Properties Of Blobs Research Articles

Segmentation and tracking of vegetable plants by exploiting vegetable shape feature for precision spray of agricultural robots

AbstractFor robotic precision spray application in vegetable farms, simultaneous accurate instance segmentation and robust tracking of plants are of great importance and a prerequisite for the following spray action. With onboard cameras, agricultural robots can apply Multiple Object Tracking and Segmentation (MOTS) methods, for instance, segmentation and tracking of plants. By assigning a unique identification for each vegetable, it ensures the robot to spray each vegetable exactly once, while traversing along the farm rows. Conventional MOTS methods, which are mostly designed for tracking pedestrians or vehicles, usually extract their color and texture features for associating different targets in consecutive images. However, vegetable plants of the same species normally show similar color and texture, which leads to degraded performance when conventional MOTS methods are used. To solve the challenging problem of associating vegetables with similar color and texture in consecutive images, in this paper, a novel MOTS method that exploits contour and blob features is proposed, for instance, segmentation and tracking of multiple vegetable plants. The method takes advantage of the fact that different plants normally possess different shape contours and blob properties. With images captured on top of them, these features of the same plant show little difference in consecutively captured images. Comprehensive experiments including ablation studies are conducted, which prove its superior performance over two state‐of‐the‐art MOTS methods. Compared with the conventional MOTS methods, the proposed method is able to re‐identify objects which have gone out of the camera field of view and re‐appear again using the proposed data association strategy, which is important to ensure each vegetable be sprayed only once when the robot travels back and forth. Although the method is tested on lettuce farm, it can be applied to other similar vegetables, such as broccoli and canola. Both the code and the dataset of this paper are publicly released for the benefit of the community: https://github.com/NanH5837/LettuceMOTS.

Optimal stereoscopic angle for 3D reconstruction of synthetic small-scale coronal transients using the CORAR technique

Context.In previous studies, we applied the CORrelation-Aided Reconstruction (CORAR) technique to reconstruct three-dimensional (3D) structures of transients in the field of view (FOV) of Heliospheric Imager-1 (HI-1) on board the spacecraft STEREO-A/B. The reconstruction quality depends on the stereoscopic angle (θSun), that is, the angle between the lines connecting the Sun and two spacecraft.Aims.To apply the CORAR technique on images from the coronagraphs COR-2 on board STEREO, the impact ofθSunon the reconstruction of coronal transients should be explored, and the optimalθSunfor reconstruction should be found.Methods.We apply the CORAR method on synthetic COR-2 images containing the small-scale transient, namely the blob, in the case of variousθSun. Based on a comparison of the synthetic blob and the corresponding reconstructed structure in location and 3D shape, we assess its level of reconstruction quality. According to the reconstruction-quality levels of blobs in various positions with various attributes, we evaluate the overall performance of reconstruction in the COR-2 FOV to determine the optimalθSunfor reconstruction.Results.In the case ofθSun > 90°, we find that the range of suitableθSun, in which the small-scale transients in the COR-2 FOV typically have high reconstruction quality, is between 120° and 150°, and the optimalθSunfor reconstruction is close to 135°. In the case ofθSun < 90°, the global reconstruction performance is similar to that of (180° −θSun). We also discuss the spatial factors in determining the range of suitableθSun, and study the influence of blob properties on the reconstruction. Our work can serve as a foundation for the design of future missions containing coronagraphs from multiple perspectives, such as the newly proposed SOlar Ring mission (SOR).

Analysis techniques for blob properties from gas puff imaging data.

Filamentary structures, also known as blobs, are a prominent feature of turbulence and transport at the edge of magnetically confined plasmas. They cause cross-field particle and energy transport and are, therefore, of interest in tokamak physics and, more generally, nuclear fusion research. Several experimental techniques have been developed to study their properties. Among these, measurements are routinely performed with stationary probes, passive imaging, and, in more recent years, Gas Puff Imaging (GPI). In this work, we present different analysis techniques developed and used on 2D data from the suite of GPI diagnostics in the Tokamak à Configuration Variable, featuring different temporal and spatial resolutions. Although specifically developed to be used on GPI data, these techniques can be employed to analyze 2D turbulence data presenting intermittent, coherent structures. We focus on size, velocity, and appearance frequency evaluation with, among other methods, conditional averaging sampling, individual structure tracking, and a recently developed machine learning algorithm. We describe in detail the implementation of these techniques, compare them against each other, and comment on the scenarios to which these techniques are best applied and on the requirements that the data must fulfill in order to yield meaningful results.

