Classification-based parameter synthesis for parametric timed automata

National Research Foundation (NRF) Singapor

Experimental study on laminar flame characteristics of methane-PRF95 dual fuel under lean burn conditions

The effects of methane addition to PRF95 (primary reference fuel with 95% volume of iso-octane and 5% volume of n-heptane) on the fundamental combustion parameters are experimentally investigated in a cylindrical combustion vessel using classical schlieren technique. In this study, methane is added with three energy fractions of 25%, 50% and 75% to PRF95. The laminar flame propagation, Markstein length and flame instability of dual fuels under different initial pressures and with different equivalence ratios, especially under lean burn condition, are well studied. Spherical flames are experimentally investigated at the initial temperature of 373 K and under the pressures of 2.5 bar, 5 bar and 10 bar. The equivalence ratios vary with 0.8, 1.0 and 1.2. The stretched flame speeds are determined by outwardly spherical flame method. The results show that at low initial pressures, the addition of methane to PRF95 increases the stretched flame speeds with lean equivalence ratios while decreases it in rich region. Laminar flame of methane-PRF95 mixtures burn faster than those of pure methane and PRF95 with equivalence ratio of 0.8 over the whole range of the initial pressures investigated, and this trend is more obvious at low pressure. Comparing the data of 25% methane dual fuel (DF25) with that of base fuels with the equivalence ratio of 0.8 and under the initial pressure of 2.5 bar, it can be seen that the flame speed of DF25 is 57% faster than that of methane and 22% faster than that of PRF95. These results provide important theoretical references to lean burn SI engine with methane-gasoline dual fuels under lean burn conditions

Contamination status and molecular typing of Legionella pneumophila in artificial water environment in Shanghai hospitals from 2019 to 2020

BackgroundThe incidence of Legionnaires' disease is increasing globally and artificial water environment is becoming a common source of outbreaks. Molecular typing techniques can help prevent and control Legionella. ObjectiveTo understand the molecular epidemiological characteristics of Legionella pneumophila in artificial water environment of Shanghai hospitals, and provide a scientific basis for the prevention and control of Legionnaires' disease. MethodsWater samples were collected from artificial water environment in 14 hospitals from May to October each year from 2019 to 2020 in Shanghai. A total of 984 water samples were collected from 8 Grade-A tertiary hospitals and 6 non-Grade-A tertiary hospitals, including 312 samples of cooling water, 72 samples of chilled water, and 600 samples of tap water. The water samples were isolated and serotyped for Legionella pneumophila and preserved, and the positive rate of Legionella pneumophila in the samples was used as an indicator of contamination. The preserved strains were resuscitated and 81 surviving strains were obtained for pulsed field gel electrophoresis (PFGE) typing analysis. ResultsA total of 124 Legionella pneumophila positive water samples were detected, with a positive rate of 12.60%. The positive rate was higher in the Grade-A tertiary hospitals (16.54%, 87/526) than in the non-Grade-A tertiary hospitals (8.08%, 37/458) (χ2=15.91, P<0.001). The positive rate of cooling water (23.40%) was the highest among different types of water samples, and the difference was statistically significant (χ2=61.19, P<0.001). The difference in positive rate of tap water was statistically significant among different hospital departments (χ2=11.37, P<0.05). The positive rate in 2019 (15.06%) was higher than that in 2020 (9.84%) (χ2=6.23, P<0.05). From May to October, August had the highest annual average positive rate (16.46%) and October had the lowest (8.54%), but the difference in positive rates among months was not statistically significant (χ2=5.39, P=0.37). The difference in positive rate among districts was statistically significant (χ2=24.88, P<0.001). A total of 131 strains of Legionella pneumophila were isolated, with serotype 1 (80.15%, 105/131) predominating. Among the 81 surviving strains of Legionella pneumophila subjected to PFGE typing, the band-based similarity coefficients ranged from 41.30% to 100%. Among the 29 PFGE band types (S1-S29) recorded, each band type included 1-10 strains, and S28 was the dominant band type. Four clusters (I-IV) of PFGE band types were identified, accounting for 66.67% (54/81) of all strains and containing 13 band types. ConclusionLegionella pneumophila contamination is present in the artificial water environment of hospitals in Shanghai from 2019 to 2020, and the contamination in tap water deserves attention. The detected serotype of Legionella pneumophila is predominantly type 1, and PFGE typing reveals the presence of genetic polymorphism. Therefore, the monitoring and control of Legionella pneumophila in hospital artificial water environment should be strengthened

Experimental investigation and modelling of the transformation of illicit drugs in a pilot-scale sewer system

In-sewer stability of illicit drug biomarkers has been evaluated by several reactor-based studies but less has been done in sewer pipes. Experiments conducted in sewer pipes have advantages over lab-scale reactors in providing more realistic biomarker stability due to the flow and biological dynamics. This study assessed the transportation and transformation of seven illicit drug biomarker compounds in a pilot-scale rising main and a gravity sewer pipe. Biomarkers presented diverse stability patterns in the pilot sewers, based on which a drug transformation model was calibrated. This model was subsequently validated using transformation datasets from literature, aiming to demonstrate the predictability of the pilot-based transformation coefficients under varying sewer conditions. Furthermore, transformation coefficients for five investigated biomarkers were generated from four studies and their prediction capabilities under the pilot sewer conditions were jointly assessed using performance statistics. The transformation model was successful in simulating the in-sewer stability for most illicit drugs. However, further study is required to delineate the sources and pathways for those compounds with potential formations to be simulated in the transformation model. Overall, the transformation model calibrated using the pilot-sewer data is a credible tool for the application of wastewater-based epidemiology

Stability of alcohol and tobacco consumption biomarkers in a real rising main sewer

