Cloud storage,a core component of cloud computing,plays a vital role in the storage and management of data.Electronic Health Records(EHRs),which document users’health information,are typically stored on cloud servers...Cloud storage,a core component of cloud computing,plays a vital role in the storage and management of data.Electronic Health Records(EHRs),which document users’health information,are typically stored on cloud servers.However,users’sensitive data would then become unregulated.In the event of data loss,cloud storage providers might conceal the fact that data has been compromised to protect their reputation and mitigate losses.Ensuring the integrity of data stored in the cloud remains a pressing issue that urgently needs to be addressed.In this paper,we propose a data auditing scheme for cloud-based EHRs that incorporates recoverability and batch auditing,alongside a thorough security and performance evaluation.Our scheme builds upon the indistinguishability-based privacy-preserving auditing approach proposed by Zhou et al.We identify that this scheme is insecure and vulnerable to forgery attacks on data storage proofs.To address these vulnerabilities,we enhanced the auditing process using masking techniques and designed new algorithms to strengthen security.We also provide formal proof of the security of the signature algorithm and the auditing scheme.Furthermore,our results show that our scheme effectively protects user privacy and is resilient against malicious attacks.Experimental results indicate that our scheme is not only secure and efficient but also supports batch auditing of cloud data.Specifically,when auditing 10,000 users,batch auditing reduces computational overhead by 101 s compared to normal auditing.展开更多
In this study, the trends in latent and sensible heat fluxes (LHF and SHF) over the Southern Ocean (oceans south of 35?S) and the contributions of the Antarctic Oscillation (AAO), the Pacific-South America teleconnect...In this study, the trends in latent and sensible heat fluxes (LHF and SHF) over the Southern Ocean (oceans south of 35?S) and the contributions of the Antarctic Oscillation (AAO), the Pacific-South America teleconnection patterns (PSA1 and PSA2) and The El Ni?o-Southern Oscillation (ENSO) to these heat fluxes were investigated using the Objectively Analyzed Air-Sea Fluxes (OAFlux) dataset from 1979 to 2008. Significant positive annual trends in LHF occur over the Agulhas Current, the Brazil Current, the oceans in the vicinity of New Zealand and southern Australia, and the eastern Pacific Ocean near between 35?S and 40?S. Significant negative seasonal trends occur in LHF which differ among the four seasons. The spatial pattern and seasonal variation of the trends in SHF over the Southern Ocean are similar to those of LHF. The spatial patterns of the trends in LHF and SHF caused by the AAO, PSA1, PSA2 and Southern Oscillation Index (SOI) indices show a wave-like feature, varying with different seasons, that can be explained by the anomalous meridional wind associated with the four indices. The above four indices account for a small portion of the trend in LHF and SHF. The residual trends in LHF over the Southern Ocean may be explained by a climate shift in the late 1990s for the four seasons. But the residual trends in SHF over the Southern Ocean are not associated with the climate shift.展开更多
Surface radiative fluxes over landfast sea ice off Zhongshan station have been measured in austral spring for five springs between 2010 and 2015.Downward and upward solar radiation vary diurnally with maximum amplitud...Surface radiative fluxes over landfast sea ice off Zhongshan station have been measured in austral spring for five springs between 2010 and 2015.Downward and upward solar radiation vary diurnally with maximum amplitudes of 473 and 290 W m^(−2),respectively.The maximum and minimum long-wave radiation values of the mean diurnal cycle are 218 and 210 W m^(−2)for downward radiation,277 and 259 W m^(−2)for upward radiation and 125 and−52 W m^(−2)for net radiation.The albedo has a U-shaped mean diurnal cycle with a minimum of 0.64 at noon.Sea ice thickness is in the growth phase for most spring days,but can be disturbed by synoptic processes.The surface temperature largely determines the occurrence of ice melting.Surface downward and upward long-wave radiation show synoptic oscillations with a 5–8 day period and intraseasonal variability with a 12–45 day period.The amplitudes of the diurnal,synoptic and intraseasonal variability show some differences during the five austral springs considered here.The intraseasonal and synoptic variability of downward and upward long-wave radiation are associated with the variability of cloud cover and surface temperature induced by the atmospheric circulation.展开更多
