Contrasting code performances for computational aeroacoustics of jets

The numerical propagation of subcritical Tollmein-Schlichting (T-S), inviscid vortical and cut-on acoustic waves is explored. For the former case, the performances of the very different NEAT, NTS, HYDRA, FLUXp and OSMIS3D codes is studied. A modest/coarse hexahedral computational grid that starkly shows differences between the different codes and schemes used in them is employed. For the same order of discretization the five codes show similar results. The unstructured codes are found to propagate vortical and acoustic waves well on triangular cell meshes but not the T-S wave. The above code contrasting exercise is then carried out using implicit LES or Smagorinsky LES for and Ma = 0.9 plane jet on modest 0.5 million cell grids moving to circa 5 million cell grids. For this case, even on the coarse grid, for all codes results were generally encouraging. In general, the spread in computational results is less than the spread of the measurements. Interestingly, the finer grid turbulence intensity levels are slightly more under-predicted than those of the coarse grid. This difference is attributed to the numerical dispersion error having a favourable coarse grid influence. For a non-isothermal jet, HYDRA and NTS also give encouraging results. Peak turbulence values along the jet centreline are in better agreement with measurements than for the isothermal jets. Copyright © 2006 by University of Wales.

Fabrication of an organic field effect transistor using nano imprinting of Ag inks and semiconducting polymers

A simple and cheap procedure for flexible electronics fabrication was demonstrated by imprinting metallic nanoparticles (NPs) on flexible substrates. Silver NPs with an average diameter of 10 nm were prepared via an improved chemical approach and Ag Np ink was produced in α-terpineol with a concentration up to 15%. Silver micro/nanostructures with a dimension varying from nanometres to microns were produced on a flexible substrate (polyimide) by imprinting the as-prepared silver ink. The fine fluidic properties of an Ag NP/α-terpineol solution and low melting temperatures of silver nanoparticles render a low pressure and low temperature procedure, which is well suited for flexible electronics fabrication. The effects of sintering and mechanical bending on the conductivity of imprinted silver contacts were also investigated. Large area organic field effect transistors (OFET) on flexible substrates were fabricated using an imprinted silver electrode and semiconducting polymer. The OFET with silver electrodes imprinted from our prepared oleic acid stabilized Ag nanoparticle ink show an ideal ohmic contact; therefore, the OFET exhibit high performance (Ion/Ioff ratio: 1 × 103; mobility: 0.071 cm2 V-1 s-1). © 2010 IOP Publishing Ltd.

Improved infrared thermal imaging of a CMOS MEMS device

We report a technique which can be used to improve the accuracy of infrared (IR) surface temperature measurements made on MEMS (Micro-Electro-Mechanical- Systems) devices. The technique was used to thermally characterize a SOI (Silicon-On-Insulator) CMOS (Complementary Metal Oxide Semiconductor) MEMS thermal flow sensor. Conventional IR temperature measurements made on the sensor were shown to give significant surface temperature errors, due to the optical transparency of the SiO 2 membrane layers and low emissivity/high reflectivity of the metal. By making IR measurements on radiative carbon micro-particles placed in isothermal contact with the device, the accuracy of the surface temperature measurement was significantly improved. © 2010 EDA Publishing/THERMINIC.

CFD-DEM simulation of propagation of sound waves in fluid particles fluidised medium

In this work, speed of sound in 2 phase mixture has been explored using CFD-DEM (Computational Fluid Dynamcis - Discrete Element Modelling). In this method volume averaged Navier Stokes, continuity and energy equations are solved for fluid. Particles are simulated as individual entities; their behaviour is captured by Newton's laws of motion and classical contact mechanics. Particle-fluid interaction is captured using drag laws given in literature.The speed of sound in a medium depends on physical properties. It has been found experimentally that speed of sound drops significantly in 2 phase mixture of fluidised particles because of its increased density relative to gas while maintaining its compressibility. Due to the high rate of heat transfer within 2 phase medium as given in Roy et al. (1990), it has been assumed that the fluidised gas-particle medium is isothermal.The similar phenomenon has been tried to be captured using CFD-DEM numerical simulation. The disturbance is introduced and fundamental frequency in the medium is noted to measure the speed of sound for e.g. organ pipe. It has been found that speed of sound is in agreement with the relationship given in Roy et al. (1990). Their assumption that the system is isothermal also appears to be valid.

