科研成果 by Year: 2016

Identifying the sanitation efficacy of reducing fecal contaminations in the environment is important for evaluating health risks of the public and developing future management strategies to improve sanitation conditions. In this study, we estimated the fecal coliforms (FC) entering into the environment in 31 provinces in China under three sanitation scenarios. Our calculation results indicated that, the current FC release is disparate among regions, and the human releases in the rural regions were dominant, accounting for over 90% of the total human releases. Compared with the human release, the FC release from the livestock was of similar magnitude, but has a quite different spatial distribution. In China Women's Development Program, the Chinese government set the target to make over 85% of the population in the rural access to the toilets in 2020. If the target set by the Chinese government is achieved, a decrease of 34% (12-54%) in the FC releases would be anticipated. In the future, the improvement in sanitation and accesses to the safe drinking water in the less developed regions, such as Tibet, Qinghai, and Ningxia, should be considered as a priority. (c) 2016 Elsevier Inc. All rights reserved.

In the last four decades, various techniques including spectroscopic, wet chemical and mass spectrometric methods, have been developed and applied for the detection of ambient nitrous acid (HONO). We developed a HONO detection system based on long path photometry which consists of three independent modules i.e., sampling module, fluid propulsion module and detection module. In the propulsion module, solenoid pumps are applied. With solenoid pumps the pulsed flow can be computer controlled both in terms of pump stroke volume and pulse frequency, which enables the attainment of a very stable flow rate. In the detection module, a customized Liquid Waveguide Capillary Cell (LWCC) is used. The customized LWCC pre-sets the optical fiber in-coupling with the liquid wave guide, providing the option of fast startup and easy maintenance of the absorption photometry. In summer 2014, our system was deployed in a comprehensive campaign at a rural site in the North China Plain. More than one month of high quality HONO data spanning from the limit of detection to 5 ppb were collected. Intercomparison of our system with another established system from Forschungszentrum Juelich is presented and discussed. In conclusion, our instrument achieved a detection limit of 10 pptV within 2 min and a measurement uncertainty of 7%, which is well suited for investigation of the HONO budget from urban to rural conditions in China. (C) 2016 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

In the last four decades, various techniques including spectroscopic, wet chemical and mass spectrometric methods, have been developed and applied for the detection of ambient nitrous acid (HONO). We developed a HONO detection system based on long path photometry which consists of three independent modules i.e., sampling module, fluid propulsion module and detection module. In the propulsion module, solenoid pumps are applied. With solenoid pumps the pulsed flow can be computer controlled both in terms of pump stroke volume and pulse frequency, which enables the attainment of a very stable flow rate. In the detection module, a customized Liquid Waveguide Capillary Cell (LWCC) is used. The customized LWCC pre-sets the optical fiber in-coupling with the liquid wave guide, providing the option of fast startup and easy maintenance of the absorption photometry. In summer 2014, our system was deployed in a comprehensive campaign at a rural site in the North China Plain. More than one month of high quality HONO data spanning from the limit of detection to 5 ppb were collected. Intercomparison of our system with another established system from Forschungszentrum Juelich is presented and discussed. In conclusion, our instrument achieved a detection limit of 10 pptV within 2 min and a measurement uncertainty of 7%, which is well suited for investigation of the HONO budget from urban to rural conditions in China. (C) 2016 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences.

Aggregation of nanoparticles impacts their reactivity, stability, transport, and fate in aqueous environments, but limited methods are available to characterize structural features and movement of aggregates in liquid. Here, liquid cell transmission electron microscopy (LCTEM) was utilized to directly observe the size, morphology, and motion of aggregates that were composed of 9 and 36 nm hematite nanoparticles, respectively, in water or NaCl solution. When mass concentrations were same, the aggregates of 9 nm nanoparticles were statistically more compact and slightly larger than those of 36 nm nanoparticles. Aggregates in both samples were typically nonspherical. Increasing ionic strength resulted in larger aggregates, and also enhanced the stability of aggregates under electron-beam irradiation. In water, small aggregates moved randomly and approached repeatedly to large aggregates before final attachment. In NaCl solution, small aggregates moved directly toward large aggregates and attached to the latter quickly. This observation provided a direct confirmation of the DLVO theory that the energy barrier to aggregation is higher in water than in salt solutions. This study not only presented the influences of particle size and ionic strength on aggregation state, but also demonstrated that LCTEM is a promising method to link aggregation state to dynamic processes of nanoparticles.

