Fracability evaluation is critical for efficiently extracting deep shale gas using hydraulic fracturing to avoid blind drilling and fracking.However,existing fracability indices often fail to systematically consider t...Fracability evaluation is critical for efficiently extracting deep shale gas using hydraulic fracturing to avoid blind drilling and fracking.However,existing fracability indices often fail to systematically consider the mechanical behavior of rocks at high temperatures and high pressures(HTHP),coupled with geostress distributions and heterogeneous reservoir characteristics.This critical omission limits their effectiveness in accurately identifying the optimal fracability sweet spots within deep reservoirs.In this work,a fracability evaluation model was proposed based on the combined weighting method,integrating the improved brittleness index,rock strength,geostresses and natural weakness characteristics.A fracability grading evaluation was carried out to determine the potential fracture characteristics corresponding to shales with different fracability levels.Additionally,the fracability index was used for field validation and applications.Results show that rock brittleness and fracability are not equivalent for deep reservoirs.The fracability index is closely related to the pay zones and actual gas production,with a correlation as high as 84%,implying that the proposed method has practical significance in both experimental and field applications.The above findings can provide theoretical guidance for the selection of fracturing candidates and the optimal design of fracturing in deep resource development.展开更多
Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstan...Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge code. The mode transitions, also known as density jumps, of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude standing helicon waves(SHWs) are responsible for the mode transitions, similar to those of a resonant cavity for laser generation.This paper intends to give a complete and quantitative SHW resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.展开更多
To study the microscopic structure,thermal and mechanical properties of sandstones under the influence of temperature,coal measure sandstones from Southwest China are adopted as the research object to carry out high-t...To study the microscopic structure,thermal and mechanical properties of sandstones under the influence of temperature,coal measure sandstones from Southwest China are adopted as the research object to carry out high-temperature tests at 25℃-1000℃.The microscopic images of sandstone after thermal treatment are obtained by means of polarizing microscopy and scanning electron microscopy(SEM).Based on thermogravimetric(TG)analysis and differential scanning calorimetric(DSC)analysis,the model function of coal measure sandstone is explored through thermal analysis kinetics(TAK)theory,and the kinetic parameters of thermal decomposition and the thermal decomposition reaction rate of rock are studied.Through the uniaxial compression experiments,the stress‒strain curves and strength characteristics of sandstone under the influence of temperature are obtained.The results show that the temperature has a significant effect on the microstructure,mineral composition and mechanical properties of sandstone.In particular,when the temperature exceeds 400℃,the thermal fracture phenomenon of rock is obvious,the activity of activated molecules is significantly enhanced,and the kinetic phenomenon of the thermal decomposition reaction of rock appears rapidly.The mechanical properties of rock are weakened under the influence of rock thermal fracture and mineral thermal decomposition.These research results can provide a reference for the analysis of surrounding rock stability and the control of disasters caused by thermal damage in areas such as underground coal gasification(UCG)channels and rock masses subjected to mine fires.展开更多
Contour bevel gears have the advantages of high coincidence,low noise and large bearing capacity,which are widely used in automobile manufacturing,shipbuilding and construction machinery.However,when the surface quali...Contour bevel gears have the advantages of high coincidence,low noise and large bearing capacity,which are widely used in automobile manufacturing,shipbuilding and construction machinery.However,when the surface quality is poor,the effective contact area between the gear mating surfaces decreases,affecting the stability of the fit and thus the transmission accuracy,so it is of great significance to optimize the surface quality of the contour bevel gear.This paper firstly analyzes the formation process of machined surface roughness of contour bevel gears on the basis of generating machining method,and