This paper presents a gradient-descent travel time tomography method for solving the acoustictype velocity model inversion problem.Similarly to the adjoint-state method,the proposed method is based on the Eikonal equa...This paper presents a gradient-descent travel time tomography method for solving the acoustictype velocity model inversion problem.Similarly to the adjoint-state method,the proposed method is based on the Eikonal equation,enabling simultaneous calculation of contributions from all common-source receivers to the gradient.This overcomes the inefficiency inherent in conventional travel time tomography methods,which rely on a two-point ray tracing process.By directly calculating Fréchet derivatives,our method avoids the complex derivation processes associated with the adjoint-state method.The key to calculating the Fréchet derivatives is to calculate a so-called ray-path term.Consequently,compared to the adjoint-state method,the proposed method can explicitly obtain the ray paths,resulting in a more concise and intuitive derivation process.Furthermore,our method retains the benefits of the adjoint-state method,such as speed,low memory usage,and robustness.This paper focuses on elucidating the principles and algorithms for calculating the raypath term based on the fast sweeping method.The algorithms could be further speeded up by using parallel computational techniques.Synthetic tests demonstrate that our proposed travel time tomographic method accurately calculates ray paths,regardless of the complexity of the model and recording geometry.展开更多
Understanding the interaction between groundwater and surface water in permafrost regions is essential to study flood frequencies and river water quality, especially in the high latitude/altitude basins. The applicati...Understanding the interaction between groundwater and surface water in permafrost regions is essential to study flood frequencies and river water quality, especially in the high latitude/altitude basins. The application of heat tracing method,based on oscillating streambed temperature signals, is a promising geophysical method for identifying and quantifying the interaction between groundwater and surface water. Analytical analysis based on a one-dimensional convective-conductive heat transport equation combined with the fiber-optic distributed temperature sensing method was applied on a streambed of a mountainous permafrost region in the Yeniugou Basin, located in the upper Heihe River on the northern Tibetan Plateau. The results indicated that low connectivity existed between the stream and groundwater in permafrost regions.The interaction between surface water and groundwater increased with the thawing of the active layer. This study demonstrates that the heat tracing method can be applied to study surface water-groundwater interaction over temporal and spatial scales in permafrost regions.展开更多
A型牛轮状病毒(BRV-A)是引起牛腹泻的重要病原之一,对养牛业危害最大。为建立一种针对BRV-A的快速、高通量、低成本检测方法,根据BRV-A的VP6基因保守区设计特异性引物,建立了检测BRV-A的SYBR Green I RT-qPCR方法。该方法对浓度梯度为4....A型牛轮状病毒(BRV-A)是引起牛腹泻的重要病原之一,对养牛业危害最大。为建立一种针对BRV-A的快速、高通量、低成本检测方法,根据BRV-A的VP6基因保守区设计特异性引物,建立了检测BRV-A的SYBR Green I RT-qPCR方法。该方法对浓度梯度为4.41×10^(8)~4.41×10^(2) copies/μL质粒标准品的扩增Ct值与拷贝数浓度呈良好的线性关系,熔解曲线为单峰;与其他引起牛腹泻的常见病原无交叉反应,最低检测限为4.41×10^(1) copies/μL,批内、批间重复性试验Ct值变异系数均低于1%;对临床粪便样品的阳性检出率高于地方标准中的PCR方法,且检测结果符合性较好。综上,本研究建立的BRV-A SYBR Green I RT-qPCR检测方法灵敏、特异、稳定,且操作简单、成本低,为临床样品的大规模BRV-A检测及其感染的早期诊断提供了技术支撑。展开更多
The classical Lagrangian particle tracing method is widely used in the evaluation of the ocean annual subduction rate.However,our analysis indicates that in addition to neglecting the effect of mixing,there are two po...The classical Lagrangian particle tracing method is widely used in the evaluation of the ocean annual subduction rate.However,our analysis indicates that in addition to neglecting the effect of mixing,there are two possible deviations in the method:one is an overestimation due to not considering that the amount of subducted water at the source location may be inadequate during the late winter of the first year when the mixed layer becomes shallow;the other one is an underestimation due to the neglect of the effective subduction caused by strong vertical pumping.Quantitative analysis shows that these two deviations mainly exist in the low-latitude subduction areas of the South Pacific and South Atlantic.The two deviations have very similar distribution areas and can partially off set each other.However,the overall deviation is still large,and the maximum relative deviation ratio can reach 50%;therefore,it cannot be ignored.展开更多
