Structural Evolution Characteristics Research Articles

New indices to capture the evolution characteristics of urban expansion structure and form

A quantitative description is the basis for correctly understanding the urban expansion process. Previous approaches were dedicated to identifying expansion types based on the boundary sharing rate, thereby depicting the evolution of urban expansion. These methods, however, focused on describing neighborhood relations and ignored urban global expansion structure and form information. In this study, we first propose a new index, the location centrality index (LCI), to capture the expansion structure characteristics by incorporating an “area-inverse distance” weighting algorithm and geometric features. Then, we propose another index, the location centrality aggregation index (LCAI), to depict the heterogeneous evolution of urban form by considering the attribute of the new patch. The location centrality and location aggregation types are identified to reflect the effect of new patches on the urban expansion structure and form based on LCI and LCAI, respectively. Two variants of LCI and LCAI are also proposed to reflect the global bottom-up characteristics of urban expansion. The LCI and LCAI were verified using four periods of Landsat images (1995, 2000, 2005, and 2010) of the Wuhan metropolitan area, China. The results show that the overall development trend of the expansion structure in the Wuhan metropolitan area was toward decentralization. The urban form had become generally separated, but tended toward aggregation from 2005 to 2010. Our findings also reveal that the LCI fills the gap in the dynamic assessment of urban expansion with previous indices by explicitly uncovering global structure characteristics. The LCAI achieves better performance than previous indices in identifying heterogeneous aggregation.

Microstructure of Liquid Co50Ni50 During Rapid Solidification.

The rapid solidification process of Co50Ni50 alloy was simulated by molecular dynamics method, and the formation and evolution characteristics of cluster structure in the solidification process were analyzed by the pair distribution function, Honeycutt-Andersen bond type index method and the largest standard cluster. The results show that during the solidification process with a cooling rate of 1×1012 K·-1, the probability of mutual bond formation between Co-Co atoms is always greater than that of Ni-Ni, and the formation of the 1421 bond type is dominant in the crystalline structure. The inflection point of the characteristic bond type 1421 varies with the crystalline transition temperature Tg of the system. The Co-Ni alloy is mainly composed of a face-centered cubic atomic group composed of the 1421 bond type. Meanwhile, there will also be a small amount of hcp structure and a smaller amount of bcc structure. Further analysis revealed that the formation of the fcc structure requires the fast decomposition of TCP structures (at 1450 K). That is to say, the TCP structure must be disassembled before the fcc structure is formed. These findings are useful to provide important guidance for the crystallization of Co50Ni50 alloy under rapid cooling in the experiment.

The evolution characteristics of organic sulfur structure in various Chinese high organic sulfur coals

Understanding the organic sulfur structure and its evolution characteristics is crucial to the desulfurization of coal, as they are the dominant factors determining the removal of organic sulfur from coal. To learn the organic sulfur structure characteristics, a series of high-organic-sulfur coals from China with different ranks were studied by coal petrology, structural chemistry, and organic geochemistry theory in this paper. Coal petrological analysis shows some of the high-organic-sulfur coals with high TPI values and low GI values indicating that they have experienced unusual conditions when the coal was forming. Through the FTIR analysis, the organic sulfur structural parameters shows the relative abundance of aliphatic sulfur (thiol, thioether and sulfone) in these coals decreased with the increasing coal rank and the relative abundance of aromatic sulfur in coal generally showed an increasing trend with increasing coalification, divided into three different evolutionary stages (0.37%–1.40%, 1.40%–1.99% and 1.99%–3.93% of Rm). Comprehensive analysis shows that EID and TPI had a significant correlation with the organic sulfur structural parameters, which means regardless of the coal rank the impact of the environment on the structure of organic sulfur is independent. These results give a new insight into organic sulfur characteristics in coal and its evolution characteristics with coal rank, which are potentially useful for the efficient remove the organic sulfur from coal.

