Position Uncertainty Research Articles

Joint Localization and Environment Sensing of Rigid Body With 5G Millimeter Wave MIMO

Accurately localizing a target in three-dimensional (3D) space assisted with the fifth generation (5G) wireless systems in an indoor environment could enable a wide variety of new applications, including precise control for factory automation, self-maneuver of the vehicle and so on. However, controlling a target in 3D space relies on a rigid body modelling with six degrees of freedom, which dramatically increases the localization difficulty and complexity. Furthermore, for radio-based localization methods, the lack of line-of-sight (LOS) and the existence of reflection points in the environment will also influence the rigid body localization process. To improve the rigid body localization accuracy as well as unravel useful environmental information from the received signal, a novel rigid body joint active localization and environment sensing scheme is proposed in this paper. Specifically, the multi-path effect of millimeter wave (mm-wave) signal with a single reflection can be exploited to enhance the rigid body localization accuracy, and it can also be utilized to locate the reflection points, which further enables a new way for environmental sensing. Hence, we first propose a two-step hierarchical compressive sensing algorithm to extract the angular and distance information of the LOS (if available) and single-bounce specular reflections. Then a particle swarm optimization (PSO) based method is derived to recover the posture of the rigid body and the location of reflection points. The Cramér-Rao lower bound (CRLB) on angle, rigid body posture and reflection points position uncertainty is also analyzed. The simulation results demonstrate that the proposed scheme can achieve high accuracy rigid body localization and locate the reflection points around the rigid body even under obstructed-line-of-sight (OLOS) conditions in an indoor scene.

Design of 3D-printed universal oral stent for tongue immobilization in head and neck radiotherapy

The primary treatment for head and neck cancer is radiotherapy, which can cause complications and effects, such as the ability to speak, taste, produce saliva, and swallow. An oral stent is an immobilization tool for minimizing the dose in the tongue (or hard palate) by locking the tongue position during radiation delivery. It can improve the treatment accuracy due to less uncertainty caused by tongue position uncertainty between treatment fractions. However, commercial oral stents are not widely adopted in developing countries due to their unaffordable price. This study aimed to design the universal oral stent (UOS) to achieve high efficiency, ease to use, and low-cost fabrication based on 3D printing technology. There were five experiments to evaluate the UOS design and fabrication versus the modified cut syringe, including finite element analysis (FEA), the usability test, the micro Vickers hardness test, single beam dose analysis, and dose calculation on treatment plan simulations. The proposed UOS design and fabrication presented a high capability to apply for clinical use.

Overcoming separation between counterparts due to unknown proper motions in catalogue cross-matching

Abstract To perform precise and accurate photometric catalogue cross-matches – assigning counterparts between two separate data sets – we need to describe all possible sources of uncertainty in object position. With ever-increasing time baselines between observations, like 2MASS in 2001 and the next generation of surveys, such as the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST), Euclid, and the Nancy Grace Romantelescope, it is crucial that we can robustly describe and model the effects of stellar motions on source positions in photometric catalogues. While Gaia has revolutionized astronomy with its high-precision astrometry, it will only provide motions for ≈10 per cent of LSST sources; additionally, LSST itself will not be able to provide high-quality motion information for sources below its single-visit depth, and other surveys may measure no motions at all. This leaves large numbers of objects with potentially significant positional drifts that may incorrectly lead matching algorithms to deem two detections too far separated on the sky to be counterparts. To overcome this, in this paper, we describe a model for the statistical distribution of on-sky motions of sources of given sky coordinates and brightness, allowing for the cross-match process to take into account this extra potential separation between Galactic sources. We further detail how to fold these probabilistic proper motions into Bayesian cross-matching frameworks, such as those of Wilson & Naylor. This will vastly improve the recovery of, for example, very red objects across optical-infrared matches, and decrease the false match rate of photometric catalogue counterpart assignment.

Quantum uncertainty effects in the dynamics of supercooled liquids: A molecular dynamics study.

Dynamics of density fluctuations in quantum supercooled liquids is analyzed using molecular dynamics simulations. In contrast to the classical case, the uncertainty in the particle position (delocalization of quantum particle in space) leads to significant differences in the dynamics of quantum liquids, both in the short- and long-time limits. The effect of uncertainty is found to be significant for length scales smaller than the uncertainty itself, and diminishes as the length scale grows. The dynamic heterogeneity of the system at short times is enhanced due to uncertainty. In the intermediate (β-relaxation) time regime, the heterogeneity tends to get suppressed due to quantum uncertainty. The probability distribution of particle displacements shows highly nonclassical behavior with double-peak structure at short timescales.

