Velocity Trends Research Articles

Ultrasound shear wave elastography for patients with sialolithiasis undergoing interventional sialendoscopy.

Ultrasound shear wave elastography is an objective tool to evaluate the stiffness of human tissues. Patients with sialolithiasis could be treated by interventional sialendoscopy with a high success rate. Sialolithiasis could be extracted, and the diseased gland could be preserved and evaluated after treatment. Whether ultrasound shear wave elastography could be used for objective outcome measurement and short-term follow-up of the parenchyma of gland in patients with sialolithiasis remains unclear. This retrospective self-controlled study was conducted. Patients with sialolithiasis treated by interventional sialendoscopy and followed by high-resolution ultrasound shear wave elastography were selected between January and September 2017. Seventeen patients with sialolithiasis (mean age: 39.63 ± 12.49 years), including 10 women and 7 men, were enrolled. Fifteen patients had sialolithiasis in the submandibular gland and two in the parotid gland. The preoperative value of shear wave velocity was significantly higher in the diseased gland than in the contralateral normal gland (p < .001; 95% confidence interval [CI], 0.3915-0.6046). After successful treatment by interventional sialendoscopy surgery, the shear wave velocity of the diseased gland decreased significantly (p=0.001; 95% CI, -0.38792 to -0.20474). However, there was a significant difference between the diseased and contralateral normal glands (p=0.001; 95% CI, 0.0423-0.2895) after 1.55 months of surgery. Ultrasound shear wave elastography could be an adjuvant tool to distinguish sialolithiasis-affected diseased glands from contralateral normal glands and assess the short-term treatment outcome objectively. The changing trend of shear wave velocity could help monitor the healing process of the parenchyma in the diseased gland after treatment. 4.

Effects of clay types and fractions on elastic properties of artificial clay-bearing sandstones: an experimental study

AbstractExperimentally understanding the effects of clay type and fraction on the elastic properties of clay-bearing sandstone is crucial for exploring hydrocarbon reservoirs. Therefore, we artificially synthesized a series of pure clay rocks and clay-bearing sandstones with different clay types and fractions, and conducted the ultrasonic measurements to investigate the elastic behaviors. According to experiments on pure clay rocks, illite rocks have the highest porosity, followed by montmorillonite rocks and chlorite rocks. In terms of elastic properties, illite rocks show the highest ultrasonic P- and S-wave velocities, followed by chlorite rocks and montmorillonite rocks. For clay-bearing sandstones, the measured results indicate that clay types and fractions significantly influence both the physical and elastic properties. Specifically, the porosity of chlorite-bearing sandstone is systematically lower than that of illite-bearing and montmorillonite-bearing sandstone. The chlorite-bearing sandstone has the highest P- and S-wave velocities, followed by illite-bearing and montmorillonite-bearing sandstone. Moreover, the clay fraction also affects porosity–velocity trends. The porosity first falls and then increases as the clay fraction rises, while the P- and S-wave velocities first rise and then fall and, in turn the turning point occurs at the ∼30% clay fraction. The potential mechanism of the turning point is analyzed based on the microscopic distribution of clay and sandstone. Additionally, the clay fraction and distribution also affect the electrical conductivity and permeability of the clay-bearing sandstone, implies that the clay types, clay fraction and clay distribution are non-negligible factors in reservoir evaluation.

Intelligent velocity picking considering an expert experience based on the Chan–Vese model and mean-shift clustering

The velocity of seismic data can initially be established by identifying energy clusters on velocity spectra at different moments, which is crucial to the migration imaging and the stacking of common midpoint (CMP) gathers in the seismic data processing. However, the identification of energy clusters currently relies on manual work, with low efficiency and different standards. With the increasing application of wide-frequency, wide-azimuth, and high-density seismic exploration technology, the amount of seismic data has increased significantly, greatly increasing the cost of manual labor and time. In this paper, an intelligent velocity picking method based on the Chan–Vese (CV) model and mean-shift clustering algorithm was proposed. It can be divided into three steps. First, a velocity trend band is set up on the velocity spectrum by experts to avoid multiples and other noises. Then, the velocity trend band is applied to the Chan–Vese model as the initial time condition to segment the velocity spectrum and obtain the velocity candidate region. Finally, mean-shift clustering is adopted to cluster the useful energy clusters retained in the candidate region derived from the Chan–Vese model. When implementing the mean-shift clustering algorithm, the Gaussian kernel function and the energy of the velocity spectrum are utilized to control the efficiency and accuracy of the cluster. The tests of the model and real data prove that the proposed method can dramatically improve the accuracy and efficiency of velocity picking compared with the K-means and manual picking method.

