Stationary Reference Point Research Articles

Experimental Verification and Analysis of the Postulate of Relativity in Relativity Theory

According to the postulate of relativity in relativity theory, a flash emits from the light source in a uniformly moving car and returns to the light source after being reflected by the mirror on the roof. The person inside the car thinks that the flash returns to the light source along a vertical line, and the person outside the car thinks that the flash returns to the light source along a curve. The time taken along the two paths is inconsistent. Now, this experiment has proved, the interpretation of the postulate of relativity on light traveling paths is inconsistent with the facts. The light is not affected by any inertial framem, and will not move with the car. Light does not belong to any inertial reference frame, nor affected by any inertial reference frame. Light is different from objects. In the absence of experimental evidence, relativity theory believed that light in the inertial frame obeys Galileo's principle of relativity, which is imprudent and wrong. The laws Galileo summarized in low-velocity macroscopic state do not apply to light. This experiment proves that light travels behind the inertial frame and does not move with the inertial frame. That is, the spatial position where the light is or light travels through is the stationary reference point for the inertial frame.

Self-organization of a wheeled robotic swarm using virtual spring-damper mesh

<p>The article analyzes the problem of self-organization of randomly placed wheeled robots around a stationary reference point, into a given shape of a regular polygon. The paper gives an answer to the question how virtual forces from virtual spring-damper connections between robots allow self-organization of the swarm into the desired shape. The presented method of control is described in detail with the description of i-th robot dynamics and tested numerically and experimentally. The swarm's self-organization is aimed at moving randomly spaced robots with a random frame orientation to a given distance to a reference point, reaching and maintaining a given distance between neighboring robots. The paper presents the results of numerical tests and experimental research and ends with discussion and conclusions. The paper's results could be expanded for applications related to spacial distribution of mobile robots.</p>

WLS algorithm for UAV navigation in satellite‐less environments

This work addresses one of the major challenges in the field of Unmanned Aerial Vehicles (UAVs), which is related to UAV navigation in 3-dimensional indoor environments. This topic is highly relevant due to limited-to-no availability of satellite signals that are usually the main sources used to govern the movement of UAVs in outdoor environments. Instead, the algorithm proposed in this work resorts to terrestrial radio measurements between the UAV and a set of stationary reference points to accomplish accurate navigation. The radio measurements are first exploited to give origin to range information that is used to calculate intersection points between a suitable subset of spheres, which serve as a coarse estimate of the UAV's position. From the intersection points, both azimuth and elevation angle estimates are obtained at each reference point. Finally, by taking advantage of estimated bearing information and applying simple geometry, the localisation problem is formulated according to the Weighted Least Squares (WLS) criterion and solved in closed form. The authors’ simulation results show good performance of the proposed approach, matching or even outperforming the state-of-the-art methods in terms of localisation accuracy with significantly lower computational complexity.

Measurement of Bridge Vibration by UAVs Combined with CNN and KLT Optical-Flow Method

A measurement method of bridge vibration by unmanned aerial vehicles (UAVs) combined with convolutional neural networks (CNNs) and Kanade–Lucas–Tomasi (KLT) optical-flow method is proposed. In this method, the stationary reference points in the structural background are required, a UAV is used to shoot the structure video, and the KLT optical-flow method is used to track the target points on the structure and the background reference points in the video to obtain the coordinates of these points on each frame. Then, the characteristic relationship between the reference points and the target points can be learned by a CNN according to the coordinates of the reference points and the target points, so as to correct the displacement time–history curves of target points containing the false displacement caused by the UAV’s egomotion. Finally, operational modal analysis (OMA) is used to extract the natural frequency of the structure from the displacement signal. In addition, the reliability of UAV measurement combined with CNN is proved by comparing the measurement results of the fixed camera and those of UAV combined with CNN, and the reliability of the KLT optical-flow method is proved by comparing the tracking results of the digital image correlation (DIC) and KLT optical-flow method in the experiment of this paper.