A Robust Model Predictive Control for Virtual Coupling in Train Sets

In recent decades, the demand for rail transport has been growing steadily and faces a double problem. Not only must the transport capacity be increased, but also a more flexible service is needed to meet the real demand. Both objectives can be achieved through virtual coupling (VC), which is an evolution of the current moving block systems. Trains under VC can run much closer together, forming what is called a virtually coupled train set (VCTS). In this paper, we propose an approach in which virtual coupling is implemented via model predictive control (MPC). For this purpose, we define a robust controller that can predict, based on a dynamic model of the train, the state of the system at later moments of time and make the appropriate control decisions. A robust MPC (RMPC) is obtained by introducing two uncertain variables. The first uncertain variable is added to the acceleration equation of the dynamic model, while the second uncertain variable is used to define the uncertainty in the train positioning. To test the RMPC for virtual coupling, two simulation cases are performed for a metro line, analysing the influence of both the uncertainties. In all cases, the results obtained show a safer operation of the virtual coupling without significantly affecting the service.

‘But then again, in the end, I decided to apply for redress’: stories of ambivalence from survivors of institutional abuse

ABSTRACT Historical abuse of children in institutional settings has increasingly been recognized as a serious issue requiring redress and reparations for survivors. This article explores the experiences of survivors of institutional childhood abuse, when they decide to apply for redress. Norwegian redress programmes are part of an international wave of survivor remedy and compensation. There is a lack of research on survivors’ experiences in this area. Data for this study were derived from qualitative interviews with 11 claimants (aged 27 to 70) of redress programmes in Norway. When we explored how our research participants experienced advocating for and applying for redress programmes, we saw that the process leading up to the decision to apply was characterized by ambivalence. By applying the theoretical concept of ‘victim capital’, we investigated the experiences and rationale of participants’ ambivalence during this decision process. Findings showed their ambivalence was centred around four themes: i) uncertainty of victim position, ii) doubt about responsibility, iii) scepticism about personal and interpersonal resources, and iv) hesitancy regarding monetary payments. As survivors seem to go through exhausting personal and social processes before even deciding to apply, we argue that information about programmes needs to be extensive, and that support during the process should be comprehensive.

Method Research and Structural Design of Segmented Shrimp Clamping

Clamping is the key factor that restricts the full-process mechanization of directional shrimp peeling. To solve the problem of difficult clamping caused by the uncertainty of shrimp position after orientation, a segmented shrimp clamping method was proposed by analyzing the relationship between shrimp conveying and clamping conditions. The contact force relationship on the shrimp meat was deduced based on mechanical analysis of the clamping process, and it was concluded that the number of segmented clamping units should be increased during the clamping process to reduce the pressure of the clamping units on the shrimp meat. A segmented shrimp clamping mechanism was designed for adaptive shrimp clamping, conveying and discharging. The profile curve model of the clamping surface was built by analyzing the shrimp section profile characteristics. According to ADAMS kinematics simulation analysis, no shrimp fell off or was damaged during the clamping process, which verified the design rationality of the segmented shrimp clamping mechanism. According to the single-factor test on a newly built shrimp clamping test bench, the optimal rotation speed range of the segmented clamping mechanism was found to be 10–20 r/min, the clamping success rate was over 92%, and the shrimp integrity rate was no less than 99%. The comparison test and performance test results showed that the segmented clamping mechanism had stronger adaptability and better clamping effect under the condition of variable interval feeding. Therefore, the segmented clamping mechanism is capable of practical application and can create stable clamping conditions for shrimp peeling.

Dispersion of Ultrarelativistic Tardyonic and Tachyonic Wave Packets on Cosmic Scales

We investigate the time propagation of tachyonic (superluminal) and tardyonic (subluminal, ordinary) massive wave packets on cosmic scales. A normalizable wave packet cannot be monochromatic in momentum space and thus acquires a positional uncertainty (or packet width) that increases with travel distance. We investigate the question of how this positional uncertainty affects the uncertainty in the detection time for cosmic radiation on Earth. In the ultrarelativistic limit, we find a unified result, δx(t)/c3=m2δpt/p03, where δx(t) is the positional uncertainty, m is the mass parameter, δp is the initial momentum spread of the wave function, and p0 is the central momentum of the wave packet, which, in the ultrarelativistic limit, is equal to its energy. This result is valid for tachyons and tardyons; its interpretation is being discussed.

