2,241 research outputs found
Smooth crossing of line in a single scalar field model
Smooth double crossing of the phantom divide line has been
found possible with a single minimally coupled scalar field for the most simple
form of generalized k-essence cosmological model, in the presence of background
cold dark matter. Such crossing is a sufficiently late time transient phenomena
and does not have any pathological behaviour.Comment: 9 pages, 6 figure
Glass transition in Ultrathin Polymer Films : A Thermal Expansion Study
Glass transition process gets affected in ultrathin films having thickness
comparable to the size of the molecules. We observe systematic broadening of
glass transition temperature (Tg) as the thickness of the polymer film reduces
below the radius of gyration but the change in the average Tg was found to be
very small. Existence of reversible negative and positive thermal expansion
below and above Tg increased the sensitivity of our thickness measurements
performed using energy dispersive x-ray reflectivity. A simple model of Tg
variation as a function of depth expected from sliding motion could explain the
results. We observe clear glass transition even for 4 nm polystyrene film that
was predicted to be absent from ellipsometry measurements of thicker films.Comment: 11 pages, 5 figure
Cooperative jumps and hop-back motion in supercooled liquids near the glass transition in binary colloids
Brownian Dynamics simulations on binary charged colloids have been performed to get a liquid to crystal (at volume fraction Φ = 0.2) or glass (Φ = 0.3) as the temperature is lowered. The subdiffusive and staircase behaviours of the mean-squared displacements as well as the behaviour of van-Hove self-correlation functions for the supercooled liquid with Φ = 0.3 indicate strongly cooperative particle motion. The van-Hove distinct correlations follow a factorization property predicted by the mode-coupling theory. Most interestingly, a few particles show an interconnected cooperative hop and subseqent hop-back motion very close to the glass transition
Coupling parameters and the form of the potential via Noether symmetry
We explore the conditions for the existence of Noether symmetries in the
dynamics of FRW metric, non minimally coupled with a scalar field, in the most
general situation, and with nonzero spatial curvature. When such symmetries are
present we find general exact solution for the Einstein equations. We also show
that non Noether symmetries can be found.
Finally,we present an extension of the procedure to the Kantowski- Sachs
metric which is particularly interesting in the case of degenerate Lagrangian.Comment: 13 pages, no figure
Noether symmetry in the higher order gravity theory
Noether symmetry for higher order gravity theory has been explored, with the
introduction of an auxiliary variable which gives the only correct quantum
desccription of the theory, as shown in a series of earlier papers. The
application of Noether theorem in higher order theory of gravity turned out to
be a powerful tool to find the solution of the field equations. A few such
physically reasonable solutions like power law inflation are presented.Comment: 9 page
Extraction of density profile for near perfect multilayers
A simple inversion scheme, based on Born approximation, to determine the electron density profile of near perfect multilayers from specular X-ray reflectivity data has been presented. This scheme is useful for semiconductor multilayers and other thin films, which are grown almost according to the designed parameters. We also indicate the possibility of separating out the contribution of interdiffusion and roughness in electron density profiles of interfaces by utilizing information obtained from the analysis of diffuse scattering data. The extracted compositional profile was used to calculate structural details of epitaxial films along the growth direction. Simulated and metal organic vapor phase epitaxy grown InP/InxGa1−xAs/InP quantum-well systems have been used to demonstrate this scheme
Biological similarity of enterotoxins of Vibrio cholerae serotypes other than type 1 to cholera toxin and Escherichia coli heat-labile enterotoxin
Vibrio cholerae serotypes other than type 1, the so-called NAG vibrios, have been recognised as an important cause of diarrhoea. A few of them have been shown to produce an enterotoxin similar, immunologically and physiologically, to cholera toxin; and cholera toxin has been shown to be structurally, functionally and immunologically identical with Escherichia coli heat-labile toxin (LT). The present investigation has demonstrated biological similarities among cholera toxin, E. coli LT and enterotoxins produced by strains of V. cholerae of 59 serotypes other than 1, in the biological models, rabbit ileal loops and rabbit skin. Culture filtrates of almost all the strains were neutralised completely and all filtrates showed some neutralisation, in enterotoxic action and increase of permeability, by cholera antitoxin and E. coli LT antiserum. The partial neutralisation observed in a few strains was probably due to high concentrations of identical toxin rather than the presence of other toxic substances
Erosion - Deposition in Hooghly Estuary
An attempt has been made to give an overall idea of erosion-deposition at theBalari-Haldia-Gangra reach of the Hooghly estuary in India. The sediment transport relationships developed by van Rijn and AcKers- White have been tried. Calculation of bed-load transport has beenmade based on'bed material sizes, flow conditions, depth and width of the channels, during 1993-97 Comparison of the results indicates the discrepancies between calculated and observed quantum of deposition/erosion to the extent of 0.6 to 0 :8 times in case ofvan Rijn ' sequation and 0.8 to 1.8 times incase of Ackers-White's model. Results sugges that the Haldia-Balari channel is deteriorating due toaccumulation of sediment
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