Cystic ganglionosis is an unusual benign condition, which presents as multiple ganglion cysts involving multiple joints. The case we report here is probably the first case of an adult reported in the literature. The only other case of multiple ganglion cysts reported in the literature is that of an 11-year-old child with ganglion cysts in multiple joints. A 57-year-old female presented with an approximately 4-year history of pain and swelling below the left knee and in the right hand. An MRI of the left knee showed multiloculated cystic-intensity lesions around the knee joint with intra-/extra-articular and intraosseous components. Similar lesions were noted around the right knee joint, right wrist and ring finger. With all the above findings and in view of multiple joint involvement, the possibility of cystic ganglionosis or multiple giant ganglion cysts was considered and confirmed by biopsy of one of the knee lesions. It is because of this rarity and the unusual presentation involving multiple joints that we have reported this case. The importance of the diagnosis is that unnecessary surgical intervention and hospitalization can be avoided, provided the patient’s symptoms are not severe. To our knowledge, no case of multiple ganglion cysts in adults has been reported in the medical literature. Only one case of multiple ganglion cysts has been reported in an 11-year-old child.2 We have reported this case because of this rare multiplicity, the unusual presentation involving the bilateral knees and Hoffa’s fat pad, together with multiple intraosseous lesions in a single patient. This is probably the first case of an adult reported in the literature.Ganglion cysts are common lesions presented by the patients. Ganglia are not true tumours. Ganglia arise from the joint capsules, bursae, ligaments, tendons and subchondral bone. Hands, wrists and feet are the sites where they are commonly seen. They are usually asymptomatic; however, the mass effect on the adjacent tissue can sometimes be the clinical presentation.T1 weighted and hyperintense on T2 weighted sequences around the knee joint with intra- and extra-articular components  with limitation of motion and paraesthesia.2About 50–70% of soft-tissue masses in the wrist region are ganglions.9 Before surgery, it is important to confirm the cystic nature of these lesions to determine their relationship to the joint and evaluate the joint for the presence of associated intra-articular disease. A demonstration of the relationship of the cyst to the capsule may be important in differentiating the ganglia from the other lesions, as failure to remove the capsular components of the cyst may lead to recurrence.10 A high rate of spontaneous resolution and recurrence after surgery argue against surgical intervention to treat them.Watchful waiting, non-operative aspiration and surgical removal are the main treatment options. High recurrence rates are noted with cyst aspiration. Surgery is better in terms of lower rates of recurrence, but has a higher incidence of complications.To our knowledge, no case of multiple ganglion cysts in adults has been reported in the medical literature. Only one case of multiple ganglion cysts has been reported in an 11-year-old child. The multifocal distribution of the ganglion cysts in our patient is unique, also bilateral involvement of the knees has never been reported previously. These may imply some inherent susceptibility of the patient to develop these lesions. The need to screen other joints and look for multifocality is highlighted by this case. We have reported this case because of this rare multiplicity, the unusual presentation involving the bilateral knees and Hoffa’s fat pad, together with multiple intraosseous lesions in a single patient. The importance of the diagnosis is that unnecessary surgical intervention and hospitalization can be avoided, provided the patient’s symptoms are not severe.Ganglion cysts are commonly seen around the joints and tendons, appearing as cystic lesions on imaging, and should be included in the differential diagnosis of any cystic lesion around the joints and tendons.Cystic ganglionosis (multiple ganglion cysts) is a very rare condition, where ganglion cysts involve multiple joints and tendons, as described in our patient. This has been hardly reported in the literature, hence its prevalence and associations are not known and further studies are needed in this regard.Awareness and recognition of this condition by the radiologist is important, as they can guide the clinician on management, which is mainly conservative.


In wireless sensor networks (WSNs), the problem of measurement origin uncertainty for observed data has a significant impact on the precision of multi-target tracking. In this paper, a novel algorithm based on least squares support vector machine (LS-SVM) is proposed to classify measurement points for adjacent targets. Extended Kalman filter (EKF) algorithm is firstly adopted to compute the predicted classification line for each sampling period, which will be used to classify sampling points and calculate observed centers of closely moving targets. Then LS-SVM algorithm is utilized to train the classified points and get the best classification line, which will then be the reference classification line for the next sampling period. Finally, the locations of the targets will be precisely estimated by using observed centers based on EKF. A series of simulations validate the feasibility and accuracy of the new algorithm, while the experimental results verify the efficiency and effectiveness of the proposal. Nowadays, with the development of precision sensors to monitor physical or environmental conditions, the applications of WSNs have been motivated by various industrial and consumer systems, as well as military usages ,2,3. AmoBroadly speaking, the traditional methods of localization and tracking contain Kalman filter (KF), extended-KF (EKF), Unscented-KF and so on ,8,9. TheIn general, there are two kinds of state-of-the-art methods dealing with sampling points for respective targets: with or without the probability model ,13,14,15The remainder of this paper is organized as follows. Recently, with the improvement of sensor resolution, the problem of extended target recognition and positioning has attracted a lot of research attention. One of the key issues is how to identify two adjacent extended targets and locate them separately.Maximum Likelihood Probabilistic Multi-Hypothesis Tracker (ML-PMHT) can reliably discriminate between the target and clutter, based on the calculation of peak point’s PDF in ML-PMHT log-likelihood ratio (LLR) due to clutter and also the peak point’s Probability Density Function (PDF) in LLR due to the target. In order to track the original target from measurement points generated by both the original target and interfering target, Steven Schoenecker replaced the clutter with a second, independently parameterizable target, on the basis of ML-PMHT . HoweverAs the applications of extended targets quickly increase, the research on target location is gradually developed for the method based on clustering. The probability-based method is used to classify each measurement point, and the great number of equivalent measurement points will lead to very large computational complexity. For this issue, adaptive weight Fuzzy C-Means clustering (AWFCM) algorithm was used to track multi-targets under the cross tracks situation , where aRelatively speaking, the clustering algorithm could quickly and effectively classify the measurement points and track the measurement points belonging to each extended target, so as to solve the problem of measurement origin uncertainty. The accuracy of the clustering algorithm to classification of measurement points will directly affect the accuracy of the target location. However, when two objects are close to each other, the overlapping phenomenon of measurement points will result in a classification error of the clustering algorithm and affect the positioning accuracy. In order to solve this problem, we use the classification method based on LSSVM to classify the measurement points for adjacent targets, which will further improve the accuracy of the target location.In this section, we will describe the proposed algorithm in detail.As shown in Here, to facilitate the description of the algorithm, we make a few points in advance. Firstly, the classification line is used hereinafter to replace the classification surface, as it is a straight line in a 2-D area. Secondly, because the sampling points always contain valid measurement points of targets and also invalid noise points, we will filter out the noise points far from targets based on the density of the sampling points. Thus, the sampling points can be considered as valid measurement points after filtering. Finally, since it is the most common case that two targets move closely compared with more targets, we will take two targets as the example to show the principle of the proposed algorithm.In order to guarantee the algorithm works well under nonlinear systems, EKF algorithm is utilized to track targets. Firstly, we build a state model for each target:The prediction equation is:The predicted positions of targets will be adopted to predict the classification line, and the observed centers In this subsection, we use the predicted positions of targets from Step 1: Input the initial parameters. The initial parameters mainly refer to the best classification line and observed centers at the very beginning of the algorithm. For the following sampling periods, the best classification line at time Step 2: Calculate the intersection point The intersection point Step 3: Compute the predicted intersection point Assume that the relative position of predicted classification line Step 4: Calculate the normal vector of The predicted classification line Step 5: Obtain the predicted classification line.lk+1|k can be described as below:The predicted classification line Step 6: Calculate the observed centers of targets.After obtaining the predicted classification line, each sampling point is put into the following formula for classification.The sampling points will be classified into two groups, the geometric center of each group is supposed to be the observed center for each target, which could be adopted to estimate the positions of targets based on EKF see .The method for predicting the classification line is presented in Algorithm 1 below.Algorithm 1 Predicting the classification lineOutput: predicted classification line and observed centers of targets at moment  1: Input the best classification line and observed centers of targets at time  parameters, get the reference classification line and predicted targets positions  and  2: Calculate the intersection point  equations; 3: Compute the predicted intersection point  predicted positions of targets  4: Calculate the normal vector of  5: Obtain the predicted classification line at moment  normal vector of  6: Calculate the observed centers of targets at time  with the predicted classification line, which will be utilized to track targets