Diffusion of small light particles in a solvent of large massive molecules

We study diffusion of small light particles in a solvent which consists of large heavy particles. The intermolecular interactions are chosen to approximately mimic a water-sucrose (or water-polysaccharide) mixture. Both computer simulation and mode coupling theoretical (MCT) calculations have been performed for a solvent-to-solute size ratio five and for a large variation of the mass ratio, keeping the mass of the solute fixed. Even in the limit of large mass ratio the solute motion is found to remain surprisingly coupled to the solvent dynamics. Interestingly, at intermediate values of the mass ratio, the self-intermediate scattering function of the solute, F_{s}(k,t) (where k is the wavenumber and t the time), develops a stretching at long time which could be fitted to a stretched exponential function with a k-dependent exponent, \beta. For very large mass ratio, we find the existence of two stretched exponentials separated by a power law type plateau. The analysis of the trajectory shows the coexistence of both hopping and continuous motions for both the solute and the solvent particles. It is found that for mass ratio five, the MCT calculations of the self-diffusion underestimates the simulated value by about 20 %, which appears to be reasonable because the conventional form of MCT does not include the hopping mode. However, for larger mass ratio, MCT appears to breakdown more severely. The breakdown of the MCT for large mass ratio can be connected to a similar breakdown near the glass transition.Comment: RevTex4, 9 pages, 10 figure

Characterization of Limestone Sample from Northeast India and its Implication on Beneficiation

Two limestone samples, from the same source (Assam, north-east India) have been petromineralogically characterized. In hand specimens, both samples are quite similar and are highly fossiliferous. Under optical microscope the fossils that are indentified belong mostly to two different Phy-llum, viz., Protozoa and Mollusca. The Protozoans are mainly Foraminifera and the Molluscans are Lamellibran-chia. Both categories have been petrified to calcium carbonate only and the fossils are embedded in a lime matrix. Due to the dominance of Nummulite fossils, the samples can be named as 'Nummulitic limestones'.The fossil records indicate that the limestones may be of Eocene age (< 65 million years)

Coal Mining in Meghalaya - a boon or bane?

Thin seams of coal occur assiciated with the Lakadong sandstones of Eocene age in the Jaintia Hills of Megha-laya. These Tertiary coals are low-ash coking coals but due to their high sulfur content they do not find proper market in the iron and steel industries. However, they are being mined rampantly for use as a fuel for other small and medium-scale industries such as power, cement, tea, fertilizer and bricks etc. Due to unscientific mining methods the environment is seriously affected destroying the land, soil, forest, water and the natural heritages. The law of the land is also a major bottleneck for persuading large-scale integrated mechanized mining by public and private sectors. Government efforts are yet to deliver a clear cut mineral and mining policy or any significant results towards protecting the environment. This is a serious issue which needs attention of the policy makers, planners, administrators, mining engineers, geo-enVironmentalists, scientists, technocrats, entre-preneurs and academicians to discuss, deliberate and suggest some solution for the benefit of the people of Meghalaya as well as for the protection of the environment

Role of B-ring of colchicine in its binding to tubulin

The chemical specificity of the colchicine-binding site of tubulin is less stringent for the presence of the B-ring than the A- and C-rings of colchicine, Colchicine analogues with modifications in the B-ring bind to tubulin at the same site as colchicine. Analogues with smaller or no substituents in the B-ring bind tubulin remarkably faster than colchicine. Thus, a compound without the B-ring [2-methoxy-5-(2',3',4'-trimethoxyphenyl)tropone] binds tubulin even at 4 °C and the binding is almost instantaneous at 37 °C. Colcemid and 2-methoxy-5-(2',3',4'-trimethoxyphenyl)tropone bind reversibly to tubulin, whereas colchicine and desacetamidocolchicine bind almost irreversibly, suggesting that the size of the B-ring moiety of colchicine is not related to the reversibility of binding. We conclude that although the presence of the B-ring of colchicine does not appear to be an essential prerequisite for the drug-tubulin interaction, the B-ring substituents play an important role in determining the binding properties of colchicine to tubulin

Effect of Fibonacci Modulation On Superconductivity

We have studied finite-sized single band models with short range pairing interactions between electrons in presence of diagonal Fibonacci modulation in one dimension. Two models, namely the attractive Hubbard model and the Penson-Kolb model, have been investigated at half-filling at zero temperature by solving the Bogoliubov-de Gennes equations in real space within a mean field approximation. The competition between ``disorder'' and the pairing interaction leads to a suppression of superconductivity (of usual pairs with zero centre-of-mass momenta) in the strong-coupling limit while an enhancement of the pairing correlation is observed in the weak-coupling regime for both the models. However, the dissimilarity of the pairing mechanisms in these two models brings about notable difference in the results. The extent to which the bond ordered wave and the $\eta$-paired (of pairs with centre-of-mass momenta = $\pi$) phases of the Penson-Kolb model are affected by the disorder has also been studied in the present calculation. Some finite size effects are also identified.Comment: 14 pages, 13 figure

Analysis of three-component aeromagnetic data

The numerical method of obtaining three field components from total field measurements, using double Fourier series expansion, is presented. The expressions for moments of the anomalous field components over a finite area are given. The magnitude and direction of the magnetization vector indicate that the vertical component of the magnetic field calculated from total field observations is more accurate at higher geomagnetic latitudes than at lower latitudes. The opposite is true for the horizontal components. The error in determining the magnetization vector directions are significantly large over most of the range of variation of declination and inclination of the vector, demonstrating the practical limitations of computing field components from total field data even under the best of conditions

Colchicine binding activity of rat brain polysomes

In this communication, we report the presence of a unique colchicine-binding activity in the polysomes of rat brain. This drug-binding property, is somewhat similar to that of tubulin isolated from many sources; however, it differs in several bio-chemical characteristics such as (i) thermal stability of colchicine-binding site, (ii) protection of binding site by vinblastine and (iii) time required for binding equilibration. Such binding of colchicine to the polysomes is most probably due to the presence of a nascent peptide chain of tubulin in the polysome

Study of Beta Equilibrated 2+1 Flavor Quark Matter in PNJL Model

We report a first case study of the phase diagram of 2+1 flavor strongly interacting matter in $\beta-$equilibrium, using the Polyakov$-$Nambu$-$Jona-Lasinio model. Physical characteristics of relevant thermodynamic observables have been discussed. A comparative analysis with the corresponding observables in the Nambu-Jona-Lasinio model is presented. We find distinct differences between the models in terms of a number of thermodynamic quantities like the speed of sound, specific heat, various number densities as well as entropy. The present study is expected to give us a better insight into the role that the superdense matter created in heavy ion collision experiments play in our understanding of the properties of matter inside the core of supermassive stars in the Universe