Currently,the BeiDou-3(BDS-3)precise point positioning(PPP)service(PPP-B2b)mostly employs the ionosphere-free(IF)combination model for precise timing,which tends to amplify the noise in observation values.To address this issue,this paper proposes a real-time BDS-3 precise unidirectional timing model based on uncombined(UC)observations using the BDS-3 PPP-B2b service.This model resolves the challenge of the amplified observation noise inherent in the IF combination model.The experiment involved selecting eight global navigation satellite system(GNSS)observation stations within China and collecting continuous observation data for 15 d.A comparative analy-sis with the traditional dual-frequency IF combination PPP timing model showed that the BDS-3 UC PPP timing based on the BDS-3 PPP-B2b service can achieve a timing preci-sion of 0.5 ns.In addition,it was found that due to global positioning system(GPS)satellite clock products in the BDS-3 PPP-B2b service not being unified to the standard time,the GPS IF PPP timing method based on the BDS-3 PPP-B2b service is not recommended for precise timing.In summary,the BDS-3 UC PPP timing model proposed in this paper is suitable for precise timing,providing observa-tion values with smaller noise,and its timing accuracy is comparable to that of the BDS-3 IF PPP,with slightly better frequency stability.
Practical applications of desulfurization gypsum are limited owing to its brittleness and low strength.To over-come these challenges,researchers have developed engi-neered desulfurization gypsum composites(EDGCs)by in-corporating ultrahigh molecular weight polyethylene(UHMWPE)fiber and sulfoaluminate cement(SAC).The mix ratio was optimized using response surface methodology(RSM).Experimental testing of EDGC under compressive and tensile loads led to the creation of a regression model that investigates the influence of variables and their interac-tions on the material's compressive and tensile strengths.Additionally,microscopic morphology and hydration prod-uct composition were analyzed to explore the influence mechanism.The results indicated that EDGC's compressive strength increased by up to 38.4%owing to a decreased water-binder ratio and higher SAC content.Similarly,ten-sile strength increased by up to 38.6%owing to increased SAC and fiber content.Moreover,EDGC demonstrated ex-cellent strain-hardening behavior and multiple cracking char-acteristics,achieving a maximum tensile strain of nearly 3%.The research findings provide valuable insights for opti-mizing the performance of desulfurization gypsum.
China's healthcare system faces increasing chal-lenges,including surging medical costs,resource allocation imbalances favoring large hospitals,and ineffective referral mechanisms.The lack of a unified strategy integrating stan-dardized coverage with personalized payment compounds these issues.To this end,this study proposes a risk-sharing reform strategy that combines equal coverage for the same disease(ECSD)with an individualized out-of-pocket(I-OOP)model.Specifically,the study employs a Markov model to capture patient transitions across health states and care levels.The findings show that ECSD and I-OOP en-hance equity by standardizing disease coverage while tailor-ing costs to patient income and facility type.This approach alleviates demand on high-tier hospitals,promoting primary care utilization and enabling balanced resource distribution.The study's findings provide a reference for policymakers and healthcare administrators by presenting a scalable frame-work that is aligned with China's development goals with the aim of fostering an efficient,sustainable healthcare sys-tem that is adaptable to regional needs.
To ensure the operational safety of railways in the landslide-prone areas of mountainous regions,a large-scale model test and numerical simulation were conducted to study the bending moment distribution,internal force distri-bution,deformation development,and crack propagation characteristics of a framed anti-sliding structure(FAS)un-der landslide thrust up to the point of failure.Results show that the maximum bending moment and its increase rate in the fore pile are greater than those in the rear pile,with the maximum bending moment of the fore pile approximately 1.1 times that of the rear pile.When the FAS fails,the dis-placement at the top of the fore pile is significantly greater,about 1.27 times that of the rear pile in the experiment.Ma-jor cracks develop at locations corresponding to the peak bending moments.Small transverse cracks initially appear on the upper surface at the intersection between the primary beam and rear pile and then spread to the side of the struc-ture.At the failure stage,major cracks are observed at the pil-beam intersections and near the anchor points.Strength-ening flexural stiffness at intersections where major cracks occur can improve the overall thrust-deformation coordina-tion of the FAS,thereby maximizing its performance.