Blob properties in I-mode and ELM-free H-mode compared to L-mode on EAST

The blob properties in I-mode and ELM-free H-mode plasmas compared to L-mode have been investigated on the EAST tokamak, including the blob detection rate size lifetime and radial velocity The blob properties in L-mode and I-mode are similar, and those in ELM-free H-mode are different to them. The blob is smaller while is larger in H-mode. The experimental blob size and velocity scalings show a good agreement with the theoretical models. The variation in blob properties during the L-I and H-L transitions, and their relations to the scrape-off layer (SOL) density, edge and SOL turbulence, and SOL collisionality are discussed. The suppression of the edge (inside the last closed flux surface) turbulence is not reflected in the blob behavior, while the blob detection rate shows a correlation with the SOL density and its low-frequency (3–50 kHz) fluctuations. In addition, the blob detection rate is found to increase with the divertor collisionality indicating a dependence of blob behavior on The differences in blob detection rates among the three operating regimes might be due to their different SOL densities and collisionalities. The investigation contributes to understanding the influences of edge and SOL plasma parameters on the blob behavior.

Simultaneous measurements of plasma parameters and blob characteristics at the far-SOL region using a hybrid probe in KSTAR

We developed a hybrid probe comprised of an electrical probe and optical probe to investigate the properties of the far scrape-off layer (SOL) plasma and the blob in Korea Superconducting Tokamak Advanced Research (KSTAR). The hybrid probe is attached to a horizontal manipulator, and the radial profiles of plasma parameters such as electron temperature, ion flux, and the Dα signals are measured with time resolution (100 μs) by varying the radial position (0.15–0.4 m away from the last closed flux surface (LCFS)). In ELMy H-mode discharge, the blob radial velocity is obtained from the time delay between the start of the peak Dα signal and the peak electrical probe current and the corresponding radial position. The obtained blob radial velocity is in good agreement with the radial velocity of the filament obtained using the two radially separated electric probes at the far-SOL in the KSTAR. The profiles of the blob radial velocity for five discharges are obtained depending on the radial position in similar experimental parameters. The blob radial velocity is estimated as 44.1–250 m/s and 25.4–135 m/s at the radial position of 0.15 m (near the LCFS) and 0.4 m (near the outer wall), respectively. It is observed that the blobs are propagated to the outer wall with various radial velocities, and the radial velocity slows down as they get closer to the outer wall. The hybrid probe measurement found that the blob properties are about 2 to 10 times larger than the background plasma, and these show the same trend with the blob radial velocity. The hybrid probe is expected to contribute to the analysis and understanding of far-SOL plasma research in fusion reactors.

Molecular crystallization directed by polymer size and overlap under dilute and crowded macromolecular conditions

We demonstrate that dissolved polymers can direct molecular crystallization behavior under dilute and crowded conditions. Larger poly(ethylene glycol)s (PEGs) accelerated caffeine crystal formation in the dilute regime of PEG solutions, which was attributed to the depletion attraction that promoted caffeine cluster aggregation into crystal nuclei. Alternatively, in the semidilute regime, the caffeine crystal formation rate was insensitive to the molecular weight (MW) of PEGs. PEGs with various MWs appeared to induce depletion attraction to a similar extent as the properties of polymer solutions in the semidilute regime described by blobs, which are constant in size at a given polymer concentration irrespective of MW. This study highlights differences between in vitro polymer solutions and crowded intracellular environments composed of folded biomacromolecules and contributes to developing the use of in vitro macromolecular crowding for the control of molecular self-assembly. Dissolved polymers directed molecular crystallization behavior under dilute and crowding conditions. Larger poly(ethylene glycol)s (PEGs) accelerated caffeine crystal formation in the dilute regime of PEG solutions, which was attributed to the depletion attraction that promoted caffeine cluster aggregation into crystal nuclei. In the semidilute regime, the crystal formation rate was insensitive to the molecular weight of PEGs. This observation was consistent with polymer blob properties, which govern depletion attraction and maintain a constant size at a given polymer concentration, irrespective of molecular weight in the semidilute regime.

