A simulation study was carried out to investigate the temporal evolution of H_(2)S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock an...A simulation study was carried out to investigate the temporal evolution of H_(2)S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock and fluid properties of the Huangcaoxia gas field, a multilayered model was built. The upper layer Jia-2 contains a high concentration of H_(2)S (27.2 g/m^(3)), and the lower layer Jia-1 contains a low concentration of H_(2)S (14.0 mg/m^(3)). There is also a low-permeability interlayer between Jia-1 and Jia-2. The multi-component fluid characterizations for Jia-1 and Jia-2 were implemented separately using the Peng-Robinson equation of state in order to perform the compositional simulation. The H_(2)S concentration gradually increased in a single cycle and peaked at the end of the production season. The peak H_(2)S concentration in each cycle showed a decreasing trend when the recovery factor (RF) of the gas field was lower than 70%. When the RF was above 70%, the peak H_(2)S concentration increased first and then decreased. A higher reservoir RF, a higher maximum working pressure, and a higher working gas ratio will lead to a higher H_(2)S removal efficiency. Similar to developing multi-layered petroleum fields, the operation of multilayered gas storage can also be divided into multi-layer commingled operation and independent operation for different layers. When the two layers are combined to build the storage, the sweet gas produced from Jia-1 can spontaneously mix with the sour gas produced from Jia-2 within the wellbore, which can significantly reduce the overall H_(2)S concentration in the wellstream. When the working gas volume is set constant, the allocation ratio between the two layers has little effect on the H_(2)S removal. After nine cycles, the produced gas’s H_(2)S concentration can be lowered to 20 mg/m^(3). Our study recommends combining the Jia-2 and Jia-1 layers to build the Huangcaoxia underground gas storage. This plan can quickly reduce the H_(2)S concentration of the produced gas to 20 mg/m^(3), thus meeting the gas export standards as well as the HSE (Health, Safety, and Environment) requirements in the field. This study helps the engineers understand the H_(2)S removal for sulfur-containing UGS as well as provides technical guidelines for converting other multilayered sour gas fields into underground storage sites.展开更多
Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity,global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbo...Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity,global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbons is thus of great necessity. Although the best method is still disputable, the acid leaching method is widely used in many laboratories because of its ease-of-use and high accuracy. The results of the elemental analysis of sediment trap samples reveal that organic and inorganic carbon contents cannot be obtained using the acid leaching method, causing an infinitely amplified error when the carbon content of the decarbonated sample is 12%±1% according to a mathematical derivation. Acid fumigation and gasometric methods are used for comparison, which indicates that other methods can avoid this problem in organic carbon analysis. For the first time, this study uncovers the pitfalls of the acid leaching method, which limits the implication in practical laboratory measurement, and recommends alternative solutions of organic/inorganic carbon determination in marine sediments.展开更多
Sediment traps are an important tool for studying the source, composition and sedimentation processes of sinking particulate matter in the ocean. An in situ observational mooring(TJ-A-1) is located in the northern Sou...Sediment traps are an important tool for studying the source, composition and sedimentation processes of sinking particulate matter in the ocean. An in situ observational mooring(TJ-A-1) is located in the northern South China Sea(20.05°N, 117.42°E) at a water depth of 2 100 m and equipped with two sediment traps deployed at 500 m and 1 950 m. Samples were collected at 18-day intervals, and 20 samples were obtained at both depths from May 2014 to May 2015. Large amounts of fecal matter and marine snow were collected in the lower trap. The fluxes of marine snow and fecal pellets exhibited a fluctuating decrease between May 2014 and early August 2014 and then stabilized at a relatively low level. Scanning electron microscopy observations revealed that the main components of the marine snow and fecal pellets were diatoms, coccolithophores, radiolarians, and other debris, all of which are planktons mostly produced in photic zone. Used in conjunction with the particle collection range estimates from the lower trap and data on ocean surface chlorophyll, these marine snow and fecal pellets were related to the lateral transport of deep water and not vertical migrations from overlying water column. Moreover, the source area might be southwest of Taiwan.展开更多
Conventional pressure-transient models have been developed under the assumption of homogeneous reservoir. However, core, log and outcrop data indicate this assumption is not realistic in most cases. But in many cases,...Conventional pressure-transient models have been developed under the assumption of homogeneous reservoir. However, core, log and outcrop data indicate this assumption is not realistic in most cases. But in many cases, the homogeneous models are still applied to obtain an effective permeability corresponding to fictitious homogeneous reservoirs. This approach seems reasonable if the permeability variation is sufficiently small. In this paper, fractal dimension and fractal index are introduced into the seepage flow mechanism to establish the fluid flow models in fractal reservoir under three outer-boundary conditions. Exact dimensionless solutions are obtained by using the Laplace transformation assuming the well is producing at a constant rate. Combining the Stehfest’s inversion with the Vongvuthipornchai’s method, the new type curves are obtained. The sensitivities of the curve shape to fractal dimension (θ) and fractal index (d) are analyzed;the curves don’t change too much when θ is a constant and d change. For a closed reservoir, the up-curving has little to do with θ when d is a constant;but when θ is a constant, the slope of the up-curving section almost remains the same, only the pressure at the starting point decreases with the increase of d;and when d = 2 and θ = 0, the solutions and curves become those of the conventional reservoirs, the application of this solution has also been introduced at the end of this paper.展开更多
