In modern industrial applications,ensuring the reliability of mechanical fittings is critical for maintaining operational safety and efficiency,particularly in power grid systems where split pins serve a pivotal role ...In modern industrial applications,ensuring the reliability of mechanical fittings is critical for maintaining operational safety and efficiency,particularly in power grid systems where split pins serve a pivotal role despite being susceptible to environmental degradation and failure.Existing UAV-based inspection systems are hampered by a low representation of split pin elements and complex backgrounds,leading to challenges in accurate fault detection and timely maintenance.To address this pressing issue,our study proposes an innovative fault detection method for split pins.The approach employs a three-step process:first,cropping operations are used to accurately isolate the fittings containing split pins;second,super-resolution reconstruction is applied to enhance image clarity and detail;and finally,an improved YOLOv8 network,augmented with inner-shape IoU and local window attention mechanisms,is utilized to refine local feature extraction and annotation accuracy.Experimental evaluations on a split pin defect dataset demonstrate robust performance,achieving an accuracy rate of 72.1%and a mean average precision(mAP)of 67.7%,thereby validating the method’s effectiveness under challenging conditions.The proposed approach contributes to the field by specifically targeting the challenges associated with split pin detection in UAV-based inspections,offering a practically applicable and reliably precise method.展开更多
Metal droplet deposition is a kind of additive manufacturing(3D Printing)technique that fabricates near-net part through droplets deposition with lower cost and higher efficiency.This paper proposed a solution to prob...Metal droplet deposition is a kind of additive manufacturing(3D Printing)technique that fabricates near-net part through droplets deposition with lower cost and higher efficiency.This paper proposed a solution to problems of electric power fittings that large inventories,high procurement costs,low manufacturing efficiency and transportation cost.Using additive Manufacturing technique-metal droplet deposition,electric power fittings fabricated on power construction site.This paper describes the manufacturing process of typical thin-walled samples(the structure optimized based on additive manufacturing principle)and ball head rings of electric power fittings.Aiming at the integral AM forming for ball and ball socket electric power fitting workpiece,a novel easy removal forming support material(ceramics and gypsum mixed with UV cured resin)have been developed.Here this support material was used to fabricate nested integral workpieces.Dimensional accuracy and microstructure of the test pieces were analyzed.The error of the height and width of the forming workpiece is within 5%.No obvious overlap trace(such as overlap line and cracks)observed,and the internal microstructure is equiaxial crystal.The average density of the component is 99.51%,which measured by drainage method and 13.39%higher than the cast raw material.展开更多
Flexible pipes function effectively in practical applications only when they are securely connected to specific components using specially designed end fittings.These end fittings must be precisely manufactured to ens...Flexible pipes function effectively in practical applications only when they are securely connected to specific components using specially designed end fittings.These end fittings must be precisely manufactured to ensure a tight connection,preventing any potential leakage.Otherwise,even perfectly manufactured flexible pipes will fail to perform their intended function.Although extensive research exists on the mechanical analysis of flexible pipes,studies on pipes connected to end fittings are scarce.The primary challenge in investigating this combined structure lies in the complex interaction between flexible pipes and end fittings after assembly,in addition to the already intricate structural behavior of flexible pipes.This paper presents both experimental and numerical analyses.Experimentally,we conducted comprehensive torsion tests on steel strip reinforced flexible pipes connected to commonly used end fittings,observing various torsional failure modes.On the numerical side,we developed a method to model the interaction between flexible pipes and end fittings.The proposed approach enables the prediction of torsional failure modes in practical applications and lays the groundwork for further failure analysis under different loading conditions and for various end fitting designs.展开更多
Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves u...Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves under varying temperatures and pre-strains,this paper conducts both tensile and stress relaxation tests on PVDF materials.To describe the stress relaxation characteristics of these materials,the Prony series is utilized.In order to identify the parameters of the series,the paper employs the Levenberg-Marquardt method of nonlinear regression.A finite element model is established to verify the accuracy of the parameter identification method.Subsequently,the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting,while taking into account fluid pressure inside the pipeline using a pressure penetration method.The impact of stress relaxation on the sealing performance is then discussed.Finally,the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.展开更多
Gauss radial basis functions(GRBF)are frequently employed in data fitting and machine learning.Their linear independence property can theoretically guarantee the avoidance of data redundancy.In this paper,one of the m...Gauss radial basis functions(GRBF)are frequently employed in data fitting and machine learning.Their linear independence property can theoretically guarantee the avoidance of data redundancy.In this paper,one of the main contributions is proving this property using linear algebra instead of profound knowledge.This makes it easy to read and understand this fundamental fact.The proof of linear independence of a set of Gauss functions relies on the constructing method for one-dimensional space and on the deducing method for higher dimensions.Additionally,under the condition of preserving the same moments between the original function and interpolating function,both the interpolating existence and uniqueness are proven for GRBF in one-dimensional space.The final work demonstrates the application of the GRBF method to locate lunar olivine.By combining preprocessed data using GRBF with the removing envelope curve method,a program is created to find the position of lunar olivine based on spectrum data,and the numerical experiment shows that it is an effective scheme.展开更多
