Characterization of luminescent properties of Sr–Ca–Al–O multi-phases oxide phosphors

Multi-phases phosphors, which could exhibit red, green, and blue emission bands simultaneously, were synthesized by the solid-state reaction method with a flux. Starting materials of SrCO₃, CaCO₃, and Al₂O₃ were mixed and fired. H₃BO₃ and Eu₂O₃ were added as a flux and a dopant, respectively. Effects of the excitation energy and the mixing ratio of starting materials on the luminescent properties were investigated. Phase transformations and variations of luminescent properties were also observed as a function of H₃BO₃ flux amounts. Emission wavelength and intensity depended on the excitation energy as well as H₃BO₃ flux amounts. The mixture of 8SrCO₃–4CaCO₃–11Al₂O₃–0.8H₃BO₃–0.18Eu₂O₃ showed red, green, and blue emission by exciting at near UV, while 8SrCO₃–4CaCO₃–11Al₂O₃–1.2 and 1.6H₃BO₃–0.18Eu₂O₃ exhibited strong red emissions.     

Features of Charging–Discharging of Supercapacitors

We present the results of experimental investigations of supercapacitors produced by Panasonic using several methods, namely, measurements of temporal dependences of charging–discharging currents, cyclic dc charging, and cyclic voltammetry. The values of the internal resistance, static and dynamic capacitance, as well as their dependences on the bias voltage of the capacitors, have been determined. Measurements have shown that the initial stage of relaxation of current is well approximated by the exponential time dependence, and then transition to a powerlike dependence occurs. This well-known effect is explained on the basis of the allowance for specific transport properties of a porous fractal-type medium. These processes are adequately described by the fractional-differential model of anomalous diffusion. A weak dependence of relaxation curves on the voltage at low values of the latter (<3 V) and the change in the power-law exponent at elevated voltages (>3 V) is explained by the appearance of new percolation paths blocked at low charging voltages due to the presence of high-potential barriers. The internal resistance and the static capacitance have been determined by measuring the voltage across the supercapacitor in the mode of dc charging. These parameters have been shown to depend on the voltage applied to the capacitor. The dependence of the dynamic capacitance on the voltage has been determined using cyclic voltammetry. It has been shown that the capacitance depends not only on the voltage, but also on the prehistory of charging and discharging of the capacitor. Comparison of the experimental results and the published data on the models and equivalent circuits with passive R, L, and C elements allows one to conclude that such models and equivalent circuits can be applied only when explaining a limited number of phenomena, in particular, behavior at small relaxation times.     

Effect of Zr/Ti ratio on piezoelectric and dielectric properties of PNW–PMS–PZT ceramics

(Pb_0.95Sr_0.05)[(Ni_1/2W_1/2)_0.02(Mn_1/3Sb_2/3)0.06(Zr_XTi_Y)_0.92]O₃ piezoelectric ceramics (abbreviated as PNW–PMS–PZT) with 1%mol excess PbO, 0.25 wt% CeO₂ and 0.2 wt% MnO₂ were prepared by traditional ceramics process. The phase structure of ceramics sintered at 1150°C were analyzed. Results show that the pure perovskite phase was in all ceramics specimens, the phase structure of PNW–PMS–PZT piezoelectric ceramics was transformed from tetragonal to rhombohedral, with Zr/Ti ratio increased in system; Effect of Zr/Ti ratio on piezoelectric and dielectric properties was investigated. Results show that ? _r , tanδ, k _p and d ₃₃ increased with an increase of Zr/Ti ratio and reached the maximum values at Zr/Ti ratio of 50/50, then decreased with further increase of Zr/Ti ratio, whereas the variation of Q _m with an increase of Zr/Ti ratio showed the opposite trend, T _c showed a tendency to decrease with an increase of Zr/Ti ratio. The piezoelectric ceramics with Zr/Ti ratio of 50/50 was applied in high-power multilayer piezoelectric transformer, and properties parameter were ? _r ?=?2100, tanδ?=?0.006, k _p ?=?0.613, Q _m ?=?1300, d ₃₃ ?=?380pC/N, T _c ?=?205 °C.     

Experimental investigation of input–output characteristics of a travelling-wave ultrasonic motor

Speed, position and load characteristics of the ultrasonic motor is considerably influenced from the input characteristics such as driving frequency, magnitude and phase difference of phase voltages. Input and output characteristics of a traveling-wave ultrasonic motor have been investigated from the experimental point of view in the present study. For this aim, a half-bridge serial-resonance inverter based drive system has been designed and then implemented. The inverter is featured with pulse width modulation and pulse frequency modulation techniques. The frequency, amplitude and phase angle of two-phase sinusoidal output of the driver has been designed to be changed for the control purpose. Then the measuring circuits and tools have been set up to obtain required measurements. Input characteristics such as duty ratio of control signal-dc reference voltage, dc reference voltage-driving frequency and output characteristics such as driving frequency-rotor speed, driving frequency-feedback voltage, phase voltage-rotor speed are obtained from the experiments. Also load characteristics are studied with experiments. Afterwards these characteristics are discussed in details. This study gives a systematical experimental approach in order to demonstrate operating and control principles and characteristics of the travelling-wave ultrasonic motor.     

