Time-varying Position Research Articles

Accounting for binaural detection as a function of masker interaural correlation: effects of center frequency and bandwidth.

Binaural detection was measured as a function of the center frequency, bandwidth, and interaural correlation of masking noise. Thresholds were obtained for 500-Hz or 125-Hz Sπ tonal signals and for the latter stimuli (noise or signal-plus-noise) transposed to 4 kHz. A primary goal was assessment of the generality of van der Heijden and Trahiotis' [J. Acoust. Soc. Am. 101, 1019-1022 (1997)] hypothesis that thresholds could be accounted for by the "additive" masking effects of the underlying No and Nπ components of a masker having an interaural correlation of ρ. Results indicated that (1) the overall patterning of the data depended neither upon center frequency nor whether information was conveyed via the waveform or by its envelope; (2) thresholds for transposed stimuli improved relative to their low-frequency counterparts as bandwidth of the masker was increased; (3) the additivity approach accounted well for the data across stimulus conditions but consistently overestimated MLDs, especially for narrowband maskers; (4) a quantitative approach explicitly taking into account the distributions of time-varying ITD-based lateral positions produced by masker-alone and signal-plus-masker waveforms proved more successful, albeit while employing a larger set of assumptions, parameters, and computational complexity.

Robust adaptive control design for rotorcraft unmanned aerial vehicles based on sliding mode approach

This paper presents a nonlinear robust control design method for a generic rotorcraft unmanned aerial vehicle (RUAV). The control objective is to let the RUAV track some pre-defined time-varying position and heading trajectories. The proposed controller employs feedback linearization process to realize the dynamic decoupling control and applies adaptive sliding mode control to compensate for the parametric uncertainties and external disturbances. The global asymptotical stability is proved via stability analysis. Compared with the cascaded controller, the proposed controller demonstrates a superior tracking performance and robustness through numerical simulation in the presence of parametric uncertainties and unknown disturbances.

Single-cell tracking with PET using a novel trajectory reconstruction algorithm.

Virtually all biomedical applications of positron emission tomography (PET) use images to represent the distribution of a radiotracer. However, PET is increasingly used in cell tracking applications, for which the "imaging" paradigm may not be optimal. Here, we investigate an alternative approach, which consists in reconstructing the time-varying position of individual radiolabeled cells directly from PET measurements. As a proof of concept, we formulate a new algorithm for reconstructing the trajectory of one single moving cell directly from list-mode PET data. We model the trajectory as a 3-D B-spline function of the temporal variable and use nonlinear optimization to minimize the mean-square distance between the trajectory and the recorded list-mode coincidence events. Using Monte Carlo simulations (GATE), we show that this new algorithm can track a single source moving within a small-animal PET system with 3 mm accuracy provided that the activity of the cell [Bq] is greater than four times its velocity [mm/s]. The algorithm outperforms conventional ML-EM as well as the "minimum distance" method used for positron emission particle tracking (PEPT). The new method was also successfully validated using experimentally acquired PET data. In conclusion, we demonstrated the feasibility of a new method for tracking a single moving cell directly from PET list-mode data, at the whole-body level, for physiologically relevant activities and velocities.

Fuzzy-PID control for the position loop of aerial inertially stabilized platform

Due to multiple-source disturbances, frame dynamic characteristics of aerial inertially stabilized platform (ISP) changes, leading to nonlinear and time-varying position loop error. Therefore, conventional PID control with fixed parameters can't bring performance of high accuracy and fast response. In this paper, control strategy that sets Kd at a certain value, and adjusts Kp and Ki in real time is proposed. Meanwhile, a fuzzy-PID controller selecting position loop error and its changing rate as observed value is designed with online modification of proportion and integration parameters. The principle prototype of aerial ISP made by our research group helps to conduct static leveling and dynamic vehicle experiments. The results indicate that overall performance of the platform is improved much for the reason that compared with conventional PID control, the fuzzy-PID control brings faster leveling speed and better steady precision.

