Comparative study of thermal degradation behavior of graft copolymers of polysaccharides and vinyl monomers

The thermal degradation of graft copolymers of both polysaccharides (guar gum and xanthan gum) showed gradual decrease in mass loss. Pure guar gum degraded about 95% but pure xanthan gum degraded about 76% up to 1173.15 K, while graft copolymers of guar gum and xanthan gum degraded only 65–76% up to 1173.15 K. Acrylic acid grafted guar gum and xanthan gum showing two-step degradation with formation of anhydride and ketonic linkage during heating, same pattern of degradation was found for xanthan gum-g-methacrylic acid. Guar gum-g-acrylamide degraded in single step and xanthan gum-g-acrylamide started to degrade above 448.15 K and it is a two-stage process and imparts thermal stability due to the formation of imide linkage with evolution NH₃. Guar gum-g-methacrylamide degraded in three steps due to the loss of NH₃ and CO₂ successively. 4-vinyl pyridine grafted both polysaccharides show single step degradation due to loss of pyridine pendent. N-vinyl formamide grafted guar gum and xanthan gum started to degrade at about 427.15 K, showed two-stage degradation process with the evolution of CO and NH₃ molecules while guar gum-g-(N-vinyl-2-pyrrolidone) degraded into two steps by the loss of pyrrolidone nucleus. Gum-g-2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) showed two-step degradation processes in two successive degradation steps, while xanthan gum-g-AMPS has started degradation at about 427.15 K and completed in five degradation steps. Overall, it was found that the grafted polysaccharides are thermally more stable than pure polysaccharides.     

Evolving networks with bimodal degree distribution

Networks with bimodal degree distribution are most robust to targeted and random attacks. We present a model for constructing a network with bimodal degree distribution. The procedure adopted is to add nodes to the network with a probability p and delete the links between nodes with probability (1 − p). We introduce an additional constraint in the process through an immunity score, which controls the dynamics of the growth process based on the feedback value of the last few time steps. This results in bimodal nature for the degree distribution. We study the standard quantities which characterize the networks, like average path length and clustering coefficient in the context of our growth process and show that the resultant network is in the small world family. It is interesting to note that bimodality in degree distribution is an emergent phenomenon.     

Charged Higgs production at hadron colliders

We study the production and decay of charged Higgs bosons,H ^±, at TEVATRON and SSC energies as a function of the top massm _t and theH ^± massm _H . We give the cross sections for events arising from bothH ^±→τν andtb decays, together with those of the competing background processes. In particular, form _t >m _H we studyH ^± W ^? andW ⁺ W ^? production and thet→bτν decay.     

Synthesis and Diels-Alder reactions of 9-(4-benzyloxazolin-2-yl) anthracene

The synthesis of 9-(4-benzyloxazolin-2-yl)anthracene is described employing a new approach for the cyclisation of β-hydroxy amides to oxazolines. Thermal Diels-Alder reactions with N-methyl maleimide were found to be considerably slower than those previously observed. Essentially no diastereoselectivity was observed in these reactions as the benzyl stereodirecting group is remote from the reactive site. Minor rate enhancements were noticeable in the presence of some added Lewis acids, but with no diastereoselection.     

Efficient use of correlation entropy for analysing time series data

The correlation dimension D ₂ and correlation entropy K ₂ are both important quantifiers in nonlinear time series analysis. However, use of D ₂ has been more common compared to K ₂ as a discriminating measure. One reason for this is that D ₂ is a static measure and can be easily evaluated from a time series. However, in many cases, especially those involving coloured noise, K ₂ is regarded as a more useful measure. Here we present an efficient algorithmic scheme to compute K ₂ directly from a time series data and show that K ₂ can be used as a more effective measure compared to D ₂ for analysing practical time series involving coloured noise.      

f-α Spectrum of circle map

We present an analytic perturbative method for calculatingf(α) and the generalized dimensionD _q of the critical invariant circle of the polynomial circle map. The scaling behaviour is found to depend onz, the exponent defining the map. The asymptotic bounds of the scaling constantsα(z) andδ(z) are verified analytically.     

Studies on the relation between chemical constitution and ultraviolet absorption spectra of optically active and racemic compounds

The ultraviolet absorption spectra of camphor-β-sulphonyl-phenyl, (o-, m- andp-) tolyl, (α- and β-) naphthylamides have been determined in methyl alcohol, ethyl alcohol, and chloroform. The absorption spectra of all the compounds show two absorption bands: one varying from 267 to 284 mμ, the longer absorption maximum (λ_max) due to selective absorption of the keto group, and the other shorter one, ranging from 226 to 230 mμ, due to general absorption of the saturated molecules. The values of the characteristic wavelengths, λ₀₈ obtained from Drude’s one-term equation, have been compared with the absorption maxima, λ_max obtained by direct measurements. There are marked discrepancies in the values of λ₀ and λ_max. An explanation of the discrepancies is given. The nature of racemic modifications of the compounds has also been discussed.     

Linear scaling relations near onset of chaos for the Josephson junction model

The transition region from order to chaos is analysed numerically in a model system, viz. the Josephson junction. This reveals linear scaling relations for Lyapunov exponents and the Lyapunov dimensions with indices close to one.     

\tilde K'_3 —A new triangulation ofR n—A new triangulation ofR n

This paper introduces a new triangulation ofR ⁿ. The triangulation is to be applied for solving system of nonlinear equation through a fixed point technique.