This paper presents a particle swarm tracking algorithm with improved inertia weight based on color features. The weighted color histogram is used as the target feature to reduce the contribution of target edge pixels in the target feature, which makes the algorithm insensitive to the target non-rigid deformation, scale variation, and rotation. Meanwhile, the influence of partial obstruction on the description of target features is reduced. The particle swarm optimization algorithm can complete the multi-peak search, which can cope well with the object occlusion tracking problem. This means that the target is located precisely where the similarity function appears multi-peak. When the particle swarm optimization algorithm is applied to the object tracking, the inertia weight adjustment mechanism has some limitations. This paper presents an improved method. The concept of particle maturity is introduced to improve the inertia weight adjustment mechanism, which could adjust the inertia weight in time according to the different states of each particle in each generation. Experimental results show that our algorithm achieves state-of-the-art performance in a wide range of scenarios. In recent years, object tracking technology has been a hot topic in the field of computer vision. For decades, a large number of scholars worldwide have been engaged in the study of object tracking algorithms ,3,4,5,6.The algorithms representative of the traditional object tracking field include the centroid tracking algorithm, the related tracking algorithm, the gate tracking algorithm, the optical flow algorithm, and the mean-shift tracking algorithm. The centroid tracking algorithm and the gate tracking algorithm have satisfactory real-time performance and low complexity, but their stability is poor. In contrast, the related tracking algorithm and the optical flow algorithm have satisfactory stability, but they have difficulty guaranteeing real-time. Compared to the advantages and disadvantages of the previous algorithms, the mean-shift tracking algorithm is the most widely used in engineering. However, the mean-shift tracking algorithm is more susceptible to the background, which is problematic since it is easy to lose the target in a complex environment. In particular, there is no robust algorithm proposed for target occlusion. Most of the solutions are confined to a specific environment and require a large amount of research.In recent years, many new algorithms have emerged in the field of target tracking. The most popular and representative new algorithms include correlation-filtering-based tracking methods and deep-learning-based tracking methods. Typical algorithms for correlation-filtering-based tracking include the kernelized correlation filter (KCF), the discriminative scale space tracker (DSST) and the spatio-temporal context (STC). The framework of these algorithms is roughly the same. In general, the principle of the correlation filter is that a high (correlation peak) is generated for each interested target and a low response is generated for the background in the scene. In 2010, Bolme proposed a Minimum Output Sum of Squared Error (MOSSE) tracking method based on adaptive correlation filtering in Reference . The algModern tracking algorithms have achieved satisfactory results in the tracking effect, but most are very complex and significantly sacrifice the operation efficiency of the algorithm. For engineering applications, we predict that the algorithm will be simple and easy to use due to its better performance than traditional algorithms and the fact that it can guarantee real-time performance.In the target tracking system, the selection of target features is related to the tracking effect of the subsequent algorithm. Color features are the most widely used visual features in video tracking. The main reason for this is that color is usually related to objects or scenes contained in images, and when the object rotates and varies in size, the color feature can improve the flexibility of the tracking algorithm. In this paper, the most widely used color histogram is used as the target feature. We have a targeted and reasonable weighting on the histogram to improve the robustness of the algorithm in a complex environment. Particle swarm optimization (PSO) has recently been a fast-growing optimization algorithm based on swarm intelligence. The algorithm has good multi-peak search ability, which means it has a good ability to search for a global optimal value and it converges quickly. When the target is occluded during the tracking process, the object similarity function will appear multi-peak. The particle swarm optimization algorithm is used to optimize the object similarity function, which could cope with the target occlusion tracking problem.In 1995, Dr. Kennedy and Dr. Eberhart proposed a particle swarm optimization algorithm for the optimization of nonlinear functions . The algHowever, the inertial weight adjustment mechanisms proposed in the above paragraph have some limitations, including a constant or random inertia weight adjustment mechanism that is not universally applicable, the linear or non-linear inertia weight adjustment mechanism adjusts inertial weight only by the number of iterations without taking the state of each particle into account, and the adaptive inertia weight adjustment mechanism is generally adjusted by a feedback parameter. However, the feedback parameter cannot be used as a reliable criterion for evaluating inertial weight.To deal with these problems, this paper introduces the concept of the particle maturity rate to improve the adjustment of inertia weight by taking full account of the different situations of each particle in each generation. The inertial weight is adjusted accurately according to the state of particles to optimize the solution of the object similarity function. The improved particle swarm optimization object tracking algorithm can reduce the number of iterations to achieve the same fitness, which improves the operation efficiency and realizes the tracking of object occlusion.(1)We use a weighted color histogram as the object feature description. The object is normalized to a unit circle to reduce the contribution of the object edge pixel in the object feature, which effectively solves the problem of non-rigid deformation, rotation, and scale variation during the object tracking. At the same time, the influence of partial occlusion on the object feature description is reduced.(2)When the target is blocked in the object tracking process, the object similarity function will reach the “multi-peak” target. Combined with the multi-peak search ability of the particle swarm optimization algorithm, the algorithm is used to optimize the object similarity function to achieve accurate positioning under the object occlusion situation.(3)An improved particle swarm optimization object tracking algorithm is proposed. The method solves the limitation of the inertia weight adjustment mechanism when the particle swarm optimization algorithm is applied in the field of object tracking.(4)Experimental results show that the particle swarm optimization object tracking algorithm with improved inertia weight can significantly improve computational efficiency.(5)Experiments show that the proposed method shows more advantages compared with eleven state-of-the-art algorithms. It is a satisfactory solution to non-rigid deformation, rotation, scale variation, and object occlusion during object tracking.The main contributions of this paper are summarized below.The rest of the paper is organized as follows. Ever since color indexing was proposed by Swain and Ballard in 1991 , color fThe color feature has less dependence on the size, orientation, and viewing angle of the image, which is why it has higher robustness. Firstly, the image-oriented color feature needs to choose the appropriate color space to describe the color features. Then, we quantify the color features. Finally, we need to define a similarity criterion to measure the color similarity between the images. There are several ways to describe color features, such as histograms, color sets, and color moments. The histogram is not the best nonparametric representation, but it is mostly adequate for use in the tracking process. The histogram is the most widely used color feature in many color tracking fields ,22,23. WA weighted color histogram of the image region in which the center position of the image is (1)The amount of the calculation is small. The histogram is a reduced dimension representing the target image, which can reduce the computational complexity of pattern matching.(2)The histogram generated by a reasonable color model is insensitive to scale variation and rotation. The weighted color histogram also has great advantages for partial occlusion, especially for edge occlusion.