http://hdl.handle.net/2289/22 Search the Channel search http://dspace.rri.res.in:8080/jspui/simple-search http://hdl.handle.net/2289/5586 Title: The structure of TGBA and TGBC phases near the lower critical twist<br/><br/>Authors: Venkatramanan, P.R.<br/><br/>Description: Restricted Access Sat, 29 Oct 2011 22:58:59 GMT http://hdl.handle.net/2289/5581 Title: Partitioning of ethanol in multi-component membranes: Effects on membrane structure<br/><br/>Authors: Polley, Anirban; Vemparala, Satyavani<br/><br/>Abstract: The molecular mechanism of ethanol and its effects on neurological function is far from clear. In this study, we investigate the effects of ethanol on various structural and dynamical properties of mixed bilayers consisting of different ratios of dipalmitoylphosphatidylcholine (DPPC), sphingomyelin (SM) and cholesterol that are typical constituents of neural cell membranes (Calderon et al., 1995) using molecular dynamics (MD) simulations. The bilayer properties such as thickness, hydrophobic chain order, and diffusive motion of individual lipids as well collective properties like lateral pressure profiles are affected by the presence of ethanol molecules. The simulations show that the percentage of cholesterol present in the bilayers significantly affects the depth of penetration of ethanol molecules. In particular, presence of very high concentration of cholesterol molecules enhances the rigidity of the bilayer and renders them resistant to the penetration of the ethanol molecules, consistent with experiments. Ethanol molecules compete with cholesterol molecules for hydrogen bonding and disrupt cholesterol–lipid interactions, especially those between SM and cholesterol. Ethanol molecules also affect the lateral pressure profiles in the bilayer systems. These results may have implications in understanding the general anesthetic mechanism and role played by cholesterol on partitioning of such anesthetic/alcohol molecules into cell membranes<br/><br/>Description: Restricted Access. Sat, 29 Dec 2012 22:58:59 GMT http://hdl.handle.net/2289/5579 Title: The diffeomorphism constraint operator in loop quantum gravity<br/><br/>Authors: Varadarajan, Madhavan<br/><br/>Abstract: We construct the diffeomorphism constraint operator at finite triangulation from the basic holonomy- flux operators of Loop Quantum Gravity, and show that the action of its continuum limit provides an anomaly free representation of the Lie algebra of diffeomorphisms of the 3- manifold. Key features of our analysis include: (i) finite triangulation approximants to the curvature, F-ab(i) of the Ashtekar- Barbero connection which involve not only small loop holonomies but also small surface fluxes as well as an explicit dependence on the edge labels of the spin network being acted on (ii) the dependence of the small loop underlying the holonomy on both the direction and magnitude of the shift vector field (iii) continuum constraint operators which do not have finite action on the kinematic Hilbert space, thus implementing a key lesson from recent studies of parameterised field theory by the authors. Features (i) and (ii) provide the first hints in LQG of a conceptual similarity with the so called "mu-bar" scheme of Loop Quantum Cosmology. We expect our work to be of use in the construction of an anomaly free quantum dynamics for LQG.<br/><br/>Description: Open Access. Sat, 29 Oct 2011 22:58:59 GMT http://hdl.handle.net/2289/5570 Title: Dynamics of passive and active particles in the cell nucleus<br/><br/>Authors: Hameed, Feroz M.; Rao, Madan; Shivashankar, G.V.<br/><br/>Abstract: Inspite of being embedded in a dense meshwork of nuclear chromatin, gene loci and large nuclear components are highly dynamic at C. To understand this apparent unfettered movement in an overdense environment, we study the dynamics of a passive micron size bead in live cell nuclei at two different temperatures ( and C) with and without external force. In the absence of a force, the beads are caged over large time scales. On application of a threshold uniaxial force (about 10 pN), the passive beads appear to hop between cages; this large scale movement is absent upon ATP-depletion, inhibition of chromatin remodeling enzymes and RNAi of lamin B1 proteins. Our results suggest that the nucleus behaves like an active solid with a finite yield stress when probed at a micron scale. Spatial analysis of histone fluorescence anisotropy (a measure of local chromatin compaction, defined as the volume fraction of tightly bound chromatin) shows that the bead movement correlates with regions of low chromatin compaction. This suggests that the physical mechanism of the observed yielding is the active opening of free-volume in the nuclear solid via chromatin remodeling. Enriched transcription sites at C also show caging in the absence of the applied force and directed movement beyond a yield stress, in striking contrast with the large scale movement of transcription loci at C in the absence of a force. This suggests that at physiological temperatures, the loci behave as active particles which remodel the nuclear mesh and reduce the local yield stress.<br/><br/>Description: Open Access. Fri, 28 Sep 2012 22:58:59 GMT