Fluctuation effects on the plasma density profiles measured by using a frequency modulated continuous wave reflectometer

Scanning diagnostics requires that for the correct measurement the target should not move during the scan. However, even if a frequency modulated continuous wave reflectometer is operated with a frequency modulation (FM) time of 10 µs, the high-temperature fusion plasma fluctuates even for such a short duration. The fluctuation effect on the reflectometer measurements is investigated by simulating the reflectometer response for various plasma conditions. Because the uncertainty of the zero density position might give an additional distortion to the reconstructed profile, this effect is also investigated. The simulation results show that the density profile reconstruction is not very sensitive to the zero density position but very sensitive to the fluctuations. The FM rate must be 100 times faster than the fluctuation frequency in order to suppress the radial distortion below about 20% of the fluctuation radial amplitude. An algorithm is proposed to reduce the distortion more effectively even at much lower FM rates. The distortion is canceled out by averaging two profiles, one of which is measured as increasing the frequency and the other as decreasing the frequency. The algorithm is applied to the experimental data analysis to confirm the simulation results. Through this study, it is concluded that the FM time of the Korea Superconducting Tokamak Advanced Research reflectometer should be reduced to 2 µs to be able to measure the H-mode plasma density profiles.

Detection of Targets in Complex Backgrounds: Partial Whitening, Reliability Weighting, and Intrinsic Position Uncertainty

Detection of Targets in Complex Backgrounds: Partial Whitening, Reliability Weighting, and Intrinsic Position Uncertainty

Dynamic obstacle avoidance for Multi-rotor UAV using chance-constraints based on obstacle velocity

To ensure the safety of autonomous Multi-rotor UAVs flying in urban airspace, they should be capable of avoiding collisions with unpredictable dynamic obstacles, such as birds. UAVs must consider both relative position and relative velocity to avoid moving obstacles. Model predictive control (MPC) can consider the multiple collision avoidance constraints in a constrained optimisation framework. This study proposes a chance-constraints based on obstacle velocity (CCOV) method, which can be combined with previous positional chance constraint methods to account for uncertainty in both position and velocity. This effectively prevents collision with high-velocity obstacles, even in a noisy environment. The proposed method has been performed on a numerical simulation built in MATLAB.

Estimation of soil radioactivity-depth profiles using Bayesian inversion of borehole gamma spectrometry data

Inversion of in situ borehole gamma spectrometry data is a faster and relatively less laborious method for calculating the vertical distribution of radioactivity in soil than conventional soil sampling method. However, the efficiency calculation of a detector for such measurements is a challenging task due to spatial and temporal variation of the soil properties and other measurement parameters. In this study, the sensitivity of different soil characteristics and measurement parameters on simulated efficiencies for a 662 keV photon peak were investigated. In addition, a Bayesian data inversion with a Gaussian process model was used to calculate the activity concentration of 137Cs and its uncertainty considering the sources of uncertainty identified during the sensitivity analysis, including soil density, borehole radius, and the uncertainty in detector position in the borehole. Several soil samples were also collected from the borehole and surrounding area, and 137Cs activity concentration was measured to compare with the inversion results. The calculated 137Cs activity concentrations agree well with those obtained from soil samples. Therefore, it can be concluded that the vertical radioactivity distribution can be calculated using the probabilistic method using in situ gamma spectrometric measurements.

Orbital error propagation considering atmospheric density uncertainty

Due to the influence of various errors, the orbital uncertainty propagation of artificial celestial objects while orbit prediction is required, especially in some applications such as conjunction analysis. In the orbital error propagation of artificial celestial objects in low Earth orbits (LEOs), atmospheric density uncertainty is one of the important factors that require special attention. In this paper, on the basis of considering the uncertainties of position and velocity, the atmospheric density uncertainty is also taken into account to further investigate the orbital error propagation of artificial celestial objects in LEOs. Artificial intelligence algorithms are introduced, the MC Dropout neural network and the heteroscedastic loss function are used to realize the correction of the empirical atmospheric density model, as well as to provide the quantification of model uncertainty and input uncertainty for the corrected atmospheric densities. It is shown that the neural network we built achieves good results in atmospheric density correction, and the uncertainty quantization obtained from the neural network is also reasonable. Moreover, using the Gaussian mixture model - unscented transform (GMM-UT) method, the atmospheric density uncertainty is taken into account in the orbital uncertainty propagation, by adding a sampled random term to the corrected atmospheric density when calculating atmospheric density. The feasibility of the GMM-UT method considering atmospheric density uncertainty is proved by the further comparison of abundant sampling points and GMM-UT results (with and without considering atmospheric density uncertainty).

