Model evaluation and optimisation of nutrient removal potential for sequencing batch reactors

Performance of sequencing batch reactors for simultaneous nitrogen and phosphorus removal is evaluated by means of model simulation, using the activated sludge model, ASM2d, involving anoxic phosphorus uptake, recently proposed by the IAWQ Task group. The evaluation includes all major process configurations with different aerobic, anoxic, anaerobic sequences, and fill conditions. Basic relationships between modelling and design based on overall process stoichiometry are established for the interpretation of nutrient profiles associated with different operation modes. A similar approach is also used for the assessment of the effect of major operating parameters on system performance. WaterSA Vol.28(4) 2002: 423-43

Investigation of AlInN HEMT structures with different AlGaN buffer layers grown on sapphire substrates by MOCVD

Cataloged from PDF version of article.We investigate the structural and electrical properties of AlxIn1-xN/AlN/GaN heterostructures with AlGaN buffers grown by MOCVD, which can be used as an alternative to AlInN HEMT structures with GaN buffer. The effects of the GaN channel thickness and the addition of a content graded AlGaN layer to the structural and electrical characteristics were studied through variable temperature Hall effect measurements, high resolution XRD, and AFM measurements. Enhancement in electron mobility was observed in two of the suggested AlxIn1-xN/AlN/GaN/Al0.04Ga0.96N heterostructures when compared to the standard AlxIn1-xN/AlN/GaN heterostructure. This improvement was attributed to better electron confinement in the channel due to electric field arising from piezoelectric polarization charge at the Al0.04Ga0.96N/GaN heterointerface and by the conduction band discontinuity formed at the same interface. If the growth conditions and design parameters of the AlxIn1-xN HEMT structures with AlGaN buffers can be modified further, the electron spillover from the GaN channel can be significantly limited and even higher electron mobilities, which result in lower two-dimensional sheet resistances, would be possible. (C) 2012 Elsevier B.V. All rights reserved

Electron transport properties in Al0.25Ga0.75N/AIN/GaN hetrostructures with different InGaN back barrier layers and GaN channel thickness grown by MOCVD

Cataloged from PDF version of article.The electron transport properties in Al0.25Ga0.75N/AlN/GaN/InxGa1-xN/GaN double heterostructures with various indium compositions and GaN channel thicknesses were investigated. Samples were grown on c-plane sapphire substrates by MOCVD and evaluated using variable temperature Hall effect measurements. In order to understand the observed transport properties, various scattering mechanisms, such as acoustic phonon, optical phonon, interface roughness, background impurity, and alloy disorder, were included in the theoretical model that was applied to the temperature-dependent mobility data. It was found that low temperature (T 160 K), optical phonon scattering is the dominant scattering mechanism for AlGaN/AlN/GaN/InGaN/GaN heterostructures. The higher mobility of the structures with InGaN back barriers was attributed to the large conduction band discontinuity obtained at the channel/buffer interface, which leads to better electron confinement. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Double subband occupation of the two-dimensional electron gas in InxAl1− xN/AlN/ GaN/AlN heterostructures with a low indium content (0.064≤x≤0.140) barrier

Cataloged from PDF version of article.We present a carrier transport study on low indium content (0.064≤x≤0.140) InxAl1−xN/AlN/GaN/AlN heterostructures. Experimental Hall data were carried out as a function of temperature (33–300 K) and a magnetic field (0–1.4 T). A two-dimensional electron gas (2DEG) with single or double subbands and a twodimensional hole gas were extracted after implementing quantitative mobility spectrum analysis on the magnetic field dependent Hall data. The mobility of the lowest subband of 2DEG was found to be lower than the mobility of the second subband. This behavior is explained by way of interface related scattering mechanisms, and the results are supported with a one-dimensional self-consistent solution of non-linear Schrödinger–Poisson equations

Contributions of impurity band and electron-electron interactions to magnetoconductance in AlGaN

