Changes In Direction Of Motion Research Articles

A stochastic model of ant trail formation and maintenance in static and dynamic environments

AbstractColonies of ants can complete complex tasks without the need for centralised control as a result of interactions between individuals and their environment. Particularly remarkable is the process of path selection between the nest and food sources that is essential for successful foraging. We have designed a stochastic model of ant foraging in the absence of direct communication. The motion of ants is governed by two components - a random change in direction of motion that improves ability to explore the environment, and a non-random global indirect interaction component based on pheromone signalling. Our model couples individual-based off-lattice ant simulations with an on-lattice characterisation of the pheromone diffusion. Using numerical simulations we have tested three pheromone-based model alternatives: (1) a single pheromone laid on the way toward the food source and on the way back to the nest; (2) single pheromone laid on the way toward the food source and an internal imperfect compass to navigate toward the nest; (3) two different pheromones, each used for one direction. We have studied the model behaviour in different parameter regimes and tested the ability of our simulated ants to form trails and adapt to environmental changes. The simulated ants behaviour reproduced the behaviours observed experimentally. Furthermore we tested two biological hypotheses on the impact of the quality of the food source on the dynamics. We found that increasing pheromone deposition for the richer food sources has a larger impact on the dynamics than elevation of the ant recruitment level for the richer food sources.

An 8-week injury prevention exercise program combined with change-of-direction technique training limits movement patterns associated with anterior cruciate ligament injury risk

Knee ligament sprains are common during change-of-direction (COD) maneuvers in multidirectional team sports. This study aimed to compare the effects of an 8-week injury prevention exercise program containing COD-specific exercises and a similar program containing linear sprint exercises on injury- and performance-related variables during a 135° COD task. We hypothesized that the COD-specific training would lead to (H1) stronger reductions in biomechanical variables associated with anterior cruciate ligament (ACL) injury risk during COD, i.e. knee abduction moment and angle, hip internal rotation angle and lateral trunk lean, and (H2) more effective improvements in COD performance according to the COD completion time, executed angle, ground contact time, and approach speed. Twenty-two sports science students (40% female) completed biomechanical assessments of COD movement strategies before and after participating in two supervised 25-min training sessions per week over 8 weeks. We observed significant ‘training x group’ interaction effects in support of H1: the COD-specific training but not the linear sprint training led to reduced peak knee abduction moments (interaction, p = 0.027), initial knee abduction (interaction, p < 0.001), and initial lateral trunk lean angles (interaction, p < 0.001) compared to baseline. Although the COD-specific training resulted in sharper executed angles (interaction, p < 0.001), the sprint-specific training group showed reduced COD completion (interaction, p = 0.037) and ground contact times (interaction, p < 0.001). In conclusion, a combination of generic and COD-specific injury prevention training resulted in COD technique adaptations that can help to avoid ACL injury-prone COD movements but may negatively affect COD speed.

