Numerical simulations to study kinetic Alfvén wave and whistler wave spectra in solar wind plasma     

Navin Kumar Dwivedi  R. P. Sharma  Karuna Batra 《Astrophysics and Space Science》2013,343(1):19-26

The numerical simulations of the model equation governing the nonlinear evolution of kinetic Alfvén wave (KAW) in solar wind plasmas are performed. The nonlinear dynamical equation of KAW satisfies the modified nonlinear Schrödinger MNLS equation when the ponderomotive nonlinearity is incorporated in the KAW dynamics. The effect of Landau damping is taken into account in the KAW dynamics. The coherent (in the absence of Landau damping) and damped (with Landau damping) localized structures of pump KAW as a consequence of ponderomotive nonlinearity have been studied in the solar wind at 1 AU. A weak whistler signal propagating in these localized structures is amplified which leads to the development of its own coherent and damped localized structures. Magnetic field (KAW) and electric field (whistler wave) power spectra and their spectral indices are calculated. Our results reveal the change in spectral index because of the damping effect which has good agreement with the observations. These damped structures and steeper spectra may be one of the reasons responsible for the plasma heating and particles acceleration in solar wind.  相似文献   

Morphological Features of Co-Rich Manganese Deposits and Their Relation to Seabed Slopes     

Tetsuo Yamazaki  Rahul Sharma 《Marine Georesources & Geotechnology》2013,31(1):43-76

Abstract

The morphological features associated with Co-rich manganese deposits, the size variations of nodules, and the occurrence of different substrates have been analyzed, to evaluate the influence of various seabed slope angles on the distribution of these features. The coverage and size of the crusts depend on their surface morphology and seabed topography, resulting in cobble-type, lineated, or step-like outcrops. Small nodules (1–4 cm in diameter) dominate all seabed slopes, with a few locations having nodules ranging from 1 to 8 or 1 to 10 cm. Sediments invariably occur as substrates for nodules and as cover for crusts, their coverage being inversely proportional to that of the nodules and crust outcrops.

Steeper seafloor areas have large crust outcrops exposed with no or few nodules and sediments associated with them. The intermediate slopes have a combination of nodules, sediments, and crusts in various proportions, depending on topography and gradient. Large-scale nodule occurrences, followed by sediment fields and crust outcrops on seabed slopes of < 3°, 3–7°, and > 15°, respectively, represent typical morphological distribution zones of the Co-rich manganese deposits on a seamount in the central Pacific Ocean. A transition zone between nodule-dominated fields and large crust outcrops occurs for slopes from 7° to 15°. This detailed study on distribution of Co-rich deposits gives a better understanding for purposes of their exploitation.  相似文献   

Interannual Variation of Eddy Kinetic Energy from TOPEX Altimeter Observations     

Rashmi Sharma  A.K.S. Gopalan  M.M. Ali 《Marine Geodesy》2013,36(4):239-248

Monthly mesoscale eddy kinetic energy (EKE) per unit mass has been computed for four years, 1993-1996, from TOPEX altimeter data in the Indian Ocean. It ranges from 50 cm²/s² to 2,700 cm²/s² (about 4,000 cm²/s² near the Somali region in a few months). In the Arabian Sea and the Bay of Bengal, regions of high energies associated with various current systems under the influence of monsoonal winds have been delineated. Monthly variation of EKE near the Somali region has been studied. In this region the maximum EKE per unit mass has been observed during August every year, with variations in magnitude from year to year. The mesoscale eddy kinetic energy computed from TOPEX altimeter-derived SSH during 1993-1996 is highest near the Somali region during the SW monsoon, due to formation of mesoscale eddies and also because of upwelling. In the Bay of Bengal, high eddy kinetic energy is seen toward the western side during nonmonsoonal months due to the western boundary current. In the South Indian Ocean, it is high at a few places in some of the months. A large part of the Indian Ocean exhibits low eddy kinetic energy (less than 300 cm²/s²) year-round.  相似文献   

