A rapid GC-FID method was developed to simultaneously determine residual levels of triethylamine(TEA), 1,1,3,3-tetramethylguanidine(TMG), and diisopropylamine(DIPA) in the synthetic route of an active pharmaceutical i...A rapid GC-FID method was developed to simultaneously determine residual levels of triethylamine(TEA), 1,1,3,3-tetramethylguanidine(TMG), and diisopropylamine(DIPA) in the synthetic route of an active pharmaceutical ingredient(API). Due to the severe absorption of amines on GC stationary phases,GC columns with various stationary phases were evaluated for optimal peak shape and reproducibility.The final conditions used the Agilent CP-Volamine column to resolve the three amines in 12 min. Various inlet liners were also screened to further improve the sensitivity of the analysis. The Restek Siltek~? liner was selected to achieve the desired detectability for the method. The quantitation limits were 4, 3, and 4 mg/mL for TEA, DIPA, and TMG in the presence of API, respectively. All three amines showed good linearity(r > 0.999) and recoveries(> 90%) over the concentration range of 3 to 16 mg/mL. The testing of residual amines was initially performed at the penultimate stage of the synthesis. However, this work demonstrates that TMG can act as a proton sponge to react with salicylic acid, the counter ion of the penultimate, to form a volatile component that elutes at a different retention time. Consequently, in the final method, these three amines were monitored in the final API to circumvent the matrix interference.Key parameters of the method were qualified per method validation requirements in ICH guidelines. The method was successfully applied for batch testing during development and implemented as an inprocess control procedure at manufacturing sites.展开更多
Gas chromatography equipped with an electron capture detector （GC-ECD） has been widely used for measuring atmospheric N2O,but nonlinear response and the influence of atmospheric CO2 have been recognized as defects f...Gas chromatography equipped with an electron capture detector （GC-ECD） has been widely used for measuring atmospheric N2O,but nonlinear response and the influence of atmospheric CO2 have been recognized as defects for quantification.An original GCECD method using N 2 as carrier gas was improved by introducing a small flow rate of CO2 makeup gas into the ECD,which could well remedy the above defects.The N2O signal of the improved method was 4-fold higher than that of the original method and the relative standard deviation was reduced from 〉 1% to 0.31%.N2O concentrations with different CO2 concentrations （172.2×10-6-1722×10-6mol/mol） measured by the improved GC-ECD method were in line with the actual N2O concentrations.However,the N2O concentrations detected by the original method were largely biased with a variation range of-4.5%～7%.The N2O fluxes between an agricultural field and the atmosphere measured by the original method were greatly overestimated in comparison with those measured by the improved method.Good linear correlation （R2=0.9996） between the response of the improved ECD and N2O concentrations （93×10-9-1966×10-9mol/mol） indicated that atmospheric N2O could be accurately quantified via a single standard gas.Atmospheric N2O concentrations comparatively measured by the improved method and a high precision GC-ECD method were in good agreement.展开更多
To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fract...To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.展开更多
Modal parameters can accurately characterize the structural dynamic properties and assess the physical state of the structure.Therefore,it is particularly significant to identify the structural modal parameters accordi...Modal parameters can accurately characterize the structural dynamic properties and assess the physical state of the structure.Therefore,it is particularly significant to identify the structural modal parameters according to the monitoring data information in the structural health monitoring(SHM)system,so as to provide a scientific basis for structural damage identification and dynamic model modification.In view of this,this paper reviews methods for identifying structural modal parameters under environmental excitation and briefly describes how to identify structural damages based on the derived modal parameters.The paper primarily introduces data-driven modal parameter recognition methods(e.g.,time-domain,frequency-domain,and time-frequency-domain methods,etc.),briefly describes damage identification methods based on the variations of modal parameters(e.g.,natural frequency,modal shapes,and curvature modal shapes,etc.)and modal validation methods(e.g.,Stability Diagram and Modal Assurance Criterion,etc.).The current status of the application of artificial intelligence(AI)methods in the direction of modal parameter recognition and damage identification is further discussed.Based on the pre-vious analysis,the main development trends of structural modal parameter recognition and damage identification methods are given to provide scientific references for the optimized design and functional upgrading of SHM systems.展开更多