2D scrape-off layer turbulence measurement using Deuterium beam emission spectroscopy on KSTAR

Intermittent events in the scrape-off layer (SOL) of magnetically confined plasmas, often called blobs and holes, contribute significantly to the particle and heat loss across the magnetic field lines. In this article, the results of the scrape-off layer and edge turbulence measurements are presented with the two-dimensional Deuterium Beam Emission Spectroscopy system (DBES) at KSTAR (Korea Superconducting Tokamak Advanced Research). The properties of blobs and holes are determined in an L-mode and an H-mode shot with statistical tools and conditional averaging. These results show the capabilities and limitations of the SOL turbulence measurement of a 2D BES system. The results from the BES study were compared with the analysis of probe measurements. It was found that while probes offer a better signal-to-noise ratio and can measure blobs down to 3 mm size, BES can monitor the two-dimensional dynamics of larger events continuously during full discharges, and the measurement is not limited to the SOL on KSTAR.

Blob Formation and Ejection in Coronal Jets due to the Plasmoid and Kelvin–Helmholtz Instabilities

Abstract We perform 2D resistive magnetohydrodynamic simulations of coronal jets driven by flux emergence along the lower boundary. The reconnection layers are susceptible to the formation of blobs that are ejected in the jet. Our simulation with low plasma β (Case I) shows that magnetic islands form easily and propagate upward in the jet. These islands are multithermal and thus are predicted to show up in hot channels (335 Å and 211 Å) and the cool channel (304 Å) in observations by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory. The islands have maximum temperatures of 8 MK, lifetimes of 120 s, diameters of 6 Mm, and velocities of 200 km s−1. These parameters are similar to the properties of blobs observed in extreme-ultraviolet (EUV) jets by AIA. The Kelvin–Helmholtz instability develops in our simulation with moderately high plasma β (Case II) and leads to the formation of bright vortex-like blobs above the multiple high magnetosonic Mach number regions that appear along the jet. These vortex-like blobs can also be identified in the AIA channels. However, they eventually move downward and disappear after the high magnetosonic Mach number regions disappear. In the lower plasma β case, the lifetime for the jet is shorter, the jet and magnetic islands are formed with higher velocities and temperatures, the current-sheet fragments are more chaotic, and more magnetic islands are generated. Our results show that the plasmoid instability and Kelvin–Helmholtz instability along the jet are both possible causes of the formation of blobs observed at EUV wavelengths.

Blob properties in full-turbulence simulations of the TCV scrape-off layer

To investigate blob properties in the tokamak scrape-off layer (SOL), we perform dedicated numerical nonlinear simulations of plasma turbulence in the SOL of a TCV discharge using the Global Braginskii Solver code. A blob detection technique is used for the first time in a three-dimensional (3D) full-turbulence simulation to track the motion of the filaments in the SOL. The specific size, density amplitude and radial velocity of the blobs are computed, with the typical values being , and , respectively. The analysis of blob structure in the parallel direction shows that the blobs are partially detached from the limiter. The cross correlation analysis shows how the blobs are born all along the entire field line, not being generated primarily on the low field side SOL and expanding towards the limiter. The blob radial velocity agrees well with the inertial branch of the existing scaling law. The radial particle and heat fluxes given by blobs are shown to be responsible of up to 100% and 70% of the turbulent particle and heat flux in the far SOL, respectively. The results of a second simulation with a 40 times higher resistivity are also discussed.

