Chang'an University
  • Xi’an, China
Recent publications
Elemental carbon has been successfully used to tune the light emission properties of zinc oxide (ZnO) through artificially doping but the underlying mechanism remains controversial. At present, carbon-related defect complexes are the main explanation. Nevertheless, the possibility of forming semiconducting Zn-C compounds has not been discussed. In this study, we reveal the existence of various stable semiconducting Zn-C compounds. Based on particle swarm optimization and first-principles calculations, we perform a structural search of Zn-C binary compounds and report four stable semiconducting structures, in which the covalent Zn-C bonding characteristics are stronger compared with that in the metal rocksalt zinc carbide (ZnC). Crucially, three of the four Zn-C compounds have direct or quasi-direct band gaps in the range of 1.09–2.94 eV which are energies highly desirable for optoelectronic applications. Electronic transitions across the band gaps of these Zn-C structures could contribute to blue and near-infrared light emissions of C-doped ZnO. Our results have not only unraveled a new perspective to explain and tailor the light emission properties of ZnO but also provide a deeper understanding of possible Zn-C compounds.
Whether the shield tunnel can be adopted to cross the ground fissure is an important issue in the field of metro construction in Xi'an, China. To study this issue, the model test and numerical simulation on a metro shield tunnel that obliquely crosses a ground fissure were carried out. The lining internal force, segment deformation and failure characteristics under the action of ground fissure dislocation were investigated. The results show that the shield tunnel obliquely crossing ground fissure exhibits three-dimensional deformation of axial bending, horizontal local torsion, and axial tension–compression, if the ground fissure dislocation takes place. The segments near ground fissure present uneven vertical dislocation, horizontal slight deflection, and axial tilt. The lining is in bias pressure state, and cracks around segment bolts nearby the vault and inverted arch of shield tunnel when the actual ground fissure dislocation reaches 24 cm. The deformation and failure of shield tunnel obliquely intersecting with the ground fissure is in the torsional-shear mode, which affects the 8 rings in the hanging wall and the 5 rings in the footwall respectively, and these segments need to be strengthened. Also, some countermeasures and suggestions are proposed to deal with the adverse impacts of ground fissure on metro shield tunnel.
We form portfolios consisting of diverse quarterly forward freight agreement (FFA) contracts to maximize the market participant's expected utility. The empirical findings indicate that individual FFA returns display clear autocorrelation, seasonality, fat tail, and heteroscedasticity. The multivariate positively skewed t copula is suggested for constructing maximum utility FFA portfolios, implying that the constituent FFA returns exhibit higher correlations when they rise together. The out-of-sample trading strategy performance metrics and various robustness checks further indicate that the aforementioned copula performs best and robustly for all portfolios. These findings provide profound methodological and managerial implications for market participants to improve risk management.
The simply supported slab bridge is a typical perfricated reinforced concrete bridge. Under the influence of increasing vehicle loads and natural environmental erosion, the hinge joints between slabs suffer from damage that cannot be easily evaluated, which brings negative effects on the load carrying capacity of bridges. In the present study, a hybrid method for damage detection and condition assessment of hinge joints in hollow slab bridges using physical models and vision-based measurements was proposed. The stiffness reduction of hinge joints is taken as the damage degree and condition level of the inspected hinge joints. An analytical model of a simplified spring-mass system was firstly built to demonstrate the applicability of using the relative displacement ratio as the damage index of hinge joints. The relationship between the relative displacement ratio and the stiffness reduction of hinge joints was then studied thoroughly through a parametric study on finite element models considering different damage levels of hinge joints. Thresholds of the relative displacement ratio were defined to classify the damage states of hinge joints. The damage index of target hinge joints can be calculated from the actual data provided by using computer vision-based multi-camera and multi-point displacement measurements. Lastly, the application of a real-life bridge under normal traffic was demonstrated to verify the feasibility of the quantitative evaluation of the service status of joints in hinged-slab bridges. It indicated that the proposed method could evaluate the damage degree of joints quantitatively, effectively and economically.
Two graphs G and H are cospectral if they share the same spectrum. Constructing cospectral non-isomorphic graphs has been investigated for many years and various constructions are known in the literature, among which, the GM-switching, invented by Godsil and McKay in 1982, is proved to a simple and powerful one. Motivated by this, we address the following problem: “For which graphs G with adjacency matrix A(G), does there exist a rational orthogonal matrix Q (not a permutation matrix) with constant row sum, such that QTA(G)Q is a (0,1)-matrix?” We focus on a special case that 2Q is an integral matrix with one fully indecomposable block. Some partial answers to the above question are given by associating a directed graph ΓG with G. We find that there exists an interesting relationship between the existence of the above Q and the structure of ΓG. Based on the results obtained, we present a new method for the construction of cospectral graphs.
