A two-dimensional partially coherent geometric model of a distributed radar object

The possibility of the substitution of a two-dimensional distributed radar object by a 4-point partly coherent model is considered. As a criterion of adequacy we accepted the coincidence of the angle noise distribution function for the model and the substituted object. It is shown that the proposed four-point configuration can be represented as two orthogonal equivalent two-point models. Relations are obtained for calculating the parameters (power ratios of the signals and coefficients of the correlation matrix) of the signals of the four-point model through the parameters of the signals of the equivalent two-point models. The signal parameters of the equivalent two-point models can be calculated for the given parameters of the joint distribution of azimuthal and elevation noises. These relations obtained for the two-dimensional model are the result of this work. The results obtained were tested using numerical experiments for the test values of the parameters of the angle noise distribution function. To generate samples of signals whose correlation matrix has the required form the linear transformation method was used. The parameters of the distribution function of the simulated angle noise were estimated by the method of matching moments. The results of numerical experiments confirm the reliability of the obtained ratios. They can be used in mathematical and simulation modeling of distributed radar objects.

Semiautomatically Register MMS LiDAR Points and Panoramic Image Sequence Using Road Lamp and Lane

We propose using the feature points of road lamp and lane to register mobile mapping system (MMS) LiDAR points and panoramic image sequence. Road lamp and lane are the common sobjects on roads; the spatial distributions are regular, and thus our registration method has wide applicability and high precision. First, the road lamp and lane were extracted from the LiDAR points by horizontal grid and reflectance intensity and then by optimizing the endpoints as the feature points of road lamp and lane. Second, the feature points were projected onto the panoramic image by initial parameters and then by extracting corresponding feature points near the projection location. Third, the direct linear transformation method was used to solve the registration model and eliminate mismatching feature points. In the experiments, we compare the accuracy of our registration method with other registration methods by a sequence of panoramic images. The results show that our registration method is effective; the registration accuracy of our method is less than 10 pixels and averaged 5.84 pixels in all 31 panoramic images (4000 × 8000 pixels), which is much less than that of the 56.24 pixels obtained by the original registration method.

Kinematic Analysis of Volleyball Attack in the Net Center with Various Types of Take-Off

The aim of the study was to describe and compare kinematics in two types of execution of attack hit, the goofy approach and regular approach. The research group consisted of players from the Czech Republic’s top league (n = 12, age 28.0 ± 4.3 years, body height 196.6 ± 5.6 cm, body mass 89.7 ± 6.7 kg) divided into two groups according to the individual type of approach in the attack. Analysis of movement was performed by 3D kinematics video analysis, space coordinates were calculated by the DLT (Direct Linear Transformation) method together with interpretation software TEMA Bio 2.3 (Image Systems AB, Sweden). The players started their run-up from a distance of about 4 – 4.5 m from the net with similar maximal vertical velocity (2.91 – 2.96 m⋅s-1). The trajectory of players with goofy approach seemed to be convenient for the rotation of shoulders and hips in the moment of ball contact. Differences between both groups were observed. Players with a goofy approach had a longer flight phase compared to regularly approaching players.

Water Sensation During Passive Propulsion for Expert and Nonexpert Swimmers

This study determined whether expert swimmers, compared with nonexperts, have superior movement perception and physical sensations of propulsion in water. Expert (national level competitors, n = 10) and nonexpert (able to swim 50 m in > 3 styles, n = 10) swimmers estimated distance traveled in water with their eyes closed. Both groups indicated their subjective physical sensations in the water. For each of two trials, two-dimensional coordinates were obtained from video recordings using the two-dimensional direct linear transformation method for calculating changes in speed. The mean absolute error of the difference between the actual and estimated distance traveled in the water was significantly lower for expert swimmers (0.90 ± 0.71 meters) compared with nonexpert swimmers (3.85 ± 0.84 m). Expert swimmers described the sensation of propulsion in water in cutaneous terms as the “sense of flow” and sensation of “skin resistance.” Therefore, expert swimmers appear to have a superior sense of distance during their movement in the water compared with that of nonexpert swimmers. In addition, expert swimmers may have a better perception of movement in water. We propose that expert swimmers integrate sensations and proprioceptive senses, enabling them to better perceive and estimate distance moved through water.

Transformation Method to Control Shear Horizontal Waves

The transformation method is of great interest to control electromagnetic waves and acoustic waves in recent years, but it does not always work to manipulate elastic waves. In this paper, a detailed analysis of controlling the shear horizontal (SH) wave, which is a special form of elastic waves, is presented by employing the transformation method. Two scenarios of setting needed materials are provided, and the equivalence of them is proved theoretically. To reduce the complexity of required material parameters, the case of a changing out-of-plane coordinate is studied. The linear transformation method and the effective medium theory are introduced to control SH waves by using homogeneous and isotropic materials. Moreover, numerical simulations confirm the validity of this approach even in the cases of anisotropic and inhomogeneous background media, which are rarely investigated before. Finally, the multiple transformations method is proposed as a strategy of designing multi-domain and multi-function devices.