GTRS-Based Algorithm for UAV Navigation in Indoor Environments Employing Range Measurements and Odometry

This work addresses the problem of unmanned aerial vehicle (UAV) navigation in indoor environments. Due to unavailability of satellite signals, the proposed algorithm takes advantage of terrestrial radio measurements between the UAV and a set of stationary reference points, from which it extracts range information, as well as odometry by means of inertial sensors, such as accelerometer. On the one hand, based on maximum a posteriori (MAP) criterion, the range information and accumulated knowledge throughout the UAV's movement are employed to derive a generalized trust region sub-problem (GTRS), that is solved exactly via bisection procedure. On the other hand, by using the UAV's transform in relation to the world, another position estimation is obtained by employing odometry. Finally, the two position estimates are combined through a Kalman filter (KF) to enhance the positioning accuracy and obtain the final UAV's position estimation. The UAV is then navigated to a desired destination, by simply calculating the velocity components in the shortest path. Our results show that the proposed algorithm is robust to various model parameters for high precision (HP) UAV sensors, achieving reasonably good positioning accuracy. Besides, the results corroborate that the proposed algorithm is suitable for real-time applications, consuming (on average) only 21 ms to estimate the UAV position.

Programming the trajectories of machine-tractor units

The control of trajectories of self-propelled agricultural vehicles and machine and tractor units (MTU) is carried out according to certain programs stored in memory of the tractor driver or in the system of autonomous driving. In the tractor driver’s memory, the programs are laid down at the stage of studying and mastering the specialty, and are specified when receiving a task to perform a specific job. A common opinion about programming a trajectory following a previous MTU passage is erroneous as the trace is the coordinate line used to bind the desired trajectory to the terrain. The quality of trajectory driving depends on the tractor’s driver, his experience and qualification but not the system of coordinates. Similarly, for autonomous driving of MTU the possible driving programs must be put into the autonomous system at the design stage, and be specified with settings before work start. The quality of autonomous driving is defined by technological level of a system of autonomous driving, which integral part is the coordinate system. There are various ways to define system of coordinates. The most promising of them is to stationary reference points in the form of underground current-carrying wires. Such systems have the high definition, universality, autonomous waymarks, noise stability and long-term stability. To realize all the advantages of coordinates systems set by underground current-carrying wires it is necessary to determine the location of MTU by point-to-point differential and amplitude method by a projection of magneto-field vector to a cross axis of the tractor or a single-point two-level amplitude and phase method. High programming accuracy is achieved by means of current-carrying wires made by commutable ones, power supply of adjacent wires by counter currents and creation of navigation magnetic field by currents of three adjacent wires, where the middle wire is a contact line. The high definition of the guidelines and the noise immunity of the algorithms allow determining both the path mismatch and the direction of the longitudinal axis of the tractor and the direction of the velocity vector as well. Introduction of these parameters into the control law of steering mechanism allows increasing the stability of systems of autonoumus driving and accuracy of trajectories control of working bodies of technological machine tools.

Robust vision sensor for multi-point displacement monitoring of bridges in the field

Computer vision sensors have great potential for accurate remote displacement monitoring in the field. This paper presents InnoVision, a video image processing technique developed by the authors to address a number of difficulties associated with the application of the vision sensors to monitoring structural displacement responses in the outdoor condition that are rarely comprehensively studied in literatures. First, limited lighting condition in the field presents a challenge to tracking low contrast features on the structural surface using intensity-based template matching algorithms. For tackling this challenge, a gradient based template matching algorithm is formulated. Second, to cost-effectively monitor structural displacements at multiple points using one camera, widely used interpolation subpixel methods are investigated and incorporated into InnoVision. Third, camera vibration in the field causes displacement measurement errors. A practical solution is proposed by applying the multi-point monitoring to track both the structure and a stationary reference point. The effect of the camera vibration can be canceled by subtracting the reference displacement from the structural displacements. Several laboratory and field tests are conducted to evaluate the InnoVision’s performance. One of the field tests is conducted in a challenging low lighting condition at night on a steel girder bridge to validate the robustness of InnoVision in comparison with two other vision sensing methods. Another field test is carried out on the Manhattan Bridge to demonstrate the efficacy of the proposed technique for canceling camera vibration and the capability of InnoVision to simultaneously monitor multiple points under the effect of camera vibration.

