Closest Point Of Approach Research Articles

Muon radiography technology for detecting high-Z materials

This paper studies the possibility of using the scattering of cosmic muons to identify threatening high-Z materials. Various scenarios of threat material detection are simulated with the Geant4 toolkit. PoCA (Point of Closest Approach) algorithm reconstructing muon track gives 3D radiography images of the target material. Z-discrimination capability, effects of the placement of high-Z materials, shielding materials inside the cargo, and spatial resolution of position sensitive detector for muon radiography are carefully studied. Our results show that a detector position resolution of 50 μm is good enough for shielded materials detection.

Interaction of Saturn's magnetosphere and its moons: 2. Shape of the Enceladus plume

The Saturnian moons in the inner magnetosphere are immersed in a plasma disk that rotates much faster than the moon's Keplerian speed. The interaction of the rotating plasma with the moons results in a disturbance in the Saturnian magnetospheric plasma that depends on the nature of obstacle that the moon represents. In particular at Enceladus, such perturbations in the magnetic field and flowing plasma enable us to infer the 3‐D shape of the Enceladus plume and its outgassing rate. In this paper, we apply our 3‐D magnetohydrodynamic model to extensively study the effects of different plume and disk plasma conditions on the interaction. By finding the best agreement with the observations of two diagnostic flybys, one with its point of closest approach on the upstream side and the other on the downstream side, we determine the plume intensity and configuration. We find that mass loading in the plume is less efficient close to the surface of the moon, where the neutral density is the highest. For E2 and E5, the opening angle of the plume is about 20°, and the plume is tilted toward the corotating direction. The upstream density has a significant effect on the mass loading rate, while its effect on the magnitude of the magnetic perturbation is less significant. An upstream velocity component in the Saturn direction helps to explain the observed magnetic perturbation in the By component and signals the need to consider Enceladus's effect on the global plasma circulation in addition to the local effect. Quantitative comparisons of the simulated and observed interaction are provided.

Channel Energy Based Estimation of Target Trajectories Using Distributed Sensors With Low Communication Rate

Sensor localization using channel energy measurements of distributed sensors has been studied in various scenarios. However, it is usually assumed that the target does not move significantly during the time needed to collect and process the data from the sensors. We want to estimate the trajectory of a moving target using a network of distributed sensors that measure only the received signal strength (RSS), sampled and as a function of time, without knowledge of the target amplitude/source level. To reduce the communication load, sensors communicate a reduced data set to the fusion center (FC), generated through local processing. It consists of three characteristic parameters: i) the maximum measured amplitude, corresponding to the closest-point-of-approach (CPA); ii) the corresponding time index; and iii) the time it takes for the amplitude to diminish by 6 dB relative to the CPA. To generate the reduced data sets, each sensor calculates a local maximum likelihood (ML) estimate of its parameters. The accuracy of these local estimates can be reasonably described by their respective Fisher information matrices (FIMs). The FC combines the data transmitted by the sensors using a ML-like formulation based on the local FIMs. This results in a heavily nonlinear least-squares problem, which we initialize via geometrical considerations. This approach has a very low communication load, performs comparably to a centralized estimator, and due to the modularized setup, any measurement model at the sensors can be considered.

A Study on the Method of Safe Shiphandling in Violently Rough Sea by Typoon or Hurricane

The object of this study is to develop the method of safe conducting of a vessel through stormy sea when we encounter typoon or hurricane on ocean. The scope of investigation in this paper will be limited to safe maneuvering related only with rolling motions of a vessel. The processes of investigations are as follows; Firstly, we decide a CPA(Closest Point of Approach) with the center of the storm and decide significant wave height(<TEX>$H_{1/3}$</TEX>) by SMB method and then calculate wave height of the highest of 1000 waves(<TEX>$H_{1/1000}$</TEX>) and other data. Secondly, we make mathematical model of rolling motions of the vessel on the stormy sea and calculate the biggest rolling angle of the vessel and etc. Thirdly, we decide the most safe maneuvering method to ride out the stormy sea. By the above mentioned method we are able to calculate the status of the stormy sea and ships motions to be encountered and ride out safely through violently rough sea.

