We analyze the frequencies of three known roAp stars,TIC 96315731,TIC 72392575,and TIC 318007796,using the light curves from the Transiting Exoplanet Survey Satellite.For TIC 96315731,the rotational and pulsational fr...We analyze the frequencies of three known roAp stars,TIC 96315731,TIC 72392575,and TIC 318007796,using the light curves from the Transiting Exoplanet Survey Satellite.For TIC 96315731,the rotational and pulsational frequencies are 0.1498360 day^(-1)and 165.2609 day^(-1),respectively.In the case of TIC 72392575,the rotational frequency is 0.25551 day^(-1).We detect a quintuplet of pulsation frequencies with a center frequency of135.9233 day^(-1),along with two signals within the second pair of rotational sidelobes of the quintuplet separated by the rotation frequency.These two signals may correspond to the frequencies of a dipole mode.In TIC318007796,the rotational and pulsational frequencies are 0.2475021 day^(-1),192.73995 day^(-1),and196.33065 day^(-1),respectively.Based on the oblique pulsator model,we calculate the rotation inclination(i)and magnetic obliquity angle(b)for the stars,which provide the geometry of the pulsation modes.Combining the phases of the frequency quintuplets,the pulsation amplitude and phase modulation curves,and the results of spherical harmonic decomposition,we conclude that the pulsation modes of frequency quintuplets in TIC96315731,TIC 72392575,and TIC 318007796 correspond to distorted dipole mode,distorted quadrupole mode,and distorted dipole mode,respectively.展开更多
In this paper Pi2 pulsations at Zhongshan Station of Antarctica are analyzed from October 1 - 31, 1996. Their characteristics e. g. occurrence frequency,frequency, and polarization are studied. The characteristics of ...In this paper Pi2 pulsations at Zhongshan Station of Antarctica are analyzed from October 1 - 31, 1996. Their characteristics e. g. occurrence frequency,frequency, and polarization are studied. The characteristics of Pi2 pulsations are summerized as follows: (1 ) Pi2 pulsations at Zhongshan Station usually take place from 2000 MLT to 0200 MLT; the main frequencies are between 6. 79 mHz and 13. 58mHZ; (2 ) Pi2 pulsations with low frequencies are dominent. The range of main frequencies becomes narrow at midnight; (3) The Polarization of Pi2 pulsations are almost linear; (4) About the orientation of major axes the NW-SE direction is dominent before 2200 MLT and NE-SW is dominent after 2200 MLT. The generation mechanism of Pi2 pulsations at Zhongshan Station is discussed theoretically.展开更多
In this paper Pc3 pulsations at Great Wall Station of Antarctica are analyzed statistically from August 16 to November 20,1990.The occurrence frequency,frequency and polarization are studied for Pc3 pulsation events.T...In this paper Pc3 pulsations at Great Wall Station of Antarctica are analyzed statistically from August 16 to November 20,1990.The occurrence frequency,frequency and polarization are studied for Pc3 pulsation events.The mechanisms of excitation and propagation of Pc3 pulsations at Great Wall Station are discussed theoretically.展开更多
In this paper Pi2 pulsation events at Great Wall Station of Antarctica are analyzed from August 16,1990 to November 20,1990.Their main characteristics e. g.occurrence frequency, frequency,and polarizations are recogni...In this paper Pi2 pulsation events at Great Wall Station of Antarctica are analyzed from August 16,1990 to November 20,1990.Their main characteristics e. g.occurrence frequency, frequency,and polarizations are recognize. The mechanism of excitation for Pi2 pulsations at Great Wall Station is here discussed theoretically.展开更多
A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of t...A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of the pumping station in both the time domain and the frequency domain. The pressure pulsation field of the whole flow passage was structured on the basis of pressure pulsations recorded at some locations of the physical model test. Dynamic time-history analysis of the pump house under pressure pulsations was carried out. At the same time, according to spectrum characteristics of the pressure pulsations at measuring points and results of free vibration characteristics analysis of the pump house, the spectrum analysis method of random vibration was used to calculate dynamic responses of the pump house. Results from both methods are consistent, which indicates that they are both reasonable. The results can be used for reference in anti-vibration safety evaluation of the Huaiyin third pumping station.展开更多
Two induction magnetometers have been installed at Zhongshan Station and Davis Station, Antarctica respectively. We adopt with cross-spectral analysis technique to analyze the data of the two induction magnetometers, ...Two induction magnetometers have been installed at Zhongshan Station and Davis Station, Antarctica respectively. We adopt with cross-spectral analysis technique to analyze the data of the two induction magnetometers, in June, September,December 1996 and March 1997. to investigate the Pc3 frequency range pulsation occurrence and propagation characteristics in the cusp latitudes. The results are summarized as following:At Zhongshan-Davis Stations, the Pc3 frequency range pulsations occur mainly around the local noon/ local magnetic noon and local magnetic midnight respectively. In daytime, the pulsations have a seasonal variation in amplitude, occurrence and temporal range, all of them are sma1lest in winter. But in nighttime, the pulsations have no such a variation. The pu1sation amplitude in nighttime is much larger than the one in daytime all oveI the year. The pulsation propagating direction is mainly western in daytime and irregularly in nighttime. It can be thought that the different sources of the pulsation and the ionospheric electric conductivity are mainly responsible for these characteristics.展开更多
