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.

Determination of the critical thickness of misfit dislocation multiplication using in situ double-crystal x-ray diffraction

Abstract: Two different kinds of critical thicknesses in the relaxation process were determined by means of in situ synchrotron double-crystal x-ray reflection topography and in situ synchrotron double-crystal x-ray diffractometry during the growth of an epilayer on a GaAs (001) substrate. The first critical thickness, derived from the in situ x-ray topographs, has been found to be in agreement with the Matthews and Blakeslee theory of misfit dislocation generation. We present measurements of the lattice constant perpendicular to the interface employing the rocking curves of the symmetric reflection and show that the deep drop in the plot of the lattice constant versus epilayer thickness may be related to misfit dislocation multiplication rather than to misfit dislocation generation processes. Our second critical thickness, derived from the in situ x-ray diffraction data has been found to be in reasonable agreement with recently published theories of misfit dislocation multiplication and substantial relaxation. .

Simulation of spacecraft secondary particle emissions and their energy deposition in CCD X-ray detectors

Abstract: A radiation transport suite has been used to simulate gamma-ray emissions produced in the X-ray Multi-Mirror Mission spacecraft by interactions of cosmic-rays and solar protons. Their energy deposition in charge coupled device detectors is a significant source of background.

Unsteady 3D Flow in a Single-Stage Transonic Fan: Part II — Unsteady Stator Exit Flow Field

Abstract: Detailed unsteady aerodynamic measurements have been taken in a single-stage transonic fan with a very high stator-hub loading. 2D dynamic yawmeter probes, capable of measuring mean and fluctuating levels of stagnation pressure, static pressure and yaw angle have been traversed at rotor exit, and downstream of the stator along with several types of pneumatic 3D probe. Part I of this paper describes the dynamic yawmeters and their performance, and presents ensemble-averaged stagnation pressure and random stagnation pressure unsteadiness measurements taken at rotor exit. These are used to illustrate the salient features of the rotor flow field, and the effects of compressor aerodynamic loading. Part II presents measurements taken at stator exit.Copyright © 1994 by ASME

Composite compatible printed circuit technology for the distribution of electrical signals

Abstract: The combination of sensing and actuating technologies within composite structures without affecting their structural performance is a major problem in the development, and acceptance, of smart materials technologies. A technique has been developed which uses a woven polyester cloth material, patterned with thin, integral, conductors to create a flexible, composite compatible, method of distributing electrical power throughout a structural panel. The cloths can be considered as printed circuit boards for inclusion within composite structures. It is capable of distributing power throughout a structure in a predetermined, controlled manner. This allows embedded components to be accurately positioned and many external connections to be made to the structure, via a PCB like connector, at a convenient position. The technique therefore considerably simplifies the construction of complex systems. The technology is demonstrated with reference to a piezoelectric actuated composite structure.

A discrete firing event analysis of the adaptive cluster expansion network.

Abstract: This paper describes how a hierarchical network for encoding sensor data (the adaptive cluster expansion network) can be constructed by linking together a number of elementary modules, each of which is a simple two-layer encoder/decoder network. To achieve this goal, a Bayesian analysis is applied to the discrete neural firing events that occur within each layer of the network.