Perovskite solar cells(PSCs) are the most promising commercial photoelectric conversion technology in the future.The planar p–i–n structure cells have advantages in negligible hysteresis, low temperature preparation...Perovskite solar cells(PSCs) are the most promising commercial photoelectric conversion technology in the future.The planar p–i–n structure cells have advantages in negligible hysteresis, low temperature preparation and excellent stability.However, for inverted planar PSCs, the non-radiative recombination at the interface is an important reason that impedes the charge transfer and improvement of power conversion efficiency. Having a homogeneous, compact, and energy-levelmatched charge transport layer is the key to reducing non-radiative recombination. In our study, NiO_(x)/Sr:NiO_(x)bilayer hole transport layer(HTL) improves the holes transmission of NiO_(x)based HTL, reduces the recombination in the interface between perovskite and HTL layer and improves the device performance. The bilayer HTL enhances the hole transfer by forming a driving force of an electric field and further improves J_(sc). As a result, the device has a power conversion efficiency of 18.44%, a short circuit current density of 22.81 m A·cm^(-2) and a fill factor of 0.80. Compared to the pristine PSCs, there are certain improvements of optical parameters. This method provides a new idea for the future design of novel hole transport layers and the development of high-performance solar cells.展开更多
Tumor progression is usually characterized by proliferation,migration,and angiogenesis,which is essential for supplying both nutrients and oxygen to the tumor cells.Therefore,targeting angiogenesis has been considered...Tumor progression is usually characterized by proliferation,migration,and angiogenesis,which is essential for supplying both nutrients and oxygen to the tumor cells.Therefore,targeting angiogenesis has been considered a promising therapeutic strategy for cancer prevention and treatment.In the present study,we demonstrated that in addition to suppressing lung cancer cell proliferation and migration in vitro,10-hydroxycamptothecin(10-HCPT)is also capable of inhibiting angiogenesis in vivo with a miR-181a-dependent manner.Mechanistically,by upregulating miR-181a,which in turn downregulating FOXP1,10-HCPT can inhibit the PI3K/Akt/ERK signaling pathwaymediated angiogenesis.Furthermore,reduced levels of miR-181a have been found in both lung cancer cell lines and xenograft with concurrently elevated levels of FOXP1,VEGF,bFGF,and HDGF.Consistent with the findings from the in vitro experiments,miR-181a impairs neovascularization in our xenograft model.In summary,our findings have not only established the anti-oncogenic role of miR-181a in lung cancer angiogenesis but also suggest that 10-HCPT could be a potential therapeutic reagent for lung cancer treatment.展开更多
Introduction:Laiza and nearby areas(LNA)in Myanmar are identified as the primary malaria hotspots in the bordering regions of Yunnan Province,China.Methods:Six sentinel surveillance sites were established at the China...Introduction:Laiza and nearby areas(LNA)in Myanmar are identified as the primary malaria hotspots in the bordering regions of Yunnan Province,China.Methods:Six sentinel surveillance sites were established at the China-Myanmar border in LNA to monitor malaria.Data from 2019 was used as a baseline to analyze malaria incidence and trends in LNA and Myanmar,as well as the importation of malaria cases into China from 2019 to 2023.Results:Plasmodium vivax was the predominant species,representing 99.95%(14,060/14,066)of confirmed malaria cases in LNA.A total of 8,356 malaria cases were identified in 2023,with an annual parasite incidence(API)of 19.78 per 100 person-years.Compared to 2019,the incidence rate ratio was 21.47(95%confidence interval:18.84,24.48),indicating that the API in 2023 was 21.47 times higher than that in 2019.In Yunnan,out of 1,016 reported cases,545 imported cases(53.64%)originated from LNA and spread to 18(13.95%)out of 129 counties.Ten provinces in China,including Yunnan,reported imported malaria cases from LNA in Myanmar.Conclusions:The increase in population,particularly among internally displaced persons,along with inadequate healthcare services,has led to a notable resurgence of malaria in LNA.This resurgence poses a risk to preventing the re-emergence of malaria transmission in China.There is an urgent need for novel collaborative policies,as well as financial and technical assistance,to enhance malaria control efforts in LNA,Myanmar.展开更多
Lead-free bismuth sodium titanate(Bi_(0.5)Na_(0.5))TiO_(3)(BNT)and related solid solutions are potential piezoelectric materials for such applications as actuators and transducers if their excellent strain responses a...Lead-free bismuth sodium titanate(Bi_(0.5)Na_(0.5))TiO_(3)(BNT)and related solid solutions are potential piezoelectric materials for such applications as actuators and transducers if their excellent strain responses and piezoelectric properties can be optimized.In this work,a large strain response of 0.61%is achieved in lead-free(0.94-x%)(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)-x%NaNbO_(3)(x=0 e6,BNT-6BT-xNN)ceramics with the composition of x=3.5 in a pseudo-cubic structure.Coexistence of ferroelectric(FE)and relaxor(RE)domain structures is observed in all the unpoled ceramics and the enhanced strain response is believed to be related to the evolution of the ergodic relaxor(ER)and non-ergodic(NR)states thanks to the substitution of antiferroelectric NN.BNT-6BT-3.5NN is a critical composition near the FE/NR/ER phase boundary close to room temperature(RT)and its high strain response arises from a synergistic combination of a reversible electric-field-induced phase transition and an active domain switching in the mixed NR/ER state.This work provides new insights into the dynamic interplay between mesoscopic domains and macroscopic electrical properties in the BNT-based piezoceramics.展开更多
Lead-free piezoelectric sodium bismuth titanate((Bi0.5Na0.5)TiO3,BNT)thin films were epitaxially grown onto(001)-,(110)-,and(111)-oriented Nb:SrTiO3(STO)single crystal substrates prepared by sol-gel processing.Highly ...Lead-free piezoelectric sodium bismuth titanate((Bi0.5Na0.5)TiO3,BNT)thin films were epitaxially grown onto(001)-,(110)-,and(111)-oriented Nb:SrTiO3(STO)single crystal substrates prepared by sol-gel processing.Highly oriented growth in(001),(110),and(111)BNT thin films was obtained in this work benefiting from the lattice match between the BNT film and the STO substrate.The different growth models in thin films with various orientations result in various surface morphologies dependent on the film orientation.The piezoresponse of the BNT thin films was represented exhibiting a strong orientation dependence that(110)>(001)>(111).This is contributed by the various domain switching contribution related to the crystal symmetry and polarization distribution in the three oriented thin films.展开更多
探索具有优异导电性和稳定性的非贵金属电催化剂对氢经济至关重要.本研究将杂原子掺杂和石墨烯包覆相结合,以控制NiCo_(2)S_(4)(NCS)蛋黄壳微球的电子性能,并抵抗酸性介质中H_(2)O和O_(2)的腐蚀.密度泛函理论(DFT)模拟结合综合表征和实...探索具有优异导电性和稳定性的非贵金属电催化剂对氢经济至关重要.本研究将杂原子掺杂和石墨烯包覆相结合,以控制NiCo_(2)S_(4)(NCS)蛋黄壳微球的电子性能,并抵抗酸性介质中H_(2)O和O_(2)的腐蚀.密度泛函理论(DFT)模拟结合综合表征和实验首次揭示了在NCS中引入P杂原子不仅加速了电子从体相向表面的转移动力学,而且降低了掺杂P原子附近活性S位上的析氢反应势垒.利用DFT计算的穿透能垒预测了rGO覆盖层在P掺杂NCS(P-NCS)表面对质子的渗透性和对H_(2)O和O_(2)分子的抵抗性等重要功能,并用X射线光电子能谱对新催化剂和回收催化剂进行了验证.利用P掺杂剂和rGO覆盖层分别辅助电荷传递和质子传递,通过二者的协同作用获得了催化活性和耐久性之间的平衡.因此,优化后的P-NCS/rGO在70 mV的低过电位下实现了10 mA cm^(-2)的电流密度,并具有令人满意的80小时耐用性.本工作阐明了石墨烯覆盖硫化物催化剂可通过调控电子结构和质子/分子穿透提高电催化性能.展开更多
