Traffic engineering such as tunnels in various altitudinal gradient zone are at risk of accidental explosion,which can damage personnel and equipment.Accurate prediction of the distribution pattern of explosive loads ...Traffic engineering such as tunnels in various altitudinal gradient zone are at risk of accidental explosion,which can damage personnel and equipment.Accurate prediction of the distribution pattern of explosive loads and shock wave propagation process in semi-enclosed structures at various altitude environment is key research focus in the fields of explosion shock and fluid dynamics.The effect of altitude on the propagation of shock waves in tunnels was investigated by conducting explosion test and numerical simulation.Based on the experimental and numerical simulation results,a prediction model for the attenuation of the peak overpressure of tunnel shock waves at different altitudes was established.The results showed that the peak overpressure decreased at the same measurement points in the tunnel entrance under the high altitude condition.In contrast,an increase in altitude accelerated the propagation speed of the shock wave in the tunnel.The average error between the peak shock wave overpressure obtained using the overpressure prediction formula and the measured test data was less than15%,the average error between the propagation velocity of shock waves predicted values and the test data is less than 10%.The method can effectively predict the overpressure attenuation of blast wave in tunnel at various altitudes.展开更多
The thermochemical non-equilibrium phenomena encountered by hypersonic vehicles present significant challenges in their design.To investigate the thermochemical reaction flow behind shock waves,the non-equilibrium rad...The thermochemical non-equilibrium phenomena encountered by hypersonic vehicles present significant challenges in their design.To investigate the thermochemical reaction flow behind shock waves,the non-equilibrium radiation in the visible range using a shock tube was studied.Experiments were conducted with a shock velocity of 4.7 km/s,using nitrogen at a pressure of 20 Pa.To address measurement difficulties associated with weak radiation,a special square section shock tube with a side length of 380 mm was utilized.A high-speed camera characterized the shock wave’s morphology,and a spectrograph and a monochromator captured the radiation.The spectra were analyzed,and the numerical spectra were compared with experimental results,showing a close match.Temperature changes behind the shock wave were obtained and compared with numerical predictions.The findings indicate that the vibrational temperatures are overestimated,while the vibrational relaxation time is likely underestimated,due to the oversimplified portrayals of the non-equilibrium relaxation process in the models.Additionally,both experimental and simulated time-resolved profiles of radiation intensity at specific wavelengths were analyzed.The gathered data aims to enhance computational fluid dynamics codes and radiation models,improving their predictive accuracy.展开更多
To explore the design criteria for composite charges and reveal the intrinsic relationship between the detonation wave propagation in composite charges and the overall energy distribution of shock waves,this study ana...To explore the design criteria for composite charges and reveal the intrinsic relationship between the detonation wave propagation in composite charges and the overall energy distribution of shock waves,this study analyzes the propagation and interaction processes of detonation waves in composite charges with different structural dimensions and explosive combinations. It also investigates the spatial distribution characteristics of the resulting shock wave loads. Based on dimensional analysis theory, a theoretical analysis of the shock wave overpressure distribution in free air fields is conducted. Utilizing the derived dimensionless function relationships, the hydrocode AUTODYN is employed to investigate the effects of charge structure parameters and explosive combinations on the internal overdriven detonation phenomena and the distribution of shock wave loads. It is found that the overdriven detonation phenomenon in the inner layer of composite charges increases the strength of the axial detonation wave,thereby enhancing the intensity of the primary end wave formed upon refraction into the air, which affects the distribution characteristics of the shock wave overpressure. Research has shown that increasing the thickness ratio and detonation velocity ratio of composite charges is beneficial for exacerbating the phenomenon of overdriven detonation, improving the primary end wave intensity and axial overpressure. This gain effect gradually weakens with the propagation of shock waves. When overdriven detonation occurs inside the composite charge, the detonation pressure first increases and then decreases. The Mach reflection pressure of the composite charge with a larger aspect ratio is attenuated to a greater extent. In addition, as the aspect ratio of the composite charge increases, the shock wave energy gradually flows from the axial direction to the radial direction. Therefore, as the aspect ratio of the composite charge increases, the primary end wave intensity and axial overpressure gradually decrease.展开更多
BACKGROUND Various stone factors can affect the net results of shock wave lithotripsy(SWL).Recently a new factor called variation coefficient of stone density(VCSD)is being considered to have an impact on stone free r...BACKGROUND Various stone factors can affect the net results of shock wave lithotripsy(SWL).Recently a new factor called variation coefficient of stone density(VCSD)is being considered to have an impact on stone free rates.AIM To assess the role of VCSD in determining success of SWL in urinary calculi.METHODS Charts review was utilized for collection of data variables.The patients were subjected to SWL,using an electromagnetic lithotripter.Mean stone density(MSD),stone heterogeneity index(SHI),and VCSD were calculated by generating regions of interest on computed tomography(CT)images.Role of these factors were determined by applying the relevant statistical tests for continuous and categorical variables and a P value of<0.05 was gauged to be statistically significant.RESULTS There were a total of 407 patients included in the analysis.The mean age of the subjects in this study was 38.89±14.61 years.In total,165 out of the 407 patients could not achieve stone free status.The successful group had a significantly lower stone volume as compared to the unsuccessful group(P<0.0001).Skin to stone distance was not dissimilar among the two groups(P=0.47).MSD was significantly lower in the successful group(P<0.0001).SHI and VCSD were both significantly higher in the successful group(P<0.0001).CONCLUSION VCSD,a useful CT based parameter,can be utilized to gauge stone fragility and hence the prediction of SWL outcomes.展开更多
The manipulation of intense shock waves to either attenuate or enhance damage has long been a key goal in the domain of impact dynamics.Effective methods for such manipulation,however,remain elusive owing to the wide ...The manipulation of intense shock waves to either attenuate or enhance damage has long been a key goal in the domain of impact dynamics.Effective methods for such manipulation,however,remain elusive owing to the wide spectrum and irreversible destructive nature of intense shock waves.This work proposes a novel approach for actively controlling intense shock waves in solids,inspired by the principles of optical and explosive lenses.Specifically,by designing a shock wave convex lens composed of a low-shock-impedance material embedded in a high-shock-impedance matrix,we prove the feasibility of transforming a planar shock into a spherically converging shock.This is based on oblique shock theory,according to which shock waves pass through an oblique interface and then undergo deflection.Both experimental and simulation results demonstrate that,as expected,the obtained local spherical shock wave has a wavefront that is nearly perfectly spherical and uniform in pressure.Thus,this work proves the possibility of generating spherical shock waves using plate-impact experiments and highlights the potential of further exploration of the manipulation of shock waves in solids.It also contributes an innovative perspective for both armor penetration technologies and shock wave mitigation strategies.展开更多
