A hybrid parallel cellular automata model for urban growth simulation over GPU/CPU heterogeneous architectures

As an important spatiotemporal simulation approach and an effective tool for developing and examining spatial optimization strategies (e.g., land allocation and planning), geospatial cellular automata (CA) models often require multiple data layers and consist of complicated algorithms in order to deal with the complex dynamic processes of interest and the intricate relationships and interactions between the processes and their driving factors. Also, massive amount of data may be used in CA simulations as high-resolution geospatial and non-spatial data are widely available. Thus, geospatial CA models can be both computationally intensive and data intensive, demanding extensive length of computing time and vast memory space. Based on a hybrid parallelism that combines processes with discrete memory and threads with global memory, we developed a parallel geospatial CA model for urban growth simulation over the heterogeneous computer architecture composed of multiple central processing units (CPUs) and graphics processing units (GPUs). Experiments with the datasets of California showed that the overall computing time for a 50-year simulation dropped from 13,647 seconds on a single CPU to 32 seconds using 64 GPU/CPU nodes. We conclude that the hybrid parallelism of geospatial CA over the emerging heterogeneous computer architectures provides scalable solutions to enabling complex simulations and optimizations with massive amount of data that were previously infeasible, sometimes impossible, using individual computing approaches.     

2020年“1·24”广西大范围冰雹天气过程分析

2020年1月24-25日,广西出现近20年来范围最大的一次冰雹天气过程。利用常规观测资料、雷达、卫星以及再分析资料,对此次天气过程进行分析和诊断。结果表明:(1)500hPa宽槽、高空急流、低层切变、地面冷锋以及辐合线相配合提供有利环流背景,异常偏冷的中层导致大温度直减率,大气不稳定增强;(2)深层强垂直风切变、热力不稳定层结以及适宜的0℃、-20℃层高度为冰雹产生提供适宜的热动力条件;(3)对流云团呈“长椭圆”型,具有造成区域性冰雹天气的典型特征,雷达回波图上的回波悬垂结构、超过60dBz的强反射率因子、VIL跃增、持久深厚中气旋以及高层辐散低层辐合等特征,对于冰雹天气的识别和预警具有指示意义。     

Seismic hazard assessment of northern Pakistan

This article presents probabilistic seismic hazard analyses of northern Pakistan region carried out to produce macro-seismic hazard maps for the region that define new regional ground motion design parameters for 95-, 475-, 975- and 2475-year return period earthquakes as regional contour maps and horizontal uniform hazard at important cities. The Cornell–McGuire approach (Cornell in Bull Seismol Soc Am 58(05):1583–1606, 1968; McGuire in FORTRAN computer program for seismic risk analysis. US Geological Survey, Open file Report, 76-6768, 1976) is used to carry out the analyses at 0.1° rectangular grid. The seismotectonic model of the region used in analysis consists of shallow and deep area zones differentiated based on the focal depths of the earthquakes. Earthquake catalogue compiled and used in the analysis is a composite catalogue composed of 19,373 events. Ground motion prediction equations (GMPEs) used are calibrated using goodness-of-fitness measures and visual inspection with local strong motion data. Epistemic uncertainty in the GMPEs is taken into account through the logic tree approach. Comparison of ground motions due to deep earthquakes is made for the first time for the region. The comparison between ground motion due to shallow and deep earthquakes indicates that the seismic hazard would be underestimated if the deep earthquakes are excluded. Ground motion values obtained in this study considering all the earthquakes suggest ground motions are dominant towards the north east of the region. The proposed study indicates that the ground motion hazard values suggested by the current Building Code of Pakistan underestimate the seismic hazard. Final results of this study are in close agreement with the recent studies on the region.     

Study on the freezing temperature of saline soil

Freezing temperature is an important parameter in studying the freezing mechanism of saline soil. An equation for calculating the freezing temperature is proposed based on the phase transition theory in porous medium, including two main influencing factors, the water activity and pore size. In this equation, the effect of the water activity on the freezing temperature of soil is calculated by Pitzer model, while the impact of pore size is replaced by water content. Through comparing the calculated results with the published experimental data, the equation is proved to be competent in predicting the freezing temperature for the saline soil with sodium chloride or calcium chloride. For the saline soil with sodium carbonate, the effect of salt hydrate crystallization should be taken into consideration. With respect to the saline soil with sodium sulfate, it is difficult to determine the freezing temperature, since there is uncertainty of the resultant when freezing (that is, heptahydrate or decahydrate). In addition, the effects of pore size and multi-component solutes on freezing temperature are also discussed. The study would be helpful for revealing the freezing mechanism and also providing a useful theoretical method for engineering design of saline soil in cold regions.     

The influence of fractionation of REE-enriched minerals on the zircon partition coefficients

Zircon is widely used to simulate melt generation, migration and evolution within the crust and mantle.The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients(D).However, a large range of D_(REE)values for zircon from natural samples and experimental studies has been reported, with values spanning up to 3 orders of magnitude.Unfortunately, a gap of knowledge on this variability is evident.In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon D_(REE)would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon.Nevertheless, compared to zircon D_(REE)values measured from experimental studies, this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon.Combined with recently published studies, this work supports that analysis of natural zircon/host groundmass pairs provides more robust D_(REE)values applicable to natural systems than those measured from experimental studies, which can be used to constrain the provenance of detrital zircons.     

