Influence of ZnO nanowire array morphology on field emission characteristics

In this work the growth and field emission properties of vertically aligned and spatially ordered and unordered ZnO nanowires are studied. Spatially ordered nanowire arrays of controlled array density are synthesised by both chemical bath deposition and vapour phase transport using an inverse nanosphere lithography technique, while spatially unordered arrays are synthesised by vapour phase transport without lithography. The field emission characteristics of arrays with 0.5 µm, 1.0 µm, and 1.5 µm inter-wire distances, as well as unordered arrays, are examined, revealing that with the range of values examined field emission properties are mainly determined by variations in nanowire height, and show no correlation with nanowire array density. Related to this, we find that a significant variation in nanowire height in an array also leads to a reduction in catastrophic damage observed on samples during field emission because arrays with highly uniform heights are found to suffer significant arcing damage. We discuss these results in light of recent computational studies of comparable nanostructure arrays and find strong qualitative agreement between our results and the computational predictions. Hence the results presented in this work should be useful in informing the design of ZnO nanowire arrays in order to optimise their field emission characteristics generally

Pulsed laser ablation in liquid (PLAL) for nanoparticle generation

Nanoparticles, broadly spherical pieces of material with diameters in the nanoscale range, have a number of advantageous physical, chemical, electrical, and optical properties. These unique properties make them suitable for a wide range of applications including sensing, medical therapeutics, printed electronics, and anti-fouling/anti-microbial surfaces. Pulsed laser ablation in liquid (PLAL), also known as laser ablation synthesis in solution (LASIS), is an attractive, green method for producing ligand-free nanoparticles in solution. These nanoparticles can be produced from a wide range of target materials and avoids the use of hazardous, environmentally-unfriendly chemicals. In this chapter, the key applications, conventional generation methods of nanoparticles, as well as the background and cutting edge of PLAL are reviewe

Investigating the morphology, hardness, and porosity of copper filters produced via Hydraulic Pressing

This paper presents an examination of the production of copper air filters via the Hydraulic Pressing (HP) method. Processing conditions examined included powder particle type (spherical and dendritic), varying compaction pressures (635, 714, and 793 MPa) and different pore forming (polyvinyl alcohol (PVA)) concentrations (1, 2, and 3 wt.%). Following compaction, the samples were thermally sintered in a two stage sintering regime at 200 ◦C and 750 ◦C. The morphology, porosity, and mechanical properties of the sintered samples were characterised. Morphological analysis demonstrated better consolidation and over-lapping of the copper powder particles in samples with a higher weight percentage of the PVA. Highest porosity was achieved in the sample produced using the dendritic copper powder mixed with highest weight percentage of PVA. As the samples were very porous, the hardness of the samples varied greatly. Samples prepared with spherical powders at high pressure demonstrated the highest hardness. The results in this study show that copper filters with 14%e26% porosity can effectively be produced using spherical and dendritic copper powders by controlling the compaction pressure and PVA concentration

Effect of powder metallurgy synthesis parameters for pure aluminium on resultant mechanical properties

In this work, pure aluminium powders of different average particle size were compacted, sintered into discs and tested for mechanical strength at different strain rates. The effects of average particle size (15, 19, and 35 μm), sintering rate (5 and 20 °C/min) and sample indentation test speed (0.5, 0.7, and 1.0 mm/min) were examined. A compaction pressure of 332 MPa with a holding time of six minutes was used to produce the green compacted discs. The consolidated green specimens were sintered with a holding time of 4 h, a temperature of 600 °C in an argon atmosphere. The resulting sintered samples contained higher than 85% density. The mechanical properties and microstructure were characterized using indentation strength measurement tests and SEM analysis respectively. After sintering, the aluminium grain structure was observed to be of uniform size within the fractured samples. The indentation test measurements showed that for the same sintering rate, the 35 μm powder particle size provided the highest radial and tangential strength while the 15 μm powder provided the lowest strengths. Another important finding from this work was the increase in sintered sample strength which was achieved using the lower sinter heating rate, 5 °C/min. This resulted in a tangential stress value of 365 MPa which was significantly higher than achieved, 244 MPa, using the faster sintering heating rate, 20 °C/min

Upper limits on the strength of periodic gravitational waves from PSR J1939+2134

The first science run of the LIGO and GEO gravitational wave detectors presented the opportunity to test methods of searching for gravitational waves from known pulsars. Here we present new direct upper limits on the strength of waves from the pulsar PSR J1939+2134 using two independent analysis methods, one in the frequency domain using frequentist statistics and one in the time domain using Bayesian inference. Both methods show that the strain amplitude at Earth from this pulsar is less than a few times $10^{-22}$.Comment: 7 pages, 1 figure, to appear in the Proceedings of the 5th Edoardo Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July 200

Improving the sensitivity to gravitational-wave sources by modifying the input-output optics of advanced interferometers

We study frequency dependent (FD) input-output schemes for signal-recycling interferometers, the baseline design of Advanced LIGO and the current configuration of GEO 600. Complementary to a recent proposal by Harms et al. to use FD input squeezing and ordinary homodyne detection, we explore a scheme which uses ordinary squeezed vacuum, but FD readout. Both schemes, which are sub-optimal among all possible input-output schemes, provide a global noise suppression by the power squeeze factor, while being realizable by using detuned Fabry-Perot cavities as input/output filters. At high frequencies, the two schemes are shown to be equivalent, while at low frequencies our scheme gives better performance than that of Harms et al., and is nearly fully optimal. We then study the sensitivity improvement achievable by these schemes in Advanced LIGO era (with 30-m filter cavities and current estimates of filter-mirror losses and thermal noise), for neutron star binary inspirals, and for narrowband GW sources such as low-mass X-ray binaries and known radio pulsars. Optical losses are shown to be a major obstacle for the actual implementation of these techniques in Advanced LIGO. On time scales of third-generation interferometers, like EURO/LIGO-III (~2012), with kilometer-scale filter cavities, a signal-recycling interferometer with the FD readout scheme explored in this paper can have performances comparable to existing proposals. [abridged]Comment: Figs. 9 and 12 corrected; Appendix added for narrowband data analysi

Analysis of nitinol actuator response under controlled conductive heating regimes

In the last few decades, Nitinol (NiTi) actuators have created a massive impact at the commercial level due to their application in various engineering and medical fields. In this paper, an experimental analysis study is presented on commercially manufactured nitinol tubes for performance enhancement. As received tubes were super-elastic at room temperature with Af temperature of 1.7°C. The nitinol tubes were heat treated at 500°C for different time ranging from 30 min to 60 min to raise the Af temperature. Metallography was performed on pristine and heat-treated samples to analyse the changes in the physical properties. XRD analysis revealed the crystalline structure present in the tubes (as received and heat treated) was nitinol cubic (110) while nitinol cubic (211) at room temperature. Moreover, dilatometry was performed which showed thermal expansion coefficients very close as noted in the literature as 11.4x10-6/°C. In the last section of this paper, the actuation force of the tubes was experimentally measured and analysed using different springs attached to the tubes connected to a conductive heating stage. A full factorial Design of Experiments (DoE) was used based on factors of time, temperature, and spring constant. For a surface temperature of 125°C and a spring constant of 2.39 kN/m, 131 N force was attained from the tube. The maximum actuation force of 145 N was obeserved for surface temperature of 145°C at an exposure time of 60 s with k = 2.39 kN/m

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Peer reviewed: NoNRC publication: Ye