Magneto acoustical emission in nanocrystalline Mn-Zn ferrites

Mn0.4Zn0.6Fe2O4 powders were prepared by microwave hydrothermal method. The powders were characterized by X-ray diffraction, transmission electron microscope. The powders were sintered at different temperatures 400, 500, 600, 700, 800 and 900 degrees C/30 min using microwave sintering method. The grain size was estimated by scanning electron microscope. The room temperature dielectric and magnetic properties were studied in the frequency range (100 kHz-1.8 GHz). The magnetization properties were measured upto 1.5 T. The acoustic emission has been measured along the hysteresis loops from 80 K to Curie temperature. It is found that the magneto-acoustic emission (MAE) activity along hysteresis loop is proportional to the hysteresis losses during the same loop. This law has been verified on series of polycrystalline ferrites and found that the law is valid whatever the composition, the grain size and temperature. It is also found that the domain wall creation/or annihilation processes are the origin of the MAE. (C) 2013 Published by Elsevier Ltd.

DEPRESSION OF MAGNETlCALLY FIXED EMISSION ZONE IN LOW PRESSURE MERCURY ARCS

A transverse magnetic field was used to fix the cathode spot of a low pressure mercury arc with liquid cathode It was noticed that such fixation causes consider-abledepression of the emission zone below the mercury level.This depression varies with the arc current and the magnetic field and is associated with an increase in the arc voltage drop. It indicates appreciable pressure in the emission zone.

Studies on the wobble mode stability of a three-wheeled vehicle

A wobble instability is one of the major problems of a three-wheeled vehicle commonly used in India, and these instabilities are of great interest to industry and academia. In this paper, we studied this instability using a multi-body dynamic model and with experiments conducted on a prototype three-wheeled vehicle on a test track. The multi-body dynamic model of a three-wheeled vehicle is developed using the commercial software ADAMS/Car. In an initial model, all components including main structures such as the frame, the steering column and the rear forks are assumed to be rigid bodies. A linear eigenvalue analysis, which is carried out at different speeds, reveals a mode that has predominantly a steering oscillation, also called a wobble mode, with a frequency of around 5-6Hz. The analysis results shows that the damping of this mode is low but positive up to the maximum speed of the three-wheeled vehicle. However, the experimental study shows that the mode is unstable at speeds below 8.33m/s. To predict and study this instability in detail, a more refined model of the three-wheeled vehicle, with flexibilities of three important bodies, was constructed in ADAMS/Car. With flexible bodies, three modes of a steering oscillation were observed. Two of these are well damped and the other is lightly damped with negative damping at lower speeds. Simulation results with flexibility incorporated show a good match with the instability observed in the experimental studies. Further, we investigated the effect of each flexible body and found that the flexibility of the steering column is the major contributor for wobble instability and is similar to the wheel shimmy problem in aircraft.

Acoustic emission techniques for NDE & structural health monitoring of advanced composite materials

Structural Health Monitoring (SHM) is an effective extension of NDE to reduce down time and cost of Inspection of structural components. On – line monitoring is an essential part of SHM. Acoustic Emission Techniques have most of the desirable requirements of an effective SHM tool. With the kind of advancement seen in the last couple of decades in the field of electronics, computers and signal processing technologies it can only be more helpful in obtaining better and meaningful quantitative results which can further enhance the potential of AET for the purpose. Advanced Composite materials owing to their specific high performance characteristics are finding a wide range of engineering applications. Testing and Evaluation of this category of materials and SHM of composite structures have been very challenging problems due to the very nature of these materials. Mechanical behaviour of fiber composite materials under different loading conditions is complex and involves different types of failure mechanisms. This is where the potential of AET can be exploited effectively. This paper presents an over view of some relevant studies where AET has been utilised to test, evaluate and monitor health of composite structures.

Nonlinear and linear autopilot performance comparison of tactical flight vehicle

n this paper, three-axis autopilot of a tactical flight vehicle has been designed for surface to air application. Both nonlinear and linear design synthesis and analysis have been carried out pertaining to present flight vehicle. Lateral autopilot performance has been compared by tracking lateral acceleration components along yaw and pitch plane at higher angles of attack in presence of side force and aerodynamic nonlinearity. The nonlinear lateral autopilot design is based on dynamic inversion and time scale separation principle. The linear lateral autopilot design is based on three-loop topology. Roll autopilot robustness performance has been enhanced against unmodeled roll disturbances by backstepping technique. Complete performance comparison results of both nonlinear and linear controller based on six degrees of freedom simulation along with stability and robustness studies with respect to plant parameter variation have been discussed in the paper.

