During the propagation of high-power lasers within internal channels,the laser beam heats the propagation medium,causing the thermal blooming effect that degrades the beam quality at the output.The intricate configura...During the propagation of high-power lasers within internal channels,the laser beam heats the propagation medium,causing the thermal blooming effect that degrades the beam quality at the output.The intricate configuration of the optical path within the internal channel necessitates complex and time-consuming efforts to assess the impact of thermal blooming effect on the optical path.To meet the engineering need for rapid evaluation of thermal blooming effect in optical paths,this study proposed a rapid simulation method for the thermal blooming effect in internal optical paths based on the finite element method.This method discretized the fluid region into infinitesimal elements and employed finite element method for flow field analysis.A simplified analytical model of the flow field region in complex internal channels was established,and regions with similar thermal blooming effect were divided within this model.Based on the calculated optical path differences within these regions,numerical simulations of phase distortion caused by thermal blooming were conducted.The calculated result were compared with those obtained using the existing methods.The findings reveal that for complex optical paths,the discrepancy between the two approaches is less than 3.6%,with similar phase distortion patterns observed.For L-type units,this method and the existing methods identify the same primary factors influencing aberrations and exhibit consistent trends in their variation.This method was used to analyze the impact of thermal blooming effect in a straight channel under different gravity directions.The results show that phase distortion varies with changes in the direction of gravity,and the magnitude of the phase difference is strongly correlated with the component of gravity perpendicular to the optical axis.Compared to the existing methods,this approach offers greater flexibility,obviates the need for complex custom analysis programming.The analytical results of this method enable a rapid assessment of the thermal blooming effect in optical paths within the internal channel.This is especially useful during the engineering design.These results also provide crucial references for developing strategies to suppress thermal blooming effect.展开更多
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 highly selective catalytic hydrogenation of halogenated nitroaromatics was achieved by employing Pd‑based catalysts that were co‑modified with organic and inorganic ligands.It was demonstrated that the catalysts c...The highly selective catalytic hydrogenation of halogenated nitroaromatics was achieved by employing Pd‑based catalysts that were co‑modified with organic and inorganic ligands.It was demonstrated that the catalysts contained Pd species in mixed valence states,with high valence Pd at the metal‑support interface and zero valence Pd at the metal surface.While the strong coordination of triphenylphosphine(PPh3)to Pd0 on the Pd surface prevents the adsorption of halogenated nitroaromatics and thus dehalogenation,the coordination of sodium metavanadate(NaVO3)to high‑valence Pd sites at the interface helps to activate H2 in a heterolytic pathway for the selective hydrogenation of nitro‑groups.The excellent catalytic performance of the interfacial active sites enables the selective hydrogenation of a wide range of halogenated nitroaromatics.展开更多
A functional interlayer based on two-dimensional(2D)porous modified vermiculite nanosheets(PVS)was obtained by acid-etching vermiculite nanosheets.The as-obtained 2D porous nanosheets exhibited a high specific surface...A functional interlayer based on two-dimensional(2D)porous modified vermiculite nanosheets(PVS)was obtained by acid-etching vermiculite nanosheets.The as-obtained 2D porous nanosheets exhibited a high specific surface area of 427 m^(2)·g^(-1)and rich surface active sites,which help restrain polysulfides(LiPSs)through good physi-cal and chemical adsorption,while simultaneously accelerating the nucleation and dissolution kinetics of Li_(2)S,effec-tively suppressing the shuttle effect.The assembled lithium-sulfur batteries(LSBs)employing the PVS-based inter-layer delivered a high initial discharge capacity of 1386 mAh·g^(-1)at 0.1C(167.5 mAh·g^(-1)),long-term cycling stabil-ity,and good rate property.展开更多
Thermally activated delayed fluorescence(TADF)molecules have outstanding potential for applications in organic light-emitting diodes(OLEDs).Due to the lack of systematic studies on the correlation between molecular st...Thermally activated delayed fluorescence(TADF)molecules have outstanding potential for applications in organic light-emitting diodes(OLEDs).Due to the lack of systematic studies on the correlation between molecular structure and luminescence properties,TADF molecules are far from meeting the needs of practical applications in terms of variety and number.In this paper,three twisted TADF molecules are studied and their photophysical properties are theoretically predicted based on the thermal vibrational correlation function method combined with multiscale calculations.The results show that all the molecules exhibit fast reverse intersystem crossing(RISC)rates(kRISC),predicting their TADF luminescence properties.In addition,the binding of DHPAzSi as the donor unit with different acceptors can change the dihedral angle between the ground and excited states,and the planarity of the acceptors is positively correlated with the reorganization energy,a property that has a strong influence on the non-radiative process.Furthermore,a decrease in the energy of the molecular charge transfer state and an increase in the kRISC were observed in the films.This study not only provides a reliable explanation for the observed experimental results,but also offers valuable insights that can guide the design of future TADF molecules.展开更多
In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ra...In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.展开更多
