49 results on '"Xiang-Yang Li"'
Search Results
2. A novel trusted third party based signcryption scheme
- Author
-
Shamsher Ullah, Zhang Lan, and Xiang-Yang Li
- Subjects
Computer Networks and Communications ,Computer science ,business.industry ,Hash function ,020207 software engineering ,Cloud computing ,02 engineering and technology ,Trusted third party ,Encryption ,Elliptic curve point multiplication ,Hardware and Architecture ,Forward secrecy ,0202 electrical engineering, electronic engineering, information engineering ,Media Technology ,Session key ,business ,Software ,Signcryption ,Computer network - Abstract
To prevent man-in-the-middle attack, Diffie-Hellman first proposed the concept of the session key exchange protocol, in which the author remove the long term keying material at the end of the session. In our scheme, we apply the session key concept of Diffie-Hellman for cloud computing in the presence of the Trusted Third Party (TTP). Our proposed scheme provides SEVEN security properties by using the session key exchange protocols as symmetric. In our scheme, TTP becomes free from a burden of activities, like to encrypt the requests (Ri) of the Cloud Service Users (CSUs) and to decrypt the services (Si) of the Cloud Service Providers (CSPs) again and again. By using S Performance (EP) for Elliptic Curve Point Multiplication (ECPM), Hash (H), Inversion (Inv), Exclusive oR (XoR), Encryption (Enc), and Decryption (Dec) is (87.5%, 62.5%, 57.14%), (87.5% and 75%), (75%), (97.82% and ≤ 1%), (92.85%) and (50%) respectively. The security requirements of our scheme are; data integrity, data confidentiality, authenticity, non-repudiation, forward secrecy, unforgeability, and untraceability. Our proposed scheme also outperformed performance in terms of flexibility, reliability, and efficiency as compared to existing schemes.
- Published
- 2020
3. An Experimental Study on Scale-Dependent Velocity and Anisotropy in Fractured Media Based on Artificial Rocks with Controlled Fracture Geometries
- Author
-
Xiang-Yang Li, Ding Wang, and Pinbo Ding
- Subjects
Materials science ,Scale (ratio) ,Scattering ,0211 other engineering and technologies ,Geology ,02 engineering and technology ,Mechanics ,010502 geochemistry & geophysics ,Geotechnical Engineering and Engineering Geology ,01 natural sciences ,Measure (mathematics) ,Physics::Fluid Dynamics ,Scale dependent ,Fluid dynamics ,Fracture (geology) ,Porosity ,Anisotropy ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Civil and Structural Engineering - Abstract
The scale of the fractures can vary, making the seismic velocity and anisotropy substantially scale dependent. Two mechanisms of the scale-dependent phenomenon may be considered: scattering and wave-induced fluid flow. In this study, we measure the scale-dependent velocity and anisotropy effects through laboratory experiments on porous and non-porous artificial rocks containing aligned fractures. This allows us to isolate the effects of these two mechanisms for the first time, yielding some insights into the scale-dependent phenomenon. For short-wavelength waves, scattering dominates with less wave-induced fluid flow effects. For intermediate- and long-wavelength waves, the P-wave is strongly scale dependent mainly due to wave-induced fluid flow mechanism, and the slow shear-wave is also strongly scale dependent but due to both scattering and wave-induced fluid flow. However, the fast shear-wave is almost scale independent. Moreover, a multi-scale equivalent medium theory can model the P-wave propagation accurately.
- Published
- 2020
4. Elastic anisotropy and its influencing factors in organic-rich marine shale of southern China
- Author
-
Feng Zhang, Xiang-Yang Li, and Zichun Liu
- Subjects
chemistry.chemical_classification ,Maturity (geology) ,Seismic anisotropy ,010504 meteorology & atmospheric sciences ,Mineralogy ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry ,Ordovician ,General Earth and Planetary Sciences ,Organic matter ,Clay minerals ,Anisotropy ,Oil shale ,Quartz ,Geology ,0105 earth and related environmental sciences - Abstract
Shale is observed to have strong anisotropy due to its unique mineralogy and microstructure, and this anisotropy property has significant impact on seismic and well-log data. The organic-rich marine shale in the southern and eastern Sichuan Basin is one of the most important shale-gas reservoir formations in China. To investigate the elastic anisotropy of this shale and its influencing factors, we performed ultrasonic velocity measurements, X-ray diffraction analysis, rock-eval pyrolysis and vitrinite reflectance measurement on the samples from the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation. The experimental results show the that: (1) the velocity anisotropy of the Wufeng-Longmaxi (WL) shale varies from 10% to 50%, and most samples have strong anisotropy; (2) the P- and S-wave anisotropy parameters (Thomsen’s e and γ) increase with clay contents, but this relationship can be greatly affected by the clay orientation index; (3) organic matter content (OMC) is found to have little influence in seismic anisotropy for the over mature WL shale, whereas the OMC determines the magnitude of anisotropy of immature/mature shales (e.g. the Bakken shale or the Bazhenov shale) according to the published literatures, because organic matters in shales of different maturity have different morphologies and distributions; (4) the OMC of WL shale has positive correlation with quartz content, and this weakens the correlation between OMC and the magnitude of anisotropy to a certain extent. The results of this study provide an important rock-physics basis and data support for seismic anisotropy exploration, quantitative interpretation and resource evaluation of the organic-rich marine shales in southern China.
- Published
- 2019
5. Amplitude anisotropy of shear-wave splitting and fluid detection in thin-layer reservoir
- Author
-
Xiang-Yang Li, Yun Wang, and Chunying Yang
- Subjects
Thin layers ,010504 meteorology & atmospheric sciences ,Thin layer ,Inverse transform sampling ,Shear wave splitting ,Mechanics ,010502 geochemistry & geophysics ,01 natural sciences ,Viscoelasticity ,Physics::Fluid Dynamics ,Geophysics ,Quality (physics) ,Amplitude ,Anisotropy ,Geology ,0105 earth and related environmental sciences - Abstract
Thin interbeds are typical reservoirs in eastern China. Thin layers and fractures bring huge challenge to fluid identification in anisotropic reservoir. This study focuses on thin-fractured reservoirs and amplitude attributes of shear-wave splitting, and consequently predicted fluid type in fractured reservoir based on the response of fast and slow S-waves to fluids. 3D HTI viscoelastic equation was employed to analyze amplitudes of split S-waves through fluid-filled and fractured media, including oil- and water-saturated synthetic models. Similar to velocity anisotropy, amplitude anisotropy was proposed to avoid the calculation of S-wave quality factor. Amplitude ratio and substation derived from amplitude anisotropy were used to identify fluid type. Example from the Luojia area of Shengli oilfield was used to demonstrate the effectiveness of the inversion method. Results show that amplitude ratio and amplitude subtraction are useful to distinguish fluids, while the former works better than the latter.
- Published
- 2019
6. Generating evacuation task plans for community typhoon emergencies: an integration of case-driven and model-driven approaches
- Author
-
Xiang-yang Li, Zhao-ge Liu, and Dilawar Khan Durrani
- Subjects
0209 industrial biotechnology ,Numerical Analysis ,021103 operations research ,Emergency management ,Computer science ,business.industry ,Strategy and Management ,0211 other engineering and technologies ,Computational intelligence ,02 engineering and technology ,Management Science and Operations Research ,Integrated approach ,Complement (complexity) ,Task (project management) ,020901 industrial engineering & automation ,Computational Theory and Mathematics ,Risk analysis (engineering) ,Management of Technology and Innovation ,Modeling and Simulation ,Typhoon ,Statistics, Probability and Uncertainty ,business - Abstract
In community emergency management, it is crucial to generate evacuation task plans (ETPs) to help reduce risks in complex disaster situations. Case-driven and model-driven approaches have their respective advantages in generating ETPs, which can complement each other. With case-driven approach, historical experience can be fully used to establish the relationship between typhoon scenarios and historical ETPs. Through model-driven approach, the continuity of ETPs can be guaranteed when required information to operate the plans is missing. This study aims at proposing an integrated approach that can combine the benefits of both case-driven approaches and model-driven approaches. Based on the structural modeling of evacuation tasks, this paper proposes an integrated approach to generate ETPs for community typhoon emergencies. Finally, a case that is based on actual problems is provided to verify the reasonability and effectiveness of the proposed method.
