The transport behavior of pollutants under dynamic groundwater conditions has attracted significant attention recently.However,there is limited research on the simultaneous effects of groundwater table fluctuations on...The transport behavior of pollutants under dynamic groundwater conditions has attracted significant attention recently.However,there is limited research on the simultaneous effects of groundwater table fluctuations on the transport of co-existing pollutants,especially combined dense and light non-aqueous phase liquids(DNAPLs and LNAPLs).In this study,column experiments investigated toluene and dichloromethane transport in a controlled water table system with varying fluctuation conditions.Results showed that both dichloromethane and toluene accumulated near the groundwater table under static water table conditions,but the concentration of dichloromethane declined more rapidly than toluene due to differences in their physicochemical properties,such as solubility,density,and hydrophobicity.Groundwater fluctuations facilitated pollutants transportation towards deeper layers,potentially resulting in unforeseen increases in pollutant volatilization and downward fluxes.The interactions between dichloromethane and toluene,including competitive adsorption,enhanced dissolution,and altered kinematic viscosities,resulted in the reduced transport potential of dichloromethane while enhancing that of toluene.Furthermore,compared to dichloromethane,the initial upward fluctuation of the water table had a more pronounced impact on toluene due to its lower solubility and volatility.The downward transport risk index assessment indicated that among various factors considered,groundwater fluctuation amplitude exerted the most significant influence on pollutant migration risk.These new findings will provide important insights into understanding and assessment of the potential transport risk associated with combined LNAPLs and DNAPLs in the natural environment.展开更多
Thermal fluctuations have been found to significantly influence the dissipation range of turbulence,an effect beyond the scope of the classical Navier-Stokes equations.In this study,we investigate their impact on turb...Thermal fluctuations have been found to significantly influence the dissipation range of turbulence,an effect beyond the scope of the classical Navier-Stokes equations.In this study,we investigate their impact on turbulent channel flow by numerically solving the fluctuating hydrodynamic equations.Simulation results confirm theoretical predictions that the energy spectrum,dominated by thermal fluctuations,follows a k2 power law.When thermal fluctuations reach sufficient intensity,they disrupt the dominant turbulent structures responsible for most of the kinetic energy,leading to a reduction in large-scale spectral energy.Additionally,thermal fluctuations increase wall skin friction by modifying mean velocity profiles.The injected energy amplifies Reynolds normal stresses while maintaining the magnitude of Reynolds shear stress.Furthermore,thermal fluctuations enhance the symmetry and homogeneity of velocity fluctuations while reducing their intermittency.Despite these effects,the balance between kinetic energy production and dissipation,including both turbulent and thermal contributions,remains preserved.展开更多
Quantum dot systems emerge as promising platforms for studying nanoscale thermoelectric effects and quantum fluctuation phenomena.In this work,we investigate the thermodynamic performance of a Coulomb-blockaded quantu...Quantum dot systems emerge as promising platforms for studying nanoscale thermoelectric effects and quantum fluctuation phenomena.In this work,we investigate the thermodynamic performance of a Coulomb-blockaded quantum dot operating as a quantum heat engine using the quantum master equation approach.By incorporating full counting statistics,we analyze both average transport properties and current fluctuations in this nanoscale system.We demonstrate that electron-electron interactions significantly enhance thermoelectric performance by increasing both the output power and energy conversion efficiency.Furthermore,we show that Coulomb interactions suppress current fluctuations while preserving the validity of the thermodynamic uncertainty relation.Our results provide important insights into the interplay between quantum effects and thermodynamic principles in nanoscale heat engines.展开更多
In this paper,we analyze the physical layer security(PLS)performance of a free-space optical(FSO)communication system composed of a transmitting satellite and ground users.Specifically,the FSO fading channels follow t...In this paper,we analyze the physical layer security(PLS)performance of a free-space optical(FSO)communication system composed of a transmitting satellite and ground users.Specifically,the FSO fading channels follow the Málaga distribution.Further,we scrutinize the influence of non-zero boresight pointing errors and angle-of-arrival fluctuations on the PLS performance for the first time.We derived the probability density function and cumulative density function of the FSO link,followed by the closed-form expressions of the secrecy outage probability(SOP)and the probability of strictly positive secrecy capacity(SPSC).The asymptotic SOP expression at the high signal-to-noise ratio regime and diversity order are also provided to reveal the physical mechanism of the PLS of the considered system.Finally,Monte Carlo simulation results are presented to verify the correctness of the analytical expressions.The results afford helpful insights for the future design of satellite FSO communication systems.展开更多
The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and th...The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and the three dimensional unsteady turbulent simulation concerning the rotor-stator interaction is executed by a Navier-Stoke solver embedded with k -ε turbulence model and with appropriate moving interface boundary conditions. Detecting points are distributed in the flow passage in different radial and circumferential positions to capture the static pressure fluctuation character for one cycle of the impeller. The time-domain spectrums show that the static pressure curves are periodic and have five peaks and five valleys. With the radius increasing, the pressure fluctuation peak-to-peak values in the impeller are increasing, and reach the maximum value on the interface. In the casing flow passage, those values are about 7% of local static pressure except some ones near the tongue. The values become decreasingly in the diffuser pipe. The frequency spectrums transformed by fast Fourier transform （FFT） show that the dominant frequency is approximate with the blade passing frequency, and the pressure fluctuations in impeller passage have high frequency content while those in casing ones have no such information.展开更多
