Objective:To assess prenatal Bisphenol A(BPA)exposure levels and explore their preliminary associations with maternal and fetal characteristics in a population from Northeastern Yunnan.Methods:A cross-sectional analys...Objective:To assess prenatal Bisphenol A(BPA)exposure levels and explore their preliminary associations with maternal and fetal characteristics in a population from Northeastern Yunnan.Methods:A cross-sectional analysis was performed using data and urine samples from 70 pregnant women in their third trimester recruited at Qujing Central Hospital.Urinary BPA was measured by HPLC-MS/MS.Participants were stratified into high and low BPA exposure groups based on the median concentration.Results:BPA was detected in all samples(100%)with a median concentration of 2.41μg/L(IQR:0.68-4.96).The high BPA exposure group(≥2.41μg/L)had a significantly higher proportion of gestational diabetes mellitus(GDM)(42.9%vs.17.1%,p=0.021)and a lower median fetal birth weight(3250 g vs.3450 g,p=0.048)compared to the low exposure group.Conclusion:This pilot study reveals ubiquitous BPA exposure in pregnant women from Northeastern Yunnan.The observed preliminary associations with GDM and reduced fetal birth weight warrant further investigation in larger,longitudinal studies.展开更多
Ultra-high-strength aluminumalloy profile is an ideal choice for aerospace structuralmaterials due to its excellent specific strength and corrosion resistance.However,issues such as uneven metal flow,stress concentrat...Ultra-high-strength aluminumalloy profile is an ideal choice for aerospace structuralmaterials due to its excellent specific strength and corrosion resistance.However,issues such as uneven metal flow,stress concentration,and forming defects are prone to occur during their extrusion.This study focuses on an Al-Zn-Mg-Cu ultra-high-strength aluminum alloy profile with a double-U,multi-cavity thin-walled structure.Firstly,hot compression experiments were conducted at temperatures of 350○C,400○C,and 450○C,with strain rates of 0.01 and 1.0 s^(−1),to investigate the plastic deformation behavior of the material.Subsequently,a 3D coupled thermo-mechanical extrusion simulation model was established using Deform-3D to systematically analyze the influence of die structure and process parameters on metal flow velocity,effective stress/strain,and temperature distribution.The simulation revealed significant velocity differences,stress concentration,and uneven temperature distribution.Key parameters,including mesh density,extrusion ratio,die fillet,and bearing length,were optimized through full-factorial experiments.This optimization,combined with a stepped flow-guiding die design,effectively improved the metal flow pattern during extrusion.Trial production based on both the initial and optimized parameters were carried out.A comparative analysis demonstrates that the optimized scheme results in a final profile whose cross-section matches the target design closely,with complete filling of complex features and no obvious forming defects.This research provides a valuable reference for the extrusion process optimization and die design of complex-section profiles made from ultra-high-strength aluminum alloys.展开更多
Objective This study aimed to determine the temporal trends in sleep duration among Chinese adults.Methods In this series of repeated nationally representative cross-sectional surveys(China Chronic Disease and Risk Fa...Objective This study aimed to determine the temporal trends in sleep duration among Chinese adults.Methods In this series of repeated nationally representative cross-sectional surveys(China Chronic Disease and Risk Factors Surveillance)conducted between 2010 and 2018,a total of 645,420 adult participants(97,741 in 2010;175,749 in 2013;187,777 in 2015;and 184,153 in 2018)were included in the trend analysis.Linear and logistic regression models were utilized to assess trends in sleep duration.Results In 2018,the estimated overall mean sleep duration among the Chinese adult population was7.58(SD,1.45)hours per day,with no significant trend from 2010.A significant increase in short sleep duration(≤6 hours)was observed in the total population,from 15.3%(95%CI:14.1%–16.5%)in 2010 to18.5%(95%CI:17.7%–19.3%)in 2018(P<0.001).Similarly,the trend in long sleep duration(>9 hours)was also significant,increasing in weighted prevalence from 7.2%(95%CI:6.3%–8.1%)in 2010 to 9.0%(95%CI:8.2%–9.9%)in 2018(P<0.001).Conclusion The prevalence of both short and long sleep durations significantly increased among Chinese adults from 2010 to 2018,highlighting the urgency of health initiatives to promote optimal sleep duration in China.展开更多
Energy shortage has become one of themost concerning issues in the world today,and improving energy utilization efficiency is a key area of research for experts and scholars worldwide.Small-diameter heat exchangers of...Energy shortage has become one of themost concerning issues in the world today,and improving energy utilization efficiency is a key area of research for experts and scholars worldwide.Small-diameter heat exchangers offer advantages such as reduced material usage,lower refrigerant charge,and compact structure.However,they also face challenges,including increased refrigerant pressure drop and smaller heat transfer area inside the tubes.This paper combines the advantages and disadvantages of both small and large-diameter tubes and proposes a combined-diameter heat exchanger,consisting of large and small diameters,for use in the indoor units of split-type air conditioners.There are relatively few studies in this area.In this paper,A theoretical and numerical computation method is employed to establish a theoretical-numerical calculation model,and its reliability is verified through experiments.Using this model,the optimal combined diameters and flow path design for a combined-diameter heat exchanger using R32 as the working fluid are derived.The results show that the heat transfer performance of all combined diameter configurations improves by 2.79%to 8.26%compared to the baseline design,with the coefficient of performance(COP)increasing from 4.15 to 4.27~4.5.These designs can save copper material,but at the cost of an increase in pressure drop by 66.86%to 131.84%.The scheme IIIH,using R32,is the optimal combined-diameter and flow path configuration that balances both heat transfer performance and economic cost.展开更多
We investigated the impact of convexity and isoperimetric deficits on the accuracy of sectional area estimates of tree stems using traditional methods(caliper,tape,formulas based on stem diameter and circumference).In...We investigated the impact of convexity and isoperimetric deficits on the accuracy of sectional area estimates of tree stems using traditional methods(caliper,tape,formulas based on stem diameter and circumference).In two complementary experiments,the use of photographs to estimate cross-sectional areas was first validated,then the use of a caliper and diameter tape was computer-simulated.The results indicated that the photographic method offers high precision,with mean relative errors below 0.1%,minimal deviation,and no significant bias,and the traditional methods led to substantial and systematic errors,with deviations from circularity and convexity significantly increasing the errors in area estimation.展开更多
We present the first systematic experimental validation of return-current-driven cylindrical implosion scaling in micrometer-sized Cu and Al wires irradiated by J-class femtosecond laser pulses.Employing XFEL-based im...We present the first systematic experimental validation of return-current-driven cylindrical implosion scaling in micrometer-sized Cu and Al wires irradiated by J-class femtosecond laser pulses.Employing XFEL-based imaging with sub-micrometer spatial and femtosecond temporal resolution,supported by hydrodynamic and particle-in-cell simulations,we reveal how return current density depends precisely on wire diameter,material properties,and incident laser energy.We identify deviations from simple theoretical predictions due to geometrically influenced electron escape dynamics.These results refine and confirm the scaling laws essential for predictive modeling in high-energy-density physics and inertial fusion research.展开更多
