科研成果

Attaining control on charge injection properties is significant for meaningful applications of organic field-effect transistors (OFETs). Here, molecular electron-doping is applied with an air-stable dimer dopant for n-type OFETs based on (naphthalene diimide-diketopyrrolopyrrole) polymer hosts. Through investigating the doping effect on contact and transport properties, it is found that the electron transport increases in n-doped OFETs at low doping regime with remaining large on/off ratios. These favorable meliorations are reconciled by the mitigated impacts of contact resistance and interfacial traps, as well as the surface morphology exhibiting features of increased ordering. The occurrence of doping in the presence of dimer dopants is evidenced by the observed shift of Fermi level toward vacuum level coupled with compositional analysis. Without applying vacuum-deposition-based contact doping, charge injection efficiencies are gained without losing OFET characteristics using the solution-based methodology.

OBJECTIVE: To investigate whether improving adherence to healthy dietary patterns interacts with the genetic predisposition to obesity in relation to long term changes in body mass index and body weight. DESIGN: Prospective cohort study. SETTING: Health professionals in the United States. PARTICIPANTS: 8828 women from the Nurses' Health Study and 5218 men from the Health Professionals Follow-up Study. EXPOSURE: Genetic predisposition score was calculated on the basis of 77 variants associated with body mass index. Dietary patterns were assessed by the Alternate Healthy Eating Index 2010 (AHEI-2010), Dietary Approach to Stop Hypertension (DASH), and Alternate Mediterranean Diet (AMED). MAIN OUTCOME MEASURES: Five repeated measurements of four year changes in body mass index and body weight over follow-up (1986 to 2006). RESULTS: During a 20 year follow-up, genetic association with change in body mass index was significantly attenuated with increasing adherence to the AHEI-2010 in the Nurses' Health Study (P=0.001 for interaction) and Health Professionals Follow-up Study (P=0.005 for interaction). In the combined cohorts, four year changes in body mass index per 10 risk allele increment were 0.07 (SE 0.02) among participants with decreased AHEI-2010 score and -0.01 (0.02) among those with increased AHEI-2010 score, corresponding to 0.16 (0.05) kg versus -0.02 (0.05) kg weight change every four years (P<0.001 for interaction). Viewed differently, changes in body mass index per 1 SD increment of AHEI-2010 score were -0.12 (0.01), -0.14 (0.01), and -0.18 (0.01) (weight change: -0.35 (0.03), -0.36 (0.04), and -0.50 (0.04) kg) among participants with low, intermediate, and high genetic risk, respectively. Similar interaction was also found for DASH but not for AMED. CONCLUSIONS: These data indicate that improving adherence to healthy dietary patterns could attenuate the genetic association with weight gain. Moreover, the beneficial effect of improved diet quality on weight management was particularly pronounced in people at high genetic risk for obesity.

This study assesses the impact of revised volatile organic compound (VOC) and organic aerosol (OA) emissions estimates in the GEM-MACH (Global Environmental Multiscale-Modelling Air Quality and CHemistry) chemical transport model (CTM) on air quality model predictions of organic species for the Athabasca oil sands (OS) region in Northern Alberta, Canada. The first emissions data set that was evaluated (base-case run) makes use of regulatory-reported VOC and particulate matter emissions data for the large oil sands mining facilities. The second emissions data set (sensitivity run) uses total facility emissions and speciation profiles derived from box-flight aircraft observations around specific facilities. Large increases in some VOC and OA emissions in the revised-emissions data set for four large oil sands mining facilities and decreases for others were found to improve the modeled VOC and OA concentration maxima in facility plumes, as shown with the 99th percentile statistic and illustrated by case studies. The results show that the VOC emission speciation profile from each oil sand facility is unique and different from standard petrochemical-refinery emission speciation profiles used for other regions in North America. A significant increase in the correlation coefficient is reported for the long-chain alkane predictions against observations when using the revised emissions based on aircraft observations. For some facilities, larger long-chain alkane emissions resulted in higher secondary organic aerosol (SOA) production, which improved OA predictions in those plumes. Overall, the use of the revised-emissions data resulted in an improvement of the model mean OA bias; however, a decrease in the OA correlation coefficient and a remaining negative bias suggests the need for further improvements to model OA emissions and formation processes. The weight of evidence suggests that the top-down emission estimation technique helps to better constrain the fugitive organic emissions in the oil sands region, which are a challenge to estimate given the size and complexity of the oil sands operations and the number of steps in the process chain from bitumen extraction to refined oil product. This work shows that the top-down emissions estimation technique may help to constrain bottom-up emission inventories in other industrial regions of the world with large sources of VOCs and OA.

