Showing papers in "Journal of Physics D in 1994"
TL;DR: In this article, the collective behavior of weakly ionized RF dusty plasmas is investigated, where negatively charged SiO2 fine particles are generated and suspended in an SiH4/O2/Ar discharge.
Abstract: The collective behaviour of weakly ionized RF dusty plasmas is investigated. Negatively charged SiO2 fine particles are generated and suspended in an SiH4/O2/Ar discharge. At high pressure (300 mTorr), the random fluctuations of the discharge and particle motions are suppressed. Coulomb solids with particle diameters from a few micrometres to a millimetre have been observed. At low pressure, the coupling between particles and the background plasma causes large-amplitude low-frequency fluctuations of the dusty plasma.
314 citations
TL;DR: In this article, a model describing the process of deep-penetration laser welding has been developed by calculating the keyhole profile using a point-by-point determination of the energy balance at the key hole wall.
Abstract: A model describing the process of deep-penetration laser welding has been developed by calculating the keyhole profile using a point-by-point determination of the energy balance at the keyhole wall. A formula for heat conduction was derived from the model of a moving line source of heat. The various absorption mechanisms were modelled. The corresponding absorbed power transferred to the keyhole wall balances the conduction losses, which yields the local inclination of the wall. The thermodynamics and the flow of metal vapour inside the keyhole have been calculated. Accordingly, beam damping due to the plasma plume above the workpiece and the mean plasma absorption coefficient in the keyhole could be estimated. The keyhole profile tends to a geometry that distributes the major part of the beam to the front wall owing to higher conduction losses at the upstream side. The reasons for decreasing energy absorption with increasing welding speed are discussed.
279 citations
TL;DR: In this paper, the effect of thermal resistance, heat leakage and internal irreversibility resulting from the working fluid on the performance of a Carnot heat engine was investigated using a new cyclic model.
Abstract: The effect of thermal resistance, heat leakage and internal irreversibility resulting from the working fluid on the performance of a Carnot heat engine is investigated using a new cyclic model. The power output and efficiency of the heat engine are adopted as objective functions for heat engine optimization. The optimal performance of the heat engine is analysed systematically. Some significant results are obtained. For example, the maximum power output and maximum efficiency are determined. The efficiency of the heat engine at maximum power output and the power output of the heat engine at maximum efficiency are also calculated. Curves of the power output varying with the efficiency of the heat engine are obtained. These curves can indicate clearly the rational regions of efficiency and power output for an irreversible Carnot heat engine. It is pointed out that all the conclusions concerning a reversible Carnot heat engine, an endoreversible Carnot heat engine only affected by thermal resistance and an irreversible Carnot heat engine with internal irreversibility and/or heat leakage can be deduced from the results in this paper.
246 citations
TL;DR: An electroaffinity column containing an interdigitated microelectrode array was used to retain human leukaemia cells dielectrophoretically and thereby separate them from normal blood cells.
Abstract: An electroaffinity column containing an interdigitated microelectrode array was used to retain human leukaemia cells dielectrophoretically and thereby separate them from normal blood cells. The leukaemic cells could be subsequently released by removal of the dielectrophoretic field and collected. This novel approach exploits the differential dielectric properties of cells as a sorting criterion and has applications in medicine, biotechnology and environmental settings.
207 citations
TL;DR: In this paper, it was shown that a particle in a non-uniform AC electric field experiences a dielectrophoretic force arising from spatial nonuniformities of the magnitude and phase of the field interacting, respectively, with the in-phase and out-of-phase components of the induced dipole moment.
Abstract: We show for the first time that a particle in a non-uniform AC electric field experiences a dielectrophoretic force arising from spatial non-uniformities of the magnitude and phase of the field interacting, respectively, with the in-phase and out-of-phase components of the induced dipole moment.
203 citations
TL;DR: In this article, a physical model of the positive discharge in long air gaps is presented, using the classical equations for conservation of mass, momentum and energy for each particle species, which are simplified according to the dominant electrostatic, hydrodynamic or thermodynamic processes involved in each step of the spark development.
