Estimation of electric stress and surface potential for traction insulators

Traction insulators are solid core insulators widely used for railway electrification. Constant exposure to detrimental effects of vandalism, and mechanical vibrations begets certain faults like shorting of sheds or cracks in the sheds. Due to fault in one/two sheds, stress on the remaining healthy sheds increases, owing to atmospheric pollution the stress may lead to a flashover of the insulator. Presently due to non availability of the electric stress data for the insulators, simulation study is carried out to find the potential and electric field for most widely used traction insulators in the country. The results of potential and electric field stress obtained for normal and faulty imposed insulators are presented.

Surface Instabilities and Generation of Multielectron Bubbles Under Pulsed Electric Fields

We studied the development of surface instabilities leading to the generation of multielectron bubbles (MEBs) in superfluid helium upon the application of a pulsed electric field. We found the statistical distribution of the charge of individual instabilities to be strongly dependent on the duration of the electric field pulse. The rate and probability of generation of these instabilities in relation to the temporal characteristics of the applied field was also investigated.

Sub-band envelope approach to obtain instants of significant excitation in speech

In this paper, we propose a new sub-band approach to estimate the glottal activity. The method is based on the spectral harmonicity and the sub-band temporal properties of voiced speech. We propose a method to represent glottal excitation signal using sub-band temporal envelope. Instants of maximum glottal excitation or Glottal Closure Instants (GCI) are extracted from the estimated glottal excitation pattern and the result is compared with a standard GCI computation method, DYPSA [1]. The performance of the algorithm is also compared for the noisy signal and it is shown that the proposed method is less variant to GCI estimation under noisy conditions compared to DYPSA. The algorithm is evaluated on the CMU-ARCTIC database.

Excitation- and power-dependent photoluminescence from oxidized Ge

Wafer/microcrystallites of oxidized Ge with holes/nanoholes synthesized by thermal oxidation strategy from Ge wafer/microcrystallites can convert one wavelength to another. Both oxidized Ge wafer and microcrystallites shows excitation- and power-dependent luminescence. Red-shift is observed as the excitation wavelength is increased, while blue-shift is observed as power density is increased. Over all, blue-green-yellow-orange luminescence is observed depending on the excitation wavelength and the morphology of oxidized Ge. The various defects level associated with germanium-oxygen vacancies in GeO2 and Ge/GeO2 interface are responsible for the excitation-dependent luminescence. Being a light-conversion material, oxidized Ge is expected to find potential applications in solid-state lighting, photovoltaic devices and photocatalysis.

Lead-free piezoelectric system (Na0.5Bi0.5)TiO3-BaTiO3: Equilibrium structures and irreversible structural transformations driven by electric field and mechanical impact

The structure-property correlation in the lead-free piezoelectric (1 - x)(Na0.5Bi0.5)TiO3-(x)BaTiO3 has been systematically investigated in detail as a function of composition (0 < x <= 0.11), temperature, electric field, and mechanical impact by Raman scattering, ferroelectric, piezoelectric measurement, x-ray, and neutron powder diffraction methods. Although x-ray diffraction study revealed three distinct composition ranges characterizing different structural features in the equilibrium state at room temperature: (i) monoclinic (Cc) + rhombohedral (R3c) for the precritical compositions, 0 <= x <= 0.05, (ii) cubiclike for 0.06 <= x <= 0.0675, and (iii) morphotropic phase boundary (MPB) like for 0.07 <= x < 0.10, Raman and neutron powder diffraction studies revealed identical symmetry for the cubiclike and the MPB compositions. The cubiclike structure undergoes irreversible phase separation by electric poling as well as by pure mechanical impact. This cubiclike phase exhibits relaxor ferroelectricity in its equilibrium state. The short coherence length (similar to 50A degrees) of the out-of-phase octahedral tilts does not allow the normal ferroelectric state to develop below the dipolar freezing temperature, forcing the system to remain in a dipolar glass state at room temperature. Electric poling helps the dipolar glass state to transform to a normal ferroelectric state with a concomitant enhancement in the correlation length of the out-of-phase octahedral tilt.

Pulsed electric field mediated in vitro cellular response of fibroblast and osteoblast-like cells on conducting austenitic stainless steel substrate

This article reports the intermittent pulse electric field stimulus mediated in vitro cellular response of L929 mouse fibroblast/SaOS2 osteoblast-like cells on austenitic steel substrates in reference to the field strength dependent behavior. The cellular density and morphometric analyses revealed that the optimal electric (E) fields for the maximum cell density of adhered L929 (similar to 270 % to that of untreated sample) and SaOS2 (similar to 280 % to that of untreated sample) cells are 1 V (0.33 V/cm) and 2 V (0.67 V/cm), respectively. The trend in aspect ratio of elongated SaOS2 cells did not indicate any significant difference among the untreated and treated (up to 3.33 V/cm) cells. The average cell and nucleus areas (for SaOS2 cells) were increased with an increase in the applied voltage up to 8 V (2.67 V/cm) and reduced thereafter. However, the ratio of nucleus to total cell area was increased significantly on the application of higher voltages (2-10 V), indicating the possible influence of E-field on cell growth. Further, the cell density results were compared with earlier results obtained with sintered Hydroxyapatite (HA) and HA-BaTiO3 composites and such comparison revealed that the enhanced cell density on steel sample occurs upon application of much lower field strength and stimulation time. This indicates the possible role of substrate conductivity towards cell growth in pulsed E-field mediated culture conditions.

