Low nitrous oxide production through nitrifier-denitrification in intermittent-feed high-rate nitritation reactors

Nitrous oxide (N2O) production from autotrophic nitrogen conversion processes, especially nitritation systems, can be significant, requires understanding and calls for mitigation. In this study, the rates and pathways of N2O production were quantified in two lab-scale sequencing batch reactors operated with intermittent feeding and demonstrating long-term and high-rate nitritation. The resulting reactor biomass was highly enriched in ammonia-oxidizing bacteria, and converted ∼93 ± 14% of the oxidized ammonium to nitrite. The low DO set-point combined with intermittent feeding was sufficient to maintain high nitritation efficiency and high nitritation rates at 20–26 °C over a period of ∼300 days. Even at the high nitritation efficiencies, net N2O production was low (∼2% of the oxidized ammonium). Net N2O production rates transiently increased with a rise in pH after each feeding, suggesting a potential effect of pH on N2O production. In situ application of 15N labeled substrates revealed nitrifier denitrification as the dominant pathway of N2O production. Our study highlights operational conditions that minimize N2O emission from two-stage autotrophic nitrogen removal systems

Hot Deformation Behavior of As-Cast 30Cr2Ni4MoV Steel Using Processing Maps

The hot deformation behavior of as-cast 30Cr2Ni4MoV steel was characterized using processing maps in the temperature range 850 to 1200 °C and strain rate range 0.01 to 10 s−1. Based on the obtained flow curves, the power dissipation maps at different strains were developed and the effect of the strain on the efficiency of power dissipation was discussed in detail. The processing maps at different strains were obtained by superimposing the instability maps on the power dissipation maps. According to the processing map and the metallographic observation, the optimum domain of hot deformation was in the temperature range of 950–1200 °C and strain rate range of 0.03–0.5 s−1, with a peak efficiency of 0.41 at 1100 °C and 0.25 s−1 which were the optimum hot working parameters

Effect of Parameters on Internal Crack Healing in 30Cr2Ni4MoV Steel for 600-Ton Ultra-Super Ingots

The effect of parameters on internal crack healing in 30Cr2Ni4MoV steel for 600-ton ultra-super ingots was systematically investigated. The results show that the degree of crack healing increases with increasing healing temperature, holding time, reduction ratio, and hot pressure, and with decreasing strain rate. Internal crack healing in 30Cr2Ni4MoV steel should be conducted at less than 1200 °C to avoid grain coarsening. Hot pressure, in the high-temperature elastic zone and perpendicular to the crack faces, not only promotes the rapid crack healing, but also prevents grain coarsening of the matrix

Crack Healing and Mechanical Properties Recovery in SA 508–3 Steel

Internal cracks could be healed under the process of hot plastic deformation. In this study, mechanical properties recovery after crack healing in SA 508–3 steel were investigated. Microstructures of the crack healing zones were observed using an optical microscope (OM) and electron back scattered diffraction (EBSD) technology, and the recovery degrees of mechanical properties in the crack healing zones with the healing temperature and a reduction ratio were tested systematically. The results showed that the internal cracks in SA 508–3 steel disappeared and were replaced by newly formed grains, achieved by recrystallization and abnormal grain growth. The tensile properties of crack healing zones could be fully restored, while their impact and low cycle fatigue properties could only be partially achieved. The recovery degrees of mechanical properties in crack healing zones increased with increasing the healing temperature and reduction ratio in the temperature range of 950–1050 °C. When the temperature was above 1150 °C, the impact properties began to deteriorate because of grain coarsening and larger MA (martensite–austenite) constituents. The microstructural evolution of the crack zone in the SA 508–3 steel was sketched

Study on Improving the Air Quality with Emission Enhanced Control Measures in Beijing during a National Parade Event

Research on the enhanced control and emission-reduction measures to improve air quality during major events could provide data theory and scientific support for air-quality improvement during non-activities. Based on the air-quality data published by the China Environmental Monitoring Station and the meteorological elements and weather conditions released by the China Meteorological Administration, this paper explored the characteristics of air-quality evolution in Beijing from 5 August to 18 September 2015 and the weather situation during the Military Parade. The results showed that: (1) Emission-reduction measures implemented for air quality by Beijing and its surrounding area were induced, and we explored the contribution of these measures to pollutants or AQI in the locality. (2) During the 2015 Military Parade, Beijing was in the front or lower part of the high-pressure system. Due to the strong effect of North or Northeast winds, the weather situation was conducive to the diffusion of pollutants. When before or after the implementation, once the atmospheric diffusion was poor, the pollutants would accumulate gradually. Thus, it can be seen that the weather situation had a great impact on air quality. (3) During the implementation, PM2.5, PM10, NO2 and other pollutants decreased significantly, of which the concentration of PM10 decreased the most, from 109 μg·m−3 down to 34 μg·m−3, and the concentration of PM2.5 decreased by 72.73%. According to the changes between before and during the implementation or during and after the implementation, the concentration of PM10 and PM2.5 increased when the implementation of the emission-reduction measures had been finished, indicating that the enhanced control measures made a great contribution to the emission reduction in particles. (4) In addition, the annual average of AQI in the three years is 87.49, and the average value of a normal year was the average value of 2013 and 2014. The average value of the normal year during the military parade is 64.63, which was 70.40% lower than the average value of AQI during the military parade. The goal of reaching the secondary standard of GB-3095-2012 was achieved, and there was still a long way to go from the primary standard. In a few words, in order to achieve the goal of better air quality throughout the year, all parties still needed to coordinate control and make joint efforts