Classifying the satellite plane membership of Centaurus A’s dwarf galaxies using orbital alignment constraints

ABSTRACT The flattened, possibly co-rotating plane of satellite galaxies around Centaurus A, if more than a fortuitous alignment, adds to the pre-existing tension between the well-studied Milky Way and M31 planes and the Lambda cold dark matter model of structure formation. It was recently reported that the Centaurus A satellite plane (CASP) may be rotationally supported, but a further understanding of the system’s kinematics is elusive in the absence of full 3D velocities. We constrain the transverse velocities of 27 satellites that would rotationally stabilize the Centaurus A plane, and classify the satellites by whether their possible orbits are consistent with the CASP. Five satellites are identified to be unlikely to participate in the plane, two of which are clearly non-members. Despite their previously reported line-of-sight velocity trend suggestive of a common co-rotating motion, 17 out of 22 potential CASP members are consistent with either orbital direction within both the full range of possible kinematics as well as when limiting orbits to those within the plane. On the other hand, disregarding the 5 off-plane satellites found to be inconsistent with CASP membership enhances the significance of the CASP’s line-of-sight velocity trend fivefold. Our results are robust with different mass estimates of the Centaurus A halo, and the adoption of either spherical or triaxial NFW potentials.

Cell counting and velocity algorithms for hydrodynamic study of unsteady biological flows in micro-channels.

In this paper, the combination of two algorithms, a cell counting algorithm and a velocity algorithm based on a Digital Particle Image Velocimetry (DPIV) method, is presented to study the collective behavior of micro-particles in response to hydrodynamic stimuli. A wide experimental campaign was conducted using micro-particles of different natures and diameters (from to ), such as living cells and silica beads. The biological fluids were injected at the inlet of a micro-channel with an external oscillating flow, and the process was monitored in an investigated area, simultaneously, through a CCD camera and a photo-detector. The proposed data analysis procedure is based on the DPIV-based algorithm to extrapolate the micro-particles velocities and a custom counting algorithm to obtain the instantaneous micro-particles number. The counting algorithm was easily integrated with the DPIV-based algorithm, to automatically run the analysis to different videos and to post-process the results in time and frequency domain. The performed experiments highlight the difference in the micro-particles hydrodynamic responses to external stimuli and the possibility to associate them with the micro-particles physical properties. Furthermore, in order to overcome the hardware and software requirements for the development of a real-time approach, it was also investigated the possibility to detect the flows by photo-detector signals as an alternative to camera acquisition. The photo-detector signals were compared with the velocity trends as a proof of concept for further simplification and speed-up of the data acquisition and analysis. The algorithm flexibility underlines the potential of the proposed methodology to be suitable for real-time detection in embedded systems.

Impact of seasonal fluctuations of ice velocity on decadal trends observed in Southwest Greenland

By tracking the feature displacement between satellite images spaced approximately one year apart, surface runoff has been shown to have a long-term impact on the average ice flow of a land-terminating sector of Greenland. In this study, we revisit the multi-year trends in ice flow by assessing more carefully the impact of seasonal fluctuation in velocity on the annual mean ice velocity. We find that, depending on the length and period used to measure displacement, seasonal fluctuations do have an impact on observed velocities on up to 15%, and can affect decadal trends. Nevertheless, the magnitude of this fluctuation is small enough to confirm the general slowdown observed during the 2000–2012 period. Between 2012 and 2019, we find significant re-acceleration of low-lying glaciers tongue but velocity trends elsewhere are generally insignificant and not spatially consistent. Finally, we propose a more selective approach to recovering velocity trends using satellite imagery that involves using only measurements where the image pair starting date is before summer, in order to have comparable measurements for every year, sampling a melt season and the following winter.