In this companion paper, flow patterns in the upstream and downstream tubes of a sudden-expansion cross-section (SECS) in a vertical straight pipe were presented. The effect of SECS on flow patterns upstream and down...In this companion paper, flow patterns in the upstream and downstream tubes of a sudden-expansion cross-section (SECS) in a vertical straight pipe were presented. The effect of SECS on flow patterns upstream and downstream was analyzed by comparing with flow patterns in uniform cross-section vertical tubes. It is found the effect is great. There exist great instabilities of two-phase flow in the neighboring areas of the SECS both downstream and upstream.展开更多
Flow patterns upstream and downstream of a sudden-contraction cross-section in a vertical straight pipe were presented. By comparing with flow patterns in uniform cross-section vertical tubes, the effect of the sudde...Flow patterns upstream and downstream of a sudden-contraction cross-section in a vertical straight pipe were presented. By comparing with flow patterns in uniform cross-section vertical tubes, the effect of the sudden change in pipe diameter on flow patterns was analyzed. Flow pattern transition mechanisms were discussed and transition criteria for flow pattern transitions were deduced accordingly using the dimensional analysis.展开更多
Objective The relationship between non-high-density lipoprotein(NHDL)cholesterol to high-density lipoprotein cholesterol(HDL-C)ratio(NHHR)and stoke remains unknown.This study aimed to evaluate the association between ...Objective The relationship between non-high-density lipoprotein(NHDL)cholesterol to high-density lipoprotein cholesterol(HDL-C)ratio(NHHR)and stoke remains unknown.This study aimed to evaluate the association between the adult NHHR and stroke occurrence in the United States of America(USA).Methods To clarify the relationship between the NHHR and stroke risk,this study used a multivariable logistic regression model and a restricted cubic spline(RCS)model to investigate the association between the NHHR and stroke,and data from the National Health and Nutrition Examination Survey(NHANES)from 2005 to 2018.Subgroup and sensitivity analyses were conducted to test the robustness of the results.Results This study included 29,928 adult participants,of which 1,165 participants had a history of stroke.Logistic regression analysis of variables demonstrated a positive association between NHHR and stroke(OR 1.24,95%CI:1.03-1.50,P=0.026).Compared with the lowest reference group of NHHR,participants in the second,third,and fourth quartile had a significantly increased risk of stroke after full adjustments(OR:1.35,95%CI:1.08-1.69)(OR:1.83,95%CI:1.42-2.36)(OR:2.04,95%CI:1.50-2.79).In the total population,a nonlinear dose-response relationship was observed between the NHHR and stroke risk(P non-linearity=0.002).This association remained significant in several subgroup analyses.Further investigation of the NHHR may enhance our understanding of stroke prevention and treatment.Conclusion Our findings suggest a positive correlation between the NHHR and an increased prevalence of stroke,potentially serving as a novel predictive factor for stroke.Timely intervention and management of the NHHR may effectively mitigate stroke occurrence.Prospective studies are required to validate this association and further explore the underlying biological mechanisms.展开更多
The umbilical,a key component in offshore energy extraction,plays a vital role in ensuring the stable operation of the entire production system.The extensive variety of cross-sectional components creates highly comple...The umbilical,a key component in offshore energy extraction,plays a vital role in ensuring the stable operation of the entire production system.The extensive variety of cross-sectional components creates highly complex layout combinations.Furthermore,due to constraints in component quantity and geometry within the cross-sectional layout,filler bodies must be incorporated to maintain cross-section performance.Conventional design approaches based on manual experience suffer from inefficiency,high variability,and difficulties in quantification.This paper presents a multi-level automatic filling optimization design method for umbilical cross-sectional layouts to address these limitations.Initially,the research establishes a multi-objective optimization model that considers compactness,balance,and wear resistance of the cross-section,employing an enhanced genetic algorithm to achieve a near-optimal layout.Subsequently,the study implements an image processing-based vacancy detection technique to accurately identify cross-sectional gaps.To manage the variability and diversity of these vacant regions,the research introduces a multi-level filling method that strategically selects and places filler bodies of varying dimensions,overcoming the constraints of uniform-size fillers.Additionally,the method incorporates a hierarchical strategy that subdivides the complex cross-section into multiple layers,enabling layer-by-layer optimization and filling.This approach reduces manufac-turing equipment requirements while ensuring practical production process feasibility.The methodology is validated through a specific umbilical case study.The results demonstrate improvements in compactness,balance,and wear resistance compared with the initial cross-section,offering novel insights and valuable references for filler design in umbilical cross-sections.展开更多
Objectives:This study aimed to classify young breast cancer patients into distinct ambivalence over emotional expression and to explore the factors influencingthe level of ambivalence over emotional expression.Methods...Objectives:This study aimed to classify young breast cancer patients into distinct ambivalence over emotional expression and to explore the factors influencingthe level of ambivalence over emotional expression.Methods:A total of 217 young breast cancer patients were enrolled from a tertiary Grade A oncology hospital in Tianjin,China,using the convenience sampling method.All participants completed the general questionnaire,Ambivalence over Emotion Expression Questionnaire(AEQ),and Family Adapt-Ability and Cohesion Evaluation Scales-Chinese Version(FACES-CV).We employed exploratory latent profileanalysis for ambivalence over emotional expression profilingand logistic regression analysis to identify the influentialfactors Results:The results of the latent profileanalysis supported the models of four latent profiles,which were definedas“low conflict-lowexpression reflection”(19.2%),“high conflict-high inhibition expression”(43.9%),“moderate conflict-highregret expression”(18.1%),and“moderate conflict-desire understand”(18.8%).Logistic regression revealed that family cohesion,marital status,residence,per capita monthly income,and cancer stage were the influencingfactors of ambivalence over emotional expression in young breast cancer patients(P<0.05)Conclusions:Levels of ambivalence over emotional expression ameast cancer patients with breast cancer were highly heterogeneous.Medical staff should provide psychological counseling and health education tailored to the unique characteristics of emotional expression ambivalence in different patient groups to promote healthy emotional expression among patients.展开更多
OBJECTIVE:To investigate the difference in gut microbiota between population with damp-heat constitution(DHC)and balanced constitution(BC).METHODS:A multi-centered cross-sectional casecontrol study was conducted,which...OBJECTIVE:To investigate the difference in gut microbiota between population with damp-heat constitution(DHC)and balanced constitution(BC).METHODS:A multi-centered cross-sectional casecontrol study was conducted,which included 249 participants with damp-heat constitution or balanced constitution.Baseline information of participants was collected,and stool samples were collected for gut microbiota analysis.Principal coordinate analysis,linear discriminant analysis effect size analysis,receiver operating characteristic,random forest model,and phylogenetic investigation of communities by reconstruction of unobserved states methods were used to reveal the relationship between gut microbiota and the damp-heat constitution.RESULTS:Compared to those in the BC group,the richness and diversity of the microbiota,specifically those of several short-chain fatty acid producing genera such as Barnesiella,Coprobacter,and Butyricimonas,were significantly decreased in the DHC group.Regarding biological functions,flavonoid biosynthesis,propanoate metabolism,and nucleotide sugar metabolism were suppressed,while arachidonic acid metabolism and glutathione metabolism were enriched in the DHC group.Finally,a classifier based on the microbiota was constructed to discriminate between the DHC and BC populations.CONCLUSION:The gut microbiota of the DHC population exhibits significantly reduced diversity and is closely related to inflammation,metabolic disorders,and liver steatosis,which is consistent with clinical observations,thus serving as a potential diagnostic tool for traditional Chinese medicine constitution discrimination.展开更多
