Observations of isoprene, methacrolein (MAC) and methyl vinyl ketone (MVK) at a mountain site in Hong Kong

A field campaign was carried out in September-November 2010 near the summit of Mt. Tai Mo Shan in Hong Kong. Isoprene, methyl vinyl ketone (MVK) and methacrolein (MAC) were measured. The average isoprene mixing ratio was 109 pptv, and the average MAC and MVK levels were 68 pptv and 164 pptv, respectively. The average daytime levels of isoprene (14920 pptv, average95% confidence interval, p<0.01), MAC (709 pptv, p<0.01) and MVK (16922 pptv, p<0.1) were significantly higher than the average nighttime values (205 pptv, 498 pptv and 13925 pptv, respectively). The relationship between MVK and MAC indicated that nearby isoprene oxidation dominated their daytime abundances, while NO3 chemistry and regional transport of anthropogenic sources from inland Pearl River Delta region could explain the higher MVK to MAC ratios at night. Correlation analysis of [MVK]/[isoprene] versus [MAC]/[isoprene] found that the isoprene photochemical ages were between 10 and 64min. Regression analysis of total O3 (O3+NO2) versus MVK resulted in an estimated contribution of isoprene oxidation to ozone production of 12.5%, consistent with the simulated contribution of 10-11% by an observation-based model. © 2012 American Geophysical Union. All Rights Reserved

Coulomb Luttinger liquid

[[abstract]]Accurate expressions, valid in experimentally relevant regimes, are presented for the effect of a long-ranged Coulomb interaction on the low-energy properties (momentum distribution function, density of states, electron spectral function, and 4k(F) correlation function) of one-dimensional electron systems. The importance of plasmon dispersion (as opposed to exponent) effects in the spectral function is demonstrated.[[fileno]]2010142010005[[department]]物理

Many-body effects on excitonic optical properties of photoexcited semiconductor quantum wire structures

[[abstract]]We study carrier-interaction-induced many-body effects on the excitonic optical properties of highly photoexcited one-dimensional semiconductor quantum wire systems by solving the dynamically screened Bethe-Salpeter equation using realistic Coulomb interaction between carriers. Including dynamical screening effects in the electron-hole self-energy and in the electron-hole interaction vertex function. we find that the excitonic absorption is essentially peaked at a constant energy for a large range of photoexcitation density (n = 0-6 x 10(5) cm(-1)), above which the absorption peak disappears without appreciable gain; i.e., no exciton to free electron-hole plasma Mott transition is observed, in contrast to previous theoretical results but in agreement with recent experimental findings. This absence of gain (or the nonexistence of a Mott transition) arises from the strong inelastic scattering by one-dimensional plasmons or charge density excitations, closely related to the non-Fermi-liquid nature of one-dimensional systems. Our theoretical work demonstrates a transition or a crossover in one-dimensional photoexcited electron-hole systems from an effective Fermi liquid behavior associated with a dilute gas of noninteracting excitons in the low-density region (n 10(5) cm(-1)). The conventional quasistatic approximation for this problem is also carried out to compare with the full dynamical results. Numerical results for exciton binding energy and absorption spectra are given as functions of carrier density and temperature.[[fileno]]2010142010006[[department]]物理

Acetone in the Atmosphere of Hong Kong, Abundance, Sources and Photochemical Precursors

Intensive field measurements were carried out at a mountain site and an urban site at the foot of the mountain from September to November 2010 in Hong Kong. Acetone was monitored using both canister air samples and 2,4-dinitrophenylhydrazine cartridges. The spatiotemporal patterns of acetone showed no difference between the two sites (p > 0.05), and the mean acetone mixing ratios on O3 episode days were higher than those on non-O3 episode days at both sites (p < 0.05). The source contributions to ambient acetone at both sites were estimated using a receptor model i.e. Positive Matrix Factorization (PMF). The PMF results showed that vehicular emission and secondary formation made the most important contribution to ambient acetone, followed by the solvent use at both sites. However, the contribution of biogenic emission at the mountain site was significantly higher than that at the urban site, whereas biomass burning made more remarkable contribution at the urban site than that at the mountain site. The mechanism of oxidation formation of acetone was investigated using a photochemical box model. The results indicated that i-butene was the main precursor of secondary acetone at the mountain site, while the oxidation of i-butane was the major source of secondary acetone at the urban site.Department of Civil and Environmental Engineerin