A new linear stability analysis approach for microchannel flow based on the Boltzmann Bhatnagar–Gross–Krook equation

Microchannels are important components of microelectromechanical systems (MEMSs) that encounter rarefaction effects due to their small-scale characteristics. The influence of rarefaction effects on the flow stability of microchannels should be investigated to improve MEMS performance. Based on kinetic theory, a linear stability analysis approach for low-speed rarefied flows was developed by using the Bhatnagar–Gross–Krook (BGK) model of the Boltzmann equation with an external force term. This approach was applied to study the linear temporal stability of microchannel flows. A slip flow model was introduced for comparison. The corresponding eigenvalue problem was solved with a Chebyshev collocation method. This novel approach yielded a critical Reynolds number of 5778. Analysis of the validity and accuracy of the slip flow model shows that although this model cannot capture the Knudsen layer structure, this approach effectively improves the prediction accuracy of the growth rate of the least stable mode. However, the prediction accuracy gradually decreases with increasing Knudsen number. Compared with the stability results obtained from the BGK equation, the Navier–Stokes equations-based stability analysis method always underestimates the disturbance growth rate, regardless of whether a slip flow model is used. The stability analysis results show that rarefaction effects stabilize the flow. The degree of rarefaction does not affect the trends of growth rate and phase velocity with wavenumber, nor does it affect the shape of the velocity eigenfunctions. For a rarefied case, increasing the Mach number has a destabilizing effect on low-speed microchannel flows.

ESPRESSO observations of HE 0107−5240 and other CEMP-no stars with [Fe/H] ≤ –4.5

Context. HE 0107−5240 is a hyper metal-poor star with [Fe/H] = −5.39, one of the lowest-metallicity stars known. Its stellar atmosphere is enhanced in carbon, with [C/Fe] = +4.0, without a detectable presence of neutron-capture elements. Therefore, it belongs to the carbon-enhanced metal-poor (CEMP−no) group, along with the majority of the most metal-poor stars known to date. Recent studies have revealed variations in the line-of-sight velocity of HE 0107−5240, suggesting it belongs to a binary system. CEMP-no stars are the closest descendants of the very first Pop III stars, and binarity holds important clues for the poorly known mechanism that leads to their formation. Aims. We performed high-resolution observations with the ESPRESSO spectrograph at the VLT to constrain the kinematical properties of the binary system HE 0107−5240 and to probe the binarity of the sample of the eight most metal-poor stars with [Fe/H] ≤ −4.5. Methods. Radial velocities are obtained by using a cross-correlation function in the interval 4200−4315 Å , which contains the relatively strong CH band, against a template that could be either a synthetic spectrum or a combined observed spectrum in an iterative process. A Bayesian method is applied to calculate the orbit using the ESPRESSO measurements and others from the literature. Chemical analysis has also been performed for HE 0107−5240, employing spectral synthesis with the SYNTHE and ATLAS codes. Results. Observations of HE 0107−5240 spanning more than 3 years show a monotonic decreasing trend in radial velocity at a rate of approximately 0.5 m s−1 d−1. A maximum vrad was reached between March 13, 2012, and December 8, 2014. The period is constrained at Porb = 13009−1370+1496 d. New, more stringent upper limits have been found for several elements: (a) [Sr/Fe] and [Ba/Fe] are lower than −0.76 and +0.2, respectively, confirming the star is a CEMP-no; (b) A(Li) &lt; 0.5 is well below the plateau at A(Li) = 1.1 found in the lower red giant branch stars, suggesting Li was originally depleted; and (c) the isotopic ratio 12C/13C is 87 ± 6, showing very low 13C in contrast to what is expected from a ‘spinstar’ progenitor. Conclusions. We confirm that HE 0107−5240 is a binary star with a long period of about 13 000 d (∼36 yr). The carbon isotopic ratio excludes the possibility that the companion has gone through the asymptotic giant branch phase and transferred mass to the currently observed star. The binarity of HE 0107−5240 implies that some of the first generations of low-mass stars formed in multiple systems and indicates that the low metallicity does not preclude the formation of binaries. Finally, a solid indication of vrad variation has also been found in SMSS 1605−1443.

