of a linear polarization were measured with a temporal resolution of 1–7 ms, and the longitudinal distributions of these parameters were constructed for each pulsar at one or more of these frequencies. These are the first such measurements for pulsars B0031-07, B0320 + 39, B0628-28, and B2217 + 47. Apart from B0628-28, all the pulsars are characterized by the simultaneous presence of orthogonal polarization modes in at least one component of the integral profile. The secondary polarization mode increases at frequencies ≤100 MHz for pulsars whose integrated pulses contain pairs of conal components (B0031-07, B0329 + 54, B0834 + 06, B1133 + 16, B2020 + 28). This is manifested both as an expansion of the longitudinal range where the secondary polarization mode is observed and an increase in its contribution to the emission at a given longitude. New data confirming the dependence of the linear polarization of individual pulses on the intensity and mode of the pulsar emission have been obtained.     

Mantle Structure Beneath the SW Slave Craton, Canada: Constraints from Garnet Geochemistry in the Drybones Bay Kimberlite

This study describes the petrography of peridotite xenoliths,and the major and trace element geochemistry of garnets in bothxenoliths and coarse concentrate from the Drybones Bay kimberlite.The temperature and depth of equilibration of clinopyroxeneand garnet show that the mantle lithosphere beneath the SW marginof the Slave Province was at least 160 km thick at the timeof kimberlite emplacement (     

From geometry to dynamics of microstructure: using boundary lengths to quantify boundary misorientations and anisotropy

The microstructure of a quartzite experimentally deformed and partially recrystallised at 900 °C, 1.2 GPa confining pressure and strain rate 10⁻⁶/s was investigated using orientation contrast and electron backscatter diffraction (EBSD). Boundaries between misoriented domains (grains or subgrains) were determined by image analysis of orientation contrast images. In each domain, EBSD measurements gave the complete quartz lattice orientation and enabled calculation of misorientation angles across every domain boundary. Results are analysed in terms of the boundary density, which for any range of misorientations is the boundary length for that range divided by image area. This allows a more direct comparison of misorientation statistics between different parts of a sample than does a treatment in terms of boundary number.The strain in the quartzite sample is heterogeneous. A 100×150 μm low-strain partially recrystallised subarea C was compared with a high-strain completely recrystallised subarea E. The density of high-angle (>10°) boundaries in E is roughly double that in C, reflecting the greater degree of recrystallisation. Low-angle boundaries in C and E are produced by subgrain rotation. In the low-angle range 0–10° boundary densities in both C and E show an exponential decrease with increasing misorientation. The densities scale with exp(−θ/λ) where λ is approximately 2° in C and 1° in E; in other words, E has a comparative dearth of boundaries in the 8–10° range. We explain this dearth in terms of mobile high-angle boundaries sweeping through and consuming low-angle boundaries as the latter increase misorientation through time. In E, the density of high-angle boundaries is larger than in C, so this sweeping would have been more efficient and could explain the relative paucity of 8–10° boundaries.The boundary density can be generalised to a directional property that gives the degree of anisotropy of the boundary network and its preferred orientation. Despite the imposed strain, the analysed samples show that boundaries are not, on average, strongly aligned. This is a function of the strong sinuosity of high-angle boundaries, caused by grain boundary migration. Low-angle boundaries might be expected, on average, to be aligned in relation to imposed strain but this is not found.Boundary densities and their generalisation in terms of directional properties provide objective measures of microstructure. In this study the patterns they show are interpreted in terms of combined subgrain rotation and migration recrystallisation, but it may be that other microstructural processes give distinctive patterns when analysed in this fashion.     

Dinosaur coprolites from the Late Cretaceous (Maastrichtian) Lameta Formation of India: isotopic and other markers suggesting a C3plant diet

A single locality of the Late Cretaceous (Maastrichtian) Lameta Formation at Pisdura in Central India has yielded a large number of coprolites attributed to titanosaurian dinosaurs. Internally the coprolites are dark grey and contain abundant plant tissues and other organic materials. The plant tissues are mostly of gymnospermous origin. In addition, remains of bacterial colonies, fungal spores and algae are seen in the macerated fraction under scanning electron microscope. The dark grey appearance is probably attributable to fine-grained organic matter within voids in tracheids or xylem. The average ¹³C/¹²C ratio of the organic matter in the coprolites is -24‰ (relative to PDB) suggesting that plants of C₃type were the main diet of their producers. A comparison of δ¹⁵N value (about 4‰ w.r.t. air) of the coprolites with that of faecal matter of modern herbivores and carnivores suggests that gut fermentation may not have been an active mechanism in the digestion process of titanosaurs.     