FMS 기능성 동작훈련이 중국 대학 에어로빅 선수의 신체자세 조절 능력에 미치는 영향에 관한 실험적 연구

The present study explores the effects of FMS functional movement training on aerobic athletes' body posture coordination, and explores the application of FMS functional movement training to the promotion of aerobic athletes' physical performance. In aerobic exercise, body posture control ability is an important criterion for the expression of technical movements, the display of form art aesthetics, and the evaluation of aerobic competition performance. Physical training is the most basic way to improve body posture control, and FMS functional movement training is an emerging physical training mode in recent years, which attaches more importance to functional training than traditional physical training, does not improve athletes' self-confidence in a purposeful way, and has a relatively good improvement effect on technical movements with relatively high movement requirements.40 college aerobic athletes were randomly divided into two groups: Traditional physical training Group (T, N=20) and FMS functional movement training Group (F, N=20). The control group adopts the traditional physical training method, and the functional training group adopts the training method based on the functional movement design of FMS. The results showed that compared with before training, after the traditional physical training group and the FMS functional movement training group intervened, the subjects' FMS test improved significantly in all six motility movements (P&lt;0.05), but there was no significant difference in the straight bow squat and active orthogonal lifting test (P&gt;0.05). The body posture coordination in the dynamic movement and static movement of aerobics was significantly improved only in the FMS functional movement training group (P&lt;0.05).Conclusion: FMS functional training can relatively well promote aerobic athletes' body control ability and body posture coordination in the movement process, which is suitable for further application and dissemination in the physical fitness training of college aerobic athletes.After 12 weeks of training, the scores of various indicators of the experimental group were significantly higher than those of the control group before the experiment, and the results of the FMS test were significantly improved; the effect of the experimental group was better than that of the control group, reducing the incidence of exercise damage; the physical stability, flexibility and asymmetry of the experimental group athletes were improved, but the effect on active right angle rise and straight lunge squat was not obvious. In the body posture control ability test under the static movement plane change condition, the 8-step ventral bridge, 5-step lateral bridge and hexagonal bridge of the experimental group and the control group showed significant differences, and the experimental configuration results were better than the control group, and the before-and-after comparison of the experimental group was significant.It shows that FMS functional movement training can improve the body posture control ability of aerobic athletes in the static movement plane. In the test of aerobic athletes' body posture control ability under the condition of dynamic movement direction change, the results show that the improvement effect of the T-shaped, W-shaped and Y-shaped tests of aerobic combination steps of the experimental group before and after the experiment is better than that of the control group, and each indicator has a significant difference within the group, indicating that FMS functional movement training has improved the body posture control ability of aerobic athletes.

Does Soundpeaking Affect the Behavior of Chub (Squalius cephalus) and Brown Trout (Salmo trutta)? An Experimental Approach

Increased turbulent flow and sediment transport during flood or hydropeaking events often induces rapid changes in underwater sound pressure levels, which is here referred to as soundpeaking. This study is the first to investigate such a change in the underwater soundscape in relation to fish behavior using an experimental approach. Trials were conducted in an experimental channel stocked with either adult chub (Squalius cephalus) or brown trout (Salmo trutta). To mimic soundpeaking, the underwater soundscape of a small alpine river was recorded during a flood event and later played back through an underwater speaker during treatment trials. Furthermore, trials were recorded with a video camera, and based on the fish position, movement variables (swimming distance, number of movement direction changes, variance of the acceleration), the aggregation of individuals, the longitudinal and the lateral position in the experimental area were compared between control (no sound played) and treatment trials. During treatment trials, brown trout changed their movement direction significantly more often, chub showed a significantly higher variation of the acceleration, and individuals from both species were significantly more aggregated. Furthermore, the soundpeaking treatment had a significant effect on the longitudinal position of brown trout in the experimental area. However, the overall results did not provide any indication for a stronger soundpeaking effect in chub despite being equipped with much more refined hearing abilities in comparison to brown trout. Based on these results and findings from other studies, soundpeaking is discussed as a behavioral trigger as well as a source of acoustic stress.

Effect of motion state variability on error-related potentials during continuous feedback paradigms and their consequences for classification

BackgroundAn erroneous motion would elicit the error-related potential (ErrP) when humans monitor the behavior of the external devices. This EEG modality has been largely applied to brain-computer interface in an active or passive manner with discrete visual feedback. However, the effect of variable motion state on ErrP morphology and classification performance raises concerns when the interaction is conducted with continuous visual feedback. New MethodIn the present study, we designed a cursor control experiment. Participants monitored a continuously moving cursor to reach the target on one side of the screen. Motion state varied multiple times with two factors: (1) motion direction and (2) motion speed. The effects of these two factors on the morphological characteristics and classification performance of ErrP were analyzed. Furthermore, an offline simulation was performed to evaluate the effectiveness of the proposed extended ErrP-decoder in resolving the interference by motion direction changes. ResultsThe statistical analyses revealed that motion direction and motion speed significantly influenced the amplitude of feedback-ERN and frontal-Pe components, while only motion direction significantly affected the classification performance. Comparison with existing methodsSignificant deviation was found in ErrP detection utilizing classical correct-versus-erroneous event training. However, this bias can be alleviated by 16% by the extended ErrP-decoder. ConclusionThe morphology and classification performance of ErrP signal can be affected by motion state variability during continuous feedback paradigms. The results enhance the comprehension of ErrP morphological components and shed light on the detection of BCI’s error behavior in practical continuous control.

