One of the practical approaches in identifying structures is the non-linear resonant decay method which identifies a non-linear dynamic system utilizing a model based on linear modal space containing the underlying li...One of the practical approaches in identifying structures is the non-linear resonant decay method which identifies a non-linear dynamic system utilizing a model based on linear modal space containing the underlying linear system and a small number of extra terms that exhibit the non-linear effects.In this paper,the method is illustrated in a simulated system and an experimental structure.The main objective of the non-linear resonant decay method is to identify the non-linear dynamic systems based on the use of a multi-shaker excitation using appropriated excitation which is obtained from the force appropriation approach.The experimental application of the method is indicated to provide suitable estimates of modal parameters for the identification of non-linear models of structures.展开更多
Surface potential decay of polymers for electrical insulation can help to determine the dark conductivity for spacecraft charging analysis. Due to the existence of radiation-induced conductivity, it decays fast in the...Surface potential decay of polymers for electrical insulation can help to determine the dark conductivity for spacecraft charging analysis. Due to the existence of radiation-induced conductivity, it decays fast in the first few hours after irradiation and exponentially slowly for the remaining time. The measurement of dark conductivity with this method usually takes the slow part and needs a couple of days. Integrating the Fowler formula into the deep dielectric charging equations, we obtain a new expression for the fast decay part. The experimental data of different materials, dose rates and temperatures are fitted by the new expression. Both the dark conductivity and the radiation-induced conductivity are derived and compared with other methods. The result shows a good estimation of dark conductivity and radiation-induced conductivity in high-resistivity polymers, which enables a fast measurement of dielectric conductivity within about 600 rain after irradiation.展开更多
Night-time OH levels have been determined for UK urban surface environments using two methods, the decay and steady state approximation methods. Measurement data from the UK National Environmental Technology Centre ar...Night-time OH levels have been determined for UK urban surface environments using two methods, the decay and steady state approximation methods. Measurement data from the UK National Environmental Technology Centre archive for four urban sites （Bristol, Harwell, London Eltham and Edinburgh） over the time period of 1996 to 2000 have been used in this study. Three reactive alkenes, namely isoprene, 1,3-butadiene and trans-2-pentene were chosen for the calculation of OH levels by the decay method. Hourly measurements of NO, NO〉 03, CO and 20 VOCs were used to determine night-time OH level using the steady state approximation method. Our results showed that the night-time OH levels were in the range of 1 × 10^3-1× 10^6 molecules/cm3 at these four urbap sites in the UK. The application of a t-test of these analyses indicated that except Bristol, there was no significant difference between the OH levels found from the decay and steady state approximation methods. Night-time levels of the OH radical appeared to peak in summer and spring time tracking the night-time 03 levels which also passed through a maximum at this time.展开更多
When using the plug pulse decay method to measure shale permeability,a comprehensive analysis of various factors influencing the measurement and analysis precision is conducive to improving the accuracy of the test re...When using the plug pulse decay method to measure shale permeability,a comprehensive analysis of various factors influencing the measurement and analysis precision is conducive to improving the accuracy of the test result.A great number of nano-scale pores are developed in shale,so the lower the test pressure is,the more easily the non-Darcy flow tends to emerge.In order to ensure the gas is in the form of Darcy flow in the process of measurement,we put forward the lower pressure limit of Darcy flow in pores according to the definition of Knudsen number.Then,the gas desorption-flow coupling model for the gas flow process during the plug pulse decay measurement was established by considering the effects of gas on the adsorption in organic pores.After the partial differential equation set was solved and derived,the corresponding permeability calculation method was proposed.Finally,after the plug pulse decay measurement,the supporting nitrogen isothermal adsorption test and methane isothermal adsorption test were conducted on shale samples.And the following research results were obtained.First,during the plug pulse decay measurement,the flow of gas in rock samples is one-dimensional linear,so when establishing the flow equation,the gas pseudopressure can be replaced with the gas pressure to simplify the calculation.Second,the adsorption of nitrogen in shale is much less than that of methane in shale,so the influence of nitrogen desorption on the flow is negligible when the pressure difference(i.e.<5%)of upstream and downstream changes within 5%of the initial pore pressure.In conclusion,the available industrial standards don't take into consideration the influence of gas adsorption,but the shale permeability measurement can still satisfy the accuracy requirement.展开更多