Objective:Postpartum nutrition plays a critical role in maternal recovery and long-term health.However,the nutritional status of working mothers in the postpartum period remains understudied.This study aimed to assess...Objective:Postpartum nutrition plays a critical role in maternal recovery and long-term health.However,the nutritional status of working mothers in the postpartum period remains understudied.This study aimed to assess the dietary quality of postpartum women in urban Beijing,identify occupational-related factors influencing their diet,and explore potential interventions to improve maternal nutrition during the postpartum period.Methods:In this cross-sectional analysis,554 women one year after delivery were recruited from ten community health centers.Sociodemographic,occupational and postpartum care variables were collected via questionnaire.Dietary intake over the preceding year was assessed using a food frequency questionnaire.The modified dietary balance index for postpartum women were used for dietary quality assessment.Results:The study revealed severe dietary imbalances among postpartum women,characterized by excessive consumption of cereals,eggs,and meats,while their intake of vegetables,fruits,and dairy products was inadequate.According to dietary balance index for postpartum women,66.25%of mothers showed varying degrees of excessive intake.45.31%of mothers experienced varying levels of insufficient intake,with only 19.86%of participants having a relatively balanced diet.Occupational differences were observed,with women in the commercial employment group showing higher levels of excessive food intake.The analysis of influencing factors showed that family monthly income,maternity leave,and postpartum care significantly affected the dietary quality.Conclusions:Postpartum women in Beijing experience widespread dietary imbalances,with both excesses and deficiencies.Occupational context and related factors significantly shape diet quality.These findings highlight the need for targeted nutritional interventions tailored to the specific challenges of different occupational groups.展开更多
To investigate the effects of the maximum principal stress direction(θ)and cross-section shape on the failure characteristics of sandstone,true-triaxial compression experiments were conducted using cubic samples with...To investigate the effects of the maximum principal stress direction(θ)and cross-section shape on the failure characteristics of sandstone,true-triaxial compression experiments were conducted using cubic samples with rectangular,circular,and D-shaped holes.Asθincreases from 0°to 60°in the rectangular hole,the left failure location shifts from the left corner to the left sidewall,the left corner,and then the floor,while the right failure location shifts from the right corner to the right sidewall,right roof corner,and then the roof.Furthermore,the initial failure vertical stress first decreases and then increases.In comparison,the failure severity in the rectangular hole decreases for variousθvalues as 30°>45°>60°>0°.With increasingθ,the fractal dimension(D)of rock slices first increases and then decreases.For the rectangular and D-shaped holes,whenθ=0°,30°,and 90°,D for the rectangular hole is less than that of the D-shaped hole.Whenθ=45°and 60°,D for the rectangular hole is greater than that of the D-shaped hole.Theoretical analysis indicates that the stress concentration at the rectangular and D-shaped corners is greater than the other areas.The failure location rotates with the rotation ofθ,and the failure occurs on the side with a high concentration of compressive stress,while the side with the tensile and compressive stresses remains relatively stable.Therefore,the fundamental reason for the rotation of failure location is the rotation of stress concentration,and the external influencing factor is the rotation ofθ.展开更多
The performance and price of copper-based micro linear products are determined by the diameter uniformity.How to accurately detect the wire diameter of long-length copper based micro linear products without cutting or...The performance and price of copper-based micro linear products are determined by the diameter uniformity.How to accurately detect the wire diameter of long-length copper based micro linear products without cutting or damage has always been a technical concern for production enterprises.Herein,a novel approach was developed for nondestructive detection of the average diameter at any given segment of a long copper wire by assessing the adsorption capacity of arginine on its surface.The amount of adsorbent on the surface of the copper wire exhibits a positive correlation with the area,which can be detected by extractive electrospray ionization mass spectrometry(EESI-MS)after online elution with ammonia.The experimental results demonstrated that the analysis can be completed within 15 min,with a good linear relationship between copper wires with different diameters and the adsorption capacity of arginine.The linear correlation coefficient R2was 0.995,the relative standard deviation was 1.10%-2.81%,and the detection limit reached 2.5μm(length of segment=4 cm),showing potential applications for facile measurement of the average diameter of various metal wires.展开更多
Background:The bibliometrics of acupuncture are growing rapidly.However,the absence of reporting guidelines may lead to significant duplication and waste,thereby undermining the research’s value.To address this,a kno...Background:The bibliometrics of acupuncture are growing rapidly.However,the absence of reporting guidelines may lead to significant duplication and waste,thereby undermining the research’s value.To address this,a knowledge mapping was generated based on published studies to investigate the characteristics of bibliometric studies on acupuncture and the extent of duplicate publications,with the overarching goal of providing a comprehensive overview of the knowledge structure in this field.Methods:This cross-sectional study used three databases(PubMed,Web of Science,and Scopus)to identify relevant studies up to May 1,2024.In addition,the reference lists were retrieved as a supplement.To track research trends,we employed Microsoft Excel and R software to extract,code,and analyze information.Study selection,data extraction,and validation were performed independently by at least two reviewers.The reporting quality of included studies was assessed using the Preliminary guideline for reporting bibliometric reviews of the biomedical literature(BIBLIO).Results:Among the 6,221 bibliometric reviews examined,113 relevant publications were identified,80 focusing on various diseases/conditions.The annual number of publications has gradually increased,with the output in the past four years being 3.52 times higher than that before 2020.China(106)and Chengdu University of Traditional Chinese Medicine(16)have the highest number of publications.The most prolific author is Fan-Rong Liang,with six articles.The first bibliometric study,by Hai-Yan Li,was published in 2010.Journal of Pain Research,with 36 articles,holds the most publications.The top three diseases:diseases of the nervous system;symptoms,signs,or clinical findings not elsewhere classified;and mental,behavioral,or neurodevelopmental disorders.There may be potential duplication in research on 13 diseases/conditions,notably stroke,migraine,pain/analgesia,cancer pain,shoulder pain,facial paralysis/bell’s palsy,chronic pain,and cognitive impairment.In BIBLIO,the most frequently missing items are issues/topics(item 2),quality assessment(item 11),and descriptive findings(item 13).Conclusion:This study demonstrates that acupuncture bibliometrics is actively utilized to identify dominant diseases/conditions,aiding scholars in understand the knowledge structure and main topics.Although the number of related studies is increasing,with an average of 25 studies annually,overlap in some areas highlights the need for adherence to reporting guidelines and careful topic selection to ensure truly valuable insights and knowledge contributions.The adherence to BIBLIO’s 20 proposed items across analyzed articles,highlighting important in reporting practices.展开更多