Background:Physical fitness is a key indicator of current and future health in children and adolescents.Evidence suggests that fitness levels have declined then stagnated in recent decades,but it remains unclear how t...Background:Physical fitness is a key indicator of current and future health in children and adolescents.Evidence suggests that fitness levels have declined then stagnated in recent decades,but it remains unclear how the coronavirus disease 2019(COVID-19)pandemic has impacted this trend.Methods:We conducted a systematic review and meta-analyses to assess pandemic-related changes in physical fitness among children and adolescents(0-19 years)in the World Health Organization European Region.Seven databases were searched up to February 28,2025 for studies reporting validated pre-and during/post-pandemic fitness measurements.Two reviewers independently performed screening,data extraction,risk-of-bias assessment(Risk Of Bias In Non-randomized Studies-of Exposure)(ROBINS-E),and certainty grading(Grading of Recommendations,Assessment,Development and Evaluation)(GRADE).Random-effects meta-analyses yielded standardized mean differences(SMDs)with 95%confidence intervals(95%CIs).Subgroup analyses examined sex,age,year,and national restriction severity(Oxford Stringency Index).Results:Thirty-two studies comprising 270,179 participants and 1,519,386 fitness measurements from 17 European countries were included.Cardiorespiratory fitness declined significantly during the pandemic,especially in 2021,with reductions in endurance(SMD=-0.43;95%CI:-0.61 to-0.25)and speed(SMD=-0.29;95%CI:-0.61 to 0.03).While speed returned to baseline by 2023,endurance remained below pre-pandemic levels(SMD=-0.10;95%CI:-0.12 to-0.08).Girls and adolescents were disproportionately affected.In contrast to cardiorespiratory fitness,muscular fitness remained largely unchanged.Stricter national regulations were associated with greater declines in cardiorespiratory fitness.Conclusion:COVID-19 pandemic restrictions were associated with a marked decline in cardiorespiratory fitness in European children and adolescents,with levels not recovered by 2023.These findings call for urgent,targeted public health interventions to improve physical fitness and prevent long-term health consequences.展开更多
Background:Midlife lifestyle factors,including physical activity,are associated with late-life brain health,yet the role of aerobic exercise on structural brain health in early and mid-adulthood remains poorly underst...Background:Midlife lifestyle factors,including physical activity,are associated with late-life brain health,yet the role of aerobic exercise on structural brain health in early and mid-adulthood remains poorly understood.This study aimed to examine the effect of aerobic exercise on structural brain age and to explore potential mediators.Methods:In a single-blind,12-month randomized clinical trial,130 healthy participants aged 26-58 years were randomized into a moderate-to-vigorous intensity aerobic exercise group or a usual-care control group.The exercise group attended two supervised 60-min sessions per week in a laboratory setting plus engaged in home-based exercise to achieve 150 min of exercise per week.Brain-predicted age difference(brain-PAD)and cardiorespiratory fitness(CRF)were assessed at baseline and 12 months.Both intention-to-treat(ITT)and completers analyses(including participants who completed post-intervention assessments)were performed.Results:The 130 participants(67.7%female)had an age of 41.28±9.93 years(mean±SD).At baseline,higher CRF(peak oxygen uptake,VO_(2peak))was associated with smaller brain-PAD(β=-0.309,p=0.012).After the intervention,the exercise group showed a decrease in brainPAD(estimated mean difference(EMD)=-0.60;95%confidence interval(95%CI):-1.15 to-0.04;p=0.034)compared to the control group(EMD=0.35;95%CI:-0.21 to 0.92;p=0.217);time×group interaction(between-group difference(BGD)=-0.95;95%CI:-1.72 to-0.17;p=0.019).VO2peak improved in the exercise group(EMD=1.60;95%CI:0.29-2.90;p=0.017)compared to the control group(EMD=-0.78;95%CI:-2.17 to 0.60;p=0.265);time×group interaction(BGD=2.38;95%CI:0.52-4.25;p=0.015).Body composition,blood pressure,and brain-derived neurotrophic factor levels were unaffected.None of the proposed pathways statistically mediated the effect of exercise on brain-PAD.The results from completers were similar.Conclusion:Engaging in 12 months of moderate-to-vigorous exercise reduced brain-PAD in early-to-midlife adults.The pathways by which these effects occur remain unknown.展开更多
The Haoping 40 m radio telescope at the National Time Service Center,Chinese Academy of Sciences was built in 2014 and is primarily used to observe navigation satellites and pulsars.Since the first successful very lon...The Haoping 40 m radio telescope at the National Time Service Center,Chinese Academy of Sciences was built in 2014 and is primarily used to observe navigation satellites and pulsars.Since the first successful very long baseline interferometry(VLBI)observation of L-band radio source fringes in 2022,ten observations have been made so far.The stations involved in the observations include the Haoping 40 m radio telescope(Haoping),the Tianma 65 m radio telescope(Tianma),the Nanshan 26 m radio telescope(Urumqi),the Guizhou 500 m radio telescope(FAST),the Jilin 13 m radio telescope(Jilin),the Effelsberg 100 m radio telescope(Effelsberg),the Onsala 25 m radio telescope(Onsala),and the Chiang Mai 40 m radio telescope(Chiang Mai).This paper presents details on the specifications of the Haoping 40 m radio telescope,as well as the design of the VLBI experiment,the observation process,and the data processing.We also discuss the analysis of the fringe results involving the Haoping 40 m radio telescope,using Distributed FX Correlator to obtain excellent results.We confirm that the telescope is capable of participating in VLBI observations and performing specific data processing tasks.It can therefore play a greater role in future VLBI observations.展开更多
With the development of the semiconductor industry below the 7 nm scale,critical dimension small-angle X-ray scattering(CD-SAXS)has emerged as a powerful tool for quantitatively measuring nanoscale deviations.In this ...With the development of the semiconductor industry below the 7 nm scale,critical dimension small-angle X-ray scattering(CD-SAXS)has emerged as a powerful tool for quantitatively measuring nanoscale deviations.In this study,the effects of X-ray beam size and photon energy on the accuracy of critical dimension measurements were investigated.Critical dimensions measured using beams with different spot sizes showed different deviations from the expected values.Beam sizes that were either too large or too small did not improve confidence intervals.As the incident energy increased,the X-ray transmission rate increased,while the scattering cross section decreased,resulting in a gradual decrease in the signal-to-noise ratio of the diffraction peaks,which reduced the accuracy of the CD-SAXS measurements.An optimal accuracy was obtained at 12 keV with a smaller beam size.Using an effective trapezoid model,the results yielded an average pitch of 100.4±0.2 nm,width of 49.8±0.2 nm,height of 130.0±0.2 nm,and a sidewall angle below 1.1°±0.1°.These results provide crucial guidance for the future development of CD-SAXS laboratories and the construction of X-ray machines as well as robust support for research in related fields.展开更多