This study explores the use of the Global Naviga-tion Satellite System(GNSS)precise point positioning(PPP)technology to determine the natural vibration periods of towering structures through simulations and field testing.During the simulation phase,a GNSS receiver captured vi-bration waveforms generated by a single-axis motion simula-tor based on preset signal parameters,analyzing how differ-ent satellite system configurations affect the efficiency of ex-tracting vibration parameters.Subsequently,field tests were conducted on a high-rise steel single-tube tower.The results indicate that in the simulation environment,no mat-ter the PPP positioning data under single GPS or multisys-tem combination,the vibration frequency of single-axis mo-tion simulator can be accurately extracted after frequency do-main analysis,with multisystem setups providing more pre-cise amplitude parameters.In the field test,the natural vi-bration periods of the main vibration modes of high-rise steel single-tube tower measured by PPP technology closely match the results of the first two modes derived from finite el-ement analysis.The first mode period calculated by the em-pirical formula is approximately 6%higher than those deter-mined through finite element analysis and PPP.This study demonstrates the potential of PPP for structural vibration analysis,offering significant benefits for assessing dynamic responses and monitoring the health of towering structures.
A novel bidirectional tuned rolling mass damper(Bi-TRMD)device is proposed,and its dynamic character-istics and vibration reduction performance are investigated.The device achieves the performance goal of bidirectional vi-bration reduction for a tuned rolling mass damper with a single concave structure.First,the Bi-TRMD device is in-troduced,and its three-dimensional(3D)mechanical model is established.The motion equations of the model are de-rived using the Gibbs-Appell equation,and a trajectory pre-diction method for the sphere and structure within the model is developed.This method demonstrates that the rolling mo-tion of the sphere around orthogonal axes is nearly indepen-dent within a limited range,enabling the simplification of the 3D model into a two-dimensional(2D)model.The ac-curacy of this simplification is validated through case analy-sis.The vibration reduction parameters are optimized using the 2D model and Den Hartog theory,leading to the deriva-tion of mathematical expressions for the optimal frequency ratio and damping ratio.Subsequently,the bidirectional vi-bration reduction performance of the Bi-TRMD is analyzed.The results show that under white noise excitation,the Bi-TRMD achieves a bidirectional peak acceleration reduc-tion rate that is 9.92%and 7.79%higher than that of trans-lational tuned mass dampers(TMD)with the same mass.These findings demonstrate that the proposed Bi-TRMD ef-fectively achieves two-directional vibration reduction with a single concave structure,offering superior vibration reduc-tion performance.
The traditional detailed model of the dual active bridge(DAB)power electronic transformer is characterized by the high dimensionality of its nodal admittance matrix and the need for a small simulation step size,which limits the speed of electromagnetic transient(EMT)simulations.To overcome these limitations,a novel EMT equivalent model based on a generalized branch-cutting method is pro-posed to improve the simulation efficiency of the DAB model.The DAB topology is first decomposed into two sub-networks through branch-cutting and node-tearing meth-ods without the introduction of a one-time-step delay.Sub-sequently,the internal nodes of each sub-network are elimi-nated through network simplification,and the equivalent cir-cuit for the port cascade module is derived.The model is then validated through simulations across various operating conditions.The results demonstrate that the model avoids the loss of accuracy associated with one-time-step delay,the relative error across different conditions remains below 1%,and the simulation acceleration ratios improve as the number of modules increases.
To investigate the effects of the spraying process and different fibers on the mechanical properties and failure patterns of ultrahigh performance concrete(UHPC),three types of fibers were used.These fibers were formed using both spraying and molding methods.Uniaxial compression tests were conducted,and two nondestructive monitoring techniques,acoustic emission(AE)and digital image cor-relation,were employed to monitor the uniaxial compres-sion tests.The results indicated that the compressive strength of UHPC with single steel fibers and hybrid fibers increased by about 19%and 14%compared with those of UHPC with polyoxymethylene fibers.In comparison with molded UHPC,sprayed UHPC showed a slight improve-ment in compressive strength.Specimens containing steel fibers exhibited better post-cracking ductility,whereas those with only polyoxymethylene fibers displayed a certain degree of brittle failure.In sprayed UHPC,the onset of sig-nificant internal damage was delayed,which was related to the redistribution of internal fibers.The failure of UHPC was characterized by primary tensile cracks,supplemented by shear cracks.The spraying process can better restrict the development of tensile cracks in UHPC.Sprayed UHPC typically exhibited multiple crack developments leading to failure,whereas molded UHPC generally failed in the form of a single main crack penetrating the specimen.The addi-tion of steel fibers delayed the occurrence of local stress concentration zones,aligning well with AE monitoring data.
