Line Of Sight Research Articles

Solar prominence diagnostics and their associated estimated errors from 1D NLTE Mg II h&k modelling

We present further development of the rolling root mean square (rRMS) algorithm. These improvements consist of an increase in computational speed and an estimation of the uncertainty on the recovered diagnostics. This improved algorithm is named the cross root mean square (xRMS) algorithm. We used the quantile method to recover the statistics of the line profiles in order to study the evolution of the prominence observed by IRIS on 1 October 2019. We then introduced the improvements to rRMS. These improvements greatly increased the computational speed, and this increase in speed allowed us to use a large model grid. Thus, we utilised a grid of 23 940 models to recover the thermodynamic diagnostics. We used the `good' (but not `best') fitting models to recover an estimate of the uncertainty on the recovered diagnostics. The maximum line-of-sight (LOS) velocities were found to be $70$ km s$^ The line widths were mostly 0.4 with the asymmetries of most pixels around zero. The central temperature of the prominence was found to range from 10 kK to 20 kK with uncertainties of approximately pm 5 to pm 15 kK . The central pressure was around 0.2 dyn cm$^ $, with uncertainties of pm 0.2 to pm 0.3 dyn cm$^ . The ionisation degree ranged from 1 to 1000, with uncertainties mostly in the range pm 10 to pm 100 . The electron density was mostly $ cm$^ with uncertainties of mostly The new xRMS algorithm finds an estimation of the errors of the recovered thermodynamic properties. To our knowledge, this is the first attempt at systematically determining the errors from forward modelling. The large range of errors found may hint at the degeneracies present when using a single ion and/or species from forward modelling. In the future, co-aligned observations of more than one ion and/or species should be used to attempt to constrain this problem.

ARUDINO BASED OBSTACLE AVOIDING ROBOT CAR P VAYUNANDA SAI KUMAR

This project involves the design and implementation of an intelligent obstacle-avoiding robot car. The objective of this project is to implement a robot car, which while moving should have the ability to detect obstacles in its path and change direction where obstacles are present without any form of external influence. The new direction to be taken to avoid collision is the direction that has the most distance between the obstacle and the sensor and this is determined by the robot based on sensor inputs. This implementation was done using an ultrasonic wave sensor, which measures distance by sending pulses. Also, the movement of the servo motor (for sensor movement) and the DC motors (for wheel movement) are controlled by the motor driver shield in order to enable the obstacle avoidance function. The commands are sent to the Arduino microcontroller chip which serves as the main control of the robot car, as it controls the sensor and car movement. The implemented robot car was able to successfully detect and avoid obstacles within the line of sight of the Ultrasonic sensor used. Keywords: Arduino UNO, ultrasonic sensor, DC motor, Servo Motor

An Empirical Approach to Rerouting Visible Light Pathways Using an Adjustable-Angle Mirror to Sustain Communication between Vehicles on Curvy Roads

In this paper, a novel method is demonstrated to sustain vehicle-to-vehicle (V2V) communication on curvy roads via the arrangement of the lateral position of a self-angle-adjustable mirror–reflective road sign (SAAMRS) and light-direction-sensing wide-angle complementary photodiodes (CPDs). Visible light communication (VLC) between vehicles attracts attention as a complementary technology to radio-frequency-based (RF-based) communication technologies due to its wide, license-free spectrum and immunity to interferences. However, V2V VLC may be interrupted on curvy roads due to the limited field of view (FOV) of the receiver or the line of sight (LOS) being interrupted. To solve this problem, an experiment was developed using an SAAMRS along with wide-angle light-direction-sensing CPDs that used a precise peak detection (PPD) method to sustain communication between vehicles in dynamic environments by rerouting the incident light with the highest signal intensity level to the receiver vehicle on curvy roads. We also used real images of curvy roads simulated as polynomials to calculate the necessary rotation angles for the SAAMRS and regions where communication exist. Our experimental results overlapped almost completely with our simulations, with small errors of approximately 4.8% and 4.4% for the SAAMRS angle and communication region, respectively.

