Role of IUC-DAEF in promoting neutron beam research in India

Inter University Consortium for Department of Atomic Energy Facilities (IUC-DAEF) is an autonomous institute of the University Grants Commission and provides an interface between the university fraternity and the institutions of Department of Atomic Energy. Mumbai Centre of IUC-DAEF promotes and supports the use of neutron facilities at Dhruva reactor by the university scientists. To augment the existing neutron scattering facilities, IUC-DAEF has developed a neutron beam line at Dhruva reactor. The present paper gives a brief survey of the activities and achievements of Mumbai Centre of IUC-DAEF.     

N2O emission in the 4.5 μM region: high excitation of the bending mode transitions v1v2v3→v1v2(v3−1) with (2v1+v2)=5

Eight emission spectra of pure N₂O and N₂O + N₂ + He mixtures excited by a radio frequency discharge were recorded by Fourier Transform Spectroscopy at a resolution of 0.005 and 0.004 cm⁻¹ in the 4.5 μm region. Results (wavenumbers, band centers, and spectroscopic constants) concerning nine new vibrational transitions which have not been observed before, and which occur between highly excited levels of the bending mode are reported. The derived spectroscopic parameters allow us to reproduce the experimental wavenumbers with an RMS error lower than 4.5 × 10⁻⁴ cm⁻¹.     

Colossal magnetoresistance manganites: A new approach

Manganites of the LA_1−x Ca _x MnO₃ family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee _g states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and spatial correlation is the key to manganite physics. Dedicated to Professor C N R Rao on his 70th birthday     

Eulerian limit for 2D Navier-Stokes equation and damped/driven KdV equation as its model

We discuss the inviscid limits for the randomly forced 2D Navier-Stokes equation (NSE) and the damped/driven KdV equation. The former describes the space-periodic 2D turbulence in terms of a special class of solutions for the free Euler equation, and we view the latter as its model. We review and revise recent results on the inviscid limit for the perturbed KdV and use them to suggest a setup which could be used to make a next step in the study of the inviscid limit of 2D NSE. The proposed approach is based on an ergodic hypothesis for the flow of the 2D Euler equation on iso-integral surfaces. It invokes a Whitham equation for the 2D Navier-Stokes equation, written in terms of the ergodic measures.     

Magnetic structure of the interface between ferromagnet and antiferromagnet with parallel anisotropy axes

The structure of a spin spiral arising in the vicinity of the interface between a ferromagnet and a compensated antiferromagnet is studied in the case where the anisotropy axes of the layers are parallel to each other, and the evolution of this spiral in an external magnetic field is investigated.     

Charge injection in study of ferroelectric film properties

A model of a capacitor with a two-layer insulator has been considered. The current density exponentially depends on voltage in one of layers and is negligible in the other layer. The dependences of current on the time of voltage action and the charge-voltage characteristics of the two-layer capacitor have been calculated. The results obtained can be used to detect and study charge injection during polarization of ferroelectrics.