With modern power utilities going green by utilising renewable energy technologies and the development of the smart power grid,high-voltage direct current(HVDC)technologies become more and more important in the energy...With modern power utilities going green by utilising renewable energy technologies and the development of the smart power grid,high-voltage direct current(HVDC)technologies become more and more important in the energy transmission.In particular,HVDC cable systems play a prominent role in undersea power transmission and offshore renewable energy integration.As an essential part of a complete HVDC cable system,the cable termination is one of the most critical components.The mathematical and physical background of HVDC cable systems is discussed and the development of various types of HVDC cable terminations is reviewed.Regarding the non-uniform field distribution,the influence of temperature on the non-linear conductivity is briefly discussed.Furthermore,faults of terminations caused by inappropriate installation and testing of cable systems are discussed.展开更多
High voltage direct current(HVDC)power transmission cable is critical for realising sustainability through renewable energy revolution.Eco-friendly thermoplastic polypropylene(PP)-based polymers/nanocomposites are reg...High voltage direct current(HVDC)power transmission cable is critical for realising sustainability through renewable energy revolution.Eco-friendly thermoplastic polypropylene(PP)-based polymers/nanocomposites are regarded as promising candidates for replacing current thermoset crosslinked polyethylene(XLPE)cables.As an essential component of the extruded HVDC cable for improving conductor/insulation interface and suppressing charge injection to insulation at high DC electrical stresses,developing semiconducting(SC)screens that are compatible with PP-based insulation is of similar importance but has not been well studied yet.This work aims at designing PP-based semiconducting screens and investigating space charge behaviours of SC/PP/SC sandwich specimen to unfold the effect of semiconducting materials,bonding methods,applied DC electric field,and temperature on charge injection,accumulation,transportation,and dissipation in PP-based insulation.Although conventional thermal,mechanical,and low field electrical characterisations demonstrated that all of the developed semiconducting materials meet the performance criteria of commercial semiconducting materials,their space charge and local electric field distribution varied significantly at high DC fields.Compared with the traditional non-bonded configuration used at lab-scale,charge injection was enhanced in hot-pressed SC/PP/SC samples with tightly bonded interfaces,which better reflects the real situation in extruded cables.High temperature further intensified charge injections.Besides,our results also revealed that high temperature and electric field strongly influence charge mobilities and consequently their distribution and local electric field in PP-based insulations.展开更多
A detailed analysis of a sea breeze front(SBF)that penetrated inland in the Beijing–Tianjin–Hebei urban agglomeration of China was conducted.We focused on the boundary layer structure,turbulence intensity,and fluxes...A detailed analysis of a sea breeze front(SBF)that penetrated inland in the Beijing–Tianjin–Hebei urban agglomeration of China was conducted.We focused on the boundary layer structure,turbulence intensity,and fluxes before and after the SBF passed through two meteorological towers in the urban areas of Tianjin and Beijing,respectively.Significant changes in temperature,humidity,winds,CO_(2),and aerosol concentrations were observed as the SBF passed.Differences in these changes at the two towers mainly resulted from their distances from the ocean,boundary layer conditions,and background turbulences.As the SBF approached,a strong updraft appeared in the boundary layer,carrying near-surface aerosols aloft and forming the SBF head.This was followed by a broad downdraft,which destroyed the near-surface inversion layer and temporarily increased the surface air temperature at night.The feeder flow after the thermodynamic front was characterized by low-level jets horizontally,and downdrafts and occasional updrafts vertically.Turbulence increased significantly during the SBF’s passage,causing an increase in the standard deviation of wind components in speed.The increase in turbulence was more pronounced in a stable boundary layer compared to that in a convective boundary layer.The passage of the SBF generated more mechanical turbulences,as indicated by increased friction velocity and turbulent kinetic energy(TKE).The shear term in the TKE budget equation increased more significantly than the buoyancy term.The atmosphere shifted to a forced convective state after the SBF’s passage,with near isotropic turbulences and uniform mixing and diffusion of aerosols.Sensible heat fluxes(latent heat and CO_(2)fluxes)showed positive(negative)peaks after the SBF’s passage,primarily caused by horizontal and vertical transport of heat(water vapor and CO_(2))during its passage.This study enhances understanding of boundary layer changes,turbulences,and fluxes during the passage of SBFs over urban areas.展开更多