Feasibility analysis of line of sight (LOS) underwater wireless optical communications (UWOCs) via link budget

Feasibility analysis of line of sight (LOS) underwater wireless optical communications (UWOCs) via link budget

Towards flow field measurements around dynamic cross-country skiers

Flow field measurements around cross-country skiers (xc skiers) are lacking in the literature to date. The aim was therefore to investigate the possibility of using particle tracking velocimetry for visualization and measurement of the flow field around xc skiers roller skiing on a treadmill in a wind tunnel. The airflow was seeded with neutrally buoyant helium-filled soap bubbles as tracer particles, following the flow without affecting it. As illumination, two different approaches were tested: first, a laser in the cameras’ line of sight (sagittal plane), then an LED unit directed vertically in a narrow slice, clearly limiting the depth of the measurement volume in the cameras’ line of sight. The flow field was studied at various speeds (3-7 m/s) around a single skier as well as around two skiers in line with the streaming airflow. It was found that the experimental approach has the potential to provide detailed insights, both qualitatively and quantitatively, into the flow field dynamics. The main challenges regarding setup, illumination, seeding, and cameras were identified, and possible improvements to streamline the experimental methodology were discussed.

Experimental validation of the appropriate channel model for an indoor Visible Light Communication system

Visible light communication (VLC) is a technology with significant potential to revolutionize indoor communication performance and satisfy the demands of fifth-generation (5G) and beyond technologies. To achieve an efficient VLC system that delivers optimal performance and coverage, it is imperative to create a reliable channel model. As a result, this research is centered around the evaluation of existing channel models for planning the VLC network coverage within indoor environments. The primary focus of this study is to enforce three types of channel models, Line of Sight (LoS), Nakagawa’s first reflection model, and the Spherical model through MATLAB simulations and obtain simulation results by varying the distance parameter. Furthermore, this research intends to implement a physical prototype representing a real-world scenario, and thereby determine the nearest channel model that aligns with the physical measurements obtained from the physical prototype.

Multi-wavelength pulse profiles from the force-free neutron star magnetosphere

The last two decades have witnessed dramatic progress in our understanding of neutron star magnetospheres thanks to force-free and particle-in-cell simulations. However, the associated particle dynamics and its emission mechanisms and locations have not been fully constrained, notably in X-rays. In this paper, we compute a full atlas of radio, X-ray, and gamma -ray pulse profiles, relying on the force-free magnetosphere model. Our goal is to use such a data bank of multi-wavelength profiles to fit a substantial number of radio-loud gamma -ray pulsars that have also been detected in non-thermal X-rays to decipher the X-ray radiation mechanism and sites. Using results from the third gamma -ray pulsar catalogue (3PC), we investigate the statistical properties of this population. We assume that radio emission emanates from field lines rooted to the polar caps, at varying height above the surface, close to the surface, at an altitude about 5-10<!PCT!> of the light cylinder radius, rlight . The X-ray photons are produced in the separatrix region within the magnetosphere; that is, the current sheet formed by the jump from closed to open magnetic field lines. We allow for substantial variations in emission height. The gamma -rays are produced within the current sheet of the striped wind, outside the light cylinder. A comprehensive set of radio, X-ray, and gamma -ray light curves was computed. Based on only geometric considerations about magnetic obliquity, line-of-sight inclination, and the radio beam cone opening angle, pulsars can be classified as radio-loud or quiet and as gamma -ray-loud or quiet. We found that the 3PC sample is compatible with an isotropic distribution of obliquity and line of sight. The atlases constructed in this work are the fundamental tools with which to explore individual pulsars and fit their multi-wavelength pulse profiles in order to constrain their magnetic topology, the emission sites, and the observer's line of sight.

