Dominant Mechanism Research Articles

Microstructure and microwave‐absorbing properties of B4C/C composite powders produced by combustion synthesis with an AC foaming agent

AbstractTo develop microwave‐absorbing properties of dielectric ceramics, B4C/C composite powders were prepared by combustion synthesis with B2O3, polyvinyl alcohol, and Mg as the raw materials in this work. The XRD, Raman, scanning electron microscope with energy‐dispersive spectroscopy, and VNA network analysis carried out the effects of the addition of azodicarbonamide (AC) foaming agent on the phase compositions, microstructure, and dielectric and microwave‐absorbing properties of the products. The results indicated that the addition of an AC foaming agent contributed to the formation of distinct morphologies with a larger specific surface area and uniform distribution of the free carbon in the B4C/C composite powders and improved its graphitization degree, which resulted in the formation of equivalent microcapacitors, enhanced interfacial polarization, improved conductive network, and leading to a low reflection loss (RL) and a broadened effective absorb bandwidth (EAB). Due to the dielectric loss as the dominant loss mechanism, C‐1.5 (1.5 wt.% AC foaming agent addition) exhibits the EAB of 3.02 GHz and the minimum RL (RLmin) of −22.90 dB at the thickness of 2.20 mm.

Extracellular Vesicles for Drug Delivery and Theranostics In Vivo.

Extracellular vesicles (EVs) are lipid bilayer-enclosed nanopouches generated by all cells and are abundant in various body fluids. Depending on the parent and recipient cells, EVs exchange diverse constituents including nucleic acids, proteins, carbohydrates, and metabolites. Morphologically, EVs suffer from low zeta potentials and short circulation times, but they also offer low intrinsic immunogenicity and inherent stability. Some crucial factors for the effective clinical application of EVs include controlling immune system clearance, achieving the large-scale production of EVs with efficient quality control, and determining the dominant mechanism of the in vivo action of EVs. In this Perspective, we shed light on how these intriguing nano-objects are utilized in cellular imaging and drug delivery for disease therapeutics. We also discuss potential strategies for overcoming the associated limitations.

Discrete element modeling of rock-filled gabions under successive boulder impacts

A discrete element model consisting of irregular crushable filling particles and a flexible wire mesh is established. The numerical model is validated against the static net punching test and the dynamic pendulum impact test to ensure that the large irreversible plastic deformations and the impact forces during successive impacts can be captured. The impact force reduces at small friction coefficients, which is associated with the significant particle rearrangement during the impact process. The important role of friction is further confirmed by the energy evolution, showing that friction is the dominant mechanism for energy dissipation, instead of the more intuitionistic collision or particle crushing. Besides, the increase of impact force with the number of impacts becomes more significant at a higher impact energy due to the faster rate of momentum exchange. A bounce-back behavior of the boulder is observed when the impact energy is low, which may attenuate the impact force like the reflection waves in real debris flow events where multiple boulders are present. Our results highlight the combined effects of contact properties and impact energy, which are valuable in the design of rigid barriers shielded by rock-filled gabions for hazard mitigation in engineering practice.

Second-scale rotational coherence and dipolar interactions in a gas of ultracold polar molecules

Ultracold polar molecules combine a rich structure of long-lived internal states with access to controllable long-range anisotropic dipole–dipole interactions. In particular, the rotational states of polar molecules confined in optical tweezers or optical lattices may be used to encode interacting qubits for quantum computation or pseudo-spins for simulating quantum magnetism. As with all quantum platforms, the engineering of robust coherent superpositions of states is vital. However, for optically trapped molecules, the coherence time between rotational states is typically limited by inhomogeneous differential light shifts. Here we demonstrate a rotationally magic optical trap for 87Rb133Cs molecules that supports a Ramsey coherence time of 0.78(4) s in the absence of dipole–dipole interactions. This is estimated to extend to >1.4 s at the 95% confidence level using a single spin-echo pulse. In our trap, dipolar interactions become the dominant mechanism by which Ramsey contrast is lost for superpositions that generate oscillating dipoles. By changing the states forming the superposition, we tune the effective dipole moment and show that the coherence time is inversely proportional to the strength of the dipolar interaction. Our work unlocks the full potential of the rotational degree of freedom in molecules for quantum computation and quantum simulation.