Magnetron-sputtered MoS_(2) has applications in piezoresistive functional materials research owing to its unique nanostructure.However,the controlled incorporation of sulfur vacancies and realization of en-hanced piez...Magnetron-sputtered MoS_(2) has applications in piezoresistive functional materials research owing to its unique nanostructure.However,the controlled incorporation of sulfur vacancies and realization of en-hanced piezoresistive performance remain significant challenges.In this work,the direct growth of large-area MoS_(2) films with tunable sulfur vacancy concentrations was successfully achieved via magnetron sputtering at various temperatures.Microstructural analysis revealed that the application of strain al-tered the number of conductive channels between the vertical MoS_(2) nanosheets,changing the measured resistance and leading to excellent piezoresistive properties.More importantly,the unsaturated electrons due to the sulfur vacancies increased the in-plane carrier concentration of the MoS_(2)nanosheets.A de-position temperature of 50℃afforded the highest concentrations of sulfur vacancies and carriers.These MoS_(2)films possessed a carrier concentration of 6.58×10^(17)cm^(−3),which was 40.9%higher than that ob-tained at 150°C,and displayed superior piezoresistive performance.The films exhibited high gage factors of 2.66 and 23.22 under tensile and compressive strain of≤0.29%,respectively.These values were 118%and 323%higher,respectively,than those obtained for films deposited at 150°C.This work provides an effective route for modulating and mass producing MoS_(2)-based piezoresistive electronic devices.展开更多
Highly rarefied gas flows through a rough channel of finite length with small bumps appended to its surfaces are investigated,by varying the accommodation coefficientin Maxwell’s diffuse-specular boundary condition,t...Highly rarefied gas flows through a rough channel of finite length with small bumps appended to its surfaces are investigated,by varying the accommodation coefficientin Maxwell’s diffuse-specular boundary condition,the characteristic size and position of the bumps,and the channel length.First,we study the influence of the surface bumps and consider the rarefied gas flow in a unit channel with periodic boundary conditions to remove the end effect.It is found that the surface bumps have a significant impact on the flow permeability.Whenis very small(i.e.,nearly specular reflection of gas molecules at the channel surface),the apparent gas permeability is dramatically reduced,even in the presence of small bumps,to a value that is almost comparable to the one when fully diffuse gas-surface scattering is assumed.This impact can be taken into account through an effective accommodation coefficient,i.e.,the permeability of the rough channel is taken equivalently as that of a smooth channel without bumps but having gas-surface scattering under the effective accommodation coefficient.Second,we study the end effect by connecting a smooth channel of length L_(0) to two huge gas reservoirs.It is found that(i)the end correction length is large at small.Consequently,the mass flow rate barely reduces with increasing L_(0) rather than scales down by a factor of 1/L_(0) as predicted by the classical Knudsen diffusion theory;and(ii)the end correction is related to the channel’s aspect ratio.Finally,based on the effective accommodation coefficient and end correction,we explain the exotic flow enhancement in graphene angstrom-scale channels observed by Geim’s research group(Keerthi et al,Nature 558:420-424,2018).展开更多
Global warming poses a serious threat to crops.Calcium-dependent protein kinases(CDPKs)/CPKs play vital roles in plant stress responses,but their exact roles in plant thermotolerance remains elusive.Here,we explored t...Global warming poses a serious threat to crops.Calcium-dependent protein kinases(CDPKs)/CPKs play vital roles in plant stress responses,but their exact roles in plant thermotolerance remains elusive.Here,we explored the roles of heat-induced ZmCDPK7 in thermotolerance in maize.ZmCDPK7-overexpressing maize plants displayed higher thermotolerance,photosynthetic rates,and antioxidant enzyme activity but lower H2 O2 and malondialdehyde(MDA)contents than wild-type plants under heat stress.ZmCDPK7-knockdown plants displayed the opposite patterns.ZmCDPK7 is attached to the plasma membrane but can translocate to the cytosol under heat stress.ZmCDPK7 interacts with the small heat shock protein sHSP17.4,phosphorylates sHSP17.4 at Ser-44 and the respiratory burst oxidase homolog RBOHB at Ser-99,and up regulates their expression.Site-directed mutagenesis of sHSP17.4 to generate a Ser-44-Ala substitution reduced ZmCDPK7’s enhancement of catalase activity but enhanced ZmCDPK7’s suppression of MDA accumulation in heat-stressed maize protoplasts.sHSP17.4,ZmCDPK7,and RBOHB were less strongly upregulated in response to heat stress in the abscisic acid-deficient mutant vp5 versus the wild type.Pretreatment with an RBOH inhibitor suppressed sHSP17.4 and ZmCDPK7 expression.Therefore,abscisic acid-induced ZmCDPK7 functions both upstream and downstream of RBOH and participates in thermotolerance in maize by mediating the phosphorylation of sHSP17.4,which might be essential for its chaperone function.展开更多
The temporal and spatial evolution of a deep-reaching anticyclonic eddy(AE) is studied using a combination of satellite measurements, moored observations and ocean model reanalysis data in the South China Sea(SCS). Th...The temporal and spatial evolution of a deep-reaching anticyclonic eddy(AE) is studied using a combination of satellite measurements, moored observations and ocean model reanalysis data in the South China Sea(SCS). Three evolutionary stages in eddy's lifecycle are identified from changes in eddy dynamical characteristics estimated from satellite altimetry: birth(22 days), growth(64 days), and decay(47 days). Similar patterns are also distinguished from dynamic signals in HYCOM.Further, flows reversal and upwelling of cold water below 1500 m were captured by the in-situ records when this energetic,highly nonlinear and long-lived(over 19 weeks) AE passed by our mooring position. Its detailed vertical structure is examined through temperature anomalies, vertical shear of horizontal velocities, and horizontal streamlines estimated from ocean model reanalysis data. Results from the model reveal a mesoscale AE with first-mode baroclinic structure: a bowl-shaped anticyclonic flow in the upper ocean connected to a slant-cylinder cyclonic flow at depth, with a transition layer at depths between 400 and 700 m. It is in good agreement with moored observations but showing a shallower transition depth, suggesting