期刊文献+
共找到4,616篇文章
< 1 2 231 >
每页显示 20 50 100
Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source
1
作者 Ilya ZADIRIEV Elena KRALKINA +2 位作者 Konstantin VAVILIN Alexander NIKONOV Georgy SHVIDKIY 《Plasma Science and Technology》 SCIE EI CAS CSCD 2023年第2期131-145,共15页
The paper describes an experimental study of the characteristics of a pulse-modulated radiofrequency(RF)discharge sustained at low pressures,typical of the operating modes of RF gridded ion sources.The motivation for ... The paper describes an experimental study of the characteristics of a pulse-modulated radiofrequency(RF)discharge sustained at low pressures,typical of the operating modes of RF gridded ion sources.The motivation for the study is the question of whether the RF pulsemodulated mode can increase the efficiency of the ion source.The ion current values extracted from an RF inductive ion source operating in continuous and pulse-modulated modes were compared.The experimental data were also compared with the parameter calculations based on a0D numerical model of the discharge.The measurements showed that the pulse-modulated operation mode of the RF ion source had a noticeable advantage when the power of the RF generator was 140 W or lower.However,as the generator power increased,the advantage was lost because the pulse-modulated operation mode,having a higher RF power instant value,entered the region of existence sooner than the continuous mode,where the ion production cost begins to grow with RF power. 展开更多
关键词 discharge plasma radio frequency(RF) pulse ELECTRONS ions
下载PDF
Long-Pulse Single-Frequency All-Fiber Amplifier
2
作者 Kuiyan Song Jingdao Yang Kun Zhang 《Journal of Applied Mathematics and Physics》 2023年第12期4153-4160,共8页
In this paper, we report a high power long-pulse single-frequency all-fiber amplifier at 1064 nm with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). By applyi... In this paper, we report a high power long-pulse single-frequency all-fiber amplifier at 1064 nm with near-diffraction-limited beam quality based on a polarization-maintaining tapered Yb-doped fiber (T-YDF). By applying square wave pulse modulation to the diodes, with a frequency of 50 Hz and a pulse width of 668 μs, the peak power of the output laser reached 257 W with an average power of 8.65 W, linewidth of 10.6 kHz and M<sup>2</sup> < 1.5. . 展开更多
关键词 Long-pulse SINGLE-frequency Fiber Laser Stimulated Brillouin Scattering
下载PDF
An Optoelectronic Pulse Frequency Modulation Circuit for Retinal Prosthesis
3
作者 刘金彬 陈弘达 +2 位作者 高鹏 裴为华 隋晓红 《Journal of Semiconductors》 EI CAS CSCD 北大核心 2006年第4期700-704,共5页
A pulse frequency modulation(PFM) circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the ... A pulse frequency modulation(PFM) circuit for retinal prosthesis,which generates electrical pulses with frequency proportional to the intensity of incident light, is presented. The fundamental characteristic of the circuit is described and analyzed. The circuit is realized in 0.6μm CMOS process,and the simulation results testify to the possibility of sub-retinal implantation. 展开更多
关键词 retinal prosthesis sub-retinal implant pulse frequency modulation
下载PDF
A NOVEL AERONAUTICAL STATIC INVERTER WITH HIGH FREQUENCY PULSE DC LINK
4
作者 陈道炼 刘志政 +1 位作者 严仰光 胡育文 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI 1999年第1期48-54,共7页
A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft swi... A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft switching of two stage cascade converters. It lays technical foundation for high power density, high efficiency and low cost aeronautical static inverter. The operation and design approach of this topology are carefully analyzed and studied. The validity of this topology is verified by simulation and test. 展开更多
关键词 INVERTERS high frequency links active clamp circuits combined soft switching techniques three state discrete pulse modulation
下载PDF
Variable frequency of pulse hydraulic fracturing for improving permeability in coal seam 被引量:12
5
