Raman and photoluminescence characterization of focused ion beam patterned InGaN/GaN multi-quantum-wells nanopillar array

High crystal quality GaN nanopillar arrays containing InGaN/GaN multi-quantum wells (MQWs) have been fabricated by focused ion beam followed by wet etch treatments to remove the ion damage. The first order Raman spectra reveal a well-built additional peak when the diameter of the nanopillars is less than 220 nm. This peak is also observed in the GaN pillars without MQW and is clearly assigned to the surface optical (SO) mode originating from the A 1 phonon in wurtzite GaN. The frequency of this SO mode is found to be sensitive with the diameter and surface roughness of the nanopillars. Temperature-variable photoluminescence measurements show that a broadband emission in the as-grown sample split into the two well-resolved bands for nanopillars and the emission band at the higher energy side quickly thermally quenched. © 2011 American Institute of Physics.published_or_final_versio

An affected pedigree member analysis of linkage between the dopamine D2 receptor gene Taql polymorphism and obesity and hypertension

BACKGROUND: Dopamine modulates a variety of physiological functions including natriuresis and satiety. We have previously reported that the TaqI polymorphism of the dopamine D2 receptor (DD2R) gene is associated with both blood pressure and obesity indices in a normoglycaemic Hong Kong Chinese population. In this study, we present evidence confirming the linkage between this gene polymorphism, obesity and hypertension. METHODS: Two hundred and seventy-four siblings from 96 normoglycaemic hypertensive families were recruited, including 133 who were hypertensive. Central obesity was defined as a waist-to-hip ratio of > or = 0.9 and > or = 0.85 in males and females, respectively, and was identified in 99 of the siblings. The DD2R gene TaqI polymorphism was identified with a polymerase chain reaction based restriction fragment length polymorphism protocol. The affected pedigree member (APM) linkage analysis (sib-pair program, version 0.99.9, by D.L. Duffy) was used to assess for linkage between this gene polymorphism, obesity and hypertension in 73 families with siblings discordant for hypertension. RESULTS: The A1 allele frequencies were similar in the 133 hypertensive, and 141 normotensive siblings, including the 99 centrally obese siblings at 0.431, 0.421 and 0.418, respectively. APM linkage analysis suggested that the DD2R gene TaqI polymorphism had evidence of linkage with blood pressure (T = -1.86, P = 0.013), as well as with obesity (T = -1.58, P = 0.007). CONCLUSION: Our data in normoglycaemic Hong Kong Chinese supports that the DD2R gene TaqI polymorphism is a marker associated with the pathogenesis of obesity and hypertension.postprin

Temperature dependent distinct coupling and dispersions of heavy- and light-hole excitonic polaritons in ZnO

Distinct coupling behavior of heavy- and light-hole excitonic polaritons in ZnO was unveiled by investigating the optical reflectance spectra of a high quality ZnO single crystal as a function of temperature both experimentally and theoretically. A resonance like coupling region was found at a temperature of around 50 K at which several relevant physical quantities such as the transverse exciton transition energy, polarizability, and damping parameters of the two kinds of excitonic polaritons were revealed to overturn. Calculated dispersions correctly reflect the nature of coupled photon and exciton and reproduce the spectral structures of the interacting polaritons. © 2012 American Institute of Physics.published_or_final_versio

418 cm-1 Raman scattering from gallium nitride nanowires: Is it a vibration mode of N-rich Ga-N bond configuration?

A Raman-active vibration mode at 418 cm-1 is observed in wurtzite gallium nitride (GaN) nanowires synthesized by different growth methods. In particular, Raman scattering measurements of a number of GaN nanowires systematically prepared by nitriding Β- Ga2 O3 nanowires at different temperatures show an interesting evolution of the mode, revealing that it is most likely the vibration mode of N-rich octahedral Ga- N6 bonds. This idea is further supported by the high-resolution transmission electron microscopic observation. © 2007 American Institute of Physics.published_or_final_versio

Localized surface optical phonon mode in the InGaN/GaN multiple-quantum- wells nanopillars: Raman spectrum and imaging

An interesting phonon mode at around 685-705 cm -1 was clearly observed in the Raman spectra of InGaN/GaN multiple-quantum-wells nanopillars with different diameters at room temperature. The Raman peak position of this mode is found to show a distinct dependence on the nanopillar size, which is in well agreement with theoretical calculation of the surface optical (SO) phonon modes of nanopillars. Moreover, this kind of SO phonon was evidenced to be located on the pillar surface by using scanning confocal micro-Raman microscopy. © 2011 American Institute of Physics.published_or_final_versio

Inner surface enhanced femtosecond second harmonic generation in thin ZnO crystal tubes

2010-2011 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Early intervention for psychotic disorders: Real-life implementation in Hong Kong