- Published
- 2019
7. Pre-stack AVA Inversion by Using Propagator Matrix Forward Modeling
- Author
-
Cong Luo, Guangtan Huang, and Xiang-Yang Li
- Subjects
Bayesian probability ,Mathematical analysis ,Inversion (meteorology) ,010502 geochemistry & geophysics ,Wave equation ,01 natural sciences ,Zoeppritz equations ,Geophysics ,Amplitude ,Geochemistry and Petrology ,Regularization (physics) ,Multiple ,0105 earth and related environmental sciences ,Mathematics ,Propagator matrix - Abstract
Most existing amplitude variation with angle (AVA) inversions are based on the exact Zoeppritz equation or its approximations. These modeling methods, which are ray-tracing-based and describe P-wave primary reflections only, lead to exacting requirements for pre-processing of the input data. Current processing is inadequate to satisfy these demands, especially for removing the effects of transmission losses, P-wave multiples and various converted-wave modes. By using input data with processing errors, inversion results of primary-only methods are predictably not accurate enough. The propagator matrix (PM), like the reflectivity method, uses an analytical solution to the wave equation and considers full-wave propagation effects in horizontal or nearly horizontal multilayered earth models. The numerical examples verify that a PM can effectively estimate transmission losses, multi-reflections and the comprehensive responses of thin interbedded layers, and also has higher reflection sensitivities to P-wave and S-wave velocity and density, as compared with ray-tracing-based AVA modelling. A pre-stack AVA three-parameter inversion by using a PM as the forward engine is proposed. Following a Bayesian approach, the inversion is stabilized by including the correlation of P-wave velocity, S-wave velocity and density. For inversion accuracy, the limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) optimization method is used to solve the augmented function, and the generalized cross-validation (GCV) criterion (Huang et al. in J Geophys Eng 14(1):100–112, 2017) is introduced to adaptively acquire the regularization parameter. Theoretical model inversion analysis shows that the proposed inversion can make use of transmission losses, P-wave multiples and converted wave modes, which not only cost-effectively simplifies the pre-processing, but also generates reasonable inverted results for multilayered conditions. The proposed inversion is then applied to a set of real data, and a comparison with Zoeppritz equation-based inversion demonstrates that PM inversion is clearly superior to Zoeppritz equation-based inversion in terms of stability and accuracy.
- Published
- 2019
8. Decision-making in highly stressful emergencies: The interactive effects of trait emotional intelligence
- Author
-
Xiang-yang Li, Muhammad Adeel Anjum, Dilawar Khan Durrani, and Syeda Maryam Dilawar
- Subjects
Interactive effects ,Turnover ,Emotional intelligence ,Multilevel model ,Applied psychology ,Stress (linguistics) ,Trait ,Sample (statistics) ,Psychology ,General Psychology ,Test (assessment) - Abstract
The purpose of this study was to examine whether, how, and when trait emotional intelligence (EI) influences the relationships between operational stress and decision-making styles for personnel working in highly stressful professions. Data for this study were collected via a cross-sectional and voluntary survey from a sample of 268 professionals (doctors = 60, paramedics = 99, police = 50 and personnel from paramilitary troops = 59) who frequently encounter emergencies as a part of their jobs. Hierarchical regression analysis and PROCESS macro for SPSS was used to test hypotheses. Results indicated that EI significantly moderated the relationships between: i) operational stress and rational decision-making, and ii) operational stress and intuitive decision-making such that the relationship of operational stress with rational and intuitive decision styles was significantly positive when EI was high and significantly negative when EI was low. EI also moderated the relationships between: i) operational stress and dependent style and ii) operational stress and avoidant style such that these relationships were positive when EI was low, and negative when EI was high. Along with its theoretical contributions, this study offers several implications for practice that are discussed at the end.
- Published
- 2019
9. Investigation of the Effects of Fracture Orientation and Saturation on the Vp/Vs Ratio and Their Implications
- Author
-
Guidong Di, Ding Wang, Pinbo Ding, and Xiang-Yang Li
- Subjects
Wave propagation ,0211 other engineering and technologies ,Geology ,Shear wave splitting ,Fluid saturation ,02 engineering and technology ,010502 geochemistry & geophysics ,Geotechnical Engineering and Engineering Geology ,01 natural sciences ,Hydraulic fracturing ,Geotechnical engineering ,Horizontal stress ,Anisotropy ,Saturation (chemistry) ,021101 geological & geomatics engineering ,0105 earth and related environmental sciences ,Civil and Structural Engineering - Abstract
Fractures are widely distributed within the Earth’s crust and have a substantial influence on wave propagation. Although many studies have been conducted on fracture characterization based on seismic anisotropic attributes, natural horizontal fractures and hydraulic fracture networks have yet to be characterized. Here, we investigate the influence of the fracture orientation and saturation on the Vp/Vs ratio via laboratory observations and theoretical modeling. Then, we discuss the feasibility of using the Vp/Vs ratio to predict natural horizontal fractures and evaluate hydraulic fracture networks. Our study demonstrates that an abnormally low Vp/Vs ratio, together with a lack of shear wave splitting, could be used to predict horizontal fractures. Fracture network development that results from hydraulic fracturing stimulation is associated with a much higher Vp/Vs ratio and no shear wave splitting; these two characteristics could be used to estimate fracture development and evaluate hydraulic fracturing stimulation.
- Published
- 2019
10. Corrosion behavior of low-carbon Cr micro-alloyed steel for grounding grids in simulated acidic soil
- Author
-
Li Li, Li Jian, Hang Su, Hui-min Meng, Feng Chai, Xiang-yang Li, and Xue Dongmei
- Subjects
Materials science ,Scanning electron microscope ,020209 energy ,Metallurgy ,Metals and Alloys ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Corrosion ,Metal ,Chromium ,X-ray photoelectron spectroscopy ,chemistry ,Mechanics of Materials ,visual_art ,Soil pH ,0202 electrical engineering, electronic engineering, information engineering ,Materials Chemistry ,visual_art.visual_art_medium ,0210 nano-technology ,Polarization (electrochemistry) ,Corrosion behavior - Abstract
To improve the corrosion resistance of steels for grounding grids, a low-carbon Cr micro-alloyed steel was developed (C1 steel), and corrosion behavior of Q235 steel and newly developed C1 steel in simulated acidic soil was investigated. The corrosion rate was evaluated with the mass loss measurements, while the corrosion morphology of surface and cross section of rust layer was observed by scanning electron microscopy. The corrosion products were analyzed by energy-dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy, and the polarization curve was measured using potentiodynamic polarization method. Results indicated that C1 steel displayed good corrosion resistance in the simulated acidic soil, of which the corrosion rate was only 30% of that of Q235 steel after corrosion for 360 h. The analysis of rust layer showed that lower carbon content in steel could reduce the tendency of micro cell corrosion and appropriate amount of chromium could improve the corrosion potential of metal matrix. Moreover, the analysis of X-ray photoelectron spectroscopy revealed that the chromium enriched in inner rust layer of C1 steel existed mainly in the form of Fe2CrO4, which facilitated the formation of Cr-goethite and improved the protection of corrosion products.
- Published
- 2018
11. Prediction of brittleness based on anisotropic rock physics model for kerogen-rich shale
- Author
-
Keran Qian, Zhi-Liang He, Xiwu Liu, Xiang-Yang Li, and Ye-Quan Chen
- Subjects
010504 meteorology & atmospheric sciences ,Lithology ,Modulus ,010502 geochemistry & geophysics ,01 natural sciences ,chemistry.chemical_compound ,Geophysics ,Brittleness ,chemistry ,Physical information ,Kerogen ,Statistical physics ,Anisotropy ,Porosity ,Oil shale ,0105 earth and related environmental sciences - Abstract
The construction of a shale rock physics model and the selection of an appropriate brittleness index (BI) are two significant steps that can influence the accuracy of brittleness prediction. On one hand, the existing models of kerogen-rich shale are controversial, so a reasonable rock physics model needs to be built. On the other hand, several types of equations already exist for predicting the BI whose feasibility needs to be carefully considered. This study constructed a kerogen-rich rock physics model by performing the selfconsistent approximation and the differential effective medium theory to model intercoupled clay and kerogen mixtures. The feasibility of our model was confirmed by comparison with classical models, showing better accuracy. Templates were constructed based on our model to link physical properties and the BI. Different equations for the BI had different sensitivities, making them suitable for different types of formations. Equations based on Young’s Modulus were sensitive to variations in lithology, while those using Lame’s Coefficients were sensitive to porosity and pore fluids. Physical information must be considered to improve brittleness prediction.
- Published
- 2017
12. Measurements of Seismic Anisotropy in Synthetic Rocks with Controlled Crack Geometry and Different Crack Densities
- Author
-
Jianxin Wei, Xiang-Yang Li, Ding Wang, Bangrang Di, and Pinbo Ding
- Subjects
Seismic anisotropy ,010504 meteorology & atmospheric sciences ,Theoretical models ,Mineralogy ,Geometry ,010502 geochemistry & geophysics ,01 natural sciences ,Azimuth ,Astron ,Geophysics ,Geochemistry and Petrology ,S-wave ,Ultrasonic sensor ,Anisotropy ,Intensity (heat transfer) ,Geology ,0105 earth and related environmental sciences - Abstract
Seismic anisotropy can help to extract azimuthal information for predicting crack alignment, but the accurate evaluation of cracked reservoir requires knowledge of degree of crack development, which is achieved through determining the crack density from seismic or VSP data. In this research we study the dependence of seismic anisotropy on crack density, using synthetic rocks with controlled crack geometries. A set of four synthetic rocks containing different crack densities is used in laboratory measurements. The crack thickness is 0.06 mm and the crack diameter is 3 mm in all the cracked rocks, while the crack densities are 0.00, 0.0243, 0.0486, and 0.0729. P and S wave velocities are measured by an ultrasonic investigation system at 0.5 MHz while the rocks are saturated with water. The measurements show the impact of crack density on the P and S wave velocities. Our results are compared to the theoretical prediction of Chapman (J App Geophys 54:191–202, 2003) and Hudson (Geophys J R Astron Soc 64:133–150, 1981). The comparison shows that measured velocities and theoretical results are in good quantitative agreement in all three cracked rocks, although Chapman’s model fits the experimental results better. The measured anisotropy of the P and S wave in the four synthetic rocks shows that seismic anisotropy is directly proportional to increasing crack density, as predicted by several theoretical models. The laboratory measurements indicate that it would be effective to use seismic anisotropy to determine the crack density and estimate the intensity of crack density in seismology and seismic exploration.
