期刊文献+
共找到14,798篇文章
< 1 2 250 >
每页显示 20 50 100
Multi-layer quasi-zero-stiffness meta-structure for high-efficiency vibration isolation at low frequency
1
作者 Jiahao ZHOU Jiaxi ZHOU +3 位作者 Hongbin PAN Kai WANG Changqi CAI Guilin WEN 《Applied Mathematics and Mechanics(English Edition)》 SCIE EI CSCD 2024年第7期1189-1208,共20页
An easily stackable multi-layer quasi-zero-stiffness(ML-QZS)meta-structure is proposed to achieve highly efficient vibration isolation performance at low frequency.First,the distributed shape optimization method is us... An easily stackable multi-layer quasi-zero-stiffness(ML-QZS)meta-structure is proposed to achieve highly efficient vibration isolation performance at low frequency.First,the distributed shape optimization method is used to design the unit cel,i.e.,the single-layer QZS(SL-QZS)meta-structure.Second,the stiffness feature of the unit cell is investigated and verified through static experiments.Third,the unit cells are stacked one by one along the direction of vibration isolation,and thus the ML-QZS meta-structure is constructed.Fourth,the dynamic modeling of the ML-QZS vibration isolation metastructure is conducted,and the dynamic responses are obtained from the equations of motion,and verified by finite element(FE)simulations.Finally,a prototype of the ML-QZS vibration isolation meta-structure is fabricated by additive manufacturing,and the vibration isolation performance is evaluated experimentally.The results show that the vibration isolation performance substantially enhances when the number of unit cells increases.More importantly,the ML-QZS meta-structure can be easily extended in the direction of vibration isolation when the unit cells are properly stacked.Hence,the ML-FQZS vibration isolation meta-structure should be a fascinating solution for highly efficient vibration isolation performance at low frequency. 展开更多
关键词 quasi-zero stiffness(QZS) meta-structure high efficiency low frequency vibration isolation
下载PDF
Precision measurement and suppression of low-frequency noise in a current source with double-resonance alignment magnetometers 被引量:1
2
作者 郑锦韬 张洋 +3 位作者 鱼在洋 熊志强 罗晖 汪之国 《Chinese Physics B》 SCIE EI CAS CSCD 2023年第4期35-41,共7页
Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz... Low-noise high-stability current sources have essential applications such as neutron electric dipole moment measurement and high-stability magnetometers. Previous studies mainly focused on frequency noise above 0.1 Hz while less on the low-frequency noise/drift. We use double resonance alignment magnetometers(DRAMs) to measure and suppress the low-frequency noise of a homemade current source(CS) board. The CS board noise level is suppressed by about 10 times in the range of 0.001-0.1 Hz and is reduced to 100 n A/√Hz at 0.001 Hz. The relative stability of CS board can reach2.2 × 10^(-8). In addition, the DRAM shows a better resolution and accuracy than a commercial 7.5-digit multimeter when measuring our homemade CS board. Further, by combining the DRAM with a double resonance orientation magnetometer,we may realize a low-noise CS in the 0.001-1000 Hz range. 展开更多
关键词 precision measurement current noise suppression low frequency double-resonance alignment magnetometer
下载PDF
A direct laser-synthesized magnetic metamaterial for low-frequency wideband passive microwave absorption 被引量:1
3
作者 Yihe Huang Yize Li +10 位作者 Kewen Pan Yixian Fang Kai Chio Chan Xiaoyu Xiao Chao Wei Kostya S Novoselov John Gallop Ling Hao Zhu Liu Zhirun Hu Lin Li 《International Journal of Extreme Manufacturing》 SCIE EI CAS CSCD 2023年第3期667-680,共14页
Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-ba... Microwave absorption in radar stealth technology is faced with challenges in terms of its effectiveness in low-frequency regions.Herein,we report a new laser-based method for producing an ultrawideband metamaterial-based microwave absorber with a highly uniform sheet resistance and negative magnetic permeability at resonant frequencies,which results in a wide bandwidth in the L-to S-band.Control of the electrical sheet resistance uniformity has been achieved with less than 5%deviation at 400Ωsq^(-1)and 6%deviation at 120Ωsq^(-1),resulting in a microwave absorption coefficient between 97.2%and 97.7%within a1.56–18.3 GHz bandwidth for incident angles of 0°–40°,and there is no need for providing energy or an electrical power source during the operation.Porous N-and S-doped turbostratic graphene 2D patterns with embedded magnetic nanoparticles were produced simultaneously on a polyethylene terephthalate substrate via laser direct writing.The proposed low-frequency,wideband,wide-incident-angle,and high-electromagnetic-absorption microwave absorber can potentially be used in aviation,electromagnetic interference(EMI)suppression,and 5G applications. 展开更多
关键词 laser direct writing degrees of crystallization Fe_(3)O_(4)nanoparticles wide bandwidth low frequency
下载PDF
Deformation characteristics and novel strain criteria of strainbursts induced by low-frequency cyclic disturbance 被引量:2
4
作者 Lihua Hu Minghe Ju +1 位作者 Peng Zhao Xiaozhao Li 《Deep Underground Science and Engineering》 2023年第1期52-60,共9页
Strainbursts induced by cyclic disturbance with low frequency(termed as cyclicinduced strainbursts)are major dynamic disasters during deep excavation and mining.There is currently no quantitative criterion available f... Strainbursts induced by cyclic disturbance with low frequency(termed as cyclicinduced strainbursts)are major dynamic disasters during deep excavation and mining.There is currently no quantitative criterion available for the prediction of such disastrous events.In this study,based on true triaxial experiments,we analyzed the deformation characteristics,established two novel strain criteria for the cyclic-induced strainbursts,and explained the physical meaning of these criteria.Characteristic strains for the cyclic-induced strainbursts were defined,including the control strain ε_(ctr),the strain caused by the combined dynamic and static loading ε_(sd),and the ultimate strain ε_(u) after strainbursts.As indicated by the results,the deformation evolution of the cyclic-induced strainbursts shows remarkable fatigue characteristics,which resemble that of rock subjected to cyclic loading and unloading.In other words,there are three stages during deformation evolution,namely,initial rapid growth,uniform velocity growth after several periods of disturbance,and sudden sharp growth preceding the burst.The ultimate strain ε_(u) is insensitive to the tangential static stress and disturbance amplitude,but it changes nonlinearly with disturbance frequency.From the perspective of deformation,the occurrence of a cyclic-induced strainburst is controlled by the control strainε_(ctr).Thus,a control strain criterion is proposed;that is,when the stain ε_(sd) is larger than the control strain ε_(ctr),a strainburst will be induced by cyclic disturbance.Moreover,based on the statistical results,a strain ratio criterion is proposed;that is,when the strain ratio ε_(sd)/ε_(u) is greater than 30%,a cyclic-induced strainburst will be induced. 展开更多
关键词 dynamic disturbance low frequency strainbursts strain criteria true triaxial
下载PDF
TRPV4-induced Neurofilament Injury Contributes to Memory Impairment after High Intensity and Low Frequency Noise Exposures
5
作者 YANG Yang WANG Ju +7 位作者 QUAN Yu Lian YANG Chuan Yan CHEN Xue Zhu LEI Xue Jiao TAN Liang FENG Hua LI Fei CHEN Tu Nan 《Biomedical and Environmental Sciences》 SCIE CAS CSCD 2023年第1期50-59,共10页
Objective Exposure to high intensity, low frequency noise(HI-LFN) causes vibroacoustic disease(VAD),with memory deficit as a primary non-auditory symptomatic effect of VAD. However, the underlying mechanism of the mem... Objective Exposure to high intensity, low frequency noise(HI-LFN) causes vibroacoustic disease(VAD),with memory deficit as a primary non-auditory symptomatic effect of VAD. However, the underlying mechanism of the memory deficit is unknown. This study aimed to characterize potential mechanisms involving morphological changes of neurons and nerve fibers in the hippocampus, after exposure to HILFN.Methods Adult wild-type and transient receptor potential vanilloid subtype 4 knockout(TRPV4^(-/-)) mice were used for construction of the HI-LFN injury model. The new object recognition task and the Morris water maze test were used to measure the memory of these animals. Hemoxylin and eosin and immunofluorescence staining were used to examine morphological changes of the hippocampus after exposure to HI-LFN.Results The expression of TRPV4 was significantly upregulated in the hippocampus after HI-LFN exposure. Furthermore, memory deficits correlated with lower densities of neurons and neurofilamentpositive nerve fibers in the cornu ammonis 1(CA1) and dentate gyrus(DG) hippocampal areas in wildtype mice. However, TRPV4^(-/-)mice showed better performance in memory tests and more integrated neurofilament-positive nerve fibers in the CA1 and DG areas after HI-LFN exposure.Conclusion TRPV4 up-regulation induced neurofilament positive nerve fiber injury in the hippocampus,which was a possible mechanism for memory impairment and cognitive decline resulting from HI-LFN exposure. Together, these results identified a promising therapeutic target for treating cognitive dysfunction in VAD patients. 展开更多