Role of atmospheric ammonia in the formation of inorganic secondary particulate matter: A study at Kanpur,India   总被引：1，自引：0，他引：1  

Mukesh Sharma  Shyam Kishore  S. N. Tripathi  S. N. Behera 《Journal of Atmospheric Chemistry》2007,57(1):1-17

Levels of fine Particulate Matter (PM_fine), SO₂ and NO_x are interlinked through atmospheric reactions to a large extent. NO_x, NH₃, SO₂, temperature and humidity are the important atmospheric constituents/conditions governing formation of fine particulate sulfates and nitrates. To understand the formation of inorganic secondary particles (nitrates and sulfates) in the atmosphere, a study was undertaken in Kanpur, India. Specifically, the study was designed to measure the atmospheric levels of covering winter and summer seasons and day and night samplings to capture the diurnal variations. Results showed are found to be significantly high in winter season compared to the summer season. In winter, the molar ratio of to was found to be greater than 2:1. This higher molar ratio suggests that in addition to (NH₄)₂SO₄, NH₄NO₃ will be formed because of excess quantity of present. In summer, the molar ratio was less than 2:1 indicating deficit of to produce NH₄NO₃. The nitrogen conversion ratio (NO₂ to NO₃) was found to be nearly 50% in the study area that suggested quick conversion of NO₂ into nitric acid. As an overall conclusion, this study finds that NH₃ plays a vital role in the formation of fine inorganic secondary particles particularly so in winter months and there is a need to identify and assess sources of ammonia emissions in India.  相似文献   

Cavitation by Nonlinear Interaction Between Inertial Alfvén Waves and Magnetosonic Waves in Low Beta Plasmas     

Sanjay Kumar  R. P. Sharma  H. D. Singh 《Solar physics》2011,270(2):523-535

This paper presents the model equations governing the nonlinear interaction between dispersive Alfvén wave (DAW) and magnetosonic wave in the low-β plasmas (β≪m _e/m _i; known as inertial Alfvén waves (IAWs); here \upbeta = 8pn₀T /B₀²\upbeta = 8\pi n_{0}T /B_{0}^{2} is thermal to magnetic pressure, n ₀ is unperturbed plasma number density, T(=T _e≈T _i) represents the plasma temperature, and m _e(m _i) is the mass of electron (ion)). This nonlinear dynamical system may be considered as the modified Zakharov system of equations (MZSE). These model equations are solved numerically by using a pseudo-spectral method to study the nonlinear evolution of density cavities driven by IAW. We observed the nonlinear evolution of IAW magnetic field structures having chaotic behavior accompanied by density cavities associated with the magnetosonic wave. The relevance of these investigations to low-β plasmas in solar corona and auroral ionospheric plasmas has been pointed out. For the auroral ionosphere, we observed the density fluctuations of ∼ 0.07n ₀, consistent with the FAST observation reported by Chaston et al. (Phys. Scr. T84, 64, 2000). The heating of the solar corona observed by Yohkoh and SOHO may be produced by the coupling of IAW and magnetosonic wave via filamentation process as discussed here.  相似文献   

A record of ductile syn-intrusional fabrics to post solidification cataclasis: Magnetic fabric analysis of neoproterozoic Mirpur and Mt. Abu Granitoids,NW India     

Helga de Wall  Stefan Schöbel  Manoj K. Pandit  Kamal K. Sharma  J. Just 《Journal of the Geological Society of India》2010,75(1):239-253

