The many-body ground state wave function of a fractional Chern insulator (FCI) can be constructed by mapping a fractional quantum Hall state to a FCI state through a substitution of the Bloch state of the flat Chern band for the magnetic Bloch state of the Landau level. There is a gauge freedom in choosing the single particle Bloch basis of the flat Chern band. Instead of considering only one form of interaction in FCI when choosing the gauge as done in previous works, we determine the optimal gauges for FCIs with different forms of interaction, including a short-range interaction, the Coulomb interaction, and an interpolation between them, by applying the variational principle proposed by Zhang et al. [Phys. Rev. B 93, 165129 (2016)]. We find that the optimal gauge strongly depends on the form of interaction. It contradicts with the common belief that the wave function of FCI is not sensitive to the interaction. In comparing the optimal gauge with the previous gauges proposed by Qi [Phys. Rev. Lett. 107, 126803 (2011)] and Wu et al. [Phys. Rev. B 86, 085129 (2012)], we find Wu et al.'s gauge is close to the optimal one when the interaction is a certain mixture of the Coulomb interaction and the short-range interaction, while Qi's gauge is qualitatively different from the optimal gauge in all the cases.
Experimental and simulation I–V characteristics of the cap gate high electron mobility transistor (HEMT) are reported. The two-dimensional simulations results are in conformity with the realistic HEMT perfectly, indicating reliable and acceptable of the TCAD simulation method in GaN-based devices. Depending on this, further researches on the cap gate HEMT are carried out by TCAD software, which analyzes the impact of recessed depth of gate barrier, the dimension of LG and cap gate structure on GaN HEMT performances.
An intensive field campaign was conducted in Chongqing during the summer of 2015 to explore the formation mechanisms of ozone pollution. The sources of ozone, the local production rates, and the controlling factors, as well as key species of volatile organic compounds (VOCs), were quantified by integrating a local ozone budget analysis, calculations of the relative incremental reactivity, and an empirical kinetic model approach. It was found that the potential for rapid local ozone formation exists in Chongqing. During ozone pollution episodes, the ozone production rates were found to be high at the upwind station Nan Quan, the urban station Chao Zhan, and the downwind station Jin-Yun Shan. The average local ozone production rate was 30x10(-9) V/V h(-1) and the daily integration of the produced ozone was greater than 180x10(-9) V/V. High ozone concentrations were associated with urban and downwind air masses. At most sites, the local ozone production was VOC-limited and the key species were aromatics and alkene, which originated mainly from vehicles and solvent usage. In addition, the air masses at the northwestern rural sites were NO (x) -limited and the local ozone production rates were significantly higher during the pollution episodes due to the increased NO (x) concentrations. In summary, the ozone abatement strategies of Chongqing should be focused on the mitigation of VOCs. Nevertheless, a reduction in NO (x) is also beneficial for reducing the regional ozone peak values in Chongqing and the surrounding areas.
Lake eutrophication has become a worldwide challenge, and the empirical chlorophyll a-total phosphorus (Chla-TP) relationship provides a management target for TP concentrations. Neglecting the dynamics of the relationship at the lake-specific scale would mislead the eutrophication control strategy. The Bayesian hierarchical model (BHM) is a flexible tool to explore dynamics of the Chla-TP relationship and improves the overall estimation accuracy by partial pooling of data. In this study, we used the BHMto show the spatial and seasonal dynamics of the Chla-TP relationship in one of themost eutrophic lakes in China (Lake Dianchi). We defined an indicator (the Chla/TP ratio, CPR), to represent the susceptibility of Chla to TP. We conducted a model selection process and used the CPR-TP curves to show the spatial and seasonal dynamics of the ChlaTP relationships. We determined that the wind caused the spatial dynamics due to the horizontal transport of phytoplankton, while the water temperature and the percentage of soluble reactive phosphorus led to the seasonal dynamics via increasing the growth rate of phytoplankton. These findings helped the eutrophication control in Lake Dianchi. We found that compared with the strategy to decrease the TP concentration, decreasing the susceptibility is expected to be more effective. Finally, we concluded that exploring the dynamics of the Chla-TP relationship provided an important basis for eutrophication control at the lake-specific scale.
We present the in-situ measurements in Chengdu, a major city in south west of China, in September 2016. The concentrations of ozone and its precursor were measured at four sites. Although the campaign was conducted in early autumn, up to 100 ppbv (parts per billion by volume) daily maximum ozone was often observed at all sites. The observed ozone concentrations showed good agreement at all sites, which implied that ozone pollution is a regional issue in Chengdu. To better understand the ozone formation in Chengdu, an observation based model is used in this study to calculate the ROx radical concentrations (ROx = OH + HO2 + RO2) and ozone production rate (P(O3)). The model predicts OH daily maximum is in the range of 4–8 × 106 molecules cm−3 , and HO2 and RO2 are in the range of 3–6 × 108 molecules cm−3 . The modelled radical concentrations show a distinct difference between ozone pollution and attainment period. The relative incremental reactivity (RIR) results demonstrate that anthropogenic VOCs reduction is the most efficient way to mitigate ozone pollution at all sites, of which alkenes dominate >50% of the ozone production. Empirical kinetic modelling approach shows that three out of four sites are under the VOC-limited regime, while Pengzhou is in a transition regime due to the local petrochemical industry. The ozone budget analysis showed that the local ozone production driven by the photochemical process is important to the accumulation of ozone concentrations.
