Direct Tracking Research Articles

Implementation of a novel robust model reference adaptive controller-based MPPT for stand-alone and grid-connected photovoltaic system

ABSTRACT The fast advancement of photovoltaic (PV) power generation technologies led to the integration of solar-based generation systems into several modes of transportation, including aircraft, automobiles, and trains. In these PV systems, solar irradiation levels fluctuate significantly and invalidate specific maximum power point (MPP) tracking (MPPT) control strategies, lowering the energy conversion efficiency. It is evident that the new robust model reference adaptive control (MRAC) proposed in this paper alleviates these problems by reducing tracking direction loss and oscillations near MPP. To evaluate the proposed controller’s performance, MATLAB/Simulink is utilized and compared with well-known techniques (P&O, VSPO, INC, ANFIS, and swarm-based MPPT) under three different modes, i.e. stand-alone, grid-connected, and real-time mode. The proposed scheme has tracking efficacy lies between 99.02% and 99.96% and achieved MPP in just 4 msec under highly fluctuating radiation and temperature conditions. It takes only 0.08 sec to capture the global MPP, which is on average two times faster than swarm-based global MPPT methods. Furthermore, the effectiveness is tested in a 50 kW three-phase grid-connected mode with and without cloud effects in realistic weather situations. Finally, real-time validation on the OPAL-RT simulator demonstrates the proposed technique’s practicality in real-world applications.

Direct tracking of noncircular sources for multiple arrays via improved unscented particle filter method

AbstractDirect tracking problem of moving noncircular sources for multiple arrays is investigated in this study. Here, we propose an improved unscented particle filter (I‐UPF) direct tracking method, which combines system proportional symmetry unscented particle filter and Markov Chain Monte Carlo (MCMC) algorithm. Noncircular sources can extend the dimension of sources matrix, and the direct tracking accuracy is improved. This method uses multiple arrays to receive sources. Firstly, set up a direct tracking model through consecutive time and Doppler information. Subsequently, based on the improved unscented particle filter algorithm, the proposed tracking model is to improve the direct tracking accuracy and reduce computational complexity. Simulation results show that the proposed improved unscented particle filter algorithm for noncircular sources has enhanced tracking accuracy than Markov Chain Monte Carlo unscented particle filter algorithm, Markov Chain Monte Carlo extended Kalman particle filter, and two‐step tracking method.

Numerical simulation of aluminum particle agglomeration near the burning surface of solid propellants

Aluminum is an important additive in solid propellants used to improve energy efficiency, but agglomeration of aluminum particles can reduce the specific impulse of the engine, increase two-phase flow losses and cause ablation of the adiabatic layer. Therefore, it is important to understand the mechanism of formation, mode of movement and particle size characteristics of aluminum agglomerates in solid propellants to study the inhibition of agglomeration. In this paper, a three-dimensional numerical simulation of aluminum particle agglomeration near the burning surface of solid propellants was conducted using the discrete unit method based on direct tracking calculations of the detailed motion of individual particles. The model considered physical processes such as burning surface motion, aluminum particle precipitation, turbulent pulsation and the heating and melting of aluminum particle and used a grid-based contact detection method to accelerate the computational process. The agglomeration process of a solid propellant with specific formulation was experimentally investigated. Aluminum particle aggregates underwent splitting, and the final aluminum particle agglomerates were spherical droplets with typical structure. The agglomeration process of this propellant was investigated by means of a simulation. The accuracy of the agglomeration model was verified by comparing the results of the model for the agglomeration process and the shape and size distribution of agglomerates with available experimental data. Compared with the experimental results, the deviations of the equivalent particle sizes of agglomerates D10, D50, D90, D4,3, and D3,2 obtained by using the simulation results were 6.3%, 6.3%, 9.4%, 7.5% and 6.7%, respectively. The aluminum particle agglomeration model established in this paper can predict the particle size distribution of aluminum agglomerates near the burning surface of solid propellants. The model was also used to further investigate the effects of aluminum particle content, ammonium perchlorate (AP) particle size and environmental pressure on aluminum particle agglomeration. Increasing the aluminum content or AP particle size aggravated aluminum particle agglomeration, whereas increasing pressure weakened it.

In Vivo Tracking of Persistent Organic Pollutants via a Coaxially Integrated and Implanted Photofuel Microsensor.