In this paper,we develop an orthogonal frequency-division multiplexing(OFDM)-based over-theair(OTA)aggregation solution for wireless federated learning(FL).In particular,the local gradients in massive Internet of thin...In this paper,we develop an orthogonal frequency-division multiplexing(OFDM)-based over-theair(OTA)aggregation solution for wireless federated learning(FL).In particular,the local gradients in massive Internet of things(IoT)devices are modulated by an analog waveform and are then transmitted using the same wireless resources.To this end,achieving perfect waveform superposition is the key challenge,which is difficult due to the existence of frame timing offset(TO)and carrier frequency offset(CFO).In order to address these issues,we propose a two-stage waveform pre-equalization technique with a customized multiple access protocol that can estimate and then mitigate the TO and CFO for the OTA aggregation.Based on the proposed solution,we develop a hardware transceiver and application software to train a real-world FL task,which learns a deep neural network to predict the received signal strength with the global positioning system information.Experiments verify that the proposed OTA aggregation solution can achieve comparable performance to offline learning procedures with high prediction accuracy.展开更多
This study sets out to discuss the challenges that need to be addressed effectively to facilitate the adoption of long distance high-voltage and ultra-high-voltage direct current(UHVDC)power transmission cables.As in ...This study sets out to discuss the challenges that need to be addressed effectively to facilitate the adoption of long distance high-voltage and ultra-high-voltage direct current(UHVDC)power transmission cables.As in the alternating current case,the desire to minimise the losses has involved the use of increasingly high transmission voltages,which presents particular problems where UHVDC cables are concerned.Specifically,this study presents the case for a novel,integrated approach to the problem,which links three distinct aspects of the problem,namely:(i)cable ratings and network operability;(ii)cable design and constituent insulating material requirements;and(iii)potential strategies for the design of novel insulation materials,where the required properties are actively‘designed in’.The study concludes that the impact of these factors acting in concert on network operation/performance requires a more integrated approach to the problem than has traditionally been the case.A number of complementary strategies for the development of novel material technologies and UHVDC cable designs are required that can meet the service performance and ultimate service lifetimes expected for new network applications.展开更多
The potential of using eco-friendly thermoplastic polypropylene(PP)-based insulation for high voltage direct current(HVDC)cable has been widely investigated but much less work on the PP-based semiconducting screen(SC)...The potential of using eco-friendly thermoplastic polypropylene(PP)-based insulation for high voltage direct current(HVDC)cable has been widely investigated but much less work on the PP-based semiconducting screen(SC).Considering a long service life(>30 years)under high temperature and high electrical stress is required for typical HVDC cables,and investigations on the effect of antioxidant(AO)concentration and thermal oxidative sta-bility,mechanical,and electrical properties of PP-based SCs have been conducted.It has been demonstrated that an appropriate combination and amounts of AOs are critical for achieving high thermal stability and maintaining the mechanical properties of SC after ageing in a harsh environment(150°C,with Cu,in air,7 days).Although higher amounts of space charges have been observed in SC/PP/SC samples with higher AO concentrations,the impact on space charge behaviours is less after ageing,suggesting that ageing(or operating at high temperature)leads to microstructure evolution in SC and can potentially mitigate space accumulation in PP-based insulating materials.展开更多
基金supported by National Natural Science Foundation of China(No.62172436)Additionally,it is supported by Natural Science Foundation of Shaanxi Province(No.2023-JC-YB-584)Engineering University of PAP’s Funding for Scientific Research Innovation Team and Key Researcher(No.KYGG202011).
