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Laser induced effects in PbO-Bi₂O₃-Ga₂O₃-BaO: Eu glasses

OPTICS COMMUNICATIONS 2010年第15期283卷 3049-3051页

作者： Reshak, A. H. Lakshminarayana, G. Proskurina, G. Yushanin, V. G. Calus, S. Chmiel, M. Miedzinski, R. Brik, M. G. Univ S Bohemia Inst Phys Biol Nove Hrady 37333 Czech Republic Nagoya Inst Technol Dept Mat Sci & Engn Showa Ku Nagoya Aichi 4668555 Japan Univ Tartu Inst Phys EE-51014 Tartu Estonia Opt Res Ctr Belmont CA USA Czestochowa Tech Univ Dept Elect Engn Czestochowa Poland State Fire Serv Cent Sch Czestohcowa Poland Univ Malaysia Perlis Inst Nano Elect Engn Kangar 01000 Perlis Malaysia

We have observed a several times enhancement of the optical second harmonic generation in newly synthesized Europium doped PbO-Bi2O3-Ga2O3-BaO glasses for the fundamental wavelength 1320 nm during optical treatment by coherent fundamental and doubled frequency beams with a pulse duration about 15 ns. We have found that the maximal optical second harmonic generation was achieved for the Eu content of about 1.4% at fundamental beam average power equal to about 3 GW/cm(2), temperature of about 300 K and intensity ratio between the fundamental and doubled frequency beams of about 9. Frequency repetition of the optical pulses was equal to about 10 Hz. It was shown that doping by other rare earth ions, particularly by Dysprosium does not give a sufficient contribution to the effect. (C) 2010 Elsevier B.V. All rights reserved.

关键词： SECOND harmonic generation EUROPIUM WAVELENGTHS pulse-width modulation LASER beams DYSPROSIUM RARE earth ions OPTICAL glass

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The effect of finite diffusion gradient pulse duration on fibre orientation estimation in diffusion MRI

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NEUROIMAGE 2010年第2期51卷 743-751页

作者： Yeh, Chun-Hung Tournier, J-Donald Cho, Kuan-Hung Lin, Ching-Po Calamante, Fernando Connelly, Alan Natl Yang Ming Univ Dept Biomed Imaging & Radiol Sci Taipei 112 Taiwan Florey Neurosci Inst Austin Brain Res Inst Melbourne Vic Australia Univ Melbourne Dept Med Melbourne Vic Australia Natl Yang Ming Univ Inst Neurosci Brain Connect Lab Taipei 112 Taiwan

An essential step for fibre-tracking is the accurate estimation of neuronal fibre orientations within each imaging voxel, and a number of methods have been proposed to reconstruct the orientation distribution function based on sampling three-dimensional q-space. In the q-space formalism, very short (infinitesimal) gradient pulses are the basic requirement to obtain the true spin displacement probability density function. On current clinical MR systems however, the diffusion gradient pulse duration (delta) is inevitably finite due to the limit on the achievable gradient intensity. The failure to satisfy the short gradient pulse (SGP) requirement has been a recurrent criticism for fibre orientation estimation based on the q-space approach. In this study, the influence of a finite delta on the DW signal measured as a function of gradient direction is described theoretically and demonstrated through simulations and experimental models. Our results suggest that the current practice of using long delta for DW imaging on human clinical MR scanners, which is enforced by hardware limitations, might in fact be beneficial for estimating fibre orientations. For a given b-value, the prolongation of delta is advantageous for estimating fibre orientations for two reasons: first, it leads to a boost in DW signal in the transverse plane of the fibre. Second, it stretches out the shape of the measured diffusion profile, which improves the contrast between DW orientations. This is especially beneficial for resolving crossing fibres, as this contrast is essential to discriminate between different fibre directions. (C) 2010 Elsevier Inc. All rights reserved.

关键词： NEUROFIBRILS FINITE element method pulse-width modulation ESTIMATION theory DIFFUSION magnetic resonance imaging BRAIN imaging

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modulation Schemes for Five-Phase to Three-Phase AC-AC Matrix Converters

Modulation Schemes for Five-Phase to Three-Phase AC-AC Matri...

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IEEE Energy Conversion Congress and Exposition (ECCE)

作者： Mihret, Melaku Abreham, Meharegzi Ojo, Olorunfemi Karugaba, Sosthenes Tennessee Technol Univ Dept Elect & Comp Engn Ctr Energy Syst Res Cookeville TN 38505 USA

ISBN: (纸本)9781424452873

The AC-AC matrix converters are pulse-width modulated using either a carrier-based or space vector modulation techniques. This paper presents these two approaches as they relate to the non-square 5 x 3 converter design targeted for a five-phase voltage source providing real and active powers for three-phase power systems found in high power applications such as on-board ship power systems. It is desirable to be able to synthesize the three-phase voltages with minimum harmonics and the highest voltage gain possible. Furthermore, the input power factor of the converter is to be variable, even to be unity. These goals are achieved with the determined modulation schemes. Computer simulations are given to validate the analytic modulation methods set forth, to demonstrate the waveform synthesis and the achievement of the unity input power factor.

