Radial Expansion Velocity Research Articles

Morphology and growth of convective cold pools observed by a dense station network in Germany

AbstractThis study explores the morphology of convective cold pools, that is, their size, shape, and structure, as well as factors controlling their growth using surface‐based observations of the Field Experiment on Sub‐mesoscale Spatio Temporal Variability in Lindenberg (FESSTVaL). FESSTVaL featured a dense network of 99 custom‐built, low‐cost measurement stations covering a circular area of 30 km in diameter at sub‐mesoscale resolution (distances between 0.1 and 4.8 km) and was held at the Lindenberg Observatory near Berlin (Germany) from May–August 2021. The station network sampled 42 cold‐pool events during the 103‐day measurement period. The morphological properties of cold pools are derived by interpolating the temperature observations spatially to a Cartesian grid and defining cold pools as individual objects at a given time with a temperature perturbation stronger than K. The sample of 1232 cold‐pool objects with extents sufficiently captured by the network has a median equivalent diameter of 8.5 km. The objects exhibit aspect ratios between 1.5 and 1.6 independent of their size and strength, meaning they are generally not circularly shaped. On average, is strongest at the cold‐pool center and decreases linearly towards the edge. For the growth phase of four selected events, the cold‐pool object area scales linearly with the radar‐observed, area‐integrated rainfall accumulation, while the object‐mean temperature perturbation strengthens most efficiently early in the life cycle. The global, radial expansion velocity decreases as the cold pool gets stronger and larger, in contradiction of density‐current theory. Instead, is a better predictor of the expansion rate. These findings identify cold‐air import by precipitation, through both evaporative cooling and convective downdrafts, as the dominant driver of the observed growth.

High strain rate responses of some metals and alloys using a plate impact driven ring expansion test (PIDRET)

A plate impact driven ring expansion test (PIDRET) has been developed to investigate the high strain rate response of metals and alloys under radial expansion. Combining photonic Doppler velocimetry (PDV) probes and ultra-high-speed cameras, it allows for measuring the radial expansion velocity of the ring and for recording the different stages of the ring deformation until necking and ultimate fragmentation. Four metallic materials with different physical and mechanical properties are tested under the same loading conditions leading to strain rates around 104 s−1. The materials exhibit different responses in terms of deformation history and fracture. A comparison is made on (i) the postmortem microstructure and ductility between low strain rate tension loaded specimens and high-strain rate expansion loaded rings and (ii) numbers of necks and fragments between experimental results and theoretical estimations.

Real-time spatiotemporal characterization of mechanics and sonoporation of acoustic droplet vaporization in acoustically responsive scaffolds.

Phase-shift droplets provide a flexible and dynamic platform for therapeutic and diagnostic applications of ultrasound. The spatiotemporal response of phase-shift droplets to focused ultrasound, via the mechanism termed acoustic droplet vaporization (ADV), can generate a range of bioeffects. Although ADV has been used widely in theranostic applications, ADV-induced bioeffects are understudied. Here, we integrated ultra-high-speed microscopy, confocal microscopy, and focused ultrasound for real-time visualization of ADV-induced mechanics and sonoporation in fibrin-based, tissue-mimicking hydrogels. Three monodispersed phase-shift droplets-containing perfluoropentane (PFP), perfluorohexane (PFH), or perfluorooctane (PFO)-with an average radius of ∼6 μm were studied. Fibroblasts and tracer particles, co-encapsulated within the hydrogel, were used to quantify sonoporation and mechanics resulting from ADV, respectively. The maximum radial expansion, expansion velocity, induced strain, and displacement of tracer particles were significantly higher in fibrin gels containing PFP droplets compared to PFH or PFO. Additionally, cell membrane permeabilization significantly depended on the distance between the droplet and cell (d), decreasing rapidly with increasing d. Significant membrane permeabilization occurred when d was smaller than the maximum radius of expansion. Both ultra-high-speed and confocal images indicate a hyper-local region of influence by an ADV bubble, which correlated inversely with the bulk boiling point of the phase-shift droplets. The findings provide insight into developing optimal approaches for therapeutic applications of ADV.