- Published
- 2017
13. Rotavirus NSP486–175 interacts with H9c2(2-1) cells in vitro, elevates intracellular Ca2+ levels and can become cytotoxic: a possible mechanism for extra-intestinal pathogenesis
- Author
-
Yinyin Hu, Xiang-yang Li, Cai-xia Liu, and Xiaoshun Xiong
- Subjects
0301 basic medicine ,030106 microbiology ,General Medicine ,Biology ,Actin cytoskeleton ,Actin cytoskeleton organization ,Calcium in biology ,Cell biology ,03 medical and health sciences ,030104 developmental biology ,Virology ,Genetics ,Extracellular ,Cytotoxic T cell ,Cytoskeleton ,Molecular Biology ,Intracellular ,Cytopathic effect - Abstract
Rotavirus (RV) is the predominant cause of infantile gastroenteritis with multiple pathogenic factors, among which enterotoxin NSP4 is the most significant factor. NSP4 has been shown to induce elevation of the intracellular calcium concentration, alteration of the cytoskeleton organization, and cytopathic effect among other processes. However, increasing evidence suggests that RVs can escape from the gastrointestinal tract and invade other organs and tissues to cause extra-intestinal diseases. In this study, we investigated whether NSP4 has a pathogenic effect on extra-intestinal cells and examined possible molecular mechanisms in vitro. Our results showed that NSP486-175 has important functions in increasing intracellular Ca2+ concentration, altering actin cytoskeleton organization and inducing cellular damage in H9c2(2-1) cells. Blockade of the integrin α2 receptor using a specific antibody attenuated the increase of intracellular Ca2+ concentration and alleviated the observed cytopathic effects, suggesting that integrin α2 may be a receptor for NSP486-175. Collectively, these results indicate that extracellular NSP486-175 can induce elevation of the intracellular Ca2+ concentration, cause cytotoxic changes, and disrupt the actin cytoskeleton in H9c2(2-1) cells, which may constitute a possible mechanism for RV extra-intestinal pathogenesis.
- Published
- 2016
14. Link scheduling for throughput maximization in multihop wireless networks under physical interference
- Author
-
Min Liu, Xiaohua Xu, Yaqin Zhou, Zhongcheng Li, and Xiang-Yang Li
- Subjects
Mathematical optimization ,Job shop scheduling ,Computer Networks and Communications ,Wireless network ,Computer science ,020206 networking & telecommunications ,Throughput ,02 engineering and technology ,Throughput maximization ,Scheduling (computing) ,0202 electrical engineering, electronic engineering, information engineering ,Graph (abstract data type) ,020201 artificial intelligence & image processing ,Electrical and Electronic Engineering ,Information Systems - Abstract
We consider the problem of link scheduling for throughput maximization in multihop wireless networks. Majority of previous methods are restricted to graph-based interference models. In this paper we study the link scheduling problem using a more realistic physical interference model. Through some key observations about this model, we develop efficient link scheduling algorithms by exploiting the intrinsic connections between the physical interference model and the graph-based interference model. For one variant of the problem where each node can dynamically adjust its transmission power, we design a scheduling method with O(g(E)) approximation to the optimal throughput capacity where g(E) denotes length diversity. For the other variant where each node has a fixed but possible different transmission powers for different nodes, we design a method with O(g(E))-approximation ratio when the transmission powers of all nodes are within a constant factor of each other, and in general with an approximation ratio of $$O(g(E)\log \rho )$$ where $$\log \rho$$ is power diversity. We further prove that our algorithm for fixed transmission power case retains O(g(E)) approximation for any length-monotone, sub-linear fixed power setting. Furthermore, all these approximation factors are independent of network size .
- Published
- 2016
15. The application study on the multi-scales integrated prediction method to fractured reservoir description
- Author
-
Shuangquan Chen, Xiang-Yang Li, Wan-Lu Zhang, Shao-Han Sun, Lianbo Zeng, and Ping Huang
- Subjects
010504 meteorology & atmospheric sciences ,Lithology ,Attenuation ,Inversion (geology) ,Seismic attribute ,010502 geochemistry & geophysics ,01 natural sciences ,Geophysics ,Reservoir modeling ,Fracture (geology) ,Macro ,Anisotropy ,Geology ,Seismology ,0105 earth and related environmental sciences - Abstract
In this paper, we implement three scales of fracture integrated prediction study by classifying it to macro- (> 1/4λ), meso- (> 1/100λ and < 1/4λ) and micro- (< 1/100λ) scales. Based on the multi-scales rock physics modelling technique, the seismic azimuthal anisotropy characteristic is analyzed for distinguishing the fractures of meso-scale. Furthermore, by integrating geological core fracture description, image well-logging fracture interpretation, seismic attributes macro-scale fracture prediction and core slice micro-scale fracture characterization, an comprehensive multi-scale fracture prediction methodology and technique workflow are proposed by using geology, well-logging and seismic multi-attributes. Firstly, utilizing the geology core slice observation (Fractures description) and image well-logging data interpretation results, the main governing factors of fracture development are obtained, and then the control factors of the development of regional macro-scale fractures are carried out via modelling of the tectonic stress field. For the meso-scale fracture description, the poststack geometric attributes are used to describe the macro-scale fracture as well, the prestack attenuation seismic attribute is used to predict the meso-scale fracture. Finally, by combining lithological statistic inversion with superposed results of faults, the relationship of the meso-scale fractures, lithology and faults can be reasonably interpreted and the cause of meso-scale fractures can be verified. The micro-scale fracture description is mainly implemented by using the electron microscope scanning of cores. Therefore, the development of fractures in reservoirs is assessed by valuating three classes of fracture prediction results. An integrated fracture prediction application to a real field in Sichuan basin, where limestone reservoir fractures developed, is implemented. The application results in the study area indicates that the proposed multi-scales integrated fracture prediction method and the technique procedureare able to deal with the strong heterogeneity and multi-scales problems in fracture prediction. Moreover, the multi-scale fracture prediction technique integrated with geology, well-logging and seismic multi-information can help improve the reservoir characterization and sweet-spots prediction for the fractured hydrocarbon reservoirs.
- Published
- 2016
16. Modeling and analysis of azimuthal AVO responses from a viscoelastic anisotropic reflector
- Author
-
Xiwu Liu, Xiang-Yang Li, Wei Fu, and Zhiqi Guo
- Subjects
Physics ,business.industry ,Attenuation ,Velocity dispersion ,Reflector (antenna) ,Interference (wave propagation) ,Azimuth ,Geophysics ,Amplitude ,Optics ,Reflection (physics) ,Nuclear Experiment ,Dispersion (water waves) ,business - Abstract
We propose a method for modeling azimuthal AVO responses from a fractured reflector. The method calculates the integrated reflected wavetrains, and the wavetrains contain elastodynamic information including the contrast in impedance and anelasticity across interfaces, the internal anisotropic propagation, the dispersion and attenuation along the wave path, and tuning and interference. The results suggest that for large angles of incidence, the velocity dispersion and attenuation increase the amplitudes of PP waves from the top and decrease those from the bottom. For azimuthal responses at specific angles of incidence, the reflected wavetrains of PP waves tend to have longer duration with increasing azimuth. In contrast, model-converted PSV and PSH reflections show stable azimuthal features and are less affected by the reflector thickness. The amplitudes of PSV reflections increase with increasing azimuth; moreover, the waves have no reflection energy at 0° and 90° azimuth and maximum amplitude at 45° azimuth.
- Published
- 2015
17. Seismic signatures of reservoir permeability based on the patchy-saturation model
- Author
-
Cai Liu, Xiang-Yang Li, and Zhiqi Guo
- Subjects
Permeability (earth sciences) ,Geophysics ,Amplitude ,Frequency domain ,Attenuation ,Mineralogy ,Velocity dispersion ,Seismic inversion ,Saturation (chemistry) ,Electrical impedance ,Geology ,Seismology - Abstract
Modeling of seismic responses of variable permeability on the basis of the patchy-saturation model provides insights into the seismic characterization of fluid mobility. We linked rock-physics models in the frequency domain and seismic modeling on the basis of the propagator matrix method. For a layered patchy-saturated reservoir, the seismic responses represent a combination of factors, including impedance contrast, the effect of dispersion and attenuation within the reservoir, and the tuning and interference of reflections at the top and bottom of the reservoir. Numerical results suggest that increasing permeability significantly reduces the P-wave velocity and induces dispersion between the high- and low-frequency elastic limit. Velocity dispersion and the layered structure of a reservoir lead to complex reflection waveforms. Seismic reflections are sensitive to permeability if the impedance of the reservoir is close to that of the surroundings. For variable layer thickness, the stacked amplitudes increase with permeability for high-velocity surrounding shale, whereas the stacked amplitudes decrease with permeability for low-velocity surrounding shale.
