Circular Source Research Articles

Odd radio circles as supernovae remnants in the intragroup medium

ABSTRACT A measurable fraction (∼8 per cent) of recently discovered arcmin-size circular diffuse radio sources termed as odd radio circles or ORCs can be supernovae remnants in the intragroup medium, within the Local Group and its immediate neighbour groups of galaxies. This estimate is based on the optical detection rate of the intragroup supernovae events in the nearby (z ∼ 0.1−0.2) galaxy groups. A rate of about 5400 intragroup supernovae per million year is expected within the local and its immediate neighbour groups of galaxies. For a radio detectability period of about 104 yr, on average 1.3 intragroup medium supernovae remnants per 1000 deg2 are expected to be detected in the radio surveys with a sensitivity that led to discovery of ORCs. The angular size, surface brightness, and radio flux of the supernova remnants up to a distance of ∼3 Mpc in the intragroup medium can be expected to be similar to the five known ORCs. The intragroup supernovae remnants are not residing in the dense and cold interstellar medium of the galaxies but evolving in low-density (10−4−10−5 cm−3) warm medium (105−106 K) in galactic haloes or beyond, and may find their progenitors in the diffuse stellar light associated with various tidal streamers surrounding the Milky Way and other nearby galaxies.

Detecting Magnetic Permeability and Electrical Conductivity Fluctuations in Metallic Ferromagnetic Sheets through the Shielding Effect

In this report, a method is proposed for determining the fluctuations of physical and structural properties in metallic ferromagnetic samples by magnetic scanning. The method is based on the shielding of a circular loop electromagnetic field source using a ferromagnetic and metallic sheet. The shielding of the electromagnetic field depends on the field frequency and amplitude as well as the electrical conductivity and magnetic permeability of the sheet. The proposed method does not require winding around the sheet. The experimental AC shielding results are reported.

A real-time method for detecting weld deviation of corrugated plate fillet weld by laser vision sensor

In the process of arc welding of the corrugated plate fillet weld, both the modification of weld position and the change of welding torch attitude are required. In general, it is difficult to accurately detect the weld position with the advanced weld detection method, and there is short of real-time in advanced weld detection. In this paper, a unique new sensor and detection method were proposed. The laser vision sensor mainly includes a camera and two circular spot laser light sources. The two laser light sources are separately fixed at two sides of the welding torch clamping piece. The axes of the two laser sources and the axis of the welding torch are parallel and coplanar, and the laser spots on both sides of corrugated plate fillet weld are symmetrically distributed on both sides of welding point. When the welding torch moves horizontally or vertically, the image position of the two laser spots in the video camera will change. Through analysis and calculation, the direction of the welding torch migration was determined, and the offset was calculated to realize the real-time detection of the position of the corrugated plate fillet weld. The experimental results showed that when the welding torch moved ±4.5 mm horizontally or vertically, the detection accuracy of the weld was 0.5 mm.

Investigation of two coronal mass ejections from circular ribbon source region:Origin, Sun-Earth propagation and Geoeffectiveness

In this article, we compare the properties of two coronal mass ejections (CMEs) that show similar source region characteristics but different evolutionary behaviors in the later phases. We discuss the two events in terms of their near-Sun characteristics, interplanetary evolution and geoeffectiveness. We carefully analyzed the initiation and propagation parameters of these events to establish the precise CME-interplanetary CME (ICME) connection and their near-Earth consequences. The first event is associated with poor geomagnetic storm disturbance index (Dst ≈-20 nT) while the second event is associated with an intense geomagnetic storm of DST ≈-119 nT. The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager (HMI). For source region imaging, we rely on data obtained from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) and Hα filtergrams from the Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences (ARIES). For both the CMEs, flux rope eruptions from the source region triggered flares of similar intensities (≈M1). At the solar source region of the eruptions,we observed a circular ribbon flare (CRF) for both cases, suggesting fan-spine magnetic configuration in the active region corona. The multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament eruption. Within the Large Angle and Spectrometric Coronograph (LASCO) field of view (FOV) thetwo CMEs propagated with linear speeds of 671 and 631 km s−1, respectively. These CMEs were tracked up to the Earth by Solar Terrestrial Relations Observatory (STEREO) instruments. We find that the source region evolution of CMEs, guided by the large-scale coronal magnetic field configuration, along with near-Sun propagation characteristics, such as CME-CME interactions, played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffectiveness.