In this paper the data of geomagnetic pulsations at Zhongshan Station from February 3 to Novernber 30 in 1996 are analyzed in ordcr to study polarization characteristics of Zhongshan Station Pc3 pulsations which compr...In this paper the data of geomagnetic pulsations at Zhongshan Station from February 3 to Novernber 30 in 1996 are analyzed in ordcr to study polarization characteristics of Zhongshan Station Pc3 pulsations which comprises the cusp Pc3 pulsation and the nightside Pc3 pulsation. For the cusp Pc3 pulsation. the right-handed polarization is always dominant. But their orientation of major axes of polarizations changes with season, NW-SE is dominant in summer and NE-SW in winter. For the nightside Pc3 pulsation,the right-handed with NE-SW is always dominant before midnight. But the left-handed with the mixing orientation of major axes is dominant in summer and the NE-SW with the mixing polarization sense is dominant in winter after midnight. It means that the two types of Zongshan Station Pc3 pulsations have different sources.展开更多
δScuti(δSct)stars are potential distance tracers for studying the Milky Way structure.We conduct a comprehensive analysis of the period-luminosity(PL)and period-luminosity-metallicity(PLZ)relations forδSct stars,in...δScuti(δSct)stars are potential distance tracers for studying the Milky Way structure.We conduct a comprehensive analysis of the period-luminosity(PL)and period-luminosity-metallicity(PLZ)relations forδSct stars,integrating data from the Zwicky Transient Facility,the Transiting Exoplanet Survey Satellite,Large Sky Area Multi-Object Fiber Spectroscopic Telescope,Apache Point Observatory Galactic Evolution Experiment,and Gaia.To mitigate the impact of the Gaia parallax zero point offset,we applied a correction method,determining the optimal zero point value to be zp(?)=35±2μas.Using the three best bands,by varying the parallax error threshold,we found that the total error of the PLR zero point was minimized to 0.9%at a parallax error threshold of 6%.With this threshold,we derived the PL and PLZ relations for nine bands(from optical to mid-infrared)and five Wesenheit bands.Through our analysis,we conclude that the influence of metallicity on the PLR ofδSct stars is not significant,and the differences across various bands are minimal.展开更多
Simultaneous measurements from THEMIS spacecraft, GOES11 and ground stations （Canadian Array for Realtime Investiga tions of Magnetic Activity or CARISMA, and 210 magnetic meridian or MM） on March 18, 2009 allow the...Simultaneous measurements from THEMIS spacecraft, GOES11 and ground stations （Canadian Array for Realtime Investiga tions of Magnetic Activity or CARISMA, and 210 magnetic meridian or MM） on March 18, 2009 allow the study of dynamic processes in the nearEarth magnetotail and corresponding Pi2 pulsations on the ground in great detail. Fast earthward flows along with traveling Alfv6n waves and fast mode waves in the Pi2 band were observed by three Time History of Events and Macroscale Interactions during Substorms （THEM/S） probes （P3, P4 and P5） in the nearEarth plasmasbeet. At the mid to highlatitude nightside, the CARISMA stations located near the foot points of the three probes recorded Pi2s with two periods, about 80 s after the earthward fast flows observed by the P4 probe. The longperiod Pi2 （140-150 s） belongs to the transient response Pi2 （TR Pi2）, since the travel time of the Alfv6n waves between the plasma sheet and CARISMA stations is very close to half the period of the longperiod Pi2. The shortperiod Pi2 （60-80 s） has the same period band as the perpendicular velocity of the fast flows, which indicates that it may relate to the inertial current caused by periodic braking of the earthward fast flows. The 210 MM stations located at the lowlatitude duskside also observed Pi2s with the same start time, waveform and frequency, about 120 s after the earthward fast flows. Strong poloidal oscillations are shown by GOES11 （23 MLT） and the compressional component （Bb） is highly correlated with H components of the 210 MM stations, whereas the other two components （Br and Be） are not. These results confirm that the lowlatitude Pi2s are generated by cavity mode resonance, which is driven by an impulsive broadband source in the nearEarth magnetotail.展开更多
In this paper, we give a rigorous mathematical and complete parameter analysis for the rheodynamic model of cardiac and obtain the conditions and parameter region for global existence and uniqueness of limit cycle and...In this paper, we give a rigorous mathematical and complete parameter analysis for the rheodynamic model of cardiac and obtain the conditions and parameter region for global existence and uniqueness of limit cycle and the global bifurcation diagram of limit cycles. We also discuss the resonance phenomenons of the perturbed system.展开更多
Chinese coal reservoirs are characterized by low pressure and low permeability,which need to be enhanced so as to increase production.However,conventional methods for permeability enhancement can only increase the per...Chinese coal reservoirs are characterized by low pressure and low permeability,which need to be enhanced so as to increase production.However,conventional methods for permeability enhancement can only increase the permeability in fractures,but not the ultra-low permeability in coal matrices.Attempts to enhance such impermeable structures lead to rapid attenuation of gas production,especially in the late stage of gas extraction.Thermal stimulation by injecting high-temperature steam is a promising method to increase gas production.The critical scientific challenges that still hinder its widespread application are related to the evolution law of permeability of high-temperature steam in coal and the thermal deformation of coal.In this study,an experimental approach is developed to explore the high-temperature steam seepage coupled with the