In vivo tracking of persistent organic pollutants (POPs) is of great significance for assessing their risks to the ecological environment and human health. However, existing in vivo POPs detection methods are limited by the lethal sampling of living organisms, complex sample preparation processes, or bulky testing equipment. Photoelectrochemical (PEC) sensing with the merits of high sensitivity and simple equipment is a fast-developed method for in vivo analysis. A major obstacle for in vivo PEC sensors is the separated implantation of multiple electrodes and a light source, which raises concerns like multielectrode biofouling and electroactive molecules interference in the complex environment, uncertain electrode implant distance, and multiple insertion operations. Here, a coaxially implanted photofuel microsensor was developed by hiding the optical fiber-based photoanode inside the glass capillary-based biocathode, and the model target PCB77 can be detected with an ultralow detection limit (2.8 fg/mL). This unique photoanode-biocathode-light source integrated structure ensures excellent selectivity, good antifouling ability and biocompatibility, high accuracy, and less implant mechanical damage. Combined with a handheld pH meter, our sensor achieved convenient and direct tracking of the bioaccumulation levels of PCB77 in freely swimming fish.

Genomic architecture of migration timing in a long-distance migratory songbird

The impact of climate change on spring phenology poses risks to migratory birds, as migration timing is controlled predominantly by endogenous mechanisms. Despite recent advances in our understanding of the underlying genetic basis of migration timing, the ways that migration timing phenotypes in wild individuals may map to specific genomic regions requires further investigation. We examined the genetic architecture of migration timing in a long-distance migratory songbird (purple martin, Progne subis subis) by integrating genomic data with an extensive dataset of direct migratory tracks. A moderate to large amount of variance in spring migration arrival timing was explained by genomics (proportion of phenotypic variation explained by genomics = 0.74; polygenic score R2 = 0.24). On chromosome 1, a region that was differentiated between migration timing phenotypes contained genes that could facilitate nocturnal flights and act as epigenetic modifiers. Overall, these results advance our understanding of the genomic underpinnings of migration timing.

BirdFlow: Learning seasonal bird movements from eBird data

Abstract Large‐scale monitoring of seasonal animal movement is integral to science, conservation and outreach. However, gathering representative movement data across entire species ranges is frequently intractable. Citizen science databases collect millions of animal observations throughout the year, but it is challenging to infer individual movement behaviour solely from observational data. We present BirdFlow, a probabilistic modelling framework that draws on citizen science data from the eBird database to model the population flows of migratory birds. We apply the model to 11 species of North American birds, using GPS and satellite tracking data to tune and evaluate model performance. We show that BirdFlow models can accurately infer individual seasonal movement behaviour directly from eBird relative abundance estimates. Supplementing the model with a sample of tracking data from wild birds improves performance. Researchers can extract a number of behavioural inferences from model results, including migration routes, timing, connectivity and forecasts. The BirdFlow framework has the potential to advance migration ecology research, boost insights gained from direct tracking studies and serve a number of applied functions in conservation, disease surveillance, aviation and public outreach.

Investigation on the drainage condition within the ballast layer based on 3D CFD simulations

Drainage capability is vital to the performance of ballasted railway tracks. Over the decades, many efforts have been made to develop practical ballast maintenance methods to improve the ballast drainage capability. Although some researchers have attempted to quantify the drainage improvement after a specific maintenance activity, the flow within the ballast lacks thorough understanding. In the study, the effect of five different maintenance activities and the presence of the crosstie on ballast drainage are studied and compared through three-dimensional computational fluid dynamics (CFD) simulations. The five maintenance activities are Cribbing All, Cribbing Interval, Scarifying, Shoulder Cleaning, and Combination. The cleaning profiles of different maintenance activities are based on field practices. The properties of the fouled ballast are derived from the field-collected fouled ballast permeability data to ensure the fidelity of the simulations. Lateral Flow Rate (LaFR) and Longitudinal Flow Rate (LoFR) are introduced to uncover the flow within the ballast layer in both lateral (along with the crosstie) and longitudinal (along with the track) directions. The results suggest that the five maintenance activities affect internal flow characteristics differently. The drainage path within the ballast layer is sensitive to the cleaned volume, and the area, especially the shoulder region is essential for drainage improvement.

Direct Target Joint Detection and Tracking Based on Passive Multi-Static Radar

Traditional target tracking is carried out based on the point measurements extracted from the radar resolution cells. This is not suitable for situations of low signal-to-noise ratio (SNR). In this paper, we aim to investigate the problem of the joint detection and tracking (JDT) of a target by directly using the received signals of passive multi-static radar without feeding the signals to matched filters. To this end, a novel likelihood function is proposed exploiting the statistical properties of coherent processing between the reference and surveillance signals. With such a likelihood function, the particle Bernoulli filter is employed to perform direct JDT (DJDT) of the target. A remarkable feature of the proposed method is that it is able to achieve satisfactory performance when the SNR of received signals is low. Furthermore, the proposed method cannot only achieve the existence and kinematic state of the target, but also the time-varying SNR of each receiver, which serves as an important input for sensor adjustment. The performance of the proposed method is verified via simulations.

