Beacon Trajectory Research Articles

4-Dimensional Cone Beam Computed Tomography–Measured Target Motion Underrepresents Actual Motion

Four-dimensional cone beam computed tomography (4DCBCT) facilitates verification of lung tumor motion before each treatment fraction and enables accurate patient setup in lung stereotactic ablative body radiation therapy. This work aims to quantify the real-time motion represented in 4DCBCT, depending on the reconstruction algorithm and the respiratory signal utilized for reconstruction. Eight lung cancer patients were implanted with electromagnetic Calypso beacons in airways close to the tumor, enabling real-time motion measurements. 4DCBCT scans were reconstructed from projections for treatment setup CBCT for 1 to 2 fractions of 8 patients with the Feldkamp-Davis-Kress (FDK) algorithm or the prior image constrained compressed sensing (PICCS) method and internal real-time Calypso beacon trajectories or an external respiratory signal (bellows belt). The real-time beacon centroid ("target") motion was compared with beacon centroid positions segmented in the 4DCBCT reconstructions. We tested the hypotheses that (1) the actual target motion was accurately represented in the reconstructions and (2) the reconstruction/respiratory signal combinations performed similarly in the representation of the real-time motion. On average the target motion was significantly underrepresented and exceeded the 4DCBCT motion for 48%, 25%, and 40% of the time in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions, respectively. The average underrepresentation for the LR, SI, and AP direction was 1.7mm, 4.2mm, and 2.5mm, respectively. No difference could be shown between the reconstruction algorithms or respiratory signals in LR direction (FDK vs PICCS: P=.47, Calypso vs bellows: P=.19), SI direction (FDK vs PICCS: P=.49, Calypso vs bellows: P=.22), and AP direction (FDK vs PICCS: P=.62, Calypso vs bellows: P=.34). The 4DCBCT scans all underrepresented the real-time target motion. The selection of the reconstruction algorithm and respiratory signal for the 4DCBCT reconstruction does not have an impact on the reconstructed motion range.

Optimal mobile beacon trajectories for nodes localisation in wireless sensor networks

The random deployment of nodes is commonly used in wireless sensor networks (WSNs), because of either the hostility of the monitored area or its large scale. However, many applications and protocols are position-based. Hence, it's necessary to determine the position of sensors even after their deployment. Localisation techniques using mobile beacon have been proposed in this context, to localise unknown sensor nodes. However, to save nodes energy it's useful to send an optimal number of messages. Thus, an optimal trajectory of mobile beacon helps to achieve such objective. In this paper, we propose two novel optimal mobile beacon trajectories based on Hilbert curve. The first proposal aims at minimising the trajectory length and improving the localisation accuracy, moreover, the second one minimises both the trajectory and the energy consumption. In this study, we compare the proposed techniques with mobile Hilbert beacon trajectory. The analytical analysis and the performance evaluation with simulations show that our proposed methods improve, compared to the existing methods, the accuracy, the length of trajectories and the energy consumption.

Optimal mobile beacon trajectories for nodes localisation in wireless sensor networks

The random deployment of nodes is commonly used in wireless sensor networks (WSNs), because of either the hostility of the monitored area or its large scale. However, many applications and protocols are position-based. Hence, it's necessary to determine the position of sensors even after their deployment. Localisation techniques using mobile beacon have been proposed in this context, to localise unknown sensor nodes. However, to save nodes energy it's useful to send an optimal number of messages. Thus, an optimal trajectory of mobile beacon helps to achieve such objective. In this paper, we propose two novel optimal mobile beacon trajectories based on Hilbert curve. The first proposal aims at minimising the trajectory length and improving the localisation accuracy, moreover, the second one minimises both the trajectory and the energy consumption. In this study, we compare the proposed techniques with mobile Hilbert beacon trajectory. The analytical analysis and the performance evaluation with simulations show that our proposed methods improve, compared to the existing methods, the accuracy, the length of trajectories and the energy consumption.