Three-dimensional optimal multi-level Monte–Carlo approximation of the stochastic drift–diffusion–Poisson system in nanoscale devices

The three-dimensional stochastic drift–diffusion–Poisson system is used to model charge transport through nanoscale devices in a random environment. Applications include nanoscale transistors and sensors such as nanowire field-effect bio- and gas sensors. Variations between the devices and uncertainty in the response of the devices arise from the random distributions of dopant atoms, from the diffusion of target molecules near the sensor surface, and from the stochastic association and dissociation processes at the sensor surface. Furthermore, we couple the system of stochastic partial differential equations to a random-walk-based model for the association and dissociation of target molecules. In order to make the computational effort tractable, an optimal multi-level Monte–Carlo method is applied to three-dimensional solutions of the deterministic system. The whole algorithm is optimal in the sense that the total computational cost is minimized for prescribed total errors. This comprehensive and efficient model makes it possible to study the effect of design parameters such as applied voltages and the geometry of the devices on the expected value of the current.     

Study of Temperature Dependence of Electrode–Glass Ceramic Interface Using Impedance Spectroscopy

The electrical behavior of strontium titanate borosilicate glass ceramics (SrO.TiO₂- 2SiO₂.B₂O₃) with additives K₂O, La₂O₃, CoO and Nb₂O₅ was studied by using Impedance Spectroscopy as a function of temperature and composition. An equivalent circuit model having three parallel RC's connected in series with a capacitor C₄ could represent the data well. By comparing the complex modulus plots with simulated ones and looking at the values of the time constants these RC's were attributed to represent crystalline, glassy and glass-crystal interface regions of the glass- ceramic whereas C₄ represented the glass-ceramic sample and contact electrode interface. When the glass ceramic sample contained only SrTiO₃ crystalline phase and the remaining glassy matrix, the interface capacitance showed an Arrhenius type of nature with an activation energy (0.11 ± 0.04) eV and when the glass- ceramic sample contained number of crystalline phases no clear cut trend appeared. These findings are useful in selecting suitable electrodes for applications as well as in deciding upon experimental techniques for measurement of dielectric constants of materials.     

Nitrogen impurity effects of W–B–C–N quaternary thin film for diffusion barrier for Cu metallization

To investigate the thermal stability of nitrogen stuffing effect of tungsten–boron–carbon–nitrogen (W–B–C–N) thin diffusion barrier, the binding energy shift was studied for various annealing temperature. The X-ray diffraction patterns, the deposition rates and the resistivities of W–B–C–N thin film were measured as a function of nitrogen gas ratios for various annealing temperatures and the binding energy between tungsten and nitrogen was determined by the X-ray photoemission spectroscopy. The interface of Cu/W–B–C–N/Si multilayer was characterized for various nitrogen impurity concentration. Our experimental results indicate that W–B–C–N thin films are effective diffusion barriers to prevent the interdiffusion between Cu and Si interface after annealing up to 850 °C for 30 min.     

Modeling and analysis method of fractional-order buck–boost converter

In this paper, the equivalent small parameter method (ESPM) is used to establish the nonlinear mathematical model of the fractional-order buck–boost converter in continuous current mode (CCM), and the analytical expression of approximate steady-state period of converter state variable is obtained by using equivalent small parameter method and combining with harmonic balance principle. The Matlab/Simulink is used to construct the fractional-order capacitance and inductance and to build the circuit model as well as the simulation model of fractional-order buck–boost converter. Moreover, the simulation results of Oustaloup circuit model and numerical simulation model are compared with those of ESPM model to verify the validity and accuracy of the ESPM. The model is simulated by changing the orders of the capacitor and inductor to obtain the influence rule of the order of fractional element on harmonic characteristics of the state variables.     

Physical and dielectric properties of BaTiO3–fluoride–glass systems for nitrogen-fireable embedded capacitors

BaTiO₃-based dielectrics containing the selective additive combinations from Pb-free glasses and fluoride compounds such as AlF₃, BaF₂, CaF₂, LiF and ZnF₂ were studied mainly for a potential N₂-fireable embedded capacitor in printed circuit board with Cu metallization. The physical and dielectric properties, such as dielectric constant (k), loss tangent (tanδ) and T _c, strongly depended on the choice of additive combination. A bismuth borosilicate glass was most promising in terms of the degree of densification and dielectric constant. The samples containing LiF and ZnF₂ and sintered at 950 °C looked most beneficial in that these additives produced high k of >1,200 and low tanδ of < 0.022 at room temperature regardless of sintering atmosphere. As an example, the 95BaTiO₃–2LiF–3(Bi borosilicate) sample exhibited k?~?1,340 and tanδ?~?0.022 at room temperature when fired at 950 °C in N₂.     