(3)Histogram models are well-suited for modeling non-rigid objects. It is difficult to use shape features to represent a non-rigid object. However, the color distribution is still the same, no matter how the non-rigid object deforms.The tracking method based on color features has the following advantages.A similarity measurement is usually expressed in Hausdorff distance. For two finite point sets The Hausdorff measurement has different representations depending on the different selected features. The Hausdorff measurement of the gray features mainly includes the mean square error evaluation function (MSE), the sum of absolute difference (SAD), and the normalized cross correlation evaluation function (NC). For the color features, the Bhattacharyya coefficient can be used to express the Hausdorff measurement based on the color histogram.It is assumed that the normalized color histogram of the template image is Particle swarm optimization simulates the predation behavior of birds. It is based on the assumption that a flock of birds randomly searches for food when there is only one piece of food in the area. All of the birds do not know where the food is, but they know how far the current location is from food. Then, the best way to find food is to search for the area around the birds that are currently closest to the food. The particle swarm optimization learns from this model and uses it to solve optimization problems. In particle swarm optimization, the solution to each optimization problem is a bird in the search space, which is called the “particle”. Each particle has a fitness value determined by the objective function. The high fitness value indicates that the obtained solution is accurate. Each particle moves in the solution space whose direction and distance will be determined by a velocity. Then, the particles follow the movement of the current optimal particle in the solution space.n-dimensional search space, the ith particle position is presented as c1 and c2 are acceleration constants, t denotes the algebra of the current iteration, and The mathematical equations of the particle swarm optimization algorithm are as follows . In the g groups .The research shows that the particle swarm optimization algorithm has an effective global convergence ability when the inertia weight is large, while the small inertia weight facilitates local convergence. Based on the important influence of inertia weight on the algorithm search behavior, many researchers improve the algorithm optimization performance by changing the inertia weight. At present, the improved method can be divided into a fixed or random inertia weight adjustment mechanism, the linear or non-linear inertia weight adjustment mechanism, and the adaptive inertia weight adjustment mechanism.In order to further explore the effect of inertia weight on particle swarm optimization, the problem is simplified to a unimodal function optimization. We first define that the particle closest to the optimal solution in the particle swarm is the optimal particle and the other particles are suboptimal particles. It should be noted that the fitness value of suboptimal particles may exceed the fitness value of the optimal particle in the process of the particle swarm approaching the optimal solution. At this point, the suboptimal particle that has a better fitness value becomes the optimal particle. This situation constantly happens during the algorithm operation. In For the first case shown in For the second case shown in Both of these situations may occur during the algorithm operation. Fixed or random inertia weight adjustment mechanisms are not appropriate. The method of adjusting the inertia weight linearly or non-linearly by the number of particle iterations is to use a moderate inertia weight to make the optimization achieve satisfactory results without taking full account of the different situations of each particle in each generation. The adaptive inertia weight adjustment mechanism adjusts the inertia weight according to the feedback parameter. Usually, the feedback parameter will use the fitness value or its derived value. However, the fitness value is not a reliable standard for evaluating inertia weights. When the particle has a high fitness value, it may require different values of inertia weight to adjust because of the different situations of the particle. When the fitness value of the particle is low, it may have different requirements for inertia weight.In order to solve the above problems, this paper presents an improved inertial weight adjustment mechanism, which introduces the concept of the particle maturity rate as a description of particle states. When the particle maturity rate is relatively high, it indicates that the particles are clustered in a position far from the optimal solution and the whole population is slowly approaching the optimal solution. This is shown in First of all, we define coefficient ith particle at tth iteration is defined by the equation below:ith particle at the tth iteration. Combined with the particle maturity rate formula, the maturity of the entire population can be described by Equation (10):The maturity rate of the The inertia weight varies between the maximum and the minimum. In this paper, the improved particle swarm optimization object tracking method is combined with the concept of the particle maturity rate to calculate the maturity rate of the entire population by taking into full account the situation of each particle in each generation. The maturity rate of the entire population is used to adjust the inertia weight, which means the adjustment of the inertia weight is more reasonable and the algorithm efficiency is improved. The main steps of the algorithm are provided in Algorithm 1.Algorithm 1. Improved particle swarm optimization object tracking method1: Initial parameters of the particle swarm. Initial 2: Initialize the target box in the first frame. Determine the object feature description and similarity measure.For frame = 2, 3, ... to the last frame.3: Fort = 1, 2, ... to the maximum number of iterations.4: 5: Calculate the 6: Calculate the If fitness value of the current particle is better compared to individual optimal solution.7: 8: Update the individual optimal solution End.9: If fitness value of the current particle is better compared to global optimal solution.10: 11: Update global optimal solution, End.12: 13: Adjust inertia weight according to Equation (6).End.14: 15: Locate the target by using the maximum fitness value position.End.16: We performed the experiments on a PC with Intel i5-5200U CPU (2.2 GHz), 8 GB RAM memory, and Windows 7 operating system. The experiments in this paper were implemented in MATLAB 2016. We compared the performance of the improved algorithm with eleven state-of-the-art algorithms including TLD , Struck Dancer, Dancer2, and Skater were used as the representative test sequences, and the partial tracking results are shown in Dancer sequence, the TLD algorithm began to lose the target after the target was deformed for a period of time, which would not accurately track the target. In the Dancer2 sequence, when the object was non-rigidly deformed for a period of time, the TLD and CT algorithms showed tracking frame drift. In the Skater sequence, DFT and DSST algorithms failed to track the target after a period of time after target deformation. During the whole tracking process, our algorithm was more accurate and stable. The image single frame processing speed was better than 23 milliseconds. This can be attributed to the use of color features, which are not sensitive to appearance deformation.For the non-rigid deformation in the object tracking process, Carscale, Human6, and Singer1 were used as the test sequences with scale variation during the object movement. In the Carscale sequence, there are not only obvious changes in scale, but there is partial occlusion. In the 152nd frame, when the target size varies greatly, the algorithm proposed in this paper started to show clear advantages. In the Human6 sequence, DFT and CT algorithms began to lose the object from the 191nd frame. In subsequent image sequences, the target scale changes more significantly and the proposed algorithm could always track the target steadily. In the Singer1 sequence, our algorithm and DSST algorithm showed satisfactory tracking performance compared to other algorithms. Throughout the tracking process, our tracking window could mostly contain the object and the single frame image processing speed was better than 36 milliseconds.In Jump, Diving, and Skiing are classic target rotation sequences, and were used as the test image sequences. In the Jump sequence, the target starts rotating from frame 10 and the algorithm proposed in this paper could solve the rotation problem better than other algorithms. In the Diving sequence, starting from frame 76, other algorithms began to lose the target, in addition to the proposed algorithm. In the Skiing sequence, our algorithm and the DLSSVM algorithm showed good performance and achieved a stable tracking target in fast rotation. In the entire process of tracking, the proposed algorithm could stably lock the target. In this scenario, the single frame image processing speed was better than 40 milliseconds.Suv, Tiger2, Human3, Basketball, and Walking2 as test sequences to track the occluded object. The tracking results are shown in Suv sequence, CT and DFT algorithms lost the target when the target passed through the blocking card while the tracking algorithm proposed in this paper could accurately and stably track the target. In the Tiger2 sequence, the object was repeatedly obscured by the green leaves and most of the tracking algorithms deviated from the object. The tracking algorithm proposed in this paper has obvious advantages, and the tracking box covered the object position accurately. In the Human3 sequence, the object is blocked completely for a short period of time. Starting from frame 53, tracking algorithms such as VTD, TLD, and Struck—which are traditionally well-behaved when dealing with occlusion—started to lose the object. However, the tracking algorithm proposed in this paper still stably locked the object. When the object appeared again in the image, the proposed tracking algorithm immediately identified the object to achieve the robustness of the entire tracking process. In the Basketball sequence, the object is heavily or even completely blocked. The algorithm proposed in this paper had good performance in managing the occlusion problem. In the Walking2 sequence, when the target is out of occlusion, only a few algorithms  could continue to track the target. It can be seen that the improved particle swarm optimization tracking algorithm has an effective anti-occlusion ability, which basically