Molecular dynamics simulation of deformation behavior of nanocrystal CuNiAlCo medium-entropy alloys

Applying the molecular simulation method, the melting, elastic, and plastic properties of nanocrystal CuNiAlCo medium entropy alloy are investigated in this work. The results show that the melting point in nanocrystal CuNiAlCo is decreased with decreasing crystallite size from 5.0 to 3.1 nm. Compared to the bulk modulus, the crystallite size has a discernible influence on both the shear and Young's modulus. The uniaxial tension calculations suggest that the tensile strength decreases with decreasing crystallite size, and the inverse Hall–Petch relationship is found in nanocrystal CuNiAlCo. The polyhedral template matching analysis illustrates that the FCC constitution of CuNiAlCo gradually decreases with the decrease in crystallite size. When the strain is 30%, the amorphization would occur in uniaxial tension. The atomic structural evolution of CuNiAlCo with the crystallite size of 5.0 nm under the uniaxial strain verifies that the stacking fault reconstruction and amorphization are the dominant plastic deformation mechanism for nanocrystal CuNiAlCo medium entropy alloy. The shockley dislocation plays an essential role in uniaxial tension.

Tuning phase separation in DPPDTT/PMMA blend to achieve molecular self-assembly in the conducting polymer for organic field effect transistors.

The semiconductor/insulator blends for organic field-effect transistors are a potential solution to improve the charge transport in the active layer by inducing phase separation in the blends. However, the technique is less investigated for long-chain conducting polymers such as Poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]thiophene)] (DPPDTT), and lateral phase separation is generally reported due to the instability during solvent evaporation, which results in degraded device performance. Herein, we report how to tailor the dominant mechanism of phase separation in such blends and the molecular assembly of the polymer. For DPPDTT/PMMA blends, we found that for higher DPPDTT concentrations (more than 75%) where the vertical phase separation mechanism is dominant, PMMA assisted in the self-assembly of DPPDTT to form nanowires and micro-transport channels on top of PMMA. The formation of nanowires yielded 13 times higher mobility as compared to pristine devices. For blend ratios with DPPDTT ≤ 50%, both the competing mechanisms, vertical and lateral phase separation, are taking place. It resulted in somewhat lower charge carrier mobilities. Hence, our results show that by systematic tuning of the blend ratio, PMMA can act as an excellent binding material in long-chain polymers such as DPPDTT and produce vertically stratified and aligned structures to ensure high mobility devices.

The Constitutive Equation-Based Recrystallization Mechanism of Ti-6Al-4V Alloy during Superplastic Forming

The present paper is concerned with the dynamic recrystallization of the Ti-6Al-4V alloy. Electron Backscatter Diffraction (EBSD) observations are performed after high-temperatures tensile tests, with the temperature ranging from 700 to ~950 °C, and the strain rates varying between 10−4 and 10−2/s. Based on the analysis of flow behavior, the dominant mechanism is identified, and a mechanism map is proposed. In particular, the conditions of 890 °C and strain rates ranging from 10−3 to ~10−2/s serve as the delineating boundary of dynamic recovery (DRV) and dynamic recrystallization (DRX). For superplastic deformation, the dominant softening mechanism is DRV. Consequently, the occurrence of continuous dynamic recrystallization (CDRX) can naturally be ascribed to the process of grain refinement. Then, a multi-scales physical-based constitutive model of CDRX is developed, demonstrating a good agreement is obtained between the experimental and calculated grain sizes, so the above model could be used to describe the grain growth for superplastic deformation. In conclusion, DRV and DRX in the superplastic forming of Ti-6Al-4V are studied in this study, the condition boundaries of their occurrence are distinguished, and a constitutive equation-based CDRX recrystallization mechanism is given, which might be employed in the fracture mechanism research.

Compressor Tip Leakage Mechanisms

Abstract The over tip leakage flow in an unshrouded compressor blade row is highly three dimensional, yet in order for aerodynamicists to analyze and improve designs, they must be able to simplify the problem down to a limited number of mechanisms. In this article, the behaviors of the dominant loss mechanisms are investigated using a multi-order methodology that combines rapid experimental tests of different geometries, detailed measurements in a large rotating rig, large numbers of industry-standard 3D Reynolds-averaged Navier–Stokes (RANS) simulations, and a single direct numerical simulation (DNS) of the datum geometry. The three loss mechanisms identified are ultimately caused by mismatches in flow velocity: separation of the flow as it enters the gap, mixing of the leakage jet with the mainstream close to the suction surface, and endwall shear acting on the jet itself at mid passage. This article is presented in three sections: First, the loss mechanisms are visualized and examined in detail using experiment, simulation, and models. Second, the uncertainty in industry-standard predictions is analyzed and improvements to turbulence modeling are presented. Finally, a matrix of blades with different 3D designs is used to investigate the balance of loss mechanisms and a reduction in total loss generation.