A reasonable process plan is an important basis for implementing wire arc additive and subtractive hybrid manu-facturing(ASHM),and a new optimization method is pro-posed.Firstly,the target parts and machining tools are mod-eled by level set functions.Secondly,the mathematical model of the additive direction optimization problem is es-tablished,and an improved particle swarm optimization al-gorithm is designed to decide the best additive direction.Then,the two-step strategy is used to plan the hybrid manu-facturing alternating sequence.The target parts are directly divided into various processing regions;each processing re-gion is optimized based on manufacturability and manufac-turing efficiency,and the optimal hybrid manufacturing al-ternating sequence is obtained by merging some processing regions.Finally,the method is used to outline the process plan of the designed example model and applied to the ac-tual hybrid manufacturing process of the model.The manu-facturing result shows that the method can meet the main considerations in hybrid manufacturing.In addition,the de-gree of automation of process planning is high,and the de-pendence on manual intervention is low.
This study examined the influence of the built en-vironment surrounding rail stations on rail transit ridership and its spatiotemporal variations,aiming to enhance rail transit operational efficiency and inform station planning and development.Data from 159 metro stations in Nanjing,collected over a 14-d period,were analyzed to identify changes in weekday and weekend ridership patterns.The analysis included explanatory variables grouped into three categories:urban spatial variables,socioeconomic vari-ables,and transit service variables.A geographically and temporally weighted regression(GTWR)model was devel-oped,and its performance was compared with that of ordi-nary least squares(OLS)and geographically weighted re-gression(GWR)models.The results demonstrated that the GTWR model outperformed others in analyzing the relation-ship between rail transit ridership and the built environment.In addition,the coefficients of explanatory variables showed significant variation across spatiotemporal dimensions,re-vealing distinct patterns.Notably,the influence of com-muter flows led to more pronounced temporal heterogeneity in the coefficients observed on weekdays.These findings of-fer valuable insights for optimizing urban public transporta-tion systems and advancing integrated urban rail develop-ment.
A buckling-restrained steel plate shear wall(BRSPSW)structure with butterfly-shaped links on the lat-eral sides is introduced to improve the cooperative perfor-mance between the BRSPSW and the boundary frames.A one-span two-story concrete-filled steel tube(CFT)column frame specimen equipped with lateral-side butterfly-shaped linked BRSPSWs(LBL-BRSPSWs)is evaluated under low-cycle reversed loading.A finite element(FE)model is developed and validated based on the test results.This FE model accurately simulates the failure modes and load-dis-placement curves.Parametric analyses are conducted on the butterfly-shaped links.The results show that the interactions between the CFT column frame and LBL-BRSPSWs are sig-nificantly influenced by the width ratio of the butterfly-shaped links,while the taper ratio and aspect ratio have relatively minor influences.Compared with traditional steel shear walls with four-sided connections,LBL-BRSPSWs reduce the additional axial forces and bend-ing moments in the frame columns by 28%to 73%and 17%to 87%,respectively,with only a 9%to 30%decrease in the lateral resistance.The experimental and parametric analysis results indicate that setting butterfly-shaped links on the lateral sides of BRSPSWs can significantly enhance their cooperative performance with the boundary frame.The butterfly-shaped link width ratio has a linear relationship with the lateral-resistance performance of the specimens and the additional internal forces in the frame columns.To en-sure that LBL-BRSPSW fails prior to the column frames,the link width ratio should be optimized.
To analyze the band gap characteristics of pho-nonic crystals,a two-dimensional phononic crystal plate model with an elastic foundation was first established.The plane wave expansion method was used to compute the dis-persion curves of this phononic crystal model,and the re-sults were compared with those from the finite element method to verify their accuracy.Subsequently,a parameter study explored the effects of the elastic foundation coeffi-cient and coverage ratio on the band gap.The results indi-cate that as the coverage ratio of the elastic foundation in-creases,the band gap significantly expands,reaching its maximum value at 100%coverage.Additionally,as the elastic foundation stiffness increases,the band gap gradu-ally widens and converges toward fixed boundary condi-tions.The study also investigated the band gap of phononic crystal plates with defects,finding that the vibrational en-ergy concentrates at the defect unit cell.Furthermore,the defect band frequency can be effectively modulated by ad-justing the coefficient of the elastic foundation,providing a theoretical basis for achieving efficient energy conversion.