guarantees the real-time value.In order to fully reflect the advantage of the algorithm proposed in this paper in the case of the similarity function occurring at “multi-peak”, we used In order to show that the improved particle swarm optimization object tracking method proposed in this paper has fewer iterations and higher tracking efficiency than other particle swarm optimization object tracking methods, the five sets of image sequences in the previous section were compared experimentally using the nonlinear inertia weight adjustment mechanism, the adaptive inertia weight adjustment mechanism, and the improved inertial weight adjustment mechanism, respectively. Because the linear and nonlinear inertia weight adjustment mechanisms are relatively similar, this paper uses the non-linear adjustment mechanism as its representative. We applied different PSO weight adjustment mechanisms to complete 20 experiments for each group of image sequences and recorded the experimental data to calculate the average single frame. When the object similarity function value reached 0.98, the results are shown in Method 1 is a non-linear decreasing inertia weight adjustment method. Method 2 is an adaptive method that dynamically changes the value of the inertia weight. Method 3 is the improved inertial weight adjustment method proposed in this paper.Suv sequence, the three methods could basically guarantee robustness and real-time due to less obstruction. However, the computational efficiency of the improved particle swarm tracking algorithm was clearly higher than the nonlinear method and the adaptive method. For Tiger2 sequences, the computational efficiency of Method 1 and Method 2 were significantly reduced because of the more serious occlusion of image sequences. However, the improved method proposed in this paper could basically guarantee real-time tracking under partial occlusion, showing that the improved method has greatly enhanced algorithm efficiency. For Human3, Basketball, and Walking2 sequences, the efficiency of the improved method was obviously better than the non-linear method. Compared with the adaptive method, the improved method significantly reduced the number of iterations when the object was severely obstructed, and it improved the efficiency of the algorithm. Experimental results showed that the improved algorithm could accurately meet the algorithm requirements by adjusting the inertia weight according to the different states of each particle in each generation, which can effectively improve the computational efficiency of the algorithm.As can be seen from In this subsection, we evaluate the algorithm performance with one-pass evaluation (OPE), which is proposed in Reference . We usedCarscale sequence. It can be seen that the particle swarm tracking algorithm with a color histogram feature has clear advantages in dealing with non-rigid deformation and rotation. This may be due to the fact that the weighted color histogram feature is insensitive to deformation and rotation. Our algorithm also had good performance in dealing with scale variation. However, our algorithm ranked after the DSST algorithm in success plots. As described in This paper presents a new object tracking method. A weighted color histogram normalized to a unit circle is used as the target feature description. Particle swarm optimization is used to optimize the object similarity function. When the target undergoes occlusion, the object similarity function will appear at the multi-peak situation and the multi-peak search ability of the particle swarm optimization algorithm is utilized to realize the accurate positioning in the occlusion situation. When the particle swarm optimization algorithm is applied to object tracking, the inertia weight adjustment mechanism has some limitations, and we present an improved method. We introduce the concept of particle maturity to achieve efficient optimization. The algorithm can adjust the inertia weight in time according to different conditions of each particle in each generation and greatly reduce the amount of computation. The experimental results show that the improved particle swarm optimization object tracking method achieves the same fitness with a smaller number of iterations. The proposed algorithm shows the most advanced performance in a wide range of scenarios.


In order to realize reliable Vehicle-to-Vehicle (V2V) communication systems for autonomous driving, the recognition of radio propagation becomes an important technology. However, in the current wireless distributed network systems, it is difficult to accurately estimate the radio propagation characteristics because of the locality of the radio propagation caused by surrounding buildings and geographical features. In this paper, we propose a measurement-based radio environment database for improving the accuracy of the radio environment estimation in the V2V communication systems. The database first gathers measurement datasets of the received signal strength indicator (RSSI) related to the transmission/reception locations from V2V systems. By using the datasets, the average received power maps linked with transmitter and receiver locations are generated. We have performed measurement campaigns of V2V communications in the real environment to observe RSSI for the database construction. Our results show that the proposed method has higher accuracy of the radio propagation estimation than the conventional path loss model-based estimation. Along with the rapid development of wireless communication technology, the number of mobile terminals has significantly increased during the last decade. As can be seen from a prediction by Cisco , 50 billThe use of the empirical propagation model is the most fundamental method for the radio propagation estimation because these models had been constructed by many discussions with the huge measurement campaigns in various environments. Although the accuracy of the path loss models is limited, the error characteristics are well known; these models enable the simple system design. However, because empirical models generalize radio propagation environments to typical environments such as urban, suburban, and rural, the propagation model cannot include site-specific dispersions: the estimation accuracy is limited . In addiIn order to solve the problem, a radio environment database based on measurement results has attracted attention in recent years ,9,10. Thcrowdsourcing. By using crowdsourcing, the huge number of datasets can be gathered from huge number of locations. In order to evaluate the accuracy of the database, a measurement campaign with Vehicle-to-Vehicle (V2V) communication is conducted over a suburban area in Japan. In IEEE 802.11p, the existing communication standard for the V2V, the transmitter position is typically included into the transmission packet for traffic safety support. Therefore, by using the global positioning systems at the received vehicle, the Received Signal Strength Indicator (RSSI) and the both transmitter/receiver position can be stored without additional operation. After the observation experiment, we create radio environment maps (REMs) related to the transmission positions using MySQL server. Experimental results show that the RSSI can be accurately predicted compared with the path loss-based method. In addition, we apply the proposed database to the power control in the unicast system in order to discuss the effect of the proposed database on the communication efficiency. Evaluation results show that the proposed method can minimize the transmission power, i.e., interference with vehicles other than the destination, while guaranteeing the desired communication quality.In this paper, we propose a novel architecture of the measurement-based radio environment database for the wireless distributed network situations. In the proposed database, the datasets of different transmitters and different receivers are gathered by users obtaining from the usual communication packets. Such kind of data gathering enabled by distributed users is called This paper is organized as follows. Note that this paper is a revised and extend version of our work presented in Reference . Based oN maps are stored at the maximum when the area is divided into N meshes. Although there are several methods for the map construction such as empirical path loss models and ray tracing, we focus on the measurement-based approach. In this way, it becomes possible to grasp statistical radio environment characteristics based on measurement data and radio environment can be estimated more accurately than the existing propagation model.As shown in The dataset accumulated after the initial database construction should be utilized again for averaging. This is because the average characteristic of radio propagation, i.e., sum of path loss and shadowing, is generally static over time domain. We anticipate that the accuracy of averaged multipath fading improves, as the number of samples increases. On the other hand, in the realistic situation, the shadowing effect will fluctuate when there is a change in the environment of the structure. One candidate of the countermeasure for this problem is to investigate the change of structure by time series analysis of observed values such as comparing the latest observation result with the probability density function (PDF) that consists of past observation results. If a change of the structure is detected, we can reconstruct the accurate database by removing the past observation results for the database construction or by taking weighted averaging with forgetting factors. Because this problem requires new algorithms and is far beyond the focus of this paper, we consider that this is a future work.After the database construction, the transmitter can adjust the communication parameters