a slight deficiency in the model due to limited deep-sea observations. Last, we estimate eddy heat transport at different depths and stages along the AE's path based on the model data. The result reveals that pronounced heat fluxes occur during growth stage(depths <400 m),counting for 73.03% of the total value. In the decay stage, major heat transport occurs at deeper depth(depths >700–1500 m).Dynamical characteristics suggest that the vertical structure and temporal evolution of the eddy play significant roles in basinscale movement and heat transferring. Considering that mesoscale eddies are ubiquitous in the SCS, our results support a recently-proposed mechanism, whereby upper ocean flows produce changes in the deep-sea circulation, potentially influencing boundary layer dynamics. For the first time to track and link an individual AE observed by satellite altimetry and ocean model,comparisons indicate that assimilative HYCOM outputs may be useful for examining the deep ocean properties within the SCS,especially under the impact of such an intensified surface-detected eddy.展开更多
Tides are the major energy source for ocean mixing, regulating the variation of oceanic circulation and sediment transport in the deep sea. Here twenty months of high-resolution current profiles, which were observed v...Tides are the major energy source for ocean mixing, regulating the variation of oceanic circulation and sediment transport in the deep sea. Here twenty months of high-resolution current profiles, which were observed via a mooring system at a water depth of 2100 m in the northern South China Sea(SCS), are used to investigate seasonal variability in deep-sea tides.Spectral analysis shows that tides in this region are dominated by diurnal tide, and both diurnal and semidiurnal tide are vertical mode-1 dominant. Baroclinic diurnal tidal current exhibits pronounced seasonal variability, showing its kinetic energy was the strongest in summer, and the maximum depth-averaged value was up to 86.7 cm^2 s^(-2), which was about 1.5 times of that in winter and twice that in spring and autumn. In contrast, baroclinic semidiurnal tide displays no evident seasonal variability. Such seasonal variability in baroclinic tide was mainly modulated by the barotropic forcing from the Luzon Strait. On the other hand,two anticyclonic eddies and one cyclonic eddy, which originated off southwestern Taiwan in winter, crossed the mooring system.The cyclonic eddy had weak impact on current velocity in the deep sea, but the two deep-reaching anticyclonic eddies enhanced the current velocity through the full-water column by inducing strong subinertial flows. Consequently, the kinetic energy of tides was strengthened and the incoherent variance of baroclinic diurnal tide increased in winter, which contributed ~85% of the variability in diurnal tide. Meanwhile, the velocity of baroclinic diurnal tide was reduced in winter, which was attributed to the weakened stratification induced by the passage of anticyclonic eddies in the deep sea. The seasonal variability of tides in the deep northern SCS can provide a dynamic mechanism for interpreting sediment transport processes in the deep sea on different time scales.展开更多
The inner shelf mud wedge of the East China Sea(ECS) is a high-sedimentation-rate fine-grained sediment unit that has preserved a continuous environmental evolution history since the last deglaciation. We present a hi...The inner shelf mud wedge of the East China Sea(ECS) is a high-sedimentation-rate fine-grained sediment unit that has preserved a continuous environmental evolution history since the last deglaciation. We present a high-resolution clay mineralogical study from Core MD06-3040 to semi-quantitatively evaluate terrigenous sediment contributions from various potential provenances throughout the Holocene. The results showed that the clay mineral assemblage is composed of dominant illite(34–49%), moderate smectite(16–41%) and chlorite(15–28%), and minor kaolinite(5–12%). Provenance analysis suggested that most fine-grained terrigenous sediments originated from the Yangtze River, with minor sediments derived from Taiwan island and negligible sediments from nearby Zhejiang and Fujian provinces. Time series variation in the contribution of the Yangtze source fluctuated in the range of 38–80%, whereas that of Taiwan island had a converse variation pattern from ~10%to ~55%, and the contribution of Fujian was relatively stable in the range of 7–11% throughout the Holocene. The fluctuations of clay mineral assemblages and variations of clay mineral contributions from different provenances of Core MD06-3040 were controlled by the variability of precipitation in the Yangtze drainage associated with periodic fluctuations in the East Asian monsoonal circulation.展开更多
Abstract A novel micro-electromechanical systems piezoresistive pressure sensor with a diagonally positioned peninsula-island structure has high sensitivity for ultra- low-pressure measurement. The pressure sensor was...Abstract A novel micro-electromechanical systems piezoresistive pressure sensor with a diagonally positioned peninsula-island structure has high sensitivity for ultra- low-pressure measurement. The pressure sensor was designed with a working range of 0-500 Pa and had a high sensitivity of 0.06 mV-V^-1-Pa-1. The trade-off between high sensitivity and linearity was alleviated. Moreover, the influence of the installation angle on the sensing chip output was analyzed, and an application experiment of the sensor was conducted using the built pipettor test platform. Findings indicated that the proposed pressure sensor had sufficient resolution ability and accuracy to detect the pressure variation in the pipettor chamber. Therefore, the proposed pressure sensor has strong potential for medical equipment application.展开更多
The influence of temperature on the inverse Hall-Petch effect in nanocrystalline (NC) materials is investigated using phase field crystal simulation method. Simulated results indicate that the inverse Hall-Petch eff...The influence of temperature on the inverse Hall-Petch effect in nanocrystalline (NC) materials is investigated using phase field crystal simulation method. Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature. The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect. At elevated temperature, grain rotation and grain boundary (GB) migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect. However, at low temperature, both grain rotation and GB migration occur with great difficulty, instead, the dislocations nucleated from the cusp of serrated GBs become active. The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect. Furthermore, it is found that since small grain size is favorable for GB migration, the degree of weakening decreases with decreasing average grain size at low temperature.展开更多
基金supported by the China Postdoctoral Science Foundation(2022M722637)as well as the Natural Science Foundation of Sichuan Province(2022NSFSC0190).