The methods of determination of 6-methyl coumarin in cosmetics by HPLC-DAD and GC-FID were compared. The positive samples were confirmed by GC-MS. Methanol was used to extract 6-methyl coumarin from cosmetics. The chr...The methods of determination of 6-methyl coumarin in cosmetics by HPLC-DAD and GC-FID were compared. The positive samples were confirmed by GC-MS. Methanol was used to extract 6-methyl coumarin from cosmetics. The chromatographic conditions of the two methods were optimized and the samples were determined. The recovery, precision, correlation coefficient, detection limit and quantitative limit of the two methods were compared. The results showed that the linear relationship between the two methods was good. The percentage recovery of standard addition by HPLC-DAD was 92.20%~102.80%, by RSD was 0.77%~2.00%;the detection limit was 0.05 mg/kg, the quantitative limit was 0.17 mg/kg. The percentage recovery of standard addition by GC-FID was 97.30%~103.28%, by RSD was 0.47%~4.87%;the detection limit was 1.3 mg/kg, the quantitative limit was 5.0 mg/kg. The detection limit by HPLC-DAD was lower and more sensitive than that by GC-FID , which also shows that HPLC-DAD has more advantages for the detection of low content samples.展开更多
A reliable and sensitive method is developed for the detection of common diuretics in human urine. diuretics along with probenecid are methylated and subjected to GC-MS analysis.Both chromatographic and mass spectrom...A reliable and sensitive method is developed for the detection of common diuretics in human urine. diuretics along with probenecid are methylated and subjected to GC-MS analysis.Both chromatographic and mass spectrometric data are obtained in selected ion monitoring and full scanning modes.The average detection limit is 0.1-1.0 ag/mi urine.This method is suitable to large-scale and routine screening or confirmation of diuretics in doping control.展开更多
A reliable method is described for the detection of amitoride,triamterene. canrenone and spironolactone in human urine using GC-MS analysis after trimethytsitytation.The mass spectrometric and metabotic features of th...A reliable method is described for the detection of amitoride,triamterene. canrenone and spironolactone in human urine using GC-MS analysis after trimethytsitytation.The mass spectrometric and metabotic features of the compounds are discussed展开更多
This study investigated the physicochemical properties,enzyme activities,volatile flavor components,microbial communities,and sensory evaluation of high-temperature Daqu(HTD)during the maturation process,and a standar...This study investigated the physicochemical properties,enzyme activities,volatile flavor components,microbial communities,and sensory evaluation of high-temperature Daqu(HTD)during the maturation process,and a standard system was established for comprehensive quality evaluation of HTD.There were obvious changes in the physicochemical properties,enzyme activities,and volatile flavor components at different storage periods,which affected the sensory evaluation of HTD to a certain extent.The results of high-throughput sequencing revealed significant microbial diversity,and showed that the bacterial community changed significantly more than did the fungal community.During the storage process,the dominant bacterial genera were Kroppenstedtia and Thermoascus.The correlation between dominant microorganisms and quality indicators highlighted their role in HTD quality.Lactococcus,Candida,Pichia,Paecilomyces,and protease activity played a crucial role in the formation of isovaleraldehyde.Acidic protease activity had the greatest impact on the microbial community.Moisture promoted isobutyric acid generation.Furthermore,the comprehensive quality evaluation standard system was established by the entropy weight method combined with multi-factor fuzzy mathematics.Consequently,this study provides innovative insights for comprehensive quality evaluation of HTD during storage and establishes a groundwork for scientific and rational storage of HTD and quality control of sauce-flavor Baijiu.展开更多
Due to the heterogeneity of rock masses and the variability of in situ stress,the traditional linear inversion method is insufficiently accurate to achieve high accuracy of the in situ stress field.To address this cha...Due to the heterogeneity of rock masses and the variability of in situ stress,the traditional linear inversion method is insufficiently accurate to achieve high accuracy of the in situ stress field.To address this challenge,nonlinear stress boundaries for a numerical model are determined through regression analysis of a series of nonlinear coefficient matrices,which are derived from the bubbling method.Considering the randomness and flexibility of the bubbling method,a parametric study is conducted to determine recommended ranges for these parameters,including the standard deviation(σb)of bubble radii,the non-uniform coefficient matrix number(λ)for nonlinear stress boundaries,and the number(m)and positions of in situ stress measurement points.A model case study provides a reference for the selection of these parameters.Additionally,when the nonlinear in situ stress inversion method is employed,stress distortion inevitably occurs near model boundaries,aligning with the Saint Venant's principle.Two strategies are proposed accordingly:employing a systematic reduction of nonlinear coefficients to achieve high inversion accuracy while minimizing significant stress distortion,and excluding regions with severe stress distortion near the model edges while utilizing the central part of the model for subsequent simulations.These two strategies have been successfully implemented in the nonlinear in situ stress inversion of the Xincheng Gold Mine and have achieved higher inversion accuracy than the linear method.Specifically,the linear and nonlinear inversion methods yield root mean square errors(RMSE)of 4.15 and 3.2,and inversion relative errors(δAve)of 22.08%and 17.55%,respectively.Therefore,the nonlinear inversion method outperforms the traditional multiple linear regression method,even in the presence of a systematic reduction in the nonlinear stress boundaries.展开更多