Massive black hole binaries in LISA: Multimessenger prospects and electromagnetic counterparts

In the next decade, the Laser Interferometer Space Antenna (LISA) will detect the coalescence of massive black hole binaries (MBHBs) in the range $[10^4, 10^8] \, \rm M_{\odot}$, up to $z\sim10$. Their gravitational wave (GW) signal is expected to be accompanied by an electromagnetic counterpart (EMcp), generated by the gas accreting on the binary or on the remnant BH. In this work, we present the number and characteristics (such as redshift and mass distribution, apparent magnitudes or fluxes) of EMcps detectable jointly by LISA and some representative EM telescopes. We combine state-of-the-art astrophysical models for the galaxies formation and evolution to build the MBHBs catalogues, with Bayesian tools to estimate the binary sky position uncertainty from the GW signal. Exploiting additional information from the astrophysical models, such as the amount of accreted gas and the BH spins, we evaluate the expected EM emission in the soft X-ray, optical and radio bands. Overall, we predict between 7 and 21 EMcps in 4 yrs of joint observations by LISA and the considered EM facilities, depending on the astrophysical model. We also explore the impact of the hydrogen and dust obscuration of the optical and X-ray emissions, as well as of the collimation of the radio emission: these effects reduce the number to EMcps to 2 or 3, depending on the astrophysical model, again in 4 yrs of observations. Most of the EMcps are characterised by faint EM emission, challenging the observational capabilities of future telescopes. Finally, we also find that systems with multi-modal sky position posterior distributions represent only a minority of cases and do not affect significantly the number of EMcps.

Three-Dimensional ANP Evaluation Method Based on Spatial Position Uncertainty under RNP Operation

Performance-based navigation (PBN) operations based on the required navigation performance (RNP) operations are the trend for civil aviation in the future. In order to further ensure the safety and efficiency of civil aviation operation, RNP will transition from 2D to 3D/4D. Accurately evaluating the actual navigation performance in three-dimensional directions (3D ANP) under civil aircraft RNP operation is important to guarantee the safe flight of civil aircraft. However, the traditional two-dimensional ANP evaluation method mainly focuses on plane navigation performance along the track, lacks the evaluation of the vertical direction. Moreover, the traditional three-dimensional accuracy evaluation method is based on the assumption of three-dimensional independence and uniformity, which can only carry out approximate calculation, and the evaluation result is inaccurate. Therefore, this paper constructs a three-dimensional ellipsoid error probability (EEP) evaluation model for the spatial position uncertainty of the navigation output of the flight management system in three-dimensional directions, and gives the three-dimensional accurate ANP calculation results through iterative numerical integration. The simulation results show that the evaluation method proposed in this paper can accurately evaluate the actual navigation performance of the airborne navigation system in all directions of 3D space, and has higher evaluation accuracy and precision than the traditional ANP evaluation method, which is of great significance to ensure the flight safety of civil aircraft under 3D/4D RNP operation in the future.

Premerger localization of intermediate mass binary black holes with LISA and prospects of joint observations with Athena and LSST

The planned Laser Interferometric Space Antenna (LISA) will be able to detect gravitational waves (GWs) from intermediate mass binary black holes (IMBBHs) in the mass range $\sim 10^{2} \mbox{-} 10^{4}\,M_{\odot}$ up to a redshift $z\sim20$. Modulation effects due to orbital motion of LISA around the Sun facilitate precise premerger localization of the sources, which in turn would help in electromagnetic (EM) followups. In this work, we calculate the uncertainties in sky position, luminosity distance, and time of coalescence as a function of time to coalescence. For representative masses of the IMBBHs, we synthesize a population of binaries uniformly located and oriented on a sphere of radius 3 Gpc and compute the projected parameter measurement uncertainties using the Fisher information matrix. We find that for systems with a total mass of $10^3\,M_{\odot}$, the errors in the sky position and luminosity distance are $\sim 0.4\,\text{deg}^2$ and $\sim 6\%$, respectively, one day prior to coalescence. The coalescence time can be predicted with an uncertainty $\lesssim 10$ sec, one day before coalescence. We also find that for $10^3\,M_{\odot}$, around $40\%$ ($100\%$) of the population has a source localization that is smaller than the field of view of Athena (LSST) one day before the merger. These extremely precise measurements can be used to alert ground-based GW detectors and EM telescopes about the time and location of these mergers. We also discuss mechanisms that may produce EM emission from IMBBH mergers and study its detectability using the planned Legacy Survey of Space and Time (LSST) in the optical and Athena in the x-ray bands. Detection of an EM transient may provide us vital clues about the environments where these mergers occur and the distance estimation can pave the way for cosmography.