In perovskite solar cells, the morphology of the porous TiO2 electron transport layer (ETL) largely determines the quality of the perovskites. Here, we chose micro-scale TiO2 (0.2 mu m) and compared it with the conventional nanoscale TiO2 (20 nm) in relation to the crystallinity of perovskites. The results show that the micro-scale TiO2 is favorable for increasing the grain size of the perovskites and enhancing the light scattering. However, the oversized TiO2 results in an uneven surface. The evenness of the perovskites can be improved by nanoscale TiO2, while the crystallinity and compactness are not as good as those of the films based on micro-scale TiO2. To combine the advantages of both micro-scale and nanoscale TiO2, by mixing 0.2 mu m/20nm TiO2 with a ratio of 1 : 2 as the composite ETL, the device average power conversion efficiency was increased to 11.2% from 9.9% in the case of only 20 nm TiO2. (C) 2018 The Japan Society of Applied Physics

Copulas provide an attractive approach to the construction of multivariate distributions with flexible marginal distributions and different forms of dependences. Of particular importance in many areas is the possibility of forecasting the tail-dependences explicitly. Most of the available approaches are only able to estimate tail-dependences and correlations via nuisance parameters, and cannot be used for either interpretation or forecasting. We propose a general Bayesian approach for modeling and forecasting tail-dependences and correlations as explicit functions of covariates, with the aim of improving the copula forecasting performance. The proposed covariate-dependent copula model also allows for Bayesian variable selection from among the covariates of the marginal models, as well as the copula density. The copulas that we study include the Joe-Clayton copula, the Clayton copula, the Gumbel copula and the Student’s t-copula. Posterior inference is carried out using an efficient MCMC simulation method. Our approach is applied to both simulated data and the S&P 100 and S&P 600 stock indices. The forecasting performance of the proposed approach is compared with those of other modeling strategies based on log predictive scores. A value-at-risk evaluation is also performed for the model comparisons.

During ferrihydrite precipitation, metal ions can be sequestered in it to form impurity-bearing ferrihydrite (IBF). Using grazing-incidence small-angle X-ray scattering (GISAXS), heterogeneous precipitation/deposition of pure and IBF nanoparticles on quartz (SiO2) and corundum (Al2O3) was quantified in 0.1 mM Fe3+ solutions in the absence and presence of 1 mM Mn2+ or Al3+ (pH = 3.8 ± 0.1). The impurity ions (Mn and Al) greatly affected ferrihydrite nanoparticle precipitation/deposition on substrates. On SiO2, ferrihydrite nanoparticle precipitation/deposition was promoted in the presence of Mn but was inhibited in the presence of Al. On Al2O3, Mn- and Al-bearing ferrihydrite nanoparticle precipitation/deposition was slower than for pure ferrihydrite. Compared with on SiO2, pure and IBF nanoparticle precipitation/deposition on Al2O3 was significantly inhibited. To understand the mechanisms, interactions among impurity ions, substrates, and precipitates were explored. Surface enrichment of Mn and Al on precipitates was found to increase the zeta potential of ferrihydrite nanoparticles. The changes in surface charges of the precipitates and substrates affected heterogeneous IBF precipitation/deposition significantly. The rates and mechanisms of heterogeneous IBF precipitation/deposition provided here can help predict pollutant transport and design catalyst synthesis.

Electron sources driven by femtosecond laser have important applications in many aspects, and the research about the intrinsic emittance is becoming more and more crucial. The intrinsic emittance of polycrystalline copper cathode, which was illuminated by femtosecond pulses (FWHM of the pulse duration was about 100 fs) with photon energies above and below the work function, was measured with an extremely low bunch charge (single-electron pulses) based on free expansion method. A minimum emittance was obtained at the photon energy very close to the effective work function of the cathode. When the photon energy decreased below the effective work function, emittance increased rather than decreased or flattened out to a constant. By investigating the dependence of photocurrent density on the incident laser intensity, we found the emission excited by pulsed photons with sub-work-function energies contained two-photon photoemission. In addition, the portion of two-photon photoemission current increased with the reduction of photon energy. We attributed the increase of emittance to the effect of two-photon photoemission. This work shows that conventional method of reducing the photon energy of excited light source to approach the room temperature limit of the intrinsic emittance may be infeasible for femtosecond laser. There would be an optimized photon energy value near the work function to obtain the lowest emittance for pulsed laser pumped photocathode. (C) 2018 Author(s).

