Table of Contents - Volume 12 Number 1

Polymer gel dosimeter is a radiation sensitive chemical dosimeter that can measure 3 D dose distribution with high resolution. Due to the increasing complexity of radiotherapy treatment planning and delivery, accurate experimental radiation dosimetry plays an important role in the implementation and quality assurance of new treatment techniques. A polymer gel dosimeter must possess several important characteristics of a dosimeter to be able to measure absorbed dose precisely. two important dosimetric properties of a dosimeter were determined in this study; accuracy and precision. The MAGAT gels were made of 5% gelatin, 6% methacrylic acid and 10 mM tetrakis-hydroxy-methyl-phosphonium chloride (THPC). The irradiation of MAGAT gel was performed by 6-MV photon beam at a dose range 1 to 10 Gy and was imaged by 1.5 T Magnetic Resonance Imaging (MRI). The dose response of MAGAT gel dosimeter was obtained from spin-spin relaxation rate (R2) of MRI signal. The accuracy of MAGAT gel dosimeter has a range within 4% for doses greater than and equal to 3 Gy. The reproducibility of the MAGAT gel dosimeter at one irradiation was less than 1% whilst the long term reproducibility was within 3% over the five month period. For temporal stability, the dose sensitivity of MAGAT gel dosimeter irradiate at 1 to 11 days post-manufacturing decreased over time. While the dose sensitivity imaged at 1 to 9 days post-irradiation increased up to 4 days post-irradiation and subsequently starts decreasing after 4 days till 9 days. From the study of two dosimetric properties, MAGAT gel dosimeter shows a great dose response with a superior dose response. Thus the MAGAT gel dosimeter can be apply as a 3 D radiotherapy dosimeter.

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In this work, pure and doped with Al (Aluminum) strontium hexaferrite (SrFe_12-xAl_xO₁₉) were fabricated by solid state reaction method. The Al concentration (x) for the fabricated samples was varied from x=0.0 to x=0.6. Structural and magnetic properties of the fabricated samples were investigated. Analyses of XRD data showed that all samples of high quality, since the measured XRD patterns found to match the standard pattern for single phase of SrFe₁₂O₁₉. The lattice constants a and c were calculated. It was found that the replacement of Fe³⁺ with Al³⁺ ions in hexagonal strontium ferrite led to a negligible changes in lattice constant a, whereas the hexagonal lattice constant c found to decrease with increasing the substitution amount of Al. The crystallite size was also determined using the XRD data. It has been found that that Al³⁺ substitution for Fe³⁺ does not appreciably disturb the crystallinity of SrFe_12-xAl_xO₁₉, since the crystallite size for all samples ranged from 83 – 72 nm. The magnetic data showed that doping of strontium with Al leads to a small decrease in saturation magnetization. Also it has been found that the doping of strontium ferrite with Al leads to an increase in the coercivity as a result of increasing of the anisotropy field.

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The structural and optical properties of four samples of cobalt phthalocyanine (CoPc) thin films having almost the same thickness deposited onto silicon substrates by organic molecular beam deposition (OMBD) were investigated. The intensity distributions of the X-ray diffraction (XRD) patterns confirm the crystalline nature of the films and presents a single sharp dominant peak at 2q=6.9^o (d=12.72 ) of the α-CoPc phase unit cells, which indicates to a preferential orientation (200) direction, then undergoes a phase transition into β- form in a preferential orientation (001) direction after annealing at 250 and 350^◦C. Furthermore it was shown that an increasing in the crystallite size (L) occurs upon annealing. The small values of the roughness (7.04 nm, 7.2 nm) obtained from atomic force microscopy (AFM) measurements show relatively smooth and flat surfaces. Despite the identity of the samples deposition conditions, the post growth annealed films show different morphological features of a mean grain size about of 11-26 nm. The optical energy gap was estimated from the absorption coefficient using Tauc's relation.

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The present work is a comparative analysis of the properties of undoped and L-Proline doped ADP crystals. Slow evaporation solution growth technique was employed for growing undoped and L-Proline doped ADP crystals. The unit cell parameters were estimated by single crystal X-Ray diffraction analysis. The crystalline nature of the samples was revealed by Powder X-Ray diffraction analysis. The presence of functional groups and the spectral properties was identified by FTIR spectral analysis. The optical property of the material was examined by UV-Visible spectral analysis. The surface morphology and the elemental composition of the material was studied by SEM and EDS analysis.  The nonlinear optical property of the samples was tested by Kurtz and Perry experimental setup.

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In this work, a single phase strontium ferrite sample was mechanically milled for 60 h. It has been found that the crystallite size reduced by 85%. A dramatic drop (from 4500 to 1600 Oe) in the coercive filed was also observed. The observed reduction in the coercivity was attributed to the reduction of the single domain particle size.

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In this study, directional freezing technique was employed to prepare pure gallium antimonide (GaSb) compound and purified samples were also been characterized to ascertain their and purity level and crystalline quality.  The select impurities that were targeted for reduction include Al, Ca, Mg, Sb, Si, Sn, Ge,  Cu, Fe, Zn and Ag.  Controlled melting and freezing conditions were followed to homogenize the sample. A multi-pass directional freezing experiment on the pre-homogenized GaSb sample was conducted. The experimental conditions and parameters such as temperature gradient, sample tube movement rate, crucible geometry was established and optimized. The prepared homogenous GaSb sample was cleaned under contamination controlled conditions aided by 1000 class clean room and 100 class clean benches.  Then the homogenous sample was loaded in the high quality quartz ampoule for further purification process.  The sample containing ampoule was subjected to melting-freezing scheme with 20 passes cycle and the 4N+ pure GaSb crystalline ingot thus prepared. The purified and crystallised sample was characterized for its purity employing ICP-MS and crystalline quality through XRD techniques respectively and the  results are discussed.