关键词 low frequency noise Memory impairment TRPV4 NEUROFILAMENT Nerve fibers Hippocampuslow frequency noise Memory impairment TRPV4 NEUROFILAMENT Nerve fibers HIPPOCAMPUS
下载PDF
Low-frequency oscillations in Hall thrusters 被引量:2
6
作者 魏立秋 韩亮 +1 位作者 于达仁 郭宁 《Chinese Physics B》 SCIE EI CAS CSCD 2015年第5期117-126,共10页
In this paper, we summarize the research development of low-frequency oscillations in the last few decades. The findings of physical mechanism, characteristics and stabilizing methods of low-frequency oscillations are... In this paper, we summarize the research development of low-frequency oscillations in the last few decades. The findings of physical mechanism, characteristics and stabilizing methods of low-frequency oscillations are discussed. It shows that it is unreasonable and incomplete to model an ionization region separately to analyze the physical mechanism of low-frequency oscillations. Electro-dynamics as well as the formation conditions of ionization distribution play an important role in characteristics and stabilizing of low-frequency oscillations. Understanding the physical mechanism and characteristics of low- frequency oscillations thoroughly and developing a feasible method stabilizing this instability are still important research subjects. 展开更多
关键词 low-frequency oscillations plasma discharge Hall thrusters
下载PDF
THE CHARACTERISTICS OF LOW-FREQUENCY OSCILLATIONS OVER THE SOUTH CHINA SEA 被引量:1
7
作者 林爱兰 《Journal of Tropical Meteorology》 SCIE 1998年第2期141-147,共7页
Using 1975-1993 (with 1978 missing) data of the outgoing longwave radiation (OLR), characteristics of seasonal variation of low-frequency oscillations in the South China Sea and its relation to the establishment and a... Using 1975-1993 (with 1978 missing) data of the outgoing longwave radiation (OLR), characteristics of seasonal variation of low-frequency oscillations in the South China Sea and its relation to the establishment and activity of the summer monsoon there are studied. As is shown in the result, the low-frequency oscillation in the South China Sea is much stronger in the period of summer monsoon than in that of winter monsoon and the summer monsoon there usually begins to set up in a negative phase of the first significant low-frequency oscillation for the early summer. The study also reveals that the circulation for the low-frequency oscillation during the summer monsoon in the Sea is embodied as north-south fluctuations of the ITCZ and east-west shifts of western ridge point of the West Pacific subtropical high, suggesting close correlation between the low-frequency oscillation and the active and break (decay) of the South China Sea monsoon. In the meantime. the work illustrates how the low-frequency oscillation in the South China Sea are superimposed with the seasonal variation of the general circulation. so that the summer inonsoon covers the establishment of the I st, intensification of the 2nd and 3rd the low-frequency oscillations and decay of the 4th oscillation. 展开更多
关键词 SOUTH China Sea SUMMER MONSOON low-frequency OSCILLATION
下载PDF
The low frequency oscillations of the sea surface temperature in the Equatorial Eastern Pacific and El Nino formation
8
作者 Zhou Faxiu and Yu Shenyu Ocean University of Oingdao, Qingdao, China 《Acta Oceanologica Sinica》 SCIE CAS CSCD 1989年第4期521-533,共13页
-In this paper the variations of the sea surface temperature anomalies (SSTA) in the Equatorial Eastern Pacific are analysed. The results show that there are two peaks in the spectrum. One is the low frequency oscilla... -In this paper the variations of the sea surface temperature anomalies (SSTA) in the Equatorial Eastern Pacific are analysed. The results show that there are two peaks in the spectrum. One is the low frequency oscillation with a period of 3 - 5 years, and the other is the quasi-biennial oscillation. The former shows a westward migration in the warm episode of SSTA and the latter has the opposite trend. The El Nino events will be formed while the two frquency bands are in phase in the warming stage of SSTA in the Equatorial Eastern Pacific 展开更多
