Hydrogen-acetylene gas ratio and catalyst thickness effect on the growth of uniform layer of carbon nanotubes

Effect of catalyst thickness (2, 4, and 6 nm) and acetylene-hydrogen gas ratio (1/4, 2/4, and 3/4) on the synthesis of carbon nanotubes is reported in this article. Synthesized nanotubes are characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and Raman effect. From SEM results, nanotubes growth is less for higher thickness, as at higher thickness catalyst nanoparticles agglomerate which suppress the growth of nanotubes. Raman spectroscopy results reveal that at higher thickness defects density increases. Nanotube of better crystallinity and graphitic outer walls grows for lower acetylene-hydrogen gas ratio and at smaller thickness of catalyst layer. The sheet resistance of carbon nanotube thin film is measured by using Hall effect measurement systems. Smallest sheet resistance among synthesized multi-walled carbon nanotubes sample is obtained for nanotubes grown on 2 nm thick catalyst film and is 0.9 kΩ/square.     

Nutrition and physical activity interventions for low-income populations.

A systematic review was conducted of community-based nutrition and physical activity strategies for chronic disease prevention targeting low-income populations. A computer search of the relevant published literature from 1996 to 2004 was done using Medline, EMBASE, ERIC, CINAHL, PubMed, and HealthSTAR databases. The primary objective was to develop an inventory of intervention strategies. The interventions ranged in approach from traditional group sessions taught by allied health professionals, peer-led workshops, one-on-one counselling print material, and home-based telephone and mail interventions to multimedia strategies and experiential activities such as food demonstrations and group exercise. The results suggest that nutrition and physical activity interventions aimed at low-income audiences tend to be delivered in an interactive visual format, to be culturally appropriate, to be administered in accessible primary care settings, and to provide incentives.     

Modeling of laser scanning system to determine its associated uncertainty of measurement

In the fabrication of fine wires such as filaments of lamps and optical fibers, it is always necessary to measure the diameter in real-time and correct the extrusion process. For metrological purposes, laser beam scanning technique will produce similar results as comparative to diffraction-assisted methods. A computerized laser beam scanning measurement system (LSM) is designed and fabricated. The LSM consists of a low power helium-neon gas laser source, a specially designed collimating lens, a hysteresis synchronous motor, a photo detector and a protective replaceable window along with temperature sensor. The LSM is mathematically modeled to identify various error contributing sources. The LSM is calibrated using a set of national reference standard cylindrical pins and a set of national reference standard slots to determine its relative calibration factor. The uncertainty of measurement achieved in the range of (0–35) mm is ± (0.55 +39.2L/m) μm.     

Investigation on the phase behaviour of gelatin/agarose mixture in an environment of reduced solvent quality

Investigation on the phase behaviour of a biopolymer mixture has been performed using 7.5% (w/w) gelatin and 1.5% (w/w) agarose in the presence of variable amounts of polydextrose as the co-solute from low to high levels of total solids. Mechanical observation of the system was performed using small deformation dynamic oscillation in shear along with thermal studies using modulated differential scanning calorimetry. Micrographs provided images of the changing morphology of the network with the addition of co-solute. Agarose and gelatin form non-interactive bicontinuous phases in the aqueous environment. Systematic increase in the concentration of polydextrose prevents the formation of a stable agarose network, with the polysaccharide chains dispersing in the high solids environment. Gelatin, on the other hand, retains its conformational stability even at a saturating co-solute environment through enhanced protein structuring. Vitrification studies on the high solids system at subzero temperatures provides information on the structural and molecular relaxation identified as a glass transition phenomenon. Fourier transform infrared spectroscopy was used to analyse potential direct interaction between polymers and co-solute. The extent of amorphicity in the system was confirmed using wide angle X-ray diffraction.     

On the Residual Resistivity Ratio in $hbox{MgB}_{2}$ Superconductors

It is found that there exist two different but related parameters that control the value of the residual resistivity ratio (RRR) in $hbox{MgB}_{2}$, namely, the stoichiometry of the starting powder and the synthesis parameters. The origin of the high RRR in the polycrystalline $hbox{MgB}_{2}$ samples has been attributed to the enhanced crystallinity of the samples due to higher Mg concentration in the starting composition. Scanning-electron-microscope images show the improved crystalline nature of the tape samples synthesized with the excess Mg in the starting powder mixture.