Adiabatic eigenfunction-based approach for coherent excitation transfer: An almost analytical treatment of the Fenna-Matthews-Olson complex

We suggest a method of studying coherence in finite-level systems coupled to the environment and use it for the Hamiltonian that has been used to describe the light-harvesting pigment-protein complex. The method works with the adiabatic states and transforms the Hamiltonian to a form in which the terms responsible for decoherence and population relaxation are separated out. Decoherence is then accounted for nonperturbatively and population relaxation using a Markovian master equation. Almost analytical results can be obtained for the seven-level system, and the calculations are very simple for systems with more levels. We apply the treatment to the seven-level system, and the results are in excellent agreement with the exact numerical results of Nalbach et al. Nalbach, Braun, and Thorwart, Phys. Rev. E 84, 041926 (2011)]. Our approach is able to account for decoherence and population relaxation separately. It is found that decoherence causes only damping of oscillations and does not lead to transfer to the reaction center. Population relaxation is necessary for efficient transfer to the reaction center, in agreement with earlier findings. Our results show that the transformation to the adiabatic basis followed by a Redfield type of approach leads to results in good agreement with exact simulation.

Determination of electric field at and near the focus of a cylindrical lens for applications in fluorescence microscopy

We present an explicit computable integral solution of the electric field generated at the focal region of a cylindrical lens. This representation is based on vectorial diffraction theory and further enables the computation of the system point spread function of a cylindrical lens. It is assumed that there is no back-scattering and the contribution from the evanescent field is negligible. Stationary phase approximation along with the Fresnel transmission coefficients are employed for evaluating the polarization dependent electric field components. Studies were carried out to determine the polarization effects and to calculate the system resolution. The effect of s -, p - and randomly polarized light is studied on the fixed sample (electric dipole is fixed in space). Proposed approach allows better understanding of electric field effects at the focus of a cylindrical aplanatic system. This opens up future developments in the field of fluorescence microscopy and optical imaging. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Electric current-induced mass flow in very thin infinite metallic films

This paper reports on the mass transport behavior of infinitely extended, continuous, and very thin metallic films under the influence of electric current. Application of direct current of high densities (> 10(8) A/m(2)) results in visible melting of thin film at only one of the electrodes, and the melt then flows towards the other electrode in a circularly symmetric fashion forming a microscale ring pattern. For the two tested thin film systems, namely Cr and Al, of thicknesses ranging from 4 to 20 nm, the above directional flow consistently occurred from cathode to anode and anode to cathode, respectively. Furthermore, application of alternating electric current results in flow of the liquid material from both the electrodes. The dependence of critical flow behavior parameters, such as flow direction, flow velocity, and evolution of the ring diameter, are experimentally determined. Analytical models based on the principles of electromigration in liquid-phase materials are developed to explain the experimental observations.

Numerical simulations of bubble formation from submerged needles under non-uniform direct current electric field

In several chemical and space industries, small bubbles are desired for efficient interaction between the liquid and gas phases. In the present study, we show that non-uniform electric field with appropriate electrode configurations can reduce the volume of the bubbles forming at submerged needles by up to three orders of magnitude. We show that localized high electric stresses at the base of the bubbles result in slipping of the contact line on the inner surface of the needle and subsequent bubble formation occurs with contact line inside the needle. We also show that for bubble formation in the presence of highly non-uniform electric field, due to high detachment frequency, the bubbles go through multiple coalescences and thus increase the apparent volume of the detached bubbles. (C) 2013 AIP Publishing LLC.

Vertical electric field stimulated neural cell functionality on porous amorphous carbon electrodes

We demonstrate the efficacy of amorphous macroporous carbon substrates as electrodes to support neuronal cell proliferation and differentiation in electric field mediated culture conditions. The electric field was applied perpendicular to carbon substrate electrode, while growing mouse neuroblastoma (N2a) cells in vitro. The placement of the second electrode outside of the cell culture medium allows the investigation of cell response to electric field without the concurrent complexities of submerged electrodes such as potentially toxic electrode reactions, electro-kinetic flows and charge transfer (electrical current) in the cell medium. The macroporous carbon electrodes are uniquely characterized by a higher specific charge storage capacity (0.2 mC/cm(2)) and low impedance (3.3 k Omega at 1 kHz). The optimal window of electric field stimulation for better cell viability and neurite outgrowth is established. When a uniform or a gradient electric field was applied perpendicular to the amorphous carbon substrate, it was found that the N2a cell viability and neurite length were higher at low electric field strengths (<= 2.5 V/cm) compared to that measured without an applied field (0 V/cm). While the cell viability was assessed by two complementary biochemical assays (MTT and LDH), the differentiation was studied by indirect immunostaining. Overall, the results of the present study unambiguously establish the uniform/gradient vertical electric field based culture protocol to either enhance or to restrict neurite outgrowth respectively at lower or higher field strengths, when neuroblastoma cells are cultured on porous glassy carbon electrodes having a desired combination of electrochemical properties. (C) 2013 Elsevier Ltd. All rights reserved.

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.

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.

Magnetoresistance and electroresistance effects in Fe3O4 nanoparticle system

Nearly monodisperse spherical magnetite (Fe3O4) nanoparticles are prepared by colloidal chemistry route. Magnetic and electronic transport properties of the annealed pellets of these nanoparticles are reported. Effect of external magnetic and electric fields on the magnetic and transport properties of the material are studied as a function of temperature. We find that the highest resistance state of the ferromagnetic system occurs at a magnetic field which is approximately equal to its magnetic coercivity; this establishes the magnetoresistance (MR) in this system to be of the conventional tunnelling type MR as against the spin-valve type MR found more recently in some ferromagnetic oxide systems. The material also shows electroresistance (ER) property with its low-temperature resistance being strongly dependent on the excitation current that is used for the measurement. This ER effect is concluded to be intrinsic to the material and is attributed to the electric field-induced melting of the charge-order state in magnetite.