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Intracavity Laser Spectroscopy of CH₄ and NH₃ Gases by Using a pulse-Periodic Cr²⁺:ZnSe Laser

OPTICS AND SPECTROSCOPY 2012年第1期112卷 32-35页

作者： Zakharov, N. G. Savikin, A. P. Sharkov, V. V. Eremeykin, O. N. NI Lobachevsky State Univ Nizhni Novgorod Nizhnii Novgorod 603950 Russia

The results of studying the characteristics of an intracavity laser spectrometer based on a polycrystalline Cr2+:ZnSe laser operating in a pulse-periodic regime with the pulse-repetition rate of 3 kHz and pulse duration of similar to 50 ns are presented. Intracavity spectra of absorption of NH3 and CH4 gases in the vicinity of 2.35 mu m are measured. The estimate of the spectrometer sensitivity is provided.

关键词： LASER spectroscopy POLYCRYSTALS SPECTRUM analysis SPECTROMETERS LIGHT absorption pulse-width modulation

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Quantification of liquid mixing enhanced by alternatively pulsed injection in a confined jet configuration

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JOURNAL OF VISUALIZATION 2012年第1期15卷 57-66页

作者： Xia, Qingfeng Zhong, Shan Univ Manchester Sch Mech Aerosp & Civil Engn Manchester M13 9PL Lancs England

In this paper, mixing between the fluid from a primary planar jet and two surrounding secondary planar jets which are pulsated out-of-phase is studied experimentally. Solenoid values are used to control the flow injection into the mixing channel with pulse-width modulation. The experiments are conducted using water at a range of pulsation frequency, two duty cycles (25 and 50%) and a mean Reynolds number between 100 and 250. The flow rate ratio between the primary and secondary flow is kept as unity. Both particle-image velocimetry and planar laser-induced fluorescence techniques are used to visualise the flow patterns and to quantify the mixing degree in the mixing channel. This mixing enhancement method is shown to be effective with a mixing degree as high as 0.9 achieved at a mean Reynolds number of about 166. A combination of different mixing mechanisms is found at play, including sequential segmentation, shearing and stretching, vortex entrainment and breakup. At a given Reynolds number, an optimal frequency exists which scales approximately with a Strouhal number (St = fh/U) of unity. Furthermore, at a given mean Reynolds number a lower duty cycle is found to produce a better mixing due to a resultant higher instantaneous Reynolds number in the jet flow.

关键词： pulse-width modulation Jet mixing PLIF Mixing quantification

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pth Moment Exponential Stability of Stochastic PWM Feedback Systems with Time-Varying Delays

ABSTRACT AND APPLIED ANALYSIS

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ABSTRACT AND APPLIED ANALYSIS 2012年第Spe17期000卷 1-19页

作者： Zhang, Zhong Ye, Lixia Chongqing Univ Coll Math & Stat Chongqing 400044 Peoples R China

This paper further studies the pth moment exponential stability of stochastic pulse-width-modulated (PWM) feedback systems with distributed time-varying delays. We establish several globally exponential stability criteria for such PWM feedback systems by using Lyapunov-Krasovskii functional and then present an upper bound of the parameter of PWM when the system is stable and such system has stronger anti-interference performance than the system without time-varying delays. Furthermore, we present two examples to show the effectiveness and conservativeness of the theoretical results.

关键词： pulse-width modulation EXPONENTIAL stability STOCHASTIC processes FEEDBACK control systems LYAPUNOV functions TIME-varying systems PERFORMANCE evaluation

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Method of alleviating overcompensation problem in zero-voltage-transition pulse-width-modulation boost converters

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ELECTRONICS LETTERS 2008年第6期44卷 444-445页

作者： Lai, Y. M. Tan, S. C. Chan, S. N. Hong Kong Polytech Univ Dept Elect & Informat Engn Kowloon Hong Kong Peoples R China

Presented is a fast control strategy to improve the transient response of a zero-voltage-transition pulse-width-modulation (PWM) boost converter. A prototype circuit based on the proposed control strategy was designed and constructed. Experimental results show that the proposed controller can reduce the load transient response time significantly compared to those obtained by conventional PWM controllers.

