Irregular Regions Research Articles

The Structure and Liquid Flow Effect of Melt during NaCl Crystal Growth

AbstractThe quasi‐lattice model of NaCl melt is proposed by the ion movement characteristics, melt structure, and radial distribution function of ions, which is composed of regular and irregular regions. These regions are connected by an irregular interface with a thickness of several sublayers, and the ions on the interface are continuously and rapidly transferred. The mixed transmission kinetic equation of NaCl melt is analyzed theoretically by using the heat transfer equation and hydrodynamic equation. The liquid flow effect of NaCl melt and the temperature distribution in crystal are analyzed according to the numerical results. It is found that the shape of a solid–liquid interface will change with the rotation rate or diameter increase. The related properties of the NaCl melt are calculated. These studies of the NaCl melt provide theoretical support to a further study on crystal growth, other alkali halide, and alkaline earth metal halide melt.

Small-Scale Ionospheric Irregularities of Auroral Origin at Mid-latitudes during the 22 June 2015 Magnetic Storm and Their Effect on GPS Positioning

Small-scale ionospheric irregularities affect navigation and radio telecommunications. We studied small-scale irregularities observed during the 22 June 2015 geomagnetic storm and used experimental facilities at the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) located near Irkutsk, Russia (~52°N, 104°E). The facilities used were the DPS-4 ionosonde (spread-F width), receivers of the Irkutsk Incoherent Scatter Radar (Cygnus A signal amplitude scintillations), and GPS/GLONASS receivers (amplitude and phase scintillations), while 150 MHz Cygnus A signal recording provides a unique data set on ionosphere small-scale structure. We observed increased spread-F, Cygnus A signal amplitude scintillations, and GPS phase scintillations near 20 UT on 22 June 2015 at mid-latitudes. GPS/GLONASS amplitude scintillations were at a quiet time level. By using global total electron content (TEC) maps, we conclude that small-scale irregularities are most likely caused by the auroral oval expansion. In the small-scale irregularity region, we recorded an increase in the precise point positioning (PPP) error. Even at mid-latitudes, the mean PPP error is at least five times that of the quiet level and reaches 0.5 m.

Hydrodynamical backflow in X-shaped radio galaxy PKS 2014−55

ABSTRACT We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index images covering the giant (projected length l ≈ 1.57 Mpc) X-shaped radio source PKS 2014−55 with an unprecedented combination of brightness sensitivity and angular resolution. They show the clear ‘double boomerang’ morphology of hydrodynamical backflows from the straight main jets deflected by the large and oblique hot-gas halo of the host galaxy PGC 064440. The magnetic field orientation in PKS 2014−55 follows the flow lines from the jets through the secondary wings. The radio source is embedded in faint ($T_\mathrm{b} \approx 0.5 \mathrm{\, K}$) cocoons having the uniform brightness temperature and sharp outer edges characteristic of subsonic expansion into the ambient intragroup medium. The position angle of the much smaller (l ∼ 25 kpc) restarted central source is within 5° of the main jets, ruling out models that invoke jet re-orientation or two independent jets. Compression and turbulence in the backflows probably produce the irregular and low polarization bright region behind the apex of each boomerang as well as several features in the flow with bright heads and dark tails.

A three dimensional coupled VOF and Level set (VOSET) method with and without phase change on general curvilinear grids

A 3D coupled VOF and LS method (VOSET) on general curvilinear grids is developed for two-phase flow simulations in complex domains. The evolution of volume fraction with time is updated by calculating fluid volume fraction flux polyhedron passing through each face with geometrical approaches. The level set function is obtained by an iterative geometric operation. The level set based continuum surface tension model is derived to compute surface tension. Subsequently the model and the proposed coupled interfacial tracking method are incorporated into IDEAL, an incompressible Navier-Stokes solver. Finally, several benchmark problems including static bubble, sphere deformation, 3D Taylor instability growth, single bubble rising, two bubble merge and microchannel flow boiling are tested on irregular regions to validate the accuracy and robustness of the proposed method. The results show good agreement with previous literature results, indicating the present method is able to accurately simulate incompressible 3D two-phase flows in complex domains.