Abstract: The main purpose of this paper is to present a physical model of the positive discharge in long air gaps. A large number of previous experimental and theoretical studies led to the identification of the different successive phases of the spark development: formation and propagation of first corona streamers, inception of the conductive stem at the electrode tip, formation and development of second corona (or 'leader corona') from the stem, and, eventually, the propagation of the leader and leader corona system until the final jump preceding the arc onset. Details of the specific modelling of each phase is presented, using the classical equations for conservation of mass, momentum and energy for each particle species. These basic equations are simplified according to the dominant electrostatic, hydrodynamic or thermodynamic processes involved in each step of the spark development. The resulting models for simulation of the corona and leader phases are coupled with an analytical calculation of the electric field due to the electrodes, the leader channel and the space charge injected into the gap. The different phase simulation models are expressed with a homogeneous simplification level and then linked sequentially into a complete model, which performs the step-by-step simulation of all the successive discharges phases until the final jump. The model described here is self-consistent since the only input data are the electrode geometry and the applied potential wave-shape. A good agreement between computed and experimental results has been obtained in various test configurations; the model has been also used to simulate the discharge behaviour with perturbations of the applied potential wave and permits the analysis of the conditions for stable propagation of the positive leader. It is shown that some parameters of practical interest, as the 50% breakdown voltage or the time to breakdown can be derived from the proposed model.
200 citations
TL;DR: In this paper, the authors describe various analytical procedures that account for the influence of the geometry of a rigid indenter on the measured contact compliance of a smooth perfectly elastic half space.
Abstract: The paper describes various analytical procedures that account for the influence of the geometry of a rigid indenter upon the measured contact compliance of a smooth perfectly elastic half space. The analytical solutions provide a means of interrelating the reaction force, P, and the displacement, h, characteristics in terms of the contact geometry and the reduced elastic modulus E*. The general form is P=gE*hn, where g and n are functions only of the indenter geometry. This relationship is incorporated into a curve-fitting procedure and used to evaluate the influence of the indenter geometry upon the computed modulus of a poly(isobutylene) rubber. The method described provides a viable means of incorporating the imperfections, associated with the geometry of an indenter, into the interpretation of contact compliance data.
182 citations
TL;DR: In this paper, a simple model for bipolar charge injection, subsequent transport and trapping has been developed, and numerical simulations for charge density generated, as a function of position, time and field, are compared to the experimentally obtained profiles.
Abstract: Measurements of the space charge density across the width of a plane parallel sample of degassed crosslinked polyethene (XLPE) have been made recently. Repeated at intervals throughout a period of applied high voltage, these measurements provide data on the dynamics of charge injection and space charge development in the sample under the influence of a stepped high DC voltage. In order to analyse these data, a simple model for bipolar charge injection, subsequent transport and trapping has been developed. This model is reported in this paper, and numerical simulations for charge density generated, as a function of position, time and field, are compared to the experimentally obtained profiles.
172 citations
TL;DR: In this article, a perturbation solution is obtained, which satisfies the momentum equation for the case in which the amplitude ratio (wave amplitude:channel half width) is small.
Abstract: Peristaltic pumping by a sinusoidal travelling wave in the walls of a two-dimensional channel filled with a viscous incompressible couple-stress fluid, is investigated theoretically. A perturbation solution is obtained, which satisfies the momentum equation for the case in which the amplitude ratio (wave amplitude:channel half width) is small. The results show that the mean axial velocity decreases with increasing couple-stress parameter eta . The phenomenon of reflux (mean flow reversal) is discussed. A reversal of velocity in the neighbourhood of the centre line occurs when the pressure gradient is greater than that of the critical reflux condition. It is found that the critical reflux pressure increases with the couple-stress parameter. Numerical results are reported for various values of the physical parameters of interest.