Assessment of a bascule lift bridge using digital image correlation

The LaSalle Causeway lift bridge is a 100 year old highway bridge that is integral to the transportation network of Kingston, Ontario, Canada. Rehabilitation of the bridge was planned to address corrosion of the bottom chord and a gap identified at the support of the lifting end. To determine the effectiveness of this rehabilitation, the displacements of the bridge were monitored before and after the rehabilitation, during a static load test, and under regular traffic loading. Since the bridge crosses the Cataraqui River, there are no stationary reference points near midspan from which to measure displacement using conventional sensors. For this reason, digital image correlation was selected as an appropriate monitoring technology. Displacements at the midspan and supports of the bridge were recorded and used to assess the performance of the bridge. The results of this research indicate that the bridge complies with displacement limits and that the rehabilitation of the bridge was successful in rehabilitating the support conditions of the bridge.

No apparent superluminal motion in the first-known jetted tidal disruption event Swift J1644+5734

Abstract The first-known tidal disruption event (TDE) with strong evidence for a relativistic jet – based on extensive multiwavelength campaigns – is Swift J1644+5734. In order to directly measure the apparent speed of the radio jet, we performed very long baseline interferometry (VLBI) observations with the European VLBI network (EVN) at 5 GHz. Our observing strategy was to identify a very nearby and compact radio source with the real-time e-EVN, and then utilize this source as a stationary astrometry reference point in the later five deep EVN observations. With respect to the in-beam source FIRST J1644+5736, we have achieved a statistical astrometric precision about 12 μas (68 per cent confidence level) per epoch. This is one of the best phase-referencing measurements available to date. No proper motion has been detected in the Swift J1644+5734 radio ejecta. We conclude that the apparent average ejection speed between 2012.2 and 2015.2 was less than 0.3c with a confidence level of 99 per cent. This tight limit is direct observational evidence for either a very small viewing angle or a strong jet deceleration due to interactions with a dense circum-nuclear medium, in agreement with some recent theoretical studies.

2-tier in-plane motion correction and out-of-plane motion filtering for contrast-enhanced ultrasound.