by utilizing the statistical information stored in the database. When the transmitter accesses to the database, the database provides the map corresponding to the transmitter position. By using the map, the transmitting vehicle can confirm the statistical communication quality at the arbitrary received location, and can modify the communication parameters. For example, when the estimated received signal power is lower than the desired value, the transmitter can improve the packet reception probability by using higher transmission power, low rate modulation schemes, and relay communications. In addition, if the estimated quality is higher than the desired value, the transmitter can choose the high rate communication with higher-order modulation or the interference mitigation with lower transmission power. The effect of the database-assisted communication parameter setting is discussed in Note that this paper does not consider the use of spatial interpolation for the REM construction. This is because the main purpose of this paper is to show that the proposed database can estimate the site-specific propagation attenuation using meshes related to the pair of transmission and reception locations. It should be noted that the spatial interpolation can be implemented by the path loss model that is fitted to the actually observed datasets. This is discussed in In order to construct a radio environment database for wireless distributed networks and evaluate the accuracy of the database, V2V communications were conducted in Chofu City and Mitaka City, typical suburban areas in Tokyo, Japan over three days in January 2017. Measurement conditions are shown in Three vehicles shown in A signal is transmitted from the onboard device at a cycle of 100 ms, and the other vehicle records the received signal power, the received time, the ID of both transmitter and receiver, and the received/transmitted position. Note that the transmitted position was extracted from the transmitted packet, and the received position and the time was obtained from the GPS connected to the onboard device. Note that Garmin GPS 18x, a USB-connected device, was used for the GPS system. The GPS acquires the location and time information once per second, and the accuracy of the position information is 95% within 15 m.Here, specifications of the onboard device are shown in The measured datasets are reported from each vehicle to the database.The database server registers the reported datasets to the table in the MySQL server.The database server performs the statistical processing of the dataset. In this scheme, the database calculates the average RSSI for each pair of transmission and reception meshes using a PHP program. Then, the calculated statistical data is stored in the table for the statistical data.According to the request from the terminal, the database server attempts to get the statistical data from the MySQL.The terminal can get the radio environment maps.A radio environment database was constructed by statistical process to the measured datasets. In our measurement campaign, the receiving vehicles record the above information into a comma-separated values (CSV) file when the packet is successfully decoded. The stored CSV file is uploaded to the database server offline after the measurement campaign. In the database server, the RSSI is stored for each pair of transmission and reception meshes and statistical processing is performed. Here, transmission and reception meshes are calculated by normalizing latitude and longitude in the database server. In the local PC, download the statistical data in which RSSI is averaged for each pair of transmission and reception meshes in the CSV file. In this section, we discuss the constructed database. After several maps are shown as examples, the accuracy of the database is evaluated by using Root Mean Squared Error (RMSE).These facts suggest that the measurement-based maps can contain the effect of structure in the radio propagation estimation. The accuracy of the constructed database is evaluated in In addition, we evaluated the calculation time for statistical processing of the datasets. Statistical processing is implemented by PHP 7.0.12 in Cent OS 7 with Intel(R) Xeon(R) CPU E5-2407@ 2.20 GHz. d (m) is then calculated and the scatter diagram was obtained. Note that the noise floor of our equipment in the communication bandwidth is about −96.0 dBm. In order to eliminate effects of the noise floor, we limit the maximum distance in the performance evaluation between links to 100 m. If we process the datasets over longer communication distances, the average received power is overestimated because we cannot obtain RSSIs below the noise floor. Because this is a challenging problem, this paper saves this issue for a future work. A similar problem is pointed out in some papers . ReferrIn this paper, we model the distance attenuation characteristics as follows :(2)Rb=4hTherefore, the path loss index can be calculated as 3.1925 for an areas ,27,28.Next, we evaluate the accuracy of the constructed database. We constructed the database using the datasets observed on days 1 and 2. Statistical processing was performed with 2 m-, 5 m-, and 10 m-squared meshes, and the average received power value for each mesh was calculated. The datasets observed on day 3 were treated as the instantaneous signal power, and RMSE was calculated from the difference between the constructed database and the instantaneous values.For comparison, path loss-based estimation method is also evaluated. The model in this communication area was calculated from the datasets observed on days 1 and 2. Although there are more complex path loss models that consider a larger number of variables , they do not necessarily make better predictions  is inter-link distance. In addition, we compare the estimation accuracy to the ITU-R P.1411 . In thisEstimated received power was derived by subtracting the propagation loss that corresponded to Equation  from traIn addition, we compare the estimation accuracies of the two-ray path loss model  and the Here, it should be noted that the fitted path loss can be used for estimating the received signal power where there is no statistical data. Thus, the RMSE of the fitted path loss also shows the performance of fitted path loss-aided interpolation.The database with 10-m mesh is constructed with the datasets observed on days 1 and day 2.The empirical cumulative distribution function (CDF) of multipath fading factor in the evaluated area is estimated by taking the difference between each instantaneous dataset used for the database construction and the average received signal power in the database. We assume that the shape of CDF is static in the evaluation area.The datasets observed on day 3 are treated as the instantaneous true received signal power. The database estimates the instantaneous received power at the reception mesh via the constructed database.The database calculates the transmission power from the estimated average received signal power and the empirical CDF of the multipath fading so that the outage probability is guaranteed. Note that we limit the maximum transmission power to 19.2 dBm, which is the rated output in our equipment.This power control is applied for all the instantaneous datasets observed on day 3.Finally, we discuss the effect of the proposed database-assisted communications. In the unicast communication, unlike the broadcast communication, the transmitted signal becomes the interference power at the vehicles other than the destination. Thus, suppressing the transmission power to the minimum, i.e., suppressing the spatial interference power, improves the communication efficiency. Motivated by this fact, we consider a simple power control situation where the transmitter designs its own transmission power according to the database so that we guarantee the outage probability that the received signal power falls below the desired value. The performance of the power control is performed according to the following procedure:The evaluation is performed around the intersection shown in Note that parameters in this equation are different from Equations  and 4)  4) becauUncertainty of estimation of the tail in the empirical CDF. Although achieving a high packet delivery ratio requires accurate information of the tail, it is difficult to obtain such information in the empirical CDF with limited samples.Limitation of the maximum transmission power.We performed the power control where the permissible outage probability is 0.1–0.2 and the desired received power is –82.0 dBm. In order to keep the permissible outage probability under the above conditions, we set the margin to the transmit power. The dotted line in The proposed method can achieve the desired value with a small margin of less than 1 dB and, even if the margin is taken into consideration, the average transmission power is lower than the path loss based method. These results mean that the proposed method can achieve the desired communication quality with lower transmission power: spectral efficiency can be improved.The measurement-based radio environment databases were proposed in the V2V communication environment. The evaluation results showed that the proposed database accurately estimates the radio environment fluctuations compared to some path loss models including the measurement-based path loss model and ITU-R P.1411. We conclude that the measurement-based radio environment database can be used for predicting radio environment characteristics in not only conventional applications where the transmitter is fixed, but also V2V communication systems.In addition, we have shown that the proposed database can improve power control in the unicast situation, and the proposed database will also improve the communication efficiency in V2V systems.


