Experimental Investigation on the Effect of Advanced Bus-Clamping Pulsewidth Modulation on Motor Acoustic Noise

Voltage source inverters (VSIs) supply nonsinusoidal voltages to induction motor drives, leading to line current distortion and torque pulsation. Conventional space vector pulsewidth modulation (PWM) techniques are widely used in VSIs on the account of good waveform quality and high dc bus utilization. In a conventional space vector PWM technique, the switching sequence begins with one zero state and ends with the other zero state in a subcycle. Some novel switching sequences have been proposed, which employ only one zero state but apply one of the two active states twice in a subcycle. One pair of such special switching sequences has recently been shown to reduce the pulsating torque considerably. In this paper, the conventional and special switching sequences are compared experimentally in terms of acoustic noise. In the low-and medium-speed ranges, the special switching sequence is seen to reduce the amplitude of the tonal component of noise at the switching frequency considerably and is also found to result in spread spectrum.

Bromenium-Catalysed Tandem Ring Opening/Cyclisation of Vinylcyclopropanes and Vinylcyclobutanes: A Metal-Free 3+2+1]/4+2+1] Cascade for the Synthesis of Chiral Amidines and Computational Investigation

We present a detailed study of a 3+2+1] cascade cyclisation of vinylcyclopropanes (VCP) catalysed by a bromenium species (Brd+?Xd-) generated in situ, which results in the synthesis of chiral bicyclic amidines in a tandem one-pot operation. The formation of amidines involves the ring-opening of VCPs with Br?X, followed by a Ritter-type reaction with chloramine-T and a tandem cyclisation. The reaction has been further extended to vinylcyclobutane systems and involves a 4+2+1] cascade cyclisation with the same reagents. The versatility of the methodology has been demonstrated by careful choice of VCPs and VCBs to yield bicyclo4.3.0]-, -4.3.1]- and -4.4.0]amidines in enantiomerically pure form. On the basis of the experimental observations and DFT calculations, a reasonable mechanism has been put forth to account for the formation of the products and the observed stereoselectivity. We propose the existence of a p-stabilised homoallylic carbocation at the cyclopropane carbon as the reason for high stereoselectivity. DFT studies at B3LYP/6-311+G** and M06-2X/6-31+G* levels of theory in gas-phase calculations suggest the ring-opening of VCP is initiated at the p-complex stage (between the double bond and Br?X). This can be clearly perceived from the solution-phase (acetonitrile) calculations using the polarisable continuum model (PCM) solvation model, from which the extent of the ring opening of VCP was found to be noticeably high. Studies also show that the formation of zero-bridge bicyclic amidines is favoured over other bridged bicyclic amidines. The energetics of competing reaction pathways is compared to explain the product selectivity.

Experimental and theoretical investigation of thermoacoustic prime mover

The thermoacoustic prime mover is part of an interesting class of prime movers that can be used to generate clean energy and to drive cryogenic refrigeration systems. A thermoacoustic prime mover has been built based on the linear thermoacoustic model, which consumes thermal energy and produces acoustic energy. The objective of this article is to design a thermoacoustic prime mover that can be used as a drive for a thermoacoustic refrigerator. It is found that stack plate length and its distance from the closed end have a significant effect on the thermal efficiency of the prime mover. For different stack center positions, there is an optimum length of stack plate that has a significant effect on the performance of the thermoacoustic prime mover in terms of temperature gradient, frequency, and pressure amplitude. In this study, the experiments have been done on the thermoacoustic prime mover by varying stack position and its length with constant blockage ratio and resonator length. The results obtained from the experiments have been compared to the theoretical results acquired from DeltaEc Software.

An EQCM investigation of capacitance of MnO2 in electrolytes containing multivalent cations

MnO2 is electrochemically deposited on Au coated quartz crystal to study the electrochemical capacitance properties and to monitor the mass variations that accompany reversible adsorption/desorption of Na+, Mg2+ and La3+ ions during discharge/charge cycling. There is an increase in the values of specific capacitance of MnO2 with increase in charge of the cation in the electrolyte. Also, there is an increase in mass during discharge due to adsorption of cations from the electrolyte resulting from reduction of MnO2. Mass decreases during charging process due to desorption of cations. The magnitude of mass variation is approximately proportional to the atomic weight of the cationic element. (C) 2012 Elsevier B.V. All rights reserved.

Numerical Investigation on Laminar Flow Due to Sudden Expansion Using Nanofluids

Laminar two-dimensional sudden expansion flow of different nanofluids is studied numerically. The governing equations are solved using stream function-vorticity method. The effect of volume fraction of the nanoparticles and type of nanoparticles on flow behaviour is examined and found significant impact. The flow response to Reynolds number in the presence of nanoparticles is examined. The presence of nanoparticles decreases the flow bifurcation Reynolds number. The size and the reattachment length of the bottom wall recirculation increase with increasing volume fraction and particle density. The effect of volume fraction and density of nanoparticles on friction factor is reported. The bottom wall recirculation strongly respond to the variation in volume faction and type of particles. However, weak response is observed for top wall recirculation.