Strain rate-dependent tensile response and deformation mechanism of laser powder bed fusion 316L stainless steel

The laser powder bed fusion (LPBF) process is renowned for producing metal parts with exceptional mechanical properties, attributed to their unique microstructures. However, there is a lack of discussion in the literature regarding the plastic deformation mechanism at wide strain rates. To address this research gap, this study employs both quasi-static tensile (QST) tests and dynamic Split-Hopkinson tensile bar (SHTB) experiments to investigate the tensile properties and deformation mechanisms of a well-characterized material, 316L stainless steel (SS), across an extensive range of strain rates spanning from 10−3 s−1 to 103 s−1. Our results reveal the superior quasi-static and dynamic stretching behavior exhibited by LPBF specimen in comparison to the wrought 316L counterpart. This enhanced behavior can be primarily attributed to the cellular and hierarchical structures inherent to LPBF specimen. Notably, the cellular structure emerges as the primary controlling factor in mechanical deformation due to its capacity for increasing the critical strain required for deformed twinning and martensite transition. Consequently, under quasi-static loading, twinning and martensite transition act as the dominant deformation mechanism, while dynamic loading conditions are characterized by a prevalence of dislocation interactions. This comprehensive understanding of the deformation mechanism and strain rate-dependent behavior of LPBF 316L SS provides valuable insight for optimizing its mechanical properties under a wide range of loading conditions.

Inheritance Pattern of A1 Cytoplasmic-nuclear Male Sterility System in Commercial Pearl Millet Hybrids [Pennisetum glaucum (L). R. Br.] in Summer and Post-rainy Seasons

Background: This study aimed to understand the genetic aspects and inheritance patterns that control the process of restoring fertility in the context of the A1 system of Cytoplasmic-Nuclear Male Sterility (CMS) in pearl millet. Methods: The experimentation was conducted in commercial pearl millet hybrids, utilizing three F2 populations and three BC1 populations. These populations underwent assessment during the rainy and post-rainy seasons at Rallis India Limited, Hyderabad During the Post-rainy (November-February) and summer (March-June) seasons of 2022-2023. Segregation data derived from observations on pollen shedding and seed set were gathered and subsequently, statistical analysis was performed. The Chi-square (χ2) test was employed to assess the conformity of the observed segregation data to the expected genetic ratios, thus evaluating the goodness of fit. Result: The hybrid combinations MP13P025A ×MP16P050R (MP7171) and MP18P069A × MP20P081R (MP7214) consistently displayed a 3:1 segregation ratio in the F2 generation and a 1:1 ratio in the BC1 generation, regardless of the rainy or post-rainy seasons. However, the cross between MP14030A and MP15P038R (MP7878) showed irregularities in both seasons due to modifiers and environmental factors. These irregularities stemmed from an excess of fertile plants (FF) in the post-rainy season or an excess of sterile plants (FS) in the summer season. These observations provide valuable insights into the genetic dynamics of the A1 Cytoplasmic-Nuclear Male Sterility (CMS) system within commercial pearl millet hybrids. The study indicates that fertility restoration in the A1-based CMS system is strongly influenced by a single Dominant gene control mechanism governing the interplay between male sterility and fertility restoration in these crosses.

Effect of Temperature-Dependent Low Oxygen Partial Pressure Annealing on SiC MOS.

Oxygen post annealing is a promising method for improving the quality of the SiC metal oxide semiconductor (MOS) interface without the introduction of foreign atoms. In addition, a low oxygen partial pressure annealing atmosphere would prevent the additional oxidation of SiC, inhibiting the generation of new defects. This work focuses on the effect and mechanism of low oxygen partial pressure annealing at different temperatures (900-1250 °C) in the SiO2/SiC stack. N2 was used as a protective gas to achieve the low oxygen partial pressure annealing atmosphere. X-ray photoelectron spectroscopy (XPS) characterization was carried out to confirm that there are no N atoms at or near the interface. Based on the reduction in interface trap density (Dit) and border trap density (Nbt), low oxygen partial pressure annealing is proven to be an effective method in improving the interface quality. Vacuum annealing results and time of flight secondary ion mass spectrometry (ToF-SIMS) results reveal that the oxygen vacancy (V[O]) filling near the interface is the dominant annealing mechanism. The V[O] near the interface is filled more by O2 in the annealing atmosphere with the increase in temperature.