The pressure and temperature increase resulting from the impact of different threats onto target materials is analyzed with a unified laboratory-scale setup.This allows deriving qualitative information on the occurrin...The pressure and temperature increase resulting from the impact of different threats onto target materials is analyzed with a unified laboratory-scale setup.This allows deriving qualitative information on the occurring phenomenology as well as quantitative statements about the relative effects sizes as a function of target material and threat.The considered target materials are steel,aluminum,and magnesium.As threats,kinetic energy penetrator,explosively formed projectile,and shaped charge jet are used.For the investigated combinations,the measured overpressures vary by a factor of up to 5 for a variation of the material,by a factor of up to 7 for a variation of the threat,and by a factor larger than 15for a simultaneous variation of both.The obtained results as well as the experimental approach are relevant for the basic understanding of impact effects and risks due to material reactivity.The paper combines two main aims.Firstly,to provide a summary of own prior work in a coherent journal article and,secondly,to review and discuss these earlier results with a new perspective.展开更多
The Hydrodynamic Ram(HRAM)effect occurs when a high kinetic energy projectile penetrates a fluid filled area,e.g.,a liquid filled tank.The projectile transfers its momentum and kinetic energy to the fluid,what causes ...The Hydrodynamic Ram(HRAM)effect occurs when a high kinetic energy projectile penetrates a fluid filled area,e.g.,a liquid filled tank.The projectile transfers its momentum and kinetic energy to the fluid,what causes a sudden,local pressure rise,further expanding as primary shock wave in the fluid and developing a cavity.It is possible that the entire tank ruptures due to the loads transferred through the fluid to its surrounding structure.In the past decades,additionally to experimental investigations,HRAM has been studied using various computational approaches particularly focusing on the description of the Fluid-Structure Interaction(FSI).This article reviews the published experimental,analytical and numerical results and delivers a chronological overview since the end of World War II.Furthermore,HRAM mitigation measures are highlighted,which have been developed with the experimental,analytical and numerical toolboxes matured over the past 80 years.展开更多
Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting t...Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting their potential applications.Therefore,it is imperative to study the creation of lowfrequency signals using antennas with suitable dimensions.In contrast to conventional mechanical antenna techniques,our study generates low-frequency signals in the spatial domain utilizing the principle of the Doppler effect.We also defines the antenna array architecture,the timing sequency,and the radiating element signal waveform,and provides experimental prototypes including 8/64 antennas based on earlier research.In the conducted experiments,121 MHz,40 MHz,and 10 kHz composite signals are generated by 156 MHz radiating element signals.The composite signal spectrum matches the simulations,proving our low-frequency signal generating method works.This holds significant implications for research on generating low-frequency signals with small-sized antennas.展开更多
In existing studies, most slope stability analyses concentrate on conditions with constant temperature, assuming the slope is intact, and employ the Mohr-Coulomb (M-C) failure criterion for saturated soil to character...In existing studies, most slope stability analyses concentrate on conditions with constant temperature, assuming the slope is intact, and employ the Mohr-Coulomb (M-C) failure criterion for saturated soil to characterize the strength of the backfill. However, the actual working temperature of slopes varies, and natural phenomena such as rainfall and groundwater infiltration commonly result in unsaturated soil conditions, with cracks typically present in cohesive slopes. This study introduces a novel approach for assessing the stability of unsaturated soil stepped slopes under varying temperatures, incorporating the effects of open and vertical cracks. Utilizing the kinematic approach and gravity increase method, we developed a three-dimensional (3D) rotational wedge failure mechanism to simulate slope collapse, enhancing the traditional two-dimensional analyses. We integrated temperature-dependent functions and nonlinear shear strength equations to evaluate the impact of temperature on four typical unsaturated soil types. A particle swarm optimization algorithm was employed to calculate the safety factor, ensuring our method’s accuracy by comparing it with existing studies. The results indicate that considering 3D effects yields a higher safety factor, while cracks reduce slope stability. Each unsaturated soil exhibits a distinctive temperature response curve, highlighting the importance of understanding soil types in the design phase.展开更多
Exploring the effective and efficient path of agricultural carbon emission reduction in Henan Province is of great significance to optimizing the strategic layout of China's agricultural emission reduction and car...Exploring the effective and efficient path of agricultural carbon emission reduction in Henan Province is of great significance to optimizing the strategic layout of China's agricultural emission reduction and carbon sequestration.Accordingly,the agricultural carbon emissions of each county were measured scientifically and then the spatial measurement model was utilized to clarify the spatial and temporal evolution trend and spatial effect mechanism of agricultural carbon emissions based on the county data of Henan Province from 2010 to 2020.The results showed that:(1)in 2020,the total agricultural carbon emissions were 134.7274 million tons,with the high distribution in the southeast and low distribution in the northwest;(2)the spatial dependence of agricultural carbon emissions showed a four-stage trend of fluctuating down-continuing up-plummeting-fluctuating up again,and the spatial heterogeneity was dominated by low-low agglomeration,followed by high-low agglomeration;(3)there was an inverted U curve relationship between the level of agricultural economic development and agricultural carbon emissions.The increase in the level of agricultural mechanization and urbanization rate significantly reduced agricultural carbon emissions.The opposite was true for the financial support for agriculture,the income level of rural residents and the structure of the agricultural industry;(4)in terms of spatial spillover effects,the increase in the level of agricultural development in neighbor counties first increased and then decreased agricultural carbon emissions in Henan Province.The mechanization level and urbanization rate of neighbor counties reduced agricultural carbon emissions in Henan Province,and the opposite was true for the income level of rural residents and the scale utilization of agricultural land.展开更多
Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsatur...Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsaturated seepage multi-field coupling,resulting in inaccurate estimates.To address these deficiencies,this paper proposed a calculation method for seismic passive earth pressure in unsaturated narrow backfill,based on inclined thin-layer units.It considers the interlayer shear stress,arching effect,and the multi-field coupling of seismic-unsaturated seepage.Additionally,this paper includes a parametric sensitivity analysis.The outcomes indicate that the earthquake passive ground pressure of unsaturated narrow backfill can be reduced by increasing the aspect ratio,seismic acceleration coefficient,and unsaturation parameterα.It can also be reduced by decreasing the effective interior friction angle,soil cohesion,wallearth friction angle,and vertical discharge.Furthermore,for any width soil,lowering the elevation of the action point of passive thrust can be attained by raising the effective interior friction angle,wall-earth friction angle,and unsaturation parameterα.Reducing soil cohesion,seismic acceleration coefficient,and vertical discharge can also lower the height of the application point of passive thrust.展开更多
Investigating the blast effects and mechanisms on typical finite-sized obstacles is essential for optimizing defense strategies and designing more robust barriers to deter terrorists and protect critical locations.Thi...Investigating the blast effects and mechanisms on typical finite-sized obstacles is essential for optimizing defense strategies and designing more robust barriers to deter terrorists and protect critical locations.This study investigates the blasting effects and underlying mechanisms of concrete frustums subjected to contact explosions,employing both numerical simulations and field tests.It focuses on the effects of top and side blasting,with particular emphasis on fracture modes,damage patterns,and fragment sizes,as well as the causes of different failure modes and the propagation of stress waves.The study also explores the blasting effects of detonating explosives at varying positions along the side and with different charge amounts.The results show that side-blasting leads to complete fragmentation,with tensile waves playing a significant role in creating extensive damage zones that propagate parallel to the frustum's outer surface,concentrating damage near the surface.During top-blasting,the upper half of the frustum undergoes fragmentation,while the lower half experiences cracking.Tensile waves propagate from the top to the bottom surface,forming larger blocks in regions with lower wave intensity.Three distinct damage zones within the frustum were identified,and a series of mathematical formulas were derived to describe the relationship between the maximum fragment size and charge mass.As the charge mass increased from 1.0 kg to 4.0 kg,the maximum fragment size decreased.Detonation at the center of the frustum's side resulted in the most severe fragmentation,with a 51.8%reduction in fragment size compared to other detonation positions.Finally,four broken modes were classified,each influenced by charge mass and explosive location.This study provides valuable insights for optimizing civil blasting operations and designing protective engineering structures.展开更多
Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which d...Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which depicts the shear properties of concrete.The experiments on the EoS of concrete is always challenging due to the technical difficulties and equipment limitations,especially for the specimen size effect on the EoS.Although some researchers investigate the shock properties of concretes by fly-plate impact tests,the specimens used in their tests are usually in one size.In this paper,the fly-plate impact tests on concrete specimens with different sizes are performed to investigate the size effect on the shock properties of concrete materials.The mechanical background of the size effect on the shock properties are revealed,which is related to the lateral rarefaction effect and the deviatoric stress produced in the specimen.According to the tests results,the modified EoS considering the size effect on the shock properties of concrete are proposed,which the bulk modulus of concrete is unpredicted by up to 20% if size effects are not accounted for.展开更多
This paper realizes the full-domain collaborative deployment of multiple interference sources of the global satellite navigation system(GNSS)and evaluates the deployment effect to enhance the ability to disturb the at...This paper realizes the full-domain collaborative deployment of multiple interference sources of the global satellite navigation system(GNSS)and evaluates the deployment effect to enhance the ability to disturb the attacker and the capability to defend the GNSS during navigation countermeasures.Key evaluation indicators for the jamming effect of GNSS suppressive and deceptive jamming sources are first created,their evaluation models are built,and their detection procedures are sorted out,as the basis for determining the deployment principles.The principles for collaboratively deploying multi-jamming sources are developed to obtain the deployment structures(including the required number,structures in demand,and corresponding positions)of three single interference sources required by collaboratively deploying.Accordingly,simulation and hardware-in-loop testing results are presented to determine a rational configuration of the collaborative deployment of multi-jamming sources in the set situation and further realize the full-domain deployment of an interference network from ground,air to space.Varied evaluation indices for the deployment effect are finally developed to evaluate the deployment effect of the proposed configuration and further verify its reliability and rationality.展开更多
