A novel MPT noise prediction methodology for highly-integrated propulsion systems with inlet flow distortion

Embedded propulsion systems, such as for example used in advanced hybrid-wing body aircraft, can potentially offer major fuel burn and noise reduction benefits but introduce challenges in the aerodynamic and acoustic integration of the high-bypass ratio fan system. A novel approach is proposed to quantify the effects of non-uniform flow on the generation and propagation of multiple pure tone noise (MPTs). The new method is validated on a conventional inlet geometry first. The ultimate goal is to conduct a parametric study of S-duct inlets in order to quantify the effects of inlet design parameters on the acoustic signature. The key challenge is that the mechanism underlying the distortion transfer, noise source generation and propagation through the non-uniform flow field are inherently coupled such that a simultaneous computation of the aerodynamics and acoustics is required. The technical approach is based on a body force description of the fan blade row that is able to capture the distortion transfer and the MPT noise generation mechanisms while greatly reducing computational cost. A single, 3-D full-wheel unsteady CFD simulation, in which the Euler equations are solved to second-order spatial and temporal accuracy, simultaneously computes the MPT noise generation and its propagation in distorted mean flow. Several numerical tools were developed to enable the implementation of this new approach. Parametric studies were conducted to determine appropriate grid and time step sizes for the propagation of acoustic waves. The Ffowcs-Williams and Hawkings integral method is used to propagate the noise to far field receivers. Non-reflecting boundary conditions are implemented through the use of acoustic buffer zones. The body force modeling approach is validated and proof-of-concept studies demonstrate the generation of disturbances at both blade-passing and shaft-order frequencies using the perturbed body force method. The full methodology is currently being validated using NASA's Source Diagnostic Test (SDT) fan and inlet geometry. Copyright © 2009 by Jeff Defoe, Alex Narkaj & Zoltan Spakovszky.

YBa2Cu3O7 tapes prepared by sol-gel deposition techniques: Microstructure and structural characterizations

We report on the preparation conditions of YBa2Cu3O7 polycrystalline superconducting tapes by a sol-gel deposition technique. We present some discussion on the compatibility between the nature of the substrate, the use of a buffer layer, and the conditions used to prepare appropriate superconducting YBa2Cu3O7 materials. We report also on the microstructural characterizations performed in order to evaluate the crystallites size, degree of orientation and connectivity. © 2002 Elsevier Science B.V. All rights reserved.

Precursor flow rate manipulation for the controlled fabrication of twin-free GaAs nanowires on silicon substrates

Vertically oriented GaAs nanowires (NWs) are grown on Si(111) substrates using metal-organic chemical vapor deposition. Controlled epitaxial growth along the 111 direction is demonstrated following the deposition of thin GaAs buffer layers and the elimination of structural defects, such as twin defects and stacking faults, is found for high growth rates. By systematically manipulating the AsH 3 (group-V) and TMGa (group-III) precursor flow rates, it is found that the TMGa flow rate has the most significant effect on the nanowire quality. After capping the minimal tapering and twin-free GaAs NWs with an AlGaAs shell, long exciton lifetimes (over 700ps) are obtained for high TMGa flow rate samples. It is observed that the Ga adatom concentration significantly affects the growth of GaAs NWs, with a high concentration and rapid growth leading to desirable characteristics for optoelectronic nanowire device applications including improved morphology, crystal structure and optical performance. © 2012 IOP Publishing Ltd.

Taper-free and vertically oriented Ge nanowires on Ge/Si substrates grown by a two-temperature process

Taper-free and vertically oriented Ge nanowires were grown on Si (111) substrates by chemical vapor deposition with Au nanoparticle catalysts. To achieve vertical nanowire growth on the highly lattice mismatched Si substrate, a thin Ge buffer layer was first deposited, and to achieve taper-free nanowire growth, a two-temperature process was employed. The two-temperature process consisted of a brief initial base growth step at high temperature followed by prolonged growth at lower temperature. Taper-free and defect-free Ge nanowires grew successfully even at 270 °C, which is 90 °C lower than the bulk eutectic temperature. The yield of vertical and taper-free nanowires is over 90%, comparable to that of vertical but tapered nanowires grown by the conventional one-temperature process. This method is of practical importance and can be reliably used to develop novel nanowire-based devices on relatively cheap Si substrates. Additionally, we observed that the activation energy of Ge nanowire growth by the two-temperature process is dependent on Au nanoparticle size. The low activation energy (∼5 kcal/mol) for 30 and 50 nm diameter Au nanoparticles suggests that the decomposition of gaseous species on the catalytic Au surface is a rate-limiting step. A higher activation energy (∼14 kcal/mol) was determined for 100 nm diameter Au nanoparticles which suggests that larger Au nanoparticles are partially solidified and that growth kinetics become the rate-limiting step. © 2011 American Chemical Society.

