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Scaling behavior in the convection-driven Brazil nut effect
No full textOpen AccessThe Brazil nut effect is the phenomenon in which a large intruder particle immersed in a vertically shaken bed of smaller particles rises to the top, even when it is much denser. The usual practice while describing these experiments has been to use the dimensionless acceleration Γ=aω2/g, where a and ω are, respectively, the amplitude and the angular frequency of vibration and g is the acceleration due to gravity. Considering a vibrated quasi-two-dimensional bed of mustard seeds, we show here that the peak-to-peak velocity of shaking v=aω, rather than Γ, is the relevant parameter in the regime where boundary-driven granular convection is the main driving mechanism. We find that the rise time τ of an intruder is described by the scaling law τ˜(v-vc)-α, where vc is identified as the critical vibration velocity for the onset of convective motion of the mustard seeds. This scaling form holds over a wide range of (a,ω), diameter, and density of the intrude
Phase behavior of phospholipid-phytosterol membranes
No full textRestricted Access.We have studied the influence of some major phytosterols on the structure and phase behavior of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) membranes. Phase diagrams of the binary systems have been determined from X-ray diffraction data. All DPPC-phytosterol membranes studied exhibit a sterol-induced modulated phase (P beta) below the main transition, first reported in DPPC-cholesterol membranes. Structural features of this phase have been deduced from electron density maps calculated from the diffraction data. In addition, a re-entrant ripple phase is observed in DPPC-stigmasterol membranes as a function of temperature. The increase in the bilayer thickness in the fluid phase, due to the ordering of the lipid chains by the sterol molecules, has also been determined from the electron density profiles of the bilayers. All the phytosterols studied are found to increase the bilayer thickness, but to a lower extent compared to cholesterol. Some of the phytosterols phase separate from POPE even at very low concentrations, whereas the others have a similar effect on the phase behavior of POPE, with the temperature range over which the fluid lamellar phase occurs first decreasing and then increasing with increasing phytosterol concentration
Online reference zone: a gateway to reference resources in science and technology
No full textRestricted AccessA gateway named 'Online Reference Zone' has been designed, developed and hosted on the Indian
Statistical Institute, Bangalore centre libraiy in an effort to enhance visibility of open source online reference sources in science and technology. . The portal lists the open access onIine reference resources in select subjects which will be of great use to the scientific community at large. The paper explains the process of compiling comprehensive lists of open access reference resources in select subjects in Science and Tecl~nologyli ke Physics, Chemistiy, etc. The paper explains the federated search facility which searches the given web pages at the same time has been built and also an additional feature called 'Share a Link!' which lets the user to submit relevant links related to the site
Microwave controlled electromagnetically induced transparency inside an RF cavity.
No full textRestricted Access. Book chapter from Proceedings of International Conference on Fibre Optics and Photonics on Tera-Hertz Imaging (T3A)held at Chennai India, December 9-12, 2012We detail the construction of a microwave cavity resonator at 3.0357 GHz. We describe the effect of this resonator on the Electromagnetically Induced Transparency (EIT) phenomenon shown by Rubidium-85 atoms enclosed within the resonator
Effect of functionalized carbon nanotube on electro-optic and dielectric properties of a liquid crystal
No full textRestricted Access.The effect of octadecylamine functionalized carbon nanotube (ODACNT) on the electro-optic response and dielectric measurements of a liquid crystal (LC) were investigated. The threshold electric field of ODACNT doped LC 'less as compared to that of pure LC whereas the dielectric anisotropy is enhanced. The dielectric measurements reveal that the ODACNT doped LC exhibits a relaxation frequency of 30 Hz as compared to 3 Hz for pure LC. The tunneling current images obtained using atomic force microscope in spreading resistance mode indicate presence of ODACNT in close proximity of alignment layer. These results clearly indicate that ODACNT is influencing the nematic anchoring as well as the ordering in the bulk due to π − π interaction between LC, ODACNT and the alignment layer
A comparative study on the optical limiting properties of different nano spinel ferrites with Z-scan technique
No full textRestricted Access.We report the optical limiting properties of five different spinel ferrites, NiFe2O4, Ni0.5Zn0.5Fe2O4,
ZnFe2O4, Ni0.5Co0.5Fe2O4, and CoFe2O4 with an average particle grain size of 8 nm. The optical limiting
properties are investigated using the open aperture Z-scan technique. The obtained nonlinearity fits to a
two-photon like absorption process. Except for NiFe2O4, the observed nonlinearity has contributions
from excited state absorption. The optical limiting response is also studied against particle size and the
nonlinearity is found to increase with increasing particle size within the range of our investigations. On
comparing the optical limiting properties, ZnFe2O4 is found to be a better candidate for the optical
limiting applications. To the best of our knowledge, this is the first report where the optical limiting
properties of spinel ferrites are compare