The separation-of-variable(SOV)methods,such as the improved SOV method,the variational SOV method,and the extended SOV method,have been proposed by the present authors and coworkers to obtain the closed-form analytica...The separation-of-variable(SOV)methods,such as the improved SOV method,the variational SOV method,and the extended SOV method,have been proposed by the present authors and coworkers to obtain the closed-form analytical solutions for free vibration and eigenbuckling of rectangular plates and circular cylindrical shells.By taking the free vibration of rectangular thin plates as an example,this work presents the theoretical framework of the SOV methods in an instructive way,and the bisection–based solution procedures for a group of nonlinear eigenvalue equations.Besides,the explicit equations of nodal lines of the SOV methods are presented,and the relations of nodal line patterns and frequency orders are investigated.It is concluded that the highly accurate SOV methods have the same accuracy for all frequencies,the mode shapes about repeated frequencies can also be precisely captured,and the SOV methods do not have the problem of missing roots as well.展开更多
Soil improvement is one of the most important issues in geotechnical engineering practice.The wide application of traditional improvement techniques(cement/chemical materials)are limited due to damage ecological en-vi...Soil improvement is one of the most important issues in geotechnical engineering practice.The wide application of traditional improvement techniques(cement/chemical materials)are limited due to damage ecological en-vironment and intensify carbon emissions.However,the use of microbially induced calcium carbonate pre-cipitation(MICP)to obtain bio-cement is a novel technique with the potential to induce soil stability,providing a low-carbon,environment-friendly,and sustainable integrated solution for some geotechnical engineering pro-blems in the environment.This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy.It systematically summarizes and overviews the mineralization mechanism,influ-encing factors,improved methods,engineering characteristics,and current field application status of the MICP.Additionally,it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement.This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand.Furthermore,we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future.The current review purports to provide insights for engineers and interdisciplinary researchers,and guidance for future engineering applications.展开更多
文摘A rapid GC-FID method was developed to simultaneously determine residual levels of triethylamine(TEA), 1,1,3,3-tetramethylguanidine(TMG), and diisopropylamine(DIPA) in the synthetic route of an active pharmaceutical ingredient(API). Due to the severe absorption of amines on GC stationary phases,GC columns with various stationary phases were evaluated for optimal peak shape and reproducibility.The final conditions used the Agilent CP-Volamine column to resolve the three amines in 12 min. Various inlet liners were also screened to further improve the sensitivity of the analysis. The Restek Siltek~? liner was selected to achieve the desired detectability for the method. The quantitation limits were 4, 3, and 4 mg/mL for TEA, DIPA, and TMG in the presence of API, respectively. All three amines showed good linearity(r > 0.999) and recoveries(> 90%) over the concentration range of 3 to 16 mg/mL. The testing of residual amines was initially performed at the penultimate stage of the synthesis. However, this work demonstrates that TMG can act as a proton sponge to react with salicylic acid, the counter ion of the penultimate, to form a volatile component that elutes at a different retention time. Consequently, in the final method, these three amines were monitored in the final API to circumvent the matrix interference.Key parameters of the method were qualified per method validation requirements in ICH guidelines. The method was successfully applied for batch testing during development and implemented as an inprocess control procedure at manufacturing sites.
基金supported by the Special Fund for Environmental Research in the Public Interest(No.201009001)the National Natural Science Foundation of China(No.41075094,21177140 and 40830101)the National Basic Research and the Development Program(973)of China(No.2010CB732304)
文摘Gas chromatography equipped with an electron capture detector （GC-ECD） has been widely used for measuring atmospheric N2O,but nonlinear response and the influence of atmospheric CO2 have been recognized as defects for quantification.An original GCECD method using N 2 as carrier gas was improved by introducing a small flow rate of CO2 makeup gas into the ECD,which could well remedy the above defects.The N2O signal of the improved method was 4-fold higher than that of the original method and the relative standard deviation was reduced from 〉 1% to 0.31%.N2O concentrations with different CO2 concentrations （172.2×10-6-1722×10-6mol/mol） measured by the improved GC-ECD method were in line with the actual N2O concentrations.However,the N2O concentrations detected by the original method were largely biased with a variation range of-4.5%～7%.The N2O fluxes between an agricultural field and the atmosphere measured by the original method were greatly overestimated in comparison with those measured by the improved method.Good linear correlation （R2=0.9996） between the response of the improved ECD and N2O concentrations （93×10-9-1966×10-9mol/mol） indicated that atmospheric N2O could be accurately quantified via a single standard gas.Atmospheric N2O concentrations comparatively measured by the improved method and a high precision GC-ECD method were in good agreement.
