Effect of the interval between two shocks on ejecta formation from the grooved aluminum surface

This work focuses on the effect of the interval between two shocks on the ejecta formation from the grooved aluminum(Al_(1100))surface by using smoothed particle hydrodynamics numerical simulation.Two unsupported shocks are obtained by the plate-impact between sample and two flyers at interval,with a peak pressure of approximately 30 GPa for each shock.When the shock interval varies from 2.11 to 7.67 times the groove depth,the bubble velocity reduces to a constant,and the micro jetting factor R_(J) from spike to bubble exhibits a non-monotonic change that decreases initially and then increases.At a shock interval of 3.6 times the groove depth,micro jetting factor R_(J) from spike to bubble reaches its minimum value of approximately 0.6.While,the micro jetting factor R_(F) from spike to free surface decreases linearly at first,and stabilizes around 0.25 once the shock interval surpasses 4.18 times the groove depth.When the shock interval is less than 4.18 times the groove depth,the unloading wave generated by the breakout of the first shock wave is superimpose with the unloading part of the second shock wave to form a large tensile area.

STABILITY OF TRANSONIC SHOCKS TO THE EULER-POISSON SYSTEM WITH VARYING BACKGROUND CHARGES

This paper is devoted to studying the stability of transonic shock solutions to the Euler-Poisson system in a one-dimensional nozzle of finite length.The background charge in the Poisson equation is a piecewise constant function.The structural stability of the steady transonic shock solution is obtained by the monotonicity argument.Furthermore,this transonic shock is proved to be dynamically and exponentially stable with respect to small perturbations of the initial data.One of the crucial ingredients of the analysis is to establish the global well-posedness of a free boundary problem for a quasilinear second order equation with nonlinear boundary conditions.

High-Order DG Schemes with Subcell Limiting Strategies for Simulations of Shocks,Vortices and Sound Waves in Materials Science Problems

Shock waves,characterized by abrupt changes in pressure,temperature,and density,play a significant role in various materials science processes involving fluids.These high-energy phenomena are utilized across multiple fields and applications to achieve unique material properties and facilitate advanced manufacturing techniques.Accurate simulations of these phenomena require numerical schemes that can represent shock waves without spurious oscillations and simultaneously capture acoustic waves for a wide range of wavelength scales.This work suggests a high-order discontinuous Galerkin(DG)method with a finite volume(FV)subcell limiting strategies to achieve better subcell resolution and lower numerical diffusion properties.By switching to the FV discretization on an embedded sub-cell grid,the method displays advantages with respect to both DG accuracy and FV shock-capturing ability.The FV scheme utilizes a class of high-fidelity schemes that are built upon the boundary variation diminishing(BVD)reconstruction paradigm.The method is therefore able to resolve discontinuities and multi-scale structures on the subcell level,while preserving the favorable properties of the high-order DG scheme.We have tested the present DG method up to the 6th-order accuracy for both smooth and discontinuous noise problems.

VANISHING VISCOSITY FOR NON-ISENTROPIC GAS DYNAMICS WITH INTERACTING SHOCKS

In this paper, we study the vanishing viscosity limit for non-isentropic gas dy- namics with interacting shocks. Given any entropy solution of non-isentropic gas dynamics which consists of two different families of shocks interacting at some positive time, we show that such solution is the vanishing viscosity limit of a family of smooth global solutions for a viscous system of conservation law. We remark that, after the interacting time, not only shocks but also contact discontinuity are generated.

Experimental and numerical studies on interactions of a spherical flame with incident and reflected shocks

Observations are presented from experiments and calculations where a laminar spherical CH4/air flame is perturbed successively by incident and reflected shock waves. The experiments are performed in a standard shock tube arrangement, in which a high-speed shadowgraph imaging system is used to record evolutions of the flame. Numerical simulations are conducted by using second-order wave propagation algorithms, based on two-dimensional axisymmetric Navier-Stokes equations with detailed chemical reactions. Qualitative agreements are obtained between the experimental and numerical results. Under actions of incident shock waves, Richtmyer-Meshkov instability responsible for the flame deformation is induced in the flame, and the distoned flame takes a barrel shape. Then, under subsequent actions of the shock wave reflected from a planar wall, the flame takes an inclined non-symmetrical kidney shape in a symmetric cross section, which means a mushroom-like shape of the flame comes finally into being. The vorticity direction in the ring cap has been altered by the reflected shock＇s action, which makes the head of the mushroom-like flame extend quickly to the side wall.

