The L-1 norm regularized least squares method is often used for finding sparse approximate solutions and is widely used in signal restoration. Basis pursuit denoising (BPD) performs noise reduction in this way. However, the shortcoming of using L-1 norm regularization is the underestimation of the true solution. Recently, a class of non-convex penalties have been proposed to improve this situation. This kind of penalty function is non-convex itself, but preserves the convexity property of the whole cost function. This approach has been confirmed to offer good performance in 1-D signal denoising. This paper demonstrates the aforementioned method to 2-D signals (images) and applies it to multisensor image fusion. The problem is posed as an inverse one and a corresponding cost function is judiciously designed to include two data attachment terms. The whole cost function is proved to be convex upon suitably choosing the non-convex penalty, so that the cost function minimization can be tackled by convex optimization approaches, which comprise simple computations. The performance of the proposed method is benchmarked against a number of state-of-the-art image fusion techniques and superior performance is demonstrated both visually and in terms of various assessment measures. (c) 2020 Elsevier B.V. All rights reserved.

Optical coherence tomography (OCT) is an essential medical imaging tool for retinal disease diagnosis. Nevertheless, as with all optical imaging techniques, image degradation is a very common phenomenon, affecting the quality of the images. In this paper, we address issues related to the resolution of OCT images and propose solutions based on solving inverse problems. A cost function for deconvolution and super-resolution is formulated and the alternating direction method of multiplier (ADMM) and forward-backward splitting (FBS) algorithms are then employed for its minimisation. On the one hand, the standard Ll norm regularisation with soft thresholding is compared with a total variation (TV) regularisation within an ADMM scheme. On the other hand, nonconvex regularisation is also considered via a multivariate generalisation of the minimax-concave scheme in FBS. In the latter case, the regularisation function is judiciously chosen in order to preserve the overall convexity of the cost function. To be able to evaluate our algorithms qualitatively, a number of standard images are initially used. Then, we also assess our algorithms subjectively by applying them to real OCT images of the human eye. Given that the point spread function (PSF) of OCT images is generally unknown, we also propose ways of estimating it in the deconvolution component of our methods. Our results show that the ADMM scheme with soft thresholding achieves the best performance in terms of enhancing the overall quality of OCT images.=20

Drowsiness as one of the impaired driving behaviour is an important area of concern in ground transportation safety. It can coincide with skill-demanding situations that may lead to vehicle control loss and possibly traffic accidents. Although drowsiness effects on driving performances have been widely investigated, there are few studies that propose a description of its effect on human neuromuscular state. To address this issue, this study aims to investigate the effects of drowsiness on driver neuromuscular state via the estimation of mechanical arm admittance. Mechanical arm admittance is a car dedicated parameter that gives information about arm stiffness of driver and its corresponding response in the frequency domain. Ten participants performed an experiment on a driving simulator, where they experienced steering disturbances, which aims to estimate variations of mechanical arm admittance as well as variations of driving performances between alert and drowsy states. Moreover, variation in driving performances were assessed by the variation of steering reversal rate and standard deviation of lane position. Results indicate that drowsiness increases the gain of mechanical arm admittance for arm movements <2.5Hz and also deteriorates car steering control, increasing the steering operations amplitude and leading to larger vehicle lateral deviations.

In developing automatic platooning of trucks as an energy-saving technology, the reliable driving of the platooned trucks is a primary objective for public implementation and future applications. At the same time, there is also an emergency requirement to ensure the safety of the driving experiment in the automatic platooning of trucks, including the conditions of a system failure. This paper presents a detailed experimental study on emergency avoidance braking for the automatic platooning of trucks using a driving simulator (DS) and an actual-vehicle experiment. In addition, a modification on the braking capability of the trucks of a platoon was applied for safety control. Therefore, human drivers can brake without risking a rear-end collision, in the case of an emergency for a failure in automatic platooning. Initially, an experimental platform was built to reproduce the automatic platooning of trucks in an advanced DS system. Assuming system failure and the emergency deceleration of the preceding truck without warning, the behavior of the driver in the following truck was studied in terms of emergency avoidance of a collision. In particular, with different settings for the mean maximum decelerations of the brake system of the following truck, the stopping gap distances and driver reaction times were analyzed in the driving experiment using the advanced DS and an actual vehicle. The experimental results indicated that emergency braking is an effective method for avoiding a rear-end collision when there is a system failure in the automatic platooning, resulting in the mean maximum deceleration for the following truck being higher than that for the preceding truck.

