查看更多>>摘要：Non-sensitive axis feedback control is crucial for cross-coupling noise suppression in the application of fullmaglev vertical superconducting gravity instruments. This study proposes the non-sensitive axis feedback control of a test mass in a custom-made full-maglev vertical superconducting accelerometer. In the feedback system, special superconducting circuits are designed to decouple and detect multiple degree-of-freedom motions of the test mass. The decoupled motion signals are then passed through a PID controller and fed back to the side-wall coils to control the test mass. The displacement of the test mass is controlled within +/- 2 nm and is reduced by approximately one order of magnitude in a laboratory environment. Accordingly, the noise level of the vertical superconducting accelerometer in the sensitive axis is reduced by a factor of 4-6 @ 0.03-0.1 Hz.
Wu, Thomas Y.Murashima, YoshikoSakurai, HiromuIida, Kenjiro...
9页
查看更多>>摘要：The first bilateral comparison of particle number concentration (PNC) standards via calibrating the counting efficiency (CE) of an optical particle counter (OPC) at high concentration of 1000 cm(-3) is reported. An OPC (GRIMM 11-D) has been used as the transfer standard between NMC and NMIJ, with its CE being calibrated using monodisperse polystyrene latex (PSL) particles around 0.3 mu m by the Faraday Cup Aerosol Electrometers (FCAE) of both metrology institutes. The CE of the OPC has been evaluated for a series of increasing concentrations to determine the highest concentration level which is free from coincidence loss. The OPC was also calibrated at 0.5 mu m using an inkjet aerosol generator (IAG) and FCAE to compare its CE at different concentration levels. We have analysed the CE's stability at decreasing concentration levels from 1228 to 0.5 cm(-3) to derive the evidence for the equivalence of CE at different concentration levels. The CE values of the OPC around 0.3 and 0.5 mu m measured by two institutes have agreement within 1.5% (normalized error E-n < 1), which can serve as evidence of the equivalence of the PNC standards of both metrology institutes for concentrations up to 1000 cm(-3). The measurement setup, comparison results and uncertainty analysis for the OPC calibration have been presented.
查看更多>>摘要：We extend the use of the intrinsic properties calibration method for triaxial accelerometers that we reported previously from discrete angular steps to using a constant rotation rate to produce a time varying sinusoidal excitation in the earth's gravitational field. We show that this extension yields the low frequency calibration response of the device under test. Whereas traditional vibration-based methods using shakers generally exhibit an increased measurement uncertainty with decreased excitation frequency, we show that this approach does not. We report results obtained from a commercial triaxial digital accelerometer from DC up to a 0.5 Hz rotation rate. The maximum rotation rate that we report is limited by our rotation stage; but we expect that the method can be extended to higher rotation rates with an upper limit constrained by what can be tolerated as a maximum centripetal acceleration.
查看更多>>摘要：Absolute wavefield amplitude information is essential to amplitude-based distributed acoustic sensing (DAS) studies such as attenuation analysis, source inversion, and subsurface imaging. Here, we report the results of a pilot experimental study aimed at exploring whether and how the strain present in a fiber-optic cable would affect the amplitude response of a DAS system. Using a precise strain-controlled setup, we find that DAS amplitudes drop sharply as the fiber shifts from a loose to a strained state. This is followed by an exponential decrease in amplitude as a function of tensile strain up to 16,000 mu epsilon. Additionally, the observed strain effect weakens with increasing vibration intensity. Overall, the revealed fiber strain dependence of DAS amplitude measurements may have implications for the accurate interpretation of DAS recordings acquired by preexisting telecommunications cables. It is also relevant to the design and optimal deployment of fit-for-purpose DAS cables in oil and gas wells, tunnels, and other engineering systems.
查看更多>>摘要：Enhanced envelope spectrum (EES) and improved envelope spectrum (IES) generated from spectral coherence (SCoh) are proven to be more robust fault detection tools than squared envelope spectrum (SES). However, EES cannot effectively detect the fault-induced components under strong interference noise and IES can only capture the information of a fault-sensitive resonance spectral frequency band. To overcome these problems, weighted combined envelope spectrum (WCES) from SCoh is proposed as a novel fault detector. WCES integrates the fault components distributed in multiple resonance frequency bands using normalized feature energy and removes the envelope spectrum slices with less fault information to exclude disturbance noises. The performance of WCES is validated using simulations and experiments and compared with the advanced envelope spectra. The results demonstrate that WCES can effectively detect bearing faults under strong interference noise and multiple resonances compared with the SES, EES and IES, and has potential application value in bearing diagnostics.