Numerical investigation of Richtmyer-Meshkov instability driven by cylindrical shocks

In this paper, a numerical method with high order accuracy and high resolution was developed to simulate the Richtmyer-Meshkov（RM） instability driven by cylindrical shock waves. Compressible Euler equations in cylindrical coordinate were adopted for the cylindrical geometry and a third order accurate group control scheme was adopted to discretize the equations. Moreover, an adaptive grid technique was developed to refine the grid near the moving interface to improve the resolution of numerical solutions. The results of simulation exhibited the evolution process of RM instability, and the effect of Atwood number was studied. The larger the absolute value of Atwood number, the larger the perturbation amplitude. The nonlinear effect manifests more evidently in cylindrical geometry. The shock reflected from the pole center accelerates the interface for the second time, considerably complicating the interface evolution process, and such phenomena of reshock and secondary shock were studied.

Ejecta from periodic grooved Sn surface under unsupported shocks

Dynamic failure and ejection characteristics of a periodic grooved Sn surface under unsupported shock loading are studied using a smoothed particle hydrodynamics method. An ＂Eiffel Tower＂ spatial structure is observed, which is com- posed of high-speed jet tip, high-density jet slug, longitudinal tensile sparse zone, and complex broken zone between grooves. It is very different from the spike-bubble structure under supported shocks, and has been validated by detonation loading experiments. In comparison with that under supported shocks at the same peak pressure, the high-speed ejecta decreases obviously, whereas the truncated location of ejecta moves towards the interior of the sample and the total mass of ejecta increases due to the vast existence of low-speed broken materials. The shock wave profile determines mainly the total ejection amount, while the variation of V-groove angle will significantly alter the distribution of middle- and high-speed ejecta, and the maximum ejecta velocity has a linear corretation with the groove angle.

TRIPLOIDY INDUCTION WITH HEAT SHOCKS TO PENAEUS CHINENSIS AND THEIR EFFECTS ON GONAD DEVELOPMENT

Heat shocks effectively produced triploids in Penaeus chinensis . Fertilized eggs heat shocked (28-32℃) for 8 to 16 minutes, starting from 8 to 20 minutes after spawning, resulted in triploidy induction rates of 39%-75%. Several triploid populations were cultured to 10 cm. In a triploid population, two kinds of ovaries were observed. Histological examination showed apparent differences between these two kinds of ovaries, whereas among male shrimp, there were no such differences.

A Physical Method of Analyzing theMechanism of Continental StrongShocks from Crustal Movement

In order to analyze the mechanism of continental strong shocks from the angle of crustal movement using the data of repeated geodetic survey, this paper has proposed a physical method; it analyzes the mechanism of density change due to the occurrence of strong shocks by use of the physical quantity that reflects the time change of crustal density. (1) The general theory of the time change of density in the earth’ s interior and the theory of the time change of single layer density have been introduced, and an algorithm of stepwise iteration has been proposed; (2) The effect of the change of single layer density caused by fault dislocation has been analyzed in brief; (3) The characteristics of the time change of crustal density in the south of the seismogenic region before the 1996 Lijiang earthquake with M_L =7.0 have been studied; (4) The precursor model or causal mechanism of strong shocks possibly existing in the time change of crustal density has been investigated preliminarily.

Early acceleration of electrons and protons at the nonrelativistic quasiparallel shocks with different obliquity angles

The early acceleration of protons and electrons in the nonrelativistic collisionless shocks with three obliquities are investigated through 1D particle-in-cell simulations. In the simulations, the charged particles possessing a velocity of 0.2c flow towards a reflecting boundary, and the shocks with a sonic Mach number of 13.4 and an Alfven Mach number of 16.5 in the downstream shock frame are generated.In these quasi-parallel shocks with the obliquity angles θ = 15°, 30° and 45°, some of the protons and the electrons can be injected into the acceleration processes, and their downstream spectra in the momentum space show a power law tail at a time of 1.89 × 10^5ω^-1pe, where ωpe is the electron plasma frequency.Moreover, the charged particles reflected at the shock excite magnetic waves upstream of the shock. The shock drift acceleration is more prominent with a larger obliquity angle for the shocks, but the accelerated particles diffuse parallel to the shock propagation direction more easily to participate in the diffusive shock acceleration. In the early acceleration stage, more energetic protons and electrons appear in the downstream of the shock for θ = 15° compared with the other two obliquities. Moreover, in the upstream region, the spectrum of the accelerated electrons is the hardest for θnB = 45° among the three obliquities, whereas the proton spectra for θnB = 15° and 45° are similar as a result of the competition of the effectiveness of the shock drift acceleration and the diffusive shock acceleration.