thermal deformation in coal under triaxial stress.The tests were conducted using cylindrical coal specimens of?50 mm×100 mm.The permeability and thermal strain in coal were investigated when high-temperature steam was injected at151.11,183.20,213.65,and 239.76°C.The experimental results reveal for the first time that as the amount of injected fluid increases,the steam permeability shows periodic pulsation changes.This paper introduces and explains the main traits of this discovery that may shed more light on the seepage phenomenon.When the injected steam temperature increases,the amplitude of pulsating permeability decreases,whereas the frequency increases;meanwhile,the period becomes shorter,the pulsation peak appears earlier,and the stabilization time becomes longer.The average peak permeability shows a“U-shaped”trend,decreasing first and then increasing as the steam temperature increases.Meanwhile,with the extension of steam injection time,the axial,radial,and volumetric strains of coal show a stage-wise expansion characteristic at different temperatures of steam injection,except for the radial strains at 151.11°C.A two-phase flow theory of gas–liquid is adopted to elucidate the mechanism of pulsating seepage of steam.Moreover,the influencing mechanism of inward and outward thermal expansion on the permeability of coal is interpreted.The results presented in this paper provide new insight into the feasibility of thermal gas recovery by steam injection.展开更多
By large-scale cold mold experiments,pressure pulsation signals within the jet influence zone of riser reactor are processed by using Hilbert-Huang analysis(HHT)in this study.Effects of different jet forms and operati...By large-scale cold mold experiments,pressure pulsation signals within the jet influence zone of riser reactor are processed by using Hilbert-Huang analysis(HHT)in this study.Effects of different jet forms and operating conditions on the intrinsic mode function(IMF)energy and Hilbert-Huang spectrum are compared.Results show that the IMF energy and Hilbert-Huang spectrum of pressure pulsation signals show significant differences under the influence of upward and downward jets.Moreover,the change of jet velocity will also lead to significant changes in IMF energy and Hilbert-Huang spectrum.Among them,energy values and energy proportions corresponding to high-frequency pressure pulsations show a good correlation with the jet velocity.On this basis,energy value and energy proportion data in the high frequency range of the original pressure signal are clustered and analyzed by using the K-means clustering algorithm.Based on clustering results,the jet influence zone of riser can be defined into three regions.From partitioning results,it is found that the introduction of downward inclined jets could effectively improve the gas-solid mixing in the feed injection zone of riser.展开更多
Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater mani...Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater manipulator with different postures using the user-defined function (UDF) method. The lift coefficient (C_(L)), drag coefficient (C_(D)), and vortex shedding of the underwater manipulator in single-and dualarm forms were obtained. Results indicated that the maximum increase in the lift and drag coefficients subjected to the pulsation parameters was 24.45%and 28%, respectively, when the fluid flowed past a single arm. Compared with the single arm, the lift and drag coefficients of the arms were higher than those of the single arm when arm 2 was located upstream. Additionally, the pulsation frequency had no obvious effect on the manipulator, but the C_(L) and C_(D) of arm 2 showed an obvious increasing trend with an increase in pulsation amplitude. Meanwhile, when arm 2 was located downstream, the C_(L) and C_(D) of arm 2 were reduced by 16.38%and 1.15%, respectively, with an increase in the pulse frequency,and the maximum increase in the lift and dragcoefficients was 33.33%and 16.78%,respectively,with increasing pulsation amplitude.Moreover, the downstream wake morphology changed significantly, and a combined vortex phenomenon appeared. Finally, a theoretical basis for examining the hydrodynamic characteristics of marine engineering equipment was established to aid future marine resource exploitation.展开更多
This study systematically investigated the effects of different gas stove structures on flame combustion characteristics using spectral diagnostic techniques,aiming to provide optimized design guidelines for clean ene...This study systematically investigated the effects of different gas stove structures on flame combustion characteristics using spectral diagnostic techniques,aiming to provide optimized design guidelines for clean energy applications.To explore the combustion behaviors of various gas stove structures,UV cameras,high-speed cameras,and K-type thermocouples were employed to measure parameters such as flame OH radicals(OH*),flame morphology,pulsation frequency,flame temperature,and heat flux.The results demonstrate that flame stability was achieved at an inner/outer cover flow rate ratio of 0.5/4.0 L/min,beyond which further flow rate increases led to reduced combustion efficiency.Compared to covered stoves,top-uncovered stove exhibited 5.5%and 12.4%higher temperatures at the inner and outer covers,respectively,along with a 35%increase in heat flux.Comprehensive analysis revealed an approximately 20%enhancement in overall flame intensity.The experimental results show that top-uncovered gas stoves exhibit higher flame intensity,greater combustion efficiency,and overall higher stove efficiency.In contrast,covered gas stoves feature a more controllable and stable flame with a gentler temperature rise.This study underscores the importance of optimizing gas stove designs to enhance combustion efficiency and reduce emissions,contributing to the transition from fossil fuels to renewable energy sources and promoting sustainable development.展开更多