Defect-free GaAs/AlGaAs Core-shell nanowires on Si substrates

We report straight and vertically aligned defect-free GaAs nanowires grown on Si(111) substrates by metal-organic chemical vapor deposition. By deposition of thin GaAs buffer layers on Si substrates, these nanowires could be grown on the buffer layers with much less stringent conditions as otherwise imposed by epitaxy of III-V compounds on Si. Also, crystal-defect-free GaAs nanowires were grown by using either a two-temperature growth mode consisting of a short initial nucleation step under higher temperature followed by subsequent growth under lower temperature or a rapid growth rate mode with high source flow rate. These two growth modes not only eliminated planar crystallographic defects but also significantly reduced tapering. Core-shell GaAs-AlGaAs nanowires grown by the two-temperature growth mode showed improved optical properties with strong photoluminescence and long carrier life times. © 2011 American Chemical Society.

Structural and optical characterization of vertical GaAs/GaP core-shell nanowires grown on Si substrates

GaAs nanowires were grown on Si (111) substrates. By coating a thin GaAs buffer layer on Si surface and using a two-temperature growth, the morphology and crystal structure of GaAs nanowires were dramatically improved. The strained GaAs/GaP core-shell nanowires, based on the improved GaAs nanowires with a shell thickness of 25 nm, showed a significant shift in emission energy of 260 meV from the unstrained GaAs nanowires. © 2010 IEEE.

Novel growth and properties of GaAs nanowires on Si substrates.

Straight, vertically aligned GaAs nanowires were grown on Si(111) substrates coated with thin GaAs buffer layers. We find that the V/III precursor ratio and growth temperature are crucial factors influencing the morphology and quality of buffer layers. A double layer structure, consisting of a thin initial layer grown at low V/III ratio and low temperature followed by a layer grown at high V/III ratio and high temperature, is crucial for achieving straight, vertically aligned GaAs nanowires on Si(111) substrates. An in situ annealing step at high temperature after buffer layer growth improves the surface and structural properties of the buffer layer, which further improves the morphology of the GaAs nanowire growth. Through such optimizations we show that vertically aligned GaAs nanowires can be fabricated on Si(111) substrates and achieve the same structural and optical properties as GaAs nanowires grown directly on GaAs(111)B substrates.

Improvement of morphology, structure, and optical properties of GaAs nanowires grown on Si substrates

We investigate vertical and defect-free growth of GaAs nanowires on Si (111) substrates via a vapor-liquid-solid (VLS) growth mechanism with Au catalysts by metal-organic chemical vapor deposition (MOCVD). By using annealed thin GaAs buffer layers on the surface of Si substrates, most nanowires are grown on the substrates straight, following (111) direction; by using two temperature growth, the nanowires were grown free from structural defects, such as twin defects and stacking faults. Systematic experiments about buffer layers indicate that V/III ratio of precursor and growth temperature can affect the morphology and quality of the buffer layers. Especially, heterostructural buffer layers grown with different V/III ratios and temperatures and in-situ post-annealing step are very helpful to grow well arranged, vertical GaAs nanowires on Si substrates. The initial nanowires having some structural defects can be defect-free by two-temperature growth mode with improved optical property, which shows us positive possibility for optoelectronic device application. ©2010 IEEE.

Measuring the composition of AlGaN layers in GaN based structures grown on 150 mm Si substrates using (2 0 5) reciprocal space maps

A critical element for the successful growth of GaN device layers on Si is accurate control of the AlGaN buffer layers used to manage strain. Here we present a method for measuring the composition of the AlGaN buffer layers in device structures which makes use of a one-dimensional x-ray detector to provide efficient measurement of a reciprocal space map which covers the full compositional range from AlN to GaN. Combining this with a suitable x-ray reflection with low strain sensitivity it is possible to accurately determine the Al fraction of the buffer layers independent of their relaxation state. © 2013 IOP Publishing Ltd.

Dynamic compression of foam supported plates impacted by high velocity soil

The response of back-supported buffer plates comprising a solid face sheet and foam core backing impacted by a column of high velocity particles (sand slug) is investigated via a lumped parameter model and coupled discrete/continuum simulations. The buffer plate is either resting on (unattached) or attached to a rigid stationary foundation. The lumped parameter model is used to construct maps of the regimes of behaviour with axes of the ratio of the height of the sand slug to core thickness and the normalised core strength. Four regimes of behaviour are identified based on whether the core compression ends prior to the densification of the sand slug or vice versa. Coupled discrete/continuum simulations are also reported and compared with the lumped parameter model. While the model predicted regimes of behaviour are in excellent agreement with numerical simulations, the lumped parameter model is unable to predict the momentum transmitted to the supports as it neglects the role of elasticity in both the buffer plate and the sand slug. The numerical calculations show that the momentum transfer is minimised for intermediate values of the core strength when the so-called "soft-catch" mechanism is in play. In this regime the bounce-back of the sand slug is minimised which reduces the momentum transfer. However, in this regime, the impulse reduction is small (less than 10% of that transferred to a rigid structure). For high values of the core strength, the response of the buffer plate resembles a rigid plate with nearly no impulse mitigation while at low values of core strength, a slap event occurs when the face sheet impinges against the foundation due to full densification of the foam core. This slap event results in a significant enhancement of the momentum transfer to the foundation. The results demonstrate that appropriately designed buffer plates have potential as impulse mitigators in landmine loading situations. © 2013 Elsevier Ltd. All rights reserved.

