Non-linear analysis of the stability of the Screw Pinch

Non-linear effects on the stability of the Screw Pinch in cylindrical system surrounded by a uniform pitch magnetic field in an incompressible pressureless plasma have been studied. A linear dispersion relation governing the stability of interface has been obtained with the help of normal mode analysis. Perturbation technique has been used to obtain the non-linear Schrödinger equation for the time variation of amplitudeA(t) which evolves according to . This can lead to non-linear stabilization, explosive instability or eventual decay, depending on the sign of . The whole calculations have been made form=1, kink modes in a sharp boundary plasma pinch. Non-linear analysis for -pinch (0) andz-pinch () have also been discussed in detail. It has been found that non-linear theory have a destabilizing influence on both - andz-pinches.     

Treatment of Loose to Medium Dense Sands by Granular Piles: Improved SPT ‘N<Subscript>1</Subscript>’ Values

The effect of granular pile installation on the modifications induced in loose to medium dense granular deposits is studied. SPT is the most often used to evaluate the in situ soil properties. Expressions for modified SPT N₁ values for different soils, i.e., for different initial SPT N₁ values, were determined as functions of replacement ratio from the available field data. Improvements in the ground are presented in the form of modified or improved SPT N₁ values versus replacement ratio charts, which can then be used to design the required degree of treatment for the expected improvement or to estimate the improved values of treated ground for different initial states of sands.     

Adsorption of heavy metals in glacial till soil

The charged sites on soil particles are important for the retention/adsorption of metals. Metallic counterions can neutralize the intrinsic charges on the surfaces of soil particles by forming complexes. In this study, efforts have been made to determine the effect of surface potential, pH, and ionic strength on the adsorption of four metal ions, hexavalent chromium Cr(VI), trivalent chromium Cr(III), nickel Ni(II) and cadmium Cd(II), in glacial till soil. Batch tests were performed to determine the effect of pH (2–12) and ionic strength (0.001–0.1 M KCl) on zeta potential of the glacial till soil. The point of zero charge (pH _PZC ) of glacial till was found to be 7.0±2.5. Surface charge experiments revealed the high buffering capacity of the glacial till. Batch adsorption experiments were conducted at natural pH (8.2) using various concentrations of selected metals. The adsorption data was described by the Freundlich adsorption model. Overall glacial till shows lower adsorption affinity to Cr(VI) as compared to cationic metals, Cr(III), Ni(II) and Cd(II).     

Influence of PDO on South Asian summer monsoon and monsoon–ENSO relation

This study has investigated the possible relation between the Indian summer monsoon and the Pacific Decadal Oscillation (PDO) observed in the sea surface temperature (SST) of the North Pacific Ocean. Using long records of observations and coupled model (NCAR CCSM4) simulation, this study has found that the warm (cold) phase of the PDO is associated with deficit (excess) rainfall over India. The PDO extends its influence to the tropical Pacific and modifies the relation between the monsoon rainfall and El Niño-Southern Oscillation (ENSO). During the warm PDO period, the impact of El Niño (La Niña) on the monsoon rainfall is enhanced (reduced). A hypothesis put forward for the mechanism by which PDO affects the monsoon starts with the seasonal footprinting of SST from the North Pacific to the subtropical Pacific. This condition affects the trade winds, and either strengthens or weakens the Walker circulation over the Pacific and Indian Oceans depending on the phase of the PDO. The associated Hadley circulation in the monsoon region determines the impact of PDO on the monsoon rainfall. We suggest that knowing the phase of PDO may lead to better long-term prediction of the seasonal monsoon rainfall and the impact of ENSO on monsoon.     

Cosmic ray synthesis of organic molecules in Titan's atmosphere

We have studied the possible synthesis of organic molecules by the absorption of galactic cosmic rays in an N₂CH₄H₂ Titan model atmosphere. The cosmic-ray-induced ionization results in peak electron densities of 2 × 10³ cm^?3, with NH₄⁺, C₃H₉⁺, and C₄H₉⁺ being among the important positive ions. Details of the ion and neutral chemistry relevant to the production of organic molecules are discussed. The potential importance of $\text{N}\text{(}{}^2\text{D)}$ reactions with CH₄ and H₂ is also demonstrated. Although the integrated production rate of organic matter due to the absorption of the cosmic ray cascade is much less than that by solar ultraviolet radiation, the production of nitrogen-bearing organic molecules by cosmic rays may be greater.     