- Published
- 2015
18. Simulated corrosion test of Q235 steel in diatomite soil
- Author
-
Feng Chai, Xiang-yang Li, Jian Li, Hang Su, Hui-min Meng, and Xiao-ping Chen
- Subjects
Materials science ,Mechanics of Materials ,Scanning electron microscope ,Soil pH ,Metallurgy ,Metallic materials ,Materials Chemistry ,Metals and Alloys ,Corrosion behavior ,Water content ,Corrosion - Abstract
Through the study of the corrosion behavior of Q235 steel in actual Yingtan soil and two simulated acidic soils with different water contents, the calculation of corrosion mass losses, and the analysis of the corrosion morphologies and products by means of scanning electron microscope (SEM) and X-ray diffraction (XRD), the results demonstrated that the diatomite soil could simulate the corrosion in actual soil veritably. In both actual soil and simulated soil with 16.4% water content, the corrosion rates of Q235 steel were approximately 0.1 mm/a, the corrosion morphologies were mainly extension and connection of corrosion spots on sample surface, and the corrosion products were composed of α-FeOOH, γ-FeOOH, Fe3O4 and Fe2O3. When other media conditions remained unchanged, the corrosion area of Q235 steel was larger in simulated soil with 34.5% water content, and the corrosion rate reached 0.48 mm/a after 360 h of corrosion, which was nearly 5 times as the value in actual soil. Compared with the corrosion products in actual soil, the proportion of γ-FeOOH in simulated soil with 34.5% water content was higher, and the wα-FeOOH/wγ-FeOOH ratio was 1.4, which was only 1/3 of the value in actual soil.
- Published
- 2015
19. Application of the double absorbing boundary condition in seismic modeling
- Author
-
Xiang-Yang Li, Shuangquan Chen, and Yang Liu
- Subjects
Absorption (acoustics) ,Geophysics ,Perfectly matched layer ,Seismic modeling ,Mathematical analysis ,Reflection (physics) ,Finite difference method ,Boundary (topology) ,Boundary value problem ,Stability (probability) ,Mathematics - Abstract
We apply the newly proposed double absorbing boundary condition (DABC) (Hagstrom et al., 2014) to solve the boundary reflection problem in seismic finite-difference (FD) modeling. In the DABC scheme, the local high-order absorbing boundary condition is used on two parallel artificial boundaries, and thus double absorption is achieved. Using the general 2D acoustic wave propagation equations as an example, we use the DABC in seismic FD modeling, and discuss the derivation and implementation steps in detail. Compared with the perfectly matched layer (PML), the complexity decreases, and the stability and flexibility improve. A homogeneous model and the SEG salt model are selected for numerical experiments. The results show that absorption using the DABC is considerably improved relative to the Clayton-Engquist boundary condition and nearly the same as that in the PML.
- Published
- 2015
20. Assessing Diagnosis Approaches for Wireless Sensor Networks: Concepts and Analysis
- Author
-
Kebin Liu, Jizhong Zhao, Meng Wan, Yuan He, Rui Li, Zhi Wang, Wei Xi, and Xiang-Yang Li
- Subjects
Skyline ,Property (programming) ,Computer science ,business.industry ,Distributed computing ,Reliability (computer networking) ,computer.software_genre ,Computer Science Applications ,Theoretical Computer Science ,Computational Theory and Mathematics ,Hardware and Architecture ,Overhead (computing) ,Wireless ,Data mining ,business ,Wireless sensor network ,computer ,Software - Abstract
Diagnosis is of great importance to wireless sensor networks due to the nature of error prone sensor nodes and unreliable wireless links. The state-of-the-art diagnostic tools focus on certain types of faults, and their performances are highly correlated with the networks they work with. The network administrators feel difficult in measuring the effectiveness of their diagnosis approaches and choosing appropriate tools so as to meet the reliability demand. In this work, we introduce the D-vector to characterize the property of a diagnosis approach. The D-vector has five dimensions, namely the degree of coupling, the granularity, the overhead, the tool reliability and the network reliability, quantifying and evaluating the effectiveness of current diagnostic tools in certain applications. We employ a skyline query algorithm to find out the most effective diagnosis approaches, i.e., skyline points (SPs), from five dimensions of all potential D-vectors. The selected skyline D-vector points can further guide the design of various diagnosis approaches. In our trace-driven simulations, we design and select tailored diagnostic tools for GreenOrbs, achieving high performance with relatively low overhead.
- Published
- 2014
21. Communicating Is Crowdsourcing: Wi-Fi Indoor Localization with CSI-Based Speed Estimation
- Author
-
Zhi Wang, Bo Xiao, Shaojie Tang, Wei Xi, Kun Zhao, Jizhong Zhao, Zhiping Jiang, Jin Song Han, and Xiang-Yang Li
- Subjects
Scheme (programming language) ,Service (systems architecture) ,Computer science ,business.industry ,RSS ,Fingerprint (computing) ,Real-time computing ,computer.file_format ,Crowdsourcing ,Computer Science Applications ,Theoretical Computer Science ,Computational Theory and Mathematics ,Hardware and Architecture ,Channel state information ,business ,computer ,Software ,computer.programming_language ,Computer network - Abstract
Numerous indoor localization techniques have been proposed recently to meet the intensive demand for location-based service (LBS). Among them, the most popular solutions are the Wi-Fi fingerprint-based approaches. The core challenge is to lower the cost of fingerprint site-survey. One of the trends is to collect the piecewise data from clients and establish the radio map in crowdsourcing manner. However the low participation rate blocks the practical use. In this work, we propose a passive crowdsourcing channel state information (CSI) based indoor localization scheme, C2IL. Despite a crowdsourcing based approach, our scheme is totally transparent to the client and the only requirement is to connect to our 802.11n access points (APs). C2IL is built upon an innovative method to accurately estimate the moving speed solely based on 802.11n CSI. Knowing the walking speed of a client and its surrounding APs, a graph matching algorithm is employed to extract the received signal strength (RSS) fingerprints and establish the fingerprint map. For localization phase, we design a trajectory clustering based localization algorithm to provide precise real-time indoor localization and tracking. We develop and deploy a practical working system of C2IL in a large office environment. Extensive evaluations indicate that the error of speed estimation is within 3%, and the localization error is within 2 m at 80% time in a very complex indoor environment.
- Published
- 2014
22. SA-MAC: Self-Stabilizing Adaptive MAC Protocol for Wireless Sensor Networks
- Author
-
Yue Tao, Paul R. Anderson, Shangping Ren, Fouad Teymour, Xiang-Yang Li, and Cheng Bo
- Subjects
business.industry ,Computer science ,Network packet ,ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS ,Real-time computing ,Energy consumption ,Computer Science Applications ,Theoretical Computer Science ,Key distribution in wireless sensor networks ,Computational Theory and Mathematics ,Transmission (telecommunications) ,Hardware and Architecture ,Sensor node ,Mobile wireless sensor network ,business ,Protocol (object-oriented programming) ,Wireless sensor network ,Software ,Computer network - Abstract
A common method of prolonging the lifetime of wireless sensor networks is to use low power duty cycling protocol. Existing protocols consist of two categories: sender-initiated, and receiver-initiated. In this paper, we present SA-MAC, a Self-stabilizing Adaptive MAC protocol for wireless sensor networks. SA-MAC dynamically adjusts the transmission time-slot, waking up time-slot, and packet detection patten according to current network working condition, such as packet length and wake-up patterns of neighboring nodes. In the long run, every sensor node will find its own transmission phase so that the network will enter a stable stage when the network load and qualities are static. We conduct extensive experiments to evaluate the energy consumption, packet reception rate of SA-MAC in real sensor networking systems. Our results indicate that SA-MAC outperforms other existing protocols.
- Published
- 2014
23. The analysis and application of simplified two-parameter moveout equation for C-waves in VTI anisotropy media
- Author
-
Shuangquan Chen, Xiang-Yang Li, and Xiao-Ming Li
- Subjects
Physics ,Data processing ,Geophysics ,Matching (graph theory) ,Estimation theory ,Transverse isotropy ,Mathematical analysis ,Isotropy ,Stacking ,Mineralogy ,Anisotropy ,Interpretation (model theory) - Abstract
Several parameters are needed to describe the converted-wave (C-wave) moveout in processing multi-component seismic data, because of asymmetric raypaths and anisotropy. As the number of parameters increases, the converted wave data processing and analysis becomes more complex. This paper develops a new moveout equation with two parameters for C-waves in vertical transverse isotropy (VTI) media. The two parameters are the C-wave stacking velocity (V C2) and the squared velocity ratio (γ vti ) between the horizontal P-wave velocity and C-wave stacking velocity. The new equation has fewer parameters, but retains the same applicability as previous ones. The applicability of the new equation and the accuracy of the parameter estimation are checked using model and real data. The form of the new equation is the same as that for layered isotropic media. The new equation can simplify the procedure for C-wave processing and parameter estimation in VTI media, and can be applied to real C-wave processing and interpretation. Accurate V C2 and γ vti can be deduced from C-wave data alone using the double-scanning method, and the velocity ratio model is suitable for event matching between P- and C-wave data.