Refinement and derivation of statistical resolution limits for circular or rectilinear correlated sources in CES data models

This paper analyzes the deterministic (DCRB) and the stochastic (SCRB) Cramér-Rao bound on direction-of-arrival (DOA) estimation for two equi-powered correlated complex circular or rectilinear sources affected by complex circular white noise in different complex elliptically symmetric (CES) data models. Beginning by decomposing these CRBs, into factors depending on signal and noise parameters, and on geometric parameters of the array, some new interpretable closed-form expressions are derived in particular scenarios. These expressions provide useful insight into the behavior of these CRB’s dependence on the correlation factor. Approximate closed-form expressions of these CRBs for small DOA separation are also derived. These results lead to new formulas for statistical resolution limit (SRL) based on the Smith criterion at which an unbiased DOA estimation algorithm can resolve two closely-spaced circular or rectilinear sources. These SCRB-derived formulas are much less optimistic than those which have so far been deduced only from the DCRB under the assumption of known sources.

Event-Based Circular Detection for AUV Docking Based on Spiking Neural Network.

In this paper, a circular objects detection method for Autonomous Underwater Vehicle (AUV) docking is proposed, based on the Dynamic Vision Sensor (DVS) and the Spiking Neural Network (SNN) framework. In contrast to the related work, the proposed method not only avoids motion blur caused by frame-based recognition during docking procedure but also reduces data redundancy with limited on-chip resources. First, four coplanar and rectangular constrained circular light sources are constructed as the docking landmark. By combining asynchronous Hough circle transform with the SNN model, the coordinates of landmarks in the image are detected. Second, a Perspective-4-Point (P4P) algorithm is utilized to calculate the relative pose between AUV and the landmark. In addition, a spatiotemporal filter is also used to eliminate noises generated by the background. Finally, experimental results are demonstrated from both software simulation and experimental pool, respectively, to verify the proposed method. It is concluded that the proposed method achieves better performance in accuracy and efficiency in underwater docking scenarios.

Shielding of rotor noise by plates and wings

A method of noise reduction proposed for the next generation of aircraft is to shield noise from the propulsion system, by positioning the noise source over a wing or another surface. In this paper, an approximate analysis is developed for the acoustic field far from a circular source placed near the edge of a semi-infinite plate, a model problem for shielding of noise by a wing and for scattering by a trailing edge. The approximation is developed for a source of small radius and is found to be accurate when compared to full numerical evaluation of the field.

Interface reflection wave of axisymmetric directional spherical-wave

The sound radiation field of a circular piston source in an infinite plane rigid baffle can be approximated as an axisymmetric directional spherical-wave. The interface response expressions of the axisymmetric directional spherical-wave for the piston parallel with the interface has already been obtained in previous studies. On condition that the distance from the piston center to the interface is much greater than the piston radius, we first derive the conical wave expansion of the axisymmetric directional spherical-wave which is obtained by using the conical wave expansion of the homogeneous spherical-wave and the formula of the axisymmetric directional spherical-wave excited by a circular piston in an rigid infinite plane, and then derive the expression of the interface reflection wave of the axisymmetric directional spherical-wave for the piston non-parallel to the interface. The expression of the interface reflection wave is simplified into a simplified expression by saddle point method on condition that the source distance is much larger than the acoustic wavelength. The simplified expression is not only simple in the calculation, but also clear in the physical meaning. The simplified expression shows that the interface reflection wave of the axisymmetric directional spherical-wave can be regarded as the product of the axisymmetric directional spherical-wave excited by the piston mirror image and the reflection coefficient. The calculations show that when the piston radius is smaller than the acoustic wavelength, the reflected wave is less sensitive to the angle included between the piston and the interface and the azimuth of the receiving point, and the directivity of the reflected wave is weak. When the piston radius is greater than the acoustic wavelength, the reflected wave is very sensitive to the angle included between the piston and the interface and the azimuth of the receiving point, and the directivity of the reflected wave is strong. Increasing the angle included between the piston and the interface, the reflected wave and its directivity both first increase and then decrease. The reflected wave is largest and the directivity of the reflected wave is strongest when the angle included between the piston and the interface is equal to that between the interface normal and the connecting line between the mirror image of the piston center and the receiving point.