The operating performance of positive discharge blower is markedly influenced by the pulsation of the discharge flow, but difficult to be measured with experimental methods. The internal and discharge flow of positive...The operating performance of positive discharge blower is markedly influenced by the pulsation of the discharge flow, but difficult to be measured with experimental methods. The internal and discharge flow of positive discharge blower with involute type three-lobe are numerically investigated, both in air cooling and countercurrent cooling conditions by means of computational fluid dynamics （CFD）. The unsteady compressible flow equations are solved using RNG x-ε turbulent model. The finite difference method and the second order upwind difference scheme are applied into discrete equations. In the numerical simulation, the dynamic mesh techniques are used to approach the rotating displacement of cell cubage and the alterability of inlet, outlet flow area. The non-uniform mesh is applied to the rotor-stator coupled area. The reliability of the numerical method is verified by simulating the inner flow and comparing with the semi-empirical theory. The flow flux curves and the distributing of velocity vector showed obvious vortex motion in all the discharge process, both in air cooling and countercurrent cooling conditions. These vortexes with different positions, intension and numbers at different rotating angles have remarkable influences on the discharge flux. For air cooling, the vortex produced a second pulsation with big-amplitude in a cycle, and led to the early appearance of maximum of backflow. For countercurrent cooling, the frequency of pulsation increased due to the pre-inflow, but the backflow at the outlet is prevented, also the pulsation strength has greatly decreased.展开更多
A three-dimensional transient numerical simulation was conducted to study the pressure fluctuations in low-specific-speed centrifugal pumps. The characteristics of the inner flow were investigated using the SST k-ω t...A three-dimensional transient numerical simulation was conducted to study the pressure fluctuations in low-specific-speed centrifugal pumps. The characteristics of the inner flow were investigated using the SST k-ω turbulence model. The distributions of pressure fluctuations in the impeller and the volute were recorded, and the pressure fluctuation intensity was analyzed comprehensively, at the design condition, using statistical methods. The results show that the pressure fluctuation intensity increases along the impeller streamline from the leading edge to the trailing edge. In the impeller passage, the intensity near the shroud is much higher than that near the hub at thc inlet. However, the intensity at the middle passage is almost equal to the intensity at the outlet. The pressure fluctuation intensity is the highest at the trailing edge on the pressure side and near the tongue because of the rotor-stator interaction. The distribution of pressure fluctuation intensity is symmetrical in the axial cross sections of the volute channel. However, this intensity decreases with increasing radial distance. Hence, the pressure fluctuation intensity can be reduced by modifying the geometry of the leading edge in the impeller and the tongue in the volute.展开更多
Pressure fluctuation due to rotor-stator interaction in turbomachinery is unavoidable,inducing strong vibration in the equipment and shortening its lifecycle.The investigation of optimization methods for an industrial...Pressure fluctuation due to rotor-stator interaction in turbomachinery is unavoidable,inducing strong vibration in the equipment and shortening its lifecycle.The investigation of optimization methods for an industrial centrifugal pump was carried out to reduce the intensity of pressure fluctuation to extend the lifecycle of these devices.Considering the time-consuming transient simulation of unsteady pressure,a novel optimization strategy was proposed by discretizing design variables and genetic algorithm.Four highly related design parameters were chosen,and 40 transient sample cases were generated and simulated using an automatic program.70%of them were used for training the surrogate model,and the others were for verifying the accuracy of the surrogate model.Furthermore,a modified discrete genetic algorithm(MDGA)was proposed to reduce the optimization cost owing to transient numerical simulation.For the benchmark test,the proposed MDGA showed a great advantage over the original genetic algorithm regarding searching speed and effectively dealt with the discrete variables by dramatically increasing the convergence rate.After optimization,the performance and stability of the inline pump were improved.The efficiency increased by more than 2.2%,and the pressure fluctuation intensity decreased by more than 20%under design condition.This research proposed an optimization method for reducing discrete transient characteristics in centrifugal pumps.展开更多
Unsteady fluid flows and level fluctuations in a thin slab continuous casting mould have significant influence on product quality. In this study, the phenomena concerning transient flow features and free surface motio...Unsteady fluid flows and level fluctuations in a thin slab continuous casting mould have significant influence on product quality. In this study, the phenomena concerning transient flow features and free surface motions were analyzed by means of the large eddy simulation （LES） software with the smagorinsky SGS model--VisualCast （VCast） II, where the Simpler algorithm on a body-fitted mesh was used to resolve governing equations. A series of water analog experiments on the fluid flow and the surface wave in the moulds of thin slab continuous casting were also performed. The results of fluid regions, middle of vortex and level fluctuation from digital simulations were identical with the results of the water analog experiments.展开更多
Smoke-wire flow visualization is conducted carefully in a laminar junction to explore the physical behavior of laminar junction flows. The two-dimensional(2 D)velocity fields in the 30?plane of a laminar junction flow...Smoke-wire flow visualization is conducted carefully in a laminar junction to explore the physical behavior of laminar junction flows. The two-dimensional(2 D)velocity fields in the 30?plane of a laminar junction flow are acquired by a time-resolved particle image velocimetry(PIV) system at a frame rate of 1 kHz, based on which the unsteady fluctuating pressure fields can be calculated by the multi-path integration method proposed in the literature(GAND, F., DECK, S., BRUNET,V., and SAGAUT, P. Flow dynamics past a simplified wing body junction. Physics of Fluids, 22(11), 115111(2010)).A novel control strategy is utilized to attenuate the unsteadiness of the horseshoe vortices of the laminar junction flow, and the consequent effect on pressure fields is analyzed.展开更多
Recent advances in two-dimensional layered systems have greatly enriched electronic transport studies, particularly in inter-layer Coulomb drag research. Here, systematic transport measurements were conducted in graph...Recent advances in two-dimensional layered systems have greatly enriched electronic transport studies, particularly in inter-layer Coulomb drag research. Here, systematic transport measurements were conducted in graphene-based electronic double-layer structures, revealing giant yet reproducible drag fluctuations at cryogenic temperatures. These fluctuations' characteristics, including amplitude and peak/valley spacing, are mainly determined by the drag layer's carrier dynamics rather than the drive layer's, resulting in violation of the Onsager reciprocity relation. Notably, the drag fluctuations remain observable up to 35 K, far exceeding universal conductance fluctuations within individual layers. This suggests enhanced phase coherence in inter-layer drag compared to single-layer transport, as further confirmed by quantitative analysis of auto-correlation fields of fluctuations under magnetic fields. Our findings provide new insights into quantum interference effects and their interplay with Coulomb interactions in solids. The observations of significant drag fluctuations could potentially help address chaotic signals between nearby components in nanoscale devices.展开更多
