Geo-engineering properties of expansive soil treated with xanthan gum biopolymer

ABSTRACT

This paper presents the effectiveness of xanthan gum (XG) biopolymer in stabilising the expansive soil. The XG biopolymer is mixed with expansive soil in different proportions such as 0%, 0.2%, 0.5%, 0.8% and 1.0% by weight of the dry soil mass. The plasticity, compaction, swelling, compressibility, hydraulic conductivity, strength and durability characteristics of the treated and un-treated expansive soil are examined. Results show that the plasticity index of the treated soil mass initially increases but beyond 0.5% biopolymer addition it decreases sharply. The optimum moisture content and maximum dry density of treated soil, found out from light and heavy compaction tests, do not follow any definite trend. It is also found that increasing XG content increases compressibility slightly but, it reduces swelling pressure, differential free swelling value and hydraulic conductivity remarkably. On the other hand, time-dependent compressive strength and resistance to mass loss increases with increasing XG content. Microscopic examination confirms the formation of gel-like linkage, which brings about the modifications in the treated expansive soil.     

Emerging Flux and X-class Flares in NOAA 6555

The active region NOAA 6555 had several locations of highly sheared magnetic field structure, yet, only one of them was the site for all the five X-class flares during its disk passage in March 1991. The pre-flare observations of high-resolution H filtergrams, vector magnetograms and H Dopplergrams of the 2B/X5.3 flare on 25 March 1991 show that the flaring site was characterized by a new rising emerging flux region (EFR) near the highly sheared magnetic field configuration. The polarity axis of the emerging flux was nearly perpendicular to the pre-existing magnetic neutral line. The location of the EFR was the site of initial brightening in H. The post-flare magnetograms show higher magnetic shear at the flare location compared to the post-flare magnetograms, which might indicate that the EFR was sheared at the time of its emergence. As the new EFR coincided with the occurrence of the flare, we suggest that it might have triggered the observed flare. Observations from Big Bear Solar Observatory and Marshall Space Flight Center also show that there was emergence of new flux at the same location prior to two other X-class flares. We find that out of five observed X-class flares in NOAA 6555, at least in three cases there are clear signatures of flare-related flux emergence. Therefore, it is concluded that EFRs might play an important role in destabilizing the observed sheared magnetic structures leading to large X-class flares of NOAA 6555.     

Hydrogen photoproduction ofA. Variabilis incorporated in a photobioreactor

H₂ photoproduction and nitrogenase activities in two strains ofAnabaena variabilis marked wild type ATCC 29413 and mutant PK84 exposed to thermal stress (temperature higher than the normal incubation temperature of 30°C) were studied. Cultures of both strains collected from any interval of logarithmic growth phase exhibited high H₂ photoproduction and nitrogenase activities when exposed to limited time heat shock during the assay process. In contrast, the algal H₂ photoproduction rate of both strains fluctuated with long term thermal stress caused by increasing the growth temperature from 30°C to 36°C.

The changes of nitrogenase (the key H₂ photobiosynthetic enzyme) activities in the mutant PK84 showed variation tendency similar to that of H₂ photoproduction during exposure to thermal stress, indicating that fluctuation of H₂ photoproduction in the mutant was mainly due to the variation of nitrogenase activities. A temporary maximal H₂ photoproduction in the mutant PK84 (wild type ATCC29413) was observed when cells grew at 36°C for 14 (6) days. However, the responses of nitrogenase activities in the wild type to thermal stress were not completely similar to those in the mutant in spite of similar variations of H₂ photoproduction in both strains. The data obtained in these studies suggested that the activities of other enzymes (in the wild strain) involved in H₂ photoproduction were affected by thermal stress since H₂ photoproduction maximized or dropped to 0 without variation tendency similar to that of nitrogenase activities.

Furthermore, an enhancement of H₂ photoproduction speed of the mutant strain cultured in a 4.4 L laboratory photobioreactor was also observed when it was subjected to short time continuous charge of argon, and temperature rise.

All these results indicated that high temperature plays an important role in the photo-autotrophic H₂ photoproduction, and that long term thermal stress is unfavourable for net H₂ photoproduction in both strains ofA. variabilis though short-time heat shock is conducive to H₂ photoproduction.

     

Some applications of humidity profiles estimated from INSAT infra red digital cloud imagery data

Moisture profiles have been estimated over the region bounded by the latitudes 40°N and 40°S and longitudes 30°E to 130°E using INSAT digital infra red cloud imagery data. The representativeness of these profiles in representing moisture field associated with the development and movement of synoptic scale systems during the period September 15th, 1996 to March 31st, 1997 has been examined. It has been shown that the changes in the moisture field associated with the withdrawal of the southwest and northeast monsoons from the Indian sub-continent, development and movement of synoptic scale sytems (depressions, tropical cyclones and waves in easterlies) and equatorial troughs in the Indian Ocean could be clearly seen in humidity profiles. The initial development of tropical systems is first seen in the humidity field in the upper troposphere. These profiles could be used in monitoring the initial development and subsequent movement of tropical systems. Further the data on moisture distribution from the data gap regions of the Indian Ocean could be used as an additional source of moisture in numerical analysis and prognosis.     