- Published
- 2013
24. Microstructure and Properties of Hot Working Die Steel H13MOD
- Author
-
Zai-zhi Chen, Dang-shen Ma, Hong-xiao Chi, Xiang-yang Li, and Jian Zhou
- Subjects
Austenite ,Quenching ,Toughness ,Hot working ,Materials science ,Mechanics of Materials ,Metallurgy ,Materials Chemistry ,Metals and Alloys ,Tempering ,Microstructure ,Die casting ,Eutectic system - Abstract
Compared with H13 steel, the influences of different heat treatment process on the microstructure and properties of the new type of hot working die steel H3MOD were studied. The results show that the complete austenitizing temperature of H13MOD is around 1030 °C and the quenching hardness achieves the maximum value at this temperature. While for H13, the complete austenitizing temperature is above 1100 °C and the quenching hardness rise constantly with the quenching temperature increasing. In quenching process, the undissolved MCcarbides can prevent the coarsening of grain in both steels. With the rise of quenching temperature, when MCcarbides dissolve completely, the grain grows quickly. The hardness and strength of H13MOD at higher tempering temperature (above 570 °C ) are nearly the same as those of H13, but its toughness is higher than that of H13. Mo2C carbide is the main strengthening phase in H13MOD, which is atributed to the higher content of Mo. The quantity of VC eutectic carbides is reduced because of lower content of V in H13MOD, which plays an important role in enhancing the impact toughness of H13MOD. Under a certain strength condition, H13MOD steel can be used in the environment that higher toughness is required and the service life of die casting mold can be improved.
- Published
- 2013
25. The influence of mesoscopic flow on the P-wave attenuation and dispersion in a porous media permeated by aligned fractures
- Author
-
Jianguo Zhao, Shangxu Wang, Jixin Deng, Xiang-Yang Li, and Gengyang Tang
- Subjects
Materials science ,business.industry ,Attenuation ,Poromechanics ,Velocity dispersion ,Mechanics ,Physics::Geophysics ,Geophysics ,Optics ,Geochemistry and Petrology ,Dispersion relation ,Dispersion (optics) ,business ,Porous medium ,Acoustic attenuation ,Longitudinal wave - Abstract
In sedimentary rocks attenuation/dispersion is dominated by fluid-rock interactions. Wave-induced fluid flow in the pores causes energy loss through several mechanisms, and as a result attenuation is strongly frequency dependent. However, the fluid motion process governing the frequency dependent attenuation and velocity remains unclear. We propose a new approach to obtain the analytical expressions of pore pressure, relative fluxes distribution and frame displacement within the double-layer porous media based on quasi-static poroelastic theory. The dispersion equation for a P-wave propagating in a porous medium permeated by aligned fractures is given by considering fractures as thin and highly compliant layers. The influence of mesoscopic fluid flow on phase velocity dispersion and attenuation is discussed under the condition of varying fracture weakness. In this model conversion of the compression wave energy into Biot slow wave diffusion at the facture surface can result in apparent attenuation and dispersion within the usual seismic frequency band. The magnitude of velocity dispersion and attenuation of P-wave increases with increasing fracture weakness, and the relaxation peak and maximum attenuation shift towards lower frequency. Because of its periodic structure, the fractured porous media can be considered as a phononic crystal with several pass and stop bands in the high frequency band. Therefore, the velocity and attenuation of the P-wave show an oscillatory behavior with increasing frequency when resonance occurs. The evolutions of the pore pressure and the relative fluxes as a function of frequency are presented, giving more physical insight into the behavior of P-wave velocity dispersion and the attenuation of fractured porous medium due to the wave-induced mesoscopic flow. We show that the specific behavior of attenuation as function of frequency is mainly controlled by the energy dissipated per wave cycle in the background layer.
- Published
- 2013
26. Study of S-wave ray elastic impedance for identifying lithology and fluid
- Author
-
Shuangquan Chen, Feng Zhang, Xue-ping Gong, and Xiang-Yang Li
- Subjects
Physics ,Sample group ,Geophysics ,Lithology ,Mathematical analysis ,S-wave ,Reflection (physics) ,Mineralogy ,Data application ,Reflection coefficient ,Electrical impedance - Abstract
In this paper, we derive an approximation of the SS-wave reflection coefficient and the expression of S-wave ray elastic impedance (SREI) in terms of the ray parameter. The SREI can be expressed by the S-wave incidence angle or P-wave reflection angle, referred to as SREIS and SREIP, respectively. Our study using elastic models derived from real log measurements shows that SREIP has better capability for lithology and fluid discrimination than SREIS and conventional S-wave elastic impedance (SEI). We evaluate the SREIP feasibility using 25 groups of samples from Castagna and Smith (1994). Each sample group is constructed by using shale, brine-sand, and gas-sand. Theoretical evaluation also indicates that SREIP at large incident angles is more sensitive to fluid than conventional fluid indicators. Real seismic data application also shows that SREIP at large angles calculated using P-wave and S-wave impedance can efficiently characterize tight gas-sand.
- Published
- 2013
27. Numerical modeling of PP- and PS-wave azimuthal anisotropy in HTI media
- Author
-
Na Lei, Bo Zhao, Xiang-Yang Li, Zhongping Qian, and Shao-Hua Zhang
- Subjects
Physics ,Offset (computer science) ,business.industry ,Observable ,Geometry ,Ellipse ,Azimuth ,Geophysics ,Amplitude ,Optics ,Perpendicular ,business ,Anisotropy ,Elliptical distribution - Abstract
This study focuses on the factors that may affect the feasibility of performing elliptical anisotropy analysis on azimuthal PP- and PS-wave data in HTI media, with the aim of using the modeling results as guidance in real seismic data application. Our results reveal that there is an offset limitation for both PP- and PS-waves in elliptical anisotropy fitting, and that PS-waves show a wider applicable offset range and larger observable azimuthal anisotropy than PP-waves. The major axis of the elliptical fit to the amplitudes of the R-component is perpendicular to the fracture strike, which is opposite to that in PP-wave analysis. The azimuthal interval travel time of PS-waves shows a nearly elliptical distribution and the major axis of the fit ellipse is perpendicular to the fracture strike, which is same as that in PP-wave analysis. For data within the applicable offset range, the anisotropic magnitude obtained from amplitude and travel time attributes of PP- and PS-waves exhibits a dependence on fracture density, and the major to minor axis ratio of the fit ellipse may be used to infer the relative distribution of fracture densities.
- Published
- 2012
28. SmartLoc: sensing landmarks silently for smartphone-based metropolitan localization
- Author
-
Xiang-Yang Li, Yu Wang, Taeho Jung, Xufei Mao, and Cheng Bo
- Subjects
Computer Networks and Communications ,Computer science ,Real-time computing ,02 engineering and technology ,Accelerometer ,GPS signals ,01 natural sciences ,law.invention ,law ,Inertial measurement unit ,Compass ,11. Sustainability ,0202 electrical engineering, electronic engineering, information engineering ,Simulation ,business.industry ,010401 analytical chemistry ,020206 networking & telecommunications ,Gyroscope ,0104 chemical sciences ,Computer Science Applications ,13. Climate action ,Assisted GPS ,Signal Processing ,Global Positioning System ,Noise (video) ,business - Abstract
We present SmartLoc, a system to estimate the location and the traveling distance of a vehicle in urban environments by leveraging the lower-power inertial sensors (e.g., accelerometer, gyroscope, compass) embedded in smartphones. It has been well documented that the inherent noise in the data measured from these sensors will result in a huge drift in the final estimated moving distance and hurt the performance of location-based applications. In SmartLoc, we designed, tested, and evaluated a sequence of techniques to address this notoriously challenging task of noise canceling. By exploiting the intermittent strong GPS signals, we use the linear regression to build a prediction model from the trace estimated from inertial sensors and the trace computed from GPS. We extensively rely on automatically detected landmarks (e.g., bridge, traffic lights) and special driving patterns (e.g., turning, uphill, and downhill) from inertial sensors data to improve the localization accuracy when the GPS signal is weak. Our evaluations of SmartLoc in a large city demonstrate its technique viability and significant localization accuracy improvement compared with GPS and other approaches: the error is approximately within 20 m for 90 % of the time. SmartLoc system can also reduce the energy consumption for localization by carefully turning off GPS under certain scenarios.
- Published
- 2016
29. Asymptotic throughput for large-scale wireless networks with general node density
- Author
-
Changjun Jiang, Yunhao Liu, Cheng Wang, and Xiang-Yang Li
- Subjects
Discrete mathematics ,Multicast ,Computer Networks and Communications ,Wireless network ,Wireless ad hoc network ,business.industry ,Computer science ,Node (networking) ,Throughput ,Scale (descriptive set theory) ,Computer Science::Networking and Internet Architecture ,Electrical and Electronic Engineering ,Unicast ,business ,Throughput (business) ,Information Systems ,Computer network - Abstract
We study the asymptotic throughput for a large-scale wireless ad hoc network consisting of n nodes under the generalized physical model. We directly compute the throughput of multicast sessions to unify the unicast and broadcast throughputs. We design two multicast schemes based on the so-called ordinary arterial road system and parallel arterial road system, respectively. Correspondingly, we derive the achievable multicast throughput by taking account of all possible cases of n s = ?(1) and 1 ? n d ? n ? 1, rather than only the cases of $$n_s=\Uptheta(n)$$ as in most related works, where n s and n d denote the number of sessions and the number of destinations of each session, respectively. Furthermore, we consider the network with a general node density $$\lambda \in [1,n]$$ , while the models in most related works are either random dense network (RDN) or random extended network (REN) where the density is ? = n and ? = 1, respectively, which further enhances the generality of this work. Particularly, for the special case of our results by letting ? = 1 and $$n_s=\Uptheta(n)$$ , we show that for some regimes of n d , the multicast throughputs achieved by our schemes are better than those derived by the well-known percolation-based schemes.