作者 Li Quangui Lin Baiquan +4 位作者 Zhai Cheng Ni Guanhua Peng Shen Sun Chen Cheng Yanying 《International Journal of Mining Science and Technology》 SCIE EI 2013年第6期847-853,共7页
Variable frequency,a new pattern of pulse hydraulic fracturing,is presented for improving permeability in coal seam.A variable frequency pulse hydraulic fracturing testing system was built,the mould with triaxial load... Variable frequency,a new pattern of pulse hydraulic fracturing,is presented for improving permeability in coal seam.A variable frequency pulse hydraulic fracturing testing system was built,the mould with triaxial loading was developed.Based on the monitor methods of pressure sensor and acoustic emission,the trials of two patterns of pulse hydraulic fracturing of single frequency and variable frequency were carried out,and at last fracturing mechanism was analyzed.The results show that the effect of variable frequency on fracture extension is better than that of single frequency based on the analysis of macroscopic figures and AE.And the shortage of single frequency is somewhat remedied when the frequency is variable.Under variable frequency,the pressure process can be divided into three stages:low frequency band,pressure stability band and high frequency band,and rupture pressure of the sample is smaller than that of the condition of single frequency.Based on the Miner fatigue theory,the effect of different loading sequences on sample rupture is discussed and the results show that it is better to select the sequence of low frequency at first and then high frequency.Our achievements can give a basis for the improvement and optimization of the pulse hydraulic fracturing technology. 展开更多
关键词 Variable frequency pulse hydraulic fracturing FRACTURE AE FATIGUE
下载PDF
Effects of initial frequency chirp on the linear propagation characteristics of the exponential optical pulse 被引量:8
6
作者 郑宏军 刘山亮 《Chinese Physics B》 SCIE EI CAS CSCD 2006年第8期1831-1837,共7页
In this paper, the linear propagation characteristics of the exponential optical pulse with initial linear and nonlinear frequency chirp are numerically studied in a single mode fibre for β2 〈 0. It can be found tha... In this paper, the linear propagation characteristics of the exponential optical pulse with initial linear and nonlinear frequency chirp are numerically studied in a single mode fibre for β2 〈 0. It can be found that the temporal full width at half maximum and time-bandwidth product of exponential pulse monotonically increase with the increase of propagation distance and decrease with the increase of linear chirp C for C 〈 0.5, go through an initial decreasing stage near ζ= 1, then increase with the increase of propagation distance and linear chirp C for C 〉 0.5. The broadening of pulses with negative chirp is faster than that with positive chirp. The exponential pulse with linear chirp gradually evolves into a near-Gaussian pulse. The effect of nonlinear chirp on waveform of the pulse is much greater than that of linear chirp. The temporal waveform breaking of exponential pulse with nonlinear chirp is first observed in linear propagation. Furthermore, the expressions of the spectral width and time-bandwidth product of the exponential optical pulse with the frequency chirp are given by use of the numerical analysis method. 展开更多
关键词 fibre optics frequency chirp numerical analysis exponential optical pulse
下载PDF
Effect of pulse M-Arc frequency on Tri-Arc DE droplet transfer and weld forming 被引量:3
7
作者 Zheng Jia Wang Tianqi +1 位作者 Zhong Pu Cheng Liqiang 《China Welding》 EI CAS 2019年第1期1-5,共5页
In view of the unstable welding process of Tri-Arc DE,surfacing test with Q235 steel plate was completed with the help of the self-built high-speed camera and waveform synchronous acquisition system using the Tri-Arc ... In view of the unstable welding process of Tri-Arc DE,surfacing test with Q235 steel plate was completed with the help of the self-built high-speed camera and waveform synchronous acquisition system using the Tri-Arc DE technology. The effects of pulsed M-Arc frequency on Tri-Arc DE droplet transfer and weld formation were analyzed. The results show that while the gradual increase of pulse frequency,the droplet transfer frequency gradually decreases,which is followed by several drops per pulse,one drop per pulse,and one drop within several pulses. The most ideal transfer form is one drop per pulse,of which the welding process is the most stable,and the quality of weld formation is the most satisfied. 展开更多