The present work deals with the numerical study of the two-phase flow pattern and heat transfer characteristics of single-loop pulsating heat pipes(PHPs)under three modified surfaces(superhydrophilic evaporation secti...The present work deals with the numerical study of the two-phase flow pattern and heat transfer characteristics of single-loop pulsating heat pipes(PHPs)under three modified surfaces(superhydrophilic evaporation section paired with superhydrophilic,superhydrophobic,and hybrid condensation section).The Volume of Fluid(VOF)model was utilized to capture the phase-change process within the PHPs.The study also evaluated the influence of surface wettability on fluid patterns and thermo-dynamic heat transfer performance under various heat fluxes.The results indicated that the effective nucleation and detachment of droplets are critical factors influencing the thermal performance of the PHPs.The overall heat transfer performance of the superhydrophobic surface was significantly improved at low heat flux.Under medium to high heat flux,the superhydrophilic condensation section exhibits a strong oscillation effect and leads to the thickening of the liquid film.In addition,the hybrid surface possesses the heat transfer characteristics of both superhydrophilic and superhydrophobic walls.The hybrid condensation section exhibited the lowest thermal resistance by 0.45 K/W at the heat flux of 10731 W/m^(2).The thermal resistance is reduced by 13.1%and 5.4%,respectively,compared to the superhydrophobic and superhydrophilic conditions.The proposed surface-modification method for achieving highly efficient condensation heat transfer is helpful for the design and operation of device-cooling components.展开更多
The arterial pulse tapping artifact,known as Aslanger’s sign,is an electrocardiographic artifact resulting from the transmission of arterial pulsation onto the limb electrodes of the standard 12-lead electrocardiogra...The arterial pulse tapping artifact,known as Aslanger’s sign,is an electrocardiographic artifact resulting from the transmission of arterial pulsation onto the limb electrodes of the standard 12-lead electrocardiograph(ECG)which are placed near the radial or posterior tibial arteries.[1-16]This electromechanical artifact is of cardiac origin and is synchronous with the cardiac cycle.[17]Nearly all reported cases of Aslanger’s sign exhibit an unusual waveform morphology in all 12 leads except one limb lead.[1-14,16]However,we previously reported a case of Aslanger’s sign that showed distorted waveforms from the ST to TP segments observed only in five limb leads among 12 leads.展开更多
This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary ...This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary conditions,the system is subject to the combined external lateral loads and internal pulsating fluid excitations.The nonlinear dynamic model is established with the Euler-Lagrange equations and then systematically discretized via the Galerkin method.The multi-scale analysis reveals how material properties and geometric imperfections influence the internal resonance.Particular emphasis is placed on elucidating,through the modal energy analysis,the energy exchange mechanisms between the first two vibration modes.展开更多
Achieving broadband solar thermal absorption via dilute nanofluids is still a daunting challenge since the absorption peaks of common metal particles are usually located in the visible part of the radiation spectrum.T...Achieving broadband solar thermal absorption via dilute nanofluids is still a daunting challenge since the absorption peaks of common metal particles are usually located in the visible part of the radiation spectrum.This paper aims to present the results of experimental investigations on the thermal performance of heat pipe-type evacuated solar collectors.The experimented system consists of 15 tubes,providing the hot nanofluid to 100-L storage in a closed flow loop.The solar collector with a gross area of 2.1 m^(2)is part of the solar hot water test system located in Baghdad-Iraq.Al2O3 nanofluid at 0.5%volume concentration in water as working fluid was used in three flow rates of 3.3,6.6,and 10 L/min over two months,March and April.The experimental results indicated that maximum solar irradiation was 1070 and 1270 W/m^(2)in March and April,respectively.The maximum daily average of rate heat gain 11,270 and 12,040 W was recorded in March and April,respectively.In terms of the best operational flow rate,the system performs better at 3.3 L/min nanofluid flow rate.For the considered study period,the average monthly maximum energy efficiencies of the solar collector in March and April were 86%and 80%,respectively.展开更多
The volute tongue,as the crucial component inducing rotor-stator interaction,is detrimental to unsteady pressure pulsations of centrifugal pumps.In the present paper,to investigate the effect of the volute tongue cut ...The volute tongue,as the crucial component inducing rotor-stator interaction,is detrimental to unsteady pressure pulsations of centrifugal pumps.In the present paper,to investigate the effect of the volute tongue cut on pressure pulsations of a low specific speed centrifugal pump,three volute tongues are obtained through twice cuts,named cases 1,2,3.Twenty measuring points are evenly mounted on periphery of the volute casing to obtain unsteady pressure signals using high response transducers.Pressure amplitudes at the blade passing frequency fBPF and root mean square(rms)values in 0 Hz-500 Hz frequency band are applied to evaluate the cutting effect.Results show that pressure spectrum is significantly affected by the volute tongue cut,especially for the component at fBPF.For different measuring points,influences of the volute tongue cut on three cases are not identical.From nns values,it is evident that cutting the volute tongue will lead to pressure energy increasing for most of the concerned measuring points,especially for the points at the far away region from the volute tongue.Finally,from comparison with the original shape case 1,the averaged increment of the twenty points is more than 20%.So it is concluded that for this type centrifugal pump,cutting the volute tongue is not reasonable considering low pressure pulsation requirement.展开更多