关键词 Nino EI SSTA The low frequency oscillations of the sea surface temperature in the Equatorial Eastern Pacific and El Nino formation EL
下载PDF
Low Frequency Oscillations of the Heat Distribution in the Global Upper Ocean Layers
9
作者 FANG Mingqiang 《Journal of Ocean University of China》 SCIE CAS 2006年第1期35-38,共4页
The heat distributions in the upper layers of the ocean have been studied and some important low frequency oscillations (LFOs) are already found and quantified by using various characteristic factors. In this paper,... The heat distributions in the upper layers of the ocean have been studied and some important low frequency oscillations (LFOs) are already found and quantified by using various characteristic factors. In this paper, the ‘heat center' of a sea area is defined with a simple method. Then the temperature data set of the upper layer of the global ocean (from surface down to 400 m, 1955-2003) is analyzed to detect the possible LFOs. Not only some zonal LFOs, which were reported early, but also some strong LFOs of the vertical and meridional heat distribution, which might imply some physical sense, are detected. It should be noted that the similar vertical oscillation pattern can be found in the Pacific Ocean, Atlantic Ocean and Indian Ocean. Results from some preliminary studies show that the vertical LFO might be caused by the solar irradiance anomalies. This study may help reveal some unknown dynamical processes in the global oceans and may also benefit other related studies. 展开更多
关键词 upper ocean layer leat distribution low frequency oscillation
下载PDF
Characteristics of low-frequency oscillations in course of SCS summer monsoon onset
10
作者 毛江玉 谢安 +1 位作者 宋焱云 叶谦 《Acta Oceanologica Sinica》 SCIE CAS CSCD 2000年第3期65-72,共8页
Some of the low-frequency oscillation (LFO) characteristics of summer moan onset over the South China Sea (SCS) are examined based on NCEP/NCAR reanalysis data and OLR from NOAA in the period of 1979-1996. It is found... Some of the low-frequency oscillation (LFO) characteristics of summer moan onset over the South China Sea (SCS) are examined based on NCEP/NCAR reanalysis data and OLR from NOAA in the period of 1979-1996. It is found that the SCS summer monsoon is characterized by predominance of low-frequency activities with significant interannual variability closely related with onset time. The LFOs over the SCS strengthen after onset. Composite analyses for LFO components of OLR and kinetic energy indicate that the eastward propagation of LFO over the equatorial Indian Ocean and LFO coming from the western Pacific strongly affect the physical processes responsible for the SCS summer monsoon onset. The SCS is the place where the Indian Ocean LFO links with low-frequency activities over the western pacific during summer monsoon onset. 展开更多
关键词 low -frequency oscillation the South China Sea summer moan onset
下载PDF
Novel Adaptive Neural Controller Design Based on HVDC Transmission System to Damp Low Frequency Oscillations and Sub Synchronous Resonance
11
作者 Samad Goli Ahad Goli Naser Taheri 《Energy and Power Engineering》 2015年第10期451-464,共14页
This paper presents the effect of the high voltage direct current (HVDC) transmission system based on voltage source converter (VSC) on the sub synchronous resonance (SSR) and low frequency oscillations (LFO) in power... This paper presents the effect of the high voltage direct current (HVDC) transmission system based on voltage source converter (VSC) on the sub synchronous resonance (SSR) and low frequency oscillations (LFO) in power system. Also, a novel adaptive neural controller based on neural identifier is proposed for the HVDC which is capable of damping out LFO and sub synchronous oscillations (SSO). For comparison purposes, results of system based damping neural controller are compared with a lead-lag controller based on quantum particle swarm optimization (QPSO). It is shown that implementing adaptive damping controller not only improves the stability of power system but also can overcome drawbacks of conventional compensators with fixed parameters. In order to determine the most effective input of HVDC system to apply supplementary controller signal, analysis based on singular value decomposition is performed. To evaluate the performance of the proposed controller, transient simulations of detailed nonlinear system are considered. 展开更多