The seminal report ofα-diimine palladium and nickel catalysts in 1995 represented a major breakthrough in the preparation of functionalized polyolefin materials.Owing to the high abundance and low cost of nickel,nick...The seminal report ofα-diimine palladium and nickel catalysts in 1995 represented a major breakthrough in the preparation of functionalized polyolefin materials.Owing to the high abundance and low cost of nickel,nickel-based catalysts have great application prospects in the industrialization process of olefin coordination polymerization.In this work,various N-aryl substituents with different electronic effects were synthesized and introduced intoα-diimine ligands.The aspreparedα-diimine nickel catalysts showed high polymerization activity(0.9×10^(7)–3.0×10^(7)g·mol^(−1)·h^(−1))in ethylene polymerization,generating polyethylene products with adjustable molecular weights(Mn values:7.4×10^(4)–146.9×10^(4)g·mol^(−1))and branching densities(31/1000 C–68/1000 C).The resulting polyethylene products showed excellent mechanical properties,with high tensile strength(up to 25.0 MPa)and high strain at break values(up to 3890%).The copolymerization of ethylene and polar monomers can also be achieved by these nicekel complexes,ultimately preparing functionalized polyolefins.展开更多
With the analysis of experiment and theory on GaN HEMT devices under DC sweep,an improved model for kink effect based on advanced SPICE model for high electron mobility transistors(ASM-HEMT)is pro⁃posed,considering th...With the analysis of experiment and theory on GaN HEMT devices under DC sweep,an improved model for kink effect based on advanced SPICE model for high electron mobility transistors(ASM-HEMT)is pro⁃posed,considering the relationship between the drain/gate-source voltage and kink effect.The improved model can not only accurately describe the trend of the drain-source current with the current collapse and kink effect,but also precisely fit different values of drain-source voltages at which the kink effect occurs under different gatesource voltages.Furthermore,it well characterizes the DC characteristics of GaN devices in the full operating range,with the fitting error less than 3%.To further verify the accuracy and convergence of the improved model,a load-pull system is built in ADS.The simulated result shows that although both the original ASM-HEMT and the improved model predict the output power for the maximum power matching of GaN devices well,the im⁃proved model predicts the power-added efficiency for the maximum efficiency matching more accurately,with 4%improved.展开更多
Electrocatalytic water splitting provides an efficient method for the production of hydrogen.In electrocatalytic water splitting,the oxygen evolution reaction(OER)involves a kinetically sluggish four-electron transfer...Electrocatalytic water splitting provides an efficient method for the production of hydrogen.In electrocatalytic water splitting,the oxygen evolution reaction(OER)involves a kinetically sluggish four-electron transfer process,which limits the efficiency of electrocatalytic water splitting.Therefore,it is urgent to develop highly active OER catalysts to accelerate reaction kinetics.Coupling single atoms and clusters in one system is an innovative approach for developing efficient catalysts that can synergistically optimize the adsorption and configuration of intermediates and improve catalytic activity.However,research in this area is still scarce.Herein,we constructed a heterogeneous single-atom cluster system by anchoring Ir single atoms and Co clusters on the surface of Ni(OH)_(2)nanosheets.Ir single atoms and Co clusters synergistically improved the catalytic activity toward the OER.Specifically,Co_(n)Ir_(1)/Ni(OH)_(2)required an overpotential of 255 mV at a current density of 10 mA·cm^(−2),which was 60 mV and 67 mV lower than those of Co_(n)/Ni(OH)_(2)and Ir1/Ni(OH)_(2),respectively.The turnover frequency of Co_(n)Ir_(1)/Ni(OH)_(2)was 0.49 s^(−1),which was 4.9 times greater than that of Co_(n)/Ni(OH)_(2)at an overpotential of 300 mV.展开更多
Roof disaster has always been an important factor restricting coal mine safety production.Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics,which is an effective way t...Roof disaster has always been an important factor restricting coal mine safety production.Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics,which is an effective way to control the hard limestone roof.In this study,the effects of various factors on the reaction characteristics and mechanical properties of limestone were analyzed.The results show that the acid with stronger hydrogen production capacity after ionization(pK_(a)<0)has more prominent damage to the mineral grains of limestone.When pKa increases from−8.00 to 15.70,uniaxial compressive strength and elastic modulus of limestone increase by 117.22%and 75.98%.The influence of acid concentration is manifested in the dissolution behavior of mineral crystals,the crystal defects caused by large-scale acid action will lead to the deterioration of limestone strength,and the strength after 15%concentration reformation can be reduced by 59.42%.The effect of acidification time on limestone has stages and is the most obvious in the initial metathesis reaction stage(within 60 min).The key to the strength damage of acidified limestone is the participation of hydrogen ions in the reaction system.Based on the analytic hierarchy process method,the influence weights of acid type,acid concentration and acidification time on strength are 24.30%,59.54% and 16.16%,respectively.The research results provide theoretical support for the acidification control of hard limestone roofs in coal mines.展开更多