ON LOCAL STRUCTURAL STABILITY OF ONE-DIMENSIONAL SHOCKS IN RADIATION HYDRODYNAMICS

In this paper, we are concerned with the local structural stability of one-dimensional shock waves in radiation hydrodynamics described by the isentropic Euler-Boltzmann equations. Even though in this radiation hydrodynamics model, the radiative effects can be understood as source terms to the isentropic Euler equations of hydrodynamics, in general the radiation field has singularities propagated in an angular domain issuing from the initial point across which the density is discontinuous. This is the major difficulty in the stability analysis of shocks. Under certain assumptions on the radiation parameters, we show there exists a local weak solution to the initial value problem of the one dimensional Euler-Boltzmann equations, in which the radiation intensity is continuous, while the density and velocity are piecewise Lipschitz continuous with a strong discontinuity representing the shock-front. The existence of such a solution indicates that shock waves are structurally stable, at least local in time, in radiation hydrodynamics.

Web software reliability modeling with random impulsive shocks

As the web-server based business is rapidly developed and popularized, how to evaluate and improve the reliability of web-servers has been extremely important. Although a large num- ber of software reliability growth models （SRGMs）, including those combined with multiple change-points （CPs）, have been available, these conventional SRGMs cannot be directly applied to web soft- ware reliability analysis because of the complex web operational profile. To characterize the web operational profile precisely, it should be realized that the workload of a web server is normally non-homogeneous and often observed with the pattern of random impulsive shocks. A web software reliability model with random im- pulsive shocks and its statistical analysis method are developed. In the proposed model, the web server workload is characterized by a geometric Brownian motion process. Based on a real data set from IIS server logs of ICRMS website （www.icrms.cn）, the proposed model is demonstrated to be powerful for estimating impulsive shocks and web software reliability.

Generation of Ultrahigh-Velocity Collisionless Electrostatic Shocks Using an Ultra-Intense Laser Pulse Interacting with Foil-Gas Target

Ultra high-velocity collisionless shocks are generated using an ultra-intense laser interacting with foil-gas target,which consists of copper foil and helium gas.The energy of helium ions accelerated by shock and the proton probing image of the shock electrostatic field show that the shock velocity is 0.02c,where c is the light speed.The numerical and theory studies indicate that the collisionless shock velocity exceeding 0.1c can be generated by a laser pulse with picosecond duration and an intensity of 1020 W/cm2.This system may be relevant to the study of mildly relativistic velocity collisionless shocks in astrophysics.

Spillover and quantile linkage between oil price shocks and stock returns: new evidence from G7 countries

The link between crude oil price and stock returns of the Group of Seven(G7)countries(Canada,France,Germany,Italy,Japan,the United Kingdom,and the United States)was analyzed in this study using monthly data from January 1999 to March 2020.We adopt a similar approach to Kilian(Am Econ Rev 99(3):1053–1069,2009)and construct a structural vector autoregression framework to decompose crude oil price shocks into oil supply shock,oil aggregate demand shock,and oil-specific demand shock.We then explore the distinct effects of different kinds of oil price shocks from various sources.Based on the decomposed oil price shocks,we apply the connectedness approach and QQ regression to find time-varying co-movements and tail dependence between oil price shocks and G7 stock returns.There is no general correlation between the decomposed oil prices and stock returns in these countries.The effects of oil price shocks on stock returns across different stock market conditions appear to be heterogeneous.Oil supply shock appears to be a net transmitter of spillover effects for all G7 countries within the sample period.

Dynamics of oil price shocks and stock market behavior in Pakistan:evidence from the 2007 financial crisis period

Background:The aim of this study is to investigate the effect of the oil price and its volatility on the stock market of Pakistan before and after the 2007 financial crisis period.Methods:The analyses are carried out on daily data for the period from July 31,2000 to July 31,2014.This study uses several econometric techniques for the analyses,namely,the Johansen-Juselius cointegration test,generalized autoregressive conditional heteroskedasticity(GARCH)model,exponential generalized autoregressive conditional heteroskedasticity(EGARCH)model,variance decomposition method,and impulse response function.Results:The results of the cointegration method indicate a significant long-run association between stock market and oil prices in the pre-crisis period.The EGARCH model shows that oil price returns have a significant effect on stock market returns in both sub-periods,while the result for the GARCH model is significant only in the postcrisis period.We find a significant effect of oil price volatility on the stock market in both sub-periods from the GARCH model.Furthermore,the EGARCH model shows an asymmetric effect of oil price volatility on the stock market in the pre-crisis period.Variance decomposition shows that stock market variations are mostly explained by selfinnovation.Moreover,the impulse response function results show that oil price shocks affected the stock market adversely in the pre-crisis period but positively in the postcrisis period.Conclusions:This study suggests that economic policymakers and investors should consider the oil price as an important factor affecting stock market returns.

