Zhou Z, Zeng J, Ma X, Pang X, Yi H, Chen Q, Meltzer M, He M, Rozelle S, Congdon* NG. Accuracy of rural refractionists in western China. Investigative Ophthalmology & Visual Science. 2014;55:154-161.
Although new particle formation accounts for about 50% of the global aerosol production in the troposphere, the chemical species and mechanism responsible for the growth of freshly nucleated nanoparticles remain largely uncertain. Here we show large size growth when sulfuric acid nanoparticles of 4-20 nm are exposed to epoxide vapors, dependent on the particle size and relative humidity. Composition analysis of the nanoparticles after epoxide exposure reveals the presence of high molecular weight organosulfates and polymers, indicating the occurrence of acid-catalyzed reactions of epoxides. Our results suggest that epoxides play an important role in the growth of atmospheric newly nucleated nanoparticles, considering their large formation yields from photochemical oxidation of biogenic volatile organic compounds.
Li J, Zheng S, Tan Y. Adaptive fireworks algorithm, in 2014 IEEE Congress on Evolutionary Computation (CEC). IEEE; 2014:3214–3221. 访问链接
Tan S, Si J, Ma S, Wang S, Gao W. Adaptive frame level rate control in 3D-HEVC, in 2014 IEEE Visual Communications and Image Processing Conference, VCIP 2014, Valletta, Malta, December 7-10, 2014.; 2014:382–385. 访问链接
Shibasaki's REMB catalysts (REMB; RE = Sc, Y, La-Lu; M = Li, Na, K; B = 1,1'-bi-2-naphtholate; RE/M/B = 1/3/3) are among the most enantioselective asymmetric catalysts across a broad range of mechanistically diverse reactions. However, their widespread use has been hampered by the challenges associated with their synthesis and manipulation. We report here the self-assembly of novel hydrogen-bonded rare earth metal BINOLate complexes that serve as bench-stable precatalysts for Shibasaki's REMB catalysts. Incorporation of hydrogen-bonded guanidinium cations in the secondary coordination sphere leads to unique properties, most notably, improved stability toward moisture in solution and in the solid state. We have exploited these properties to develop straightforward, high-yielding, and scalable open-air syntheses that provide rapid access to crystalline, nonhygroscopic complexes from inexpensive hydrated RE starting materials. These compounds can be used as precatalysts for Shibasaki's REMB frameworks, where we have demonstrated that our system performs with comparable or improved levels of stereoselectivity in several mechanistically diverse reactions including Michael additions, aza-Michael additions, and direct Aldol reactions.
Trifluoroacetic acid (TFA) has been attracting increasing attention worldwide because of its increased environmental concentrations and high aquatic toxicity. Atmospheric deposition is the major source of aquatic TFA, but only a few studies have reported either air concentrations or deposition fluxes for TFA. This is the first study to report the atmospheric concentrations of TFA in China, where an annular denuder and filter pack collection system were deployed at a highly urbanized site in Beijing. In total, 14-4 air samples were collected over the course of 1 year (from May 2012 to April 2013) and analyzed directly using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) or following derivatization by gas chromatography-mass spectrometry (GC-MS). The annual mean atmospheric concentration of TFA was 1580 +/- 558 pg/m(3), higher than the previously reported annual mean levels in Germany and Canada. For the first time, it was demonstrated that maximum concentrations of TFA were frequently observed in the afternoon, following a diurnal cycle and suggesting that a major source of airborne TFA is likely degradation of volatile precursors. Using a deposition model, the annual TFA deposition flux was estimated to be 619 +/- 264 mu g m(-2) year(-1). Nevertheless, a box model estimated that the TFA deposition flux from the degradation of HFC-134a contributed only 14% (6-33%) to the total TFA deposition flux in Beijing. Source analysis is quite important for future TFA risk predictions; therefore, future research should focus on identifying additional sources.
Trifluoroacetic acid (TFA) has been attracting increasing attention worldwide because of its increased environmental concentrations and high aquatic toxicity. Atmospheric deposition is the major source of aquatic TFA, but only a few studies have reported either air concentrations or deposition fluxes for TFA. This is the first study to report the atmospheric concentrations of TFA in China, where an annular denuder and filter pack collection system were deployed at a highly urbanized site in Beijing. In total, 144 air samples were collected over the course of 1 year (from May 2012 to April 2013) and analyzed directly using high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS) or following derivatization by gas chromatography–mass spectrometry (GC–MS). The annual mean atmospheric concentration of TFA was 1580 ± 558 pg/m3, higher than the previously reported annual mean levels in Germany and Canada. For the first time, it was demonstrated that maximum concentrations of TFA were frequently observed in the afternoon, following a diurnal cycle and suggesting that a major source of airborne TFA is likely degradation of volatile precursors. Using a deposition model, the annual TFA deposition flux was estimated to be 619 ± 264 μg m–2 year–1. Nevertheless, a box model estimated that the TFA deposition flux from the degradation of HFC-134a contributed only 14% (6–33%) to the total TFA deposition flux in Beijing. Source analysis is quite important for future TFA risk predictions; therefore, future research should focus on identifying additional sources.
Trifluoroacetic acid (TFA) has been attracting increasing attention worldwide because of its increased environmental concentrations and high aquatic toxicity. Atmospheric deposition is the major source of aquatic TFA, but only a few studies have reported either air concentrations or deposition fluxes for TFA. This is the first study to report the atmospheric concentrations of TFA in China, where an annular denuder and filter pack collection system were deployed at a highly urbanized site in Beijing. In total, 144 air samples were collected over the course of 1 year (from May 2012 to April 2013) and analyzed directly using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) or following derivatization by gas chromatography-mass spectrometry (GC-MS). The annual mean atmospheric concentration of TFA was 1580 +/- 558 pg/m(3), higher than the previously reported annual mean levels in Germany and Canada. For the first time, it was demonstrated that maximum concentrations of TFA were frequently observed in the afternoon, following a diurnal cycle and suggesting that a major source of airborne TFA is likely degradation of volatile precursors. Using a deposition model, the annual TFA deposition flux was estimated to be 619 +/- 264 mug m(-2) year(-1). Nevertheless, a box model estimated that the TFA deposition flux from the degradation of HFC-134a contributed only 14% (6-33%) to the total TFA deposition flux in Beijing. Source analysis is quite important for future TFA risk predictions; therefore, future research should focus on identifying additional sources.
We report a high-performance normally-off Al2O3/AlN/GaN MOS-channel-high electron mobility transistor (MOSC-HEMT) featuring a monocrystalline AlN interfacial layer inserted between the amorphous Al2O3 gate dielectric and the GaN channel. The AlN interfacial layer effectively blocks oxygen from the GaN surface and prevents the formation of detrimental Ga-O bonds. Frequency-dispersion in C-V characteristics and threshold voltage hysteresis are effectively suppressed, owing to improved interface quality. The new MOSC-HEMTs exhibit a maximum drain current of 660 mA/mm, a field-effect mobility of 165 cm(2)/V . s, a high ON/OFF drain current ratio of similar to 10(10), and low dynamic ON-resistance degradation.