Reference-frame-independent quantum key distribution(RFI-QKD)can avoid real-time calibration operation of reference frames and improve the efficiency of the communication process.However,due to imperfections of optica...Reference-frame-independent quantum key distribution(RFI-QKD)can avoid real-time calibration operation of reference frames and improve the efficiency of the communication process.However,due to imperfections of optical devices,there will inevitably exist intensity fluctuations in the source side of the QKD system,which will affect the final secure key rate.To reduce the influence of intensity fluctuations,an improved 3-intensity RFI-QKD scheme is proposed in this paper.After considering statistical fluctuations and implementing global parameter optimization,we conduct corresponding simulation analysis.The results show that our present work can present both higher key rate and a farther transmission distance than the standard method.展开更多
Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal st...Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal stress level to induce the martensitic transformation and experiences premature failure before the formation of martensite during tensile testing.By utilizing in situ characterization technologies,in this study,we demonstrate that by fabricating a NiTi sample with complete<001>_(B2) texture using wire-fed electron beam directed energy deposition,a sluggish martensitic transformation can be achieved to re-tard the initiation of fracture under tensile loading.To discern the origins of this tensile response,we combine experiments with molecular dynamics simulations to systematically analyze the micro-scale de-tails on how internal lattice defects can select the variety of martensite variants.Using both quasi in situ transmission electron microscopy analysis and calculations of the different atomic configurations,our results indicate that the pre-existing precipitates and accumulated dislocation defects,rather than columnar boundaries,can have a positive influence on the sluggish formation of variants that can cou-ple with plastic deformation within a much wider stress interval.Specifically,only the variant favored by both internal strain/stress fluctuations around local defects and external tensile load will overcome the high-energy transition barrier of<001>_(B2)-oriented tension to nucleate and grow sluggishly.The cur-rent findings not only show how the mechanical responses can be controlled in additively manufactured NiTi alloys with<001>_(B2) texture,but also regard this understanding to be a step forward in decoding the salient underlying mechanisms for the correlating texture,defects,and phase transformation of these functional materials.展开更多
A coalescence model was employed to form deuterons(d),tritons(t),and helium-3(^(3)He)nuclei from a uniformly-distributed volume of protons(p)and neutrons(n).We studied the ratio N_(t)N_(p)/N_(d)^(2)of light nuclei yie...A coalescence model was employed to form deuterons(d),tritons(t),and helium-3(^(3)He)nuclei from a uniformly-distributed volume of protons(p)and neutrons(n).We studied the ratio N_(t)N_(p)/N_(d)^(2)of light nuclei yields as a function of the neutron density fluctuations.We investigated the effect of finite transverse momentum(p_(T))acceptance on the ratio,in particular,the“extrapolation factor”(f)for the ratio as a function of the p_(T)spectral shape and the magnitude of neutron density fluctuations.The nature of f was found to be monotonic in p_(T)spectra“temperature”parameter and neutron density fluctuation magnitude;variations in the latter are relatively small.We also examined f in realistic simulations using the kinematic distributions of protons measured from the heavy-ion collision data.The nature of f was found to be smooth and monotonic as a function of the beam energy.Therefore,we conclude that extrapolation from limited p_(T)ranges does not create,enhance,or reduce the local peak of the N_(t)N_(p)/N_(d)^(2)ratio in the beam energy.Our study provides a necessary benchmark for light nuclei ratios as a probe for nucleon density fluctuations,an important observation in the search for the critical point of nuclear matter.展开更多
The floodplain of the Yellow River is a typical area characterized by redox fluctuations and heavy metal pollution.However,the mobilization behavior of heavy metals in floodplain sediments during redox fluctuations re...The floodplain of the Yellow River is a typical area characterized by redox fluctuations and heavy metal pollution.However,the mobilization behavior of heavy metals in floodplain sediments during redox fluctuations remains poorly understood.In this study,reductive mobilization of Fe and Mn was observed under reducing environments through reduction and dissolution,leading to the subsequent release of adsorbed As.In contrast,the mobilization of U occurred under oxic conditions,as the oxidative state of U(VI)has higher solubility.Furthermore,insignificant effects on the mobilization of Cd,Cu,Pb,and Hg were noticed during redox fluctuations,indicating higher stability of these heavymetals.Additionally,we demonstrated that carbon sources can play a key role in the mobilization of heavy metals in floodplain sediments,amplifying the reductive mobilization of Fe,Mn,As and the oxidative mobilization of U.Our findings contribute to the understanding of the biogeochemical cycling of heavy metal in floodplain sediments of the Yellow River and the factors that control this cycling.展开更多
This study investigated the fluctuations in the relationship between the Silk Road Pattern(SRP)and the boreal summer North Atlantic Oscillation(SNAO).The results indicated that the SRP–SNAO relationship was relativel...This study investigated the fluctuations in the relationship between the Silk Road Pattern(SRP)and the boreal summer North Atlantic Oscillation(SNAO).The results indicated that the SRP–SNAO relationship was relatively weak during 1958–2022,which was primarily due to fluctuations,particularly the reversal in their relationship since the late 1990s.Using wavelet coherence analysis,the authors identified a strong SRP–SNAO linkage on a 4–8-yr timescale,in particular during the mid-1970s to the early/mid-1990s.This strong linkage is mainly attributable to the intensification and eastward movement of the southern part of the SNAO around the mid/late 1970s,which favored the strong connection between the SNAO and the SRP.Additionally,the interdecadal changes of the atmospheric circulations over the North Atlantic and Eurasia around the mid/late 1970s that resembled the circulation anomalies related to the strong SRP–SNAO linkage,may also have provided a favorable background for the strong connection between the two teleconnections.These findings on the fluctuations in the SRP–SNAO linkage may offer important implications for understanding the impact of the SNAO on the SRP and the variability of the SRP.展开更多