Heavy metals distribution in agricultural topsoils in urban area

Intensive urbanisation of the Croatian capital of Zagreb has led to a situation where very good agricultural soils, developed mostly on Pleistocene eolian sediments and alluvial and proluvian Holocene sediments are entrapped within urban and suburban areas. Therefore the influence of urban and industrialised environments on the accumulation of metals in agricultural topsoils has been investigated. On an area of 860 km² of the wider Zagreb region, 331 samples were taken according to a regular 1ǵ km square mesh. Samples were dissolved in aqua regia and analysed for Cd, Cu, Fe, Mn, Ni, Pb and Zn with flame atomic aqua regia absorption spectroscopy. The following concentration ranges have been determined: Cd 0.25-3.85 mg kg^-1 (average 0.66 mg kg^-1), Cu 4.30-183 mg kg^-1 (average 20.8 mg kg^-1), Fe 5.8-51.8 g kg^-1 (average 27 g kg^-1), Mn 79.2-1282 mg kg^-1 (average 613 mg kg^-1), Ni 0.70-282 mg kg^-1 (average 49.5 mg kg^-1), Pb 1.50-139 mg kg^-1 (average 25.9 mg kg^-1), and Zn 15.2-277 mg kg^-1 (average 77.9 mg kg^-1). Visualisation of the spatial data is made by the aid of GIS, and selected maps of the heavy metal concentrations in topsoils are displayed. Statistical multivariate analysis was carried out for quantitative study and data were processed by means of R-mode factor analysis, applying the varimax-raw rotational technique. F1, which grouped Cd, Pb, Cu, Zn and partially Ni, is characterized as a factor with strongly scattered anthropogenic influence. The elements in F2, Fe, Mn and partially Ni are mainly of geogenic, i.e. pedogenic, origin. The variations in concentrations of the investigated elements are thus of both natural and anthropogenic origins. The variations in the main soil constituents, particularly Fe and Mn, are determined primarily by the composition of different regolithic substrates of the fluvial origin in recent pedogenesis. High concentrations of nickel are also related to morphogenetic characteristics of the wider region, primarily basic and ultrabasic magmatic rocks of the surrounding mountain range. It is, however, assumed that the anomalous nickel concentrations in the vicinity of the highway and the airport are of anthropogenic origin, i.e. caused by fuel combustion. Copper is characterized by strongly scattered anthropogenic influence, which is related particularly to uncontrolled solid waste disposals or discharges of liquid waste from households or agricultural enterprises. With Zn, Pb and Cd, there are two possible ways of diffuse pollution. The Sava River, which drains the area and feeds the abundant Quaternary aquifer spreading below the major part of the investigated agricultural areas, has been exposed to intensive pollution by mining, industry and cities in the recent history. The part of the area with the highest determined concentrations of Zn, Pb and Cd was repeatedly flooded as recently as the previous decade; therefore, the recent sedimentation of the river deposits exposed to pollution is a very probable cause of the accumulation of metals in this until recently inundation area. The other way is atmospheric deposition of particles from urban sources (industrial emission, traffic, waste disposals, heating plants, etc.). In addition to agricultural enterprises, several economically important, but ecologically risky, facilities are situated in the vicinity of the water-protection area. The area is intersected by a very busy ring road, while a marshalling yard, the city dump, pharmaceutical and chemical industry, the district-heating plant and the airport are all located in close proximity. The geochemical maps show a clear relationship between human activities and metal concentration gradients.     