The COVID-19 pandemic has underscored the critical need for rapid and accurate diagnostic tools.Current methods,including Polymerase Chain Reaction and rapid antigen tests(RAT),have limitations in speed,sensitivity,an...The COVID-19 pandemic has underscored the critical need for rapid and accurate diagnostic tools.Current methods,including Polymerase Chain Reaction and rapid antigen tests(RAT),have limitations in speed,sensitivity,and the requirement for specialized equipment and trained personnel.Nanotechnology,particularly upconversion nanoparticles(UCNPs),offer a promising alternative due to their unique optical properties.UCNPs can convert low-energy near-infrared light into higher-energy visible light,making them ideal for use as optical probes in single molecule detection and point of care applications.This study,initiated in early 2020,explores the opportunity of using highly doped UCNPs(40%Yb^(3+)/4%Er^(3+))in lateral flow assay(LFA)for the early diagnosis of COVID-19.The UCNPsbased LFA testing demonstrated a minimum detection concentration of 100 pg/mL for SARS-CoV-2 antigen and 10^(5)CCID_(50)/mL for inactivated virus.Clinical trials,conducted in Malaysia and Western Australia independently,showed that the technique was at least 100 times more sensitive than commercial RAT kits,with a sensitivity of 100%and specificity of 91.94%.The development process involved multidisciplinary collaborations,resulting in the Virulizer device,an automated strip reader for point-of-care testing.This work sets a reference for future development of highly sensitive and quantitative RAT,aiming for the Limits of Detection in the range of sub-ng/mL.展开更多
An optical emission spectroscopy(OES)method with a non-invasive measurement capability,without inducing disturbance to the discharge,represents an effective method for material monitoring.However,when the OES method i...An optical emission spectroscopy(OES)method with a non-invasive measurement capability,without inducing disturbance to the discharge,represents an effective method for material monitoring.However,when the OES method is employed to monitor the trace erosion product within the ceramic channel of a Hall thruster,it becomes challenging to distinguish between signal and noise.In this study,we propose a model filtering method based on the signal characteristics of the Hall thruster plume spectrometer.This method integrates the slit imaging and spectral resolution features of the spectrometer.Employing this method,we extract the spectral signals of the erosion product and working gas from the Hall thruster under different operating conditions.The results indicate that our new method performs comparably to the traditional method without model filtering when extracting atom signals from strong xenon working gas.However,for trace amounts of the erosion product,our approach significantly enhances the signal-to-noise ratio(SNR),enabling the identification of extremely weak spectral signals even under low mass flow rate and low-voltage conditions.We obtain boron atom concentration of 3.91×10^(-3) kg/m^(3) at a mass flow rate of 4×10^(-7) kg/s and voltage of 200 V while monitoring a wider range of thruster operating conditions.The new method proposed in this study is suitable for monitoring other low-concentration elements,making it valuable for materials processing,environmental monitoring and space propulsion applications.展开更多
The intersection method is one of the basic approaches for locating earthquakes and is not only robust but also efficient. However, its location accuracy is not high, especially for focal depth because the velocity mo...The intersection method is one of the basic approaches for locating earthquakes and is not only robust but also efficient. However, its location accuracy is not high, especially for focal depth because the velocity model used for the conventional intersection method is based on homogeneous or laterally homogeneous media, which is too simple. In order to improve the accuracy, we have modified the existing intersection method. In the modified approach, the earthquake loci are not assumed to be circular or hyperbolic and calculation accuracy is improved using a minimum traveltime tree algorithm for tracing rays. The numerical model shows that the modified method can locate earthquakes in complex velocity models.展开更多