关键词： Telecommunication pulse-width modulation Signal theory (Telecommunication) modulation (Electronics) modulation theory Electronic systems Electronics

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An effective TDLS setup using homemade driving modules for evaluation of pulsed QCL

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APPLIED PHYSICS B-LASERS AND OPTICS 2012年第3期109卷 541-548页

作者： Zhang, Y. G. Gu, Y. Li, Y. Y. Li, A. Z. Li, C. Cao, Y. Y. Zhou, L. Chinese Acad Sci State Key Lab Funct Mat Informat Shanghai Inst Microsyst & Informat Technol Shanghai 200050 Peoples R China Chinese Acad Sci Grad Sch Beijing 100049 Peoples R China

Integrated, compact, and economical pulse driving and TE control modules for pulsed quantum cascade lasers (QCL) have been developed. Based on those modules, an effective tunable diode laser spectroscopy (TDLS) setup has been constructed for the evaluation of pulsed QCL and demonstration of TDLS concepts. Connecting our mid-infrared QCL module to the driving module using cable of 10 Omega characteristic impedance results in down chirp light pulses suitable for intrapulse scheme of TDLS;a usable down chirp of about 0.78 cm(-1) is achieved for current pulse with 240-ns pulse width. Connecting the QCL module to the driving module using stripline of characteristic impedance < 1 Omega results in narrow Gaussian-like light pulses that are suitable for interpulse scheme of TDLS;the light pulse width of 15 ns is achieved. The absorption features of N2O at 1289.86 cm(-1) have been measured using a homemade distributed feedback QCL around about 7.75 mu m adopting intrapulse scheme;the measurement limit below 1 ppmv is achieved with a 10-m white cell.

关键词： LASER spectroscopy QUANTUM cascade lasers INFRARED spectroscopy ABSORPTION spectra DISTRIBUTED feedback lasers pulse-width modulation

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Two-dimensional Random PWM Technique for Full-Bridge DC/DC Converter

Two-dimensional Random PWM Technique for Full-Bridge DC/DC C...

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38th Annual Conference on IEEE-Industrial-Electronics-Society (IECON )

作者： Lai, Yen-Shin Chen, Bo-Yuan Natl Taipei Univ Technol Ctr Elect Power Taipei Taiwan

ISBN: (纸本)9781467324212

PWM techniqnes for full-bridge DC/DC converter are investigated and a new multi-dimension random PWM technique is proposed in this paper. Three PWM techniques with constant switching frequency are discussed and the related random PWM techniques are which spread the harmonic clusters and give constant average inductor current to reduce the output voltage ripple are discussed. The pros and cons of three constant switching frequency PWM techniques and the related random counterparts are investigated. Experimental results show there is significant efficiency drop of the random PWM technique due to significant increase of switching counts. Therefore, this paper presents a two-dimensional random PWM technique to significantly reduce the harmonic intensity while not causing relevant impact on the efficiency. An FPGA-based digital controlled isolated full-bridge DC/DC converter prototype is built to verify the performance of conventional and proposed PWM techniques. The specifications of the converter include: input voltage = 400 V, output voltage = 12 V, output power = 120 Wand switching frequency = 100 kHz. Measured efficiency and Harmonic Spread Factor will be used for the evaluation of these PWM techniques.

关键词： pulse-width modulation Full-Bridge DC/DC Converter Harmonic Spread Factor

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On the Design of Low-Frequency Broadcasting System and Its Applications to Disaster Management

On the Design of Low-Frequency Broadcasting System and Its A...

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IEEE International Conference on Communications (ICC)

作者： Liu, Chia-Horng Shen, June-Ming Wang, Chung-Ho Kuo, Yu-Chen Wu, Neal Chunghwa Telecom Co Ltd Telecom Labs Wireless Commun Dept Tao Yuan Taiwan

ISBN: (纸本)9781457720536

In this paper, we present a new and dependable disaster broadcasting network. The urgent information is broadcasted in the low-frequency band of 40-80kHz and modulated with reliable pulse width modulation(PWM). The coverage of one low-frequency broadcasting station is more than 500km. With excellent propagation characteristics, the low-frequency signal could penetrate into remote areas which are usually lack of telecommunication infrastructure. To promulgate the hazard information to general people of one specific area, the hierarchical data structure is proposed. A series of field measurement, test and theoretical comparisons are conducted to evaluate the performance of low-frequency system. It is shown from our experimental results that the low-frequency broadcasting network is a dependable and cost-effective solution in disaster management. Finally, a sustainable heterogeneous and layered ICT network designed for disaster management is drawn.