文摘During the propagation of high-power lasers within internal channels,the laser beam heats the propagation medium,causing the thermal blooming effect that degrades the beam quality at the output.The intricate configuration of the optical path within the internal channel necessitates complex and time-consuming efforts to assess the impact of thermal blooming effect on the optical path.To meet the engineering need for rapid evaluation of thermal blooming effect in optical paths,this study proposed a rapid simulation method for the thermal blooming effect in internal optical paths based on the finite element method.This method discretized the fluid region into infinitesimal elements and employed finite element method for flow field analysis.A simplified analytical model of the flow field region in complex internal channels was established,and regions with similar thermal blooming effect were divided within this model.Based on the calculated optical path differences within these regions,numerical simulations of phase distortion caused by thermal blooming were conducted.The calculated result were compared with those obtained using the existing methods.The findings reveal that for complex optical paths,the discrepancy between the two approaches is less than 3.6%,with similar phase distortion patterns observed.For L-type units,this method and the existing methods identify the same primary factors influencing aberrations and exhibit consistent trends in their variation.This method was used to analyze the impact of thermal blooming effect in a straight channel under different gravity directions.The results show that phase distortion varies with changes in the direction of gravity,and the magnitude of the phase difference is strongly correlated with the component of gravity perpendicular to the optical axis.Compared to the existing methods,this approach offers greater flexibility,obviates the need for complex custom analysis programming.The analytical results of this method enable a rapid assessment of the thermal blooming effect in optical paths within the internal channel.This is especially useful during the engineering design.These results also provide crucial references for developing strategies to suppress thermal blooming effect.
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.
文摘The highly selective catalytic hydrogenation of halogenated nitroaromatics was achieved by employing Pd‑based catalysts that were co‑modified with organic and inorganic ligands.It was demonstrated that the catalysts contained Pd species in mixed valence states,with high valence Pd at the metal‑support interface and zero valence Pd at the metal surface.While the strong coordination of triphenylphosphine(PPh3)to Pd0 on the Pd surface prevents the adsorption of halogenated nitroaromatics and thus dehalogenation,the coordination of sodium metavanadate(NaVO3)to high‑valence Pd sites at the interface helps to activate H2 in a heterolytic pathway for the selective hydrogenation of nitro‑groups.The excellent catalytic performance of the interfacial active sites enables the selective hydrogenation of a wide range of halogenated nitroaromatics.
文摘A functional interlayer based on two-dimensional(2D)porous modified vermiculite nanosheets(PVS)was obtained by acid-etching vermiculite nanosheets.The as-obtained 2D porous nanosheets exhibited a high specific surface area of 427 m^(2)·g^(-1)and rich surface active sites,which help restrain polysulfides(LiPSs)through good physi-cal and chemical adsorption,while simultaneously accelerating the nucleation and dissolution kinetics of Li_(2)S,effec-tively suppressing the shuttle effect.The assembled lithium-sulfur batteries(LSBs)employing the PVS-based inter-layer delivered a high initial discharge capacity of 1386 mAh·g^(-1)at 0.1C(167.5 mAh·g^(-1)),long-term cycling stabil-ity,and good rate property.
文摘Thermally activated delayed fluorescence(TADF)molecules have outstanding potential for applications in organic light-emitting diodes(OLEDs).Due to the lack of systematic studies on the correlation between molecular structure and luminescence properties,TADF molecules are far from meeting the needs of practical applications in terms of variety and number.In this paper,three twisted TADF molecules are studied and their photophysical properties are theoretically predicted based on the thermal vibrational correlation function method combined with multiscale calculations.The results show that all the molecules exhibit fast reverse intersystem crossing(RISC)rates(kRISC),predicting their TADF luminescence properties.In addition,the binding of DHPAzSi as the donor unit with different acceptors can change the dihedral angle between the ground and excited states,and the planarity of the acceptors is positively correlated with the reorganization energy,a property that has a strong influence on the non-radiative process.Furthermore,a decrease in the energy of the molecular charge transfer state and an increase in the kRISC were observed in the films.This study not only provides a reliable explanation for the observed experimental results,but also offers valuable insights that can guide the design of future TADF molecules.
基金Project(51975167)supported by the National Natural Science Foundation of China。
文摘In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.
文摘The pressure and temperature increase resulting from the impact of different threats onto target materials is analyzed with a unified laboratory-scale setup.This allows deriving qualitative information on the occurring phenomenology as well as quantitative statements about the relative effects sizes as a function of target material and threat.The considered target materials are steel,aluminum,and magnesium.As threats,kinetic energy penetrator,explosively formed projectile,and shaped charge jet are used.For the investigated combinations,the measured overpressures vary by a factor of up to 5 for a variation of the material,by a factor of up to 7 for a variation of the threat,and by a factor larger than 15for a simultaneous variation of both.The obtained results as well as the experimental approach are relevant for the basic understanding of impact effects and risks due to material reactivity.The paper combines two main aims.Firstly,to provide a summary of own prior work in a coherent journal article and,secondly,to review and discuss these earlier results with a new perspective.