Three-dimensional curved shock wave/boundary layer interaction with streamwise and spanwise curvatures widely exists in practical aerodynamic design.To explore the effects of composite shock curvatures on boundary lay...Three-dimensional curved shock wave/boundary layer interaction with streamwise and spanwise curvatures widely exists in practical aerodynamic design.To explore the effects of composite shock curvatures on boundary layer separation,a canonical model with a cone placed above plate was utilized as a reference.Configurations of straight,convex,and concave conical shock waves inducing the curved conical shock wave/boundary layer interactions were studied,using CFD based on Reynolds-averaged numerical simulation method.The flow structure and separation region of each case were discussed quantitively on the symmetry plane,flat plate,and plane perpendicular to flow direction,respectively.The focus of the analysis was on the characteristic patterns of separation scale variation in the streamwise and spanwise directions,which were observed to consistently change with respect to both directions with alterations in the incident shock wave shape.A simplified control volume model was established to qualitatively discuss the influence source of curved shock waves on separation scales,based on mass conservation equations.The results suggest that the curved shock wave has a holistic effect on separation,which is not solely dependent on the shock foot strength.展开更多
This paper focuses on the application of the adaptive mesh method in the study of underwater shock waves near the water surface.By integrating theoretical analysis with a five-equation model under axisymmetric coordin...This paper focuses on the application of the adaptive mesh method in the study of underwater shock waves near the water surface.By integrating theoretical analysis with a five-equation model under axisymmetric coordinates,we developed an optimized computational framework for multi-material fluid simulations.The moving mesh method(r-method)is used to accurately capture complex underwater shock wave systems.Multiple numerical experiments are conducted,including deep-water explosions,near-surface explosions for both spherical charge and cylindrical charge,and regular–irregular reflection interface calculations.The results show that compared to the fixed mesh method,the adaptive mesh method provides results closer to the theoretical values and achieves local high-resolution computation of multi-material fluids.By adjusting the adaptive function,different mesh refinement effects can be obtained.This method also has certain advantages in calculating the regular–irregular reflection interface in underwater explosions.This study establishes a validated computational framework for underwater explosion research,enhancing the predictive accuracy for underwater shock wave propagation in engineering assessments and providing new insights into the fundamental physics of multi-material explosion phenomena.展开更多
This study focuses on High-Amplitude Wall Heat Flux events(HAWHFs) occurring during the interaction between a supersonic flat-plate Turbulent Boundary Layer(TBL) at a Mach number of2.25 and an oblique shock wave impin...This study focuses on High-Amplitude Wall Heat Flux events(HAWHFs) occurring during the interaction between a supersonic flat-plate Turbulent Boundary Layer(TBL) at a Mach number of2.25 and an oblique shock wave impinging at 33.2.. A database from a validated direct numerical simulation is analyzed using conditional averaging and a two-dimensional clustering methodology to elucidate the statistical characteristics of both positive and negative HAWHFs within the interaction region. The results reveal that the interaction considerably affects the temporal attributes of the HAWHFs, leading to an extended lifespan for the positive HAWHFs and an increased interval between the occurrences of negative HAWHFs. The structural characteristics of the identified HAWHFs are delineated based on the evolution of population density, aspect ratio, and both absolute and relative distances throughout the interaction. The joint probability density functions of the relative positioning of two adjacent structures indicate that, away from the reattachment point, the positive HAWHFs align in the spanwise direction, displaying similarities with the negative HAWHFs. Moreover, a conditional analysis of flow structures associated with HAWHFs is conducted. This analysis of the conditionally averaged three-dimensional fields reveals that the interaction fosters larger-scale organizational patterns in the downstream region. However, the formation of positive and negative HAWHFs remains largely unaffected by the interaction, with the former predominantly linked to a two-layer temperature structure and the latter primarily associated with a pair of oblique vortices.展开更多
BACKGROUND Recovering from anterior cruciate ligament(ACL)reconstruction can be challenging.While standard rehabilitation helps restore knee function,many patients still face a slow or incomplete recovery.Extracorpore...BACKGROUND Recovering from anterior cruciate ligament(ACL)reconstruction can be challenging.While standard rehabilitation helps restore knee function,many patients still face a slow or incomplete recovery.Extracorporeal shockwave therapy(ESWT)has recently gained attention as a potential way to speed up healing and improve outcomes when added to traditional rehab.AIM To explore whether combining ESWT with standard postoperative rehabilitation truly leads to better recovery compared with rehab alone.METHODS A systematic review and meta-analysis were conducted using the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines,evaluating participant status following ACL reconstruction with standard rehabilitation and without augmented ESWT.This meta-analysis included six studies(five randomized controlled trials,one non-randomized clinical study).The outcome measures were the Lysholm score,International Knee Documentation Committee score,visual analog score,and KT-1000 measurements.To compare the control and intervention groups,the weighted mean differences were calculated along with the 95%confidence intervals.The heterogeneity of the studies and publication bias were analyzed.RESULTS ESWT modestly improved Lysholm scores(weighted mean difference:3.72;95%confidence interval:-0.27 to 7.71)with high heterogeneity(I2:96%,P<0.001)when compared with standard rehabilitation.Focused ESWT showed greater benefits compared with radial ESWT.No significant differences were found in the International Knee Documentation Committee scores,visual analog score,or KT-1000 measurements.Substantial variability and publication bias were noted.CONCLUSION ESWT improved Lysholm scores but did not show other significant benefits.Due to the limited evidence,further standardized,placebo-controlled trials are needed to confirm its effectiveness in ACL reconstruction.展开更多
[Objectives]To quantify the efficacy of Extracorporeal Shock Wave Therapy(ESWT)for upper limb spasticity in stroke patients using Modified Ashworth Scale(MAS)across three timeframes:immediate,short-term(24 h-4 wks),an...[Objectives]To quantify the efficacy of Extracorporeal Shock Wave Therapy(ESWT)for upper limb spasticity in stroke patients using Modified Ashworth Scale(MAS)across three timeframes:immediate,short-term(24 h-4 wks),and long-term(>4 wks).[Methods]Six databases(PubMed,EMBASE,CENTRAL,CINAHL,Scopus,Web of Science)until May 2025,were systematically searched,identifying 11 RCTs(n=505)meeting inclusion criteria(adults≥18 yrs old with stroke-related spasticity[MAS≥1]).Risk of bias was rigorously assessed using Cochrane criteria,revealing uniformly low risk across all domains.Random-effects meta-analyses(REML model)calculated Hedges'g with 95%CI for MAS outcomes,with subgroup analyses for joint-specific effects.[Results]ESWT demonstrated non-significant immediate MAS reduction(g=-0.69,p=0.07;=93.95%),but statistically significant short-term(g=-0.58,p=0.02;I^(2)=89.64%)and long-term effects(g=-0.52,p=0.02;I^(2)=78.72%).Effects were driven by composite MAS scores(short-term g=-0.63;long-term g=-0.56,both p<0.05)rather than isolated joints(elbow/finger/wrist all non-significant).Substantial heterogeneity persisted across analyses,particularly in joint-specific subgroups(I^(2)>90%).[Conclusions]ESWT provides statistically significant,clinically relevant reductions in global upper limb spasticity with durable efficacy beyond four weeks,supporting its use as a non-invasive adjunct therapy despite substantial heterogeneity warranting protocol standardization.展开更多