A train body's cross-sectional shape has a significant impact on aerodynamic drag and operational safety in high-speed trains(HSTs).This study extracts five design variables from a real-world HST body:height,width...A train body's cross-sectional shape has a significant impact on aerodynamic drag and operational safety in high-speed trains(HSTs).This study extracts five design variables from a real-world HST body:height,width,side arc radius,arc radius at the connection between the side and the roof,and arc radius at the connection between the side and the train's bottom.The cross-validated Kriging surrogate model and the genetic algorithm are used to perform two types of aerodynamic optimization,with the cross-sectional area as a constraint.Cross-sectional shapes are optimized in both windless and windy conditions.Numerical results indicate that in a windless environment,the aerodynamic drag coefficient of the whole train is reduced by 2.4%;in a windy condition,the aerodynamic drag coefficient of the entire vehicle is reduced by 2.4%,and the aerodynamic lateral force of the leading car is reduced by 37.8%.These suggest that a flat and wide shape helps to reduce not only overall aerodynamic drag in a windless environment but also aerodynamic load in a windy environment,which can be accomplished by reducing the area of the side wall and top region,lowering the train body's height,increasing its width,and lowering the radius of the side and top arcs.展开更多
Carbon nanotubes are uniquely featured by the nanoscale tubular structure with a highly-curved surface and defined chirality.The diameter and chirality fundamentally determine their stability and electrical and therma...Carbon nanotubes are uniquely featured by the nanoscale tubular structure with a highly-curved surface and defined chirality.The diameter and chirality fundamentally determine their stability and electrical and thermal properties.Up to now,the relationship between the intrinsic thermal conductivity and the atomic features of CNTs has not been established,due to the challenges in precise measurements and characterizations.In this work,we develop a micro electro-thermal device enabling simultaneous thermal measurements by Raman spectroscopy and atomic structural characterization by transmission electron microscopy for individual CNTs.The influence of diameter and chirality is systematically investigated.In addition,the temperature dependence of the thermal conductivity was extracted from parameter optimization of finite-element modeling.It is found that the thermal transport of CNTs depends mainly on the diameter,while the chiral angle has no significant influence.Along with increasing diameter,the room temperature thermal conductivity increases and eventually approaches the limit of flat graphene.展开更多
The coconut structure exhibits inherent impact resistance,with the macroscopically ordered distribution of variable crosssection fibers in its husk playing a crucial role in stress wave propagation and scaling.Inspire...The coconut structure exhibits inherent impact resistance,with the macroscopically ordered distribution of variable crosssection fibers in its husk playing a crucial role in stress wave propagation and scaling.Inspired by the natural structure and fibers,this study proposes a stress wave propagation model for a variable cross-section bar considering viscous effects.A theoretical model for stress wave propagation in a fusiform-shaped bar with variable cross-section is established,elucidating the stress wave scaling effect observed in coconut fibers.Additionally,a quasi-one-dimensional method for analyzing and measuring stress wave propagation is introduced,and an experimental setup is assembled.Experimental validation of the stress wave scaling effect confirms the theory’s accuracy for stress wave scaling in variable cross-section bars.This research provides theoretical guidance and measurement methods for the design of space landers,automobile anti-collision beams,stress wave collectors,and scalers,as well as for impact testing of macro and micro materials and the design of sustainable plant-based materials for impact protection.展开更多
With the increasing development of deepburied engineering projects,rockburst disasters have become a frequent concern.Studies have indicated that tunnel diameter is a critical factor influencing the occurrence of rock...With the increasing development of deepburied engineering projects,rockburst disasters have become a frequent concern.Studies have indicated that tunnel diameter is a critical factor influencing the occurrence of rockbursts.To investigate the influence of tunnel diameter on the deformation and failure characteristics of surrounding rock,large-sized rocklike gypsum specimens were tested using a selfdeveloped true triaxial rockburst loading system containing circular tunnels with three different diameters(D=0.07 m,0.11 m,and 0.15 m).Acoustic emission monitoring,together with a miniature intelligent camera,was employed to analyze the entire process,focusing on macroscopic failure patterns,fragment characteristics,and underlying failure mechanisms.In addition,theoretical analyses were carried out and combined with numerical simulations to investigate the differences in energy evolution associated with rockburst physical models.The results indicate that:(1)The rockburst process with different tunnel diameters consistently evolved through three distinct stages—initial particle ejection,crack propagation accompanied by flake spalling,and,finally,fragment ejection leading to the formation of a‘V'-shaped notch.(2)Increasing tunnel diameter reduces rockburst failure load while increasing surrounding rock damage extent,total mass and average size of ejected fragments.Additionally,shear failure proportion decreases with tensile failure becoming increasingly dominant.(3)Larger tunnel diameters reduce the attenuation rate of elastic strain energy,thereby expanding the zone of elastic strain energy accumulation and disturbance and creating conditions for larger volume rockburst.(4)Larger tunnel diameters result in a smaller principal stress ratio at equivalent distances in the surrounding rock,indicating a higher likelihood of tensile failure.(5)Numerical analyses further reveal that larger tunnel diameters reduce the maximum elastic strain energy density around the tunnel,lowering the energy released per unit volume of rockburst fragments and their ejection velocities.However,both the total failure volume and overall energy release from rockburst increase.Model experiments with different tunnel diameters are of great significance for optimizing engineering design and parameter selection,as well as guiding tunnel construction under complex geological conditions.展开更多
文摘Objective:To assess prenatal Bisphenol A(BPA)exposure levels and explore their preliminary associations with maternal and fetal characteristics in a population from Northeastern Yunnan.Methods:A cross-sectional analysis was performed using data and urine samples from 70 pregnant women in their third trimester recruited at Qujing Central Hospital.Urinary BPA was measured by HPLC-MS/MS.Participants were stratified into high and low BPA exposure groups based on the median concentration.Results:BPA was detected in all samples(100%)with a median concentration of 2.41μg/L(IQR:0.68-4.96).The high BPA exposure group(≥2.41μg/L)had a significantly higher proportion of gestational diabetes mellitus(GDM)(42.9%vs.17.1%,p=0.021)and a lower median fetal birth weight(3250 g vs.3450 g,p=0.048)compared to the low exposure group.Conclusion:This pilot study reveals ubiquitous BPA exposure in pregnant women from Northeastern Yunnan.The observed preliminary associations with GDM and reduced fetal birth weight warrant further investigation in larger,longitudinal studies.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFB3710805).
