Concept of spinsonde for multi-cycle measurement of vertical wind profile of tropical cyclones

Tropical cyclones and cyclogenesis are active areas of research. Chute-operated dropsondes jointly developed by NASA and NCAR are capable of acquiring high resolution vertical wind profile of tropical cyclones. This paper proposes a chute-free vertical retardation technique (termed as spinsonde) that can accurately measure vertical wind profile. Unlike the expendable dropsondes, the spinsonde allows multi-cycle measurement to be performed within a single flight. Proof of principle is demonstrated using a simulation software and results indicate that the GPS ground speed correlates with the wind speeds to within +/-5 km/h. This technique reduces flying weight and increases payload capacity by eliminating bulky chutes. Maximum cruising speed (Vh) achieved by the spinsonde UAV is 372 km/h.Comment: arXiv admin note: substantial text overlap with arXiv:1407.845

Opto-VLSI processing for reconfigurable optical devices

The implementation of Wavelength Division Multiplexing system (WDM) optical fibre transmission systems has the potential to realise this high capacity data rate exceeding 10 Tb/s. The ability to reconfigure optical networks is a desirable attribute for future metro applications where light paths can be set up or taken down dynamically as required in the network. The use of microelectronics in conjunction with photonics enables intelligence to be added to the high-speed capability of photonics, thus realising reconfigurable optical devices which can revolutionise optical telecommunications and many more application areas. In this thesis, we investigate and demonstrate the capability of Opto-VLSI processors to realise a reconfigurable WDM optical device of many functions, namely, optical multiband filtering, optical notch filtering, and reconfigurable-Optical-Add-Drop Multiplexing (ROADM). We review the potential technologies available for tunable WDM components, and discuss their advantages and disadvantages. We also develop a simple yet effective algorithm that optimises the performance of Opto-VLSI processors, and demonstrate experimentally the multi-function WDM devices employing Opto-VLSI processors. Finally, the feasibility of Opto-VLSI-based WDM devices in meeting the stringent requirements of the optical communications industry is discussed

Journey to the Typhoon

Abstract Application of UAVs (unmanned aerial vehicles) for tropical cyclone missions is an emerging area of research and recent advances include the concept of spinsonde for multi-cycle measurement of vertical wind profile within the storm. This work proposes the design of a typhoon UAV as part of a cost-effective approach for acquiring atmospheric data to improve prediction and refine models. Land-and carrier-based flight schemes are proposed in this study and computer simulations are carried out to investigate the flight performance. Results suggest that the UAV achieves a maximum cruising speed in excess of 350 km·h −1 with excellent spinsonde performance. Furthermore, the UAV is capable of performing high-alpha maneuvers as well as vertical landing, thus rendering it suitable for space-efficient operation whether on land or aircraft carrier

Demonstration of Tunable Optical Notch Filter Using 1-D Opto-VLSI Processor

An opto-very-large-scale-integrated (opto-VLSI)-based tunable optical filter structure is demonstrated. Filter tunability is achieved by reconfiguring the holographic diffraction grating of an opto-VLSI processor, allowing virtually any type of filter response to be synthesized. A proof-of-concept tunable notch filter with wavelength span of 7 nm is experimentally verifie

Density functional based tight binding study on the thermal evolution of amorphous carbon

Density functional based tight binding (DFTB) model is employed to study the sp3-to-sp2 transformation of diamond-like carbon at elevated temperatures. The understanding of which could lead to the direct-growth of graphene on a wide variety of substrates

Metallic nanostructures, ultrathin films and optical technologies for hydrogen storage and switchable mirrors

The ability of some hydrides to reversibly absorb hydrogen under the right conditions makes them potential candidates for hydrogen storage, while the change in electrical or optical properties during the metal-insulator transition can be used to realize devices of technological interests such as two-dimensional hydrogen diffusion indicators and smart windows. This thesis focuses primarily on the investigation of metal hydrides based on magnesium and palladium, in the form of both nanopowders and thin films. In general, samples prepared in the form of nanopowders were intended for hydrogen storage applications, while samples prepared in the form of thin film were intended for switchable mirror applications. Nanopowder samples were synthesized by ball milling, while the thin films were prepared by physical vapor deposition techniques such as pulsed laser deposition and thermal evaporation. The desorption capacity, thermodynamics, and kinetics of Ti- and Ni/Ti-catalyzed Mg hydrides were investigated using Sieverts-type apparatus and differential scanning calorimetry. Based on analysis of the van’t Hoff equation and the Kissinger equation, the addition of Ti and Ni as catalysts has been found to play a key role in improving the thermodynamic and kinetic properties of magnesium hydride by decreasing the desorption temperature and the activation energy. A combination of Ti and Ni is a more effective catalyst than either Ti or Ni alone, suggesting the existence of a synergetic effect. We propose and demonstrate a simple but effective real-time optical method to determine the Tdes and kinetics of freshly fabricated magnesium nanowires inside a transparent quartz tube, while it is still under the protective gas environment. The proposed characterization technique based on optical reflection requires only milligrams of sample and helps to eliminate the common problem of oxidation associated with removal and transport of the freshly fabricated nanostructures into an inert protective environment. This optical technique could be applied to any hydrogen storage material in powder form which shows a significant difference in its optical absorption between the hydride and the non-hydride phase. A three-color, 8-bit, 240 × 320 pixel imager was used to acquire the optical signals, and the image processing was peformed in MATLAB®. Magnesium films of various thicknesses were fabricated by pulsed laser deposition and capped with a palladium protective layer. The change in the kinetics as a function of film thickness was measured. Raman spectroscopy on the 11 nm magnesium hydride film reveals a small but detectable peak arising from the Eg phonon mode. The Raman frequencies of bulk magnesium hydride predicted by CASTEP calculations are included for comparison. We propose and demonstrate a multi-stacked structure intended for low-nanometer ultrathin films of various metal hydrides, which would enable them to simultaneously achieve an enhanced optical contrast equivalent to that of thicker films, yet be able to retain much of the rapid switching kinetics characteristic of low-nanometer ultrathin films. Such improvement in the performance will help to further extend the scope of applications, particularly in the area of dynamic switchable mirrors, where switching speed and high switching contrast are crucial. Future work will also be based on resonant photodesorption of hydrogen, as well as surface plasmon nanophotonics, both of which are aimed at improving the efficiency of hydrogen desorption of promising hydrides such as MgH2 or LiBH4

Characterization of Pd nano-thin films for high-speed switchable mirrors

We fabricated Pd thin films from 2 to 35 nm thick via thermal evaporation, and a hermetically sealed hydrogen optical cell was used to characterize the films for properties such as hydrogen fractional ratio, optical switching contrast (Weber contrast), and response and recovery times. An atomic force microscope with a high resolution scanning tip was used to study the evolution of the film morphology

Organic solar cells: evaluation of the stability of P3HT using time-delayed degredation

Despite the fact that the performance of organic solar cells is generally susceptible to degradation by moisture exposure, there has been suggestion that the photoactive layer (P3HT) is surprisingly resilient. This work attempts to confirm the stability of P3HT as an organic solar cell material by deliberately introducing water into the photoactive layer. A dramatic step drop in device performance during cell characterization is observed approximately one day after the device has been fabricated. The time-delayed step drop in output efficiency strongly suggests that moisture has little effect on the P3HT conducting polymer