Direct Observation and Real-Time Tracking of an Extraordinarily Stable Folding Intermediate in Mitotic Arrest Deficient Protein 2 Folding by Single-Molecule Fluorescence Resonance Energy Transfer.

Although ensemble experiments have suggested that mitotic arrest deficient protein 2 (Mad2), a metamorphic protein, has folding intermediates, direct evidence and characterization are not available. It remains an outstanding challenge to capture the folding intermediates in real time, which is crucial to elucidate the folding mechanism, but the folding intermediates are normally unstable and only exist transiently. By combining confocal-microscopy-based and total internal reflection fluorescence (TIRF)-microscopy-based single-molecule Förster resonance energy transfer (sm-FRET) techniques, we have investigated the folding/unfolding process of Mad2 and captured its folding intermediate at the single-molecule level. This provides direct evidence for the existence of an intermediate along the folding pathway of Mad2. The folding intermediate proved to be extraordinarily stable, with an extremely long average dwell time of 2.3 s under the conditions of 3 M GdmCl at ambient temperature. The folding trajectories obtained from TIRF experiments further suggest that the intermediate is on-pathway to native Mad2.

Direct Tracking of Charge Carrier Drift and Extraction from Perovskite Solar Cells by Means of Transient Electroabsorption Spectroscopy.

The best perovskite solar cells currently demonstrate more than 25% efficiencies, yet many fundamental processes that determine the operation of these devices are still not fully understood. In particular, even though the device performance strongly depends on charge carrier transport across the perovskite layer to selective electrodes, information about this process is still very controversial. Here, we investigate charge carrier motion and extraction from an archetypical CH3NH3PbI3 (MAPI) perovskite solar cell. We use the ultrafast electric-field-modulated transient absorption technique, which allows us to evaluate the electric field dynamics from the time-resolved electroabsorption spectra and to visualize the motion of charge carriers with subpicosecond time resolution. We demonstrate that photogenerated holes drift across the mesoporous TiO2/perovskite layer during hundreds of picoseconds. On the other hand, their extraction into the spiro-OMeTAD hole transporting layer lasts for more than 1 nanosecond, suggesting that the hole extraction is limited by the perovskite/spiro-OMeTAD interface rather than by the hole transport through the perovskite layer. Additionally, we use the ultrafast time-resolved fluorescence technique that reveals fluorescence decay during tens of picoseconds, which we attribute to the spatial separation of electrons and holes.

Algorithmic support of the adaptive system of controlled flight into terrain avoidance (CFITA)

The article considers the restrictions algorithms for the trajectory parameters of aircraft motion. Three groups of algorithms are under consideration. They are distinguished by the volume of airborne database about terrain, modes of aircraft operation. The first group (the full SFITA mode) uses the maximum digital cartographic information (DCI) about the terrain. In the SFITA algorithms, the terrain is approximated in the form of planes in space in some predictable, pre-emptive area in the flight path direction. Terrain following is carried out in space in the assigned direction. The equation of the adjacent plane is solved. The distance, the approach speed, and the time to reach the plane are enumerated. The net acceleration to reduce the approach speed to the plane of restriction is calculated under the specified constraint controls. The required time is calculated to reduce the approach speed towards the obstacle to zero. Having equated the expressions for the time of reaching and the required time, transition towards the distance to the plane of restriction, on which it is imperative to utilize constraint controls. The second group (the major SFITA mode) uses the DCI about the terrain in the direction of track in a pre-emptive area. The terrain is approximated by a line in the plane. The specified normal overload is used as a means of control. Terrain following is conducted in the vertical or slant planes. Subsequently, the same procedures are used as in the first group. The third group (the minimum SFITA mode) does not use DCI. The radio and barometric pressure altimeters are used as information systems about the terrain. The given SFITA mode is selected only for flights in a flat terrain. The algorithm includes the similar procedures as in the first and in the second groups. The analytical analysis, confirming the adaptive properties of algorithmic support based on the fundamental law of uniformly retarded motion, is given. The considered algorithms efficiency is confirmed by a comprehensive amount of simulation. The presented algorithms can become the foundation for developing Russian TAWS analogues.