Feature selection serves as a critical preprocessing step inmachine learning,focusing on identifying and preserving the most relevant features to improve the efficiency and performance of classification algorithms.Par...Feature selection serves as a critical preprocessing step inmachine learning,focusing on identifying and preserving the most relevant features to improve the efficiency and performance of classification algorithms.Particle Swarm Optimization has demonstrated significant potential in addressing feature selection challenges.However,there are inherent limitations in Particle Swarm Optimization,such as the delicate balance between exploration and exploitation,susceptibility to local optima,and suboptimal convergence rates,hinder its performance.To tackle these issues,this study introduces a novel Leveraged Opposition-Based Learning method within Fitness Landscape Particle Swarm Optimization,tailored for wrapper-based feature selection.The proposed approach integrates:(1)a fitness-landscape adaptive strategy to dynamically balance exploration and exploitation,(2)the lever principle within Opposition-Based Learning to improve search efficiency,and(3)a Local Selection and Re-optimization mechanism combined with random perturbation to expedite convergence and enhance the quality of the optimal feature subset.The effectiveness of is rigorously evaluated on 24 benchmark datasets and compared against 13 advancedmetaheuristic algorithms.Experimental results demonstrate that the proposed method outperforms the compared algorithms in classification accuracy on over half of the datasets,whilst also significantly reducing the number of selected features.These findings demonstrate its effectiveness and robustness in feature selection tasks.展开更多
The original online version of this article was revised:The layout update for Article 758 has impacted the page range in the published issue,but did not affect the scholarly content.To ensure consistency with the orig...The original online version of this article was revised:The layout update for Article 758 has impacted the page range in the published issue,but did not affect the scholarly content.To ensure consistency with the originally assigned pages(2595-2614),we will need to publish an erratum to correct the article and restore the original page range.The original article has been corrected.展开更多
The search for mechanical properties of materials reached a highly acclaimed level, when indentations could be analysed on the basis of elastic theory for hardness and elastic modulus. The mathematical formulas proved...The search for mechanical properties of materials reached a highly acclaimed level, when indentations could be analysed on the basis of elastic theory for hardness and elastic modulus. The mathematical formulas proved to be very complicated, and various trials were published between the 1900s and 2000s. The development of indentation instruments and the wish to make the application in numerous steps easier, led in 1992 to trials with iterations by using relative values instead of absolute ones. Excessive iterations of computers with 3 + 8 free parameters of the loading and unloading curves became possible and were implemented into the instruments and worldwide standards. The physical formula for hardness was defined as force over area. For the conical, pyramidal, and spherical indenters, one simply took the projected area for the calculation of the indentation depth from the projected area, adjusted it later by the iterations with respect to fused quartz or aluminium as standard materials, and called it “contact height”. Continuously measured indentation loading curves were formulated as loading force over depth square. The unloading curves after release of the indenter used the initial steepness of the pressure relief for the calculation of what was (and is) incorrectly called “Young’s modulus”. But it is not unidirectional. And for the spherical indentations’ loading curve, they defined the indentation force over depth raised to 3/2 (but without R/h correction). They till now (2025) violate the energy law, because they use all applied force for the indenter depth and ignore the obvious sidewise force upon indentation (cf. e.g. the wood cleaving). The various refinements led to more and more complicated formulas that could not be reasonably calculated with them. One decided to use 3 + 8 free-parameter iterations for fitting to the (poor) standards of fused quartz or aluminium. The mechanical values of these were considered to be “true”. This is till now the worldwide standard of DIN-ISO-ASTM-14577, avoiding overcomplicated formulas with their complexity. Some of these are shown in the Introduction Section. By doing so, one avoided the understanding of indentation results on a physical basis. However, we open a simple way to obtain absolute values (though still on the blackbox instrument’s unsuitable force calibration). We do not iterate but calculate algebraically on the basis of the correct, physically deduced exponent of the loading force parabolas with h3/2 instead of false “h2” (for the spherical indentation, there is a calotte-radius over depth correction), and we reveal the physical errors taken up in the official worldwide “14577-Standard”. Importantly, we reveal the hitherto fully overlooked phase transitions under load that are not detectable with the false exponent. Phase-transition twinning is even present and falsifies the iteration standards. Instead of elasticity theory, we use the well-defined geometry of these indentations. By doing so, we reach simple algebraically calculable formulas and find the physical indentation hardness of materials with their onset depth, onset force and energy, as well as their phase-transition energy (temperature dependent also its activation energy). The most important phase transitions are our absolute algebraically calculated results. The now most easily obtained phase transitions under load are very dangerous because they produce polymorph interfaces between the changed and the unchanged material. It was found and published by high-enlargement microscopy (5000-fold) that these trouble spots are the sites for the development of stable, 1 to 2 µm long, micro-cracks (stable for months). If however, a force higher than the one of their formation occurs to them, these grow to catastrophic crash. That works equally with turbulences at the pickle fork of airliners. After the publication of these facts and after three fatal crashing had occurred in a short sequence, FAA (Federal Aviation Agency) reacted by rechecking all airplanes for such micro cracks. These were now found in a new fleet of airliners from where the three crashed ones came. These were previously overlooked. FAA became aware of that risk and grounded 290 (certainly all) of them, because the material of these did not have higher phase-transition onset and energy than other airplanes with better material. They did so despite the 14577-Standard that does not find (and thus formally forbids) phase transitions under indenter load with the false exponent on the indentation parabola. However, this “Standard” will, despite the present author’s well-founded petition, not be corrected for the next 5 years.展开更多