dry milling experiments of contour bevel gears are conducted to analyze the effects of cutting speed and feed rate on the machined surface roughness and surface topography of the workpiece.Then,the surface defects on the machined surface of the workpiece are studied by SEM,and the causes of the surface defects are analyzed by EDS.After that,XRD is used to compare the microscopic grains of the machined surface and the substrate material for diffraction peak analysis,and the effect of cutting parameters on the microhardness of the workpiece machined surface is investigated by work hardening experiment.The research results are of great significance for improving the machining accuracy of contour bevel gears,reducing friction losses and improving transmission efficiency.展开更多
In this study,a code,named Peking University Helicon Discharge(PHD),which can simulate helicon discharge processes under both a background magnetic field greater than 500 G and a pressure less than 1 Pa,is developed.I...In this study,a code,named Peking University Helicon Discharge(PHD),which can simulate helicon discharge processes under both a background magnetic field greater than 500 G and a pressure less than 1 Pa,is developed.In the code,two fluid equations are used.The PHD simulations led to two important findings:(1)the temporal evolution of plasma density with the background magnetic field exhibits a second rapid increase(termed as the second density jump),similar to the transition of modes in helicon plasmas;(2)in the presence of a magnetic field,the peak positions of electron power absorption appeared near the central axis,unlike in the case of no magnetic field.These results may lead to an enhanced understanding of the discharge mechanism.展开更多
The widespread popularity of new social media has a huge impact on college students’life,study,social behavior,and physical and mental health,and has also posed new challenges to the ideological and political educati...The widespread popularity of new social media has a huge impact on college students’life,study,social behavior,and physical and mental health,and has also posed new challenges to the ideological and political education work in colleges and universities.By analyzing the impact of new social media on college students’behavioral habits,this paper explores and proposes strategies to guide college students to form correct new social media behavioral habits.展开更多
Conventional flat-plate photovoltaic-thermal(PV-T)collectors generate electricity and heat simultaneously;however,the outlet temperature of the latter is typically below 60℃,limiting their widespread application.The ...Conventional flat-plate photovoltaic-thermal(PV-T)collectors generate electricity and heat simultaneously;however,the outlet temperature of the latter is typically below 60℃,limiting their widespread application.The use of optical concentration can enable higher-temperature heat to be generated,but this can also lead to a rise in the operating temperature of the PV cells in the collector and,in turn,to a deterioration in their electrical performance.To overcome this challenge,an optical spectral-splitting filter that absorbs the infrared and transmits the visible portion of the solar spectrum can be used,such that wavelengths below the bandgap are sent to the cells for electricity generation,while those above it are sent to a thermally decoupled absorber for the generation of heat at a temperature that is considerably higher than that of the cells.In this study,a triangular primary PV-T channel,wherein the primary heat transfer fluid(water)flows,is integrated into a parabolic trough concentrator of geometrical concentration ratio~10,while a secondary liquid filter(water,AgSiO_(2)-eg or Therminol-66)is introduced for spectral splitting.Optical,electrical and thermal-fluid(sub-)models are developed and coupled to study the performance of this collector.Each sub-model is individually checked against results taken from the literature with maximum deviations under 10%.Subsequently,the optical and electrical models are coupled with a 3-D thermal-fluid CFD model(using COMSOL Multiphysics 6.1)to predict the electrical and thermal performance of the collector.Results show that when water is used as the optical filter,the maximum overall thermal(filter channel plus primary channel)and electrical efficiencies of the collector reach~45%and 15%,respectively.A comparison between water,AgSiO_(2)-eg and Therminol-66 reveals that AgSiO_(2)-eg improves the thermal efficiency of the filter channel by~25%(absolute)compared to Therminol-66 and water,however,this improvement–which arises from the thermal performance of the filter–comes at an expense of a~5%electrical efficiency loss.展开更多