The accurate measurement of parameters such as the cavity-loaded quality factor(Q_(L))and half bandwidth(f_(0.5))is essential for monitoring the performance of superconducting radio-frequency cavities.However,the conv...The accurate measurement of parameters such as the cavity-loaded quality factor(Q_(L))and half bandwidth(f_(0.5))is essential for monitoring the performance of superconducting radio-frequency cavities.However,the conventional"field decay method"employed to calibrate these values requires the cavity to satisfy a"zero-input"condition.This can be challenging when the source impedance is mismatched and produce nonzero forward signals(V_(f))that significantly affect the measurement accuracy.To address this limitation,we developed a modified version of the"field decay method"based on the cavity differential equation.The proposed approach enables the precise calibration of f_(0.5) even under mismatch conditions.We tested the proposed approach on the SRF cavities of the Chinese Accelerator-Driven System Front-End Demo Superconducting Linac and compared the results with those obtained from a network analyzer.The two sets of results were consistent,indicating the usefulness of the proposed approach.展开更多
A new air exchange rate （AER） monitoring method using continuous CO2 sensors was developed and validated through both laboratory experiments and field studies. Controlled laboratory simulation tests were conducted i...A new air exchange rate （AER） monitoring method using continuous CO2 sensors was developed and validated through both laboratory experiments and field studies. Controlled laboratory simulation tests were conducted in a 1-m3 environmental chamber at different AERs （0.1-10.0 hr-1）. AERs were determined using the decay method based on box model assumptions. Field tests were conducted in classrooms, dormitories, meeting rooms and apartments during 2-5 weekdays using CO2 sensors coupled with data loggers. Indoor temperature, relative humidity （RH）, and CO2 concentrations were continuously monitored while outdoor parameters combined with on-site climate conditions were recorded. Statistical results indicated that good laboratory performance was achieved： duplicate precision was within 10%, and the measured AERs were 90%-120% of the real AERs. Average AERs were 1.22, 1.37, 1.10, 1.91 and 0.73 hr-l in dormitories, air-conditioned classrooms, classrooms with an air circulation cooling system, reading rooms, and meeting rooms, respectively. In an elderly particulate matter exposure study, all the homes had AER values ranging from 0.29 to 3.46 hr-1 in fall, and 0.12 to 1.39 hr-1 in winter with a median AER of 1.15.展开更多
Several direct or indirect approaches have been proposed to measure diffusion coefficient of gases into liquids.The main complexity of indirect techniques such as pressure decay method is interpreting early pressure-t...Several direct or indirect approaches have been proposed to measure diffusion coefficient of gases into liquids.The main complexity of indirect techniques such as pressure decay method is interpreting early pressure-time data which strongly affected by incubation period effect or convective instability.In the current approach,accurate apparatus and precise experimental setup including a high pressure and temperature PVT cell,a high precision Sanchez pump,heating and recording sub-system are implemented and a novel data analysis procedure is applied to modify pressure decay method.The effect of incubation period is reduced remarkably and diffusion coefficient of carbon dioxide in water in wide range of pressures and temperatures is determined and the effects of temperature,pressure and carbon dioxide phase alteration from gas to supercritical are investigated and the value of uncertainty is estimated.Furthermore,diffusion coefficient of CO_(2) and methane in an oil sample from one of the Iranian southwest oil formations is determined precisely using the experimental approach while no incubation period is detected.The results showed that incubation period duration decreases with increasing diffusion coefficient.Additionally,when CO_(2) state is gas,rate of increasing diffusion coefficient with pressure is decreased with temperature and when CO_(2) state is supercritical,the rate of increasing diffusion coefficient with pressure is decreased significantly.展开更多
The vibration attenuation and damping characteristics of carbon fiber reinforced composite laminates with different thicknesses were investigated by hammering experiments under free boundary constraints in different d...The vibration attenuation and damping characteristics of carbon fiber reinforced composite laminates with different thicknesses were investigated by hammering experiments under free boundary constraints in different directions.The dynamic signal testing and analysis system is applied to collect and analyze the vibration signals of the composite specimens,and combine the self-spectrum analysis and logarithmic decay method to identify the fundamental frequencies of different specimens and calculate the damping ratios of different directions of the specimens.The results showed that the overall stiffness of the specimen increased with the increase of the specimen thickness,and when the thickness of the sample increases from 24mm to 32mm,the fundamental frequency increases by 35.1%,the vibration showed the same vibration attenuation and energy dissipation characteristics in the 0°and 90°directions of the specimen,compared with the specimen in the 45°direction,which was less likely to be excited and had poorer vibration attenuation ability,while the upper and lower surfaces of the same specimen showed slightly different attenuation characteristics to the vibration,the maximum difference of damping capacity between top and bottom surfaces of CFRP plates is about 70%.展开更多