Study on the cylinder test of aluminized explosives with different content of Al powder

To investigate the effect of the content of Al powder on the acceleration ability of the aluminized explosives, a series of 25mm cylinder experiments was conducted, and the content of Al/LiF powder is 0%, 15%, 30%. The radial expansion velocities of the cylinder wall were measured through the Photonic Doppler Velocimetry (PDV) system. The cylinder experiments verify that Al powder could react with detonation products to release energy, which enhance the accelerating ability of explosives. By comparing the different content of Al powder of aluminized explosives, it is found that the accelerating ability of aluminized explosives is related to the content of Al powder, and the optimal content of Al powder is 15% in this experiment. By comparing the same content of Al/LiF powder, it is indicated that the reaction delay time of Al powder in RDX80/Al15 explosive does not exceed 2.8µs, and as RDX65/Al30, the reaction delay time is less than 3µs. Finally, through normalization method, the specific reaction delay time of Al powder are 0.147 and 0.203, with the content of Al powder 15% and 30%.

Investigating emission characteristics and plasma properties in a long-pulse magnetically insulated coaxial diode with different cathode materials

Magnetically insulated coaxial diodes are widely used in O-type high power microwave device for intensive annular electron beam generation. This study reports on a series of electrical and optical measurements on a long-pulse magnetically insulated coaxial diodes in which the emission characteristics and the plasma properties were observed. The impact of cathode material, blade angle, diode voltage and guiding magnetic field on the emission characteristics and the plasma properties of six types of annular cathodes were studied. Two configurations of these cathodes have been used, one with a sharp edge for aluminum, bronze, graphite, stainless-steel, silicon-aluminum alloy and another metal–dielectric. The impressing diode performance was achieved with the metal-dielectric cathode characterized on the excellent emission characteristics and plasma properties. Moreover, high voltage and small blade angle are beneficial to the emission capability and emission uniformity. For the cathode with smaller blade angle, its axial plasma expansion velocity is smaller during the pulse plateau. The strong magnetic field or the large diode voltage is confirmed to reduce the axial and radial expansion velocities.

Evidence for episodic and patchy mass ejection in the circumstellar envelope of AGB star R Leonis

ABSTRACT The morpho-kinematics of the circumstellar envelope of oxygen-rich AGB star R Leonis is probed using Atacama Large Millimeter/submillimeter Array observations of the emission of molecular lines, including in particular CO(2–1) and 29SiO(5–4). Evidence is found for an episode of enhanced mass-loss, a few centuries ago, that produced a broad expanding shell of mean radius ∼6 arcsec and mean radial expansion velocity ∼5.5 km s−1. Detailed scrutiny of its structure, as displayed by the emission of the CO(2–1) line, reveals strong inhomogeneity and patchy morphology. Evidence is also found, in particular from the morpho-kinematics of the emission of SiO, SO, and SO2 lines probing the close neighbourhood of the star, for distinct gas outflows covering broad solid angles in the south-eastern, south-western, and north-western quadrants, suggesting significant contribution of the convective cell granulation in defining the pattern of mass ejection. A study of relative molecular abundances in these outflows suggests that a local thermal equilibrium description applies approximately beyond ∼10 stellar radii from the centre of the star but not at the smaller angular separations where the SO and SO2 molecules are found to be confined. Near the stellar disc, masers of the vibrationally excited SiO lines are found to probe north-western parts of a layer of hot gas, consistent with the earlier observation of an asymmetric expanding shell within 1–2 stellar radii from the centre of the star. Globally, a picture dominated by episodic and patchy mass ejections is found to prevail.

Addressing the critical parameters for overdamped underwater electrical explosion of wire

Experimental and magnetohydrodynamic numerical simulation results and analysis of a μs- and sub-μs-timescale overdamped underwater electrical explosion of copper wires having different lengths and diameters are presented. For these explosions, ∼80% of the energy stored in the pulse generator is deposited into the wire during a time comparable or shorter than a quarter period of the underdamped discharge. It was found that the threshold values of the deposited energy density, energy density rate, and energy density per unit area, which satisfy overdamped discharge, depend on the wire parameters and on the timescale of the explosion. It was shown that the mechanism responsible for this is the process during which the wire experiences phase transitions to a low-ionized plasma, the resistivity of which is determined by the electron–neutral collision rate, which, in turn, depends on the wire radial expansion velocity, current density, and temperature.