Research on preprocessing of winding trajectory of composite type IV pressure vessel based on robot

Herein, a smooth preprocessing method of robotic end-effector trajectory, based on Nurbs curve is proposed for obtaining the complete and stable envelope trajectory of the robot. Initially, the winding pattern of pressure vessel based on non-geodesic is deduced, followed by positioning of yarn point based on doffing point distribution and preprocessing of the trajectory through Nurbs curve. Variation trend and stationarity of velocity and acceleration in carriage and cross-carriage directions in Cartesian coordinate system are analyzed. Finally, the winding experiment of type IV pressure vessel is wound with the robotic winding workstation. Results show that the fiber winding can be carried out stably by the end of the robot. The realtime movement curve of the robot is consistent with the simulation curve, and the pressure liner is completely covered without yarn sliding and overhead problems, verifying the feasibility of the as-reported preprocessing method.

Rapid variations of Si IV spectra in a flare observed by interface region imaging spectrograph at a sub-second cadence

We report on observations of highly-varying Si IV 1402.77 Å line profiles observed with the Interface Region Imaging Spectrograph (IRIS) during the M-class flare from 18 January 2022 at an unprecedented 0.8 s cadence. Moment analysis of this line observed in flare ribbon kernels showed that the intensity, Doppler velocity, and non-thermal broadening exhibited variations with periods below 10 s. These variations were found to be correlated with properties of the Gaussian fit to a well-resolved secondary component of the line redshifted by up to 70 km s−1, while the primary component was consistently observed near the rest wavelength of the line. A particularly high correlation was found between the non-thermal broadening of the line resulting from the moment analysis and the redshift of the secondary component. This means that the oscillatory enhancements in the line broadening were due to plasma flows (away from the observer) with varying properties. A simple de-projection of the Doppler velocities of the secondary component based on a three-dimensional reconstruction of flare loops rooted in the kernel suggests that the observed flows were caused by downflows and compatible with strong condensation flows recently predicted by numerical simulations. Furthermore, peaks of the intensity and the trends of Doppler velocity of the Gaussian fit to the secondary component (averaged in the ribbon) were found to correspond to one of the quasi-periodic pulsations (QPPs) detected during the event in the soft X-ray flux (as measured by the Geostationary Operational Environmental Satellite, GOES) and the microwave radio flux (as measured by the Expanded Owens Valley Solar Array, EOVSA). This result supports a scenario in which the QPPs were driven by repeated magnetic reconnection.

Design of signal processing circuit for acoustic Doppler Current Profiler

according to the measurement principle and performance requirements of acoustic Doppler velocity profile, a circuit for weak frequency signal processing is designed. The measurement principle, circuit structure, data comparison before and after signal processing and frequency measurement accuracy data analysis are introduced. The performance comparison and application of the instrument are carried out according to the relevant standards. The experimental results show that the signal processing circuit realizes the constant amplitude amplification of the wide dynamic range frequency signal, and the processed signal is converted by A / D and then measured by digital frequency to obtain a high frequency accuracy. In the application of channel flow measurement, the velocity profile can reflect the change trend of cross-section velocity and complete the accurate measurement of flow rate. It shows that the flow profile instrument based on the signal processing circuit can meet the requirements of on-line monitoring of flow velocity and flow of river and channel.

