Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

Device Applications of Side-Chain Ferroelectric Liquid Crystalline Polymer Films

Abstract: Side-chain ferroelectric liquid crystalline polymers are currently used in a number of applications, including displays and electrical sensors. Comparisons with existing technologies and materials indicate that relative to ceramics, such polymers have lower figures of merit but offer greater durability in sensor applications.

A theory of word frequencies and its application to dialogue move recognition

Abstract: Dialogue move recognition is taken as being representative of a class of spoken-language applications where inference about high-level semantic meaning is required from lower-level acoustic, phonetic or word-based features. Topic identification is another such application. In the particular case of inference from words, the multinomial distribution is shown to be inadequate for modelling word frequencies, and the multivariate Poisson distribution is a more reasonable choice. Zipf's law is used to model a prior distribution. This more rigorous mathematical formulation is shown to improve dialogue move classification both subjectively and quantitatively.

New synthesis routes for energetic materials using dinitrogen pentoxide. Discussion

Abstract: The harsh and unselective nature of conventional nitrating agents, based on nitricsulphuric acid mixtures or pure nitric acid, has led to the development of new nitration methodologies based on dinitrogen pentoxide (N 2 O 5 ) that overcome many of the draw backs of conventional media, especially when dealing with sensitive substrates. Two principal nitration system s have been developed : (i) N 2 O 5 in pure nitric acid, and (ii) N 2 O 5 in organic solvents, mainly chlorinated hydrocarbons. The former system possesses strength similar to mixed acid (HNO 3 - H 2 SO 4 ) system s and is therefore potent, but displays advantages such as ease of generation of the nitration reagent by electrolysis and com patibility with nitram ine products, facilitating the synthesis of nitram ine explosives as well as certain aromatic nitro compounds. The second system (N 2 O 5 /organic solvent) encompasses a much wider range of nitrations, and with suitable choice of substrate permits the generation of polynitrated species directly without the formation of acidic by-products, an important environmental consideration. These conditions are also compatible with sensitive substrates, particularly those possessing strained-ring heterocyclic skeletons; thus the nitration of such compounds with N2O5 perm its precursors for energetic polymers (e.g. polyNIMMO) to be prepared by selective nitration. Likewise, nitrated derivatives of suitably functionalized elastomeric pre-polymers (e.g. NHTPB ) can also be manufactured; both of the latter category of compound find important application as energetic binders for novel explosive and propellant compositions, notably low-vulnerability (LOVA) propellant charges.

Analysis of multilayer semiconductor rib waveguides with high refractive index substrates

Abstract: The waveguiding properties of semiconductor rib waveguides with high refractive index substates are studied using the spectral index method. The propagation constants of leaky modes in such two-dimensional structures are calculated for the first time. The method is applied to the design of high wall GaAs/AlGaAs rib waveguides. Results indicate that the number of low-loss modes can be controlled by careful positioning of the substrate relative to the guiding region.