based on EKF.Input: best classification line and observed centers of targets at time By using the predicted classification line to classify the sampling points, we could effectively find the observed centers of targets at each time. However, the predicted classification line obtained at time quations . AccordiBy solving the linear Equations (23), we can get the best classification line. The method for training the best classificiation line is shown in Algorithm 2.Algorithm 2 Training the best classification lineOutput: best classification line at moment  1: Input the predicted classification line and observed measure point set   2: Classify the observed measure point set  classification line according to Equation (19), which will get the classified  sampling point set  3: Substituting  Input: predicted classification line and observed measure point set In this section, the classification and tracking performance of the presented method will be simulated for algorithm validation.The parameter γ, which is shown in (20), is needed to be determined before program running. Theoretically, a bigger γ will increase the difficulty of calculation, while a smaller one will reduce the balance effect. In order to determine a proper γ, we simulated a classification by using the measurement points of two targets in different overlapping ranges and optimized the value of γ/2 from 1 to 10000. The overlap range is set from 0% to 30% for simulation, with the simulation result listing in In order to verify the classification performance of the proposed algorithm, we firstly simulate the classification of the two targets within 11 groups of continuous sampling periods, which is shown in Moreover, a Monte Carlo simulation with In order to evaluate the performance of the proposed algorithm for tracking adjacent targets, several simulations have been done and compared with some existing algorithms, namely K-means , Fuzzy CThe RMSE and MMSE of position are respectively defined as follows:Besides algorithm simulation, a series of experiments are conducted to validate the efficiency and effectiveness of our proposal. In this section, we firstly introduce the implementation of experiments and then analyze and discuss experimental results.A WSN platform with 12 sensor nodes was set up  coveringThe sensor node consists of five parts: infrared ranging (IR) sensor, angle control module, wireless communication module, control module, and power supply module, which is shown in Besides, in order to compare the tracking efficiency of these algorithms, it is necessary to obtain true positions of each target. Therefore, a kind of device for recording time and imprinting on the ground is installed on the shoes of every person. When people walk, a mark will be printed on the ground for each footstep as well as the exact time will be recorded by the device. After the experiment is completed, all the marks will be detected and the center between the two adjacent marks is perceived as the true position of target. Then, the true positions will be coupled with the recorded time. Finally, the actual positions for each sampling time can be calculated by the interpolation method according to the detected positions and recorded time.Based on the above experimental setup, sequence data were collected from two closely moving persons and then used to estimate the target trajectory by the presented algorithm, K-means, and FCM methods separately, see We counted the positional errors (PE) between the locations from each algorithm and truth locations, as shown in This paper mainly focuses on the classification problem among the sampling points of two adjacent targets. The proposed algorithm combined EKF and LS-SVM methods to obtain the best classification line for each sampling period, which was then devoted to precisely classify sampling points and calculate the observed centers of targets, as well as estimate the positions for closely moving targets based on EKF. Several simulations were conducted to demonstrate the feasibility and accuracy of the presented algorithm for tracking two closely moving targets in WSNs. Moreover, in contrast with state-of-the-art K-means, FCM and EKFCM methods, experimental and quantitative results further validate the efficiency and effectiveness of our proposal. In the near future, algorithm optimization and its extension to track more than two targets will be fully investigated.


Endoscopic nasobiliary drainage (ENBD) is widely used for biliary decompression in patients with biliary disease. However, it is difficult to reposition a nasobiliary catheter from the mouth to nostril. We developed a new device, which has a curved flexible loop and bar-handle, for repositioning of ENBD catheter. The aim of this study was to evaluate the usefulness of the new loop-device for facilitating the repositioning of an ENBD catheter from the mouth to nostril.Between January 2015 and December 2017, a comparative observational study was performed to evaluate the time taken for repositioning a nasobiliary catheter during endoscopic retrograde cholangiopancreatography (ERCP) and compare the results of ENBD procedure between the new loop-device and conventional techniques. In the subgroup analysis, we evaluated the occurrence of oral cavity injury and the time taken to transfer ENBD catheter from the mouth to nostril.p < 0.001). The total success rate of new device technique was 97.3%. No complication, including oral cavity injury, was observed.In all, 145 ENBD procedures were performed using these two techniques. The procedure time was significantly shorter in the new technique group than in the conventional group. (44 s vs. 194 s, The technique using our new loop-device was useful for repositioning a nasobiliary catheter from the mouth to nostril in ERCP. The new device does not require the removal of the mouthpiece before ENBD positioning, which can help perform the ENBD procedure rapidly and avoid the finger injury of endoscopists. Endoscopic retrograde cholangiopancreatography (ERCP) is an important procedure for the treatment of biliary diseases. In patients with cholangitis or biliary obstruction, endoscopic nasobiliary drainage (ENBD) can be required for effective drainage of bile juice , 2. ENBDFor completing the ENBD after ERCP, a drainage catheter repositioning from the mouth to nostril has to be performed. The conventional technique involves inserting a nasal plastic tube, catching the tip of the tube in the mouth, pulling out the tip, connecting the ENBD catheter with the tube and completing the repositioning by extracting the catheter toward the nose. However, the conventional technique has several disadvantages. The mouthpiece had to be removed from the mouth in sedated patients before the ENBD repositioning. It may take a long time to wait for the patients to wake up. Moreover, the finger injury of the operator often occurs from biting by poorly cooperative patients. When using the forceps, there is a risk of oral cavity injury while grasping the tip of the plastic tube.Prior investigators have suggested modified techniques to facilitate the ENBD repositioning –7. In a We have developed a new device composed of a curved wire-loop and bar-handle. In this study, we compared the outcomes between the conventional technique and our new technique using the device we developed for the ENBD repositioning.This is a comparative observational study using endoscopic data in patients who underwent ERCP at a tertiary medical center in Seoul, Korea between January 2015 and December 2017. We selected patients who underwent the ENBD procedure with the conventional catheter repositioning technique or the new technique using our device. The inclusion criteria were as follows: (1) age above 18 years, (2) patients who underwent the ENBD procedure with medical records of the procedure time, (3) no medical history of nasopharyngeal deformity, and (4) written informed consent. The conventional catheter repositioning technique was used from January 2015 to August 2016, and the new technique was used since September 2016 in our center. The patients who underwent ERCP from January 2015 to August 2016 were allocated to the conventional technique group, and those who underwent ERCP from September 2016 to December 2017 were allocated to the J-Loop technique group. Total of 160 patients were enrolled, 80 patients for each group, and 9 patients from conventional technique group and 6 patients from J-loop technique group, who were without sufficient medical data such as procedure time record or Mallampati score, were excluded.This study was conducted in accordance with the Declaration of Helsinki and was approved by the institutional human research committee. The study was reviewed and approved by the Ethics Committee of Korea University Anam Hospital(2019AN0313). All patients signed a written informed consent before the procedure.The conventional technique for ENBD has the following steps: (1) the ENBD catheter located in the oral cavity with the scope is withdrawn from the mouth, (2) the mouth piece is removed and the mouth is opened using the operator’s fingers, (3) a plastic tube is inserted into the nasal cavity, (4) the tip of plastic tube is grasped using fingers or forceps in the oral cavity, (5) the plastic tube is pulled from the oval cavity and connected with the ENBD catheter, and (6) the plastic tube, connected with the ENBD catheter, is pulled toward the nose.The new technique was performed by using the new device. The device set composed of a loop-shaped holder and a plastic tube with markings .Normally distributed data were expressed as mean ± standard deviation (SD), and student t-test was used to compare the parameters. Not normally distributed data were expressed as median (range), and Mann-Whitney U test was used to compare the parameters. Chi-square test or Fisher’s exact test was used for compare the distribution of a categorical variable. P < 0.001). The technical success of the new technique was achieved in 97.3% (72/74) of cases. Two patients who underwent the new technique experienced difficulty due to deep insertion of the J-loop into the throat, and were barely successful with conventional method. A high Mallampati score was related to difficult ENBD repositioning using the conventional technique. However, there was no significant difference in the repositioning time using J-Loop (Table A total of 145 patients were included in this study. The baseline characteristics of the patients are shown in Table In this study, the new ENBD device, J-Loop, was easy, convenient, fast and safe for repositioning the ENBD catheter from the mouth to nostril. The outcomes showed that the new technique is more efficient than the conventional technique for the ENBD repositioning. The conventional technique took an average of 194 s for the ENBD repositioning, which was similar to the results from other studies . Using tIn the conventional technique, operators had to insert a plastic tube into the nose and pull out its tip through the pharynx and oral cavity using a finger or forcep. However, it is difficult to catch the tip of a plastic