Harbor seals respond with aversion to 69-kHz pings: Implications for weighting procedures for marine mammal noise metrics.

Author Shane tracked cultured white seabass (Atractoscion nobilis) instrumented with 69-kHz ultrasonic coded transmitters (UCTs) in the vicinity of harbor seals (Phoca vitulina), later finding the bones of fish associated with UCTs. This led the authors to suspect that seals had targeted and eaten instrumented fish. To determine whether seals could detect pings, four harbor seals and a ringed seal at SeaWorld San Diego were exposed to pings from two 69-kHz and one 83-kHz UCTs and their spontaneous responses observed. The seals were not expected to respond strongly because most of the energy in the pings was close to the upper limit of hearing, but three of the four harbor seals reacted with aversion to the 69-kHz pinger with the highest source level (147 dB re 1 μPa), swimming into a refuge pool or jumping out of the water. The received level at the closest point of approach was estimated at 20 dB above sensation level or less. The results suggest that seals may be especially responsive to high-frequency tonal signals, and that broadband weighting functions may not consistently yield efficient exposure metrics. [Funded by NOAA; in-kind support from SeaWorld San Diego.]

An analysis of the Doppler shifted aircraft noise signature as measured by a hydrophone located within an evanescent field and implication for localization.

Simultaneous measurements of the acoustic pressure field across the air‐water interface, at site in Puget Sound, WA, are analyzed in terms of the Doppler signature of propeller driven aircraft. Measurements in the 50–300‐Hz range are considered for various aircraft over flights. The Doppler shift recorded in air by a microphone placed 3 m above the air‐water interface is modeled using standard Doppler theory. The hydrophone, placed at a depth 2.5 m below the air‐water interface, reveals two Doppler shifts; one associated with the propagating transmitted acoustic field and the other associated with an evanescent field. A parametrized model for these two observed Doppler shifts is presented, utilizing ray theory and Snell’s law applied to a plane wave decomposition of the source wave fronts with, kH ≫ 1, where H is the source height and k is the wave number. It will be shown that analysis of the underwater acoustic field can be used to determine the altitude and closest point of approach (CPA) of a passing tonal source, with support from experimental data recorded by the hydrophone lying within the detection limits of the evanescent field. [Work supported by Washington Sea Grant and ONR.]

Geoacoustic Inversions of Horizontal and Vertical Line Array Acoustic Data From a Surface Ship Source of Opportunity

The application of an inversion methodology produces the first demonstration of a simultaneous solution for geoacoustic and source track parameters from acoustic data collected in a shallow-water, sandy sediment environment. Inversion solutions from data collected in the 2006 Shallow Water Experiment (SW06) are extracted from noise measurements of a surface ship source on an L-array. The methodology includes a screening algorithm to determine a set of frequencies for the inversion data. In addition, the methodology assesses the accuracy of the inversion solution and incorporates an estimation of parameter value uncertainties. The solution from the inversion of the horizontal component of the L-array data from the surface ship source before its closest point of approach (CPA) is used to construct modeled propagation loss for comparison with observed received level (RL) structure as the source departs from CPA. Inversion of the data from a single element in the vertical component of the L-array produces a solution that agrees with the solution obtained from the inversion of horizontal subaperture data. Also, modeled transmission loss (TL) structure obtained from the single-element inversion solution reproduces the depth dependence of the RL structure observed at other elements of the vertical component of the L-array.

Charge Interaction between Particle-Laden Fluid Interfaces

Experiments are described where two oil/water interfaces laden with charged particles move at close proximity relative to one another. The particles on one of the interfaces were observed to be attracted toward the point of closest approach, forming a denser particle monolayer, while the particles on the opposite interface were repelled away from this point, forming a particle depletion zone. Such particle attraction/repulsion was observed even if one of the interfaces was free of particles. This phenomenon can be explained by the electrostatic interaction between the two interfaces, which causes surface charges (charged particles and ions) to redistribute in order to satisfy surface electric equipotential at each interface. In a forced particle oscillation experiment, we demonstrated the control of charged particle positions on the interface by manipulating charge interaction between interfaces.

