Suspended barite as a tracer of biological activity in the Southern Ocean

During two cruises in the Southern Ocean (INDIGO 3, Indian sector and EPOS 2, Scotia-Weddell Confluence) suspended matter samples were collected for analysis of several biogenic elements including Ba, Si and particulate organic carbon (POC).The good agreement between particulate barium in subsurface water with oxygen minimum concentrations as well as with nitrate depletions suggests that it reflects the intensity of new production over the past season. As a consequence of new production in the Southern Ocean being performed mainly by diatoms, the occurrences of barite and diatoms are related in the water column. In areas characterized by diatom-poor phytoplankton, barite does occur, but in lower concentrations.     

Geochemical variation in ferromanganese nodules and associated sediments from the Pacific Ocean

The major and minor element compositions of a suite of abyssal sea-floor ferromanganese nodules and associated sediments from the eastern central Pacific have been used to examine inter-element relationships and the mineralogy of the nodules, the relationship between the composition of nodules and their associated sediments and regional variations in composition with respect to likely modes of formation of such deposits. Apart from Mn and Fe, significant proportions of the total Ti, Ca, Mg, K, Ba, Sr, Th and Y and almost all the P, As, Ce, Co, Cu, Mo, Ni, Pb, Zn and Zr are present in the oxide fractions of the nodules. The Mg, Ba, Cu, Mo, Ni and Zn contents are significantly correlated with the Mn content, while Ti, P, As, Pb, Sr, Y and Zr are similarly correlated with the total Fe content.Nodules from the northeastern tropical Pacific have Mn/Fe ratios higher than those in the oxide fractions of their associated sediments, todorokite as the principal Mn phase and relatively high concentrations of minor elements associated with Mn. Nodules from the south central Pacific have Mn/Fe ratios similar to those in the oxide fractions of the associated sediments, δ-MnO₂ as the only Mn-phase, and relatively high concentrations of minor elements associated with Fe. There appears to be a smooth gradation in composition in the tropical Pacific between these two end members.The regional compositional variation is interpreted as a reflection of different sources of metals for, and different growth mechanisms of, sea-floor nodules. The oxide precipitate from sea water consists of δ-MnO₂, has a relatively low Mn/Fe ratio and minor element contents related to the total Fe and Mn(δ-MnO₂) content. The oxide precipitate forming in areas of very low sedimentation as a result of diagenetic remobilisation in the surface sediment consists of todorokite, and has a high Mn/Fe ratio and enhanced metal content in the Mn-(todorokite)phase. Available information on the morphology and compositional variation of individual nodules from the tropical Pacific corroborates these contrasting metal sources and suggests that they can be resolved on the scale of an individual oxide concretion.     

Stellar flare statistics — Physical consequences

The observational data permit us to establish clear statistical correlations between different parameters of stellar flare activity and the characteristics of quiet stars. These relations are:

1. between energies and frequencies of flares on stars of different luminosities;
2. between total radiation energies of flares and quiet stars both in X-ray and Balmer emission lines;
3. between flare decay rates just after the maxima and flare luminosities at maxima.

     

Optical interferometric observations of a transient event of 1986 March 13 in the coma of Comet Halley

During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H₂ O⁺ emission was recorded in thecoma at ～ 0^h UT on 1986 March 13. Observations were carried out using a special IHW filter for H₂ O⁺ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24?39’N,72? 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ～ 35km s^?1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet     

The University of Durham Southern Hemisphere VHE gamma ray telescope

The design of very high energy (VHE) gamma ray telescopes is discussed and it is shown that a triple-mirror telescope operating in threefold fast coincidence provides an effective instrument. The design, construction and operation of a large VHE gamma ray telescope with an energy threshold of 300 GeV (at the zenith) and incorporating several novel features is described. The use of a coincidence guard ring technique is shown to result in the rejection of about 50% of the off-source (proton) events which form a high background and limit the sensitivity of such telescopes.     