Confirmation and characterisation of three giant planets detected by TESS from the FIES/NOT and Tull/McDonald spectrographs

We report the confirmation and characterisation of TOI-1820 b, TOI-2025 b, and TOI-2158 b, three Jupiter-sized planets on short-period orbits around G-type stars detected by TESS. Through our ground-based efforts using the FIES and Tull spectrographs, we have confirmed these planets and characterised their orbits, and find periods of around 4.9 d, 8.9 d, and 8.6 d for TOI-1820 b, TOI-2025 b, and TOI-2158 b, respectively. The sizes of the planets range from 0.96 to 1.14 Jupiter radii, and their masses are in the range from 0.8 to 4.4 Jupiter masses. For two of the systems, namely TOI-2025 and TOI-2158, we see a long-term trend in the radial velocities, indicating the presence of an outer companion in each of the two systems. For TOI-2025 we furthermore find the star to be well aligned with the orbit, with a projected obliquity of 9−31+33°. As these planets are all found in relatively bright systems (V ~ 10.9–11.6 mag), they are well suited for further studies, which could help shed light on the formation and migration of hot and warm Jupiters.

Deep learning strategy for salt model building

Velocity models are crucial intermediate products generated in seismic data processing, and the model’s accuracy is essential for constructing quality seismic images. Conventional approaches to velocity-model building (VMB) use a family of inversion methods, among which are ray-based tomography and full-waveform inversion. These methods have been highly optimized throughout the years but are still heavily dependent on continuous human curation of the results, which leads to an overall high time cost, especially in areas with high structural complexity, such as those containing salt tectonics. We have investigated a deep learning (DL) approach that accurately defines salt geometries for VMB. We train our convolutional neural network on synthetic shot gather data, explore a manner of leveraging information through summation of shot data, and determine the influence that the choice of loss function has on the quality and aspect of predicted velocity models. Our residual U-Net model trained on data containing only randomly shaped salt bodies can estimate geologically complex salt geometries such as those in 2D SEG/EAGE salt model slices. Our results find that deeper encoder-decoder models with shortcut connections resolve velocity model structures better than shallower models. Moreover, network models trained with a composite loss function — combining mean absolute error and the multiscale structural similarity index — better delineate the contours of areas with high-velocity contrast and better recover regions with a uniform velocity trend than network models trained with conventional loss functions like the mean squared error. The residual U-Net and loss functions that we use are not task-specific and can be extended to other DL approaches to VMB.

Magnetite water based ferrofluid flow and convection heat transfer on a vertical flat plate: Mathematical and statistical modelling

The unique magnetic properties of ferrofluid when exposed to the magnetic field led to the ferrofluid formulation in wide applications, especially as a thermal transfer. To picture the effective ferrofluid flow configurations and heat transfer mechanism at a surface, it is crucial to figure out the phenomenology of boundary layer and convective heat transfer. This study investigates a numerical solution of the mixed convection boundary layer flow of ferrofluid at the stagnation point on a vertical flat plate. Ferrofluid composed of magnetite (Fe3O4) water based exposure to the magnetic field and thermal radiation is considered. The complicated governing differential equations of fluid flow and heat transfer are simplified into simple equations using boundary layer approximation, Boussinesq approximation and similarity transformations. Then, the equations are solved numerically by employing the Keller-box method. Numerical results discovered that the ferroparticles volume fraction is the predominant factor in contributing to the trend of ferrofluid velocity, reduced skin friction and reduced Nusselt number. Further, the influence of the ferroparticles volume fraction on reduced skin friction and reduced Nusselt number are analyzed using regression analysis.

Experimental study of coherent structures downstream mixing vaned spacer grid of different inclination angles in a 5 × 5 rod bundle by TR-PIV

