Anodic-oxide-induced interdiffusion in quantum wells structure

Enhancement of interdiffusion in GaAs/AlGaAs quantum wells (QWs) due to anodic oxides was studied. Photoluminescence and diffused QW modeling were used to understand the effects of intermixing on the QW structure. The activation energy is similar to those obtained from SiO 2 cap annealed quantum well structures.published_or_final_versio

Occurrence, fate and health risk assessment of 10 common antibiotics in two drinking water plants with different treatment processes

© 2019 Elsevier B.V. The occurrence of antibiotics in drinking water has become a serious problem worldwide as they are a potential and real threat to human health. In this study, the variability of 10 typical antibiotics in two drinking water plants was investigated in two seasons (n = 12). The total concentrations of target antibiotics in raw water were significantly higher in winter than in summer, which may be attributed to the more frequent occurrence of colds and respiratory diseases as well as less rainfall in winter. The efficiency in removing the antibiotics varied from −46.5% to 45.1% in water plant A (WP-A) using a conventional process and 40.3% to 70.3% in water plant B (WP-B) with an advanced treatment process. Results indicated that the antibiotics in WP-A were mainly removed via the coagulation process. However in WP-B, the ultraviolet + chlorination process played a key role in antibiotics removal, followed by the pre-ozone + coagulation process. According to the human health risk assessment, it was suggested that the risk of drinking water was significantly higher than that of skin contact. However, the risk of carcinogenesis and non-carcinogenesis caused by antibiotics was at an acceptable level

Removal of antibiotics (sulfamethazine, tetracycline and chloramphenicol) from aqueous solution by raw and nitrogen plasma modified steel shavings

© 2017 Elsevier B.V. The removal of sulfamethazine (SMT), tetracycline (TC) and chloramphenicol (CP) from synthetic wastewater by raw (M3) and nitrogen plasma modified steel shavings (M3-plN2) was investigated using batch experiments. The adsorption kinetics could be expressed by both pseudo-first-order kinetic (PFO) and pseudo-second-order kinetic (PSO) models, where correlation coefficient r2 values were high. The values of PFO rate constant k1p and PSO rate constant k2p decreased as SMT-M3 > SMT-M3-plN2 > TC-M3-plN2 > TC-M3 > CP-M3 > CP-M3-plN2 and SMT-M3 > SMT-M3-plN2 > TC-M3 > TC-M3-plN2 > CP-M3 > CP-M3-plN2, respectively. Solution pH, adsorbent dose and temperature exerted great influences on the adsorption process. The plasma modification with nitrogen gas cleaned and enhanced 1.7-fold the surface area and 1.4-fold the pore volume of steel shavings. Consequently, the removal capacity of SMT, TC, CP on the adsorbent rose from 2519.98 to 2702.55, 1720.20 to 2158.36, and 2772.81 to 2920.11 μg/g, respectively. Typical chemical states of iron (XPS in Fe2p3 region) in the adsorbents which are mainly responsible for removing antibiotics through hydrogen bonding, electrostatic and non- electrostatic interactions and redox reaction were as follows: Fe3O4/Fe2 +, Fe3O4/Fe3 +, FeO/Fe2 + and Fe2O3/Fe3 +

Nitrous oxide generation in denitrifying phosphorus removal process: Main causes and control measures

Despite the many benefits of denitrifying phosphorus removal process, the significant generation of nitrous oxide (N2O), a potent greenhouse gas, remains a problem for this innovative and promising process. To better understand and more effectively control N2O generation in denitrifying phosphorus removal process, batch experiments were carried out to investigate the main causes of N2O generation, based on which the control measures were subsequently proposed. The results showed that N2O generation accounted for 0.41 % of the total nitrogen removal in denitrifying phosphorus removal process, whereas, in contrast, almost no N2O was generated in conventional denitrification process. It was further demonstrated that the weak competition of N2O reductase for electrons and the high nitrite accumulation were the two main causes for N2O generation, evidenced by N2O production and reduction rates under different conditions. Accordingly, the reduction of N2O generation was successfully achieved via two control measures: (1) the use of continuous nitrate addition reducing N2O generation by around 91.4 % and (2) the use of propionate as the carbon source reducing N2O generation by around 69.8 %. © 2013 Springer-Verlag Berlin Heidelberg

Food waste based biochars for ammonia nitrogen removal from aqueous solutions

© 2019 Elsevier Ltd Biochar derived from waste has been increasingly considered as a potential green adsorbent due to its significant ability and affordable production costs. This study prepared and evaluated 7 types of food waste-based biochars (FWBBs) (including meat and bone, starchy staples, leafy stemmed vegetables, nut husks, fruit pericarp, bean dreg and tea leaves). The impacts of raw materials, pyrolysis temperatures (300, 400, 500, 600 and 700 °C), and residence time (2 h and 4 h) on the removal of ammonia nitrogen at different ammonia nitrogen concentrations (5, 10, 20, 50, 100, 150 mg/L) were investigated. The batch equilibrium and kinetic experiments confirmed that a FWBB dosage of 3 g/L at 25 °C could remove up to 92.67% ammonia nitrogen. The Langmuir isotherm model had the best fit to equilibrium experimental data with a maximum adsorption capacity of 7.174 mg/g at 25 °C. The pseudo-second order kinetic model well describes the ammonia nitrogen adsorption

N<inf>2</inf>O reduction during municipal wastewater treatment using a two-sludge SBR system acclimatized with propionate

