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  • 1
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    A smart city used low-latency seamless positioning system based on inverse global navigation satellite system technology (2019)
    Hindawi
    Details
    Publication Date: 2019
    Description: International Journal of Distributed Sensor Networks, Volume 15, Issue 9, September 2019. 〈br/〉People have to move between indoor and outdoor frequently in city scenarios. The global navigation satellite system signal cannot provide reliable indoor positioning services. To solve the problem, this article proposes a seamless positioning system based on an inverse global navigation satellite system signal, which can extend the global navigation satellite system service into the indoor scenario. In this method, a signal source is arranged at a key position in the room, and the inverse global navigation satellite system signal is transmitted to the global navigation satellite system receiver to obtain a preset positioning result. The indoor positioning service is continued with the inertial navigation system after leaving the key position. The inverse global navigation satellite system seamless positioning system proposed in this article can unify indoor and outdoor positioning using the same receiver. The receiver does not need to re-receive navigation information when the scene changes, which avoids the switching process. Through the design of signal layer coverage, the receiver is in a warm start state, and the users can quickly fix the position when the scenario changes, realizing quick access in a true sense. This enables the ordinary commercial global navigation satellite system receiver to obtain indoor positioning capability without modification, and the algorithm can perform accurate positioning indoors and outdoors without switching.
    Print ISSN: 1550-1477
    Electronic ISSN: 1550-1477
    Topics: Electrical Engineering, Measurement and Control Technology
    Published by Hindawi
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  • 2
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    Large earthquake cycles and intermittent criticality on heterogeneous faults due to evolving stress and seismicity (2003)
    In:  J. Geophys. Res., Beijing, Pergamon, vol. 108, no. B6, pp. ESE 4-1 to ESE 4-21, pp. 2307
    Details
    Publication Date: 2003
    Description: We analyze evolving stress and seismicity generated by three realizations of a discrete model of a strike-slip fault in a 3D elastic half-space using five functions of stress and five functions of seismicity. The first model (F) has realistic dynamic weakening (static minus dynamic frictions), the second (FC) has zero critical dynamic weakening, and the third (SYS) is constrained to produce only system-size events. The results for model F show cyclical development, saturation, and destruction of fluctuations and long range correlations on the fault, punctuated by the system-size events. The development stage involves evolution of stress and seismicity to distributions having broad ranges of scales, evolution of response functions toward scale-invariant behavior, increasing seismicity rate and event sizes, and increasing hypocenter diffusion. Most functions reach asymptotically stable values around 2/3 of the cycle and then fluctuate until one event cascades to become the next large earthquake. In model FC the above evolution is replaced by scale-invariant statistical fluctuations, while in model SYS the signals show simple cyclic behavior. The results suggest that large earthquake cycles on heterogeneous faults with realistic positive dynamic weakening are associated with intermittent criticality, produced by spontaneous evolution of stress heterogeneities toward a critical level of disorder having a broad range of scales. The stress evolution and development of large earthquake cycles may be tracked with seismicity functions.