文摘The Hydrodynamic Ram(HRAM)effect occurs when a high kinetic energy projectile penetrates a fluid filled area,e.g.,a liquid filled tank.The projectile transfers its momentum and kinetic energy to the fluid,what causes a sudden,local pressure rise,further expanding as primary shock wave in the fluid and developing a cavity.It is possible that the entire tank ruptures due to the loads transferred through the fluid to its surrounding structure.In the past decades,additionally to experimental investigations,HRAM has been studied using various computational approaches particularly focusing on the description of the Fluid-Structure Interaction(FSI).This article reviews the published experimental,analytical and numerical results and delivers a chronological overview since the end of World War II.Furthermore,HRAM mitigation measures are highlighted,which have been developed with the experimental,analytical and numerical toolboxes matured over the past 80 years.
基金Science and Technology Project of Aerospace Information Research Institute,Chinese Academy of Sciences(Y910340Z2F)Science and Technology Project of BBEF(E3E2010201)。
文摘Low-frequency signals have been proven valuable in the fields of target detection and geological exploration.Nevertheless,the practical implementation of these signals is hindered by large antenna diameters,limiting their potential applications.Therefore,it is imperative to study the creation of lowfrequency signals using antennas with suitable dimensions.In contrast to conventional mechanical antenna techniques,our study generates low-frequency signals in the spatial domain utilizing the principle of the Doppler effect.We also defines the antenna array architecture,the timing sequency,and the radiating element signal waveform,and provides experimental prototypes including 8/64 antennas based on earlier research.In the conducted experiments,121 MHz,40 MHz,and 10 kHz composite signals are generated by 156 MHz radiating element signals.The composite signal spectrum matches the simulations,proving our low-frequency signal generating method works.This holds significant implications for research on generating low-frequency signals with small-sized antennas.
基金Project(51378510) supported by the National Natural Science Foundation of China。
文摘In existing studies, most slope stability analyses concentrate on conditions with constant temperature, assuming the slope is intact, and employ the Mohr-Coulomb (M-C) failure criterion for saturated soil to characterize the strength of the backfill. However, the actual working temperature of slopes varies, and natural phenomena such as rainfall and groundwater infiltration commonly result in unsaturated soil conditions, with cracks typically present in cohesive slopes. This study introduces a novel approach for assessing the stability of unsaturated soil stepped slopes under varying temperatures, incorporating the effects of open and vertical cracks. Utilizing the kinematic approach and gravity increase method, we developed a three-dimensional (3D) rotational wedge failure mechanism to simulate slope collapse, enhancing the traditional two-dimensional analyses. We integrated temperature-dependent functions and nonlinear shear strength equations to evaluate the impact of temperature on four typical unsaturated soil types. A particle swarm optimization algorithm was employed to calculate the safety factor, ensuring our method’s accuracy by comparing it with existing studies. The results indicate that considering 3D effects yields a higher safety factor, while cracks reduce slope stability. Each unsaturated soil exhibits a distinctive temperature response curve, highlighting the importance of understanding soil types in the design phase.
基金Supported by the Humanities and Social Sciences Planning Program of the Ministry of Education(23YJA790027)。
文摘Exploring the effective and efficient path of agricultural carbon emission reduction in Henan Province is of great significance to optimizing the strategic layout of China's agricultural emission reduction and carbon sequestration.Accordingly,the agricultural carbon emissions of each county were measured scientifically and then the spatial measurement model was utilized to clarify the spatial and temporal evolution trend and spatial effect mechanism of agricultural carbon emissions based on the county data of Henan Province from 2010 to 2020.The results showed that:(1)in 2020,the total agricultural carbon emissions were 134.7274 million tons,with the high distribution in the southeast and low distribution in the northwest;(2)the spatial dependence of agricultural carbon emissions showed a four-stage trend of fluctuating down-continuing up-plummeting-fluctuating up again,and the spatial heterogeneity was dominated by low-low agglomeration,followed by high-low agglomeration;(3)there was an inverted U curve relationship between the level of agricultural economic development and agricultural carbon emissions.The increase in the level of agricultural mechanization and urbanization rate significantly reduced agricultural carbon emissions.The opposite was true for the financial support for agriculture,the income level of rural residents and the structure of the agricultural industry;(4)in terms of spatial spillover effects,the increase in the level of agricultural development in neighbor counties first increased and then decreased agricultural carbon emissions in Henan Province.The mechanization level and urbanization rate of neighbor counties reduced agricultural carbon emissions in Henan Province,and the opposite was true for the income level of rural residents and the scale utilization of agricultural land.