The roll motions are influenced by significant viscous effects such as the flow separation.The 3D simulations of free decay roll motions for the ship model DTMB 5512 are carried out by Reynold averaged NavierStokes(RA...The roll motions are influenced by significant viscous effects such as the flow separation.The 3D simulations of free decay roll motions for the ship model DTMB 5512 are carried out by Reynold averaged NavierStokes(RANS) method based on the dynamic mesh technique.A new moving mesh technique is adopted and discussed in details for the present simulations.The purpose of the research is to obtain accurate numerical prediction for roll motions with their respective numerical/modeling errors and uncertainties.Errors and uncertainties are estimated by performing the modern verification and validation(V&V) procedures.Simulation results for the free-floating surface combatant are used to calculate the linear,nonlinear damping coefficients and resonant frequencies including a wide range of forward speed.The present work can provide a useful reference to calculate roll damping by computational fluid dynamics(CFD) method and simulate a general ship motions in waves.展开更多
Lifetimes of the 2_(1)^(+),4_(1)^(+),7_(2)^(-),10_(2)^(+),12_(2)^(+),and 14_(1)^(+) states in 138 Nd populated via the 123 Sb(19 F,4n)138 Nd fusion–evaporation reaction were measured with the recoil distance Doppler ...Lifetimes of the 2_(1)^(+),4_(1)^(+),7_(2)^(-),10_(2)^(+),12_(2)^(+),and 14_(1)^(+) states in 138 Nd populated via the 123 Sb(19 F,4n)138 Nd fusion–evaporation reaction were measured with the recoil distance Doppler shift technique in combination with the differential decay curve method.The B(E2;2_(1)^(+)→0_(1)^(+))value fit well with the systematic trend in the Nd isotope chain and Grodzins rule,which proved that 138Nd is a transitional nucleus.展开更多
Sustaining or enhancing nature's contributions to people(NCPs)requires a comprehensive understanding of both nature's contributions and people's needs.However,the 2 aspects for water-related NCPs are spati...Sustaining or enhancing nature's contributions to people(NCPs)requires a comprehensive understanding of both nature's contributions and people's needs.However,the 2 aspects for water-related NCPs are spatially mismatched.We introduced an assessment framework for water-related NCPs from a spatial flow perspective,considering the local nature's contributions assessed using the In VEST(Integrated Valuation of Ecosystem Services and Tradeoffs)model,as well as people's needs in the downstream assessed via a distance decay method.We assessed 3 water-related NCPs'spatial distribution and correlation on the Loess Plateau from 2000 to 2020,where a large-scale ecological restoration was implemented that may affect downstream people.The results showed that NCP6(downstream needs from water yield)showed no increasing trend in the majority watersheds over the past 20 years,in contrast to NCP7(downstream needs from water purification)and NCP8(downstream needs from soil conservation).There are spatial synergies among NCP6,NCP7,and NCP8.From 2000 to 2020,the spatial synergy between NCP7 and NCP8 increased while decreased between other NCPs.The temporal dynamics of NCP6 and NCP8 showed a trade-off,while NCP6 and NCP7 showed a synergy.NCP7 and NCP8,in turn,showed a transition from synergy to trade-off.Guided by nature's contributions and people's needs,we proposed 3 ecological measures:thinning and intermediate cutting measures,control nonpoint source pollution,and soil and water conservation projects to promote ecological restoration.This assessment can offer multifunctional guidance for planning ecological conservation and restoration in the upstream based on people's needs in the downstream.展开更多
Purpose Precise measurements of the cavity-loaded quality factor(Q_(L))are essential for monitoring the performance of superconducting radio frequency cavities.The conventional“field-decay method”cannot be used to m...Purpose Precise measurements of the cavity-loaded quality factor(Q_(L))are essential for monitoring the performance of superconducting radio frequency cavities.The conventional“field-decay method”cannot be used to measure Q_(L)accurately when the impedance is mismatched.Researchers at the China ADS Front End Demo Linac(CAFe)therefore introduced a new Q_(L)calibration algorithm for mismatched impedance conditions,which they validated through testing at the CAFe facility.The Test Stand 2(TS2)facility at the European Spallation Source(ESS),which is equipped with a high-power circulator having an adjustable reflection coefficient,provides increased experimental flexibility for