Experimental Investigation on Shear Strength of Hooking-type Beam-to-column Joints, Applied in One of High Storage Pallet Racking Systems

The article presents the results of experimental investigation carried on the structural members of a typical high storage racking system. The assessment of the mechanical characteristics and behaviour of the hooking beam-to-column joints were done in terms of shearing strength for one-sided configuration of beams attached. The experiments were performed in accordance with the guidelines contained in European standard EN 15512 “Steel static storage systems. Adjustable pallet racking systems. Principles for structural design”. Shear strength, just right after the bending moment resistance is the basic mechanical parameter, characterizing this type of connections. The specific way the storage systems are performing their function, associated with the use of time-varying position of the beams and the exceptionally high rate of change in the size and position of the loads acting on the joints, tend to in-depth analysis of the shear phenomenon for this type of joints, very rarely used in any other structures.

Containment control of multi-agent systems with time delay

This paper studies the containment control issue of multi-agent systems with time delay. By adopting continuous-time and sampled-data-based control protocols, we establish some necessary and sufficient containment control criteria for multi-agent systems with time delay. For the continuous-time case, our results show that both topology structure and time delay play an important role in the containment control of multi-agent systems, no matter whether the leaders are stationary (first-order system) or dynamic with constant velocity and time-varying position (second-order system). Furthermore, the maximum value of time delay to guarantee the achievement of containment control is given by the Hopf bifurcation theory. Moreover, we extend the results to the sampled-data case. Finally, numerical simulations are given to illustrate our main results.

Consensus of second-order multi-agent systems with a time-varying reference signal via sampled control

For second-order multi-agent systems with both a time-varying reference velocity signal, and time-varying reference position and velocity signals, respectively, this paper studies the corresponding consensus issue in a sampling setting under directed communicated topology. Firstly, necessary and sufficient consensus criteria are established for both cases. Moreover, whether the communicated topology graph has a directed spanning tree has nothing to do with the consensus of multi-agent system with time-varying position and velocity reference signals. Then we further extend the results to the complicated case where the Cartesian coordinate coupling is introduced and give the specific size of Euler angle of the rotation matrix. Finally, numerical examples are given to show the effectiveness of our results.

Asymptotic differentiation of signals in the trajectory tracking control of a differentially flat nonlinear magnetic suspension system

This paper deals with the problem of time-varying desired position reference trajectory tracking tasks for an object in a differentially flat nonlinear magnetic levitation system using position measurements only. A novel scheme for signal differentiation is proposed for asymptotic estimation of velocity and acceleration. This differentiator can be utilized in many control applications of practical engineering systems where the differentiation of any signal is required. The differentiation of signals is combined with a differential flatness-based controller for asymptotic tracking of reference trajectories. Simulation results are provided to show the efficient performance of the proposed differentiator-control scheme. Two issues for reference trajectory tracking tasks are performed. The first one considers the rest-to-rest position transfer problem of the object from a nominal position to another, while the second one focuses on the sinusoidal position trajectory tracking problem.

Vibrational Analysis of Planetary Gear Trains by Finite Element Method

Planetary gear trains produce several advantages, including high speed reduction, compactness, greater load sharing and higher torque to weight ratio, which are used widely in wind turbine, automobiles, robot and other applications. In some important transmission applications, the noise and vibration are key concerns in design. In this paper, a 3D dynamic contact and impact analysis model of planetary gear trains has been proposed. Tooth surface friction, backlash, tolerance of peg hole, and time-varying stiffness were considered in this dynamic model. The ANSYS / LS-DYNA were utilized to analyze the dynamic responses of gear transmission of the planetary gears. The vibration behavior of an actual gear set under dynamic loading was simulated in the dynamic model. The stiffness and elastic deformation of gear teeth are calculated using the finite element method with actual geometry and positions of the gears. The time-varying position of the carrier defined as the vibration and noise source. After impact analysis, the numerical results of vibration of carrier involved with the transient and steady states. Through the Fast Fourier Transform (FFT) methods, frequency spectrums of the transient and steady states of the calculated vibration of planet carrier are obtained for the gearbox designer to avoid the resonance zone.