The Beep-Speed Illusion Cannot Be Explained With a Simple Selection Bias.

An object appears to move at higher speed than another equally fast object when brief nonspatial tones coincide with its changes in motion direction. We refer to this phenomenon as the beep-speed illusion (Meyerhoff et al., 2022, Cognition, 219, 104978). The origin of this illusion is unclear; however, attentional explanations and potential biases in the response behavior appear to be plausible candidates. In this report, we test a simple bias explanation that emerges from the way the dependent variable is assessed. As the participants have to indicate the faster of the two objects, participants possibly always indicate the audio-visually synchronized object in situations of perceptual uncertainty. Such a response behavior potentially could explain the observed shift in perceived speed. We therefore probed the magnitude of the beep-speed illusion when the participants indicated either the object that appeared to move faster or the object that appeared to move slower. If a simple selection bias would explain the beep-speed illusion, the response pattern should be inverted with the instruction to indicate the slower object. However, contrary to this bias hypothesis, illusion emerged indistinguishably under both instructions. Therefore, simple selection biases cannot explain the beep-speed illusion.

Change of direction deficit is an important indicator for agility test

&lt;p&gt;變向 (change of direction, COD) 是運動員執行多方向移動的必要能力，變向能力可以透過專項訓練、敏捷性訓練、和技術發展提升，俾使競技運動比賽時的戰略成功達到攻防合一。過去發展許多關於變向、敏捷性的測驗，如：折返跑、505敏捷測驗或專業敏捷測驗等，這些田野方法通常用動作時間測量敏捷性，而變向動作則有採用生物力學研究方法的量化分析探討其動作特徵。但是，這些動作時程較長的單一測驗結果，卻也夾雜了衝刺能力、無氧代謝能力等因素。方向變換逆差 (change of direction deficit, CODD) 參數的發展，乃是通過數學的扣除方法，結合了純粹衝刺與變向衝刺等二項測驗的結果，能夠更精準地獲得敏捷能力的指標。本文整合了敏捷測驗、變向技能個別差異與生物力學特徵的過去相關文獻，提供教練員、肌力與體能訓練專家、運動員、體育教師在運動現場監控敏捷表現的資訊，也提醒方向變換逆差的參數是國際正發展評估敏捷能力具高靈敏度及準確度的指標，其信度與效度議題則有發展及探索的價值。&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;&lt;p&gt;Change of direction (COD) is an essential ability for athletes to perform multi-directional locomotion. COD can be enhanced through specific training, agility training, and technique development in order to successfully achieve the tactics of defense and offense within sport activities. Previous studies have developed many COD and agility tests, such as shuttle runs, 505 agility tests, and pro-agility tests. These field tests are used to assess agility by measuring movement time. There has been quantitative analysis of COD movements through a biomechanical approach to identify movement characteristics. However, using single outcome measures with long movement duration can blend the factors of sprint ability and anaerobic capacity. The development of the parameter of change-of-direction deficit (CODD) is a subtractive method in mathematics that combines two measurements to evaluate the index of agility precisely. This article summarizes previously published material on individual differences and biomechanical characteristics of COD skills to provide sport instructors, strength and conditioning specialists, athletes, or physical educators with information to monitor agility performance in the field. CODD is a sensitive and precise indicator for assessing agility. It is worth developing and exploring the issues of reliability and validity.&lt;/p&gt; &lt;p&gt;&amp;nbsp;&lt;/p&gt;

Effects of Game-Specific Demands on Accelerations during Change of Direction Movements: Analysis of Youth Female Soccer