基金Project(42277175)supported by the National Natural Science Foundation of ChinaProject(NRMSSHR-2022-Z08)supported by the Key Laboratory of Natural Resources Monitoring and Supervision in Southern Hilly Region,Ministry of Natural Resources,China。
文摘Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsaturated seepage multi-field coupling,resulting in inaccurate estimates.To address these deficiencies,this paper proposed a calculation method for seismic passive earth pressure in unsaturated narrow backfill,based on inclined thin-layer units.It considers the interlayer shear stress,arching effect,and the multi-field coupling of seismic-unsaturated seepage.Additionally,this paper includes a parametric sensitivity analysis.The outcomes indicate that the earthquake passive ground pressure of unsaturated narrow backfill can be reduced by increasing the aspect ratio,seismic acceleration coefficient,and unsaturation parameterα.It can also be reduced by decreasing the effective interior friction angle,soil cohesion,wallearth friction angle,and vertical discharge.Furthermore,for any width soil,lowering the elevation of the action point of passive thrust can be attained by raising the effective interior friction angle,wall-earth friction angle,and unsaturation parameterα.Reducing soil cohesion,seismic acceleration coefficient,and vertical discharge can also lower the height of the application point of passive thrust.
基金the support provided by the Technology Innovation Project (Grant No. KYGYZB002201) for the research work
文摘Investigating the blast effects and mechanisms on typical finite-sized obstacles is essential for optimizing defense strategies and designing more robust barriers to deter terrorists and protect critical locations.This study investigates the blasting effects and underlying mechanisms of concrete frustums subjected to contact explosions,employing both numerical simulations and field tests.It focuses on the effects of top and side blasting,with particular emphasis on fracture modes,damage patterns,and fragment sizes,as well as the causes of different failure modes and the propagation of stress waves.The study also explores the blasting effects of detonating explosives at varying positions along the side and with different charge amounts.The results show that side-blasting leads to complete fragmentation,with tensile waves playing a significant role in creating extensive damage zones that propagate parallel to the frustum's outer surface,concentrating damage near the surface.During top-blasting,the upper half of the frustum undergoes fragmentation,while the lower half experiences cracking.Tensile waves propagate from the top to the bottom surface,forming larger blocks in regions with lower wave intensity.Three distinct damage zones within the frustum were identified,and a series of mathematical formulas were derived to describe the relationship between the maximum fragment size and charge mass.As the charge mass increased from 1.0 kg to 4.0 kg,the maximum fragment size decreased.Detonation at the center of the frustum's side resulted in the most severe fragmentation,with a 51.8%reduction in fragment size compared to other detonation positions.Finally,four broken modes were classified,each influenced by charge mass and explosive location.This study provides valuable insights for optimizing civil blasting operations and designing protective engineering structures.
基金supported by the National Natural Science Foundation of China[Grant Nos.51938011 and 51908405]Australian Research Council。
文摘Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which depicts the shear properties of concrete.The experiments on the EoS of concrete is always challenging due to the technical difficulties and equipment limitations,especially for the specimen size effect on the EoS.Although some researchers investigate the shock properties of concretes by fly-plate impact tests,the specimens used in their tests are usually in one size.In this paper,the fly-plate impact tests on concrete specimens with different sizes are performed to investigate the size effect on the shock properties of concrete materials.The mechanical background of the size effect on the shock properties are revealed,which is related to the lateral rarefaction effect and the deviatoric stress produced in the specimen.According to the tests results,the modified EoS considering the size effect on the shock properties of concrete are proposed,which the bulk modulus of concrete is unpredicted by up to 20% if size effects are not accounted for.
基金the National Natural Science Foundation of China(Grant No.42174047 and No.42174036)the National Science Foundation Project for Outstanding Youth(No.42104034).
文摘This paper realizes the full-domain collaborative deployment of multiple interference sources of the global satellite navigation system(GNSS)and evaluates the deployment effect to enhance the ability to disturb the attacker and the capability to defend the GNSS during navigation countermeasures.Key evaluation indicators for the jamming effect of GNSS suppressive and deceptive jamming sources are first created,their evaluation models are built,and their detection procedures are sorted out,as the basis for determining the deployment principles.The principles for collaboratively deploying multi-jamming sources are developed to obtain the deployment structures(including the required number,structures in demand,and corresponding positions)of three single interference sources required by collaboratively deploying.Accordingly,simulation and hardware-in-loop testing results are presented to determine a rational configuration of the collaborative deployment of multi-jamming sources in the set situation and further realize the full-domain deployment of an interference network from ground,air to space.Varied evaluation indices for the deployment effect are finally developed to evaluate the deployment effect of the proposed configuration and further verify its reliability and rationality.
基金supported by the National Key R&D Program of China(2021YFA1501700)Fundamental Research Funds for the Central Universities(WK9990000142).