tube especially in patients with a short neck or a small oral cavity. Poor visualization of the oral cavity is an obstacle to a successful ENBD repositioning. When using the conventional technique, the ENBD repositioning time was significantly longer in the higher Mallampati score patients than that in the lower Mallampati score patients.However, the new technique does not require observing the oral cavity or catching the tip of a plastic tube. As the plastic tube can be dragged out while pulling out the J-loop, operators just have to push the J-loop into the mouth and plastic tube into the nostril up to a marking, and pull the J-loop out. Appropriate depths were marked on plastic tube. There was no significant difference related to the Mallampati scores of the group while using the new technique.Another advantage of the new repositioning technique is that the ENBD repositioning with J-loop can be performed to the sedated patient immediately after removing the endoscope. As the operator does not need to touch the patient’s oral cavity, there is no risk of causing injury to the patient, such as a mucosal scratch or broken tooth. Moreover, as the entire procedure is completed in the sedated state, the patient does not feel any discomfort during the ENBD repositioning. Above all, the operator is able to avoid an unexpected injury or trauma to the finger and can be free from the fear of ENBD, either fear of failure or pain. This study was performed in patients who underwent ERCP under sedation, not under general anesthesia with endotracheal intubation. Therefore, further studies are needed to determine whether the J-Loop is also convenient for ERCP under general anesthesia.In summary, the new technique is useful and effective for repositioning of the ENBD catheter from the mouth to nostril. The technique using the J-loop allows the operator to easily maneuver the ENBD procedure and helps avoid injury to both the operator and patients.Additional file 2: Figure S1. Visualization of nasobiliary catheter under fluoroscopy


This article introduces a novel approach for a functional electrical stimulation (FES) controller intended for FES-induced cycling based on inertial measurement units (IMUs). This study aims at simplifying the design of electrical stimulation timing patterns while providing a method that can be adapted to different users and devices. In most of studies and commercial devices, the crank angle is used as an input to trigger stimulation onset. We propose instead to use thigh inclination as the reference information to build stimulation timing patterns. The tilting angles of both thighs are estimated from one inertial sensor located above each knee. An IF–THEN rule algorithm detects, online and automatically, the thigh peak angles in order to start and stop the stimulation of quadriceps muscles, depending on these events. One participant with complete paraplegia was included and was able to propel a recumbent trike using the proposed approach after a very short setting time. This new modality opens the way for a simpler and user-friendly method to automatically design FES-induced cycling stimulation patterns, adapted to clinical use, for multiple bike geometries and user morphologies. Functional electrical stimulation (FES) refers to the activation of muscle contractions by the application of short electrical pulses. In some conditions, the FES technique can be used in paralyzed muscles to provide functional or therapeutic benefits. In individuals with spinal cord injury (SCI), a clinical use of FES to activate lower limb muscles has proven to reduce risk factors for cardiovascular disease and decrease other risks related to a prolonged sitting posture  by maintaining muscular activity ,2. FES-aIn most of these studies, FES cycling is achieved while the user is installed in a fixed ergocycle at a rehabilitation center. However, multiple studies have demonstrated that adding a recreational dimension to this physical exercise could improve the attractiveness of FES-assisted training and increase the psychological wellness of the user . This caUsing inertial measurement units (IMUs) to analyze gait and posture, as well as to control electrical stimulation delivery, has been deeply investigated in prior studies led by the authors ,24,25,26In the work by Wiesener et al. , the autMost of the existing solutions are globally complex and time consuming. They highlight the inherent difficulties in designing a stimulation pattern able to produce active cycling. On the other hand, it is essential to keep in mind that most of these applications are intended for clinical or personal use. The final users are either medical practitioners or the pilots themselves, and providing intuitive interfaces to adapt the stimulation patterns in a simple and quick manner would probably be valuable in FES-cycling practice. Based on the arguments of Wiesener et al., and on our personal experience in FES cycling ,31,32, wOne participant , the so-called pilot, with complete spinal cord lesion  was included in this protocol. The study was approved by the French national ethics committee (Comité de Protection des Personnes) and the participant gave his written informed consent. Prior to joining the study, the pilot got acquainted with the stimulation by taking part in a 2-year training FES-cycling protocol .Installed on a tricycle  with a fixed-gear rear wheel, the pilot was equipped with two inertial measurement units  located on each thigh . IMUs weIMU data were processed online to detect the ‘Peak Thigh Flexion’ (PTF) and ‘Peak Thigh Extension’ (PTE) chosen as the start and stop events of the quadriceps stimulation. Thigh tilting angles (θ) relative to the horizontal were computed for each new sample (n) using the method detailed in , by combAs illustrated in The stimulation electrodes were positioned over quadriceps  and the two inertial sensors were fixed on the thigh with rubber bands. After this, the participant was transferred from his wheelchair to the bike, with minimum assistance in order to guarantee his safety regarding sharp metallic elements. Feet were stabilized using calf supports.During the first part of the experiment, the tricycle was installed on the home trainer support  adjustedFor the second part of the experiment, the bike was removed from the home trainer and installed in a 40-meter corridor.The algorithm presented previously was tested successfully. The participant was able to cycle on the recumbent trike in stationary conditions , several data-points were monitored over crank cycles: Crank angle distribution, thigh angles evolution, power developed on the rear wheel and stimulation onset for both legs . The estThe cyclic behavior can be appreciated by plotting the angular velocity as a function of the angular position .The exact same set of parameters was used for over-ground and stationary cycling. In stationary conditions the thigh angles range was  and angular velocity range . In over-ground conditions the thigh angles range was  and angular velocity range . The thigh angle was relative to the horizontal, which explains the shift in values due to different trike inclinations on the home-trainer and flat surface, despite the same 40° range of motion. The cycling velocity was lower in over-ground conditions compared to stationary, as the resistive forces were higher. Furthermore, the trial was performed at the end of the session and some muscular fatigue was already influencing the performance.This study aimed at investigating and developing a new method to simplify the design of stimulation patterns in FES-induced cycling, without requiring any sensor installation on the recumbent trike used. The goal was to demonstrate the feasibility of further simplifying existing approaches for setting any tricycle as an FES-cycling device for an individual with complete SCI, without any prior stimulation timing pattern tuning, nor adaptation due to the bike geometry or the size and position of the pilot, using only two inertial sensors. The present case-study experiment intends to be a proof of concept of this new control modality.In our experience of FES-cycling, adjusting the stimulation timing of the different muscles to be activated using crank angle is time consuming and the optimization regarding power consumption may be complex. The pattern needs to be adapted for different situations: Sitting position, leg length, bike geometry, etc. We believe it is more intuitive and generalizable to define triggering events relative to the pilot instead of the bike. Setting a stimulation onset at a predefined crank angle cannot be translated to multiple bikes or pilots. When tuning a crank-angle-based stimulation pattern, it is necessary to manually correlate each crank value to the pilot oneself; the users take into account the seat height compared to the crank, the lower limb lengths and possible asymmetry, the seat tilting, the length of the boom, and the length of the crank handles. If the position of the pilot varies, the stimulation pattern needs to be entirely defined again.Detecting peak knee angles was initially intended as a stimulation event. Meanwhile, depending on each individual, when the peak knee flexion is reached over the crank cycle, the hip flexion could modify the starting event regarding the seat height compared to the crank, it also requires more sensors. We have observed that the time when the pedal crank reached few degrees before its vertical position corresponds to the time when the thigh reaches its maximum tilting angle. This event detection was supposed to be the same no matter the leg length or bike geometry while enabling to start the stimulation a few degrees before the pedal was vertical, in order to obtain the best muscle mechanical response at the optimal timing. Therefore, the hypothesis was made of detecting this event as the simplest and universal stimulation onset event. Furthermore, this can be done using only two inertial sensors.The result obtained here in one participant confirmed the feasibility of this very simple approach compared to the state-of-the-art, i.e., crank-angle-based stimulation patterns. Further work is needed to validate the approach with other participants.More refined control laws may be considered to optimize cycling performances and robustness , but theIn this study, only the quadriceps were stimulated. A more efficient pedaling could be achieved by adding hamstrings and glutei stimulation, but could require the need to define other detectable stimulation events.Using the instrumented home trainer, we observed that the effective mechanical response of the quadriceps stimulation associated to the pushing phase was less than a 200-ms duration at 47 rpm (cadency used for our participation to the Cybathlon competition ). This oAutomatically adjusting the stimulation parameters to counteract muscle fatigue or ground surface changes remains an open problem.https://youtu.be/gbgGxbBD-VM.A video of the experiment is available online here:


A polarization-modulation-based Goos–Hanchen (GH) sensing scheme leveraging the polarization-dependence of the Bloch surface wave enhanced GH shift is proposed and experimentally demonstrated. Based on a simple setup utilizing a liquid crystal modulator to switch the polarization state of the input beam periodically, the alternating positions of the reflected beam for both polarizations are monitored by a lock-in amplifier to handily retrieve the GH shift signal. The conventional direct measurement of the beam position for the target state of polarization is vulnerable to instabilities in the optomechanical setup and alignment. Our proposed scheme provides a sensitive yet robust GH shift-sensing setup where the common mode drift and noise could be suppressed to ensure better system stability. For a couple of decades, surface plasmon resonance (SPR) has been extensively studied as a powerful diagnostic tool for real-time, label-free bio-related detection . This kiThe GH effect is an interesting physical optical phenomenon that occurs during the nonspecular reflection, where the position of the reflected beam deviates from geometric optic prediction with a lateral displacement . It coulIn contrast to SPR, another type of surface electromagnetic waves, Bloch surface wave (BSW) can be excited at the interface of a truncated one-dimensional photonic crystal (PC) slab and shares certain similarities to the surface plasmon wave . As it pIn such a BSW-induced GH shift sensing system, the position of the reflected beam is measured using a position-sensitive detector (PSD) or an image sensor like charge-coupled device (CCD). Compared to conventional surface wave-based sensing systems where the optical power is monitored, the stability of the position measurement directly affects the system performance of the GH shift sensing system. Yet, in real-world systems, the inevitable changes in instrument temperature, vibration of the mechanical parts, and more would contribute to the results read from the PSD, which would greatly affect the capability of a GH shift sensing system to realize high-sensitivity detection. Therefore, it is of critical importance to reduce or eliminate such drift and instability in a GH shift sensing setup. As is known, the excitation of the surface wave that could enhance the GH shift, including SPW and BSW, depends strongly on the polarization. It is noted that a BSW structure can be designed to possess highly different GH responses for different states of polarization. Based on this, we propose and experimentally demonstrate a polarization-modulated GH sensing scheme using a BSW enhanced GH shift sensor. By measuring the alternating position of the reflected beam with and without the GH response, the retrieved GH shift is free from the common mode noise and drift compared to the conventional direct position measuring systems. Therefore, a sensitive yet robust GH sensing system could be realized with a simple setup.The schematic diagram of the proposed sensing scheme is shown in 10H’/cladding. For P-polarized incident light at the wavelength of 980 nm, the device is designed to be able to excite the BSW mode with water as the cladding (n = 1.33). The substrate is made up of ZF10 glass (nS = 1.668), with TiO2 and SiO2 evaporated alternatively as high index layer  and low index layer , respectively, where the buffer layer adjacent to the external medium is also TiO2 (H’) with a different thickness. The thicknesses of the high index layer, the low index layer, and the buffer layer are 163 nm, 391 nm, and 23 nm, respectively. In order to represent the intrinsic loss of the material and the scattering loss from the interfacial roughness induced through the fabrication process, an extinction coefficient of 2 × 10−4 is added to the imaginary part for the refractive index of the TiO2 for calculation to match the experimental observation [n = 1.33) is just beyond the rising edge of the forbidden band, and the excited BSW mode sits in the forbidden band and lies closely to the light line for water, which means that a slight refractive index change in water would strongly affect the excitation of the BSW, i.e., the design is suitable for sensing in an aqueous solution environment. The excitation of the BSW mode could be observed from reflectance simulation using Fresnel equations, as shown in The structure of the BSW enhanced GH shift sensor chip is sketched in In the experimental setup as shown in At the beginning of the experiment, it is important to confirm the excitation of the BSW, which could be observed by angular scanning the reflected intensity , or the −4 RIU [−4 V without much effort for environment control and vibration suppression of the setup.The real-time record of the retrieved GH shifts from the polarization-modulated PSD signal measured through the lock-in amplifier for different injections is shown in −4 RIU ) were usFor the previous direct position measurement-based sensing schemes ,22, thouWe note that the current modulation frequency is only in the order of ~1 Hz, and the switching speed is limited by the specific LCM device that happens to be available to this experiment. Under the current limitation, the rising/falling time of the signal takes near half of the high/low period, which might reduce the retrieved GH shift signal by average. Further, the limited modulation rate prevents us from removing more environmental disturbance with higher frequency components from the signal. However, LCMs with much faster modulation speed  have become widely available, and it is noted that the response time for liquid crystal modulators could be shortened to submillisecond . In thatA polarization-modulated, GH shift sensing system for common mode noise and drift suppression is proposed and experimentally demonstrated for a Bloch surface wave sensor. By switching the polarization state of the input light between S and P, the position of the reflected beam under the influence of the GH shift effect was recorded for both polarizations periodically. A lock-in amplifier can be utilized to conveniently retrieve the GH shift information by extracting the modulation depth of the reflected beam position signal. Compared to the previous GH sensing schemes, the common mode noise and drift introduced by the mechanical instability of the opto-mechanical setup could be removed easily. Therefore, by utilizing a liquid crystal modulator, a sensitive yet robust GH sensing system is presented with a simple and compact configuration. By introducing spatial light modulators with higher modulation speed, the overall performance of our scheme could be further improved by suppressing more noise at higher frequencies.


Corpus selection bias in international relations research presents an epistemological problem: How do we know what we know? Most social science research in the field of text analytics relies on English language corpora, biasing our ability to understand international phenomena. To address the issue of corpus selection bias, we introduce results that suggest that machine translation may be used to address non-English sources. We use human translation and machine translation (Google Translate) on a collection of aligned sentences from United Nations documents extracted from the Multi-UN corpus, analyzed with a “bag of words” analysis tool, Linguistic Inquiry Word Count (LIWC). Overall, the LIWC indices proved relatively stable across machine and human translated sentences. We find that while there are statistically significant differences between the original and translated documents, the effect sizes are relatively small, especially when looking at psychological processes. The motivation for this paper is to address the lack of linguistic diversity among text-as-data scholarship by quantifying the effects of machine translation on linguistic measures across a variety of languages. The primary goal is not to determine whether there are statistically significant differences, as for most indices there are, but rather to determine the effect size of the machine translation. This will enable future researchers to determine whether an observed effect might reasonably be attributed to the effects of translation or whether an alternative explanation, such as corpus irregularities, is more plausible. We employ the MultiUN corpus to test the stability of LIWC (Linguistic Inquiry Word Count) measures across machine and human translation because it was developed specifically to facilitate the improvement of machine translation techniques.LIWC is a useful tool for identifying linguistic patterns, threatening language and deception ,2, gendeBecause the MultiUN corpus provides expert translations into, or between, the UN’s official languages, it provides an unparalleled source for comparing the LIWC indices of machine translated sentences against the LIWC indices of human translated documents for five non-English languages simultaneously. We find that while there are statistically significant differences between machine and human translated documents across LIWC indices, the effect sizes are very small. This means that scholars can reliably use Google Translate alongside off-the-shelf, bag-of-words analysis programs for political science research.The structure of this paper proceeds as follows. We first provide an orientation the problems researchers face in dealing with multilingual corpora and discuss some of the relevant literature on this topic. We then describe the methodology of our analysis of the effects of machine translation on LIWC indices. Following this, we present our results, including the substantive differences between human and computer-translated documents. We conclude with a discussion of how using machine translation can impact the scope of social science inquiry.Much of quantitative text analysis for political research is done using English-language sources, introducing corpus selection bias at the level of the data generating process that may influence the outcome of results . AdditioBroadly speaking, the field of “text as data" has become well-established in political science scholarship, particularly in the field of American politics, using English-language corpora –23. ThouIn the case of LIWC, this limitation is due to the reliance on curated word lists to compute its indices. In the case of Coh-Metrix this limitation arises from the use of word lists for some indices such as lists of connectives and age-of-acquisition lists, from the reliance on parsing , and from the dependence of some indices on English grammatical constructs. For example, left-embeddedness does not make sense as an index for S-O-V languages .Given the language limitations of computational linguistics programs, one potential solution is to employ expert human translators to translate the documents from the original language to the target language, usually English. Expert human translation, however, is both expensive and time-consuming. Automated translation programs, on the other hand, are efficient and cost-effective ,36, and An area of concern in machine translation is whether the computer program is able to approximate the skill and accuracy of human translation ,40,41. AChecking the stability of a linguistic