基金funded by the project of the Major Scientific and Technological Projects of CNOOC in the 14th Five-Year Plan(No.KJGG2022-0701)the CNOOC Research Institute(No.2020PFS-03).
文摘To analyze the differences in the transport and distribution of different types of proppants and to address issues such as the short effective support of proppant and poor placement in hydraulically intersecting fractures,this study considered the combined impact of geological-engineering factors on conductivity.Using reservoir production parameters and the discrete elementmethod,multispherical proppants were constructed.Additionally,a 3D fracture model,based on the specified conditions of the L block,employed coupled(Computational Fluid Dynamics)CFD-DEM(Discrete ElementMethod)for joint simulations to quantitatively analyze the transport and placement patterns of multispherical proppants in intersecting fractures.Results indicate that turbulent kinetic energy is an intrinsic factor affecting proppant transport.Moreover,the efficiency of placement and migration distance of low-sphericity quartz sand constructed by the DEM in the main fracture are significantly reduced compared to spherical ceramic proppants,with a 27.7%decrease in the volume fraction of the fracture surface,subsequently affecting the placement concentration and damaging fracture conductivity.Compared to small-angle fractures,controlling artificial and natural fractures to expand at angles of 45°to 60°increases the effective support length by approximately 20.6%.During hydraulic fracturing of gas wells,ensuring the fracture support area and post-closure conductivity can be achieved by controlling the sphericity of proppants and adjusting the perforation direction to control the direction of artificial fractures.
基金supported by the Innovation Foundation of Provincial Education Department of Gansu(2024B-005)the Gansu Province National Science Foundation(22YF7GA182)the Fundamental Research Funds for the Central Universities(No.lzujbky2022-kb01)。
文摘Modal parameters can accurately characterize the structural dynamic properties and assess the physical state of the structure.Therefore,it is particularly significant to identify the structural modal parameters according to the monitoring data information in the structural health monitoring(SHM)system,so as to provide a scientific basis for structural damage identification and dynamic model modification.In view of this,this paper reviews methods for identifying structural modal parameters under environmental excitation and briefly describes how to identify structural damages based on the derived modal parameters.The paper primarily introduces data-driven modal parameter recognition methods(e.g.,time-domain,frequency-domain,and time-frequency-domain methods,etc.),briefly describes damage identification methods based on the variations of modal parameters(e.g.,natural frequency,modal shapes,and curvature modal shapes,etc.)and modal validation methods(e.g.,Stability Diagram and Modal Assurance Criterion,etc.).The current status of the application of artificial intelligence(AI)methods in the direction of modal parameter recognition and damage identification is further discussed.Based on the pre-vious analysis,the main development trends of structural modal parameter recognition and damage identification methods are given to provide scientific references for the optimized design and functional upgrading of SHM systems.
文摘The methods of determination of 6-methyl coumarin in cosmetics by HPLC-DAD and GC-FID were compared. The positive samples were confirmed by GC-MS. Methanol was used to extract 6-methyl coumarin from cosmetics. The chromatographic conditions of the two methods were optimized and the samples were determined. The recovery, precision, correlation coefficient, detection limit and quantitative limit of the two methods were compared. The results showed that the linear relationship between the two methods was good. The percentage recovery of standard addition by HPLC-DAD was 92.20%~102.80%, by RSD was 0.77%~2.00%;the detection limit was 0.05 mg/kg, the quantitative limit was 0.17 mg/kg. The percentage recovery of standard addition by GC-FID was 97.30%~103.28%, by RSD was 0.47%~4.87%;the detection limit was 1.3 mg/kg, the quantitative limit was 5.0 mg/kg. The detection limit by HPLC-DAD was lower and more sensitive than that by GC-FID , which also shows that HPLC-DAD has more advantages for the detection of low content samples.
文摘A reliable and sensitive method is developed for the detection of common diuretics in human urine. diuretics along with probenecid are methylated and subjected to GC-MS analysis.Both chromatographic and mass spectrometric data are obtained in selected ion monitoring and full scanning modes.The average detection limit is 0.1-1.0 ag/mi urine.This method is suitable to large-scale and routine screening or confirmation of diuretics in doping control.