Shaking table tests are widely used to evaluate seismic effects on railway structures,but accurately measur-ing rail displacement remains a significant challenge owing to the nonlinear characteristics of large displacements,ambi-ent noise interference,and limitations in displacement meter installation.In this paper,a novel method that integrates the Kanade-Lucas-Tomasi(KLT)feature tracker with an ex-tended Kalman filter(EKF)is presented for measuring rail displacement during shaking table tests.The method em-ploys KLT feature tracker and a random sample consensus algorithm to extract and track key feature points,while EKF optimally estimates dynamic states by accounting for system noise and observation errors.Shaking table test results dem-onstrate that the proposed method achieves an acceleration root mean square error of 0.300 m/s2 and a correlation with accelerometer data exceeding 99.7%,significantly outper-forming the original KLT approach.This innovative method provides a more efficient and reliable solution for measuring rail displacement under large nonlinear vibrations.
To tackle the issue of notch frequency and center frequency drift of the L(0,1)mode guided wave in ultra-sonic guided wave-based stress monitoring of prestressed steel strands,a method using higher-order mode plateau fre-quencies is adopted.First,the correlation between group velocity peaks and phase velocities at these plateau frequen-cies is analyzed.This analysis establishes a quantitative rela-tionship between phase velocity and stress in the steel strand,providing a theoretical foundation for stress monitor-ing.Then the two-dimensional Fourier transform is em-ployed to separate wave modes.Dynamic programming techniques are applied in the frequency-velocity domain to extract higher-order modes.By identifying the group veloc-ity peaks of these separated higher-order modes,the plateau frequencies of guided waves are determined,enabling indi-rect measurement of stress in the steel strand.To validate this method,finite element simulations are conducted under three scenarios.Results show that the higher-order modes of transient signals from three different positions can be ac-curately extracted,leading to successful cable stress moni-toring.This approach effectively circumvents the issue of guided wave frequency drift and improves stress monitoring accuracy.Consequently,it significantly improves the appli-cation of ultrasonic guided wave technology in structural health monitoring.
To tackle the path planning problem,this study in-troduced a novel algorithm called two-stage parameter adjustment-based differential evolution(TPADE).This al-gorithm draws inspiration from group behavior to implement a two-stage scaling factor variation strategy.In the initial phase,it adapts according to environmental complexity.In the following phase,it combines individual and global expe-riences to fine-tune the orientation factor,effectively im-proving its global search capability.Furthermore,this study developed a new population update method,ensuring that well-adapted individuals are retained,which enhances popu-lation diversity.In benchmark function tests across different dimensions,the proposed algorithm consistently demon-strates superior convergence accuracy and speed.This study also tested the TPADE algorithm in path planning simula-tions.The experimental results reveal that the TPADE algo-rithm outperforms existing algorithms by achieving path lengths of 28.527 138 and 31.963 990 in simple and com-plex map environments,respectively.These findings indi-cate that the proposed algorithm is more adaptive and effi-cient in path planning.
To investigate the impact of digital literacy on the health of older adults,based on the four-wave micropanel data from the China Family Panel Studies,a digital literacy indicator system was constructed using the factor analysis method.The health of older adults was characterized from the perspectives of overall health levels and internal health inequalities among older adults,and the theoretical mecha-nism was empirically examined through fixed-effects regres-sion,threshold,and moderating-effects models.Policy rec-ommendations are proposed to accelerate the construction of a digital literacy cultivation system for the elderly,promote digitally empowered public health services,and encourage age-appropriate upgrading of digital health facilities.The re-sults show that for every 1-unit increase in digital literacy,the overall self-assessed health level of the elderly increases by approximately 0.052 units on average,and the health relative deprivation index,which reflects health inequalities of older adults,decreased by about 0.013 units on average.There was heterogeneity in the effect of digital literacy on the health of the elderly,which was more significant among rural-dwelling elderly people,those aged more than 65 years,and females.The mechanism analysis shows that the variables reflecting medical experience and health manage-ment awareness play a moderating role in channels through which digital literacy affects older adults'health.