Energy expenditure estimation can be used to measure the exercise load and physical condition of different individuals, such as soldiers, athletes, firemen, etc., during their training and work. Energy expenditure est...Energy expenditure estimation can be used to measure the exercise load and physical condition of different individuals, such as soldiers, athletes, firemen, etc., during their training and work. Energy expenditure estimation methods based on computer vision have rapidly developed in recent years. Compared with sensor-based methods, such methods are capable of monitoring several target persons at the same time, and the subjects do not need to wear different sensor devices that hamper their movement. In this paper, we propose a cross-attention spatial–temporal convolutional neural network to predict the energy expenditure of people under different exercise intensities. The model explores the relationship between changes in the human skeleton and energy expenditure intensity. In addition, a cross-attention correction module is used to reduce the negative effects of individual physical fitness characteristics during energy expenditure estimation. The experimental results show that our proposed method achieves high accuracy for energy expenditure estimation and performs better than existing computer vision-based energy expenditure estimation methods do. The proposed method can be widely used in various physical activity scenarios to measure energy expenditure, increasing the convenience of usage.展开更多
Background:Physicalfitness in childhood and adolescence is associated with a variety of health outcomes and is a powerful marker of current and future health.However,inconsistencies in tests and protocols limit interna...Background:Physicalfitness in childhood and adolescence is associated with a variety of health outcomes and is a powerful marker of current and future health.However,inconsistencies in tests and protocols limit international monitoring and surveillance.The objective of the study was to seek international consensus on a proposed,evidence-informed,Youth Fitness International Test(YFIT)battery and protocols for health monitoring and surveillance in children and adolescents aged 618 years.Methods:We conducted an international modified Delphi study to evaluate the level of agreement with a proposed,evidence-based,YFIT of core health-relatedfitness tests and protocols to be used worldwide in 6-to 18-year-olds.This proposal was based on previous European and North American projects that systematically reviewed the existing evidence to identify the most valid,reliable,health-related,safe,and feasiblefitness tests to be used in children and adolescents aged 618 years.We designed a single-panel modified Delphi study and invited 216 experts from all around the world to answer this Delphi survey,of whom one-third are from low-to-middle income countries and one-third are women.Four experts were involved in the piloting of the survey and did not participate in the main Delphi study to avoid bias.We pre-defined an agreement of 80%among the expert participants to achieve consensus.Results:We obtained a high response rate(78%)with a total of 169fitness experts from 50 countries and territories,including 63 women and 61 experts from low-or middle-income countries/territories.Consensus(>85%agreement)was achieved for all proposed tests and protocols,supporting the YFIT battery,which includes weight and height(to compute body mass index as a proxy of body size/composition),the 20-m shuttle run(cardiorespiratoryfitness),handgrip strength,and standing long jump(muscularfitness).Conclusion:This study contributes to standardizingfitness tests and protocols used for research,monitoring,and surveillance across the world,which will allow for future data pooling and the development of international and regional sex-and age-specific reference values,health-related cut-points,and a global picture offitness among children and adolescents.展开更多
1.Introduction。There is abundant evidence that the amount of habitual physical activity(PA)and the level of cardiorespiratory fitness(CRF)are inversely related to developing chronic diseases,including cardiovascular(...1.Introduction。There is abundant evidence that the amount of habitual physical activity(PA)and the level of cardiorespiratory fitness(CRF)are inversely related to developing chronic diseases,including cardiovascular(CV)disease(CVD).Relative to the CV and all-cause mortality reductions associated with exercise,intensity and duration also appear to be inversely related.For example,the mortality reductions that are associated with a regular 5-min run~a 15-min walk,and a 25-min run~a 105-min walk.1 In addition,at comparable levels of total energy expenditure,vigorous exercise seems to be more effective than moderate-intensity exercise in reducing CV risk.2 Vigorous exercise training is also more effective than moderate intensity training at increasing CRF,expressed as metabolic equivalents or METs,which has been shown to confer a lower risk of mortality.3 Accordingly,the optimal physiologic,clinical,and survival benefits of exercise are most likely to be achieved by progressing from moderate intensity exercise(usually defined as 40%-59%of functional capacity or 55%-69%of the maximal heart rate)to vigorous training regimens,corresponding to≥60%of functional capacity or 70%-89%of the measured maximal heart rate.展开更多
基金Fundamental Research Funds for the Central Universities(2023MS134)。
文摘In modern industrial applications,ensuring the reliability of mechanical fittings is critical for maintaining operational safety and efficiency,particularly in power grid systems where split pins serve a pivotal role despite being susceptible to environmental degradation and failure.Existing UAV-based inspection systems are hampered by a low representation of split pin elements and complex backgrounds,leading to challenges in accurate fault detection and timely maintenance.To address this pressing issue,our study proposes an innovative fault detection method for split pins.The approach employs a three-step process:first,cropping operations are used to accurately isolate the fittings containing split pins;second,super-resolution reconstruction is applied to enhance image clarity and detail;and finally,an improved YOLOv8 network,augmented with inner-shape IoU and local window attention mechanisms,is utilized to refine local feature extraction and annotation accuracy.Experimental evaluations on a split pin defect dataset demonstrate robust performance,achieving an accuracy rate of 72.1%and a mean average precision(mAP)of 67.7%,thereby validating the method’s effectiveness under challenging conditions.The proposed approach contributes to the field by specifically targeting the challenges associated with split pin detection in UAV-based inspections,offering a practically applicable and reliably precise method.
