Yaokui Cui

Formation and structure of Al-Zr metallic glasses studied by Monte Carlo simulations

Based on the recently constructed n-body potential, both molecular dynamics and Monte Carlo simulations revealed that the Al-Zr amorphous alloy or metallic glass can be obtained within the composition range of 24–66 at. % Zr. The revealed composition range could be considered the intrinsic glass-forming range and it quantitatively indicates the glass-forming ability of the Al-Zr system. The underlying physics of the finding is that, within the composition range, the amorphous alloys are energetically favored to form. In addition, it is proposed that the energy difference between a solid solution and the amorphous phase could serve as the driving force of the crystalline to amorphous transition and the driving force should be sufficiently large for amorphization to take place. The minimum driving forces for fcc Al-based and hcp Zr-based Al-Zr solid solutions to amorphize are calculated to be about −0.05 and −0.03 eV/atom, respectively, whereas the maximum driving force is found to be −0.23 eV/atom at the a...

A comprehensive data set of lake surface water temperature over the Tibetan Plateau derived from MODIS LST products 2001–2015

Lake surface water temperature (LSWT) is sensitive to long-term changes in thermal structure of lakes and regional air temperature. In the context of global climate change, recent studies showed a significant warming trend of LSWT based on investigating 291 lakes (71% are large lakes, ≥50 km2 each) globally. However, further efforts are needed to examine variation in LSWT at finer regional spatial and temporal scales. The Tibetan Plateau (TP), known as ‘the Roof of the World’ and ‘Asia’s water towers’, exerts large influences on and is sensitive to regional and even global climates. Aiming to examine detailed changing patterns and potential driven mechanisms for temperature variations of lakes across the TP region, this paper presents the first comprehensive data set of 15-year (2001–2015) nighttime and daytime LSWT for 374 lakes (≥10 km2 each), using MODIS (Moderate Resolution Imaging Spectroradiometer) Land Surface Temperature (LST) products as well as four lake boundary shapefiles (i.e., 2002, 2005, 2009, and 2014) derived from Landsat/CBERS/GaoFen-1 satellite images. The data set itself reveals significant information on LSWT and its changes over the TP and is an indispensable variable for numerous applications related to climate change, water budget analysis (particularly lake evaporation), water storage changes, glacier melting and permafrost degradation, etc.

Interatomic potential to predict the favored and optimized compositions for ternary Cu-Zr-Hf metallic glasses

Under the framework of smoothed and long range second-moment approximation of tight-binding, a realistic interatomic potential was first constructed for the Cu-Zr-Hf ternary metal system. Applying the constructed potential, Monte Carlo simulations were carried out to compare the relative stability of crystalline solid solution versus its disordered counterpart over the entire composition triangle of the system (as a function of alloy composition). Simulations not only reveal that the origin of metallic glass formation but also determine, in the composition triangle, a quadrilateral region, within which metallic glass formation is energetically favored. It is proposed to define the energy differences between the crystalline solid solutions and disordered states as the driving force for amorphization and the corresponding calculations pinpoint an optimized composition locating at an composition of Cu55Zr10Hf35, around which the driving force for metallic glass formation reaches its maximum, suggesting that ...

Spatiotemporal Dynamics in Vegetation GPP over the Great Khingan Mountains Using GLASS Products from 1982 to 2015

Gross primary productivity (GPP) is an important parameter that represents the productivity of vegetation and responses to various ecological environments. The Greater Khingan Mountain (GKM) is one of the most important state-owned forest bases, and boreal forests, including the largest primeval cold-temperature bright coniferous forest in China, are widely distributed in the GKM. This study aimed to reveal spatiotemporal vegetation variations in the GKM on the basis of GPP products that were generated by the Global LAnd Surface Satellite (GLASS) program from 1982 to 2015. First, we explored the spatiotemporal distribution of vegetation across the GKM. Then we analyzed the relationships between GPP variation and driving factors, including meteorological elements, growing season length (GSL), and Fraction of Photosynthetically Active Radiation (FPAR), to investigate the dominant factor for GPP dynamics. Results demonstrated that (1) the spatial distribution of accumulated GPP (AG) in spring, summer, autumn, and the growing season varied due to three main reasons: understory vegetation, altitude, and land cover; (2) interannual AG in summer, autumn, and the growing season significantly increased at the regional scale during the past 34 years under climate warming and drying; (3) interannual changes of accumulated GPP in the growing season (AGG) at the pixel scale displayed a rapid expansion in areas with a significant increasing trend (p < 0.05) during the period of 1982–2015 and this trend was caused by the natural forest protection project launched in 1998; and finally, (4) an analysis of driving factors showed that daily sunshine duration in summer was the most important factor for GPP in the GKM and this is different from previous studies, which reported that the GSL plays a crucial role in other areas.