Abstract For a long time, there has been an excessive use of synthetic fertilizers applied to the decreasing area of arable land to help meet the increasing food demand, which causes NH3 volatilization and land degradation. In this study, we conducted a nationwide inventory of NH3 emissions from synthetic nitrogen fertilizers in China from 1991 to 2013. We estimated that NH3 emissions increased from 3.20 to 5.21 Tg NH3 yr−1. Because of the different agricultural practices, fertilizer use schedules, and ambient temperature, monthly NH3 emissions have varied greatly. NH3 emissions during the spring and summer accounted for approximately 83% of the national total in 1991, 1998, 2005, and 2013. Similarly, the spatial distribution of NH3 emissions exhibited large heterogeneity in 1991, 1998, 2005, and 2013. High emissions occurred in the eastern and central provinces and eastern Sichuan. Based on NH3 emissions in Chinese counties for 1991–1998, 1999–2005, and 2006–2013, the Pearson correlation coefficient was applied to compute the changing trends in NH3 emissions and fertilization rates. The results showed that the NH3 emissions from the major grain-producing regions increased, whereas those from the eastern provinces, which experienced rapid economic development, decreased. In addition, fertilizer amount, arable land area, grain yield, and primary industry have been shown to be largely correlated to NH3 emissions based on principal component analysis. Therefore, the results of this study have significant implications for improving the efficient use of fertilizers and preventing soil and/or land degradation.

Epidemiological and toxicological studies suggest that exposure to ambient fine particles (PM2.5) can reduce human reproductive capacity. We previously reported, based on spatial epidemiology, that higher levels of PM2.5 exposure were associated with a lower fertility rate (FR) in China. However, that study was limited by a lack of temporal variation. Using first-difference regression, we linked temporal changes in FR and PM2.5 with adjustment for ecological covariates across 2806 counties in China during 2000-2010. Next, we performed a sensitivity analysis of the variation in the PM2.5 -FR association according to (1) geographic region, (2) indicators of the level of development, and (3) PM2.5 concentrations. Also, we quantified the reduction in the FR attributable to ambient PM2.5 in China for the first time. The FR decreased by 3.3% (1.2%, 5.3%) for each 10 mu g/m(3) increment in PM2.5 . The association varied significantly among the geographic regions, but not with the level of development. Nonlinearity analysis suggested a linear exposure-response function with an effect threshold of -8 mu g/m(3). We also found that comparing to the 2000 scenario, increment of PM2.5 in 2010 might result in a reduction of 2.50 (2.44, 2.60) infants per 1000 women aged 15-44 years per year in China. Our results confirm the statistical association between ambient particles and FR and suggest that poor air quality may contribute to childlessness in China. (C) 2018 Elsevier B.V. All rights reserved.

© The Author(s) 2018. Lacking of floor plans is a fundamental obstacle to ubiquitous indoor location-based services. Recent work have made significant progress to accuracy, but they largely rely on slow crowdsensing that may take weeks or even months to collect enough data. In this chapter, we propose Knitter that can generate accurate floor maps by a single random user's one-hour data collection efforts, and demonstrate how such maps can be used for indoor navigation. Knitter extracts high-quality floor layout information from single images, calibrates user trajectories, and filters outliers. It uses a multi-hypothesis map fusion framework that updates landmark positions/orientations and accessible areas incrementally according to evidences from each measurement. Our experiments on three different large buildings and 30+ users show that Knitter produces correct map topology, and 90-percentile landmark location and orientation errors of 3∼5m and 4 ∼ 6 ∘ , comparable to the state of the art at more than 20 × speed up: data collection can finish in about one hour even by a novice user trained just a few minutes.

OBJECTIVES: We assessed relationships between indoor black carbon (BC) exposure and urinary oxidative stress biomarkers, 8-hydroxy-2'-deoxyguanosine (8-OHdG) and malondialdehyde (MDA), in participants with chronic obstructive pulmonary disease (COPD). METHODS: Eighty-two participants completed in-home air sampling for one week prior to providing urine samples up to four times in a year. Weekly indoor and daily outdoor concentrations were used to estimate indoor daily lags and moving averages. There were no reported in-home BC sources, thus indoor levels closely represented outdoor BC infiltration. Mixed effects regression models with a random intercept for each participant were used to assess relationships between indoor BC and 8-OHdG and MDA, adjusting for age, race, BMI, diabetes, heart disease, season, time of urine collection, urine creatinine, and outdoor humidity and temperature. RESULTS: There were positive effects of BC on 8-OHdG and MDA, with the greatest effect the day before urine collection (6.9% increase; 95% CI 0.9-13.3%, per interquartile range: 0.22mug/m(3)) for 8-OHdG and 1 to 4days before collection (8.3% increase; 95% CI 0.03-17.3% per IQR) for MDA. Results were similar in models adjusting for PM2.5 not associated with BC and NO2 (10.4% increase, 95% CI: 3.5-17.9 for 8-OHdG; 8.1% increase, 95% CI: -1.1-18.1 for MDA). Effects on 8-OHdG were greater in obese participants. CONCLUSIONS: We found positive associations between BC exposure and 8-OHdG and MDA, in which associations with 8-OHdG were stronger in obese participants. These results suggest that exposure to low levels of traffic-related pollution results in lipid peroxidation and oxidative DNA damage in individuals with COPD.