A Discrete Boltzmann Method(DBM)with a Maxwell-type boundary condition is constructed to investigate the influence of rarefaction on laminar Shock Wave/Boundary Layer Interaction(SWBLI).Due to the complexity of compre...A Discrete Boltzmann Method(DBM)with a Maxwell-type boundary condition is constructed to investigate the influence of rarefaction on laminar Shock Wave/Boundary Layer Interaction(SWBLI).Due to the complexity of compressible flow,a Knudsen number vector Kn,whose components include the local Knudsen numbers such as Kn_(ρ)and Kn_(U),is introduced to characterize the local structures,where Kn_(ρ)and Kn_(U)are Knudsen numbers defined in terms of the density and velocity interfaces,respectively.Since first focusing on the steady state of SWBLI,the DBM considers up to the second-order Kn_(ρ)(rarefaction/non-equilibrium)effects.The model is validated using Mach number 2 SWBLI and the necessity of using DBM with sufficient physical accuracy is confirmed by the shock collision problem.Key findings include the following:the leading-edge shock wave increases the local density Knudsen number Kn_(ρ)and eventually leads to the failure of linear constitutive relations in the Navier-Stokes(N-S)model and surely also in the lower-order DBM;the non-equilibrium effect differences in regions behind the leading-edge shock wave are primarily correlated with Kn_(ρ),while in the separation region are primarily correlated with Kn_(U);the non-equilibrium quantities D_(2)and D_(4,2),as well as the viscous entropy production rate S_(NOMF)can be used to identify the separation zone.The findings clarify various effects and main mechanisms in different regions associated with SWBLI,which are concealed in N-S model.展开更多
Cowl-induced incident Shock Wave/Boundary Layer Interactions (SWBLI) under the influence of gradual expansion waves are frequently observed in supersonic inlets. However, the analysis and prediction of interaction len...Cowl-induced incident Shock Wave/Boundary Layer Interactions (SWBLI) under the influence of gradual expansion waves are frequently observed in supersonic inlets. However, the analysis and prediction of interaction lengths have not been sufficiently investigated. First, this study presents a theoretical scaling analysis and validates it through wind tunnel experiments. It conducts detailed control volume analysis of mass conservation, considering the differences between inviscid and viscous cases. Then, three models for analysing interaction length under gradual expansion waves are derived. Related experiments using schlieren photography are conducted to validate the models in a Mach 2.73 flow. The interaction scales are captured at various relative distances between the shock impingement location and the expansion regions with wedge angles ranging from 12° to 15° and expansion angles of 9°, 12°, and 15°. Three trend lines are plotted based on different expansion angles to depict the relationship between normalised interaction length and normalised interaction strength metric. In addition, the relationship between the coefficients of the trend line and the expansion angles is introduced to predict the interaction length influenced by gradual expansion waves. Finally, the estimation of normalised interaction length is derived for various coefficients within a unified form.展开更多
With different structural forms of ventilation pipes have various attenuation effects on incident shock waves while meeting ventilation requirements.The attenuation mechanism and the propagation law of shock waves in ...With different structural forms of ventilation pipes have various attenuation effects on incident shock waves while meeting ventilation requirements.The attenuation mechanism and the propagation law of shock waves in ventilation pipes of different structures are investigated by experiments and numerical simulations.Furthermore,for the same structure,the effects of peak pressure and positive pressure time on the attenuation rate are discussed.It is found that the attenuation rate increases with the incident shock wave pressure,and the shock wave attenuation rate tends to reach its limiting value k for the same structure and reasonably short positive pressure time.Under the same conditions,the attenuation rate is calculated using the pressure of the shock wave as follows:diffusion chamber pipe,branch pipe and selfconsumption pipe;the attenuation rate per unit volume is calculated as follows:self-consumption pipe,branch pipe and diffusion chamber pipe.In addition,an easy method is provided to calculate the attenuation rate of the shock wave in single and multi-stage ventilation pipes.Corresponding parameters are provided for various structures,and the margin of error between the formulae and experimental results is within 10%,which is significant for engineering applications.展开更多
The propagation properties of ion-acoustic solitary and shock waves in the magnetized viscous plasma with nonthermal trapped electrons are investigated.The Cairns-Gurevich distribution as the electron distribution is ...The propagation properties of ion-acoustic solitary and shock waves in the magnetized viscous plasma with nonthermal trapped electrons are investigated.The Cairns-Gurevich distribution as the electron distribution is considered to describe the plasma nonthermality and particle trapping.By adopting the reductive perturbation technique,we derived the nonlinear Schamel-Korteweg-de Vries-Burgers(SKdVB)equation,and then obtained the ion-acoustic shock and solitary wave solutions of the SKdVB equation for different limiting cases.It is found that the impact of nonthermal parameterα,external magnetic fieldΩ,obliqueness lz,wave speed U0,and the ion kinematic viscosityη0can significantly change the characteristics of the shock and solitary waves.These results may be useful for better understanding the propagation of nonlinear structures in space(i.e.Earth's magnetosphere and ionosphere,auroral regions)and laboratory plasma with nonthermal trapped electrons.展开更多
Biochar and biochar composites are versatile materials that can be used in many applications.In this study,biochar was prepared from sawdust and combined with the yttrium iron garnet(YIG)nanocrystal to investigate the...Biochar and biochar composites are versatile materials that can be used in many applications.In this study,biochar was prepared from sawdust and combined with the yttrium iron garnet(YIG)nanocrystal to investigate the shielding effectiveness of the composite structure.Firstly,the effect of the pyrolysis temperature on the shielding effectiveness of biochar was investigated.Secondly,biochars combined with YIG nanocrystals with different contents and shielding effectiveness of the composites were investigated.The electromagnetic effectiveness of the samples was investigated within the X band(8-12 GHz).The findings indicate that biochar demonstrates enhanced absorption properties with elevated pyrolysis temperatures.Biochars demonstrated an approximate 40 d B shielding effectiveness,while YIG exhibited approximately 7 d B,corresponding to absorption at 8 GHz.However,the combination of biochar and YIG exhibited exceptional absorption,reaching 67.12 d B at 8 GHz.展开更多
Tellurene,a chiral chain semiconductor with a narrow bandgap and exceptional strain sensitivity,emerges as a pivotal material for tailoring electronic and optoelectronic properties via strain engineering.This study el...Tellurene,a chiral chain semiconductor with a narrow bandgap and exceptional strain sensitivity,emerges as a pivotal material for tailoring electronic and optoelectronic properties via strain engineering.This study elucidates the fundamental mechanisms of ultrafast laser shock imprinting(LSI)in two-dimensional tellurium(Te),establishing a direct relationship between strain field orientation,mold topology,and anisotropic structural evolution.This is the first demonstration of ultrafast LSI on chiral chain Te unveiling orientation-sensitive dislocation networks.By applying controlled strain fields parallel or transverse to Te’s helical chains,we uncover two distinct deformation regimes.Strain aligned parallel to the chain’s direction induces gliding and rotation governed by weak interchain interactions,preserving covalent intrachain bonds and vibrational modes.In contrast,transverse strain drives shear-mediated multimodal deformations—tensile stretching,compression,and bending—resulting in significant lattice distortions and electronic property modulation.We discovered the critical role of mold topology on deformation:sharp-edged gratings generate localized shear forces surpassing those from homogeneous strain fields via smooth CD molds,triggering dislocation tangle formation,lattice reorientation,and inhomogeneous plastic deformation.Asymmetrical strain configurations enable localized structural transformations while retaining single-crystal integrity in adjacent regions—a balance essential for functional device integration.These insights position LSI as a precision tool for nanoscale strain engineering,capable of sculpting 2D material morphologies without compromising crystallinity.By bridging ultrafast mechanics with chiral chain material science,this work advances the design of strain-tunable devices for next-generation electronics and optoelectronics,while establishing a universal framework for manipulating anisotropic 2D systems under extreme strain rates.This work discovered crystallographic orientation-dependent deformation mechanisms in 2D Te,linking parallel strain to chain gliding and transverse strain to shear-driven multimodal distortion.It demonstrates mold geometry as a critical lever for strain localization and dislocation dynamics,with sharp-edged gratings enabling unprecedented control over lattice reorientation.Crucially,the identification of strain field conditions that reconcile severe plastic deformation with single-crystal retention offers a pathway to functional nanostructure fabrication,redefining LSI’s potential in ultrafast strain engineering of chiral chain materials.展开更多
Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in ...Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in this paper.The five-point central difference method is used for spatial discretization,and the fourth-order Adams predictor-corrector scheme is employed for marching in time.The domain-decomposition method is applied for the wave-current generation and absorption.The effects of currents on the wave profile and velocity field are examined under two conditions:the same velocity of currents at the still-water level and the constant flow volume of currents.Wave profiles and velocity fields demonstrate substantial differences in three types of currents owing to the diverse vertical distribution of current velocity and vorticity.Then,loads on small-scale vertical cylinders subjected to regular waves and three types of background currents with the same flow volume are investigated.The maximum load intensity and load fluctuation amplitude in uniform,linear shear,and quadratic shear currents increase sequentially.The stretched superposition method overestimates the maximum load intensity and load fluctuation amplitude in opposing currents and underestimates these values in following currents.The stretched superposition method obtains a poor approximation for strong nonlinear waves,particularly in the case of the opposing quadratic shear current.展开更多
This study investigates the relationship between atmospheric stratification (i.e., static stability given by N^(2)) and the vertical energy transfer of stationary planetary waves, and further illustrates the underlyin...This study investigates the relationship between atmospheric stratification (i.e., static stability given by N^(2)) and the vertical energy transfer of stationary planetary waves, and further illustrates the underlying physical mechanism. Specifically, for the simplified case of constant stratospheric N^(2), the refractive index square of planetary waves has a theoretical tendency to increase first and then decrease with an increased N^(2), whereas the group velocity weakens. Mechanistically, this behavior can be understood as an intensified suppression of vertical isentropic surface displacement caused by meridional heat transport of planetary waves under strong N^(2) conditions. Observational analysis corroborates this finding, demonstrating a reduction in the vertical-propagation velocity of waves with increased N^(2). A linear, quasi- geostrophic, mid-latitude beta-plane model with a constant background westerly wind and a prescribed N^(2) applicable to the stratosphere is used to obtain analytic solutions. In this model, the planetary waves are initiated by steady energy influx from the lower boundary. The analysis indicates that under strong N^(2) conditions, the amplitude of planetary waves can be sufficiently increased by the effective energy convergence due to the slowing vertical energy transfer, resulting in a streamfunction response in this model that contains more energy. For N^(2) with a quasi-linear vertical variation, the results bear a resemblance to the constant case, except that the wave amplitude and oscillating frequency show some vertical variations.展开更多
The electromagnetic wave absorption of silicon carbide nanowires is improved by their uniform and diverse cross-structures.This study introduces a sustainable and high value-added method for synthesizing silicon carbi...The electromagnetic wave absorption of silicon carbide nanowires is improved by their uniform and diverse cross-structures.This study introduces a sustainable and high value-added method for synthesizing silicon carbide nanowires using lignite and waste silicon powder as raw materials through carbothermal reduction.The staggered structure of nanowires promotes the creation of interfacial polarization,impedance matching,and multiple loss mechanisms,leading to enhanced electromagnetic absorption performance.The silicon carbide nanowires demonstrate outstanding electromagnetic absorption capabilities with the minimum reflection loss of-48.09 d B at10.08 GHz and an effective absorption bandwidth(the reflection loss less than-10 d B)ranging from 8.54 to 16.68 GHz with a thickness of 2.17 mm.This research presents an innovative approach for utilizing solid waste in an environmentally friendly manner to produce broadband silicon carbide composite absorbers.展开更多
Using a recognition model of atmospheric gravity waves(AGWs),we identified 519 AGW events from the OH airglow images observed at the Dandong and Lhasa stations from 2015 to 2017.The 317 AGW events detected at the Dand...Using a recognition model of atmospheric gravity waves(AGWs),we identified 519 AGW events from the OH airglow images observed at the Dandong and Lhasa stations from 2015 to 2017.The 317 AGW events detected at the Dandong station have wavelengths ranging from 30 to 60 km,periods from 14 to 20 min,horizontal speeds from 30 to 60 m/s,and relative intensities from 0.4%to 0.6%,respectively.The parameters of 202 events recorded at the Lhasa station mainly vary within 15-35 km in horizontal wavelength,4-6 min in period,40-100 m/s in horizontal velocity,and 0.1%-0.3%in relative intensity.The occurrence rate peaks in winter and summer at Dandong and the peak in summer are absent at Lhasa because of the lack of convective weather.The seasonal propagation directions of the waves are influenced by both the wind field-filtering effect and the distribution of wave sources.In spring,because of the southeastward background wind field,fewer southeastward events are observed at the Dandong station.The situation at the Lhasa station is similar.In summer,both the Lhasa and Dandong stations are dominated by northeastward AGWs,which can be attributed to the southwestward wind.In autumn,ray-tracing results show that the events at Dandong mainly originate from wind shear,whereas the events at the Lhasa station are triggered by convective weather.The location of the wave sources determines the trend of the propagation directions at the Dandong and Lhasa stations in autumn.In winter,because of the eastward wind,more events are propagating to the southwest at the Dandong station.展开更多
基金financially supported by National Natural Science Foundation of China(Grant Nos.52378401,52278504)the Fundamental Research Funds for the Central Universities(Grant No.30922010918)。
文摘Traffic engineering such as tunnels in various altitudinal gradient zone are at risk of accidental explosion,which can damage personnel and equipment.Accurate prediction of the distribution pattern of explosive loads and shock wave propagation process in semi-enclosed structures at various altitude environment is key research focus in the fields of explosion shock and fluid dynamics.The effect of altitude on the propagation of shock waves in tunnels was investigated by conducting explosion test and numerical simulation.Based on the experimental and numerical simulation results,a prediction model for the attenuation of the peak overpressure of tunnel shock waves at different altitudes was established.The results showed that the peak overpressure decreased at the same measurement points in the tunnel entrance under the high altitude condition.In contrast,an increase in altitude accelerated the propagation speed of the shock wave in the tunnel.The average error between the peak shock wave overpressure obtained using the overpressure prediction formula and the measured test data was less than15%,the average error between the propagation velocity of shock waves predicted values and the test data is less than 10%.The method can effectively predict the overpressure attenuation of blast wave in tunnel at various altitudes.