An analytical approach of heat transfer modelling with thermal stresses in circular plate by means of Gaussian heat source and stress function

In the proposed research work we have used the Gaussian circular heat source. This heat source is applied with the heat flux boundary condition along the thickness of a circular plate with a finite radius. The research work also deals with the formulation of unsteady-state heat conduction problems along with homogeneous initial and non-homogeneous boundary condition around the temperature distribution in the circular plate. The mathematical model of thermoelasticity with the determination of thermal stresses and displacement has been studied in the present work. The new analytical method, Reduced Differential Transform has been used to obtain the solution. The numerical results are shown graphically with the help of mathematical software SCILAB and results are carried out for the material copper.

Lattice optimization of a fourth-generation synchrotron radiation light source in Novosibirsk

We discuss the choice of the magnetic lattice and parameter optimization of the fourth-generation light source SKIF (Russian acronym for Siberian Circular Photon Source) under construction in Novosibirsk. The study compares several basic lattice cells to procure one with low emittance and large dynamic aperture. The result is a developed lattice of SKIF with 72 pm natural emittance (at zero beam current and absent betatron coupling) at 3 GeV beam energy and 476 m circumference. Only two families of sextupoles provide horizontal and vertical dynamic apertures of 12 mm and 3.5 mm, respectively, and energy acceptance more than 5%. To check the potential of the found solution, we used slightly modified SKIF lattice to design 6 GeV light source and reached 33 pm natural emittance for 1075 m circumference with 40 straight sections. Again, only two sextupole families ensure sufficient dynamic aperture (7 mm horizontal and 4 mm vertical) and energy acceptance more than 5% for simple efficient injection and sufficient beam lifetime.

Heat transfer and cost analysis of circular heating source based tubular rods loaded with thermal oil-MWCNT nanofluid

Nanofluid is a suspension of nanoparticles (NPs) in conventional fluids. It has emerged as a smart material for transferring heat efficiently and has a great potential to be used as a coolant. In this work, nanofluid is designed by considering multi walled carbon nanotubes (MWCNT) suspended in heat transfer oil. The focus is on the heat transfer through natural convection for a specific geometry of circular heating source based tubular rods. In particular, this is representative of heating by micro-processors and other electronic components. Comsol Multi-Physics 5.5 software has been used for investigating the temperature and velocity profile for different concentrations of MWCNT NPs in this geometry. Significant enhancement in outlet temperature of the nanofluid even at low concentration of the NPs has been observed. This signifies an efficient heat extraction from the circular heat point sources (microprocessors) in the tube. On the basis of mathematical formulation, cost analysis of the proposed system has been performed and the cost per heat point source (Chps) has been estimated for fixed concentration of CNTs (0.5%) with interest rates of 4%,8%,and10%. For life spans of 30 and 50 years of the system, the corresponding Chps is found to be 12.34$,14.10$,15.55$and10.06$,12.98$,14.74$ respectively using CNTs. Moreover, the outlet of the proposed system can be coupled with other photovoltaic thermal (PVT) based systems as an application i.e., solar distillation and solar water heaters in order to improve their efficiency.

Device cooling features in wiggler synchrotron workstations

Construction of the 4+ generation Siberian circular photon source (SKIF synchrotron) has started in Novosibirsk. It will initially be equipped with six research workstations. For two stations, synchrotron radiation is generated by superconducting wigglers, whose radiation power approaches 49 kW, and the power density on the axis is 92 kW/mrad2. Most of the optical devices of the stations operate in a vacuum. The high energy density of the synchrotron beamline and the requirements for the values of thermal deformations lead to difficult conditions for the thermal management of optical elements. The article provides an overview of the applied and promising cooling systems; an example of a 3D calculation of a thermal diamond filter of workstation 1-5 is given, the limit for the thermal load of the filter, at which the temperature of the diamond plate will not exceed 600 °C, is estimated.