基金This research was funded by National Natural Science Foundation of China under grant number 51575313 and 51775420.This paper got help from Du Jun and Wang Xin of Xi’an Jiaotong University.
文摘Metal droplet deposition is a kind of additive manufacturing(3D Printing)technique that fabricates near-net part through droplets deposition with lower cost and higher efficiency.This paper proposed a solution to problems of electric power fittings that large inventories,high procurement costs,low manufacturing efficiency and transportation cost.Using additive Manufacturing technique-metal droplet deposition,electric power fittings fabricated on power construction site.This paper describes the manufacturing process of typical thin-walled samples(the structure optimized based on additive manufacturing principle)and ball head rings of electric power fittings.Aiming at the integral AM forming for ball and ball socket electric power fitting workpiece,a novel easy removal forming support material(ceramics and gypsum mixed with UV cured resin)have been developed.Here this support material was used to fabricate nested integral workpieces.Dimensional accuracy and microstructure of the test pieces were analyzed.The error of the height and width of the forming workpiece is within 5%.No obvious overlap trace(such as overlap line and cracks)observed,and the internal microstructure is equiaxial crystal.The average density of the component is 99.51%,which measured by drainage method and 13.39%higher than the cast raw material.
文摘Flexible pipes function effectively in practical applications only when they are securely connected to specific components using specially designed end fittings.These end fittings must be precisely manufactured to ensure a tight connection,preventing any potential leakage.Otherwise,even perfectly manufactured flexible pipes will fail to perform their intended function.Although extensive research exists on the mechanical analysis of flexible pipes,studies on pipes connected to end fittings are scarce.The primary challenge in investigating this combined structure lies in the complex interaction between flexible pipes and end fittings after assembly,in addition to the already intricate structural behavior of flexible pipes.This paper presents both experimental and numerical analyses.Experimentally,we conducted comprehensive torsion tests on steel strip reinforced flexible pipes connected to commonly used end fittings,observing various torsional failure modes.On the numerical side,we developed a method to model the interaction between flexible pipes and end fittings.The proposed approach enables the prediction of torsional failure modes in practical applications and lays the groundwork for further failure analysis under different loading conditions and for various end fitting designs.
基金the National Natural Science Foundation of China[Grant No.52088102,52001208,52111530135]Joint Funds of the National Natural Science Foundation of China[Grant No.U19B2013]+2 种基金Young Elite Scientists Sponsorship Program by CAST[Grant No.2020QNRC001]Chenguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commission[Grant No.21CGA15,19CG10]Natural Science Foundation of Shanghai[Grant No.21ZR1434500,22ZR1434100].
文摘Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures,which ultimately affects the sealing performance of end sealing systems.To assess stress relaxation curves under varying temperatures and pre-strains,this paper conducts both tensile and stress relaxation tests on PVDF materials.To describe the stress relaxation characteristics of these materials,the Prony series is utilized.In order to identify the parameters of the series,the paper employs the Levenberg-Marquardt method of nonlinear regression.A finite element model is established to verify the accuracy of the parameter identification method.Subsequently,the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting,while taking into account fluid pressure inside the pipeline using a pressure penetration method.The impact of stress relaxation on the sealing performance is then discussed.Finally,the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.
基金Supported by the National Basic Research Program of China(2012CB025904)Zhengzhou Shengda University of Economics,Business and Management(SD-YB2025085)。
文摘Gauss radial basis functions(GRBF)are frequently employed in data fitting and machine learning.Their linear independence property can theoretically guarantee the avoidance of data redundancy.In this paper,one of the main contributions is proving this property using linear algebra instead of profound knowledge.This makes it easy to read and understand this fundamental fact.The proof of linear independence of a set of Gauss functions relies on the constructing method for one-dimensional space and on the deducing method for higher dimensions.Additionally,under the condition of preserving the same moments between the original function and interpolating function,both the interpolating existence and uniqueness are proven for GRBF in one-dimensional space.The final work demonstrates the application of the GRBF method to locate lunar olivine.By combining preprocessed data using GRBF with the removing envelope curve method,a program is created to find the position of lunar olivine based on spectrum data,and the numerical experiment shows that it is an effective scheme.
