科研成果 by Year: 2018

Ammonium sulfate (AS) and ammonium nitrate (AN) are key components of urban fine particles. Both field and model studies showed that heterogeneous reactions of SO2, NO2, and NH3 on wet aerosols accelerated the haze formation in northern China. However, little is known on phase transitions of AS-AN containing haze particles. Here hygroscopic properties of laboratory-generated AS-AN particles and individual particles collected during haze events in an urban site were investigated using an individual particle hygroscopicity system. AS-AN particles showed a two-stage deliquescence at mutual deliquescence relative humidity (MDRH) and full deliquescence relative humidity (DRH) and three physical states: solid before MDRH, solid-aqueous between MDRH and DRH, and aqueous after DRH. During hydration, urban haze particles displayed a solid core and aqueous shell at RH=60-80% and aqueous phase at RH>80%. Most particles were in aqueous phase at RH>50% during dehydration. Our results show that AS content in individual particles determines their DRH and AN content determines their MDRH. AN content increase can reduce MDRH, which indicates occurrence of aqueous shell at lower RH. The humidity-dependent phase transitions of nitrate-abundant urban particles are important to provide reactive surfaces of secondary aerosol formation in the polluted air. Plain Language Summary Recently, aerosol water has received more attention because heterogeneous reactions of SO2, NO2, and NH3 on wet particles accelerate the severe haze formation in north China. Ammonium sulfate and ammonium nitrate (AS-AN) are key components of fine urban particles. Especially, nitrate concentration keeps increasing in polluted air in China. Our study indicates that the increase of AN content promotes the occurrence of aqueous shell at lower RH. Here we find that most of urban particles generally keep solid core and aqueous shell at RH=60-80% and aqueous phase at RH>80%. These findings can clearly explain the role of nitrate in phase transitions and make up the discussion about heterogeneous reactions on particle surfaces during the severe hazes in north China. Humidity-dependent phase states of particles are useful for interpreting the secondary aerosols' formation in severe hazes as well as in modeling studies.

A new planar MISHEMT structure is proposed with the drain surrounded (D-S) by the gate channel. The gate channel serves as the stop-ring of the drain voltage, eliminating the damages from the high voltage on the mesa edge and isolation area. As a result, the leakage of the D-S MISHEMT is found to be reduced by almost 3 orders comparing with the source surrounded (S-S) MISHEMT. A saturated output current density of 740 mA/mm and an ON-resistance of 13.09 Ω-mm are obtained for device with LG/LGS/LGD/WC = 1.5/5/20/250 μm. Meanwhile, the degradation of dynamic ON-resistance and off-state breakdown performance are investigated in both D-S and S-S MISHEMT, which indicates excellent reliability of the D-S MISHEMT.

Telomere length (TL) has been established as a biomarker of aging and aging-related health outcomes, but showed only a weak or inconsistent association with all-cause mortality in previous epidemiological studies. Recently, an epigenetic 'mortality risk score' (MS) based on whole blood DNA methylation at 10 mortality-related CpG sites has been demonstrated to be strongly related to all-cause mortality at the population level. This study aimed to address the association between TL and this MS, and to assess and compare their associations with all-cause mortality. The MS was derived from the DNA methylation profiles measured by Illumina Human Methylation450K Beadchip and TL was measured by quantitative PCR at baseline among 1517 participants aged 50-75 of the German ESTHER cohort study. In cross-sectional bi- and multivariable analyses, the MS was strongly associated and showed monotonic dose-response relationships with TL (p-values <0.05). However, only the MS but not TL was associated with all-cause mortality during a median follow-up of 12.5 years. After controlling for potential covariates and TL, hazard ratios (95% CI) for all-cause mortality for low, moderate and high levels of the MS defined by 1, 2-5 and >5 CpG sites with aberrant methylation were 2.24 (1.13-4.41), 3.31 (1.76-6.22) and 6.33 (3.22-12.41) compared to a MS of 0, respectively. Our investigation shows that the epigenetic-based MS is strongly associated with TL, a broadly accepted aging biomarker, and at the same time shows much stronger associations with all-cause mortality than the latter.

In this letter, we demonstrate a recessed-anode Schottky barrier diode (SBD) on a double AlGaN/GaN heterojunction structure. A self-terminated, oxidation/wet etching with low-pressure chemical vapor deposition (LPCVD) Si3N4 mask is applied in the anode recess process. Unlike common plasma-based, dry etching techniques, the etched surface is not subjected to ion bombardment, and the etch depth is precisely controlled. As a result, a high effective channel mobility of 1079 cm2/V . s is maintained in the channel beneath the recess surface. The fabricated devices with a 15-mum anode-to-cathode distance (LAC) are found to exhibit a uniform, low turn-ON voltage (VON) of 0.69 +or- 0.03 V, and a low specific on-resistance (RON,SP) of 2.83 mQ . cm2. The SBDs also show excellent off-state blocking characteristics due to the smooth recess interface together with the assistance of LPCVD grown Si3N4. A breakdown voltage of 1190 V is achieved for the SBDs with 15-mum LAC at a leakage current criteria of 1 muA/mm, and the Baliga's figure-of-merit is 500 MW/cm2.

Compelling evidence indicates that lipid metabolism is in partial control of the circadian system. In this context, it has been reported that the melatonin receptor 1B (MTNR1B) genetic variant influences the dynamics of melatonin secretion, which is involved in the circadian system as a chronobiotic. The objective was to analyze whether the MTNR1B rs10830963 genetic variant was related to changes in lipid levels in response to dietary interventions with different macronutrient distribution in 722 overweight/obese subjects from the POUNDS Lost trial. We did not find a significant association between the MTNR1B genotype and changes in lipid metabolism. However, dietary fat intake significantly modified genetic effects on 2 year changes in total and LDL cholesterol (P interaction = 0.006 and 0.001, respectively). In the low-fat diet group, carriers of the sleep disruption G allele (minor allele) showed a greater reduction of total cholesterol (beta +/- SE = -5.78 +/- 2.88 mg/dl, P = 0.04) and LDL cholesterol (beta +/- SE = -7.19 +/- 2.37 mg/dl, P = 0.003). Conversely, in the high-fat diet group, subjects carrying the G allele evidenced a smaller decrease in total cholesterol (beta +/- SE = 5.81 +/- 2.65 mg/dl, P = 0.03) and LDL cholesterol (beta +/- SE = 5.23 +/- 2.21 mg/dl, P = 0.002). Subjects carrying the G allele of the circadian rhythm-related MTNR1B variant may present a bigger impact on total and LDL cholesterol when undertaking an energy-restricted low-fat diet.