Performance and mechanism of phosphorus removal in an integrated vertical flow constructed wetland treating eutrophic lake water

Phosphorus removal performance and a possible mechanism for the phosphorus removal from an eutrophic lake water were investigated using a medium-scale integrated vertical constructed wetland (combined vertical and reverse-vertical systems) from April, 11, 2001 to September, 28, 2004. Environmental factors affecting phosphorus removal and release profiles were monitored simultaneously under hydraulic loads from 400 to 2000 mm per day. The phosphorus removal rate varied with the environmental conditions. The removal rate for acidic influent water was superior to that for alkaline influent water. The substrate in the wetland chamber acted as a buffer to regulate the pH value of the water sample. As regards the water temperature, no significant differences were observed for the removal rate of total phosphorus (TP) and soluble reactive phosphorus (SRP) between low (lower than 15 degrees C) medium (16-25 degrees C) and high temperature (higher than 26 degrees C) conditions. Under a hydraulic load of 400 mm per day, the removal rate reached over 70%, the highest value achieved in this work. In addition, the highest hydraulic load of 2000 mm/d did not result in the lowest removal rate, as had been expected. After a two-year high hydraulic load test, the removal rate decreased significantly. Phosphorous release from the substrate was examined using a spatial sampling method. Depth profiles of total phosphorus and different states of phosphorus present in the substrate were recorded. This further study demonstrated that binding of phosphorus by iron and calcium might be another major factor in the removal and release of TP and SRP in this wetland system. The distribution of the speciated phosphorus showed that the amount of phosphorus captured in the substrate of the down-flow chamber was significantly higher than that captured in the up-flow chamber, suggesting that the up-flow chamber was the main source of phosphorus release in this constructed wetland.

Environmental mechanism of change in cyanobacterial species composition in the northeastern part of Lake Dianchi (China)

Environmental mechanism of change in cyanobacterial species composition in the northeastern part of Lake Dianchi (also called Macun Bay and Haidong Bay) was studied using canonical correlation analysis (CCA), but also bottom-up control and top-down control were fully discussed. Results from CCA suggest: (1) the abundance and dominance of Microcystis aeruginosa in Macun Bay and Haidong Bay are influenced by total phosphorus (TP), nitrate (NO3--N), nitrite (NO2--N), dissolved oxygen (DO) and water temperature (WT); (2) water temperature has a positive correlation with the abundance of M. aeruginosa and it also has negative correlations with the abundances of Anabaena flos-aquae and Aphanizomenonon flos-aquae; and (3) abundances of both Anabaena flos-aquae and Aphanizomenon flos-aquae have positive correlations with ammonia-N (NH4+-N). Furthermore, cyanobacterial species composition has no significant correlations with light and size-fractioned iron in this study. Grazers, cyanophages and viruses were able to control cyanobacterial blooms and change the composition of cyanobacterial species. Though we studied physical and chemical factors intensely enough, we still are not able to predict the change in the composition of cyanobacterial blooms, because of plankton system in a chaotic behavior.

Modeling current-voltage behaviour in oxide TFTs combining trap-limited conduction with percolation

Current-voltage behaviour of oxide TFTs is modeled based on trap-limited conduction and percolation theories. The mobility has a power-law dependence, in which percolation controls the exponent while trap states determine constant term in the power law. The proposed model, which is fully physically-based, provides a good agreement with measured transistor characteristics as well as transient operations of fabricated pixel test circuits for oxide-based OLED displays. © 2013 Society for Information Display.