基金Funding for the TESS mission is provided by the NASA Explorer Programsupport of the National Natural Science Foundation of China(NSFC,grant Nos.U2031204,12373038,12163005,and 12288102)+1 种基金the science research grants from the China Manned Space Project with No.CMSCSST-2021-A10the Natural Science Foundation of Xinjiang Nos.2022D01D85 and 2022TSYCLJ0006。
文摘We analyze the frequencies of three known roAp stars,TIC 96315731,TIC 72392575,and TIC 318007796,using the light curves from the Transiting Exoplanet Survey Satellite.For TIC 96315731,the rotational and pulsational frequencies are 0.1498360 day^(-1)and 165.2609 day^(-1),respectively.In the case of TIC 72392575,the rotational frequency is 0.25551 day^(-1).We detect a quintuplet of pulsation frequencies with a center frequency of135.9233 day^(-1),along with two signals within the second pair of rotational sidelobes of the quintuplet separated by the rotation frequency.These two signals may correspond to the frequencies of a dipole mode.In TIC318007796,the rotational and pulsational frequencies are 0.2475021 day^(-1),192.73995 day^(-1),and196.33065 day^(-1),respectively.Based on the oblique pulsator model,we calculate the rotation inclination(i)and magnetic obliquity angle(b)for the stars,which provide the geometry of the pulsation modes.Combining the phases of the frequency quintuplets,the pulsation amplitude and phase modulation curves,and the results of spherical harmonic decomposition,we conclude that the pulsation modes of frequency quintuplets in TIC96315731,TIC 72392575,and TIC 318007796 correspond to distorted dipole mode,distorted quadrupole mode,and distorted dipole mode,respectively.
文摘In this paper Pi2 pulsations at Zhongshan Station of Antarctica are analyzed from October 1 - 31, 1996. Their characteristics e. g. occurrence frequency,frequency, and polarization are studied. The characteristics of Pi2 pulsations are summerized as follows: (1 ) Pi2 pulsations at Zhongshan Station usually take place from 2000 MLT to 0200 MLT; the main frequencies are between 6. 79 mHz and 13. 58mHZ; (2 ) Pi2 pulsations with low frequencies are dominent. The range of main frequencies becomes narrow at midnight; (3) The Polarization of Pi2 pulsations are almost linear; (4) About the orientation of major axes the NW-SE direction is dominent before 2200 MLT and NE-SW is dominent after 2200 MLT. The generation mechanism of Pi2 pulsations at Zhongshan Station is discussed theoretically.
文摘In this paper Pc3 pulsations at Great Wall Station of Antarctica are analyzed statistically from August 16 to November 20,1990.The occurrence frequency,frequency and polarization are studied for Pc3 pulsation events.The mechanisms of excitation and propagation of Pc3 pulsations at Great Wall Station are discussed theoretically.
文摘In this paper Pi2 pulsation events at Great Wall Station of Antarctica are analyzed from August 16,1990 to November 20,1990.Their main characteristics e. g.occurrence frequency, frequency,and polarizations are recognize. The mechanism of excitation for Pi2 pulsations at Great Wall Station is here discussed theoretically.
基金supported by the National Science and Technology Support Program of China (Program for theEleventh Five-Year Plan, Grant No. 2006BAB04A03)the National Natural Science Foundation of China(Grant No. 10702019)
文摘A 3D finite element model of the Huaiyin third pumping station of the Eastern Route of the South-to-North Water Transfer is described in this paper. Two methods were used in the calculation and vibration analysis of the pumping station in both the time domain and the frequency domain. The pressure pulsation field of the whole flow passage was structured on the basis of pressure pulsations recorded at some locations of the physical model test. Dynamic time-history analysis of the pump house under pressure pulsations was carried out. At the same time, according to spectrum characteristics of the pressure pulsations at measuring points and results of free vibration characteristics analysis of the pump house, the spectrum analysis method of random vibration was used to calculate dynamic responses of the pump house. Results from both methods are consistent, which indicates that they are both reasonable. The results can be used for reference in anti-vibration safety evaluation of the Huaiyin third pumping station.
文摘Two induction magnetometers have been installed at Zhongshan Station and Davis Station, Antarctica respectively. We adopt with cross-spectral analysis technique to analyze the data of the two induction magnetometers, in June, September,December 1996 and March 1997. to investigate the Pc3 frequency range pulsation occurrence and propagation characteristics in the cusp latitudes. The results are summarized as following:At Zhongshan-Davis Stations, the Pc3 frequency range pulsations occur mainly around the local noon/ local magnetic noon and local magnetic midnight respectively. In daytime, the pulsations have a seasonal variation in amplitude, occurrence and temporal range, all of them are sma1lest in winter. But in nighttime, the pulsations have no such a variation. The pu1sation amplitude in nighttime is much larger than the one in daytime all oveI the year. The pulsation propagating direction is mainly western in daytime and irregularly in nighttime. It can be thought that the different sources of the pulsation and the ionospheric electric conductivity are mainly responsible for these characteristics.