文摘Ultra-high-strength aluminumalloy profile is an ideal choice for aerospace structuralmaterials due to its excellent specific strength and corrosion resistance.However,issues such as uneven metal flow,stress concentration,and forming defects are prone to occur during their extrusion.This study focuses on an Al-Zn-Mg-Cu ultra-high-strength aluminum alloy profile with a double-U,multi-cavity thin-walled structure.Firstly,hot compression experiments were conducted at temperatures of 350○C,400○C,and 450○C,with strain rates of 0.01 and 1.0 s^(−1),to investigate the plastic deformation behavior of the material.Subsequently,a 3D coupled thermo-mechanical extrusion simulation model was established using Deform-3D to systematically analyze the influence of die structure and process parameters on metal flow velocity,effective stress/strain,and temperature distribution.The simulation revealed significant velocity differences,stress concentration,and uneven temperature distribution.Key parameters,including mesh density,extrusion ratio,die fillet,and bearing length,were optimized through full-factorial experiments.This optimization,combined with a stepped flow-guiding die design,effectively improved the metal flow pattern during extrusion.Trial production based on both the initial and optimized parameters were carried out.A comparative analysis demonstrates that the optimized scheme results in a final profile whose cross-section matches the target design closely,with complete filling of complex features and no obvious forming defects.This research provides a valuable reference for the extrusion process optimization and die design of complex-section profiles made from ultra-high-strength aluminum alloys.
基金supported by the National Natural Science Foundation of China(82341245,82371491)the Chinese Central Government(Key Project of Public Health Program)the National Key Research and Development Program of China(2018YFC1311706,2018YFC1311702)。
文摘Objective This study aimed to determine the temporal trends in sleep duration among Chinese adults.Methods In this series of repeated nationally representative cross-sectional surveys(China Chronic Disease and Risk Factors Surveillance)conducted between 2010 and 2018,a total of 645,420 adult participants(97,741 in 2010;175,749 in 2013;187,777 in 2015;and 184,153 in 2018)were included in the trend analysis.Linear and logistic regression models were utilized to assess trends in sleep duration.Results In 2018,the estimated overall mean sleep duration among the Chinese adult population was7.58(SD,1.45)hours per day,with no significant trend from 2010.A significant increase in short sleep duration(≤6 hours)was observed in the total population,from 15.3%(95%CI:14.1%–16.5%)in 2010 to18.5%(95%CI:17.7%–19.3%)in 2018(P<0.001).Similarly,the trend in long sleep duration(>9 hours)was also significant,increasing in weighted prevalence from 7.2%(95%CI:6.3%–8.1%)in 2010 to 9.0%(95%CI:8.2%–9.9%)in 2018(P<0.001).Conclusion The prevalence of both short and long sleep durations significantly increased among Chinese adults from 2010 to 2018,highlighting the urgency of health initiatives to promote optimal sleep duration in China.
基金supported by Supported by the Scientific Research Foundation for High-Level Talents of Zhoukou Normal University(ZKNUC2024018).
文摘Energy shortage has become one of themost concerning issues in the world today,and improving energy utilization efficiency is a key area of research for experts and scholars worldwide.Small-diameter heat exchangers offer advantages such as reduced material usage,lower refrigerant charge,and compact structure.However,they also face challenges,including increased refrigerant pressure drop and smaller heat transfer area inside the tubes.This paper combines the advantages and disadvantages of both small and large-diameter tubes and proposes a combined-diameter heat exchanger,consisting of large and small diameters,for use in the indoor units of split-type air conditioners.There are relatively few studies in this area.In this paper,A theoretical and numerical computation method is employed to establish a theoretical-numerical calculation model,and its reliability is verified through experiments.Using this model,the optimal combined diameters and flow path design for a combined-diameter heat exchanger using R32 as the working fluid are derived.The results show that the heat transfer performance of all combined diameter configurations improves by 2.79%to 8.26%compared to the baseline design,with the coefficient of performance(COP)increasing from 4.15 to 4.27~4.5.These designs can save copper material,but at the cost of an increase in pressure drop by 66.86%to 131.84%.The scheme IIIH,using R32,is the optimal combined-diameter and flow path configuration that balances both heat transfer performance and economic cost.
文摘We investigated the impact of convexity and isoperimetric deficits on the accuracy of sectional area estimates of tree stems using traditional methods(caliper,tape,formulas based on stem diameter and circumference).In two complementary experiments,the use of photographs to estimate cross-sectional areas was first validated,then the use of a caliper and diameter tape was computer-simulated.The results indicated that the photographic method offers high precision,with mean relative errors below 0.1%,minimal deviation,and no significant bias,and the traditional methods led to substantial and systematic errors,with deviations from circularity and convexity significantly increasing the errors in area estimation.
基金partially supported by the Center for Advanced Systems Understanding(CASUS)financed by Germany’s Federal Ministry of Education and Research(BMBF)+2 种基金the Saxon State Government out of the State Budget approved by the Saxon State Parliamentfunding from the European Union’s Just Transition Fund(JTF)within the project Röntgenlaser-Optimierung der Laserfusion(ROLF),Contract No.5086999001co-financed by the Saxon State Government out of the State Budget approved by the Saxon State Parliament.
文摘We present the first systematic experimental validation of return-current-driven cylindrical implosion scaling in micrometer-sized Cu and Al wires irradiated by J-class femtosecond laser pulses.Employing XFEL-based imaging with sub-micrometer spatial and femtosecond temporal resolution,supported by hydrodynamic and particle-in-cell simulations,we reveal how return current density depends precisely on wire diameter,material properties,and incident laser energy.We identify deviations from simple theoretical predictions due to geometrically influenced electron escape dynamics.These results refine and confirm the scaling laws essential for predictive modeling in high-energy-density physics and inertial fusion research.
基金the National Natural Science Foundation of China (No. 59236130).