Impact of static trajectories on localization in wireless sensor networks

A Wireless Sensor Network (WSN) consists of many sensors that communicate wirelessly to monitor a physical region. Location information is critical essential and indispensable for many applications of WSNs. A promising solution for localizing statically deployed sensors is to benefit from mobile location-aware nodes called beacons. However, the essential problem is to find the optimum path that the mobile beacon should travel in order to improve localization accuracy, time and success as well as energy efficiency. In this paper, we evaluate the performance of five mobile beacon trajectories; Random Way Point, Scan, Hilbert, Circles and Localization algorithm with a Mobile Anchor node based on Trilateration (LMAT) based on three different localization techniques such as Weighted Centroid Localization and trilateration with time priority and accuracy priority. This evaluation aims to find effective and essential properties that the trajectory should have. Our simulations show that a random movement cannot guarantee the performance of localization. The results also show the efficiency of LMAT regarding accuracy, success and collinearity while the Hilbert space filling curve has lower energy consumption. Circles path planning can help to localize unknown sensors faster than others at the expense of lower localization precision.

Superior Path Planning Mechanism for Mobile Beacon-Assisted Localization in Wireless Sensor Networks

In many wireless sensor network applications, such as warning systems or healthcare services, it is necessary to update the captured data with location information. A promising solution for statically deployed sensors is to benefit from mobile beacon-assisted localization. The main challenge is to design and develop an optimum path planning mechanism for a mobile beacon to decrease the required time for determining location, increase the accuracy of the estimated position, and increase the coverage. In this paper, we propose a novel superior path planning mechanism called Z-curve. Our proposed trajectory can successfully localize all deployed sensors with high precision and the shortest required time for localization. We also introduce critical metrics, including the ineffective position rate for further evaluation of mobile beacon trajectories. In addition, we consider an accurate and reliable channel model, which helps to provide more realistic evaluation. Z-curve is compared with five existing path planning schemes based on three different localization techniques such as weighted centroid localization and trilateration with time priority and accuracy priority. Furthermore, the performance of the Z-curve is evaluated at the presence of obstacles and Z-curve obstacle-handling trajectory is proposed to mitigate the obstacle problem on localization. Simulation results show the advantages of our proposed path planning scheme over the existing schemes.

On coherent ice drift features in the southern Beaufort sea

Previous studies have highlighted reversals in the Beaufort Gyre on regional scales during summer months, and more recently, throughout the annual cycle. In this study we investigate coherent ice drift features associated with individual ice beacons during winter 2008 that may be a signature of ice–coast interactions, atmospheric and/or oceanic forcing. Examined in particular are three case studies associated with reversals in ice beacon trajectories in January and April of 2008; case I corresponds to a meander reversal event in January, case II to a loop reversal event in April, and case III to a meander reversal event located to the northeast of the Mackenzie Canyon in April. An assessment of atmospheric and oceanic conditions during these reversal events shows enhanced ocean–sea-ice–atmosphere dynamical coupling during the Case I meander reversal event in January and comparatively weak coupling during the Case II loop and Case III meander reversal event in April. Absolute (single-particle/beacon) and relative (two-particle/beacon) dispersion results demonstrate dominant meridional ice drift displacement and inter-beacon separation for Case I relative to Cases II and III indicative of ice–ice and ice–coast interactions in January. The results from this investigation provide an ice drift case study analysis relevant to, and template for, high-resolution sea ice dynamic modeling studies essential for safety and hazard assessments of transportation routes and shipping lanes, ice forecasting, and nutrient and contaminant transport by sea ice in the Arctic.

Obstacle‐avoidance path planning of a mobile Beacon for localisation

Location is important for most wireless sensor network applications. A potential localisation method uses a mobile beacon instead of numerous static beacons. This method includes planning a beacon trajectory as a fundamental and interesting problem. Obstacles in practical scenarios often restrict the free locomotion of beacons. This study examines the obstacle-avoidance path-planning method, which consists of three stages. First, the network deployment region is partitioned into cells by adaptive cell decomposition, and the corresponding connectivity graph is constructed. Second, a modified max–min ant system algorithm is provided to obtain the approximate shortest global path that covers the connectivity graph. Finally, a sequence of concentric circles of adjustable radii is utilised as the local path within an obstacle-free cell. We prove that all sensor nodes deployed in obstacle-free cells can be localised by using the proposed path. Simulation results show that more than 90% of the sensor nodes in the obstacle-free region can be localised by using the given trajectory.

