BACKGROUND Heart rate variability(HRV) and pulse-wave velocity(PWV),indicators of cardiac function,are altered in patients with spinal cord injury(SCI),suggesting that autonomic cardiac function and arterial stiffness...BACKGROUND Heart rate variability(HRV) and pulse-wave velocity(PWV),indicators of cardiac function,are altered in patients with spinal cord injury(SCI),suggesting that autonomic cardiac function and arterial stiffness may underlie the high risk of cardiovascular complications in these patients.No study has simultaneously investigated HRV and PWV in the same patients.AIM To evaluate cardiovascular complications in SCI patients by comparing HRV and PWV between patients with and without SCI.METHODS In this cross-sectional pilot study,patients with(n = 60) and without SCI(n = 60) were recruited from December 7,2019 to January 21,2020.Each participant received a five-minute assessment of HRV and the cardiovascular system using the Medicore HRV Analyzer SA-3000 P.Differences in HRV and PWV parameters between participants with and without SCI were statistically examined.RESULTS We observed a significant difference between participants with and without SCI with respect to the standard deviation of all normal-to-normal intervals,square root of the mean sum of squared successive risk ratio interval differences,physical stress index,total power,very-low frequency,low frequency,high frequency,and arterial elasticity.CONCLUSION Patients with SCI have weaker sympathetic and parasympathetic activity as well as lower arterial elasticity compared to those without,suggesting that SCI may increase cardiac function loading.展开更多
This study presents a machine learning-based method for predicting fragment velocity distribution in warhead fragmentation under explosive loading condition.The fragment resultant velocities are correlated with key de...This study presents a machine learning-based method for predicting fragment velocity distribution in warhead fragmentation under explosive loading condition.The fragment resultant velocities are correlated with key design parameters including casing dimensions and detonation positions.The paper details the finite element analysis for fragmentation,the characterizations of the dynamic hardening and fracture models,the generation of comprehensive datasets,and the training of the ANN model.The results show the influence of casing dimensions on fragment velocity distributions,with the tendencies indicating increased resultant velocity with reduced thickness,increased length and diameter.The model's predictive capability is demonstrated through the accurate predictions for both training and testing datasets,showing its potential for the real-time prediction of fragmentation performance.展开更多
The transformation from multibody models to lumped-parameter models is a crucial aspect of vehicle dynamics research.The velocity transformation method is adopted in this research,and the suspension multibody model is...The transformation from multibody models to lumped-parameter models is a crucial aspect of vehicle dynamics research.The velocity transformation method is adopted in this research,and the suspension multibody model is described using only one degree of freedom.It is found that the equivalent mass of the system is time-dependent during the simulation process,as observed in numerical simulations.Further symbolic calculations are conducted to derive the analytical form of the equivalent mass,and the results show that once the static parameters are determined,the equivalent mass of the suspension system is determined solely by the vertical position of the suspension upright,which reveals the kinematics characteristic of the equivalent mass of the suspension system.It is found that the equivalent mass experiences smaller changes when the suspension is compressed from the middle position,but larger changes when the suspension is extended.Furthermore,by comparing the multibody model,the lumped-parameter model with static mass,and the proposed lumped-parameter model considering the kinematics characteristic of the equivalent unsprung mass,the proposed model produces simulation results that more closely match the original multibody model than the model with static mass.The improvements in accuracy can be up to 20%under certain evaluation metrics.展开更多
This study presents an inversion method to recover the tidal flow velocity using tidal signals extracted from geomagnetic satellite dataset.By integrating the latest Earth conductivity profile and the Earth's magn...This study presents an inversion method to recover the tidal flow velocity using tidal signals extracted from geomagnetic satellite dataset.By integrating the latest Earth conductivity profile and the Earth's magnetic field model,the limited memory quasi-Newton method(L-BFGS)is used to directly invert seawater flow velocities.We used the radial component of the induced magnetic field as the observed data,constructed an L_(2)-norm-based data misfit term using theoretical response and observed data,and applied smoothness constraints to the ocean flow velocity.The results agree well with the widely used HAMTIDE model in low-and mid-latitude regions,which is attributed to Macao Science Satellite-1's(MSS-1)unique low-inclination orbit of full coverage in these areas.These findings underscore MSS-1's potential to advance research on tidal-induced magnetic fields and their applications in ocean dynamics studies.展开更多
The Sichuan-Yunnan Block is located on the southeastern margin of the Qinghai-Xizang Plateau and has frequent seismic activity on the western border,posing a potential threat to human society and economic development....The Sichuan-Yunnan Block is located on the southeastern margin of the Qinghai-Xizang Plateau and has frequent seismic activity on the western border,posing a potential threat to human society and economic development.Therefore,it is important to understand its geological evolution,assess earthquake risks,and formulate scientific and reasonable disaster prevention and mitigation strategies.Using 23 months of continuous ambient noise records from 81 seismic stations,we obtained 1248 phasevelocity dispersion curves of the fundamental Rayleigh wave at 5–50 s.The three-dimensional(3D)S-wave velocity structure in the northwestern Sichuan-Yunnan Block was obtained by pure-path and depth inversion.The results show that three lowvelocity anomalous bands were distributed nearly north-to-south(N-S)at depths of 10–35 km.The overall shape of the lowvelocity channel gradually shifted from southeast to southwest because of the influence of the Panzhihua high-velocity blocks.The low-velocity strip consists of three branches,with the first branch extending southwest from the northern part of the Lancangjiang Fault.The second branch is distributed in the N-S direction and is blocked by two high-velocity bodies near the Longpan-Qiaohou and Honghe faults.The third branch crosses the research area from N-S and gradually extends from southeast to southwest and from shallow to deep.The three low-velocity anomaly distribution areas are likely the most severely deformed areas of the collision between the Qinghai-Xizang Plateau and Yangtze Block.The results provide a more detailed understanding of the deep structure of the western boundary of the Sichuan-Yunnan Block crustal low-velocity anomalies and reliable geophysical evidence for the morphology and continuity of crustal flows.展开更多