Two rest-frame wavelength measurements of galaxy sizes at z < 1: the evolutionary effects of emerging bulges and quenched newcomers

ABSTRACT We analyse the size evolution of 16 000 star-forming galaxies (SFGs) and 5000 quiescent galaxies (QGs) with mass M* > 109.5 M⊙ at 0.1 < z < 0.9 from the COSMOS field using deep CLAUDS + HSC imaging in two rest-frame wavelengths, 3000 Å (UV light) and 5000 Å (visible light). With half-light radius (Re) as proxy for size, SFGs at characteristic mass M0 = 5 × 1010 M⊙ grow by 20 per cent (30 per cent) in UV (visible) light since z ∼ 1 and the strength of their size evolution increases with stellar mass. After accounting for mass growth due to star formation, we estimate that SFGs grow by 75 per cent in all stellar mass bins and in both rest-frame wavelengths. Redder SFGs are more massive, smaller and more concentrated than bluer SFGs and the fraction of red SFGs increases with time. These results point to the emergence of bulges as the dominant mechanism for the average size growth of SFGs. We find two threshold values for the stellar mass density within central 1 kpc (Σ1): all SFGs with log Σ1 ≳ 9 are red and only QGs have log Σ1 ≳ 9.7. The size of M* = M0 QGs grows by 50 per cent (110 per cent) in the UV (visible) light. Up to $\sim 20~{{\rm per\,cent}}$ of this increase in size of massive QGs is due to newcomers (recently quenched galaxies). However, newcomers cannot explain the observed pace in the size growth of QGs; that trend has to be dominated by processes affecting individual galaxies, such as minor mergers and accretion.

Multi-response optimization of M2 steel coatings deposited by co-axial laser cladding on A2 steel tool surfaces

Laser cladding is a highly effective technique used in additive manufacturing to enhance the surface properties of workpieces. It is employed to improve wear resistance, corrosion resistance, and high-temperature resilience of materials. This study explores the utilization of laser cladding technology to repair the surface of AISI A2 tool steel by applying a coating of M2 steel. Sixteen experiments were designed using an orthogonal methodology to investigate the intricate relationship between various processing parameters, including laser power, scan speed, powder feed rate, and overlapping ratio. These parameters were examined in conjunction with key mechanical properties of the coating, such as micro-hardness, friction-wear characteristics, and shear bond strength.Additionally, analytical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) were employed to gain insights into the microstructure of the coatings and elucidate the underlying failure modes. Shear testing of the coatings indicated a tendency towards a brittle fracture mode within the coating, with the dominant wear mechanism involving a combination of abrasive and oxidative wear.Finally, a TOPSIS-Grey Relational Analysis (GRA) method was utilized to identify the optimal process parameters. These optimal parameters were determined to be a laser power of 1200 W, a scan speed of 5 mm/s, a powder feed rate of 14 g/min, and an overlapping ratio of 30 %. Subsequent validation experiments carried out with these parameters demonstrated superior performance compared to the optimal group identified in the orthogonal experiment.

Preparation of a novel magnetic calcium-based biochar for arsenic removal: Behavior and dominant mechanism

Engineered biochar as conventional adsorbents, was typically fabricated by pyrolyzing waste biomass first and then modified with reagents or techniques. In this work, the carbothermal reduction method was employed to produce magnetic calcium-based biochar composites (MCBB) by combusting shrimp shells impregnated with FeCl3 solutions at 800 °C. The adsorption capacity of MCBB3 for As(V) exceeded that of many conventional adsorbents, reaching 119.7 mg/g. The spontaneous and endothermic nature of the As(V) adsorption process by MCBB3 was confirmed, and both the Freundlich model and pseudo-second-order model adequately described the adsorption data. The potential adsorption mechanism was investigated and analyzed according to the results of the characterization. The removal of As(V) was achieved through surface complexation and electrostatic attraction, while the deposition occurred by substituting the hydroxyl group on the MCBB3 surface with Fe and Ca to generate bidentate complexes. Moreover, MCBB3 exhibited exceptional performance in various water matrices, establishing its potential as a promising adsorbent for the remediation of As-containing water in environmental applications. The proposed MCBB adsorbents manufactured via a pyrolysis-loading approach, provide new insights into design facile production.