Characteristics of industrial structure evolution and isomorphism in Central Asia

This study undertakes a systematic examination of characteristics of the spatio-temporal evolution of industrial economies in Central Asia from the perspectives of industrial scale, structural rationality, industrial competitiveness, and industrial isomorphism. The results show that industrial structures in Central Asian countries are becoming increasingly advanced, with certain differences among them in the characteristics of this evolution. Kazakhstan has long had a tertiary-secondary-primary industrial pattern, and productive services have played an increasingly prominent role in the development of its tertiary industry. The transformation of the industrial structure in Uzbekistan, from a secondary-tertiary- primary pattern at its independence from the Soviet Union to a tertiary-secondary-primary pattern, is apparent. Tajikistan’s industrial structure has also changed significantly in recent times. Its secondary industries shrunk while tertiary industries developed rapidly. In Kyrgyzstan, the ratios of secondary and tertiary industries to total industrial output have fluctuated significantly while considerable progress has been made in the service sector. The industrial structure of Turkmenistan is significantly lower than the other countries, and Turkmenistan is the only country in the Central Asian region which still shows a tertiary-secondary-primary industrial pattern. The feasibility and competitiveness of the industrial structures of these five Central Asian countries have different characteristics. Kazakhstan has structural advantages but lags in competitiveness, Uzbekistan is driven by both structural and competitive advantages, Tajikistan enjoys structural advantages while Kyrgyzstan lags behind in competitiveness, and Turkmenistan has a competitiveness-driven economy. Furthermore, values of the similar coefficient index of the three industrial structures in these countries were mostly above 0.95, the coefficients of the secondary industrial subdivisions in some countries were below 0.85, and those of tertiary industrial subdivisions among most countries were above 0.89, indicating considerable similarities in industrial structure among them. These findings are important in the context of establishing an effective industrial development strategy for the Silk Road Economic Belt, improving international cooperation, and upgrading industrial structures to achieve economic prosperity.

Impact assessment of climate change and human activities on GHG emissions and agricultural water use

The agriculture sector is one of the largest users of water and a significant source of greenhouse gas (GHG) emissions. The development of low-GHG-emission and water-conserving agriculture will inevitably be the trend in the future. Because of the physiological differences among crops and their response efficiency to external changes, changes in planting structure, climate and input of production factors will have an impact on regional agricultural water use and GHG emissions. This paper systematically analyzed the spatial-temporal evolution characteristics of crop planting structure, climate, and production factor inputs in Heilongjiang Province, the main grain-producing region of China, from 2000 to 2015, and quantified the regional agricultural water use and GHG emissions characteristics under different scenarios by using the Penman-Monteith formula and the Denitrification-Decomposition (DNDC) model. The results showed that the global warming potential (GWP) increased by 15% due to the change in planting structure. A large increase in the proportion of rice and corn sown was the main reason. During the study period, regional climate change had a positive impact on the water-saving and emission reduction of the agricultural industry. The annual water demand per unit area decreased by 19%, and the GWP decreased by 12% compared with that in 2000. The input of fertilizer and other means of production will have a significant impact on GHG emissions from farmlands. The increase in N fertilizer input significantly increased N2O emissions, with a 5% increase in GWP. Agricultural water consumption and carbon emissions are affected by changes in climate, input of means of production, and planting structure. Therefore, multiple regulatory measures should be taken in combination with regional characteristics to realize a new layout of planting structure with low emissions, water conservation, and sustainability.

A Study on the Effect of Incorporation of SiC Particles during Friction Stir Welding of Al 5059 Alloy

Friction stir welding (FSW) was performed in the current research on Al 5059 alloy. Nano-sized SiC (n-SiC) particles were incorporated during FSW for improving mechanical characteristics of welds. Effect of tool rotating speed and multiple FSW passes was studied on SiC dispersion, micro structural changes and mechanical characteristics of composite joints. Results reflected that rotational speed and multiple FSW passes have significant impact over the distribution of SiC reinforcement. Further, the pattern of SiC distribution in the base metal strongly affects the micro structural evolution and mechanical characteristics of welds. An increase of ~55% in microhardness values was achieved in the stir zone of composite joint. Correspondingly, higher ultimate tensile strength (342 MPa) value was obtained as compared to base metal (321 MPa). The increase in mechanical characteristics is mainly owing to grain refinement caused by recrystallization and pinning effect of SiC particles. Micro structural study was carried out using metallurgical microscope and dispersion of n-SiC was observed using TEM. The results of mechanical testing of the present study are in strong corroboration with the micro structural analysis.