The Mirpur granite body represents a relatively small (10 km²) pluton intruded along the northern margin of the adjacent Mt. Abu batholith (∼125 km²) in NW India. It is a visibly undeformed alkali feldspar rich pink granite; in contrast, the Mt. Abu is a composite granitoid body and variably deformed. Both are intruded by rhyolitic dykes and the terminal magmatic events in both the cases are mafic dykes. The AMS (Anisotropy of Magnetic Susceptibility) data identify the Mt. Abu with SE-dipping foliations and subvertical lineations as a single structural domain while the Mirpur granite body shows two domains characterized by predominantly E — W trend of magnetic foliation in the eastern part (domain I) and N — S orientations in the western part (domain II). The domain I shows magmatic fabrics, typical for the peraluminous granites of Malani Igneous Suite (MIS). Change in fabric orientation in the domain II has resulted from cataclasis wherein the samples show destruction of the original E — W fabric and complete transposition by N — S trends. The foliations in the Mt. Abu granites have been related to SE orientation of maximum horizontal stress. The same maximum stress direction can be inferred from dyke orientation in the Mirpur granite, which is interpreted as continuation of the tectonic imprint in this region during emplacement of both the granites. Age of the cataclastic overprint with a predominant N — S orientation is not yet constrained but corresponds with the trend of the nearby Sindreth basin within the Malani Igneous Suite. The Neoproterozoic tectonic scenario for the region has been interpreted in terms of an ongoing crustal convergence and granitic magma emplacement against the back stop offered by the rigid Delhi Fold Belt.  相似文献   

Dissociation Constants of Protonated Oxidized Glutathione in Seawater Media at Different Salinities     

Pasquale Crea  Concetta De Stefano  Frank J. Millero  Silvio Sammartano  Virender K. Sharma 《Aquatic Geochemistry》2010,16(3):447-466

Oxidized glutathione (GSSG), which has four carboxylic and two amino groups, interacts with metal ions and may affect the bioavailability and geochemistry of metals in natural waters. In the present paper, six stepwise protonation constants K^\textH_i K^{\text{H}}_{i} for GSSG were measured as a function of salinity, S = 5–35‰ at t = 25°C (and in NaCl/MgCl₂ mixtures at different ionic strengths), in order to provide thermodynamic data for their acid base properties, which are useful for studying the interaction with metals in these media. The protonation enthalpies (ΔH _i /kJ mol⁻¹) were also determined at t = 25°C. The results were interpreted using the SIT model and Pitzer equations. The seawater model with the interaction parameters accounts for the differences between the values in NaCl and seawater. The results suggest that it is important to consider all of the ionic interactions in natural waters in examining the proton dissociation of GSSG.  相似文献   

Landslide susceptibility zonation of the Chamoli region, Garhwal Himalayas, using logistic regression model   总被引：5，自引：2，他引：3  

Shivani Chauhan  Mukta Sharma  Manoj K. Arora 《Landslides》2010,7(4):411-423

A remote sensing and Geographic Information System-based study has been carried out for landslide susceptibility zonation in the Chamoli region, part of Garhwal Himalayas. Logistic regression has been applied to correlate the presence of landslides with independent physical factors including slope, aspect, relative relief, land use/cover, lithology, lineament, and drainage density. Coefficients of the categories of each factor have been obtained and used to assess the landslide probability value to ultimately categorize the area into various landslide susceptibility zones; very low, low, moderate, high, and very high. The results show that 71.13% of observed landslides fall in 21.96% of predicted very high and high susceptibility zone, which in fact should be the case. Furthermore, lineament first buffer category (0–500 m) and the east and south aspects are the most influential in causing landslides in the region.  相似文献   

Numerical model and flume experiments of single- and two-layered hillslope flow related to slope failure   总被引：1，自引：0，他引：1  

Raj Hari Sharma  Hajime Nakagawa 《Landslides》2010,7(4):425-432

A hillslope flow model is developed considering 3D saturated and unsaturated flow of water during rainfall events. A finite difference-based numerical model of hillslope flow processes is developed. Four different experiments are done to see the effects of a single- and double-layered soil in pore-water pressure dynamics and slope failure. Results from the numerical model are verified with experimental results. The numerical and experimental values of the pore-water pressure and moisture contents are in good agreement. The results show that the hillslope heterogeneity caused by multiple layers of soil has greater influence on hillslope pore-pressure dynamics and slope failure patterns. The depth of slope failure shows high dependency on layering characteristics of the soil slope and pattern of rainfall. The proposed model provides a perspective on failure mechanism of a single- or double-layered slope under rainfall infiltration.  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