    Keywords: Recurrence of earthquakes ; Chaotic behaviour ; SOC ; Inhomogeneity ; Fault zone ; Stress ; Seismicity ; 3220 ; Mathematical ; Geophysics: ; Nonlinear ; dynamics ; 7209 ; Seismology: ; Earthquake ; dynamics ; and ; mechanics ; 7223 ; Seismic ; hazard ; assessment ; and ; prediction ; 7260 ; Theory ; and ; modeling ; 8164 ; Tectonophysics: ; Stresses--crust ; and ; lithosphere ; JGR
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    A viscoelastic damage model with applications to stable and unstable fracturing (2004)
    In:  Geophys. J. Int., Basel, Birkhäuser Verlag, vol. 159, no. 3, pp. 1155-1165, pp. B05S07, (ISBN: 0534351875, 2nd edition)
    Details
    Publication Date: 2004
    Keywords: Rheology ; Inelastic ; Fracture ; Rock mechanics ; cracks and fractures (.NE. fracturing) ; cracked ; media, ; rheology, ; viscoelasticity ; GJI
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Systematic analysis of shear-wave splitting in the aftershock zone of the 1999 Chi-Chi, Taiwan, earthquake: Shallow crustal anisotropy and lack of precursory variations (2004)
    In:  Bull. Seism. Soc. Am., Kunming, China, Inst. f. Theoret. Geodäsie, vol. 94, no. 6, pp. 2330-2347, pp. B08307, (ISSN: 1340-4202)
    Details
    Publication Date: 2004
    Keywords: Seismology ; AnisotropyS ; Aftershocks ; Earthquake ; China ; Earthquake precursor: prediction research ; Earthquake precursor: Vp/Vs anomalies ; BSSA
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    BIBLIOGRAPHY SEISMOLOGY
  • 5
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    Near-surface seismic anisotropy, attenuation and dispersion in the aftershock region of the 1999 Chi-Chi earthquake (2005)
    In:  Geophys. J. Int., Kunming, China, Inst. f. Theoret. Geodäsie, vol. 160, no. 2, pp. 695-706, pp. B08307, (ISSN: 1340-4202)
    Details
    Publication Date: 2005
    Keywords: AnisotropyS ; shallow ; Attenuation ; Quality factor ; Dispersion ; Aftershocks ; Earthquake ; Taiwan ; China ; GJI ; attenuation, ; borehole, ; crust, ; Q, ; seismic ; anisotropy, ; shear ; wave ; splitting
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    BIBLIOGRAPHY SEISMOLOGY
  • 6
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    Materials, Vol. 12, Pages 2656: Bitumen Recovery from Crude Bitumen Samples from Halfaya Oilfield by Single and Composite Solvents—Process, Parameters, and Mechanism (2019)
    MDPI
    In: Materials
    Details
    Publication Date: 2019
    Description: Since 2007, heterogeneous, high-viscosity active bituminous formations have often occurred during the drilling process in Yadavaran oilfield (Iran), Halfaya oilfield (Iraq), and tar sands (Canada). The formation of bitumen exhibits plastic and creep properties, and its adhesion is strong, so drilling accidents are easily caused, such as adhering vibrating screen, drill pipe sticking, lost circulation, and even well abandonment. These complex problems cause huge economic losses. Solvents used to dissolve bitumen are a feasible technology to remove bitumen effectively. In order to solve this problem, we used crude bitumen samples from Halfaya oilfield to study the relation between the bitumen component and different solvents. In this study, the temperature, crude bitumen sample to solvent ratio, stirring rate, stirring time, and ultrasound time on bitumen recovery by toluene were investigated by a single factor experiment. The optimum process parameter for bitumen recovery was obtained. Toluene, n-heptane, tetrahydrofuran, cyclohexane, cyclopentane, ethyl acetate, and n-pentane were chosen as the solvents for single solvent extraction and composite solvent extraction. The bitumen recovery increased significantly with the use of a composite solvent compared to a single solvent. The composite solvent ratio was 1:1. The highest bitumen recovery was 98.9 wt% by toluene/cyclohexane composite solvent. The SARA (saturates, aromatics, resins, and asphaltenes) components of the bitumen were analyzed. The toluene showed the highest asphaltene content, while the n-alkanes showed the lowest asphaltene content. The higher the asphaltene content, the higher the bitumen recovery. The composite solvent obtained the highest asphaltene content and bitumen recovery. The viscosity of bitumen extraction by different solvents was measured. The lower the bitumen viscosity, the higher the bitumen recovery. The element analysis indicated the solvent’s ability to extract bitumen colloids with the C/H ratio. This study provides a reliable theoretical basis for the subsequent adoption of effective anti-bitumen polluted drilling fluid additives.
    Electronic ISSN: 1996-1944
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by MDPI
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  • 7
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    Sensors, Vol. 19, Pages 1544: Temperature-Insensitive Structure Design of Micromachined Resonant Accelerometers (2019)
    MDPI
    In: Sensors
    Details
    Publication Date: 2019
    Description: Micromachined resonant accelerometers (MRAs), especially those devices fabricated by silicon on glass technology, suffer from temperature drift error caused by inherent thermal stress. This paper proposes two structure designs to attenuate the effect of thermal stress. The first MRA structure is realized by optimizing the locations of the bonding anchors and utilizing a special-shaped substrate to isolate the thermal stress generated during the die attach process. The second structure is designed using an isolation frame fixed by a single anchor to replace all dispersed anchors associated with the suspension beams and micro-levers. Simulated and experimental results show that both of the MRA structures can effectively reduce the thermal stress effect. The experimental results on one MRA prototype indicate that the differential temperature sensitivity reduces down to 1.9 μg/°C and its 15-day bias stability reaches 1.4 μg.