measure under machine translation is difficult. One obviously wants to take the same sentence in two different languages, but what does this mean? There are four natural approaches ,42,43: fIn our workflow, we eliminate the last two possibilities. Of the two involving translating and then retranslating the translated sentence, we prefer to apply the human translator first. Human translators remain the gold standard, so we prefer to input the “better'' human translation to the machine translator, rather than have the human struggle with the lower fidelity machine translation. The fourth possibility seems to test the reversibility of the translation algorithm rather than its fidelity. One can imagine an algorithm which is highly reversible, but which nonetheless provides translations of low fidelity. This leaves us with the first two possibilities. The nature of our corpus means that we in fact employ both strategies (and a fifth strategy where a sentence in one language is human translated into a second and third language and then machines translated from the second into the third) and cannot say which we are employing for any given sentence.Skeptics might identify an issue using the MultiUN corpus, namely that it likely was included in the document set to train Google Translate algorithms. It is difficult to address this concern given that Google does not make the training data for their translation algorithms public. It is probable that our sample from the MultiUN corpus was indeed included in the training set as it is one of the “gold standard parallel corpora.” However, because it would likely represent such a small proportion of the total available United Nations documents used to generate translation algorithms, the effect would likely be insignificant.The accuracy of machine translations is often scored using the bilingual evaluation understudy (BLEU) metric, used to evaluate the quality of text that has been machine-translated from one natural language to another . The BLEThere is some debate about the use of off-the-shelf, dictionary-based, bag-of-words sentiment analysis programs such as LIWC . Young aGiven that LIWC takes a "bag of words" approach to computational linguistics analysis, meaning it is not dependent on word order or syntax, can automated translation approximate the reliability associated with human translation? Using the MultiUN data set, we address this question and find that while there are statistically significant differences between the LIWC scoring of machine and human translations, the effect sizes are quite small. In other words, we can say with confidence that the error associated with LIWC results is sufficiently tiny that any substantial differences in LIWC values should be attributed to the corpus, not the translation.The MultiUN corpus aligns parallel translations across meaning units. Each parallel sentence in the MultiUN corpus is represented in the corpus map as a link, and each document as a list of links called a link group. A link defines the position of sentences in their language’s respective corpora as well as a certainty score. This certainty score is an output of the hunalign algorithm used to automatically align the individual sentences . HunaligTo facilitate navigating and searching through MultiUN’s large XML files, the first step was to insert the link groups from every corpus map into a document-oriented database. To that end, we constructed an event-based XML parser to read through the corpus map files and populate a MongoDB database with link groups and their constituent links.Recalling its previous resolutions concerning the situation in Somalia, in particular resolution 733 (1992) of 23 January 1992 …), due to the hunalign algorithm finding increased certainty in numerical and ordinal language [We then constructed a list of every unique document that had a representation in all of the following languages: English, French, German, Chinese, Russian, and Arabic. For each unique document in the resulting list, we filtered the link group based on two criteria. First, we excluded any sentence whose English representation was fewer than 140 characters. This thresholding was performed to avoid sampling headers, footers, and other such artifacts present in UN documents that do not express a unit of speech. Secondly, we excluded any sentence whose certainty score > 0.5. Initially, we tried excluding any sentence whose certainty did not fall between the 60th and 80th percentile of the entire MultiUN corpus; however, it was observed that sentences with certainties higher than 0.5 skewed heavily towards formulaic, procedural statements  we were left with a corpus of 3,447 sextuplets of English sentences . This comprises a total of 157,595 words in the English corpus. Each sentence was then analyzed using LIWC 2015. A table of the summary statistics from the Multi-UN corpus appears as The primary goal of this paper is to quantify the effect of machine translation upon LIWC indices. Our primary measure is the correlation between the “original” English variable and the one computed from the machine translation see . We consAn alternative way of looking at the effect size is to look at confidence intervals for the mean difference and compare these with the mean for the English corpus see . This leFinally, we compute a variant of the Cohen’s d effect size. The standard Cohen’s d for paired difference, useful for power analysis, is not useful for determining whether the difference is of practical importance since it normalizes with respect to the standard deviation of the difference. Instead, we use a variant of the Cohen’s d for independent samples, which normalizes the difference with respect to a measure of standard deviation for one or both of the variables. We choose to compute the variant that uses the scale of the English variable to normalize the difference. Thus, our effect size is given byσTranslated or the average A reasonable case could be made for using We remark that, though it may be tempting to use statistical tests for proportions on the LIWC proportions this is not valid. LIWC proportions are proportions of total words and at the level of words no assumption of independence is valid.From this table we can see that the Summary Language Variables and the Psychological Processes categories have high mean correlation and Linguistic Dimensions the lowest correlations. Overall Russian is the most stable and Mandarin the least. Despite the lower correlations in other categories Mandarin still shows high correlation in the Psychological Processes category.The Summary Language Variables are not proportions but the remaining categories are all reported as proportions. If we consider the associated word counts then then correlations are generally higher (75% of pairs have higher correlation), see This indicates that in many cases the observed effect on the proportion is due to the uniform change in the word count, the denominator in the proportion, and not in the actual category word count, the numerator in the proportion. The authors prefer the use of word counts to word proportions.When we look at the Psychological Processes, we see that every primary category variable is correlated at above 0.8. The category of time orientation (which has no associated primary variable) has all three of its constituent measures correlated at less than 0.8. Within the affective language category, the primary variable (affect) and the two secondary components  are correlated at better than 0.8. Switching from proportions to word counts would see pronoun, prep, reward, and focusfuture leave the list while percept and feel enter the list.While we view the correlation and Cohen’s d effect size measurements as the most pertinent, we have also produced confidence intervals for the paired differences and their associated t-tests  and sum the differences and the variances of the English variables.Text-as-data research in political science usually employs English-language corpora, even in international relations research. To internationalize this line of inquiry, our findings suggest that Google Translate may help scholars to overcome the deficit of non-English corpora. Human translation is time-consuming and expensive; machine translation, on the other hand, is quick and less costly.To summarize, the LIWC indices do change under translation but in most cases the change is small relative to the standard deviation of the variable and as a percentage of the mean value of the variable in the English corpus. The Linguistic Dimensions and Other Grammar parts of LIWC output are the most unstable under translation and care should be exercised when trying to use these in analyses involving translated documents. Fortunately, many of the popular Psychological Processes, including all the core categories are very stable under translation.While much of the computational analysis of political language has moved beyond using simple word count tools like LIWC ,45, thisOne issue that any bag-of-words analysis falls short in addressing, is that of translating words versus translating meaning. Meanings of words vary across language, culture, and time; it is not clear whether direct translation via Google Translate will accurately capture the intended meaning from one actor to another. Issues of polysemy–the simultaneous existence of multiple interpretations of words and phrases–cannot always be captured by bag-of-words approaches. This requires more computationally intensive programs that examine the syntactic and semantic properties of language; such a project is currently under development for English, Chinese, French, Spanish, German, Arabic, and Russian .Overall, we are encouraged by our findings from this study of expert human and computer translations. We acknowledge potential endogeneity concerns given that Google drew linguistic information from United Nations documents; however, the MultiUN corpus represents only a tiny proportion of the total number of parallel documents presumably used in generating statistical machine translation algorithms, and our analyzed subset is smaller still. Given the preponderance of questions that scholars receive about the validity of linguistic measures across translated documents, we believe that this study will help to assuage concerns about the generalizability of findings. Further, we have demonstrated that Google Translate is a reliable venue for accurate automated document translation. In summary, typically, the more frequent the word category the more stable it was under translation. Thus, if you observe a medium or large effect size change in a category that appears frequently then it is unlikely to have arisen purely as an artifact of translation.S1 Table(DOCX)Click here for additional data file.S2 Table(DOCX)Click here for additional data file.S3 Table(DOCX)Click here for additional data file.S4 Table(DOCX)Click here for additional data file.S5 Table(DOCX)Click here for additional data file.S6 Table(DOCX)Click here for additional data file.S7 Table(DOCX)Click here for additional data file.S8 Table(DOCX)Click here for additional data file.


