Editorial

At the dawn of the devastating events of the COVID-19 pandemic, in the editorial of the first issue of 2020, as well as in the articles, topics related to the overwhelming impact of the emerging crisis were explored (Van der Maesen 2020). In particular, reference was made to the topical performances of the federal governments of the United States and Brazil, as well as the British government. As an introduction to this special issue, it is interesting to recall and extend some of the observations that were made last year.In the case of the United States, when COVID-19 appeared, the hazards of the virus were downplayed and even neglected. The president countered the opinion of public health experts with false, misleading comparisons to other countries (Qiu 2020). It was proposed to cut the budget of the US Centres for Disease Control and Prevention by 16 percent starting in October 2020. Long-lasting contacts and collaboration with the World Health Organization were broken. Due to export restrictions on medical products, importing countries were unable to obtain sufficient medical equipment, resulting in a shortage in healthcare equipment that had to be made for up via a mandatory increase in local production. This came at a high cost and with serious delays (Krueger 2020). For the United States itself, the initial attitude of the government resulted in a dramatic blow to its public health resources and capabilities. The quality of hundreds of health departments around the country suggests that the nation may be less prepared for the next pandemic than it was for the current one (Baker and Ivory 2021). The violence toward public health professions is gradually taking shape (Schreiber 2021). An overriding societal pattern, which in the United States undermines the principles of effective public health, is the primacy of personal rights over collective responsibility and solidarity. More than half of US states have introduced new laws to restrict public health measures, including policies requiring quarantine and mandating vaccines and/or masks.

The Analysis and Compensation of Elastic Unbalance Torque of the Three-axis Air-bearing Simulator

The most important interfering torque of a three-axis air-bearing simulator is the displacement of the center of mass in the gravity field caused by structural elasticity. In order to characterize the torque, a mathematical model of the interference moment was established. Based on the model, it is suggested that the vertical stiffness and horizontal stiffness of the structure should be equal as far as possible during the structural design, and the elastic unbalance moment can be compensated by the vertical offset of the center of mass of the air floating platform relative to the rotation center after the initial attitude leveling. ABAQUS was used to build a simulation model of the air floating platform, and the changes of the structure’s centroid before and after the gravitational field was applied were extracted by software to simulate the centroid deviation caused by the elastic deformation of the structure, which was used as the characterization to conduct discrete optimization of the structure. The optimal structural parameters were obtained. Then the disturbance torque curve and the corresponding initial centroid offset after initial centroid compensation were calculated by mathematical model. The results are of positive guiding significance to the design of three-axis air-bearing simulator.

Research on the Shearer Positioning Method Based on SINS and LiDAR with Velocity and Absolute Position Constraints

Accurate positioning of the shearer with a strapdown inertial navigation system (SINS) is the key technology to realize the automation of the longwall face. Unfortunately, the existing positioning methods have a strong dependence on the attitude accuracy of the SINS. The position errors gradually increase with the drift of the SINS attitude. To reduce the dependence on the SINS attitude and further increase the shearer positioning accuracy, this paper proposes a positioning method based on SINS and light detection and ranging (LiDAR) with velocity and absolute position constraints. A Kalman filter (KF) model based on these constraints was established. Simulation analysis shows that the attitude calibration between the shearer body, SINS and LiDAR, and the initial attitude alignment of the SINS are the keys to determining the shearer positioning accuracy. Even if there are small horizontal bends in the running track of the shearer and the features have small horizontal errors, an excellent positioning effect can still be obtained. In addition, four cutting processes were simulated with a reciprocating travel of 44.6 m and an advance distance of 1.2 m. Compared with the relative positioning method, the positioning accuracy of the proposed method was improved by 37%, 63%, 76%, and 69% from the first to the fourth cutting cycle, respectively, calculated by spherical error probable (SEP) values, and positioning accuracy had a lower dependence on the installation deflection angles between the SINS, the LiDAR, and the SINS attitude accuracy.

Interlaced Attitude Estimation for Spacecraft Using Vector Observations

This paper proposes an interlaced attitude estimation method for spacecraft using vector observations, which can simultaneously estimate the constant attitude at the very start and the attitude of the body frame relative to its initial state. The arbitrary initial attitude, described by constant attitude at the very start, is determined using quaternion estimator which requires no prior information. The multiplicative extended Kalman filter (EKF) is competent for estimating the attitude of the body frame relative to its initial state since the initial value of this attitude is exactly known. The simulation results show that the proposed algorithms could achieve better performance compared with the state-of-the-art algorithms even with extreme large initial errors. Meanwhile, the computational burden is also much less than that of the advanced nonlinear attitude estimators.