Measures of effective use of the capacity of twotrack sections of JSC “Uzbekistan Railways”

The article first presents the analysis of the complete structure of all two-track sections of JSC “Uzbekistan Railways” with mixed traffic, and then the proposals of local and foreign scientists regarding the determination of the coefficient of displacement of freight trains from the graph on two-track sections in conditions of mixed traffic of trains are described in detail. In addition, the factors affecting the displacement coefficient of freight trains from the graph were analyzed, as well as the reduction of the time interval of the arrival of freight and high-speed passenger trains that arrive at the separation points in a row in the track direction, and as a result of the organization of train movement based on the technology of connecting, increasing the maximum number of freight trains in the sections suggestions were made regarding the issues.

Kinematic analysis of upper limb coordination during a multi-directional reaching task: specific examination of shoulder girdle movement.

[Purpose] This study was conducted to show the directional specificity of a reaching motion and to verify the three-joint coordination of the sternoclavicular joint, shoulder joint, and elbow joint. [Participants and Methods] The participants in this study were 10 healthy adult males. A reaching task for the upper limbs in a horizontal plane was assessed and measured. The trajectory, joint angle, and joint range of motion were calculated using a three-dimensional motion analyzer. [Results] The joint angle changes of the three joints were related in a circular radiation pattern. The sternoclavicular joint and shoulder joint were related in a fan-shaped radiation pattern. On the other hand, the sternoclavicular joint and elbow joint were related in a linear functional relation except for T3 and T8. [Conclusion] The results suggest that the coordinated motion of the shoulder joint and elbow joint controls the direction and extent of the motion track, while the coordinated motion of the sternoclavicular joint and elbow joint finely regulates the track. There also is a degree of difficulty in motion depending on the direction, which is apparently defined by a combination of joint motions.

Disturbance Rejection Extremum Seeking: A Sliding Mode Control Approach

This paper investigates the sliding mode extremum seeking control problem for nonlinear systems with disturbances to improve the disturbance rejection capability, delivering promising searching accuracy and efficiency under disturbances. The existing results in sliding mode extremum seeking control suffer from the drawback of unsatisfactory transient performance and slow convergence speed when disturbances, especially unmatched disturbances, are injected into the system. To this end, a disturbance rejection sliding mode extremum seeking control approach is proposed in this paper. A nonlinear disturbance observer is developed for disturbance estimation, and then a disturbance rejection sliding mode extremum seeking control algorithm is proposed by exploiting the disturbance estimation. Under the proposed approach, the disturbances can be online estimated and compensated. As a result, the cost function is less disturbed by unknown disturbances, and faster convergence speed as well as shorter recovery time can be obtained. The proposed method is applied for directional antenna automatic tracking system. Simulation results show that the newly proposed searching control approach outperforms the baseline extremum searching approaches in terms of much more reliable and high efficiency searching performance under disturbances.

A TENS Based System for 2-Dimensional Balance Biofeedback Under Muscle Fatigue Condition

Many balance assist or training systems have been developed to improve postural control, however these have limitations such as being bulky or unable to provide 2-dimensional feedback. Furthermore, efficiency of the commonly used vibro-tactile feedback modality can be reduced due to muscle fatigue. Therefore, we suggest a transcutaneous electrical nerve stimulation (TENS) based electro-tactile biofeedback system to provide efficient balance biofeedback even under muscle fatigue condition. A feedback scheme based on Stevens’ power law is devised to provide 2-dimensional feedback using only four electrodes attached to the user’s leg. A pilot test involving the tracking of directions indicated by stimuli was done to select the algorithm appropriate for use in the directional perception test and the balance study. The perception, in 8 directions, of electro-tactile cues delivered using the developed scheme is compared with that of vibro-tactile cues under both normal and fatigued conditions. In addition, we have done standing balance experiments to verify the effectiveness of the developed balance biofeedback scheme. 20 healthy participants took part in these experiments that were conducted under two conditions. The perception results show that under the fatigued condition, the electro-tactile modality is more perceptible than the vibro-tactile modality. Results of the balance biofeedback experiment with no feedback, continuous stimulation with and without dead-zone and directional feedback conditions show that directional electro-tactile feedback helped the most in improving the users’ balance under normal and fatigued conditions. These promising results pave the way for future studies on the applications of this scheme for balance rehabilitation.

Research on Attitude Maneuver and Solar Panel Vibration Suppression of Flexible Satellite

Due to the improvement of the complexity and diversity of modern aviation work, there are more requirements for the large altitude posture, the maneuverability and the accuracy of the tracking direction of flexible satellite for observing and tracking the ground. In this context, this paper discusses the large inclination maneuver attitude control theory and stability method of flexible satellites, and designs a shape memory alloy compression release device, which is expected to be used as a reference for relevant workers.