文摘In this companion paper, flow patterns in the upstream and downstream tubes of a sudden-expansion cross-section (SECS) in a vertical straight pipe were presented. The effect of SECS on flow patterns upstream and downstream was analyzed by comparing with flow patterns in uniform cross-section vertical tubes. It is found the effect is great. There exist great instabilities of two-phase flow in the neighboring areas of the SECS both downstream and upstream.
基金the National Natrual Science Foundation of China (No. 59236130).
文摘Flow patterns upstream and downstream of a sudden-contraction cross-section in a vertical straight pipe were presented. By comparing with flow patterns in uniform cross-section vertical tubes, the effect of the sudden change in pipe diameter on flow patterns was analyzed. Flow pattern transition mechanisms were discussed and transition criteria for flow pattern transitions were deduced accordingly using the dimensional analysis.
文摘Objective The relationship between non-high-density lipoprotein(NHDL)cholesterol to high-density lipoprotein cholesterol(HDL-C)ratio(NHHR)and stoke remains unknown.This study aimed to evaluate the association between the adult NHHR and stroke occurrence in the United States of America(USA).Methods To clarify the relationship between the NHHR and stroke risk,this study used a multivariable logistic regression model and a restricted cubic spline(RCS)model to investigate the association between the NHHR and stroke,and data from the National Health and Nutrition Examination Survey(NHANES)from 2005 to 2018.Subgroup and sensitivity analyses were conducted to test the robustness of the results.Results This study included 29,928 adult participants,of which 1,165 participants had a history of stroke.Logistic regression analysis of variables demonstrated a positive association between NHHR and stroke(OR 1.24,95%CI:1.03-1.50,P=0.026).Compared with the lowest reference group of NHHR,participants in the second,third,and fourth quartile had a significantly increased risk of stroke after full adjustments(OR:1.35,95%CI:1.08-1.69)(OR:1.83,95%CI:1.42-2.36)(OR:2.04,95%CI:1.50-2.79).In the total population,a nonlinear dose-response relationship was observed between the NHHR and stroke risk(P non-linearity=0.002).This association remained significant in several subgroup analyses.Further investigation of the NHHR may enhance our understanding of stroke prevention and treatment.Conclusion Our findings suggest a positive correlation between the NHHR and an increased prevalence of stroke,potentially serving as a novel predictive factor for stroke.Timely intervention and management of the NHHR may effectively mitigate stroke occurrence.Prospective studies are required to validate this association and further explore the underlying biological mechanisms.
基金financially supported by Guangdong Province Basic and Applied Basic Research Fund Project(Grant No.2022B1515250009)Liaoning Provincial Natural Science Foundation-Doctoral Research Start-up Fund Project(Grant No.2024-BSBA-05)+1 种基金Major Science and Technology Innovation Project in Shandong Province(Grant No.2024CXGC010803)the National Natural Science Foundation of China(Grant Nos.52271269 and 12302147).
文摘The umbilical,a key component in offshore energy extraction,plays a vital role in ensuring the stable operation of the entire production system.The extensive variety of cross-sectional components creates highly complex layout combinations.Furthermore,due to constraints in component quantity and geometry within the cross-sectional layout,filler bodies must be incorporated to maintain cross-section performance.Conventional design approaches based on manual experience suffer from inefficiency,high variability,and difficulties in quantification.This paper presents a multi-level automatic filling optimization design method for umbilical cross-sectional layouts to address these limitations.Initially,the research establishes a multi-objective optimization model that considers compactness,balance,and wear resistance of the cross-section,employing an enhanced genetic algorithm to achieve a near-optimal layout.Subsequently,the study implements an image processing-based vacancy detection technique to accurately identify cross-sectional gaps.To manage the variability and diversity of these vacant regions,the research introduces a multi-level filling method that strategically selects and places filler bodies of varying dimensions,overcoming the constraints of uniform-size fillers.Additionally,the method incorporates a hierarchical strategy that subdivides the complex cross-section into multiple layers,enabling layer-by-layer optimization and filling.This approach reduces manufac-turing equipment requirements while ensuring practical production process feasibility.The methodology is validated through a specific umbilical case study.The results demonstrate improvements in compactness,balance,and wear resistance compared with the initial cross-section,offering novel insights and valuable references for filler design in umbilical cross-sections.
基金funded by Tianjin Key Medical Discipline(Specialty)Construction Project,China(Grant No.TJYXZDXK-011A)Tianjin Medical University Cancer Institute&Hospital Nursing Special Fund Project(H2304)。
文摘Objectives:This study aimed to classify young breast cancer patients into distinct ambivalence over emotional expression and to explore the factors influencingthe level of ambivalence over emotional expression.Methods:A total of 217 young breast cancer patients were enrolled from a tertiary Grade A oncology hospital in Tianjin,China,using the convenience sampling method.All participants completed the general questionnaire,Ambivalence over Emotion Expression Questionnaire(AEQ),and Family Adapt-Ability and Cohesion Evaluation Scales-Chinese Version(FACES-CV).We employed exploratory latent profileanalysis for ambivalence over emotional expression profilingand logistic regression analysis to identify the influentialfactors Results:The results of the latent profileanalysis supported the models of four latent profiles,which were definedas“low conflict-lowexpression reflection”(19.2%),“high conflict-high inhibition expression”(43.9%),“moderate conflict-highregret expression”(18.1%),and“moderate conflict-desire understand”(18.8%).Logistic regression revealed that family cohesion,marital status,residence,per capita monthly income,and cancer stage were the influencingfactors of ambivalence over emotional expression in young breast cancer patients(P<0.05)Conclusions:Levels of ambivalence over emotional expression ameast cancer patients with breast cancer were highly heterogeneous.Medical staff should provide psychological counseling and health education tailored to the unique characteristics of emotional expression ambivalence in different patient groups to promote healthy emotional expression among patients.
基金National Nonprofit Institute Research Grant for the Institute of Basic Theory for Chinese Medicine,China Academy of Chinese Medical Sciences:Mechanism of Regulating Phlegm-Dampness Constitution to Prevent Metabolic Diseases based on Gut Microbiota-host DNA Methylation(No.YZ-202151)。
文摘OBJECTIVE:To investigate the difference in gut microbiota between population with damp-heat constitution(DHC)and balanced constitution(BC).METHODS:A multi-centered cross-sectional casecontrol study was conducted,which included 249 participants with damp-heat constitution or balanced constitution.Baseline information of participants was collected,and stool samples were collected for gut microbiota analysis.Principal coordinate analysis,linear discriminant analysis effect size analysis,receiver operating characteristic,random forest model,and phylogenetic investigation of communities by reconstruction of unobserved states methods were used to reveal the relationship between gut microbiota and the damp-heat constitution.RESULTS:Compared to those in the BC group,the richness and diversity of the microbiota,specifically those of several short-chain fatty acid producing genera such as Barnesiella,Coprobacter,and Butyricimonas,were significantly decreased in the DHC group.Regarding biological functions,flavonoid biosynthesis,propanoate metabolism,and nucleotide sugar metabolism were suppressed,while arachidonic acid metabolism and glutathione metabolism were enriched in the DHC group.Finally,a classifier based on the microbiota was constructed to discriminate between the DHC and BC populations.CONCLUSION:The gut microbiota of the DHC population exhibits significantly reduced diversity and is closely related to inflammation,metabolic disorders,and liver steatosis,which is consistent with clinical observations,thus serving as a potential diagnostic tool for traditional Chinese medicine constitution discrimination.
