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Surface waves are excited by mechanical vibration of a cylindrical container having an air/water interface pinned at the rim, and the dynamics of pattern formation is analysed from both an experimental and theoretical perspective. The wave conforms to the geometry of the container and its spatial structure is described by the mode number pair ($n,\ell$) that is identified by long exposure time white light imaging. A laser light system is used to detect the surface wave frequency, which exhibits either a (i) harmonic response for low driving amplitude edge waves or (ii) sub-harmonic response for driving amplitude above the Faraday wave threshold. The first 50 resonant modes are discovered. Control of the meniscus geometry is used to great effect. Specifically, when flat, edge waves are suppressed and only Faraday waves are observed. For a concave meniscus, edge waves are observed and, at higher amplitudes, Faraday waves appear as well, leading to complicated mode mixing. Theoretical predictions for the natural frequency of surface oscillations for an inviscid liquid in a cylindrical container with a pinned contact line are made using the Rayleigh–Ritz procedure and are in excellent agreement with experimental results.
Polystyrene (PS), polymethyl-methacrylate (PMMA) and multi-walled carbon nanotubes (MWNT) were used to fabricate conductive nanocomposites using various mixing methods, followed by compression molding to analyze their electrical properties. The main objective of this research project was to evaluate how using different mixing techniques alter the composite microstructure and hence the properties of the resultant composite material. Three fabrication techniques were selected to be investigated: mechanical mixing, melt-mixing, and solution mixing. The concentration of the fillers was kept constant at 2 wt% MWNT to simplify comparisons. After mixing, the composite mixtures were compression molded at the same temperature of 180°C. It was found that each mixing method yielded uniquely different AC conductivity profiles which can be attributed to how the fabrication method used affected the arrangement of the CNTs in the composite structure. This newfound control of the electrical properties of the composite materials could definitely be useful to researchers because one can choose the proper fabrication technique based on what properties are desired.
This paper describes some key points in the history and development of the European Microwave Conference, the European Microwave Week, and the European Microwave Association, starting from 1969. It captures the way in which the conference since the earliest days has sought to create a successful blend of scientific and industry interests and has adapted itself to and indeed shaped the many existing technical changes that have characterized and continue to be at the core of the field of microwave engineering.
Silver nanoparticles have shown immense potential in many biomedical applications, specifically wound healing. These nanoparticles reduce the degree of inflammation in wounds and increase the rate of wound healing overall in a dose-dependent manner. Moreover, silver nanoparticles exhibit antibacterial and antimicrobial properties. While the mechanism of action for silver nanoparticles is not clear, current studies focus on the effect of silver nanoparticles on recipient cells and tissues. It is shown that silver nanoparticles are more toxic to these recipient cells in comparison to other metal nanoparticles. This suggests that the bactericidal properties of the silver nanoparticles are size dependent. Our present work investigates the toxicity level of silver nanoparticles on specific immune circulating cells. The approach is to report the LD50 level as a function of the ratio of the nanoparticles concentration (ppm) to the cell concentration (cell number/ml) used in the assays. This method allows a normalization of the LD50 capable to compare the toxicity of the nanoparticle on different types of cells. Next, the localization of the silver nanoparticles within the cells will be determined, and the toxic mode of action of the nanoparticles will be modulated by the modification of the synthesis method.
Cytotaxonomic analysis of the polytene chromosomes from larvae of the Simulium damnosum Theobald complex from the island of Bioko in Equatorial Guinea is reported, and a new endemic cytoform is described. Chromosomally this cytoform is close to both S. squamosum (Enderlein) and S. yahense Vajime & Dunbar, but is not identical to either. However, it is morphologically and enzymatically identical to S. yahense. The Bioko form was also found to differ from other cytoforms of the S. damnosum complex in West Africa in the copy number or RFLP pattern of several different repetitive DNA sequences. It is clear that the Bioko form is genetically distinct from other populations of the S. damnosum complex, and whilst it is closest to S. yahense, it shows features that suggest a high degree of geographical and genetic isolation. Such isolation is an important consideration in the assessment of the potential for onchocerciasis vector eradication on Bioko.
We have (1) accumulated long-term (up to 15 years) photoelectric photometry of 76 bright pulsating red giants (PRGs) and related stars, with V amplitudes of 0.04 to ≥ 1 magnitude; (2) used a variety of techniques, including autocorrelation, to determine both “short” radial pulsation periods, and long secondary periods; (3) determined pulsation modes using the Q-value method; the modes range from fundamental to second overtone, independent of temperature; (4) tested wavelet analysis on small-amplitude PRGs; (5) made a special study of PRGs with amplitudes less than 0.1 magnitude; and (6) called further attention to the problem of the long secondary periods of these stars. Our studies provide a “model” for the analysis and interpretation of larger, fainter surveys such as MACHO and OGLE.