A decoupling control algorithm for Woofer–Tweeter adaptive optics system in generalized irregular pupil region

We proposed a decoupling control algorithm to accomplish the application of woofer–tweeter (W–T) adaptive optics system in generalized irregular pupil region. This algorithm firstly modifies the response matrix of woofer and tweeter by setting corresponding value at some sub-apertures of Shack–Hartmann(S–H) sensor to zero and constructs a slope-based orthogonal basis used to distribute different spatial frequency aberration to dual deformable mirrors (DMs). Then a limited condition is used to calculate the pseudo-inverse matrix of modified response matrix of dual DMs through single value decomposition. Finally, to restrain tweeter generating cross-coupling shape with woofer, a constraint matrix used to reset control vector of tweeter is constructed with the slope-based orthogonal basis and modified response matrix of tweeter. Numeral simulation of W–T adaptive optics system is built to verify the performance of this algorithm and results demonstrate that this algorithm has a good performance to control the W–T adaptive optics system in generalized irregular pupil region, and achieve better performance to suppress the cross-coupling between woofer and tweeter than Zernike decomposition algorithm. At the same time, the experimental results for the W–T AO system demonstrated that this algorithm is practical for the AO system with dual DMs in generalized irregular pupil region.

Trace fossil evidence for infaunal moulting in a Middle Devonian non-trilobite euarthropod

Trace fossils represent the primary source of information on the evolution of animal behaviour through deep time, and provide exceptional insights into complex life strategies that would be otherwise impossible to infer from the study of body parts alone. Here, we describe unusual trace fossils found in marginal-marine, storm- and river-flood deposits from the Middle Devonian Naranco Formation of Asturias (northern Spain) that constitute the first evidence for infaunal moulting in a non-trilobite euarthropod. The trace fossils are preserved in convex hyporelief, and include two main morphological variants that reflect a behavioural continuum. Morphotype 1 consists of a structure that superficially resembles a Rusophycus with an oval outline that possesses a distinctly three lobed axis with an elevated central ridge and regularly spaced transverse furrows that convey the appearance of discrete body segments. The anterior part is the most irregular region of the structure, and it is not always recorded. Morphotype 2 displays more elongated, tubular morphology. Careful observation, however, reveals that it comprises up to three successive morphotype 1 specimens organised in a linear fashion and partially truncating each other. Trilobate morphology and effaced transverse furrows are locally evident, but the predominant morphological feature is the continuous, elevated ridge. The detailed morphology of morphotype 1 and well-preserved, discrete segments of morphotype 2 closely resemble the dorsal exoskeleton of the enigmatic late Carboniferous euarthropod Camptophyllia, suggesting the possible affinities of the producer. Comparisons with patterns of Devonian phacopid trilobite exuviation suggest that the Naranco Formation trace fossils may have been produced by the infaunal activities of an euarthropod that anchored its dorsal exoskeleton in the firm sediment during the body inversion moult procedure. Our findings expand the phylogenetic and environmental occurrence of infaunal moulting in Palaeozoic euarthropods, and suggest a defensive strategy against predation, previously only known from trilobites preserved in open-marine deposits.

Investigation of Midlatitude Nighttime Ionospheric E‐F Coupling and Interhemispheric Coupling by Using COSMIC GPS Radio Occultation Measurements