Centrifugal pumps are extensively employed in ocean engineering,such as ship power systems,water transportation,and mineral exploitation.Pressure fluctuation suppression is essential for the operation stability and se...Centrifugal pumps are extensively employed in ocean engineering,such as ship power systems,water transportation,and mineral exploitation.Pressure fluctuation suppression is essential for the operation stability and service life of the centrifugal pump.In this paper,a new method of bionic structure is proposed for the blade surface of a centrifugal pump,which is inspired by the fish scale and comprises a leading edge,a trailing edge,and two symmetrical side edges.This fish scale structure is applied to the blade pressure and suction surfaces,and an impeller with a fish scale structure is constructed.A test rig for a centrifugal pump is developed to determine the pressure fluctuation in the pump with a prototype impeller and fish scale structure impeller.Results reveal that the dominant frequency of pressure fluctuation in volute is the blade passing frequency(f_(bpf))of 193.33 Hz,which is triggered by the interaction between the tongue and the impeller.The bionic structure of the fish scale effectively suppresses the pressure fluctuation amplitude at f_(bpf).From flow rates of 0.6 Q_(d)to 1.2 Q_(d),the average suppressions in pressure fluctuation amplitudes at f_(bpf)are 20.98%,5.85%,19.20%,and 25.77%.展开更多
Natural grazing land plays a crucial role in extensive ruminant livestock systems,especially in semi-arid tropical regions such as East Nusa Tenggara(ENT),Indonesia.The availability and quality of forage during the dr...Natural grazing land plays a crucial role in extensive ruminant livestock systems,especially in semi-arid tropical regions such as East Nusa Tenggara(ENT),Indonesia.The availability and quality of forage during the dry season present significant challenges.This study aimed to identify variations in grass species composition and fluctuations in forage nutritional content in natural grazing lands of ENT during the dry season(July–October 2024).Sampling was conducted in four sub-districts:two representing lowland zones and two representing highland zones.In each sub-district,four grazing fields were selected,and ten plots were sampled per grazing field,totaling 160 sampling plots.Species identification and nutrient analysis included crude protein,crude fiber,energy content,and proteinenergy ratio.Statistical analyses using ANOVA and Tukey’s multiple comparison test were performed to evaluate significant differences in nutritional parameters across months and zones.Dominant species identified were Themeda arguens,Heteropogon contortus,Brachiaria decumbens,Ischaemum timorense,Cynodon dactylon,and Pennisetum clandestinum.Results showed significant monthly fluctuations in crude protein and fiber contents(p<0.05),with protein levels decreasing from July(9.31±2.66%)to October(7.53±3.10%).Energy content and protein-energy ratio also varied significantly across the dry season.A monthly shift in dominant grass species composition was observed,influenced by environmental conditions and species adaptability.The protein-energy ratio of forage remained below optimal levels throughout the dry season,potentially limiting livestock productivity.These findings provide important scientific insights for developing climate-resilient feeding strategies and support policy formulation for sustainable tropical livestock farming in semi-arid regions.展开更多
The global supply chain turbulence has increased the difficulty of protecting foreign well-known trademarks.Although there are many studies on cross-border trademark rights protection in academia,there is relatively l...The global supply chain turbulence has increased the difficulty of protecting foreign well-known trademarks.Although there are many studies on cross-border trademark rights protection in academia,there is relatively little research on its risk mitigation effectiveness in the context of supply chain fluctuations.Based on case studies of commercial law and data statistics,the study explores the relationship between protection efficiency and market response through legal applicability.Due to the long litigation cycle and uneven law enforcement,there are differences in market regulation,weakening the protection of well-known trademarks and exacerbating supply chain uncertainty.Strengthening international legal framework cooperation and promoting law enforcement linkage can enhance protection effectiveness.In theory,enriching the theory of cross-border trademark protection and expanding research on brand rights protection in the context of global supply chains.In practice,it helps enterprises adjust their trademark layout,avoid legal risks,and improve market competitiveness.Due to the complexity of the legal environment and limitations in data acquisition,future research will strengthen data analysis,promote international cooperation in intelligent supervision,and build a more efficient cross-border well-known trademark protection mechanism.展开更多
Photovoltaic(PV)systems are being increasingly implemented in the grid,and their intermittent output fluctuations threaten the stability of the grid,thereby requiring effective power ramp control(PRRC)strategies.In th...Photovoltaic(PV)systems are being increasingly implemented in the grid,and their intermittent output fluctuations threaten the stability of the grid,thereby requiring effective power ramp control(PRRC)strategies.In this study,we proposed a power fluctuation identification method to optimize the PRRC strategy.The K-means++cluster based on DTW used in this method,which clusters the historical PV power generation data into power curves corresponding to a specific weather type(sunny,cloudy,and rainy)in a time zone.Subsequently,wavelet decomposition is applied to discretize the power curves with extreme RR overrun to accurately identify the extreme fluctuation time zones.We conducted an analysis using minute-level data from a 100 kW PV plant in Arizona,which demonstrates that the proposed method can effectively identify high-risk periods.Weather patterns within the time zones were quantitatively identified using a weather probability model.A hardware-in-the-loop experimental platform was employed to validate two days of actual power data in Arizona,demonstrating the weather zoning accuracy of the method and the reasonableness of the control.The proposed methodology contributes significantly to PRRC strategy selection and parameter optimization(e.g.,ESS capacity storage allocation and APC power reserveΔP)in different time zones and weather conditions.展开更多
基金supported by the National Key Research and Development Project of China(Nos.2024YFC3713802 and 2023YFC3709700)the Strategic Priority Research Program of the Chinese Academy of Sciences,China(No.XDA23030202)the Science and Technology Program for Foreign Cooperation in Fujian Province of China(No.2022I0040).