关键词 Tri-Arc double electrode pulse frequency the metal transfer behavior WELD formation
下载PDF
Clinical usefulness of transpapillary removal of common bile duct stones by frequency doubled double pulse Nd:YAG laser 被引量:20
8
作者 Tae Hyeon Kim Hyo Jeong Oh +2 位作者 Chang-Soo Choi Dong Han Yeom Suck Chei Choi 《World Journal of Gastroenterology》 SCIE CAS CSCD 2008年第18期2863-2866,共4页
AIM: To study the efficacy and the safety of laser lithotripsy without direct visual control by using a balloon catheter in patients with bile duct stones that could not be extracted by standard technique. METHODS: Th... AIM: To study the efficacy and the safety of laser lithotripsy without direct visual control by using a balloon catheter in patients with bile duct stones that could not be extracted by standard technique. METHODS: The seventeen patients (7 male and 10 female; mean age 67.8 years) with difficult common bile duct (CBD) stones were not amenable for conventional endoscopic maneuvers such as sphincterotomy and mechanical lithotripsy were included in this study. Laser wavelengths of 532 nm and 1064 nm as a double pulse were applied with pulse energy of 120 mJ. The laser fiber was advanced under fluoroscopic control through the ERCP balloon catheter. Laser lithotripsy was continued until the fragment size seemed to be less than 10 mm. Endoscopic extraction of the stones and fragments was performed with the use of the Dormia basket and balloon catheter. RESULTS: Bile duct clearance was achieved in 15 of 17 patients (88%). The mean number of treatment sessions was 1.7 ± 0.6. Endoscopic stone removal could not be achieved in 2 patients (7%). Adverse effects were noted in three patients (hemobilia, pancreatitis, and cholangitis). CONCLUSION: The Frequency Doubled Double Pulse Nd:YAG (FREDDY) laser may be an effective and safe technique in treatment of difficult bile duct stones. 展开更多
关键词 Bile duct stones frequency doubled double pulse Nd:YAG laser Transpapillary removal Mechanical lithotripsy Balloon catheter
下载PDF
The effect of pulse frequency on the electrochemical properties of micro arc oxidation coatings formed on magnesium alloy 被引量:6
9
作者 Xianghua Song Jianhong Lu +2 位作者 Xijiang Yin Jianping Jiang Jing Wang 《Journal of Magnesium and Alloys》 SCIE EI CAS 2013年第4期318-322,共5页
Micro arc oxidation(MAO)coatings were formed on magnesium alloy AZ31B to improve the corrosion resistance using environmental friendly electrolyte solution under single-polar pulse power supply.The effect of electrica... Micro arc oxidation(MAO)coatings were formed on magnesium alloy AZ31B to improve the corrosion resistance using environmental friendly electrolyte solution under single-polar pulse power supply.The effect of electrical parameters of pulse frequency on the coating performance was studied at frequencies of 2.5 Hz,25 Hz and 250 Hz.The coating performance at different frequencies was characterized by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS)and potentiodynamic polarization testing method.It was found that the corrosion resistance of the MAO coatings was improved when increasing the pulse frequencies from 2.5 Hz to 250 Hz.The corrosion current in 250 Hz case decreased by three orders of magnitude as compared with bare Mg alloy and the corrosion impedance also increased remarkably,means significantly enhanced corrosion resistance than bare Mg alloy.The results give us more insight in the optimization of electrical parameters to improve the MAO coating performance.The MAO technology is attractive for application on magnesium and other light alloys for surface protection in automotive and space industries. 展开更多
关键词 Micro arc oxidation Magnesium alloys pulse frequency Corrosion resistance Potentiodynamic polarization
下载PDF
Broadband mid-infrared pulse via intra-pulse difference frequency generation based on supercontinuum from multiple thin plates 被引量:1
10
作者 Hang-Dong Huang Chen-Yang Hu +4 位作者 Hui-Jun He Hao Teng Zhi-Yuan Li Kun Zhao Zhi-Yi Wei 《Chinese Physics B》 SCIE EI CAS CSCD 2019年第11期168-172,共5页
We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation(DFG) in ... We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation(DFG) in β-barium borate crystal(β-BBO) and passively carrier-envelope-phase(CEP) stabilized. The DFG is induced by few-cycle pulses initiated from spectral broadening in multiple thin plates driven by a Ti: sapphire chirped-pulse amplifier. Furthermore, a numerical simulation is developed to estimate the conversion efficiency and output spectrum of the DFG. Our results show that the pulses from the DFG have the potential for seeding intense mid-infrared(MIR) laser generation and amplification to study strong-field physics and attosecond science. 展开更多
关键词 infrared pulseS DIFFERENCE frequency generation ULTRAFAST laser
下载PDF
Microstructure,tribological behavior and magnetic properties of Fe−Ni−TiO_(2) composite coatings synthesized via pulse frequency variation 被引量:3
11
作者 Ebrahim YOUSEFI Shahriar SHARAFI Ahmad IRANNEJAD 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2021年第12期3800-3813,共14页
The Fe−Ni−TiO_(2) nanocomposite coatings were electrodeposited by pulse frequency variation.The results showed that the nanocomposite with a very dense coating surface and a nanocrystalline structure was produced at h... The Fe−Ni−TiO_(2) nanocomposite coatings were electrodeposited by pulse frequency variation.The results showed that the nanocomposite with a very dense coating surface and a nanocrystalline structure was produced at higher frequencies.By increasing the pulse frequency from 10 to 500 Hz,the iron and TiO_(2) nanoparticles contents were increased in expense of nickel content.XRD patterns showed that by increasing the frequency to 500 Hz,an enhancement of BCC phase was observed and the grain size of deposits was reduced to 35 nm.The microhardness and the surface roughness were increased to 647 HV and 125 nm at 500 Hz due to the grain size reduction and higher incorporation of TiO_(2) nanoparticles into the Fe−Ni matrix(5.13 wt.%).Moreover,the friction coefficient and wear rate values were decreased by increasing the pulse frequency;while the saturation magnetization and coercivity values of the composite deposits were increased. 展开更多
关键词 Fe−Ni alloy coatings ELECTRODEPOSITION pulse frequency tribomechanical properties magnetic behaviors
下载PDF
Temporal evolution of atmospheric cascade glow discharge with pulsed discharge and radio frequency discharge 被引量:2
12
作者 Qianhan HAN Chenyu WU +1 位作者 Ying GUO Jianjun SHI 《Plasma Science and Technology》 SCIE EI CAS CSCD 2020年第3期101-106,共6页
Atmospheric cascade discharges with pulsed discharge and radio frequency(RF)discharge were experimentally investigated by the temporal evolution of discharge spatial profile and intensity.The indium tin oxide(ITO)coat... Atmospheric cascade discharges with pulsed discharge and radio frequency(RF)discharge were experimentally investigated by the temporal evolution of discharge spatial profile and intensity.The indium tin oxide(ITO)coated glass was employed as the transparent electrode to capture the discharge distribution above the electrode surface.It is demonstrated that in the pulsed discharge with dielectric barrier,the first discharge at the rising edge of pulse voltage is uniformly ignited and then forms an expanding plasma ring on the ITO electrode surface,which shrinks to the same diameter as that of bare stainless steel electrode with the generation of second discharge at the falling edge of pulse voltage.The discharge profiles along the electrode surface and discharge gap of the successive RF discharge are dependent on the intensity and spatial distribution of residual plasma species generated by the pulsed discharge,which is determined by the time interval between the pulsed discharge and RF discharge.It is demonstrated that the residual plasma species before the RF discharge ignition help to achieve the stable operation of RF discharge with elevated intensity. 展开更多
