Free vibration of semisubmersibles: A parametric study

Like any other engineering structure, the dynamic aspects of semisubmersible offshore platforms require serious consideration. The free vibrations of the semisubmersible structures have been investigated in the present work, in which the effect of the variation of the length, draft and hull spacings on the natural frequencies and mode shapes has been studied and the nature of the variations and their reasons have been discussed.     

Chemistry of snow and lake water in Antarctic region

Surface snow and lake water samples were collected at different locations around Indian station at Antarctica, Maitri, during December 2004–March 2005 and December 2006–March 2007. Samples were analyzed for major chemical ions. It is found that average pH value of snow is 6.1. Average pH value of lake water with low chemical content is 6.2 and of lake water with high chemical content is 6.5. The Na⁺ and Cl^? are the most abundantly occurring ions at Antarctica. Considerable amount of SO ₄ ^2? is also found in the surface snow and the lake water which is attributed to the oxidation of DMS produced by marine phytoplankton. Neutralization of acidic components of snow is mainly done by NH ₄ ⁺ and Mg²⁺. The Mg²⁺, Ca²⁺ and K⁺ are nearly equally effective in neutralizing the acidic components in lake water. The NH ₄ ⁺ and SO ₄ ^2? occur over the Antarctica region mostly in the form of (NH₄)₂SO₄.     

Selection of a Landfill Site for Solid Waste Management: An Application of AHP and Spatial Analyst Tool

Selection of a suitable landfill site for Solid Waste Management (SWM) forms an important component of urban planning. The problem of SWM has assumed significant proportion for the municipal authorities in the wake of rapid industrialization, urbanization and resultant pressure on existing resources. Many criteria such as distance from residential locations, transport connectivity, presence of water-bodies (drains, ponds, rivers etc.) and forests, ground water table and geology are taken into consideration while planning for suitable sites. Spatial Analyst Tool along with Analytic Hierarchy Process (AHP) model is extremely useful in such multicriteria decision making process. The present study, based on these tools/techniques, endeavours to identify a suitable location for landfill site in a part of the National Capital Territory of Delhi. The study identifies six potential sites out of which one has been proposed and recommended as the best suitable site.     

Anisotropic universe with cosmic strings and bulk viscosity

Spatially homogeneous and anisotropic LRS Bianchi type-I string cosmological models are studied in the frame work of general relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the models are discussed. The role of bulk viscosity in getting an inflationary phase in the universe is studied.     

Silicate and carbonate weathering in the drainage basins of the Ganga-Ghaghara-Indus head waters: Contributions to major ion and Sr isotope geochemistry

The role of silicate and carbonate weathering in contributing to the major cation and Sr isotope geochemistry of the headwaters of the Ganga-Ghaghara-Indus system is investigated from the available data. The contributions from silicate weathering are determined from the composition of granites/ gneisses, soil profiles developed from them and from the chemistry of rivers flowing predominantly through silicate terrains. The chemistry of Precambrian carbonate outcrops of the Lesser Himalaya provided the data base to assess the supply from carbonate weathering. Mass balance calculations indicate that on an average ∼ 77% (Na + K) and ∼ 17% (Ca + Mg) in these rivers is of silicate origin. The silicate Sr component in these waters average ∼40% and in most cases it exceeds the carbonate Sr. The observations that (i) the⁸⁷Sr/⁸⁶Sr and Sr/Ca in the granites/gneisses bracket the values measured in the head waters; (ii) there is a strong positive correlation between⁸⁷Sr/⁸⁶Sr of the rivers and the silicate derived cations in them, suggest that silicate weathering is a major source for the highly radiogenic Sr isotope composition of these source waters. The generally low⁸⁷Sr/⁸⁶Sr (< 0.720) and Sr/Ca (∼ 0.2 nM/ μM) in the Precambrian carbonate outcrops rules them out as a major source of Sr and⁸⁷Sr/⁸⁶Sr in the headwaters on a basin-wide scale, however, the high⁸⁷Sr/⁸⁶Sr (∼ 0.85) in a few of these carbonates suggests that they can be important for particular streams. The analysis of⁸⁷Sr/⁸⁶Sr and Ca/Sr data of the source waters show that they diverge from a low⁸⁷Sr/⁸⁶Sr and low Ca/Sr end member. The high Ca/Sr of the Precambrian carbonates precludes them from being this end member, other possible candidates being Tethyan carbonates and Sr rich evaporite phases such as gypsum and celestite. The results of this study should find application in estimating the present-day silicate and carbonate weathering rates in the Himalaya and associated CO₂ consumption rates and their global significance.     