An Enhanced CPA Algorithm for Real-Time Target Tracking in Wireless Sensor Networks

Real-time tracking of moving targets using wireless sensor networks has been a challenging problem because of the high velocity of the targets and the limited resources of the sensors. CPA (closest point of approach) algorithms are appropriate for tracking fast-moving targets since the tracking error is roughly inversely proportional to the square root of the target velocity. However, this approach requires a specific node configuration with reference to the target trajectory which may not always be possible in randomly deployed sensor networks. Moreover, our mathematical analysis of the original CPA algorithm shows that it suffers from huge localization errors due to inaccuracies in sensor location and measured CPA times. To address these issues, we propose an enhanced CPA (ECPA) algorithm which requires only five sensors around the target to achieve the reliability and efficiency we want for computing the bearing of the target trajectory, the relative position between the sensors and the trajectory, and the velocity of the target. To validate the ECPA algorithm, we designed and implemented this algorithm over an actual data-centric acoustic sensor network as well as simulating it in an NS-2 simulator. The results of our field experiments and simulations show that we can achieve our goals of detecting the target and predicting its location, velocity and direction of travel with reasonable accuracy.

UAV Conflict Detection and Resolution Based on Geometric Approach

A method of conflict detection and resolution is described by using simple geometric approach. Two VAVs are dealt with and considered as point masses with constant velocity. This paper discusses en route aircraft which are assumed to be linked by real time data bases like ADS-B. With this data base, all DAVs share the information each other. Calculating PCA (Point of Closest Approach), we can evaluate the worst conflict condition between two VAVs. This paper proposes one resolution maneuvering logic, which can be called 'Vector Sharing Resolution'. In case of conflict, using miss distance vector in PCA, we can decide the directions for two VAVs to share the conflict region. With these directions, VAVs are going to maneuver cooperatively. First of all, this paper describes some '2-D' conflict scenarios and then extends to '3-D' conflict scenarios.

Inversions from source of opportunity data collected on horizontal and vertical line arrays.

Environmental and source track parameter values were extracted by coherent spatial and temporal field processing of data from a ship of opportunity source that were recorded on collocated horizontal and vertical arrays. The data were collected during the Shallow Water 2006 (SW06) experiment in a continental shelf, sandy sediment environment with a water depth of approximately 70 m. Inversion solutions for environmental and source track parameter values were obtained from both conventionally and adaptively beamformed subaperture data over a 5‐km range scale. The inversion solution for the data from the source to the closest point of approach (CPA) is presented and compared to the prior information on the seabed parameter values provided by geophysical measurements and inversions using other measured acoustic data. The coherent received field structure for the source departing from CPA is compared to the model predictions obtained from the inversion solution for the seabed parameter values. Inversion soluti...

An Evidence Accumulation Model for Conflict Detection Performance in a Simulated Air Traffic Control Task

The aim of this article is to develop a formal model of conflict detection performance. Our model assumes that participants iteratively sample evidence regarding the state of the world and accumulate it over time. A decision is made when the evidence reaches a threshold that changes over time in response to the increasing urgency of the task. Two experiments were conducted to examine the effects of conflict geometry and timing on response proportions and response time. The model is able to predict the observed pattern of response times, including a nonmonotonic relationship between distance at point of closest approach and response time, as well as effects of angle of approach and relative velocity. The results demonstrate that evidence accumulation models provide a good account of performance on a conflict detection task. Evidence accumulation models are a form of dynamic signal detection theory, allowing for the analysis of response times as well as response proportions, and can be used for simulating human performance on dynamic decision tasks.