文摘A simulation study was carried out to investigate the temporal evolution of H_(2)S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock and fluid properties of the Huangcaoxia gas field, a multilayered model was built. The upper layer Jia-2 contains a high concentration of H_(2)S (27.2 g/m^(3)), and the lower layer Jia-1 contains a low concentration of H_(2)S (14.0 mg/m^(3)). There is also a low-permeability interlayer between Jia-1 and Jia-2. The multi-component fluid characterizations for Jia-1 and Jia-2 were implemented separately using the Peng-Robinson equation of state in order to perform the compositional simulation. The H_(2)S concentration gradually increased in a single cycle and peaked at the end of the production season. The peak H_(2)S concentration in each cycle showed a decreasing trend when the recovery factor (RF) of the gas field was lower than 70%. When the RF was above 70%, the peak H_(2)S concentration increased first and then decreased. A higher reservoir RF, a higher maximum working pressure, and a higher working gas ratio will lead to a higher H_(2)S removal efficiency. Similar to developing multi-layered petroleum fields, the operation of multilayered gas storage can also be divided into multi-layer commingled operation and independent operation for different layers. When the two layers are combined to build the storage, the sweet gas produced from Jia-1 can spontaneously mix with the sour gas produced from Jia-2 within the wellbore, which can significantly reduce the overall H_(2)S concentration in the wellstream. When the working gas volume is set constant, the allocation ratio between the two layers has little effect on the H_(2)S removal. After nine cycles, the produced gas’s H_(2)S concentration can be lowered to 20 mg/m^(3). Our study recommends combining the Jia-2 and Jia-1 layers to build the Huangcaoxia underground gas storage. This plan can quickly reduce the H_(2)S concentration of the produced gas to 20 mg/m^(3), thus meeting the gas export standards as well as the HSE (Health, Safety, and Environment) requirements in the field. This study helps the engineers understand the H_(2)S removal for sulfur-containing UGS as well as provides technical guidelines for converting other multilayered sour gas fields into underground storage sites.
基金The National Natural Science Foundation of China under contract Nos 41530964,41776047,41876048 and 91528304。
文摘Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity,global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbons is thus of great necessity. Although the best method is still disputable, the acid leaching method is widely used in many laboratories because of its ease-of-use and high accuracy. The results of the elemental analysis of sediment trap samples reveal that organic and inorganic carbon contents cannot be obtained using the acid leaching method, causing an infinitely amplified error when the carbon content of the decarbonated sample is 12%±1% according to a mathematical derivation. Acid fumigation and gasometric methods are used for comparison, which indicates that other methods can avoid this problem in organic carbon analysis. For the first time, this study uncovers the pitfalls of the acid leaching method, which limits the implication in practical laboratory measurement, and recommends alternative solutions of organic/inorganic carbon determination in marine sediments.
基金The National Natural Science Foundation of China under contract Nos 91528304 and 41376043.
文摘Sediment traps are an important tool for studying the source, composition and sedimentation processes of sinking particulate matter in the ocean. An in situ observational mooring(TJ-A-1) is located in the northern South China Sea(20.05°N, 117.42°E) at a water depth of 2 100 m and equipped with two sediment traps deployed at 500 m and 1 950 m. Samples were collected at 18-day intervals, and 20 samples were obtained at both depths from May 2014 to May 2015. Large amounts of fecal matter and marine snow were collected in the lower trap. The fluxes of marine snow and fecal pellets exhibited a fluctuating decrease between May 2014 and early August 2014 and then stabilized at a relatively low level. Scanning electron microscopy observations revealed that the main components of the marine snow and fecal pellets were diatoms, coccolithophores, radiolarians, and other debris, all of which are planktons mostly produced in photic zone. Used in conjunction with the particle collection range estimates from the lower trap and data on ocean surface chlorophyll, these marine snow and fecal pellets were related to the lateral transport of deep water and not vertical migrations from overlying water column. Moreover, the source area might be southwest of Taiwan.
文摘Conventional pressure-transient models have been developed under the assumption of homogeneous reservoir. However, core, log and outcrop data indicate this assumption is not realistic in most cases. But in many cases, the homogeneous models are still applied to obtain an effective permeability corresponding to fictitious homogeneous reservoirs. This approach seems reasonable if the permeability variation is sufficiently small. In this paper, fractal dimension and fractal index are introduced into the seepage flow mechanism to establish the fluid flow models in fractal reservoir under three outer-boundary conditions. Exact dimensionless solutions are obtained by using the Laplace transformation assuming the well is producing at a constant rate. Combining the Stehfest’s inversion with the Vongvuthipornchai’s method, the new type curves are obtained. The sensitivities of the curve shape to fractal dimension (θ) and fractal index (d) are analyzed;the curves don’t change too much when θ is a constant and d change. For a closed reservoir, the up-curving has little to do with θ when d is a constant;but when θ is a constant, the slope of the up-curving section almost remains the same, only the pressure at the starting point decreases with the increase of d;and when d = 2 and θ = 0, the solutions and curves become those of the conventional reservoirs, the application of this solution has also been introduced at the end of this paper.
基金supported by the Fundamental Research Funds for the Central Universities, China (Grant No. 2021QN1110)。
文摘Perovskite solar cells(PSCs) are the most promising commercial photoelectric conversion technology in the future.The planar p–i–n structure cells have advantages in negligible hysteresis, low temperature preparation and excellent stability.However, for inverted planar PSCs, the non-radiative recombination at the interface is an important reason that impedes the charge transfer and improvement of power conversion efficiency. Having a homogeneous, compact, and energy-levelmatched charge transport layer is the key to reducing non-radiative recombination. In our study, NiO_(x)/Sr:NiO_(x)bilayer hole transport layer(HTL) improves the holes transmission of NiO_(x)based HTL, reduces the recombination in the interface between perovskite and HTL layer and improves the device performance. The bilayer HTL enhances the hole transfer by forming a driving force of an electric field and further improves J_(sc). As a result, the device has a power conversion efficiency of 18.44%, a short circuit current density of 22.81 m A·cm^(-2) and a fill factor of 0.80. Compared to the pristine PSCs, there are certain improvements of optical parameters. This method provides a new idea for the future design of novel hole transport layers and the development of high-performance solar cells.