文摘The seminal report ofα-diimine palladium and nickel catalysts in 1995 represented a major breakthrough in the preparation of functionalized polyolefin materials.Owing to the high abundance and low cost of nickel,nickel-based catalysts have great application prospects in the industrialization process of olefin coordination polymerization.In this work,various N-aryl substituents with different electronic effects were synthesized and introduced intoα-diimine ligands.The aspreparedα-diimine nickel catalysts showed high polymerization activity(0.9×10^(7)–3.0×10^(7)g·mol^(−1)·h^(−1))in ethylene polymerization,generating polyethylene products with adjustable molecular weights(Mn values:7.4×10^(4)–146.9×10^(4)g·mol^(−1))and branching densities(31/1000 C–68/1000 C).The resulting polyethylene products showed excellent mechanical properties,with high tensile strength(up to 25.0 MPa)and high strain at break values(up to 3890%).The copolymerization of ethylene and polar monomers can also be achieved by these nicekel complexes,ultimately preparing functionalized polyolefins.
基金Supported by the National Key R&D Program of China(2022YFF0707800,2022YFF0707801)Primary Research&Development Plan of Jiangsu Province(BE2022070,BE2022070-2)。
文摘With the analysis of experiment and theory on GaN HEMT devices under DC sweep,an improved model for kink effect based on advanced SPICE model for high electron mobility transistors(ASM-HEMT)is pro⁃posed,considering the relationship between the drain/gate-source voltage and kink effect.The improved model can not only accurately describe the trend of the drain-source current with the current collapse and kink effect,but also precisely fit different values of drain-source voltages at which the kink effect occurs under different gatesource voltages.Furthermore,it well characterizes the DC characteristics of GaN devices in the full operating range,with the fitting error less than 3%.To further verify the accuracy and convergence of the improved model,a load-pull system is built in ADS.The simulated result shows that although both the original ASM-HEMT and the improved model predict the output power for the maximum power matching of GaN devices well,the im⁃proved model predicts the power-added efficiency for the maximum efficiency matching more accurately,with 4%improved.
基金supported by the National Key Research and Development Program of China(2021YFA1500500,2019-YFA0405600)the CAS Project for Young Scientists in Basic Research(YSBR-051)+6 种基金the National Science Fund for Distinguished Young Scholars(21925204)the National Natural Science Foundation of China(22202192,U19A2015,22221003,22250007,22163002)the Collaborative Innovation Program of Hefei Science Center,CAS(2022HSCCIP004)the International Partnership,the DNL Cooperation Fund,CAS(DNL202003)the USTC Research Funds of the Double First-Class Initiative(YD9990002016,YD999000-2014)the Program of Chinese Academy of Sciences(123GJHZ2022101GC)the Fundamental Research Funds for the Central Universities(WK9990000095,WK999000-0124).
文摘Electrocatalytic water splitting provides an efficient method for the production of hydrogen.In electrocatalytic water splitting,the oxygen evolution reaction(OER)involves a kinetically sluggish four-electron transfer process,which limits the efficiency of electrocatalytic water splitting.Therefore,it is urgent to develop highly active OER catalysts to accelerate reaction kinetics.Coupling single atoms and clusters in one system is an innovative approach for developing efficient catalysts that can synergistically optimize the adsorption and configuration of intermediates and improve catalytic activity.However,research in this area is still scarce.Herein,we constructed a heterogeneous single-atom cluster system by anchoring Ir single atoms and Co clusters on the surface of Ni(OH)_(2)nanosheets.Ir single atoms and Co clusters synergistically improved the catalytic activity toward the OER.Specifically,Co_(n)Ir_(1)/Ni(OH)_(2)required an overpotential of 255 mV at a current density of 10 mA·cm^(−2),which was 60 mV and 67 mV lower than those of Co_(n)/Ni(OH)_(2)and Ir1/Ni(OH)_(2),respectively.The turnover frequency of Co_(n)Ir_(1)/Ni(OH)_(2)was 0.49 s^(−1),which was 4.9 times greater than that of Co_(n)/Ni(OH)_(2)at an overpotential of 300 mV.
基金Project(2021YFC2902102)supported by the National Key Research and Development Program of ChinaProject(52374142)supported by the National Natural Science Foundation of ChinaProject(JSTU-2022-066)supported by the Young Talent Support Project of Jiangsu Association for Science and Technology,China。
文摘Roof disaster has always been an important factor restricting coal mine safety production.Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics,which is an effective way to control the hard limestone roof.In this study,the effects of various factors on the reaction characteristics and mechanical properties of limestone were analyzed.The results show that the acid with stronger hydrogen production capacity after ionization(pK_(a)<0)has more prominent damage to the mineral grains of limestone.When pKa increases from−8.00 to 15.70,uniaxial compressive strength and elastic modulus of limestone increase by 117.22%and 75.98%.The influence of acid concentration is manifested in the dissolution behavior of mineral crystals,the crystal defects caused by large-scale acid action will lead to the deterioration of limestone strength,and the strength after 15%concentration reformation can be reduced by 59.42%.The effect of acidification time on limestone has stages and is the most obvious in the initial metathesis reaction stage(within 60 min).The key to the strength damage of acidified limestone is the participation of hydrogen ions in the reaction system.Based on the analytic hierarchy process method,the influence weights of acid type,acid concentration and acidification time on strength are 24.30%,59.54% and 16.16%,respectively.The research results provide theoretical support for the acidification control of hard limestone roofs in coal mines.