The Central 300 pc of the Galaxy Probed by Infrared Spectra of H3 + and CO. III. Locations of Sgr B2 and Star Iota

Abstract Using a simple relation between the radial expansion velocity of diffuse gas in the Central Molecular Zone (CMZ) of the Galaxy and its distance from Sgr A* we estimate the physical depths within the CMZ of Star ι (2MASS J17470898-2829561) and two Sgr B2 far-infrared continuum sources with respect to the location of Sgr A*. To do this we use velocity profiles of infrared absorption lines of H 3 + and of far-infrared absorption lines of H2O+, OH+, and 13CH+. The distances to Star ι and to the Sgr B2 sources are found to be ∼90 pc greater than the distance to Sgr A*. Our conclusion that Sgr B2 lies toward the rear of the CMZ is contrary to most previous models in which it has been placed shallower than Sgr A*.

Dust release from cold ring particles as a mechanism of spoke formation in Saturn's rings

Spokes in Saturn's rings are radially-extended structures consisting of dust grains. Although spacecraft and space telescope observations have revealed various detailed features of the spokes and their time variation, their formation mechanism is still under debate. Previous models examined charging mechanisms to attempt at explaining dust release from cm-sized ring particles; however, the attempt has been unsuccessful, because the electrostatic force caused by such charging mechanisms is much weaker than the cohesive force acting on dust grains at ordinary conditions in the ring environment. Here we propose a novel model for the formation of the spokes, where the temperature dependence of cohesion plays an essential role. Ring particles with a temperature below 60 K adsorb an O2 ring atmosphere, which facilitates release of dust grains from them by reduction in the cohesive force between the grains and the particles on the morning ansa. Then, intense electrostatic forces sufficient to overcome the cohesive force are generated on the surface of ring particles and the released dust grains form the structure of spokes. Our model explains observational features of the spokes including their longitudinal location, lifetime, radial expansion velocity, and seasonality.

The growth of H ii regions around massive stars: the role of metallicity and dust

ABSTRACT Gas metallicity (Z) and the related dust-to-gas ratio (fd) can influence the growth of H ii regions via metal line cooling and ultraviolet (UV) absorption. We model these effects in star-forming regions containing massive stars. We compute stellar feedback from photoionization and radiation pressure (RP) using Monte Carlo radiative transfer coupled with hydrodynamics, including stellar and diffuse radiation fields. We follow a $10^{5}\, \mathrm{M}_{\odot }$ turbulent cloud with Z/Z⊙ = 2, 1, 0.5, and 0.1, and $f_\textrm{d} = 0.01\, Z/Z_{\odot }$ with a cluster-sink particle method for star formation. The models evolve for at least 1.5 Myr under feedback. Lower Z results in higher temperatures and therefore larger H ii regions. For Z ≥ Z⊙, RP (Prad) can dominate locally over the gas pressure (Pgas) in the inner half-parsec around sink particles. Globally, the ratio of Prad/Pgas is around 1 (2 Z⊙), 0.3 (Z⊙), 0.1 (0.5 Z⊙), and 0.03 (0.1 Z⊙). In the solar model, excluding RP results in an ionized volume several times smaller than the fiducial model with both mechanisms. Excluding RP and UV attenuation by dust results in a larger ionized volume than the fiducial case. That is, UV absorption hinders growth more than RP helps it. The radial expansion velocity of ionized gas reaches +15 km s−1 outwards, while neutral gas has inward velocities for most of the runtime, except for 0.1 Z⊙ that exceeds +4 km s−1. Z and fd do not significantly alter the star formation efficiency, rate, or cluster half-mass radius, with the exception of 0.1 Z⊙ due to the earlier expulsion of neutral gas.