文摘In this paper the data of geomagnetic pulsations at Zhongshan Station from February 3 to Novernber 30 in 1996 are analyzed in ordcr to study polarization characteristics of Zhongshan Station Pc3 pulsations which comprises the cusp Pc3 pulsation and the nightside Pc3 pulsation. For the cusp Pc3 pulsation. the right-handed polarization is always dominant. But their orientation of major axes of polarizations changes with season, NW-SE is dominant in summer and NE-SW in winter. For the nightside Pc3 pulsation,the right-handed with NE-SW is always dominant before midnight. But the left-handed with the mixing orientation of major axes is dominant in summer and the NE-SW with the mixing polarization sense is dominant in winter after midnight. It means that the two types of Zongshan Station Pc3 pulsations have different sources.
基金supported by the National Natural Science Foundation of China(NSFC)through grants 12173047,12373035,12322306,12373028,12233009 and 12133002X.C.and S.W.acknowledge supports from the Youth Innovation Promotion Association of the Chinese Academy of Sciences(CAS,Nos.2022055 and 2023065)+2 种基金support from the National Key Research and Development Program of China,grant 2022YFF0503404Funding for the DPAC has been provided by national institutions,in particular the institutions participating in the Gaia Multilateral AgreementFunding for the project has been provided by the National Development and Reform Commission。
文摘δScuti(δSct)stars are potential distance tracers for studying the Milky Way structure.We conduct a comprehensive analysis of the period-luminosity(PL)and period-luminosity-metallicity(PLZ)relations forδSct stars,integrating data from the Zwicky Transient Facility,the Transiting Exoplanet Survey Satellite,Large Sky Area Multi-Object Fiber Spectroscopic Telescope,Apache Point Observatory Galactic Evolution Experiment,and Gaia.To mitigate the impact of the Gaia parallax zero point offset,we applied a correction method,determining the optimal zero point value to be zp(?)=35±2μas.Using the three best bands,by varying the parallax error threshold,we found that the total error of the PLR zero point was minimized to 0.9%at a parallax error threshold of 6%.With this threshold,we derived the PL and PLZ relations for nine bands(from optical to mid-infrared)and five Wesenheit bands.Through our analysis,we conclude that the influence of metallicity on the PLR ofδSct stars is not significant,and the differences across various bands are minimal.
基金supported by the National Key Basic Research Program of China (Grant No.2012CB825604)the National Natural Science Foundation of China (Grant Nos.41104093 & 41204122).
文摘Simultaneous measurements from THEMIS spacecraft, GOES11 and ground stations （Canadian Array for Realtime Investiga tions of Magnetic Activity or CARISMA, and 210 magnetic meridian or MM） on March 18, 2009 allow the study of dynamic processes in the nearEarth magnetotail and corresponding Pi2 pulsations on the ground in great detail. Fast earthward flows along with traveling Alfv6n waves and fast mode waves in the Pi2 band were observed by three Time History of Events and Macroscale Interactions during Substorms （THEM/S） probes （P3, P4 and P5） in the nearEarth plasmasbeet. At the mid to highlatitude nightside, the CARISMA stations located near the foot points of the three probes recorded Pi2s with two periods, about 80 s after the earthward fast flows observed by the P4 probe. The longperiod Pi2 （140-150 s） belongs to the transient response Pi2 （TR Pi2）, since the travel time of the Alfv6n waves between the plasma sheet and CARISMA stations is very close to half the period of the longperiod Pi2. The shortperiod Pi2 （60-80 s） has the same period band as the perpendicular velocity of the fast flows, which indicates that it may relate to the inertial current caused by periodic braking of the earthward fast flows. The 210 MM stations located at the lowlatitude duskside also observed Pi2s with the same start time, waveform and frequency, about 120 s after the earthward fast flows. Strong poloidal oscillations are shown by GOES11 （23 MLT） and the compressional component （Bb） is highly correlated with H components of the 210 MM stations, whereas the other two components （Br and Be） are not. These results confirm that the lowlatitude Pi2s are generated by cavity mode resonance, which is driven by an impulsive broadband source in the nearEarth magnetotail.
文摘In this paper, we give a rigorous mathematical and complete parameter analysis for the rheodynamic model of cardiac and obtain the conditions and parameter region for global existence and uniqueness of limit cycle and the global bifurcation diagram of limit cycles. We also discuss the resonance phenomenons of the perturbed system.