© The Author(s) 2018. Mainstream indoor localization technologies rely on RF signatures that require extensive human efforts to measure and periodically recalibrate signatures. The progress to ubiquitous localization remains slow. In this chapter, we explore Sextant, an alternative approach that leverages environmental reference objects such as store logos. A user uses a smartphone to obtain relative position measurements to such static reference objects for the system to triangulate the user location. Sextant leverages image matching algorithms to automatically identify the chosen reference objects by photo-taking, and we propose two methods to systematically address image matching mistakes that cause large localization errors. We formulate the benchmark image selection problem, prove its NP-completeness, and propose a heuristic algorithm to solve it. We also propose a couple of geographical constraints to further infer unknown reference objects. To enable fast deployment, we propose a lightweight site survey method for service providers to quickly estimate the coordinates of reference objects. Extensive experiments have shown that Sextant prototype achieves 2–5 m accuracy at 80-percentile, comparable to the industry state of the art, while covering a 150 × 75 m mall and 300 × 200 m train station requires a one-time investment of only 2–3 man-hours from service providers.

© The Author(s) 2018. The lack of indoor maps is a critical reason behind the current sporadic availability of indoor localization service. Service providers have to go through effort-intensive and time-consuming business negotiations with building operators, or hire dedicated personnel to gather such data. In this chapter, we propose Jigsaw, a floor plan reconstruction system that leverages crowdsensed data from mobile users. It extracts the position, size, and orientation information of individual landmark objects from images taken by users. It also obtains the spatial relation between adjacent landmark objects from inertial sensor data, and then computes the coordinates and orientations of these objects on an initial floor plan. By combining user mobility traces and locations where images are taken, it produces complete floor plans with hallway connectivity, room sizes, and shapes. It also identifies different types of connection areas (e.g., escalators, stairs) between stories, and employs a refinement algorithm to correct detection errors. Our experiments on three stories of two large shopping malls show that the 90-percentile errors of positions and orientations of landmark objects are about 1 \~ 2m and 5 \~ 9°, while the hallway connectivity and connection areas between stories are 100% correct.

The influence of the moving on the radiation characteristics is an important research direction on the field of the microwave remote sense. This paper has investigated the influence of the aerodynamic heating effect caused by high-speed moving on the radiation property of the typical plane. Firstly, the temperature distributions on the plane skin under different flight speeds have been calculated through Fluent simulation. Secondly, the emissivity of the skin under different observation angles has been calculated by the method of equivalent transmission lines. Finally, the radiation brightness temperatures of the stealth plane and the background have been calculated based on the blackbody radiation law and the atmospheric radiation transfer model. The results show that the high-speed moving has a significant influence on the radiation characteristic of the stealth target.

Plastic particles are widely present in the natural environment and are highly likely to interact with bacteria (the ubiquitous microbes in the natural environment), which might affect the transport and deposition of bacteria in porous media. In this study, the significance of plastic particles from nanoscale to micrometer-scale (0.02-2 μm) on the transport and deposition behaviors of bacteria (Escherichia coli) in quartz sand was examined under environmentally relevant conditions in both NaCl and CaCl2 solutions at pH 6. The results showed that the presence of different-sized plastic particles did not affect bacterial transport behaviors at low ionic strength (10 mM NaCl and 1 mM CaCl2), whereas, at high ionic strength conditions (50 mM NaCl and 5 mM in CaCl2), plastic particles increased bacterial transport in quartz sand. At low ionic strength conditions, the mobility of both plastic particles and bacteria was high, which might drive the negligible effects of plastic particles on bacterial transport behaviors. The mechanisms driving the enhanced cell transport at high ionic strength were different for different-sized plastic particles. Specifically, for 0.02 μm nanoplastic particles, the adsorption of plastic particles onto cell surfaces and the repel effect induced by suspended plastic particles contributed to the increased cell transport. As for 0.2 μm microplastics (MPs), the suspended plastic particles induced repel effect contributed to the increased cell transport, whereas, for 2 μm MPs, the competition deposition sites by the plastic particles were the contributor to the increased cell transport. © 2018 American Chemical Society.