Riparian vegetation dynamics across two different landscapes along the river Cauvery in the Kodagu region of Western Ghats

Decades of commercial planting and other anthropogenic processes are posing a threat to the riparian landscapes of the Cauvery river basin, which supports a high floral diversity. Despite this, the habitats in the upstream sections of the River Cauvery are still intact, as they are located in sacred groves. To understand the dynamism of riparian forests exposed to anthropogenic pressures, the upstream stretch of Cauvery extending from Kushalanagara to Talacauvery (~102 km) was categorized into two landscapes: agro ecosystem and sacred (i.e. preserved). The tree species were sampled using belt transects at 5 km intervals and the regeneration status of endemic species assessed using quadrats. A total of 128 species belonging to 47 families, and representing 1,590 individuals, was observed. Amongst them, 65% of unique species were exclusive to sacred landscapes. A rarefaction plot confirmed higher species richness for the sacred compared to the agro ecosystem landscapes, and diversity indices with more evenness in distribution were evident in sacred landscapes. A significant loss of endemic tree species in the agro ecosystem landscapes was found. Overall, this study demonstrates that an intense biotic pressure in terms of plantations and other anthropogenic activities have altered the species composition of the riparian zone in non-sacred areas. A permanent policy implication is required for the conservation of riparian buffers to avoid further ecosystem degradation and loss of biodiversity.     

Temporal variation of b value associated with M ��4 earthquakes in the reservoir-triggered seismic environment of the Koyna�CWarna region, Western India

It is generally found that the b values associated with reservoir-triggered seismicity (RTS) are higher than the regional b values in the frequency magnitude relation of earthquakes. In the present study, temporal and spatial variation of b value is investigated using a catalog of 3,000 earthquakes from August 2005 through December 2010 for the Koyna?CWarna region in Western India, which is a classical site of RTS globally. It is an isolated (30?×?20?km²) zone of seismicity where earthquakes of up to M ??5 are found to occur during phases of loading and unloading of the Koyna and Warna reservoirs situated 25?km apart. For the Warna region, it is found that low b values of 0.6?C0.9 are associated with earthquakes of M ??4 during the loading phase. The percentage correlation of the occurrence of an M????4 earthquake with a low b value outside the 1?? or 2?? level is as high as 78?%. A drastic drop in the b value of about 50?% being reported for an RTS site may be an important precursory parameter for short-term earthquake forecast in the future.     

Calibration of AGRS System Using Transportable Pads in India: An Application to AGRS Data of Aravalli Basin,Banswada Block,South Rajasthan

Calibration of airborne gamma ray spectrometric system (AGRS) over standard radioactive sources of known elemental abundances is essential before carrying out airborne surveys. In India, fixed calibration pads were constructed in 1985. Since then calibration of AGRS system was carried out over the fixed pads. However the fixed pads are expensive to build and maintain. Also the large pads are subject to variations in radiation output due to variable moisture content and radon loss. Alternate approach is to construct transportable calibration pads which are discussed in this paper.Atomic Minerals Directorate for Exploration & Research (AMD) under Department of Atomic Energy has recently constructed five transportable calibration pads. Three pads i.e. K, U and Th have been spiked with the respective radioelements while keeping the minor radioelements to the least in order to obtain pure spectra. A composite pad has been constructed which contains all the three radioelements. This helps in cross verifying the obtained calibration results. A background pad has also been constructed which is helpful to obtain the background values during calibration.Analysis of the data acquired over the transportable pads with airborne gamma ray spectrometer (16.8 ltr) has been carried out and presented in this paper. A comparison with the data acquired over the fixed calibration pads is also included. There is a good agreement of results which suggests the use of transportable pads in future.     

Influence of multipurpose trees on agricultural crops in arid regions of Haryana, India

The effects of multipurpose trees on the productivity of agricultural crops were studied in the arid regions of Haryana. In one of the experiments, wheat was grown on irrigated farms having scattered trees ofDalbergia sissoo, Azadirachta indica, Prosopis cinerariaandAcacia nilotica. Data of wheat yield for each tree species at different distances (1, 3, 5, and 7 m) and four directions (East, West, North and South) from the tree bases and control (no trees) were collected. Results indicate thatAzadirachta indicaandProsopis cinerariadid not produce any significant difference in the wheat yield while the other two species (Dalbergia sissooandAcacia nilotica) gave a reduction in yield.A. niloticahad a more significant and prominent effect and a reduction of 40 to 60 % wheat yield was observed.Dalbergia sissooreduced yield by 4 to 30 % but the reduction was only up to a distance of 3 m. In general, the impact of trees on productivity was observed up to 3 m distance and there was little, if any, impact up to 5 m and almost no impact at 7 m.In another experiment,D. sissoo(18-years-old) was raised as windbreak and productivity of cotton was assessed. The tree belt reduced the wind speed by 15 to 45 %, depending on season and wind speed. The influence of trees on cotton yield was observed to be negative up to 2H (36 m), where H is tree height, i.e. 18 m. Cotton productivity was observed to be maximum between 2H and 5H. Depending upon orientation of tree belt, the increase in cotton yield was found to be 4 to 10 %.