- Published
- 2012
30. Converted-wave diodic moveout and application in the land gas cloud area
- Author
-
Xiang-Yang Li, Heng-Chang Dai, and Si-Hai Zhang
- Subjects
business.industry ,Computation ,Mineralogy ,Perturbation (astronomy) ,Cloud computing ,Residual ,Geophysics ,Natural gas ,business ,Statics ,Perturbation method ,Astrophysics::Galaxy Astrophysics ,Geology ,Seismology - Abstract
PS converted-waves (C-waves) have been commonly used to image through gas clouds but the C-wave imaging may also be degraded by the diodic effect introduced by the gas cloud. It may be compensated for using a velocity perturbation method which decouples the diodic moveout into two parts: the base velocity and the velocity perturbation. Gas clouds are widely distributed in the Sanhu area in the Qaidam basin of northwest China which is rich in natural gas. A land 2D3C seismic dataset is analyzed from the Sanhu area and significant diodic effects are observed in the data which harm the C-wave imaging. The diodic correction is applied to this data and the resultant C-wave imaging and the details of the reservoir structure are significantly improved. The diodic moveout plays an important role in working out the residual shear wave statics and the association of diodic correction and shear wave residual statics computation is a key step of C-wave high fidelity imaging in the gas cloud area. Finally, the new process workflow with diodic moveout is given.
- Published
- 2011
31. Impact of deployment size on the asymptotic capacity for wireless ad hoc networks under Gaussian channel model
- Author
-
Shaojie Tang, Xiang-Yang Li, Xufei Mao, and Cheng Wang
- Subjects
Multicast ,Computer Networks and Communications ,Computer science ,business.industry ,Wireless ad hoc network ,Wireless network ,Node (networking) ,ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS ,Signal-to-interference-plus-noise ratio ,Throughput ,Topology ,Computer Science::Networking and Internet Architecture ,Wireless ,Electrical and Electronic Engineering ,Unicast ,business ,Computer Science::Information Theory ,Information Systems ,Computer network - Abstract
We study the throughput capacity and transport capacity for both random and arbitrary wireless networks under Gaussian Channel model when all wireless nodes have the same constant transmission power P and the transmission rate is determined by Signal to Interference plus Noise Ratio (SINR). We consider networks with n wireless nodes $$\{v_1,v_2,\ldots,v_n\}$$ (randomly or arbitrarily) distributed in a square region B a with a side-length a. We randomly choose n s node as the source nodes of n s multicast sessions. For each source node v i , we randomly select k points and the closest k nodes to these points as destination nodes of this multicast session. We derive achievable lower bounds and some upper bounds on both throughput capacity and transport capacity for both unicast sessions and multicast sessions. We found that the asymptotic capacity depends on the size a of the deployment region, and it often has three regimes.
- Published
- 2011
32. Flow admission control for multi-channel multi-radio wireless networks
- Author
-
Xufei Mao, Xiang-Yang Li, and Guojun Dai
- Subjects
Wireless mesh network ,Computer Networks and Communications ,business.industry ,Computer science ,Wireless network ,Call Admission Control ,Quality of service ,Distributed computing ,ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS ,Mesh networking ,Time division multiple access ,Order One Network Protocol ,Admission control ,Metrics ,Scheduling (computing) ,Hop (networking) ,Distributed algorithm ,Wireless ,Network performance ,Electrical and Electronic Engineering ,business ,Information Systems ,Computer network - Abstract
Providing Quality of Service (QoS) is a major challenge in wireless networks. In this paper we propose a distributed call admission control protocol (DCAC) to do both bandwidth and delay guaranteed call admission for multihop wireless mesh backbone networks, by exploiting the multi-channel multi-radio (mc-mr) feature. We propose a novel routing metric for route setup, and present an efficient distributed algorithm for link reservation that satisfies the required bandwidth and reduces the delay by a local scheduling that minimizes one hop delay. To the best of our knowledge, this is the first distributed protocol that embeds mc-mr feature in Time Division Medium Access (TDMA) to do QoS call admission in wireless backbone networks. Extensive simulation studies show that our protocol significantly improves network performance on supporting QoS sessions compared with some widely used protocols.
- Published
- 2010
33. Capacity of data collection in randomly-deployed wireless sensor networks
- Author
-
Siyuan Chen, Yu Wang, Xiang-Yang Li, and Xinghua Shi
- Subjects
Combinatorics ,Computer Networks and Communications ,Computer science ,Network packet ,TheoryofComputation_ANALYSISOFALGORITHMSANDPROBLEMCOMPLEXITY ,Data mining ,Electrical and Electronic Engineering ,computer.software_genre ,computer ,Wireless sensor network ,Information Systems - Abstract
Data collection is one of the most important functions provided by wireless sensor networks. In this paper, we study theoretical limitations of data collection and data aggregation in terms of delay and capacity for a wireless sensor network where n sensors are randomly deployed. We consider different communication scenarios such as with single sink or multiple sinks, regularly-deployed or randomly-deployed sinks, with or without aggregation. For each scenario, we not only propose a data collection/aggregation method and analyze its performance in terms of delay and capacity, but also theoretically prove whether our method can achieve the optimal order (i.e., its performance is within a constant factor of the optimal). Particularly, with a single sink, the capacity of data collection is in order of $$\Uptheta(W)$$ where W is the fixed data-rate on individual links. With k regularly deployed sinks, the capacity of data collection is increased to $$\Uptheta(kW)$$ when $$k=O\left({\frac{n}{\log n}}\right)$$ or $$\Uptheta\left({\frac{n}{\log n}}W\right)$$ when $$k=\Upomega\left({\frac{n}{\log n}}\right)$$ . With k randomly deployed sinks, the capacity of data collection is between $$\Uptheta\left({\frac{k}{\log k}}W\right)$$ and $$\Uptheta(kW)$$ when $$k=O\left({\frac{n}{\log n}}\right)$$ or $$\Uptheta\left({\frac{n}{\log n}}W\right)$$ when $$k=\omega\left({\frac{n}{\log n}}\right)$$ . If each sensor can aggregate its receiving packets into a single packet to send, the capacity of data collection with a single sink is also increased to $$\Uptheta\left({\frac{n}{\log n}}W\right)$$ .
- Published
- 2010
34. Long-term large-scale sensing in the forest: recent advances and future directions of GreenOrbs
- Author
-
Jizhong Zhao, Lufeng Mo, Kebin Liu, Guomo Zhou, Yuan He, Wei Xi, Xiang-Yang Li, Ming Gu, Yunhao Liu, Wei Dong, Mo Li, Guojun Dai, Huadong Ma, and Wang Jiliang
- Subjects
Key distribution in wireless sensor networks ,General Computer Science ,Computer science ,Software deployment ,Scale (chemistry) ,Systems engineering ,Wireless sensor network ,Simulation ,Theoretical Computer Science ,Term (time) - Abstract
We introduce GreenOrbs, our recent effort in exploring the fundamental challenges and future direction of long-term large-scale applications of wireless sensor networks. An integrated framework with more than 1000 sensors has been implemented, including the indoor test bed, prototype systems, and forest deployment: comprehensively supporting research, development, and forestry applications.
- Published
- 2010
35. Microstructure and Transformation Characteristics of Acicular Ferrite in High Niobium-Bearing Microalloyed Steel
- Author
-
Dong-bai Sun, Xiang-yang Li, Qing-you Liu, and Jing-hong Yang
- Subjects
Materials science ,Misorientation ,Beta ferrite ,Metallurgy ,Metals and Alloys ,Niobium ,chemistry.chemical_element ,Continuous cooling transformation ,engineering.material ,Microstructure ,Acicular ferrite ,chemistry ,Mechanics of Materials ,Ferrite (iron) ,Materials Chemistry ,engineering ,Microalloyed steel - Abstract
The transformation behavior and microstructural characteristics of a low carbon high niobium-bearing microalloyed pipeline steel were investigated by deformation dilatometry and microstructure observation. The continuous cooling transformation curves of the test steel were constructed. The results showed that high niobium content and deformation enhanced the formation of acicular ferrite; the microstructures changed from polygonal ferrite, quasi-polygonal ferrite to acicular ferrite with increasing cooling rates from 0.5 to 50 °C/s and was dominated by acicular ferrite in a broadened cooling rate higher than 5 °C/s. The chaotic microstructure consisted of non-equiaxed ferrite and interwoven ferrite laths with high density dislocations and subunits. The results of isothermal holding treatment showed that acicular ferrite microstructure was formed at 550 — 600 °C and consisted of highly misoriented plate packets having internal low angle boundaries. With increasing the holding time or temperature, some low misorientation boundaries changed to high misorientation owing to the movement of dislocations and coarsening of grain.