Effect of waste rubber particles on the shear behaviour of bio-cemented calcareous sand

Calcareous sand, a special type of sand commonly used for the construction of coastal engineering in tropical coasts, is usually required to be strengthened due to its poor engineering mechanical properties. Microbially induced carbonate precipitation has been proved to be a promising method for this purpose. A higher cementation level generally leads to a greater strength enhancement, but tends to cause brittle failure of bio-cemented calcareous sand, which in turn brings great potential risks for the coastal engineering. Therefore, the shear behaviour, especially the brittle behaviour, of bio-cemented calcareous sand needs to be understood properly, and taking some measures to improve its brittle behaviour is also necessary. In this regard, a series of triaxial compression tests were conducted to study the shear behaviour of bio-cemented calcareous sand with various cementation levels, and the waste rubber particles are used to improve the brittle behaviour of bio-cemented calcareous sand. The test results show that the shear strength of bio-cemented calcareous sand increases with the increase in cementation level, and the brittle behaviour is significant gradually. The waste rubber particles contribute to improve the brittle behaviour of bio-cemented calcareous sand, reducing the dilation of bio-cemented calcareous sand and slowing the changes in dilatancy with the increment of stress.

     

Ground shaking scenarios at the town of Vicoforte,Italy

Vicoforte is a small town in Northern Italy, which hosts a Cathedral with the world's largest elliptical dome. The name of the Basilica is “Regina Montis Regalis” and it is of extraordinary architectural and structural importance. The main objective of this study is the definition of the seismic hazard at the site of Vicoforte following a deterministic approach. Although Vicoforte is located in an area of moderate seismicity, the calculation of the most unfavourable seismic ground shaking scenarios is of great interest due to the importance of the Basilica and its vulnerability to even a moderate seismic excitation.The closest active faults to Vicoforte were identified in order to simulate the potentially most severe ground shaking scenarios compatibly with the tectonic and seismic setting of the region. Subsequently, numerical simulations were conducted through finite faults numerical models using two different approaches: the extended kinematic source model of Hisada and Bielak [24] and the stochastic method of Motazedian and Atkinson [38]. They, respectively, simulate the low and high frequency ranges of predicted ground motion. The numerical models used for the simulations were calibrated by a comparison between synthetic results and recorded data. A parametric study was finally carried out to identify the most critical fault rupture mechanisms.     

Magma mixing origin for the post-collisional adakitic monzogranite of the Triassic Yangba pluton, Northwestern margin of the South China block: geochemistry, Sr–Nd isotopic, zircon U–Pb dating and Hf isotopic evidences

Petrogenesis of high Mg# adakitic rocks in intracontinental settings is still a matter of debate. This paper reports major and trace element, whole-rock Sr–Nd isotope, zircon U–Pb and Hf isotope data for a suite of adakitic monzogranite and its mafic microgranular enclaves (MMEs) at Yangba in the northwestern margin of the South China Block. These geochemical data suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived from subcontinental lithospheric mantle (SCLM) may account for the origin of high Mg# adakitic rocks in the intracontinental setting. The host monzogranite and MMEs from the Yangba pluton have zircon U–Pb ages of 207 ± 2 and 208 ± 2 Ma, respectively. The MMEs show igneous textures and contain abundant acicular apatite that suggests quenching process. Their trace element and evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.707069–0.707138, and ε_Nd(t) = −6.5] indicate an origin from SCLM. Some zircon grains from the MMEs have positive ε_Hf(t) values of 2.3–8.2 with single-stage Hf model ages of 531–764 Ma. Thus, the MMEs would be derived from partial melts of the Neoproterozoic SCLM that formed during rift magmatism in response to breakup of supercontinent Rodinia, and experience subsequent fractional crystallization and magma mixing process. The host monzogranite exhibits typical geochemical characteristics of adakite, i.e., high La/Yb and Sr/Y ratios, low contents of Y (9.5–14.5 ppm) and Yb, no significant Eu anomalies (Eu/Eu* = 0.81–0.90), suggesting that garnet was stable in their source during partial melting. Its evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.7041–0.7061, and ε_Nd(t) = −3.1 to −4.3] and high contents of K₂O (3.22–3.84%) and Th (13.7–19.0 ppm) clearly indicate an origin from the continental crust. In addition, its high Mg# (51–55), Cr and Ni contents may result from mixing with the SCLM-derived mafic magma. Most of the zircon grains from the adakitic monzogranite show negative ε_Hf(t) values of −9.4 to −0.1 with two-stage Hf model ages of 1,043–1,517 Ma; some zircon grains display positive ε_Hf(t) of 0.1–3.9 with single-stage Hf ages of 704–856 Ma. These indicate that the source region of adakitic monzogranite contains the Neoproterozoic juvenile crust that has the positive ε_Hf(t) values in the Triassic. Thus, the high-Mg adakitic granites in the intracontinental setting would form by mixing between the crustal-derived adakitic magma and the SCLM-derived mafic magma. The mafic and adakitic magmas were generated coevally at Late Triassic, temporally consistent with the exhumation of deeply subducted continental crust in the northern margin of the South China Block. This bimodal magmatism postdates slab breakoff at mantle depths and therefore is suggested as a geodynamic response to lithospheric extension subsequent to the continental collision between the South China and North China Blocks.