Experimental study of coherent structures downstream of a spacer grid with different inclination angles (20°, 25°, 30°) of split-type mixing vanes in a 5 × 5 rod bundle was conducted by time-resolved particle image velocimetry (TR-PIV) under Reynolds number from 6.6 × 103 to 3.96 × 104. The fluorinated ethylene propylene (FEP) tubes and water are used as the matched index of refraction (MIR) materials. The maximum standard uncertainty of time-averaged velocity is less than 2 % of bulk flow velocity (Wb), and that of Reynolds stress is less than 2 % Wb2.The secondary flow structures downstream spacer grid with mixing vanes of different inclination angles change with several similar patterns, including vortices shedding from mixing vanes and fast dissipation near spacer grid, counter-current shear-flow development and shear-flow induced vortices formation, shear-flow induced vortices decaying and dissipation. The development trends of spanwise time-averaged velocity, Reynolds stress, integral spatial length scales and integral temporal length scales are determined by coherent structures. With Reynolds number increasing, smaller coherent structures are generated and the time-averaged velocity, Reynolds stress, spatial and temporal length scales decrease. Larger inclination angle generates larger coherent structures, and spatial and temporal length scales increase with inclination angle increasing.The experimental findings provide valuable information for understanding sub-channel mixing phenomena caused by mixing vaned spacer grids. The experimental data can be used for sub-channel mixing model developments and validations of turbulent models.

Supraglacial lake expansion, intensified lake drainage frequency, and first observation of coupled lake drainage, during 1985–2020 at Ryder Glacier, Northern Greenland

Along the Greenland Ice Sheet margin, supraglacial lakes store and redistribute ice sheet surface run off, and comprise an important potential hydrological link between the ice surface and the base, with ramifications for subglacial drainage systems and ice flow. As a consequence of increasing global mean surface air temperatures, these lakes have been predicted to expand further inland and to affect larger areas of the ice sheet. However, as contemporary dynamics of such supraglacial lake expansion are not well studied, any assessment of their future implications remains afflicted with uncertainty. Here, recent changes in supraglacial lake distribution and expansion, and in their drainage behavior and frequency, are presented for Ryder Glacier, Northern Greenland, as concluded from a remote sensing based analysis. The 35-year time span covered in the analysis allows for the detection of trends in lake processes and ice velocity, which otherwise were found to exhibit large inter-annual variability. It also reveals the first occurrence of a coupled lake drainage event in 2002. By linking supraglacial lake expansion, drainage modes, and drainage frequency to the efficiency of the subglacial drainage system and ice flow on seasonal and decadal timescales, a contribution is made to better understand the complexity of coupled glacio-hydrological processes, and to help reduce uncertainties in predictions of future mass loss from the Greenland Ice Sheet.

Rock-physics modeling for the elastic properties of gas hydrate-bearing sediments under varying fluid saturation and temperature

The microscale physical properties of gas hydrate-bearing sediments (HBSs) are significant for understanding their macroscale elastic responses and further facilitating seismic exploration. Several models have been developed to investigate the microscale properties of gas HBSs, whereas most of them place emphasis on the construction of the rock frame, ignoring the influence of mixing patterns of pore fluids. Based on laboratory observations, we have developed a rock-physics model that integrates the spatial distribution of gas hydrate, water, and free gas in pores; in addition, this model considers the variable stress-strain relationship of the pore fluids depending on hydrate saturation. We also attempt to incorporate the effect of temperature on the elastic properties of gas HBSs through theoretical modeling. Our approach of handling hydrate-gas spatial relationship reasonably delineates the velocity trends, ensuring that prediction results are congruent with field data. Moreover, the variable stress-strain relationship of the pore fluids allows for the achievement of better simulation results than those by conventional iso-stress and iso-strain fluid mixing schemes. Integrating the factors tied to hydrate dissociation and hydrate moduli reduction during heating processes enables the prediction of a declining trend in the velocity-temperature relation, which is congruent with laboratory-measured data. This model provides an alternative approach to predict the elastic properties of gas HBSs and can reasonably explain the effects of fluid saturation and temperature.