基金supported by the Key-Area Research and Development Program of Guangdong Province(Grant No.2021B0909060004)the National Natural Science Foundation of China(Grant Nos.12072355 and 92271117)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0620202).
文摘The thermochemical non-equilibrium phenomena encountered by hypersonic vehicles present significant challenges in their design.To investigate the thermochemical reaction flow behind shock waves,the non-equilibrium radiation in the visible range using a shock tube was studied.Experiments were conducted with a shock velocity of 4.7 km/s,using nitrogen at a pressure of 20 Pa.To address measurement difficulties associated with weak radiation,a special square section shock tube with a side length of 380 mm was utilized.A high-speed camera characterized the shock wave’s morphology,and a spectrograph and a monochromator captured the radiation.The spectra were analyzed,and the numerical spectra were compared with experimental results,showing a close match.Temperature changes behind the shock wave were obtained and compared with numerical predictions.The findings indicate that the vibrational temperatures are overestimated,while the vibrational relaxation time is likely underestimated,due to the oversimplified portrayals of the non-equilibrium relaxation process in the models.Additionally,both experimental and simulated time-resolved profiles of radiation intensity at specific wavelengths were analyzed.The gathered data aims to enhance computational fluid dynamics codes and radiation models,improving their predictive accuracy.
基金funded by the National Natural Science Foundation of China(Grant No. 12302437)Jiangsu Provincial Natural Science Foundation (Grant No.SBK2023045424)。
文摘To explore the design criteria for composite charges and reveal the intrinsic relationship between the detonation wave propagation in composite charges and the overall energy distribution of shock waves,this study analyzes the propagation and interaction processes of detonation waves in composite charges with different structural dimensions and explosive combinations. It also investigates the spatial distribution characteristics of the resulting shock wave loads. Based on dimensional analysis theory, a theoretical analysis of the shock wave overpressure distribution in free air fields is conducted. Utilizing the derived dimensionless function relationships, the hydrocode AUTODYN is employed to investigate the effects of charge structure parameters and explosive combinations on the internal overdriven detonation phenomena and the distribution of shock wave loads. It is found that the overdriven detonation phenomenon in the inner layer of composite charges increases the strength of the axial detonation wave,thereby enhancing the intensity of the primary end wave formed upon refraction into the air, which affects the distribution characteristics of the shock wave overpressure. Research has shown that increasing the thickness ratio and detonation velocity ratio of composite charges is beneficial for exacerbating the phenomenon of overdriven detonation, improving the primary end wave intensity and axial overpressure. This gain effect gradually weakens with the propagation of shock waves. When overdriven detonation occurs inside the composite charge, the detonation pressure first increases and then decreases. The Mach reflection pressure of the composite charge with a larger aspect ratio is attenuated to a greater extent. In addition, as the aspect ratio of the composite charge increases, the shock wave energy gradually flows from the axial direction to the radial direction. Therefore, as the aspect ratio of the composite charge increases, the primary end wave intensity and axial overpressure gradually decrease.
文摘BACKGROUND Various stone factors can affect the net results of shock wave lithotripsy(SWL).Recently a new factor called variation coefficient of stone density(VCSD)is being considered to have an impact on stone free rates.AIM To assess the role of VCSD in determining success of SWL in urinary calculi.METHODS Charts review was utilized for collection of data variables.The patients were subjected to SWL,using an electromagnetic lithotripter.Mean stone density(MSD),stone heterogeneity index(SHI),and VCSD were calculated by generating regions of interest on computed tomography(CT)images.Role of these factors were determined by applying the relevant statistical tests for continuous and categorical variables and a P value of<0.05 was gauged to be statistically significant.RESULTS There were a total of 407 patients included in the analysis.The mean age of the subjects in this study was 38.89±14.61 years.In total,165 out of the 407 patients could not achieve stone free status.The successful group had a significantly lower stone volume as compared to the unsuccessful group(P<0.0001).Skin to stone distance was not dissimilar among the two groups(P=0.47).MSD was significantly lower in the successful group(P<0.0001).SHI and VCSD were both significantly higher in the successful group(P<0.0001).CONCLUSION VCSD,a useful CT based parameter,can be utilized to gauge stone fragility and hence the prediction of SWL outcomes.
基金supported by the National Key R&D Program of China(Grant No.2021YFB3802303)the National Natural Science Foundation of China(Grant Nos.12302493 and 12525211).
文摘The manipulation of intense shock waves to either attenuate or enhance damage has long been a key goal in the domain of impact dynamics.Effective methods for such manipulation,however,remain elusive owing to the wide spectrum and irreversible destructive nature of intense shock waves.This work proposes a novel approach for actively controlling intense shock waves in solids,inspired by the principles of optical and explosive lenses.Specifically,by designing a shock wave convex lens composed of a low-shock-impedance material embedded in a high-shock-impedance matrix,we prove the feasibility of transforming a planar shock into a spherically converging shock.This is based on oblique shock theory,according to which shock waves pass through an oblique interface and then undergo deflection.Both experimental and simulation results demonstrate that,as expected,the obtained local spherical shock wave has a wavefront that is nearly perfectly spherical and uniform in pressure.Thus,this work proves the possibility of generating spherical shock waves using plate-impact experiments and highlights the potential of further exploration of the manipulation of shock waves in solids.It also contributes an innovative perspective for both armor penetration technologies and shock wave mitigation strategies.