A two-sludge denitrifying phosphorus removal process (A2N-SBR), acclimatized with propionate, was proposed as an efficient method for nitrous oxide (N2O) reduction during municipal wastewater treatment. Compared with the conventional nitrification-denitrification process (AO-SBR) operated in parallel, the A2N-SBR not only significantly improved total nitrogen and soluble phosphorus removal efficiencies by around 32.3% and 23.5%, respectively, but also greatly reduced N2O generation by around 31.5%. Moreover, like the anoxic stage of AO-SBR, nearly zero N2O (merely 0.054% of the removed nitrogen) was generated during the anoxic stage of A2N-SBR. The substantial N2O reduction achieved in the proposed A2N-SBR can be reasonably explained by: (i) the use of independent nitrification reactor resulting in higher activity of nitrifying bacteria and no occurrence of heterotrophic denitrification in aerobic stage, and (ii) the use of propionate as carbon source decreasing nitrite accumulation in anoxic stage. © 2013 Elsevier B.V

Effect of plant harvesting on the performance of constructed wetlands during winter: radial oxygen loss and microbial characteristics

© 2014, Springer-Verlag Berlin Heidelberg. The aboveground tissue of plants is important for providing roots with constant photosynthetic resources. However, the aboveground biomass is usually harvested before winter to maintain the permanent removal of nutrients. In this work, the effects of harvest on plants’ involvement in oxygen input as well as in microbial abundance and activity were investigated in detail. Three series of constructed wetlands with integrated plants (“unharvested”), harvested plants (“harvested”), and fully cleared plants (“cleared”) were set up. Better performance was found in the unharvested units, with the radial oxygen loss (ROL) rates ranging from 0.05 to 0.59 μmol O2/h/plant, followed by the harvested units that had relatively lower ROL rates (0.01 to 0.52 μmol O2/h/plant). The cleared units had the lowest removal efficiency, which had no rhizome resources from the plants. The microbial population and activity were highest in the unharvested units, followed by the harvested and cleared units. Results showed that bacterial abundances and enhanced microbial activity were ten times higher on root surfaces compared with sands. These results indicate that late autumn harvesting of the aboveground biomass exhibited negative effects on plant ROL as well as on the microbial population and activity during the following winter

In situ reconstruction of long-term extreme flooding magnitudes and frequencies based on geological archives

© 2019 Extreme flooding magnitudes and frequencies are essentially related to assessment of risk and reliability in hydrological design. Extreme flooding and its discharge are highly sensitive to regional climate change. Presently, its discharge can be reconstructed by a geological archive or record along the river valley. Two units of typical extreme flooding deposits (EFDs) carrying long-term information preserved in the Holocene loess–palaeosol sequence were found at Xipocun (XPC), which is located in Chengcheng County, China. It is situated in the downstream section of the Beiluohe (hereafter BLH) River. Based on multiple sedimentary proxy indices (grain-size distribution (GSD), magnetic susceptibility (MS), and loss-on-ignition (LOI), etc.), EFDs were interpreted as well-sorted clayey silt in suspension. They were then deposited as a result of riverbank flooding in a stagnant environment during high water level. Through the Optically Stimulated Luminescence (OSL) dating technique and stratigraphic correlations, chronologies of two identified extreme flooding periods were 7600–7400 a B.P. and 3200–3000 a B.P. Two phases of extreme flooding occurrence under climate abnormality scenarios were characterized as having high frequencies of hydrological extremes in river systems. According to simulation and verification using the Slope–Area Method and Hydrologic Engineering Center's River Analysis System (HEC-RAS) model, the extreme flooding discharges at the XPC site were reconstructed between 9625 m 3 /s and 16,635 m 3 /s. A new long-term flooding frequency and peak discharge curve, involved gauged flooding, historical flooding at Zhuangtou station and in situ reconstructed extreme flooding events, was established for the downstream BLH River. The results improve the accuracy of low-frequency flooding risk assessment and provide evidence for predicting the response of fluvial systems to climate instability. Thus, this improves the analysis of the BLH River watershed

Predicting the Next Best View for 3D Mesh Refinement

3D reconstruction is a core task in many applications such as robot navigation or sites inspections. Finding the best poses to capture part of the scene is one of the most challenging topic that goes under the name of Next Best View. Recently, many volumetric methods have been proposed; they choose the Next Best View by reasoning over a 3D voxelized space and by finding which pose minimizes the uncertainty decoded into the voxels. Such methods are effective, but they do not scale well since the underlaying representation requires a huge amount of memory. In this paper we propose a novel mesh-based approach which focuses on the worst reconstructed region of the environment mesh. We define a photo-consistent index to evaluate the 3D mesh accuracy, and an energy function over the worst regions of the mesh which takes into account the mutual parallax with respect to the previous cameras, the angle of incidence of the viewing ray to the surface and the visibility of the region. We test our approach over a well known dataset and achieve state-of-the-art results.Comment: 13 pages, 5 figures, to be published in IAS-1

Livenet: A low-latency video transport network for large-scale live streaming

Low-latency live streaming has imposed stringent latency requirements on video transport networks. In this paper we report on the design and operation of the Alibaba low-latency video transport network, LiveNet. LiveNet builds on a flat CDN overlay with a centralized controller for global optimization. As part of this, we present our design of the global routing computation and path assignment, as well as our fast data transmission architecture with fine-grained control of video frames. The performance results obtained from three years of operation demonstrate the effectiveness of LiveNet in improving CDN performance and QoE metrics. Compared with our prior state-of-The-Art hierarchical CDN deployment, LiveNet halves the CDN delay and ensures 98% of views do not experience stalls and that 95% can start playback within 1 second. We further report our experiences of running LiveNet over the last 3 years