Exponential decay for damped Klein-Gordon equations on asymptotically cylindrical and conic manifolds

We study the decay of the global energy for the damped Klein-Gordon equation on non-compact manifolds with finitely many cylindrical and subconic ends up to bounded perturbation. We prove that under the Geometric Control Condition, the decay is exponential, and that under the weaker Network Control Condition, the decay is logarithmic, by developing the global Carleman estimate with multiple weights

The contribution of sidewall light extraction to efficiencies of polygonal light-emitting diodes shaped with laser micromachining

The light extraction efficiencies of InGaN/GaN blue light-emitting diodes (LEDs) of different geometries ranging from a triangle to a decagon have been simulated by ray-tracing. The conventional rectangular LED was found to be the most inefficient among the investigated polygons, and light extraction through the device sidewalls was the key factor. The results were experimentally verified by fabricating LEDs shaped into polygons by nanosecond-pulsed laser micromachining, which proved the simulated results. The mechanism of light extrac-tion in polygonal LEDs is discussed in detail. © 2010 American Institute of Physics.published_or_final_versio

Laser micro-machining of three-dimensional microstructures in optical materials

We demostrate an advanced precision cutting tool using a 349 nm nanosecond pulsed UV laser micromachining setup. After expansion and collimation, the laser beam is directed vertically and focused with a high performance triplet lens. With an Al mirror inserted in the path of the convergent beam, the beam can be focused on a horizontal machining plane at any desired tilting angles. Microstructures of a wide range of geometries on hard materials can be formed using this custom machining method. Conventional linear and rotary machining on sapphire materials have been demonstrated.published_or_final_versionThe 2009 Spring Meeting of the Materials Research Society (MRS), San Francisco, CA., 13-17 April 2009. In Materials Research Society Symposium Proceedings, 2009, v. 1179, p. 99-10

Laser micromachining of optical microstructures with inclined sidewall profile

Laser micromachining has been proved to be a useful tool for the formation of microstructures in semiconductor and optical materials. It is also widely adopted for dicing of light-emitting diode chips. The authors propose a modified laser micromachining setup which enables three-dimensional structures to be formed. A mirror is inserted in the optical path between the focusing optics and the machining plane so that the beam strikes the sample at an oblique angle. By translating and/or rotating the sample as micromachining is carried out, various three-dimensional structures such as a pyramid or a conic section can be obtained. Trenches as small as 10 μm on sapphire have been realized with nanosecond ultraviolet laser pulses. Laser-induced damage, due to resolidification of the ablation melt, accumulates with increasing scans of the beam; it can be removed by chemical and mechanical treatment. © 2009 American Vacuum Society.published_or_final_versio

Behavioural insights into housing relocation decisions: The effects of the Beijing Olympics

This article examines the impact of mega events on Beijing housing market from a behavioural perspective. By exploring the situation surrounding the Beijing 2008 Summer Olympics, we analyse the relationship between mega-event regeneration and expected residential relocation outcomes. Our findings suggest that Beijing Olympic regeneration caused disadvantaged groups to anticipate relocation to undesirable areas, as a result of improved infrastructure, public security, and urban environment. Behavioural sciences research indicates that expectation influences decision-making by serving as a salient reference point. Agents who perceived themselves as in a disadvantaged position or holding a gloomy prospect of their future are more likely to end up in such a situation. This paper offers insights into an effect of mega event regeneration projects that has been largely overlooked in the literature, i.e., the expected housing relocation outcomes. The research calls for government intervention and public attention to this important behavioural aspect of mega-event effects.This is the accepted manuscript for a paper published in Habitat International Volume 47, June 2015, Pages 20–28, DOI: 10.1016/j.habitatint.2015.01.00

Laser micro-machining of three-dimensional microstructures in optical materials

We demostrate an advanced precision cutting tool using a 349 nm nanosecond pulsed UV laser micromachining setup. After expansion and collimation, the laser beam is directed vertically and focused with a high performance triplet lens. With an Al mirror inserted in the path of the convergent beam, the beam can be focused on a horizontal machining plane at any desired tilting angles. Microstructures of a wide range of geometries on hard materials can be formed using this custom machining method. Conventional linear and rotary machining on sapphire materials have been demonstrated.published_or_final_versionThe 2009 Spring Meeting of the Materials Research Society (MRS), San Francisco, CA., 13-17 April 2009. In Materials Research Society Symposium Proceedings, 2009, v. 1179, p. 99-10

Effects of sputtering and annealing temperatures on MOS capacitor with HfTiON gate dielectric

In this work, Al/HfTiON/n-Si capacitors with different sputtering and annealing temperatures are studied. Larger accumulation capacitance and flat-band voltage are observed for samples with higher sputtering or post-deposition annealing temperature. Gate conduction mechanisms are only affected by sputtering temperature slightly. The flat-band voltage shift and interface-state density at midgap under high-field gate injection and substrate injection are investigated, and the results imply electron detrapping in the gate dielectric. ©2009 IEEE.published_or_final_versionThe IEEE International Conference of Electron Devices and Solid-State Circuits (EDSSC 2009), Xi'an, China, 25-27 December 2009. In Proceedings of EDSSC, 2009, p. 209-21

Self-sensing composites: in-situ detection of fibre fracture

The primary load-bearing component in a composite material is the reinforcing fibres. This paper reports on a technique to study the fracture of individual reinforcing fibres or filaments in real-time. Custom-made small-diameter optical fibres with a diameter of 12 (±2) micrometres were used to detect the fracture of individual filaments during tensile loading of unreinforced bundles and composites. The unimpregnated bundles were end-tabbed and tensile tested to failure. A simple technique based on resin-infusion was developed to manufacture composites with a negligible void content. In both cases, optical fibre connectors were attached to the ends of the small-diameter optical fibre bundles to enable light to be coupled into the bundle via one end whilst the opposite end was photographed using a high-speed camera. The feasibility of detecting the fracture of each of the filaments in the bundle and composite was demonstrated. The in-situ damage detection technique was also applied to E-glass bundles and composites; this will be reported in a subsequent publication

Evaluation of InGaN/GaN light-emitting diodes of circular geometry

Blue GaN light emitting diodes (LEDs) in the shape of cuboids and circular disks have been fabricated by laser micromachining. The proposed circular geometry serves to enhance overall light extraction on a macro-scale and to improve uniformity of the emission pattern due to the rotational symmetry of the chip. Analysis of the chip shaping effect is carried out by ray-tracing simulations and further supported with mathematical modeling using ideal LED models, and subsequently verified with fabricated devices. In comparison, a 10% improvement in overall emission was observed for circular LEDs over the regular cuboids, consistent with simulations and calculations. The measured emission pattern from the circular LED confirms the axial symmetry of the emission beam. © 2009 Optical Society of America.published_or_final_versio

Angularly uniform white light-emitting diodes using an integrated reflector cup

We report on white light-emitting diodes (LEDs) with a truncated-conical (TC) geometry produced by laser micromachining. A blue LED was shaped into a circular disc with 50°-inclined sidewall using a modified laser micromachining setup. A layer of Al was coated onto the inclined sidewall and the bottom surface to form an integrated reflector. Due to the highly reflective mirror, laterally propagating photons are redirected into the upward direction, contributing to an increase of 21.7% of light intensity in the normal direction. With quantum dots applied to the surface, white light emission from this TC-LED structure demonstrated a 37% enhancement in color uniformity, compared with a conventional device. © 2010 IEEE.published_or_final_versio