Acoustic source localization in anisotropic plates

The conventional triangulation technique cannot locate the acoustic source in an anisotropic plate because this technique requires the wave speed to be independent of the propagation direction which is not the case for an anisotropic plate. All methods proposed so far for source localization in anisotropic plates require either the knowledge of the direction dependent velocity profile or a dense array of sensors. In this paper for the first time a technique is proposed to locate the acoustic source in large anisotropic plates with the help of only six sensors without knowing the direction dependent velocity profile in the plate. Experimental results show that the proposed technique works for both isotropic and anisotropic structures. For isotropic plates the required number of sensors can be reduced from 6 to 4.     

Bivariate Birnbaum–Saunders distribution and associated inference

Univariate Birnbaum–Saunders distribution has been used quite effectively to model positively skewed data, especially lifetime data and crack growth data. In this paper, we introduce bivariate Birnbaum–Saunders distribution which is an absolutely continuous distribution whose marginals are univariate Birnbaum–Saunders distributions. Different properties of this bivariate Birnbaum–Saunders distribution are then discussed. This new family has five unknown parameters and it is shown that the maximum likelihood estimators can be obtained by solving two non-linear equations. We also propose simple modified moment estimators for the unknown parameters which are explicit and can therefore be used effectively as an initial guess for the computation of the maximum likelihood estimators. We then present the asymptotic distributions of the maximum likelihood estimators and use them to construct confidence intervals for the parameters. We also discuss likelihood ratio tests for some hypotheses of interest. Monte Carlo simulations are then carried out to examine the performance of the proposed estimators. Finally, a numerical data analysis is performed in order to illustrate all the methods of inference discussed here.     

Kinetics and mechanism of the oxidation of oxalic acid and bioxalate ion by [ethylene bis (biguanide)] silver (III) cation in aqueous perchlorate media

In acidic aqueous media the complex [Ag^IIILL⁻)³⁺[L = ethylenebis (bi-guanide)] reacts quantitatively with oxalic acid and bioxalate ion to produce CO₂, Ag⁺ and L. Kinetic evidence indicates preequilibrium adduct formation, but the reactions appear to be outer-sphere with these adducts (I₁ and I₂) acting as kinetic dead ends.No Ag⁺ catalysis could be detected.     

Reconstruction of a tree from its homomorphic images and other related transforms

It is shown that a tree is uniquely reconstructable from its homomorphic images. In addition, the classes of elementary contractions and elementary partitions of a tree are also shown to possess this property. In each case, only the isomorphically distinct transforms of the tree are assumed given for the reconstruction. In the case of elementary contractions the proof uses the reconstruction property of a tree from its endpoint deleted subtrees, which is well-known.     

Working group report: Collider and B physics

The activities of the working group including some of the seminars are summarized. The written reports received are included.     

Base catalyzed intramolecular transamidation of 2-aminoquinazoline derivatives on solid phase

A novel intramolecular cyclo-elimination via transamidation on the Rink Amide AM resin under mild basic conditions is presented. The methodology led to the synthesis of an important class of cardiotonic agents: imdiazo- and pyrimido-quinazolines from the corresponding 2-aminoquinazoline hydrobromide salt under mild basic conditions. NMR based titration studies revealed the role of hydrobromide as a molecular switch, which on removal triggers the cyclisation of aminoquinazoline to tricyclic structures. The main advantage of transamidation under basic conditions over the TFA cleavage is the recyclability of the resin obtained after cyclo-elimination. This has been demonstrated by successive synthesis of four structurally diverse imidazoquianzolin-2-ones using the same batch of resin without any cross contamination.     

Construction of nonlinear σ-models in two and higher space-dimensions

An algorithm for constructing nonlinear σ-models in arbitrary space-dimensions m (m ≥ 2) is proposed and Hamiltonian estimates are found through the degree of mapping. The field models are constructed in general forms and the scaling-neutral models are shown to have exact soliton solutions which are (anti) self-dual when the corresponding topological charge is the degree of mapping. All known field models are shown to be particular cases of the general models proposed, which also give new models not investigated before.     

A theoretical study of stress-induced effects on Mössbauer impurities forming dislocations in some b.c.c. and f.c.c. metals

Pramana - The external stress values required to move the dislocations in phase with the Mössbauer impurities, forming edge dislocations in different crystals are evaluated. The vibrating...     

A new synthesis of n-blocked dihydrouracil and dihydroorotic acid derivatives using lithium tri-sec-butyl borohydride as reducing agent

1,3-Di-N-substituted uracil and its derivatives have been reduced with lithium-tri-$\text{sec}$-butyl borohydride to the corresponding 5,6-dihydro compounds in excellent yields. Alkylation of 5-position of uracil is also very conveniently accomplished.