查看更多>>摘要：Due to the global problem with plastic contaminating the environment, with bisphenol A (BPA) being one of the highest demand, effective monitoring and purification of the pollutants are required. The electrochemical methods constitute a good solution but, due to polymerization of electrochemical oxidation bisphenol A products and their adsorption to the surfaces, measurement head elements are clogged by the formed film. In this research, we propose a nanocrystalline diamond sheet protection for securing elements in direct contact with bisphenol A during electrochemical processes. The solution was presented on the example of a zinc oxide (ZnO) coating deposited on a fiber-optic end-face by Atomic Layer Deposition. Series of optical and electrochemical measurements were performed in a dedicated hybrid setup. The results show that ZnO can be modified during the electrochemistry leading to the drastic change of its properties. Such degradation did not show in case of nanocrystalline diamond sheet-protected sample proving the solution's effectiveness, giving a possibility of reusing the measurement element and prolonging its lifespan.
查看更多>>摘要：This paper is focused on the performance of Global Navigation Satellite System (GNSS) Kinematic Precise Point Positioning (PPP) methods for monitoring the engineering structures based on harmonic oscillation tests using a single-axis shake table. To examine the performance of kinematic PPP methods, shake table oscillated harmonically for different amplitudes and frequencies. Data were processed using the online Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP) service. Results were analyzed by time series analysis and Fast Fourier transform techniques. The kinematic PPP method's accuracy under different satellite configurations was determined by comparing the frequency and amplitude values obtained by PPP processing with the linear variable differential transformer (LVDT) results. As a result of experiments, the effectiveness of the multi-GNSS high-rate kinematic PPP methods in determining the structural movements were demonstrated and the frequencies of the structural movements could be determined exactly and their amplitudes with a maximum difference of 3.9 mm.
查看更多>>摘要：Despite the considerable success achieved by deep learning-based fault diagnosis methods, a powerful deep learning model must require a substantial set of training data to obtain a strong generalization ability in practical application. Focusing on the fault diagnosis case under small data sets, an enhanced non-local weakly supervised fault diagnosis method is proposed in this paper. In the proposed method, the few-shot learning strategy is presented to perform learning task augmentation to alleviate the overfitting problem caused by scarce training data, and the non-local operation is investigated to further enhance the feature extraction ability of convolutional neural network through capturing the long-range dependency. Two fault diagnosis experiments which were conducted on rolling bearing and bevel gear are carried out. The proposed method obtains 97.23% and 99.76% fault diagnosis accuracy in bearing data sets and gear data sets, which outperforms the traditional fault diagnosis methods.
查看更多>>摘要：Latent environmental variable-based methods are popular for diagnosing structural damage in bridges under varying environmental temperatures. However, it is still a shortage of researches on distinguishing and selecting the damage features suitable for this type of method in order to improve the validity of damage detection in terms of their application to actual bridges. To address this issue, a method based on the characteristics of the narrow dimension (CND) of damage features is proposed for damage detection in actual bridges under changing environmental temperatures. First, the definition of the CND of damage features is presented in detail by analysing the influencing factors of latent environmental variable-based methods for damage detection. Second, based on the correlations among damage features, an index is presented for determining whether the damage features possess CND. If so, these damage features are suitable for latent environmental variable-based methods, which are beneficial for detecting damage to bridges while considering environmental influences; if not, then other types of methods must be considered in using the above damage features. Consequently, combined with novelty detection and variational mode decomposition, a method based on CND is implemented for detecting the damage to actual bridges. Finally, examples of numerical simulations and actual bridges are provided to demonstrate the effectiveness of the proposed method.
查看更多>>摘要：Flexible strain sensors are significant components for smart wearable electronic devices because of wide appli-cations. However, the design and construction of high-performance strain sensors through facile fabrication remains a challenge. In this study, we designed a simple and high-performance flexible strain sensor based on gold nanoparticles and a polyimide substrate. The fabrication included drop-casting and high-temperature annealing, enhancing the connections between the nanoparticles. The results reveal that the sensor can sensi-tively detect subtle strains (GF = 19.94). It exhibits excellent linearity (R-2 = 0.99) when sensing outward bending strain and low power consumption (<2.5 mW). Furthermore, it can be adhered to human skin to detect human physiological parameters. The strain sensor can detect the angles of the cervical vertebra in different bending states. It can show the distinctions of artery pulse waveforms at different conditions (before and after exercise) and in people (pregnant and unpregnant) with a high precision.
NSTL
Elsevier