关键词 ATMOSPHERIC CASCADE GLOW DISCHARGE pulseD DISCHARGE radio frequency DISCHARGE
下载PDF
NEW TYPE OF WINDOWS FOR DIGITAL PULSE COMPRESSION IN FREQUENCY DOMAIN FOR BROADBAND LFM SIGNALS 被引量:3
13
作者 HuangWei FangKeying HuTe XiangJingcheng 《Journal of Electronics(China)》 2005年第2期149-152,共4页
A new type of window called combined window is designed to get higher Ratio of Mainlobe to Sidelobes (RMS) and lower Mainlobe Widening Factor (MWF). Simulation results prove that the new window can solve the contradic... A new type of window called combined window is designed to get higher Ratio of Mainlobe to Sidelobes (RMS) and lower Mainlobe Widening Factor (MWF). Simulation results prove that the new window can solve the contradiction between RMS and MWF better than classic windows. 展开更多
关键词 Linear frequency modulation WINDOWS pulse compression
下载PDF
Development of high frequency pulse power source using two powersfor TIG welding 被引量:1
14
作者 张广军 耿正 +1 位作者 吴林 梁群 《China Welding》 EI CAS 1999年第2期38-42,共5页
A high frequency pulse power source for TIG welding is developed. The structure of two powers is adopted. The by pass circuit effectively eliminates the effect of the cable equivalent inductance. The maximum frequenc... A high frequency pulse power source for TIG welding is developed. The structure of two powers is adopted. The by pass circuit effectively eliminates the effect of the cable equivalent inductance. The maximum frequency of the output pulse current reaches to 16 kHz . The base current and the peak current can be regulated separately. 展开更多
关键词 high frequency pulse TIG welding arc welding power source
下载PDF
Effect of pulse frequency on hardness characteristics of Al-Cu alloy HPVP-GTAW joints 被引量:1
15
作者 欧阳瑞洁 从保强 +1 位作者 杨明轩 齐铂金 《China Welding》 EI CAS 2015年第1期62-67,共6页
AA 2219-0 Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding (HPVP-GTAW) process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardn... AA 2219-0 Al-Cu alloy single bead welds were obtained by hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding (HPVP-GTAW) process with pulse frequency varying from 25 kHz to 70 kHz. Weld hardness characteristics which mainly depicted by microhardness and its gradient were investigated systematically. The results show that pulse frequency has a great effect on the hardness characteristics. The weld zone microhardness and its gradient with different pulse frequency present an evident fluctuant trend. The fluctuation of gradient is slight, illustrating that the mierostructure is uniform with pulse frequcncy varied from 35 kHz to 60 kHz. The fusion zone microhardness and its gradient foUow the similar trends but fluetuate greatly. Maximum value of gradient appears around the fusion boundary due to the coarse and non- uniform microstrueture. The maximum gradient at 60 kHz is only 25.5 % of that at 45 kHz. According to the study, the best hardness characteristics are achieved at 60 kHz frequency. 展开更多
关键词 high frequency pulse current microhardness gradient variable polarity gas tungsten are welding aluminum alloy
下载PDF
Effect of pulsed electromagnetic frequency on the microstructure, wear and solid erosion resistance of CrAlN coatings deposited by arc ion plating 被引量:1
16
作者 WANG Di LIN Song-sheng +5 位作者 LIU Ling-yun XUE Yu-na YANG Hong-zhi YANG Chao YANG Zhen ZHOU Ke-song 《Journal of Central South University》 SCIE EI CAS CSCD 2022年第9期3065-3076,共12页