Numerical study of the Rayleigh–Bénard convection in two-dimensional cavities heated by elliptical heat sources using the lattice Boltzmann method

This study aims to investigate numerically the Rayleigh–Bénard Convection using an in-house Fortran 90 code based on the lattice Boltzmann method. The bottom wall is equipped with two hot circular/elliptical sources and the right wall is open. The non-linear coupled differential governing equations are formulated using the lattice Boltzmann equation associated with the Boussinesq approximation. The simulations are conducted for (103 ≤ Ra ≤ 106) and Pr = 0.7 (corresponding to air). The code verification showed a good reliability of the present mesoscopic numerical approach. Several configurations related to the size and shape of the heaters were studied. It was found that elliptically shaped heat sources provide higher heat transfer rates compared to circular sources.

Three-Dimensional Lattice Boltzmann Model for Acoustic Waves Emitted by a Source

This paper implements the lattice Boltzmann method to simulate the propagation of sound waves in three dimensions. The numerical model is exercised on the lid-driven cavity flow. Tests are then proposed on acoustic situations. The results are first confronted with analytical solutions of the spherical waves emitted by a single point source inside a cubic cavity. Then, we studied the case where the waves are emitted from a circular sound source placed at the center of the left boundary of a parallelepipedic cavity filled with water. With the circular source discretized as a set of point sources, we were able to simulate the wave propagation in 3D and calculate the sound pressure amplitude. Tests using different emission conditions and LBM relaxation times finally allowed us to get good comparisons with analytical expressions of the pressure amplitude along the source axis, highlighting the performance of the lattice Boltzmann simulations in acoustics.

Sustainable Production of Lignocellulolytic Enzymes in Solid-State Fermentation of Agro-Industrial Waste: Application in Pumpkin (Cucurbita maxima) Juice Clarification

Valorization of agro-industrial waste through greener and biotechnological processes are promising approaches to minimize the generation of agro-industrial waste. Therefore, the study aimed to produce lignocellulolytic enzymes from agro-industrial waste under solid-state fermentation (SSF) conditions and study their application in the clarification of pumpkin juice. The SSF was performed with three different combinations of wheat bran + rice bran (WBRB), wheat bran + wheat straw (WBWS), and rice bran + wheat straw (RBWS) as dry solid substrates (1:1) using Fusarium oxysporum (MTCC 7229). The protein, carboxymethyl cellulase (CMCase), and xylanase contents ranged from 0.98–3.90 mg/g, 5.89–6.84 U/g substrate, and 10.08–13.77 U/g substrate, respectively in different agro-industrial waste as substrates (WBRB, WBWS, RBWS, and control). The increase in enzyme concentration (0.50–2.40%) added to pumpkin juice exhibited an increased juice yield (16.30–55.60%), reduced browning index (1.03–0.70), and an increase in clarity (5.31–13.77 %T), which was further confirmed by a total variance of 84.83% by principal component analysis. Thus, the low-cost lignocellulolytic enzymes can be produced from agro-industrial waste that might have applications in food and beverage industries. Hence, this approach could be used as a long-term sustainable and circular source to valorize agro-industrial waste towards the greener future and the preservation of ecosystems.

Stochastic Simulation of Strong Ground Motions From Two M > 5 Uttarakhand Earthquakes

Many studies based on the geodetic data and statistical analysis of seismicity have pointed out that sufficient amount of stress accumulated in the Himalayan plate boundary may host a big earthquake. Consequently, high seismic activities and infrastructural developments in the major cities around Himalayan regions are always of major concern. The ground motion parameter estimation plays a vital role in the near real time evaluation of potentially damaged areas and helps in mitigating the seismic hazard. Therefore, keeping in mind the importance of estimation of ground motion parameters, we targeted two moderate-size earthquakes that occurred recently within a gap of 10 months in Uttarakhand region with M > 5.0 on 06/02/2017 and 06/12/2017. The ground motions are simulated by adopting a stochastic modeling technique. The source is assumed as ω−2, a circular point source (Brune’s model). The average value of reported anelastic attenuation from various studies, the quality factor, Qs= 130.4*(f0.996), and stress drop values obtained through iterative procedure are considered for simulations. The stochastic spectra are generated between 0.1 and 10 Hz of frequency range. The site effect is also estimated by using the H/V method in the same frequency range. The synthetic spectra are compared with the observed Fourier amplitude spectra obtained from the recorded waveform data and converted back to the time histories. The stochastic time histories are compared with the observed waveforms and discussed in terms of amplitude (PGA). The simulated and observed response spectra at different structural periods are also discussed. The mismatch between the observed and simulated PGA values along with the GMPE existing for shallow crustal earthquakes is also discussed in the present work.