162 citations
TL;DR: Porosity superlattices have been investigated by transmission electron microscopy, photoluminescence and reflectance spectroscopy in this article, and the results are in good agreement with the values calculated from the etching rate and time.
Abstract: Porosity superlattices have been investigated by transmission electron microscopy, photoluminescence and reflectance spectroscopy. The superlattices were formed on p-type doped Si using two different techniques. Firstly, for homogeneously doped substrates we have periodically varied the formation current density and thereby the porosity. Secondly, the current density was kept constant while etching was performed on periodically doped Si layers. For the first type of superlattices the layer thicknesses were determined by transmission electron microscopy. The results are in good agreement with the values calculated from the etching rate and time. For both types of superlattices, reflectance and photoluminescence spectra show strong modulation due to the periodicity of the superlattice.
158 citations
TL;DR: Ozone formation efficiencies in a homogeneous glow discharge at atmospheric pressure have been measured and compared with that in a filamentary silent electric discharge, which is the usual ozone generation method as discussed by the authors.
Abstract: Ozone formation efficiencies in a homogeneous glow discharge at atmospheric pressure have been measured and compared with that in a filamentary silent electric discharge, which is the usual ozone generation method. The ozone efficiencies in the homogeneous glow clearly increased to about 10% in air and to a maximum of 15% in oxygen. This increase is attributed to better collision efficiency among electrons and molecules, and to a lower increase in temperature than in discharge filaments of a silent electric discharge.
TL;DR: In this article, a review of recent developments in highly magnetostrictive terbium-dysprosium-iron alloys is presented, including discussion of domain structure, the magnetization process, microstructure, sample preparation, magnetostriction, effects of different chemical compositions on magnetic properties of the alloys, and possible applications of these materials.
Abstract: This paper reviews recent developments in highly magnetostrictive terbium-dysprosium-iron alloys. This includes discussion of domain structure, the magnetization process, microstructure, sample preparation, magnetostriction, effects of different chemical compositions on magnetic properties of the alloys, and possible applications of these materials. It has been found over recent years that there has been a steady improvement in material properties, both in terms of increased strain amplitude and reduction in variability from sample to sample. The material is now finding applications in magnetostrictive transducers, actuators and adaptive vibration control systems.
TL;DR: In this paper, the edge effects for crack-like defects have been calculated using the Wiener-Hopf technique and it is found that the crack surface temperature is reduced over a distance of a thermal diffusion length by heat flow around the crack edge to the cold underside of the crack.
Abstract: Thermal edge effects for crack-like defects have been calculated using the Wiener-Hopf technique. It is found that the crack surface temperature is reduced over a distance of a thermal diffusion length by heat flow around the crack edge to the cold underside of the crack. Surface thermal images have been computed for a straight-edged and a circular crack. Comparisons are presented of image profiles computed with and without inclusion of edge effects. Edge effects lead to the prediction that transient thermographic defect images should shrink with elapsed time. Experimental data are presented, which are in agreement with this prediction and demonstrate a simple means of defect sizing.
TL;DR: In this paper, current-voltage characteristics and electrical switching behavior of bulk As-Te-Se glasses have been investigated over a wide composition range, and most of the glasses studied have been found to exhibit a current controlled negative-resistance behavior with memory.
Abstract: Tne current-voltage characteristics and electrical switching behaviour of bulk $As_xTe_{100-x-y}Se_y$ glasses have been investigated over a wide composition range $(25\leq x \leq 60; 10 \leq y \leq 25)$. Most of the glasses studied have been found to exhibit a current-controlled negative-resistance behaviour with memory. A sharp switching is observed in the glass of composition $As_{50}Te_{30}Se_{20}$. A strong dependence of the switching fields on composition, which resembles the variation of crystallization temperatures with X, has been noticed. Further, a current pulse of 100 mA amplitude and 10 $\mu s$ duration is found to re-set the memory-switched As-Te-Se glasses to the original high-resistance state. The sample can be made to switch again, with $\pm2%$ variation in the swtiching fields. This indicates the possible application of these materials in 'read mostly' memories.