Distortions of the Hubble diagram: Line-of-sight signatures of local galaxy clusters

The Universe expansion rate is modulated around local inhomogeneities due to their gravitational potential. Velocity waves are then observed around galaxy clusters in the Hubble diagram. This paper studies them in a sim 738 Mpc-wide, 2048$^3$-particle cosmological simulation of our cosmic environment (a.k.a. CLONE: Constrained LOcal Nesting Environment Simulation). For the first time, the simulation shows that velocity waves that arise in the lines of sight of the most massive dark matter halos agree with those observed in local galaxy velocity catalogs in the lines of sight of Coma and several other local (Abell) clusters. For the best-constrained clusters such as Virgo and Centaurus -- that is, those closest to us -- secondary waves caused by galaxy groups, further into the non-linear regime, also stand out. This match was not utterly expected given that before being evolved into a fully non-linear z=0 state, assuming Lambda CDM, CLONE initial conditions are constrained solely with linear theory, the power spectrum, and highly uncertain and sparse local peculiar velocities. Additionally, Gaussian fits to velocity wave envelopes show that wave properties are tightly tangled with cluster masses. This link is complex, though, and involves the environment and formation history of the clusters. A proposed metric, measuring the distance between the observed and several re-centred simulated lines of sight, waves included, is shown to be capable of providing a tight mass range estimate for massive local clusters. Using machine learning techniques to grasp more thoroughly the complex wave-mass relation, velocity waves could in the near future be used to provide additional and independent mass estimates from galaxy dynamics within large cluster radii.

Preliminary design of an AXUV photodiode-based bolometer camera for MT-I spherical tokamak

The MT-I is a spherical tokamak at the Pakistan Tokamak Plasma Research Institute, and has a major radius of 15 cm and a minor radius of 9 cm. This paper presents the design and computational analysis of the Absolute eXtreme Ultra-Violet (AXUV) photodiode-based bolometer camera, which will be used for the first time in the MT-I tokamak. The bolometer camera contains a single array of 16 AXUV photodiodes placed behind an aperture to compute the line of sight (LOS) and field of view (FOV) of the system. This array is located at the midplane of the vessel, which provides a radial resolution of about 16 mm. The individual FOV of each photodiode and the collective FOV of the array are ±34.5° and 4.1°°, respectively. The impurity densities and their cooling rates for elements like carbon, oxygen, and iron are used to compute the plasma emissivity distribution, the power incident on the photodiode array, and signal-to-noise ratio (SNR) analysis. The analysis reveals that the radiated power loss is about 10 % of the ohmic heating input power. The geometrical etendue falls within the range of 2.2 × 10−5 to 3.2 × 10−5 Sr cm2. The bolometer exhibits a frequency response bandwidth of 10 kHz, and its temporal resolution is around 0.1 milliseconds.

Mechanical design of ITER radial neutron camera Ex-Port system

The Radial Neutron Camera is an ITER diagnostic designed to measure the un-collided 14 MeV and 2.5 MeV neutrons from deuterium-tritium (DT) and deuterium-deuterium (DD) fusion reactions, through an array of detectors covering a poloidal plasma section along collimated Lines Of Sight (LOS). It is composed by two fan-shaped collimating structures viewing the plasma radially through vertical slots in the diagnostic shielding module of ITER Equatorial Port 1: the In-Port RNC, devoted to plasma edge coverage, and the Ex-Port RNC, devoted to the plasma core coverage. This paper presents an overview of the mechanical design of the Ex-Port RNC at the Preliminary Design Review (PDR) stage. The Ex-Port RNC is located in the Port Interspace and consists of a massive shielding structure hosting the detector units and two sets of collimators lying on different toroidal planes. The Ex-Port RNC design is presented both from the point of view of functional requirements (e.g. LOS positions and angles, radiation shielding, weight limitations) and of manufacturability. Finally, the Ex-port RNC structural integrity is assessed, and its design validated against the main loads and load combinations.