基金Fundamental Research Funds for the Universities of Henan Province,Grant/Award Number:NSFRF180305。
文摘Chinese coal reservoirs are characterized by low pressure and low permeability,which need to be enhanced so as to increase production.However,conventional methods for permeability enhancement can only increase the permeability in fractures,but not the ultra-low permeability in coal matrices.Attempts to enhance such impermeable structures lead to rapid attenuation of gas production,especially in the late stage of gas extraction.Thermal stimulation by injecting high-temperature steam is a promising method to increase gas production.The critical scientific challenges that still hinder its widespread application are related to the evolution law of permeability of high-temperature steam in coal and the thermal deformation of coal.In this study,an experimental approach is developed to explore the high-temperature steam seepage coupled with the thermal deformation in coal under triaxial stress.The tests were conducted using cylindrical coal specimens of?50 mm×100 mm.The permeability and thermal strain in coal were investigated when high-temperature steam was injected at151.11,183.20,213.65,and 239.76°C.The experimental results reveal for the first time that as the amount of injected fluid increases,the steam permeability shows periodic pulsation changes.This paper introduces and explains the main traits of this discovery that may shed more light on the seepage phenomenon.When the injected steam temperature increases,the amplitude of pulsating permeability decreases,whereas the frequency increases;meanwhile,the period becomes shorter,the pulsation peak appears earlier,and the stabilization time becomes longer.The average peak permeability shows a“U-shaped”trend,decreasing first and then increasing as the steam temperature increases.Meanwhile,with the extension of steam injection time,the axial,radial,and volumetric strains of coal show a stage-wise expansion characteristic at different temperatures of steam injection,except for the radial strains at 151.11°C.A two-phase flow theory of gas–liquid is adopted to elucidate the mechanism of pulsating seepage of steam.Moreover,the influencing mechanism of inward and outward thermal expansion on the permeability of coal is interpreted.The results presented in this paper provide new insight into the feasibility of thermal gas recovery by steam injection.
基金sponsored by the National Key Research and Development Program of China(No.2022YFA1506200)the CNPC Innovation Found(No.2024DQ02-0203)the open foundation of State Key Laboratory of Chemical Engineering(No.SKL-ChE-23B02).
文摘By large-scale cold mold experiments,pressure pulsation signals within the jet influence zone of riser reactor are processed by using Hilbert-Huang analysis(HHT)in this study.Effects of different jet forms and operating conditions on the intrinsic mode function(IMF)energy and Hilbert-Huang spectrum are compared.Results show that the IMF energy and Hilbert-Huang spectrum of pressure pulsation signals show significant differences under the influence of upward and downward jets.Moreover,the change of jet velocity will also lead to significant changes in IMF energy and Hilbert-Huang spectrum.Among them,energy values and energy proportions corresponding to high-frequency pressure pulsations show a good correlation with the jet velocity.On this basis,energy value and energy proportion data in the high frequency range of the original pressure signal are clustered and analyzed by using the K-means clustering algorithm.Based on clustering results,the jet influence zone of riser can be defined into three regions.From partitioning results,it is found that the introduction of downward inclined jets could effectively improve the gas-solid mixing in the feed injection zone of riser.
基金the National Natural Science Foundation of China (No. 51905211)China Postdoctoral Science Foundation (Grant No. 2020M672128)+1 种基金University of Jinan Research Startup and Discipline Construction Fund (Grant No.1009435)a Project of the “20 Regulations for New Universities” funding program of Jinan (No.202228116)。
文摘Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater manipulator with different postures using the user-defined function (UDF) method. The lift coefficient (C_(L)), drag coefficient (C_(D)), and vortex shedding of the underwater manipulator in single-and dualarm forms were obtained. Results indicated that the maximum increase in the lift and drag coefficients subjected to the pulsation parameters was 24.45%and 28%, respectively, when the fluid flowed past a single arm. Compared with the single arm, the lift and drag coefficients of the arms were higher than those of the single arm when arm 2 was located upstream. Additionally, the pulsation frequency had no obvious effect on the manipulator, but the C_(L) and C_(D) of arm 2 showed an obvious increasing trend with an increase in pulsation amplitude. Meanwhile, when arm 2 was located downstream, the C_(L) and C_(D) of arm 2 were reduced by 16.38%and 1.15%, respectively, with an increase in the pulse frequency,and the maximum increase in the lift and dragcoefficients was 33.33%and 16.78%,respectively,with increasing pulsation amplitude.Moreover, the downstream wake morphology changed significantly, and a combined vortex phenomenon appeared. Finally, a theoretical basis for examining the hydrodynamic characteristics of marine engineering equipment was established to aid future marine resource exploitation.
基金supported by Ningxia Natural Science Foundation Innovative Group Project(2023AAC01001)the Postdoctoral Research Excellence Funding Project of Zhejiang Province ofChina(ZJ2023135).
文摘This study systematically investigated the effects of different gas stove structures on flame combustion characteristics using spectral diagnostic techniques,aiming to provide optimized design guidelines for clean energy applications.To explore the combustion behaviors of various gas stove structures,UV cameras,high-speed cameras,and K-type thermocouples were employed to measure parameters such as flame OH radicals(OH*),flame morphology,pulsation frequency,flame temperature,and heat flux.The results demonstrate that flame stability was achieved at an inner/outer cover flow rate ratio of 0.5/4.0 L/min,beyond which further flow rate increases led to reduced combustion efficiency.Compared to covered stoves,top-uncovered stove exhibited 5.5%and 12.4%higher temperatures at the inner and outer covers,respectively,along with a 35%increase in heat flux.Comprehensive analysis revealed an approximately 20%enhancement in overall flame intensity.The experimental results show that top-uncovered gas stoves exhibit higher flame intensity,greater combustion efficiency,and overall higher stove efficiency.In contrast,covered gas stoves feature a more controllable and stable flame with a gentler temperature rise.This study underscores the importance of optimizing gas stove designs to enhance combustion efficiency and reduce emissions,contributing to the transition from fossil fuels to renewable energy sources and promoting sustainable development.