基金supported by an Innovation Fund for Medical Sciences of the Chinese Academy of Medical Sciences (Grant No.2019-I2M-2-007).
文摘Objective:Postpartum nutrition plays a critical role in maternal recovery and long-term health.However,the nutritional status of working mothers in the postpartum period remains understudied.This study aimed to assess the dietary quality of postpartum women in urban Beijing,identify occupational-related factors influencing their diet,and explore potential interventions to improve maternal nutrition during the postpartum period.Methods:In this cross-sectional analysis,554 women one year after delivery were recruited from ten community health centers.Sociodemographic,occupational and postpartum care variables were collected via questionnaire.Dietary intake over the preceding year was assessed using a food frequency questionnaire.The modified dietary balance index for postpartum women were used for dietary quality assessment.Results:The study revealed severe dietary imbalances among postpartum women,characterized by excessive consumption of cereals,eggs,and meats,while their intake of vegetables,fruits,and dairy products was inadequate.According to dietary balance index for postpartum women,66.25%of mothers showed varying degrees of excessive intake.45.31%of mothers experienced varying levels of insufficient intake,with only 19.86%of participants having a relatively balanced diet.Occupational differences were observed,with women in the commercial employment group showing higher levels of excessive food intake.The analysis of influencing factors showed that family monthly income,maternity leave,and postpartum care significantly affected the dietary quality.Conclusions:Postpartum women in Beijing experience widespread dietary imbalances,with both excesses and deficiencies.Occupational context and related factors significantly shape diet quality.These findings highlight the need for targeted nutritional interventions tailored to the specific challenges of different occupational groups.
基金supported by the National Natural Science Foundation of China (Grant Nos.52304227 and 52104133)Scientific and Technological Research Platform for Disaster Prevention and Control of Deep Coal Mining (Anhui University of Science and Technology) (Grant No.DPDCM2208).
文摘To investigate the effects of the maximum principal stress direction(θ)and cross-section shape on the failure characteristics of sandstone,true-triaxial compression experiments were conducted using cubic samples with rectangular,circular,and D-shaped holes.Asθincreases from 0°to 60°in the rectangular hole,the left failure location shifts from the left corner to the left sidewall,the left corner,and then the floor,while the right failure location shifts from the right corner to the right sidewall,right roof corner,and then the roof.Furthermore,the initial failure vertical stress first decreases and then increases.In comparison,the failure severity in the rectangular hole decreases for variousθvalues as 30°>45°>60°>0°.With increasingθ,the fractal dimension(D)of rock slices first increases and then decreases.For the rectangular and D-shaped holes,whenθ=0°,30°,and 90°,D for the rectangular hole is less than that of the D-shaped hole.Whenθ=45°and 60°,D for the rectangular hole is greater than that of the D-shaped hole.Theoretical analysis indicates that the stress concentration at the rectangular and D-shaped corners is greater than the other areas.The failure location rotates with the rotation ofθ,and the failure occurs on the side with a high concentration of compressive stress,while the side with the tensile and compressive stresses remains relatively stable.Therefore,the fundamental reason for the rotation of failure location is the rotation of stress concentration,and the external influencing factor is the rotation ofθ.
基金supported by the National Natural Science Foundation of China(No.22422402)National Key Research and Development Program of China(No.2022YFF0705300)Key Research and Development Program of Jiangxi Province(No.20232BBG70004)。
文摘The performance and price of copper-based micro linear products are determined by the diameter uniformity.How to accurately detect the wire diameter of long-length copper based micro linear products without cutting or damage has always been a technical concern for production enterprises.Herein,a novel approach was developed for nondestructive detection of the average diameter at any given segment of a long copper wire by assessing the adsorption capacity of arginine on its surface.The amount of adsorbent on the surface of the copper wire exhibits a positive correlation with the area,which can be detected by extractive electrospray ionization mass spectrometry(EESI-MS)after online elution with ammonia.The experimental results demonstrated that the analysis can be completed within 15 min,with a good linear relationship between copper wires with different diameters and the adsorption capacity of arginine.The linear correlation coefficient R2was 0.995,the relative standard deviation was 1.10%-2.81%,and the detection limit reached 2.5μm(length of segment=4 cm),showing potential applications for facile measurement of the average diameter of various metal wires.
基金supported by the Innovation Team and Talents Cultivation Program of National Administration of Traditional Chinese Medicine(ZYYCXTD-C-202006)the High-level traditional Chinese medicine key subject construction project of National Administration of Traditional Chinese Medicine-Evidence-based Traditional Chinese Medicine(ZYYZDXK-2023249).
文摘Background:The bibliometrics of acupuncture are growing rapidly.However,the absence of reporting guidelines may lead to significant duplication and waste,thereby undermining the research’s value.To address this,a knowledge mapping was generated based on published studies to investigate the characteristics of bibliometric studies on acupuncture and the extent of duplicate publications,with the overarching goal of providing a comprehensive overview of the knowledge structure in this field.Methods:This cross-sectional study used three databases(PubMed,Web of Science,and Scopus)to identify relevant studies up to May 1,2024.In addition,the reference lists were retrieved as a supplement.To track research trends,we employed Microsoft Excel and R software to extract,code,and analyze information.Study selection,data extraction,and validation were performed independently by at least two reviewers.The reporting quality of included studies was assessed using the Preliminary guideline for reporting bibliometric reviews of the biomedical literature(BIBLIO).Results:Among the 6,221 bibliometric reviews examined,113 relevant publications were identified,80 focusing on various diseases/conditions.The annual number of publications has gradually increased,with the output in the past four years being 3.52 times higher than that before 2020.China(106)and Chengdu University of Traditional Chinese Medicine(16)have the highest number of publications.The most prolific author is Fan-Rong Liang,with six articles.The first bibliometric study,by Hai-Yan Li,was published in 2010.Journal of Pain Research,with 36 articles,holds the most publications.The top three diseases:diseases of the nervous system;symptoms,signs,or clinical findings not elsewhere classified;and mental,behavioral,or neurodevelopmental disorders.There may be potential duplication in research on 13 diseases/conditions,notably stroke,migraine,pain/analgesia,cancer pain,shoulder pain,facial paralysis/bell’s palsy,chronic pain,and cognitive impairment.In BIBLIO,the most frequently missing items are issues/topics(item 2),quality assessment(item 11),and descriptive findings(item 13).Conclusion:This study demonstrates that acupuncture bibliometrics is actively utilized to identify dominant diseases/conditions,aiding scholars in understand the knowledge structure and main topics.Although the number of related studies is increasing,with an average of 25 studies annually,overlap in some areas highlights the need for adherence to reporting guidelines and careful topic selection to ensure truly valuable insights and knowledge contributions.The adherence to BIBLIO’s 20 proposed items across analyzed articles,highlighting important in reporting practices.