validating the proposed CAFe algorithm.The present study further validates the proposed algorithm at the ESS TS2 facility.Methods In this study,we utilized the CAFe algorithm to measure Q_(L)at the ESS TS2 facility in the presence of mismatched impedance.The CAFe algorithm is a modified version of the“field-decay method,”which is based on the cavity differential equation.A more concise alternative derivation of the proposed CAFe algorithm is given in Appendix.The experimental setup at the TS2 facility enables the adjustment of the circulator bias current to vary the reflection coefficient,thereby introducing an impedance mismatch.Our primary focus here is to calibrate the actual values Q_(L)and the cavity detuning Q_(L)under these mismatch conditions.Results Our results reconfirm the effectiveness of the CAFe algorithm by accurately calibrating Q_(L)andΔf at the ESS TS2 facility,even when the impedance is mismatched.Our successful calibration of Q_(L)andΔf under mismatched conditions highlights the practicality and reliability of the CAFe proposed algorithm.When calibrating the cavity half bandwidth and detuning,the Lorentz force detuning and direct current offset may introduce uncertainties of approximately±5 Hz and±4 Hz,respectively.展开更多
Injecting CO2 into oil reservoirs can improve the oil recovery,meanwhile achieve CO2 storage.The diffusion of CO2 in oil-water systems has a substantial impact on this process.The interface significantly affects the m...Injecting CO2 into oil reservoirs can improve the oil recovery,meanwhile achieve CO2 storage.The diffusion of CO2 in oil-water systems has a substantial impact on this process.The interface significantly affects the mass transfer of CO2 between oil and water phase.In this paper,based on the determination of the CO2 diffusion coefficient in oil or water phases,the diffusion processes of CO2 from oil to water were experimentally investigated under different pressures.A numerical method was proposed to calculate the pressure drop and the diffusion coefficient in the process of CO2 diffusion from oil to water.The experimental results indicated that the CO2 diffusion coefficient in oil or water increased rapidly with pressure up to the critical pressure of CO2 and gradually slowed down thereafter.The CO2 diffusion from oil to water was much slower than that in oil or water.The diffusion coefficient of CO2 from oil to water was one magnitude lower than that in the single liquid phase of oil or water,and the effect of pressure was not significant.Based on the diffusion coefficient of CO2 in a single liquid phase and the proposed numerical method,the pressure drop and the numerical diffusion coefficient in the process of CO2 diffusion from oil to water were calculated.The relative errors between the experimental and numerical results were within 9%.Therefore,the numerical method proposed herein can be used to predict the diffusion process of CO2 from oil to water and the diffusion coefficient associated with this process.展开更多
The lifetime of the 2^+1 state in ^106Cd populated via the ^94Zr(^16O,4n)^106Cd reaction has been measured with the Recoil Distance Doppler Shift technique in combination with the Differential Decay Curve Method.By su...The lifetime of the 2^+1 state in ^106Cd populated via the ^94Zr(^16O,4n)^106Cd reaction has been measured with the Recoil Distance Doppler Shift technique in combination with the Differential Decay Curve Method.By subtracting the contamination in the data,the mean lifetime of the I^π=2^+1633 keV state was determined as 9.9(12)ps.The B(E2)value calculated in this study is in good agreement with the experimental systematics and was compared to the shell model calculations.展开更多
A transfer-reaction experiment of ~9Be(~9Be,^(10)Be)~8Be was performed at a beam energy of 45 Me V.Excited states in ^(10)Be up to 18.80 Me V are produced using missing mass and invariant mass methods.Most of the obse...A transfer-reaction experiment of ~9Be(~9Be,^(10)Be)~8Be was performed at a beam energy of 45 Me V.Excited states in ^(10)Be up to 18.80 Me V are produced using missing mass and invariant mass methods.Most of the observed high-lying resonant states,reconstructed from theα+~6He and t+~7Li decay channels,agree with the previously reported results.In addition,two new resonances at 15.6 and 18.8 Me V are identified from the present measurement.The 18.55 Me V state is found to decay into both the t + ~7Lig:s: and t + ~7Li?(0.478 MeV) channels, with a relative branching ratio of 0:93 ± 0:33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.展开更多
文摘One of the practical approaches in identifying structures is the non-linear resonant decay method which identifies a non-linear dynamic system utilizing a model based on linear modal space containing the underlying linear system and a small number of extra terms that exhibit the non-linear effects.In this paper,the method is illustrated in a simulated system and an experimental structure.The main objective of the non-linear resonant decay method is to identify the non-linear dynamic systems based on the use of a multi-shaker excitation using appropriated excitation which is obtained from the force appropriation approach.The experimental application of the method is indicated to provide suitable estimates of modal parameters for the identification of non-linear models of structures.