Hong Kong is among the first few cities in Asia to have implemented early intervention for psychosis in 2001. Substantial changes in psychosis service have since taken place. We reviewed available outcome data in Hong Kong, with reference to the philosophy of early intervention in psychosis, discussing experience and lessons learned from the implementation process, and future opportunities and challenges. Data accumulated in the past decade provided evidence for the benefits and significance of early intervention programmes: patients under the care of early intervention service showed improved functioning, milder symptoms, and fewer hospitalizations and suicides. Early intervention is more cost-effective compared with standard care. Stigma and misconception remains an issue, and public awareness campaigns are underway. In recent years, a critical mass is being formed, and Hong Kong has witnessed the unfolding of public service extension, new projects and organizations, and increasing interest from the community. Several major platforms are in place for coherent efforts, including the public Early Assessment Service for Young people with psychosis (EASY) programme, the Psychosis Studies and Intervention (PSI) research unit, the independent Hong Kong Early Psychosis Intervention Society (EPISO), the Jockey Club Early Psychosis (JCEP) project, and the postgraduate Psychological Medicine (Psychosis Studies) programme. The first decade of early intervention work has been promising; consolidation and further development is needed on many fronts of research, service and education. © 2012 Elsevier B.V.postprin

Comprehensive eco-environmental effects of the shelter-forest ecological engineering along the Tarim Desert Highway

In this work, we report a comprehensive study about the eco-environmental effects of the shelter forest along the Tarim Desert Highway, including the effects on aeolian environment, soil, micro-climate, biodiversity, and groundwater. The results show that: (1) The movement of windblown sand near the ground surface was affected by the shelter forest. The wind speed and sediment transport rate in the shelter forest decreased by 64%-80% and 87.45%-99.02%, respectively. In addition, there were also significant changes in the sand flux structure, the sand grain size, and the deflation and deposition on the ground surface. (2) Compared to the natural mobile sand, the soil bulk density in the forest area decreased while the total salt content, the total porosity, and the water content increased. In addition, the soil fertility was significantly improved in the forest area, and showed the "first rapid, then slow" variation pattern. (3) The shelter forest showed positive effects on the micro-climate. Within the 6 m height above the ground, the air temperature in the shelter forest at different heights was lower than that in the mobile sand, while the air humidity was higher, while, the soil temperature was also lower in the shelter forest than mobile sand. (4) The number of soil microbial species increased significantly with the improvement of habitat in the shelterbelt. However, the population of different species was not distributed evenly across the surveyed area. (5) Currently, no significant effects of groundwater-pumping and forest-irrigation water have been found on the groundwater level and its salinity. The variation amplitude of both groundwater level and salinity was at the level of centimeters and 1g/L, respectively. No obvious variation trend has been observed

Balancing hydrogen adsorption/desorption by orbital modulation for efficient hydrogen evolution catalysis

Hydrogen adsorption/desorption behavior plays a key role in hydrogen evolution reaction (HER) catalysis. The HER reaction rate is a trade-off between hydrogen adsorption and desorption on the catalyst surface. Herein, we report the rational balancing of hydrogen adsorption/desorption by orbital modulation using introduced environmental electronegative carbon/nitrogen (C/N) atoms. Theoretical calculations reveal that the empty d orbitals of iridium (Ir) sites can be reduced by interactions between the environmental electronegative C/N and Ir atoms. This balances the hydrogen adsorption/ desorption around the Ir sites, accelerating the related HER process. Remarkably, by anchoring a small amount of Ir nanoparticles (7.16 wt%) in nitrogenated carbon matrixes, the resulting catalyst exhibits significantly enhanced HER performance. This includs the smallest reported overpotential at 10 mA cm(-2) (4.5 mV), the highest mass activity at 10 mV (1.12 A mg(Ir)(-1)) and turnover frequency at 25 mV (4.21 H2 s(-1)) by far, outperforming Ir nanoparticles and commercial Pt/C

Identification of key parameters controlling demographically structured vegetation dynamics in a land surface model: CLM4.5(FATES)

Vegetation plays an important role in regulating global carbon cycles and is a key component of the Earth system models (ESMs) that aim to project Earth's future climate. In the last decade, the vegetation component within ESMs has witnessed great progress from simple "big-leaf" approaches to demographically structured approaches, which have a better representation of plant size, canopy structure, and disturbances. These demographically structured vegetation models typically have a large number of input parameters, and sensitivity analysis is needed to quantify the impact of each parameter on the model outputs for a better understanding of model behavior. In this study, we conducted a comprehensive sensitivity analysis to diagnose the Community Land Model coupled to the Functionally Assembled Terrestrial Simulator, or CLM4.5(FATES). Specifically, we quantified the first- and second-order sensitivities of the model parameters to outputs that represent simulated growth and mortality as well as carbon fluxes and stocks for a tropical site with an extent of 1×1°. While the photosynthetic capacity parameter (Vc;max25) is found to be important for simulated carbon stocks and fluxes, we also show the importance of carbon storage and allometry parameters, which determine survival and growth strategies within the model. The parameter sensitivity changes with different sizes of trees and climate conditions. The results of this study highlight the importance of understanding the dynamics of the next generation of demographically enabled vegetation models within ESMs to improve model parameterization and structure for better model fidelity