Experimental investigation on switching characteristics of IGBTs for traction application

In traction application, inverters need to have high reliability on account of wide variation in operating conditions, extreme ambient conditions, thermal cycling and varying DC link voltage. Hence it is important to have a good knowledge of switching characteristics of the devices used. The focus of this paper is to investigate and compare switching characteristics and losses of IGBT modules for traction application. Dependence of device transition times and switching energy losses on dc link voltage, device current and operating temperature is studied experimentally.

EQCM investigation of electrochemical deposition and stability of Co-Pi oxygen evolution catalyst of solar energy storage

Photoassisted electrolysis of water is considered as an effective way of storing solar energy in the form of hydrogen fuel. This overall reaction involves the oxidation of water to oxygen at the anode and the reduction of protons to hydrogen at the cathode. Cobalt-phosphate-based catalyst (Co-Pi) is a potentially useful material for oxygen evolution reaction. In the present study, electrochemical deposition of Co-Pi catalyst is carried out on Au-coated quartz crystal from 0.1 M phosphate buffer (pH 7) containing 0.5 mM Co2+ ion, along with the simultaneous measurement of mass changes at the electrode surface. Cyclic voltammograms and mass variations are recorded during the course of deposition. A current peak is observed at 0.92 V vs Ag/AgCl, 3 M KCl corresponding to oxidation of Co2+ ion. The mass of the electrode starts increasing at this potential, suggesting the deposition of a Co(III)-based insoluble product on the electrode surface. The stability of the catalyst is also studied at several potentials in both buffered and nonbuffered electrolyte by monitoring the real-time mass variations.

Investigation of phase separation in bulk heterojunction solar cells via supramolecular chemistry

In this work, we have prepared two donor-acceptor-donor (D-A-D) pi-conjugated oligomers to investigate the effect of phase separation on the performance of bulk heterojunction (BHJ) solar cells. These charge transfer low band gap pi-conjugated oligomers (TTB and NMeTTB) were synthesized by Knoevenagel condensation of terthiophenecarbaldehyde and barbiturate appended pyran derivative. The thin film morphology of both the oligomers and along with electron acceptor 6,6]-phenyl-C60-butyric acid methyl ester (PC61BM) was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The blend of NMeTTB and PC61BM thin film yield highly ordered thin film, whereas there was clear phase separation between TTB and PC61BM in thin film. The BHJ solar cell was fabricated using a blend of NMeTTB and TTB with PC61BM acceptor in 1:1 ratio as active layer, and a power conversion efficiency of 1.8% was obtained. This device characteristic was compared with device having TTB:PC61BM as active layer, and large difference is observed in photocurrents. This poor performance of TTB in BHJ devices was attributed to the difference in the nanoscale morphology of the corresponding derivatives. We rationalize our findings based on the low charge carrier mobility in organic field-effect transistors and miscibility/phase separation parameter of binary components (oligomers and PC61BM) in the active layer of bulk heterojunction solar cells.

Investigation of the origin of glassiness in La0.5Sr0.5CoO3

A comprehensive magnetic study has been carried out on the two sets of La0.5Sr0.5CoO3 samples with a view to understand the origin of low temperature glassiness in the ferromagnetic state. The samples prepared by the conventional solid-state synthesis method show a low temperature shoulder in both dc magnetization as well as in the ac susceptibility measurements, which exhibit characteristics of glassiness such as the frequency dependence and memory effect. These observations suggest the existence of a distinct low temperature cluster-glass like phase within dominant ferromagnetic phase. But, once the same sample is properly homogenized by repeated grinding and annealing process, the low temperature glassy phase disappears, and it shows a pure ferromagnetic behavior. Our comparative study clearly reveals that the reentrant spin-glass like nature is not intrinsic to La0.5Sr0.5CoO3 system, in fact this is an outcome of the compositional inhomogeneity.

Does aluminium bind to histidine? an NMR investigation of Amyloid beta 12 and Amyloid beta 16 fragments

Aluminium and zinc are known to be the major triggering agents for aggregation of amyloid peptides leading to plaque formation in Alzheimer's disease. While zinc binding to histidine in A (amyloid ) fragments has been implicated as responsible for aggregation, not much information is available on the interaction of aluminium with histidine. In the NMR study of the N-terminal A fragments, DAEFRHDSGYEV (A12) and DAEFRHDSGYEVHHQK (A16) presented here, the interactions of the fragments with aluminium have been investigated. Significant chemical shifts were observed for few residues near the C-terminus when aluminium chloride was titrated with A12 and A16 peptides. Surprisingly, it is nonhistidine residues which seem to be involved in aluminium binding. Based on NMR constrained structure obtained by molecular modelling, aluminium-binding pockets in A12 were around charged residues such as Asp, Glu. The results are discussed in terms of native structure propagation, and the relevance of histidine residues in the sequences for metal-binding interactions. We expect that the study of such short amyloid peptide fragments will not only provide clues for plaque formation in aggregated conditions but also facilitate design of potential drugs for these targets.