Piezoelectric energy harvesting using cantilever-type structures has been extensively investigated due to its potential application in providing power supplies for wireless sensor networks, but the low output power has been a bottleneck for its further commercialization. To improve the power conversion capability, a piezoelectric beam with different electrode coverage ratios is studied theoretically and experimentally in this paper. A distributed-parameter theoretical model is established for a bimorph piezoelectric beam with the consideration of the electrode coverage area. The impact of the electrode coverage on the capacitance, the output power and the optimal load resistance are analyzed, showing that the piezoelectric beam has the best performance with an electrode coverage of 66.1%. An experimental study was then carried out to validate the theoretical results using a piezoelectric beam fabricated with segmented electrodes. The experimental results fit well with the theoretical model. A 12% improvement on the Root-Mean-Square (RMS) output power was achieved with the optimized electrode converge ratio (66.1%). This work provides a simple approach to utilizing piezoelectric beams in a more efficient way. Energy harvesting, as an alternative energy source for low-power electronics, has prompted great research interest in the last decade. Three conversion mechanisms, i.e. piezoelectric, electromagnetic and electrostatic, have been extensively investigated for harvesting ambient kinetic energy from the environment ,2. AmongThe low output power is mainly caused by the low power generation capability of piezoelectric transducers , and thiThe size and shape of the piezoelectric transducer also affect the performance of harvesters. Friswell and Adhikari investigated the influence of the length and width of the piezoelectric layer of a rectangular beam on the power output . The widIn addition, electrode coverage is another important factor for piezoelectric harvester design. For piezoelectric transducers, along with the piezoelectric layer, there are normally two additional metal layers as electrodes for transferring the electrons from the piezoelectric material to the subsequent load circuits . Using pFor micro-harvesting devices, the resonant frequency for high order vibration modes is normally much higher than the frequency of ambient vibrations in the environment, which are characterized as low frequency and broadband ,20. TherIn this paper, we present a theoretical model to analyze the influence of electrode coverage on the electromechanical behaviour of the piezoelectric harvester under tip excitation. Compared with base excitation, the tip excitation method  demonstrates broadband capability by beam plucking using magnetic force ,28 or diThe variation of the electrode coverage not only affects the electrical behaviour of the harvester, but also its mechanical performance, namely the vibration response. Therefore, a complete model considering both the mechanical and electrical fields are needed to optimize the design.Q is the electric charge on the electrodes, A. The current output of the harvester can be obtained from the integral form of Gauss’s Law , which iThe axial strain mid-way through each piezoelectric layer is proportional to the curvature of the beam at that point:The electrical equation of piezoelectric beams are then obtained from Equation  as(4)e¯z-axis is The strain distribution can be deduced from the vibration response of the cantilever under tip excitation. In terms of the excitation mechanism, a magnetic-force plucking method is adopted in this analysis, as this is the typical solution for the tip excitation method, and the force model has been verified by several researchers ,31. The YI is the bending stiffness, m is the mass per unit length of the beam, L is the length of the beam. Details on the solution to this equation are referred to Ref. [Erturk and Inman built a distributed-parameter model for piezoelectric beams under base excitation . In our  to Ref. .J and Due to the three-dimensional distribution of the driving magnet and the tip magnet, a 3D theoretical model is needed to calculate the magnetic force. Akoun and Yonnet established a reliable theoretical model for calculating 3D magnetic force between cuboidal magnets . The magi, j, k, l, p and q, are equal to 0 or 1 according to the specific corner. x-axis and z-axis when the rotor is static, with the driving magnet’s angular position These lengths, refer to .Combining Equations  and 5),,5), we cThe theory introduced above is solved using Matlab/Simulink . The parameters of the harvester are listed in Piezoelectric energy harvesters can be regarded as a current source in parallel with the electrode capacitance Cp . The intThe tip displacement, however, stays unchanged for different coverage ratios, which indicates that the electrode coverage has a limited influence on the mechanical behaviour of the harvester. Furthermore, it also indicates that the electrical energy collected from the vibrating piezoelectric beam is marginal compared with the mechanical energy in the beam. Therefore, the improved electrical output power is not indicated on the tip displacement curves. In order to enable the piezoelectric energy harvester to work more effectively, other methods should be adopted to enhance the electrical damping of the system, such as the pre-biasing method , the fliIn order to verify the theoretical analysis, an experimental validation was conducted for piezoelectric energy harvesters with different electrode coverage ratios. The piezoelectric beam is a commercial product from Johnson Matthey. The varying electrode coverage was achieved by dividing the electrodes using laser cutting. The segmented beam is shown in The experimental set-up is demonstrated in In order to get the optimal electrode coverage ratio for the maximum output power, piezoelectric beams with different electrode coverage ratios were tested for different load resistance. The theoretical and experimental results are compared in In this paper, the electrode coverage ratio is investigated in order to improve the output power of piezoelectric energy harvesters under tip excitation. A distributed-parameter model was built for a bimorph piezoelectric cantilever beam with consideration of the electrode coverage. The influence of the electrode coverage on beam vibration, internal capacitance, optimal load resistance and output power is analysed theoretically and then verified experimentally.The optimal coverage was found to be 66.1% with a 12.8% improvement of the output power in theoretical analysis. The optimal load resistance increases with the decrease of the electrode coverage ratio, as the internal capacitance decreases. The output voltage, however, increases with decrease of the electrode coverage ratio, which means that the performance of the harvester can be improved with the optimized electrode design. The tip displacement remains the same for the harvester with different coverage ratios working at the optimal load condition. It indicates that, compared with the mechanical energy in the vibrating beam, the extracted electrical energy is marginal. Other mechanisms to improve the electrical damping are needed to further improve the performance of piezoelectric harvesters.In experiments, a piezoelectric beam was cut into seven segments using laser machining. The beam tip displacement and output voltage were measured for the harvester with different coverage ratios. The experimental results verify the theoretical analysis from both the mechanical and the electrical perspective, showing that partial electrode coverage is beneficial to enhancing the performance of energy harvesting using piezoelectric cantilever beams. This study provides a simple and effective way to improve the power generating capability of piezoelectric energy harvesters under tip excitation.


Early hospital readmission of patients after discharge is a public health problem. One major cause of hospital readmission is dysfunctions in integrated pathways between community and hospital care that can cause adverse drug events. Furthermore, the French ENEIS 2 study showed that 1.3% of hospital stays originated from serious adverse drug events in 2009. Pharmacy-led medication reviews at hospital transitions are an effective means of decreasing medication discrepancies when conducted at admission or discharge. However, it is difficult to assess the true impact of pharmacist-led medication reviews in specific high-risk populations, such as pediatric and geriatric populations.In such a context, it is important to demonstrate the effectiveness of medication reconciliation as part of a standardized medication review process—in pediatric and elderly populations—on all-cause readmissions in a large randomized controlled clinical trial.The aim of this study is to assess the impact of the pharmacist-led medication review on the rate of readmissions and/or death after hospital discharge and patient treatment satisfaction.The study is a randomized controlled clinical trial. A total of 1400 hospitalized patients will be randomized in two groups: (1) the experimental group (group receiving a pharmacist-led medication review) and (2) the control group . The pharmacist-led medication review process includes medication reconciliation, treatment review and medication liaison service. The primary endpoint will be the rate of readmissions and/or death at 30 days following initial hospitalization discharge. The secondary endpoints will be the rate of hospital readmission, the rate of emergency department visits, the rate of mortality, the number of consultations and patient treatment satisfaction at 30 days following initial hospitalization discharge.A randomized controlled trial provides the most extensive evidence on the impact of pharmacist-led medication reviews on early hospital readmission for extreme age populations.NCT02734017. Registered on 4 May 2016.Current Controlled Trials, The online version of this article (doi:10.1186/s13063-017-1798-6) contains supplementary material, which is available to authorized users. Early hospital readmission of patients after discharge is a public health problem. One major cause of hospital readmission is dysfunctions in integrated pathways between community and hospital care that can cause adverse drug events (ADE). An ADE is generally defined as a side effect (anticipated or unanticipated) of an administered medication; it may be due to an adverse drug reaction or a medication error . FurtherIn accordance with the World Health Organization (WHO) ("Assuring medication accuracy at transitions in care”) and French health authorities , developIn this context, the pharmacist-led medication review may appear to be a way to improve patient safety. The medication review is a