基金supported by the National Natural Science Foundation of China(Nos.81702296,81772281)the Shandong Science and Technology Committee(Nos.2017GSF18124,ZR2019PC019,ZR2019MH022)+1 种基金the Health Commission of Shandong Province(Nos.2017WS737,2019KJK014)the Shandong Province Taishan Scholar Project(No.ts201712067).
文摘Tumor progression is usually characterized by proliferation,migration,and angiogenesis,which is essential for supplying both nutrients and oxygen to the tumor cells.Therefore,targeting angiogenesis has been considered a promising therapeutic strategy for cancer prevention and treatment.In the present study,we demonstrated that in addition to suppressing lung cancer cell proliferation and migration in vitro,10-hydroxycamptothecin(10-HCPT)is also capable of inhibiting angiogenesis in vivo with a miR-181a-dependent manner.Mechanistically,by upregulating miR-181a,which in turn downregulating FOXP1,10-HCPT can inhibit the PI3K/Akt/ERK signaling pathwaymediated angiogenesis.Furthermore,reduced levels of miR-181a have been found in both lung cancer cell lines and xenograft with concurrently elevated levels of FOXP1,VEGF,bFGF,and HDGF.Consistent with the findings from the in vitro experiments,miR-181a impairs neovascularization in our xenograft model.In summary,our findings have not only established the anti-oncogenic role of miR-181a in lung cancer angiogenesis but also suggest that 10-HCPT could be a potential therapeutic reagent for lung cancer treatment.
基金Supported by the National Key Research and Development Program of China(2020YFC1200105).
文摘Introduction:Laiza and nearby areas(LNA)in Myanmar are identified as the primary malaria hotspots in the bordering regions of Yunnan Province,China.Methods:Six sentinel surveillance sites were established at the China-Myanmar border in LNA to monitor malaria.Data from 2019 was used as a baseline to analyze malaria incidence and trends in LNA and Myanmar,as well as the importation of malaria cases into China from 2019 to 2023.Results:Plasmodium vivax was the predominant species,representing 99.95%(14,060/14,066)of confirmed malaria cases in LNA.A total of 8,356 malaria cases were identified in 2023,with an annual parasite incidence(API)of 19.78 per 100 person-years.Compared to 2019,the incidence rate ratio was 21.47(95%confidence interval:18.84,24.48),indicating that the API in 2023 was 21.47 times higher than that in 2019.In Yunnan,out of 1,016 reported cases,545 imported cases(53.64%)originated from LNA and spread to 18(13.95%)out of 129 counties.Ten provinces in China,including Yunnan,reported imported malaria cases from LNA in Myanmar.Conclusions:The increase in population,particularly among internally displaced persons,along with inadequate healthcare services,has led to a notable resurgence of malaria in LNA.This resurgence poses a risk to preventing the re-emergence of malaria transmission in China.There is an urgent need for novel collaborative policies,as well as financial and technical assistance,to enhance malaria control efforts in LNA,Myanmar.
基金supported by the Natural Science Foundation of China(Grant No.51902246,12161141012,and 12174299)the China National Key R&D Program(Grant No.2021YFB3201800 and 2020YFC0122100)+5 种基金the Natural Science Fundamental Research Project of Shaanxi Province of China(No.2019JQ590)the Key R&D Program of Shaanxi Province of China(2020GY-271)the Fundamental Research Funds for the Central Universities(xzd012020059)the“111 Project”of China(B14040)the Natural Sciences&Engineering Research Council of Canada(NSERC,Discovery Grant No.RGPIN-2017-06915)Xijiang Innovation Team Introduction Program of Zhaoqing(Jiecheng).
文摘Lead-free bismuth sodium titanate(Bi_(0.5)Na_(0.5))TiO_(3)(BNT)and related solid solutions are potential piezoelectric materials for such applications as actuators and transducers if their excellent strain responses and piezoelectric properties can be optimized.In this work,a large strain response of 0.61%is achieved in lead-free(0.94-x%)(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)-x%NaNbO_(3)(x=0 e6,BNT-6BT-xNN)ceramics with the composition of x=3.5 in a pseudo-cubic structure.Coexistence of ferroelectric(FE)and relaxor(RE)domain structures is observed in all the unpoled ceramics and the enhanced strain response is believed to be related to the evolution of the ergodic relaxor(ER)and non-ergodic(NR)states thanks to the substitution of antiferroelectric NN.BNT-6BT-3.5NN is a critical composition near the FE/NR/ER phase boundary close to room temperature(RT)and its high strain response arises from a synergistic combination of a reversible electric-field-induced phase transition and an active domain switching in the mixed NR/ER state.This work provides new insights into the dynamic interplay between mesoscopic domains and macroscopic electrical properties in the BNT-based piezoceramics.
基金supported by the Natural Science Foundation of China(Grant No.51902246)the Natural Science Fundamental Research Project of Shaanxi Province of China(No.2019JQ590)the Fundamental Research Funds for the Central Universities,and the“111 Project”of China(B14040).
文摘Lead-free piezoelectric sodium bismuth titanate((Bi0.5Na0.5)TiO3,BNT)thin films were epitaxially grown onto(001)-,(110)-,and(111)-oriented Nb:SrTiO3(STO)single crystal substrates prepared by sol-gel processing.Highly oriented growth in(001),(110),and(111)BNT thin films was obtained in this work benefiting from the lattice match between the BNT film and the STO substrate.The different growth models in thin films with various orientations result in various surface morphologies dependent on the film orientation.The piezoresponse of the BNT thin films was represented exhibiting a strong orientation dependence that(110)>(001)>(111).This is contributed by the various domain switching contribution related to the crystal symmetry and polarization distribution in the three oriented thin films.
