查看更多>>摘要：? 2022 Elsevier LtdThe non-holonomic constraint (NHC) is a common auxiliary information based on the motion characteristics of land vehicles to improve navigation accuracy. Affected by Ackermann turning geometry, the accuracy of the velocity of the vehicle frame will decline in the maneuvering process. In this paper, the error above is modeled and compensated based on Ackermann turning geometry to improve the navigation accuracy, so as to enhance the system reliability: (1) Analysis shows that there is a velocity measurement error when the vehicle has angular motion without considering the lever arm effect; (2) A continuous linear 19dimensional (19D) Strapdown inertial navigation system (SINS)/NHC error model considering the lever arm effect based on Ackermann turning geometry is derived in this paper and (3) Kalman filter is utilized to estimate the error parameters. Field test results show that the proposed method can effectively improve the accuracy of positioning compared with the traditional method.
查看更多>>摘要：? 2022Air pollution related to fine dust is increasing globally with rapid industrialization and modernization. With the rising environmental and health concerns with respect to air quality, it is imperative to develop an advanced system for detecting harmful components from airborne particles. Based on spark-induced plasma spectroscopy (SIPS), a novel instrument was designed for measurements of fine dust atomic components in situ. All the functional parts related to plasma generation, measurement, and data visualization of time-resolved electric signals were integrated into a compact single module with embedded software. Quantitative measurements were conducted to investigate and verify the performance of the all-in-one module for key components of fine dust, namely, Fe, Mg, Si, Ca, Al, and K. Along with the enhanced limit of detection by ～ 1.4 times the previous setup, the quantitative monitoring of fine dust in the atmospheric environment is illustrated via the compact SIPS module.
查看更多>>摘要：? 2022 Elsevier LtdDirect imaging method has been proved to be quite convenient and importance for measuring bubble shape parameters of gas–liquid two-phase flow due to its advantages of non-contact and visualization. The accuracy of flow pattern segmentation and measurement has an importantly impact on flow characteristic. For bubble recognition (pattern segmentation and extraction) with low-quality image, the aim of this paper is to propose a novel hybrid image analysis model (U-net-QR-EMD) combining the U-net algorithm with the quantile regression method (QR) and empirical mode decomposition (EMD). For a direct-contact gas–liquid mixing system, both the synthetic and experimental images of bubble swarm are respectively captured and used to verify the feasibility of the new model. The main findings of our study are as follows. (1) Computing and experimental results show that it is effective in the recognition of bubbles with irregular shape and have a potential in recognizing other bubbles taken under different working conditions. The number of iterations with the proposed model is 90 in the training process, leading to the prediction accuracy with more than 90%. Specifically, it can accurately and reliably identify the individual small and large bubbles in a direct-contact gas–liquid mixing system, but the classical Otsu and K-means methods cannot. (2) Using QR method, it is found that with the increase of gas–liquid mixing time, the number of the identified bubbles decreases but the gas holdup increases. Meanwhile, 90% of the bubble number are between the 5% and 95% quantile regression curves. Both the time series of bubble number and gas holdup tend to be non-stationary and non-linear, but intrinsic mode function (IMF) components and residual obtained by EMD display a higher stability and stronger periodicity. (3) The six parameters (area, perimeter, deformation coefficient, equivalent diameter, aspect ratio and eccentricity) related to bubble patterns can be measured and agree with each other in the evolution process of the mixing state quality with the help of the new model. The proposed model can not only successfully identify the micro-details of small-scale bubbles in low-quality images of gas–liquid two-phase flow, but also improve the ability to obtain low-quality deep processing of other two-phase flow taking advantage of direct imaging method.
查看更多>>摘要：? 2022 Elsevier LtdThermistor-based measurement systems at constant temperature have been widely used in multiple applications. In this type of hot-wire measurement applications, either analog circuits or digital processors can be used to regulate the thermistor temperature. The sampled-data control is an interesting alternative for temperature regulation because measurement signals are commonly handled by digital processors nowadays. However, the temperature control of Negative Temperature Coefficient (NTC) sensors present a nonlinear behavior in closed-loop operation. Furthermore, measurement variance depends on the temperature of the ambient and the dissipated power, but these relationships are nonlinear. This work proposes an approximated closed-loop propagation model for the output variance of an NTC-based measurement system at constant temperature. The thermistor temperature is regulated with a digital controller. Simulation and experimental results are presented in order to illustrate the benefits of the proposed model.
查看更多>>摘要：? 2022We argue that the assessment of the Calibration and Measurement Capabilities, CMCs, by means of the results of a Key Comparison is a bona fide exercise of conformity assessment, and as such should be treated, using the appropriate tools, including risk assessment. This position contrasts with the current practice, in which acceptance or rejection of a CMC claim are based on the normalised error. We show that, behind this seemingly unique acceptance criterion, different decision rules – guarded acceptance, simple acceptance and guarded rejection – exist in reality, depending on the characteristics of the comparison. This variety of decision rules impairs the fairness of the current equivalence arrangement. We suggest that the conformance probability should be the key parameter to be considered in the assessment of a CMC claim. Using a suitable Probability Density Function, PDF, for the measurand, we calculate the conformance probability for the possible scenarios, and show that using the current acceptance criterion the conformance probability can attain unacceptably low values. Therefore, we maintain that the current acceptance criterion is ambiguous and inadequate, and suggest to rather adopt a criterion based on the calculation of the conformance probability and the establishment of a minimum threshold for acceptance. We demonstrate our proposal by applying it to a practical case and to a fictitious example in mass metrology.