structured, critical examination of a patient’s medicines; the objective is to reach agreement with the patient regarding treatment to optimize the impact of medicines, minimize the number of medication-related problems and reduce waste . When peThe pharmacist-led medication review has been demonstrated to be an effective strategy to reduce medication discrepancies at admission and discharge , 10. HowMeta-analysis shows that pharmacist-led medication reviews have brought substantial reductions in the rate of readmission . This enIn such a context, it is important to demonstrate the effectiveness of a pharmacist-led medication review in high-risk populations (geriatrics and pediatrics) using a high level of evidence based on a large randomized controlled clinical trial. In our study, we hypothesized that this pharmacist-led medication review—which consists of (1) preventing medication errors at transitions (admission or discharge) through medication reconciliation, (2) analyzing and revising treatment, (3) informing and educating patients and (4) coordinating health professionals—may decrease hospital readmissions.The primary objective of this study is to assess the impact of the pharmacist-led medication review on the rate of all-cause hospital readmissions and/or all-cause death at 30 days following initial hospitalization discharge. The secondary objectives are to assess the impact of the pharmacists-led medication review on the rate of all-cause readmission in care units, the rate of emergency department visits, the rate of mortality, the number of consultations post-discharge and patient treatment satisfaction.This is a prospective, randomized, controlled and open-label study comparing two patient care strategies: 1) the experimental group, receiving a pharmacist-led medication review; (2) the control group, receiving typical care. The open procedure is the only possible option because of the nature of the intervention, which requires that healthcare workers and participants not be blinded. The study protocol was designed using the recommendations of the Consolidated Standard of Reporting Trials (CONSORT) statement. The Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) checklist . This work is supported by institutional grants from the French 2014 National Program of Clinical Research (Programme de Recherche sur la Performance du Système de Soins). All details are provided in Table The recruitment will be performed in a pediatric department and a geriatric and internal medicine department. The methodological support will be provided by the Clinical Research Unit . The central pharmacy of AP-HM is in charge of overall coordination of the study and implementation of interventions.The details of the inclusion and exclusion criteria are provided in Table To the adult patient or caregiver in the case of demented patients ;To the parents in the case of minor patients.Participants will be recruited within 24 h after admission in the care service. When a new patient is eligible according to the selection criteria, a participant information sheet presenting the objectives of the study as well as procedures is provided and explained:To reach the target sample, when a patient is admitted into the service, the physician performing the clinical examination of entry reviews the patient's inclusion criteria and considers whether the patient is eligible for study. He or she then informs the pharmacist of the study.Computer-generated randomized lists will be drawn up before the beginning of the study using a permuted block design under the responsibility of the clinical research unit (AP-HM). The randomization will be stratified by center. The patients will be randomized to the control group or the experimental group using a computer-generated randomization schedule with a 1:1 allocation ratio. The open-label study is the only option because of the involvement of the patient in the medication reconciliation procedure.Each patient included in the study will be randomized in one of the following two groups see Fig. :Fig. 2CoIn the control group, the pharmaceutical team is only involved in dispensing drugs, including standard pharmaceutical analysis prescription, during the hospital stay. At admission, the medical staff collects the list of current medications. At discharge, the medical team provides a prescription without intervention by the hospital pharmacy team. A report is sent to the community physician at the end of hospitalization.Participants in the experimental group receive a pharmacist-led medication review including the following: (1) a medical and pharmaceutical admission medication reconciliation and treatment review, (2) a medical and pharmaceutical medication reconciliation at discharge and treatment review and (3) medication liaison service.Medication reconciliation (MedRec) at admission will be performed by a pharmacist or a pharmacy resident within 24 h after patient admission. On Saturdays and Sundays, admission MedRec will take place the following Monday morning, and for patients admitted on holidays, the MedRec will be performed the day after.The admission MedRec first involves completion of the medication history, with research into information about patient treatment. Data from several sources should be gathered; previous medical and pharmaceutical records before admission or information from the patient him- or herself and/or the family or caregivers, the community pharmacist and physician should be gathered by phone. First, the pharmacist or a pharmacy resident interviews the patient, and then the interview is conducted with the community pharmacist. If there are insufficient data, the pharmacist should call the general practitioner or the specialist. Based on these data, it is possible to formalize the complete list of medications taken by the patient before hospitalization. Then, the list is compared to the admission prescription. Differences from the admission prescription are discussed between the hospital pharmacist and hospital physician. If these are intentional, the hospital physician is asked to note the reason in the medical record. In the case of medication errors, the hospital physician issues a revised prescription.A pharmacist-led treatment review is systematically associated with MedRec. It consists of pharmaceutical analysis of the prescription.The medical and pharmaceutical MedRec at discharge consists of comparing the medication history to the hospital discharge prescription to identify possible discrepancies. Differences between medication history and the hospital discharge prescription are discussed between the hospital pharmacist and hospital physician. The differences may be intentional, and if this is the case, the hospital physician notes the changes in the patient record. In the case of unintentional discrepancies (medication errors), the hospital physician issues a new prescription.A pharmacist-led treatment review is systematically associated with MedRec. It consists of pharmaceutical analysis of the prescription.A comprehensive medication history contains the list of medications that the patient was taking prior to hospitalization and the list of new medications with comments, making it possible to understand the evolution of the treatment.Counseling: A session with the patient explaining the comprehensive medication history, the main adverse drug reactions, warning signs, biological monitoring, indications and an indication of the importance of drug adherence.A discharge letter faxed to the community pharmacist and general practitioner (community physician). This discharge letter will also present medications prescribed before and after hospitalization. Additional comments allow the community pharmacy and physician to understand the patient's revised treatment.At discharge, the medication liaison service includes the following:The primary endpoint is the rate of all-cause hospital readmission and/or all-cause death and/or emergency department visits occurring within 30 days after the patient discharge from initial hospitalization.All-cause hospital readmission is defined as an unscheduled hospital stay in a medical or surgery department or intensive care unit, regardless of the reason for admission or duration of stay.Death is defined as an occurrence of death between discharge and day 30.Not considered are inpatient services, post-acute care and rehabilitation (PACR) or nursing homes.The rate of all-cause hospital readmission, as defined in the primary endpoint, within 30 days after the patient discharge from the initial hospitalization.The rate of all-cause emergency department visits occurring within 30 days after the patient discharge from the initial hospitalization. This is the proportion of emergency department visits.The rate of all-cause mortality occurring within 30 days after the patient discharge from the initial hospitalization. This is the proportion of deaths.The number of consultations scheduled or not within 30 days post-hospitalization will be studied. Consultations are defined as interviews with the attending physician, a specialist physician or a nurse.Patient satisfaction with regards to its drug treatment will be measured using the standardized questionnaire “Satisfaction with Medicines Questionnaire (SatMed-Q®)”  validateThe evaluation will be performed at three different time points: baseline (T1), discharge at the hospital (T2) and 30 days after discharge from the hospital (T3). The study procedure and date collection are detailed in Table As regards the computerized processing of data relating to this project, which is intended for health research, it falls within the scope of legislative requirements, in particular the law of 9 August 2004, and will directly or indirectly identify the persons concerned.The calculation of the required number of subjects was made from the primary endpoint, i.e., the rate of re-hospitalization and/or death.Based on the literature, mainly a recent meta-analysis including the RCTs working on a pharmacist-led medication review , and datp < 0.05. The methodology is based on the Consolidated Standards of Reporting Trials Statement  [The major principles of the analysis are reported below. However, a specific protocol of the analysis will be provided a second time before the initialization of the study . The data will be analyzed using SPSS version 17.0 software. Statistical significance is defined as tement/) .The full analysis population  will be used in the primary analysis, and the per protocol population  will be used in the secondary analysis to assess the robustness of the results. No interim analysis is planned. Demographic and baseline characteristics will be summarized for the two groups . Missing data will not be replaced.2 test or Fisher’s exact test). Proportions will be presented with 95% confidence intervals. Logistic