Metal and dust evolution in ALMA REBELS galaxies: insights for future JWST observations

ABSTRACT Atacama Large Millimeter/submillimeter Array (ALMA) observations revealed the presence of significant amounts of dust in the first Gyr of Cosmic time. However, the metal and dust build-up picture remains very uncertain due to the lack of constraints on metallicity. JWST has started to reveal the metal content of high-redshift targets, which may lead to firmer constraints on high-redshift dusty galaxies evolution. In this work, we use detailed chemical and dust evolution models to explore the evolution of galaxies within the ALMA Reionization Era Bright Emission Line Survey (REBELS) survey, testing different metallicity scenarios that could be inferred from JWST observations. In the models, we track the build-up of stellar mass using non-parametric star formation histories for REBELS galaxies. Different scenarios for metal and dust evolution are simulated by allowing different prescriptions for gas flows and dust processes. The model outputs are compared with measured dust scaling relations, by employing metallicity-dependent calibrations for the gas mass based on the [C ii] 158 μm line. Independently of the galaxies metal content, we found no need for extreme dust prescriptions to explain the dust masses revealed by ALMA. However, different levels of metal enrichment will lead to different dominant dust production mechanisms, with stardust production dominant over other interstellar medium dust processes only in the metal-poor case. This points out how metallicity measurements from JWST will significantly improve our understanding of the dust build-up in high-redshift galaxies. We also show that models struggle to reproduce observables such as dust-to-gas and dust-to-stellar ratios simultaneously, possibly indicating an overestimation of the gas mass through current calibrations, especially at high metallicities.

Performance evolution analysis of solid oxide electrolysis cells operating at high current densities

Hydrogen generation by water electrolysis using solid oxide electrolysis cells (SOECs) is highly promising because of the favorable thermodynamics and kinetics. Commercial applications require SOEC operating at high current densities (ǀiǀ≥1 A·cm−2) to achieve substantial hydrogen production rates. This study demonstrates the operation of a full-size Ni–yttria-stabilized zirconia (Ni–YSZ) cell with an effective area of 16 cm2 at −2 A·cm−2 for 336 h, illustrating the feasibility of operating SOECs at a high current density. The electrochemical characteristics of the SOEC evolved during constant current electrolysis, exhibiting an activation stage with a degradation rate (DR) of 54.6 mV/100 h, followed by a rapid decline process(DR: 180.9 mV/100 h), a gentle decline period (DR: 105.5 mV/100 h), and a stable stage (DR: 11.0 mV/100 h). The contributions of individual processes to cell degradation during each process are identified using the distribution of relaxation times (DRT) and subsequent equivalent circuit model (ECM) fitting. The results suggest that the Ohmic resistance, ionic transport and charge-transfer reaction in the Ni-YSZ fuel electrode contribute the most to performance loss. Ni redistribution is regarded as the dominant degradation mechanism, as verified by detailed post-test characterization.

Coping with disruptive patients: Perspectives of primary care employees.

The impact of patient aggression on primary health care employees is underexplored, yet imperative to address, given high rates of burnout. We qualitatively explore perceptions of patient aggression among staff in women's health primary care at the Veterans Health Administration (VA). Our objective is to identify coping strategies that staf devised in response to aggressive behavior. We conducted semi-structured interviews with 60 VA women's health primary care employees in 2021 and 2022. Informed by the Job Demands-Resources theoretical model, we used rapid qualitative analysis to identify themes related to patient aggression and employee coping strategies. Disruptive behaviors reported by participants included verbal and physical aggression. Staff cited disruptive patient behavior as emotionally draining and perceived a lack of consequences for low-level aggression. Respondents used coping strategies in response to patient aggression at three time points: before, during, and after a negative interaction. At each point, support from team members emerged as a dominant coping mechanism, as well as rapport-building with patients. Patient aggression can negatively impact the work experiences of primary care employees. At VA, women's health primary care staff have devised multiple strategies to cope with these interactions. However, the ability to effectively prevent and manage patient aggression is limited by the lack of meaningful repercussions for aggression at the organizational level, which has important implications for employee well-being and retention. Retention of women's health employees in VA is critical given the need for a highly specialized workforce to address the complex health needs of women veterans.