Transformer-Based Maneuvering Target Tracking.

When tracking maneuvering targets, recurrent neural networks (RNNs), especially long short-term memory (LSTM) networks, are widely applied to sequentially capture the motion states of targets from observations. However, LSTMs can only extract features of trajectories stepwise; thus, their modeling of maneuvering motion lacks globality. Meanwhile, trajectory datasets are often generated within a large, but fixed distance range. Therefore, the uncertainty of the initial position of targets increases the complexity of network training, and the fixed distance range reduces the generalization of the network to trajectories outside the dataset. In this study, we propose a transformer-based network (TBN) that consists of an encoder part (transformer layers) and a decoder part (one-dimensional convolutional layers), to track maneuvering targets. Assisted by the attention mechanism of the transformer network, the TBN can capture the long short-term dependencies of target states from a global perspective. Moreover, we propose a center-max normalization to reduce the complexity of TBN training and improve its generalization. The experimental results show that our proposed methods outperform the LSTM-based tracking network.

A Location-Aware RF-Assisted MAC Protocol for Sectorized Vehicular Visible Light Communications

Vehicular Visible Light Communications (V-VLC) has emerged as a viable technology complementing RF-based communication in automotive scenarios. This is mainly due to properties such as the large unlicensed spectrum and the intrinsic security due to the Line Of Sight (LOS) requirement. In this context, one aspect of V-VLC needs further attention given the current state of the art, namely medium access under multi-user interference. In this paper, we extensively study interference in typical vehicular scenarios. Based on the findings from this study, we propose a novel approach for medium access. We follow a location-aware cross-layer approach that exploits the Space Division Multiple Access (SDMA) feature of modern matrix lighting modules to avoid interference and thus collisions. Making use of heterogeneous communication concepts, in which vehicles share their positions via the Radio Frequency (RF) channel, V-VLC transmissions can be scheduled accordingly. In an extensive simulation study using a realistic urban scenario, we first identify critical interference scenarios and then assess the efficacy of our proposed solution. We also investigate the impact of position uncertainty due to, e.g., GPS errors. Our results clearly indicate the benefits of a location-aware protocol that exploits the space-division features of the matrix lights.

Gaia Early Data Release 3

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13–21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 µas yr–1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution.

Constraining the Nature of the 18 min Periodic Radio Transient GLEAM-X J162759.5-523504.3 via Multiwavelength Observations and Magneto-thermal Simulations

We observed the periodic radio transient GLEAM-X J162759.5-523504.3 (GLEAM-X J1627) using the Chandra X-ray Observatory for about 30 ks on 2022 January 22–23, simultaneously with radio observations from the Murchison Widefield Array, MeerKAT, and the Australia Telescope Compact Array. Its radio emission and 18 min periodicity led the source to be tentatively interpreted as an extreme magnetar or a peculiar highly magnetic white dwarf. The source was not detected in the 0.3–8 keV energy range with a 3σ upper limit on the count rate of 3 × 10−4 counts s−1. No radio emission was detected during our X-ray observations either. Furthermore, we studied the field around GLEAM-X J1627 using archival European Southern Observatory and DECam Plane Survey data, as well as recent Southern African Large Telescope observations. Many sources are present close to the position of GLEAM-X J1627, but only two within the 2″ radio position uncertainty. Depending on the assumed spectral distribution, the upper limits converted to an X-ray luminosity of L X < 6.5 × 1029 erg s−1 for a blackbody with temperature kT = 0.3 keV, or L X < 9 × 1029 erg s−1 for a power law with photon index Γ = 2 (assuming a 1.3 kpc distance). Furthermore, we performed magneto-thermal simulations for neutron stars considering crust- and core-dominated field configurations. Based on our multiband limits, we conclude that (i) in the magnetar scenario, the X-ray upper limits suggest that GLEAM-X J1627 should be older than ∼1 Myr, unless it has a core-dominated magnetic field or has experienced fast cooling; (ii) in the white dwarf scenario, we can rule out most binary systems, a hot sub-dwarf, and a hot magnetic isolated white dwarf (T ≳ 10.000 K), while a cold isolated white dwarf is still compatible with our limits.