Discrete global grid systems (DGGSs) are considered to be promising structures for global geospatial information representation. Square and triangular DGGSs have had the advantage over hexagonal ones in geospatial data processing over the past few decades. Despite a significant body of research supporting hexagonal grids as the superior alternative, the application thereof has been hindered partly owing to the lack of a hierarchy. This study presents an original perspective to combine two types of aperture 4 hexagonal discrete grid systems into a hierarchy. Each cell of the hierarchy is assigned a unique code using a linear quadtree that constructs the hexagonal quaternary balanced structure (HQBS). The mathematical system described by HQBS addressing and the vector operations, including addition, subtraction, multiplication, and division, are defined. Essential spatial operations for HQBS cell retrieval, transformation between HQBS codes and other coordinate systems, and arrangement of HQBS cells on spherical surfaces were studied and implemented. The accuracy and efficiency of algorithms were validated through experiments. The results indicate that the average efficiency of cell retrieval using the HQBS is higher than that using other schemes, thus proving it to be more efficient. 相似文献
From 2000 to 2010, monitoring of radio emission from the Crab pulsar at Xinjiang Observatory detected a total of nine glitches. The occurrence of glitches appears to be a random process as described by previous researches. A persistent change in pulse frequency and pulse frequency derivative after each glitch was found. There is no obvious correlation between glitch sizes and the time since last glitch. For these glitches Δνp and D[(n)\dot]p\Delta\dot{\nu}_{p} span two orders of magnitude. The pulsar suffered the largest frequency jump ever seen on MJD 53067.1. The size of the glitch is ∼6.8×10−6 Hz, ∼3.5 times that of the glitch occurred in 1989 glitch, with a very large permanent changes in frequency and pulse frequency derivative and followed by a decay with time constant ∼21 days. The braking index presents significant changes. We attribute this variation to a varying particle wind strength which may be caused by glitch activities. We discuss the properties of detected glitches in Crab pulsar and compare them with glitches in the Vela pulsar. 相似文献
Journal of Oceanology and Limnology - In this study, a programmable freezing technique has been developed for strip spawned sperm in the blue mussel, Mytilus galloprovincialis. The optimized key... 相似文献
Oil from the Oligocene oil sands of the Lower Ganchaigou Formation in the Northern Qaidam Basin and the related asphaltenes was analyzed using bulk and organic geochemical methods to assess the organic matter source input, thermal maturity, paleo-environmental conditions, kerogen type, hydrocarbon quality, and the correlation between this oil and its potential source rock in the basin. The extracted oil samples are characterized by very high contents of saturated hydrocarbons (average 62.76%), low contents of aromatic hydrocarbons (average 16.11%), and moderate amounts of nitrogen–sulfur–oxygen or resin compounds (average 21.57%), suggesting that the fluid petroleum extracted from the Oligocene oil sands is of high quality. However, a variety of biomarker parameters obtained from the hydrocarbon fractions (saturated and aromatic) indicate that the extracted oil was generated from source rocks with a wide range of thermal maturity conditions, ranging from the early to peak oil window stages, which are generally consistent with the biomarker maturity parameters, vitrinite reflectance (approximately 0.6%), and Tmax values of the Middle Jurassic carbonaceous mudstones and organic-rich mudstone source rocks of the Dameigou Formation, as reported in the literature. These findings suggest that the studied oil is derived from Dameigou Formation source rocks. Furthermore, the source- and environment-related biomarker parameters of the studied oil are characterized by relatively high pristane/phytane ratios, the presence of tricyclic terpanes, low abundances of C27 regular steranes, low C27/C29 regular sterane ratios, and very low sterane/hopane ratios. These data suggest that the oil was generated from source rocks containing plankton/land plant matter that was mainly deposited in a lacustrine environment and preserved under sub-oxic to oxic conditions, and the data also indicate a potential relationship between the studied oil and the associated potential source rocks. The distribution of pristane, phytane, tricyclic terpanes, regular steranes and hopane shows an affinity with the studied Oligocene Lower Ganchaigou Formation oil to previously published Dameigou Formation source rocks. In support of this finding, the pyrolysis–gas chromatography results of the analyzed oil asphaltene indicate that the oil was primarily derived from type II organic matter, which is also consistent with the organic matter of the Middle Jurassic source rocks. Thus, the Middle Jurassic carbonaceous mudstones and organic rock mudstones of the Dameigou Formation could be significantly contributing source rocks to the Oligocene Lower Ganchaigou Formation oil sand and other oil reservoirs in the Northern Qaidam Basin.
Due to high gas content, high geo-stress and complex geological conditions, gas disasters occur frequently in deep coal mining. The hard thick roof (HTR) greatly increases the difficulty of coalbed gas control besides causing dynamic disasters. In this paper, the effects of HTR on gas migration were numerically analyzed based on a multi-field coupling model. Results indicated that the hanging arch leads to remarkable stress concentration and induces a “cap-shaped” low-permeable zone above the gob, which greatly prevents gas from migrating upwards. Meanwhile, HTR hinders the subsidence movements of the upper rock strata, contributing to very few roof fractures and bed-separated fractures. Without the formation of roof-fractured zone, coalbed gas completely loses the possibility of upward concentration and will accumulate in the gob, forming a major safety hazard. To overcome these problems, borehole artificially guided pre-splitting (BAGP) technology was proposed. Three different pre-splitting boreholes were constructed as a group to generate artificial fractures in advance in HTR via deep-hole blasting, promoting the evolution of roof fractures. With the effects of mining stress, a fracture network is eventually formed in HTR, which provides a preferential passage for the upward flow of coalbed gas. Moreover, the controllable breaking of HTR was achieved and the roof strata could deform and subside regularly, forming an “O-shaped” roof-fractured zone above the gob which greatly improves the gas extraction efficiency of roof high-level boreholes. In addition, after BAGP, several extraction measures can be applied in the gob-side entry to drain the gas in different concentrated areas. In the field experiment, the roof periodic breaking length was reduced by half, and the average gas extraction rate was increased by 4 times to 67.7%. The synergetic controls of HTR and coalbed gas were effectively realized. This study provides valuable insight into gas control in other deep coal mines with similar geological conditions.
ABSTRACT Cellular automata (CA) models are in growing use for land-use change simulation and future scenario prediction. It is necessary to conduct model assessment that reports the quality of simulation results and how well the models reproduce reliable spatial patterns. Here, we review 347 CA articles published during 1999–2018 identified by a Scholar Google search using ‘cellular automata’, ‘land’ and ‘urban’ as keywords. Our review demonstrates that, during the past two decades, 89% of the publications include model assessment related to dataset, procedure and result using more than ten different methods. Among all methods, cell-by-cell comparison and landscape analysis were most frequently applied in the CA model assessment; specifically, overall accuracy and standard Kappa coefficient respectively rank first and second among all metrics. The end-state assessment is often criticized by modelers because it cannot adequately reflect the modeling ability of CA models. We provide five suggestions to the method selection, aiming to offer a background framework for future method choices as well as urging to focus on the assessment of input data and error propagation, procedure, quantitative and spatial change, and the impact of driving factors. 相似文献