基金Supported by the Fundamental Research Funds for the Central Universities in Nanjing University of Aeronautics and Astronautics under Grant No NS2014089
文摘Surface potential decay of polymers for electrical insulation can help to determine the dark conductivity for spacecraft charging analysis. Due to the existence of radiation-induced conductivity, it decays fast in the first few hours after irradiation and exponentially slowly for the remaining time. The measurement of dark conductivity with this method usually takes the slow part and needs a couple of days. Integrating the Fowler formula into the deep dielectric charging equations, we obtain a new expression for the fast decay part. The experimental data of different materials, dose rates and temperatures are fitted by the new expression. Both the dark conductivity and the radiation-induced conductivity are derived and compared with other methods. The result shows a good estimation of dark conductivity and radiation-induced conductivity in high-resistivity polymers, which enables a fast measurement of dielectric conductivity within about 600 rain after irradiation.
文摘Night-time OH levels have been determined for UK urban surface environments using two methods, the decay and steady state approximation methods. Measurement data from the UK National Environmental Technology Centre archive for four urban sites （Bristol, Harwell, London Eltham and Edinburgh） over the time period of 1996 to 2000 have been used in this study. Three reactive alkenes, namely isoprene, 1,3-butadiene and trans-2-pentene were chosen for the calculation of OH levels by the decay method. Hourly measurements of NO, NO〉 03, CO and 20 VOCs were used to determine night-time OH level using the steady state approximation method. Our results showed that the night-time OH levels were in the range of 1 × 10^3-1× 10^6 molecules/cm3 at these four urbap sites in the UK. The application of a t-test of these analyses indicated that except Bristol, there was no significant difference between the OH levels found from the decay and steady state approximation methods. Night-time levels of the OH radical appeared to peak in summer and spring time tracking the night-time 03 levels which also passed through a maximum at this time.
基金supported by the National Major Science and Technology Project under the 13th Five-year Plan“Development of large oil/gas fields and coalbed methane”(No.:2016ZX05034-002-006 and 2016ZX05066003-003).
文摘When using the plug pulse decay method to measure shale permeability,a comprehensive analysis of various factors influencing the measurement and analysis precision is conducive to improving the accuracy of the test result.A great number of nano-scale pores are developed in shale,so the lower the test pressure is,the more easily the non-Darcy flow tends to emerge.In order to ensure the gas is in the form of Darcy flow in the process of measurement,we put forward the lower pressure limit of Darcy flow in pores according to the definition of Knudsen number.Then,the gas desorption-flow coupling model for the gas flow process during the plug pulse decay measurement was established by considering the effects of gas on the adsorption in organic pores.After the partial differential equation set was solved and derived,the corresponding permeability calculation method was proposed.Finally,after the plug pulse decay measurement,the supporting nitrogen isothermal adsorption test and methane isothermal adsorption test were conducted on shale samples.And the following research results were obtained.First,during the plug pulse decay measurement,the flow of gas in rock samples is one-dimensional linear,so when establishing the flow equation,the gas pseudopressure can be replaced with the gas pressure to simplify the calculation.Second,the adsorption of nitrogen in shale is much less than that of methane in shale,so the influence of nitrogen desorption on the flow is negligible when the pressure difference(i.e.<5%)of upstream and downstream changes within 5%of the initial pore pressure.In conclusion,the available industrial standards don't take into consideration the influence of gas adsorption,but the shale permeability measurement can still satisfy the accuracy requirement.
基金supported by the project of Large Research Infrastructures"China initiative Accelerator-Driven System"(No.2017-000052-75-01-000590)"Studies of intelligent LLRF control algorithms for superconducting RF cavities"(No.E129851YR0)the National Natural Science Foundation of China(No.12205344).