Upaya Meningkatkan Hasil Belajar Keterampilan Passing Atas Bolavoli Dalam Pembelajaran Pendidikan Jasmani Menggunakan Metode Bermain Untuk Siswa SMK

The research objective was to improve the results of learning passing on volleyball for class X Catering Services 3 SMK Negeri 1 Batu Kota. This study uses quantitative data analysis with classroom action research (CAR), and uses a test instrument. The research subjects were students of class X Catering Services 3 at SMKN 1 Batu, totaling 35 students. Based on the results of the study, it can be concluded that the initial attitude, attitude attitude, and final attitude on volleyball passing skills showed a significant increase, which was included in the very good category. Abstrak: Tujuan penelitian adalah untuk meningkatkan hasil belajar passing atas bolavoli siswa kelas X Jasa Boga 3 SMK Negeri 1 Batu Kota. Penelitian ini menggunakan analisis data secara kuantitatif dengan metode penelitian tindakan kelas (PTK), serta menggunakan instrumen berupa tes. Subjek penelitian adalah siswa kelas X Jasa Boga 3 SMKN 1 Batu yang berjumlah 35 siswa. Berdasarkan hasil penelitian dapat disimpulkan bahwa sikap awal, sikap perkenaan, dan sikap akhir pada keterampilan passing atas bolavoli menunjukkan adanya peningkatan yang signifikan yaitu masuk pada pada kategori baik sekali.

A Rapid Target Searching Scheme for a Small Satellite with Device Limits

In recent years, small satellites, which are more and more popular and affordable, have been already widely applied in observation and monitoring missions. However, it is a tough problem to meet the different mission requirements with such limits as space, energy, and devices. In this paper, we propose a practical target searching scheme for a small satellite which suffers from the device limits during the first 7.5 seconds after the launch separation. Due to the device limits at the beginning of the separation, the initial attitude of the satellite and the position of the target that the following observation task is based on are both unknown. In order to solve this problem, a backward integral strategy used to estimate the initial attitude and a target searching method intended to ensure the satellite acquires the target rapidly are included in the scheme. Simulation results proved that this scheme enabled the satellite, regardless of the initial conditions, to acquire the target within the limited observation time.

A New Perspective on Low-Cost MEMS-Based AHRS Determination

Attitude and heading reference system (AHRS) is the term used to describe a rigid body’s angular orientation in three-dimensional space. This paper describes an AHRS determination and control system developed for navigation systems by integrating gyroscopes, accelerometers, and magnetometers signals from low-cost MEMS-based sensors in a complementary adaptive Kalman filter. AHRS estimation based on the iterative Kalman filtering process is required to be initialized first. A new method for AHRS initialization is proposed to improve the accuracy of the initial attitude estimates. Attitude estimates derived from the initialization and iterative adaptive filtering processes are compared with the orientation obtained from a high-end reference system. The improvement in the accuracy of the initial orientation as significant as 45% is obtained from the proposed method as compared with other selected techniques. Additionally, the computational process is reduced by 96%.

Study of Body Attitude Criteria of Indoor Hockey Players Based on Body Height to Obtain Accurate Passing Techniques

In this study, the authors analyzed the posture of indoor hockey players for ball passing techniques based on posture which consists of initial attitude, implementation attitude, and final attitude. These three gestures have been demonstrated by a male indoor hockey player from the Sports Science Faculty, Jakarta State University. Data was collected in September at Hall B, Room Hockey Field, Faculty of Sports Science, Jakarta State University. The data obtained in this study were obtained through filling out questionnaires, observations, and interviews. The aim of this research is to determine the ideal height of a indoor hockey player who has accurate passing techniques. The samples in this study were all male indoor hockey athletes at the State University of Jakarta who followed a quasi-experimental research method with a time series design on indoor hockey passing techniques. As a result, we will get data on height and body position when doing the passing technique and the accuracy of the technique. Then from this study the respondents stated that the experience of playing, comfort, and body posture of the respondents supported the ability of the passing technique, which respectively indicated by the percentages of strongly agreeing and agreeing that were 63% and 30%, 52% and 48%, 56% and 37%. Furthermore, in terms of height, the largest percentage was 45% disagreed, 11% strongly disagreed and 33% doubted. Whereas in the case of 52% disagree, 4% strongly disagree and 33% are doubtful and in terms of the distance between hand grips it affects the accuracy of the passing technique with a percentage of 59% agree and 4% strongly agree. We're going to give some recommendations for coaches and hockey players to have multiple height classifications with postures that give better accuracy for passing the ball.

Study of Body Attitude Criteria of Indoor Hockey Players Based on Body Height to Obtain Accurate Shooting Techniques

The purpose of this study was to make a preliminary study of the criteria for accurate shooting techniques based on height. Researchers in this study analyzed an accurate ball shooting technique based on body posture consisting of the initial attitude, the execution attitude, and the final attitude. The posture of the ball shooting technique has been demonstrated by indoor hockey players at the Sports Science Faculty, Jakarta State University. The data obtained in this study were taken through observation, interviews, and filling out questionnaires. This study uses a qualitative method by distributing questionnaires to each player. The population used was the hockey athlete at the State University of Jakarta. The sample was taken in this study using a total sampling technique. The results of this study the respondents stated that playing experience, comfort, The body postures of the respondents support the ability to shoot the ball accurately, respectively, shown by the percentage strongly agree and agree are 45% and 44%, 52% and 44%, 70% and 30%. Furthermore, for height, the largest percentage was 44% disagreed and 26% doubtful, for arm length the largest percentage was 45% doubtful and 41% disagreed. This means that height and arm length do not affect the respondent's accuracy in shooting the ball accurately. However, the distance between the hand grips affects the accuracy and comfort, this is reinforced by the percentage strongly agree and agree that the hand grip distance affects the accuracy is 19% and 59% and the distance between the handles based on comfort is 33% and 56%. The results of this study will be given to athletes and coaches as evaluation material.