基金the support of the National Natural Science Foundation of China(Nos.12372295,U21B6003,U20A2069,12302389 and 123B2037)。
文摘Three-dimensional curved shock wave/boundary layer interaction with streamwise and spanwise curvatures widely exists in practical aerodynamic design.To explore the effects of composite shock curvatures on boundary layer separation,a canonical model with a cone placed above plate was utilized as a reference.Configurations of straight,convex,and concave conical shock waves inducing the curved conical shock wave/boundary layer interactions were studied,using CFD based on Reynolds-averaged numerical simulation method.The flow structure and separation region of each case were discussed quantitively on the symmetry plane,flat plate,and plane perpendicular to flow direction,respectively.The focus of the analysis was on the characteristic patterns of separation scale variation in the streamwise and spanwise directions,which were observed to consistently change with respect to both directions with alterations in the incident shock wave shape.A simplified control volume model was established to qualitatively discuss the influence source of curved shock waves on separation scales,based on mass conservation equations.The results suggest that the curved shock wave has a holistic effect on separation,which is not solely dependent on the shock foot strength.
基金supported by the Overall Planning and Development Project of China Academy of Engineering Physics(CAEP)(Grant No.TCGH0909)the Science and Technology Development Fund of the Chinese Academy of Meteorological Sciences(CAMS)(Grant No.2023KJ048)the Basic Research Fund of the Chinese Academy of Meteorological Sciences(Grant No.2023Z001)。
文摘This paper focuses on the application of the adaptive mesh method in the study of underwater shock waves near the water surface.By integrating theoretical analysis with a five-equation model under axisymmetric coordinates,we developed an optimized computational framework for multi-material fluid simulations.The moving mesh method(r-method)is used to accurately capture complex underwater shock wave systems.Multiple numerical experiments are conducted,including deep-water explosions,near-surface explosions for both spherical charge and cylindrical charge,and regular–irregular reflection interface calculations.The results show that compared to the fixed mesh method,the adaptive mesh method provides results closer to the theoretical values and achieves local high-resolution computation of multi-material fluids.By adjusting the adaptive function,different mesh refinement effects can be obtained.This method also has certain advantages in calculating the regular–irregular reflection interface in underwater explosions.This study establishes a validated computational framework for underwater explosion research,enhancing the predictive accuracy for underwater shock wave propagation in engineering assessments and providing new insights into the fundamental physics of multi-material explosion phenomena.
基金supported by the National Natural Science Foundation of China(Nos.12232018,12072360)The authors are very grateful to Dr.DONG Siwei for his helpful recommendation on the clustering method.
文摘This study focuses on High-Amplitude Wall Heat Flux events(HAWHFs) occurring during the interaction between a supersonic flat-plate Turbulent Boundary Layer(TBL) at a Mach number of2.25 and an oblique shock wave impinging at 33.2.. A database from a validated direct numerical simulation is analyzed using conditional averaging and a two-dimensional clustering methodology to elucidate the statistical characteristics of both positive and negative HAWHFs within the interaction region. The results reveal that the interaction considerably affects the temporal attributes of the HAWHFs, leading to an extended lifespan for the positive HAWHFs and an increased interval between the occurrences of negative HAWHFs. The structural characteristics of the identified HAWHFs are delineated based on the evolution of population density, aspect ratio, and both absolute and relative distances throughout the interaction. The joint probability density functions of the relative positioning of two adjacent structures indicate that, away from the reattachment point, the positive HAWHFs align in the spanwise direction, displaying similarities with the negative HAWHFs. Moreover, a conditional analysis of flow structures associated with HAWHFs is conducted. This analysis of the conditionally averaged three-dimensional fields reveals that the interaction fosters larger-scale organizational patterns in the downstream region. However, the formation of positive and negative HAWHFs remains largely unaffected by the interaction, with the former predominantly linked to a two-layer temperature structure and the latter primarily associated with a pair of oblique vortices.
文摘BACKGROUND Recovering from anterior cruciate ligament(ACL)reconstruction can be challenging.While standard rehabilitation helps restore knee function,many patients still face a slow or incomplete recovery.Extracorporeal shockwave therapy(ESWT)has recently gained attention as a potential way to speed up healing and improve outcomes when added to traditional rehab.AIM To explore whether combining ESWT with standard postoperative rehabilitation truly leads to better recovery compared with rehab alone.METHODS A systematic review and meta-analysis were conducted using the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines,evaluating participant status following ACL reconstruction with standard rehabilitation and without augmented ESWT.This meta-analysis included six studies(five randomized controlled trials,one non-randomized clinical study).The outcome measures were the Lysholm score,International Knee Documentation Committee score,visual analog score,and KT-1000 measurements.To compare the control and intervention groups,the weighted mean differences were calculated along with the 95%confidence intervals.The heterogeneity of the studies and publication bias were analyzed.RESULTS ESWT modestly improved Lysholm scores(weighted mean difference:3.72;95%confidence interval:-0.27 to 7.71)with high heterogeneity(I2:96%,P<0.001)when compared with standard rehabilitation.Focused ESWT showed greater benefits compared with radial ESWT.No significant differences were found in the International Knee Documentation Committee scores,visual analog score,or KT-1000 measurements.Substantial variability and publication bias were noted.CONCLUSION ESWT improved Lysholm scores but did not show other significant benefits.Due to the limited evidence,further standardized,placebo-controlled trials are needed to confirm its effectiveness in ACL reconstruction.
文摘[Objectives]To quantify the efficacy of Extracorporeal Shock Wave Therapy(ESWT)for upper limb spasticity in stroke patients using Modified Ashworth Scale(MAS)across three timeframes:immediate,short-term(24 h-4 wks),and long-term(>4 wks).[Methods]Six databases(PubMed,EMBASE,CENTRAL,CINAHL,Scopus,Web of Science)until May 2025,were systematically searched,identifying 11 RCTs(n=505)meeting inclusion criteria(adults≥18 yrs old with stroke-related spasticity[MAS≥1]).Risk of bias was rigorously assessed using Cochrane criteria,revealing uniformly low risk across all domains.Random-effects meta-analyses(REML model)calculated Hedges'g with 95%CI for MAS outcomes,with subgroup analyses for joint-specific effects.[Results]ESWT demonstrated non-significant immediate MAS reduction(g=-0.69,p=0.07;=93.95%),but statistically significant short-term(g=-0.58,p=0.02;I^(2)=89.64%)and long-term effects(g=-0.52,p=0.02;I^(2)=78.72%).Effects were driven by composite MAS scores(short-term g=-0.63;long-term g=-0.56,both p<0.05)rather than isolated joints(elbow/finger/wrist all non-significant).Substantial heterogeneity persisted across analyses,particularly in joint-specific subgroups(I^(2)>90%).[Conclusions]ESWT provides statistically significant,clinically relevant reductions in global upper limb spasticity with durable efficacy beyond four weeks,supporting its use as a non-invasive adjunct therapy despite substantial heterogeneity warranting protocol standardization.