Improved jet noise modeling using a new time-scale.

To calculate the noise emanating from a turbulent flow using an acoustic analogy knowledge concerning the unsteady characteristics of the turbulence is required. Specifically, the form of the turbulent correlation tensor together with various time and length-scales are needed. However, if a Reynolds Averaged Navier-Stores calculation is used as the starting point then one can only obtain steady characteristics of the flow and it is necessary to model the unsteady behavior in some way. While there has been considerable attention given to the correct way to model the form of the correlation tensor less attention has been given to the underlying physics that dictate the proper choice of time-scale. In this paper the authors recognize that there are several time dependent processes occurring within a turbulent flow and propose a new way of obtaining the time-scale. Isothermal single-stream flow jets with Mach numbers 0.75 and 0.90 have been chosen for the present study. The Mani-Gliebe-Balsa-Khavaran method has been used for prediction of noise at different angles, and there is good agreement between the noise predictions and observations. Furthermore, the new time-scale has an inherent frequency dependency that arises naturally from the underlying physics, thus avoiding supplementary mathematical enhancements needed in previous modeling.

TRANSIENT SCANNING ELECTRON BEAM ANNEALING METHODS USED TO STUDY DIFFUSION AND DEFECTS IN IMPLANTED SILICON.

Rapid thermal annealing of arsenic and boron difluoride implants, such as those used for source/drain regions in CMOS, has been carried out using a scanning electron beam annealer, as part of a study of transient diffusion effects. Three types of e-beam anneal have been performed, with peak temperatures in the range 900 -1200 degree C; the normal isothermal e-beam anneals, together with sub-second fast anneals and 'dual-pulse' anneals, in which the sample undergoes an isothermal pre-anneal followed by rapid heating to the required anneal temperature is less than 0. 5s. The diffusion occuring during these anneal cycles has been modelled using SPS-1D, an implant and diffusion modelling program developed by one of the authors. This has been modified to incorporate simulated temperature vs. time cycles for the anneals. Results are presented applying the usual equilibrium clustering model, a transient point-defect enhancement to the diffusivity proposed recently by Fair and a new dynamic clustering model for arsenic. Good agreement with SIMS measurements is obtained using the dynamic clustering model, without recourse to a transient defect model.

Innovative fabrication of PZT pillar arrays by a colloidal approach

An innovative approach for fabricating pillar arrays for ultrasonic transducer applications is disclosed. It involves the preparation of concentrated piezoelectric lead zirconate titanate (PZT) suspensions in aqueous solutions of epoxy resin and its polymerization upon adding a polyamine based hardener. Zeta potential and rheological measurements revealed that 1wt.% dispersant, 20wt.% of epoxy resin and a hardener/epoxy resin ratio of 0.275mLg -1, were the optimized contents to obtain strong PZT samples with high green strength (35.21±0.39MPa). Excellent ellipsoidal and semi-circle shaped pillar arrays presenting lateral dimensions lower than 10μm and 100μm height were successfully achieved. The organics burning off was conducted at 500°C for 2h at a heating rate of 1°Cmin -1. Sintering was then carried out in the same heating cycle at 1200°C for 1h. The microstructures of the green and sintered ceramics were homogeneous and no large defects could be detected. © 2011 Elsevier Ltd.