regression will be performed to adjust potential confounding factors; variables relevant to the models will be selected based on their clinical interest and/or a threshold p-value ≤ 0.1 during univariate analysis. The center will be automatically entered into the model. The final models expressed the odd ratios and their 95% confidence intervals. The unadjusted analysis will be the primary analysis, and the adjusted analysis will be the complementary analysis.Primary endpoint. The proportions of readmission and/or death at day 30 will be compared between the two groups (chit test or Mann-Whitney test. Multivariate approaches (logistic or linear regressions) will be performed using the same procedure.Secondary endpoints. Qualitative variables will be compared between the two groups using the same procedure. The number of consultations and satisfaction scores will be compared between the two groups using Student’s Quality assurance and control, under the responsibility of the promoter, will be conducted in accordance with Good Clinical Practice (decisions of 24 November 2006) to guarantee the integrity of the data collected and the protection of patients as well as to respect the protocol and legislation throughout the entire period of patient inclusion and follow-up by a clinical researcher mandated by the sponsor.The nature and frequency of monitoring are established according to the definition of the level of monitoring according to the patient's risk and will depend on the number of patients included, the rhythm of the inclusions and the difficulties observed during the study  .In this test, the level of monitoring is classified as "minimal" with a patient risk of type A. This will be to verify the consents. If one or more consents are not compliant, files will be monitored randomly.This study is sponsored by the French Ministry of Health (PREPS 2014 no. 14–0330). The Assistance Publique-Hôpitaux de Marseille is the promoter and is in charge of all the administrative measures. As required by French law, all patients or their relatives will provide written informed consent to participate . The FreTo our knowledge, this is the first study to assess the effectiveness of pharmacist-led medication reviews in two extreme populations at high risk of medication errors, i.e., pediatric and geriatric populations. Moreover, the impact of pharmacist-led medication reviews on all-cause readmissions is not clear, and to our knowledge, there are no randomized controlled trials involving a large number of subjects .In our study, we will evaluate patient satisfaction with their drug treatments. We hypothesize that a patient with a more precise explanation of his or her treatment will be more satisfied. Satisfaction being correlated with adherence, we believe this may decrease ADE .We will use a randomized, open-label, controlled design, which is the most appropriate design to demonstrate the efficacy of pharmacist-led medication reviews in accordance with an Evidence-Based Medicine Working Group.However, some issues related to the content of the protocol study should be discussed.The open procedure is justified because the nature of intervention meant that personnel and participants could not be blinded. Indeed, the patients and the pharmacist are players in the intervention effect.A cluster design should be proposed. Indeed, the experimental program is applied to the whole center and may affect all the individuals within it. To conform to the intervention application and to avoid contamination within the unit, cluster randomization may be advocated. However, this design requires the inclusion of several centers, and we have chosen to restrict the number of centers; we consider it easier to implement the experimentation in adherent centers, where the pharmacist teams and medical teams are working together, the best guarantee of the feasibility of the study. This risks minimizing the experimentation effect. Moreover, it is possible that our trial has less power because the pharmacist intervenes in both groups. However, it is not possible that the pharmacist does not intervene in the controlled group as required by law. Our tests therefore evaluate additional activities that have not yet shown their superiority.The outcomes will be collected during a telephone follow-up 30 days after hospital discharge. We will call patients in the case of a patient who is older than 65 years, parents in the case of a minor patient or caregivers in the case of an elderly patient who is not able to consent. Moreover, if the patient reports a hospitalization or a visit to the emergency department during the 30 days post-discharge, a verification will be made by telephone call in the care unit.At the time of manuscript submission (April 2016), the status of the trial is “open for participant recruitment.”


Recently, progress has been made in the development of mechanical joints with variable intrinsic stiffness, opening up the search for application areas of such variable-stiffness joints. By varying the stiffness of its joints, the resonant frequency of a system can be tuned to perform cyclical tasks most energy-efficiently, making the variable-stiffness joint a candidate element for an advanced prosthetic device specifically designed for the cyclical task of drumming. A prerequisite for a successful variable-stiffness drumming prosthesis is the ability of human drummers to profitably employ different stiffness levels for playing different beats. In this pilot study, 29 able-bodied subjects (20 drumming novices and 9 experts) wear a cuff on the forearm, to which a drumstick is connected using changeable adapters, consisting of several leaf springs with different stiffness and one maximally stiff connection element. The subjects are asked to play simple regular drum beats at different frequencies, one of which is the resonant frequency of the adapter-drumstick system. The subject's performance of each drumming task is rated in terms of accuracy and precision, and the effort is measured using questionnaires for the perceived stress as well as electromyography (EMG) for the muscular activity. The experiments show that using springs instead of the stiff connection leads to lower muscular activity, indicating that humans are able to use the energy-storing capabilities of the springs, or that muscular activity is reduced due to the lower mass of the springs. However, the perceived stress is increased and the novices' performance lowered, possibly due to a higher cerebral load for controlling the elastic system. The hypothesis that “matching the resonant frequency of the spring-drumstick system to the desired frequency leads to better performance and lower effort” is not confirmed. Possible explanations are discussed. In conclusion, a series-elastic element appears to lower the muscular effort of drumming, while a stiff connection appears to minimize the mental load and has a positive effect on the performance of drumming novices. Series-elastic actuators (SEAs) as well as variable-stiffness actuators (VSAs) have been recently introduced into robotics  reduce impacts of collisions for motors and gears . A prosthetic drumstick holder is commercially available, including an elastic element, but without variable stiffness  that subjects play best with diagonal-type variable stiffness, and, (b) that experts are better in taking benefit of the variable stiffness, since they are familiar with the general task of drumming, which probably frees their mental capacities for adapting to the new device.This study involved 20 unimpaired drumming novices and 9 unimpaired drumming experts who wore a cuff on the forearm, to which a drumstick was attached using stiff and elastic adapters. Hence, the subjects' intact wrists were not used but replaced with an experimental prosthetic attachment, simulating the situation of a missing hand. The subjects were asked to play all combinations of adapter types and desired frequencies shown in the combination matrix in Figure The experiment setup is shown in Figure The subject wore a cuff constraining movements of the wrist . The cuff was coupled to the drumstick via a changeable adapter. The set of changeable adapters consisted of four leaf springs with different stiffness values . This sensor was used for determining the design frequency of each adapter element, which corresponds to the resonant frequency of the whole cuff including force-torque sensor, spring and drumstick. For this, the cuff was fixed in a bench vise, and the drumstick was jolted into free oscillation. From the force-torque sensor data, the frequencies of the oscillation were found to be at 3.7, 4.4, 5, and 6.3 Hz for the springs and at 27 Hz for the stiff connection. The force sensor remained between spring and cuff during the experiments to avoid changing the design frequencies. The springs were approximately 70–90 g lighter than the stiff connection, leading to a reduction of the moment of inertia around the elbow flexion axis of about 5–6%.Between spring and cuff a force-torque sensor ATI Mini45 SI-290-10 was placed . The sensor was covered with rubber mats for damping the noise and making the drumming more comfortable , pectoralis major (humerus adduction), deltoideus posterior (shoulder extension), deltoideus medius (shoulder abduction), deltoideus anterior (shoulder flexion), anconeus (elbow extension), triceps brachii long head (elbow and shoulder extension), and triceps brachii lateral head (elbow extension). The mean of the EMG values over all trials of each electrode was subtracted subject-wise to remove any constant DC offset. Furthermore, after subtracting the DC offset, the EMG values of each electrode were normalized subject-wise by dividing by the RMS value over all trials. This eliminates differences in electrodes due to location-specific tissue resistance and gives the variations between trials of the signal of each electrode the same weights.aRDnet  to read out the force-torque and EMG sensors at 1 kHz. The marker positions were recorded by the Windows computer and transferred to the Linux host using the DLR communication protocol A total of 29 healthy subjects, 25 male and 4 female, all right-handed and initially fully naive to the experiment, performed the experimental protocol as described below. 