基金supported by 14th Five-Year Plan major science and technology projects(no.KJGG2022-0201)。
文摘This paper presents a gradient-descent travel time tomography method for solving the acoustictype velocity model inversion problem.Similarly to the adjoint-state method,the proposed method is based on the Eikonal equation,enabling simultaneous calculation of contributions from all common-source receivers to the gradient.This overcomes the inefficiency inherent in conventional travel time tomography methods,which rely on a two-point ray tracing process.By directly calculating Fréchet derivatives,our method avoids the complex derivation processes associated with the adjoint-state method.The key to calculating the Fréchet derivatives is to calculate a so-called ray-path term.Consequently,compared to the adjoint-state method,the proposed method can explicitly obtain the ray paths,resulting in a more concise and intuitive derivation process.Furthermore,our method retains the benefits of the adjoint-state method,such as speed,low memory usage,and robustness.This paper focuses on elucidating the principles and algorithms for calculating the raypath term based on the fast sweeping method.The algorithms could be further speeded up by using parallel computational techniques.Synthetic tests demonstrate that our proposed travel time tomographic method accurately calculates ray paths,regardless of the complexity of the model and recording geometry.
基金supported by the National Natural Science Foundation of China(41690141,41671067)the second Tibetan Plateau Scientific Expedition and Research Program(STEP)(2019QZKK0605)+1 种基金the Fundamental Research Funds for Central Universities(lzujbky-2019-40)CAS"Light of West China"and the State Key Laboratory of Cryospheric Science,CAS(SKLCS-ZZ-2020).
文摘Understanding the interaction between groundwater and surface water in permafrost regions is essential to study flood frequencies and river water quality, especially in the high latitude/altitude basins. The application of heat tracing method,based on oscillating streambed temperature signals, is a promising geophysical method for identifying and quantifying the interaction between groundwater and surface water. Analytical analysis based on a one-dimensional convective-conductive heat transport equation combined with the fiber-optic distributed temperature sensing method was applied on a streambed of a mountainous permafrost region in the Yeniugou Basin, located in the upper Heihe River on the northern Tibetan Plateau. The results indicated that low connectivity existed between the stream and groundwater in permafrost regions.The interaction between surface water and groundwater increased with the thawing of the active layer. This study demonstrates that the heat tracing method can be applied to study surface water-groundwater interaction over temporal and spatial scales in permafrost regions.
文摘A型牛轮状病毒(BRV-A)是引起牛腹泻的重要病原之一,对养牛业危害最大。为建立一种针对BRV-A的快速、高通量、低成本检测方法,根据BRV-A的VP6基因保守区设计特异性引物,建立了检测BRV-A的SYBR Green I RT-qPCR方法。该方法对浓度梯度为4.41×10^(8)~4.41×10^(2) copies/μL质粒标准品的扩增Ct值与拷贝数浓度呈良好的线性关系,熔解曲线为单峰;与其他引起牛腹泻的常见病原无交叉反应,最低检测限为4.41×10^(1) copies/μL,批内、批间重复性试验Ct值变异系数均低于1%;对临床粪便样品的阳性检出率高于地方标准中的PCR方法,且检测结果符合性较好。综上,本研究建立的BRV-A SYBR Green I RT-qPCR检测方法灵敏、特异、稳定,且操作简单、成本低,为临床样品的大规模BRV-A检测及其感染的早期诊断提供了技术支撑。
基金Supported by the National Natural Science Foundation of China(No.41676009)the National Key R&D Program of China(No.2016YFC0301203)the State Key Program of National Natural Science of China(No.41730534)。
文摘The classical Lagrangian particle tracing method is widely used in the evaluation of the ocean annual subduction rate.However,our analysis indicates that in addition to neglecting the effect of mixing,there are two possible deviations in the method:one is an overestimation due to not considering that the amount of subducted water at the source location may be inadequate during the late winter of the first year when the mixed layer becomes shallow;the other one is an underestimation due to the neglect of the effective subduction caused by strong vertical pumping.Quantitative analysis shows that these two deviations mainly exist in the low-latitude subduction areas of the South Pacific and South Atlantic.The two deviations have very similar distribution areas and can partially off set each other.However,the overall deviation is still large,and the maximum relative deviation ratio can reach 50%;therefore,it cannot be ignored.