Computational–Experimental Verification of Technologies of Utilization of the Concentrate Formed in the Reverse-Osmosis Water Demineralization Cycle

Technologies for utilizing the wastewater of the reverse-osmosis plants (ROPs) to prepare the make-up water for power-generating plants of combined heat and power plants and nuclear power plants are proposed and substantiated using mathematical models and full-scale experiments. The ROPs use natural feedwater with a wide range of quality characteristics. For the first time, variants of the treatment of the concentrate formed in the ROP cycle have been proposed for the reuse of the latter by acidifying it in H-type cation- exchange filters charged with a weakly acidic cation-exchange resin. By admixing part of the filtrate processed in the H-type cation-exchange filters to the feedwater, the latter is acidified thus reducing the probability of formation of carbonaceous sediments and water consumption. The rest of the filtrate subjected to a conversion process is used as a constituent of the make-up feedwater of the heating system or potable water, which eliminates the discharge of the reverse-osmosis plant wastewater into the environment. Another feature of the proposed technology is that the H-type cation-exchange filters are integrated into a regenerant solution reuse circuit (RSRC). As a result, the consumption rate of sulfuric acid for regeneration equals the stoichiometric rate and the regeneration yields gypsum used to produce a binding agent for construction. The kinetics of separation of gypsum from the spent regenerant solutions with different chemical compositions was studied experimentally as applied to the RSRC conditions. The procedure of operating filters charged with the Lewatit CNP-LF cation-exchange resin was trialed under production conditions. It was established that the height of the filtering cation-exchange resin layer should be 1.0–1.5 m and the concentration of the regenerant solution should not exceed 0.8% at a rate of 10–15 m/h. The basic components of the technological scheme were trialed under production conditions on a water treatment plant in service.     

Digital QFT robust control of DC–DC current-mode converters

A new digital robust control law for dc–dc converters is analyzed and implemented in this paper. The robust control QFT technique, which has been successfully used with analog implementations, has been adapted to the digital domain. Concretely, this paper considers the design of a power conditioning unit, which must take into account the uncertainty of the converter, as the conduction mode, the load, the input voltage or the storage elements while assuring that the specifications of a well-known standard are met. The robust control has been implemented by means of a digital device. The sampling frequency is a critical parameter for this kind of system which exhibits fast dynamics. The paper shows a procedure to analyze the minimum sampling frequency of the regulation loop. The procedure consists of transforming an standard analog QFT design to a digital controller by means of an accurate transformation from the s to z domain. After this transformation, we assure the robust stability of the converter by means of the Kharitonov theorem. This approach allows the designer to avoid iterations while finding an appropriate sampling frequency. The experimental prototype has been implemented by means of a FPGA device where the sampling frequency is 100 kHz for a buck power stage with a switching frequency of 200 kHz. The experimental results that are in good agreement with theoretical derivations.     

Stability Analysis of Cascaded DC–DC Power Electronic System

Stability analysis of the cascaded dc-dc power electronic system is analyzed in this paper. For demonstration boost converter supplying, the hybrid switched capacitor converter considered as an example. The boost converter is acting as the bus converter, 42 V bus, while the switched capacitor converter is serving as the point of load converter. The two converters are provided with voltage-mode and peak current-mode controllers, respectively. Converter state-space, two-port network models are developed and then stability of the cascaded system has been analyzed. Cascaded system interaction effects, (i) source converter power handling capability with switching load and (ii) load converter interfacing capability with bus converter, are analyzed. Simulation and experimental results are provided for verification purpose. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