The Ship Domain – A Criterion of Navigational Safety Assessment in an Open Sea Area

One of the basic tasks in shipping is to ensure safe navigation of vessels. The concept of the ship domain is of major importance in the assessment of a navigational situation and the avoidance of ship collisions. It is difficult to determine a ship domain as its shape and size depend on a number of factors. One question to be answered before the determination of the ship domain is which method to use: statistical, analytic, or expert method using artificial intelligence tools; other questions are connected with domain interpretation. The authors have analyzed the ship domain as a criterion for the assessment of ship navigational safety in an encounter situation in the open sea. The research results are used to answer some of the questions.Part 2 includes definitions of the ship domain and ship fuzzy domain. Part 3, in turn, presents methods of their determination as well as relevant questions. The results of the authors' research, described in Part 4, make up a basis for the determination of the domain and ship fuzzy domain. These have been determined with the so-called dynamic domains as a point of departure. The criteria of ship domain and closest point of approach are compared and discussed. Encounters of various size ships are considered in Part 5. The research and its results are described. Both ship domains and ship fuzzy domains of encountering ships are analyzed. Then, conclusions have been formulated in relation to the effect of the sizes of encountering ships on the shapes and sizes of their domains. Final conclusions are given in Part 6.

A Probabilistic Algorithm for Multi-aircraft Collision Detection and Resolution in 3-D

This paper presents a real-time algorithm for collision detection, collision avoidance and guidance. Three-dimensional point-mass aircraft models are used. For collision detection, conflict probability is calculated by using the Monte-Carlo Simulation. Time at the closest point of approach(CPA) and distance at CPA are needed to determine the collision probability, being compared to certain threshold values. For collision avoidance, one of possible maneuver options is chosen to minimize the collision probability. For guidance to a designated way-point, proportional navigation guidance law is used. Two scenarios on encounter situation are studied to demonstrate the performance of proposed algorithm.

3차원 일대일 충돌 감지 및 회피 알리고리듬

This paper presents the development of a real-time algorithm for collision detection, collision avoidance and guidance to way-point. Three-dimensional point-mass aircraft models are used. For collision detection, time of closest point of approach(CPA) and distance at CPA are compared to threshold values. For collision avoidance, optimal acceleration input which maximizes the terminal relative distance is calculated based on optimal control theory. For guidance to way-point, proportional navigation guidance, the well-known method, is used. Two scenarios of encounter situation are illustrated to validate performance of proposed algorithm.

Ship's Fuzzy Domain – a Criterion for Navigational Safety in Narrow Fairways

The concept of ship's domain plays an important role in navigating a ship. It is a criterion of safety in the process of making decisions by the navigator – in analyzing and assessing a navigational situation and in performing the right manoeuvre. This concept is particularly useful in restricted areas, including narrow fairways, which results from the fact that in such waters a manoeuvring area is restricted so that the criterion of the closest point of approach (CPA) cannot be used. This author has analyzed definitions of ship's domain and methods of its determination found in the literature on the subject. Then a method of navigational safety assessment using the fuzzy domain concept is proposed in reference to a ship in a restricted area. The concept and method of determination have been, respectively, defined and described. The method is based on relevant navigators' knowledge. The methods and tools for knowledge acquisition and representation make use of artificial intelligence. Ships and navigational areas of various size have been considered.