The aim of this study was to assess center of mass (COM) acceleration and movement during change of direction (COD) maneuvers during a competitive soccer game to elucidate situation-specific demands of COD performance. This information can assist in developing soccer-specific tests and training methods. Fifteen elite-level female youth soccer players were tracked for one game with inertial measurement units (IMU) attached to the lower back. COD movements in combination with situational patterns were identified using high-speed video. LASSO regression was used to identify the most important predictors associated with higher vertical peak accelerations (PAv) of the COM during COD movements. COD angle, running speed, contact, and challenge from the opposition were identified as important features related to higher PAv. This study adds to the literature on the demands of COD performance in soccer match-play. The unique approach with game-specific situational data from female youth players provides increased insight into the game-demands of COD and agility performance. PAv in games was higher with larger COD angles, increased running speed, or with contact when the player was challenged by the opposition. A larger study including more games is warranted to increase confidence in using these variables as a basis for training or testing agility.

Effects of athletic socks with high frictional properties on in-shoe foot sliding and performance in football-specific movements

The purpose of this study was to examine the efficacy of high friction socks on in-shoe foot sliding and running performance of male footballers during change of direction movements. Twelve recreational football players (mean age 20.3 ± 1.1 years) completed a 26 m dynamic agility course at their maximum running speed. 3D kinematic and kinetic data were collected for three maximum speed 45° side-cuts, and 180° turns in two different sock conditions. Comparisons were made between a sock with a high static coefficient of friction (GripSock) and a regular sock (CompressionS). The Gripsock condition significantly increased utilized traction (COFu) and a reduction of GRF angle (GRFα) was identified during the braking phase of the side cut (COFu: + 9.3 ± 10%; GRFα: −3.1 ± 2.9%) but not in the side-cut propulsion, turn braking and turn propulsion phases. Speed perception was raised in the GripSock condition (+18 ± 30%). However, wearing a sock with high frictional properties did not significantly reduce in-shoe foot sliding in any examined direction nor did it significantly reduce running times over a functional traction course. The relationship between in-shoe traction and running performance is complex and likely dependent on the overall interaction of shoe properties and the type of athletic sock.

Development of Transmission Control Algorithm for Power Shuttle Transmission System for an Agricultural Tractor

A tractor is a versatile machine and is used in many applications other than agriculture, like in mining, transportation, and construction. One such application is with front end loader where it requires a frequent change in direction of motion. To meet this requirement a power shuttle transmission system is used in agricultural tractors. The present research focuses on the transmission control algorithm development for one such a power shuttle transmission system. The development and testing of the control algorithm were carried out in MATLAB & Simulink environments with an additional specific strategy for the clutch pressure modulation. Further National Instruments CompactRIO (NI-cRIO) was used to verify the system’s functionality in a real-time environment. The obtained simulation results were in close accordance with the real system in terms of system functionality and response time. The alikeness between the simulated and actual response time varies from − 20 to 11% and the tractor intended functionality is verified as per the developed control logic. This research provides an approach for the development of control strategies for tractor transmission systems and their rapid prototype development and testing.

Intra-Positional and Inter-Positional Differences in Agility Tests among Youth Female Volleyball Players

In their structure, indoor sports require quick changes of movement direction. Players should possess a high level of ability to change the direction and speed of movement in response to a stimulus, which is one of the major prerequisites for a high level of performance. During a volleyball match, players are involved in different defensive and offensive activities in which agility plays an important role. The aim of this study was to determine the differences between less successful and more successful youth female volleyball players, as well as their inter-positional and intra-positional differences in agility. The study was conducted on a sample of 204 youth female volleyball players whose mean chronological age was 14.11±0.84 years. The players were divided into 5 subgroups according to their playing position (setters, opposite players, passer-hitters, middle blockers, and libero players). The variable sample used to assess agility consisted of 3 tests: Side steps, 9-3-6-3-9 test, and Step-hop test. Methods of data analysis included the determination of metric characteristics for all three agility tests. The analysis of covariance revealed a significant impact of biological age indicators on all agility tests. Furthermore, discriminant analysis of differences showed that more successful volleyball players achieved better results in all three agility tests. High reliability of the test was determined by Cronbach’s Alpha coefficient (0.87-0.96). The results of this study showed a positive effect of agility tests in differentiating less successful and more successful players regardless of their position. More successful players achieved better results than less successful players in all tests. Greater biological maturity and training experience represent great competitive advantage in this age group. The obtained inter-positional and intra-positional differences and the influence of the biological age indicator on inter-positional and intra-positional differences in agility tests imply that higher biological maturity and training experience are great competitive advantages in this age group. The primary goal of training in younger age groups should not be the current success in the competition, but rather the preparation for achieving the best possible results in senior competition.