Structure and composition of Earth are fundamental importance in exploring the dynamic evolution of the crust and mantle.The Qinling Orogenic Belt(QOB)is located between the North China plate and the South China Plate...Structure and composition of Earth are fundamental importance in exploring the dynamic evolution of the crust and mantle.The Qinling Orogenic Belt(QOB)is located between the North China plate and the South China Plate,and is one of the main orogenic belts in China.To explore the composition and origin of anisotropy and the low wave velocity zone of the QOB,ten rock samples(gneiss and schist)were collected from the five sites of the QOB and the P-and S-wave velocities of these samples were measured under 0.6 to 2.0 GPa and 100 to 550℃.The wave velocities increase with increasing pressure and decreasing temperature.The V_(P)and V_(S)of the schist and gneiss match the velocity of the middle and lower crust of the QOB,indicating that schist and gneiss are important component of the QOB.All the schist and gneiss samples exhibit obvious seismic anisotropy with 1.64%-17.42%for V_(S)and 2.93%-14.78%for V_(P)under conditions of crust and upper mantle.The CPO/LPO and layering distribution of mica in rock samples are the main reasons for this anisotropy.The V_(S)structures below the five sampled sites from seismic ambient noise tomography were built to explore the effect of schist and gneiss on the composition and structure of the QOB.The results indicate that orientation-arranged gneiss and schist driven by the tectonic stresses might be a new origin of the character of V_(P)/V_(S),seismic anisotropy,and the low velocity zone in the QOB.展开更多
Flow velocity uniformity of the microchannel plate is a major factor affecting the performance of microchannel devices.In order to improve the velocity distribution uniformity of the microchannel plate,we designed two...Flow velocity uniformity of the microchannel plate is a major factor affecting the performance of microchannel devices.In order to improve the velocity distribution uniformity of the microchannel plate,we designed two new microchannel structures:V-type and A-type.The effects of various structural parameters of the manifolds on the velocity distribution are reported.The V-type and A-type microchannel plates had a more uniform velocity distribution compared to the Z-type microchannel plate.The final result showed that it is beneficial for the V-type microchannel plate to obtain a more uniform velocity distribution when the manifold structure parameters are X_(in)=-1,X_(out)=0,Y_(in)=10,Y_(out)=6,Hin=4,H_(out)=1,and R=0.5.展开更多
Identifying potential hazards is crucial for maintaining the structural stability of opencast mining area.To address the limitations of irregular structure and sparse microseismic events in opencast mining monitoring,...Identifying potential hazards is crucial for maintaining the structural stability of opencast mining area.To address the limitations of irregular structure and sparse microseismic events in opencast mining monitoring,this paper proposes an active-source imaging method for identifying potential hazards precisely based on velocity structure.This method innovatively divides the irregular structure into unstructured grids and introduces a damping and smoothing regularization operator into the inversion process,mitigating the ill-posedness caused by the sparse distribution of events and rays.Numerical and laboratory experiments were conducted to verify the reliability and effectiveness of the proposed method.The results demonstrate the competitive performance of the method in identifying hazard areas of varying sizes and numbers.The proposed method shows potential for meeting hazard identification requirements in the complex opencast mining structure.Furthermore,field experiments were conducted on an rare earth mine slope.It confirms that the proposed method provides a more concrete and intuitive scheme for stability monitoring for the microseismic monitoring system.This paper not only demonstrates the application of acoustic structure velocity imaging technology in detecting unstructured potential hazard regions but also provides valuable insights into the construction and maintenance of stable opencast mining area.展开更多
This study investigates the paradoxical detonation behavior of TKX-50,a nitrogen-rich energetic material,exhibiting higher detonation velocities but lower metal acceleration ability compared to HMX.Through experimenta...This study investigates the paradoxical detonation behavior of TKX-50,a nitrogen-rich energetic material,exhibiting higher detonation velocities but lower metal acceleration ability compared to HMX.Through experimental measurements and theoretical calculations,we propose a novel three-factor competition mechanism to explain this phenomenon.TKX-50-based PBX formulations achieved detonation velocities up to 9100 m/s,surpassing HMX-based counterparts.However,cylinder expansion tests revealed a 15%reduction in metal acceleration ability.Thermochemical measurements showed lower detonation heat for TKX-50(4900 J/g)versus HMX(5645 J/g).Our mechanism involves:(1)compositional effects prevailing at high pressures;(2)Energy release becoming essential as pressure drops;(3)Pressure-dependent product composition evolution functioning at low pressure.VLW code calculations unveiled a"crossover"in Hugoniot curves,lending support to this mechanism.This study furnishes a new framework for comprehending the performance of nitrogen-rich energetic materials,with significant implications for the design and optimization of future high-energy density materials.展开更多
INTRODUCTION.Crustal velocity model is crucial for describing the subsurface composition and structure,and has significant implications in offshore oil and gas exploration and marine geophysical engineering(Xie et al....INTRODUCTION.Crustal velocity model is crucial for describing the subsurface composition and structure,and has significant implications in offshore oil and gas exploration and marine geophysical engineering(Xie et al.,2024).Currently,travel time tomography is the most commonly used method for velocity modeling based on ocean bottom seismometer(OBS)data(Zhang et al.,2023;Sambolian et al.,2021).This method usually assumes that the sub-seafloor structure is layered,and therefore faces challenges in high-precision modeling with strong lateral discontinuities.展开更多
The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(...The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(Qingzang)Plateau and adjacent blocks,plateau uplift,and strong earthquake mechanisms.P-wave velocity and crustal composition provide key constraints on the properties of distinct tectonic units and their evolutionary modification processes.Based on the results of 8 Deep Seismic Sounding(DSS)profiles completed in the Bayan Har block and surrounding areas over the past 20 years,We constructed one-dimensional P-wave velocity models for the crust of Bayan Har block,Qilian fold belt,Qinling fold belt,Alxa block,Ordos block and Sichuan basin.Furthermore,crustal composition models for different tectonic units were established based on these results.The results reveal that the crustal thickness of the Bayan Har block gradually decreases towards the NNE,NE,and SE directions,while the average crustal velocity increases correspondingly.The felsic layer in the crust accounts for more than half of the total crustal thickness.The mafic content within the crust of different tectonic units exhibits notable variations,which may reflect that the Bayan Har block,Qilian fold belt,and Qinling fold belt have experienced more intensive lithospheric evolution processes compared to Ordos basin and Sichuan basin.The seismicity distribution in this region is significantly controlled by crustal velocity and composition heterogeneity across the Bayan Har block and adjacent areas,which demonstrates that earthquakes within and around the Bayan Har block exhibit both high frequency and larger magnitudes.These seismic characteristics primarily result from intense crustal stress accumulation and release during the outward expansion of the Qingzang Plateau.展开更多