Contrast-enhanced ultrasound (CEUS) cines of focal liver lesions (FLLs) can be quantitatively analyzed to measure tumor perfusion on a pixel-by-pixel basis for diagnostic indication. However, CEUS cines acquired freehand and during free breathing cause nonuniform in-plane and out-of-plane motion from frame to frame. These motions create fluctuations in the time-intensity curves (TICs), reducing the accuracy of quantitative measurements. Out-of-plane motion cannot be corrected by image registration in 2-dimensional CEUS and degrades the quality of in-plane motion correction (IPMC). A 2-tier IPMC strategy and adaptive out-of-plane motion filter (OPMF) are proposed to provide a stable correction of nonuniform motion to reduce the impact of motion on quantitative analyses. A total of 22 cines of FLLs were imaged with dual B-mode and contrast specific imaging to acquire a 3-minute TIC. B-mode images were analyzed for motion, and the motion correction was applied to both B-mode and contrast images. For IPMC, the main reference frame was automatically selected for each cine, and subreference frames were selected in each respiratory cycle and sequentially registered toward the main reference frame. All other frames were sequentially registered toward the local subreference frame. Four OPMFs were developed and tested: subsample normalized correlation (NC), subsample sum of absolute differences, mean frame NC, and histogram. The frames that were most dissimilar to the OPMF reference frame using 1 of the 4 above criteria in each respiratory cycle were adaptively removed by thresholding against the low-pass filter of the similarity curve. Out-of-plane motion filter was quantitatively evaluated by an out-of-plane motion metric (OPMM) that measured normalized variance in the high-pass filtered TIC within the tumor region-of-interest with low OPMM being the goal. Results for IPMC and OPMF were qualitatively evaluated by 2 blinded observers who ranked the motion in the cines before and after various combinations of motion correction steps. Quantitative measurements showed that 2-tier IPMC and OPMF improved imaging stability. With IPMC, the NC B-mode metric increased from 0.504 ± 0.149 to 0.585 ± 0.145 over all cines (P < 0.001). Two-tier IPMC also produced better fits on the contrast-specific TIC than industry standard IPMC techniques did (P < 0.02). In-plane motion correction and OPMF were shown to improve goodness of fit for pixel-by-pixel analysis (P < 0.001). Out-of-plane motion filter reduced variance in the contrast-specific signal as shown by a median decrease of 49.8% in the OPMM. Two-tier IPMC and OPMF were also shown to qualitatively reduce motion. Observers consistently ranked cines with IPMC higher than the same cine before IPMC (P < 0.001) as well as ranked cines with OPMF higher than when they were uncorrected. The 2-tier sequential IPMC and adaptive OPMF significantly reduced motion in 3-minute CEUS cines of FLLs, thereby overcoming the challenges of drift and irregular breathing motion in long cines. The 2-tier IPMC strategy provided stable motion correction tolerant of out-of-plane motion throughout the cine by sequentially registering subreference frames that bypassed the motion cycles, thereby overcoming the lack of a nearly stationary reference point in long cines. Out-of-plane motion filter reduced apparent motion by adaptively removing frames imaged off-plane from the automatically selected OPMF reference frame, thereby tolerating nonuniform breathing motion. Selection of the best OPMF by minimizing OPMM effectively reduced motion under a wide variety of motion patterns applicable to clinical CEUS. These semiautomated processes only required user input for region-of-interest selection and can improve the accuracy of quantitative perfusion measurements.

Development of a Wireless Displacement Measurement System Using Acceleration Responses

Displacement measurements are useful information for various engineering applications such as structural health monitoring (SHM), earthquake engineering and system identification. Most existing displacement measurement methods are costly, labor-intensive, and have difficulties particularly when applying to full-scale civil structures because the methods require stationary reference points. Indirect estimation methods converting acceleration to displacement can be a good alternative as acceleration transducers are generally cost-effective, easy to install, and have low noise. However, the application of acceleration-based methods to full-scale civil structures such as long span bridges is challenging due to the need to install cables to connect the sensors to a base station. This article proposes a low-cost wireless displacement measurement system using acceleration. Developed with smart sensors that are low-cost, wireless, and capable of on-board computation, the wireless displacement measurement system has significant potential to impact many applications that need displacement information at multiple locations of a structure. The system implements an FIR-filter type displacement estimation algorithm that can remove low frequency drifts typically caused by numerical integration of discrete acceleration signals. To verify the accuracy and feasibility of the proposed system, laboratory tests are carried out using a shaking table and on a three storey shear building model, experimentally confirming the effectiveness of the proposed system.

Sunlight Intensity Based Global Positioning System for Near-Surface Underwater Sensors

Water monitoring is important in domains including documenting climate change, weather prediction and fishing. This paper presents a simple and energy efficient localization strategy for near surface buoy based sensors. Sensors can be dropped randomly in the ocean and thus self-calibrate in terms of geographic location such that geo-tagged observations of water quality can be made without the need for costly and energy consuming GPS-hardware. The strategy is based on nodes with an accurate clock and light sensors that can regularly sample the level of light intensity. The measurements are fitted into a celestial model of the earth motion around the sun. By identifying the trajectory of the sun across the skies one can accurately determine sunrise and sunset times, and thus extract the longitude and latitude of the sensor. Unlike previous localization techniques for underwater sensors, the current approach does not rely on stationary or mobile reference points.