9 out of the 29 subjects had at least 1 year of drumming experience and were therefore considered as experts, and the other 20 were counted as novices. All subjects participated voluntarily and gave written informed consent to the procedures, which were conducted in partial accordance with the principles of the Helsinki agreement . Approval was received from the works council of the German Aerospace Center, as well as its institutional board for data privacy ASDA; the collection and processing of experimental data were approved by both committees. For all subjects and experiments the right hand was used, which was restricted by the design of the cuff. Subjects stood upright in all experimental conditions.The experiment session lasted between 20 and 25 min per subject. At the beginning of each experiment session, the participant was instructed about the experiment using a standardized presentation.The subjects were asked to play all 20 trials consisting of the combinations of adapter types and desired frequencies shown in the combination matrix in Figure Before each trial, subjects had the possibility to get used to the current combination of desired frequency and adapter type within a time of 10 s, followed by a phase of 15 s of collecting drumming data. The 10 s of training data were not recorded. After each trial, subjects were asked to fill in a questionnaire about the combined physical and mental stress level that they felt during playing at the respective combination of desired frequency and adapter type. The question was “How high was the perceived stress while playing of each frequency, with respect to physical and mental effort” 1: very low, 8: very highBefore and after the trials, base noise EMG during rest of the arm was measured, as well as EMG and maximum force during maximum voluntary contraction in a lifting-up and a pushing-down task. This was used for checking whether the signals look plausible. Unfortunately, for unknown reasons, the electrodes of pectoralis major and anconeus showed very noisy signals for many subjects. We therefore discarded the results of these two electrodes.The inaccuracy, i.e., the difference between the desired time interval and the mean played time interval between two drum strokes, which tells how well the desired frequency could be met; a lower inaccuracy means a better performance:the imprecision, i.e., the standard deviation of the time between two strokes, which tells how evenly the frequency was played; a lower imprecision means a better performance:the perceived stress consisting of physical and mental effort, i.e., the result of the questionnaire; lower stress means higher comfort:the measured muscular activity, i.e., the mean normalized root-mean-square (RMS) EMG signals, where normalizing means subtracting the per-electrode DC offset and dividing by the per-electrode RMS of the signals of all trials; again, a lower muscular activity means a higher comfort:To answer our research questions and evaluate our hypotheses, we predefined four outcome measures, which are gathered for each subject and trial:elt is the measured EMG signal of electrode e at time sample t in trial l, with nelectrodes = 6, ntrials = 20 and nsamples = 3,000.where EMGTo statistically analyze the results we built and applied a mixed-effects regression model with fixed and random effects. It allowed to directly include the two hypotheses as fixed effects into our model. The formula of the mixed-effects model is:yijklmn is the response variable, i.e., any of the four above-mentioned outcome measures, i is the adapter type, j is the desired frequency, k is the expert status, l is the diagonal status, which is 1 if the combination of adapter type and desired frequency is on the diagonal and 0 otherwise, m is the within-subject trial number, n is the subject number, β0 is the intercept, which is a constant term, βiadapter_type, is the fixed effect of the adapter type, βjdesired_frequency, is the fixed effect of the desired frequency, βkexpert_status, is the fixed effect of the expert status, βldiagonal, is the fixed effect of playing on the diagonal, βkldiagonal×expert_status, is the fixed effect of the interaction between the expert status and playing on the diagonal, βikadapter_type×expert_status, is the fixed effect of the interaction between expert status and adapter type, mβtrial_number is the trial-number-dependent fixed effect of learning or fatigue, ϵnsubject, is the subject-specific random effect and ϵmn is the residual random error. The random effects are assumed to follow normal distributions as follows:where The factors adapter type, desired frequency, expert status and diagonal status can assume the levels shown in Table lmer function of the lme4 library  and their interactions with the expert status, are shown in Figure The first hypothesis, that variable stiffness provides the best performance and comfort, and the second hypothesis, that experts are better able to make use of the variable stiffness, can be tested by regarding the differences between playing on or off the diagonal shown in Figure Figure Since the use of diagonal-type variable stiffness shows a beneficial effect on the accuracy of experts but the use of some of the springs shows a detrimental effect with a similar magnitude, it is interesting to see the differences in inaccuracy of experts between using the springs in diagonal-type variable stiffness mode and using the stiff connection. These effects of the springs on the diagonal are the sum of the effect of the diagonal Figure  and the In this study, we investigated whether drummers can take advantage of a variable-stiffness joint in a prosthetic wrist. We asked 20 novices and 9 experts to play different frequencies using different elastic elements and one stiff element in a connection between a cuff on the forearm and a drumstick. We hypothesized that subjects will perform best and require the least effort when playing the elastic elements at their resonant frequencies, which is one main argument for variable-stiffness actuation. Moreover, we hypothesized that such an effect will be more obvious for an expert drummer.Can drummers take advantage of a variable-stiffness joint in a prosthetic wrist? Our experimental design was unable to verify that variable stiffness is useful for a prosthetic wrist. Even if experts showed a trend for a reduced inaccuracy when playing the diagonal, they showed the opposite trend for imprecision, and it is difficult to judge which of the two is more relevant. For novices, both inaccuracy and imprecision increased when using the diagonal-type variable stiffness.The results showed the expected influence of elasticity on the EMG-measured effort, namely that elasticity reduces the effort, and that experts are better than novices in doing so. Despite that, there was a clear discrepancy between measured and perceived effort for both groups. While the muscular activity decreased with decreasing stiffness of the adapter, the perceived stress increased. We find this effect surprising.A possible interpretation is that subjects are indeed able to save muscular effort by making use of the energy-storing capabilities of the spring. However, the effort by the brain for controlling the more complex dynamics of the system involving the springs is likely higher than for controlling the system involving the stiff connection. In the answers to the questionnaire, the increased cerebral effort might therefore outweigh the reduced muscular effort.A further explanation for the lower EMG-measured effort when using the springs lies in the fact that the they are more lightweight than the stiff connection and that less muscular effort might have been necessary to accelerate and decelerate it. However, the reduction of inertia (5–6%) is considerably lower than the reduction of EMG-measured effort (16–25%). Assuming that muscular activity is roughly proportional to accelerated inertia, we therefore estimate that the influence of the different weights on the EMG-measured effort is small and that the effect of the adapter types on muscular activity is dominated by their elasticity.These findings somewhat confirm the study of Fujisawa and Miura , who fouIn interpreting the results with respect to variable stiffness, three main limitations of our experimental design have to also be considered. (a) We measured the resonant frequency of the cuff including the elastic element and the drumstick. The influence of the rebound of the drum skin as well as the elasticity of the soft tissue and the (variable) stiffness of the joints due to muscle contraction and cocontraction were not gathered when measuring the resonant frequency of the cuff-spring-drumstick combination. This possibly leads to lower resonant frequencies of the whole system including the human arm, which could explain the better performance of the stiffer springs. (b) There might be variable-stiffness strategies other than matching the resonant frequency of the system to the desired frequency. In order to potentially discover those other variable-stiffness strategies, in future experiments, one could ask subjects to play a more fine grained set of frequencies and try to discover patterns in the outcome measures. (c) Even the expert drummers were naive to the experiment and the time to become acquainted with the system for any combination of adapter type and desired frequency was limited to 10 s. While this was helpful for achieving a reasonable experiment duration, allowing a subject to practice using a variable-stiffness drumming system for weeks or months might show long-term learning effects.Future experiments into variable-stiffness drumming prostheses might use the following improvements to possibly find a beneficial effect of variable stiffness. A new device with continuously variable stiffness instead of separate adapters with different stiffness levels could be built so that subjects can better match the resonant frequency of the whole system including the rebound of the drum to the desired frequency or employ a different variable-stiffness strategy. This would also remove the problem of different masses of the stiff connection adapter and the springs. Furthermore, subjects could be given more time  to become more acquainted with the system in order to learn the more complex dynamics.Conclusively, our experimental results argue that series-elastic elements can be used to reduce the muscular activity of drumming, but that their stiffness does not need to be variable. However, the elastic elements appear to initially put an increased control burden on the user. While expert drummers seem to be able to deal with their more complex dynamics, novice drummers seem to reach a better performance with a stiff connection. Prosthesis users may benefit from this study if its results or the results of a future, improved study are incorporated into the design of an actual prosthetic device.GS, HH, and JV were involved in planning and design of the experiments. HH and GS were involved in the statistical analysis. JS was involved in setting up and conducting the experiments. HN, HH, and GS were involved in the statistical design. HH and GS wrote the manuscript. JV provided corrections to the manuscript. All authors contributed to manuscript revision, read and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer NC and handling Editor declared their shared affiliation.