Global Navigation Satellite System(GNSS)imaging method(GIM)has been successfully applied to global regions to investigate vertical land motion(VLM)of the Earth's surface.GNSS images derived from conventional GIM m...Global Navigation Satellite System(GNSS)imaging method(GIM)has been successfully applied to global regions to investigate vertical land motion(VLM)of the Earth's surface.GNSS images derived from conventional GIM method may present fragmented patches and encounter problems caused by excessive smoothing of velocity peaks,leading to difficulty in short-wavelength deformation detection and improper geophysical interpretation.Therefore,we propose a novel GNSS imaging method based on Gaussian process regression with velocity uncertainty considered(GPR-VU).Gaussian processing regression is introduced to describe the spatial relationship between neighboring site pairs as a priori weights and then reweight velocities by known station uncertainties,converting the discrete velocity field to a continuous one.The GPR-VU method is applied to reconstruct VLM images in the southwestern United States and the eastern Qinghai-Xizang Plateau,China,using the GNSS position time series in vertical direction.Compared to the traditional GIM method,the root-mean-square(RMS)and overall accuracy of the confusion matrix of the GPR-VU method increase by 5.0%and 14.0%from the 1°×1°checkerboard test in the southwestern United States.Similarly,the RMS and overall accuracy increase by 33.7%and 15.8%from the 6°×6°checkerboard test in the eastern Qinghai-Xizang Plateau.These checkerboard tests validate the capability to effectively capture the spatiotemporal variations characteristics of VLM and show that this algorithm outperforms the sparsely distributed network in the Qinghai-Xizang Plateau.The images from the GPR-VU method using real data in both regions show significant subsidence around Lassen Volcanic in northern California within a 30 km radius,slight uplift in the northern Sichuan Basin,and subsidence in its central and southern sections.These results further qualitatively illustrate consistency with previous findings.The GPR-VU method outperforms in diminishing the effect by fragmented patches,excessive smoothing of velocity peaks,and detecting potential short-wavelength deformations.展开更多
In this study,the flow characteristics around a group of three piers arranged in tandem were investigated both numerically and experimentally.The simulation utilised the volume of fluid(VOF)model in conjunction with t...In this study,the flow characteristics around a group of three piers arranged in tandem were investigated both numerically and experimentally.The simulation utilised the volume of fluid(VOF)model in conjunction with the k–ɛmethod(i.e.,for flow turbulence representations),implemented through the ANSYS FLUENT software,to model the free-surface flow.The simulation results were validated against laboratory measurements obtained using an acoustic Doppler velocimeter.The comparative analysis revealed discrepancies between the simulated and measured maximum velocities within the investigated flow field.However,the numerical results demonstrated a distinct vortex-induced flow pattern following the first pier and throughout the vicinity of the entire pier group,which aligned reasonably well with experimental data.In the heavily narrowed spaces between the piers,simulated velocity profiles were overestimated in the free-surface region and underestimated in the areas near the bed to the mid-stream when compared to measurements.These discrepancies diminished away from the regions with intense vortices,indicating that the employed model was capable of simulating relatively less disturbed flow turbulence.Furthermore,velocity results from both simulations and measurements were compared based on velocity distributions at three different depth ratios(0.15,0.40,and 0.62)to assess vortex characteristic around the piers.This comparison revealed consistent results between experimental and simulated data.This research contributes to a deeper understanding of flow dynamics around complex interactive pier systems,which is critical for designing stable and sustainable hydraulic structures.Furthermore,the insights gained from this study provide valuable information for engineers aiming to develop effective strategies for controlling scour and minimizing destructive vortex effects,thereby guiding the design and maintenance of sustainable infrastructure.展开更多
A three-dimensional path-planning approach has been developed to coordinate multiple fixed-wing unmanned aerial vehicles(UAVs)while avoiding collisions.The hierarchical path-planning architecture that divides the path...A three-dimensional path-planning approach has been developed to coordinate multiple fixed-wing unmanned aerial vehicles(UAVs)while avoiding collisions.The hierarchical path-planning architecture that divides the path-planning process into two layers is proposed by designing the velocityobstacle strategy for satisfying timeliness and effectiveness.The upper-level layer focuses on creating an efficient Dubins initial path considering the dynamic constraints of the fixed wing.Subsequently,the lower-level layer detects potential collisions and adjusts its flight paths to avoid collisions by using the threedimensional velocity obstacle method,which describes the maneuvering space of collision avoidance as the intersection space of half space.To further handle the dynamic and collisionavoidance constraints,a priority mechanism is designed to ensure that the adjusted path is still feasible for fixed-wing UAVs.Simulation experiments demonstrate the effectiveness of the proposed method.展开更多
This study analyzed ambient seismic noise using the MSNoise package to monitor temporal changes in the underground seismic wave velocity in Mining Area 6 of the Dongtan Coal Mine in China.The data was recorded continu...This study analyzed ambient seismic noise using the MSNoise package to monitor temporal changes in the underground seismic wave velocity in Mining Area 6 of the Dongtan Coal Mine in China.The data was recorded continuously over 76 days by 7 three-component stations and 10 single-component microseismic stations deployed in Dongtan Coal Mine,with station spacing ranging from 0.1 km to approximately 3 km.Using the causal and non-causal components of the Z-component cross-correlation function,along with moving-window cross-spectrum analysis and cumulative calculations with a 5-day window overlay,stable seismic velocity changes were obtained in the frequency band of 0.1 to 2 Hz.We found a correlation between the timing of average velocity changes and seismic events caused by underground mining processes.In particular,when the relative seismic velocity increased by 0.23%,larger energy minequakes typically occurred.This study shows that ambient noise correlation has great potential for predicting minequakes,guiding pressure-relief production,and providing warnings about the impact of overburden pressure.展开更多
The surface velocity is one of the most important characteristics of glaciers.Monitoring and mapping glacier movements are of great significance for the studies of sea-level rise,glacier mass balance and dynamics,glob...The surface velocity is one of the most important characteristics of glaciers.Monitoring and mapping glacier movements are of great significance for the studies of sea-level rise,glacier mass balance and dynamics,global warming,and the management of freshwater resources.It is also essential for the early warnings of hazards caused by ice avalanches.SAR imaging geodesy has been developed for measuring glacier velocity,especially the pixel-offset tracking method.This paper introduces some basic concepts of glaciology and principles of various SAR imaging geodesy methods,with a detailed presentation about the developments in the applications of the pixel-offset tracking method.Finally,the challenges and future prospects of SAR imaging geodesy in glacier monitoring are discussed.展开更多