Implosion dynamics and radiation characteristics of preconditioned hybrid X-pinch driven by double pulse current

Preconditioned hybrid X-pinch (HXP) experiments have been performed on the Qin-1 facility to investigate the effect of the prepulse current on the implosion dynamics and radiation characteristics. HXPs with molybdenum wires of ∼1.2 mm in length and 25 to 50 μm in diameter have been tested. Driven by the prepulse current, the molybdenum wire is heated to a core-corona structure with a Joule energy deposition of 0.5–4.8 eV/atom, which is smaller than its atomization enthalpy. The radial expansion velocity of the wire core is 0.5–3 km/s. The main current of 450 kA/400 ns is applied ∼610 ns after the prepulse current. The implosion dynamics of the preconditioned HXP is characterized by two-shell structure implosion. Immediately after the main current starts, the current mainly passes through the corona plasma located in a large radius, and the implosion of corona plasma lasts for ∼100 ns until the corona plasma collides with the wire core. Then, the current distribution switches from the corona plasma to the wire core, which results in the onset of implosion of the wire core. The implosion of the wire core generates hot spots and x-ray radiation. The calculated inductance and radius of the current sheath agree with the experimental results. The corona plasma performs as a current switch, which allows the main current passing through the wire core after 100 ns. It indirectly contributes to sharpening the main current used for implosion of the wire core. A single hot spot with x-rays over 2.5 keV is measured using the preconditioned HXP.

The Constant of the Universe Expansion Acceleration ΓH, the Einstein Variation of c and Parameters VH, Ω, Ʌ and ɣ

The Hubble-Lemaitre equation v=H∙r  (cm∙s-1) represented a linear function of the radial Space expansion velocity, if H would be a constant. Sometimes it has been assumed as H = 1/t, which sends back to the classical v = r/t. However, the later discovered acceleration required the additional condition for H to be, also, a function of time; or, opposed, the existence of a not yet defined dark energy. In a previous paper [1] it had been proposed a provisional expression for a constant Universe expansion acceleration as function of distance: Γ= H2( cm∙s-2). Now, the substitution of r as a function of time, takes to five new equations of H, the Hubble velocity vH , the Hubble acceleration ΓH and the positive Hubble potential VH of the Space. So the proposed Hubble functions for the Space: H, rH , vH, ΓH and VH result higher than those in a gravitational field. All of these Hubble functions act in the total Space expansion though, into the Physical Universe, ΓH is not perceived as it does, continuously, the opposed gravitational acceleration g. Otherwise, a revision is made of the Einstein equation for the c value as function of the gravitational potential φ. Additional proposals are made about the horizons definitions and parameters Ω, Ʌ and ɣ.

Nuclear system size scan for freeze-out properties in relativistic heavy-ion collisions by using a multiphase transport model

A system size scan program was recently proposed for the STAR experiments at the Relativistic Heavy Ion Collider(RHIC). In this study, we employ a multiphase transport (AMPT) model for considering the bulk properties at the freeze-out stage for $\mathrm{^{10}B+^{10}B}$, $\mathrm{^{12}C+^{12}C}$, $\mathrm{^{16}O+^{16}O}$, $\mathrm{^{20}Ne+^{20}Ne}$, $\mathrm{^{40}Ca+^{40}Ca}$, $\mathrm{^{96}Zr+^{96}Zr}$, and $\mathrm{^{197}Au+^{197}Au}$ collisions at RHIC energies $\sqrt{s_{NN}}$ of 200, 20, and 7.7 GeV. The results for $\mathrm{^{197}Au+^{197}Au}$ collisions are comparable with those of previous experimental STAR data. The transverse momentum $p_{T}$ spectra of charged particles ($\pi^{\pm}$, $K^{\pm}$, $p$, and $\bar{p}$) at the kinetic freeze-out stage, based on a blast-wave model, are also discussed. In addition, we use a statistical thermal model to extract the parameters at the chemical freeze-out stage, which agree with those from other thermal model calculations. It was found that there is a competitive relationship between the kinetic freeze-out parameter $T_{kin}$ and the radial expansion velocity $\beta_{T}$, which also agrees with the STAR or ALICE results. We found that the chemical freeze-out strangeness potential $\mu_{s}$ remains constant in all collision systems and that the fireball radius $R$ is dominated by $\left\langle \mathrm{N_{Part}}\right\rangle$, which can be well fitted by a function of $a \left\langle \mathrm{N_{Part}}\right\rangle^{b}$ with $b \approx 1/3$. In addition, we calculated the nuclear modification factors for different collision systems with respect to the $ \mathrm{{}^{10}B} + \mathrm{{}^{10}B}$ system, and found that they present a gradual suppression within a higher $p_{T}$ range from small to large systems.