Mechanism of Paradoxical Ventricular Septal Motion After Coronary Artery Bypass Grafting

Paradoxical septal motion is commonly noted on echocardiography after coronary artery bypass grafting (CABG), but its mechanism is unclear. Cardiac magnetic resonance imaging was performed before and 3 months after CABG in 23 patients. On a mid-left ventricular short-axis cine image, the motion of myocardial landmarks during the cardiac cycle was ascertained relative to a stationary anterior reference point. Before CABG, the movement of the ventricular septum in systole was either posterior or neutral (median -2 mm) in 19 patients, whereas after CABG, the septum moved anteriorly in all 23 patients (+4 mm; p<0.001). (A positive sign indicates anterior motion in ventricular systole, and a negative sign denotes posterior motion.) The motion of the right ventricular free wall was reduced after CABG (-5 vs -3 mm; p=0.002), whereas anterior movement of the lateral left ventricular wall in systole increased (+4 vs +9 mm; p<0.001). There was a positive correlation between degree of anterior movement of the ventricular septum and right ventricular ejection fraction (r=0.47, p=0.023). In conclusion, after CABG, the entire left ventricle translocated anteriorly in systole. Despite preserved right ventricular function, there was restricted motion of the right ventricular free wall suggestive of postoperative adhesions. The pattern of movement observed offers a sound explanation for postoperative paradoxical septal motion.

1012 Cardiac surgery results in anterior translocation of the left ventricle in systole and tethering of the right ventricular free wall – an explanation for post-operative paradoxical septal motion

Methods Patients scheduled for coronary artery bypass surgery were prospectively enrolled to undergo cardiac MRI before and three months after surgery. On a mid left ventricular (LV) short axis cine image the positions of myocardial landmarks were ascertained relative to a stationary anterior reference point. Systolic wall thickening (SWT) in the mid septum was assessed on the same images. Viability images and echocardiography results were also reviewed.

Location of Spinal Cord Pathways That Control Hindlimb Movement Amplitude and Interlimb Coordination During Voluntary Swimming in Turtles

We performed mechanical lesions of the midbody (D2-D3; second to third postcervical spinal segments) spinal cord in otherwise intact turtles to locate spinal cord pathways that 1) activate and control the amplitude of voluntary hindlimb swimming movements and 2) coordinate hindlimb swimming with the movement of other limbs. Pre- and postlesion turtles were held by a band clamp around the carapace just beneath the water surface in a clear Plexiglas tank and videotaped from below so that kinematic measurements could be made of voluntary forward swimming with motion analysis software. Movements of the forelimbs (wrists) and hindlimbs (knees and ankles) were tracked relative to stationary reference points on the plastron to obtain bilateral measurements of hip and forelimb angles as functions of time along with foot trajectories. We measured changes in limb movement amplitude, cycle period, and interlimb phase before and after spinal lesions. Our results indicate that locomotor command signals that activate and regulate the amplitude of voluntary hindlimb swimming travel primarily in the dorsolateral funiculus (DLF) at the D2-D3 level and cross over to drive contralateral hindlimb movements. This suggests that electrical stimulation of the D3 DLF, which was previously shown to evoke swimming movements in the contralateral hindlimb of low-spinal turtles, activated the same locomotor command pathways that the animal uses during voluntary behavior. We also show that forelimb-hindlimb coordination is maintained by longitudinal spinal pathways that are largely confined to the ventrolateral funiculus (VLF) and mediate phase coupling of ipsilateral limbs, presumably by interenlargement propriospinal fibers.

Subkelvin cooling of a gram-sized oscillator

Mechanical oscillators have a long tradition in measuring very small forces, particularly of gravitational nature. Oscillators have thermal energy of kBT∕2 in each degree of freedom. Here, we demonstrate the dynamical cooling of a gram-sized oscillator to 300mK in equivalent temperature, a reduction of noise by a factor of 106 compared to the seismic background level. A simple physical model is provided for the cooling process. We also demonstrate the dynamic control of the oscillator’s eigenfrequency, aiming at providing a stationary reference point for position measurements. The method may find applications in precision measurements of weak forces.