文摘The transport behavior of pollutants under dynamic groundwater conditions has attracted significant attention recently.However,there is limited research on the simultaneous effects of groundwater table fluctuations on the transport of co-existing pollutants,especially combined dense and light non-aqueous phase liquids(DNAPLs and LNAPLs).In this study,column experiments investigated toluene and dichloromethane transport in a controlled water table system with varying fluctuation conditions.Results showed that both dichloromethane and toluene accumulated near the groundwater table under static water table conditions,but the concentration of dichloromethane declined more rapidly than toluene due to differences in their physicochemical properties,such as solubility,density,and hydrophobicity.Groundwater fluctuations facilitated pollutants transportation towards deeper layers,potentially resulting in unforeseen increases in pollutant volatilization and downward fluxes.The interactions between dichloromethane and toluene,including competitive adsorption,enhanced dissolution,and altered kinematic viscosities,resulted in the reduced transport potential of dichloromethane while enhancing that of toluene.Furthermore,compared to dichloromethane,the initial upward fluctuation of the water table had a more pronounced impact on toluene due to its lower solubility and volatility.The downward transport risk index assessment indicated that among various factors considered,groundwater fluctuation amplitude exerted the most significant influence on pollutant migration risk.These new findings will provide important insights into understanding and assessment of the potential transport risk associated with combined LNAPLs and DNAPLs in the natural environment.
基金supported by the National Natural Science Foundation of China(Grant Nos.12202437,12172352,and 12388101)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0500300)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.WK2090000086)the Key Laboratory of Cross Domain Flight Interdisciplinary technology(Grant No.2023ZY0101).
文摘Thermal fluctuations have been found to significantly influence the dissipation range of turbulence,an effect beyond the scope of the classical Navier-Stokes equations.In this study,we investigate their impact on turbulent channel flow by numerically solving the fluctuating hydrodynamic equations.Simulation results confirm theoretical predictions that the energy spectrum,dominated by thermal fluctuations,follows a k2 power law.When thermal fluctuations reach sufficient intensity,they disrupt the dominant turbulent structures responsible for most of the kinetic energy,leading to a reduction in large-scale spectral energy.Additionally,thermal fluctuations increase wall skin friction by modifying mean velocity profiles.The injected energy amplifies Reynolds normal stresses while maintaining the magnitude of Reynolds shear stress.Furthermore,thermal fluctuations enhance the symmetry and homogeneity of velocity fluctuations while reducing their intermittency.Despite these effects,the balance between kinetic energy production and dissipation,including both turbulent and thermal contributions,remains preserved.
基金supported by the National Natural Science Foundation of China(Grant No.12305050)the Natural Science Foundation of Jiangsu Higher Education Institutions of China(Grant No.23KJB140017)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ25A050001)。
文摘Quantum dot systems emerge as promising platforms for studying nanoscale thermoelectric effects and quantum fluctuation phenomena.In this work,we investigate the thermodynamic performance of a Coulomb-blockaded quantum dot operating as a quantum heat engine using the quantum master equation approach.By incorporating full counting statistics,we analyze both average transport properties and current fluctuations in this nanoscale system.We demonstrate that electron-electron interactions significantly enhance thermoelectric performance by increasing both the output power and energy conversion efficiency.Furthermore,we show that Coulomb interactions suppress current fluctuations while preserving the validity of the thermodynamic uncertainty relation.Our results provide important insights into the interplay between quantum effects and thermodynamic principles in nanoscale heat engines.
基金National Natural Science Foundation of China(Grant No.62271202,62027802)Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ25F010004)。
文摘In this paper,we analyze the physical layer security(PLS)performance of a free-space optical(FSO)communication system composed of a transmitting satellite and ground users.Specifically,the FSO fading channels follow the Málaga distribution.Further,we scrutinize the influence of non-zero boresight pointing errors and angle-of-arrival fluctuations on the PLS performance for the first time.We derived the probability density function and cumulative density function of the FSO link,followed by the closed-form expressions of the secrecy outage probability(SOP)and the probability of strictly positive secrecy capacity(SPSC).The asymptotic SOP expression at the high signal-to-noise ratio regime and diversity order are also provided to reveal the physical mechanism of the PLS of the considered system.Finally,Monte Carlo simulation results are presented to verify the correctness of the analytical expressions.The results afford helpful insights for the future design of satellite FSO communication systems.
基金supported by National Outstanding Young Scientists Funds of China (Grand No.50825902)
文摘The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and the three dimensional unsteady turbulent simulation concerning the rotor-stator interaction is executed by a Navier-Stoke solver embedded with k -ε turbulence model and with appropriate moving interface boundary conditions. Detecting points are distributed in the flow passage in different radial and circumferential positions to capture the static pressure fluctuation character for one cycle of the impeller. The time-domain spectrums show that the static pressure curves are periodic and have five peaks and five valleys. With the radius increasing, the pressure fluctuation peak-to-peak values in the impeller are increasing, and reach the maximum value on the interface. In the casing flow passage, those values are about 7% of local static pressure except some ones near the tongue. The values become decreasingly in the diffuser pipe. The frequency spectrums transformed by fast Fourier transform （FFT） show that the dominant frequency is approximate with the blade passing frequency, and the pressure fluctuations in impeller passage have high frequency content while those in casing ones have no such information.