In the present study,three layers of aluminum(Al)and a single layer of copper(Cu)were joined by resistance rolling welding(RRW)and the impact of welding velocity on microstructure,mechanical property and electrical pr...In the present study,three layers of aluminum(Al)and a single layer of copper(Cu)were joined by resistance rolling welding(RRW)and the impact of welding velocity on microstructure,mechanical property and electrical property was investigated.The results showed that the welding velocity was identified as the most significant parameter.With decreasing the welding velocity from 11 mm/s to 1 mm/s,the mechanical property of the joints initially showed an increase,reaching a maximum coach-peel peak load of 185.25 N,due to the larger well bonded region,then decreased owing to the high-temperature softening of the base metal.The elec-trical resistance of the joint demonstrated a consistent varying,characterized by an initial decrease owing to the larger completely bonded region and then increased with the decreasing welding velocity due to the excessive generation of Al2Cu with high electrical resistance.A cooling system was thus utilized to reduce the welding temperature to relieve the high-temperature softening,that suc-cessfully improved the welding quality of the joint by an 11.5%increase in the coach-peel peak load.展开更多
Based on the observational data from 60 short-period stations deployed in the Jishishan M6.2 earthquake epicenter and adjacent regions(Gansu Province,2023),this study inverted the near-surface S-wave velocity structur...Based on the observational data from 60 short-period stations deployed in the Jishishan M6.2 earthquake epicenter and adjacent regions(Gansu Province,2023),this study inverted the near-surface S-wave velocity structure through teleseismic receiver function analysis by using the amplitude of direct P-wave.The results reveal that the epicentral area(Liugou Township and surroundings)exhibits markedly low S-wave velocities of 400-600 m/s,with a mean value of(500±50)m/s.In contrast,intermountain basins-Guanting Basin and Dahejia Basin-demonstrate significantly elevated velocities,exceeding the epicentral zone by 100-300 m/s,with values concentrated at 600-900 m/s.Notably,localized areas such as Jintian Village and Caotan Village maintain stable S-wave velocities of(700±30)m/s.The western margin tectonic belt of Jishishan displays distinctive velocity differentiation:A pronounced velocity gradient zone along the 35.8°N latitude boundary separates northern areas(<550 m/s)from southern regions(>750 m/s).These findings demonstrate significant spatial heterogeneity in shallow S-wave velocity structures,primarily controlled by three factors:(1)topographic-geomorphic units,(2)stratigraphic lithological contrasts,and(3)anthropogenic modifications.The persistent low-velocity anomalies(<600 m/s)in the epicentral zone and northern Yellow River T2 terrace likely correlate with Quaternary unconsolidated sediments,enhanced groundwater circulation,and bedrock weathering.These results provide critical geophysical constraints for understanding both the seismogenic environment of the Jishishan earthquake and its damage distribution patterns.Furthermore,they establish a foundational framework for regional seismic intensity evaluation,site amplification analysis,and secondary hazard risk assessment.展开更多
Modeling the boundary layer flow of ternary hybrid nanofluids is important for understanding and optimizing their thermal performance,particularly in applications where enhanced heat transfer and fluid dynamics are es...Modeling the boundary layer flow of ternary hybrid nanofluids is important for understanding and optimizing their thermal performance,particularly in applications where enhanced heat transfer and fluid dynamics are essential.This study numerically investigates the boundary layer flow of alumina-copper-silver/water nanofluid over a permeable stretching/shrinking sheet,incorporating both first and second-order velocity slip.The mathematical model is solved in MATLAB facilitated by the bvp4c function that employs the finite difference scheme and Lobatto IIIa formula.The solver successfully generates dual solutions for the model,and further analysis is conducted to assess their stability.The findings reported that only one of the solutions is stable.For the shrinking sheet case,increasing the first-order velocity slip delays boundary layer separation and enhances heat transfer,while,when the sheet is stretched,the second-order velocity slip accelerates separation and improves heat transfer.Boundary layer separation is most likely to occur when the sheet is shrinking;however,this can be controlled by adjusting the velocity slip with the inclusion of boundary layer suction.展开更多
Objective:To evaluate the effectiveness of cardiac rehabilitation therapy in the treatment of patients with chronic heart failure(CHF).Methods:76 patients with CHF who were treated in the hospital from January 2023 to...Objective:To evaluate the effectiveness of cardiac rehabilitation therapy in the treatment of patients with chronic heart failure(CHF).Methods:76 patients with CHF who were treated in the hospital from January 2023 to December 2024 were selected and randomly divided into two groups using a random number table.The experimental group(38 patients)received cardiac rehabilitation therapy,while the reference group(38 patients)received conventional drug therapy.The total effective rate,cardiac function indicators,lung function indicators,and pulse wave velocity(PWV)were compared between the two groups.Results:The total effective rate was higher in the experimental group than in the reference group.After treatment,the cardiac and lung function indicators were better in the experimental group than in the reference group,and the PWV was lower in the experimental group(P<0.05).Conclusion:Cardiac rehabilitation therapy for patients with CHF can improve treatment efficacy,enhance cardiopulmonary function,and regulate PWV levels,with high professionalism and feasibility.展开更多
文摘BACKGROUND Heart rate variability(HRV) and pulse-wave velocity(PWV),indicators of cardiac function,are altered in patients with spinal cord injury(SCI),suggesting that autonomic cardiac function and arterial stiffness may underlie the high risk of cardiovascular complications in these patients.No study has simultaneously investigated HRV and PWV in the same patients.AIM To evaluate cardiovascular complications in SCI patients by comparing HRV and PWV between patients with and without SCI.METHODS In this cross-sectional pilot study,patients with(n = 60) and without SCI(n = 60) were recruited from December 7,2019 to January 21,2020.Each participant received a five-minute assessment of HRV and the cardiovascular system using the Medicore HRV Analyzer SA-3000 P.Differences in HRV and PWV parameters between participants with and without SCI were statistically examined.RESULTS We observed a significant difference between participants with and without SCI with respect to the standard deviation of all normal-to-normal intervals,square root of the mean sum of squared successive risk ratio interval differences,physical stress index,total power,very-low frequency,low frequency,high frequency,and arterial elasticity.CONCLUSION Patients with SCI have weaker sympathetic and parasympathetic activity as well as lower arterial elasticity compared to those without,suggesting that SCI may increase cardiac function loading.
