Controlled engineering of spin polarized transport properties in a zigzag graphene nanojunction

We investigate a novel way to manipulate the spin polarized transmission in a two terminal zigzag graphene nanoribbon in presence of Rashba spin-orbit (SO) interaction with circular shaped cavity engraved into it. A usual technique to control the spin polarized transport behaviour of a nanoribbon can be achieved by tuning the strength of the SO coupling, while we show that an efficient engineering of the spin polarized transport properties can also be done via cavities of different radii engraved in the nanoribbon. Simplicity of the technique in creating such cavities in the experiments renders an additional handle to explore transport properties as a function of the location of the cavity in the nanoribbon. Further, a systematic assessment of the interplay of the Rashba interaction and the dimensions of the nanoribbon is presented. These results should provide useful input to the spintronic behaviour of such devices. In addition to the spin polarization, we have also included an interesting discussion on the charge transmission properties of the nanoribbon, where, in absence of any SO interaction a metal-insulator transition induced by the presence of a cavity is observed.Comment: 7 pages, 9 figures (Accepted in Europhysics Letters

Chirality Reversing Active Brownian Motion in Two Dimensions

We study the dynamics of a chirality reversing active Brownian particle, which models the chirality reversing active motion common in many microorganisms and microswimmers. We show that, for such a motion, the presence of the two time-scales set by the chirality reversing rate $\gamma$ and rotational diffusion constant $D_R$ gives rise to four dynamical regimes, namely, (I) $t \ll \text{min}(\gamma^{-1}, D_R^{-1})$, (II) $\gamma^{-1} \ll t \ll D_R^{-1}$, (III) $D_R^{-1} \ll t \ll \gamma^{-1}$ and (IV) $t \gg \text{max}(\gamma^{-1}, D_R^{-1})$, each showing different behaviour. The short-time regime (I) is characterized by a strongly anisotropic and non-Gaussian position distribution, which crosses over to a diffusive Gaussian behaviour in the long-time regime (IV) via an intermediate regime (II) or (III), depending on the relative strength of $\gamma$ and $D_R$. In regime (II), the chirality reversing active Brownian motion reduces to that of an ordinary active Brownian particle, with an effective rotation diffusion coefficient which depends on the angular velocity. Finally, we find that, the regime (III) is characterized by an effective chiral active Brownian motion.Comment: 13 pages, 7 figure

Evaluation of impact of landscape changes on large Mammal Habitats in Pench Tiger Reserve, Madhya Pradesh, India

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Real time simulation of rail dispacher operations

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (leaf 120).by Santanu Basu.S.M

Glutamate and cyclic AMP regulate the expression of galactokinase in Mycobacterium smegmatis

It was found that Mycobacterium smegmatis is unable to utilize galactose as the sole carbon source because the sugar alone cannot induce galactokinase. However, galactokinase was induced by glutamate alone, and was further stimulated by galactose. Rifampicin completely inhibited the glutamate-mediated expression of galK in both the absence and presence of galactose. Extracellular cAMP stimulated the expression of the enzyme only in the presence of glutamate plus galactose. The galK gene from M. smegmatis, including its upstream promoter region, was cloned in a plasmid in Escherichia coli. The expression of kinase from these clones in E. coli was dependent on cAMP and its receptor protein (CRP). The expression of UDP-galactose 4-epimerase was constitutive. This and other evidence suggests that the galK gene is not linked to galT and galE in the mycobacterial genome. In a glutamate-independent galactose-utilizing mutant (gin-1 mutant) of M. smegmatis, galK was expressed in the absence of both galactose and glutamate, while in the presence of galactose this expression was increased twofold in the absence of glutamate and fourfold in its presence. Extracellularly added cAMP reduced the expression of the enzyme in the presence of galactose plus glutamate nearly to the basal level. It is proposed that in M. smegmatis the galK gene is expressed from two different promoters; the expression from one promoter is dependent on glutamate but not on galactose and cAMP, while that from the other requires all three components. The role of galactose is possibly to derepress the latter promoter