Background:Senescent human skin primary fibroblast(FB)models have been established for studying aging-related,proliferative,and inflammatory skin diseases.The aim of this study was to compare the transcriptome charact...Background:Senescent human skin primary fibroblast(FB)models have been established for studying aging-related,proliferative,and inflammatory skin diseases.The aim of this study was to compare the transcriptome characteristics of human primary dermal FBs from children and the elderly with four senescence models.Methods:Human skin primary FBs were obtained from healthy children(FB-C)and elderly donors(FB-E).Senescence models were generated by ultraviolet B irradiation(FB-UVB),D-galactose stimulation(FB-D-gal),atazanavir treatment(FB-ATV),and replication exhaustion induction(FB-P30).Flow cytometry,immunofluorescence staining,real-time quantitative polymerase chain reaction,co-culturing with immune cells,and bulk RNA sequencing were used for systematic comparisons of the models.Results:In comparison with FB-C,FB-E showed elevated expression of senescence-related genes related to the skin barrier and extracellular matrix,proinflammatory factors,chemokines,oxidative stress,and complement factors.In comparison with FB-E,FB-UVB and FB-ATV showed higher levels of senescence and expression of the genes related to the senescence-associated secretory phenotype(SASP),and their shaped immune microenvironment highly facilitated the activation of downstream immune cells,including T cells,macrophages,and natural killer cells.FB-P30 was most similar to FB-E in terms of general transcriptome features,such as FB migration and proliferation,and aging-related characteristics.FB-D-gal showed the lowest expression levels of senescence-related genes.In comparisons with the single-cell RNA sequencing results,FB-E showed almost complete simulation of the transcriptional spectrum of FBs in elderly patients with atopic dermatitis,followed by FB-P30 and FB-UVB.FB-E and FB-P30 showed higher similarity with the FBs in keloids.Conclusions:Each senescent FB model exhibited different characteristics.In addition to showing upregulated expression of natural senescence features,FB-UVB and FB-ATV showed high expression levels of senescence-related genes,including those involved in the SASP,and FB-P30 showed the greatest similarity with FB-E.However,D-galactose-stimulated FBs did not clearly present aging characteristics.展开更多
The occurrence of debris flow events in small-scale watersheds with dense vegetation in mountainous areas that result in significant loss of life and missing individuals challenges our understanding and expertise in i...The occurrence of debris flow events in small-scale watersheds with dense vegetation in mountainous areas that result in significant loss of life and missing individuals challenges our understanding and expertise in investigating and preventing these disasters. This has raised concerns about the occurrence of large debris flow disasters from small watersheds. This study focused on a catastrophic debris flow that took place in Longtou Gully(0.45 km^(2)) in Tianquan County, Ya'an City on 25 September 2021, which resulted in 14 deaths and missing individuals. Through comprehensive field investigations, highprecision remote sensing data analyses, and numerical simulations, we analyzed the triggering mechanisms and dynamic processes of this event. Our results indicate that the convergence hollow at the channel head exhibited higher hydraulic conditions during rainfall compared to gentle slopes and convex terrains, leading to the instability of colluvial soil due to the expansion of the saturated zone near the soil–bedrock interface. The entrainment of material eroded from the channel resulted in an approximately 4.7 times increase in volume, and the channel scarp with a height of about 200 m amplified the destructive power of the debris flow. We emphasize the need to take seriously the possibility of catastrophic debris flows in small-scale watersheds, with colluvial deposits in hollows at the channel head under vegetation cover that serve as precursor material sources, and the presence of channel scarps formed by changes in the incision rate of the main river, which is common in the small watershed on both sides. This study provides insights for risk assessment of debris flows in small-scale catchments with dense vegetation cover in mountainous areas, highlighting the importance of vigilance in addressing disasters in small-scale catchments, particularly in regions with increasing human–environment conflicts.展开更多
基金supported by the National Natural Science Foun-dation of China(Nos.U24B2035 and U22A20166)the Postdoctoral Fellowship Program and China Postdoctoral Science Foundation(Nos.BX20250034 and 2024M763503)the Natural Science Foundation of Hubei Province of China(No.2024AFD374).