Trajectory Deviation Estimation Method for UAV-Borne Through-Wall Radar

Mini–unmanned aerial vehicles (mini-UAVs) are emerging as a promising platform for through-wall radar to sense the enclosed space in cities, especially high-rise buildings, due to their excellent maneuverability. However, due to unavoidable environmental interference such as airflow, mini-UAVs are prone to trajectory deviation thus degrading their sensing accuracy. Most of the existing approaches model the impact of trajectory deviation into a polynomial phase error on the received signal, which cannot fit the space-variant motion error well. Moreover, the large trajectory deviations of UAVs introduce the unavoidable envelope error. This article proposes an autofocusing algorithm based on the back projection (BP) image, which directly estimates the trajectory deviations between the actual and measured track. Thus, the problem of the 2D space variability of the motion error can be circumvented. The proposed method mainly consists of two steps. First, we estimate the trajectory deviation in the line-of-sight (LOS) direction by exploring the underlying linear property of the wall embedded in the BP imaging result. Then, the estimated trajectory deviation in the LOS direction is compensated for to obtain an updated BP image, followed by a Particle Swarm Optimization (PSO) approach to estimate the trajectory deviation along the track through focusing targets behind the wall. Simulations and practical experiments show that the proposed algorithm can accurately estimate the serious trajectory deviations larger than the range resolution, improving the sensing robustness of UAV-borne through-wall radar greatly.

Improving Target Geolocation Accuracy with Multi-View Aerial Images in Long-Range Oblique Photography

Target geolocation in long-range oblique photography (LOROP) is a challenging study due to the fact that measurement errors become more evident with increasing shooting distance, significantly affecting the calculation results. This paper introduces a novel high-accuracy target geolocation method based on multi-view observations. Unlike the usual target geolocation methods, which heavily depend on the accuracy of GNSS (Global Navigation Satellite System) and INS (Inertial Navigation System), the proposed method overcomes these limitations and demonstrates an enhanced effectiveness by utilizing multiple aerial images captured at different locations without any additional supplementary information. In order to achieve this goal, camera optimization is performed to minimize the errors measured by GNSS and INS sensors. We first use feature matching between the images to acquire the matched keypoints, which determines the pixel coordinates of the landmarks in different images. A map-building process is then performed to obtain the spatial positions of these landmarks. With the initial guesses of landmarks, bundle adjustment is used to optimize the camera parameters and the spatial positions of the landmarks. After the camera optimization, a geolocation method based on line-of-sight (LOS) is used to calculate the target geolocation based on the optimized camera parameters. The proposed method is validated through simulation and an experiment utilizing unmanned aerial vehicle (UAV) images, demonstrating its efficiency, robustness, and ability to achieve high-accuracy target geolocation.

Identifying H i Emission and UV Absorber Associations near the Magellanic Stream

We present a new technique to identify associations of H i emission in the Magellanic Stream (MS) and ultraviolet (UV) absorbers from 92 QSO sight lines near the MS. We quantify the level of associations of individual H i elements to the main H i body of the Stream using Wasserstein distance-based models, and derive characteristic spatial and kinematic distances of the H i emission in the MS. With the emission-based model, we further develop a comparison metric, which identifies the dominant associations of individual UV absorbers with respect to the MS and nearby galaxies. For ionized gas associated with the MS probed by C ii, C iv, Si ii, Si iii, Si iv, we find that the ion column densities are generally ∼0.5 dex higher than those that are not associated, and that the gas is more ionized toward the tail of the MS as indicated by the spatial trend of the C ii/C iv ratios. For nearby galaxies, we identify potential new absorbers associated with the circumgalactic medium of M33 and NGC 300, and affirm the associations of absorbers with IC 1613 and the Wolf–Lundmark–Mellote galaxy. For M31, we find the previously identified gradient in column densities as a function of the impact parameter, and that absorbers with higher column densities beyond M31's virial radius are more likely to be associated with the MS. Our analysis of absorbers associated with the Magellanic Clouds reveals the presence of continuous and blended diffuse ionized gas between the Stream and the Clouds. Our technique can be applied to future applications of identifying associations within physically complex gaseous structures.