A thermalization energy analysis of the threshold voltage shift in amorphous indium gallium zinc oxide thin film transistors under simultaneous negative gate bias and illumination

It has been previously observed that thin film transistors (TFTs) utilizing an amorphous indium gallium zinc oxide (a-IGZO) semiconducting channel suffer from a threshold voltage shift when subjected to a negative gate bias and light illumination simultaneously. In this work, a thermalization energy analysis has been applied to previously published data on negative bias under illumination stress (NBIS) in a-IGZO TFTs. A barrier to defect conversion of 0.65-0.75 eV is extracted, which is consistent with reported energies of oxygen vacancy migration. The attempt-to-escape frequency is extracted to be 10 6-107 s-1, which suggests a weak localization of carriers in band tail states over a 20-40 nm distance. Models for the NBIS mechanism based on charge trapping are reviewed and a defect pool model is proposed in which two distinct distributions of defect states exist in the a-IGZO band gap: these are associated with states that are formed as neutrally charged and 2+ charged oxygen vacancies at the time of film formation. In this model, threshold voltage shift is not due to a defect creation process, but to a change in the energy distribution of states in the band gap upon defect migration as this allows a state formed as a neutrally charged vacancy to be converted into one formed as a 2+ charged vacancy and vice versa. Carrier localization close to the defect migration site is necessary for the conversion process to take place, and such defect migration sites are associated with conduction and valence band tail states. Under negative gate bias stressing, the conduction band tail is depleted of carriers, but the bias is insufficient to accumulate holes in the valence band tail states, and so no threshold voltage shift results. It is only under illumination that the quasi Fermi level for holes is sufficiently lowered to allow occupation of valence band tail states. The resulting charge localization then allows a negative threshold voltage shift, but only under conditions of simultaneous negative gate bias and illumination, as observed experimentally as the NBIS effect. © 2014 AIP Publishing LLC.

Changes in the patterns of inorganic nitrogen and TN/TP ratio and the associated mechanism of biological regulation in the shallow lakes of the middle and lower reaches of the Yangtze River

The changes of NH3-N, NO3-N, NO2-N and TN/TP were studied during growth and non-growth season in 33 subtropical shallow lakes in the middle and lower reaches of the Yangtze River. There were significant positive correlations among all nutrient concentrations, and the correlations were better in growth season than in non-growth season. When TP > 0.1 mgL(-1), NH3-N increased sharply in non-growth season with increasing TP, and NO3-N increased in growth season but decreased in non-growth season with TP. These might be attributed to lower dissolved oxygen and low temperature in non-growth season of the hypereutrophic lakes, since nitrification is more sensitive to dissolved oxygen and temperature than anti nitrification. When 0.1 mgL(-1)> TP > 0.035 mgL(-1), TN and all kinds of inorganic nitrogen were lower in growth season than in non-growth season, and phytoplankton might be the vital regulating factor. When TP < 0.035 mgL(-1), inorganic nitrogen concentrations were relatively low and NH3-N, NO2-N had significant correlations with phytoplankton, indicating that NH3-N and NO2-N might be limiting factors to phytoplankton. In addition, TN/TP went down with decline in TIP concentration, and TN and inorganic nitrogen concentrations were obviously lower in growth season than in non-growth season, suggesting that decreasing nitrogen (especially NH3-N and NO3-N) was an important reason for the decreasing TN/TP in growth season. The ranges of TN/TP were closely related to trophic level in both growth and non-growth seasons, and it is apparent that in the eutrophic and hypertrophic state the TN/TP ratio was obviously lower in growth season than in non-growth season. The changes of the TN/TP ratio were closely correlated with trophic levels, and both declines of TN in the water column and TP release from the sediment were important factors for the decline of the TN/TP ratio in growth season.

Growth mechanism of graphene on platinum: Surface catalysis and carbon segregation

A model of the graphene growth mechanism of chemical vapor deposition on platinum is proposed and verified by experiments. Surface catalysis and carbon segregation occur, respectively, at high and low temperatures in the process, representing the so-called balance and segregation regimes. Catalysis leads to self-limiting formation of large area monolayer graphene, whereas segregation results in multilayers, which evidently "grow from below." By controlling kinetic factors, dominantly monolayer graphene whose high quality has been confirmed by quantum Hall measurement can be deposited on platinum with hydrogen-rich environment, quench cooling, tiny but continuous methane flow and about 1000°C growth temperature. © 2014 AIP Publishing LLC.