Pedestrian gaze pattern before crossing road in a naturalistic traffic setting

Abstract Background Gaze is the primary way for pedestrians to obtain clues from traffic scenes before making decisions. Therefore, understanding pedestrian gaze pattern is vital for traffic safety in general and for the design of autonomous vehicles. Methods In this study, participants made road-crossing decisions in a naturalistic traffic scene, with an eye-tracker recording their gaze behaviors. We manually encoded the recorded videos with 14,898 fixations, and then analyzed the gaze pattern at three levels from general to specific: gaze towards overall scenes, gaze towards vehicles and gaze towards components of vehicles. Findings At the first level, our findings indicate that frequent fixations began to appear at the distance of 100 m and peaked around 5–30 m away from pedestrians. Transversely pedestrians mainly gazed at the two lanes adjacent to themselves. Pedestrians allocated 53% gaze duration to motor vehicles. For a specific vehicle, which is the second level, the gaze duration varied with vehicles' attributes such as distances, sizes, and types. Finally, at the third level, we discovered that pedestrians’ gaze duration on different vehicle components varied with the longitudinal distance. As vehicles approach, the main area of fixation expanded from the near side headlight to the whole front and near side, and finally shift to the near side of a vehicle. Implications The distribution of fixations in space and vehicle components before pedestrian crossing can provide fundamental information for understanding and modeling of pedestrian's road-crossing behaviors. In practice, our findings can guide the timing and position of information displays on autonomous vehicles to facilitate friendly interaction with pedestrians

Study on Improving the Air Quality with Emission Enhanced Control Measures in Beijing during a National Parade Event

Research on the enhanced control and emission-reduction measures to improve air quality during major events could provide data theory and scientific support for air-quality improvement during non-activities. Based on the air-quality data published by the China Environmental Monitoring Station and the meteorological elements and weather conditions released by the China Meteorological Administration, this paper explored the characteristics of air-quality evolution in Beijing from 5 August to 18 September 2015 and the weather situation during the Military Parade. The results showed that: (1) Emission-reduction measures implemented for air quality by Beijing and its surrounding area were induced, and we explored the contribution of these measures to pollutants or AQI in the locality. (2) During the 2015 Military Parade, Beijing was in the front or lower part of the high-pressure system. Due to the strong effect of North or Northeast winds, the weather situation was conducive to the diffusion of pollutants. When before or after the implementation, once the atmospheric diffusion was poor, the pollutants would accumulate gradually. Thus, it can be seen that the weather situation had a great impact on air quality. (3) During the implementation, PM2.5, PM10, NO2 and other pollutants decreased significantly, of which the concentration of PM10 decreased the most, from 109 μg·m−3 down to 34 μg·m−3, and the concentration of PM2.5 decreased by 72.73%. According to the changes between before and during the implementation or during and after the implementation, the concentration of PM10 and PM2.5 increased when the implementation of the emission-reduction measures had been finished, indicating that the enhanced control measures made a great contribution to the emission reduction in particles. (4) In addition, the annual average of AQI in the three years is 87.49, and the average value of a normal year was the average value of 2013 and 2014. The average value of the normal year during the military parade is 64.63, which was 70.40% lower than the average value of AQI during the military parade. The goal of reaching the secondary standard of GB-3095-2012 was achieved, and there was still a long way to go from the primary standard. In a few words, in order to achieve the goal of better air quality throughout the year, all parties still needed to coordinate control and make joint efforts

Switched safe tracking control design for unmanned autonomous helicopter with disturbances

International audienceIn this paper, the switched safe tracking control scheme is investigated for the attitude and altitude system of a medium-scale unmanned autonomous helicopter with output constraints and unknown external disturbances. To keep the attitude angles and altitude within the desired constrained range, an output boundary protection approach is adopted to generate an output constrained trajectory which is piecewise differentiable. The disturbance observer-based control method is employed to handle the unknown external disturbances of the system. Because of the piecewise differentiability of the output constrained trajectory, the closed-loop error system with the safe tracking controller can be seen as a switched system with jump dynamics. The multiple Lyapunov function method is adopted to guarantee the tracking performance with designed average dwell time. Simulation results of an example are provided to illustrate the effectiveness of the proposed control scheme for the unmanned autonomous helicopter system