On-Line Smoothing for an Integrated Navigation System with Low-Cost MEMS Inertial Sensors

The integration of the Inertial Navigation System (INS) and the Global Positioning System (GPS) is widely applied to seamlessly determine the time-variable position and orientation parameters of a system for navigation and mobile mapping applications. For optimal data fusion, the Kalman filter (KF) is often used for real-time applications. Backward smoothing is considered an optimal post-processing procedure. However, in current INS/GPS integration schemes, the KF and smoothing techniques still have some limitations. This article reviews the principles and analyzes the limitations of these estimators. In addition, an on-line smoothing method that overcomes the limitations of previous algorithms is proposed. For verification, an INS/GPS integrated architecture is implemented using a low-cost micro-electro-mechanical systems inertial measurement unit and a single-frequency GPS receiver. GPS signal outages are included in the testing trajectories to evaluate the effectiveness of the proposed method in comparison to conventional schemes.

Hybrid MV-kV 3D respiratory motion tracking during radiation therapy with low imaging dose

A novel real-time adaptive MV-kV imaging framework for image-guided radiation therapy is developed to reduce the thoracic and abdominal tumor targeting uncertainty caused by respiration-induced intrafraction motion with ultra-low patient imaging dose. In our method, continuous stereoscopic MV-kV imaging is used at the beginning of a radiation therapy delivery for several seconds to measure the implanted marker positions. After this stereoscopic imaging period, the kV imager is switched off except for the times when no fiducial marker is detected in the cine-MV images. The 3D time-varying marker positions are estimated by combining the MV 2D projection data and the motion correlations between directional components of marker motion established from the stereoscopic imaging period and updated afterwards; in particular, the most likely position is assumed to be the position on the projection line that has the shortest distance to the first principal component line segment constructed from previous trajectory points. An adaptive windowed auto-regressive prediction is utilized to predict the marker position a short time later (310 ms and 460 ms in this study) to allow for tracking system latency. To demonstrate the feasibility and evaluate the accuracy of the proposed method, computer simulations were performed for both arc and fixed-gantry deliveries using 66 h of retrospective tumor motion data from 42 patients treated for thoracic or abdominal cancers. The simulations reveal that using our hybrid approach, a smaller than 1.2 mm or 1.5 mm root-mean-square tracking error can be achieved at a system latency of 310 ms or 460 ms, respectively. Because the kV imaging is only used for a short period of time in our method, extra patient imaging dose can be reduced by an order of magnitude compared to continuous MV-kV imaging, while the clinical tumor targeting accuracy for thoracic or abdominal cancers is maintained. Furthermore, no additional hardware is required with the proposed method.

Can proprioceptive training improve motor learning?

Recent work has investigated the link between motor learning and sensory function in arm movement control. A number of findings are consistent with the idea that motor learning is associated with systematic changes to proprioception (Haith A, Jackson C, Mial R, Vijayakumar S. Adv Neural Inf Process Syst 21: 593-600, 2008; Ostry DJ, Darainy M, Mattar AA, Wong J, Gribble PL. J Neurosci 30: 5384-5393, 2010; Vahdat S, Darainy M, Milner TE, Ostry DJ. J Neurosci 31: 16907-16915, 2011). Here, we tested whether motor learning could be improved by providing subjects with proprioceptive training on a desired hand trajectory. Subjects were instructed to reproduce both the time-varying position and velocity of novel, complex hand trajectories. Subjects underwent 3 days of training with 90 movement trials per day. Active movement trials were interleaved with demonstration trials. For control subjects, these interleaved demonstration trials consisted of visual demonstration alone. A second group of subjects received visual and proprioceptive demonstration simultaneously; this group was presented with the same visual stimulus, but, in addition, their limb was moved through the target trajectory by a robot using servo control. Subjects who experienced the additional proprioceptive demonstration of the desired trajectory showed greater improvements during training movements than control subjects who only received visual information. This benefit of adding proprioceptive training was seen in both movement speed and position error. Interestingly, additional control subjects who received proprioceptive guidance while actively moving their arm during demonstration trials did not show the same improvement in positional accuracy. These findings support the idea that the addition of proprioceptive training can augment motor learning, and that this benefit is greatest when the subject passively experiences the goal movement.