Secondary eclipse and day-night modulation of exoplanets observed by transiting exoplanet survey satellite

Astronomers have identified over five thousand extrasolar planets since the discovery of the first solar-like star in 1995. These systems exhibit greater diversity than our solar system, providing insights into their formation and evolution. To understand these exoplanets and their habitability, it is crucial to examine their atmosphere composition. The Transiting Exoplanet Survey Satellite (TESS) can detect reflected light from exoplanets with high accuracy, providing valuable insights into their formation and potential for life in the Universe. Planetary reflection can be detected by monitoring the light curve, which is the sum of stellar flux and planetary reflection. Orbiting planets may also reveal their presence by modulating reflected starlight, showing day-night variations in observers sight lines. However, these flux variations are extremely small, at a level of 0.01%, making detection difficult. This study developed an efficient Python program to search for secondary eclipse and day-night modulation on the TESS light curves of over four hundred known short-period transiting exoplanets. The program automatically identifies and rejects low-quality photometric data points in light curves, folding high-quality light curves in the orbital phase determined by primary transits. The phase-folded average light curves have high photometric precision, suitable for detecting secondary eclipse and day-night modulation. The program successfully identified planetary reflection in seventeen transiting exoplanetary systems, larger than the current TESS sample by twice. The program plans to upgrade to search for orbital phase modulation in non-transit exoplanets, taking advantage of the high precision of TESS photometry.

Received signal evaluation for Ultra High Frequency (UHF)terrestrial television; Case of Ekiti State, Nigeria

This paper presents the evaluation of the received signal for UHF channel 41, (transmitting frequency of 631.25 MHz) and Star-times (transmitting frequency of 618 MHz). Using a Digital Field Strength Meter, the signal strength from the two UHF Transmitting Stations was measured throughout the state along two routes. The elevation, geographic coordinates, and line of sight of the various data points from the base stations were determined using a global positioning system (GPS) receiver. Regression analysis and correlation were used in the signal assessment process. Analysis of the data collected from the field measurements indicated that as line of sight increases signal strength reduces along all the routes for Ekiti Television (EKTV) and Star-times except along Route B for Star-times. Line of Sight and Elevation have a strong negative connection in almost all routes except along route A for star-times. Elevation and Signal strength correlation indicated negatively very high except for that along route B for EKTV and route A for Star-times. Regression analysis revealed that variance in Line of Sight and Elevation accounted for high significant changes in signal strength for EKTV and consistently very high changes for Star-times. Generally, it was observed that distance from the base station, topography/elevation, power of the transmitter, nature of signal (Digital/Analog) as shown for regression analysis and other factors affected the quality of service of the propagated signal. Terrestrial Television stations should ensure they transmit with the standard parameters. To improve service quality, the transition from analog to digital should be accelerated in Nigeria such that most stations transmit via the standard Digital method of transmission.

3D physical structure and angular expansion of the remnant of the recurrent nova T Pyx

Abstract We present the analysis of archival VLT MUSE and multi-epoch HST WFPC2 and WFC3/UVIS narrow-band observations of the remnant associated with the ejecta of the mid-nineteenth century outburst of the recurrent nova T Pyx. These data sets are used to investigate its true 3D physical structure and the nebular expansion patterns along the line of sight and on the plane of the sky. The VLT MUSE emission line maps and 3D visualisations based on position-position-velocity diagrams reveal T Pyx as a bipolar nebula, with a knotty toroidal structure at its waist best seen in Hβ and two open bowl-shaped bipolar lobes (a diabolo) best revealed by the [O iii] emission lines. The comparison of multi-epoch HST WFPC2 and WFC3/UVIS narrow-band images and VLT MUSE emission line maps of T Pyx reveals the angular expansion of the remnant through the proper motion of individual knots and nebular features. The angular expansion is confirmed to be homologous in the period from 1994.2 to 2007.4 before the recent 2011 outburst, but there is suggestive evidence that the inner knots have experienced a higher expansion rate since then.

Trajectory Tracking Control of Variable Sweep Aircraft Based on Reinforcement Learning

An incremental deep deterministic policy gradient (IDDPG) algorithm is devised for the trajectory tracking control of a four-wing variable sweep (FWVS) aircraft with uncertainty. The IDDPG algorithm employs the line-of-sight (LOS) method for path tracking, formulates a reward function based on position and attitude errors, and integrates long short-term memory (LSTM) units into IDDPG algorithm to enhance its adaptability to environmental changes during flight. Finally, environmental disturbance factors are introduced in simulation to validate the designed controller’s ability to track climbing trajectories of morphing aircraft in the presence of uncertainty.