文摘Cloud storage,a core component of cloud computing,plays a vital role in the storage and management of data.Electronic Health Records(EHRs),which document users’health information,are typically stored on cloud servers.However,users’sensitive data would then become unregulated.In the event of data loss,cloud storage providers might conceal the fact that data has been compromised to protect their reputation and mitigate losses.Ensuring the integrity of data stored in the cloud remains a pressing issue that urgently needs to be addressed.In this paper,we propose a data auditing scheme for cloud-based EHRs that incorporates recoverability and batch auditing,alongside a thorough security and performance evaluation.Our scheme builds upon the indistinguishability-based privacy-preserving auditing approach proposed by Zhou et al.We identify that this scheme is insecure and vulnerable to forgery attacks on data storage proofs.To address these vulnerabilities,we enhanced the auditing process using masking techniques and designed new algorithms to strengthen security.We also provide formal proof of the security of the signature algorithm and the auditing scheme.Furthermore,our results show that our scheme effectively protects user privacy and is resilient against malicious attacks.Experimental results indicate that our scheme is not only secure and efficient but also supports batch auditing of cloud data.Specifically,when auditing 10,000 users,batch auditing reduces computational overhead by 101 s compared to normal auditing.
基金supported by the National Natural Science Foundation(41175010,40930848 and 41106164)Marine Public Welfare Project(201205007)+1 种基金National Program on Key Basic Research Project of China(2010CB950301)sponsored by the National Science Foundation
文摘In this study, the trends in latent and sensible heat fluxes (LHF and SHF) over the Southern Ocean (oceans south of 35?S) and the contributions of the Antarctic Oscillation (AAO), the Pacific-South America teleconnection patterns (PSA1 and PSA2) and The El Ni?o-Southern Oscillation (ENSO) to these heat fluxes were investigated using the Objectively Analyzed Air-Sea Fluxes (OAFlux) dataset from 1979 to 2008. Significant positive annual trends in LHF occur over the Agulhas Current, the Brazil Current, the oceans in the vicinity of New Zealand and southern Australia, and the eastern Pacific Ocean near between 35?S and 40?S. Significant negative seasonal trends occur in LHF which differ among the four seasons. The spatial pattern and seasonal variation of the trends in SHF over the Southern Ocean are similar to those of LHF. The spatial patterns of the trends in LHF and SHF caused by the AAO, PSA1, PSA2 and Southern Oscillation Index (SOI) indices show a wave-like feature, varying with different seasons, that can be explained by the anomalous meridional wind associated with the four indices. The above four indices account for a small portion of the trend in LHF and SHF. The residual trends in LHF over the Southern Ocean may be explained by a climate shift in the late 1990s for the four seasons. But the residual trends in SHF over the Southern Ocean are not associated with the climate shift.
基金the National Natural Science Foundation of China[nos.41376005,41606222]the Chinese Polar Environmental Comprehensive Investigation and Assessment Program under contract[no.CHINARE2017-04-04]The National Center for Atmospheric Research is sponsored by the U.S.National Science Foundation.
文摘Surface radiative fluxes over landfast sea ice off Zhongshan station have been measured in austral spring for five springs between 2010 and 2015.Downward and upward solar radiation vary diurnally with maximum amplitudes of 473 and 290 W m^(−2),respectively.The maximum and minimum long-wave radiation values of the mean diurnal cycle are 218 and 210 W m^(−2)for downward radiation,277 and 259 W m^(−2)for upward radiation and 125 and−52 W m^(−2)for net radiation.The albedo has a U-shaped mean diurnal cycle with a minimum of 0.64 at noon.Sea ice thickness is in the growth phase for most spring days,but can be disturbed by synoptic processes.The surface temperature largely determines the occurrence of ice melting.Surface downward and upward long-wave radiation show synoptic oscillations with a 5–8 day period and intraseasonal variability with a 12–45 day period.The amplitudes of the diurnal,synoptic and intraseasonal variability show some differences during the five austral springs considered here.The intraseasonal and synoptic variability of downward and upward long-wave radiation are associated with the variability of cloud cover and surface temperature induced by the atmospheric circulation.