Heat transfer enhancement analysis of a cylindrical surface by a piezoelectric fan

Piezoelectric fans consist of a thin flexible blade attached to a vibrating piezoelectric patch, and provide an effective means of enhancing the heat transfer in low convective regions. In this study, the characteristics of the three-dimensional heat and fluid flow fields generated by the vibrating fan are examined by performing numerical simulations and experimental measurements. In performing the simulations, the fluid domain is discretized using a dynamic meshing scheme to take account of the time-varying shape and position of the vibrating blade. The results show that two counter-rotating screw-type flow structures on either side of the blade appeared on either edge of the blade, and a pair of asymmetric vortex is formed around the fan tip. The experiment is conducted with a total of eighteen T-type thermocouples attaching to the cylindrical surface to measure the variation of temperature. The experimental and numerical results indicate that the piezoelectric fan improves the heat transfer coefficient by 1.2–2.4 times. Moreover, the augmentation of local heat transfer coefficient can be achieved by 2.85 times.

Design of Embedded Wireless Sensor and its Soft Encapsulation for Embedded Monitoring of Helicopter Planetary Gear Set

Planetary gear set, as an important part of helicopter, is with the characteristics of multi-point and time-varying position engagement. For the revolution of planetary gears round sun gear, directions of vibration and pulse created by tooth damage change continuously. If an accelerometer fixed on the surface of gearbox, the angle between the directions of pulse force and accelerometer sensitivity will change continuously, which will causes that the components of pulse force on the sensitivity direction vary with time and the features of damage are very difficult to extract from the signals. Aiming at this problem, a type of embedded wireless sensor node was designed firstly, which can be fixed on the carrier of planetary gear, and acquires the damage-related vibration signals in a fixed direction of pulse force. Then, to avoid the corrosion of electronic components by the lubrication oil in gearbox, the protect restrictions of the sensor node was investigated and a kind of soft encapsulation method is applied. Finally, real vibration signal is measured and transmitted by the designed and/or encapsulated sensor node. The experiments show that the sensor can measure vibration effectively.

Non-Linear, Non-Gaussian Estimation for INS/GPS Integration

Mobile mapping system (MMS) has developed rapidly over the past two decades. In that system, a direct geo-referencing system using Global Positioning System (GPS) and Inertial Navigation System (INS) is applied to determine the time-variable position and orientation parameters. The Kalman filter or Extended Kalman Filter (EKF) is popularly used as the optimal estimation tool for real-time INS/GPS integrated kinematic position and orientation determination. In such those estimation strategies, linearization and assuming Gaussian distribution are utilized. However, the fact that the state model and measurement model in INS/GPS integration are originally non-linear and the noise arising during operation may be non-Gaussian distribution. This characteristic may lead to the degraded performance of the system utilizing KF or EKF in case of non-linear models and non-Gaussian noises. This paper investigates some of non-linear, non-Gaussian estimation strategies in order to improve the performance of system. Firstly, the fundamental of algorithms will be introduced, those estimation strategies is then applied on simulation scenario to find the optimal method, finally, real data from field test will be implemented for the real aspects and final conclusions.

Analysis of three-dimensional heat and fluid flow induced by piezoelectric fan

In this study, the characteristics of the three-dimensional heat and fluid flow fields generated by the vibrating fan are examined by performing numerical simulations and experimental measurements. This paper considers two different arrangements of the heat source, namely vertical and horizontal. In performing the simulations, the fluid domain is meshed using a dynamic meshing scheme in order to take account of the time-varying shape and position of the vibrating blade. The results show that the interaction between the normal force exerted on the air surrounding the moving blade and the impingement jet flow produced at the blade tip prompts the formation of two counter-rotating screw-type flow circulations on either edge of the blade. An infrared thermal camera is used to measure the temperature distribution on the heated surface to examine the numerical results. It is indicated that the piezoelectric fan improves the heat transfer coefficient by 1.6–3.4 times when the heat source is vertically arranged and 1.8–3.6 times when the heat source is horizontally arranged.