Low temperature electrical measurements of conductivity, the Hall effect and magnetoconductance were performed on a degenerate AlGaN sample. The sample exhibited negative magnetoconductance at low magnetic fields and low temperatures, with the magnitude being systematically dependent on temperature. The measured magnetoconductance was compared with models proposed previously by Sondheimer and Wilson [Proc. R. Soc. Lond. Ser. A 190 (1947) p. 435] and Lee and Ramakrishan [Rev. Mod. Phys. 57 (1985) p. 287]. Data were analyzed as the sum of the contribution of a two-band and electron-electron interactions to the magnetoconductance, applying these models to describe the observed behavior. Least-squares fits to the data are presented. In the sample, magnetoconductance can be explained reasonably well by assuming these contributions to the measured magnetoconductance. It was found that theoretical and experimental data were in excellent agreement. © 2010 Taylor & Francis

Late Cretaceous-Early Eocene tectonic development of the Tethyan suture zone in the Erzincan area, Eastern Pontides, Turkey

Six individual tectonostratigraphic units are identified within the Izmir-Ankara-Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayikayasi Formation of Campanian-Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayikayasi Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of similar to 75 % (by volume) serpentinized peridotite (mainly harzburgite), similar to 20 % diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally Occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak Melange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karadag Formation, of Campanian-Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian-Early Eocene Sutpinar Formation (similar to 1500 m thick) is a coarsening-Upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene-Eocene Sipikor Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, supra-subduction zone-type oceanic lithosphere and volcanic are units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian-Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, supra-subduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys

Investigation of AlInN HEMT structures with different AlGaN buffer layers grown on sapphire substrates by MOCVD

We investigate the structural and electrical properties of Al xIn 1-xN/AlN/GaN heterostructures with AlGaN buffers grown by MOCVD, which can be used as an alternative to AlInN HEMT structures with GaN buffer. The effects of the GaN channel thickness and the addition of a content graded AlGaN layer to the structural and electrical characteristics were studied through variable temperature Hall effect measurements, high resolution XRD, and AFM measurements. Enhancement in electron mobility was observed in two of the suggested Al xIn 1 -xN/AlN/GaN/Al 0.04Ga 0.96N heterostructures when compared to the standard Al xIn 1 -xN/AlN/GaN heterostructure. This improvement was attributed to better electron confinement in the channel due to electric field arising from piezoelectric polarization charge at the Al 0.04Ga 0.96N/GaN heterointerface and by the conduction band discontinuity formed at the same interface. If the growth conditions and design parameters of the Al xIn 1-xN HEMT structures with AlGaN buffers can be modified further, the electron spillover from the GaN channel can be significantly limited and even higher electron mobilities, which result in lower two-dimensional sheet resistances, would be possible. © 2012 Elsevier B.V. All rights reserved

Well parameters of two-dimensional electron gas in Al0.88In 0.12N/AlN/GaN/AlN heterostructures grown by MOCVD

Resistivity and Hall effect measurements were carried out as a function of magnetic field (0-1.5 T) and temperature (30-300 K) for Al0.88In 0.12N/AlN/GaN/AlN heterostructures grown by Metal Organic Chemical Vapor Deposition (MOCVD). Magnetic field dependent Hall data were analyzed by using the quantitative mobility spectrum analysis (QMSA). A two-dimensional electron gas (2DEG) channel located at the Al0.88In 0.12N/GaN interface with an AlN interlayer and a two-dimensional hole gas (2DHG) channel located at the GaN/AlN interface were determined for Al 0.88In0.12N/AlN/GaN/AlN heterostructures. The interface parameters, such as quantum well width, the deformation potential constant and correlation length as well as the dominant scattering mechanisms for the Al 0.88In0.12N/GaN interface with an AlN interlayer were determined from scattering analyses based on the exact 2DEG carrier density and mobility obtained with QMSA. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA

Grain boundary related electrical transport in Al-rich AlxGa1 - xN layers grown by metal-organic chemical vapor deposition

Electrical transport data for Al-rich AlGaN layers grown by metal-organic chemical vapor deposition (MOCVD) are presented and analyzed in the temperature range 135-300 K. The temperature dependence of electrical conductivity indicated that conductivity in the films was controlled by potential barriers caused by carrier depletion at grain boundaries in the material. The Seto's grain boundary model provided a complete framework for understanding of the conductivity behavior. Various electrical parameters of the present samples such as grain boundary potential, donor concentration, surface trap density, and Debye screening length were extracted. © 2011 Pleiades Publishing, Ltd

High Rate of Mobilization for blaCTX-Ms

The blaCTX-Ms have been mobilized to plasmids more frequently than other class A β-lactamases