Zeno blocking of interplanar tunneling by intraplane inelastic scattering in layered superconductors: a generalized spin-boson analysis

Following an earlier proposal that the observed temperature dependence of the normal-state c-axis resistivity of oxide superconductors can be understood as arising from the inhibition of electron transport along the c axis due to in-plane incoherent inelastic scatterings suffered by the tagged electron, we consider a specific form for the interaction Hamiltonian. In this, the tagged electron is coupled to bosonic baths at adjacent planes (the baths at any two planes being uncorrelated) and is coupled also to the intraplane momentum-flip degree of freedom via the bath degrees of freedom. Thus our model Hamiltonian incorporates the earlier proposed picture that each in-plane inelastic scattering event is like a measurement of which plane the electron is in, and this, as in the quantum Zeno effect, leads to the suppression of interplane tunneling. In the present scenario it is the baths which bring about a coupling between the intraplane and interplane degrees of freedom. For simplicity we confine ourselves to dynamics in two adjacent planes and allow for two states only, as far as momentum flips due to scattering are concerned. In the case when the intraplane dynamics is absent, our model reduces effectively to the usual spin-boson model. We solve for the reduced tunneling dynamics of the electron using a non-Markovian master equation approach. Our numerical results on the survival probability of the electron in the initial plane show that the intraplane momentum flips lead to further inhibition of the interplane tunneling over and above the inhibition effected by pure spin-boson dynamics

Mechanical activation of solids in processing of minerals and wastes

Recently, there has been an increasing interest in mechanical/mechanochemical activation of solids for developing new materials and metallurgical processes. In this paper, a brief overview of our research in this area is presented. Select applications of mechanical activation are discussed with emphasis on characterisation of activated materials, and the prospects and possibilities of developing improved/novel processes. The main applications covered include the Bayer process of alumina production, and blended cement manufacturing

Geopolymers, fly ash reactivity and mechanical activation

The foucs this paper is on the reactivity of fly ash in relation to its geopolymerisation, that is structure and properies of geopolymer. A comparision of the mechanically induced reactivity by vibration and attrition milling and glass content induced reactivity obtained through size classification in a high speed air classifier has been made. It has been shown that for the fly ash of nearly same size (~ 5 µm), mechanical activation results in higher reactivity or geopoymerisation rate as compared to the air classified samples. Reactvity can also be altered by mixing raw fly ash with processed fly ash. Much wider variation in the reactivity is possible by mixing raw fly ash with mechanically activated fly ash than with classified fly ash. Higher reactivity of the mechanically activated fly ash results higher strength vis-à-vis raw and air classified fly ash

Mechanical activation in blended cement processing

The foucs this paper is on the mechanically induced reactivity of granulated blast furnace slag and fly ash. Mechanical activation of blast furnace and fly ash is mill specific, that is, it depends on milling mechanism and mill dynamics. Slag after wet milling in an attrition mill hydrates completely in sharp contrast with ball milled slag of same fineness (~ 12 µm). The hydration product of attrition milled slag shows a number of unique characteristics, for example : increased crystallinity of the phases in the hydration product with an increase in the milling time, formation of cement phases that forms under hydrothermal conditions, etc. The vibratory milled fly ash showed higher lime reactivity vis-à-vis raw and attrition milled fly ash. The origin of mechanically induced reactivity, development of improved blended cements and their prospects are presented