Calculation of driving force and local order to predict the favored and optimized compositions for Mg-Cu-Ni metallic glass formation

Based on a newly constructed Mg-Cu-Ni n-body potential, atomistic simulations revealed the underlying mechanism of metallic glass formation is the crystalline lattice collapsing while solute concentration exceeding a critical value, and predicted a quadrilateral region in the composition triangle, energetically favoring the formation of ternary Mg-Cu-Ni metallic glasses. Moreover, an optimized stoichiometry area around Mg60Cu17Ni23 was further located, at which the driving force for transforming the crystalline solid solution into a disordered state, i.e., the glassy phase reaches its maximum. Furthermore, by characterizing the local environments, the frustration of crystallization favorable short-range orders was revealed to be correlated with the optimum glass forming ability (GFA) in Mg-Cu-Ni system, interpreting the structural orgin of GFA and lending further support to the prediction results.

Evaluation of the FY-3B/MWRI soil moisture product on the central Tibetan Plateau

Soil moisture is a key variable in the exchange of water and energy between the land surface and atmosphere, especially over the Tibetan Plateau. The Fengyun-3B Microwave Radiation Imager (FY-3B/MWRI) soil moisture product is one of relatively new passive microwave products. This paper validated the FY-3B/MWRI soil moisture product using in-suit measurements within two soil moisture networks (1°×1° and 0.25°×0.25°) on the central Tibetan Plateau, and compared it with other fourteen products from satellite and land surface models based on published studies. Results showed that the FY-3B/MWRI soil moisture product is comparable with AMSR2, and outperforms LPRM_C, LPRM_X, ASCAT, AMSR-E (NASA), AMSR-E (JAXA), SMOS, and outputs from CLM, Noah, VIC, and Mosaic models. The good performance indicates that the FY-3B/MWRI soil moisture products could be valuable in studying meteorology, hydrology, the environment, agriculture, etc. on the central Tibetan Plateau.

Microchemical inhomogeneity to characterize atomic configurations in the heating and quenching of a CuHf2 alloy

Based on the constructed Cu-Hf interatomic potential, Monte Carlo simulations were conducted to reveal the atomic configurations in heating and quenching of a CuHf(2) alloy through scrutinizing the evolution of microchemical inhomogeneity. Simulations show that the CuHf(2) crystalline structure becomes more homogeneous during heating but an obvious drop in microchemical inhomogeneity appears when reaching its melting point. During the quenching process, the CuHf(2) melt becomes increasingly inhomogeneous and shows a change in the slope in the microchemical inhomogeneity around glass transition temperature. Simulation results were evidenced by the atomic packing analysis through the Voronoi tessellation method. The implications of our study suggest that the glass transition could be visualized as a process involving increase of microchemical inhomogeneity from the liquid to glassy state.

Developing the Remote Sensing-Gash Analytical Model for Estimating Vegetation Rainfall Interception at Very High Resolution: A Case Study in the Heihe River Basin

Accurately quantifying the vegetation rainfall interception at a high resolution is critical for rainfall-runoff modeling and flood forecasting, and is also essential for understanding its further impact on local, regional, and even global water cycle dynamics. In this study, the Remote Sensing-based Gash model (RS-Gash model) is developed based on a modified Gash model for interception loss estimation using remote sensing observations at the regional scale, and has been applied and validated in the upper reach of the Heihe River Basin of China for different types of vegetation. To eliminate the scale error and the effect of mixed pixels, the RS-Gash model is applied at a fine scale of 30 m with the high resolution vegetation area index retrieved by using the unified model of bidirectional reflectance distribution function (BRDF-U) for the vegetation canopy. Field validation shows that the RMSE and R2 of the interception ratio are 3.7% and 0.9, respectively, indicating the model’s strong stability and reliability at fine scale. The temporal variation of vegetation rainfall interception and its relationship with precipitation are further investigated. In summary, the RS-Gash model has demonstrated its effectiveness and reliability in estimating vegetation rainfall interception. When compared to the coarse resolution results, the application of this model at 30-m fine resolution is necessary to resolve the scaling issues as shown in this study.

Coupled patterns between the surface chlorophyll-a and the physical factors in the Pacific Ocean

The ocean bio-physical co-variability and its response to climate change have received increasing attention with the accumulation of satellite ocean data sets. Most of the present studies focus either on regional ocean or short time span, lacking a systemetic study of the co-variability of bio-physical parameters in the Pacific. Based on the satellite datasets and re-analyzed datasets from 1997 to 2012, the co-variability and coupled patterns between the surface chlorophyll-a (CHL) and the physical factors, i.e. sea surface temperature (SST), sea level anomaly (SLA) and sea winds in the Pacific Ocean were studied through the canonical correlation analysis. We found that the bio-physical coupled patterns in the Pacific Ocean were corresponding to the Pacific climate variability patterns, i.e. El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO).