Electric field activated nonlinear anisotropic charge transport in doped polypyrrole

Electric field activated nonlinear transport is investigated in polypyrrole thin film in both in-plane and out-of-plane geometries down to 5 K and strong anisotropy is observed. A morphological model is suggested to explain the anisotropy through inter-chain and intra-chain transport. The deviation from the variable range hopping at low temperature is accounted by fluctuation assisted transport. From Zabrodaskii plots, it is found that electric field can tune the transport from insulating to metallic regime. Glazman-Matveev model is used to describe the nonlinear conduction. Field scaling analysis shows that conductance data at different temperature falls on to a single curve. Nonlinearity exponent, m(T) and characteristic length, L-E are estimated to characterize the transport in both the geometries. (C) 2013 AIP Publishing LLC.

Long ranged structural modulation in the pre-morphotropic phase boundary cubic-like state of the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3

The nature of the pre-morphotropic phase boundary (MPB) cubic-like state in the lead-free piezoelectric ceramics (1-x)Na1/2Bi1/2TiO3-(x)BaTiO3 at x similar to 0.06 has been examined in detail by electric field and temperature dependent neutron diffraction, x-ray diffraction, dielectric and ferroelectric characterization. The superlattice reflections in the neutron diffraction patterns cannot be explained with the tetragonal P4bm and the rhombohedral (R3c) phase coexistence model. The cubic like state is rather a result of long ranged modulated complex octahedral tilt. This modulated structure exhibits anomalously large dielectric dispersion. The modulated structure transforms to a MPB state on poling. The field-stabilized MPB state is destroyed and the modulated structure is restored on heating the poled specimen above the Vogel-Fulcher freezing temperature. The results show the predominant role of competing octahedral tilts in determining the nature of structural and polar states in Na1/2Bi1/2TiO3-based ferroelectrics. (C) 2013 AIP Publishing LLC.

Improved magneto-electric response in Na0.5Bi0.5TiO3-MnFe2O4 composites

Magneto-electric composites comprising Na0.5Bi0.5TiO3 (NBT) and MnFe2O4 (MFO) were fabricated using their fine powders obtained via sol-gel method. X-ray diffraction and scanning electron microscopy results confirmed the single-phase formation of NBT and MFO and the composite nature when these were mixed and sintered at appropriate temperatures. The dielectric constant (epsilon(r)) and dielectric loss (D) decreased with increase in frequency (40-110 MHz). Room temperature magnetization measurements established these composites to be soft magnetic. Further, the nature of these composites were established to be magneto-electric at 300 K. The highest ME response of 0.19 % was observed in 30NBT-70MFO composite. The ME coefficient (alpha) was 240 mV/cm Oe for the same composition. The present study demonstrated the effectiveness of NBT/MFO as a lead-free multiferroic composite and provides an alternative for environment-friendly ME device applications.

Electric field induced ultra-high actuation in a bulk carbon nanotube structure

Electric-field induced nonlinear actuation behavior is demonstrated in a bulk nanotube (CNT) structure under ambient conditions. Completely recoverable and non-degradable actuation over several cycles of electric-field is measured in these structures. A symmetric and polarity independent displacement corresponding up to an axial strain of 14% is measured upon application of a low strength electric field of 4.2 kV/m in the axial direction. However, a much lower strain of similar to 1% is measured in the radial (or, transverse) direction. Furthermore, the electric field induced actuation increases by more than a factor of 2 upon impregnating the CNT cellular structure with copper oxide nano-particles. An electrostriction mechanism, based on the electric-field induced polarization of CNT strands, is proposed to account for the reported actuation behavior. (C) 2013 Elsevier Ltd. All rights reserved.

Hypersonic interference heating on flat plate with short three-dimensional protuberances

Experiments were conducted to measure the heat flux in the vicinity of a three-dimensional protuberance placed on a flat plate facing a hypersonic flow at zero angle of attack. The effects of flow enthalpy and height of the protuberance on the interference heating in its vicinity were studied. Evidence of disturbed flow with highly three-dimensional characteristics and heightened vorticity was observed near the protrusion. A parametric study by changing the deflection angle of the protuberance was also made. Correlations exist in the open literature for enthalpy values lower than 2  MJ/kg. This effort has yielded a new correlation that is valid for enthalpies up to 6  MJ/kg. The Z-type schlieren technique was used to visualize the flow features qualitatively for one of the flow conditions studied.

Suppression of air bubble in microfluidic channel using electro-acoustic excitation

A simple method to study the air bubble dynamics and to burst the air bubbles formed on the electrode– electrolyte interface in a parallel gate electrode fluidic channel is demonstrated. Upon application of a voltage across the electrodes,volume of water contained between them begins to electrolyzing depending on the conductivity, as well as it boils due to heating effect. This results in bubble formation within. These bubbles grow in radius with higher potential difference applied across the electrodes. As an approach towards removing these bubbles, an alternating current is applied at low potential difference of a 5 volts and high frequency at few megahertz. The alternating electric field had a heating effect on the bubbles where the energy input due to current heats up water and bursts the bubble. The bubbles of size up to 480μm were burst at 2500 V/m using this approach.