    Electronic ISSN: 1424-8220
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Published by MDPI
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  • 8
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    Sensors, Vol. 18, Pages 3901: Spin Rate Effects in a Micromachined Electrostatically Suspended Gyroscope (2018)
    MDPI
    In: Sensors
    Details
    Publication Date: 2018
    Description: Spin rate of a high-speed spinning-rotor gyroscope will make a significant impact on angular rate sensor performances such as the scale factor, resolution, measurement range, and bias stability. This paper presents the spin rate effects on performance indicators of a microelectromechanical systems (MEMS) gyroscope where a free-spinning rotor is electrostatically suspended in an evacuated vacuum cavity and functions as a dual-axis angular rate sensor. Theoretical models of the scale factor and measurement range of such a spinning-rotor gyroscope are derived. The experimental results indicate that the measured scale factors at different settings of the spin rate match well with the theoretical predication. In order to separate the disturbance component of the rotation control loop on the gyroscope output, a testing strategy is proposed by operating the gyroscope at different spin rates. Experimental results on a prototype gyroscope show that the squared drive voltage generated by the rotation control loop is approximately proportional to the noise of the gyroscope output. It was further investigated that an improved performance of such spinning-rotor gyroscopes can be achieved by operating the gyroscope rotor at an optimal spin rate.
    Electronic ISSN: 1424-8220
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Published by MDPI
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  • 9
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    Force measurement using strain-gauge balance in a shock tunnel with long test duration (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-25
    Description: Force tests were conducted at the long-duration-test shock tunnel JF12, which has been designed and built in the Institute of Mechanics, Chinese Academy of Sciences. The performance tests demonstrated that this facility is capable of reproducing a flow of dry air at Mach numbers from 5 to 9 at more than 100 ms test duration. Therefore, the traditional internal strain-gauge balance was considered for the force tests use in this large impulse facility. However, when the force tests are conducted in a shock tunnel, the inertial forces lead to low-frequency vibrations of the test model and its motion cannot be addressed through digital filtering because a sufficient number of cycles cannot be found during a shock tunnel run. The post-processing of the balance signal thus becomes extremely difficult when an averaging method is employed. Therefore, the force measurement encounters many problems in an impulse facility, particularly for large and heavy models. The objective of the present study is to develop pulse-type sting balance by using a strain-gauge sensor that can be applied in the force measurement of 100 ms test time, especially for the force test of the large-scale model. Different structures of the S-series (i.e., sting shaped balances) strain-gauge balance are proposed and designed, and the measuring elements are further optimized to overcome the difficulties encountered during the measurement of aerodynamic force in a shock tunnel. In addition, the force tests were conducted using two large-scale test models in JF12 and the S-series strain-gauge balances show good performance in the force measurements during the 100 ms test time.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 10
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    Sensors, Vol. 16, Pages 389: A Novel Digital Closed Loop MEMS Accelerometer Utilizing a Charge Pump (2016)
    MDPI Publishing
    In: Sensors
    Details
    Publication Date: 2016-03-19
    Description: This paper presents a novel digital closed loop microelectromechanical system (MEMS) accelerometer with the architecture and experimental evaluation. The complicated timing diagram or complex power supply in published articles are circumvented by using a charge pump system of adjustable output voltage fabricated in a 2P4M 0.35 µm complementary metal-oxide semiconductor (CMOS) process, therefore making it possible for interface circuits of MEMS accelerometers to be integrated on a single die on a large scale. The output bitstream of the sigma delta modulator is boosted by the charge pump system and then applied on the feedback comb fingers to form electrostatic forces so that the MEMS accelerometer can operate in a closed loop state. Test results agree with the theoretical formula nicely. The nonlinearity of the accelerometer within ±1 g is 0.222% and the long-term stability is about 774 µg.
    Electronic ISSN: 1424-8220
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Published by MDPI Publishing
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