Experimental study on damage evolution characteristics of segment structure of shield tunnel with cracks based on acoustic emission information

Cracks are constantly observed in segments due to adverse geological conditions and loads during shield construction. However, crack propagation can have a negative impact on the stress deformation of the segment structures in the long run. Revealing the characteristics of energy release during crack propagation can effectively reflect the damage evolution process. Based on an investigation of segment cracks in a subway tunnel project, this paper conducts an in-depth analysis of AE data of segments through similar model tests, and explores the influence of cracks of different lengths, quantities and positions on the damage evolution of segments of shield tunnels. The results show that cracks reduce the overall stiffness of the structure when compared with that of a segment ring with no prepared cracks, and the elastic bearing range increases slightly, while the plastic bearing range decreases obviously. With the increase of the length and number of prepared cracks, the number of ladders of AE events decreases and the height of ladders increases, and the number of AE events of segments increases continuously at the critical point of instability. The damage of segments appears earlier, and the development process of the damage and is relatively gentle if cracks are located at the arch waist. By contrast, the damage of segments is more serious if cracks are located at the arch roof and arch bottom. The results provide theoretical basis for design optimization, disease analysis and evaluation of shield tunnel.

Geological and tectonic evolution characteristics of polymetallic metallogenic belt

According to the geological structure evolution characteristics of the polymetallic metallogenic belt, the key to solve the problem of mineral resources shortage is to analyze the dominant deposit types, metallogenic mechanism, and metallogenic process of the polymetallic metallogenic belt. On this basis, the analysis method of geological structure evolution characteristics of polymetallic metallogenic belt is put forward. Taking the Wuyishan polymetallic metallogenic belt as the research object, the comprehensive investigation methods of 2D seismic exploration, drilling, geophysical logging, and sampling test are used to control the structural morphology and polymetallic in Wuyishan area. Through drilling, logging, and laboratory tests, the occurrence range, buried depth, thickness, and structure of the polymetallic metallogenic belt are controlled. According to the evaluation results of mineral resources potential in China, it is proposed that the main mineral exploration directions of Wuyishan polymetallic metallogenic belt are rare earth, fluorite, copper-molybdenum, lead-zinc, tin, gold, and silver. The main types of ore deposits include weathering crust-type (ion adsorption type) rare earth deposit, porphyry copper-molybdenum gold deposit, and sedimentary reformed lead-zinc polymetallic deposit. Hydrothermal fluorite deposit and hydrothermal w-sn-bi-mo-ta deposit related to acid rocks are delineated, and eight key prospecting areas in the metallogenic belt are delineated.

Transparent characterization of spatial-temporal evolution of gangue solid wastes' void structures during compression based on CT scanning

In the solid backfill mining, gangue solid wastes (GSW) are used as the main filling materials. The void ratio and void structure of GSW filling materials under the loaded compression in the goaf are the key factors that affect the heavy metal ion migration with the mine water. In this paper, the transparency of the internal structure of GSW filling materials was realized by CT scanning experiment and 3D reconstruction technology, and then the spatial-temporal evolution characteristics of void ratio and void structure of GSW filling materials were studied under the loaded compression. The results show that: (a) With the progress of loading process, the connectivity between adjacent voids is getting worse, and closed voids are gradually formed; (b) The void's equivalent diameter is mainly concentrated in the range of 15 mm - 25 mm; (c) The change in the overall void ratio of GSW is mainly caused by the change of large voids, and the change of small voids has slight contribution to the change of the overall void ratio. However, the sharp increase in the number of small voids can reflect the poor connectivity and permeability between the voids. This research is of great significance to further understand the migration mechanism of heavy metal ions in the filled goaf, and protect the groundwater environment.