Dynamic Beacon Mobility Scheduling for Sensor Localization

In mobile-beacon assisted sensor localization, beacon mobility scheduling aims to determine the best beacon trajectory so that each sensor receives sufficient beacon signals and becomes localized with minimum delay. We propose a novel DeteRministic dynamic bEAcon Mobility Scheduling (DREAMS) algorithm, without requiring any prior knowledge of the sensory field. In this algorithm, the beacon trajectory is defined as the track of Depth-First Traversal (DFT) of the network graph, thus deterministic. The mobile beacon performs DFT dynamically, under the instruction of nearby sensors on the fly. It moves from sensor to sensor in an intelligent heuristic manner according to Received Signal Strength (RSS)-based distance measurements. We prove that DREAMS guarantees full localization (every sensor is localized) when the measurements are noise-free, and derive the upper bound of beacon total moving distance in this case. Then, we suggest to apply node elimination and Local Minimum Spanning Tree (LMST) to shorten beacon tour and reduce delay. Further, we extend DREAMS to multibeacon scenarios. Beacons with different coordinate systems compete for localizing sensors. Loser beacons agree on winner beacons' coordinate system, and become cooperative in subsequent localization. All sensors are finally localized in a commonly agreed coordinate systems. Through simulation we show that DREAMS guarantees full localization even with noisy distance measurements. We evaluate its performance on localization delay and communication overhead in comparison with a previously proposed static path-based scheduling method.

Some Algorithms of AUV Positioning Based on One Moving Beacon

The report is devoted to designing of algorithms for AUV mobile navigation system operation. The navigation system includes AUV onboard reckoning system and acoustic positioning system with long base line that uses single moving beacon. The approach is described where at first the initial AUV position and sound velocity in water are estimated and than AUV position is calculated on the base of the Kalman filtering. The algorithm for mobile beacon trajectory creation is discussed that allows minimizing the AUV positioning error. Some modeling results of proposed approach operation are supplemented.

On the scaling laws derived from ice beacon trajectories in the southern Beaufort Sea during the International Polar Year - Circumpolar Flaw Lead study, 2007–2008

[1] Sea ice motion is an important element in mass balance calculations, ice thermodynamic modeling, ice management plans for industry, and ecosystems studies. In the historical literature, sea ice motion in the Beaufort Sea was characterized by a predominantly anticyclonic motion during winter months, with episodic reversals to cyclonic activity during summer. However, recent studies have shown an increase in cyclonic activity throughout the annual cycle. In this paper we examine circulation in the Beaufort Sea based on the trajectories of 22 ice beacons launched in the Franklin Bay area during the International Polar Year - Circumpolar Flaw Lead (IPY-CFL) study during an over-wintering experiment in 2007–2008. Dispersion characteristics of ice motion show that absolute zonal dispersion follows a t2 scaling law characteristic of advection associated with Beaufort Gyre circulation, whereas absolute meridional dispersion follows a scaling law of t5/4 characteristic of floaters and dispersion in 2-D turbulence. Temporal autocorrelations of ice velocity fluctuations highlight definitive timescales with values of 1.2 (0.7) days in the zonal (meridional) direction. Near-Gaussian behavior is reflected in higher-order moments for ice velocity fluctuation probability density functions (pdfs). Non-Gaussian behavior for absolute displacement pdfs indicates spatial heterogeneity in the ice motion fields. Atmospheric forcing of sea ice is explored through analysis of daily North American Regional Reanalysis and in situ wind data, where it is shown that ice in the CFL study region travels with an average speed of approximately 0.2% and an average angle of 51.5° to the right of the surface winds during the 2007–2008 winter. The results from this analysis further demonstrate seasonality in ice drift to wind ratios and angles that corresponds to stress buoy data indicative of increases in internal ice stress and connectivity due to consolidation of the seasonal ice zone to the coast and perennial ice pack during winter in the Beaufort Sea region.