Single‐step geolocation for a non‐circular source in the presence of satellite orbit perturbations

This study addresses the problem of geolocating a strictly non-circular source on the surface of Earth by a cluster of passive satellites. The known satellite positions and velocities are subject to random errors. The authors propose a single-step satellite geolocation algorithm that directly localises the transmitter from sensor outputs using the information of time delays and Doppler shifts but without explicitly estimating them. It exploits the non-circular property of signals and a priori information of satellite orbit error distribution to jointly calibrate orbit errors and determine the longitude and latitude of the transmitter based on the ellipsoidal Earth model, which integrates an alternating iteration scheme for the estimation of various unknowns instead of the exhaustive grid search. Additionally, a detailed Cramér-Rao bound (CRB) derivation is presented for the single-step satellite geolocation of a non-circular source on Earth with and without satellite orbit perturbations, and it is proved that these CRBs are lower than the associated CRBs for a circular source. The simulation results illustrate that the proposed method asymptotically attains the associated CRB, and shows greater performance robustness to signal-to-noise ratio (SNR) and satellite orbit errors compared with conventional two-step satellite geolocation approaches.

New findings in vorticity dynamics of turbulent buoyant plumes

The vorticity dynamics of turbulent, buoyant, and pure plumes released into the quiescent ambience has been investigated using large-eddy simulations with plume Reynolds number in the range of 6 × 107 to 108. The plume is generated by a circular heat source and sustained by buoyancy forcings generated by heating. As the starting plume rises vertically, it expands radially, entraining ambient fluid into the plume and two distinct stages of evolution are evident. During stage one (initial stage), in the near-source region the plume is accelerating characterized by developing turbulence. During the next stage (mixing stage), the plume is significantly altered by turbulence resulting in significant entrainment and expansion in the radial direction. As turbulent intensities decay during the mixing stage, the enstrophy decays in an exponential manner with height with an exponent of −7/4. The turbulent kinetic energy budget analysis reveals—baroclinic torque, stretching, and compression—as the three dominant mechanisms for the plume growth. The probability distribution function (PDF) of vorticity shows that vorticity is mainly aligned along the transverse direction near the source and slowly reaches to a quasi-isotropy state downstream. Turbulence spectra demonstrate the presence of a buoyancy-regime with a −3 spectral slope. The PDF of vorticity further shows extreme dominance of the strain rate rather than rotation within the plume. Consistent with studies in the literature, the vorticity fluctuations align with the intermediate eigen-vector of strain-rate tensor.

In vitro glucose concentration measurement by a reusable enzymatic glucose sensor and a highly stable circular heterodyne polarimeter

A reliable glucose concentration measurement system was proposed that consisted of a circular heterodyne polarimeter and a reusable enzymatic sensor. The circular heterodyne polarimeter was constructed using a highly stable circular heterodyne light source and a compact alignment-free apparatus that provided phase stability of less than 1° within 20 min. The reusable enzymatic glucose sensor can be reused more than 100 times and retain 90% of its initial performance under optimum storage conditions within a month. The proposed method can be used to determine glucose concentrations in aqueous solutions and human serum. The optimum resolution of the proposed method was approximately 0.88 mg/dl for the glucose solution and 0.68 mg/dl for the serum-based sample.

Asymptotic approximations for swirling turbulent plume rising from circular sources

Swirling turbulent plumes are investigated with the Morton, Taylor, and Turner model (MTT) and the $\mathrm{\ensuremath{\Gamma}}$-approach. We derive the asymptotic solutions using regular perturbation methods, and discuss the influence of swirling motions on the plume properties for lazy and forced plumes, respectively. Specially and intriguingly, by introducing a swirl, a forced plume can even be turned into a lazy one in the near field during the vertical evolution.