基金supported by National Natural Science Foundation of China (Grant No. 10802058)
文摘The operating performance of positive discharge blower is markedly influenced by the pulsation of the discharge flow, but difficult to be measured with experimental methods. The internal and discharge flow of positive discharge blower with involute type three-lobe are numerically investigated, both in air cooling and countercurrent cooling conditions by means of computational fluid dynamics （CFD）. The unsteady compressible flow equations are solved using RNG x-ε turbulent model. The finite difference method and the second order upwind difference scheme are applied into discrete equations. In the numerical simulation, the dynamic mesh techniques are used to approach the rotating displacement of cell cubage and the alterability of inlet, outlet flow area. The non-uniform mesh is applied to the rotor-stator coupled area. The reliability of the numerical method is verified by simulating the inner flow and comparing with the semi-empirical theory. The flow flux curves and the distributing of velocity vector showed obvious vortex motion in all the discharge process, both in air cooling and countercurrent cooling conditions. These vortexes with different positions, intension and numbers at different rotating angles have remarkable influences on the discharge flux. For air cooling, the vortex produced a second pulsation with big-amplitude in a cycle, and led to the early appearance of maximum of backflow. For countercurrent cooling, the frequency of pulsation increased due to the pre-inflow, but the backflow at the outlet is prevented, also the pulsation strength has greatly decreased.
基金Projects(51239005,51009072) supported by the National Natural Science Foundation of ChinaProject(2011BAF14B04) supported by the National Science&Technology Pillar Program of ChinaProject(13JDG084) supported by the Research Foundation for Advanced Talents of Jiansu University,China
文摘A three-dimensional transient numerical simulation was conducted to study the pressure fluctuations in low-specific-speed centrifugal pumps. The characteristics of the inner flow were investigated using the SST k-ω turbulence model. The distributions of pressure fluctuations in the impeller and the volute were recorded, and the pressure fluctuation intensity was analyzed comprehensively, at the design condition, using statistical methods. The results show that the pressure fluctuation intensity increases along the impeller streamline from the leading edge to the trailing edge. In the impeller passage, the intensity near the shroud is much higher than that near the hub at thc inlet. However, the intensity at the middle passage is almost equal to the intensity at the outlet. The pressure fluctuation intensity is the highest at the trailing edge on the pressure side and near the tongue because of the rotor-stator interaction. The distribution of pressure fluctuation intensity is symmetrical in the axial cross sections of the volute channel. However, this intensity decreases with increasing radial distance. Hence, the pressure fluctuation intensity can be reduced by modifying the geometry of the leading edge in the impeller and the tongue in the volute.
基金Supported by National Key Research and Development Program of China(Grant No.2022YFC3202901)Natural Science Foundation of China(Grant No.51879121)+1 种基金Jiangsu Provincial Primary Research&Development Plan(Grant No.BE2019009-1)China Scholarship Council(Grant No.202108690020).
文摘Pressure fluctuation due to rotor-stator interaction in turbomachinery is unavoidable,inducing strong vibration in the equipment and shortening its lifecycle.The investigation of optimization methods for an industrial centrifugal pump was carried out to reduce the intensity of pressure fluctuation to extend the lifecycle of these devices.Considering the time-consuming transient simulation of unsteady pressure,a novel optimization strategy was proposed by discretizing design variables and genetic algorithm.Four highly related design parameters were chosen,and 40 transient sample cases were generated and simulated using an automatic program.70%of them were used for training the surrogate model,and the others were for verifying the accuracy of the surrogate model.Furthermore,a modified discrete genetic algorithm(MDGA)was proposed to reduce the optimization cost owing to transient numerical simulation.For the benchmark test,the proposed MDGA showed a great advantage over the original genetic algorithm regarding searching speed and effectively dealt with the discrete variables by dramatically increasing the convergence rate.After optimization,the performance and stability of the inline pump were improved.The efficiency increased by more than 2.2%,and the pressure fluctuation intensity decreased by more than 20%under design condition.This research proposed an optimization method for reducing discrete transient characteristics in centrifugal pumps.
文摘Unsteady fluid flows and level fluctuations in a thin slab continuous casting mould have significant influence on product quality. In this study, the phenomena concerning transient flow features and free surface motions were analyzed by means of the large eddy simulation （LES） software with the smagorinsky SGS model--VisualCast （VCast） II, where the Simpler algorithm on a body-fitted mesh was used to resolve governing equations. A series of water analog experiments on the fluid flow and the surface wave in the moulds of thin slab continuous casting were also performed. The results of fluid regions, middle of vortex and level fluctuation from digital simulations were identical with the results of the water analog experiments.
基金Project supported by the National Natural Science Foundation of China(Nos.11102188 and 91852101)
文摘Smoke-wire flow visualization is conducted carefully in a laminar junction to explore the physical behavior of laminar junction flows. The two-dimensional(2 D)velocity fields in the 30?plane of a laminar junction flow are acquired by a time-resolved particle image velocimetry(PIV) system at a frame rate of 1 kHz, based on which the unsteady fluctuating pressure fields can be calculated by the multi-path integration method proposed in the literature(GAND, F., DECK, S., BRUNET,V., and SAGAUT, P. Flow dynamics past a simplified wing body junction. Physics of Fluids, 22(11), 115111(2010)).A novel control strategy is utilized to attenuate the unsteadiness of the horseshoe vortices of the laminar junction flow, and the consequent effect on pressure fields is analyzed.
基金supported by the National Natural Science Foundation of China (Grant Nos.12474051 and 92165201)the Chinese Academy of Sciences Project for Young Scientists in Basic Research (Grant No.YSBR-046)+1 种基金the National Key Research and Development Program of China (Grant No.2023YFA1406300)the Anhui Provincial Natural Science Foundation (Grant Nos.2308085J11 and2308085QA14)。
文摘Recent advances in two-dimensional layered systems have greatly enriched electronic transport studies, particularly in inter-layer Coulomb drag research. Here, systematic transport measurements were conducted in graphene-based electronic double-layer structures, revealing giant yet reproducible drag fluctuations at cryogenic temperatures. These fluctuations' characteristics, including amplitude and peak/valley spacing, are mainly determined by the drag layer's carrier dynamics rather than the drive layer's, resulting in violation of the Onsager reciprocity relation. Notably, the drag fluctuations remain observable up to 35 K, far exceeding universal conductance fluctuations within individual layers. This suggests enhanced phase coherence in inter-layer drag compared to single-layer transport, as further confirmed by quantitative analysis of auto-correlation fields of fluctuations under magnetic fields. Our findings provide new insights into quantum interference effects and their interplay with Coulomb interactions in solids. The observations of significant drag fluctuations could potentially help address chaotic signals between nearby components in nanoscale devices.