Getting Obstacle Avoidance Trajectory of Mobile Beacon for Localization

Localization is one of the most important technologies in wireless sensor network, and mobile beacon assisted localization is a promising localization method. The mobile beacon trajectory planning is a basic and important problem in these methods. There are many obstacles in the real world, which obstruct the moving of mobile beacon. This paper focuses on the obstacle avoidance trajectory planning scheme. After partitioning the deployment area with fixed cell decomposition, the beacon trajectory are divided into global and local trajectory. The approximate shortest global trajectory is obtained by depth-first search, greedy strategy method and ant colony algorithm, while local trajectory is any existing trajectories. Simulation results show that this method can avoid obstacles in the network deployment area, and the smaller cell size leads to longer beacon trajectory and more localizable sensor nodes.

Designing reduced beacon trajectory for sensor localization

Localization is one of the substantial issues in wireless sensor networks. The key problem for the mobile beacon localization is how to choose the appropriate beacon trajectory. However, little research has been done on it. In this paper, firstly, we deduce the number of positions for a beacon to send a packet according to the acreage of ROI (region of interest); and next we present a novel method based on virtual force to arrange the positions in arbitrary ROI; then we apply TSP (travelling salesman problem) algorithm to the positions sequence to obtain the optimal touring path, i.e. the reduced beacon trajectory. When a mobile beacon moves along the touring path, sending RF signals at every position, the sensors in ROI can work out their position with trilateration. Experimental results demonstrate that the localization method, based on the beacon reduced path, is efficient and has flexible accuracy.

Coronary artery bypass grafting without cardiopulmonary bypass and without interruption of native coronary flow using a novel anastomosis site restraining device (“Octopus”)

Objective. This study assessed the feasibility of coronary artery bypass grafting on the beating heart without interruption of native coronary blood flow using a novel anastomosis site restraining device.Background. Recently, an end-to-side bypass technique was described that does not require interruption of flow in the recipient artery.Methods. By means of a suction device (“Octopus”), in 31 pigs the epicardium was grasped and immobilized through an arm contraption fixed to the operating table. In the first 15 consecutive pigs (study 1), the two-dimensional motion of an epicardial beacon was monitored. In 16 subsequent pigs (study II), an internal mammary artery was grafted under the microscope in two steps to a proximal coronary artery segment, without cardiopulmonary bypass. First, the internal mammary artery was sutured end-to-side to the outside of the coronary artery. Secondly, an orifice was ponched in the partitioning coronary wall by an excimer laser catheter introduced through a temporary side-branch of the internal mammary artery.Results. Study II: During 43 suction periods in four anastomosis areas, immobilization was achieved for 15 to 169 min (> 30 h in total) in 13 open- and 9 closed-chest procedures without hemodynamic deterioration. The area circumscribed by the edges of the beacon trajectory (area in which the anastomosis is to be tracked) was reduced from 73.0 ± 43.0 mm2(mean ± SD) to 1.3 ± 0.5 mm2(p < 0.001) in the open-chest and to 0.2 ± 0.2 mm2in the closed-chest procedure. At 6 weeks, no myocardial or coronary suction lesions were found. Study II: Nonocclusive anastomosis surgery required 25 ± 3 min. No leakage, serious arrhythmias, graft closure or hemodynamic deterioration occurred during the procedure or for 2 h after ligating the coronary artery proximally. At 6 weeks, all seven grafts were patent.Conclusions. Coronary bypass on the beating heart without interruption of coronary flow is feasible. In both open- and in closed-chest procedures, the “Octopus” reduced anastomosis site motion to about 1 × 1 mm without adverse consequences.

Detection of the Labrador current using ice‐floe movement in synthetic aperture radar imagery and ice beacon trajectories

Abstract Two sets of Synthetic Aperture Radar (SAR) images were collected, as part of the Labrador Ice Margin Experiment (LIMEX), over the Newfoundland Shelf on consecutive days in April 1990. Ice movement is detected from the displacement of ice floes between the two images sets and compared with ice drift data from six satellite‐tracked beacons and in situ CTD data. The ice velocity data derived from the SAR images and the beacons are used to generate a map of ice velocity vectors. A streamfunction map of ocean currents is produced by removing the direct wind‐driven component in the ice movement data, and by using an objective analysis method. The resulting flow pattern contains the offshore branch of the Labrador Current with a speed of 30 to 50 cm s−1. The current closely follows the shelf break topography from north to south through the study area (47–50.5°N) as a continuous flow. In comparison, if the wind effect was not removed from the ice velocity data, the calculated Labrador Current north of 50...