文摘Fracability evaluation is critical for efficiently extracting deep shale gas using hydraulic fracturing to avoid blind drilling and fracking.However,existing fracability indices often fail to systematically consider the mechanical behavior of rocks at high temperatures and high pressures(HTHP),coupled with geostress distributions and heterogeneous reservoir characteristics.This critical omission limits their effectiveness in accurately identifying the optimal fracability sweet spots within deep reservoirs.In this work,a fracability evaluation model was proposed based on the combined weighting method,integrating the improved brittleness index,rock strength,geostresses and natural weakness characteristics.A fracability grading evaluation was carried out to determine the potential fracture characteristics corresponding to shales with different fracability levels.Additionally,the fracability index was used for field validation and applications.Results show that rock brittleness and fracability are not equivalent for deep reservoirs.The fracability index is closely related to the pay zones and actual gas production,with a correlation as high as 84%,implying that the proposed method has practical significance in both experimental and field applications.The above findings can provide theoretical guidance for the selection of fracturing candidates and the optimal design of fracturing in deep resource development.
基金supported by the National Key R&D Program of China(No.2017YFE0301201)National Natural Science Foundation of China(No.11975038)the funding support from the State Key Laboratory of Nuclear Physics and Technology,Peking University(No.NPT2021ZZ03)。
文摘Helicon wave plasma sources have the well-known advantages of high efficiency and high plasma density, with broad applications in many areas. The crucial mechanism lies with mode transitions, which has been an outstanding issue for years. We have built a fluid simulation model and further developed the Peking University Helicon Discharge code. The mode transitions, also known as density jumps, of a single-loop antenna discharge are reproduced in simulations for the first time. It is found that large-amplitude standing helicon waves(SHWs) are responsible for the mode transitions, similar to those of a resonant cavity for laser generation.This paper intends to give a complete and quantitative SHW resonance theory to explain the relationship of the mode transitions and the SHWs. The SHW resonance theory reasonably explains several key questions in helicon plasmas, such as mode transition and efficient power absorption, and helps to improve future plasma generation methods.
基金supported by the Scientific Research Foundation of State Key Laboratory of Coal Mine Disaster Dynamics and Control(Grant No.2011DA105287-zd201804)Jiangxi Provincial Natural Science Foundation of China(Grant No.20232BAB214036).
文摘To study the microscopic structure,thermal and mechanical properties of sandstones under the influence of temperature,coal measure sandstones from Southwest China are adopted as the research object to carry out high-temperature tests at 25℃-1000℃.The microscopic images of sandstone after thermal treatment are obtained by means of polarizing microscopy and scanning electron microscopy(SEM).Based on thermogravimetric(TG)analysis and differential scanning calorimetric(DSC)analysis,the model function of coal measure sandstone is explored through thermal analysis kinetics(TAK)theory,and the kinetic parameters of thermal decomposition and the thermal decomposition reaction rate of rock are studied.Through the uniaxial compression experiments,the stress‒strain curves and strength characteristics of sandstone under the influence of temperature are obtained.The results show that the temperature has a significant effect on the microstructure,mineral composition and mechanical properties of sandstone.In particular,when the temperature exceeds 400℃,the thermal fracture phenomenon of rock is obvious,the activity of activated molecules is significantly enhanced,and the kinetic phenomenon of the thermal decomposition reaction of rock appears rapidly.The mechanical properties of rock are weakened under the influence of rock thermal fracture and mineral thermal decomposition.These research results can provide a reference for the analysis of surrounding rock stability and the control of disasters caused by thermal damage in areas such as underground coal gasification(UCG)channels and rock masses subjected to mine fires.
基金National Key R&D Program of China(Grant No.2019YFE0121300)Yancheng Hali Power Transmission and Intelligent Equipment Industrial Research Institute Project。
文摘Contour bevel gears have the advantages of high coincidence,low noise and large bearing capacity,which are widely used in automobile manufacturing,shipbuilding and construction machinery.However,when the surface quality is poor,the effective contact area between the gear mating surfaces decreases,affecting the stability of the fit and thus the transmission accuracy,so it is of great significance to optimize the surface quality of the contour bevel gear.This paper firstly analyzes the formation process of machined surface roughness of contour bevel gears on the basis of generating machining method,and dry milling experiments of contour bevel gears are conducted to analyze the effects of cutting speed and feed rate on the machined surface roughness and surface topography of the workpiece.Then,the surface defects on the machined surface of the workpiece are studied by SEM,and the causes of the surface defects are analyzed by EDS.After that,XRD is used to compare the microscopic grains of the machined surface and the substrate material for diffraction peak analysis,and the effect of cutting parameters on the microhardness of the workpiece machined surface is investigated by work hardening experiment.The research results are of great significance for improving the machining accuracy of contour bevel gears,reducing friction losses and improving transmission efficiency.
