Compact slotline fed enhanced gain dipole antenna for 5.2 GHz/5.8‐GHz applications

A high‐efficiency and high‐gain slotline fed directive dipole antenna is developed for microwave applications. The antenna offers an average gain of 7.9 dBi with a front to back ratio better than 20 dB and a cross polar level better than ?20 dB. Design equations of the antenna are developed and validated on different substrates. The simulation and experimental results show that the proposed antenna exhibits high gain and robust radiation patterns in the entire frequency band. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Peristrophic multiplexing studies in silver doped photopolymer film

The peristrophic multiplexing technique with rotation of the film in a plane normal to the bisector of the incident beams was employed for recording plane-wave transmission gratings at the same location of silver doped acrylamide photopolymer film. Both constant and variable exposure scheduling methods were adopted for storing gratings using a 632.8 nm HeNe laser. The diffraction efficiency (DE) and M number (M/#) obtained from both methods were compared to determine which method enabled the greatest number of gratings to be recorded with uniform diffraction efficiencies. By the variable exposure energy scheduling method, 30 nearly uniform plane wave gratings with M/# equal to 4.7, could be recorded in a 130 µm thick photopolymer layer.     

Effect of Substituted Dithiobiurets—Tetramethyl Thiuram Disulfide (TMTD) Binary Accelerator Systems in the Vulcanization of NR-SBR Blends

1-Phenyl 2,4-dithiobiuret and 1,5-diphenyl 2,4-dithiobiuret were studied as secondary accelerators along with tetramethyl thiuram disulfide (TMTD) in the vulcanization of a blend of natural rubber (NR) and styrene-butadiene rubber (SBR). These binary systems were found to be very effective and reduced the optimum vulcanization time considerably. 1-Phenyl 2,4-dithiobiuret, which is more nucleophilic than 1,5-diphenyl 2,4-dithiobiuret, reduced the vulcanization time more, indicating a nucleophilic reaction mechanism in the vulcanization reactions under review. In both cases the optimum dosage of the secondary accelerator was derived. Physical properties such as modulus, tensile strength, elongation at break, hardness, compression set, heat buildup, resilience, etc., of the vulcanizates were studied before and after heat aging and compared with a reference mix. There is substantial increase in many of these properties compared with TMTD alone or with the reference mix. Chemical characterization of the vulcanizates was also carried out to correlate the physical properties with the type of chemical crosslinks formed in these systems.     

Fabrication of a ternary PANI@Fe3O4@CFs nanocomposite as a high performance electrode for solid-state supercapacitors

In this work, a solid-state high performance supercapacitor is fabricated based on a ternary polyaniline@Fe₃O₄@carbon fibers nanocomposite. To prepare the polyaniline@Fe₃O₄@carbon fibers electrodes, a two-step method including electrophoretic deposition of Fe₃O₄ nanoparticles on carbon fibres followed by an in situ polymerization process of polyaniline is utilized. The results show that the polyaniline@Fe₃O₄@carbon fibers nanocomposite with a layer by layer microstructure is successfully formed. The fabricated nanocomposite represents a specific surface area of 3.12 m² g⁻¹. The electrochemical measurements in a three-electrode configuration reveals a high specific capacitance of 245.5 F g⁻¹ at 0.5 A g⁻¹ and an excellent cycle stability (82.44% after 1000 cycle) of the polyaniline@Fe₃O₄@carbon fibers electrode. The as-fabricated solid-state supercapacitor based on the polyaniline@Fe₃O₄@carbon fiber nanocomposite cloth with a surface area of 25 cm² powers up a blue light-emitting diode for 4 min and delivers a high energy density of 78.6 Wh.kg⁻¹ at a power density of 1047.5 W kg⁻¹.     

Ferrofluid thin films as optical gaussmeters proposed for field and magnetic moment sensing

Ferrofluids belonging to the series, Ni _x Fe_1-x Fe₂O₄ and Zn _x Fe_1-x Fe₂O₄, were synthesized using cold co-precipitation. Liquid films of these ferrofluids were prepared by encapsulating the ferrofluids in between two optically smooth and ultrasonically cleaned glass plates. Magnetic field induced laser transmission through these ferrofluid films has been investigated. Magnetic field values can be calibrated in terms of output laser power in the low field region in which the variation is linear. This set up can be used as a cheap optical gaussmeter in the low field regime. Using the same set-up, the saturation magnetization of the sample used can also be calculated with a sample that is pre-characterized. Hence both magnetization of the sample, as well as applied magnetic field can be sensed and calculated with a precalibrated sample.     

One-step versus two-step mechanism of Diels-Alder reaction of 1-chloro-1-nitroethene with cyclopentadiene and furan

DFT computational study shows that Diels-Alder (DA) reactions of 1-chloro-1-nitroethene with cyclopentadiene and furan have polar nature. However, their mechanism is substantially different. In particular, 1-chloro-1-nitroethene react with cyclopentadiene according to one-step mechanism. In the same time, more favourable channel associated with the P-DA reaction between furan and 1-chloro-1-nitroethene is a domino process, that comprises an initial hetero-Diels-Alder reaction yielding a [2 + 4] cycloadduct, which experiences a subsequent [3,3] sigmatropic shift to yield the expected formal [4 + 2] cycloadduct. This is a consequence of more polar nature of reaction, due to higher nucleophilicity of furan in comparison to cyclopentadiene.     

Design of experiments for thermo-mechanical behavior of polypropylene/high-density polyethylene/nanokaolinite clay composites

This paper deals with the preparation of nanocomposites using polypropylene (PP)/high-density polyethylene (PE) blend and low-cost nanokaolinite clay by melt compounding in a Thermo Haake Rheocord mixer. The optimization of processing parameters and nanoclay content is done using Box–Behnken design of response surface methodology. Mechanical properties are modeled in terms of processing parameters and nanoclay content and results are verified using statistical analysis. Most reports suggest that kaolinite clay is difficult to disperse in polymer matrix compared to costly montmorillonite clay. This difficulty is overcome by surface modification of nanokaolinite clay by an organic group and the effect of modification is studied using melt flow index, thermal stability and dynamic mechanical behavior. Morphological characterization is done by scanning electron microscopy and X-ray diffraction. Study shows that cheap and abundantly occurring nanokaolinite clay is an efficient reinforcing agent for PP/PE blend. Design of experiments can be effectively used to model such a system, which is influenced by a number of variables. It is also observed that surface modification of the nanoclay with an organic group leads to remarkable improvement in the thermal and mechanical properties of the blend.     

TiO2 nanotube-based field effect transistors and their application as humidity sensors

TiO₂ nanotubes are the building units of various devices of energy- and environment-related applications and the property studies of individual TiO₂ nanotubes are important to understand and improve the performance of TiO₂ nanotubes-based devices. Here we report the electrical property study of individual TiO₂ nanotubes enabled by the construction of field effect transistors based on individual TiO₂ nanotubes. It is found that individual TiO₂ nanotubes exhibit typical n-type electrical conduction characteristics, with electron mobility of 6.9 × 10^?3 cm²/V s at V_ds = 1 V, and electron concentration of 2.8 × 10¹⁷ cm^?3. Moreover, the on–off ratio of the TiO₂ nanotube-based field effect transistors is as high as 10³. Humidity sensing test shows the sensitive response of the individual TiO₂ nanotubes to water vapor.