Multi-laminate framework of soil models—plasticity formulation

This paper presents plasticity formulation of the multi-laminate framework of soil models. Soil element is assumed to be an assemblage of perfectly fitting polyhedral blocks and irreversible deformations are assumed to occur due to sliding, separation/closing of the boundaries. Using an appropriate summation of mechanisms, the total plastic strains are obtained by evaluating contributions from an infinite number of randomly oriented planes in space. The paper provides a general plasticity formulation and examines various constitutive theories which can be incorporated into the framework.     

Hydromagnetic thermal boundary-layer flow near an oscillating limiting surface

Unsteady hydromagnetic thermal boundary layer flow of an electrically conducting, viscous, incompressible fluid near a harmonically oscillating limiting surface (e.g. in stellar atmospheres) is considered when the viscous dissipation and the Joule heating terms are retained in the energy equation. Exact solution of the problem, with the aid of the Laplace transform technique, is obtained when the magnetic Prandtl number is unity. For the purpose of application and discussion of the results, the variations of the temperature and the rate of heat transfer (expressed in the form of the Nusselt number) are presented for different sets of values of the magnetic parameter for the case of two particular fluids — air and water — when the limiting surface is under the condition of either cooling or heating.     

Time delay between Hα and hard X-ray emissions during impulsive solar flares

This investigation shows that statistically there are significant time delays between H and hard X-ray (HXR) emissions during solar flares; most impulsive flares produce HXR emissions up to 1 min before and up to 2 min after the onset of H emission. HXR emissions are also found to be peaked up to 2 min before the H emissions.     

On the presence of SH in the sunspot spectrum

The expected equivalent widths of individual rotational lines of the most intense Q ₂ branch of the 0-0 band of the A ²-X²_i; system of S³²H and S³⁴H have been calculated in the umbral spectrum for five disk positions using Zwaan's (1974) sunspot model. Percentage abundance of S³⁴ in the terrestrial case has been considered valid in our calculations.Strong lines of S³²H and S³⁴H of the A-X band system should be detectable in the sunspot spectrum. The molecule SH may play a possible role as a major opacity source in the ultraviolet spectrum of sunspots along with the molecule OH in the upper layers (up to _0.5m = 1.0) wherefrom most of the continuum arises. Study of this molecule in the umbral spectrum may also provide the solar isotopic abundance ratio N(S³²)/N(S³⁴).     

Molecular line haze opacity in sunspots

It has been shown that bound-bound opacity due to electronic transitions of molecules CN, CaH, MgH, and TiO explains, in a first approximation, the line haze opacity postulated by Zwaan (1974) for the region 0.5 m to 0.9 m of the umbral spectrum.     

Unsteady hydromagnetic thermal boundary layer flow

With viscous dissipation and Joule heating taken into account, solution of the energy equation is obtained for unsteady hydromagnetic thermal boundary layer flow past a porous wall (e.g., surface of a star) in presence of a transverse magnetic field, under the condition of zero heat transfer between the fluid and the boundary — the so-called plate thermometer problem in MHD. Solution of the problem, in the form of power series, is obtained under certain valid simplifying assumptions, when (i) the wall is subjected to a normal velocity of suction/injection which is proportional tot ^–1/2, and (ii) the wall has a velocity given by t ⁿ . The variation of temperature is shown graphically and is followed by a quantitative discussion therein also signifying the importance of retaining the Joule heating term in the energy equation.Part I is the article inAstrophysics and Space Science, Vol.45, No. 2, 1976, pp. 397–410.On study-leave from Defence Science Laboratory, Delhi, India.     

Biogeochemical responses to late-winter storms in the Sargasso Sea,III—Estimates of export production using 234Th:238U disequilibria and sediment traps