基金supported by National Natural Science Foundation of China(No.11975038)。
文摘In this study,a code,named Peking University Helicon Discharge(PHD),which can simulate helicon discharge processes under both a background magnetic field greater than 500 G and a pressure less than 1 Pa,is developed.In the code,two fluid equations are used.The PHD simulations led to two important findings:(1)the temporal evolution of plasma density with the background magnetic field exhibits a second rapid increase(termed as the second density jump),similar to the transition of modes in helicon plasmas;(2)in the presence of a magnetic field,the peak positions of electron power absorption appeared near the central axis,unlike in the case of no magnetic field.These results may lead to an enhanced understanding of the discharge mechanism.
文摘The widespread popularity of new social media has a huge impact on college students’life,study,social behavior,and physical and mental health,and has also posed new challenges to the ideological and political education work in colleges and universities.By analyzing the impact of new social media on college students’behavioral habits,this paper explores and proposes strategies to guide college students to form correct new social media behavioral habits.
基金supported by the UK Engineering and Physical Sciences Research Council(EPSRC)(Grant No.EP/R045518/1)the Royal Society under an International Collaboration Award 2020(Grant No.ICA\R1\201302)+2 种基金UK company Solar Flow Ltd.This work has also been funded by the European Union under the SPECTRUM project(Grant Agreement No.101172891)support for this research was provided by Tecnologico de Monterrey Challenge-Based Research Funding Programsupporting this publication can be obtained on request from cep-laboratory@imperial.ac.uk.For the purpose of Open Access,the authors have applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission.
文摘Conventional flat-plate photovoltaic-thermal(PV-T)collectors generate electricity and heat simultaneously;however,the outlet temperature of the latter is typically below 60℃,limiting their widespread application.The use of optical concentration can enable higher-temperature heat to be generated,but this can also lead to a rise in the operating temperature of the PV cells in the collector and,in turn,to a deterioration in their electrical performance.To overcome this challenge,an optical spectral-splitting filter that absorbs the infrared and transmits the visible portion of the solar spectrum can be used,such that wavelengths below the bandgap are sent to the cells for electricity generation,while those above it are sent to a thermally decoupled absorber for the generation of heat at a temperature that is considerably higher than that of the cells.In this study,a triangular primary PV-T channel,wherein the primary heat transfer fluid(water)flows,is integrated into a parabolic trough concentrator of geometrical concentration ratio~10,while a secondary liquid filter(water,AgSiO_(2)-eg or Therminol-66)is introduced for spectral splitting.Optical,electrical and thermal-fluid(sub-)models are developed and coupled to study the performance of this collector.Each sub-model is individually checked against results taken from the literature with maximum deviations under 10%.Subsequently,the optical and electrical models are coupled with a 3-D thermal-fluid CFD model(using COMSOL Multiphysics 6.1)to predict the electrical and thermal performance of the collector.Results show that when water is used as the optical filter,the maximum overall thermal(filter channel plus primary channel)and electrical efficiencies of the collector reach~45%and 15%,respectively.A comparison between water,AgSiO_(2)-eg and Therminol-66 reveals that AgSiO_(2)-eg improves the thermal efficiency of the filter channel by~25%(absolute)compared to Therminol-66 and water,however,this improvement–which arises from the thermal performance of the filter–comes at an expense of a~5%electrical efficiency loss.
基金supported by grants from the National Key R&D Program of China(No.2022YFC3601800)National Natural Science Foundation of China(Nos.82103735,82373489,and 82273542)CAMS Innovation Fund for Medical Sciences(Nos.CIFMS,2021-I2M-1-059,2022-I2M-C&T-B-096).
