A concise overview on historical black carbon in ice cores and remote lake sediments in the northern hemisphere

Black Carbon(BC),as a driver of environmental change,could significantly impact the snow by accelerating melting and decreasing albedo.Systematic documentation ...     

Utilization of Basic Oxygen Furnace (BOF) slag in the production of a hydraulic cement binder

Basic Oxygen Furnace (BOF) slag is a major waste product generated during the steelmaking process. In India and in most industrial countries, the use of BOF slag as a road ballast and land filler has had a very long history. This being a low end use, a study was conducted to examine the possibility of converting the slag into a hydraulic binder. This paper describes the effect of cooling rate on mineralogy and cementing characteristics of normal BOF slag as well as iron oxide-devoid BOF slag. Specifically, the mineralogy and compressive strengths of heat-treated slags were compared with a conventional ordinary Portland cement. It was found that the slowly cooled slags did not show any cementing properties. The iron oxide-devoid slag, on slow cooling, disintegrated into fine powder. The water-cured cubic specimens of quenched slag products were tested for their compressive strengths. The cementing properties of the quenched slag products were improved by formation of hydraulic phases and showed considerable strength after 28 days of water curing.     

Excitation equilibrium for low lying levels in Cii,Niii, Oiv,Nevi, Mgviii,Six, and Siii

The populations of the excited state ² P _3/2 relative to the ground state ² P _1/2 have been investigated in C ii, N iii, O iv, Ne vi, Mg viii, Si x, and Si ii by considering all the radiative and collisional processes including the collisional transitions to the higher states which cascade to the upper level. The relative populations are used for the calculation of the line emissivities. The intensities of 76 320, 30 258 and 14 302 lines of Nevi, Mgviii, and Six ions respectively in the chromosphere-corona transition region are also calculated.     

Cometary impacts and ice-ages

Cycles of glaciation with an average period of 100 kyr are mediatedby impacts of cometary bolides. Ice-age conditions are dry and dusty withlow rates of precipitation. Comets in the mass range 10¹⁵ -10¹⁶ gimpacting the oceans could release enough water vapour into the atmosphereto enhance a depleted greenhouse effect. The energy deposited in the oceanswould also warm the surface layers, thus starting up anevaporation-precipitation cycle which ushers in warmer interglacialinterludes. The latter have neutral stability and are necessarilyshort-lived, eventually drifting back to glacial conditions on timescalesof 10 kyr.     

GEOLOGICAL STUDIES OF METAMORPHIC ROCKS IN THE VICINITY OF M.C.T./LESSER HIMALAYAN SHEAR ZONE, PARTS OF SIKKIM HIMALAYAS

GEOLOGICAL STUDIES OF METAMORPHIC ROCKS IN THE VICINITY OF M.C.T./LESSER HIMALAYAN SHEAR ZONE, PARTS OF SIKKIM HIMALAYAS     

Performance evaluation of soil mixtures treated with graphite and used as barrier fill material for high-level radioactive waste repository

Buffer/backfill material is an important engineering barrier in a deep geological repository of high-level radioactive waste (HLW). Its thermo-hydro-mechanical (THM) performance is very important for the safe and stable operation of the HLW repository system. Natural graphite powder mixed with sodium bentonite forms a buffer/backfill material that can dissipate heat quickly and provide strong isolation. In this paper, the THM characteristics of bentonite–sand–graphite–polypropylene fiber (BSGF) mixtures, used as a buffer/backfill material, were studied through a series of laboratory tests. The influence of graphite and polypropylene fiber contents on thermal conductivity, swelling pressure, hydraulic conductivity, and strength properties of BSGF mixtures with different sand contents was analyzed. Experimental results indicated that the graphite content, the maximum graphite mesh number, and the initial dry density of bentonite–graphite mixtures influenced the thermal conductivity of bentonite–graphite mixtures. The addition of polypropylene fiber was found to enhance the shear strength and inhibit cracking without significantly affecting the expansivity, permeability, and thermal conductivity of the BSGF mixtures. This study provides a new buffer/backfill material that can improve the stability, functionality, and thermal efficiency of the HLW repository.

     

Analysis of Families of Triple Close Approaches Occurring inStellar Systems in Three Dimensions (II)

This is the second paper of a trilogy dealing with the role of triple encounters with low initial velocities and equal masses in the evolution of stellar systems in three dimensional space. It shows how a condition of complete collapse may be perturbed to obtain well-established families of asymmetric triple close approaches with systematic regularity of escape with the formation of a binary. The main result is that when perturbation is introduced two close approaches called the first close approach and the second close approach occur in the same plane but the binary formed and the escaper are not in that plane. Further it is observed that the conjecture of Szebehely (1977) viz. `The measure of escaping orbits is significantly higher than the measure of stable orbits' is likely to be true. The third and last paper offers applications in stellar systems. This revised version was published online in July 2006 with corrections to the Cover Date.