Behavior of Overlying Strata at the Working Face of in a Multi-fault Zone

Fault is one of the common geological structures in coal mining, the concentrated development of several faults has changed the movement form and structure shape of overlying strata, which caused the instability of overburden strata easily and induced dynamic disasters. Taking the 10,416 working face of Yangliu coal mine as the research object, the plane numerical model of overburden structure with two faults (a reverse fault and a normal fault) was established by using UDEC numerical simulation software. The dip angle of normal fault is 50°, the dip angle of normal fault is 70°. The distances between the two faults are 30 m, 60 m, 90 m. The evolution characteristics of overburden structure in working face are studied respectively from hanging wall to footwall and from footwall to hanging wall, and the dynamic hazard law induced by the activation of different faults is analyzed. The results prove that: when the working face is mined from footwall to hanging wall, the overlying strata on the working surface form “trapezoid” and “triangle” structures. When the working face is mined from hanging wall to footwall, the overlying strata form the structure of “inverted trapezoid” and “inverted triangle”. The low-level fault activation caused by overburden movement is easy to induce dynamic response. Finally, the research results are verified by using the microseismic activity of 10,416 working face in Yangliu coal mine.

Physico-chemical structure evolution characteristics of coal char during gasification in the presence of iron-based waste catalyst

The present study aims to explore the physico-chemical structure evolution characteristic during Yangchangwan bituminous coal (YCW) gasification in the presence of iron-based waste catalyst (IWC). The catalytic gasification reactivity of YCW was measured by thermogravimetric analyzer. Scanning electron microscope–energy dispersive system, nitrogen adsorption analyzer and laser Raman spectroscopy were employed to analyze the char physico-chemical properties. The results show that the optimal IWC loading ratio was 5 wt% at 1000 °C. The distribution of IWC on char was uneven and Fe catalyst concentrated on the surface of some chars. The specific surface area of YCW gasified semi-char decreased significantly with the increase of gasification time. i.e., the specific surface area reduced from 382 m2/g (0 min) to 192 m2/g (3 min), meanwhile, the number of micropores and mesopores decreased sharply at the late gasification stage. The carbon microcrystalline structure of YCW gasified semi-char was gradually destroyed with the increase of gasification time, and the microcrystalline structure with small size was gradually generated, resulting in the decreasing order degree of carbon microcrystalline structure. IWC can catalyze YCW gasification which could provide theoretical guidance for industrial solid waste recycling.

Investigation on plasma structure evolution and discharge characteristics of a single-stage planar-pulsed-inductive accelerator under ambient fill condition* *Project supported by the Hunan Provincial Natural Science Foundation of China (Grant No. 2018JJ3592).

The physical process of a single-stage planar-pulsed-inductive accelerator is investigated. Measurements include the waveforms of circuit current, capacitor voltage, plasma radiation intensity, and temporal plasma structure photos captured by a high-speed camera. Experiments are conducted under static ambient fill condition using argon as propellant. Varied values of capacitor voltage and gas pressure are compared. Further discussions quantify the EM interaction between circuit and plasma, as well as their energy deposition and current sheet acceleration. Based on the results of experiments, physical mechanisms of the initial ionization phase and the following acceleration phase are analyzed theoretically.

A review of shale pore structure evolution characteristics with increasing thermal maturities

Pore structure has a significant effect on the occurrence state of shale hydrocarbons and the hydrocarbon storage capability of shale reservoirs. Consequently, it is quite meaningful to clarify the shale pore structure evolution characteristics for understanding the migration and enrichment mechanisms of hydrocarbons within shale reservoirs during different geological stages. The abundant existence of organic matter within shales complicates the shale pore structure evolution process by hydrocarbon generation, migration and cracking. Many studies have been conducted to reveal the shale pore structure evolution characteristics and the controlling factors. Basically, these studies could be divided into two categories based on the sample source: comparing the pore structure of natural shale samples with different thermal maturities; obtaining shale samples with different thermal maturities by conducting thermal simulation experiments on low-mature shale samples and comparing the pore structure of these simulated shale samples. However, no consistent viewpoint on shale pore structure evolution has been reached. This review presents the state of the art of shale pore structure evolution studies. It is widely recognized in the literature that both the inorganic and organic diagenesis control the shale pore structure evolution process. However, it is found that the shale pore structure evolution models proposed in the literature were largely dependent on the samples used. And it is recommended to conduct the two categories of studies simultaneously in order to obtain more reliable shale pore structure evolution characteristics in future investigations. Cited as : Gao, Z., Fan, Y., Xuan, Q., Zheng, G. A review of shale pore structure evolution characteristics with increasing thermal maturities. Advances in Geo-Energy Research, 2020, 4(3): 247-259, doi: 10.46690/ager.2020.03.03

