Study of relaxations in poly(methyl methacrylate)–magneto electrets by thermally stimulated depolarization current and surface‐charge‐decay mechanisms

The effect of the forming temperature and the magnetic field was investigated for the charge retention and stability of poly(methyl methacrylate) (PMMA)–magneto electret (ME) samples with thermally stimulated discharge currents (TSDCs) and a surface‐charge‐decay mechanism. The measurements were performed on a pristine PMMA sample with a thickness of 20 mm. The comparative studies of charge decay with TSDC indicated a strong resemblance between the results of the two techniques of MEs of PMMA and were characterized by two TSDC peaks, that is, an α peak at 110°C and a ρ peak at 160°C. The low‐temperature peak (i.e., the α peak) was associated with dipolar relaxation, and the high‐temperature peak (i.e., the ρ peak) was attributed to the self‐motion of space charges in PMMA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Structural,electrical and optical properties of sintered SnO2 pellets

Tin dioxide (SnO₂) powder was prepared by the co-precipitation method using SnCl₂ solution as a precursor. The powder was then pelletized and sintered. Structural characterization of the samples with XRD confirmed that all the pellets were of SnO₂ having polycrystalline nature with the crystallite size of the order of 90 nm. SEM-EDAX was used to confirm the morphology and composition of the samples. The measurements of electrical properties were carried out in the frequency range of 100 Hz to 100 kHz at various fixed temperatures from 40 °C to 160 °C. The a.c. conductivity and the dielectric constant were found to be dependent on both frequency and temperature. The frequency and temperature dependent conduction properties of SnO₂ are found to be in accordance with correlated barrier hoping model. Infrared and visible spectroscopic studies show that a strong vibration band characteristic of the SnO₂ stretching mode was present at around 620 cm^?1 and the samples exhibited optical transmittance in the visible range.     

Solvent Free Microwave Assisted Isomerization of N‐Nitropyrazoles

This paper describes solvent‐free isomerization of N‐nitropyrazoles under microwave irradiation to achieve a new green chemistry procedure for the synthesis of C‐ nitropyrazoles in good to excellent yields. The presented procedure requires less time, offers simplified workup procedure, needs no obnoxious solvents, and may be used for the preparation of several C‐nitropyrazoles.     

Kinetic and fluid dynamics modeling of methane/hydrogen jet flames in diluted coflow

MILD combustion is a recent development in the combustion of hydrocarbon fuels which promises high efficiencies and low NO_x emissions. In this paper we analyze the mathematical and numerical modeling of a Jet in Hot Coflow (JHC) burner, which is designed to emulate a moderate and intense low oxygen dilution (MILD) combustion regime [1]. This paper initially discusses the effects of several modeling strategies on the prediction of the JHC flame structure using the CFD code FLUENT 6.3.26. Effects of various turbulence models and their boundary conditions have been studied. Moreover, the detailed kinetic mechanism adopted in the CFD simulations is successfully validated in the conditions of interest using recent literature data [2] on the effect of nitrogen dilution on the flame speeds of several CH₄/H₂/air lean mixtures. One of the aims of this paper is also to describe a methodology for computing pollutant formation in steady turbulent flows to verify its applicability to the MILD combustion regime. CFD results are post-processed for calculating the NO_x using a numerical tool called Kinetic Post Processor (KPP). The modeling results agree with the experimental results [1] and support the proposed approach as a useful tool for optimizing the design of new burners also in the MILD combustion regime.     

Development of refractory silicate-yttria-stabilized zirconia dual-layer thermal barrier coatings

Development of advanced thermal barrier coatings (TBCs) is the most promising approach for increasing the efficiency and performance of gas turbine engines by enhancing the temperature capability of hot section metallic components. Spallation of the yttria-stabilized zirconia (YSZ) top coat, induced by the oxidation of the bond coat coupled with the thermal expansion mismatch strain, is considered to be the ultimate failure mode for current state-of-the-art TBCs. Enhanced oxidation resistance of TBCs can be achieved by reducing the oxygen conductance of TBCs below that of thermally grown oxide (TGO) alumina scale. One approach is incorporating an oxygen barrier having an oxygen conductance lower than that of alumina scale. Mullite, rare earth silicates, and glass ceramics have been selected as potential candidates for the oxygen barrier. This paper presents the results of cyclic oxidation studies of oxygen barrier/YSZ dual-layer TBCs.     

Seating discomfort for tractor operators – a critical review

A large number of studies have been conducted and researchers have suggested several criteria for evaluating discomfort and the suitability of a tractor seat in a given working condition. The studies have led to various parameters, viz. the body pressure distributed under and supporting both the buttocks, thighs and the back of an operator, control of posture in static or dynamic condition, ride vibration, exposure time on task and other factors. But in the absence of a more definitive and the most logical criteria particularly from biomechanical viewpoint, the researchers will continue to design conditions and procedures to understand the seat dynamics and evaluate the seating discomfort. Therefore, this paper reviews the research information available in this regard and attempts to set the most appropriate procedure for assessment of seating discomfort during tractor driving.

Relevance to industry

This paper attempts to project the most appropriate method of assessment and selection of tractor seats from engineering and biomechanical view point which could be adopted by the tractor seat manufacturers. It is designed to enhance the feeling of comfort, safety, convenience, and results in higher work output from the operator.     

Structural,dielectric and electrical characteristics of BiFeO3-NaNbO3 solid solutions

The paper mainly reports the effect of NaNbO₃ (as a doping material) on the structural (crystal data and microstructure), dielectric (permittivity, dissipation of energy) and electrical (impedance, modulus, and conductivity) characteristics of BiFeO₃ forming a solid solution of Bi_.8Na_.2Fe_.8Nb_.2O_3. By analysis of the room temperature X-ray diffraction data, the formation of pure-phase material and its crystal data were obtained. The comprehensive studies of dielectric parameters (relative dielectric constant (ε_r), and tangent loss (tan δ) were measured in a wide range of temperature (25–450?°C) and frequency (1?kHz-1?MHz). The surface morphology, obtained with a gold-coated pellet sample, exhibits the high density of the sample. The frequency-temperature dependence of conductivity follows the Jonscher’s Universal Power law. The electrical behavior of the compound has been studied using complex impedance and modulus data. The effect of grain and grain boundary on the capacitive and resistive properties of the material has been studied from complex impedance spectroscopy.     

Sail rotor regulation by self-activated twin spoilers (SATS)

A new method for regulation of small wind turbine rotors is described. The blade (a cambered surface in this instance) is provided with two span-wise slits which are normally kept closed with the help of chord-wise rubber strips or tension springs. In low wind speeds, the blade is a smooth arc, but it progressively distorts, resembling an inverted omega () in moderate wind speeds. Such a distortion in the camber causes flow separation and results in rotor speed regulation. At higher wind speeds the gaps open-up, resulting in a reduced thrust coefficient, besides the power and speed regulation. This is a significant advantage over conventional spoiler regulation. Wind-tunnel test results for $\text{1}\text{10}\text{th}$ and $\text{1}\text{5}\text{th}$ scale models of a 7.5 m rotor diameter prototype are discussed, along with field data for the rotor power coefficient.