基金supported by Poongsan-KAIST Future Research Center Projectthe fund support provided by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(Grant No.2023R1A2C2005661)。
文摘This study presents a machine learning-based method for predicting fragment velocity distribution in warhead fragmentation under explosive loading condition.The fragment resultant velocities are correlated with key design parameters including casing dimensions and detonation positions.The paper details the finite element analysis for fragmentation,the characterizations of the dynamic hardening and fracture models,the generation of comprehensive datasets,and the training of the ANN model.The results show the influence of casing dimensions on fragment velocity distributions,with the tendencies indicating increased resultant velocity with reduced thickness,increased length and diameter.The model's predictive capability is demonstrated through the accurate predictions for both training and testing datasets,showing its potential for the real-time prediction of fragmentation performance.
基金This work was supported by the National Natural Science Foundation of China(Grant No.12272141)The financial support is gratefully acknowledged.
文摘The transformation from multibody models to lumped-parameter models is a crucial aspect of vehicle dynamics research.The velocity transformation method is adopted in this research,and the suspension multibody model is described using only one degree of freedom.It is found that the equivalent mass of the system is time-dependent during the simulation process,as observed in numerical simulations.Further symbolic calculations are conducted to derive the analytical form of the equivalent mass,and the results show that once the static parameters are determined,the equivalent mass of the suspension system is determined solely by the vertical position of the suspension upright,which reveals the kinematics characteristic of the equivalent mass of the suspension system.It is found that the equivalent mass experiences smaller changes when the suspension is compressed from the middle position,but larger changes when the suspension is extended.Furthermore,by comparing the multibody model,the lumped-parameter model with static mass,and the proposed lumped-parameter model considering the kinematics characteristic of the equivalent unsprung mass,the proposed model produces simulation results that more closely match the original multibody model than the model with static mass.The improvements in accuracy can be up to 20%under certain evaluation metrics.
基金financially supported by the National Natural Science Foundation of China(42250102,42250101)the Macao Foundation。
文摘This study presents an inversion method to recover the tidal flow velocity using tidal signals extracted from geomagnetic satellite dataset.By integrating the latest Earth conductivity profile and the Earth's magnetic field model,the limited memory quasi-Newton method(L-BFGS)is used to directly invert seawater flow velocities.We used the radial component of the induced magnetic field as the observed data,constructed an L_(2)-norm-based data misfit term using theoretical response and observed data,and applied smoothness constraints to the ocean flow velocity.The results agree well with the widely used HAMTIDE model in low-and mid-latitude regions,which is attributed to Macao Science Satellite-1's(MSS-1)unique low-inclination orbit of full coverage in these areas.These findings underscore MSS-1's potential to advance research on tidal-induced magnetic fields and their applications in ocean dynamics studies.
基金support from the National Natural Science Foundation of China(No.42474081)Basic Research Business of the Institute of Geophysics,China Earthquake Administration(Nos.DQJB 22R29 and DQJB19B30)Basic Research Business Special Project of the Earthquake Prediction Institute of the China Earthquake Administration(No.CEAIEF20220204).
文摘The Sichuan-Yunnan Block is located on the southeastern margin of the Qinghai-Xizang Plateau and has frequent seismic activity on the western border,posing a potential threat to human society and economic development.Therefore,it is important to understand its geological evolution,assess earthquake risks,and formulate scientific and reasonable disaster prevention and mitigation strategies.Using 23 months of continuous ambient noise records from 81 seismic stations,we obtained 1248 phasevelocity dispersion curves of the fundamental Rayleigh wave at 5–50 s.The three-dimensional(3D)S-wave velocity structure in the northwestern Sichuan-Yunnan Block was obtained by pure-path and depth inversion.The results show that three lowvelocity anomalous bands were distributed nearly north-to-south(N-S)at depths of 10–35 km.The overall shape of the lowvelocity channel gradually shifted from southeast to southwest because of the influence of the Panzhihua high-velocity blocks.The low-velocity strip consists of three branches,with the first branch extending southwest from the northern part of the Lancangjiang Fault.The second branch is distributed in the N-S direction and is blocked by two high-velocity bodies near the Longpan-Qiaohou and Honghe faults.The third branch crosses the research area from N-S and gradually extends from southeast to southwest and from shallow to deep.The three low-velocity anomaly distribution areas are likely the most severely deformed areas of the collision between the Qinghai-Xizang Plateau and Yangtze Block.The results provide a more detailed understanding of the deep structure of the western boundary of the Sichuan-Yunnan Block crustal low-velocity anomalies and reliable geophysical evidence for the morphology and continuity of crustal flows.
基金supported by the National Natural Science Foundation of China(42174115 and 42330311)the Special Fund of the Institute of Earthquake Forecasting,China Earthquake Administration(CEAIEF20230301)the State key laboratory of earthquake dynamics(LED2021B02).