关键词： AC-AC power convertors PWM power convertors active powers computer simulations five-phase AC-AC matrix converters five-phase voltage source matrix convertors modulation schemes on-board ship power systems power factor power factor pulse-width modulation space vector modulation three-phase AC-AC matrix converters three-phase power systems

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Assessment of pulse-width modulation Techniques for Brushless DC Motor Drives

Assessment of Pulse-Width Modulation Techniques for Brushles...

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41st Annual Meeting of the IEEE Industry-Applications-Society (IAS)

作者： Lai, Yen-Shin Lin, Yong-Kai Natl Taipei Univ Technol Dept Elect Engn Taipei 106 Taiwan

ISBN: (纸本)9781424403646

The purpose of this paper is to assess the pulse-width modulation (PWM) techniques for Brushless DC Motor (BLDCM) motor drives. The criteria for assessment include driver circuit, reversal DC-link current, circulating current of floating phase, and back Electro-Magnetic Force (EMF) detection. The advantages and disadvantages of five PWM techniques for BLDCM drives will be analyzed and confirmed by experimental results. The results presented in this paper are expected to provide whole picture for applications reference.

关键词： pulse-width modulation brushless DC motor drives

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Seven-Level Cascaded ANPC-Based Multilevel Converter

Seven-Level Cascaded ANPC-Based Multilevel Converter

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IEEE Energy Conversion Congress and Exposition (ECCE)

作者： Pulikanti, Sridhar R. Konstantinou, Georgios S. Agelidis, Vassilios G. Univ Sydney Sch Elect & Informat Engn Sydney NSW Australia Univ New South Wales Sch Elect Engn & Telecommun Sydney NSW Australia

ISBN: (纸本)9781424452873

A seven-level converter based on the cascaded connection of a three-level active neutral-point-clamped (ANPC) converter and individual H-bridge cells per phase is presented in this paper. This converter only requires a single DC source for all three phases and extends the amplitude of output voltage of the converter with similar DC-link voltage. The operation principles and control strategies based on a fundamental frequency harmonic elimination PWM are discussed. The regulation of FC voltage depends on the positions of switching angles over a quarter period in the available solutions and on the load power factor. In order to extend the regulation of the FC voltage into higher modulation indices an additional switching in the top voltage level is also considered. Experimental results taken from a low-power single-phase laboratory setup that verify the theoretical considerations and simulation results are presented.

关键词： Active neutral-point-clamped multilevel converter selective harmonic elimination pulse-width modulation flying capacitor voltage control

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Border-collision bifurcations in a DC/DC converter with multilevel pulse-width modulation

Border-collision bifurcations in a DC/DC converter with mult...

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IEEE International Conference on Industrial Technology

作者： Zhusubaliyev, Zhanybai T. Mosekilde, Erik Kursk State Tech Univ Dept Comp Sci 50 Yrs Oct Str94 Kursk 305040 Russia Tech Univ Denmark Dept Phys Complex Syst Grp Lyngby Denmark

ISBN: (纸本)9781424407255

Considering a pulse-width modulated DC/DC converter as an example, this paper describes a border-collision bifurcation that can lead to the appearance of quasiperiodicity in piecewise-smooth dynamical systems. We demonstrate how a two-dimensional torus can arise from a periodic orbit through a bifurcation in which two complex-conjugated Poincare characteristic multipliers abruptly jump from the inside to the outside of the unit circle. The torus may be ergodic or resonant. In both cases, however, the diameter of the torus develops approximately linearly with the distance to the bifurcation point as opposed to the characteristic parabolic form of the well-known Neimark-Sacker bifurcation.

关键词： border-collision bifurcations quasiperiodicity torus birth bifurcation multilevel converters pulse-width modulation

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Calibrated continuous-time sigma -delta modulators

Calibrated continuous-time sigma -delta modulators

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作者： Lu, Cho-Ying Texas A&M University

学位级别：Ph.D.