T-test as a post hoc test to ascertain pairwise differences between the three taping conditions. Significance was set at 0.05. The fractal analyses of the dynamic changes in center of mass showed significant differences between the control and both the static tape and kinesiology tape groups . The current study developed a novel measure of dynamic changes in the center of mass during a set movement that indicated real-time processing effects during a balance task associated with the type of taping used to enhance postural stability.Static taping of the ankle or knee joint is a common method of reducing risk of injury by providing mechanical stability. An alternative taping technique employs kinesiology tape, which has the additional benefit of improving functionality by stimulating proprioception. There is substantial disagreement whether kinesiology tape shows significant differences in proprioception and postural stability as compared to rigid/static tape when applied at the lower limb. The current study investigated the effects of kinesiology tape and static tape during a Y Balance Test on center of mass as an indicator for postural stability. Forty-one individuals, free of injury, performed the Y Balance Test under the three conditions; no tape, kinesiology tape, and static tape applied at the lower limb to the quadriceps, triceps surae and ankle joint. All participants completed the Y Balance Test to determine whether any significant differences could be observed using center of mass movement as a surrogate measure for balance and proprioception. The Minkowski-Bouligand and box-counting fractal dimension analyses were used as measures of the dynamic changes in the center of mass whilst undertaking the Y Balance Test. Statistical analyses included the Kruskal Wallis test to allow for non-normally distributed data and a Bonferroni corrected pairwise  Proprioception is a sensory modality important in monitoring body position in space, balance and movement , and the Y Balance Test (YBT). These tests can be used to evaluate physical performance, investigate dynamic postural control, identify athletes at greater risk for injury, and provide quantitative data during rehabilitation. Both tests require reaching of the non-stance leg in set directions from a central standing position. The YBT uses three  of the eight SEBT directions. No significant differences in terms of reliability and information gained from the two tests have been reported  or center of mass analyses are based on position time series but also include spatial measures such as sway path length, the area covered by CoP/CoM dispersion, as well as range, maximal sway trajectory and peak velocity . All participants provided written consent to take part in the research following receipt of an information package.All participants were tested on two separate occasions, using kinesiology tape (Kinesio Tex®) on one occasion, and rigid tape on the other. The order of tape allocation was randomized. Both occasions included a no Tape trial. A single strip of tape was applied without tension to the muscle belly of rectus femoris and the medial head of gastrocnemius while the muscle was under stretch. An anti-inversion ankle strapping was also applied using a single strip of tape without tension starting from the medial lower leg, passing inferiorly over the lateral malleolus , under the arch of the foot, passing superiorly over the medial malleolus, and finishing at the lateral aspect of the lower leg  was used to investigate the effect of taping. The goal of the YBT is to reach as far as possible with one leg in three directions while maintaining balance with the dominant leg. The participant stands at a central point and extends the non-dominant leg anteriorly, posterolaterally, and posteromedially Figure . Each paTraditional common features extracted from the spatial dispersion of the center of mass included total path length, maximum and minimum trajectory in each direction and total area . Spearman's correlation was determined to investigate whether the fractal dimension was correlated with maximum reach. Descriptive statistics were calculated for male and female groups. Significance was set at p < 0.05.The Shapiro-Wilk Test was used to check for normality as recommended for sample size below 50 and based on regression and correlation, whereas the Kolmogorov-Smirnov test is based on the empirical distribution function and only considers the largest discrepancy between observed and hypothesized distributions . Table A linear mixed effects model was applied to consider the three experimental interventions of no tape, KT and ST tape as well as gender. The The box-counting results are shown in Table Fractal dimension results close to 1 may reflect a transition phase between Euclidean and fractal forms or are a function of the smoothness of the Minkowski-Bouligand dimension (dilation method) that is more sensitive to linear features.MB) or box-counting (DfBC) method. The model showed a significant difference for KT and ST groups as compared to control with the Minkowski-Bouligand method (p = 0.0216 and p = 0.0098 respectively), and for ST with the box-counting method (p = 0.0048). The same model was applied for males only and females only. Analysing effects of taping within gender showed that both DfMB and DfBC were significant. A difference was found for KT for males according to the DfMB method (p = 0.0464) and for ST according to the box-counting method (p = 0.0249) but not for females. A post hoc comparison using Bonferroni correction indicated a significant result for no tape vs. rigid tape for both the Minkowski-Bouligand and box-counting methods (p = 0.052 and p = 0.0093) but no significant difference within gender. The fractal data and maximum reach data showed that a correlation existed for anterior reach and posteromedial reach when using ST taping . When maximum reach points in the three directions of the YBT were connected to form a sway area description of maximum reach in the three directions, there was no correlation between the fractal dimension results and the triangle area and perimeter (r = 0.04 and p = 0.9).Significant differences were found when the fixed effects were the Minkowski-Bouligand (DfMB) and box-counting (DfBC) dimensions. Larger fractal dimension values of the CoM trajectory are associated with greater activity of the sensori-motor system in retaining balance during a dynamic movement task. In contrast, in previous studies applying KT did not improve knee or ankle proprioception in a group of healthy young adults, did not decrease or increase performance, and had no effects on muscle activation  and gender, and showed a significant difference in males for DfThe fractal dimension reflects the degree of complexity associated with changes in the CoM trajectory in the anterior-posterior and medial–lateral directions during the YBT. In general, a higher fractal dimension represents more complex movement patterns, possibly reflecting better dynamic control and postural stability (Costa et al., MB and DfBC that could be due to ST decreasing joint movement more than KT. A previous study which investigated the fractal structure of force plate signals suggested that the center of pressure was more useful and sensitive in the evaluation of the age-related decline of postural stability than the CoM (Błaszczyk and Klonowski, In our study, with a young adult cohort free of injury, the fractal dimension for KT and ST was higher than the control for both methods. This suggests that rigid or kinesiology tapes applied on healthy subjects may improve postural stability. Rigid tape led to slightly higher DfAn association between fractal dimension and maximum leg extension was not found in the current study, suggesting that the CoM is not a function of maximum reach. Consequently, the improved postural stability may not be associated with a shorter reach. According to this result, the fractal dimension represents the dynamics of movement and is not a function of the maximum reach of any movement, which suggests that taping in general does not affect the extent of movement but rather postural stability.The findings of this study indicate both KT and ST application contribute to increased complexity of CoM movement during a dynamic balance task, however it was only ST that achieved significance when compared to no tape. This is contrary to claims KT has the potential to facilitate changes in proprioception and postural stability. While the findings are of clinical interest, the use of fractal analysis to achieve these findings offers a novel, and potentially more appropriate method for future investigation of movement complexity.LD and HJ conceived of the study, interpreted the results and finalized the manuscript. KK contributed to interpretation of results and writing the manuscript. LH collected the data, analyzed the data, and contributed to the writing of the manuscript. PA undertook the fractal analysis and contributed to the interpretation of the results and writing of the manuscript.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 capability of landing on previously unvisited areas is a fundamental challenge for an unmanned aerial vehicle (UAV). In this paper, we developed a vision-based motion estimation as an aid to improve landing performance. As an alternative to the common scenarios accompanying by external infrastructures or well-defined marker, the proposed hybrid framework can successfully land on a new area without any prior information about guiding marks. The implementation was based on the optical flow technique associated with a multi-scale strategy to overcome the decreasing field-of-view during the UAV descending. Compared with a commercial Global Positioning System (GPS) through a sequence of flight trials, the vision-aided scheme can effectively minimize the possible sensing error, thus, leading to a more accurate result. Moreover, this work has potential to integrate the fast-growing image learning process and yields more practical versatility for UAV applications in the future. Landing is the most critical and dangerous phase of a flight due to the uncertainty from complex terrains or unpredictable occurrence. Unlike the manned aircraft with pilots capable of responding to various environmental interferences, an Unmanned Aerial Vehicle (UAV) needs to equip a vision system to retrieve related information, especially when a UAV lands on an unvisited area. In this study, we attempt to develop a vision system as an aid for UAV landing purposes. Unlike conventional scenarios structured with external infrastructures such as Differential Global Positioning System (DGPS) and trajectory measurement system, the proposed vision-based scheme provides more versatilities in integrating the fast-growing imaging techniques into aircraft control. Vision-based motion estimation for aerial vehicles firstly experimented on a fixed-wing manned aircraft . This woAccordingly, some studies have aimed to assess the landing risk by evaluating the planarity and slope of the terrain or construct a partial map for navigation purposes ,11,12. TThe optical flow techniques, correlating two consecutive image frames, were proven to be effective in motion detection ,16. Two The Gunnar–Farnebäck Algorithm (GFA)  is a comIn this paper, we proposed a novel scheme that compromises both the advantages of sparse and dense optical flow techniques. We presented a vision-aided landing system developed for rotorcraft UAV to land on a previously unvisited area. The major functions of the proposed system are to track the landing spot with no marker and provide accurate and reliable measures of both position and velocity to replace the existing GPS measurement in a UAV control system. The remainder is organized as follows. In In the hybrid optical flow technique, correlating multiple image frames, was proposed to estimate two dynamic measures: velocity and position. As shown in While flying a UAV in an unvisited area there is no prior information as the landing reference. Since motion detection is mainly achieved by comparing the image patterns, it is unlikely to retrieve sufficient information as the scene has plain texture. Compared with the conventional global feature-based methods, the Gunnar–Farnebäck optical flow  with pixTo speed up the computational time, the above algorithm can be modified by the iterative scheme with a prior estimate, whereas a coarse to fine image pyramid was built. As the illustration in For position estimation with long working range, it is no longer adequate to keep track on every pixel in the ROI due to the large displacement. Instead, we employed the PC method to obtain the translational offset between two images based on the Fourier Shift theorem ,34. ConsThe typical PC algorithm only allows a small range of scale variance between the two images. However, the image-based motion detection would experience a large-scale difference during the whole landing process. Instead of using spatial correlation methods which are computationally intensive , we propFurthermore, as the UAV was descending, an instant updating reference ROI image was essential to make sure that it contains enough area for extracting the ROI out of the subsequently measured images. This section reveals the experiment of vision-aided UAV landing in an outdoor environment. After describing the experimental setup, we examined the capability of the hybrid framework for motion estimation. Then, we proceed to present the results of vision-based landing in comparison to GPS-based landing. While the vision function was in effect, the system would simultaneously collect the GPS signal as the benchmark. In terms of velocity, we calculated the mean and the standard deviation of the difference between these two systems. On the other hand, due to the reason that the position measurement from the GPS may have a drifting problem , we evaluated the position accuracy by template matching method  after flTM , was pre-installed with a flight control system (Jupiter JM-1 Autopilot), an inertial measurement unit (IMU), a laser altimeter and a GPS module, respectively. For the visual aspect, the image processing system consisted of the NVIDIATM Jetson TK1 module  and the GoProTM camera . The embedded program executed the algorithms of motion estimation as well as communicated with the flight control computer which runs the proportional–integral–derivative (PID) control scheme.The testing UAV as shown in Our goal was to aid the landing with visual feedback and improve the landing accuracy without controller tuning. In order to legitimate the GFA and PC algorithm in motion estimation, a ground truth was given in different operational conditions. For position estimation, the difference between the Nth and the reference frame shown in  by both To verify the effectiveness of the vision-based landing, we involved the GPS-based landing as the benchmark. The UAV was commanded to hover above a selected landing area, and then steadily descend until the vehicle touched down on the ground. http://tinyurl.com/y656uerp. The flight data along with the captured images were presented in x and y directions. The close agreement suggested that the vision-based aid is competitive with the conventional GPS-based in terms of velocity estimation. A video demo for the experiment was shared below: position , we veriFor comparison purposes, we conducted the landing process using the measurements from GPS instead of the proposed vision system. Like the previous case, the flight control system set the designated landing spot at the center of the camera view when the landing control starts (black cross in nditions  and obtaIn this paper, we proposed a hybrid vision-based framework to maneuver UAV landing without prior knowledge about the landing spot. Unlike the past experiences in which a well-defined marker is required for motion detection, we introduced a hybrid scheme to select the operating images and algorithms based on the estimated motion; thus, meeting the need to land in an unvisited area with no target recognition required. In this work, the GFA and PC methods were combined to compromise both advantages of dense and sparse optical flow in terms of accuracy and robustness, and a multi-scale strategy is proposed to tackle the field-of-view problem during UAV descent. The experimental results indicated that the UAV is able to stabilize its velocity and position in the absence of GPS signals. Finally, with the vision-based motion estimation system, we successfully carried out the UAV landing more precisely than is achieved by using a GPS in an outdoor environmentThe proposed vision-aided system not only accomplished the landing mission with a superior performance to the conventional GPS but had full potential to incorporate fast-growing imaging and learning procedures. For an autonomous UAV to land safely at an unvisited airfield, a survey to assess the planarity of the landing surface must be considered prior to the final approach phase. Therefore, based on this work, we will extend the machine vision upon landing site selection and apply self-supervised learning to autonomously locate a safe landing spot in an unsurveyed environment.


