查看更多>>摘要：? 2022 Elsevier LtdThis work addresses an innovative processing strategy to improve the classification of Steady-State Visually Evoked Potentials (SSVEPs). This strategy resorts to the combined use of fast Fourier transform and Canonical Correlation Analysis in time domain, and manages to outperform by over 5% previous results obtained for highly wearable, single-channel Brain–Computer Interfaces. In fact, a classification accuracy of 90% is reached with only 2-s time response. Then, the proposed algorithm is employed for an experimental characterization of three different Augmented Reality (AR) devices (namely, Microsoft Hololens I, Epson Moverio BT-350, and Oculus Rift S). These devices are used to generate the flickering stimuli necessary to the SSVEP induction. Also, in the three pieces of instrumentation under test, the number of simultaneous visual stimuli was increased with respect to the state-of-art solutions. The aim of the experimental characterization was to evaluate the influence of different AR technologies on the elicitation of user's SSVEPs. Classification accuracy, time response, and information transfer rate were used as figures of merit on nine volunteers for each piece of instrumentation. Experimental results show that choosing an adequate AR headset is crucial for obtaining satisfying performance: in fact, it can be observed that the classification accuracy obtained with Microsoft Hololens is about 20% greater than Epson Moverio one.
查看更多>>摘要：? 2022 Elsevier LtdSensor localization is an important step of wireless sensor network (WSN) before conducting a common surveillance task. We propose a robust multiple sensor cooperative localization method against the uncertainty of anchor position estimate based on Time of Flight (TOF) measurements. A key feature is that it makes no statistic assumption on the anchor position uncertainties, which are often difficult to obtain, and only assumes that the error modulus of anchor position is upper bounded. The Maximum likelihood (ML) problem is formulated, where both the TOF measurements between anchors and sensors and the measurements among sensors are utilized in a cooperative way. The semidefinite relaxation technique is provided to transform the nonconvex ML problem into a convex one. The Cramer–Rao lower bounds with and without anchor position uncertainties are also derived. The simulation and experimental results show that our method can yield a good estimate compared to other localization methods.
查看更多>>摘要：? 2022 Elsevier LtdComposite structures are susceptible to impacts capable of producing Barely Visible Impact Damage (BVID). The existence and extent of the damage cannot be clearly determined without further inspection but could lead to an important weakening of the structure. This work investigates the usefulness of Frequency Response Function (FRF) Correlation analysis (based on the analysis of differences between FRFs corresponding to intact and damage states) for BVID detection in carbon/epoxy plates due to multi-impact events. Several indexes are proposed to detect internal damage, all of them proved as useful to detect delamination areas lower than 8% of the composite plate surface, and some of them even lower than 4%. In addition, the influence of the number of measurements was studied through quick tests (reducing the test effort) proving its feasibility. The conclusion is that the proposed method can be applied to efficient structural health monitoring systems for composite structures.
查看更多>>摘要：? 2022 Elsevier LtdData quality plays a strong role in modelling and is fundamental to ensure that obtained analyses and results are reliable. Data uncertainty is related to the measurement's imperfections that will cause an error in the obtained numerical value. In this way, data quality could be measured through uncertainty. Although there are well-established methods for uncertainty evaluation in independent measurements, there is a gap of methods in the case of time-dependent measurements. This study aims to propose a general methodology to evaluate the uncertainty of time-dependent measurements. Fitting an appropriate model to the measurements and then resampling and refitting a model, the uncertainty estimation of each data point is possible. The approach was validated using measurements obtained from typical time series models and compared with theoretical values. Further, real data from a water system is also used to illustrate the method’ capacity for uncertainty estimation of single time measurements.
查看更多>>摘要：? 2022 Elsevier LtdVoltage harmonics are present in various forms and compositions in both power distribution and transmission systems as well as in an industrial environment. This paper presents the influence of harmonics on partial discharge (PD) measurements and the interpretation of phase-resolved patterns. The measurement of partial discharges in the high-voltage insulation of power equipment is perceived as a key diagnostic and prognostic indicator. Partial discharge evolution due to harmonics in both deterministic and stochastic models was evaluated. Since modern diagnostics and prognostics rely more and more on partial discharge phase-resolved patterns, the awareness of the harmonics’ impact is essential. Voltage harmonics result in the additional modulation of PD images; in this context, the harmonic sensitivity of statistical distributions (often derived in diagnostics systems from PD patterns) was demonstrated. With DC voltage, the superimposed harmonics may influence the PD development; for example, in HVDC systems, where they may infiltrate from the grid side or can be created by power electronics-based voltage conversion. Further complication brings voltage harmonic variations over time, which was highlighted by using a time–frequency analysis. The limitations of a harmonic content evaluation based on total harmonic distortion (THD) is shown, indicating potential misinterpretation cases. The presented simulation and measurements results increase the awareness of partial discharge analysis in the presence of harmonics at high voltages. Hence, for modern diagnostics and future autonomous expert systems, it is of paramount significance to properly analyze the presence of harmonics when evaluating and interpreting partial discharges.