TL;DR: In this article, the authors focused on the use of corona discharge in electroseparation processes and showed that stable corona discharges were obtained when energizing that electrode at both positive and negative polarities from a reversible non-filtered full-bridge high-voltage rectifier.
Abstract: The physics of corona charging phenomena is of paramount importance for the development of such electrotechnologies as precipitation of dust, spraying of powders and selective sorting of particulate mixtures. This study focused on the use of corona discharge in electroseparation processes. Crude theoretical evaluations pointed out that the required corona current density and high-voltage level in this application depend on various factors, such as material characteristics, feed rate and configuration of the electrode system. Experiments carried out on a laboratory roll-type electroseparator demonstrated the capability of a new corona electrode design to generate an extended and quasi-uniform corona field. Stable corona discharges were obtained when energizing that electrode at both positive and negative polarities from a reversible non-filtered full-bridge high-voltage rectifier. The voltage-current characteristics of the corona discharge from the new electrode were determined under various operating conditions: (i) without material in the inter-electrode gap; (ii) with a monolayer of a 50% aluminium-50% polyvinyl chloride particulate mixture on the surface of the grounded electrode; (iii) with a similar monolayer of metallic particles (99% aluminium); and (iv) with a layer of insulating particles (99% polyvinyl chloride). In each case, attention was paid to the upper acceptable limit of operating voltage, as well as to some side effects of corona discharges, such as audible noise and ozone generation. The efficacy of corona charging was assessed by electroseparation tests involving two groups of particulate materials: (i) barley grains, impurified with weeds and soil particulates; and (ii) granular mixtures of metals and plastics, yielded by chopping electric wire and cable scrap. Several practical considerations were formulated, based on a critical evaluation of the experimental results.
TL;DR: In this article, the thermodynamic properties and transport coefficients of thermal plasmas formed in SF6-copper vapour mixtures were calculated as a function of temperature and pressure for molar concentrations of copper between 0 and 10%.
Abstract: The thermodynamic properties and the transport coefficients of thermal plasmas formed in SF6-copper vapour mixtures were calculated as a function of temperature and pressure for molar concentrations of copper between 0 and 10%. The material property that is most affected by the presence of copper is the electrical conductivity for temperatures up to 10000 K. The results given in this paper enabled a data bank to be built up for modelling arcs in SF6 seeded with copper vapour.
TL;DR: In this paper, an automatic iterative method by which material constants of piezoelectric ceramics may be determined in complex form is described, and the profiles for the conductance, resistance, susceptance and reactance are calculated, for the same sample, in the frequency range containing resonance and anti-resonance.
Abstract: An automatic iterative method by which material constants of piezoelectric ceramics may be determined in complex form is described. Measurements are reported on samples with different shapes: thickness expansion and shear plates, and length expansion bars. With the constants provided by this method, the profiles for the conductance, resistance, susceptance and reactance are calculated, for the same sample, in the frequency range containing resonance and anti-resonance, and very good agreement is obtained with respect to the experimental data.
TL;DR: In this paper, electron energy distribution functions in glow discharges (I=5-50 mA, p=200-1000 Pa) were derived from the intensities of Ar and He spectral lines and N2 molecular bands with different excitation thresholds.
Abstract: Electron energy distribution functions in glow discharges (I=5-50 mA, p=200-1000 Pa) were derived from the intensities of Ar and He spectral lines and N2 molecular bands with different excitation thresholds. The relevant rate coefficients represent weighted integrals in the range from 12 to 24 eV. In molecular gases, structures in the low-energy region was inferred from theoretical calculations. An analytical formula with one experimentally adjusted parameter was used to describe the energy distribution. The total electron density was calculated from the electrical conductivity. The mean electron energies from three spectroscopic criteria, as well as those from an ionization-diffusion model of the discharge, are in close agreement for values of the fitting parameter characteristic for the particular plasma conditions. The high-energy part of the distribution functions is not far from a Druyvesteyn shape both in pure nitrogen and in noble gases. The electron densities in nitrogen and mixture plasmas were also measured from N2+ molecular band intensities. Because of the rapid decrease in electron population at higher energies, the ionization of neutral N2 into the upper N2+ level can be ignored and these bands reflect the N2+ ion ground state population. The excitation rate coefficients were calibrated in pure nitrogen and then applied to mixture plasmas, where the N2+ ion fraction was calculated including charge exchange processes. Agreement with ne results from electrical conductivity is very good over the entire parameter range investigated.