Filament transport, warm ions and erosion in ASDEX Upgrade L-modes

The dynamics of blob filaments are investigated in the scrape-off layer of ASDEX Upgrade by means of lithium beam emission spectroscopy. A comparison of the measurements in L-mode with a recently developed analytical blob model based on a drift-interchange-Alfvén fluid model indicates an influence of a finite ion temperature on the blob dynamics which has typically been neglected in other blob models. The blob dynamics agree well with the sheath-connected regime at lower plasma densities, and inertial effects play only a minor role. At higher densities, a transition into another regime with large blob amplitudes and increased transport is found. This points to a prominent role of blob transport at higher Greenwald fractions. On the basis of the measured blob properties, the erosion on plasma facing components is estimated. For pure deuterium plasmas, the high ion temperatures of blobs lead to a dominant erosion induced by blobs. However, if an impurity concentration of 1% is taken into account, the blob-induced erosion plays a minor role and background plasma parameters determine the total gross erosion.

Blob properties in L- and H-mode from gas-puff imaging in ASDEX upgrade

Blob properties are studied in the scrape-off layer of the tokamak ASDEX Upgrade with a fast camera. The gas-puff imaging technique is used to investigate the detection rate as well as the blob size and velocity scaling. The experiments were performed in L- and H-mode phases of the same discharges to study the change in blob properties after the L-H transition. In both regimes the detection rate is of the order of a few thousand blobs per second, which is compatible with the picture of blob generation by edge micro instabilities. The blob size increases in H-mode, while the radial velocity decreases slightly. The changes are, however, not indicating a drastic change in the blob dynamics in both phases. The experimentally found blob properties were compared to predictions from a novel blob model including effects due to a finite ion temperature, which should be more appropriate for the conditions in the SOL of fusion plasmas.

The influence of plasma edge dynamics on blob properties in the stellarator TJ-K

Blob properties are studied in the scrape-off layer of the stellarator TJ-K. Langmuir probes and a fast camera are used to investigate the generation rate as well as the blob size and velocity scaling. Discharges with different ion species and magnetic field strengths provide access to a large range of plasma parameters. It was found that almost every large amplitude drift wave in the edge of the confined plasma triggers blob generation in the scrape-off layer, which implies that the birth rate of blobs is determined by the turbulence in the edge. Furthermore, the cross-field size of the blobs seems to correlate with the size of the generating drift waves. Since the observed radial propagation velocity of the blobs is well described by a size dependent blob velocity model, the size coupling between the drift waves and the blobs also has an impact on the blob velocities. Thus, the presented results imply that the dynamics in the edge have a large influence on the blob properties in the scrape-off layer.

Profiles and Fluctuations in Edge and SOL Turbulence

AbstractThe time and space averaged profiles of temperature, particle density, and momentum are in the scrape off layer determined by the intermittent transport generated at the edge shear layer. The distinction between profiles and fluctuations becomes arbitrary for situations where the transport is highly intermittent and shows long range correlations. Without this distinction the full range in parameter variability has to be taken into account for simulations, posing extreme demands on the used models. Numerical investigations and experimental results show how the interplay between radially propagating structures and parallel transport sets up the observed profiles and how intermittency influences edge conditions. The filamentary blob structures also transport and generate currents in the SOL, which can be investigated by means of local magnetic diagnostics. Finally, the ratio of ion to electron temperature in the SOL is an important measure for the influence of finite larmor radius effects on the propagation properties of blobs. Numerical investigations indicate that these effects can lead to an increased self confinement and radial reach of these structures (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Blob birth and transport in the tokamak edge plasma: Analysis of imaging data

High-speed high-spatial-resolution data obtained by the gas puff imaging (GPI) diagnostic on the National Spherical Torus Experiment [M. Ono, M.G. Bell, R.E. Bell et al. Plasma Phys. Control. Fusion 45, A335 (2003).] is analyzed and interpreted in light of recent theoretical models for electrostatic edge turbulence and blob propagation. The experiment is described in terms of theoretical regimes that predict different dependencies for the radial velocity of blob convection. Using the GPI data, atomic physics analysis, and blob tracking on a restricted dataset, it is shown that the observed blob velocities in the scrape-off layer are bounded by a theory-based minimum velocity associated with the sheath-connected regime. A similar maximum velocity bound associated with the resistive-ballooning regime is also observed. Turning to the question of blob creation, it is shown that blobs are born with a density and temperature characteristic of the plasma conditions where underlying linear edge drift-curvature instabilities are localized. Finally, statistical variations in blob properties and in the radial blob velocity for given edge conditions are significant, and tend to mask any systematic changes among discharges with different conditions.