Spatial distribution of near-surface CO over bay of Bengal during winter: role of transport     

Girach Imran Asatar  Prabha R Nair 《Journal of Atmospheric and Solar》2010,72(17):1241-1250

As part of Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), cruise-based measurements of near-surface CO were carried out over Bay of Bengal (BoB) covering the latitude–longitude sector 3.5°N–21.0°N and 76.0°E–98.0°E, during winter months of December 2008 to January 2009. These in-situ measured CO mixing ratio varied in the range of 80–480 ppbv over this marine environment with the distinct spatial pattern. The highest mixing ratios were measured over southeast-BoB with mean value of 379±58 ppbv. CO mixing ratios were high over north-BoB compared to southern BoB. These in-situ measurements were compared with the satellite-measured surface CO obtained from Measurements of Pollution in the Troposphere (MOPITT) onboard TERRA and found to be in good agreement over most of the regions, except at southeast-BoB. Surface CO and column CO from MOPITT data showed a similar spatial pattern. Based on the analysis of airmass back-trajectories, satellite-based spatial map of CO distribution over Asian region and Potential Source Contribution Function analysis, different pathways of transport of CO were identified. Transport from northern landmass as well as from south-east Asia has a significant influence in the spatial variation of CO over BoB. Winter-time mixing ratio of CO was found to be higher compared to those measured during other campaigns conducted during February–March 1999, 2001 (pre-monsoon) and September–October, 2002 (post-monsoon).  相似文献   

The linearity of the Wesenheit function for the Large Magellanic Cloud Cepheids     

Chow-Choong Ngeow  Shashi M. Kanbur 《Monthly notices of the Royal Astronomical Society》2005,360(3):1033-1039

There is strong evidence that the period–luminosity (PL) relation for the Large Magellanic Cloud (LMC) Cepheids shows a break at a period around 10 d. Because the LMC PL relation is extensively used in distance scale studies, the non-linearity of the LMC PL relation may affect the results based on this LMC calibrated relation. In this paper we show that this problem can be remedied by using the Wesenheit function in obtaining Cepheid distances. This is because the Wesenheit function is linear, although recent data suggest that the PL and the period–colour (PC) relations that make up the Wesenheit function are not. We test the linearity of the Wesenheit function and find strong evidence that the LMC Wesenheit function is indeed linear. This is because the non-linearity of the PL and PC relations cancel out when the Wesenheit function is constructed. We discuss this result in the context of distance scale applications. We also compare the distance moduli obtained from  μ₀=μ _V − R (μ _V −μ _I )  (equivalent to Wesenheit functions) constructed with the linear and the broken LMC PL relations, and we find that the typical difference in distance moduli is  ∼ ±0.03 mag  . Hence, the broken LMC PL relation does not seriously affect current distance scale applications. We also discuss the random error calculated with equation  μ₀=μ _V − R (μ _V −μ _I )  , and show that there is a correlation term that exists from the calculation of the random error. The calculated random error will be larger if this correlation term is ignored.  相似文献   

The nature and engineering behavior of carbonate soils at Bombay High,India     

Manoj Datta  G. Venkatappa Rao  Shashi K. Gulhati 《Marine Georesources & Geotechnology》2013,31(4):307-341

Abstract

This paper presents the results of a laboratory investigation undertaken to study the nature of two submarine carbonate soils from Bombay High off the west coast of India, as well as to study the shear and plasticity behavior of their sand and silt‐clay fractions, respectively. Scanning electron micrographs reveal that the carbonate content in both soils is comprised primarily of nonskeletal particles of various types. X‐ray diffraction and infrared absorption analyses indicate that in one soil the carbonate fraction consists of calcite and aragonite minerals, whereas in the other soil dolomite is also present. The non‐carbonate fraction of both soils is comprised primarily of quartz and feldspar, and also some clay minerals. The nature of the carbonate fraction of the two soils indicates that they were formed by different depositional processes.

During drained triaxial shear the nonskeletal sand grains of both soils exhibit a lower degree of crushing when compared with that of the skeletal carbonate sands, and thus appear to be stronger foundation material.

Although the carbonate contents of the silt‐clay fractions of the two soils are similar, they exhibit markedly different plasticity characteristics . This is probably because of the microlevel cementation produced by carbonate material in one soil.

This study leads one to the conclusion that carbonate content alone should not be treated as a parameter which controls the engineering behavior of submarine soils; the nature and form of carbonate material must also be identified.  相似文献   

Integrated very low-frequency EM, electrical resistivity, and geological studies on the Lanta Khola landslide, North Sikkim, India     

Shashi Prakash Sharma  K. Anbarasu  Saibal Gupta  A. Sengupta 《Landslides》2010,7(1):43-53

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   

In Situ Bioremediation of Toluene‐Polluted Vadose Zone: Integrated Column and Wetland Study     

Shreejita Basu  Brijesh Kumar Yadav  Shashi Mathur  Pankaj Kumar Gupta 《洁净——土壤、空气、水》2020,48(5-6)

A vertical soil column setup integrated with wetlands is developed to study the biodegradation and transport of toluene, a light non‐aqueous phase liquid (LNAPL), in the subsurface environment. LNAPL‐contaminated water is applied to infiltrate from the top of the soil column. The observed and simulated breakthrough curves show high equilibrium concentration at top ports rather than at lower ports, indicating effective toluene biodegradation with soil depth. The observed equilibrium concentration of toluene is higher in the case of unplanted wetland, asserting an accelerated biodegradation rate in the planted case. A difference in the relative concentration of toluene between input and output fluxes at 100 h is found as 13.34% and 30.86% for planted and unplanted wetland setups, respectively. Estimated biodegradation rates show that toluene degradation is 2.5 times faster in the planted wetland setup. In addition, the difference in the observed bacterial count and dissolved oxygen prove that toluene degraded aerobically at a faster rate in the planted setup. Simulations show that as time reached 80–100 h, there is no significant change in concentration profile, thereby confirming the equilibrium condition. The results of this study will be useful to frame plant‐assisted bioremediation techniques for LNAPL‐contaminated soil–water resources in the field.  相似文献   

Settlement of soil due to water uptake by plant roots     

Shashi Mathur 《国际地质力学数值与分析法杂志》1999,23(12):1349-1357

The settlement of soil occurs whenever there is an increase in effective confining stress. The withdrawal of water by plant roots results in a change in water pressure and moisture content in the soil. The variation in the moisture content leads to a change in the effective stress that causes a decrease in porosity which eventually results in the settlement of soil. The driving force for the uptake of water by the roots is the difference in the plant water and soil water potential existing between the soil solution adjacent to the roots and the root xylem. In case of transpiring plants, this driving force is mainly due to the tension (negative pressure) produced in the roots. A finite element solution of the governing equation yields the variation of moisture content with depth and the total settlement of the soil column due to the extraction of water by the plant roots. The simulated results indicate the damaging situation due to changes in the soil moisture content on account of transpiring trees and plants grown around the perimeter of structures. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献