基金support from the National Key R&D Program of China(No.2020YFC2201100)the Foundation of National Key Laboratory of Shock Wave and Detonation Physics,China(No.JCKYS2023212003)+1 种基金the National Natural Science Foundation of China(No.12172061)the Opening Project of State Key Laboratory of Explosion Science and Safety Protection(Beijing Institute of Technology)(No.KFJJ25-02M).
文摘A Discrete Boltzmann Method(DBM)with a Maxwell-type boundary condition is constructed to investigate the influence of rarefaction on laminar Shock Wave/Boundary Layer Interaction(SWBLI).Due to the complexity of compressible flow,a Knudsen number vector Kn,whose components include the local Knudsen numbers such as Kn_(ρ)and Kn_(U),is introduced to characterize the local structures,where Kn_(ρ)and Kn_(U)are Knudsen numbers defined in terms of the density and velocity interfaces,respectively.Since first focusing on the steady state of SWBLI,the DBM considers up to the second-order Kn_(ρ)(rarefaction/non-equilibrium)effects.The model is validated using Mach number 2 SWBLI and the necessity of using DBM with sufficient physical accuracy is confirmed by the shock collision problem.Key findings include the following:the leading-edge shock wave increases the local density Knudsen number Kn_(ρ)and eventually leads to the failure of linear constitutive relations in the Navier-Stokes(N-S)model and surely also in the lower-order DBM;the non-equilibrium effect differences in regions behind the leading-edge shock wave are primarily correlated with Kn_(ρ),while in the separation region are primarily correlated with Kn_(U);the non-equilibrium quantities D_(2)and D_(4,2),as well as the viscous entropy production rate S_(NOMF)can be used to identify the separation zone.The findings clarify various effects and main mechanisms in different regions associated with SWBLI,which are concealed in N-S model.
基金co-supported by the National Natural Science Foundation of China (No. 12172175)the National Science and Technology Major Project, China (No. J2019-II0014-0035)the Science Center for Gas Turbine Project, China (Nos. P2022-C-II-002-001, P2022-A-II-002-001)
文摘Cowl-induced incident Shock Wave/Boundary Layer Interactions (SWBLI) under the influence of gradual expansion waves are frequently observed in supersonic inlets. However, the analysis and prediction of interaction lengths have not been sufficiently investigated. First, this study presents a theoretical scaling analysis and validates it through wind tunnel experiments. It conducts detailed control volume analysis of mass conservation, considering the differences between inviscid and viscous cases. Then, three models for analysing interaction length under gradual expansion waves are derived. Related experiments using schlieren photography are conducted to validate the models in a Mach 2.73 flow. The interaction scales are captured at various relative distances between the shock impingement location and the expansion regions with wedge angles ranging from 12° to 15° and expansion angles of 9°, 12°, and 15°. Three trend lines are plotted based on different expansion angles to depict the relationship between normalised interaction length and normalised interaction strength metric. In addition, the relationship between the coefficients of the trend line and the expansion angles is introduced to predict the interaction length influenced by gradual expansion waves. Finally, the estimation of normalised interaction length is derived for various coefficients within a unified form.
文摘With different structural forms of ventilation pipes have various attenuation effects on incident shock waves while meeting ventilation requirements.The attenuation mechanism and the propagation law of shock waves in ventilation pipes of different structures are investigated by experiments and numerical simulations.Furthermore,for the same structure,the effects of peak pressure and positive pressure time on the attenuation rate are discussed.It is found that the attenuation rate increases with the incident shock wave pressure,and the shock wave attenuation rate tends to reach its limiting value k for the same structure and reasonably short positive pressure time.Under the same conditions,the attenuation rate is calculated using the pressure of the shock wave as follows:diffusion chamber pipe,branch pipe and selfconsumption pipe;the attenuation rate per unit volume is calculated as follows:self-consumption pipe,branch pipe and diffusion chamber pipe.In addition,an easy method is provided to calculate the attenuation rate of the shock wave in single and multi-stage ventilation pipes.Corresponding parameters are provided for various structures,and the margin of error between the formulae and experimental results is within 10%,which is significant for engineering applications.
文摘The propagation properties of ion-acoustic solitary and shock waves in the magnetized viscous plasma with nonthermal trapped electrons are investigated.The Cairns-Gurevich distribution as the electron distribution is considered to describe the plasma nonthermality and particle trapping.By adopting the reductive perturbation technique,we derived the nonlinear Schamel-Korteweg-de Vries-Burgers(SKdVB)equation,and then obtained the ion-acoustic shock and solitary wave solutions of the SKdVB equation for different limiting cases.It is found that the impact of nonthermal parameterα,external magnetic fieldΩ,obliqueness lz,wave speed U0,and the ion kinematic viscosityη0can significantly change the characteristics of the shock and solitary waves.These results may be useful for better understanding the propagation of nonlinear structures in space(i.e.Earth's magnetosphere and ionosphere,auroral regions)and laboratory plasma with nonthermal trapped electrons.
基金support provided by the Center for Fabrication and Application of Electronic Materials at Dokuz Eylül University,Türkiye。
文摘Biochar and biochar composites are versatile materials that can be used in many applications.In this study,biochar was prepared from sawdust and combined with the yttrium iron garnet(YIG)nanocrystal to investigate the shielding effectiveness of the composite structure.Firstly,the effect of the pyrolysis temperature on the shielding effectiveness of biochar was investigated.Secondly,biochars combined with YIG nanocrystals with different contents and shielding effectiveness of the composites were investigated.The electromagnetic effectiveness of the samples was investigated within the X band(8-12 GHz).The findings indicate that biochar demonstrates enhanced absorption properties with elevated pyrolysis temperatures.Biochars demonstrated an approximate 40 d B shielding effectiveness,while YIG exhibited approximately 7 d B,corresponding to absorption at 8 GHz.However,the combination of biochar and YIG exhibited exceptional absorption,reaching 67.12 d B at 8 GHz.
基金financial support from NSF ExpandQISE program.The synthesis of tellurene was supported by NSF under grant no.CMMI-2046936supports from Purdue Research Foundation.