The role of exocentric reference frames in the perception of visual direction

One classic piece of evidence for an efference copy signal of eye position is that a small, positive afterimage viewed in darkness is perceived to move with the eye. When a small stationary reference point is visible the afterimage appears to move relative to the reference point. However, this is true only when the afterimage is localized to a small area. We have observed that when an extended afterimage of a complex scene is generated by a brief, bright flash it does not appear to move, even with large changes in eye position. When subjects were instructed to maintain their direction of gaze, we observed small saccades (typically < 1 deg) and slow drift movements often totalling more than 10 deg over a 30 sec period. When the instructions were to simply inspect the extended afterimage, subjects made larger saccades (up to 5 deg) which were not accompanied by afterimage movement. The smaller movements observed under the first instructions are greater than those observed in the dark or with small afterimages. When a visible reference is present with these large afterimages, the afterimage appears stationary, while the reference point appears to move. Eye position was monitored following the generation of such afterimages. In general, the perceived motion of the stationary reference point was in a direction opposite to the motion of the eye. Similar drift movements of smaller magnitude were observed with localized afterimages, but the motion was attributed to the afterimage. This suggests that with whole scene afterimages, extraretinal information about slow movements and small to moderate saccades is absent or suppressed, and that stationarity is assigned to the complex scene. This indicates a perceptual disposition to rely on visual information (when it is available) for maintaining constancy of visual direction, despite substantial changes in eye position. We found that changes in gaze as large as 13 deg produced no change in reported position of the large scene afterimage. When a small, stationary reference light was present it appeared to move in the afterimage scene in a way consistent with the recorded eye movements. When observers attempted to maintain their direction of gaze, most of the eye movements were slow drift, with occasional small saccades. When the instruction to hold gaze was relaxed, larger saccades up to about 5 deg were observed which were not accompanied by afterimage movement.

Correcting two-dimensional kinematic errors for chick embryonic movements in ovo

In motor behavior studies of chick embryos in ovo, kinematic recording is limited to a single camera system and produces kinematic data that are distorted if out-of-plane movements are not considered. CONVERT is a rule based algorithm designed to calculate 3D limb movements given 2D kinematic data. CONVERT's calculations are based on a stationary reference point, limited translation of the chick embryo's trunk point, a multi-linked model of the body, and approximate limb segment lengths. Simulations indicate CONVERT calculates joint movements from 2D data with a maximum error of 6° compared to a maximum error of 79° if out-of-plane considerations are ignored. The approach used to correct two-dimensional kinematic measurement errors can be readily applied to other experimental conditions that restrict video recording to single camera systems.

An Alternate Solution of the Deformation of a Cylinder Between Two Flat Plates

Using the method of conformal mapping, an alternate solution is obtained for the line contact deformation of a cylinder loaded between two flat plates. In this method, the elastic deformation of two half spaces, assuming an elliptical pressure distribution across the width of contact, does not have to be calculated relative to an arbitrarily selected stationary reference point.

The Role of Vision in Producing Motion Sickness

To investigate the ways in which visual cues affect the sensation of motion, the visual component was isolated by presenting stationary subjects with a moving visual field. This induced a sensation of vection or illusory self-rotation in the subjects. The effect of various visual variables such as the eccentricity of the visual display and the distance of the display from the plane of focus were investigated by varying the position of a stationary visual reference point. More vection was observed when this reference was held by the subject than when it was secured to ground, and when held in the peripheral visual field. Less vection was observed when the reference was held closer to the subject than the moving visual display. In addition to establishing the role of visual cues in the perception of motion, these results can be helpful in inducing or inhibiting the sensation of motion through visual displays.