Since alcohol and tobacco consumption are among the leading causes of population health harm, it is very important to understand the consumption behaviour to develop effective harm reduction strategies. Wastewater-based epidemiology (WBE) is a potential tool for estimating their consumption, but there are several uncertainties that need to be determined, including the stability of biomarkers in the sewer. Utilizing a real rising main sewer, this study investigated the stability of alcohol and tobacco consumption biomarkers. Rhodamine and acesulfame were used as flow tracer and benchmarker to understand the transportation of wastewater in the sewer with a hydraulic retention time between 2.7 and 5.0 h. Ethyl sulphate (EtS) and ethyl glucuronide (EtG), two biomarkers of alcohol consumption, were found to have different in-sewer stability, with EtS much more stable than EtG. The degradation rate of EtS is approximately 8% per hour, while EtG has a half-life of 1.9 h. Formation of nicotine, cotinine and trans-3'-hydroxycotinine, three biomarkers for tobacco consumption, was observed during the experiment, probably due to deconjugation of their glucuronide chemicals. The deconjugation process has prevented the determination of actual stability of the three chemicals. However, it is suggested that cotinine is relatively stable, while nicotine and trans-3'-hydroxycotinine degrade to a certain degree in the sewer system. According to our findings, the in-sewer degradation is more important during the interpretation of alcohol consumption estimation than for tobacco consumption estimation

Systematic evaluation of biomarker stability in pilot scale sewer pipes

Transformation of biomarkers (or their stability) during sewer transport is an important issue for wastewater-based epidemiology (WBE). Most studies so far have been conducted in the laboratory, which usually employed unrealistic conditions. In the present study, we utilized a pilot sewer system including a gravity pipe and a rising main pipe to investigate the fate of 24 pharmaceutical biomarkers. A programmable logic controller was used to control and monitor the system including sewer operational conditions and wastewater properties. Sequential samples were collected that can represent hydraulic retention time (HRT) of up to 8 h in a rising main and 4 h in a gravity sewer. Wastewater parameters and biomarker concentrations were analysed to evaluate the stability and transformation kinetics. The wastewater parameters of the pilot system were close to the conditions of real sewers. The findings of biomarker transformation were also close to real sewer data with seventeen biomarkers reported as stable while buprenorphine, caffeine, ethyl-sulfate, methadone, paracetamol, paraxanthine and salicylic acid degraded to variable extents. Both zero-order and first-order kinetics were used to model the degradation of unstable biomarkers and interestingly the goodness of fit R for the zero-order model was higher than the first-order model for all unstable biomarkers in the rising main. The pilot sewer system simulates more realistic conditions than benchtop laboratory setups and may provide a more accurate approach for assessing the in-sewer transformation kinetics and stability of biomarkers

Exceptionally low charge trapping enables highly efficient organic bulk heterojunction solar cells

In this study, we investigate the underlying origin of the high performance of PM6:Y6 organic solar cells. Employing transient optoelectronic and photoemission spectroscopies, we find that this blend exhibits greatly suppressed charge trapping into electronic intra-bandgap tail states compared to other polymer/non-fullerene acceptor solar cells, attributed to lower energetic disorder. The presence of tail states is a key source of energetic loss in most organic solar cells, as charge carriers relax into these states, reducing the quasi-Fermi level splitting and therefore device VOC. DFT and Raman analyses indicate this suppression of tail state energetics disorder could be associated with a higher degree of conformational rigidity and uniformity for the Y6 acceptor. We attribute the origin of such conformational rigidity and uniformity of Y6 to the presence of the two alkyl side chains on the outer core that restricts end-group rotation by acting as a conformation locker. The resultant enhanced carrier dynamics and suppressed charge carrier trapping are proposed to be a key factor behind the high performance of this blend. Low energetic disorder is suggested to be a key factor enabling reasonably efficient charge generation in this low energy offset system. In the absence of either energetic disorder or a significant electronic energy offset, it is argued that charge separation in this system is primarily entropy driven. Nevertheless, photocurrent generation is still limited by slow hole transfer from Y6 to PM6, suggesting pathways for further efficiency improvement

Experimental study on laminar flame characteristics of methane-PRF95 dual fuel under lean burn conditions

This article was published in the journal Fuel [© Elsevier Ltd.] and the definitive version is available at: http://dx.doi.org/10.1016/j.fuel.2016.07.065The effects of methane addition to PRF95 (primary reference fuel with 95% volume of iso-octane and 5% volume of n-heptane) on the fundamental combustion parameters are experimentally investigated in a cylindrical combustion vessel using classical schlieren technique. In this study, methane is added with three energy fractions of 25%, 50% and 75% to PRF95. The laminar flame propagation, Markstein length and flame instability of dual fuels under different initial pressures and with different equivalence ratios, especially under lean burn condition, are well studied. Spherical flames are experimentally investigated at the initial temperature of 373 K and under the pressures of 2.5 bar, 5 bar and 10 bar. The equivalence ratios vary with 0.8, 1.0 and 1.2. The stretched flame speeds are determined by outwardly spherical flame method. The results show that at low initial pressures, the addition of methane to PRF95 increases the stretched flame speeds with lean equivalence ratios while decreases it in rich region. Laminar flame of methane-PRF95 mixtures burn faster than those of pure methane and PRF95 with equivalence ratio of 0.8 over the whole range of the initial pressures investigated, and this trend is more obvious at low pressure. Comparing the data of 25% methane dual fuel (DF25) with that of base fuels with the equivalence ratio of 0.8 and under the initial pressure of 2.5 bar, it can be seen that the flame speed of DF25 is 57% faster than that of methane and 22% faster than that of PRF95. These results provide important theoretical references to lean burn SI engine with methane-gasoline dual fuels under lean burn conditions