基金supported by the National Key R&D Program of China(2021YFA1501900)the National Natural Science Foundation of China-Yunnan Joint Fund(U2102215)+4 种基金the National Natural Science Foundation of China(22209203)China Postdoctoral Science Foundation(2021M693419)Jiangsu Key Laboratory of Coal-based Greenhouse Gas Control and Utilization(PCSX202202)the Material Science and Engineering Discipline Guidance Fund of China University of Mining and Technology(CUMTMS202202 and CUMTMS202207)the Open Sharing Fund for the Large-scale Instruments and Equipment of China University of Mining and Technology。
文摘探索具有优异导电性和稳定性的非贵金属电催化剂对氢经济至关重要.本研究将杂原子掺杂和石墨烯包覆相结合,以控制NiCo_(2)S_(4)(NCS)蛋黄壳微球的电子性能,并抵抗酸性介质中H_(2)O和O_(2)的腐蚀.密度泛函理论(DFT)模拟结合综合表征和实验首次揭示了在NCS中引入P杂原子不仅加速了电子从体相向表面的转移动力学,而且降低了掺杂P原子附近活性S位上的析氢反应势垒.利用DFT计算的穿透能垒预测了rGO覆盖层在P掺杂NCS(P-NCS)表面对质子的渗透性和对H_(2)O和O_(2)分子的抵抗性等重要功能,并用X射线光电子能谱对新催化剂和回收催化剂进行了验证.利用P掺杂剂和rGO覆盖层分别辅助电荷传递和质子传递,通过二者的协同作用获得了催化活性和耐久性之间的平衡.因此,优化后的P-NCS/rGO在70 mV的低过电位下实现了10 mA cm^(-2)的电流密度,并具有令人满意的80小时耐用性.本工作阐明了石墨烯覆盖硫化物催化剂可通过调控电子结构和质子/分子穿透提高电催化性能.
基金supported by the National Natural Science Foundation of China(No.U20A201293)the Ningbo Ma-jor Special Project“Science and Technology Innovation 2025”(No.2020Z023),and the National Key Research and Development Pro-gram(No.2021YFB3201100).
文摘Magnetron-sputtered MoS_(2) has applications in piezoresistive functional materials research owing to its unique nanostructure.However,the controlled incorporation of sulfur vacancies and realization of en-hanced piezoresistive performance remain significant challenges.In this work,the direct growth of large-area MoS_(2) films with tunable sulfur vacancy concentrations was successfully achieved via magnetron sputtering at various temperatures.Microstructural analysis revealed that the application of strain al-tered the number of conductive channels between the vertical MoS_(2) nanosheets,changing the measured resistance and leading to excellent piezoresistive properties.More importantly,the unsaturated electrons due to the sulfur vacancies increased the in-plane carrier concentration of the MoS_(2)nanosheets.A de-position temperature of 50℃afforded the highest concentrations of sulfur vacancies and carriers.These MoS_(2)films possessed a carrier concentration of 6.58×10^(17)cm^(−3),which was 40.9%higher than that ob-tained at 150°C,and displayed superior piezoresistive performance.The films exhibited high gage factors of 2.66 and 23.22 under tensile and compressive strain of≤0.29%,respectively.These values were 118%and 323%higher,respectively,than those obtained for films deposited at 150°C.This work provides an effective route for modulating and mass producing MoS_(2)-based piezoresistive electronic devices.
基金the National Natural Science Foundation of China(No.52222402,No.52074235).
文摘Highly rarefied gas flows through a rough channel of finite length with small bumps appended to its surfaces are investigated,by varying the accommodation coefficientin Maxwell’s diffuse-specular boundary condition,the characteristic size and position of the bumps,and the channel length.First,we study the influence of the surface bumps and consider the rarefied gas flow in a unit channel with periodic boundary conditions to remove the end effect.It is found that the surface bumps have a significant impact on the flow permeability.Whenis very small(i.e.,nearly specular reflection of gas molecules at the channel surface),the apparent gas permeability is dramatically reduced,even in the presence of small bumps,to a value that is almost comparable to the one when fully diffuse gas-surface scattering is assumed.This impact can be taken into account through an effective accommodation coefficient,i.e.,the permeability of the rough channel is taken equivalently as that of a smooth channel without bumps but having gas-surface scattering under the effective accommodation coefficient.Second,we study the end effect by connecting a smooth channel of length L_(0) to two huge gas reservoirs.It is found that(i)the end correction length is large at small.Consequently,the mass flow rate barely reduces with increasing L_(0) rather than scales down by a factor of 1/L_(0) as predicted by the classical Knudsen diffusion theory;and(ii)the end correction is related to the channel’s aspect ratio.Finally,based on the effective accommodation coefficient and end correction,we explain the exotic flow enhancement in graphene angstrom-scale channels observed by Geim’s research group(Keerthi et al,Nature 558:420-424,2018).
基金supported by the National Natural Science Foundation of Henan Joint Fund(U1604101 to XLH)the Key R&D and Promotion Projects of Henan Province(192102110009 to XLH,192102110004 to HY)。
文摘Global warming poses a serious threat to crops.Calcium-dependent protein kinases(CDPKs)/CPKs play vital roles in plant stress responses,but their exact roles in plant thermotolerance remains elusive.Here,we explored the roles of heat-induced ZmCDPK7 in thermotolerance in maize.ZmCDPK7-overexpressing maize plants displayed higher thermotolerance,photosynthetic rates,and antioxidant enzyme activity but lower H2 O2 and malondialdehyde(MDA)contents than wild-type plants under heat stress.ZmCDPK7-knockdown plants displayed the opposite patterns.ZmCDPK7 is attached to the plasma membrane but can translocate to the cytosol under heat stress.ZmCDPK7 interacts with the small heat shock protein sHSP17.4,phosphorylates sHSP17.4 at Ser-44 and the respiratory burst oxidase homolog RBOHB at Ser-99,and up regulates their expression.Site-directed mutagenesis of sHSP17.4 to generate a Ser-44-Ala substitution reduced ZmCDPK7’s enhancement of catalase activity but enhanced ZmCDPK7’s suppression of MDA accumulation in heat-stressed maize protoplasts.sHSP17.4,ZmCDPK7,and RBOHB were less strongly upregulated in response to heat stress in the abscisic acid-deficient mutant vp5 versus the wild type.Pretreatment with an RBOH inhibitor suppressed sHSP17.4 and ZmCDPK7 expression.Therefore,abscisic acid-induced ZmCDPK7 functions both upstream and downstream of RBOH and participates in thermotolerance in maize by mediating the phosphorylation of sHSP17.4,which might be essential for its chaperone function.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91128206, 41576005, 91528304 & 41530964)
文摘The temporal and spatial evolution of a deep-reaching anticyclonic eddy(AE) is studied using a combination of satellite measurements, moored observations and ocean model reanalysis data in the South China Sea(SCS). Three evolutionary stages in eddy's lifecycle are identified from changes in eddy dynamical characteristics estimated from satellite altimetry: birth(22 days), growth(64 days), and decay(47 days). Similar patterns are also distinguished from dynamic signals in HYCOM.Further, flows reversal and upwelling of cold water below 1500 m were captured by the in-situ records when this energetic,highly nonlinear and long-lived(over 19 weeks) AE passed by our mooring position. Its detailed vertical structure is examined through temperature anomalies, vertical shear of horizontal velocities, and horizontal streamlines estimated from ocean model reanalysis data. Results from the model reveal a mesoscale AE with first-mode baroclinic structure: a bowl-shaped anticyclonic flow in the upper ocean connected to a slant-cylinder cyclonic flow at depth, with a transition layer at depths between 400 and 700 m. It is in good agreement with moored observations but showing a shallower transition depth, suggesting a slight deficiency in the model due to limited deep-sea observations. Last, we estimate eddy heat transport at different depths and stages along the AE's path based on the model data. The result reveals that pronounced heat fluxes occur during growth stage(depths <400 m),counting for 73.03% of the total value. In the decay stage, major heat transport occurs at deeper depth(depths >700–1500 m).Dynamical characteristics suggest that the vertical structure and temporal evolution of the eddy play significant roles in basinscale movement and heat transferring. Considering that mesoscale eddies are ubiquitous in the SCS, our results support a recently-proposed mechanism, whereby upper ocean flows produce changes in the deep-sea circulation, potentially influencing boundary layer dynamics. For the first time to track and link an individual AE observed by satellite altimetry and ocean model,comparisons indicate that assimilative HYCOM outputs may be useful for examining the deep ocean properties within the SCS,especially under the impact of such an intensified surface-detected eddy.