文摘Structure and composition of Earth are fundamental importance in exploring the dynamic evolution of the crust and mantle.The Qinling Orogenic Belt(QOB)is located between the North China plate and the South China Plate,and is one of the main orogenic belts in China.To explore the composition and origin of anisotropy and the low wave velocity zone of the QOB,ten rock samples(gneiss and schist)were collected from the five sites of the QOB and the P-and S-wave velocities of these samples were measured under 0.6 to 2.0 GPa and 100 to 550℃.The wave velocities increase with increasing pressure and decreasing temperature.The V_(P)and V_(S)of the schist and gneiss match the velocity of the middle and lower crust of the QOB,indicating that schist and gneiss are important component of the QOB.All the schist and gneiss samples exhibit obvious seismic anisotropy with 1.64%-17.42%for V_(S)and 2.93%-14.78%for V_(P)under conditions of crust and upper mantle.The CPO/LPO and layering distribution of mica in rock samples are the main reasons for this anisotropy.The V_(S)structures below the five sampled sites from seismic ambient noise tomography were built to explore the effect of schist and gneiss on the composition and structure of the QOB.The results indicate that orientation-arranged gneiss and schist driven by the tectonic stresses might be a new origin of the character of V_(P)/V_(S),seismic anisotropy,and the low velocity zone in the QOB.
基金supported by Scientific Research Project of Guangdong Provincial Department of Education(2024KQNCX152).
文摘Flow velocity uniformity of the microchannel plate is a major factor affecting the performance of microchannel devices.In order to improve the velocity distribution uniformity of the microchannel plate,we designed two new microchannel structures:V-type and A-type.The effects of various structural parameters of the manifolds on the velocity distribution are reported.The V-type and A-type microchannel plates had a more uniform velocity distribution compared to the Z-type microchannel plate.The final result showed that it is beneficial for the V-type microchannel plate to obtain a more uniform velocity distribution when the manifold structure parameters are X_(in)=-1,X_(out)=0,Y_(in)=10,Y_(out)=6,Hin=4,H_(out)=1,and R=0.5.
基金Project(2021YFC2900500)supported by the National Key Research and Development Program of China。
文摘Identifying potential hazards is crucial for maintaining the structural stability of opencast mining area.To address the limitations of irregular structure and sparse microseismic events in opencast mining monitoring,this paper proposes an active-source imaging method for identifying potential hazards precisely based on velocity structure.This method innovatively divides the irregular structure into unstructured grids and introduces a damping and smoothing regularization operator into the inversion process,mitigating the ill-posedness caused by the sparse distribution of events and rays.Numerical and laboratory experiments were conducted to verify the reliability and effectiveness of the proposed method.The results demonstrate the competitive performance of the method in identifying hazard areas of varying sizes and numbers.The proposed method shows potential for meeting hazard identification requirements in the complex opencast mining structure.Furthermore,field experiments were conducted on an rare earth mine slope.It confirms that the proposed method provides a more concrete and intuitive scheme for stability monitoring for the microseismic monitoring system.This paper not only demonstrates the application of acoustic structure velocity imaging technology in detecting unstructured potential hazard regions but also provides valuable insights into the construction and maintenance of stable opencast mining area.
基金support provided by the National Natural Science Foundation of China(Grant No.12102405)the Presidential Foundation of CAEP(Grant No.YZJJZQ2023008).
文摘This study investigates the paradoxical detonation behavior of TKX-50,a nitrogen-rich energetic material,exhibiting higher detonation velocities but lower metal acceleration ability compared to HMX.Through experimental measurements and theoretical calculations,we propose a novel three-factor competition mechanism to explain this phenomenon.TKX-50-based PBX formulations achieved detonation velocities up to 9100 m/s,surpassing HMX-based counterparts.However,cylinder expansion tests revealed a 15%reduction in metal acceleration ability.Thermochemical measurements showed lower detonation heat for TKX-50(4900 J/g)versus HMX(5645 J/g).Our mechanism involves:(1)compositional effects prevailing at high pressures;(2)Energy release becoming essential as pressure drops;(3)Pressure-dependent product composition evolution functioning at low pressure.VLW code calculations unveiled a"crossover"in Hugoniot curves,lending support to this mechanism.This study furnishes a new framework for comprehending the performance of nitrogen-rich energetic materials,with significant implications for the design and optimization of future high-energy density materials.
基金financially supported by the National Key R&D Program of China(No.2023YFF0803404)the Zhejiang Provincial Natural Science Foundation(No.LY23D040001)+4 种基金the Open Research Fund of Key Laboratory of Engineering Geophysical Prospecting and Detection of Chinese Geophysical Society(No.CJ2021GB01)the Open Re-search Fund of Changjiang River Scientific Research Institute(No.CKWV20221011/KY)the ZhouShan Science and Technology Project(No.2023C81010)the National Natural Science Foundation of China(No.41904100)supported by Chinese Natural Science Foundation Open Research Cruise(Cruise No.NORC2019–08)。
文摘INTRODUCTION.Crustal velocity model is crucial for describing the subsurface composition and structure,and has significant implications in offshore oil and gas exploration and marine geophysical engineering(Xie et al.,2024).Currently,travel time tomography is the most commonly used method for velocity modeling based on ocean bottom seismometer(OBS)data(Zhang et al.,2023;Sambolian et al.,2021).This method usually assumes that the sub-seafloor structure is layered,and therefore faces challenges in high-precision modeling with strong lateral discontinuities.