- Published
- 2010
36. Multicast throughput for large scale cognitive networks
- Author
-
Changjun Jiang, Cheng Wang, Yunhao Liu, and Xiang-Yang Li
- Subjects
Multicast ,Computer Networks and Communications ,Computer science ,business.industry ,Wireless ad hoc network ,Distributed computing ,Time division multiple access ,Throughput ,Cognitive network ,Metric (mathematics) ,Electrical and Electronic Engineering ,Unicast ,Routing (electronic design automation) ,business ,Throughput (business) ,Information Systems ,Computer network - Abstract
In this paper, we focus on the achievable throughput of cognitive networks consisting of the primary ad hoc network (PaN) and the secondary ad hoc network (SaN). We construct PaN and SaN by placing nodes according to Poisson point processes of density n and m respectively over a unit square region. We directly study the multicast throughput of cognitive network to unify that of unicast and broadcast sessions. In order to ensure the priority of primary users in meanings of throughput, we design a metric called throughput decrement ratio (TDR) to measure the ratio of the throughput of PaN in presence of SaN to that of PaN in absence of SaN. Endowing PaN with the right to determine the threshold of the TDR, we propose multicast schemes based on TDMA and multihop routing for the two networks respectively and derive their achievable multicast throughput depending on the given threshold. Specially, we show when PaN has sparser density than SaN, to be specific, $$n=o\left({\frac{m} {(\log m)^2}}\right),$$ and if PaN only cares about the order of its throughput, SaN can simultaneously achieve the same order of the aggregated multicast throughput as it were a stand-alone network in absence of PaN.
- Published
- 2010
37. Cost sharing and strategyproof mechanisms for set cover games
- Author
-
Zheng Sun, Xiang-Yang Li, Wei Lou, and Weizhao Wang
- Subjects
Cost allocation ,Mechanism design ,Mathematical optimization ,Control and Optimization ,Total cost ,Applied Mathematics ,Set cover problem ,Computer Science Applications ,Combinatorics ,Core (game theory) ,Bayesian game ,Computational Theory and Mathematics ,Discrete Mathematics and Combinatorics ,Cost sharing ,Greedy algorithm ,Mathematics - Abstract
We develop for set cover games several general cost-sharing methods that are approximately budget-balanced, in the core, and/or group-strategyproof. We first study the cost sharing for a single set cover game, which does not have a budget-balanced mechanism in the core. We show that there is no cost allocation method that can always recover more than $\frac{1}{\ln n}$ of the total cost and in the core. Here n is the number of all players to be served. We give a cost allocation method that always recovers $\frac{1}{\ln d_{\mathit{max}}}$ of the total cost, where d max is the maximum size of all sets. We then study the cost allocation scheme for all induced subgames. It is known that no cost sharing scheme can always recover more than $\frac{1}{n}$ of the total cost for every subset of players. We give an efficient cost sharing scheme that always recovers at least $\frac{1}{2n}$ of the total cost for every subset of players and furthermore, our scheme is cross-monotone. When the elements to be covered are selfish agents with privately known valuations, we present a strategyproof charging mechanism, under the assumption that all sets are simple sets; further, the total cost of the set cover is no more than ln?d max times that of an optimal solution. When the sets are selfish agents with privately known costs, we present a strategyproof payment mechanism to them. We also show how to fairly share the payments to all sets among the elements.
- Published
- 2009
38. Recrystallization Behavior of Deformed Austenite in High Strength Microalloyed Pipeline Steel
- Author
-
Jing-hong Yang, Dong-bai Sun, Xiang-yang Li, and Qing-you Liu
- Subjects
Austenite ,Materials science ,Metallurgy ,Metals and Alloys ,Recrystallization (metallurgy) ,Strain rate ,engineering.material ,Flow stress ,Hot working ,Mechanics of Materials ,Materials Chemistry ,Stress relaxation ,Dynamic recrystallization ,engineering ,Microalloyed steel - Abstract
Using methods of single-hit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator, the curves of flow stress and stress relaxation, the microstructure and the recrystallization behavior of Nb-V-Ti high strength microalloyed low carbon pipeline steel were studied, and the influence of the thermomechanical treatment parameters on dynamic and static recrystallization of the steel was investigated. It was found that microalloying elements improved the deformation activation energy and produced a retardation of the recrystallization due to the solid solution and precipitation pinning. The deformation conditions such as deformation temperature, strain, and strain rate influenced the recrystallization kinetics and the microstructure respectively. Equations obtained can be used to valuate and predict the dynamic and static recrystallizations.
- Published
- 2009
39. OVSF-CDMA Code Assignment in Wireless Ad Hoc Networks
- Author
-
Peng-Jun Wan, Xiang-Yang Li, and Ophir Frieder
- Subjects
General Computer Science ,Applied Mathematics ,Computer Science Applications - Published
- 2007
40. Localized Construction of Low Weighted Structure and Its Applications in Wireless Ad Hoc Networks
- Author
-
Xiang-Yang Li
- Subjects
Computer Networks and Communications ,business.industry ,Wireless network ,Wireless ad hoc network ,Computer science ,Mobile ad hoc network ,Minimum spanning tree ,Ad hoc wireless distribution service ,Energy conservation ,Broadcasting (networking) ,Optimized Link State Routing Protocol ,Broadcast communication network ,Computer Science::Networking and Internet Architecture ,Wireless ,Electrical and Electronic Engineering ,business ,Information Systems ,Computer network - Abstract
We consider a wireless network composed of a set of n wireless nodes distributed in a two dimensional plane. The signal sent by every node can be received by all nodes within its transmission range, which is uniform and normalized to one unit. We present the first distributed method to construct a bounded degree planar connected structure LRNG, whose total link length is within a constant factor of the minimum spanning tree1 using total O(n) messages under the broadcast communication model. Moreover, in our method, every node only uses its two-hop information to construct such structure, i.e., it is localized method. We show that some two-hop information is necessary to construct any low-weighted structure. We also study the application of this structure in efficient broadcasting in wireless ad hoc networks. We prove that, for broadcasting, the relative neighborhood graph (RNG), which is the previously best-known sparse structure that can be constructed locally, could use energy O(n) times the total energy used by our structure LRNG. Our simulations show that the broadcasting based on LRNG consumes energy about 36% more than that by MST, and broadcasting based on RNG consumes energy about 64% more than that by MST. We also show that no localized method can construct a structure for broadcasting with total power consumption asymptotically better than LRNG.
- Published
- 2005
41. Converted-wave seismology in anisotropic media Revisited, Part II: Application to parameter estimation
- Author
-
Xiang-Yang Li and Jianxin Yuan
- Subjects
Physics ,Propagation of uncertainty ,Geophysics ,Transverse isotropy ,Estimation theory ,Stacking ,Group velocity ,Anisotropy ,Seismology - Abstract
In transversely isotropic media with a vertical symmetry axis (VTI), the converted-wave (C-wave) moveout over intermediate-to-far offsets is determined by four parameters. These are the C-wave stacking velocity V C2, the vertical and effective velocity ratios γ 0and γ eff, and the anisotropic parameter X eff. We refer to the four parameters as the C-wave stacking velocity model. The purpose of C-wave velocity analysis is to determine this stacking velocity model. The C-wave stacking velocity model V C2, γ 0, γ geff, and X eff can be determined from P- and C-wave reflection moveout data. However, error propagation is a severe problem in C-wave reflection-moveout inversion. The current short-spread stacking velocity as deduced from hyperbolic moveout does not provide sufficient accuracy to yield meaningful inverted values for the anisotropic parameters. The non-hyperbolic moveout over intermediate-offsets (x/z from 1.0 to 1.5) is no longer negligible and can be quantified using a background γ. Non-hyperbolic analysis with a γ correction over the intermediate offsets can yield V C2 with errors less than 1% for noise free data. The procedure is very robust, allowing initial guesses of γ with up to 20% errors. It is also applicable for vertically inhomogeneous anisotropic media. This improved accuracy makes it possible to estimate anisotropic parameters using 4C seismic data. Two practical work flows are presented for this purpose: the double-scanning flow and the single-scanning flow. Applications to synthetic and real data show that the two flows yield results with similar accuracy but the single-scanning flow is more efficient than the double-scanning flow.
- Published
- 2005
42. Efficient Topology Control for Ad-Hoc Wireless Networks with Non-Uniform Transmission Ranges
- Author
-
Wen-Zhan Song, Yu Wang, and Xiang-Yang Li
- Subjects
Euclidean distance ,Computer Networks and Communications ,Computer science ,Wireless ad hoc network ,Wireless network ,Topology control ,business.industry ,Bounded function ,Electrical and Electronic Engineering ,business ,Network topology ,Information Systems ,Computer network - Abstract
Wireless network topology control has drawn considerable attention recently. Priori arts assumed that the wireless ad hoc networks are modeled by unit disk graphs (UDG), i.e., two mobile hosts can communicate as long as their Euclidean distance is no more than a threshold. However, practically, the networks are never so perfect as unit disk graphs: the transmission ranges may vary due to various reasons such as the device differences, the network control necessity, and the perturbation of the transmission ranges even the transmission ranges are set as the same originally. Thus, we assume that each mobile host has its own transmission range. The networks are modeled by mutual inclusion graphs (MG), where two nodes are connected iff they are within the transmission range of each other. Previously, no method is known for topology control when the networks are modeled as mutual inclusion graphs.The paper proposes the first distributed mechanism to build a sparse power efficient network topology for ad hoc wireless networks with non-uniform transmission ranges. We first extend the Yao structure to build a spanner with a constant length and power stretch factor for mutual inclusion graph. We then propose two efficient localized algorithms to construct connected sparse network topologies. The first structure, called extended Yao-Yao, has node degree at most O(log γ), where γ = maxu maxuv∈MG ru/rv. The second structure, called extended Yao and Sink, has node degree bounded by O(log γ), and is a length and power spanner. The methods are based on a novel partition strategy of the space surrounded each mobile host. Both algorithms have communication cost O(n) under a local broadcasting communication model, where each message has O(log n) bits.