Photospheric and Chromospheric Activity Associated with 3B Flare of February 27, 1992

We have analyzed the H filtergrams and vector magnetograms of the active region NOAA 7070, in which a 3B/X3.3 flare occurred on February 27, 1992. The average area per sunspot of this active region was in declining phase at the time of the flare. The vector magnetograms indicate that the magnetic field was non-potential at the flaring site. Besides non-potentiality, the longitudinal field gradient was found to be the highest at the region showing initial H brightening. Further, in H filtergrams no appreciable change in the morphology of the filament tracing the magnetic neutral line was noticed in the post-flare stage. Also, the photospheric vector magnetograms show considerable shear in post-flare magnetic field of the active region. In this paper we present the observations and discuss the possible mechanism responsible for the 3B/X3.3 flare.     

Soil survey of command area for planning of water management: A case study of an area in Hardoi district,U.P.

Development of irrigation potential for increasing agricultural production is the main aim of Command Area Development. This involves interaction amongst various factors; the soil, the crop, the climate, the topograpny and others. Water management in Command Area requires careful planning, based upon adequate data regarding soils, land use and topography. It is essential to make the best possible use of the available water without creating waterlogging, salinity and alkalinity problems in the command area. The use of aerial photographs is a well recognized expedient, convenient and economical method of data collection, which appreciably suits the requirement of the survey of Command Areas. As large areas have to be surveyed for data collection, the best way to accomplish this is by taking up survey of command area in different levels: reconnaissance, semi-detailed and detailed. The reconnaissance and semi-detailed survey would enable us to identify problem areas. Detailed survey are needed in these areas for taking up reclamation measures. A case study of soil survey carried out in the Sharda Sahayak Command Area of a part of Hardoi District is given as an example to illustrate the use of aerial photographs for planning of water management practices.     

The structure of the natural stratosphere and the impact of chlorofluoromethanes on the ozone layer investigated in a 2-D time dependent model

two-dimensional time dependent model of the stratosphere incorporating the major interactions between radiative-photochemical and dynamical processes is described. The main prognostic equations considered are the thermodynamic equation and the general conservation equation for the minor chemical constituents representing the odd oxygen (O _x =O+('D)+O₃), odd hydrogen (HO _x =HO+HO₂), N₂O, odd nitrogen (NO _x =NO+NO₂+HNO₃), CF₂Cl₂, CFCl₃ and odd chlorine (Cl _x =Cl+ClO+HCl). The zonal wind and mean meridional circulations are determined diagnostically by the integration of the thermal wind equation and the stream function equation in the meridional plane espectively. The large scale eddy processes are parameterized in terms of zonal mean quantities using the generalized diffusion formulation on a sloping surface. The radiative heating and cooling and the hotochemical sources and sinks are incorporated in a form which allows for the major interactions among the minor trace constituents, temperature and mean circulation.Two integrations consisting of natural stratosphere and a stratosphere contaminated by the chlorofluoromethanes through lower boundary fluxes are carried out for 23 model years by changing the declination of the sun every day and using 6-hour time step. The model simulations of temperature, mean circulation, ozone, HO _x , N₂O and NO _x in the meridional plane for the normal stratosphere, show satisfactory agreement with the available observations. Based on the results of second integration it is found that the injection of chlorofluoromethanes in the atmosphere at the estimated current production rates can lead to significant changes in the meridional distribution of ozone, temperature and NO _x in the middle and upper stratosphere. The results also indicate that the percentage total ozone depletion increases from tropics to high latitudes and from summer to winter high latitudes. Also discussed are the results of additional experiments incorporating the reaction of HO₂ with NO and the reactions involving ClNO₃.     

Seaward dipping reflectors along the SW continental margin of India: Evidence for volcanic passive margin

Multi-channel seismic reflection profiles across the southwest continental margin of India (SWCMI) show presence of westerly dipping seismic reflectors beneath sedimentary strata along the western flank of the Laccadive Ridge — northernmost part of the Chagos-Laccadive Ridge system. Velocity structure, seismic character, 2D gravity model and geographic locations of the dipping reflectors suggest that these reflectors are volcanic in origin, which are interpreted as Seaward Dipping Reflectors (SDRs).     

Distribution of arsenic and mercury in subtropical coastal beachrock,Gulf of Mannar,India

An assessment of coastal pollution was made on the basis of trace element concentrations (arsenic — As, mercury — Hg) in the Gulf of Mannar. The beachrock samples were collected along the coastal tracts between Rameswaram and Kanyakumari. The samples were dried and digested to determine the As and Hg using atomic absorption spectrophotometer (AAS-air-acetylene and nitrous oxide method). The As and Hg accumulation status of the beachrock was assessed using geo-accumulation index values (I _geo). The accumulation of As and Hg in the beachrock ranges from 2.75 to 20.72 μg g⁻¹ and from 0.06 to 0.31 μg g⁻¹, respectively. The As and Hg concentrations in the beachrocks are compared with crustal average values and average of other region sediments. The possible source of the contamination is from atmospheric deposition and anthropogenic activities.