文摘The accurate measurement of parameters such as the cavity-loaded quality factor(Q_(L))and half bandwidth(f_(0.5))is essential for monitoring the performance of superconducting radio-frequency cavities.However,the conventional"field decay method"employed to calibrate these values requires the cavity to satisfy a"zero-input"condition.This can be challenging when the source impedance is mismatched and produce nonzero forward signals(V_(f))that significantly affect the measurement accuracy.To address this limitation,we developed a modified version of the"field decay method"based on the cavity differential equation.The proposed approach enables the precise calibration of f_(0.5) even under mismatch conditions.We tested the proposed approach on the SRF cavities of the Chinese Accelerator-Driven System Front-End Demo Superconducting Linac and compared the results with those obtained from a network analyzer.The two sets of results were consistent,indicating the usefulness of the proposed approach.
基金supported by the Scientific Research Projects for State Environmental Protection and Commonweal (No. 200709048)the National Natural Science Foundation of China (No. 20977054/B070704)+1 种基金the Innovation Fund of Nankai UniversityJoint Research Grant to Both Nankai University and Tianjin University sponsored by the Ministry of Education,China
文摘A new air exchange rate （AER） monitoring method using continuous CO2 sensors was developed and validated through both laboratory experiments and field studies. Controlled laboratory simulation tests were conducted in a 1-m3 environmental chamber at different AERs （0.1-10.0 hr-1）. AERs were determined using the decay method based on box model assumptions. Field tests were conducted in classrooms, dormitories, meeting rooms and apartments during 2-5 weekdays using CO2 sensors coupled with data loggers. Indoor temperature, relative humidity （RH）, and CO2 concentrations were continuously monitored while outdoor parameters combined with on-site climate conditions were recorded. Statistical results indicated that good laboratory performance was achieved： duplicate precision was within 10%, and the measured AERs were 90%-120% of the real AERs. Average AERs were 1.22, 1.37, 1.10, 1.91 and 0.73 hr-l in dormitories, air-conditioned classrooms, classrooms with an air circulation cooling system, reading rooms, and meeting rooms, respectively. In an elderly particulate matter exposure study, all the homes had AER values ranging from 0.29 to 3.46 hr-1 in fall, and 0.12 to 1.39 hr-1 in winter with a median AER of 1.15.
文摘Several direct or indirect approaches have been proposed to measure diffusion coefficient of gases into liquids.The main complexity of indirect techniques such as pressure decay method is interpreting early pressure-time data which strongly affected by incubation period effect or convective instability.In the current approach,accurate apparatus and precise experimental setup including a high pressure and temperature PVT cell,a high precision Sanchez pump,heating and recording sub-system are implemented and a novel data analysis procedure is applied to modify pressure decay method.The effect of incubation period is reduced remarkably and diffusion coefficient of carbon dioxide in water in wide range of pressures and temperatures is determined and the effects of temperature,pressure and carbon dioxide phase alteration from gas to supercritical are investigated and the value of uncertainty is estimated.Furthermore,diffusion coefficient of CO_(2) and methane in an oil sample from one of the Iranian southwest oil formations is determined precisely using the experimental approach while no incubation period is detected.The results showed that incubation period duration decreases with increasing diffusion coefficient.Additionally,when CO_(2) state is gas,rate of increasing diffusion coefficient with pressure is decreased with temperature and when CO_(2) state is supercritical,the rate of increasing diffusion coefficient with pressure is decreased significantly.
基金supported by the Fundamental Research Funds for the Central Universities [grant nos.DUT21LAB108,DUT22LAB401].
文摘The vibration attenuation and damping characteristics of carbon fiber reinforced composite laminates with different thicknesses were investigated by hammering experiments under free boundary constraints in different directions.The dynamic signal testing and analysis system is applied to collect and analyze the vibration signals of the composite specimens,and combine the self-spectrum analysis and logarithmic decay method to identify the fundamental frequencies of different specimens and calculate the damping ratios of different directions of the specimens.The results showed that the overall stiffness of the specimen increased with the increase of the specimen thickness,and when the thickness of the sample increases from 24mm to 32mm,the fundamental frequency increases by 35.1%,the vibration showed the same vibration attenuation and energy dissipation characteristics in the 0°and 90°directions of the specimen,compared with the specimen in the 45°direction,which was less likely to be excited and had poorer vibration attenuation ability,while the upper and lower surfaces of the same specimen showed slightly different attenuation characteristics to the vibration,the maximum difference of damping capacity between top and bottom surfaces of CFRP plates is about 70%.