By analyzing the bus operation environment and accounting for prediction uncertainties,a bus arrival inter-val prediction model was developed utilizing a gated recur-rent unit(GRU)neural network.To reduce the impact of ir-relevant data and boost prediction accuracy,an attention mechanism was integrated into the point model to concen-trate on important input sequence information.Based on the point predictions,the lower upper bound estimation(LUBE)method was used,providing a range for the bus in-terval times predicted by the model.The model was vali-dated using data from 169 bus routes in Nanchang,Jiangxi Province.The results indicated that the attention-GRU model outperformed neural network,long short-term memory and GRU models.Compared with the Bootstrap method,the LUBE method has a narrower average interval width.The coverage width-based criterion(CWC)was re-duced by 8.1%,2.2%,and 5.7%at confidence levels of 85%,90%,and 95%,respectively,during the off-peak pe-riod,and by 23.2%,26.9%,and 27.3%at confidence lev-els of 85%,90%,and 95%,respectively,during the peak period.Therefore,it can accurately describe the fluctuation range in bus arrival times with higher accuracy and stability.
Main cable displacement-controlled devices(DCDs)are key components for coordinating the vertical de-formation of the main cable and main girder in the side span of continuous suspension bridges.To reveal the mechanical ac-tion mechanisms of DCD on bridge structures,a three-span continuous suspension bridge was taken as the engineering background in this study.The influence of different forms of DCD on the internal force and displacement of the compo-nents in the side span of the bridge and the structural dynamic characteristics were explored through numerical simulations.The results showed that the lack of DCD caused the main cable and main girder to have large vertical displacements.The stresses of other components were redistributed,and the safety factor of the suspenders at the side span was greatly re-duced.The setting of DCD improved the vertical stiffness of the structure.The rigid DCD had larger internal forces,but its control effect on the internal forces at the side span was slightly better than that of the flexible DCD.Both forms of DCD effectively coordinated the deformation of the main cable and main girder and the stress distribution of compo-nents in the side span area.The choice of DCD form de-pends on the topographic factors of bridge sites and the de-sign requirements of related components at the side span.
Transmission towers,serving as the support struc-ture of transmission lines,are significant for the functional-ity of an electric transmission system.Bolt joint loosening is one of the critical factors that can affect the safety and sta-bility of transmission towers.In this study,the effects of bolt joint loosening on the dynamic characteristics of a 220-kV angle steel transmission tower are the main topic of concern.First,the mechanical properties of typical joints subjected to different degrees of bolt loosening are studied by finite solid-element simulation,based on which a finite hybrid-element modeling method is developed for a tower structure suffering varying loose degrees in the joints.Tak-ing a 220-kV angle steel transmission tower as the object,the influence of the position and degree of loosening on the tower's natural frequencies and mode shapes are simulated and discussed.The results demonstrate that the main-member splice joint and the main diagonal-horizontal member gusset plate joint account for the dominant impact on the dynamic characteristics of the tower.In addition,the dominant joint shifts from the main-member splice joint to the main diagonal-horizontal member gusset plate joint as the considered modal order increases.In the case of double joints loosening simultaneously,the loosening of nondomi-nant joints has nonnegligible effects on the tower as well.
To improve the seismic performance of unrein-forced masonry(URM)buildings in the Himalayan re-gions,including Western China,India,Nepal,and Paki-stan,a low-cost bonded scrap tire rubber isolator(BSTRI)is proposed,and a series of vertical compression and hori-zontal shear tests are conducted.Incremental dynamic analyses are conducted for five types of BSTRI-supported URM buildings subjected to 22 far-field and 28 near-field earthquake ground motions.The resulting fragility curves and probability of damage curves are presented and utilized to evaluate the damage states of these buildings.The results show that in the base-isolated(BI)URM buildings under seismic ground motion at a peak ground acceleration(PGA)of 1.102g,the probability of exceeding the collapse preven-tion threshold is less than 25%under far-field earthquake ground motions and 31%under near-field earthquake ground motions.Furthermore,the maximum average vul-nerability index for the BI-URM buildings,which are de-signed to withstand rare earthquakes with 9°(PGA=0.632g),is 40.87%for far-field earthquake ground mo-tions and 41.83%for near-field earthquake ground mo-tions.Therefore,the adoption of BSTRIs can significantly reduce the collapse probability of URM buildings.