In this master thesis, we explore the probability theory, statistical inference and numerical computation of discrete compound Poisson (DCP) distribution. In particular, we do a very comprehensive literature review of DCP distributions and its applications in related statistical models of count data fields, and especially, we discuss penalized generalized linear model of count data regression.The discrete compound Poisson distributions have the probability generating function in the form of the following: The famous Feller’s characterization of the compound Poisson states that a discrete distribution is compound Poisson if and only if its distribution is discrete infinitely divisible. This is a special case of Levy-Khinchine formula. When the{ai}i=1∞, may take negative values and the sum is absolutely convergent, it is called pseudo discrete compound Poisson distribution.In the first chapter, we introduce an important tool (probability generating function and Fourier transform) as preliminaries and improve the flawed proof of Feller’s characterization, and then we give a short introduction of variable selection method about Lasso and generalization. We close this chapter with the infinitely divisibile prior distribution in Bayesian Lasso and we envisages appropriate zero-inflated distribution as prior distribution which obtains the nonzero sparse estimation of coefficients. The chapter Ⅱ discusses characterizations of DCP distribution(process) with ten methods to prove the probability mass function are given in Appendix, and we give over a hundred kinds of special cases or sub-families of DCP distribution which are listed in a table with references. We use Stein-Chen method and operator semigroup method to obtain the upper bound of the total variation between a sum of independent discrete r.v. and a related discrete compound Poisson r.v., and use row sum in random triangular array to approximate discrete compound Poisson distribution. Chapter Ⅳ studys statistics, parameters estimation, FFT of DCP probability mass. Chapter Ⅴ firstly uses cumulants estimation and Fourier transform estimation to actuarial claim data with zero-inflated and overdispersion properties, then compares its Kolmogorov-Smimov test and Chi-squared test. We give a theorem that a set of count data obeys discrete pseudo compound Poisson distribution if its. probability of zero is larger than the probability of nonzero. Further more, we use this zero-inflated property of pseudo discrete compound Poisson with adding virtual frequency techniques; we get an algorithm to fit any discrete distributions. Chapter V also discusses count GLM related to the DCP distribution and use penalized estimation to select important regression variables. In particular, we consider the Elastic net estimates of negative binomial regression, and we give a necessary and sufficient condition(like Karush-Kuhn-Tucker conditions) for non-zero(zero) coefficient estimates. Using a spider count data, we analysis this real example by negative binomial regression with MLE, Lasso, Elastic net penalties. Next, we set forth the survival functions in discrete frailty model and cured rate models (or long term survivor models with competing causes) which are derived from some DCP distributions. In the last section, we look forword to the future study that mixed Poisson distribution to approximate any discrete distribution, and states the problem of variable selection in mixture components. Due to the complexity of the mixture, it results the high-dimentional problem. 

The significance of perfluorooctanoic acid (PFOA) on the transport and deposition behaviors of bacteria (Gram-negative Escherichia coli and Gram-positive Bacillus subtilis) in quartz sand is examined in both NaCl and CaCl2 solutions at pH 5.6 by comparing both breakthrough curves and retained profiles with PFOA in solutions versus those without PFOA. All test conditions are found to be highly unfavorable for cell deposition regardless of the presence of PFOA; however, 7%-46% cell deposition is observed depending on the conditions. The cell deposition may be attributed to micro- or nanoscale roughness and/or to chemical heterogeneity of the sand surface. The results show that, under all examined conditions, PFOA in suspensions increases cell transport and decreases cell deposition in porous media regardless of cell type, presence or absence of extracellular polymeric substances, ionic strength, and ion valence. We find that the additional repulsion between bacteria and quartz sand caused by both acid-base interaction and steric repulsion as well as the competition for deposition sites on quartz sand surfaces by PFOA are responsible for the enhanced transport and decreased deposition of bacteria with PFOA in solutions. © 2016 American Chemical Society.