文摘Tellurene,a chiral chain semiconductor with a narrow bandgap and exceptional strain sensitivity,emerges as a pivotal material for tailoring electronic and optoelectronic properties via strain engineering.This study elucidates the fundamental mechanisms of ultrafast laser shock imprinting(LSI)in two-dimensional tellurium(Te),establishing a direct relationship between strain field orientation,mold topology,and anisotropic structural evolution.This is the first demonstration of ultrafast LSI on chiral chain Te unveiling orientation-sensitive dislocation networks.By applying controlled strain fields parallel or transverse to Te’s helical chains,we uncover two distinct deformation regimes.Strain aligned parallel to the chain’s direction induces gliding and rotation governed by weak interchain interactions,preserving covalent intrachain bonds and vibrational modes.In contrast,transverse strain drives shear-mediated multimodal deformations—tensile stretching,compression,and bending—resulting in significant lattice distortions and electronic property modulation.We discovered the critical role of mold topology on deformation:sharp-edged gratings generate localized shear forces surpassing those from homogeneous strain fields via smooth CD molds,triggering dislocation tangle formation,lattice reorientation,and inhomogeneous plastic deformation.Asymmetrical strain configurations enable localized structural transformations while retaining single-crystal integrity in adjacent regions—a balance essential for functional device integration.These insights position LSI as a precision tool for nanoscale strain engineering,capable of sculpting 2D material morphologies without compromising crystallinity.By bridging ultrafast mechanics with chiral chain material science,this work advances the design of strain-tunable devices for next-generation electronics and optoelectronics,while establishing a universal framework for manipulating anisotropic 2D systems under extreme strain rates.This work discovered crystallographic orientation-dependent deformation mechanisms in 2D Te,linking parallel strain to chain gliding and transverse strain to shear-driven multimodal distortion.It demonstrates mold geometry as a critical lever for strain localization and dislocation dynamics,with sharp-edged gratings enabling unprecedented control over lattice reorientation.Crucially,the identification of strain field conditions that reconcile severe plastic deformation with single-crystal retention offers a pathway to functional nanostructure fabrication,redefining LSI’s potential in ultrafast strain engineering of chiral chain materials.
基金Supported by the Development and Application Project of Ship CAE Software.
文摘Studies of wave-current interactions are vital for the safe design of structures.Regular waves in the presence of uniform,linear shear,and quadratic shear currents are explored by the High-Level Green-Naghdi model in this paper.The five-point central difference method is used for spatial discretization,and the fourth-order Adams predictor-corrector scheme is employed for marching in time.The domain-decomposition method is applied for the wave-current generation and absorption.The effects of currents on the wave profile and velocity field are examined under two conditions:the same velocity of currents at the still-water level and the constant flow volume of currents.Wave profiles and velocity fields demonstrate substantial differences in three types of currents owing to the diverse vertical distribution of current velocity and vorticity.Then,loads on small-scale vertical cylinders subjected to regular waves and three types of background currents with the same flow volume are investigated.The maximum load intensity and load fluctuation amplitude in uniform,linear shear,and quadratic shear currents increase sequentially.The stretched superposition method overestimates the maximum load intensity and load fluctuation amplitude in opposing currents and underestimates these values in following currents.The stretched superposition method obtains a poor approximation for strong nonlinear waves,particularly in the case of the opposing quadratic shear current.
基金supported by the National Natural Science Foundation of China(Grant No.42261134532,42405059,and U2342212)。
文摘This study investigates the relationship between atmospheric stratification (i.e., static stability given by N^(2)) and the vertical energy transfer of stationary planetary waves, and further illustrates the underlying physical mechanism. Specifically, for the simplified case of constant stratospheric N^(2), the refractive index square of planetary waves has a theoretical tendency to increase first and then decrease with an increased N^(2), whereas the group velocity weakens. Mechanistically, this behavior can be understood as an intensified suppression of vertical isentropic surface displacement caused by meridional heat transport of planetary waves under strong N^(2) conditions. Observational analysis corroborates this finding, demonstrating a reduction in the vertical-propagation velocity of waves with increased N^(2). A linear, quasi- geostrophic, mid-latitude beta-plane model with a constant background westerly wind and a prescribed N^(2) applicable to the stratosphere is used to obtain analytic solutions. In this model, the planetary waves are initiated by steady energy influx from the lower boundary. The analysis indicates that under strong N^(2) conditions, the amplitude of planetary waves can be sufficiently increased by the effective energy convergence due to the slowing vertical energy transfer, resulting in a streamfunction response in this model that contains more energy. For N^(2) with a quasi-linear vertical variation, the results bear a resemblance to the constant case, except that the wave amplitude and oscillating frequency show some vertical variations.
基金supported by the National Natural Science Foundation of China(No.52436008)the Inner Mongolia Science and Technology Projects,China(Nos.JMRHZX20210003 and 2023YFCY0009)+3 种基金the Huaneng Group Co Ltd.,China(No.HNKJ23-H50)the National Natural Science Foundation of China(No.22408044)the China Postdoctoral Science Foundation(No.2024M761877)the National Key R&D Program of China(No.SQ2024YFD2200039)。
文摘The electromagnetic wave absorption of silicon carbide nanowires is improved by their uniform and diverse cross-structures.This study introduces a sustainable and high value-added method for synthesizing silicon carbide nanowires using lignite and waste silicon powder as raw materials through carbothermal reduction.The staggered structure of nanowires promotes the creation of interfacial polarization,impedance matching,and multiple loss mechanisms,leading to enhanced electromagnetic absorption performance.The silicon carbide nanowires demonstrate outstanding electromagnetic absorption capabilities with the minimum reflection loss of-48.09 d B at10.08 GHz and an effective absorption bandwidth(the reflection loss less than-10 d B)ranging from 8.54 to 16.68 GHz with a thickness of 2.17 mm.This research presents an innovative approach for utilizing solid waste in an environmentally friendly manner to produce broadband silicon carbide composite absorbers.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0711402)the Specialized Research Fund for State Key Laboratories。
文摘Using a recognition model of atmospheric gravity waves(AGWs),we identified 519 AGW events from the OH airglow images observed at the Dandong and Lhasa stations from 2015 to 2017.The 317 AGW events detected at the Dandong station have wavelengths ranging from 30 to 60 km,periods from 14 to 20 min,horizontal speeds from 30 to 60 m/s,and relative intensities from 0.4%to 0.6%,respectively.The parameters of 202 events recorded at the Lhasa station mainly vary within 15-35 km in horizontal wavelength,4-6 min in period,40-100 m/s in horizontal velocity,and 0.1%-0.3%in relative intensity.The occurrence rate peaks in winter and summer at Dandong and the peak in summer are absent at Lhasa because of the lack of convective weather.The seasonal propagation directions of the waves are influenced by both the wind field-filtering effect and the distribution of wave sources.In spring,because of the southeastward background wind field,fewer southeastward events are observed at the Dandong station.The situation at the Lhasa station is similar.In summer,both the Lhasa and Dandong stations are dominated by northeastward AGWs,which can be attributed to the southwestward wind.In autumn,ray-tracing results show that the events at Dandong mainly originate from wind shear,whereas the events at the Lhasa station are triggered by convective weather.The location of the wave sources determines the trend of the propagation directions at the Dandong and Lhasa stations in autumn.In winter,because of the eastward wind,more events are propagating to the southwest at the Dandong station.