GLOBAL INSTABILITY OF MULTI-DIMENSIONAL PLANE SHOCKS FOR ISOTHERMAL FLOW

In this paper,we are concerned with the long time behavior of the piecewise smooth solutions to the generalized Riemann problem governed by the compressible isothermal Euler equations in two and three dimensions.A non-existence result is established for the fan-shaped wave structure solution,including two shocks and one contact discontinuity which is a perturbation of plane waves.Therefore,unlike in the one-dimensional case,the multi-dimensional plane shocks are not stable globally.Moreover,a sharp lifespan estimate is established which is the same as the lifespan estimate for the nonlinear wave equations in both two and three space dimensions.

Remote monitoring of implantable defibrillators is associated with fewer inappropriate shocks and reduced time to medical assessment in a remote and rural area

BACKGROUND Implantable cardioverter defibrillators(ICDs)and cardiac resynchronisation therapy with defibrillators(CRT-D)reduce mortality in certain cardiac patient populations.However,inappropriate shocks pose a problem,having both adverse physical and psychological effects on the patient.The advances in device technology now allow remote monitoring(RM)of devices to replace clinic follow up appointments.This allows real time data to be analysed and actioned and this may improve patient care.AIM To determine if RM in patients with an ICD is associated with fewer inappropriate shocks and reduced time to medical assessment.METHODS This was a single centre,retrospective observational study,involving 156 patients implanted with an ICD or CRT-D,followed up for 2 years post implant.Both appropriate and inappropriate shocks were recorded along with cause for inappropriate shocks and time to medical assessment.RESULTS RM was associated with fewer inappropriate shocks(13.6%clinic vs 3.9%RM;P=0.030)and a reduced time to medical assessment(15.1±6.8 vs 1.0±0.0 d;P<0.001).CONCLUSION RM in patients with an ICD is associated with improved patient outcomes.

STABILIZATION EFFECT OF FRICTIONS FOR TRANSONIC SHOCKS IN STEADY COMPRESSIBLE EULER FLOWS PASSING THREE-DIMENSIONAL DUCTS

Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock solutions in rectilinear ducts with square cross-sections.In this article,we are devoted to proving rigorously that a large class of these transonic shock solutions are stable,under multidimensional small perturbations of the upcoming supersonic flows and back pressures at the exits of ducts in suitable function spaces.This manifests that frictions have a stabilization effect on transonic shocks in ducts,in consideration of previous works which shown that transonic shocks in purely steady Euler flows are not stable in such ducts.Except its implications to applications,because frictions lead to a stronger coupling between the elliptic and hyperbolic parts of the three-dimensional steady subsonic Euler system,we develop the framework established in previous works to study more complex and interesting Venttsel problems of nonlocal elliptic equations.

Numerical method for simulating rarefaction shocks in the approximation of phase-flip hydrodynamics

A finite-difference algorithm is proposed for numerical modeling of hydrodynamic flows with rarefaction shocks, in which the fluid undergoes a jump-like liquid-gas phase transition. This new type of flow discontinuity, unexplored so far in computational fluid dynamics, arises in the approximation of phase-flip(PF) hydrodynamics, where a highly dynamic fluid is allowed to reach the innermost limit of metastability at the spinodal, upon which an instantaneous relaxation to the full phase equilibrium(EQ) is assumed. A new element in the proposed method is artificial kinetics of the phase transition, represented by an artificial relaxation term in the energy equation for a "hidden"component of the internal energy, temporarily withdrawn from the fluid at the moment of the PF transition. When combined with an appropriate variant of artificial viscosity in the Lagrangian framework, the latter ensures convergence to exact discontinuous solutions, which is demonstrated with several test cases.

NUMERICAL SIMULATION OF 1-D UNSTEADY TWO-PHASE FLOWS WITH SHOCKS

In the present paper, random-choice method (RCM) and second-order GRP difference method, which are high resolution methods used for pure gas flows with shocks, are extended and employed to study the problem of one-dimensional unsteady two-phase flows. The two-phase shock wave and the flow field behind it in a dusty gas shock tube are calculated and the time-dependent change of the flow parameters for the gas and particle phase are obtained. The numerical results indicate that both the two methods can give the relaxation structure of the two-phase shocks with a sharp discontinuous front and that the GRP method has the advantages of less time-consuming and higher accuracy over the RCM method.