A novel modeling method was proposed to provide an improved representation of the actual microstructure of TiB/Ti-6Al-4V discontinuously-reinforced titanium matrix composite (DRTMC). Based on the Thiessen polygon structure, the representative volume element (RVE) containing the complex microstructures of the DRTMC was first generated. Thereafter, by using multiple user-defined subroutines in the commercial finite element software ABAQUS, the application of asymmetric mesh periodic boundary conditions on the RVE was realized, and the equivalent elastic modulus of the DRTMC was determined according to the homogenization method. Through error analyses on the experimental and calculated results regarding the equivalent elastic parameters of the DRTMC, the rationality of generating the DRTMC finite element model by using the present method was validated. Finally, simulations based on four types of network-like models revealed that the present simplifications to the particle shape of the reinforcement phase had less of an influence on the overall composite strength. Moreover, the present study demonstrates that the DRTMC enhancement is mainly attributed to the matrix strengthening, rather than the load-transferring mechanism. The strengthening influences of the distribution forms of the reinforcement phases, including their distribution density and orientation, were studied further. It was found that both the higher distribution density and limited distribution orientation of the particles would increase the probability of overlapping and merging between particles, and; therefore, higher strength could be yielded when the volume fraction of the reinforcement phase reached a certain threshold. Owing to the versatility of the developed methods and programs, this work can provide a useful reference for the characterization of the mechanical properties of other composites types. With the development of the aerospace industry, the requirements for the adopted materials have become more focused on lightweight, but high strength, ductility, and toughness. In order to meet the development trends, studies on lightweight titanium alloy and composites have become an important direction in material development, owing to their high performance and lightweight features. In particular, discontinuously-reinforced titanium matrix composite (DRTMC), which not only maintains the excellent properties of titanium alloy, but also possesses a higher specific strength and specific modulus, is expected to become a key structural metal material in the aerospace field. Therefore, this area has received increasing attention in material research in recent years ,2.4C hybrid-enhanced discontinuously-reinforced titanium matrix composites (DRTMCs) based on a yield strength model, by accounting for strengthening from the reinforcement phase, matrix grain refinement, and solid solution simultaneously. Their results indicated that the increase in the composite yield strength is mainly owing to grain refinement and solid solution strengthening. Zherebtsov et al.  = [L]−1. Therefore, by comparing Equations (12) and (13), the equivalent elastic parameters of the DRTMC can be acquired, as listed in iE is the elastic modulus, μij is the Poisson’s ratio, and ijG is the shear modulus.Taking V2  as an example, the calculation of its equivalent stiffness matrix is briefly described. The equivalent material stiffness matrix of the RVE indicated in Equation (11) can be obtained through calculation based on the homogenization method mentioned previously. It is well known that the flexibility matrix for the orthogonal anisotropic material, ion (13) , which iE1 is quite close to E2 for each case, corresponding to different volume fractions. Therefore, the present composite can be regarded as isotropic material. Furthermore, this signifies that the generated RVE model may be reasonable, as it contains sufficient reinforcement phase material. Moreover, from E1 + E2)/2, exhibits a slight underestimate. However, the maximum error of these three cases is only 2.3%, which is acceptable in engineering applications. From these calculated equivalent elastic parameters, it can also be observed that the elastic module increases with the volume fraction of the reinforcement phase, but the Poisson’s ratio μ12 decreases. Therefore, all of the conclusions mentioned above fulfill our expectations. This implies that the developed modeling and analysis methods, as well as the generated RVE models, are reasonable and effective.Obviously, if the RVE is excessively small, it cannot represent the composite material behavior. However, an overly large RVE will lead to significant computational expenses and waste time. Although the generated RVE, including its size, appears reasonable according to the above discussion, its size convergence study was further conducted in our work. Firstly, a sufficiently large composite geometrical model was generated using our method, in which the same configuration and size of the microstructure as the actual material were considered. Thereafter, the domain size was changed to generate different sizes of RVE models, as illustrated in The reinforcement phase is an important component in the composite, which will significantly affect the overall composite mechanical properties. Because the configuration of the DRTMC reinforcement phase is extremely complex, it needs to be simplified for simulation. However, different simplifications will generally lead to varying results . To ensuDuring the numerical simulations of the above five model types, the same settings as in the previous verification were considered, including the material constitutive relationship and its associated material parameters. A 2D RVE model of the DRTMC and its boundary conditions are illustrated in In our work, the nonlinear true stress–strain response curves for V2, V3.5, and V5, as illustrated in As discussed previously, the literature studies demonstrate that the DRTMC strengthening mechanism is mainly attributed to two factors: the load-transferring mechanism between the reinforcement phase and matrix, and the strengthening caused by the metal matrix owing to grain refinement and the solid solution, among others. In our work, the load-transferring mechanism was first investigated through theoretical calculations.cyσ is the composite yield strength, myσ is the matrix yield strength, eV is the content of the reinforcement phase, S is the aspect ratio of particles in the reinforcement phase, and mV is the content of the matrix. Actually, the present analytical formula itself does not consider the effect of the particle distribution forms in composites. Therefore, it was also applied to predict the yield strength of the composites with network-like microstructure, σcy=e.g., in ,37,38). e.g., in , namely In general, compared to the uniformly distributed particle model (Model V), the network-like model (Model I) appears to possess a significantly stronger load-transferring capability. The reason is that the particles in the network-like model form a load-transferring channel much more easily, owing to nearer distances between particles and a higher probability of the particles merging. Therefore, in our work, a comparison between these two model types was further carried out to conduct an investigation. The simulation results are displayed in In In addition to the above two mechanisms, our investigations also found that other factors, such as the distribution density and orientation of the reinforcement phase, will affect the DRTMC enhancement. In this paper, we explored such an influence from the above two factors in order to aid in further understanding the strengthening mechanism of the present composite material types. Furthermore, the reasonability of the 3D model simplified to a 2D model is discussed. As the enhancement phase is simplified to be linear and elastic, the calculated stress values are approximately larger than the real situation.Because the network-like RVE model illustrated in It is worth noting that there existed a significant difference in the density of the reinforcement phase, although the reinforcement phase contents for both models were maintained constant. For the network-like model illustrated in As mentioned previously, it can be determined that the particle densities in the above models differed, although they had the same particle contents. In our work, the effective elastic and shear moduli were also evaluated from the above two models with three different particle contents, and their results are illustrated in x-axis) and vertical (y-axis) directions were implemented to obtain the mechanical responses along these two directions. x-axis), as illustrated in As the distribution orientation of the reinforcement phase particles of the current composite material may have certain influence on the overall performance, the influence of the distribution orientation of the particles is discussed further here. In our work, the model with uniformly distributed rectangular particles was selected as the research object. The particle orientation was defined as the direction located with a larger size in the rectangular particle. The previous material properties were still adopted in these simulations. The loads in the horizontal  in Case II may be smaller than those in Case I. It can be understood that the limitation of the particle orientation signifies a lower intersection probability between particles. Therefore, for the medium particle contents, although from a statistical viewpoint slightly more particle materials were located along the x-axis than the y-axis, the probability of particles intersecting with one another in Case II may be lower than that in Case I, which would result in both shear moduli (xG and yG) in Case II being smaller than those in Case I. This implies that material strengthening owing to intersections between particles will be higher than that with slightly more reinforcement particles.In addition to the single axial tension loading mentioned above, a comparison under the pure shear loading condition was also conducted between the non-limited and limited particle orientations. y-axis) obviously resulted in a slightly higher effective yield stress than that in the horizontal direction (x-axis). This was caused by more particles intersecting along the horizontal direction. The presence of intersecting particles could