Accelerated and real-time creep and creep-rupture results for aramid fibers

This article presents results from conventional creep tests (CCT) and two accelerated test methods (the stepped isothermal method (SIM) and the stepped isostress method (SSM)) to determine the creep and creep-rupture behavior of two different aramid fibers, Kevlar 49 and Technora. CCT are regarded as the true behavior of the yarn, but they are impractical for long-term use where failures are expected only after many years. All the tests were carried out on the same batches of yarns, and using the same clamping arrangements, so the tests should be directly comparable. For both materials, SIM testing gives good agreement with CCT and gave stress-rupture lifetimes that followed the same trend. However, there was significant variation for SSM testing, especially when testing Technora fibers. The results indicate that Kevlar has a creep strain capacity that is almost independent of stress, whereas Technora shows a creep strain capacity that depends on stress. Its creep strain capacity is approximately two to three times that of Kevlar 49. The accelerated test methods give indirect estimates for the activation energy and the activation volume of the fibers. The activation energy for Technora is about 20% higher than that for Kevlar, meaning that it is less sensitive to the effects of increasing temperature. The activation volume for both materials was similar, and in both cases, stress dependent. Copyright © 2012 Wiley Periodicals, Inc.

Rapid Electron Beam Reacted Tantalum/Titanium Bilayers on Silicon : Semiconductors and Semiconductor Devices

The electrical and structural characteristics of tantalum-titanium bilayers on silicon reacted by electron beam heating have been investigated over a wide range of temperature and time conditions. The reacted layers exhibit low sheet resistance and stable electrical characteristics up to at least 1100℃. Titanium starts reacting from 750℃ onwards for 100 milliseconds reaction times whereas tantalum starts reacting only above 900℃ for such short reaction times. RBS results confirm that silicon is the major diffusing species and there is no evidence for the formation of ternary silicides. Reactions have also been explored on millisecond time scales by non-isothermal heating.

Plasma stabilisation of metallic nanoparticles on silicon for the growth of carbon nanotubes

Ammonia (NH 3) plasma pretreatment is used to form and temporarily reduce the mobility of Ni, Co, or Fe nanoparticles on boron-doped mono- and poly-crystalline silicon. X-ray photoemission spectroscopy proves that NH 3 plasma nitrides the Si supports during nanoparticle formation which prevents excessive nanoparticle sintering/diffusion into the bulk of Si during carbon nanotube growth by chemical vapour deposition. The nitridation of Si thus leads to nanotube vertical alignment and the growth of nanotube forests by root growth mechanism. © 2012 American Institute of Physics.

Synthesis of 10 nm Ag nanoparticle polymer composite pastes for low temperature production of high conductivity films

The conversion of silver nanoparticle (NP) paste films into highly conductive films at low sintering temperature is an important requirement for the developing areas of additive fabrication and printed electronics. Ag NPs with a diameter of ∼10 nm were prepared via an improved chemical process to produce viscous paste with a high wt%. The paste consisted of as-prepared Ag NP and an organic vehicle of ethylcellulose that was deposited on glass and Si substrates using a contact lithographic technique. The morphology and conductivity of the imprinted paste film were measured as a function of sintering temperature, sintering time and the percentage ratio of Ag NP and ethylcellulose. The morphology and conductivity were examined using scanning electron microscopy (SEM) and a two-point probe electrical conductivity measurement. The results show that the imprinted films were efficiently converted into conducting states when exposed to sintering temperature in the range of 200-240 °C, this temperature is lower than the previously reported values for Ag paste. © 2010 Elsevier B.V. All rights reserved.

Sintered metal foams for acoustic absorption

Metal foams fabricated via sintering offer novel mechanical and acoustic properties. Previously, polymer foams have been used as a means of absorbing acoustic energy. However, the structural applications of these foams are limited. The metal sintering approach offers a cost-effective means for the mass-production of open-cell metal foams. The static flow resistance of sintered metal foams was characterized for a range of practical pore sizes and porosities. The measured values for the flow resistance were subsequently used in a phenomenological acoustic model to predict the impedances and propagation constants of the foams. The predictions were then compared to acoustic measurements. At low frequencies (0-1000Hz), the phenomenological model captures the magnitude and frequency dependence of the absorption. At higher frequencies, as expected, the phenomenological model underpredicted the acoustic properties of the foams. However, an alternative microstructural model demonstrated good correlation to the measured results in this frequency range. The effects of foam type and arrangement on the absorption pattern were examined. General trends were identified for enhancing the low frequency performance of an acoustic absorber incorporating sintered foams.