查看更多>>摘要：? 2022 Elsevier LtdA polymer-based micro-bottle resonator coated with graphene oxide (GO) film is presented to improve the relative humidity (RH) sensing performance. Polymeric material Loctite 3525 was coated onto a quartz fiber and cured by using UV light irradiation and thermal reflow technology. A layer of GO film was prepared on the micro-bottle resonator by the dip impregnation method, which realized a high Q-factor (>104) transmission of energy by appropriately designing a wave-guide resonator coupling. By optimizing the concentration of GO dip impregnation solution, high sensitivity and figure of merit (FoM) of 0.161 nm/%RH and 2.01/%RH were achieved in the RH range of 22–81%. In addition, after high-temperature annealing at 300 °C, the temperature sensitivity decreased by an order of magnitude from 0.793 nm/°C to 0.068 nm/°C, which significantly reduces the cross-sensitivity between humidity and temperature. The proposed resonator has the advantages of being compact in size, low in cost, high sensitivity, and low in temperature crosstalk.
查看更多>>摘要：? 2022 Elsevier LtdThis paper focuses on performance evaluation of Hestenes–Stiefel conjugate gradient (CG) method along with two well-known line search conditions, which are weak Wolfe conditions (WWC) and strong Wolfe conditions (SWC), and a new step length computation algorithm in geometry fitting of five primitive geometries (i.e., circle, square, equilateral triangle, ellipse and rectangle). A coordinate measuring machine (CMM) is used to acquire 2D profiles of these geometries. Total number of function evaluations, when the CG method-step length computation technique combination being used successfully completes the geometry fitting, are considered to be performance criteria of the combination. It has been seen that the step length computation techniques for the line search crucially affect the success and performance of the Hestenes–Stiefel CG method in the geometry fitting. Therefore, they require a special care for optimal computational efficiency in addition to the line search direction.
查看更多>>摘要：? 2022 Elsevier LtdThe large environmental noise interference has a negative impact on the fault diagnosis of vibration signals. To solve the problems, we present novel global multi-attention deep residual shrinkage networks (GMA-DRSNs), by using attention mechanism. In this paper, the self-adaptive Leaky Thresholding shrinkage function is firstly proposed to substitute the original soft thresholding function in the deep residual shrinkage networks (DRSNs), where all the inner parameters of the approach are automatically inferred based on the attention sub-networks. Secondly, a novel activation function is further presented based on the above improvement, in order to realize the corresponding adaptive nonlinear transformation of each signal. Various experimental results show that our work can achieve better performance compared with the previous works. Finally, we systematically analyze the threshold's tendency, and surprisingly find the same consistency with the receptive field of convolutional neural networks, which is the first geometry explanation work about DRSNs’ structure.
查看更多>>摘要：? 2022 Elsevier LtdIn the domain of inspection of civil structures, the evaluation of permeability in the field is a major problem of durability for all engineering structures using concrete. Specifically, tightness of the enclosure vessels of nuclear plants has to be controlled regularly. The work presented here aims to estimate the capability of non-destructive techniques (permeameters, capacitive and resistive techniques) to evaluate the leakage flow of concrete structures during their service life or after mechanical, hydric and thermal damage induced by accidental loading. The methodology followed to reach this objective is based on three scales, from laboratory samples to real structures, with an intermediate step on large concrete slabs. The analysis highlights the interest of combining permeability, capacitive and resistive measurements for the evaluation of the air tightness of concrete in the field. Global measurements, performed on large slabs in steady state, and evaluation on representative specimens by Cembureau and the surface permeameter, were in accordance for most of the situations analysed in this work. From the saturation degree evaluated by permittivity and resistivity, it was possible to evaluate the apparent permeability of concrete by means of a van Genuchten law calibrated in the laboratory on representative specimens of the structural concrete.
查看更多>>摘要：? 2022 Elsevier LtdThis paper experimentally investigates the characteristics of the velocity field induced by the slipstream from the leading carriage model of a CR 400 high-speed train. The tests were carried out using a 1:16.8 scale model on a moving model rig developed at the Central South University, PRC. The slipstream velocity field was measured at a point cloud involving 25 locations on a plane orthogonal to the track orientation. Aiming at understanding the slipstream ensemble characteristics, especially those unique to the CR400 train, observations were analyzed to evaluate the ensemble-averaged profiles, spatial variations, gusts and time–frequency characteristics of velocity fluctuations in the slipstream. The results suggest that the moving train model and testing rig used in this study capture the unsteady and time-variant features of the slipstream. The spatiotemporal profile of the slipstream usually includes a primary and a secondary peak at the nose tip and the region immediately next to it, respectively. Among the collection of locations studied, the primary peak reaches its maximum at a lateral location close to the train side at the nose height. Finally, the time–frequency portraits of the spatiotemporal variations of the slipstream were obtained using wavelet scalograms of the velocity field, which offered an insightful understanding of the various scales of velocity fluctuations around the nose and their locale.
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