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141.
A. Das K V. S. S. Krishna R. Kumar M. C. Saha S. Sengupta J. G. Ghosh 《International Journal of Environmental Science and Technology》2018,15(1):159-172
Street dust from 29 locations, in some of the busiest parts of north and south Kolkata, was analysed for heavy metal composition. The decreasing order of average metal concentrations (mg kg?1) found was Mn (390) > Pb (380) > Zn (300) > As (96) > Cu (61) > Cr (40) > Co (13) > Ag (2.1). The heavy metal composition of the Kolkata dust was compared with reported data for other cities. Enrichment factors of Pb and As were high. Multivariate statistical analysis of the heavy metals and analysis of lead isotopic ratios of the dust revealed a predominant anthropogenic influence in the contamination. The range of lead isotopic ratios found in the dust was between 0.8789 and 0.8998 with a mean Pb concentration of 383 mg kg?1. The three Pb isotope plots of street dust, diesel and rainwater clustered linearly, while coal did not fit into this trend. The highest 207/206 lead isotopic ratio obtained was from diesel with a mean value of 0.9015, followed by the rainwater sample. The application of the binary mixing model showed that about 66.86% of lead contamination in the street dust was sourced from the atmosphere. The two components extracted by the principal component analysis explained 64.34% of the total variance. Vehicular and industrial emissions appeared to be an important contributor to the accumulation of heavy metals in the dust. The health risk assessment study of the dust indicated carcinogenic risk associated with As and Cr. 相似文献
142.
Sachin Kumar Tripathi Debasis Sengupta Resmi Sathikumar Satyendra Baraik Amitava Lahiri 《Arabian Journal of Geosciences》2018,11(20):639
Sundarban is a largest mangrove forest delta developed along the NE-SW direction covering parts of India and Bangladesh. Little work has been done on Indian part of Sundarban in respect of heterogeneity in channel morphology which could be mostly due to the effect of tilting and basin subsidence. These changes might have played a major role on development of high marshes, which offers a congenial environment for survival of Haplophragmoides wilberti, Jadammina macrescens, Trochammina inflata, and Miliammina fusca. These marsh benthonic foraminiferal assemblages provide a direct evidence of recent past sea level changes. To establish the depositional pattern and their effects rendered by merciless changing environment, 11 pit sections have been excavated along three E-W transects from Indian Sundarban. Depth of these pit sections varies from 2 to 3 m. Generally, top 20 cm sediment (in pit section W-1 to W-11) deposited under the intertidal environment, as indicated by the presence of Ammonia tepida. However, sediment below 20 cm in some of the pit sections (W-3 and W-5) exhibits fresh water signatures as indicated by the presence of Charophytes algae. In other pit sections (W-1, W-2, W-6, W-7, W-8, W-9 and W-11), the intertidal assemblage is noticed just above the upper marshes assemblage and vice versa, signifying that depositional environment is in proximity to the mangrove dominated area as indicated by the presence of marsh benthonic foraminiferal assemblage containing T. inflata, H. wilberti, Haplophragmoides sp., J. macrescens and M. fusca. Bottom sediment in most of the pit sections from south to north have different depositional environment with alternate presence of intertidal to subtidal faunal assemblages. The peculiar presence of intertidal assemblage above the upper marshes assemblages in recent sediment points towards the theory of submergence due to relative rise in the sea level. But the effect of relative sea level rise is not uniform throughout the area because of differential subsidence due to varied rate of sediment supply (0.5 to 3.3 cm/year) and eastward tilting of the basin. Based on the upper marshes benthonic foraminiferal assemblage and radiocarbon age (in W-1 at 100 cm ~?150 years age), the average subsidence rate as recorded is approximately 0.3 to 0.5 cm/year. Hence, such depositional sequence conjectures that the Indian part of Sundarban is undergoing a phase of submergence concomitant to basin subsidence. 相似文献
143.
Sujan Sengupta 《Journal of Astrophysics and Astronomy》2013,34(2):151-155
Planets which are old and close to their parent stars are considered as reflecting planets because their intrinsic temperature is extremely low but they are heated strongly by the impinging stellar radiation and hence radiation of such planets are the reflected star light that is governed by the stellar radiation, orbital distance and albedo of the planet. These planets cannot be resolved from the host stars. The second kind of exoplanets are those which are very young and hence they have high intrinsic temperature. They are far away from their star and so they can be resolved by blocking the star-light. It is now realized that radiation of such planets are linearly polarized due to atmospheric scattering and polarization can determine various physical properties including the mass of such directly detected self-luminous exoplanets. It is suggested that a spectropolarimeter of even low spectral resolution and with a capacity to record linear polarization of 0.5–1% at the thirty-meter telescope would immensely help in understanding the atmosphere, especially the cloud chemistry of the self-luminous and resolvable exoplanets. 相似文献
144.
Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to
heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required
to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of
the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide
are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust
passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important
to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of
slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can
be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta
Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available
worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this high-altitude mountainous terrain.
VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was
delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient
resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the
slide parallel to the geological gneiss–schist contact within the Lanta Khola slide. This indicates that the conductive feature
correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive
structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out
water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide. 相似文献
145.
The ophiolitic rocks of Naga Hills-Andaman belt occur as rootless slices, gently dipping over the Paleogene flyschoid sediments,
the presence of blue-schists in ophiolite melange indicates an involvement of the subduction process. Subduction was initiated
prior to mid-Eocene as proved by the contemporaneous lower age limit of ophiolite-derived cover sediment as against the accreted
ophiolites and olistostromal trench sediment. During the late Oligocene terminal collision between the Indian and Sino-Burmese
blocks, basement slivers from the Sino-Burmese block, accreted ophiolites and trench sediments from the subduction zone were
thrust westward as nappe and emplaced over the down-going Indian plate. The geometry of the ophiolites and the presence of
a narrow negative gravity anomaly flanking their map extent, run counter to the conventional view that the Naga-Andaman belt
marks the location of the suture. The root-zone of the ophiolite nappe representing the suture is marked by a partially-exposed
eastern ophiolite belt of the same age and gravity-high zone, passing through central Burma-Sumatra-Java.
The ophiolites of the Andaman and Naga Hills are also conventionally linked with the subduction activity, west of Andaman
islands. This activity began only in late Miocene, much later than onland emplacement of the ophiolites; it further developed
west of the suture in its southern part. Post-collisional northward movement of the Indian plate subparallel to the suture,
also developed leaky dextral transcurrent faults close to the suture and caused Neogene-Quatemary volcanism in central Burma
and elsewhere. 相似文献