Cyclohexanol is obtained from abundant lignocellulosic biomass sources at low cost, and it is a promising alternative fuel for diesel engines. In this study, cyclohexanol was blended with diesel at various volume ratios and the mixtures were denoted as D100 (100 % diesel + 0 % cyclohexanol), D90CH10 (90 % diesel + 10 % cyclohexanol), and D80CH20 (80 % diesel + 20 % cyclohexanol), respectively. Subsequently, the effects of exhaust gas recirculation and pilot plus main injections at various pilot injection timings on the combustion and emissions of the diesel engine fueled with various mixtures were evaluated. The results demonstrated that diesel/cyclohexanol blends had a longer ignition delay, but shorter combustion duration. D80CH20 had the highest oxygen content, peak combustion temperature (PCT), and peak heat release rate (PHRR) at medium and high loads. Cyclohexanol blending with diesel significantly decreased the particulate number (PN) and volume concentrations at the expense of higher NOx emissions. Advancing the pilot injection timing prolonged the ignition delay and combustion duration, and increased the PCT and PHRR. Therefore, it emitted higher NOx emissions, but lower PN emissions. D80CH20 with 8 % EGR can simultaneously reduce the PN and NOx emissions at medium and high loads.
The suspenders bear the repeated stress caused by various cyclic actions during the bridge operation while the stress amplitude under dynamic load is smaller than under dead load. The steel wire degradation process is a typical corrosion fatigue degradation, in which the initial defects caused by surface corrosion are the main source of fatigue cracks and the crack development under operating load leads to the failure of the steel wire. The steel wires of the suspender are considered as a co-deformed parallel structural system. The corrosion process of steel wires in different layers are different for the diffusion paths of corrosion medium, which makes the bearing capacity of steel wires differs from each other. The suspender strength depends on the wire of lowest strength due to the Daniels effect, interlayer corrosion variance should be considered in the evaluation of suspender reliability. This paper investigates the interlayer corrosion variance of parallel steel wire suspenders on the basis of neutral salt spray test. It proposes a corrosion variance coefficient, and considers the stochastic degradation process of suspender. Combined with the daily traffic model, it establishes a sophisticated reliability evaluation method of suspender. The results are shown: The steel wires in each layer of test specimens are all severely corroded when the corrosion time reaches a certain degree. For the specimens with different damage types, the overall corrosion condition of the annular damaged specimen is the most severe; whereas that of the vertical damaged specimen is the least. Under experimental environment, the corrosion variance coefficients of sheath damaged specimens follow normal distribution. In the application of suspender evaluation, the service lifespan of wires varies obviously with the corrosion variance coefficient. The distribution of steel wire lifespan under different corrosion variance coefficients also follows normal distribution. The service lifespan of outer layer wires is longer than inner layer wires, and the overall reliability lies between the reliability of outer and inner layers.
The use of bio-based materials to partially replace petroleum-based materials in road engineering can not only reduce the consumption of natural resources but also contribute to environmental protection and sustainable development. In this study, a rosin-based acid anhydride curing agent, maleic rosin anhydride (MRA), was used to prepare a polyurethane/epoxy resin/MRA modified asphalt (PEMMA) binder. The mechanical properties, viscosity characteristics, storage stability, and high- and low-temperature performances were studied, and the appropriate modifier content was determined. Meanwhile, Fourier transform infrared spectroscopy and atomic force microscope were used to explore its microscopic modification mechanism. In addition, the PEMMA mixture was prepared, and its pavement performance was tested and evaluated. The results revealed that the PEMMA binder has satisfactory mechanical properties and storage stability. Except for the PEMMA binder with 60 wt% modifier content, the construction allowable time range for the remaining binders met the specification. Compared to the base binder, the PEMMA binder had excellent high-temperature strain recovery ability but reduced its low-temperature performance. The change of the functional groups in the PEMMA binder verified the occurrence of the curing reaction; its microscopic morphology had changed significantly, with the bee-shaped structure becoming blurred and the roughness increasing significantly. The low-temperature performance of the PEMMA mixture was improved compared to the epoxy asphalt mixture. Overall, the comprehensive performance of the PEMMA mixture was more equitable but inferior to that of the mixture prepared with the petroleum-based curing agent.