Hydroxylated metabolites of polychlorinated biphenyls and their endocrine disrupting mechanism

Hydroxylated polychlorinated biphenyls (OH-PCBs a group of main active metabolites of polychlorinated biphenyl (PCBs) which are typical persistent organic pollutants (Pops) I have been identified in wild animals and human. The endocrine disruption of OH-PCBs has been drawn great attention due to the similarity of their chemical structures to the natural estrogens and thyroid hormones. The metabolic pathways of PCBs, the levels of OHPCBs in organism, the endocrine disruption and other adverse effects of OH-PCBs are reviewed. The further investigation of OH-PCBs will not only reveal the toxicological mechanism of PCBs, but also can lay scientific basis for setting up the risk assessment of POPs contamination and early-warning system in China.

Nutritional homeostasis in carnivorous southern catfish (Silurus meridionalis): is there a mechanism for increased energy expenditure during carbohydrate overfeeding?

In previous growth experiments with carnivorous southern catfish (Silurus meridionalis), the non-fecal energy lose was positively related to dietary. carbohydrate level. To test whether metabolic energy expenditure accounts for such energy loss, an experiment was performed with southern catfish juveniles (33.2-71.9 g) to study the effect of dietary carbohydrate level on fasting metabolic rate and specific dynamic action (SDA) at 27.5 degreesC. The fasting metabolic rate in this catfish was increased with dietary carbohydrate level, and the specific dynamic action (SDA) coefficient (energy expended on SDA as percent of assimilated energy) was not affected by dietary carbohydrate level. The results suggest that in southern catfish, carbohydrate overfeeding increases metabolic rate to oxidize unwanted assimilated carbohydrate. A discussion on the poor capacity of intermediate metabolism for adapting dietary carbohydrate in carnivorous fish and its possible relationship with facultative component of SDA was also documented in this paper. (C) 2004 Elsevier Inc. All rights reserved.

Guided self-organization in a dynamic embodied system based on attractor selection mechanism

Guided self-organization can be regarded as a paradigm proposed to understand how to guide a self-organizing system towards desirable behaviors, while maintaining its non-deterministic dynamics with emergent features. It is, however, not a trivial problem to guide the self-organizing behavior of physically embodied systems like robots, as the behavioral dynamics are results of interactions among their controller, mechanical dynamics of the body, and the environment. This paper presents a guided self-organization approach for dynamic robots based on a coupling between the system mechanical dynamics with an internal control structure known as the attractor selection mechanism. The mechanism enables the robot to gracefully shift between random and deterministic behaviors, represented by a number of attractors, depending on internally generated stochastic perturbation and sensory input. The robot used in this paper is a simulated curved beam hopping robot: a system with a variety of mechanical dynamics which depends on its actuation frequencies. Despite the simplicity of the approach, it will be shown how the approach regulates the probability of the robot to reach a goal through the interplay among the sensory input, the level of inherent stochastic perturbation, i.e., noise, and the mechanical dynamics. © 2014 by the authors; licensee MDPI, Basel, Switzerland.

Cementing mechanism of algal crusts from desert area

34-, 17-, 4-, 1.5-year old natural algal crusts were collected from Shapotou Scientific Station of the Chinese Academy of Sciences, 40-day old field and greenhouse artificial algal crusts were in situ developed in the same sandy soil and the same place (37degrees27'N, 104degrees57'E). Their different cohesions both against wind force and pressure were measured respectively by a sandy wind-tunnel experiment and a penetrometer. On the basis of these algal crusts, the cementing mechanism was revealed from many subjects and different levels. The results showed that in the indoor artificial crusts with the weakest cohesion bunchy algal filaments were distributed in the surface of the crusts, produced few extracellular polymers (EPS), the binding capacity of the crusts just accomplished by mechanical bundle of algal filaments. For field crusts, most filaments grew toward the deeper layers of algal crusts, secreted much more EPS, and when organic matter content was more than 2.4 times of chlorophyll a, overmuch organic matter (primarily is EPS) began to gather onto the surface of the crusts and formed an organic layer in the relatively lower micro-area, and this made the crust cohesion increase 2.5 times. When the organic layer adsorbed and intercepted amounts of dusts, soil particles and sand grains scattered down from wind, it changed gradually into an inorganic layer in which inorganic matter dominated, and this made the crusts cohesion further enhanced 2-6 times. For crust-building species Microcoleus vaginatus, 88.5% of EPS were the acidic components, 78% were the acidic proteglycan of 380 kD. The uronic acid content accounted for 8% of proteglycan, and their free carboxyls were important sites of binding with metal cations from surrounding matrix.