INFLUENCE OF LONG-TERM TAI-CHI CHUAN TRAINING ON STANDING BALANCE IN THE ELDERLY

Tai-Chi Chuan (TCC) is thought to be a low-impact and effective exercise to improve balance capability in the elderly. However, the effects of TCC exercise on balance improvement remain controversial. The purpose of the current study was to investigate the effects of long-term Yang-Style TCC training on balance variables such as stable standing time and center of pressure (COP) movement patterns. Fifteen long-term Yang-Style TCC practitioners and fifteen age-matched adults performed different static balance tests each for 30 seconds. For each test, the time-varying COP positions were measured by two forceplates. The sway area of the COP was described by an equivalent ellipse, the two principal axes of which were obtained by using principal component analysis. The results showed that elderly subjects with long-term Yang-Style TCC training were able to maintain stable standing longer than those without TCC training, with reduced COP sway area during challenging tasks such as single-leg stance and tandem stance. It is suggested that long-term TCC exercise is a good choice in a training program aimed at reducing the risk of falling in the elderly.

Time-Varying Characteristics of Bending Deformation of Work-Piece in the Turning Process

Based on the geometrical description of work-pieces cutting process, the time-varying differential equations of deflection curve under two different conditions were obtained using the singular function: one with thimble and one without thimble constraint. Using the Mathcad software, we have solved the time-varying differential equations analytically and have studied the deflection changing of work piece with the position of turning tool and given the distribution characteristic for the time-varying deflection of each section. The results indicate that (1) the deflection of an arbitrary section is time-varying due to the time-varying position of the turning tool and the time-varying inertia moment; (2) for the shaft with thimble constraint, the position of the maximal deflection is not at the section with turning tool; (3) for the shaft without thimble constraint, when the turning tool is at the free end, the deflection at each section of the work-piece is the maximal compared with the other positions of turning tool.

Electrokinetic techniques applied to electrochemical DNA biosensors

Electrokinetic techniques are contact-free methods currently used in many applications, where precise handling of biological entities, such as cells, bacteria or nucleic acids, is needed. These techniques are based on the effect of electric fields on molecules suspended in a fluid, and the corresponding induced motion, which can be tuned according to some known physical laws and observed behaviours. Increasing interest on the application of such strategies in order to improve the detection of DNA strands has appeared during the recent decades. Classical electrode-based DNA electrochemical biosensors with combined electrokinetic techniques present the advantage of being able to improve the working electrode's bioactive part during their fabrication and also the hybridization yield during the sensor detection phase. This can be achieved by selectively manipulating, driving and directing the molecules towards the electrodes increasing the speed and yield of the floating DNA strands attached to them. On the other hand, this technique can be also used in order to make biosensors reusable, or reconfigurable, by simply inverting its working principle and pulling DNA strands away from the electrodes. Finally, the combination of these techniques with nanostructures, such as nanopores or nanochannels, has recently boosted the appearance of new types of electrochemical sensors that exploit the time-varying position of DNA strands in order to continuously scan these molecules and to detect their properties. This review gives an insight into the main forces involved in DNA electrokinetics and discusses the state of the art and uses of these techniques in recent years.

Time-varying Position Error Compensation of Machine Tools Based on Dynamic Fuzzy Neural Networks

A new time-varying position error compensation method for machine tools based on dynamic fuzzy neural networks(D-FNN) is presented to improve the positioning accuracy of numerical control(NC) machine tools.In view of the complexity of influencing factors of NC machine tool positioning accuracy and the difficulty to obtain fuzzy rules,the D-FNN is improved to fit for multiple-input multiple-output system,and also to automatically online identify and generate fuzzy rules.Through measuring the temperature and positioning accuracy of NC machine tool,a NC machine tool time-varying position error prediction model is build on the basis of the improved D-FNN.Then this model is used to compensate the NC machine tool's positioning error,and its effect is compared with the compensation effect of a radial basis function(RBF) neural network model,which shows that the D-FNN model features high accuracy,strong generalization ability and excellent robustness,thus being more suitable for long-time,high-precision real time compensation of NC machine tools.