查看更多>>摘要：? 2022 Elsevier LtdAsphalt mixtures behave as linear viscoelastic materials when subjected to loading conditions that are similar to pavement operating conditions. Thus, this study proposed a novel method for extracting the linear viscoelastic properties of asphalt mixture at 25 °C using digital image correlation and repeated-load semi-circular bending (SCB) test. Digital image correlation was utilised successfully for extracting creep compliance using semi-circular samples under repeated loading conditions. A fractional time-dependent viscoelastic element converted the creep compliance data into relaxation modulus. The extracted relaxation modulus data were verified by simulating the viscoelastic response of control and modified asphalt mixtures using the extended finite element model (XFEM). The findings presented in this paper showed that digital image correlation has a high potential for bridging the gap between experimental and simulation work. The strain map provided by the prediction model was compatible with the DIC strain.
查看更多>>摘要：? 2022In recent years, with the acceleration of the aging of the population, the safety of the elderly living alone has attracted great attention, and the falls have become one of the main factors leading to elderly casualties. In order to obtain a high precision and low cost fall detection system for the elderly, a fall detection system based on infrared array sensor and multi-dimensional feature fusion is proposed in this paper. First, we propose a new data acquisition method using infrared array sensor, which effectively enlarges the detection area. Then the personnel positioning is performed before fall detection, which can ensure real-time detection while reducing computational complexity. In addition, a sliding window algorithm is developed and four representative features of a fall are extracted from the collected data, which is fitful to the online detection. Among them, the four characteristics include the change in the center of mass of the falling process, the change in the speed, the change in the area of the person, and the change in variance. Finally, based on the refined features, the support vector machine (SVM) classifier is introduced to identify falls and improve the classification accuracy. The experimental results validate that the proposed fall detection system shows good fall detection accuracy and great practicability.
查看更多>>摘要：? 2022The vibration signals of variable speed rotating machines are non-stationary. Time-frequency analysis (TFA) can effectively analyze non-stationary signals in time–frequency (TF) plane and polynomial chirplet transform (PCT) is one of widely adopted TFA methods. In PCT, a vital step is to approximate the instantaneous frequency (IF) of signals through polynomial approximation. However, the solution of polynomial approximation is easily affected by noise or disturbance, which greatly limits the ability of PCT to analyze noisy signals. To solve this issue, kernel ridge regression-based chirplet transform (KRR-CT) is developed to precisely characterize the TF features of non-stationary signals and produce an energy concentrated TF plane. In the KRR-CT, even in the presence of severe noise, a stable solution can be obtained in the approximation step implemented through KRR. Moreover, KRR-CT based iterative algorithm is further constructed for the analysis of common multi-component signals. The efficacy of proposed KRR-CT based iterative algorithm is confirmed by synthetic and real signals, and the feasibility of applying it for machine fault detection is illustrated. The results indicate that the proposed methods can produce a more energy concentrated TF plane and provide more precise IF information for machine fault detection under varying speed conditions than four comparison methods.
查看更多>>摘要：? 2022 Elsevier LtdTo improve the spatial resolution for mapping of small-scale cylindrical plant root zones using electrical impedance tomography, this paper presents a novel sensor structure, where a ring of 16 external electrodes and an inner ring of 8 internal electrodes are included in an electrode layer. To assess the ability of the structure in the electrode plane as well as the effects of measurement noise, conductivity contrast, radial position of internal electrodes, and measurement strategy on its performance, various simulations and experiments were conducted. Results show that the increased noise level or the decreased conductivity contrast will cause the decrease in resolution. Moreover, half the radius of the imaged domain is a good and compromised choice for the radial position of internal electrodes, and the extended adjacent strategy is an available and relatively better choice. Overall, the internal-external electrodes exhibit benefits in improving and uniforming the resolution.
查看更多>>摘要：? 2022 Elsevier LtdSmartphone applications are increasingly being used to measure gait due to their portability and cost-effectiveness. Important reliability metrics are not available for most of these devices. The purpose of this article was to evaluate the test-retest reliability and concurrent validity of spatiotemporal gait using the novel Gait Analyzer smartphone application compared to the Tekscan Strideway. Healthy participants (n = 23) completed 12 trials of 10-meter walking, at two separate time points, using Gait Analyzer and while walking across the Tekscan Strideway. The results suggest excellent test-retest reliability for the Gait Analyzer and good test-retest reliability for the Tekscan Strideway for both velocity and cadence. At both time points, these devices were moderately to strongly correlated to one another for both velocity and cadence. These data suggest that the Gait Analyzer and Tekscan Strideway are reliable over time and can comparably calculate velocity and cadence.
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