TL;DR: In this article, free oscillations of the keyhole in penetration laser beam welding are studied theoretically with regard to characteristic frequencies, damping rates and stability at large amplitudes, and the normal modes form a discrete set which may be characterized by axial and azimuthal numbers.
Abstract: Free oscillations of the keyhole in penetration laser beam welding are studied theoretically with regard to characteristic frequencies, damping rates and stability at large amplitudes. The normal modes form a discrete set which may be characterized by axial and azimuthal numbers. Due to viscous damping, only the lowest modes survive many oscillation periods, which yields a limited range of frequencies for the dynamic response of the keyhole to fluctuations of external welding parameters.
TL;DR: In this article, an integrated mathematical model for laser welding of thin metal sheets under a variety of laser material processing conditions has been developed and tested against the results of experiments, and results calculated from the model are found to agree well with experiment for appropriate values of the keyhole radius.
Abstract: An integrated mathematical model for laser welding of thin metal sheets under a variety of laser material processing conditions has been developed and tested against the results of experiments. Full account is taken in the model of the interaction of the laser-generated keyhole with the weld pool. Results calculated from the model are found to agree well with experiment for appropriate values of the keyhole radius. The analysis yields values for power absorption in the metal. In a complementary calculation the total absorption of the laser energy is determined from detailed consideration of the inverse Bremsstrahlung absorption in the plasma and Fresnel absorption at the keyhole walls. To test these results, experiments were performed on 1 mm mild steel using a high-speed video camera, which measured the surface dimensions of the melt pool. Processing parameters were varied to study the effect on the melt pool; parameters considered included traverse speed, laser power and shroud gas species. The general shape of the weld pool was found to depend on whether penetration was full, partial or blind; only the results for full penetration were compared with the theory, which is for complete penetration only.
TL;DR: In this article, the gaseous nature of filamentary positive streamers is demonstrated by the influence of hydrostatic pressure on their propagation in cyclohexane and pentane up to 7 MPa.
Abstract: In this first part, the gaseous nature of filamentary positive streamers is demonstrated by the influence of hydrostatic pressure on their propagation in cyclohexane and pentane up to 7 MPa. At a fixed voltage, when the pressure is increased, the propagation velocity is found to be constant whereas the stopping length of streamers is greatly reduced. Correlated to this effect, the duration of transient currents and light emission signals is reduced. These effects are discussed in terms of the hypothesis that the conductivity of the streamer results from a gas discharge mechanism occurring within the filaments. These results constitute the experimental basis on which a study of the filament dynamics has been developed (part II).
TL;DR: In this article, a practical review of the use of laser ablation for the deposition of thin films of oxide superconductors and metals is presented, together with the influence of operating parameters such as laser wavelength and power density on the film growth.
Abstract: A practical review of the use of laser ablation for the deposition of thin films of oxide superconductors and metals is presented. Details of the design and operation of a laser ablation deposition system are discussed, together with the influence of operating parameters such as laser wavelength and power density on the film growth, with the aim of assisting the researcher beginning to use and/or study laser ablation deposition.
TL;DR: In this article, it has been found that the dominant emission band observed can be assigned to Eu2+ occupying MII sites of the apatite system having C1h symmetry.