基金the National Key Research and Development Program of China in its project entitle‘Critical Technologies for Designing and Manufacturing±500 kV DC Cables and their Accessories’(grant no.2016YFB0900703).
文摘With modern power utilities going green by utilising renewable energy technologies and the development of the smart power grid,high-voltage direct current(HVDC)technologies become more and more important in the energy transmission.In particular,HVDC cable systems play a prominent role in undersea power transmission and offshore renewable energy integration.As an essential part of a complete HVDC cable system,the cable termination is one of the most critical components.The mathematical and physical background of HVDC cable systems is discussed and the development of various types of HVDC cable terminations is reviewed.Regarding the non-uniform field distribution,the influence of temperature on the non-linear conductivity is briefly discussed.Furthermore,faults of terminations caused by inappropriate installation and testing of cable systems are discussed.
基金Science and Technology Project of SGCC,Grant/Award Number:5500-201958504A-0-0-00。
文摘High voltage direct current(HVDC)power transmission cable is critical for realising sustainability through renewable energy revolution.Eco-friendly thermoplastic polypropylene(PP)-based polymers/nanocomposites are regarded as promising candidates for replacing current thermoset crosslinked polyethylene(XLPE)cables.As an essential component of the extruded HVDC cable for improving conductor/insulation interface and suppressing charge injection to insulation at high DC electrical stresses,developing semiconducting(SC)screens that are compatible with PP-based insulation is of similar importance but has not been well studied yet.This work aims at designing PP-based semiconducting screens and investigating space charge behaviours of SC/PP/SC sandwich specimen to unfold the effect of semiconducting materials,bonding methods,applied DC electric field,and temperature on charge injection,accumulation,transportation,and dissipation in PP-based insulation.Although conventional thermal,mechanical,and low field electrical characterisations demonstrated that all of the developed semiconducting materials meet the performance criteria of commercial semiconducting materials,their space charge and local electric field distribution varied significantly at high DC fields.Compared with the traditional non-bonded configuration used at lab-scale,charge injection was enhanced in hot-pressed SC/PP/SC samples with tightly bonded interfaces,which better reflects the real situation in extruded cables.High temperature further intensified charge injections.Besides,our results also revealed that high temperature and electric field strongly influence charge mobilities and consequently their distribution and local electric field in PP-based insulations.
基金Supported by the Beijing Natural Science Foundation(8222048)Open Grants of the State Key Laboratory of Severe Weather(2022LASW-A03)+2 种基金Key Innovation Team of China Meteorological Administration(CMA2022ZD09)China Meteorological Administration Innovation Development Project(CXFZ2023J061)Tianjin Meteorology Service Project(202113ybxm05)。
文摘A detailed analysis of a sea breeze front(SBF)that penetrated inland in the Beijing–Tianjin–Hebei urban agglomeration of China was conducted.We focused on the boundary layer structure,turbulence intensity,and fluxes before and after the SBF passed through two meteorological towers in the urban areas of Tianjin and Beijing,respectively.Significant changes in temperature,humidity,winds,CO_(2),and aerosol concentrations were observed as the SBF passed.Differences in these changes at the two towers mainly resulted from their distances from the ocean,boundary layer conditions,and background turbulences.As the SBF approached,a strong updraft appeared in the boundary layer,carrying near-surface aerosols aloft and forming the SBF head.This was followed by a broad downdraft,which destroyed the near-surface inversion layer and temporarily increased the surface air temperature at night.The feeder flow after the thermodynamic front was characterized by low-level jets horizontally,and downdrafts and occasional updrafts vertically.Turbulence increased significantly during the SBF’s passage,causing an increase in the standard deviation of wind components in speed.The increase in turbulence was more pronounced in a stable boundary layer compared to that in a convective boundary layer.The passage of the SBF generated more mechanical turbulences,as indicated by increased friction velocity and turbulent kinetic energy(TKE).The shear term in the TKE budget equation increased more significantly than the buoyancy term.The atmosphere shifted to a forced convective state after the SBF’s passage,with near isotropic turbulences and uniform mixing and diffusion of aerosols.Sensible heat fluxes(latent heat and CO_(2)fluxes)showed positive(negative)peaks after the SBF’s passage,primarily caused by horizontal and vertical transport of heat(water vapor and CO_(2))during its passage.This study enhances understanding of boundary layer changes,turbulences,and fluxes during the passage of SBFs over urban areas.