关键词 SYNCHRONOUS RESONANCE Neural Network Damping Controller Quantum Particle SWARM Optimization HVDC Transmission Systems low frequency oscillations
下载PDF
Numerical study of low-frequency discharge oscillations in a 5kW Hall thruster
12
作者 Le YANG Tianping ZHANG +1 位作者 Juanjuan CHEN Yanhui JIA 《Plasma Science and Technology》 SCIE EI CAS CSCD 2018年第7期145-151,共7页
A two-dimensional particle-in-cell plasma model is built in the R-Z plane to investigate the low- frequency plasma oscillations in the discharge channel of a 5 kW LHT-140 Hall thruster. In addition to the elastic, exc... A two-dimensional particle-in-cell plasma model is built in the R-Z plane to investigate the low- frequency plasma oscillations in the discharge channel of a 5 kW LHT-140 Hall thruster. In addition to the elastic, excitation, and ionization collisions between neutral atoms and electrons, the Coulomb collisions between electrons and electrons and between electrons and ions are analyzed. The sheath characteristic distortion is also corrected. Simulation results indicate the capability of the built model to reproduce the low-frequency oscillation with high accuracy. The oscillations of the discharge current and ion density produced by the model are consistent with the existing conclusions. The model predicts a frequency that is consistent with that calculated by the zero-dimensional theoretical model. 展开更多
关键词 Hall thruster low-frequency oscillations SHEATH Coulomb collisions
下载PDF
The Propagation of Disturbances Excited by Low-Frequency Oscillations in the Tropics
13
作者 卢佩生 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 1993年第3期287-295,共9页
The propagation of disturbances excited by low-frequency oscillations in the tropics is investigated by applying the theory of wave packet dynamics. For simplicity, a linearized barotropic model is adopted and the zon... The propagation of disturbances excited by low-frequency oscillations in the tropics is investigated by applying the theory of wave packet dynamics. For simplicity, a linearized barotropic model is adopted and the zonal circulation is taken as basic current. Suppose that the disturbances or waves are superimposed on jet-like westerly basic cur-rent and excited by the forcing in the tropics. We have (1) only the eastward propagating (m>0, n>0 and σ>0) low-frequency disturbances and the stationary (σ = 0) waves can propagate into the middle and high latitudes in the Northern Hemisphere; the others, such as the westward propagating low-frequency wave (m>0, n<0, σ<0) and the high-frequency waves, are restricted only in the vicinity of source region; (2) a stationary wave (σ = 0) reaches a given latitude even more quickly than some low-frequency ones (σ>0) due to the fact that the group velocity of stationary wave is larger; (3) there is a whole wave train excited by the forcing in the tropics and extended into the middle and high latitudes, if the amplitude of the source is independent on time, especially, the low-frequency wave (σ > 0) is of travelling type propagating along the ray; (4) if the source lasts only for an interval of time, namely, its amplitude also has the character of low-frequency oscillation, the excited wave train is not always a whole one, but is restricted in the vicinity of source region in the beginning, extended from the source region to the middle and high latitudes in its saturated stage, after that it gradually becomes weaker and weaker and is detectable only in some area at high latitude, and eventually disappears. Undoubtedly, case (4) is closer to the reality, even though case (3) gives a more impressive wavy pattern. 展开更多
关键词 Wave packet. low-frequency oscillation Quasi-stationary source Non-stationary source
下载PDF
Production of super-high strength aluminum alloy billets by low frequency electromagnetic casting 被引量:6
14
作者 张海涛 崔建忠 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2011年第10期2134-2139,共6页
The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by th... The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods.Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting(LFEC) process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field:an entirely changed direction and remarkably increased velocity of melt flow;a uniform distribution and a decreased gradient of temperature;elevated isothermal lines;a reduced sump depth;decreased stress and plastic deformation.Further,the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field. 展开更多