基金the National Natural Science Foundation of China(No.51579147)
文摘The roll motions are influenced by significant viscous effects such as the flow separation.The 3D simulations of free decay roll motions for the ship model DTMB 5512 are carried out by Reynold averaged NavierStokes(RANS) method based on the dynamic mesh technique.A new moving mesh technique is adopted and discussed in details for the present simulations.The purpose of the research is to obtain accurate numerical prediction for roll motions with their respective numerical/modeling errors and uncertainties.Errors and uncertainties are estimated by performing the modern verification and validation(V&V) procedures.Simulation results for the free-floating surface combatant are used to calculate the linear,nonlinear damping coefficients and resonant frequencies including a wide range of forward speed.The present work can provide a useful reference to calculate roll damping by computational fluid dynamics(CFD) method and simulate a general ship motions in waves.
基金This work was supported by the National Natural Science Foundation of China(Nos.U1932209,11975315,U1867210,and 11905134)the Leading Innovation Project(Nos.LC192209000701 and LC202309000201)+1 种基金the Continuous Basic Scientific Research Project(Nos.BJ20002501 and WDJC-2019-13)the China National Nuclear Corporation(No.FA18000201).
文摘Lifetimes of the 2_(1)^(+),4_(1)^(+),7_(2)^(-),10_(2)^(+),12_(2)^(+),and 14_(1)^(+) states in 138 Nd populated via the 123 Sb(19 F,4n)138 Nd fusion–evaporation reaction were measured with the recoil distance Doppler shift technique in combination with the differential decay curve method.The B(E2;2_(1)^(+)→0_(1)^(+))value fit well with the systematic trend in the Nd isotope chain and Grodzins rule,which proved that 138Nd is a transitional nucleus.
基金supported by the National Natural Science Foundation of China(Nos.42041007,U2243601,and 42201306)the Fundamental Research Funds for the Central Universities of China
文摘Sustaining or enhancing nature's contributions to people(NCPs)requires a comprehensive understanding of both nature's contributions and people's needs.However,the 2 aspects for water-related NCPs are spatially mismatched.We introduced an assessment framework for water-related NCPs from a spatial flow perspective,considering the local nature's contributions assessed using the In VEST(Integrated Valuation of Ecosystem Services and Tradeoffs)model,as well as people's needs in the downstream assessed via a distance decay method.We assessed 3 water-related NCPs'spatial distribution and correlation on the Loess Plateau from 2000 to 2020,where a large-scale ecological restoration was implemented that may affect downstream people.The results showed that NCP6(downstream needs from water yield)showed no increasing trend in the majority watersheds over the past 20 years,in contrast to NCP7(downstream needs from water purification)and NCP8(downstream needs from soil conservation).There are spatial synergies among NCP6,NCP7,and NCP8.From 2000 to 2020,the spatial synergy between NCP7 and NCP8 increased while decreased between other NCPs.The temporal dynamics of NCP6 and NCP8 showed a trade-off,while NCP6 and NCP7 showed a synergy.NCP7 and NCP8,in turn,showed a transition from synergy to trade-off.Guided by nature's contributions and people's needs,we proposed 3 ecological measures:thinning and intermediate cutting measures,control nonpoint source pollution,and soil and water conservation projects to promote ecological restoration.This assessment can offer multifunctional guidance for planning ecological conservation and restoration in the upstream based on people's needs in the downstream.
基金supported by the project of Large Research Infrastructures“National Natural Science Foundation of China”(Grant No.U22A20261)the“Studies of intelligent LLRF control algorithms for superconducting RF cavities”(Grant No.E129851YR0)the“National Natural Science Foundation of China”(Grant No.12205344).