Post-Crisis Financial Integration in East Asia

organized by HKSAR Central Policy Unit / Centre of Asian Studies, University of Hong KongFinancial integration is less pronounced in East Asia than among states in Europe and North America, or compared to economic integration within the region. Cross-border trade flows, direct investment and investment in capital goods have long been greater and faster growing than other investment flows, while regional institutional and legal structures are scarce and frequently insubstantive. This dichotomy persists despite suggestions since the early 1990s that Asian financial integration would accelerate, most especially following the East Asian financial crisis of 1997-98, including the growth of regional representative organizations and in national enthusiasm for the World Trade Organization. In particular, it defies post-crisis expectations that greater financial integration might prevent or lessen the impact of future financial shocks. This article suggests explanations in legal, governance and institutional frameworks for the paradox of modest financial integration accompanying robust economic growth and trade integration. First, cultural norms militate against regional innovation in financial markets and systems. Second, other economic institutions have tended to resist market-orientated regional reform. Above all, states failed to collaborate effectively in solutions to regional contagion during and following the 1997-98 financial crisis. Without improving financial integration, Asia will maintain a reliance on risk averse portfolio selection and excessive international reserve accumulation, all to the detriment of its financial markets.published_or_final_versio

In situ loading and delivery of short single- And double-stranded dna by supramolecular organic frameworks

Short DNA represents an important class of biomacromolecules that are widely applied in gene therapy, editing, and modulation. However, the development of simple and reliable methods for their intracellular delivery remains a challenge. Herein, we describe that seven water-soluble, homogeneous supramolecular organic frameworks (SOFs) with a well-defined pore size and high stability in water that can accomplish in situ inclusion of single-stranded (ss) and double-stranded (ds) DNA (21, 23, and 58 nt) and effective intracellular delivery (including two noncancerous and six cancerous cell lines). Fluorescence quenching experiments for single and double endlabeled ss- and ds-DNA support that the DNA sequences can be completely enveloped by the SOFs. Confocal laser scanning microscopy and flow cytometry reveal that five of the SOFs exhibit excellent delivery efficiencies that, in most of the studied cases, outperform the commercial standard Lipo2000, even at low SOF-nucleic acid ratios. In addition to high delivery efficiencies, the watersoluble, self-assembled SOF carriers have a variety of advantages, including convenient preparation, high stability, and in situ DNA inclusion, which are all critical for practical applications in nucleic acid delivery

Graphene-Based Planar Microsupercapacitors: Recent Advances and Future Challenges

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The continuous development of integrated electronics such as maintenance-free biosensors, remote and mobile environmental sensors, wearable personal electronics, nanorobotics etc. and their continued miniaturization has led to an increasing demand for miniaturized energy storage units. Microsupercapacitors with graphene electrodes hold great promise as miniaturized, integrated power sources thanks to their fast charge/discharge rates, superior power performance, and long cycling stability. In addition, planar interdigitated electrodes also have the capability to reduce ion diffusion distances leading to a greatly improved electrochemical performance. Either as standalone power sources or complementing energy harvesting units, it is expected that graphene-based microsupercapacitors will play a key role as miniaturized power sources in electronic microsystems. This review highlights the recent development, challenges, and perspectives in this area, with an emphasis on the link between material and geometry design of planar graphene-based electrodes and their electrochemical performance and integrability

An Electrocorticographic Brain Interface in an Individual with Tetraplegia

Brain-computer interface (BCI) technology aims to help individuals with disability to control assistive devices and reanimate paralyzed limbs. Our study investigated the feasibility of an electrocorticography (ECoG)-based BCI system in an individual with tetraplegia caused by C4 level spinal cord injury. ECoG signals were recorded with a high-density 32-electrode grid over the hand and arm area of the left sensorimotor cortex. The participant was able to voluntarily activate his sensorimotor cortex using attempted movements, with distinct cortical activity patterns for different segments of the upper limb. Using only brain activity, the participant achieved robust control of 3D cursor movement. The ECoG grid was explanted 28 days post-implantation with no adverse effect. This study demonstrates that ECoG signals recorded from the sensorimotor cortex can be used for real-time device control in paralyzed individuals