关键词： Low-frequency pulse-width modulation broadcasting hierarchical data structurestyling heterogeneous network

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Switched Capacitor DC-DC Converter Based Current Equalization Scheme For Maximum Power Extraction From Partially Shaded PV Modules Without Bypass Diodes

Switched Capacitor DC-DC Converter Based Current Equalizatio...

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38th IEEE Photovoltaic Specialists Conference (PVSC)

作者： Peter, Pradeep K. Sharma, Pooja Agarwal, Vivek Indian Space Res Org Bangalore 562140 Karnataka India Indian Inst Technol Bombay 400076 Maharashtra India

ISBN: (纸本)9781467300667

The use of 'by pass' diodes to prevent damage to series connected photovoltaic (PV) modules of a PV array in case of partial shading leads to complete power loss from the shaded modules. This paper explains the use of Switched Capacitor (SC) dc-dc converters in place of module by pass diodes to prevent power loss from partially shaded modules. SC converters have the advantage of being compact, cost effective and highly efficient under certain operating conditions. An SC converter is connected across each PV module. The SC converter injects an equalization current across the PV module while maintaining the module at its maximum power point voltage. The injected equalization current is the difference between the maximum current generated by any of the series connected PV modules and the current of that particular PV module. This enables the PV array to conduct the current corresponding to the current of the module generating maximum current. Thus partially shaded modules are allowed to generate what ever power they can. The choice of an optimum charge transfer capacitor for the SC converter and its efficiency issues are also discussed.

关键词： DC-DC power converters photovoltaic system pulse-width modulation solar power generation switched capacitor circuits

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Topology and PWM Method Dependency of High Frequency Leakage Current Characteristics of Voltage Source Inverter Driven AC Motor Drives

Topology and PWM Method Dependency of High Frequency Leakage...

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IEEE Energy Conversion Congress and Exposition (ECCE)

作者： Cetin, N. Onur Hava, Ahmet M. Middle E Tech Univ Dept Elect & Elect Engn TR-06800 Ankara Turkey

ISBN: (纸本)9781467308014

In PWM inverter based AC motor drives, high frequency common-mode voltage (CMV) causes high frequency common-mode current (CMC, motor leakage current). With its magnitude reaching ampere levels, the CMC can induce bearing failures, drive nuisance trips, EMC issues etc. The CMC is dependent on the inverter topology (two or three-level), PWM method (pulse pattern), and the filters if active/passive mitigation methods used. This paper investigates the CMV/CMC properties of the two and three-level VSIs [with and without common-mode inductor (CMI)] for various PWM methods. It shows the peak CMC is highly dependent on the PWM method and pulse sequence (in addition to dv/dt). The PWM methods pulse pattern and sequence analyses are supported by detailed experiments to illustrate that the reduced CMV PWM methods with proper pulse sequences yield low peak CMC and the inclusion of a CMI filter provides further suppression. Furthermore, the high frequency CMV/CMC spectra for various PWM methods are provided comparatively. It is shown that when the common-mode resonant frequency coincides with the dominant CMV frequency, the CMC can be amplified. As a result a comprehensive leakage current evaluation is provided in the paper. The information is useful for design and implementation of motor drive PWM algorithms and high frequency EMC filters in terms of CMV/CMC performance considering CMV/CMC reduction.

关键词： AC motor common-mode inverter leakage current pulse-width modulation

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Field-free orientation of CO by a terahertz few-cycle pulse

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Physical Review A 2012年第5期85卷 053415-053415页

作者： Chaochao Qin Ying Tang Yanmei Wang Bing Zhang []State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics Wuhan Institute of Physics and Mathematics Chinese Academy of Sciences Wuhan Hubei 430071 People's Republic of China and Graduate School of the Chinese Academy of Sciences Beijing 100049 People's Republic of China

The field-free molecular orientation of CO by a terahertz few-cycle pulse was studied theoretically. The effects of the laser intensity and pulse duration on the molecular orientation, which is created by the terahertz few-cycle pulse, were discussed. Furthermore, it was shown that the enhancement or suppression of the molecular orientation can be coherently manipulated by precisely controlling the carrier-envelope phase of the terahertz few-cycle pulse. Compared with other orientation techniques, better orientation can be achieved by a terahertz few-cycle pulse at lower intensities.

关键词： CARBON monoxide SUBMILLIMETER waves pulse-width modulation NUCLEAR orientation PHASE transformations (Physics) LASER beams

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