基金supported by the National Key R&D Program of China(No.2023YFC3012002)the National Natural Science Foundation of China(42374073)。
文摘The Bayan Har block,one of China's most seismically active regions,has experienced multiple major earthquakes(≥M 7.0)in recent years.It is a key area for investigating the interactions between the Qinghai-Xizang(Qingzang)Plateau and adjacent blocks,plateau uplift,and strong earthquake mechanisms.P-wave velocity and crustal composition provide key constraints on the properties of distinct tectonic units and their evolutionary modification processes.Based on the results of 8 Deep Seismic Sounding(DSS)profiles completed in the Bayan Har block and surrounding areas over the past 20 years,We constructed one-dimensional P-wave velocity models for the crust of Bayan Har block,Qilian fold belt,Qinling fold belt,Alxa block,Ordos block and Sichuan basin.Furthermore,crustal composition models for different tectonic units were established based on these results.The results reveal that the crustal thickness of the Bayan Har block gradually decreases towards the NNE,NE,and SE directions,while the average crustal velocity increases correspondingly.The felsic layer in the crust accounts for more than half of the total crustal thickness.The mafic content within the crust of different tectonic units exhibits notable variations,which may reflect that the Bayan Har block,Qilian fold belt,and Qinling fold belt have experienced more intensive lithospheric evolution processes compared to Ordos basin and Sichuan basin.The seismicity distribution in this region is significantly controlled by crustal velocity and composition heterogeneity across the Bayan Har block and adjacent areas,which demonstrates that earthquakes within and around the Bayan Har block exhibit both high frequency and larger magnitudes.These seismic characteristics primarily result from intense crustal stress accumulation and release during the outward expansion of the Qingzang Plateau.
基金supported by the National Natural Science Foundation of China(Grant No.42274035)the Major Science and Technology Program for Hubei Province(No.2022AAA002)the Hunan Provincial Land Surveying and Mapping Project(HNGTCH-2023-05)。
文摘Global Navigation Satellite System(GNSS)imaging method(GIM)has been successfully applied to global regions to investigate vertical land motion(VLM)of the Earth's surface.GNSS images derived from conventional GIM method may present fragmented patches and encounter problems caused by excessive smoothing of velocity peaks,leading to difficulty in short-wavelength deformation detection and improper geophysical interpretation.Therefore,we propose a novel GNSS imaging method based on Gaussian process regression with velocity uncertainty considered(GPR-VU).Gaussian processing regression is introduced to describe the spatial relationship between neighboring site pairs as a priori weights and then reweight velocities by known station uncertainties,converting the discrete velocity field to a continuous one.The GPR-VU method is applied to reconstruct VLM images in the southwestern United States and the eastern Qinghai-Xizang Plateau,China,using the GNSS position time series in vertical direction.Compared to the traditional GIM method,the root-mean-square(RMS)and overall accuracy of the confusion matrix of the GPR-VU method increase by 5.0%and 14.0%from the 1°×1°checkerboard test in the southwestern United States.Similarly,the RMS and overall accuracy increase by 33.7%and 15.8%from the 6°×6°checkerboard test in the eastern Qinghai-Xizang Plateau.These checkerboard tests validate the capability to effectively capture the spatiotemporal variations characteristics of VLM and show that this algorithm outperforms the sparsely distributed network in the Qinghai-Xizang Plateau.The images from the GPR-VU method using real data in both regions show significant subsidence around Lassen Volcanic in northern California within a 30 km radius,slight uplift in the northern Sichuan Basin,and subsidence in its central and southern sections.These results further qualitatively illustrate consistency with previous findings.The GPR-VU method outperforms in diminishing the effect by fragmented patches,excessive smoothing of velocity peaks,and detecting potential short-wavelength deformations.
文摘In this study,the flow characteristics around a group of three piers arranged in tandem were investigated both numerically and experimentally.The simulation utilised the volume of fluid(VOF)model in conjunction with the k–ɛmethod(i.e.,for flow turbulence representations),implemented through the ANSYS FLUENT software,to model the free-surface flow.The simulation results were validated against laboratory measurements obtained using an acoustic Doppler velocimeter.The comparative analysis revealed discrepancies between the simulated and measured maximum velocities within the investigated flow field.However,the numerical results demonstrated a distinct vortex-induced flow pattern following the first pier and throughout the vicinity of the entire pier group,which aligned reasonably well with experimental data.In the heavily narrowed spaces between the piers,simulated velocity profiles were overestimated in the free-surface region and underestimated in the areas near the bed to the mid-stream when compared to measurements.These discrepancies diminished away from the regions with intense vortices,indicating that the employed model was capable of simulating relatively less disturbed flow turbulence.Furthermore,velocity results from both simulations and measurements were compared based on velocity distributions at three different depth ratios(0.15,0.40,and 0.62)to assess vortex characteristic around the piers.This comparison revealed consistent results between experimental and simulated data.This research contributes to a deeper understanding of flow dynamics around complex interactive pier systems,which is critical for designing stable and sustainable hydraulic structures.Furthermore,the insights gained from this study provide valuable information for engineers aiming to develop effective strategies for controlling scour and minimizing destructive vortex effects,thereby guiding the design and maintenance of sustainable infrastructure.
基金supported by the National Science Fund for Distinguished Young Scholars(52425211)BIT Research Fund Program for Young Scholars(XSQD-202201005).
文摘A three-dimensional path-planning approach has been developed to coordinate multiple fixed-wing unmanned aerial vehicles(UAVs)while avoiding collisions.The hierarchical path-planning architecture that divides the path-planning process into two layers is proposed by designing the velocityobstacle strategy for satisfying timeliness and effectiveness.The upper-level layer focuses on creating an efficient Dubins initial path considering the dynamic constraints of the fixed wing.Subsequently,the lower-level layer detects potential collisions and adjusts its flight paths to avoid collisions by using the threedimensional velocity obstacle method,which describes the maneuvering space of collision avoidance as the intersection space of half space.To further handle the dynamic and collisionavoidance constraints,a priority mechanism is designed to ensure that the adjusted path is still feasible for fixed-wing UAVs.Simulation experiments demonstrate the effectiveness of the proposed method.
文摘This study analyzed ambient seismic noise using the MSNoise package to monitor temporal changes in the underground seismic wave velocity in Mining Area 6 of the Dongtan Coal Mine in China.The data was recorded continuously over 76 days by 7 three-component stations and 10 single-component microseismic stations deployed in Dongtan Coal Mine,with station spacing ranging from 0.1 km to approximately 3 km.Using the causal and non-causal components of the Z-component cross-correlation function,along with moving-window cross-spectrum analysis and cumulative calculations with a 5-day window overlay,stable seismic velocity changes were obtained in the frequency band of 0.1 to 2 Hz.We found a correlation between the timing of average velocity changes and seismic events caused by underground mining processes.In particular,when the relative seismic velocity increased by 0.23%,larger energy minequakes typically occurred.This study shows that ambient noise correlation has great potential for predicting minequakes,guiding pressure-relief production,and providing warnings about the impact of overburden pressure.