Beyond radial profiles: Using log-normal distributions to model the multiphase circumgalactic medium

Abstract Recent observations and simulations reveal that the circumgalactic medium (CGM) surrounding galaxies is multiphase, with the gas temperatures spanning a wide range at most radii, ∼104 K to the virial temperature (∼106 K for Milky Way). Traditional CGM models using simple density profiles are inadequate at reproducing observations that indicate a broad temperature range. Alternatively, a model based on probability distribution functions (PDFs) with parameters motivated by simulations can better match multi-wavelength observations. In this work, we use log-normal distributions, commonly seen in the simulations of the multiphase interstellar and circumgalactic media, to model the multiphase CGM. We generalize the isothermal background model by Faerman et al. 2017 to include more general CGM profiles. We extend the existing probabilistic models from 1D-PDFs in temperature to 2D-PDFs in density-temperature phase space and constrain its parameters using a Milky Way-like Illustris TNG50-1 halo. We generate various synthetic observables such as column densities of different ions, UV/X-ray spectra, and dispersion and emission measures. X-ray and radio (Fast Radio Burst) observations mainly constrain the hot gas properties. However, interpreting cold/warm phase diagnostics is not straightforward since these phases are patchy, with inherent variability in intercepting these clouds along arbitrary lines of sight. We provide a tabulated comparison of model predictions with observations and plan to expand this into a comprehensive compilation of models and data. Our modeling provides a simple analytic framework that is useful for describing important aspects of the multiphase CGM.

Line-of-sight Initial Pointing Model of Space Dynamic Optical Network and Its Verification

In dynamic space networks, achieving high precision and fast initial pointing of the optical line of sight (LOS) is the key goal in developing this technology. It is the premise and basis of realizing optical LOS capture. Based on the composition and working principle of space optical networking systems, and the effect of real-time position and attitude changes on LOS initial pointing between networks, the matrix transformation and transfer principle is used to establish a multi-link LOS initial pointing model and analyze the factors affecting the size of the field of uncertainty (FOU). In a dynamic space optical networking experiment, the “one-to-two” simultaneous LOS pointing test is carried out, which shows that the model can realize the function of multi-link LOS initial pointing. The sizes of the FOU of the test terminal are 8.67 mrad and 8.34 mrad, respectively, with an average capture time of 18.3 s.

A Steep Decline in the Galaxy Space Density beyond Redshift 9 in the CANUCS UV Luminosity Function

We present a new sample of 158 galaxies at redshift z > 7.5 selected from deep James Webb Space Telescope (JWST) NIRCam imaging of five widely separated sight lines in the CANUCS survey. Two-thirds of the pointings and 80% of the galaxies are covered by 12–14 NIRCam filters, including seven to nine medium bands, providing accurate photometric redshifts and robustness against low-redshift interlopers. A sample of 28 galaxies at z > 7.5 with spectroscopic redshifts shows a low systematic offset and scatter in the difference between photometric and spectroscopic redshifts. We derive the galaxy UV luminosity function at redshifts 8–12, finding a slightly higher normalization than previously seen with the Hubble Space Telescope at redshifts 8–10. We observe a steeper decline in the galaxy space density from z = 8 to 12 than found by most JWST Cycle 1 studies. In particular, we find only eight galaxies at z > 10 and none at z > 12.5, with no z > 10 galaxies brighter than F277W AB = 28 or M UV = −20 in our unmasked, delensed survey area of 53.4 arcmin2. We attribute the lack of bright z > 10 galaxies in CANUCS compared to GLASS and CEERS to intrinsic variance in the galaxy density along different sight lines. The evolution in the CANUCS luminosity function between z = 8 and 12 is comparable to that predicted by simulations that assume a standard star formation efficiency without invoking any special adjustments.