关键词 super-high strength aluminum alloy low frequency electromagnetic casting DC casting macro-physical field CRACK MICROSTRUCTURE
下载PDF
Effect of Acute Low Temperature Stress on Oxygen Consumption Rate and Respiration Frequency in Silurus meridionalis and Pelteobag vachelli 被引量:2
15
作者 彭姜岚 曹振东 付世建 《Agricultural Science & Technology》 CAS 2007年第3期73-78,共6页
The objective of the study was to explore the effect of acute low temperature stress on VO2 and Vf of Silurus meridionalis and Pelteobag vachelli after 10 minutes cold water bath with different temperature.The investi... The objective of the study was to explore the effect of acute low temperature stress on VO2 and Vf of Silurus meridionalis and Pelteobag vachelli after 10 minutes cold water bath with different temperature.The investigation was operated under the temperature of 24 ℃.It was found that the VO2 and Vf of Silurus meridionalis after 6 and 0 ℃ stress showed a decrease-increase-decrease trend while other groups showed a rapid increase then slowly recovery trend.The VO2 and Vf of Pelteobag vachelli after 0 ℃stress showed a decrease-increase-decrease trend while other groups showed an increase then slowly recovery process.It was suggested that Pelteobag vachelli was more adaptive to acute cold stress,but it cost more energy adapting to cold stress compared to Silurus meridionalis. 展开更多
关键词 Pelteobag vachelli Richardson Silurus meridionalis Chen Oxygen consumption VO2 Ventilation frequency (Vf) Acute low temperature stress
下载PDF
A wideband low-phase-noise LC VCO for DRM/DAB frequency synthesizer
16
作者 雷雪梅 王志功 王科平 《Journal of Southeast University(English Edition)》 EI CAS 2010年第4期528-531,共4页
The wideband CMOS voltage-controlled oscillator(VCO)with low phase noise and low power consumption is presented for a DRM/DAB(digital radio mondiale and digital audio broadcasting)frequency synthesizer.In order to... The wideband CMOS voltage-controlled oscillator(VCO)with low phase noise and low power consumption is presented for a DRM/DAB(digital radio mondiale and digital audio broadcasting)frequency synthesizer.In order to obtain a wide band and a large tuning range,a parallel switched capacitor bank is added in the LC tank.The proposed VCO is implemented in SMIC 0.18-μm RF CMOS technology and the chip area is 750 μm×560 μm,including the test buffer circuit and the pads.Measured results show that the tuning range is 44.6%;i.e.,the frequency turning range is from 2.27 to 3.57 GHz.The measured phase noise is-122.22 dBc/Hz at a 1 MHz offset from the carrier.The maximum power consumption of the core part is 6.16 mW at a 1.8 V power supply. 展开更多
关键词 CMOS voltage-controlled oscillator switched capacitor bank MOS varactors WIDEBAND low phase noise DRM/DAB frequency synthesizer
下载PDF
Nested Miller Active-Capacitor Frequency Compensation for Low-Power Three-Stage Amplifiers 被引量:1
17
作者 马海峰 周锋 +1 位作者 牛祺 吕昌辉 《Journal of Semiconductors》 EI CAS CSCD 北大核心 2008年第9期1698-1702,共5页
A new frequency compensation technique for low-power, area-efficient multistage amplifiers is introduced. Using nested active capacitors, our scheme achieves better bandwidth-to-power and slew-rate-to-power performanc... A new frequency compensation technique for low-power, area-efficient multistage amplifiers is introduced. Using nested active capacitors, our scheme achieves better bandwidth-to-power and slew-rate-to-power performances than previous works. Implemented in standard 0.35μm CMOS technology, our three-stage amplifier achieves 105dB DC gain, 3.3M GBW,68 phase margin, and 2.56V/μs average slew rate under a 150pF capacitive load. All of these are realized with only 40μW power consumption under a 2V power supply,with very small compensation capacitors. 展开更多
关键词 multistage amplifier frequency compensation low power
下载PDF
The Seasonal Climate and Low Frequency Oscillation in the Simulated Mid-Holocene Megathermal Climate 被引量:12
18
作者 王会军 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2000年第3期445-457,共13页