Extraction of genomic DNA using a new amino silica monolithic column

A new amino silica monolithic column was developed for DNA extraction in a miniaturized format. The monolithic column was prepared in situ by polymerization of tetraethoxysilane (TEOS) and N-(beta-aminoethyl)-gamma-aminopropylmethyldimethoxysilane (AEAPMDMS). DNA was loaded in 50 mM tris(hydroxylmethyl)aminomethane-EDTA buffer at pH 7.0 and eluted with 300 mM potassium phosphate solution at pH 10.0. Under optimal condition, a 6.0-cm monolithic column provided a capacity of 56 ng DNA with an extraction efficiency of 71 +/- 5.2% (X +/- RSD). When the amino silica monolithic column was applied to extract genomic DNA from the whole blood of crucian carp, an extraction efficiency of 52 +/- 5.6% (X +/- SD) was obtained by three extractions. Since the chaotropic-based sample loading and organic solvent wash steps were avoided in this procedure, the purified DNA was suitable for downstream processes such as PCR. This amino silica monolithic column was demonstrated to allow rapid and efficient DNA purification in microscale.

Phosphorus in suspended matter and sediments of a hypertrophic lake. A case study: Lake Dianchi, China

From June 2004 to December 2004, Lake Dianchi, which had large scale of cyanobacterial blooms was investigated in order to study P-fractionation in the suspended matter and the sediment. The investigation improves our understanding of phosphorus in Lake Dianchi and the relationship between phosphorus and cyanobacterial blooms. It contributes to the available literature on the behavior of P in hypertrophic lakes. The distribution of P-fractions in Lake Dianchi was not uniform from northwest to south, but was closely related to the trophic status of the whole lake. The concentrations of total phosphorus, labile P (NH4Cl-P), Organic P (NaOH-NRP) and loss on ignition in suspended matter were positively correlated with the strength of cyanobacterial blooms. Total phosphorus in suspended matter was relatively stable for almost half an year and closely related to Chl. a concentration. The main content of organic phosphorus is in the cyanobacterial blooms. The concentrations of phosphorus bound to metal oxides and carbonates (NaOH-SRP and HCl-P) in sediment were similar to NaOH-SRP and HCl-P in the corresponding suspended matter. The latter two forms of P in suspended matter were not affected by cyanobacterial blooms, indicating that the inorganic phosphorus is derived from the sediment after resuspension from the sediment due to wind and wave action. The contribution of the different P-fractions to TP in sediment and in suspended matter indicates that NH4Cl-P in the suspended matter is an important buffer for maintaining dissolved phosphorus in water.

High performance non-volatile ferroelectric copolymer memory based on a ZnO nanowire transistor fabricated on a transparent substrate

A high performance ferroelectric non-volatile memory device based on a top-gate ZnO nanowire (NW) transistor fabricated on a glass substrate is demonstrated. The ZnO NW channel was spin-coated with a poly (vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) layer acting as a top-gate dielectric without buffer layer. Electrical conductance modulation and memory hysteresis are achieved by a gate electric field induced reversible electrical polarization switching of the P(VDF-TrFE) thin film. Furthermore, the fabricated device exhibits a memory window of ∼16.5 V, a high drain current on/off ratio of ∼105, a gate leakage current below ∼300 pA, and excellent retention characteristics for over 104 s. © 2014 AIP Publishing LLC.

Optical investigations of the effect of solvent and thermal annealing on the optoelectronic properties of Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) films

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most promising conducting polymers that can be used as transparent electrode or as buffer layer for organic electronic devices. However, when used as an electrode, its conductivity has to be optimized either by the addition of solvents or by post-deposition processing. In this work, we investigate the effect of the addition of the polar solvent dimethylsulfoxide (DMSO) to an aqueous PEDOT:PSS solution on its optical and electrical properties by the implementation of the Drude model for the analysis of the measured pseudo-dielectric function by Spectroscopic Ellipsometry from the near infrared to the visible-far ultraviolet spectral range. The results show that the addition of DMSO increases significantly the film conductivity, which reaches a maximum value at an optimum DMSO concentration as it has confirmed by experimentally measured conductivity values. The post-deposition thermal annealing has been found to have a smaller effect on the film conductivity. © 2013 Elsevier B.V.

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.