基金supported by the National Natural Science Foundation of China(Grant Nos.41576005,91528304&41876048)
文摘Tides are the major energy source for ocean mixing, regulating the variation of oceanic circulation and sediment transport in the deep sea. Here twenty months of high-resolution current profiles, which were observed via a mooring system at a water depth of 2100 m in the northern South China Sea(SCS), are used to investigate seasonal variability in deep-sea tides.Spectral analysis shows that tides in this region are dominated by diurnal tide, and both diurnal and semidiurnal tide are vertical mode-1 dominant. Baroclinic diurnal tidal current exhibits pronounced seasonal variability, showing its kinetic energy was the strongest in summer, and the maximum depth-averaged value was up to 86.7 cm^2 s^(-2), which was about 1.5 times of that in winter and twice that in spring and autumn. In contrast, baroclinic semidiurnal tide displays no evident seasonal variability. Such seasonal variability in baroclinic tide was mainly modulated by the barotropic forcing from the Luzon Strait. On the other hand,two anticyclonic eddies and one cyclonic eddy, which originated off southwestern Taiwan in winter, crossed the mooring system.The cyclonic eddy had weak impact on current velocity in the deep sea, but the two deep-reaching anticyclonic eddies enhanced the current velocity through the full-water column by inducing strong subinertial flows. Consequently, the kinetic energy of tides was strengthened and the incoherent variance of baroclinic diurnal tide increased in winter, which contributed ~85% of the variability in diurnal tide. Meanwhile, the velocity of baroclinic diurnal tide was reduced in winter, which was attributed to the weakened stratification induced by the passage of anticyclonic eddies in the deep sea. The seasonal variability of tides in the deep northern SCS can provide a dynamic mechanism for interpreting sediment transport processes in the deep sea on different time scales.
基金supported by the National Natural Science Foundation of China (Grant Nos. 91528304, 41530964 & 41676028)
文摘The inner shelf mud wedge of the East China Sea(ECS) is a high-sedimentation-rate fine-grained sediment unit that has preserved a continuous environmental evolution history since the last deglaciation. We present a high-resolution clay mineralogical study from Core MD06-3040 to semi-quantitatively evaluate terrigenous sediment contributions from various potential provenances throughout the Holocene. The results showed that the clay mineral assemblage is composed of dominant illite(34–49%), moderate smectite(16–41%) and chlorite(15–28%), and minor kaolinite(5–12%). Provenance analysis suggested that most fine-grained terrigenous sediments originated from the Yangtze River, with minor sediments derived from Taiwan island and negligible sediments from nearby Zhejiang and Fujian provinces. Time series variation in the contribution of the Yangtze source fluctuated in the range of 38–80%, whereas that of Taiwan island had a converse variation pattern from ~10%to ~55%, and the contribution of Fujian was relatively stable in the range of 7–11% throughout the Holocene. The fluctuations of clay mineral assemblages and variations of clay mineral contributions from different provenances of Core MD06-3040 were controlled by the variability of precipitation in the Yangtze drainage associated with periodic fluctuations in the East Asian monsoonal circulation.
文摘Abstract A novel micro-electromechanical systems piezoresistive pressure sensor with a diagonally positioned peninsula-island structure has high sensitivity for ultra- low-pressure measurement. The pressure sensor was designed with a working range of 0-500 Pa and had a high sensitivity of 0.06 mV-V^-1-Pa-1. The trade-off between high sensitivity and linearity was alleviated. Moreover, the influence of the installation angle on the sensing chip output was analyzed, and an application experiment of the sensor was conducted using the built pipettor test platform. Findings indicated that the proposed pressure sensor had sufficient resolution ability and accuracy to detect the pressure variation in the pipettor chamber. Therefore, the proposed pressure sensor has strong potential for medical equipment application.
基金financially supported by the National Natural Science Foundation of China(Nos.51174168 and 51274167)Northwestern Polytechnical University Foundation for Fundamental Research(No.NPU-FFR-JC20120222)
文摘The influence of temperature on the inverse Hall-Petch effect in nanocrystalline (NC) materials is investigated using phase field crystal simulation method. Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature. The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect. At elevated temperature, grain rotation and grain boundary (GB) migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect. However, at low temperature, both grain rotation and GB migration occur with great difficulty, instead, the dislocations nucleated from the cusp of serrated GBs become active. The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect. Furthermore, it is found that since small grain size is favorable for GB migration, the degree of weakening decreases with decreasing average grain size at low temperature.