The mid—Holocene climate about 6000 years ago was simulated by using the atmospheric general circulation model. The orbital parameters for 6 ka BP (before present) were prescribed and other forcing factors were set i... The mid—Holocene climate about 6000 years ago was simulated by using the atmospheric general circulation model. The orbital parameters for 6 ka BP (before present) were prescribed and other forcing factors were set in the modern conditions. Results show that the large—scale climate change in the African—Asian monsoon areas during the summer—time is strongly compared to the present climate, while the changes in other seasons and regions are generally weak. The results also revealed the change of the low frequency oscillation in the atmosphere. Key words Seasonal climate - Low frequency oscillation - Mid—Holocene This research was jointly supported by the National Natural Science Foundation of China (NSFC) key project “ Variation of Paleo—environment over East Asia and Its Dynamic Relation with the Global Change” under contract 49894170 and the NSFC project “ Coupling of the AGCM with an Biome Model and the Simulation on the Mid-Holocene Climate” under contract 49975018. 展开更多
关键词 Seasonal climate low frequency oscillation Mid—Holocene
下载PDF
Dust Storms in North China in 2002: A Case Study of the Low Frequency Oscillation 被引量:3
19
作者 范可 王会军 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2007年第1期15-23,共9页
The low frequency oscillation in both hemispheres and its possible role in the dust weather storm events over North China in 2002 are analyzed as a case study. Results show that the Aleutian Low is linked with the Cir... The low frequency oscillation in both hemispheres and its possible role in the dust weather storm events over North China in 2002 are analyzed as a case study. Results show that the Aleutian Low is linked with the Circumpolar Vortex in the Southern Hemisphere on a 30-60-day oscillation, with a weak Circumpolar Vortex tending to deepen the Aleutian Low which may be helpful for the generation of dust storm events. The possible mechanism behind this is the inter-hemispheric interaction of the mean meridional circulation, with the major variability over East Asia. The zonal mean westerly wind at high latitudes of the Southern Hemisphere in the upper level troposphere may lead that of the Northern Hemisphere, which then impacts the local circulation in the Northern Hemisphere. Thus, the low frequency oscillation teleconnection is one possible linkage in the coupling between the Southern Hemisphere circulation and dust events over North China. However, the interannual variation of the low frequency oscillation is unclear. 展开更多
关键词 dust storm events low frequency oscillation mean meridional circulation and local circulation relationship
下载PDF
Active Low-frequency Vertical Vibration Isolation System for Precision Measurements 被引量:5
20
作者 WU Kang LI Gang +1 位作者 HU Hua WANG Lijun 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2017年第1期164-169,共6页
Low-fi'equency vertical vibration isolation systems play important roles in precision measurements to reduce seismic and environmental vibration noise. Several types of active vibration isolation systems have been de... Low-fi'equency vertical vibration isolation systems play important roles in precision measurements to reduce seismic and environmental vibration noise. Several types of active vibration isolation systems have been developed. However, few researches focus on how to optimize the test mass install position in order to improve the vibration transmissibility. An active low-frequency vertical vibration isolation system based on an earlier instrument, the Super Spring, is designed and implemented. The system, which is simple and compact, consists of two stages: a parallelogram-shaped linkage to ensure vertical motion, and a simple spring-mass system. The theoretical analysis of the vibration isolation system is presented, including terms erroneously ignored before. By carefully choosing the mechanical parameters according to the above analysis and using feedback control, the resonance frequency of the system is reduced from 2.3 to 0.03 Hz, a reduction by a factor of more than 75. The vibration isolation system is installed as an inertial reference in an absolute gravimeter, where it improved the scatter of the absolute gravity values by a factor of 5. The experimental results verifies the improved performance of the isolation system, making it particularly suitable for precision experiments. The improved vertical vibration isolation system can be used as a prototype for designing high-performance active vertical isolation systems. An improved theoretical model of this active vibration isolation system with beam-pivot configuration is proposed, providing fundamental guidelines for vibration isolator design and assembling. 展开更多
关键词 vibration isolation VERTICAL low frequency ACTIVE
下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部