In this work,the chromium aluminum nitride(CrAlN)coatings were prepared on TC11 titanium alloy by composite magnetic field cathodic arc ion plating with controllable pulse electromagnetic combined with permanent magne... In this work,the chromium aluminum nitride(CrAlN)coatings were prepared on TC11 titanium alloy by composite magnetic field cathodic arc ion plating with controllable pulse electromagnetic combined with permanent magnet.The effects of electromagnetic frequency on the morphology,microstructure,nano-hardness and elastic modulus of the coatings were investigated by scanning electron microscope(SEM),X-ray diffraction(XRD)and nano-indenter.This paper has mainly studied the influence of CrAlN coatings which are prepared at various electromagnetic frequencies on the wear and erosion resistance through a series of wear and solid particle erosion experiments.It was found that the deposition rate of CrAlN coatings increases with the increase of electromagnetic frequency.And CrAlN coatings all preferentially grew along the(111)crystal plane.At 16.7 Hz,with the increase of pulsed electromagnetic frequency,the hardness is the highest(23.6 GPa)and the adhesion is the highest(41.5 N).In addition,the coating deposition exhibited the best wear and solid erosion resistance at 16.7 Hz and 33.3 Hz,the friction coefficient is about 0.35,and the erosion rate is about 0.2μm/g at 30°and less than 1μm/g at 90°,respectively.These results indicate that the CrAlN coating formed at an appropriate pulsed electromagnetic frequency can achieve excellent mechanical properties,wear and solid erosion resistance. 展开更多
关键词 CrAlN coating compound magnetic field pulse electromagnetic frequency mechanical property
下载PDF
Effect of Pulse Frequency on Microstructure of 21% Cr Ferritic Stainless Steel in Pulsed Gas Tungsten Arc Welding 被引量:1
17
作者 胡绳荪 韩瑞峰 +2 位作者 申俊琦 韩俭 许海刚 《Transactions of Tianjin University》 EI CAS 2013年第2期127-129,共3页
Thin plates of 21% Cr ferritic stainless steel welded by pulsed gas tungsten arc welding at different pulse frequencies were investigated for the microstructure characteristics and hardness behavior.The welds containe... Thin plates of 21% Cr ferritic stainless steel welded by pulsed gas tungsten arc welding at different pulse frequencies were investigated for the microstructure characteristics and hardness behavior.The welds contained columnar grains in the outer part and fine equiaxed grains in the central region due to the pulsed process. 展开更多
关键词 ferritic stainless steel MICROSTRUCTURE pulse frequency
下载PDF
Spectrum for Pulse Frequency Modulation 被引量:1
18
作者 HUANG Yuan SUN Jianjun(Jinan University, Guangzhou 510632, CHN) 《Semiconductor Photonics and Technology》 CAS 1996年第3期194-198,共5页
This paper gives a spectrum expression which is simple and has a clear physical conception for pulse frequency modulation signal, and has been confirmed by an experiment simultaneously.
关键词 Spectral Analysis pulse frequency Modulation MODULATION Instanta neous frequency
下载PDF
Pulse frequency classification based on BP neural network 被引量:1
19
作者 WANG Rui WANG Xu +1 位作者 YANG Dan FU Rong 《哈尔滨工程大学学报》 EI CAS CSCD 北大核心 2006年第B07期471-473,共3页
关键词 反向神经网络 脉搏频率 中医学 分类 脉搏形式
下载PDF
Pulse-Width Pulse-Frequency Based Optimal Controller Design for Kinetic Kill Vehicle Attitude Tracking Control 被引量:3
20
作者 Xingyuan Xu Yuanli Cai 《Applied Mathematics》 2011年第5期565-574,共10页
The attitude control problem of the kinetic kill vehicle is studied in this work. A new mathematical model of the kinetic kill vehicle is proposed, the linear quadratic regulator technique is used to design the optima... The attitude control problem of the kinetic kill vehicle is studied in this work. A new mathematical model of the kinetic kill vehicle is proposed, the linear quadratic regulator technique is used to design the optimal attitude controller, and the pulse-width pulse-frequency modulator is used to shape the continuous control command to pulse or on-off signals to meet the requirements of the reaction thrusters. The methods to select the appropriate parameters of pulse-width pulse-frequency are presented in detail. Numerical simulations show that the performance of the LQR/PWPF approach can achieve good control performance such as pseudo-linear operation, high accuracy, and fast enough tracking speed. 展开更多
关键词 ATTITUDE Control Kinetic KILL Vehicle Linear QUADRATIC pulse-Width pulse-frequency
下载PDF
上一页 1 2 231 下一页 到第
使用帮助 返回顶部