文摘The surface velocity is one of the most important characteristics of glaciers.Monitoring and mapping glacier movements are of great significance for the studies of sea-level rise,glacier mass balance and dynamics,global warming,and the management of freshwater resources.It is also essential for the early warnings of hazards caused by ice avalanches.SAR imaging geodesy has been developed for measuring glacier velocity,especially the pixel-offset tracking method.This paper introduces some basic concepts of glaciology and principles of various SAR imaging geodesy methods,with a detailed presentation about the developments in the applications of the pixel-offset tracking method.Finally,the challenges and future prospects of SAR imaging geodesy in glacier monitoring are discussed.
基金supported by the National Key Research and Development Program of China(Grant No.2023YFB3407400)the National Natural Science Foundation of China(Grant No.52475386,Grant No.52025058).
文摘In the present study,three layers of aluminum(Al)and a single layer of copper(Cu)were joined by resistance rolling welding(RRW)and the impact of welding velocity on microstructure,mechanical property and electrical property was investigated.The results showed that the welding velocity was identified as the most significant parameter.With decreasing the welding velocity from 11 mm/s to 1 mm/s,the mechanical property of the joints initially showed an increase,reaching a maximum coach-peel peak load of 185.25 N,due to the larger well bonded region,then decreased owing to the high-temperature softening of the base metal.The elec-trical resistance of the joint demonstrated a consistent varying,characterized by an initial decrease owing to the larger completely bonded region and then increased with the decreasing welding velocity due to the excessive generation of Al2Cu with high electrical resistance.A cooling system was thus utilized to reduce the welding temperature to relieve the high-temperature softening,that suc-cessfully improved the welding quality of the joint by an 11.5%increase in the coach-peel peak load.
基金project is supported in part by Broadband Seismic 3D Array Detection(PhaseⅠ),Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(Grant No.2024ZD1000300)National Natural Science Foundation of China(42204061)Gansu Jishishan 6.2 magnitude earthquake scientific investigation(DQJB23Y45)program。
文摘Based on the observational data from 60 short-period stations deployed in the Jishishan M6.2 earthquake epicenter and adjacent regions(Gansu Province,2023),this study inverted the near-surface S-wave velocity structure through teleseismic receiver function analysis by using the amplitude of direct P-wave.The results reveal that the epicentral area(Liugou Township and surroundings)exhibits markedly low S-wave velocities of 400-600 m/s,with a mean value of(500±50)m/s.In contrast,intermountain basins-Guanting Basin and Dahejia Basin-demonstrate significantly elevated velocities,exceeding the epicentral zone by 100-300 m/s,with values concentrated at 600-900 m/s.Notably,localized areas such as Jintian Village and Caotan Village maintain stable S-wave velocities of(700±30)m/s.The western margin tectonic belt of Jishishan displays distinctive velocity differentiation:A pronounced velocity gradient zone along the 35.8°N latitude boundary separates northern areas(<550 m/s)from southern regions(>750 m/s).These findings demonstrate significant spatial heterogeneity in shallow S-wave velocity structures,primarily controlled by three factors:(1)topographic-geomorphic units,(2)stratigraphic lithological contrasts,and(3)anthropogenic modifications.The persistent low-velocity anomalies(<600 m/s)in the epicentral zone and northern Yellow River T2 terrace likely correlate with Quaternary unconsolidated sediments,enhanced groundwater circulation,and bedrock weathering.These results provide critical geophysical constraints for understanding both the seismogenic environment of the Jishishan earthquake and its damage distribution patterns.Furthermore,they establish a foundational framework for regional seismic intensity evaluation,site amplification analysis,and secondary hazard risk assessment.
基金The authors acknowledged Universiti Putra Malaysia for the Putra Grant that was received(GP-IPM 9787700)supported by Grant PN-III-P4-PCE-2021-0993,UEFISCDI,Romania.
文摘Modeling the boundary layer flow of ternary hybrid nanofluids is important for understanding and optimizing their thermal performance,particularly in applications where enhanced heat transfer and fluid dynamics are essential.This study numerically investigates the boundary layer flow of alumina-copper-silver/water nanofluid over a permeable stretching/shrinking sheet,incorporating both first and second-order velocity slip.The mathematical model is solved in MATLAB facilitated by the bvp4c function that employs the finite difference scheme and Lobatto IIIa formula.The solver successfully generates dual solutions for the model,and further analysis is conducted to assess their stability.The findings reported that only one of the solutions is stable.For the shrinking sheet case,increasing the first-order velocity slip delays boundary layer separation and enhances heat transfer,while,when the sheet is stretched,the second-order velocity slip accelerates separation and improves heat transfer.Boundary layer separation is most likely to occur when the sheet is shrinking;however,this can be controlled by adjusting the velocity slip with the inclusion of boundary layer suction.
基金Study on the Efficacy and Safety of Hyperbaric Oxygen Therapy Combined with Exercise in Improving Heart Rate Variability in Patients with Stable Chronic Cardiac Insufficiency(Project No.:2023-E-49)。
文摘Objective:To evaluate the effectiveness of cardiac rehabilitation therapy in the treatment of patients with chronic heart failure(CHF).Methods:76 patients with CHF who were treated in the hospital from January 2023 to December 2024 were selected and randomly divided into two groups using a random number table.The experimental group(38 patients)received cardiac rehabilitation therapy,while the reference group(38 patients)received conventional drug therapy.The total effective rate,cardiac function indicators,lung function indicators,and pulse wave velocity(PWV)were compared between the two groups.Results:The total effective rate was higher in the experimental group than in the reference group.After treatment,the cardiac and lung function indicators were better in the experimental group than in the reference group,and the PWV was lower in the experimental group(P<0.05).Conclusion:Cardiac rehabilitation therapy for patients with CHF can improve treatment efficacy,enhance cardiopulmonary function,and regulate PWV levels,with high professionalism and feasibility.