Unified egg ellipse critical threshold estimation for the deformation behavior of ultrahigh arch dams

This paper presents an innovative critical threshold estimation approach using unified egg-shaped ellipsoid modelling to study the deformation behavior of ultrahigh arch dams. First, the deformation variation law is regarded as a direct indicator of the overall stability and potential damage of ultrahigh arch dams based on comprehensively comparison with the results of theoretical calculations, experimental tests, numerical simulations and monitoring data. Subsequently, a novel geometric center of an irregular deformation plane constituted by all the deflection curves is proposed according to the measured distribution characteristics of the deformation spatial fields of the Xiaowan and Jinping I arch dams. Furthermore, unified egg-shaped ellipse equations are proposed to systematically identify the deformation critical attributes of Jinping I dam. Eventually, based on the peaks over threshold model, critical indexes are estimated considering the abnormal probabilities. The proposed methods are applied to Xiaowan dam as well. Results demonstrate that unified ellipsoid modelling can uniformly describe the abnormal features of the deformation behaviors of different ultrahigh arch dams, thereby the universal structural evolution characteristics to be understood in a wider range during their long-term operations.

Cavity influence on fatigue performance of heavy haul railway Tunnel’s bottom structure

The smoothness of tunnel base directly affects the safety of train operation, and tunnel base diseases are usually difficult to detect and deal with due to the distinguishing features of heavy haul railway, the base diseases become one of the most harmful tunnel diseases. Therefore, with the increasing axle load and the basal deterioration of the existing heavy haul railway in China, studying the fatigue performance of the tunnel bottom structure is essential. A 3D train-tunnel-surrounding rock numerical model is established to obtain the dynamic response of the tunnel bottom structure under 30 t axle load trains. Then refer to the stress state and fatigue vulnerable position which are originated from the numerical simulation, a series bending fatigue tests are carried out to study the cavity influence on fatigue performance of heavy haul railway tunnel’s bottom structure in this paper. A non-linear cumulative damage model is proposed to quantify fatigue damage evolution characteristics of tunnel bottom structure with base cavity through the tests. The results suggest that, the base rock cavity remarkably reduces the fatigue life of the specimen and increases the development rate of damage; the existence of cavity not only deteriorates the bearing capacity of the structure, but also greatly improves the dynamic response and stress level of the bottom structure and base rock, which has multiple adverse effects on the fatigue performance of the tunnel bottom structure, and also accelerates the expansion of the cavity itself.

Studying effects of solid structure evolution on gasification reactivity of coal chars by in-situ Raman spectroscopy

This study focuses on characteristics of structure evolution during pyrolysis and subsequent char gasification of lignite and bituminous coal. Coal pyrolysis was conducted on induction-heating reactor. As pyrolysis temperature increased, the graphitization degree of char increased, and the amount of C-O and -CH in char decreased, resulting in poorer gasification reactivity of char. Char gasification was conducted by thermogravimetric analyzer (TGA), high-temperature stage microscope (HTSM) and in-situ Raman system to investigate gasification reactivity, in-situ evolution of morphology structure and in-situ evolution of carbon structure, respectively. As gasification proceeded, the projected area of char particle decreased rapidly first and then kept consistent, and degree of graphitization of char gradually increased. In-situ Raman parameters indicated difference in increasing rate of graphitization between lignite char and bituminous char decreased with increasing temperature. Higher temperature deactivated the alkali metals, leading to attenuation of their inhibitory effect on graphitization. Gasification reactivity index R0.9 was in positively correlated with in-situ ID1/IG value, and corresponding correlation coefficient (R2) for TGA and HTSM were 0.8108 and 0.9829, respectively. The higher R2 for HTSM was due to the weaker diffusion effect. In-situ Raman parameter was more suitable for predicting gasification reactivity of single particle char.

Pore Structure and Compressibility Characteristics of Heat-Treated Coals by N2 Adsorption/Desorption and Mercury Intrusion Porosimetry

To improve the physical properties of a coal reservoir with heat treatment and enhance the coalbed methane recovery, the characteristics of gas generation and pore structure evolution of different ...