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The temperature distribution profile above the graphite die used to grow multi-crystalline silicon (Si) sheets by Capillary Action Shaping Technique (CAST) in a resistive heated system, has been controlled by forced argon (Ar) gas cooling. A theoretical model is proposed in which the temperature on the top of the die is related with the gas flow and the solutions to these equations are simulated and plotted using Mathematica 6.0 program. While the crystal growth is better controlled with the forced cooling, the theoretical model helps to set the optimum flow rates for obtaining desired growth speed and thickness of the Si sheets. Thus the experimental growth variables such as thickness and growth rates of the growing silicon sheets have been controlled. Temperature gradient values at the growth interface observed experimentally have also been compared to the theoretical values, which agree closely.

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Stainless steel foams are produced via powder metallurgy process taking acicular urea as space holder contributing porosity with 40-70 volume %. The resulting changes in microstructure of compact after each operation comprising cold compaction, pre-heating and sintering are discussed along with causes with the help of SEM micrograph. The processed foam samples using 40 % urea by volume are quite regular and acicular in shape but with increase in porosity regularity starts diminishing. It is observed that the foam samples with 40 % porosity doesn’t show any plateau stress as in aluminum foams but those with 50 % porosity (approximately 80 MPa maximum plateau stress) and 60 % porosity (approx.45MPa) shows plateau region in true stress-strain diagram during compression test due before final densification process. It is observed that with increasing porosity plateau stress decreases, since lesser force is required to densify the foam. Therefore the stainless steel foams with low porosity can be used in light weight high strength applications e.g. structures whereas with high porosity have impact energy absorbing applications e.g. damping elements in buildings or vehicles, etc.

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The technique of pattern synthesis using potentiostatic electroless deposition is a very weighty process for fabrication of micro/nano structures and is cheap and simple. In this paper, electrochemical/electroless deposition have been used to develop copper micro/nanostructures within the micro/nanochannels of single ion track membranes. Scanning electron microscope  was used for morphological studies. These micro/nanostructures have uniform diameters of 5µm and 200nm which is equivalent to the pore shape and size of the pattern used. 

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The present investigation focuses on the fabrication and mechanical characterization of alkali treated natural abaca fiber reinforced urea formaldehyde composites. The composites were prepared by means of compression moulding, and then the effects of fiber loading on mechanical properties such as tensile strength, flexural strength and impact strength were investigated. The composite with 40 wt% abaca fibers gave excellent tensile strength and flexural strength showing that it has the most superior bonding and adhesion of all the composites. In particular, the highest value, 10.02 kJ/m² of charpy impact strength is observed in the composite with 50 wt% abaca fiber. This work revealed the potential of using abaca fibers in fiberboard.

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Ionic thermocurrent (ITC) spectrum is much similar to a thermoluminescence (TL) glow curve involving monomolecular kinetics. Like TL processes, it is found that the ITC spectrum involves different orders of kinetics which depends on the experimental conditions of polarization and rate of rapid cooling. In the present work a generalized equation has been developed which is capable of explaining the occurrence of ITC spectrum involving various order of kinetics. Dielectric relaxation parameters, order of kinetics and approximate number of dipoles per unit volume can be evaluated easily using the proposed model.

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The effect of marine algae Chaetomorpha antennia extract on corrosion inhibition of brass in phosphoric acid was investigated by weight-loss method, potentiodynamic polarization and electrochemical impedance spectroscopy studies. The inhibition efficiency is found to increase with increasing concentration of extract and decreases with rise in temperature. The activation energy, thermodynamic parameters (free energy, enthalpy and entropy change) and kinetic parameters (rate constant and half-life) for inhibition process were calculated. These thermodynamic and kinetic parameters indicate a strong interaction between the inhibitor and the brass surface. The inhibition is assumed to occur via adsorption of inhibitor molecules on the brass surface, which obeys Temkin adsorption isotherm. The adsorption of inhibitor on the brass surface is exothermic, physical, and spontaneous, follows first order kinetics. The polarization measurements showed that the inhibitor behaves as a mixed type inhibitor and the higher inhibition surface coverage on the brass was predicted. Inhibition efficiency values were found to show good trend with weight-loss method, potentiodynamic polarization and electrochemical impedance spectroscopy studies. SEM was carried out to ascertain the inhibitive nature of the algal extract on the brass surface.

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Piezoelectric Materials have played a pivotal role in the progress of Science and Technology since the First World War, being used historically as naturally occurring transducer for precise measurement or to transform energy from one form to the other while currently being used in the MEMS domain for sensing or energy harvesting. Thus this paper reviews piezoelectric materials and their applications in MEMS as thin films by categorizing the known materials in 3 types namely Naturally Occurring Materials, Piezoelectric Ceramics and Piezoelectric Polymers. Piezoelectric constants of the above mentioned materials are also enlisted.

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The polyaniline belongs to the group of electronically conducting polymers. The graphite is anisotropic, being a good electrical and thermal conductor within the layers. One of the more important groups of materials in our lives today is composite material. The nano-composites provide reinforcing efficiency because of their high aspect ratios In this paper, synthesis and characterization polyaniline- graphite as a novel eco-friendly nano-composite material is reported.

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