Biogeochemistry and paleoclimate variability during the Holocene: a record from Mansar Lake,Lesser Himalaya

Investigation of biogeochemistry and amino acids on a 30-m-long core from Mansar Lake has thrown light on palaeoclimate variability during the Holocene period. The C/N ratio between 6 and 10 with some deviations and δ13C mostly between −20 and −22‰ in the shallow core, as well as a C/N ratio greater than 13 reaching from 19 to 20 and correspondingly lower δ13C of –28‰ in the deeper core suggest an aquatic source of carbon in the former and a cellulose-rich land plant source in the latter. This is supported by the abrupt increase in organic carbon content in the deeper core compared to the shallow core, which indicates a hot and wet climatic regime during the early Holocene and dry and cold during the late Holocene period. The amino acid data AA-C/C% and AA-N/N% are higher in shallow sediments compared to deeper sediments, indicating an aquatic plant source in the shallow core and greater supply of land plant sources in the deeper core. The lower percentage of the non-protein amino acids β-alanine (ALA) and γ-amino-butyric acid in the shallow core compared to the deeper core indicates different sources of organic matter in the lake basin. The higher amino acid ratio Asp/β-Ala (16.99 av.) and Glu/γ-Aba (18.18 av.) in the shallow core and lower ratios (10.32 and 12.41 av.) in the deeper core, and Asp/Glu (1.52 av.) and β-Ala/γ-Aba (1.61 av.) ratios in the former, which are potential indicators of the nature of the organic matter, are higher in the shallow core relative to the deeper core (1.33 and 1.23 av.), indicating relative biodegradation of organic matter in deeper sediments. It has been observed that the organic matter associated with the dry season is relatively less biodegraded, as evidenced from their higher ratios, and is more biodegraded in the wet season as their ratios are lower in the river sediments. In the absence of a bacterial contribution of organic matter from the soil source in this lake, since Mansar Lake is a non-drainage type, it is envisaged that the climatic variation may be responsible for biodegradation in the deeper core sediments. Therefore, the C/N ratio and δ13C values supported by amino acid data, the latter being significant in revealing primary productivity and a terrestrial source of organic matter, suggest a hot and wet climatic regime during the early Holocene (ca. 7580 bp) and a dry and cold in the late Holocene period (ca. 4050 bp).     

The stability of inner cometo-sheath with large Larmor radius effects

An investigation of the linear stability of the cometary inner sheath, the boundary layer surrounding the ionopause which separates the outflowing unmagnetized plasma from an inflowing magnetized plasma, has been carried out by taking into account the large Larmor radius effects. The structure of the boundary layer is determined by the balance between an outward ion-neutral collisional drag force and an inward magnetic stress. The eigenvalues and the eigenfunctions are obtained numerically by treating the cometary ionosphere as a layer of finite thickness, bounded by the contact surface, i.e., the diamagnetic cavity boundary. Certain limiting cases of the wave equations are also discussed. In general, the cometary ionosphere is structurally linearly unstable and the effects of recombination, photoionization, plasma pressure, though stabilizing are unable to quench the instability completely. The large Larmor radius also has a destabilizing effect on the system. The instability of the cometosheath is further proved by the _c/_i assuming a value greater than 30 that is sufficient for the convection of perturbations down into the cavity surface and this is in agreement with the observations of ripples in the ionopause.     

Locating oceanic Tuna resources in the Eastern Arabian sea using remote sensing

Tuna fishery resources are currently under exploited. The resource potential of tunas in the Indian Exclusive Economic Zone (EEZ) beyond 50 m depths is around 2.09 lakh tonnes as estimated by Fishery Survey of India. The distribution and availability of the tuna are governed by environmental factors like temperature, thermocline depth, availability of prey, visibility etc. Remote sensing provides synoptic information on productivity in terms of chlorophyll and Sea Surface Temperature (SST). In the present paper, satellite remote sensing data from Indian Remote Sensing Satellite IRS- P4 Ocean Colour Monitor (OCM) sensor for chlorophyll-a and diffuse attenuation coefficient (K) and National Oceanic and Atmospheric Administration (NOAA) - Advanced Very High Resolution Radiometer (AVHRR) sensor data for sea surface temperature were analysed and correlated within situ catch data of oceanic tunas, Skipjack(Katsuwonus pelamis) and Yellowfin tuna(Thunnus albacares), off Maharashtra coast. Higher catches were found to be associated with moderate to good primary productivity and in the vicinity of thermal fronts. Relationship between Hooking rate and SST has shown that SST of 28–30°C range is optimum for skipjack and 28–31°C for yellowfin tuna. Besides satellite derived chlorophyll and SST for identification of potential tuna fishing zones, role of diffuse attenuation coefficient (K) for visibility factor is also discussed.