Revisiting the color-motion asynchrony.

Color-motion asynchrony (CMA) refers to an illusion in which we perceive a change in color earlier than a change in motion direction when the two changes occur simultaneously. This phenomenon may indicate that color is processed earlier than motion in the visual system. However, the very existence of CMA is under question owing to contradictory findings and methodological deficits in previous studies. Here, we used both the motion and color correspondence tasks (experiment 1) and the temporal order judgment (TOJ) task (experiment 2) to re-examine CMA. Colored dots moved in one direction and changed their color/direction at some time, whereas the relative timing between color and direction changes varied across trials. In the correspondence task, participants reported which direction/color of dots with a particular color/direction lasted longer, the one before or after the change? In the TOJ task, participants reported whether the change in color or the change in motion direction occurred earlier. Results indicated that participants perceived the change in color earlier than the change in motion direction in either the motion or color correspondence task, with a stronger asynchrony in the former. In the TOJ task, although participants showed no difference in psychophysical measures, they responded faster when the change in color occurred before (versus after) the change in direction. Drift-diffusion modeling (DDM) revealed a lower decision threshold when the change in color occurred before (versus after) the change in direction, indicating less cautiousness was excised in judgment when the color changed earlier. These results confirmed the veracity of CMA in different tasks and point to the viability of analyzing response times in traditional psychophysical studies.

The Practicality and Effectiveness of Soccer Scoring Techniques Revealed by Top Elite Soccer Scorers

Background: Although there are 43 soccer scoring techniques (SSTs) identified in the elite soccer games, most of them are overlooked by the current coaching practice. Obviously, the lack of scientific quantification on the fundamental issues related to SSTs could be one of the reasons for the crisis. Therefore, improving coaching practice requires efforts on fundamental researches to supply evidences that can be used to better guide the SST research and the development of SST training systems. Two of the fundamental aspects are the practicality and effectiveness of SSTs. The current study aims to uncover these two aspects. Method: All repeated nominees of the FIFA Puskás Award were selected as study subjects. The terminology system and the identification method developed by Zhang in 2021 were applied in scoring video analysis of the subjects’ career goals. The percentage of goal obtained by each SST (practicality) and ball possessions before shooting for each goal (effectiveness) were determined to reveal the SSTs’ practicality and shooting effectiveness of the top elite scorers. In total, 2315 goals were quantified. Results and Conclusion: The study has unveiled: 1) the practicality is increased if a SST can be applied in shots under all-body-orientation regardless of the ball spatial position at the instant of shooting, 2) the practicality is also associated with the SSTs that can provide either sudden change of ball motion direction at the instant of shooting or unpredictable ball flight, 3) the effectiveness is linked to shots taken with no or one setting of the ball, and 4) the practicality and effectiveness do not always go along with each other and anthropometrically-dependent characteristics should be considered in SST development. As the 1st pilot investigation on the topic, this study would supply a foundation and rich food for speculative thoughts in further explorations that aim to innovatively develop SSTs’ training systems in the future.

Method of Changing Running Direction of Cheetah-Inspired Quadruped Robot.

The rapid change of motion direction during running is beneficial to improving the movement flexibility of the quadruped robot, which is of great relevance to its research. How to make the robot change its motion direction during running and achieve good dynamic stability is a problem to be solved. In this paper, a method to change the running direction of the cheetah-inspired quadruped robot is proposed. Based on the analysis of the running of the cheetah, a dynamic model of the quadruped robot is established, and a two-level stability index system, including a minimum index system and a range index system, is proposed. On this basis, the objective function based on the stability index system and optimization variables, including leg landing points, trunk movement trajectory, and posture change rule, are determined. Through these constraints, the direction changes with good dynamic stability of the cheetah-inspired quadruped robot during running is realized by controlling the leg parameters. The robot will not roll over during high-speed movement. Finally, the correctness of the proposed method is proven by simulation. This paper provides a theoretical basis for the quadruped robot's rapid change of direction in running.