Abstract: M5(PO4)3X apatites are well known for their technological importance as phosphors, laser hosts and biocompatible materials. Divalent-europium-activated alkaline earth chloroapatites are of special importance for their application as the blue component in high-efficiency trichromatic fluorescent lamps. In these apatites, Eu2+ yields narrow-band emission in the blue region corresponding to the 4f65d to 8S7/2 allowed electric dipole transition. It has been found that the dominant emission band observed can be assigned to Eu2+ occupying MII sites of the apatite system having C1h symmetry. In the case of barium chloroapatites one could also observe Eu2+ emission from a second type of site (MI) that is available in the apatite system. The weak emission observed in the latter can be attributed to the intense spectral overlap with the former site(s) and thermal quenching effects. The exchange coupling between the 4f6 and 5d electrons of Eu2+ manifests itself in 'stair-case' features in the excitation spectrum and the strength of the exchange interaction is highly dependent on the host apatite(s). Also, in the Eu2+, Mn2+ co-doped system, energy transfer is found to occur from the former to the latter and the transfer is regulated by an exchange process. Various results based on these facts are discussed in detail.
TL;DR: In this paper, it was shown that the Poisson equation for electric field can be replaced by a much simpler current conservation law so that the solution would automatically obey the poisson equation.
Abstract: A novel technique of simulation of low-temperature gas-discharge plasmas when space-charge effects are dominant is described. It is shown that the Poisson equation for electric field can be replaced by a much simpler current conservation law so that the solution would automatically obey the Poisson equation. A one-dimensional version of this method was tested on the problem of cathode region formation in pre-ionized atmospheric pressure nitrogen. A two-dimensional scheme for cylindrical coordinates is described. The method proposed allows one to simulate fully the two-dimensional problem of streamer dynamics in an over-volted gap on a personal computer, as described in the companion paper.
TL;DR: In this paper, a study of the dynamics of positive streamer filaments in pentane using an optical method described in the text for pressures up to 9 MPa is presented.
Abstract: This paper presents a study of the dynamics of positive streamer filaments in pentane using an optical method described in the text for pressures up to 9 MPa. It is observed that filaments expand and collapse, in a similar way to cavitation bubbles. Good agreement with the Rayleigh model shows that the dynamics of filaments is determined by liquid inertia. The influence of electric forces (electrostatic pressure) on the dynamics is found to be negligible. An evaluation of the energies involved shows that filaments are mainly composed of vapour, whose pressure varies with time and space and is on average higher than the hydrostatic pressure. Vaporization results mainly from energy dissipated at the filament extremity, which may be compared to a propagating point heat source of about 10 W power. At low pressure, a significant influence of energy dissipation within the filament, attributed to the transient current flowing during propagation, is also observed. At high pressure and/or high voltage, the stopping of the streamer is due to collapse of the gaseous filaments.
TL;DR: In this article, the authors investigated the influence of microwave power both on the discharge characteristics on the H atom density, which has been measured by actinometry, and found that dissociation levels of H2 are much higher at low microwave power than at high power.
Abstract: We investigate a source of H atoms generated by a low-pressure surface wave discharge (2.45 GHz). We study the influence of microwave power both on the discharge characteristics on the H atom density, which has been measured by actinometry. Dissociation levels of H2 are much higher (75%) at low microwave power than at high power (10%). Unlike what has been found in oxygen surface wave plasmas, discharge characteristics depend strongly on microwave power, due to an important coupling between discharge equilibrium and kinetics of the atomic hydrogen. These results are explained taking into account the effect of discharge tube wall temperature on atomic recombination. The wall recombination probability gamma is estimated as a function of the microwave power: it ranges from 6*10-3 to 6*10-2, which is very high in comparison with values determined previously under post-discharge conditions.
TL;DR: In this article, two integrals over radiation frequency, designated Som and Delta Sim, are used in the approximate method of "partial characteristics", as formulated by Sevast'yanenko, and the validity of this method of partial characteristics has been demonstrated by comparing exact calculations with the approximate calculations to evaluate radiation intensities, radiation fluxes and divergence of radiation fluxe for specified temperature profiles.