D-Tyrosine inhibits formation and triggers disassembly of bacterial biofilm and has been proposed for biofouling control applications. This study probes the impact of D-tyrosine in different biofilm formation stages in both G+ and G- bacteria, and reveals a non-monotonic correlation between D-tyrosine concentration and biofilm inhibition effect. In the attachment stage, cell adhesion was studied in a flow chamber, where D-tyrosine caused significant reduction in cell attachment. Biofilms formed by Pseudomonas aeruginosa and Bacillus subtilis were characterized by confocal laser scanning microscopy as well as quantitative analysis of cellular biomass and extracellular polymeric substances. D-Tyrosine exhibited strong inhibitive effects on both biofilms with  an effective concentration as low as 5 nM; the biofilms responded to D-tyrosine concentration change in a non-monotonic, bi-modal pattern. In addition, D-tyrosine showed notable and different impact on EPS production by G+ and G- bacteria. Extracellular protein was decreased in P. aeruginosa biofilms, but increased in those of B. subtilis. Exopolysaccharides production by P. aeruginosa was increased at low concentrations and reduced at high concentrations while no impact was found in B. subtilis. These results suggest that distinct mechanisms are at play at different D-tyrosine concentrations and they may be species specific. Dosage of D-tyrosine must be carefully controlled for biofouling control applications.

Crystalline Si nanowire (SiNW) springs, produced via a low temperature (<350 degrees C) thin film technology, are ideal building blocks for stretchable electronics. Herein, a novel cyclic crystallographic-index-lowering self-turning and twin dynamics is reported, during a tin-catalyzed in-plane growth of SiNWs, which results in a periodic zigzag SiNW without any external parametric intervention. More interestingly, a unique twin-reflected interlaced crystal-domain structure has been identified for the first time, while in situ and real-time scanning electron microscopy observations reveal a new twin-triggering growth mechanism that is the key to reset a complete zigzag growth cycle. Direct "stress-strain" testing of the SiNW springs demonstrates a large stretchability of 12% under tensile loading, indicating a whole new strategy and capability to engineer mono-like SiNW channels for high performance stretchable electronics

Multiple approaches were used to investigate the evolution of surface aerosols in Beijing during the passage of a dust event at high altitude, which was from the Gobi areas of southern Mongolia and covered a wide range of North China. Single particle analysis with electron microscope showed that the majority of coarse particles were mineral ones, and most of them were in the size range of 1-7 mu m with a peak of number concentration at about 3.5 mu m. Based on elemental composition and morphology, the mineral particles could be classified into several groups, including Si-rich (71%), Ca-rich (15%), Fe-rich (6%), and halite-rich (2%), etc., and they were the main contributors to the aerosol optical depth as the dust occurred. The sizedistributions of surface aerosols were significantly affected by the dust intrusion. The average number concentration of accumulation mode particles during the event was about 400 cm(-3), which was much lower than that in heavily polluted days (6300 cm(-3)). At the stage of floating dust, the number concentration of accumulation mode particles decreased, and coarse particles contributed to total volume concentration of particulate matter as much as 90%. The accumulation mode particles collected in this stage were mostly in the size range of 0.2-0.5 mu m, and were rectangular or spherical. They were considered to be particles consisting of ammonium sulfate. New particle formation (NPF) was observed around noon in the three days during the dust event, indicating that the passage of the dust was probably favorable for NPF. (C) 2016 Elsevier B.V. All rights reserved.