Extracting Human-Exoskeleton Interaction Torque for Cable-Driven Upper-Limb Exoskeleton Equipped With Torque Sensors

Powered exoskeletons have global trends in broad applications, such as rehabilitation and human strength amplification in industry, military, and activities of daily livings. The motion intention of the exoskeleton wearer can be obtained using the interaction force at the physical human-machine interface. This article implements joint torque sensors in a custom-made cable-driven exoskeleton. The model of the torque sensor signal is established to extract the human-exoskeleton interaction (HEI) torque, which can be used to predict the human upper-limb motion intention. To accurately decouple the HEI torque from other components in the torque sensor signal, a nonlinear numerical friction model composed of the cable and joint parts is investigated based on the LuGre friction model. A protocol for parameter identification of the proposed friction model is verified experimentally. Furthermore, a coefficient combining the two friction models is designed for antagonistic directions in a joint to account for the bidirectional cable drive's backlash and hysteresis characteristics. Owing to this coefficient, the error of the friction model is reduced by approximately 90% during motion direction change. Finally, the accuracy of the torque sensor model is verified experimentally, and the root-mean-square error (RMSE) is about 0.038 N·m (2.8%). The RMSE of extracted interaction torque is about 0.25 N·m (8.1%). This article validates the feasibility of extracting HEI torque via a torque sensor implemented in the upper-limb exoskeleton, which can promote the development of new generations of upper-limb exoskeleton for active rehabilitation or assistance and research on intuitive control of exoskeleton in future.

Seeing and extrapolating motion trajectories share common informative activation patterns in primary visual cortex.

The natural environment is dynamic and moving objects become constantly occluded, engaging the brain in a challenging completion process to estimate where and when the object might reappear. Although motion extrapolation is critical in daily life-imagine crossing the street while an approaching car is occluded by a larger standing vehicle-its neural underpinnings are still not well understood. While the engagement of low-level visual cortex during dynamic occlusion has been postulated, most of the previous group-level fMRI-studies failed to find evidence for an involvement of low-level visual areas during occlusion. In this fMRI-study, we therefore used individually defined retinotopic maps and multivariate pattern analysis to characterize the neural basis of visible and occluded changes in motion direction in humans. To this end, participants learned velocity-direction change pairings (slow motion-upwards; fast motion-downwards or vice versa) during a training phase without occlusion and judged the change in stimulus direction, based on its velocity, during a following test phase with occlusion. We find that occluded motion direction can be predicted from the activity patterns during visible motion within low-level visual areas, supporting the notion of a mental representation of motion trajectory in these regions during occlusion.

Are sprint accelerations related to groin injuries? A biomechanical analysis of adolescent soccer players

ABSTRACT Groin injuries have one of the highest incidences in soccer and can be career threatening, especially for adolescents, due to their high recurrence rate. Quick accelerations have been connected to groin injuries along with kicking and change of directions. Purpose of this study was to examine the hip joint kinematics, kinetics and the muscle forces of adductor longus and gracilis during first ground contact of a linear sprint acceleration performed by adolescent soccer players. Twenty-two male participants were investigated with 3D motion capture and two force plates. Inverse dynamics were used to calculate the kinematics, kinetics and muscle forces. The kinematics show a constant extension during the stance phase and a quick transition from an abduction to an adduction movement at 90% stance, which coincides with the highest forces in adductor longus and gracilis. This indicates a high load on the adductor muscles due to eccentric contractions combined with high muscle forces in the adductors. Compared to previously investigated inside passing and change of direction movements, adductor muscle forces and angular velocities are higher in this study. Therefore, it is suggested that sprint accelerations are likely to be connected to the development of groin injuries in adolescent soccer players.

Estimating the time structure of descending activation that generates movements at different speeds.