Gallium nitride films were grown by rf-plasma assisted molecular beam epitaxy. A small indium flux was used as surfactant during the growth. The optical and electrical properties of the films grown with and without In surfactant were characterized by investigating the photoluminescence (PL), high resolution x-ray diffraction (HRXRD) and low-frequency noise power spectra. The sample grown in the presence of In surfactant showed a suppressed yellow luminescence (YL) compared to the one grown without In surfactant. Significant reduction in the full width at half maximum of the GaN (0002) x-ray diffraction peak, indicating a better film quality, was obtained when In surfactant was used during growth. Atomic force microscopy studies show that the root mean squared surface roughness for films grown with and without the In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. This is attributed to the enhanced 2-dimensional growth by In surfactant. A smaller Hooge parameter was obtained from the low-frequency noise measurement for the sample grown with In surfactant indicating that application of In surfactant led to significant reduction in the trap density of the material.
A new fast fabrication method entailing, two step anodization of silicon with different HF solutions was used to form a high aspect ratio silicon Field Emitter Array on n-type silicon (resistivity of 0.01cm). A Silicon oxide mask was used to define the field emitter array. The silicon substrate was pre-anodized with low current density for 1 minute in the dark and then anodized in HF:H2O:Ethanol solution. Finally, the porous silicon was removed by isotropic solution etching. The turn-on voltage of the fabricated field emitters was approximately 27V/μm when the emission current density reaches 1μA/cm2. This compares with the turn-on field of about 35V/μm on silicon tip array fabricated by using an isotropic etching solution of HNO3. We obtained field emitter arrays with good uniformity and reproducibility.
Planar SiC/Si heterostructures were formed by high dose carbon implantation using a metal vapor vacuum arc ion source. The variations of the field emission properties with the implant dose and annealing conditions were studied. A remarkably low turn-on field of IV/μm was observed from a sample implanted at 35 keV to a dose of 1.0×1018 cm−2 with subsequent annealing in nitrogen at 1200°C for 2h. The chemical composition depth profiles were determined from x-ray photoelectron spectroscopy and the surface morphology was observed by atomic force microscopy. The formation of a thin surface stoichiometric SiC layer and the formation of densely distributed small protrusions on the surface are believed to be the two factors responsible for the efficient electron field emission.
The surface morphology of high dose Co implanted Si has been studied by atomic force microscopy. The Co implantation was performed using a metal vapor vacuum arc (MEVVA) ion source at an extraction voltage of 60 or 70 kV to a dose of 2×l017 or 4×l017 ions cm-2 at substrate temperatures Ts ranging from 210°C to 700°C. When Ts is less than about 600°C, the surface morphology of the implanted samples shows largely similar features of densely distributed narrow asperities. However, for the sample with Ts of 700°C, the surface morphology is significantly different and shows hillocks of much larger size. It is also found that when other parameters are fixed, for Ts less than about 600°C, the root-mean-square roughness Rrms increases exponentially with 7^, from the subnanometer scale to several nanometers. But for the sample with Ts of 700°C, there is an abrupt increase in Rrms to 35 nm. The variation of the surface morphology with other parameters is also discussed.
As part of the Australia Telescope's commissioning astronomy, three antennas of the Compact Array, with spacings of 0.5, 1.5 and 2 km, were used to produce the instrument's first spectral-line images - OH excited-state transitions from the southern spiral galaxy NGC 4945. For the 6030- and 6035-MHz transitions of the 2π3/2, J = 5/2 state, well-defined line absorption was detected towards the 6 × 2 arcsec2 radio continuum nucleus. The line profiles are wide, with heliocentric radial velocities extending from 350 to 770 km s−1, and with overall shapes similar to the corresponding ground-state transitions at 1665 and 1667 MHz (Whiteoak & Gardner 1975). The respective maximum line-to-continuum ratios of 0.04 and 0.07 occur near 650 km s−1. A comparison of the 6035- and 1667-MHz results yields an OH temperature of 36 K. The position of the absorption changes systematically with velocity along a line at position angle 45°. Such behaviour is consistent with that for a rotating molecular cloud which surrounds the nucleus.
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