基金financial support from the Industrial Prospect and Key Core Technology Projects of Jiangsu Provincial Key R&D Program(Grant No.BE2022071)the Natural Science Foundation of Jiangsu Province(Grant No.BK20192001)+1 种基金the National Natural Science Foundation of China(Grant No.12074194)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX220954)。
文摘Reference-frame-independent quantum key distribution(RFI-QKD)can avoid real-time calibration operation of reference frames and improve the efficiency of the communication process.However,due to imperfections of optical devices,there will inevitably exist intensity fluctuations in the source side of the QKD system,which will affect the final secure key rate.To reduce the influence of intensity fluctuations,an improved 3-intensity RFI-QKD scheme is proposed in this paper.After considering statistical fluctuations and implementing global parameter optimization,we conduct corresponding simulation analysis.The results show that our present work can present both higher key rate and a farther transmission distance than the standard method.
基金supported by the National Natural Science Foundation of China(Nos.52101037,52401040 and 52171034)the Postdoctoral Fellowship Program of CPSF(No.GZB20230944)with the computational resources provided by LvLiang Cloud Comput-ing Center.
文摘Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal stress level to induce the martensitic transformation and experiences premature failure before the formation of martensite during tensile testing.By utilizing in situ characterization technologies,in this study,we demonstrate that by fabricating a NiTi sample with complete<001>_(B2) texture using wire-fed electron beam directed energy deposition,a sluggish martensitic transformation can be achieved to re-tard the initiation of fracture under tensile loading.To discern the origins of this tensile response,we combine experiments with molecular dynamics simulations to systematically analyze the micro-scale de-tails on how internal lattice defects can select the variety of martensite variants.Using both quasi in situ transmission electron microscopy analysis and calculations of the different atomic configurations,our results indicate that the pre-existing precipitates and accumulated dislocation defects,rather than columnar boundaries,can have a positive influence on the sluggish formation of variants that can cou-ple with plastic deformation within a much wider stress interval.Specifically,only the variant favored by both internal strain/stress fluctuations around local defects and external tensile load will overcome the high-energy transition barrier of<001>_(B2)-oriented tension to nucleate and grow sluggishly.The cur-rent findings not only show how the mechanical responses can be controlled in additively manufactured NiTi alloys with<001>_(B2) texture,but also regard this understanding to be a step forward in decoding the salient underlying mechanisms for the correlating texture,defects,and phase transformation of these functional materials.
基金supported in part by the U.S.Department of Energy(No.DE-SC0012910)National Nature Science Foundation of China(Nos.12035006 and 12075085)the Ministry of Science and Technology of China(No.2020YFE020200)。
文摘A coalescence model was employed to form deuterons(d),tritons(t),and helium-3(^(3)He)nuclei from a uniformly-distributed volume of protons(p)and neutrons(n).We studied the ratio N_(t)N_(p)/N_(d)^(2)of light nuclei yields as a function of the neutron density fluctuations.We investigated the effect of finite transverse momentum(p_(T))acceptance on the ratio,in particular,the“extrapolation factor”(f)for the ratio as a function of the p_(T)spectral shape and the magnitude of neutron density fluctuations.The nature of f was found to be monotonic in p_(T)spectra“temperature”parameter and neutron density fluctuation magnitude;variations in the latter are relatively small.We also examined f in realistic simulations using the kinematic distributions of protons measured from the heavy-ion collision data.The nature of f was found to be smooth and monotonic as a function of the beam energy.Therefore,we conclude that extrapolation from limited p_(T)ranges does not create,enhance,or reduce the local peak of the N_(t)N_(p)/N_(d)^(2)ratio in the beam energy.Our study provides a necessary benchmark for light nuclei ratios as a probe for nucleon density fluctuations,an important observation in the search for the critical point of nuclear matter.
基金supported by the National Key Research and Development Program of China(No.2022YFC3203604)the National Natural Science Foundation of China(Nos.51808541,and U1904205).
文摘The floodplain of the Yellow River is a typical area characterized by redox fluctuations and heavy metal pollution.However,the mobilization behavior of heavy metals in floodplain sediments during redox fluctuations remains poorly understood.In this study,reductive mobilization of Fe and Mn was observed under reducing environments through reduction and dissolution,leading to the subsequent release of adsorbed As.In contrast,the mobilization of U occurred under oxic conditions,as the oxidative state of U(VI)has higher solubility.Furthermore,insignificant effects on the mobilization of Cd,Cu,Pb,and Hg were noticed during redox fluctuations,indicating higher stability of these heavymetals.Additionally,we demonstrated that carbon sources can play a key role in the mobilization of heavy metals in floodplain sediments,amplifying the reductive mobilization of Fe,Mn,As and the oxidative mobilization of U.Our findings contribute to the understanding of the biogeochemical cycling of heavy metal in floodplain sediments of the Yellow River and the factors that control this cycling.
基金jointly supported by the National Natural Science Foundation of China[grant numbers 41605058 and 41831175]the Joint Open Project of the Key Laboratory of Meteorological Disaster,the Ministry of Education,the Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters,NUIST[grant number KLME202104]。
文摘This study investigated the fluctuations in the relationship between the Silk Road Pattern(SRP)and the boreal summer North Atlantic Oscillation(SNAO).The results indicated that the SRP–SNAO relationship was relatively weak during 1958–2022,which was primarily due to fluctuations,particularly the reversal in their relationship since the late 1990s.Using wavelet coherence analysis,the authors identified a strong SRP–SNAO linkage on a 4–8-yr timescale,in particular during the mid-1970s to the early/mid-1990s.This strong linkage is mainly attributable to the intensification and eastward movement of the southern part of the SNAO around the mid/late 1970s,which favored the strong connection between the SNAO and the SRP.Additionally,the interdecadal changes of the atmospheric circulations over the North Atlantic and Eurasia around the mid/late 1970s that resembled the circulation anomalies related to the strong SRP–SNAO linkage,may also have provided a favorable background for the strong connection between the two teleconnections.These findings on the fluctuations in the SRP–SNAO linkage may offer important implications for understanding the impact of the SNAO on the SRP and the variability of the SRP.