AbstractThis study presents the statistical features of ionospheric E‐F coupling and interhemispheric coupling at midlatitudes. Nighttime ionospheric E and F region irregularity occurrences are investigated by using Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation measurements during 2006–2018. We presented four typical events of simultaneous observations of E and F region irregularities in the local hemisphere and F region irregularities in both conjugate hemispheres. Results of case studies indicate the coincidence of ionospheric irregularities in both E and F regions, as well as the coincidence of ionospheric irregularities in both F regions of two conjugate hemispheres. Statistical analysis of occurrences of E and F region irregularities shows that the concurrence of ionospheric irregularities in both E and F regions reaches a maximum (nearly 70%) during June (December) solstice in the Northern (Southern) Hemisphere. Nearly 50% (45%) of the F region irregularity in the Northern (Southern) Hemisphere occurs simultaneously with F region irregularity occurrence in the Southern (Northern) Hemisphere during December (June) solstice. These results provide the observational evidences showing that the effect of E‐F coupling and interhemispheric coupling may be important in generation of midlatitude nighttime F region irregularity. In addition, our results also reveal that mapping efficiency of electrodynamic coupling has a different seasonal variation in the Northern and Southern Hemispheres, which shows dependence on both the integrated Pedersen conductivity of F region ( ) and the integrated Hall conductivity of ES layer ( ).

Multi-scale superpatch matching using dual superpixel descriptors

Over-segmentation into superpixels is a very effective dimensionality reduction strategy, enabling fast dense image processing. The main issue of this approach is the inherent irregularity of the image decomposition compared to standard hierarchical multi-resolution schemes, especially when searching for similar neighboring patterns. Several works have attended to overcome this issue by taking into account the region irregularity into their comparison model. Nevertheless, they remain sub-optimal to provide robust and accurate superpixel neighborhood descriptors, since they only compute features within each region, poorly capturing contour information at superpixel borders. In this work, we address these limitations by introducing the dual superpatch, a novel superpixel neighborhood descriptor. This structure contains features computed in reduced superpixel regions, as well as at the interfaces of multiple superpixels to explicitly capture contour structure information. A fast multi-scale non-local matching framework is also introduced for the search of similar descriptors at different resolution levels in an image dataset. The proposed dual superpatch enables to more accurately capture similar structured patterns at different scales, and we demonstrate the robustness and performance of this new strategy on matching and supervised labeling applications.

Influence of chemical pretreatments on plant fiber cell wall and their implications on the appearance of fiber dislocations

AbstractThe cell wall of plant fibers may contain irregular regions called dislocations. This study evaluated the effect of chemical pretreatment as a mechanochemical dislocation initiator in unbleached and bleachedEucalyptussp. fibers. Accordingly, bleached and unbleached pulps of eucalyptus were subjected to chemical pretreatments with sodium hydroxide at concentrations of 5% for 2 h, 10% for 1 h and 10% for 2 h or with hydrogen peroxide. The extent of dislocations was evaluated by polarized light microscopy. Based on the observation, an index of dislocations (ID) expressing their ratio of cell wall as per two-dimensional (2D) imaging and their angle relative to the longitudinal direction of the fiber were estimated. Chemical pretreatments increased the ID for bleached and unbleached fibers as well as increased the changes in the curl of bleached and unbleached fibers for chemical pretreatments. Chemical pretreatment extracted the hemicellulose of the fiber cell wall causing some fiber to curl, which in turn generated new dislocations and modifications in the dislocation angles which may be useful for improving the deconstruction process of the cellulose fibers.

A study of the stability for a generalized finite-difference scheme applied to the advection–diffusion equation

A great number of phenomena can be modelled by using evolution equations. These equations can model different behaviors according to the problem of interest. The advection–diffusion equation models the dispersion of pollutants in water bodies such as rivers, lakes, and groundwater.In previous works, different results for the stability of generalized finite-difference applied to the advection equation and the diffusion equation have been presented.This paper deals with a study of the stability of a generalized finite-difference approximation of the advection–diffusion equation solved on non-rectangular and highly irregular regions using convex, logically rectangular grids. The discussed bounds for the time step are valid for any second-order finite difference scheme, regardless of a grid structure.