基金Project(RE-KRIS/FF67/020)supported by the King Mongkut's Institute of Technology Ladkrabang(Fundamental Fund by National Science Research and Innovation Fund(NSRF)),Thailand。
文摘A train body's cross-sectional shape has a significant impact on aerodynamic drag and operational safety in high-speed trains(HSTs).This study extracts five design variables from a real-world HST body:height,width,side arc radius,arc radius at the connection between the side and the roof,and arc radius at the connection between the side and the train's bottom.The cross-validated Kriging surrogate model and the genetic algorithm are used to perform two types of aerodynamic optimization,with the cross-sectional area as a constraint.Cross-sectional shapes are optimized in both windless and windy conditions.Numerical results indicate that in a windless environment,the aerodynamic drag coefficient of the whole train is reduced by 2.4%;in a windy condition,the aerodynamic drag coefficient of the entire vehicle is reduced by 2.4%,and the aerodynamic lateral force of the leading car is reduced by 37.8%.These suggest that a flat and wide shape helps to reduce not only overall aerodynamic drag in a windless environment but also aerodynamic load in a windy environment,which can be accomplished by reducing the area of the side wall and top region,lowering the train body's height,increasing its width,and lowering the radius of the side and top arcs.
基金financially supported by the National Key Research and Development Program of China(Grant No.2022YFA1203302)the National Natural Science Foundation of China(Grant Nos.52130209,52188101)+4 种基金the JSPS Kakenhi(Grant Nos.JP25820336,JP20K05281,and JP23H01796)the JST-FOREST Program(Grant No.JPMJFR223T)the WPI-MANA“Challenging Research Program(CRP)”the National Institute for Materials Science(NIMS)“Support system for curiosity-driven research”the“Advanced Research Infrastructure for Materials and Nanotechnology in Japan(ARIM)”of the Ministry of Education,Culture,Sports,Science and Technology(MEXT)(Grant No.JPMXP1223NM5306).
文摘Carbon nanotubes are uniquely featured by the nanoscale tubular structure with a highly-curved surface and defined chirality.The diameter and chirality fundamentally determine their stability and electrical and thermal properties.Up to now,the relationship between the intrinsic thermal conductivity and the atomic features of CNTs has not been established,due to the challenges in precise measurements and characterizations.In this work,we develop a micro electro-thermal device enabling simultaneous thermal measurements by Raman spectroscopy and atomic structural characterization by transmission electron microscopy for individual CNTs.The influence of diameter and chirality is systematically investigated.In addition,the temperature dependence of the thermal conductivity was extracted from parameter optimization of finite-element modeling.It is found that the thermal transport of CNTs depends mainly on the diameter,while the chiral angle has no significant influence.Along with increasing diameter,the room temperature thermal conductivity increases and eventually approaches the limit of flat graphene.
基金supported by the National Natural Science Foundation of China(Grant Nos.11922206 and 11832011)theMajor Project of Science and Technology Innovation 2030(Grant No.2021ZD0113100)the 111 Project(Grant No.B16015).
文摘The coconut structure exhibits inherent impact resistance,with the macroscopically ordered distribution of variable crosssection fibers in its husk playing a crucial role in stress wave propagation and scaling.Inspired by the natural structure and fibers,this study proposes a stress wave propagation model for a variable cross-section bar considering viscous effects.A theoretical model for stress wave propagation in a fusiform-shaped bar with variable cross-section is established,elucidating the stress wave scaling effect observed in coconut fibers.Additionally,a quasi-one-dimensional method for analyzing and measuring stress wave propagation is introduced,and an experimental setup is assembled.Experimental validation of the stress wave scaling effect confirms the theory’s accuracy for stress wave scaling in variable cross-section bars.This research provides theoretical guidance and measurement methods for the design of space landers,automobile anti-collision beams,stress wave collectors,and scalers,as well as for impact testing of macro and micro materials and the design of sustainable plant-based materials for impact protection.
基金funded by the National Natural Science Foundation of China(Nos.42077228,52174085)。
文摘With the increasing development of deepburied engineering projects,rockburst disasters have become a frequent concern.Studies have indicated that tunnel diameter is a critical factor influencing the occurrence of rockbursts.To investigate the influence of tunnel diameter on the deformation and failure characteristics of surrounding rock,large-sized rocklike gypsum specimens were tested using a selfdeveloped true triaxial rockburst loading system containing circular tunnels with three different diameters(D=0.07 m,0.11 m,and 0.15 m).Acoustic emission monitoring,together with a miniature intelligent camera,was employed to analyze the entire process,focusing on macroscopic failure patterns,fragment characteristics,and underlying failure mechanisms.In addition,theoretical analyses were carried out and combined with numerical simulations to investigate the differences in energy evolution associated with rockburst physical models.The results indicate that:(1)The rockburst process with different tunnel diameters consistently evolved through three distinct stages—initial particle ejection,crack propagation accompanied by flake spalling,and,finally,fragment ejection leading to the formation of a‘V'-shaped notch.(2)Increasing tunnel diameter reduces rockburst failure load while increasing surrounding rock damage extent,total mass and average size of ejected fragments.Additionally,shear failure proportion decreases with tensile failure becoming increasingly dominant.(3)Larger tunnel diameters reduce the attenuation rate of elastic strain energy,thereby expanding the zone of elastic strain energy accumulation and disturbance and creating conditions for larger volume rockburst.(4)Larger tunnel diameters result in a smaller principal stress ratio at equivalent distances in the surrounding rock,indicating a higher likelihood of tensile failure.(5)Numerical analyses further reveal that larger tunnel diameters reduce the maximum elastic strain energy density around the tunnel,lowering the energy released per unit volume of rockburst fragments and their ejection velocities.However,both the total failure volume and overall energy release from rockburst increase.Model experiments with different tunnel diameters are of great significance for optimizing engineering design and parameter selection,as well as guiding tunnel construction under complex geological conditions.