文摘Background:Physical fitness is a key indicator of current and future health in children and adolescents.Evidence suggests that fitness levels have declined then stagnated in recent decades,but it remains unclear how the coronavirus disease 2019(COVID-19)pandemic has impacted this trend.Methods:We conducted a systematic review and meta-analyses to assess pandemic-related changes in physical fitness among children and adolescents(0-19 years)in the World Health Organization European Region.Seven databases were searched up to February 28,2025 for studies reporting validated pre-and during/post-pandemic fitness measurements.Two reviewers independently performed screening,data extraction,risk-of-bias assessment(Risk Of Bias In Non-randomized Studies-of Exposure)(ROBINS-E),and certainty grading(Grading of Recommendations,Assessment,Development and Evaluation)(GRADE).Random-effects meta-analyses yielded standardized mean differences(SMDs)with 95%confidence intervals(95%CIs).Subgroup analyses examined sex,age,year,and national restriction severity(Oxford Stringency Index).Results:Thirty-two studies comprising 270,179 participants and 1,519,386 fitness measurements from 17 European countries were included.Cardiorespiratory fitness declined significantly during the pandemic,especially in 2021,with reductions in endurance(SMD=-0.43;95%CI:-0.61 to-0.25)and speed(SMD=-0.29;95%CI:-0.61 to 0.03).While speed returned to baseline by 2023,endurance remained below pre-pandemic levels(SMD=-0.10;95%CI:-0.12 to-0.08).Girls and adolescents were disproportionately affected.In contrast to cardiorespiratory fitness,muscular fitness remained largely unchanged.Stricter national regulations were associated with greater declines in cardiorespiratory fitness.Conclusion:COVID-19 pandemic restrictions were associated with a marked decline in cardiorespiratory fitness in European children and adolescents,with levels not recovered by 2023.These findings call for urgent,targeted public health interventions to improve physical fitness and prevent long-term health consequences.
基金funded by the National Institutes of Health and the National Heart,Lung,and Blood Institute(P01HL040962)。
文摘Background:Midlife lifestyle factors,including physical activity,are associated with late-life brain health,yet the role of aerobic exercise on structural brain health in early and mid-adulthood remains poorly understood.This study aimed to examine the effect of aerobic exercise on structural brain age and to explore potential mediators.Methods:In a single-blind,12-month randomized clinical trial,130 healthy participants aged 26-58 years were randomized into a moderate-to-vigorous intensity aerobic exercise group or a usual-care control group.The exercise group attended two supervised 60-min sessions per week in a laboratory setting plus engaged in home-based exercise to achieve 150 min of exercise per week.Brain-predicted age difference(brain-PAD)and cardiorespiratory fitness(CRF)were assessed at baseline and 12 months.Both intention-to-treat(ITT)and completers analyses(including participants who completed post-intervention assessments)were performed.Results:The 130 participants(67.7%female)had an age of 41.28±9.93 years(mean±SD).At baseline,higher CRF(peak oxygen uptake,VO_(2peak))was associated with smaller brain-PAD(β=-0.309,p=0.012).After the intervention,the exercise group showed a decrease in brainPAD(estimated mean difference(EMD)=-0.60;95%confidence interval(95%CI):-1.15 to-0.04;p=0.034)compared to the control group(EMD=0.35;95%CI:-0.21 to 0.92;p=0.217);time×group interaction(between-group difference(BGD)=-0.95;95%CI:-1.72 to-0.17;p=0.019).VO2peak improved in the exercise group(EMD=1.60;95%CI:0.29-2.90;p=0.017)compared to the control group(EMD=-0.78;95%CI:-2.17 to 0.60;p=0.265);time×group interaction(BGD=2.38;95%CI:0.52-4.25;p=0.015).Body composition,blood pressure,and brain-derived neurotrophic factor levels were unaffected.None of the proposed pathways statistically mediated the effect of exercise on brain-PAD.The results from completers were similar.Conclusion:Engaging in 12 months of moderate-to-vigorous exercise reduced brain-PAD in early-to-midlife adults.The pathways by which these effects occur remain unknown.
基金supported by the National Science and Technology Major Project(E152KJ1201)the Natural Science Basic Research Program of Shaanxi(2024JC-YBQN-0036)+1 种基金the National Natural Science Foundation of China(42030105 and 11973046)the National SKA Program of China(2020SKA0120200).
文摘The Haoping 40 m radio telescope at the National Time Service Center,Chinese Academy of Sciences was built in 2014 and is primarily used to observe navigation satellites and pulsars.Since the first successful very long baseline interferometry(VLBI)observation of L-band radio source fringes in 2022,ten observations have been made so far.The stations involved in the observations include the Haoping 40 m radio telescope(Haoping),the Tianma 65 m radio telescope(Tianma),the Nanshan 26 m radio telescope(Urumqi),the Guizhou 500 m radio telescope(FAST),the Jilin 13 m radio telescope(Jilin),the Effelsberg 100 m radio telescope(Effelsberg),the Onsala 25 m radio telescope(Onsala),and the Chiang Mai 40 m radio telescope(Chiang Mai).This paper presents details on the specifications of the Haoping 40 m radio telescope,as well as the design of the VLBI experiment,the observation process,and the data processing.We also discuss the analysis of the fringe results involving the Haoping 40 m radio telescope,using Distributed FX Correlator to obtain excellent results.We confirm that the telescope is capable of participating in VLBI observations and performing specific data processing tasks.It can therefore play a greater role in future VLBI observations.