A Ray Tracing Simulation of HF Ionospheric Radar Performance at African Equatorial Latitudes

AbstractHigh‐frequency (HF) coherent radars are widely applied for studying electrodynamic processes in the Earth's upper atmosphere and ionosphere. Super Dual Auroral Radar Network (SuperDARN) is an international network of such radars located at high‐ and middle‐latitude regions in the Northern and Southern Hemispheres. A major criterion of the HF coherent radar technique entails that the HF waves propagate orthogonal to the geomagnetic field lines (aspect angle 1°) in the ionospheric irregularity region from where backscatter originates. In this paper we present an HF ray tracing simulation of the performance of three proposed equatorial HF radar systems for the African equatorial sector. We use a number of realistic average ionospheres deduced from the International Reference Ionosphere (IRI) 2012 model and magnetic field geometries from the International Geomagnetic Reference Field (IGRF) to determine likely propagation paths and orthogonality conditions for such radar systems. The east‐west azimuth ( 25° range) has a significant likelihood of achieving a SuperDARN‐type backscatter in the African equatorial sector, mainly due to the prevailing magnetic field geometry. This analysis provides a feasibility study for developing a SuperDARN‐like radar for studying the equatorial ionosphere over the African longitude sector, for example, in determining the technical radar characteristics such as preferable operating frequencies, antenna boresight orientation, and azimuth coverage and provides a simulation of the expected localization of radar backscatter as a function of radar location and beam direction, as well as the time of day, season, and sunspot number.

Investigation of the Occurrence of Nighttime Topside Ionospheric Irregularities in Low-Latitude and Equatorial Regions Using CYGNSS Satellites.

By using multi-satellite observations of the L1 signal-to-noise ratio (SNR) from the Cyclone Global Navigation Satellite System (CYGNSS) taken in 2017, we present the occurrence of nighttime topside ionospheric irregularities in low-latitude and equatorial regions. The most significant finding of this study is the existence of longitudinal structures with a wavenumber 4 pattern in the topside irregularities. This suggests that lower atmospheric waves, especially a daytime diurnal eastward-propagating zonal wave number-3 nonmigrating tide (DE3), might play an important role in the generation of topside plasma bubbles during the low solar minimum. Observations of scintillation events indicate that the maximum occurrence of nighttime topside ionospheric irregularities occurs on the magnetic equator during the equinoxes. The current work, which could be regarded as an important update of the previous investigations, would be readily for the further global analysis of the topside ionospheric irregularities.

Bacterial nanocellulose membranes loaded with vitamin B-based ionic liquids for dermal care applications

The development of innovative bio-based skin care products has received an increased attention in the latter years. In the present work, the synthesis of original active principle ingredients based on ionic liquids (ILs) with cholinium cation and vitamins B anions, followed by their incorporation in bacterial nanocellulose (BC) membranes for topical applications, is reported. Three ILs, namely cholinium nicotinate [Ch][B3], cholinium pantothenate [Ch][B5] and cholinium pyridoxylate [Ch][B6], were synthesized through a metathesis reaction and their structure characterized in detail. Thermal analysis confirmed their denomination as ILs and their high thermal resistance. The solubility of these ILs was higher than their vitamin precursors, especially in the case of [Ch][B3] whose solubility increased 30.6-fold enhancing the bioavailability of this vitamin. The incorporation of ILs in BC led to translucent and homogeneous membranes stable up to 190 °C. ILs acted as plasticizers reducing BC brittleness that facilitated their application on irregular skin regions. Moreover, the re-hydration ability of BC-ILs membranes was improved 2.9 to 4.8-fold in comparison to BC, ensuring adequate hydration for ILs release, while the release of ILs in buffer solutions was more complete and faster than the release of vitamins. Finally, BC-ILs were proven not cytotoxic to skin epithelial cells and thus are suitable materials for skin care applications.

Rapid numerical approximation method for integrated covariance functions over irregular data regions

In many practical applications, spatial data are often collected at areal levels (i.e., block data), and the inferences and predictions about the variable at points or blocks different from those at which it has been observed typically depend on integrals of the underlying continuous spatial process. In this paper, we describe a method based on Fourier transforms by which multiple integrals of covariance functions over irregular data regions may be numerically approximated with the same level of accuracy as traditional methods, but at a greatly reduced computational expense.