Pore structure evolution and fractal characteristics of Zhaotong lignite during drying

While the drying of lignite is critical prior to its usage, the fragmentation and pulverization of lignite during drying inhibit the safe operation of this process. In this study, the changes in the physical structure of Zhaotong lignite during the drying process were examined by study its microstructure. Microstructure aspects like pore size distribution, pore volume distribution, and fractal dimension were used to determine the variation in pore structure, and the relationship between fractal dimension and water content was established. The results showed that open pores and pore connectivity decreased as the degree of drying increased. During the drying process, the number of pores larger than 100 nm decreased first, followed by a decrease in the number of pores smaller than 100 nm. The total pore volume and the pore volume of four types of pores showed a general trend of downward at different drying temperatures. The change in the fractal dimensions of Zhaotong lignite during drying can be divided into three stages. The change in the fractal dimension of the second stage (water content decreasing from 1.19 to 0.62 g/g) was found to be the most significant, since it entailed the destruction of the Zhaotong lignite pore structure.

An enhanced coalbed methane recovery technique based on CO2 phase transition jet coal-breaking behavior

In recent years, CO2 phase transition jet (CPTJ) coal-breaking technology has been reported to increase coal seam permeability. However, the structural evolution effect of coal subjected to CPTJ technology is unclear, which restricts widespread CPTJ technology application. In this study, a laboratory experimental system and field technical equipment were developed, and coal-breaking experiments under different CPTJ pressure conditions were conducted. We investigated pore structure changes by combining scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) to better understand the coal pore structure evolution characteristics under different CPTJ pressures. Furthermore, an enhanced coalbed methane (ECBM) recovery experiment using CPTJ coal-breaking technology was conducted with the self-developed technical equipment. The results show that notable damage occurs in the coal body influenced by CPTJ, and the damage area increases with increasing jet pressure. The SEM results revealed that more pores and cracks are produced due to liquid CO2 CPTJ, and the porosity and crack size increase with increasing jet pressure. MIP analysis indicates that the pore structure of the breaking coal samples mainly includes macropores, and coal sample macroporosity increases significantly with increasing jet pressure. The field ECBM experiment showed that CPTJ technology can reduce the coalbed methane (CBM) drainage decay coefficient and increase the CBM extraction pure flow rate and recovery efficiency 8.3–10.4 and 20.4 times, respectively.

Experimental study of strength, pore structure and phase evolution characteristics of iron tailings cemented paste backfill under high-temperature

With the deepening of mining depth, the geothermal temperature faced by the pit backfill is getting higher and higher, so the spontaneous combustion probability of sulfur-bearing minerals increases. In addition, sudden fires can expose the backfill to high temperatures, which will endanger the structural safety of the backfill. Therefore, in order to fully understand the mechanical response and pore structure evolution characteristics of backfills under high-temperature loading, the compressive strength and splitting tensile strength of backfills with different ages: 7 days, 28 days and 60 days and cement-tailings ratios: 1:6, 1:8 and 1:10 were tested using high-temperature furnace to simulate different temperature loads: 100, 200, 400, 600 and 800°C. The pore structure characteristics of the backfill after high temperature are analyzed by mercury intrusion porosimetry. To further understand the mechanism of backfill transformation at high temperature, the phase evolution characteristics of iron tailings and cementitious materials are analyzed by X-ray diffractometer and differential ther-mal/thermogravimetric analyzer. The results show that the strength and pore structure of iron tailings backfi ll at high temperature are related to the curing age. The strength and most probable pore size of backfill cured at 7 days increased fi rst and then decreased with the increase of temperature. Among them, the compressive strength and splitting tensile strength reached their peak values at 200°C and 100°C, respectively. While after 28 days, the pore size increased with the increase of high temperature, and the strength of backfill decreased continuously with increasing temperature. No matter what age of backfill is, it almost loses its tensile strength after being subjected to a high temperature above 400°C. These characteristics are closely related to the expansion of mica in iron tailings and the dehydration and decomposition of cementing material hydration products, such as ettringite and C-S-H phase at high temperature.