To provide more information mobility, many wireless communication systems such as WCDMA and EDGE in phone systems, bluetooth and WIMAX in communication networks have been recently developed. Recent efforts have been made to build the all-in-one next generation device which integrates a large number of wireless services into a single receiving path in order to raise the competitiveness of the device. Among all the receiver architectures, the high-IF receiver presents several unique properties for the next generation receiver by digitalizing the signal at the intermediate frequency around a few hundred MHz. In this architecture, the modulation/demodulation schemes, protocols, equalization, etc., are all determined in a software platform that runs in the digital signal processor (DSP) or FPGA. The specifications for most of front-end building blocks are relaxed, except the analog-to-digital converter (ADC). The requirements of large bandwidth, high operational frequency and high resolution make the design of the ADC very challenging. Solving the bottleneck associated with the high-IF receiver architecture is a major focus of many ongoing research efforts. In this work, a 6th-order bandpass continuous-time sigma-delta ADC with measured 68.4dB SNDR at 10MHz bandwidth to accommodate video applications is proposed. Tuned at 200 MHz, the fs/4 architecture employs an 800 MHz clock frequency. By making use of a unique software-based calibration scheme together with the tuning properties of the bandpass filters developed under the umbrella of this project, the ADC performance is optimized automatically to fulfill all requirements for the high-IF architecture. In a separate project, other critical design issues for continuous-time sigma-delta ADCs are addressed, especially the issues related to unit current source mismatches in multi-level DACs as well as excess loop delays that may cause loop instability. The reported solutions are revisited to find more efficient architecture

关键词： Calibration sigma-delta modulator continuous-time ADC bandpass lowpass PWM pulse-width modulation Book Thesis

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Novel analog pulse-width-modulated 15-μm SiGe micromirrors

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JOURNAL OF THE SOCIETY FOR INFORMATION DISPLAY 2010年第10期18卷 855-861页

作者： Beernaert, Roel Avci, Aykut De Smet, Jelle De Smet, Herbert De Coster, Jeroen Severi, Simone Witvrouw, Ann Univ Ghent ELINT TFCG Microsyst B-9052 Ghent Belgium

A novel six-electrode SiGe micromirror pixel enabling analog pulse-width modulation (PWM) in display applications is presented. Instead of utilizing bitplanes, arbitrary duty cycles can be realized, resulting in an analog gray-level distribution. This eliminates the posterization (contouring) effect that is typical for digital micromirrors. Moreover, the pixel design does not require the incorporation of electronic comparators and the gamma compensation can be processed externally. Two out of the six electrodes are used as landing electrodes. The other four attracting electrodes are driven by two anti-phase saw-tooth signals and two fixed analog voltage signals. By applying this signal scheme, the duty cycle of the mirror is modulated in an analog manner. Test vehicles were manufactured where SiGe is the microelectromechanical systems (MEMS) material. The use of SiGe as a structural layer is advantageous to build MEMS since the CMOS and MEMS layers can be deposited in a monolithic manner. Measurements using a Laser Doppler Vibrometer (LDV) have confirmed the feasibility of analog PWM for 15-mu m SiGe micromirrors.

关键词： Microelectromechanical systems MEMS SiGe micromirror pixel analog pulse-width modulation contouring posterization

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On the plume splitting of pulsed laser ablated Fe and Al plasmas

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PHYSICS OF PLASMAS 2010年第10期17卷 103105-103105页

作者： Mahmood, S. Rawat, R. S. Darby, M. S. B. Zakaullah, M. Springham, S. V. Tan, T. L. Lee, P. Nanyang Technol Univ NSSE NIE Singapore 637616 Singapore Univ Karachi Dept Phys Karachi 75270 Pakistan Univ Southampton Optoelect Res Ctr Southampton SO17 1BJ Hants England Quaid I Azam Univ Dept Phys Islamabad 45320 Pakistan

A time resolved imaging study of pulsed laser ablated Fe and Al plasma plumes with specific interest in the splitting of plumes into the slow and fast moving components as they expand through the background argon gas at different pressures is reported. The material ablation was achieved using a Q-switched Nd: YAG (yttrium aluminum garnet) laser operating at 532 nm with a pulse duration of similar to 8 ns full width at half maximum and a fluence of 30 Jcm(-2) at the target surface. Typical time resolved images with low magnification show that the splitting occurs at moderate background gas pressures (0.5 and 1.0 mbar for Fe, and 0.2 mbar for Al plasma plumes). The plume splitting did not occur for higher background gas pressures. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3491410]

关键词： LASER ablation ND-YAG lasers pulse-width modulation ARGON SURFACE chemistry LASER plasmas ARGON plasmas

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Loop Model and Quasi Limit Cycle for Digitally Controlled Switching DC-DC Converters

Loop Model and Quasi Limit Cycle for Digitally Controlled Sw...

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The 2010 International Conference on Computer Application and System Modeling(2010计算机应用与系统建模国际会议 ICCASM 2010)

作者： Feng Li Tingcun Wei Han Yan Ran Zheng School of Computer Science and Technology Northwestern Polytechnical University Xi'an China

ISBN: (纸本)9781424472352

Loop model and controlled object model for digitally controlled switching dc-dc converters are set up in this paper, and buck converters stability for both digital control and analog control are comparatively analyzed based on the proposed models. This paper also discusses the presence of one oscillation, called as quasi limit cycle, caused by one additional switching cycle delay in the digital feedback loop, and three methods to remove it are introduced and studied. Simulation results are provided to verify the correctness of proposed models and the validity of removal methods.

关键词： switching dc-dc converter limit cycle pulse-width modulation

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