An Automatic Drift-Measurement-Data-Processing Method with Digital Ionosondes

Drift detection is one of the important detection modes in a digital ionosonde system. In this paper, a new data processing method is presented for boosting the automatic and high-quality drift measurement, which is helpful for long-term ionospheric observation, and has been successfully applied to the Chinese Academy of Sciences, Digital Ionosonde (CAS-DIS). Based on Doppler interferometry principle, this method can be successively divided into four constraint steps: extracting the stable echo data; restricting the ionospheric detection region; extracting the reliable reflection cluster, including Doppler filtering and coarse clustering analysis; and calculating the drift velocity. Ordinary wave (O-wave) data extraction, complementary code pulse compression and other data preprocessing techniques are used to improve the signal-to-noise ratio (SNR) of echo data. For the purpose of eliminating multiple echoes, the ionospheric region is determined by combining the optimal height range and detection frequencies obtained from the ionogram. Successively, Doppler filtering and coarse clustering analysis extract reliable reflection clusters. Finally, the weighting factor is brought in, and then weighted least-squares (WLS) is used to fit the drift velocity. The entire data processing process can be implemented automatically without constantly changing parameter settings due to changes in external conditions. This is the first time coarse clustering analysis has been used to extract the paracentral reflection cluster to eliminate scattered reflection points and outer reflection clusters, which further reduces the impacts of external conditions on parameter settings and improves the ability of automatic drift measurement. Compared with the previous method possessed by Digisonde Protable Sounder 4D (DPS4D), the new method can achieve comparable drift detection precision and results even with fewer reflection points. In 2021–2022, several experiments on F region drift detection were carried out in Hainan, China. Results indicate that drift velocities fitted by the new method have diurnal variation and change more gently; the trends of drift velocities fitted by the new method and the previous method are semblable; and this new method can be widely applied to digital ionosondes.

Research on Numerical Simulation of Tantalum Explosively Formed Projectile Forming Driven by Detonation

In order to study the formation characteristics of tantalum explosively formed projectile (EFP), based on LS-DYNA finite-element software, this article analyzes the influence of mesh size on tantalum EFP forming, compares the accuracy of JC constitutive parameters in different literature on the characterization of tantalum EFP forming, calculates the effective action time of detonation that drives EFP formation, and carries out experimental verification. The results show that the EFP forming velocity was less sensitive to grid size; however, the EFP shape was highly sensitive to grid size, among which the liner had the greatest influence. Besides, for the same density and different constitutive parameters, the velocity of the stabilized EFP was the same, but the change trend of velocity was different, which led to the difference in morphology. The verification test showed that a selection of appropriate JC constitutive parameters could simulate tantalum EFP forming. Finally, the effect of detonation products on EFP forming was reflected mainly in the axial acceleration and radial contraction of the tail skirt. The influence of explosives and detonation products on EFP forming can be ignored 80 μs after the charge detonates. In this work, the numerical simulation method of tantalum EFP forming was studied, which provides guidance for the design and engineering application of tantalum EFP.

Thermotaxic diel vertical migration of the harmful dinoflagellate Cochlodinium (Margalefidinium) polykrikoides: Combined field and laboratory studies

The harmful dinoflagellate Cochlodinium polykrikoides, a species that causes mass mortality of farmed fish, uses diel vertical migration (DVM) as an ecological strategy. In summer 2018, a bloom of C. polykrikoides occurred on the southern coast of Korea when the surface water temperature exceeded 29 °C, as a result of a marine heatwave. To understand the effect of high temperature conditions on the DVM of C. polykrikoides, vertical profiles of environmental variables and the occurrence of the dinoflagellate were investigated through a 48 h field survey. In addition, a thermally stratified environment (6–12 °C difference between the surface and bottom layers) was established in a laboratory study to investigate the effect of temperature difference between water layers on the DVM of C. polykrikoides. In the field, most of the C. polykrikoides population was at a depth of 3–6 m during the day, where the water temperature was significantly lower (p < 0.01; Chi square = 57.98; Kruskal–Wallis test) than in the surface layer (0 m), and only the water temperature at 0 m was not correlated with weighted mean depth of C. polykrikoides, suggesting the usage of DVM to avoid high temperature stress. According to our field and laboratory results, there was a trend of greater DVM velocity by thermotaxis when moving from “unfavorable” water temperature (30 °C hot and 12 °C cold) to “favorable” water temperature for growth (optimal 24 °C) of C. polykrikoides. Our findings suggest that thermotaxic DVM is an important ecological strategy used by C. polykrikoides to optimize environmental conditions for growth through vertical positioning and changing migration velocity.