An inducible CO2 concentrating mechanism in cyanobacterium Anabaena sp strain PCC7120

In order to define its characteristics of the photosynthetic utilization of CO2 and HCO3- when the ambient inorganic carbon changed, HCG (High-CO2-Growing Cells) of cyanobacterium Anabaena sp. strain PCC7120 were prepared. The growth rate of HCG was higher than that of LCG (low-CO2-growing cells, i.e. air-growing cells). When the HCG cells were transferred from 5% CO2 to air levels of CO2 , a series of changes took place: its carbonic anhydrase activity as well as its photosynthetic affinity to the external inorganic carbon significantly increased; the number of the carboxysomes, which is one of the most important components of CCM in cyanobacteria also increased. These facts indicated that the CCM activity of Anabaena PCC 7120 was induced. When the pH in the medium increased from 6 to 9, the photosynthetic affinity to external inorganic carbon of both HCG and LCG declined, while the apparent photosynthetic affinity to external CO2 increased. In the light of these findings, this inducible CCM in cyanobacteria provided a good model for the study of the photosynthetic Ci utilization in the phototrophic microoganisms.

UV-sensitive P compounds: Release mechanism, seasonal fluctuation and inhibitory effects on alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Filtrable phosphorus compounds in a shallow Chinese freshwater lake (Donghu Lake) were fractionated by Sephadex G-25 gel-filtration chromatography. Some portions of those compounds released soluble reactive phosphorus upon irradiation with low dose ultraviolet light. Catalase and a hydroxyl radical scavenger (mannitol) markedly prevented photosensitive phosphorus release. The observed effects may be explained by the action of oxidizing reagents such as hydroxyl radicals, produced in photochemical reactions between UV irradiation and humic substances in the water. There was a strong seasonality in UV-sensitive P (UVSP) release. Michaels constants (K-m) of total alkaline phosphatase in the lake water showed a direct positive relation to UVSP. Plot of K-m against the UVSP/phosphomonoester ratio reveals a strong relationship between the two variables. These results suggest that in some situations UVSP may be a competitive inhibitor of alkaline phosphatase activity in the lake. The competitive inhibition of fractionated UVSP on alkaline phosphatase reagent (Sigma) apparently supports this hypothesis.

Mechanism on Effect of Surface Plasmons Coupling with InGaN/GaN Quantum Wells: Enhancement and Suppression of Photoluminescence Intensity

The photoluminescence (PL) intensity enhancement and suppression mechanism on surface plasmons (SPs) coupling with InGaN/GaN quantum wells (QWs) have been systematically studied. The SP-QW coupling behaviors in the areas of GaN cap layer coated with silver thin film were compared at different temperatures and excitation powers. It is found that the internal quantum efficiency (IQE) of the light emitting diodes (LEDs) varies with temperature and excitation power, which in turn results in anomalous emission enhancement and suppression tendency related to SP-QW coupling. The observation is explained by the balance between the extraction efficiency of SPs and the IQE of LEDs

Mechanism of enhancing output power of plasmonic very-small-aperture lasers

Light transmission through a single subwavelength slit surrounded by periodic grooves in layered films consisting of Au and dielectric material is analyzed by the finite difference time domain method in two dimensions. The results show that the transmission field can be enhanced by the corrugations on the output plane, which is a supplementary explanation for the extraordinary optical transmission.