This article addresses a cooperative game-oriented optimal constraint-following problem for fuzzy mechanical systems. The state of the concerned system is affected by possibly (fast) time-varying uncertainty. The fuzzy set theory is adopted to describe such uncertainty. The task is to drive the system to obey a set of prescribed constraints optimally. Since the control objective may be changing along with the system uncertainty, a time-varying β-measure is defined to gauge the constraint-following error; based on which, an adaptive robust control scheme with two tunable parameters is then proposed to render it to be uniform boundedness and uniform ultimate boundedness. For the seeking of the optimal design parameters, two cost functions, each of which is dominated by one tunable parameter, are developed with the fuzzy information, and thereout a two-player cooperative game is formulated. Finally, the optimal design problem is successfully solved: with the existence, uniqueness, and analytical expression of the Pareto optimality.
The detection technology and identification method of blasting fragmentation can be used to quickly quantify and feed back the blasting effect. In this paper, aiming at the phenomenon of false edge or missing edge in image edge detection operator, an improved Canny operator edge detection method is proposed. Firstly, statistical filtering is used to solve the problem of image edge blur. Then, based on the 3 × 3 gradient template of the operator, the gradient amplitude and direction of the burst image are calculated. Finally, the natural iterative method is used to obtain the image threshold, and the discontinuous edge is repaired by morphological closure operation and thinning operator to obtain the final detected edge. The experimental results show that the improved Canny operator removes the granular and flake noise of the blasting block, maintains the integrity of the edge of the explosive pile image, and has high authenticity and feasibility.
Efficient visible-light-driven H2 production without noble metal is one of the major challenges in photocatalysis. Herein, SrTiO3 nanoparticles synthesized from a facile hydrothermal process are adopted as supporting material for a fluorescein-sensitized photocatalytic system, and considerable H2 production is obtained without cocatalyst due to the relatively large surface area for sufficient adsorption of dye molecules. Upon further modification with earth-abundant Ni cocatalyst, the activity of H2 production from the as-established noble-metal-free fluorescein-sensitized photocatalytic system could be drastically enhanced, achieving an apparent quantum yield of ∼4.1% at 500 nm. The excellent photocatalytic performance is attributed to the synergistic contribution of the efficient electron excitation and injection, the significantly promoted charge transfer, and the abundant reactive sites provided by Ni cocatalyst.
Urban transport sector's transition to cleaner energy is needed to help stop global warming. To reduce the sector's dependence on fossil fuels, government are promoting green mode of transportation and it can help reduce air pollution in cities. Our study examines Chinese consumers' environmental awareness and attitude toward new energy vehicle (NEV) policy, and its impact on their attitude toward NEV. Using the theories of planned behavior and social exchange we examine the relative impact of Chinese consumers' attitude toward NEV, subjective norms, and perceived behavioral control on their purchase intention. Our findings show that consumers' favorable attitude toward government policy and environmental awareness improves the consumers' attitude toward NEV, and a positive attitude toward NEV and the impact of social pressures or evaluations of early adopters help the transition to cleaner energy use by increasing the adoption of NEV. And this study suggests that consumers' education level has a significant moderating effect on their NEV purchase intentions. The study findings provide direction for the government's NEV promotion and application policy for city residents.
The use of renewable methanol partly substituting diesel fuel can support the transition to low-carbon engines, in the form of diesel/methanol dual-fuel combustion. Particulate filters are still required for diesel/methanol dual-fuel combustion engines to meet the emission standard. Their periodical regeneration depends on the soot oxidation reactivity and nanostructure. We therefore assessed the influences of premixing methanol on soot oxidation reactivity and nanostructure at both engine loads. The results showed that increasing methanol substitution ratio shifted thermogravimetric profiles towards low temperature direction. The average activation energies of M20 and M40 samples (the methanol substitutions of 20% and 40%) dropped by 41.1–43.9 kJ/mol and 53.2–99.7 kJ/mol compared to diesel one at both engine loads, respectively. With an increase in methanol substitution ratio, a notable reduction in primary particle size was observed, with the shorter and more tortuous fringes as well as larger separation distance between the stacked fringes. The increasing trend in soot oxidation reactivity with methanol addition correlated well with the changes in primary particle size and fringe parameters, which means that soot oxidation reactivity highly depends on its morphology and nanostructure. It can be expected from the results that diesel/methanol dual-fuel operation has the advantages in engine fuel economy improvement regarding the regeneration of particulate filters.