Omni-Directional Obstacle Detection for Vehicles Based on Depth Camera

At present, the vehicle obstacle detection system usually uses different devices or sensors to perceive and obtain the obstacle information. However, omni-directional obstacle detection is difficult to realize because these devices or sensors are usually easy to be affected by environmental lighting and the material properties of the obstacle surface. Furthermore, most sensors have limited information regarding distance, which limits their application to omni-directional obstacle detection. To solve this problem, this paper proposes a method using depth camera for omni-directional obstacle detection. A method applying region growth for depth image and a fast inpainting method for depth image are proposed to extract and repair the obstacle regions in the depth images obtained by installing depth cameras around the car body. An improved method applying iterative normalized cut is also proposed to cluster and segment fragmentary and irregular obstacle regions to generate the complete obstacle regions. Finally, the obstacle regions are overviewed using a three-dimensional visualization method to realize omni-directional obstacle viewing. The results of experiments conducted in an environment with different obstacles during the day and night demonstrate that, compared with other methods, our proposed approach can effectively promote the ability to detect complex obstacles, and largely improve the detection speed; furthermore, obstacle detection using our method will be unaffected by environmental lighting. Each of these advantages provided by our method can significantly promote the driving safety of unmanned or other types of vehicles.

Multiscale Dynamic Graph Convolutional Network for Hyperspectral Image Classification

Convolutional neural network (CNN) has demonstrated impressive ability to represent hyperspectral images and to achieve promising results in hyperspectral image classification. However, traditional CNN models can only operate convolution on regular square image regions with fixed size and weights, and thus, they cannot universally adapt to the distinct local regions with various object distributions and geometric appearances. Therefore, their classification performances are still to be improved, especially in class boundaries. To alleviate this shortcoming, we consider employing the recently proposed graph convolutional network (GCN) for hyperspectral image classification, as it can conduct the convolution on arbitrarily structured non-Euclidean data and is applicable to the irregular image regions represented by graph topological information. Different from the commonly used GCN models that work on a fixed graph, we enable the graph to be dynamically updated along with the graph convolution process so that these two steps can be benefited from each other to gradually produce the discriminative embedded features as well as a refined graph. Moreover, to comprehensively deploy the multiscale information inherited by hyperspectral images, we establish multiple input graphs with different neighborhood scales to extensively exploit the diversified spectral–spatial correlations at multiple scales. Therefore, our method is termed multiscale dynamic GCN (MDGCN). The experimental results on three typical benchmark data sets firmly demonstrate the superiority of the proposed MDGCN to other state-of-the-art methods in both qualitative and quantitative aspects.

Mixed-Unit Lattice Approach for Area Determination of Cellular and Subcellular Structures

Even small changes in the dimensions of cellular and subcellular structures can inform an ongoing disease. An increase in glomerular dimensions is associated with kidney disease and can predict glomerulosclerosis, whereas an increase in the size of fluid-filled renal cysts is predictive of end-stage polycystic kidney disease. In the absence of set formulae to define the area of curvilinear irregular regions, such as glomeruli and cysts, the method of counting unit squares is used. Nonetheless, as infinitesimally small as the unit square may be, this 2D space-filling method still underestimates the area of a curvilinear region. Developed herein is a mixed-unit lattice approach that represents an improvement over the existing method for estimating the areas of cellular and subcellular structures. In test cases comprising images of glomeruli and renal cysts, this method outperformed the conventional unit-squares method, and may form the foundation for refining the current method used by most types of software for estimating the area of irregular curvilinear regions.

