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121.
This paper presents the study of a nonlinear process in the solar corona where dispersive Alfvén waves (DAWs) may lead to coronal heating. We present the model equations governing the nonlinear excitation of the fast waves (FWs) by DAWs in low-β plasmas (β≪m
e/m
i as applicable to the solar corona). By properly considering the ponderomotive nonlinearity, we have derived the equations
for the decay waves, namely the FWs and other DAWs. The expressions for the coupling coefficients of the three-wave interaction
have been derived. The growth rate of the instability is also calculated; we have found that the value of the decay growth
time turns out to be of the order of milliseconds at the pump DAW amplitude B
0y
/B
0=10−3. This time scale is much shorter than the observed time scales (a minute or less) for coronal heating, as inferred from images
obtained by instruments on board Yohkoh and the Solar and Heliospheric Observatory (SOHO). 相似文献
122.
Source and distribution of trace metals and nutrients in Narmada and Tapti river basins,India 总被引:2,自引:1,他引:1
The study was designed to establish the distributions of trace metals, dissolved organic carbon, and inorganic nutrients as
well as to assess the extent of anthropogenic inputs into the Narmada and Tapti rivers. Water and sediment qualities are variable
in the rivers, and there are major pollution problems at certain locations, mainly associated with urban and industrial centers.
The metal concentrations of samples of the aquatic compartments investigated were close to the maximum permissible concentration
for the survival of aquatic life, except for higher values of Cu (5–763 μg l−1), Pb (24–376 μg l−1), Zn (24–730 μg l−1), and Cr (70–740 μg l−1) and for drinking water except for elevated concentrations of metals such as Pb, Fe (850–2,060 μg l−1), Cr, and Ni (20–120 μg l−1). In general, the concentrations of trace metals in the rivers vary down stream which may affect the “health” of the aquatic
ecosystem and may also affect the health of the rural community that depends on the untreated river water directly for domestic
use. The assessment of EF, I
geo, and PLI in the sediments reveals overall moderate pollution in the river basins. 相似文献
123.
Sanjay Kumar Mehta M. Venkat Ratnam B.V. Krishna Murthy 《Journal of Atmospheric and Solar》2011,73(17-18):2462-2473
The characteristics of the cold point tropopause (CPT), convective tropopause (COT) and tropical tropopause layer (TTL) in the tropical region at different longitudes are studied using radiosonde data at 5 stations in the tropical belt (±15°) and high resolution GPS radiosonde data from April 2006 to December 2008 at Gadanki (13.5°N, 79.2°E) also a tropical station. The CPT over Gadanki is found to be higher than over the rest of the stations. This aspect is further confirmed using COSMIC GPS RO observations. In the Northern Hemisphere (NH) winter, the CPT is coldest over stations in the Pacific region compared to the other stations while in the NH summer, it is coldest at Gadanki, a station in the Indian monsoon region. The range of seasonal variation of the CPT temperature is found to be quite small over Gadanki compared to the other stations whereas that of the CPT altitude is nearly the same. 相似文献
124.
M. Venkat Ratnam M. Roja Raman Sanjay Kumar Mehta Debashis Nath B.V. Krishnamurthy M. Rajeevan S. Vijaya Bhaskara Rao D. Narayana Rao 《Journal of Atmospheric and Solar》2011,73(7-8):731-740
To investigate the sub-daily variation in Tropical Easterly Jet (TEJ), a few special experiments have been conducted with mesosphere–stratosphere–troposphere (MST) radar located at Gadanki(13.5°N, 79.2°E) under Study on Atmospheric Forcing and Responses (SAFAR) campaign during 2008–2009. Large sub-daily changes in the TEJ characteristics are observed within a day in addition to day-to-day changes. Based on this observational study, three possible mechanisms for the sub-daily variations are proposed i.e., (1) motion of TEJ core, (2) large updrafts and downdrafts, and (3) strong wave activity. Interestingly, TEJ peak altitude is seen above the Cold Point Tropopause altitude for about 42% of the days. 相似文献
125.
Simultaneous Estimation of Geologic and Reservoir State Variables Within an Ensemble-Based Multiple-Point Statistic Framework 总被引:1,自引:1,他引:0
Liangping Li Sanjay Srinivasan Haiyan Zhou J. Jaime Gómez-Hernández 《Mathematical Geosciences》2014,46(5):597-623
Assessment of uncertainty due to inadequate data and imperfect geological knowledge is an essential aspect of the subsurface model building process. In this work, a novel methodology for characterizing complex geological structures is presented that integrates dynamic data. The procedure results in the assessment of uncertainty associated with the predictions of flow and transport. The methodology is an extension of a previously developed pattern search-based inverse method that models the spatial variation in flow parameters by searching for patterns in an ensemble of reservoir models. More specifically, the pattern-searching algorithm is extended in two directions: (1) state values (such as piezometric head) and parameters (such as conductivities) are simultaneously and sequentially estimated, which implies that real-time assimilation of dynamic data is possible as in ensemble filtering approaches; and (2) both the estimated parameter and state variables are considered when pattern searching is implemented. The new scheme results in two main advantages—better characterization of parameters, especially for delineating small scale features, and an ensemble of head states that can be used to update the parameter field using the dynamic data at the next instant, without running expensive flow simulations. An efficient algorithm for pattern search is developed, which works with a flexible search radius and can be optimized for the estimation of either large- or small-scale structures. Synthetic examples are employed to demonstrate the effectiveness and robustness of the proposed approach. 相似文献
126.
In this note, we compare the LiNbO3 and Piezo-Electrically(PE) servo controlled air gap Fabry-Perot etalons for observing the Sun. An identical test setup was
used to evaluate the instrumental parameters of the two etalons. It is found that for the etalons with similar finesse the
advantage of using PE Etalons is tunability over entire Free Spectral Range. On the other hand, the LiNbO3 etalons have advantage of wider acceptance angle.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
127.
Sanjay Jain 《Journal of Astrophysics and Astronomy》1997,18(4):363-379
In a universe whose elementary constituents are point particles there does not seem to be any obvious mechanism for avoiding
the initial singularities in physical quantities in the standard model of cosmology. In contrast in string theory these singularities
can be absent even at the level where spacetime is treated classically. This is a consequence of the basic degrees of freedom
of strings in compact spaces, which necessitate a reinterpretation of what one means by a very small universe. We discuss
the basic degrees of freedom of a string at the classical and quantum level, the minimum size of strings (string uncertainty
principle), the t-duality symmetry, and string thermodynamics at high energy densities, and then describe how these considerations
suggest a resolution of the initial singularity problem. An effort has been made to keep this writeup self-contained and accessible
to non-string theorists. 相似文献
128.
Natural Hazards - The precise focal depth of earthquakes is a crucial parameter for better characterising of complex tectonic zones, especially where seismogenic faults occur at different depths.... 相似文献
129.
Pallabee Choudhury Kalpna Gahalaut Rakesh Dumka V. K. Gahalaut Abhay Kumar Singh Sanjay Kumar 《Environmental Earth Sciences》2018,77(22):770
A continuous GPS measurement site, ISRR, at Gandhinagar (Western India), documented ~?5 mm/year of surface subsidence rate during 2009–2016. Preliminary modelling using an analytical solution indicates that the observed surface subsidence rate at the ISRR site is consistent with the ground water depletion reported from Gandhinagar. An assessment of data from GPS sites at Lucknow and Varanasi in the Indo-Gangetic plains in Northern India does not indicate any significant subsidence at these sites which is also consistent with the in situ observations of insignificant depletion of ground water in the region. 相似文献
130.