Prolonged driving on monotonous roads often leads to a reduction in task load that causes drivers passive fatigue. Passive fatigue results in loss of driver alertness and is detrimental to driver safety. This paper focuses on the effect of a haptic guidance steering system on improving behaviors of passively fatigued drivers. By continuously exerting active torque on a steering wheel, the haptic system guides drivers to follow the centerline of a lane; meanwhile, the drivers sense the torque and interact with it while operating the steering wheel. An experiment was conducted with 12 healthy participants in a high-fidelity driving simulator. A monotonous driving course was designed, and vehicle speed was fixed in order to induce drivers' passive fatigue. A treatment session was arranged with the haptic guidance steering system, and a control session was conducted as a comparison. Driving performance, assessed by standard deviation of lane position, mean absolute lateral error, and time-to-lane crossing, was significantly improved when haptic guidance was activated. Results of physiological measures, including heart rate variability and percentage of eye closure, revealed that passively fatigued drivers were aroused when they were aware of the active torque on the steering wheel. In conclusion, the activation of haptic guidance can be regarded as an effective countermeasure for the passively fatigued drivers who have performed a prolonged monotonous driving task.

Drivers always suffer varying degrees of performance decrements under insufficient visual feedback (VF) conditions. Nowadays, haptic guidance (HG) is a developing assistance technology to enhance steering performance; however, driver reactions to HG under degraded VF conditions are still unclear. Therefore, this study focuses on the influence of HG on driving behaviour when part of the road ahead is occluded. The experimental conditions combined three levels of HG, namely none, weak, and strong torques, with four scenarios of VF: whole, near, mid, and far segments. The driving experiment was conducted using a high-fidelity driving simulator with 12 participants. By analysing the standard deviation of lane position and time-to-lane crossing, it was shown that the lane keeping performance became worse without the HG for the degraded VF of near and far segments compared to that of whole and mid-segments. Furthermore, it indicates that the performance decrement in the worse cases was compensated by the implementation of HG, and the strong torque was significantly more effective than the weak torque. Additionally, the use of HG always resulted in an improved turning manoeuvre while approaching curves in the degraded VF of near and far segments.

Millions of drivers could experience shoulder muscle overload when rapidly rotating steering wheels and reduced steering ability at increased steering wheel angles. In order to address these issues for drivers with disability, surface electromyography (sEMG) sensors measuring biceps brachii muscle activity were incorporated into a steering assistance system for remote steering wheel rotation. The path-following accuracy of the sEMG interface with respect to a game steering wheel was evaluated through driving simulator trials. Human participants executed U-turns with differing radii of curvature. For a radius of curvature equal to the minimum vehicle turning radius of 3.6 m, the sEMG interface had significantly greater accuracy than the game steering wheel, with intertrial median lateral errors of 0.5 m and 1.2 m, respectively. For a U-turn with a radius of 7.2 m, the sEMG interface and game steering wheel were comparable in accuracy, with respective intertrial median lateral errors of 1.6 m and 1.4 m. The findings of this study could be utilized to realize accurate sEMG-controlled automobile steering for persons with disability.

In the development of the multi-dimensional force sensor, dimension coupling is the ubiquitous factor restricting the improvement of the measurement accuracy. To effectively reduce the influence of dimension coupling on the parallel multi-dimensional force sensor, a novel parallel three-dimensional force sensor is proposed using a mechanical decoupling principle, and the influence of the friction on dimension coupling is effectively reduced by making the friction rolling instead of sliding friction. In this paper, the mathematical model is established by combining with the structure model of the parallel three-dimensional force sensor, and the modeling and analysis of mechanical decoupling are carried out. The coupling degree (epsilon) of the designed sensor is defined and calculated, and the calculation results show that the mechanical decoupling parallel structure of the sensor possesses good decoupling performance. A prototype of the parallel three-dimensional force sensor was developed, and FEM analysis was carried out. The load calibration and data acquisition experiment system are built, and then calibration experiments were done. According to the calibration experiments, the measurement accuracy is less than 2.86% and the coupling accuracy is less than 3.02%. The experimental results show that the sensor system possesses high measuring accuracy, which provides a basis for the applied research of the parallel multi-dimensional force sensor.

Stochastic resonance is a physical phenomenon where large vibration occurs when a weak sinusoidal force is applied to a bi-stable system. It is expected that a larger vibrational response can be produced than for a typical resonance. Then the authors utilize this system as an energy harvester, which converts energy from vibration. The energy balance between the converted energy and the energy consumed to produce the necessary weak sinusoidal force is analyzed through numerical simulations. It is shown the proposed harvester can convert more energy than a system using a typical linear system resonance.