All‐Sky Interferometric Meteor Radar Observations of Zonal Structure and Drifts of Low‐Latitude Ionospheric E Region Irregularities

AbstractAll‐sky interferometric meteor radar has been operated worldwide for the measurements of neutral winds in the mesopause region. In this paper, we employ an all‐sky meteor radar and an ionospheric radar, which are situated at Ledong (18.4°N,109°E) and Sanya (18.3°N,109.6°E), respectively, and both have the interferometry capability, to study the zonal structure and drifts of ionospheric E region irregularities producing continuous and quasiperiodic echoes. We use the collocated optical meteor observations to calibrate the radar system phase offsets for interferometry measurements. A good correspondence between the irregularity measurements from both radars was found. The observations show that the quasiperiodic striations with both negative and positive slopes in radar range‐time‐intensity maps were produced by spatially separated irregularity structures, which drift through the radar field of view. The continuous echoes were due to irregularities generated locally. Specifically, comparing with ionospheric radar, all‐sky meteor radar has a much wider field of view that can provide E region irregularity information over a large zonal region of more than 300 km. It is suggested that all‐sky meteor radar provides a capability to probe ionospheric E region irregularities and to trace their movements.

Limited One-time Sampling Irregularity Map (LOTS-IM) for Automatic Unsupervised Assessment of White Matter Hyperintensities and Multiple Sclerosis Lesions in Structural Brain Magnetic Resonance Images

We present the application of limited one-time sampling irregularity map (LOTS-IM): a fully automatic unsupervised approach to extract brain tissue irregularities in magnetic resonance images (MRI), for quantitatively assessing white matter hyperintensities (WMH) of presumed vascular origin, and multiple sclerosis (MS) lesions and their progression. LOTS-IM generates an irregularity map (IM) that represents all voxels as irregularity values with respect to the ones considered ”normal”. Unlike probability values, IM represents both regular and irregular regions in the brain based on the original MRI's texture information. We evaluated and compared the use of IM for WMH and MS lesions segmentation on T2-FLAIR MRI with the state-of-the-art unsupervised lesions’ segmentation method, Lesion Growth Algorithm from the public toolbox Lesion Segmentation Toolbox (LST-LGA), with several well established conventional supervised machine learning schemes and with state-of-the-art supervised deep learning methods for WMH segmentation. In our experiments, LOTS-IM outperformed unsupervised method LST-LGA on WMH segmentation, both in performance and processing speed, thanks to the limited one-time sampling scheme and its implementation on GPU. Our method also outperformed supervised conventional machine learning algorithms (i.e., support vector machine (SVM) and random forest (RF)) and deep learning algorithms (i.e., deep Boltzmann machine (DBM) and convolutional encoder network (CEN)), while yielding comparable results to the convolutional neural network schemes that rank top of the algorithms developed up to date for this purpose (i.e., UResNet and UNet). LOTS-IM also performed well on MS lesions segmentation, performing similar to LST-LGA. On the other hand, the high sensitivity of IM on depicting signal change deems suitable for assessing MS progression, although care must be taken with signal changes not reflective of a true pathology.

Theoretical Study of Twinning Boundaries in Twinned Gold Nanorod Using Evolutionary Algorithms Aided Computational Simulations

Fivefold twinned gold nanorods have been widely used in many different fields. It is crucial to understand their twinning structures and related activities. In this work, we conducted computational simulations of the twinning boundaries of the 5-fold twinned gold nanorod, which consists of five single crystal regions and one irregular boundary region with a 7.5° wedge angle. Force-field calculations aided by an evolutionary algorithm based optimization scheme were performed to extensively sample the twinning boundary structures, and several analytical schemes were used to describe the differences among the various located structures, which also help better understand their relationship with stabilities. Moreover, adsorptions of probe molecules at different regions of the twinned gold nanorods, as well as those at single crystalline Au surfaces, were also calculated to illustrate their catalytic activities. The calculated results show that the charge transfer from the twinning boundary to the single crystal regions occurs due to its irregular atomic arrangement, and the accumulated electrons at the single crystal regions can significantly increase their surface activities.