Narrow Results

The effect of processing atmosphere on the microstructure and superconducting properties of MgB₂ was studied for bulk samples made using the in situ reaction technique under argon gas with three different levels of purity: ultra-high, high, and welding grade. The critical temperature, T_c, decreased by 0.5 K, while the full width at half maximum (FWHM) of the MgB₂ peaks, and the resistivity showed an increase in the sample processed in welding Ar. The critical current density, J_c, and the upper critical field, H_c2, for the welding Ar sample were improved in comparison with the samples treated in ultra-high and high purity argon. Optimal J_c in MgB₂ can be achieved by using readily available and economical welding grade Ar as the protective atmosphere instead of using ultra-high or high purity Ar.

The crucial role of nonlinear propagation effects in the self-guiding of femtosecond laser pulses required accurate representation of nonlinearities to describe them. In this paper, an improved theoretical model has been proposed to study the height distribution of the atmospheric nonlinear refractive index. The results show that the revised model obviously improves accurate estimation of nonlinear index at the long wavelength band. Based on the model, we also found the atmospheric nonlinear refractive index differs much from the lower atmosphere to the upper atmosphere. Our results are essential for engineering applications based on the long-distance ultrashort laser pulses’ transmission in diverse atmosphere.

A large number of clear nights at a given location is one of the key prerequisites for establishing an astronomical observatory. This parameter needs to be reliably determined before the site location is finalized. For an already exiting observatory site, monitoring of clouds on real-time basis helps automating many observing procedures, thus optimizing the scientific returns from the facility. We have developed an infrared (IR) scanning cloud monitor which generates a local sky-map and provides reliable information about the changing sky conditions. Our device measures the IR sky brightness temperature using a circular array of thermopile sensors mounted on a rotating system. In this paper, we give a detailed description of the instrument hardware, laboratory and on-site calibration procedures and further tests carried out to check the reliability of the device. The cloud monitor has been in regular use since its installation at the Indian Astronomical Observation (IAO), Hanle, Ladakh in 2015 December. We also present the analysis of a year long sky data to demonstrate the usefulness of the device.

This paper concerns with the adaptive based autolanding controller design by the means of MRAS (Model Reference Adaptive Systems) method. In that, Adaptive controller is used to design a controller which can land the aircraft smoothly on runway in severe conditions like gusts. A PID controller has also been designed to compare its performance with that of Adaptive controller. Two kinds of wind patterns, Strong and Very Strong in comparison to JFK Airport Downburst, have been induced to investigate the performance of the proposed controllers. Simulation results show that both controllers satisfy necessary conditions in presence of the strong wind but only Adaptive controller meets the necessary performance conditions, in presence of Very Strong wind. Therefore, this controller can expand the safety flight envelope of the aircraft.