- Published
- 2005
43. Converted-wave seismology in anisotropic media revisited, Part I: Basic theory
- Author
-
Xiang-Yang Li and Jianxin Yuan
- Subjects
Physics ,Travel time ,Data processing ,Geophysics ,Transverse isotropy ,Estimation theory ,Point (geometry) ,Reflector (antenna) ,Anisotropy ,Model building ,Seismology - Abstract
We have developed new basic theories for calculating the conversion point and the travel time of the P-SV converted wave (C-wave) in anisotropic, inhomogeneous media. This enables the use of conventional procedures such as semblance analysis, Dix-type model building and Kirchhoff summation, to implement anisotropic processing, and makes anisotropic processing affordable. Here we present these new developments in two parts: basic theory and application to velocity analysis and parameter estimation. This part deals with the basic theory, including both conversion-point calculation and moveout analysis. Existing equations for calculating the PS-wave (C-wave) conversion point in layered media with vertical transverse isotropy (VTI) are strictly limited to offsets about half the reflector depth (an offset-depth ratio, xlz, of 0.5), and those for calculating the C-wave traveltimes are limited to offsets equal to the reflector depth (x/z=l.0). In contrast, the new equations for calculating the conversion-point extend into offsets about three-times the reflector depth (x/z=3.0), those for calculating the C-wave traveltimes extend into offsets twice the reflector depth (x/z=2.0). With the improved accuracy, the equations can help in C-wave data processing and parameter estimation in anisotropic, inhomogeneous media.
- Published
- 2005
44. [Untitled]
- Author
-
Gruia Calinescu, Ophir Frieder, Peng-Jun Wan, and Xiang-Yang Li
- Subjects
Mathematical optimization ,Optimization problem ,Computer Networks and Communications ,Computer science ,Wireless network ,Wireless ad hoc network ,Wireless Routing Protocol ,Minimum spanning tree ,Ad hoc wireless distribution service ,Connected dominating set ,Energy conservation ,Optimized Link State Routing Protocol ,Computer Science::Networking and Internet Architecture ,Destination-Sequenced Distance Vector routing ,Electrical and Electronic Engineering ,Unicast ,Information Systems - Abstract
Energy conservation is a critical issue in ad hoc wireless networks for node and network life, as the nodes are powered by batteries only. One major approach for energy conservation is to route a communication session along the route which requires the lowest total energy consumption. This optimization problem is referred to as Minimum-Energy Routing. While the minimum-energy unicast routing problem can be solved in polynomial time by shortest-path algorithms, it remains open whether the minimum-energy broadcast routing problem can be solved in polynomial time, despite the NP-hardness of its general graph version. Recently three greedy heuristics were proposed in [11]: MST (minimum spanning tree), SPT (shortest-path tree), and BIP (broadcasting incremental power). They have been evaluated through simulations in [11], but little is known about their analytical performances. The main contribution of this paper is a quantitative characterization of their performances in terms of approximation ratios. By exploring geometric structures of Euclidean MSTs, we have been able to prove that the approximation ratio of MST is between 6 and 12, and the approximation ratio of BIP is between 13/3 and 12. On the other hand, we show that the approximation ratio of SPT is at least n/2, where n is the number of receiving nodes. To the best of our knowledge, these are the first analytical results for the minimum-energy broadcasting problem.
- Published
- 2002
45. Numerical analysis of the flow field inside an entrained-flow gasifier
- Author
-
Jae Ho Kim, Tae Jun Park, Jae Goo Lee, Young Chan Choi, and Xiang Yang Li
- Subjects
geography ,geography.geographical_feature_category ,Computer simulation ,Wood gas generator ,Turbulence ,General Chemical Engineering ,Numerical analysis ,Flow (psychology) ,General Chemistry ,Mechanics ,Inlet ,Physics::Fluid Dynamics ,Combustor ,Coal gasification - Abstract
The flow field of an entrained-flow gasifier was numerically simulated to describe coal gasification process. The standard k-e turbulence model and SIMPLE procedure were used with the Primitive-Variable method during computation. In order to investigate the influencing factors on the flow field that may have a great effect on coal gasification process, some parametric studies were performed by changing the gas injection angle, gas inlet diameter, gas inlet velocity, extension in burner length and gasifier geometry. The calculation results showed that the basic patterns of the flow field inside the gasifier were nearly the same with a parabolic distribution irrespective of the change in parameters. There existed an obvious external recirculation zone with axial length less than 1.0 m and a narrow internal recirculation region was observed in the entrance of gasifier inlet. The geometry parameters of the burner, such as the oxygen inlet diameter and angle, influenced the flow field at the inlet region near the burner. But after a certain length along the gasifier, the flow field was nearly the same as that in the basic case.
- Published
- 2001
46. Simultaneous Refinement and Coarsening for Adaptive Meshing
- Author
-
Shang-Hua Teng, Alper Üngör, and Xiang-Yang Li
- Subjects
Microstructural evolution ,Mathematical optimization ,Computer simulation ,Delaunay triangulation ,Adaptive mesh refinement ,General Engineering ,Boundary (topology) ,Computer Science Applications ,Constant factor ,Sphere packing ,Combustion process ,Modeling and Simulation ,Algorithm ,Software ,ComputingMethodologies_COMPUTERGRAPHICS ,Mathematics - Abstract
In the numerical simulation of the combustion process and microstructural evolution, we need to consider the adaptive meshing problem for a domain that has a moving boundary. During the simulation, the region ahead of the moving boundary needs to be refined (to satisfy stronger numerical conditions), and the submesh in the region behind the moving boundary should be coarsened (to reduce the mesh size). We present a unified scheme for simultaneously refining and coarsening a mesh. Our method uses sphere packings and guarantees that the resulting mesh is well-shaped and is within a constant factor of the optimal possible in the number of mesh elements. We also present several practical variations of our provably good algorithm.
- Published
- 1999
47. Novel transient outward K + current of mature murine hippocampal neurones
- Author
-
Xiang-Yang Li and Joseph J. McArdle
- Subjects
Neurons ,Potassium Channels ,Time Factors ,Tetraethylammonium ,Dose-Response Relationship, Drug ,Physiology ,Clinical Biochemistry ,4-Aminopyridine ,Time constant ,Dendrotoxin ,Hippocampal formation ,Hippocampus ,Mice ,chemistry.chemical_compound ,Decay time ,Delayed rectifier ,chemistry ,Physiology (medical) ,Biophysics ,medicine ,Animals ,Receptor ,Neuroscience ,medicine.drug - Abstract
Hippocampal neurones were freshly isolated from the brain of adult mice and voltage-dependent K+ currents were recorded with the whole-cell patch-clamp technique. Three components of transient K+ current (IA) were isolated when analyzing data with exponential functions or treating neurones with a variety of voltage protocols and pharmacologic agents. Subtraction of the delayed rectifier current (I K) from the K+ currents elicited after prepulses to –120 mV of varying duration revealed fast (IAf) and slow (IAs) components with decay time constants of 45 ± 8 and 612 ± 140 ms, respectively; the corresponding time constants for the removal of inactivation were 12.3 and 189.6 ms. Both tetraethylammonium and dendrotoxin selectively inhibited IAs. 4-Aminopyridine (4-AP) specifically blocked IAf and 40% of IAs with different affinities. Therefore, the properties of a 4-AP-resistant (IAsR) and a 4-AP-sensitive (IAsS) component of IAs were compared. These data suggest that three distinct subtypes of K+ currents contribute to the IA of mature murine hippocampal neurones.
- Published
- 1997
48. Erratum: Minimum-Energy Broadcast in Static Ad Hoc Wireless Networks
- Author
-
Gruia Calinescu, Peng-Jun Wan, Xiang-Yang Li, and Ophir Frieder
- Subjects
Computer Networks and Communications ,Computer science ,Wireless network ,Analytical chemistry ,Electrical and Electronic Engineering ,Energy (signal processing) ,Information Systems - Abstract
(S(α + β − θ) + S(θ)) − (S(α) + S(β)) = (S(α + β) − S(α) − S(β)) − (S(α + β) − S(α + β − θ) − S(θ ))
- Published
- 2005
49. MONET Special Issue on Non-Cooperative Wireless Networking and Computing
- Author
-
Ophir Frieder, Xiang-Yang Li, Yantai Shu, and Xiaohua Jia
- Subjects
Wi-Fi array ,Computer Networks and Communications ,Wireless network ,Computer science ,Service set ,business.industry ,Wireless WAN ,Networking hardware ,law.invention ,Key distribution in wireless sensor networks ,Hardware and Architecture ,law ,Wi-Fi ,business ,Software ,Municipal wireless network ,Information Systems ,Computer network - Published
- 2005
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.