基金supported by the Open Fund of Science and Technology on Thermal Energy and Power Laboratory[TPL2021A02]the State Key Laboratory of Hydroscience and Engineering[sklhse-2023-E-01].
文摘Centrifugal pumps are extensively employed in ocean engineering,such as ship power systems,water transportation,and mineral exploitation.Pressure fluctuation suppression is essential for the operation stability and service life of the centrifugal pump.In this paper,a new method of bionic structure is proposed for the blade surface of a centrifugal pump,which is inspired by the fish scale and comprises a leading edge,a trailing edge,and two symmetrical side edges.This fish scale structure is applied to the blade pressure and suction surfaces,and an impeller with a fish scale structure is constructed.A test rig for a centrifugal pump is developed to determine the pressure fluctuation in the pump with a prototype impeller and fish scale structure impeller.Results reveal that the dominant frequency of pressure fluctuation in volute is the blade passing frequency(f_(bpf))of 193.33 Hz,which is triggered by the interaction between the tongue and the impeller.The bionic structure of the fish scale effectively suppresses the pressure fluctuation amplitude at f_(bpf).From flow rates of 0.6 Q_(d)to 1.2 Q_(d),the average suppressions in pressure fluctuation amplitudes at f_(bpf)are 20.98%,5.85%,19.20%,and 25.77%.
基金supported by the Ministry of Education,Culture,Research,and Technology of the Republic of Indonesia through the Directorate of Research,Technology,and Community Service under the Primary Contract Number:073/E5/PG.02.00.PL/2024 and the Secondary Contract Number:432/UN15.22/SP2H/PL/2024.
文摘Natural grazing land plays a crucial role in extensive ruminant livestock systems,especially in semi-arid tropical regions such as East Nusa Tenggara(ENT),Indonesia.The availability and quality of forage during the dry season present significant challenges.This study aimed to identify variations in grass species composition and fluctuations in forage nutritional content in natural grazing lands of ENT during the dry season(July–October 2024).Sampling was conducted in four sub-districts:two representing lowland zones and two representing highland zones.In each sub-district,four grazing fields were selected,and ten plots were sampled per grazing field,totaling 160 sampling plots.Species identification and nutrient analysis included crude protein,crude fiber,energy content,and proteinenergy ratio.Statistical analyses using ANOVA and Tukey’s multiple comparison test were performed to evaluate significant differences in nutritional parameters across months and zones.Dominant species identified were Themeda arguens,Heteropogon contortus,Brachiaria decumbens,Ischaemum timorense,Cynodon dactylon,and Pennisetum clandestinum.Results showed significant monthly fluctuations in crude protein and fiber contents(p<0.05),with protein levels decreasing from July(9.31±2.66%)to October(7.53±3.10%).Energy content and protein-energy ratio also varied significantly across the dry season.A monthly shift in dominant grass species composition was observed,influenced by environmental conditions and species adaptability.The protein-energy ratio of forage remained below optimal levels throughout the dry season,potentially limiting livestock productivity.These findings provide important scientific insights for developing climate-resilient feeding strategies and support policy formulation for sustainable tropical livestock farming in semi-arid regions.
文摘The global supply chain turbulence has increased the difficulty of protecting foreign well-known trademarks.Although there are many studies on cross-border trademark rights protection in academia,there is relatively little research on its risk mitigation effectiveness in the context of supply chain fluctuations.Based on case studies of commercial law and data statistics,the study explores the relationship between protection efficiency and market response through legal applicability.Due to the long litigation cycle and uneven law enforcement,there are differences in market regulation,weakening the protection of well-known trademarks and exacerbating supply chain uncertainty.Strengthening international legal framework cooperation and promoting law enforcement linkage can enhance protection effectiveness.In theory,enriching the theory of cross-border trademark protection and expanding research on brand rights protection in the context of global supply chains.In practice,it helps enterprises adjust their trademark layout,avoid legal risks,and improve market competitiveness.Due to the complexity of the legal environment and limitations in data acquisition,future research will strengthen data analysis,promote international cooperation in intelligent supervision,and build a more efficient cross-border well-known trademark protection mechanism.
基金supported by the Natural Science Research Project of Jiangsu Higher Education Institutions(23KJB470019)the Natural Science Foundation of Jiangsu Province under Grant BK20240594.
文摘Photovoltaic(PV)systems are being increasingly implemented in the grid,and their intermittent output fluctuations threaten the stability of the grid,thereby requiring effective power ramp control(PRRC)strategies.In this study,we proposed a power fluctuation identification method to optimize the PRRC strategy.The K-means++cluster based on DTW used in this method,which clusters the historical PV power generation data into power curves corresponding to a specific weather type(sunny,cloudy,and rainy)in a time zone.Subsequently,wavelet decomposition is applied to discretize the power curves with extreme RR overrun to accurately identify the extreme fluctuation time zones.We conducted an analysis using minute-level data from a 100 kW PV plant in Arizona,which demonstrates that the proposed method can effectively identify high-risk periods.Weather patterns within the time zones were quantitatively identified using a weather probability model.A hardware-in-the-loop experimental platform was employed to validate two days of actual power data in Arizona,demonstrating the weather zoning accuracy of the method and the reasonableness of the control.The proposed methodology contributes significantly to PRRC strategy selection and parameter optimization(e.g.,ESS capacity storage allocation and APC power reserveΔP)in different time zones and weather conditions.