Compatibility between asphalt and polyurethane (PU) additives is the most challenging issue affecting the performance of PU modified asphalt. This study aims to investigate the influence of shearing temperature and PU content on compatibility between PU and asphalt via experiments and molecular dynamics (MD) simulation. Herein, the molecular models of base asphalt, PU molecules, and PU/asphalt blends were first constructed in Materials Studio (MS) software. Based on a reasonable model, the influence of shearing temperature on the storage stability of PU modified asphalt was measured by calculating the solubility parameters (δ) and diffusion coefficient. In addition, the effect of PU content on the compatibility of PU and asphalt was evaluated through cohesive energy density (CED), hydrogen bonding, and radial distribution function (RDF). Finally, the simulation results were compared with results from the segregation test and fluorescence microscope (FM). The simulation results indicate that PU and asphalt obtain optimal compatibility when the temperature is 135 °C, at which the diffusion coefficient of PU modified asphalt is enhanced significantly. The CED of modified asphalt is enhanced with the increase of PU content. Meanwhile, PU shows a significant effect on the RDF of each asphalt component. All these changes in asphalt molecules demonstrate that PU plays a positive role in improving the tightness of asphalt molecular structure, and the optimal content is 15 wt%. The simulation results are consistent with experimental results.
Novel frame beams differ from the traditional steel-concrete composite frame beam, named as steel-hollow partially encased composite spliced frame beam (SHSFB) and steel-partially encased composite spliced frame beam (SPSFB) is proposed herein. SHSFB and SPSFB are “false steel-concrete composite structures”, actually, they are regarded as steel structure in mechanism analysis. Plastic hinge is located on the stub beam, while the mid-span of the beam is a steel-concrete composite beam. Their deformation and bearing capacity are similar to that of the steel structures. The novel frame beams also have the advantages of easy construction, steel saving, and good lateral stiffness. In order to study the seismic performance of the novel structures, five specimens were tested under cyclic loading. All specimens showed excellent seismic capacity. When the stub beam was long, its hysteretic curve was more similar to that of the steel frame beam; when the stub beam was short, the ductility, energy dissipation capacity, and drift ratio of the specimen were better, especially for SHSFB. In addition, the flexural capacity of the novel frame beam was calculated. According to the test results and analysis, the thickness of independent beam flange, filling amount of concrete, and length of stub beam are optimized.
Sustainable economic development is the primary goal of each economy. In this regard, the role of natural resources has been extensively debated in the existing literature; however, the studies on the natural resource's influence on the financial development of developing countries are scarce. This study investigates the validity of the resource curse hypothesis related to financial development by recruiting fiscal decentralization, technology innovation, and economic policy uncertainty in China. The study employed the contemporary and innovative approach of quantile autoregressive distribution lag (QARDL) to evaluate the asymmetric association between variables from 1990 to 2020. Empirical findings validate the resource curse hypothesis in China, which implies that the natural resource rent compressed financial development. Likewise, economic policy uncertainty also adversely affected financial development. In contrast, fiscal decentralization and technological innovation accelerated financial development and neutralized the negative consequences of natural resources. Based on the findings, conductive short-run and long-run business strategies and regulations should be implemented, including the adequate consumption of natural resources, reallocation of funds at regional government levels, and transformation toward sustainable technologies to shift the curse into a blessing.
The implications of petrogenesis and tectonics of Paleoproterozoic (ca. 2.1–1.9 Ga) granitoid rocks in Dunhuang Terrane have hitherto received less attention. According to data from zircon UPb dating, the ages of dioritic gneiss, granodioritic gneiss and potassic granite are 2045 ± 44 Ma, 1998 ± 15 Ma and 1950 ± 38 Ma, respectively. The dioritic gneiss has MgO = 1.87–2.93 wt% (Mg# = 46.8–50.9), Yb ≤ 1.9 ppm and Y ≤ 18 ppm, with variable εHf(t) (−2.8 − +5.5) and εNd(t) (−5.6 − +1.3) values, indicating that the mantle wedge source above the subducted slab contributed with subduction fluids and ocean sediment melt in an arc setting. The granodioritic gneiss has relatively high MgO (3.00–1.83 wt%), variable Cr (13.5–106 ppm) and Ni (12.2–72.9 ppm), negative εHf(t) (−20.4 to −10.1) and εNd(t) (−15.2 to −12.8) values, and high P2O5 and TiO2 saturation temperatures (∼800 °C). These data indicate magma source of late Paleo- to early Mesoarchean (∼3.2–3.1 Ga) continental crust rocks. The potassic granite has high K2O (5.52–6.79 wt%) and low MgO (0.10–0.19 wt%) concentrations, low Mg# (37.7–44.6) values, and negative εHf(t) (−12.8 to −2.5) and εNd(t) (−10.6 to −4.8) values. These results suggest that pre-existing Neoarchean crustal rocks were partially melted possibly under transitional stage from syn- to post-collision. Compared with the adjacent areas, Paleoproterozoic (ca. 2.1–1.8 Ga) evolutionary period related to assembly of Columbia supercontinent in Dunhuang Terrane is comparable with that in northeastern Tarim Craton and southwestern Alxa Block, but terminated ∼100 Ma later than that in southeastern Tarim Craton (Aketashtage Terrane).