Environmental impact assessment in the Moradabad industrial area (rivers Ramganga-Ganga interfluve), Ganga Plain,India

Sediment samples collected in the Moradabad area, lying in the interfluve of the Ganga and Ramganga Rivers, were analysed for heavy metals, after studying the geomorphology of the area. Geomorphologically, the area can be divided into three terraces - the T₀, T₁ and T₂ surfaces. The rivers on these three surfaces show varying amounts of pollution depending upon the input from industries and urban settlements. The Ramganga River on the T₀ surface shows the highest amount of pollution. However, the pollution levels in all these rivers show a downstream dilution effect. The characteristic feature of the vast interfluve area (T₂ surface) is the presence of several, independent basins which are closed and rarely interact with each other or with any river. The sediments are redistributed and redeposited within the basin itself, and thus these basins serve as sinks. The sediments of one such basin in the study area show significant concentrations of arsenic, chromium, copper, nickel, lead, zinc and organic carbon. The concentrations of heavy metals in such a basin will show exponential increases with time, because there is no activity to funnel out the sediments and dilute the effect of pollution. This increase will pose more threats, as ultimately it will make its way laterally and vertically through the sediments, thereby polluting groundwater.     

Constraints on the thermal evolution of continental lithosphere from U-Pb accessory mineral thermochronometry of lower crustal xenoliths,southern Africa

U-Pb isotopic thermochronometry of rutile, apatite and titanite from kimberlite-borne lower crustal granulite xenoliths has been used to constrain the thermal evolution of Archean cratonic and Proterozoic off-craton continental lithosphere beneath southern Africa. The relatively low closure temperature of the U-Pb rutile thermochronometer (~400-450 °C) allows its use as a particularly sensitive recorder of the establishment of "cratonic" lithospheric geotherms, as well as subsequent thermal perturbations to the lithosphere. Contrasting lower crustal thermal histories are revealed between intracratonic and craton margin regions. Discordant Proterozoic (1.8 to 1.0 Ga) rutile ages in Archean (2.9 to 2.7 Ga) granulites from within the craton are indicative of isotopic resetting by marginal orogenic thermal perturbations influencing the deep crust of the cratonic nucleus. In Proterozoic (1.1 to 1.0 Ga) granulite xenoliths from the craton-bounding orogenic belts, rutiles define discordia arrays with Neoproterozoic (0.8 to 0.6 Ga) upper intercepts and lower intercepts equivalent to Mesozoic exhumation upon kimberlite entrainment. In combination with coexisting titanite and apatite dates, these results are interpreted as a record of postorogenic cooling at an integrated rate of approximately 1 °C/Ma, and subsequent variable Pb loss in the apatite and rutile systems during a Mesozoic thermal perturbation to the deep lithosphere. Closure of the rutile thermochronometer signals temperatures of 𙠂 °C in the lower crust during attainment of cratonic lithospheric conductive geotherms, and such closure in the examined portions of the "off-craton" Proterozoic domains of southern Africa indicates that their lithospheric thermal profiles were essentially cratonic from the Neoproterozoic through to the Late Jurassic. These results suggest similar lithospheric thickness and potential for diamond stability beneath both Proterozoic and Archean domains of southern Africa. Subsequent partial resetting of U-Pb rutile and apatite systematics in the cratonic margin lower crust records a transient Mesozoic thermal modification of the lithosphere, and modeling of the diffusive Pb loss from lower crustal rutile constrains the temperature and duration of Mesozoic heating to 𙡦 °C for ₞ ka. This result indicates that the thermal perturbation is not simply a kimberlite-related magmatic phenomenon, but is rather a more protracted manifestation of lithospheric heating, likely related to mantle upwelling and rifting of Gondwana during the Late Jurassic to Cretaceous. The manifestation of this thermal pulse in the lower crust is spatially and temporally correlated with anomalously elevated and/or kinked Cretaceous mantle paleogeotherms, and evidence for metasomatic modification in cratonic mantle peridotite suites. It is argued that most of the geographic differences in lithospheric thermal structure inferred from mantle xenolith thermobarometry are likewise due to the heterogeneous propagation of this broad upper mantle thermal anomaly. The differential manifestation of heating between cratonic margin and cratonic interior indicates the importance of advective heat transport along pre-existing lithosphere-scale discontinuities. Within this model, kimberlite magmatism was a similarly complex, space- and time-dependent response to Late Mesozoic lithospheric thermal perturbation.