Photometry of the bright stars inside and outside associations in the spiral arm S5 of the andromeda galaxy

Photometry of more than 1000 bright stars of 20 associations and some fields in its vicinity is made, usingUBV plates taken with a 2-m Ritchey-Chrétien telescope of the National Observatory at the Bulgarian Academy of Sciences with limited magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitudes of about 20.6 inU andV, 21.6 inB. The colour-magnitude and colour-colour diagrams of 12 associations and 8 fields are constructed and the brightest blue and red stars colour excesses, ages, and integrated luminosities of the associations are determined. The composite diagrams for all association and nonassociation measured stars are constructed too. Inside associations bright stars as well as non-stellar objects occur more often than outside. The brightest stars in S5 are withM _v7 and do not differ considerably from the brightest ones in the spiral arm S4 of M31. Approximately the same are the absolute magnitudes of the brightest stars in our Galaxy and M33. A small difference between the brightest stars of the latter galaxy with those of M31 is possible because the stars in M33 are younger. This is in agreement with the concept that Sc galaxies (for example M33) are younger than Sb ones (for example M31). The same could be the reason for the smaller ratio of blue to red supergiants in M33 than in M31. The age estimations of the associations in S5 together with those in S4 in M31 show that they are older than the associations in M33 which is in agreement with the above mentioned concept.     

Distribution analysis of salt affected soils under canal and non-canal command area in a part of Etah district,U. P., using remote sensing technique

A World Bank-aided project on sodic land reclamation in Uttar Pradesh is being executed by U.P. Bhumi Sudhar Nigam, Lucknow, and Remote Sensing Applications Centre, U.P., Lucknow has the responsibility of sodic land mapping for the execution of land reclamation programme at the cadastral level. Sodic lands are mainly concentrated in the Gangetic alluvial plains but the problem of sodicity is particularly acute in the canal-irrigated areas. A study of the distribution pattern of sodic lands in canal and noncanal command areas in a reclamation site (covering 60 villages out of which sodic lands were mapped in 51 villages) of Etah district in Uttar Pradesh, indicates that 18.39 per cent area of the canal command villages was barren sodic which was 13.41 per cent of the total geographical area of the site (15417 ha), however, 11.69 per cent area was recorded to be barren sodic in the non-canal command villages which was only 3.16 per cent of the geographical area of the site. The results of soil chemical analysis indicate that barren sodic lands of canal command area are saline-sodic with higher concentration of soluble salts (pH₂ >8.5, EC₂ >4 dSm⁻¹), however, those of non-canal command area are sodic (pH₂ >8.5, EC₂ <4 dSm⁻¹). The post-monsoon ground level in the canal-irrigated areas was in the critical and semicritical zone (< 3.0 mbgl) whereas it was well below the semi-critical zone in the non-canal command area, which indicates that the high ground water level is a major factor to higher the area under sodicity.     

Urban cadastral mapping using very high resolution remote sensing data

With growing urban expanses, one of the pre-requisites for effective governance is Urban Information Systems (UIS) with content down to individual properties (and individuals). The basic input i.e., a map, in UIS should show individual property boundaries showing the plan outline of all structures existing within, at a scale of 1:1000 and larger with sub-metre to centimeters planimetric and geometric accuracy. With very high resolution remote sensing data of the order of 1m available in hand, it is possible to prepare maps with high resolution spatial content. The present exercise demonstrates a method of preparing a geometrically and planimetrically accurate urban cadastral map on very large scale for a small area of about 5 sq km. IKONOS merged data with 1m resolution is used for the purpose. Mapping was done in conjunction with on-site measurements and sketches. Guides are used to maintain shape symmetry and accuracy of buildings and other features. Working out cost of mapping per unit area is another objective in the present exercise. For want of fully or semi-automatic methods of information extraction from very high resolution remote sensing data, it is imperative that mapping should be carried out in conjunction with some on-site measurements wherever necessary.