Dynamic Characteristics of the Spark Channel Plasma in Nitrogen Trigatron Investigated by the Laser Mach–Zehnder Interferometer

The spark channel plasma generated in the atmospheric nitrogen trigatron is studied with the laser Mach–Zehnder (M–Z) interferometer. The development of the spark channel plasma is described by analyzing the temporal and spatial evolution of the plasma electron density from the interferograms. The regions of the shock wave and the plasma are distinguished by the phase shift. Different spatial distributions of the anodic and cathodic plasma channels are obtained. The anodic spark channel shows good axial symmetry with constant radial expansion velocity. On the periphery of the main spark channel, a secondary spark channel occurs simultaneously in the cathodic region. After the collision of the two channels, the stagnation forms in the overlapping region and the secondary channel merges with the main one gradually. The leftward expansion velocity of the secondary channel is higher than the rightward velocity of the main channel, but both of them are lower than that near anode. The speculation on the production of the secondary spark channel is given and its influence on the development of the spark discharge in the gap is discussed in this work.

Fragmentation behavior of large-caliber PELE impacting RHA plate at low velocity

Abstract Impact experiments of large-caliber PELE with various inner-outer diameter ratio perforating RHA plate at low velocity were performed. Experimental results showed the size of perforated holes on plate, average diameter of damage area on witness plate, and number of behind-armor fragments will increase as d/D increasing from 0.72 to 0.84. Expansion and fragmentation of large-caliber PELE in this condition were also numerically studied with ANSYS Autodyn. Then, an analytical model accounting for an additional radial shock wave was presented to predict radial expansion velocity and fragmentation of jacket, as well as an empirical approach to estimate diameter of damage area. Calculation results by these approaches were in good agreement with experiments and numerical simulations. Further discussion revealed that Shock/rarefaction wave interactions behavior varying with inner-outer diameter ratio is an important mechanism resulting in different lateral effect by PELE projectiles with various configurations.

Time-and-Space Resolved Cathode Plasma Expansion Velocities in Magnetically Insulated Coaxial Diode With a Metal–Dielectric Cathode

Time-and-space resolved cathode plasma expansion velocities in magnetically insulated coaxial diodes (MICD) with edged cathodes made of bronze dielectric, bronze, and graphite have been compared through optical diagnosis. The voltage and current of the diode pulse of 260 ns are about 400 kV and 2.8 kA, respectively. The axial and radial expansion velocities of the cathode plasma were obtained through the angled lateral view by utilizing high-speed framing camera combined with the digital image processing methods. In addition, the evolution of the cathode and collector plasmas was visible firstly on the front view at the same time. The bronze-dielectric cathode not only showed low expansion velocity of about 0.5 cm/μs but also had other superior characteristics indicated by the strong emission capability, the fast plasma formation and the uniform plasma distribution. Thereby, the metal-dielectric cathode is a good candidate for applications in a long-pulsed MICD.

Distinct Phenotypic Clusters of Glioblastoma Growth and Response Kinetics Predict Survival.