Thermocapillary migration of thin droplet on wettability-confined track

The thermocapillary migration of droplets on a solid surface is widely used in daily life and industrial fields. Regulating droplet thermocapillary migration by changing surface wettability has received extensive attention. According to the lubrication theory and slip boundary conditions, we establish a mathematical model of the thermocapillary migration dynamics of a droplet on wettability-confined tracks subjected to a uniform temperature gradient. Combined with the contact line dynamics, a method of determining the velocity of the contact line in a different direction of the three-dimensional droplet is proposed, the simulation is carried out with FreeFEM++. The evolution of droplet migration is examined, and the effects of track width and wettability on the droplet migration dynamics are emphatically investigated. The results show that the main part of the droplet moves from the high-temperature region to the low-temperature region, the trailing edge of the droplet forms a small bulge during the movement, and a thin liquid film is formed between the bulge and the main part of the droplet. The droplet spreading perpendicular to the track direction is inhibited and remains pinned after shrinking to the track edge. Negative correlation between the velocity of the advancing contact line and the track width is observed. The velocity of the advancing line first rapidly and then slowly decrease to a steady state. The squeezing effect caused by the wettability confined perpendicular to the track direction accelerates the thermocapillary migration of the droplet on the track in the initial short time. The enhanced track wettability increases the initial velocity of the receding contact line but has little effect on its stable value. The velocity of the advancing contact line is positively correlated with track wettability. Changing the track width is possibly easier to regulate the thermocapillary migration of a droplet than varying the track wettability.

Shadow-Assisted Moving Target Tracking Based on Multidiscriminant Correlation Filters Network in Video SAR

Moving targets always defocus and shift outside the scene in video synthetic aperture radar (video SAR) image sequences. However, the shadows of moving targets are immune to these issues and can reveal the true position of the moving targets. As such, by tracking the shadows of moving targets in the video SAR image sequence, it becomes feasible to keep track of these targets. Nevertheless, due to the small pixel size and time-varying characteristics of the target shadow, current prevailing tracking methods often prove insufficient for direct tracking of the shadow. In this paper, a shadow-assisted tracking method for moving targets based on multilevel discriminant correlation filters network (MDCFnet) is proposed. Primarily, we designed a Reverse Feature Pyramid Network (RFPN) that integrates multiple high-level features into low-level features to obtain multiple features with higher distinguishability and resolution, thereby enhancing the final tracking accuracy and precision. Furthermore, we devised Multi-level Discriminative Correlation Filters (MDCF) to perform filtering tracking under multiple feature maps. Real dataset processing results are provided to demonstrate that the proposed method outperforms other state-of-the-art methods.

Semi-Direct Multimap SLAM System for Real-Time Sparse 3-D Map Reconstruction

The lack of a sufficient number of reliable corners in low-textured environments is a big challenge for classical visual simultaneous localization and mapping (SLAM), especially for point feature-based methods. Many other features (i.e., line and plane segments) are often combined with points to restore an environmental structure. However, using such features requires much computational time. This work focuses on the reliable and high-performance real-time operation of a SLAM system in low-textured scenarios. It proposes a semi-direct multi-map monocular SLAM system (SM-SLAM) that combines direct tracking and feature-based map maintenance with point features and line segments. The proposed system tracks non-keyframes based on a sparse image alignment method for fast tracking, extracts and matches point features and line segments in keyframes for high-quality environment structure and motion optimization. We present an extensive evaluation on two widely-used public datasets and some challenging real-world scenarios. Experimental results show that SM-SLAM can well reconstruct a sparse 3D map with geometrical structure information in 30-40 Hz. Notably, SM-SLAM shows an accuracy improvement of more than 20% than the Oriented FAST and Rotated BRIEF feature-based SLAM (ORB-SLAM) on some low-speed, small-range camera motion datasets and performs well in low-texture scenarios.

Differentially private stochastic gradient descent via compression and memorization

We propose a novel approach for achieving differential privacy for neural network training models through compression and memorization of gradients. The compression technique, which makes gradient vectors sparse, reduces the sensitivity so that differential privacy can be achieved with less noise; whereas the memorization technique, which remembers unused gradient parts, keeps track of the descent direction and thereby maintains the accuracy of the proposed algorithm. Our differentially private algorithm, called dp-memSGD for short, converges mathematically at the same rate of 1/T as standard stochastic gradient descent (SGD) algorithm, where T is the number of training iterations. Experimentally, we demonstrate that dp-memSGD converges with reasonable privacy losses on many benchmark datasets.