基金support by Beijing Natural Science Foundation(3194046)BUCEA Post Graduate Innovation Project.
文摘The present work deals with the numerical study of the two-phase flow pattern and heat transfer characteristics of single-loop pulsating heat pipes(PHPs)under three modified surfaces(superhydrophilic evaporation section paired with superhydrophilic,superhydrophobic,and hybrid condensation section).The Volume of Fluid(VOF)model was utilized to capture the phase-change process within the PHPs.The study also evaluated the influence of surface wettability on fluid patterns and thermo-dynamic heat transfer performance under various heat fluxes.The results indicated that the effective nucleation and detachment of droplets are critical factors influencing the thermal performance of the PHPs.The overall heat transfer performance of the superhydrophobic surface was significantly improved at low heat flux.Under medium to high heat flux,the superhydrophilic condensation section exhibits a strong oscillation effect and leads to the thickening of the liquid film.In addition,the hybrid surface possesses the heat transfer characteristics of both superhydrophilic and superhydrophobic walls.The hybrid condensation section exhibited the lowest thermal resistance by 0.45 K/W at the heat flux of 10731 W/m^(2).The thermal resistance is reduced by 13.1%and 5.4%,respectively,compared to the superhydrophobic and superhydrophilic conditions.The proposed surface-modification method for achieving highly efficient condensation heat transfer is helpful for the design and operation of device-cooling components.
文摘The arterial pulse tapping artifact,known as Aslanger’s sign,is an electrocardiographic artifact resulting from the transmission of arterial pulsation onto the limb electrodes of the standard 12-lead electrocardiograph(ECG)which are placed near the radial or posterior tibial arteries.[1-16]This electromechanical artifact is of cardiac origin and is synchronous with the cardiac cycle.[17]Nearly all reported cases of Aslanger’s sign exhibit an unusual waveform morphology in all 12 leads except one limb lead.[1-14,16]However,we previously reported a case of Aslanger’s sign that showed distorted waveforms from the ST to TP segments observed only in five limb leads among 12 leads.
基金supported by the Shanghai Shuguang Program(No.18SG36)。
文摘This study investigates the nonlinear dynamics of geometrically imperfect graphene platelet-reinforced metal foam(GPLRMF)fluid-conveying pipes under the 1:1 internal resonance condition.With simply supported boundary conditions,the system is subject to the combined external lateral loads and internal pulsating fluid excitations.The nonlinear dynamic model is established with the Euler-Lagrange equations and then systematically discretized via the Galerkin method.The multi-scale analysis reveals how material properties and geometric imperfections influence the internal resonance.Particular emphasis is placed on elucidating,through the modal energy analysis,the energy exchange mechanisms between the first two vibration modes.
基金The University of Technology,specifically the Department of Electromechanical Engineering,provided invaluable assistance during the experimental work,for which the authors are quite grateful.
文摘Achieving broadband solar thermal absorption via dilute nanofluids is still a daunting challenge since the absorption peaks of common metal particles are usually located in the visible part of the radiation spectrum.This paper aims to present the results of experimental investigations on the thermal performance of heat pipe-type evacuated solar collectors.The experimented system consists of 15 tubes,providing the hot nanofluid to 100-L storage in a closed flow loop.The solar collector with a gross area of 2.1 m^(2)is part of the solar hot water test system located in Baghdad-Iraq.Al2O3 nanofluid at 0.5%volume concentration in water as working fluid was used in three flow rates of 3.3,6.6,and 10 L/min over two months,March and April.The experimental results indicated that maximum solar irradiation was 1070 and 1270 W/m^(2)in March and April,respectively.The maximum daily average of rate heat gain 11,270 and 12,040 W was recorded in March and April,respectively.In terms of the best operational flow rate,the system performs better at 3.3 L/min nanofluid flow rate.For the considered study period,the average monthly maximum energy efficiencies of the solar collector in March and April were 86%and 80%,respectively.
基金Supported by the National Natural Science Foundation of China(Grant Nos.51706086,51576090).
文摘The volute tongue,as the crucial component inducing rotor-stator interaction,is detrimental to unsteady pressure pulsations of centrifugal pumps.In the present paper,to investigate the effect of the volute tongue cut on pressure pulsations of a low specific speed centrifugal pump,three volute tongues are obtained through twice cuts,named cases 1,2,3.Twenty measuring points are evenly mounted on periphery of the volute casing to obtain unsteady pressure signals using high response transducers.Pressure amplitudes at the blade passing frequency fBPF and root mean square(rms)values in 0 Hz-500 Hz frequency band are applied to evaluate the cutting effect.Results show that pressure spectrum is significantly affected by the volute tongue cut,especially for the component at fBPF.For different measuring points,influences of the volute tongue cut on three cases are not identical.From nns values,it is evident that cutting the volute tongue will lead to pressure energy increasing for most of the concerned measuring points,especially for the points at the far away region from the volute tongue.Finally,from comparison with the original shape case 1,the averaged increment of the twenty points is more than 20%.So it is concluded that for this type centrifugal pump,cutting the volute tongue is not reasonable considering low pressure pulsation requirement.
