Identify Finger Rotation Angles with ArUco Markers and Action Cameras

Measuring the motions of human hand joints is often a challenge due to the high number of degrees of freedom. In this study, we proposed a hand tracking system utilizing action cameras and ArUco markers to continuously measure the rotation angles of hand joints. Three methods were developed to estimate the joint rotation angles. The pos-based method transforms marker positions to a reference coordinate system (RCS) and extracts a hand skeleton to identify the rotation angles. Similarly, the orient-x-based method calculates the rotation angles from the transformed x-orientations of the detected markers in the RCS. In contrast, the orient-mat-based method first identifies the rotation angles in each camera coordinate system using the detected orientations, and then, synthesizes the results regarding each joint. Experiment results indicated that the repeatability errors with one camera regarding different marker sizes were around 2.64 to 27.56 degrees and 0.60 to 2.36 degrees using the marker positions and orientations respectively. When multiple cameras were employed to measure the joint rotation angles, the angles measured by using the three methods were comparable with that measured by a goniometer. Despite larger deviations occurred when using the pos-based method. Further analysis indicated that the results of using the orient-mat-based method can describe more types of joint rotations, and the effectiveness of this method was verified by capturing hand movements of several participants. Thus it is recommended for measuring joint rotation angles in practical setups.

Propagation conditions of 10 MHz signals along the paths between Rostov and Moscow

To determine the conditions for the propagation of HF signals through the ionosphere along various paths, there are several possibilities: (1) ionograms of vertical sounding, (2) ionograms of oblique sounding between transmission and receiver points, (3) receiving signals from transmitters of exact time at fixed frequencies (here ~10 MHz), (4) using ionospheric models. This paper presents the results of a comprehensive study that implements all these possibilities. They refer to the propagation of HF signals on reciprocal paths between Rostov and Moscow during the period of the lowest solar activity of cycle 24 (April-May 2020). It is shown that the maximum usable frequency (MUF) of propagation through the F2 layer of the ionosphere in the overwhelming majority of cases did not exceed 10 MHz both in the experiment and according to model calculations. The signals were propagated through the Es layer. If earlier it was shown that such a joint experiment allows revealing the presence of traveling ionospheric disturbances, the results of this work emphasize the role of the Es layer.

Ponies, Joints, Complexity and the Method of Indifference

An important discipline in biomedical science is the repair of damaged organs by in vitro cultured differentaited stem cells. This article evaluates an article in this field, entitled "The complexity of joint regeneration", by Diloloksumpan et al. (2021), who described a regeneration experiment of artificial damage of the joint of ponies. The experiment failed an I describe the possible cause of this failure by discussing the design of the experiment in the light of J.S.Mill's Method of Difference, published in 1848. I continue with a discussion of the concept of complexity that was introduced by the authors of the paper, by pointing out that three types of complexity may be distinguished; one of these is complicatedness which characterizes the assumed complexity of the joint experiment. I propose that this complicatedness can be solved by the use of the method of difference.

Dynamical signatures from competing, nonadiabatic fragmentation pathways of S-nitrosothiophenol

A joint experiment-theory study of the UV photolysis of S-nitrosothiophenol reveals competing photodissociation pathways that produce NO in its spin–orbit ground state and thiophenoxy radical in either its ground or excited electronic state.