Investigation of Magnon Assisted Resistivity in Permalloy Thin Films

Magnon contribution to the resistance of ferromagnetic film like Permalloy is investigated by magnetotransport measurements. We are able to observe and distinguish Anisotropic-Magnetoresistance(AMR)(1) and Magnon Magnetoresistance(MMR)(2) contributions clearly in PLD grown Permalloy films. A linear non-saturating longitudinal MR observed in high field regime for permalloy films could never be explained using AMR but only MMR can account for it.

Critical investigation on hydrogen bonding by Fourier transform infrared spectroscopy in hydrogenated amorphous silicon thin films

Fourier Transform Infrared (FTIR) spectroscopic analysis has been carried out on the hydrogenated amorphous silicon (a-Si:H) thin films deposited by DC, pulsed DC (PDC) and RF sputtering process to get insight regarding the total hydrogen concentration (C-H) in the films, configuration of hydrogen bonding, density of the films (decided by the vacancy and void incorporation) and the microstructure factor (R*) which varies with the type of sputtering carried out at the same processing conditions. The hydrogen incorporation is found to be more in RF sputter deposited films as compared to PDC and DC sputter deposited films. All the films were broadly divided into two regions namely vacancy dominated and void dominated regions. At low hydrogen dilutions the films are vacancy dominated and at high hydrogen dilutions they are void dominated. This demarcation is at C-H = 23 at.% H for RF, C-H = 18 at.% H for PDC and C-H = 14 at.% H for DC sputter deposited films. The microstructure structure factor R* is found to be as low as 0.029 for DC sputter deposited films at low C-H. For a given C-H, DC sputter deposited films have low R* as compared to PDC and RF sputter deposited films. Signature of dihydride incorporation is found to be more in DC sputter deposited films at low C-H.

Forming limit investigation of friction stir welded sheets: influence of shoulder diameter and plunge depth

The main aim of the present work is to analyze the influence of shoulder diameter and plunge depth on the formability of friction stir welded sheets. The base material used for welding and forming was AA6061-T6. Formability evaluation was performed through limiting dome height tests. The forming limit curve, FLC (only in the stretching region), thickness distribution, and strain hardening exponent of the weld region were monitored during formability studies. It is found from the work that the forming limit of friction stir welded sheets is better than unwelded sheets. In general, with an increase in shoulder diameter and plunge depth, the forming limit is found to improve considerably. With a decrease in thickness gradient severity and an increase in strain hardening exponent (n) of the weld region, the forming limit is found to increase. The increase in n value of the weld region is believed to occur because of the reduction in dislocation density. The maximum thickness difference is higher in the retreating side, rather than in the advancing side, of the weld. This is due to the differential straining and hardness levels attained by both sides during friction stir welding.

Experimental Investigation of Heat Fluxes in the Vicinity of Protuberances on a Flat Plate at Hypersonic Speeds

Heat transfer rates measured in front and to the side of a protrusion on an aluminum flat plate subjected to hypersonic flow at zero angle of attack are presented for two flow enthalpies of approximately 2 MJ/kg and 4.5 MJ/kg. Experiments were conducted in the hypersonic shock tunnel (HST2) and free piston driven HST3 at a freestream Mach number of 8. Heat transfer data was obtained for different geometries of the protrusion of a height of 4 mm, which is approximately the local boundary layer thickness. Comparatively high rates of heat transfer were obtained at regions of flow circulation in the separated region, with the hottest spot generally appearing in front of the protuberance. Experimental values showed moderate agreement with existing empirical correlations at higher enthalpy but not at all for the lower enthalpy condition, although the correlations were coined at enthalpy values nearer to the lower value. Schlieren visualization was also done to investigate the flow structures qualitatively.

Investigation on non-exchange spring behaviour and exchange spring behaviour: A first order reversal curve analysis

The First Order Reversal Curve (FORC) method has been utilised to understand the magnetization reversal and the extent of the irreversible magnetization of the soft CoFe2O4-hard SrFe12O19 nanocomposite in the nonexchange spring and the exchange spring regime. The single peak switching behaviour in the FORC distribution of the exchange spring composite confirms the coherent reversal of the soft and hard phases. The onset of the nucleation field and the magnetization reversal by domain wall movement are also evident from the FORC measurements. (C) 2013 AIP Publishing LLC.