基金supported by the National Natural Science Foundation of China(No.12175295)the National Key R&D Program of China(2021YFA1601000)the Shanghai Municipal Science and Technology Major Project。
文摘With the development of the semiconductor industry below the 7 nm scale,critical dimension small-angle X-ray scattering(CD-SAXS)has emerged as a powerful tool for quantitatively measuring nanoscale deviations.In this study,the effects of X-ray beam size and photon energy on the accuracy of critical dimension measurements were investigated.Critical dimensions measured using beams with different spot sizes showed different deviations from the expected values.Beam sizes that were either too large or too small did not improve confidence intervals.As the incident energy increased,the X-ray transmission rate increased,while the scattering cross section decreased,resulting in a gradual decrease in the signal-to-noise ratio of the diffraction peaks,which reduced the accuracy of the CD-SAXS measurements.An optimal accuracy was obtained at 12 keV with a smaller beam size.Using an effective trapezoid model,the results yielded an average pitch of 100.4±0.2 nm,width of 49.8±0.2 nm,height of 130.0±0.2 nm,and a sidewall angle below 1.1°±0.1°.These results provide crucial guidance for the future development of CD-SAXS laboratories and the construction of X-ray machines as well as robust support for research in related fields.
基金supported by National Natural Science Foundation of China(62106092)Natural Science Foundation of Fujian Province(2024J01822,2024J01820,2022J01916)Natural Science Foundation of Zhangzhou City(ZZ2024J28).
文摘Feature selection serves as a critical preprocessing step inmachine learning,focusing on identifying and preserving the most relevant features to improve the efficiency and performance of classification algorithms.Particle Swarm Optimization has demonstrated significant potential in addressing feature selection challenges.However,there are inherent limitations in Particle Swarm Optimization,such as the delicate balance between exploration and exploitation,susceptibility to local optima,and suboptimal convergence rates,hinder its performance.To tackle these issues,this study introduces a novel Leveraged Opposition-Based Learning method within Fitness Landscape Particle Swarm Optimization,tailored for wrapper-based feature selection.The proposed approach integrates:(1)a fitness-landscape adaptive strategy to dynamically balance exploration and exploitation,(2)the lever principle within Opposition-Based Learning to improve search efficiency,and(3)a Local Selection and Re-optimization mechanism combined with random perturbation to expedite convergence and enhance the quality of the optimal feature subset.The effectiveness of is rigorously evaluated on 24 benchmark datasets and compared against 13 advancedmetaheuristic algorithms.Experimental results demonstrate that the proposed method outperforms the compared algorithms in classification accuracy on over half of the datasets,whilst also significantly reducing the number of selected features.These findings demonstrate its effectiveness and robustness in feature selection tasks.
文摘The original online version of this article was revised:The layout update for Article 758 has impacted the page range in the published issue,but did not affect the scholarly content.To ensure consistency with the originally assigned pages(2595-2614),we will need to publish an erratum to correct the article and restore the original page range.The original article has been corrected.
文摘The search for mechanical properties of materials reached a highly acclaimed level, when indentations could be analysed on the basis of elastic theory for hardness and elastic modulus. The mathematical formulas proved to be very complicated, and various trials were published between the 1900s and 2000s. The development of indentation instruments and the wish to make the application in numerous steps easier, led in 1992 to trials with iterations by using relative values instead of absolute ones. Excessive iterations of computers with 3 + 8 free parameters of the loading and unloading curves became possible and were implemented into the instruments and worldwide standards. The physical formula for hardness was defined as force over area. For the conical, pyramidal, and spherical indenters, one simply took the projected area for the calculation of the indentation depth from the projected area, adjusted it later by the iterations with respect to fused quartz or aluminium as standard materials, and called it “contact height”. Continuously measured indentation loading curves were formulated as loading force over depth square. The unloading curves after release of the indenter used the initial steepness of the pressure relief for the calculation of what was (and is) incorrectly called “Young’s modulus”. But it is not unidirectional. And for the spherical indentations’ loading curve, they defined the indentation force over depth raised to 3/2 (but without R/h correction). They till now (2025) violate the energy law, because they use all applied force for the indenter depth and ignore the obvious sidewise force upon indentation (cf. e.g. the wood cleaving). The various refinements led to more and more complicated formulas that could not be reasonably calculated with them. One decided to use 3 + 8 free-parameter iterations for fitting to the (poor) standards of fused quartz or aluminium. The mechanical values of these were considered to be “true”. This is till now the worldwide standard of DIN-ISO-ASTM-14577, avoiding overcomplicated formulas with their complexity. Some of these are shown in the Introduction Section. By doing so, one avoided the understanding of indentation results on a physical basis. However, we open a simple way to obtain absolute values (though still on the blackbox instrument’s unsuitable force calibration). We do not iterate but calculate algebraically on the basis of the correct, physically deduced exponent of the loading force parabolas with h3/2 instead of false “h2” (for the spherical indentation, there is a calotte-radius over depth correction), and we reveal the physical errors taken up in the official worldwide “14577-Standard”. Importantly, we reveal the hitherto fully overlooked phase transitions under load that are not detectable with the false exponent. Phase-transition twinning is even present and falsifies the iteration standards. Instead of elasticity theory, we use the well-defined geometry of these indentations. By doing so, we reach simple algebraically calculable formulas and find the physical indentation hardness of materials with their onset depth, onset force and energy, as well as their phase-transition energy (temperature dependent also its activation energy). The most important phase transitions are our absolute algebraically calculated results. The now most easily obtained phase transitions under load are very dangerous because they produce polymorph interfaces between the changed and the unchanged material. It was found and published by high-enlargement microscopy (5000-fold) that these trouble spots are the sites for the development of stable, 1 to 2 µm long, micro-cracks (stable for months). If however, a force higher than the one of their formation occurs to them, these grow to catastrophic crash. That works equally with turbulences at the pickle fork of airliners. After the publication of these facts and after three fatal crashing had occurred in a short sequence, FAA (Federal Aviation Agency) reacted by rechecking all airplanes for such micro cracks. These were now found in a new fleet of airliners from where the three crashed ones came. These were previously overlooked. FAA became aware of that risk and grounded 290 (certainly all) of them, because the material of these did not have higher phase-transition onset and energy than other airplanes with better material. They did so despite the 14577-Standard that does not find (and thus formally forbids) phase transitions under indenter load with the false exponent on the indentation parabola. However, this “Standard” will, despite the present author’s well-founded petition, not be corrected for the next 5 years.