文摘A reliable method is described for the detection of amitoride,triamterene. canrenone and spironolactone in human urine using GC-MS analysis after trimethytsitytation.The mass spectrometric and metabotic features of the compounds are discussed
文摘This study investigated the physicochemical properties,enzyme activities,volatile flavor components,microbial communities,and sensory evaluation of high-temperature Daqu(HTD)during the maturation process,and a standard system was established for comprehensive quality evaluation of HTD.There were obvious changes in the physicochemical properties,enzyme activities,and volatile flavor components at different storage periods,which affected the sensory evaluation of HTD to a certain extent.The results of high-throughput sequencing revealed significant microbial diversity,and showed that the bacterial community changed significantly more than did the fungal community.During the storage process,the dominant bacterial genera were Kroppenstedtia and Thermoascus.The correlation between dominant microorganisms and quality indicators highlighted their role in HTD quality.Lactococcus,Candida,Pichia,Paecilomyces,and protease activity played a crucial role in the formation of isovaleraldehyde.Acidic protease activity had the greatest impact on the microbial community.Moisture promoted isobutyric acid generation.Furthermore,the comprehensive quality evaluation standard system was established by the entropy weight method combined with multi-factor fuzzy mathematics.Consequently,this study provides innovative insights for comprehensive quality evaluation of HTD during storage and establishes a groundwork for scientific and rational storage of HTD and quality control of sauce-flavor Baijiu.
基金funded by the National Key R&D Program of China(Grant No.2022YFC2903904)the National Natural Science Foundation of China(Grant Nos.51904057 and U1906208).
文摘Due to the heterogeneity of rock masses and the variability of in situ stress,the traditional linear inversion method is insufficiently accurate to achieve high accuracy of the in situ stress field.To address this challenge,nonlinear stress boundaries for a numerical model are determined through regression analysis of a series of nonlinear coefficient matrices,which are derived from the bubbling method.Considering the randomness and flexibility of the bubbling method,a parametric study is conducted to determine recommended ranges for these parameters,including the standard deviation(σb)of bubble radii,the non-uniform coefficient matrix number(λ)for nonlinear stress boundaries,and the number(m)and positions of in situ stress measurement points.A model case study provides a reference for the selection of these parameters.Additionally,when the nonlinear in situ stress inversion method is employed,stress distortion inevitably occurs near model boundaries,aligning with the Saint Venant's principle.Two strategies are proposed accordingly:employing a systematic reduction of nonlinear coefficients to achieve high inversion accuracy while minimizing significant stress distortion,and excluding regions with severe stress distortion near the model edges while utilizing the central part of the model for subsequent simulations.These two strategies have been successfully implemented in the nonlinear in situ stress inversion of the Xincheng Gold Mine and have achieved higher inversion accuracy than the linear method.Specifically,the linear and nonlinear inversion methods yield root mean square errors(RMSE)of 4.15 and 3.2,and inversion relative errors(δAve)of 22.08%and 17.55%,respectively.Therefore,the nonlinear inversion method outperforms the traditional multiple linear regression method,even in the presence of a systematic reduction in the nonlinear stress boundaries.
基金supported by the National Natural Science Foundation of China(12172023).
文摘The separation-of-variable(SOV)methods,such as the improved SOV method,the variational SOV method,and the extended SOV method,have been proposed by the present authors and coworkers to obtain the closed-form analytical solutions for free vibration and eigenbuckling of rectangular plates and circular cylindrical shells.By taking the free vibration of rectangular thin plates as an example,this work presents the theoretical framework of the SOV methods in an instructive way,and the bisection–based solution procedures for a group of nonlinear eigenvalue equations.Besides,the explicit equations of nodal lines of the SOV methods are presented,and the relations of nodal line patterns and frequency orders are investigated.It is concluded that the highly accurate SOV methods have the same accuracy for all frequencies,the mode shapes about repeated frequencies can also be precisely captured,and the SOV methods do not have the problem of missing roots as well.
基金funded by the National Natural Science Foundation of China(No.41962016)the Natural Science Foundation of NingXia(Nos.2023AAC02023,2023A1218,and 2021AAC02006).
文摘Soil improvement is one of the most important issues in geotechnical engineering practice.The wide application of traditional improvement techniques(cement/chemical materials)are limited due to damage ecological en-vironment and intensify carbon emissions.However,the use of microbially induced calcium carbonate pre-cipitation(MICP)to obtain bio-cement is a novel technique with the potential to induce soil stability,providing a low-carbon,environment-friendly,and sustainable integrated solution for some geotechnical engineering pro-blems in the environment.This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy.It systematically summarizes and overviews the mineralization mechanism,influ-encing factors,improved methods,engineering characteristics,and current field application status of the MICP.Additionally,it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement.This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand.Furthermore,we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future.The current review purports to provide insights for engineers and interdisciplinary researchers,and guidance for future engineering applications.