Active yaw control of a vehicle using a Fuzzy logic algorithm

Yaw rate of a vehicle is highly influenced by the lateral forces generated at the tire contact patch to attain the desired lateral acceleration, and/or by external disturbances resulting from factors such as crosswinds, flat tire or, split-μ braking. The presence of the latter and the insufficiency of the former may lead to undesired yaw motion of a vehicle. This paper proposes a steer-by-wire system based on fuzzy logic as yaw-stability controller for a four-wheeled road vehicle with active front steering. The dynamics governing the yaw behavior of the vehicle has been modeled in MATLAB/Simulink. The fuzzy controller receives the yaw rate error of the vehicle and the steering signal given by the driver as inputs and generates an additional steering angle as output which provides the corrective yaw moment. The results of simulations with various drive input signals show that the yaw stability controller using fuzzy logic proposed in the current study has a good performance in situations involving unexpected yaw motion. The yaw rate errors of a vehicle having the proposed controller are notably smaller than an uncontrolled vehicle's, and the vehicle having the yaw stability controller recovers lateral distance and desired yaw rate more quickly than the uncontrolled vehicle.

Enhanced Field Emission Properties from CNT Arrays Synthesized on Inconel Superalloy

One of the most promising materials for fabricating cold cathodes for next generation high-performance flat panel devices is carbon nanotubes (CNTs). For this purpose, CNTs grown on metallic substrates are used to minimize contact resistance. In this report, we compare properties and field emission performance of CNTs grown via water assisted chemical vapor deposition using Inconel vs silicon (Si) substrates. Carbon nanotube forests grown on Inconel substrates are superior to the ones grown on silicon; low turn-on fields (similar to 1.5 V/mu m), high current operation (similar to 100 mA/cm(2)) and very high local field amplification factors (up to similar to 7300) were demonstrated, and these parameters are most beneficial for use in vacuum microelectronic applications.

Robust Reentry Guidance of a Reusable Launch Vehicle Using Model Predictive Static Programming

A robust suboptimal reentry guidance scheme is presented for a reusable launch vehicle using the recently developed, computationally efficient model predictive static programming. The formulation uses the nonlinear vehicle dynamics with a spherical and rotating Earth, hard constraints for desired terminal conditions, and an innovative cost function having several components with associated weighting factors that can account for path and control constraints in a soft constraint manner, thereby leading to smooth solutions of the guidance parameters. The proposed guidance essentially shapes the trajectory of the vehicle by computing the necessary angle of attack and bank angle that the vehicle should execute. The path constraints are the structural load constraint, thermal load constraint, bounds on the angle of attack, and bounds on the bank angle. In addition, the terminal constraints include the three-dimensional position and velocity vector components at the end of the reentry. Whereas the angle-of-attack command is generated directly, the bank angle command is generated by first generating the required heading angle history and then using it in a dynamic inversion loop considering the heading angle dynamics. Such a two-loop synthesis of bank angle leads to better management of the vehicle trajectory and avoids mathematical complexity as well. Moreover, all bank angle maneuvers have been confined to the middle of the trajectory and the vehicle ends the reentry segment with near-zero bank angle, which is quite desirable. It has also been demonstrated that the proposed guidance has sufficient robustness for state perturbations as well as parametric uncertainties in the model.

Morphology controlled synthesis of wurtzite ZnS nanostructures through simple hydrothermal method and observation of white light emission from ZnO obtained by annealing the synthesized ZnS nanostructures

A controllable synthesis of phase pure wurtzite (WZ) ZnS nanostructures has been reported in this work at a low temperature of similar to 220 degrees C using ethylenediamine as the soft template and by varying the molar concentration of zinc to sulphur precursors as well as by using different precursors. A significant reduction in the formation temperature required for the synthesis of phase pure WZ ZnS has been observed. A strong correlation has been observed between the morphology of the synthesized ZnS nanostructures and the precursors used during synthesis. It has been found from Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) image analyses that the morphology of the ZnS nanocrystals changes from a block-like to a belt-like structure having an average length of similar to 450 nm when the molar ratio of zinc to sulphur source is increased from 1 : 1 to 1 : 3. An oriented attachment (OA) growth mechanism has been used to explain the observed shape evolution of the synthesized nanostructures. The synthesized nanostructures have been characterized by the X-ray diffraction technique as well as by UV-Vis absorption and photoluminescence (PL) emission spectroscopy. The as-synthesized nanobelts exhibit defect related visible PL emission. On isochronal annealing of the nanobelts in air in the temperature range of 100-600 degrees C, it has been found that white light emission with a Commission Internationale de I'Eclairage 1931 (CIE) chromaticity coordinate of (0.30, 0.34), close to that of white light (0.33, 0.33), can be obtained from the ZnO nanostructures obtained at an annealing temperature of 600 degrees C. UV light driven degradation of methylene blue (MB) dye aqueous solution has also been demonstrated using as-synthesized nanobelts and similar to 98% dye degradation has been observed within only 40 min of light irradiation. The synthesized nanobelts with visible light emission and having dye degradation activity can be used effectively in future optoelectronic devices and in water purification for cleaning of dyes.