文摘Purpose Precise measurements of the cavity-loaded quality factor(Q_(L))are essential for monitoring the performance of superconducting radio frequency cavities.The conventional“field-decay method”cannot be used to measure Q_(L)accurately when the impedance is mismatched.Researchers at the China ADS Front End Demo Linac(CAFe)therefore introduced a new Q_(L)calibration algorithm for mismatched impedance conditions,which they validated through testing at the CAFe facility.The Test Stand 2(TS2)facility at the European Spallation Source(ESS),which is equipped with a high-power circulator having an adjustable reflection coefficient,provides increased experimental flexibility for validating the proposed CAFe algorithm.The present study further validates the proposed algorithm at the ESS TS2 facility.Methods In this study,we utilized the CAFe algorithm to measure Q_(L)at the ESS TS2 facility in the presence of mismatched impedance.The CAFe algorithm is a modified version of the“field-decay method,”which is based on the cavity differential equation.A more concise alternative derivation of the proposed CAFe algorithm is given in Appendix.The experimental setup at the TS2 facility enables the adjustment of the circulator bias current to vary the reflection coefficient,thereby introducing an impedance mismatch.Our primary focus here is to calibrate the actual values Q_(L)and the cavity detuning Q_(L)under these mismatch conditions.Results Our results reconfirm the effectiveness of the CAFe algorithm by accurately calibrating Q_(L)andΔf at the ESS TS2 facility,even when the impedance is mismatched.Our successful calibration of Q_(L)andΔf under mismatched conditions highlights the practicality and reliability of the CAFe proposed algorithm.When calibrating the cavity half bandwidth and detuning,the Lorentz force detuning and direct current offset may introduce uncertainties of approximately±5 Hz and±4 Hz,respectively.
基金financially supported by National Natural Science Foundation of China (No. 51574264)National Science and Technology Major Project of the Ministry of Science and Technology of China (No. 2016ZX05056-001)Shandong Provincial Natural Science Foundation, China (ZR2015EL015)
文摘Injecting CO2 into oil reservoirs can improve the oil recovery,meanwhile achieve CO2 storage.The diffusion of CO2 in oil-water systems has a substantial impact on this process.The interface significantly affects the mass transfer of CO2 between oil and water phase.In this paper,based on the determination of the CO2 diffusion coefficient in oil or water phases,the diffusion processes of CO2 from oil to water were experimentally investigated under different pressures.A numerical method was proposed to calculate the pressure drop and the diffusion coefficient in the process of CO2 diffusion from oil to water.The experimental results indicated that the CO2 diffusion coefficient in oil or water increased rapidly with pressure up to the critical pressure of CO2 and gradually slowed down thereafter.The CO2 diffusion from oil to water was much slower than that in oil or water.The diffusion coefficient of CO2 from oil to water was one magnitude lower than that in the single liquid phase of oil or water,and the effect of pressure was not significant.Based on the diffusion coefficient of CO2 in a single liquid phase and the proposed numerical method,the pressure drop and the numerical diffusion coefficient in the process of CO2 diffusion from oil to water were calculated.The relative errors between the experimental and numerical results were within 9%.Therefore,the numerical method proposed herein can be used to predict the diffusion process of CO2 from oil to water and the diffusion coefficient associated with this process.
基金Supported by National Key Research and Development Program of China(2017YFF0106501)National Natural Science Foundation of China(11905134,11975315,U1932209,11575118,11605114)+3 种基金NSFC-CNNC Joint Project for Nuclear Technology Innovation(U1867210)Continuous Basic Scientific Research Project(WDJC-2019-13)Project funded by China Post-doctoral Science Foundation(2019M652999)and National Natural Science Foundation of Guangdong China(2016A030310042)。
文摘The lifetime of the 2^+1 state in ^106Cd populated via the ^94Zr(^16O,4n)^106Cd reaction has been measured with the Recoil Distance Doppler Shift technique in combination with the Differential Decay Curve Method.By subtracting the contamination in the data,the mean lifetime of the I^π=2^+1633 keV state was determined as 9.9(12)ps.The B(E2)value calculated in this study is in good agreement with the experimental systematics and was compared to the shell model calculations.
基金supported by the National Basic Research Program of China (Grant No. 2013CB834402)the National Natural Science Foundation of China (Grant Nos. 11535004, 11275011, 11375017, and 11275001)
文摘A transfer-reaction experiment of ~9Be(~9Be,^(10)Be)~8Be was performed at a beam energy of 45 Me V.Excited states in ^(10)Be up to 18.80 Me V are produced using missing mass and invariant mass methods.Most of the observed high-lying resonant states,reconstructed from theα+~6He and t+~7Li decay channels,agree with the previously reported results.In addition,two new resonances at 15.6 and 18.8 Me V are identified from the present measurement.The 18.55 Me V state is found to decay into both the t + ~7Lig:s: and t + ~7Li?(0.478 MeV) channels, with a relative branching ratio of 0:93 ± 0:33. Further theoretical investigations are encouraged to interpret this new information on cluster structure in neutron-rich light nuclei.