The application of stochastic resonance to mechanical energy harvesting is currently of topical interest, and this paper concentrates on an analytical and experimental investigation in which stochastic resonance is deliberately exploited within a bistable mechanical system for optimised energy harvesting. The condition for the occurrence of stochastic resonance is defined conventionally by the Kramers rate, and the modelling of a theoretical nonlinear oscillator driven by a small periodic modulating excitation and a harvestable noise source, which, together satisfy this condition, is developed in the paper. A novel experiment is also discussed which validates this particular form of stochastic resonance, showing that the response can indeed be amplified when the frequency of the weak periodic modulating excitation fulfills the correct occurrence condition. The experimental results indicate that the available power generated under this condition of stochastic resonance is noticeably higher than the power that can be collected under other harvesting conditions. (C) 2014 Elsevier Ltd. All rights reserved.

The kinetics analysis of ankle, knee and hip joints during gait is fundamental for rehabilitation and clinical diagnosis but data are commonly obtained by means of the laboratory-restricted equipment such as a force plate and optical camera system, which usually require complicated computing programs and professional operation. In this study, we have developed a wearable sensor system to facilitate joint kinetics analysis to assess body movement in daily activities. The sensor system is composed of a shoe-based force sensor which measures ground reaction force (GRF) and center of pressure (CoP), and a leg-attached motion sensor consisting of three uniaxial gyroscopes units which detect lower limbs movement. This paper presents a kinetics analysis of ankle, knee and hip joints in the sagittal plane by using the sensor system on human normal level walking during whole gait phases. In order to estimate the joint kinetics, an inverse kinetics method based on the sensing signals and gait characteristics was developed. In the validation experiments with 10 subjects, joint kinetics was calculated using data synchronously measured by the sensor system and a force plate & optical camera system. The root mean square (RMS) differences of the ankle, knee and hip joints moments between the two systems in a gait cycle were (2±0.34) (mean±standard deviation) Nm, (7.2±1.34) Nm and (11.2±1.3) Nm, being (5.4±0.7)%, (6±0.32)% and (6.1±0.25)% of the maximal magnitude of ankle, knee and hip joints moments respectively. The RMS differences of the ankle, knee and hip joints powers between the two systems in a gait cycle were (4.2±0.4) W, (5.7±2.1) W and (5.7±0.3) W, being (8.4±0.4)%, (4.1±0.5)% and (6.4±0.4)% of the maximal magnitude of joint powers respectively. The experimental results demonstrate the feasibility and effectiveness of the joint kinetics analysis using the wearable sensor system for a daily application in gait analysis.

The non-linearity of a hardening-type oscillator provides a wider bandwidth and a higher energy harvesting capability under harmonic excitations. Also, both low- and high-energy responses can coexist for the same parameter combinations at relatively high excitation levels. However, if the oscillator's response happens to coincide with the low-energy orbit then the improved performance achieved by the non-linear oscillator over that of its linear counterpart, could be impaired. This is therefore the main motivation for stabilisation of the high-energy orbit. In the present work, a schematic harvester design is considered consisting of a mass supported by two linear springs connected in series, each with a parallel damper, and a third-order non-linear spring. The equivalent linear stiffness and damping coefficients of the oscillator are derived through variation of the damper element. From this adjustment the variation of the equivalent stiffness generates a corresponding shift in the frequency-amplitude response curve, and this triggers a jump from the low-energy orbit to stabilise the high-energy orbit. This approach has been seen to require little additional energy supply for the adjustment and stabilisation, compared with that needed for direct stiffness tuning by mechanical means. Overall energy saving is of particular importance for energy harvesting applications. Subsequent results from simulation and experimentation confirm that the proposed method can be used to trigger a jump to the desirable state, thereby introducing a beneficial addition to the performance of the non-linear hardening-type energy harvester that improves overall efficiency and broadens the bandwidth.

With the advent of global positioning system technology, smart phones are used as portable navigation systems. Guidelines that ensure driving safety while using conventional on-board navigation systems have already been published but do not extend to portable navigation systems; therefore, this study focused on the analysis of the eye-gaze tracking of drivers interacting with portable navigation systems in an urban area. Combinations of different display sizes and positions of portable navigation systems were adopted by 20 participants in a driving simulator experiment. An expectation maximum algorithm was proposed to classify the measured eye-gaze points; furthermore, three measures of glance frequency, glance time, and total glance time as a percentage were calculated. The results indicated that the convenient display position with a small visual angle can provide a significantly shorter glance time but a significantly higher glance frequency; however, the small-size display will bring on significantly longer glance time that may result in the increasing of visual distraction for drivers. The small-size portable display received significantly lower scores for subjective evaluation of acceptability and fatigue; moreover, the small-size portable display on the conventional built-in position received significantly lower subjective evaluation scores than that of the big-size one on the upper side of the dashboard. In addition, it indicated an increased risk of rear-end collision that the proportion of time that the time-to-collision was less than 1 s was significantly shorter for the portable navigation than that of traditional on-board one.