基金supported by the National Key Research and Development Program of China (Grant No.2022YFC3600403)Emerging Interdisciplinary Platform for Medicine and Engineering in Sports (EIPMES),Beijing,China。
文摘Energy expenditure estimation can be used to measure the exercise load and physical condition of different individuals, such as soldiers, athletes, firemen, etc., during their training and work. Energy expenditure estimation methods based on computer vision have rapidly developed in recent years. Compared with sensor-based methods, such methods are capable of monitoring several target persons at the same time, and the subjects do not need to wear different sensor devices that hamper their movement. In this paper, we propose a cross-attention spatial–temporal convolutional neural network to predict the energy expenditure of people under different exercise intensities. The model explores the relationship between changes in the human skeleton and energy expenditure intensity. In addition, a cross-attention correction module is used to reduce the negative effects of individual physical fitness characteristics during energy expenditure estimation. The experimental results show that our proposed method achieves high accuracy for energy expenditure estimation and performs better than existing computer vision-based energy expenditure estimation methods do. The proposed method can be widely used in various physical activity scenarios to measure energy expenditure, increasing the convenience of usage.
基金supported by the Grant PID2020-120249RB-I00PID2023-148404OB-100funded by MCIN/AEI/10.13039/501100011033+4 种基金by the Andalusian Government(Junta de Andalucía,Plan Andaluz de Investigación,ref.P20_00124)by the Erasmus+Sport Programme of the European Union within the project FitBack4Literacy(No.101089829)Additional support is provided by the University of Granada,Plan Propio de Inves-tigación,Units of ExcellenceUnit of Excellence on Exercise,Nutrition and Health(UCEENS)by theCIBERobn Physiopa-thology of Obesity and Nutrition,and by the Spanish Network in Exercise and Health,EXERNET Network(RED2022-134800-Tand EXP_99828).
文摘Background:Physicalfitness in childhood and adolescence is associated with a variety of health outcomes and is a powerful marker of current and future health.However,inconsistencies in tests and protocols limit international monitoring and surveillance.The objective of the study was to seek international consensus on a proposed,evidence-informed,Youth Fitness International Test(YFIT)battery and protocols for health monitoring and surveillance in children and adolescents aged 618 years.Methods:We conducted an international modified Delphi study to evaluate the level of agreement with a proposed,evidence-based,YFIT of core health-relatedfitness tests and protocols to be used worldwide in 6-to 18-year-olds.This proposal was based on previous European and North American projects that systematically reviewed the existing evidence to identify the most valid,reliable,health-related,safe,and feasiblefitness tests to be used in children and adolescents aged 618 years.We designed a single-panel modified Delphi study and invited 216 experts from all around the world to answer this Delphi survey,of whom one-third are from low-to-middle income countries and one-third are women.Four experts were involved in the piloting of the survey and did not participate in the main Delphi study to avoid bias.We pre-defined an agreement of 80%among the expert participants to achieve consensus.Results:We obtained a high response rate(78%)with a total of 169fitness experts from 50 countries and territories,including 63 women and 61 experts from low-or middle-income countries/territories.Consensus(>85%agreement)was achieved for all proposed tests and protocols,supporting the YFIT battery,which includes weight and height(to compute body mass index as a proxy of body size/composition),the 20-m shuttle run(cardiorespiratoryfitness),handgrip strength,and standing long jump(muscularfitness).Conclusion:This study contributes to standardizingfitness tests and protocols used for research,monitoring,and surveillance across the world,which will allow for future data pooling and the development of international and regional sex-and age-specific reference values,health-related cut-points,and a global picture offitness among children and adolescents.
文摘1.Introduction。There is abundant evidence that the amount of habitual physical activity(PA)and the level of cardiorespiratory fitness(CRF)are inversely related to developing chronic diseases,including cardiovascular(CV)disease(CVD).Relative to the CV and all-cause mortality reductions associated with exercise,intensity and duration also appear to be inversely related.For example,the mortality reductions that are associated with a regular 5-min run~a 15-min walk,and a 25-min run~a 105-min walk.1 In addition,at comparable levels of total energy expenditure,vigorous exercise seems to be more effective than moderate-intensity exercise in reducing CV risk.2 Vigorous exercise training is also more effective than moderate intensity training at increasing CRF,expressed as metabolic equivalents or METs,which has been shown to confer a lower risk of mortality.3 Accordingly,the optimal physiologic,clinical,and survival benefits of exercise are most likely to be achieved by progressing from moderate intensity exercise(usually defined as 40%-59%of functional capacity or 55%-69%of the maximal heart rate)to vigorous training regimens,corresponding to≥60%of functional capacity or 70%-89%of the measured maximal heart rate.