文摘Background:Senescent human skin primary fibroblast(FB)models have been established for studying aging-related,proliferative,and inflammatory skin diseases.The aim of this study was to compare the transcriptome characteristics of human primary dermal FBs from children and the elderly with four senescence models.Methods:Human skin primary FBs were obtained from healthy children(FB-C)and elderly donors(FB-E).Senescence models were generated by ultraviolet B irradiation(FB-UVB),D-galactose stimulation(FB-D-gal),atazanavir treatment(FB-ATV),and replication exhaustion induction(FB-P30).Flow cytometry,immunofluorescence staining,real-time quantitative polymerase chain reaction,co-culturing with immune cells,and bulk RNA sequencing were used for systematic comparisons of the models.Results:In comparison with FB-C,FB-E showed elevated expression of senescence-related genes related to the skin barrier and extracellular matrix,proinflammatory factors,chemokines,oxidative stress,and complement factors.In comparison with FB-E,FB-UVB and FB-ATV showed higher levels of senescence and expression of the genes related to the senescence-associated secretory phenotype(SASP),and their shaped immune microenvironment highly facilitated the activation of downstream immune cells,including T cells,macrophages,and natural killer cells.FB-P30 was most similar to FB-E in terms of general transcriptome features,such as FB migration and proliferation,and aging-related characteristics.FB-D-gal showed the lowest expression levels of senescence-related genes.In comparisons with the single-cell RNA sequencing results,FB-E showed almost complete simulation of the transcriptional spectrum of FBs in elderly patients with atopic dermatitis,followed by FB-P30 and FB-UVB.FB-E and FB-P30 showed higher similarity with the FBs in keloids.Conclusions:Each senescent FB model exhibited different characteristics.In addition to showing upregulated expression of natural senescence features,FB-UVB and FB-ATV showed high expression levels of senescence-related genes,including those involved in the SASP,and FB-P30 showed the greatest similarity with FB-E.However,D-galactose-stimulated FBs did not clearly present aging characteristics.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFC3008301)the Postdoctoral Fellowship Program of CPSF(Grant No.GZC20232571,2024M753153)+3 种基金the Special Research Assistant Program of CAS(Grant No.2024IMHE01)the National Natural Science Foundation of China(Grant No.42361144880)the Basic Research Program of Qinghai Province(2024-ZJ-904)the International Cooperation Overseas Platform Project,CAS(Grant No.131C11KYSB20200033).
文摘The occurrence of debris flow events in small-scale watersheds with dense vegetation in mountainous areas that result in significant loss of life and missing individuals challenges our understanding and expertise in investigating and preventing these disasters. This has raised concerns about the occurrence of large debris flow disasters from small watersheds. This study focused on a catastrophic debris flow that took place in Longtou Gully(0.45 km^(2)) in Tianquan County, Ya'an City on 25 September 2021, which resulted in 14 deaths and missing individuals. Through comprehensive field investigations, highprecision remote sensing data analyses, and numerical simulations, we analyzed the triggering mechanisms and dynamic processes of this event. Our results indicate that the convergence hollow at the channel head exhibited higher hydraulic conditions during rainfall compared to gentle slopes and convex terrains, leading to the instability of colluvial soil due to the expansion of the saturated zone near the soil–bedrock interface. The entrainment of material eroded from the channel resulted in an approximately 4.7 times increase in volume, and the channel scarp with a height of about 200 m amplified the destructive power of the debris flow. We emphasize the need to take seriously the possibility of catastrophic debris flows in small-scale watersheds, with colluvial deposits in hollows at the channel head under vegetation cover that serve as precursor material sources, and the presence of channel scarps formed by changes in the incision rate of the main river, which is common in the small watershed on both sides. This study provides insights for risk assessment of debris flows in small-scale catchments with dense vegetation cover in mountainous areas, highlighting the importance of vigilance in addressing disasters in small-scale catchments, particularly in regions with increasing human–environment conflicts.