In targeted movements of the hand, descending activation patterns must not only generate muscle activation but also adjust spinal reflexes from stabilizing the initial to stabilizing the final postural state. We estimate descending activation patterns that change minimally while generating a targeted movement within a given movement time based on a model of the biomechanics, the muscle dynamics, and the stretch reflex. The estimated descending activation patterns predict human movement trajectories quite well. Their temporal structure varies across workspace and with movement speed, from monotonic profiles for slow movements to nonmonotonic profiles for fast movements. Descending activation patterns at different speeds thus do not result from a mere rescaling of invariant templates but reflect varying needs to compensate for interaction torques and muscle dynamics. The virtual attractor trajectories, on which active muscle torques are zero, lie within reachable workspace and are largely invariant when represented in end-effector coordinates. Their temporal structure along movement direction changes from linear ramps to "N-shaped" profiles with increasing movement speed.NEW & NOTEWORTHY The descending activation patterns driving movement must be integrated with spinal reflexes, which would resist movement if left unchanged. We estimate the descending activation patterns at different movement speeds using a model of the stretch reflex and of muscle and limb dynamics. The descending activation patterns we find are temporally structured to compensate for interaction torques as predicted by internal models but also shift the reflex threshold, solving the posture-movement problem.

Study of anisotropy of convective optical underwater turbulence and the effect of the mean water temperature in the presence of a varying temperature gradient on it

In this paper, the anisotropy of optical convective underwater turbulence is investigated in terms of the variance of angle of arrival (AOA) fluctuations of a narrow laser beam propagating through it in different sections of the medium. The collimated laser beam with a wavelength 532 nm and a diameter 1 cm, which passes through a convective underwater turbulence. The turbulence is generated in a water tank with dimensions of 20 cm × 36 cm × 20 cm, which is installed on a flat surface electrical heater. During the experiments, the mean water temperature (MWT) can be changed from room temperature to 34 ∘C by increasing the heater temperature. The use of the heater also generates a temperature gradient in the medium. The laser beam propagates along a horizontal path with a length of 20 cm inside the tank at different altitudes from the heater source, as well as at different distances from one of the side walls of the turbulent medium. After passing the laser beam through the turbulent medium, the fluctuations of the AOA components in the vertical and horizontal directions are measured. From the time series of the measured AOA fluctuations, their variances are determined. The anisotropy of the medium is investigated by comparing the variance of AOA components measured in the vertical and horizontal directions. We show that the variances of both of vertical and horizontal components of the AOA fluctuations are increased with the MWT, and they are saturated at higher MWTs. In addition, different anisotropic behaviors are observed for the variances of the measured AOA fluctuations at the vicinity of the lateral wall and upper surface of the water. At the vicinity of the lateral wall the variances of the AOA fluctuations in the horizontal component are larger, but at the vicinity of the upper surface the variances of the AOA fluctuations in the vertical component are dominant. This behavior may be caused by the change of the convection motion direction in the turbulent fluid.

Edge-Assisted Intelligent Video Compression for Live Aerial Streaming

The ultra-low latency transmission, high speed broadband and ubiquitous access points in modern cities have greatly alleviated the last mile problem of live streaming services. Yet, the sophisticated video compression of high definition videos is still inevitable before transmission, which leads to overwhelming workloads in the light-weighted video collectors. In this paper, we are motivated to explore the computation offloading of live streaming video compression for UAVs, which are featured by limited capacity and fixed trajectory. In particular, the global motion model is utilized for inter frame residual coding instead of motion vector estimation, which usually takes more than 50% computation complexity in traditional H.264/265. We propose an edge-based Joint Video Coding (eJVC) scheme, which can save up to 84.04% encoding complexity of UAV video collector. Specifically, the attention network is used to distinguish foreground blocks and background blocks in the frame. LSTM neural network is used on the edge server to predict the auxiliary data needed by UAV video collector for video coding. In addition, our proposed solution can also accommodate the movement direction change when the control signal is notified in advance. Finally, the prototype system is implemented with the real world data set, and the experiment results show that our proposed solution can significantly save the computation time with little bitrate distortion performance loss.