Direct CO2 capture from simulated and Ambient Air over aminosilane-modified hierarchical silica

Aminosilane-modified Hierarchical silica, HSA and HST-based adsorbents were synthesized by aminosilanization using Hierarchical silica (HS) with 3-aminopropyltriethoxysilane (APS) and N1-(3-trimethoxysilylpropyl)diethylenetriamine (TMPTA), respectively, and characterized to establish their physicochemical, structural, morphological, and porosity properties. Their CO2 adsorption performance was evaluated under direct air capture (DAC) conditions: 1) simulated air with CO2 concentration of 400 ppm in helium (He) at 30 °C and 2) indoor air with CO2 concentration ≥400 ppm at 30 °C, where HSA and HST modified with 70 wt% of respective aminosilanes outperformed others. The modified HS adsorbents showed an increase in kinetics, CO2 uptake under dry and humid conditions, stable cyclic adsorption-desorption performance, moderate enthalpy of desorption indicating a dominant chemisorption mechanism. Under dry and humid simulated air conditions (400 ppm CO2 in He), HSA-70 displayed a CO2 uptake of 0.82 mmol/g and 1.70 mmol/g, respectively, while HST-70 exhibited enhanced CO2 uptake of 1.54 mmol/g and 2.08 mmol/g, respectively. Cyclic stability of HSA-70 and HST-70 was confirmed through five thermal swing adsorption (TSA) cycles. In addition to this, their use for indoor air CO2 capture was also explored through ten short TSA cycles. Developed HSA-70 and HST-70 adsorbents exhibited more selectivity for CO2 over water, demonstrating their usage in practical direct air CO2 capture application.

Artificial humic acid coated ferrihydrite strengthens the adsorption of phosphate and increases soil phosphate retention

Phosphorus (P) leaching loss from farmland soils is one of the main causes of water eutrophication. Thus, effective methods must be developed to maintain sustainability in agricultural soils. Herein, we design artificial humic acid (A-HA) coated ferrihydrite (Fh) particles for fixing P in soil. The experiments in water and soil are successively conducted to explore the phosphate adsorption mechanism and soil P retention performance of A-HA coated ferrihydrite particles (A-Fh). Compared with unmodified ferrihydrite (Fh), the phosphate adsorption capacity of A-Fh is increased by 15 %, the phosphate adsorption speed and selectivity are also significantly improved. The ligand exchange, electrostatic attraction and hydrogen bonding are the dominant mechanisms of phosphate adsorption by A-Fh. In soil experiments, the addition of 2 % A-Fh increases the soil P retention performance from 0.15 to 0.7 mg/kg, and A-Fh are able to convert more phosphate adsorbed by itself into soil available P to improve soil fertility. Overall, this work highlights the importance of this a highly effective amendment for improving poor soils.

Water vapour exchange between the atmospheric boundary layer and free troposphere over eastern China: seasonal characteristics and the El Niño–Southern Oscillation anomaly

Abstract. This study develops a quantitative climatology of water vapour exchange between the atmospheric boundary layer (ABL) and free troposphere (FT) over eastern China. The exchange flux is estimated for January, April, July and October over 7 years based on a water vapour budget equation using simulated meteorological data. The spatiotemporal characteristics and occurrence mechanism of ABL–FT water vapour exchange and its relationship with the El Niño–Southern Oscillation (ENSO) are revealed: (1) the vertical exchange flux varies regionally and seasonally, with downward transport to maintain ABL moisture during winter and autumn in the northern region and persistent output to humidify the FT in the southern region, particularly in summer. Additionally, the vertical exchange flux is also topographic dependent. (2) The vertical motion at the ABL top, which is produced by the dynamic forcing of the terrain on synoptic winds, is the dominant mechanism for the water vapour vertical exchange over the long-term average. The evolution of the vertical exchange flux within 1 d scale is driven by the ABL diurnal cycle. (3) The interannual variation of water vapour vertical exchange is correlated with ENSO. A triple antiphase distribution with negative–positive–negative anomalies from north to south exists in La Niña years (and vice versa in El Niño years), which corresponds to the spatial pattern of anomalous precipitation. This phenomenon is mainly due to the alteration of vertical velocity and water vapour content at the ABL top varying with ENSO phases. These results provide new insight into understanding the atmospheric water cycle.