The conventional manual sand-patch method of mean texture depth (MTD) measurement is unsuitable for network level pavement condition monitoring. Relying on 2-D mean linear profile depth (MPD) to estimate 3-D MTD is also unsuitable because MTD-MPD regression relationship varies from one pavement mix type to another. This problem of network level MTD measurements and monitoring can be overcome if MTD could be numerically determined from 3-D digital laser images. All the numerical MTD determination methods proposed by researchers in recent years made a common invalid assumption that the MTD top surface was defined by the high texture peaks of the test surface. This study presents evidence to show that the top surface defining MTD actually lies below the highest peaks of the test surface. Next, applying the concept of planation surface, a novel numerical procedure is proposed to identify a reference surface for MTD calculation by means of a second-derivative plot of peak-height percentiles. The validity of the proposed method was verified experimentally with measured MTD values of both laboratory fabricated specimens and in-service pavements. For four different surface course materials, the errors in the predicted MTD values range from 0.20 to 7.31 %. The proposed method produced improved accuracy in MTD predictions compared with the existing methods which were based on incorrectly assumed MTD top surfaces.
Three-dimensional (3D) surface information is becoming the data of choice for pavement inspection and maintenance. Pavement digital reconstruction still faces various challenges, including field-of-view (FOV) limits, traffic influences, data acquisition speed and cost. This paper presents a full-FOV pavement stereo reconstruction framework integrating unmanned aerial vehicle (UAV) photography, object detection and multi-view occlusion optimization. A UAV-YOLO vehicle detector embedding depth-wise separable convolution and resolution adjustment unit is developed for noise localization. To improve reconstruction quality and speed, multi-view occlusion optimization is proposed for determining the optimal image series spatial distribution. The results show that the UAV-YOLO detector achieves an overall AP75 of 93.69% with an inference speed of 157 FPS. Through multi-criterion evaluation, the pavement digital models reconstructed under dynamic traffic conditions have satisfactory performance in terms of point cloud noise, density, similarity and accuracy. In addition, the proposed stereo reconstruction workflow saves 30.27% processing time over conventional SfM workflow.
The expansion and deterioration (E&D) of cement treated road base has become one of the common road problems in northwest and northern China, which seriously affected driving safety and increased road maintenance costs. In order to explore the influencing laws and mechanism of external salt on the expansion of cement treated road base in desert Gobi area with large temperature difference, based on the climate in Xinjiang and cement stabilized macadam (CSM) mixture, a laboratory accelerated simulation test under the coupling effect of water-heat-salt was designed to restore the working condition of the base course in Xinjiang. The expansion deformation and deterioration laws of CSM specimens under different gradation types, temperature, humidity and temperature-humidity cycle change were studied. Combined with MIP and computed tomography (CT), the air-void structure change, micro-pore morphology and accumulation of expansion products in the mixture were studied. The results showed that after 360-days' coupling effect, the damage height of the specimen was SD (suspension-dense structure) > FP (frame-pore structure) > FD (frame-dense structure). The mass of the partially-immersed specimens increased first, and the mass loss began to appear at about day 120. After 360-days' temperature and humidity cycle change, the mass loss rate of SD, FD and FP were 4.15 %, 2.4 % and 4.9 %, respectively, which were 2.75, 2.53 and 2.62 times of that at 25 • C. Moreover, the expansion rate increased by about 20 %, and the performance deterioration decreased by 24.9 %-30 %. Additionally, the MIP and CT test results indicated that the aggregate proportion had a significant effect on the spatial distribution of the air-voids and the change of pore structure with coupling ages. This study provides reference for the design of cement-based composites and the acknowledgement of cement-treated base expansion in desert Gobi area.
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3,537 members
Yonggang Wang
  • College of Transportation Engineering
Zhaowen Qiu
  • school of automobile
Zengping Zhang
  • Key Laboratory for Special Area Highway Engineering of Ministry of Education
Chaoying Zhao
  • School of Geology Engineering and Geomatics
Zhenhong Li
  • College of Geological Engineering and Geomatics
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Xi’an, China