Urban residents spend the majority of time in indoor environments, which, however, may not be a safe haven for staying away from outdoor air pollution, especially in China. To examine this hypothesis, the particle mass concentrations (0.056-18 mu m) and number concentrations (14-660 nm) were simultaneously measured in and outside of three typical urban indoor settings (n = 9), i.e., school, office and residence in Guangzhou, China from October-November 2014 (dry weather season) and June-August 2015 (wet weather season). The indoor and outdoor particle number concentrations were positively correlated with each other at all three sampling settings for both dry and wet weather seasons (r(2) = 0.13-0.65, p < 0.001). The infiltration factors and indoor/outdoor ratios of particles (14-660 nm) were estimated at 0.30-0.75 and 0.85-1.5, respectively, which were comparable to or higher than those (0.12-0.76 and 0.03-1.1) found in cites of other countries under infiltration conditions. Furthermore, the average infiltration factor of fine particle numbers (50-660 nm) in an office was 0.61 during a severe haze episode, indicating that approximately 60% of outdoor particles penetrated indoors. All findings suggested an efficient transport of outdoor particle sources into indoor environment, confirming that exposure of the general public to indoor particles in China should not be overlooked due to effective infiltration of outdoor particles and frequent heavy haze episodes.
A novel early gate dielectric AIGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) process is reported. With the highquality Si3N4 dielectric by low-pressure chemical vapor deposition and damage free, self-terminating passivation layer etching at the gate area, the MIS-HEMTs on 150-mm Si substrate demonstrate excellent output performance and good uniformity. The interface trap density between the gate insulator and the barrier layer is as low as 2 x 10(12) cm(-2).eV(-1) extracted by the conductance method. The MIS-HEMT fabricated on the wafer delivers an extremely small gate leakage current of 10(-9) mA/mm and a high I-on/I-off ratio of 10(11). The subthreshold swing (SS) is around 80 mV/dec, and the saturated output current density is 750 mA/mm. The dynamic on-resistance increases about 42% at a quiescent drain bias of 600 V. The V-th shift is -0.63 and -0.89 V at a high temperature of 200 degrees C and negative gate-bias stress of -25 V, respectively, indicating a comparable stability with the state-of-the-art MIS-HEMTs. An excellent threshold voltage and SS uniformity (1 - sigma/mu) with the value of 94.5% and 95.2% are achieved on the 150-mm wafer.
A novel early gate dielectric AlGaN/GaNmetal–insulator–semiconductorhigh-electron-mobilitytransistors (MIS-HEMTs) process is reported. With the highqualitySi3N4 dielectric by low-pressure chemical vapordeposition and damage free, self-terminating passivationlayer etching at the gate area, the MIS-HEMTs on 150-mmSi substrate demonstrate excellent output performanceand good uniformity. The interface trap density betweenthe gate insulator and the barrier layer is as low as2 × 1012 cm−2 · eV−1 extracted by the conductancemethod. The MIS-HEMT fabricated on the wafer delivers anextremely small gate leakage current of 10−9 mA/mm anda high Ion/Ioff ratio of 1011. The subthreshold swing (SS) isaround 80mV/dec, and the saturated output current densityis 750 mA/mm. The dynamic on-resistance increases about42% at a quiescent drain bias of 600 V. The Vth shift is−0.63 and −0.89 V at a high temperature of 200 °C andnegative gate-bias stress of −25 V, respectively, indicatinga comparable stability with the state-of-the-art MIS-HEMTs.An excellent threshold voltage and SS uniformity (1 − σ/μ)with the value of 94.5% and 95.2% are achieved on the150-mm wafer.
Abstract Magnetic Fe3O4@BiOI@AgI (FBA) spheres were synthesized through a multi-step process. The fabricated photocatalysts were characterized by different techniques. To testify the visible light driven photocatalytic activity of FBA, Rhodamine B and Bisphenol A were chosen as model common and emerging organic contaminants, respectively. While, gram-negative strain Escherichia coli was selected as model waterborne bacteria. The results showed that under visible light irradiation, \FBA\ contained strong photocatalytic degradation capacity towards both RhB and BPA. Moreover, \FBA\ was also found to exhibit excellent disinfection activity towards E. coli. The photocatalytic mechanisms for different pollutants by \FBA\ were determined and found to vary for different pollutants. Specifically, scavenger experiments, degradation intermediates determination, as well as theoretical density functional theory (DFT) analysis showed that RhB and \BPA\ were degraded via photosensitization (dominated by e- and ·O2−) and direct photocatalytic oxidation (contributed by h+, e- and ·O2−), respectively. Whereas, E. coli cells yet were found to be inactivated by the generation of e- and ·O2− rather than by the released Ag+. Since it contained superparamagnetic property, \FBA\ could be easily separated from the reaction suspension after use. Due to the excellent photo stability, \FBA\ exhibited strong photocatalytic activity in the fourth reused recycle. Therefore, \FBA\ could serve as a promising alternative for water purification.