Speed control of brushed DC motor for low cost electric cars

As petrol prices are going up in developing countries in upcoming decades low cost electric cars will become more and more popular in developing world. One of the main deciding factors for success of electric cars specially in developing world in upcoming decades will be its cost. This paper shows a cost effective method to control the speed of low cost brushed D.C. motor by combining a IC 555 Timer with a High Boost Converter. The main purpose of using High Boost Converter since electric cars needs high voltage and current which a High Boost Converter can provide even with low battery supply.

Electric current induced flow of liquid metals: Mechanism and substrate-surface effects

Long range, continuous flow of liquid metals occurs upon application of an electric current. Here, we report experimental results elucidating the mechanism of current-induced liquid metal flow, and its dependence on substrate surface condition. It is shown that the observed flow is diffusion-controlled, with the flow-rate depending linearly on applied current density, indicating that it is driven by electromigration. The effective charge number for liquid electromigration, Z*, of several pure metals, such as Al, Bi, Ga, Sn, and Pb, were deduced from the experimental results and were found to be close to the elemental valency. With the exception of liquid Pb, Z* for all liquid metals tested in this study were positive, indicating that: (i) electron wind contributes much less to Z* in liquid metals than in solids, and (ii) with a few exceptions, liquid metals generally flow in the direction of the electric current. On smooth substrates which are wetted well by the liquid metal, flow occurs in a thin, continuous stream. On rough surfaces which are poorly wetted, on the other hand, discrete beads of liquid form, with mass transport between adjacent beads occurring by surface diffusion on the substrate. A rationale for the role of substrate roughness in fostering this observed transition in flow mechanism is presented. (C) 2014 AIP Publishing LLC.

Influence of exhaust gas heating and L/D ratios on the discharge efficiencies for an activated carbon natural gas storage system

A transient 2D axi-symmetric and lumped parameter (LP) model with constant outflow conditions have been developed to study the discharge capacity of an activated carbon bed. The predicted discharge times and variations in bed pressure and temperature are in good agreement with experimental results obtained from a 1.82 l adsorbed natural gas (ANG) storage system. Under ambient air conditions, a maximum temperature drop of 29.5 K and 45.5 K are predicted at the bed center for discharge rates of 1.0 l min(-1) and 5.0 l min(-1) respectively. The corresponding discharge efficiencies are 77% and 71.5% respectively with discharge efficiencies improving with decreasing outflow rates. Increasing the LID ratio from 1.9 to 7.8 had only a marginal increase in the discharge efficiency. Forced convection (exhaust gas) heating had a significant effect on the discharge efficiency, leading to efficiencies as high as 92.8% at a discharge of 1.0 l min(-1) and 88.7% at 5 l min(-1). Our study shows that the LP model can be reliably used to obtain discharge times due to the uniform pressure distributions in the bed. Temperature predictions with the LP model were more accurate at ambient conditions and higher discharge rates, due to greater uniformity in bed temperatures. For the low thermal conductivity carbon porous beds, our study shows that exhaust gas heating can be used as an effective and convenient strategy to improve the discharge characteristics and performance of an ANG system. (C) 2013 Elsevier Ltd. All rights reserved.

A Gibbs-ensemble based technique for Monte Carlo simulation of electric double layer capacitors (EDLC) at constant voltage

Current methods for molecular simulations of Electric Double Layer Capacitors (EDLC) have both the electrodes and the electrolyte region in a single simulation box. This necessitates simulation of the electrode-electrolyte region interface. Typical capacitors have macroscopic dimensions where the fraction of the molecules at the electrode-electrolyte region interface is very low. Hence, large systems sizes are needed to minimize the electrode-electrolyte region interfacial effects. To overcome these problems, a new technique based on the Gibbs Ensemble is proposed for simulation of an EDLC. In the proposed technique, each electrode is simulated in a separate simulation box. Application of periodic boundary conditions eliminates the interfacial effects. This in addition to the use of constant voltage ensemble allows for a more convenient comparison of simulation results with experimental measurements on typical EDLCs. (C) 2014 AIP Publishing LLC.

Film thickness mediated transition in the kinetics of electric current induced flow of thin liquid metal films

Application of high electric-field between two points in a thin metallic film results in liquefaction and subsequent flow of the liquid-film from one electrode to another in a radially symmetric fashion. Here, we report the transition of the flow kinetics driven by the liquid film thickness varying from 3 to 100 nm. The mechanism of the flow behavior is observed to be independent of the film thickness; however, the kinetics of the flow depends on the film thickness and the applied voltage. An analytical model, incorporating viscosity and varying electrical resistivity with film thickness, is developed to explain the experimental observations. (C) 2014 AIP Publishing LLC.

Hypersonic interference heating on cones with short three-dimensional protuberances

Heat fluxes around short, three-dimensional protuberances on sharp and blunt cones in hypersonic flow were experimentally measured using platinum thin-film sensors deposited on macor inserts. A parametric study of different protrusion geometries and flow conditions were conducted. Excessive heating was observed at locations near the protrusion where increased vorticity is expected, with the hottest spot being presented at the foot of the protuberance immediately upstream of it. If left unchecked, these hot spots could prove detrimental to hypersonic flight vehicles. Z-type schlieren technique was used to visualize the flow features qualitatively. New correlations to predict the heat flux at the hot spot have been proposed. (C) 2014 Elsevier Inc. All rights reserved.