Multistage effect in enhancing the field emission behaviour of ZnO branched nanostructures

We report the synthesis of branched ZnO nanostructures by vapour phase transport and their multistage effect in enhancing the field emission behaviour. First, the ZnO nanowires (first generation) are grown and second generation nanowires are grown on first one and so on to obtain the branched structures. The number of branches increases and the diameter of the branches decreases till the third generation nanowires. Fourth generation onwards, dense branched structures are obtained eventually yielding nanoforest-like morphology. The field emission behaviour is found to improve till the third generation and is assigned to smaller diameter of the branches. (C) 2014 AIP Publishing LLC.

Study of liquid fuel transport in a small carburetted engine in the context of cold-start HC emission control

In the present study, a detailed visualization of the transport of fuel film has been performed in a small carburetted engine with a transparent manifold at the exit of the carburettor. The presence of fuel film is observed significantly on the lower half of the manifold at idling, while at load conditions, the film is found to be distributed all throughout the manifold walls. Quantitative measurement of the fuel film in a specially-designed manifold of square cross section has also been performed using the planar laser-induced fluorescence (PLIF) technique. The measured fuel film thickness is observed to be of the order of 1 nun at idling, and in the range of 0.1 to 0.4 mm over the range of load and speed studied. These engine studies are complemented by experiments conducted in a carburettor rig to study the state of the fuel exiting the carburettor. Laser-based Particle/Droplet Image Analysis (PDIA) technique is used to identify fuel droplets and ligaments and estimate droplet diameters. At a throttle position corresponding to idling, the fuel exiting the carburettor is found to consist of very fine droplets of size less than 15 mu m and large fuel ligaments associated with length scales of the order of 500 mu m and higher. For a constant pressure difference across the carburettor, the fuel consists of droplets with an SMD of the order of 30 mu m. Also, the effect of liquid fuel film on the cold start HC emissions is studied. Based on the understanding obtained from these studies, strategies such as manifold heating and varying carburettor main jet nozzle diameter are implemented. These are observed to reduce emissions under both idling and varying load conditions.

Fine-Tuning Dual Emission and Aggregation-Induced Emission Switching in NPI-BODIPY Dyads

Three new NPI-BODIPY dyads 1-3 (NPI = 1,8-naphthalimide, BODIPY = boron-dipyrromethene) were synthesized, characterized, and studied. The NPI and BODIPY moieties in these dyads are electronically separated by oxoaryl bridges, and the compounds only differ structurally with respect to methyl substituents on the BODIPY fluorophore. The NPI and BODIPY moieties retain their optical features in molecular dyads 1-3. Dyads 1-3 show dual emission in solution originating from the two separate fluorescent units. The variations of the dual emission in these compounds are controlled by the structural flexibilities of the systems. Dyads 13, depending on their molecular flexibilities, show considerably different spectral shapes and dissimilar intensity ratios of the two emission bands. The dyads also show significant aggregation-induced emission switching (AIES) on formation of nano-aggregates in THF/H2O with changes in emission color from green to red. Whereas the flexible and aggregation-prone compound 1 shows AIES, rigid systems with less favorable intermolecular interactions (i.e., 2 and 3) show aggregation-induced quenching of emission. Correlations of the emission intensity and structural flexibility were found to be reversed in solution and aggregated states. Photophysical and structural investigations suggested that intermolecular interactions (e. g., pi-pi stacking) play a major role in controlling the emission of these compounds in the aggregated state.

Rainbow Emission from an Atomic Transition in Doped Quantum Dots

Although semiconductor quantum dots are promising materials for displays and lighting due to their tunable emissions, these materials also suffer from the serious disadvantage of self-absorption of emitted light. The reabsorption of emitted light is a serious loss mechanism in practical situations because most phosphors exhibit subunity quantum yields. Manganese-based phosphors that also exhibit high stability and quantum efficiency do not suffer from this problem but in turn lack emission tunability, seriously affecting their practical utility. Here, we present a class of manganese-doped quantum dot materials, where strain is used to tune the wavelength of the dopant emission, extending the otherwise limited emission tunability over the yellow-orange range for manganese ions to almost the entire visible spectrum covering all colors from blue to red. These new materials thus combine the advantages of both quantum dots and conventional doped phosphors, thereby opening new possibilities for a wide range of applications in the future.