Elastic properties of crystalline-amorphous core-shell silicon nanowires

The pressure behavior of Raman frequencies and line widths of crystalline core-amorphous shell silicon nanowires (SiNWs) with two different core-to-shell ratio thicknesses was studied at pressures up to 8 GPa. The obtained isothermal compressibility (bulk modulus) of SiNWs with a core-to-shell ratio of about 1.8 is ∼20% higher (lower) than reported values for bulk Si. For SiNWs with smaller core-to-shell ratios, a plastic deformation of the shell was observed together with a strain relaxation. A significant increase in the full width at half-maximum of the Raman LTO-peak due to phonon decay was used to determine the critical pressure at which LTO-phonons decay into LO + TA phonons. Our results reveal that this critical pressure in strained core-shell SiNWs (∼4 GPa) is different from the reported value for bulk Si (∼7 GPa), whereas no change is observed for relaxed core-shell SiNWs. © 2013 American Chemical Society.

Nanobodies raised against monomeric α-synuclein distinguish between fibrils at different maturation stages.

Nanobodies are single-domain fragments of camelid antibodies that are emerging as versatile tools in biotechnology. We describe here the interactions of a specific nanobody, NbSyn87, with the monomeric and fibrillar forms of α-synuclein (αSyn), a 140-residue protein whose aggregation is associated with Parkinson's disease. We have characterized these interactions using a range of biophysical techniques, including nuclear magnetic resonance and circular dichroism spectroscopy, isothermal titration calorimetry and quartz crystal microbalance measurements. In addition, we have compared the results with those that we have reported previously for a different nanobody, NbSyn2, also raised against monomeric αSyn. This comparison indicates that NbSyn87 and NbSyn2 bind with nanomolar affinity to distinctive epitopes within the C-terminal domain of soluble αSyn, comprising approximately amino acids 118-131 and 137-140, respectively. The calorimetric and quartz crystal microbalance data indicate that the epitopes of both nanobodies are still accessible when αSyn converts into its fibrillar structure. The apparent affinities and other thermodynamic parameters defining the binding between the nanobody and the fibrils, however, vary significantly with the length of time that the process of fibril formation has been allowed to progress and with the conditions under which formation occurs, indicating that the environment of the C-terminal domain of αSyn changes as fibril assembly takes place. These results demonstrate that nanobodies are able to target forms of potentially pathogenic aggregates that differ from each other in relatively minor details of their structure, such as those associated with fibril maturation.

La 0.7Ca 0.3MnO 3 / Mn 3O 4 composites: Does an insulating secondary phase always enhance the low field magnetoresistance of manganites

Composites of magnetoresistive La 0.7Ca 0.3MnO 3 (LCMO) with insulating Mn 3O 4 are useful as a model system because no foreign cation is introduced in the LCMO phase by interdiffusion during the heat treatment. Here we report the magnetotransport properties as a function of sintering temperature T sinter for a fixed LCMO/Mn 3O 4 ratio. Decreasing T sinter from 1250 °C to 800 °C causes an increase in low field magnetoresistance (LFMR) that correlates with the decrease in crystallite size (CS) of the LCMO phase. When plotting LFMR at (77 K, 0.5 T) versus 1/CS, we find that the data for the LCMO/Mn 3O 4 composites sintered between 800 °C and 1250 °C follow the same trend line as data from the literature for pure LCMO samples with crystallite size >∼25 nm. This differs from the LFMR enhancement observed by many authors in the usual manganite composites, i.e., composites where the insulating phase contains cations other than La, Ca or Mn. This difference suggests that diffusion of foreign cations into the grain boundary region is a necessary ingredient for the enhanced LFMR. © 2012 American Institute of Physics.