STOCHASTIC “BEADS ON A STRING” IN THE ACCRETION TAIL OF ARP 285

We present Spitzer infrared, Galaxy Evolution Explorer UV, and Sloan Digitized Sky Survey and Southeastern Association for Research in Astronomy optical images of the peculiar interacting galaxy pair Arp 285 (NGC 2856/4), and compare with a new numerical model of the interaction. We estimate the ages of clumps of star formation in these galaxies using population synthesis models, carefully considering the uncertainties on these ages. This system contains a striking example of on a string: a series of star-formation complexes ~1 kpc apart. These beads are found in a tail-like feature that is perpendicular to the disk of NGC 2856, which implies that it was formed from material accreted from the companion NGC 2854. The extreme blueness of the optical/UV colors and redness of the mid-infrared colors implies very young stellar ages (~4-20 Myr) for these star-forming regions. Spectral decomposition of these beads shows excess emission above the modeled stellar continuum in the 3.6 μm and 4.5 μm bands, indicating either contributions from interstellar matter to these fluxes or a second older stellar population. These clumps have –12.0 < M_B < –10.6, thus they are less luminous than most dwarf galaxies. Our model suggests that bridge material falling into the potential of the companion overshoots the companion. The gas then piles up at apogalacticon before falling back onto the companion, and star formation occurs in the pile-up. There was a time delay of ~500 Myr between the point of closest approach between the two galaxies and the initiation of star formation in this feature. A luminous (M_B ~ –13.6) extended (FWHM ~ 1.3 kpc) bright spot is visible at the northwestern edge of the NGC 2856 disk, with an intermediate stellar population (400-1500 Myr). Our model suggests that this feature is part of a expanding ripple-like arc created by an off-center ring-galaxy-like collision between the two disks.

Equivalence of the waveguide invariant and two path ray theory methods for range prediction based on Lloyd's mirror patterns

For shallow, range‐independent environments where the sound is dominated by low‐order modes, the constant which characterizes the modal interference pattern, the waveguide invariant, is approximately equal to one. The speed of a contact which maintains a constant course and speed as it passes through its closest point of approach (CPA) can be determined from the asymptotic behavior of its tonal frequencies from the Doppler shift. This information can be used along with the change in broadband striation frequencies in a Lloyd's mirror pattern over time to extract the range of the contact as it transits through CPA. If instead of using normal mode theory, the Lloyd's mirror pattern is derived as the coherent interference between a straight‐line direct and surface‐reflected path, a relationship between the striation frequencies and time of a crossing contact can also be derived. This relationship can be shown to be identical to the result obtained from the normal mode approach when the value of the waveguide invariant is equal to one. Thus, the same equations can be used to extract range information from a Lloyd's mirror pattern regardless of contact range as long as the environmental conditions support a waveguide invariant close to one.

Effects of Air Traffic Geometry on Pilots' Conflict Detection With Cockpit Display of Traffic Information

This experiment attempted to identify the features of air traffic geometry that would influence the difficulty and biases of pilots' conflict detection using a cockpit display of traffic information (CDTI). There was previously no systematic study on effects of such features on conflict detection using the CDTI. Twenty-four pilots viewed dynamic encounters between their own aircraft and an intruder aircraft on a simulated CDTI; difficulty was varied by the intruder aircraft's distance and time to closest point of approach (CPA), relative speed, miss distance at CPA, approach side, and conflict angle. Participants estimated the intruder's location at, and its time to, CPA. Effects on three estimation error measures were explored: intruder's miss distance at CPA, orientation at CPA, and time to CPA. (a) Estimation errors increased with slower speeds, longer times to CPA, and longer distances to CPA and with longer miss distances at CPA; (b) the best performance occurred at a conflict angle of 90 degrees; (c) there was a bias to judge conflicts to be more risky than was actually the case; and (d) there was a "distance-over-speed" bias, such that two aircraft farther apart and converging rapidly were perceived as less risky than when they were closer to each other and converging at a slower rate, despite identical time to CPA. Pilots' conflict detection with CDTI was subject to various errors and biases, which has important safety implications. The design of procedures, displays, and decision support tools for the free flight environment needs to take these human performance limitations into account.

Entanglement, avoided crossings, and quantum chaos in an Ising model with a tilted magnetic field

We study a one-dimensional Ising model with a magnetic field and show that tilting the field induces a transition to quantum chaos. We explore the stationary states of this Hamiltonian to show the intimate connection between entanglement and avoided crossings. In general, entanglement gets exchanged between the states undergoing an avoided crossing with an overall enhancement of multipartite entanglement at the closest point of approach, simultaneously accompanied by diminishing two-body entanglement as measured by concurrence. We find that both for stationary as well as nonstationary states, nonintegrability leads to a destruction of two-body correlations and distributes entanglement more globally.