Despite the intra- and intertumoral heterogeneity seen in glioblastoma multiforme (GBM), there is little definitive data on the underlying cause of the differences in patient survivals. Serial imaging assessment of tumor growth allows quantification of tumor growth kinetics (TGK) measured in terms of changes in the velocity of radial expansion seen on imaging. Because a systematic study of this entire TGK phenotype-growth before treatment and during each treatment to recurrence -has never been coordinately studied in GBMs, we sought to identify whether patients cluster into discrete groups on the basis of their TGK. From our multi-institutional database, we identified 48 patients who underwent maximally safe resection followed by radiotherapy with imaging follow-up through the time of recurrence. The patients were then clustered into two groups through a k-means algorithm taking as input only the TGK before and during treatment. There was a significant survival difference between the clusters ( P = .003). Paradoxically, patients among the long-lived cluster had significantly larger tumors at diagnosis ( P = .027) and faster growth before treatment ( P = .003) but demonstrated a better response to adjuvant chemotherapy ( P = .048). A predictive model was built to identify which cluster patients would likely fall into on the basis of information that would be available to clinicians immediately after radiotherapy (accuracy, 90.3%). Dichotomizing the heterogeneity of GBMs into two populations-one faster growing yet more responsive with increased survival and one slower growing yet less responsive with shorter survival-suggests that many patients who receive standard-of-care treatments may get better benefit from select alternative treatments.

Correlation of axial and radial breakdown dynamics in dielectric barrier discharges

Experimental studies of single-filament dielectric barrier discharges (DBDs) in a 0.1 vol% O2 in N2 gas mixture were performed with high spatial and temporal resolution. For the first time, the axial and radial dynamics and electrical characteristics of the DBDs were recorded by high-resolution imaging of the discharge emission combined with synchronised, fast electrical measurements. The axial propagation of the positive streamer and the radial expansion of the discharge channel were studied and correlated to each other. The analysis of the radial dynamics allowed the separation of the streamer propagation and the transient glow phase during channel formation. It was found that the discharge channel widens when the streamer hits the cathode surface and that both the diameter and the radial expansion velocities of the streamer increase with increasing axial propagation velocity. The synchronised quantification of the axial and radial streamer dynamics allowed the estimation of the electric field in the streamer head. Additionally, the time-resolved current density was determined by combining current measurements with fast imaging of the radial discharge development during streamer and glow phase.

Experimental research on time-resolved evolution of cathode plasma expansion velocity in a long pulsed magnetically insulated coaxial diode

Unlike planar diodes, separate research of the axial and radial plasma expansion velocities is difficult for magnetically insulated coaxial diodes. Time-resolved electrical diagnostic which is based on the voltage-ampere characteristics has been employed to study the temporal evolution of the axial and radial cathode plasma expansion velocities in a long pulsed magnetically insulated coaxial diode. Different from a planar diode with a “U” shaped profile of temporal velocity evolution, the temporal evolution trend of the axial expansion velocity is proved to be a “V” shaped profile. Apart from the suppression on the radial expansion velocity, the strong magnetic field is also conducive to slowing down the axial expansion velocity. Compared with the ordinary graphite cathode, the carbon velvet and graphite composite cathode showed superior characteristics as judged by the low plasma expansion velocity and long-term electrical stability as a promising result for applications where long-pulsed and reliable operation at high power is required.

A two-phase model for aluminized explosives on the ballistic and brisance performance

The performance of aluminized high explosives is considered by varying the aluminum (Al) mass fraction in a heterogeneous mixture model. Since the time scales of the characteristic induction and combustion of high explosives and Al particles differ, the process of energy release behind the leading detonation wave front occurs over an extended period of time. For simulating the performance of aluminized explosives with varying Al mass fraction, HMX (1,3,5,7-tetrahexmine-1,3,5,7-tetrazocane) is considered as a base explosive when formulating the multiphase conservation laws of mass, momentum, and energy exchanges between the HMX product gases and Al particles. In the current study, a two-phase model is utilized in order to determine the effects of the Al mass fraction in a condensed phase explosive. First, two types of confined rate stick tests are considered to investigate the detonation velocity and the acceleration ability, which refers to the radial expansion velocity of the confinement shell. The simulation results of the confined rate stick test are compared with the experimental data for the Al mass fraction range of 0%–25%, and the optimal Al mass fraction is provided, which is consistent with the experimental observations. Additionally, a series of plate dent test simulations are conducted, the results of which show the same tendency as those of the experimental tests with varying Al mass fractions.