基金approved by the Ethics Committee at the University of Technology Sydney(ETH22-7241)written informed consent(according to the UTS clinical trial declaration)was obtained from all patients before the COVID-19 testing.
文摘The COVID-19 pandemic has underscored the critical need for rapid and accurate diagnostic tools.Current methods,including Polymerase Chain Reaction and rapid antigen tests(RAT),have limitations in speed,sensitivity,and the requirement for specialized equipment and trained personnel.Nanotechnology,particularly upconversion nanoparticles(UCNPs),offer a promising alternative due to their unique optical properties.UCNPs can convert low-energy near-infrared light into higher-energy visible light,making them ideal for use as optical probes in single molecule detection and point of care applications.This study,initiated in early 2020,explores the opportunity of using highly doped UCNPs(40%Yb^(3+)/4%Er^(3+))in lateral flow assay(LFA)for the early diagnosis of COVID-19.The UCNPsbased LFA testing demonstrated a minimum detection concentration of 100 pg/mL for SARS-CoV-2 antigen and 10^(5)CCID_(50)/mL for inactivated virus.Clinical trials,conducted in Malaysia and Western Australia independently,showed that the technique was at least 100 times more sensitive than commercial RAT kits,with a sensitivity of 100%and specificity of 91.94%.The development process involved multidisciplinary collaborations,resulting in the Virulizer device,an automated strip reader for point-of-care testing.This work sets a reference for future development of highly sensitive and quantitative RAT,aiming for the Limits of Detection in the range of sub-ng/mL.
基金financially supported by National Natural Science Foundation of China(No.U22B2094)。
文摘An optical emission spectroscopy(OES)method with a non-invasive measurement capability,without inducing disturbance to the discharge,represents an effective method for material monitoring.However,when the OES method is employed to monitor the trace erosion product within the ceramic channel of a Hall thruster,it becomes challenging to distinguish between signal and noise.In this study,we propose a model filtering method based on the signal characteristics of the Hall thruster plume spectrometer.This method integrates the slit imaging and spectral resolution features of the spectrometer.Employing this method,we extract the spectral signals of the erosion product and working gas from the Hall thruster under different operating conditions.The results indicate that our new method performs comparably to the traditional method without model filtering when extracting atom signals from strong xenon working gas.However,for trace amounts of the erosion product,our approach significantly enhances the signal-to-noise ratio(SNR),enabling the identification of extremely weak spectral signals even under low mass flow rate and low-voltage conditions.We obtain boron atom concentration of 3.91×10^(-3) kg/m^(3) at a mass flow rate of 4×10^(-7) kg/s and voltage of 200 V while monitoring a wider range of thruster operating conditions.The new method proposed in this study is suitable for monitoring other low-concentration elements,making it valuable for materials processing,environmental monitoring and space propulsion applications.
基金This work is supported by the National Natural Science Foundation of China(40674044)the Special Foundation for Basic Professional Scientific Research (DQJB06A02)
文摘The intersection method is one of the basic approaches for locating earthquakes and is not only robust but also efficient. However, its location accuracy is not high, especially for focal depth because the velocity model used for the conventional intersection method is based on homogeneous or laterally homogeneous media, which is too simple. In order to improve the accuracy, we have modified the existing intersection method. In the modified approach, the earthquake loci are not assumed to be circular or hyperbolic and calculation accuracy is improved using a minimum traveltime tree algorithm for tracing rays. The numerical model shows that the modified method can locate earthquakes in complex velocity models.