基金This work was supported by Innovation and Technology Fund under Grant GHP/016/18GD and Guangdong Special Fund for Science and Technology Development under Grant 2019A050503001.
文摘In this paper,we develop an orthogonal frequency-division multiplexing(OFDM)-based over-theair(OTA)aggregation solution for wireless federated learning(FL).In particular,the local gradients in massive Internet of things(IoT)devices are modulated by an analog waveform and are then transmitted using the same wireless resources.To this end,achieving perfect waveform superposition is the key challenge,which is difficult due to the existence of frame timing offset(TO)and carrier frequency offset(CFO).In order to address these issues,we propose a two-stage waveform pre-equalization technique with a customized multiple access protocol that can estimate and then mitigate the TO and CFO for the OTA aggregation.Based on the proposed solution,we develop a hardware transceiver and application software to train a real-world FL task,which learns a deep neural network to predict the received signal strength with the global positioning system information.Experiments verify that the proposed OTA aggregation solution can achieve comparable performance to offline learning procedures with high prediction accuracy.
基金the National Key Research and Development Program of China in its project entitled‘Critical Technologies for Designing and Manufacturing±500 kV DC Cables and their Accessories’(no.2016YFB0900703)the State Grid Corporation of China in its project entitled‘Preliminary Feasibility Study on±800 kV DC Cable System’(no.SGRIDGKJ[2016]1185).
文摘This study sets out to discuss the challenges that need to be addressed effectively to facilitate the adoption of long distance high-voltage and ultra-high-voltage direct current(UHVDC)power transmission cables.As in the alternating current case,the desire to minimise the losses has involved the use of increasingly high transmission voltages,which presents particular problems where UHVDC cables are concerned.Specifically,this study presents the case for a novel,integrated approach to the problem,which links three distinct aspects of the problem,namely:(i)cable ratings and network operability;(ii)cable design and constituent insulating material requirements;and(iii)potential strategies for the design of novel insulation materials,where the required properties are actively‘designed in’.The study concludes that the impact of these factors acting in concert on network operation/performance requires a more integrated approach to the problem than has traditionally been the case.A number of complementary strategies for the development of novel material technologies and UHVDC cable designs are required that can meet the service performance and ultimate service lifetimes expected for new network applications.
基金State Grid Corporation of China,Grant/Award Number:5108-202218280A-2-78-XG。
文摘The potential of using eco-friendly thermoplastic polypropylene(PP)-based insulation for high voltage direct current(HVDC)cable has been widely investigated but much less work on the PP-based semiconducting screen(SC).Considering a long service life(>30 years)under high temperature and high electrical stress is required for typical HVDC cables,and investigations on the effect of antioxidant(AO)concentration and thermal oxidative sta-bility,mechanical,and electrical properties of PP-based SCs have been conducted.It has been demonstrated that an appropriate combination and amounts of AOs are critical for achieving high thermal stability and maintaining the mechanical properties of SC after ageing in a harsh environment(150°C,with Cu,in air,7 days).Although higher amounts of space charges have been observed in SC/PP/SC samples with higher AO concentrations,the impact on space charge behaviours is less after ageing,suggesting that ageing(or operating at high temperature)leads to microstructure evolution in SC and can potentially mitigate space accumulation in PP-based insulating materials.