hinder the possibility of matrix plasticity in the shear direction.Therefore, a specific distribution orientation of particles will cause the composite to behave with the feature of anisotropy; that is, strengthening of mechanical performance at certain orientations and weakening at others.The microstructure of the present composite is rather complicated, and it is nearly impossible to generate a 3D model perfectly mimicking the actual microstructure configuration. During the generation of the 3D finite element model, various issues will be encountered, such as failure to create an overlapping operation between different volumes, failure to generate the proper mesh owing to the existence of a small volume, and heavy computational costs. It is known that certain differences definitely exist between the 3D simulation and the 2D simulation simplified from the 3D model, particularly for the complicated composite material. Here, the differences between these two simulation types are further investigated. From the previous discussions, it can be concluded that the volume fraction of particles is the key influencing factor on the material properties of the present composite. Although the distribution form of the particle would also contribute a certain difference, it would not intrinsically change the mechanical behavior of the present composite. Therefore, the 3D modeling was simplified according to the following principles. Firstly, the particle volume fraction was maintained the same as the experimental data and that adopted in the 2D simulation. Secondly, relatively larger particles were considered in the 3D model. If the particle was excessively small, it would result in numerous modeling issues, which may cause abortion of the modeling.In our work, the previous three materials with different particle volume fractions were modeled, as illustrated in In order to disclose the DRTMC strengthening mechanism, a novel modeling approach was developed, and implementation of the homogenization theory in ABAQUS was introduced. Ultimately, different microstructure models were generated, and the modified TNT model considering two strengthening mechanisms was used to investigate the influences of the load-transferring and strengthening mechanisms of the matrix material on the DRTMC mechanical response. The main conclusions can be drawn as follows.(1) The present developed modeling method using the Thiessen polygon can realistically represent the network-like microstructure feature of the DRTMC. It can also easily be extended to describe other similar composite microstructures, and provides valuable insights into the optimization and design of this type of composite material.(2) Based on the commercial finite element software ABAQUS and the developed user-defined subroutines, AMPBC can be conveniently applied in the RVE finite element model. With the aid of the homogenization method and the present implementation scheme in ABAQUS, the equivalent elastic parameters of the composites can be calculated effectively.(3) The comparisons of simulation results from several simplified network-like distributed models indicates that the different simplifications of the reinforcement phase will not have any significant influences on the overall mechanical response of the studied DRTMC.(4) The simulated results based on the present material constitutive relationship exhibit good agreement with the experimental results. By comparing the numerical predictions with the experimental data and analytical solution, it can be concluded that the strengthening of the matrix phase is the main cause of the overall strengthening of the present DRTMC material.(5) By comparing the simulation results based on the models with different distribution forms of the reinforcement phase, including the distribution density and orientation, it is found that the specific distribution forms will also result in the strengthening effect, including producing the anisotropy feature, when the particle contents reach a certain threshold.(6) For the studied composite with a lower volume fraction of reinforcement particles, the operation regarding simplification to the 2D model will not have a significant influence on the related factors.


Additive manufacturing is becoming a technique with great prospects for the production of components with new designs or shapes that are difficult to obtain by conventional manufacturing methods. One of the most promising techniques for printing metallic components is binder jetting, due to its time efficiency and its ability to generate complex parts. In this process, a liquid binding agent is selectively deposited to adhere the powder particles of the printing material. Once the metallic piece is generated, it undergoes a subsequent process of curing and sintering to increase its density (hot isostatic pressing). In this work, we propose subjecting the manufactured component to an additional post-processing treatment involving the application of a high hydrostatic pressure (5000 bar) at room temperature. This post-processing technique, so-called cold isostatic pressing (CIP), is shown to increase the yield load and the maximum carrying capacity of an additively manufactured AISI 316L stainless steel. The mechanical properties, with and without CIP processing, are estimated by means of the small punch test, a suitable experimental technique to assess the mechanical response of small samples. In addition, we investigate the porosity and microstructure of the material according to the orientations of layer deposition during the manufacturing process. Our observations reveal a homogeneous distribution independent of these orientations, evidencing thus an isotropic behaviour of the material. Additive manufacturing (AM) is experiencing an increasing popularity in both academic and industrial applications; see the work by Frazier  for a reIn this paper, we propose and investigate the effect of applying a high hydrostatic pressure as an additional post-processing technique to further increase material density and mechanical performance. The so-called cold isostatic pressing (CIP) technique is used to subject metallic samples to high pressures at room temperature. CIP post-processing has been used in combination with HIP in the context of conventional powder metallurgy, see for example the pioneering work by Ng et al. , but itsThe remainder of this manuscript is structured as follows. The present study was conducted on a stainless steel studied by Nastac et al. , AISI 31L. Orientation defined by the advance direction of the printhead;T. Orientation defined by the direction perpendicular to the advance of the printhead, i.e., normal to the L orientation;S. Orientation perpendicular to the plane LT and coincident with the vertical movement of the printing bed.The microstructure analysis reveals the existence of numerous pores. A representative scanning electron microscope (SEM) micrograph is shown in As described schematically in The cold isostatic pressing (CIP) procedure was performed in three steps: first, the hydrostatic pressure was raised up to 5000 bar, then it was maintained for 3 min and, finally, the pressure was removed in a controlled manner. Once the pressure unloading had finished, the device was disassembled and the specimens could be collected and tested.The mechanical assessment of the effect of the CIP process on the material properties was conducted by means of the small punch test (SPT). Extensive details of the testing equipment and the experimental procedure are given in the SPT CEN code of practice . As descOne of the most influencing works on SPT correlations for determining the mechanical properties is the one by Mao and Takahashi . They esHere, y García  for the SPT specimens were extracted from a component printed by the binder jetting method, obtaining square specimens of 10 × 10 mm in each of the defined planes: LT, LS and TS. The small specimens were polished to achieve a uniform thickness of roughly 0.5 mm. SPT experiments were carried out, at room temperature, for 316L samples with and without CIP post-processing. The tests were quasi-static, with the punch displacement rate being equal to The resulting force versus displacement curves obtained from the experiment were normalised by the measured specimen thickness a et al. , we deteThe following expression was employed for load normalisation after this point:To ensure reproducibility, three experiments were conducted for every combination of specimen orientation  and post-processing treatment (with and without CIP).The values measured with the small punch test (SPT) for the load at yield t et al. . Sket anThe representative load versus displacement curves obtained from the SPT are shown in Remarkably, two of the tested specimens suffered a premature failure in orientation L, which is defined by the advance direction of the printhead. The two samples, B3 and E3, correspond to the LS plane. We propose and assess the use of cold isostatic pressing (CIP) post-processing techniques to compact samples of AISI 316L steel that have been additively manufactured (AM) by binder jetting. Pressures of 5000 bar are applied by means of a novel device that builds upon high pressure processing (HPP) technology; the aim is to improve the mechanical response of the AM specimens. Due to the limited size of the samples that can be accommodated in this device, the small punch test is employed to characterise material performance with and without CIP post-processing. Specifically, three material parameters are extracted: the yield load Our main findings are twofold. First, little differences are observed in the microstructure along the three characteristic planes intrinsic to the binder jetting process. However, mechanical testing reveals early cracking and cleavage-like features in the LS plane samples. Second, the use of CIP post-processing appears to improve the mechanical performance of AM steels. Small punch test measurements show that, when the CIP technique is employed as an additional post-processing of the material, there is a 6.5% increase in the yield resistance, a 3.1% increase in the critical load, and a 1.4% increase in the displacement to failure. In addition, this enhancement due to CIP appears to be sensitive to the characteristic orientations intrinsic to the binder jetting process. Future work will involve gaining further insight into this effect.