Abstract: Radiation emission and absorption in SF6 arc plasmas are important energy transfer processes. Exact calculations, though possible in principle, are usually impossible in practice because of the need to treat about 400 spectral lines and also continuum radiation spanning wavelengths from 10 nm to 10 mu m. From calculated spectral absorptivities at 300000 radiation frequency points for SF6 plasmas of 1, 5 and 10 bar from 300 K to 35000 K, we have calculated two integrals over radiation frequency. These integrals, designated Som and Delta Sim are used in the approximate method of 'partial characteristics', as formulated by Sevast'yanenko. The validity of this method of partial characteristics has been demonstrated by comparing exact calculations with the approximate calculations to evaluate radiation intensities, radiation fluxes and divergence of radiation fluxes for specified temperature profiles. Agreement to within 20% is obtained with exact calculations, but with a reduction of computation time of about four orders of magnitude. Furthermore, the new method has been used to evaluate net emission of radiation as a function of position in an algorithm to predict temperature profiles of wall stabilized arcs of any given current. Fair agreement is obtained between predicted and experimental values of central are temperatures and electric field strengths as a function of current for SF6 arcs of radius 0.25 cm at a pressure of 1 bar.
TL;DR: In this article, the linear stability of power law liquid film flows down an inclined plane is investigated and the integral method is used to derive nonlinear evolution equations for film thickness and local flow rate.
Abstract: The linear stability of power law liquid film flows down an inclined plane is investigated. The integral method is used to derive nonlinear evolution equations for film thickness and local flow rate. After linearizing the nonlinear evolution equations, the method of normal mode is applied to study its linear stability. The results reveal that, in the case of fixing the value of power law exponent n, the stability characteristics in terms of generalized Reynolds number Ren and generalized Weber number Wen are the same as those of Newtonian liquids, i.e. to increase the Reynolds number, or to decrease the Weber number will destabilize the film flow system. Furthermore, decreasing only the magnitude of n will cause more unstable film flow, and make the dimensional wave speed faster.
TL;DR: In this paper, a simple accumulated damage analysis method and an empirical field-driven tree growth model are proposed to characterize and describe the spatial and temporal development of electrical trees, showing that tree structural characteristics change progressively from branch to bush structures as the stressing voltage is increased.
Abstract: A simple accumulated damage analysis method and an empirical field-driven tree growth model are proposed to characterize and describe the spatial and temporal development of electrical trees. Examples are presented for trees grown in CT200 and CY1311 epoxy resin pin-plane samples subjected to a wide range of 50 Hz alternating current electrical stress. It is shown that a material's resistance to treeing may be described quantitatively, allowing the relative performance of different synthetic resins to be easily compared. For CY1311 epoxy resin, tree structural characteristics change progressively from branch to bush structures as the stressing voltage is increased. It is shown that the time to failure is primarily influenced by the local electric field and the resultant tree geometry and fractal dimension of tree growth and is not simply dependent on the applied voltage.
TL;DR: In this paper, a narrowbandwidth interference filter was developed using volume holography in photorefractive LiNbO3 crystals, which works as a Bragg reflector using a volume hologram recorded, fixed and developed in a Li NbO 3 sample.
Abstract: A narrow-bandwidth interference filter has been developed using volume holography in photorefractive LiNbO3 crystals. The device works as a Bragg reflector using a volume hologram recorded, fixed and developed in a LiNbO3 sample. With a 2 mm thick LiNbO3 plate the following performances have been achieved: a peak reflectivity above 32%, a full-width at half-maximum bandwidth below 0.05 nm, an angular field of view of about 3 degrees and a peak wavelength of 518.45 nm (for green Ar laser writing wavelength). These performances compare well with that exhibited by the conventional Lyot-Ohman and Solc filters. A complete explanation of the fabrication procedure is given, including practical details needed for producing such an efficiency with fixed holograms in LiNbO3.