Direct measurements of new production and carbon export in the subtropical North Atlantic Ocean appear to be too low when compared to geochemical-based estimates. It has been hypothesized that episodic inputs of new nutrients into surface water via the passage of mesoscale eddies or winter storms may resolve at least some of this discrepancy. Here, we investigated particulate organic carbon (POC), particulate organic nitrogen (PON), and biogenic silica (BSiO₂) export using a combination of water column ²³⁴Th:²³⁸U disequilibria and free-floating sediment traps during and immediately following two weather systems encountered in February and March 2004. While these storms resulted in a 2–4-fold increase in mixed layer NO₃ inventories, total chlorophyll a and an increase in diatom biomass, the systems were dominated by generally low ²³⁴Th:²³⁸U disequilibria, suggesting limited particle export. Several ²³⁴Th models were tested, with only those including non-steady state and vertical upwelling processes able to describe the observed ²³⁴Th activities. Although upwelling velocities were not measured directly in this study, the ²³⁴Th model suggests reasonable rates of 2.2–3.7 m d^?1.Given the uncertainties associated with ²³⁴Th derived particle export rates and sediment traps, both were used to provide a range in sinking particle fluxes from the upper ocean during the study. ²³⁴Th particle fluxes were determined applying the more commonly used steady state, one-dimensional model with element/²³⁴Th ratios measured in sediment traps. Export fluxes at 200 m ranged from 1.91±0.20 to 4.92±1.22 mmol C m^?2 d^?1, 0.25±0.08 to 0.54±0.09 mmol N m^?2 d^?1, and 0.22±0.04 to 0.50±0.06 mmol Si m^?2 d^?1. POC export efficiencies (Primary Production/Export) were not significantly different from the annual average or from time periods without storms, although absolute POC fluxes were elevated by 1–11%. This increase was not sufficient, however, to resolve the discrepancy between our observations and geochemical-based estimates of particle export. Comparison of PON export rates with simultaneous measurements of NO₃^? uptake derived new production rates suggest that only a fraction, <35%, of new production was exported as particles to deep waters during these events. Measured bSiO₂ export rates were more than a factor of two higher (p<0.01) than the annual average, with storm events contributing as much as 50% of annual bSiO₂ export in the Sargasso Sea. Furthermore it appears that 65–95% (average 86±14%) of the total POC export measured in this study was due to diatoms.Combined these results suggest that winter storms do not significantly increase POC and PON export to depth. Rather, these storms may play a role in the export of bSiO₂ to deep waters. Given the slower remineralization rates of bSiO₂ relative to POC and PON, this transport may, over time, slowly decrease water column silicate inventories, and further drive the Sargasso Sea towards increasing silica limitation. These storm events may further affect the quality of the POC and PON exported, given the large association of this material with diatoms during these periods.     

North–south asymmetry of different solar activity features during solar cycle 23

A study on north–south (N–S) asymmetry of different solar activity features (DSAF) such as solar proton events, solar active prominences [total, low (?40°) and high (?50°) latitudes], Hα flare indices, soft X-ray flares, monthly mean sunspot areas and monthly mean sunspot numbers carried out from May 1996 to October 2008. Study shows a southern dominance of DSAF during this period. During the rising phase of the cycle 23 the number of DSAF approximately equals on both, the northern and the southern hemispheres. But these activities tend to shift from northern to southern hemisphere during the period 1998–1999. The statistical significance of the asymmetry time series using a χ²-test of goodness of fit indicates that in most of the cases the asymmetry is highly significant, meaning thereby that the asymmetry is a real feature in the N–S distribution of DSAF.     

Geoseismological investigation of the January 26, 2001 Bhuj earthquake in western peninsular India

Of the intraplate seismic events, the January 26, 2001 Bhuj earthquake (Mw 7.7) would be remembered as one of the deadliest, in which 13,805 human lives were lost, 0.177 million injured and a total of 1,205,198 houses were fully or partly damaged in 16 districts of Gujarat state with an estimated overall loss of Rs. 284, 23 million. The brunt of the calamity was borne by five districts, namely Kachchh, Ahmadabad, Rajkot, Jamnagar and Surendranagar, where 99?% of the total casualties and damage occurred. In the neighbouring parts of Sindhh Province of Pakistan, 40 human casualties were reported, and some buildings cracked in the Karachi city as well. In the Kachchh district of Gujarat state, the telecommunication links and power supply were totally disrupted, road and rail links partially impaired and water supply snapped at many places. The Bhuj airbase had to be closed for some time due to damage to the infrastructure. The macroseismic survey carried out by the Geological Survey of India in an area as large as 1.2 million?sq?km indicated an epicentral intensity as high as X on the MSK scale in an area of 780?sq?km in the central part of Kachchh rift basin. Apart from damages to civil structures, the January 26 earthquake induced conspicuous terrain deformation in the form of liquefaction features, structural ground deformation and low-order slope failures that were mainly prevalent within the higher intensity isoseists. Liquefaction occurred in an area of about 50,000?sq?km. The extensive plains of Rann of Kachchh, the marshy tracts of the Little Rann and the shallow groundwater table zones of Banni Land provided the most conducive geotechnical environments for the development of seismites. The liquefaction activity was profuse in seismic intensity zones X and IX, widespread in intensity VIII, subdued in intensity VII and stray in intensity VI. The common forms of liquefaction were sand blows/boils, ground fissures, craters, lateral spreading and slumping. Ground deformation of tectonic origin was witnessed in the epicentral tract. Such features, though much less subdued in comparison with the 1819 large earthquake (Mw 7.8) in region, occurred along the Kachchh Mainland fault (KMF) and along a transverse lineament, referred to as Manfara?CKharoi fault. The manifestations were in the form of fractures, displacement of strata, linear subsidence, upheaval, formation of micro-basins/micro-ridges, ripping off of rock surface, and at places violent forms of liquefaction. The localities where coseismic deformations were observed include Bodhormora, Sikra, Vondh, Chobari, Manfara and Kharoi. The 2001 event has demonstrated the role of local geology in influencing the ground motion characteristics and, therefore, the hazard estimation.