High-efficiency condenser of steam from a steam–gas mixture

The design of a module for a high-efficiency condenser of steam with a high content (up to 15%) of noncondensable gases (NCGs) with a nearly constant steam–gas mixture (SGM) velocity during the condensation of steam has been developed. This module provides the possibility to estimate the operational efficiency of six condenser zones during the motion of steam from the inlet to the SGM suction point. Some results of the experimental tests of the pilot high-efficiency condenser module are presented. The dependence of the average heat transfer coefficient k? on the volumetric NCG concentration v? has been derived. It is shown that the high-efficiency condenser module can provide a moderate decrease in k? from 4400–4600 to 2600–2800 W/(m² K) at v? ≈ 0.5–9.0%. The heat transfer coefficient distribution over different module zones at a heat duty close to its nominal value has been obtained. From this distribution, it can be seen that the average heat transfer coefficient decreases to 2600 W/(m² K) at an NCG concentration v? = 7.5%, but the first condenser sections (1–3) retain high values of k? at a level of no lower than 3200 W/(m² K), and the last sections operate less well, having k? at a level of 1700 W/(m² K). The dependence of the average heat transfer coefficient on the water velocity in condenser tubes has been obtained at a nearly nominal duty such that the extrapolation of this dependence to the water velocity of 2 m/s may be expected to give k? = 5000 W/(m² K) for relatively pure steam, but an increase in k? at v? = 8% will be smaller. The effect of the gas removal device characteristic on the operation of the high-efficiency condenser module is described. The design developed for the steam condenser of a gas-turbine plant with a power of 25 MW, a steam flow rate of 40.2 t/h, and a CO₂ concentration of up to 12% with consideration for the results of performed studies is presented.     

Study of piezoelectric fibre/cement 1–3 composites

To improve the compatibility between the sensor material and civil engineering structural material, a new functional cement-based composite for smart structure applications has been studied. Piezoelectric lead zirconate titanate (PZT) fibres, fabricated using a slurry method, are embedded in a cement matrix to form PZT/cement 1–3 composites. By incorporating PZT fibres into the cement matrix, composites with low PZT volume fractions ranging from 0.05 to 0.22 have been fabricated. The 1–3 composites have good piezoelectric properties that agree quite well with theoretical modeling. The thickness electromechanical coupling coefficient of the composites could reach ～0.5 even for low volume fraction of PZT. These composites have potential to be used as sensors in civil structure health monitoring systems.     

Experimental Determination of Numerical–Analytical Model Coefficients of Electrophysical Processes in Silicon Power Devices

A method has been presented of experimental determination of numerical–analytical model coefficients describing electrophysical processes in silicon power devices that does not use “transistance” (the effect of on-again modes) to decrease loss of power in a device. It has been demonstrated that experimental determination of the coefficients allows one to dispense with numerical solutions of the fundamental systems of equations of semiconductors and use a low-level model for solution of practical problems related to the maximum permissible current loads of silicon power devices in regimes specified by a customer.     

Coupled circuit–field formulation for analysis of parallel operation of converters with interphase transformer

This paper deals with the coupled circuit–field analysis of an interphase transformer (IPT) required for two three-pulse controlled converters operating in parallel for the typical low voltage high current electrolysis application. Two-dimensional nonlinear transient finite element (FE) model of the IPT is coupled with external power electronic circuit comprised of switching thyristors. Output current is maintained constant at 6000 A by implementing current feedback control system. The resulting system of transient nonlinear equations is solved by backward Euler and Newton–Raphson methods, and analyzed under balanced, unbalanced and short circuit conditions. The results obtained from short circuit condition are verified with experimental results and design values, making them helpful for design purpose.     

Impurity behaviors of nitrogen in W–C–N thin diffusion barriers for Cu metallization schemes

To investigate the effect of nitrogen impurities in the tungsten–carbon thin films, the electrical and structural properties of W–C–N thin films deposited with rf magnetron sputtering method were measured. Interface characteristics of W–C–N/Si were studied with resistivity and crystal structure as a function of nitrogen impurity concentrations of as-deposited and annealed state for various annealing temperature. We also investigate the interface of Cu/W–C–N/Si for various nitrogen concentration by using XRD pattern and Nomarski microscope. Our experimental results indicate that nitrogen impurity provides stuffing effect for preventing the interdiffusion between Cu and Si interface after annealing up to 800°C for 30 min, because W–C–N thin films serve as a good diffusion barrier and this may be due to the role of nitrogen and carbon inside the W–C–N film not as bonded state but impurities     

A comparison of time-average power losses in insulated-gate bipolar transistors and hybrid SIT–MOS–transistors

Switching of equivalent silicon insulated-gate bipolar transistors, such as carrier-stored trenchgate bipolar transistors (CSTBTs) and hybrid static induction transistor/metal–oxide–semiconductor (SIT–MOS) thyristors (HSMTs), from a blocking state to a conducting state and vice versa is numerically simulated in two dimensions. It is shown that on–off switching losses in an HSMT are greater than in a fully equivalent CSTBT. Thus, time-average power P that dissipates in an HSMT becomes smaller than the power in the equivalent CSTBTh only at a long current pulse duration. However, a decrease in lifetime τ₀ of nonequilibrium charge carriers in an SIT makes it possible to significantly reduce HSMT switching losses while maintaining its advantage in the on state. Consequently, for each set of CSTBT parameters, such τ₀, it can be selected in the almost equivalent HSMT that power P dissipating in the HSMT will be smaller than the power in the equivalent CSTBT in any given range of amplitude J _a and duration T _on of the current pulses.